Inhibitory Effect Of Grapefruit Juice Research Articles

Abstract 639: The effect of grapefruit intake on endogenous serum estrogen levels in postmenopausal women

Abstract The inhibitory effect of grapefruit juice on the intestinal cytochrome P450 3A4 system interacts with more than 60% of orally administered drugs leading to elevation of their serum concentrations. While grapefruit has been shown to lead to elevated serum levels of estrogens when hormones are administered orally, there are no published data on the effect of grapefruit intake on endogenous levels. To begin to address that data gap, we conducted a dietary intervention study among healthy postmenopausal volunteers to determine whether endogenous estrogen levels are significantly affected by grapefruit consumption. We tested 4 grapefruit products: whole fresh grapefruit, fresh squeezed juice “not from concentrate,” shelf-stable juice from concentrate, and grapefruit soda. The majority of volunteers were recruited through the Love/Avon Army of Women. The six-week study consisted of a run-in period of three weeks, a two-week period of grapefruit consumption, and a one-week wash-out period. Eight fasting blood samples were collected during the study. An additional 5 samples drawn at 1, 2, 4, 8 and 10 hours after initial grapefruit intake were collected during an acute-phase study. Serum assays for estrone (E1), estradiol (E2), estrone-3- sulfate (E1S), and sex hormone-binding globulin (SHBG) were conducted. Sixty-two women participated in the study, 10 of whom also participated in the acute phase. Only the whole grapefruit had statistically significant effects on endogeneous estrogen levels. The largest increases were seen in the women with the highest BMI. The changes were evident at 24 hours and remained relatively constant over the 2 week period. With whole grapefruit at the average BMI of 26.6 kg/m2, E1S increased overall by 10.6% (p=0.031), and at a BMI of 30 kg/m2 this increased to 16.4% (p=0.003). Approximately double the effects were seen around 10 hours after whole grapefruit consumption. The effects of fresh juice consumption were around 25% of these increases but were not statistically significant. Small increases in E1 were seen with whole grapefruit, but no increase was seen in E2. The findings of the present study suggest an important interaction between grapefruit consumption and serum levels of endogenous E1S. The increase in E1S is difficult to interpret in term of risk of breast cancer as we found only a small increase in E1 and failed to find any increase in E2. More detailed studies are needed to gain an understanding how the increased levels of E1S are not reflected in similar increases in E1 and E2, and whether the increased E1S levels are reflected in an increase in E1 and E2 levels in the breast itself. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 639. doi:1538-7445.AM2012-639

Inhibitory effect of grapefruit juice on the genotoxicity induced by hydrogen peroxide in human lymphocytes

By means of the comet assay we demonstrated a strong effect by hydrogen peroxide (HP) and no damage by grapefruit juice (GJ) in human lymphocytes. Cells exposed to HP and treated with three concentrations of GJ (10–90min) showed an increase of DNA damage by HP over the control level, and a decrease of such damage by GJ. With the comet assay plus formamidopyrimidine-DNA-glycosylase we found the strongest increase of DNA damage by HP over the control level, and the strongest reduction of such damage by GJ. By applying the comet/FISH method we determined 98% of the p53 gene signals in the comet head of control cells along the experiment (10–90min), in contrast with about 90% signals in the comet tail of cells exposed to HP. Cells treated with both agents showed a significant, concentration/time dependent return of p53 signals to the head, suggesting enhancement of the gene repair. Finally, with the annexin V assay we found an increase in apoptosis and necrosis by HP, and no effect by GJ; when GJ was added to HP treated cells no modification was observed in regard to apoptosis, although a decrease of necrosis was observed.

Inhibitory Effect of Grapefruit Juice on the Genotoxic Damage Induced by Ifosfamide in Mouse

The consumption of grapefruit juice (GJ) has been associated with various activities potentially beneficial for human health, including protection against the DNA damage produced by various compounds. In the present report, we evaluated the capability of this juice to inhibit the rate of micronucleated polychromatic erythrocytes (MNPE) and sister chromatid exchanges (SCE) induced by the antineoplastic alkylating agent ifosfamide (IF). We tested the effect of administering 100, 500, and 1000 mg/kg of GJ in mouse and obtained the following results: a) with the high dose, a reduction of 72% in the rate of SCE induced by IF; b) a mean reduction of 65.3% in the rate of MNPE compared with the damage induced by IF at 48 h post-administration; c) no modification induced by GJ either on the cellular proliferation kinetics or in the mitotic index; and d) neither induction of bone marrow cytotoxicity by GJ nor a protective effect of the juice against the cytotoxicity induced by IF. These data showed a significant inhibitory effect of GJ against the chromosome damage induced by the tested agent; they also suggest the relevance of carrying out studies to clarify the involved mechanism of action as well as to determine the cancer chemopreventive capacity of the juice.

