Epoxidation of cholesterol by hepatic microsomal lipid hydroperoxides

doi:10.1016/0006-291X(82)90889-0

Biochemical and Biophysical Research Communications

Volume 108, Issue 2, 30 September 1982, Pages 724-730

https://doi.org/10.1016/0006-291X(82)90889-0 Get rights and content

Abstract

[1,2-³H]Cholesterol was epoxidized to radioactive cholesterol α- and β-epoxides (5,6α-epoxy-5α- and 5,6β-epoxy-5β-cholestan-3β-ols) in the ratio 1:4 by hepatic microsomal lipid hydroperoxides (MsOOH, 1 mM as active oxygen) in the presence of ferrous ion. MsOOH could be replaced by methyl linoleate hydroperoxides (MOOH) under the same conditions although the latter was less effective than the former. None of cumene hydroperoxide, t-butyl hydroperoxide, and hydrogen peroxide was an effective oxidant even at 10 mM. Neither ADP nor EDTA had an effect on the epoxidation of cholesterol by MsOOH as well as by MOOH. Ferrous ion could not be replaced by ferric ion in the hydroperoxide-mediated epoxidation. Cyanide anion potentially inhibited the reaction.

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Citation Excerpt :
5,6 ECs were found to be produced in rat liver homogenates as a consequence of lipid peroxidation [53] with the 5,6β-EC being the major isomer formed [54]. It has been reported by several authors that lipoxygenase [35,36,54], myeloperoxidase [55] and heme oxygenase 1 [56] were involved in the endogenous production of 5,6-ECs. A stereospecific transformation of cholesterol into 5,6α-EC was reported in the microsomal fraction of the bovine adrenal cortex by Watabe and Sawata [42].
In the nineteen sixties it was proposed that cholesterol might be involved in the etiology of cancers and cholesterol oxidation products were suspected of being causative agents. Researchers had focused their attention on cholesterol-5,6-epoxides (5,6-ECs) based on several lines of evidence: 1) 5,6-ECs contained an oxirane group that was supposed to confer alkylating properties such as those observed for aliphatic and aromatic epoxides. 2) cholesterol-5,6-epoxide hydrolase (ChEH) was induced in pre-neoplastic lesions of skin from rats exposed to ultraviolet irradiations and ChEH was proposed to be involved in detoxification processes like other epoxide hydrolases. However, 5,6-ECs failed to induce carcinogenicity in rodents which ruled out a potent carcinogenic potential for 5,6-ECs. Meanwhile, clinical studies revealed an anomalous increase in the concentrations of 5,6β-EC in the nipple fluids of patients with pre-neoplastic breast lesions and in the blood of patients with endometrious cancers, suggesting that 5,6-ECs metabolism could be linked with cancer. Paradoxically, ChEH has been recently shown to be totally inhibited by therapeutic concentrations of tamoxifen (Tam), which is one of the main drugs used in the hormonotherapy and the chemoprevention of breast cancers. These data would suggest that the accumulation of 5,6-ECs could represent a risk factor, but we found that 5,6-ECs were involved in the induction of breast cancer cell differentiation and death induced by Tam suggesting a positive role of 5,6-ECs. These observations meant that the biochemistry and the metabolism of 5,6-ECs needed to be extensively studied. We will review the current knowledge and the future direction of 5,6-ECs chemistry, biochemistry, metabolism, and relationship with cancer.
Linoleic acid peroxidation - The dominant lipid peroxidation process in low density lipoprotein-and its relationship to chronic diseases
1998, Chemistry and Physics of Lipids
Modern separation and identification methods enable detailed insight in lipid peroxidation (LPO) processes. The following deductions can be made: (1) Cell injury activates enzymes: lipoxygenases generate lipid hydroperoxides (LOOHs), proteases liberate Fe ions—these two processes are prerequisites to produce radicals. (2) Radicals attack any activated CH₂-group of polyunsaturated fatty acids (PUFAs) with about a similar probability. Since linoleic acid (LA) is the most abundant PUFA in mammals, its LPO products dominate. (3) LOOHs are easily reduced in biological surroundings to corresponding hydroxy acids (LOHs). LOHs derived from LA, hydroxyoctadecadienoic acids (HODEs), surmount other markers of LPO. HODEs are of high physiological relevance. (4) In some diseases characterized by inflammation or cell injury HODEs are present in low density lipoproteins (LDL) at 10–100 higher concentration, compared to LDL from healthy individuals.
Subunit Ya-specific glutathione peroxidase activity toward cholesterol 7-hydroperoxides of glutathione S-transferases in cytosols from rat liver and skin
1997, Journal of Biological Chemistry
