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Vol. 27, Issue 4, 517-525, April 1999
Department of Pharmacology and Molecular Toxicology,
University of Massachusetts Medical Center, Worcester, Massachusetts
To study cytochrome P-450 (CYP) 2B6 contribution to
methoxychlor metabolism within human liver microsomes and to initiate an investigation of CYP2B6 protein expression, we developed a polyclonal antibody targeted to a 20-residue peptide within that protein. The antibody was found to be highly sensitive and monospecific for CYP2B6 on immunoblots. Although many immunological studies have
described the absence or low expression of CYP2B6 in human livers, in
the present investigation, we have found this not to be the case. We
immunoquantified CYP2B6 apoprotein expression in a panel of 28 livers
and found concentrations ranging from 2 to 82 pmol/mg protein, with a
mean value of 25 pmol/mg protein. Five livers (~18%) displayed
relatively high levels of CYP2B6 (>40 pmol/mg protein). There were no
sex-related differences, although the highest level was observed in a
1-week postpartum donor given several medications. A marked diminution
in variability was found in individuals aged 56 or older
(n = 12), but there were no age-related trends in
mean CYP2B6 content. We suggest that CYP2B6 represents a significant
portion of total CYP in human liver. The exquisite sensitivity of this
antibody (fmol quantities are detected easily on immunoblots) may
explain our detection of CYP2B6 in 100% of livers versus its detection
in a limited number of livers by certain other investigators. The
antibody also was found to immunoinhibit CYP2B6-catalyzed
N-demethylation of (S)-mephenytoin in human liver
microsomes by 68 to 79%. The utility of this antibody for determining
human liver microsomal CYP2B6 contribution to the
ortho-hydroxylation of methoxychlor was demonstrated.
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