Adipocyte fatty acid binding protein 4 (FABP4) inhibitors. An update from 2017 to early 2022

The fatty acid binding protein 4 (FABP4) is a protein predominantly expressed in macrophages and adipose tissue, where it regulates fatty acids storage and lipolysis and is an essential mediator of inflammation. Small molecule inhibitors of FABP4 have attracted interest following the recent publications of beneficial pharmacological effects of these compounds for the treatment of metabolic syndrome and, more recently, for other pathologies. Since the synthesis of the BMS309403, one of the first selective and effective FABP4 inhibitors, hundreds of other inhibitors have been synthesized (i.e., derivatives of niacin, quinoxaline, aryl-quinoline, bicyclic pyridine, urea, aromatic compounds and other novel heterocyclic compounds). This review updates the recently reported (2017 to early 2022) molecules as adipocyte fatty acid binding protein 4 inhibitors.

Fatty acid-binding protein 4: a key regulator of ketoacidosis in new-onset type 1 diabetes

AIMS/HYPOTHESIS

Fatty acid-binding protein 4 (FABP4) is an adipokine with a key regulatory role in glucose and lipid metabolism. We prospectively evaluated the role of FABP4 in the pathophysiology of diabetic ketoacidosis (DKA) in new-onset type 1 diabetes.

METHODS

Clinical and laboratory data were prospectively collected from consecutive children presenting with new-onset type 1 diabetes. In addition to blood chemistry and gases, insulin, C-peptide, serum FABP4 and NEFA were collected upon presentation and 48 h after initiation of insulin treatment. In a mouse model of type 1 diabetes, glucose, insulin, β-hydroxybutyrate and weight were compared between FABP4 knockout (Fabp4^-/-) and wild-type (WT) mice.

RESULTS

Included were 33 children (mean age 9.3 ± 3.5 years, 52% male), of whom 14 (42%) presented with DKA. FABP4 levels were higher in the DKA group compared with the non-DKA group (median [IQR] 10.1 [7.9-14.2] ng/ml vs 6.3 [3.9-7] ng/ml, respectively; p = 0.005). The FABP4 level was positively correlated with HbA_1c at presentation and inversely correlated with venous blood pH and bicarbonate levels (p < 0.05 for all). Following initiation of insulin therapy, a marked reduction in FABP4 was observed in all children. An FABP4 level of 7.22 ng/ml had a sensitivity of 86% and a specificity of 78% for the diagnosis of DKA, with an area under the receiver operating characteristic curve of 0.78 (95% CI 0.6, 0.95; p = 0.008). In a streptozotocin-induced diabetes mouse model, Fabp4^-/- mice exhibited marked hypoinsulinaemia and hyperglycaemia similar to WT mice but displayed no significant increase in β-hydroxybutyrate and were protected from ketoacidosis.

CONCLUSIONS/INTERPRETATION

FABP4 is suggested to be a necessary regulator of ketogenesis in insulin-deficient states.

Computational Tools in the Discovery of FABP4 Ligands: A Statistical and Molecular Modeling Approach

Small molecule inhibitors of adipocyte fatty-acid binding protein 4 (FABP4) have received interest following the recent publication of their pharmacologically beneficial effects. Recently, it was revealed that FABP4 is an attractive molecular target for the treatment of type 2 diabetes, other metabolic diseases, and some type of cancers. In past years, hundreds of effective FABP4 inhibitors have been synthesized and discovered, but, unfortunately, none have reached the clinical research phase. The field of computer-aided drug design seems to be promising and useful for the identification of FABP4 inhibitors; hence, different structure- and ligand-based computational approaches have been used for their identification. In this paper, we searched for new potentially active FABP4 ligands in the Marine Natural Products (MNP) database. We retrieved 14,492 compounds from this database and filtered through them with a statistical and computational filter. Seven compounds were suggested by our methodology to possess a potential inhibitory activity upon FABP4 in the range of 97–331 nM. ADMET property prediction was performed to validate the hypothesis of the interaction with the intended target and to assess the drug-likeness of these derivatives. From these analyses, three molecules that are excellent candidates for becoming new drugs were found.

