Cytoplasmic fatty acid-binding proteins: emerging roles in metabolism and atherosclerosis

Discovery of FDA-approved drugs as inhibitors of fatty acid binding protein 4 using molecular docking screening

We first identified fluorescein, ketazolam, antrafenine, darifenacin, fosaprepitant, paliperidone, risperidone, pimozide, trovafloxacin, and levofloxacin as inhibitors of fatty acid binding protein 4 using molecular docking screening from FDA-approved drugs. Subsequently, the biochemical characterizations showed that levofloxacin directly inhibited FABP4 activity in both the in vitro ligand displacement assay and cell-based function assay. Furthermore, levofloxacin did not induce adipogenesis in adipocytes, which is the major adverse effect of FABP4 inhibitors.

Mechanism and clinical evidence of lipocalin-2 and adipocyte fatty acid-binding protein linking obesity and atherosclerosis

Obesity is considered to be a chronic inflammatory state in which the dysfunction of adipose tissue plays a central role. The adipokines, which are cytokines secreted by adipose tissue, are key links between obesity and related diseases such as metabolic syndrome and atherosclerosis. LCN2 and A-FABP, both of which are major adipokines predominantly produced in adipose tissue, have recently been shown to be pivotal modulators of vascular function. However, different adipokines modulate the development of atherosclerosis in distinctive manners, which are partly attributable to their unique regulatory mechanisms and functions. This review highlights recent advances in the understanding of the role of two adipokines in mediating chronic inflammation and the pathogenesis of atherosclerosis.

Associations between adipocyte fatty acid-binding protein and clinical parameters in polycystic ovary syndrome

PURPOSE

We evaluated a possible association between serum adipocyte fatty acid-binding protein (A-FABP) levels and clinical parameters in women with polycystic ovary syndrome (PCOS).

METHODS

Our study included 86 women: 49 with PCOS (study group), 37 with non-PCOS (control group). We recorded and analyzed age, body mass index [BMI = weight (kg)/height (m)(2)], waist circumference, and blood pressure and follicle-stimulating hormone (FSH), luteinizing hormone (LH), LH/FSH, free testosterone (fT), dehydroepiandrosterone sulfate, 17-OH progesterone, insulin, glucose, triglyceride, high-density lipoprotein, low-density lipoprotein, very low density lipoprotein, HOMA-IR, and A-FABP levels.

RESULTS

The mean BMI, waist circumference, and levels of serum LH, fT, LH/FSH, fasting insulin, and HOMA-IR were significantly higher in PCOS patients (p < 0.05). Pearson correlation analysis showed positive correlations of A-FABP levels with BMI and HOMA-IR levels and a negative correlation between A-FABP and fT levels. A ROC curve analysis found that BMI, waist circumference, and levels of fT, A-FABP, and HOMA-IR were discriminative parameters.

CONCLUSION

Serum A-FABP levels may be a good prognostic marker in predicting metabolic syndrome and cardiovascular diseases in PCOS patients.

Exogenous fatty acid binding protein 4 promotes human prostate cancer cell progression

Epidemiologic studies have found that obesity is associated with malignant grade and mortality in prostate cancer. Several adipokines have been implicated as putative mediating factors between obesity and prostate cancer. Fatty acid binding protein 4 (FABP4), a member of the cytoplasmic fatty acid binding protein multigene family, was recently identified as a novel adipokine. Although FABP4 is released from adipocytes and mean circulating concentrations of FABP4 are linked with obesity, effects of exogenous FABP4 on prostate cancer progression are unclear. In this study, we examined the effects of exogenous FABP4 on human prostate cancer cell progression. FABP4 treatment promoted serum-induced prostate cancer cell invasion in vitro. Furthermore, oleic acid promoted prostate cancer cell invasion only if FABP4 was present in the medium. These promoting effects were reduced by FABP4 inhibitor, which inhibits FABP4 binding to fatty acids. Immunostaining for FABP4 showed that exogenous FABP4 was taken up into DU145 cells in three-dimensional culture. In mice, treatment with FABP4 inhibitor reduced the subcutaneous growth and lung metastasis of prostate cancer cells. Immunohistochemical analysis showed that the number of apoptotic cells, positive for cleaved caspase-3 and cleaved PARP, was increased in subcutaneous tumors of FABP4 inhibitor-treated mice, as compared with control mice. These results suggest that exogenous FABP4 might promote human prostate cancer cell progression by binding with fatty acids. Additionally, exogenous FABP4 activated the PI3K/Akt pathway, independently of binding to fatty acids. Thus, FABP4 might be a key molecule to understand the mechanisms underlying the obesity-prostate cancer progression link.

FABP4 attenuates PPARγ and adipogenesis and is inversely correlated with PPARγ in adipose tissues

Fatty acid binding protein 4 (FABP4, also known as aP2) is a cytoplasmic fatty acid chaperone expressed primarily in adipocytes and myeloid cells and implicated in the development of insulin resistance and atherosclerosis. Here we demonstrate that FABP4 triggers the ubiquitination and subsequent proteasomal degradation of peroxisome proliferator-activated receptor γ (PPARγ), a master regulator of adipogenesis and insulin responsiveness. Importantly, FABP4-null mouse preadipocytes as well as macrophages exhibited increased expression of PPARγ, and complementation of FABP4 in the macrophages reversed the increase in FABP4 expression. The FABP4-null preadipocytes exhibited a remarkably enhanced adipogenesis compared with wild-type cells, indicating that FABP4 regulates adipogenesis by downregulating PPARγ. We found that the FABP4 level was higher and PPARγ level was lower in human visceral fat and mouse epididymal fat compared with their subcutaneous fat. Furthermore, FABP4 was higher in the adipose tissues of obese diabetic individuals compared with healthy ones. Suppression of PPARγ by FABP4 in visceral fat may explain the reported role of FABP4 in the development of obesity-related morbidities, including insulin resistance, diabetes, and atherosclerosis.

Cardiac Surgery Increases Serum Concentrations of Adipocyte Fatty Acid-Binding Protein and Its mRNA Expression in Circulating Monocytes but Not in Adipose Tissue

Adipocyte fatty acid binding protein (A-FABP) is a novel adipokine involved in the regulation of lipid and glucose metabolism and inflammation. To evaluate its potential role in the development of postoperative hyperglycemia and insulin resistance we assessed A-FABP serum concentrations and mRNA expression in skeletal and myocardial muscle, subcutaneous and epicardial adipose tissue and peripheral monocytes in 11 diabetic and 20 age- and sex-matched non-diabetic patients undergoing elective cardiac surgery. Baseline serum A-FABP did not differ between the groups (31.1±5.1 vs. 25.9±4.6 ng/ml, p=0.175). Cardiac surgery markedly increased serum A-FABP in both groups with a rapid peak at the end of surgery followed by a gradual decrease to baseline values during the next 48 h with no significant difference between the groups at any timepoint. These trends were analogous to postoperative excursions of plasma glucose, insulin and selected proinflammatory markers. Cardiac surgery increased A-FABP mRNA expression in peripheral monocytes, while no effect was observed in adipose tissue or muscle. Our data suggest that circulating A-FABP might be involved in the development of acute perioperative stress response, insulin resistance and hyperglycemia of critically ill irrespectively of the presence of diabetes mellitus.

FABP4 induces vascular smooth muscle cell proliferation and migration through a MAPK-dependent pathway

Purpose

The migration and proliferation of vascular smooth muscle cells play crucial roles in the development of atherosclerotic lesions. This study examined the effects of fatty acid binding protein 4 (FABP4), an adipokine that is associated with cardiovascular risk, endothelial dysfunction and proinflammatory effects, on the migration and proliferation of human coronary artery smooth muscle cells (HCASMCs).

Methods and Results

A DNA 5-bromo-2′-deoxy-uridine (BrdU) incorporation assay indicated that FABP4 significantly induced the dose-dependent proliferation of HCASMCs with a maximum stimulatory effect at 120 ng/ml (13% vs. unstimulated cells, p<0.05). An anti-FABP4 antibody (40 ng/ml) significantly inhibited the induced cell proliferation, demonstrating the specificity of the FABP4 proliferative effect. FABP4 significantly induced HCASMC migration in a dose-dependent manner with an initial effect at 60 ng/ml (12% vs. unstimulated cells, p<0.05). Time-course studies demonstrated that FABP4 significantly increased cell migration compared with unstimulated cells from 4 h (23%vs. 17%, p<0.05) to 12 h (74%vs. 59%, p<0.05). Pretreatment with LY-294002 (5 µM) and PD98059 (10 µM) blocked the FABP4-induced proliferation and migration of HCASMCs, suggesting the activation of a kinase pathway. On a molecular level, we observed an up-regulation of the MAPK pathway without activation of Akt. We found that FABP4 induced the active forms of the nuclear transcription factors c-jun and c-myc, which are regulated by MAPK cascades, and increased the expression of the downstream genes cyclin D1 and MMP2, CCL2, and fibulin 4 and 5, which are involved in cell cycle regulation and cell migration.

