Nuclear receptor regulation of cholesterol and bile acid metabolism

Transcriptome analysis of macrophages during Brucella abortus infection clarifies the survival mechanisms of the bacteria

Brucellosis is a critical zoonotic disease impacting humans and animals globally, causing symptoms like fever and arthritis in humans and reproductive issues in animals. The disease stems from the Brucella genus, adept at evading the immune system and proliferating within host cells. This study explores how Brucella abortus manipulates host cellular mechanisms to sustain infection, focusing on the interaction with murine macrophages over 24 h. Initial host defenses involve innate immune responses, while Brucella's survival strategies include evading lysosomal degradation and modulating host cell functions through various pathways. The research identified significant transcriptional changes in macrophages post-infection, highlighting pathways such as cytokine storm, pyroptosis signaling, Toll-like receptor pathways, and LXRs/RXRs signaling. The findings shed light on Brucella's complex mechanisms to undermine host defenses and underscore the need for further investigation into therapeutic targets to combat brucellosis.

Comprehensive bibliometric and visualized analysis of research on gut-liver axis published from 1998 to 2022

Background

The concept of the gut-liver axis was proposed by Marshall in 1998, and since then, this hypothesis has been gradually accepted by the academic community. Many publications have been published on the gut-liver axis, making it important to assess the scientific implications of these studies and the trends in this field.

Methods

Publications were retrieved from the Web of Science Core Collection. Microsoft Excel, CiteSpace, VOSviewer, and Scimago Graphica software were used for bibliometric analysis.

Results

A total of 776 publications from the Web of Science core database were included in this study. In the past 25 years, the number of publications on the gut-liver axis has shown an upward trend, particularly in the past 3 years (2020-2022). China had the highest number of publications (267 articles, 34.4%). However, the United States was at the top regarding influence and international cooperation in this field. The University of California San Diego had contributed the most publications. Suk, Ki Tae and Schnabl, Bernd were tied for the first rank in most publications. Thematic hotspots and frontiers were focused on gut microbiota, microbial metabolite, intestinal permeability, bacterial translocation, bile acid, non-alcoholic steatohepatitis, and alcoholic liver disease.

Conclusion

Our study is the first bibliometric analysis of literature using visualization software to present the current research status of the gut-liver axis over the past 25 years. The damage and repair of intestinal barrier function, as well as the disruption of gut microbiota and host metabolism, should be a focus of attention. This study can provide a reference for later researchers to understand the global research trends, hotspots, and frontiers in this field.

Oncogenic role of an uncharacterized cold-induced zinc finger protein 726 in breast cancer

The unobtrusive cold environmental temperature can be linked to the development of cancer. This study, for the first time, envisaged cold stress-mediated induction of a zinc finger protein 726 (ZNF726) in breast cancer. However, the role of ZNF726 in tumorigenesis has not been defined. This study investigated the putative role of ZNF726 in breast cancer tumorigenic potency. Gene expression analysis using multifactorial cancer databases predicted overexpression of ZNF726 in various cancers, including breast cancer. Experimental observations found that malignant breast tissues and highly aggressive MDA-MB-231 cells showed an elevated ZNF726 expression as compared to benign and luminal A type (MCF-7), respectively. Furthermore, ZNF726 silencing decreased breast cancer cell proliferation, epithelial-mesenchymal transition, and invasion accompanied by the inhibition of colony-forming ability. Concordantly, ZNF726 overexpression significantly demonstrated opposite outcomes than ZNF726 knockdown. Taken together, our findings propose cold-inducible ZNF726 as a functional oncogene demonstrating its prominent role in facilitating breast tumorigenesis. An inverse correlation between environmental temperature and total serum cholesterol was observed in the previous study. Furthermore, experimental outcomes illustrate that cold stress elevated cholesterol content hinting at the involvement of the cholesterol regulatory pathway in cold-induced ZNF726 gene regulation. This observation was bolstered by a positive correlation between the expression of cholesterol-regulatory genes and ZNF726. Exogenous cholesterol treatment elevated ZNF726 transcript levels while knockdown of ZNF726 decreased the cholesterol content via downregulating various cholesterol regulatory gene expressions (e.g., SREBF1/2, HMGCoR, LDLR). Moreover, an underlying mechanism supporting cold-driven tumorigenesis is proposed through interdependent regulation of cholesterol regulatory pathway and cold-inducible ZNF726 expression.

Bile components affect the functions and transcriptome of the rainbow trout intestinal epithelial cell line RTgutGC

The concomitant increase in cultivation of fish and decrease in supply of marine ingredients, have greatly increased the demand for new nutrient sources. This also regards so-called functional ingredients which may benefit health and welfare of the fish. In vitro cell line-based intestinal epithelial barrier models may serve as tools for narrowing down the broad range of ingredient options, to identify the most promising candidates before in vivo feeding trials are run. In vivo, differentiation of the various epithelial cells in the fish intestine, from the multipotent stem cells, takes place in the presence of a variety of substances from dietary and endogenous origin. Among these, bile salts have recently received attention as regulators of epithelial function in health and disease but have not, until now, been included in the medium when culturing fish gut epithelial cells in vitro. As bile salts are present at high levels in the chyme of the fish intestine, in particular in salmon and rainbow trout, mostly as taurocholate (>90%), their role for effects of diet ingredients on the in vitro gut cell model should be understood. With this study, we wanted to investigate whether inclusion of bile from rainbow trout or pure taurocholate in the culture media would modulate functions of the RTgutGC epithelial cells. Here, we demonstrated that the rainbow trout intestinal epithelial cell line RTgutGC responded significantly to the presence of bile components. Treatment with rainbow trout bile taken from the gall bladder (RTbile) or pure taurocholate (TC) at taurocholate concentrations of ≤0.5 mg/mL retained normal cell morphology, cell viability as in cell oxidation-reduction metabolic activity and membrane integrity, and barrier features, while high concentrations of bile salts (≥1 mg/mL) were cytotoxic to the cells. After long-term (4 days) bile treatment, transcriptome responses showed how bile salts play important roles in intestinal epithelial cell metabolism. qPCR data demonstrated that barrier function genes, brush border enzyme genes and immune genes were significantly affected. Although similar trends were seen, treatment with bile salt as a component of rainbow trout bile or pure taurocholate, induced somewhat different effects. In conclusion, this study clearly indicates that bile salts should be included in the cell medium when running in vitro studies of gut cell functions, not at least immune functions, preferably at the level of ∼0.5 mg/mL supplemented as pure taurocholate to ensure reproducibility.

Human adaptation to high altitude: a review of convergence between genomic and proteomic signatures

Both genomics- and proteomics-based investigations have identified several essential genes, proteins, and pathways that may facilitate human adaptive genotype/phenotype in a population-specific manner. This comprehensive review provides an up-to-date list of genes and proteins identified for human adaptive responses to high altitudes. Genomics studies for indigenous high-altitude populations like Tibetans, Andeans, Ethiopians, and Sherpas have identified 169 genes under positive natural selection. Similarly, global proteomics studies have identified 258 proteins (± 1.2-fold or more) for Tibetan, Sherpa, and Ladakhi highlanders. The primary biological processes identified for genetic signatures include hypoxia-inducible factor (HIF)-mediated oxygen sensing, angiogenesis, and erythropoiesis. In contrast, major biological processes identified for proteomics signatures include 14–3-3 mediated sirtuin signaling, integrin-linked kinase (ILK), phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT), and integrin signaling. Comparing genetic and protein signatures, we identified 7 common genes/proteins (HBB/hemoglobin subunit beta, TF/serotransferrin, ANGPTL4/angiopoietin-related protein 4, CDC42/cell division control protein 42 homolog, GC/vitamin D-binding protein, IGFBP1/insulin-like growth factor-binding protein 1, and IGFBP2/insulin-like growth factor-binding protein 2) involved in crucial molecular functions like IGF-1 signaling, LXR/RXR activation, ferroptosis signaling, iron homeostasis signaling and regulation of cell cycle. Our combined multi-omics analysis identifies common molecular targets and pathways for human adaptation to high altitude. These observations further corroborate convergent positive selection of hypoxia-responsive molecular pathways in humans and advocate using multi-omics techniques for deciphering human adaptive responses to high altitude.

