Usefulness of gas chromatographic profiles of plasma total lipids in diagnosis of phytosterolemia

Activation of the liver X receptor stimulates trans-intestinal excretion of plasma cholesterol

Recent studies have indicated that direct intestinal secretion of plasma cholesterol significantly contributes to fecal neutral sterol loss in mice. The physiological relevance of this novel route, which represents a part of the reverse cholesterol transport pathway, has not been directly established in vivo as yet. We have developed a method to quantify the fractional and absolute contributions of several cholesterol fluxes to total fecal neutral sterol loss in vivo in mice, by assessing the kinetics of orally and intravenously administered stable isotopically labeled cholesterol combined with an isotopic approach to assess the fate of de novo synthesized cholesterol. Our results show that trans-intestinal cholesterol excretion significantly contributes to removal of blood-derived free cholesterol in C57Bl6/J mice (33% of 231 micromol/kg/day) and that pharmacological activation of LXR with T0901317 strongly stimulates this pathway (63% of 706 micromol/kg/day). Trans-intestinal cholesterol excretion is impaired in mice lacking Abcg5 (-4%), suggesting that the cholesterol transporting Abcg5/Abcg8 heterodimer is involved in this pathway. Our data demonstrate that intestinal excretion represents a quantitatively important route for fecal removal of neutral sterols independent of biliary secretion in mice. This pathway is sensitive to pharmacological activation of the LXR system. These data support the concept that the intestine substantially contributes to reverse cholesterol transport.

Stigmasterol reduces plasma cholesterol levels and inhibits hepatic synthesis and intestinal absorption in the rat

Plant sterols compete with cholesterol (cholest-5-en-3beta-ol) for intestinal absorption to limit absorption and lower plasma concentrations of cholesterol. Stigmasterol (24-ethyl-cholesta-5,22-dien-3beta-ol; Delta(22) derivative of sitosterol [24-ethyl-cholest-5-en-3beta-ol]), but not campesterol (24-methyl-cholest-5-en-3beta-ol) and sitosterol, is reported to inhibit cholesterol biosynthesis via inhibition of sterol Delta(24)-reductase in human Caco-2 and HL-60 cell lines. We studied the effect of feeding 0.5% stigmasterol on plasma and liver sterols and intestinal cholesterol and sitosterol absorption in 12 wild-type Kyoto (WKY) and 12 Wistar rats. After 3 weeks of feeding, cholesterol and sitosterol absorption was determined in 6 rats from each group by plasma dual-isotope ratio method. After 3 more weeks, plasma and hepatic sterols and hepatic enzyme activities were determined in all rats. After feeding stigmasterol, baseline plasma cholesterol was 1.3 times and plant sterols 3 times greater in WKY compared with Wistar rats. Stigmasterol feeding lowered plasma cholesterol by approximately 11%, whereas plasma campesterol and sitosterol levels were virtually unchanged in both rat strains, and stigmasterol constituted 3.2% of plasma sterols in WKY rats and 1% in Wistar rats. After 6 weeks of feeding, cholesterol and sitosterol absorption decreased 23% and 30%, respectively, in WKY, and 22% and 16%, respectively, in the Wistar rats as compared with untreated rats. The intestinal bacteria in both rat strains metabolized stigmasterol to mainly the 5beta-H stanol (>40%), with only small amounts of 5alpha-H derivative (approximately 1.5%), whereas the C-22 double bond was resistant to bacterial metabolism. Hepatic stigmasterol levels increased from 11 microg/g liver tissue to 104 mug/g in WKY rats and from 5 microg/g liver tissue to 21 microg/g in Wistar rats. 3-Hydroxy-3-methylglutaryl coenzyme A reductase activity was suppressed 4-fold in the WKY and almost 1.8-fold in Wistar rats, cholesterol 7alpha-hydroxylase activity was suppressed 1.6-fold in the WKY and 3.5-fold in Wistar rats, whereas cholesterol 27-hydroxylase activity was unchanged after feeding. In conclusion, stigmasterol, when fed, lowers plasma cholesterol levels, inhibits intestinal cholesterol and plant sterol absorption, and suppresses hepatic cholesterol and classic bile acid synthesis in Wistar as well as WKY rats. However, plasma and hepatic incorporation of stigmasterol is low.

