| Abstract
| - Grapefruit juice (GFJ) has been found to interact with several medications, increasing their oralbioavailability and the risk of toxicity. Inhibition of CYP3A4 in the small intestine by flavonoids (suchas naringin and naringenin) and furanocoumarins (including bergamottin and 6‘,7‘-dihydroxybergamottin) present in GFJ seems to be the predominant mechanism, although P-glycoprotein and influxtransporters in the small intestine are also involved. The quantity of interactive compounds ingestedmay affect the magnitude and mechanism of the food−drug interaction. Therefore, these fourcompounds were quantified by HPLC analysis in commercially available and fresh-squeezed GFJand in grapefruit tissues. Considerable variability in naringin (174−1492 μmol/L), bergamottin (1.0−36.6 μmol/L), and 6‘,7‘-dihydroxybergamottin (0.22−52.5 μmol/L) was observed, whereas naringenincould not be detected. White grapefruit showed higher concentrations of naringin and furanocoumarinslocated in the albedo and flavedo compared with red varieties. Findings from this study suggestconsidering concentrations of components with a potential for drug interactions in GFJ−drug interactionstudies. The concentration of potentially contributing compounds may crucially influence the magnitudeof observed interaction and impair direct comparison of studies in which different juices have beenused. Keywords: Grapefruit; flavonoids; furanocoumarins; HPLC; grapefruit−drug interaction; cytochromeP-450
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