Induction of intestinal ATP-binding cassette transporters by a phytosterol-derived liver X receptor agonist

Ergosterol and its metabolites as agonists of Liver X receptor and their anticancer potential in colorectal cancer

Aberrant cholesterol homeostasis is a well-recognized hallmark of cancer and is implicated in metastasis as well as chemotherapeutic resistance, the two major causes of cancer associated mortality. Liver X receptors (LXRs) are the key transcription factors that induce cholesterol efflux via enhancing the expression of ABCA1 and ABCG1. Therefore, a comprehensive analysis of several novel sterols namely ergosta-7,22,24(28)-trien-3β-ol (Erg1), ergosta-5,22,25-trien-3-ol (Erg2), ergosta-5,7,22,24(28)-tetraen-3β-ol (Erg3), and ergosta-7,22-dien-3β-ol (Erg4) as LXR agonists has been performed. Molecular docking studies have shown that these sterols possess higher binding affinities for LXRs as compared to the reference ligands (GW3965 and TO901317) and also formed critical activating interactions. Molecular dynamic (MD) simulations further confirmed that docking complexes made of these sterols possess significant stability. To assess the extent of LXR activation, ABCA1 promoter was cloned into luciferase reporter plasmid and transfected into HCT116 cells. It was observed that treatment with Erg, Erg2 and Erg4 led to a significant LXR activation with an EC50 of 5.64 µM, 4.83 and 3.03 µM respectively. Furthermore, a significant increase in mRNA expression of NR1H2 and LXR target genes i.e. ABCA1, ABCG1 and ApoE was observed upon Erg treatment. Flow cytometric analysis have revealed a significant increase in the accumulation of ABCA1 upon Erg treatment. Cytotoxicity studies conducted on colorectal cancer cell and normal epithelial cell line showed that these sterols are selectively toxic towards cancer cells. Taken together, our findings suggests that ergosterol activates LXRs, have significant anticancer activity and could be a likely candidate to manage aberrant cholesterol homeostasis.

Nuclear receptors behind the therapeutic effects of plant sterols on metabolism: A review

Plant sterols are known for their hypocholesterolemic action, and the molecular mechanisms behind this within the gut have been extensively discussed and demonstrated to the point that there is a degree of consensus. However, recent studies show that these molecules exert an additional umbrella of therapeutic effects in other tissues, which are related to immune function, lipid metabolism, and glucose metabolism. A strong hypothesis to explain these effects is the structural relationship between plant sterols and the ligands of a group of nuclear receptors. This review delves into the molecular aspects of therapeutic effects related with lipid and energy metabolism that have been observed and demonstrated for plant sterols, and turns the perspective to explore the involvement of nuclear receptors as part of these mechanisms.

β-Sitosterol as a Promising Anticancer Agent for Chemoprevention and Chemotherapy: Mechanisms of Action and Future Prospects

Cancer is one of the primary causes of death worldwide, and its incidence continues to increase yearly. Despite significant advances in research, the search for effective and nontoxic preventive and therapeutic agents remains greatly important. Cancer is a multimodal disease, where various mechanisms play significant roles in its occurrence and progression. This highlights the need for multitargeted approaches that are not only safe and inexpensive but also provide effective alternatives for current therapeutic regimens. β-Sitosterol (SIT), the most abundant phytosterol found in various plant foods, represents such an option. Preclinical evidence over the past few decades has overwhelmingly shown that SIT exhibits multiple anticancer activities against varied cancers, such as liver, cervical, colon, stomach, breast, lung, pancreatic, and prostate cancers, in addition to leukemia, multiple myeloma, melanoma, and fibrosarcoma. In this article, we present the latest advances and perspectives on SIT-systematically summarizing its antitumor mechanisms of action into 7 main sections and combining current challenges and prospects-for its use as a promising agent for cancer prevention and treatment. In particular, SIT plays a role in cancer prevention and treatment mainly by enhancing apoptosis, inducing cell cycle arrest, bidirectionally regulating oxidative stress, improving metabolic reprogramming, inhibiting invasion and metastasis, modulating immunity and inflammation, and combating drug resistance. Although SIT holds such great promise, the poor aqueous solubility and bioavailability coupled with low targeting efficacy limit its therapeutic efficacy and clinical application. Further research on novel drug delivery systems may improve these deficiencies. Overall, through complex and pleiotropic mechanisms, SIT has good potential for tumor chemoprevention and chemotherapy. However, no clinical trials have yet proven this potential. This review provides theoretical basis and rationality for the further design and conduct of clinical trials to confirm the anticancer activity of SIT.

Flindissone, a Limonoid Isolated from Trichilia prieuriana, Is an LXR Agonist

In this study, the ability of six limonoids from Trichilia prieuriana (Meliaceae) to activate the liver X receptor (LXR) was assessed. One of these limonoids, flindissone, was shown to activate LXR by reporter-gene assays. Flindissone is a ring-intact limonoid, structurally similar to sterol-like LXR ligands. In endogenous cellular settings, flindissone showed an activity profile that is characteristic of LXR agonists. It induced cholesterol efflux in THP-1 macrophages by increasing the cholesterol transporter ABCA1 and ABCG1 gene expression. In HepG2 cells, flindissone induced the expression of IDOL, an LXR-target gene that is associated with the downregulation of the LDL receptor. However, unlike synthetic and similarly to sterol-based LXR agonists, flindissone did not induce the expression of the SREBP1c gene, a major transcription factor regulating de novo lipogenesis. Additionally, flindissone also appeared to be able to inhibit post-translational activation of SREBP1c. The results presented here reveal a natural product as a new LXR agonist and point to an additional property of T. prieuriana and other plant extracts containing flindissone.