Sitosterolaemia in Switzerland: molecular genetics links the US Amish-Mennonites to their European roots

Sitosterolaemia is a rare autosomal recessive disease characterized by increased intestinal absorption of plant sterols, decreased hepatic excretion into bile and elevated concentrations in plasma phytosterols. Homozygous or compound heterozygous loss of function mutations in either of the ATP-binding cassette (ABC) proteins ABCG5 and ABCG8 explain the increased absorption of plant sterols. Here we report a Swiss index patient with sitosterolaemia, who presented with the classical symptoms of xanthomas, but also had mitral and aortic valvular heart disease. Her management over the last 20 years included a novel therapeutic approach of high-dose cholesterol feeding that was semi-effective. Mutational and extended haplotype analyses showed that our patient shared this haplotype with that of the Amish-Mennonite sitosterolaemia patients, indicating they are related ancestrally.

Effect of high plant sterol-enriched diet and cholesterol absorption inhibitor, SCH 58235, on plant sterol absorption and plasma concentrations in hypercholesterolemic wild-type Kyoto rats

BACKGROUND AND AIMS

Plant sterols are widely distributed in human diet but are poorly absorbed so that their plasma levels are very low. However, when fed in large amounts, they lower plasma cholesterol levels by interfering with cholesterol absorption. We have studied the effect of 4 weeks of feeding a chow diet supplemented with 1% plant sterols [brassicasterol (6.3%), campesterol (28.5%), stigmasterol (15.6%) and sitosterol (49.6%)], with or without SCH 58235 (a derivative of ezetimibe), 30 mg/kg per day, known to suppress intestinal cholesterol absorption, on plasma, tissue, biliary, and fecal sterols in Wistar and wild-type Kyoto (WKY) rats, and their metabolism by intestinal bacteria.

METHODS

After 2 weeks of feeding control or experimental diet, rats were given [3alpha-(3)H]sitosterol intravenously and [4-(14)C]sitosterol by mouth, and blood was collected after 1, 2, 3, and 5 days after labeling to determine sitosterol absorption. Feces were collected during the last 3 days and freeze dried. At the end of feeding, bile fistulas were created in 3 rats of each strain and bile was collected for 1 hour. All rats were then sacrificed and plasma and liver were collected for sterol measurements and activities of hepatic HMG-CoA reductase, cholesterol 7alpha-hydroxylase, and cholesterol 27-hydroxylase.

RESULTS

Wild-type Kyoto rats were hypercholesterolemic compared to Wistar rats and had increased plant sterols in the plasma. Plasma cholesterol tended to be lower in WKY rats after feeding with plant sterol-enriched diet whereas plant sterol levels rose to approximately 31% of plasma sterols in WKY and 14% in Wistar rats. However, brassicasterol and stigmasterol, with a double bond at C-22, constituted less than 3.5% of total plasma plant sterols. After feeding, biliary plant sterols increased 2.25-fold in Wistar and 1.5-fold in WKY rats, suggesting less hepatic clearance in WKY rats. SCH 58235 feeding significantly increased plasma as well as biliary cholesterol levels in both the untreated and plant sterol-fed WKY rats, and the plasma plant sterols showed a tendency to increase but did not reach significant level. Intestinal bacteria in both rat strains metabolized all plant sterols to mainly the 5beta-H-stanols. However, the C-22 double bond was stable to bacterial degradation. Intestinal absorption of sitosterol and cholesterol was increased 1.5- and 1.3-fold, respectively, in the WKY rats as compared to the Wistar rats, and plant sterol feeding lowered absorption of these sterols in both strains. Absorption of both these sterols was also lowered in SCH 58235-treated rats in both strains and was further lowered when SCH 58235 and plant sterols were simultaneously fed. The activity of the rate-limiting enzyme, HMG-CoA reductase, was increased 1.57-fold in Wistar rats and 1.27-fold in WKY rats that were fed plant sterols as compared to untreated rats.

CONCLUSIONS

(1) Plant sterol absorption was increased whereas hepatic elimination of all sterols was diminished in WKY rats accounting for elevated cholesterol and plant sterol levels. (2) The 1% plant sterol-enriched diet tended to lower plasma cholesterol levels whereas SCH 58235 feeding significantly increased plasma cholesterol levels in the WKY rats. (3) Intestinal absorption of sterols with C-22 double bond is diminished and the side-chain double bond is resistant to intestinal bacteria.

