Mechanisms of perfused kidney cytoprotection by alanine and glycine

Abstract

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.