Exogenous N-terminal fragments of galanin, which are agonists of the GalR2 receptor, have therapeutic potential in experimental cardiac pathology. This implies the need to study their proteolytic stability in biological environments. The aim of this work was to evaluate the proteolytic degradation of galanin G1 (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2), its natural and modified fragments G2 and G3 (WTLNSAGYLLGPHA-OH and WTLNSAGYLLGPβAH-OH, respectively) in human plasma. The peptides were obtained by solid-phase synthesis using the Fmoc methodology, purified by HPLC; their structure was confirmed by MALDI-TOF mass spectrometry and 1H-NMR spectroscopy. The kinetics of galanins G1-G3 degradation in blood plasma was studied by 1H-NMR spectroscopy based on changes in the intensity of Trp2 signals at 310 K. The results indicate a higher proteolytic stability of the G3 peptide compared to the natural G2 fragment and full-length galanin G1. They indicate the potential of using modified peptide agonists of GalR2 receptors to protect vital organs in pathophysiological conditions.

Type 1 diabetes mellitus (T1DM) is the most severe form of diabetes, which is characterized by absolute insulin deficiency induced by the destruction of pancreatic beta cells. The aim of this study was to evaluate the effect of a structural analogue of apelin-12 ((NαMe)Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-OH, metilin) on hyperglycemia, mitochondrial (MCh) respiration in permeabilized cardiac left ventricular (LV) fibers, the myocardial energy state, and cardiomyocyte membranes damage in a model of streptozotocin (STZ) diabetes in rats. Metilin was prepared by solid-phase synthesis using the Fmoc strategy and purified using HPLC. Four groups of animals were used: initial state (IS); control (C), diabetic control (D) and diabetic animals additionally treated with metilin (DM). The following parameters have been studied: blood glucose, MCh respiration in LV fibers, the content of cardiac ATP, ADP, AMP, phosphocreatine (PCr) and creatine (Cr), the activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) in blood plasma. Administration of metilin to STZ-treated rats decreased blood glucose, increased state 3 oxygen consumption, the respiratory control ratio in MCh of permeabilized LV fibers, and increased the functional coupling of mitochondrial CK (mt-CK) to oxidative phosphorylation compared with these parameters in group D. In STZ-treated animals metilin administration caused an increase in the PCr content and prevention of the loss of total creatine (ΣCr=PCr+Cr) in the diabetic hearts, as well as restoration of the PCr/ATP ratio in the myocardium and a decrease in the activity of CK-MB and LDH in plasma to initial values. Thus, metilin prevented energy disorders disturbances in cardiomyocytes of animals with experimental T1DM.

Creation of bioactive molecules for treatment of cardiovascular diseases based on natural peptides is the focus of intensive experimental research. In the recent years, it has been established that C-terminal fragments of apelin, an endogenous ligand of the APJ receptor, reduce metabolic and functional disorders in experimental heart damage. The review presents literature data and generalized results of our own experiments on the effect of apelin-13, [Pyr]apelin-13, apelin-12, and their chemically modified analogues on the heart under normal and pathophysiological conditions in vitro and in vivo . It has been shown that the spectrum of action of apelin peptides on the damaged myocardium includes decrease in the death of cardiomyocytes from necrosis, reduction of damage to cardiomyocyte membranes, improvement in myocardial metabolic state, and decrease in formation of reactive oxygen species and lipid peroxidation products. The mechanisms of protective action of these peptides associated with activation of the APJ receptor and manifestation of antioxidant properties are discussed. The data presented in the review show promise of the molecular design of APJ receptor peptide agonists, which can serve as the basis for the development of cardioprotectors that affect the processes of free radical oxidation and metabolic adaptation.

Objectives: The aim of this work was to elucidate the role of GalR2 receptor activation in protecting the rat heart in vivo from ischemia/reperfusion (I/R) damage by a pharmacological peptide agonist WTLNSAGYLLGP beta AH-OH (G1) and full-length rat galanin GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2 (G2) using M871, a selective inhibitor of GalR2. Methods: The peptides were prepared by the automatic solid-phase synthesis using the Fmoc-strategy and purified by high-performance liquid chromatography (HPLC). A 40-min left anterior descending (LAD) coronary artery occlusion followed by a 60-min reperfusion was performed. The criteria for damage/protection of the heart were the infarct size (IS) and plasma activity of creatine kinase-MB (CK-MB) at the end of reperfusion. Results: Intravenous injection of G1 or G2 at an optimal dose of 1 mg/kg at the fifth minute of reperfusion significantly reduced the IS (by 35% and 32%, respectively) and activity of CK-MB at the end of reperfusion (by 43% and 38%, respectively) compared with the control. Administration of M871 (8 mg/kg) 5 min before the onset of reperfusion abolished the effects of G1 on IS and CK-MB activity, returning them to control values. Co-administration of M871 (8 mg/kg) with G2 attenuated protective effect of G2 on both IS and plasma CK-MB activity. However, differences in these parameters between the M871+G2 and G2 groups did not reach statistical significance (P = 0.139 and P = 0.121, respectively). Conclusion: Thus, GalR2 is the principal receptor subtype that transduces the protective effects of galanin and ligand G1 in myocardial I/R injury. This suggests that GalR2-specific peptide agonists could be used as drug candidates for treating ischemic heart disease.

