title: Role of metabolism in cocaine-induced immunosuppression in splenocyte cultures from B6C3F1 female mice.
abstract: Cocaine has been reported to directly suppress the in vitro immune responses at very high concentrations. In the present study, the possible role of metabolism in cocaine-induced immunosuppression was investigated in splenocyte cultures isolated from B6C3F1 female mice. Since cocaine can be metabolized by both esterase and P-450 monooxygenase, we studied the direct effects of cocaine, benzoylecgonine and norcocaine on the in vitro T-dependent antibody response to SRBC. Direct exposure to cocaine only produced a modest (30%) but nonsignificant suppression of the antibody response, while benzoylecgonine, a primary product of metabolism by the esterase pathway, was devoid of activity. In contrast, direct exposure to norcocaine, the initial product of N-demethylation by the P-450 pathway, produced significant suppression at concentrations greater than or equal to 10 microM. Similar results were observed in studies measuring LPS and Con A mitogenicity. Furthermore, a significant suppression was observed when splenocytes were preincubated for 1 h with 1 mM cocaine in the presence of liver S-9 fractions isolated from phenobarbital-induced mice. Meanwhile, no suppression was obtained when splenocytes were preincubated in the presence of untreated S-9 fractions. To characterize the mechanism of our results, the capacity of both untreated and phenobarbital-induced microsomes to produce formaldehyde from cocaine was compared. The N-demethylation of cocaine was NADPH-dependent and phenobarbital-induced microsomes produced approx. 6-times higher amounts of formaldehyde, indicating a greater portion of cocaine could be metabolized through the P-450 pathway to its toxic metabolites. Finally, because benzoylecgonine shares with cocaine the presence of a methyl group on the tropane nitrogen, we also compared the ability of N-demethylation from cocaine and benzoylecgonine in mouse liver microsomes. Our results indicated that benzoylecgonine could not be demethylated as determined by a failure to generate any formaldehyde. These results offer further support that the N-demethylation pathway is a critical step to cause its immunotoxicity.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Virginia/Virginia Commonwealth University, Richmond, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Jeong
authors.forename: R A
authors.initials: RA
authors.lastname: Matulka
authors.forename: S D
authors.initials: SD
authors.lastname: Jordan
authors.forename: K H
authors.initials: KH
authors.lastname: Yang
authors.forename: M P
authors.initials: MP
authors.lastname: Holsapple
mesh_terms: D000818:Animals; D000917:Antibody Formation; D002478:Cells, Cultured; D003042:Cocaine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism / Q000633:toxicity*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004912:Erythrocytes / Q000166:cytology; D005260:Female; D006520:Hepatitis, Animal / Q000276:immunology / Q000503:physiopathology; D007108:Immune Tolerance / Q000187:drug effects* / Q000502:physiology; D007165:Immunosuppression Therapy / Q000009:adverse effects; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D011897:Random Allocation; D012756:Sheep; D013154:Spleen / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
chemical_list: C008671:norcocaine; C005618:benzoylecgonine; D003577:Cytochrome P-450 Enzyme System; D003042:Cocaine