4beta-hydroxycholesterol as a marker of CYP3A4 inhibition in vivo - effects of itraconazole in man.
OBJECTIVE
Itraconazole, a triazole antifungal agent, has been demonstrated to act as an inhibitor of the ligand induced pregnane X receptor-mediated transcriptional regulation of the CYP3A4 gene. Here, we study the potential endogenous serum marker of CYP3A4 activity, 4beta-hydroxycholesterol, during therapy with itraconazole.


METHODS
8 male patients with onychomycosis received two 1-week cycles of treatment with 400 mg itraconazole once daily in an open, prospective exploratory trial. Fasting serum samples were taken at the beginning and at the end of each cycle. The levels of cholesterol were measured using gas chromatography-flame ionization detection, while cholesterol and bile acid precursors were quantified by gas chromatography-mass spectrometry.


RESULTS
Total cholesterol decreased by 10% (p < 0.0005) during the itraconazole treatment. Concentrations of the cholesterol precursor lanosterol and 24, 25-dihydrolanosterol increased 10- and 240-fold, respectively (p < 0.001 for both). Interestingly, the ratio of serum lathosterol to cholesterol, an indicator of endogenous cholesterol synthesis downstream from lanosterol, remained unchanged. Absolute and cholesterol-corrected concentrations of 4beta-hydroxycholesterol, formed by CYP3A4-mediated oxidation, decreased significantly during both cycles, on average by 29.1% (p = 0.0006) and 20.8% (p = 0.0062), respectively. The brain-specific cholesterol metabolite 24S-hydroxycholesterol as well as its ratio to cholesterol increased by 19.7% (p = 0.0422) and 34.9% (p = 0.0013), respectively, while the concentrations of the other bile acid precursors, 7alpha-hydroxycholesterol and 27-hydroxycholesterol, remained unchanged.


CONCLUSIONS
In conclusion, 4beta-hydroxycholesterol appears to be a sensitive endogenous surrogate marker in human serum for inhibition of CYP3A4 by itraconazole.
Lütjohann
D
D
Institute of Clinical Chemistry and Pharmacology, University Clinic, Bonn, Germany. dieter.luetjohann@ukb.uni-bonn.de
Marinova
M
M
Schneider
B
B
Oldenburg
J
J
von Bergmann
K
K
Bieber
T
T
Björkhem
I
I
Diczfalusy
U
U
D000935:Antifungal Agents / Q000627:therapeutic use; D054316:Biomarkers, Pharmacological / Q000097:blood*; D002784:Cholesterol / Q000097:blood / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D065692:Cytochrome P-450 CYP3A Inhibitors; D006801:Humans; D006888:Hydroxycholesterols / Q000097:blood*; D017964:Itraconazole / Q000627:therapeutic use; D008297:Male; D014009:Onychomycosis / Q000188:drug therapy
D000935:Antifungal Agents; D054316:Biomarkers, Pharmacological; D065692:Cytochrome P-450 CYP3A Inhibitors; D006888:Hydroxycholesterols; C099828:cholest-5-ene-3,4-diol; D017964:Itraconazole; D002784:Cholesterol; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human