CHARACTERIZATION OF THE INHIBITION OF RENAL TRANSLATION IN THE SPRAGUE-DAWLEY RAT FOLLOWING INVIVO CYCLOSPORINE-A

''Run-off'' translation assays in microsomes isolated from Sprague - Dawley rats were used to examine the capacity of cyclosporin A (CsA) to alter translation elongation. CsA added in vitro in concentrations of up to 100 mug/ml did not reduce ''run-off'' translation measured as H-3-L-leucine incorporation in microsomes isolated from the rat kidney or thymus. In contrast, the oral administration of CsA at 50 mg/kg/day for 6 days resulted in reductions in H-3-L-leucine incorporation by microsomes isolated from rat kidneys and unstimulated thymus to 21.6 and 83.0% of control values, respectively. In cross-over experiments between renal microsomal and cytoplasmic fractions, H-3-L-leucine incorporation was inhibited following the addition of renal cytoplasm from CsA treated rats to renal microsomal fractions from control vehicle treated rats. Translation inhibition was still observed when renal cytoplasm from CsA treated rats was added along with renal cytoplasm from control rats to renal microsomes isolated from rats treated with control vehicle. Reductions in renal H-3-L-leucine incorporation were not due to a stimulation of renal protease activity. Experiments varying the concentration of individual components of the microsomal translation assays suggested that renal microsomes from CsA treated animals were saturated with substrate or cofactor at lower concentrations than control microsomes. Time course experiments showed a marked reduction in the duration and extent of H-3-L-leucine incorporation by renal microsomes from CsA treated animals compared to controls. Sucrose density gradient analysis of microsomes from CsA treated animals confirmed that elongation was inhibited. These findings suggest that the in vivo administration of CsA results in the formation of a direct-acting inhibitor of renal translation rather than reducing translation by producing changes in renal transcription. The observation that renal translation is inhibited only after in vivo CsA suggests that a CsA metabolite formed in, or taken up by, the kidney produces translation inhibition, or that a cellular product involved in translation or translation regulation is formed or induced. We propose that the CsA induced inhibition of renal translation elongation accounts, at least in part, for CsA-induced nephrotoxicity.