Sitosterolemia in ABC-transporter G5-deficient mice is aggravated on activation of the liver-X receptor

BACKGROUND AND AIMS

Mutations in either adenosine triphosphate- binding cassette (ABC) half-transporter G5 or G8 cause sitosterolemia. It has been proposed that ABCG5/ABCG8 heterodimers mediate secretion of plant sterols and cholesterol by hepatocytes into bile and their efflux from enterocytes into the intestinal lumen.

METHODS

To test whether deficiency of ABCG5 alone is sufficient to induce sitosterolemia, Abcg5-null mice were generated and characterized with respect to sterol metabolism.

RESULTS

Abcg5 deficiency was associated with strongly elevated plasma levels of beta-sitosterol (37-fold) and campesterol (7.7-fold) as well as reduced plasma cholesterol concentrations (-40%). Retention of orally administered [(3)H]beta-sitosterol in the intestinal wall (+550%) and plasma (+640%) was higher in Abcg5-null mice than in wild-type controls. Surprisingly, high plasma beta-sitosterol and campesterol concentrations were even further elevated in Abcg5-null mice on treatment with the synthetic LXR agonist T0901317 (0.015% dietary supplementation, 10 days), whereas these concentrations were reduced by approximately 75% in wild-type mice. Both cholesterol and phospholipid concentrations in gallbladder bile were decreased, but, unexpectedly, cholesterol/phospholipid ratios were unchanged in the absence of Abcg5 and increased in both genotypes on LXR activation. Hepatic expression of Abcg8 was reduced by about 35% in Abcg5-deficient mice when compared with controls. No compensatory overexpression of other ABC transporters potentially involved in hepatic cholesterol trafficking was observed on messenger RNA level.

CONCLUSIONS

Our data show that disruption of the Abcg5 gene alone is sufficient to cause hyperabsorption of dietary plant sterols and sitosterolemia in mice, whereas the ability to secrete cholesterol into bile is maintained.

Down-regulation of hepatic and intestinal Abcg5 and Abcg8 expression associated with altered sterol fluxes in rats with streptozotocin-induced diabetes

AIM/HYPOTHESIS

Type I diabetes is associated with altered hepatic bile formation and increased intestinal cholesterol absorption. The aim of this study was to evaluate whether altered expression of the ATP-Binding Cassette half-transporters Abcg5 and Abcg8, recently implicated in control of both hepatobiliary cholesterol secretion and intestinal cholesterol absorption, contributes to changed cholesterol metabolism in experimental diabetes.

METHODS

mRNA and protein expression of Abcg5 and Abcg8 were determined in the liver and intestine of rats with streptozotozin-induced diabetes and related to relevant metabolic parameters in plasma, liver and bile.

RESULTS

Hepatic mRNA expression of both Abcg5 (-76%) and Abcg8 (-71%) was reduced in diabetic rats when compared to control rats. In spite of increased HDL cholesterol, considered a major source of biliary cholesterol, secretion of the sterol into bile relative to that of bile salts was reduced by 65% in diabetic animals. Intestinal mRNA expression of Abcg5 (-47%) and Abcg8 (-43%) as well as Abcg5 protein contents were also reduced in insulin-deficient animals. This was accompanied by a three- to four-fold increase in plasma beta-sitosterol and campesterol concentrations and by a doubling of the calculated apparent cholesterol absorption. These effects partially normalized upon insulin supplementation.

CONCLUSION/INTERPRETATION

Our data indicate that effects of insulin-deficiency on bile composition and cholesterol absorption in rats are, at least partly, attributable to changes in hepatic and intestinal Abcg5 and Abcg8 expression.

Plasma non-cholesterol sterols

Increased levels of plasma sterols other than cholesterol can serve as markers for abnormalities in lipid metabolism associated with clinical disease. Premature atherosclerosis and xanthomatosis occur in two rare lipid storage diseases, Cerebrotendinous xanthomatosis (CTX) and sitosterolemia. In CTX, cholestanol is present in all tissues. In sitosterolemia, dietary campesterol and sitosterol accumulate in plasma and red blood cells. Plasma accumulation of oxo-sterols is associated with inhibition of bile acid synthesis and other abnormalities in plasma lipid metabolism. Inhibition of cholesterol biosynthesis is associated with plasma appearance of precursor sterols. The increases in non-cholesterol sterols, while highly significant, represent only minor changes in plasma sterols, which require capillary gas-liquid chromatography and MS for effective detection, identification and quantification.

