Analysis of plasma cholesterol oxidation products using gas- and high-performance liquid chromatography/mass spectrometry

Cholesterol is more readily oxidized than phospholipid linoleates in cell membranes to produce cholesterol hydroperoxides

Cholesterol is an essential component of cell membranes and serves as an important precursor of steroidal hormones and bile acids, but elevated levels of cholesterol and its oxidation products have been accepted as a risk factor for maintenance of health. The free and ester forms of cholesterol and fatty acids are the two major biological lipids. The aim of this hypothesis paper is to address the long-standing dogma that cholesterol is less susceptible to free radical peroxidation than polyunsaturated fatty acids (PUFAs). It has been observed that cholesterol is peroxidized much slower than PUFAs in plasma but that, contrary to expectations from chemical reactivity toward peroxyl radicals, cholesterol appears to be more readily autoxidized than linoleates in cell membranes. The levels of oxidation products of cholesterol and linoleates observed in humans support this notion. It is speculated that this discrepancy is ascribed to the fact that cholesterol and phospholipids bearing PUFAs are localized apart in raft and non-raft domains of cell membranes respectively and that the antioxidant vitamin E distributed predominantly in the non-raft domains cannot suppress the oxidation of cholesterol lying in raft domains which are relatively deficient in antioxidant.

Dietary phytochemicals in the protection against oxysterol-induced damage

The intake of fruits and vegetables is associated with reduced incidence of many chronic diseases. These foods contain phytochemicals that often possess antioxidant and free radical scavenging capacity and show anti-inflammatory action, which are also the basis of other bioactivities and health benefits, such as anticancer, anti-aging, and protective action for cardiovascular diseases, diabetes mellitus, obesity and neurodegenerative disorders. Many factors can be included in the etiopathogenesis of all of these multifactorial diseases that involve oxidative stress, inflammation and/or cell death processes, oxysterols, i.e. cholesterol oxidation products (COPs) as well as phytosterol oxidation products (POPs), among others. These oxidized lipids result from either spontaneous and/or enzymatic oxidation of cholesterol/phytosterols on the steroid nucleus or on the side chain and their critical roles in the pathophysiology of the abovementioned diseases has become increasingly evident. In this context, many studies investigated the potential of dietary phytochemicals (polyphenols, carotenoids and vitamins C and E, among others) to protect against oxysterol toxicity in various cell models mimicking pathophysiological conditions. This review, summarizing the mechanisms involved in the chemopreventive effect of phytochemicals against the injury by oxysterols may constitute a step forward to consider the importance of preventive strategies on a nutritional point of view to decrease the burden of many age-related chronic diseases.

p-TsOH-Catalyzed one-pot transformation of di- and trihydroxy steroids towards diverse A/B-ring oxo-functionalization

A milder, facile, and greener transformative protocol, specifically on solid supports, to yield A-ring and/or B-ring oxo-functionalized steroids has been accomplished.

Dietary indicaxanthin from cactus pear (Opuntia ficus-indicaL. Mill) fruit prevents eryptosis induced by oxysterols in a hypercholesterolaemia-relevant proportion and adhesion of human erythrocytes to endothelial cell layers

Toxic oxysterols in a hypercholesterolaemia-relevant proportion cause suicidal death of human erythrocytes or eryptosis. This process proceeds through early production of reactive oxygen species (ROS), release of prostaglandin (PGE2) and opening of PGE2-dependent Ca channels, membrane phosphatidylserine (PS) externalisation, and cell shrinkage. The present study was the first to reveal that a bioavailable phytochemical, indicaxanthin (Ind) from cactus pear fruit, in a concentration range (1·0–5·0 μM) consistent with its plasma level after a fruit meal, prevents PS externalisation and cell shrinkage in a dose-dependent manner when incubated with isolated healthy human erythrocytes exposed to an oxysterol mixture for 48 h. Dietary Ind inhibited ROS production, glutathione (GSH) depletion, PGE2 release and Ca2+entry. Ind alone did not modify the erythrocyte redox environment or affect other parameters.Ex vivospiking of normal human blood with the oxysterol mixture for 48 h induced eryptosis, resulting in the production of ROS and decreased levels of GSH, which was prevented by concurrent exposure to 5 μm-Ind. The adherence of eryptotic erythrocytes to the endothelium causes vascular tissue injury. Erythrocytes isolated from blood incubated with the oxysterol mixture plus 5 μm-Ind did not adhere to endothelial cell monolayers. Eryptotic erythrocytes may contribute to thrombotic complications in hypercholesterolaemia. Our findings suggest the positive effects of diets containing Ind on erythrocytes in hypercholesterolaemic subjects.

Quantitative detection of free 24S-hydroxycholesterol, and 27-hydroxycholesterol from human serum

Background

Cholesterol metabolism is important for the maintenance of myelin and neuronal membranes in the central nervous system. Blood concentrations of the brain specific cholesterol metabolite 24S-hydroxysterol to the peripheral metabolite 27-hydroxycholesterol may be useful surrogate markers for neurodegenerative diseases including Alzheimer’s disease, Huntington’s disease, HIV-Associated Neurocognitive Disorders, and Multiple Sclerosis. However, current methods to isolate hydroxycholesterols are labor intensive, prone to produce variable extraction efficiencies and do not discriminate between free and esterfied forms of hydroxycholesterols. Since free hydroxycholesterols are the biologically active form of these sterols, separating free from esterfied forms may provide a sensitive measure to identify disease-associated differences in brain sterol metabolism.

Results

We found that average human serum concentrations were 12.3 ± 4.79 ng/ml for free 24(s)-hydroxycholesterol and 17.7 ± 8.5 ng/ml for 27-hydroxycholesterol.

Conclusion

Serum measurements of these biologically active oxysterols may be useful surrogate measures for brain health in a variety of neurodegenerative conditions.

CD36-dependent 7-ketocholesterol accumulation in macrophages mediates progression of atherosclerosis in response to chronic air pollution exposure

RATIONALE

Air pollution exposure has been shown to potentiate plaque progression in humans and animals. Our previous studies have suggested a role for oxidized lipids in mediating adverse vascular effect of air pollution. However, the types of oxidized lipids formed in response to air pollutants and how this occurs and their relevance to atherosclerosis are not fully understood.

OBJECTIVE

To investigate the mechanisms by which particulate matter <2.5 μm (PM2.5) induces progression of atherosclerosis.

METHODS AND RESULTS

Atherosclerosis-prone ApoE(-/-) or LDLR(-/-) mice were exposed to filtered air or concentrated ambient PM2.5 using a versatile aerosol concentrator enrichment system for 6 months. PM2.5 increased 7-ketocholesterol (7-KCh), an oxidatively modified form of cholesterol, in plasma intermediate density lipoprotein/low-density lipoprotein fraction and in aortic plaque concomitant with progression of atherosclerosis and increased CD36 expression in plaque macrophages from PM2.5-exposed mice. Macrophages isolated from PM2.5-exposed mice displayed increased uptake of oxidized lipids without alterations in their efflux capacity. Consistent with these finding, CD36-positive macrophages displayed a heightened capacity for oxidized lipid uptake. Deficiency of CD36 on hematopoietic cells diminished the effect of air pollution on 7-KCh accumulation, foam cell formation, and atherosclerosis.

