Pharmacokinetic and pharmacogenomic modelling of the CYP3A activity marker 4ß-hydroxycholesterol during efavirenz treatment and efavirenz/rifampicin co-treatment.

OBJECTIVES: To assess the effect of the major efavirenz metabolizing enzyme (CYP2B6) genotype and the effects of rifampicin co-treatment on induction of CYP3A by efavirenz. PATIENTS AND METHODS: Two study arms (arm 1, n = 41 and arm 2, n = 21) were recruited into this study. In arm 1, cholesterol and 4ß-hydroxycholesterol were measured in HIV treatment-naive patients at baseline and then at 4 and 16 weeks after initiation of efavirenz-based antiretroviral therapy. In arm 2, cholesterol and 4ß-hydroxycholesterol were measured among patients taking efavirenz during rifampicin-based tuberculosis (TB) treatment (efavirenz/rifampicin) just before completion of TB treatment and then serially following completion of TB treatment (efavirenz alone). Non-linear mixed-effect modelling was performed. RESULTS: A one-compartment, enzyme turnover model described 4ß-hydroxycholesterol kinetics adequately. Efavirenz treatment in arm 1 resulted in 1.74 (relative standard error = 15%), 3.3 (relative standard error = 33.1%) and 4.0 (relative standard error = 37.1%) average fold induction of CYP3A for extensive (CYP2B6*1/*1), intermediate (CYP2B6*1/*6) and slow (CYP2B6*6/*6) efavirenz metabolizers, respectively. The rate constant of 4ß-hydroxycholesterol formation [mean (95% CI)] just before completion of TB treatment [efavirenz/rifampicin co-treatment, 7.40 × 10(-7) h(-1) (5.5 × 10(-7)-1.0 × 10(-6))] was significantly higher than that calculated 8 weeks after completion [efavirenz alone, 4.50 × 10(-7) h(-1) (4.40 × 10(-7)-4.52 × 10(-7))]. The CYP3A induction dropped to 62% of its maximum by week 8 of completion. CONCLUSIONS: Our results indicate that efavirenz induction of CYP3A is influenced by CYP2B6 genetic polymorphisms and that efavirenz/rifampicin co-treatment results in higher induction than efavirenz alone.

Pharmacogenetic and pharmacokinetic aspects of CYP3A induction by efavirenz in HIV patients.

We investigated the effects of pharmacogenetic variations and efavirenz pharmacokinetics on inter-individual differences in the extent of CYP3A induction by efavirenz using 4ß-hydroxycholesterol/cholesterol (4ß-OHC/Chol) as a marker for CYP3A induction. Plasma 4ß-hydroxycholesterol and cholesterol concentrations were determined at baseline, and at the 4th, 16th and 48th week of efavirenz-based highly active antiretroviral therapy in antiretroviral therapy-naive HIV patients (n=77). Efavirenz plasma concentrations were quantified at weeks 4 and 16. CYP2B6, CYP3A5, ABCB1, UGT2B7 genotyping were done. Compared with baseline, the median plasma 4ß-OHC/Chol ratio increased at the 4th (257%), 16th (291%) and 48th (165%) week (P<0.0001). CYP2B6*6 genotype significantly influenced 4ß-OHC/Chol ratio at weeks 16 (P=0.02) and 48 (P=0.04) being highest in CYP2B6*6/*6>*1/*6>*1/*1. There were positive correlations between plasma efavirenz and 4ß-OHC/Chol ratios (week 4: P=0.02, week 16: P=0.001). CYP3A enzyme induction by efavirenz is pronounced in CYP2B6 slow metabolizers who have high efavirenz plasma exposure.

High levels of 15-oxygenated steroids in circulation of patients with multiple sclerosis: fact or fiction?

