Improvement of Cardiac Function and Subcellular Defects Due to Chronic Diabetes upon Treatment with Sarpogrelate

In order to investigate the subcellular mechanisms underlying the beneficial effects of sarpogrelate-a 5-HT2A receptor antagonist-on diabetic cardiomyopathy, diabetes was induced in rats by injecting streptozotocin (65 mg/kg). Diabetic animals were treated with or without sarpogrelate (5 mg/kg daily) for 6 weeks; diabetic animals were also treated with insulin (10 units/kg daily) for comparison. Elevated plasma levels of glucose and lipids, depressed insulin levels, hemodynamic alterations and cardiac dysfunction in diabetic animals were partially or fully attenuated by sarpogrelate or insulin treatment. Diabetes-induced changes in myocardial high-energy phosphate stores, as well as depressed mitochondrial oxidative phosphorylation and Ca2+-uptake activities, were significantly prevented by these treatments. Reductions in sarcolemma Na+-K+ ATPase, Na+-Ca2+ exchange, Ca2+-channel density and Ca2+-uptake activities were also attenuated by treatments with sarpogrelate and insulin. In addition, decreases in diabetes-induced sarcoplasmic reticulum Ca2+-uptake, Ca2+-release and Ca2+-stimulated ATPase activities, myofibrillar Mg2+-ATPase and Ca2+-stimulated ATPase activities, and myosin Mg2+-ATPase and Ca2+-ATPase activities were fully or partially prevented by sarpogrelate and insulin treatments. Marked alterations in different biomarkers of oxidative stress, such as malondialdehyde, superoxide dismutase and glutathione peroxidase, in diabetic hearts were also attenuated by treating the animals with sarpogrelate or insulin. These observations suggest that therapy with sarpogrelate, like that with insulin, may improve cardiac function by preventing subcellular and metabolic defects as a consequence of a reduction in oxidative stress.

Dual Roles of 5-Hydroxytryptamine in Ischemia-Reperfusion Injury in Isolated Rat Hearts

Background: 5-Hydroxytryptamine (5-HT) has been shown to be involved in exacerbating cardiac ischemia-reperfusion injury; however, the role of 5-HT in the injury has yet to be established. This study demonstrates that 5-HT has dual roles in ischemia-reperfusion injury.

Methods and Results: The role of 5-HT in cardiac ischemia-reperfusion injury was examined in isolated rat hearts perfused with oxygenated Krebs-Henseleit solution. A 30-minute global ischemia and 30-minute reperfusion exacerbated functional cardiac parameters such as left ventricular end-diastolic pressure, coronary flow, heart rate, and total lactate dehydrogenase release. The 5-HT2A receptor antagonist sarpogrelate (0.3-1.0 μM) improved cardiac function during ischemia-reperfusion. High-performance liquid chromatography analysis revealed an elevation in the level of 5-HT in the coronary effluent immediately after ischemia, suggesting that 5-HT is released from the ischemic heart and that sarpogrelate protects the heart from ischemia-reperfusion injury by blocking 5-HT2A receptors. However, 5-HT (0.3-1.0,μM) applied exogenously unexpectedly improved the cardiac mechanical parameters during ischemia-reperfusion, increased coronary flow, and increased the level of NO in the effluent, which was inhibited by L-NG-nitro-arginine methyl ester, a NO synthase blocker.

Conclusions: Present results suggest dual roles of 5-HT in ischemia-reperfusion injury. During ischemia, 5HT is released endogenously, constricts coronary smooth muscles via 5-HT2A receptors, and aggravates cardiac function. In contrast, 5-HT applied exogenously affects predominantly non-5HT2A receptors on the endothelium and induces coronary vasodilatation via endothelial NO production, which is protective against ischemia-reperfusion injury.

