Angiotoxicity and atherogenicity of cholesterol oxides

Association of Cholesterol and Oxysterols in Adipose Tissue With Obesity and Metabolic Syndrome Traits

OBJECTIVE

Adipose tissue stores a substantial amount of body cholesterol in humans. Obesity is associated with decreased concentrations of serum cholesterol. During weight gain, adipose tissue dysfunction might be one of the causes of metabolic syndrome. The aim of this study is to evaluate cholesterol storage and oxidized metabolites in adipose tissue and their relationship with metabolic clinical characteristics.

METHODS

Concentrations of cholesterol and oxysterols (27-hydroxycholesterol and 24S-hydroxycholesterol) in subcutaneous and visceral adipose tissue were determined by high-performance liquid chromatography with tandem mass spectrometry in 19 adult women with body mass index between 23 and 40 kg/m2 from the FAT expandability (FATe) study. Tissue concentration values were correlated with biochemical and clinical characteristics using nonparametric statistics.

RESULTS

Insulin correlated directly with 24S-hydroxycholesterol in both adipose tissues and with 27-hydroxycholesterol in visceral tissue. Leptin correlated directly with 24S-hydroxycholesterol in subcutaneous adipose tissue. Tissue cholesterol correlated directly with 27-hydroxycholesterol in both adipose tissues and with 24S-hydroxycholesterol in visceral tissue, where cholesterol correlation with 24S-hydroxycholesterol was higher than with 27-hydroxycholesterol. In addition, some tendencies were observed: serum high-density lipoprotein cholesterol tended to be inversely correlated with visceral adipose tissue cholesterol; high-sensitivity C-reactive protein tended to be correlated directly with subcutaneous adipose 24S-hydroxycholesterol and inversely with visceral 27-hydroxycholesterol.

CONCLUSIONS

Adipose tissue oxysterols are associated with blood insulin and insulin resistance. Tissue cholesterol correlated more with 27-hydroxycholesterol in subcutaneous adipose tissue and with 24S-hydroxycholesterol in visceral adipose tissue. Levels of adipose 24S-hydroxycholesterol seem to be correlated with some metabolic syndrome symptoms and inflammation while adipose 27-hydroxycholesterol could represent some protection against them.

Vitamin D toxicity related to its physiological and unphysiological supply

Vitamin D is defined as a nutrient despite its rare occurrence in food. Vitamin D status is determined mainly by solar UV light action in skin. However, the strategy to combat vitamin D deficiency has been to increase oral intake of vitamin D in greater amounts than could be obtained from food. Persistent large intakes of vitamin D can cause hypercalcaemic toxicity. Although the amounts recommended to prevent deficiency are far less than those causing such toxicity, the possibility of other toxic actions from increased intake of vitamin D has been ignored. Animal experiments have demonstrated that moderate amounts of oral vitamin D over time result in atherosclerosis. Differences in the fate of vitamin D could explain this angiotoxicity.

Effect of Linseed Supplementation on Total Longissimus Muscle Lipid Composition and Shelf-Life of Beef From Young Maremmana Bulls

Twenty young Maremmana bulls were randomly allotted to two dietary groups during a finishing period (~90 days): C diet (without lipid supplementation), and L diet (with linseed supplementation, 20% concentrate feed). The aim was to investigate the effects of dietary linseed supplementation on the intramuscular fat composition, and the shelf-life of minced beef. The L diet did not alter the dressing rate and daily weight gain, whereas the C18:3n-3 content in the intramuscular fat significantly increased (from 0.85 to 1.78 g/100 g of total fatty acid, +109%), leading to a reduction in a n-6/n-3 ratio below four and an increase in the overall proportion of long chain n-3 fatty acids in beef lipids. These effects were principally related to differences in the distribution of fatty acids between the neutral and polar lipids. The results demonstrated that linseed supplementation modified the lipid composition of beef, without negatively impacting overall productivity, in the period from weaning the bull until its slaughter. However, the total amount of n-3 fatty acids in the beef of young bulls on the L diet, was not sufficient for the aliquot of humans' n-3 fatty acid requirements. This was mainly related to the low levels of fat in the beef. Comparing beef samples from animals on the L diet, with samples from animals on the C diet, the higher levels of n-3 polyunsaturated fatty acids led to a significant reduction of shelf-life starting after 2 days of storage at 4°C, because of fatty acid and cholesterol oxidation. The L diet group samples showed a higher level of TBARS (+80%) and COPs (+73%), two important parameters to estimate the oxidation level of beef. This suggests that enriching beef with n-3 fatty acids should be coupled with packaging techniques that consider the higher susceptibility to lipid oxidation. In conclusion, dietary linseed supplementation led to a higher proportion of n-3 fatty acids in beef lipids, however, the natural content of antioxidant substances was not able to protect intramuscular fat from oxidation during storage at 4°C.

Current knowledge on the mechanism of atherosclerosis and pro-atherosclerotic properties of oxysterols

Due to the fact that one of the main causes of worldwide deaths are directly related to atherosclerosis, scientists are constantly looking for atherosclerotic factors, in an attempt to reduce prevalence of this disease. The most important known pro-atherosclerotic factors include: elevated levels of LDL, low HDL levels, obesity and overweight, diabetes, family history of coronary heart disease and cigarette smoking. Since finding oxidized forms of cholesterol – oxysterols – in lesion in the arteries, it has also been presumed they possess pro-atherosclerotic properties. The formation of oxysterols in the atherosclerosis lesions, as a result of LDL oxidation due to the inflammatory response of cells to mechanical stress, is confirmed. However, it is still unknown, what exactly oxysterols cause in connection with atherosclerosis, after gaining entry to the human body e.g., with food containing high amounts of cholesterol, after being heated. The in vivo studies should provide data to finally prove or disprove the thesis regarding the pro-atherosclerotic prosperities of oxysterols, yet despite dozens of available in vivo research some studies confirm such properties, other disprove them. In this article we present the current knowledge about the mechanism of formation of atherosclerotic lesions and we summarize available data on in vivo studies, which investigated whether oxysterols have properties to cause the formation and accelerate the progress of the disease. Additionally we will try to discuss why such different results were obtained in all in vivo studies.