Fatty Acid-Binding Protein 4 in Cardiovascular and Metabolic Diseases

Fatty acid-binding proteins (FABPs), a family of lipid chaperones, contribute to systemic metabolic regulation via several lipid signaling pathways. Fatty acid-binding protein 4 (FABP4), known as adipocyte FABP (A-FABP) or aP2, is mainly expressed in adipocytes and macrophages and plays important roles in the development of insulin resistance and atherosclerosis in relation to metabolically driven low-grade and chronic inflammation, referred to as ‘metaflammation’. FABP4 is secreted from adipocytes in a non-classical pathway associated with lipolysis and acts as an adipokine for the development of insulin resistance and atherosclerosis. Circulating FABP4 levels are associated with several aspects of metabolic syndrome and cardiovascular disease. Ectopic expression and function of FABP4 in cells and tissues are also related to the pathogenesis of several diseases. Pharmacological modification of FABP4 function by specific inhibitors, neutralizing antibodies or antagonists of unidentified receptors would be novel therapeutic strategies for several diseases, including obesity, diabetes mellitus, atherosclerosis and cardiovascular disease. Significant roles of FABP4 as a lipid chaperone in physiological and pathophysiological conditions and the possibility of FABP4 being a therapeutic target for metabolic and cardiovascular diseases are discussed in this review.

3D-QSAR assisted identification of FABP4 inhibitors: An effective scaffold hopping analysis/QSAR evaluation

Following on the recent publication of pharmacologically relevant effects, small molecule inhibitors of adipocyte fatty-acid binding protein 4 (FABP4) have attracted high interest. FABP4 is mainly expressed in macrophages and adipose tissue, where it regulates fatty acid storage and lipolysis, being also an important mediator of inflammation. In this regard, FABP4 recently demonstrated an interesting molecular target for the treatment of type 2 diabetes, other metabolic diseases and some type of cancers. In the past years, hundreds of effective FABP4 inhibitors have been synthesized. In this paper, a quantitative structure-activity relationship (QSAR) model has been produced, in order to predict the bioactivity of FABP4 inhibitors. The methodology has been combined with a scaffold-hopping approach, allowing to identify three new molecules that act as effective inhibitors of this protein. These molecules, synthesized and tested for their FABP4 inhibitor activity, showed IC₅₀ values between 3.70 and 5.59 μM, with a high level of agreement with the predicted values.

Lessons from Cre-Mice and Indicator Mice

The adult human adipose tissue is predominantly composed of white adipocytes. However, within certain depots, adipose tissue contains thermogenically active brown-like adipocytes, which have been evolutionarily conserved in mammals. This chapter will give a brief overview on the methods used to genetically target and trace both white and brown adipocytes using techniques such as bacterial artificial chromosome (BAC) cloning to create transgenic mouse models and the tools with which genetic recombination is mediated in vivo (e.g., Cre-loxP, CreERT, and Tet-On). The chapter furthermore critically discusses the strength and limitation of the various systems used to target mature white and brown adipocytes (ap2-Cre, Adipoq-Cre, and Ucp1-Cre). Based on these systems, it is evident that our knowledge of mature adipocyte categorization into brown, white, brite, or beige adipocytes is strongly influenced by the use of the various genetic mouse models described in this chapter. Our evaluation of different studies using the aforementioned systems focuses on key genes, which have been reported to maintain adipocyte's function (insulin receptor, Raptor, or Atgl).

