Inhibition of CYP3A4 by 6',7'-dihydroxybergamottin in human CYP3A4 over-expressed hepG2 cells.

OBJECTIVES: We previously established HepG2-GS-3A4, a cell line from hepatoblastoma with overexpression of human CYP3A4 and glutamine synthetase (GS). We further reported that these cells can be applied for screening inhibitors of CYP3A4 in vitro. The purpose of this study was to determine whether our CYP3A4-overexpresed cell could be applied to evaluate mechanisms of CYP3A4 inhibition by 6',7'-dihydroxybergamottin (DHB), which is one of the major furanocoumarins in grapefruit juice, by using these cells. METHODS: Nifedipine oxidation, activity and protein expression of NADPH-cytochrome reductase (POR) of HepG2-GS-3A4 cell were measured. CO-binding spectrumassay in microsomal fraction of the cells was also evaluated. KEY FINDINGS: DHB and ketoconazole, a well-known inhibitor of CYP3A4, inhibited nifedipine oxidation in a concentration-dependent manner. DHB at a concentration of 3.0 µm, sufficient to inhibit the nifedipine oxidation, decreased POR activity; however, ketoconazole at a concentration of 0.9 µm, sufficient to inhibit the oxidation, did not affect the activity. The expression of POR protein in HepG2-GS-3A4 cells was not changed by either DHB or ketoconazole. The expression of CYP3A4 mRNA and protein was not changed by the addition of DHB or ketoconazole. DHB also reduced the absorption rate at 450 nm in a CO-binding spectrum assay without alteration of the wavelength of maximum absorption. The mean absorption value at 450 nm slightly decreased with ketoconazole; however, the difference was not significant. CONCLUSIONS: We concluded that inhibition of CYP3A4 activity by DHB includes the inhibition of POR activity. HepG2-GS-3A4 might be a good tool to evaluate the mechanisms.

Cranberry juice suppressed the diclofenac metabolism by human liver microsomes, but not in healthy human subjects.

AIM: To investigate a potential interaction between cranberry juice and diclofenac, a substrate of CYP2C9. METHODS: The inhibitory effect of cranberry juice on diclofenac metabolism was determined using human liver microsome assay. Subsequently, we performed a clinical trial in healthy human subjects to determine whether the repeated consumption of cranberry juice changed the diclofenac pharmacokinetics. RESULTS: Cranberry juice significantly suppressed diclofenac metabolism by human liver microsomes. On the other hand, repeated consumption of cranberry juice did not influence the diclofenac pharmacokinetics in human subjects. CONCLUSIONS: Cranberry juice inhibited diclofenac metabolism by human liver microsomes, but not in human subjects. Based on the present and previous findings, we think that although cranberry juice inhibits CYP2C9 activity in vitro, it does not change the pharmacokinetics of medications metabolized by CYP2C9 in clinical situations.

Effects of selenium status and supplementary seleno-chemical sources on mouse T-cell mitogenesis.

Although selenium is thought to be essential for various immune responses, the excess supplementation may have an adverse effect on certain immunological functions. The present study was designed to determine the effective chemical forms of selenium and their optimal levels on T-cell mitogenesis with splenic cells from mice given a selenium-deficient diet for 8 weeks to avoid effects of cellular selenium sources. Although selenium in tissues, except for spleen and thymus, was almost depleted by feeding selenium-deficient diet, the lymphoid organs still contained low levels of selenium. Both activities of cellular glutathione peroxidase (cGPx) and thioredoxin reductase (TR) in liver and splenic cells showed a tendency to decrease by selenium deficiency. However, splenic cells were tolerant against decrease of the selenoenzyme activities, and TR was also more tolerant than cGPx. T-cell proliferation of the selenium-insufficient splenic cells induced by concanavalin A was increased by addition of Na2SeO3, Na2SeO4, Na2Se, seleno-DL-cystine, seleno-L-methionine and selenocystamine. Their promoting action was observed at levels lower than 0.1 micromol/L and was completely suppressed at the highest concentration (1 micromol/L), except for selenocystamine. Na2SeO3 was one of the efficient selenocompounds for the mitogenesis, which was concomitant with the significant induction of cGPx and TR. However, recovery of cGPx activity in the selenium-insufficient cells by supplementary Na2SeO3 was only partial,while TR activity was readily recovered from selenium deficiency. These results therefore indicate that only low levels of selenium is essential for T-cell mitogenesis even in selenium-insufficient splenic cells, and TR, which is readily recovered by Na2SeO3, may be the critical enzyme.