Xenobiotic lipids: The inclusion of xenobiotic compounds in pathways of lipid biosynthesis

Dodds, Peter F.

doi:10.1016/0163-7827(95)00007-m

Cited by 41 publications

(28 citation statements)

References 150 publications

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“…Fenbufen is a nonsteroidal anti-inflammatory drug (NSAID), which has been reported to be incorporated into diacylglycerols using 3T3-L1 cells . Similarly ibuprofen, also a NSAID, is also known to be incorporated into triacyglycerol and diacylglycerol under various conditions [Dodds, 1995;Vickery and Dodds, 2004]. In this study, it was found that fenbufen-DG and ibuprofen-DG were capable of inducing increased micronucleus frequency in a dosedependent manner, which was statistically significant (P < 0.001).…”

Section: Discussionsupporting

confidence: 51%

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In vitro genotoxic assessment of xenobiotic diacylglycerols in an in vitro micronucleus assay

Kayani

Parry

Vickery

et al. 2009

Environ and Mol Mutagen

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Xenobiotic diacylglycerols (DG) may induce pathological disorders by causing abnormal chromosomal segregation, which could be aneuploid. In this study, seven xenobiotic-diacylglycerols (four of drug origin and three of pesticide origin) were evaluated for their ability to induce aneuploidy in mammalian cultures using in vitro cytokinesis blocked micronucleus (CBMN) assay coupled with kinetochore labeling and interphase fluorescent in situ hybridization. Out of seven xeno-DGs, two (ibuprofen-DG and fenbufen-DG) induced statistically significant (P < 0.001) and dose-dependent increase in micronucleus induction, but this apparent micronucleus induction was very weak in case of fenbufen-DG. These MN were produced predominantly by aneugenic and clastogenic mechanisms, respectively, confirmed by immunofluorescent labeling of kinetochores. Fluorescent in situ hybridization analysis revealed that ibuprofen-DG induced significantly higher nondisjunction for chromosomes 10, 17, and 18. Other xenobiotic diacylglycerols (indomethacin-DG, salicylic acid-DG, 4-(2-methyl-4-chlorophenoxy) butanoic acid-DG (MCPB-DG), 2-(2-methyl-4-chlorophenoxy) propanoic acid-DG (MCPP-DG) and 2-(4-dichlorophenoxy)-butanoic acid-DG (2,4 DB-DG) did not induce micronuclei, but the concentrations tested did not reach levels that caused the marked growth suppression typically required for testing for regulatory testing purposes. However, the levels of growth suppression achieved were similar to that seen with ibuprofen-DG, which was positive. This study shows that xeno-DGs, which have been neglected in the past for their possible link to any pathological disorders, need serious assessment of their mutagenic potential.

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Section: Discussionsupporting

confidence: 51%

“…consequences of their occurrence [Dodds, 1995]. To our knowledge, there had been no studies on the ability of xenobiotic diacylglycerols to induce aneuploidy.…”

Section: Discussionmentioning

confidence: 96%

In vitro genotoxic assessment of xenobiotic diacylglycerols in an in vitro micronucleus assay

Kayani

Parry

Vickery

et al. 2009

Environ and Mol Mutagen

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“…PPAR␣ activators such as clofibric acids or GW4647 up to 50 M had no effect on ACS1, ACS4, or ACS5 (Table II) despite the ability of PPAR␣ ligands to improve insulin sensitivity and reduce adiposity (28). We also tested a variety of xenobiotic carboxylic acids, which contain hydrophobic and carboxylic acid moieties, are known to be incorporated into complex lipids, and either resemble natural fatty acids or are aromatic derivatives of short chain fatty acids (29). The long chain cyclopropane (bridged) analogue of oleic acid, (Ϯ)-cis-9,10-methylene octadecanoic acid, inhibited ACS1 and ACS4 activities 50% at 25 and 30 -40 M, respectively, but had no effect on ACS5.…”

Section: Fig 2 Triton X-100 Activates Acs5mentioning

confidence: 99%

Expression and Characterization of Recombinant Rat Acyl-CoA Synthetases 1, 4, and 5