Mechanism of sarpogrelate action in improving cardiac function in diabetes

Although sarpogrelate, a 5-HT(2A) receptor antagonist, has been reported to exert beneficial effects in diabetes, the mechanisms of its action are not understood. In this study, diabetes was induced in rats by an injection of streptozotocin (65 mg/kg) and the animals were assessed 7 weeks later. Decreased serum insulin as well as increased serum glucose, cholesterol, and triglyceride levels in diabetic animals were associated with increased blood pressure and heart/body weight ratio. Impaired cardiac performance in diabetic animals was evident by decreased heart rate, left ventricular developed pressure, rate of pressure development, and rate of pressure decay. Treatment of diabetic animals with sarpogrelate (5 mg/kg) or insulin (10 units/kg) daily for 6 weeks attenuated the observed changes in serum insulin, glucose, and lipid levels as well as blood pressure and cardiac function by varying degrees. Protein content for membrane glucose transporters (GLUT-1 and GLUT-4) was depressed in diabetic heart; the observed alteration in GLUT-4 was partially prevented by both sarpogrelate and insulin, whereas that in GLUT-1 was attenuated by sarpogrelate only. Incubation of myoblast cells with sarpogrelate and insulin stimulated glucose uptake; these effects were additive. 5-hydroxytryptamine was found to inhibit glucose-induced insulin release from the pancreas; this effect was prevented by sarpogrelate. These results suggest that sarpogrelate may improve cardiac function in chronic diabetes by promoting the expression of membrane glucose transporters as well as by releasing insulin from the pancreas.

Antiplatelet agents sarpogrelate and cilostazol affect experimentally-induced ventricular arrhythmias and mortality

Antiplatelet agents, sarpogrelate (SAR), a 5-hydroxy tryptamine 2A receptor antagonist and cilostazol (CIL), a phosphodiesterase-III inhibitor, were observed to be beneficial in attenuating cardiac remodeling and improving cardiac function in congestive heart failure due to myocardial infarction in rats; however, CIL increased ventricular tachycardia and mortality. In order to study the effects of these antiplatelet agents on arrhythmias, Sprague-Dawley rats were pretreated with either SAR or CIL (5 mg/kg/day) for 2 weeks and were then either injected cumulative doses of epinephrine (Epi) or subjected to coronary occlusion. Saline-treated animals served as controls. Electrocardiographic analysis revealed that SAR pretreatment decreased the incidence and severity of ventricular arrhythmias (time of onset of arrhythmias as well as the occurrence of premature ventricular contractions, salvos, tachycardia, and fibrillations), whereas CIL treatment augmented the incidence of cardiac arrhythmias due to both Epi and coronary occlusion. None of the drugs affected the corrected QT interval significantly. Furthermore, the levels of cyclic adenosine monophosphate (cAMP) in left ventricle were markedly higher in CIL-pretreated rats when compared to SAR-pretreated or control rats. It is suggested that an excessive level of cAMP may contribute to increase incidence of ventricular arrhythmias and mortality in animals pretreated with CIL, unlike the SAR-pretreated rats.

Targeting platelets for prevention and treatment of cardiovascular disease

Platelets play an important role in the development of thrombosis, atherosclerosis, hypertension, heart attack and stroke. As a result, pharmacologic interventions that influence platelet functions, such as adhesion, aggregation and the release of different factors, are considered useful for the prevention and treatment of cardiovascular disease. Although classical anti-platelet agents have proven beneficial effects for the treatment of some specific cardiovascular diseases, there are limitations for their use as these drugs target platelet function directly. In contrast, newly developed anti-platelet agents have broad applications for the treatment of cardiovascular disease as they not only influence platelet function but are also considered to affect cardiac and vascular smooth muscle cell functions. Natural food products and nutraceutical agents also appear to modify cardiovascular abnormalities by affecting various platelet functions; however, the mechanisms of their actions remain to be investigated. Accordingly, this article is focused to discuss emerging pharmacologic, nutritional and nutraceutical interventions that may influence the prevention or progression of a broad range of cardiovascular diseases.

