Active immunization against nicotine alters the distribution of nicotine but not the metabolism to cotinine in the rat

We have previously shown that active immunization with the nicotine immunoconjugate IP18-KLH attenuates the reinforcing effects of nicotine, i.e., suppresses the nicotine-induced brain dopamine release and prevents reinstatement of the nicotine-seeking behavior in rats. These effects are thought to be due to an alteration of the kinetics of nicotine distribution by the antibodies, resulting in an attenuated nicotine distribution to the brain. In this study, the distribution of nicotine administered at doses corresponding to those used in our previous studies, was investigated in immunized rats and controls. Male Wistar rats received two immunizations with IP18-KLH in Freund's incomplete adjuvant, 21 days apart, and experiments were performed 7-11 days post-immunization under chloral hydrate anesthesia. Blood samples were collected to determine antibody titer and nicotine selectivity using enzyme-linked immunosorbent assay (ELISA) techniques. The animals received an intravenous nicotine dose and were sacrificed either 3 min or 60 min after nicotine administration. Trunk blood was collected and the brains were removed for analysis of nicotine content. The results showed that immunization against nicotine increases the nicotine concentration in blood and significantly decreases the amount of nicotine that reaches the brain. The present findings thus demonstrate an altered distribution of nicotine after immunization with IP18-KLH. Despite the sustained nicotine binding by the antibodies, the active immunization did not alter the metabolism of nicotine to cotinine, the major nicotine metabolite. In conclusion, the attenuation of the reinforcing effect of nicotine after immunization with IP18-KLH, shown previously, is indeed associated with an altered distribution of nicotine.