Metabolite Of Molsidomine Research Articles

Relaxations to Endothelium-Derived Relaxing Factor and the Metabolite of Molsidomine, SIN-1, in the Aorta and the Hindquarters of the Rat

The effects of SIN-1 were studied on isolated aortic rings and perfused hindquarters of the rat and were compared with the effects of nitroglycerin and endothelium-derived relaxing factor (EDRF) released by acetylcholine or histamine (aorta) and carbachol (hindquarters). SIN-1 relaxes rat aortic rings in a dose-dependent and endothelium-independent way. Aortic rings made tolerant to nitroglycerin in vitro show cross-tolerance to isosorbide dinitrate but no cross-tolerance to EDRF, sodium nitroprusside, or SIN-1. Aortic rings made tolerant to nitroglycerin by in vivo treatment show an important cross-tolerance to isosorbide dinitrate, a small degree of tolerance to sodium nitroprusside, but no significant tolerance to SIN-1 or EDRF. Also, in the nitroglycerin-tolerant hindquarter vasculature, no cross-tolerance is found to EDRF or SIN-1. In the aorta of renal hypertensive rats, in which the relaxation to EDRF-dependent dilators is impaired, no depression of the maximal response to SIN-1 occurs.

Molecular Aspects Underlying the Vasodilator Action of Molsidomine

Using different techniques, we measured the kinetics of nitric oxide (NO) liberation from SIN-1, the metabolite of molsidomine, and some related sydnonimines like its thiomorpholinyl analog, compound C 78-0698, and compared it under identical experimental conditions with its biological action at the guanylate cyclase (GC) site, taking this target enzyme as a suitable bioassay. There was a close relationship between half-maximal activation of GC and the velocity of NO release. The thiomorpholinyl analog was slightly more active in NO liberation than SIN-1 and activated the enzyme more rapidly. The kinetics of SIN-1A and SIN-1C formation, determined by high-performance liquid chromatography, could be accurately described by a Bateman equation. Oxyhemoglobin shifted the concentration-response curve of SIN-1 at the isolated soluble GC concentration to the right, whereas methemoglobin was without any effect. The results of our chemical and biochemical studies suggest that velocity and amount of NO formation are the only rate-limiting factors of guanylate cyclase activation by sydnonimines like SIN-1. NO, therefore, exclusively is the mediator of their pharmacodynamic action. In remarkable contrast to nitrate esters like glyceryl trinitrate or isosorbide dinitrate, NO liberation is not dependent on the interaction with thiol-containing compounds like cysteine.

Interaction Between SIN-1 and Prostacyclin in Inhibiting Platelet Aggregation

SIN-1, the metabolite of molsidomine, caused a dose-dependent inhibition of the aggregation of rabbit platelets induced by adenosine diphosphate (ADP) and the stable thromboxane mimetic U-46619. Molsidomine was inactive in this respect. In the presence of a threshold concentration of prostacyclin, the antiaggregating activity of SIN-1 became more pronounced. As a result, the dose-response curve of SIN-1 was shifted to the left. These findings suggest that SIN-1 could be of therapeutic value to suppress platelet aggregation during atherosclerotic disease when the endogenous supply of endothelium-derived relaxing factor is compromised.

Modulation of Platelet Function by SIN-1A, a Metabolite of Molsidomine

Molsidomine or its active metabolite SIN-1A have antithrombotic properties in experimental models. This effect seems to be related, at least in part, to their antiplatelet activities. SIN-1A inhibited platelet adhesion to collagen, platelet aggregation, and the release reaction in in vitro experiments. SIN-1A acts as an early step of platelet activation by inhibiting calcium influx and phospholipase activity, which leads to inhibition of thromboxane formation and fibrinogen binding. Antiplatelet properties were observed after oral absorption in healthy volunteers and in patients with myocardial infarction after intravenous infusion.

