Introduction

Angioedema is a rare but potentially fatal side effect of angiotensin-converting enzyme inhibitor (ACEi) treatment. A recent systematic review by Aygoren-Pursun et al. found a prevalence between 0.12% and 0.3% [1]. In a recent retrospective cohort study by Do in heart failure patients starting ACEi, the incidence of angioedema was 3.27 per 1000 person years (PY) in the first year of treatment with a higher incidence in patients of African descendance (6.24 per 1000 PY) and women (5.16 per 1000 PY) [2]. The incidence was the highest in the first 30 days of treatment. These data confirm earlier findings of Reichman et al. [3]. The prevalence of mortality associated with drugs was 136 cases (8%) according to Kim et al. [4••]. Although this is a quite well-known side effect, diagnosis of angioedema caused by ACEi can take up to several years and is often mistaken for allergic symptoms despite the absence of urticaria or other symptoms of anaphylaxis. Consequently, treatment often consists of antihistamines and corticosteroids, which are considered to be not effective [5]. Since ACEi–induced angioedema can lead to life-threatening symptoms, more effective treatment is warranted. In this article, we will discuss clinical presentation, pathophysiology, and current developments in treatment.

Clinical Presentation

Usually, angiotensin-converting enzyme inhibitor–induced angioedema (ACEia) presents itself as swelling without urticaria, most prevalent in the face, lips, tongue, the floor of the mouth, and the upper airways, leading to hoarseness, inability to swallow, and difficulty of breathing. Other manifestations of angioedema, such as gastrointestinal or genital swellings, are rarely caused by ACE inhibitors [6]. The differential diagnosis of solitary angioedema includes hereditary or acquired C1 inhibitor deficiency, hereditary angioedema (HAE) with normal C1-inhibitor (former nomenclamenture HAE type III), angioedema caused by other drugs, and eosinophilic disorders such as Melkersson-Rosenthal’s syndrome. When urticaria is present, an allergic cause is more likely [6].

The major risk of angioedema occurring in the head and neck region is a compromised airway. While swelling of the lips and/or mucosa in the oral cavity is usually harmless in this respect (given that the patient is able to breathe through the nose), edema of the pharynx and especially larynx is potentially life-threatening. Indeed, several authors have described asphyxiation as a result of angioedema, for example, in patients with HAE [7,8,9]. At the level of the vocal cords, the larynx represents the narrowest part of the upper airway. As such, a subtle mucosal swelling already gives rise to a significant reduction of the airway lumen. Therefore, the airway should always be evaluated by an ear-nose-throat (ENT) specialist in case of angioedema.

Several signs and symptoms indicate (relevant) edema in the upper airway, such as increased breathing frequency, use of accessory muscles of respiration, audible breathing, or even stridor. As the oxygen saturation will deteriorate only in the later stages of respiratory failure, it is dangerous to rely on a good saturation alone. In case a patient has signs of impaired breathing due to laryngeal edema (as confirmed with laryngoscopy), intubation might be necessary. In milder cases, admitting a patient for close observation and repeating the laryngoscopy after several hours can be sufficient.

Pathophysiology

Etiology of Angioedema

Angioedema can be driven by the contact activation route or by inappropriate release of histamine. The latter form, which is usually associated with urticaria and/or anaphylaxis, is primarily seen in allergic reactions and is beyond the scope of this review. The contact activation system consists of the zymogens factor XII, prekallikrein, high molecular weight kininogen, and factor XI. Factor XII is able to autoactivate through a conformational change following contact with negatively charged surfaces, e.g., glycosaminoglycans, mast cell heparin, inorganic polyphosphates, and misfolded proteins [10,11,12,13,14].

Activated factor XII is the initiator of the contact activation route, but it is also able to activate the intrinsic coagulation pathway, the fibrinolytic pathway, and the classical complement pathway. The contact-driven forms of angioedema occur as a result of either uncontrolled formation or inadequate degradation of the nonapeptide bradykinin (BK). BK is released after proteolytic cleavage from its precursor high molecular weight kininogen (HK) by kallikrein (KK) which in turn is cleaved from prekallikrein by factor XIIa (Fig. 1 see image) [15]. BK produces its effect through stimulation of the G-coupled receptors and the BK2-receptors (and subsequently, its proteolytically cleaved form desargylated BK through the BK1 receptor) [16]. Release of BK results ultimately in smooth muscle cell relaxation, vasodilation, and increased vascular permeability, most notably of the postcapillary venules [17••]. These processes are mediated by nitric oxide and prostaglandines. Uncontrolled formation of BK is typically seen in patients with C1 inhibitor deficiency (such as HAE), a condition that is characterized by impaired inhibition of both the classical complement pathway and the contact activation route (through impaired inhibition of factor XIIa and kallikrein [KK]). Angioedema can also occur due to inadequate degradation of BK, besides excessive formation. BK has a very short half-life of ± 17 s as it is rapidly metabolized by various metalloproteinases, such as ACE (also known as kininase II), carboxypeptidase N (kininase I), neutral endopeptidase (NEP), aminopeptidase P (APP), and—to a lesser extent—also dipeptidyl peptidase IV (DPPIV) [18].

