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PubMed2002

Delineating novel metabolic pathways of DPC 963, a non-nucleoside reverse transcriptase inhibitor, in rats. Characterization of glutathione conjugates of postulated oxirene and benzoquinone imine intermediates by LC/MS and LC/NMR.

The metabolic activation of (S)-5,6-difluoro-4-cyclopropylethynyl-4-trifluoromethyl-3,4-dihydro-2(1H)-quinazolinone, DPC 963, in rats was investigated by identifying and characterizing the GSH and mercapturic acid conjugates excreted in the bile and urine, respectively. The structures of these adducts, which were unequivocally elucidated by LC/MS/MS and NMR experiments, revealed the existence of at least three distinct metabolic pathways leading to these products. One of the pathways, which has been described previously, involves the activation of the acetylene group after an initial hydroxylation on the methine carbon of the cyclopropyl ring. Metabolite M1 was demonstrated to be formed via this pathway after an enzymatic addition of GSH across the triple bond of the substituted acetylene. The second pathway, also previously described, leads to diastereoisomeric GSH adducts M3 and M4 after the formation of a highly reactive oxirene intermediate. This postulated oxirene subsequently rearranges to an alpha, beta-unsaturated cyclobutenyl ketone intermediate capable of undergoing a 1,4-Michael addition with a nucleophile such as GSH. In addition to these pathways, DPC 963 was found to undergo a metabolic activation previously undescribed for structural analogues of this compound. It is postulated that an oxidative defluorination mediated by cytochrome P450 leads to the formation of a putative benzoquinone imine intermediate which subsequently reacts with GSH to form two aromatic ring-substituted regioisomeric conjugates, M5 and M6. In addition to forming the GSH adducts, the benzoquinone imine was also found to be reduced to its unreactive hydroquinone metabolite, which was excreted as the glucuronide conjugate in rat bile. Studies with induced rat microsomes, cDNA-expressed rat P450 isozymes, and polyclonal antibodies against rat P450 clearly demonstrated that the rat P450s 3A1/3A2 were responsible for the formation of postulated oxirene and benzoquinone intermediates.

Animals↗
PubMed1981

Bacterial mutagenicity and toxicity of cycloaliphatic epoxides.

The mutagenicity of 12 cycloaliphatic epoxides was investigated using the Ames Salmonella assay without the addition of liver homogenate fractions. Base-pair substitution mutagenic activity was detected for 8 members of this series of compounds, confirming our laboratory's previous observations of weak mutagenic response at high dose levels for cis-1,2-disubstituted epoxides. While mutagenicity decreased with expanding ring size, inhibition of bacterial growth increased for increases in ring size. Toxicity accompanying the required high doses for the demonstration of mutagenicity for these compounds prevented the establishment of meaningful dose-response ranges for the remaining epoxides tested. The volatility observed with these oxiranes also made dose-response establishment difficult but was countered by the use of petri dish sealing bands during incubation. Mutagenicity in this series was found to be generally more pronounced in TA1535 while toxicity was detected with greater sensitivity by TA100. The use of the less permeable strains TA92, TA1950 and TA2410, all having normal lipopolysaccharide cell wall coatings, failed to reduce this marked toxicity. The repair test compared results in TA1535 (repair-deficient strain) with TA1975 (repair-proficient strain) and demonstrated that the bacteria were not being killed by damage to DNA since toxicity was not reduced in TA1975.

Epoxy Compounds↗
PubMed1988

The role of intestinal microflora in the metabolism of trichothecene mycotoxins.

The role of faecal and intestinal microflora on the metabolism of trichothecene mycotoxins was examined in this study. Suspensions of microflora obtained from the faeces of horses, cattle, dogs, rats, swine and chickens were incubated anaerobically with the trichothecene mycotoxin, diacetoxyscirpenol (DAS). Micro-organisms from rats, cattle and swine completely biotransformed DAS, primarily to the deacylated deepoxidation products, deepoxy monoacetoxyscirpenol (DE MAS) and deepoxy scirpentriol (DE SCP). By contrast, faecal microflora from chickens, horses and dogs failed to reduce the epoxide group in DAS and yielded only the deacylation products, monoacetoxyscirpenol (MAS) and scirpentriol (SCP), in addition to unmetabolized parent compound. Intestinal microflora obtained from rats completely biotransformed DAS to DE MAS, DE SCP and SCP; and T-2 toxin to the deepoxy products, deepoxy HT-2 (DE HT-2) and deepoxy T-2 triol (DE TRIOL). Rat intestinal microflora also biotransformed the polar trichothecenes, T-2 tetraol and scirpentriol, to their corresponding deepoxy analogues. Deepoxy T-2 toxin (DE T-2) was synthesized from T-2 toxin and demonstrated to be 400 times less toxic than T-2 toxin in the rat skin irritation bioassay and non-toxic to mice given 60 mg/kg ip, demonstrating that epoxide reduction is a significant single step detoxification reaction for trichothecene mycotoxins.

