Barley intake induces bile acid excretion by reduced expression of intestinal ASBT and NPC1L1 in C57BL/6J mice

Impact of whole grain highland hull-less barley on the denaturing gradient gel electrophoresis profiles of gut microbial communities in rats fed high-fat diets

Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) is a traditional non-culture technique that can provide a fingerprint of the microbial community. In the field of gut microbiota analysis, PCR-DGGE still holds potential for development. In the present study, we utilized an improved nested PCR-DGGE approach targeting the V3 region of 16S ribosomal DNA to investigate the impact of whole grain highland hull-less barley (WHLB), a cereal known for its significant hypocholesterolemic effect, on the gut microbiota profiles of high-fat diet rats. Seventy-two male Sprague-Dawley rats were divided into four groups and fed a normal control diet, a high-fat diet, or a high-fat diet supplemented with a low or high dose of WHLB for 4 or 8 weeks. The results revealed that the dominant bands varied among different dose groups and further changed with different treatment times. The compositions of bacterial communities in feces and cecal content were similar, but the dominant bacterial bands differed. After performing double DGGE, extracting the bands, sequencing the DNA, and aligning the sequences, a total of 19 bands were classified under the Firmicutes and Bacteroidetes phyla, while two bands were identified as unclassified uncultured bacteria. The relative abundance of Lactobacillus gasseri, Uncultured Prevotella sp., and Clostridium sp. increased following the administration of WHLB. Illumina-based sequencing was employed to assess the reliability of DGGE, demonstrating its reliability in analyzing the dominant taxonomic composition, although it may have limitations in accurately detecting the alpha diversity of bacterial species.

IMPORTANCE

While next-generation sequencing has overshadowed polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), the latter still holds promise for advancing gut microbiota analysis due to its unique advantages. In this study, we used optimized nested PCR-DGGE to investigate the gut microbiota profile of high-fat diet rats after administering whole grain highland hull-less barley. High-throughput sequencing was employed to validate the DGGE results. Our results proved the reliability of PCR-DGGE for analyzing the dominant taxonomic composition while also providing visual evidence of a notable relationship between the composition of cecal and fecal microbial communities, highlighting substantial differences in both richness and abundance.

Structural Characteristics of Insoluble Dietary Fiber from Okara with Different Particle Sizes and Their Prebiotic Effects in Rats Fed High-Fat Diet

Dietary fiber, which is utilized to make functional meals, is an important component for promoting human health and managing calorie consumption. In this study, three different particle sizes of OIDF (Okara insoluble dietary fiber) were characterized. Their lipid-lowering effects and the impacts on gut microbiota were determined by OIDF intervention in high-fat diet rats. Scanning electron microscopy (SEM) results showed that the three particle sizes of OIDF have different morphologies. Fourier transform infrared spectroscopy (FT-IR) results showed that the three sources of IDF samples have similar active groups, but the thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and X-ray diffraction (XRD) showed that three different particle sizes of OIDF have different retention and crystallinity. Among the three OIDFs, OIDF-10 exhibited the stronger WSC, OHC, CAC, and SCAC. The results after the feeding showed that the OIDF of three particle sizes could improve the elevation of blood lipids and the disturbance of gut microbiota caused by the high-fat diet. Therefore, this study demonstrated the functional significance of the three particle sizes of OIDF and provided a reference for its application in functional food processing, aiming at maintaining healthy blood lipid and intestinal flora levels.

Enterohepatic circulation of bile acids and their emerging roles on glucolipid metabolism

Bile acids (BAs) are amphiphilic molecules with a nonpolar steroid carbon skeleton and a polar carboxylate side chain. Recently, BAs have aroused the attention of scholars due to their potential roles on metabolic diseases. As important endogenous ligands, BAs are wildly active in the enterohepatic circulation, during which microbiota play a significant role in promoting the hydrolysis and dehydroxylation of BAs. Besides, many pathways initiated by BAs including glucolipid metabolism and inflammation signaling pathways have been reported to regulate the host metabolism and maintain immune homeostasis. Herein, the characteristics on the enterohepatic circulation and metabolism of BAs are systematically summarized. Moreover, the regulation mechanism of the glucolipid metabolism by BAs is intensively discussed. Worthily, FXR and TGR5, which are involved in glucolipid metabolism, are the prime candidates for targeted therapies of chronic metabolic diseases such as diabetes and hypercholesterolemia.

