1. Introduction
It is known that in recent years the main cause of mortality and disability in the population of industrially developed countries is cardiovascular diseases [
1,
2]. Among all cardiovascular diseases, chronic heart failure (CHF) is a complex and major health problem in many countries. Despite the progress achieved over the past 20 years in the treatment of CHF, the problem remains relevant [
3,
4,
5]. The reason for the importance of the problem of CHF is that this disease has an extremely unfavorable prognosis. Thus, the annual mortality rate among patients with functional class III-IV CHF reaches 60% and only half of less severe patients survive for 5 years from the date of diagnosis [
6,
7,
8,
9]. To date, recommendations have been developed for the treatment of CHF, which include the prescription of ACE inhibitors, diuretics, cardiac glycosides and beta blockers [
10,
11]. It is beta blockers, along with ACE inhibitors, that are considered first-line drugs in the treatment of CHF, as they can improve survival rates and hospitalization of patients, effectively increase ejection fraction (EF), reduce the mass and sphericity of the left ventricle (LV) [
12]. The leading component of this effect of beta blockers is their cardioprotective properties [
13]. Currently, depending on the pharmacological action, there are three generations of beta blockers.
First generation beta blockers - non-selective block β1- and β2-receptors (Propranolol (Anaprilin), Nadolol, Timolol), exhibit negative effects on carbohydrate and lipid metabolism, the central nervous system, erectile function in men, increase the tone of bronchial smooth muscles, vascular walls, myometrium, which significantly limits their use in clinical practice; Second-generation β-blockers are cardioselective, since they block only β1-receptors (Metoprolol, Bisoprolol, Atenolol), which have fewer side effects compared to first-generation drugs and have more favorable tolerability with long-term use and a convincing evidence base for long-term prognosis life during the treatment of CHF. Third generation β-blockers, which can be either highly selective for β1 receptors (Nebivalol, Betaxolol) or non-selective (Carvedilol, Labetalol, Carteolol), and have antiischemic, endotheliotropic, antioxidant, antiproliferative, antihypertrophic and antiapoptotic activity, with minimal side effects. Also, 1st and 2nd generation beta blockers are called traditional, and 3rd generation - beta blockers with additional pharmacological properties [
14,
15,
16].
A potential drug Hypertril (1-(b-phenylethyl)-4-amino-1,2,4-triazolium bromide) exhibiting β1-blocking, vasodilatory, antihypertensive and cardioprotective effects and belonging to class IV toxicity (LD50 is 683.4 mg/kg after intragastric administration to rats) is a result of our multi-year efforts [
17]. SPA "Pharmatron" together with the scientific and technological complex "Institute of Single Crystals" of the National Academy of Sciences of Ukraine has developed methods for the synthesis and standardization of the substance "Hypertril" and the technology of parenteral solutions (certificate No. 2, series 020213). According to the decision of the State Expert Center of the Ministry of Health of Ukraine, phase 1 has been successfully completed and phase 2 of clinical trials of Hypertril as an antihypertensive drug is underway. There are the first experimental positive results of using Hypertril for CHF and its advantages over other beta blockers [
18,
19].
It is known that CHF is accompanied by mitochondrial dysfunction and persistent disturbances in myocardial energy metabolism leading to macroerg deficiency, ROS production, oxidative stress and apoptosis [
20,
21]. Such disorders, on the one hand, can be considered as a component of the pathogenesis of CHF, and, on the other, as a key factor in its progression. The mechanism of action of traditional beta blockers and, especially, beta blockers with additional properties suggests the possibility of the drugs influencing myocardial energy metabolism when prescribed for CHF. However, these data are very limited and demonstrate a variable effect depending on the class of the drug. Thus, Propronalol (Anaprilin), a non-selective beta-blocker, enhances disturbances in myocardial energy metabolism due to a negative effect on mitochondria (inhibition of complex II of the respiratory chain, collapse of mitochondrial membrane potential) [
22,
23]. At the same time, Timolol had a mitoprotective effect and improved metabolism, directly related to the activity of myocardial mitochondria [
24]. Interesting data have been obtained on the effect of a beta blocker with additional properties - Carvedilol - on energy metabolism [
25].
