Assessing the effect of leptin central administration on plasma proteins in insulin deficient mice.

Leptin monotherapy (i.e. without the use of administered insulin and/or any other molecule) corrects ID-induced metabolic aberrancies and promotes survival of insulin deficient rodents. These results generated great interest in the possibility of treating insulin deficient patients with leptin and/or molecule(s) underlying its beneficial effects. Hence, with the goal of identifying circulating molecule(s) underlying the advantageous effect of leptin we performed quantitative proteomic analysis of plasma and identified S100A9 as a putative peripheral mediator of leptin action. Here, to identify circulating molecule(s) underlying the advantageous effect of leptin we compared the results obtained by quantitative proteomic analysis of plasma between 2 groups of mice: streptozotocin (STZ)-treated mice that underwent intracerebroventricular (icv) leptin treatment for 12 days (STZ-Leptin) and ii) STZ-treated mice that underwent icv leptin treatment for 10 days and were withdrawn from leptin treatment for the following two days (STZ-Leptin-STOP). STZ treatment led to a massive loss of pancreatic insulin-producing β-cells, diminished pancreatic Proinsulin mRNA level, and caused severe insulinopenia, and hyperglycemia. icv leptin administration normalized hyperglycemia. However, two days after leptin delivery was halted hyperglycemia reappeared. We hypothesized that change in plasmatic protein(s) content could underlie re-emergence of hyperglycemia following decrease of leptin action.