Conclusions

These findings indicate a direct effect of FABP4 on the migration and proliferation of HCASMCs, suggesting a role for this adipokine in vascular remodelling. Taken together, these results demonstrate that the FABP4-induced DNA synthesis and cell migration are mediated primarily through a MAPK-dependent pathway that activates the transcription factors c-jun and c-myc in HCASMCs.

Curcumin modulation of high fat diet-induced atherosclerosis and steatohepatosis in LDL receptor deficient mice

OBJECTIVE

Consuming curcumin may benefit health by modulating lipid metabolism and suppressing atherogenesis. Fatty acid binding proteins (FABP-4/aP2) and CD36 expression are key factors in lipid accumulation in macrophages and foam cell formation in atherogenesis. Our earlier observations suggest that curcumin's suppression of atherogenesis might be mediated through changes in aP2 and CD36 expression in macrophages. Thus, this study aimed to further elucidate the impact of increasing doses of curcumin on modulation of these molecular mediators on high fat diet-induced atherogenesis, inflammation, and steatohepatosis in Ldlr(-/-) mice.

METHODS

Ldlr(-/-) mice were fed low fat (LF) or high fat (HF) diet supplemented with curcumin (500 HF + LC; 1000 HF + MC; 1500 HF + HC mg/kg diet) for 16 wks. Fecal samples were analyzed for total lipid content. Lipids accumulation in THP-1 cells and expression of aP2, CD36 and lipid accumulation in peritoneal macrophages were measured. Fatty streak lesions and expression of IL-6 and MCP-1 in descending aortas were quantified. Aortic root was stained for fatty and fibrotic deposits and for the expression of aP2 and VCAM-1. Total free fatty acids, insulin, glucose, triglycerides, and cholesterol as well as several inflammatory cytokines were measured in plasma. The liver's total lipids, cholesterol, triglycerides, and HDL content were measured, and the presence of fat droplets, peri-portal fibrosis and glycogen was examined histologically.

RESULTS

Curcumin dose-dependently reduced uptake of oxLDL in THP-1 cells. Curcumin also reduced body weight gain and body fat without affecting fat distribution. During early intervention, curcumin decreased fecal fat, but at later stages, it increased fat excretion. Curcumin at medium doses of 500-1000 mg/kg diet was effective at reducing fatty streak formation and suppressing aortic expression of IL-6 in the descending aorta and blood levels of several inflammatory cytokines, but at a higher dose (HF + HC, 1500 mg/kg diet), it had adverse effects on some of these parameters. This U-shape like trend was also present when aortic root sections were examined histologically. However, at a high dose, curcumin suppressed development of steatohepatosis, reduced fibrotic tissue, and preserved glycogen levels in liver.

CONCLUSION

Curcumin through a series of complex mechanisms, alleviated the adverse effects of high fat diet on weight gain, fatty liver development, dyslipidemia, expression of inflammatory cytokines and atherosclerosis in Ldlr(-/-) mouse model of human atherosclerosis. One of the mechanisms by which low dose curcumin modulates atherogenesis is through suppression of aP2 and CD36 expression in macrophages, which are the key players in atherogenesis. Overall, these effects of curcumin are dose-dependent; specifically, a medium dose of curcumin in HF diet appears to be more effective than a higher dose of curcumin.

Beneficial effects of flaxseed oil and fish oil diet are through modulation of different hepatic genes involved in lipid metabolism in streptozotocin-nicotinamide induced diabetic rats

Dietary omega-3 fatty acids have been demonstrated to have positive physiological effects on lipid metabolism, cardiovascular system and insulin resistance. Type-2 diabetes (T2DM) is known for perturbations in fatty acid metabolism leading to dyslipidemia. Our objective was to investigate beneficial effects of dietary flaxseed oil and fish oil in streptozotocin-nicotinamide induced diabetic rats. Thirty-six adult, male, Wistar rats were divided into six groups: three diabetic and three non-diabetic. Diabetes was induced by an injection of nicotinamide (110 mg/kg) and STZ (65 mg/kg). The animals received either control, flaxseed oil or fish oil (10 % w/w) enriched diets for 35 days. Both diets lowered serum triglycerides and very low-density lipoprotein cholesterol levels and elevated serum high-density lipoprotein cholesterol levels in diabetic rats, while serum total cholesterol and LDL-C levels remained unaffected. Both the diets increased omega-3 levels in plasma and RBCs of diabetic rats. Flaxseed oil diet significantly up-regulated the key transcription factor peroxisome proliferator-activated receptor-α (PPAR-α ) and down-regulated sterol regulatory element-binding protein-1 (SREBP-1) in diabetic rats, which would have increased β-oxidation of fatty acids and concomitantly reduced lipogenesis respectively, thereby reducing TG levels. Fish oil diet, on the contrary lowered serum TG levels without altering PPAR-α while it showed a non-significant reduction in SREBP-1 expression in diabetic rats. Another key finding of the study is the activation of D5 and D6 desaturases in diabetic rats by flaxseed oil diet or fish oil diets, which may have resulted in an improved omega-3 status and comparable effects shown by both diets. The reduced expression of Liver-fatty acid binding protein in diabetic rats was restored by fish oil alone, while both diets showed equal effects on adipocyte fatty acid-binding protein expression. We also observed down-regulation of atherogenic cytokines tumor necrosis factor-α and interleukin-6 by both the diets. In conclusion, dietary flaxseed oil and fish oil have therapeutic potential in preventing lipid abnormalities in T2DM.

Serum liver fatty acid binding protein levels correlate positively with obesity and insulin resistance in Chinese young adults

Background

Liver fatty acid–binding protein (FABP1) plays an inconclusive role in adiposity. We investigated the association of serum FABP1 levels with obesity and insulin resistance in Chinese young people under 30 years old.

Methodology and Principal Findings

Cross-sectional analysis including 200 obese and 172 normal-weight subjects matched for age and sex, anthropometric measurements were performed and serum FABP1 and biochemical characteristics were measured. Insulin resistance was determined by homeostasis model assessment of insulin resistance (HOMA-IR) and by the insulin sensitivity index (S_i) derived from Bergman’s minimal model. FABP1 levels in obese subjects were significantly higher than those in normal-weight subjects (p<0.001) and the significance remained after adjustment for age, gender, alanine and aspartate aminotransferases (p<0.001). Serum FABP1 levels were significantly correlated with many metabolic-related parameters, with BMI and triglycerides as the independent determinants. FABP1 levels remained an independent risk factor of insulin resistance assessed by binary S_i (OR = 1.868 per SD unit, 95% CI [1.035–3.373], p = 0.038) after adjustment for age, sex, BMI, waist circumference, systolic blood pressure, serum triacylglycerol, total cholesterol, HDL- and LDL-cholesterol,. FABP1 levels were also elevated with an increasing number of components of the metabolic syndrome (p for trend <0.001). Multiple regression modeling for the MetS and its components demonstrated that hypertriglyceridemia and low HDL-cholesterol were significantly correlated to serum FABP1 levels.

Conclusions and Significance

Serum FABP1 correlates positively with obesity and insulin resistance in Chinese young adults. Our data supports the fact that FABP1 might be an important mediator participating in fatty acid metabolism and energy balance.

Periodontal therapy decreases serum levels of adipocyte fatty acid-binding protein in systemically healthy subjects: a pilot clinical trial

BACKGROUND AND OBJECTIVE

Adipocyte fatty acid-binding protein (A-FABP) is expressed in adipocytes, macrophages and microvascular endothelial cells, and it plays a central role in inflammation, atherosclerosis and metabolic responses. This pilot study investigated the effect of nonsurgical periodontal therapy on the serum levels of A-FABP in subjects with chronic periodontitis.

MATERIAL AND METHODS

A pilot clinical trial was conducted in 24 otherwise healthy Chinese subjects with moderate to severe chronic periodontitis. The treatment group (n = 12) received nonsurgical periodontal therapy immediately, whereas in the control group (n = 12) the treatment was delayed for 3 months. The serum levels of A-FABP were measured by ELISAs. Other inflammatory and endothelial biomarkers and periodontal conditions were evaluated at baseline and at the 3-month follow-up appointment.

RESULTS

A-FABP levels decreased significantly in the treatment group compared with the control group (treatment effect: -1.7 ng/mL; 95% confidence interval: -2.8 to -0.6; p = 0.003). The treatment also significantly improved periodontal conditions but had no significant effect on other biomarkers. In the multivariable regression model, the change in the percentage of sites with detectable plaque was significantly associated with the change in the level of A-FABP (beta: 0.04, 95% confidence interval: 0.01-0.06, p = 0.004).

CONCLUSION

Within the limitations of this pilot study, the current findings suggest that treatment of periodontitis may significantly decrease the serum levels of A-FABP. Further longitudinal study with a large sample size is warranted to confirm this finding and elaborate the relevant clinical implications.