Naringenin attenuates hepatitis B virus X protein-induced hepatic steatosis

BACKGROUND

Naringenin (Nar), a common dietary flavonoid abundantly present in fruits, vegetables, and Chinese herbs, is believed to possess strong anti-inflammatory properties and to modulate hepatic apolipoprotein and lipid synthesis. However, there are no reports describing Nar's effects on the hepatitis B virus protein X (HBx) -induced hepatic steatosis, and the detailed molecular mechanisms of the compound's effects are still unclear.

METHODS

Nar was administered by oral gavage to HBx-transgenic mice from 4 to 6 weeks of age. Mice were sacrificed after 14 days of once-daily naringenin administration. Liver tissues and sera were collected for histopathology and biochemical analysis.

RESULTS

Nar counteracted hepatic lipid accumulation and liver dysfunction in HBx-transgenic mice. In addition, Nar significantly decreased expression of adipogenic and lipogenic genes in mice, suggesting that the compound may have therapeutic effects in the early stages of HBx-mediated hepatic steatosis. These results indicated that naringenin inhibits HBx-induced expression of hepatic adipogenic and lipogenic genes through suppression of HBx-induced gene expression, including decreases in the transcriptional activity of SREBP1c, LXRα, and PPARγ in HBx-trangenic mice and HBx-transfected HepG2 cells.

CONCLUSIONS

Results from this study suggested that Nar may serve as a therapeutic agent for preventing HBx-infected hepatic steatosis in humans.

Adipocyte fatty acid binding protein 4 (FABP4) inhibitors. A comprehensive systematic review

Small molecule inhibitors of adipocyte fatty acid binding protein 4 (FABP4) have attracted interest following the recent publications of beneficial pharmacological effects of these compounds. FABP4 is predominantly expressed in macrophages and adipose tissue where it regulates fatty acids (FAs) storage and lipolysis and is an important mediator of inflammation. In the past years, hundreds FABP4 inhibitors have been synthesized for effective atherosclerosis and diabetes treatments, including derivatives of niacin, quinoxaline, aryl-quinoline, bicyclic pyridine, urea, aromatic compounds and other novel heterocyclic compounds. This review provides an overview of the synthesized and discovered molecules as adipocyte fatty acid binding protein 4 inhibitors (FABP4is) since the synthesis of the putative FABP4i, BMS309403, highlighting the interactions of the different classes of inhibitors with the targets.

Monascus ruber-Fermented Buckwheat (Red Yeast Buckwheat) Suppresses Adipogenesis in 3T3-L1 Cells

Although various treatments have been used for weight loss to date, obese people rarely have safe and effective treatment options. Therefore, the antiobesity effects of several natural compounds are being actively investigated. This study was conducted to investigate the antiadipogenic effects of Monascus ruber-fermented Fagopyrum esculentum (red yeast buckwheat, RYB) in 3T3-L1 cells. We assessed the intracellular lipid content and adipocyte differentiation by oil red O staining and the expression of genes and proteins associated with adipocyte differentiation by reverse transcription-polymerase chain reaction and western blotting in 3T3-L1 cells. RYB dose dependently inhibited 3T3-L1 cell differentiation at concentrations of 50-800 μg/mL, without cytotoxic effects. It also suppressed the expression of adipogenic transcription factors, including peroxisome proliferator-activated receptor γ and CCAAT/enhancer-binding protein α, and adipocyte-specific genes, such as adipocyte fatty acid-binding protein (aP2), fatty acid synthase, and leptin, during preadipocyte differentiation into adipocytes. Furthermore, RYB reduced cyclin-dependent kinase 2 and cyclin expression and increased p21 and p27 expression, thus causing cell cycle arrest at the G1/S phase. Collectively, these results suggest that RYB may be an effective nutraceutical for weight loss as indicated by its ability to suppress adipogenesis-specific gene expression and cause cell cycle arrest at the G1/S interphase.

