Apparent lack of conversion of sitosterol into C24-bile acids in humans

Advances and Challenges in Plant Sterol Research: Fundamentals, Analysis, Applications and Production

Plant sterols (PS) are cholesterol-like terpenoids widely spread in the kingdom Plantae. Being the target of extensive research for more than a century, PS have topped with evidence of having beneficial effects in healthy subjects and applications in food, cosmetic and pharmaceutical industries. However, many gaps in several fields of PS's research still hinder their widespread practical applications. In fact, many of the mechanisms associated with PS supplementation and their health benefits are still not fully elucidated. Furthermore, compared to cholesterol data, many complex PS chemical structures still need to be fully characterized, especially in oxidized PS. On the other hand, PS molecules have also been the focus of structural modifications for applications in diverse areas, including not only the above-mentioned but also in e.g., drug delivery systems or alternative matrixes for functional foods and fats. All the identified drawbacks are also superimposed by the need of new PS sources and technologies for their isolation and purification, taking into account increased environmental and sustainability concerns. Accordingly, current and future trends in PS research warrant discussion.

Oxidation of sitosterol and transport of its 7-oxygenated products from different tissues in humans and ApoE knockout mice

The most common phytosterols in the human diet are sitosterol and campesterol, which originate exclusively from plant derived food. These phytosterols are taken up by NPC1L1 transport from the intestine into the enterocytes together with cholesterol and other xenosterols. Phytosterols are selectively pumped back from the enterocytes into the intestinal lumen and on the liver site from hepatocytes into bile by heterodimeric ABCG5/G8 transporters. Like cholesterol, both phytosterols are prone to ring and side chain oxidation. It could be shown that oxyphytosterols, found in atherosclerotic tissue, are most likely of in situ oxidation (Schött et al.; Biochem. Biophys. Res. Commun. 2014 Apr 11;446(3):805-10). However, up to now, the entire mechanism of phytosterol oxidation is not clearly understood. Here, we provide further information about the oxidation of sitosterol and the transport of its oxidation products out of tissue. Our survey includes data of 104 severe aortic stenosis patients that underwent an elective aortic valve cusp replacement. We studied their phytosterol concentrations, as well as absolute and substrate corrected oxyphytosterol levels in plasma and valve cusp tissue. In addition, we also examined phytosterol and oxyphytosterol concentrations in plasma and tissues (from brain and liver) of 10 male ApoE knockout mice. The ratio of 7-oxygenated-sitosterol-to-sitosterol exceeds the ratio for 7-oxygenated-campesterol-to-campesterol in plasma and tissue of both humans and mice. This finding indicates that sitosterol is oxidized to a higher amount than campesterol and that a selective oxidative mechanism might exist which can differentiate between certain phytosterols. Secondly, the concentrations of oxyphytosterols found in plasma and tissue support the idea that oxysitosterols are preferably transported out of individual tissues. Selective oxidation of sitosterol and preferred transport of sitosterol oxidation products out of tissue seem to be a metabolic pathway of forced sitosterol clearance from tissue compartments.

Mechanisms for the effects of fish oil lipid emulsions in the management of parenteral nutrition-associated liver disease

Parenteral nutrition (PN) can be life saving for infants unable to adequately absorb enteral nutrients due to intestinal failure from inadequate bowel length or function. However, long-term PN carries significant morbidity and mortality, with 30 to 60% of patients developing progressive liver dysfunction. The etiology of PN-associated liver disease (PNALD) is poorly understood, however the involvement of lipid emulsions in its pathogenesis has been clearly established, with new emphasis emerging on the role of omega-6 polyunsaturated fatty acids and omega-3 polyunsaturated fatty acids. Recent studies evaluating the use of parenteral fish oil lipid emulsions instead of soybean oil lipid emulsions have demonstrated marked improvements in cholestasis, morbidity, and mortality in patients with PNALD treated with fish oil. This review provides an overview of the role of lipid emulsions in the pathogenesis of PNALD and the proposed mechanisms by which parenteral fish oil lipid emulsions may be exerting their beneficial effects.

Differential regulation of bile acid and cholesterol metabolism by the farnesoid X receptor in Ldlr -/- mice versus hamsters

Modulating bile acid synthesis has long been considered a good strategy by which to improve cholesterol homeostasis in humans. The farnesoid X receptor (FXR), the key regulator of bile acid synthesis, was, therefore, identified as an interesting target for drug discovery. We compared the effect of four, structurally unrelated, synthetic FXR agonists in two fat-fed rodent species and observed that the three most potent and selective agonists decreased plasma cholesterol in LDL receptor-deficient (Ldlr (-/-)) mice, but none did so in hamsters. Detailed investigation revealed increases in the expression of small heterodimer partner (Shp) in their livers and of intestinal fibroblast growth factor 15 or 19 (Fgf15/19) in mice only. Cyp7a1 expression and fecal bile acid (BA) excretion were strongly reduced in mice and hamsters by all four FXR agonists, whereas bile acid pool sizes were reduced in both species by all but the X-Ceptor compound in hamsters. In Ldlr (-/-) mice, the predominant bile acid changed from cholate to the more hydrophilic β-muricholate due to a strong repression of Cyp8b1 and increase in Cyp3a11 expression. However, FXR agonists caused only minor changes in the expression of Cyp8b1 and in bile acid profiles in hamsters. In summary, FXR agonist-induced decreases in bile acid pool size and lipophilicity and in cholesterol absorption and synthesis could explain the decreased plasma cholesterol in Ldlr (-/-) mice. In hamsters, FXR agonists reduced bile acid pool size to a smaller extent with minor changes in bile acid profile and reductions in sterol absorption, and consequently, plasma cholesterol was unchanged.

