Clinical Research Of Relationship Between Serum C-peptide And Type 2 Diabetic Retinopathy

Background and ObjectiveDiabetic retinopathy (DR) is an increasingly more common cause of blindness in the world.The prevalence of DR stepped up with the extension of duration of diabetes.DR occurs in about 95% of patients with type 1 DM and in 60% of type 2 DM patients.Chronic hyperglycemia of DM is the major determinant of diabetic retinopathy.Good glycemic control significantly prevents the development and progression of DR and decreases the visual loss,but it does not offer sufficient protection from the development of DR.Now,the final pathogenesis causing DR is unknown.Besides hyperglycemia, other factors appear to contribute to the development of diabetic complications, one such factor is C-peptide. The proinsulin connecting peptide, C-peptide, is a cleavage product of insulin synthesis that is co-secreted with insulin by pancreatic (3-cells following glucose stimulation, and is important for the biosynthesis of insulin. C-peptide has long been thought to be an inert byproduct of insulin production, but it has become apparent, and accepted, that C-peptide has important biological properties.Many studies suggest that C-peptide has important effects in a number of diabetes-associated complications. Animal and clinical studies have shown that C-peptide could improve kidney function by its ability to stimulate the Na+-K+-ATPase activity,reduces diabetes-induced glomerular hyperfiltration,and resulting in regression of fibrosis;C-peptide has been shown to prevent diabetic neuropathy by improving endoneural blood flow, preventing neuronal apoptosis and by preventing axonal swelling;C-peptide has been shown to prevent vascular dysfunction in diabetic rats, and to possess anti-proliferative effects on vascular smooth muscle cells.The relationship between C-peptide and DR is poorly known in type 2 DM and is conflicting.So, we want to explore the relationship of serum C-peptide with DR and provide basis for the prevention of DR by this study.MethodsSubjects A total of 167 inpatients (115 males and 52 females) with type 2 diabetes collected from September 2009 to March 2010 were enrolled. Their age were from 27 to 80 years old, with an average age 54.8 years.The average duration of diabetes was 8 years, between 1 and 29 years.Measurements Their fasting serum C-peptide (FCP) and postprandial 2h C-peptide(PCP) were tested with chemiluminescent immunoassay.Body mass index (MBI),systolic blood pressure(SBP),diastolic blood pressure(DBP), fasting blood glucose(FBG), glycosylated hemoglobin (HbAlc), total cholesterol(TCH), triglyceride(TG),low-density lipoprotein(LDL-C) and high-density lipoprotein (HDL-C) were measured by OLYMPUS AU5400 auto-chemical analysis instrument, Japan.Grouping All these patients were separated into three groups based on presence or absence of DR and their degree of DR.NDR group:no signs of diabetic retinopathy;BDR group:background diabetic retinopathy,including microaneurysms, retinal haemorrhages,hard exudates, cotton wool spots;PDR group:proliferative diabetic retinopathy, including new vessels,vitrous haemorrhages,vitreoretinal traction,or retinal detachment.Then all the patients were divided according to their C-peptide fasting levels in quartiles again, low C-peptide group(LCP)[n=37], normal C-peptide group(NCP)[n=78],high C-peptide group(HCP)[n=52]. Statistical TreatmentThese datas were analyzed by statistical software SPSS 17.0.Comparisons among subjects of NDR,BDR and PDR group were performed by ANOVA test for continuous variables, frequency between NDR and DR were compared by using theχ2 test;Logistic regression models were used to analyze the importance of C-peptide and other factors for the development of DR. The relevance of C-peptide and other factors were analyzed by using Pearson test. A P value of less than 0.05 was considered significant.Results①Of all these 167 patients,60(35.93%)patients were classified as NDR,76 (45.51%) patients as BDR and 31(18.56%)patients as PDR.Druation of diabetes[(4.10±3.10) years vs (8.93±4.71)years vs (15.13±6.07)years, P<0.01],BMI[(27.69±3.42) kg/ m2 vs (25.78±2.99) kg/m2 vs (23.56±3.59) kg/m2, P<0.01],FCP[(2.11±0.80) ng/ml vs (1.34±0.68) ng/ml vs (0.61±0.33) ng/ml, P<0.01],PCP[(3.69±1.38) ng/ml vs (2.68±1.23) ng/ml vs (1.20±0.60) ng/ml, P<0.01] were statistically different among the three groups.②The incidence of DR among LCP group,NCP group and HCP group showed a significant difference (χ2=46.702,P<0.01).③Logistic regression analysis showed that only fasting C-peptide (B=-1.411, P=0.005) and duration of diabetes (B=0.404, P=0.000)were independently associated with DR.④negative correlation was evident between fasting C-peptide levels and duration of diabetes(r=-0.459, P=0.000),a negative correlation was also found between fasting C-peptide levels and DR (r=-0.629,P=0.000). A negative correlation was evident between postprandial 2h C-peptide levels and duration of diabetes (r=-0.434, P=0.000), a negative correlation was found between postprandial 1h C-peptide levels and DR (r=-0.588,P=0.000)ConclusionsSerum C-peptide may have important significance in pathological form of Type 2 DR. The decrease of C-peptide levels may be a maker of the development of DR in type 2 diabetes.