Liver X Receptors and their Agonists: Targeting for Cholesterol Homeostasis and Cardiovascular Diseases

Protective effect of liver X receptor on cigarette smoke and lipopolysaccharide induced airway inflammation and emphysema in mice

OBJECTIVE

The aim of this study is to assess the impact of Liver X receptors (LXRs) on airway inflammation, airway remodeling, and lipid deposition induced by cigarette smoke and lipopolysaccharide (LPS) exposure in the lung.

METHODS

Wild mice and LXR-deficient mice were exposed to cigarette smoke and LPS to induce airway inflammation and remodeling. In addition, some wild mice received intraperitoneal treatment with the LXR agonist GW3965 before exposure to cigarette smoke and LPS. Lung tissue and bronchoalveolar lavage fluid were collected to evaluate airway inflammation, airway remodeling and lipid deposition.

RESULTS

Exposure to cigarette smoke and LPS resulted in airway inflammation, emphysema and lipid accumulation in wild mice. These mice also exhibited downregulated LXRα and ABCA1 in the lung. Treatment with GW3965 mitigated inflammation, remodeling and lipid deposition, while the deletion of LXRs exacerbated these effects. Furthermore, GW3965 treatment following exposure to cigarette smoke and LPS increased LXRα and ABCA1 expression and attenuated MyD88 expression in wild mice.

CONCLUSION

LXRs demonstrate the potential to mitigate cigarette smoke and LPS- induced airway inflammation, emphysema and lipid disposition in mice.

Obesity-associated Airway Hyperresponsiveness: Mechanisms Underlying Inflammatory Markers and Possible Pharmacological Interventions

Obesity is rapidly becoming a global health problem affecting about 13% of the world's population affecting women and children the most. Recent studies have stated that obese asthmatic subjects suffer from an increased risk of asthma, encounter severe symptoms, respond poorly to anti-asthmatic drugs, and ultimately their quality-of-life decreases. Although, the association between airway hyperresponsiveness (AHR) and obesity is a growing concern among the public due to lifestyle and environmental etiologies, however, the precise mechanism underlying this association is yet to establish. Apart from aiming at the conventional antiasthmatic targets, treatment should be directed towards ameliorating obesity pathogenesis too. Understanding the pathogenesis underlying the association between obesity and AHR is limited, however, a plethora of obesity pathologies have been reported viz., increased pro-inflammatory and decreased anti-inflammatory adipokines, depletion of ROS controller Nrf2/HO-1 axis, NLRP3 associated macrophage polarization, hypertrophy of WAT, and down-regulation of UCP1 in BAT following down-regulated AMPKα and melanocortin pathway that may be correlated with AHR. Increased waist circumference (WC) or central obesity was thought to be related to severe AHR, however, some recent reports suggest body mass index (BMI), not WC tends to exaggerate airway closure in AHR due to some unknown mechanisms. This review aims to co-relate the above-mentioned mechanisms that may explain the copious relation underlying obesity and AHR with the help of published reports. A proper understanding of these mechanisms discussed in this review will ensure an appropriate treatment plan for patients through advanced pharmacological interventions.

Danlou Recipe promotes cholesterol efflux in macrophages RAW264.7 and reverses cholesterol transport in mice with hyperlipidemia induced by P407

INTRODUCTION

Liver X Receptor (LXR) agonists could attenuate the development of atherosclerosis but bring excess lipid accumulation in the liver. Danlou Recipe was believed to be a benefit for improving the lipid profile. Thus, it is unclear whether Danlou Recipe could attenuate hyperlipidemia without excess lipid accumulated in the liver of mice. This study aimed to clarify if Danlou Recipe could alleviate the progression of hyperlipidemia in mice without extra lipids accumulated in the liver.

METHODS

Male murine macrophage RAW264.7 cells and murine peritoneal macrophages were used for the in vitro experiments. Cellular cholesterol efflux was determined using the fluorescent cholesterol labeling method. Those genes involved in lipid metabolism were evaluated by qRT-PCR and western blotting respectively. In vivo, a mouse model of hyperlipidemia induced by P407 was used to figure out the effect of Danlou Recipe on reverse cholesterol transport (RCT) and hyperlipidemia. Ethanol extract of Danlou tablet (EEDL) was prepared by extracting the whole powder of Danlou Prescription from ethanol, and the chemical composition was analyzed by ultra-performance liquid chromatography (UPLC).

RESULTS

EEDL inhibits the formation of RAW264.7 macrophage-derived foam cells, and promotes ABCA1/apoA1 conducted cholesterol efflux in RAW264.7 macrophages and mouse peritoneal macrophages. In the P407-induced hyperlipidemia mouse model, oral administration of EEDL can promote RCT in vivo and improve fatty liver induced by a high-fat diet. Consistent with the findings in vitro, EEDL promotes RCT by upregulating the LXR activities.

CONCLUSION

Our results demonstrate that EEDL has the potential for targeting RCT/LXR in the treatment of lipid metabolism disorders to be developed as a safe and effective therapy.

MicroRNA-206-3p suppresses hepatic lipogenesis and cholesterol synthesis while driving cholesterol efflux

BACKGROUND AND AIMS

Hepatosteatosis, hypertriglyceridemia, and hypercholesterolemia are interconnected metabolic disorders. This study is designed to characterize how microRNA-206-3p (miR-206) simultaneously prevents de novo lipogenesis (DNL), cholesterol synthesis, and VLDL production in hepatocytes while promoting cholesterol efflux in macrophages.

APPROACH AND RESULTS

MiR-206 levels were reduced in hepatocytes and macrophages of mice subjected to a high-fat, high-cholesterol diet. A negative feedback between LXRα (liver X receptor alpha) and miR-206 is formed to maintain high LXRα and low miR-206 in hepatocytes. Systemic administration of miR-206 alleviated hepatosteatosis, hypertriglyceridemia, and hypercholesterolemia in mice. A significant reduction in LDL cholesterol and VLDL cholesterol but unaltered HDL cholesterol was observed in miR-206-treated mice. Mirroring these findings, miR-206 reprogrammed the transcriptome of hepatocytes towards the inhibition of DNL, cholesterol synthesis, and assembly and secretion of VLDL. In macrophages, miR-206 activated the expression of genes regulating cholesterol efflux. Hepatocyte-specific expression of miR-206 reduced hepatic and circulating triglycerides and cholesterol, as well as VLDL production, while transplantation of macrophages bearing miR-206 facilitated cholesterol efflux. Mechanistically, miR-206 directly targeted Lxrα and Hmgcr in hepatocytes but facilitated expression of Lxrα in macrophages by targeting macrophage-specific tricho-rhino-phalangeal syndrome 1 (TRPS1), a transcription repressor of Lxrα . By targeting Hmgc r and Lxrα , miR-206 inhibited DNL, VLDL production, and cholesterol synthesis in hepatocytes, whereas it drove cholesterol efflux by activating the TRPS1-LXRα axis.

CONCLUSIONS

MiR-206, through differentially modulating LXRα signaling in hepatocytes and macrophages, inhibits DNL, promotes cholesterol efflux, and concurrently hinders cholesterol synthesis and VLDL production. MiR-206 simulates the functions of lipid-lowering medications, statins, and LXRα agonists.

A crosstalk between epigenetic modulations and non-alcoholic fatty liver disease progression

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a major public health concern worldwide due to its rapidly rising prevalence and its potential to progress into end-stage liver disease. While the precise pathophysiology underlying NAFLD remains incompletely understood, it is strongly associated with various environmental triggers and other metabolic disorders. Epigenetics examines changes in gene expression that are not caused by alterations in the DNA sequence itself. There is accumulating evidence that epigenetics plays a key role in linking environmental cues to the onset and progression of NAFLD. Our understanding of how epigenetic mechanisms contribute to NAFLD pathophysiology has expanded considerably in recent years as research on the epigenetics of NAFLD has developed. This review summarizes recent insights into major epigenetic processes that have been implicated in NAFLD pathogenesis including DNA methylation, histone acetylation, and microRNAs that have emerged as promising targets for further investigation. Elucidating epigenetic mechanisms in NAFLD may uncover novel diagnostic biomarkers and therapeutic targets for this disease. However, many questions have remained unanswered regarding how epigenetics promotes NAFLD onset and progression. Additional studies are needed to further characterize the epigenetic landscape of NAFLD and validate the potential of epigenetic markers as clinical tools. Nevertheless, an enhanced understanding of the epigenetic underpinnings of NAFLD promises to provide key insights into disease mechanisms and pave the way for novel prognostic and therapeutic approaches.

