SUSCEPTIBILITY OF HUMAN PROXIMAL TUBULAR CELLS TO HYPOXIA - EFFECT OFHYPOXIC PRECONDITIONING AND COMPARISON TO GLOMERULAR CELLS

In animal models, exposure of the brain, heart, or kidneys to subletha l ischemia induces tolerance for subsequent ischemia. However the abil ity of human renal cells to undergo hypoxic preconditioning has not be en evaluated. In addition, it is unclear if renal ischemic preconditio ning induces resistance at the cellular level, or if preconditioning i s a result of altered postischemic hemodynamics or the azotemic enviro nment. In this study, we tested the ability of cultured human proximal tubular epithelial cells (PTEC) to undergo hypoxic preconditioning at the cellular level. Hypoxia was induced by incubating cells in an ana erobic incubator in glucose-free buffer (combined oxygen-glucose depri vation; COGD). Cell injury was assessed by lactate dehydrogenase (LDH) efflux, release of arachidonic acid metabolites, and light microscopy . PTEC preconditioned with 12 h of COGD and a 24-h recovery period had less LDH efflux than control PTEC after subsequent exposure to 20 h o f COGD (15.0 +/- 2.5% vs. 44.0 +/- 3.4%, p < 0.05). Preconditioned PTE C also retained relatively normal morphology and had less release of a rachidonic acid metabolites than control PTEC. Because renal ischemia is characterized predominately by tubular injury with relative sparing of the glomerulus, we determined if PTEC are more susceptible to hypo xic injury than glomerular cells. For further comparison, we also asse ssed the susceptibility to hypoxia of the porcine tubular epithelial c ell line LLC-PK1. After exposure to 18 h of COGD, LDH efflux from PTEC (25.5 +/- 3.3%, mean +/- SEM) was lower than from LLC-PK1 cells (47.6 +/- 4.0%; p < 0.01), but not mesangial cells (22.7 +/- 5.0%) or glome rular endothelial cells (38.2 +/- 6.2%). In conclusion, we have demons trated that cultured PTEC are as resistant to hypoxic injury as glomer ular cells, and that PTEC attain cytoresistance after hypoxic precondi tioning. Characterization of the molecular changes that occur in human PTEC after hypoxic preconditioning may reveal innate survival mechani sms that can be manipulated to promote protection from renal ischemia in patients.