Current and new insights on phytosterol oxides in plant sterol-enriched food

Over the past 15 years, plant sterol-enriched foods have faced a great increase in the market, due to the asserted cholesterol-lowering effect of plant sterols. However, owing to their chemical structures, plant sterols can oxidize and produce a wide variety of oxidation products with controversial biological effects. Although oxyphytosterols can derive from dietary sources and endogenous formation, their single contribution should be better defined. The following review provides an overall and critical picture on the current knowledge and future perspectives of plant sterols-enriched food, particularly focused on occurrence of plant sterol oxidation products and their biological effects. The final objective of this overview is to evince the different aspects of plant sterols-enriched food that require further research, for a better understanding of the influence of plant sterols and their oxides on consumers' health.

Metabolism of a novel side chain modified Delta8(14)-15-ketosterol, a potential cholesterol lowering drug: 28-hydroxylation by CYP27A1

The synthetic inhibitors of sterol biosynthesis, 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one and 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one, are of interest as potential cholesterol lowering drugs. Rapid metabolism of synthetic 15-ketosterols may lead to a decrease, or loss, of their potency to affect lipid metabolism. 3beta-Hydroxy-5alpha-cholest-8(14)-en-15-one is reported to be rapidly side chain oxygenated by rat liver mitochondria. In an attempt to reduce this metabolism, the novel side chain modified 15-ketosterol 3beta-Hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one was synthesized. We have examined the metabolism by recombinant human CYP27A1 of this novel side chain modified 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one and compared the rate of metabolism with that of the previously described 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. Both sterols were found to be efficiently metabolized by recombinant human CYP27A1. None of the two 15-ketosterols was significantly metabolized by microsomal 7alpha-hydroxylation. Interestingly, CYP27A1-mediated product formation was much lower with the side chain modified 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one than with the previously described 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one. A surprising finding was that this novel side chain modified sterol was metabolized mainly in the C-28 position by CYP27A1. The data on 28-hydroxylation by human CYP27A1 provide new insights on the catalytic properties and substrate specificity of this enzyme. The finding that 3beta-hydroxy-24S-methyl-5alpha-cholesta-8(14),22-dien-15-one with a modified side chain is metabolized at a dramatically slower rate than the previously described 15-ketosterol with unmodified side chain may be important for future development of synthetic cholesterol lowering sterols.

The lipid-lowering effect of ezetimibe in pure vegetarians

Results of previous studies have shown that ezetimibe (10 mg/day) reduces LDL cholesterol in patients with mild hypercholesterolemia on a normal-cholesterol diet (dietary intake of 200-500 mg/day) by 16-22%. However, the LDL cholesterol-lowering effect of ezetimibe in subjects with an extremely low dietary cholesterol intake (vegetarians) has not been studied. We conducted a randomized, double-blind, placebo-controlled, two-phase crossover study in 18 healthy pure vegetarians to assess the effect of ezetimibe (10 mg/day) on plasma lipids, cholesterol absorption, and its synthesis. Treatment periods lasted 2 weeks each, with an intervening 2 week washout period. Fractional cholesterol absorption was determined using the continuous dual stable isotope feeding method. Mean dietary cholesterol intake in the pure vegetarians was extremely low and averaged 29.4 +/- 16.8 and 31.4 +/- 14.4 mg/day during the placebo and ezetimibe administration phases, respectively. Fractional cholesterol absorption during the placebo phase was 48.2 +/- 8.2% and was decreased by 58% during ezetimibe treatment to 20.2 +/- 6.2% (P < 0.001). This change in intestinal cholesterol absorption was followed by a significant reduction in LDL cholesterol of 17.3%. In individuals with extremely low dietary cholesterol intake, treatment with ezetimibe (10 mg/day) leads to a significant reduction of cholesterol absorption and a clinically relevant decrease of plasma LDL cholesterol, comparable to that of subjects with a normal dietary cholesterol intake. Thus, the lipid-lowering effect of ezetimibe is mediated mainly through a reduction of the absorption of endogenous (biliary) cholesterol.

