Differences in 27-hydroxycholesterol concentrations in plasma and liver of baboons with high and low responses to dietary cholesterol and fat

Diet-induced early-stage atherosclerosis in baboons: Lipoproteins, atherogenesis, and arterial compliance

BACKGROUND

The purpose of this study was to determine whether dietary manipulation can reliably induce early-stage atherosclerosis and clinically relevant changes in vascular function in an established, well-characterized non-human primate model.

METHODS

We fed 112 baboons a high-cholesterol, high-fat challenge diet for two years. We assayed circulating biomarkers of cardiovascular disease (CVD) risk, at 0, 7, and 104 weeks into the challenge; assessed arterial compliance noninvasively at 104 weeks; and measured atherosclerotic lesions in three major arteries at necropsy.

RESULTS

We observed evidence of atherosclerosis in all but one baboon fed the two-year challenge diet. CVD risk biomarkers, the prevalence, size, and complexity of arterial lesions, plus consequent arterial stiffness, were increased in comparison with dietary control animals.

CONCLUSIONS

Feeding baboons a high-cholesterol, high-fat diet for two years reliably induces atherosclerosis, with risk factor profiles, arterial lesions, and changes in vascular function also seen in humans.

Serum concentration of 27-hydroxycholesterol predicts the effects of high-cholesterol diet on plasma LDL cholesterol level

AIM

The effect of dietary cholesterol on plasma cholesterol concentrations varies widely among individuals. Recent studies suggest that the synthesis of oxysterols is up-regulated when tissue cholesterol is saturated. The present study was undertaken to test the hypothesis that a serum high concentration of 27-hydroxycholesterol, one of the oxysterols, reflects positive cholesterol balance in the body and predicts intolerance to a high-cholesterol diet.

METHODS

In 30 subjects, 750 mg/day of cholesterol was added for 4 weeks to the ordinary diet. Blood samples were collected at the start and finish of the supplementation. Serum sterol and oxysterol concentrations were measured by high-resolution GC-MS.

RESULTS

A receiver operating characteristic curve was drawn and the cutoff point (80 ng/mg cholesterol) was chosen to maximize sensitivity (81.3%) and specificity (64.3%) for predicting a positive change of LDL cholesterol concentration after cholesterol loading. Subjects with higher serum 27-hydroxycholesterol concentrations (>/= 80 ng/mg cholesterol) showed significantly (P < 0.05) high values for the change of LDL cholesterol concentration (+7.4 +/- 3.4%, mean +/- SEM, n = 17) compared with those with lower 27-hydroxycholesterol levels (-5.3 +/- 2.7%, n = 13).

CONCLUSIONS

In subjects with high serum 27-hydroxycholesterol concentrations were unable to adapt to a high-cholesterol diet. The concentration of serum 27-hydroxycholesterol appears to reflect cholesterol saturation in the body and predicts to some extent a responsiveness to dietary cholesterol.

Prevalence and clinical significance of sonographic detection of enlarged regional lymph nodes in Crohn's disease

OBJECTIVE

Reactive regional lymph node enlargement is a frequent ultrasonographic finding in patients with Crohn's disease. However, the prevalence of this condition and its clinical significance are unknown. This study assesses the prevalence of enlarged regional mesenteric lymph nodes and its clinical significance in Crohn's disease, and in particular whether there is a correlation between the sonographic detection of enlarged regional lymph nodes and the degree of clinical or biochemical activity of the disease.

MATERIAL AND METHODS

A total of 240 in- and outpatients with Crohn's disease underwent intestinal ultrasound to assess the presence of enlarged regional lymph nodes as well as the thickness and echopattern of the bowel wall, the site and extent of Crohn's disease and the presence of stenosis, fistulas and abscesses. Demographic, clinical and biochemical parameters were also collected for each patient. A multivariate model by means of multiple regression analysis was used to identify independent variables linked to regional lymph node enlargement.