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.

Genetic basis of sitosterolemia

The molecular mechanisms regulating the amount of dietary cholesterol retained by the body, as well as the body's ability to exclude other dietary sterols selectively, are poorly understood. An average Western diet will contain approximately 250-500 mg of dietary cholesterol and approximately 200-400 mg of non-cholesterol sterols, of which plant sterols are the major constituents. Approximately 50-60% of dietary cholesterol is absorbed and retained by the normal human body, but less than 1% of the non-cholesterol sterols are retained. There thus exists a subtle mechanism that allows the body to distinguish between cholesterol and non-cholesterol sterols. In sitosterolemia, a rare autosomal recessive disorder, affected individuals hyperabsorb and retain not only cholesterol but also all other sterols, including plant and shellfish sterols from the intestine. Consequently, patients with this disease have very high levels of plant sterols in the plasma, and develop tendon and tuberous xanthomas, accelerated atherosclerosis, and premature coronary artery disease. The STSL locus has been mapped to human chromosome 2p21. Mutations in two tandem ABC genes, ABCG5 and ABCG8, encoding sterolin-1 and -2, respectively, are now known to be mutant in sitosterolemia. The identification of these genes should now lead to a better understanding of the molecular mechanism(s) governing the highly selective absorption and retention of cholesterol by the body. Indeed, it is the very existence of this disease that has given credence to the hypothesis that there is a molecular pathway that regulates dietary cholesterol absorption and sterol excretion by the body.

Chromatographic methods in the analysis of cholesterol and related lipids

Methods using thin-layer chromatography, solid-phase extraction, gas chromatography, high-performance liquid chromatography and supercritical fluid chromatography are described for the analysis of single cholesterol, esterified and sulfated cholesterol, and for cholesterol in the context of other lipid components, like other sterols and lipid classes. In connection with these techniques several clinical applications are mentioned.

Identification of core aldehydes among in vitro peroxidation products of cholesteryl esters

Synthetic cholesteryl 5-oxovalerate and 9-oxononanoate were used as reference standards for the isolation and identification of cholesteryl ester core aldehydes from tert-butyl hydroperoxide/Fe++ oxidation of synthetic and natural cholesteryl esters. The core aldehydes were recovered from the peroxidation products by thin-layer chromatography as the free aldehydes or the 2,4-dinitrophenylhydrazones and were identified, respectively, by gas-liquid chromatography (GLC) and by GLC combined with mass spectrometry (GC/MS) or by reverse-phase high-performance liquid chromatography (HPLC) and by HPLC with MS (LC/MS). The core aldehydes produced by peroxidation of cholesteryl linoleate were identified as mainly 9-oxononanoates of cholesterol and oxycholesterols, with smaller amounts of the 8-oxooctenoates, 10-oxodecenoates, 11-oxoundecenoates and 12-oxododecenoates. Peroxidation of cholesteryl arachidonate yielded 5-oxovalerates of cholesterol and the oxycholesterols as the main products with smaller amounts of the 4-oxobutyrates, 6-oxohexenoates, 7-oxoheptenoates, 8-oxooctenoates, 9-oxononenoates, 9-oxononadienoates and 10-oxodecadienotes. The oxycholesterols resulting from the peroxidation of the steroid ring were identified as mainly 7-keto-, 7 alpha-hydroxy- and 7 beta-hydroxy-cholesterols and 5 alpha,6 alpha- and 5 beta,6 beta-epoxy-cholestanols. Cholesteryl palmitate and oleate did not yield core aldehydes in the present peroxidation system. In these esters, the sterol and linoleic acid moieties appeared to be oxygenated at about the same rate, while the arachidonic acid moiety reacted more rapidly than did the sterol moiety.

