Adipocyte fatty acid-binding protein, aP2, alters late atherosclerotic lesion formation in severe hypercholesterolemia

Inhibition of Adipocyte-Derived FABP4 Reduces Adipocyte Inflammation, Improves Angiogenesis, and Facilitates Wound Healing in Metabolic Dysfunctions

Dermal white adipose tissue may participate in the wound-healing process. Obesity-mediated chronic low-grade inflammation impairs wound healing by suppressing vascularity. Given that FABP4 is upregulated in the skin tissue of animals with obesity, this study aimed to investigate the effects of FABP4 inhibition on wound healing in mice with high-fat diet-induced metabolic dysfunction in vivo. The interaction between adipocyte-derived FABP4 and vascular endothelial cell function was also investigated. In mice with high-fat diet-induced metabolic dysfunction, FABP4 inhibition increased angiogenesis and facilitated wound healing with reduced wound inflammation. FABP4 inhibition not only attenuated systemic inflammation, decreased body weight, and reduced insulin resistance but also improved the sizes of adipocytes and hypoxic conditions in dermal white adipose tissue. In vitro hypoxia was used to induce adipocyte inflammation, and the supernatants from hypoxia-stimulated adipocytes impaired the function and angiogenetic capability of human dermal microvascular endothelial cells (HDMECs). Both of them were improved by FABP4 inhibition. Altogether, FABP4 inhibition reduced systemic and adipocyte inflammation, improved vascular endothelial cell function, and facilitated wound healing in metabolic dysfunctions. Given the complex involvement of wound healing, future studies may be required to validate FABP4 as a potential therapeutic target for wound repair in metabolic dysfunctions.

Fatty Acids and their Proteins in Adipose Tissue Inflammation

Chronic low-grade adipose tissue inflammation is associated with metabolic disorders. Inflammation results from the intertwined cross-talks of pro-inflammatory and anti-inflammatory pathways in the immune response of adipose tissue. In addition, adipose FABP4 levels and lipid droplet proteins are involved in systemic and tissue inflammation. Dysregulated adipocytes help infiltrate immune cells derived from bone marrow responsible for producing cytokines and chemokines. When adipose tissue expands in excess, adipocyte exhibits increased secretion of adipokines and is implicated in metabolic disturbances due to the release of free fatty acids. This review presents an emerging concept in adipose tissue fat metabolism, fatty acid handling and binding proteins, and lipid droplet proteins and their involvement in inflammatory disorders.

FABP4 Expression in Subcutaneous Adipose Tissue Is Independently Associated with Circulating Triglycerides in Obesity

Hypertriglyceridemia (HTG) has been associated with an increased risk of pancreatitis and cardiovascular disease. Adipose tissue plays a major role in lipid metabolism, mobilization and distribution. We have compared the histological and transcriptomic profiles of the subcutaneous (SAT) and visceral (VAT) adipose tissues from subjects with severe obesity undergoing bariatric surgery with (Ob-HTG, n = 37) and without HTG (Ob-NTG, n = 67). Mean age and BMI were 51.87 ± 11.21 years, 45.78 ± 6.96 kg/m² and 50.03 ± 10.17 years, 44.04 ± 4.69 kg/m², respectively. The Ob-HTG group showed higher levels of glycosylated hemoglobin, fasting plasma glucose, high-sensitivity C-reactive protein and prevalence of hypertension. The degree of fibrosis was increased by 14% in SAT from the Ob-HTG group (p = 0.028), while adipocyte size distribution was comparable. Twenty genes were found differentially expressed in SAT and VAT between study groups. Among them, only SAT expression of FABP4 resulted significantly associated with circulating triglyceride levels after adjusting for other covariates and independently explained 5% of the variance in triglyceride levels in the combined model. This relationship was not found in the cohort of lean or overweight patients with normotriglyceridemia (non-Ob, n = 21). These results emphasize the contribution of SAT to triglyceride concentrations in obesity and indicate that FABP4 may be a potential drug target for the treatment of HTG.

Serum Adipocyte Fatty-Acid Binding Protein as an Independent Marker of Peripheral Artery Disease in Patients with Type-2 Diabetes Mellitus

The adipocyte fatty-acid binding protein (A-FABP) is predominantly expressed in macrophages and adipocytes and is an essential mediator of inflammation and atherosclerosis pathogenesis. Atherosclerosis is an aggravating factor for peripheral arterial disease (PAD). Our study intended to study the association between PAD and serum A-FABP levels in type-2 diabetes mellitus (T2DM) patients. One hundred and twenty T2DM subjects were enrolled in the study. Fasting blood samples were collected to determine biochemical data and A-FABP levels. By the automatic oscillometric method, the ankle−brachial index (ABI) was measured. Low ABI was defined as any value < 0.9. Twenty participants with T2DM (16.7%) were included in the low ABI group. Low ABI T2DM participants had an increased mean body mass index, body fat mass, systolic blood pressure, C-reactive protein, urine albumin−creatinine ratio, and A-FABP levels compared to those in the normal ABI group. After variables significantly associated with PAD were adjusted by multivariate logistic regression analyses, circulating A-FABP levels (odds ratio [OR]: 1.138; 95 percent confidence interval [CI]: 1.023−1.266; p = 0.017) were identified as the independent marker of PAD. In conclusion, fasting serum A-FABP value has positive association with PAD in T2DM patients.

2,2',4,4'-Tetrabromodiphenyl Ether (PBDE 47) Selectively Stimulates Proatherogenic PPARγ Signatures in Human THP-1 Macrophages to Contribute to Foam Cell Formation

2,2',4,4'-Tetrabromodiphenyl ether (PBDE 47) is one of the most prominent PBDE congeners detected in the human body, suggesting that the potential health risks of PBDE 47 should be thoroughly considered. However, the cardiovascular toxicity of PBDE 47 remains poorly understood. Here, toxic outcomes of PBDE 47 in human THP-1 macrophages concerning foam cell formation, which play crucial roles in the occurrence and development of atherosclerosis, were elucidated. First, our results indicated that PBDE 47 affected the PPARγ pathway most efficiently in THP-1 macrophages by transcriptomic analysis. Second, the PPARγ target genes CD36 and FABP4, responsible for lipid uptake and accumulation in macrophages, were consistently upregulated both at transcriptional and translational levels in THP-1 macrophages upon PBDE 47. Unexpectedly, PBDE 47 failed to activate the PPARγ target gene LXRα and PPARγ-LXRα-ABCA1/G1 cascade, which is activated by the PPARγ full agonist rosiglitazone and enables cholesterol efflux in macrophages. Thus, coincident with the selective upregulation of the PPARγ target genes CD36 and FABP4, PBDE 47, distinct from rosiglitazone, functionally resulted in more lipid accumulation and oxLDL uptake in THP-1 macrophages through high-content analysis (HCA). Moreover, these effects were markedly abrogated by the addition of the PPARγ antagonist T0070907. Mechanistically, the structural basis of selective activation of PPARγ by PBDE 47 was explored by molecular docking and dynamics simulation, which indicated that PBDE 47 interacted with the PPARγ ligand binding domain (PPARγ-LBD) distinctively from that of rosiglitazone. PBDE 47 was revealed to interact with helix 3 and helix 5 but not helix 12 in the PPARγ-LBD. Collectively, these results unraveled the potential cardiovascular toxicity of PBDE 47 by selective activation of PPARγ to facilitate foam cell formation for the first time.

