N-acetylcysteine for the prevention of non-contrast media agent-induced kidney injury: from preclinical data to clinical evidence
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- Hosseinjani, H., Moghaddas, A. & Khalili, H. Eur J Clin Pharmacol (2013) 69: 1375. doi:10.1007/s00228-013-1494-8
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To review available evidence on the effectiveness of N-acetylcysteine (NAC) as a prophylactic agent in the prevention of non-contrast media agent-induced kidney injury.
Data were collected by searching Scopus, PubMed, Medline, Science direct and Cochrane database systematic reviews. A total of 26 relevant experimental studies up to the date of publication were included in the review.
Available evidence shows that NAC has the potential to exert significant protective or ameliorative effects against drug-induced kidney injury in experimental models. The possible suggested renoprotective mechanisms of NAC in different experimental settings were acting as an antioxidant by restoring the pool of intracellular reduced glutathione, scavenging of free radicals, and/or interacting with reactive oxygen species.
Whether the administration of NAC could be an effective protective clinical strategy to prevent drug-induced kidney injury or not is a question that remains to be answered in future clinical trials.
KeywordsN-acetylcysteineDrug-induced kidney injuryRenoprotective mechanismsAmeliorative effects
N-acetylcysteine (NAC), the acetylated variant of the amino acid cysteine, is a rich source of sulfhydryl groups. NAC has antioxidant properties and, as a sulfhydryl donor, contributes to the regeneration of endothelium-derived relaxing factor and glutathione (GSH). Additional protective effects of NAC result from its ability to reduce oxygen radicals produced following oxidative processes. This effect can be shown directly by interfering with the oxidants, up-regulating antioxidant systems such as superoxide dismutase (SOD), or enhancing the catalytic activity of GSH peroxidase (GSH-Px) [1–5].
The results of several studies support the involvement of reactive oxygen species (ROS) in the development of various forms of acute kidney injury (AKI) [6–9]. Among the proposed interventions, several lines of evidence supports the potential role of NAC in the prevention of AKI . NAC has been suggested to ameliorate renal vasoconstriction via potentiation of nitric oxide (NO) production and NO-independent mechanisms. Local NO production plays a major role in the maintenance of adequate blood supply to the renal medulla. In addition to contributing to the preservation of renal microcirculation, NAC can improve mitochondrial function by lowering the concentration of ROS [11–13].
Although the exact mechanism responsible for the nephroprotective activity of NAC remains unclear, the antioxidant and vasodilatory properties of NAC have been suggested as the main effects [14, 15]. The protective effect of NAC against kidney injury has been reported in various experimental models, such as contrast media agents [16, 17], ischemia–reperfusion injury (IRI) [18, 19] and chronic kidney disease (CKD) .
In this review, we collected and analyzed current experimental evidence on the effectiveness of NAC as a prophylactic agent in the prevention of non-contrast media agent-induced kidney injury.
The data were collected by searching Scopus, PubMed, Medline, Science direct, and Cochrane database systematic reviews. The keywords used as search terms were “N-acetylcysteine,” “acetylcysteine,” “NAC,” “ARF,” “AKI,” “kidney injury,” “kidney failure,” “renal injury,” “renal failure,” “renal toxicity,” “nephrotoxicity,” and “nephropathy.” Experimental studies that have assessed the protective effects of NAC in non-contrast media agent-induced kidney injury were included in this review. One article was retrieved on NAC and folic acid, two on NAC and glycerol, four on NAC and ifosfamide, one on NAC and colistin, six on NAC and cisplatin, two on NAC and gentamicin, two on NAC and cyclosporine A, one on NAC and vancomycin, one on NAC and nonsteroidal anti-inflammatory drugs (NSAIDs), two on NAC and amphotericin B, one on NAC and adriamycin, one on NAC and lithium, one on NAC and isoflurane, and one on NAC and methotrexate (MTX). Irrelevant articles (basic experimental studies, non-English language reports, studies that did not include clinical end-point assessments, and case reports) were excluded. A total of 26 relevant animal studies up to the date of publication were included.
NAC and adriamycin
Adriamycin is a potent chemotherapeutic agent that has been widely used to treat many solid tumors, such as head, neck, lung, liver, testis, ovary and breast cancers, and hematologic malignancies, including lymphoma and leukemia . Adriamycin causes direct toxic damage to the glomerulus with subsequent glomerulosclerosis and tubulointerstitial injury, characterized by reductions in the glomerular filtration rate (GFR) and proteinuria. The proposed molecular mechanism for the pathogenesis of adriamycin-induced renal toxicity is free oxygen radical production. In addition, adriamycin administration has been found to deplete the level of GSH as an antioxidant and elevate lipid peroxide levels in the liver, kidney, and heart .
Sang-Woong et al.  studied the effects of antioxidants on adriamycin-induced nephropathy and evaluated the expression of transforming growth factor (TGF) β1 and laminin β1 in a rat kidney model. In this study, the experimental group received a single injection of adriamycin at a dose of 2 mg/kg, and the control group were injected with an equal volume of saline. The animals were followed for 6 weeks, following which time the adriamycin-treated rats were randomly divided into two groups, with one group receiving 1 g/kg/day NAC in the drinking water for additional 6 weeks and the other group not receiving any supplement. Monitoring was done at weeks 0, 6, and 12 by measuring the systolic blood pressure and 24-h urine collection. The expression of TGF-β1 and laminin β1was determined in the renal cortex by reverse-transcription PCR, western blotting, immunohistochemistry, and immunogold electron microscopy methods.
The results of this study demonstrate that NAC was able to ameliorate the adriamycin-induced proteinuric nephropathy and blood pressure as well as the glomerulosclerosis and tubulointerstitial injury. NAC was also shown to return the TGF-β1 mRNA and protein expression to the control level. However, it was not able to significantly alter the expression of laminin β1 proteins, suggesting that the expression of laminins may play an important role in various glomerular diseases, such as glomerulosclerosis and tubulointerstitial fibrosis. This study also demonstrates that NAC had renoprotective effects in association with the suppression of over-expressed TGF-β1 in an established nephropathy model .
Based on the results of this study, the role of ROS in the progression of adriamycin-induced nephropathy by inducing glomerulosclerosis and tubulointerstitial lesions and enhancing the expression of TGF-β1 must be considered. NAC had a protective effect against oxidative damage through its direct free radical scavenging properties and the ability to modulate intracellular GSH levels. However, further experimental and human studies are needed before NAC can be recommended for the prevention of adriamycin-induced nephrotoxicity in clinical practice.
NAC and ifosfamide
Ifosfamide is a potent alkylating agent that is widely used for the treatment of a variety of solid organ tumors, such as lung, ovarian, testicular and breast cancers. Unfortunately, severe hemorrhagic cystitis and nephrotoxicity are the most common adverse effects of this drug. Ifosfamide-associated severe hemorrhagic cystitis can be prevented through the concomitant administration of mesna, but to date no effective agent for the prevention of ifosfamide-induced nephrotoxicity has been found [24–26].
The exact mechanism of ifosfamide-induced nephrotoxicity has not been fully described. Some experimental data suggest that its toxic metabolites (e.g., 4-hydroxy-ifosfamide, chloracetaldehyde and, in particular, acrolein) causes nephrotoxic effects through the side-chain oxidation of ifosfamide in renal cells. Ifosfamide-induced nephrotoxicity is usually manifested as Fanconi syndrome, whereas CKD has been only rarely described [27–29].