Changes in the plasma membrane in metabolic disease: impact of the membrane environment on G protein-coupled receptor structure and function

Drug development targeting GPCRs often utilizes model heterologous cell expression systems, reflecting an implicit assumption that the membrane environment has little functional impact on these receptors or on their responsiveness to drugs. However, much recent data have illustrated that membrane components can have an important functional impact on intrinsic membrane proteins. This review is directed toward gaining a better understanding of the structure of the plasma membrane in health and disease, and how this organelle can influence GPCR structure, function and regulation. It is important to recognize that the membrane provides a potential mode of lateral allosteric regulation of GPCRs and can affect the effectiveness of drugs and their biological responses in various disease states, which can even vary among individuals across the population. The type 1 cholecystokinin receptor is reviewed as an exemplar of a class A GPCR that is affected in this way by changes in the plasma membrane.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Monitoring the formation of cholesterol oxidation products in model systems using response surface methodology

BACKGROUND

Cholesterol oxidation products (COPs) are produced during thermal processing of animal origin foods and are considered to have negative health impacts. The model systems are helpful to understand the impact of various factors on oxidation changes in foods during cooking process.

METHODS

The study presented herein investigates the effects of pH, presence of unsaturated fatty acids, and heat on the formation of cholesterol oxidation products (COPs). Two model systems were designed to investigate the formation of cholesterol oxidation products in different lipid environments. The cholesterol oxides produced were quantified using gas chromatography.

RESULTS

The level of cholesterol oxidation products decreased significantly at higher pH (above 5.8) and shorter heating time (3 h). The presence of unsaturated fatty acids (linoleic and oleic acids) significantly increased the amount of COPs under low-temperature heating conditions (100 °C and 1 h) but did not affect the production of COPs at higher temperature (150 °C). Increasing the temperature to 200 °C significantly increased the amount of COPs during the first hour of heating and this amount decreased upon further heating. The most frequently observed COPs in samples were α-epoxide, 20α-hydroxycholesterol, and 25-hydroxycholesterol.

CONCLUSIONS

In conclusion, pH below 5.8, presence of unsaturated fatty acid, and high cooking temperature (>150 °C) leads to increased production of cholesterol oxidation products.

Dietary olive cake reduces the oxidation of lipids, including cholesterol, in lamb meat enriched in polyunsaturated fatty acids

Over 40 days, lambs were fed: concentrate (C), concentrate containing 20% linseed (L), concentrate containing 35% olive cake (OC), or concentrate containing 10% linseed and 17% olive cake (OCL). The polyunsaturated fatty acids (PUFA) and peroxidation index (PI) in phospholipids were increased by the L and OCL treatments (P=0.007 and P=0.003, respectively). The OC and OCL diets increased the concentration of tocopherol in muscle (P<0.001). Compared to the OC and OCL diet, the L diet increased fatty acid oxidation, measured as conjugated dienes (CD; P=0.003), peroxides (PV; P<0.001) and TBARS (P=0.002) in minced muscle over 11 days of storage in high-oxygen atmosphere. Also, the L diet increased (P<0.001) the levels cholesterol oxidation products (COPs). In conclusion, feeding olive cake improved the oxidative stability of lamb meat and the combination of olive cake and linseed improved the fatty acid composition of meat without compromising its oxidative stability.

Hepatic function and lipid metabolism are modulated by short-term feeding of cholesterol oxidation products in rats

Dietary cholesterol oxidation products (COPs) modulate various metabolic processes, particularly lipid metabolism. In this study, we observed that dietary COPs perturbed hepatic function, linoleic acid desaturation, and cholesterol catabolism in rats that were fed with diets containing 0.5% COPs for a short duration (7 days). The rats (age, 8 weeks) were fed American Institute of Nutrition (AIN)-purified diets containing 0.5% cholesterol or 0.5% COPs for 7 days. The glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and lactate dehydrogenase (LDH) levels were significantly high in rats fed with dietary COPs, but no such increase was observed in rats fed with dietary cholesterol, thereby indicating that dietary COPs may impair the hepatic function. The mRNA expression levels of Delta6 desaturase in the liver were significantly increased by dietary COPs, while these levels were significantly decreased by dietary cholesterol. However, the mRNA expression level of cholesterol 7alpha-hydroxylase (CYP7A1) in the liver was significantly decreased by dietary COPs and significantly increased by dietary cholesterol. Therefore, dietary COPs may modulate lipid metabolic processes such as linoleic acid desaturation and cholesterol catabolism even when they are consumed for a short duration. Hence, processed animal foods containing COPs should be consumed with caution.

Oxysterols in heart failure

Oxysterols are biologically active molecules that result from the oxidation of cholesterol. Several oxysterols are found in macrophages and macrophage-derived 'foam cells' in atherosclerotic tissue. Lipophilic oxysterols penetrate cell membranes and, therefore, their concentrations can reach harmful levels in endothelial and smooth muscle cells located in close proximity to the atherosclerotic plaques or inflammatory zones. New findings suggest that the effects of oxysterols on cardiomyocytes can lead to cell hypertrophy and death. This may make oxysterols one of the major factors precipitating morbidity in atherosclerosis-induced cardiac diseases and inflammation-induced heart complications. The pathological actions of oxysterols on muscle cells were shown to depend on dysfunctional Ca(2+) signaling; however, the mechanisms of the effects remain to be elucidated. Understanding the effects of oxysterols could lead to therapies that modulate malfunction of cardiomyocytes. This review discusses the experimental findings and the relevance of oxysterols to heart failure, and suggests strategies for important future investigations.

