Cholesterol absorption is mainly regulated by the jejunal and ileal ATP-binding cassette sterol efflux transporters Abcg5 and Abcg8 in mice

Lemon Flavonoid Extract Eriomin Improves Pro/Antioxidant Status and Interferes with Cholesterol Metabolism without Affecting Serum Cholesterol Levels in Aged Rats

This study aimed to assess the antioxidant capacity of lemon flavonoid extract Eriomin® (LE) and its impact on cholesterol metabolism in the context of healthy aging. We orally treated 24-month-old male Wistar rats with an LE (40 mg/kg) suspended in 0.3 mL of sunflower oil. At the same time, control groups received an equal volume of sunflower oil (CON) or remained untreated (ICON) daily for 4 weeks. We examined LE's effects on superoxide dismutase and catalase- and glutathione-related enzyme activities, the concentration of lipid peroxides and protein carbonyls, total oxidant status (TOS) and antioxidant status (TAS), and oxidative stress index (OSI) in the liver, jejunum, and ileum. We also measured total cholesterol, its biosynthetic precursors (lanosterol, lathosterol, desmosterol), its degradation products (bile acid precursors) in the serum, liver, jejunum, and ileum, and serum phytosterols (intestinal absorption markers). LE reduced TOS, TAS, and OSI (p < 0.05) compared with control values, indicating its consistent antioxidant action in all examined organs. LE lowered hepatic desmosterol (p < 0.05) while also reducing 7α- and 24-hydroxycholesterol levels in the liver and ileum (p < 0.01). Serum cholesterol, hepatic gene expression, and the immunostaining intensity of CYP7A1 were unchanged. In conclusion, LE exerted non-enzymatic antioxidant effects and reduced cholesterol degradation, reducing its biosynthesis products, thereby maintaining serum cholesterol levels.

Pentapeptide IIAEK ameliorates cholesterol metabolism via the suppression of intestinal cholesterol absorption in mice

Dietary protein-derived peptides are effective in improving dyslipidemia and hypercholesterolemia. We previously identified a novel cholesterol-lowering pentapeptide IIAEK from milk beta-lactoglobulin. However, it remains unclear whether IIAEK affects the micellar solubility of cholesterol and the bile acid-binding ability to lower cholesterol. Moreover, there is no direct evidence that IIAEK inhibits intestinal cholesterol absorption and affects hepatic cholesterol and fecal steroid excretion in vivo. Herein, we showed that IIAEK did not affect the micellar solubility of cholesterol and the bile acid-binding ability. However, we found that IIAEK decreased serum and liver cholesterol levels and increased fecal steroid excretion in mice. Interestingly, IIAEK markedly suppressed the intestinal absorption of [3H]-cholesterol in mice. In conclusion, we found that IIAEK ameliorated cholesterol metabolism by suppressing intestinal cholesterol absorption without affecting in vitro micellar solubility of cholesterol and the bile acid-binding ability in mice.

Differences in Cholesterol Metabolism, Hepato-Intestinal Aging, and Hepatic Endocrine Milieu in Rats as Affected by the Sex and Age

Age and sex influence serum cholesterol levels, but the underlying mechanisms remain unclear. To investigate further, we measured cholesterol, precursors (surrogate synthesis markers), degradation products (oxysterols and bile acid precursors) in serum, the liver, jejunum, and ileum, as well as serum plant sterols (intestinal absorption markers) in male and female Wistar rats (4 and 24 months old). The analysis of histomorphometric and oxidative stress parameters (superoxide dismutase, catalase, glutathione-related enzyme activities, lipid peroxide, and protein carbonyl concentrations) in the liver and jejunum offered further insights into the age- and sex-related differences. The hepatic gene expression analysis included AR, ERα, and sex-specific growth hormone-regulated (Cyp2c11 and Cyp2c12) and thyroid-responsive (Dio1, Tbg, and Spot 14) genes by qPCR. We observed age-related changes in both sexes, with greater prominence in females. Aged females had significantly higher serum cholesterol (p < 0.05), jejunum cholesterol (p < 0.05), and serum plant sterols (p < 0.05). They exhibited poorer hepato-intestinal health compared with males, which was characterized by mild liver dysfunction (hydropic degeneration, increased serum ALT, p < 0.05, and decreased activity of some antioxidant defense enzymes, p < 0.05), mononuclear inflammation in the jejunal lamina propria, and age-related decreases in jejunal catalase and glutathione peroxidase activity (p < 0.05). Aged females showed increased levels of 27-hydroxycholesterol (p < 0.05) and upregulated ERα gene expression (p < 0.05) in the liver. Our study suggests that the more significant age-related increase in serum cholesterol in females is associated with poorer hepato-intestinal health and increased jejunal cholesterol absorption. The local increase in 27-hydroxycholesterol during aging might reduce the hepatoprotective effects of endogenous estrogen in the female liver.

Gene expressions between obligate bamboo-eating pandas and non-herbivorous mammals reveal converged specialized bamboo diet adaptation

BACKGROUND

It is inevitable to change the function or expression of genes during the environmental adaption of species. Both the giant panda (Ailuropoda melanoleuca) and red panda (Ailurus fulgens) belong to Carnivora and have developed similar adaptations to the same dietary switch to bamboos at the morphological and genomic levels. However, the genetic adaptation at the gene expression level is unclear. Therefore, we aimed to examine the gene expression patterns of giant and red panda convergent specialized bamboo-diets. We examined differences in liver and pancreas transcriptomes between the two panda species and other non-herbivorous species.

RESULTS

The clustering and PCA plots suggested that the specialized bamboo diet may drive similar expression shifts in these two species of pandas. Therefore, we focused on shared liver and pancreas DEGs (differentially expressed genes) in the giant and red panda relative to other non-herbivorous species. Genetic convergence occurred at multiple levels spanning carbohydrate metabolism, lipid metabolism, and lysine degradation. The shared adaptive convergence DEGs in both organs probably be an evolutionary response to the high carbohydrate, low lipid and lysine bamboo diet. Convergent expression of those nutrient metabolism-related genes in both pandas was an intricate process and subjected to multi-level regulation, including DNA methylation and transcription factor. A large number of lysine degradation and lipid metabolism related genes were hypermethylated in promoter regions in the red panda. Most genes related to carbohydrate metabolism had reduced DNA methylation with increased mRNA expression in giant pandas. Unlike the red panda, the core gene of the lysine degradation pathway (AASS) doesn't exhibit hypermethylation modification in the giant panda, and dual-luciferase reporter assay showed that transcription factor, NR3C1, functions as a transcriptional activator in AASS transcription through the binding to AASS promoter region.

CONCLUSIONS

Our results revealed the adaptive expressions and regulations of the metabolism-related genes responding to the unique nutrients in bamboo food and provided data accumulation and research hints for the future revelation of complex mechanism of two pandas underlying convergent adaptation to a specialized bamboo diet.

Expression of ABC transporters during syncytialization in preeclampsia

Preeclampsia complicates 2-8% of pregnancies and is associated with prematurity and intrauterine growth restriction. Cholesterol and sterol transport is a key function of the placenta and it is elicited through ATP binding cassette (ABC) transporters. ABCA1 expression changes during trophoblast cell fusion, a process required to form the placental syncytium that enables maternal-fetal nutrient transfer. ABCA1 expression is dysregulated in preeclamptic placentas. But whether ABC transporters expression during trophoblast fusion is disrupted in preeclampsia remains unknown. We investigated if cholesterol and sterol ABC transporters are altered in term and preterm preeclampsia placentas and during human cytotrophoblast syncytialization. Human placental biopsies were collected from healthy term (≥37 weeks; n = 11) and term preeclamptic (≥36 6/7 weeks; n = 8) and pre-term preeclamptic (28-35 weeks; n = 8) pregnancies. Both, protein and mRNA expression for ABCA1, ABCG1, ABCG5, and ABCG8 were evaluated. Primary cytotrophoblasts isolated from a subset of placentas were induced to syncytialize for 96 h and ABCA1, ABCG1 and ABCG8 mRNA expression evaluated at 0 h and 96 h. Protein and gene expression of ABC transporters were not altered in preeclamptic placentas. In the healthy Term group, ABCA1 expression was similar before and after syncytialization. After 96 h of syncytialization, mRNA expression of ABCA1 and ABCG1 increased significantly, while ABCG8 decreased significantly in term-preeclampsia, but not pre-term preeclampsia. While placental expression of ABCA1 and ABCG1 remained unaltered in term preeclampsia, the disruption in their dynamic expression pattern during cytotrophoblast syncytialization suggests that cholesterol transport may contribute to the pathophysiologic role of the placenta in preeclampsia.

