Pharmacological inhibition of adipocyte fatty acid binding protein alleviates both acute liver injury and non-alcoholic steatohepatitis in mice

Islet-Resident Memory T Cells Orchestrate the Immunopathogenesis of Type 1 Diabetes through the FABP4-CXCL10 Axis

Type 1 diabetes (T1D) is a chronic disease characterized by self-destruction of insulin-producing pancreatic β cells by cytotoxic T cell activity. However, the pathogenic mechanism of T cell infiltration remains obscure. Recently, tissue-resident memory T (TRM) cells have been shown to contribute to cytotoxic T cell recruitment. TRM cells are found present in human pancreas and are suggested to modulate immune homeostasis. Here, the role of TRM cells in the development of T1D is investigated. The presence of TRM cells in pancreatic islets is observed in non-obese diabetic (NOD) mice before T1D onset. Mechanistically, elevated fatty acid-binding protein 4 (FABP4) potentiates the survival and alarming function of TRM cells by promoting fatty acid utilization and C-X-C motif chemokine 10 (CXCL10) secretion, respectively. In NOD mice, genetic deletion of FABP4 or depletion of TRM cells using CD69 neutralizing antibodies resulted in a similar reduction of pancreatic cytotoxic T cell recruitment, a delay in diabetic incidence, and a suppression of CXCL10 production. Thus, targeting FABP4 may represent a promising therapeutic strategy for T1D.

Development of a therapeutic monoclonal antibody against circulating adipocyte fatty acid binding protein to treat ischaemic stroke

BACKGROUND AND PURPOSE

Adipocyte fatty acid-binding protein (A-FABP) exacerbates cerebral ischaemia injury by disrupting the blood-brain barrier (BBB) through inducing expression of MMP-9. Circulating A-FABP levels positively correlate with infarct size in stroke patients. We hypothesized that targeting circulating A-FABP by a neutralizing antibody would alleviate ischaemic stroke outcome.

EXPERIMENTAL APPROACH

Monoclonal antibodies (mAbs) against A-FABP were generated using mouse hybridoma techniques. Binding affinities of a generated mAb named 6H2 towards various FABPs were determined using Biacore. Molecular docking studies were performed to characterize the 6H2-A-FABP complex structure and epitope. The therapeutic potential and safety of 6H2 were evaluated in mice with transient middle cerebral artery occlusion (MCAO) and healthy mice, respectively.

KEY RESULTS

Replenishment of recombinant A-FABP exaggerated the stroke outcome in A-FABP-deficient mice. 6H2 exhibited nanomolar to picomolar affinities to human and mouse A-FABP, respectively, with minimal cross-reactivities with heart and epidermal FABPs. 6H2 effectively neutralized JNK/c-Jun activation elicited by A-FABP and reduced MMP-9 production in macrophages. Molecular docking suggested that 6H2 interacts with the "lid" of the fatty acid binding pocket of A-FABP, thus likely hindering the binding of its substrates. In mice with transient MCAO, 6H2 significantly attenuated BBB disruption, cerebral oedema, infarction, neurological deficits, and decreased mortality associated with reduced cytokine and MMP-9 production. Chronic 6H2 treatment showed no obvious adverse effects in healthy mice.

CONCLUSION AND IMPLICATIONS

These results establish circulating A-FABP as a viable therapeutic target for ischaemic stroke, and provide a highly promising antibody drug candidate with high affinity and specificity.

Integrated multi-omic analysis identifies fatty acid binding protein 4 as a biomarker and therapeutic target of ischemia-reperfusion injury in steatotic liver transplantation

BACKGROUND AND AIMS

Due to a lack of donor grafts, steatotic livers are used more often for liver transplantation (LT). However, steatotic donor livers are more sensitive to ischemia-reperfusion (IR) injury and have a worse prognosis after LT. Efforts to optimize steatotic liver grafts by identifying injury targets and interventions have become a hot issue.

METHODS

Mouse LT models were established, and 4D label-free proteome sequencing was performed for four groups: normal control (NC) SHAM, high-fat (HF) SHAM, NC LT, and HF LT to screen molecular targets for aggravating liver injury in steatotic LT. Expression detection of molecular targets was performed based on liver specimens from 110 donors to verify its impact on the overall survival of recipients. Pharmacological intervention using small-molecule inhibitors on an injury-related target was used to evaluate the therapeutic effect. Transcriptomics and metabolomics were performed to explore the regulatory network and further integrated bioinformatics analysis and multiplex immunofluorescence were adopted to assess the regulation of pathways and organelles.

RESULTS

HF LT group represented worse liver function compared with NC LT group, including more apoptotic hepatocytes (P < 0.01) and higher serum transaminase (P < 0.05). Proteomic results revealed that the mitochondrial membrane, endocytosis, and oxidative phosphorylation pathways were upregulated in HF LT group. Fatty acid binding protein 4 (FABP4) was identified as a hypoxia-inducible protein (fold change > 2 and P < 0.05) that sensitized mice to IR injury in steatotic LT. The overall survival of recipients using liver grafts with high expression of FABP4 was significantly worse than low expression of FABP4 (68.5 vs. 87.3%, P < 0.05). Adoption of FABP4 inhibitor could protect the steatotic liver from IR injury during transplantation, including reducing hepatocyte apoptosis, reducing serum transaminase (P < 0.05), and alleviating oxidative stress damage (P < 0.01). According to integrated transcriptomics and metabolomics analysis, cAMP signaling pathway was enriched following FABP4 inhibitor use. The activation of cAMP signaling pathway was validated. Microscopy and immunofluorescence staining results suggested that FABP4 inhibitors could regulate mitochondrial membrane homeostasis in steatotic LT.

CONCLUSIONS

FABP4 was identified as a hypoxia-inducible protein that sensitized steatotic liver grafts to IR injury. The FABP4 inhibitor, BMS-309403, could activate of cAMP signaling pathway thereby modulating mitochondrial membrane homeostasis, reducing oxidative stress injury in steatotic donors.

A study integrated metabolomics and network pharmacology to investigate the effects of Shicao in alleviating acute liver injury

ETHNOPHARMACOLOGICAL RELEVANCE

Shicao is the aerial part of Achillea alpina L., a common herb found mainly in Europe, Asia, and North America. Traditional Chinese medicine has a history of thousands of years and is widely used to treat various diseases.

AIM OF STUDY

To explore the hepatoprotective effects of Shicao on CCl4-induced acute liver injury.

METHODS

A rat model of acute liver injury was established and liver function indices were assessed to evaluate the protective effect of Shicao on the liver. Untargeted metabolomics of the serum and liver tissues was conducted using UPLC-Q-TOF/MS to identify differential metabolites related to acute liver injury. A network of metabolite-reaction-enzyme-gene constituents was constructed using network pharmacology. Hub targets and key components of the effect of Shicao on acute liver injury were screened from the network.

RESULTS

Compared to the model group, Shicao improved the degree of liver damage through the assessment of the liver index, ALT and AST levels, and hepatic pathology slices, demonstrating its hepatoprotective effect against acute liver injury in rats. 10 and 38 differential metabolites involved in acute liver injury were identified in serum and liver tissues, respectively. Most of these were regulated or restored following treatment with Shicao, which mainly consisted of bile acids, lipids, and nucleotides such as taurocholic acid, LysoPC (17:0), and adenosine diphosphate ribose. Through the network of metabolite-reaction-enzyme-gene-constituents, 10 key components and 5 hub genes, along with 7 crucial differential metabolites, were mainly involved in glycerophospholipid metabolism, purine metabolism, biosynthesis of unsaturated fatty acids, and primary bile acid biosynthesis, which may play important roles in the prevention of acute liver injury by Shicao.

CONCLUSION

This study revealed that Shicao had protective effects against CCl4-induced liver injury in rats. It was speculated that the ingredients of Shicao might be closely related to the hub targets, thereby regulating the levels of key metabolites, affecting inflammatory response and oxidative stress and attenuate the liver injury consequently. This study provides a basis for further investigation of its therapeutic potential and the mechanism of action.