Based on the above, we can outline the main direction of the ongoing research, which, in our opinion, will allow us to form a theoretical foundation for a clearer understanding of the possible and potential mechanisms of action of beta blockers of various generations on energy metabolism, which will, perhaps, resolve some practical issues, associated with the treatment of CHF. Purpose of the study: to investigate the effect of beta blockers of various generations (Bisoprolol, Metoprolol, Carvedilol, Nebivalol and the new drug Hypertril on indicators of myocardial energy metabolism in a model of doxorubicin-induced CHF.
3. Results and Discussion
Biochemical studies revealed disturbances in myocardial energy metabolism and energy deficiency in the group of animals with CHF. Thus, a 14-day administration of doxorubicin led on the 45th day of the experiment to a decrease in the level of ATP in the myocardial cytosol by 50% and in mitochondria by 55%. In parallel, a decrease in the ADP content in the myocardial cytosol of rats with CHF by 42% was recorded against the background of an increase in the ADP level by 75.3% (
Table 1). Our results correspond to generally accepted ideas about disturbances in the energy supply of the myocardium under conditions of ischemia [
31].
We also recorded a 70% malate deficiency in the cytosolic fraction with a 62% decrease in the activity of mitochondrial NAD-dependent MDH (
Table 2 and
Table 3), which indicates possible inhibition of the malate-aspartate shuttle mechanism of transport of reduced equivalents into the mitochondria [
32,
33] and the formation of secondary mitochondrial dysfunction.
Among the causes of mitochondrial dysfunction in CHF are oxidative stress, disruption of NO biosynthesis, production of its cytotoxic derivatives, and development of nitrosating stress [
34,
35,
36]. It is currently known that the main manifestations of mitochondrial dysfunction are a decrease in the level of ATP in the cell, an increase in the level of lactate and a decrease in pyruvate, activation of cell death mechanisms and the production of reactive oxygen species (ROS) by mitochondria [
37]. Currently, the effect of impaired ATP synthesis in mitochondria on the functional activity of the myocardium has been studied to the greatest extent [
38]. It has been established that with a decrease in the content of ATP in the mitochondria and cytosol of the myocardium by 10–20%, the activity of all energy-dependent processes decreases by 80%. The effects of an insufficient amount of ATP include suppression of the disruption of ion pumps, ion homeostasis and, accordingly, the contractile function of the heart [
39]. Inhibition of energy production processes in the mitochondria of cardiomyocytes is accompanied by a weakening of lipid beta-oxidation, which results in a violation of lipid homeostasis in the cell and the accumulation of acyl-CoA thioesters, acylcarnitines, ceramides and triglycerides, which enhance the formation of myocardial hypertrophy in CHF [
40,
41].
Under the influence of mitochondria-formed ROS, there is an increase in the opening of mitochondrial pores, expression and release of proapoptotic proteins into the cytosol. The opening of the pores occurs due to the oxidation of the thiol groups of the cysteine-dependent region of the protein of the inner mitochondrial membrane (ATP/ADP antiporter) by cytotoxic derivatives of NO, which turns it into a permeable non-specific channel - a pore [
42,
43]. ROS generated by mitochondria also participate in the transmission of intracellular signals of receptors for endothelin, TGF-β1, PDGF, AT-II, FGF-2, etc. ROS are also capable of changing the activity of various transcription factors, including NF-κB, AP-1, and the proapoptotic protein p66Shc. In general, an increase in ROS production, by affecting the intracellular signaling mechanisms discussed above, can contribute to the activation of the inflammatory process in heart tissue, the development of hypertrophic and fibrotic changes [
44,
45].