Antiplatelet therapy attenuates subcellular remodelling in congestive heart failure

Antiplatelet agents, sarpogrelate (SAR), a 5-HT(2A) receptor antagonist, and cilostazol (CIL), a phosphodiesterase III (PDE-III) inhibitor, are used for the treatment of peripheral vascular disease. We tested whether these agents affect cardiac function and subcellular remodelling in congestive heart failure (CHF) induced by myocardial infarction (MI). Three weeks after MI, rats were treated daily with 5 mg/kg SAR or CIL as well as vehicle for 5 weeks. Sham-operated animals served as controls. At end of the treatment period, haemodynamic measurements were performed and the left ventricle was processed for the determination of sarcoplasmic reticulum (SR) Ca(2+)-uptake and -release activities, and expression of SR Ca(2+)-pump, phospholamban and ryanodine receptors, as well as myofibrillar ATPase activities, expression of alpha- and beta-myosin heavy chain (MHC) isoforms, and phosphorylation of phospholamban and cardiac troponin-I (c Tn-I). Marked haemodynamic changes in the MI-induced CHF were associated with depressions in SR Ca (+)-uptake and -release activities as well as in protein content and gene expression for SR proteins. Furthermore, myofibrillar Ca(2+)-stimulated ATPase activity, as well as protein content and gene expression for alpha-MHC were decreased whereas those for beta-MHC were increased in the failing heart. Also, phosphorylation levels of phospholamban and cTn-I were reduced in failing hearts. The MI-associated changes in cardiac function, SR and myofibillar activities, as well as SR and myofibrillar protein and gene expression were attenuated by treatment with SAR or CIL. The results suggest that SAR and CIL improve cardiac function by ameliorating subcellular remodelling in the failing heart and indicate the potential therapy of CHF with antiplatelet agents.

Induction of Indefinite Survival of Fully Mismatched Cardiac Allografts and Generation of Regulatory Cells by Sarpogrelate Hydrochloride

BACKGROUND

At initiation of the immunologic response, platelets rapidly release chemical mediators such as serotonin (5-hydroxytryptamine, [5-HT]) and cytokines. Sarpogrelate hydrochloride (SH), a selective 5-HT2-receptor antagonist, is used to treat patients with peripheral arterial disease. We investigated the effect of SH on the alloimmune response in a murine cardiac transplantation model.

METHODS

CBA mice underwent transplantation of a C57BL/10 heart and received a short course of SH treatment. Survival of the allograft was recorded. An adoptive transfer study was performed to determine whether regulatory cells were generated. Immunohistochemistry studies of intercellular adhesion molecule 1 (ICAM-1), histological, cell-proliferation, and cytokine assessments were performed.

RESULTS

Untreated CBA mice rejected C57BL/10 cardiac grafts acutely (median survival time [MST], 8 days). In mice given 10 mg/kg of SH, all allografts survived indefinitely (MST, >100 days); these mice also had significantly prolonged survival of donor-specific skin grafts but acute rejection of third-party skin grafts. Secondary CBA recipients given not only whole but also CD4 splenocytes from primary SH-treated CBA recipients with C57BL/10 cardiac allograft had indefinite survival of C57BL/10 hearts (MST, >100 days). SH inhibited upregulation of ICAM-1 on endothelial cells in the allografts. Graft acceptance and hyporesponsiveness were confirmed by the histological and cell-proliferation studies, respectively. Production of interleukin-4 and interleukin-10 from splenocytes of SH-treated transplant recipients increased compared to that from splenocytes of untreated recipients.

CONCLUSION

SH induced indefinite survival of fully allogeneic cardiac allografts, generated CD4 regulatory cells, inhibited ICAM-1 expression in the allografts, and upregulated IL-4 and IL-10 production.

