Studies On Protective Effects And Mechanisms Of Taurine On Myocardial Ishemia

The incidence, mutilation rate and lethality rate of cardiovasculardiseases turns on the increasing trends all over the world in recent years.Ishemic heart disease (IHD) is one of the most common cardiovasculardiseases in clinical practice, IHD is caused by coronary blood circulationchanges resulting in the imbalance of myocardial supply and demand.Acute myocardial ischemia or acute myocardial infarction happened whencoronary artery was occluded suddenly and for a long time. Drug therapyis one of important ways to cure myocardial ischemia. Although nitrate,calcium-channel blocker and β-receptor antagonist are effective in thetherapy of myocardial ischemia, they all have some adverse reactions.Studies on the new agents used to treat myocardium ischemia are still apivotal issue.Taurine (2-aminoethylsulfonic acid), a β-amino acid, is lookedupon as an "essential amino acid" in the body. Taurine has multiplephysiological and pharmacological functions: this sulfur-containing aminoacid plays an important part in promoting optic nerve fuction, nutrition thecenter, osmoregulation, anti-inflammatory, relieving pain, decreasingblood glucose, improving microcirculation, resisting senile anddefatigation. Clinically, taurine has been used in asthenopia, eliminatinginflammatory and relieving pain. The protective effects of taurine oncardiovascular disease have been paid little attention by people, sodeveloping the new preparation of taurine on cardiovascular disease hasgood prospect.It is demonstrated that taurine is effective on viral myocarditis andcardiomyopathy. The effect on myocardial ischemia and its mechanismshas not been brought to light completely, the objectives of the presentstudy are to copy the model of myocardial ischemia in vivo and in vitro toinvesgate the protective effects and possible mechanisms of taurine on thecardiovascular disease and to provide a theoretical basis for better, saferuse and targeting application in clinical practice.Acute myocardium ishemia model in rats by ligating the descendinganterior branch of the coronary artery for 6h was developed, the effects oftaurine on the serum level of lactate dehydrogenase(LDH), superoxidedismutase(SOD), malondialdehyde(MDA) were measured andmyocardium infarction area was detected by nitroterrazolium blue chloride(NBT) staining. At the same time, samples were taken to store in thefixation liquid for HE and TUNEL immunohistochemical performance.Myocardial Chronic damage model in rats by administratingadriamycin(ADR) was set up and the effects of taurine on the content ofLDH and SOD in myocardial tissue and GOT in the serum were measured ,Histopathology changes and ultramicrostructure in myocardium tissue wasrelatively detected by HE staining and electron microscope.Ligating the left anterior descending coronary artery oradminiatrating ADR in rat simulated the patho-physiological process-theincreasing of free radicals in myocardial ischemia. Experiments results invivo showed that taurine could significantly reduce content of MDA, andincrease the activity of SOD in serum or myocardium tissue, and reduceLDH and GOT releasing from myocardial cell. Taurine could decrease thepositive percent of cardiac myocyte apoptosis, and reduce the infarctionarea. In addition, taurine could increase the survival rate and inhibit themitochondria hyperplasia in myocyte damaged by ADR. It is demonstratedthat taurine is effective on the therapy of myocardium ischemia in animals.It was presumed that taurine protected the cellular membrane, inhibitedthe cardiac myocyte enzymes release, reducing myocardium apoptosispercentage and reducing the infarction area probably by increasing theenzyme activity of anti-oxidation and the ability of removing free radicals.The primary cultured cardiac myocytes in neonatal rats damaged by0.3mmol/L hydrogen peroside(H2O2) simulated the oxidative stress model.The survival ability were detected by Methyl thiazolyl tetrazolium(MTT)method. The content of LDH in cultured conditions, SOD and MDA inmyocytes were measured by the instruments. The percentage of apoptosisrate and mitochondrial memberane pertential(△Ψm) were measured byflowcytometry, and intracellular calcium change by Fluo-3/AM stainingbefore and after H2O2 damage was observed by laser-confocal-microscopysystem. Meanwhile, the protein expression of Bcl-2 , Bax and CaMKIIwere analyzed by Western-blotting. In addition,Cacium-calmodulin-calmodulin independent protein kinase Ⅱ(Ca2+-CaM-CaMKII)signal transduction pathway were investigate by detectingthe content of mRNA of CaM and CaMKII with the method of one stepRT-PCR. The results in vitro experiments showed that taurine couldincrease the survival rate of cardiac myocytes, reduce the release of LDHfrom the myocytes and the generation of MDA, increase the activity ofSOD in myocytes, reduce apoptosis percentage, stablize the mitochondrialmembrane potential, reduce the intracellular calcium overload, increacethe content of CaM and CaMKII mRNA, increase the protein expressionof Bcl-2 and CaMKII ,meanwhile decrease the protein expression of Bax.Oxidative stress in myocytes was simulated by adding the finalconcentration of 0.3mol/L H2O2 to the cultured conditions, resulting incalcium overload and the damage of motrochondria. These three factorsmay work separately or interact with each other to cause cellular structure,function and metabolism obstruction, and eventual cell death. Taurinereducing the the generation of MDA and increasing the activity of SOD inmyocytes damaged by H2O2 indirectly demonstrated that taurine couldprotect the activities of antioxidase and inhibit the formation of lipidperoxidation production, this accorded with the finding of researchersabroad and also hinted that one of probably mechanisms of taurine onprotecting myocardium is inhibiting the production of oxygen free radicals.Taurine reducing the change of intracellular Ca2+ fluorescent intensitybefore and after the myocytes damaged by H2O2 indicated that tarineattenuated calcium overload probably owning to protectingCaMKⅡprotein expression in damaged myocytes, because Ca2 + -CaM-CaMKⅡ signal transduction play a pivotal role in modulatingintracellular Ca2+ and CaMKⅡmodulated calcium cycle byphosphorylating calcium release channel(such as ryanodine receptor) andcalcium pump in sarcoplasmic reticulum. In addition, It indicated thattaurine inhibited the opening of mitochondrial permeability transitionpores to stabilize mitochondria membrane potential. Taurine inhibitmyocytes apoptosis by several ways ① Taurine inhibit the initiation ofapoptosis by reducing the formation of oxygen free radicals andintracellular calcium overload. ② Taurine inhibited the opening ofmitochondrial transition pores, thus reducing the release ofapoptosis-inducing proteins, such as Cyt C,Smac,AIF.③ Taurinemodulated the protein in signal transduction of apoptosis, such asupregulating anti-apoptosis Bcl-2 protein family and downregulatingpro-apoptosis Bax protein。In conclusion, taurine protected from acute myocardium infarctionby ligating the left anterior descending coronary artery, myocardialChronic damage inducing by ADR in rats and oxidative stress in theprimary cultured cardiac myocytes in neonatal rats damaged by H2O2.Based on the above experiments in vivo and in vitro, it has been proventaurine protected the cardiac myocyte from hypoxia damage probablyowing to reducing free radical damnification, decreasing intracellularcalcium overload, protecting the mitochondrion and inhibitingcardiomyocyte apoptosis.