Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and ...

Oxysterols: modulators of cholesterol metabolism and other processes.

Organisms are exposed to epoxide-containing compounds from both exogenous and endogenous sources. In mammals, the hydration of these compounds by various epoxide hydrolases (EHs) can not only regulate their genotoxicity but also, for lipid-derived epoxides, their endogenous roles as chemical mediators. Recent findings suggest that the EHs as a family represent novel drug discovery targets for regulation of blood pressure, inflammation, cancer progression, and the onset of several other diseases. Knowledge of the EH mechanism provides a solid foundation for the rational design of inhibitors, and this review summarizes the current understanding of the catalytic mechanism of the EHs. Although the overall EH mechanism is now known, the molecular basis of substrate selectivity, possible allosteric regulation, and many fine details of the catalytic mechanism remain to be solved. Finally, recent development in the design of EH inhibitors and the EH biological role are discussed.

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Epoxide hydrolases: Mechanisms, inhibitor designs, and biological roles

Isothiocyanates, glutathione S-transferase M1 and T1 polymorphisms, and lung-cancer risk: a prospective study of men in Shanghai, China.

https://ucanr.org/sites/hammocklab/files/125268.pdf

Epoxide hydrolases: their roles and interactions with lipid metabolism.

Background: Members of the glutathione S-transferase (GST) superfamily are important in cellular defense mechanisms. These enzymes attach reduced glutathione to electrophilic groups in a wide variety of toxic compounds, including chemotherapeutic agents. Certain polymorphisms in GSTs are associated with changes in enzyme activity, sensitivity to chemotherapy, and overall patient survival. In a retrospective study, we investigated associations between common polymorphisms in genes for several GST subclasses (GSTP1, GSTT1, GSTM1) and survival of patients with metastatic colorectal cancer receiving 5-fluorouracil (5-FU)/oxaliplatin chemotherapy. Methods: During 1998–2000, 107 previously treated patients with advanced colorectal cancer received 5-FU/oxaliplatin combination chemotherapy. Associations between deletion polymorphisms in GSTM1 and GSTT1 genes and between a polymorphism in the GSTP1 gene that generates an Ile 105 Val in the GSTP1 protein and survival were evaluated using relative risks (RRs) of dying and the log-rank test. All statistical tests were two-sided. Results: Patients heterozygous for the GSTP1 polymorphism had an RR = 0.47 (95% confidence interval [CI] = 0.27 to 0.81) compared with patients homozygous for the GSTP1 105 Ile allele. Patients homozygous for the mutant polymorphism had an RR = 0.16 (95% CI = 0.04 to 0.63). After adjustment for performance status and tumor site, the stratified RRs were 0.28 (95% CI = 0.07 to 1.10) for patients with two 105 Val alleles and 0.64 (95% CI = 0.36 to 1.16) for those with one 105 Val allele (P = .042). Patients with the 105 Val/ 105 Val genotype survived a median of 24.9 months, those with the 105 Ile/ 105 Ile genotype a median of 7.9 months, and those with the 105 Ile/ 105 Val genotype a median of 13.3 months (P<.001). The GSTM1 and GSTT1 genotypes were not associated with survival or clinical response. Conclusions: The GSTP1 Ile 105 Val polymorphism is associated in a dose-dependent fashion with increased survival of patients with advanced colorectal cancer receiving 5-FU/oxaliplatin chemotherapy. [J Natl Cancer Inst 2002;94:936–42]

/pdf/association-between-glutathione-s-transferase-p1-t1-and-m1-4bcupr15ue.pdf

Association Between Glutathione S-Transferase P1, T1, and M1 Genetic Polymorphism and Survival of Patients With Metastatic Colorectal Cancer

A multiplex polymerase chain reaction protocol for the simultaneous analysis of the glutathione S-transferase GSTM1 and GSTT1 polymorphisms.

Mammalian soluble and microsomal epoxide hydrolases have been proposed to belong to the family of alpha/beta-hydrolase-fold enzymes. These enzymes hydrolyse their substrates by a catalytic triad, with the first step of the enzymatic reaction being the formation of a covalent enzyme-substrate ester. In the present paper, we describe the direct visualization of the ester formation between rat microsomal epoxide hydrolase and its substrate. Microsomal epoxide hydrolase was precipitated with acetone after brief incubation with [1-(14)C]epoxystearic acid. After denaturing SDS gel electrophoresis the protein-bound radioactivity was detected by fluorography. Pure epoxide hydrolase and crude microsomes showed a single radioactive signal of the expected molecular mass that could be suppressed by inclusion of the competitive inhibitor 1,1,1-trichloropropene oxide in the incubation mixture. In a similar manner, 4-fluorochalcone-oxide-sensitive binding of epoxystearic acid to rat soluble epoxide hydrolase could be demonstrated in rat liver cytosol. Under similar conditions, no covalent binding of [26-(14)C]cholesterol-5alpha,6alpha-epoxide to microsomal proteins or solubilized fractions tenfold enriched in cholesterol epoxide hydrolase activity could be observed. Our data provide definitive proof for the formation of an enzyme-substrate-ester intermediate formed in the course of epoxide hydrolysis by microsomal epoxide hydrolase, show no formation of a covalent intermediate between cholesterol epoxide hydrolase and its substrate under the same conditions as those under which an intermediate was shown for both microsomal and soluble epoxide hydrolases and therefore indicate that the cholesterol epoxide hydrolase apparently does not act by a similar mechanism and is probably not structurally related to microsomal and soluble epoxide hydrolases.

https://ucanr.edu/sites/hammocklab/files/125194.pdf

Lars Winkler

Papers

A multiplex polymerase chain reaction protocol for the simultaneous analysis of the glutathione S-transferase GSTM1 and GSTT1 polymorphisms.

Visualization of a Covalent Intermediate between Microsomal Epoxide Hydrolase, but not Cholesterol Epoxide Hydrolase, and their Substrates