Metabolic-induced cytotoxicity of diosbulbin B in CYP3A4-expressing cells.

As a candidate antitumor agent, diosbulbin B (DB) can induce serious liver toxicity and other adverse reactions. DB is mainly metabolized by CYP3A4 in vitro and in vivo, but the cytotoxicity and anti-tumor mechanisms of DB have yet to be clarified. This study aimed to determine whether the cytotoxicity and anti-tumor effects of DB are related to the metabolism-induced activation of CYP3A4 in various cell models, including CYP-free NIH3T3 cells, primary rat hepatocytes, HepG2 and L02 cells of high CYP3A4 expression and wild-type. Results showed that DB did not markedly decrease the viability of NIH3T3 cells. DB metabolites, obtained from the metabolism by mouse liver microsomes, did not elicit cytotoxicity on NIH3T3 cells either. By contrast, DB could induce significant cytotoxicity on primary rat hepatocytes. The DB induced cytotoxicity on HepG2 or L02 cells with high CYP3A4 expression were stronger than those on wild-type cells. As a metabolic biomarker, the metabolite conjugate (M31) of DB with GSH was detected in the incubation system. A higher amount of M31 was generated in the transfected HepG2 and L02 cells than in the wild-type cells at different time points. Ketoconazole, however, could restrain DB induced cytotoxicity on primary rat hepatocytes and in CYP3A4 transfected HepG2 and L02 cells. Therefore, the cytotoxicity of DB was closely related to CYP3A4-metabolized reactive DB metabolites.

Differential metabolism of 3FDT and docetaxel in RLMs, rats, and HLMs.

3FDT, an analog of docetaxel with a blocked metabolism at its 3'-N-tert-butyloxyl group with three fluorine atoms, exhibits more potent cytotoxicity than docetaxel both with human cancer cell line SK-OV-3 in vitro and with human non-small cell lung cancer A549 xenografts in vivo. To further develop pharmacodynamically and pharmacokinetically favorable fluorinated docetaxel analogs as anticancer agents, we chose 3FDT as the model compound to identify the metabolites of 3FDT in RLMs, rats, and HLMs and the cytochrome P450 enzymes responsible for the metabolism of 3FDT. Our findings indicated that the major metabolic site switched from the C3' appendage for docetaxel to the taxane ring for 3FDT, and the main metabolizing P450 enzymes switched from CYP3A to CYP3A4 and CYP2E1.

[Metabolism of mitomycin C by human liver microsomes in vitro].

To provide the profiles of metabolism of mitomycin C (MMC) by human liver microsomes in vitro, MMC was incubated with human liver microsomes, then the supernatant component was isolated and detected by HPLC. Types of metabolic enzymes were estimated by the effect of NADPH or dicumarol (DIC) on metabolism of MMC. Standard, reaction, background control (microsomes was inactivated), negative control (no NADPH), and inhibitor group (adding DIC) were assigned, the results were analyzed by Graphpad Prism 4. 0 software. Reaction group compared with background control and negative control groups, 3 NADPH-dependent absorption peaks were additionally isolated by HPLC after MMC were incubated with human liver microsomes. Their retention times were 10. 0, 14. 0, 14. 8 min ( named as Ml, M2, M3) , respectively. Their formation was kept as Sigmoidal dose-response and their Km were 0. 52 (95% CI, 0. 40 - 0.67) mmol x L(-1), 0. 81 (95% CI, 0. 59 - 1. 10) mmol x L(-1), 0. 54 (95% CI, 0. 41 -0. 71) mmol x L(-1) , respectively. The data indicated that the three absorption peaks isolated by HPLC were metabolites of MMC. DIC can inhibit formation of M2, it' s dose-effect fitted to Sigmoidal curve and it' s IC50 was 59. 68 (95% CI, 40. 66 - 87. 61) micromol x L(-1) , which indicated DT-diaphorase could take part in the formation of M2. MMC can be metabolized by human liver microsomes in vitro, and at least three metabolites of MMC could be isolated by HPLC in the experiment, further study showed DT-diaphorase participated in the formation of M2.

[Effects of chronic HBV infection on human hepatic cytochrome P450 3A4].