Kim

Lewin

Coleman

2001

Journal of Biological Chemistry

216

181

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Inhibition by triacsins and troglitazone of long chain fatty acid incorporation into cellular lipids suggests the existence of inhibitor-sensitive and -resistant acyl-CoA synthetases (ACS, EC 6.2.1.3) that are linked to specific metabolic pathways. In order to test this hypothesis, we cloned and purified rat ACS1, ACS4, and ACS5, the isoforms present in liver and fat cells, expressed the isoforms as ACS-Flag fusion proteins in Escherichia coli, and purified them by Flag affinity chromatography. The Flag epitope at the C terminus did not alter the kinetic properties of the enzyme. Purified ACS1-, 4-, and 5-Flag isoforms differed in their apparent K m values for ATP, thermolability, pH optima, requirement for Triton X-100, and sensitivity to N-ethylmaleimide and phenylglyoxal. The ACS inhibitor triacsin C strongly inhibited ACS1 and ACS4, but not ACS5. The thiazolidinedione (TZD) insulin-sensitizing drugs and peroxisome proliferator-activated receptor ␥ (PPAR␥) ligands, troglitazone, rosiglitazone, and pioglitazone, strongly and specifically inhibited only ACS4, with an IC 50 of less than 1.5 M. Troglitazone exhibited a mixed type inhibition of ACS4. ␣-Tocopherol, whose ring structure forms the non-TZD portion of troglitazone, did not inhibit ACS4, indicating that the thiazolidine-2,4-dione moiety is the critical component for inhibition. A non-TZD PPAR␥ ligand, GW1929, which is 7-fold more potent than rosiglitazone, inhibited ACS1 and ACS4 poorly with an IC 50 of greater than 50 M, more than 100-fold higher than was required for rosiglitazone, thereby demonstrating the specificity of TZD inhibition. Further, the PPAR␣ ligands, clofibrate and GW4647, and various xenobiotic carboxylic acids known to be incorporated into complex lipids had no effect on ACS1, -4, or -5. These results, together with previous data showing that triacsin C and troglitazone strongly inhibit triacylglycerol synthesis compared with other metabolic pathways, suggest that ACS1 and ACS4 catalyze the synthesis of acyl-CoAs used for triacylglycerol synthesis and that lack of inhibition of a metabolic pathway by triacsin C does not prove lack of acyl-CoA involvement. The results further suggest the possibility that the insulin-sensitizing effects of the thiazolidinedione drugs might be achieved, in part, through direct interaction with ACS4 in a PPAR␥-independent manner.Acyl-CoA synthetase (ACS, 1 EC 6.2.1.3) catalyzes the ligation of long chain fatty acids with coenzyme A (CoA) to produce long chain acyl-CoAs (1). The resulting acyl-CoAs can be further metabolized in pathways of ␤-oxidation, glycerolipid synthesis, cholesteryl ester (CE) synthesis, desaturation, elongation, and protein acylation and can serve as signaling molecules (2-4). Although ACS was first believed to be a constitutive enzyme because the activity in liver was not altered by changes in nutritional status or hormonal stimuli (5-9), the cloning of ACS1 from rat liver in 1990 disclosed that hepatic ACS1 mRNA expression is sensitively regulated by fasting and refeeding as well a...

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“…Practically all the carboxylic acids are thought to covalently modify proteins by this mechanism (Hertz and BarTana, 1988). This pathway may also lead to the inclusion of xenobiotic compounds in pathways of lipid biosynthesis (Tracy et al, 1993;Dodds, 1995). Grillo and Benet (1996) first reported in abstract form a tolmetin-glycine amino acid conjugate formed in vitro in freshly isolated rat hepatocytes exposed to tolmetin.…”

Section: Discussionmentioning

confidence: 99%

Glucuronidation and Covalent Protein Binding of Benoxaprofen and Flunoxaprofen in Sandwich-Cultured Rat and Human Hepatocytes

Dong

Smith²

2009

Drug Metab Dispos

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ABSTRACT:Benoxaprofen (BNX), a nonsteroidal anti-inflammatory drug (NSAID) that was withdrawn because of hepatotoxicity, is more toxic than its structural analog flunoxaprofen (FLX) in humans and rats. Acyl glucuronides have been hypothesized to be reactive metabolites and may be associated with toxicity. Both time-and concentration-dependent glucuronidation and covalent binding of BNX, FLX, and ibuprofen (IBP) were determined by exposing sandwich-cultured rat hepatocytes to each NSAID. The levels of glucuronide and covalent protein adduct measured in cells followed the order BNX > FLX > IBP. These results indicate that 1) BNXglucuronide (G) is more reactive than FLX-G, and 2) IBP-G is the least reactive metabolite, which support previous in vivo studies in rats. The proportional increases of protein adduct formation for BNX, FLX, and IBP as acyl glucuronidation increased also support the hypothesis that part of the covalent binding of all three NSAIDs to hepatic proteins is acyl glucuronide-dependent. Moreover, theses studies confirmed the feasibility of using sandwich-cultured rat hepatocytes for studying glucuronidation and covalent binding to hepatocellular proteins. These studies also showed that these in vitro methods can be applied using human tissues for the study of acyl glucuronide reactivity. More BNX-protein adduct was formed in sandwich-cultured human hepatocytes than FLX-protein adduct, which not only agreed with its relative toxicity in humans but also was consistent with the in vitro findings using rat hepatocyte cultures. These data support the use of sandwich-cultured human hepatocytes as an in vitro screening model of acyl glucuronide exposure and reactivity.Many types of acidic drugs form acyl glucuronides, and other xenobiotics are metabolized to carboxylic acids (Phase I metabolites), which subsequently undergo Phase II conjugation to form acyl glucuronides. Often such a glucuronide conjugate constitutes the major metabolite. The major site of conjugation for most compounds in humans is believed to be the liver. Modification of critical hepatic proteins by covalent binding of acidic drugs through reactive acyl glucuronides may provide a basis for direct hepatocyte toxicity or immune-mediated adverse reactions (Gillette, 1974;Faed, 1984;Boelsterli, 2002;Bailey and Dickinson, 2003).Some pharmaceutical companies have been conducting in vitro experiments by incubating acyl glucuronides with model proteins or peptides (Wang et al., 2004) to determine their reactivity, and hence possibly predict the relative extent of covalent protein binding in vivo in humans. This method requires chemical synthesis or biosynthesis of individual glucuronides for each drug candidate, a process that can be tedious and costly. In addition, hepatic tissue proteins are not present in the incubation, which makes it less likely to correlate covalent protein binding with hepatotoxicity. In vitro models involving hepatic materials, including liver homogenates, microsomal subcellular preparation, and isolated hepatocyte s...

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Xenobiotic lipids: The inclusion of xenobiotic compounds in pathways of lipid biosynthesis

Cited by 41 publications

References 150 publications

In vitro genotoxic assessment of xenobiotic diacylglycerols in an in vitro micronucleus assay

In vitro genotoxic assessment of xenobiotic diacylglycerols in an in vitro micronucleus assay

Expression and Characterization of Recombinant Rat Acyl-CoA Synthetases 1, 4, and 5

Glucuronidation and Covalent Protein Binding of Benoxaprofen and Flunoxaprofen in Sandwich-Cultured Rat and Human Hepatocytes

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