The Bioavailability and Biological Activities of Phytosterols as Modulators of Cholesterol Metabolism

Phytosterols are natural sterols widely found in plants that have a variety of physiological functions, and their role in reducing cholesterol absorption has garnered much attention. Although the bioavailability of phytosterols is only 0.5–2%, they can still promote cholesterol balance in the body. A mechanism of phytosterols for lowering cholesterol has now been proposed. They not only reduce the uptake of cholesterol in the intestinal lumen and affect its transport, but also regulate the metabolism of cholesterol in the liver. In addition, phytosterols can significantly reduce the plasma concentration of total cholesterol, triglycerides, and low-density lipoprotein cholesterol (LDL-C), with a dose-response relationship. Ingestion of 3 g of phytosterols per day can reach the platform period, and this dose can reduce LDL-C by about 10.7%. On the other hand, phytosterols can also activate the liver X receptor α-CPY7A1 mediated bile acids excretion pathway and accelerate the transformation and metabolism of cholesterol. This article reviews the research progress of phytosterols as a molecular regulator of cholesterol and the mechanism of action for this pharmacological effect.

Albino mice with the point mutation at the tyrosinase locus show high cholesterol diet-induced NASH susceptibility

Non-alcoholic fatty liver disease (NAFLD) constitutes a metabolic disorder with high worldwide prevalence and increasing incidence. The inflammatory progressive state, non-alcoholic steatohepatitis (NASH), leads to liver fibrosis and carcinogenesis. Here, we evaluated whether tyrosinase mutation underlies NASH pathophysiology. Tyrosinase point-mutated B6 (Cg)-Tyr^c-2J/J mice (B6 albino) and C57BL/6J black mice (B6 black) were fed with high cholesterol diet (HCD) for 10 weeks. Normal diet-fed mice served as controls. HCD-fed B6 albino exhibited high NASH susceptibility compared to B6 black, a phenotype not previously reported. Liver injury occurred in approximately 50% of B6 albino from one post HCD feeding, with elevated serum alanine aminotransferase and aspartate aminotransferase levels. NASH was induced following 2 weeks in severe-phenotypic B6 albino (sB6), but B6 black exhibited no symptoms, even after 10 weeks. HCD-fed sB6 albino showed significantly higher mortality rate. Histological analysis of the liver revealed significant inflammatory cell and lipid infiltration and severe fibrosis. Serum lipoprotein analysis revealed significantly higher chylomicron and very low-density lipoprotein levels in sB6 albino. Moreover, significantly higher small intestinal lipid absorption and lower fecal lipid excretion occurred together with elevated intestinal NPC1L1 expression. As the tyrosinase point mutation represents the only genetic difference between B6 albino and B6 black, our work will facilitate the identification of susceptible genetic factors for NASH development and expand the understanding of NASH pathophysiology.

Neurotrophin-4 is essential for survival of the majority of vagal afferents to the mucosa of the small intestine, but not the stomach

Vagal afferents form the primary gut-to-brain neural axis, communicating signals that regulate gastrointestinal (GI) function and promote satiation, appetition and reward. Neurotrophin-4 (NT-4) is essential for the survival of vagal smooth muscle afferents of the small intestine, but not the stomach. Here we took advantage of near-complete labeling of GI vagal mucosal afferents in Nav1.8cre-Rosa26tdTomato transgenic mice to determine whether these afferents depend on NT-4 for survival. We quantified the density and distribution of vagal afferent terminals in the stomach and small intestine mucosa and their central terminals in the solitary tract nucleus (NTS) and area postrema in NT-4 knockout (KO) and control mice. NT-4KO mice exhibited a 75% reduction in vagal afferent terminals in proximal duodenal villi and a 55% decrease in the distal ileum, whereas, those in the stomach glands remained intact. Vagal crypt afferents were also reduced in some regions of the small intestine, but to a lesser degree. Surprisingly, NT-4KO mice exhibited an increase in labeled terminals in the medial NTS. These findings, combined with previous results, suggest NT-4 is essential for survival of a large proportion of all classes of vagal afferents that innervate the small intestine, but not those that supply the stomach. Thus, NT-4KO mice could be valuable for distinguishing gastric and intestinal vagal afferent regulation of GI function and feeding. The apparent plasticity of central vagal afferent terminals - an increase in their density - could have compensated for loss of peripheral terminals by maintaining near-normal levels of satiety signaling.

Recent Advances in the Critical Role of the Sterol Efflux Transporters ABCG5/G8 in Health and Disease

Cardiovascular disease is characterized by lipid accumulation, inflammatory response, cell death, and fibrosis in the arterial wall and is the leading cause of morbidity and mortality worldwide. Cholesterol gallstone disease is caused by complex genetic and environmental factors and is one of the most prevalent and costly digestive diseases in the USA and Europe. Although sitosterolemia is a rare inherited lipid storage disease, its genetic studies led to identification of the sterol efflux transporters ABCG5/G8 that are located on chromosome 2p21 in humans and chromosome 17 in mice. Human and animal studies have clearly demonstrated that ABCG5/G8 play a critical role in regulating hepatic secretion and intestinal absorption of cholesterol and plant sterols. Sitosterolemia is caused by a mutation in either the ABCG5 or the ABCG8 gene alone, but not in both simultaneously. Polymorphisms in the ABCG5/G8 genes are associated with abnormal plasma cholesterol metabolism and may play a key role in the genetic determination of plasma cholesterol concentrations. Moreover, ABCG5/G8 is a new gallstone gene, LITH9. Gallstone-associated variants in ABCG5/G8 are involved in the pathogenesis of cholesterol gallstones in European, Asian, and South American populations. In this chapter, we summarize the latest advances in the critical role of the sterol efflux transporters ABCG5/G8 in regulating hepatic secretion of biliary cholesterol, intestinal absorption of cholesterol and plant sterols, the classical reverse cholesterol transport, and the newly established transintestinal cholesterol excretion, as well as in the pathogenesis and pathophysiology of ABCG5/G8-related metabolic diseases such as sitosterolemia, cardiovascular disease, and cholesterol gallstone disease.

