I. Gardner et al., A COMPARISON OF THE COVALENT BINDING OF CLOZAPINE AND OLANZAPINE TO HUMAN NEUTROPHILS IN-VITRO AND IN-VIVO, Molecular pharmacology, 53(6), 1998, pp. 999-1008
Covalent binding of a reactive metabolite of clozapine to neutrophils
or their precursors is thought to play a role in the development of cl
ozapine-induced agranulocytosis. immunoblotting studies with an anti-c
lozapine antiserum detected covalent binding of clozapine to human neu
trophils in vitro when HOCl was used to generate clozapine reactive me
tabolite (major clozapine adducts of 31, 49, 58, 78, 86, 126, 160, and
204 kDa). In addition, incubating neutrophils with clozapine and H2O2
(major clozapine adducts of 49 and 58 kDa) or clozapine, H2O2, and hu
man myeloperoxidase (major clozapine adducts of 31, 49, 58, and 126 kD
a) also resulted in covalent binding of clozapine to the neutrophils.
The covalent binding of clozapine to neutrophils was inhibited by extr
acellular glutathione when HOCl, but not H2O2 was used to generate rea
ctive metabolite. We found that the antiserum against clozapine also r
ecognized olanzapine, an antipsychotic drug that forms a similar react
ive metabolite to clozapine but has not been associated with induction
of agranulocytosis. Repeating the in vitro experiments with olanzapin
e revealed that the major olanzapine-modified polypeptides had molecul
ar masses of 96, 130-170, and 218 kDa. Only relatively low levels of 3
1, 49, and 58 kDa adducts were observed. Clozapine-modified polypeptid
es also were detected in neutrophils from patients being treated with
clozapine. A major 58-kDa clozapine-modified polypeptide was detected
in all patients tested. In contrast, no drug-modified polypeptides wer
e detected in neutrophils from patients taking olanzapine. The differe
nces in covalent binding exhibited by the two compounds and, in partic
ular, the lack of olanzapine binding to human neutrophils in vivo may
help to explain the difference in toxicity of these two drugs.