Animals↗
PubMedDate not supplied

In vitro assessment of individual and interactive effects of aromatic hydrocarbons on embryonic development of the rat.

There have been reports of disruption of embryonic development following exposure of pregnant women to aromatic hydrocarbons. In the present study, the embryotoxicity of toluene, xylene, benzene, styrene, and its metabolite, styrene oxide, was evaluated using the in vitro culture of postimplantation rat embryos. Possible interactions between toluene, xylene, and benzene were also studied using mixtures of these solvents. The results of the study showed that toluene, xylene, benzene, and styrene all have a concentration-dependent embryotoxic effect on the developing rat embryo in vitro. Styrene was embryotoxic at a lower concentration (1.00 mumol/mL) than benzene (1.56 mumol/mL), toluene (2.25 mumol/mL), or xylene (1.89 mumol/mL). The metabolite of styrene, styrene oxide, was embryotoxic at a concentration (0.038 mumol/mL). more than 20 times less than the parent compound. There was no evidence of a synergistic interaction between toluene, xylene, and benzene in causing embryotoxicity; the solvents interacted in an additive manner. The embryos were exposed to the solvents for 40 h of the organogenic period. When the levels of solvents found to be embryotoxic in the present study are compared to blood levels in the human following industrial exposure or solvent abuse, it appears unlikely that the threshold blood levels for embryotoxicity would be exceeded in the workplace. However, the possibility that exposure to solvents earlier or later or throughout the entire organogenic period might result in a different conclusion cannot be excluded.

Animals↗
PubMed1977

Benzo[a]pyrene carcinogenesis: a biochemical selection mechanism.

Separation of the metabolic products of benzo[a]pyrene has been readily accomplished by high-pressure liquid chromatography. This technique is uniquely suited for compounds labile to air and light and resolving positional isomers of phenolic or other types of oxygenated metabolites of this carcinogen. This procedure has been utilized to separate and compare benzo[a]pyrene activation and detoxification products between rat, mouse, and hamster hepatic microsomes and mouse and hamster embryo cell cultures. While metabolic profiles exhibited the same types of derivatives, marked quantitative variation was observed. Microsomal preparation produced large amounts of noncarcinogenic phenols, while intact cell metabolism favored diol formation. These results are in agreement with reactivation of metabolic diols as substrates for further activation to a more proximate carcinogenic species of benzo[a]pyrene and caution against extrapolating metabolic results from any single test system to other species or tissues.

Animals↗
PubMed2002

Epothilone B analogue (BMS-247550)-mediated cytotoxicity through induction of Bax conformational change in human breast cancer cells.

Epothilone B is a novel nontaxane antimicrotubule agent that is active even against paclitaxel (Taxol)-resistant cancer cells. The present study further explores the mechanisms underlying epothilone B-mediated cytotoxicity in human breast cancer cells. We show that BMS-247550 (EpoB), a novel epothilone B analogue, induces cell cycle arrest at the G(2)-M phase transition and subsequent apoptotic cell death of MDA-MB-468 (468) cells. Treating cells with EpoB triggers a conformational change in the Bax protein and its translocation from the cytosol to the mitochondria, which is accompanied by cytochrome c release from the inter-membrane space of mitochondria into the cytosol. Overexpression of Bcl-2 delays Bax conformational change, cytochrome c release, and apoptosis induced by EpoB. Conversely, the Bcl-2 antagonist Bak-BH3 peptide or HA14-1 compound abrogates the antiapoptotic effects of Bcl-2 and enhances apoptosis of 468 cells pretreated with EpoB (to induce mitotic arrest). In synchronized 468 cells, EpoB is more potent in inducing Bax conformational change and apoptosis at G(2)-M phase compared with G(1)-S phase of the cell cycle. Taken together, these findings demonstrate that EpoB induces apoptosis through a Bcl-2-suppressible pathway that controls a conformational change of the proapoptotic Bax protein. The enhanced cytotoxicity of EpoB by blocking Bcl-2 at mitochondria implies a potential application of the combination of EpoB and Bcl-2 antagonists in the treatment of human breast cancer.

Antineoplastic Agents↗
PubMed1996

Inhibition of the reconstituted mitochondrial oxoglutarate carrier by arginine-specific reagents.