5-HT2 receptor blocker sarpogrelate prevents downregulation of antiapoptotic protein Bcl-2 and protects the heart against ischemia–reperfusion injury

Even though reperfusion is the treatment of choice in patients admitted with acute myocardial infarction, reperfusion itself has been demonstrated to activate various pathological factors especially following procedures of cardiac revascularization. 5-hydroxytryptamine (5HT) is one such factor activated during reperfusion and is known to trigger the post ischemic contractile dysfunction and pathological apoptosis. Here we demonstrate the potential effects of the 5-HT(2)A antagonist sarpogrelate in protecting the myocardium against reperfusion injury of heart. Male Wistar rats weighing between 220 and 240 g were subjected to 30 min left coronary artery (LCA) occlusion and 120 min reperfusion. Sarpogrelate (4 mg/kg) was infused intravenously for 30 min either before LCA occlusion or at reperfusion. Following reperfusion the samples were collected for infarction area, immunohistochemistry, western blotting and myocardial metabolite analysis. Sarpogrelate infusion before ischemia resulted in (a) significant recovery of post ischemic cardiac functions (LVDP, EDP), (b) significant reduction in the infarct size among the risk area after triphenyl tetrazolium chloride staining (p<0.001), (c) decreased tissue water content (p<0.05), (d) well preserved myocardial ATP (p<0.05), (e) reduction in Bcl-2 downregulation and caspase 3 activation and (g) less prevalence of apoptotic cells (3.1+/-0.4% to 15.2+/-0.6%, drug versus control). Treating the rats with sarpogrelate during reperfusion also showed similar results. This study thus demonstrates the protective effects of sarpogrelate and supports the role for 5-HT2A inhibition in preventing the reperfusion injury of the heart.

Therapeutic Potentials of Sarpogrelate in Cardiovascular Disease*

In view of the pivotal role of serotonin (5-HT) in a wide variety of cardiovascular disorders, extensive effort has been made to develop different types of 5-HT receptor antagonists for therapeutic use. On the basis of experimental studies, this article is focused on the potentials of sarpogrelate, a specific 5-HT2A receptor antagonist as an antiplatelet, antithrombotic, antiatherosclerotic and antianginal agent. The major effects of sarpogrelate are due to the inhibition of 5-HT-induced platelet aggregation and smooth muscle cell proliferation. This agent was found to attenuate the 5-HT-mediated increase in intracellular Ca2+ and ischemia-reperfusion injury in the heart. Sarpogrelate has been found to have beneficial effects in peripheral vascular disease, restenosis after coronary stenting, pulmonary hypertension, acute and chronic myocardial infarction.

Oxidative Stress by Monoamine Oxidase Mediates Receptor-Independent Cardiomyocyte Apoptosis by Serotonin and Postischemic Myocardial Injury

BACKGROUND

Serotonin (5-hydroxytryptamine [5-HT]), released by activated platelets during cardiac ischemia, is metabolized by the mitochondrial enzyme monoamine oxidase A (MAO-A). Because hydrogen peroxide is one of the byproducts of 5-HT degradation by MAO-A, we investigated the potential role of reactive oxygen species generated by MAOs in 5-HT-dependent cardiomyocyte death and post-ischemia-reperfusion cardiac damage.

METHODS AND RESULTS

Treatment of isolated adult rat cardiomyocytes with 5-HT induced intracellular oxidative stress and cell apoptosis. The apoptotic cascade triggered by 5-HT involves release of cytochrome c, upregulation of proapoptotic Bax protein, and downregulation of antiapoptotic Bcl-2 protein. These effects were prevented by inhibition of amine transporter or MAO, antioxidants, or iron chelation. In contrast, cardiomyocyte apoptosis was only slightly affected by the 5-HT(2B) receptor antagonist SB 206553. In vivo, inhibition of MAO-A largely reduced myocardial ultrastructural damage induced by 30 minutes of ischemia followed by 60 minutes of reperfusion in the rat heart. Cardioprotective effects of MAO inhibitors were associated with the prevention of postischemic oxidative stress, neutrophil accumulation, and mitochondrial-dependent cell death and were not reverted by SB 206553. Administration of MAO-A inhibitors during ischemia was still effective in preventing cardiac damage.