The apelin/APJ system is involved in many physiological functions and pathophysiological effects in cardiovascular diseases, making it a promising drug target. This narrative review briefly summarizes data on experimental conditioning of the heart with modified structural analogues of apelin-12. Apelin-12 analogues resistant to proteolytic cleavage in human plasma were synthetized by targeted substitution of amino acid residues in the structure of natural apelin-12 by an automated solid-phase method using Fmoc technology. These peptides are able to mimic the protective effect of apelin-12 in both ex vivo and in vivo models of ischaemia/reperfusion (I/R) myocardial injury. Intravenous administration of apelin-12 analogues at the onset of reperfusion reduces the size of acute myocardial infarction in rats, preserves the metabolic and antioxidant state of the area at risk during reperfusion, and improves cardiomyocyte membrane integrity. Postconditioning effects are mediated by signaling via PLC and survival kinases, PI3K and MEK1/2, with further activation of downstream targets, NO synthase and mitochondrial KATP channels, and sarcolemmal Na+/H+ and Na+/Ca2+ exchangers. Given the role of apelin/APJ in cardiovascular diseases, future perspectives of development of pharmacological postconditioning with apelin-12 analogues are discussed. This strategy may provide important therapeutic benefits in the treatment of cardiovascular disease.

The neuropeptide galanin (G) and its N-terminal fragments reduce the formation of reactive oxygen species and normalize myocardial metabolic and antioxidant state in experimental cardiomyopathy and ischemia/reperfusion injury. This study intends to elucidate the cardioprotective effect of G in rats treated with streptozotocin (STZ). The rat galanin (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2) was prepared by the solid phase peptide synthesis using the Fmoc-strategy and purified by preparative HPLC. Its chemical structure was identified by 1H-NMR spectroscopy and MALDI-TOF mass spectrometry. The animals were divided in four groups: C—normal control; S—STZ control, a single i.p. injection of STZ (35 mg/kg); SG—a single i.p. injection of STZ (35 mg/kg) and i.p. injections of G (5 nmol/kg/day for 4 weeks); and G—normal animals treated with G (5 nmol/kg/day for 4 weeks). Treatment with G prevented hyperglycemia in STZ rats. G significantly improved maximal ADP-stimulated respiration and respiratory control ratio in saponin-skinned myocardial fibers in SG group compared to S group. G enhanced myocardial metabolic state in animals treated with STZ by reducing ATP, phosphocreatine (PCr) and total creatine (ΣCr = PCr + Cr) losses, and decreasing lactate accumulation in parallel with elevation of glucose level. Administration of G reduced the increased activity of creatine kinase-MB and lactate dehydrogenase in blood plasma of STZ-treated rats. G also prevented the formation of STZ-induced lipid peroxidation products, thiobarbituric acid reactive substances, in blood plasma to a value not different from baseline. The results suggest that G may be a promising tool for reducing myocardial metabolic disorders in diabetes mellitus.

Neuropeptide galanin and its N-terminal fragments reduce the generation of reactive oxygen species and normalize metabolic and antioxidant states of myocardium in experimental cardiomyopathy and ischemia/reperfusion injury. The aim of this study was to elucidate the effect of WTLNSAGYLLGPβAH-OH (peptide G), a pharmacological agonist of the galanin receptor GalR2, on the cardiac injury induced by administration of streptozotocin (STZ) in rats. Peptide G was prepared by solid phase peptide synthesis using the Fmoc strategy and purified by preparative HPLC; its structure was confirmed by 1H-NMR spectroscopy and MALDI-TOF mass spectrometry. Experimental animals were randomly distributed into five groups: C, control; S, STZ-treated; SG10, STZ + peptide G (10 nmol/kg/day); SG50, STZ + peptide G (50 nmol/kg/day); G, peptide G (50 nmol/kg/day). Administration of peptide G prevented hyperglycemia in SG50 rats. By the end of the experiment, the ATP content, total pool of adenine nucleotides, phosphocreatine (PCr) content, and PCr/ATP ratio in the myocardium of animals of the SG50 group were significantly higher than in rats of the S group. In the SG50 and SG10 groups, the content of lactate and lactate/pyruvate ratio in the myocardium were reduced, while the glucose content was increased vs. the S group. Both doses of peptide G reduced the activation of creatine kinase-MB and lactate dehydrogenase, as well as the concentration of thiobarbituric acid reactive products in the blood plasma of STZ-treated rats to the control values. Taken together, these results suggest that peptide G has cardioprotective properties in type 1 diabetes mellitus. Possible mechanisms of peptide G action in the STZ-induced diabetes are discussed.