Modulation of Platelet Function by SIN-1A, a Metabolite of Molsidomine

Modulation of Platelet Function by SIN-1A, a Metabolite of Molsidomine

Relaxations to SIN-1, Nitric Oxide, and Sodium Nitroprusside in Canine Arteries and Veins

SUMMARY Experiments were designed to compare the vasodilator properties of SIN-1, the active metabolite of molsidomine, with nitric oxide (NO) and sodium nitroprusside. Rings of canine femoral arteries and veins with and without endothelium were suspended in organ chambers for the measurement of isometric force. SIN-1 and sodium nitroprusside relaxed rings of blood vessels in the presence and in the absence of the endothelium. However, these relaxations were reduced by the endothelial cells in arteries contracted with endothelin and in veins contracted with prostaglandin F2α. In the arteries, SIN-1, sodium nitroprusside, and NO were equipotent in relaxing rings without endothelium contracted with either norepinephrine or prostaglandin F2α; NO was less potent than the other two vasodilators when the arteries were contracted with endothelin. In the veins without endothelium, the potency of the three nitrovasodilators was comparable; the veins were more sensitive to the effects of the dilators when contracted with prostaglandin F2α than with either endothelin or norepinephrine. These results indicate that SIN-1, sodium nitroprusside, and NO are potent dilators of arterial and venous smooth muscle, and that the potency of the dilators can be altered by endothelial cells and the contractile agonist differentially in arteries and veins.

Differential Effect of SIN-1 on Thromboxane and Prostacyclin Formation in Platelets and Endothelial Cells

The effect of SIN-1, the active metabolite of molsidomine that inhibits platelet aggregation, was tested upon the oxidation of arachidonic acid in platelets and endothelial cells. The metabolism of arachidonic acid from both exogenous and endogenous sources was investigated by determining the formation of thromboxane and prostacyclin. These prostanoids were measured in platelets and endothelial cells alone or during their interaction, in the absence or presence of SIN-1. The presence of endothelial cells decreased the generation of thromboxane by the platelets, especially from endogenous arachidonate, whereas the platelets tended to increase that of prostacyclin under basal conditions. SIN-1 significantly reduced the production by the platelets of metabolites from endogenous arachidonic acid but did not affect those from exogenous sources. The reduction in metabolism of endogenous arachidonate was more pronounced in the presence of endothelial cells. In contrast, SIN-1 did not alter the production of cyclo-oxygenase metabolites of arachidonic acid in endothelial cells. Thus, the liberation of arachidonic acid, leading to prostanoid synthesis, may be regulated differentially in platelets and endothelial cells: molsidomine might be a potential antithrombogenic drug because it alters specifically the phospholipase activity in the platelets.

Relaxations to SIN-1, Nitric Oxide, and Sodium Nitroprusside in Canine Arteries and Veins

Experiments were designed to compare the vasodilator properties of SIN-1, the active metabolite of molsidomine, with nitric oxide (NO) and sodium nitroprusside. Rings of canine femoral arteries and veins with and without endothelium were suspended in organ chambers for the measurement of isometric force. SIN-1 and sodium nitroprusside relaxed rings of blood vessels in the presence and in the absence of the endothelium. However, these relaxations were reduced by the endothelial cells in arteries contracted with endothelin and in veins contracted with prostaglandin F2 alpha. In the arteries, SIN-1, sodium nitroprusside, and NO were equipotent in relaxing rings without endothelium contracted with either norepinephrine or prostaglandin F2 alpha; NO was less potent than the other two vasodilators when the arteries were contracted with endothelin. In the veins without endothelium, the potency of the three nitrovasodilators was comparable; the veins were more sensitive to the effects of the dilators when contracted with prostaglandin F2 alpha than with either endothelin or norepinephrine. These results indicate that SIN-1, sodium nitroprusside, and NO are potent dilators of arterial and venous smooth muscle, and that the potency of the dilators can be altered by endothelial cells and the contractile agonist differentially in arteries and veins.