Interaction Analysis of FABP4 Inhibitors by X-ray Crystallography and Fragment Molecular Orbital Analysis

X-ray crystal structural determination of FABP4 in complex with four inhibitors revealed the complex binding modes, and the resulting observations led to improvement of the inhibitory potency of FABP4 inhibitors. However, the detailed structure-activity relationship (SAR) could not be explained from these structural observations. For a more detailed understanding of the interactions between FABP4 and inhibitors, fragment molecular orbital analyses were performed. These analyses revealed that the total interfragment interaction energies of FABP4 and each inhibitor correlated with the ranking of the K i value for the four inhibitors. Furthermore, interactions between each inhibitor and amino acid residues in FABP4 were identified. The oxygen atom of Lys58 in FABP4 was found to be very important for strong interactions with FABP4. These results might provide useful information for the development of novel potent FABP4 inhibitors.

The effects of androgen deprivation therapy with weight management on serum aP2 and adiponectin levels in prostate cancer patients

Androgen deprivation therapy (ADT) for the treatment of prostate cancer (PCa) causes an increase in total body fat, leading to a net gain in body weight. Moreover, the use of the luteinizing hormone-releasing hormone agonists in ADT causes a decrease in serum androgen levels, leading to the development of metabolic syndrome (MetS). Androgen blockade significantly increases plasma adiponectin levels, which has some efficacy against MetS, whereas ADT increases fasting plasma insulin and decreases insulin sensitivity, suggesting that there are other mechanisms involved in the onset of MetS besides adiponectin activation. We investigated the effects of ADT on serum aP2 and adiponectin in PCa patients. Six months post-ADT, serum aP2 and adiponectin levels were significantly increased, although there were no changes in patient body weight and no correlation between the changes in serum aP2 and total adiponectin levels. The serum adiponectin and aP2 levels have independent implications in ADT for PCa; therefore, their combined measurement will clarify the impact on the development of obesity-related diseases during ADT. Contrary to adiponectin, high serum aP2 levels were correlated with the late development of MetS. Further studies are needed to investigate the future occurrence of metabolic diseases post-ADT.

Promoting effect of triterpenoid compound from Agrimonia pilosa Ledeb on preadipocytes differentiation via up-regulation of PPARγ expression

Background:

Agrimonia Pilosa Ledeb (APL), a traditional Chinese medicine, has been reported a variety of biological activities, including treating T2DM.

Objective:

Triterpenoid compound (TC) was collected from APL. The aim of this study was to investigate the effects of TC on 3T3-L1 preadipocytes differentiation and genes related to differentiation and IR.

Materials and Methods:

Column chromatography was used to collect TC from ALP. 3T3-L1 cell differentiation was induced typically in the presence of various concentrations of TC or pioglitazone. Oil red O staining and measurement of intracellular TG content were performed on the seventh day of differentiation. Then quantitative polymerase chain reaction (Q-PCR) was used to test the expressions of three transcription factors (PPARγ, CCAAT enhancer binding protein-α (C/EBP-α), and sterol regulatory element-binding protein 1 (SREBP-1)) and the target genes of PPARγ including glucose transporter (GLUT4), lipoprotein lipase (LPL), fat acid binding protein (AP2), and adiponectin in 3T3-L1 cells.

Results:

At the concentration of 5, 25 and 125 μg/mL, TC significantly promoted triglyceride accumulation. Further study showed that TC could promote the expression of PPARγ, C/EBPα and ADD1/SREBP1 significantly at 125 μg/mL. As for downstream genes controlled by PPARγ, TC at 25 and 125 μg/mL could significantly promote the expression of GLUT4 and adiponectin. However, the expression of aP2 related to lipid metabolism and adiposity in the TC group was significantly lower than that in the pioglitazone group.

Conclusion:

TC could promote preadipocytes differentiation through activating PPARγ and downstream controlled genes. TC has the ideal insulin sensitization with lower adipogenic action than classical TZDs in vitro. So TC from Agrimonia Pilosa Ledeb has a good prospect as a natural drug for IR and T2DM.