Species Difference in the Effect of Grapefruit Juice on Intestinal Absorption of Talinolol between Human and Rat

Bioavailability of talinolol, a beta(1)-adrenergic receptor antagonist, was enhanced by coadministration with grapefruit juice (GFJ) in rats, whereas GFJ ingestion markedly reduced the absorption of talinolol in humans. Because our recent study indicated that the inhibitory effect of GFJ on organic anion-transporting polypeptide (Oatp)- and P-gp-mediated talinolol absorption depends on the concentration of naringin in ingested GFJ, the apparent inconsistent findings may be explained by the species difference in the affinity of naringin for OATP/Oatp and P-gp multidrug resistance 1 (MDR1/Mdr1) between humans and rats. Although human MDR1-mediated talinolol transport was not inhibited by 2000 microM naringin, naringin inhibited human OATP1A2-, rat Oatp1a5-, and rat Mdr1a-mediated talinolol transport with IC(50) values of 343, 12.7, and 604 microM, respectively, in LLC-PK1 cell and Xenopus laevis oocyte systems. Because the naringin concentration in commercially prepared GFJ was found to be approximately 1200 microM, these results suggested that GFJ would reduce the intestinal absorption of talinolol through inhibition of OATP1A2-mediated talinolol uptake in humans, whereas an increase of talinolol absorption is mainly through inhibition of Mdr1a-mediated efflux in rats. The rat intestinal permeability of talinolol measured by the in situ closed loop method was indeed significantly increased in the presence of GFJ, whereas a significant decrease was observed with 6-fold diluted GFJ, in which the naringin concentration was approximately 200 microM. The present study indicated that the species difference in the effect of GFJ on intestinal absorption of talinolol between humans and rats may be due to differences in the affinity of naringin for OATP/Oatp and MDR1/Mdr1 transporters between the two species.

The activity of liver oxidative enzymes after single and multiple grapefruit juice ingestion

In the recent time, several in vitro and in vivo studies have shown the inhibitory effect of grapefruit juice on metabolism of xenobiotics catalyzed by liver oxidative enzymes including cytochrome P450 izoenzymes. However, all these experiments were done with a single dose of grapefruit juice. The primary aim of this study was to evaluate if the chronical ingestion of grapefruit juice can cause enzyme activity alteration as well as a single dose. Three groups of male mice were used: the control group, the group which was administered 0.2 mL of grapefruit juice per os 10 days and the group which was administered single dose of 0.5 mL grapefruit juice per os 90 min. before the sacrificing. After the sacrificing of animals, liver was homogenized with appropriate buffer, and the activity of oxidative liver enzymes: xanthine oxidase (XOD), peroxidase (Px), catalase (CAT), lipid peroxidase (LPx), glutathion peroxidase (GSH-Px) and liver glutathion contents (GSH) were detected by standard methods. The results show that the enzyme activity of liver MFO was changed according to a single or multiple grapefruit juice ingestion. The grapefruit juice in a single oral dose significantly decreases the activity of xanthine oxidase, glutathion peroxidase, lipid peroxidase and liver glutathion contents, and has no effect on activity of catalase and peroxidase. The multiple grapefruit ingestion increases the activity of XOD, GSH-Px, LPx, Px and GSH, while the activity of CAT enzyme is unchanged. The chronical and single grapefruit ingestion has no effect on relative liver weight, but the liver protein content is significantly decreased after the multiple oral grapefruit juice ingestion.

EFFECT OF GRAPEFRUIT JUICE AND OTHER JUICES ON P-GLYCOPROTEIN FUNCTION OF DRUG ABSORPTION IN THE INTESTINE

We investigated the inhibitory effect of components in grapefruit juice (GFJ) and orange juice (OJ) on the uptake of vinblastine, a substrate of P-glycoprotein, by Caco-2 cells. Significantly increased uptake of [3H] vinblastine at the steady state by Caco-2 cells was observed in the presence of GFJ and OJ. This suggests that the both juices involve compounds inhibiting P-gp function. We examined the effect of three organic solvent extracts, ethyl acetate, diethyl ether and methylene chrolide, of GO and OJ on the uptake of [3H] vinblastine. The inhibitory effect was shown more in ethyl acetate extracts than the other two extracts, in the both case of GFJ and OJ. Furthermore, the ethyl acetate extracts of GFJ and OJ were fractionated by cosmosil column chromatography with stepwise methanol solution. Inhibitory effect of GFJ on P-gp function was maximun in the fraction eluted with 60% methanol solution, while OJ's was maximun in 70% methanol solution. Each fraction contained different component. Moreover, inhibitory effect of GFJ on CYP3A4 was maximun in the fraction eluted with 80% methanol solution. This study suggested the existence of unknown specific inhibitory compounds in GFJ and OJ for the P-gp, but not for CYP3A4 function.