Endothelium-Dependent Vasodilatation in Human Epicardial Coronary Arteries

Human epicardial coronary arteries were obtained from the hearts of 15 patients who received cardiac transplantation for cardiomyopathy. Transverse strips of these arteries were mounted in organ baths for isometric tension recording. The arteries were constricted with prostaglandin F2 alpha and then exposed to the endothelium-dependent relaxants substance P (1 nM), bradykinin (1 nM-1 microM), and the Ca2+ ionophore A23187 (1 nM-1 microM). The effects of the endothelium-independent relaxants glyceryl trinitrate (1 nM-10 microM) and SIN-1, the active metabolite of molsidomine (1 nM-10 microM), were also tested. In control strips of human coronary arteries, all vasodilators caused concentration-dependent relaxations. Pretreatment of human coronary arteries with glyceryl trinitrate (0.5 mM for 60 min) shifted the concentration-response curve to glyceryl trinitrate to the right by a factor of approximately 800 (increase in EC50 from 10 nM to 8 microM). In contrast, endothelium-dependent relaxations to substance P, bradykinin, and A23187 and relaxations to SIN-1 were not changed significantly. Previous exposure of human coronary arteries to SIN-1 (0.5 mM for 60 min) did not modify relaxations to any of the agents tested. Our results show that (a) the responsiveness to SIN-1 is not modified in nitrate-tolerant strips of human coronary arteries, (b) prolonged exposure of human coronary arteries to SIN-1 does not cause tolerance, and (c) endothelium-dependent relaxations are not influenced by exposure of human coronary arteries to either glyceryl trinitrate or SIN-1.

Generation of NO from Molsidomine (SIN-1) in vitro and Its Relationship to Changes in Coronary Vessel Tone

The release of NO from SIN-1, the active metabolite of molsidomine, was measured in vitro in Langendorff-perfused rabbit hearts. NO in the coronary effluent was determined on-line using the oxyhemoglobin technique. Left ventricular and coronary perfusion pressure were also recorded continuously. Glyceryl trinitrate and iloprost were used as reference compounds. Infusion of SIN-1 or glyceryl trinitrate into the coronary inflow resulted in a significant and dose-dependent NO release. An apparently identical response was seen when SIN-1 was infused into the coronary effluent while the response to glyceryl trinitrate was greatly reduced or abolished. The glyceryl trinitrate-induced coronary vasodilation was only slightly diminished in presence of oxyhemoglobin whereas the response to SIN-1 was abolished. This is explained by complete scavenging of NO by oxyhemoglobin within the vessel lumen. In isolated porcine aortic endothelial cells, SIN-1 induced a significant and dose-dependent increase in cyclic GMP, whereas glyceryl trinitrate was ineffective. This would argue against biotransformation of glyceryl trinitrate to NO by endothelial cells. Finally, glyceryl trinitrate-tolerant heart preparations exhibited a considerably reduced or even undetectable release of NO, whereas the response to SIN-1 was unchanged.

Mitochondrial sulfhydryl groups under oligomycin-inhibited, aging, and uncoupling conditions: Beneficial influence of cardioprotective drugs

Uncoupling, oligomycin-inhibited, and aging/swelling conditions comprise three models for mitochondrial dysfunction. In these models, the effects of Cardioprotective agents on rat heart mitochondrial membrane SH reactivity have been studied. For -SH detection two different chromophores were used: dithionitrobenzoate (Nbs 2) and mono-bromobimane (MB). The objective of this study is to reveal the influence of three Cardioprotective substances against the loss of membrane -SH reactivity: (i) The thiol reagent 2-mercaptopropionylglycine (MPG) prevents the decrease of thiols caused by carbonylcyanide- p-trifluoromethoxyphenylhydrazone (FCCP), aging, and oligomycin measured with MB and Nbs 2, and the diminution by oleate detected with MB. The small amount of MPG (6 nmol/mg protein), necessary for the protection, agrees with oligomycin sensitivity of the SH groups concerned. (ii) The active metabolite of molsidomine, 3-morpholinosydnonimine (SIN-1), protects against the decrease of thiols by FCCP, oleate, and aging monitored with MB. In the case of oligomycin -SH groups accessible to Nbs 2 are protected. (iii) Another antianginal drug, isosorbidedinitrate (ISDN) does not protect membrane thiol groups. In contrast to SIN-1, ISDN probably requires enzymatic activation. It is suggested that MPG as well as SIN-1 may help to restitute the original -SH status of the mitochondrial membrane.

