STUDIES ON THE NEUROTOXICITY OF -DIHYDROXY-1-METHYL-1,2,3,4-TETRAHYDROISOQUINOLINE (SALSOLINOL) IN SH-SY5Y CELLS

We have studied the hypothesis that -dihydroxy-1-methyl-1,2,3,4-tetrah ydroisoquinoline (salsolinol) is neurotoxic. Salsolinol induced a sign ificant time and dose related inhibition of 3 [4,5-dimethylthiazol-2-y l]-2, 5-diphenyltetrazolium bromide; thiazoyl blue (MTT) reduction, an d increased lactate dehydrogenase release (LDH) release from human SH- SY5Y neuroblastoma cells, at concentrations within the range of 1-meth yl-4-phenylpyridinium (MPP(+)) cytotoxicity, in vitro. Cytotoxicity wa s not inhibited by the addition of antioxidants, monoamine oxidase inh ibitors or imipramine. In confluent monolayers, salsolinol stimulated catecholamine uptake with EC(50) values of 17 mu M and 11 mu M, for no radrenaline and dopamine,respectively. Conversely, at concentrations a bove 100 mu M, salsolinol inhibited the uptake of noradrenaline and do pamine, with IC50 values of 411 mu M and 379 mu M, respectively. The i nhibition of catecholamine uptake corresponded to the increased displa cement of [H-3]nisoxetine from the uptake(1) site by salsolinol, as th e K-i (353 mu M) for displacement was similar to the IC50 (411 and 379 mu M) for uptake. salsolinol stimulated catecholamine uptake does not involve the uptake recognition site, or elevation of cAMP, cGMP, or i nhibition of protein kinase C. Salsolinol also inhibited both carbacho l (1 mM) and K+ (100 mM, Na+ adjusted) evoked release of noradrenaline from SH-SY5Y cells, with IC50 values of 500 mu M and 120 mu M, respec tively. In conclusion, salsolinol appears to be cytotoxic to SH-SY5Y c ells, via a mechanism that does not require uptake(1), bioactivation b y monoamine oxidase, or membrane based free radical damage. The effect s of salsolinol on catecholamine uptake, and the mechanism of toxicity require further investigation.