Chen et al. performed a study in 2007 using a porcine renal proximal tubular (LLCPK-1) cell model with two different interventions including pretreatment and concurrent treatment with NAC [30, 31]. In the pretreatment group, cells were first pre-treated with 0.4 mM of NAC for 24 h and then with 50 μM of buthionine sulfoximine (BSO), a GSH synthesis inhibitor, plus 1 mM of ifosfamide daily for 96 h. In the treatment group, cells were exposed to 50 μM of BSO plus 1 mM of ifosfamide, concurrently with 0.4 mM/day of NAC for 96 h. Cellular viability was assessed by the alamarBlue® assay (AbD Serotec, Oxford, UK) at 96 h, and the levels of reduced and intracellular oxidized GSH were determined by a GSH colorimetric assay kit. There was a significant decrease in cellular viability detected following exposure to BSO and ifosfamide in the both groups, but this decrease was more significant in the concurrently treated group than in the pre-treatment group. Intracellular and total GSH levels improved significantly following NAC administration. Based on these results, the authors concluded that NAC can be a potential option for the prevention of ifosfamide-induced nephrotoxicity by acting as a precursor for GSH synthesis. In this study NAC at a concentration of 0.4 mM prevented ifosfamide-induced nephrotoxicity in vitro. However, this in vitro concentration of NAC needs to be compared to levels used in human studies since the in vitro pharmacological effect of a compound is usually achieved at concentrations exceeding those used in clinical settings [30, 31].
In another study carried out in 2008, Chen et al. evaluated the effects of NAC on ifosfamide-induced AKI . Four groups of male Wistar albino rats (6 in each group) received saline [0.5 ml intraperitoneal (i.p.) for 5 days], ifosfamide (50 mg/kg/day or 80 mg/kg/day i.p. for 5 days), NAC (1.2 g/kg/day i.p. for 6 days), or ifosfamide +NAC i.p. (for 6 days). Twenty-four hours after the last injection, the rats were sacrificed, and serum and urine were collected for biochemical analysis, including creatinine, sodium, potassium, urea, phosphate, albumin, magnesium, glucose, and β2-microglobulin. GSH, glutathione S-transferase, and lipid peroxide activity were also analyzed in the kidney tissue.
The results showed that ifosfamide significantly increased the serum creatinine level and urinary magnesium and β2-microglobulin excretion when compared with the control group. NAC significantly reversed the elevation of serum creatinine as well as the increased excretion of magnesium and β2-microglobulin in the urine. Moreover, NAC significantly improved the ifosfamide-induced GSH depletion and glutathione S-transferase activity and decreased lipid peroxides .
In a subsequent study, Hanly et al.  compared the data reported by Chen et al. with data on the use of NAC in children for acetaminophen overdose [in terms of area under the curve (AUC) over time]. The aim of these authors was to translate the systemic exposure associated with a therapeutic effect in the rat model to the needed systemic exposure in children. The mean systemic exposure in the rat model was 18.72 (range 9.92–30.02) mM · h) and that found in children was 14.48 (range 6.22–32.96) mM · h. Finally the authors reported two pediatric cases in which NAC ameliorated AKI associated with ifosfamide when given concurrently with their chemotherapy treatment. Systemic exposure to NAC measured in one of these cases was comparable with children who treated for acetaminophen overdose . The results indicate that NAC with its clinically approved dose schedule has the potential to protect against ifosfamide-induced nephrotoxicity in children.
In a very recent study, El-Sisi et al.  compared the protective effect of alpha lipoic acid versus NAC against ifosfamide-induced nephrotoxicity. Three groups of male albino rats were treated with ifosfamide (50 mg/kg daily for 5 days), ifosfamide + ALA (100 mg/kg daily for 8 days) or ifosfamide + NAC (200 mg/kg daily for 8 days). The kidney malondialdehyde (MDA), NO and GSH contents, serum biochemical parameters, and histopathological analysis were evaluated as end-points. The results showed that both ALA and NAC markedly reduced the severity of renal dysfunction induced by ifosfamide, but that NAC was more nephroprotective than ALA .
The results of these experimental studies support the potential benefits of NAC in the prevention of ifosfamide-induced nephrotoxicity. However, more evidence is needed before this intervention can be introduced into clinical practice.
NAC and cisplatin
Cisplatin is an alkylating agent introduced for the treatment of various solid tumors in, for example, the testes, ovaries, lungs, bladder, head, and neck . Cisplatin acts through the activation of multiple signal transduction pathways leading to the regulation of cell survival and apoptosis in various cell types. The major dose limiting toxicity which occurs in 28–36 % of patients treated with a single dose of cisplatin is nephrotoxicity .
Cisplatin is partially metabolized into toxic species which have multiple intracellular effects, including gene regulation, direct cytotoxicity with ROS, activation of mitogen-activated protein kinases, induction of apoptosis, and stimulation of inflammation and fibrogenesis. These events cause tubular damage and tubular dysfunction leading to sodium, potassium, and magnesium wasting. Cisplatin also induces renal vasculature injury and consequently a decline in GFR [36, 37]. When the probable mechanisms of cisplatin-induced nephrotoxicity are taken into account, NAC as a potent antioxidant may be an effective agent for the prevention of this event.
Amany et al.  evaluated the renoprotective role of NAC on experimental cisplatin-induced nephrotoxicity in a rat model. In this study 40 albino rats were divided into four groups, with the control group receiving i.p. isotonic saline daily for 7 days, the second group receiving cisplatin 1 mg/kg/day i.p. for 7 days. to induce nephrotoxicity, the hird group receiving a daily oral dose of NAC 400 mg/kg for 7 days, 1 h before cisplatin administration, and the last group receiving NAC in the same dose and duration as the third group but 1 h after cisplatin administration. Evaluations in this experiment were based on DNA extraction, apoptosis detection, caspase-3 reaction, and histopathological findings. In comparison with the control group, in the cisplatin-treated rats the authors detected higher levels of serum creatinine and blood urea nitrogen (BUN), marked DNA fragmentation, a significant increase in caspase-3 reaction, and the presence of proximal convoluted tubules vacuolations. In addition, the administration of NAC 1 h after cisplatin was more effective than pretreatment with NAC in terms of reversing the nephrotoxicity parameters .
In similar study conducted in 1 year later in 2009, Abdelrahman et al.  evaluated the effects of NAC on renal hemodynamic parameters in cisplatin-induced renal failure in a Wistar-Kyoto rat model. These authors divided the animals into four groups (n = 5 or 6) and treated them as follows; the first and the second groups received normal saline (control) and i.p. NAC (500 mg/kg/day for 9 days) respectively; the third and the fourth groups received a single i.p. injection of cisplatin (5 mg/kg) and cisplatin (5 mg/kg as a single i.p. injection) + NAC (500 mg/kg/day for 9 days), respectively. Following the treatment hemodynamic parameters such as blood pressure, renal blood flow, serum creatinine, BUN, urinary creatinine, N-acetyl-β-D-glucosaminidase activity, and renal platinum concentration were monitored. The results showed that cisplatin caused a significant reduction in renal blood flow but did not affect norepinephrine-induced renal vasoconstriction.