Fatty acid-binding protein 4 circulating levels in non-segmental vitiligo

Background

Vitiligo is an acquired and progressive mucocutaneous disease resulting from the loss of active epidermal melanocytes. Metabolic syndrome (MetS) affects about 25% of the world’s population and is linked to inflammatory skin diseases including vitiligo. Fatty Acid-Binding Protein 4 (FABP4) is an intracellular lipid chaperone. FABP4 is closely associated with MetS.

Objectives

To evaluate the serum level of FABP4 in vitiligo patients and its relation to MetS in the investigated cases.

Methods

This case control study was conducted on 45 patients having non segmental vitiligo and 45 matched controls. Their lipid profile, blood glucose and serum FABP4 levels were measured.

Results

There were significant elevations in FABP4 (p < 0.001), cholesterol (p < 0.001), triglycerides (p = 0.005), and glucose (fasting [p = 0.001] and 2 hours post prandial [p < 0.001]) levels in patients in comparison with controls. MetS was significantly more prevalent among vitiligo patients (p < 0.001) and associated with high FABP4 serum levels (p = 0.037). In vitiligo patients, there were significant positive correlations between FABP4 serum levels and triglycerides (p = 0.047), cholesterol (p = 0.001) and LDL (p = 0.001) levels and negative correlation regarding HDL level (p = 0.009). FABP4 level was a significantly good diagnostic test for early detection of vitiligo (p < 0.001).

Study limitations

The small number of studied subjects.

Conclusions

FABP4 may play an active role in the disease process of vitiligo that could be mediated through associated dyslipidemia and hyperglycemia. FABP4 may be a marker of vitiligo helping in its early diagnosis, but it does not appear to be useful for determining vitiligo severity, activity or associated MetS.

Regulation of macrophage functions by FABP-mediated inflammatory and metabolic pathways

Macrophages are almost everywhere in the body, where they serve pivotal functions in maintaining tissue homeostasis, remodeling, and immunoregulation. Macrophages are traditionally thought to differentiate from bone marrow-derived hematopoietic stem cells (HSCs). Emerging studies suggest that some tissue macrophages at steady state originate from embryonic precursors in the yolk sac or fetal liver and are maintained in situ by self-renewal, but bone marrow-derived monocytes can give rise to tissue macrophages in pathogenic settings, such as inflammatory injuries and cancer. Macrophages are popularly classified as Th1 cytokine (e.g. IFNγ)-activated M1 macrophages (the classical activation) or Th2 cytokine (e.g. IL-4)-activated M2 macrophages (the alternative activation). However, given the myriad arrays of stimuli macrophages may encounter from local environment, macrophages exhibit notorious heterogeneity in their phenotypes and functions. Determining the underlying metabolic pathways engaged during macrophage activation is critical for understanding macrophage phenotypic and functional adaptivity under different disease settings. Fatty acid binding proteins (FABPs) represent a family of evolutionarily conserved proteins facilitating lipid transport, metabolism and responses inside cells. More specifically, adipose-FABP (A-FABP) and epidermal-FABP (E-FABP) are highly expressed in macrophages and play a central role in integrating metabolic and inflammatory pathways. In this review we highlight how A-FABP and E-FABP are respectively upregulated in different subsets of activated macrophages and provide a unique perspective in defining macrophage phenotypic and functional heterogeneity through FABP-regulated lipid metabolic and inflammatory pathways.

FABP5 Is a Sensitive Marker for Lipid-Rich Macrophages in the Luminal Side of Atherosclerotic Lesions

Lipid-rich macrophages in atherosclerotic lesions are thought to be derived from myeloid and vascular smooth muscle cells. A series of studies with genetic and pharmacological inhibition of fatty acid binding protein 4 (FABP4) and FABP5 and bone marrow transplant experiments with FABP4/5 deficient cells in mice have demonstrated that these play an important role in the development of atherosclerosis. However, it is still uncertain about the differential cell-type specificity and distribution between FABP4- and FABP5-expressing cells in early- and late-stage atherosclerotic lesions. In this study, we first explored spatial distribution of FABP4/5 in atherosclerotic lesions in apolipoprotein E deficient (ApoE-/-) mice. FABP4 was only marginally detected in early and advanced lesions, whereas FABP5 was abundantly expressed in these lesions. In advanced lesions, the FABP5-positive area was mostly restricted to the foam cell layer adjacent to the lumen above collagen and elastic fibers with a high signal/noise ratio. Oil red O (ORO) staining revealed that FABP5-positive cells were lipid-rich in early and advanced lesions. Together, most of lipid-rich FABP5-positive cells reside adjacent to the lumen above collagen and elastic fibers. We next studied involvement of FABP5 in lesion formation of atherosclerosis using ApoE-/- FABP5-/- mice. However, deletion of FABP5 did not affect the development of atherosclerosis. These findings, along with previous reports, suggest a novel notion that FABP5 is a sensitive marker for bone marrow-derived lipid-rich macrophages in the luminal side of atherosclerotic lesions, although its functional significance remains elusive.

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.

Apple Supplementation Improves Hemodynamic Parameter and Attenuates Atherosclerosis in High-Fat Diet-Fed Apolipoprotein E-Knockout Mice

Epidemiological studies describe the association between apple consumption and improved cardiovascular and metabolic dysfunction. Our recent multiparametric screening on cellular model studies has shown that apples exhibit vascular tropism including Granny Smith (GS) variety independently of the storage condition. The present study aimed to evaluate the cardiovascular and metabolic protection of supplementation of GS variety after storage in classic cold (GSCC) and extreme ultra-low oxygen conditions (GSXO) in the apolipoprotein E-deficient 8-week-old mice fed with high fat diet for 14 weeks. Supplementation with GSCC and GXO decreases circulating triglycerides, the expression of genes involved in lipogenesis, without change in cholesterol and glucose concentrations and HOMA-IR. Only GSXO supplementation ameliorates body weight gain, insulin level, and HDL/LDL ratio. GSXO supplementation does not modify cardiac parameters; while supplementation with GSCC decreases heart rate and improves cardiac output. Interestingly, GSCC and GSXO reduce systolic and diastolic blood pressure with a differential time course of action. These effects are associated with substantial decrease of atherosclerotic lesions. These data reinforce the knowledge about the vascular tropism of apple supplementation and underscore their ability to improve both cardiovascular and metabolic alterations in a mouse model of atherosclerosis.

Role of the Fatty Acid Binding Proteins in Cardiovascular Diseases: A Systematic Review

Cardiovascular diseases (CVD) remain a global pandemic and leading cause of deaths worldwide. While several guidelines have been developed to control the development of CVDs, its prevalence keeps on increasing until this day. Cardiovascular risk factors, such as reduced exercises and high fat or glucose diets, culminate in the development of the metabolic syndrome and eventually atherosclerosis, which is driven by high blood lipid and cholesterol levels, and by endothelial dysfunction. Late complications of atherosclerosis give rise to serious clinical cardiovascular manifestations such as myocardial infarction and hypertension. Therefore, endothelial functions and the lipid metabolism play critical roles in the pathogenesis of CVDs. Fatty acid-binding proteins are a family of intracellular proteins expressed in many cell types known mainly for their interaction with and trafficking of cellular lipids. The roles of a number of isoforms in this family have been implicated in lipid metabolic homeostasis, but their influence on endothelial function and vascular homeostasis remain largely unknown. This review's purpose is to update fundamentals about the connection between cardiovascular disease, metabolism, endothelial function, and mainly the roles of fatty acid-binding proteins.

Metabolic Reprogramming of Macrophages in Atherosclerosis: Is It All about Cholesterol?