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.

Oxysterols, cholesterol homeostasis, and Alzheimer disease

Aberrant cholesterol metabolism has been implicated in Alzheimer disease (AD) and other neurological disorders. Oxysterols and other cholesterol oxidation products are effective ligands of liver X activated receptor (LXR) nuclear receptors, major regulators of genes subserving cholesterol homeostasis. LXR receptors act as molecular sensors of cellular cholesterol concentrations and effectors of tissue cholesterol reduction. Following their interaction with oxysterols, activation of LXRs induces the expression of ATP-binding cassette, sub-family A member 1, a pivotal modulator of cholesterol efflux. The relative solubility of oxysterols facilitates lipid flux among brain compartments and egress across the blood-brain barrier. Oxysterol-mediated LXR activation induces local apoE biosynthesis (predominantly in astrocytes) further enhancing cholesterol re-distribution and removal. Activated LXRs invoke additional neuroprotective mechanisms, including induction of genes governing bile acid synthesis (sterol elimination pathway), apolipoprotein elaboration, and amyloid precursor protein processing. The latter translates into attenuated beta-amyloid production that may ameliorate amyloidogenic neurotoxicity in AD brain. Stress-induced up-regulation of the heme-degrading enzyme, heme oxygenase-1 in AD-affected astroglia may impact central lipid homeostasis by promoting the oxidation of cholesterol to a host of oxysterol intermediates. Synthetic oxysterol-mimetic drugs that activate LXR receptors within the CNS may provide novel therapeutics for management of AD and other neurological afflictions characterized by deranged tissue cholesterol homeostasis.

Oxyphytosterols are present in plasma of healthy human subjects

The oxidised derivatives of phytosterols (oxyphytosterols) were identified in plasma samples from thirteen healthy human volunteers, using MS. All the samples contained noticeable quantities of (24R)-5β,6β-epoxy-24-ethylcholestan-3β-ol (β-epoxysitostanol) and (24R)-ethylcholestan-3β,5α,6β-triol (sitostanetriol) and also trace levels of (24R)-5α,6α-epoxy-24-ethylcholestan-3β-ol (α-epoxysitostanol), (24R)-methylcholestan-3β,5α,6β-triol (campestanetriol) and (24R)-ethylch olest-5-en-3β-ol-7-one(7-ketositosterol). The amounts of these oxyphytosterols in plasma varied from 4·8 to 57·2 ng/ml. There are two possibilities concerning the origin of these compounds. First, they could come from the small amounts of oxyphytosterols in food. Second, they could originate from thein vivooxidation of phytosterols in plasma. Very few data actually exist concerning these compounds. Their identification in human samples suggests that further research is necessary in this field.

The effect of oxysterols, individually and as a representative mixture from food, on in vitro cultured bovine ovarian granulosa cells

The cytotoxicity of five oxysterols identified in cooked fish, 7-ketocholesterol, 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one, was investigated in primary cultures of bovine ovarian granulosa cells. Cells were exposed to the oxysterols individually and to a mixture of the same oxysterols for 24 h. Cell viability as determined by trypan blue exclusion and mitochondrial integrity (3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) reduction) was reduced by 0.5 and 2.5 microM 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one, but not by 0.5 or 2.5 microM 7-ketocholesterol under the same culture conditions. A mixture of 7-ketocholesterol, 7beta-hydroxycholesterol, cholesterol 5alpha,6alpha-epoxide, cholestanetriol and 4-cholesten-3-one 0.5 microM each; 2.5 microM oxysterol in total) did not change cell viability relative to controls. Lipid peroxidation, as determined by thiobarbituric acid reactive substances assay, was unaffected by a 24-hour exposure of granulosa cells to individual oxysterols but was increased slightly by the oxysterol mixture. The specific activities of antioxidant enzymes superoxide dismutase and catalase were increased to different extents (1.17- to 6.43-fold), relative to controls, by the administration of individual oxysterols and the oxysterol mixture. These results indicate that while some individual oxysterols can induce cytotoxic effects and defensive responses in bovine ovarian granulosa cells, administration of the same oxysterols as a mixture does not elicit the same responses. In addition, the oxysterols tested exerted a pro-apoptotic effect on granulosa cells when administered individually at concentrations of 0.5 and 2.5 microM, but not when administered as a 2.5 microM oxysterol mixture. The results suggest that major oxysterols are not universally cytotoxic, they may complete with other oxysterols for receptor sites, and that the simultaneous presence of several different oxysterol species may reduce the adverse effects of individual oxysterols.

Increase in cholesterol and cholesterol oxidation products, and role of cholesterol oxidation products in kainate-induced neuronal injury

Little is known about changes in sterols, in particular cholesterol, and cholesterol oxidation products (COPs) in oxidative injury in neural tissues. We have therefore examined changes in cholesterol and COPs using a model of excitotoxic injury. Intracerebroventricular injections of kainate in rats resulted in an increase in immunoreactivity to cholesterol in the affected CA fields of the hippocampus. The increase was confirmed by increased filipin staining of cholesterol in adjacent sections from the same animals, and in hippocampal slice or neuronal cultures after kainate treatment. In neuronal cultures, addition of lovastatin, an inhibitor of cholesterol synthesis, attenuated the increased filipin staining after kainate treatment, indicating that the increase in cholesterol could involve increased cholesterol synthesis. Furthermore, gas chromatographic mass spectrometric (GC/MS) analysis of cholesterol and COPs in kainate-injected rat brain showed a marked increase in cholesterol and COPs including 7-ketocholesterol, 3 days after kainate treatment. The addition of some COPs, including 7-ketocholesterol and cholesterol epoxides to hippocampal slices resulted in neuronal injury as reflected by decreased staining of a neuronal marker in the affected CA fields. The ability of these COPs to produce neuronal injury was attenuated by glutathione, suggesting that oxidative mechanisms are involved in neuronal injury induced by these products. These results, together with GC/MS results that showed significant increase in 7-ketocholesterol at 3 days post-kainate injury suggest that 7-ketocholesterol may be a factor in aggravating oxidative damage to neurons, after the initial stages of kainate-induced neuronal injury.