A course of administration of Hypertril tablets to rats with CHF resulted in a reduction in manifestations of secondary mitochondrial dysfunction. Thus, in animals treated with a course of Hypertril, there was a decrease in the opening of the mitochondrial pore (MP) by 51% (
p < 0.05), as well as an increase in the charge of the inner membrane of the myocardial mitochondria by 82% (
p < 0.05) compared to the group of untreated animals (
Table 3). In these indicators, Hypertril is superior to the action of both traditional beta-blockers - Metoprolol and Bisoprolol, as well as Carvedilol and Nebivalol. Biochemical studies of the myocardium of rats with CHF made it possible to identify the features of the mitoprotective and anti-ischemic action of Hypertril. Thus, the ATP content in the cytosolic and mitochondrial fractions in rats treated with Hypertril increased (p < 0.05) by 42% and 33%, respectively. Along with an increase of 24% in the ADP content and a decrease of AMP by 54% were observed in the cytosol of the heart (p<0.05) compared with the corresponding indicators of the control group (
Table 1,
Table 2 and
Table 3). In the cytosolic and mitochondrial fractions of the myocardial homogenate of animals with myocardial infarction under the influence of Hypertril, a decrease in lactate by 38.8 and 37%, respectively, was observed, which indicated a decrease in the activity of low-productive glycolysis (
Table 2). At the same time, in the myocardial mitochondria of rats with CHF treated with Hypertril, the activity of SDH increased by 72% (
p < 0.05) and NAD-MDH by 75.3% (
p < 0.05) compared with the group of untreated animals. In the cytosolic fraction of the myocardial homogenate of rats with CHF, against the background of Hypertril administration, the level of malate by 90% and pyruvate by 24% significantly increased. The positive changes in the myocardium of animals under the influence of Hypertril indicate a decrease in the manifestations of mitochondrial dysfunction and activation of compensatory cytosolic-mitochondrial shunts of ATP synthesis and a decrease in energy deficiency. Administration of Nebivalol to rats with CHF also had a positive effect on the energy metabolism of the myocardium. Thus, Nebivalol reduced mitochondrial swelling by 25% (
p < 0.05) and increased the mitochondrial charge by 41% (
p < 0.05) compared to the parameters of the group of untreated animals. Nebivalol increased the concentration of ATP in the cytosol and mitochondria of the myocardium of rats with CHF by 21% (
p < 0.05) and 18% (
p < 0.05), respectively, against the background of a decrease in AMP (
p < 0.05) compared to the control. Administration of Nebivalol increased the activity of SDH by 44% (
p < 0.05) and NAD-MDH by 21.5% (
p < 0.05) in the myocardial mitochondria of rats with CHF compared to the control. Administration of Nebivalol resulted in a decrease in lactate (in the cytosol by 33% and in the mitochondria by 18%) (
p < 0.05) and an increase in malate by 27% (
p < 0.05) and pyruvate by 12% (
p < 0.05) in the cardiac cytosol of rats with CHF compared to the group of untreated animals with CHF.
Administration of Carvedilol had a significant effect on the indices of mitochondrial swelling reduction (30%) and mitochondrial charge increase (39%) in the myocardium of rats with CHF (
Table 3). Carvedilol also significantly increased the activity of SDH (15%) in the mitochondria of rats with CHF compared to the control. Administration of Carvedilol had no significant effect on the other studied indices of energy metabolism in the myocardium of rats with CHF (
Table 1,
Table 2 and
Table 3). Traditional beta-blockers – Metoprolol and Bisoprolol had no significant effect on the studied indices of energy metabolism in the myocardium of rats with CHF (
Table 1,
Table 2 and
Table 3). The only thing that attracts attention in the group of rats with CHF that received a course of Bisoprolol in the mitochondrial fraction of the myocardium was a decrease in lactate by 14% (p<0.05) compared to the control.
Analyzing the obtained results of biochemical studies of myocardial energy metabolism in experimental CHF and against the background of the use of Hypertril, it can be concluded that the starting mechanism of the anti-ischemic action of Hypertril is its effect on the dysfunction of the mitochondria of cardiomyocytes. Apparently, Hypertril, by reducing the damaging effect of ROS and free radicals on the SH-groups of the cysteine-dependent region of the protein of the inner mitochondrial membrane, prevents the opening of the mitochondrial pore and maintains the functional activity of the mitochondria, which subsequently improves the energy metabolism of the myocardium under ischemic conditions [
42]. This statement is also confirmed by our previous study, which showed that Hypertril, unlike Metoprolol, Bisoprolol, Carvedilol and Nebivalol, leads to a decrease in systolic and diastolic dysfunction, restoration of autonomic mechanisms of heart rhythm regulation, a decrease in the amplitude of the ST interval (
p < 0.05), which, in combination with the restoration of the amplitude of the R wave, indicates the preservation of high performance of cardiomyocytes in doxorubicin-induced CHF [
19]. The mechanism of such an effect of Hypertril on energy metabolism parameters in rats with CHF is apparently associated not only with its β1-adrenergic blocking effect, but is also possibly realized through additional mechanisms identified earlier – antioxidant and NO-mimetic [
46]. The viability of such assumptions is based on various studies that have shown that patients with mitochondrial disorders have a deficiency of NO, and the administration of NO-mimetics leads to an improvement in mitochondrial function and energy metabolism [
47,
48].