OBJECTIVE: To study the effect of HBV on human hepatic cytochrome P450 3A4 (CYP3A4) in patients with chronic HBV infection. METHODS: Liver tissue samples were obtained from 21 patients undergoing hepatic surgery with (n = 10) or without (n = 11) chronic HBV infection and were homogenized, then hepatic microsomes were separated from the homogenate using a differential centrifugation method. The activity of CYP3A4 was determined by HPLC, and the expression of CYP3A4 protein was determined by Western-blotting. RESULTS: The V(max) of CYP3A4 in patients with chronic HBV infection was 493 +/- 297 pmol/min/mg, significantly reduced (P = 0.03) comparing to the normal control group: 741 +/- 189 pmol/min/mg. Western-blotting showed the the CYP3A4 protein expression in patients with chronic HBV infection was 3.04 +/- 1.63, which was significantly lower than that of the normal control group: 5.67 +/- 1.52 (P = 0.003). In contrast, no significant alteration of the K(m) of CYP3A4 was observed between two groups: 0.142 +/- 0.057 micromol/L; 0.121 +/- 0.024 micromol/L (P = 0.103). The enzymatic activity and protein expression of each liver sample had a high correlation. Correlation index was 0.7683 (P < 0.001). CONCLUSION: Chronic HBV infection tends to down-regulate the expression of hepatic CYP3A4 and reduce its activity, but does not affect its structure. When patients with chronic HBV infection are given drugs metabolized by CYP3A4, the drugs' side-effects brought by the variation of their metabolism should be taken into account.

[The combined effect of isoniazid and rifampicin on the activities of CYP4501A2 and CYP4503A4 in primary hepatocytes from healthy human adults].

OBJECTIVE: To study the combined effect of isoniazid and rifampicin on the activities of CYP1A2 and 3A4 in primary hepatocytes from healthy human adults. METHODS: The primary hepatocytes were isolated from adult healthy human livers, and cultured for 3 days. Then the cells were divided into 15 groups including two negative control groups (culture media alone) and 13 drug intervention groups, to which the following drugs were added: isoniazid (25 micromol/L, 50 micromol/L), rifampicin (12.5 micromol/L, 25 micromol/L) or both of them with different concentrations (CYP 1A2: rifampicin 12.5 micromol/L + isoniazid 50 micromol/L, rifampicin 25 micromol/L + isoniazid 50 micromol/L; CYP3A4: rifampicin 12.5 micromol/L + isoniazid 50 micromol/L, rifampicin 25 micromol/L + isoniazid 25 micromol/L, rifampicin 25 micromol/L + isoniazid 50 micromol/L) respectively. All the concentrations were consistent with the range of maximum clinical blood concentrations. After culture for 2 days, substrates (phenacetin for CYP1A2 , testosterone for CYP3A4) were added, and then the peak area (unit: mAU. min) of their metabolites was measured with high performance liquid chromatography (HPLC) to assess the activities of CYP450 1A2 and 3A4. RESULTS: (1) The activity of CYP1A2 in isoniazid groups with concentrations of 25 micromol/L and 50 micromol/L was (3.33 +/- 0.65), (3.03 +/- 0.38) mAU.min respectively, significantly different compared with that in the negative control group [(5.23 +/- 0.31) mAU.min, P < 0.01]. The activity of CYP450 1A2 in rifampicin groups with a concentration of 12.5 micromol/L was (6.07 +/- 0.55) mAU.min, which had significant difference compared with that in the negative control group (P < 0.05). There was no statistical difference of CYP1A2 activity between rifampicin with 25 micromol/L [(4.93 +/- 0.57) mAU.min] and the negative control group (P > 0.05). The activity of CYP1A2 of groups with two kinds of different concentrations of isoniazid and rifampicin combined groups was (3.27 +/- 0.96), (3.97 +/- 0.25) mAU.min respectively, which had significant difference compared with that in the negative control group (P < 0.05). (2) The activity of CYP3A4 in isoniazid groups with concentrations of 25 micromol/L and 50 micromol/L was (5.40 +/- 1.35), (2.63 +/- 0.06) mAU.min respectively, which had significant difference compared with that in the negative control group [(12.53 +/- 0.51) mAU.min, P < 0.01]. The activity of CYP3A4 in rifampicin groups with concentrations of 12.5 micromol/L and 25 micromol/L was (165.17 +/- 11.47), (120.20 +/- 15.73) mAU.min respectively, which had significant difference compared with that in the negative control group (P < 0.01). The activity of CYP3A4 in the three isoniazid and rifampicin combined groups with three kinds of different concentrations was (118.37 +/- 8.90), (77.53 +/- 6.91), (68.73 +/- 4.72) mAU.min respectively, which had significant difference compared with that in the negative control group (P < 0.01), but they were lower than those in rifampicin groups with corresponding concentrations (P < 0.05). CONCLUSIONS: Isoniazid and rifampicin in the range of maximum clinical blood concentration have no significant inducing or inhibiting effect on the activity of CYP1A2 of healthy adult human primary hepatocytes. Isoniazid in the range of maximum clinical blood concentration can inhibit the activity of CYP3A4, while rifampicin can induce the activity of CYP3A4; the combined effect of isoniazid and rifampicin being the induction of CYP3A4 activity, but the inducing effect was less than that of rifampicin alone with the same concentration.