Eric Seree

Serum induces a transcriptional activation of CYP1A1 gene in HepG2 independently of the AhR pathway

CYP1A1 is largely implicated in carcinogenesis. To date, it is known that this gene is induced by xenobiotics such as polycyclic aromatic hydrocarbons. In this study, we evaluated the effect of serum in the regulation of CYP1A1 gene expression. CYP1A1 mRNA level is induced 1) in HepG2 and HT29-D4 cells by 3-methylcholanthrene 2) only in HepG2 after treatment by serum. The CYP1A1 mRNA induction in HepG2 is the consequence at least in part of a transcriptional activation as was demonstrated by evaluation of the hnRNA level. HepG2 cells were transfected by a plasmid containing the 7.5 Kb of the CYP1A1 promoter and the CAT reporter gene. No CAT stimulation was observed after serum treatment. These results demonstrated that CYP1A1 is induced at a transcriptional level by a physiological compound contained in serum independently of the Ah receptor and the 7.5 Kb promoter region.

Metabolism of carbamazepine by CYP3A6: a model for in vitro drug interactions studies.

Carbamazepine (CBZ) is widely used in the treatment of epilepsy. The drug is principally metabolized by CYPs to 10, 11-epoxy carbamazepine (CBZ-E) but this metabolite more toxic than the parent drug, does possess anticonvulsant properties. In humans, CYP3A4, CYP2C8 and CYP1A2 have been shown to be implicated in CBZ biotransformation. Our purpose was to establish an experimental model to determine the interaction of CBZ with other antiepileptic drugs. We first identified the CYP isoforms that metabolized CBZ in rabbit. We used liver microsomes from rabbit treated with various compounds known to induce principally some CYPs subfamilies. Having tested all the compounds we demonstrated that only the animals treated with CYP3A inducers were able to metabolize CBZ strongly. The CBZ biotransformation was inhibited by anti CYP3A antibodies. All the CYP3A subfamily substrates specifically decrease CBZ-E formation. In our experiment we did not observe any inhibition with CYP2C substrate. These data provide evidence that in rabbit the CYP3A subfamily is primarily involved in CBZ metabolism. Using this model we investigated the interaction of CBZ with phenobarbital, phenytoin, ethosuccimide, primidone, progabide, vigabatrin and lamotrigine.

Dietary lipids affect human ethanol-inducible CYP2E1 gene expression in vivo in mononuclear cells.

We tested the hypothesis that dietary cholesterol modulate human ethanol-inducible CYP2E1 expression in vivo in circulating mononuclear cells. Healthy volunteers (n= 10) were submitted to a low fat low cholesterol diet for 4 days (day 0-day 3, LFLC). Cholesterol (595 +/- 56 mg/day) was then reintroduced for 7 days (day 4-day 10, LFHC). In the same time, controls subjects (n=7) did not change their habitual daily diet. CYP2E1 mRNA levels, evaluated in mononuclear cells, decreased in experimental subjects during both LFLC and LFHC from 100% to 53 +/- 5%, (p<0.001) with a main decrease during LFLC period (100% to 71 +/- 16%, p=0.05). Immunoreactive CYP2E1 showed a similar pattern and decreased from 100 to 62 +/- 12% during the trial (p<0.05). No significant change occured in control subjects. Between day 0 and day 11, changes in CYP2E1 mRNA correlated positively with plasma cholesterol (r2=0.67, p<0.001) and HDL cholesterol concentrations (r2=0.61, p<0.001). In contrast, no correlation was found between plasma fatty acids concentrations and CYP2E1 expression. The present results suggest that lipid factors regulate CYP2E1 expression, in vivo, in human mononuclear cells. In particular, plasma cholesterol concentrations may play an important role in this regulation.

Serum increases CYP1A1 induction by 3-methylcholanthrene

CYP1A1 is largely involved in carcinogenesis through the bioactivation of numerous procarcinogens. Exposure to environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs) leads to induction of CYP1A1 via AhR pathway. We have previously demonstrated that fetal bovine serum (FBS) induces CYP1A1 gene transcription. In this work, we show evidence that the serum does not contain an AhR ligand and we evaluated the effect of a 3-methylcholanthrene (3-MC) and FBS cotreatment on CYP1A1 expression. CYP1A1 activity was potentiated by this treatment. This potentiation was at least in part associated with an increase of the CYP1A1 mRNA and gene transcription levels. FBS potentiation of CYP1A1 PAH-mediated induction was related to a significant increase of single strand breaks of DNA as compared to a single 3-MC treatment. Moreover, we demonstrated that human serum induces CYP1A1 with a high interindividual variability. The potentiation by serum of polycyclic aromatic hydrocarbon CYP1A1 induction could be involved in the etiology of some human cancers.