Mechanisms of perfused kidney cytoprotection by alanine and glycine

We examined the cytoprotective action of individual amino acids in isolated perfused kidneys during perfusion with either 10 mM lactate or 5 mM glucose. In the absence of amino acids inulin clearance fell rapidly, whereas fractional excretion of phosphate, lactate, or glucose increased to more than 30%; lactate dehydrogenase was released into perfusate and alkaline phosphatase into the urine. Functional deterioration was less in kidneys from rats rendered chronically water diuretic by drinking 5% glucose. Adding 5 mM glycine, L-alanine, beta-alanine, or D-alanine to the perfusate also prevented functional deterioration and release of enzymes. Glycine perfusion increased total phospholipid per microgram DNA by 6%. Aspartate, glutamate, glutamine, taurine, isoleucine, leucine, and valine were not protective. Serine, proline, and alpha-aminoisobutyric acid had small protective effects. Micropuncture measurements of proximal tubular free- and stop-flow pressures showed no effect of L-alanine on glomerular hemodynamics. L-Alanine increased oxygen consumption by both glucose- and lactate-perfused kidneys and increased gluconeogenesis by lactate-perfused kidneys but did not alter renal ATP content or energy charge. L-Alanine was not consumed during 70 min of perfusion and its protective action was not inhibited by blocking transamination with 0.5 mM amino-oxyacetate. The protective action of glycine was not inhibited by blocking glycine metabolism with 0.1 mM cysteamine. Thus the beneficial effects of L-alanine and glycine do not require their metabolism. These observations suggest that small neutral amino acids prevent tubular disruption through their physicochemical effects, which can stabilize membrane protein tertiary structure.