A new LC/APCI-MS method for the determination of cholesterol oxidation products in food

Cholesterol oxidation products (COPs) can be formed in the body or in animal foods from cholesterol during food processing. A new method for the extraction and quantification of cholesterol, 7-ketocholesterol, cholestane-3beta-5alpha-6beta-triol, 25-hydroxycholesterol, 5,6alpha-epoxycholesterol, and 7beta-hydroxycholesterol by means of reversed-phase LC/atmospheric pressure chemical ionization mass spectrometry is presented. A baseline separation of all COPs was achieved, allowing a separate quantification also for isobaric compounds. The limits of detection were 15-30 ng/mL, quantification was performed from 100 ng/mL to 10 microg/mL with RSD < 2%. The method was applied successfully to the determination of cholesterol and COPs in processed foods such as pork, beef, chicken, and egg.

Epoxide hydrolases: their roles and interactions with lipid metabolism

The epoxide hydrolases (EHs) are enzymes present in all living organisms, which transform epoxide containing lipids by the addition of water. In plants and animals, many of these lipid substrates have potent biologically activities, such as host defenses, control of development, regulation of inflammation and blood pressure. Thus the EHs have important and diverse biological roles with profound effects on the physiological state of the host organisms. Currently, seven distinct epoxide hydrolase sub-types are recognized in higher organisms. These include the plant soluble EHs, the mammalian soluble epoxide hydrolase, the hepoxilin hydrolase, leukotriene A4 hydrolase, the microsomal epoxide hydrolase, and the insect juvenile hormone epoxide hydrolase. While our understanding of these enzymes has progressed at different rates, here we discuss the current state of knowledge for each of these enzymes, along with a distillation of our current understanding of their endogenous roles. By reviewing the entire enzyme class together, both commonalities and discrepancies in our understanding are highlighted and important directions for future research pertaining to these enzymes are indicated.

Decreased membrane fluidity and altered susceptibility to peroxidation and lipid composition in overweight and obese female erythrocytes

The increased generation of reactive oxygen species that occurs in the condition of obesity may be responsible for oxidative injury to erythrocyte membranes, which could lead to a decrease in tissue oxygenation. Therefore, we have looked into the effects of obesity on both indexes of oxidative damage and physical-chemical properties of erythrocyte membranes in 50 overweight or obese [25 < body mass index (BMI) < 33], normotensive, nondiabetic women and 50 age-matched lean healthy women (BMI < 25). In the obese group compared with the lean group, we found that a) the onset of free radical-induced erythrocyte hemolysis and the ratio between reduced and oxidized glutathione were reduced, whereas the rate of free radical-induced damage increased; b) the n-3 fatty acid and the phospholipid contents decreased; c) the ratio between cholesterol and phospholipids increased; and d) the membrane fluidity decreased. These findings suggest an impairment of erythrocyte membrane physical-chemical properties in overweight and obese people as a consequence of oxidative injury that might be part of a pathogenetic mechanism responsible for obesity-related pathologies such as atherosclerosis and hypertension.

Oxidized products of cholesterol: dietary and metabolic origin, and proatherosclerotic effects (review)

Cholesterol oxidation products, termed oxysterols, are increasingly considered of potential interest in the pathogenesis of atherosclerotic lesions. Of dietary or endogenous origin, oxysterols may occur in significant amounts in low density lipoprotein (LDL) particles, especially in hypercholesterolemic subjects. They likely contribute to the uptake of modified LDL by scavenger receptors and some of them finally accumulate in the subintimal space of major arteries; here cholesterol oxides may favor the perpetuation of a chronic inflammatory state, through their ability to trigger irreversible damage of vascular cells with consequent activation of phagocytes. Furthermore, practically all oxysterols of major pathophysiologic interest have been shown to markedly up-regulate expression and synthesis of adhesion molecules, inflammatory cytokines and chemokines. Cholesterol oxidation thus appears to be an important biochemical pathway through which it exerts toxic, inflammatory and finally atherogenic effects.

High dietary iron concentrations enhance the formation of cholesterol oxidation products in the liver of adult rats fed salmon oil with minimal effects on antioxidant status

The aim of this study was to investigate the effect of high dietary iron concentrations on the antioxidant status of rats fed two different types of fat. Four groups of male adult Sprague-Dawley rats were fed diets with adequate (50 mg iron supplemented per kg diet) or high (500 mg iron supplemented per kg diet) iron concentrations with either lard or salmon oil as dietary fat at 100 g/kg for 12 wk. The antioxidant status of the rats was profoundly influenced by the type of fat. Rats fed salmon oil diets had higher concentrations of thiobarbituric acid-reactive substances (TBARS) (P < 0.001), various cholesterol oxidation products (COP) (P < 0.001), total and oxidized glutathione (P < 0.05) and a lower concentration of alpha-tocopherol (P < 0.05) in liver and plasma than rats fed lard diets. The iron concentration of the diet did not influence the concentrations of TBARS, the activities of superoxide dismutase and glutathione peroxidase or the concentration of alpha-tocopherol in plasma or liver. The activity of catalase (P < 0.01) and the concentrations of total, oxidized and reduced glutathione (P < 0.05) in liver were slightly but significantly higher in rats fed high iron diets than in rats fed adequate iron diets, irrespective of the dietary fat. Rats fed the high iron diets with salmon oil, moreover, had higher concentrations of various COP in the liver (P < 0.001) than rats fed adequate iron diets with salmon oil. These results suggest that feeding a high iron diet does not generally affect the antioxidant status of rats but enhances the formation of COP, particularly if the diet is rich in polyunsaturated fatty acids.