Fatty acid-binding protein 4 impairs the insulin-dependent nitric oxide pathway in vascular endothelial cells

Background

Recent studies have shown that fatty acid-binding protein 4 (FABP4) plasma levels are associated with impaired endothelial function in type 2 diabetes (T2D). In this work, we analysed the effect of FABP4 on the insulin-mediated nitric oxide (NO) production by endothelial cells in vitro.

Methods

In human umbilical vascular endothelial cells (HUVECs), we measured the effects of FABP4 on the insulin-mediated endothelial nitric oxide synthase (eNOS) expression and activation and on NO production. We also explored the impact of exogenous FABP4 on the insulin-signalling pathway (insulin receptor substrate 1 (IRS1) and Akt).

Results

We found that eNOS expression and activation and NO production are significantly inhibited by exogenous FABP4 in HUVECs. FABP4 induced an alteration of the insulin-mediated eNOS pathway by inhibiting IRS1 and Akt activation. These results suggest that FABP4 induces endothelial dysfunction by inhibiting the activation of the insulin-signalling pathway resulting in decreased eNOS activation and NO production.

Conclusion

These findings provide a mechanistic linkage between FABP4 and impaired endothelial function in diabetes, which leads to an increased cardiovascular risk.

Obesity, obstructive sleep apnoea and metabolic syndrome

OSA is increasingly recognized as a major health problem in developed countries. Obesity is the most common risk factor in OSA and hence, the prevalence of OSA is undoubtedly rising given the epidemic of obesity. Recent data also suggest that OSA is highly associated with the metabolic syndrome, and it is postulated that OSA contributes to cardiometabolic dysfunction, and subsequently vasculopathy. Current evidence regarding the magnitude of impact on ultimate cardiovascular morbidity or mortality attributable to OSA-induced metabolic dysregulation is scarce. Given the known pathophysiological triggers of intermittent hypoxia and sleep fragmentation in OSA, the potential mechanisms of OSA-obesity-metabolic syndrome interaction involve sympathetic activation, oxidative stress, inflammation and neurohumoral changes. There is accumulating evidence from human and animal/cell models of intermittent hypoxia to map out these mechanistic pathways. In spite of support for an independent role of OSA in the contribution towards metabolic dysfunction, a healthy diet and appropriate lifestyle modifications towards better control of metabolic function are equally important as CPAP treatment in the holistic management of OSA.

Elevated serum adipocyte fatty acid-binding protein concentrations are independently associated with renal dysfunction in patients with stable angina pectoris

Background

Chronic kidney disease (CKD) is associated with cardiovascular events. Adipocyte fatty acid-binding protein (A-FABP) plays an important role in atherosclerosis. We investigated whether plasma A-FABP is involved in renal function in patients with stable angina pectoris.

Methods

A total of 221 patients with significant coronary artery stenosis were enrolled after coronary angiography. CKD was defined as an estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m². The severity of coronary stenosis was assessed using a modified Gensini score and coronary angiography. Serum A-FABP levels were determined by enzyme-linked immunosorbent assay.

Results

Serum A-FABP levels were significantly correlated with both eGFR (r = -0.41, p < 0.01) and the severity of coronary artery stenosis (r = 0.16, p = 0.02), and these relationships remained significant after adjusting for confounding factors. The prevalence of CKD and multi-vessel disease was significantly higher among patients with serum A-FABP levels above the median value of 20.3 ng/ml than among patients with serum A-FABP levels below the median value (57% vs. 27%, p < 0.01 and 64% vs. 48%, p = 0.02, respectively). Multivariate analysis revealed that the presence of three-vessel disease in comparison with single-vessel disease was independently associated with the higher A-FABP (per doubling) (odds ratio; 2.26, 95% confidential interval; 1.28-3.98, p < 0.01) and tended to be associated with the lower eGFR (p = 0.06).

Conclusion

Serum A-FABP may have a significant role in the interplay between renal dysfunction and coronary atherosclerosis.

A cross-sectional characterization of insulin resistance by phenotype and insulin clamp in East Asian Americans with type 1 and type 2 diabetes

OBJECTIVE

Classic features of type 1 and type 2 diabetes may not apply in Asian Americans, due to shared absence of common HLA DR-DQ genotype, low prevalence of positive anti-islet antibodies and low BMI in both types of diabetes. Our objective was to characterize diabetic phenotypes in Asian Americans by clamp and clinical features.

MATERIALS/METHODS

This was a cross-sectional study conducted in a referral center. Thirty East young Asian American adult volunteers (27.6±5.5 years) with type 1, type 2 diabetes or controls underwent hyperinsulinemic euglycemic clamp to assess insulin resistance and DEXA to assess adiposity.

RESULTS

Gender, BMI, waist/hip ratio, leptin, LDL, anti-GAD, anti-IA2 antibodies and C-reactive protein were similar among three groups. Serum C-peptide, adiponectin, free fatty acid, HDL concentrations and truncal fat by DEXA, were different between diabetic groups. Glucose disposal rate by clamp was lowest in type 2 diabetes, followed by type 1 diabetes and controls (5.43±2.70, 7.62±2.59, 8.61±2.37 mg/min/kg, respectively, p = 0.001). Free fatty acid concentration universally plummeted during steady state of the clamp procedure regardless of diabetes types in all three groups. Adipocyte fatty acid binding protein in the entire cohort (r = -0.625, p = 0.04) and controls (r = -0.869, p = 0.046) correlated best with insulin resistance, independent of BMI.

CONCLUSIONS

Type 2 diabetes in Asian Americans was associated with insulin resistance despite having low BMI as type 1 diabetes, suggesting a potential role for targeting insulin resistance apart from weight loss. Adipocyte fatty acid binding protein, strongly associated with insulin resistance, independent of adiposity in the young Asian American population, may potentially serve as a biomarker to identify at-risk individuals. Larger studies are needed to confirm this finding.

Serum A-FABP is increased and closely associated with elevated NT-proBNP levels in type 2 diabetic patients treated with rosiglitazone

Background

Adipocyte fatty acid-binding protein (A-FABP) has been shown to play important roles in the development of metabolic syndrome, diabetes, and cardiovascular diseases. In this study we investigated the possible role of A-FABP in the development of cardiac dysfunction related to rosiglitazone treatment.

Methodology/Principal Findings

A total of 84 patients with newly diagnosed type 2 diabetes were treated with rosiglitazone for 48 weeks. Circulating A-FABP and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were determined at baseline and repeated at 24 and 48 weeks. After the 48-week rosiglitazone treatment period, serum levels of both A-FABP and NT-proBNP increased progressively and significantly (P<0.01). Serum levels of A-FABP were demonstrated to be positively correlated with gender and waist circumference both at baseline and the end of the study, and with age, body mass index (BMI), total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and NT-proBNP at 48 weeks (all P<0.05). In addition, changes in A-FABP were significantly and positively correlated with changes in NT-proBNP (r = 0.239, P = 0.039). Furthermore, multiple stepwise regression analysis showed that the changes in A-FABP were independently and positively associated with changes in NT-proBNP after adjusting for confounding factors (β = 0.320, P = 0.007).

Conclusions/Significance

Rosiglitazone-mediated increase of A-FABP is closely associated with the elevation of NT-proBNP, a well-established marker of cardiac dysfunction. The findings of our study imply that A-FABP may mediate the cross-talk between heart and adipose tissue.

Expression and regulation of adipocyte fatty acid binding protein in granulosa cells and its relation with clinical characteristics of polycystic ovary syndrome

Increased expression of adipocyte fatty acid binding protein (FABP4) is associated with type 2 diabetic, high triglycerides, increased lipid peroxidation, and inflammation markers. To study the expression of FABP4 mRNA in granulosa cells of patients with polycystic ovary syndrome (PCOS) and the impact of testosterone, insulin, and PPARγ agonist rosiglitazone on granulosa cells (GCs), and to investigate the relationship of serum FABP4 levels with clinical characteristics in patients with PCOS. The expression of FABP4 mRNA in GCs of patients with PCOS and normal controls were assayed by RT-PCR. We assessed the level of FABP4 mRNA after treatment with testosterone, insulin, and rosiglitazone in GCs from normal controls. Serum FABP4 were assayed from 96 patients with PCOS (obese and nonobese 48 cases, respectively) and 80 healthy normal controls (obese and the nonobese 40 cases, respectively). The expression of FABP4 mRNA was higher in the GCs of PCOS than that of the controls (P<0.05). FABP4 mRNA expression was up-regulated by testosterone, insulin, and rosiglitazone at different dosages. Serum FABP4 levels were higher in the nonobese PCOS group than that of the nonobese controls (8.9±5.1 ng/ml vs. 4.8±0.7 ng/ml), and in the obese PCOS group than that of the obese controls (28.2±14.0 ng/ml vs. 15.6±6.6 ng/ml), respectively (P<0.05). Multiple linear regression analyses showed that serum FABP4 level was independently associated with HOMA-IR, BMI, and testosterone (P<0.05). Increased FABP4 was related to the clinical characteristics of PCOS.

