Metabolism Of Foreign Chemicals Research Articles

Response mechanisms of pipe wall biofilms in water supply networks under different disinfection strategy pressures and the effect of mediating halogenated acetonitrile formation

Residual chlorine and biofilm coexistence is inevitable in drinking water transmission and distribution networks. Understanding the microbial response and its mediated effects on disinfection byproducts under different categories of residual chlorine stress is essential to ensure water safety. The aim of our study was to determine the response of pipe wall biofilms to residual chlorine pressure in chlorine and chloramine systems and to understand the microbially mediated effects on the formation and migration of haloacetonitriles (HANs), typical nitrogenous disinfection byproducts. According to the experimental results, the biofilm response changes under pressure, with significant differences noted in morphological characteristics, the extracellular polymeric substances (EPS) spatial structure, bacterial diversity, and functional abundance potential. Upon incubation with residual chlorine (1.0 ± 0.2 mg/L), the biofilm biomass per unit area, EPS, community abundance, and diversity increased in the chloramine group, and the percentage of viable bacteria increased, potentially indicating that the chloramine group provides a richer variety of organic matter precursors. Compared with the chloramine group, the chlorination group exhibited increased haloacetonitrile formation potential (HANFP), with Rhodococcus (43.2%) dominating the system, whereas the prediction abundance of metabolic functions was advantageous, especially with regard to amino acid metabolism, carbohydrate metabolism, and the biodegradation and metabolism of foreign chemicals. Under chlorine stress, pipe wall biofilms play a stronger role in mediating HAN production. It is inferred that chlorine may stimulates microbial interactions, and more metabolites (e.g., EPS) consume chlorine to protect microbial survival. EPS dominates in biofilms, in which proteins exhibit greater HANFP than polysaccharides.

The phenotype of a flavin-containing monooyxgenase knockout mouse implicates the drug-metabolizing enzyme FMO1 as a novel regulator of energy balance

Flavin-containing monooxygenases (FMOs) of mammals are thought to be involved exclusively in the metabolism of foreign chemicals. Here, we report the unexpected finding that mice lacking Fmos 1, 2 and 4 exhibit a lean phenotype and, despite similar food intake, weigh less and store less triglyceride in white adipose tissue (WAT) than wild-type mice. This is a consequence of enhanced whole-body energy expenditure, due mostly to increased resting energy expenditure (REE). This is fuelled, in part, by increased fatty acid β-oxidation in skeletal muscle, which would contribute to depletion of lipid stores in WAT. The enhanced energy expenditure is attributed, in part, to an increased capacity for exercise. There is no evidence that the enhanced REE is due to increased adaptive thermogenesis; instead, our results are consistent with the operation in WAT of a futile energy cycle. In contrast to FMO2 and FMO4, FMO1 is highly expressed in metabolic tissues, including liver, kidney, WAT and BAT. This and other evidence implicates FMO1 as underlying the phenotype. The identification of a novel, previously unsuspected, role for FMO1 as a regulator of energy homeostasis establishes, for the first time, a role for a mammalian FMO in endogenous metabolism. Thus, FMO1 can no longer be considered to function exclusively as a xenobiotic-metabolizing enzyme. Consequently, chronic administration of drugs that are substrates for FMO1 would be expected to affect energy homeostasis, via competition for endogenous substrates, and, thus, have important implications for the general health of patients and their response to drug therapy.

The Flavin-Containing Monoooxygenases (FMOs): Genetic Variation and its Consequences for the Metabolism of Therapeutic Drugs

Flavin-containing monoooxygenases (FMOs) are a family of enzymes involved in the metabolism of foreign chemicals, including many therapeutic drugs. In this review we focus on the functional FMOs of humans (FMOs 1, 2, 3, 4 and 5). For each FMO we describe its gene organization, developmental- and tissue-specific pattern of expression, substrate specificity and the identity, frequency and functional effect of polymorphic variants. We also review the consequences of genetic variation in the FMOs for the metabolism of therapeutic drugs and the implications of this for drug efficacy and response. Some key points are: the majority of humans are homozygous for an allele (FMO2ast;2) that encodes a truncated, non-functional polypeptide, but a substantial proportion of individuals of African descent possess a copy of the functional ancestral (FMO2*1) allele and thus are predicted to respond differently to drugs and other foreign chemicals that are substrates for FMO2; FMO3 polymorphisms that decrease catalytic activity have been linked to increased drug efficacy; rare mutations in FMO3 are causative of the disorder trimethylaminuria; and the role of FMO1 and FMO3 in the oxidation of the antiestrogen tamoxifen and the antitubercular drug thiacetazone are discussed. Keywords: human FMO1 gene, cytochrome P450, coding variants, FMO2 expression, Trimethylaminuria