In addition, cisplatin significantly increased plasma urea and creatinine concentrations, urinary NAG activity and also kidney relative weight whereas it decreased body weight and creatinine clearance. The histopathological arm of the study showed that cisplatin caused remarkable renal insults compared with the control group. No significant changes in variables were detected in the NAC alone group compared with the control group, but all of the biochemical parameters and histopathological changes were improved following cisplatin administration. All of these findings support the role of NAC in reversing the decline in renal blood flow and increase in renal vascular resistance following cisplatin therapy, but the authors were unable to determine whether the reduction of renal cisplatin concentration by NAC interferes with its anticancer properties or not .
In an earlier study carried out in 1993, Appenroth et al.  reported similar results. These authors proposed that nephroprotective effects of NAC are related to the increase in renal GSH concentration or a change in the pharmacokinetic behavior of cisplatin. In this study, Wistar rats were assigned into four groups: a control group [saline 5 ml/100 g body weight (BW) + NAC 100 mg/00 g BW], a cisplatin group (0.6 or 0.3 mg/100 g BW), a cisplatin + NAC group, and a cisplatin + NAC mixed group which received cisplatin and NAC as a pre-mixed i.p. solution. A small increase in protein excretion with no oliguria was detected in the cisplatin + NAC group compared with the group that received cisplatin alone. Also, cisplatin concentration in the kidney tissue decreased significantly following the administration of NAC. These authors reported that these changes occurred concurrently with a decreased renal tubular reabsorption of the cisplatin–NAC complex and, consequently, the increased urinary excretion of cisplatin. The same effects were detected when cisplatin and NAC were dissolved together in a solution prior to injection. This was the first report of the formation of a non-reabsorbable cisplatin–NAC complex .
p38 mitogen-activated protein kinase (MAPK) has been reported to play an important role in AKI induced by ischemia–reperfusion and nephrotoxic agents. The MAPK pathways are a series of serine/threonine kinases which regulate cell proliferation, differentiation and survival. In 2008, Luo et al.  examined the effects of NAC on oxidative stress and oxidation-associated signals, including MAPK, nuclear factor NF-kappa-B p105 subunit (NF-κB), and tumor necrosis factor alpha (TNF-α), in cisplatin-induced nephrotoxicity in a rat model, comparing these to the effects of melatonin (MT), one of the physiological TNF-α inhibitors, and pyrrolidine dithiocarbamate (PDTC), a NF-κB inhibitor.
In their experimental design, rats were divided into five different groups (6–9 rats in each group) as follows: saline-treated control rats; rats treated once daily with cisplatin (5 mg/kg, intravenous injection) + i.p. injection of vehicle (5 ml/kg) or NAC (250 mg/kg) or MT (5 mg/kg) or (5) PDTC (80 mg/kg). The administration of these agents was started 2 days prior to the administration of a single dose of cisplatin. Four days after cisplatin treatment, blood samples were obtained and all histological parameters, expression of related protein, renal GSH content and TNF-α mRNA level were analyzed. The authors found that NAC inhibited oxidative stress, p38 MAPK activation, caspase-3 cleavage, tissue apoptosis, renal dysfunction, and morphological damages. Cisplatin caused the translocation of NF-κB into the nucleus and increased TNF-α mRNA level in kidney which had been inhibited by NAC. None of the agents, such as MT which down-regulated the TNF-α mRNA level, and PDTC which inhibited the increases in both NF-κB translocation and TNF-α mRNA, were capable to interfere with oxidative stress, p38 MAPK phosphorylation, caspase-3 cleavage, tissue apoptosis, and kidney injury induced by cisplatin.
These data support the critical role of oxidative stress and consequent activation of p38 in the induction of apoptosis and the pathogenesis of cisplatin-induced AKI which is blocked by NAC. However, enhanced NF-κB activation and increased TNF-α mRNA levels seem to be less attributable to cisplatin in terms of renal damage .
In a similar study performed in 2011, this same Japanese group assessed the effects of NAC on cisplatin-induced AKI and its relationship with the MAPK pathway. Cisplatin was used for induction of AKI in a rat model . The animals were randomly divided into six groups, including a control group, AKI group, NAC (50 mg/kg) group, NAC (100 mg/kg) group, NAC (200 mg/kg) group, and MAPK-specific inhibitor SB203580 (10 mg/kg) group. NAC and SB203580 were administered once a day for 3 days before cisplatin administration and continuously given once daily for 5 days thereafter. Apoptosis and caspase-3 content in the kidney in relation to the expression of caspase-3, Bcl-2, and phosphorylated MAPK were evaluated in this study. The results demonstrated that NAC and SB203580 reduced apoptotic cells, suppressed caspase-3 and MAPK expression, and augmented the expression of Bcl-2 to protect kidney from cisplatin injury. The authors concluded that NAC prevents cisplatin-induced renal damage via the MAPK pathway .
The protective effect of GSH against cisplatin-induced nephrotoxicity was found to be critically dependent on the timing of thiol administration. Delayed treatment was not consistently protective against nephrotoxicity. It has been reported that if GSH precursors are started within 2 h of cisplatin administration, they are effective, and this effect will be decreased after 4 h and is minimal by 6 h .
NAC and cyclosporine
Cyclosporine is a potent immunosuppressant which is widely used in the treatment of several autoimmune diseases. It is associated with a number of adverse effects on the renal, hepatic, cardiac, alimentary tract, and nervous systems . Cyclosporine nephrotoxicity may be divided into acute and chronic episodes. Acute nephrotoxicity is characterized by vasoconstriction leading to reduced renal blood flow, reduced GFR, and an increase in renal vascular resistance. Imbalance in vasoactive substance release, increased endothelin activity and angiotensin II level, and a reduction of NO synthesis and secretion from the endothelium are responsible for this phenomenon. In contrast, the chronic form of nephrotoxicity is characterized not only by renal vasoconstriction but also by the development of structural damage. Chronic cyclosporine nephrotoxicity is thought to be mediated by several different mediators, such as TGF-β1, platelet-derived growth factor, fibroblast growth factor, andTNF-α [45, 46].
In 2008 Duru et al.  evaluated the contribution of oxidative stress to cyclosporine-induced nephrotoxicity and the protective role of high dose NAC in a rat model. In this study, Wistar albino rats were divided into four groups (n = 7 in each) in which group 1 rats were treated with sodium chloride (control group), group 2 rats received cyclosporine [15 mg/kg/day subcutaneous (s.c.) for 10 days], group 3 rats received NAC [150 mg/kg/day intramuscular (i.m.) for 11 days] initiated 1 day before the cyclosporine injection and then together with cyclosporine, and group 4 rats received NAC alone (150 mg/kg/day i.m. for 10 days). On day 10 of cyclosporine therapy, the animals were sacrificed and blood samples collected for the analysis of BUN, serum creatinine, MDA and NO levels, as well as SOD and GSH-Px activities. Kidney tissue sections were evaluated for histopathological findings, MDA and NO levels, and SOD and GSH-Px activities.
