Diet-induced obesity and hepatic steatosis in L-Fabp / mice is abrogated with SF, but not PUFA, feeding and attenuated after cholesterol supplementation

The proximal intestinal Fatty Acid-Binding Proteins liver FABP (LFABP) and intestinal FABP (IFABP) differentially modulate whole body energy homeostasis but are not centrally involved in net dietary lipid absorption: Studies of the LFABP/IFABP double knockout mouse

Proximal intestinal enterocytes expresses both intestinal-fatty acid binding protein (IFABP; FABP2) and liver-FABP (LFABP; FABP1). These FABPs are thought to be important in the net uptake of dietary lipid from the intestinal lumen, however their specific and potentially unique functions in the enterocyte remain incompletely understood. We previously showed markedly divergent phenotypes in LFABP^-/- vs. IFABP^-/- mice fed high-fat diets, with the former becoming obese and the latter remaining lean relative to wild-type (WT) mice, supporting different functional roles for each protein. Interestingly, neither mouse model displayed increased fecal lipid concentration, raising the question of whether the presence of one FABP was sufficient to compensate for absence of the other. Here, we generated an LFABP and IFABP double knockout mouse (DKO) to determine whether simultaneous ablation would lead to fat malabsorption, and to further interrogate the individual vs. overlapping functions of these proteins. Male WT, IFABP^-/-, LFABP^-/-, and DKO mice were fed a low-fat (10 % kcal) or high-fat (45 % kcal) diet for 12 weeks. The body weights and fat mass of the DKO mice integrated those of the LFABP^-/- and IFABP^-/- single knockouts, supporting the notion that IFABP and LFABP have distinct functions in intestinal lipid assimilation that result in downstream alterations in systemic energy metabolism. Remarkably, no differences in fecal fat concentrations were found in the DKO compared to WT, revealing that the FABPs are not required for net intestinal uptake of dietary lipid.

Intestinal peroxisome proliferator-activated receptor α-fatty acid-binding protein 1 axis modulates nonalcoholic steatohepatitis

BACKGROUND AND AIMS

Peroxisome proliferator-activated receptor α (PPARα) regulates fatty acid transport and catabolism in liver. However, the role of intestinal PPARα in lipid homeostasis is largely unknown. Here, intestinal PPARα was examined for its modulation of obesity and NASH.

APPROACH AND RESULTS

Intestinal PPARα was activated and fatty acid-binding protein 1 (FABP1) up-regulated in humans with obesity and high-fat diet (HFD)-fed mice as revealed by using human intestine specimens or HFD/high-fat, high-cholesterol, and high-fructose diet (HFCFD)-fed C57BL/6N mice and PPARA -humanized, peroxisome proliferator response element-luciferase mice. Intestine-specific Ppara or Fabp1 disruption in mice fed a HFD or HFCFD decreased obesity-associated metabolic disorders and NASH. Molecular analyses by luciferase reporter assays and chromatin immunoprecipitation assays in combination with fatty acid uptake assays in primary intestinal organoids revealed that intestinal PPARα induced the expression of FABP1 that in turn mediated the effects of intestinal PPARα in modulating fatty acid uptake. The PPARα antagonist GW6471 improved obesity and NASH, dependent on intestinal PPARα or FABP1. Double-knockout ( Ppara/Fabp1ΔIE ) mice demonstrated that intestinal Ppara disruption failed to further decrease obesity and NASH in the absence of intestinal FABP1. Translationally, GW6471 reduced human PPARA-driven intestinal fatty acid uptake and improved obesity-related metabolic dysfunctions in PPARA -humanized, but not Ppara -null, mice.

CONCLUSIONS

Intestinal PPARα signaling promotes NASH progression through regulating dietary fatty acid uptake through modulation of FABP1, which provides a compelling therapeutic target for NASH treatment.

Defects in the expression of colonic host defense factors associate with barrier dysfunction induced by a high-fat/high-cholesterol diet

The effect of Western diets in the gastrointestinal system is largely mediated by their ability to promote alterations in the immunity and physiology of the intestinal epithelium, and to affect the composition of the commensal microbiota. To investigate the response of the colonic epithelium to high-fat/high-cholesterol diets (HFHCDs), we evaluated the synthesis of host defense factors involved in the maintenance of the colonic homeostasis. C57BL/6 mice were fed an HFHCD for 3 weeks and their colons were evaluated for histopathology, gene expression, and microbiota composition. In addition, intestinal permeability and susceptibility to Citrobacter rodentium were also studied. HFHCD caused colonic hyperplasia, loss of goblet cells, thinning of the mucus layer, moderate changes in the composition of the intestinal microbiota, and an increase in intestinal permeability. Gene expression analyses revealed significant drops in the transcript levels of Muc1, Muc2, Agr2, Atoh1, Spdef, Ang4, Camp, Tff3, Dmbt1, Fcgbp, Saa3, and Retnlb. The goblet cell granules of HFHCD-fed mice were devoid of Relmβ and Tff3, indicating defective production of those two factors critical for intestinal epithelial defense and homeostasis. In correspondence with these defects, colonic bacteria were in close contact with, and invading the epithelium. Fecal shedding of C. rodentium showed an increased bacterial burden in HFHCD-fed animals accompanied by increased epithelial damage. Collectively, our results show that HFHCD perturbs the synthesis of colonic host defense factors, which associate with alterations in the commensal microbiota, the integrity of the intestinal barrier, and the host's susceptibility to enteric infections.

Exendin-4 alleviates steatosis in an in vitro cell model by lowering FABP1 and FOXA1 expression via the Wnt/-catenin signaling pathway

Non-alcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide. Agonists of the glucagon-like peptide-1 receptor (GLP-1R), currently approved to treat type 2 diabetes, hold promise to improve steatosis and even steatohepatitis. However, due to their pleiotropic effects, the mechanisms underlying their protective effect on NAFLD remain elusive. We aimed to investigate these mechanisms using an in vitro model of steatosis treated with the GLP-1R agonist Exendin-4 (Ex-4). We established steatotic HepG2 cells by incubating the cells with 400 µM oleic acid (OA) overnight. Further treatment with 200 nM Ex-4 for 3 h significantly reduced the OA-induced lipid accumulation (p < 0.05). Concomitantly, Ex-4 substantially reduced the expression levels of Fatty Acid-Binding Protein 1 (FABP1) and its primary activator, Forkhead box protein A1 (FOXA1). Interestingly, the silencing of β-catenin with siRNA abolished the effect of Ex-4 on these genes, suggesting dependency on the Wnt/β-catenin pathway. Additionally, after β-catenin silencing, OA treatment significantly increased the expression of nuclear transcription factors SREBP-1 and TCF4, whereas Ex-4 significantly decreased this upregulation. Our findings suggest that direct activation of GLP-1R by Ex-4 reduces OA-induced steatosis in HepG2 cells by reducing fatty acid uptake and transport via FABP1 downregulation.

Modulation of PPAR signaling disrupts pancreas development in the zebrafish, Danio rerio

Peroxisome Proliferator Activated Receptors (PPARs) are transcription factors that regulate processes such as lipid and glucose metabolism. Synthetic PPAR ligands, designed as therapeutics for metabolic disease, provide a tool to assess the relationship between PPAR activity and pancreas development in vivo, an area that remains poorly characterized. Here, we aim to assess the effects of PPAR agonists and antagonists on gene expression, embryonic morphology and pancreas development in transgenic zebrafish embryos. To evaluate developmental perturbations, we assessed gross body and pancreas morphology at 4 days post fertilization (dpf) in response to developmental exposures with PPARα, PPARγ, and PPARβ/δ agonists and antagonists at 0, 0.01, 0.1, 1, and 10 μM concentrations. All ligand exposures, with the exception of the PPARα agonist, resulted in significantly altered fish length and yolk sac area. PPARγ agonist and antagonist had higher incidence of darkened yolk sac and craniofacial deformities, whereas PPARα antagonist had higher incidence of pericardial edema and death. Significantly reduced endocrine pancreas area was observed in both PPARγ ligands and PPARα agonist exposed embryos, some of which also exhibited aberrant endocrine pancreas morphology. Both PPARβ/δ ligands caused reduced exocrine pancreas length and novel aberrant phenotype, and disrupted gene expression of pancreatic targets pdx1, gcga, and try. Lipid staining was performed at 8 dpf and revealed altered lipid accumulation consistent with isoform function. These data indicate chronic exposure to synthetic ligands may induce morphological and pancreatic defects in zebrafish embryos.

α-Lipoic Acid Alleviates Hepatic Lipid Deposition by Inhibiting FASN Expression via miR-3548 in Rats

Excessive liver lipid deposition is a vital risk factor for the development of many diseases. Here, we fed Sprague-Dawley rats with a control or α-lipoic acid-supplemented diet (0.2%) for 5 weeks to elucidate the effects of α-lipoic acid on preventive ability, hepatic lipid metabolism-related gene expression, and the involved regulatory mechanisms. In the current study, α-lipoic acid supplementation lowered plasma triglyceride level and hepatic triglyceride content. Reduced hepatic lipid deposition was closely associated with inhibiting fatty acid-binding protein 1 and fatty acid synthase expression, as well as increasing phosphorylated hormone-sensitive lipase expression at the protein level in α-lipoic acid-exposed rats. Hepatic miRNA sequencing revealed increased expression of miR-3548 targeting the 3'untranslated region of Fasn mRNA, and the direct regulatory link between miRNA-3548 and FASN was verified by dual-luciferase reporter assay. Taken together, α-lipoic acid lowered hepatic lipid accumulation, which involved changes in miRNA-mediated lipogenic genes.