Molecular evolution and balancing selection in the flavin-containing monooxygenase 3 gene (FMO3)

Flavin-containing monooxygenase 3 (FMO3) is involved in the metabolism of foreign chemicals, including therapeutic drugs, and thus mediates interactions between humans and their chemical environment. Loss-of-function mutations in the gene cause the inherited disorder trimethylaminuria, or fish-odour syndrome. The objective was to gain insights into the evolutionary history of FMO3. Genetic diversity within FMO3 was characterized by sequencing 6.3 kb of genomic DNA, encompassing the entire coding sequence, some intronic and 3'-untranslated region, and 3.4 kb of 5'-flanking sequence, in 23 potential trimethylaminuric Japanese, and the same 3.4 kb 5'-flanking region in 45 unaffected Japanese. Mutational relationships among haplotypes were inferred from a reduced-median network. The time depth of the variation and ages of individual mutations were estimated by maximum-likelihood coalescent analysis. Test statistics were used to investigate whether the variation is compatible with neutral evolution. Sixteen single-nucleotide polymorphisms (SNPs) were identified, which segregated as seven distinct haplotypes. Estimated ages of the mutations indicate that almost all predated migration out of Africa. Analysis of the heterozygosity of FMO3 SNPs indicates that genetic differentiation among continental populations is low (FST=0.050). Test statistics, based on allele-frequency spectrum, number and diversity of haplotypes, linkage disequilibrium and interspecific sequence comparisons, showed a significant departure from neutral expectations, because of an excess of intermediate-frequency SNPs and haplotypes, a ragged pairwise mismatch distribution and an excess of replacement polymorphisms. The results provide evidence that FMO3 has been the subject of balancing selection. Finally, we identify mutations that are potential targets for selection.

Induction of cellular glutathione and glutathione S-transferase by 3H-1,2-dithiole-3-thione in rat aortic smooth muscle A10 cells: protection against acrolein-induced toxicity

There is increasing evidence that aldehydes, including acrolein generated endogenously during the degradation process of biological molecules or the metabolism of foreign chemicals may be involved in the pathogenesis of cardiovascular diseases, such as atherosclerosis. Because glutathione (GSH) and GSH S-transferase (GST) are a major cellular defense against the toxic effects of reactive aldehydes, in this study we have characterized the inducibility of GSH and GST by the unique chemoprotective agent, 3H-1,2-dithiole-3-thione (D3T) and their protective effects against acrolein-induced toxicity in rat aortic smooth muscle A10 cells. Incubation of rat aortic A10 cells with micromolar concentrations of D3T resulted in a concentration- and time-dependent induction of both GSH and GST. Treatment of A10 cells with D3T also led to induction of gamma-glutamylcysteine synthetase, the key enzyme involved in GSH biosynthesis. Notably, the levels of GSH and GST remained higher than basal levels 72 h after removal of D3T from the culture media. To examine the protective effects of D3T-induced GSH and GST against reactive aldehyde-mediated toxicity, A10 cells were pretreated with D3T and then exposed to acrolein. Pretreatment of A10 cells with D3T resulted in a marked decrease of acrolein-induced toxicity as determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction assay and morphological changes. To further demonstrate the involvement of GSH and GST in protecting against acrolein-induced toxicity, buthionine sulfoximine (BSO) and sulfasalazine were used to inhibit cellular GSH biosynthesis and GST activity, respectively. Either depletion of cellular GSH by BSO or inhibition of cellular GST by sulfasalazine led to a marked potentiation of acrolein-induced toxicity in A10 cells. Furthermore, co-treatment of cells with BSO was found to greatly abolish the protective effects of D3T on acrolein-induced toxicity. Taken together, our results demonstrate for the first time that both GSH and GST in aortic smooth muscle cells can be induced by D3T, and that this increased cellular defense affords great protection against reactive aldehyde-induced cardiovascular cell injury.

