Irreversible blockade of sigma-1 receptors by haloperidol and its metabolites in guinea pig brain and SH-SY5Y human neuroblastoma cells

We evaluated the effect of haloperidol (HP) and its metabolites on [H-3](+)-pentazocine binding to sigma(1) receptors in SH-SY5Y human neuroblastorna cells and guinea pig brain P-1, P-2 and P-3 subcellular fractions. Three days after a single i.p. injection in guinea pigs of HP (but not of other a, antagonists or (-)-sulpiride), [H-3](+)-pentazocine binding to brain membranes was markedly decreased. Recovery of a, receptor density to steady state after HP-induced inactivation required more than 30 days. HP-metabolite 11 (reduced HP, 4-(4-chlorophenyl)-alpha-(4-fluorophenyl)-4-hydroxy-1 -piperidinebutanol), but not HP-metabolite I (4-(4-chlorophenyl)-4-hydroxypiperidine), irreversibly blocked sigma(1) receptors in guinea pig brain homogenate and P-2 fraction in vitro. We found similar results in SH-SY5Y cells, which suggests that this process may also take place in humans. HP irreversibly inactivated sigma(1) receptors when it was incubated with brain homogenate and SH-SY5Y cells, but not when incubated with P-2 fraction membranes, which suggests that HP is metabolized to inactivate a, receptors. Menadione, an inhibitor of the ketone reductase activity that leads to the production of HPmetabolite II, completely prevented HP-induced inactivation of a, receptors in brain homogenates. These results suggest that HP may irreversibly inactivate sigma(1) receptors in guinea pig and human cells, probably after metabolism to reduced HP.