Yves Barra

Identification of the human and animal hepatic cytochromes P450 involved in clonazepam metabolism

Summary— This report characterizes the cytochrome P450 isozyme involved in clonazepam metabolism. This study was undertaken using a library of liver microsomal fractions prepared from untreated rabbits or those treated with drugs known to specifically induce various cytochrome P450 isozymes (ie P450 2B4 by phenobarbital, P450 1A1 and P450 1A2 by 3‐methylcholanthrene and β‐naphthoflavone, P450 2E1 by acetone and ethyl alcohol, and P450 3A6 by erythromycin). Only microsomes obtained from phenobarbital‐treated rabbits exhibited a type II binding spectrum upon addition of clonazepam (Ks(app) = 31.4±3.8 μM) and significantly metabolized clonazepam to 7‐aminoclonazepam. Benzphetamine, which is a known substrate for P450 2B1 was also extensively metabolized by microsomes prepared from phenobarbital treated rabbits. This indicates that the same isozyme (P450 2B subfamily) was involved in the biotransformation of both substrates. Experiments performed on 14 human liver microsomal preparations showed a wide inter‐individual variability (from 1–4) and a good correlation (r = 0.70) between benzphetamine and clonazepam metabolism. Since P450 3A4 (nf25) was involved in benzphetamine metabolism, clonazepam was probably nitroreduced by the same isozyme. An oligonucleotide specific for the P450 3A4 gene subfamily was synthetized and used for hybridization on total RNA from human liver samples. Two transcripts of 2.2 and 3.0 kb were detected and the level of the 2.2 kb mRNA expression was significantly correlated (r = 0.61) with the intensity of clonazepam nitroreduction by the corresponding microsome batches.

Involvement of the macrolide antibiotic inducible cytochrome P-450 LM3c in the metabolism of midazolam by microsomal fractions prepared from rabbit liver

This report characterizes the cytochrome P-450 isozyme involved in midazolam metabolism. This study was undertaken into liver microsomal fractions prepared from untreated rabbits or animals treated with drugs known to specifically induce various cytochrome P-450 isozymes such as form LM2 by phenobarbital, LM4 and LM6 by 3-methylcholanthrene and beta-naphthoflavone, LM3a by ethyl alcohol and acetone, and LM3c by macrolide antibiotics (rifampicin, erythromycin and triacetyloleandomycin). Among this library of characterized microsomal preparations, only those obtained from macrolide antibiotic-treated rabbits exhibited a Type I binding spectrum upon addition of midazolam (Ks = 3.2-5.3 micrograms/ml; 10.6-17.5 microM) and significantly metabolized midazolam to its various hydroxylated metabolites (Km = 2.52 +/- 0.22 micrograms/ml; 8.32 +/- 0.73 microM and Vmax = 20 micrograms metabolites formed/min/mg proteins; 66 nmoles metabolites formed/min/mg proteins). The following observations further confirmed the specific involvement of the cytochrome P-450 LM3c isozyme: (i) only anti-cytochrome P-450 LM3c isozyme antibodies intensively inhibited midazolam metabolism, (ii) incubation of microsomes, prepared from TAO-treated rabbits, with midazolam in the presence of potassium ferricyanide which restored the functional cytochrome P-450 LM3c isozyme, increased midazolam metabolism to a similar extent, and (iii) in the presence of Cyclosporin A, a specific substrate of the rabbit cytochrome P-450 LM3c isozyme, midazolam metabolism was inhibited in a concentration-dependent manner. These data demonstrated that the rabbit cytochrome P-450 LM3c isozyme was predominantly involved in midazolam metabolism.

Decrease in c-Myc activity enhances cancer cell sensitivity to vinblastine.

