Vitamin D receptor activation down-regulates the small heterodimer partner and increases CYP7A1 to lower cholesterol

2', 3', 5'-tri-O-acetyl-N6-(3-hydroxyphenyl) adenosine alleviates diet-induced hyperlipidemia by modulating intestinal gene expression profiles and metabolic pathway

There is a growing body of evidence suggesting that the composition of intestinal flora plays a significant role in regulating lipid metabolism. 2', 3', 5'-tri-O-acetyl-N6-(3-hydroxyphenyl) adenosine (IMMH007) is a new candidate compound for regulating blood cholesterol and other lipids. In this study, we conducted metagenomic and metabolomic analyses on samples from high-fat diet-fed (HFD) hamsters treated with IMMH007. Our findings revealed that IMM-H007 reversed the imbalance of gut microbiota caused by a high-fat diet. Additionally, it activated adiponectin receptor and pantothenate and CoA biosynthesis pathway-related genes, which are known to regulate lipid and glucose metabolism. Furthermore, IMM-H007 promotes cholesterol metabolism by reducing the abundance of genes and species associated with 7α-dehydroxylation and bile salt hydrolase (BSH). Metabolomics and pharmacological studies have shown that IMM-H007 effectively improved glucose and lipid metabolism disorders caused by HFD, reduced the aggregation of secondary bile acids (SBAs), significantly increased the content of hyodeoxycholic acid (HDCA), and also activated the expression of VDR in the small intestine. As a result, there was a reduction in the leakage of diamine oxidase (DAO) into the bloodstream in hamsters, accompanied by an upregulation of ZO-1 expression in the small intestine. The results suggested that IMM-H007 regulated glucose and lipid metabolism, promoted cholesterol metabolism through activating the expression of VDR, inhibiting inflammatory and improving the permeability of the intestinal barrier. Thus, our study provides new understanding of how IMM-H007 interacts with intestinal function, microbiota, and relevant targets, shedding light on its mechanism of action.

Role of the microbiota-gut-heart axis between bile acids and cardiovascular disease

Bile acid (BA) receptors (e.g., farnesoid X-activated receptor, muscarinic receptor) are expressed in cardiomyocytes, endothelial cells, and vascular smooth muscle cells, indicating the relevance of BAs to cardiovascular disease (CVD). Hydrophobic BAs are cardiotoxic, while hydrophilic BAs are cardioprotective. For example, fetal cardiac insufficiency in maternal intrahepatic cholestasis during pregnancy, and the degree of fetal cardiac abnormality, is closely related to the level of hydrophobic BAs in maternal blood and infant blood. However, ursodeoxycholic acid (the most hydrophilic BA) can reverse/prevent these detrimental effects of increased levels of hydrophobic BAs on the heart. The gut microbiota (GM) and GM metabolites (especially secondary BAs) have crucial roles in hypertension, atherosclerosis, unstable angina, and heart failure. Herein, we describe the relationship between CVD and the GM at the BA level. We combine the concept of the "microbiota-gut-heart axis" (MGHA) and postulate the role and mechanism of BAs in CVD development. In addition, the strategies for treating CVD with BAs under the MGHA are proposed.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Aging and brain free cholesterol concentration on amyloid-β peptide accumulation in guinea pigs

Alzheimer's disease is a complex multifactorial neurodegenerative disorder wherein age is a major risk factor. The appropriateness of the Hartley guinea pig (GP), which displays high sequence homologies of its amyloid-β (Aβ40 and Aβ42) peptides, Mdr1 and APP (amyloid precursor protein) and similarity in lipid handling to humans, was appraised among 9-40 weeks old guinea pigs. Protein expression levels of P-gp (Abcb1) and Cyp46a1 (24(S)-hydroxylase) for Aβ40, and Aβ42 efflux and cholesterol metabolism, respectively, were decreased with age, whereas those for Lrp1 (low-density lipoprotein receptor related protein 1), Rage (receptor for advanced glycation endproducts) for Aβ efflux and influx, respectively, and Abca1 (the ATP binding cassette subfamily A member 1) for cholesterol efflux, were unchanged among the ages examined. There was a strong, negative correlation of the brain Aβ peptide concentrations and Abca1 protein expression levels with free cholesterol. The correlation of Aβ peptide concentrations with Cyp46a1 was, however, not significant, and concentrations of the 24(S)-hydroxycholesterol metabolite revealed a decreasing trend from 20 weeks old toward 40 weeks old guinea pigs. The composite data suggest a role for free cholesterol on brain Aβ accumulation. The decreases in P-gp and Lrp1 protein levels should further exacerbate the accumulation of Aβ peptides in guinea pig brain.

Vitamin D Receptor Activation Reduces Hepatic Inflammation via Enhancing Macrophage Autophagy in Cholestatic Mice

Macrophage autophagy dysfunction aggravates liver injury by activating inflammasomes, which can cleave pro-IL-1β to its active, secreted form. We investigated whether the vitamin D/vitamin D receptor (VDR) axis could up-regulate macrophage autophagy function to inhibit the activation of inflammasome-dependent IL-1β during cholestasis. Paricalcitol (PAL; VDR agonist) was intraperitoneally injected into bile duct-ligated mice for 5 days. Up-regulation of VDR expression by PAL reduced liver injury by reducing the oxidative stress-induced inflammatory reaction in macrophages. Moreover, PAL inhibited inflammasome-dependent IL-1β generation. Mechanistically, the knockdown of VDR increased IL-1β generation, whereas VDR overexpression exerted the opposite effect following tert-butyl hydroperoxide treatment. The inflammasome antagonist glyburide, the caspase-1-specific inhibitor YVAD, and the reactive oxygen species (ROS) scavenger N-acetyl-l-cysteine (NAC) blocked the increase in Vdr shRNA-induced IL-1β production. Interestingly, up-regulation of VDR also enhanced macrophage autophagy. Autophagy reduction impaired the up-regulation of VDR-inhibited macrophage inflammasome-generated IL-1β, whereas autophagy induction showed a synergistic effect with VDR overexpression through ROS-p38 mitogen-activated protein kinase (MAPK) pathway. This result was confirmed by p38 MAPK inhibitor, MAPK activator, and ROS inhibitor NAC. Collectively, PAL triggered macrophage autophagy by suppressing activation of the ROS-p38 MAPK pathway, which, in turn, suppressed inflammasome-generated cleaved, active forms of IL-1β, eventually leading to reduced inflammation. Thus, triggering the VDR may be a potential target for the anti-inflammatory treatment of cholestatic liver disease.

The unique association between serum 25-hydroxyvitamin D concentrations and blood lipid profiles in agriculture, forestry, and fishing occupations: Insights from NHANES 2001-2014

BACKGROUND

The relationship of serum 25(OH)D levels and hyperlipidemia has not been explored in the Agriculture, Forestry, and Fishing (AFF) occupation. We aimed to explore the impact of serum 25(OH)D levels on lipid profiles in AFF workers, traffic drivers, and miners.

METHODS

Data from 3937 adults aged 18-65 years old with completed information were obtained from the National Health and Examination Survey from 2001 to 2014. Multivariate linear regression models were used to examine the associations between serum 25(OH)D concentrations and triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and HDL-C/LDL-C ratio. Subgroup analyses for AFF workers considered age, sex, BMI, work activity, months worked, and alcohol consumption. Non-linear relationships were explored using curve fitting.

RESULTS

Serum 25(OH)D levels differed between groups (AFF: 60.0 ± 21.3 nmol/L, drivers: 56.6 ± 22.2 nmol/L, miners: 62.8 ± 22.3 nmol/L). Subgroup analysis of the AFF group showed that participants with serum 25(OH)D ≥50 nmol/L, females, and BMI <30 kg/m2 demonstrated improved HDL-C levels correlating with higher serum 25(OH)D. Serum 25(OH)D in AFF workers had a reversed U-shaped relationship with TG and TC, and a U-shaped relationship with HDL-C, with HDL-C, with inflection points at 49.5 nmol/L for TG and TC, and 32.6 nmol/L for HDL-C.