ESS2 controls prostate cancer progression through recruitment of chromodomain helicase DNA binding protein 1

Molecular targeted therapy using poly (ADP-ribose) polymerase inhibitors has improved survival in patients with castration-resistant prostate cancer (CRPC). However, this approach is only effective in patients with specific genetic mutations, and additional drug discovery targeting epigenetic modulators is required. Here, we evaluated the involvement of the transcriptional coregulator ESS2 in prostate cancer. ESS2-knockdown PC3 cells dramatically inhibited proliferation in tumor xenografts in nude mice. Microarray analysis revealed that ESS2 regulated mRNA levels of chromodomain helicase DNA binding protein 1 (CHD1)-related genes and other cancer-related genes, such as PPAR-γ, WNT5A, and TGF-β, in prostate cancer. ESS2 knockdown reduced nuclear factor (NF)-κB/CHD1 recruitment and histone H3K36me3 levels on the promoters of target genes (TNF and CCL2). In addition, we found that the transcriptional activities of NF-κB, NFAT and SMAD2/3 were enhanced by ESS2. Tamoxifen-inducible Ess2-knockout mice showed delayed prostate development with hypoplasia and disruption of luminal cells in the ventral prostate. Overall, these findings identified ESS2 acts as a transcriptional coregulator in prostate cancer and ESS2 can be novel epigenetic therapeutic target for CRPC.

Syntheses of 25-Adamantyl-25-alkyl-2-methylidene-1α,25-dihydroxyvitamin D3 Derivatives with Structure-Function Studies of Antagonistic and Agonistic Active Vitamin D Analogs

The active form of vitamin D₃, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], is a major regulator of calcium homeostasis through activation of the vitamin D receptor (VDR). We have previously synthesized vitamin D derivatives with large adamantane (AD) rings at position 24, 25, or 26 of the side chain to study VDR agonist and/or antagonist properties. One of them-ADTK1, with an AD ring and 23,24-triple bond-shows a high VDR affinity and cell-selective VDR activity. In this study, we synthesized novel vitamin D derivatives (ADKM1-6) with an alkyl group substituted at position 25 of ADTK1 to develop more cell-selective VDR ligands. ADKM2, ADKM4, and ADKM6 had VDR transcriptional activity comparable to 1,25(OH)₂D₃ and ADTK1, although their VDR affinities were weaker. Interestingly, ADKM2 has selective VDR activity in kidney- and skin-derived cells-a unique phenotype that differs from ADTK1. Furthermore, ADKM2, ADKM4, and ADKM6 induced osteoblast differentiation in human dedifferentiated fat cells more effectively than ADTK1. The development of vitamin D derivatives with bulky modifications such as AD at position 24, 25, or 26 of the side chain is useful for increased stability and tissue selectivity in VDR-targeting therapy.

Phytosterols as bioactive food components against nonalcoholic fatty liver disease

Phytosterols are bioactive food components widely present in cell membranes of plants, especially in nuts and oilseeds. In recent years, many studies have shown that phytosterols possess therapeutic potentials for nonalcoholic fatty liver disease (NAFLD). This review summarizes the effects of phytosterols from in vitro and in vivo studies to lower the levels of total cholesterol (TC) and triglycerides (TG), and the evidence supporting the potential of phytosterols against NAFLD. The potential mechanisms by which phytosterols improve NAFLD may include (i) competition with cholesterol; (ii) regulation of key factors involved in cholesterol and TG metabolism; and (iii) inhibition of liver inflammation and (iv) regulation of liver fatty acid composition. In summary, phytosterols are potential natural ingredients with good safety profile against NAFLD, which deserve more future studies.

Phytosterols: Targeting Neuroinflammation in Neurodegeneration

Plant-derived sterols, phytosterols, are well known for their cholesterol-lowering activity in serum and their anti-inflammatory activities. Recently, phytosterols have received considerable attention due to their beneficial effects on various non-communicable diseases, and recommended use as daily dietary components. The signaling pathways mediated in the brain by phytosterols have been evaluated, but little is known about their effects on neuroinflammation, and no clinical studies have been undertaken on phytosterols of interest. In this review, we discuss the beneficial roles of phytosterols, including their attenuating effects on inflammation, blood cholesterol levels, and hallmarks of the disease, and their regulatory effects on neuroinflammatory disease pathways. Despite recent advancements made in phytosterol pharmacology, some critical questions remain unanswered. Therefore, we have tried to highlight the potential of phytosterols as viable therapeutics against neuroinflammation and to direct future research with respect to clinical applications.

Common targets for a deadly duo of diabetes mellitus and colon cancer: Catching two fish with one worm

Colon cancer is a major health issue and number of cases are increasing every year. Diabetes mellitus is also a significant health issue that is growing day by day worldwide having negative influences on the survival of individuals. Research has shown a strong relationship between the two malignant diseases. The risk of colon cancer with patients who have type 2 diabetes mellitus has spiked by 30%. The scientific research suggests insulin has a major role in the spread of cancer and the condition unifying between the two diseases is hyperinsulinemia. Several anti-diabetic agents are used for the treatment of type 2 diabetesmellitus. However, their mechanism of action against cancer activity is a question and only a few agents have shown positive signs of action in colon cancer associated with type 2 diabetesmellitus. Hence, the identification of targets, which is common for both colon cancer, associated with type 2 diabetesmellitus has become an urgent requirement. Novel targets such as Liver X receptors, Histone deacetylase inhibitors (HDACi), Glucose Transporters (GLUTs), Peroxisome proliferator activator receptors (PPARs), Dipeptidyl peptidase-IV inhibitors (DPP4i), Cyclin-dependent kinase 4 inhibitors (CDK4i), Estrogen receptors,Mechanistic target of rapamycin (mTOR), Insulin-like growth factor receptors (IGF) are some of the targets which are common for both, type 2 diabetesmellitus and colon cancer. This current review gives an overview of the targets (using one worm) which are common for both viz. diabetes mellitus and colon cancer (two fish).

Nuclear receptors in the kidney during health and disease

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.