The results showed that the treatment of rats with cyclosporine alone produced significant increases in NO and MDA levels and significant decreases in SOD and GSH-Px activities in the serum and renal samples. In this group of rats, morphological changes, such as tubular epithelial atrophy, vacuolizations, and cellular desquamations, were clearly observed. Co-administration of NAC with cyclosporine improved renal function, as exhibited by lower serum creatinine and BUN values. NAC-treated rats consequently showed a significant reduction in MAD and NO levels and increased SOD and GSH-Px activities in serum and renal tissue, and NAC apparently provided a protective histological manifestation against cyclosporine-induced nephrotoxicity. The authors concluded that the mechanism for cyclosporine-induced nephrotoxicity may be secondary to free oxygen radicals and that the protective effects of NAC may related to anti-oxidative and radical-scavenging effects .
The possible role of NAC in th prevention of cyclosporine-induced renal damage was investigated using biochemical and histopathological parameters . Thirty-two rats were randomly assigned to control (saline treated), cyclosporine (20 mg/kg/day, i.p.), NAC alone (20 mg/kg/day, i.p.), and cyclosporine + NAC (20 mg/kg/day, i.p) groups. Cyclosporine caused a significant increase in serum creatinine, urea, uric acid, and BUN levels; these effects were significantly ameliorated by NAC administration. The authors also observed a significant decrease in total antioxidant level in serum and kidney following cyclosporine treatment which was prevented by NAC co-administration. The histopathological evaluation revealed that cyclosporine caused severe glomerular atrophy, blood vessel thickening, and moderate tubular necrosis, all of which were significantly prevented by NAC .
Thus, the concomitant use of NAC-like antioxidants may provide protection against cyclosporine nephrotoxicity. However, this theory needs to be investigated in more detail.
NAC and MTX
Methotrexate is a folic acid antagonist which is widely used for treatment of malignant cancers, such as those of the blood, lymph, breast, uterus, and some non-malignant diseases including rheumatoid arthritis or psoriasis. Renal toxicity and tubular morphological changes are the most serious toxic effects of MTX. The pathogenesis of MTX-induced nephrotoxicity is believed to be mediated by the precipitation of MTX and its metabolites into the renal tubules or via a direct toxic effect of MTX on the renal tubules. It is believed that the metabolites of MTX may affect membrane permeability and endostotic activity [49–51].
Çağlar et al. recently investigated the protective effect of NAC against MTX-induced nephrotoxicity . They divided 15 rats into three equally sized groups, with one group receiving MTX alone (18 mg/kg/day, i.p.), one group receiving MTX (300 mg/kg/day, i.p.) + NAC (18 mg/kg/day, i.p.), and one group receiving normal saline (control group, with the treatment lasting 3 days in all groups. The histological evaluation revealed that MTX principally induced prominent large vacuolization in the proximal convoluted tubule cells and focal thickening in the glomerular basal lamina of some glomeruli. A decrease in tissue SOD and GSH-Px and an increase in serum urea nitrogen, serum creatinine and tissue MDA levels were also detected following MTX therapy. All of these changes were significantly reversed, and most of vacuoles in the proximal convoluted tubule cells disappeared following NAC administration .
The effects of NAC on MTX-induced nephrotoxicity require more evaluation in future studies in order to confirm these findings.
NAC and gentamicin
Aminoglycosides are antibiotics used in the clinical setting for the treatment of serious infections due to Gram-negative bacteria . Nephrotoxicity due to aminoglycosides occur in 10–20 % of therapeutic regimes. A main part of gentamicin-induced nephrotoxicity is related to its tubular effect which is triggered by drug accumulation in the epithelial tubular cells. Gentamicin acts on mitochondria and induces oxidative stress and apoptosis. Ultimately, gentamicin causes glomerular congestion, the generation of renal free radicals, reduction in antioxidant defense mechanisms, and acute tubular necrosis [53–55].
In 2001 Mazzon et al.  evaluated the protective effect of NAC against gentamicin-mediated nephropathy based on both biochemical and morphological parameters. These authors divided 40 rats into four equally sized groups, including a control group which received a daily s.c. injection of 0.5 ml isotonic saline for 5 days, a control + NAC group which received a daily s.c. injection of 0.5 ml isotonic saline + 10 mg/kg/day i.p. injection of NAC for 5 days, a gentamicin group which received gentamicin sulfate 100 mg/kg/day s.c. in 0.5 ml of saline solution for 5 days, and a gentamicin + NAC group which received gentamicin sulfate 100 mg/kg/day s.c. in 0.5 ml of saline solution + 10 mg/kg/day i.p. injection of NAC for 5 days. Renal function was evaluated based on the light microscopy examination, immunohistochemical assay, and laboratory parameters (such as urine and serum creatinine, creatinine clearance, fractional excretion of sodium and lithium, urinary excretion of gamma glutamyltransferase, and daily urine volume). These authors also assessed myeloperoxidase activity, MDA concentration, and nitrotyrosine formation in the kidney. The results showed that the gentamicin-treated group had significantly reduced creatinine clearance and increased blood creatinine levels, fractional excretion of sodium and lithium, urine gamma glutamyltransferase, and daily urine output. A significant increase in kidney myeloperoxidase activity, lipid peroxidation, nitrotyrosine formation, poly (ADP-ribose) synthase activation, and proximal tubular necrosis was also detected in gentamicin-treated rats. Previous biochemical and histopathological parameters were normalized following NAC administration. In addition, NAC significantly prevented the gentamicin-induced tubular necrosis. Based on these results the authors proposed that NAC exerts its nephroprotective effects against gentamicin-induced nephropathy by interaction with peroxynitrite-related pathways. NAC ameliorated nephrotoxicity development, morphological injury, neutrophil infiltration, and renal clearance disturbance and significantly reduced myeloperoxidase activity, kidney MDA levels, nitrotyrosine staining and poly (ADP-ribose) synthase expression following gentamicin administration .
In a similar manner, Gupta et al.  investigated the efficacy of the combination of NAC and desferrioxamine (DFX) in the prevention and treatment of gentamicin-induced acute renal failure (ARF) in a rat model. For this purpose male Wistar rats were randomly divided into five groups (7 animals in each group), namely, (1) saline, (2) gentamicin, (3) gentamicin + NAC, (4) gentamicin + DFX and (5) gentamicin + NAC and DFX. These groups were further subdivided in two arms of the study: prevention and treatment. Blood creatinine and urea concentrations were considered as markers of renal function, and oxidative stress and lipid peroxidation were also evaluated. In the prevention protocol, animals received gentamicin (70 mg/kg i.p. every 12 h for 7 days) + NAC (20 mg/kg s.c. every 8 h for 7 days) and/or DFX (20 mg/kg s.c. on first, fourth and seventh days). In the treatment protocol, animals were first treated with gentamicin and then with antioxidants (NAC and/or DFX at the same doses and duration of administration as in the prevention protocol) 4 days after the gentamicin treatment.
The results showed that the NAC + DFX combination was superior to either agent alone in preventing gentamicin-induced nephrotoxicity. This effect primarily could be described by the cumulative antioxidant effects of NAC and DFX and could be secondary to the competitive binding of DFX and iron that impedes iron–gentamycin binding and free radical generation. In addition, DFX was able to decrease NAC iron-depended oxidative metabolism. This combination attenuated kidney oxidative damage for the treatment of gentamicin-induced ARF but did not improve blood creatinine levels. It appeared that the use of NAC alone was superior to the NAC–DFX combination in the treatment protocol .