High serum phytosterol levels in short bowel patients on parenteral nutrition support

BACKGROUND & AIMS

Patients with short bowel syndrome (SBS) are often depending on parenteral nutrition support (PNS), sometimes complicated by liver dysfunction. Phytosterols in parenteral lipid emulsions have been suspected to be responsible for cholestasis in paediatric nutrition support. The aim of the present study was to evaluate phytosterol intake and serum phytosterol levels in adult SBS patients.

METHODS

We quantified serum levels of phytosterols, cholesterol, and markers for bile acid and cholesterol synthesis, by gas or liquid chromatography in 21 healthy controls, and in 24 adult SBS-patients, 8 with and 16 without PNS. Phytosterols and cholesterol in parenteral lipid emulsions were also quantified.

RESULTS

Serum levels in SBS-patients without PNS; with PNS; and in controls, were on average for phytosterols 11; 63; and 23 micromol/l (P<0.05 for differences), cholesterol 4,2; 3,8; and 5,1 mmol/l, lathosterol 808; 824; and 228 micromol/100 mmol cholesterol, and 7alpha-hydroxy-4-cholesten-3-one 207;191; and 18 nmol/l, respectively (P<0.05 between controls and SBS). Phytosterols in lipid emulsions ranged from 591 to 958 micromol/l.

CONCLUSIONS

SBS-patients on PNS have higher serum levels of phytosterols than other SBS-patients and controls, possibly because of phytosterols in lipid emulsions. Patients with SBS, regardless of nutrition support, have lower serum levels of cholesterol but higher cholesterol and bile acid synthesis compared to controls.

[New delta8(14)-ketosterols with an oxygenated side chain]

New analogues of 3beta-hydroxy-5alpha-cholest-8(14)-en-15-one (15-ketosterol) with modified 17-chains [(22S,23S,24S)- and (22R,23R,24S)-3beta-hydroxy-24-methyl-22,23-oxido-5alpha-cholest-8(14)-en-15-ones and (22RS,23xi,24S)-24-methyl-5alpha-cholesta-3beta,22,23-triol-15-one] were synthesized from (22E,24S)-3beta-acetoxy-24-methyl-5alpha-cholesta-8(14),22-dien-15-one. The chiralities of their 22 and 23 centers were determined by NMR spectroscopy. The isomeric 22,23-epoxides effectively inhibited cholesterol biosynthesis in hepatoma Hep G2 cells (IC50 0.9 +/- 0.2 and 0.7 +/- 0.2 microM, respectively), and their activities significantly exceeded those of 15-ketosterol (IC50 4.0 +/- 0.5 microM), (22E,24S)-3beta-hydroxy-24-methyl-5alpha-cholesta-8(14),22-dien-15-one (IC50 3.1 +/- 0.4 microM), and the 3beta,22,23-triol synthesized (IC50 6.0 +/- 1.0 microM). The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 3; see also http://www.maik.ru.

Cholesterol and plant sterol absorption: recent insights

The recent discovery of transporters in the intestinal mucosa and the canalicular membrane has given new insights into the regulation of intestinal absorption as well as the biliary output of cholesterol and plant sterols. The 2 adenosine triphosphate (ATP)-binding cassette (ABC) half-transporters ABCG5 and ABCG8 are expressed in the mucosa cells and the canalicular membrane, and they resecrete sterols, especially absorbed plant sterols, back into the intestinal lumen and from the liver into bile. Defects of either of these cotransporters lead to the rare inherited disease of phytosterolemia, which is clinically defined by hyperabsorption and diminished biliary excretion of plant sterols. Furthermore, it has been recently demonstrated that the Niemann-Pick C1-Like 1 (NPC1L1) transporter is most likely responsible for the transport of cholesterol and plant sterols from the brush border membrane into the intestinal mucosa. Ezetimibe interferes with NPC1L1, reducing the intestinal uptake of cholesterol and plant sterols. These new findings contribute to our understanding of cholesterol and plant sterol concentrations in serum, and the effect of dietary and drug intervention to reduce serum concentrations of sterols.

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.

Sterol transporters: targets of natural sterols and new lipid lowering drugs

Recent insights in the role of ATP-binding cassette (ABC) transporters ABCG5 and ABCG8, the discovery of ezetimibe, the first approved direct cholesterol absorption inhibitor, as well as the identification of Niemann-Pick C1 Like 1 (NPC1L1) protein as sterol transporter in the gut, focused attention on sterol transport processes in the small intestine and the liver. The identification of defective structures in the ABCG5 or ABCG8 transporters in patients with the rare disease of sitosterolemia elucidated their role as sterol efflux pumps regulating at least in parts the intestinal sterol absorption and the hepatic sterol output. ABCG5 and ABCG8 themselves are regulated by cholesterol via liver X receptors (LXRs), which are also activated by oxysterols and some derivatives of plant sterols. NPC1L1 could recently be identified as a major sterol transporter for the intestinal uptake of cholesterol as well as plant sterols. Studies in NPC1L1 knockout mice indicate that this transporter is essential for the intestinal uptake of sterols and that NPC1L1 might also be involved in the mechanism of action of ezetimibe. However, studies with photoreactive cholesterol as well as with photoreactive ezetimibe analogues suggest that other processes might also be involved in the mechanism of action of ezetimibe.