CONCLUSIONS

Our results suggest a potential role for CD36-mediated abnormal accumulations of oxidized lipids, such as 7-KCh, in air pollution-induced atherosclerosis progression.

The major cholesterol metabolite cholestane-3β,5α,6β-triol functions as an endogenous neuroprotectant

Overstimulation of NMDA-type glutamate receptors is believed to be responsible for neuronal death of the CNS in various disorders, including cerebral and spinal cord ischemia. However, the intrinsic and physiological mechanisms of modulation of these receptors are essentially unknown. Here we report that cholestane-3β,5α,6β-triol (triol), a major metabolite of cholesterol, is an endogenous neuroprotectant and protects against neuronal injury both in vitro and in vivo via negative modulation of NMDA receptors. Treatment of cultured neurons with triol protects against glutamate-induced neurotoxicity, and administration of triol significantly decreases neuronal injury after spinal cord ischemia in rabbits and transient focal cerebral ischemia in rats. An inducible elevation of triol is associated with ischemic preconditioning and subsequent neuroprotection in the spinal cord of rabbits. This neuroprotection is effectively abolished by preadministration of a specific inhibitor of triol synthesis. Physiological concentrations of triol attenuate [Ca(2+)]i induced by glutamate and decrease inward NMDA-mediated currents in cultured cortical neurons and HEK-293 cells transiently transfected with NR1/NR2B NMDA receptors. Saturable binding of [(3)H]triol to cerebellar granule neurons and displacement of [(3)H]MK-801 binding to NMDA receptors by triol suggest that direct blockade of NMDA receptors may underlie the neuroprotective properties. Our findings suggest that the naturally occurring oxysterol, the major cholesterol metabolite triol, functions as an endogenous neuroprotectant in vivo, which may provide novel insights into understanding and developing potential therapeutics for disorders in the CNS.

3β,5α,6β-Cholestanetriol and 25-hydroxycholesterol accumulate in ATP-binding cassette transporter G1 (ABCG1)-deficiency

OBJECTIVE

Oxysterols are oxidized derivatives of sterols that have cytotoxic effects and are potent regulators of diverse cellular functions. Efficient oxysterol removal by the sub-family G member 1 of the ATP-binding cassette transporters (ABCG1) is essential for cell survival and control of cellular processes. However, the specific role of ABCG1 in the transport of various oxysterol species has been not systematically investigated to date. Here, we examined the involvement of ABCG1 in the oxysterol metabolism by studying oxysterol tissue levels in a mouse model of Abcg1-deficiency.

METHODS AND RESULTS

Analysis of lung tissue of Abcg1(-/-) mice on a standard diet revealed that 3β,5α,6β-cholestanetriol (CT) and 25-hydroxycholesterol (HC) accumulated at more than 100-fold higher levels in comparison to wild-type mice. 24S-HC and 27-HC levels were also elevated, but were minor constituents. A radiolabeled assay employing regulable ABCG1-expressing HeLa cell lines revealed that 25-HC export to albumin was dependent on functional ABCG1 expression and could be blocked by an excess of unlabeled 25-HC or 27-HC. In this cell line, 25-HC at low doses triggered mitochondrial membrane potential, and reactive oxygen species production, which are both indirect indicators of cellular energy expenditure.

CONCLUSION

Our results suggest that 25-HC and CT are physiologic substrates for ABCG1. Excessive accumulation of these oxysterols may explain the increased rate of cell death and the inflammatory phenotype observed in Abcg1-deficient animals and cells.

Determination of 7-ketocholesterol in plasma by LC-MS for rapid diagnosis of acid SMase-deficient Niemann-Pick disease

Acid sphingomyelinase (ASMase)-deficient Niemann-Pick disease (NPD) is caused by mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene, resulting in accumulation of sphingomyelin in the lysosomes and secondary changes in cholesterol metabolism. We hypothesized that the oxidation product of cholesterol, 7-ketocholesterol (7-KC), might increase in the plasma of patients with ASMase-deficient NPD. In this study, a rapid and nonderivatized method of measurement of plasma 7-KC by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Plasma samples from healthy subjects, patients with ASMase-deficient NPD, nonaffected ASMase-deficient NPD heterozygotes, Niemann-Pick type C (NPC) disease, glycogen storage disorder type II (GSDII), Gaucher disease (GD), mucopolysaccharidosis type II (MPSII), Krabbe disease (KD), and metachromatic leukodystrophy (MLD) were tested retrospectively. Markedly elevated 7-KC was found in patients with ASMase-deficient NPD and NPC disease that showed significant differences from ASMase-deficient NPD heterozygotes; patients with GSDII, GD, MPSII, KD, and MLD; and normal controls. The analysis of plasma 7-KC by LC-MS/MS offers the first simple, quantitative, and highly sensitive method for detection of ASMase-deficient NPD and could be useful in the diagnosis of both ASMase-deficient NPD and NPC disease.

Derivatization-independent cholesterol analysis in crude lipid extracts by liquid chromatography/mass spectrometry: applications to a rabbit model for atherosclerosis

Direct measurement of various sterols in crude lipid extracts in a single experiment from limited biological samples is challenging. Current mass spectrometry (MS) based approaches usually require chemical derivatization before subjecting to MS analysis. Here, we present a derivatization-independent method for analyzing various sterols, including cholesterol and its congeners, using liquid chromatography and atmospheric pressure chemical ionization mass spectrometry. Based on the specific tandem mass spectrometry pattern of cholesterol, multiple reaction monitoring (MRM) transitions were used to quantify free cholesterol and its fatty acyl esters. Several cholesterol oxidation products could also be measured using the upfront liquid chromatography separation and specific MRM transitions. The method was validated alongside established enzymatic assays in measuring total cholesterol. As a proof of concept, we analyzed plasma sterols in rabbits administrated with a high cholesterol diet (HCD) which is a classical atherosclerotic model. Free cholesterol, cholesterol esters, 7-hydroxycholesterol, and 7-ketocholesterol were elevated in plasma of rabbits on HCD. This method could also serve as an excellent tool for quantitative analysis of other sterols such as ergosterol and sitosterol in other organisms beside mammalian. In Saccharomyces cerevisiae, our results indicated dramatic increases of the ratio of ergosterol esters to free ergosterol in both yeh2Δ and tgl1Δ cells, which are consistent with the function of the respective enzymes.