Analysis of the regulation of fatty acid binding protein 7 expression in human renal carcinoma cell lines

Background

Improving the treatment of renal cell carcinoma (RCC) will depend on the development of better biomarkers for predicting disease progression and aiding the design of appropriate therapies. One such marker may be fatty acid binding protein 7 (FABP7), also known as B-FABP and BLBP, which is expressed normally in radial glial cells of the developing central nervous system and cells of the mammary gland. Melanomas, glioblastomas, and several types of carcinomas, including RCC, overexpress FABP7. The abundant expression of FABP7 in primary RCCs compared to certain RCC-derived cell lines may allow the definition of the molecular components of FABP7's regulatory system.

Results

We determined FABP7 mRNA levels in six RCC cell lines. Two were highly expressed, whereas the other and the embryonic kidney cell line (HEK293) were weakly expressed FABP7 transcripts. Western blot analysis of the cell lines detected strong FABP7 expression only in one RCC cell line. Promoter activity in the RCC cell lines was 3- to 21-fold higher than that of HEK293. Deletion analysis demonstrated that three FABP7 promoter regions contributed to upregulated expression in RCC cell lines, but not in the HEK293 cell. Competition analysis of gel shifts indicated that OCT1, OCT6, and nuclear factor I (NFI) bound to the FABP7 promoter region. Supershift experiments indicated that BRN2 (POU3F2) and NFI bound to the FABP7 promoter region as well. There was an inverse correlation between FABP7 promoter activity and BRN2 mRNA expression. The FABP7-positive cell line's NFI-DNA complex migrated faster than in other cell lines. Levels of NFIA mRNA were higher in the HEK293 cell line than in any of the six RCC cell lines. In contrast, NFIC mRNA expression was lower in the HEK293 cell line than in the six RCC cell lines.

Conclusions

Three putative FABP7 promoter regions drive reporter gene expression in RCC cell lines, but not in the HEK293 cell line. BRN2 and NFI may be key factors regulating the expression of FABP7 in certain RCC-derived cell lines.

Fatty acid binding proteins (FABPs) in prostate, bladder and kidney cancer cell lines and the use of IL-FABP as survival predictor in patients with renal cell carcinoma

Background

Fatty acid binding proteins (FABP) play an important role in carcinogenesis. Modified FABP expression patterns were described for prostate, bladder and for renal cell carcinoma. Studies on metabolic relationships and interactions in permanent cell lines allow a deeper insight into molecular processes. The aim of this study is therefore a systematic overview on mRNA and protein expressions of seven FABPs in frequently used urological cell lines.

Methods

Nine cell lines of renal carcinomas, seven of urinary bladder carcinomas, and five of prostate carcinomas were investigated. Quantitative RT-qPCR and western blotting were used to determine different FABPs. In addition, 46 paired cancerous and noncancerous tissue samples from nephrectomy specimen with renal cell carcinomas were investigated regarding the ileum FABP mRNA expression level and associated with survival outcome.

Results

General characteristics of all urological carcinoma cell lines were the expression of E-and IL-FABP on mRNA and protein level, while the expressions differed between the cell lines. The protein expression was not always congruent with the mRNA expression. Renal cell carcinoma cell lines showed expressions of L-, H- and B-FABP mRNA in addition to the general FABP expression in five out of the eight investigated cell lines. In bladder cancer cell lines, we additionally found the expression of A-FABP mRNA in six cell lines, while H-FABP was present only in three cell lines. In prostate cancer cell lines, a strong reduction of A- and E- FABP mRNA was observed. The expression of B-FABP mRNA and protein was observed only in the 22 RV-1 cells. IL-FABP mRNA was over-expressed in renal tumour tissue. The IL-FABP ratio was identified as an independent indicator of survival outcome.

Conclusions

Distinctly different FABP expression patterns were observed not only between the cell lines derived from the three cancer types, but also between the cell lines from the same cancer. The FABP patterns in the cell lines do not always reflect the real situation in the tumours. These facts have to be considered in functional studies concerning the different FABPs.

Association of increased plasma adipocyte fatty acid-binding protein with coronary artery disease in non-elderly men

Background

Adipocyte fatty acid-binding protein (A-FABP) has been reported to play critical roles in the development of atherosclerosis. We investigated whether an increased in plasma A-FABP level can be independently associated with the presence of coronary artery disease (CAD).

Methods

Two hundred eleven consecutive male patients (mean age: 66 years, range: 33-87 years) were enrolled from inpatients who underwent coronary angiography. Age-matched male subjects (n = 211) having no evidence of CAD served as controls. Plasma A-FABP levels were measured by enzyme-linked immunosorbent assays.

Results

Plasma A-FABP levels in CAD patients were significantly higher than in control subjects (median [IQR], 20.6 [15.7-27.8] ng/mL vs. 15.1 [11.7-19.9] ng/mL, p < 0.01). Multivariate logistic regression analysis revealed that an increased plasma A-FABP level was independently associated with the presence of CAD in all subjects (adjusted odds ratio: 1.76, 95% confidence interval: 1.14 to 2.70, p = 0.01). Furthermore, sub-analysis based on age showed that this association remained significant in subjects aged < 65 years (adjusted odds ratio: 3.06, 95% confidence interval: 1.34 to 6.98, p < 0.01), but not in subjects aged ≥65 years.

Conclusions

Increased plasma A-FABP in non-elderly men had a significant association with the presence of CAD, independent of established CAD risk factors.

Serum levels of adipocyte fatty acid-binding protein are associated with the severity of coronary artery disease in Chinese women

Background

Adipocyte fatty acid-binding protein (A-FABP) has been described as a novel adipokine, playing an important role in the development of metabolic syndrome, type 2 diabetes and atherosclerosis. In this study, we investigated the relationship between serum levels of A-FABP and the presence and severity of coronary artery disease (CAD) in Chinese subjects.

Methodology/Principal Findings

Circulating A-FABP level was determined by ELISA in 341 Chinese subjects (221 men, 120 women) who underwent coronary angiography. A-FABP levels in patients with CAD were significantly higher compared with non-CAD subjects (P = 0.029 in men; P = 0.031 in women). Serum A-FABP increased significantly in multi-vessel diseased patients than in non-CAD subjects (P = 0.011 in men, P = 0.004 in women), and showed an independent correlation with coronary atherosclerosis index (standardized β = 0.173, P = 0.025). In multiple logistic regression analysis, serum A-FABP was an independent risk factor for CAD in women (OR = 5.637, 95%CI: 1.299-24.457, P = 0.021). In addition, amino terminal pro-brain natriuretic peptide (NT-proBNP) was demonstrated to be positively and independently correlated with A-FABP (standardized β = 0.135, P = 0.027).

Conclusions/Significance

Serum A-FABP is closely associated with the presence and severity of CAD in Chinese women.

Fasting serum fatty acid-binding protein 4 level positively correlates with metabolic syndrome in hemodialysis patients

BACKGROUND AND AIMS

Serum fatty acid-binding protein 4 (FABP4) level increases in patients with metabolic syndrome (MetS). The interrelationships between fasting FABP4 levels and MetS have not been analyzed in hemodialysis (HD) patients.

METHODS

Fasting blood samples were obtained from 101 chronic HD patients. MetS was defined according to the diagnostic criteria of the International Diabetes Federation.

RESULTS

In total, 48 HD patients (47.5%) had MetS. Fasting FABP4 levels positively correlated with MetS (p = 0.022). Univariate linear regression analysis showed that the pre-HD body weight (p <0.001), waist circumference (p = 0.003), body mass index (p = 0.003), total cholesterol (TCH) (p <0.001), triglyceride (TG) (p <0.001), creatinine (p = 0.042), insulin level (p = 0.014), and homeostasis model assessment of insulin resistance (HOMA-IR; p = 0.015) were positively correlated with serum FABP4 levels, whereas high-density lipoprotein-cholesterol (HDL-C) (p = 0.049) and adiponectin level (p = 0.004) were negatively correlated with fasting serum FABP4 levels in HD patients.

CONCLUSIONS

MetS was positively correlated with fasting FABP4 levels in our chronic HD patients. TG, TCH, and waist circumference were independent predictors of serum FABP4 levels in HD patients.

The role of low-grade inflammation in the polycystic ovary syndrome

PCOS is not only the most frequent cause of oligomenorrhea in young women, but also a metabolic disorder characterized by insulin resistance, glucose intolerance, dyslipidemia, and obesity, especially the visceral phenotype. PCOS represents a broad spectrum of endocrine and metabolic alterations which change with age and with increasing adiposity. In fact, during adolescence and youth the predominant clinical manifestations of PCOS are menstrual abnormalities, hirsutism and acne, whereas in peri-menopausal and post-menopausal periods metabolic disorders and an increased risk for cardiovascular diseases prevail. The pathogenetic links between PCOS and metabolic or cardiovascular complications are still debated. However, recent evidence has been focused on a condition of low-grade chronic inflammation as a potential cause of the long-term consequence of the syndrome. In this review we describe the state of low-grade inflammation observed in PCOS. In addition, we hypothesize the potential mechanisms responsible for the generation of this inflammatory state and the role played by low-grade inflammation in linking hyperandrogenism and insulin resistance with the metabolic and cardiovascular long-term complications of the syndrome.

