ACEIs
The primary action of ACE inhibitors is inhibition of ACE activity and thus blockade or reduction in conversion of ang-I to ang-II resulting in decreased stimulation of AT1R receptors. Therefore, ACEIs lead to the reduction of total peripheral resistance, decrease in blood pressure, decreased afterload and thus increased stroke volume. Additionally, ACE inhibition through reduction of ang-II production decrease activation of intracellular signaling pathways from ang-II receptors.
Possible mechanism of ACEIs action in the prevention of AIC include the following: direct modulation of the cardiac and systemic renin–angiotensin system by inhibiting ang-II formation, reducing vascular resistances and then reducing myocardial afterload, indirect action against degradation of bradykinin and consequently enhancing NO synthesis, preserving sarcoplasmic reticulum Ca
2+ homeostasis and thus the contractility of the myocardium [
93‐
95]. In the animal models of AIC, pretreatment or co-treatment with ACEIs led to decrease of mortality, improvement of hemodynamic function, reduction of hypertrophy, decrease in level of serum markers of myocardial damage, or heart failure induced by doxorubicin [
69,
96]. Similar observations have been noted for majority of available ACEIs, however some variations are observed. It is caused mostly by additional functions besides blockade of ACE that results from differences in the chemical structure. Based on their molecular structure ACEIs can be divided into three groups: dicarboxylate-containing agents (enalapril, ramipril, perindopril, lisinopril), sulfhydryl-containing agents (captopril, zofenopril) and phosphonate-containing agents (fosinopril).
Enalapril is probably the most extensively studied ACEI that showed efficacy in preventing AIC in various animal models [
80,
97‐
99], but the data are inconsistent. Generally, enalapril do not protect against acute cardiotoxicity but have protective effect in chronic AIC induced by repeated small doses of Dox administered on a weekly basis [
89]. Enalapril used in the dose of 10 mg/kg/day, for 1 week before, during, and 3 weeks after DOX, significantly attenuated the decrease in percent fractional shortening and prevented the doxorubicin-associated reduction in respiratory efficiency and cytosolic ATP content [
98]. Importantly, enalapril abolished also the robust doxorubicin-induced increase in free radical formation. Interestingly, increase in cardiac apoptosis (measured by caspase-3 and -9 activity) was not significantly attenuated by enalapril [
98]. This stay in line with another study, in which enalapril failed to normalize sub-acute daunorubicin-associated decrease in hemodynamic parameters and did not prevented absolute ventricular mass loss and weight loss [
99]. However, QT prolongation, basal cardiac cell shortening and impaired catecholaminergic response were completely prevented by enalapril [
80,
98]. Those data suggest that enalapril has only limited protective action on early development of anthracycline cardiomyopathy in rats.
The enalapril treatment comes along with increased phosphorylation of Akt and increased activation of PI3K, mTOR, and S6, when compared with Dox-treated mice what suggest that enalapril acts via activation of pro-survival AKT/PI3K pathway [
89]. Enalapril exerts a protective effect not only by decreasing ang-II/AT-1R-mediated responses but also upon improving mitochondrial function in doxorubicin-treated rats and maintaining mitochondrial O2 consumption at control levels, preventing the depletion of cellular ATP content, and lowering the mitochondrial free radical leak [
98]. Pretreatment with ACE inhibitor
captopril or
enalapril significantly reduces the thiobarbituric acid reactive substances concentration in the heart and ameliorate the inhibition of cardiac superoxide dismutase activity, suggesting that captopril and enalapril possess antioxidative potential that may protect the heart against doxorubicin-induced acute oxidative toxicity. This protective effect might be mediated, at least in part, by the limitation of culprit free radicals and the amelioration of oxidative stress [
100]. Captopril contains in its structure a thiol and sulfhydryl group and thus can act as a free radical scavenger because sulfhydryl compounds are able to neutralize oxygen radicals by either a hydrogen donating or electron transferring mechanism [
101].