LXR agonist improves peripheral neuropathy and modifies PNS immune cells in aged mice

Background

Peripheral neuropathy is a common and progressive disorder in the elderly that interferes with daily activities. It is of importance to find efficient treatments to treat or delay this age-related neurodegeneration. Silencing macrophages by reducing foamy macrophages showed significant improvement of age-related degenerative changes in peripheral nerves of aged mice. We previously demonstrated that activation of the cholesterol sensor Liver X receptor (LXR) with the potent agonist, GW3965, alleviates pain in a diet-induced obesity model. We sought to test whether LXR activation may improve neuropathy in aged mice.

Methods

21-month-old mice were treated with GW3965 (25 mg/Kg body weight) for 3 months while testing for mechanical allodynia and thermal hyperalgesia. At termination, flow cytometry was used to profile dorsal root ganglia and sciatic nerve cells. Immune cells were sorted and analyzed for cholesterol and gene expression. Nerve fibers of the skin from the paws were analyzed. Some human sural nerves were also evaluated. Comparisons were made using either t test or one-way ANOVA.

Results

Treatment with GW3965 prevented the development of mechanical hypersensitivity and thermal hyperalgesia over time in aged mice. We also observed change in polarization and cholesterol content of sciatic nerve macrophages accompanied by a significant increase in nerve fibers of the skin.

Conclusions

These results suggest that activation of the LXR may delay the PNS aging by modifying nerve-immune cell lipid content. Our study provides new potential targets to treat or delay neuropathy during aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02423-z.

Bile Acid Receptors and the Gut-Liver Axis in Nonalcoholic Fatty Liver Disease

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been significantly increased due to the global epidemic of obesity. The disease progression from simple steatosis (NAFL) to nonalcoholic steatohepatitis (NASH) is closely linked to inflammation, insulin resistance, and dysbiosis. Although extensive efforts have been aimed at elucidating the pathological mechanisms of NAFLD disease progression, current understanding remains incomplete, and no effective therapy is available. Bile acids (BAs) are not only important physiological detergents for the absorption of lipid-soluble nutrients in the intestine but also metabolic regulators. During the last two decades, BAs have been identified as important signaling molecules involved in lipid, glucose, and energy metabolism. Dysregulation of BA homeostasis has been associated with NAFLD disease severity. Identification of nuclear receptors and G-protein-coupled receptors activated by different BAs not only significantly expanded the current understanding of NAFLD/NASH disease progression but also provided the opportunity to develop potential therapeutics for NAFLD/NASH. In this review, we will summarize the recent studies with a focus on BA-mediated signaling pathways in NAFLD/NASH. Furthermore, the therapeutic implications of targeting BA-mediated signaling pathways for NAFLD will also be discussed.

Atorvastatin Induces FXR and CYP7A1 Activation as a Result of the Sequential Action of PPARγ/PGC-1α/HNF-4α in Hep3B Cells

Backgrounds/Aims

PPARγ, farnesoid X receptor (FXR) and CYP7A1 are associated with solubility of bile. This study was performed to understand a mechanism and interactions of statin-induced PPARγ, PGC-1α and HNF-4α related to the statin-induced activation of FXR and CYP7A1, and verify whether the mevalonate pathway is involved in the mechanism.

Methods

MTT assays were performed using cultured human Hep3B cells to determine the effect of atorvastatin on the cell proliferation. Expression levels of indicated proteins were measured using Western blotting assays by inhibiting the protein expression or not.

Results

Atorvastatin increased expression of PPARγ, PGC-1α, HNF-4α, FXR, and CYP7A1 in Hep3B cells. PPARγ ligand of troglitazone upregulated the expression of PGC-1α, HNF-4α, FXR, and CYP7A1 in Hep3B cells. Silencing of PPARγ, PGC1α, and HNF4α using respective siRNA demonstrated that atorvastatin-induced FXR and CYP7A1 activation required sequential action of PPARγ /PGC-1α/HNF-4α. The silencing of PPARγ completely inhibited atorvastatin-induced PGC-1α expression, and the PGC1α silencing partially inhibited atorvastatin-induced PPARγ expression. The inhibition of HNF4α did not affect atorvastatin-induced PPARγ expression, but partially inhibited atorvastatin-induced PGC-1α expression. Besides, mevalonate completely reversed the effect of atorvastatin on PPARγ, PGC-1α, HNF-4α, FXR, and CYP7A1.

Conclusions

Atorvastatin induces FXR and CYP7A1 activation as a result of sequential action of PPARγ/PGC-1α/HNF-4α in human hepatocytes. We propose that atorvastatin enhances solubility of cholesterol in bile by simultaneously activating of FXR and CYP7A1.

Berberine Prevents Disease Progression of Nonalcoholic Steatohepatitis through Modulating Multiple Pathways

The disease progression of nonalcoholic fatty liver disease (NAFLD) from simple steatosis (NAFL) to nonalcoholic steatohepatitis (NASH) is driven by multiple factors. Berberine (BBR) is an ancient Chinese medicine and has various beneficial effects on metabolic diseases, including NAFLD/NASH. However, the underlying mechanisms remain incompletely understood due to the limitation of the NASH animal models used. Methods: A high-fat and high-fructose diet-induced mouse model of NAFLD, the best available preclinical NASH mouse model, was used. RNAseq, histological, and metabolic pathway analyses were used to identify the potential signaling pathways modulated by BBR. LC-MS was used to measure bile acid levels in the serum and liver. The real-time RT-PCR and Western blot analysis were used to validate the RNAseq data. Results: BBR not only significantly reduced hepatic lipid accumulation by modulating fatty acid synthesis and metabolism but also restored the bile acid homeostasis by targeting multiple pathways. In addition, BBR markedly inhibited inflammation by reducing immune cell infiltration and inhibition of neutrophil activation and inflammatory gene expression. Furthermore, BBR was able to inhibit hepatic fibrosis by modulating the expression of multiple genes involved in hepatic stellate cell activation and cholangiocyte proliferation. Consistent with our previous findings, BBR's beneficial effects are linked with the downregulation of microRNA34a and long noncoding RNA H19, which are two important players in promoting NASH progression and liver fibrosis. Conclusion: BBR is a promising therapeutic agent for NASH by targeting multiple pathways. These results provide a strong foundation for a future clinical investigation.

Neuronal LXR Regulates Neuregulin 1 Expression and Sciatic Nerve-Associated Cell Signaling in Western Diet-fed Rodents

Neuropathic pain caused by peripheral nerve injuries significantly affects sensory perception and quality of life. Accumulating evidence strongly link cholesterol with development and progression of Obesity and Diabetes associated-neuropathies. However, the exact mechanisms of how cholesterol/lipid metabolism in peripheral nervous system (PNS) contributes to the pathogenesis of neuropathy remains poorly understood. Dysregulation of LXR pathways have been identified in many neuropathic models. The cholesterol sensor, LXR α/β, expressed in sensory neurons are necessary for proper peripheral nerve function. Deletion of LXR α/β from sensory neurons lead to pain-like behaviors. In this study, we identified that LXR α/β expressed in sensory neurons regulates neuronal Neuregulin 1 (Nrg1), protein involved in cell-cell communication. Using in vivo cell-specific approaches, we observed that loss of LXR from sensory neurons altered genes in non-neuronal cells located in the sciatic nerve (potentially representing Schwann cells (SC)). Our data suggest that neuronal LXRs may regulate non-neuronal cell function via a Nrg1-dependent mechanism. The decrease in Nrg1 expression in DRG neurons of WD-fed mice may suggest an altered Nrg1-dependent neuron-SC communication in Obesity. The communication between neurons and non-neuronal cells such as SC could be a new biological pathway to study and understand the molecular and cellular mechanism underlying Obesity-associated neuropathy and PNS dysfunction.