Nostoc sphaeroids Kütz ameliorates hyperlipidemia and maintains the intestinal barrier and gut microbiota composition of high-fat diet mice

Hyperlipidemia is associated with chronic inflammation and intestinal dysbiosis. The purpose of this study was to investigate the protective effect of Nostoc sphaeroids Kütz (NO) on diet-induced hyperlipidemia in mice. Experimental animals received a high-fat diet (HFD) for 4 weeks, then an HFD supplemented with 2.5% or 7.5% NO for 6 weeks. HFD-fed mice exhibited a significant increase in serum total cholesterol, triglycerides, and low-density lipid cholesterol, and a decrease in high-density lipid cholesterol. NO supplementation was associated with significantly lower dyslipidemia, decreased intestinal inflammation, and inhibition of toll-like receptor 4 gene repression in HFD-fed mice. Results suggest that NO treatment protected the integrity of the intestinal barrier. NO treatment was also associated with significant changes in the intestinal microbiota induced by HFD and an increase in the Firmicutes-to-Bacteroidetes ratio. Furthermore, NO treatment was also inversely correlated with mice obesity and hyperlipidemia NO and was associated with no significant in fecal short-chain fatty acids. In conclusion, NO significantly ameliorated hyperlipidemia induced by a HFD in mice, potentially via a decrease intestinal inflammation, increase in intestinal barrier integrity, and amelioration in the gut microbiota.

Comparative Effects and Mechanisms of Chitosan and Its Derivatives on Hypercholesterolemia in High-Fat Diet-Fed Rats

The present study investigated and compared the effects of different molecular weights of chitosan (high molecular weight chitosan (HC) and low molecular weight chitosan (LC)) and its derivatives (chitosan oligosaccharide (CO)) on cholesterol regulation in high-fat (HF) diet-fed rats. A diet supplementation of 5% HC, 5% LC, or 5% CO for 8 weeks showed hypocholesterolemic potential in HF diet-fed rats. Unexpectedly, a 5% CO-supplemented diet exerted hepatic damage, producing increased levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and tumor necrosis factor-alpha (TNF-α). The supplementation of HC and LC, unlike CO, significantly decreased the hepatic total cholesterol (TC) levels and increased the fecal TC levels in HF diet-fed rats. The hepatic protein expression of the peroxisome proliferator-activated receptor-α (PPARα) in the HF diet-fed rats was markedly decreased, which could be significantly reversed by both HC and LC, but not CO, supplementation. Unlike the supplementation of CO, both HC and LC supplementation could effectively reverse the HF-inhibited/induced gene expressions of the low-density lipoprotein receptor (LDLR) and cholesterol 7α-hydroxylase (CYP7A1), respectively. The upregulated intestinal acyl-CoA cholesterol acyltransferase 2 (ACAT2) protein expression in HF diet-fed rats could be reversed by HC and LC, but not CO, supplementation. Taken together, a supplementation of 5% CO in HF diet-fed rats may exert liver damage via a higher hepatic cholesterol accumulation and a higher intestinal cholesterol uptake. Both HC and LC effectively ameliorated the hypercholesterolemia and regulated cholesterol homeostasis via the activation and inhibition of hepatic (AMPKα and PPARα) and intestinal (ACAT2) cholesterol-modulators, respectively, as well as the modulation of downstream signals (LDLR and CYP7A1).

The intestinal microbiota regulates host cholesterol homeostasis

BACKGROUND

Management of blood cholesterol is a major focus of efforts to prevent cardiovascular diseases. The objective of this study was to investigate how the gut microbiota affects host cholesterol homeostasis at the organism scale.

RESULTS

We depleted the intestinal microbiota of hypercholesterolemic female Apoe^-/- mice using broad-spectrum antibiotics. Measurement of plasma cholesterol levels as well as cholesterol synthesis and fluxes by complementary approaches showed that the intestinal microbiota strongly regulates plasma cholesterol level, hepatic cholesterol synthesis, and enterohepatic circulation. Moreover, transplant of the microbiota from humans harboring elevated plasma cholesterol levels to recipient mice induced a phenotype of high plasma cholesterol levels in association with a low hepatic cholesterol synthesis and high intestinal absorption pattern. Recipient mice phenotypes correlated with several specific bacterial phylotypes affiliated to Betaproteobacteria, Alistipes, Bacteroides, and Barnesiella taxa.