CONCLUSIONS

Serum 25(OH)D levels are associated with lipid profiles, and the relationship varies among occupational groups. AFF workers, facing unique occupational challenges, may benefit from maintaining adequate serum 25(OH)D levels to mitigate adverse lipid profiles and reduce cardiovascular risk.

Effect of Nutrition Education on Health Science University Students to Improve Cardiometabolic Profile and Inflammatory Status

The inadequate lifestyle associated with university life may have a negative impact on various cardiometabolic factors. The aim of this study was to evaluate the effect of a one-year nutrition education course on cardiometabolic parameters in undergraduate health science students. During the 2021-22 academic year, 1.30 h nutrition sessions were conducted twice a week. Capillary blood samples were collected and centrifuged to measure cardiometabolic and inflammatory biomarkers in serum. The sample studied consisted of 49 students: 20.4% male and 79.6% female. The nutritional intervention resulted in changes in dietary patterns, with increased consumption of vegetables, nuts and legumes. After the course, females showed an increase in HDL-cholesterol levels (p = 0.007) and no change in LDL-cholesterol levels (p = 0.189). On the other hand, males showed significant changes in HDL-cholesterol (p = 0.001) and LDL-cholesterol (p = 0.043) levels. The atherogenic index was also significantly reduced (p < 0.001) in both males (p = 0.009) and females (p = 0.002). Differences were also observed in the increase in vitamin D levels in both males and females, although the magnitude of the increase was greater in the men (Δ = 7.94, p = 0.016 in men vs. Δ = 4.96, p = 0.001 in women). The monocyte-to-HDL ratio (MHR) showed a significant reduction, although these differences were only significant in males. Students with low vitamin D levels had higher LDL-cholesterol values (p = 0.01) and atherogenic index (p = 0.029). Adjusted linear regression analysis showed a significant association between post-course vitamin D MHR (β = -0.42, IC: -0.29, -0.06, p < 0.01). These findings suggest the importance of including nutrition education programs during the university stage for the prevention of long-term health problems.

Vitamin D/vitamin D receptor pathway in non-alcoholic fatty liver disease

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, but underlying mechanisms are not fully understood. In recent years, a growing body of evidence has emphasized the therapeutic role of vitamin D in NAFLD, but the specific mechanism remains to be investigated.

AREAS COVERED

This review summarized the roles of vitamin D/VDR (vitamin D receptor) pathway in different types of liver cells (such as hepatocytes, hepatic stellate cells, liver macrophages, T lymphocytes, and other hepatic immune cells) in case of NAFLD. Meanwhile, the effects of pathways in the gut-liver axis, adipose tissue-liver axis, and skeletal muscle-liver axis on the development of NAFLD were further reviewed. Relevant literature was searched on PubMed for the writing of this review.

EXPERT OPINION

The precise regulation of regional vitamin D/VDR signaling pathway based on cell-specific or tissue-specific function will help clarify the potential mechanism of vitamin D in NAFLD, which may provide new therapeutic targets to improve the safety and efficacy of vitamin D based drugs.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D₃ or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for β-amyloid peptide efflux and influx, the sodium phosphate transporters (NaP_i), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTβ) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aβ) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Biomarkers of vitamin D status in healthy adults: Associations with serum lipid parameters: A pilot study

Vitamin D deficiency is among important healthcare challenges today. Traditionally, vitamin D status is assessed through determination of 25-hydroxy metabolite (25(OH)D), but novel data point to 24,25(OH)2D and 25(OH)D/24,25(OH)2D ratio (VDMR) as promising biomarkers. It is widely accepted that the biological role of vitamin D exceeds its well-known contribution to bone turnover. However, its effects on overall energy metabolism and lipid status alterations are not completely understood. In this study, we analyzed the relationship of vitamin D status assessed as concentrations of 25(OH)D3 and 24,25(OH)2D3 determined by liquid chromatography-tandem mass spectrometry, as well as VDMR with advanced lipid status parameters. Vitamin D status biomarkers, routine parameters of lipid status and size and distribution of lipoprotein subclasses were determined in 89 healthy adults (35 with adequate vitamin D status and 54 with vitamin D deficiency). Our results indicated a preponderance of proatherogenic small, dense LDL particles (sdLDL) in vitamin D deficient subjects. Both 25(OH)D and 24,25(OH)2D were associated with a relative proportion of sdLDL (B: -0.410; SE: 0.154; P=0.010; and B: -2.041; SE: 0.969; P=0.039, respectively). Positive correlation was found for VDMR and relative proportion of HDL 3a particles (r=0.251; P=0.024). VDMR value was decreased in subjects with vitamin D deficiency (P=0.001), thus implying its usefulness as a biomarker. A thorough investigation of novel vitamin D biomarkers and advanced lipid status parameters can be useful in the estimation of individual risk for the development of cardiometabolic alterations.

Association of changes in lipid levels with changes in vitamin D levels in a real-world setting

In clinical trials, vitamin D supplementation has been reported to reduce serum levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG) but not high-density lipoprotein cholesterol (HDL-C). In this cohort study we evaluated the association between changes in vitamin D (25-hydroxyvitamin D) and changes in lipid levels in a real-world setting. Changes in lipid levels over a 1-year period were evaluated among individuals whose vitamin D levels increased (group 1) or decreased (group 2) by ≥ 10 ng/mL in year 2018 versus 2017 (cohort 1; n = 5580), in 2019 versus 2018 (cohort 2, n = 6057), or in 2020 versus 2019 (cohort 3, n = 7249). In each cohort, levels of TC, LDL-C, and TG decreased in group 1 and increased in group 2. Between-group differences in average changes in the 3 cohorts ranged from 10.71 to 12.02 mg/dL for TC, from 7.42 to 8.95 mg/dL for LDL-C, and from 21.59 to 28.09 mg/dL for TG. These differences were significant after adjusting for age, sex, race, education, body mass index, blood pressure, smoking status, geographical location, and baseline levels of vitamin D and lipids (P < 0.001). Changes in vitamin D levels were not significantly associated with changes in HDL-C levels.

Measuring Amyloid-β Peptide Concentrations in Murine Brain with Improved ELISA Assay

The amyloid-β (Aβ) peptides of 40 and 42 amino acids that are implicated in Alzheimer's disease may potentially aggregate into toxic oligomers and form neuritic plaques. The enzyme-linked immunosorbent assay (ELISA) is a facile method used for the determination of Aβ concentrations in biological matrices, namely plasma, cerebrospinal fluid, and brain. The method is mostly used for the measurement of Aβ concentrations in transgenic mice, but it is unknown whether the ELISA method is suitable for measuring low, endogenous levels of Aβ in the brains of wild-type mice. The Aβ ELISA kit manufacturer recommends use of 5 M guanidine hydrochloride (GuHCl), a protein-denaturing agent, for homogenization of the brain tissue, followed by dilution back down to 0.1 M to avoid quenching by GuHCl. Components of brain matrices and GuHCl that could interfere with the quantitation have not been investigated. In this article, we describe an improved method involving homogenization of mouse brain with 1 M instead of 5 M GuHCl, reducing the dilution factor by 5× to provide a higher sensitivity. The modified ELISA assay is improved for the quantitation of brain Aβ peptides in wild-type mice, where Aβ peptide levels are much lower than those in transgenic mouse models. © 2021 Wiley Periodicals LLC.

Impact of age, hypercholesterolemia, and the vitamin D receptor on brain endogenous β-amyloid peptide accumulation in mice

Age, hypercholesterolemia, and vitamin D deficiency are risk factors that increase the brain accumulation of pathogenic β-amyloid peptides (40 and 42), precursors leading to Alzheimer's disease (AD) in humans. The relative changes accompanying aging, high cholesterol, and/or treatment of calcitriol, active vitamin D receptor (VDR) ligand, under normal physiology are unknown. We examined these relative changes in C57BL/6 mice of ages 2, 4-8, and more than 10 months old, which were fed a normal or high fat / high cholesterol diet and treated with calcitriol, active ligand of the vitamin D receptor (0 or 2.5 μg/kg ×4, intraperitoneally, every other day to elicit cholesterol lowering in liver). Aβ₄₀ but not Aβ₄₂ accumulation in brain and lower P-glycoprotein (P-gp) and neprilysin protein expressions for Aβ efflux and degradation, respectively, were found to be associated with aging. But there was no trend for BACE1 (β-secretase 1, a cholesterol-sensitive enzyme) toward Aβ synthesis with age. In response to calcitriol treatment, P-gp was elevated, mitigating partially the age-related changes. Although age-dependent decreasing trends in mRNA expression levels existed for Cyp46a1, the brain cholesterol processing enzyme, whose inhibition increases BACE1 and ApoE to facilitate microglia Aβ degradation, mRNA changes for other cholesterol transporters: Acat1 and Abca1, and brain cholesterol levels remained unchanged. There was no observable change in the mRNA expression of amyloid precursor protein (APP) and the influx (RAGE) and efflux (LRP1) transporters with respect to age, diet, or calcitriol treatment. Overall, aging poses as a risk factor contributing to Aβ accumulation in brain, and VDR-mediated P-gp activation partially alleviates the outcome.