15-Oxygenated cholesterol species such as 5α-cholest-8(14)ene-3ß,15α-diol (15HC) and 3ß-hydroxy-5α-cholest-8(14)-en-15-one (15KC) are commercially available synthetic products unlikely to occur in biological systems. Surprisingly, Farez et al. recently reported that these two steroids occur in human circulation at levels considerably higher than those of any other endogenous oxysterol [Farez, M. et al. 2009. Toll-like receptor 2 and poly(ADP-ribose) polymerase 1 promote central nervous system neuroinflammation in progressive EAE. Nat. Immunol. 10: 958-964]. The levels were reported to be increased in patients with multiple sclerosis in a progressive phase and the authors suggested that this could be utilized diagnostically. Based on extensive in vitro experiments exposing cells to the same high levels of 15HC as found in vivo (1000 ng/ml) the authors concluded that 15HC may be an important pathogenetic factor in multiple sclerosis. Using combined gas chromatography-mass spectrometry we fail to detect significant plasma levels of 15HC either in healthy controls or in patients with multiple sclerosis (levels < 2 ng/ml). If 15KC is present in these plasma samples, the concentration of it must be <10 ng/ml. Our failure to detect significant levels of the above steroids could not be due to loss during hydrolysis and work-up because recovery of the added two oxysterols was close to 100%. Autoxidation of lipoprotein-bound cholesterol resulted in extensive conversion of cholesterol into 7-oxygenated but not 15-oxygenated sterols. We conclude that if present there are trace amounts only of the above 15-oxygenated steroids in human circulation and that the role of such oxysterols as pathogenetic factors and biomarkers must be reconsidered.

Sex and CYP3A5 genotype influence total CYP3A activity: high CYP3A activity and a unique distribution of CYP3A5 variant alleles in Ethiopians.

The objectives of the this study were to assess the influence of CYP3A5 genotype and sex on the variability in total CYP3A activity and to compare 4ß-hydroxycholesterol and omeprazole sulfoxidation as phenotypic markers for CYP3A activity in Ethiopians. Healthy subjects (n=150) were genotyped for CYP3A5*3, *6 and *7 using allele-specific PCR and Taqman genotyping assays. Plasma levels of 4ß-hydroxycholesterol, 3 h post-dose omeprazole and omeprazole sulfone, were determined by gas chromatography-mass spectrometry and high performance liquid chromatography, respectively. The frequency of CYP3A5*1, *3, *6 and *7 was 20.5, 67.3, 12.2 and 0%, respectively. The mean plasma 4ß-hydroxycholesterol level was 35.4 ng ml⁻¹. The mean 4ß-hydroxycholesterol level (P=0.0001) and the 4ß-hydroxycholesterol/cholesterol ratio (P=0.004) were higher in women than in men. CYP3A5 genotype significantly correlated with the plasma 4ß-hydroxycholesterol concentration (P=0.003) and 4ß-hydroxycholesterol/cholesterol ratio (P=0.0002). The omeprazole/omeprazole sulfone ratio was significantly correlated with 4ß-hydroxycholesterol and 4ß-hydroxycholesterol/cholesterol ratio in CYP3A5*0/*0 genotypes but not in individuals carrying the CYP3A5*1 allele. No correlation of omeprazole/omeprazole sulfone ratio with sex or CYP3A5 genotype was observed. A clear gene-dose effect implies plasma 4ß-hydroxycholesterol level as a useful endogenous biomarker for total CYP3A activity (CYP3A5 plus CYP3A4) whereas the omeprazole/omeprazole sulfone ratio reflects mainly CYP3A4 activity. Sex and CYP3A5 genotype influence total CYP3A activity. Ethiopians display high total CYP3A activity and a unique distribution of CYP3A5 variant alleles not described hitherto.

4beta-hydroxycholesterol as a marker of CYP3A4 inhibition in vivo - effects of itraconazole in man.