ABCA1 and metabolic syndrome; a review of the ABCA1 role in HDL-VLDL production, insulin-glucose homeostasis, inflammation and obesity

ATP-binding cassette transporter A1 (ABCA1) is an integral cell-membrane protein that mediates the rate-limiting step of high density lipoprotein (HDL) biogenesis and suppression of inflammation by triggering a number of signaling pathways via interacting with an apolipoprotein acceptor. The hepatic ABCA1 is involved in regulation of very low density lipoprotein (VLDL) production by affecting the apolipoprotein B trafficking and lipidation of VLDL particles. This protein is involved in protecting the function of pancreatic β-cells and insulin secretion by cholesterol homeostasis. Adipose tissue lipolysis is associated with ABCA1 activity. This transporter is involved in controlling obesity and insulin sensitivity by regulating triglyceride (TG) lipolysis and influencing on adiponectin, visfatin, leptin, and GLUT4 genes expression. The ABCA1 of skeletal muscle cells play a role in increasing the glucose uptake by enhancing the Akt phosphorylation and transferring GLUT4 to the plasma membrane. Abnormal status of ABCA1-regulated phenotypes is observed in metabolic syndrome. This syndrome is associated with the occurrence of many diseases. This review is a summary of the role of ABCA1 in HDL and VLDL production, homeostasis of insulin and glucose, suppression of inflammation and obesity controlling to provide a better insight into the association of this protein with metabolic syndrome.

Comparative potency of obeticholic acid and natural bile acids on FXR in hepatic and intestinal in vitro cell models

Obeticholic acid (OCA) is a semisynthetic farnesoid X receptor (FXR) agonist, an analogue of chenodeoxycholic acid (CDCA) which is indicated for the treatment of primary biliary cholangitis (PBC) in combination with ursodeoxycholic acid (UDCA). OCA efficiently inhibits bile acid synthesis and promotes bile acid efflux via activating FXR-mediated mechanisms in a physiologically relevant in vitro cell system, Sandwich-cultured Transporter Certified ™ human primary hepatocytes (SCHH). The study herein evaluated the effects of UDCA alone or in combination with OCA in SCHH. UDCA (≤100 μmol/L) alone did not inhibit CYP7A1 mRNA, and thus, no reduction in the endogenous bile acid pool observed. UDCA ≤100 μmol/L concomitantly administered with 0.1 μmol/L OCA had no effect on bile acid synthesis beyond what was observed with OCA alone. Furthermore, this study evaluated human Caco-2 cells (clone C2BBe1) as in vitro intestinal models. Glycine conjugate of OCA increased mRNA levels of FXR target genes in Caco-2 cells, FGF-19, SHP, OSTα/β, and IBABP, but not ASBT, in a concentration-dependent manner, while glycine conjugate of UDCA had no effect on the expression of these genes. The results suggested that UDCA ≤100 μmol/L did not activate FXR in human primary hepatocytes or intestinal cell line Caco-2. Thus, co-administration of UDCA with OCA did not affect OCA-dependent pharmacological effects.

Metformin and AMP Kinase Activation Increase Expression of the Sterol Transporters ABCG5/8 (ATP-Binding Cassette Transporter G5/G8) With Potential Antiatherogenic Consequences

OBJECTIVE

The mechanisms underlying the cardiovascular benefit of the anti-diabetic drug metformin are poorly understood. Recent studies have suggested metformin may upregulate macrophage reverse cholesterol transport. The final steps of reverse cholesterol transport are mediated by the sterol transporters, ABCG5 (ATP-binding cassette transporter G5) and ABCG8 (ATP-binding cassette transporter G8), which facilitate hepato-biliary transport of cholesterol. This study was undertaken to assess the possibility that metformin induces Abcg5 and Abcg8 expression in liver and to elucidate the underlying mechanisms.

APPROACH AND RESULTS

Metformin-treated mouse or human primary hepatocytes showed increased expression of Abcg5/8 and the bile salt export pump, Bsep. Administration of metformin to Western-type diet-fed mice showed significant upregulation of Abcg5/8 and Bsep. This resulted in increased initial clearance of ³H-cholesteryl ester HDL (high-density lipoprotein) from plasma. However, fecal ³H-cholesterol output was only marginally increased, possibly reflecting increased hepatic Ldlr (low-density lipoprotein receptor) expression, which would increase nonradiolabeled cholesterol uptake. Abcg5/8 undergo strong circadian variation. Available chromatin immunoprecipitation-Seq data suggested multiple binding sites for Period 2, a transcriptional repressor, within the Abcg5/8 locus. Addition of AMPK (5' adenosine monophosphate-activated protein kinase) agonists decreased Period 2 occupancy, suggesting derepression of Abcg5/8. Inhibition of ATP citrate lyase, which generates acetyl-CoA from citrate, also decreased Period 2 occupancy, with concomitant upregulation of Abcg5/8. This suggests a mechanistic link between feeding-induced acetyl-CoA production and decreased cholesterol excretion via Period 2, resulting in inhibition of Abcg5/8 expression.

CONCLUSIONS

Our findings provide partial support for the concept that metformin may provide cardiovascular benefit via increased reverse cholesterol transport but also indicate increased Ldlr expression as a potential additional mechanism. AMPK activation or ATP citrate lyase inhibition may mediate antiatherogenic effects through increased ABCG5/8 expression.

Comparison of Effects of Sleeve Gastrectomy and Gastric Bypass on Lipid Profile Parameters in Indian Obese: a Case Matched Analysis

BACKGROUND

Obesity is associated with increased mortality due to higher cardiovascular risk. A proportion of this risk is attributed to impaired lipid profile in the form of high levels of serum total cholesterol, triglycerides, and low levels of HDL cholesterol. Both sleeve gastrectomy (LSG) and gastric bypass (LGB) have been shown to have favourable effects on lipid profile with some variability in improvement. We aimed to study the difference in changes in lipid profile after LSG and LGB.

METHODS

We performed a retrospective case-matched study comparing effects of LSG and LGB on lipid profile of patients who underwent bariatric surgery from September 2014 to September 2015. The matching was done based on criteria of age and body mass index (BMI).

RESULTS

Out of a total of 92 selected patients, 69 patients underwent LSG and 23 patients underwent LGB. There was a significant improvement in serum triglycerides and HDL cholesterol with no significant reduction in serum total cholesterol in both LSG and LGB group. There was a significant reduction in cardiovascular risk calculated as total cholesterol: HDL cholesterol ratio following bariatric surgery (p = 0.002).

CONCLUSION

Both LSG and LGB have similar effects on lipid profile cardiovascular risk attributed to it in Indian obese. Thus, sleeve gastrectomy may be considered as effective as a gastric bypass for dyslipidaemia improvement in Indian patients.

Pluronic based β-cyclodextrin polyrotaxanes for treatment of Niemann-Pick Type C disease

Niemann-Pick Type C disease (NPC) is a rare metabolic disorder characterized by disruption of normal cholesterol trafficking within the cells of the body. There are no FDA approved treatments available for NPC patients. Recently, the cycloheptaglucoside 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) has shown efficacy as a potential NPC therapeutic by extending lifetime in NPC mice, delaying neurodegeneration, and decreasing visceral and neurological cholesterol burden. Although promising, systemic HP-β-CD treatment is limited by a pharmacokinetic profile characterized by rapid loss through renal filtration. To address these shortcomings, we sought to design a family of HP-β-CD pro-drug delivery vehicles, known as polyrotaxanes (PR), capable of increasing the efficacy of a given injected dose by improving both pharmacokinetic profile and bioavailability of the HP-β-CD agent. PR can effectively diminish the cholesterol pool within the liver, spleen, and kidney at molar concentrations 10-to-100-fold lower than monomeric HP-β-CD. In addition to this proof-of-concept, use of PR scaffolds with differing physiochemical properties reveal structure-activity relationships in which PR characteristics, including hydrophobicity, threading efficiency and surface charge, were found to both decisively and subtly effect therapeutic efficacy. PR scaffolds exhibit absorption, pharmacokinetics, and biodistribution patterns that are significantly altered from monomeric HP-β-CD. In all, PR scaffolds hold great promise as potential treatments for visceral disease in NPC patients.