Liver injury after small bowel resection is prevented in obesity-resistant 129S1/SvImJ mice

Intestinal failure-associated liver disease is a major morbidity associated with short bowel syndrome. We sought to determine if the obesity-resistant mouse strain (129S1/SvImJ) conferred protection from liver injury after small bowel resection (SBR). Using a parenteral nutrition-independent model of resection-associated liver injury, C57BL/6J and 129S1/SvImJ mice underwent a 50% proximal SBR or sham operation. At postoperative week 10, hepatic steatosis, fibrosis, and cholestasis were assessed. Hepatic and systemic inflammatory pathways were evaluated using oxidative markers and abundance of tissue macrophages. Potential mechanisms of endotoxin resistance were also explored. Serum lipid levels were elevated in all mouse lines. Hepatic triglyceride levels were no different between mouse strains, but there was an increased accumulation of free fatty acids in the C57BL/6J mice. Histological and serum markers of hepatic fibrosis, steatosis, and cholestasis were significantly elevated in resected C57BL/6J SBR mice as well as oxidative stress markers and macrophage recruitment in both the liver and visceral white fat in C57BL/6J mice compared with sham controls and the 129S1/SvImJ mouse line. Serum endotoxin levels were significantly elevated in C57BL/6J mice with significant elevation of hepatic TLR4 and reduction in PPARα expression levels. Despite high levels of serum lipids, 129S1/SvImJ mice did not develop liver inflammation, fibrosis, or cholestasis after SBR, unlike C57BL/6J mice. These data suggest that the accumulation of hepatic free fatty acids as well as increased endotoxin-driven inflammatory pathways through PPARα and TLR4 contribute to the liver injury seen in C57BL/6J mice with short bowel syndrome.NEW & NOTEWORTHY Unlike C57BL/6 mice, the 129S1/SvImJ strain is resistant to liver inflammation and injury after small bowel resection. These disparate outcomes are likely due to the accumulation of hepatic free fatty acids as well as increased endotoxin-driven inflammatory pathways through PPARα and TLR4 in C57BL/6 mice with short bowel syndrome.

From Congenital Disorders of Fat Malabsorption to Understanding Intra-Enterocyte Mechanisms Behind Chylomicron Assembly and Secretion

During the last two decades, a large body of information on the events responsible for intestinal fat digestion and absorption has been accumulated. In particular, many groups have extensively focused on the absorptive phase in order to highlight the critical "players" and the main mechanisms orchestrating the assembly and secretion of chylomicrons (CM) as essential vehicles of alimentary lipids. The major aim of this article is to review understanding derived from basic science and clinical conditions associated with impaired packaging and export of CM. We have particularly insisted on inborn metabolic pathways in humans as well as on genetically modified animal models (recapitulating pathological features). The ultimate goal of this approach is that "experiments of nature" and in vivo model strategy collectively allow gaining novel mechanistic insight and filling the gap between the underlying genetic defect and the apparent clinical phenotype. Thus, uncovering the cause of disease contributes not only to understanding normal physiologic pathway, but also to capturing disorder onset, progression, treatment and prognosis.

Circulating fatty acid-binding protein 1 (FABP1) and nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus

Background: Fatty acid-binding protein 1 (FABP1) (also known as liver-type fatty acid-binding protein or LFABP) is a protein that is mainly expressed in the liver, and is associated with hepatocyte injury in acute transplant rejection. Reduced levels of FABP1 in mice livers have been shown to be effective against nonalcoholic fatty liver disease (NAFLD). In this study, we investigated the association between plasma FABP1 levels and NAFLD in patients with type 2 diabetes mellitus (T2DM). Methods: We enrolled 267 T2DM patients. Clinical and biochemical parameters were measured. The severity of NAFLD was assessed by ultrasound. FABP1 levels were determined using by enzyme-linked immunosorbent assays. Results: FABP1 levels were higher in patients with overt NAFLD, defined as more than a moderate degree of fatty liver compared to those without NAFLD. Age- and sex-adjusted analysis of FABP1 showed positive associations with body mass index (BMI), waist circumference, homeostasis model assessment estimate of β-cell function, creatinine, and fatty liver index, but showed negative associations with albumin and estimated glomerular filtration rate (eGFR). The odds ratio (OR) for the risk of overt NAFLD with increasing levels of sex-specific FABP1 was significantly increased (OR 2.63 [95% CI 1.30-5.73] vs. 4.94 [2.25-11.48]). The OR in the second and third tertiles of FABP1 remained significant after adjustments for BMI, triglycerides, high-density lipoprotein cholesterol, HbA1C, homeostasis model assessment estimate of insulin resistance, white blood cell count, hepatic enzymes, and eGFR. Conclusion: Our results indicate that FABP1 may play a role in the pathogenesis of NAFLD in patients with T2DM.

Dietary grape seed proanthocyanidin extract regulates metabolic disturbance in rat liver exposed to lead associated with PPARα signaling pathway

Lead, a pervasive environmental hazard worldwide, causes a wide range of physiological and biochemical destruction, including metabolic dysfunction. Grape seed proanthocyanidin extract (GSPE) is a natural production with potential metabolic regulation in liver. This study was performed to investigate the protective role of GSPE against lead-induced metabolic dysfunction in liver and elucidate the potential molecular mechanism of this event. Wistar rats received GSPE (200 mg/kg) daily with or without lead acetate (PbA, 0.5 g/L) exposure for 56 d. According to biochemical and histopathologic analysis, GSPE attenuated lead-induced metabolic dysfunction, oxidative stress, and liver dysfunction. Liver gene expression profiling was assessed by RNA sequencing and validated by qRT-PCR. Expression of some genes in peroxisome proliferator-activated receptor alpha (PPARα) signaling pathway was significantly suppressed in PbA group and revived in PbA + GSPE group, which was manifested by Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis and validated by western blot analysis. This study supports that dietary GSPE ameliorates lead-induced fatty acids metabolic disturbance in rat liver associated with PPARα signaling pathway, and suggests that dietary GSPE may be a protector against lead-induced metabolic dysfunction and liver injury, providing a novel therapy to protect liver against lead exposure.

Perilipin 5 and liver fatty acid binding protein function to restore quiescence in mouse hepatic stellate cells

Hepatic stellate cell (HSC) activation occurs along with decreased Perilipin5 (Plin5) and liver fatty acid-binding protein (L-Fabp) expression and coincident lipid droplet (LD) depletion. Conversely, the activated phenotype is reversible in WT HSCs upon forced expression of Plin5. Here, we asked if L-Fabp expression is required for Plin5-mediated rescue of the quiescent phenotype. Lentiviral Plin5 transduction of passaged L-Fabp^-/- HSCs failed to reverse activation markers or restore lipogenic gene expression and LD formation. However, adenoviral L-Fabp infection of lentiviral Plin5 transduced L-Fabp^-/- HSCs restored both the quiescent phenotype and LD formation, an effect also mediated by adenoviral intestine-Fabp or adipocyte-Fabp. Expression of exogenous Plin5 in activated WT HSCs induced a transcriptional program of lipogenic gene expression including endogenous L-Fabp, but none of the other FABPs. We further demonstrated that selective, small molecule inhibition of endogenous L-Fabp also eliminated the ability of exogenous Plin5 to rescue LD formation and reverse activation of WT HSCs. This functional coordination of L-Fabp with Plin5 was 5'-AMP-activated protein kinase (AMPK)-dependent and was eliminated by AMPK inhibition. Taken together, our results indicate that L-Fabp is required for Plin5 to activate a transcriptional program that restores LD formation and reverses HSC activation.

Ablating both Fabp1 and Scp2/Scpx (TKO) induces hepatic phospholipid and cholesterol accumulation in high fat-fed mice

Although singly ablating Fabp1 or Scp2/Scpx genes may exacerbate the impact of high fat diet (HFD) on whole body phenotype and non-alcoholic fatty liver disease (NAFLD), concomitant upregulation of the non-ablated gene, preference for ad libitum fed HFD, and sex differences complicate interpretation. Therefore, these issues were addressed in male and female mice ablated in both genes (Fabp1/Scp2/Scpx null or TKO) and pair-fed HFD. Wild-type (WT) males gained more body weight as fat tissue mass (FTM) and exhibited higher hepatic lipid accumulation than WT females. The greater hepatic lipid accumulation in WT males was associated with higher hepatic expression of enzymes in glyceride synthesis, higher hepatic bile acids, and upregulation of transporters involved in hepatic reuptake of serum bile acids. While TKO had little effect on whole body phenotype and hepatic bile acid accumulation in either sex, TKO increased hepatic accumulation of lipids in both, specifically phospholipid and cholesteryl esters in males and females and free cholesterol in females. TKO-induced increases in glycerides were attributed not only to complete loss of FABP1, SCP2 and SCPx, but also in part to sex-dependent upregulation of hepatic lipogenic enzymes. These data with WT and TKO mice pair-fed HFD indicate that: i) Sex significantly impacted the ability of HFD to increase body weight, induce hepatic lipid accumulation and increase hepatic bile acids; and ii) TKO exacerbated the HFD ability to induce hepatic lipid accumulation, regardless of sex, but did not significantly alter whole body phenotype in either sex.