Advances in methods for the determination of biologically relevant lipid peroxidation products

Lipid peroxidation is recognized to be an important contributor to many chronic diseases, especially those of an inflammatory pathology. In addition to their value as markers of oxidative damage, lipid peroxidation products have also been shown to have a wide variety of biological and cell signalling effects. In view of this, accurate and sensitive methods for the measurement of lipid peroxidation products are essential. Although some assays have been described for many years, improvements in protocols are continually being reported and, with recent advances in instrumentation and technology, highly specialized and informative techniques are increasingly used. This article gives an overview of the most currently used methods and then addresses the recent advances in some specific approaches. The focus is on analysis of oxysterols, F(2)-isoprostanes and oxidized phospholipids by gas chromatography or liquid chromatography mass spectrometry techniques and immunoassays for the detection of 4-hydroxynonenal.

Rapid, direct analysis of cholesterol by charge labeling in reactive desorption electrospray ionization

Direct and rapid analysis of cholesterol was accomplished in the ambient environment using reactive desorption electrospray ionization (DESI) mass spectrometry. This was achieved by electrospraying reagent solutions in the form of high velocity charged droplets at surfaces such as dried serum samples and animal tissue sections. Betaine aldehyde, incorporated into the spray solvent, reacts selectively and rapidly with the alcohol group of cholesterol by nucleophilic addition, forming a hemiacetal salt. Limits of detection for pure cholesterol and related compounds were approximately 1 ng when a solution of cholesterol of 1 microg/mL was spotted onto the surface. Quantitative analysis of free cholesterol in serum using reactive DESI was demonstrated using cholesterol-d7 as internal standard. High throughput analysis of small volumes of serum spotted onto a suitable substrate was achieved at an analysis rate of approximately 14 s per sample, with a relative standard deviation (RSD) of ca. 6%. Use of reactive DESI in the imaging mode allowed 2D spatial distributions of phospholipids and cholesterol to be recorded simultaneously in rat brain tissues.

Cholesterol oxides inhibit cholesterol esterification by lecithin: cholesterol acyl transferase

Cholesterol oxides are atherogenic and can affect the activity of diverse important enzymes for the lipidic metabolism. The effect of 7β-hydroxycholesterol, 7-ketocholesterol, 25-hydroxycholesterol, cholestan-3β,5α,6β-triol,5,6β-epoxycholesterol, 5,6α-epoxycholesterol and 7α-hydroxycholesterol on esterification of cholesterol by lecithin:cholesterol acyl transferase (LCAT, EC 2.3.1.43) and the transfer of esters of cholesterol oxides from high density lipoprotein (HDL) to low density lipoproteins (LDL) and very low density lipoproteins (VLDL) by cholesteryl ester transfer protein (CETP) was investigated. HDL enriched with increasing concentrations of cholesterol oxides was incubated with fresh plasma as source of LCAT. Cholesterol and cholesterol oxides esterification was followed by measuring the consumption of respective free sterol and oxysterols. Measurements of cholesterol and cholesterol oxides were done by gas-chromatography. 14C-cholesterol oxides were incorporated into HDL2 and HDL3 subfractions and then incubated with fresh plasma containing LCAT and CETP. The transfer of cholesterol oxide esters was followed by measuring the 14C-cholesterol oxide-derived esters transferred to LDL and VLDL. All the cholesterol oxides studied were esterified by LCAT after incorporation into HDL particles, competing with cholesterol by LCAT. Cholesterol esterification by LCAT was inversely related to the cholesterol oxide concentration. The esterification of 14C-cholesterol oxides was higher in HDL3 and the transfer of the derived esters was greater from HDL2 to LDL and VLDL. The results suggest that cholesterol esterification by LCAT is inhibited in cholesterol oxide-enriched HDL particles. Moreover, the cholesterol oxides-derived esters are efficiently transferred to LDL and VLDL. Therefore, we suggest that cholesterol oxides may exert part of their atherogenic effect by inhibiting cholesterol esterification on the HDL surface and thereby disturbing reverse cholesterol transport.

Cholesterol, Linoleic Acid or/and Tyrosine Yield Different Spectra of Products when Oxidized Alone or in a Mixture: Studies in Various Oxidative Systems

Identification of reliable biomarkers for oxidative stress for the prediction of the early development of pathological conditions is essential. The detection of biomarkers for oxidative stress such as degradation products of polyunsaturated fatty acid (PUFA), oxysterols, and oxidized proteins, as indicators of oxidative stress are in use, but suffers from insufficient specificity, accuracy and reliability. The overall aim of the present study was to develop new markers which will not only provide information about the presence and level of oxidative stress in biological systems but also on the type of reactive oxygen species (ROS) involved and their metabolic consequences. In the first stage of the study, we compared the level and type of oxidized products formed when different ROS were applied onto three major biomolecules, i.e. cholesterol, linoleic acid (LH) and tyrosine, representing sterols, PUFA and protein, when each compounds was exposed alone or in a mixture to the ROS [copper ions, 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) and hypochlorous acid (HOCl)]. It was found that different types of oxidants resulted in the formation of different types of oxidation products. Furthermore, oxidation pattern differs when the substrates (cholesterol, PUFA or amino acid) were present alone or in a mixture. As biological systems such as lipoproteins and cell membranes are composed of the above studied molecules, the need for simultaneous detection of the major oxidized products is requires for better characterization of the oxidative stress outcome.

Biomarcadores de peroxidação lipídica na aterosclerose

A aterosclerose é caracterizada por uma resposta inflamatória crônica da parede arterial, iniciada por uma lesão do endotélio, cuja etiologia está relacionada à modificação oxidativa da lipoproteína de baixa densidade. O objetivo deste trabalho é apresentar os principais metabólitos envolvidos nos processos bioquímicos de peroxidação lipídica, discutindo as vantagens e desvantagens dos métodos empregados para a mensuração dos biomarcadores de peroxidação lipídica relacionados com a aterosclerose. A avaliação da oxidação das lipoproteínas pode ser realizada pela determinação dos produtos gerados durante a peroxidação lipídica, como os isoprostanos, hidroperóxidos lipídicos, aldeídos, fosfolípides oxidados e os produtos da oxidação do colesterol. A suscetibilidade das partículas de lipoproteína de baixa densidade à oxidação pode ser avaliada in vitro, após a indução da peroxidação lipídica por azoiniciadores radicalares lipossolúveis, hidrossolúveis, ou mais comumente, pelos íons cobre. Por outro lado, as modificações da lipoproteína de baixa densidade, pela ação das lipoxigenases e peroxidases, ou oxidação não-enzimática, resultam no aumento da carga negativa destas partículas e podem contribuir para a geração in vivo de uma subfração de lipoproteína de baixa densidade minimamente oxidada, denominada lipoproteína de baixa densidade eletronegativa (lipoproteína de baixa densidade). A determinação das concentrações desta partícula pode ser realizada em plasma por cromatografia líquida ou por imunoensaios..Diversos métodos podem ser utilizados para a avaliação dos biomarcadores de peroxidação lipídica in vivo e in vitro, porém, a definição do marcador mais adequado, depende de uma avaliação criteriosa das vantagens, desvantagens e particularidades de cada análise, levando-se em consideração os objetivos do estudo que será conduzido.

