Effects of epigallocatechin gallate on the oral bioavailability and pharmacokinetics of tamoxifen and its main metabolite, 4-hydroxytamoxifen, in rats
College of Pharmacy, Chonnam National University, Gwangju, Republic of Korea.Anti-cancer drugs (Impact Factor: 1.78). 05/2009; 20(7):584-8. DOI: 10.1097/CAD.0b013e32832d6834
The effects of epigallocatechin gallate (EGCG) on the oral bioavailability and pharmacokinetics of tamoxifen and its metabolite, 4-hydroxytamoxifen, were investigated in rats. A single dose of tamoxifen was administered intravenously (2 mg/kg) and orally (10 mg/kg) with or without epigallocatechin (0.5, 3 and 10 mg/kg) to rats. The presence of EGCG significantly altered the pharmacokinetics of orally administered tamoxifen. Compared with the oral control group (given tamoxifen alone), the area under the plasma concentration-time curve and the peak plasma concentration of tamoxifen significantly (P<0.05 for 3 mg/kg of EGCG, P<0.01 for 10 mg/kg of EGCG) increased 48.4-77.0 and 57.1-89.7%, respectively. Consequently, the absolute bioavailability of tamoxifen in the presence of EGCG (3 and 10 mg/kg) was 48.9-78.1%, which was significantly enhanced (P<0.05 for 3 mg/kg of EGCG, P<0.01 for 10 mg/kg of EGCG) compared with the oral control group (23.7%). Moreover, the relative bioavailability of tamoxifen was 1.48-1.77-fold greater than that of the control group. EGCG at a dose of 10 mg/kg significantly increased the area under the plasma concentration-time curve (P<0.05, 40.3%) of 4-hydroxytamoxifen, but the metabolite-parent ratio of 4-hydroxytamoxifen was also significantly altered (P<0.05 for 10 mg/kg of EGCG), implying that the formation of 4-hydroxytamoxifen was considerably affected by EGCG. The increase in bioavailability of tamoxifen is likely to be due to the decrease in first-pass metabolism in the intestine and liver by inhibition of P-glycoprotein and CYP3A by EGCG. The increase in oral bioavailability of tamoxifen in the presence of EGCG should be taken into consideration of potential drug interactions between tamoxifen and EGCG.
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- "Many findings suggested that EGCG acts as a P-glycoprotein inhibitor and improves the bioavailability of its substrates viz. diltiazem, tamoxifen, doxorubicin, irinotecan (Li and Choi, 2008; Shin and Choi, 2009; Brand et al., 2006, Lin et al., 2008). However, very limited mechanistic data are available in support of these claims. "
ABSTRACT: The aim of this study was to evaluate the change in the expression and the activity of intestinal P-glycoprotein (efflux transporter) with progression of diabetes in rats. Diabetes was induced in Wistar rats using a combination of low dose streptozotocin along with high fat diet. The expression of intestinal P-glycoprotein significantly increased (P≤0.05) with the progression of diabetes which was inferred from the mRNA analysis of mdr1a and mdr1b genes in the ileum segment of rat intestine. Furthermore, a significant increase (P≤0.05) in Na(+)-K(+) ATPase activity was observed in the ileum segment of rat intestine with the progression of diabetes. As a result of this, a significant decrease in the intestinal uptake and peroral bioavailability of the P-glycoprotein substrates (verapamil and atorvastatin) was observed along with the progression of diabetes as compared to normal animals. To address this problem of impaired drug uptake and bioavailability, a reported P-glycoprotein inhibitor, epigallocatechin-3-gallate, was experimentally evaluated. The treatment with epigallocatechin-3-gallate resulted in significant reduction in the expression and activity of P-glycoprotein and subsequent improvement in the intestinal uptake and peroral bioavailability of both verapamil and atorvastatin in normal as well as in diabetic animals. The findings of this study rationalized the use and established the mechanism of action of epigallocatechin-3-gallate to overcome P-glycoprotein mediated drug efflux and will also be helpful in therapeutic drug monitoring in diabetes.
