N-METHYL-D-ASPARTATE-INDUCED EXCESSIVE FORMATION OF NITRIC-OXIDE IN CHP100 NEUROBLASTOMA-CELLS PRODUCES DEATH OF BMEL MELANOMA-CELLS IN COCULTURE

In the present experiments we planned to ascertain whether an abnormal production of nitric oxide (NO) by human CHP100 neuroblastoma cells in culture following stimulation of N-methyl-D-aspartate (NMDA) receptors, produced lethal effects in co-cultured human BMEL melanoma cells. Human BMEL melanoma cells in culture were found to be positive to the nicotinamide adenine dinucleotide phosphate diaphorase (NADPH diaphorase) histochemical reaction and produced NO as revealed by measurements of nitrite under basal culture conditions. Exposure for 50 min to aspartate (1-2 mM) or to NMDA (0.5-1.5 mM) did not evoke significant melanoma cell death. The dose of 1.0 mM NMDA applied for 1 min to BMEL cell cultures did not increase significantly nitrite concentrations in comparison to controls. Incubation for 50 min of human CHP100 neuroblastoma cells with NMDA (0.5-1.5 mM) elicited dose-dependent death of BMEL melanoma cells co-cultured in trans-wells. Under these experimental conditions, nitrite levels in cell culture-inserts containing melanoma cells increased by 120% 1 min after application of the excitotoxin (1 mM) to CHP100 neuroblastoma cultures. The lethal effects produced in BMEL cell culture-inserts by application of NMDA (1.0 mM) to CHP100 cultures were prevented by pretreatment of neuroblastoma cultures with MK801 (200 nM). Similar protection was also afforded by N-omega-nitro-L-arginine methyl ester (L-NAME; 0.2 mM) and N-omega-monomethyl-L-arginine (L-NMMA; 0.2 mM), two inhibitors of nitric oxide synthase, and by haemoglobin (10 mu M), a nitric oxide trapping agent. L-NMMA (0.2 mM) and haemoglobin (10 mu M) also prevented the increase in nitrite levels produced in BMEL culture-inserts by 1 min incubation of CHP100 cells with NMDA. In addition, sodium nitroprusside and S-nitroso-N-acetyl-penicillamine, two NO donors, produced significant death of BMEL cells in individual cultures, thus demonstrating the sensitivity of this cell line to the cytotoxic effect of NO. The present data show that BMEL melanoma cells are not sensitive to the cytotoxic effects of NMDA but they are killed by excessive NO produced by co-cultured CHP100 neuroblastoma cells exposed to NMDA.