Sitosterolemia—a rare disease

Elevated plasma plant sterol concentrations, xanthomatosis, and accelerated-often fatal-atherosclerosis at young age are the major findings in patients with homozygous sitosterolemia. A defect in the ABCG5 or ABCG8 co-transporter gene locus (STSL) causes an increased intestinal absorption and a decreased biliary elimination of all sterols, plant sterols as well as cholesterol, leading to a 50 to 200-fold increase in plasma plant sterol concentrations. A few recent publications indicate that even moderately elevated plasma plant sterol levels might be associated with an increased risk of atherosclerosis. This raises the question whether plant sterols themselves might be atherogenic or whether elevated plasma levels are a marker for a decreased ABCG5/G8 transporter activity which itself causes an increased risk for atherosclerosis. However, current data are too few to conclude that elevated plant sterol concentrations in plasma are an additional risk factor for coronary heart disease. But especially young patients suffering from xanthomatosis and/or atherosclerotic diseases with only mildly or moderately elevated plasma cholesterol should be screened for sitosterolemia by measurement of plasma plant sterol levels.

Final report of the amended safety assessment of PEG-5, -10, -16, -25, -30, and -40 soy sterol

PEGs Soy Sterol are polyethylene glycol (PEG) derivatives of soybean oil sterols used in a variety of cosmetic formulations as surfactants and emulsifying agents, skin-conditioning agents, and cleansing and solubilizing agents. When the safety of these ingredients were first reviewed, the available data were insufficient to support safety. New data have since been received and the safety of these ingredients in cosmetics has been substantiated. Current concentration of use ranges from a low of 0.05% in makeup preparations to 2% in moisturizers and several other products. PEGs Soy Sterol are produced by the reaction of the soy sterol hydroxyl with ethylene oxide. In general, ethoxylated fatty acids can contain 1,4-dioxane as a byproduct of ethoxylation. The soy sterols include campesterol, stigmasterol, and beta-sitosterol. The distribution of sterols found in oils derived from common plants is similar, with beta-sitosterol comprising a major component. Impurities include sterol hydrocarbons and cholesterol (4% to 6%) and triterpine alcohols, keto-steroids, and other steroid-like substances (4% to 6%). No pesticide residues were detected. PEGS: Because PEGs are an underlying structure in PEGs Soy Sterols, the previous assessment of PEGs was considered. It is generally recognized that the PEG monomer, ethylene glycol, and certain of its monoalkyl ethers are reproductive and developmental toxins. Given the methods of manufacture of PEGs Soy Sterol, there is no likelihood of ethylene glycol or its alkyl ethers being present. Also, the soybean oil sterol ethers in this ingredient are chemically different from the ethylene glycol alkyl ethers of concern. PEGs are not carcinogenic, although sensitization and nephrotoxicity were observed in burn patients treated with a PEG-based cream. No evidence of systemic toxicity or sensitization was found in studies with intact skin. Plant Phytosterols: Intestinal absorption of ingested plant phytosterols is on the order of 5%, with 95% of the material entering the colon. Absorbed plant phytosterols are transported to the blood. Although there are some data suggesting that sulfates of beta-sitosterol can act as abortifacients in rats and rabbits, other studies of well-characterized plant phytosterols and phytosterol esters demonstrated no effect in an estrogen-binding study, a recombinant yeast assay for estrogen or estrogen-like activity, or a juvenile rat uterotrophic assay for estrogen or estrogen-like activity. In a two-generation reproduction study using rats, plant phytosterol esters in the diet had no effect on any parameter of reproduction or fertility. Subcutaneous injections of beta-sitosterol did reduce sperm concentrations and fertility in rats. Sitosterol inhibited tumor promoting activity of 12-O-tetradecanoylphorbol-13-acetate (TPA) in mice after initiation with 7,12-dimethylbenz[a]anthracene (DMBA), and reduced the tumors produced by N-methylnitrosourea in rats. Phytosterols were not genotoxic in several bacterial, mammalian, and in vitro assay systems. Phytosterols decreased epithelial cell proliferation in the colon of mice and rats, and were cytotoxic for human epidermoid carcinoma of the nasopharynx. PEGs Soy Sterols: The acute oral LD50 in rats of PEG-5-25 Soy Sterol was >10 g/kg. The acute dermal LD50 of a liquid eyeliner containing 2%PEG-5 Soy Sterol was >2 g/kg in rabbits. PEG-5-25 Soy Sterol was not a primary irritant in rabbits when applied undiluted. Undiluted PEG-5 Soy Sterol did not cause sensitization in guinea pigs. PEGs Soy Sterol did not produce ocular toxicity in rabbits. PEG-5 Soy Sterol was negative in the Ames mutagenicity test, with or without metabolic activation. PEG-5 Soy Sterol, at concentrations up to 2%in formulation, did not cause dermal or ocular irritation, dermal sensitization, or photosensitization in clinical studies. Because of the possible presence of 1,4-dioxane reaction product and unreacted ethylene oxide residues, it was considered necessary to use appropriate procedures to remove these from PEGs Soy Sterol before blending them into cosmetic formulations. Based on the systemic toxicity and sensitization seen with PEGs applied to damaged skin, it was recommended that PEGs Soy Sterol should not be used in cosmetic products applied to damaged skin. Although no dermal absorption data were available, oral studies demonstrate that phytosterols and phytosterol esters are not significantly absorbed and do not result in significant systemic exposure. Some small amounts did appear in the ovaries, however. This raises a concern about the potential presence of free phytosterols and beta-Sitosterol, which could have antiestrogenic, antiprogestational, gonadotrophic, antigonadotrophic, and antiandrogenic effects in PEG sterols. These concerns are alleviated by the extensive data showing that well-defined phytosterols and phytosterol esters are not estrogenic and do not pose a hazard to reproduction. Likewise, the absence of impurities in plant phytosterols and phytosterol esters and extensive data demonstrating the absence of any genotoxicity in bacterial and mammalian systems mitigate against the possibility of any carcinogenic effect with those same well-characterized materials. The Cosmetic Ingredient Review (CIR) Expert Panel concluded that the PEGs Soy Sterol are safe as used in cosmetic products.