Dermal 7α- and 7β-hydroperoxycholest-5-en-3β-ols (cholesterol 7α- and 7β-hydroperoxides), regarded as good aging markers in the rat (Ozawa, N., Yamazaki, S., Chiba, K., Aoyama, H., Tomisawa, H., Tateishi, M., and Watabe, T. (1991) Biochem. Biophys. Res. Commun. 178, 242-247), were reduced in the presence of glutathione (GSH) with concomitant formation of GSSG by cytosol from rat liver in which no detectable level of the hydroperoxides had been demonstrated to occur. The GSH peroxidase (GSH Px) activity toward the toxic steroid hydroperoxides was exerted to almost the same extent by both Alpha-class GSH S-transferases (GSTs), Ya-Ya and Ya-Yc, and by selenium-containing GSH Px (Se-GSH Px) in rat liver cytosol. None of three Mu-class GSTs, Yb1-Yb1, Yb1-Yb2, and Yb2-Yb2, and a Theta-class GST, Yrs-Yrs, from rat liver and a Pi-class GST, Yp-Yp, from rat kidney showed any appreciable GSH Px activity toward the hydroperoxides. The subunit Ya-bearing GSTs and Se-GSH Px purified from rat liver cytosol showed marked differences in apparent specific activity toward the cholesterol hydroperoxides (GSTs Ya-Ya > Ya-Yc ≫ Se-GSH Px). However, a kinetic study indicated that Se-GSH Px had a higher affinity for steroid hydroperoxides than did the GSTs, so that Se-GSH Px could catalyze the reduction of lower concentrations of cholesterol 7-hydroperoxides with approximately equal V_max/K_m values to those by the GSTs. Rat skin had no GST bearing the subunit Ya but contained only a very low concentration of Se-GSH Px, possibly resulting in the accumulation of cholesterol 7-hydroperoxides in the skin but not in the liver. From rat skin cytosol, GSTs Yc-Yc, Yb1-Yb1, Yb1-Yb2, Yb2-Yb2, and Yp-Yp were isolated, purified to homogeneity, and identified with the corresponding GSTs from liver and kidney. The GSTs accounted for 0.23% of total skin cytosolic protein, and the most abundant isoform of skin GSTs was Yb2-Yb2, followed by Yc-Yc, Yp-Yp, Yb1-Yb1, and Yb1-Yb2 in decreasing order.
Comparison of the effects of cholesterol and oxysterols on phospholipid bilayer microheterogeneity: A study of fluorescence lifetime distributions
1994, Archives of Biochemistry and Biophysics
The homogenizing effect of cholesterol and its oxidative derivatives, 7-ketocholesterol, cholesterol 5α,6α-epoxide and 25-hydroxycholestero1, in liquid-crystalline 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayer vesicles was studied using the fluorescence lifetimes of 2-(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (DPH-PC). The phase and modulation data were fitted either to discrete exponential models or to models characterized by continuous distributional lifetimes. Among all the models tested, it was found that the best one to account for the experimental data was the unimodal Lorentzian distribution. Thus, the DPH-PC lifetime was adequately described by a distributional center and a full width at half-maximum, for DOPC vesicles these values being 6.23 and 0.48 ns, respectively. Increasing the concentration of cholesterol, 7-ketocholesterol, or cholesterol 5α,6α-epoxide from 0 to 30 mol% resulted in an increase of the lifetime center (e.g., 7.16 ns at 30 mol% cholesterol) and a decrease of the distributional width (e.g., 0.05 ns at 30 mol% cholesterol). On the other hand, up to 30 mol% of 25-hydroxycholesterol incorporated into the bilayer vesicles showed little influence on both lifetime parameters. Our results support the use of lifetime distributional width to evaluate membrane heterogeneity and suggest that oxysterols, depending on their molecular structural particulars, may exert cholesterol-like homogenizing effect in membranes.
Role of lipoxygenase in xenobiotic oxidation: Parathion metabolism catalyzed by highly purified soybean lipoxygenase
1991, Pesticide Biochemistry and Physiology
Earlier studies from this laboratory demonstrated that lipoxygenase catalyzes oxidation of a number of xenobiotics. This report presents data on the desulfuration and dearylation of parathion catalyzed by purified soybean lipoxygenase in the presence of linoleic acid. The formation of paraoxon was estimated from in vitro inhibition of acetylcholinesterse (electric eel) and further confirmed by using [¹⁴C]parathion. The metabolites paraoxon and p-nitrophenol were separated on thin layer chromatography and quantified by radiometry. The maximal rate of parathion metabolism occurred in the presence of 1.0 mM linoleic acid, 25.0 μM parathion, 20.0 nM enzyme at pH 8.0. The rate of desulfuration and dearylation reactions were dependent on incubation time, pH, linoleic acid, parathion, and enzyme concentration. Lipoxygenase inhibitors, like nor-dihydroguaiaretic acid and phenidone, significantly blocked the desulfuration and dearylation reactions. The turnover numbers (nmol product/min/nmol enzyme) were found to be 3.0 and 5.5 for paraoxon and p-nitrophenol, respectively. The rate of lipoxygenase-catalyzed parathion bioactivation was 3–20 times greater as compared to purified mammalian cytochrome P-450
Activation of deoxycholic acid by the lipid peroxy radical and its covalent binding to nucleic acids
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Deoxycholic acid, a colon tumor promoter, was found to bind covalently to DNA and RNA in the presence of methyl linoleate hydroperoxide and ferrous ion. This binding was shown to occur specifically with guanine residues and its covalent nature was demonstrated by analysis of hydrolysates of nucleic acid adducts. These findings are discussed in connection with the increased risk of colon cancer associated with a high fat and meat diet.

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Epoxidation of cholesterol by hepatic microsomal lipid hydroperoxides

Abstract

J. Lipid Res.

J. Lipid Res.

Biochem. Biophys. Res. Commun.

J. Biol. Chem.

J. Biol. Chem.

Tetrahedron Lett.

Cancer Res.

Lipids

Cancer

J. Chem. Soc., Chem. Commun.

Aus. J. Exp. Biol. Med. Sci.

Cancer Lett.

Lipids