Serum C peptide level and renal function in diabetes mellitus

Posted on May 25, 2010

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Serum C peptide level and renal function in diabetes mellitus C peptide is an active peptide hormone with potentially important physiological effects. C peptide has the capacity to diminish glomerular hyperfiltration and reduce urinary albumin excretion in both experimental and human type 1 diabetes. The present study is aimed at correlating the serum C peptide level with that of renal clearance, urinary albumin excretion and duration of diabetes. This is a prospective cross sectional study. Patients with diagnosis of type 2 diabetes mellitus were evaluated for their baseline clinical and laboratory profile.

Both males and females above the age of 18 years were included in the study. The laboratory investigations include fasting serum C peptide, HbA 1C , serum creatinine, blood urea nitrogen, urine albumin and creatinine. Creatinine clearance was calculated using modification of diet in renal disease formula from serum creatinine value. A total of 168 patients were included in the study, among them 90 were females (53.57%) and 78 males (46.43%). Mean age of the patients was 57.64 years. Pearson correlation test showed negative correlation of serum C peptide level with creatinine clearance, though statistically not significant.

Negative correlation was also seen between serum C peptide, and urine albumin, urine albumin creatinine ratio, HbA 1C and duration of diabetes. Mean urine albumin was higher in patients with subnormal C peptide level. Duration of disease was more in patients with lower serum C peptide level.

The study has shown weak association of serum C peptide level with microalbuminuria and creatinine clearance. Risk of albuminuria is more in patients with low serum C peptide level. In insulin bio-synthesis, C-peptide is cleaved from pro-insulin, stored in secretory granules, and eventually released into the bloodstream in amounts equimolar with those of insulin. C-peptide has an essential function in the synthesis of insulin in that it links the A and B chains in a manner that allows correct folding and inter-chain disulfide bond formation. [1]

The kidney has been suggested as the main organ for the degradation of C-peptide. Half-life of C peptide in circulation is 2-5 times longer than insulin. [2] C peptide is the more reliable indicator of insulin secretion than insulin itself. Furthermore, the concentration of C peptide is not affected by interference from insulin antibodies often present in patients receiving insulin therapy After the discovery of the mode of insulin biosynthesis, several early studies addressed the question of possible physiological effects of C-peptide.

Insulin-like effects on blood glucose levels and glucose disposal after glucose loading were looked for but not found. [7],[8] Recently, new data have been presented demonstrating specific binding of C-peptide to cell surfaces in a manner that suggests the presence of G protein-coupled membrane receptors. C-peptide may thereby stimulate specific intracellular processes, influencing renal and nerve function in C-peptide-deficient type 1 diabetes patients. [3]

The study has shown weak association of serum peptide level with microalbuminuria and creatinine clearance. Patients with low serum C peptide level may have increased risk of microalbuminuria. C-peptide replacement together with insulin administration may be beneficial in type 1 diabetes patients. Studies involving C-peptide administration of longer duration will be required to determine whether C-peptide may have a role in the prevention and treatment of diabetic nephropathy.

http://www.indianjnephrol.org/