Relationship Between Serum C-peptide And Diabetic Retinopathy In Type 2 Diabetes Mellitus

Background and purposeDiabetes mellitus(DM)is a metabolic disease caused by deficiency of insulin secretion and / or function.Chronic hyperglycemia is a typical feature of chronic mellitus.Diabetes has become a worldwide health problem due to the high lethality and morbidity caused by its chronic complications including ocular,renal,neurological and cardiovascular involvement.Diabetic microangiopathy mainly affects the kidneys and the retina.Early manifestations of microcirculation,such as glomerular filtration rate,increased albumin exudation,increased retinal blood flow.The main factors affecting the development of microvascular complications include age,duration,blood lipids,blood glucose control level.In recent years,the incidence of diabetic retinopathy(DR)has been on the rise.In severe cases,it can lead to blindness,thereby affecting the quality of life of patients.The current pathogenesis of DR has not been fully elucidated,its occurrence,development may be affected by many factors.C peptide consists of 31 amino acids,which in the proinsulin molecule is linked to the A chain of insulin and to the B chain and is therefore also referred to as a linker peptide.During the conversion of proinsulin into insulin,the C-peptide is produced as an isolysate of insulin and is eventually secreted by pancreatic B-cells.Patients with type 1 diabetes(T1DM)have an absolute lack of insulin,so serum C-peptide levels are extremely low or undetectable.C-peptide has long been considered only to aid in the formation of insulin and has no other biological activity that is clinically used to evaluate pancreatic B-cell function.In recent years,many domestic and foreign studies have found that C peptide has some biological activity,it can not only enhance insulin function,and in some T1 DM patients and diabetic animal models,short-term C peptide replacement can improve renal function,glucose utilization,skeletal muscle And skin blood flow and autonomic function.It is proposed that C-peptide may be one of the protective factors of diabetic microvascular complications.The mechanism of action of C-peptide may be binding to G protein-coupled receptors on the cell membrane,causing intracellular Ca2 + concentration to increase,activating endothelial nitric oxide synthase(NOS)and Na+-K+-ATPase,Increased flow,while reducing vascular permeability,inhibiting mesangial cell proliferation,reducing endothelial cell permeability of albumin,thereby delaying the development of diabetic microangiopathy.Numerous studies at home and abroad show that the relationship between C-peptide and T1 DM microvascular complications is closely related,but the relationship with T2 DM microvascular complications has been controversial,especially the study of C-peptide and T2 DM retinopathy.The purpose of this study was to analyze the risk factors associated with T2 DM retinopathy and to investigate the correlation between serum C-peptide levels and T2 DM retinopathy and to investigate its clinical significance.Objects and methods1.1 Subjects: According to the World Health Organization(WHO)diagnostic criteria for diabetes in 1999,209 patients with confirmed type 2 diabetes who were hospitalized in Department of Endocrinology,Qingdao Municipal Hospital from October 2016 to September 2017 were collected.All patients excluded non-DM-induced ocular disorders and retinal lesions due to glaucoma and cataracts other than retinal lesions,except for T1 DM,cardiopulmonary insufficiency,hepatobiliary disorders,hematologic disorders,neoplasms,infections and non-diabetic renal diseases Or urinary tract diseases,etc.,as well as drugs and other factors that affect the determination of C-peptide.1.2 Determination of indicators: records of selected patients gender,age,duration,height,weight and other basic information,measurement of systolic blood pressure(SBP)and diastolic blood pressure(DBP),calculate the body mass index(BMI).The DR was photographed by ophthalmologists and diagnosed according to the International Clinical Classification of Diabetic Retinopathy(2002).Fasting venous blood was collected for determination of fasting C-peptide(FCP),fasting blood glucose(FBG),Hb A1 c,TC,triglyceride(TG),low density lipoprotein(LDL-C),high density lipoprotein(HDL-C),and the morning urine test to take a single morning urine albumin / creatinine ratio(ACR).Subsequent C peptide release test measured after 0.5h,1h,2h and 3h serum C-peptide.1.3 Grouping: All 209 patients underwent mydriasis to examine the fundus.The included patients were divided into three groups according to the severity of the lesion: the group without significant retinopathy(NDR),the group with non-proliferative retinopathy(NPDR),and the proliferative diabetic retina Lesions(PDR)group.According to the normal fasting C-peptide reference range(1.1-4.4ng / m L)established by our laboratory,the patients were divided into lower normal group(LCP group),normal group(NCP group),higher than normal group HCP group).1.4 Statistical Analysis: Using SPSS 22 statistical software for statistical analysis of the data.All measurement data are expressed as mean ± standard deviation.Multiple sets of measurement data were compared using one-way analysis of variance,measurement data between the two groups using t test.The incidence of C-peptide group DR was compared using the chi-square test.Logistic regression model was used to analyze the correlation between C-peptide and other factors and DR.Pearson test was used to analyze the correlation between C-peptide and various factors.P <0.05 as the difference was statistically significant.Result 2.1 The differences of course of disease,BMI,Hb A1 C,ACR,FCP and 2h-CP between NDR group,NPDR group and PDR group were statistically significant(p <0.05).2.2 There was significant difference in the incidence of DR among C peptide groups(chi square = 72.2,P <0.01).2.3 The level of fasting C-peptide was negatively correlated with duration of diabetes,Hb A1 C,FPG and HDL levels(p <0.05),and positively correlated with TG level(p <0.05).2.4 Logistic regression analysis of the risk factors of T2 DM retinopathy showed that the disease course,BMI was the risk factor of DR,and FCP was the protective factor of DR.ConclusionsSerum C-peptide is associated with T2 DM retinopathy in T2 DM patients.The level of C-peptide gradually decreases with the severity of DR.The higher C-peptide level is protective factor,suggesting that serum C-peptide may delay T2 DM retinopathy Development took place.