CONCLUSIONS

These results indicate that the intestinal microbiota determines the circulating cholesterol level and may thus represent a novel therapeutic target in the management of dyslipidemia and cardiovascular diseases.

Undernutrition Shapes the Gut Microbiota and Bile Acid Profile in Association with Altered Gut-Liver FXR Signaling in Weaning Pigs

Bile acids, synthesized in the liver and metabolized by microbiota, have emerged as important signaling molecules regulating immune responses and cell proliferation. However, the crosstalk among nutrition, microbiota, and bile acids remains unclear. Our study indicated that undernutrition in weaning piglets led to intestinal atrophy, increased colonic production, and systemic accumulation of lithocholic acid (LCA), deoxycholic acid (DCA), or their conjugated forms, which might be associated with decreased Lactobacillus abundance. Moreover, undernutrition led to increased portal fibroblast growth factor 19 ( FGF19) level, upregulated hepatic heterodimer partner ( SHP), and downregulated cholesterol 7a-hydroxylase ( CYP7A1) expression. The detrimental effects of DCA and LCA on proliferation and barrier function were confirmed in porcine enterocytes, whereas their roles in weaning piglets warrant further research. In summary, undernutrition in weaning piglets led to increased secondary bile acids production, which might be related to altered gut microbiome and enhanced farnesoid X receptor (FXR) signaling while CYP7A1 expression was suppressed.

Whole barley prevents obesity and dyslipidemia without the involvement of the gut microbiota in germ free C57BL/6J obese mice

Whole barley (WB) consumption is the subject of renewed interest because of its health benefits.

Co-administrating apigenin in a high-cholesterol diet prevents hypercholesterolaemia in golden hamsters

Objectives

Hypercholesterolaemia is a major risk factor for developing atherosclerosis. Increased consumption of fruits and vegetables is recommended to hypercholesterolaemic patients. In this study, the hypocholesterolaemic effect of apigenin and luteolin was evaluated in a hamster model.

Methods

Hamsters were put on a high-cholesterol diet for 9 weeks, and apigenin or luteolin was administered in the diet at 60 and 300 ppm.

Key findings

Both apigenin and luteolin supplementations could attenuate the aorta plaque formation by 30% and 20%, respectively. Apigenin-fed hamsters at both dosages displayed a 1.5-fold increase in hepatic Ldlr expression and a 40% reduction in non-HDL cholesterol level as compared with those in the control fed a high-cholesterol (HC) diet. Besides, faecal elimination of cholesterol was facilitated by 20% in the hamsters with high apigenin consumption. Suppressing the expression of the cholesterol transporter ncp1l1 in the intestinal mucosa could block the cholesterol absorption and promote its elimination. The differential regulations of ncp1l1 and Ldlr appeared to be the underlying hypocholesterolaemic mechanism of apigenin in this model system. Luteolin supplementation, on the other hand, had no effect on the blood cholesterol.

Conclusions

This study illustrated that dietary administration of apigenin attenuated HC feeding-induced hypercholesterolemia in hamsters.

Hypocholesterolaemic effect of whole-grain highland hull-less barley in rats fed a high-fat diet

Whole-grain highland hull-less barley (WHLB) contains high amounts of bioactive compounds that potentially exhibit cholesterol-lowering effects. This study investigated the hypocholesterolaemic effect of WHLB. A total of seventy-two male Sprague–Dawley rats were divided into four groups and were fed with the normal control diet, high-fat diet (HFD) and HFD containing low or high dose (10 or 48·95 %) of WHLB. High dose of WHLB significantly decreased the organ indexes of liver and abdominal fat and lipid levels of plasma and liver in HFD rats. The lipid regulation effect of WHLB, which was reconfirmed through hepatocyte morphologic observation, was accompanied by a large excretion of bile acids in the small intestinal contents and the faeces. Real-time PCR analyses, which were further reconfirmed through Western blot analyses, revealed that a high dose of WHLB significantly enhanced the hepatic expressions of AMP-activated protein kinase α, cholesterol 7α-hydroxylase, LDL receptor, liver X receptor, and PPARα and decreased the expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase. It also enhanced the ileal expression of farnesoid X receptor and resulted in the decrease of expression of apical sodium-dependent bile acid transporter. WHLB exhibited hypocholesterolaemic effects mainly by inhibiting cholesterol synthesis, cholesterol accumulation in peripheral tissue, and bile acid reabsorption and by stimulating bile acid synthesis.