Hypercholesterolemia contributes to the chronic inflammatory response during the progression of atherosclerosis, in part by favoring cholesterol loading in macrophages and other immune cells. However, macrophages encounter a substantial amount of other lipids and nutrients after ingesting atherogenic lipoprotein particles or clearing apoptotic cells, increasing their metabolic load and impacting their behavior during atherosclerosis plaque progression. This review examines whether and how fatty acids and glucose shape the cellular metabolic reprogramming of macrophages in atherosclerosis to modulate the onset phase of inflammation and the later resolution stage, in which the balance is tipped toward tissue repair.

Fatty Acid Binding Protein-4 and Risk of Cardiovascular Disease: The Cardiovascular Health Study

Background

FABP‐4 (fatty acid binding protein‐4) is a lipid chaperone in adipocytes and has been associated with prognosis in selected clinical populations. We investigated the associations between circulating FABP‐4, risk of incident cardiovascular disease (CVD), and risk of CVD mortality among older adults with and without established CVD.

Methods and Results

In the Cardiovascular Health Study, we measured FABP4 levels in stored specimens from the 1992–993 visit and followed participants for incident CVD if they were free of prevalent CVD at baseline and for CVD mortality through June 2015. We used Cox regression to estimate hazard ratios for incident CVD and CVD mortality per doubling in serum FABP‐4 adjusted for age, sex, race, field center, waist circumference, blood pressure, lipids, fasting glucose, and C‐reactive protein. Among 4026 participants free of CVD and 681 with prevalent CVD, we documented 1878 cases of incident CVD and 331 CVD deaths, respectively. In adjusted analyses, FABP‐4 was modestly associated with risk of incident CVD (mean, 34.24; SD, 18.90; HR, 1.10 per doubling in FABP‐4, 95% CI, 1.00–1.21). In contrast, FABP‐4 was more clearly associated with risk of CVD mortality among participants without (HR hazard ratio 1.24, 95% CI, 1.10–1.40) or with prevalent CVD (HR hazard ratio 1.57, 95% CI, 1.24–1.98). These associations were not significantly modified by sex, age, and waist circumference.

Conclusions

Serum FABP‐4 is modestly associated with risk of incident CVD even after adjustment for standard risk factors, but more strongly associated with CVD mortality among older adults with and without established CVD.

Positive Association of Serum Adipocyte Fatty Acid Binding Protein Level With Peripheral Artery Disease in Hemodialysis Patients

Adipocyte fatty acid binding protein is positively associated with atherosclerosis. Peripheral arterial disease is associated with an increased mortality in hemodialysis patients. This study aimed to evaluate the relationship between serum adipocyte fatty acid binding protein levels and peripheral arterial disease by ankle-brachial index in hemodialysis patients. Among the 90 chronic hemodialysis recipients, 20 patients (22.2%) were in the low ankle-brachial index group who had a higher prevalence of diabetes, hyperlipidemia, statin use, older age, higher body fat mass, higher serum adipocyte fatty acid binding protein level, and lower serum creatinine level compared with patients in the control group. After statistical analysis, body fat mass (P = 0.006) and creatinine level (P = 0.018) were shown to be the independent predictors of adipocyte fatty acid binding protein level. Serum adipocyte fatty acid binding protein (P = 0.021) was found to be positively associated with peripheral arterial disease in hemodialysis patients.

Serum fatty acid binding protein 4 is positively associated with early stroke recurrence in nondiabetic ischemic stroke

Adipocyte fatty acid–binding protein (FABP4) played critical roles in metabolic syndrome, inflammatory responses and cardiovascular diseases. It aimed to investigate the associations of serum FABP4 levels with early stroke recurrence. This study included the 206 acute ischemic stroke patients hospitalized in our institution. Stroke recurrence events were assessed at the 3-month follow-up. The median of FABP level was 22.6 (IQR, 17.9-31.6) ng/mL in patients with stroke recurrence (N=36), which was higher than in patients without stroke recurrence [16.9 (IQR, 11.8-21.4) ng/mL] (P<0.001). As a continuous variable, the unadjusted and adjusted risk of stroke recurrence would be increased by 12% (OR=1.12 [95% CI 1.06–1.17], P<0.001) and 8% (1.08 [1.02–1.14], P=0.006) for every 1 ng/ml increment of FABP4. The Area under the curve (AUC) of serum FABP4 and NIH Stroke Scale (NIHSS) score for predicting stroke recurrence was 0.73 (95% CI: 0.64–0.82) and 0.72 (95% CI: 0.64–0.81), presenting no discriminating capacity (P=0.45). In the combining model, the AUC of NIHSS score was further improved to 0.77 by FABP4 (0.77; 95% CI: 0.69–0.85), which was significant (P=0.01). The risk of stroke recurrence can be predicted by elevated FABP4 levels in serum of nondiabetic patients with first-ever ischemic stroke.

Macrophage FABP4 is required for neutrophil recruitment and bacterial clearance in Pseudomonas aeruginosa pneumonia

Fatty acid binding protein 4 (FABP4), an intracellular lipid chaperone and adipokine, is expressed by lung macrophages, but the function of macrophage-FABP4 remains elusive. We investigated the role of FABP4 in host defense in a murine model of Pseudomonas aeruginosa pneumonia. Compared with wild-type (WT) mice, FABP4-deficient (FABP4-/-) mice exhibited decreased bacterial clearance and increased mortality when challenged intranasally with P. aeruginosa. These findings in FABP4-/- mice were associated with a delayed neutrophil recruitment into the lungs and were followed by greater acute lung injury and inflammation. Among leukocytes, only macrophages expressed FABP4 in WT mice with P. aeruginosa pneumonia. Chimeric FABP4-/- mice with WT bone marrow were protected from increased mortality seen in chimeric WT mice with FABP4-/- bone marrow during P. aeruginosa pneumonia, thus confirming the role of macrophages as the main source of protective FABP4 against that infection. There was less production of C-X-C motif chemokine ligand 1 (CXCL1) in FABP4-/- alveolar macrophages and lower airway CXCL1 levels in FABP4-/- mice. Delivering recombinant CXCL1 to the airways protected FABP4-/- mice from increased susceptibility to P. aeruginosa pneumonia. Thus, macrophage-FABP4 has a novel role in pulmonary host defense against P. aeruginosa infection by facilitating crosstalk between macrophages and neutrophils via regulation of macrophage CXCL1 production.-Liang, X., Gupta, K., Rojas Quintero, J., Cernadas, M., Kobzik, L., Christou, H., Pier, G. B., Owen, C. A., Çataltepe, S. Macrophage FABP4 is required for neutrophil recruitment and bacterial clearance in Pseudomonas aeruginosa pneumonia.

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.

Circulating adipocyte fatty acid-binding protein levels predict the development of subclinical atherosclerosis in type 2 diabetes

OBJECTIVE

The aim of this study was to investigate the prospective association of circulating adipocyte fatty acid-binding protein (A-FABP) levels with the development of subclinical atherosclerosis in patients with type 2 diabetes in an 8-year prospective study.

METHODS

A total of 170 patients with newly diagnosed type 2 diabetes were recruited in the study and 133 patients completed the follow-up of 8 years. Baseline plasma A-FABP levels were measured with enzyme-linked immunosorbent assays. The role of A-FABP in predicting the development of subclinical atherosclerosis over 8 years was analyzed using multiple logistic regression.

