Diabetes mellitus is today the most common cause for end-stage renal disease. Type 1 diabetes accounts for 5-10% of all diagnosed cases of diabetes. Furthermore, diabetes is the leading cause of kidney failure, accounting for 44% of all new cases in 2002. Sustained hyperglycemia is closely associated with kidney hypoxia, altered nitric oxide (NO) system and glomerular hyperfiltration. Decreased influence of NO has therefore been suggested to be involved in the diabetes-induced increase in renal cellular oxygen consumption and decreased oxygenation. This research program focuses on intracellular metabolism of a specific nitric oxide synthase (NOS) inhibitor, asymmetric dimethylarginine (ADMA), by dimethylarginine dimethylaminohydrolase (DDAH) expressed as two isoforms, DDAH-I expressed primarily in proximal tubular cells and DDAH-II expressed in the juxtaglomerular apparatus, and the intracellular availability of the NOS substrate arginine which it self depends on the plasma arginine concentration (regulated primarily by cellular uptake of arginine in the liver via a specific cationic amino acid transporter, CAT-2A), uptake of extracellular arginine into renal tubular epithelial cells (regulated primarily by a distinct cationic amino acid transporter, CAT-1), intracellular metabolism to ornithine and urea by arginase-1 (expressed in proximal tubular cells). Diabetes may impact each of these steps, thereby leading to diabetic nephropathy. The specific role of each of these parameters will be investigated using RNA interference (RNAi) in vivo in animal models of insulinopenic Diabetes Mellitus. By applying RNAi in only one kidney in the same animal we will be able to isolate the effects of specific alterations the gene product of interest. Traditional invasive micropuncture techniques will be used to measure local changes in renal blood flow, oxygenation and bioavailable NO. Additionally, we will develop and validate protocol for noninvasive measurements of renal blood, oxygen usage and glomerular filtration rate by magnetic resonance. The information gained from this research program could lead to novel targets to treat diabetesinduced renal damage in the clinic. Since metabolic alterations precede histological changes, theirs identification in this aspect could potentially be used as a clinical diagnostic tool when identifying patients at increased risk to develop diabetic nephropathy and enable early treatment.
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