Inhibition of intestinal cholesterol absorption by ezetimibe in humans

BACKGROUND

Ezetimibe has been shown to inhibit cholesterol absorption in animal models, but studies on cholesterol absorption in humans have not been performed thus far.

METHODS AND RESULTS

The effect of ezetimibe (10 mg/d) on cholesterol absorption and synthesis, sterol excretion, and plasma concentrations of cholesterol and noncholesterol sterols was investigated in a randomized, double-blind, placebo-controlled, crossover study in 18 patients with mild to moderate hypercholesterolemia. Treatment periods lasted 2 weeks with an intervening 2-week washout period. Fractional cholesterol absorption rates averaged 49.8+/-13.8% on placebo and 22.7+/-25.8% on ezetimibe, indicating a reduction of 54% (geometric mean ratio; P< 0.001). Cholesterol synthesis increased by 89% from 931+/-1027 mg/d on placebo to 1763+/-1098 mg/d on ezetimibe (P<0.001), while the ratio of lathosterol-to-cholesterol, an indirect marker of cholesterol synthesis, was increased by 72% (P<0.001). Bile acid synthesis was insignificantly increased (placebo: 264+/-209 mg/d, ezetimibe: 308+/-184 mg/d; P=0.068). Mean percent changes from baseline for LDL and total cholesterol after ezetimibe treatment were -20.4% and -15.1%, respectively (P<0.001 for both), whereas campesterol and sitosterol were decreased by -48% and - 41%, respectively.

CONCLUSION

In humans, ezetimibe inhibits cholesterol absorption and promotes a compensatory increase of cholesterol synthesis, followed by clinically relevant reductions in LDL and total cholesterol concentrations. Ezetimibe also reduces plasma concentrations of the noncholesterol sterols sitosterol and campesterol, suggesting an effect on the absorption of these compounds as well.

Serum plant sterols and biliary cholesterol secretion in humans: studies with ursodeoxycholic acid

Ratios of cholestanol, campesterol, and sitosterol to cholesterol in serum are known to reflect cholesterol absorption efficiency. Here, a possible link between these ratios and biliary secretion rates of cholesterol was investigated. Biliary lipid secretion rates and serum sterols were determined in 13 patients with gallstones. Seven were treated with ursodeoxycholic acid (UDCA) (1,000 mg/d). Serum cholesterol and non-cholesterol sterols were also measured in a cross over study in 20 healthy volunteers, who received either placebo or UDCA (750 mg/d). Biliary cholesterol secretion was significantly lower, whereas the non-cholesterol sterols and their ratio to cholesterol were higher in patients with gallstones treated with UDCA. A highly significant negative linear correlation between the ratios of non-cholesterol sterols to cholesterol and biliary cholesterol secretion was observed. In volunteers, administration of UDCA for 4 weeks was followed by a significant increase in non-cholesterol sterols and their ratios. Even 4 weeks after discontinuing UDCA administration, campesterol and sitosterol were still significantly higher than pretreatment levels, which was also true for the campesterol-cholesterol ratio after 8 weeks. The results suggest that the ratios of cholestanol, campesterol, and sitosterol to cholesterol can be used as indicators of changes in biliary cholesterol secretion rates.