Silencing of FABP1 ameliorates hepatic steatosis, inflammation, and oxidative stress in mice with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is increasing in prevalence worldwide and has been identified as a risk factor for cirrhosis and hepatocellular carcinoma. However, there is no effective pharmacologic treatment for NAFLD. FABP1 is a liver‐specific fatty acid‐binding protein (FABP) that plays important roles in intracellular lipid metabolism in the liver. We investigated the effect of repression of FABP1 expression on NAFLD, using adenovirus‐mediated silencing of FABP1. FABP1 knockdown in the liver decreased the liver weight and hepatic triglyceride (TG) accumulation. The expression of inflammatory and oxidative stress markers in the liver was also reduced. The level of thiobarbituric acid‐reactive substances, a marker of lipid peroxidation, in the liver of FABP1 knockdown mice was significantly decreased. These results suggest that FABP1 reduction in the liver is an effective approach against NAFLD.

Pyrazinamide induced hepatic injury in rats through inhibiting the PPARα pathway

Pyrazinamide (PZA) causes serious hepatotoxicity, but little is known about the exact mechanism by which PZA induced liver injury. The peroxisome proliferator-activated receptors alpha (PPARα) is highly expressed in the liver and modulates the intracellular lipidmetabolism. So far, the role of PPARα in the hepatotoxicity of PZA is unknown. In the present study, we described the hepatotoxic effects of PZA and the role of PPARα and its target genes in the downstream pathway including L-Fabp, Lpl, Cpt-1b, Acaa1, Apo-A1 and Me1 in this process. We found PZA induced the liver lipid metabolism disorder and PPARα expressionwas down-regulated which had a significant inverse correlation with liver injury degree. These changeswere ameliorated by fenofibrate, the co-treatment that acts as a PPARα agonist. In contrast, short-termstarvation significantly aggravated the severity of PZA-induced liver injury. In conclusion, this study demonstrated the critical role played by PPARα in PZA-induced hepatotoxicity and provided a better understanding of the molecular mechanisms underlying PZA-induced liver injury. Copyright © 2016 John Wiley & Sons, Ltd.

Phenotypic divergence in two lines of L-Fabp-/- mice reflects substrain differences and environmental modifiers

Phenotypic divergence in diet-induced obesity (DIO) and hepatic steatosis has been reported in two independently generated lines of L-Fabp(-/-) mice [New Jersey (NJ) L-Fabp(-/-) vs. Washington University (WU) L-Fabp(-/-) mice]. We performed side-by-side studies to examine differences between the lines and investigate the role of genetic background, intestinal microbiota, sex, and diet in the divergent phenotypes. Fasting-induced steatosis was attenuated in both L-Fabp(-/-) lines compared with C57BL/6J controls, with restoration of hepatic triglyceride levels following adenoviral L-Fabp rescue. Both lines were protected against DIO after high-saturated-fat diet feeding. Hepatic steatosis was attenuated in WU but not NJ L-Fabp(-/-) mice, although this difference between the lines disappeared upon antibiotic treatment and cohousing. In contrast, there was phenotypic divergence in L-Fabp(-/-) mice fed a high cocoa butter fat diet, with WU L-Fabp(-/-) mice, but not NJ L-Fabp(-/-) mice, showing protection against both DIO and hepatic steatosis, with some sex-dependent (female > male) differences. Dense mapping revealed no evidence of unintended targeting, duplications, or deletions surrounding the Fabp1 locus in either line and only minor differences in mRNA expression of genes located near the targeted allele. However, a C57BL/6 substrain screen showed that the NJ L-Fabp(-/-) line contains ∼40% C57BL/6N genomic DNA, despite reports that these mice were backcrossed six generations. Overall, these findings suggest that some of the phenotypic divergence between the two L-Fabp(-/-) lines may reflect unanticipated differences in genetic background, underscoring the importance of genetic background in phenotypic characterization.

Recent insights into the biological functions of liver fatty acid binding protein 1

Over four decades have passed since liver fatty acid binding protein (FABP)1 was first isolated. There are few protein families for which most of the complete tertiary structures, binding properties, and tissue occurrences are described in such detail and yet new functions are being uncovered for this protein. FABP1 is known to be critical for fatty acid uptake and intracellular transport and also has an important role in regulating lipid metabolism and cellular signaling pathways. FABP1 is an important endogenous cytoprotectant, minimizing hepatocyte oxidative damage and interfering with ischemia-reperfusion and other hepatic injuries. The protein may be targeted for metabolic activation through the cross-talk among many transcriptional factors and their activating ligands. Deficiency or malfunction of FABP1 has been reported in several diseases. FABP1 also influences cell proliferation during liver regeneration and may be considered as a prognostic factor for hepatic surgery. FABP1 binds and modulates the action of many molecules such as fatty acids, heme, and other metalloporphyrins. The ability to bind heme is another cytoprotective property and one that deserves closer investigation. The role of FABP1 in substrate availability and in protection from oxidative stress suggests that FABP1 plays a pivotal role during intracellular bacterial/viral infections by reducing inflammation and the adverse effects of starvation (energy deficiency).

Loss of L-FABP, SCP-2/SCP-x, or both induces hepatic lipid accumulation in female mice

Although roles for both sterol carrier protein-2/sterol carrier protein-x (SCP-2/SCP-x) and liver fatty acid binding protein (L-FABP) have been proposed in hepatic lipid accumulation, individually ablating these genes has been complicated by concomitant alterations in the other gene product(s). For example, ablating SCP2/SCP-x induces upregulation of L-FABP in female mice. Therefore, the impact of ablating SCP-2/SCP-x (DKO) or L-FABP (LKO) individually or both together (TKO) was examined in female mice. Loss of SCP-2/SCP-x (DKO, TKO) more so than loss of L-FABP alone (LKO) increased hepatic total lipid and total cholesterol content, especially cholesteryl ester. Hepatic accumulation of nonesterified long chain fatty acids (LCFA) and phospholipids occurred only in DKO and TKO mice. Loss of SCP-2/SCP-x (DKO, TKO) increased serum total lipid primarily by increasing triglycerides. Altered hepatic level of proteins involved in cholesterol uptake, efflux, and/or secretion was observed, but did not compensate for the loss of L-FABP, SCP-2/SCP-x or both. However, synergistic responses were not seen with the combinatorial knock out animals-suggesting that inhibiting SCP-2/SCP-x is more correlative with hepatic dysfunction than L-FABP. The DKO- and TKO-induced hepatic accumulation of cholesterol and long chain fatty acids shared significant phenotypic similarities with non-alcoholic fatty liver disease (NAFLD).

The pan-caspase inhibitor Emricasan (IDN-6556) decreases liver injury and fibrosis in a murine model of non-alcoholic steatohepatitis

BACKGROUND & AIMS

Hepatocyte apoptosis, the hallmark of non-alcoholic steatohepatitis (NASH) contributes to liver injury and fibrosis. Although, both the intrinsic and extrinsic apoptotic pathways are involved in the pathogenesis of NASH, the final common step of apoptosis is executed by a family of cysteine-proteases termed caspases. Thus, our aim was to ascertain if administration of Emricasan, a pan-caspase inhibitor, ameliorates liver injury and fibrosis in a murine model of NASH.

METHODS

C57/BL6J-mice were fed regular chow or high fat diet (HFD) for 20 weeks. All mice were treated with vehicle or Emricasan.

RESULTS

Mice fed a HFD diet demonstrate a five-fold increase in hepatocyte apoptosis by the TUNEL assay and a 1.5-fold and 1.3-fold increase in caspase-3 and-8 activities respectively; this increase in apoptosis was substantially attenuated in mice fed a HFD treated with Emricasan (HFD-Em). Likewise, liver injury and inflammation were reduced in mice fed HFD-Em as compare to HFD by measuring serum aspartate aminotransferase and alanine aminotransferase levels, NAS histological score and IL 1-β, TNF-α, monocyte chemoattractant protein (MCP-1) and C-X-C chemokine ligand-2 (CXCL2) quantitative reverse-transcription polymerase chain reaction (qPCR). These differences could not be attributed to differences in hepatic steatosis as liver triglycerides content were similar in both HFD groups. Hepatic fibrosis was reduced by Emricasan in HFD animals by decreasing αSMA (a marker for hepatic stellate cell activation), fibrosis score, Sirius red staining, hydroxyproline liver content and profibrogenic cytokines by qPCR.

CONCLUSION

In conclusion, these data demonstrate that in a murine model of NASH, liver injury and fibrosis are suppressed by inhibiting hepatocytes apoptosis and suggests that Emricasan may be an attractive antifibrotic therapy in NASH.

