Poly-L-aspartic acid does but triiodothyronine does not protect against gentamicin-induced cytotoxicity in the porcine kidney cell line LLC-PK1

This study investigated the protective effect of thyroid hormone and poly- L-aspartic acid (PAA) in an in vitro model of gentamicin nephrotoxicity. LLC- PK1 porcine renal cells were grown in Medium 199 supplemented with either fetal bovine serum or thyroid hormone-depleted fetal bovine serum. After a preincubation with or without 30 nM L-triiodothyronine for 3 days, or 0.1 mM PAA for 1 hr, cells were coincubated with 1 mM gentamicin for an additional 3 days. Determinations were made of the following indicators of cell damage and/or viability: the numbers of detached dead cells, the total lactate dehydrogenase activity and its percentage release and γ-glutamyl transpeptidase activity. Preincubation with L-triiodothyronine did not protect from gentamicin-induced cell death but did reduce cellular accumulation of gentamicin (3.2 ± 0.8 μg/mg of protein vs. 5.2 ± 1.8 μg/mg of protein in controls; P < .05). In contrast, preincubation with 0.1 mM PAA decreased gentamicin-induced cell death (gentamicin: 685 ± 416% of control dead cells and 487 ± 48% of control lactate dehydrogenase release; PAA + gentamicin: 164 ± 63% of control dead cells and 257 ± 85% of control lactate dehydrogenase release; P < .05) but failed to attenuate inhibition by gentamicin of γ-glutamyl transpeptidase activity (gentamicin: 69 ± 7% of control; PAA + gentamicin: 76 ± 3% of control) and failed to alter cellular gentamicin levels. Protection against gentamicin nephrotoxicity by L- triiodothyronine was not demonstrated in LLC-PK1 cells, indicating that its protective effect in vivo is likely due to a systemic effect of the hormone. In contrast, PAA provided protection at a cellular level despite unaltered cellular gentamicin uptake.