Pioneer Factor Foxa2 Mediates Chromatin Conformation Changes for Activation of Bile Acid Targets of FXR

BACKGROUND & AIMS

Transcription factors regulate gene expression that orchestrates liver physiology. Many bind at distal enhancers and chromatin looping is required to activate their targets. Chromatin architecture has been linked to essential functions of the liver, including metabolism and sexually dimorphic gene expression. We have previously shown that pioneer factor Foxa2 opens chromatin for binding of nuclear receptors farnesoid X receptor (FXR) and liver X receptor-α during acute ligand activation. FXR is activated by bile acids and deletion of Foxa2 in the liver results in intrahepatic cholestasis. We hypothesized that Foxa2 also enables chromatin conformational changes during ligand activation and performed genome-wide studies to test this hypothesis.

METHODS

We performed Foxa2 HiChIP (Hi-C and ChIP) to assess Foxa2-dependent long-range interactions in mouse livers treated with either vehicle control or FXR agonist GW4064.

RESULTS

HiChIP contact analysis shows that global chromatin interactions are dramatically increased during FXR activation. Ligand-treated livers exhibit extensive redistribution of topological associated domains and substantial increase in Foxa2-anchored loops, suggesting Foxa2 is involved in dynamic chromatin conformational changes. We demonstrate that chromatin conformation, including genome-wide interactions, topological associated domains, and intrachromosomal and interchromosomal Foxa2-anchored loops, drastically changes on addition of FXR agonist. Additional Foxa2 binding in ligand-activated state leads to formation of Foxa2-anchored loops, leading to distal interactions and activation of gene expression of FXR targets.

CONCLUSIONS

Ligand activation of FXR, and likely of related receptors, requires global changes in chromatin architecture. We determine a novel role for Foxa2 in enabling these conformational changes, extending its function in bile acid metabolism.

Liver X receptors: From pharmacology to nanoparticle-based drug delivery

Liver X receptors (LXRs) are master regulators of various biological processes, including metabolism, inflammation, development, and reproduction. As well-known nuclear oxysterol receptors of the nuclear receptor (NR) family, LXRs have two homologous subtypes, LXRα (NR1H3) and LXRβ (NR1H2). Since the mid-1990s, numerous LXR-targeted drugs have been designed to treat diseases such as atherosclerosis, systemic lupus erythematosus, and cancer. These modulators include agonists and antagonists, and the selectivity of them have been development from diverse aspects, including subtype-specific, cell-specific, tissue-specific types. Meanwhile, advanced delivery systems are also exploreed to facilitate the application of LXR drugs in clinical setting. One of the most promising delivery systems involves the use of nanoparticles and is expected to increase the clinical potential of LXR modulators. This review discusses our current understanding of LXR biology and pharmacology, focusing on the development of modulators for LXRα and/or LXRβ, and the nanoparticle-based delivery systems for promising LXR modulators with potential for use as drugs.

Therapeutic effect of ouabagenin, a novel liver X receptor agonist, on atherosclerosis in nonalcoholic steatohepatitis in SHRSP5/Dmcr rat model

The liver X receptor (LXR) can enhance cholesterol transporters, which could remove excess cholesterol from foam cells in atheromas. LXR has two subtypes: LXRα, which aggravates hepatic lipid accumulation, and LXRβ, which does not. In 2018, ouabagenin (OBG) was reported as a potential LXRβ-specific agonist. We aimed to examine whether OBG specifically affects LXRβ in nonalcoholic steatohepatitis (NASH); it did not aggravate hepatic steatosis and can suppress the development of atherosclerosis. SHRSP5/Dmcr rats fed a high-fat and high-cholesterol diet were divided into four groups as follows: (I) L-NAME group, (II) L-NAME/OBG group, (III) OBG (-) group, and (IV) OBG (+) group. All groups' rats were intraperitoneally administered L-NAME. The L-NAME/OBG group's rats were intraperitoneally administered OBG and L-NAME simultaneously. After L-NAME administration, the OBG (+) group's rats were administered OBG, while the OBG (-) group's rats were not. Although all rats developed NASH, OBG did not exacerbate steatosis (L-NAME/OBG and OBG (+) groups). In addition, endothelial cells were protected in the L-NAME/OBG group and foam cells in the atheroma were reduced in the OBG (+) group. OBG is an LXRβ-specific agonist and has a potential therapeutic effect on atherosclerosis without developing lipid accumulation in the liver.

Emerging Insights into Liver X Receptor α in the Tumorigenesis and Therapeutics of Human Cancers

Liver X receptor α (LXRα), a member of the nuclear receptor superfamily, is identified as a protein activated by ligands that interacts with the promoters of specific genes. It regulates cholesterol, bile acid, and lipid metabolism in normal physiological processes, and it participates in the development of some related diseases. However, many studies have demonstrated that LXRα is also involved in regulating numerous human malignancies. Aberrant LXRα expression is emerging as a fundamental and pivotal factor in cancer cell proliferation, invasion, apoptosis, and metastasis. Herein, we outline the expression levels of LXRα between tumor tissues and normal tissues via the Oncomine and Tumor Immune Estimation Resource (TIMER) 2.0 databases; summarize emerging insights into the roles of LXRα in the development, progression, and treatment of different human cancers and their diversified mechanisms; and highlight that LXRα can be a biomarker and therapeutic target in diverse cancers.

Nicotinamide Adenine Dinucleotide Augmentation in Overweight or Obese Middle-Aged and Older Adults: A Physiologic Study

CONTEXT

Nicotinamide adenine dinucleotide (NAD) levels decline with aging and age-related decline in NAD has been postulated to contribute to age-related diseases.

OBJECTIVE

We evaluated the safety and physiologic effects of NAD augmentation by administering its precursor, β-nicotinamide mononucleotide (MIB-626, Metro International Biotech, Worcester, MA), in adults at risk for age-related conditions.

METHODS

Thirty overweight or obese adults, ≥ 45 years, were randomized in a 2:1 ratio to 2 MIB-626 tablets each containing 500 mg of microcrystalline β-nicotinamide mononucleotide or placebo twice daily for 28 days. Study outcomes included safety; NAD and its metabolome; body weight; liver, muscle, and intra-abdominal fat; insulin sensitivity; blood pressure; lipids; physical performance, and muscle bioenergetics.

RESULTS

Adverse events were similar between groups. MIB-626 treatment substantially increased circulating concentrations of NAD and its metabolites. Body weight (difference -1.9 [-3.3, -0.5] kg, P = .008); diastolic blood pressure (difference -7.01 [-13.44, -0.59] mmHg, P = .034); total cholesterol (difference -26.89 [-44.34, -9.44] mg/dL, P = .004), low-density lipoprotein (LDL) cholesterol (-18.73 [-31.85, -5.60] mg/dL, P = .007), and nonhigh-density lipoprotein cholesterol decreased significantly more in the MIB-626 group than placebo. Changes in muscle strength, muscle fatigability, aerobic capacity, and stair-climbing power did not differ significantly between groups. Insulin sensitivity and hepatic and intra-abdominal fat did not change in either group.

CONCLUSIONS

MIB-626 administration in overweight or obese, middle-aged and older adults safely increased circulating NAD levels, and significantly reduced total LDL and non-HDL cholesterol, body weight, and diastolic blood pressure. These data provide the rationale for larger trials to assess the efficacy of NAD augmentation in improving cardiometabolic outcomes in older adults.