Modulation of prostacyclin/thromboxane formation by molsidomine during plateletendothelial cell interactions

Platelet and endothelial cell metabolism of both exogenous and endogenous arachidonic acid, via the cyclooxygenase pathway, was evaluated according to thromboxane and prostacyclin formations. This was investigated in platelets, endothelial cells alone or during their interactions, in the presence or absence of SIN-1, the active anti-anginal metabolite of molsidomine. This revealed that, in contrast to the generation of thromboxane, which was decreased in the presence of endothelial cells, especially from endogenous arachidonate, that of prostacyclin increased under basal conditions as well as from endogenous arachidonate to a lesser extent. SIN-1 reduced thromboxane formation solely from endogenous arachidonate, and this was more pronounced when both cell populations interacted. In contrast, SIN-1 failed to decrease prostacyclin formation, which would emphasize its anti-aggregating potential. We conclude that the liberation of arachidonic acid leading to prostanoid synthesis may be differently regulated in platelets and endothelial cells, and that molsidomine might be a potential anti-aggregating drug in altering specifically thromboxane formation.

血管系に作用する有機ニトロ,ニトロソ化合物ならびにSodium Nitroprussideの薬理学的研究

The purpose of the present study was to determine the involvement of Ca2+ (Mg2+)-ATPase, guanylate cyclase, PGI2 synthesis and/or glutathion in mechanism of vascular smooth muscle relaxation by nitro- and nitroso-vasodilator drugs. Vasodilators used in the experiment were nitroglycerin (GTN), isosorbide dinitrate (ISD), N-nitroso-morpholino aminoacetonitrile (SIN-1A, an active metabolite of molsidomine) and sodium nitroprusside (SN P).Guinea-pig thoracic aorta strips were suspended in tissue bath which permitt cotinuous recording of isometric tension. Relaxation was measured in submaximally contracted strips with noradrenaline (NA,30 μM) or PGF2α (5 μM) and dose-relaxation curves were constructed to show the effects or IC50 ovalues of vasodilators.The cumulative concentrations of GTN from 0.001 to 100.0 μM and ISD from 0.01 to 100.0 μM relaxed the contracted strips in a concentration dependent manner. IC50values in GTN and ISD were 0.26 μM and 4.8 μM, respectively in the NA-contracted preparation. When tranylcypromine (TC), indomethacin (IDM) and/or 15 HPETE, each 10 μM which inhibit the production of PGI2, were added to the bath 20 min before NA application, the relaxation by GTN or ISD was attenuated to cause a significant shift of dose-relaxation curves to the right and IC50 values obtained from the curves was larger than the control one in each case. On the other hand, TC, IDM and 15 HPETE failed to alter the enhancement by GTN and ISD in Ca2+ (Mg2+)-ATPase activity in the microsome fraction from guinea pig thoracic aorta smooth muscle.The tension develope d by NA or PGF2α was decreased by the cumulative concentrations of SIN-1A from 0.001 to 100.0 μM or SNP 0.001 to 100.0 μM in a concentration dependen t manner. The relaxation was attenuated in the presence of methylene blue (MB) or 6-anilino-5,8-quinolinedione (AQD), which is reported as a guanylate cyclase inhibitor. SIN-1A was found to stimulate the activity of Ca2+ (Mg2+)-ATPase in the microsome fraction from guinea pig aorta. Inorganic nitroso complex salt SNP in the low concentration exerted a similar effect on Ca2+ (Mg2+)-ATPase activity to SIN-1A, but not in the high concentration of the drug. MB inhibited the stimulatory effect of SIN-1A in the Ca2+ (Mg2+) -ATPase activity, while AQD had no effect on the ATPase activity. The addition of SNP to the strips in the high concentration caused a depression of contractions obtained with NA even after removal of SNP from the bath.This depression was completely reversible upon the addition of glutathion 100 μM or MB 1.0 μM. The effects of SNP on vascular tissue may be, in part, account for the decrease in glutathion content in the smooth muscle of the tissue.These results suggest that GTN and ISD elicit vasodilation, partially through the stimulation of Ca2+ pump ATPase activity and also through the accelerated production of PGI2 in arterial blood vessel, and that SIN-1A and SNP dilate the blood vessel by the stimulatory effect on the Ca2+ pump ATPase as well as guanylate cyclase activity, although the glutathion content in the vascular tissue may decrease after the application of SNP because of a possible interaction between Fe3+-prussiate and SH-group of this active peptide.

