Empagliflozin Ameliorates Free Fatty Acid Induced-Lipotoxicity in Renal Proximal Tubular Cells via the PPARγ/CD36 Pathway in Obese Mice.

High serum levels of free fatty acids (FFAs) could contribute to obesity-induced nephropathy. CD36, a class B scavenger receptor, is a major receptor mediating FFA uptake in renal proximal tubular cells. Empagliflozin, a new anti-diabetic agent, is a specific inhibitor of sodium-glucose co-transporter 2 channels presented on renal proximal tubular cells and inhibits glucose reabsorption. In addition, empagliflozin has shown renoprotective effects. However, the mechanism through which empagliflozin regulates CD36 expression and attenuates FFA-induced lipotoxicity remains unclear. Herein, we aimed to elucidate the crosstalk between empagliflozin and CD36 in FFA-induced renal injury. C57BL/6 mice fed a high-fat diet (HFD) and palmitic acid-treated HK-2 renal tubular cells were used for in vivo and in vitro assessments. Empagliflozin attenuated HFD-induced body weight gain, insulin resistance, and inflammation in mice. In HFD-fed mice, CD36 was upregulated in the tubular area of the kidney, whereas empagliflozin attenuated CD36 expression. Furthermore, empagliflozin downregulated the expression of peroxisome proliferator-activated receptor (PPAR)-γ. Treatment with a PPARγ inhibitor (GW9662) did not further decrease PPARγ expression, whereas a PPARγ antagonist reversed this effect; this suggested that empagliflozin may, at least partly, decrease CD36 by modulating PPARγ. In conclusion, empagliflozin can ameliorate FFA-induced renal tubular injury via the PPARγ/CD36 pathway.

KLF15-activating Twist2 ameliorated hepatic steatosis by inhibiting inflammation and improving mitochondrial dysfunction via NF-κB-FGF21 or SREBP1c-FGF21 pathway.

Twist-related protein 2 (TWIST2) is identified as a basic helix-loop-helix (b-HLH) transcription repressor by dimerizing with other b-HLH proteins. The significance of TWIST2 has been emphasized in various tumors; however, few studies report its functions in metabolism and metabolic diseases. Here we aimed to explore the novel role and regulation mechanism of TWIST2 in hepatic steatosis. Our results showed that Twist2 knockdown caused mice obesity, insulin resistance, and hepatic steatosis, which were accompanied with inflammation, endoplasmic reticulum stress, and mitochondrial dysfunction. In vitro, TWIST2 overexpression ameliorated hepatocellular steatosis, inhibited inflammation, and improved mitochondrial content and function with a fibroblast growth factor 21 (FGF21)-dependent pattern. NF-κB negatively regulated FGF21 transcription by directly binding to FGF21 promoter DNA, which was eliminated by TWIST2 overexpression by inhibiting NF-κB expression and translocation to nucleus. TWIST2 overexpression decreased intracellular reactive oxygen species level, increased mitochondrial DNA and biogenesis, and enhanced ATP production and antioxidation ability. Additionally, TWIST2 expression was repressed by insulin-targeting sterol regulatory element-binding protein 1c (SREBP1c) and forkhead box protein O1 and was enhanced by dexamethasone targeting Krüppel-like factor 15, which directly interacted with Twist2 promoter DNA. Together, our studies identify an important role and regulation mechanism of TWIST2 in maintaining hepatic homeostasis by ameliorating steatosis, inflammation, and oxidative stress via the NF-κB-FGF21 or SREBP1c-FGF21 pathway, which may provide a new therapeutic scheme for nonalcoholic fatty liver disease.-Zhou, L., Li, Q., Chen, A., Liu, N., Chen, N., Chen, X., Zhu, L., Xia, B., Gong, Y., Chen, X. KLF15-activating Twist2 ameliorated hepatic steatosis by inhibiting inflammation and improving mitochondrial dysfunction via NF-κB-FGF21 or SREBP1c-FGF21 pathway.

