Proinsulin and C-peptide at onset and during 12 months cyclosporin treatment of type 1 (insulin-dependent) diabetes mellitus.

An increased proinsulin to C-peptide molar ratio at the onset of Type 1 (insulin-dependent) diabetes mellitus has been suggested. We studied fasting proinsulin levels and proinsulin/C-peptide ratios in the newly diagnosed diabetic subjects participating in the Canadian/European placebo controlled cyclosporin study at entry, during the one year treatment period and six months of follow-up. Available entry data from 176 out of the 188 allocated patients were compared to 60 age and weight matched control subjects. Fasting proinsulin was significantly elevated in male patients compared to male control subjects (p less than 0.01), whereas the levels only tended to be elevated in female patients. The proinsulin/C-peptide ratio was three to fourfold elevated in the diabetic groups of both sexes, (p less than 0.001). Further, proinsulin and C-peptide were studied in 83 cyclosporin and 86 placebo-treated subjects during the trial and follow-up. An additional increase of proinsulin/C-peptide ratio was observed during the first three months of placebo treatment. It remained constantly high for nine months and then declined to entry level. This pattern was not seen in the cyclosporin-treated group, where the ratio was unchanged during the 12 months trial and follow-up. The effect of cyclosporin on the induction of non-insulin requiring remission was unrelated to fasting and glucagon stimulated C-peptide levels at entry, whereas 64% of the cyclosporin-treated against 28% of the placebo-treated subjects (p less than 0.01) went into remission if the proinsulin/C-peptide ratio at entry was above 0.024.(ABSTRACT TRUNCATED AT 250 WORDS)