Levofloxacin alleviates blood-brain barrier disruption following cerebral ischemia and reperfusion via directly inhibiting A-FABP

Reperfusion therapy is currently the most effective treatment for acute ischemic stroke, but often results in secondary brain injury. Adipocyte fatty acid-binding protein (A-FABP, FABP4, or aP2) was shown to critically mediate cerebral ischemia/reperfusion (I/R) injury by exacerbating blood-brain barrier (BBB) disruption. However, no A-FABP inhibitors have been approved for clinical use due to safety issues. Here, we identified the therapeutic effect of levofloxacin, a widely used antibiotic displaying A-FABP inhibitory activity in vitro, on cerebral I/R injury and determined its target specificity and action mechanism in vivo. Using molecular docking and site-directed mutagenesis, we showed that levofloxacin inhibited A-FABP activity through interacting with the amino acid residue Asp76, Gln95, Arg126 of A-FABP. Accordingly, levofloxacin significantly inhibited A-FABP-induced JNK phosphorylation and expressions of proinflammatory factors and matrix metalloproteinase 9 (MMP-9) in mouse primary macrophages. In wild-type mice with transient middle cerebral artery occlusion, levofloxacin substantially mitigated BBB disruption and neuroinflammation, leading to reduced cerebral infarction, alleviated neurological outcomes, and improved survival. Mechanistically, levofloxacin decreased MMP-9 expression and activity, and thus reduced degradation of extracellular matrix and endothelial tight junction proteins. Importantly, the BBB- and neuro-protective effects of levofloxacin were abolished in A-FABP or MMP-9 knockout mice, suggesting that the therapeutic effects of levofloxacin highly depended on specific targeting of the A-FABP-MMP-9 axis. Overall, our study demonstrates that levofloxacin alleviates A-FABP-induced BBB disruption and neural tissue injury following cerebral I/R, and unveils its therapeutic potential for the treatment of ischemic stroke.

Structure-based design of potent FABP4 inhibitors with high selectivity against FABP3

Fatty-acid binding protein 4 (FABP4) presents an attractive target for therapeutic intervention in metabolic and inflammatory diseases in recent years. However, highly similar three-dimensional structures and fatty acid binding ability of multiple FABP family members pose a significant challenge in design of FABP4-selective inhibitors. Particularly, inhibition of FABP3 raises safety concerns such as cardiac dysfunction and exercise intolerance. Here, we reported the discovery of new FABP4 inhibitors with high selectivity over FABP3 by exploiting the little structural difference in the ligand binding pockets of FABP4 and FABP3. On the basis of our previously reported FABP4 inhibitors with nanomolar potency, different substituents were further introduced to perfectly occupy two sub-pockets of FABP4 that are distinct from those of FABP3. Remarkably, a single methyl group introduction leads to the discovery of compound C3 that impressively exhibits a 601-fold selectivity over FABP3 when maintained nanomolar binding affinity for FABP4. Moreover, C3 also shows good metabolic stability and potent cellular anti-inflammatory activity, making it a promising inhibitor for further development. Therefore, the present study highlights the utility of the structure-based rational design strategy for seeking highly selective and potent inhibitors of FABP4 and the importance of identifying the appropriate subsite as well as substituent for gaining the desired selectivity.

Fatty acid binding protein 4 (FABP4) induces chondrocyte degeneration via activation of the NF-κb signaling pathway

The pathogenesis of osteoarthritis (OA) is still unclear. Fatty acid binding protein 4 (FABP4), a novel adipokine, has been found to play a role in OA. This study aimed to explore the role of NF-κB in FABP4-induced OA. In the in vivo study, four pairs of 12-week-old male FABP4 knockout (KO) and wild-type (WT) mice were included. The activation of NF-κB was assessed. In parallel, 24 6-week-old male C57/Bl6 mice were fed a high-fat diet (HFD) and randomly allocated to four groups: daily oral gavage with (1) PBS solution; (2) QNZ (NF-κB-specific inhibitor, 1 mg/kg/d); (3) BMS309403 (FABP4-specific inhibitor, 30 mg/kg/d); and (4) BMS309403 (30 mg/kg/d) + QNZ (1 mg/kg/d). The diet and treatment were sustained for 4 months. The knee joints were obtained to assess cartilage degradation, NF-κB activation, and subchondral bone sclerosis. In the in vitro study, a mouse chondrogenic cell line (ATDC5) was cultured. FABP4 was supplemented to stimulate chondrocytes, and the activation of NF-κB was investigated. In parallel, QNZ and NF-κB-specific siRNA were used to inhibit NF-κB. In vivo, the FABP4 WT mice had more significant NF-κB activation than the KO mice. Dual inhibition of FABP4 and NF-κB alleviated knee OA in mice. FABP4 has no significant effect on the activation of the JNK signaling pathway. In vitro, FABP4 directly activated NF-κB in chondrocytes. The use of QNZ and NF-κB-siRNA significantly alleviated the expression of catabolic markers of chondrocytes induced by FABP4. FABP4 induces chondrocyte degeneration by activating the NF-κB pathway.

Therapeutic effects of fatty acid binding protein 1 in mice with pulmonary fibrosis by regulating alveolar epithelial regeneration

INTRODUCTION

Idiopathic pulmonary fibrosis is a progressive fibrotic lung disease with limited therapeutic options and high lethality, related to alveolar type II epithelial (ATII) cell dysregulation, the abnormal repair of alveolar epithelial cells and activation of fibroblasts promote the development of pulmonary fibrosis. Fatty acid binding protein 1 (FABP1) was significantly downregulated in the fibrotic state by proteomics screening in our previous date, and the ATII cell dysregulation can be mediated by FABP1 via regulating fatty acid metabolism and intracellular transport. The aim of this study was to evaluate the role and potential mechanism of FABP1 in the development of pulmonary fibrosis.

METHODS

Proteomics screening was used to detect changes of the protein profiles in two different types (induced by bleomycin and silica, respectively) of pulmonary fibrosis models. The localisation of FABP1 in mouse lung was detected by Immunofluorescence and immunohistochemistry. Experimental methods such as lung pathology, micro-CT, western blotting, small animal imaging in vivo, EdU, etc were used to verify the role of FABP1 in pulmonary fibrosis.

RESULTS

The expression of FABP1 in the mouse lung was significantly reduced in the model of pulmonary fibrosis from our proteomic analysis and immunological methods, the double immunofluorescence staining showed that FABP1 was mainly localised in type II alveolar epithelial cells. Additionally, the expression of FABP1 was negatively correlated with the progression of pulmonary fibrosis. Further in vivo and in vitro experiments showed that overexpression of FABP1 alleviated pulmonary fibrosis by protecting alveolar epithelium from injury and promoting cell survival.

CONCLUSION

Our findings provide a proof-of-principle that FABP1 may represent an effective treatment for pulmonary fibrosis by regulating alveolar epithelial regeneration, which may be associated with the fatty acid metabolism in ATII cells.

Fatty Acid-Binding Protein 4 is Essential for the Inflammatory and Metabolic Response of Microglia to Lipopolysaccharide

Prolonged activation of microglia leads to excessive release of proinflammatory mediators, which are detrimental to brain health. Therefore, there are significant efforts to identify pathways mediating microglial activation. Recent studies have demonstrated that fatty acid-binding protein 4 (FABP4), a lipid binding protein, is a critical player in macrophage-mediated inflammation. Given that we have previously identified FABP4 in microglia, the aim of this study was to assess whether FABP4 activity contributed to inflammation, metabolism and immune function (i.e. immunometabolism) in immortalised mouse microglia (BV-2 cells) using the proinflammatory stimulus lipopolysaccharide (LPS) to induce general microglial activation. Microglial FABP4 expression was significantly increased following exposure to LPS, an outcome associated with a significant increase in microglial proliferation rate. LPS-stimulated BV-2 microglia demonstrated a significant increase in the production of reactive oxygen species (ROS) and tumour necrosis factor-alpha (TNF-α), phosphorylation of c-Jun N-terminal kinase (JNK), increased expression of Toll-like receptor 4 (TLR4), and reduced expression of uncoupling protein 2 (UCP2), all of which were reversed following FABP4 genetic silencing and chemical inhibition with BMS309403. The oxidation rate of 3H-oleic acid and microglial uptake of 3H-2-deoxy-D-glucose were modulated with LPS activation, processes which were restored with genetic and chemical inhibition of FABP4. This is the first study to report on the critical role of FABP4 in mediating the deleterious effects of LPS on microglial immunometabolism, suggesting that FABP4 may present as a novel therapeutic target to alleviate microglia-mediated neuroinflammation, a commonly reported factor in multiple neurodegenerative diseases.

FABP4 in LSECs promotes CXCL10-mediated macrophage recruitment and M1 polarization during NAFLD progression

BACKGROUND AND AIMS

Non-alcoholic liver disease (NAFLD) is emerging as the leading cause of end-stage liver disease with a serious threat to global health burden. Fatty acid-binding protein 4 (FABP4) is closely associated with metabolic syndromes. We aimed to explore the potential mechanisms of FABP4 in NAFLD progression.

MATERIALS AND METHODS

For NAFLD mice, animals were fed with high fat diet (HFD) for 20 weeks. The assays of hematoxylin and eosin, Sirius Red, oil red O staining and immunohistology were performed to evaluate hepatic pathology. Flow cytometric analysis was used to distinguish macrophage subtypes.