Bone circuitry and interorgan skeletal crosstalk

The past decade has seen significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone integrity in disease. Recent breakthroughs have arisen mainly from identifying disease-causing mutations and modeling human bone disease in rodents, in essence, highlighting the integrative nature of skeletal physiology. It has become increasingly clear that bone cells, osteoblasts, osteoclasts, and osteocytes, communicate and regulate the fate of each other through RANK/RANKL/OPG, liver X receptors (LXRs), EphirinB2-EphB4 signaling, sphingolipids, and other membrane-associated proteins, such as semaphorins. Mounting evidence also showed that critical developmental pathways, namely, bone morphogenetic protein (BMP), NOTCH, and WNT, interact each other and play an important role in postnatal bone remodeling. The skeleton communicates not only with closely situated organs, such as bone marrow, muscle, and fat, but also with remote vital organs, such as the kidney, liver, and brain. The metabolic effect of bone-derived osteocalcin highlights a possible role of skeleton in energy homeostasis. Furthermore, studies using genetically modified rodent models disrupting the reciprocal relationship with tropic pituitary hormone and effector hormone have unraveled an independent role of pituitary hormone in skeletal remodeling beyond the role of regulating target endocrine glands. The cytokine-mediated skeletal actions and the evidence of local production of certain pituitary hormones by bone marrow-derived cells displays a unique endocrine-immune-skeletal connection. Here, we discuss recently elucidated mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, crosstalk between bone and vital organs, as well as opportunities for treating diseases of the skeleton.

Endocytosis of LXRs: Signaling in liver and disease

Nuclear receptors are among one of the major transcriptional factors that induces gene regulation in the nucleus. Liver X receptor (LXR) is a transcription factor which regulates essential lipid homeostasis in the body including fatty acid, cholesterol and phospholipid synthesis. Liver X receptor-retinoid X receptor (LXR-RXR) heterodimer is activated by either of the ligand binding on LXR or RXR. The promoter region of the gene which is targeted by LXR is bound to the response element of LXR. The activators bind to the heterodimer once the corepressor is dissociated. The cellular process such as endocytosis aids in intracellular trafficking and endosomal formation in transportation of molecules for essential signaling within the cell. LXR isotypes play a crucial role in maintaining lipid homeostasis by regulating the level of cholesterol. In the liver, the deficiency of LXRα can alter the normal physiological conditions depicting the symptoms of various cardiovascular and liver diseases. LXR can degrade low density lipoprotein receptors (LDLR) by the signaling of LXR-IDOL through endocytic trafficking in lipoprotein uptake. Various gene expressions associated with cholesterol level and lipid synthesis are regulated by LXR transcription factor. With its known diversified ligand binding, LXR is capable of regulating expression of various specific genes responsible for the progression of autoimmune diseases. The agonists and antagonists of LXR stand to be an important factor in transcription of the ABC family, essential for high density lipoprotein (HDL) formation. Endocytosis and signaling mechanism of the LXR family is broad and complex despite their involvement in cellular growth and proliferation. Here in this chapter, we aimed to emphasize the master regulation of LXR activation, regulators, and their implications in various metabolic activities especially in lipid homeostasis. Furthermore, we also briefed the significant role of LXR endocytosis in T cell immune regulation and a variety of human diseases including cardiovascular and neuroadaptive.

NUDT7 regulates total hepatic CoA levels and the composition of the intestinal bile acid pool in male mice fed a Western diet

Nudix hydrolase 7 (NUDT7) is an enzyme that hydrolyzes CoA species, is highly expressed in the liver, and resides in the peroxisomes. Peroxisomes are organelles where the preferential oxidation of dicarboxylic fatty acids occurs and where the hepatic synthesis of the primary bile acids cholic acid and chenodeoxycholic acid is completed. We previously showed that liver-specific overexpression of NUDT7 affects peroxisomal lipid metabolism but does not prevent the increase in total liver CoA levels that occurs during fasting. We generated Nudt7^-/- mice to further characterize the role that peroxisomal (acyl-)CoA degradation plays in the modulation of the size and composition of the acyl-CoA pool and in the regulation of hepatic lipid metabolism. Here, we show that deletion of Nudt7 alters the composition of the hepatic acyl-CoA pool in mice fed a low-fat diet, but only in males fed a Western diet does the lack of NUDT7 activity increase total liver CoA levels. This effect is driven by the male-specific accumulation of medium-chain dicarboxylic acyl-CoAs, which are produced from the β-oxidation of dicarboxylic fatty acids. We also show that, under conditions of elevated synthesis of chenodeoxycholic acid derivatives, Nudt7 deletion promotes the production of tauromuricholic acid, decreasing the hydrophobicity index of the intestinal bile acid pool and increasing fecal cholesterol excretion in male mice. These findings reveal that NUDT7-mediated hydrolysis of acyl-CoA pathway intermediates in liver peroxisomes contributes to the regulation of dicarboxylic fatty acid metabolism and the composition of the bile acid pool.

Silibinin protects against sepsis and septic myocardial injury in an NR1H3-dependent pathway

Cardiac dysfunction resulting from sepsis causes high morbidity and mortality. Silibinin (SIL) is a secondary metabolite isolated from the seed extract of the milk thistle plant with various properties, including anti-inflammatory, anti-fibrotic, and anti-oxidative activities. This study, for the first time, examined the effects and mechanisms of SIL pretreatment, posttreatment and in combination with classical antibiotics in septic myocardial injury. The survival rate, sepsis score, anal temperature, routine blood parameters, blood biochemical parameters, cardiac function indicators, pathological indicators of myocardial injury, NR1H3 signaling pathway, and several sepsis-related signaling pathways were detected 8 h following cecal ligation and puncture (CLP). Our results showed that SIL pretreatment showed a significant protective effect on sepsis and septic myocardial injury, which was explained by the attenuation of inflammation, inhibition of oxidative stress, improvement of mitochondrial function, regulation of endoplasmic reticulum stress (ERS), and activation of the NR1H3 pathway. SIL posttreatment and the combination of SIL and azithromycin (AZI) showed a certain therapeutic effect. RNA-seq detection further clarified the myocardial protective mechanisms of SIL. Taken together, this study provides a theoretical basis for the application strategy and combination of SIL in septic myocardial injury.

Cholesterol-Lowering Phytochemicals: Targeting the Mevalonate Pathway for Anticancer Interventions

There are a plethora of cancer causes and the road to fully understanding the carcinogenesis process remains a dream that keeps changing. However, a list of role players that are implicated in the carcinogens process is getting lengthier. Cholesterol is known as bad sterol that is heavily linked with cardiovascular diseases; however, it is also comprehensively associated with carcinogenesis. There is an extensive list of strategies that have been used to lower cholesterol; nevertheless, the need to find better and effective strategies remains vastly important. The role played by cholesterol in the induction of the carcinogenesis process has attracted huge interest in recent years. Phytochemicals can be dubbed as magic tramp cards that humans could exploit for lowering cancer-causing cholesterol. Additionally, the mechanisms that are regulated by phytochemicals can be targeted for anticancer drug development. One of the key role players in cancer development and suppression, Tumour Protein 53 (TP53), is crucial in regulating the biogenesis of cholesterol and is targeted by several phytochemicals. This minireview covers the role of p53 in the mevalonate pathway and how bioactive phytochemicals target the mevalonate pathway and promote p53-dependent anticancer activities.

Review of in silico studies dedicated to the nuclear receptor family: Therapeutic prospects and toxicological concerns

Being in the center of both therapeutic and toxicological concerns, NRs are widely studied for drug discovery application but also to unravel the potential toxicity of environmental compounds such as pesticides, cosmetics or additives. High throughput screening campaigns (HTS) are largely used to detect compounds able to interact with this protein family for both therapeutic and toxicological purposes. These methods lead to a large amount of data requiring the use of computational approaches for a robust and correct analysis and interpretation. The output data can be used to build predictive models to forecast the behavior of new chemicals based on their in vitro activities. This atrticle is a review of the studies published in the last decade and dedicated to NR ligands in silico prediction for both therapeutic and toxicological purposes. Over 100 articles concerning 14 NR subfamilies were carefully read and analyzed in order to retrieve the most commonly used computational methods to develop predictive models, to retrieve the databases deployed in the model building process and to pinpoint some of the limitations they faced.

Apolipoprotein and LRP1-Based Peptides as New Therapeutic Tools in Atherosclerosis

Apolipoprotein (Apo)-based mimetic peptides have been shown to reduce atherosclerosis. Most of the ApoC-II and ApoE mimetics exert anti-atherosclerotic effects by improving lipid profile. ApoC-II mimetics reverse hypertriglyceridemia and ApoE-based peptides such as Ac-hE18A-NH2 reduce cholesterol and triglyceride (TG) levels in humans. Conversely, other classes of ApoE and ApoA-I mimetic peptides and, more recently, ApoJ and LRP1-based peptides, exhibit several anti-atherosclerotic actions in experimental models without influencing lipoprotein profile. These other mimetic peptides display at least one atheroprotective mechanism such as providing LDL stability against mechanical modification or conferring protection against the action of lipolytic enzymes inducing LDL aggregation in the arterial intima. Other anti-atherosclerotic effects exerted by these peptides also include protection against foam cell formation and inflammation, and induction of reverse cholesterol transport. Although the underlying mechanisms of action are still poorly described, the recent findings suggest that these mimetics could confer atheroprotection by favorably influencing lipoprotein function rather than lipoprotein levels. Despite the promising results obtained with peptide mimetics, the assessment of their stability, atheroprotective efficacy and tissue targeted delivery are issues currently under progress.