The Interdependency and Co-Regulation of the Vitamin D and Cholesterol Metabolism

Vitamin D and cholesterol metabolism overlap significantly in the pathways that contribute to their biosynthesis. However, our understanding of their independent and co-regulation is limited. Cardiovascular disease is the leading cause of death globally and atherosclerosis, the pathology associated with elevated cholesterol, is the leading cause of cardiovascular disease. It is therefore important to understand vitamin D metabolism as a contributory factor. From the literature, we compile evidence of how these systems interact, relating the understanding of the molecular mechanisms involved to the results from observational studies. We also present the first systems biology pathway map of the joint cholesterol and vitamin D metabolisms made available using the Systems Biology Graphical Notation (SBGN) Markup Language (SBGNML). It is shown that the relationship between vitamin D supplementation, total cholesterol, and LDL-C status, and between latitude, vitamin D, and cholesterol status are consistent with our knowledge of molecular mechanisms. We also highlight the results that cannot be explained with our current knowledge of molecular mechanisms: (i) vitamin D supplementation mitigates the side-effects of statin therapy; (ii) statin therapy does not impact upon vitamin D status; and critically (iii) vitamin D supplementation does not improve cardiovascular outcomes, despite improving cardiovascular risk factors. For (iii), we present a hypothesis, based on observations in the literature, that describes how vitamin D regulates the balance between cellular and plasma cholesterol. Answering these questions will create significant opportunities for advancement in our understanding of cardiovascular health.

Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.

Differential Effects of 1α,25-Dihydroxyvitamin D3 on the Expressions and Functions of Hepatic CYP and UGT Enzymes and Its Pharmacokinetic Consequences In Vivo

The compound 1α,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) is the active form of vitamin D₃ and a representative ligand of the vitamin D receptor (VDR). Previous studies have described the impacts of 1,25(OH)₂D₃ on a small number of cytochrome P450 (CYP) and uridine diphosphate-glucuronyltransferase (UGT) enzymes, but comparatively little is known about interactions between several important CYP and UGT isoforms and 1,25(OH)₂D₃ in vitro and/or in vivo. Thus, we investigated the effects of 1,25(OH)₂D₃ on the gene and protein expressions and functional activities of selected CYPs and UGTs and their impacts on drug pharmacokinetics in rats. The mRNA/protein expressions of Cyp2b1 and Cyp2c11 were downregulated in rat liver by 1,25(OH)₂D₃. Consistently, the in vitro metabolic kinetics (V_max and CL_int) of BUP (bupropion; a Cyp2b1 substrate) and TOL (tolbutamide; a Cyp2c11 substrate) were significantly changed by 1,25(OH)₂D₃ treatment in liver microsomes, but the kinetics of acetaminophen (an Ugt1a6/1a7/1a8 substrate) remained unaffected, consistent with Western blotting data for Ugt1a6. In rat pharmacokinetic studies, the total body clearance (CL) and nonrenal clearance (CL_NR) of BUP were significantly reduced by 1,25(OH)₂D₃, but unexpectedly, the total area under the plasma concentration versus time curve from time zero to infinity (AUC) of hydroxybupropion (HBUP) was increased probably due to a marked reduction in the renal clearance (CL_R) of HBUP. Additionally, the AUC, CL, and CL_NR for TOL and the AUC for 4-hydroxytolbutamide (HTOL) were unaffected by 1,25(OH)₂D₃ in vivo. Discrepancies between observed in vitro metabolic activity and in vivo pharmacokinetics of TOL were possibly due to a greater apparent distribution volume at the steady-state (V_ss) and lower plasma protein binding in 1,25(OH)₂D₃-treated rats. Our results suggest possible drug-drug and drug-nutrient interactions and provide additional information concerning safe drug combinations and dosing regimens for patients taking VDR ligand drugs including 1,25(OH)₂D₃.

A Villin-Driven Fxr Transgene Modulates Enterohepatic Bile Acid Homeostasis and Response to an n-6-Enriched High-Fat Diet

A diet high in n-6 polyunsaturated fatty acids (PUFAs) may contribute to inflammation and tissue damage associated with obesity and pathologies of the colon and liver. One contributing factor may be dysregulation by n-6 fatty acids of enterohepatic bile acid (BA) metabolism. The farnesoid X receptor (FXR) is a nuclear receptor that regulates BA homeostasis in the liver and intestine. This study aims to compare the effects on FXR regulation and BA metabolism of a palm oil-based diet providing 28% energy (28%E) from fat and low n-6 linoleic acid (LA, 2.5%E) (CNTL) with those of a soybean oil-based diet providing 50%E from fat and high (28%E) in LA (n-6HFD). Wild-type (WT) littermates and a transgenic mouse line overexpressing the Fxrα1 isoform under the control of the intestine-specific Villin promoter (Fxrα1^TG) were fed the CNTL or n-6HFD starting at weaning through 16 weeks of age. Compared to the CNTL diet, the n-6HFD supports higher weight gain in both WT and Fxrα^TG littermates; increases the expression of Fxrα1/2, and peroxisome proliferator-activated receptor-γ1 (Pparγ1) in the small intestine, Fxrα1/2 in the colon, and cytochrome P4507A1 (Cyp7a1) and small heterodimer protein (Shp) in the liver; and augments the levels of total BA in the liver, and primary chenodeoxycholic (CDCA), cholic (CA), and β-muricholic (βMCA) acid in the cecum. Intestinal overexpression of the Fxra1^TG augments expression of Shp and ileal bile acid-binding protein (Ibabp) in the small intestine and Ibabp in the proximal colon. Conversely, it antagonizes n-6HFD-dependent accumulation of intestinal and hepatic CDCA and CA; hepatic levels of Cyp7a1; and expression of Pparγ in the small intestine. We conclude that intestinal Fxrα1 overexpression represses hepatic de novo BA synthesis and protects against n-6HFD-induced accumulation of human-specific primary bile acids in the cecum.

Noteworthy idiosyncrasies of 1α,25-dihydroxyvitamin D3 kinetics for extrapolation from mouse to man: Commentary

Calcitriol or 1,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ] is the active ligand of the vitamin D receptor (VDR) that plays a vital role in health and disease. Vitamin D is converted to the relatively inactive metabolite, 25-hydroxyvitamin D₃ [25(OH)D₃ ], by CYP27A1 and CYP2R1 in the liver, then to 1,25(OH)₂ D₃ by a specific, mitochondrial enzyme, CYP27B1 (1α-hydroxylase) that is present primarily in the kidney. The degradation of both metabolites is mostly carried out by the more ubiquitous mitochondrial enzyme, CYP24A1. Despite the fact that calcitriol inhibits its formation and degradation, allometric scaling revealed strong interspecies correlation of the net calcitriol clearance (CL estimated from dose/AUC_∞ ), production rate (PR), and basal, plasma calcitriol concentration with body weight (BW). PBPK-PD (physiologically based pharmacokinetic-pharmacodynamic) modeling confirmed the dynamic interactions between calcitriol and Cyp27b1/Cyp24a1 on the decrease in the PR and increase in CL in mice. Close scrutiny of the literature revealed that basal levels of calcitriol had not been taken into consideration for estimating the correct AUC_∞ and CL after exogenous calcitriol dosing in both animals and humans, leading to an overestimation of AUC_∞ and underestimation of the plasma CL. In humans, CL was decreased in chronic kidney disease but increased in cancer. Collectively, careful pharmacokinetic data analysis and improved definition are achieved with PBPK-PD modeling, which embellishes the complexity of dose, enzyme regulation, and disease conditions. Allometric scaling and PBPK-PD modeling were applied successfully to extend the PBPK model to predict calcitriol kinetics in cancer patients.