OBJECTIVE: Itraconazole, a triazole antifungal agent, has been demonstrated to act as an inhibitor of the ligand induced pregnane X receptor-mediated transcriptional regulation of the CYP3A4 gene. Here, we study the potential endogenous serum marker of CYP3A4 activity, 4beta-hydroxycholesterol, during therapy with itraconazole. PATIENTS AND METHODS: 8 male patients with onychomycosis received two 1-week cycles of treatment with 400 mg itraconazole once daily in an open, prospective exploratory trial. Fasting serum samples were taken at the beginning and at the end of each cycle. The levels of cholesterol were measured using gas chromatography-flame ionization detection, while cholesterol and bile acid precursors were quantified by gas chromatography-mass spectrometry. RESULTS: Total cholesterol decreased by 10% (p < 0.0005) during the itraconazole treatment. Concentrations of the cholesterol precursor lanosterol and 24, 25-dihydrolanosterol increased 10- and 240-fold, respectively (p < 0.001 for both). Interestingly, the ratio of serum lathosterol to cholesterol, an indicator of endogenous cholesterol synthesis downstream from lanosterol, remained unchanged. Absolute and cholesterol-corrected concentrations of 4beta-hydroxycholesterol, formed by CYP3A4-mediated oxidation, decreased significantly during both cycles, on average by 29.1% (p = 0.0006) and 20.8% (p = 0.0062), respectively. The brain-specific cholesterol metabolite 24S-hydroxycholesterol as well as its ratio to cholesterol increased by 19.7% (p = 0.0422) and 34.9% (p = 0.0013), respectively, while the concentrations of the other bile acid precursors, 7alpha-hydroxycholesterol and 27-hydroxycholesterol, remained unchanged. CONCLUSIONS: In conclusion, 4beta-hydroxycholesterol appears to be a sensitive endogenous surrogate marker in human serum for inhibition of CYP3A4 by itraconazole.

Metabolism of prostaglandin F2 alpha in Zellweger syndrome. Peroxisomal beta-oxidation is a major importance for in vivo degradation of prostaglandins in humans.

We have recently shown in vitro that the peroxisomal fraction of a rat liver homogenate has the highest capacity to beta-oxidize prostaglandins. In order to evaluate the relative importance of peroxisomes for this conversion also in vivo, we administered [3H]prostaglandin F2 alpha to an infant suffering from Zellweger syndrome, a congenital disorder characterized by the absence of intact peroxisomes. As a control, labeled compound was administered to two healthy volunteers. Urine was collected, fractionated on a SEP-PAK C18 cartridge, and subjected to reversed-phase high-performance liquid chromatography. The Zellweger patient was found to excrete prostaglandin metabolites considerably less polar than those of the control subjects. The major urinary metabolite in the control subjects was practically absent in the urine from the Zellweger patient. The major urinary prostaglandin F2 alpha metabolite from the Zellweger patient was identified as an omega-oxidized C20-prostaglandin, 9,11-dihydroxy-15-oxoprost-5-ene-1,20-dioic acid. The major urinary prostaglandin F2 alpha metabolite from the control subjects had chromatographic properties of a tetranor (C16) prostaglandin, in accordance with earlier published data. The present results, in combination with our previous in vitro data, indicate that peroxisomal beta-oxidation is of major importance for in vivo chain shortening of prostaglandins.

Oxysterols present in atherosclerotic tissue decrease the expression of lipoprotein lipase messenger RNA in human monocyte-derived macrophages.

The presence of oxysterols in macrophages isolated from atherosclerotic tissue and the effect of oxysterols on the regulation of lipoprotein lipase (LPL) mRNA were studied. Both rabbit and human macrophages, freshly isolated from atherosclerotic aorta, show about the same distribution of oxysterols, analyzed by isotope dilution mass spectrometry, except that all three preparations of human arterial-derived macrophages contained high levels of 27-hydroxycholesterol, which was not found in rabbit macrophages. To determine if oxysterols regulate LPL expression, human monocyte-derived macrophages were incubated with different oxysterols. Incubation with 7 beta-hydroxycholesterol and 25-hydroxycholesterol resulted in a 70-75% reduction of LPL mRNA, analyzed by quantitative RT-PCR. Cholesterol and other tested oxysterols showed no effect on macrophage LPL mRNA expression compared with control. LPL activity in the medium was also reduced after exposure of the macrophages to 7 beta-hydroxycholesterol and 25-hydroxycholesterol. In conclusion, we have demonstrated accumulation of oxysterols in macrophage-derived foam cells isolated from atherosclerotic aorta. There was suppression of LPL mRNA in human monocyte-derived macrophages after incubation with 7 beta-hydroxycholesterol and 25-hydroxycholesterol. It is tempting to suggest that an exposure to oxysterols may explain our earlier observation of a low level of LPL mRNA in arterial foam cells.

Hepatic cholesterol metabolism and resistance to dietary cholesterol in LXRbeta-deficient mice.