RESULTS

Serum FABP4 level was positively correlate with the severity of hepatic steatosis in NAFLD patients. FABP4 expression was mainly distributed in liver sinusoidal endothelial cells (LSECs), which was significantly increased in HFD mice. The level of CXCL10 was positively correlated with FABP4 at mRNA and serum level. FABP4 inhibition resulted in decreased expression of CXCL10. The percentage of M1 macrophage and CXCR3⁺ cells in infiltrated macrophage was increased in liver of HFD mice. Inhibition of FABP4 ameliorated HFD-induced M1 macrophage polarization as well as CXCR3⁺ macrophages recruitment. Recombinant CXCL10 and co-culturing with TMNK-1 stimulated macrophage toward M1 polarization, which could be reversed by CXCR3 inhibitor. Palmitic acid treatment resulted in increased nuclear P65 expression, which could be reversed by inhibiting FABP4. Cxcl10 expression was dramatically suppressed by NF-κB inhibitor.

CONCLUSIONS

FABP4 in LSECs may play a pathogenic role in NAFLD course by promoting CXCL10-mediated macrophage M1 polarization and CXCR3⁺ macrophage infiltration via activating NF-κB/p65 signaling.

Targeting adipokines in polycystic ovary syndrome and related metabolic disorders: from experimental insights to clinical studies

Polycystic ovary syndrome (PCOS) affects approximately 15% of women of reproductive age worldwide. It is the most prevalent endocrine disorder with marked risks for female infertility, type 2 diabetes mellitus (T2DM), psychiatric disorders and gynecological cancers. Although the pathophysiology of PCOS remains largely elusive, growing evidence suggests a close link with obesity and its related metabolic disorders. As a highly active endocrine cell population, hypertrophic adipocytes in obesity have disturbed production of a vast array of adipokines, biologically active peptides that exert pleiotropic effects on homeostatic regulation of glucose and lipid metabolism. In parallel with their crucial roles in the pathophysiology of obesity-induced metabolic diseases, adipokines have recently been identified as promising targets for novel therapeutic strategies for multiple diseases. Current treatments for PCOS are suboptimal with insufficient alleviation of all symptoms. Novel findings in adipokine-targeted agents may provide important insight into the development of new drugs for PCOS. This Review presents an overview of the current understanding of mechanisms that link PCOS to obesity and highlights emerging evidence of adipose-ovary crosstalk as a pivotal mediator of PCOS pathogenesis. We summarize recent findings of preclinical and clinical studies that reveal the therapeutic potential of adipokine-targeted novel approaches to PCOS and its related metabolic disorders. We also discuss the critical gaps in knowledge that need to be addressed to guide the development of adipokine-based novel therapies for PCOS.

Adipokines in Non-Alcoholic Fatty Liver Disease: Are We on the Road toward New Biomarkers and Therapeutic Targets?

Simple Summary

Non-alcoholic fatty liver disease (NAFLD) is an unmet medical need due to its increasingly high incidence, severe clinical consequences, and the absence of feasible diagnostic tools and effective drugs. This review summarizes the preclinical and clinical data on adipokines, cytokine-like hormones secreted by adipose tissue, and NAFLD. The aim is to establish the potential of adipokines as diagnostic and prognostic biomarkers, as well as their potential as therapeutic targets for NAFLD. The limitations of current research are also discussed, and future perspectives are outlined.

Abstract

Non-alcoholic fatty liver disease (NAFLD) has become the major cause of chronic hepatic illness and the leading indication for liver transplantation in the future decades. NAFLD is also commonly associated with other high-incident non-communicable diseases, such as cardiovascular complications, type 2 diabetes, and chronic kidney disease. Aggravating the socio-economic impact of this complex pathology, routinely feasible diagnostic methodologies and effective drugs for NAFLD management are unavailable. The pathophysiology of NAFLD, recently defined as metabolic associated fatty liver disease (MAFLD), is correlated with abnormal adipose tissue–liver axis communication because obesity-associated white adipose tissue (WAT) inflammation and metabolic dysfunction prompt hepatic insulin resistance (IR), lipid accumulation (steatosis), non-alcoholic steatohepatitis (NASH), and fibrosis. Accumulating evidence links adipokines, cytokine-like hormones secreted by adipose tissue that have immunometabolic activity, with NAFLD pathogenesis and progression; however, much uncertainty still exists. Here, the current knowledge on the roles of leptin, adiponectin, ghrelin, resistin, retinol-binding protein 4 (RBP4), visfatin, chemerin, and adipocyte fatty-acid-binding protein (AFABP) in NAFLD, taken from preclinical to clinical studies, is overviewed. The effect of therapeutic interventions on adipokines’ circulating levels are also covered. Finally, future directions to address the potential of adipokines as therapeutic targets and disease biomarkers for NAFLD are discussed.

Metabolic dysfunction-associated fatty liver disease - How relevant is this to primary care physicians and diabetologists?

Metabolic-dysfunction associated fatty liver disease (MAFLD) is a newly introduced entity hoping to more precisely define fatty liver disease. Despite the controversies surrounding MAFLD, the definition is getting more widely accepted by the global liver-health community. MAFLD represents a cohort of patients enriched with more advanced liver disease, cardio-renal and metabolic complications with increased mortality. This review aims to provide all primary care physicians and diabetologists with a clinical management update from a non-hepatologist's perspective, and a summary of important findings from recent studies to raise disease awareness and highlight the relevance of MAFLD to their daily clinical practice.

Interplay between Fatty Acid Binding Protein 4, Fetuin-A, Retinol Binding Protein 4 and Thyroid Function in Metabolic Dysregulation

Signalling between the tissues integrating synthesis, transformation and utilization of energy substrates and their regulatory hormonal axes play a substantial role in the development of metabolic disorders. Interactions between cytokines, particularly liver derived hepatokines and adipokines, secreted from adipose tissue, constitute one of major areas of current research devoted to metabolic dysregulation. The thyroid exerts crucial influence on the maintenance of basal metabolic rate, thermogenesis, carbohydrate and lipid metabolism, while its dysfunction promotes the development of metabolic disorders. In this review, we discuss the interplay between three adipokines: fatty acid binding protein type 4, fetuin-A, retinol binding protein type 4 and thyroid hormones, that shed a new light onto mechanisms underlying atherosclerosis, cardiovascular complications, obesity, insulin resistance and diabetes accompanying thyroid dysfunction. Furthermore, we summarize clinical findings on those cytokines in the course of thyroid disorders.

Ginsenoside Rg2 Ameliorating CDAHFD-Induced Hepatic Fibrosis by Regulating AKT/mTOR-Mediated Autophagy

Ginsenoside Rg2 (G-Rg2) in the rhizome of Panax ginseng can modify lipid accumulation, oxidative stress, and apoptosis in the liver induced by a high-fat diet. This research adds to this by assessing the potential antifibrosis effect of G-Rg2 (including possible mechanisms). G-Rg2 significantly improved pathological changes in liver tissue induced by a choline-deficient, l-amino acid-defined, high-fat diet (CDAHFD), it inhibited serum transaminase, plasma lipopolysaccharide, and liver hydroxyproline levels; it inhibited TGF-β1, α-SMA, and COL1A1 expression, it activated the AKT/mTOR signal pathway, and it inhibited liver expression of autophagy-related proteins. The in vitro experiments showed that G-Rg2 also restored the autophagy flux impairment induced by oleic acid and inhibited TGF-β1 expression by promoting p62 degradation in hepatocytes. In hepatic stellate (HSC-T6) cells, G-Rg2 reversed lipopolysaccharide-induced activation through the AKT/mTOR signaling pathway, inhibiting autophagy. Thus, G-Rg2 ameliorates CDAHFD-induced liver fibrosis and lipopolysaccharide-induced HSC-T6 cell activation by inhibiting AKT/mTOR-mediated autophagy.

Non-alcoholic fatty liver disease and type 2 diabetes - An Update

The global prevalence of non‐alcoholic fatty liver disease (NAFLD) is rising, along with the epidemic of diabesity. NAFLD is present in >70% of individuals with type 2 diabetes. Although the mutually detrimental relationship between NAFLD and type 2 diabetes has been well established, a multitude of recent studies have further shown that type 2 diabetes is closely linked to the development of cirrhosis, hepatocellular carcinoma, liver‐related morbidity and mortality. In contrast, NAFLD also negatively impacts type 2 diabetes both in terms of its incidence and related adverse clinical outcomes, including cardiovascular and chronic kidney diseases. In response to these global health threats, clinical care pathways for NAFLD and guidelines for metabolic dysfunction‐associated fatty liver disease have been developed. Several antidiabetic agents have been evaluated for their potential hepatic benefits with promising results. Furthermore, type 2 diabetes patients are increasingly represented in clinical trials of novel therapeutics for NAFLD. However, despite the wealth of knowledge in NAFLD and type 2 diabetes, lack of awareness of the disease and the potential weight of this problem remains a major challenge, especially among clinicians who are outside the field of hepatology and gastroenterology. This review therefore aimed to provide all diabetes care providers with a summary of the latest evidence that supports NAFLD as an emerging diabetic complication of increasing importance, and to present the current recommendations, focusing on the assessment and therapeutic strategies, on the management of NAFLD among type 2 diabetes patients.