Association of L-FABP T94A and MTP I128T polymorphisms with hyperlipidemia in Chinese subjects

The purpose of this study was to evaluate the relation between the L-FABP T94A and MTP I128T polymorphisms and hyperlipidemia in Chinese subjects. We recruited 390 volunteers: 201 hyperlipidemic and 189 healthy volunteers. The L-FABP T94A and MTP I128T polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Anthropometry, lipid profile, and liver function of the subjects were determined. We observed that male carriers of the L-FABP A94 allele had significantly higher body weight (P = 0.012), higher body mass index (BMI) (P = 0.014), and higher plasma triacylglycerol levels (TAG) (P = 0.033) and lower ratios of high-density lipoprotein cholesterol (HDL-C) to total cholesterol (TC) (P = 0.008) than T94 homozygotes. The MTP T128 allele was associated with significantly lower serum TC (P < 0.001) and low-density lipoprotein cholesterol (LDL-C) (P < 0.001) levels in males. There was a direct correlation between the MTP T128 allele and a decreased risk of hyperlipidemia after adjusting for body mass index (OR = 0.327, 95 % CI: 0.178-0.600, P < 0.001). In conclusion, both the MTP I128T and the L-FABP T94A polymorphisms can affect serum lipid levels in the Chinese population. The MTP T128 allele offers protection against hyperlipidemia in the Chinese population.

Enterocyte fatty acid-binding proteins (FABPs): different functions of liver and intestinal FABPs in the intestine

Fatty acid-binding proteins (FABP) are highly abundant cytosolic proteins that are expressed in most mammalian tissues. In the intestinal enterocyte, both liver- (LFABP; FABP1) and intestinal FABPs (IFABP; FABP2) are expressed. These proteins display high-affinity binding for long-chain fatty acids (FA) and other hydrophobic ligands; thus, they are believed to be involved with uptake and trafficking of lipids in the intestine. In vitro studies have identified differences in ligand-binding stoichiometry and specificity, and in mechanisms of FA transfer to membranes, and it has been hypothesized that LFABP and IFABP have different functions in the enterocyte. Studies directly comparing LFABP- and IFABP-null mice have revealed markedly different phenotypes, indicating that these proteins indeed have different functions in intestinal lipid metabolism and whole body energy homeostasis. In this review, we discuss the evolving knowledge of the functions of LFABP and IFABP in the intestinal enterocyte.

Acetylcholinesterase (AChE) inhibition aggravates fasting-induced triglyceride accumulation in the mouse liver

Although fasting induces hepatic triglyceride (TG) accumulation in both rodents and humans, little is known about the underlying mechanism. Because parasympathetic nervous system activity tends to attenuate the secretion of very-low-density-lipoprotein-triglyceride (VLDL-TG) and increase TG stores in the liver, and serum cholinesterase activity is elevated in fatty liver disease, the inhibition of the parasympathetic neurotransmitter acetylcholinesterase (AChE) may have some influence on hepatic lipid metabolism. To assess the influence of AChE inhibition on lipid metabolism, the effect of physostigmine, an AChE inhibitor, on fasting-induced increase in liver TG was investigated in mice. In comparison with ad libitum-fed mice, 30 h fasting increased liver TG accumulation accompanied by a downregulation of sterol regulatory element-binding protein 1 (SREBP-1) and liver-fatty acid binding-protein (L-FABP). Physostigmine promoted the 30 h fasting-induced increase in liver TG levels in a dose-dependent manner, accompanied by a significant fall in plasma insulin levels, without a fall in plasma TG. Furthermore, physostigmine significantly attenuated the fasting-induced decrease of both mRNA and protein levels of SREBP-1 and L-FABP, and increased IRS-2 protein levels in the liver. The muscarinic receptor antagonist atropine blocked these effects of physostigmine on liver TG, serum insulin, and hepatic protein levels of SREBP-1 and L-FABP. These results demonstrate that AChE inhibition facilitated fasting-induced TG accumulation with up regulation of the hepatic L-FABP and SREBP-1 in mice, at least in part via the activation of muscarinic acetylcholine receptors. Our studies highlight the crucial role of parasympathetic regulation in fasting-induced TG accumulation, and may be an important source of information on the mechanism of hepatic disorders of lipid metabolism.

Structural and functional interaction of fatty acids with human liver fatty acid-binding protein (L-FABP) T94A variant

The human liver fatty acid-binding protein (L-FABP) T94A variant, the most common in the FABP family, has been associated with elevated liver triglyceride levels. How this amino acid substitution elicits these effects is not known. This issue was addressed using human recombinant wild-type (WT) and T94A variant L-FABP proteins as well as cultured primary human hepatocytes expressing the respective proteins (genotyped as TT, TC and CC). The T94A substitution did not alter or only slightly altered L-FABP binding affinities for saturated, monounsaturated or polyunsaturated long chain fatty acids, nor did it change the affinity for intermediates of triglyceride synthesis. Nevertheless, the T94A substitution markedly altered the secondary structural response of L-FABP induced by binding long chain fatty acids or intermediates of triglyceride synthesis. Finally, the T94A substitution markedly decreased the levels of induction of peroxisome proliferator-activated receptor α-regulated proteins such as L-FABP, fatty acid transport protein 5 and peroxisome proliferator-activated receptor α itself meditated by the polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid in cultured primary human hepatocytes. Thus, although the T94A substitution did not alter the affinity of human L-FABP for long chain fatty acids, it significantly altered human L-FABP structure and stability, as well as the conformational and functional response to these ligands.

Hepatic ATGL mediates PPAR-α signaling and fatty acid channeling through an L-FABP independent mechanism

Adipose TG lipase (ATGL) catalyzes the rate-limiting step in TG hydrolysis in most tissues. We have shown that hepatic ATGL preferentially channels hydrolyzed FAs to β-oxidation and induces PPAR-α signaling. Previous studies have suggested that liver FA binding protein (L-FABP) transports FAs from lipid droplets to the nucleus for ligand delivery and to the mitochondria for β-oxidation. To determine if L-FABP is involved in ATGL-mediated FA channeling, we used adenovirus-mediated suppression or overexpression of hepatic ATGL in either WT or L-FABP KO mice. Hepatic ATGL knockdown increased liver weight and TG content of overnight fasted mice regardless of genotype. L-FABP deletion did not impair the effects of ATGL overexpression on the oxidation of hydrolyzed FAs in primary hepatocyte cultures or on serum β-hydroxybutyrate concentrations in vivo. Moreover, L-FABP deletion did not influence the effects of ATGL knockdown or overexpression on PPAR-α target gene expression. Taken together, we conclude that L-FABP is not required to channel ATGL-hydrolyzed FAs to mitochondria for β-oxidation or the nucleus for PPAR-α regulation.

Fatty acid synthase mediates the epithelial-mesenchymal transition of breast cancer cells

This study aimed to investigate the role of fatty acid synthase (FASN) in the epithelial-mesenchymal transition (EMT) of breast cancer cells. MCF-7 cells and MCF-7 cells overexpressing mitogen-activated protein kinase 5 (MCF-7-MEK5) were used in this study. MCF-7-MEK5 cells showed stable EMT characterized by increased vimentin and decreased E-cadherin expression. An In vivo animal model was established using the orthotopic injection of MCF-7 or MCF-7-MEK5 cells. Real-time quantitative PCR and western blotting were used to detect the expression levels of FASN and its downstream proteins liver fatty acid-binding protein (L-FABP) and VEGF/VEGFR-2 in both in vitro and in vivo models (nude mouse tumor tissues). In MCF-7-MEK5 cells, significantly increased expression of FASN was associated with increased levels of L-FABP and VEGF/VEGFR-2. Cerulenin inhibited MCF-7-MEK5 cell migration and EMT, and reduced FASN expression and down-stream proteins L-FABP, VEGF, and VEGFR-2. MCF-7-MEK5 cells showed higher sensitivity to Cerulenin than MCF-7 cells. Immunofluorescence revealed an increase of co-localization of FASN with VEGF on the cell membrane and with L-FABP within MCF-7-MEK5 cells. Immunohistochemistry further showed that increased percentage of FASN-positive cells in the tumor tissue was associated with increased percentages of L-FABP- and VEGF-positive cells and the Cerulenin treatment could reverse the effect. Altogether, our results suggest that FASN is essential to EMT possibly through regulating L-FABP, VEGF and VEGFR-2. This study provides a theoretical basis and potential strategy for effective suppression of malignant cells with EMT.

Direct comparison of mice null for liver or intestinal fatty acid-binding proteins reveals highly divergent phenotypic responses to high fat feeding

The enterocyte expresses two fatty acid-binding proteins (FABP), intestinal FABP (IFABP; FABP2) and liver FABP (LFABP; FABP1). LFABP is also expressed in liver. Despite ligand transport and binding differences, it has remained uncertain whether these intestinally coexpressed proteins, which both bind long chain fatty acids (FA), are functionally distinct. Here, we directly compared IFABP(-/-) and LFABP(-/-) mice fed high fat diets containing long chain saturated or unsaturated fatty acids, reasoning that providing an abundance of dietary lipid would reveal unique functional properties. The results showed that mucosal lipid metabolism was indeed differentially modified, with significant decreases in FA incorporation into triacylglycerol (TG) relative to phospholipid (PL) in IFABP(-/-) mice, whereas LFABP(-/-) mice had reduced monoacylglycerol incorporation in TG relative to PL, as well as reduced FA oxidation. Interestingly, striking differences were found in whole body energy homeostasis; LFABP(-/-) mice fed high fat diets became obese relative to WT, whereas IFABP(-/-) mice displayed an opposite, lean phenotype. Fuel utilization followed adiposity, with LFABP(-/-) mice preferentially utilizing lipids, and IFABP(-/-) mice preferentially metabolizing carbohydrate for energy production. Changes in body weight and fat may arise, in part, from altered food intake; mucosal levels of the endocannabinoids 2-arachidonoylglycerol and arachidonoylethanolamine were elevated in LFABP(-/-), perhaps contributing to increased energy intake. This direct comparison provides evidence that LFABP and IFABP have distinct roles in intestinal lipid metabolism; differential intracellular functions in intestine and in liver, for LFABP(-/-) mice, result in divergent downstream effects at the systemic level.

