Pharmacokinetics and immunologic consequences of exposing macaques to purified homologous butyrylcholinesterase

Exposure to organophosphorus compounds (OPs), in the form of nerve agents and pesticides poses an ever increasing military and civilian threat. In recent years, attention has focused on the use of exogenously administered cholinesterases as an effective prophylactic treatment for protection against OPs. Clearly, a critical prerequisite for any potential bioscavenger is a prolonged circulatory residence time, which is influenced by the size of protein, the microheterogeneity of carbohydrate structures, and the induction (if any) of anti-enzyme antibodies following repeated injections of the enzyme. Previously, it was demonstrated that multiple injections of equine butyrylcholinesterase (BChE) into rabbits, rats, or rhesus monkeys, resulted in a mean residence time spanning several days, and variable immune responses. The present study sought to assess the pharmacokinetics and immunological consequences of administration of purified macaque BChE into macaques of the same species at a dose similar to that required for preventing OP toxicity. An i.v. injection of 7,000 U of homologous enzyme in monkeys demonstrated much longer mean residence times in plasma (MRT = 225 +/- 19 h) compared to those reported for heterologous Hu BChE (33.7 +/- 2.9 h). A smaller second injection of 3,000 U given four weeks later, attained predicted peak plasma levels of enzyme activity, but surprisingly, the MRT in the four macaques showed wide variation and ranged from 54 to 357 h. No antibody response was detected in macaques following either injection of enzyme. These results bode well for the potential use of human BChE as a detoxifying drug in humans.