O-201 - The effect of a Molsidomine metabolite (SIN-1A) on (Ca2+-Mg2+ )ATPase activity in sarcoplasmic reticulum from guinea-pig aortic smooth muscle

O-201 - The effect of a Molsidomine metabolite (SIN-1A) on (Ca2+-Mg2+ )ATPase activity in sarcoplasmic reticulum from guinea-pig aortic smooth muscle

Mechanism of Vasodilation by Nitrates: Role of Cyclic GMP

Nitrovasodilators relax vascular smooth muscle by stimulating soluble guanylate cyclase (GC). The resulting rise in cGMP probably initiates Ca extrusion from the smooth muscle cell which causes relaxation. Since repeated administration of organic nitrates, particularly nitroglycerin, leads to tolerance, i.e. a decrease in the vasodilator effect, it was studied whether (a) tolerance was a peripheral phenomenon occurring in the vascular smooth muscle, and (b) was due to an impairment of GC activation. In isolated circular strips of bovine coronary arteries, 90 min pretreatment with nitroglycerin greatly lowered the relaxing as well as the cGMP increasing response to nitroglycerin, indicating tolerance induction. Tolerance, although to a lesser extent, was also obtained with other organic nitrates under similar conditions, including IS 5-MN. Little (nitroprusside Na) to negligible tolerance was obtained with sodium nitrate and SIN-1, the active metabolite of molsidomine. The latter group of drugs stimulated soluble GC in vitro in the absence of cysteine whereas organic nitrates required the presence of this thiol. Preincubation with nitroglycerin almost completely inactivated GC whereas other organic nitrates had little effect. The results indicate that tolerance is caused by an impairment of GC function in the smooth muscle cell, particularly when elicited by nitroglycerin, and that differences in the degree of tolerance development by various nitrovasodilators are possibly due to different mechanisms of activation and inactivation of GC as well as differences in cysteine requirement.

Active and passive changes in coronary diameter after vasodilation with SIN-1, the active metabolite of molsidomine

The vasodilating effects of intracoronary injections of 0.4 mg of SIN-1, the active metabolite of molsidomine, on epicardial coronary arteries and coronary stenoses were evaluated in 14 patients with coronary artery disease in a double-blind, randomized fashion vs placebo. Nine additional patients with well defined coronary stenoses received 0.4 mg of SIN-1 as well. Diameter changes of nonstenotic coronary arteries in proximal, medial, and distal coronary segments as well as changes of the residual luminal diameters within coronary stenoses were determined before (K), immediately after (M1), and 10 minutes after (M2) intracoronary administration of SIN-1. Aortic pressures and heart rate were monitored continuously. After administration of SIN-1, the diameters of nonstenotic coronary arteries increased in proximal segments by 9.4% (M1) and 11.7% (M2), in medial segments by 17.9% (M1) and 17.6% (M2), and in distal segments by 25.6% (M1) and 28.8% (M2). Within coronary stenoses the residual luminal diameters showed mean increases of 31.5% (M1) and 48.3% (M2). Placebo administration did not alter coronary diameters significantly. Aortic pressure and heart rate did not change after administration of SIN-1 or placebo. SIN-1 effectively dilates nonstenotic and stenotic coronary segments, as do nitrates and calcium channel blockers. By intracoronary injections, the direct effects on coronary vessels can be evaluated without interference with systemic effects. The increase in the residual luminal diameters within dynamic coronary stenoses after administration of SIN-1 is probably an important antianginal mechanism also for molsidomine.