Small Heterodimer Partner Regulates Dichotomous T Cell Expansion by Macrophages

The involvement of small heterodimer partner (SHP) in the inhibition of hepatic bile acid synthesis from cholesterol has been established. However, extrahepatic expression of SHP implies that SHP may have regulatory functions other than those in the liver. Here, we find that SHP mRNA expression is high in murine bone marrow cells, suggesting a physiological role within macrophages. Indeed, expression of SHP in macrophages decreases the transcriptional activity and nuclear localization of nuclear factor κB, whereas downregulation of SHP has the opposite effects. Expression of genes associated with macrophage-T cell crosstalk were altered by overexpression or downregulation of SHP. Intriguingly, increasing SHP expression in macrophages resulted in decreased T cell expansion, a hallmark of T cell activation, whereas knockdown of SHP resulted in increased expansion. Analyses of the expanded T cells revealed a dichotomous skewing between effector T cells and regulatory T cells (Tregs), with SHP overexpression reducing Tregs and downregulation of SHP increasing their expansion. The expanded Tregs were confirmed to be suppressive via adoptive transfers. IL-2 and TGF-β, known inducers of Treg differentiation, were found to be regulated by SHP. Furthermore, SHP occupancy at the promoter region of IL-2 was increased after macrophages were challenged with lipopolysaccharide. Neutralizing antibodies to IL-2 and TGF-β inhibited the expansion of Tregs mediated by downregulation of SHP. This study demonstrates that expression and activity of SHP within macrophages can alter T cell fate and identifies SHP as a potential therapeutic target for autoimmune diseases or solid cancers.

Obesity and dyslipidemia

Obesity, a pandemic of the modern world, is intimately associated with dyslipidemia, which is mainly driven by the effects of insulin resistance and pro-inflammatory adipokines. However, recent evidence suggests that obesity-induced dyslipidemia is not a unique pathophysiological entity, but rather has distinct characteristics depending on many individual factors. In line with that, in a subgroup of metabolically healthy obese (MHO) individuals, dyslipidemia is less prominent or even absent. In this review, we will address the main characteristics of dyslipidemia and mechanisms that induce its development in obesity. The fields, which should be further investigated to expand our knowledge on obesity-related dyslipidemia and potentially yield new strategies for prevention and management of cardiometabolic risk, will be highlighted. Also, we will discuss recent findings on novel lipid biomarkers in obesity, in particular proprotein convertase subtilisin/kexin type 9 (PCSK9), as the key molecule that regulates metabolism of low-density lipoproteins (LDL), and sphingosine-1-phosphate (S1P), as one of the most important mediators of high-density lipoprotein (HDL) particles function. Special attention will be given to microRNAs and their potential use as biomarkers of obesity-associated dyslipidemia.

Tetrahydropalmatine Prevents High-Fat Diet-Induced Hyperlipidemia in Golden Hamsters (Mesocricetus Auratus)

Background

Hyperlipidemia is a major cause of atherosclerotic cardiovascular disease. Tetrahydropalmatine (THP) can exhibit hepatoprotective, anti-arrhythmic, and anti-inflammatory activities. The mechanism of THP on the hyperlipidemia remains unknown; therefore, the present study explored the role of THP in hyperlipidemia.

Material/Methods

We established an animal model of hyperlipidemia by high-fat diet (HFD) feeding. Blood samples were obtained for determination of serum cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c), pro-inflammatory cytokines, and CYP7A1 expression. Histology was performed and inflammation was detected in the liver using hematoxylin-eosin (HE) staining and enzyme-linked immunosorbent assay (ELISA), respectively. The mRNA and protein levels of TLR4 and TRAF-6 were determined by quantitative real-time PCR (qPCR) and Western blot, respectively.

Results

THP suppressed hepatic lipid accumulation and reduced serum levels of TC, TG, LDL-c, and HDL-c in HFD-fed golden hamsters. THP increased cholesterol 7 α-hydroxylase (CYP7A1) expression and prevented inflammation by the limited reduction in interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expressions in serum and liver. THP slightly increased the ratio of the body/liver weight. THP inhibited the mRNA and protein levels of Toll-like receptor 4 (TLR4) and TNF-receptor associated factor-6 (TRAF-6).

Conclusions

These results suggest that THP attenuates hyperlipidemia by multiple effects, including hepatoprotective and anti-inflammatory effects. Moreover, THP also suppressed the expressions of TLR4 and TRAF-6 in golden hamsters.

Protective Effects of Yinchenhao Decoction on Cholesterol Gallstone in Mice Fed a Lithogenic Diet by Regulating LXR, CYP7A1, CYP7B1, and HMGCR Pathways

The study attempted to elucidate whether lipid genes are closely associated with lipid metabolic abnormalities during the lithogenic time and how Yinchenhao Decoction (YCHD) works on the transcriptions of lipid genes against cholesterol gallstone model. C57BL/6J mice fed on lithogenic diet (LD) were used for model establishment and randomized into 5 groups. All groups received LD for different weeks with isometrically intragastric administration of YCHD or NS. Biochemical tests were measured and liver tissues were harvested for histological and genetic detection. It was found that all groups with increasing LD showed a following tendency of gallstone incidence, bile cholesterol, phospholipids, total bile acid, and cholesterol saturation index (CSI). Conversely, YCHD could significantly normalize the levels of gallstone incidence, bile lipids, and CSI (CSI<1). As lithogenic time progressed, ABCG5, ABCG8, PPAR-α, and ABCB4 were upregulated, and SREBP2, CYP7A1, and CYP7B1 were downregulated, while CYP7A1, CYP7B1, LXR, and HMGCR mRNA were increased 3-fold under the administration of YCHD. It was concluded that abnormal expressions of the mentioned genes may eventually progress to cholesterol gallstone. CYP7A1, CYP7B1, LXR, and HMGCR mRNA may be efficient targets of YCHD, which may be a preventive drug to reverse liver injury, normalize bile lipids, facilitate gallstone dissolution, and attenuate gallstone formation.

Vitamin D receptor polymorphism rs2228570 is significantly associated with risk of dyslipidemia and serum LDL levels in Chinese Han population

Background

The goal of this study was to determine if vitamin D receptor (VDR) gene polymorphisms underlie susceptibility to dyslipidemia in a Chinese Han population.

Methods

Three tag single nucleotide polymorphisms (SNPs) (rs11574129, rs2228570, and rs739837) were genotyped using TaqMan assays to determine VDR SNP associations with dyslipidemia. We genotyped 877 cases of dyslipidemia from a normotensive, non-diabetes mellitus population and 1822 non-dyslipidemia subjects in a stage I study. In a follow-up stage II study, we included a larger sample of 3124 controls and 1679 cases with dyslipidemia. Finally, we explored the potential molecular mechanism for the SNP associations using molecular modeling analysis.

Results

We found a significant association between SNP rs2228570 and dyslipidemia in the additive (adjusted odds ratio (OR) = 1.255, 95% Confidence Interval (CI) = (1.118–1.409), P < 0.001), dominant (OR = 1.384, 95% CI = 1.384 (1.136–1.6), P = 0.001) and recessive models (OR = 1.356, 95%CI = 1.1–1.671, P = 0.004) in stage I. We further established that the rs2228570 variant was significantly associated with dyslipidemia in the additive (adjusted OR = 1.146, 95% CI = 1.053–1247, P = 0.002), dominant (OR = 1.184, 95%CI =1.018–1.376, P = 0.028) and recessive models (OR = 1.209, 95%CI = 1.064–1.374, P = 0.004) in stage II. The TT genotype was significantly higher (4.93 ± 0.75 mmol/L) compared to the TC (4.67 ± 0.47 mmol/L) or CC (4.66 ± 0.44 mmol/L) genotype (P = 0.01) in cases with elevated low-density lipoprotein cholesterol (LDL-C) levels. In contrast, the cases with the TT genotype had significantly lower serum 25(OH)D levels (18.43 ± 5.04 ng/ mL) compared to the TC (26.24 ± 4.16 ng/mL) and CC (36.76 ± 8.10 ng/ mL) genotypes (P < 0.001). Multivariable linear regression analysis indicated that the rs2228750 genotype significantly correlated with serum low-density lipoprotein-C (LDL-C) levels in cases with dyslipidemia. Using molecular modeling analysis, we further found that the rs2228570 variant changed the structure and the stability of VDR and altered the binding energy of its ligand.