Parenteral nutrition-associated liver complications in children

Parenteral nutrition is a life-saving therapy for patients with intestinal failure. It may be associated with transient elevations of liver enzyme concentrations, which return to normal after parenteral nutrition is discontinued. Prolonged parenteral nutrition is associated with complications affecting the hepatobiliary system, such as cholelithiasis, cholestasis, and steatosis. The most common of these is parenteral nutrition-associated cholestasis (PNAC), which may occur in children and may progress to liver failure. The pathophysiology of PNAC is poorly understood, and the etiology is multifactorial. Risk factors include prematurity, long duration of parenteral nutrition, sepsis, lack of bowel motility, and short bowel syndrome. Possible etiologies include excessive caloric administration, parenteral nutrition components, and nutritional deficiencies. Several measures can be undertaken to prevent PNAC, such as avoiding overfeeding, providing a balanced source of energy, weaning parenteral nutrition, starting enteral feeding, and avoiding sepsis.

Cholesterol absorption inhibitors for the treatment of hypercholesterolaemia

The benefits of lipid lowering therapy on coronary heart disease have been clearly established in many clinical trials on primary and secondary prevention. Despite the availability of potent lipid lowering drugs, many patients do not reach the current treatment goals. This paper reviews new therapeutic approaches in lipid lowering drugs focusing on compounds which lower cholesterol absorption. The role of plant sterols and stanols, new acyl-CoA:cholesterol O-acyl transferase (ACAT) inhibitors, microsomal triglyceride transfer protein (MTP) inhibitors, and ezetimibe are summarised. Although the lipid lowering effect of plant sterols and plant stanols is only moderate, their use as functional foods is beneficial for patients with mild hypercholesterolaemia and is able to enhance the lipid lowering effect of HMG-CoA reductase inhibitors (statins). The role of ACAT inhibitors that might also inhibit cholesterol absorption remains unclear. Avasimibe, the first oral bioavailable ACAT inhibitor, has entered phase III trials. However, the presently available data in humans do not indicate a clear clinical benefit. The role of MTP inhibitors, which exhibit remarkable effects on all plasma lipids, also remains unclear, as safety concerns must first be addressed. Ezetimibe, the first available 2-azetidinone, succeeded in phase III trials showing remarkable effects in inhibition of cholesterol absorption as well as cholesterol lowering. The synergistic effect of co-administration of ezetimibe with statins seemingly offers a new approach in reaching the therapeutic goals.

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.

Genetic analysis of phytosterolaemia

Two women with multiple xanthomas, intermittent arthritis and thrombocytopenia were diagnosed as phytosterolaemia, an autosomal-recessive lipid storage disease, based on their increased serum concentrations of beta-sitosterol, campesterol and sitostanol. The gene responsible for this disease is located within a distance of 18 cM between microsatellite markers of D2S 1788 and D2S1352 at chromosome 2p21. We genotyped the patients and their family members with 16 microsatellite markers around this locus. The results from the homozygosity mapping of one family suggested that the gene was located within the distance of 12.6 cM between D2S2328 and D2S1352. We have shortened the genetic distance by 5.4 cM.

New approaches to understanding the etiology and treatment of total parenteral nutrition-associated cholestasis

Total parenteral nutrition-associated cholestasis (TPN-AC) may be a fatal disease. The only known effective treatment is to discontinue TPN and institute full enteral feedings. However, this is not possible for many patients with severe gastrointestinal failure. Current research supports two theories regarding the etiology of TPN-AC. One proposes that the enteral fast disrupts the enterohepatic circulation. Cholestasis, in this hypothesis, results from a combination of altered gut hormone production and endotoxins produced by bacterial translocation. The second theory implicates the direct toxicity of TPN solution. Amino acid solutions and plant sterols in intralipid have generated much interest. Ursodeoxycholic acid and S-adenosyl-L-methionine are promising treatments for TPN-AC. They have been proven to be effective in animals and adult liver diseases. Cholecystokinin also has been investigated as a possible prophylactic agent. However, results from these experiments do not conclusively show a beneficial effect.

Nutritional support of the pediatric surgical patient

This review discusses the important developments in pediatric surgical nutrition over the past year. Sepsis and total parenteral nutrition-associated cholestasis remain complex problems for patients on total parenteral nutrition. Investigations suggest that total parenteral nutrition may compromise bactericidal activity, increasing the risk of sepsis. Sepsis possibly sensitizes the liver to cholestatic injury. Small volume enteral feeds may restore immune system function. Current research does not support an association between phytosterols in parenteral lipid solutions and total parenteral nutrition-associated cholestasis. Methionine has been identified as a potential hepatotoxin. Ursodeoxycholic acid and S-adenosyl-L-methionine are the most promising treatments of total parenteral nutrition-associated cholestasis. Small bowel transplant is now a reasonable option for patients with irreversible intestinal failure. Patient and graft survival rates have improved with FK-506 (Tacrolimus) immunosuppression. Isolated intestinal grafts have the best survival rate (92% at 1 year). Most surviving graft recipients are weaned off of total parenteral nutrition. The Cox Proportional Hazard model may help to identify candidates for small bowel transplant. This equation predicts the duration of dependence on total parenteral nutrition. Patients with irreversible intestinal failure can then be referred for early small bowel transplantation.

