Calcitonin Gene-related Peptide Gene Delivery Protects Against Ischemic Myocardial Injury In Isolated Perfused Diabetic Mouse Hearts

Background:Transient receptor potential vanilloid 1(TRPV1) is mainly distributed in primary sensory nerves.It can result in the release of some neuropeptides,including calcitonin gene-related peptide(CGRP) and substance P(SP),from peripheral nerve terminals,when activated by physical and/or chemical stimuli.It has been elucidated that hearts are widely innervated by TRPV1-positive sensory nerves.Exogenous CGRP and SP have been suggested to protect against ischemic myocardial injury.TRPV1 exert a cardioprotective effect on ischemia/reperfusion injury,whereas TRPV1 gene knockout eliminates the protection.The expression of VR1 and synthesis of CGRP were impaired in DM hearts according to our previous study.We can observe significantly more recurrent myocardial infarction in patients with diabetes compared with those without, but the mechanism is still unclear.Therefore,the relationship between susceptibility of the diabetic hearts to myocardial ischemia injury and TRPV1 receptor and neurotransmitter CGRP need to be further defined.The important cardioprotective role of VR1 and CGRP in diabetic hearts needs to be further studied.Objective:To observe the protective effect of exogenous CGRP gene delivery against myocardial ischemia reperfusion injury in diabetic mouse hearts.Methods:We successfully construct recombinant adenovirus vector of CGRP gene by AdEasy system.DM was induced by intraperitoneally injection of streptozotocin(STZ) in the ICR mice.Expression of CGRP in hearts 3 days after delivery of advenoviral vectors AV-CGRP by direct injection in the LV free wall were determined by the CGRP Radioimmunoassay.The isolated hearts of DM mice or Non-DM mice were perfused in a Langendorff apparatus when hearts were subjected to 30 minutes of ischemia and 40 minutes of reperfusion.Tissue injury was determined by measuring the leakage of lactate dehydrogenase(LDH) in the effluent and tissue viability by the reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide(MTT) to blue formazan product.Results:Somatic delivery of CGRP gene could significantly increase the expression of CGRP both in Non-DM hearts and DM hearts.Impairment of postischemic recovery, defined by increased left ventricular end-diastolic pressure(LVEDP) and decreased left ventricular developed pressure(LVDP),coronary flow(CF) and heart rate(HR),was more severe in DM hearts than in Non-DM hearts.DM hearts caused a significant increase in LDH leakage and decrease in MTT reduction when compared with Non-DM hearts.However,delivery of CGRP gene produced a significant improvement in postischemic recovery and attenuation in myocardial injury in both DM and Non-DM hearts respectively.Conclusions:Delivery of CGRP gene is able to improve postischemic recovery and attenuate the myocardial injury in diabetic hearts just the same as in the normal hearts. Impaired VR1 and decreased expression of CGRP in diabetic hearts may be the plausible explanation for more severe deterioration of diabetic hearts after ischemic injury.