Compounds targeting OSBPL7 increase ABCA1-dependent cholesterol efflux preserving kidney function in two models of kidney disease

Impaired cellular cholesterol efflux is a key factor in the progression of renal, cardiovascular, and autoimmune diseases. Here we describe a class of 5-arylnicotinamide compounds, identified through phenotypic drug discovery, that upregulate ABCA1-dependent cholesterol efflux by targeting Oxysterol Binding Protein Like 7 (OSBPL7). OSBPL7 was identified as the molecular target of these compounds through a chemical biology approach, employing a photoactivatable 5-arylnicotinamide derivative in a cellular cross-linking/immunoprecipitation assay. Further evaluation of two compounds (Cpd A and Cpd G) showed that they induced ABCA1 and cholesterol efflux from podocytes in vitro and normalized proteinuria and prevented renal function decline in mouse models of proteinuric kidney disease: Adriamycin-induced nephropathy and Alport Syndrome. In conclusion, we show that small molecule drugs targeting OSBPL7 reveal an alternative mechanism to upregulate ABCA1, and may represent a promising new therapeutic strategy for the treatment of renal diseases and other disorders of cellular cholesterol homeostasis.

Untangling the Cooperative Role of Nuclear Receptors in Cardiovascular Physiology and Disease

The heart is the first organ to acquire its physiological function during development, enabling it to supply the organism with oxygen and nutrients. Given this early commitment, cardiomyocytes were traditionally considered transcriptionally stable cells fully committed to contractile function. However, growing evidence suggests that the maintenance of cardiac function in health and disease depends on transcriptional and epigenetic regulation. Several studies have revealed that the complex transcriptional alterations underlying cardiovascular disease (CVD) manifestations such as myocardial infarction and hypertrophy is mediated by cardiac retinoid X receptors (RXR) and their partners. RXRs are members of the nuclear receptor (NR) superfamily of ligand-activated transcription factors and drive essential biological processes such as ion handling, mitochondrial biogenesis, and glucose and lipid metabolism. RXRs are thus attractive molecular targets for the development of effective pharmacological strategies for CVD treatment and prevention. In this review, we summarize current knowledge of RXR partnership biology in cardiac homeostasis and disease, providing an up-to-date view of the molecular mechanisms and cellular pathways that sustain cardiomyocyte physiology.

LXR-Mediated Regulation of Marine-Derived Piericidins Aggravates High-Cholesterol Diet-Induced Cholesterol Metabolism Disorder in Mice

Reported as two antirenal cell carcinoma (RCC) drug candidates, marine-derived compounds piericidin A (PA) and glucopiericidin A (GPA) exhibit hepatotoxicity in renal carcinoma xenograft mice. Proteomics and transcriptomics reveal the hepatotoxicity related with cholesterol disposition since RCC is characterized by cholesterol accumulation. PA/GPA aggravate hepatotoxicity in high-cholesterol diet (HCD)-fed mice while exhibiting no toxicity in chow diet-fed mice. High cholesterol accumulation in liver is liver X receptor (LXR)-mediated cytochrome P450 family 7 subfamily a member 1 (CYP7A1) depression and low-density lipoprotein receptor (LDLR) activation. The farnesoid X nuclear receptor (FXR) is also depressed with a downregulated target gene OSTα. Different from PA directly combined with LXRα as an inhibitor, GPA exists as a prodrug in the liver and exerts toxic effects due to transformation into PA. Surface plasmon resonance (SPR) and docking results of 17 piericidins illustrate that glycosides exert no LXRα binding activity. A longer survival time of GPA-treated mice indicates that further exploration in anti-RCC drug research should focus on reducing glycosides transformed into PA and concentrating in the kidney tumor rather than the liver for lowering the risk of hepatotoxicity.

Liver X receptors conserve the therapeutic target potential for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic multi-system autoimmune disease with extremely complex pathogenesis. Significantly altered lipid paradox related to the inflammatory burden is reported in RA patients, inducing 50% higher cardiovascular risks. Recent studies have also demonstrated that lipid metabolism can regulate many functions of immune cells in which metabolic pathways have altered. The nuclear liver X receptors (LXRs), including LXRα and LXRβ, play a central role in regulating lipid homeostasis and inflammatory responses. Undoubtedly, LXRs have been considered as an attractive therapeutic target for the treatment of RA. However, there are some contradictory effects of LXRs agonists observed in previous animal studies where both pro-inflammatory role and anti-inflammatory role were revealed for LXRs activation in RA. Therefore, in addition to updating the knowledge of LXRs as the prominent regulators of lipid homeostasis, the purpose of this review is to summarize the effects of LXRs agonists in RA-associated immune cells, to explore the underlying reasons for the contradictory therapeutic effects of LXRs agonists observed in RA animal models, and to discuss future strategy for the treatment of RA with LXRs modulators.

Food Chemistry of Selenium and Controversial Roles of Selenium in Affecting Blood Cholesterol Concentrations

Hypercholesterolemia, one of the major risk factors of cardiovascular diseases, is a worldwide public health problem. Nutraceuticals and phytochemicals are attracting attention as a result of their cholesterol-lowering ability and minimal side effects. Among them, selenium (Se) is on the list. The amount of Se in foods varies by region. Se-enriched fertilizers and feeds can raise the Se content in plants and animals, while some processing methods decrease food Se content. This review summarizes recent studies on (1) the content distribution of Se in foods and factors influencing Se-enriched foods, (2) the bioavailability and metabolism of Se, and (3) the role of Se in affecting blood cholesterol and cholesterol metabolism. Although the hypocholesterolemic effect of Se is equivocal, its cholesterol-lowering activity may be more remarkable when the Se supplementation is 200 μg/day or the baseline blood total cholesterol is above 200 mg/dL in humans with low Se status.

Liver X receptors and skeleton: Current state-of-knowledge

The liver X receptors (LXR) is a nuclear receptor that acts as a prominent regulator of lipid homeostasis and inflammatory response. Its therapeutic effectiveness against various diseases like Alzheimer's disease and atherosclerosis has been investigated in detail. Emerging pieces of evidence now reveal that LXR is also a crucial modulator of bone remodeling. However, the molecular mechanisms underlying the pharmacological actions of LXR on the skeleton and its role in osteoporosis are poorly understood. Therefore, in the current review, we highlight LXR and its actions through different molecular pathways modulating skeletal homeostasis. The studies described in this review propound that LXR in association with estrogen, PTH, PPARγ, RXR hedgehog, and canonical Wnt signaling regulates osteoclastogenesis and bone resorption. It regulates RANKL-induced expression of c-Fos, NFATc1, and NF-κB involved in osteoclast differentiation. Additionally, several studies suggest suppression of RANKL-induced osteoclast differentiation by synthetic LXR ligands. Given the significance of modulation of LXR in various physiological and pathological settings, our findings indicate that therapeutic targeting of LXR might potentially prevent or treat osteoporosis and improve bone quality.

