Inhibitory effects of detergents on rat CYP1A1-dependent monooxygenase: comparison of mixed and fused systems consisting of rat CYP 1A1 and yeast NADPH-P450 reductase

Evaluation of surfactants as solubilizing agents in microsomal metabolism reactions with lipophilic substrates

Solubilizing agents are routinely added when investigating the biotransformation of lipophilic substrates using hepatic microsomes. For highly lipophilic compounds, the concentration of solvent or surfactant necessary for dissolution can be detrimental to enzyme activity. This study evaluates the effect of 12 surfactants on microsomal metabolism and the ability of the same surfactants to improve the aqueous solubility of the pentabrominated diphenyl ether BDE-100, a lipophilic environmental contaminant previously found to be recalcitrant to in vitro metabolism. Of the surfactants investigated, Cremophor EL and Tween 80 displayed the best combination of increased BDE-100 solubility and minimal inhibition of microsomal metabolism. However, a comparison of the in vitro metabolism products of BDE-100 in the presence of the two surfactants revealed varying amounts of metabolites depending on the surfactant used.

Production of L-malic acid by permeabilized cells of commercial Saccharomyces sp. strains

Of various yeasts tested in the conversion of fumaric to L-malic acid, Saccharomyces bayanus had the highest activity of fumarase. Cells permeabilized with 0.2% (w/v) CTAB for 5 min gave maximum enzyme activity. Under non-growth conditions, fumarase activity in the permeabilized cells was four times higher (271 U/g) than that of the intact cells (67 U/g). The proposed mathematical model for the batch production of L-malic acid was validated at different initial fumaric acid concentrations. The average conversion of fumaric acid was up to 82% and gave 21, 40, 83 and 175 mM L-malic acid from respectively, 25, 50, 100 and 210 mM: fumaric acid.

Interaction of non-ionic surfactants with hepatic CYP in Prochilodus scrofa

Cytochromes P450 (CYP) constitute a superfamily of hemeproteins that play a vital role in the metabolism of a wide variety of endogenous and xenobiotic compounds. Xenobiotic metabolism and the role of CYP are of particular interest in studies regarding the prevention of the damage caused by chemical pollutants. We investigated, in this study, the interaction of Triton X-100 and Tween 80 with CYP and antioxidant defenses in Curimbata, a Brazilian fish. Aiming to clarify the effects of non-ionic surfactants in the monooxigenase system of fish through in vitro study, the effects of Triton X-100 and Tween 80 were analyzed using monooxygenases and antioxidant system as experimental model. Total CYP and EROD were strongly inhibited by Triton X-100 and Tween 80 in a concentration-dependent way; the content of CYP was reduced until zero while EROD activity was completely inhibited in the presence of Triton X-100 and more than 40% inhibited in the presence of Tween 80. Each surfactant causes a different effect on each antioxidant enzyme. No effect was detected in SOD activity in the presence of even Triton X-100 or Tween 80. Triton X-100 increase catalase activity, while Tween 80 decreases this enzyme activity. The molecular structure of the surfactants causes the alteration of this system, since they are able to interact with the microsomal protein, especially with monooxigenase's components, altering their conformation and, consequently destroying their function. Our results suggest that surfactants can interact with components of the microsomal system leading to inhibition of CYP. Therefore, CYP activity, which has been used as a biomarker of xenobiotic exposure, should be used as a marker in association with other enzymes.

Cytochrome p450-dependent lipid metabolism in preovulatory follicles

Estrogen biosynthesis and proteolysis are both important processes involved in ovarian follicular development, which may be influenced by cytochrome P450 (CYP)-dependent fatty acid metabolites. However, CYP-dependent lipid metabolism has not been characterized with respect to follicular maturation in vivo. Therefore, follicular fluid was collected in the hours before and after the LH surge in pigs, and concentrations of epoxy, hydroxy, and dihydroxy lipids were measured by liquid chromatography tandem mass spectrometry. Arachidonate oxidation and epoxyeicosatrienoic acid hydrolysis to dihydroxyeicosatrienoic acids (DHETs) were also assessed in thecal and granulosa tissue fractions, and the expression of CYP epoxygenases was evaluated by immunoblots using available antisera. To evaluate soluble epoxide hydrolase (sEH) expression, the porcine sEH was cloned from ovarian tissue, expressed and purified for antibody generation. The follicular fluid oxylipin concentrations ranged from 1-150 nm depending on the compound and estrous stage. The follicular fluid concentrations of CYP-dependent oxylipins increased at estrus, as did sEH expression; however, significant changes in epoxides were not observed, and the 11,12-DHET peak was delayed. The ratio of 14,15-DHET:11,12-DHET across all samples correlated with the log of follicular fluid estradiol concentrations (P < 0.01). Epoxygenase activities were similar in theca and granulosa, varying little with follicular development, whereas the decline of a single CYP2J isoform at ovulation was observed by immunoblots. The sEH activity was higher in granulosa than in theca. Finally, the dynamic changes in follicular CYP-dependent arachidonic acid metabolites and their modulatory function in vascular models suggest roles for these metabolites in follicular maturation, which may include regulation of estradiol biosynthesis and preovulatory remodeling of the follicular wall that should be fully explored in future studies.