The c-myc oncogene encodes for a transcriptional factor involved in many cellular processes such as proliferation, differentiation and apoptosis. According to these different functions, the role of c-Myc protein in cellular sensitivity to anti-cancer drugs is controversial. We defined the role of c-Myc in cancer cell sensitivity to vinblastine (VLB) using human colon cancer cells: LoVo wild-type or transfected with a plasmid containing the human c-myc gene in antisense orientation (LoVo-mycANS). Analysis of VLB cytotoxicity demonstrated a 3-fold increase in VLB sensitivity in LoVo-mycANS cells. Comparison between cells revealed different apoptosis kinetics: accumulation of cells in sub-G1 phase and poly(ADP-ribose) polymerase cleavage occurred earlier in LoVo-mycANS. Then, we demonstrated a mitochondrial membrane potential disruption followed by cytochrome c release that indicates the involvement of mitochondria in this apoptotic signaling pathway. This earlier apoptosis was accompanied by a Bcl-2 decrease and a p53 increase. In conclusion, the decrease in c-Myc expression enhanced the VLB sensitivity, triggering earlier apoptosis through induction of the intrinsic pathway. Thus, c-myc induction is a resistance factor and our findings suggest that tumors carrying low levels of c-Myc protein could be more responsive to vinca alkaloids treatment. Moreover, the downregulation of c-myc oncogene by an antisense strategy might represent a useful goal for improving the efficacy of this anti-neoplastic drug family.

Effect of Tetrahydrouridine on Metabolism and Transport of 1-β-D-Arabinofuranosylcytosine in Human Cells

Deamination of cytosine arabinoside (ara-C) by cytidine deaminase is the main mode of inactivation of this drug which can be responsible for ara-C resistance. The present study was undertaken to determine the effect of tetrahydrouridine (THU; a potent inhibitor of cytidine deaminase) on ara-C transport and metabolism in human cells. A rapid transport of ara-C into freshly isolated hepatocytes and an increased intracellular accumulation of the unchanged drug were observed in the presence of 50 micrograms/ml THU. THU inhibited the intracellular deamination of ara-C by 80% and slowed elimination of the compound extracellularly. The intracellular ara-C concentrations achieved after incubation with 1 micrograms/ml ara-C plus 50 micrograms/ml THU are similar to those attained with ara-C (10 micrograms/ml) alone. Treatment of leukemic K562 cells with the combination of THU (50 micrograms/ml) and ara-C (1 micrograms/ml) led to an augmentation of intracellular ara-C triphosphate formation up to twofold.

Synthesis of two novel thioacridinic derivatives and comparison of their in vitro biological activities

Two novel compounds, 3-amino-9-(diethylaminoethylthio) acridine and 9-diethylaminoethylthioacridine, were synthesized and characterized. They were shown to be cytotoxic against K562 and Raji cell lines. A concentration of 10(-5) M killed around 40% of the cells after 3 h time of incubation. Intercalation into DNA was more efficient when a protonated nitrogen was present in a side chain of the ring system. At the cytotoxic concentrations (10(-5) M, 10(-6) M), inhibition of nucleic acid synthesis in K562, Raji cell lines and human leukocytes has been shown. The results presented suggest that the cytotoxicity and the inhibition of nucleic acid synthesis of the two compounds studied are inversely related to their intercalating capability into the DNA helix.

Variations in the levels of IgG1 and IgG2 subclasses in the sera of normal, immunized and tumor-bearing hamsters

The concentration of IgG1 and IgG2 subclasses in the sera of hamsters bearing tumors of different origins were compared to that of normal serum and to that of sera of animals rendered resistant to tumor take by immunization with viable SV40-transformed cells. In the sera of hamsters bearing tumors induced by virus-transformed cells an augmentation of IgG2 and a diminution of IgG1 was observed during the development of the tumor compared to sera of normal hamsters. In the sera of animals bearing tumors induced by methylcholanthrene ( MCH2 ) or by spontaneously transformed cells ( EHB ) the level of IgG2 was almost normal but IgG1 was barely detectable, especially in MCH2 tumors. On the other hand, the sera of animals immunized with virus-transformed cells showed a slight increase in both IgGs, but only that of IgG2 was significant. Antibody activity was tested in the sera as well as in the IgG1 and IgG2 fractions of the sera of hamsters immunized or bearing tumors induced by SV40 transformed cells. Both sera and the subclasses showed antibody activity, the activity being more pronounced in the IgG2 fraction than in the IgG1 fraction.