HVC1 ameliorates hyperlipidemia and inflammation in LDLR-/- mice

Background

HVC1 consists of Coptidis Rhizoma (dried rhizome of Coptischinensis), Scutellariae Radix (root of Scutellariabaicalensis), Rhei Rhizoma (rhizome of Rheum officinale), and Pruni Cortex (cortex of Prunusyedoensis Matsum). Although the components are known to be effective in various conditions such as inflammation, hypertension, and hypercholesterolemia, there are no reports of the molecular mechanism of its hypolipidemic effects.

Methods

We investigated the hypolipidemic effect of HVC1 in low-density lipoprotein receptor-deficient (LDLR^−/−) mice fed a high-cholesterol diet for 13 weeks. Mice were randomized in to 6 groups: ND (normal diet) group, HCD (high-cholesterol diet) group, and treatment groups fed HCD and treated with simvastatin (10 mg/kg, p.o.) or HVC1 (10, 50, or 250 mg/kg, p.o.).

Results

HVC1 regulated the levels of total cholesterol, triglyceride (TG), low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol in mouse serum. In addition, it regulated the transcription level of the peroxisome proliferator-activated receptors (PPARs), sterol regulatory element-binding proteins (SREBP)-2, 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, lipoprotein lipase (LPL), apolipoprotein B (apo B), liver X receptor (LXR), and inflammatory cytokines (IL-1β, IL-6, and TNF-α). Furthermore, HVC1 activated 5′ adenosine monophosphate-activated protein kinase (AMPK).

Conclusion

Our results suggest that HVC1 might be effective in preventing high-cholesterol diet-induced hyperlipidemia by regulating the genes involved in cholesterol and lipid metabolism, and inflammatory responses.

Novel Role for Matrix Metalloproteinase 9 in Modulation of Cholesterol Metabolism

Background

The development of atherosclerosis is strongly linked to disorders of cholesterol metabolism. Matrix metalloproteinases (MMPs) are dysregulated in patients and animal models with atherosclerosis. Whether systemic MMP activity influences cholesterol metabolism is unknown.

Methods and Results

We examined MMP‐9–deficient (Mmp9^−/−) mice and found them to have abnormal lipid gene transcriptional responses to dietary cholesterol supplementation. As opposed to Mmp9^+/+ (wild‐type) mice, Mmp9^−/− mice failed to decrease the hepatic expression of sterol regulatory element binding protein 2 pathway genes, which control hepatic cholesterol biosynthesis and uptake. Furthermore, Mmp9^−/− mice failed to increase the expression of genes encoding the rate‐limiting enzymes in biliary cholesterol excretion (eg, Cyp7a and Cyp27a). In contrast, MMP‐9 deficiency did not impair intestinal cholesterol absorption, as shown by the ¹⁴C‐cholesterol and ³H‐sitostanol absorption assay. Similar to our earlier study on Mmp2^−/− mice, we observed that Mmp9^−/− mice had elevated plasma secreted phospholipase A₂ activity. Pharmacological inhibition of systemic circulating secreted phospholipase A₂ activity (with varespladib) partially normalized the hepatic transcriptional responses to dietary cholesterol in Mmp9^−/− mice. Functional studies with mice deficient in other MMPs suggested an important role for the MMP system, as a whole, in modulation of cholesterol metabolism.

Conclusions

Our results show that MMP‐9 modulates cholesterol metabolism, at least in part, through a novel MMP‐9–plasma secreted phospholipase A₂ axis that affects the hepatic transcriptional responses to dietary cholesterol. Furthermore, the data suggest that dysregulation of the MMP system can result in metabolic disorder, which could lead to atherosclerosis and coronary heart disease.

Apolipoprotein M regulates the orphan nuclear receptor LRH-1 gene expression through binding to its promoter region in HepG2 cells

Apolipoprotein M (ApoM) is predominantly located in the high-density lipoprotein in human plasma. It has been demonstrated that ApoM expression could be regulated by several crucial nuclear receptors that are involved in the bile acid metabolism. In the present study, by combining gene-silencing experiments, overexpression studies, and chromatin immunoprecipitation assays, we showed that ApoM positively regulated liver receptor homolog-1 (LRH-1) gene expression via direct binding to an LRH-1 promoter region (nucleotides -406/ -197). In addition, we investigated the effects of farnesoid X receptor agonist GW4064 on hepatic ApoM expression in vitro. In HepG2 cell cultures, both mRNA and protein levels of ApoM and LRH-1 were decreased in a time-dependent manner in the presence of 1 μM GW4064, and the inhibition effect was gradually attenuated after 24 hours. In conclusion, our findings present supportive evidence that ApoM is a regulator of human LRH-1 transcription, and further reveal the importance of ApoM as a critical regulator of bile acids metabolism.

Dietary cholesterol supplementation to a plant-based diet suppresses the complete pathway of cholesterol synthesis and induces bile acid production in Atlantic salmon (Salmo salar L.)

Plants now supply more than 50 % of protein in Norwegian salmon aquafeeds. The inclusion of plant protein in aquafeeds may be associated with decreased lipid digestibility and cholesterol and bile salt levels, indicating that the replacement of fishmeal with plant protein could result in inadequate supplies of cholesterol in fish. A reduction in feed efficiency, fish growth and pathogen resistance is often observed in parallel to alterations in sterol metabolism. Previous studies have indicated that the negative effects induced by plant components can be attenuated when diets are supplemented with cholesterol. The present study evaluated the effects of dietary cholesterol supplementation (1·5 %) in Atlantic salmon fed a plant-based diet for 77 d. The weights of body, intestines and liver were recorded and blood, tissues, faeces, chyme and bile were sampled for the evaluation of effects on growth, nutrient utilisation and metabolism, and transcriptome and metabolite levels, with particular emphasis on sterol metabolism and organ structure and function. Cholesterol supplementation did not affect the growth or organ weights of Atlantic salmon, but seemed to promote the induction of cholesterol and plant sterol efflux in the intestine while suppressing sterol uptake. Cholesterol biosynthesis decreased correspondingly and conversion into bile acids increased. The marked effect of cholesterol supplementation on bile acid synthesis suggests that dietary cholesterol can be used to increase bile acid synthesis in fish. The present study clearly demonstrated how Atlantic salmon adjusted their metabolic functions in response to the dietary load of cholesterol. It has also expanded our understanding of sterol metabolism and turnover, adding to the existing, rather sparse, knowledge of these processes in fish.

Cholesterol transport and regulation in the mammary gland

The milk-producing alveolar epithelial cells secrete milk that remains after birth the principal source of nutrients for neonates. Milk secretion and composition are highly regulated processes via integrated actions of hormones and local factors which involve specific receptors and downstream signal transduction pathways. Overall milk composition is similar among mammalian species, although the content of individual constituents such as lipids may significantly differ from one species to another. The milk lipid fraction is essentially composed of triglycerides, which represent more than 95 % of the total lipids in human and commercialized bovine milk. Though sterols, including cholesterol, which is the major milk sterol, represent less than 0.5 % of the total milk lipid fraction, they are of key importance for several biological processes. Cholesterol is required for the formation of biological membranes especially in rapidly growing organisms, and for the synthesis of sterol-based compounds. Cholesterol found in milk originates predominantly from blood uptake and, to a certain extent, from local synthesis in the mammary tissue. The present review summarizes current knowledge on cellular mechanisms and regulatory processes determining intra- and transcellular cholesterol transport in the mammary gland. Cholesterol exchanges between the blood, the mammary alveolar cells and the milk, and the likely role of active cholesterol transporters in these processes are discussed. In this context, the hormonal regulation and signal transduction pathways promoting active cholesterol transport as well as potential regulatory crosstalks are highlighted.