These are the only two animal studies which have evaluated the effects of NAC in the prevention and treatment of aminoglycoside-induced nephrotoxicity. The results of these studies support the protective role of NAC in gentamicin-induced kidney injury. More animal and human studies are required to confirm these findings.
NAC and vancomycin
Vancomycin has been used more frequently in the recent years following the increase in the incidence of methicillin-resistant Staphylococcus aureus and S. epidermidis infections . Although the exact mechanism of vancomycin-induced renal toxicity is not well understood, the results of animal studies suggest that vancomycin has oxidative effects on proximal renal tubule, increases cell proliferation in the renal proximal tubule, stimulates oxygen consumption, elevates cellular adenosine triphosphate concentrations, and produces oxygen free radicals leading to the injury [59, 60].
The beneficial effects of caffeic acid phenethyl ester (CAPE), vitamin C, vitamin E, and NAC on vancomycin-induced nephrotoxicity were examined by Ocak et al.  in a rat model in which six groups of male Wistar albino rats (5 animals in each group) were selected as control (group 1); vancomycin, 200 mg/kg i.p. injection (group 2); vancomycin + CAPE, 10 μmol/kg i.p. injection (group 3); vancomycin + 1 g vitamin C in drinking water (group 4); vancomycin + 1,000 mg/kg vitamin Ei.m. injection (group 5); vancomycin + NAC 10 mg/kg i.p. injection (group 6). CAPE, vitamin C, vitamin E, and NAC treatments were repeated at 24-h intervals for 8 days. Vancomycin administration was started 1 day after the first dose of these agents and was continued for 7 days. Laboratory parameters, including BUN, serum creatinine, MDA, and NO levels, as well as catalase activity were measured in the homogenized kidney tissue. In this study vancomycin significantly increased kidney MDA and NO levels and significantly decreased catalase activity in comparison to the control group. All of the antioxidants in this study effectively suppressed MDA and NO levels. The co-administration of vitamin E, vitamin C, NAC, and CAPE decreased BUN levels, although significant differences were detected only in the vitamin E- and vitamin C-treated groups. NAC decreased MDA, NO, and plasma creatinine levels.
Overall, the results showed that vitamin E was the most effective agent in the prevention of vancomycin-induced renal damage, followed by vitamin C, NAC, and CAPE, in that order . However, the protective effects of NAC in the prevention of vancomycin-induced nephrotoxicity must be confirmed in the future randomized clinical trials.
NAC and colistin
Colistin is a cyclic cationic polypeptide antibiotic which has re-introduced onto the market with the increased incidence of infections caused by multidrug-resistant Gram-negative bacteria. Nephrotoxicity is the most common side effect of this drug, with a reported incidence of colistin-induced nephrotoxicity of 7.4–45 % . The mechanism responsible for colistin-induced nephrotoxicity is unknown but is mainly related to the induction of acute tubular necrosis. The proposed mechanisms for this effect are increases in tubular epithelial cell membrane permeability and the influx of cations, anions, and water, causing a local disturbance of the outer membrane [63, 64].
Ozyilmaz et al.  evaluated the protective effects of NAC on colistin-induced nephrotoxicity and reperfusion-induced ischemia in a rat model. In this study, 18 female Sprague–Dawley rats were randomly divided into three groups (6 in each group) consisting of a group receiving 1 ml/kg/day i.p. saline (control), a group receiving 300,000 IU/kg/day i.p. colistin, and a group receiving 300,000 IU/kg/day i.p. colistin + 150 mg/kg/day i.p. NAC; all treatments were for 6 days. The plasma levels of BUN, creatinine, and TNF-α, urine levels of protein and creatinine, and tissue SOD and MDA levels were measured at 24 h after the last injection. The potential role of oxidative stress in colistin-induced nephrotoxicity was evaluated by two enzymatic markers of tissue injury which induce NO synthesis [endothelial NOS (e-NOS) and inducible NOS (i-NOS)].
The results showed that colistin caused a significant increase in plasma BUN and creatinine levels and to some extent in renal tissue SOD. NAC reduced renal tissue SOD level, but its effect on biochemical parameters was not significant. NAC also reversed the immunocytochemical staining of i-NOS and neurotrophin-3, which is a well-known marker of tissue injury.
Based on these results, it would seem that colistin-induced nephrotoxicity may be related to oxidative stress and that the beneficial effects of NAC may be attributed to its antioxidant properties . This study was the first to investigate the protective effect of NAC on colistin-induced nephrotoxicity. Further research is warranted to distinguish the possible effects, appropriate dose, and duration of NAC therapy on colistin-induced nephrotoxicity in human subjects.
NAC and amphotericin B
Amphotericin B is a potent antifungal agent used for the treatment of several mycotic infections . Its major dose-limiting side effect is nephrotoxicity. Two major hypotheses for the pathogenesis of amphotericin-related nephrotoxicity are the direct effects of the drug on epithelial cell membranes and vasoconstriction. Amphotericin may lead to changes in tubular cell permeability, potassium wasting, decreased medullary tonicity, and diminished acidification capacity. Renal vasoconstriction plays a major role in renal ischemia and tubular damage [66, 67].
The possible renoprotective effect of NAC on amphotericin-mediated kidney injury was evaluated in a rat model by Feldman et al.  in 2005. These authors induced AKI in 30 Sprague–Dawley male rats with a single i.p. injection of amphotericin B (50 mg/kg). The rats were then divided into two equally sized groups, with one group receiving NAC 10 mg/kg in 1.0 ml of isotonic saline daily for 4 days, starting 1 day before amphotericin B injection, and the second group (control) receiving a daily i.p. injection of 1.0 ml isotonic saline for 4 days, starting 1 day before the administration of amphotericin B, as in group 1. Further assessments were based on an evaluation of GFR using 99 m-technetium diethylene triaminepentaacetic acid and histopathological examination. A 24-h urine sample was collected for the analysis of sodium, potassium, and magnesium determination before and following amphotericin B administration.
The results showed the GFR had significantly decreased in both groups of rats at 4 days after the administration of amphotericin B. The authors also reported that the NAC-administrated group had a significantly higher GFR than the control group. Histopathological data showed that signs of acute tubular necrosis were attenuated in the NAC-treated group. These results proved a relative preservation of tubular structure in the NAC group with no protective effects on tubular function, as exhibited by a similar daily urine output and excretion of sodium, potassium, and magnesium in both study groups, suggesting that NAC does not prevent the possible direct toxic effect of amphotericin on renal tubular cells. As a result the authors reported that NAC may be capable of preventing amphotericin-induced reduction in renal function by both improving renal hemodynamics and preventing oxidative tissue damage .
Odabasi et al.  evaluated the ameliorative effects of NAC in amphotericin B-induced renal tubular apoptosis and nephrotoxicity in a murine model. These authors administered amphotericin B deoxycholate (10 mg/kg/day i.p.) to all rats concomitantly with three doses of NAC daily at 30, 60, or 120 mg/kg, respectively (i.p. injection) (3 treatment groups) or sterile water (control group) for 5 days. The results showed that concomitant NAC at any dose significantly decreased levels of apoptosis due to amphotericin B .