Alisol B 23-acetate activates ABCG5/G8 in the jejunum via the LXRα/ACAT2 pathway to relieve atherosclerosis in ovariectomized ApoE-/- mice

Phytosterols have been shown to improve blood lipid levels and treat atherosclerosis. This research investigated the effects of phytosterol Alisol B 23-acetate (AB23A) on jejunum lipid metabolism and atherosclerosis. The results show that intragastric administration of AB23A can significantly reduce atherosclerotic plaque area and lipid accumulation in the jejunum of ovariectomized ApoE-/- mice fed a high-fat diet and can also improve the lipid mass spectra of the plasma and jejunum. In vitro studies have shown that AB23A can increase cholesterol outflow in Caco-2 cells exposed to high fat concentrations and increase the expression of ATP-binding cassette transfer proteins G5/G8 (ABCG5/G8), the liver X receptor α (LXRα). Furthermore, inhibition of LXRα can significantly eliminate the active effect of AB23A on decreasing intracellular lipid accumulation. We also confirmed that AB23A has a negative effect on Acyl-CoA cholesterol acyltransferase 2 (ACAT2) in Caco-2 cells cultured in the high concentrations of fat, and we found that AB23A further reduces ACAT2 expression in cells treated with the ACAT2 inhibitor pyripyropene or transfected with ACAT2 siRNA. In conclusion, we confirmed that AB23A can reduce the absorption of dietary lipids in the jejunum by affecting the LXRα-ACAT2-ABCG5/G8 pathway and ultimately exert an anti-atherosclerotic effect.

Stigmasterol stimulates transintestinal cholesterol excretion independent of liver X receptor activation in the small intestine

Despite advances in healthcare, cardiovascular disease (CVD) remains the leading cause of death in the United States. Elevated levels of plasma cholesterol are highly predictive of CVD and stroke and are the principal driver of atherosclerosis. Unfortunately, current cholesterol lowering agents, such as statins, are not known to reverse atherosclerotic disease once it has been established. In preclinical models, agonists of nuclear receptor, LXR, have been shown to reduce and reverse atherosclerosis. Phytosterols are bioactive non-cholesterol sterols that act as LXR agonists and regulate cholesterol metabolism and transport. We hypothesized that stigmasterol would act as an LXR agonist and alter intestinal cholesterol secretion to promote cholesterol elimination. Mice were fed a control diet, or a diet supplemented with stigmasterol (0.3% w/w) or T0901317 (0.015% w/w), a known LXR agonist. In this experiment we analyzed the sterol content of bile, intestinal perfusate, plasma, and feces. Additionally, the liver and small intestine were analyzed for relative levels of transcripts known to be regulated by LXR. We observed that T0901317 robustly promoted cholesterol elimination and acted as a strong LXR agonist. Stigmasterol promoted transintestinal cholesterol secretion through an LXR-independent pathway.

Phytosterols Inhibit Side-Chain Oxysterol Mediated Activation of LXR in Breast Cancer Cells

Low fruit and vegetable consumption and high saturated fat consumption causes elevated circulating cholesterol and are breast cancer risk factors. During cholesterol metabolism, oxysterols form that bind and activate the liver X receptors (LXRs). Oxysterols halt breast cancer cell proliferation but enhance metastatic colonization, indicating tumour suppressing and promoting roles. Phytosterols and phytostanols in plants, like cholesterol in mammals, are essential components of the plasma membrane and biochemical precursors, and in human cells can alter LXR transcriptional activity. Here, a panel of breast cancer cell lines were treated with four dietary plant sterols and a stanol, alone or in combination with oxysterols. LXR activation and repression were measured by gene expression and LXR-luciferase reporter assays. Oxysterols activated LXR in all cell lines, but surprisingly phytosterols failed to modulate LXR activity. However, phytosterols significantly inhibited the ability of oxysterols to drive LXR transcription. These data support a role for phytosterols in modulating cancer cell behaviour via LXR, and therefore suggest merit in accurate dietary recordings of these molecules in cancer patients during treatment and perhaps supplementation to benefit recovery.

Flavonoids differentially modulate liver X receptors activity-Structure-function relationship analysis

Liver X receptors (LXRs) α (NR1H3) and β (NR1H2) are nuclear receptors that have been involved in the regulation of many physiological processes, principally in the control of cholesterol homeostasis, as well as in the control of the cell death and proliferation balance. These receptors are thus promising therapeutic targets in various pathologies such as dyslipidemia, atherosclerosis, diabetes and/or cancers. These receptors are known to be activated by specific oxysterol compounds. The screening for LXR-specific ligands is a challenging process: indeed, these molecules should present a specificity towards each LXR-isoform. Because some natural products have significant effects in the regulation of the LXR-regulated homeostasis and are enriched in flavonoids, we have decided to test in cell culture the effects of 4 selected flavonoids (galangin, quercetin, apigenin and naringenin) on the modulation of LXR activity using double-hybrid experiments. In silico, molecular docking suggests specific binding pattern between agonistic and antagonistic molecules. Altogether, these results allow a better understanding of the ligand binding pocket of LXRα/β. They also improve our knowledge about flavonoid mechanism of action, allowing the selection and development of better LXR selective ligands.

The Lipid-lowering Effects and Associated Mechanisms of Dietary Phytosterol Supplementation

Phytosterols (PS) are plant-based structural analogous of mammalian cholesterol that have been shown to lower blood cholesterol concentrations by ~10%, although inter-individual response to PS supplementation due to subject-specific metabolic and genetic factors is evident. Recent work further suggests that PS may act as effective triglyceride (TG)-lowering agents with maximal TG reductions observed in hypertriglyceridemic subjects. Although PS have been demonstrated to interfere with cholesterol and perhaps TG absorption within the intestine, they also have the capacity to modulate the expression of lipid regulatory genes through liver X receptor (LXR) activation. Identification of single-nucleotide polymorphisms (SNP) in key cholesterol and TG regulating genes, in particular adenosine triphosphate binding cassette G8 (ABCG8) and apolipoprotein E (apoE) have provided insight into the potential of utilizing genomic identifiers as an indicator of PS responsiveness. While PS supplementation is deemed safe, expanding research into the atherogenic potential of oxidized phytosterols (oxyphytosterols) has emerged with their identification in arterial lesions. This review will highlight the lipid-lowering utility and associated mechanisms of PS and discuss novel applications and future research priorities for PS pertaining to in utero PS exposure for long-term cardiovascular disease risk protection and combination therapies with lipidlowering drugs.