Fig. 1
figure 1

BK is released after proteolytic cleavage from its precursor high molecular weight kininogen (HK) by kallikrein (KK) which in turn is cleaved from prekallikrein by factor XIIa.

Full size image

Angiotensin-Converting Enzyme

Angiotensin-converting enzyme (ACE) is distributed throughout the vascular endothelium of the body, with the highest concentrations in the lungs [19]. Its main function is cleavage of a dipeptide from angiotensin I, thereby converting it to angiotensin II which is a potent vasoconstrictor when it binds to its receptors. Angiotensin II contributes to the renin-angiotensin-aldosterone axis, which affects the blood pressure through regulation of vascular tonus, sympathetic activity, vagal inhibition, antidiuretic hormone secretion, and tubular sodium secretion. Inhibition of this axis by ACEi has clearly been demonstrated to improve outcomes in congestive heart failure, diabetic nephropathy, hypertension, and coronary artery disease in large-scale trials [20,20,21,23]. The widespread use of ACEi can be explained by the high efficacy, combined with their overall good tolerability.

Risk Factors for Developing ACE-Induced Angioedema

Although any patient using ACEi is at risk for developing angioedema, some individuals may be at particular risk. According to a recent survey among 276,977 new ACEi users, risk factors for developing angioedema were age 65 years and higher, asthma and allergy, COPD, and rheumatoid arthritis, while diabetes seemed a protective factor. Furthermore, the use of calcium channel blockers and NSAID was associated with a higher risk [24]. A smaller study by Hallberg confirmed calcium blockers as a risk factor but also found a significant association with male sex and smoking [25] which is in contrast with the findings by Do et al., showing higher incidence in women and patients of African origin [2].

Treatment

In recent years, several new drugs have been developed for the treatment of HAE which have also been evaluated in patients with ACEia motivated by the assumed similar pathophysiological principle, being the excessive presence of BK. Theoretically, both inhibition of production (ecallantide) and prevention of the binding of BK to the receptor (icatibant) could be of use in ACEia. Likewise, treatment with C1 inhibitor by means of fresh frozen plasma or as C1 inhibitor concentrate could be advocated. We searched the literature for double-blind placebo-controlled trials regarding production inhibitors, bradykinin receptor antagonists, C1 concentrate, and fresh frozen plasma.

Icatibant

Although the earliest reports of icatibant showed improvement of time to relief or resolution of ACEia when compared to an historical cohort or a group of patients that received standard therapy with antihistamines and corticosteroids, this observation could not be confirmed in larger randomized-controlled trials [26, 27, 28•, 29]. Sinert and colleagues randomized a total of 121 ACEia patients to either icatibant or placebo. The primary outcome, time to meeting the discharge criteria, was equal in both groups (median, 4 h) as was the secondary outcome, time to onset of symptom relief (2.0 h versus 1.6 h). A similar observation was reported from the trial performed by Straka et al., as a total of 13 ACEia patients that were randomly assigned to icatibant and 18 patients that received placebo had a similar time to relief of symptoms. Possible explanations for the lack of efficacy in the latter two trials might be the relatively long time between first symptoms and administration of icatibant (7.9 h and 10.3 h, respectively) compared to the first study by Bas, or icatibant’s incapacity to block angioedema formation through activation of the BK1 receptor by desargylated BK.