Conclusions

The VDR rs2228570 variant may increase susceptibility to dyslipidemia in the Chinese Han population.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0819-0) contains supplementary material, which is available to authorized users.

Strategies and limitations associated with in vitro characterization of vitamin D receptor activators

In vitro cell-based assays are common screening tools used for the identification of new VDR ligands. For 25-hydroxyvitamin D₃ [25(OH)D₃] and 1α-hydroxyvitamin D₃ [1α(OH)D₃], protein expressions of CYP2R1 and CYP27B1, respectively, that form the active 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] ligand were detected in human embryonic kidney (HEK293) cells expressing the GAL4-hVDR, the human brain microvessel endothelial (hCMEC/D3) and adenocarcinoma colonic (Caco-2) cells. The impact of bioactivation enzymes was shown upon the addition of ketoconazole (10 μM KTZ), a pan-CYP inhibitor, which reduced the apparent potency of 25(OH)D₃ and increased the EC₅₀ from 272 to 608 nM in HEK293 cells. EIA assays verified that 1,25(OH)₂D₃ was formed and contributed to VDR activity independently of its precursors. In hCMEC/D3 cells where enzyme protein levels were lowest, changes in MDR1/P-gp expression with KTZ were minimal. In Caco-2 cells, the induction of TRPV6 (calcium channel), CYP24A1, CYP3A4, OATP1A2 and MDR1 mRNA expression was 1,25(OH)₂D₃ > 1α(OH)D₃ > 25(OH)D₃, with the magnitude of change being blunted by KTZ. Upon inclusion of KTZ in the cell-based assays, high transcriptional activities were observed for synthetic VDR activators from Teijin Pharma. Cyclopentanone derivatives: TPD-003, TPD-005, TPD-006, TPD-008 and TPD-009 (EC₅₀s 0.06 to 67 nM, unchanged with KTZ) were found more potent over straight chain and lactone derivatives (antagonists). Most TPD compounds activated OATP1A2, CYP24A1, CYP3A4, and MDR1 (28-67%) and TRPV6 transcriptionally in Caco-2 cells. The results identified that cell-based assays with added KTZ could accurately identify new VDR activators, although these may be hypercalcemic with strong TRPV6 inducing properties.

Functional assessment of genetic variants located in the promoter of SHP1 (NR0B2)

Small heterodimer partner 1 (SHP1, NR0B2) is a member of the superfamily of nuclear receptors (NRs). Even if this orphan receptor, unlike other NRs, lacks the DNA-binding domain, it is capable of regulating transcription by repressing the activity of other NRs by direct protein-protein interaction. Accordingly, SHP1 is part of negative feedback loops of the transcriptional regulation of genes involved in drug metabolism and various metabolic pathways including bile acid and glucose homeostasis. Although it is known that several interacting partners of SHP1 also modulate its expression, there is little information about genetic variability of this regulatory mechanism. Our study aimed to identify genetic variants in the NR0B2 promoter region and to determine their impact on NR0B2 transcription. For this, DNA samples originating from 119 participants of the population-based cohort Study of Health in Pomerania were analyzed by Sanger sequencing revealing four genetic variants: NR0B2:c.-594T>C (rs71636795), NR0B2:c.-414G>C (newly identified), NR0B2:c.-423C>T (rs78182695), and NR0B2:c.-224delCTGA (rs145613139) localized in the 5' untranslated region of NR0B2. The impact of these variants on transactivation of the NR0B2 promoter by NRs known to be regulators of SHP1 expression (hepatocyte nuclear factor 4α, liver receptor homolog-1, and farnesoid X receptor) was assessed in a cell-based reporter gene assay, showing that transactivation by hepatocyte nuclear factor 4α and liver receptor homolog-1 was significantly decreased in the presence of the genetic variant NR0B2:c.-594T>C, even though this effect was cell specific. However, SHP1 mRNA expression in a small collection of human kidney samples was not affected by these genetic variants.

Serum 25-Hydroxyvitamin D, Plasma Lipids, and Associated Gene Variants in Prepubertal Children

CONTEXT

The associations of serum 25-hydroxyvitamin D [25(OH)D] with plasma lipids remain controversial in children.

OBJECTIVE

To examine the associations and interactions of 25(OH)D and related gene variants with lipids in children.

DESIGN

Cross-sectional.

SETTING

Kuopio, Finland.

PARTICIPANTS

Population sample of 419 prepubertal white children aged 6 to 8 years.

MAIN OUTCOME MEASURES

25(OH)D, total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides.

RESULTS

Serum 25(OH)D was negatively associated with total cholesterol (β = -0.141, P = 0.004), LDL cholesterol (β = -0.112, P = 0.023), HDL cholesterol (β = -0.150, P = 0.002), and triglycerides (β = -0.104, P = 0.035) adjusted for age and sex. Associations of 25(OH)D with total cholesterol, LDL cholesterol, and HDL cholesterol remained after adjustment for adiposity, physical activity, sedentary behavior, diet, daylight time, and parental education. Children in the highest quartile of 25(OH)D had the lowest total cholesterol (P = 0.022) and LDL cholesterol (P = 0.026) adjusted for age and sex. Cytochrome P450 family 2 subfamily R member 1 (CYP2R1) rs12794714, CYP2R1 rs10741657, and vitamin D binding protein (DBP) rs2282679 were associated with 25(OH)D adjusted for age and sex. CYP2R1 rs12794714 was associated with total cholesterol and LDL cholesterol and C10orf88 rs6599638 with HDL cholesterol adjusted for age, sex, and 25(OH)D. The gene variants did not explain or modify the associations of 25(OH)D with lipids.

CONCLUSIONS

25(OH)D was independently and inversely associated with total cholesterol, LDL cholesterol, and HDL cholesterol. CYP2R1 rs12794714, CYP2R1 rs10741657, and DBP rs2282679 were associated with 25(OH)D. CYP2R1 rs12794714 was associated with total cholesterol and LDL cholesterol and chromosome 10 open reading frame 88 (C10orf88) rs6599638 with HDL cholesterol independent of 25(OH)D. None of the gene variants modified the associations of 25(OH)D with lipids. Further studies are needed to detect the mechanisms for the associations of 25(OH)D with lipids.

Vitamin D supplementation does not improve CVD risk factors in vitamin D-insufficient subjects

OBJECTIVE

Low serum 25(OH)D levels are associated with cardiovascular disease (CVD) and some of its risk factors. However, in interventional studies, the effects of vitamin D supplementation have been uncertain, possibly due to inclusion of vitamin D-sufficient subjects. Our aim was therefore to examine effects of vitamin D supplementation on CVD risk factors in vitamin D-insufficient subjects.

DESIGN

Double-blinded randomized controlled trial.

METHODS

A 4-month interventional study with high-dose vitamin D (100,000 IU loading dose, followed by 20,000 IU/week) or placebo with measurements of blood pressure, lipids (total-, LDL- and HDL-cholesterol, triglycerides, apolipoproteins A1 and B), and glucose metabolism parameters (blood glucose, HbA_1c, serum human receptors for advanced glycation end products (sRAGE), insulin, C-peptide and HOMA-IR).

RESULTS

A total of 422 subjects with mean serum 25(OH)D level 34 nmol/L were included, with 411 subjects completing the study. Serum 25(OH)D levels increased with 56 nmol/L and decreased with 4 nmol/L in the vitamin D and placebo group, respectively. We found no statistically significant differences between the two groups in any of the measured CVD risk factors, except for a minor increase in sRAGE in the vitamin D group. Stratified analyses of subjects with low baseline serum 25(OH)D levels alone, or combined with blood pressure, lipid and HOMA-IR values above the median for the cohort, did not skew the results in favour of vitamin D supplementation.