Different association of circulating levels of adipocyte and epidermal fatty acid-binding proteins with metabolic syndrome and coronary atherosclerosis in Chinese adults

AIMS

Adipocyte and epidermal fatty acid-binding protein (A-FABP, E-FABP) are cytoplasmic proteins which may play an important role in metabolic diseases. In the present study, we investigated the different association of A-FABP and E-FABP with metabolic syndrome (MetS) and coronary artery disease (CAD) in Chinese adults.

METHODS

A total of 459 subjects (233 MetS and 226 non-MetS) who had undergone coronary angiography were enrolled in the present study. Serum A-FABP and E-FABP levels, glucose, lipid profiles and other biochemical markers were measured.

RESULTS

Both serum A-FABP and E-FABP levels were significantly higher in the MetS group than in the non-MetS group (P = 0.040 and 0.045, respectively). Only serum A-FABP levels in the CAD group were significantly higher than in the non-CAD group (12.30 ± 5.45 vs.10.94 ± 4.94 ng/mL, P= 0.008), and significantly increased with the increasing of number of disease vessels (P=0.004). Serum A-FABP levels were also associated with risk of CAD (odds ratio 2.956 [1.295-6.748]; P = 0.010). Adjusting for age, sex, and other conventional risk factors for CAD did not appreciably change the results. No difference was found in serum E-FABP levels between CAD status. Serum E-FABP levels were correlated with fasting and post load 2h plasma glucose, HbA1c, serum total cholesterol and LDL-C concentrations while serum A-FABP levels were correlated with fasting and post load 2h serum insulin concentrations and HOMA-IR (different P<0.05).

CONCLUSIONS

Our data indicated while both serum A-FABP and E-FABP levels had associations with MetS, only A-FABP was significantly associated with increased risk of CAD in Chinese adults.

Olmesartan reduces arterial stiffness and serum adipocyte fatty acid-binding protein in hypertensive patients

Adipocyte fatty acid binding protein (A-FABP) has been reported to be involved in insulin resistance, lipid metabolism, and atherosclerosis; however, little is known about the effect of medication on the change in circulating A-FABP in human subjects. We evaluated the effects of angiotensin II type 1 receptor blocker (ARB) on arterial stiffness and its association with serum A-FABP in patients with hypertension. Thirty patients newly diagnosed with essential hypertension were treated with olmesartan (20 mg/day), an ARB, for 6 months. Serum levels of A-FABP and high-sensitivity C-reactive protein (hsCRP) were examined and the cardio-ankle vascular index (CAVI), which is a marker of arterial stiffness, was also determined. Serum A-FABP at baseline was significantly correlated with the body mass index (r = 0.45, P = 0.01), homeostasis model assessment as a marker of insulin resistance (r = 0.53, P < 0.01), and systolic blood pressure (r = 0.37, P = 0.047), and tended to be correlated with low-density lipoprotein cholesterol, triglyceride, and CAVI. Olmesartan treatment resulted in a significant decrease in CAVI, serum A-FABP levels, and hsCRP, besides a significant reduction of blood pressure. Multiple regression analysis revealed that the change in CAVI was independently correlated with the change in serum A-FABP. Olmesartan ameliorated arterial stiffness in patients with hypertension, which may be involved in the reduction of serum A-FABP.

Unsaturated fatty acids repress the expression of adipocyte fatty acid binding protein via the modulation of histone deacetylation in RAW 264.7 macrophages

BACKGROUND

Adipocyte fatty acid binding protein (A-FABP) present in macrophages has been implicated in the integration of lipid metabolism and inflammatory response, contributing to development of insulin resistance and atherosclerosis.

AIM OF THE STUDY

This study was conducted to test the hypothesis that the role of fatty acids in the inflammatory pathways is mediated through the modulation of A-FABP expression in macrophages.

METHODS

Murine RAW 264.7 macrophages were treated with inflammatory insults and fatty acids for quantitative real-time PCR and Western blot analysis. The cells were treated with trichostatin A (TSA), a histone deacetylase inhibitor, for elucidating mechanisms for the regulation of A-FABP expression by fatty acids. RNA interference (RNAi) to knock down A-FABP was utilized to assess its role in inflammatory gene expression.

RESULTS

When RAW 264.7 were incubated with lipopolysaccharides (LPS; 100 ng/ml) or 2.5 ng/ml of tumor necrosis factor α for 18 h, A-FABP mRNA and protein levels were drastically increased. Unsaturated fatty acids (100 μmol/l in complexed with BSA) such as palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and eicosapentaenoic acid, significantly repressed the basal as well as LPS-induced A-FABP expression, whereas palmitic acid did not elicit the same effect. TSA increased A-FABP mRNA levels and abolished the repressive effect of linoleic acid on A-FABP expression in unstimulated and LPS-stimulated macrophages. Depletion of A-FABP expression by 70-80% using RNAi markedly decreased cyclooxygenase 2 mRNA abundance and potentiated the repression by linoleic acid.

CONCLUSION

Unsaturated fatty acids inhibited the basal as well as LPS-induced A-FABP expression. The mechanism may involve histone deacetylation and anti-inflammatory effect of unsaturated fatty acids may be at least in part attributed to their repression of A-FABP expression in RAW 264.7 macrophages.

Common genetic variants in fatty acid-binding protein-4 (FABP4) and clinical diabetes risk in the Women's Health Initiative Observational Study

Adipocypte fatty acid-binding protein-4 (FABP4/adipocyte P2) may play a central role in energy metabolism and inflammation. In animal models, defects of the aP2 gene (aP2(-/-)) partially protected against the development of obesity-related insulin resistance, dyslipidemia, and atherosclerosis. However, it is unclear whether common genetic variation in FABP4 gene contributes to risk of type 2 diabetes (T2D) or diabetes-related metabolic traits in humans. We comprehensively assess the genetic associations of variants in the FABP4 gene with T2D risk and diabetes-associated biomarkers in a prospective study of 1,529 cases and 2,147 controls among postmenopausal women aged 50-79 years who enrolled in the Women's Health Initiative Observational Study (WHI-OS). We selected and genotyped a total of 11 haplotype-tagging single-nucleotide polymorphisms (tSNPs) spanning 41.3 kb across FABP4 in all samples. None of the SNPs and their derived haplotypes showed significant association with T2D risk. There were no significant associations between SNPs and plasma levels of inflammatory and endothelial biomarkers, including C-reactive protein, tumor necrosis factor (TNF), interleukin-6 (IL-6), E-selectin, and intercellular adhesion molecule (ICAM-1). Among African-American women, several SNPs were significantly associated with lower levels of vascular cell adhesion molecule-1 (VCAM-1), especially among those with incident T2D. On average, plasma levels of VCAM-1 were significantly lower among carriers of each minor allele at rs1486004(C/T; -1.08 ng/ml, P = 0.01), rs7017115(A/G; -1.07 ng/ml, P = 0.02), and rs2290201(C/T; -1.12 ng/ml, P = 0.002) as compared with the homozygotes of the common allele, respectively. After adjusting for multiple testing, carriers of the rs2290201 minor allele remained significantly associated with decreasing levels of plasma VCAM-1 in these women (P = 0.02). In conclusion, our finding from a multiethnic cohort of postmenopausal women did not support the notion that common genetic variants in the FABP4 gene may trigger increased risk of T2D. The observed significant association between reduced VCAM-1 levels and FABP4 genotypes in African-American women warrant further confirmation.

Atherosclerotic lesion progression changes lysophosphatidic acid homeostasis to favor its accumulation

Lysophosphatidic acid (LPA) accumulates in the central atheroma of human atherosclerotic plaques and is the primary platelet-activating lipid constituent of plaques. Here, we investigated the enzymatic regulation of LPA homeostasis in atherosclerotic lesions at various stages of disease progression. Atherosclerotic lesions were induced in carotid arteries of low-density lipoprotein receptor-deficient mice by semiconstrictive collar placement. At 2-week intervals after collar placement, lipids and RNA were extracted from the vessel segments carrying the plaque. Enzymatic-and liquid chromatography-mass spectrometry-based lipid profiling revealed progressive accumulation of LPA species in atherosclerotic tissue preceded by an increase in lysophosphatidylcholine, a precursor in LPA synthesis. Plaque expression of LPA-generating enzymes cytoplasmic phospholipase A(2)IVA (cPLA(2)IVA) and calcium-independent PLA(2)VIA (iPLA(2)VIA) was gradually increased, whereas that of the LPA-hydrolyzing enzyme LPA acyltransferase alpha was quenched. Increased expression of cPLA(2)IVA and iPLA(2)VIA in advanced lesions was confirmed by immunohistochemistry. Moreover, LPA receptors 1 and 2 were 50% decreased and sevenfold upregulated, respectively. Therefore, key proteins in LPA homeostasis are increasingly dysregulated in the plaque during atherogenesis, favoring intracellular LPA production. This might at least partly explain the observed progressive accumulation of this thrombogenic proinflammatory lipid in human and mouse plaques. Thus, intervention in the enzymatic LPA production may be an attractive measure to lower intraplaque LPA content, thereby reducing plaque progression and thrombogenicity.