Perindopril (2 mg/kg/day) used concomitantly with doxorubicin in Wistar rats did not improve DOX-induced heart dilatation, but enhanced antioxidant defense [
102]. No improvement in cardiac function when treated with perindopril may be caused by too short treatment period or inappropriate animal model because rats in this study did not develop typical cardiotoxicity but rather mild cardiac dysfunction.
Zofenopril is an angiotensin-converting enzyme inhibitor characterized by a remarkable uptake by cardiac tissue, producing a striking and long-lasting inhibition of cardiac ACE as compared to other drugs of this class [
103]. It is known to accumulate intracellularly thanks to its lipophilic structure. Moreover due to the presence of a sulfhydryl group it can act as ROS scavenger [
104]. Sacco et al. [
105] evaluated the level of ACE inhibition by
zofenopril and
lisinopril in the myocardium and in the plasma, depending on the dose. Both, zofenopril and lisinopril produced a dose-dependent inhibition of serum and cardiac ACE in rats. Zofenopril at lowest dose of 0.1 mg/kg/day showed a significantly greater inhibition of angiotensin converting enzyme in the myocardium than in the serum (Δ 20%), indicating a tropism for cardiac tissues and for myocardial ACE. Zofenopril, at a dose 0.1 mg/kg/day which partially inhibit ACE (app. 50%) and did not affect hemodynamics, almost totally prevented the QT lengthening induced by chronic administration of doxorubicin. For comparison, lisinopril was ineffective at this dose and higher dose of 10 mg/kg/day was required to achieve the same effect. Other groups confirmed the observation regarding zofenopril in the prevention of ST segment in ECG [
106]. Moreover, zofenopril also prevented the depression of the inotropic response to isoprenaline in DOX-treated animals [
106]. Zofenopril is more potent in the prevention of cardiotoxicity than enalapril or valsartan [
107]. Presented data suggest that even low doses of zofenopril can be effective in the prevention of DOX-induced changes in ECG; however, authors did not evaluate the effect on the degree of apoptosis or ROS production. The lowest dose of zofenopril used in these experiments (0.1 mg/kg) is relatively close to that used for treatment of hypertension in humans.
Preventive effects of zofenopril or captopril lies partially besides the ACE inhibition and is based on the specific signaling pathways controlling cell survival through H
2S, originating from sulfhydryl group. It was proven in various cardiovascular disease that H
2S donors cause vasodilatation [
108], exert anti-inflammatory responses [
109], and protect from hypoxia/reperfusion damage in the heart [
110].
While most research concentrate on the prevention of doxorubicin toxicity in the myocardium, Monti et al. [
111] evaluated ACEIs in prevention of vascular damage. Zofenopril, in contrast to other ACEIs like captopril, lisinopril, or enalapril, can reverse the negative effect of doxorubicin on endothelial cells. When endothelial CVEC cells were exposed to various concentrations of doxorubicin in vivo, impaired cell survival, ERK1/2 related p53 activation and promotion of apoptosis by and induction of caspase-3 cleavage bypassing mitochondrial ROS production were observed, and could be prevented by zofenopril [
111].
Co-treatment with
fosinopril prevents from hemodynamic and morphologic changes in the heart induced by DOX [
96]. Moreover, it partially reverses increase of cardiac enzymes levels (AST, LDH, CPK, cTnI) in plasma [
112]. Importantly, fosinopril has an ability to attenuate DOX-induced decrease of sarcomplasmatic reticulum uptake of calcium ions and Ca2+-stimulated ATPase activity. Impairment of calcium homeostasis is most probably mediated by decreased expression of SERCA2 and phospholamban in sarcomplasmatic reticulum, what can be ameliorated by fosinopril [
96]. Also Maeda et al. [
112] reported that impaired calcium transients can be restored in isolated neonatal rat cardiomyocytes by concomitant treatment with ACEI. Ability to prevent remodeling of the cardiac SR membrane and attenuation of changes in myocardial Ca2+ homeostasis seems to be one of beneficial mechanism of ACEIs. This suggest involvement of ang-II in DOX-mediated downregulation of SERCA2 and phospholamban, but this mechanism has not been studied yet. Restoration of calcium ions homeostasis may significantly improve prevention and treatment of AIC because calcium ions regulate both systolic and diastolic function.
