Effects of cocaine esterase following its repeated administration with cocaine in mice

Background: A bacterial cocaine esterase (CocE) produces robust protection and reversal of cocaine toxicity. The aim of this study was to investigate how effectiveness of CocE was changed following its repeated administration together with cocaine. Methods: Cocaine toxicity was quantified by measuring the occurrence of convulsions and lethality in mice. Immunologic responses of CocE were determined using ELISA. In the protection experiment, i.v. CocE 0.3 mg was given 1 min before a lethal dose of i.p. cocaine 180 mg/kg. In the rescue experiment, i.v. CocE 0.3 mg was given 1 min after the occurrence of convulsions elicited by i.p. cocaine 100 mg/kg. In both treatment paradigms, four trials were conducted in the same animals with a 2-week interval. Results: CocE retained its effectiveness to protect or rescue mice during the first two trials and these mice did not show an immune response. In contrast, CocE's effectiveness was gradually reduced in the last two trials, accompanied by 10- and 100-fold increases in anti-CocE antibody titers. Nevertheless, effectiveness of CocE could be partially recovered by increasing the dose of CocE. In addition, escalating the dose of CocE from the minimum effective dose for repeated administration could also retain CocE's effectiveness longer and slow the production of anti-CocE antibodies. Conclusions: These results indicate that CocE is a weak antigen and it can maintain its protective and rescuing ability initially against cocaine-induced toxicity. Decreased effectiveness of CocE following repeated use can be partially improved by adjusting the dose and frequency of CocE treatment.