Molecular and biochemical characterization of a novel oxysterol-binding protein (OSBP2) highly expressed in retina

We are interested in understanding the possible function(s) of the oxysterol-binding proteins in mediating oxysterol cytotoxicity in the retina. In this study we describe the cloning, localization, and biological activity of a novel oxysterol-binding protein (OSBP2), and complete the molecular characterization of the previously known OSBP1. Both OSBP genes contain 14 exons and have similar exon sizes and splice sites suggesting they may have arisen from a gene duplication event. OSBP1 is located in chromosome 11q12.1, and OSBP2 is located in 22q12. At the protein level they share 63% overall similarity and although they have unique N termini, both have similar pleckstrin homology domains within the N terminus region. Northern blot analyses indicate that OSBP1 is broadly expressed in human and monkey tissues. OSBP2 is detected mainly in retina, testis, and fetal liver. Western blot analysis using peptide antibodies specific to OSBP1 and OSBP2 detected the proteins in different subcellular fractions in the retinal monkey tissue. OSBP1 is detected mainly in the soluble or cytosolic fraction and nuclei whereas OSBP2 is detected exclusively in the detergent soluble fraction suggesting association with membranes. Immunohistochemical localization of OSBP1 and OSBP2 in the monkey retina placed these two proteins in similar but distinct areas of the inner retina. OSBP2 was found to bind 7-ketocholesterol but to have very little affinity for cholesterol or 25-hydroxycholesterol.

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.

Tea catechins inhibit cholesterol oxidation accompanying oxidation of low density lipoprotein in vitro

Endogenous oxidized cholesterols are potent atherogenic agents. Therefore, the antioxidative effects of green tea catechins (GTC) against cholesterol oxidation were examined in an in vitro lipoprotein oxidation system. The antioxidative potency of GTC against copper catalyzed LDL oxidation was in the decreasing order (-)-epigalocatechin gallate (EGCG)=(-)-epicatechin gallate (ECG)>(-)-epicatechin (EC)=(+)-catechin (C)>(-)-epigallocatechin (EGC). Reflecting these activities, both EGCG (74%) and ECG (70%) inhibited the formation of oxidized cholesterol, as well as the decrease of linoleic and arachidonic acids, in copper catalyzed LDL oxidation. The formation of oxidized cholesterol in 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH)-mediated oxidation of rat plasma was also inhibited when the rats were given diets containing 0.5% ECG or EGCG. In addition, EGCG and ECG highly inhibited oxygen consumption and formation of conjugated dienes in AAPH-mediated linoleic acid peroxidative reaction. These two species of catechin also markedly lowered the generation of hydroxyl radical and superoxide anion. Thus, GTC, especially ECG and EGCG, seem to inhibit cholesterol oxidation in LDL by combination of interference with PUFA oxidation, the reduction and scavenging of copper ion, hydroxyl radical generated from peroxidation of PUFA and superoxide anion.

Involvement of oxysterols and lysophosphatidylcholine in the oxidized LDL-induced impairment of serum albumin synthesis by HEPG2 cells

Oxidized low density lipoproteins (Ox-LDLs) are increasingly thought to be a key element in atherogenesis. We have previously reported that serum albumin has important antioxidant properties and that a reduced synthesis of albumin may represent a crucial point in the overall antioxidant defense. In the present work, we aimed at determining whether Ox-LDL could modulate albumin synthesis in cultured human hepatocytes (HepG2 cells). With the use of enzyme immunoassay and radiolabeled leucine incorporation followed by specific immunoprecipitation, Ox-LDL was found to lead to a dose-dependent decrease in albumin secretion. Moreover, the protein synthesis and mRNA levels were decreased in the presence of Ox-LDL, as assessed by Northern blot analysis. Because oxysterols and lysophospholipids are key components of Ox-LDL, we tested the effects of oxysterols (7-ketocholesterol and 25-hydroxycholesterol) and lysophosphatidylcholine on albumin secretion and expression. In our experimental conditions, we found that incubations with oxysterols or lysophosphatidylcholine at pathophysiological concentrations similar to those measured in Ox-LDLs reproduced the above-mentioned inhibitory effects on albumin synthesis. On the basis of our in vitro data, we propose that this newly described biological effect of Ox-LDL might partly explain the findings of epidemiological studies indicating that reduced levels of serum albumin are associated with increased mortality.

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.

