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In previous studies, we showed that a high-dose intake of green tea polyphenol (GP) induced a hepatospecific decrease in the expression and activity of the drug-metabolizing enzyme cytochrome P450 3A (CYP3A). In this study, we examined whether this decrease in CYP3A expression is induced by epigallocatechin gallate (EGCG), which is the main component of GP. After a diet containing 1.5% EGCG was given to mice, the hepatic CYP3A expression was measured. The level of intestinal bacteria of Clostridium spp., the concentration of lithocholic acid (LCA) in the feces, and the level of the translocation of pregnane X receptor (PXR) to the nucleus in the liver were examined. A decrease in the CYP3A expression level was observed beginning on the second day of the treatment with EGCG. The level of translocation of PXR to the nucleus was significantly lower in the EGCG group. The fecal level of LCA was clearly decreased by the EGCG treatment. The level of intestinal bacteria of Clostridium spp. was also decreased by the EGCG treatment. It is clear that the hepatospecific decrease in the CYP3A expression level observed after a high-dose intake of GP was caused by EGCG. Because EGCG, which is not absorbed from the intestine, causes a decrease in the level of LCA-producing bacteria in the colon, the level of LCA in the liver decreases, resulting in a decrease in the nuclear translocation of PXR, which in turn leads to the observed decrease in the expression level of CYP3A.

The chronic administration of morphine to patients with neuropathic pain results in the development of a gradual tolerance to morphine. Although the detailed mechanism of this effect has not yet been elucidated, one of the known causes is a decrease in μ-opioid receptor function with regard to the active metabolite of morphine, M-6-G(morphine-6-glucuronide), in the ventrotegmental area of the midbrain. In this study, the relationship between the concentration of morphine in the brain and its analgesic effect was examined after the administration of morphine in the presence of neuropathic pain. Morphine was orally administered to mice with neuropathic pain, and the relationship between morphine's analgesic effect and its concentration in the brain was analysed. In addition, the expression levels of the conjugation enzyme, UGT2B (uridine diphosphate glucuronosyltransferase), which has morphine as its substrate, and P-gp, which is a transporter involved in morphine excretion, were examined. In mice with neuropathic pain, the concentration of morphine in the brain was significantly decreased, and a correlation was found between this decrease and the decrease in the analgesic effect. It was considered possible that this decrease in the brain morphine concentration may be due to an increase in the expression level of P-gp in the small intestine and to an increase in the expression level and binding activity of UGT2B in the liver. The results of this study suggest the possibility that a sufficient analgesic effect may not be obtained when morphine is administered in the presence of neuropathic pain due to a decrease in the total amount of morphine and M-6-G that reach the brain.

In recent years, the intake of functional foods containing high-doses of green tea polyphenols (GP) has been increasing. In this study, the long-term safety of high-dose GP was assessed from a pharmacokinetic point of view by focusing on the drug-metabolizing enzyme, cytochrome P450 (CYP). Mice were fed a diet containing 3% GP for 4weeks, and the CYP expression levels and activity were determined. The GP-treated group showed a significant decrease in the hepatic CYP3A and an increase in the hepatic CYP2C expression compared with the control group. CYP1A, CYP2D, and CYP2E expression were not different between the GP-treated and the control groups. In the small intestine, there were no differences in the CYP3A protein levels between the groups. The increase in the plasma triazolam concentration in the GP-treated group was observed. Although no changes were found in the hepatic CYP3A levels in mice receiving a diet containing 0.1% GP for 4weeks, a significant decrease was seen in the hepatic CYP3A level in mice receiving a diet containing 3% GP for only 1week. This study revealed that the intake of a high-dose GP results in a liver-specific decrease in the CYP3A expression level. The results also indicated that the effects of GP on CYP3A were not observed following the intake of a low-dose GP. In the future, caution should be taken in cases when functional foods containing a high-dose GP are concomitantly consumed with a CYP3A substrate drug.

Recent studies have reported that a high-fat diet during pregnancy exerts various effects on the foetus and newborn. The purpose of this study was to clarify the effects of a high-fat diet during pregnancy on the activity of hepatic cytochrome P450 (Cyp) 3a in offspring in mice. The protein expression level and activity of Cyp3a in the livers of 6-week-old mice born to mothers that were given a high-fat diet during pregnancy (HF group) decreased significantly compared with the Control group. Triazolam, which is a substrate of Cyp3a, was intraperitoneally administered to the mice in the HF group. Compared with the Control group, an increase in the area under the plasma concentration–time curve and a decrease in total clearance were observed in the HF group. The hepatic constitutive androstane receptor (CAR) mRNA expression level in the HF group was significantly lower than that in the Control group. An increase in phosphorylation of extracellular signal-regulated kinase (ERK) was also observed in the HF group. The results of this study revealed that a high-fat diet during pregnancy causes an increase in ERK phosphorylation and a decrease in the expression level of CAR in the livers of offspring, which leads to decreased Cyp3a expression and activity. The results suggest that individual differences in pharmacokinetics may not only be expressed by genetic predisposition but also by a mother’s living environment during pregnancy.

Patients with severe constipation are treated with combinations of several different laxatives. The purpose of this study is to examine whether the concomitant use of different laxatives enhances the laxative effect, using an osmotic laxative, magnesium sulphate (MgSO₄), and a stimulant laxative, bisacodyl. The faecal water content of rats, to which MgSO₄ and bisacodyl were coadministered, was lower than that in the MgSO₄ group, while the change in the faecal water content over time was very similar to that in the bisacodyl group. The mRNA expression of the osmotic pressure marker, sodium/myo-inositol transporter, in the coadministration group 5h after the administration was significantly higher than that in the control group and almost equal to that in the MgSO₄ group. The protein expression level of aquaporin-3 (AQP3), which plays an important role in water transfer, in the coadministration group decreased compared to the control group, as was the case in the bisacodyl group. The results of this study indicates that the coadministration of MgSO₄ and bisacodyl does not enhance the laxative effect because the expression level of AQP3 in the colon in the coadministration group was almost equal to that in the bisacodyl group.

Ethnopharmacological relevance We have previously reported that Byakkokaninjinto improves cutaneous pruritus by increasing the expression level of aquaporin-3 (AQP3). In this study, we examined the effect of Gypsum fibrosum (main component: CaSO 4 ), which is the main component of Byakkokaninjinto, on the cutaneous AQP3 expression level. Materials and methods KKAy mice were given a diet containing 0.3% Gypsum fibrosum extract, or a diet containing 0.3% CaSO 4 for 4 weeks. The urine volume, plasma glucose levels, cutaneous AQP3 protein expression, and the Ca 2+ content were measured. Results The 24-h urine volumes and the plasma glucose levels in the Gypsum fibrosum extract group were not significantly different from those in the control group. In the Gypsum fibrosum extract group, the cutaneous AQP3 protein levels increased significantly, by approximately 3.2-fold, compared to the control group. The cutaneous Ca 2+ content in the control group was approximately 35 μg/g. In the Gypsum fibrosum extract group, the Ca 2+ content increased to approximately 51 μg/g, which was significant compared to the control group. In the CaSO 4 group, an increase in the AQP3 protein expression levels and Ca 2+ content were observed; the extent of these increases were similar to those in the Gypsum fibrosum extract group. Conclusions The results of this study suggest that Gypsum fibrosum plays an important role in the increased levels of cutaneous AQP3 expression enhanced by Byakkokaninjinto. The results also indicate that the increase in AQP3 caused by Gypsum fibrosum is attributable to an increase in the cutaneous Ca 2+ content from its main component, CaSO 4 .