Liver fatty acid-binding protein (L-Fabp) modifies intestinal fatty acid composition and adenoma formation in ApcMin/+ mice

Evidence suggests a relationship between dietary fat intake, obesity, and colorectal cancer, implying a role for fatty acid metabolism in intestinal tumorigenesis that is incompletely understood. Liver fatty acid-binding protein (L-Fabp), a dominant intestinal fatty acid-binding protein, regulates intestinal fatty acid trafficking and metabolism, and L-Fabp deletion attenuates diet-induced obesity. Here, we examined whether changes in intestinal fatty acid metabolism following L-Fabp deletion modify adenoma development in Apc(Min)(/+) mice. Compound L-Fabp(-/-)Apc(Min)(/+) mice were generated and fed a 10% fat diet balanced equally between saturated, monounsaturated, and polyunsaturated fat. L-Fabp(-/-)Apc(Min)(/+) mice displayed significant reductions in adenoma number and total polyp area compared with Apc(Min)(/+)controls, reflecting a significant shift in distribution toward smaller polyps. Adenomas from L-Fabp(-/-)Apc(Min)(/+) mice exhibited reductions in cellular proliferation, high-grade dysplasia, and nuclear β-catenin translocation. Intestinal fatty acid content was increased in L-Fabp(-/-)Apc(Min)(/+) mice, and lipidomic profiling of intestinal mucosa revealed significant shifts to polyunsaturated fatty acid species with reduced saturated fatty acid species. L-Fabp(-/-)Apc(Min)(/+) mice also showed corresponding changes in mRNA expression of enzymes involved in fatty acid elongation and desaturation. Furthermore, adenomas from L-Fabp(-/-)Apc(Min)(/+) mice displayed significant reductions in mRNA abundance of nuclear hormone receptors involved in cellular proliferation and in enzymes involved in lipogenesis. These findings collectively implicate L-Fabp as an important genetic modifier of intestinal tumorigenesis, and identify fatty acid trafficking and metabolic compartmentalization as an important pathway linking dietary fat intake, obesity, and intestinal tumor formation.

Liver fatty acid binding protein (L-Fabp) modulates murine stellate cell activation and diet-induced nonalcoholic fatty liver disease

Activation of hepatic stellate cells (HSCs) is crucial to the development of fibrosis in nonalcoholic fatty liver disease. Quiescent HSCs contain lipid droplets (LDs), whose depletion upon activation induces a fibrogenic gene program. Here we show that liver fatty acid-binding protein (L-Fabp), an abundant cytosolic protein that modulates fatty acid (FA) metabolism in enterocytes and hepatocytes, also modulates HSC FA utilization and in turn regulates the fibrogenic program. L-Fabp expression decreased 10-fold following HSC activation, concomitant with depletion of LDs. Primary HSCs isolated from L-FABP(-/-) mice contain fewer LDs than wild-type (WT) HSCs, and exhibit up-regulated expression of genes involved in HSC activation. Adenoviral L-Fabp transduction inhibited activation of passaged WT HSCs and increased both the expression of prolipogenic genes and also augmented intracellular lipid accumulation, including triglyceride and FA, predominantly palmitate. Freshly isolated HSCs from L-FABP(-/-) mice correspondingly exhibited decreased palmitate in the free FA pool. To investigate whether L-FABP deletion promotes HSC activation in vivo, we fed L-FABP(-/-) and WT mice a high-fat diet supplemented with trans-fatty acids and fructose (TFF). TFF-fed L-FABP(-/-) mice exhibited reduced hepatic steatosis along with decreased LD abundance and size compared to WT mice. In addition, TFF-fed L-FABP(-/-) mice exhibited decreased hepatic fibrosis, with reduced expression of fibrogenic genes, compared to WT mice.

CONCLUSION

L-FABP deletion attenuates both diet-induced hepatic steatosis and fibrogenesis, despite the observation that L-Fabp paradoxically promotes FA and LD accumulation and inhibits HSC activation in vitro. These findings highlight the importance of cell-specific modulation of hepatic lipid metabolism in promoting fibrogenesis in nonalcoholic fatty liver disease. (Hepatology 2013).

Liver fatty acid binding protein gene-ablation exacerbates weight gain in high-fat fed female mice

Loss of liver fatty acid binding protein (L-FABP) decreases long chain fatty acid uptake and oxidation in primary hepatocytes and in vivo. On this basis, L-FABP gene ablation would potentiate high-fat diet-induced weight gain and weight gain/energy intake. While this was indeed the case when L-FABP null (-/-) mice on the C57BL/6NCr background were pair-fed a high-fat diet, whether this would also be observed under high-fat diet fed ad libitum was not known. Therefore, this possibility was examined in female L-FABP (-/-) mice on the same background. L-FABP (-/-) mice consumed equal amounts of defined high-fat or isocaloric control diets fed ad libitum. However, on the ad libitum-fed high-fat diet the L-FABP (-/-) mice exhibited: (1) decreased hepatic long chain fatty acid (LCFA) β-oxidation as indicated by lower serum β-hydroxybutyrate level; (2) decreased hepatic protein levels of key enzymes mitochondrial (rate limiting carnitine palmitoyl acyltransferase A1, CPT1A; HMG-CoA synthase) and peroxisomal (acyl CoA oxidase 1, ACOX1) LCFA β-oxidation; (3) increased fat tissue mass (FTM) and FTM/energy intake to the greatest extent; and (4) exacerbated body weight gain, weight gain/energy intake, liver weight, and liver weight/body weight to the greatest extent. Taken together, these findings showed that L-FABP gene-ablation exacerbated diet-induced weight gain and fat tissue mass gain in mice fed high-fat diet ad libitum--consistent with the known biochemistry and cell biology of L-FABP.

Susceptibility of L-FABP-/- mice to oxidative stress in early-stage alcoholic liver

Chronic ethanol consumption is a prominent cause of liver disease worldwide. Dysregulation of an important lipid uptake and trafficking gene, liver-fatty acid binding protein (L-FABP), may contribute to alterations in lipid homeostasis during early-stage alcoholic liver. We have reported the detrimental effects of ethanol on the expression of L-FABP and hypothesize this may deleteriously impact metabolic networks regulating fatty acids. Male wild-type (WT) and L-FABP(-/-) mice were fed a modified Lieber-DeCarli liquid diet for six weeks. To assess the response to chronic ethanol ingestion, standard biochemical indicators for alcoholic liver disease (ALD) and oxidative stress were measured. Ethanol ingestion resulted in attenuation of hepatic triglyceride accumulation and elevation of cholesterol in L-FABP(-/-) mice. Lipidomics analysis validated multiple alterations in hepatic lipids resulting from ethanol treatment. Increased immunohistochemical staining for the reactive aldehydes 4-hydroxynonenal and malondialdehyde were observed in WT mice ingesting ethanol; however, L-FABP(-/-) mice displayed prominent protein adducts in liver sections evaluated from pair-fed and ethanol-fed mice. Likewise, alterations in glutathione, thiobarbituric acid reactive substances (TBARS), 8-isoprostanes, and protein carbonyl content all indicated L-FABP(-/-) mice exhibit high sustained oxidative stress in the liver. These data establish that L-FABP is an indirect antioxidant protein essential for sequestering FFA and that its impairment could contribute to in the pathogenesis of ALD.

The human liver fatty acid binding protein (FABP1) gene is activated by FOXA1 and PPARα; and repressed by C/EBPα: Implications in FABP1 down-regulation in nonalcoholic fatty liver disease

Liver fatty acid binding protein (FABP1) prevents lipotoxicity of free fatty acids and regulates fatty acid trafficking and partition. Our objective is to investigate the transcription factors controlling the human FABP1 gene and their regulation in nonalcoholic fatty liver disease (NAFLD). Adenovirus-mediated expression of multiple transcription factors in HepG2 cells and cultured human hepatocytes demonstrated that FOXA1 and PPARα are among the most effective activators of human FABP1, whereas C/EBPα is a major dominant repressor. Moreover, FOXA1 and PPARα induced re-distribution of FABP1 protein and increased cytoplasmic expression. Reporter assays demonstrated that the major basal activity of the human FABP1 promoter locates between -96 and -229bp, where C/EBPα binds to a composite DR1-C/EBP element. Mutation of this element at -123bp diminished basal reporter activity, abolished repression by C/EBPα and reduced transactivation by HNF4α. Moreover, HNF4α gene silencing by shRNA in HepG2 cells caused a significant down-regulation of FABP1 mRNA expression. FOXA1 activated the FABP1 promoter through binding to a cluster of elements between -229 and -592bp, whereas PPARα operated through a conserved proximal element at -59bp. Finally, FABP1, FOXA1 and PPARα were concomitantly repressed in animal models of NAFLD and in human nonalcoholic fatty livers, whereas C/EBPα was induced or did not change. We conclude that human FABP1 has a complex mechanism of regulation where C/EBPα displaces HNF4α and hampers activation by FOXA1 and PPARα. Alteration of expression of these transcription factors in NAFLD leads to FABP1 gen repression and could exacerbate lipotoxicity and disease progression.