Update on the Molecular Mechanisms Underlying the Effect of Cholecystokinin and Cholecystokinin-1 Receptor on the Formation of Cholesterol Gallstones

Cholecystokinin (CCK) is an important neuro-intestinal peptide hormone produced by the enteroendocrine I-cells in the upper part of small intestine. Protein- and fat-enriched food plays an important role in triggering CCK secretion from the intestine. Carbohydrates stimulate only small amounts of CCK release. The CCK-1 receptor (CCK-1R) is largely localized in the gallbladder, sphincter of Oddi, pancreas, small intestine, gastric mucosa, and pyloric sphincter, where it is responsible for CCK to regulate multiple digestive processes including gallbladder contraction, pancreatic secretion, small intestinal transit, and gastric emptying. Accumulated evidence clearly demonstrates that CCK regulates gallbladder and small intestinal motility through CCK-1R signaling cascade and the effect of CCK-1R on small intestinal transit is a physiological response for regulating intestinal cholesterol absorption. Disruption of the Cck or the Cck-1r gene in mice significantly increases the formation of cholesterol gallstones by disrupting gallbladder emptying and biliary cholesterol metabolism, as well as promoting intestinal absorption of cholesterol. Abnormalities in gallbladder motility function in response to exogenously administered CCK are found primarily in patients with cholesterol gallstones. Patients with pigment gallstones display an intermediate degree of gallbladder motility defect without gallbladder inflammation and enlarged fasting gallbladder. Dysfunctional gallbladder contractility has been found under several conditions such as pregnancy, obesity, diabetes, celiac disease, and total parenteral nutrition although gallstones are not observed. The gallbladder-specific CCK-1R-selective agonist may lead to an efficacious novel way for preventing gallstone formation by promoting gallbladder emptying, particularly for pregnant women and subjects with dysfunctional gallbladder motility function such as celiac patients, as well as patients with total parenteral nutrition.

GutSelf: Interindividual Variability in the Processing of Dietary Compounds by the Human Gastrointestinal Tract

Nutritional research is currently entering the field of personalized nutrition, to a large extent driven by major technological breakthroughs in analytical sciences and biocomputing. An efficient launching of the personalized approach depends on the ability of researchers to comprehensively monitor and characterize interindividual variability in the activity of the human gastrointestinal tract. This information is currently not available in such a form. This review therefore aims at identifying and discussing published data, providing evidence on interindividual variability in the processing of the major nutrients, i.e., protein, fat, carbohydrates, vitamins, and minerals, along the gastrointestinal tract, including oral processing, intestinal digestion, and absorption. Although interindividual variability is not a primary endpoint of most studies identified, a significant number of publications provides a wealth of information on this topic for each category of nutrients. This knowledge remains fragmented, however, and understanding the clinical relevance of most of the interindividual responses to food ingestion described in this review remains unclear. In that regard, this review has identified a gap and sets the base for future research addressing the issue of the interindividual variability in the response of the human organism to the ingestion of foods.

Sterol Characteristics in Silkworm Brain and Various Tissues Characterized by Precise Sterol Profiling Using LC-MS/MS

Sterols, especially cholesterol (Chl), are fundamental for animal survival. Insects lacking the ability to synthesize Chl are sterol auxotrophic animals and utilize dietary Chl and phytosterols to survive. The sterols obtained from a diet are distributed to the tissues; however, sterol homeostasis in insect tissues remains to be elucidated. This study sought to understand the sterol characteristics of insect tissues through detailed sterol quantification and statistics. The combination of sterol quantification using liquid chromatography tandem mass spectrometry (LC-MS/MS) and principal component analysis (PCA) revealed tissue-specific sterol characteristics in the silkworm, Bombyx mori, a phytophagous insect. We found that insect tissues have tissue-intrinsic sterol profiles. The brain has a unique sterol composition as compared to other tissues—high concentration of Chl and less accumulation of phytosterols. Other tissues also have intrinsic sterol characteristics, which when defined by dietary sterols or Chl metabolites, indicate preference for a sterol and consistently manage their own sterol homeostasis. Though most tissues never change sterol profiles during development, the brain drastically changes its sterol profile at the wandering stage, indicating that it could alter sterol composition in preparation for metamorphosis. These results suggest the existence of tissue- and sterol-specific systems for sterol homeostasis in insects.

Modulation of Rat Liver Regeneration after Partial Hepatectomy by Dietary Cholesterol

INTRODUCTION

The aim of study was to evaluate impact of long-term dietary cholesterol overload on the cholesterol homeostasis and liver regeneration.

MATERIAL AND METHODS

Serum lipid parameters, 14C-cholesterol incorporation, liver DNA synthesis and protein expression was determined in partially hepatectomized (PH) rats fed with a standard (SLD) or hypercholesterolemic (CHOL) diet.

RESULTS

29-day intake of CHOL diet before PH produced increase in serum total cholesterol, LDL lipoprotein, and triglyceride concentration. PH provoked decrease in serum total cholesterol and triglyceride concentration in both groups. PH was associated with increase in serum ALT activity more pronounced in CHOL animals. Hepatic DNA synthesis was increased after PH in both groups, but lower in CHOL. Hypercholesterolemic diet reduced the absorption of radiolabelled cholesterol in intestine and then activity in blood and liver. The 14C-cholesterol hepatic activities tend to increase after PH in both groups. CHOL diet produced up-regulation of Acyl-CoA:cholesterol acyltransferase-2 protein expression. PH was associated with increase of LDL receptor and Acyl-CoA:cholesterol acyltransferase-2 protein expression in both dietary groups.

DISCUSSION

Liver regeneration after PH is negatively influenced by CHOL diet. The increased uptake of cholesterol in the liver after PH associated with up-regulation of LDL receptor protein expression suggests preferential use of extrahepatic cholesterol by the liver.

The Impact of Egg Nutrient Composition and Its Consumption on Cholesterol Homeostasis

Nutrient deficiencies and excess are involved in many aspects of human health. As a source of essential nutrients, eggs have been used worldwide to support the nutritional needs of human societies. On the other hand, eggs also contain a significant amount of cholesterol, a lipid molecule that has been associated with the development of cardiovascular diseases. Whether the increase of egg consumption will lead to elevated cholesterol absorption and disruption of cholesterol homeostasis has been a concern of debate for a while. Cholesterol homeostasis is regulated through its dietary intake, endogenous biosynthesis, utilization, and excretion. Recently, some research interests have been paid to the effects of egg consumption on cholesterol homeostasis through the intestinal cholesterol absorption. Nutrient components in eggs such as phospholipids may contribute to this process. The goals of this review are to summarize the recent progress in this area and to discuss some potential benefits of egg consumption.

Serum, liver and bile sitosterol and sitostanol in obese patients with and without NAFLD

Background and aims: Non-alcoholic fatty liver disease (NAFLD) associates with low levels of serum plant sterols in cross-sectional studies. In addition, it has been suggested that the hepatic sterol transport mechanisms are altered in NAFLD. Therefore, we investigated the association between serum, liver and bile plant sterols and sitostanol with NAFLD.

Methods: Out of the 138 individuals (age: 46.3 ± 8.9, body mass index: 43.3 ± 6.9 kg/m², 28% men and 72% women), 44 could be histologically categorized to have normal liver, and 94 to have NAFLD. Within the NAFLD group, 28 had simple steatosis and 27 had non-alcoholic steatohepatitis. Plant sterols and sitostanol were measured from serum (n=138), liver (n=38), and bile (n=41). The mRNA expression of genes regulating liver sterol metabolism and inflammation was measured (n=102).

Results: Liver and bile sitostanol ratios to cholesterol were higher in those with NAFLD compared to those with histologically normal liver (all P<0.022). Furthermore, liver sitostanol to cholesterol ratio correlated positively with histological steatosis and lobular inflammation (r_s > 0.407, P<0.01 for both). In contrast, liver sitosterol to cholesterol ratio correlated negatively with steatosis (r_s = −0.392, P=0.015) and lobular inflammation (r_s = −0.395, P=0.014). Transcriptomics analysis revealed suggestive correlations between serum plant sterol levels and mRNA expression.

Conclusion: Our study showed that liver and bile sitostanol ratios to cholesterol associated positively and liver sitosterol ratio to cholesterol associated negatively with liver steatosis and inflammation in obese individuals with NAFLD..