RESULTS

Enlarged regional lymph nodes were detected ultrasonographically in 25.4% of Crohn's disease patients. The presence of regional lymph nodes showed a weak correlation with both clinical and biochemical Crohn's disease activity. Regional lymph nodes were found more frequently in young patients (50% of patients < 30 years, 18% of patients between 30 and 50 yrs, and 7% of patients > 50 yrs; p<0.0001) and in patients with a shorter disease duration. Enlarged regional lymph nodes were strongly correlated with internal fistulas and intra-abdominal abscesses. The multiple regression analysis showed that age, duration of disease and presence of internal fistulas were the best independent predictive factors linked to the presence of enlarged mesenteric lymph nodes.

CONCLUSIONS

The sonographic detection of enlarged regional lymph nodes is more frequent in young patients, which suggests an earlier phase of Crohn's disease and the presence of septic complications such as fistulas and abscesses, but this is of limited valued in assessing disease activity.

Expression levels of genes for ATP-binding cassette transporters and sterol 27-hydroxylase in liver and intestine of baboons with high and low cholesterolemic responses to dietary lipids

Baboons with high and low lipemic responses to dietary lipids differ in intestinal cholesterol absorption and hepatic cholesterol metabolism. ATP-binding cassette (ABC) transporters play an important role in cholesterol absorption and hepatic cholesterol metabolism. Using frozen tissues from high- and low-responding baboons maintained on the cholesterol and fat-enriched diet, we determined the relative expression of ABCA1, ABCG5, ABCG8, and 27-hydroxylase genes in the liver and intestine using TaqMan real-time polymerase chain reaction. There was no consistent difference in the expression of ABC-transporters and 27-hydroxylase in the intestine between high- and low-responding baboons. However, hepatic expression of sterol 27-hydroxylase, ABCG5, and ABCG8 was higher in low-responding baboons than in high-responding baboons. There was also a significant correlation between the expression of sterol 27-hydroxylase and ABCG5, and ABCG8 in both the liver and the intestine. These results suggest that differences in hepatic lipid metabolism but not in cholesterol absorption between high- and low-responding baboons observed previously may be mediated by the differences in the expression levels of 27-hydroxylase, ABCG5, and ABCG8.

Significance of plasma 7alpha-hydroxy-4-cholesten-3-one and 27-hydroxycholesterol concentrations as markers for hepatic bile acid synthesis in cholesterol-fed rabbits

Plasma 7alpha-hydroxy-4-cholesten-3-one has been used as an index of hepatic bile acid synthesis. The aim of the current study was to ascertain whether the level of this oxysterol reflects hepatic cholesterol 7alpha-hydroxylase activity when plasma cholesterol concentrations are markedly changed. In addition, the relationship of hepatic sterol 27-hydroxylase activity with plasma concentrations of 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid was studied. We used New Zealand white rabbits fed 2% cholesterol for 5 or 10 days and/or constructed bile fistula. Feeding cholesterol markedly increased and bile drainage reduced plasma cholesterol concentrations. Initially, in these models there was no correlation between plasma 7alpha-hydroxy-4-cholesten-3-one concentrations and hepatic cholesterol 7alpha-hydroxylase activities (r = -0.24, n = 10). Cholesterol feeding was associated with downregulated 7alpha-hydroxylase activities, while plasma 7alpha-hydroxy-4-cholesten-3-one concentrations were elevated in the presence of increased plasma cholesterol levels. However, this discrepancy was overcome and significant correlation was observed (r = 0.73, P <.05, n = 10) by expressing 7alpha-hydroxy-4-cholesten-3-one levels relative to cholesterol. In contrast, hepatic sterol 27-hydroxylase activities were not significantly correlated with plasma absolute (r = 0.23, difference not significant [NS], n = 10) nor cholesterol-related levels of 27-hydroxycholesterol (r = -0.13, NS, n = 10), or 3beta-hydroxy-5-cholestenoic acid concentrations (r = 0.30, NS, n = 10). In conclusion, plasma 7alpha-hydroxy-4-cholesten-3-one concentrations reflected hepatic cholesterol 7alpha-hydroxylase activities when the sterol levels were adjusted to plasma cholesterol concentrations in rabbits with hypercholesterolemia. The results suggest that plasma 7alpha-hydroxy-4-cholesten-3-one relative to cholesterol is a better marker for hepatic cholesterol 7alpha-hydroxylase activity than the absolute concentration when hypercholesterolemia is present. In contrast, 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid levels in plasma did not reflect hepatic sterol 27-hydroxylase activities even if the levels were adjusted to plasma cholesterol concentrations.