Unveiling the Role of the Fatty Acid Binding Protein 4 in the Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD), the main cause of chronic liver disease worldwide, is a progressive disease ranging from fatty liver to steatohepatitis (metabolic-associated steatohepatitis; MASH). Nevertheless, it remains underdiagnosed due to the lack of effective non-invasive methods for its diagnosis and staging. Although MAFLD has been found in lean individuals, it is closely associated with obesity-related conditions. Adipose tissue is the main source of liver triglycerides and adipocytes act as endocrine organs releasing a large number of adipokines and pro-inflammatory mediators involved in MAFLD progression into bloodstream. Among the adipocyte-derived molecules, fatty acid binding protein 4 (FABP4) has been recently associated with fatty liver and additional features of advanced stages of MAFLD. Additionally, emerging data from preclinical studies propose FABP4 as a causal actor involved in the disease progression, rather than a mere biomarker for the disease. Therefore, the FABP4 regulation could be considered as a potential therapeutic strategy to MAFLD. Here, we review the current knowledge of FABP4 in MAFLD, as well as its potential role as a therapeutic target for this disease.

Circulating level of fatty acid-binding protein 4 is an independent predictor of metabolic dysfunction-associated fatty liver disease in middle-aged and elderly individuals

Aims/Introduction

Metabolic dysfunction‐associated fatty liver disease (MAFLD), defined as hepatosteatosis with type 2 diabetes mellitus, overweight/obesity or metabolic dysregulation, has been proposed as a new feature of chronic liver disease. Fatty acid‐binding protein 4 (FABP4) is expressed in adipose tissue, and secreted FABP4 is associated with the development of insulin resistance and atherosclerosis. However, the relationship between MAFLD and FABP4 has not been fully addressed.

Materials and Methods

Associations of MAFLD with metabolic markers, including FABP4, fibroblast growth factor 21 and adiponectin, were investigated in 627 individuals (men/women 292/335) in the Tanno‐Sobetsu Study, a population‐based cohort.

Results

The mean age was 65 years (range 19–98 years, median [interquartile range] 68 [56–76] years). Hepatosteatosis was determined by the fatty liver index (FLI), and FLI ≥35 for men and FLI ≥16 for women were used for detection of fatty liver, as previously reported using 14,471 Japanese individuals. FLI was positively correlated with systolic blood pressure and levels of FABP4 (r = 0.331, P < 0.001), fibroblast growth factor 21, homeostasis model assessment of insulin resistance as an insulin resistance index and uric acid, and was negatively correlated with levels of high‐density lipoprotein cholesterol and adiponectin. FABP4 concentration was independently associated with FLI after adjustment of age, sex, systolic blood pressure and levels of uric acid, high‐density lipoprotein cholesterol, homeostasis model assessment of insulin resistance, adiponectin and fibroblast growth factor 21 in multivariable regression analysis. Logistic regression analysis showed that FABP4 was an independent predictor of MAFLD after adjustment of age, sex, presence of diabetes mellitus, hypertension and dyslipidemia, and levels of uric acid, homeostasis model assessment of insulin resistance, adiponectin and fibroblast growth factor 21.

Conclusions

FABP4 concentration is independently associated with FLI and is an independent predictor of MAFLD in middle‐aged and elderly individuals.

Gene Signatures Detect Damaged Liver Sinusoidal Endothelial Cells in Chronic Liver Diseases

Liver sinusoidal endothelial cells have a gatekeeper function in liver homeostasis by permitting substrates from the bloodstream into the space of Disse and regulating hepatic stellate cell activation status. Maintenance of LSEC's highly specialized phenotype is crucial for liver homeostasis. During liver fibrosis and cirrhosis, LSEC phenotype and functions are lost by processes known as capillarization and LSEC dysfunction. LSEC capillarization can be demonstrated by the loss of fenestrae (cytoplasmic pores) and the manifestation of a basement membrane. Currently, no protein or genetic markers can clearly distinguish healthy from damaged LSECs in acute or chronic liver disease. Single cell (sc)RNA sequencing efforts have identified several LSEC populations in mouse models for liver disease and in human cirrhotic livers. Still, there are no clearly defined genesets that can identify LSECs or dysfunctional LSEC populations in transcriptome data. Here, we developed genesets that are enriched in healthy and damaged LSECs which correlated very strongly with healthy and early stage- vs. advanced human liver diseases. A damaged LSEC signature comprised of Fabp4/5 and Vwf/a1 was established which could efficiently identify damaged endothelial cells in single cell RNAseq data sets. In LSECs from an acute CCl₄ liver injury mouse model, Fabp4/5 and Vwf/a1 expression is induced within 1-3 days while in cirrhotic human livers these 4 genes are highly enriched in damaged LSECs. In conclusion, our newly developed gene signature of damaged LSECs can be applicable to a wide range of liver disease etiologies, implicating a common transcriptional alteration mechanism in LSEC damage.

Pre-emptive pharmacological inhibition of fatty acid-binding protein 4 attenuates kidney fibrosis by reprogramming tubular lipid metabolism

Kidney fibrosis is a hallmark of chronic kidney disease (CKD) progression that is caused by tubular injury and dysregulated lipid metabolism. Genetic abolition fatty acid-binding protein 4 (FABP4), a key lipid transporter, has been reported to suppress kidney interstitial fibrosis. However, the role and underlying mechanism of chemical inhibition of FABP4 in fibrotic kidney have not been well-documented. Here, we examined preemptive the effect of a FABP4 inhibitor, BMS309403, on lipid metabolism of tubular epithelial cells (TECs) and progression of kidney fibrosis. The expression of FABP4 was significantly elevated, concomitated with the accumulation of lipid droplets in TECs during kidney fibrosis. Treatment with BMS309403 alleviated lipid deposition of TECs, as well as interstitial fibrotic responses both in unilateral ureteral obstruction (UUO)-engaged mice and TGF-β-induced TECs. Moreover, BMS309403 administration enhanced fatty acid oxidation (FAO) in TECs by regulating peroxisome proliferator-activated receptor γ (PPARγ) and restoring FAO-related enzyme activities; In addition, BMS309403 markedly reduced cell lipotoxicity, such as endoplasmic reticulum (ER) stress and apoptosis in fibrotic kidney. Taken together, our results suggest that preemptive pharmacological inhibition of FABP4 by BMS309403 rebalances abnormal lipid metabolism in TECs and attenuates the progression of kidney fibrosis, thus may hold therapeutic potential for the treatment of fibrotic kidney diseases.

Adipocyte Fatty Acid Binding Protein Promotes the Onset and Progression of Liver Fibrosis via Mediating the Crosstalk between Liver Sinusoidal Endothelial Cells and Hepatic Stellate Cells

Development of liver fibrosis results in drastic changes in the liver microenvironment, which in turn accelerates disease progression. Although the pathological function of various hepatic cells in fibrogenesis is identified, the crosstalk between them remains obscure. The present study demonstrates that hepatic expression of adipocyte fatty acid binding protein (A-FABP) is induced especially in the liver sinusoidal endothelial cells (LSECs) in mice after bile duct ligation (BDL). Genetic ablation and pharmacological inhibition of A-FABP attenuate BDL- or carbon tetrachloride-induced liver fibrosis in mice associating with reduced collagen accumulation, LSEC capillarization, and hepatic stellate cell (HSC) activation. Mechanistically, elevated A-FABP promotes LSEC capillarization by activating Hedgehog signaling, thus impairs the gatekeeper function of LSEC on HSC activation. LSEC-derived A-FABP also acts on HSCs in paracrine manner to potentiate the transactivation of transforming growth factor β1 (TGFβ1) by activating c-Jun N-terminal kinase (JNK)/c-Jun signaling. Elevated TGFβ1 subsequently exaggerates liver fibrosis. These findings uncover a novel pathological mechanism of liver fibrosis in which LSEC-derived A-FABP is a key regulator modulating the onset and progression of the disease. Targeting A-FABP may represent a potential approach against liver fibrosis.

Adipocyte fatty acid-binding protein exacerbates cerebral ischaemia injury by disrupting the blood-brain barrier

Aims

Adipocyte fatty acid-binding protein (A-FABP) is an adipokine implicating in various metabolic diseases. Elevated circulating levels of A-FABP correlate positively with poor prognosis in ischaemic stroke (IS) patients. No information is available concerning the role of A-FABP in the pathogenesis of IS. Experiments were designed to determine whether or not A-FABP mediates blood–brain barrier (BBB) disruption, and if so, to explore the molecular mechanisms underlying this deleterious effects.

