Specific Binding of Leptin to Red Blood Cells Delivers a Pancreatic Hormone and Stimulates ATP Release

Since its discovery in 1994, leptin continues to have new potential physiological roles uncovered, including a role in the regulation of blood flow. Leptin's role in regulating blood flow is not completely understood. Red blood cell (RBC)-derived ATP is a recognized stimulus of blood flow, and multiple studies suggest that C-peptide, a hormone secreted in equimolar amounts with insulin from the pancreatic beta-cells, can stimulate that release when delivered by albumin and in combination with Zn2+. Here, we report leptin delivers C-peptide and Zn2+ to RBCs in a saturable and specific manner. We labeled leptin with technetium-99 m (Tc-99m) to perform binding studies while using albumin to block the specific binding of Tc-99m-leptin in the presence or absence of Cpeptide. Our results suggest that leptin has a saturable and specific binding site on the RBC ((K-d = 1.79 +/- 0.46) x 10(-7) M) that is statistically equal to the binding affinity in the presence of 20 nM C-peptide ((K-d = 2.05 +/- 0.20) x 10(-7) M). While the binding affinity between leptin and the RBC did not change with C-peptide, the moles of bound leptin did increase with C-peptide, suggesting a separate binding site on the cell for a leptin/C-peptide complex. The RBC-derived ATP increased in the presence of a leptin/C-peptide/Zn2+ addition, in a concentration-dependent manner. Control RBCs ATP release increased (71 +/- 5.6%) in the presence of C-peptide and Zn2+, which increased further to (94 +/- 5.6%) in the presence of Zn2+, C-peptide, and leptin.

Automated summary

Leptin plays a role in delivering C-peptide and Zn2+ to red blood cells in a saturable and specific manner, with a separate binding site for the leptin/C-peptide complex. The presence of leptin/C-peptide/Zn2+ leads to an increase in ATP release from red blood cells in a concentration-dependent manner.