Dietary Sargassum fusiforme improves memory and reduces amyloid plaque load in an Alzheimer's disease mouse model

Activation of liver X receptors (LXRs) by synthetic agonists was found to improve cognition in Alzheimer's disease (AD) mice. However, these LXR agonists induce hypertriglyceridemia and hepatic steatosis, hampering their use in the clinic. We hypothesized that phytosterols as LXR agonists enhance cognition in AD without affecting plasma and hepatic triglycerides. Phytosterols previously reported to activate LXRs were tested in a luciferase-based LXR reporter assay. Using this assay, we found that phytosterols commonly present in a Western type diet in physiological concentrations do not activate LXRs. However, a lipid extract of the 24(S)-Saringosterol-containing seaweed Sargassum fusiforme did potently activate LXRβ. Dietary supplementation of crude Sargassum fusiforme or a Sargassum fusiforme-derived lipid extract to AD mice significantly improved short-term memory and reduced hippocampal Aβ plaque load by 81%. Notably, none of the side effects typically induced by full synthetic LXR agonists were observed. In contrast, administration of the synthetic LXRα activator, AZ876, did not improve cognition and resulted in the accumulation of lipid droplets in the liver. Administration of Sargassum fusiforme-derived 24(S)-Saringosterol to cultured neurons reduced the secretion of Aβ₄₂. Moreover, conditioned medium from 24(S)-Saringosterol-treated astrocytes added to microglia increased phagocytosis of Aβ. Our data show that Sargassum fusiforme improves cognition and alleviates AD pathology. This may be explained at least partly by 24(S)-Saringosterol-mediated LXRβ activation.

Bread enriched with phytosterols with or without curcumin modulates lipoprotein profiles in hypercholesterolaemic individuals. A randomised controlled trial

A novel functional food containing phytosterols and curcumin significantly lowers blood cholesterol concentrations in hypercholesterolaemic individuals.

In vitro and in vivo testing of the hypocholesterolemic activity of ergosterol- and β-glucan-enriched extracts obtained from shiitake mushrooms (Lentinula edodes)

Herein, two shiitake fractions were obtained: the ergosterol-enriched fraction exerted higher in vitro hypocholesterolemic activity and the β-glucan-enriched fraction reduced the cholesterol levels in mice.

Liver X receptors in lipid signalling and membrane homeostasis

Liver X receptors α and β (LXRα and LXRβ) are nuclear receptors with pivotal roles in the transcriptional control of lipid metabolism. Transcriptional activity of LXRs is induced in response to elevated cellular levels of cholesterol. LXRs bind to and regulate the expression of genes that encode proteins involved in cholesterol absorption, transport, efflux, excretion and conversion to bile acids. The coordinated, tissue-specific actions of the LXR pathway maintain systemic cholesterol homeostasis and regulate immune and inflammatory responses. LXRs also regulate fatty acid metabolism by controlling the lipogenic transcription factor sterol regulatory element-binding protein 1c and regulate genes that encode proteins involved in fatty acid elongation and desaturation. LXRs exert important effects on the metabolism of phospholipids, which, along with cholesterol, are major constituents of cellular membranes. LXR activation preferentially drives the incorporation of polyunsaturated fatty acids into phospholipids by inducing transcription of the remodelling enzyme lysophosphatidylcholine acyltransferase 3. The ability of the LXR pathway to couple cellular sterol levels with the saturation of fatty acids in membrane phospholipids has implications for several physiological processes, including lipoprotein production, dietary lipid absorption and intestinal stem cell proliferation. Understanding how LXRs regulate membrane composition and function might provide new therapeutic insight into diseases associated with dysregulated lipid metabolism, including atherosclerosis, diabetes mellitus and cancer.

A Genome-Wide Screen of Deletion Mutants in the Filamentous Saccharomyces cerevisiae Background Identifies Ergosterol as a Direct Trigger of Macrophage Pyroptosis

Phagocytic cells such as macrophages play an important role in the host defense mechanisms mounted in response to the common human fungal pathogen Candida albicans. In vitro, C. albicans triggers macrophage NLRP3-Casp1/11-mediated pyroptosis, an inflammatory programmed cell death pathway. Here, we provide evidence that Casp1/11-dependent pyroptosis occurs in the kidney of infected mice during the early stages of infection. We have also used a genome-wide screen of nonessential Σ1278b Saccharomyces cerevisiae genes to identify genes required for yeast-triggered macrophage pyroptosis. The set of genes identified by this screen was enriched for those with functions in lipid and sterol homeostasis and trafficking. These observations led us to discover that cell surface localization and/or total levels of ergosterol correlate with the ability of S. cerevisiae, C. albicans, and Cryptococcus neoformans to trigger pyroptosis. Since the mammalian sterol cholesterol triggers NLRP3-mediated pyroptosis, we hypothesized that ergosterol may also do so. Consistent with that hypothesis, ergosterol-containing liposomes but not ergosterol-free liposomes induce pyroptosis. Cell wall mannoproteins directly bind ergosterol, and we found that Dan1, an ergosterol receptor mannoprotein, as well as specific mannosyltransferases, is required for pyroptosis, suggesting that cell wall-associated ergosterol may mediate the process. Taken together, these data indicate that ergosterol, like mammalian cholesterol, plays a direct role in yeast-mediated pyroptosis.

Innate immune cells such as macrophages are key components of the host response to the human fungal pathogen Candida albicans. Macrophages undergo pyroptosis, an inflammatory, programmed cell death, in response to some species of pathogenic yeast. Prior to the work described in this report, yeast-triggered pyroptosis has been observed only in vitro; here, we show that pyroptosis occurs in the initial stages of murine kidney infection, suggesting that it plays an important role in the initial response of the innate immune system to invasive yeast infection. We also show that a key component of the fungal plasma membrane, ergosterol, directly triggers pyroptosis. Ergosterol is also present in the fungal cell wall, most likely associated with mannoproteins, and is increased in hyphal cells compared to yeast cells. Our data indicate that specific mannoproteins are required for pyroptosis. This is consistent with a potential mechanism whereby ergosterol present in the outer mannoprotein layer of the cell wall is accessible to the macrophage-mediated process. Taken together, our data provide the first evidence that ergosterol plays a direct role in the host-pathogen interactions of fungi.