Methods and results

Circulating A-FABP and its cerebral expression were increased in mice after middle cerebral artery occlusion. Genetic deletion and pharmacological inhibition of A-FABP alleviated cerebral ischaemia injury with reduced infarction volume, cerebral oedema, neurological deficits, and neuronal apoptosis; BBB disruption was attenuated and accompanied by reduced degradation of tight junction proteins and induction of matrix metalloproteinases-9 (MMP-9). In patients with acute IS, elevated circulating A-FABP levels positively correlated with those of MMP-9 and cerebral infarct volume. Mechanistically, ischaemia-induced elevation of A-FABP selectively in peripheral blood monocyte-derived macrophages and cerebral resident microglia promoted MMP-9 transactivation by potentiating JNK/c-Jun signalling, enhancing degradation of tight junction proteins and BBB leakage. The detrimental effects of A-FABP were prevented by pharmacological inhibition of MMP-9.

Conclusion

A-FABP is a key mediator of cerebral ischaemia injury promoting MMP-9-mediated BBB disruption. Inhibition of A-FABP is a potential strategy to improve IS outcome.

Lampaya Medicinalis Phil. decreases lipid-induced triglyceride accumulation and proinflammatory markers in human hepatocytes and fat body of Drosophila melanogaster

BACKGROUND

Excess hepatic triglyceride (TG) accumulation (steatosis) commonly observed in obesity, may lead to non-alcoholic fatty liver disease (NAFLD). Altered regulation of intracellular lipid droplets (LD) and TG metabolism, as well as activation of JNK-mediated proinflammatory pathways may trigger liver steatosis-related disorders. Drosophila melanogaster is an animal model used for studying obesity and its associated disorders. In Drosophila, lipids and glycogen are stored in the fat body (FB), which resembles mammalian adipose tissue and liver. Dietary oversupply leads to obesity-related disorders, which are characterized by FB dysfunction. Infusions of Lampaya medicinalis Phil. (Verbenaceae) are used in folk medicine of Chile to counteract inflammatory diseases. Hydroethanolic extract of lampaya (HEL) contains considerable amounts of flavonoids that may explain its anti-inflammatory effect.

METHODS

We studied whether HEL affects palmitic acid (PA, C16:0) and oleic acid (OA; C18:1)-induced TG accumulation and proinflammatory marker content in HepG2 hepatocytes as well as impaired lipid storage and proinflammatory molecule expression in Drosophila melanogaster fed a high-fat diet (HFD).

RESULTS

In HepG2 hepatocytes, exposure to OA/PA elevated TG content, FABP4, ATGL and DGAT2 expression, and the JNK proinflammatory pathway, as well as TNF-α and IL-6 production, while diminished FAS expression. These effects were prevented by HEL co-treatment. In Drosophila larvae fed a HFD, HEL prevented TG accumulation and downregulated proinflammatory JNK pathway activation.

CONCLUSION

HEL effect counteracting OA/PA- and HFD-induced lipid accumulation and proinflammatory marker expression in HepG2 hepatocytes and Drosophila larvae may represent a preventive approach against hepatic steatosis and inflammation, associated to obesity and NAFLD.

Fatty acid binding protein 4 promotes autoimmune diabetes by recruitment and activation of pancreatic islet macrophages

Both innate and adaptive immune cells are critical players in autoimmune destruction of insulin-producing β cells in type 1 diabetes. However, the early pathogenic events triggering the recruitment and activation of innate immune cells in islets remain obscure. Here we show that circulating fatty acid binding protein 4 (FABP4) level was significantly elevated in patients with type 1 diabetes and their first-degree relatives and positively correlated with the titers of several islet autoantibodies. In nonobese diabetic (NOD) mice, increased FABP4 expression in islet macrophages started from the neonatal period, well before the occurrence of overt diabetes. Furthermore, the spontaneous development of autoimmune diabetes in NOD mice was markedly reduced by pharmacological inhibition or genetic ablation of FABP4 or adoptive transfer of FABP4-deficient bone marrow cells. Mechanistically, FABP4 activated innate immune responses in islets by enhancing the infiltration and polarization of macrophages to proinflammatory M1 subtype, thus creating an inflammatory milieu required for activation of diabetogenic CD8+ T cells and shift of CD4+ helper T cells toward Th1 subtypes. These findings demonstrate FABP4 as a possible early mediator for β cell autoimmunity by facilitating crosstalk between innate and adaptive immune cells, suggesting that pharmacological inhibition of FABP4 may represent a promising therapeutic strategy for autoimmune diabetes.

Adipocyte Fatty Acid-Binding Protein, Cardiovascular Diseases and Mortality

It has been increasingly recognized that inflammation plays an important role in the pathogenesis of cardiovascular disease (CVD). In obesity, adipose tissue inflammation, especially in the visceral fat depots, contributes to systemic inflammation and promotes the development of atherosclerosis. Adipocyte fatty acid-binding protein (AFABP), a lipid chaperone abundantly secreted from the adipocytes and macrophages, is one of the key players mediating this adipose-vascular cross-talk, in part via its interaction with c-Jun NH2-terminal kinase (JNK) and activator protein-1 (AP-1) to form a positive feedback loop, and perpetuate inflammatory responses. In mice, selective JNK inactivation in the adipose tissue significantly reduced the expression of AFABP in their adipose tissue, as well as circulating AFABP levels. Importantly, fat transplant experiments showed that adipose-specific JNK inactivation in the visceral fat was sufficient to protect mice with apoE deficiency from atherosclerosis, with the beneficial effects attenuated by the continuous infusion of recombinant AFABP, supporting the role of AFABP as the link between visceral fat inflammation and atherosclerosis. In humans, raised circulating AFABP levels are associated with incident metabolic syndrome, type 2 diabetes and CVD, as well as non-alcoholic steatohepatitis, diabetic nephropathy and adverse renal outcomes, all being conditions closely related to inflammation and enhanced CV mortality. Collectively, these clinical data have provided support to AFABP as an important adipokine linking obesity, inflammation and CVD. This review will discuss recent findings on the role of AFABP in CVD and mortality, the possible underlying mechanisms, and pharmacological inhibition of AFABP as a potential strategy to combat CVD.

Phosphatidylinositol-3,4,5-trisphosphate dependent Rac exchange factor 1 is a diagnostic and prognostic biomarker for hepatocellular carcinoma

BACKGROUND

Phosphatidylinositol-3,4,5-trisphosphate dependent Rac exchange factor 1 (P-Rex1) was reported to be a risk factor in several cancers, including breast cancer, lung cancer, and melanoma, but its expression and role in hepatocellular carcinoma (HCC) have not yet been fully studied.

AIM

To explore the expression of P-Rex1 in HCC, and further evaluate its potential application in the diagnosis and prognosis of HCC, especially in hepatitis B virus (HBV)-related patients.

METHODS

P-Rex1 expression in HCC was evaluated by real-time-quantitative polymerase chain reaction. The expression of P-Rex1 was subjected to correlation analysis with clinical features, such as lymph node invasion, distant metastasis, HBV infection, patient's age and gender. Receiver operating characteristic analysis was used to examine the potential role of P-Rex1 as a diagnostic biomarker in HCC. Kaplan-Meier analysis was used to determine the association between P-Rex1 expression and overall survival, progression-free survival and relapse-free survival. Bioinformatic analysis was used to validate the clinical findings.

RESULTS

P-Rex1 expression was significantly increased in HCC tumors than adjacent tissues. The expression of P-Rex1 was higher in HCC patients with lymph node invasion, distant metastasis, HBV infection and positive alpha-fetoprotein, respectively. The receiver operating characteristic analysis showed that P-Rex1 was a diagnostic biomarker with a higher area under the curve value, especially in patients with HBV infection. Survival analysis showed that patients with higher P-Rex1 expression had a favorable survival rate, even in early-stage patients.

CONCLUSION

P-Rex1 expression was highly increased in HCC, and the expression level of P-Rex1 was positively correlated with tumor progression. P-Rex1 has a higher efficiency in the diagnosis of HBV-related HCC, and could also be used as a favorable prognostic factor for HCC patients.