CONCLUSIONS

Our results supply the first direct evidence that oxidative stress induced by MAO is responsible for receptor-independent apoptotic effects of 5-HT in cardiomyocytes and postischemic myocardial injury. These findings provide new insight into the mechanisms of 5-HT action in the heart and may constitute the basis for novel therapies.

Sarpogrelate: cardiovascular and renal clinical potential

Sarpogrelate is a selective 5-hydroxytryptamine receptor subtype 2A (5-HT2A) antagonist. It is metabolised to racemic M-1 and both enantiomers of M-1 are also antagonists of 5-HT2A receptors. Sarpogrelate inhibits responses to 5-HT mediated by 5-HT2A receptors such as platelet aggregation, vasoconstriction and vascular smooth muscle proliferation. There is no information available on the pharmacokinetics of sarpogrelate. Sarpogrelate is efficacious in animal models of thrombosis, coronary artery spasm, atherosclerosis, restenosis, peripheral vascular disease, pulmonary hypertension, ischaemic heart disease, myocardial infarction, diabetes and kidney disease. Small clinical trials indicate that sarpogrelate may be beneficial in the treatment of coronary artery disease, angina, restenosis, heart valve prostheses surgery, diabetes mellitus, Raynaud's phenomenon, systemic sclerosis and Buerger's disease. Larger, randomised, double-blind, placebo-controlled clinical trials of sarpogrelate in intermittent claudication, coronary artery disease, restenosis and diabetes should be considered.

Protective effects of sarpogrelate, a 5-HT2A antagonist, against postischemic myocardial dysfunction in guinea-pig hearts

The protective effects of sarpogrelate (SG), a 5-HT2A antagonist, were investigated in perfused guinea-pig Langendorff hearts subjected to ischemia and reperfusion. Changes in cellular levels of high phosphorous energy, NO and Ca2+ in the heart together with simultaneous recordings of left ventricular developed pressure (LVDP) were monitored using an nitric oxide (NO) electrode, fluorometry and 31P-NMR. The recovery of LVDP from ischemia by reperfusion was 30.1% in the control, while the treatment with SG (5 x 10(-7) M) in pre- and post-ischemia hearts produced a gradual increase to 73.1 and 53.6%, respectively. At the final stage of ischemia, the intracellular concentration of Ca2+ ([Ca2+]i) and release of NO increased with no twitching and remained at a high steady level. The addition of SG increased the transient NO signal (TNO) level at the end of ischemia compared with the control, but [Ca2+]i during ischemia decreased. Meanwhile, mitochondrial Ca2+ uptake on acidification or Ca2+ content changes of the perfusate was suppressed by pre-treatment with SG or the KATP channel opener diazoxide, but not the KATP channel blocker 5-HD. The myocardial NO elevated with 5-HT in normal Langendorff hearts was suppressed by the treatment with SG. Therefore, the existence of the 5HT2A receptor in a Langendorff heart was anticipated. By in vitro EPR, SG was found to directly quench the hydroxy radical. Thus, these findings suggested that the 5-HT2A receptor induced in ischemia-reperfusion plays an important role in the mitochondrial KATP channel of hearts in close relation with NO and active oxygen radicals.

Attenuation of the serotonin-induced increase in intracellular calcium in rat aortic smooth muscle cells by sarpogrelate