25 S-Adamantyl-23-yne-26,27-dinor-1α,25-dihydroxyvitamin D3: Synthesis, Tissue Selective Biological Activities, and X-ray Crystal Structural Analysis of Its Vitamin D Receptor Complex

Both 25 R- and 25 S-25-adamantyl-23-yne-26,27-dinor-1α,25-dihydroxyvitamin D₃ (4a and 4b) were stereoselectively synthesized by a Pd(0)-catalyzed ring closure and Suzuki-Miyaura coupling between enol-triflate 7 and alkenyl-boronic ester 8. The 25 S isomer (4b) showed high vitamin D receptor (VDR) affinity (50% of that of the natural hormone 1α,25-dihydroxyvitamin D₃, 1) and transactivation potency (kidney HEK293, 90%). In endogenous gene expression, it showed high cell-type selectivity for kidney cells (HEK293, CYP24A1 160% of 1), bone cells (MG63, osteocalcin 64%), and monocytes (U937, CAMP 96%) over intestine (SW480, CYP24A1 8%) and skin (HaCaT, CYP24A1 7%) cells. The X-ray crystal structural analysis of 4b in complex with rat VDR-ligand binding domain (LBD) showed the highest Cα positional shift from the 1/VDR-LBD complex at helix 11. Helix 11 of the 4b and 1 VDR-LBD complexes also showed significant differences in surface properties. These results suggest that 4b should be examined further as another candidate for a mild preventive osteoporosis agent.

Curcumin potentiates cholesterol-lowering effects of phytosterols in hypercholesterolaemic individuals. A randomised controlled trial

BACKGROUND

Dietary phytosterols (PS) are well-known hypocholesterolaemic agents. Curcumin elicits hypolipidaemic and anti-inflammatory effects in preclinical studies, however, consistent findings in humans are lacking.

OBJECTIVE

Concurrent PS and curcumin supplementation may exhibit enhanced hypocholesterolaemic and anti-inflammatory effects to optimise cardio-protection. The objective of this trial was to investigate the effects of dietary intervention with PS with or without curcumin on blood lipids (primary outcome) in hypercholesterolaemic individuals.

METHODS

A double-blinded, randomised, placebo-controlled, 2 × 2 factorial trial was conducted in hypercholesterolaemic individuals. Participants received either placebo (PL, no phytosterols or curcumin), phytosterols (PS, 2 g/d), curcumin (CC, 200 mg/d) or a combination of PS and curcumin (PS-CC, 2 g/d-200 mg/d respectively) for four weeks. Primary outcomes included fasting total cholesterol (TC), LDL-cholesterol, HDL-cholesterol, triglycerides (TG), TC-to-HDL-C ratio (TC:HDL-C). Secondary outcomes included anthropometrics and fasting blood glucose concentrations.

RESULTS

Seventy participants with a mean (±SEM) fasting TC concentration of 6.57 ± 0.13 mmol/L completed the study (PL, n = 18; PS, n = 17; CC, n = 18; PS-CC, n = 17). PS and PS-CC supplementation significantly lowered TC, LDL-cholesterol and TC:HDL-C post-intervention (p < 0.05). Reductions from baseline in the PS group were 4.8% and 8.1% for TC and LDL-cholesterol respectively (p < 0.05). CC exhibited non-significant reduction (2.3% and 2.6%) in TC and LDL-C respectively, however, the PS-CC resulted in a greater reduction in TC (11.0%) and LDL-cholesterol (14.4%) than either of the treatments alone (p < 0.0001). The reduction in the PS-CC treatment was significantly greater compared to those for CC (p < 0.05) or PL (p < 0.01) alone. Plasma HDL-cholesterol and TG concentrations remained unchanged across all groups. No adverse side effects were reported.

CONCLUSIONS

The addition of curcumin to phytosterol therapy provides a complementary cholesterol-lowering effect that is larger than phytosterol therapy alone. Implications of these findings include the development of a single functional food containing both the active ingredients for enhanced lipid-lowering and compliance in hypercholesterolaemic individuals. ANZCTR identifier: 1261500095650.

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.

Transintestinal cholesterol excretion in humans

PURPOSE OF REVIEW

To discuss recent insights into the measurement and cellular basis of transintestinal cholesterol excretion (TICE) in humans and to explore TICE as a therapeutic target for increasing reverse cholesterol transport.

RECENT FINDINGS

TICE is the net effect of cholesterol excretion by the enterocyte into the intestinal lumen and is the balance between input and output fluxes through the enterocytes. These fluxes are: cholesterol excretion into the intestinal lumen mainly via ATP-binding cassette (ABC) G5/8, cholesterol absorption from the intestine by Niemann-Pick C1 like protein 1, the uptake of plasma lipoproteins by enterocytes at the basolateral membrane, and the excretion of cholesterol in chylomicrons into the lymph. Multiple studies have shown that TICE contributes to fecal neutral sterol (FNS) excretion in humans. TICE can be targeted with plant sterols, liver X receptor agonists, bile acids, ezetimibe, and proprotein convertase subtilisin/kexin type 9 inhibitors.

SUMMARY

TICE contributes significantly to FNS excretion in humans, independently of the biliary pathway. Knowledge about its underlying cellular mechanisms surges through in-vivo and in-vitro studies in mice and humans. TICE might be an interesting therapeutic target for increasing cholesterol disposal with the feces. Albeit multiple therapeutic options are available, studies showing clinical benefit are still needed.

Biomarkers of Amyotrophic Lateral Sclerosis: Current Status and Interest of Oxysterols and Phytosterols

Amyotrophic lateral sclerosis (ALS) is a non-demyelinating neurodegenerative disease in adults with motor disorders. Two forms exist: a sporadic form (90% of cases) and a family form due to mutations in more than 20 genes including the Superoxide dismutase 1, TAR DNA Binding Protein, Fused in Sarcoma, chromosome 9 open reading frame 72 and VAPB genes. The mechanisms associated with this pathology are beginning to be known: oxidative stress, glutamate excitotoxicity, protein aggregation, reticulum endoplasmic stress, neuroinflammation, alteration of RNA metabolism. In various neurodegenerative diseases, such as Alzheimer's disease or multiple sclerosis, the involvement of lipids is increasingly suggested based on lipid metabolism modifications. With regard to ALS, research has also focused on the possible involvement of lipids. Lipid involvement was suggested for clinical arguments where changes in cholesterol and LDL/HDL levels were reported with, however, differences in positivity between studies. Since lipids are involved in the membrane structure and certain signaling pathways, it may be considered to look for oxysterols, mainly 25-hydroxycholesterol and its metabolites involved in immune response, or phytosterols to find suitable biomarkers for this pathology.