RESULTS

Of the 133 patients without subclinical atherosclerosis at baseline, a total of 100 had progressed to subclinical atherosclerosis over 8 years. Baseline A-FABP level was significantly higher in patients who had progressed to subclinical atherosclerosis at year 8 compared with ones who had not developed subclinical atherosclerosis after adjustment for sex (15.3 [12.1-23.2] versus 13.3 [10.0-18.9] ng/ml, P = 0.021). High baseline A-FABP level was an independent predictor for the development of subclinical atherosclerosis in patients with type 2 diabetes (odds ratio: 16.24, P = 0.022).

CONCLUSIONS

Circulating A-FABP levels predict the development of subclinical atherosclerosis in type 2 diabetes patients.

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.

Molecular Dynamics Exploration of Selectivity of Dual Inhibitors 5M7, 65X, and 65Z toward Fatty Acid Binding Proteins 4 and 5

Designing highly selective inhibitors of fatty acid binding proteins 4 and 5 (FABP4 and FABP5) is of importance for treatment of some diseases related with inflammation, metabolism, and tumor growth. In this study, molecular dynamics (MD) simulations combined with molecular mechanics generalized Born surface area (MM-GBSA) method were performed to probe binding selectivity of three inhibitors (5M7, 65X, and 65Z) to FABP4/FABP5 with K_i values of 0.022/0.50 μM, 0.011/0.086 μM, and 0.016/0.12 μM, respectively. The results not only suggest that all inhibitors associate more tightly with FABP4 than FABP5, but also prove that the main forces driving the selective bindings of inhibitors to FABP4 and FABP5 stem from the difference in the van der Waals interactions and polar interactions of inhibitors with two proteins. Meanwhile, a residue-based free energy decomposition method was applied to reveal molecular basis that inhibitors selectively interact with individual residues of two different proteins. The calculated results show that the binding difference of inhibitors to the residues (Phe16, Phe19), (Ala33, Gly36), (Phe57, Leu60), (Ala75, Ala78), (Arg126, Arg129), and (Tyr128, Tyr131) in (FABP4, FABP5) drive the selectivity of inhibitors toward FABP4 and FABP5. This study will provide great help for further design of effective drugs to protect against a series of metabolic diseases, arteriosclerosis, and inflammation.

Success stories of natural product-based hybrid molecules for multi-factorial diseases

Complex diseases comprises of highly complicated etiology resulting in limited applicability of conventional targeted therapies. Consequently, conventional medicinal compounds suffer major failure when used for such disease conditions. Additionally, development of multidrug resistance (MDR), adverse drug reactions and clinical specificity of single targeted drug therapy has increased thrust for novel drug therapy. In this rapidly evolving era, natural product-based discovery of hybrid molecules or multi-targeted drug therapies have shown promising results and are trending now a days. Historically, nature has blessed human with different sources viz. plant, animal, microbial, marine and ethnopharmaceutical sources which has given a wide variety of medicinally active compounds. These compounds from natural origin are always choice of interest of medicinal chemists because of their minimum side effects. Hybrid molecules synthesized by fusing or conjugating different active molecules obtained from these sources are reported to synergistically block different pathways which contribute in the pathogenesis of complex diseases. This review strives to encompass all natural product-derived hybrid molecules which act as multi-targeting agents striking various targets involved in different pathways of complex diseased conditions reported in literature.

Adipocyte Fatty Acid-Binding Protein Promotes Palmitate-Induced Mitochondrial Dysfunction and Apoptosis in Macrophages

A high level of circulating free fatty acids (FFAs) is known to be an important trigger for macrophage apoptosis during the development of atherosclerosis. However, the underlying mechanism by which FFAs result in macrophage apoptosis is not well understood. In cultured human macrophage Thp-1 cells, we showed that palmitate (PA), the most abundant FFA in circulation, induced excessive reactive oxidative substance production, increased malondialdehyde concentration, and decreased adenosine triphosphate levels. Furthermore, PA treatment also led to mitochondrial dysfunction, including the decrease of mitochondrial number, the impairment of respiratory complex IV and succinate dehydrogenase activity, and the reduction of mitochondrial membrane potential. Mitochondrial apoptosis was also detected after PA treatment, indicated by a decrease in cytochrome c release, downregulation of Bcl-2, upregulation of Bax, and increased caspase-3 activity. PA treatment upregulated the expression of adipocyte fatty acid-binding protein (A-FABP), a critical regulator of fatty acid trafficking and lipid metabolism. Inhibition of A-FABP with BMS309403, a small-molecule A-FABP inhibitor, almost reversed all of these indexes. Thus, this study suggested that PA-mediated macrophage apoptosis through A-FABP upregulation, which subsequently resulted in mitochondrial dysfunction and reactive oxidative stress. Inhibition of A-FABP may be a potential therapeutic target for macrophage apoptosis and to delay the progress of atherosclerosis.

A Herbal Formula HT051, a Combination of Pueraria lobata and Rehmannia glutinosa, Prevents Postmenopausal Obesity in Ovariectomized Rats

Menopause is strongly associated with an increased risk of metabolic dysfunctions due to the decline in estrogen. Here, we hypothesized that dietary HT051, containing the roots of Pueraria lobata and Rehmannia glutinosa, has beneficial effects on ovariectomized (OVX) rats by regulating lipid metabolism. Forty-eight female Sprague-Dawley rats were randomly divided into 4 groups: sham-operated (Sham), OVX, OVX with low-dose HT051 supplementation, and OVX with high-dose HT051 supplementation. The rats were fed with a modified AIN-93G diet or an HT051-containing modified AIN-93G diet for 8 weeks. Body weight, fat mass, and serum levels of total cholesterol, triglyceride, glucose, alanine transaminase, and aspartate transaminase decreased in HT051-fed OVX rats. Dietary HT051 supplementation significantly decreased the mRNA expression of lipogenesis-related genes, including sterol regulatory element-binding protein 1c and fatty acid synthase, and increased the mRNA expression of β-oxidation-related genes, including peroxisome proliferator-activated receptor and carnitine palmitoyl transferase 1 in the liver of OVX rats. Moreover, the expression of genes involved in adipogenesis and inflammation was significantly lower in the adipose tissue of OVX rats fed with HT051 than in the OVX group. These findings suggest that HT051 may be a potential natural alternative for the management of postmenopausal metabolic dysfunctions.

Circulating adipocyte fatty acid-binding protein is a predictor of cardiovascular events in patients with stable angina undergoing percutaneous coronary intervention

Background

Adipocyte fatty acid-binding protein (A-FABP) is expressed in both adipocytes and macrophages. Recent studies have shown that A-FABP is secreted by adipocytes and that the A-FABP concentration is associated with obesity, insulin resistance, and atherosclerosis. We have reported that the coronary atherosclerotic burden is associated with the serum A-FABP concentration. In the present study, we investigated whether the serum A-FABP concentration is associated with prognosis in patients with stable angina pectoris who have undergone percutaneous coronary intervention (PCI).

Methods

This was a prospective single-center trial. In total, 130 patients with stable angina pectoris undergoing their first PCI were enrolled from August 2008 to July 2010 at Kagawa Prefectural Central Hospital. The primary endpoints were cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, revascularization, and hospitalization for heart failure.

Results

During the follow-up (median, 50 months; interquartile range, 23–66 months), 49 cardiovascular events occurred. Kaplan–Meier analysis showed that the cumulative incidence of the primary endpoints in the high A-FABP group (median A-FABP concentration of ≥ 18.6 ng/ml) was greater than that in the low A-FABP group. Cox analysis showed that the A-FABP concentration was an independent predictor of cardiovascular events adjusted for age and the presence of multi-vessel disease (hazard ratio, 1.03; 95% confidence interval, 1.01–1.04; p = 0.01).