Cholesterol-rich diets have different effects on lipid peroxidation, cholesterol oxides, and antioxidant enzymes in rats and rabbits

The objective of this study was to compare the effect of cholesterol feeding of rats and rabbits. The levels of lipid peroxidation products and oxysterols in the plasma of the two species plus the antioxidant enzyme activities in the liver and erythrocytes were measured to explain their different susceptibilities to atherosclerosis. Our study showed that rats are less susceptible than are rabbits to the atherogenic effect of a cholesterol-rich diet because of differences in lipid peroxidation products as well as antioxidant enzymes activities in their livers. In rabbits, cholesterol feeding produced severe hypercholesterolemia (43-fold increase) and increased plasma and liver lipid peroxidation. Total as well as the individual oxysterol contents of 7alpha-, 7beta-hydroxycholesterol, alpha-epoxy, beta-epoxycholesterol, cholestanetriol, 7-keto, and 27-hydroxycholesterol significantly increased in the plasma of hypercholesterolemic (HC) rabbits. Erythrocyte glutathione peroxidase (GSH-Px) activity significantly decreased whereas catalase activity significantly increased in HC rabbits. In rats cholesterol feeding increased the plasma cholesterol only twofold and had no effect on plasma or liver lipid peroxidation. Only 7alpha- and 7beta-hydroxycholesterol increased and no change was observed in any of the antioxidant enzymes activity in the erythrocytes. Although cholesterol feeding caused a 10-fold increase of liver cholesterol as ester in both rats and rabbits, the antioxidant enzyme GSH-Px and catalase activities in the liver significantly increased in rats but significantly decreased in rabbits. The increase of GSH-Px and catalase activities in the liver of cholesterol fed rats could have a protective role against oxidation, thus preventing the formation of lipid peroxidation and oxysterols.

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.

Effects of dietary protein type on oxidized cholesterol-induced alteration in age-related modulation of lipid metabolism and indices of immune function in rats

Exogenous oxidized cholesterol disturbs both lipid metabolism and immune functions. Therefore, it may perturb these modulations with ageing. Effects of the dietary protein type on oxidized cholesterol-induced modulations of age-related changes in lipid metabolism and immune function was examined using differently aged (4 weeks versus 8 months) male Sprague-Dawley rats when casein, soybean protein or milk whey protein isolate (WPI) was the dietary protein source, respectively. The rats were given one of the three proteins in diet containing 0.2% oxidized cholesterols mixture. Soybean protein, as compared with the other two proteins, significantly lowered both the serum thiobarbituric acid reactive substances value and cholesterol, whereas it elevated the ratio of high density lipoprotein-cholesterol/cholesterol in young rats, but not in adult. Moreover, soybean protein, but not casein and WPI, suppressed the elevation of Delta6 desaturation indices of phospholipids in both liver and spleen, particularly in young. On the other hand, WPI, compared to the other two proteins, inhibited the leukotriene B4 production of spleen, irrespective of age. Soybean protein reduced the ratio of CD4(+)/CD8(+) T-cells in splenic lymphocytes. Therefore, the levels of immunoglobulin (Ig)A, IgE and IgG in serum were lowered in rats given soybean protein in both age groups except for IgA in adult, although these observations were not shown in rats given other proteins. Thus, various perturbations of lipid metabolism and immune function caused by oxidized cholesterol were modified depending on the type of dietary protein. The moderation by soybean protein on the change of lipid metabolism seems to be susceptible in young rats whose homeostatic ability is immature. These observations may be exerted through both the promotion of oxidized cholesterol excretion to feces and the change of hormonal release, while WPI may suppress the disturbance of immune function by oxidized cholesterol in both ages. This alleviation may be associated with a large amount of lactoglobulin in WPI. These results thus showed a possibility that oxidized cholesterol-induced perturbations of age-related changes of lipid metabolism and immune function can be moderated by both the selection and combination of dietary protein.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Oxysterols from oxidized LDL are cytotoxic but fail to induce hsp70 expression in endothelial cells

Oxidized low density lipoprotein (OxLDL) possesses several proatherogenic characteristics, among which a marked cytotoxicity. In vitro, cytotoxicity of OxLDL to endothelial cells is associated with an increase in the expression of the inducible form of heat shock protein 70 (hsp70), generally regarded as a cytoprotective protein. Oxidized derivatives of cholesterol which form upon LDL oxidation are cytotoxic. Moreover, most of the OxLDL cytotoxicity is due to its lipid moiety, in particular to oxysterols. In this report we demonstrate that although oxysterols identified in OxLDL are cytotoxic, they cannot trigger the increase in hsp70 expression observed with intact oxidized lipoproteins. We speculate therefore that oxysterols may represent the most toxic form of oxidized lipids in LDL because they cannot activate a rescue mechanism (i.e. the hsp response) and may contribute significantly to cell death within atherosclerotic plaques.

Cholesterol oxidation products induce vascular foam cell lesion formation in hypercholesterolemic New Zealand white rabbits

Circulating cholesterol oxidation products (ChOx) have long been implicated in the etiology of early atherosclerosis; however, direct in vivo evidence elucidating their role in atherogenesis is only recently becoming available. This study investigated ChOx effects on vascular lesion formation in New Zealand White rabbits under controlled hypercholesterolemic conditions. By closely monitoring plasma cholesterol levels and adjusting dietary cholesterol intake during a 78-day period, total plasma cholesterol exposures (cumulative plasma cholesterol levels over time) were controlled between 27 000 and 34 000 mg/dLxday (final plasma cholesterol concentration, 467+/-77 mg/mL), representing a threshold range for sudanophilic lesion formation in the aorta. Twenty injections of a ChOx mixture (70 mg per injection) were made bearing an oxysterol composition similar to that found in circulating oxidatively modified low density lipoprotein. At sacrifice, the ChOx-injected rabbits (n=5) had (1) significantly higher plasma ChOx levels, (2) significantly increased cholesterol content in the aortas, mainly as esterified cholesterol, and (3) significantly greater sudanophilic lesion size and frequency in the aortas compared with vehicle-injected control rabbits (n=5). The aortic cholesterol content and extent of sudanophilic lesion area were correlated significantly with total plasma ChOx exposure (P<0.003 and P<0.0001, respectively) but not with total cholesterol exposure. The results indicate that for moderate experimental hypercholesterolemia, a situation more relevant to physiological hypercholesterolemia in humans, circulating ChOx may play an important role in inducing formation of early atherosclerotic lesions. Because ChOx are often present in cholesterol-containing diets, foam cell lesion formation induced by ChOx rather than cholesterol cannot be overlooked.