To confirm the renoprotective effects of NAC, we suggest that clinical studies need to be performed.
NAC and NSAIDs
Non-steroidal anti-inflammatory drugs are the most widely used analgesic drugs worldwide . Nephrotoxicity due to NSAIDs still remains a concern and is mediated via the inhibition of protective prostaglandin synthesis and, consequently, vasoconstriction in the vascular bed and acute tubular nephritis [70–73].
Efrati et al.  evaluated the renoprotective effects of NAC in a rat model of NSAID-induced ARF. ARF was induced in 40 Sprague–Dawley male rats by 3 days of water deprivation and 3 additional days of i.p. diclofenac administration at a dose of 15 mg/kg/day. The animals were randomly divided into four equally sized groups (n = 10): group1, deprived of water for 6 days combined with i.p. injection of 0.1 ml of 0.9 % saline twice a day; group 2, similar to group1 but also received i.p. injection of NAC 40 mg/kg twice a day on days 4 through 6 of the experiment; group 3, water deprivation for 6 days, combined with 15 mg/kg i.p. injection of diclofenac twice a day on days 4 through 6 of the study; group 4, water deprivation for 6 days, combined with i.p. injection of diclofenac (15 mg/kg) and NAC (40 mg/kg) twice a day on days 4 through 6 of the study. Renal function was evaluated by biochemical tests, including cystatin C, creatinine, urea, potassium, and intrarenal blood flow which measured by laser Doppler. The kidneys were subjected to histopathological examination and evaluation of intrarenal NO, hydrogen peroxide (H2O2) and PGE2.
The results showed that the injection of diclofenac caused a significant increase in the levels of serum cystatin C, creatinine, and urea compared with 6 days of water deprivation without diclofenac treatment. The authors found that the administration of NAC 15 min after the diclofenac injection (group 4) significantly reversed all abnormal renal injury parameters. The histopathological findings proved the positive effects of NAC. In the diclofenac-treated rats, intrarenal medullar blood flow dropped by approximately 51 %; this drop was significantly greater than that observed in rats which received NAC after the diclofenac injection (14 %). A moderate rise in NO concentration was observed in the renal cortex and medullae segments following NAC administration. The histopathological findings showed elevated H2O2 concentration in renal tissues of diclofenac-treated rats, while the H2O2 concentration decreased in NAC-treated animals. Also, renal PGE2 release dropped significantly (about 3-fold in medullae and about 8-fold in cortex) following diclofenac treatment and increased to the control level following NAC administration.
In this experimental model, NAC dramatically improved NSAID-induced deterioration of the renal insult by inducing renal vasodilatation, decreasing intrarenal oxidative stress via inhibition of ROS and, most importantly, restoring renal tissue PGE2 release back to normal levels. The improvement in renal blood flow was not significantly related to the change in renal tissue NO content . Although these physiological, pathological and histological findings support the renoprotective effect of NAC in NSAID-induced nephropathy, additional experimental and clinical studies are needed for confirmation.
NAC and lithium
Lithium is one of the most effective agents for the treatment of bipolar (manic-depressive) disorders, but prolonged therapy has been associated with several forms of renal damage . The postulated mechanisms of lithium-induced nephrogenic diabetes insipidus include inhibition of adenylyl cyclase, decreased density of arginine vasopressin receptors, and dysregulation of the aquaporin system in principal cells of the collecting duct with reduced expression of aquaporin 2. Another probable mechanism has arisen from the observation that lithium can induce cyclooxygenase 2 expression in the kidney medulla via GSK-3 inhibition. The pathogenic mechanisms by which lithium causes tubulointerstitial nephritis and glomerular injury are not well understood. It has been claimed that lithium plays a role in modulation of the inositol monophosphate pathway, which results in decreased inositol levels and inhibition of the cell cycle. Thus, lithium accumulation in the distal nephron through the sodium channel could account for chronic tubulointerstitial damage and minimal change disease [76, 77].
Efrati et al.  investigated the role of NAC in reducing lithium-induced kidney injury in 40 Sprague–Dawley male rats. For inducing AKI these authors used the following protocol: administration of oral 15 % lithium chloride solution for the first week, regular water for second week, 7 % lithium chloride solution for the third week, and regular water for the fourth week. The animals were then divided into two equally sized groups, with one group receiving 10 mg/kg NAC and the other receiving saline, both treatments as two daily i.p. injections. GFR, serum creatinine, BUN, 24 h urinary protein, osmolarity, and histopathological parameters were assessed in this study.
The results showed that the NAC-treated group had a higher GFR and lower serum creatinine and BUN levels compared to the control group. The histological and electron microscopy findings indicated that tubular necrosis and tubular lumen obstruction were lower in the NAC-treated group. However, at the end of the study, urine osmolarity in the NAC-treated group did not differ from that of the control group—apparently because NAC does not exert its renoprotective effect via interference with the accumulation of lithium in the collecting duct .
In conclusion these authors found that NAC treatment had protective role against lithium-induced renal failure in a rat model although further evaluations are needed.
NAC and folic acid
There is as yet no human data available on folic acid-induced renal failure, but some evidence does exist showing that high-dose folic acid supplementation in humans with CKD may improve endothelial function. Folic acid has also been shown to induce a significant decrease in plasma homocysteine in subjects with moderate to severe CKD [79–84].
The beneficial effects of the three most commonly used regimens of NAC for the prevention of AKI were evaluated in mice–folic acid models by Wang et al. . In the first model (severe), the authors induced AKI by the i.p. injection of 350 mg/kg of folic acid in Ouybred male mice. The mice were then divided into four groups: the pretreatment group (n = 15) received a s.c. injection of 300 mg/kg NAC at 24 and 6 h prior to the folic acid injection; the post-treatment group (n = 12) received 300 mg/kg NAC at 6 and 24 h after the folic acid injection; the pre- and post-treatment group (n = 15) were both treated with 300 mg/kg NAC at 24 and 6 h before folic acid treatment and at 6, 24, and 48 h post-folic acid injection; the control group received vehicle only using the pre- and/or post-treatment protocol.
In the milder AKI or lower dose of folic acid model, AKI was induced by i.p. injection of 250 mg/kg of folic acid, and the treatment and control groups (12 animals in each) were as described above for the severe model. Blood samples were drawn from all animals 4 days before the folic acid injection (baseline measurement) and on days 1, 2, 3, and 7 after the folic acid injection. Plasma concentrations of creatinine, cystatin C, and reduced GSH were measured. In addition to kidney MDA content and histological findings, survival time was assessed up to 7 days post-intervention.
The results showed that the survival rates were significantly better in the NAC pretreatment mice than in the post-treatment (73.33 vs. 46.67 %, respectively) and that AKI occurred significantly less in the former than in the placebo group. Interestingly, compared to the control group, AKI incidence was significantly more common and survival rate was significantly less common in the post-treatment group . Histological findings showed that GSH levels slightly decreased in the NAC pretreatment group compared with the placebo at the beginning but increased at day 2. GSH levels did not increase in the NAC post-treatment group.
