Variance of common flavonoids by brand of grapefruit juice
Introduction
This study was designed to characterize the differences in flavonoid concentration of several commercially available brands of grapefruit [Citrus paradisi Macf. (Rutaceae)] juice (GFJ). GFJ has been demonstrated to inhibit the metabolism of several cytochrome P450 (cP450) metabolized drugs [1], [2], [3], [4], [5], [6], [7], [8]. After our analyses were completed newly published research demonstrated that 6′,7′-dihydroxybergamottin, a furanocoumarin, is probably the major cP450 inhibitory substance in grapefruit products [9]. Even so, flavonoids have been demonstrated to exhibit a significant degree of cP450 inhibition and for this reason our data are significant. Furthermore, future plans include expanding the current database to determine if high flavonoid concentration in commercial grapefruit products correlates with high 6′,7′-dihydroxybergamottin concentration, thus demonstrating that both may play a role in cP450 inhibition. Recently, GFJ and orange juice have been demonstrated to significantly lower LDL-cholesterol in animals [10]. Flavonoids in Citrus juices might also play a significant role in lowering cholesterol in humans.
Section snippets
Investigated material
Nine commercial grapefruit juice products detailed in Table 1.
Flavonoid Standards
Rutin trihydrate (quercetin 3-rutinoside), quercetin dihydrate (3,5,7,3′,4′-pentahydroxyflavone), hesperidin (hesperitin 7-rutinoside), naringin (naringenin 7-rutinoside), kaempferol (3,5,7,4′-tetrahydroxyflavone), kaempferide (3,5,7,-trihydroxy-4′-methoxyflavone), and apigenin (5,7,4′-trihydroxyflavone) were obtained from Fluka Chemical Corp. (Ronkonkoma, NY 11779, USA). Poncirin (isosakuranetin 7-neohesperidoside), didymin
Results
High performance liquid chromatography (HPLC) using normal or reversed-phase columns has been utilized by many investigators to quantify flavonoids in Citrus juices [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. In our study a similar HPLC method was used to quantify all the major flavonoids present in GFJ. Nine commercial brands of grapefruit juice (Table 1) were analyzed for their flavonoid content. The identification of the flavonoids in the different
Discussion
The small intestine, especially the duodenum, is the site of high concentration cP450 enzymes [21]. When drugs metabolized by these enzymes are administered orally, significant pre-systemic metabolism and thus, reduced bioavailability occurs. Pre-systemic metabolism of several agents by cP450 has been confirmed [1], [2], [4], [5], [6], [7], [22]. These studies describe a variety of drugs having a propensity for increased systemic bioavailability when administered orally and simultaneously with
Acknowledgements
We are grateful to Charles D. Hufford, H. Joseph Byrd, John D. Cleary, and W.W. Widmer for their invaluable assistance.
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