Circulating adipocyte fatty acid binding protein levels in healthy preterm infants: Positive correlation with weight gain and total-cholesterol levels

BACKGROUND

Adipocyte fatty acid binding protein (a-FABP) has been suggested to play an important role in the pathogenesis of metabolic syndrome. Preterm infants are at risk for the later development of insulin resistance, and, possibly, other components of metabolic syndrome.

AIM

To determine circulating levels of a-FABP in preterm infants and examine possible associations of a-FABP with metabolic indices (serum lipids, glucose, and insulin levels, and homeostasis model assessment index of insulin resistance [HOMA-IR]), levels of leptin and adiponectin, anthropometric parameters and weight gain.

STUDY DESIGN

Prospective cohort study.

SUBJECTS

55 healthy preterm (mean [SD] gestational age 32.8 [1.8] weeks) and 23 fullterm infants (reference group).

OUTCOME MEASURES

Serum a-FABP, lipids, glucose, insulin, leptin and adiponectin levels at 31.9 [10.4] days of life.

RESULTS

Serum a-FABP levels did not differ significantly between preterm and fullterm infants. A-FABP levels correlated positively with total-cholesterol [total-C] in both preterm and fullterm infants (beta=0.33; p=0.01 and beta=0.33; p=0.04, respectively). In addition to total-C, weight gain correlated independently with a-FABP levels in preterm infants (beta=0.36, p=0.01).

CONCLUSIONS

An association between a-FABP levels and indices of insulin resistance was not present in infants studied. As the development of insulin resistance in children born prematurely is possibly associated with weight gain in early postnatal life, follow-up of our study population is necessary to demonstrate whether a-FABP levels, shown to correlate with weight gain in preterm infants, are a predictive marker for the later development of insulin resistance in these infants.

Metformin reduces lipid accumulation in macrophages by inhibiting FOXO1-mediated transcription of fatty acid-binding protein 4

OBJECTIVE

The accumulation of lipids in macrophages contributes to the development of atherosclerosis. Strategies to reduce lipid accumulation in macrophages may have therapeutic potential for preventing and treating atherosclerosis and cardiovascular complications. The antidiabetic drug metformin has been reported to reduce lipid accumulation in adipocytes. In this study, we examined the effects of metformin on lipid accumulation in macrophages and investigated the mechanisms involved.

METHODS AND RESULTS

We observed that metformin significantly reduced palmitic acid (PA)-induced intracellular lipid accumulation in macrophages. Metformin promoted the expression of carnitine palmitoyltransferase I (CPT-1), while reduced the expression of fatty acid-binding protein 4 (FABP4) which was involved in PA-induced lipid accumulation. Quantitative real-time PCR showed that metformin regulates FABP4 expression at the transcriptional level. We identified forkhead transcription factor FOXO1 as a positive regulator of FABP4 expression. Inhibiting FOXO1 expression with FOXO1 siRNA significantly reduced basal and PA-induced FABP4 expression. Overexpression of wild-type FOXO1 and constitutively active FOXO1 significantly increased FABP4 expression, whereas dominant negative FOXO1 dramatically decreased FABP4 expression. Metformin reduced FABP4 expression by promoting FOXO1 nuclear exclusion and subsequently inhibiting its activity.

CONCLUSIONS

Taken together, these results suggest that metformin reduces lipid accumulation in macrophages by repressing FOXO1-mediated FABP4 transcription. Thus, metformin may have a protective effect against lipid accumulation in macrophages and may serve as a therapeutic agent for preventing and treating atherosclerosis in metabolic syndrome.

Fasting serum level of fatty-acid-binding protein 4 positively correlates with metabolic syndrome in patients with coronary artery disease

BACKGROUND

The serum level of fatty-acid-binding protein 4 (FABP4) increases in patients with metabolic syndrome (MetS), so the relationship between FABP4 and MetS among patients with coronary artery disease (CAD) was investigated in the present study.

METHODS AND RESULTS

Fasting blood samples were obtained from 98 CAD patients. MetS and its components were defined using the diagnostic criteria of the International Diabetes Federation; 50 CAD patients (51.0%) had MetS. The fasting level of FABP4 positively correlated with MetS (P=0.037) and serum levels of FABP4 correlated with a number of MetS criteria (P=0.035). Univariate linear regression analysis showed that body fat mass (R=0.234; P=0.020) and the levels of triglycerides (R=0.348; P<0.001), and low-density lipoprotein-cholesterol (R=0.217; P=0.032) positively correlated with the serum level of FABP4, whereas the level of high-density lipoprotein-cholesterol (R=-0.243; P=0.016) negatively correlated with it. Multivariate forward stepwise linear regression analysis of the significant variables showed that the level of triglycerides (beta=0.348, R(2)=0.121, P<0.001) was the independent predictor of fasting serum level of FABP4.

CONCLUSIONS

Among CAD patients in the present study, the fasting level of FABP4 positively correlated with MetS and serum levels of FABP4 correlated with a number of MetS criteria.

FABP4: a novel candidate gene for polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complex multifactorial disorder involving a number of genetic and environmental factors. Adipocyte-fatty acid-binding protein (FABP4) is an adipokine regulating systemic insulin sensitivity, lipid and glucose metabolism. In humans serum FABP4 levels correlate significantly with features of PCOS. Previous researches showed strong evidences that FABP4 impacted the developing of PCOS possibly through its protein alteration or transcription regulation. Thus, the present study is the first attempt to identify the possible genetic role of FABP4 gene in the development of PCOS.

METHODS

About 1000 bp of the promoter region and four exons of FABP4 gene of 178 PCOS patients and 171 healthy controls were directly sequenced.

RESULTS

Three polymorphisms, rs16909225, rs3834363, and rs16909220, were identified, of which rs16909225 and rs16909220 were completely linked (r² = 1) and not associated with the development of PCOS, while the -2-bp/-2-bp genotype of rs3834363 was significantly higher in PCOS than in the controls (χ² = 7.39, df = 1, P = 0.007, OR = 1.80 95% CI: 1.18-2.75).

CONCLUSION

The present study is the first to establish an association between FABP4 gene polymorphisms and the development of PCOS.

Proteomic profiling of the prechylomicron transport vesicle involved in the assembly and secretion of apoB-48-containing chylomicrons in the intestinal enterocytes

Intracellular assembly of chylomicrons (CM) occurs in intestinal enterocytes through a series of complex vesicular interactions. CM are transported from the ER to the Golgi using a specialized vesicular compartment called the prechylomicron transport vesicle (PCTV). In this study, PCTVs were isolated from the enteric ER of the Syrian Golden hamster, and characterized using 2-DE and MS. Proteomic profiles of PCTV-associated proteins were developed with the intention of identifying proteins involved in the formation, transport, lipidation, and assembly of CM particles. Positively identified proteins included those involved in lipoprotein assembly, namely microsomal triglyceride transfer protein and apolipoprotein B-48, as well as proteins involved in vesicular transport, such as Sar1 and vesicle-associated membrane protein 7. Other groups of proteins found were chaperones, intracellular vesicular trafficking proteins, fatty acid-binding proteins, and lipid-related proteins. These findings have increased our understanding of the transport vesicle involved in the intracellular assembly and transport of CM and can provide insight into potential cellular factors responsible for dysregulation of intestinal CM production.

ADRP/ADFP and Mal1 expression are increased in macrophages treated with TLR agonists

Activation of macrophages by TLR agonists enhances foam cell formation, but the underlying mechanisms are not understood. We examined the effects of TLR agonists on ADRP/ADFP, a protein associated with forming lipid droplets, and Mal1 a fatty acid-binding protein, in two mouse macrophage cell lines and human monocytes. Low doses of LPS, a TLR4 agonist increased both mRNA and protein levels of ADRP/ADFP and Mal1 in RAW 264.7 macrophages. Following pretreatment with Intralipid, fatty acids, or acetyl-LDL to increase triglyceride or cholesterol ester storage, LPS treatment still increased ADRP/ADFP and Mal1 mRNA levels. LPS also induced ADRP/ADFP and Mal1 in J774 macrophages and ADRP/ADFP in human monocytes. Zymosan, a fungal product that activates TLR2, poly-I:C, a viral mimetic that activates TLR3, and imiquimod, a TLR7 agonist, also increased ADRP/ADFP. Zymosan, but not poly-I:C or imiquimod, induced Mal1. In contrast, neither gene was induced by TNFalpha, IL-1beta, IL-6, or interferon-gamma. Thus TLR agonists induce ADRP/ADFP and Mal1, which likely contributes to macrophage triglyceride and cholesterol ester storage leading to foam cell formation.

