| The data from N Engl J Med indicates that 92.4 million adults have diabetesand in addition, 148.2 million adults have prediabetes in China. China overtakesIndia as diabetes capital. Cardiovascular disease is a major complication ofdiabetes and the leading cause of early death among people with diabetes. About65 percent of people with diabetes die from heart disease. Diabetes has become acostly health burden in China.Strong evidence exists that diabetics suffer from increased incidence andseverity of myocardial infarction (MI) and are much more likely to suffer fromheart failure following MI compared to non-diabetics. The results from animalmodel also demonstrate that the diabetic animals have larger infarct size and poorheart function after ischemia/reperfusion injury. However, despite theoverwhelming data indicating that the diabetic heart is more sensitive to ischemicinjury, a controversy has arisen concerning this. The diabetic and non-diabeticpatients have similar or even smaller infarct size estimated by maximum levels ofserum cardiac enzymes and QRS-score gave. The diabetic heart exposed toischemia exhibits enhanced recovery of cardiac contractile function with reperfusion as compared to hearts from non-diabetic rats. This discrepancy maypartly attribute to the duration of diabetes according to some studies thatdemonstrate that diabetes at early stages have generally shown cardioprotectionagainst ischemia/reperfusion (I/R) injury compared to later stage. However theexact relationship between the duration of diabetes and the severity of MI/Rinjury remains unknown.Oxidative/nitrative stress has been implicated as a contributor to both theonset and the progression of diabetes and its associated complications. Evidenceexists that both I/R injury and diabetes increased reactive nitrogen species (RNS)and reactive oxygen species (ROS) production which can modifyposttranslationally some key proteins related to gene expression, signaltransduction, and antioxidant defense, altering the response of hearts to I/R injury.Thioredoxin is a small protein expressed in living cells. Trx not only exertscytoprotective functions against oxidative stress, but also regulates cell survivalsignaling pathways. It has been demonstrated that in addition to upregulation ordownregulation of Trx expression at the gene level, Trx activity is regulated byposttranslational modification. Trx can be nitratively modified, resulting in theirreversible inhibition of activity during the MI/R condition. Recent studydemonstrates that increased oxidative/ nitrative stress and nitrative inactivation ofthioredoxin enhanced the vulnerability of diabetic hearts to I/R injury .However,whether the relationship between the duration of diabetes and the severity ofMI/R is involved in the oxidative/ nitrative stress and nitrative inactivation ofthioredoxin remains completely unknown.Numerous studies demonstrate that intensive glucose control can reduce themicrovascular events in the type 2 patients; however whether intensive glucosecontrol can also reduce the macrovascular events remains controversial. The UK Prospective Diabetes Study (UKPDS) finds that compared with the conventionaltherapy, intensive therapy can decrease any diabetes-related endpoint, and most ofthe risk reduction in the any diabetes-related aggregate endpoint was due to therisk reduction in microvascular endpoints; however intensive therapy cannotdecrease the incidence of myocardial infarction. The Action to ControlCardiovascular Risk in Diabetes Study (ACCORD) also demonstrates that ascompared with standard therapy, the use of intensive therapy does notsignificantly reduce major cardiovascular events. The DIGAMI 1 study (Intensemetabolic control by means of insulin in patients with diabetes mellitus and acutemyocardial infarction) demonstrated that an insulin-based glucose managementimproved survival in the patients with diabetes mellitus and acute myocardialinfarction. Therefore, whether blood glucose control can result in bettercardioprotection remains to be elucidated in diabetic heart, more importantly, themechanism by which the blood glucose control serve as cardioprotective effectsremains completely unknown.Therefore, the aim of the present study was (1) to determine the relationshipbetween diabetic duration and the severity of the MI/R injury, (2) to identify themechanism by which the dynamic alteration of the severity of the MI/R injury indiabetic mice, and (3) to explore the mechanism by which the blood glucosecontrol decrease the MI/R injury in diabetic mice.MethodMethods:Part one: Establishment of diabetes and myocardial ischemia/reperfusionmodel in mice.Mice were rendered diabetic by 5 days of daily intraperitoneal injection with40 mg/kg STZ (Sigma) in 0.05 M sodium citrate, pH 4.5. Blood glucose wasmeasured 2 days after the final injection, and diabetic condition was confirmed by markedly elevated fasting-blood glucose levels (>11.1μmol/L). Myocardialischemia/reperfusion was produced by temporarily exteriorizing the heart via leftthoracic incision and placing a 6-0 silk suture slipknot at the distal 1/3 of the leftanterior descending coronary artery. After 30 min of ischemia, the slipknot wasreleased.Part two: Effects of diabetic duration on the myocardialischemia/reperfusion injury in the diabetic mice and its involved mechanismThe diabetic and age-matched non-diabetic mice were subjected tomyocardial ischemia reperfusion at 1 day, 7 days and 14 days after theestablishment of diabetes, respectively. After 30 min of ischemia, the slipknot wasreleased, and the myocardium was reperfused for 3 h (for apoptosis, Trx activity,and nitration assays) or 24 h (for LDH evaluation and infarct size assay). Shamoperatedmice underwent the same surgical procedures except that the sutureplaced under the left coronary artery was not tied.Part three: Effects of blood glucose control on the myocardialischemia/reperfusion injury in the diabetic mice and its involved mechanism1 day, 7 days, 14 days after the establishment of diabetes, the diabetic micewere received insulin (10U/kg/d) treatment by subcutaneous injection for 14 days,7 days and 1 day, respectively. 1 day after the termination of insulin treatment,MI/R were induced in the insulin-treatment mice. In order to exclude the effect ofinsulin on the myocardial injury, wortmannin (a PI3K inhibitor) wasadministrated by intraperitoneal injection 10 min before MI/R in the 14-dayinsulin-treatment mice.ResultsPart one: The fasting-blood glucose level was significantly elevated (19±4.5 mmol/L in STZ-treated mice VS 7.5±2.1 mmol/L in control mice). The hearts suffering from ischemia/reperfusion present infarcted and ischemia area by TTC.These results indicate that the diabetes condition and myocardialischemia/reperfusion model were established successfully.Part two: In 1-day DM mice, the MI/R injury, evidenced by infarct size,apoptosis and LDH release , the level of oxidative/nitrative stress, evidenced bysuperoxide generation, total NO content, and nitrotyrosine content, Trx activityand Trx nitration showed no difference compared to the age-matched no-diabeticmice. With DM progression, the MI/R injury, the level of nitrative stress and Trxnitration were increased while the Trx activity decreased in a time-dependentmanner in 7-day and 14-day DM mice.Part three: 1-day insulin-treatment had no effect on the blood glucose level, and1-day, 14-day insulin-treatment significantly decreased the blood glucose levelcompared to the vehicle. In 1-day insulin-treatment DM mice, the MI/R injury,evidenced by infarct size, and LDH release, the caspase-3 activity, nitrotyrosinecontent and Trx activity showed no difference compared to the vehicle-treatmentdiabetic mice. In 7-day and 14-day insulin-treatment DM mice, the infarct size,LDH release, caspase-3 activity, nitrotyrosine content were decreased, and the Trxactivity was recovered. Wortmannin had no effect on the MI/R injury,oxidative/nitrative stress, Trx activity and Trx nitration compared to the insulin.Wortmannin partly canceled the attenuation in the apoptosis induced by insulin.ConclusionsThe MI/R injury is time-dependently increased and blood glucose control canattenuated the MI/R injury in diabetic mice, which are both involved inoxidative/nitrative stress and nitrative thioredoxin inactivation. |
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