The nuclear oxysterol-receptor paralogues LXRalpha and LXRbeta share a high degree of amino acid identity and bind endogenous oxysterol ligands with similar affinities. While LXRalpha has been established as an important regulator of cholesterol catabolism in cholesterol-fed mice, little is known about the function of LXRbeta in vivo. We have generated mouse lines with targeted disruptions of each of these LXR receptors and have compared their responses to dietary cholesterol. Serum and hepatic cholesterol levels and lipoprotein profiles of cholesterol-fed animals revealed no significant differences between LXRbeta(-/-) and wild-type mice. Steady-state mRNA levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase, farnesyl diphosphate synthase, and squalene synthase were increased in LXRbeta(-/-) mice compared with LXRbeta(+/+) mice, when fed standard chow. The mRNA levels for cholesterol 7alpha-hydroxylase, oxysterol 7alpha-hydroxylase, sterol 12alpha-hydroxylase, and sterol 27-hydroxylase, respectively, were comparable in these strains, both on standard and 2% cholesterol chow. Our results indicate that LXRbeta(-/-) mice - in contrast to LXRalpha(-/-) mice - maintain their resistance to dietary cholesterol, despite subtle effects on the expression of genes coding for enzymes involved in lipid metabolism. Thus, our data indicate that LXRbeta has no complete overlapping function compared with LXRalpha in the liver.

Effects of high-dose itraconazole treatment on lipoproteins in men.

OBJECTIVE: Epidemiological studies have convincingly demonstrated a positive association between LDL-cholesterol (LDL-C) and coronary artery disease but, in the case of HDL-C, there is an inverse association. Administration of high doses of the antifungal agent ketoconazole (800 mg/d) reduces serum concentrations of total cholesterol and LDL-C and there is a tendency for an increase in HDL-C. Our goal was to examine whether high-dose itraconazole raises HDL-C in subjects with normal levels of cholesterol. PATIENTS AND METHODS: 8 male patients with onychomycosis received 2 one-week cycles of treatment with itraconazole at a dose of 400 mg once daily in an open, prospective exploratory trial. Serum levels of itraconazole and its active metabolite hydroxyitraconazole were determined using high-performance liquid chromatography at the end of each treatment cycle. Fasting levels of serum lipoproteins and triglycerides were measured twice using routine enzymatic assays at the beginning and end of each cycle. The effects of itraconazole and hydroxyitraconazole on HDL-C metabolism were assessed in vitro using a human Caco-2 cell line and analyzing apoA-I levels with an enzyme-linked immunosorbent assay. RESULTS: During itraconazole treatment total cholesterol and LDL-C decreased on average by 12% (p < 0.001) and 17% (p < 0.001), respectively, whereas HDL-C increased by 21% (p < 0.001). The ratio LDL: HDL-C, an index of atherogenic risk, decreased by 30% (p < 0.001). Incubation of Caco-2 cells in the presence of itraconazole and hydroxyitraconazole for 3 hours resulted in a significant increase in apoA-I concentration in the medium (913 and 412%, respectively) compared with control. CONCLUSION: In addition to its inhibitory effect on cholesterol synthesis, high-dose itraconazole (400 mg/d) causes a significant decrease in serum LDL-C and, in contrast to ketoconazole, a significant increase in HDL-C. In vitro studies with Caco-2 cells indicate that the latter observation might be caused by an increase in apoA-I levels.

Oxysterols and Alzheimer's disease.

There is a clear link between cholesterol turnover and neurodegenerative diseases and hypercholesterolemia is an established risk factor for Alzheimer's disease (AD). The failure to demonstrate a transfer of cholesterol from the circulation into the brain in humans and experimental animals makes it difficult to explain the link between hypercholesterolemia and AD. In contrast to cholesterol itself, side-chain oxidized cholesterol metabolites such as 24S-hydroxycholesterol and 27-hydroxycholesterol are able to pass the blood-brain barrier (BBB). Formation of 24S-hydroxycholesterol is the quantitatively most important mechanism for elimination of cholesterol from the brain and we recently demonstrated a significant net uptake of 27-hydroxycholesterol by the brain from the circulation. We have also shown that patients with AD have increased brain levels of 27-hydroxycholesterol, which may affect the production of beta-amyloid in the brain. The levels of 27-hydroxycholesterol in the circulation are correlated with the levels of cholesterol and the possibility must be considered that the flux of 27-hydroxycholesterol into the brain is the missing link between hypercholesterolemia and Alzheimer's disease. Current knowledge about the role of the two oxysterols for cholesterol homeostasis in the brain as well as their diagnostic potential are reviewed.

