Inhibition of human intestinal wall metabolism by macrolide antibiotics: effect of clarithromycin on cytochrome P450 3A4/5 activity and expression.
BACKGROUND
Clarithromycin increases both hepatic and intestinal availability of the selective cytochrome P450 (CYP) 3A probe midazolam. This study was designed to identify determinants of variability in the extent of intestinal wall CYP3A inhibition by clarithromycin, such as CYP3A5 genotype, and the mechanism of inhibition.


METHODS
Ten healthy volunteers received 500 mg oral clarithromycin twice a day for 7 days. Before and after administration of clarithromycin, small-bowel mucosal biopsy specimens were obtained endoscopically. Intestinal CYP3A activity was determined from the rate of 1'-hydroxymidazolam and 4-hydroxymidazolam formation by incubation of small-bowel homogenate with midazolam (25 micromol/L) and NADPH for 5 minutes. Intestinal CYP3A4 and CYP3A5 messenger ribonucleic acid was quantified by real-time reverse transcriptase-polymerase chain reaction. Intestinal CYP3A4 and CYP3A5 protein concentrations were determined by immunoblotting. Serum and homogenate concentrations of midazolam, clarithromycin, and metabolites were determined by liquid chromatography-mass spectrometry. CYP3A5 genotype was determined by real-time polymerase chain reaction.


RESULTS
The formation of 1'-hydroxymidazolam (1.36 +/- 0.46 pmol . min(-1) . mg(-1) at baseline versus 0.35 +/- 0.16 pmol . min(-1) . mg(-1) after administration) and 4-hydroxymidazolam (0.39 +/- 0.12 pmol . min(-1) . mg(-1) at baseline versus 0.12 +/- 0.05 pmol . min(-1) . mg(-1) after administration) was significantly (P < .001) reduced after clarithromycin administration. Clarithromycin administration did not result in a significant change in intestinal CYP3A4 and CYP3A5 messenger ribonucleic acid and protein expression. All subjects had detectable serum clarithromycin concentrations after 7 days of clarithromycin (3.71 +/- 2.43 micromol/L). The mean concentration of clarithromycin in the intestinal biopsy homogenate was 1.2 +/- 0.7 nmol/L (range, 0.42-2.39 nmol/L). Compared with CYP3A5 nonexpressers, subjects with at least 1 CYP3A5*1 allele (CYP3A5 expressers) had greater inhibition of intestinal CYP3A activity after treatment with clarithromycin. There was a strong linear relationship between the decrease in intestinal CYP3A activity and baseline catalytic activity (R(2) = 0.9).


CONCLUSIONS
Baseline intestinal activity of CYP3A4 was a key determinant of variability of the inhibitory effect of clarithromycin among individuals. CYP3A5*1 alleles were associated with greater baseline intestinal CYP3A activity and, therefore, greater extent of inhibition. The primary in vivo mechanism was not rapidly reversible competitive or irreversible inhibition but was likely formation of metabolic intermediate complexes.
Pinto
Amar G
AG
Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Wang
Ying-Hong
YH
Chalasani
Naga
N
Skaar
Todd
T
Kolwankar
Dhanashri
D
Gorski
J Christopher
JC
Liangpunsakul
Suthat
S
Hamman
Mitchell A
MA
Arefayene
Million
M
Hall
Stephen D
SD
D000284:Administration, Oral; D000328:Adult; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D017291:Clarithromycin / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000187:drug effects* / Q000235:genetics; D005260:Female; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D005838:Genotype; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects* / Q000503:physiopathology; D008297:Male; D008874:Midazolam / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D013997:Time Factors
D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C104464:CYP3A protein, human; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; D017291:Clarithromycin; D008874:Midazolam