Shear stress influences spatial variations in vascular Mn-SOD expression: implication for LDL nitration

Fluid shear stress modulates vascular production of endothelial superoxide anion (O2*-) and nitric oxide (*NO). Whether the characteristics of shear stress influence the spatial variations in mitochondrial manganese superoxide dismutase (Mn-SOD) expression in vasculatures is not well defined. We constructed a three-dimensional computational fluid dynamics model simulating spatial variations in shear stress at the arterial bifurcation. In parallel, explants of arterial bifurcations were sectioned from the human left main coronary bifurcation and right coronary arteries for immunohistolocalization of Mn-SOD expression. We demonstrated that Mn-SOD staining was prominent in the pulsatile shear stress (PSS)-exposed and atheroprotective regions, but it was nearly absent in the oscillatory shear stress (OSS)-exposed regions and lateral wall of arterial bifurcation. In cultured bovine aortic endothelial cells, PSS at mean shear stress (tau ave) of 23 dyn/cm2 upregulated Mn-SOD mRNA expression at a higher level than did OSS at tau ave = 0.02 dyn/cm2 +/- 3.0 dyn.cm(-2).s(-1) and at 1 Hz (PSS by 11.3 +/- 0.4-fold vs. OSS by 5.0 +/- 0.5-fold vs. static condition; P < 0.05, n = 4). By liquid chromatography and tandem mass spectrometry, it was found that PSS decreased the extent of low-density lipoprotein (LDL) nitration, whereas OSS increased nitration (P < 0.05, n = 4). In the presence of LDL, treatment with Mn-SOD small interfering RNA increased intracellular nitrotyrosine level (P < 0.5, n = 4), a fingerprint for nitrotyrosine formation. Our findings indicate that shear stress in the atheroprone versus atheroprotective regions regulates spatial variations in mitochondrial Mn-SOD expression with an implication for modulating LDL nitration.

Lack of effect of oral supplementation with antioxidants on cholesterol oxidation product concentration of human plasma, as revealed by an improved gas chromatography method

A gas chromatographic method was successfully applied to determine cholesterol oxidation products (COPs) in human plasma. The linearity, precision, recovery and sensitivity of the method were determined. Oral supplementation with a combination of vitamin E (800 IU), C (1 g) and beta-carotene (24 mg), given for 21 days to 21 patients, did not significantly decrease plasma COP content. No correlations (n = 26) were found between initial plasma COP content and the following parameters: age, body mass index, plasma content of alpha-tocopherol, cholesterol, high-density lipoprotein cholesterol and triglycerides, and fat, natural antioxidant and oxidized lipid intake. Differences in plasma COP content between type 2 diabetic (n = 6) and nondiabetic (n = 20) patients were not statistically significant. The results from this study lead us to hypothesize that the nonenzymatic oxidation of cholesterol in plasma is negligible compared to COPs originating from the diet. This article also includes a comprehensive review of the drawbacks of the analytical methods of COP determination in plasma and serum.

Redox regulation of 7-ketocholesterol-induced apoptosis by beta-carotene in human macrophages

The aim of this study was to verify the hypothesis that beta-carotene may prevent 7-ketocholesterol (7-KC)-induced apoptosis in human macrophages. Therefore, THP-1 macrophages were exposed to 7-KC (5-50 microM) alone and in combination with beta-carotene (0.25-1 microM). 7-KC inhibited the growth of macrophages in a dose- and a time-dependent manner by inducing an arrest of cell cycle progression in the G0/G1 phase and apoptosis. Concomitantly, p53, p21, and Bax expressions were increased by 7-KC, whereas the levels of AKT, Bcl-2, and Bcl-xL were decreased. beta-Carotene prevented the growth-inhibitory effects of 7-KC in a dose- and time-dependent manner as well as the effects of 7-KC on the expression of cell cycle- and apoptosis-related proteins. 7-KC also enhanced reactive oxygen species (ROS) production through an increased expression of NAD(P)H oxidase (NOX-4). The effects of 7-KC were counteracted by the addition of the NAD(P)H oxidase inhibitor DPI or by cotransfection of siNOX-4 mRNA. beta-Carotene prevented 7-KC-induced increase in ROS production and in NOX-4 expression, as well as the phosphorylation of p38, JNK, and ERK1/2 induced by 7-KC. These data suggest a possible antiatherogenic role of beta-carotene through the prevention of 7-KC toxicity in human macrophages.

Levels of lipid peroxidation in human plasma and erythrocytes: comparison between fatty acids and cholesterol

Lipid peroxidation has gained renewed attention with increasing evidence showing its biological role in producing toxic compounds and cellular signaling mediators. The assessment of lipid peroxidation levels in vivo is difficult partly because lipids are oxidized by different oxidants by different mechanisms to give versatile types of products, which may undergo metabolism and secondary reactions. In the present study, total hydroxyoctadecadienoic acids (tHODE) and 7alpha- and 7beta-hydroxycholesterol (t7-OHCh) from 44 healthy human subjects were assessed as biomarkers after reduction with sodium borohydride followed by saponification with potassium hydroxide comparing with the prevailing standard 8-isoprostaglandin F(2alpha) (t8-iso-PGF(2alpha)). The average concentrations of tHODE, total 8-isoprostaglandin F(2alpha) (t8-iso-PGF(2alpha)), t7alpha-OHCh, and t7beta-OHCh were 203, 0.727, 87.1, and 156 nmol/l plasma and 1,917, 12.8, 1,372, and 3,854 nmol/l packed erythrocytes, respectively. The ratios of tHODE and t7-OHCh to the parent substrates were 194 and 3,519 micromol tHODE/mol linoleates and 40.9 and 686 micromol t7-OHCh/mol cholesterol in plasma and erythrocytes, respectively. It was found that (1) t7-OHCh in blood was unexpectedly high, as high as or even higher than tHODE, (2) the amounts of tHODE was more than 100 fold higher than t8-iso-PGF(2alpha) (3) the level of lipid oxidation products in erythrocytes was higher than that in plasma, and (4) lipid peroxidation products level tended to increase while antioxidant level decrease with age. These products may be used as potential biomarker for assessment of lipid peroxidation and oxidative stress in vivo.

Cholesterol oxides as biomarkers of oxidative stress in type 1 and type 2 diabetes mellitus

BACKGROUND

Oxidative stress plays an important role in the pathophysiology of diabetes mellitus. The aim of this study was to evaluate the formation of cholesterol oxides (ChOx) as biomarkers of oxidative stress in subjects with impaired glucose tolerance (IGT) and diabetes.

