Oxidative stress induced by the chemotherapeutic agent arsenic trioxide
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Arsenic compounds have been used for medicinal purposes throughout history. Arsenic trioxide (As2O3) achieved dramatic remissions in patients with acute promyelocytic leukaemia. Unfortunately, the clinical usefulness of As2O3 has been limited by its toxicity. The present study was designed to investigate the toxic effects of As2O3 at its clinical concentrations. Experimental rats were administered with As2O3 2, 4 and 8 mg/kg body weight for a period of 45 days and the serum glucose, creatine kinase, lactate dehydrogenase, lipid peroxidation and antioxidant status were measured. As2O3-treated rats showed elevated serum glucose, creatine kinase and lactate dehydrogenase concentrations. Lipid peroxidation product malondialdehyde was found to be produced more in arsenic-treated rats. Reduced glutathione and glutathione-dependant antioxidant enzymes, glutathione-S-transferase and glutathione peroxidase, and the antiperoxidative enzymes, superoxide dismutase and catalase, concentrations were reduced with the As2O3 treatment. All these toxic effects were found increased with the increase in concentration of As2O3. The results of the study indicate that As2O3 produced dose-dependant toxic side effects at its clinical concentrations.
KeywordsArsenic trioxide Antioxidants Lipid peroxidation Glutathione Oxidative stress
Arsenic is widely distributed in air, water and soil in the form of either metalloids or chemical compound (Basu et al. 2001). The most toxicologically potent arsenic compounds are in the trivalent oxidation state (Hughes 2002). Exposure to arsenic occurs via ingestion, inhalation, dermal contact, and the parenteral route (Tchounwou et al. 1999). The health effects that are associated with arsenic exposure include cardiovascular and peripheral vascular disease, developmental anomalies, neurologic and neurobehavioral disorders, diabetes, portal fibrosis, and multiple cancers (Tseng et al. 2003). Haematological abnormalities associated with arsenic intoxication are haemoglobinuria, intravascular coagulation, bone marrow depression, severe pancytopenia, and normocytic normochromic anaemia and basophilic stippling (Ratnaike 2003).
The treatment with low doses of arsenic trioxide (As2O3) caused high rates of complete remission in patients suffering from acute promyelocytic leukaemia (APL) (Wang and Chen 2008). The adverse effects associated with As2O3 treatment include hyperleukocytosis, APL differentiation syndrome, electrocardiographic abnormalities (QTc-interval prolongation), peripheral neuropathy, skin rash, gastrointestinal reactions and hyperglycaemia (Rust and Soignet 2001). Arsenic compounds also showed genotoxic effects; induced gene amplification, inhibit DNA repair, and induce expression of the oxidative stress protein heme oxygenase in mammalian cells (Vega et al. 1995; Keyse et al. 1990).
Due to the toxic side effects of arsenic, it carries significant risks in their therapeutic regiment. The mechanisms of arsenic-induced toxic effects during clinical trials were not fully elucidated. So the present study was performed to understand the toxicological association between biochemical parameters and the blood antioxidant status at different clinically relevant concentrations of As2O3.
Materials and methods
Arsenic trioxide, sodium pyruvate, thiobarbituric acid and triton X-100, phenazine methosulphate, nitroblue tetrazolium were obtained from Sigma-Aldrich (Bangalore, India). l-aspartate, α-oxoglutarate, 2,4-dinitro phenyl hydrazine, nicotinamide adenine dinucleotide (reduced), 1-chloro-2,4-dinitrobenzene (CDNB), 5,5′-dithiobis-(2-nitrobenzoic acid), nicotinamide adenine dinucleotide phosphate and reduced glutathione were purchased from Merck Specialties Pvt Ltd (Mumbai, India). All other chemicals were purchased from Sisco Research Laboratories (Mumbai, Maharashtra, India).
Group 1: Normal Control
Group 2: As2O3 2 mg/kg b.wt
Group 3: As2O3 4 mg/kg b.wt
Group 4: As2O3 8 mg/kg b.wt
The duration of the study was 45 days and the route of administration was daily by oral intubation. At the end of the experimental period, blood was drawn from the orbital sinus of the rat’s eye. Anticoagulated blood was used for the analysis of blood antioxidant status and lipid peroxidation. The blood samples collected in another set of test tubes without anticoagulant were centrifuged at 3,000 rpm at 4 °C for 20 min; the clear serum obtained was used for the biochemical assays.