C24-hydroxylated stigmastane derivatives as Liver X Receptor agonists

Phytosterols are stucturally correlated to the endogenous ligands of Liver X Receptor (LXR), a ligand-activated nuclear receptor that has emerged as an attractive drug target due to its ability to integrate metabolic and inflammatory signaling. Natural and semi-synthetic phytosterol derivatives characterized by the presence of side-chain oxygenated functions have shown to be able to modulate LXR activity. Here, we describe the efficient synthesis of four stigmastane derivatives, endowed with a hydroxyl group at C24 position, namely (24R)- and (24S)-stigmasta-5,28-diene-3β,24-ols (also referred to as saringosterols, 10a and 10b) and (24R)- and (24S)-stigmasta-5-ene-3β,24-ols (11a and 11b), starting from the readily available stigmasterol. Thanks to X-ray crystallography the absolute configuration of the newly created chiral centers was definitively assigned for all the four compounds. The subsequent luciferase assays with GAL-4 chimeric receptors evidenced the ability of the two 24(S)-epimers, 10b and 11b, to interact with LXRs, showing the same degree of affinity as (22R)-hydroxycholesterol (1). With regard to the isoform selectivity both the derivatives 10b and 11b showed a preference for LXRβ, up to 4-fold in terms of efficacy for 11b. The gene expression profiling of (24S)-stigmasta-5,28-diene-3β,24-ol (10a) and (24S)-stigmasta-5-ene-3β,24-ol (11a) demonstrated the capability of both the compounds to induce the expression of four well-known LXR target genes, such as ABCA1, SREBP1c, FASN, and SCD1 in U937 monocytic cell line, thus supporting the hypothesis they were LXR positive modulators.

Molecular actions of hypocholesterolaemic compounds from edible mushrooms

Edible mushrooms contain bioactive compounds able to modulate the expression of genes related to absorption, biosynthesis and transport of cholesterol and regulation of its homeostasis.

Liver X receptors as potential targets for cancer therapeutics

Liver X receptors (LXRs) are important members of the nuclear receptor family that were originally determined to function in cholesterol transport and the regulation of immune responses. Synthetic LXR ligands have been developed to treat various diseases including diabetes, Alzheimer's disease and atherosclerosis. Previous studies have suggested that LXRs are also involved in numerous types of cancer and are therefore potential targets for cancer therapeutics. The present review summarizes LXR ligands and their mechanisms of action, the effects of LXRs in different types of cancer and their potential applications in clinical treatment. Together, the studies discussed in the present review indicate that LXRs may be potential targets for cancer therapeutics.

1α-Hydroxy derivatives of 7-dehydrocholesterol are selective liver X receptor modulators

The nuclear receptors liver X receptor (LXR) α and LXRβ are involved in the regulation of lipid metabolism, inflammation, immunity, cellular proliferation, and apoptosis. Oxysterols are endogenous LXR ligands, and also interact with other nuclear and membrane receptors. We previously reported that a phytosterol derivative with a 1α-hydroxy group acts as a potent LXR agonist with intestine-selective action and that 25-hydroxy and 26/27-hydroxy metabolites of 7-dehydrocholesterol (7-DHC) exhibit partial LXR agonism. In this study, we report that 1α-hydroxy derivatives of 7-DHC, 1α-OH-7-DHC and 1,25-(OH)₂-7-DHC, act as LXR modulators. Luciferase reporter gene assays showed that 1α-OH-7-DHC activates LXRα and LXRβ and that 1,25-(OH)₂-7-DHC activates both LXRs and vitamin D receptor. Examination of cofactor peptide association showed that the 1α-hydroxy derivatives, specifically 1,25-(OH)₂-7-DHC, induce association of coactivator/corepressor peptide in a different manner from the agonist T0901317. Docking modeling and alanine mutational analysis of LXRα demonstrated that 1,25-(OH)₂-7-DHC interacts with LXRα residues in a manner distinct from potent agonists, such as T0901317 and 24(S),25-epoxycholesterol. 1α-OH-7-DHC and 1,25-(OH)₂-7-DHC induced expression of LXR target genes in a cell type- and gene-selective manner. 1,25-(OH)₂-7-DHC effectively suppressed lipopolysaccharide-stimulated proinflammatory gene expression in an LXR-dependent manner. Therefore, 1α-hydroxy derivatives, such as 1,25-(OH)₂-7-DHC, are unique LXR modulators with selective agonistic activity and potent transrepression function. These oxysterols have potential as LXR-targeted therapeutics for inflammatory disease.

Side-Chain Modified Ergosterol and Stigmasterol Derivatives as Liver X Receptor Agonists

A series of stigmasterol and ergosterol derivatives, characterized by the presence of oxygenated functions at C-22 and/or C-23 positions, were designed as potential liver X receptor (LXR) agonists. The absolute configuration of the newly created chiral centers was definitively assigned for all the corresponding compounds. Among the 16 synthesized compounds, 21, 27, and 28 were found to be selective LXRα agonists, whereas 20, 22, and 25 showed good selectivity for the LXRβ isoform. In particular, 25 showed the same degree of potency as 22R-HC (3) at LXRβ, while it was virtually inactive at LXRα (EC₅₀ = 14.51 μM). Interestingly, 13, 19, 20, and 25 showed to be LXR target gene-selective modulators, by strongly inducing the expression of ABCA1, while poorly or not activating the lipogenic genes SREBP1 and SCD1 or FASN, respectively.