CONCLUSION

Supplementation with vitamin D in subjects with baseline vitamin D insufficiency does not improve CVD risk factor profile.

Efficacy of Vitamin D interventional strategies in saudi children and adults

Despite the amount of sunshine in Saudi Arabia, vitamin D (25(OH)D) deficiency is highly prevalent among Saudis. Several strategies are known to improve 25(OH)D status. The aim of this study was to evaluate the efficacy of different interventional strategies in improving 25(OH)D status in Saudi children and adults. This interventional study was undertaken among 593 out of 1152 Saudi subjects [530 students (aged 13-17 years) and 63 teachers (aged 26-46 years)] over a 6-month period from different secondary schools in Riyadh, Saudi Arabia. 25(OH)D status was taken at baseline and after 6 months post interventions. Subjects were divided into 3 groups and requested to implement different vitamin D correction schemes: sun-exposure, vitamin D-fortified milk consumption, and oral vitamin D supplementation (1000IU/day). Follow-up results revealed that all correction strategies used could decrease the deficiency of serum 25(OH)D with different potencies, with the highest positive percentage change observed in oral supplementation in both adults and children (11% men, 17% women, 16% boys and 8% girls). The oral vitamin D supplementation strategy also showed significant positive associations between delta (Δ) changes and HDL-cholesterol in both adults and children. In conclusion, oral vitamin D supplementation was the most effective strategy in improving vitamin D status in Saudi adults and children than sunlight exposure or consumption of vitamin D-fortified dairy products.

Alterations in gene expression in vitamin D-deficiency: Down-regulation of liver Cyp7a1 and renal Oat3 in mice

The vitamin D-deficient model, established in the C57BL/6 mouse after 8 weeks of feeding vitamin D-deficient diets in the absence or presence of added calcium, was found associated with elevated levels of plasma parathyroid hormone (PTH) and plasma and liver cholesterol, and a reduction in cholesterol 7α-hydroxylase (Cyp7a1, rate-limiting enzyme for cholesterol metabolism) and renal Oat3 mRNA/protein expression levels. However, there was no change in plasma calcium and phosphate levels. Appraisal of the liver revealed an up-regulation of mRNA expressions of the small heterodimer partner (Shp) and attenuation of Cyp7a1, which contributed to hypercholesterolemia in vitamin D-deficiency. When vitamin D-sufficient or D-deficient mice were further rendered hypercholesterolemic with 3 weeks of feeding the respective, high fat/high cholesterol (HF/HC) diets, treatment with 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ], active vitamin D receptor (VDR) ligand, or vitamin D (cholecalciferol) to HF/HC vitamin D-deficient mice lowered the cholesterol back to baseline levels. Cholecalciferol treatment partially restored renal Oat3 mRNA/protein expression back to that of vitamin D-sufficient mice. When the protein expression of protein kinase C (PKC), a known, negative regulator of Oat3, was examined in murine kidney, no difference in PKC expression was observed for any of the diets with/without 1,25(OH)₂ D₃ /cholecalciferol treatment, inferring that VDR regulation of renal Oat3 did not involve PKC in mice. As expected, plasma calcium levels were not elevated by cholecalciferol treatment of vitamin D-deficient mice, while 1,25(OH)₂ D₃ treatment led to hypercalcemia. In conclusion, vitamin D-deficiency resulted in down-regulation of liver Cyp7a1 and renal Oat3, conditions that are alleviated upon replenishment of cholecalciferol.

Calcitriol Inhibits HCV Infection via Blockade of Activation of PPAR and Interference with Endoplasmic Reticulum-Associated Degradation

Vitamin D has been identified as an innate anti-hepatitis C virus (HCV) agent but the possible mechanisms for this issue remain unclear. Here, we clarified the mechanisms of calcitriol-mediated inhibition of HCV infection. Calcitriol partially inhibited HCV infection, nitric oxide (NO) release and lipid accumulation in Huh7.5 human hepatoma cells via the activation of vitamin D receptor (VDR). When cells were pretreated with the activators of peroxisome proliferator-activated receptor (PPAR)-α (Wy14643) and -γ (Ly171883), the calcitriol-mediated HCV suppression was reversed. Otherwise, three individual stimulators of PPAR-α/β/γ blocked the activation of VDR. PPAR-β (linoleic acid) reversed the inhibition of NO release, whereas PPAR-γ (Ly171883) reversed the inhibitions of NO release and lipid accumulation in the presence of calcitriol. The calcitriol-mediated viral suppression, inhibition of NO release and activation of VDR were partially blocked by an inhibitor of endoplasmic reticulum-associated degradation (ERAD), kifunensine. Furthermore, calcitriol blocked the HCV-induced expressions of apolipoprotein J and 78 kDa glucose-regulated protein, which was restored by pretreatment of kifunensine. These results indicated that the calcitriol-mediated HCV suppression was associated with the activation of VDR, interference with ERAD process, as well as blockades of PPAR, lipid accumulation and nitrative stress.

REV-ERBα Regulates CYP7A1 Through Repression of Liver Receptor Homolog-1

Nuclear heme receptor reverse erythroblastosis virus (REV-ERB) α (a transcriptional repressor) is known to regulate cholesterol 7α-hydroxylase (CYP7A1) and bile acid synthesis. However, the mechanism for REV-ERBα regulation of CYP7A1 remains elusive. Here, we investigate the role of LRH-1 in REV-ERBα regulation of CYP7A1 and cholesterol metabolism. We first characterized the tertiary amine N-(4-chloro-2-methylbenzyl)-N-(4-chlorobenzyl)-1-(5-nitrothiophen-2-yl)methanamine (GSK2945) as a highly specific Rev-erbα/REV-ERBα antagonist using cell-based assays and confirmed expression of Rev-erbα in mouse liver. GSK2945 treatment increased hepatic mouse cholesterol 7α-hydroxylase (Cyp7a1) level and lowered plasma cholesterol in wild-type mice. Likewise, the compound increased the expression and microsomal activity of Cyp7a1 in hypercholesterolemic mice. This coincided with reduced plasma and liver cholesterol and enhanced production of bile acids. Increased levels of Cyp7a1/CYP7A1 were also found in mouse and human primary hepatocytes after GSK2945 treatment. In these experiments, we observed parallel increases in Lrh-1/LRH-1 (a known hepatic activator of Cyp7a1/CYP7A1) mRNA and protein. Luciferase reporter, mobility shift, and chromatin immunoprecipitation assays revealed that Lrh-1/LRH-1 was a direct Rev-erbα/REV-ERBα target gene. Furthermore, conditional deletion of Lrh-1 in the liver abrogated the regulatory effects of Rev-erbα on Cyp7a1 and cholesterol metabolism in mice. In conclusion, Rev-erbα regulates Cyp7a1 and cholesterol metabolism through its repression of the Lrh-1 receptor. Targeting the REV-ERBα/LRH-1 axis may represent a novel approach for management of cholesterol-related diseases.

Bile Acids in the Treatment of Cardiometabolic Diseases

Bile acids (BA), for decades considered only to have fat-emulsifying functions in the gut lumen, have recently emerged as novel cardio-metabolic modulators. They have real endocrine effects, acting via multiple intracellular receptors in various organs and tissues. BA affect energy homeostasis through the modulation of glucose and lipid metabolism, predominantly by activating the nuclear farnesoid X receptor (FXR), as well as the cytoplasmic membrane G protein-coupled BA receptor TGR5 in a variety of tissues; although numerous other intracellular targets of BA are also in play.The roles of BA in the pathogenesis of diabetes, obesity, metabolic syndrome, and cardiovascular diseases are seriously being considered, and BA and their derivatives seem to represent novel potential therapeutics to treat these diseases of civilization.