Structural analysis of ibuprofen binding to human adipocyte fatty-acid binding protein (FABP4)

Inhibition of human adipocyte fatty-acid binding protein (FABP4) has been proposed as a treatment for type 2 diabetes, fatty liver disease and atherosclerosis. However, FABP4 displays a naturally low selectivity towards hydrophobic ligands, leading to the possibility of side effects arising from cross-inhibition of other FABP isoforms. In a search for structural determinants of ligand-binding selectivity, the binding of FABP4 towards a group of small molecules structurally related to the nonsteroidal anti-inflammatory drug ibuprofen was analyzed through X-ray crystallography. Several specific hydrophobic interactions are shown to enhance the binding affinities of these compounds, whereas an aromatic edge-to-face interaction is proposed to determine the conformation of bound ligands, highlighting the importance of aromatic interactions in hydrophobic environments.

Novel insights of dietary polyphenols and obesity. J Nutr Biochem. 2014;25:1-18. [PMID: 24314860 DOI: 10.1016/j.jnutbio.2013.09.001]

The prevalence of obesity has steadily increased over the past three decades both in the United States and worldwide. Recent studies have shown the role of dietary polyphenols in the prevention of obesity and obesity-related chronic diseases. Here, we evaluated the impact of commonly consumed polyphenols, including green tea catechins, especially epigallocatechin gallates, resveratrol and curcumin, on obesity and obesity-related inflammation. Cellular studies demonstrated that these dietary polyphenols reduce viability of adipocytes and proliferation of preadipocytes, suppress adipocyte differentiation and triglyceride accumulation, stimulate lipolysis and fatty acid β-oxidation, and reduce inflammation. Concomitantly, the polyphenols modulate signaling pathways including the adenosine-monophosphate-activated protein kinase, peroxisome proliferator activated receptor γ, CCAAT/enhancer binding protein α, peroxisome proliferator activator receptor gamma activator 1-alpha, sirtuin 1, sterol regulatory element binding protein-1c, uncoupling proteins 1 and 2, and nuclear factor-κB that regulate adipogenesis, antioxidant and anti-inflammatory responses. Animal studies strongly suggest that commonly consumed polyphenols described in this review have a pronounced effect on obesity as shown by lower body weight, fat mass and triglycerides through enhancing energy expenditure and fat utilization, and modulating glucose hemostasis. Limited human studies have been conducted in this area and are inconsistent about the antiobesity impact of dietary polyphenols probably due to the various study designs and lengths, variation among subjects (age, gender, ethnicity), chemical forms of the dietary polyphenols used and confounding factors such as other weight-reducing agents. Future randomized controlled trials are warranted to reconcile the discrepancies between preclinical efficacies and inconclusive clinic outcomes of these polyphenols.

Bisphenol A increases aP2 expression in 3T3L1 by enhancing the transcriptional activity of nuclear receptors at the promoter

Environmental pollutants, such as bisphenol A (BPA), have the potential to affect the differentiation processes and the biology of the adipose tissue. The 3T3-L1 model is one of the murine cell models used extensively for the investigation of the molecular events that govern the differentiation of adipocytes from a committed preadipocyte to a mature, lipid laden adipocyte. Most of the studies investigating the effects of BPA on preadipocyte differentiation have investigated the effects of this chemical in the presence of an optimal differentiation cocktail containing high concentrations of the synthetic glucocorticoid dexamethasone, conditions that result in 90% to 100% of differentiated adipocytes. Our studies employed the 3T3-L1 cell model in the absence of exogenous glucocorticoids. We show that BPA is able to increase the differentiation of the 3T3-L1 cells under these conditions. Furthermore, the effect of BPA was observed in the absence of the synthetic glucocorticoid (dexamethasone), a hormone known to be required for the differentiation of the 3T3-L1 cells. In addition, BPA upregulated the mRNA expression and protein levels of the terminal marker of adipogenesis the fatty acid binding protein (aP2) in these cells. Interestingly, the known modulators of adipogenesis such as the peroxisome proliferator-activated receptor (PPAR) γ or CCAAT enhancer binding protein (C/EBP) α were not elevated at the mRNA or protein level in response to BPA. Furthermore, BPA upregulated the expression levels of the marker of adipogenesis aP2, through an effect on the transcriptional activity of C/EBPδ and the glucocorticoid receptor (GR) at its promoter.

