Arginine Metabolism in Youth With Type 2 Diabetes

In parallel with the youth obesity epidemic, type 2 diabetes (T2D) in youth is becoming a significant public health concern. The incidence of pediatric T2D increased by 50% during the past decade, and recent data show that T2D accounts for one in four newly-diagnosed diabetes cases in children. Youth with T2D have an aggressive disease course and a rapid decline in β-cell function, and many also have multiple cardiovascular disease risk factors at an early age. The disease is characterized by insulin resistance and impaired insulin secretion, but the molecular underpinnings of T2D are not yet fully elucidated. This study aims to uncover the role of arginine metabolism in the pathogenesis of youth with T2D and the effect of exogenous arginine administration on β-cell function in them. Arginine is a known stimulant of insulin secretion in pancreatic β-cells. Nitric oxide (NO) is synthesized from arginine by NO synthase, and arginine stimulates insulin secretion in both NO-mediated and NO-independent mechanisms by stimulating guanylate cyclase, membrane depolarization, and metabolic by-products. The effects of arginine in pancreatic β-cells are dependent on the cells' available arginine concentration. Kinetic techniques using isotope tracer infusions and targeted metabolomics provide a unique opportunity to determine "intracellular" arginine availability and its relative contribution of various pathways to this pool. Such studies in adults with T2D have shown that arginine and NO play roles in the pathogenesis of T2D by affecting insulin secretion and insulin sensitivity. In the preliminary data on children with T2D, the investigators found that children with T2D had lower fasting arginine, citrulline (arginine precursor), and glutamine (citrulline precursor) levels. In this proposal, the investigators will seek kinetic validation of these hypothesis-generating observations to investigate the role of arginine metabolism in youth with T2D. Our central hypothesis is that youth with T2D have inadequate arginine availability (Aim 1), leading to suboptimal β-cell function, which can be restored by exogenous arginine administration (Aim 2). If our hypotheses are proven, arginine supplementation will play a clinically vital role in improving diabetes outcomes in this population as a safe, low-cost, and readily available nutrient.