Mitochondrial membrane protein mitofusin 2 as a potential therapeutic target for treating free fatty acid-induced hepatic inflammation in dairy cows during early lactation.

Inflammation is critical in the progression from benign hepatic lipidosis to pathological hepatic steatosis. The objective of this study was to examine the potential role of the outer mitochondrial membrane protein mitofusin 2 (MFN2) in the etiology of hepatic steatosis in dairy cows during early lactation. Using a nested case-control design, we compared blood and liver samples from 10 healthy cows and 10 age-matched cows with moderate fatty liver. Cows with moderate fatty liver had high liver triacylglycerols, elevated plasma concentrations of free fatty acids (FFA) and ß-hydroxybutyrate, and low concentrations of glucose. Cows with moderate fatty liver had overactivated inflammatory pathways in the liver, as indicated by increased abundance of phosphorylated nuclear factor κB (NF-κB) p65, NLR family pyrin domain containing 3 (NLRP3) and caspase-1 inflammasome protein, and elevated plasma concentrations and hepatic mRNA abundance of their molecular targets IL-1ß, IL-6, and tumor necrosis factor α (TNF-α). In the cell culture model, we were able to replicate our findings in cows with moderate fatty liver: 1.2 mM exogenous FFA decreased the abundance of MFN2 and upregulated phosphorylation levels of the inhibitor of NF-κB (IκB) α and NF-κB p65, the IκB kinase ß activity, and the abundance of NLRP3, caspase-1, IL-1ß, IL-6, and TNF-α. Whereas MFN2 knockdown potentiated the FFA-induced activation of these inflammatory pathways, overexpression of MFN2 attenuated the detrimental effect of excess exogenous FFA by improving mitochondrial function and decreasing the release of reactive oxygen species, suggesting that MFN2 may be a potential therapeutic target for FFA-induced hepatic inflammation in dairy cows during early lactation.

A Protective Role for Triacylglycerols during Apoptosis.

Triacylglycerols (TAGs) are one of the major constituents of the glycerolipid family. Their main role in cells is to store excess fatty acids, and they are mostly found within lipid droplets. TAGs contain acyl chains that vary in length and degree of unsaturation, resulting in hundreds of chemically distinct species. We have previously reported that TAGs containing polyunsaturated fatty acyl chains (PUFA-TAGs) accumulate via activation of diacylglycerol acyltransferases during apoptosis. In this work, we show that accumulation of PUFA-TAGs is a general phenomenon during this process. We further show that the accumulated PUFA-TAGs are stored in lipid droplets. Because membrane-residing PUFA phospholipids can undergo oxidation and form reactive species under increased levels of oxidative stress, we hypothesized that incorporation of PUFAs into PUFA-TAGs and their localization within lipid droplets during apoptosis limit the toxicity during this process. Indeed, exogenous delivery of a polyunsaturated fatty acid resulted in a profound accumulation of PUFA phospholipids and rendered cells more sensitive to oxidative stress, causing reduced viability. Overall, our results support the concept that activation of TAG biosynthesis protects cells from lipid peroxide-induced membrane damage under increased levels of oxidative stress during apoptosis. As such, targeting triacylglycerol biosynthesis in cancer cells might represent a new approach to promoting cell death during apoptosis.

NEFA-induced ROS impaired insulin signalling through the JNK and p38MAPK pathways in non-alcoholic steatohepatitis.