Pravastatin activates the expression of farnesoid X receptor and liver X receptor alpha in Hep3B cells

BACKGROUND

Statins are suggested to preserve gallbladder function by suppressing pro-inflammatory cytokines and preventing cholesterol accumulation in gallbladder epithelial cells. They also affect cross-talk among the nuclear hormone receptors that regulate cholesterol-bile acid metabolism in the nuclei of hepatocytes. However, there is controversy over whether or how statins change the expression of peroxisome proliferator-activated receptor (PPAR)alpha, PPARgamma, liver X receptor alpha (LXRalpha), farnesoid X receptor (FXR), ABCG5, ABCG8, and 7alpha-hydroxylase (CYP7A1) which are directly involved in the cholesterol saturation index in bile.

METHODS

Human Hep3B cells were cultured on dishes. MTT assays were performed to determine the appropriate concentrations of reagents to be used. The protein expression of PPARalpha and PPARgamma was measured by Western blotting analysis, and the mRNA expression of LXRalpha, FXR, ABCG5, ABCG8 and CYP7A1 was estimated by RT-PCR.

RESULTS

In cultured Hep3B cells, pravastatin activated PPARalpha and PPARgamma protein expression, induced stronger expression of PPARgamma than that of PPARalpha, increased LXRalpha mRNA expression, activated ABCG5 and ABCG8 mRNA expression mediated by FXR as well as LXRalpha, enhanced FXR mRNA expression, and increased CYP7A1 mRNA expression mediated by the PPARgamma and LXRalpha pathways, together or independently.

CONCLUSION

Our data suggested that pravastatin prevents cholesterol gallstone diseases via the increase of FXR, LXRalpha and CYP7A1 in human hepatocytes.

Cholesterol metabolism after bariatric surgery in grade 3 obesity: differences between malabsorptive and restrictive procedures

OBJECTIVE

Malabsorptive bariatric surgery (biliopancreatic diversion and biliointestinal bypass [BIBP]) reduces serum cholesterol levels more than restrictive surgery (adjustable gastric banding [AGB]), and this is thought to be due to greater weight loss. Our aim was to evaluate the changes of cholesterol metabolism induced by malabsorptive and restrictive surgery independent of weight loss.

RESEARCH DESIGN AND METHODS

In a nonrandomized, self-selected, unblinded, active-comparator, bicenter, 6-month study, glucose metabolism (blood glucose and serum insulin levels and homeostasis model assessment of insulin resistance [HOMA-IR] index) and cholesterol metabolism (absorption: serum campesterol and sitosterol levels; synthesis: serum lathosterol levels; catabolism: rate of appearance and serum concentrations of serum 7-α- and serum 27-OH-cholesterol after infusions of deuterated 7-α- and 27-OH-cholesterol in sequence) were assessed in grade 3 obesity subjects undergoing BIBP (n = 10) and AGB (n = 10). Evaluations were performed before and 6 months after surgery.

RESULTS

Subjects had similar values at baseline. Weight loss was similar in the two groups of subjects, and blood glucose, insulin levels, HOMA-IR, and triglycerides decreased in a similar way. In contrast, serum cholesterol, LDL cholesterol, non-HDL cholesterol, serum sitosterol, and campesterol levels decreased and lathosterol levels increased only in BIBP subjects, not in AGB subjects. A significant increase in 7-α-OH-cholesterol occurred only with BIBP; serum 27-OH-cholesterol decreased in both groups.

CONCLUSIONS

Malabsorptive surgery specifically affects cholesterol levels, independent of weight loss and independent of glucose metabolism and insulin resistance. Decreased sterol absorption leads to decreased cholesterol and LDL cholesterol levels, accompanied by enhanced cholesterol synthesis and enhanced cholesterol catabolism. Compared with AGB, BIBP provides greater cholesterol lowering.

Hypolipidemic Effects of a Proprietary Commiphora Mukul Gum Resin Extract and Medium-Chain Triglyceride Preparation (GU-MCT810)

The hypolipidemic effects of the poorly soluble ayurvedic resin guggul, especially the molecular targets and mechanism, have not been well investigated to date. In the present study, we have formulated a liquid product, GU-MCT810, composed of a proprietary Commiphora mukul gum resin extract and medium-chain triglyceride and investigated its hypolipidemic effects in vitro. Treatment of HepG2 cells significantly reduced low-density lipoprotein cholesterol and increased the high-density lipoprotein/low-density lipoprotein ratio. GU-MCT810 showed direct inhibition of HMG-CoA reductase activity in a dose-dependent manner and compared very well with the inhibitory effect of statins like Pravastatin and Mevastatin. The adipocyte differentiation was also inhibited by GU-MCT810 treatment. GU-MCT810 increased the AMPKα phosphorylation and AMPK kinase activity and inhibited the phosphorylated form of mTOR expression, indicating the molecular targets affected by the nutraceutical compound. The preparation also highly upregulated the expression of LXR and PPARα genes and moderately upregulated BABP and SHP genes.

Impaired cholesterol efflux in senescent macrophages promotes age-related macular degeneration

Pathologic angiogenesis mediated by abnormally polarized macrophages plays a central role in common age-associated diseases such as atherosclerosis, cancer, and macular degeneration. Here we demonstrate that abnormal polarization in older macrophages is caused by programmatic changes that lead to reduced expression of ATP binding cassette transporter ABCA1. Downregulation of ABCA1 by microRNA-33 impairs the ability of macrophages to effectively efflux intracellular cholesterol, which in turn leads to higher levels of free cholesterol within senescent macrophages. Elevated intracellular lipid polarizes older macrophages to an abnormal, alternatively activated phenotype that promotes pathologic vascular proliferation. Mice deficient for Abca1, but not Abcg1, demonstrate an accelerated aging phenotype, whereas restoration of cholesterol efflux using LXR agonists or miR-33 inhibitors reverses it. Monocytes from older humans with age-related macular degeneration showed similar changes. These findings provide an avenue for therapeutic modulation of macrophage function in common age-related diseases.

A novel isoform of liver receptor homolog-1 is regulated by steroidogenic factor-1 and the specificity protein family in ovarian granulosa cells

Liver receptor homolog-1 (LRH-1) is a member of the nuclear receptor 5A (NR5A) subfamily. It is expressed in granulosa cells of the ovary and is involved in steroidogenesis and ovulation. To reveal the transcriptional regulatory mechanism of LRH-1, we determined its transcription start site in the ovary using KGN cells, a human granulosa cell tumor cell line. 5'-rapid amplification of cDNA ends PCR revealed that human ovarian LRH-1 was transcribed from a novel transcription start site, termed exon 2o, located 41 bp upstream of the reported exon 2. The novel LRH-1 isoform was expressed in the human ovary but not the liver. Promoter analysis and an EMSA indicated that a steroidogenic factor-1 (SF-1) binding site and a GC box upstream of exon 2o were required for promoter activity, and that SF-1 and specificity protein (Sp)-1/3 bind to the respective regions in ovarian granulosa cells. In KGN cells, transfection of SF-1 increased ovarian LRH-1 promoter activity and SF-1-dependent reporter activity was further enhanced when peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was cotransfected. In Drosophila SL2 cells, Sp1 was more effective than Sp3 in enhancing promoter activity, and co-transfection of the NR5A-family synergistically increased activity. Infection with adenoviruses expressing SF-1 or PGC-1α induced LRH-1 expression in KGN cells. These results indicate that the expression of human LRH-1 is regulated in a tissue-specific manner, and that the novel promoter region is controlled by the Sp-family, NR5A-family and PGC-1α in ovarian granulosa cells in a coordinated fashion.