Synthetic high-density lipoproteins delivering liver X receptor agonist prevent atherogenesis by enhancing reverse cholesterol transport

Liver X nuclear receptor (LXR) agonists are promising anti-atherosclerotic agents that increase the expression of cholesterol transporters on atheroma macrophages leading to increased efflux of cholesterol to endogenous high-density lipoprotein (HDL) acceptors. HDL subsequently delivers effluxed cholesterol to the liver by the process of reverse cholesterol transport, resulting in reduction of atherosclerotic plaques. However, LXR agonists administration triggers undesirable liver steatosis and hypertriglyceridemia due to increased fatty acid and sterol synthesis. LXR-induced liver toxicity, poor drug aqueous solubility and low levels of endogenous HDL acceptors in target patient populations limit the clinical translation of LXR agonists. Here, we propose a dual-antiatherogenic strategy for administration of the LXR agonist, T0901317 (T1317), by encapsulating in synthetic HDL (sHDL) nanoparticles. sHDL had been clinically proven to serve as cholesterol acceptors, resulting in plaque reduction in atherosclerosis patients. In addition, the hydrophobic core and endogenous atheroma-targeting ability of sHDL allow for encapsulation of water-insoluble drugs and their subsequent delivery to atheroma. Several compositions of sHDL were tested to optimize both T1317 encapsulation efficiency and ability of T1317-sHDL to efflux cholesterol. Optimized T1317-sHDL exhibited more efficient cholesterol efflux from macrophages and enhanced atheroma-targeting relative to free drug. Most importantly, in an apolipoprotein E deficient (ApoE-/-) atherosclerosis progression murine model, T1317-sHDL showed superior inhibition of atherogenesis and reduced hypertriglyceridemia side effects in comparison to the free drug and blank sHDL. The T1317-sHDL pharmacological efficacy was observed at doses lower than those previously described for LXR agents, which may have additional safety benefits. In addition, the established clinical manufacturing, safety and efficacy of blank sHDL nanoparticles used in this study could facilitate future clinical translation of LXR-loaded sHDLs.

The roles of liver X receptor α in inflammation and inflammation-associated diseases

Liver X receptor α (LXRα; also known as NR1H3), an isoform of LXRs, is a member of the nuclear receptor family of transcription factors and plays essential roles in the transcriptional control of cholesterol homeostasis. Previous in-depth phenotypic analyses of mouse models with deficient LXRα have also demonstrated various physiological functions of this receptor within inflammatory responses. LXRα activation exerts a combination of metabolic and anti-inflammatory actions resulting in the modulation and the amelioration of inflammatory disorders. The tight "repercussions" between LXRα and inflammation, as well as cholesterol homeostasis, have suggested that LXRα could be pharmacologically targeted in pathologies such as atherosclerosis, acute lung injury, and Alzheimer's disease. This review gives an overview of the recent advances in understanding the roles of LXRα in inflammation and inflammation-associated diseases, which will help in the design of future experimental researches on the potential of LXRα and advance the investigation of LXRα as pharmacological inflammatory targets.

Interferon-γ decreases ATP-binding cassette subfamily G member 1-mediated cholesterol efflux through small ubiquitin-like modifier/ubiquitin-dependent liver X receptor-α degradation in macrophages

The effects of interferon-γ (IFN-γ) on cholesterol accumulation and the development of foam cells are still unclear. In the present study, we found that IFN-γ promoted liver X receptor (LXR)-α degradation through the ubiquitin-proteasome system in macrophages. The process was dependent on its interactions with phosphorylated signal transducer and activator of transcription 1 (p-STAT1) and protein inhibitor of activated STAT 1 (PIAS1) because both fludarabine and PIAS1 shRNA reversed the decrease in LXR-α protein expression induced by IFN-γ. Additionally, IFN-γ enhanced the interactions of ubiquitin-conjugating enzyme 9 (UBC9), small ubiquitin-like modifier (SUMO)-1 and SUMO-2/3 with LXR-α. Moreover, treatment with shRNA specific for them not only reduced LXR-α polyubiquitination but also reversed the IFN-γ-induced decrease in its expression. Two specific sumoylation sites in LXR-α, K22 and K326, were indispensable for its IFN-γ-induced polyubiquitination because the K22R and K326R mutations inhibited the polyubiquitination and degradation of LXR-α in IFN-γ-treated macrophages. In addition, K22R or K326R mutation almost completely restored ATP-binding cassette subfamily G member 1 (ABCG1)-mediated cholesterol efflux in IFN-γ-treated macrophages. Taken together, these findings indicate that IFN-γ promotes LXR-α degradation through a SUMO-ubiquitin-dependent pathway, which may inhibit cholesterol efflux mediated by ABCG1 from macrophages and promote the development of atherosclerosis.

Oilseed crop sunflower (Helianthus annuus) as a source of food: Nutritional and health benefits

The use of biofertilizers in developing environmentally friendly agriculture as an alternative to chemical-based fertilizers in enhancing food production is promising in sustainable agriculture for the improvement in the yield of some commercial crops such as sunflowers and other oilseed crops in terms of quality and quantity. Sunflower is an important oilseed crop native to South America and currently cultivated throughout the world. Generally, the sunflower is considered important based on its nutritional and medicinal value. Due to its beneficial health effects, sunflower has been recognized as functional foods or nutraceutical, although not yet fully harnessed. Sunflower contains mineral elements and phytochemicals such as dietary fiber, manganese, vitamins, tocopherols, phytosterols, triterpene glycosides, α-tocopherol, glutathione reductase, flavonoids, phenolic acids, carotenoids, peptides, chlorogenic acid, caffeic acid, alkaloids, tannins, and saponins; and these compounds contribute to their functional and nutraceutical development. The extract from sunflower is known to be a potential source of antimicrobial, anti-inflammatory, antitumor, and antioxidants agents that protect human cells against harmful reactive oxygen molecules and pathogenic microorganisms. Also, the pharmacological survey on sunflower had revealed its curative power to different kinds of diseases. The health benefits of sunflower include blood pressure and diabetic control, skin protection, and lowering cholesterol and other functions. This review is written with appropriate referencing to previously published work and provides updated information regarding the new method of organic farming for sunflower production, nutritional and health benefits, and its by-products as human diet and livestock feed. Also, the constraints of sunflower production are elucidated.

Identifying new liver X receptor alpha modulators and distinguishing between agonists and antagonists by crystal ligand pocket screening

Background: Modulators of LXRα are of high pharmacological interest as LXRα regulates fatty acid metabolism, inflammatory processes and cancer. We aim to identify new LXRα modulators and to recognize a distinguishable feature of agonists. Results&methodology: The ligand self-dock and largest-cavity-size searching purposely located two appropriate ligand-binding sites to reach the two aims. One is identifying the new modulators from Maybridge library. 20 new compounds are confirmed by the in vitro reporter gene assay. The other is denoting an agonist by at least one best docking pose having one hydrogen bond to LXRα Helix12 His421. Conclusion: Based on the quality x-ray binding pocket, we can identify new LXRα modulators and distinguish between agonists and antagonists by molecular docking.

Hepatic Transporter Alterations by Nuclear Receptor Agonist T0901317 in Sandwich-Cultured Human Hepatocytes: Proteomic Analysis and PBPK Modeling to Evaluate Drug-Drug Interaction Risk

In vitro approaches for predicting drug-drug interactions (DDIs) caused by alterations in transporter protein regulation are not well established. However, reports of transporter regulation via nuclear receptor (NR) modulation by drugs are increasing. This study examined alterations in transporter protein levels in sandwich-cultured human hepatocytes (SCHH; n = 3 donors) measured by liquid chromatography-tandem mass spectrometry-based proteomic analysis after treatment with N-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenyl]-N-(2,2,2-trifluoroethyl)benzenesulfonamide (T0901317), the first described synthetic liver X receptor agonist. T0901317 treatment (10 μM, 48 hours) decreased the levels of organic cation transporter (OCT) 1 (0.22-, 0.43-, and 0.71-fold of control) and organic anion transporter (OAT) 2 (0.38-, 0.38-, and 0.53-fold of control) and increased multidrug resistance protein (MDR) 1 (1.37-, 1.48-, and 1.59-fold of control). The induction of NR downstream gene expression supports the hypothesis that T0901317 off-target effects on farnesoid X receptor and pregnane X receptor activation are responsible for the unexpected changes in OCT1, OAT2, and MDR1. Uptake of the OCT1 substrate metformin in SCHH was decreased by T0901317 treatment. Effects of decreased OCT1 levels on metformin were simulated using a physiologically-based pharmacokinetic (PBPK) model. Simulations showed a clear decrease in metformin hepatic exposure resulting in a decreased pharmacodynamic effect. This DDI would not be predicted by the modest changes in simulated metformin plasma concentrations. Altogether, the current study demonstrated that an approach combining SCHH, proteomic analysis, and PBPK modeling is useful for revealing tissue concentration-based DDIs caused by unexpected regulation of hepatic transporters by NR modulators. SIGNIFICANCE STATEMENT: This study utilized an approach combining sandwich-cultured human hepatocytes, proteomic analysis, and physiologically based pharmacokinetic modeling to evaluate alterations in pharmacokinetics (PK) and pharmacodynamics (PD) caused by transporter regulation by nuclear receptor modulators. The importance of this approach from a mechanistic and clinically relevant perspective is that it can reveal drug-drug interactions (DDIs) caused by unexpected regulation of hepatic transporters and enable prediction of altered PK and PD changes, especially for tissue concentration-based DDIs.