Ecallantide

Ecallantide is a KK inhibitor with a proven efficacy in hereditary angioedema. [30, 31] It is of note that ecallantide is only licensed in the USA. To date, two randomized controlled trials evaluated the effect in ACEia. The first study, executed by Lewis et al., randomized a total of 79 patients to either placebo, 10, 30, or 60 mg of ecallantide, on top of regular therapy (H1 blockers, H2 blockers, corticosteroids, and/or adrenergic agonists), and not only scoring the Ishoo stage (location of edema) but severity as well [32•]. This study was terminated early since in all treatment arms, more patients than expected achieved the primary end point, which was eligibility for discharge. Ecallantide did not show superiority over placebo in the interim analysis. A subgroup analysis comparing Ishoo stages III and IV and moderate-to-severe symptoms to placebo showed a response rate of 83% while the placebo group reached 50%. Bernstein et al. performed a triple-blind, placebo-controlled study comparing conventional therapy (antihistamines and corticosteroids) plus ecallantide to conventional therapy plus placebo. In the ecallantide group, 31% met discharge criteria within 4 h compared to 21% of the placebo group [33]. In this study, as well as in the study by Lewis et al., the majority of patients had Ishoo class 1. Therefore, ecallantide has no clinically proven efficacy in ACEia in general, but its efficacy in the more severe attacks (Ishoo stages III and IV) remains a matter of debate. From a pathophysiological point of view, inhibition of KK is unlikely to counteract the decreased (desArg-)BK degradation.

C1 Inhibitor Concentrate

To date, no phase 3 clinical studies have been performed with C1 inhibitor concentrate in ACEia. However, several case reports and case series have reported successful outcomes with C1 inhibitor concentrate. The first case report using human C1 inhibitor concentrate (Berinert P) was published by Nielsen et al. in 2006 [34]. It described a 61-year-old female patient that despite treatment with corticosteroids and antihistamines showed progressive symptoms. After a gift of 1500 units of C1 inhibitor concentrate, improvement was seen within 20 min. Several other case reports confirmed successful treatment with C1 inhibitor concentrate [35,35,36,38]. Patients showed improvement on average 88 min and complete resolution in 10.1 h, without the need for other treatment such as intubation or corticosteroids or a second gift of C1 inhibitor concentrate.

Fresh Frozen Plasma

Fresh frozen plasma (FFP) has been used in patients with ACEia with mostly good results, e.g., resolution of complaints or cessation of progression. In 8 case reports and 1 case series, a total of 16 patients were treated with FFP after failure of antihistamines, steroids, and/or adrenaline/epinephrine. So far, no double-blind placebo-controlled trial to evaluate the value of FFP over placebo has been performed [38].

Secondary Prevention

The optimal intervention to prevent patients with ACEia from future attacks is to permanently stop the administration of ACEi. It is of note, however, that ACEia can also recur in the first months after discontinuation of this treatment. Angiotensin II receptor antagonists (ARBs) can be used as a safe alternative in the large majority of ACEia patients as cross reactivity is low and ARBs do not influence BK degradation.

Genetic Susceptibility

In the past years, several groups have tried to identify genetic susceptibility for developing ACEia which could potentially lead to preventive testing as has been proven very effective for example in treatment with Abacavir [39]. A meta-analysis by Mahmoudpour et al. showed that in three smaller studies, SNPs within the XPNPEP2 gene were associated with a lower aminopeptidase P activity and higher risk at angioedema [40]. A GWAS study by the same author showed 8 SNPs within 4 genes that reached the significance level (RBFOX3, GABRG2, SH2B1, and MBOAT1) but not for the XPNPEP2 gene. However, contrary to the first 3 studies, the population study of the GWAS did not contain confirmed angioedema cases but consisted of patients that switched from an ACE inhibitor to an angiotensin II receptor antagonist [41]. A study by Moholisa suggested lower ACE activity as well as B2 receptor polymorphism as a risk factor for developing ACEia. Again, these results need to be confirmed in larger studies [42].

Discussion

Since we have no possibilities to prevent or predict the development of ACEia, we are limited to pharmacological treatment in ACEia patients; as this review shows, developments to date are disappointing. Both KK inhibitors and BK2 receptor antagonists showed no improvement over placebo or usual treatment despite several positive case reports. Two important factors to take into account is that ACE is only one of the many enzymes involved in the elimination of BK and that earlier reports have shown that patients with ACEia have lower activity of APP as well as DPP-IV [43]. Moreover, ACE not only breaks down BK but also substance P, which is also vasoactive. It could therefore well be that the effects of both KK inhibitors as well as BK2 receptor antagonists, which focus on the BK system alone, are too limited to exert clinical relevant effects, while FFP containing both ACE and C1 inhibitor could potentially improve the breakdown of both BK and substance P [44]. Since no randomized-controlled trials have been done with FFP, this point remains to be proven.

In conclusion, to date, convincing evidence warranting the use of KK inhibitors or BK2 receptor antagonists in ACE–induced angioedema is lacking. Fresh frozen plasma could be useful but has not been evaluated in randomized-controlled trials. Pharmacogenetics seems promising but also needs to be evaluated in larger trials.