Intrinsic circannual regulation of brown adipose tissue form and function in tune with hibernation

Winter hibernators repeatedly cycle between cold torpor and rewarming supported by nonshivering thermogenesis in brown adipose tissue (BAT). In contrast, summer animals are homeotherms, undergoing reproduction, growth, and fattening. This life history confers variability to BAT recruitment and activity. To address the components underlying prewinter enhancement and winter activation, we interrogated the BAT proteome in 13-lined ground squirrels among three summer and five winter states. We also examined mixed physiology in fall and spring individuals to test for ambient temperature and seasonal effects, as well as the timing of seasonal transitions. BAT form and function differ circannually in these animals, as evidenced by morphology and proteome dynamics. This intrinsic pattern distinguished homeothermic groups and early vs. late winter hibernators. Homeothermic variation derived from postemergence delay in growth and substrate biosynthesis. The heterothermic proteome varied less despite extreme winter physiological shifts and was optimized to exploit lipids by enhanced fatty acid binding, β-oxidation, and mitochondrial protein translocation. Surprisingly, ambient temperature did not affect the BAT proteome during transition seasons; rather, the pronounced summer-winter shift preceded environmental changes and phenotypic progression. During fall transition, differential regulation of two fatty acid binding proteins provides further evidence of recruitment and separates proteomic preparation from successful hibernation. Abundance of FABP4 correlates with torpor bout length throughout the year, clarifying its potential function in hibernation. Metabolically active BAT is a target for treating human obesity and metabolic disorders. Understanding the hibernator's extreme and seasonally distinct recruitment and activation control strategies offers untapped potential to identify novel, therapeutically relevant regulatory pathways.

MiR-27 orchestrates the transcriptional regulation of brown adipogenesis

OBJECTIVE

Brown adipose tissue (BAT) produces heat using chemical energy of lipids and glucose, a function induced by cold exposure or diet. The brown adipogenesis is tightly controlled in a coordinated interplay between several transcriptional factors. It is not known what enables and coordinates this robust program of concerted cooperation between the transcriptional factors and co-regulators necessary for the brown adipogenesis.

MATERIALS/METHODS

A. In vivo studies--we investigated the expression levels of miR-27a and b in mice after cold exposure. B. Using gene expression and functional studies together with high throughput imaging in primary preadipocytes, and cell culture models, we investigated the role of miR-27 in beige and brown adipogenesis. C. Using gene silencing and rescue experiments we dissected the molecular mechanisms of the miR-27 action.

RESULTS

After cold exposure, miR-27 is downregulated in BAT and subcutaneous white adipose tissue (SAT). MiR-27 is also downregulated during brown adipogenesis of primary preadipocytes in vitro, and it directly targets and negatively regulates the essential components of the brown transcriptional network: Prdm16, Pparα, Creb, and in part Pgc1β. Together with its direct effect on Pparγ, and indirect on Pgc1α, mir-27 decreases brown differentiation of cultured cells and of primary SAT preadipocytes.

CONCLUSIONS

Our results point to miR-27 as a central upstream regulator of the transcriptional network involved in beige and brown adipogenesis after cold exposure, and suggest miR-27 inhibition as a novel therapeutic approach for metabolic diseases aiming at increasing the beige/brown fat mass.