Effect of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor on sterol absorption in hypercholesterolemic subjects

To investigate the potential effects of high-dose 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor on plasma phytosterol, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG), hypercholesterolemic subjects received 40 or 80 mg/d simvastatin in a 24-week prospective clinical trial. Plasma lipid levels were analyzed enzymatically, and plasma phytosterol concentrations were determined using gas-liquid chromatography. The change in the plasma phytosterol-campesterol level was used as an indicator of cholesterol absorption in humans. Simvastatin treatment reduced plasma campesterol (-24%, P = .017) but did not affect circulating stigmasterol and sitosterol levels. A dose of 80 mg/d simvastatin produced a larger decrease (P = .050) in plasma campesterol (0.1680 mmol/L) than 40 mg/d (0.0237 mmol/L) versus baseline. There was a positive correlation between plasma campesterol and TC both before (r = .54, P = .027) and after (r = .63, P = .009) treatment. Plasma TC and TG levels did not differ between groups receiving 40 or 80 mg/d simvastatin. Simvastatin treatment reduced circulating TC, LDL-C, and TG by 40%, 50%, and 33% (P<.007), respectively. There was no significant effect of simvastatin on plasma HDL-C, but the HDL-C/LDL-C ratio increased 1.3-fold (P<.0001). In conclusion, this HMG-CoA reductase inhibitor reduces the plasma campesterol level, a marker of cholesterol absorption, which may contribute to the mechanism by which simvastatin decreases circulating cholesterol levels.

Absorption, excretion, and distribution of plant sterols after proximal gut resection and autotransplantation of porcine ileum

Contribution of different gut segments to plant sterol absorption, adaptation of plant sterol absorption after partial small bowel resection, and effects of gut transplantation (necessitates extrinsic autonomic denervation and lymphatic disruption) on plant sterol biodynamics are unclear. We studied the consequences of massive proximal small bowel resection and autotransplantation of the remaining ileum on the adaptive absorption and biodynamics of plant sterols. Dietary, fecal, biliary, hepatic and plasma plant sterols, fecal elimination and absorption of cholesterol, small bowel morphology, and intestinal transit were determined before (n = 5) and at 4, 8, and 14 wk after resection of the proximal 75% of the jejunoileum (n = 15) and autotransplantation of the remaining ileum (n = 15) or transection (n = 5). Proximal gut resection significantly reduced cholesterol absorption efficiency; percentage absorption and biliary secretion of plant sterols; plasma, biliary and hepatic campesterol-to-cholesterol proportions; and sitosterol proportions in plasma and bile. Autotransplantation of the remaining ileum further significantly decreased cholesterol absorption efficiency; percentage absorption and biliary secretion of campesterol; campesterol proportions in plasma, bile and liver; and plasma proportions of sitosterol while increasing fecal excretion of neutral and acidic steroids. Plasma proportions of the two plant sterols, but absorption of just campesterol, were gradually improved with increasing cholesterol absorption and villus height after proximal gut resection; the same result was observed to a lesser degree after ileal autotransplantation. In addition, significant positive correlations were found between percentage cholesterol and campesterol absorption and the plasma plant sterol proportions in both proximal resection groups, between campesterol absorption and ileal villus height in the resection group, and between campesterol absorption and intestinal transit time in the autotransplantation group. In conclusion, plasma campesterol and sitosterol closely reflect absorption of cholesterol and plant sterols from intact and autotransplanted ileum during adaptation to proximal gut resection. A loss of proximal gut absorptive surface impairs cholesterol and campesterol absorption more than sitosterol absorption, the latter being apparently less dependent on available jejunal villus surface area.

The role of phytosterols in the pathogenesis of liver complications of pediatric parenteral nutrition

Long-term parenteral nutrition of infants who have had major gut resections is associated with a high incidence of cholestatic liver disease. Affected infants have high plasma concentrations of phytosterols--compounds that resemble cholesterol but have an alkylated side chain. The phytosterols that accumulate in patients receiving parenteral nutrition are derived from the soya oil and/or soya lecithin used to make the intravenous lipid emulsion. There is a striking association between phytosterolemia and cholestatic liver disease. This has led us to put forward the hypothesis that phytosterols can cause cholestasis in susceptible infants. Experiments using neonatal piglets indicate that phytosterols (given without any of the other components of parenteral nutrition) can indeed reduce bile flow. We suggest that increasing the content of phytosterols in cell membranes may interfere with the function of important transport proteins involved in the secretion of bile. Other factors that might contribute to cholestasis (such as inhibition of cholesterol 7 alpha-hydroxylase) are discussed.

