Red Blood Cells Specifically Bind a C‐peptide/Albumin Complex

Abstract

People with Type 1 diabetes (T1D) require exogenous insulin due to the destruction of insulin‐secreting pancreatic β‐cells. However, even with insulin treatments, people with T1D develop complications such as retinopathy, neuropathy, and nephropathy that are often associated with poor microvascular blood flow. C‐peptide, a 31‐amino acid length peptide co‐secreted with insulin from the pancreatic β‐cells in a 1:1 mole ratio has been shown to improve microvascular blood flow in T1D rats and small‐scale human studies. C‐peptide indirectly enhances endothelium‐derived nitric oxide (NO) by stimulating the release of red blood cell (RBC) derived ATP, a recognized stimulus of endothelial NO synthase. Unfortunately, a receptor for C‐peptide has never been reported. Previously, using ELISA, we reported C‐peptide uptake by RBCs was approximately 1800 C‐peptide molecules/cell, but only when in the presence of albumin. In the absence of albumin, there was no measurable C‐peptide binding to the RBCs. We also report C‐peptide binding to albumin with a Kd of 5.7 ± (2.1) × 10−6 M; therefore, we hypothesize that C‐peptide binds to RBCs via a receptor that is specific for an albumin/Cpeptide complex. The binding of 99mTc labeled bovine serum albumin (BSA) to isolated RBCs, in the presence and absence of C‐peptide, was quantitatively determined by automatic gamma counting after repeated washing with a physiological salt solution. Sample counts per minute (CPM) were compared to a standard curve to determine the 99mTc‐BSA molecules per RBC. Results suggest BSA total binding to the RBCs saturates at approximately 1600 BSA molecules/RBC, whether or not C‐peptide is present, but that the BSA‐99mTc is specifically binding to RBCs in the presence of C‐peptide. Collectively, our data strongly suggest that the Cpeptide receptor has remained elusive because the receptor specifically binds an albumin/Cpeptide complex, as opposed to C‐peptide alone.Support or Funding InformationNIHThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.