Multiple mechanisms for doxorubicin cytotoxicity on glomerular epithelial cells ‘in vitro’

Abstract

This study was planned to define the metabolic pathways for free radical production by isolated glomeruli and glomerular epithelial cells in vitro after exposure to cytotoxic doses of doxorubicin. A net increment in glomerular superoxide anion (O · 2) synthesis was observed at doxorubicin doses between 10 and 30 μg/ml, a drug level which also induced a parallel increment in uric acid synthesis. Since the synthesis of O · 2 with production of uric acid implies an activity of xanthine oxidase, a few experiments were performed with glomeruli which had been deprived of xanthine oxidase activity. In this case doxorubicin-inducible O · 2 and uric acid synthesis by glomeruli was practically nil. A similar stimulatory effect of O · 2 synthesis was induced by doxorubicin on glomerular epithelial cells and also in this case O · 2 synthesis was suppressed by pre-treating cells with deoxyconformicin, a selective inhibitor of adenosine deaminase. Finally, equimolar amounts of the drug were equally cytotoxic even when kept constantly outside the cell by a stable linkage with an agarose macroporous bed. In summary, these data demonstrate that O · 2 is generated by isolated glomeruli and glomerular epithelial cells ‘in vitro’ when exposed to cytotoxic amounts of doxorubicin and that purine degradation to uric acid furnish the metabolic pathways for glomerular O · 2 generation. However, doxorubicin is comparably cytotoxic on glomerular epithelial cells from outside cells thus suggesting that also a membrane perturbation may activate the series of events leading to cell injury.