The aim of this study was to investigate the changes in hepatic oxidative phosphorylation (OXPHOS) complexes (COs) in patients and cows with non-alcoholic steatohepatitis (NASH) and to investigate the mechanism that links mitochondrial dysfunction and hepatic insulin resistance induced by non-esterified fatty acids (NEFAs). Patients and cows with NASH displayed high blood NEFAs, TNF-α and IL-6 concentrations, mitochondrial dysfunction and insulin resistance. The protein levels of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), mitofusin-2 (Mfn-2) and OXPHOS complexes (human: COI and COIII; cow: COI-IV) were significantly decreased in patients and cows with NASH. NEFA treatment significantly impaired mitochondrial function and, increased reactive oxygen species (ROS) production, and excessive ROS overactivated the JNK and p38MAPK pathways and induced insulin resistance in cow hepatocytes. PGC-1α and Mfn-2 overexpression significantly decreased the NEFA-induced ROS production and TNF-α and IL-6 mRNA expressions, reversed the inhibitory effect of NEFAs on mitochondrial function and attenuated the overactivation of the ROS-JNK/p38MAPK pathway, alleviated insulin resistance induced by NEFAs in cow hepatocytes and HepG2 cells. These findings indicate that NEFAs induce mitochondrial dysfunction and insulin resistance mediated by the ROS-JNK/p38MAPK pathway. PGC-1α or Mfn-2 overexpression reversed the lipotoxicity of NEFAs on mitochondrial dysfunction and insulin resistance. Our study clarified the mechanism that links hepatic mitochondrial dysfunction and insulin resistance in NASH.

The stress-regulatory transcription factors Msn2 and Msn4 regulate fatty acid oxidation in budding yeast.

The transcription factors Msn2 and Msn4 (multicopy suppressor of SNF1 mutation proteins 2 and 4) bind the stress-response element in gene promoters in the yeast Saccharomyces cerevisiae However, the roles of Msn2/4 in primary metabolic pathways such as fatty acid ß-oxidation are unclear. Here, in silico analysis revealed that the promoters of most genes involved in the biogenesis, function, and regulation of the peroxisome contain Msn2/4-binding sites. We also found that transcript levels of MSN2/MSN4 are increased in glucose-depletion conditions and that during growth in nonpreferred carbon sources, Msn2 is constantly localized to the nucleus in wild-type cells. Of note, the double mutant msn2Δmsn4Δ exhibited a severe growth defect when grown with oleic acid as the sole carbon source and had reduced transcript levels of major ß-oxidation genes. ChIP indicated that Msn2 has increased occupancy on the promoters of ß-oxidation genes in glucose-depleted conditions, and in vivo reporter gene analysis indicated reduced expression of these genes in msn2Δmsn4Δ cells. Moreover, mobility shift assays revealed that Msn4 binds ß-oxidation gene promoters. Immunofluorescence microscopy with anti-peroxisome membrane protein antibodies disclosed that the msn2Δmsn4Δ strain had fewer peroxisomes than the wild type, and lipid analysis indicated that the msn2Δmsn4Δ strain had increased triacylglycerol and steryl ester levels. Collectively, our data suggest that Msn2/Msn4 transcription factors activate expression of the genes involved in fatty acid oxidation. Because glucose sensing, signaling, and fatty acid ß-oxidation pathways are evolutionarily conserved throughout eukaryotes, the msn2Δmsn4Δ strain could therefore be a good model system for further study of these critical processes.

3-Acetyl-oleanolic acid ameliorates non-alcoholic fatty liver disease in high fat diet-treated rats by activating AMPK-related pathways.

3-Acetyl-oleanolic acid (3Ac-OA) is a derivative of oleanolic acid (OA), which has shown therapeutic beneficial effects on diabetes and metabolic syndrome. In this study we investigated whether 3Ac-OA exerted beneficial effect on non-alcoholic fatty liver disease (NAFLD) in rats and its potential underlying mechanisms. Treatment with 3Ac-OA (1-100 µmol/L) dose-dependently decreased the intracellular levels of total cholesterol (TC) and triglyceride (TG) in FFA-treated primary rat hepatocytes and human HepG2 cell lines in vitro. Furthermore, oil red staining studies showed that 3Ac-OA caused dose-dependent decrease in the number of lipid droplets in FFA-treated primary rat hepatocytes. SD rats were fed a high fat diet (HFD) for 6 weeks and subsequently treated with 3Ac-OA (60, 30, 15 mg·kg-1·d-1) for 4 weeks. 3Ac-OA administration significantly decreased the body weight, liver weight and serum TC, TG, LDL-C levels in HFD rats. Furthermore, 3AcOA administration ameliorated lipid accumulation and cell apoptosis in the liver of HFD rats. Using adipokine array analyses, we found that the levels of 11 adipokines (HGF, ICAM, IGF-1, IGFBP-3, IGFBP-5, IGFBP-6, lipocalin-2, MCP-1, M-CSF, Pref-1 and RAGE) were increased by more than twofold in the serum of 3Ac-OA-treated rats, whereas ICAM, IGF-1 and lipocalin-2 had levels increased by more than 20-fold. Moreover, 3Ac-OA administration significantly increased the expression of glucose transporter type 2 (GLUT-2) and low-density lipoprotein receptor (LDLR), as well as the phosphorylation of AMP-activated protein kinase (AMPK), protein kinase B (AKT) and glycogen synthase kinase 3ß (GSK-3ß) in the liver tissues of HFD rats. In conclusion, this study demonstrates that 3Ac-OA exerts a protective effect against hyperlipidemia in NAFLD rats through AMPK-related pathways.