Antioxidant and anti-ischemic properties of the pharmacological agonist of galanin receptor GalR2 WTLNSAGYLLGPβAH (Gal) and its C-terminal fragment, dipeptide carnosine (βAH), were studied in the model of regional ischemia and reperfusion of the rat heart in vivo in the dose range of 0.5-5.0 mg/kg and Cu²⁺-induced free radical oxidation of low density lipoproteins (LDL) of human plasma in vitro for peptide concentrations of 0.01 mM and 0.1 mM. Gal was obtained by automatic solid phase synthesis using the Fmoc methodology; its structure was characterized by 1H-NMR spectroscopy and MALDI-TOF mass spectrometry. Intravenous administration of the optimal dose of Gal (1 mg/kg) to rats after ischemia was more effective than carnosine in reducing of the myocardial infarct size and the activity of creatine kinase-MB and lactate dehydrogenase in blood plasma at the end of reperfusion. It also improved the metabolic state of the reperfused myocardium and reduced the formation of peroxidation products during reperfusion. Gal reduced more effectively the formation of adducts of hydroxyl radicals in the interstitium of the area at risk (AAR) of the rat heart than carnosine. Carnosine at a dose of 1 mg/kg more effectively increased the activity of catalase and glutathione peroxidase in the AAR by the end of reperfusion compared to Gal. In a model of Cu²⁺-initiated oxidation of human plasma LDL 0.1 mM carnosine demonstrated a significantly more pronounced reduction in the formation of lipid radicals compared to Gal. The results show that Gal can be considered as a promising agent that reduces myocardial injury during reperfusion and oxidative stress.

The dose-dependent action of the M871 synthetic peptide antagonist of the GalR2 galanin receptor (H-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu-Leu-Gly-Pro-Glu-His-Pro-Pro-Pro-Ala-Leu-Ala-Leu-Ala-NH2) and the pharmacological agonist G (H-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu-Leu-Gly-Pro-βAla-His-OH) on sizes of the myocardial infarction (MI) and an activity of creatine kinase (CK-MB) in the blood plasma was studied on the in vivo model of regional ischemia and reperfusion of the rat heart. The peptides were prepared by the automatic solid phase synthesis using the Fmoc-strategy and purified by HPLC. The peptides had the appropriate molecular mass and the homogeneity of 97–98%. A blockage of the GalR2 receptors by the intravenous injection of M871 in doses of 3, 6, and 8 mg/kg before the beginning of the reperfusion had no influence on the MI sizes and the CK-MB activity in comparison with the control. The intravenous injection of the agonist G in a dose of 1 mg/kg at the beginning of the reperfusion significantly decreased the MI sizes and the CK-MB activity in the blood plasma in comparison with the control by 38 and 40%, respectively. Peptides M871 and G did not significantly affect the hemodynamic parameters of the heart. The preliminary intravenous injection of increasing doses of peptide M871 before an administration of agonist G resulted in a gradual increase in the MI sizes and the CK-MB activity. An application of compound M871 in doses of 6 or 8 mg/kg completely abrogated the cardioprotective effects of agonist G. These results suggested the participation of the GalR2 receptor in the protective action of the chimeric agonist G on the heart that was subjected to ischemia and reperfusion and pointed to the considerable promise of the molecular engineering of the peptide agonists of the GalR2 receptor for a design of therapeutic agents for a treatment of cardiovascular diseases.