ARBs
Angiotensin receptor blockers (ARBs) are the drugs that are antagonists of AT-1 receptors. They prevent binding of ang-II with AT-1R and inhibit intracellular signaling pathways from this receptor. However, the amount of ang-II produced by ACE remains at the same or even increased level; thus, it can bind with AT-2R or be conversed to other forms, e.g., ang-(1–7). The general effect of ARBs is similar to ACEIs, even though it can be more pronounced due to increased additional signaling from AT-2 and Mas receptors [
113,
114].
Various ARBs have been tested in the preclinical models of anthracycline-induced cardiotoxicity with similar effects; however, some variations between specific drugs were observed, like those found in ACEIs.
Treatment with oral
candesartan (5 mg/kg/day) started 4 weeks after the last dose of daunorubicin and continued for 4 weeks has resulted in the reduction of animals mortality from 50 to 19%, reduction of elevated blood pressure, LVP and LVEDP, increase of fractional shortening and E/A ratio, normalization of ventricular weight/body weight ratio, decrease of percentage of apoptotic cells in myocardium and amelioration of decreased SERCA2 mRNA expression when compared to control group [
115].
Telmisartan (10 mg/kg/day) is also effective in prevention of AIC [
73,
116,
117]. Iqbal et al. [
116] evaluated the effect of telmisartan in the pre- and post-treatment model. In the pre-treatment model telmisartan (10 mg/kg/day) was administered orally 5 days before and 2 days after single injection of 20 mg DOX, while in the post-treatment model, it was administered only for 7 days after DOX. Pre- and post-treatment with telmisartan significantly attenuated AIC, however elevated tissue malondialdehyde MDA level and decreased level of glutathione GSH were normalized only by the pre-treatment with telmisartan. Histopathological examination revealed that signs of myocardial injury, such as high numbers of inflammatory cells, focal necrosis of muscle fiber, hemorrhage, and congestions, could be prevented by pretreatment with telmisartan while mild peripheral necrosis was noted in the post-treatment group [
116]. This implicates that to obtain the best cardioprotective effects ARBs should be used before, or at least during DOX treatment, not only after or when the signs of AIC become evident.
The mechanisms of telmisartan-induced protection against Dox-induced toxicities may be partially AT-1R-independent, mostly via inhibition of lipid peroxidation and protection against GSH depletion, possibly owing to its lipophilic and antioxidant structure [
118]. Besides blocking AT-1R, telmisartan poses additional partial agonistic activity on PPAR-γ which is known to have anti-inflammatory and antioxidant activities [
119]. Protection before DOX-induced iNOS expression seems to be a significant factor in the telmisartan cardioprotection because iNOS overexpression leads to release of NO that promotes redox cycling and production of ROS [
117,
120]. Moreover, Dox-induced apoptosis is associated with the increased expression of the endothelial nitric oxide synthase [
121].
In another study, animals received
losartan (30 mg/kg/daily) for 6 weeks concomitantly with doxorubicin [
73]. Treatment with losartan attenuated deterioration of left ventricular function caused by DOX in similar level to telmisartan. Moreover, losartan significantly suppressed the upregulation of AT1R. Interestingly, telmisartan and losartan were not able to prevent decrease of ang-(1–7), MasR, and AT-2R [
73]. Losartan decreased serum level of TNF-a, probably by inhibition of the ang-II ability to induce production of TNF-a by monocytes, macrophages, and vascular smooth muscle cells [
122].
Losartan (0.7 mg/kg/day) was also tested in the combination with quercetin (3,3,4,5,7-pentahydroxy flavone), the flavonoid present in a variety of foods including vegetables, fruits, and wine [
123]. The above combination resulted in more pronounce cardioprotection than losartan alone, most probably due to ability of quercetin to inhibit ACE via binding to its active site and reducing the conversion of ang-I [
124].