Free fatty acid can induce cardiac dysfunction and alter insulin signaling pathways in the heart.

BACKGROUND: Insulin resistance has been independently related to heart failure. However, the specific mechanisms of high FFA levels in the pathophysiology of heart failure in insulin-resistant states are remain largely unclear. This study investigated whether elevated circulating free fatty acids (FFA) levels result in impaired cardiac structure and function in vivo via insulin-related signaling pathways in myocardium. METHODS: Male Wistar rats were randomly divided into the intralipid group (20% intralipid plus heparin infusion) and the control group (glycerol infusion). Blood samples were collected before and after 6-, 12-, and 24-h infusions. Cardiac structure and function were measured using echocardiography. Maximum velocity of myocardial contraction (+dP/dt max) and diastole (-dP/dt max) were measured using a physiological polygraph in vivo. Heart tissues were collected for western blotting. RESULTS: Compared with the control group, plasma FFA, plasma glucose, and serum insulin levels increased significantly in the intralipid group. With increasing infusion time, cardiac function in the intralipid group decreased gradually compared with the control group. After a 24-h infusion, early (E', cm/s) diastolic peak velocities and (-dP/dt max) decreased significantly. Protein expression of phosphatidylinositol 3-kinase (PI3K), the serine/threonine kinase Akt, and phosphorylated Akt in myocardium increased after a 6-h infusion and decreased significantly after a 24-h infusion in the intralipid group. Protein expression of glucose transporter type 4 (GLUT4), Adenosine 5'-monophosphate -activated protein kinase (AMPK), phosphorylated AMPK(p-AMPK), and endothelial nitric oxide synthase (eNOS) in myocardium gradually decreased in the intralipid group. CONCLUSIONS: Elevated FFA levels may impair cardiac function and cardiac dysfunction might result from myocardial insulin resistance with significant changes to PI3K-Akt-GLUT4 and AMPK-eNOS signaling pathways with increasing FFA levels.

The Transcription Factor p8 Regulates Autophagy in Response to Palmitic Acid Stress via a Mammalian Target of Rapamycin (mTOR)-independent Signaling Pathway.

Autophagy is an evolutionarily conserved degradative process that allows cells to maintain homoeostasis in numerous physiological situations. This process also functions as an essential protective response to endoplasmic reticulum (ER) stress, which promotes the removal and degradation of unfolded proteins. However, little is known regarding the mechanism by which autophagy is initiated and regulated in response to ER stress. In this study, different types of autophagy were identified in human gastric cancer MKN45 cells in response to the stress induced by nutrient starvation or lipotoxicity in which the regulation of these pathways is mammalian target of rapamycin (mTOR)-dependent or -independent, respectively. Interestingly, we found that p8, a stress-inducible transcription factor, was enhanced in MKN45 cells treated with palmitic acid to induce lipotoxicity. Furthermore, an increase in autophagy was observed in MKN45 cells stably overexpressing p8 using a lentivirus system, and autophagy induced by palmitic acid was blocked by p8 RNAi compared with the control. Western blotting analyses showed that autophagy was regulated by p8 or mTOR in response to the protein kinase-like endoplasmic reticulum kinase/activating transcription factor 6-mediated ER stress of lipotoxicity or the parkin-mediated mitochondrial stress of nutrient starvation, respectively. Furthermore, our results indicated that autophagy induced by palmitic acid is mTOR-independent, but this autophagy pathway was regulated by p8 via p53- and PKCα-mediated signaling in MKN45 cells. Our findings provide insights into the role of p8 in regulating autophagy induced by the lipotoxic effects of excess fat accumulation in cells.