Although serotonin (5-HT) induced proliferation of vascular smooth muscle cells is considered to involve changes in intracellular Ca2+([Ca2+]i), the mechanism of Ca2+mobilization by 5-HT is not well defined. In this study, we examined the effect of 5-HT on rat aortic smooth muscle cells (RASMCs) by Fura-2 microfluorometry for [Ca2+]imeasurements. 5-HT was observed to increase the [Ca2+]iin a concentration- and time-dependent manner. This action of 5-HT was dependent upon the extracellular concentration of Ca2+([Ca2+]e) and was inhibited by both Ca2+channel antagonists (verapamil and diltiazem) and inhibitors of sarcoplasmic reticular Ca2+pumps (thapsigargin and cyclopia zonic acid). The 5-HT-induced increase in [Ca2+]iwas blocked by sarpogrelate, a 5-HT2A-receptor antagonist, but not by different agents known to block other receptor sites. 5-HT-receptor antagonists such as ketanserin, cinanserin, and mianserin, unlike methysergide, were also found to inhibit the 5-HT-induced Ca2+mobilization, but these agents were less effective in comparison to sarpogrelate. On the other hand, the increase in [Ca2+]iin RASMCs by ATP, angiotensin II, endothelin-1, or phorbol ester was not affected by sarpogrelate. These results indicate that Ca2+mobilization in RASMCs by 5-HT is mediated through the activation of 5-HT2Areceptors and support the view that the 5-HT-induced increase in [Ca2+]iinvolves both the extracellular and intracellular sources of Ca2+.Key words: sarpogrelate, serotonin, vascular smooth muscle cells, intracellular Ca2+.

The role of 5-HT on the cardiovascular and renal systems and the clinical potential of 5-HT modulation

The main peripheral sources of 5-hydroxytryptamine (5-HT) are as a neurotransmitter and local hormone in the gastrointestinal tract, and stored in circulating platelets and pulmonary neuroepithelial bodies. 5-HT has been shown to have many possible physiological and pathophysiological roles on the cardiovascular and renal systems. Thus, 5-HT may contribute to valvular heart disease, coronary artery disease, pulmonary hypertension, pulmonary embolism, pre-eclampsia, peripheral vascular disease and diabetic nephropathy. Consequently, modulators of the 5-HT system have diverse clinical potential. For instance, selective 5-HT subtype 3 receptor (5-HT(3)) antagonists may have potential in the treatment of the pain associated with myocardial infarction. MCI-9042 (sarpogrelate) or other 5-HT(2A) antagonists may have clinical potential for the treatment of vasospastic angina, ischaemic heart disease, reperfusion injury and hindlimb ischaemia. Several modulators of 5-HT (5-HT transporter inhibitors, 5-HT(1B) and (2B) antagonists) may have potential alone or in combination in the treatment of pulmonary hypertension. In hypertension, agonists at the 5-HT(7) and antagonists at the 5-HT(2B) may reduce blood pressure, and in diabetes, sarpogrelate may protect against nephropathy.

Blockade of 5-HT(2A) receptors by sarpogrelate protects the heart against myocardial infarction in rats

BACKGROUND

It has been shown that serotonin (5-hydroxytryptamine, 5-HT) is involved in exacerbating vascular abnormalities; however, its role in mediating changes in cardiac function due to myocardial injury has yet to be established. This study examined the effect of sarpogrelate, a 5-HT(2A) receptor blocker, in preventing cardiac dysfunction due to myocardial infarction (MI).

METHODS AND RESULTS

Rats were treated 3 days before surgery with or without 5 mg x kg(-1) x day(-1) sarpogrelate, and the left coronary artery was ligated for 3 weeks to induce MI. Sarpogrelate reduced the mortality from 40% to 30%, infarct size from 35% to 25%, and left ventricular end diastolic pressure from 15 mm Hg to 10 mm Hg in MI rats. Electrocardiographic (ECG) tracings showed a marked deviation in the ST-segment and prolongation of the QTc interval in MI rats during the 3 weeks; these changes were attenuated by sarpogrelate pretreatment. In another set of experiments, MI rats were treated with 5 mg x kg(-1) x day(-1) sarpogrelate 1 hour after the surgery, and the hemodynamic and electrocardiograph changes were assessed at 3 weeks. This posttreatment was also found to reduce infarct size, improve cardiac function, and attenuate ECG changes.

CONCLUSIONS

Sarpogrelate attenuates cardiac dysfunction, infarct size, and changes in the ECG due to MI. These results also support the view that serotonin and 5-HT(2A) may contribute to the deleterious effects of ischemic injury in the heart.