Hepatic Lipidomics and Molecular Imaging in a Murine Non-Alcoholic Fatty Liver Disease Model: Insights into Molecular Mechanisms

An imbalance between hepatic fatty acid uptake and removal results in ectopic fat accumulation, which leads to non-alcoholic fatty liver disease (NAFLD). The amount and type of accumulated triglycerides seem to play roles in NAFLD progression; however, a complete understanding of how triglycerides contribute to NAFLD evolution is lacking. Our aim was to evaluate triglyceride accumulation in NAFLD in a murine model and its associations with molecular mechanisms involved in liver damage and adipose tissue-liver cross talk by employing lipidomic and molecular imaging techniques. C57BL/6J mice fed a high-fat diet (HFD) for 12 weeks were used as a NAFLD model. Standard-diet (STD)-fed animals were used as controls. Standard liver pathology was assessed using conventional techniques. The liver lipidome was analyzed by liquid chromatography–mass spectrometry (LC–MS) and laser desorption/ionization–mass spectrometry (LDI–MS) tissue imaging. Liver triglycerides were identified by MS/MS. The transcriptome of genes involved in intracellular lipid metabolism and inflammation was assessed by RT-PCR. Plasma leptin, resistin, adiponectin, and FABP4 levels were determined using commercial kits. HFD-fed mice displayed increased liver lipid content. LC–MS analyses identified 14 triglyceride types that were upregulated in livers from HFD-fed animals. Among these 14 types, 10 were identified in liver cross sections by LDI–MS tissue imaging. The accumulation of these triglycerides was associated with the upregulation of lipogenesis and inflammatory genes and the downregulation of β-oxidation genes. Interestingly, the levels of plasma FABP4, but not of other adipokines, were positively associated with 8 of these triglycerides in HFD-fed mice but not in STD-fed mice. Our findings suggest a putative role of FABP4 in the liver-adipose tissue cross talk in NAFLD.

A preliminary study: proteomic analysis of exosomes derived from thyroid-stimulating hormone-stimulated HepG2 cells

BACKGROUND

Thyroid-stimulating hormone (TSH) plays an important role in the regulation of lipid metabolism. However, little is known about the role that exosomes play in the process of TSH-induced lipotoxicity in non-alcoholic fatty liver disease (NAFLD). As a preliminary step, the present study set out to investigate alterations in protein expression in exosomes derived from TSH-stimulated HepG2 cells.

METHODS

HepG2 cells were treated with TSH, exosomes were collected, and proteins were identified by mass spectrometry (MS). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genome (KEGG) pathway analysis were performed to analyze the identified proteins.

RESULTS

TSH treatment significantly increased exosomal production and changed the exosomal proteomic profile in HepG2 cells. Among the 1728 proteins, 140 identified proteins were upregulated and seven proteins were downregulated. GO analysis and KEGG analysis revealed that these proteins were involved in multiple processes including metabolism, apoptosis, and inflammation.

CONCLUSION

Our preliminary study demonstrated that exosomes derived from TSH-stimulated hepatocytes were increased and showed a specific altered spectrum of proteins, many of which were involved in metabolism, signal transduction, apoptosis, and inflammation. This study offers new insights into the pathogenesis of TSH-induced lipotoxicity in NAFLD.

Correlation of serum fatty acid binding protein-4 and interleukin-6 with airflow limitation and quality of life in stable and acute exacerbation of COPD

Background/aim

The serum fatty acid binding protein 4 (FABP-4) level increases in chronic inflammatory diseases. The present study aimed to examine serum FABP-4 and interleukin (IL)-6 levels in patients with stable and acute exacerbation of chronic obstructive pulmonary disease (COPD) and the correlation of these markers with airflow limitation.

Materials and methodsS

We measured serum FABP-4 and IL-6 levels in 60 COPD patients [30 stable COPD (SCOPD), and 30 acute exacerbation of COPD (AECOPD)], and 30 healthy subjects and compared them with airflow limitation according to the COPD stage in the Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) criteria, peripheral O2 saturation (SpO2), and COPD Assessment Test (CAT) score. We also tested the association between serum FABP-4 levels and some characteristics of study parameters.

Results

Both serum FABP-4 and IL-6 levels increased with increasing severity of GOLD grades in SCOPD (P < 0.01 for both) and AECOPD groups (P < 0.001 and P < 0.01, respectively). It also increased in patients with AECOPD group compared with SCOPD group in GOLD grades I-II (P < 0.01) and GOLD grades III-IV (P < 0.05). In addition, there was a significant positive correlation between serum FABP-4 level with IL-6, CAT score, and smoking history and inversely with FEV1 and SpO2.

Conclusion

The study revealed that serum FABP-4 level was elevated with increasing GOLD grades in COPD patients, markedly in acute exacerbation phase. The increase was associated with elevated serum levels of IL-6 and severity of hypoxia. Thus, it seems that FABP-4 may be involved in the pathogenesis of COPD.

Association of adipokines with hepatic steatosis and fibrosis in chronic hepatitis B patients on long-term nucleoside analogue

BACKGROUND & AIMS

It is unknown how concomitant hepatic steatosis affects disease progression in chronic hepatitis B (CHB). Adipokines such as fibroblast growth factor 21 (FGF21) and adipocyte fatty acid-binding protein (AFABP) have been associated with non-alcoholic fatty liver disease. We determined the significance of these metabolic markers in CHB-related liver injury.

METHODS

We recruited CHB patients on antiviral treatment for transient elastography assessment to determine liver stiffness (advanced fibrosis/cirrhosis, F3/F4, defined by EASL-ALEH criteria) and controlled attenuation parameter (hepatic steatosis, defined as ≥ 248 dB/m). Plasma FGF-21, AFABP and adiponectin levels were measured.

RESULTS

A total of 415 patients [mean age 59.6 years, 71.6% male, median treatment duration 6.2 years] were recruited. Patients with F3/F4 (N = 151) had lower FGF-21 (11.7 vs 13.6 pg/mL, P = 0.055), higher AFABP (126.8 vs 84.1 pg/mL, P < 0.001) and HOMA-IR (7.1 vs 5.1, P = 0.004) levels compared to those without F3/F4 (N = 264). Multivariate analysis showed that FGF-21 level was associated with hepatic steatosis (OR 1.005, 95% CI 1.001-1.009) and F3/F4 (OR 0.993, 95% CI 0.989-0.998), while AFABP level (OR 1.001, 95% CI 1-1.002), body mass index (BMI) (OR 1.107, 95% CI 1.037-1.182) and presence of diabetes mellitus (OR 2.059, 95% CI 1.206-3.516) were associated with F3/F4. With the combined presence of BMI ≥ 25 kg/m² , diabetes and AFABP > 105.9 pg/mL, the odds ratio for F3/F4 was 3.712 (95% CI 1.364-10.105, P = 0.010).

CONCLUSIONS

Low FGF-21 and high AFABP levels were associated with advanced fibrosis/cirrhosis in CHB patients on antiviral treatment. Plasma AFABP, together with other metabolic risk factors, may aid identification of patients lacking fibrosis improvement during antiviral treatment.

Hepatocellular iNOS protects liver from NASH through Nrf2-dependent activation of HO-1

Multiple molecular events are involved in non-alcoholic steatohepatitis (NASH). There is no consensus on the role of inducible nitric oxide synthase (iNOS) in the progression of NASH. The present study therefore investigated the role of iNOS in NASH pathogenesis using bone marrow-transplanted iNOS chimeric mice under high-fat diet (HFD) conditions. The chimeric mice were fed a HFD for 16 wk, and primary hepatocytes were stimulated with oleic acid (OA). The molecular mechanisms underlying the role of iNOS in NASH were investigated. Marked hepatic steatosis and injury observed in the HFD mice and OA-stimulated hepatocytes were reduced by hepatocyte-derived iNOS. Mechanistically, iNOS upregulated heme oxygenase 1 (HO-1) by augmenting nuclear factor erythroid 2-related factor 2 (Nrf-2) binding to the HO-1 gene promoter. In conclusion, hepatocyte-derived iNOS may play a protective role against the progression of NASH by upregulating HO-1 through Nrf-2. Upregulation of hepatocellular iNOS may represent a potentially new therapeutic paradigm to combat NASH.

Beneficial Effects of Korean Red Ginseng in the Progression of Non-Alcoholic Steatohepatitis via FABP4 Modulation

Korean red ginseng (KRG) is a traditional herbal medicine used to prevent several geriatric diseases due to its therapeutic effects on metabolic disorder, including type 2 diabetes and fatty liver disease. In this study, we investigated the effects of KRG on the progression of nonalcoholic steatohepatitis (NASH) in mice. NASH was induced by feeding a methionine- and choline-deficient high-fat or high-fat/high-sucrose diet for 6 or 13 weeks, respectively. Each diet group was also orally administered saline (group G0) or KRG extract (100, 200, or 400 mg/kg/day; groups G1, G2, and G4, respectively). KRG showed anti-inflammatory and antifibrogenic effects in the diet-induced NASH models. Furthermore, the expression levels of lipid metabolism-related genes were markedly decreased with KRG treatment in both diet-induced NASH groups. We next confirmed the expression levels of FABP4 in the liver and its ability to regulate inflammation and/or oxidative stress. We observed decreased levels of FABP4 mRNA and protein in the KRG-treated groups indicating that KRG affects the pathogenesis of NASH-related inflammatory responses by modulating FABP4 expression. Results of in vitro experiments showed similar patterns in cells treated with KRG, indicating that KRG treatment regulates the expression of FABP4 and subsequently reduces NASH related inflammation. Our findings suggest a novel role of KRG in NASH-related inflammatory responses via modulation of FABP4 expression in the liver. KRG may be a safe alternative therapy to prevent NASH progression.