Analysis of serum glucose, creatine kinase and lactate dehydrogenase
Serum Glucose, Creatine Kinase (CK) and Lactate dehydrogenase (LDH) were detected (Agappe Diagnostic Ltd., Ernakulam, Kerala, India) using semi-auto analyzer (RMS, India).
Analysis of blood antioxidant status and lipid peroxidation
Haemoglobin concentration in blood was determined according to the method of Drabkin and Austin (1932). Superoxide dismutase (SOD) activity was determined by the method of Paoletti et al. (1986). Catalase (CAT) activity was measured in the sample according to the method of Aebi (1984) by measuring the decrease in absorbance of hydrogen peroxide (H2O2) at 240 nm. Glutathione-S-Transferase (GST) activity was estimated by determining the rate of formation of glutathione and CDNB conjugates (Beutler et al. 1986). Glutathione peroxidase (GPx) activity was measured by the method of Paglia and Valentine (1967). Reduced glutathione (GSH) was estimated by the method of Beutler et al. (1963). Malondialdehyde (MDA), a product of lipid peroxidation, was determined by the method of Buege and Aust (1978).
One-way ANOVA followed by LSD post hoc multiple comparison test was used for comparison among the four groups (SPSS/PC+ version 18, SPSS Inc. Chicago, Illinois, USA). Probability (p) <0.05 was considered statistically significant.
As2O3-induced alterations in the serum Glucose, CK and LDH
As2O3-induced lipid peroxidation
Effect of As2O3 on the Blood Antioxidant Status: Normal control (Group I), As2O3 2 mg/kg b.wt (Group II), As2O3 4 mg/kg b.wt (Group III), and As2O3 8 mg/kg b.wt (Group IV)
4.09 ± 0.12
4.68 ± 0.17ac
4.9 ± 0.09ab
5.05 ± 0.11abc
5.87 ± 0.32
5.16 ± 0.2ac
4.47 ± 0.32ab
3.84 ± 0.42abc
1.59 ± 0.13
1.32 ± 0.12ac
0.98 ± 0.14ab
0.75 ± 0.17abc
10.31 ± 0.45
9.12 ± 0.85ac
8.28 ± 0.65ab
7.44 ± 0.47abc
7.94 ± 0.18
7.44 ± 0.11ac
7.12 ± 0.12ab
6.16 ± 0.1abc
2.09 ± 0.11
1.64 ± 0.09ac
1.35 ± 0.09ab
0.76 ± 0.07abc
As2O3-induced alterations in the antioxidant status
The tripeptide GSH was reduced significantly with respect to the control and was noticed in the arsenic-treated groups. As2O3 treatment also decreased the GSH-dependant antioxidant enzymes, GST and GPx, and the antiperoxidative enzymes, SOD and CAT, when compared to the group I control and between the arsenic-treated groups II, III and IV. These reductions in the antioxidant enzyme activities were in accordance with the increase concentration of As2O3 (Table 1).
As2O3 is an effective cancer therapeutic drug for acute promyelocytic leukaemia and has potential anticancer activity against a wide range of solid tumours (Lu et al. 2007). The adverse effects that have been noted in clinical trials of As2O3 are fluid retention, cardiac toxicity, hepatocellular toxicity and electrocardiographic changes (Soignet et al. 2001). The duration of the present study was selected based on the previous clinical study (Huan et al. 2000). They have reported that As2O3 treatment resulted in significant remission in APL patients. The As2O3 concentrations in our study are in the range of clinically available concentrations for anti-leukaemia treatment (Li et al. 2002).
In the present study, the treatment with As2O3 increased the glucose concentration in serum. Miller et al. (2002) reported that trivalent arsenic inhibits the uptake of glucose into cells, gluconeogenesis, fatty acid oxidation and further production of acetyl CoA. Pyruvate dehydrogenase, an enzyme of glucose metabolism, is susceptible to arsenic-induced reactive oxygen species (ROS) generation (Aposhian and Aposhian 2006). The thiol moiety is an important target for arsenic (Flora 2011). The increased concentration of glucose in this study, may be due to the binding of arsenic to the sulfhydryl groups of glucose metabolising enzymes, and thereby blocked the uptake of glucose. The altered blood sugar level may also due to islet cells toxicity, because arsenic administration caused severe pancreatic damage (Mukherjee et al. 2004). In our observation, the treatment with As2O3-induced ROS production, which may reduce insulin production by pancreatic cellular damage, leads to the increased glucose concentration in serum.
