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Effect of Cholesterol on the Interaction of Cytochrome P450 Substrate Drug Chlorzoxazone with the Phosphatidylcholine Bilayer
journal contribution
posted on 2016-06-27, 00:00 authored by Ayumi Yamada, Nobutaka Shimizu, Takaaki Hikima, Masaki Takata, Toshihide Kobayashi, Hiroshi TakahashiMany
drugs are oxidized by membrane protein cytochrome P450 (CYP)
enzymes during their metabolism process. CYPs are located mainly in
endoplasmic reticulum (ER) membranes. Recent studies have suggested
that CYP substrate drugs first bind the lipid bilayers of ER membranes
and then the drugs reach the active site of CYP by way of an access
channel. The entrance of the channel is located in the hydrophobic
regions of the lipid bilayers. One of the features of the ER membrane
is a cholesterol content that is lower than those of other biomembranes.
In this study, the cholesterol concentration dependence of the interaction
of a CYP substrate drug, chlorzoxazone (CZX), with model membranes
composed of phosphatidylcholine (PC) and cholesterol was examined
via differential scanning calorimetry (DSC), UV–visible spectroscopy,
and X-ray diffraction. Experimental results indicated that CZX can
bind to pure PC bilayers in the absence of cholesterol and that, by
contrast, a high cholesterol concentration (30–50 mol %) tends
to prevent CZX from binding to PC bilayers. Interestingly, the effect
of cholesterol on the binding and insertion of CZX was biphasic. In
the case of palmitoyloleoylphosphatidylcholine (POPC) bilayers containing
5–10 mol % cholesterol, the CZX’s binding and penetration
into the bilayer were found to be greater than those with pure POPC
bilayers. The concentration of 5–10 mol % nearly corresponds
to the cholesterol concentration of ER membranes. The low cholesterol
contents (12–20 mol %) of ER membranes might be the most suitable
for the CYP drug metabolism process in ER membranes.