Circulating Adipocyte Fatty Acid–Binding Protein Concentrations Predict Multiple Mortality Outcomes among Men and Women with Diabetes

INTRODUCTION

Raised circulating adipocyte fatty acid–binding protein (AFABP) concentrations are associated with various adverse health conditions. However, their relationship with mortality remains to be defined, especially in view of the sexual dimorphism of circulating AFABP concentrations. Here we investigated prospectively whether serum AFABP concentrations predict multiple mortality outcomes in men and women alike, using a large clinic-based cohort of individuals with type 2 diabetes, a condition with raised AFABP concentrations.

METHODS

Baseline serum AFABP concentrations were measured in 5305 research participants with a monoclonal antibody-based sandwich immunoassay. The role of circulating AFABP concentrations in predicting mortality outcomes was evaluated by multivariable Cox regression analysis.

RESULTS

Among the 5305 participants (59% men) in this study, over a median follow-up of 5 years, there were 512 deaths (19.3 deaths per 1000 person-years). Circulating AFABP concentrations, with higher levels in women at baseline, predicted all-cause mortality (P &lt; 0.001), cardiovascular mortality (P = 0.037), and infection-related deaths (P &lt; 0.002) among all participants. In sex-specific analyses, circulating AFABP concentration was an independent predictor of all-cause mortality in both men and women and a predictor of cancer-related deaths and infection-related deaths in men only. Furthermore, the addition of serum AFABP concentrations improved the time-dependent c statistics in predicting all-cause mortality in participants with type 2 diabetes (P = 0.008).

CONCLUSIONS

Circulating AFABP concentration was an independent predictor of various mortality outcomes in type 2 diabetes over and above known risk factors of reduced survival in men and women. The role of AFABP as a prognostic biomarker and therapeutic target warrants further investigation.

Knocking out or pharmaceutical inhibition of fatty acid binding protein 4 (FABP4) alleviates osteoarthritis induced by high-fat diet in mice

OBJECTIVES

Adipokines play roles in the pathogenesis of osteoarthritis (OA). Fatty acid binding protein 4 (FABP4) is a novel adipokine that is closely associated with obesity and metabolic diseases. The aim of this study was to discover the potential role of FABP4 in OA.

METHODS

Seventy-two FABP4 knockout mice (KO) in C57BL/6N background and wild-type littermates (WT) (male, 6-week-old) were fed with a high-fat diet (HFD, 60% calorie) or standard diet (STD, 11.6% calorie) for 3 months, 6 months and 9 months (n = 6 each). In the parallel study, forty-eight 6-week-old male WT mice were fed with HFD or STD, and simultaneously treated with daily oral gavage of selective FABP4 inhibitor BMS309403 (15 mg/kg/d) or vehicle for 4 months and 6 months (n = 6 each). Serum FABP4 and cartilage oligomeric matrix protein (COMP) concentration was quantified. Histological assessment of knee OA and micro-CT analysis of subchondral bone were performed.

RESULTS

HFD induced obesity in mice. After 3 months and 6 months of HFD, KO mice showed alleviated cartilage degradation and synovitis, with significantly lower COMP, modified Mankin OA score, and MMP-13/ADAMTS4 expression. After 6 months and 9 months of HFD, KO mice showed less osteophyte formation and subchondral bone sclerosis. Chronic treatment of BMS309403 for 4 months and 6 months significantly alleviated cartilage degradation, but had no effects on the subchondral bone. Knocking out or pharmaceutical inhibition of FABP4 did not have significant effects on lean mice fed with STD.

CONCLUSIONS

Knocking out or pharmaceutical inhibition of FABP4 alleviates OA induced by HFD in mice.

HDL-AuNPs-BMS Nanoparticle Conjugates as Molecularly Targeted Therapy for Leukemia

Gold nanoparticles (AuNPs) with adsorbed high-density lipoprotein (HDL) have been utilized to deliver oligonucleotides, yet HDL-AuNPs functionalized with small-molecule inhibitors have not been systematically explored. Here, we report an AuNP-based therapeutic system (HDL-AuNPs-BMS) for acute myeloid leukemia (AML) by delivering BMS309403 (BMS), a small molecule that selectively inhibits AML-promoting factor fatty acid-binding protein 4. To synthesize HDL-AuNPs-BMS, we use AuNP as a template to control conjugate size ensuring a spherical shape to engineer HDL-like nanoparticles containing BMS. The zeta potential and size of the HDL-AuNPs obtained from transmission electron microscopy demonstrate that the HDL-AuNPs-BMS are electrostatically stable and 25 nm in diameter. Functionally, compared to free drug, HDL-AuNPs-BMS conjugates are more readily internalized by AML cells and have more pronounced effects on downregulation of DNA methyltransferase 1 (DNMT1), induction of DNA hypomethylation, and restoration of epigenetically silenced tumor suppressor p15^INK4B coupled with AML growth arrest. Importantly, systemic administration of HDL-AuNPs-BMS conjugates into AML-bearing mice inhibits DNMT1-dependent DNA methylation, induces AML cell differentiation, and diminishes AML disease progression without obvious side effects. In summary, these data, for the first time, demonstrate HDL-AuNPs as an effective delivery platform with great potential to attach distinct inhibitors and HDL-AuNPs-BMS conjugates as a promising therapeutic platform to treat leukemia.

Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics for the investigation of the effect of Hugan Qingzhi on non-alcoholic fatty liver disease in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hugan Qingzhi tablet (HQT), a traditional Chinese medicine formula has been adopted for preventing and treating nonalcoholic fatty liver disease (NAFLD).

AIM

In order to explore the anti-NAFLD mechanisms of HQT, iTRAQ-based proteomic was employed to investigate the expression profiles of proteins in NAFLD rats induced by high-fat diet after HQT treatment.

MATERIALS AND METHODS

The NAFLD rat model was administrated with high-fat diet (HFD) for 12weeks. HQT was administrated in a daily basis to the HFD groups. Biochemical markers, liver histology, pro-inflammatory cytokines, and oxidative stress/antioxidant biomarkers were assayed to evaluate HQT effects in HFD-induced NAFLD rats. Furthermore, the combined strategy of iTRAQ labeling with strong cation exchange-non-liquid chromatography-tandem mass spectrometry (SCX-non-LC-MS/MS) analysis were employed to explore the mechanisms of HQT's protective effect against NAFLD in rats. Western blotting was performed to verify the proteomic results.

RESULTS

The histopathologic characteristics and biochemical data showed that HQT exhibited protective effects on HFD-induced NAFLD rats. After being analyzed by the combined strategy of iTRAQ with LC-MS/MS and subsequent investigation, we identified 275 differentially expressed proteins in the HFD group, compared to the control; 207 altered proteins in the HQT high dose + HFD group, compared to the HFD group; and 316 altered proteins in the HQT high dose + HFD group, compared to the control. Based on the Kyoto Encyclopedia of Gene and Genomes (KEGG) pathway mapping, the conclusion has reached that several pathways including microbial metabolism in diverse environments, fatty acid metabolism, inflammatory response, oxidative stress, bile secretion, and peroxisome proliferator activated receptor (PPAR) signaling pathway were closely related to the effects of HQT in HFD-induced NAFLD in rats. Furthermore, several differentially expressed proteins, including phytanoyl-CoA 2-hydroxylase (PHYH), acyl-CoA synthetase 1 long chain (ACSL1), hemopexin, Alpha-1-acid glycoprotein (ORM1), fatty acid binding protein 4 (FABP4), soluble sulphotransferase 2a1 (Sult2a1), and argininosuccinate synthase 1 (ASS1) were verified by the western blotting analysis and these results were consistent with the data obtained from the proteomics analysis.

CONCLUSIONS

Our results not only confirm that Hugan Qingzhi exhibits a significant protective effect in HFD-induced NAFLD rats but also provide a better understanding for the treatments of NAFLD.

