Nephrotoxicity of lysine and of a single dose of aminoglycoside in rats given lysine

Hyperalimentation solutions have been shown to increase aminoglycoside nephrotoxicity in rats and rabbits. Lysine is a major constituent of hyperalimentation solutions and is known to inhibit tubular reabsorption of protein. To test the effects of lysine on renal function and structure and on aminoglycoside nephrotoxicity, three groups of rats were prepared. Groups 1 and 2 were infused with lysine (55 μmol/kg/min, 1.9 gm/kg total) for 4 hours. In group 2, gentamicin (60 mg/kg) was also infused during the third hour. In group 3, dextrose was given instead of lysine, and gentamicin was given as in group 2. In group 1 (lysine-saline solution), there was a decrease in glomerular filtration rate (GFR) and an increase in ¹²⁵I-albumin clearance factored by GFR. In group 2 (lysine-gentamicin), the same effects were seen, but the reduction in GFR was significantly greater. Group 3 (dextrose-gentamicin) showed no change in GFR over the 4-hour period, but did show an increase in ¹²⁵I-albumin clearance factored by GFR. Fractional excretion of sodium rose in group 2 but not in groups 1 and 3. A gradual mild (20%) and nonsignificant fall in renal blood flow followed the combined administration of lysine and gentamicin. In separate 20-hour studies, lysine (1.9 gm/kg intraperitoneally) or gentamicin or tobramycin (60 mg/kg subcutaneously) produced mild renal failure, but the combination of lysine and an aminoglycoside produced substantially greater renal failure. Serum creatinine in experimental groups was significantly correlated with medullary cast formation and tubular necrosis (p < 0.001). Giant lysosomes with crystalloid inclusions in proximal tubular cells, individual cell necrosis in the pars recta, and casts in the thin limb of the loop of Henle were seen in rats given lysine. We conclude that lysine alone and single large doses of aminoglycosides alone are nephrotoxic, and when the two are combined, toxicity is additive. The nephrotoxicity of lysine may be related to direct tubular toxicity and to tubular obstruction.