Activation of early phase of adipogenesis through Krüppel-like factor KLF9-mediated, enhanced expression of CCAAT/enhancer-binding protein β in 3T3-L1 cells

In this study, we found that Krüppel-like factor (KLF) 9 activate the progression of the early phase of adipocyte differentiation in mouse adipocytic 3T3-L1 cells. KLF9 mRNA was detected in preadipocytes; and its level increased after the initiation of adipocyte differentiation, reached its maximum at 1h, and gradually decreased thereafter. Functional suppression of KLF9 mRNA by its siRNAs repressed the accumulation of the intracellular lipids with a reduction in the expression of CCAAT/enhancer-binding protein (C/EBP) β, but not in that of C/EBPδ. In contrast, C/EBPβ and C/EBPδ did not affect the expression of KLF9 in 3T3-L1 cells. A chromatin immunoprecipitation assay revealed that KLF9 bound the KLF binding element at position -874 of the mouse C/EBPβ promoter. Moreover, the ability of KLF9 to bind to this element was enhanced, with a peak at 1-2h after the initiation of adipogenesis, whose profile well resembled that of the expression of the C/EBPβ gene in 3T3-L1 cells. These results indicate that KLF9 activated the early phase of adipogenesis by enhancing the expression of the C/EBPβ gene in 3T3-L1 cells.

Deletion of circadian gene Per1 alleviates acute ethanol-induced hepatotoxicity in mice. Toxicology. 2013;314:193-201. [PMID: 24144995 DOI: 10.1016/j.tox.2013.09.009]

The severity of ethanol-induced liver injury is associated with oxidative stress and lipid accumulation in the liver. Core circadian clock is known to mediate antioxidative enzyme activity and lipid metabolism. However, the link between circadian clock and ethanol-induced hepatotoxicity remains unclear. Here we showed that extents of acute ethanol-induced liver injury and steatosis in mice exhibit circadian variations consistent with hepatic expression of Period (Per) genes. Mice lacking clock gene Per1 displayed less susceptible to ethanol-induced liver injury, as evidenced by lower serum transaminase activity and less severe histopathological changes. Ethanol-induced lipid peroxidation was alleviated in Per1-/- mice. However, Per1 deletion had no effect on antioxidants depletion caused by ethanol administration. Ethanol-induced triglycerides (TG) accumulation in the serum and liver was significantly decreased in Per1-/- mice compared with that in wild-type (WT) mice. Analysis of gene expression in the liver revealed peroxisome proliferators activated receptor-gamma (PPARγ) and its target genes related to TG synthesis are remarkably down-regulated in Per1-/- mice. HepG2 cells were treated with ethanol at 150 mM for 3 days. Per1 overexpression augmented lipid accumulation after treatment with ethanol in HepG2 cells, but had no effect on ethanol-induced oxidative stress. Expression of genes related to lipogenesis, including PPARγ and its target genes, was up-regulated in cells overexpressing Per1. In conclusion, these results indicated that circadian rhythms of ethanol-induced hepatotoxicity are controlled by clock gene Per1, and deletion of Per1 protected mice from ethanol-induced liver injury by decreasing hepatic lipid accumulation.

Hypoxia downregulates PPARγ via an ERK1/2-NF-κB-Nox4-dependent mechanism in human pulmonary artery smooth muscle cells