Pectin Penta-Oligogalacturonide Suppresses Intestinal Bile Acids Absorption and Downregulates the FXR-FGF15 Axis in High-Cholesterol Fed Mice

Haw pectin penta-oligogalacturonide (HPPS), purified from the hydrolysates of haw pectin, has important role in decreasing hepatic cholesterol accumulation and promoting bile acids (BA) excretion in the feces of mice fed a high-cholesterol diet (HCD). However, the mechanism is not clear. This study aims to investigate the effects of HPPS on BA reabsorption in ileum and biosynthesis in liver of mice. Results showed that HPPS increased fecal BA output by approximately 110%, but decreased ileal BA and the total BA pool size by approximately 47 and 36%, respectively, compared to HCD. Studies of molecular mechanism revealed that HPPS significantly decreased the mRNA and protein levels of farnesoid X receptor (FXR) in the small intestine of mice and inactivated the fibroblast growth factor 15 (FXR-FGF15) axis, which increased the mRNA and protein levels of CYP7A1 by approximately 204 and 104%, respectively, compared to HCD. Interestingly, the mRNA and protein levels of apical sodium-dependent bile acid transporter (ASBT) in the small intestine were approximately 128 and 73% higher in HPPS-fed mice than those in HCD-fed mice, respectively. However, no significant difference was detected for ASBT expression between HCD group and BA sequestrant cholestyramine group. These findings indicate that HPPS can suppress intestinal BA reabsorption and promoting hepatic BA biosynthesis. We speculated that HPPS could be ASBT competitive inhibitor rather than BA sequestrant in inhibiting BA reabsorption in ileum and improving cholesterol metabolism.

Effect of Whole Grain Qingke (Tibetan Hordeum vulgare L. Zangqing 320) on the Serum Lipid Levels and Intestinal Microbiota of Rats under High-Fat Diet

This study investigated the hypolipidemic effect of whole grain Qingke (WGQ) and its influence on intestinal microbiota. Changes in the serum lipid, intestinal environment, and microbiota of Sprague-Dawley rats fed high-fat diets supplemented with different doses of WGQ were determined. Results showed that high doses of WGQ significantly decreased (P < 0.05) the Lee's index, serum total cholesterol, low-density lipoprotein cholesterol, and non-high-density lipoprotein cholesterol levels whereas they increased the body weight of the rats. Cecal weight and short-chain fatty acid (SCFA) concentration increased with increasing WGQ dose. An Illumina-based sequencing approach showed that the relative abundance of putative SCFA-producing bacteria Prevotella and Anaerovibrio increased in the rats fed the WGQ diet. Principal component analysis revealed a significant difference in intestinal microbiota composition after the administration of the WGQ diet. These findings provide insights into the contribution of the intestinal microbiota to the hypolipidemic effect of WGQ.

Lactoferrin interacts with bile acids and increases fecal cholesterol excretion in rats

Lactoferrin (LF) is a multifunctional cationic protein (pI 8.2–8.9) in mammalian milk. We previously reported that enteric-LF prevented hypercholesterolemia and atherosclerosis in a diet-induced atherosclerosis model using Microminipig, although the underlying mechanisms remain unclear. Because LF is assumed to electrostatically interact with bile acids to inhibit intestinal cholesterol absorption, LF could promote cholesterol excretion. In this study, we assessed the interaction between LF and taurocholate in vitro, and the effect of LF on cholesterol excretion in rats. The binding rate of taurocholate to LF was significantly higher than that to transferrin (pI 5.2–6.3). When rats were administered a high-cholesterol diet (HCD) containing 5% LF, LF was detected using ELISA in the upper small intestine from 7.5 to 60 min after the administration. Rats were fed one of the following diets: control, HCD, or HCD + 5% LF for 21 days. Fecal neutral steroids and hepatic cholesterol levels in the HCD group were significantly higher than those in the control group. The addition of LF to a HCD significantly increased fecal neutral steroids levels (22% increase, p < 0.05) and reduced hepatic cholesterol levels (17% decrease, p < 0.05). These parameters were inversely correlated (R = −0.63, p < 0.05). These results suggest that LF promotes cholesterol excretion via interactions with bile acids.