Association of Free Fatty Acid (FFA), Fatty Acid Binding Protein (FABP) and Adiponectin with Tumor Necrosis Factor-alpha (TNF-alpha) and Interleukin-6 (IL-6) Among Obese Non Diabetic Males

BACKGROUND: The prevalence of obesity has increased dramatically in recent years. It is commonly associated with type 2 diabetes, coronary artery disease, and hypertension. White adipose tissue (WAT) is a major site of energy storage and is important for energy homeostasis. WAT has been increasingly recognized as an important endocrine organ that secretes a number of biologically active “adipokines”. The resultant higher FFA, FABP4, FABP5 concentration; and lower concentration of adiponectin is known to be correlated with inflammation. The aim of this study was to observe the correlation between FFA, FABP4, FABP5 and adiponectin with TNF-α and Interleukin-6 as markers of inflammation.METHOD: The study was observational with a cross sectional design. The analysis was done on 69 male subjects aged 30-60 years with non diabetic abdominal obesity which is characterized by waist circumference (WC) 98.7±6.5 cm and fasting blood glucose 87.1±9.7 mg/dL. FFA testing was performed by enzymatic colorimetric assay; whereas FABP4, FABP5, TNF-α, adiponectin and IL-6 were performed by ELISA. All statistical calculations were performed with the SPSS 11.5 statistical software package. We used the Pearson or Spearman’s rho correlation coefficient to assess the correlation between various anthropometric and biochemical measures. We also used path analysis Lisrel 8.30 for Windows.RESULT: This study revealed that there was no correlation between FFA, FABP4 and adiponectin with TNF-α and Interleukin-6, whereas there was correlation between FABP5 with TNF- and Interleukin-6. This study also showed there were correlations between WC and hsCRP (r=0.314, p=0.000), WC and IL-6 (r=0.276, p=0.022), FFA and FABP4 (r=0.263, p=0.029), FABP4 and WC (r=0.249, p =0.039), FABP4 and BMI (r=0.311, p=0.009), FABP5 and TNF- (r=0.408, p=0.000), FABP5 and FABP4 (r=0.296, p=0.014), FABP5 and Interleukin-6 (r=0.248, p=0.04), Adiponectin and HDL-Cholesterol (r=0.301, p=0.012).CONCLUSION: Abdominal obesity might contribute to inflammation in obese nondiabetic males. This study indicated that in abdominal obesity, FFA may induce inflammation through FABP4 and FABP5. Advancing our understanding of the function and measurement of FABP4 and FABP5 serum concentration will give insight into the clinical diagnosis of obesity-related metabolic disorders.KEYWORDS: Obesity, Waist Circumference, Free Fatty Acid (FFA), Fatty Acid Binding Protein (FABP), Adiponectin, TNF-α, Interleukin-6, Inflammation

Association between adipocyte fatty acid-binding protein levels and childhood obesity in Korean children

Adipocyte fatty acid-binding protein (A-FABP) is a newly recognized adipokine that plays a role in the development of obesity and insulin resistance in adults. We investigated the association between A-FABP levels and obesity and insulin resistance in school-aged children. One hundred sixty-one 9-year-old Korean children (80 boys and 81 girls) voluntarily participated in this study at school-based health examinations. Weight, height, waist circumference, and blood pressure were measured. Fasting plasma glucose, triglycerides, high-density lipoprotein cholesterol, insulin, and A-FABP levels were measured; and insulin resistance was estimated by the homeostasis model assessment. Subjects with higher body mass index (BMI) percentiles had correspondingly higher concentrations of A-FABP in both boys and girls. Subjects within the highest quartile of A-FABP levels had correspondingly poor metabolic risk profiles (BMI, waist circumference, triglycerides, high-density lipoprotein cholesterol, fasting insulin, and homeostasis model assessment of insulin resistance) compared with those in the lowest A-FABP quartile (P < .01). Serum A-FABP concentrations were significantly correlated with BMI (r = 0.58, P < .01) and waist circumference (r = 0.51, P < .01). However, the significant correlation between serum A-FABP and insulin resistance faded after adjustment for BMI. Adipocyte fatty acid-binding protein was closely associated with obesity or abdominal obesity in children; however, the independent relationship between A-FABP and insulin resistance in children is still unclear and remains to be determined.

Association between the FABP2 Ala54Thr, PPARα Leu162/Val, and PPARα intron7 polymorphisms and blood lipids ApoB and ApoCIII in hypertriglyceridemic subjects in Tehran

BACKGROUND

The alanine to threonine substitution at codon 54 in the FABP2 gene and PPARα Val162 allele have been associated with hypertriglyceridemia.

OBJECTIVE

We sought to determine the prevalence of the Ala54Thr polymorphism of fatty acid binding protein (FABP) 2 gene and the Leu162/Val in exon 5 and G/C in intron7 polymorphism of peroxisome proliferator-activated receptor alpha (PPARα) gene in hypertriglyceridemic patients and their associations with blood lipid concentrations.

METHODS

A total of 170 hypertriglyceridemic subjects were enrolled and genotyped for Ala54Thr, Leu162Val, and intron 7 polymorphism by the use of a polymerase chain reaction-restriction fragment length polymorphism method. Fasting blood triglyceride, total cholesterol (TC), low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apolipoprotein (Apo)B, and ApoCIII also were determined.

RESULTS

We found frequency of 81.2% for the Thr54 polymorphism among hypertriglyceridemic subjects. Positive associations were observed between this polymorphism and greater blood triglyceride, very low-density lipoprotein, and ApoCIII levels and lower blood high-density lipoprotein cholesterol concentration both in men and women. However, no association was found between the Thr54 polymorphism and TC, low-density lipoprotein cholesterol, ApoB, and body mass index. Frequency of the Leu162Val polymorphism was 21.8%. The Leu162Val polymorphism was not associated with lipid and lipoprotein concentrations in hypertriglyceridemic subjects (both in men and women). The frequency of intron7 polymorphism was 55.3% in subjects studied and, except for body mass index and TC, no association was found between the intron7 allele and blood lipids ApoB, and ApoCIII.

CONCLUSION

Frequency of the Thr54 polymorphism is high in hypertriglyceridemic subjects, and the presence of this allele may increase some blood lipid and lipoprotein concentrations. In addition, the frequency of intron7 polymorphism may be greater than Leu162Val in hypertriglyceridemic patients.

Effect of exercise training on A-FABP, lipocalin-2 and RBP4 levels in obese women

OBJECTIVE

Lipocalin family proteins, including adipocyte fatty acid-binding protein (A-FABP), lipocalin-2 and retinol-binding protein 4 (RBP4), have recently been identified as novel adipokines associated with obesity, type 2 diabetes and the metabolic syndrome. We have evaluated the effect of exercise training on lipocalin family proteins and inflammatory markers.

STUDY SUBJECTS

Thirty obese Korean women and 15 age-matched nonobese control subjects were studied.

DESIGN

Concentrations of the lipocalin family proteins were compared between obese and nonobese women and were evaluated before and 3 months after an exercise programme consisting of aerobic exercise (45 min/session, 300 kcal/day) and muscle strength training (20 min/session, 100 kcal/day) five times a week.

RESULTS

Obese women exhibited higher A-FABP levels compared to nonobese women (21.4 +/- 6.4 microg/l vs. 13.6 +/- 4.4 microg/l, P < 0.001). However, neither lipocalin-2 nor RBP4 levels were significantly different between the two groups, although the difference in lipocalin-2 was marginally significant (P = 0.054). Circulating A-FABP levels were significantly associated with body mass index (BMI), waist circumference, triglyceride, alanine aminotransferase (ALT), lipocalin-2 and high-sensitivity C-reactive protein (hsCRP) levels. After 3 months of the exercise training programme, serum A-FABP levels decreased significantly from 21.4 +/- 6.4 microg/l to 19.3 +/- 6.8 microg/l (P = 0.038), along with a reduction in weight, BMI, waist circumference, fasting glucose and total cholesterol levels. There was no significant change in the lipocalin-2 and RBP4 levels, although IL-6 levels increased after the exercise programme.

CONCLUSION

Exercise training with weight loss induced a significant reduction in circulating A-FABP levels in obese Korean women.

Fatty acid binding proteins in adipose tissue: a promising link between metabolic syndrome and atherosclerosis?

Adipocyte/macrophage fatty acid binding protein (A-FABP) has been shown to be closely associated with metabolic syndrome, obesity and development of atherosclerosis. Moreover, A-FABP has been recently suggested as a potential therapeutic target of these abnormalities in animal models. The present review aims to summarize current knowledge on A-FABP functions and regulations both in animal models and humans, since the role of A-FABP in human physiology and disease has not been presently clarified.