Conclusion

The serum A-FABP concentration is associated with prognosis in patients with stable angina undergoing PCI, suggesting that the serum A-FABP concentration could be useful for risk assessment of secondary prevention.

Trial registration

UMIN Clinical Trials Registry UMIN000029283 (registration date: September 25, 2017), retrospectively registered.

Fenugreek supplementation during high-fat feeding improves specific markers of metabolic health

To assess the metabolically beneficial effects of fenugreek (Trigonella foenum-graecum), C57BL/6J mice were fed a low- or high-fat diet for 16 weeks with or without 2% (w/w) fenugreek supplementation. Body weight, body composition, energy expenditure, food intake, and insulin/glucose tolerance were measured regularly, and tissues were collected for histological and biochemical analysis after 16 weeks of diet exposure. Fenugreek did not alter body weight, fat mass, or food intake in either group, but did transiently improve glucose tolerance in high fat-fed mice. Fenugreek also significantly improved high-density lipoprotein to low-density lipoprotein ratios in high fat-fed mice without affecting circulating total cholesterol, triglycerides, or glycerol levels. Fenugreek decreased hepatic expression of fatty acid-binding protein 4 and increased subcutaneous inguinal adipose tissue expression of adiponectin, but did not prevent hepatic steatosis. Notably, fenugreek was not as effective at improving glucose tolerance as was four days of voluntary wheel running. Overall, our results demonstrate that fenugreek promotes metabolic resiliency via significant and selected effects on glucose regulation, hyperlipidemia, and adipose pathology; but may not be as effective as behavioral modifications at preventing the adverse metabolic consequences of a high fat diet.

Identification of new susceptibility loci for type 2 diabetes and shared etiological pathways with coronary heart disease

To evaluate the shared genetic etiology of type 2 diabetes (T2D) and coronary heart disease (CHD), we conducted a genome-wide, multi-ancestry study of genetic variation for both diseases in up to 265,678 subjects for T2D and 260,365 subjects for CHD. We identify 16 previously unreported loci for T2D and 1 locus for CHD, including a new T2D association at a missense variant in HLA-DRB5 (odds ratio (OR) = 1.29). We show that genetically mediated increase in T2D risk also confers higher CHD risk. Joint T2D-CHD analysis identified eight variants-two of which are coding-where T2D and CHD associations appear to colocalize, including a new joint T2D-CHD association at the CCDC92 locus that also replicated for T2D. The variants associated with both outcomes implicate new pathways as well as targets of existing drugs, including icosapent ethyl and adipocyte fatty-acid-binding protein.

Positive correlation of serum adipocyte fatty acid binding protein levels with metabolic syndrome in kidney transplantation patients

Adipocyte fatty acid binding protein (A-FABP) is significantly expressed in white and brown adipose tissue, monocytes, and macrophages and is a central regulator of systemic insulin sensitivity. Metabolic syndrome (MetS) is a risk factor for post-transplant diabetes mellitus (PTDM), chronic graft dysfunction, graft loss, and patient death in kidney transplantation (KT) patients. This study was undertaken to evaluate the relationship between MetS and fasting serum A-FABP concentration in KT patients. Fasting blood samples were obtained from 70 KT patients. Serum A-FABP levels were measured using a commercial enzyme-linked immunosorbent assay kit. MetS and its components were defined using the diagnostic criteria of the International Diabetes Federation. Twenty-two patients (31.4%) had MetS. KT patients with hypertension (P = 0.011), diabetes (P = 0.002), body weight (P = 0.004), body mass index (BMI, P = 0.001), waist circumference (P < 0.001), body fat mass (P < 0.001), systolic blood pressure (SBP, P = 0.017), total cholesterol (TCH, P = 0.028), triglycerides (TG, P = 0.001), blood urea nitrogen (BUN, P = 0.003), insulin (P < 0.001), homeostasis model assessment of insulin resistance (HOMA-IR, P < 0.001), and A-FABP level (P < 0.001) were higher, while high-density lipoprotein cholesterol (HDL-C, P = 0.010) was lower in KT patients with MetS. Moreover, SBP (β = 0.347, adjusted R² change = 0.108, P = 0.001) and logarithmically transformed triglycerides (log-TG, β = 0.393, adjusted R² change = 0.189, P < 0.001) were associated with A-FABP levels in a multivariable forward stepwise linear regression analysis among KT patients. The results of our study showed that the fasting A-FABP level was positively associated with MetS in KT patients. SBP and log-TG were independent predictors of the serum A-FABP level among KT patients.

Macrophage functions in lean and obese adipose tissue

Interactions between macrophages and adipocytes influence both metabolism and inflammation. Obesity-induced changes to macrophages and adipocytes lead to chronic inflammation and insulin resistance. This paper reviews the various functions of macrophages in lean and obese adipose tissue and how obesity alters adipose tissue macrophage phenotypes. Metabolic disease and insulin resistance shift the balance between numerous pro- and anti-inflammatory regulators of macrophages and create a feed-forward loop of increasing inflammatory macrophage activation and worsening adipocyte dysfunction. This ultimately leads to adipose tissue fibrosis and diabetes. The molecular mechanisms underlying these processes have therapeutic implications for obesity, metabolic syndrome, and diabetes.

Fatty acid binding protein 4/aP2-dependent BLT1R expression and signaling

Previous studies have shown that reduced levels of the adipocyte fatty acid binding protein (FABP)4 (AFABP/aP2), result in metabolic improvement including potentiated insulin sensitivity and attenuated atherosclerosis. Mechanistically, pharmacologic or genetic inhibition of FABP4 in macrophages upregulates UCP2, attenuates reactive oxygen species (ROS) production, polarizes cells toward the anti-inflammatory M2 state, and reduces leukotriene (LT) secretion. At the protein level, FABP4 stabilizes LTA₄ toward chemical hydrolysis, thereby potentiating inflammatory LTC₄ synthesis. Herein, we extend the FABP4-LT axis and demonstrate that genetic knockout of FABP4 reduces expression of the major macrophage LT receptor, LTB₄ receptor 1 (BLT1R), via a ROS-dependent mechanism. Consistent with inflammation driving BLT1R expression, M1 polarized macrophages express increased levels of BLT1R relative to M2 polarized macrophages and treatment with proinflammatory lipopolysaccharide increased BLT1R mRNA and protein expression. In FABP4 knockout macrophages, silencing of UCP2, increased ROS levels and led to increased expression of BLT1R mRNA. Similarly, addition of exogenous H₂O₂ upregulated BLT1R expression, whereas the addition of a ROS scavenger, N-acetyl cysteine, decreased BLT1R levels. As compared with WT macrophages, LTB₄-BLT1R-dependent JAK2-phosphorylation was reduced in FABP4 knockout macrophages. In summary, these results indicate that FABP4 regulates the expression of BLT1R and its downstream signaling via control of oxidative stress in macrophages.

Aggressive Crosstalk Between Fatty Acids and Inflammation in Macrophages and Their Influence on Metabolic Homeostasis

From the immunological point of view, macrophages are required to maintain metabolic homeostasis. Recently, there has been an increased focus on the influence of macrophage phenotypes in adipose tissue on the maintenance of metabolic homeostasis in healthy conditions because dysregulated metabolic homeostasis causes metabolic syndrome. This review notes several types of inflammatory and anti-inflammatory mediators in metabolic homeostasis. M1 macrophage polarization mediates inflammation, whereas M2 macrophage polarization mediates anti-inflammation. Fatty acids and their related factors mediate both inflammatory and anti-inflammatory responses. Saturated fatty acids and polyunsaturated fatty acids mediate inflammation, whereas marine-derived n-3 fatty acids, such as eicosapentaenoic acid and docosahexaenoic acid, mediate anti-inflammation. In this review, we discuss the current understanding of the crosstalk between fatty acids and inflammation in macrophages and their influence on metabolic homeostasis.