Oxidant stress: the role of nutrients in cell-lipoprotein interactions

Oxidant stress is increasingly becoming an important hypothesis to explain the genesis of several pathologies, including cancer, atherosclerosis and also ageing. Beside a few rare genetic defects, dietary factors are thought to play a key role in the regulation of the production of reactive oxygenated species. An imbalance between nutrients, and in particular those involved in antioxidant status, could explain the onset of an enhanced production of free radicals. We will briefly review information concerning oxidation of lipids and lipoproteins which lead to atherothrombosis. We also present new findings supporting a role for blood platelets in generating oxidant species. New data are also described concerning the role of oxygenated derivatives of cholesterol, oxysterols, in cellular cholesterol efflux and NO production. Also, new developments relating to the influence of direct effects of free radicals on cellular cholesterol homeostasis are presented. Finally, the in vitro effects of butyrate, a natural short-chain fatty acid produced by bacterial fermentation, in the protection against free radical-mediated cytotoxicity are discussed. These data provide information on the mechanisms of dietary antioxidants in preventing oxidant stress.

Lymphatic absorption of phytosterol oxides in rats

Two of the main classes of oxyphytosterols (7-keto and epoxides) were synthesized from sitosterol and campesterol and given to mesenteric duct-cannulated adult male rats. Lymph was collected during 24 h and was analyzed for oxysterols. The results showed that the lymphatic recovery of the phytosterol oxides was low: 4.7% of the given dose for epoxy derivatives and 1.5% for 7-keto compounds. The campesterol oxides presented a better absorption than the sitosterol oxides. During the process of absorption, the epoxyphytostanols were also partly transformed in campestanetriol and stigmastanetriol.

Cholesterol oxidation in meat from chickens fed alpha-tocopherol- and beta-carotene-supplemented diets with different unsaturation grades

The production of B-ring and side-chain oxysterols was evaluated in meat from chickens fed diets differing by the kind of oil or fat added. The effect of supplementary levels of natural antioxidants, as alpha-tocopherol and beta-carotene, on the meat cholesterol oxidative stability was also studied. Lard, sunflower and olive oil were used as dietary fat. Raw and cooked meats were analyzed for oxysterols, and cholesterol was also quantified. Oxysterol analyses were carried out by combining the use of solid-phase extraction, thin-layer chromatography, capillary gas chromatography, and capillary gas chromatography-mass spectrometry. Oxysterols were detected within the 0.1-0.5 microg/g range in raw meat. Cooking increased the oxysterol content of the meat, and levels as high as 5 microg/g muscle tissue were observed. B-Ring oxysterols were mainly produced: the alpha- and the beta-epoxycholesterols, the 7alpha- and 7beta-hydroxycholesterols, and the 7-ketocholesterol. The results showed that the meat from the chickens fed the olive oil-based diet containing alpha-tocopherol at 200 mg/kg of diet presented the best cholesterol oxidative stability. A positive effect could not be found for dietary beta-carotene administered at levels of 15 and 50 mg/kg of diet. Furthermore, a significant decrease in the tissue cholesterol content was observed with the olive and the sunflower oil-based diets.

Modulation of cholestane-3 beta,5 alpha,6 beta-triol toxicity by butylated hydroxytoluene, alpha-tocopherol and beta-carotene in newborn rat kidney cells in vitro

Cholesterol oxidation products (COP) have been reported to influence vital cellular processes such as cell growth, cell proliferation, membrane function and de novo sterol biosynthesis. The objectives of the present study were: (1) to develop an in vitro model using newborn rat kidney (NRK) cells to investigate the actions of COP; (2) to investigate the effect of COP on cell viability, endogenous antioxidant enzymes activities, i.e. superoxide dismutase (EC 1.15.1.1; SOD) and catalase (EC 1.11.1.6; CAT), and the extent of lipid peroxidation in this model; (3) to determine whether the addition of 100-1000 nM-alpha-tocopherol, beta-carotene or butylated hydroxytoluene (BHT) could protect against COP-induced cytotoxicity. NRK cells were cultured in the presence of various concentrations (5-50 microM) of cholesterol or cholestane-3 beta,5 alpha,6 beta-triol (cholestantriol) for a period of 24 h. Cholesterol over the range 5-50 microM did not induce cytotoxicity as indicated by the neutral-red-uptake assay or the lactate dehydrogenase (EC 1.1.1.27)-release assay. However, cell viability was compromised by the addition of > 10 microM-cholestantriol (P < 0.05). The addition of beta-carotene (100-1000 nM) did not increase cell viability significantly in cholestantriol-supplemented cells. However, the addition of alpha-tocopherol (1000 nM) and BHT (1000 nM) significantly increased percentage cell viability above that of the cholestantriol-supplemented cells but not back to control levels. SOD and CAT activities in NRK cells significantly decreased (P < 0.05) following incubation with cholestantriol. The addition of > 750 nM-alpha-tocopherol, beta-carotene or BHT returned SOD and CAT activities to that of the control. Lipid peroxidation was significantly induced (P < 0.05) in the presence of cholestantriol. Supplementation of the cells with alpha-tocopherol (250, 500 or 1000 nM) or BHT (750 or 1000 nM) resulted in a reduction in the extent of lipid peroxidation (P < 0.05). The addition of beta-carotene over the concentration range of 250-1000 nM did not reduce lipid peroxidation significantly compared with cells exposed to cholestantriol alone. These findings suggest that addition of exogenous antioxidants may be beneficial in the prevention of COP-induced toxicity in vitro.