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.

Beta-glucosidase 2 knockout mice with increased glucosylceramide show impaired liver regeneration

BACKGROUND AND AIMS

Glycolipids have been shown to serve specialized functions in cell signalling, proliferation and differentiation processes, which are all important during liver regeneration. We previously generated beta-glucosidase 2 (GBA2) knockout mice that accumulate the glycolipid glucosylceramide in various tissues, including the liver. The present study addressed the role of GBA2-deficiency and subsequent glucosylceramide accumulation in liver regeneration.

METHODS

Gba2 knockout and wild-type mice were subjected to two-third partial hepatectomy. Mice were sacrificed at different time points, blood was collected, and the remnant liver was removed. Glucosylceramide and ceramide were quantified using mass spectrometry from whole liver and isolated hepatocytes. Serum and hepatocytic supernatant of IL-6, TNF-α and TGF-β levels were measured using ELISA. Cell signalling proteins were analysed using immunoblots.

RESULTS

Regenerating liver after partial hepatectomy showed a significant increase of hepatic glucosylceramide in GBA2-deficient mice compared to controls. Accumulation of glucosylceramide was associated with a delay in liver regeneration and reduced serum levels of IL-6 and TNF-α. Furthermore, reduced IL-6 led to decreased expression of the phosphorylated form of the signal transducer and activator of transcription 3 (P-STAT3).

CONCLUSIONS

We conclude that increased glucosylceramide affects cytokine- and growth factor-mediated signalling pathways during liver regeneration. Thus, the repression of IL-6/STAT3 signalling pathway seems to be one of the mechanisms for the delay of liver regeneration in GBA2-deficient mice.

Decreased body weight and hepatic steatosis with altered fatty acid ethanolamide metabolism in aged L-Fabp -/- mice

The tissue-specific sources and regulated production of physiological signals that modulate food intake are incompletely understood. Previous work showed that L-Fabp(-/-) mice are protected against obesity and hepatic steatosis induced by a high-fat diet, findings at odds with an apparent obesity phenotype in a distinct line of aged L-Fabp(-/-) mice. Here we show that the lean phenotype in L-Fabp(-/-) mice is recapitulated in aged, chow-fed mice and correlates with alterations in hepatic, but not intestinal, fatty acid amide metabolism. L-Fabp(-/-) mice exhibited short-term changes in feeding behavior with decreased food intake, which was associated with reduced abundance of key signaling fatty acid ethanolamides, including oleoylethanolamide (OEA, an agonist of PPARα) and anandamide (AEA, an agonist of cannabinoid receptors), in the liver. These reductions were associated with increased expression and activity of hepatic fatty acid amide hydrolase-1, the enzyme that degrades both OEA and AEA. Moreover, L-Fabp(-/-) mice demonstrated attenuated responses to OEA administration, which was completely reversed with an enhanced response after administration of a nonhydrolyzable OEA analog. These findings demonstrate a role for L-Fabp in attenuating obesity and hepatic steatosis, and they suggest that hepatic fatty acid amide metabolism is altered in L-Fabp(-/-) mice.

Fatty acid induced remodeling within the human liver fatty acid-binding protein

We crystallized human liver fatty acid-binding protein (LFABP) in apo, holo, and intermediate states of palmitic acid engagement. Structural snapshots of fatty acid recognition, entry, and docking within LFABP support a heads-in mechanism for ligand entry. Apo-LFABP undergoes structural remodeling, where the first palmitate ingress creates the atomic environment for placement of the second palmitate. These new mechanistic insights will facilitate development of pharmacological agents against LFABP.

Different functions of intestinal and liver-type fatty acid-binding proteins in intestine and in whole body energy homeostasis

It has long been known that mammalian enterocytes coexpress two members of the fatty acid-binding protein (FABP) family, the intestinal FABP (IFABP) and the liver FABP (LFABP). Both bind long-chain fatty acids and have similar though not identical distributions in the intestinal tract. While a number of in vitro properties suggest the potential for different functions, the underlying reasons for expression of both proteins in the same cells are not known. Utilizing mice genetically lacking either IFABP or LFABP, we directly demonstrate that each of the enterocyte FABPs participates in specific pathways of intestinal lipid metabolism. In particular, LFABP appears to target fatty acids toward oxidative pathways and dietary monoacylglycerols toward anabolic pathways, while IFABP targets dietary fatty acids toward triacylglycerol synthesis. The two FABP-null models also displayed differences in whole body response to fasting, with LFABP-null animals losing less fat-free mass and IFABP-null animals losing more fat mass relative to wild-type mice. The metabolic changes observed in both null models appear to occur by nontranscriptional mechanisms, supporting the hypothesis that the enterocyte FABPs are specifically trafficking their ligands to their respective metabolic fates.

Screening and identification of differentially expressed genes in goose hepatocytes exposed to free fatty acid

The overaccumulation of triglycerides in hepatocytes induces hepatic steatosis; however, little is known about the mechanism of goose hepatic steatosis. The aim of this study was to define an experimental model of hepatocellular steatosis with TG overaccumulation and minimal cytotoxicity, using a mixture of various proportions of oleate and palmitate free fatty acids (FFAs) to induce fat-overloading, then using suppressive subtractive hybridization and a quantitative PCR approach to identify genes with higher or lower expression levels after the treatment of cells with FFA mixtures. Overall, 502 differentially expressed clones, representing 21 novel genes and 87 known genes, were detected by SSH. Based on functional clustering, up- and down-regulated genes were mostly related to carbohydrate and lipid metabolism, enzyme activity and signal transduction. The expression of 20 selected clones involved with carbohydrate and lipid metabolism pathways was further studied by quantitative PCR. The data indicated that six clones similar to the genes ChREBP, FoxO1, apoB, IHPK2, KIF1B, and FSP27, which participate in de novo synthesis of fatty acid and secretion of very low density lipoproteins, had significantly lower expression levels in the hepatocytes treated with FFA mixtures. Meanwhile, 13 clones similar to the genes DGAT-1, ACSL1, DHRS7, PPARα, L-FABP, DGAT-2, PCK, ACSL3, CPT-1, A-FABP, PPARβ, MAT, and ALDOB had significantly higher expression levels in the hepatocytes treated with FFA mixtures. These results suggest that several metabolic pathways are altered in goose hepatocytes, which may be useful for further research into the molecular mechanism of goose hepatic steatosis.

Dietary fat sensing via fatty acid oxidation in enterocytes: possible role in the control of eating

Various mechanisms detect the presence of dietary triacylglycerols (TAG) in the digestive tract and link TAG ingestion to the regulation of energy homeostasis. We here propose a novel sensing mechanism with the potential to encode dietary TAG-derived energy by translating enterocyte fatty acid oxidation (FAO) into vagal afferent signals controlling eating. Peripheral FAO has long been implicated in the control of eating ( 141 ). The prevailing view was that mercaptoacetate (MA) and other FAO inhibitors stimulate eating by modulating vagal afferent signaling from the liver. This concept has been challenged because hepatic parenchymal vagal afferent innervation is scarce and because experimentally induced changes in hepatic FAO often fail to affect eating. Nevertheless, intraperitoneally administered MA acts in the abdomen to stimulate eating because this effect was blocked by subdiaphragmatic vagal deafferentation ( 21 ), a surgical technique that eliminates all vagal afferents from the upper gut. These and other data support a role of the small intestine rather than the liver as a FAO sensor that can influence eating. After intrajejunal infusions, MA also stimulated eating in rats through vagal afferent signaling, and after infusion into the superior mesenteric artery, MA increased the activity of celiac vagal afferent fibers originating in the proximal small intestine. Also, pharmacological interference with TAG synthesis targeting the small intestine induced a metabolic profile indicative of increased FAO and inhibited eating in rats on a high-fat diet but not on chow. Finally, cell culture studies indicate that enterocytes oxidize fatty acids, which can be modified pharmacologically. Thus enterocytes may sense dietary TAG-derived fatty acids via FAO and influence eating through changes in intestinal vagal afferent activity. Further studies are necessary to identify the link between enterocyte FAO and vagal afferents and to examine the specificity and potential physiological relevance of such a mechanism.