Highlighting Vitamin D Receptor-Targeted Activities of 1α,25-Dihydroxyvitamin D3 in Mice via Physiologically Based Pharmacokinetic-Pharmacodynamic Modeling

We expanded our published physiologically based pharmacokinetic model (PBPK) on 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], ligand of the vitamin D receptor (VDR), to appraise VDR-mediated pharmacodynamics in mice. Since 1,25(OH)₂D₃ kinetics was best described by a segregated-flow intestinal model (SFM) that described a low/partial intestinal (blood/plasma) flow to enterocytes, with feedback regulation of its synthesis (Cyp27b1) and degradation (Cyp24a1) enzymes, this PBPK(SFM) model was expanded to describe the VDR-mediated changes (altered/basal mRNA expression) of target genes/responses with the indirect response model. We examined data on 1) renal Trpv5 (transient receptor potential cation channel, subfamily V member 5) and Trpv6 and intestinal Trpv6 (calcium channels) for calcium absorption; 2) liver 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (Hmgcr) and cytochrome 7α-hydroxylase (Cyp7a1) for cholesterol synthesis and degradation, respectively; and 3) renal and brain Mdr1 (multidrug-resistance protein that encodes the P-glycoprotein) for digoxin disposition after repetitive intraperitoneal doses of 120 pmol 1,25(OH)₂D₃ Fitting, performed with modeling software, yielded reasonable prediction of a dominant role of intestinal Trpv6 in calcium absorption, circadian rhythm that is characterized by simple cosine models for Hmgcr and Cyp7a1 on liver cholesterol, and brain and renal Mdr1 on tissue efflux of digoxin. Fitted parameters on the E_max, EC₅₀, and turnover rate constants of VDR-target genes [zero-order production (k_in) and first-order degradation (k_out) rate constants] showed low coefficients of variation and acceptable median prediction errors (4.5%-40.6%). Sensitivity analyses showed that the E_max and EC₅₀ values are key parameters that could influence the pharmacodynamic responses. In conclusion, the PBPK(SFM)-pharmacodynamic model successfully characterized VDR gene activation and serves as a useful tool to predict the therapeutic effects of 1,25(OH)₂D₃.

Statin therapy causes gut dysbiosis in mice through a PXR-dependent mechanism

BACKGROUND

Statins are a class of therapeutics used to regulate serum cholesterol and reduce the risk of heart disease. Although statins are highly effective in removing cholesterol from the blood, their consumption has been linked to potential adverse effects in some individuals. The most common events associated with statin intolerance are myopathy and increased risk of developing type 2 diabetes mellitus. However, the pathological mechanism through which statins cause these adverse effects is not well understood.

RESULTS

Using a murine model, we describe for the first time profound changes in the microbial composition of the gut following statin treatment. This remodelling affected the diversity and metabolic profile of the gut microbiota and was associated with reduced production of butyrate. Statins altered both the size and composition of the bile acid pool in the intestine, tentatively explaining the observed gut dysbiosis. As also observed in patients, statin-treated mice trended towards increased fasting blood glucose levels and weight gain compared to controls. Statin treatment affected the hepatic expression of genes involved in lipid and glucose metabolism. Using gene knockout mice, we demonstrated that the observed effects were mediated through pregnane X receptor (PXR).

CONCLUSION

This study demonstrates that statin therapy drives a profound remodelling of the gut microbiota, hepatic gene deregulation and metabolic alterations in mice through a PXR-dependent mechanism. Since the demonstrated importance of the intestinal microbial community in host health, this work provides new perspectives to help prevent the statin-associated unintended metabolic effects.

1,25(OH)2 D3 attenuates hepatic steatosis by inducing autophagy in mice

OBJECTIVE

1,25(OH)₂ D₃ has been reported to attenuate liver steatosis; however, its exact mechanism of action remains poorly understood. This study aimed to determine whether 1,25(OH)₂ D₃ can attenuate hepatic steatosis by inducing autophagy.

METHODS

Male C57BL/6 mice fed a high-fat diet (HFD) were injected with 1,25(OH)₂ D₃ for 4 weeks. These mice were given 3-methyladenine (3-MA) to inhibit autophagy. HepG2 cells were preincubated with a free fatty acid (FFA) and then treated with 1,25(OH)₂ D₃ . Vitamin D receptor (VDR) shRNA and autophagy-related 16-like 1 (ATG16L1) siRNA were used for VDR knockdown or ATG16L1 silencing, respectively.

RESULTS

1,25(OH)₂ D₃ diminished HFD-induced liver damage and steatosis, changes accompanied by autophagy and ATG16L1 expression upregulation. Inhibition of 1,25(OH)₂ D₃ -induced autophagy mediated by 3-MA blocked the protective effects of 1,25(OH)₂ D₃ on hepatic steatosis. Additionally, 1,25(OH)₂ D₃ -induced autophagy appeared to play a role in anti-inflammation and lipid metabolism modulation in the liver. In HepG2 cells, 1,25(OH)₂ D₃ reduced lipid accumulation and increased autophagy and ATG16L1 expression; however, this effect was abrogated after VDR knockdown. The protective effects of 1,25(OH)₂ D₃ -mediated autophagy against lipid accumulation were abolished by 3-MA. Furthermore, siRNA-mediated ATG16L1 knockdown prevented 1,25(OH)₂ D₃ -induced autophagy, resulting in increased fat accumulation.

CONCLUSIONS

The data suggest that 1,25(OH)₂ D₃ may ameliorate hepatic steatosis by inducing autophagy by upregulating ATG16L1.

Effect of Osteocyte-Ablation on Inorganic Phosphate Metabolism: Analysis of Bone-Kidney-Gut Axis

In response to kidney damage, osteocytes increase the production of several hormones critically involved in mineral metabolism. Recent studies suggest that osteocyte function is altered very early in the course of chronic kidney disease. In the present study, to clarify the role of osteocytes and the canalicular network in mineral homeostasis, we performed four experiments. In Experiment 1, we investigated renal and intestinal Pi handling in osteocyte-less (OCL) model mice [transgenic mice with the dentin matrix protein-1 promoter-driven diphtheria toxin (DT)-receptor that were injected with DT]. In Experiment 2, we administered granulocyte colony-stimulating factor to mice to disrupt the osteocyte canalicular network. In Experiment 3, we investigated the role of osteocytes in dietary Pi signaling. In Experiment 4, we analyzed gene expression level fluctuations in the intestine and liver by comparing mice fed a high Pi diet and OCL mice. Together, the findings of these experiments indicate that osteocyte ablation caused rapid renal Pi excretion (P < 0.01) before the plasma fibroblast growth factor 23 (FGF23) and parathyroid hormone (PTH) levels increased. At the same time, we observed a rapid suppression of renal Klotho (P < 0.01), type II sodium phosphate transporters Npt2a (P < 0.01) and Npt2c (P < 0.05), and an increase in intestinal Npt2b (P < 0.01) protein. In OCL mice, Pi excretion in feces was markedly reduced (P < 0.01). Together, these effects of osteocyte ablation are predicted to markedly increase intestinal Pi absorption (P < 0.01), thus suggesting that increased intestinal Pi absorption stimulates renal Pi excretion in OCL mice. In addition, the ablation of osteocytes and feeding of a high Pi diet affected FGF15/bile acid metabolism and controlled Npt2b expression. In conclusion, OCL mice exhibited increased renal Pi excretion due to enhanced intestinal Pi absorption. We discuss the role of FGF23-Klotho on renal and intestinal Pi metabolism in OCL mice.

Bile Acids, Nuclear Receptors and Cytochrome P450

This review summarizes the importance of bile acids (BA) as important regulators of various homeostatic mechanisms with detailed focus on cytochrome P450 (CYP) enzymes. In the first part, synthesis, metabolism and circulation of BA is summarized and BA are reviewed as physiological ligands of nuclear receptors which regulate transcription of genes involved in their metabolism, transport and excretion. Notably, PXR, FXR and VDR are the most important nuclear receptors through which BA regulate transcription of CYP genes involved in the metabolism of both BA and xenobiotics. Therapeutic use of BA and their derivatives is also briefly reviewed. The physiological role of BA interaction with nuclear receptors is basically to decrease production of toxic non-polar BA and increase their metabolic turnover towards polar BA and thus decrease their toxicity. By this, the activity of some drug-metabolizing CYPs is also influenced what could have clinically relevant consequences in cholestatic diseases or during the treatment with BA or their derivatives.