METHODS

Blood plasma levels of cholesterol oxidation products were determined in the following groups: type 1 diabetes mellitus (DM1), type 2 diabetes (DM2), impaired glucose tolerance (IGT), children without diabetes (C1) and adults without diabetes (C2). The serum levels of cholest-5-ene-3alpha,7alpha-diol (7alpha-hydroxycholesterol, 7alpha-OH), cholest-5-ene-3beta,7beta-diol (7beta-hydroxycholesterol, 7beta-OH), 3beta-hydroxycholest-5-7-one (7-ketocholesterol, 7-K), 5alpha-cholestane-3beta,5,6beta-triol (cholestanetriol), 5,6alpha-epoxy-5alpha-cholestan-3alpha-ol (cholesterol-5alpha,6alpha-epoxide,), 5,6beta-epoxy-5beta-cholestan-3beta-ol (cholesterol-5beta,6beta-epoxide) and cholest-5-eno-3beta,25-diol (25-hydroxycholesterol, 25-OH) (trivial name and abbreviations indicated in parentheses) were quantified by gas chromatography using flame ionization detection.

RESULTS

The levels of total ChOx were elevated in the DM1 and DM2 groups compared to age-matched subjects without diabetes (p < 0.05). The concentrations of 7beta-hydroxycholesterol, cholesterol-alpha-epoxide and cholesterol-beta-epoxide were higher in the blood plasma of subjects in the DM2 group than in the blood plasma of subjects in the C2 and IGT groups (p < 0.05). Treatment of type 2 diabetic patients with oral hypoglycemic drugs associated with insulin resulted in lower concentrations of nitrotyrosine in the blood plasma without significant changes in the concentrations of glucose and glycated hemoglobin. Moreover, combination with statins in both treatments decreased the concentrations of ChOx.

CONCLUSIONS

ChOx are suitable biomarkers of oxidative stress and may be useful in clinical studies to follow drug effects on lipid oxidative modifications in diabetic patients.

Characterization of oxysterols by electrospray ionization tandem mass spectrometry after one-step derivatization with dimethylglycine

We report a novel approach to derivatize the primary, secondary, and tertiary hydroxy group(s) of oxysterols with N,N-dimethylglycine (DMG) in the presence of both 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-(N,N-dimethylamino)pyridine to yield their corresponding mono- or di-DMG esters. Eight oxysterols including 7-oxocholesterol, 5alpha,6alpha- and 5beta,6beta-epoxycholesterols, as well as 7alpha-, 7beta-, 24(S)-, 25-, and 27-hydroxycholesterols, were studied. Electrospray ionization tandem mass spectrometric characterization of these singly or doubly protonated derivatives demonstrates the presence of an informative fragmentation pattern for each oxysterol derivative. Potential dissociation pathways for the production of these unique fragmentation patterns are proposed and discussed. Collectively, these informative and unique fragmentation patterns allow rapid and direct discrimination of the identities of 7alpha-, 7beta-, 24(S)-, 25-, and 27-hydroxycholesterol isomers, as well as 5alpha,6alpha- and 5beta,6beta-epoxycholesterol isomers, thereby potentially providing a foundation for quantitative analysis of oxysterols in biological samples in combination with a chromatographic separation.

Oxidative status of human low density lipoprotein isolated by anion-exchange high-performance liquid chromatography--assessment by total hydroxyoctadecadienoic acid, 7-hydroxycholesterol, and 8-iso-prostaglandin F(2alpha)

This study aims to measure the oxidative status of LDL from human plasma (n=26) as assessed by biomarkers for lipid peroxidation, total hydroxyoctadecadienoic acid (tHODE), 7alpha- and 7beta-hydroxycholesterol (t7-OHCh), and 8-iso-prostaglandin F(2alpha) (t8-iso-PGF(2alpha)) after subfractionation of LDL with an anion-exchange HPLC (AE-HPLC). LDL was separated and quantified by AE-HPLC as LDL-1, LDL-2, and LDL-3 in the order of the anionic charge of the LDL particles. The concentrations of tHODE, t7-OHCh, and t8-iso-PGF(2alpha) in both plasma and LDL subfractions were assessed after reduction and saponification. In this method, the free and ester forms of hydroperoxides, ketones, and hydroxides of linoleic acid and cholesterol are measured as tHODE and t7-OHCh, respectively. It was found that tHODE significantly correlated with the proportion of LDL-2 and LDL-3 as well as with the concentration of malondialdehyde-modified LDL in plasma. Further, by the analyses of LDL subfractions, the concentrations of tHODE, t8-iso-PGF(2alpha), and t7-OHCh in LDL-3 were found to be significantly higher than those in LDL-1 and LDL-2. These results clearly indicate that the extent of oxidation increases in the order of LDL-1<LDL-2<<LDL-3 and that the oxidative status of LDL in plasma can be quantitatively evaluated by using AE-HPLC and biomarkers, tHODE, t7-OHCh, and t8-iso-PGF(2alpha).

17beta-Estradiol reverses shear-stress-mediated low density lipoprotein modifications

Within arterial bifurcations or branching points, oscillatory shear stress (OSS) induces oxidative stress mainly via the reduced nicotinamide adenine dinucleodtide phosphate (NADPH) oxidase system. It is unknown whether 17beta-estradiol (E(2)) can regulate OSS-mediated low-density lipoprotein (LDL) modifications. Bovine aortic endothelial cells were pretreated with E(2) at 5 nmol/L, followed by exposure to OSS (0 +/- 3.0 dynes/cm(2) s and 60 cycles/min) in a flow system. E(2) decreased OSS-mediated NADPH oxidase mRNA expression, and E(2)-mediated (.-)NO production was mitigated by the NO synthase inhibitor N(G)-nitro-l-argenine methyl ester. The rates of O(2)(-.) production in response to OSS increased steadily as determined by superoxide-dismutase-inhibited ferricytochrome c reduction; whereas, pretreatment with E(2) decreased OSS-mediated O(2)(-.) production (n = 4, p < 0.05). In the presence of native LDL (50 microg/mL), E(2) also significantly reversed OSS-mediated LDL oxidation as determined by high-performance liquid chromatography. In the presence of O(2)(-.) donor, xanthine oxidase (XO), E(2) further reversed XO-induced LDL lipid peroxidation (n = 3, p < 0.001). Mass spectra acquired in the m/z 400-1800 range, revealed XO-mediated LDL protein nitration involving tyrosine 2535 in the alpha-2 domains, whereas pretreatment with E(2) reversed nitration, as supported by the changes in nitrotyrosine intensities. Thus, E(2) plays an indirect antioxidative role. In addition to upregulation of endothelial (.-)NO synthase and downregulation of Nox4 expression, E(2) influences LDL modifications via lipid peroxidation and protein nitration.