Liver fatty acid-binding protein and obesity

While low levels of unesterified long chain fatty acids (LCFAs) are normal metabolic intermediates of dietary and endogenous fat, LCFAs are also potent regulators of key receptors/enzymes and at high levels become toxic detergents within the cell. Elevated levels of LCFAs are associated with diabetes, obesity and metabolic syndrome. Consequently, mammals evolved fatty acid-binding proteins (FABPs) that bind/sequester these potentially toxic free fatty acids in the cytosol and present them for rapid removal in oxidative (mitochondria, peroxisomes) or storage (endoplasmic reticulum, lipid droplets) organelles. Mammals have a large (15-member) family of FABPs with multiple members occurring within a single cell type. The first described FABP, liver-FABP (L-FABP or FABP1), is expressed in very high levels (2-5% of cytosolic protein) in liver as well as in intestine and kidney. Since L-FABP facilitates uptake and metabolism of LCFAs in vitro and in cultured cells, it was expected that abnormal function or loss of L-FABP would reduce hepatic LCFA uptake/oxidation and thereby increase LCFAs available for oxidation in muscle and/or storage in adipose. This prediction was confirmed in vitro with isolated liver slices and cultured primary hepatocytes from L-FABP gene-ablated mice. Despite unaltered food consumption when fed a control diet ad libitum, the L-FABP null mice exhibited age- and sex-dependent weight gain and increased fat tissue mass. The obese phenotype was exacerbated in L-FABP null mice pair fed a high-fat diet. Taken together with other findings, these data suggest that L-FABP could have an important role in preventing age- or diet-induced obesity.

L-FABP T94A decreased fatty acid uptake and altered hepatic triglyceride and cholesterol accumulation in Chang liver cells stably transfected with L-FABP

Liver fatty acid-binding protein (L-FABP, FABP1) is a highly conserved key factor in lipid metabolism. This study was undertaken to verify whether the T94A mutation in the L-FABP gene affects fatty acid uptake and intracellular esterification into specific lipid pools. Candidate SNPs were recreated using site-directed mutagenesis and tested for physical function in stably transfected Chang liver cell lines. We found that the T94A mutant of L-FABP lowered FFA uptake but had no effect on FFA efflux. L-FABP T94A-expressing cells showed decreased triglyceride content and increased cholesterol accumulation compared to the wild-type control for cells incubated with an FFA mixture (oleate: palmitate, 2:1 ratio). In conclusion, our study provided additional indications of the functional relevance of the L-FABP T94A SNP in hepatic fatty acid and lipid metabolism in humans.

Dynamic expression of L-FABP and PPAR-α mRNAs in nonalcoholic fatty liver disease in rats

AIM: To establish a rat model of nonalcoholic fatty liver disease (NAFLD) to detect the changes in the expression of liver fatty acid-binding protein (L-FABP) and peroxisome proliferator-activated receptor-α (PPAR-α) mRNAs in NAFLD and to explore the mechanism underlying the pathogenesis of the disease.

METHODS: Eighty-four male Wistar rats were randomly and equally divided into two groups: control group (fed a normal diet for 18 weeks) and model group (fed a high-fat diet for 12 wk and a normal diet for another 6 wk). Each group was further divided into 7 subgroups for testing at weeks 0, 2, 4, 8, 12, 16 and 18. Rats in the two groups were sacrificed at each time point. Blood samples were taken to measure serum ALT, TG, CHOL, HDL-C and LDL-C. Liver samples were taken for HE staining and for detection of the expression of L-FABP and PPAR-α mRNAs by real-time fluorescence quantitative RT-PCR.

RESULTS: The expression of L-FABP and PPAR-α mRNAs in control rats showed no obvious changes. No steatosis was observed at week 2 in rats fed a high-fat diet. The expression of L-FABP mRNA increased obviously in rats fed a high-fat diet at week 4 (0.59 ± 0.06 vs 0.52 ± 0.03, P < 0.05), reaching the peak at weeks 8 and 12 (0.91 ± 0.07 and 0.92 ± 0.08 vs 0.52 ± 0.03, respectively; both P < 0.01). At week 18, the expression level of L-FABP mRNA declined significantly (0.59 ± 0.04 vs 0.92 ± 0.08, P < 0.01) but was still higher than that in the control group (P < 0.05). The expression of PPAR-α mRNA decreased obviously in rats fed a high-fat diet at week 4 (1.05 ± 0.09 vs 1.13 ± 0.07, P < 0.05), reaching the lowest level at weeks 8 and 12 (0.89 ± 0.04 and 0.85 ± 0.07 vs 1.13 ± 0.07, respectively; both P < 0.01). At week 18, the expression level of PPAR-α mRNA was elevated obviously (1.04 ± 0.07 vs 0.85 ± 0.07, P < 0.01) but was still lower than that in the control group. Steatosis become worst at week 12 but was improved greatly at week 18.

CONCLUSION: In the progression of rat NAFLD, PPAR-α mRNA expression decreases and L-FABP mRNA expression increases as steatosis becomes worse. Steatosis can be improved through diet.

PPAR/RXR Regulation of Fatty Acid Metabolism and Fatty Acid omega-Hydroxylase (CYP4) Isozymes: Implications for Prevention of Lipotoxicity in Fatty Liver Disease

Fatty liver disease is a common lipid metabolism disorder influenced by the combination of individual genetic makeup, drug exposure, and life-style choices that are frequently associated with metabolic syndrome, which encompasses obesity, dyslipidemia, hypertension, hypertriglyceridemia, and insulin resistant diabetes. Common to obesity related dyslipidemia is the excessive storage of hepatic fatty acids (steatosis), due to a decrease in mitochondria β-oxidation with an increase in both peroxisomal β-oxidation, and microsomal ω-oxidation of fatty acids through peroxisome proliferator activated receptors (PPARs). How steatosis increases PPARα activated gene expression of fatty acid transport proteins, peroxisomal and mitochondrial fatty acid β-oxidation and ω-oxidation of fatty acids genes regardless of whether dietary fatty acids are polyunsaturated (PUFA), monounsaturated (MUFA), or saturated (SFA) may be determined by the interplay of PPARs and HNF4α with the fatty acid transport proteins L-FABP and ACBP. In hepatic steatosis and steatohepatitis, the ω-oxidation cytochrome P450 CYP4A gene expression is increased even with reduced hepatic levels of PPARα. Although numerous studies have suggested the role ethanol-inducible CYP2E1 in contributing to increased oxidative stress, Cyp2e1-null mice still develop steatohepatitis with a dramatic increase in CYP4A gene expression. This strongly implies that CYP4A fatty acid ω-hydroxylase P450s may play an important role in the development of steatohepatitis. In this review and tutorial, we briefly describe how fatty acids are partitioned by fatty acid transport proteins to either anabolic or catabolic pathways regulated by PPARs, and we explore how medium-chain fatty acid (MCFA) CYP4A and long-chain fatty acid (LCFA) CYP4Fω-hydroxylase genes are regulated in fatty liver. We finally propose a hypothesis that increased CYP4A expression with a decrease in CYP4F genes may promote the progression of steatosis to steatohepatitis.

Caveolin, sterol carrier protein-2, membrane cholesterol-rich microdomains and intracellular cholesterol trafficking

While the existence of membrane lateral microdomains has been known for over 30 years, interest in these structures accelerated in the past decade due to the discovery that cholesterol-rich microdomains serve important biological functions. It is increasingly appreciated that cholesterol-rich microdomains in the plasma membranes of eukaryotic cells represent an organizing nexus for multiple cellular proteins involved in transmembrane nutrient uptake (cholesterol, fatty acid, glucose, etc.), cell-signaling, immune recognition, pathogen entry, and many other roles. Despite these advances, however, relatively little is known regarding the organization of cholesterol itself in these plasma membrane microdomains. Although a variety of non-sterol markers indicate the presence of microdomains in the plasma membranes of living cells, none of these studies have demonstrated that cholesterol is enriched in these microdomains in living cells. Further, the role of cholesterol-rich membrane microdomains as targets for intracellular cholesterol trafficking proteins such as sterol carrier protein-2 (SCP-2) that facilitate cholesterol uptake and transcellular transport for targeting storage (cholesterol esters) or efflux is only beginning to be understood. Herein, we summarize the background as well as recent progress in this field that has advanced our understanding of these issues.

Initial studies of the cytoplasmic FABP superfamily

Our colleagues and we have determined the complete primary structure of a low molecular weight cytoplasmic FABP (also known as z-protein) that binds to LCFAs with high affinities, obtained from rat liver. At the same time, we were the first to propose that rat FABP1, bovine FABP8 (MP-2), bovine CRBP and rat CRABP constituted a protein superfamily in 1982. Since then, extensive investigation of structures, functions and expressions has been carried out on a whole family of FABPs. Analyses of rat heart FABP; FABP1, FABP3 and alpha(2U)-globulin expressed in rat kidney; discovery of ileal FABP6 (I-15P); and first application of FABP2 as a diagnostic marker also stand out in particular.

High dietary fat exacerbates weight gain and obesity in female liver fatty acid binding protein gene-ablated mice

Since liver fatty acid binding protein (L-FABP) facilitates uptake/oxidation of long-chain fatty acids in cultured transfected cells and primary hepatocytes, loss of L-FABP was expected to exacerbate weight gain and/or obesity in response to high dietary fat. Male and female wild-type (WT) and L-FABP gene-ablated mice, pair-fed a defined isocaloric control or high fat diet for 12 weeks, consumed equal amounts of food by weight and kcal. Male WT mice gained weight faster than their female WT counterparts regardless of diet. L-FABP gene ablation enhanced weight gain more in female than male mice-an effect exacerbated by high fat diet. Dual emission X-ray absorptiometry revealed high-fat fed male and female WT mice gained mostly fat tissue mass (FTM). L-FABP gene ablation increased FTM in female, but not male, mice-an effect also exacerbated by high fat diet. Concomitantly, L-FABP gene ablation decreased serum beta-hydroxybutyrate in male and female mice fed the control diet and, even more so, on the high-fat diet. Thus, L-FABP gene ablation decreased fat oxidation and sensitized all mice to weight gain as whole body FTM and LTM-with the most gain observed in FTM of control vs high-fat fed female L-FABP null mice. Taken together, these results indicate loss of L-FABP exacerbates weight gain and/or obesity in response to high dietary fat.

