INORGANIC FLUORIDE - DIVERGENT EFFECTS ON HUMAN PROXIMAL TUBULAR CELLVIABILITY

Fluoride (F) is a widely distributed nephrotoxin with exposure potenti ally resulting from environmental pollution and from fluorinated anest hetic use (eg, isoflurane). This study sought to characterize some of the subcellular determinants of fluoride cytotoxicity and to determine whether subtoxic F exposure affects tubular cell vulnerability to sup erimposed ATP depletion and nephrotoxic attack. Human proximal tubular cells (HK-2) were cultured with differing amounts of NaF (0 to 20 mmo l/L, overlapping with clinically relevant intrarenal/urinary levels af ter fluorinated anesthetic use). After completing 24-hour exposures, c ell injury was determined (vital dye uptake). Fluoride effects on cell deacylation ([(3)]H-C20:4 release) and PLA(2) activity were also asse ssed. To determine whether subtoxic F exposure alters tubular cell sus ceptibility to superimposed injury, cells were exposed to subtoxic NaF doses for 0 to 24 hours and them challenged with simulated ischemia ( ATP depletion plus Ca2+ overload) or a clinically relevant nephrotoxic insult (myoglobin exposure). NaF induced dose-dependent cytotoxicity (up to similar to 90% vital dye uptake and increased [H-3]C20:4 releas e). Extracellular Ca2+ chelation (EGTA) and PLA(2) inhibitor therapy ( aristolochic acid, dibucaine, or mepacrine) each conferred significant protective effects. When subtoxic NaF doses were applied, partial cyt osolic PLA(2) depletion rapidly developed (similar to 85% within 3 hou rs, determined on cell extracts). These partially PLA(2)-depleted cell s were markedly resistant to ATP depletion/Ca2+ ionophore injury and t o myoglobin-induced attack (similar to 50% decrease in cell death). We conclude that 1) F induces dose-dependent cytotoxicity in cultured hu man proximal tubular cells, 2) this occurs, in part, via Ca2+- and PLA (2)-dependent mechanism(s), 3) partial cytosolic PLA(2) depletion subs equently results, and 4) subtoxic fluoride exposure can acutely increa se cell resistance to further attack. Reductions in cytosolic PLA(2) a ctivity could potentially contribute to this result.