Liposome-delivered superoxide dismutase prevents nitric oxide-dependent motor neuron death induced by trophic factor withdrawal

Inhibition of nitric oxide synthesis prevents rat embryonic motor neurons f rom undergoing apoptosis when initially cultured without brain-derived neur otrophic factor. Using an improved cell culture medium, we found that the p artial withdrawal of trophic support even weeks after motor neurons had dif ferentiated into a mature phenotype still induced apoptosis through a proce ss dependent upon nitric oxide. However, nitric oxide itself was not direct ly toxic to motor neurons. To investigate whether intracellular superoxide contributed to nitric oxide-dependent apoptosis. we developed a novel metho d using pH-sensitive liposomes to deliver Cu, Zn superoxide dismutase intra cellularly into developed a novel method using pH-sensitive liposomes to de liver Cu, Zn superoxide dismutase intracellularly into motor neurons, Intra cellular superoxide dismutase prevented motor neuron apoptosis from trophic factor withdrawal, whereas empty liposomes, inactivated superoxide dismuta se in liposomes or extracellular superoxide dismutase did not. Neither hydr ogen peroxide nor nitrite added separately or in combination affected motor neuron survival. Our results suggest that a partial reduction in trophic s upport induced motor neuron apoptosis by a process requiring the endogenous a process requiring the endogenous production of both nitric oxide and sup eroxide, irrespective of the extent of motor neuron maturation in culture. (C) 2000 Elsevier Science Inc.