Nuclear receptors in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) pose a considerable health burden and at present are only managed surgically since there is no proven pharmacotherapy that will retard their expansion or reduce the incidence of fatal rupture. This pathology shares several pathophysiological mechanisms with atherosclerosis, such as macrophage infiltration, inflammation, and degradation of extracellular matrix. Therefore, therapeutic targets proven effective in the treatment of atherosclerosis could also be considered for treatment of AAA. Different members of the nuclear receptor (NR) superfamily have been extensively studied as potential targets in the treatment of cardiovascular disease (CVD) and therefore might also be suited for AAA treatment. In this context, this review summarizes the role of different NRs in CVD, mostly atherosclerosis, and discusses in detail the current knowledge of their implications in AAA. From this overview it becomes apparent that NRs that were attributed a beneficial or adverse role in CVD have similar roles in AAA. Together, this overview provides compelling evidence to consider several NRs as attractive targets for future treatment of AAA.

LXRs regulate features of age-related macular degeneration and may be a potential therapeutic target

Effective treatments and animal models for the most prevalent neurodegenerative form of blindness in elderly people, called age-related macular degeneration (AMD), are lacking. Genome-wide association studies have identified lipid metabolism and inflammation as AMD-associated pathogenic pathways. Given liver X receptors (LXRs), encoded by the nuclear receptor subfamily 1 group H members 2 and 3 (NR1H3 and NR1H2), are master regulators of these pathways, herein we investigated the role of LXR in human and mouse eyes as a function of age and disease and tested the therapeutic potential of targeting LXR. We identified immunopositive LXR fragments in human extracellular early dry AMD lesions and a decrease in LXR expression within the retinal pigment epithelium (RPE) as a function of age. Aged mice lacking LXR presented with isoform-dependent ocular pathologies. Specifically, loss of the Nr1h3 isoform resulted in pathobiologies aligned with AMD, supported by compromised visual function, accumulation of native and oxidized lipids in the outer retina, and upregulation of ocular inflammatory cytokines, while absence of Nr1h2 was associated with ocular lipoidal degeneration. LXR activation not only ameliorated lipid accumulation and oxidant-induced injury in RPE cells but also decreased ocular inflammatory markers and lipid deposition in a mouse model, thereby providing translational support for pursuing LXR-active pharmaceuticals as potential therapies for dry AMD.

Differences in microRNA-29 and Pro-fibrotic Gene Expression in Mouse and Human Hypertrophic Cardiomyopathy

Background: Hypertrophic cardiomyopathy (HCM) is characterized by myocyte hypertrophy and fibrosis. Studies in two mouse models (R92W-TnT/R403Q-MyHC) at early HCM stage revealed upregulation of endothelin (ET1) signaling in both mutants, but TGFβ signaling only in TnT mutants. Dysregulation of miR-29 expression has been implicated in cardiac fibrosis. But it is unknown whether expression of miR-29a/b/c and profibrotic genes is commonly regulated in mouse and human HCM.

Methods: In order to understand mechanisms underlying fibrosis in HCM, and examine similarities/differences in expression of miR-29a/b/c and several profibrotic genes in mouse and human HCM, we performed parallel studies in rat cardiac myocyte/fibroblast cultures, examined gene expression in two mouse models of (non-obstructive) HCM (R92W-TnT, R403Q-MyHC)/controls at early (5 weeks) and established (24 weeks) disease stage, and analyzed publicly available mRNA/miRNA expression data from obstructive-HCM patients undergoing septal myectomy/controls (unused donor hearts).

Results: Myocyte cultures: ET1 increased superoxide/H₂O₂, stimulated TGFβ expression/secretion, and suppressed miR-29a expression in myocytes. The effect of ET1 on miR-29 and TGFβ expression/secretion was antagonized by N-acetyl-cysteine, a reactive oxygen species scavenger. Fibroblast cultures: ET1 had no effect on pro-fibrotic gene expression in fibroblasts. TGFβ1/TGFβ2 suppressed miR-29a and increased collagen expression, which was abolished by miR-29a overexpression. Mouse and human HCM: Expression of miR-29a/b/c was lower, and TGFB1/collagen gene expression was higher in TnT mutant-LV at 5 and 24 weeks; no difference was observed in expression of these genes in MyHC mutant-LV and in human myectomy tissue. TGFB2 expression was higher in LV of both mutant mice and human myectomy tissue. ACE2, a negative regulator of the renin-angiotensin-aldosterone system, was the most upregulated transcript in human myectomy tissue. Pathway analysis predicted upregulation of the anti-hypertrophic/anti-fibrotic liver X receptor/retinoid X receptor (LXR/RXR) pathway only in human myectomy tissue.

Conclusions: Our in vitro studies suggest that activation of ET1 signaling in cardiac myocytes increases reactive oxygen species and stimulates TGFβ secretion, which downregulates miR-29a and increases collagen in fibroblasts, thus contributing to fibrosis. Our gene expression studies in mouse and human HCM reveal allele-specific differences in miR-29 family/profibrotic gene expression in mouse HCM, and activation of anti-hypertrophic/anti-fibrotic genes and pathways in human HCM.

Novel lipid-modifying therapies addressing unmet needs in cardiovascular disease

Cardiovascular disease (CVD) remains a major cause of morbidity and mortality worldwide. Currently, it is well established that dyslipidemia is one of the major risk factors leading to the development of atherosclerosis and CVD. Statins remain the standard-of-care in the treatment of hypercholesterolemia and their use has significantly reduced cardiovascular morbidity and mortality. In addition, recent advances in lipid-modifying therapies, such as the development of proprotein convertase subtilisin/kexin type 9 inhibitors, have further improved cardiovascular outcomes in patients with hypercholesterolemia. However, despite significant progress in the treatment of dyslipidemia, there is still considerable residual risk of recurring cardiovascular events. Furthermore, in some cases, an effective therapy for the identified primary cause of a specific dyslipidemia has not been found up to date. Thus, a number of novel pharmacological interventions are under early human trials, targeting different molecular pathways of lipid formation, regulation and metabolism. This editorial aims to discuss the current clinical and scientific data on new promising lipid-modifying therapies addressing unmet needs in CVD, which may prove beneficial in the near future.

Adenosine and the Cardiovascular System

Adenosine is an endogenous nucleoside with a short half-life that regulates many physiological functions involving the heart and cardiovascular system. Among the cardioprotective properties of adenosine are its ability to improve cholesterol homeostasis, impact platelet aggregation and inhibit the inflammatory response. Through modulation of forward and reverse cholesterol transport pathways, adenosine can improve cholesterol balance and thereby protect macrophages from lipid overload and foam cell transformation. The function of adenosine is controlled through four G-protein coupled receptors: A₁, A_2A, A_2B and A₃. Of these four, it is the A_2A receptor that is in a large part responsible for the anti-inflammatory effects of adenosine as well as defense against excess cholesterol accumulation. A_2A receptor agonists are the focus of efforts by the pharmaceutical industry to develop new cardiovascular therapies, and pharmacological actions of the atheroprotective and anti-inflammatory drug methotrexate are mediated via release of adenosine and activation of the A_2A receptor. Also relevant are anti-platelet agents that decrease platelet activation and adhesion and reduce thrombotic occlusion of atherosclerotic arteries by antagonizing adenosine diphosphate-mediated effects on the P2Y12 receptor. The purpose of this review is to discuss the effects of adenosine on cell types found in the arterial wall that are involved in atherosclerosis, to describe use of adenosine and its receptor ligands to limit excess cholesterol accumulation and to explore clinically applied anti-platelet effects. Its impact on electrophysiology and use as a clinical treatment for myocardial preservation during infarct will also be covered. Results of cell culture studies, animal experiments and human clinical trials are presented. Finally, we highlight future directions of research in the application of adenosine as an approach to improving outcomes in persons with cardiovascular disease.