Identification of the major urinary metabolite of prostaglandin E3 in the rat.

[11,12-3H2]Prostaglandin E3 was administered subcutaneously into male Sprague-Dawley rats in doses of 0.4 microgram-10 mg/kg body weight. 40-60% of the administered radioactivity was excreted in the urine. The major metabolite was isolated by solid phase extraction followed by three steps of high-performance liquid chromatography. The structure of the major metabolite (5-11% of the administered radioactivity) was 7 alpha,11 alpha-dihydroxy-5-ketotetranorprosta-9,13-dienoic acid as shown by gas-liquid chromatography-mass spectrometry and by its conversion into 11 alpha-hydroxy-5-ketotetranorprosta-4(8),9, 13-trienoic acid.

Transport of side-chain oxidized oxysterols in the human circulation.

To study the transport of 24-hydroxycholesterol, 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid in the circulation, the distribution of these oxysterols was determined in plasma, very low density lipoprotein, low density lipoprotein, high density lipoprotein, and lipoprotein-free plasma. An accurate method based on isotope dilution-mass spectrometry with use of individual deuterium labeled internal standards was used. 24-Hydroxycholesterol and 27-hydroxycholesterol were found to be associated mainly with HDL and LDL, whereas 3beta-hydroxy-5-cholestenoic acid was found predominantly in the lipoprotein-free fraction. While both 24-hydroxycholesterol and 27-hydroxycholesterol are present mainly in esterified form in plasma, 3beta-hydroxy-5-cholestenoic acid was present as free acid only. For reasons of comparison, a number of other oxysterols were determined in plasma and in isolated lipoprotein fractions. Significant amounts of these oxysterols were formed by cholesterol autoxidation during fractionation of plasma. It was therefore not possible to calculate the distribution of these oxysterols in the different plasma fractions. The present results are consistent with our previous finding that the less polar cholesterol metabolite 27-hydroxycholesterol competes with cholesterol for transport out of cells using HDL as an acceptor molecule, whereas the transport of the more polar compound 3beta-hydroxy-5-cholestenoic acid is facilitated by albumin.

Formation of 15-HETE as a major hydroxyeicosatetraenoic acid in the atherosclerotic vessel wall.

Atherosclerosis was induced in New Zealand White rabbits through cholesterol feeding. Aortae were taken out from treated animals and incubated with arachidonic acid. Aortae from cholesterol-fed animals converted arachidonic acid into 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE). This conversion was not seen in aortae from control animals. The immediate precursor of 15-HETE, 15-HPETE, is an inhibitor of prostacyclin synthetase and might hamper prostacyclin production.

Clofibrate treatment increases stearoyl-CoA desaturase mRNA level and enzyme activity in mouse liver.

Stearoyl-CoA desaturase activity is encoded by two highly homologous genes, SCD1 and SCD2, which show tissue-specific expression and regulation. SCD1, which is expressed in the liver, showed a marked diurnal variation with the highest expression during the feeding period. Treatment of mice with the peroxisome proliferator clofibrate, which induces several lipid metabolizing enzymes, increased both the enzyme activity and mRNA level in the liver, indicating regulation at the transcriptional level. The highest expression of both SCD1 and SCD2 was found in brown adipose tissue, which was slightly down-regulated by feeding a fat-free diet.

Formation of oxysterols from different pools of cholesterol as studied by stable isotope technique: cerebral origin of most circulating 24S-hydroxycholesterol in rats, but not in mice.