Hepatic phenotype of liver fatty acid binding protein gene-ablated mice

Although the function of liver fatty acid binding protein in hepatic fatty acid metabolism has been extensively studied, its potential role in hepatic cholesterol homeostasis is less clear. Although hepatic cholesterol accumulation was initially reported in L-FABP-null female mice, that study was performed with early N2 backcross generation mice. To resolve whether the hepatic cholesterol phenotype in these L-FABP(-/-) mice was attributable to genetic inhomogeneity, these L-FABP(-/-) mice were further backcrossed to C57Bl/6 mice up to the N10 (99.9% homogeneity) generation. Hepatic total cholesterol accumulation was observed in female, but not male, L-FABP(-/-) mice at all (N2, N4, N6, N10) backcross generations examined. The greater total cholesterol was due to increased hepatic levels of both unesterified (free) cholesterol and esterified cholesterol. Altered hepatic cholesterol accumulation correlated directly with L-FABP's ability to bind cholesterol with high affinity as shown by direct L-FABP binding of fluorescent cholesterol analogs (NBD-cholesterol, dansyl-cholesterol), a photoactivatable cholesterol analog [free cholesterol benzophenone (FCBP)], and free cholesterol (circular dichroism, isothermal titration microcalorimetry). One mole of fluorescent sterol was bound per mole of L-FABP. This was confirmed by photo-cross-linking studies with the photoactivatable cholesterol analog FCBP and by isothermal titration calorimetry with free cholesterol, which showed that L-FABP bound only one sterol molecule per L-FABP molecule. In contrast, the hepatic phenotype of male, but not female, L-FABP(-/-) mice was characterized by decreased hepatic triacylglycerol levels at all backcross generations examined. Taken together, these data support the hypothesis that L-FABP plays a role in physiological regulation of not only hepatic fatty acid metabolism, but also that of hepatic cholesterol.

Specific role for acyl CoA:Diacylglycerol acyltransferase 1 (Dgat1) in hepatic steatosis due to exogenous fatty acids

Nonalcoholic fatty liver disease, characterized by the accumulation of triacylglycerols (TGs) and other lipids in the liver, often accompanies obesity and is a risk factor for nonalcoholic steatohepatitis and fibrosis. To treat or prevent fatty liver, a thorough understanding of hepatic fatty acid and TG metabolism is crucial. To investigate the role of acyl CoA:diacylglycerol acyltransferase 1 (DGAT1), a key enzyme of TG synthesis, in fatty liver development, we studied mice with global and liver-specific knockout of Dgat1. DGAT1 was required for hepatic steatosis induced by a high-fat diet and prolonged fasting, which are both characterized by delivery of exogenous fatty acids to the liver. Studies in primary hepatocytes showed that DGAT1 deficiency protected against hepatic steatosis by reducing synthesis and increasing the oxidation of fatty acids. In contrast, lipodystrophy (aP2-SREBP-1c436) and liver X receptor activation (T0901317), which increase de novo fatty acid synthesis in liver, caused steatosis independently of DGAT1. Pharmacologic inhibition of Dgat1 with antisense oligonucleotides protected against fatty liver induced by a high-fat diet.

CONCLUSION

Our findings identify a specific role for hepatic DGAT1 in esterification of exogenous fatty acids and indicate that DGAT1 contributes to hepatic steatosis induced by this mechanism.

Differential expression of lumican and fatty acid binding protein-1: new insights into the histologic spectrum of nonalcoholic fatty liver disease

The basis of hepatocellular injury and progressive fibrosis in a subset of patients with nonalcoholic fatty liver disease (NAFLD) is poorly understood. We sought to identify hepatic proteins that are differentially abundant across the histologic spectrum of NAFLD. Hepatic protein abundance was measured in liver samples from four groups (n = 10 each) of obese (body mass index >30 kg/m(2)) patients: (1) obese normal group (normal liver histology), (2) simple steatosis (SS), (3) nonalcoholic steatohepatitis (NASH)-mild (steatohepatitis with fibrosis stage 0-1), and (4) NASH-progressive (steatohepatitis with fibrosis stage 2-4). Hepatic peptides were analyzed on an API Qstar XL quadrupole time-of-flight mass spectrometer using Analyst QS software. Linear trends tests were performed and used to screen for differential abundance. Nine known proteins were expressed with differential abundance between study groups. For seven proteins differential abundance is likely to have been on the basis increased hepatic lipid content and/or inflammation. Lumican, a 40-kDa keratin sulfate proteoglycan that regulates collagen fibril assembly and activates transforming growth factor-beta and smooth muscle actin, was expressed similarly in obese normal and SS but was overexpressed in a progressive manner in NASH-mild versus SS (124%, P < 0.001), NASH-progressive versus NASH-mild (156%, P < 0.001) and NASH-progressive versus obese normal (178%, P < 0.001). Fatty acid binding protein-1 (FABP-1), which is protective against the detergent effects of excess free fatty acids, facilitates intracellular free fatty acid transport and is an important ligand for peroxisome proliferator-activated receptor-mediated transcription, was overexpressed in SS when compared to the obese normal group (128%, P < 0.001), but was paradoxically underexpressed in NASH-mild versus SS (73%, P < 0.001), NASH-progressive versus NASH-mild (81%, P < 0.001), and NASH-progressive versus obese normal (59%, P < 0.001).

CONCLUSION

Histologically progressive NAFLD is associated with overexpression of lumican, an important mediator of fibrosis in nonhepatic tissues, whereas FABP-1 is paradoxically underexpressed in NASH, suggesting a new potential mechanism of lipotoxicity in NAFLD. Further studies are needed to determine the biologic basis of lumican and/or FABP-1 dysregulation in NAFLD.

Increased susceptibility to diet-induced gallstones in liver fatty acid binding protein knockout mice

Quantitative trait mapping identified a locus colocalizing with L-Fabp, encoding liver fatty acid binding protein, as a positional candidate for murine gallstone susceptibility. When fed a lithogenic diet (LD) for 2 weeks, L-Fabp(-/-) mice became hypercholesterolemic with increased hepatic VLDL cholesterol secretion. Seventy-five percent of L-Fabp(-/-) mice developed solid gallstones compared with 6% of wild-type mice with an increased gallstone score (3.29 versus 0.62, respectively; P < 0.01). Hepatic free cholesterol content, biliary cholesterol secretion, and the cholesterol saturation index of hepatic bile were increased in LD-fed L-Fabp(-/-) mice. Chow-fed L-Fabp(-/-) mice demonstrated increased fecal bile acid (BA) excretion accompanied by decreased ileal Asbt expression. By contrast, there was an increased BA pool and decreased fecal BA excretion in LD-fed L-Fabp(-/-) mice, associated with increased proximal intestinal Asbt mRNA expression, suggesting that intestinal BA absorption was enhanced in LD-fed L-Fabp(-/-) mice. The increase in biliary BA secretion and enterohepatic pool size in LD-fed L-Fabp(-/-) mice was accompanied by downregulation of Cyp7a1 mRNA and increased intestinal mRNA abundance of Fgf-15, Fxr, and Fabp6. These findings suggest that changes in hepatic cholesterol metabolism and biliary lipid secretion as well as changes in enterohepatic BA metabolism increase gallstone susceptibility in LD fed L-Fabp(-/-) mice.

Diet-induced alterations in intestinal and extrahepatic lipid metabolism in liver fatty acid binding protein knockout mice

Liver fatty acid binding protein (L-FABP) is highly expressed in both enterocytes and hepatocytes and binds multiple ligands, including saturated (SFA), unsaturated fatty acids (PUFA), and cholesterol. L-fabp (-/-) mice were protected against obesity and hepatic steatosis on a high saturated fat (SF), high cholesterol "Western" diet and manifested a similar phenotype when fed with a high SF, low cholesterol diet. There were no significant differences in fecal fat content or food consumption between the genotypes, and fatty acid (FA) oxidation was reduced, rather than increased, in SF-fed L-fabp (-/-) mice as evidenced by decreased heat production and serum ketones. In contrast to mice fed with a SF diet, L-fabp (-/-) mice fed with a high PUFA diet were not protected against obesity and hepatic steatosis. These observations together suggest that L-fabp (-/-) mice exhibit a specific defect in the metabolism of SFA, possibly reflecting altered kinetics of FA utilization. In support of this possibility, microarray analysis of muscle from Western diet-fed mice revealed alterations in genes regulating glucose uptake and FA synthesis. In addition, intestinal cholesterol absorption was decreased in L-fabp (-/-) mice. On the other hand, and in striking contrast to other reports, female L-fabp (-/-) mice fed with low fat, high cholesterol diets gained slightly less weight than control mice, with minor reductions in hepatic triglyceride content. Together these data indicate a role for L-FABP in intestinal trafficking of both SFA and cholesterol.