Carvedilol, a β-adrenergic receptor antagonist with strong antioxidant activity, provides a high degree of cardioprotection in various experimental models of ischemic heart injury. Data on the effect of Carvedilol on mitochondrial bioenergetic functions and ROS formation have been obtained. Thus, Carvedilol is able to reduce the formation of H
2O
2, increase the level of reduced glutathione, and restore mitochondrial respiration due to its antioxidant effect [
49]. Carvedilol exhibits the properties of an ROS scavenger and also inhibits the formation of ROS in mitochondria due to “soft uncoupling” and a slight decrease in the potential of the mitochondrial membrane; it is able to directly protect the ultrastructure of mitochondria, reduce Ca++ overload of mitochondria, but does not affect the indicators of mitochondrial respiration after 7-week administration of doxorubicin [
50,
51]. It has been shown that the direct mitoprotective properties of Carvedilol are associated with its properties to suppress the formation of ROS in the xanthine oxidase reaction of mitochondria and by increasing the activity of cytosolic Cu, Zn-SOD and mitochondrial Mn-SOD, as well as catalase [
51,
52]. It has also been shown that "antioxidant" concentrations of Carvedilol and its metabolite BM-910228 do not affect mitochondrial respiration parameters [
50]. Some studies have shown that Carvedilol, due to its uncoupling effect, can also exhibit prooxidant properties [
25].
Our results, which show that Metoprolol does not have a reliable effect on the energy metabolism of the myocardium, coincide with the data of other researchers. Thus, it was shown that this selective beta-blocker, prescribed for the treatment of CHF [
12], does not improve the mitochondrial ultrastructure after the introduction of doxorubicin, did not reduce peroxidation processes, did not reduce the degree of Ca
++ overload of mitochondria [
53,
54,
55]. Metoprolol attenuates post-infarction structural remodeling without concomitant improvement in myocardial energy metabolism in rats with chronic CHF [
56]. Bisoprolol was the first beta blocker to show clinical efficacy in heart failure [
57]. Our results demonstrated the absence of a clear reliable effect of Bisoprolol on myocardial energy metabolism in CHF (except for the effect on LDH), which is consistent with other researchers [
58]. It has been shown that the protective effect of Bisoprolol on the heart is not associated with the optimization of energy metabolism, but has other mechanisms [
59]. Bisoprolol has also been shown to inhibit mitochondrial respiration and ATP synthesis in cancer cells [
60]. It has been shown that blockade of cardiac β1 receptors with traditional beta blockers via the PKA/cAMP signaling pathway suppresses the nuclear-encoded mitochondrial protein IF1 and inhibits oxidative phosphorylation in cardiac mitochondria [
60]. Nebivalol is a latest generation beta blocker with additional metabolitotropic properties – NO-mimetic and antioxidant, and is actively used in the treatment of arterial hypertension and CHF [
61]. To date, there are no complete data on the effect of Nebivalol on myocardial energy metabolism in CHF, and it is difficult for us to compare our modest results with the data of other researchers. It is known that Nebivalol is an ROS scavenger and is able to protect mitochondrial membranes, affect various mechanisms of mitoptosis, increase ATP, creatine phosphate and normalize the [lactate]/[pyruvate] ratio. Moreover, the effect on energy metabolizum is not associated with its NO-mimetic effect [
62,
63]. There are, however, other studies demonstrating the involvement of Nebivalol in enhancing the formation of mitochondrial dysfunction in cancer cells [
60,
64]. Other researchers do not confirm a direct negative effect of Nebivalol on mitochondria in non-tumor cells, which emphasizes its specificity and excludes any antimitotic toxicity [
60,
65].