High and low responding strains of laboratory opossums differ in sterol 27-hydroxylase and acyl-coenzyme A:cholesterol acyltransferase activities on a high cholesterol diet

Two partially inbred strains of laboratory opossums exhibit extremely high or low levels of VLDL+LDL cholesterol concentrations, respectively, when challenged with a high cholesterol and high fat diet. The present studies were conducted to determine whether the high and low responding strains differ in activities of important enzymes that have been shown to affect lipemic responsiveness to diet. We measured plasma 27-hydroxycholesterol and hepatic activities of 27-hydroxylase and 7alpha-hydroxylase in high and low responding opossums while consuming the basal diet and cholesterol-enriched diets. Plasma 27-hydroxycholesterol concentration and 27-hydroxylase activity in liver did not differ between groups on the basal diet, but both were significantly higher in low responders than in high responders on the cholesterol-enriched diet with unsaturated fat (10.79 +/- 0.56 in low vs. 7.31 +/- 0.50 &mgr;g/dl in high responders for 27-hydroxycholesterol and 14.14 +/- 0.79 in low vs. 10.07 +/- 0.80 pmol/mg protein/min in high responders for 27-hydroxylase activity). On the other hand, 7alpha-hydroxylase activity was significantly higher in high responding opossums (75.72 +/- 6.81 pmol/mg protein/min) than in low responding opossums (51.39 +/- 6.18 pmol/mg protein/min) on the basal diet, but it did not differ on the high cholesterol and high fat diet. We measured hepatic ACAT and extrahepatic hepatic 27-hydroxylase activities in high and low responding opossums on the cholesterol enriched diet. Hepatic ACAT activity was significantly higher in high responding opossums (137.00 +/- 18.33 pmol/mg protein/min) than in low responding opossums (47.67 +/- 2.71 pmol/mg protein/min), whereas extrahepatic 27-hydroxylase activity was higher in low responding opossums (33.00 +/- 2.10 pmol/mg protein/min in lungs and 3.69 +/- 0.20 in kidneys) than in high responding opossums (21.17 +/- 1.54 pmol/mg protein/min in lungs and 2.82 +/- 0.31 in kidneys). We also compared the composition of bile between high and low responders. The concentration of taurine conjugates of cholic acid in bile of both groups was similar, but concentration of taurine conjugates of chenodeoxycholic acid in bile of low responding animals was higher than in high responding animals (124.9 +/- 17.3 in low vs. 59.2 +/- 13.2 &mgr;mol/ml in high responders). The results of these studies suggest two enzymes may affect the lipemic response to diet in laboratory opossums: sterol 27-hydroxylase and ACAT. Each of these enzymes may influence diet-induced hyperlipidemia at a different step of lipoprotein metabolism.

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.