Changes in the expression of hepatic genes involved in cholesterol homeostasis in dairy cows in the transition period and at different stages of lactation

This study was performed to investigate changes in expression level of genes involved in hepatic cholesterol metabolism in the transition from pregnancy to lactation and during different stages of lactation in dairy cows. Therefore, relative mRNA abundances of several genes involved in various pathways of cholesterol homeostasis in liver biopsy samples of 20 dairy cows, taken in late pregnancy (3 wk prepartum) and early lactation (1, 5, and 14 wk postpartum), were determined. At 1 wk postpartum, hepatic mRNA abundances of genes involved in cholesterol synthesis (3-hydroxy-3-methylglutaryl-coenzyme A reductase, mevalonate kinase, and farnesyl diphosphate synthase), cholesterol uptake from blood (low-density lipoprotein receptor), bile acid synthesis (cholesterol-7α-hydroxylase), cholesterol efflux [ATP-binding cassette (ABC) transporter A1 and ABCG1], esterification of cholesterol (acyl-coenzyme A:cholesterol acyltransferase), and proteins involved in assembly and secretion of very low-density lipoproteins (microsomal triglyceride transfer protein, ApoB100) were increased compared with 3 wk prepartum. The mRNA abundances of most of these genes decreased after 1 wk of lactation and reached levels in 5 and 14 wk of lactation similar to those at 3 wk prepartum. Only mRNA abundances of cholesterol-7α-hydroxylase, ABC transporters, and ApoB100 remained at 5 and 14 wk postpartum at levels higher than those at 3 wk prepartum. Hepatic cholesterol abundance was highest at 1 wk postpartum and was, thereafter, decreasing to values similar to that at 3 wk prepartum. Overall, this study shows that the onset of lactation is associated with an increased expression of various genes involved in cholesterol metabolism in the liver of dairy cows, suggesting that pronounced changes in hepatic cholesterol metabolism take place in the periparturient phase.

Therapeutic potential of cyclodextrins in the treatment of Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is an autosomal recessive neurovisceral lipid and storage disorder characterized by abnormal sequestration of unesterified cholesterol within the late endosomal/lysosomal compartment of all cells in the body. This disease primarily affects children and is characterized by hepatic and pulmonary dysfunction, neurodegeneration and death at an early age. Currently, there is no effective treatment for NPC disease. It was recently discovered that 2-hydroxypropyl-β-cyclodextrin (2HPBCD), when administered systemically to a murine model of either NPC1 or NPC2 disease, significantly reduced lysosomal cholesterol accumulation in almost every organ, delayed the progression of neurodegeneration and significantly prolonged lifespan by allowing trapped cholesterol within the late endosome/lysosome to be released. When 2HPBCD was administered directly into the CNS of Npc1^-/- mice, neurodegeneration was completely prevented. This review will explore the pathophysiology of NPC disease and the use of 2HPBCD as a possible therapeutic modality.

Nuclear receptors as drug targets for metabolic disease

Nuclear hormone receptors comprise a superfamily of ligand-activated transcription factors that control development, differentiation, and homeostasis. Over the last 15 years a growing number of nuclear receptors have been identified that coordinate genetic networks regulating lipid metabolism and energy utilization. Several of these receptors directly sample the levels of metabolic intermediates including fatty acids and cholesterol derivatives and use this information to regulate the synthesis, transport, and breakdown of the metabolite of interest. In contrast, other family members sense metabolic activity via the presence or absence of interacting proteins. The ability of these nuclear receptors to impact metabolism will be discussed and the challenges facing drug discovery efforts for this class of targets will be highlighted.

Intestinal FXR-mediated FGF15 production contributes to diurnal control of hepatic bile acid synthesis in mice

Hepatic bile acid synthesis is subject to complex modes of transcriptional control, in which the bile acid-activated nuclear receptor farnesoid X receptor (FXR) in liver and intestine-derived, FXR-controlled fibroblast growth factor 15 (Fgf15) are involved. The Fgf15 pathway is assumed to contribute significantly to control of hepatic bile acid synthesis. However, scientific evidence supporting this assumption is primarily based on gene expression data. Using intestine-selective FXR knockout mice (iFXR-KO), we show that contribution of intestinal FXR-Fgf15 signalling in regulation of hepatic cholesterol 7α-hydroxylase (Cyp7A1) expression depends on time of the day with increased hepatic Cyp7A1 expression in iFXR-KO mice compared with controls exclusively during the dark phase. To assess the physiological relevance hereof, we determined effects of intestine-selective deletion of FXR on physiological parameters such as bile formation and kinetics of the enterohepatic circulation of bile acids. It appeared that intestinal FXR deficiency leads to a modest but significant increase in cholic acid pool size, without changes in fractional turnover rate. As a consequence, bile flow and biliary bile acid secretion rates were increased in iFXR-KO mice compared with controls. Feeding a bile acid-containing diet or treatment with a bile acid sequestrant similarly affected bile formation in iFXR-KO and control mice and induced similar changes in Cyp7A1 and Cyp8B1 expression patterns. In conclusion, this study is the first to demonstrate the physiological relevance of the contribution of the intestinal FXR-Fgf15 signalling pathway in control of hepatic bile acid synthesis. Fgf15 contributes to the regulation of hepatic bile acid synthesis in mice mainly during the dark phase. Expansion of the circulating bile acid pool as well as bile acid sequestration diminishes the contribution of intestinal FXR-Fgf15 signalling in control of hepatic bile acid synthesis and bile formation.

Expression, localization, and functional model of cholesterol transporters in lactating and nonlactating mammary tissues of murine, bovine, and human origin

Members of the ATP-binding cassette (ABC) transporters play a pivotal role in cellular lipid efflux. To identify candidate cholesterol transporters implicated in lipid homeostasis and mammary gland (MG) physiology, we compared expression and localization of ABCA1, ABCG1, and ABCA7 and their regulatory genes in mammary tissues of different species during the pregnancy-lactation cycle. Murine and bovine mammary glands (MGs) were investigated during different functional stages. The abundance of mRNAs was determined by quantitative RT-PCR. Furthermore, transporter proteins were localized in murine, bovine, and human MGs by immunohistochemistry. In the murine MG, ABCA1 mRNA abundance was elevated during nonlactating compared with lactating stages, whereas ABCA7 and ABCA1 mRNA profiles were not altered. In the bovine MG, ABCA1, ABCG1, and ABCA7 mRNAs abundances were increased during nonlactating stages compared with lactation. Furthermore, associations between mRNA levels of transporters and their regulatory genes LXRα, PPARγ, and SREBPs were found. ABCA1, ABCG1, and ABCA7 proteins were localized in glandular MG epithelial cells (MEC) during lactation, whereas during nonlactating stages, depending on species, the proteins showed distinct localization patterns in MEC and adipocytes. Our results demonstrate that ABCA1, ABCG1, and ABCA7 are differentially expressed between lactation and nonlactating stages and in association with regulatory genes. Combined expression and localization data suggest that the selected cholesterol transporters are universal MG transporters involved in transport and storage of cholesterol and in lipid homeostasis of MEC. Because of the species-specific expression patterns of transporters in mammary tissue, mechanisms of cholesterol homeostasis seem to be differentially regulated between species.

