Cardioprotective Efficacy Of Methylcobalamin Treatment In Heart Of Diabetic Peripheral Neuropathy Mouse And Its Possible Mechanism

Part I Cardioprotective efficacy of Methylcobalamin Treatment against Ischemia/Reperfusion Injury in Isolated Heart of Diabetic Peripheral Neuropathy Mouse and Its Possible MechanismBackground:Diabetes mellitus (DM) is considered as one of the most important risk factors and prognostic risks of coronary heart disease. As the most common and troublesome complication of diabetes mellitus, diabetic peripheral neuropathy (DPN) involves the degeneration of motor, sensory and autonomic nerves. The transient receptor potential vanilloid type 1 (TRPV1), which distributes widely in sensory nerve endings, is an important sensor to detect myocardium ischemia. It could be activated by capsaicin, noxious heat and protons and could result in the release of neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P (SP). A series of evidence indicated that diabetes mellitus could impair the expression and function of TRPV1 in sensory nerve. In our previous study of diabetic mice hearts, we also found that the expression of TRPV1 and its main neuropeptides was remarkably decreased. Methylcobalamin is commonly applied in the treatment of peripheral neuropathy; however, its effect on cardiovascular system has not been well investigated.Aims:We performed this study to investigate the cardioprotection of Methylcobalamin therapy against ischemia/reperfusion (I/R) in isolated heart of diabetic peripheral neuropathy mouse, and the involvement of TRPV1 in this procedure.Methords:Streptozotocin(STZ)-induced diabetes mellitus was carried out in ICR mice.4 weeks treatment of Methylcobalamin (1mg/kg/day I.M.) was executed. Isolated mouse heart was perfused in Langendorff apparatus. Hemodynamic parameters and release of lactate dehydrogenase (LDH), calcitonin gene-related peptide (CGRP) and substance P (SP) in coronary effluent during reperfusion were measured. Expression of TRPV1, calcitonin receptor-like receptor(CRLR) and SP receptor(SPR) in myocardium was detected by Western Blot.Results:Compared with normal mice, the DM mice had slower SNCV (p<0.01) and longer hot plate latency (p<0.01), indicating the impairment of sensory nerve function in experimental DPN. After 4-week Methylcobalamin treatment, treated DM mice had faster SNCV (p<0.01) and shorter hot plate latency (p<0.05) than untreated ones. Untreated DM hearts got much severer ischemic/reperfusion injuries than treated ones, an observation validated by raised left ventricular end-diastolic pressure (LVEDP) (p<0.05), decreased left ventricular developed pressure (LVDP) (p<0.01), reduced coronary flow (CF) (p<0.01), and increased LDH release (p<0.05). The ischemic injuries manifested in normal hearts were not as severe as in DM hearts. Unlike the untreated DM hearts, treated ones had higher concentration of SP in coronary effluent (p<0.01) and higher expression of TRPV1 (p<0.01) and SPR (p<0.01) in myocardium. Normal hearts had more intensive release of CGRP and SP as well as higher expression of myocardium TRPV1, CRLR and SPR than DM ones (p<0.01).Conclusions:Thus, these data provide important evidence that the cardioprotection of Methylcobalamin therapy in isolated DM mice hearts is related to the recovery of the expression and activation of TRPV1 and SPR. Part II Effect of Methylcobalamin Treatment on the Cardiac Function of Diabetic Peripheral Neuropathy Mouse after Acute Myocardial InfarctionBackground:Myocardial infarction is one of the main causes of death in diabetic patients, and a considerable part of these patients undergo myocardial ischemia without chest pain, which is so called silent myocardial ischemia. Diabetic peripheral neuropathy (DPN) id one of the most complications of diabetes mellitus. Sensory nerve dysfunction caused by DPN might be responsible for the silent myocardial ischemia of DM patients. The lack of ischemic nociception remarkably increases the risk of sudden cardiac death in DM patients. In the research of Part I, we demonstrated the cardiacprotective efficacy of Methylcobalamin treatment in isolated DPN mice hearts, and this effect might be related to the recovery of the expression and activation of TRPV1 and SPR in myocardium. How about the result in the experiment in vivo? We will figure it out in this part, and the result may have an important clinical implication for the future anti-ischemia therapies.Aims:We performed this study to investigate the effect of Methylcobalamin therapy on the cardiac function and infarct area in diabetic peripheral neuropathy mouse after acute myocardial infarction.Methords:Streptozotocin(STZ)-induced diabetes mellitus was carried out in ICR mice.4 weeks treatment of Methylcobalamin (1mg/kg/day I.M.) was executed. Myocadial infarction was generated by ligating the left anterior descending coronary artery. Left ventricular end-diastolic diameter(LVEDD), left ventricular end-systolic diameter (LVESD), interventricular septal thickness at end-diastole(IVSd), left ventricular posterior wall thickness at end-diastole(LVPWd), fraction shortening(FS) and ejection fraction(EF) were measured by echocardiography 2 days after operation. Releases of LDH, CGRP and SP in plasma were measured. Infarct size was measured by 2,3,5-triphenyltetrazolium chloride staining.Results:Compared with normal mice, the DM mice had slower SNCV (p<0.01) and longer hot plate latency (p<0.01), indicating the impairment of sensory nerve function in experimental DPN. After 4-week Methylcobalamin treatment, treated DM mice had faster SNCV (p<0.01) and shorter hot plate latency (p<0.01) than untreated ones. The cardiac function of untreated DM hearts got much severer impairment than treated ones, an observation validated by longer LVESD (p<0.01), longer LVEDD (p<0.05), lower FS (p<0.05) and lower EF (p<0.01). The untreated DM hearts also got severer myocardial injuries than treated ones, which can be demonstrated by higher plasma LDH level (p<0.01) and larger infarct size (p<0.01). The ischemic injuries manifested in normal hearts were not as severe as in DM hearts. Unlike the untreated DM hearts, treated ones had higher concentration of SP (p<0.05)and CGRP (p<0.05) in plasma. Normal hearts had more intensive release of CGRP and SP as well than DM ones (p<0.01).Conclusions:Thus, these data indicated the cardioprotection of Methylcobalamin therapy in DPN mice undergoing myocardial infarction, and this efficacy might be related to the recovery of the expression and activation of TRPV1 and the following-up increases in SP and CGRP releases.