A potential role for sterol 27-hydroxylase in atherogenesis

OBJECTIVE

27-hydroxycholesterol is the product of the mitochondrial cytochrome P450 sterol 27-hydroxylase, a key enzyme in cholesterol metabolism present in most tissues of the body. 27-hydroxycholesterol increases in abundance with progression of human atherosclerotic lesions, therefore the aim of this study was to determine the pattern of sterol 27-hydroxylase gene expression in normal and diseased arteries and to identify the cell types responsible for its expression.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR) analysis and in situ hybridisation, utilising a sterol 27-hydroxylase cDNA probe, and immunohistochemistry, utilising an antibody to sterol 27-hydroxylase, together with an antibody to smooth muscle cell alpha-actin and an antibody to CD68, a marker for macrophages, were used to study expression of 27-hydroxylase in arterial specimens. In addition, RT-PCR was used to study expression of 27-hydroxylase in cultured macrophages and smooth muscle cells.

RESULTS

Semi-quantitative RT-PCR analysis of normal and atherosclerotic human aortas showed that 27-hydroxylase is constitutively expressed in the normal artery wall, and is substantially up-regulated in atherosclerosis. RT-PCR analysis of 27-hydroxylase expression in vitro demonstrated that macrophages constitutively express high levels throughout their differentiation in culture whilst de-differentiated vascular smooth muscle cells express very low levels. In situ hybridisation revealed that in normal artery and fatty streaks, expression of mRNA for 27-hydroxylase was low in the media, but higher in intimal smooth muscle cells. The macrophages of fatty streaks expressed low or undetectable levels of 27-hydroxylase. However in advanced lesions the highest expression of 27-hydroxylase was detectable in macrophages. Immunohistochemistry demonstrated that high levels of 27-hydroxylase protein occurred in macrophages near the shoulder region of plaques, at the edge of the lipid core.

CONCLUSIONS

27-hydroxylase may constitute a protective mechanism for removing cholesterol from macrophages and smooth muscle cells. Genetic heterogeneity resulting in differences in sterol 27-hydroxylase activity between individuals may affect their ability to deal with accumulated cholesterol in the arterial intima, and hence their relative degree of predisposition to atherosclerosis.

Kinetics and plasma concentrations of 26-hydroxycholesterol in baboons

26-Hydroxycholesterol (26OHC), a major oxysterol in human blood, is believed to play an important role in reverse cholesterol transport, bile acid formation, and regulation of various cellular processes. Using isotope dilution mass spectrometry, we measured plasma 26OHC concentrations in baboons fed either a high cholesterol/saturated fat (HC-SF) or normal chow diet. Plasma 26OHC levels in baboons were comparable to those reported for humans and were positively correlated with plasma cholesterol concentrations. Animals on the HC-SF diet had significantly higher 26OHC levels (0.274+/-0.058 microM, mean+/-S.D.) than those on the chow diet (0.156+/-0.046 microM). In separate experiments, [(3)H]26OHC was injected into four tethered baboons, and multiple blood samples drawn over a 1-h period were analyzed for [(3)H]26OHC and 26OHC. Fitting the specific radioactivity data to a two-pool compartmental model indicated a rapidly turning over plasma compartment (t(1/2) 2.9-6.0 min) and a second compartment with slow turnover (t(1/2) 76-333 min). The calculated 26OHC production rate was 2.5 micromol/kg body weight/day. Assuming all 26OHC is converted to bile acids, the 26OHC production rate corresponds to about 10% of total bile acid production in adult baboons. These results indicate that rapid turnover of plasma 26OHC at submicromolar concentrations could significantly contribute to bile acid synthesis.

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.

Comparative regulation of hepatic sterol 27-hydroxylase and cholesterol 7alpha-hydroxylase activities in the rat, guinea pig, and rabbit: effects of cholesterol and bile acids