REV-ERB agonism suppresses osteoclastogenesis and prevents ovariectomy-induced bone loss partially via FABP4 upregulation

REV-ERBs (REV-ERBα and REV-ERBβ) are transcription repressors and circadian regulators. Previous investigations have shown that REV-ERBs repress the expression of target genes, including MMP9 and CX3CR1, in macrophages. Because MMP9 and CX3CR1 reportedly participate in receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis, we inferred that REV-ERBs might play a role in osteoclastogenesis. In the present study, we found that the REV-ERBα level decreased significantly during RANKL-induced osteoclast differentiation from primary bone marrow-derived macrophages (BMMs). REV-ERBα knockdown by small interfering RNA in BMMs resulted in the enhanced formation of osteoclasts, whereas REV-ERBβ knockdown showed no effect on osteoclast differentiation. Moreover, the REV-ERB agonist SR9009 inhibited osteoclast differentiation and bone resorption. Intraperitoneal SR9009 administration prevented ovariectomy-induced bone loss; this effect was accompanied by decreased serum RANKL and C-terminal telopeptide of type I collagen levels and increased osteoprotegerin levels. Further investigation revealed that NF-κB and MAPK activation and nuclear factor of activated T cells, cytoplasmic 1, and c-fos expression were suppressed by SR9009. The level of reactive oxygen species was also decreased by SR9009, with NADPH oxidase subunits also being down-regulated. In addition, an expression microarray showed that FABP4, an intracellular lipid-binding protein, was up-regulated by REV-ERB agonism. BMS309403, an inhibitor of FABP4, partially prevented the suppression of osteoclastogenesis by SR9009 through stabilizing phosphorylation of p65. To summarize, our results proved that the REV-ERB agonism inhibited osteoclastogenesis partially via FABP4 up-regulation.-Song, C., Tan, P., Zhang, Z., Wu, W., Dong, Y., Zhao, L., Liu, H., Guan, H., Li, F. REV-ERB agonism suppresses osteoclastogenesis and prevents ovariectomy-induced bone loss partially via FABP4 upregulation.

The Importance of Liver-Fatty Acid Binding Protein in Diagnosis of Liver Damage in Patients with Acute Hepatitis

INTRODUCTION

Acute hepatitis is acute inflammation of liver elicited by a large number of causes. It sometimes spontaneously recovers, sometimes may progress to chronic hepatitis. Liver- Fatty Acid Binding Protein (L-FABP) is a small protein that is abundant in hepatocytes, and which binds most of the long-chain fatty acids present in the cytosol.

AIM

The present study was aimed to investigate the levels of serum and urine L-FABP in acute hepatitis and diagnostic value of serum and urine L-FABP levels in patients with acute hepatitis.

MATERIALS AND METHODS

The present study included a total of 85 patients. Total number of patients with acute hepatitis were 17 (five of acute hepatitis B, one of acute hepatitis A, two of acute hepatitis C, five of autoimmune hepatitis and four of toxic hepatitis), 19 of hepatic encephalopathy, 29 of liver cirrhosis, and 20 controls were included. Serum and urinary L-FABP levels were analyzed by the Enzyme-Linked Immunosorbent Assay (ELISA).

RESULTS

Serum L-FABP levels were 9110±3352.5, 9410±1355, 9715±2462 and 3672±982.5 ng/l in patients with acute hepatitis, hepatic encephalopathy and cirrhosis and control subjects, respectively. There were statistically significant positive correlations between serum levels of L-FABP and Aspartate Aminotransferases (AST), Alanine Aminotransferases (ALT), Creatinine (Cre) and Gamma Glutamyl Transferases (GGT) (p<0.001, p<0.001, p<0.001 and p<0.001, respectively). While the cut-off value of serum L-FABP for all of the patients was 5183 ng/l {p<0.001 and Area Under Curve (AUC) 0.985}, the sensitivity and specificity were 95.4% and 100%, respectively. Positive and negative predictive values for serum L-FABP were 100% and 87%, respectively.

CONCLUSION

Serum and urine L-FABP may be a new diagnostic marker for liver damage in patients with acute hepatitis. However, our study showed that except of aminotransferases, L-FABP should be used for diagnosis of liver damage in patients with acute hepatitis, chronic hepatitis and also cirrhosis.

Hepatic Induction of Fatty Acid Binding Protein 4 Plays a Pathogenic Role in Sepsis in Mice

Sepsis is defined as the host's deleterious systemic inflammatory response to microbial infections. Herein, we report an essential role of the fatty acid binding protein 4 (FABP4; alias adipocyte protein 2 or aP2), a lipid-binding chaperone, in sepsis response. Bioinformatic analysis of the Gene Expression Omnibus data sets showed the level of FABP4 was higher in the nonsurvival sepsis patients' whole blood compared to the survival cohorts. The expression of Fabp4 was induced in a liver-specific manner in cecal ligation and puncture (CLP) and lipopolysaccharide treatment models of sepsis. The induction of Fabp4 may have played a pathogenic role, because ectopic expression of Fabp4 in the liver sensitized mice to CLP-induced inflammatory response and worsened the animal's survival. In contrast, pharmacological inhibition of Fabp4 markedly alleviated the CLP responsive inflammation and tissue damage and improved survival. We conclude that FABP4 is an important mediator of the sepsis response. Early intervention by pharmacological inhibition of FABP4 may help to manage sepsis in the clinic.

Adipocyte Fatty Acid Binding Protein Potentiates Toxic Lipids-Induced Endoplasmic Reticulum Stress in Macrophages via Inhibition of Janus Kinase 2-dependent Autophagy

Lipotoxicity is implicated in the pathogenesis of obesity-related inflammatory complications by promoting macrophage infiltration and activation. Endoplasmic reticulum (ER) stress and adipocyte fatty acid binding protein (A-FABP) play key roles in obesity and mediate inflammatory activity through similar signaling pathways. However, little is known about their interplay in lipid-induced inflammatory responses. Here, we showed that prolonged treatment of palmitic acid (PA) increased ER stress and expression of A-FABP, which was accompanied by reduced autophagic flux in macrophages. Over-expression of A-FABP impaired PA-induced autophagy associating with enhanced ER stress and pro-inflammatory cytokine production, while genetic ablation or pharmacological inhibition of A-FABP reversed the conditions. PA-induced expression of autophagy-related protein (Atg)7 was attenuated in A-FABP over-expressed macrophages, but was elevated in A-FABP-deficient macrophages. Mechanistically, A-FABP potentiated the effects of PA by inhibition of Janus Kinase (JAK)2 activity, thus diminished PA-induced Atg7 expression contributing to impaired autophagy and further augmentation of ER stress. These findings suggest that A-FABP acts as autophagy inhibitor to instigate toxic lipids-induced ER stress through inhibition of JAK2-dependent autophagy, which in turn triggers inflammatory responses in macrophages. A-FABP-JAK2 axis may represent an important pathological pathway contributing to obesity-related inflammatory diseases.

Association of recently described adipokines with liver histology in biopsy-proven non-alcoholic fatty liver disease: a systematic review

The prevalence of non-alcoholic fatty liver disease (NAFLD) is rising, as is the prevalence of obesity and type 2 diabetes. It is increasingly recognized that an impaired pattern in adipokine secretion could play a pivotal role in the development of NAFLD. We performed a systematic review to evaluate the potential link between newly described adipokines and liver histology in biopsy-proven NAFLD patients. A computerized literature search was performed in PubMed, EMBASE and Web of Science electronic databases. Thirty-one cross-sectional studies were included, resulting in a total of seven different investigated adipokines. Studies included in this review mainly had a good methodological quality. Most adipokines were suggested to be involved in the inflammatory response that develops within the context of NAFLD, either at hepatic or systemic level, and/or hepatic insulin resistance. Based on literature, clinical studies suggest that chemerin, resistin and adipocyte-fatty-acid-binding protein potentially are involved in NAFLD pathogenesis and/or progression. However, major inconsistency still exists, and there is a high need for larger studies, together with the need of standardized assays to determine adipokine levels.

Intimate association of visceral obesity with non-alcoholic fatty liver disease in healthy Asians: A case-control study

BACKGROUND AND AIM

To identify factors associated with non-alcoholic fatty liver disease (NAFLD) in healthy Asian subjects.

METHODS

A propensity score-matched case-control study was designed. To investigate the effects of demographic and clinical factors on the presence of NAFLD, a baseline-category logit model was used. Potential living liver donors with no hepatic steatosis (< 5%: n = 1353, group 1) were considered the baseline category, and subjects with mild (5-33%: n = 724, group 2) and moderate/severe (> 33%: n = 116, group 3) hepatic steatosis were defined as cases. Age and gender were matched between cases and controls, which resulted in 83 matched subjects in each of the three groups. The area of abdominal (visceral and subcutaneous) fat was directly measured in all subjects by unenhanced computed tomography.

RESULTS

Serum aspartate aminotransferase, alanine aminotransferase (ALT), gamma-glutamyltranspeptidase, total cholesterol and triglyceride levels, and visceral fat amount were directly correlated with the grade of hepatic steatosis, and high-density lipoprotein cholesterol levels were inversely correlated with it (all P values < 0.05). In a multivariate model, visceral fat amount was significantly correlated with both mild (group 2) and moderate to severe (group 3) NAFLD, with respective odds ratios (ORs) of 1.03 relative to group 1 (Ps < 0.05). Body mass index (BMI), ALT, and subcutaneous fat were significant predictors of only moderate to severe NAFLD (ORs of 0.54, 1.20, and 1.02, respectively, for group 3 vs group 1; Ps < 0.05).

CONCLUSIONS

Our results indicate that visceral adiposity makes non-obese subjects more susceptible to NAFLD, compared with subcutaneous fat and BMI.