Fatty acid binding protein regulate antimicrobial function via Toll signaling in Chinese mitten crab

Fatty acid binding proteins (FABPs) are members of the lipid binding protein superfamily and play crucial role in fatty acid transport and lipid metabolism. In macrophages, Adipocyte-type FABP is an important mediator of inflammation. However, the immune functions of FABPs in invertebrates are not well understood; here, we obtained the gene structure of Eriocheir sinensis FABP 3 and FABP 9 (EsFABP 3 and EsFABP 9), and compared with EsFABP 10. The mRNA expression profiles show that all three FABPs were significantly up-regulated in hemocytes after being challenged with bacteria. Of the three, EsFABP 3 was the most stable and also the most highly up-regulated. Further studies showed that knockdown of EsFABP 3 led to higher bacterial counts in the hemocyte culture medium and a significant decrease in the mRNA expression of some antimicrobial peptides following bacterial stimulation. Moreover, a subcellular study demonstrated that EsFABP 3 can affect nuclear translocation of the dorsal after Gram-positive bacterial stimulation in hemocytes. These findings support the notion that EsFABP 3 could inhibit bacterial proliferation by regulating antimicrobial peptides expression via the Toll signaling pathway.

Adipokines: Potential Therapeutic Targets for Vascular Dysfunction in Type II Diabetes Mellitus and Obesity

Adipokines are bioactive molecules that regulate several physiological functions such as energy balance, insulin sensitization, appetite regulation, inflammatory response, and vascular homeostasis. They include proinflammatory cytokines such as adipocyte fatty acid binding protein (A-FABP) and anti-inflammatory cytokines such as adiponectin, as well as vasodilator and vasoconstrictor molecules. In obesity and type II diabetes mellitus (DM), insulin resistance causes impairment of the endocrine function of the perivascular adipose tissue, an imbalance in the secretion of vasoconstrictor and vasodilator molecules, and an increased production of reactive oxygen species. Recent studies have shown that targeting plasma levels of adipokines or the expression of their receptors can increase insulin sensitivity, improve vascular function, and reduce the risk of cardiovascular morbidity and mortality. Several reviews have discussed the potential of adipokines as therapeutic targets for type II DM and obesity; however, this review is the first to focus on their therapeutic potential for vascular dysfunction in type II DM and obesity.

Adipocyte and epidermal fatty acid-binding protein serum concentrations in patients with lipodystrophy

OBJECTIVE

Lipodystrophy (LD) syndromes are associated with diabetes mellitus, hypertriglyceridemia, and coronary artery disease. One pathogenetic factor of LD is dysregulation of several adipokines. However, the insulin resistance- and dyslipidemia-promoting adipokines adipocyte (AFABP) and epidermal (EFABP) fatty acid-binding protein have not been investigated in non-HIV-associated LD so far.

MATERIAL AND METHODS

We performed a cross-sectional analysis of AFABP and EFABP serum concentrations in 37 LD patients and 37 age-, gender-, and body mass index-matched healthy controls. Moreover, AFABP and EFABP were correlated to clinical and biochemical parameters of inflammation, glucose control, and lipid metabolism.

RESULTS

There was no significant difference in median circulating AFABP and EFABP levels between LD patients (21.7μg/l and 7.5μg/l, respectively) and healthy controls (24.5μg/l and 8.6μg/l, respectively). Neither AFABP nor EFABP were related to markers of impaired glucose control or lipid metabolism. Multiple linear regression analysis showed a positive and independent association of AFABP with gender, serum leptin levels, and body mass index.

CONCLUSIONS

Circulating levels of AFABP and EFABP are not decreased in LD despite adipose tissue loss in contrast to other adipokines including leptin and adiponectin.

Adipose inflammation at the heart of vascular disease

Visceral adipose tissue is a primary site of chronic inflammation in obesity and may contribute to systemic inflammation and development of atherosclerotic vascular disease. Few studies identify molecular mechanisms and secretory pathways which mediate this process. In this edition of Clinical Science, Kwok et al. utilize a transgenic mouse in which dominant-negative c-Jun NH2 terminal kinase (dnJNK) expression is restricted to adipose tissue to implicate JNK-driven expression of adipocyte fatty acid binding protein (A-FABP) in visceral adipose tissue as a key secretory pathway to exacerbate development of atherosclerosis in ApoE-/- mice. They further demonstrate that ApoE-/- mice transplanted with visceral adipose tissue in which JNK has been inactivated display less systemic inflammation and develop significantly less atherosclerosis compared with control mice. Together, the findings of the present study reinforce our understanding of visceral adipose tissue as a secretory organ and the importance of the JNK/A-FABP pathway in mediating adipose vascular cross-talk and exacerbation of atherosclerosis.

Macrophage Apoptosis and Efferocytosis in the Pathogenesis of Atherosclerosis

Macrophage apoptosis and the ability of macrophages to clean up dead cells, a process called efferocytosis, are crucial determinants of atherosclerosis lesion progression and plaque stability. Environmental stressors initiate endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR). Unresolved ER stress with activation of the UPR initiates apoptosis. Macrophages are resistant to apoptotic stimuli, because of activity of the PI3K/Akt pathway. Macrophages express 3 Akt isoforms, Akt1, Akt2 and Akt3, which are products of distinct but homologous genes. Akt displays isoform-specific effects on atherogenesis, which vary with different vascular cell types. Loss of macrophage Akt2 promotes the anti-inflammatory M2 phenotype and reduces atherosclerosis. However, Akt isoforms are redundant with regard to apoptosis. c-Jun NH₂-terminal kinase (JNK) is a pro-apoptotic effector of the UPR, and the JNK1 isoform opposes anti-apoptotic Akt signaling. Loss of JNK1 in hematopoietic cells protects macrophages from apoptosis and accelerates early atherosclerosis. IκB kinase α (IKKα, a member of the serine/threonine protein kinase family) plays an important role in mTORC2-mediated Akt signaling in macrophages, and IKKα deficiency reduces macrophage survival and suppresses early atherosclerosis. Efferocytosis involves the interaction of receptors, bridging molecules, and apoptotic cell ligands. Scavenger receptor class B type I is a critical mediator of macrophage efferocytosis via the Src/PI3K/Rac1 pathway in atherosclerosis. Agonists that resolve inflammation offer promising therapeutic potential to promote efferocytosis and prevent atherosclerotic clinical events. (Circ J 2016; 80: 2259-2268).

Plasma Levels of Fatty Acid-Binding Protein 4, Retinol-Binding Protein 4, High-Molecular-Weight Adiponectin, and Cardiovascular Mortality Among Men With Type 2 Diabetes: A 22-Year Prospective Study

OBJECTIVE

To examine select adipokines, including fatty acid-binding protein 4, retinol-binding protein 4, and high-molecular-weight (HMW) adiponectin in relation to cardiovascular disease (CVD) mortality among patients with type 2 diabetes mellitus.