Activation of the NFκB Pathway Enhances AhR Expression in Intestinal Caco-2 Cells

Recent data suggest that apart from its well-known role in the regulation of xenobiotic metabolizing enzymes, AhR is also involved in inflammation. However, the influence of inflammation on AhR expression remains unknown. Here, we demonstrated that proinflammatory conditions induced by either PMA or IL-1β enhance AhR expression in Caco-2 cells. This was associated with an increase in AhR promoter activity. By means of directed mutagenesis experiments and the use of proteasome inhibitors, we demonstrated that inflammation-induced AhR expression involved the NFκB pathway but not AP-1. Moreover, conditioned media from PMA-treated Caco-2 cells were also able to induce AhR expression, and this induction was repressed by anti-IL-1β blocking antibodies. Similar results were obtained with conditioned media from PMA-treated THP-1 cells. Taken together, these data suggest that AhR could be involved in vivo in an inflammatory loop. AhR was recently suspected to be implicated in inflammatory bowel disease. Our results support this hypothesis and suggest that AhR could be a new target for inflammatory bowel disease patient management.

Hybridization of a mouse T-cell lymphocyte line (HB1) with a polyoma virus-transformed mouse fibroblast line

The establishment of permanent T-lymphocyte cell lines by transformation with DNA viruses has not yet been achieved. This paper reports the successful transfer of polyoma virus genome into T-lymphocyte cells by somatic hybridization. A T-lymphocyte clone, HB1, derived from (DBA/ 2J×AKR) spleen cells, isolated in vitro by cloning in semi-solid agar, was fused with a polyoma (Py) virus-transformed fibroblast C3HPy, clone 1. The authenticity of the hybrid C3H/HB was established by chromosome and histocompatibility antigen studies. This initial population and the various clones retained T-lymphocyte characteristics such as morphological appearance, growth properties (suspension culture) and differentiation antigen (Thy 1–2). The hybrid cell line and the various clones presented all the characteristics of Py transformation. Namely, they carried the Py genome originating from the fibroblastic parent and maintained Py virus tumour-associated antigens (TSTA, TSSA and T antigens). In most respects, this hybrid population resembled the C3HPy/C11 parent and exhibited the same tumorigenicity.

Calculation of individual dosage regimen of cytosine arabinoside (ara-C) based on metabolite levels in leukemic cells.

Patients with acute nonlymphocytic leukemia (ANLL) were treated by continuous infusion of ara-C (100 mg/m2/d ± 10 days). During ara-C treatment, cellular arabinofuranosyl cytosine triphosphate (ara-CTP) pharmacokinetics was assessed in the circulating blasts of these patients using a high-performance liquid chromatography (HPLC) and an associated radioimmunoassay. Since a strong correlation was found between achievement of complete remission and cellular ara-CTP levels, we propose a calculation scheme that allows steady-state adjustment of ara-CTP levels during administration of ara-C. To improve the complete remission rate in patients with low ara-CTP levels, we sought optimum ara-C dosing. In order to achieve an optimal therapeutic response, in vivo ara-CTP formation has to be >50 μM in leukemic cells. Conversely, using the same pharmacokinetic approach, the infusion rate at which to administer ara-C in order to reach in vivo ara-CTP concentration threshold and to achieve complete remission could be calculated for each patient.

Mécanismes moléculaires de l’altération du métabolisme cellulaire par les polluants de la chaîne alimentaire

Resume Les aliments peuvent presenter des risques s’ils contiennent une molecule toxique dont la presence est soit naturelle, soit liee a l’activite humaine. Parmi les differents toxiques detectes dans l’alimentation on note: les PCB et les dioxines, les phtalates, les pesticides organochlores. Toutes ces molecules ont la particularite d′etre bioaccumulables. Les dioxines agissent via le recepteur AhR et leurs principaux effets sur la population sont: atteintes des fonctions de reproduction, augmentation des cancers, chloracnee, diabete, atteintes cardiovasculaires. Les phtalates, retrouves dans le lait, le fromage, les poissons, les viandes, activent le recepteur PPARα. Ils diminuent chez l’animal et l’homme la fertilite du mâle, et augmentent la cancerogenese animale. Les pesticides organochlores (OCs) sont des perturbateurs endocriniens agissant notamment via le recepteur ER (recepteur aux œstrogenes). Ils conduisent a une diminution de la fertilite chez l’animal et chez l’homme et a une augmentation probable du risque de cancer du sein.