In order to study the origin of different oxysterols in the circulation, in particular 24S-hydroxycholesterol, different pools of cholesterol in rat and mouse were labelled by feeding the animals with a diet supplemented with 0.3 or 0.5% hexadeuterium-labelled cholesterol, respectively, for 10 days. The incorporation of deuterium label in cholesterol and different oxysterols was measured by combined gas chromatography-mass spectrometry in selected tissues and in the circulation. In both rat and mouse, a high incorporation of label was found in cholesterol present in serum and liver (up to 77%). Incorporation of label was similar in 7 alpha- and 7 beta-hydroxycholesterol of the same origin. There was no significant incorporation of deuterium in brain cholesterol, and little or no incorporation in the brain oxysterols investigated, in both animals. In the testis, the incorporation of the deuterium label in cholesterol was less than half of that in the liver, with similarly reduced labelling of the testicular oxysterols. 24S-Hydroxycholesterol in the circulation contained a deuterium content that was about 50% of that of serum and liver cholesterol in the mouse experiment and about 30% in the rat experiment. Thus, about 50% of circulating 24S-hydroxycholesterol in the mouse and about 70% of this fraction in the rat must originate from pools of cholesterol that are not in equilibrium with plasma and liver cholesterol. The liver is probably responsible for a considerable part of the extracerebral formation of 24S-hydroxycholesterol, since this organ contained detectable amounts of 24S-hydroxycholesterol with a relatively high incorporation of deuterium in both animal species. The results are consistent with a cerebral origin of more than half of the 24S-hydroxycholesterol in the circulation of rats, but not in mice.

The oxysterols cholest-5-ene-3 beta,4 alpha-diol, cholest-5-ene-3 beta,4 beta-diol and cholestane-3 beta,5 alpha,6 alpha-triol are formed during in vitro oxidation of low density lipoprotein, and are present in human atherosclerotic plaques.

Isolated human low density lipoprotein (LDL) was oxidized with either cupric ions or soybean lipoxygenase and linoleic acid. Cholesterol oxidation products (oxysterols) were determined by isotope dilution gas chromatography-mass spectrometry. A new cholestane-3,5,6-triol isomer, cholestane-3 beta,5 alpha,6 alpha-triol, which has not previously been recognized as a cholesterol autoxidation product, was found at similar concentrations as the well-known cytotoxic cholestane-3 beta,5 alpha,6 beta-triol during both copper- and lipoxygenase-mediated LDL oxidation. Furthermore, two epimeric cholest-5-ene-3 beta,4-diols were identified in the oxidized LDL at similar concentrations. These two isomers were also identified in human atherosclerotic tissue in a ratio of 1:1 at a concentration more than 10-times higher than in non-atherosclerotic vessels. In vitro oxidation of LDL under an 18O2 atmosphere revealed that molecular oxygen was the only source of the oxygen functions at C-4 in the cholest-5-ene-3 beta,4-diols. Taken together, these findings suggest that the cholest-5-ene-3 beta,4-diols in atherosclerotic plaques are formed by autoxidation.

Identification of intermediates in the peroxisomal beta-oxidation of linoleic acid.

Rat liver peroxisomes contain a beta-oxidation system different from that present in the mitochondria. Intermediates in this oxidation have not hitherto been identified by direct methods. Incubation of linoleic acid with isolated peroxisomes (in the absence of detergent) resulted in the accumulation of polar products in addition to the chain-shortened products. Omission of NAD in the incubation mixture considerably increased the accumulation of these products. Two of the products were isolated and characterized by gas chromatography-mass spectrometry. They were identified as 2,3-dehydrolinoleic acid and 3-hydroxylinoleic acid, based on identical chromatographic behaviour and mass spectra compared to synthetic reference compounds. Stereochemical analysis of catalytically hydrogenated 3-hydroxylinoleic acid showed a D/L ratio near to one. The mechanism behind the apparent lack of stereospecificity is discussed in relation to the recently described novel peroxisomal 2-enoyl-CoA hydratase (Smeland, T.E., Li, J., Chu, C.-h., Cuebas, D. and Schultz, H. (1989) Biochem. Biophys. Res. Commun. 160, 988-992 and Hiltunen, J.K., Palosaari, P.M. and Kunau, W.-H. (1989) J. Biol. Chem. 264, 13536-13540). In previous work we have demonstrated that beta-oxidation intermediates accumulate also in the peroxisomal metabolism of C27-bile acid intermediates and prostaglandins. The possibility is discussed that the peroxisomal beta-oxidation system is less tightly coupled than the corresponding system in mitochondria.

Localization of sterol 27-hydroxylase immuno-reactivity in human atherosclerotic plaques.