Butyrate from pectin fermentation inhibits intestinal cholesterol absorption and attenuates atherosclerosis in apolipoprotein E-deficient mice

Short-chain fatty acids (SCFAs), the major products of dietary fiber fermentation by intestinal microflora, exert beneficial effects on pathogenesis of multiple metabolic diseases. The aim of this study was to determine whether SCFAs from fermentation of pectin (PE), a soluble dietary fiber, prevent the development of atherosclerosis in apolipoprotein E-deficient (apoE^-/-) mice. Male apoE^-/- mice (8-week-old) were fed a high-fat, high-cholesterol diet (HCD; 21% wt/wt fat, 0.15% wt/wt cholesterol) or HCD supplemented with 20% wt/wt PE (HCD+PE) alone or with antibiotics (HCD+PE + A) in drinking water for 12 weeks. Serum lipids and SCFAs concentrations, atherosclerotic lesion area, and intestinal morphology and function were measured. Caco-2 cells were treated with SCFAs to determine whether they affected the expression of genes involved in cholesterol absorption. HCD+PE-treated mice exhibited decreased serum total and low-density lipoprotein cholesterol, and reduced atherosclerotic lesion area compared with HCD mice. These beneficial effects of PE were not observed in the HCD+PE+A group. Incubation of Caco-2 cells with butyrate, but not acetate and propionate, down-regulated the expression of Niemann-Pick C1-Like 1 but up-regulated the ATP-binding cassette transporters G5 and G8 (ABCG5 and G8) at the mRNA level. Butyrate treatment also increased transcriptional activity of liver X receptor in Caco-2 cells. Our data suggest that butyrate from PE intestinal fermentation protects mice from the progression of diet-induced atherosclerosis in apoE^-/- mice. These findings suggest a novel mechanism by which dietary fiber may prevent the development of atherosclerosis.

Cholesterol and Lipoprotein Metabolism and Atherosclerosis: Recent Advances In reverse Cholesterol Transport

Atherosclerosis is characterized by lipid accumulation, inflammatory response, cell death and fibrosis in the arterial wall, and is major pathological basis for ischemic coronary heart disease (CHD), which is the leading cause of morbidity and mortality in the USA and Europe. Intervention studies with statins have shown to reduce LDL cholesterol levels and subsequently the risk of developing CHD. However, not all the aggressive statin therapy could decrease the risk of developing CHD. Many clinical and epidemiological studies have clearly demonstrated that the HDL cholesterol is inversely associated with risk of CHD and is a critical and independent component of predicting its risk. Elucidations of HDL metabolism give rise to therapeutic targets with potential to raising plasma HDL cholesterol levels, thereby reducing the risk of developing CHD. The concept of reverse cholesterol transport is based on the hypothesis that HDL displays an cardioprotective function, which is a process involved in the removal of excess cholesterol that is accumulated in the peripheral tissues (e.g., macrophages in the aortae) by HDL, transporting it to the liver for excretion into the feces via the bile. In this review, we summarize the latest advances in the role of the lymphatic route in reverse cholesterol transport, as well as the biliary and the non-biliary pathways for removal of cholesterol from the body. These studies will greatly increase the likelihood of discovering new lipid-lowering drugs, which are more effective in the prevention and therapeutic intervention of CHD that is the major cause of human death and disability worldwide.

ABC Transport Proteins in Cardiovascular Disease-A Brief Summary

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters may play an important role in the pathogenesis of atherosclerotic vascular diseases due to their involvement in cholesterol homeostasis, blood pressure regulation, endothelial function, vascular inflammation, as well as platelet production and aggregation. In this regard, ABC transporters, such as ABCA1, ABCG5 and ABCG8, were initially found to be responsible for genetically-inherited syndromes like Tangier diseases and sitosterolemia. These findings led to the understanding of those transporter’s function in cellular cholesterol efflux and thereby also linked them to atherosclerosis and cardiovascular diseases (CVD). Subsequently, further ABC transporters, i.e., ABCG1, ABCG4, ABCB6, ABCC1, ABCC6 or ABCC9, have been shown to directly or indirectly affect cellular cholesterol efflux, the inflammatory response in macrophages, megakaryocyte proliferation and thrombus formation, as well as vascular function and blood pressure, and may thereby contribute to the pathogenesis of CVD and its complications. Furthermore, ABC transporters, such as ABCB1, ABCC2 or ABCG2, may affect the safety and efficacy of several drug classes currently in use for CVD treatment. This review will give a brief overview of ABC transporters involved in the process of atherogenesis and CVD pathology. It also aims to briefly summarize the role of ABC transporters in the pharmacokinetics and disposition of drugs frequently used to treat CVD and CVD-related complications.

Lipocalin 2 alleviates iron toxicity by facilitating hypoferremia of inflammation and limiting catalytic iron generation

Iron is an essential transition metal ion for virtually all aerobic organisms, yet its dysregulation (iron overload or anemia) is a harbinger of many pathologic conditions. Hence, iron homeostasis is tightly regulated to prevent the generation of catalytic iron (CI) which can damage cellular biomolecules. In this study, we investigated the role of iron-binding/trafficking innate immune protein, lipocalin 2 (Lcn2, aka siderocalin) on iron and CI homeostasis using Lcn2 knockout (KO) mice and their WT littermates. Administration of iron either systemically or via dietary intake strikingly upregulated Lcn2 in the serum, urine, feces, and liver of WT mice. However, similarly-treated Lcn2KO mice displayed elevated CI, augmented lipid peroxidation and other indices of organ damage markers, implicating that Lcn2 responses may be protective against iron-induced toxicity. Herein, we also show a negative association between serum Lcn2 and CI in the murine model of dextran sodium sulfate (DSS)-induced colitis. The inability of DSS-treated Lcn2KO mice to elicit hypoferremic response to acute colitis, implicates the involvement of Lcn2 in iron homeostasis during inflammation. Using bone marrow chimeras, we further show that Lcn2 derived from both immune and non-immune cells participates in CI regulation. Remarkably, exogenous rec-Lcn2 supplementation suppressed CI levels in Lcn2KO serum and urine. Collectively, our results suggest that Lcn2 may facilitate hypoferremia, suppress CI generation and prevent iron-mediated adverse effects.

Plasma Cholesterol-Lowering Activity of Lard Functionalized with Mushroom Extracts Is Independent of Niemann-Pick C1-like 1 Protein and ABC Sterol Transporter Gene Expression in Hypercholesterolemic Mice

Interest in food matrices supplemented with mushrooms as hypocholesterolemic functional foods is increasing. This study was to (i) investigate the hypocholesterolemic activity of lard functionalized with mushroom extracts (LF) including fungal β-glucans, water-soluble polysaccharides, or ergosterol and (ii) examine the LF influence on transcriptional mechanisms involved in cholesterol metabolism. mRNA levels of 17 cholesterol-related genes were evaluated in jejunum, cecum, and liver of high cholesterol-fed mice. The four tested LFs decreased plasma cholesterol by 22-42%, HDLc by 18-40%, and LDLc by 27-51%, and two of them increased mRNA levels of jejunal Npc1l1 and Abcg5 and hepatic Npc1l1. mRNA levels of other cholesterol-related genes were unchanged. These findings suggest that LF may have potential as a dietary supplement for counteracting diet-induced hypercholesterolemia and could be a source for the development of novel cholesterol-lowering functional foods. However, the cholesterol-lowering effect was unrelated to transcriptional changes, suggesting that post-transcriptional mechanisms could be involved.