The new long-acting coronary artery dilator molsidomine and its metabolite SIN-1

We studied the effects of intracoronary injections of SIN-1 (0.8 mg), the active metabolite of molsidomine, on coronary artery diameters and coronary stenoses. In nine patients with abnormal angiograms measurements were made 4 and 8 minutes after SIN-1 administration. There was a statistically significant increase in coronary luminal diameter in proximal, medial, and distal segments as well as at the level of the stenoses. At 4 minutes after administration distal segments showed a mean increase in diameter of 50%, compared to a mean increase of 26% in proximal segments. In six patients with normal angiograms SIN-1 abolished three of four coronary spasms induced by ergonovine maleate. A protective effect of SIN-1 against the vasoconstrictor effects of ergonovine was still present at 8 minutes after administration. Heart rate and blood pressure remained unchanged throughout the study. We conclude that the vasodilation induced by SIN-1 in normal and stenotic coronary arteries is probably an important contribution to the antianginal efficacy of molsidomine and suggests that molsidomine may be effective in the prophylaxis of variant angina.

The Effects of Molsidomine and Its Metabolite SIN-1 on Coronary Vessel Tone, Platelet Aggregation, and Eicosanoid Formation In Vitro???Inhibition of 12-HPETE Biosynthesis

We studied the action of the biologically active metabolite of molsidomine, N-morpholino-N-nitrosoamino-acetonitrile (SIN), on eicosanoid formation and functional behavior of bovine coronary arteries and human platelets in vitro. Glyceryltrinitrate (GTN) and prostaglandin (PG) I2 were used as reference compounds. SIN dose-dependently inhibited the thrombin-, collagen-, and primary ADP-induced platelet aggregation. The IC50 was in the range of 0.1-0.8 mumol/L. At these concentrations SIN also inhibited thromboxane formation, but did not influence the PGI2 biosynthesis of coronary vessels. Molsidomine itself was inactive. GTN stimulated vascular PGI2 formation, but did not modify the platelet aggregation at comparable concentrations. A particularly interesting finding was the dose-dependent and apparently complete inhibition of formation of the hydroperoxide of 12L-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HPETE) in human platelets by SIN. The IC50 amounted to 1.7 +/- 0.4 mumol/L and was in the same range as with 5,8,11,14-eicosatetraynoic acid (2.0 +/- 0.3 mumol/L). Although the results may not suggest a common mechanism of the antiaggregatory action of GTN and SIN, they provide no evidence of a similar or dissimilar mechanism of action in vascular smooth muscle.

Effects of molsidomine and other NO-containing vasodilators on cyclic GMP formation.

Organic nitrates, molsidomine and sodium nitroprusside belong to a group of vasodilators containing an NO-group. Although some of them have already been used in the therapy of cardiovascular diseases for decades and although numerous results have been accumulated on their effects on the cardiovascular system as well as on isolated organs, the mechanism of their action on a cellular level is still to be explained. The metabolite of molsidomine used in ischemic heart disease, 3-morpholino-syndnonimine (SIN-I) and other sydnonimines have a vasodilatory effect and, like sodium nitroprusside, inhibit platelet aggregation, which possibly contributes to the therapeutic effect. It was shown that SIN-I raises the content of cyclic GMP of various blood vessels and, like other sydnonimines. raises the cyclic GMP concentration of platelets to an extent similar to that seen with sodium nitroprusside. SIN-I and other sydnonimines stimulate the soluble cyclic GMP-forming enzyme from hog spleen arteries and from human platelets: the same holds true for the soluble guanylate cyclase purified from bovine lung. On the basis of results from reaction-kinetic experiments performed with sydnonimines and soluble guanylate cyclase, it can be assumed that the enzyme is directly activated by the A-forms of sydnonimines which are non-enzymatically formed and contain an N-NO-group. On the basis of these and other findings, it is likely that the active metabolites of NO-containing vasodilators are compounds whose NO-group can be bound through nitrogen, oxygen or sulfur. The findings obtained so far on the regulation of cyclic GMP formation by hormonal factors and drugs as well as on the effects of cyclic GMP derivatives on smooth muscle and platelets suggest that cyclic GMP-dependent regulatory processes are involved in the effects of NO-containing vasodilators. It can be expected that the elucidation of cyclic GMP-dependent regulatory processes will contribute significantly to the understanding of the differences in effects of these drugs on capacity and resistance vessels, of the tolerance development when organic nitrates are used and of possible interferences with other cardiovascular-active drugs such as β-blockers or calcium antagonists.