The challenges and promise of targeting the Liver X Receptors for treatment of inflammatory disease

The Liver X Receptors (LXRs) are oxysterol-activated transcription factors that upregulate a suite of genes that together promote coordinated mobilization of excess cholesterol from cells and from the body. The LXRs, like other nuclear receptors, are anti-inflammatory, inhibiting signal-dependent induction of pro-inflammatory genes by nuclear factor-κB, activating protein-1, and other transcription factors. Synthetic LXR agonists have been shown to ameliorate atherosclerosis and a wide range of inflammatory disorders in preclinical animal models. Although this has suggested potential for application to human disease, systemic LXR activation is complicated by hepatic steatosis and hypertriglyceridemia, consequences of lipogenic gene induction in the liver by LXRα. The past several years have seen the development of multiple advanced LXR therapeutics aiming to avoid hepatic lipogenesis, including LXRβ-selective agonists, tissue-selective agonists, and transrepression-selective agonists. Although several synthetic LXR agonists have made it to phase I clinical trials, none have progressed due to unforeseen adverse reactions or undisclosed reasons. Nonetheless, several sophisticated pharmacologic strategies, including structure-guided drug design, cell-specific drug targeting, as well as non-systemic drug routes have been initiated and remain to be comprehensively explored. In addition, recent studies have identified potential utility for targeting the LXRs during therapy with other agents, such as glucocorticoids and rexinoids. Despite the pitfalls encountered to date in translation of LXR agonists to human disease, it appears likely that this accelerating field will ultimately yield effective and safe applications for LXR targeting in humans.

Role of Intestinal LXRα in Regulating Post-prandial Lipid Excursion and Diet-Induced Hypercholesterolemia and Hepatic Lipid Accumulation

Post-prandial hyperlipidemia has emerged as a cardiovascular risk factor with limited therapeutic options. The Liver X receptors (Lxrs) are nuclear hormone receptors that regulate cholesterol elimination. Knowledge of their role in regulating the absorption and handling of dietary fats is incomplete. The purpose of this study was to determine the role of intestinal Lxrα in post-prandial intestinal lipid transport. Using Lxrα knockout (nr1h3^−/−) and intestine-limited Lxrα over-expressing [Tg(fabp2a:EGFP-nr1h3)] zebrafish strains, we measured post-prandial lipid excursion with live imaging in larvae and physiological methods in adults. We also conducted a long-term high-cholesterol dietary challenge in adults to examine the chronic effect of modulating nr1h3 gene dose on the development of hypercholesterolemia and hepatic lipid accumulation. Over-expression of Lxrα in the intestine delays the transport of ingested lipids in larvae, while deletion of Lxrα increases the rate of lipid transport. Pre-treating wildtype larvae with the liver-sparing Lxr agonist hyodeoxycholic acid also delayed the rate of intestinal lipid transport in larvae. In adult males, deletion of Lxrα accelerates intestinal transport of ingested lipids. Adult females showed higher plasma Lipoprotein lipase (Lpl) activity compared to males, and lower post-gavage blood triacylglycerol (TAG) excursion. Despite the sexually dimorphic effect on acute intestinal lipid handling, Tg(fabp2a:EGFP-nr1h3) adults of both sexes are protected from high cholesterol diet (HCD)-induced hepatic lipid accumulation, while nr1h3^−/− mutants are sensitive to the effects of HCD challenge. These data indicate that intestinal Lxr activity dampens the pace of intestinal lipid transport cell-autonomously. Selective activation of intestinal Lxrα holds therapeutic promise.

Ligands of Therapeutic Utility for the Liver X Receptors

Liver X receptors (LXRs) have been increasingly recognized as a potential therapeutic target to treat pathological conditions ranging from vascular and metabolic diseases, neurological degeneration, to cancers that are driven by lipid metabolism. Amidst intensifying efforts to discover ligands that act through LXRs to achieve the sought-after pharmacological outcomes, several lead compounds are already being tested in clinical trials for a variety of disease interventions. While more potent and selective LXR ligands continue to emerge from screening of small molecule libraries, rational design, and empirical medicinal chemistry approaches, challenges remain in minimizing undesirable effects of LXR activation on lipid metabolism. This review provides a summary of known endogenous, naturally occurring, and synthetic ligands. The review also offers considerations from a molecular modeling perspective with which to design more specific LXRβ ligands based on the interaction energies of ligands and the important amino acid residues in the LXRβ ligand binding domain.

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.

Lipid Homeostasis and Ligands for Liver X Receptors: Identification and Characterization

Screening of bona fide ligands for nuclear receptors is a real tour de force as the identified molecules are supposed to be able to activate the targeted proteins in cell culture as well as in vivo. Indeed orphan nuclear receptors are putative pharmacologically targets for various diseases. It is thus necessary to have quick and reproductive systems that help in identifying new ligands, agonist or antagonist, before using them in vivo in animal models to check for secondary effects. Here, we describe the transient transfections (homologous and heterologous) used for the screening of ligands for liver X receptor α (LXRα, NR1H3) in HeLa cells.

The emerging roles of liver X receptors and their ligands in cancer

INTRODUCTION

Liver X receptors (LXRs) are nuclear receptors with well-known functions in cholesterol transport, fatty acid and glucose metabolism, and modulation of immune responses. Natural and synthetic ligands have been identified and are under development for the treatment of metabolic and inflammatory conditions and diseases. There is mounting evidence pointing to functional roles for LXRs in a variety of malignancies and the potential therapeutic efficacy of their ligands.

AREAS COVERED

This review summarizes the discovery and characterization of LXRs and their ligands, surveys their effects and mechanisms of action in cell-based and animal models of cancer, and proposes the future direction of basic and translational studies of LXRs and their ligands in cancer research and therapeutics.

EXPERT OPINION

Targeting LXRs is a promising strategy for cancer treatment, particularly for those cancers which do not have effective treatment options. Key questions remain, however, regarding the specific mechanisms of action, effects on other target cells within the tumor microenvironment, and receptor status in patient populations. Moreover, LXR ligands optimized for disease-specific functions and cancer-related endpoints are currently not available. These issues represent both challenges and significant opportunities for future research and development efforts.