It has recently been shown that extrahepatic cells can eliminate intracellular cholesterol by enzymatic conversion into 27-hydroxy-cholesterol and 3 beta-hydroxy-5-cholestenoic acid. Using immunohistochemical methods, we studied the presence of the enzyme responsible for these conversions, sterol 27-hydroxylase, in human carotid atherosclerotic plaques. All plaques examined were found to contain sterol 27-hydroxylase immuno-reactive cells. While some endothelial cells stained for sterol 27-hydroxylase, the majority of the immunoreactive cells co-localized with macrophages. Accumulation of sterol 27-hydroxylase-positive cells were often observed in macrophage-rich core regions of complicated lesions. High concentrations of 27-hydroxycholesterol were found in plaques, while the concentration in non-atherosclerotic human vessels was lower by two orders of magnitude. The rabbit, which is particularly sensitive to dietary cholesterol and easily develops fatty streaks, had low plasma levels of 27-hydroxycholesterol, 3 ng/ml compared to 150 ng/ml in humans. The concentration of 27-hydroxycholesterol in the atherosclerotic rabbit vessels was also lower compared to human atherosclerotic plaques. The results are consistent with our hypothesis that sterol 27-hydroxylase may be utilized by human macrophages as a defence towards a high cholesterol load. This mechanism may be less important in some other species.

On the anti-atherogenic effect of the antioxidant BHT in cholesterol-fed rabbits: inverse relation between serum triglycerides and atheromatous lesions.

We have shown that inclusion of the antioxidant butylated hydroxytoluene (BHT) in the diet protects against development of atherosclerotic lesions in cholesterol-fed rabbits. In parallel, BHT treatment results in increased plasma triglyceride levels. The present study explores the relationship between the triglyceride-inducing and protective effects of BHT in two different studies. The combined material contains 22 rabbits fed cholesterol and 18 rabbits fed cholesterol in combination with 1% BHT. In the BHT group there was an inverse relationship between triglyceride exposure/cholesterol exposure and extent of lesions with r=0.74 (P=0.0005). Our results show that increased triglyceride exposure parallels the anti-atherogenic effect of BHT. There was no significant correlation between atheromatosis and serum BHT levels. beta-very low density lipoprotein (beta-VLDL) from cholesterol and BHT animals was triglyceride-enriched and smaller compared to beta-VLDL from cholesterol-fed animals, but there was no significant association between the anti-atherogenic effect of BHT and particle size or apolipoprotein pattern of LDL or beta-VLDL. LDL isolated from rabbits treated with cholesterol and BHT was less sensitive to oxidative modification than LDL isolated from rabbits treated with cholesterol only. In conclusion, our results demonstrate that the degree of triglyceride exposure may be an important modulator of the anti-atherogenic effect of an antioxidant.

Bioavailability of vitamin E as function of food intake in healthy subjects: effects on plasma peroxide-scavenging activity and cholesterol-oxidation products.

Clinical trials with vitamin E have yielded contrasting results. In these trials, the amount of vitamin E given was different, and the compliance was not assessed in all studies. In addition, the modality of intake, ie, in relation to food, was not specified in any trial. Vitamin E is lipophilic, and its absorption is expected to be increased by food. We studied the bioavailability of vitamin E in relation to food intake and the effect on the lipid peroxide-scavenging activity of plasma and on 7beta-hydroxycholesterol and 7-ketocholesterol (oxysterols) as markers of oxidant stress. Twenty healthy Italian subjects were randomly assigned to take vitamin E at 300 mg/d on an empty stomach (group A) or during dinner (group B) for 15 days. Plasma vitamin E markedly increased in group B (84%) compared with group A (29%). The lipid peroxide-scavenging activity of plasma increased significantly in group B (14%, P=0.005) but did not change in group A. All subjects showed very low levels of plasma oxysterols, which were not affected by vitamin E supplementation in either group. This study shows that plasma concentration of vitamin E and plasma antioxidant activity in response to oral supplementation are markedly affected by food intake. Healthy Italian subjects show very low levels of cholesterol oxidation products; these low levels are possibly related to the Mediterranean diet. To obtain maximal absorption, vitamin E must be given at meals. These data should be taken into account in clinical trials with vitamin E.