F2-isoprostanes are bioactive prostaglandin (PG)-like compounds that are produced from arachidonic acid through a nonenzymatic process of lipid peroxidation catalyzed by oxygen free-radicals. 8-Epi-PGF2 alpha may amplify the platelet response to agonists, circulates in plasma, and is excreted in urine. We examined the hypothesis that the formation of 8-epi-PGF2 alpha is altered in patients with hypercholesterolemia and contributes to platelet activation in this setting. Urine samples were obtained from 40 hypercholesterolemic patients and 40 age- and sex-matched control subjects for measurement of immunoreactive 8-epi-PGF2 alpha. Urinary excretion of 11-dehydro-thromboxane (TX) B2, a major metabolite of TXA2, was measured as an in vivo index of platelet activation. Low-dose aspirin, indobufen, and vitamin E were used to investigate the mechanism of formation and effects of 8-epi-PGF2 alpha on platelet activation. Urinary 8-epi-PGF2 alpha was significantly (P = .0001) higher in hypercholesterolemic patients than in control subjects: 473 +/- 305 versus 205 +/- 95 pg/mg creatinine. Its rate of excretion was inversely related to the vitamin E content of LDL and showed a positive correlation with urinary 11-dehydro-TXB2. Urinary 8-epi-PGF2 alpha was unchanged after 2-week dosing with aspirin and indobufen despite complete suppression of TX metabolite excretion. Vitamin E supplementation was associated with dose-dependent reductions in both urinary 8-epi-PGF2 alpha and 11-dehydro-TXB2 by 34% to 36% and 47% to 58% at 100 and 600 mg daily, respectively. We conclude that the in vivo formation of the F2-isoprostane 8-epi-PGF2 alpha is enhanced in the vast majority of patients with hypercholesterolemia. This provides an aspirin-insensitive mechanism possibly linking lipid peroxidation to amplification of platelet activation in the setting of hypercholesterolemia. Dose-dependent suppression of enhanced 8-epi-PGF2 alpha formation by vitamin E supplementation may contribute to the beneficial effects of antioxidant treatment.
Populations that consume a diet rich in marine lipids may have a lower risk of atherosclerotic disease. Fish oil contains the N-3 polyunsaturated fatty acid eicosapentaenoate, and the biosynthesis of thromboxanes and prostacyclins from eicosapentaenoate (thromboxane A3 and prostaglandin I3), rather than from the usual precursor arachidonate (thromboxane A2 and prostaglandin I2), may help to reduce the risk. To examine this hypothesis, we studied the effect of eicosapentaenoate supplementation (10 g per day) for one month on the synthesis of thromboxanes and prostacyclins, as assessed by urinary metabolite excretion, in six patients with peripheral vascular disease and seven normal controls. Supplementation markedly increased the eicosapentaenoate content of phospholipids from red cells and platelets. Synthesis of the platelet agonist thromboxane A2, which was elevated in the patients at base line, declined by 58 percent during supplementation but did not reach normal values. The decline in thromboxane A2, which is synthesized from arachidonate, coincided with the formation of the inactive thromboxane A3, which is synthesized from eicosapentaenoate. A lower dose of eicosapentaenoate (1 g per day) was not sufficient to maintain the changes in thromboxane A2 synthesis. Platelet function was only moderately inhibited during eicosapentaenoate supplementation, consistent with incomplete suppression of thromboxane A2 synthesis. These studies show that a high dose of eicosapentaenoate alters the pattern of synthesis of thromboxanes and prostacyclins. However, effects comparable to those of aspirin require long-term administration in high doses. Whether other properties of fish oil might render it a more attractive antithrombotic therapy remains to be determined.
Objective-To better understand the role of lecithin:cholesterol acyltransferase (LCAT) in lipoprotein metabolism through the genetic and biochemical characterization of families carrying mutations in the LCAT gene. Methods and Results-Thirteen families carrying 17 different mutations in the LCAT gene were identified by Lipid Clinics and Departments of Nephrology throughout Italy. DNA analysis of 82 family members identified 15 carriers of 2 mutant LCAT alleles, 11 with familial LCAT deficiency (FLD) and 4 with fish-eye disease (FED). Forty-four individuals carried 1 mutant LCAT allele, and 23 had a normal genotype. Plasma unesterified cholesterol, unesterified/total cholesterol ratio, triglycerides, very-low-density lipoprotein cholesterol, and pre- high-density lipoprotein (LDL) were elevated, and high-density lipoprotein (HDL) cholesterol, apolipoprotein A-I, apolipoprotein A-II, apolipoprotein B, LpA-I, LpA-I:A-II, cholesterol esterification rate, LCAT activity and concentration, and LDL and HDL 3 particle size were reduced in a gene-dose-dependent manner in carriers of mutant LCAT alleles. No differences were found in the lipid/lipoprotein profile of FLD and FED cases, except for higher plasma unesterified cholesterol and unesterified/total cholesterol ratio in the former. Conclusion-In a large series of subjects carrying mutations in the LCAT gene, the inheritance of a mutated LCAT genotype causes a gene-dose-dependent alteration in the plasma lipid/lipoprotein profile, which is remarkably similar between subjects classified as FLD or FED. Key Words: familial lecithin:cholesterol acyltransferase deficiency Ⅲ fish eye disease Ⅲ high-density lipoproteins Ⅲ lecithin:cholesterol acyltransferase Ⅲ mutation T he lecithin:cholesterol acyltransferase (LCAT) (phosphatidylcholine:sterol-O-acyltransferase; EC 2.3.1.43) enzyme is responsible for the synthesis of cholesteryl esters (CE) in plasma. 1 Through this action, LCAT plays a central role in the formation and maturation of high-density lipoproteins (HDL), and in the intravascular stage of reverse cholesterol transport, the major mechanism by which HDL modulate the development and progression of atherosclerosis. A defect in LCAT function would be expected to enhance atherosclerosis by interfering with this process.The human LCAT gene encompasses 4.2 kilobases and is localized in the q21-22 region of chromosome 16. Methods SubjectsProbands with primary hypoalphalipoproteinemia (HALP), defined by a plasma HDL-C level below the fifth percentile for the age-and sex-matched general population, were identified by Lipid Clinics and Departments of Nephrology throughout Italy. Plasma samples were analyzed for total and unesterified cholesterol; in 18 unrelated index cases, the results were suggestive of a defect in the LCAT gene. Genetic analysis revealed that 13 of 18 index cases carried at least 1 mutant LCAT allele. Relatives of the 13 probands were invited to participate in the study. All subjects gave an informed consent. Blood samples were collected after an overni...
Supplementation with pharmacological doses of vitamin E has no detectable effects on lipid peroxidation and thromboxane biosynthesis in vivo in healthy subjects with a mild degree of oxidant stress. These findings are consistent with the hypothesis that the basal rate of lipid peroxidation is a major determinant of the response to vitamin E supplementation and have implications for the use of vitamin E in healthy subjects as well as for the design and interpretation of clinical trials of antioxidant intervention.
Background-Mutations in the LCAT
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