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- "Commercially, Tmx is available only as tablet and oral solution containing Tmx citrate in a daily dose of 10e20 mg. However Tmx citrate also showed the poor oral bioavailability (20e30%) due to its precipitation as free base in the acidic environment of stomach and also due to extensive hepatic and intestinal first pass metabolism, so as to increase its does . So in spite of a clinical choice in advanced and metastatic stages of breast cancer, it suffers from large inter subject variability and several dose and concentration dependent side effects [6e8]. "
ABSTRACT: The present investigation reports on the conditions for preparation of tamoxifen loaded PLGA nanoparticles (Tmx-NPs) for oral administration. Tmx-NPs with >85% entrapment efficiency and 165.58 ± 3.81 nm particle size were prepared and freeze dried. Freeze dried Tmx-NPs were found to be stable in various simulated GIT media (pH 1.2, pH 3.5, pH 6.8, SGF & SIF). No significant changes in characteristics of Tmx-NPs were observed after 3 months accelerated stability studies. The cell viability in C127I cells was found to be relatively lower in Tmx-NP treated cells as compared to free Tmx treated cells. CLSM imaging reveled that nanoparticles were efficiently localized into the nuclear region of C127I cells. Oral bioavailability of Tmx was increased by 3.84 and 11.19 times as compared to the free Tmx citrate and Tmx base respectively, when formulated in NPs. In vivo oral antitumor efficacy of Tmx-NPs was carried out in DMBA induced breast tumor model and tumor size was reduced up to 41.56% as compared to untreated groups which showed an increase in tumor size up to 158.66%. Finally, Tmx-NPs showed the marked reduction in hepatotoxicty when compared with free Tmx citrate as evidenced by histopathological examination of liver tissue as well as AST, ALT and MDA levels. Therefore Tmx-NPs could have the significant value for the oral chronic breast cancer therapy with reduced hepatotoxicity.
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ABSTRACT: The effects of silybinin, an antioxidant, on the pharmacokinetics of tamoxifen and its metabolite, 4-hydroxytamoxifen, were investigated in rats. A single dose of tamoxifen was administered intravenously (2 mg/kg) and orally (10 mg/kg) without or with silybinin (0.5, 2.5 and 10 mg/kg) to rats. Silybinin significantly altered the pharmacokinetics of orally administered tamoxifen. Compared to those in the oral control group (given tamoxifen alone), the area under the plasma concentration-time curve (AUC(0-infinity)) and the peak plasma concentration (C(max)) of tamoxifen were significantly (p<0.05 for 2.5 mg/kg, p<0.01 for 10 mg/kg) increased by 40.2-71.3% and 45.2-78.6%, respectively, with silybinin. Consequently, the absolute bioavailability (AB) of tamoxifen in the presence of silybinin (2.5 and 10 mg/kg) was 31.1-38.1%, which was significantly enhanced (p<0.05) compared to that in the oral control group (22.2%). Moreover, the relative bioavailability (RB) of tamoxifen was 1.40- to 1.72-fold greater than that in the control group. Silybinin (10 mg/kg) significantly increased the AUC(0-infinity) (p<0.05, 40.0%) of 4-hydroxytamoxifen, but the metabolite-parent ratio (MR) of 4-hydroxytamoxifen was significantly altered (p<0.05 for 10 mg/kg), implying that the formation of 4-hydroxytamoxifen was considerably affected by silybinin. The enhanced bioavailability of tamoxifen by silybinin might be due to the promotion of intestinal absorption in the small intestine and the reduction of first-pass metabolism of tamoxifen in the small intestine and in the liver. If these results are confirmed in clinical trials, the tamoxifen dosage should be adjusted when tamoxifen is administered with silybinin or silybinin-containing dietary supplements.
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