The increase of fatty acid-binding protein aP2 in overweight and obese children: interactions with dietary fat and impact on measures of subclinical inflammation

BACKGROUND

In adults, circulating aP2 may link obesity, inflammation and the metabolic syndrome, but there are few data in children. Experimental models support that dietary factors, particularly dietary fat, may be major determinants of phenotype.

OBJECTIVE

The aim of this study was to investigate, in normal, overweight and obese children, the relationships among aP2, the metabolic syndrome, inflammation and diet.

DESIGN

This was a cross-sectional study conducted in Northern Switzerland.

SUBJECTS

Subjects for this study were 6- to 14-year-old, prepubertal and early pubertal, normal weight, overweight and obese children (n=124).

MAIN OUTCOME MEASURES

Body mass index (BMI), body fat percent, waist-to-hip ratio, blood pressure, circulating aP2, fasting insulin, C-reactive protein (CRP), plasma lipids and dietary intakes of macro- and micronutrients were determined.

RESULTS

Circulating aP2 markedly increased with increasing central and total adiposity, and predicted measures of insulin resistance. Independent of BMI standard deviation scores and puberty, aP2 correlated with intake of the antioxidant vitamins A, C and E as well as circulating concentrations of CRP, leptin and low-density lipoprotein cholesterol. Children with lower aP2 concentrations consuming high-fat diets did not show an increase in fasting insulin or CRP, whereas those with higher aP2 concentrations showed marked increases in these measures with high intakes of fat or saturated fat.

CONCLUSIONS

Increased central and overall adiposity in children are associated with higher circulating aP2 concentrations. In children with high dietary intakes of total fat and saturated fat, but not those with low intakes, higher aP2 concentrations are associated with measures of insulin resistance and inflammation.

Epidermal fatty-acid-binding protein: a new circulating biomarker associated with cardio-metabolic risk factors and carotid atherosclerosis

AIMS

Epidermal fatty-acid-binding protein (E-FABP) is highly homologous to adipocyte FABP (A-FABP), which mediates obesity-related metabolic syndrome (MetS), diabetes and atherosclerosis in animals. Combined deficiency of E-FABP and A-FABP protects against the MetS and atherosclerosis in mice. This study investigated the association of serum E-FABP with cardio-metabolic risk factors and carotid atherosclerosis in humans.

METHODS AND RESULTS

The presence of E-FABP in human plasma was detected by tandem mass spectrometry. Serum E-FABP levels, determined by an enzyme-linked immunosorbent assay in 479 Chinese subjects (age: 55.4 ± 13.5 years; M/F: 232/247), correlated positively (P < 0.05 to <0.001, age-adjusted) with parameters of adiposity, adverse lipid profiles, serum insulin, A-FABP, and C-reactive protein levels and were higher in subjects with the MetS (P < 0.001 vs. no MetS). The association of E-FABP with the MetS was independent of A-FABP. Furthermore, serum E-FABP correlated with carotid intima-media thickness (IMT; P < 0.001) and was independently associated with carotid IMT in men (adjusted P = 0.03).

CONCLUSION

E-FABP is a new circulating biomarker associated with increased cardio-metabolic risk. It may contribute to the development of the MetS and carotid atherosclerosis in humans, independent of the effect of A-FABP.

Association between fatty acid binding protein 3 gene variants and essential hypertension in humans

BACKGROUND

We have earlier identified a quantitative trait locus (QTL) on rat chromosome 5 that appears to be primarily under the control of the sympathetic nervous system. Because sympathetic overactivity is related to both hypertension and insulin resistance, FABP3 is a candidate gene for the link between this QTL and blood pressure regulation. In this study, therefore, we explored the role of FABP3 genetic variations in essential hypertension (EH) in humans.

METHODS

We evaluated two single-nucleotide polymorphisms (SNPs) (rs2279885 and rs2271072) in 758 patients with EH and 726 controls. Polymorphism-related genotypes were determined using TaqMan assays, while haplotypes were estimated from the genotype data.

RESULTS

The frequencies of occurrence of the G allele of rs2279885 and the C allele of rs2271072 were significantly higher in subjects with EH than in normotensive (NT) subjects (P = 0.0339, P = 0.0209, respectively). However, the genotype distributions did not exhibit any significant differences.

CONCLUSION

We found an association between FABP3 gene polymorphisms and EH in a Japanese population, thereby suggesting that FABP3 is a susceptibility locus for EH.

Plasma fatty acid binding protein 4 is associated with atherogenic dyslipidemia in diabetes

The aim of this study was to evaluate the impact of adipocyte fatty acid binding protein 4 (FABP4) on the lipid profile in type 2 diabetic subjects. Plasma levels of FABP4 and adiponectin and an extensive lipid profile were analyzed in 169 type 2 diabetic subjects and 105 controls. Type 2 diabetic subjects were categorized according the presence of atherogenic dyslipidemia. Univariate statistical analyses, partial correlation tests, and binary logistic regression models were applied. In type 2 diabetic subjects, FABP4 was positively correlated with plasma triglycerides (P = 0.007), apolipoprotein C-III (apoC-III) (P = 0.009), and all the components of triglyceride-rich lipoproteins, including VLDL triglycerides (P = 0.002), VLDL-cholesterol (P = 0.001), and VLDL apoB (P = 0.001). FABP4 was inversely correlated with apoA-I (P = 0.038), HDL-cholesterol (P = 0.002), and HDL apoA-I (P = 0.010) in type 2 diabetic subjects. These correlations are not significantly affected by age, gender, body mass index, adiponectin, insulin, or any pharmacological treatment. The associations are even stronger when the FABP4/adiponectin ratio is considered. None of these associations were observed in controls. High FABP4 and low adiponectin levels are independent predictors of atherogenic dyslipidemia. In conclusion, FABP4 plasma concentrations hold strong potential for development as a clinical biomarker for atherogenic dyslipidemia, independent of obesity and insulin resistance, in type 2 diabetic subjects.

Inflammatory biomarkers associated with obesity and insulin resistance: a focus on lipocalin-2 and adipocyte fatty acid-binding protein

Obesity is an important risk factor for a cluster of metabolic and cardiovascular diseases, including insulin resistance, Type 2 diabetes, nonalcoholic fatty liver disease and atherosclerosis. Systemic low-grade inflammation, characterized by elevated circulating concentrations of proinflammatory factors, has recently been proposed to be a key mediator that links obesity with its medical complications. Adipose tissue is now recognized as the major contributor to systemic inflammation associated with obesity. As obesity develops, adipose tissue is infiltrated with activated macrophages. The 'inflamed' adipose tissue secretes a large number of proinflammatory adipokines and/or cytokines, which can act either in an autocrine manner to perpetuate local inflammation or in an endocrine manner to induce insulin resistance and endothelial dysfunction. In this review, we summarize recent advances in several newly identified adipose tissue-derived inflammatory factors, with the focus on lipocalin-2 and adipocyte fatty acid-binding protein (A-FABP). Both lipocalin-2 and A-FABP possess lipid-binding properties and are important integrators of metabolic and inflammatory pathways. A growing body of evidence from experimental, epidemiological and genetic studies suggests that both lipocalin-2 and A-FABP represent a novel class of serum biomarkers for risk prediction and therapeutic intervention of obesity-related medical complications.

Adipocyte fatty acid-binding protein in obese children before and after weight loss

Adipocyte fatty acid-binding protein (A-FABP) has been reported to be increased in obese adults and to be related to metabolic syndrome. Because studies concerning A-FABP in weight loss are limited and studies in obese children are missing, we analyzed A-FABP in obese children before and after weight loss. Fasting serum A-FABP, leptin, insulin, glucose, triglycerides, low-and high-density lipoprotein cholesterol, high-sensitivity C-reactive protein, and tumor necrosis factor alpha concentrations as markers of the metabolic syndrome, and weight status (body mass index and percentage body fat based on skinfold measurements) were determined in 30 obese children (median age, 11.9 years) before and after participating in a 1-year obesity intervention. Furthermore, A-FABP levels were measured in 10 nonobese children of similar age, sex, and pubertal stage. Obese children had significantly (P < .001) higher A-FABP concentrations compared with nonobese children. In backward multivariate linear regression analysis, A-FABP correlated significantly (P < .05) with percentage body fat and leptin, but not with any of the markers of the metabolic syndrome. Changes of A-FABP concentrations correlated significantly with changes of percentage body fat (r = 0.53, P = .001) and leptin (r = 0.55, P < .001), but not with any changes of parameters of the metabolic syndrome. Substantial weight loss in 10 children led to a significant (P < .05) decrease in A-FABP levels in contrast to the 20 children without change of weight status. In cross-sectional as well as longitudinal analyses, A-FABP levels were related to weight status and leptin levels. Further longitudinal studies are necessary to study the relationship between A-FABP concentrations and parameters of the metabolic syndrome.