Bioactive phytochemicals in barley

Epidemiological studies have consistently shown that regular consumption of whole grain barley reduces the risk of developing chronic diseases. The presence of barley fiber, especially β-glucan in whole grain barley, has been largely credited for these health benefits. However, it is now widely believed that the actions of the fiber component alone do not explain the observed health benefits associated with the consumption of whole grain barley. Whole grain barley also contains phytochemicals including phenolic acids, flavonoids, lignans, tocols, phytosterols, and folate. These phytochemicals exhibit strong anti-oxidant, antiproliferative, and cholesterol lowering abilities, which are potentially useful in lowering the risk of certain diseases. Therefore, the high concentration of phytochemicals in barley may be largely responsible for its health benefits. This paper reviews available information regarding barley phytochemicals and their potential to combat common nutrition-related diseases including cancer, cardiovascular disease, diabetes, and obesity.

Antihyperlipidemic effect of Acanthopanax senticosus (Rupr. et Maxim) Harms leaves in high-fat-diet fed mice

BACKGROUND

Metabolic syndrome is a major risk factor for a variety of obesity-related diseases. Recently, the effects of functional foods have been investigated on lipid metabolism as a means to reduce lipid content in the blood, liver and adipose tissues associated with carnitine O-palmitoyltransferase (CPT) activity. Acanthopanax senticosus (Rupr. et Maxim) Harms (AS) is a medicinal herb possessing a wide spectra of functions including antioxidant, anti-inflammatory and anti-fatigue actions. Despite much research being focused on the cortical roots of AS, little information is available regarding its leaves, which are also expected to promote human health, for example by improving abnormal lipid metabolism. Here, we explored whether AS leaves affect lipid metabolism in mice fed a high-fat diet.

RESULTS

The administration of AS to BALB/c mice fed a high-fat diet significantly decreased plasma triglycerides (TG). CPT activity in the liver of these mice was significantly enhanced by AS treatment.

CONCLUSION

These findings indicate that AS leaves have the potential to alleviate increase in plasma TG levels due to high-fat diet intake in mice, possibly by increasing mitochondrial fatty acid β-oxidation, especially via CPT activation. Consequently, daily intake of AS leaves could promote beneficial health effects including the prevention of metabolic syndrome. © 2015 Society of Chemical Industry.

Ursolic acid improves lipid and glucose metabolism in high-fat-fed C57BL/6J mice by activating peroxisome proliferator-activated receptor alpha and hepatic autophagy

SCOPE

This study investigated metabolic effects of ursolic acid (UA), a peroxisome proliferation-activated receptor (PPAR)-α activator, in vivo.

METHODS AND RESULTS

High-fat diet (HFD)-fed C57BL/6J mice were orally administered UA (50 or 200 mg/kg body weight) for 8 wk. UA reduced liver and adipose tissue mass, adipocyte size, and plasma leptin concentrations, plasma triglyceride and low-density-lipoprotein cholesterol concentrations, while it elevated the high-density-lipoprotein cholesterol and adiponectin concentrations significantly compared with controls. UA induced the expression of PPARα and its responsive genes involved in fatty acid uptake and β-oxidation in the livers, whereas genes involved in lipogenesis, including sterol regulatory element-binding proteins-1c, were downregulated. UA administration improved glucose tolerance and insulin sensitivity significantly compared with the HFD-fed control livers. UA administration also activated hepatic autophagy as assessed by the expression of microtubule-associated protein 1A/1B-light chain 3 (LC3)-II and other key proteins in the autophagy pathway.

CONCLUSION

Our findings suggest that UA ameliorates lipid and glucose metabolism in HFD-fed mice primarily by the activation of PPARα and induction of the hepatic autophagy pathway. Thus, intake of UA in the diet or in an isolated form may ameliorate lipid and glucose metabolism.