Cyclodextrin overcomes the transport defect in nearly every organ of NPC1 mice leading to excretion of sequestered cholesterol as bile acid

A mutation in NPC1 leads to sequestration of unesterified cholesterol in the late endosomal/lysosomal compartment of every cell culminating in the development of pulmonary, hepatic, and neurodegenerative disease. Acute administration of 2-hydroxypropyl-beta-cyclodextrin (CYCLO) rapidly overcomes this transport defect in both the 7-day-old pup and 49-day-old mature npc1(-/-) mouse, even though this compound is cleared from the body and plasma six times faster in the mature mouse than in the neonatal animal. The liberated cholesterol flows into the cytosolic ester pool, suppresses sterol synthesis, down-regulates SREBP2 and its target genes, and reduces expression of macrophage-associated inflammatory genes. These effects are seen in the liver and brain, as well as in peripheral organs like the spleen and kidney. Only the lung appears to be resistant to these effects. Forty-eight h after CYCLO administration to the 49-day-old animals, fecal acidic, but not neutral, sterol output increases, whole-animal cholesterol burden is reduced, and the hepatic and neurological inflammation is ameliorated. However, lifespan is extended only when the CYCLO is administered to the 7-day-old animals. These studies demonstrate that CYCLO administration acutely reverses the cholesterol transport defect seen in the NPC1 mouse at any age, and this reversal allows the sequestered sterol to be excreted from the body as bile acid.

Regulation of metabolism by nuclear hormone receptors

The worldwide epidemic of metabolic disease indicates that a better understanding of the pathways contributing to the pathogenesis of this constellation of diseases need to be determined. Nuclear hormone receptors comprise a superfamily of ligand-activated transcription factors that control development, differentiation, and metabolism. Over the last 15 years a growing number of nuclear receptors have been identified that coordinate genetic networks regulating lipid metabolism and energy utilization. Several of these receptors directly sample the levels of metabolic intermediates and use this information to regulate the synthesis, transport, and breakdown of the metabolite of interest. In contrast, other family members sense metabolic activity via the presence or absence of interacting proteins. The ability of these nuclear receptors to impact metabolism and inflammation will be discussed and the potential of each receptor subfamily to serve as drug targets for metabolic disease will be highlighted.

Biliary pancreatic diversion and laparoscopic adjustable gastric banding in morbid obesity: their long-term effects on metabolic syndrome and on cardiovascular parameters

Background

Bariatric surgery is able to improve glucose and lipid metabolism, and cardiovascular function in morbid obesity. Aim of this study was to compare the long-term effects of malabsorptive (biliary pancreatic diversion, BPD), and restrictive (laparoscopic gastric banding, LAGB) procedures on metabolic and cardiovascular parameters, as well as on metabolic syndrome in morbidly obese patients.

Methods

170 patients studied between 1989 and 2001 were called back after a mean period of 65 months. 138 patients undergoing BPD (n = 23) or LAGB (n = 78), and control patients (refusing surgery and treated with diet, n = 37) were analysed for body mass index (BMI), blood glucose, cholesterol, and triglycerides, blood pressure, heart rate, and ECG indexes (QTc, Cornell voltage-duration product, and rate-pressure-product).

Results

After a mean 65 months period, surgery was more effective than diet on all items under evaluation; diabetes, hypertension, and metabolic syndrome disappeared more in surgery than in control patients, and new cases appeared only in controls. BPD was more effective than LAGB on BMI, on almost all cardiovascular parameters, and on cholesterol, not on triglyceride and blood glucose. Disappearance of diabetes, hypertension, and metabolic syndrome was similar with BPD and with LAGB, and no new cases were observed.

Conclusion

These data indicate that BPD, likely due to a greater BMI decrease, is more effective than LAGB in improving cardiovascular parameters, and similar to LAGB on metabolic parameters, in obese patients. The greater effect on cholesterol levels is probably due to the different mechanism of action.

The cell cholesterol exporter ABCA1 as a protector from cardiovascular disease and diabetes

ATP-binding cassette transporter A1 (ABCA1) is an integral cell membrane protein that exports cholesterol from cells and suppresses macrophage inflammation. ABCA1 exports cholesterol by a multistep pathway that involves forming cell-surface lipid domains, solubilizing these lipids by apolipoproteins, binding of apolipoproteins to ABCA1, and activating signaling processes. Thus, ABCA1 behaves both as a lipid exporter and a signaling receptor. ABCA1 transcription is highly induced by sterols, and its expression and activity are regulated post-transcriptionally by diverse processes. ABCA1 mutations can reduce plasma HDL levels, accelerate cardiovascular disease, and increase the risk for type 2 diabetes. Genetic manipulations of ABCA1 expression in mice also affect plasma HDL levels, inflammation, atherogenesis, and pancreatic beta cell function. Metabolites elevated in individuals with the metabolic syndrome and diabetes destabilize ABCA1 protein and decrease cholesterol export from macrophages, raising the possibility that an impaired ABCA1 pathway contributes to the enhanced atherogenesis associated with common inflammatory and metabolic disorders. The ABCA1 pathway has therefore become a promising new therapeutic target for treating cardiovascular disease and diabetes.

Where does fetal and embryonic cholesterol originate and what does it do?

The development of a single-celled fertilized egg, through the blastocyst stage of a ball of cells and the embryonic stage when almost all organ systems begin to develop, and finally to the fetal stage where growth and physiological maturation occurs, is a complex and multifaceted process. A change in metabolism during gestation, especially when organogenesis occurs, can lead to abnormal development and congenital defects. Although many studies have described the roles of specific proteins in development, the roles of specific lipids, such as sterols, have not been studied as intensely. Sterol's functions in development range from being a structural component of membranes to regulating the patterning of the forebrain through sonic hedgehog to regulating expression of key proteins involved in metabolic processes. This review focuses on the roles of sterols in embryonic and fetal development and metabolism. Potential sources of cholesterol for the fetus and embryo are also discussed.

Androgen deprivation by activating the liver X receptor

Prostate cancer is the most commonly diagnosed and the second leading cause of cancer death in men. The androgens-androgen receptor signaling plays an important role in normal prostate development, as well as in prostatic diseases, such as benign hyperplasia and prostate cancer. Accordingly, androgen ablation has been the most effective endocrine therapy for hormone-dependent prostate cancer. Here, we report a novel nuclear receptor-mediated mechanism of androgen deprivation. Genetic or pharmacological activation of the liver X receptor (LXR) in vivo lowered androgenic activity by inducing the hydroxysteroid sulfotransferase 2A1, an enzyme essential for the metabolic deactivation of androgens. Activation of LXR also inhibited the expression of steroid sulfatase in the prostate, which may have helped to prevent the local conversion of sulfonated androgens back to active metabolites. Interestingly, LXR also induced the expression of selected testicular androgen synthesizing enzymes. At the physiological level, activation of LXR in mice inhibited androgen-dependent prostate regeneration in castrated mice. Treatment with LXR agonists inhibited androgen-dependent proliferation of prostate cancer cells in a LXR- and sulfotransferase 2A1-dependent manner. In summary, we have revealed a novel function of LXR in androgen homeostasis, an endocrine role distinct to the previously known sterol sensor function of this receptor. LXR may represent a novel therapeutic target for androgen deprivation, and may aid in the treatment and prevention of hormone-dependent prostate cancer.

Screening for nutritive peptides that modify cholesterol 7alpha-hydroxylase expression

Bioactive peptides with a variety of effects have been described from several nutritive proteins. They exhibit antimicrobial, blood-pressure lowering, antithrombotic, immunomodulatory, and cholesterol-modulating effects. In this study, we have examined whether peptides derived from food proteins might influence bile acid synthesis. A reporter gene cell line that carries a cholesterol 7alpha-hydroxylase promoter fragment fused to firefly luciferase ( cyp7a-luc) was used to screen for nutritive peptides affecting cyp7a expression, the enzyme catalyzing the rate-limiting step in bile acid synthesis. Proteolytic hydrolysates were prepared from soy protein and bovine casein with pepsin, trypsin, chymotrypsin, and elastase and size fractionated using ultrafiltration. Several bioactive hydrolysates could be identified that inhibited luciferase expression. Also, an activation of kinase (AKT, ERK, p38-MAPK) signaling could be observed. Selected hydrolysates were further fractionated by reversed-phase HPLC. Bioactive HPLC-fractions were obtained from casein but not from soy hydrolysates; however, activity could not be recovered in single peak fractions. Peptides in such fractions were identified by mass spectrometry. Five selected peptides from alpha S1-casein present in active fractions were synthesized, but none of these showed activity in the cyp7a-luc screening system. However, two of them activated MAP-kinase signaling similar to the hydrolysates, which suggests, that these peptides are involved in cyp7a regulation by the casein hydrolysates.