Drosophila melanogaster NADPH–cytochrome P450 oxidoreductase: pronounced expression in antennae may be related to odorant clearance

Insects perceive a large number of airborne chemicals as olfactory components mainly through the antenna. It is thought that detection of the odorants by specific receptors is followed by a degradative pathway that clears the olfactory organ from accumulating chemicals. In Drosophila, a number of P450 monooxygenases are involved in the metabolism of foreign chemicals [ Dunkov et al. (1996)Cytochrome P450 gene cluster in Drosophila melanogaster, Mol. Gen. Genet. 251, 290–297]. NADPH–cytochrome P450 oxidoreductases serve to transfer reducing equivalents to P450 monooxygenases. We isolated cDNA and genomic clones coding for a Drosophila NADPH–cytochrome P450 oxidoreductase (CPR). The largest cDNA of 2471 nucleotides in length contained an open reading frame of 693 amino acids that includes the putative CPR sequence. CPR is a single copy gene as shown by genomic Southern hybridisation and maps to the cytogenetic map position 26C on the second chromosome. Comparison of genomic and cDNA CPR sequences revealed a gene structure that is split into at least six exons. The CPR protein sequence is almost identical with that of house fly and remarkably conserved when compared to vertebrates and yeast. RNA expression is high in embryos and antennae as compared to adult heads, adult bodies and larvae. High expression in antennae may reflect the putative function in olfactory clearance. © 1997 Elsevier Science B.V. All rights reserved.

Metabolic biomarkers of Parkinson's disease

Enzymic systems involved with metabolism of foreign chemicals, xenobiotics, have been studied in Parkinson's disease. Enzymes involved with sulphur oxidation and methylation are under-active. Cysteine levels are high and sulphate levels low. Differences in the activity of the enzyme monoamine oxidase-B are evident. Pathways involved with N-methylation of pyridines are different from controls leading to a rise in potentially toxic N-methylated derivatives.

Mechanism of induction of hepatic drug metabolizing enzymes: recent advances

The function of the readily-inducible microsomal drug metabolizing enzymes is to oxidize ‘foreign’ chemicals (drugs, steroids, pollutants, etc.) which are thereby rendered more polar and more readily excretable. Although metabolism of foreign chemicals may generally be considered to be desirable, in some cases toxic or carcinogenic metabolic intermediates may be formed en route. Understanding of this complex mono-oxygenase system is therefore of importance to both pharmacologists and toxicologists. In this review Joyce Goldstein describes the advances that application of DNA recombinant technology has made in the elucidation of the mechanism of regulation of cytochrome P-450 by two classes of chemicals.

Isolation and culture of adult hepatocytes from liver biopsies.

Hepatocytes were isolated from liver biopsies of rats, guinea pigs, rabbits, dogs, and humans. The procedure is based on cannulation of large veins in the cut face of the biopsy, followed by collagenase perfusion. Yields averaged 19 x 10(6) viable hepatocytes/g liver. Viability averaged 84%, as determined by trypan blue dye exclusion. Cultures were prepared from the isolated hepatocytes and were found to be comparable in morphology and N-demethylase activity to hepatocyte cultures prepared by the in situ perfusion of the liver. The development of this method should facilitate comparative studies of the cytotoxicity, genotoxicity, and metabolism of foreign chemicals in primary hepatocyte cultures.

Effect of dietary factors and environmental chemicals on intestinal drug metabolizing enzymes

The liver is the major site of metabolism of foreign chemicals, but contribution from intestinal biotransformation can influence the overall disposition of chemicals. The intestinal drug‐metabolizing enzymes are located in the endoplasmic reticulum and they possess biochemical properties similar to those of the hepatic system. In general, the rate of in vitro metabolism of drug substrates in intestines is lower than in the liver. There seem to be differences in regulation and induction of hepatic and intestinal drug‐metabolizing enzymes. The in vitro intestinal metabolism of foreign chemicals is affected by several factors including the nutritional status of the animal. Dietary components such as vitamins, lipids and vegetables can modify the activities of intestinal drug‐metabolizing enzymes. Phenobarbital or 3‐methyl‐cholanthrene (3‐MC) pre‐treatment induces the hepatic metabolism of a wide variety of drug substrates in a number of species, while the stimulation of intestinal enzymes is both substrate a...