The ligand-activated transcription factor peroxisome proliferator-activated receptor γ (PPARγ) regulates metabolism, cell proliferation, and inflammation. Pulmonary hypertension (PH) is associated with reduced PPARγ expression, and hypoxia exposure regimens that cause PH reduce PPARγ expression. This study examines mechanisms of hypoxia-induced PPARγ downregulation in vitro and in vivo. Hypoxia reduced PPARγ mRNA and protein levels, PPARγ activity, and the expression of PPARγ-regulated genes in human pulmonary artery smooth muscle cells (HPASMCs) exposed to 1% oxygen for 72 h. Similarly, exposure of mice to hypoxia (10% O₂) for 3 weeks reduced PPARγ mRNA and protein in mouse lung. Inhibiting ERK1/2 with PD98059 or treatment with siRNA directed against either NF-κB p65 or Nox4 attenuated hypoxic reductions in PPARγ expression and activity. Furthermore, degradation of H₂O₂ using PEG-catalase prevented hypoxia-induced ERK1/2 phosphorylation and Nox4 expression, suggesting sustained ERK1/2-mediated signaling and Nox4 expression in this response. Mammalian two-hybrid assays demonstrated that PPARγ and p65 bind directly to each other in a mutually repressive fashion. We conclude from these results that hypoxic regimens that promote PH pathogenesis and HPASMC proliferation reduce PPARγ expression and activity through ERK1/2-, p65-, and Nox4-dependent pathways. These findings provide novel insights into mechanisms by which pathophysiological stimuli such as hypoxia cause loss of PPARγ activity and pulmonary vascular cell proliferation, pulmonary vascular remodeling, and PH. These results also indicate that restoration of PPARγ activity with pharmacological ligands may provide a novel therapeutic approach in selected forms of PH.

Ubiquitin-specific protease 2-69 in macrophages potentially modulates metainflammation

Macrophages play a critical role in chronic inflammation and metabolic diseases. We identified a longer splice variant of ubiquitin specific protease (USP) 2-69 as a novel molecule that modulates pathways implicated in metabolic disorders. Expression levels of aP2/FABP4 and PAI-1/SERPINE1 genes were increased by 4- and 1.8-fold, respectively, after short hairpin RNA-mediated knockdown (KD) of the USP2 gene, and such expression was alleviated by overexpression of USP2-69 in human myeloid cell lines. Supernatants derived from USP2-KD cells induced IL6 (∼6-fold) and SAA3 (∼15-fold) in 3T3-L1 adipocytes to suggest the anti-inflammatory properties of USP2. In addition, we observed a 30% decrease in the number of macrophages in mesenteric adipose tissue derived from USP2-69 transgenic mice fed a high-fat diet for 14 wk compared with that in their C57BL/6 littermates (P<0.01), which was consistent with a ∼40% decrease in transcription of aP2 and PAI-1. The aP2 locus exhibited elevated chromatin accessibility (>2.1-fold), methylation of histone H3 lysine 4 (>4.5-fold), and acetylation of histone H4 (>2.5-fold) in USP2-KD cells. Transfection of isopeptidase-mutated USP2-69 did not alter chromatin conformation on the aP2 locus in USP2-KD cells. Our results suggest that USP2-69 suppresses meta-inflammatory molecules involved in the development of type-2 diabetes.

Piperine reverses high fat diet-induced hepatic steatosis and insulin resistance in mice

This study examined the effect of piperine on hepatic steatosis and insulin resistance induced in mice by feeding a high-fat diet (HFD) for 13 weeks and elucidated potential underlying molecular mechanisms. Administration of piperine (50 mg/kg body weight) to mice with HFD-induced hepatic steatosis resulted in a significant increase in plasma adiponectin levels. Also, elevated plasma concentrations of insulin and glucose and hepatic lipid levels induced by feeding a HFD were reversed in mice when they were administered piperine. However, piperine did not reduce body weight and other biochemical markers to an extent where they became equal to the levels found in the CD-fed mice. Piperine reversed HFD-induced down-regulation of adiponecitn-AMP-activated protein kinase (AMPK) signalling molecules which play an important role in mediating lipogenesis, fatty acid oxidation and insulin signalling in the livers of mice. The expressions of lipogenic target genes were decreased, whereas the expression of carnitine palmitoyltransferase 1 (CPT1) gene involved in fatty acid oxidation was increased in the livers of the Pin50 group. Piperine significantly decreased the phosphorylation of insulin receptor substrate-1 (IRS-1) compared with the HFD-fed mice. Administration of piperine appeared to reverse preexisting HFD-induced hepatic steatosis and insulin resistance, probably by activation of adiponectin-AMPK signalling in mice.