| Diabetes mellitus is a state of chronic hyperglycemia due to an absolute or relative deficiency of insulin secretion that may or may not be associated with insulin resistance. The world wide prevalence of diabetes was estimated to be 2.8% in 2000 and is projected to reach 4.4% by 2030. Diabetic cardiomyopathy, characterized by structure changes and function impairment of cardiomyocytes, is one of the most prevalent cardiovascular complications of diabetes mellitus that occurs independently of coronary artery disease, microangiopathy and autonomic neuropathy of the heart. Many epidemiological and clinical studies have shown that chronic hyperglycemia is a major initiator of diabetic cardiovascular complications, as high glucose may regulate the growth of cardiomyocytes via activating several signal transduction pathways. The characteristic of diabetic heart failure, manifested by early diastolic dysfunction, followed by late systolic dysfunction, is faster deteriorating with high mortality and is difficult to diagnose in the early stage. Thus, we tried to seek for an ideal treatment to inhibit the pathway towards heart failure in the earlier period of diabetic cardiomyopathy.There was a consensus that there were excessive activity of sympathetic nerve system, oxidative stress as well as higher expression and activation of protein kinase C isoforms in the early stage of diabetic cardiomyopathy, all of which accelerated cardiac remodeling and dysfunction. Studies have revealed that hyperglycemia could increase the formation and activity of PKC isoforms, and PKC signal pathway is now considered to be one of the most important intracellular transduction pathways that functions as a core effect in the onset and progression of diabetic cardiomyopathy. Increased PKC activity in diabetic cardiomyopathy could regulate the growth, contractility and permeability of cardiomyocytes, and is associated with remodeling of extracellular matrix, thickening in basement membrane, hypertrophy of cardiomyocytes, as well as microangiopathy and autonomic neuropathy of the heart, which eventually lead to the structure and function impairment of cardiomyocytes in diabetic cardiomyopathy. So inhibiting the expression of PKC and blockade of PKC signal transduction pathway may have preventative and therapeutical effect on the diabetic cardiomyopathy.Breviscapine is a flavonoid extracted from Erigeron breviscapus and prepared into a Chinese patent medicine, its essential active ingredient is flavones. Its pharmacologic action is dilating blood vessel, reducing blood viscosity and improving microcirculation. It also possesses an anti-platelet action and can decrease plasma fibrin content and promote fibrinolytic activity. Recent studies have also shown that breviscapine could inhibit the expression of PKC, and decrease the protein expression of c-jun, c-fos and synthesis of type IV collagen induced by hyperglycaemia. There were also researches indicated that breviscapine had a protective effect on diabetic nephropathy through inhibiting the increased expression and activity of PKC-P2. But little is known about the influence of breviscapine on diabetic cardiomyopathy and its underlying mechanisms.On the basis of above considerations that PKC is activated in diabetic mellitus, and breviscapine could inhibit the activation and expression of PKC, we hypothesized that breviscapine may have protective effect on the structure and function injury of cardiomyocytes in diabetic cardiomyopathy via inhibiting the cardiac overexpression of PKC. In this study, we use diabetic rats as an animal model to investigate the influence of breviscapine treatment on the cardiac structure and function in diabetic cardiomyopathy, as well as the myocardial expression of PKC and associated proteins and its underlying mechanisms. Part 1 Breviscapine ameliorates cardiac dysfunction and regulates the myocardial Ca2+-cycling proteins in diabetic ratsObjective:To investigate the influence of breviscapine on the cardiac function in diabetic rats as well as the expression of PKC-α,PKC-β2 and Ca2+-cycling proteins.Methods:Diabetes were induced in male Sprague-Dawley rats by a single intraperitoneal injection of streptozotocin and the control rats were injected with citrate buffer solution. After the induction of diabetes for 4 weeks, the animals were divided into four groups:(1)normal rats as control; (2)diabetic rats; (3)diabetic rats treated with low dose of breviscapine(10mg/kg/day); (4)diabetic rats treated with high dose of breviscapine(25mg/kg/day). After treatment with breviscapine for 6 weeks, the echocardiographic parameters and invasive cardiac function were measured. The expression of PKC-α,p-PKC-α,PKC-β2,p-PKC-β2 and calcium handling regulators, such as protein phosphatase inhibitor-1(PPI-1), phospholamban(PLB) and sarco/endoplasmic reticulum Ca2+-ATPase-2(SERCA-2) were detected by western blot. The activity of Ca2+-ATPase was measured using Ca2+-ATPase kit.Result:Diabetic rats showed impaired cardiac function compared with control rats. The expression of PKC-α,p-PKC-α,PKC-β2,p-PKC-β2 and PLB in diabetic rats increased significantly compared with control rats, while the expression of PPI-1, p-PLB, SERCA-2 and activity of Ca2+-ATPase decreased. Treatment with breviscapine could reverse the cardiac dysfunction in diabetic cardiomyopathy rats, and decrease the expression of PKC-α,p-PKC-α,PKC-β2,p-PKC-β2 and PLB, as well as increase the expression of PPI-1, p-PLB, SERCA-2 and the activity of Ca2+-ATPase.Conclusion:This study showed that breviscapine could ameliorate cardiac dysfunction in diabetic rats, and have protective effect on diabetic cardiomyopathy via regulating the expression of PKC and Ca2+-cycling proteins. Part 2 Breviscapine ameliorates cardiac hypertrophy of diabetic rats via inhibiting the expression of PKC and its mechanismsObjective:To investigate the influence and mechanism of breviscapine on the hypertrophy of cardiomyocytes in diabetic cardiomyopathy rats.Methods:Diabetes were induced in male Sprague-Dawley rats by a single intraperitoneal injection of streptozotocin and the control rats were injected with citrate buffer solution. After the induction of diabetes for 4 weeks, the animals were divided into four groups:(1)normal rats as control; (2)diabetic rats; (3)diabetic rats treated with low dose of breviscapine(10mg/kg/day); (4)diabetic rats treated with high dose of breviscapine(25mg/kg/day). After treatment with breviscapine for 6 weeks, heart tissues were obtained for HE stain and electron microscopestudy. The expression of PKC-α,p-PKC-α,PKC-β2,p-PKC-β2 and NF-kB,p-NF-KB,TNF-α,c-fos were detected by western blot or RT-PCR.Result:Diabetic rats showed cardiac hypertrophy and impaired cardiac structure compared with control rats, the protein expression of PKC-α,p-PKC-α,PKC-β2,p-PKC-β2,NF-kB,p-NF-KB,c-fos and the mRNA expression of TNF-αall increased significantly. Treatment with breviscapine could reverse the cardiac hypertrophy and structure impairment in diabetic cardiomyopathy rats, as well as decrease the protein expression of PKC-α,p-PKC-α,PKC-β2,p-PKC-β2,NF-kB,p-NF-kB,c-fos and the mRNA expression of TNF-a.Conclusion:This study showed that breviscapine could ameliorate cardiac hypertrophy and structure impairment in diabetic rats, and have protective effect on diabetic cardiomyopathy via inhibiting the activity of PKC and then the subsequent expression of NF-kB,TNF-αand c-fos. |