Contribution of mass spectrometry to assess quality of milk-based products

The vast knowledge of milk chemistry has been extensively used by the dairy manufacturing industry to develop and optimize the modern technology required to produce high-quality milk products to which we are accustomed. A thorough understanding of the chemistry of milk and its numerous components is essential for designing processing equipment and conditions needed for the manufacture and distribution of high-quality dairy products. Knowledge and application of milk chemistry is also indispensable for fractionating milk into its principal components for use as functional and nutritional ingredients by the food industry. For all these reasons, powerful analytical methods are required. Because of the complexity of the milk matrix, mass spectrometry, coupled or not to separation techniques, constitutes a key tool in this area. In the present manuscript, we review the contribution and potentialities of mass spectrometry-based techniques to assess quality of milk-based products.

Acyl-coenzyme A:cholesterol acyltransferase promotes oxidized LDL/oxysterol-induced apoptosis in macrophages

7-Ketocholesterol (7KC) is a cytotoxic component of oxidized low density lipoproteins (OxLDLs) and induces apoptosis in macrophages by a mechanism involving the activation of cytosolic phospholipase A2 (cPLA2). In the current study, we examined the role of ACAT in 7KC-induced and OxLDL-induced apoptosis in murine macrophages. An ACAT inhibitor, Sandoz 58-035, suppressed 7KC-induced apoptosis in P388D1 cells and both 7KC-induced and OxLDL-induced apoptosis in mouse peritoneal macrophages (MPMs). Furthermore, compared with wild-type MPMs, ACAT-1-deficient MPMs demonstrated significant resistance to both 7KC-induced and OxLDL-induced apoptosis. Macrophages treated with 7KC accumulated ACAT-derived [14C]cholesteryl and [3H]7-ketocholesteryl esters. Tandem LC-MS revealed that the 7KC esters contained primarily saturated and monounsaturated fatty acids. An inhibitor of cPLA2, arachidonyl trifluoromethyl ketone, prevented the accumulation of 7KC esters and inhibited 7KC-induced apoptosis in P388D1 cells. The decrease in 7KC ester accumulation produced by the inhibition of cPLA2 was reversed by supplementing with either oleic or arachidonic acid (AA); however, only AA supplementation restored the induction of apoptosis by 7KC. These results suggest that 7KC not only initiates the apoptosis pathway by activating cPLA2, as we have reported previously, but also participates in the downstream signaling pathway when esterified by ACAT to form 7KC-arachidonate.

Trojan horse-like behavior of a biologically representative mixture of oxysterols

Oxysterols, 27-carbon atoms cholesterol oxidation products, are consistently detectable in minimally oxidized low density lipoproteins (oxLDLs) and accumulate in the core of fibrotic plaques. Several oxysterols of pathophysiological interest have been shown to possess many and diverse biochemical activities. In particular, 7-ketocholesterol (7K), a major cholesterol oxide both in oxLDLs and in atherosclerotic lesions, is able to lead vascular cells to apoptosis. Indeed, when 7K is added to cells of the macrophage lineage, in a concentration range actually detectable in hypercholesterolemic patients, a marked apoptotic effect was observed. However, when identical concentrations of 7K are given to the same cells in a mixture with other oxysterols, also detectable in human low density lipoprotein (LDL), cell apoptosis was dramatically reduced. Of note, identical amounts of unoxidized cholesterol did not show any significant pro-apoptotic effect. With the aim to investigate the mechanisms underlying the quenching of 7K-dependent apoptosis by the oxysterol mixture, we found that the combined oxysterol mixture counteracted the ability of 7K given alone to strongly increase the steady-state level of reactive oxygen species (ROS) in macrophages as well as the up-regulation of the pro-apoptotic factor p21 and the triggering of the mitochondria-dependent pathway of apoptosis. Competition among oxysterols, apparently at NADPH oxidase level, diminishes the macrophage ROS production and direct toxicity that is evoked by defined oxysterols, as for instance, 7-ketocholesterol.

Determination of 24S- and 27-hydroxycholesterol in plasma by high-performance liquid chromatography-mass spectrometry

24S-Hydroxycholesterol (24S-OH-Chol) and 27-hydroxycholesterol (27-OH-Chol) are oxidized derivatives of cholesterol and of potential diagnostic interest because their circulating levels may reflect the cholesterol metabolism of the brain and macrophages, respectively. We developed a sensitive and specific HPLC-MS method for the quantification of 24S-OH-Chol and 27-OH-Chol in human plasma. In contrast to currently available procedures based on gas chromatography-mass spectrometry, this methodology offers the advantage that no time-consuming derivatization is needed. After saponification, solid-phase extraction, and HPLC separation under reversed-phase column conditions, detection by MS was performed using atmospheric pressure chemical ionization and selected ion monitoring mode. The standard curves were linear throughout the calibration range for both oxysterols. Within-day and between-day coefficients of variation were less than 9%, and the recoveries ranged between 98% and 103%. The quantification limits were 40 and 25 microg/l for 24S-OH-Chol and 27-OH-Chol, respectively. Mean values for both oxysterols were determined in plasma from 22 healthy volunteers. The sensitive and selective HPLC-MS method described here combined with the appropriate workup procedure allow the quantification of 24S-OH-Chol and 27-OH-Chol in plasma samples, for example in clinical studies to elaborate the clinical usefulness of these two oxysterols.

Oxysterol mixtures prevent proapoptotic effects of 7-ketocholesterol in macrophages: implications for proatherogenic gene modulation

Oxysterols are common components of oxidized low-density lipoprotein and accumulate in the core of fibrotic plaques as a mixture of cholesterol and cholesteryl ester oxidation products. The proapoptotic effects of a biologically representative mixture of oxysterols was compared with equimolar amounts of 7-ketocholesterol and unoxidized cholesterol. The oxysterol mixture in a concentration range actually detectable in hypercholesterolemic patients did not stimulate programmed cell death in cultivated murine macrophages. Unoxidized cholesterol also produced no effect. By contrast, when given alone, 7-ketocholesterol strongly stimulated the mitochondrial pathway of apoptosis with cytochrome c release, caspase-9 activation, and eventually caspase-3 activation. Subsequent experiments showed that when 7-ketocholesterol was administered to cells together with another oxysterol, namely 7betaOH-cholesterol, the strong proapoptotic effect of 7-ketocholesterol was markedly attenuated. As regards the mechanism underlying this quenching, we found that the combined oxysterol treatment counteracted the ability of 7-ketocholesterol, when administered alone, to strongly up-regulate the steady-state levels of reactive oxygen species (ROS) without interfering with sterol uptake. Furthermore, this increase in intracellular ROS appeared to be responsible for the up-regulation of proapoptotic factor, p21, after treatment with 7-ketocholesterol but not in cells challenged with the oxysterol mixture. Competition among oxysterols, apparently at the level of NADPH oxidase, diminishes the ROS induction and direct toxicity that is evoked by specific oxysterols. As a consequence, a more subtle gene modulation by oxysterols becomes facilitated in vascular cells.