The character of inhibition of the metabolism of 1,2-benzopyrone (coumarin) by grapefruit juice in human.

Constituents of grapefruit juice are known to interfere with mammalian cytochrome P450 isozymes such as intestinal CYP3A4 and hepatic CYP2A6, lowering the biotransformation of drugs and increasing their bioavailability. The aim of this study was to investigate whether the presence of naringin is demanded for the inhibition of the coumarin 7-hydroxylase in man or other compounds are responsible for it. In cross-over studies, doses of 10 mg coumarin, together with combinations of grapefruit juice, water and naringin, were given orally to one healthy male volunteer, We investigated increasing amounts of grapefruit juice, keeping the volume of liquid constant at 1 L; increasing doses of naringin given in water; increasing amounts of juice, keeping the dose of naringin constant; or increasing doses of naringin, keeping the amount of juice constant. Urine samples were collected up to 24 h after dosing and 7-hydroxycoumarin was quantified fluorimetrically in urine hydrolysates after HPLC separation to determine the excretion rates. While increasing amounts of grapefruit juice delay the excretion of 7-hydroxycoumarin by 2 h, increasing doses of naringin in water up to twofold (i.e. naringin content of 2 L grapefruit juice) do not cause any alteration in the time course of excretion. Experiments with increasing amounts of juice, keeping the dose of naringin constant, indicate that the inhibitory potency of small amounts of grapefruit juice can be amplified by naringin. The same is true when the ratio between juice constituents and naringin is enhanced up to threefold by adding naringin. As naringin alone is ineffective, the inhibitory effect of grapefruit juice on the metabolism of coumarin is caused by at least one compound other than naringin. The persistency of the primary inhibitor not identified yet can obviously be modulated by the naring(en)in-system.

Effect of Grapefruit Juice on the Urinary 6.BETA.-hydroxycortisol/cortisol Ratio.

The effect of grapefruit juice on the urinary 6β-hydroxycortisolicortisol ratio was investigated in healthy volunteers. The urinary concentration of cortisol was virtually unaffected by the administration of grapefruit juice whereas the concetration of 6β-hydroxycortisol in the urine decreased when grapefruit juice was given every 3 hours. The administration of grapefruit juice was thus considered to result in a decrease in the urinary 6β-hydroxycortisol/cortisol ratio. In addition, both diurnal and individual differences were also observed in the extent of the inhibitory effect of grapefruit juice.

Grapefruit Component Interacting with Rat and Human P450 CYP3A: Possible Involvement of Non-Flavonoid Components in Drug Interaction.

Active components in grapefruit juice, which modulate a cytochrome P450 (CYP3A) activity, were investigated. CYP3A-catalyzed 6beta-hydroxylation of testosterone in livers of rat and human was inhibited by the addition of an ethyl acetate-extract of grapefruit juice. Several components of grapefruit juice, including naringin, naringenin, limonin and obacunone, also showed inhibitory effects in human liver microsomes. However, the amounts of these components in grapefruit juice are too low to account for the inhibition by the ethyl acetate-extracts. Analyses with HPLC indicate the existence of inhibitory components in the extract, which are distinct from these known compounds and are specific to grapefruit juice. These results suggest that hydrophobic components other than flavonoids, probably coumarin derivatives, are responsible for the inhibitory effect of grapefruit juice.

Inhibitory effect of grapefruit juice and its bitter principal, naringenin, on CYP1A2 dependent metabolism of caffeine in man.

1. The effects of grapefruit juice and naringenin on the activity of the human cytochrome P450 isoform CYP1A2 were evaluated using caffeine as a probe substrate. 2. In vitro naringin was a potent competitive inhibitor of caffeine 3-demethylation by human liver microsomes (Ki = 7-29 microM). 3. In vivo grapefruit juice (1.2 l day-1 containing 0.5 g l-1 naringin, the glycone form of naringenin) decreased the oral clearance of caffeine by 23% (95% CI: 7%-30%) and prolonged its half-life by 31% (95% CI: 20%-44%) (n = 12). 4. We conclude that grapefruit juice and naringenin inhibit CYP1A2 activity in man. However, the small effect on caffeine clearance in vivo suggests that in general the ingestion of grapefruit juice should not cause clinically significant inhibition of the metabolism of other drugs that are substrates of CYPIA2.