As2O3 administration caused myocardial damage and increased release of CK and LDH in serum (Raghu et al. 2009). In our recent report, the As2O3 treatment caused oxidative stress and structural aberrations in the cardiac tissue of experimental rats (Mathews et al. 2013). So the increased concentration of CK and LDH observed in this investigation may be due to the exudation of enzymes from cells to the systemic circulation because of cellular damage induced by the As2O3.
From our observation, it is found that the MDA production in blood is significantly increased with As2O3 treatment. MDA is a marker of endogenous lipid peroxidation. Liu et al. (2001) reported that the treatment with arsenic caused a significant increase in the rate of formation of ROS such as superoxide anion radical, hydroxyl radical and hydrogen peroxide. The toxic potential exerted by these compounds is through their reactivity with sulphur containing compounds and the generation of ROS (Hughes et al. 2011). Arsenic-induced MDA production could be due to the impairment of cells’ natural protective system and could be directly related to the GSH depletion in blood cells (Wang et al. 2006). Higher the rate of MDA production corresponds to As2O3 inversely associated with GSH. Depletion of GSH results in the increased production of arsenic-induced ROS, which may enhance the lipid peroxidation as observed in the present study.
The most significant alteration in the antioxidant defence is the decrease in GSH concentration, and GSH has direct antioxidant activity (Schulz et al. 2000). In this study, As2O3-treated rats showed decreased concentration of GSH and GSH-dependant antioxidant enzymes GPx and GST. This reduction is suggested to be due to the consumption of glutathione while protecting against the arsenic-induced oxidative stress, for maintaining cellular redox status (Hughes 2002). As2O3 administration reduced the antioxidant and antiperoxidative enzyme concentration in liver tissue of experimental rats (Mathews et al. 2012a). GPx and GST play an important role in arsenic detoxification and the arsenic-induced oxidative stress (Thompson et al. 2009). GST utilises GSH as a cofactor, and therefore, the decrease in the activity of GST after As2O3 treatment may suggest coming from the paucity of GSH.
The exposure to arsenic decreased the activities of antiperoxidative enzymes SOD and CAT. The decreased SOD activity in serum suggested that the accumulation of superoxide anion radical might be responsible for increased lipid peroxidation following arsenic treatment (Maiti and Chatterjee 2000). ROS can themselves reduce the activity of the antioxidant enzymes CAT and GPx (Datta et al. 2000). Reduction in the antioxidant and antiperoxidative enzymes during As2O3 treatment may leads to the deposition of arsenic in tissues (Mathews et al. 2012b). SOD catalyses the dismutation of superoxide anions and prevents the subsequent formation of hydroxyl radicals in blood cells (Wang et al. 2006). In the present study, the decreased SOD activity may suggest that the accumulation of superoxide anion radical; might be responsible for increased lipid peroxidation following arsenic treatment as observed by Maiti and Chatterjee (2000). Exposure to arsenic decreased the CAT activity. CAT catalyses the removal of H2O2 formed during the reaction catalysed by SOD (Lee and Ho 1995). In the present study, the decreased CAT activity indicates the impaired ability to detoxify H2O2 and may leads to the accumulation of H2O2 and thereby oxidative stress.
In the current investigation, As2O3 treatment at its clinically different concentrations induced toxic effects by varying the blood glucose, CK, LDH and the oxidative status. As2O3-induced oxidative stress and the lipid peroxidation may be due to the reduced activity of GSH and GSH-dependant antioxidant and antiperoxidative enzymes. We also suggest that further studies are necessary for identifying the cellular and molecular mechanism of toxicity of arsenic at its clinical concentrations.
We thank the University Grants Commission, New Delhi for rendering financial support for the study (F. No: 39-683/2010SR) and the award of research fellowship in sciences for meritorious student to Mr. Mathews. V. Varghese (No. F.4-1/2006 (BSR)/11-29/2008(BSR)).
Conflict of interest
The authors declare that they have no conflict of interest.
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