Activation of microglial poly(ADP-ribose)-polymerase-1 by cholesterol breakdown products during neuroinflammation: a link between demyelination and neuronal damage

Multiple sclerosis (MS) is a chronic demyelinating disease in which it has only recently been suggested that damage to neuronal structures plays a key role. Here, we uncovered a link between the release of lipid breakdown products, found in the brain and cerebrospinal fluid (CSF) of MS patients as well as in experimental autoimmune encephalomyelitis, and neuronal damage mediated by microglial activation. The concentrations of the breakdown product 7-ketocholesterol detected in the CSF of MS patients were capable of inducing neuronal damage via the activation and migration of microglial cells in living brain tissue. 7-ketocholesterol rapidly entered the nucleus and activated poly(ADP-ribose)-polymerase (PARP)-1, followed by the expression of migration-regulating integrins CD11a and intercellular adhesion molecule 1. These findings reveal a novel mechanism linking demyelination and progressive neuronal damage, which might represent an underlying insidious process driving disease beyond a primary white matter phenomenon and rendering the microglial PARP-1 a possible antiinflammatory therapeutic target.

Pulsatile versus oscillatory shear stress regulates NADPH oxidase subunit expression: implication for native LDL oxidation

Shear stress regulates endothelial nitric oxide and superoxide (O2-*) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 microg/mL of native LDL were exposed to (1) pulsatile flow with a mean shear stress (tau(ave)) of 25 dyne/cm2 and (2) oscillating flow at tau(ave) of 0. After 4 hours, aliquots of culture medium were collected for high-performance liquid chromatography analyses of electronegative LDL species, described as LDL- and LDL2-. In response to oscillatory shear stress, gp91phox mRNA expression was upregulated by 2.9+/-0.3-fold, and its homologue, Nox4, by 3.9+/-0.9-fold (P<0.05, n=4), with a corresponding increase in O2-* production rate. The proportion of LDL- and LDL2- relative to static conditions increased by 67+/-17% and 30+/-7%, respectively, with the concomitant upregulation of monocyte chemoattractant protein-1 expression and increase in monocyte/BAEC binding (P<0.05, n=5). In contrast, pulsatile flow downregulated both gp91phox and Nox4 mRNA expression (by 1.8+/-0.2-fold and 3.0+/-0.12-fold, respectively), with an accompanying reduction in O2-* production, reduction in the extent of LDL modification (51+/-12% for LDL- and 30+/-7% for LDL2-), and monocyte/BAEC binding. The flow-dependent LDL oxidation is determined in part by the NADPH oxidase activity. The formation of modified LDL via O2-* production may also affect the regulation of monocyte chemoattractant protein-1 expression and monocyte/BAEC binding.

Oxysterols: friends, foes, or just fellow passengers?

Oxysterols are oxygenated derivatives of cholesterol that are intermediates or even end products in cholesterol excretion pathways. Because of their ability to pass cell membranes and the blood-brain barrier at a faster rate than cholesterol itself, they are also important as transport forms of cholesterol. In addition, oxysterols have been ascribed a number of important roles in connection with cholesterol turnover, atherosclerosis, apoptosis, necrosis, inflammation, immunosuppression, and the development of gallstones. According to current concepts, oxysterols are physiological mediators in connection with a number of cholesterol-induced metabolic effects. However, most of the evidence for this is still indirect, and there is a discrepancy between the documented potent effects of oxysterols under in vitro conditions and the studies demonstrating that they are of physiological importance in vivo. Oxysterol-binding proteins, such as liver X receptor-alpha (a nuclear receptor), do have a regulatory role in cholesterol turnover, but the physiological ligand of the protein has not yet been defined with certainty. Recently developed genetically engineered mouse models with markedly reduced or increased concentration of some of the oxysterols have exhibited surprisingly small changes in cholesterol turnover and homeostasis. The present review is a critical evaluation of the literature on oxysterols, in particular, the in vivo evidence for a role of oxysterols as physiological regulators of cholesterol homeostasis and as atherogenic factors.

Concentration of chosen oxycholesterols in plasma of pregnant women with pregnancy-induced hypertension

Solid-phase extraction (SPE) was applied for isolation of oxycholesterols from plasma lipid extract from pregnant women with hypertension and from a control group. Separation of oxycholesterols fraction was performed in an SD II horizontal chamber (Chromdes, Poland) using silica gel and octadecyl RPC18 silica gel TLC plates (Merck and Machery Nagel). Visualization was carried out under UV light after Liebermann-Burchard reaction specific for cholesterol and its derivatives. The oxycholesterols (5-cholestene-3beta-ol-7-one, sum of 5-cholestene-3beta, 7beta-diol and 5-cholestene-3beta, 7alpha-diol and sum of 5alpha,6alpha-epoxycholestan-3beta-ol and 5beta, 6beta-epoxycholestan-3beta-ol) were quantified by chromatograms scanning in reflectance and fluorescence mode using a CS 9301 densitometer (Shimadzu). The total concentration of the investigated oxycholesterols in the plasma of pregnant women was up to 5000 ng/mL and was statistically significantly higher in women with pregnancy induced hypertension (PIH).

Analysis of steroidal lipids by gas and liquid chromatography

This article describes the most commonly used procedures and recent laboratory methodologies using gas and liquid chromatography developed for separation and quantitation of non-saponifiable steroidal lipids from clinical (human) studies, edible fats and oils or fatty foods.

Selective distribution of oxysterols in atherosclerotic lesions and human plasma lipoproteins

The presence of oxidized sterols (oxysterols) in human serum and lesions has been linked to the initiation and progression of atherosclerosis. Data concerning the origin, identity and quantity of oxysterols in biological samples are controversial and inconsistent. This inconsistency may arise from different analytical methods or handling conditions used by different investigators. In the present study, oxysterol levels and distribution were analyzed by an optimized GC-MS method, in human atherosclerotic coronary and carotid lesions, in atherosclerotic apolipoprotein E deficient mice (E degrees mice) and in native and in vitro oxidized human low and high density lipoproteins. Oxysterol levels were analyzed with a limit of detection of 0.06 - 0.24 ng, with 25-hydroxycholesterol (25-OH) being the least sensitive. In human coronary and carotid lesions, obtained from endatherectomic samples, 27-hydroxycholesterol (27-OH) was the major oxysterol, with about 85% as sterols esterified to fatty acids. While total cholesterol and oxysterols levels were similar in both kinds of human lesions, oxysterol distribution was significantly different. In coronary lesions the mean levels of 27-OH and 7beta-hydroxycholesterol (7beta-OH) were 38% and 20% of total oxysterols, whereas in carotid lesions their mean levels were 66% and 5%, respectively. Unlike in human aortic lesions, 27-OH was entirely absent in E degrees mice, whereas the level of 7alpha-hydroxycholesterol (7alpha-OH) was 28% of the total oxysterols, vs. 5% in human coronary lesions. As 27-OH is an enzymatic product of cholesterol oxidation, this finding may indicate that such an enzymatic process does not take place in E degrees mice.