Effects of 12-month, 2000IU/day vitamin D supplementation on treatment naïve and vitamin D deficient Saudi type 2 diabetic patients

Objectives:

To determine whether 12-month, 2000IU/day vitamin D supplementation cardiometabolically improves treatment naïve type 2 diabetes mellitus (T2DM) Saudi patients with vitamin D deficiency.

Methods:

This 12-month interventional study was conducted at primary health centers in 5 different residential areas in Riyadh, Saudi Arabia between January 2013 and January 2014. Forty-five Saudi T2DM patients were enrolled. Baseline anthropometrics, glycemic, and lipid profiles were measured and repeated after 6 and 12 months. All subjects were provided with 2000IU vitamin D supplements for one year.

Results:

Vitamin D deficiency at baseline was 46.7%, 31.8% after 6 months, and 35.6% after 12 months, indicating an overall improvement in the vitamin D status in the entire cohort. Insulin and homeostatic model assessment-insulin resistance (HOMA-IR) after 12 months were significantly lower than a 6 months (p<0.05), but comparable to baseline values. Mean levels of triglycerides increased overtime from baseline (1.9±0.01 mmol/l) to 12 months (2.1±0.2 mmol). This modest increase in serum triglycerides was parallel to the insignificant decrease in circulating high-density lipoprotein -cholesterol levels.

Conclusion:

Twelve-month vitamin D supplementation of 2000IU per day in a cohort of treatment naïve Saudi patients with T2DM resulted in improvement of several cardiometabolic parameters including systolic blood pressure, insulin, and HOMA-IR. Further studies that include a placebo group are suggested to reinforce findings.

Hepatocyte vitamin D receptor regulates lipid metabolism and mediates experimental diet-induced steatosis

BACKGROUND & AIMS

The pathogenesis and progression of non-alcoholic fatty liver disease (NAFLD) is still incompletely understood. Several nuclear receptors play a role in liver lipid metabolism and can promote hepatosteatosis, but the possible role of vitamin D receptor (VDR) in NAFLD has not been investigated.

METHODS

The expression of liver VDR was investigated in apolipoprotein E knockout (apoE(-/-)) mice on a high fat diet, in wild-type mice on methionine and choline deficient diet and in NAFLD patients with hepatosteatosis and non-alcoholic steatohepatitis. The relevance of VDR was assessed in apoE(-/-) mice by deletion of VDR or paricalcitol treatment and in human HepG2 cells by VDR transfection or silencing. The role of VDR in fibrosis was also determined in VDR knockout mice (VDR(-/-)) treated with thioacetamide.

RESULTS

Expression of liver VDR was markedly induced in two mouse models of NAFLD, as well as in patients with hepatosteatosis, but decreased in non-alcoholic steatohepatitis. VDR deletion in high fat diet-fed apoE(-/-) mice protected against fatty liver, dyslipidemia and insulin resistance, and caused a decrease in taurine-conjugated bile acids, but did not influence fibrosis by thioacetamide. apoE(-/-)VDR(-/-) mouse livers showed decreased gene expression of CD36, DGAT2, C/EBPα and FGF21, and increased expression of PNPLA2, LIPIN1 and PGC1α. Treatment of apoE(-/-) mice on high fat diet with paricalcitol had modest opposite effects on steatosis and gene expression. Finally, this set of genes showed concordant responses when VDR was overexpressed or silenced in HepG2 cells.

CONCLUSIONS

Induced hepatocyte VDR in NAFLD regulates key hepatic lipid metabolism genes and promotes high fat diet-associated liver steatosis. Therapeutic inhibition of liver VDR may reverse steatosis in early NAFLD.

LAY SUMMARY

The amount of vitamin D receptor is induced early in the livers of mice and humans when they develop non-alcoholic fatty liver disease. If the gene for the vitamin D receptor is deleted, hepatic lipid metabolism changes and mice do not accumulate fat in the liver. We conclude that the vitamin D receptor can contribute to the fatty liver disease promoted by a high fat diet.

High Dietary Selenium Intake Alters Lipid Metabolism and Protein Synthesis in Liver and Muscle of Pigs

BACKGROUND

Prolonged high intakes of dietary selenium have been shown to induce gestational diabetes in rats and hyperinsulinemia in pigs.

OBJECTIVE

Two experiments were conducted to explore metabolic and molecular mechanisms for the diabetogenic potential of high dietary selenium intakes in pigs.

METHODS

In Expt. 1, 16 Yorkshire-Landrace-Hampshire crossbred pigs (3 wk old, body weight = 7.5 ± 0.81 kg, 50% males and 50% females) were fed a corn-soybean meal basal diet supplemented with 0.3 or 1.0 mg Se/kg (as selenium-enriched yeast for 6 wk). In Expt. 2, 12 pigs of the same crossbreed (6 wk old, body weight = 16.0 ± 1.8 kg) were fed a similar basal diet supplemented with 0.3 or 3.0 mg Se/kg for 11 wk. Biochemical and gene and protein expression profiles of lipid and protein metabolism and selenoproteins in plasma, liver, muscle, and adipose tissues were analyzed.

RESULTS

In Expt. 1, the 1-mg-Se/kg diet did not affect body weight or plasma concentrations of glucose and nonesterified fatty acids. In Expt. 2, the 3-mg-Se/kg diet, compared with the 0.3-mg-Se/kg diet, increased (P < 0.05) concentrations of plasma insulin (0.2 compared with 0.4 ng/mL), liver and adipose lipids (41% to 2.4-fold), and liver and muscle protein (10-14%). In liver, the 3-mg-Se/kg diet upregulated (P < 0.05) the expression, activity, or both of key factors related to gluconeogenesis [phosphoenolpyruvate carboxykinase (PEPCK); 13%], lipogenesis [sterol regulatory element binding protein 1 (SREBP1), acetyl-coenzyme A carboxylase (ACC), and fatty acid synthase (FASN); 46-90%], protein synthesis [insulin receptor (INSR), P70 ribosomal protein S6 kinase (P70), and phosphorylated ribosomal protein S6 (P-S6); 88-105%], energy metabolism [AMP-activated protein kinase (AMPK); up to 2.8-fold], and selenoprotein glutathione peroxidase 3 (GPX3; 1.4-fold) and suppressed (P < 0.05) mRNA levels of lipolysis gene cytochrome P450, family 7, subfamily A, polypeptide 1 (CYP7A1; 88%) and selenoprotein gene selenoprotein W1 (SEPW1; 46%). In muscle, the 3-mg-Se/kg diet exerted no effect on the lipid profiles but enhanced (P < 0.05) expression of P-S6 and mammalian target of rapamycin (mTOR; 42-176%; protein synthesis); selenoprotein P (SELP; 40-fold); and tumor suppressor protein 53 (P53) and peroxisome proliferator-activated receptor γ (PPARG; 52-58%; lipogenesis) and suppressed (P < 0.05) expression of INSR (59%; insulin signaling); selenoprotein S (SELS); deiodinases, iodothyronine, type I (DIO1); and thioredoxin reductase 1 (TXNRD1; 50%; selenoproteins); and ACC1 and FASN (35-51%; lipogenesis).

CONCLUSION

Our research showed novel roles, to our best knowledge, and mechanisms of high selenium intakes in regulating the metabolism of protein, along with that of lipid, in a tissue-specific fashion in pigs.

The role of bile acids in metabolic regulation

Bile acids (BA), long believed to only have lipid-digestive functions, have emerged as novel metabolic modulators. They have important endocrine effects through multiple cytoplasmic as well as nuclear receptors in various organs and tissues. BA affect multiple functions to control energy homeostasis, as well as glucose and lipid metabolism, predominantly by activating the nuclear farnesoid X receptor and the cytoplasmic G protein-coupled BA receptor TGR5 in a variety of tissues. However, BA also are aimed at many other cellular targets in a wide array of organs and cell compartments. Their role in the pathogenesis of diabetes, obesity and other 'diseases of civilization' becomes even more clear. They also interact with the gut microbiome, with important clinical implications, further extending the complexity of their biological functions. Therefore, it is not surprising that BA metabolism is substantially modulated by bariatric surgery, a phenomenon contributing favorably to the therapeutic effects of these surgical procedures. Based on these data, several therapeutic approaches to ameliorate obesity and diabetes have been proposed to affect the cellular targets of BA.