Targeting liver X receptors in cancer therapeutics

Members of the nuclear receptor superfamily of ligand-dependent transcription factors carry out vital cellular functions and are highly druggable therapeutic targets. Liver X receptors (LXRs) are nuclear receptor family members that function in cholesterol transport, glucose metabolism and the modulation of inflammatory responses. There is now accumulating evidence to support the involvement of LXRs in a variety of malignancies and the potential efficacy of their ligands in these diseases. This Review summarizes the discovery and characterization of LXRs and their ligands, their effects and mechanisms in preclinical cancer models, and the future directions of basic and translational LXR research in cancer therapeutics.

An acute intake of plant stanol esters alters immune-related pathways in the jejunum of healthy volunteers

Plant sterols and stanols inhibit intestinal cholesterol absorption and consequently lower serum LDL-cholesterol (LDL-C) concentrations. The underlying mechanisms are not yet known. In vitro and animal studies have suggested that changes in intestinal sterol metabolism are attributed to the LDL-C-lowering effects of plant stanol esters. However, similar studies in human subjects are lacking. Therefore, we examined the effects of an acute intake of plant stanol esters on gene expression profiles of the upper small intestine in healthy volunteers. In a double-blind cross-over design, fourteen healthy subjects (eight female and six male; age 21–55 years), with a BMI ranging from 21 to 29 kg/m2, received in random order a shake with or without plant stanol esters (4 g). At 5 h after consumption of the shake, biopsies were taken from the duodenum (around the papilla of Vater) and from the jejunum (20 cm distal from the papilla of Vater). Microarray analysis showed that the expression profiles of genes involved in sterol metabolism were not altered. Surprisingly, the pathways involved in T-cell functions were down-regulated in the jejunum. Furthermore, immunohistochemical analysis showed that the number of CD3 (cluster of differentiation number 3), CD4 (cluster of differentiation number 4) and Foxp3+ (forkhead box P3-positive) cells was reduced in the plant stanol ester condition compared with the control condition, which is in line with the microarray data. The physiological and functional consequences of the plant stanol ester-induced reduction of intestinal T-cell-based immune activity in healthy subjects deserve further investigation.

The effect of two novel cholesterol-lowering agents, disodium ascorbyl phytostanol phosphate (DAPP) and nanostructured aluminosilicate (NSAS) on the expression and activity of P-glycoprotein within Caco-2 cells

Background

Many drugs are substrates for P-glycoprotein (P-gp) and interactions involving P-gp may be relevant to clinical practice. Co-administration with P-gp inhibitors or inducers changes the absorption profile as well as the risk for drug toxicity, therefore it is important to evaluate possible P-gp alterations. The purpose of this study was to investigate the effect of two novel cholesterol-lowering agents, disodium ascorbyl phytostanol phosphate (DAPP) and nanostructured aluminium silicate (NSAS), a protonated montmorillonite clay, on mdr-1 gene expression and its protein, P-glycoprotein (P-gp) within Caco-2 cells.

Methods

The effects of DAPP and NSAS on the regulation of mdr-1 gene, P-gp protein expression and activity within Caco-2 cells, were determined using cell viability and cytotoxicity tests, RT-PCR, Western Blot analysis and bi-directional transport studies.

Results

We observed a significant down-regulation of mdr-1 mRNA (e.g. 38.5 ± 17% decrease vs. control at 5 μM DAPP and 61.2 ± 25% versus control at 10 μM DAPP; n = 6, P* < 0.05) within Caco-2 cells. Western Blot analysis of P-gp expression showed that changes in mdr-1 gene expression lead to correlating changes in P-gp protein expression. This down-regulation of P-glycoprotein also resulted in decreased activity of P-glycoprotein compared to untreated control. In contrast, when Caco-2 cells were treated with NSAS, no changes in mdr-1 gene expression, P-gp protein expression nor P-gp activity were observed.

Conclusions

DAPP but not NSAS decreases P-gp mediated drug efflux through decreased mdr-1 gene expression and consequently decreased P-gp protein expression. These findings have to be taken into consideration when DAPP is concurrently given with other drugs that are substrates for P-gp since drug-drug interactions harbour a safety issue and alter bioavailability profiles.

NSAS does not have any P-gp altering properties and therefore might not affect drug-drug interactions. We conclude from this study that NSAS might make a safer drug candidate compared to DAPP for lowering LDL-cholesterol.

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.

7-Dehydrocholesterol metabolites produced by sterol 27-hydroxylase (CYP27A1) modulate liver X receptor activity

7-Dehydrocholesterol (7-DHC) is a common precursor of vitamin D3 and cholesterol. Although various oxysterols, oxygenated cholesterol derivatives, have been implicated in cellular signaling pathways, 7-DHC metabolism and potential functions of its metabolites remain poorly understood. We examined 7-DHC metabolism by various P450 enzymes and detected three metabolites produced by sterol 27-hydroxylase (CYP27A1) using high-performance liquid chromatography. Two were further identified as 25-hydroxy-7-DHC and 26/27-hydroxy-7-DHC. These 7-DHC metabolites were detected in serum of a patient with Smith-Lemli-Opitz syndrome. Luciferase reporter assays showed that 25-hydroxy-7-DHC activates liver X receptor (LXR) α, LXRβ and vitamin D receptor and that 26/27-hydroxy-7-DHC induces activation of LXRα and LXRβ, although the activities of both compounds on LXRs were weak. In a mammalian two-hybrid assay, 25-hydroxy-7-DHC and 26/27-hydroxy-7-DHC induced interaction between LXRα and a coactivator fragment less efficiently than a natural LXR agonist, 22(R)-hydroxycholesterol. These 7-DHC metabolites did not oppose agonist-induced LXR activation and interacted directly to LXRα in a manner distinct from a potent agonist. These findings indicate that the 7-DHC metabolites are partial LXR activators. Interestingly, 25-hydroxy-7-DHC and 26/27-hydroxy-7-DHC suppressed mRNA expression of sterol regulatory element-binding protein 1c, an LXR target gene, in HepG2 cells and HaCaT cells, while they weakly increased mRNA levels of ATP-binding cassette transporter A1, another LXR target, in HaCaT cells. Thus, 7-DHC is catabolized by CYP27A1 to metabolites that act as selective LXR modulators.