Enhanced placental cholesterol efflux by fetal HDL in Smith-Lemli-Opitz syndrome

Previous studies from this laboratory have shown that maternal-derived cholesterol can be effluxed from trophoblasts to fetal HDL and plasma. We had the opportunity to study for the first time the ability of HDL and plasma from a fetus with the Smith-Lemli-Opitz syndrome (SLOS) to efflux cholesterol from trophoblasts. It was unclear whether cholesterol could be effluxed to fetuses with SLOS since lipoprotein levels are often very low. To answer this question, cord blood was collected from the placentas of an SLOS fetus and unaffected fetuses just after delivery. Plasma cholesterol concentrations were very low in the affected fetus; cholesterol, 7-dehydrocholesterol, and 8-dehydocholesterol concentrations were 14.1, 4.5, and 5.2 mg/dl, respectively. The HDL from the fetal SLOS effluxed approximately 50% more cholesterol from a trophoblast cell line, were smaller in size, and had a lower cholesterol to phospholipid ratio as compared to HDL from unaffected fetuses or adults. Plasma from the SLOS fetus effluxed cholesterol to a similar percentage as unaffected fetal plasma or adult plasma, possibly due to fewer HDL particles as demonstrated in previous SLOS patients. These novel data demonstrate that the cholesterol-deficient SLOS fetus is able to obtain cholesterol from trophoblasts at a time when cholesterol is playing a critical role in development, and has implications for design of treatments for cholesterol deficiency syndromes as well as understanding of prenatal cholesterol transport in humans.

The pharmacological exploitation of cholesterol 7alpha-hydroxylase, the key enzyme in bile acid synthesis: from binding resins to chromatin remodelling to reduce plasma cholesterol

Mammals dispose of cholesterol mainly through 7alpha-hydroxylated bile acids, and the enzyme catalyzing the 7alpha-hydroxylation, cholesterol 7alpha-hydroxylase (CYP7A1), has a deep impact on cholesterol homeostasis. In this review, we present the study of regulation of CYP7A1 as a good exemplification of the extraordinary contribution of molecular biology to the advancement of our understanding of metabolic pathways that has taken place in the last 2 decades. Since the cloning of the gene from different species, experimental evidence has accumulated, indicating that the enzyme is mainly regulated at the transcriptional level and that bile acids are the most important physiological inhibitors of CYP7A1 transcription. Multiple mechanisms are involved in the control of CYP7A1 transcription and a variety of transcription factors and nuclear receptors participate in sophisticated regulatory networks. A higher order of transcriptional regulation, stemming from the so-called histone code, also applies to CYP7A1, and recent findings clearly indicate that chromatin remodelling events have profound effects on its expression. CYP7A1 also acts as a sensor of signals coming from the gut, thus representing another line of defence against the toxic effects of bile acids and a downstream target of agents acting at the intestinal level. From the pharmacological point of view, bile acid binding resins were the first primitive approach targeting the negative feed-back regulation of CYP7A1 to reduce plasma cholesterol. In recent years, new drugs have been designed based on recent discoveries of the regulatory network, thus confirming the position of CYP7A1 as a focus for innovative pharmacological intervention.

Mechanisms in the regulation of aromatase in developing ovary and placenta

During human gestation, the placental syncytiotrophoblast develops the capacity to synthesize large amounts of estrogen from C(19)-steroids secreted by the fetal adrenals. The conversion of C(19)-steroids to estrogens is catalyzed by aromatase P450 (P450arom), product of the CYP19 gene. The placenta-specific promoter of the hCYP19 gene lies approximately 100,000 bp upstream of the translation initiation site in exon II. In studies using transgenic mice and transfected human trophoblast cells we have defined a 246-bp region upstream of placenta-specific exon I.1 that mediates placental cell-specific expression. Using transgenic mice, we also observed that as little as 278 bp of DNA flanking the 5'-end of ovary-specific hCYP19 exon IIa was sufficient to target ovary-specific expression. This ovary-specific promoter contains response elements that bind cAMP-response element-binding protein (CREB) and the orphan nuclear receptors SF-1 and LRH-1, which are required for cAMP-mediated stimulation of CYP19 expression in granulosa and luteal cells during the estrous cycle and pregnancy. In this article, we review our studies to define genomic regions and response elements that mediate placenta-specific expression of the hCYP19 gene. The temporal and spatial expression of LRH-1 versus SF-1 in the developing gonad during mouse embryogenesis and in the postnatal ovary also will be considered.

Bile acids, farnesoid X receptor, atherosclerosis and metabolic control

PURPOSE OF REVIEW

Bile acids are amphiphilic molecules synthesized from cholesterol exclusively in the liver that are essential for effective absorption of dietary fat. In addition to this 'classical role', bile acids act as signalling molecules that control their own metabolism by activating the nuclear receptor, farnesoid X receptor.

RECENT FINDINGS

Recent work demonstrates that farnesoid X receptor exerts metabolic control beyond bile acid homeostasis, notably effects on HDL, triglyceride and glucose metabolism. Farnesoid X receptor influences insulin sensitivity of tissues that are not part of the enterohepatic circulation, for example, adipose tissue. Certain metabolic effects in the liver appear to be mediated via farnesoid X receptor-stimulated release of an intestinal growth factor. In addition, novel signalling pathways independent of farnesoid X receptor have been identified that may contribute to bile acid-mediated metabolic regulation.

SUMMARY

Farnesoid X receptor represents a potentially attractive target for treatment of various aspects of the metabolic syndrome and for prevention of atherosclerosis. Yet, in view of its pleiotropic effects and apparent species-specificity, it is evident that successful interference of the farnesoid X receptor signalling system will require the development of gene-specific and/or organ-specific farnesoid X receptor modulators and extensive testing in human models of disease.

Bioavailability and hypoglycemic activity of the semisynthetic bile acid salt, sodium 3α,7α-dihydroxy-12-0X0-5β-cholanate, in healthy and diabetic rats

Previous studies in our laboratory have shown that the semisynthetic bile acid derivative, sodium 3alpha,7alpha-dihydroxy-12-oxo-5beta-cholanate (MKC), has hypoglycemic activity. The aim of this study was to investigate the relationship between the pharmacokinetics and hypoglycemic activity of MKC in healthy and diabetic rats. Groups of healthy and alloxan-induced diabetic rats were dosed intravenously (i.v.) and orally with MKC (4 mg/kg). Blood samples were taken before administration of the dose and at 20, 40, 60, 80, 120, 150, 180, 210 and 240 minutes post-dose. MKC serum concentration was measured by HPLC, and pharmacokinetic parameters determined using the WinNonlin program. The absolute bioavailability of MKC was found to be low in healthy and diabetic rats (29 and 23% respectively) and was not significantly different between the two groups. Mean residence time (MRT), volume of distribution (Vd) and half-life (t1/2) of MKC after oral administration were significantly lower in diabetic than in healthy rats (21, 31 and 29% respectively). After the i.v. dose, the change in blood glucose concentration was not significant in either healthy or diabetic rats. After the oral dose, the decrease in blood glucose concentration was significant, reaching a maximum decrease from baseline of 24% in healthy rats and 15% in diabetic rats. The results suggest that a first-pass effect is crucial for the hypoglycemic activity of MKC, indicating that a metabolite of MKC and/or interference with metabolism and glucose transport is responsible.