Phytosterolaemia: diagnosis, characterization and therapeutical approaches

Phytosterolaemia (sitosterolaemia) is a very rare inherited sterol storage disease characterized by tendon and tuberous xanthomas and by a strong predisposition to premature coronary atherosclerosis. In addition to increased or normal serum cholesterol, patients are found to have markedly elevated concentrations of the phytosterols sitosterol and campesterol. These sterols accumulate in all tissues, except the brain. Increased intestinal absorption of plant sterols, impaired biliary excretion, and decreased cholesterol synthesis are suggested as causes for this disease. However, the primary defect has not yet been identified. As well as dietary restrictions of cholesterol and plant sterols, therapeutic approaches based on interruption of the enterohepatic circulation of bile acids by administration of bile acid-binding resins or ileal bypass surgery have been recommended as therapeutic approaches to reduce all serum sterols. Administration of sitostanol, a nonabsorbable saturated plant sterol, showed a significant reduction of serum plant sterols and cholesterol in two patients with phytosterolaemia, presumably by competitive inhibition of sterol absorption.

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.

Dietary phytosterols: a review of metabolism, benefits and side effects

Most animal and human studies show that phytosterols reduce serum/or plasma total cholesterol and low density lipoprotein (LDL) cholesterol levels. Phytosterols are structurally very similar to cholesterol except that they always contain some substitutions at the C24 position on the sterol side chain. Plasma phytosterol levels in mammalian tissue are normally very low due primarily to poor absorption from the intestine and faster excretion from liver compared to cholesterol. Phytosterols are able to be metabolized in the liver into C21 bile acids via liver other than normal C24 bile acids in mammals. It is generally assumed that cholesterol reduction results directly from inhibition of cholesterol absorption through displacement of cholesterol from micelles. Structure-specific effects of individual phytosterol constituents have recently been shown where saturated phytosterols are more efficient compared to unsaturated compounds in reducing cholesterol levels. In addition, phytosterols produce a wide spectrum of therapeutic effects in animals including anti-tumour properties. Phytosterols have been shown experimentally to inhibit colon cancer development. With regard to toxicity, no obvious side effects of phytosterol have been observed in studies to date, except in individual with phytosterolemia, an inherited lipid disorder. Further characterization of the influence of various phytosterol subcomponents on lipoprotein profiles in humans is required to maximize the usefulness of this non-pharmacological approach to reduction of atherosclerosis in the population.

Phytosterolemia in children with parenteral nutrition-associated cholestatic liver disease

BACKGROUND

Lipid emulsions used for parenteral nutrition (PN) contain phytosterols. Our hypothesis was that these phytosterols can accumulate and contribute to cholestatic liver disease and other complications of PN, e.g., thrombocytopenia (which occurs in hereditary phytosterolemia).

METHODS

Using gas chromatography-mass spectrometry, plasma concentrations of sterols were measured in 29 children aged 2 months to 9 years receiving PN and in 29 age-matched controls. The children receiving PN fell into two subgroups: 5 with severe PN-associated cholestatic liver disease (bilirubin level, > 100 mumol/L; aspartate aminotransferase [AST] level, > 200 U/L) and 24 with a bilirubin level of < 100 mumol/L and/or AST level of < 200 U/L.

RESULTS

The 5 children with severe PN-associated liver disease had plasma concentrations of phytosterols and sitostanol that were as high as those seen in patients with hereditary phytosterolemia (total phytosterols 1.3-1.8 mmol/L). All 5 had intermittent thrombocytopenia. A reduction in intake of lipid emulsion to < 50 mL.kg-1.wk-1 was associated with a decrease in plasma phytosterol concentrations and an improvement in liver function tests and platelet counts in two patients. Children with less severe PN-associated liver disease had lower plasma phytosterol concentrations than the 5 with severe disease.

CONCLUSIONS

Children receiving PN who have high plasma phytosterol concentrations also have cholestatic liver disease and thrombocytopenia; phytosterolemia might contribute to the pathogenesis of complications of PN.

Cholesterol and bile acid biodynamics after total small bowel resection and bile diversion in humans

BACKGROUND

In humans, the patterns of cholesterol and bile acid biodynamics in the absence of the small intestine are not yet known. They are described in two parenterally fed patients several months after total enterectomy and bile diversion.

METHODS

After an intravenous pulse of [3H]cholesterol, a long-term study involved the analysis of both the decay in the specific activity of plasma cholesterol and the biliary outputs of sterols and bile acids.

RESULTS

Plasma cholesterol input reached 2-3 g/day (vs. 1 g/day in healthy patients), mostly from synthesis. As assessed by sterol balance, whole body cholesterol synthesis approximated 6 g/day (vs. 0.6-0.8 g/day). Unusually, about 60% of the newly synthesized cholesterol was eliminated, without prior transit into the bloodstream, from the liver into the bile. Bile acid conversion concerned over 90% (vs. 40%-50%) of the cholesterol meant to be excreted, issued from plasma or hepatic synthesis. In addition to cholic and chenodeoxycholic acids, one patient secreted up to 1 g/day of 7-epicholic acid.

CONCLUSIONS

The stimulation (up to 10-fold) of the cholesterol and bile acid synthesis, stronger than that observed following ileal bypass or resection or complete bile diversion, could well be partially linked to the absence of small bowel tissue per se.