Determination of cholesterol oxides in processed food using high-performance liquid chromatography-mass spectrometry with atmospheric pressure chemical ionisation

The present work describes the development and application of an on-line atmospheric pressure ionisation (APCI) LC-MS interface for the simultaneous determination of seven toxicologically relevant cholesterol oxides (7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, 25-hydroxycholesterol, 7-ketocholesterol, 5,6alpha-, 5,6beta-epoxycholesterol and cholestan-3beta,5alpha,6beta-triol). The HPLC method has been optimised to reach better separation of all tested compounds. The influences of APCI parameters (nebulising temperature, cone voltage, source temperature) on signal intensity and fragmentation pattern were investigated for all tested cholesterol oxides compounds. This is the first report on optimisation and determination of two compounds 7alpha-hydroxycholesterol and 5,6beta-epoxycholesterol in processed food using LC-MS. After extraction with hexane, clean-up was carried out using solid-phase extraction on a silica column. For the chromatographic separation of cholesterol oxides an Aquasil C18 column was used with acetonitrile-methanol (60:40) as mobile phase. For the first time we report the use of such a C18 column with a relatively hydrophilic nature for the separation of cholesterol oxides. APCI-MS detection was then applied in selected ion monitoring and positive ion modes by using the molecular ions and the main fragments. The developed method shows good linearity, high repeatability and good recovery for all tested cholesterol oxides. The method was applied for determination of seven selected cholesterol oxidation products in different foodstuffs such as butter, butteroil, lard and egg powder.

Effect of oxidized cholesterol on age-associated changes to immune parameters in spleen lymphocytes and peritoneal exudate cells derived from rats

The effects of oxidized cholesterol on immune parameters were examined by using spleen lymphocytes and peritoneal exudate cells (PEC) derived from 5-week- (Young) and 9-month-old (Adult) rats. The immunoglobulin (Ig) G and IgM production was inhibited by oxidized cholesterol in the rats of both ages when lymphocytes were exposed to 30 micrograms/ml of oxidized cholesterol for 24 hr. The intracellular IgA level was also lowered by 30 micrograms/ml of oxidized cholesterol, irrespective of age. In contrast, IgE production was significantly increased by the addition of 30 micrograms/ml of oxidized cholesterol in only young lymphocytes. Moreover, oxidized cholesterol enhanced the intracellular histamine accumulation in only adult PEC, although the total histamine level produced by PEC was similar in the rats of both ages. These results thus suggest the possibility that oxidized cholesterol can have different effects on the age-related modulation of immune functions such as Igs production and histamine release.

The effect of vitamin E, probucol, and lovastatin on oxidative status and aortic fatty lesions in hyperlipidemic-diabetic hamsters

Diabetes mellitus is associated with an increased risk of premature atherosclerosis, which may be due in part to an increased rate of low density lipoprotein (LDL) oxidation. Previous studies have shown that vitamin E, probucol, and lovastatin can reduce the oxidative susceptibility of LDL in normoglycemic animal models; however, few studies have investigated this in conjunction with aortic fatty streak lesion formation in diabetic hyperlipidemic models. Forty-eight Syrian hamsters were made diabetic by intraperitoneal injection of low dose streptozotocin. Diabetic animals (12 animals/groups) received a high saturated fat and cholesterol diet for 12.5 weeks. At 2.5 week of dietary treatments, the diet was supplemented with either: (1) 500 IU/day vitamin E (D+E); (2) 1% probucol w/w of the diet (D+P); (3) 25 mg/kg lovastatin (D+L); or (4) diabetic control (D). An age-matched group of hamsters (n=6) receiving the same diet but not made diabetic (ND) was used as control. At the end of the study, aortic arch foam cell-rich fatty streak lesion, plasma glucose, total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), non-HDL-C, triglycerides (TG), phospholipids, alpha-tocopherol, plasma lipid peroxide and the susceptibility of LDL to copper-catalyzed oxidation were determined. Diabetes increased plasma glucose, and when combined with an atherogenic diet resulted in a further increase of plasma lipids. Vitamin E, probucol, and lovastatin significantly reduced plasma TG in the diabetic hamsters fed the atherogenic diet. Vitamin E treatment increased TC, probucol reduced HDL-C without affecting TC; whereas lovastatin reduced TC and selectively decreased non-HDL-C, and significantly reduced fatty streak lesion formation in the aortic arch. While vitamin E and probucol were effective in reducing several indices of oxidative stress including plasma lipid peroxides, cholesterol oxidation products and in vitro LDL oxidation, they had no effect on fatty streak lesion formation. Our results indicate that the LDL in diabetic animals is more susceptible to oxidation than in non-diabetic hamsters and that not only vitamin E and probucol but also lovastatin provide antioxidant protection. It appears that in this combined model of diabetes and hypercholesterolemia, progression of fatty streak lesion formation is mainly associated with changes in TC and non-HDL-C as affected by lovastatin, and is less dependent on the extent of LDL oxidation, changes in plasma TG level and oxidative stress status.

Lysosomal destabilization during macrophage damage induced by cholesterol oxidation products

We have previously shown that oxidized low-density lipoprotein (LDL) induces damage to the macrophage lysosomal membranes, with ensuing leakage of lysosomal contents and macrophage cell death. Cholesterol oxidation products (ChOx) have been reported to be the major cytotoxic components of oxidized LDL/LDL- and also to stimulate cholesterol accumulation in vascular cells. In the present study, we characterized the initial events during macrophage damage induced by cholesterol oxidation products (ChOx). Within 24 h of exposure, ChOx caused lysosomal destabilization, release to the cytosol of the lysosomal marker-enzyme cathepsin D, apoptosis, and postapoptotic necrosis. Enhanced autophagocytosis and chromatin margination was found 12 h after the exposure to ChOx, whereas apoptosis and postapoptotic necrosis was pronounced 24 and 48 h after the exposure. Some lysosomal vacuoles were then filled with degraded cellular organelles, indicating phagocytosis of apoptotic bodies by surviving cells. Because caspase-3 activation was detected in the ChOx-exposed cells, lysosomal destabilization may associate with the leakage of lysosomal enzymes, and activation of the caspase cascade. MnSOD mRNA levels were markedly increased after 24 h of exposure to ChOx, suggesting associated induction of mitochondrial protection repair or turnover. We conclude that ChOx-induced damage to lysosomes and mitochondria are sequelae to the cascade of oxysterol cytotoxic events. The early disruption of lysosomes induced by ChOx, with resultant autophagocytosis may be a critical event in apoptosis and/or necrosis of macrophages/foam cells during the development of atherosclerotic lesions.