The design of new drugs for treatment of cardiovascular diseases based on endogenous peptide hormones is of undoubted interest and stimulates intensive experimental research. One of the approaches for development in this area is synthesis of the short bioactive peptides that mimic effects of the larger peptide molecules and have improved physicochemical characteristics. In recent years, it has been found that the N-terminal fragments of the neuropeptide galanin reduce metabolic and functional disorders in the experimental heart damage. The review presents literature data and generalized results of our own experiments on the effects of the full-size galanin and its chemically modified N-terminal fragments (2-11) and (2-15) on the heart in normal conditions and in modeling pathophysiological conditions in vitro and in vivo. It has been shown that the spectrum of the peptide actions on the damaged myocardium includes decrease in the necrotic death of cardiomyocytes, decrease in the damage of sarcolemma, improvement in the metabolic state of myocardium, decrease in the formation of reactive oxygen species (ROS) and lipid peroxidation (LPO) products. Mechanisms of the protective action of the modified galanin fragments associated with activation of the GalR2 receptor subtype and manifestation of antioxidant properties are discussed. The data summarized in the review indicate that the molecular design of pharmacological agonists of the GalR2 receptor is a promising approach, because they can serve as a basis for the development of cardioprotectors influencing processes of free radical oxidation and metabolic adaptation.

A correction to this paper has been published: https://doi.org/10.1007/s10989-021-10233-9

Antioxidant properties of rat galanin GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2 (Gal), N-terminal fragment of galanin (2-15 aa) WTLNSAGYLLGPHA (G1), and its modified analogue WTLNSAGYLLGPβAH (G2) were studied in vivo in the rat model of regional myocardial ischemia and reperfusion and in vitro in the process of Cu2+-induced free radical oxidation of human blood plasma low-density lipoproteins. Intravenous administration of G1, G2, and Gal to rats after ischemia induction reduced the infarction size and activities of the necrosis markers, creatine kinase-MB and lactate dehydrogenase, in blood plasma at the end of reperfusion. G1, G2, and Gal reduced formation of the spin adducts of hydroxyl radicals in the interstitium of the area at risk during reperfusion, moreover, G2 and Gal also reduced formation of the secondary products of lipid peroxidation in the reperfused myocardium. It was shown in the in vivo experiments and in the in vitro model system that the ability of galanin peptides to reduce formation of ROS and attenuate lipid peroxidation during myocardial reperfusion injury was not associated directly with their effects on activities of the antioxidant enzymes of the heart: Cu,Zn-superoxide dismutase, catalase, and glutathione peroxidase. The peptides G1, G2, and Gal at concentrations of 0.01 and 0.1 mM inhibited Cu2+-induced free radical oxidation of human low-density lipoproteins in vitro. The results of oxidative stress modeling demonstrated that the natural and synthetic agonists of galanin receptors reduced formation of the short-lived ROS in the reperfused myocardium, as well as of lipid radicals in blood plasma. Thus, galanin receptors could be a promising therapeutic target for cardiovascular diseases.

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia–reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

Chemically modified peptide apelin-12 ([MeArg1, NLe10]-apelin12, peptide M) is able to reduce reactive oxygen species (ROS) formation, cell death, and metabolic and ionic homeostasis disorders in experimental myocardial ischemia-reperfusion injury. These beneficial effects indicate the therapeutic potential of this compound in cardiovascular diseases. The goals of this work were to optimize the synthesis of peptide M, and to study its proteolytic stability and effect on the heart function of rabbits with doxorubicin (Dox) cardiomyopathy. We have developed a rational method of solid-phase synthesis of peptide M using the Fmoc methodology in combination with the temporary protection of the guanidine function of arginine residues by protonation (salt formation) during the formation of the amide bond. It avoids the formation of by-products, and simplifies the post-synthetic procedures, providing an increase in the yield of the final product of higher purity. Comparative evaluation of the proteolytic stability of peptide M and apelin-12 in human blood plasma was carried out using 1H NMR spectroscopy. It was shown that the half-life of peptide M in plasma is approximately three times longer than that of apelin-12. Intravenous infusion of increasing doses of peptide M caused a gradual increase in left ventricular (LV) fractional shortening and ejection fraction in rabbits after 8 weeks of Dox administration (2 mg/kg weekly). The effect of the modified peptide on LV systolic dysfunction was significantly more pronounced than the effect of apelin-12, which suggests the promise of using this pharmacological agonist of the APJ receptor in patients with heart failure.