ABCG5/G8 deficiency in mice reduces dietary triacylglycerol and cholesterol transport into the lymph

The adenosine triphosphate-binding cassette (ABC) transporter G5/G8 is critical in protecting the body from accumulating dietary plant sterols. Expressed in the liver and small intestine, it transports plant sterols into the biliary and intestinal lumens, thus promoting their excretion. The extent to which G5/G8 regulates cholesterol absorption remains unclear. G5/G8 is also implicated in reducing the absorption of dietary triacylglycerols (TAG) by unknown mechanisms. We hypothesized that G5/G8 suppresses the production of chylomicrons, and its deficiency would enhance the absorption of both dietary TAG and cholesterol. The aim of this study was to investigate the effects of G5/G8 deficiency on lipid uptake and secretion into the lymph under steady-state conditions. Surprisingly, compared with wild-type mice (WT) (n = 9), G5/G8 KO (n = 13) lymph fistula mice given a continuous intraduodenal infusion of [3H]-TAG and [14C]-cholesterol showed a significant (P < 0.05) reduction in lymphatic transport of both [(3)H]-TAG and [(14)C]-cholesterol, concomitant with a significant (P < 0.05) increase of [(3)H]-TAG and [(14)C]-cholesterol accumulated in the intestinal lumen. There was no difference in the total amount of radiolabeled lipids retained in the intestinal mucosa between the two groups. G5/G8 KO mice given a bolus of TAG showed reduced intestinal TAG secretion compared with WT, suggesting an independent role for G5/G8 in facilitating intestinal TAG transport. Our data demonstrate that G5/G8 deficiency reduces the uptake and secretion of both dietary TAG and cholesterol by the intestine, suggesting a novel role for the sterol transporter in the formation and secretion of chylomicrons.

Cholesterol and Plant Sterol Efflux from Cultured Intestinal Epithelial Cells Is Mediated by ATP-Binding Cassette Transporters

In this study we analyzed functions of ATP-binding cassette (ABC) transporters involved in sterol transport from Caco-2 cells. Treatment with a synthetic liver x receptor ligand elevated both mRNA and protein levels of ABCG5, G8, and ABCA1. The ligand stimulated cholesterol efflux, suggesting that ABC transporters are involved in it. To identify the acceptors of cholesterol, potential molecules such as apolipoprotein A-I, glycocholic acid, phosphatidylcholine, and bile acid micelles were added to the medium. Apo A-I, a known acceptor of cholesterol transported by ABCA1, elevated cholesterol efflux on the basal side, whereas the others raised cholesterol efflux on the apical side. Moreover, bile acid micelles preferentially augmented plant sterol efflux rather than cholesterol. Finally, in HEK293 cells stably expressing ABCG5/G8, bile acid micelle-mediated sterol efflux was significantly accelerated. These results indicate that ABCG5/G8, unlike ABCA1, together with bile acids should participate in sterol efflux on the apical surface of Caco-2 cells.

New insights into the molecular mechanism of intestinal fatty acid absorption

BACKGROUND

Dietary fat is one of the most important energy sources of all the nutrients. Fatty acids, stored as triacylglycerols (also called triglycerides) in the body, are an important reservoir of stored energy and derived primarily from animal fats and vegetable oils.

DESIGN

Although the molecular mechanisms for the transport of water-insoluble amphipathic fatty acids across cell membranes have been debated for many years, it is now believed that the dominant means for intestinal fatty acid uptake is via membrane-associated fatty acid-binding proteins, that is, fatty acid transporters on the apical membrane of enterocytes.

RESULTS

These findings indicate that intestinal fatty acid absorption is a multistep process that is regulated by multiple genes at the enterocyte level, and intestinal fatty acid absorption efficiency could be determined by factors influencing intraluminal fatty acid molecules across the brush border membrane of enterocytes. To facilitate research on intestinal, hepatic and plasma triacylglycerol metabolism, it is imperative to establish standard protocols for precisely and accurately measuring the efficiency of intestinal fatty acid absorption in humans and animal models. In this review, we will discuss the chemical structure and nomenclature of fatty acids and summarize recent progress in investigating the molecular mechanisms underlying the intestinal absorption of fatty acids, with a particular emphasis on the physical chemistry of intestinal lipids and the molecular physiology of intestinal fatty acid transporters.

CONCLUSIONS

A better understanding of the molecular mechanism of intestinal fatty acid absorption should lead to novel approaches to the treatment and the prevention of fatty acid-related metabolic diseases that are prevalent worldwide.

Induction of intestinal stem cells by R-spondin 1 and Slit2 augments chemoradioprotection

Cancer research has been rightly and successfully focused on prevention, early detection, and identification of specific molecular targets that distinguish the malignant cells from the neighbouring benign cells. However, reducing lethal tissue injury caused by intensive chemoradiotherapy during treatment of late-stage metastatic cancers remains a key clinical challenge. Here we tested whether the induction of adult stem cells could repair chemoradiation-induced tissue injury and prolong overall survival in mice. We found that intestinal stem cells (ISCs) expressed Slit2 and its single-span transmembrane cell-surface receptor roundabout 1 (Robo1). Partial genetic deletion of Robo1 decreased ISC numbers and caused villus hypotrophy, whereas a Slit2 transgene increased ISC numbers and triggered villus hypertrophy. During lethal dosages of chemoradiation, administering a short pulse of R-spondin 1 (Rspo1; a Wnt agonist) plus Slit2 reduced ISC loss, mitigated gut impairment and protected animals from death, without concomitantly decreasing tumour sensitivity to chemotherapy. Therefore Rspo1 and Slit2 may act as therapeutic adjuvants to enhance host tolerance to aggressive chemoradiotherapy for eradicating metastatic cancers.

Chronic ethanol consumption alters mammalian gastrointestinal content metabolites

Chronic ethanol consumption is associated with not only the alteration of metabolic profiles in biofluids but also the composition of the gut microbiome. Our understanding of the importance of the intestinal microbiota as well as the disturbances elicited by ethanol intervention is limited by the fact that previous analyses have primarily focused on biofluids and liver tissue metabolome; the metabolic profiles of the gastrointestinal (GI) contents are rarely investigated. In this study, we applied a metabonomics approach using a high performance liquid chromatography-time-of-flight mass spectrometry (HPLC-TOF MS) and gas chromatography-mass spectrometry (GC-MS) to characterize the metabolic alterations of the contents within the GI tract (stomach, duodenum, jejunum, ileum, cecum, colon, and rectum) in male Sprague-Dawley rats following 8 weeks of ethanol exposure. We obtained a snapshot of the distinct changes of the intestinal content metabolite composition in rats with ethanol exposure, which indicated a profound impact of ethanol consumption on the intestinal metabolome. Many metabolic pathways that are critical for host physiology were affected, including markedly altered bile acids, increased fatty acids and steroids, decreased carnitines and metabolites involved in lipid metabolism, a significant decrease of all amino acids and branched chain amino acids, and significantly decreased short chain fatty acids except for acetic acid, which rapidly elevated as a product of ethanol metabolism. These results provide an improved understanding of the systemic alteration of intestinal content metabolites in mammals and the interplay between the host and its complex resident microbiota and may aid in the design of new therapeutic strategies that target these interactions.

Role of the ABCG8 19H risk allele in cholesterol absorption and gallstone disease

BACKGROUND

Gallstone disease is associated with p.D19H of ABCG8 as well as alterations of cholesterol and bile acid metabolism. However, molecular mechanisms have not been fully elucidated. It is important to understand the link between the sterol transporters ABCG5/8 and NPC1L1 and intestinal cholesterol absorption as well as de novo synthesis in gallstone patients stratified according to 19H risk allele. Moreover, the functional importance of the 19H variant on intestinal ABCG8 feature remains to be clarified.

METHODS

Measurements of serum surrogate markers of cholesterol absorption (plant sterols: sitosterol, campesterol) and synthesis (cholesterol precursor: lathosterol) were carried out by gas chromatography/mass spectrometry (GC/MS). For expression studies, total RNA was isolated from 168 ileal biopsies of study participants with (34) and without gallstone disease (134). Messenger RNA was measured by LightCycler real-time PCR. Genomic DNA was obtained from blood leukocytes. Genotype frequencies of p.D19H were established using MALDI-TOF mass spectrometry.