APPROACH AND RESULTS

Plasma levels of fatty acid-binding protein 4, retinol-binding protein 4, and HMW adiponectin were measured in 950 men with type 2 diabetes mellitus in the Health Professionals Follow-up Study. After an average of 22 years of follow-up (1993-2015), 580 deaths occurred, of whom 220 died of CVD. After multivariate adjustment for covariates, higher levels of fatty acid-binding protein 4 were significantly associated with a higher CVD mortality: comparing extreme tertiles, the hazard ratio and 95% confidence interval of CVD mortality was 1.78 (1.22-2.59; P trend=0.001). A positive association was also observed for HMW adiponectin: the hazard ratio (95% confidence interval) was 2.07 (1.42-3.06; P trend=0.0002), comparing extreme tertiles, whereas higher retinol-binding protein 4 levels were nonsignificantly associated with a decreased CVD mortality with an hazard ratio (95% confidence interval) of 0.73 (0.50-1.07; P trend=0.09). A Mendelian randomization analysis suggested that the causal relationships of HMW adiponectin and retinol-binding protein 4 would be directionally opposite to those observed based on the biomarkers, although none of the Mendelian randomization associations achieved statistical significance.

CONCLUSIONS

These data suggest that higher levels of fatty acid-binding protein 4 and HMW adiponectin are associated with elevated CVD mortality among men with type 2 diabetes mellitus. Biological mechanisms underlying these observations deserve elucidation, but the associations of HMW adiponectin may partially reflect altered adipose tissue functionality among patients with type 2 diabetes mellitus.

Co-treatment of Pitavastatin and Dexamethasone Exacerbates the High-fat Diet-induced Atherosclerosis in apoE-deficient Mice

Activation of macrophage adipocyte fatty acid-binding protein (FABP4) induces development of atherosclerosis in animal models. We previously reported that statin inhibited while dexamethasone activated macrophage FABP4 expression. However, co-treatment of macrophages with statin and dexamethasone induced FABP4 expression in a synergistic manner, which implies that this co-treatment may exacerbate high-fat diet (HFD)-induced atherosclerosis. In this study, we fed apoE-deficient (apoE) mice with HFD or HFD containing dexamethasone or pitavastatin or both for 16 weeks. Compared with HFD alone, pitavastatin or dexamethasone had little effect on lesions in both en face aortas and aortic root cross sections. However, the co-treatment exacerbated HFD-induced lesions. In addition, the co-treatment decreased collagen content and disturbed the integrity of lesion caps. Both serum total cholesterol and LDL cholesterol levels were reduced by pitavastatin and increased by dexamethasone, respectively. However, the co-treatment had little effect on both total cholesterol and LDL cholesterol levels, indicating that the exacerbation of lesions is independent of total cholesterol or LDL cholesterol levels. FABP4 expression in aortic lesion area was significantly induced by the co-treatment, suggesting that activation of FABP4 expression is a main contributor to lesions. In conclusion, our study demonstrates that co-treatment of pitavastatin and dexamethasone exacerbates HFD-induced atherosclerosis and defines a potential risk to use the dual treatment for patients in clinics.

Carnitine transport and fatty acid oxidation

Carnitine is essential for the transfer of long-chain fatty acids across the inner mitochondrial membrane for subsequent β-oxidation. It can be synthesized by the body or assumed with the diet from meat and dairy products. Defects in carnitine biosynthesis do not routinely result in low plasma carnitine levels. Carnitine is accumulated by the cells and retained by kidneys using OCTN2, a high affinity organic cation transporter specific for carnitine. Defects in the OCTN2 carnitine transporter results in autosomal recessive primary carnitine deficiency characterized by decreased intracellular carnitine accumulation, increased losses of carnitine in the urine, and low serum carnitine levels. Patients can present early in life with hypoketotic hypoglycemia and hepatic encephalopathy, or later in life with skeletal and cardiac myopathy or sudden death from cardiac arrhythmia, usually triggered by fasting or catabolic state. This disease responds to oral carnitine that, in pharmacological doses, enters cells using the amino acid transporter B(0,+). Primary carnitine deficiency can be suspected from the clinical presentation or identified by low levels of free carnitine (C0) in the newborn screening. Some adult patients have been diagnosed following the birth of an unaffected child with very low carnitine levels in the newborn screening. The diagnosis is confirmed by measuring low carnitine uptake in the patients' fibroblasts or by DNA sequencing of the SLC22A5 gene encoding the OCTN2 carnitine transporter. Some mutations are specific for certain ethnic backgrounds, but the majority are private and identified only in individual families. Although the genotype usually does not correlate with metabolic or cardiac involvement in primary carnitine deficiency, patients presenting as adults tend to have at least one missense mutation retaining residual activity. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Therapeutic potential of a synthetic FABP4 inhibitor 8g on atherosclerosis in ApoE-deficient mice: the inhibition of lipid accumulation and inflammation

We discovered a synthetic FABP4 inhibitor that ameliorated the symptoms of atherosclerosis and suppressed lipid accumulation.

Development of a therapeutic monoclonal antibody that targets secreted fatty acid-binding protein aP2 to treat type 2 diabetes

The lipid chaperone aP2/FABP4 has been implicated in the pathology of many immunometabolic diseases, including diabetes in humans, but aP2 has not yet been targeted for therapeutic applications. aP2 is not only an intracellular protein but also an active adipokine that contributes to hyperglycemia by promoting hepatic gluconeogenesis and interfering with peripheral insulin action. Serum aP2 levels are markedly elevated in mouse and human obesity and strongly correlate with metabolic complications. These observations raise the possibility of a new strategy to treat metabolic disease by targeting serum aP2 with a monoclonal antibody (mAb) to aP2. We evaluated mAbs to aP2 and identified one, CA33, that lowered fasting blood glucose, improved systemic glucose metabolism, increased systemic insulin sensitivity, and reduced fat mass and liver steatosis in obese mouse models. We examined the structure of the aP2-CA33 complex and resolved the target epitope by crystallographic studies in comparison to another mAb that lacked efficacy in vivo. In hyperinsulinemic-euglycemic clamp studies, we found that the antidiabetic effect of CA33 was predominantly linked to the regulation of hepatic glucose output and peripheral glucose utilization. The antibody had no effect in aP2-deficient mice, demonstrating its target specificity. We conclude that an aP2 mAb-mediated therapeutic constitutes a feasible approach for the treatment of diabetes.

Metabolic functions of FABPs--mechanisms and therapeutic implications

Intracellular and extracellular interactions with proteins enables the functional and mechanistic diversity of lipids. Fatty acid-binding proteins (FABPs) were originally described as intracellular proteins that can affect lipid fluxes, metabolism and signalling within cells. As the functions of this protein family have been further elucidated, it has become evident that they are critical mediators of metabolism and inflammatory processes, both locally and systemically, and therefore are potential therapeutic targets for immunometabolic diseases. In particular, genetic deficiency and small molecule-mediated inhibition of FABP4 (also known as aP2) and FABP5 can potently improve glucose homeostasis and reduce atherosclerosis in mouse models. Further research has shown that in addition to their intracellular roles, some FABPs are found outside the cells, and FABP4 undergoes regulated, vesicular secretion. The circulating form of FABP4 has crucial hormonal functions in systemic metabolism. In this Review we discuss the roles and regulation of both intracellular and extracellular FABP actions, highlighting new insights that might direct drug discovery efforts and opportunities for management of chronic metabolic diseases.

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.

Nutrition and metabolic correlates of obesity and inflammation: clinical considerations

Since 1980, the global prevalence of obesity has doubled; in the United States, it has almost tripled. Billions of people are overweight and obese; the WHO reports that >65% of the world's population die of diseases related to overweight rather than underweight. Obesity is a complex disease that can be studied from "metropolis to metabolite"—that is, beginning at the policy and the population level through epidemiology and intervention studies; to bench work including preclinical models, tissue, and cell culture studies; to biochemical assays; and to metabolomics. Metabolomics is the next research frontier because it provides a real-time snapshot of biochemical building blocks and products of cellular processes. This report comments on practical considerations when conducting metabolomics research. The pros and cons and important study design concerns are addressed to aid in increasing metabolomics research in the United States. The link between metabolism and inflammation is an understudied phenomenon that has great potential to transform our understanding of immunometabolism in obesity, diabetes, cancer, and other diseases; metabolomics promises to be an important tool in understanding the complex relations between factors contributing to such diseases.