The full-length rat galanin (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2, G29) was prepared by the solid phase peptide synthesis using the Fmoc-strategy. The peptide chain was elongated both by one amino acid and by a fragment condensation. Fragments with the C-terminal glycine residue were synthesized by the solid phase method on the 2-chlorotrityl chloride resin or by the method of conventional peptide synthesis in solution. After the reversed phase HPLC, galanin had the correct molecular weight and 98% purity. We studied the G29 cardioprotective properties on a model of acute myocardial infarction in rats. The G29 administration reduced the infarct size by 40% and decreased the activity of necrosis markers CK-MB (Creatine Kinase-MB) and LDH (Lactate Dehydrogenase) in the blood plasma. The peptide improved metabolic state of the infarcted heart, increased the ATP content, the total adenine nucleotide pool, phosphocreatine, and total creatine, and decreased the lactate level compared to a control. These results indicated the possibility of the G29 use as a drug for reducing the myocardial reperfusion injury. In addition, the mechanisms of the G29 action should be studied.

Резюме Цель исследования. Настоящая работа предпринята с целью изучения влияния митохондриального антиоксиданта пластомитина (ПМ, препарат SkQ1) на энергетическое состояние и функцию сердца крыс с кардиомиопатией, вызванной введением доксорубицина (Докс). Материалы и методы. Использовали крыс-самцов Вистар, которым вводили подкожно Докс (2 мг/кг/нед.) в течение 5 недель (группа Докс). Животным группы Докс+ПМ наряду с доксорубицином 5 недель подкожно вводили ПМ в дозе 0,32 мг/кг ежедневно. Контрольной группе животных в течение 5 недель вводили такой же объем физиологического раствора. Перед началом введения препаратов и через 8 недель у всех крыс была выполнена эхокардиография (ЭхоКГ) левого желудочка (ЛЖ). Дополнительно у части животных была изучена сократительная функция ЛЖ при помощи PV-катетера. Содержание адениннуклеотидов (АТФ, АДФ и АМФ), фосфокреатина (ФКр), креатина (Кр) и лактата в безбелковых экстрактах сердец определяли энзиматическими методами. Дыхание митохондрий в скинированных сапонином волокнах ЛЖ определяли полярографическим методом. Результаты. В конце исследования у животных группы Докс фракция выброса и фракция укорочения были достоверно снижены, а диастолический объём ЛЖ уменьшен по сравнению с этими показателями в контрольной группе. В группе Докс+ПМ фракция выброса, фракция укорочения, индекс сократимости миокарда, максимальная скорость развития давления и работа сердца были выше, чем в группе Докс и недостоверно отличались от величин в контроле. Эти изменения сочетались с достоверным увеличением содержания общего фонда адениннуклеотидов и креатина в сердце животных группы Докс+ПМ по сравнению с этими показателями у животных, получавших только Докс. Показатели скорости дыхания митохондрий в волокнах ЛЖ, выделенных из сердец животных группы Докс+ПМ, были выше, чем в группе Докс. Заключение. Применение ПМ предотвращало развитие систолической дисфункции у животных, получавших Докс. Это было связано с улучшением окислительного фосфорилирования и сохранением фонда адениннуклеотидов в сердце Summary Aim. This study was designed to explore effects of the mitochondrial antioxidant plastomitin (PM) on the energy state and heart function of rats with cardiomyopathy induced by doxorubicin (Dox) administration. Material and methods. Male Wistar rats were injected subcutaneously with Dox (2 mg / kg / weekly) for 5 weeks (Dox group). Animals of the Dox + PM group were subcutaneously injected with PM for 5 weeks at a dose of 0.32 mg/kg daily along with Dox. The control group of animals was injected for 5 weeks with the same volume of saline. Before the administration of drugs and after 8 weeks of the study, all rats were underwented echocardiography of the left ventricle (LV). Additionally, the LV contractile function was studied using a PV catheter in some animals. The contents of adenine nucleotides (ATP, ADP and AMP), phosphocreatine (PCr), creatine (Cr) and lactate in protein-free extracts of hearts were determined by enzymatic methods. Mitochondrial respiration in saponin-skinned LV fibers was determined using the polarographic method. Results. At the end of the study, in animals of Dox group, the ejection fraction, fractional shortening and LV diastolic volume were significantly reduced in comparison with these indices in the control group. In Dox + PM group, the ejection fraction, fractional shortening, myocardial contractility index, maximum rate of pressure development and heart work were significantly higher than in Dox group and did not differ from the control values. These functional alterations were combined with a significant increase in the content of myocardial adenine nucleotide pool and creatine in animals of Dox + PM group compared with these parameters in animals treated with Dox alone.The rate of mitochondrial respiration in LV fibers isolated from the hearts of animals of Dox + PM group was higher than in Dox group. Conclusion. Treatment with PM prevented the development of LV systolic dysfunction in animals received Dox. This beneficial effect was due to an improvement in oxidative phosphorylation and preservation of myocardial adenine nucleotide pool.