Bile acid promotes liver regeneration via farnesoid X receptor signaling pathways in rats

Bile acids, which are synthesized from cholesterol in the hepatocytes of the liver, are amphipathic molecules with a steroid backbone. Studies have shown that bile acid exhibits important effects on liver regeneration. However, the mechanism underlying these effects remains unclear. The aim of the present study was to investigate the effect of bile acid and the farnesoid X receptor (FXR) on hepatic regeneration and lipid metabolism. Rats were fed with 0.2% bile acid or glucose for 7 days and then subjected to a 50 or 70% hepatectomy. Hepatic regeneration rate, serum and liver levels of bile acid, and expression of FXR and Caveolin‑1, were detected at 24, 48 or 72 h following hepatectomy. The expression of proliferating cell nuclear antigen (PCNA) in the liver was measured using immunohistochemistry at the end of the study. Hepatocytes isolated from rats were treated with bile acid, glucose, FXR agonist and FXR antagonist, separately or in combination. Lipid metabolism, the expression of members of the FXR signaling pathway and energy metabolism‑related factors were measured using ELISA kits or western blotting. Bile acid significantly increased the hepatic regeneration rate and the expression of FXR, Caveolin‑1 and PCNA. Levels of total cholesterol and high density lipoprotein were increased in bile acid‑ or FXR agonist‑treated hepatocytes in vitro. Levels of triglyceride, low density lipoprotein and free fatty acid were decreased. In addition, bile acid and FXR agonists increased the expression of bile salt export pump and small heterodimer partner, and downregulated the expression of apical sodium‑dependent bile acid transporter, Na+/taurocholate cotransporting polypeptide and cholesterol 7α‑hydroxylase. These results suggested that physiological concentrations of bile acid may promote liver regeneration via FXR signaling pathways, and may be associated with energy metabolism.

The dipeptide H-Trp-Arg-OH (WR) Is a PPARα agonist and reduces hepatic lipid accumulation in lipid-loaded H4IIE cells

Dipeptides absorbed by the intestinal epithelium are delivered to circulation, but their metabolic roles are not yet clearly understood. We investigated the biological activities of a dietary dipeptide, H-Trp-Arg-OH (WR), on the regulation of peroxisome proliferator-activated receptor (PPAR) α activity. Reporter gene assays revealed that WR dose-dependently induced PPARα transactivation. Surface plasmon resonance experiments demonstrated that WR interacts directly with the PPARα ligand binding domain, and time-resolved fluorescence energy transfer analyses revealed recruitment of a co-activator peptide, fluorescein-PGC1α, to PPARα, confirming the direct binding of WR to PPARα and occurrence of conformational changes. WR induced cellular fatty acid uptake and the expression of PPARα response genes in fatty acid oxidation, thus reducing intracellular triglyceride accumulation in lipid-loaded hepatocytes. In conclusion, the dietary dipeptide WR activates PPARα and reduces hepatic lipid accumulation in lipid-loaded hepatocytes.

trans-Caryophyllene is a natural agonistic ligand for peroxisome proliferator-activated receptor-α

Intake of dietary aroma compounds may regulate cellular lipid metabolism. We demonstrated that trans-caryophyllene, a flavor compound in plant foods and teas, activates peroxisome proliferator-activated receptor (PPAR)-α through direct interaction with the ligand-binding domain of PPAR-α. The agonistic activity of trans-caryophyllene was investigated by the luciferase reporter assay, surface plasmon resonance, and time-resolved fluorescence resonance energy transfer assay. Following the stimulation of cells with trans-caryophyllene, intracellular triglyceride concentrations were significantly reduced by 17%, and hepatic fatty acid uptake was significantly increased by 31%. The rate of fatty acid oxidation was also significantly increased. The expressions of PPAR-α and its target genes and proteins in fatty acid uptake and oxidation were significantly up-regulated as well. In HepG2 cells transfected with small interfering RNA of PPAR-α, the effects of trans-caryophyllene on PPAR-α responsive gene expressions, intracellular triglyceride, fatty acid uptake and oxidation were disappeared. These results indicate that the aroma compound, trans-caryophyllene, is PPAR-α agonist thus regulates cellular lipid metabolism in PPAR-α dependent manners.