Supplementation of chitosan alleviates high-fat diet-enhanced lipogenesis in rats via adenosine monophosphate (AMP)-activated protein kinase activation and inhibition of lipogenesis-associated genes

This study investigated the role of chitosan in lipogenesis in high-fat diet-induced obese rats. The lipogenesis-associated genes and their upstream regulatory proteins were explored. Diet supplementation of chitosan efficiently decreased the increased weights in body, livers, and adipose tissues in high-fat diet-fed rats. Chitosan supplementation significantly raised the lipolysis rate; attenuated the adipocyte hypertrophy, triglyceride accumulation, and lipoprotein lipase activity in epididymal adipose tissues; and decreased hepatic enzyme activities of lipid biosynthesis. Chitosan supplementation significantly activated adenosine monophosphate (AMP)-activated protein kinase (AMPK) phosphorylation and attenuated high-fat diet-induced protein expressions of lipogenic transcription factors (PPAR-γ and SREBP1c) in livers and adipose tissues. Moreover, chitosan supplementation significantly inhibited the expressions of downstream lipogenic genes (FAS, HMGCR, FATP1, and FABP4) in livers and adipose tissues of high-fat diet-fed rats. These results demonstrate for the first time that chitosan supplementation alleviates high-fat diet-enhanced lipogenesis in rats via AMPK activation and lipogenesis-associated gene inhibition.

Increased plasma levels of FABP4 and PTEN is associated with more severe insulin resistance in women with gestational diabetes mellitus

BACKGROUND

The aim of this study was to investigate the relationship between plasma fatty acid binding protein 4 (FABP4), phosphatase and tensin homolog (PTEN), and insulin resistance in patients with gestational diabetes mellitus (GDM).

MATERIAL AND METHODS

Plasma FABP4 and PTEN were determined by ELISA in GDM patients (GDM group, n=30) and in euglycemic pregnant women (control group, n=30). The clinical features, body mass index (BMI), homeostasis model assessment of insulin resistance (HOMA-IR), and lipid profiles were compared between the 2 groups. The influence of risk factors on insulin resistance, including BMI, lipid profiles, FABP4, and PTEN, were further investigated by multiple-factor stepwise regression analysis.

RESULTS

Higher levels of BMI, ΔBMI, triglyceride (TG), fasting plasma glucose (FPG), 2-hour plasma glucose (2hPG), fasting insulin, HOMA-IR, FABP4, PTEN, and lower level of high-density lipoprotein cholesterol (HDL-C) were found in the GDM patients than in the controls (all P<0.005). The plasma FABP4 was 1.47±0.25 vs. 0.20±0.07 ng/ml in the GDM and control group, respectively (P<0.0001). Plasma PTEN was 6.46±1.57 vs. 4.72±0.82 ng/ml in the GDM and control group, respectively (P<0.0001). There was a positive relation between plasma FABP4 and PTEN when all blood samples, including GDM and control groups, were analyzed (P<0.05). The multiple-factor regression analysis revealed that plasma FABP4, TG, and PTEN were independent risk factors for increased insulin resistance.

CONCLUSIONS

GDM patients have more severe insulin resistance compared to euglycemic pregnant women. Higher levels of plasma FABP4 and PTEN are associated with increased insulin resistance and may participate in the pathogenesis of insulin resistance during gestation.

Mature adipocyte proteome reveals differentially altered protein abundances between lean, overweight and morbidly obese human subjects

Overweight (OW) and obese individuals are considered to be graded parts of the scale having increasing weight as a common feature. They may not, however, be part of the same continuum and may differ metabolically. In this study we applied an untargeted proteomic approach to compare protein abundances in mature adipocytes derived from the subcutaneous adipose tissue of overweight and morbidly obese female subjects to those of lean age matched controls. Mature adipocytes were isolated from liposuction samples of abdominal subcutaneous adipose tissue collected from both lean (L; n = 7, 23.3 ± 0.4 kg/m(2); mean BMI ± SD), overweight (OW; n = 8, 27.9 ± 0.6 kg/m(2); mean BMI ± SD) and morbidly obese (MOB; n = 7, 44.8 ± 3.8 kg/m(2); mean BMI ± SD) individuals. Total protein extracts were then compared by two-dimensional difference in gel electrophoresis (2D DIGE). One hundred and ten differentially expressed protein spots (i.e., fitting the statistical criteria ANOVA test, p < 0.05; fold-change ≥1.5) were detected, and of these, 89 were identified by MALDI-TOF mass spectrometry. Of these, 66 protein spots were common to both groups whereas 23 were unique to the MOB group. Significant differences were evident in the abundances of key proteins involved in glucose and lipid metabolism, energy regulation, cytoskeletal structure and redox control signaling pathways. Differences in the abundance of some chaperones were also evident. The differentially abundant proteins were investigated using Ingenuity Pathway Analysis (IPA) to establish their associations with known biological functions. The network identified in the OW group with the highest score relates to-: cell-to-cell signaling and interaction; in contrast, in the MOB group the major interacting pathways are associated with lipid metabolism, small molecule biochemistry and cancer. The differences in abundance of the differentially regulated proteins were validated by immunoblotting. These findings provide insights into metabolic differences in OW and MOB individuals.

Fatty Acid-Binding Protein 4 (FABP4): Pathophysiological Insights and Potent Clinical Biomarker of Metabolic and Cardiovascular Diseases

Over the past decade, evidences of an integration of metabolic and inflammatory pathways, referred to as metaflammation in several aspects of metabolic syndrome, have been accumulating. Fatty acid-binding protein 4 (FABP4), also known as adipocyte FABP (A-FABP) or aP2, is mainly expressed in adipocytes and macrophages and plays an important role in the development of insulin resistance and atherosclerosis in relation to metaflammation. Despite lack of a typical secretory signal peptide, FABP4 has been shown to be released from adipocytes in a non-classical pathway associated with lipolysis, possibly acting as an adipokine. Elevation of circulating FABP4 levels is associated with obesity, insulin resistance, diabetes mellitus, hypertension, cardiac dysfunction, atherosclerosis, and cardiovascular events. Furthermore, ectopic expression and function of FABP4 in several types of cells and tissues have been recently demonstrated. Here, we discuss both the significant role of FABP4 in pathophysiological insights and its usefulness as a biomarker of metabolic and cardiovascular diseases.

Imaging of atherosclerotic plaques in obesity: excessive fat accumulation, plaque progression and vulnerability

Obesity is becoming a major health issue in the world due to sedentary lifestyles and increasing intake of Western diets. Obesity is associated with metabolic abnormalities and atherosclerotic cardiovascular diseases. Adipose tissue has been increasingly considered to play a critical role in inducing metabolic disturbances and promoting atherogenesis. Arterial wall imaging permits direct visualization of atheroma burden in various vascular beds. In addition, recent advances in imaging technology help characterize components, microstructures and functional features of atherosclerotic plaques. These imaging modalities have contributed to elucidating factors associated with atherosclerosis in obese patients. Also, it provides opportunities to evaluate the effect of novel therapies on plaques in the setting of obesity. The findings of recent imaging studies and the clinical implications will be reviewed.