SPHINGOSINE - A MEDIATOR OF ACUTE RENAL TUBULAR INJURY AND SUBSEQUENTCYTORESISTANCE

The goal of this study was to determine whether sphingosine and cerami de, second messengers derived from sphingolipid breakdown, alter kidne y proximal tubular cell viability and their adaptive responses to furt her damage. Adult human kidney proximal tubular (HK-2) cells were cult ured for 0-20 hr in the presence or absence of sphingosine, sphingosin e metabolites (sphingosine 1-phosphate, dimethylsphingosine), or C2, C 8, or C16 ceramide, Acute cell injury was assessed by vital dye exclus ion and tetrazolium dye transport. Their subsequent impact on superimp osed ATP depletion/Ca2+ ionophore-induced damage was also assessed. Sp hingosine (greater than or equal to 10 mu M), sphingosine 1-phosphate, dimethylsphingosine, and selected ceramides (C2 and C8, but not C16) each induced rapid, dose-dependent cytotoxicity. This occurred in the absence of DNA laddering or morphologic changes of apoptosis, suggesti ng a necrotic form of cell death. Prolonged exposure (20 hr) to subtox ic sphingosine doses (less than or equal to 7.5 mu M) induced substant ial cytoresistance to superimposed ATP depletion/Ca2+ ionophore-mediat ed damage, Conversely, neither short-term sphingosine treatment (less than or equal to 8.5 hr) nor 20-hr exposures to any of the above sphin gosine/ceramide derivatives/metabolites or various free fatty acids re produced this effect. Sphingosine-induced cytoresistance was dissociat ed from the extent of cytosolic Ca2+ loading (indo-1 fluorescence), in dicating a direct increase in cell resistance to attack. We conclude t hat sphingosine can exert dual effects on proximal renal tubular viabi lity: in high concentrations it induces cell necrosis, whereas in low doses it initiates a cytoresistant state. These results could be repro duced in human foreskin fibroblasts, suggesting broad-based relevance to the area of acute cell injury and repair.