The solute carrier family 10 (SLC10): beyond bile acid transport

The solute carrier (SLC) family 10 (SLC10) comprises influx transporters of bile acids, steroidal hormones, various drugs, and several other substrates. Because the seminal transporters of this family, namely, sodium/taurocholate cotransporting polypeptide (NTCP; SLC10A1) and the apical sodium-dependent bile acid transporter (ASBT; SLC10A2), were primarily bile acid transporters, the term "sodium bile salt cotransporting family" was used for the SLC10 family. However, this notion became obsolete with the finding of other SLC10 members that do not transport bile acids. For example, the sodium-dependent organic anion transporter (SOAT; SLC10A6) transports primarily sulfated steroids. Moreover, NTCP was shown to also transport steroids and xenobiotics, including HMG-CoA inhibitors (statins). The SLC10 family contains four additional members, namely, P3 (SLC10A3; SLC10A3), P4 (SLC10A4; SLC10A4), P5 (SLC10A5; SLC10A5) and SLC10A7 (SLC10A7), several of which were unknown or considered hypothetical until approximately a decade ago. While their substrate specificity remains undetermined, great progress has been made towards their characterization in recent years. Explicitly, SLC10A4 may participate in vesicular storage or exocytosis of neurotransmitters or mastocyte mediators, whereas SLC10A5 and SLC10A7 may be involved in solute transport and SLC10A3 may have a role as a housekeeping protein. Finally, the newly found role of bile acids in glucose and energy homeostasis, via the TGR5 receptor, sheds new light on the clinical relevance of ASBT and NTCP. The present mini-review provides a brief summary of recent progress on members of the SLC10 family.

Fucosterol is a selective liver X receptor modulator that regulates the expression of key genes in cholesterol homeostasis in macrophages, hepatocytes, and intestinal cells

Fucosterol, a sterol that is abundant in marine algae, has hypocholesterolemic activity, but the mechanism underlying its effect is not clearly understood. Because data suggest that fucosterol can increase plasma high-density lipoprotein concentrations, we investigated whether it could activate liver X receptors (LXRs), critical transcription factors in reverse cholesterol transport. Fucosterol dose-dependently stimulated the transcriptional activity of both LXR-α and -β in a reporter gene assay, responses that were attenuated by the LXR antagonist As(2)O(3). Fucosterol also activated co-activator recruitment in cell-free time-resolved fluorescence resonance energy transfer analysis. In THP-1-derived macrophages, it induced the transcriptional activation of ABCA1, ABCG1, and ApoE, key genes in reverse cholesterol transport, and thereby significantly increased the efflux of cholesterol. Fucosterol also regulated intestinal NPC1L1 and ABCA1 in Caco-2 cells. Notably, fucosterol did not induce cellular triglyceride accumulation in HepG2 cells, primarily because of its upregulation of Insig-2a, which delays nuclear translocation of SREBP-1c, a key hepatic lipogenic transcription factor. These results suggest that fucosterol is a dual-LXR agonist that regulates the expression of key genes in cholesterol homeostasis in multiple cell lines without inducing hepatic triglyceride accumulation.

Taurine is a liver X receptor-α ligand and activates transcription of key genes in the reverse cholesterol transport without inducing hepatic lipogenesis

SCOPE

Taurine, which is abundant in seafood, has antiatherogenic activities in both animals and humans; however, its molecular target has been elusive. We examined whether taurine could activate liver X receptor-α (LXR-α), a critical transcription factor in the regulation of reverse cholesterol transport in macrophages.

METHODS AND RESULTS

Taurine bound directly to LXR-α in a reporter gene assay, time-resolved fluorescence resonance energy transfer analysis, and limited protease digestion experiment. Macrophage cells incubated with taurine showed reduced cellular cholesterol and induced medium cholesterol in a dose-dependent manner with the induction of ATP-binding cassette transporter A1 and G gene and protein expression. In hepatocytes, taurine significantly induced Insig-2a levels and delayed nuclear translocation of the sterol regulatory element-binding protein 1 (SREBP-1) protein, resulting in a dose-dependent reduction in the cellular lipid levels without inducing the expression of fatty acid synthesis genes.

CONCLUSION

Taurine is a direct LXR-α ligand, represses cholesterol accumulation, and modulates the expression of genes involved in reverse cholesterol transport in macrophages, without inducing hepatic lipogenesis. The induction of Insig-2a suppressed the nuclear translocation of SREBP-1c.