Direct cytotoxicity of hypoxia-reoxygenation towards sinusoidal endothelial cells in the rat

AIMS/BACKGROUND: Sinusoidal endothelial cells are the primary target of ischemia-reperfusion injury following liver preservation. The present study was undertaken to examine the susceptibility of sinusoidal endothelial cells to hypoxia-reoxygenation and the potential role of oxygen free radicals in the induction of cell injury. METHODS: Sinusoidal endothelial cells were isolated from rat liver. After 2 3 days of primary culture, the cells were exposed to hypoxia (N2/CO2 95/5) for 120 min and reoxygenation (O2/CO2 95/5) for 90 min. Control cells were exposed to hypoxia alone, to 95% O2 alone or were maintained under normoxic conditions. Human umbilical vein endothelial cells were used as a model of vascular endothelial cells and submitted to the same protocol. Cell viability and lipid peroxidation were assessed by LDH leakage and malondialdehyde production, respectively. In order to test the potential role of xanthine oxidase and mitochondrial dysfunction in cell injury, the cells were treated with allopurinol and potassium cyanide (KCN) respectively. RESULTS: The different gaseous treatments did not affect LDH leakage in human umbilical vein endothelial cells. In sinusoidal endothelial cells, the sequential hypoxia-reoxygenation caused a significant increase in LDH release, malondialdehyde production and xanthine oxidase activity while hypoxia alone had no effect except on xanthine oxidase activity. Allopurinol inhibited xanthine oxidase without preventing cell injury or lipid peroxidation in this latter cell type. CONCLUSIONS: The results suggest that sinusoidal endothelial cells, as opposed to vascular endothelial cells, are susceptible to a direct cytotoxic effect of hypoxia-reoxygenation. This effect occurs in combination with an increase in xanthine oxidase activity and lipid peroxidation, although cell injury is mediated at least in part by mechanisms independent of xanthine oxidase such as mitochondrial dysfunction.