Relationships of serum plant sterols (phytosterols) and cholesterol in 595 hypercholesterolemic subjects, and familial aggregation of phytosterols, cholesterol, and premature coronary heart disease in hyperphytosterolemic probands and their first-degree relatives

To assess relationships of serum phytosterols (plant sterols [P]) to serum cholesterol (C), P were measured by gas-liquid chromatography (GLC) in 595 hypercholesterolemics (top C quintile in screening of 3,472 self-referred subjects). A second specific aim was to determine whether high serum P would track over time and whether they would predict familial aggregation of high C, high low-density lipoprotein cholesterol (LDLC), high apolipoprotein (apo) B, and increased premature coronary heart disease (CHD) in hyperphytosterolemic probands and their first-degree relatives. Mean +/- (SD) C was 260 +/- 56 mg/dL, campesterol (CAMP) was 2.10 +/- 1.6 micrograms/mL, stigmasterol (STIG) 1.71 +/- 1.67, sitosterol (SIT) 2.98 +/- 1.61, and total P 6.79 +/- 3.66 micrograms/mL. Serum C correlated with CAMP (r = .15, P less than or equal to .001), STIG (r = .10, P less than or equal to .02), SIT (r = .34, P less than or equal to .0001), and total P (r = .29, P less than or equal to .0001). High serum CAMP and STIG were associated with a personal or family history of CHD in subjects less than or equal to age 55 years (premature CHD). In 21 hyperphytosterolemic probands who initially had at least one P at or above the 95th percentile and a second P at or above the 75th percentile, P were remeasured 2 years later. Initial and 2-year follow-up CAMP, STIG, and SIT did not differ (P greater than .7). Initial and follow-up CAMP were correlated (r = .47, P = .03).(ABSTRACT TRUNCATED AT 250 WORDS)

Gas chromatographic profiles of plasma total lipids as indicators of dietary history. Correlation with fat intake based on 24-h dietary recall

Fasting plasma total lipid profiles were determined by high-temperature gas chromatography on a total of 1246 free living urban subjects, ages 20-59 years, from the Toronto-McMaster Lipid Research Clinic Population Study. Quantitative estimates of the major molecular species, lipid classes and lipid class ratios were correlated with a total of twelve dietary lipid components, including total saturated and unsaturated fats. oleic and linoleic acids, and cholesterol, to give appropriate Spearman coefficients (rS) and tests of significance (P) for groups of 775 males and 471 females. The intake of the various nutrients was derived from a 24-h dietary recall. The most significant correlations varying from rs +/- 0.1-0.4 and P less than 0.0001-0.0005 were between the intake of total fat, individual saturated and unsaturated fats, and the ratios of C50/C54 triacylglycerols and the C34/C36 phosphatidylcholines, which reflected the nature and quantity of the dietary fat consumed. Increases in dietary cholesterol and saturated fat produced small increases in plasma cholesterol and saturated triacylglycerols, while unsaturated dietary fat produced small decreases in saturated and increases in unsaturated plasma triacylglycerols. These changes in the plasma lipid parameters are consistent with those observed previously in much more limited dietary experiments with accurately known composition of ingested fats. It is, therefore, concluded that direct gas chromatographic profiling of plasma total lipids provides a simple and rapid method of verifying the overall correctness of the dietary recall.

Gas chromatographic analysis of intact steryl esters in wild type Saccharomyces cerevisiae and in an ester accumulating mutant

The steryl ester faction from wild type and mutant strains of the yeast Saccharomyces cerevisiae was analyzed without saponification by a non-polar capillary gas chromatographic column. When expressed as microgram ester/mg dry wt, the total ester fraction remained constant or declined slightly from log to stationary phase in the wild type. In the mutant the decrease was more dramatic. No individual ergosteryl ester species was dominant throughout the culture cycle in the wild type. A compound tentatively identified as zymosteryl palmitate was the most prevalent ester in wild type log phase cells, ergosta-5,7-dienyl palmitate and ergosta-5,7-dienyl palmitoleate were the major esters in stationary cells. In the mutant strain, ergosteryl esters of palmitate, palmitoleate, oleate, and stearate were the major ester components throughout the culture cycle. Like the wild type, however, the mutant showed an increase in the proportion of ergosta-5,7-dienyl esters in the stationary phase of the culture cycle. The data did not indicate a sterol/fatty acid specificity during the culture cycle.