Metabolic pathways of dioxin by CYP1A1: species difference between rat and human CYP1A subfamily in the metabolism of dioxins

Metabolism of polychlorinated dibenzo-p-dioxins by CYP1A subfamily was examined by using the recombinant yeast microsomes. In substrate specificity and reaction specificity, considerable species differences between rats and humans were observed in both CYP1A1- and CYP1A2-dependent metabolism of dioxins. Among four CYPs, rat CYP1A1 showed the highest activity toward dibenzo-p-dioxin (DD) and mono-, di-, and trichloroDDs. To reveal the mechanism of dioxin metabolism, we examined rat CYP1A1-dependent metabolism of 2-chloro-dibenzo-p-dioxin. In addition to hydroxylation at an unsubstituted position, hydroxylation with migration of a chloride substituent, hydroxylation with elimination of a chloride substituent, and cleavage of an ether linkage of the dioxin ring were observed. In particular, the cleavage of an ether linkage of the dioxin ring appeared most important for the detoxication of dioxins. Based on these results, the metabolic pathways of 2-chloro-dibenzo-p-dioxin by rat CYP1A1 were proposed. The metabolic pathways contain most of the metabolites observed in vivo using experimental animals, suggesting that P450 monooxygenase systems including CYP1A1 are greatly responsible for dioxin metabolism in vivo.

Metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) by human cytochrome P450-dependent monooxygenase systems

Metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) by monooxygenase systems dependent on 12 forms of human cytochrome P450 (CYP) was examined with the recombinant yeast microsomes containing each of the human CYP. The metabolites of PCDDs were analyzed by HPLC and GC-MS. Remarkable metabolism by the multiple CYP forms was observed toward dibenzo-p-dioxin (DD) and mono-, di-, and trichloroDDs. The metabolism contained multiple reactions such as hydroxylation at an unsubstituted position, hydroxylation with migration of a chloride substituent, and hydroxylation with elimination of a chloride substituent. Although major CYPs in human liver such as CYP2C8, CYP2C9, and CYP3A4 showed no significant metabolism toward the PCDDs, CYP1A1 and CYP1A2 showed high catalytic activity toward DD and mono-, di-, and trichloroDDs. The kinetic parameters K(m)(app) and V(max) of the CYP1A1-dependent 8-hydroxylation activity of 2,3,7-trichloro-DD (2,3,7-triCDD) were estimated to be 0.30 microM and 51 (mol/min/mol of P450), respectively, suggesting that 2,3,7-triCDD was a good substrate for CYP1A1. However, none of the CYPs showed any detectable activity [<0.01 mol/min/mol of P450)] toward 2,3,7,8-tetraCDD. Substrate-induced absorption spectrum and inhibition studies indicated that CYP1A1 could bind 2,3,7,8-tetraCDD with considerably high affinity. It was strongly suggested that the long half-life (7.1 years) of 2,3,7,8-tetraCDD in humans was due to an extremely low activity of CYPs toward 2,3,7,8-tetraCDD in addition to its chemical stability.

Biodegradation of polychlorinated dibenzo-p-dioxins by recombinant yeast expressing rat CYP1A subfamily

Metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) by recombinant yeast cells expressing either rat CYP1A1 or CYP1A2 was examined. When each of the dibenzo-p-dioxins (DDs), mono-, di-, and tri-chloroDDs, was added to the cell culture of the recombinant yeast, a remarkable metabolism was observed. The metabolism contained multiple reactions such as hydroxylation at an unsubstituted position, hydroxylation with migration of a chloride substituent, hydroxylation with elimination of a chloride substituent, and opening of dioxin ring. The distinct difference was observed in substrate specificity and reaction specificity between CYP1A1 and CYP1A2. Kinetic analysis using microsomal fractions prepared from the recombinant yeast cells revealed that 2,7-dichloroDD and 2,3,7-trichloroDD were good substrates for both CYP1A1 and CYP1A2. When 2,3,7-trichloroDD was added to the yeast cells expressing each of rat CYP1A1 and CYP1A2, most of 2,3,7-trichloroDD was first converted to 8-hydroxy-2,3,7-trichloroDD, and further metabolized to more hydrophilic compounds whose ethereal bridges were cleaved. These findings give essential information on the metabolism of PCDDs in mammalian liver. In addition, this study indicates the possibility of application of microorganisms expressing mammalian cytochrome P450 to bioremediation of contaminated soils with dioxins.