NAC neither significantly improved nor worsened renal function in the model of milder AKI, although NAC pretreatment was effective in reducing the incidence and severity of AKI as well as increasing survival time. The authors therefore proposed that only NAC pretreatment is able to increase GSH in both mild and severe models. These results show that the protective effect of NAC is apparently related to the replenishing depleted GSH, whereas the harmful effect might be due to NAC’s pro-oxidative actions in the setting of injury and inflammation .
NAC and alcohols
Rhabdomyolysis-induced renal injury accounts for about 10–40 % of all cases of ARF. The intramuscular administration of hypertonic glycerol in the rat model induces myolysis and hemolysis which is widely used as a model of heme protein-induced renal injury. Heme protein-induced renal injury is due to a combination of factors, including severe intrarenal vasoconstriction, heme-mediated oxidant injury to tubular cells, and obstruction of distal tubules by casts of acid hematin. Additionally, the binding of NO to the heme group of myoglobin and hemoglobin would lead to a decrease in NO activity and also to a decrease in NO oxidation to nitrite. Moreover, the heme-iron-driven hydroxyl radical (·OH) generation is a critical mediator of the evolving tubular damage. Intrarenal hemodynamic changes which caused endothelium damage due to ischemia are also considered as important pathogenic events in the early phase after glycerol administration [86–88].
Kim et al.  investigated the role of NAC as an antioxidant in the prevention of myoglobin-induced AKI in glycerol-induced rhabdomyolysis in a rat model. Two major pathways, including c-Jun N-terminal kinase (JNK) and p38 are associated with the induction of apoptosis in the response to environmental stress. Induction of the balance between cell survival and apoptosis can be established through the activation of the extracellular signal-regulated kinase and JNK/p38 kinase pathway. These MAPKs determine the outcome of the renal tubular cells. The authors claimed that rhabdomyolysis decreases the renal anti-oxidant reserves and that these changes are associated with the expression of the MAPK regulatory pathways leading to signaling of renal tubular apoptosis. They proposed that NAC plays a major renoprotective role through controlling the signaling pathway and renal tubular apoptosis.
In their study, male Sprague–Dawley rats were deprived of water for 16 h before receiving an injection of glycerol. They were then divided into four groups: a control group (n = 7), which received normal saline (8 ml/kg i.m.) and three treatment groups (n = 7 in all groups) which were treated with 150 mg/kg NAC administered as an intravenous (i.v.) injection, 8 ml/kg of 50 % glycerol administered as an i.m. injection, or150 mg/kg NAC administered as an i.v. injection 30 min prior to glycerol administration. The results showed that glycerol induced severe kidney injury with marked renal oxidative stress, leading to a significant elevation in BUN and serum creatinine levels. Kidney tissue GSH depletion, increase in the number of apoptotic cells, and activation of JNK and ERK were also detected following glycerol injection. The histopathological evaluation showed cast formation, tubular necrosis, and expression of signal-regulatory kinase. The authors concluded that the increase in BUN and serum creatinine, morphological injury, and biochemical changes were prevented by NAC .
In another study done by Polo-Romero et al. , AKI was induced by an i.m. injection of glycerol (50 % v/v in sterile saline, 10 ml/kg) in 40y Spraue-Dawley rats which were then divided in four groups. The first group (n = 10) was pretreated with NAC, 10 mg/100g BW i.p. injection, 1 h before the induction of rhabdomyolysis; the second group (n = 10) received an i.p. injection of saline solution (0.9 %) in the same manner as the first group; the third group (n = 10) was treated with NAC 10 mg/100 g BW i.p. injection, immediately after rhabdomyolysis induction; the fourth group (n = 10) received saline solution (0.9 %), at the same dose and injection time as the third group. Variations in serum total antioxidant capacity and GSH reductase activity were evaluated in the study. The critical role of released iron from myoglobin following rhabdomyolysis, which causes the generation of highly reactive free oxygen radicals and tubular cell destruction, was emphasized by the investigators. NAC ameliorated antioxidant activity through an increase in the total antioxidant status and GSH reductase levels in the serum. This effect was much greater when NAC was administered before the induction of rhabdomyolysis, which had a more significant effect on GSH reductase levels than total antioxidant status .
Based on the results of these two studies, it can be assumed that NAC is a potential agent for prevention of rhabdomyolysis-induced AKI, but this must be confirmed in future clinical studies.
The administration of ethanol (10 ml/kg) orally to fasted mice induced extensive renal failure following the production of free radicals . The effects of chronic ethanol exposure on renal function and oxidative stress-related parameters in the kidney have been also evaluated. In one study , chronic ethanol exposure (1.6 g/kg/day) did not show any significant changes in the relative weight of kidneys, serum calcium level, or GSH S-transferase activity. However, urea and creatinine concentration in the serum and the level of thiobarbituric acid reactive substance (TBARS) in the kidney was significantly elevated after 12 weeks of ethanol exposure. Elevated TBARS levels indicate that prolonged ethanol consumption increases lipid peroxidation in the kidney . The authors of another study reported a rise in serum urea and creatinine levels and a significantly reduced GSH concentration after the administration of 5 g/kg/day ethanol for 60 days in rats . Ethanol oxidation by the kidney in chronic ethanol-treated rats suggests a pathogenic role for acetaldehyde in the nephrotoxic effect of ethanol ingestion. Also, increased ROS, partly generated from acetaldehyde oxidation, may contribute to the oxidative stress .
In contrast to previous results, antecedent ethanol exposure by single bolus i.p. injection in rats was found to protect the kidneys against IRI by enhancing antioxidant capacity and preventing lipid peroxidation .
NAC is protective against ethanol-induced lipid peroxidation by attenuation-increased oxidative stress parameters such as MDA and NO, and restoration diminished antioxidant enzymes and substances such as GSH-Px, catalase, SOD, and GSH .
Methanol toxicity is a significant problem in substance abusers. The primary metabolic pathway of methanol is oxidation to formaldehyde and formate. This process is accompanied by an elevation of in nicotinamide adenine dinucleotide (NADH) level and the formation of superoxide anion and H2O2. Methanol toxicity is also associated with the increased production of oxygen radicals due to mitochondrial damage and increased microsomal proliferation. All of these factors have an essential role in lipid peroxidation. The production of formaldehyde and free radicals during methanol intoxication (3 g/kg) in rats has been found to cause modification of proteins and lipid molecules and the inhibition of GSH-Px and GSH reductase activities . Hemolysis and myoglobinuria are other contributing factors in renal injury following methanol intoxication .
NAC with free sulfhydryl groups have been found to directly react with electrophilic compounds such as formaldehyde and free radicals. NAC also inhibits the formation of extracellular reactive oxygen intermediates. In one study, after methanol ingestion NAC diminished lipid peroxidation, elevated the GSH level in the liver and erythrocytes, and increased the activity of GSH-related enzymes in the serum, erythrocytes, and liver .
NAC and volatile anesthetic agents
Volatile anesthetics are powerful modulators of inflammation and IRI in several organs, such as heart, lung, liver and kidney.
Data on the renal safety of volatile anesthetics are very conflicting. Obal et al.  reported that the administration of desflurane during early reperfusion protects against IRI in rats. On the other hand, methoxyflurane-induced interstitial fibrosis and chronic renal failure have been reported in a number of studies. Two phases were described for methoxyflurane-induced nephrotoxicity: an acute phase characterized by a vasopressin-resistant polyuria and renal failure (possibly due to toxic concentrations of fluoride) and a chronic phase in which renal failure persists and interstitial fibrosis becomes evident (possibly secondary to oxalic acid crystal deposition). This agent was subsequently withdrawn from the market due to renal injury .