RESULTS

Compared to controls, cholesterol absorption but not synthesis in gallstone carriers was diminished by about 21% based on low serum sitosterol (P = 0.0269) and campesterol (P = 0.0231) to cholesterol ratios. D19H was found to be significantly associated with gallstones (odds ratio [OR] = 2.9, P = 0.0220, 95% confidence interval [CI]:1.22-6.89), particularly in the overweight cohort (OR = 3.2, P = 0.0430, 95% CI:1.07-9.26). Cholesterol absorption was about 24% lower in individuals carrying p.D19H compared to wild type (Psitosterol = 0.0080, Pcampesterol = 0.0206). Moreover, irrespective of phenotype, carriers of p.D19H displayed a significant lower absorption than carriers of the major allele. The most pronounced effect on cholesterol absorption ratio was observed for serum campesterol levels (wild type controls to mutated controls 28%, P = 0.0347 and wild type controls to gallstone carriers with 19H allele 37%, P = 0.0030). Notably, ABCG5/8 and NPC1L1 expression was similar in gallstone carriers and controls regardless of p.D19H presence.

CONCLUSIONS

Both gallstone disease and p.D19H of ABCG8 are associated with diminished cholesterol absorption. However, p.D19H is not responsible for the differences in small intestinal sterol transporter expression.

Effects of diet and development on the Drosophila lipidome

Cells produce tens of thousands of different lipid species, but the importance of this complexity in vivo is unclear. Analysis of individual tissues and cell types has revealed differences in abundance of individual lipid species, but there has been no comprehensive study comparing tissue lipidomes within a single developing organism. Here, we used quantitative shotgun profiling by high-resolution mass spectrometry to determine the absolute (molar) content of 250 species of 14 major lipid classes in 6 tissues of animals at 27 developmental stages raised on 4 different diets. Comparing these lipidomes revealed unexpected insights into lipid metabolism. Surprisingly, the fatty acids present in dietary lipids directly influence tissue phospholipid composition throughout the animal. Furthermore, Drosophila differentially regulates uptake, mobilization and tissue accumulation of specific sterols, and undergoes unsuspected shifts in fat metabolism during larval and pupal development. Finally, we observed striking differences between tissue lipidomes that are conserved between phyla. This study provides a comprehensive, quantitative and expandable resource for further pharmacological and genetic studies of metabolic disorders and molecular mechanisms underlying dietary response.

Ezetimibe blocks the internalization of NPC1L1 and cholesterol in mouse small intestine

The multiple transmembrane protein Niemann-Pick C1 like1 (NPC1L1) is essential for intestinal cholesterol absorption. Ezetimibe binds to NPC1L1 and is a clinically used cholesterol absorption inhibitor. Recent studies in cultured cells have shown that NPC1L1 mediates cholesterol uptake through vesicular endocytosis that can be blocked by ezetimibe. However, how NPC1L1 and ezetimibe work in the small intestine is unknown. In this study, we found that NPC1L1 distributed in enterocytes of villi and transit-amplifying cells of crypts. Acyl-CoA cholesterol acyltransferase 2 (ACAT2), another important protein for cholesterol absorption by providing cholesteryl esters to chylomicrons, was mainly presented in the apical cytoplasm of enterocytes. NPC1L1 and ACAT2 were highly expressed in jejunum and ileum. ACAT1 presented in the Paneth cells of crypts and mesenchymal cells of villi. In the absence of cholesterol, NPC1L1 was localized on the brush border of enterocytes. Dietary cholesterol induced the internalization of NPC1L1 to the subapical layer beneath the brush border and became partially colocalized with the endosome marker Rab11. Ezetimibe blocked the internalization of NPC1L1 and cholesterol and caused their retention in the plasma membrane. This study demonstrates that NPC1L1 mediates cholesterol entering enterocytes through vesicular endocytosis and that ezetimibe blocks this step in vivo.

The sterols isolated from Evening Primrose oil modulate the release of proinflammatory mediators

Evening Primrose oil is a natural product extracted by cold-pressed from Oenothera biennis L. seeds. The unsaponifiable matter of this oil is an important source of interesting minor compounds, like long-chain fatty alcohols, sterols and tocopherols. In the present study, sterols were isolated from the unsaponifiable matter of Evening Primrose oil, and the composition was identified and quantified by GC and GC-MS. The major components of sterols fraction were β-Sitosterol and campesterol. We investigated the ability of sterols from Evening Primrose oil to inhibit the release of different proinflammatory mediators in vitro by murine peritoneal macrophages stimulated with lipopolysaccharide. Sterols significantly and dose-dependently decreased nitric oxide production. Western blot analysis showed that nitric oxide reduction was a consequence of the inhibition of inducible nitric oxide synthetase expression. Sterols also reduced tumor necrosis factor-α, interleukine 1β and tromboxane B₂. However, sterols did not reduce prostaglandin E₂. The reduction of eicosanoid release was related to the inhibition of cyclooxygenase-2 expression. These results showed that sterols may have a protective effect on some mediators involved in inflammatory damage development, suggesting its potential value as a putative functional component of Evening Primrose oil.

High-dose supplemental selenite to male Syrian hamsters fed hypercholesterolaemic diets alters Ldlr, Abcg8 and Npc1l1 mRNA expression and lowers plasma cholesterol concentrations

The aim of the present study was to elucidate possible cholesterol-lowering mechanism(s) of high-dose supplemental Se in the form of selenite, a known hypocholesterolaemic agent. Male Syrian hamsters (four groups, ten per group) were fed semi-purified diets for 4 weeks containing 0·1 % cholesterol and 15 % saturated fat with selenite corresponding to varying levels of Se: (1) Se 0·15 parts per million (ppm), control diet; (2) Se 0·85 ppm; (3) Se 1·7 ppm; (4) Se 3·4 ppm. Lipids were measured in the bile, faeces, liver and plasma. The mRNA expression of several known regulators of cholesterol homeostasis (ATP-binding cassette transporters g5 (Abcg5) and g8 (Abcg8), 7-hydroxylase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, LDL receptor (LdLr) and Nieman-Pick C1-like 1 protein (Npc1l1)) were measured in the liver and/or jejunum. Oxysterols including 24-(S)-hydroxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol (27-OHC) were measured in the liver. Significantly lower total plasma cholesterol concentrations were observed in hamsters consuming the low (0·85 ppm) and high (3·4 ppm) Se doses. The two highest doses of Se resulted in decreased plasma LDL-cholesterol concentrations and increased mRNA levels of hepatic Abcg8, Ldlr and jejunal Ldlr. Higher hepatic 27-OHC and TAG concentrations and lower levels of jejunal Npc1l1 mRNA expression were noted in the 1·7 and 3·4 ppm Se-treated hamsters. Overall, Se-induced tissue changes in mRNA expression including increased hepatic Abcg8 and Ldlr, increased jejunal Ldlr and decreased jejunal Npc1l1, provide further elucidation regarding the hypocholesterolaemic mechanisms of action of Se in the form of selenite.

Ezetimibe: its novel effects on the prevention and the treatment of cholesterol gallstones and nonalcoholic Fatty liver disease

The cholesterol absorption inhibitor ezetimibe can significantly reduce plasma cholesterol concentrations by inhibiting the Niemann-Pick C1-like 1 protein (NPC1L1), an intestinal sterol influx transporter that can actively facilitate the uptake of cholesterol for intestinal absorption. Unexpectedly, ezetimibe treatment also induces a complete resistance to cholesterol gallstone formation and nonalcoholic fatty liver disease (NAFLD) in addition to preventing hypercholesterolemia in mice on a Western diet. Because chylomicrons are the vehicles with which the enterocytes transport cholesterol and fatty acids into the body, ezetimibe could prevent these two most prevalent hepatobiliary diseases possibly through the regulation of chylomicron-derived cholesterol and fatty acid metabolism in the liver. It is highly likely that there is an intestinal and hepatic cross-talk through the chylomicron pathway. Therefore, understanding the molecular mechanisms whereby cholesterol and fatty acids are absorbed from the intestine could offer an efficacious novel approach to the prevention and the treatment of cholesterol gallstones and NAFLD.

