Two major grapefruit juice components differ in time to onset of intestinal CYP3A4 inhibition.
Grapefruit juice elevates blood levels of some drugs taken orally, primarily by inhibiting intestinal CYP3A4-mediated first-pass metabolism. Two prominent furanocoumarins in the juice, 6',7'-dihydroxybergamottin (DHB) and bergamottin (BG), have been demonstrated as important contributors to grapefruit juice-drug interactions. Using CYP3A4-expressing Caco-2 cells and representative probes from distinct CYP3A4 substrate subgroups (midazolam, testosterone), we compared the time-dependent inhibitory properties of DHB and BG. DHB rapidly inhibited CYP3A4 activity in a substrate-independent fashion with maximal inhibition (>/=85%) generally occurring within 30 min. In contrast, BG had a slower onset and exhibited substrate-dependent inhibition. Whereas testosterone 6beta-hydroxylation was inhibited by >50% with all exposure times (0.5-3 h), midazolam 1'-hydroxylation was unaffected, or even activated, with short exposure times (<1 h). After a 3-h exposure, however, BG had begun to "catch up" with DHB, causing >/=70% inhibition, independent of substrate. Likewise, loss of CYP3A4 protein, believed to reflect rapid intracellular degradation of the enzyme following mechanism-based inactivation, was comparable between the furanocoumarins (40-50%). The time course of BG-mediated inhibition was similar after just a 30-min exposure, indicating that the short exposure presumed to occur after juice ingestion is sufficient to initiate the events required to cause substantial inhibition (>/=50%). These results suggest that after ingestion of a glass of grapefruit juice, CYP3A4 is maximally inhibited by DHB before BG has the opportunity to act. However, foods containing BG but not DHB (e.g., lime juice) could produce a substrate-dependent interaction with drugs consumed concomitantly, but a substrate-independent interaction with drugs taken several hours after food consumption.
Paine
Mary F
MF
General Clinical Research Center, Room 3005 Bldg. APCF, CB# 7600, UNC Hospitals, Chapel Hill, NC 27599-7600, USA. mpaine@med.unc.edu
Criss
Anne B
AB
Watkins
Paul B
PB
D018938:Caco-2 Cells; D002384:Catalysis; D032083:Citrus paradisi; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D011564:Furocoumarins / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D013997:Time Factors
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D011564:Furocoumarins; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; C068337:bergamottin; C104774:6',7'-dihydroxybergamottin