Protective effects of isoflurane against renal IRI in mice have been reported [100, 101]. Isoflurane activates HIF-1α (a transcription factor) which mediates a highly conserved adaptive mechanism for oxygen homeostasis in all mammalian cell types and protects them against oxygen deprivation . Isoflurane also significantly attenuates renal IRI in mice by reducing inflammation and modulating leukocyte influx [100, 103].
Degradation of sevoflurane produces Compound A (penta fluorisoprenyl fluoromethyl ether), a vinyl halide which is an inorganic fluoride that causes necrosis of the renal tubules at the corticomedullary junction in rats. However, to date, there is no evidence showing an association between inorganic fluoride metabolites and sevoflurane-induced renal injury in human subjects [104, 105].
The renoprotective effect of NAC against IRI when administered early after anesthesia induction with isoflurane has been evaluated. Eighteen rats were administered isoflurane and then randomly divided into a NAC (300 mg/kg i.v.) group or a control (saline) group. After 30 min, the investigators performed a right nephrectomy, and the left renal artery was clamped for 45 min to induce ischemia, following which the renal artery was unclamped. Variation in serum creatinine and tubular necrosis after 48 h of reperfusion was significantly lower in the NAC group . Studies on renal IRI following ischemic preconditioning in rats demonstrated beneficial nephroprotective effects when isoflurane was administered associated with remifentanil .
Drug-induced AKI is a major cause of patient mortality and morbidity. Several options, such as drug dose adjustment, hydration, and avoidance of nephrotoxic agents, have been suggested to prevent or ameliorate drug-induced nephrotoxicity. This review focused on the effects of NAC as a known and potent antioxidant in the prevention of drug-induced kidney injury in experimental models. The protective effects of NAC may be related to its ability to reduce oxidative stress by either directly interfering with the oxidant molecules and ROS due to its scavenging properties or up-regulating antioxidant systems, such as SOD and GSH-Px. Some researchers also assume anti-apoptosis properties for NAC. Most of the evidence originates from animal and in vitro cellular models, which make it difficult to extrapolate the results to human subjects. Also, in the most studies serum creatinine was used as a marker of renal function. The accuracy of serum creatinine for the detection of AKI is questionable due to either false positives (true tubular injury but no significant change in serum creatinine) or false negatives (absence of true tubular injury, but elevations in serum creatinine due to pre-renal causes) [107, 108]. The emergence of numerous renal tubular damage-specific biomarkers offers an opportunity to diagnose AKI at an early time point, to facilitate the differential diagnosis of structural and functional AKI, and to predict the outcome of established AKI. The most promising AKI biomarkers include plasma and urinary neutrophil gelatinase-associated lipocalin, urinary interleukin-18, urinary liver-type fatty acid binding protein, cystatin C, and urinary kidney injury molecule [109–117].
Other concerns regarding the studies are dose, route, and time of NAC administration. Following a constant 24 h infusion of 4.2 mg/kg/h of NAC in infants, the steady state concentration (Css) of NAC was 0.51 mM . In comparison, the Css of NAC at a dose of 200 mg i.v. and 400 mg orally in healthy subjects was 0.037 mM , and that in another study with an infusion rate of 125 mg/kg/h for 15 min followed by 25 mg/kg/h was 0.9 mM . Very similar values of steady-state plasma concentrations of NAC have been reported in the pediatric use of the drug (0.51 mM) . The wide range of the Css of NAC found in healthy adults may be due to the use of different pharmacokinetic analysis programs .
Some studies have evaluated the total NAC concentration; however, the value probably does not reflect its true pharmacokinetics in vivo. Total NAC consists of free reduced and oxidized forms, disulphides, and mixed disulphides with other low-molecular-weight thiols, such as cysteine and GHS. As NAC acts primarily as a precursor of cysteine, only the free reduced form can diffuse through the cell and be deacetylated to cysteine. Hence, the plasma concentration of total NAC at any time may not be a reliable indication of its biological activity [31, 121].
Marenzi et al.  conducted a clinical study with the aim of gaining an understanding of the dose–response relationship of NAC. They investigated the effect of NAC in the prevention of contrast medium-induced nephropathy in patients undergoing primary angioplasty. The patients were randomly assigned to receive NAC at a standard dose (standard-dose group), at a double dose (high-dose group), or placebo (control group). Patients in the standard-dose group received an i.v. bolus of 600 mg of NAC before primary angioplasty and a 600-mg dose orally twice daily for the 48 h after intervention (total dose of NAC 3,000 mg). Patients in the high-dose group received an i.v. bolus of 1,200 mg of NAC before intervention and 1,200 mg orally twice daily for the 48 h after intervention (total dose of NAC 6,000 mg). After intervention, all treated patients and those in the control group underwent hydration with intravenous isotonic saline. The rate of contrast medium–induced nephropathy was 33 % in the control group, 15 % in the standard-dose group, and 8 % in the high-dose group (P < 0.001). These results show that the incidence of contrast medium-induced nephropathy was significantly lower in patients who received a cumulative dose of 6,000 mg than in those who were treated with a cumulative dose of 3,000 mg of NAC.
In another study in patients with chronic renal failure, high doses of NAC (1,200 mg orally twice daily) showed more nephroprotective effects than standard doses (600 mg orally twice daily) against contrast media agent-induced kidney injury. These studies confirmed the dose-dependent effects of NAC in patients with normal and impaired renal function [122, 123].
In a study conducted by Sandilands et al. , the high peak plasma concentration that resulted from the rapid initial infusion of NAC in cases of Paracetamol poisoning produced nausea and anaphylactoid reactions in about 40 and 20 % of the patients, respectively. Slow infusion of same dose of NAC over 7 h produced a lower peak acetylcysteine concentration and a lower likelihood of nausea and anaphylactoid reactions . Potential benefits of NAC in patients with systemic inflammatory response syndrome (SIRS) or sepsis was recently reviewed in a meta-analysis. In this analysis, NAC did not show any significant effect on the patients’ length of stay, duration of mechanical ventilation, or incidence of new organ failure. Based on the lack of sufficient information on the safety and utility of NAC as an adjuvant therapy in oxidato-inflammatory conditions such as SIRS and sepsis, it can be concluded that NAC is not effective in reducing patients’ mortality and may even be harmful due to cardiovascular depression, especially when administered later than 24 h after the onset of symptoms. However, future studies are needed to confirm this important issue . These important clinical findings can serve as a warning that we should be more cautious when using NAC in clinical settings in comparison to experimental studies.
Whether NAC can be an effective clinical strategy to prevent drug-induced nephrotoxicity or not is a question that remains to be answered in future clinical trials and human studies.
Proposed future research
Further research is needed to determine the appropriate time, route of administration, dose and duration of NAC in prevention of drug-induced nephrotoxicity.
Positive effects of NAC in non-human studies must be confirmed in well-designed human clinical trials with sufficient sample sizes.
Most animal studies support nephroprotective effects of NAC, but whether NAC is effective in the treatment of drug-induced nephrotoxicity or not must be evaluated in future studies.