The regulation of the classic and alternative bile acid synthetic pathways by key hepatic enzyme activities (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase, respectively) was examined in bile acid depletion and replacement and cholesterol-feeding experiments with rats, guinea pigs, and rabbits. The bile acid pool was depleted by creating a bile fistula (BF) and collecting bile for 2 to 5 days, and it was replaced by intraduodenal infusion of the major biliary bile acids (taurocholic acid [TCA], glycochenodeoxycholic acid [GCDCA], and glycocholic acid [GCA] in the rat, guinea pig, and rabbit, respectively) at rates equivalent to the measured hepatic flux of the bile acids. To study the effects of cholesterol, the animals were fed for 7 days on a basal diet with and without 2% cholesterol. Cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities, measured by isotope incorporation assays, were related to bile acid output and composition and hepatic cholesterol concentrations. Intraduodenal infusion of bile acids increased the output of the tested bile acids, but did not significantly change hepatic cholesterol concentrations and had no effect on sterol 27-hydroxylase activity. Neither bile acid depletion nor replacement affected sterol 27-hydroxylase activity when three different substrates (cholesterol, 5beta-cholestane-3alpha,7alpha-diol, and 5beta-cholestane-3alpha,7alpha,12alpha-triol) were tested. In contrast, feeding 2% cholesterol increased hepatic cholesterol concentrations in rats, guinea pigs, and rabbits threefold, twofold, and eightfold, respectively, and increased hepatic mitochondrial sterol 27-hydroxylase activity (conversion of cholesterol to 27-hydroxycholesterol) in all three animal models. The stimulation and feedback inhibition of cholesterol 7alpha-hydroxylase activity by bile acid depletion and replacement were observed in all three animal models, whereas the effect of cholesterol feeding was species-dependent (cholesterol 7alpha-hydroxylase activity increased in the rat, did not change in the guinea pig, and was inhibited in the rabbit). Thus, in contrast to sterol 27-hydroxylase, which was upregulated by cholesterol but not affected by bile acid depletion and replacement in all three animal models, cholesterol 7alpha-hydroxylase activity was controlled consistently and inversely by the hepatic flux of bile acids, but was species-dependent in its response to a 1-week feeding with 2% cholesterol.

Effect of dietary lipids on hepatic and extrahepatic sterol 27-hydroxylase activity in high- and low-responding baboons

Our previous studies found that low low-density lipoprotein (LDL)-responding baboons compared with high LDL-responding baboons have higher hepatic sterol 27-hydroxylase activity when consuming a high-cholesterol and high-fat (HCHF) diet. The present studies were conducted to determine whether the extrahepatic activity of sterol 27-hydroxylase is also higher in low-responding baboons and to assess whether the enzyme is regulated at the protein level. We measured the hepatic sterol 27-hydroxylase activity and protein level and plasma 27-hydroxycholesterol concentration in six low- and six high-responding baboons on both the basal and the HCHF diet. We also compared the sterol 27-hydroxylase activity in the adrenal gland and 27-hydroxycholesterol concentration in blood lymphocytes from high- and low-responding baboons consuming the HCHF diet. With the HCHF diet, the plasma 27-hydroxycholesterol concentration and hepatic sterol 27-hydroxylase activity and protein level increased rapidly in low responders, but not in high responders. Blood lymphocytes of low-responding baboons cultured in the presence of lipoprotein-deficient serum (LPDS) had lower cholesterol concentrations than those from high-responding baboons. Addition of exogenous 27-hydroxycholesterol to the culture medium of blood lymphocytes decreased the cellular cholesterol concentration. Plasma 27-hydroxycholesterol and hepatic sterol 27-hydroxylase activity and protein levels were negatively correlated with the plasma VLDL + LDL cholesterol concentration and VLDL + LDL/HDL cholesterol ratio after 6 weeks on the HCHF diet, but not on the chow diet. The results suggest that sterol 27-hydroxylase activity in both hepatic and extrahepatic tissues attenuates the dietary responsiveness in baboons, and the enzyme activity is not regulated by the specific activity of the protein.