The effect of arginine-specific reagents on the function of the purified and reconstituted oxoglutarate carrier protein of the inner mitochondrial membrane has been investigated. The alpha-dicarbonyl reagents 2,3-butanedione, 2,3-pentanedione, 2,3- and 3,4-hexanedione, 1-phenyl-1,2-propanedione, phenylglyoxal, and phenylglyoxal derivatives caused a concentration-dependent inhibition of oxoglutarate transport with an IC50 of 0.05 mM for 2,3-hexanedione, 0.08 mM for 4-hydroxy-3-nitrophenylglyoxal, and 0.17 mM for 2,3-pentanedione. The inhibition increased with pH from 6.0 to 8.0, indicating that the pK of the reacting group(s) is rather high. Mersalyl and pyridoxal 5'-phosphate (or 4,4'-dinitrostilbene-2,2'-disulfonate), which are known to react specifically and reversibly with cysteine residues and lysine residues, respectively, were unable to protect the oxoglutarate carrier against inhibition by alpha-dicarbonyl reagents. Other diketone compounds, which do not react with arginine residues, had no significant effect on the oxoglutarate transport activity. Oxoglutarate and L-malate effectively protected the oxoglutarate carrier against inactivation caused by arginine-specific reagents; other dicarboxylates, which are not substrates of the carrier, had no protective effect. A 50% substrate protection was observed at half-saturation of the external binding site. These results indicate that the arginine-specific reagents used in this investigation interact with the oxoglutarate carrier at the level of an arginine residue(s), which is essential for binding and/or translocation of substrates and which may be localized in, or near, the substrate-binding site.

Animals↗
PubMed1991

Stereospecificity of the inhibition by etomoxir of fatty acid and cholesterol synthesis in isolated rat hepatocytes.

The racemates of substituted 2-oxiranecarboxylates are potent inhibitors of fatty acid oxidation and fatty acid and cholesterol synthesis. We show in the accompanying paper [Agius L, Peak M and Sherratt HSA, Biochem Pharmacol 42: 1711-1715, 1991] that only the R-enantiomer of etomoxir, a potent hypoglycaemic compound, inhibits fatty acid oxidation in hepatocytes. We demonstrate in this paper that although the R-enantiomer of etomoxir is esterified to its CoA-ester more readily than the S-enantiomer, both the R- and S-enantiomers are equally potent inhibitors of fatty acid and cholesterol synthesis from acetate in rat hepatocytes. The inhibition of fatty acid synthesis is not due to direct inhibition of fatty acid synthetase and the inhibition of cholesterol synthesis occurs at a site proximal to formation of mevalonate. Since the S-enantiomer inhibits fatty acid and cholesterol synthesis but not fatty acid oxidation the inhibition of the biosynthetic pathways is not coupled to inhibition of fatty acid oxidation.

Animals↗
PubMed2005

Inhibitory effect of triptolide on chemokine expression induced by proinflammatory cytokines in human corneal fibroblasts.

PURPOSE: Synthesis of various chemokines, including interleukin (IL)-8 and monocyte chemotactic protein (MCP)-1, as well as the surface expression of intercellular adhesion molecule (ICAM)-1 in corneal fibroblasts contribute to corneal inflammation. The effects of triptolide, the major constituent of extracts of the herb Tripterygium wilfordii hook f, on the expression of these proteins in human corneal fibroblasts were examined in comparison with those of dexamethasone. METHODS: The release of IL-8 and MCP-1 from and the surface expression of ICAM-1 on cultured corneal fibroblasts were measured with enzyme-linked immunosorbent assays. The cellular abundance of the mRNAs for these proteins was determined by reverse transcription and real-time polymerase chain reaction analysis. The activities of the transcription factors NF-kappaB and AP-1 were assessed by cell transfection with secretory alkaline phosphatase reporter genes. RESULTS: Both triptolide and dexamethasone inhibited in a dose-dependent manner the expression of IL-8 and MCP-1 in corneal fibroblasts induced by the proinflammatory cytokines IL-1beta or tumor necrosis factor (TNF)-alpha. These inhibitory effects were apparent at both the mRNA and protein levels. Both compounds also had a lesser inhibitory effect on cytokine-induced ICAM-1 expression. The activation of NF-kappaB by IL-1beta was markedly inhibited by both triptolide and dexamethasone, whereas the activity of AP-1 was not affected by either agent. CONCLUSIONS: Like dexamethasone, triptolide inhibited IL-8 and MCP-1 expression in cultured human corneal fibroblasts exposed to proinflammatory cytokines, an action most likely mediated by inhibition of NF-kappaB activation. Similar effects of triptolide in vivo may be expected to limit the infiltration of neutrophils and monocytes into the cornea.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1984

Biologically-active and chemically-reactive polycyclic hydrocarbon metabolites.