Dietary Lipids Differentially Shape Nonalcoholic Steatohepatitis Progression and the Transcriptome of Kupffer Cells and Infiltrating Macrophages

A crucial component of nonalcoholic fatty liver disease (NAFLD) pathogenesis is lipid stress, which may contribute to hepatic inflammation and activation of innate immunity in the liver. However, little is known regarding how dietary lipids, including fat and cholesterol, may facilitate innate immune activation in vivo. We hypothesized that dietary fat and cholesterol drive NAFLD progression to steatohepatitis and hepatic fibrosis by altering the transcription and phenotype of hepatic macrophages. This hypothesis was tested by using RNA-sequencing methods to characterize and analyze sort-purified hepatic macrophage populations that were isolated from mice fed diets with varying amounts of fat and cholesterol. The addition of cholesterol to a high-fat diet triggered hepatic pathology reminiscent of advanced nonalcoholic steatohepatitis (NASH) in humans characterized by signs of cholesterol dysregulation, generation of oxidized low-density lipoprotein, increased recruitment of hepatic macrophages, and significant fibrosis. RNA-sequencing analyses of hepatic macrophages in this model revealed that dietary cholesterol induced a tissue repair and regeneration phenotype in Kupffer cells (KCs) and recruited infiltrating macrophages to a greater degree than fat. Furthermore, comparison of diseased KCs and infiltrating macrophages revealed that these two macrophage subsets are transcriptionally diverse. Finally, direct stimulation of murine and human macrophages with oxidized low-density lipoprotein recapitulated some of the transcriptional changes observed in the RNA-sequencing study. These findings indicate that fat and cholesterol synergize to alter macrophage phenotype, and they also challenge the dogma that KCs are purely proinflammatory in NASH. Conclusion: This comprehensive view of macrophage populations in NASH indicates mechanisms by which cholesterol contributes to NASH progression and identifies potential therapeutic targets for this common disease.

Identification of the fructose transporter GLUT5 (SLC2A5) as a novel target of nuclear receptor LXR

Fructose has become a major constituent of our modern diet and is implicated as an underlying cause in the development of metabolic diseases. The fructose transporter GLUT5 (SLC2A5) is required for intestinal fructose absorption. GLUT5 expression is induced in the intestine and skeletal muscle of type 2 diabetes (T2D) patients and in certain cancers that are dependent on fructose metabolism, indicating that modulation of GLUT5 levels could have potential in the treatment of these diseases. Using an unbiased screen for transcriptional control of the human GLUT5 promoter we identified a strong and specific regulation by liver X receptor α (LXRα, NR1H3). Using promoter truncations and site-directed mutagenesis we identified a functional LXR response element (LXRE) in the human GLUT5 promoter, located at −385 bp relative to the transcriptional start site (TSS). Finally, mice treated with LXR agonist T0901317 showed an increase in Glut5 mRNA and protein levels in duodenum and adipose tissue, underscoring the in vivo relevance of its regulation by LXR. Together, our findings show that LXRα regulates GLUT5 in mice and humans. As a ligand-activated transcription factor, LXRα might provide novel pharmacologic strategies for the selective modulation of GLUT5 activity in the treatment of metabolic disease as well as cancer.

Role of Liver X Receptor in Mastitis Therapy and Regulation of Milk Fat Synthesis

Mastitis is important disease that causes huge economic losses in the dairy industry. In recent years, antibiotic therapy has become the primary treatment for mastitis, however, due to drug residue in milk and food safety factors, we lack safe and effective drugs for treating mastitis. Therefore, new targets and drugs are urgently needed to control mastitis. LXRα, one of the main members of the nuclear receptor superfamily, is reported to play important roles in metabolism, infection and immunity. Activation of LXRα could inhibit LPS-induced mastitis. Furthermore, LXRα is reported to enhance milk fat production, thus, LXRα may serve as a new target for mastitis therapy and regulation of milk fat synthesis. This review summarizes the effects of LXRα in regulating milk fat synthesis and treatment of mastitis and highlights the potential agonists involved in both issues.

Regulation of ABCA1-mediated cholesterol efflux by sphingosine-1-phosphate signaling in macrophages

Sphingolipid and cholesterol metabolism are closely associated at the structural, biochemical, and functional levels. Although HDL-associated sphingosine-1-phosphate (S1P) contributes to several HDL functions, and S1P signaling regulates glucose and lipid metabolism, no study has addressed the involvement of S1P in cholesterol efflux. Here, we show that sphingosine kinase (Sphk) activity was induced by the LXR agonist 22(R)-hydroxycholesterol and required for the stimulation of ABCA1-mediated cholesterol efflux to apolipoprotein A-I. In support, pharmacological Sphk inhibition and Sphk2 but not Sphk1 deficiency abrogated efflux. The involved mechanism included stimulation of both transcriptional and functional ABCA1 regulatory pathways and depended for the latter on the S1P receptor 3 (S1P3). Accordingly, S1P3-deficient macrophages were resistant to 22(R)-hydroxycholesterol-stimulated cholesterol efflux. The inability of excess exogenous S1P to further increase efflux was consistent with tonic S1P3 signaling by a pool of constitutively generated Sphk-derived S1P dynamically regulating cholesterol efflux. In summary, we have established S1P as a previously unrecognized intermediate in LXR-stimulated ABCA1-mediated cholesterol efflux and identified S1P/S1P3 signaling as a positive-feedback regulator of cholesterol efflux. This constitutes a novel regulatory mechanism of cholesterol efflux by sphingolipids.

AMP-activated protein kinase sparks the fire of cardioprotection against myocardial ischemia and cardiac ageing

AMP-activated protein kinase (AMPK) is a pivotal regulator of some endogenous defensive molecules in various pathological processes, particularly myocardial ischemia (MI), a high risk of myocardial infarction. Thereby it is of great significance to explore the inherent mechanism between AMPK and myocardial infarction. In this review, we first introduce the structure and role of AMPK in the heart. Next, we introduce the mechanisms of AMPK in the heart; followed by the energy regulation of AMPK in MI. Lastly, the attention will be expanded to some potential directions and further perspectives. The information compiled here will be helpful for further research and drug design in the future before AMPK might be considered as a therapeutic target of MI.

The effects of LXR agonist GW3965 on vascular reactivity and inflammation in hypertensive rat aorta

AIMS

Liver X receptors (LXRs) play an important role in the regulation of cholesterol, fatty acid and glucose metabolisms together with inflammatory processes. In the present study, the effects of LXR agonist GW3965 on vascular reactivity and expression of functional proteins in DOCA-Salt induced hypertension were examined.

MAIN METHODS

Hypertension was induced through unilateral nephrectomy and deoxycorticosterone-acetate (DOCA) injection (20 mg/kg, twice a week) for 6 weeks in male Wistar albino rats (8 weeks old). An LXR agonist GW3965 (10 mg/kg/day, i.p.) was administered to animals for last seven days.

KEY FINDINGS

GW3965 treatment reduced systolic blood pressures in hypertensive rats. Acetylcholine-induced endothelium-dependent and sodium nitroprusside-induced endothelium-independent vasorelaxations were decreased in hypertensive rats but not affected by GW3965. GW3965 treatment enhanced plasma nitrite levels in normotensive rats. KCl and phenylephrine (Phe)-induced vasocontractions were reduced in hypertensive groups and increased with GW3965 treatment. Decreased sarco/endoplasmic reticulum Ca²⁺-ATPase2 (SERCA2) expression in the hypertensive aorta was not changed by GW3965 treatment. Expression of inositoltrisphosphate receptor1 (IP3R1) was increased by GW3965 in normotensive animals. The nuclear factor kappaB (NF-κB) and tumor necrosis factor alpha (TNF-α) expressions were increased in hypertensive rats and reduced by GW3965 treatment.

SIGNIFICANCE

The results of study indicate that the LXR agonist, GW3965, exhibited a beneficial effect on increased blood pressure and improved hypertension-induced impairment in contractile activity of vessel and inflammatory markers in vascular tissue. Therefore, these effects of LXR agonists on vessel should be taken into account in experimental or therapeutic approaches to hypertension.

Role of SREBPs in Liver Diseases: A Mini-review

Sterol regulator element binding proteins (SREBPs) are a family of transcription factors involved in the biogenesis of cholesterol, fatty acids and triglycerides. They also regulate physiological functions of many organs, such as thyroid, brain, heart, pancreas and hormone synthesis. Beside the physiological effects, SREBPs participate in some pathological processes, diabetes, endoplasmic reticulum stress, atherosclerosis and chronic kidney disease associated with SREBP expression changes. In the liver, SREBPs are involved in the pathogenesis of nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, hepatitis and hepatic cancer. There are several SREBP inhibitors that have potential for treating obesity, diabetes and cancer. This review assesses the recent findings about the roles of SREBPs in the physiology of organs' function and pathogenesis of liver diseases.