Sakr et al. [
125] evaluated different protocols of treatment with
valsartan (10 mg/kg/daily): pre-treatment (2 weeks of valsartan followed by 2 weeks of doxorubicin), concomitant treatment, or post-treatment (2 weeks of doxorubicin followed by 2 weeks of valsartan). Concurrent or post- but not pre-treatment with valsartan of doxorubicin-treated rats reduced the cardiac enzymes serum levels, attenuated the oxidative stress, improved hemodynamic parameters, prevented from changes in ECG, ameliorated apoptosis and improved cell senescence. Importantly, there was no difference between concomitant and-post treatment use of valsartan, but the short duration of the study and treatment strongly limits the translation of this results into humans, where treatment with doxorubicin lasts for few months.
Treatment with
olmesartan (10 mg/kg/day) for 12 days concomitantly with daunorubicin reversed worsening cardiac function, elevation of malondialdehyde (MDA) level in heart tissue, and decrease in the level of total glutathione peroxidase activity in the male SPRD rats [
67]. Furthermore, ARB treatment downregulated matrix metalloproteinase-2 (MMP-2) expression, myocardial expression of ang-II, attenuated the increased protein expressions of p67 phox and Nox4, and reduced oxidative stress-induced DNA damage [
67]. The reduction in the levels of MDA in the heart tissue of olmesartan-treated rats suggests that it protects myocardium against DOX induced lipid peroxidation.
Normalization of MMP2 expression by olmesartan is important observation because previous studies have shown that anthracyclines upregulate it by increased stimulation via AT-1R [
126,
127]. Activation of MMPs can be one of mechanism leading to cardiac remodeling, dysfunction, and increase of cTnI due to its proteolysis, as observed in other cardiac diseases, like myocarditis or inflammatory cardiomyopathy [
128,
129].
Also,
fimasartan significantly improved survival of doxorubicin treated animals, protected from the ejection fraction decline and cardiac remodeling in dose dependent manner in the rat model. Effects were more pronounce when higher doses were used (10 mg/kg/day vs 5 mg/kg/day) [
130].
Aldosterone antagonists
Aldosterone antagonist, such as spironolactone or eplerenone, antagonize action of aldosterone at mineralocorticoid receptor. Spironolactone is the first and most used drug in this class; however, eplerenone is much more selective than spironolactone on target, but somewhat less potent. These drugs are widely used in the treatment of hypertension but they also exert protective action in treatment of heart failure. They exert positive effects on preventing cardiac fibrosis and remodeling induced by heart failure and myocardial infarction, which conclusively reduces the risk of both morbidity and death [
131]. Considering that fact, there were few animal and human studies evaluating cardioprotective effects of aldosterone antagonists in AIC.
Spironolactone can prevent deterioration of systolic and diastolic function as well as attenuate cardiac fibrosis and myocyte apoptosis caused by DOX treatment [
92]. Moreover, the expressions of TGF-β1 which plays important role in the induction of cardiac fibrosis, increased after DOX treatment, is significantly reduced by coadministration of spironolactone [
92]. In one of preclinical studies, eplerenone (200 mg/kg/day), when started 5 days before doxorubicin, prevented the impairment of left ventricular ejection fraction and contractility. In the acute model, eplerenone was able to attenuate the interstitial fibrosis but in the chronic model this effect was not observed [
90]. In another study, eplerenone did not protect from the acute or chronic cardiotoxicity in male mice. Moreover, the observations suggest that eplerenone synergistically amplifies Dox-induced molecular changes via sustained release of aldosterone and possible crosstalk with the ang-II signaling resulting in higher expression of AT-1R and connective tissue growth factor (CTGF) [
89]. Summing up, the data concerning aldosterone and its antagonists in the prevention of AIC in animal models are highly limited and inconsistent.