The mechanism by which polycyclic hydrocarbons produce tumours in mammalian tissues exposed to them involves biotransformation of the compounds to chemically-reactive species that covalently modify cellular informational macromolecules. In all cases known, epoxides of some form are the reactive species involved. The most common pathway is the formation of vicinal diol-epoxides, the reactive centre of the molecule commonly being adjacent to the 'bay-region'. With some hydrocarbons, the involvement in DNA binding of non-'bay-region' diol-epoxides, of a phenol epoxide and of a 'bay-region' diol-epoxide containing a phenolic function (a triol-epoxide) has also been demonstrated. The relative importance to the carcinogenic process of the different pathways leading to DNA-binding products may be reflected by the biological activities of the intermediates involved.

Animals↗
PubMed2003

Biocatalytic conversion of epoxides.

Epoxides are attractive intermediates for producing chiral compounds. Important biocatalytic reactions involving epoxides include epoxide hydrolase mediated kinetic resolution, leading to the formation of diols and enantiopure remaining substrates, and enantioconvergent enzymatic hydrolysis, which gives high yields of a single enantiomer from racemic mixtures. Epoxides can also be converted by non-hydrolytic enantioselective ring opening, using alternative anionic nucleophiles; these reactions can be catalysed by haloalcohol dehalogenases. The differences in scope of these enzymatic conversions is related to their different catalytic mechanisms, which involve, respectively, covalent catalysis with an aspartate carboxylate as the nucleophile and non-covalent catalysis with a tyrosine that acts as a general acid-base. The emerging new possibilities for enantioselective biocatalytic conversion of epoxides suggests that their importance in green chemistry will grow.

Catalysis↗
PubMed1996

[Evaluation of blood absorption, hemostatic ability and purity of a polyepoxy compound cross-linked cotton type collagen hemostat].

A polyepoxy compound cross-linked cotton type collagen hemostat (CCH) made of highly purified atelocollagen in a fine filament shape was developed. To evaluate blood absorption, hemostatic ability and purity of the CCH, Avitene and Oxycel were used for comparison. Blood absorption speed of the CCH was faster than Avitene and Oxycel. The handling characteristics of the CCH were much better than those of Avitene and Oxycel. Hemostatic ability was better in the CCH compared to Avitene in a canine study. The purity of the CCH was better than in Avitene which contained albumin and other proteins. Those results suggest that the developed hemostat with excellent blood absorption, handling characteristics, hemostatic ability and purity, could be useful in clinicals.

Absorption↗
PubMed2005

Anthracene-induced turnover enhancement in the manganese porphyrin-catalyzed epoxidation of olefins.

Anthracene and related compounds function as lifetime-extending cofactors in the (meso-tetraphenylporphine)Mn(III) chloride-catalyzed epoxidation of olefins. An experiment with a chiral porphyrin catalyst shows that enantioselectivity is preserved in the presence of the cofactor. Additional experiments show that (a) turnover number enhancement is greatest for the least reactive substrates, (b) derivatization of anthracene at the 9 and 10 positions largely eliminates the enhancement effect, and (c) anthracene is ultimately converted to anthraquinone. The origin of the observed enhancements is in the reaction of anthracene with the normally unreactive dimeric oxo-bridged form of the catalyst. This reaction, which produces anthraquinone, regenerates the catalytically active monomeric form of the manganese porphyrin.

Alkenes↗
PubMed2005

Analogues of key precursors of aspartyl protease inhibitors: synthesis of trifluoromethyl amino epoxides.

The synthesis of the title compound is described through original and tailored synthetic protocols. The addition of vinylmagnesium bromide to CF(3)-N-aryl and N-alkyl aldimines was efficient and did not require an activating N-substituent. The resultant CF3-allylamines were converted in an efficient and completely stereoselective route to syn CF3-epoxides 3 via formation of bromhydrins 8. The same sequence performed from the aldimine substituted with the methyl ether of the (R)-phenylglycinol provided the homochiral (R,R)-amino epoxide (de >98%). This study has allowed access to the novel racemic and homochiral trifluoromethyl beta-amino epoxides, analogues of key precursors of various HIV protease inhibitors.

Amines↗
PubMed1977

Effect of trichloropropene oxide on the ability of polyaromatic hydrocarbons and their "K-region" oxides to initiate skin tumors in mice and to bind to DNA in vitro.