Sex steroids increase cholesterol 7alpha-hydroxylase mRNA in nonhuman primates

One mechanism that may account for our prior observation that oral contraceptives decrease the hepatic cholesterol concentration independently of the low-density lipoprotein (LDL) receptor in sexually intact nonhuman primates is that sex hormones increase biliary cholesterol secretion by increasing hepatic mRNA abundance for cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the conversion of cholesterol into bile acids. To examine the independent effect of estrogen, progestin, and combined estrogen and progestin on the hepatic cholesterol concentration and cholesterol 7alpha-hydroxylase mRNA abundance, 34 ovariectomized adult female cynomolgus monkeys were fed a moderately atherogenic diet for 12 weeks with either oral conjugated equine estrogen ([CEE] n = 8), medroxyprogesterone acetate ([MPA] n = 9), or combined CEE + MPA (n = 9) and compared with a control group (n = 8) that did not receive exogenous sex hormones. After 12 weeks, hepatic cholesterol was significantly lower in CEE-treated (6.2 +/- 1.2 mg/g liver) and CEE + MPA-treated (6.4 +/- 0.9 mg/g liver) animals compared with the control (12.6 +/- 1.9 mg/g liver) and MPA-treated (14.6 +/- 1.6 mg/g liver) groups. Hepatic cholesterol 7alpha-hydroxylase mRNA abundance was significantly increased in CEE-treated (0.553 +/- 0.08 pg/microg RNA), MPA-treated (0.734 +/- 0.12 pg/microg RNA), and CEE + MPA-treated (0.487 +/- 0.07 pg/microg RNA) animals compared with the controls (0.318 +/- 0.03 pg/microg RNA). There was no significant difference in the plasma LDL cholesterol concentration and hepatic LDL receptor mRNA abundance between the groups. These data support but do not prove the hypothesis that low-dose oral estrogen induces an increase in cholesterol 7alpha-hydroxylase mRNA abundance, which is correlated with biliary cholesterol secretion and may result in depletion of hepatic cholesterol.

Effect of naturally reduced ovarian function on plasma lipoprotein and 27-hydroxycholesterol levels in baboons (Papio sp.)

Female baboons over 15 years of age develop irregular menstrual cycles, an indication of declining ovarian function similar to that occurring in perimenopausal women. To determine the effect of declining ovarian function on plasma lipoprotein metabolism and plasma oxysterols, we measured plasma lipoprotein and 27-hydroxycholesterol levels in 86 female baboons from 15-28 years of age with regular (n = 51) and irregular (n = 35) menstrual cycles. We sampled blood and liver while they were consuming a basal diet and after consuming a high cholesterol and high fat diet for 7 weeks. On the basal diet, baboons with irregular cycles had higher VLDL + LDL/HDL cholesterol ratios (P = 0.034). After consuming the HCHF diet for 7 weeks, total plasma (P < 0.001) and VLDL + LDL (P < 0.001) cholesterol concentrations and VLDL + LDL/HDL sterol ratios (P < 0.001) increased in both cycle groups; whereas HDL cholesterol concentrations increased only in baboons with regular cycles (P = 0.009). As a result, HDL cholesterol concentrations (P = 0.006) were lower and VLDL + LDL/HDL cholesterol ratios (P = 0.002) were higher in baboons with irregular cycles on the HCHF diet. Plasma 27-hydroxycholesterol concentrations were higher in baboons with regular cycles than in those with irregular cycles on both basal (P = 0.018) and HCHF (P = 0.037) diets and were positively correlated (P < 0.001) with hepatic sterol 27-hydroxylase activities on both diets. Hepatic sterol 27-hydroxylase activities were negatively correlated with the VLDL + LDL/HDL cholesterol ratios on the HCHF diet (r = -0.342, P = 0.033). These results suggest that declining ovarian function changes the plasma lipoprotein pattern to one that is more atherogenic. Ovarian failure is also associated with decreased concentrations of plasma 27-hydroxycholesterol (the major oxysterol of plasma), and the decrease in plasma 27-hydroxycholesterol concentration was due to the decrease in hepatic sterol 27-hydroxylase activity. The effects of ovarian failure on plasma lipoprotein metabolism and plasma 27-hydroxycholesterol may be mediated by the decreased production of estrogen in perimenopausal baboons. Thus, the perimenopausal baboon is an excellent model for menopause and can be used for studies that cannot be conducted in women.