Targeting the ACE2/ang-(1–7)/MASR axis
Above mentioned observations on the role of ACE2/ang-(1–7)/MASR axis in AIC has led to the studies analyzing the cardioprotective utility of targeting ACE2. Based on the findings that autophagy-deficient mouse embryonic fibroblasts overexpress ACE2 [
134], the hypothesis that ACE2 provides cardioprotection by reduction of myocardial autophagy was proposed and tested [
135]. Lai et al. [
136] reported that treatment of SPRD rats with human recombinant ACE2 after doxorubicin-induced cardiotoxicity has significantly reduced mortality from 32 to 4% and improved echocardiographic parameters compared to non-treated animals. Similar observations were reported by Ma et al. [
137] who obtained myocardial ACE2 overexpression by intramyocardial injection of ACE2 adenoviral vectors. Animals overexpressing ACE2 had significantly lower 4-week mortality rates associated with doxorubicin treatment compared to Mock group and group with control vector: 18.75%, 71.88%, and 75%, respectively. At the molecular level, ACE2 overexpression resulted in decreased levels of oxidative stress markers, inflammation, and lower myocardial collagen depositions. Markers of autophagy and apoptosis, which were significantly increased in AIC rats, were attenuated by recombinant ACE2 or cardiomyocyte transfection with cDNA for ACE2 [
136,
137]. The key explanation of this is the fact that ACE2 overexpression has changed the proportion of RAAS components. Ang-II and ACE expressions were decreased whereas levels of ang-(1–7) were higher than in the control group [
137]. The proposed mechanisms behind the protective action of ACE2 is decreased stimulation of AT-1R due to higher conversion of Ang-I and Ang-II to Ang-(1–7) that further acting via Mas receptor leads to activation of PI3K-Akt/AMPK pathways and inhibition of the ERK pathway, which have known activity in inhibition of cardiac apoptosis [
138‐
140]. That stays in line with Liu et al. who showed that ang-(1–7) infusions could significantly attenuate the left ventricular dysfunction and myocardial apoptosis by downregulating the pro-apoptotic protein caspase-3 and Bax and upregulating anti-apoptotic protein Bcl-xl expression in the rat AIC model [
141].
The other possible mechanism includes suppression of DOX-triggered overexpression of TGF-β1 and thus reduction of heart fibrosis and hypertrophy [
137], as well as inhibition inflammation [
137,
142]. It seems that the protective effects of ACE2 can be also mediated by the miR-30e, which expression was significantly decreased in the myocardium of AIC rats and effectively prompted by ACE2 overexpression [
136]. Silencing of the miR-30e inverted cardioprotective function of ACE2 both at the molecular level and in the echocardiography [
136]. Physiologically, miR-30e is a negative regulator for Becclin-1 [
143], a functional protein that interacts with Bcl-2 and is regarded as a mediator of autophagy [
144] which stays in line with hypothesis on the involvement of ACE2 in protection against myocardial autophagy.
It is worth mentioning that effects obtained by ACE2 overexpression are at some extend like those observed upon ACEIs. ACE inhibition leads to the accumulation of ang-I and activation of collateral pathway, including upregulation of ACE2 that converts ang-I to ang-(1–7). ACE2 activity can be increased not only by ACEIs but also by overexpression of its gene (e.g., by using adenoviral vector). Both approaches are enough to reduce degree of cardiotoxic effect of doxorubicin, however in case of some parameters ACEIs are less effective than adenoviral vector. The difference may be due to the fact that ACEIs inhibits ang-II synthesis catalyzed by ACE but cannot inhibit process catalyzed by chymase and may not completely inhibit RAAS in the hearts of animals with AIC. On the other hand, ACE2 cleaves ang-II into protective ang-(1–7) and reduce level of ang-II, exhibiting stronger effect than ACEI [
137]. For example, animals receiving ACEI cilazapril had lower mortality than controls but higher than ACE2-overexpressing rats (46.88 vs 71.88% vs 18.75%) [
137]. Based on those observations it seems reasonable to search for new strategies aiming at increasing ACE2 activity as cardioprotection against AIC. For the moment, beside studies with ACEIs, there were no trials in humans with therapies affecting ACE2. Use of viral vectors to overexpress ACE2 is highly limited in humans due to lack of evidence, ethical issues, and safety considerations, but in the future, it can become a groundbreaking strategy.