The potent epoxide hydrase inhibitor, 1,1,1-trichloro-2,3-propene oxide (TCPO), enhanced the tumor-initiating ability of benzo[alpha]pyrene (BP) and 3-methylcholanthrene (MCA) but had no effect on 9,10-dimethyl-1,2-anthracene (DMBA) initiation in a two-stage system of tumorigenesis in female Charles River CD-1 mice. The tumor-initiating ability of dibenz[alpha,h]-anthracene (DBA) was decreased by prior topical treatment with 10 mumoles of TCPO. The tumor latency period of BP and MCA was decreased by TCPO but had no effect on DMBA or DBA. Topical treatment with 10 mumoles of TCPO did not initiate tumors in a two-stage system in mouse skin nor did it cause any histopathologic changes in the skin. The "K-region" epoxides of BP, DMBA, and MCA were weak tumor initiators when compared to the parent compounds. TCPO only slightly increased or had no effect on the tumor-initiating activity of the above epoxides. Pretreatment with Croton oil 18 hours prior to initiation with BP-4,5-epoxide also slightly enhanced the tumorigenic response in mouse skin. DBA-5,6-epoxide, when tested as a complete carcinogen at high doses (1 mg daily/10 days), was found to be a weak carcinogen but with activity comparable to that of DBA. TCPO only slightly increased the in vitro epidermally mediated covalent binding of the above parent polycyclic hydrocarbons to DNA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1994

Chemical mutagenesis testing in Drosophila. IX. Results of 50 coded compounds tested for the National Toxicology Program.

Fifty chemicals were tested for mutagenic activity in post-meiotic and meiotic germ cells of male Drosophila melanogaster using the sex-linked recessive lethal (SLRL) assay. As in the previous studies in this series, feeding was chosen as the first route of administration. If the compound failed to induce mutations by this route, injection exposure was used. One gaseous chemical (1,3-butadiene) was tested only by inhalation. Those chemicals that were mutagenic in the sex-linked recessive lethal assay were further tested for the ability to induce reciprocal translocations. Eleven of the 50 chemicals tested were mutagenic in the SLRL assay. These included bis(2-chloroethyl) ether, 1,4-butanediol diglycidyl ether, 1-chloro-2-propanol, dimethyl methylphosphonate, dimethyl morpholinophosphoramidate, dimethyloldihydroxyethylene urea, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isatin-5-sulfonic acid (Na salt), isopropyl glycidyl ether, and urethane. Five of these, including 1,4-butanediol diglycidyl ether, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isopropyl glycidyl ether, and urethane, also induced reciprocal translocations.

Animals↗
PubMed2004

Styrene 7,8-oxide induces mitochondrial damage and oxidative stress in neurons.

Styrene 7,8-oxide (SO) is the main metabolite of styrene, a neurotoxic compound used industrially. Neurons exposed to SO undergo apoptosis with characteristic features including chromatin rearrangements and caspase activation. We report that the execution phase of apoptosis induced by SO (0.3 mM) in SK-N-MC neurons is triggered by translocation of apoptogenic factors (e.g., cytochrome c) into the cytosol. In addition, mitochondria exhibit lower Ca2+ capacity and loss of mitochondrial membrane potential (DeltaPsi). Lipid peroxidation, measured as thiobarbituric acid reactive substances (TBARS), is increased after 12 h. Pre-treatment with the antioxidant MnTBAP (100 microM) prevents the decrease of Ca2+ capacity, cytochrome c release, activation of caspases, exposure of phosphatidylserine and cell death. Hence, the neurotoxic effects of SO are related to mitochondrial damage and oxidative stress.

Apoptosis↗
PubMed1977

Measurement of carbamazepine and its epoxide metabolite by high-performance liquid chromatography, and a comparison of assay techniques for the analysis of carbamazepine.

We describe a modified high-performance liquid-chromatographic method for the simultaneous analysis of carbamazepine andits biologically active metabolite, carbamazepine-10, 11-epoxide. Concentrations of both these compounds in the plasma of 35 epileptic patients receiving chronic carbamazepine therapy are presented. Concentrations of carbamazepine in plasma were related to those of carbamazepine-10, 11-epoxide (r - 0.495, P less than 0.05). Total daily doses of carbamazepine were better correlated with plasma concentrations of carbamazepine-10, 11-epoxide (r = 0.714, P less than 0.001) than of carbamazepine (r = 0.269, P greater than 0.05). Close correlations were found between results of the three assay procedures we used to measure plasma carbamazepine concentrations: high-performance liquid chromatography, gas-liquid chromatography, and enzyme immunoassay. Correlation coefficients exceeded 0.97 and regression slopes were near unity, indicating that all three procedures were individually specific for the quantification of plasma carbamazepine.

Carbamazepine↗