Absorption of dietary cholesterol oxidation products and incorporation into rat lymph chylomicrons

Cholesterol oxidation products (oxysterols) induce macrophage lipid loading and accumulate in early arterial fatty streaks. The origin of lesion oxysterols has not been elucidated. The absorption of oxysterols from the diet and transport to the arterial wall by postprandial lipoprotein remnants may be a significant source. This study aimed to investigate the extent of oxysterol absorption and the effect on chylomicron composition. Cholesterol was heat-treated, causing 30% oxidation; the major oxidation products were 7 beta-hydroxycholesterol, 7-keto-cholesterol, 5 alpha,6 alpha-epoxycholesterol, and 5 beta,6 beta-epoxycholesterol. Conscious lymph-cannulated rats were given a bolus gastric infusion of 50 mg oxidized cholesterol or 50 mg purified cholesterol in a vehicle of triglyceride. In the rats given the oxidized cholesterol, 6% of the oxysterol load was absorbed and incorporated into lymph chylomicrons. Rats given pure cholesterol had no increase in oxysterols above baseline levels. The incorporation of oxysterols into lymph chylomicrons differed over time with 7 beta-hydroxycholesterol, having peak absorption at 3 h, followed by 7-ketocholesterol at 4 h and 5 alpha,6 alpha-epoxy-cholesterol at 5 h. The absorption of oxysterols in animals given the oxidized cholesterol gastric infusate was associated with lymph chylomicron compositional changes at 2-4 h. The oxidized cholesterol-treated group had a twofold increase in the cholesterol (890 +/- 84 micrograms vs. 440 +/- 83 microgram at 3 h) and triglyceride content (19.76 +/- 3.4 micrograms vs. 8.49 +/- 3.8 micrograms at 3 h). This led to a doubling of chylomicron size over this postprandial period, with particles having a mean diameter of 294 nm in the oxidized cholesterol-treated animals, compared to 179 nm in the purified cholesterol group. In conclusion, dietary oxysterols appear to influence postprandial lipoprotein particle size and composition. These changes may have effects on the clearance of chylomicrons from plasma, arterial delivery of oxysterols, and possible deposition in arterial lesions.

Macrophages isolated from human atherosclerotic plaques produce IL-8, and oxysterols may have a regulatory function for IL-8 production

Oxysterols are biologically active molecules generated during oxidation of LDL. Several of these oxysterols were found in macrophage-derived foam cells from human atherosclerotic tissue (eg, 7-hydroxycholesterol, 7-ketocholesterol, 5-epoxycholesterol, and 25-hydroxycholesterol). A specific stimulation of interleukin-8 (IL-8) production by oxidized LDL (oxLDL) has been shown by other investigators. In foam cells from human atherosclerotic tissue, we found high levels of IL-8 (183.1 pg/10(6) cells) compared with monocytes (23.2 pg/10(6) cells) or monocyte-derived macrophages in culture (1.5 pg/10(6) cells). When monocytes and monocyte-derived macrophages, in vitro, were exposed to a series of different oxysterols, we found that all oxysterols tested had a tendency to stimulate IL-8 production but that 25-hydroxycholesterol was the most potent one. This stimulation of IL-8 production was time and dose dependent and could be blocked by cycloheximide. These results indicate that oxysterols in oxLDL may have a regulatory effect on IL-8 production. IL-8, a potent chemoattractant, may play a role in the recruitment of T lymphocytes and smooth muscle cells into the subendothelial space and may contribute to the formation of atherosclerotic lesions.

Impaired cellular cholesterol efflux by oxysterol-enriched high density lipoproteins

One of the proposed antiatherogenicity role of high-density lipoproteins (HDL) is believed to stimulate removal of cholesterol from the peripheral cells back to the liver for excretion. We have investigated the effects of oxidation-related modifications of HDL on their ability to stimulate cholesterol efflux from cultured cells. Human HDL (HDL3, 1.13 < d < 1.21 g/ml) have been modified either by malondialdehyde or by copper-mediated oxidation (Ox-HDL3). Compared with native HDL3, the modified HDL3 resulted in a significantly reduced efflux of labeled cholesterol from preloaded macrophages (P388D1 cell line). Analysis of lipid composition of Ox-HDL3 by gas chromatography revealed the presence of oxysterols (OS). Enrichment of native HDL3 with oxysterols resulted in a reduced capacity to stimulate cholesterol efflux. The reduced ability of OS-enriched HDL3 to elicit cholesterol efflux may contribute to cellular cholesterol accumulation and subsequently to atherosclerosis.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Biological effects of oxysterols: current status

A review of relevant literature on biological activities of oxysterols (OS) and cholesterol is presented. The data clearly demonstrate manifold biological activities, often detrimental, for OS compared with little or no such activity of a deleterious nature for cholesterol itself. Cholesterol is perhaps the single most important compound in animal tissue and, as such, it is difficult to imagine it as a toxin or hazard. In contrast, OS exhibit cytotoxicity to a wide variety of cells leading to angiotoxic and atherogenic effects; alter vascular permeability to albumin; alter prostaglandin synthesis and stimulate platelet aggregation, an important process facilitating atherosclerosis and thrombosis; alter the functionality of low density lipoprotein (LDL) receptors, possibly stimulating hypercholesterolaemia; modify cholesteryl ester accumulation in various cells, inducing foam cell formation; and enrich the LDL particle in cholesteryl esters, possibly increasing its atherogenicity. Furthermore, OS are mutagenic and carcinogenic, although some have been studied as antitumour agents based on their cytotoxic properties. Moreover, numerous studies have implicated OS in membrane and enzyme alterations that are interrelated with many of the foregoing effects. The authors find that OS deserve much more attention than cholesterol itself in terms of research activity but that unfortunately the reverse is true with regard to funding.