Effect of estrogen and progesterone on the expression of hepatic and extrahepatic sterol 27-hydroxylase in baboons (Papio sp)

Sterol 27-hydroxylase plays an important role in cholesterol metabolism in hepatic and extrahepatic tissues. To determine whether female sex steroid hormones influence its expression, we measured plasma and hepatic 27-hydroxycholesterol, hepatic mRNA levels, activity of sterol 27-hydroxylase, and adrenal mRNA levels of this enzyme in baboons (n = 6 per group) treated with placebo, estrogen, estrogen + progesterone, and progesterone. We also measured hepatic cholesterol concentration and hepatic acyl coenzyme A:cholesterol acyltransferase (ACAT) activity to determine their relationship with hepatic sterol 27-hydroxylase activity. Plasma 27-hydroxycholesterol concentration was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P = .090) and LDL (P = .026) cholesterol concentrations. Similarly, hepatic sterol 27-hydroxylase activity was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P = .056) and LDL (P = .052) cholesterol concentrations but was positively correlated with hepatic and plasma 27-hydroxycholesterol concentrations (P < .001). Hepatic ACAT activity was increased by progesterone (P < .004) and was positively correlated with plasma (P = .002) and LDL (P = .009) cholesterol concentrations but was negatively correlated with hepatic sterol 27-hydroxylase activity (P = .035). Hepatic and adrenal gland mRNA levels for sterol 27-hydroxylase were increased by estrogen alone or in combination with progesterone (P < .05). Hepatic sterol 27-hydroxylase activity was positively correlated with hepatic mRNA levels (P < .001), an observation suggesting that estrogen increases the activity of sterol 27-hydroxylase by increasing its synthesis. Hepatic cholesterol concentration was not influenced by the hormone treatment. These observations suggest that estrogen alone or in combination with progesterone increases the synthesis of sterol 27-hydroxylase in hepatic and extrahepatic tissues, and the increased activity of hepatic sterol 27-hydroxylase resulting from the increased synthesis is associated with a hypolipidemic effect on plasma LDL levels. Furthermore, progesterone alone increases the hepatic ACAT activity, but given in combination with estrogen progesterone does not have the same effect on hepatic ACAT activity. The effect of estrogen on hepatic ACAT activity may be mediated by sterol 27-hydroxylase and its effect on cholesterol metabolism (decreased cholesterol synthesis and increased output of cholesterol in the bile) in liver.

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.

Effect of dietary cholesterol and fat on the expression of hepatic sterol 27-hydroxylase and other hepatic cholesterol-responsive genes in baboons (Papio species)

Our studies of baboons with low and high responses to dietary cholesterol and fat suggest that low-responding baboons increase the activity of hepatic sterol 27-hydroxylase, an important enzyme of bile acid synthesis, considerably more than do high-responding baboons when challenged with a high-cholesterol, high-fat (HCHF) diet. The present studies were conducted to determine whether hepatic sterol 27-hydroxylase mRNA levels and plasma 27-hydroxycholesterol concentrations also differed with dietary responsiveness. Sixteen adult male baboons with a wide range of VLDL cholesterol plus LDL cholesterol (VLDL+LDL cholesterol) response to an HCHF diet were selected. They were examined first while on a chow diet and then after 1, 3, 6, 10, 18, 26, 36, 52, 72, and 104 weeks on the HCHF diet. Plasma and lipoprotein cholesterol concentrations increased rapidly during the first 3 weeks and stabilized thereafter. On the basis of the response in VLDL/LDL cholesterol, we selected five low-responding, four medium-responding, and five high-responding baboons for more intensive study in more detail. In low responders, the major increase in serum cholesterol concentration was in HDL cholesterol, whereas in medium and high responders it was in both VLDL+LDL and HDL cholesterol. In low and medium responders, serum or VLDL+LDL cholesterol did not change after 3 weeks of consumption of the HCHF diet, whereas in high responders VLDL+LDL cholesterol declined between 78 and 104 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships of plasma and hepatic variables with rates of plasma low-density lipoprotein apolipoprotein B metabolism in baboons fed low- and high-fat diets