Mechanisms and genetic determinants regulating sterol absorption, circulating LDL levels, and sterol elimination: implications for classification and disease risk

This review integrates historical biochemical and modern genetic findings that underpin our understanding of the low-density lipoprotein (LDL) dyslipidemias that bear on human disease. These range from life-threatening conditions of infancy through severe coronary heart disease of young adulthood, to indolent disorders of middle- and old-age. We particularly focus on the biological aspects of those gene mutations and variants that impact on sterol absorption and hepatobiliary excretion via specific membrane transporter systems (NPC1L1, ABCG5/8); the incorporation of dietary sterols (MTP) and of de novo synthesized lipids (HMGCR, TRIB1) into apoB-containing lipoproteins (APOB) and their release into the circulation (ANGPTL3, SARA2, SORT1); and receptor-mediated uptake of LDL and of intestinal and hepatic-derived lipoprotein remnants (LDLR, APOB, APOE, LDLRAP1, PCSK9, IDOL). The insights gained from integrating the wealth of genetic data with biological processes have important implications for the classification of clinical and presymptomatic diagnoses of traditional LDL dyslipidemias, sitosterolemia, and newly emerging phenotypes, as well as their management through both nutritional and pharmaceutical means.

A novel model of cholesterol efflux from lipid-loaded cells

Cholesterol efflux from lipid-loaded cells is a key athero-protective event that counteracts cholesterol uptake. The imbalance between cholesterol efflux and uptake determines the prevention or development of atherosclerosis. Many proteins and factors participate in the cholesterol efflux event. However, there are currently no systematic models of reverse cholesterol transport (RCT) that include most RCT-related factors and events. On the basis of recent research findings from other and our laboratories, we propose a novel model of one center and four systems with coupling transportation and networking regulation. This model represents a common way of cholesterol efflux; however, the systems in the model consist of different proteins/factors in different cells. In this review, we evaluate the novel model in vascular smooth muscle cells (VSMCs) and macrophages, which are the most important original cells of foam cells. This novel model consists of 1) a caveolae transport center, 2) an intracellular trafficking system of the caveolin-1 complex, 3) a transmembrane transport system of the ABC-A1 complex, 4) a transmembrane transport system of the SR-B1 complex, and 5) an extracelluar trafficking system of HDL/Apo-A1. In brief, the caveolin-1 system transports cholesterol from intracellular compartments to caveolae. Subsequently, both ABC-A1 and SR-B1 complex systems transfer cholesterol from caveolae to extracellular HDL/Apo-A1. The four systems are linked by a regulatory network. This model provides a simple and concise way to understand the dynamic process of atherosclerosis.

Study of molecular targets influencing homocysteine and cholesterol metabolism in growing rats by manipulation of dietary selenium and methionine concentrations

Inconsistent results exist from human and animal studies for Se and methionine (Met) regarding their influence on homocysteine (HCys) and cholesterol (Chol) metabolism. To elucidate these contradictions, sixty-four weanling albino rats were divided into eight groups of 8, and were fed diets containing four different Se levels (15, 50, 150 and 450 microg/kg) either in combination with the recommended Met level of 3 g/kg (C15, C50, C150 and C450) or with an increased Met concentration of 15 g/kg (M15, M50, M150 and M450) for 8 weeks. Plasma HCys was twofold higher in the Se-supplemented C groups than in group C15. Met addition also doubled plasma HCys compared with the respective C groups. In contrast, the expression of the key enzymes of glutathione biosynthesis in the liver was significantly lowered by Se and in particular by Met. Liver Chol concentration was significantly higher in all the Se-supplemented C and M groups than in groups C15 and M15. Plasma Chol was, however, lowered. The uninfluenced expression of sterol-regulatory element-binding protein 2 and of hydroxymethyl-glutaryl-CoA reductase, the increased LDL receptor expression and the reduced expression of the hepatobiliary Chol exporter ATP-binding-cassette-transporter 8 (ABCG8) by Se and/or Met explain these findings. We conclude that the elevation of plasma HCys in rats by Se and Met results from a higher export into plasma. The fact that Se in particular combined with Met increases liver Chol but reduces plasma Chol should be addressed in future investigations focussing on the regulation of ABCG8, which is also selectively involved in the reverse transport of phytosterols in the small intestine.

Tissue-specific liver X receptor activation promotes macrophage reverse cholesterol transport in vivo

OBJECTIVE

We previously reported that a systemic liver X receptor (LXR) agonist promoted macrophage reverse-cholesterol transport (mRCT) in vivo. Because LXR are expressed in multiple tissues involved in RCT (macrophages, liver, intestine), we analyzed the effect of tissue-specific LXR agonism on mRCT.

METHODS AND RESULTS

In initial studies, the systemic LXR agonist GW3965 failed to promote mRCT in a setting in which LXR was expressed in macrophages but not in liver or intestine. To evaluate the effect of LXR activation specifically in small intestine on mRCT, wild-type mice were treated with either intestinal-specific LXR agonist (GW6340) or systemic LXR agonist (GW3965). Both GW3965 and GW6340 significantly promoted excretion of [(3)H]-sterol in feces by 162% and 52%, respectively. To evaluate the requirement for macrophage LXR activation, we assessed the ability of GW3965 to promote mRCT in wild-type mice using primary macrophages deficient in LXR alpha/beta vs wild-type macrophages. Whereas GW3965 treatment promoted fecal excretion compared with vehicle, its overall ability to promote mRCT was significantly attenuated using LXR alpha/beta knockout macrophages.

CONCLUSIONS

We demonstrate that intestinal-specific LXR agonism promotes macrophage RCT in vivo and that macrophage LXR itself plays an important, but not predominant, role in promoting RCT in response to an LXR agonist.

Role of naturally-occurring plant sterols on intestinal cholesterol absorption and plasmatic levels

Cardiovascular disease is a major health problem in developed countries although its incidence is relatively lower in Mediterranean countries which is partly ascribed to dietary habits. Epidemiologic evidence shows that elevated serum cholesterol, specifically low-density lipoprotein cholesterol (c-LDL), increases cardiovascular disease. Phytosterols are bioactive compounds, found in all vegetable foods, which inhibit intestinal cholesterol absorption and, therefore, have a serum cholesterol-lowering effect. Intestinal cholesterol absorption is a multistep process where plant sterols and stanols may act: a) attenuating the NPC1L1 gene expression, which may result in a lower cholesterol uptake from the lumen; b) lowering the cholesterol esterification rate by the ACAT2 (acyl-CoA cholesterol acyltransferase) and, consequently, the amount of cholesterol secreted via the chylomicrons and c) upregulating the expression of ABC-transporters ABCG5 and ABCG8 in intestinal cells, which may result in an increased excretion of cholesterol by the enterocyte back into the lumen. Many clinical trials proved that commercial products enriched with phytosterols reduce cholesterol levels. Likewise, recent studies show that phytosterols present in natural food matrices are also effective and could be an important component of cardioprotective dietary patterns such as the Mediterranean diet.

Soy constituents: modes of action in low-density lipoprotein management

Reviewed here are the modes of action of soy components used as ingredients in foods, which can lower plasma levels of low-density lipoprotein (LDL) and cholesterol, which are markers for the risk for atherosclerosis. Soy ingredients act via more than one mode of action including the following: LDL absorption suppression, cholesterol efflux stimulation, LDL resorption stimulation, LDL oxidation prevention, LDL particle size increase, cholesterol synthesis reduction, and bile secretion increase. Individual genetics, lifestyle, and nutrition habits alter LDL management and a better understanding of the various modes of actions of soy ingredients may facilitate the composition of effective ingredient cocktails. The optimization of food components offers further alternatives to LDL management to augment drug therapy for patients who are unable to reach their target LDL cholesterol levels or who are suffering from side effects or drug insensitivity.