Maternal fructose induces gender-dependent changes in both LXRα promoter methylation and cholesterol metabolism in progeny

Fructose consumption from added sugars correlates with the epidemic rise in obesity, metabolic syndrome and cardiovascular diseases. However, consumption of beverages containing fructose is allowed during gestation. We have investigated whether maternal fructose intake produces subsequent changes in cholesterol metabolism of progeny. Carbohydrates were supplied to pregnant rats in drinking water (10% w/v solution) throughout gestation. Adult male and female descendants from fructose-fed, control or glucose-fed mothers were studied. Male offspring from fructose-fed mothers had elevated plasma HDL-cholesterol levels, whereas female progeny from fructose-fed mothers presented lower levels of non-HDL cholesterol vs. the other two groups. Liver X-receptor (LXR), an important regulator of cholesterol metabolism, and its target genes such as scavenger receptor B1, ATP-binding cassette (ABC)G5 and cholesterol 7-alpha hydroxylase showed decreased gene expression in males from fructose-fed mothers and the opposite in the female progeny. Moreover, the expression of a number of LXRα target genes related to lipogenesis paralleled to that for LXRα expression. In accordance with this, LXRα gene promoter methylation was increased in males from fructose-fed mothers and decreased in the corresponding group of females. Surprisingly, plasma folic acid levels, an important methyl-group donor, were augmented in males from fructose-fed mothers and diminished in female offspring. Maternal fructose intake produces a fetal programming that influences, in a gender-dependent manner, the transcription factor LXRα epigenetically, and both hepatic mRNA gene expression and plasma parameters of cholesterol metabolism in adult progeny. Changes in the LXRα promoter methylation might be related to the availability of the methyl donor folate.

Effects of a combined intervention with a lentil protein hydrolysate and a mixed training protocol on the lipid metabolism and hepatic markers of NAFLD in Zucker rats

Metabolic syndrome is a cluster of metabolic alterations characterized by central obesity, dyslipidemia, elevated plasma glucose, insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD). In this study, a combined intervention of a lentil protein hydrolysate and a mixed training protocol was assessed in an animal experimental model of genetic obesity and metabolic syndrome. Thirty-two male obese and 32 lean Zucker rats were divided into eight different experimental groups. Rats performed a mixed exercise protocol or had a sedentary lifestyle and were administered a lentil protein hydrolysate or placebo. Daily food intake, weekly body weight gain, plasma parameters of glucose and lipid metabolisms, body composition, hepatic weight, total fat content and fatty acid profile, as well as gene expression of lipogenic and lipolytic nuclear transcription factors and their target genes were measured. Obese Zucker rats exhibited higher body and liver weight and fat content than did their lean counterparts. Such alterations were related to modifications in aerobic capacity, plasma biochemical parameters of glucose and lipid metabolisms, hepatic fatty acid profile and gene expression of nuclear transcription factors SREBP1c, PPARα, LXR and associated lipogenic and lipolytic enzymes. The interventions tested did not affect body weight gain but improved aerobic capacity, reduced hepatomegalia and steatosis associated with NAFLD and relieved the adverse effects produced by this condition in glucose and lipid metabolisms through the modulation in the expression of different genes involved in diverse metabolic pathways.

Lipid reducing activity of novel cholic acid (CA) analogs: Design, synthesis and preliminary mechanism study

Bile acids, initially discovered as endogenous ligands of farnesoid X receptor (FXR), play a central role in the regulation of triglyceride and cholesterol metabolism and have recently emerged as a privileged structure for interacting with nuclear receptors relevant to a large array of metabolic processes. In this paper, phenoxy containing cholic acid derivatives with excellent drug-likeness have been designed, synthesized, and assayed as agents against cholesterol accumulation in Raw264.7 macrophages. The most active compound 14b reduced total cholesterol accumulation in Raw264.7 cells up to 30.5% at non-toxic 10 μM and dosage-dependently attenuated oxLDL-induced foam cell formation. Western blotting and qPCR results demonstrate that 14b reduced both cholesterol and lipid in Raw264.7 cells through (1) increasing the expression of cholesterol transporters ABCA1 and ABCG1, (2) accelerating ApoA1-mediated cholesterol efflux. Through a cell-based luciferase reporter assay and molecular docking analysis, LXR was identified as the potential target for 14b. Interestingly, unlike conventional LXR agonist, 14b did not increase lipogenesis gene SREBP-1c expression. Overall, these diverse properties disclosed herein highlight the potential of 14b as a promising lead for further development of multifunctional agents in the therapy of cardiovascular disease.

Downregulation of microRNA-1 attenuates glucose-induced apoptosis by regulating the liver X receptor α in cardiomyocytes

Diabetic cardiomyopathy (DCM) is characterized by abnormal myocardial structure or performance. It has been suggested that microRNA-1 (miR-1) may be abnormally expressed in the hearts of patients with diabetes. In the present study, the role of miR-1 in glucose-induced apoptosis and its underlying mechanism of action was investigated in rat cardiomyocyte H9C2 cells. Cells were transfected with anti-miR-1 or miR-1-overexpression plasmids and the expression of miR-1 and liver X receptor α (LXRα) were determined by reverse transcription-quantitative polymerase chain reaction analysis. The proportion of apoptotic cells was determined using an Annexin-V-FITC apoptosis detection kit and the mitochondrial membrane potential (ΔΨ) was measured following staining with rhodamine 123. In addition, the expression of apoptosis-associated proteins was measured by western blot analysis. The results demonstrated that expression of miR-1 was significantly increased, whereas the expression of LXRα was significantly decreased in H9C2 cells following treatment with glucose. miR-1 knockdown significantly inhibited apoptosis, increased the ΔΨ and suppressed the cleavage of poly (adenosine diphosphate-ribose) polymerase, caspase-3 and caspase-9. It also significantly downregulated the expression of Bcl-2 and upregulated the expression of Bax. In addition, it was demonstrated that miR-1 regulates LXRα; transfection with anti-miR-1 significantly increased the expression of LXRα. Furthermore, treatment of cells with the LXR agonist GW3965 inhibited apoptosis in glucose-induced anti-miR-1 cells. These results suggest a novel function of miR-1: The regulation of cardiomyocyte apoptosis via LXRα, and provide novel insights into regarding the complex mechanisms involved in DCM.

Identfication of Potent LXRβ-Selective Agonists without LXRα Activation by In Silico Approaches

Activating Liver X receptors (LXRs) represents a promising therapeutic option for dyslipidemia. However, activating LXRα may cause undesired lipogenic effects. Discovery of highly LXRβ-selective agonists without LXRα activation were indispensable for dyslipidemia. In this study, in silico approaches were applied to develop highly potent LXRβ-selective agonists based on a series of newly reported 3-(4-(2-propylphenoxy)butyl)imidazolidine-2,4-dione-based LXRα/β dual agonists. Initially, Kohonen and stepwise multiple linear regression SW-MLR were performed to construct models for LXRβ agonists and LXRα agonists based on the structural characteristics of LXRα/β dual agonists, respectively. The obtained LXRβ agonist model gave a good predictive ability (R²_train = 0.837, R²_test = 0.843, Q²_LOO = 0.715), and the LXRα agonist model produced even better predictive ability (R²_train = 0.968, R²_test = 0.914, Q²_LOO = 0.895). Also, the two QSAR models were independent and can well distinguish LXRβ and LXRα activity. Then, compounds in the ZINC database met the lower limit of structural similarity of 0.7, compared to the 3-(4-(2-propylphenoxy)butyl)imidazolidine-2,4-dione scaffold subjected to our QSAR models, which resulted in the discovery of ZINC55084484 with an LXRβ prediction value of pEC₅₀ equal to 7.343 and LXRα prediction value of pEC₅₀ equal to −1.901. Consequently, nine newly designed compounds were proposed as highly LXRβ-selective agonists based on ZINC55084484 and molecular docking, of which LXRβ prediction values almost exceeded 8 and LXRα prediction values were below 0.