These studies were conducted to determine relationships of plasma low-density lipoprotein (LDL) cholesterol concentrations and hepatic mRNA levels for apolipoprotein (apo) B, LDL receptor, and hepatic hydroxymethyl glutaryl coenzyme A (HMG CoA) synthase with plasma LDL apo B production and catabolic rates in baboons maintained on a low-cholesterol, low-fat chow diet and on a high-cholesterol, high-fat (HCHF) diet. Twelve baboons with LDL cholesterol levels ranging from low to high on the HCHF diet but with similar high-density lipoprotein (HDL) cholesterol levels were selected from a colony of selectively bred pedigreed baboons. LDL apo B turnover and hepatic mRNA concentrations for apo B, LDL receptor, and HMG CoA synthase were measured on a chow diet and again on a HCHF diet fed for 14 weeks. LDL apo B fractional catabolic rates decreased and production rates increased on the HCHF diet. Hepatic mRNA concentrations for apo B were not affected by the HCHF diet. Hepatic LDL receptor and HMG CoA synthase mRNA concentrations decreased on the HCHF diet as compared with the chow diet. LDL apo B fractional catabolic rate was negatively correlated with plasma cholesterol, LDL cholesterol, LDL apo B, and LDL apo B production and positively correlated with hepatic LDL receptor and HMG CoA synthase mRNA concentrations and with plasma LDL triglyceride to cholesterol ratio on the chow diet but not on the HCHF diet. LDL apo B production was positively correlated with plasma cholesterol, LDL cholesterol, and LDL apo B on the HCHF diet and negatively correlated with LDL triglyceride to cholesterol ratio on both chow and HCHF diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipids and oxidised lipids in human atherosclerotic lesions at different stages of development

Lipids and oxidised lipids were analysed by GC and GC-MS in human necropsy samples of normal artery and individual atherosclerotic lesions, from aorta and common carotid artery, including fatty streaks, intermediate lesions and advanced lesions. Age-related increases were seen for linoleate, oleate and cholesterol in normal artery, but not in lesions. Each category of lesion was much richer than normal artery in all the lipids measured and in oxidised lipids (oxysterols and hydroxyoctadecadienoic acids), although a degree of overlap existed between the compositions of the various categories of lesion. 26-Hydroxycholesterol and 7 beta-hydroxycholesterol levels were extremely low or undetectable in normal artery, but significantly higher in each of the categories of lesions. The generally wide variation in lipid composition of individual lesions within each category, and the fact that a few individual lesions showed no detectable 26-hydroxycholesterol or 7 beta-hydroxycholesterol, suggested that the lipid oxidation in lesions and therefore perhaps the progression of lesions may be intermittent. Fatty streaks showed the highest concentration of 7 beta-hydroxycholesterol relative to cholesterol, and the lowest ratio of linoleate to oleate, suggesting that this type of lesion experiences the greatest concentration of free radical activity. Levels of the enzymatic product 26-hydroxycholesterol were approximately proportional to cholesterol in all the categories of lesions. 26-Hydroxycholesterol was significantly more abundant in advanced lesions than in intermediate lesions or fatty streaks. 26-Hydroxycholesterol levels were higher in macrophage-rich intermediate and advanced lesions than in their fibrous counterparts. This distinction between macrophage-rich and fibrous lesions was also true for most of the other lipid components, consistent with the involvement of macrophages in lipid accumulation, lipid oxidation and lesion development.