Influence of class B scavenger receptors on cholesterol flux across the brush border membrane and intestinal absorption

To learn more about how the step of cholesterol uptake into the brush border membrane (BBM) of enterocytes influences overall cholesterol absorption, we measured cholesterol absorption 4 and 24 h after administration of an intragastric bolus of radioactive cholesterol in mice with scavenger receptor class B, type 1 (SR-BI) and/or cluster determinant 36 (CD36) deleted. The cholesterol absorption efficiency is unaltered by deletion of either one or both of the receptors. In vitro determinations of the cholesterol uptake specific activity of the BBM from the mice reveal that the scavenger receptors facilitate cholesterol uptake into the proximal BBM. It follows that cholesterol uptake into the BBM is not normally rate-limiting for the cholesterol absorption process in vivo; a subsequent step, such as NPC1L1-mediated transfer from the BBM into the interior of the enterocyte, is rate-limiting. The absorption of dietary cholesterol after 4 h in mice lacking SR-BI and/or CD36 and fed a high-fat/high-cholesterol diet is delayed to more distal regions of the small intestine. This effect probably arises because ATP binding cassette half transporters G5 and G8-mediated back flux of cholesterol from the BBM to the lumen of the small intestine limits absorption and causes the local cholesterol uptake facilitated by SR-BI and CD36 to become rate-limiting under this dietary condition.

Effect of ezetimibe on plasma cholesterol levels, cholesterol absorption, and secretion of biliary cholesterol in laboratory opossums with high and low responses to dietary cholesterol

Partially inbred lines of laboratory opossums differ in plasma low-density lipoprotein cholesterol concentration and cholesterol absorption on a high-cholesterol diet. The aim of the present studies was to determine whether ezetimibe inhibits cholesterol absorption and eliminates the differences in plasma cholesterol and hepatic cholesterol metabolism between high and low responders on a high-cholesterol diet. Initially, we determined that the optimum dose of ezetimibe was 5 mg/(kg d) and treated 6 high- and 6 low-responding opossums with this dose (with equal numbers of controls) for 3 weeks while the opossums consumed a high-cholesterol and low-fat diet. Plasma and low-density lipoprotein cholesterol concentrations decreased significantly (P < .05) in treated but not in untreated high-responding opossums. Plasma cholesterol concentrations increased slightly (P < .05) in untreated low responders but not in treated low responders. The percentage of cholesterol absorption was significantly higher in untreated high responders than in other groups. Livers from high responders with or without treatment were significantly (P < .01) heavier than livers from low responders with or without treatment. Hepatic cholesterol concentrations in untreated high responders were significantly (P < .05) higher than those in low responders with or without treatment (P < .001). The gall bladder bile cholesterol concentrations in untreated high responders were significantly (P < .05) lower than those in other groups. A decrease in biliary cholesterol in low responders treated with ezetimibe was associated with a decrease in hepatic expression of ABCG5 and ABCG8. These studies suggest that ezetimibe decreases plasma cholesterol levels in high responders mainly by decreasing cholesterol absorption and increasing biliary cholesterol concentrations. Because ezetimibe's target is NPC1L1 and NPC1L1 is expressed in the intestine of opossums, its effect on cholesterol absorption may be mediated by inhibiting NPC1L1 function in the intestine.

Cholesterol and non-cholesterol sterol transporters: ABCG5, ABCG8 and NPC1L1: a review

1. Whole-body sterol (cholesterol and xenosterol) balance is delicately regulated by the gastrointestinal tract and liver, which control sterol absorption and excretion, respectively, in addition to the contribution to the cholesterol pool by whole-body cholesterol synthesis. In the past ten years enormous strides have been made not only in establishing that specific transporters mediate the entry and exit of sterols and how these may regulate selective sterol access to the body pools, but also in how these pathways operate to integrate these physiological pathways. 2. The entry of sterols from the gastrointestinal and biliary canalicular lumen into the body is mediated by NPC1L1, which was discovered by a novel method, via a genomics-bioinformatics approach. 3. Identification of the genetic basis responsible for causing sitosterolaemia, characterized by plant sterol accumulation, led to the identification of two half-transporters (ABCG5 and ABCG8) that normally efflux plant sterols (and cholesterol) into the intestinal and biliary lumen for faecal excretion. 4. The objective of this review is to provide up-to-date knowledge on genomics, proteomics and function of these two transporter systems.

New insights into the molecular actions of plant sterols and stanols in cholesterol metabolism

Plant sterols and stanols (phytosterols/phytostanols) are known to reduce serum low-density lipoprotein (LDL)-cholesterol level, and food products containing these plant compounds are widely used as a therapeutic dietary option to reduce plasma cholesterol and atherosclerotic risk. The cholesterol-lowering action of phytosterols/phytostanols is thought to occur, at least in part, through competition with dietary and biliary cholesterol for intestinal absorption in mixed micelles. However, recent evidence suggests that phytosterols/phytostanols may regulate proteins implicated in cholesterol metabolism both in enterocytes and hepatocytes. Important advances in the understanding of intestinal sterol absorption have provided potential molecular targets of phytosterols. An increased activity of ATP-binding cassette transporter A1 (ABCA1) and ABCG5/G8 heterodimer has been proposed as a mechanism underlying the hypocholesterolaemic effect of phytosterols. Conclusive studies using ABCA1 and ABCG5/G8-deficient mice have demonstrated that the phytosterol-mediated inhibition of intestinal cholesterol absorption is independent of these ATP-binding cassette (ABC) transporters. Other reports have proposed a phytosterol/phytostanol action on cholesterol esterification and lipoprotein assembly, cholesterol synthesis and apolipoprotein (apo) B100-containing lipoprotein removal. The accumulation of phytosterols in ABCG5/G8-deficient mice, which develop features of human sitosterolaemia, disrupts cholesterol homeostasis by affecting sterol regulatory element-binding protein (SREBP)-2 processing and liver X receptor (LXR) regulatory pathways. This article reviews the progress to date in studying these effects of phytosterols/phytostanols and the molecular mechanisms involved.

Physical chemistry of intestinal absorption of biliary cholesterol in mice

Although many putative sterol transporters influencing cholesterol absorption and physical-chemical factors affecting dietary cholesterol absorption have been extensively investigated, it is still unclear how biliary cholesterol contributes to the regulation of intestinal cholesterol absorption. We studied whether the gallbladder can modulate the microaggregates of cholesterol carriers, which may in turn influence the intestinal absorption of biliary cholesterol. Supersaturated, crystallized, or micellar model biles were delivered via a duodenal catheter to conscious, freely moving C57L mice daily for 2 days. Intestinal uptake and absorption of biliary cholesterol and its fecal excretion, as well as expression levels of intestinal sterol transporters, were analyzed. Cholesterol uptake and absorption by the enterocyte were dramatically reduced in mice treated with crystallized biles compared with supersaturated biles. This correlated with the higher cumulative radioactivity of cholesterol recovered in the feces at 24 hours. Such findings were absent with the added reference compound sitostanol. After removing cholesterol crystals from crystallized biles, micellar biles showed essentially identical effects on intestinal absorption but with lower fecal cholesterol excretion compared with the original samples containing crystals. Expression levels of the jejunal Abcg5 (ATP-binding cassette transporter G5) and Abcg8, but not Npc1l1 (Niemann-Pick C1 like 1), were significantly increased by supersaturated biles compared with crystallized biles.

CONCLUSION

Different physical forms of biliary cholesterol dramatically determine intestinal uptake and absorption of cholesterol. Solid plate-like cholesterol monohydrate crystals in bile are probably not absorbed and are totally excreted in feces from the body. The gallbladder may have a role in regulating cholesterol homeostasis by modulating the physical forms of biliary cholesterol.