A novel method to generate monocyte-derived dendritic cells during coculture with HaCaT facilitates detection of weak contact allergens in cosmetics.

The in vitro sensitization assay LCSA (Loose-fit Coculture-based Sensitization Assay) has proved reliable for the detection of contact sensitizers in the past. However, the coculture of human monocyte-derived dendritic cells (DCs) with primary human keratinocytes (KCs) in serum-free medium is relatively complex compared to other sensitization assays which use continuous cell lines. To facilitate high-throughput screening of chemicals, we replaced KCs with the HaCaT cell line under various culture conditions. Coculture of HaCaT with peripheral blood mononuclear cells in serum-supplemented medium leads to generation of CD1a+/CD1c+ DCs after addition of GM-CSF, IL-4, and TGF-ß1 (as opposed to CD1a-/CD1c- DCs which arise in the "classic" LCSA coculture). These cells resemble monocyte-derived DCs generated in monoculture, but, unlike those, they show a marked upregulation CD86 after treatment with contact allergens. All of the nine sensitizers in this study were correctly identified by CD1a+/CD1c+ DCs in coculture with HaCaT. Among the substances were weak contact allergens such as propylparaben (which is false negative in the local lymph node assay in mice) and resorcinol (which was not detected by CD1a-/CD1c- DCs in the "classic" LCSA). The level of CD86 upregulation on CD1a+/CD1c+ DCs was higher for most allergens compared to CD1a-/CD1c- DCs, thus improving the assay's discriminatory power. Three out of four non-sensitizers were also correctly assessed by the coculture assay. A false-positive reaction to caprylic (octanoic) acid confirms earlier results that some fatty acids are able to induce CD86 on DC in vitro. In conclusion, change of the LCSA protocol led to reduction of time and cost while even increasing the assay's sensitivity and discriminatory power.

Curcumin protects hearts from FFA-induced injury by activating Nrf2 and inactivating NF-κB both in vitro and in vivo.

Obesity and increased free fatty acid (FFA) level are tightly linked, leading to the development of cardiovascular disorders. Curcumin is a natural product from Curcuma longa with multiple bioactivities and is known to have cardioprotective effects in several cellular and animal models. The current study was designed to evaluate the cardioprotective effects of curcumin and demonstrate the underlying mechanism in FFA-induced cardiac injury. Using cell culture studies and high fat in vivo model, we explored the mechanistic basis of anti-inflammatory and antioxidant activities of curcumin. We observed that palmitate (PA) treatment in cardiac derived H9C2 cells induced a marked increase in reactive oxygen species, inflammation, apoptosis and hypertrophy. All of these changes were effectively suppressed by curcumin treatment. In addition, oral administration of curcumin at 50mg/kg completely suppressed high fat diet-induced oxidative stress, inflammation, apoptosis, fibrosis, hypertrophy and tissue remodeling in mice. The beneficial actions of curcumin are closely associated with its ability to increase Nrf2 expression and inhibit NF-κB activation. Thus, both in vitro and in vivo studies showed a promising role of curcumin as a cardioprotective agent against palmitate and high fat diet mediated cardiac dysfunction. We indicated the regulatory roles of Nrf2 and NF-κB in obesity-induced heart injury, and suggested that they may be important therapeutic targets in the treatment of obesity-related disorders.

Lactoferrin attenuates fatty acid-induced lipotoxicity via Akt signaling in hepatocarcinoma cells.

Nonalcoholic fatty liver disease (NAFLD) describes a spectrum of lesions ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). The excess influx of fatty acids (FAs) into the liver is recognized as a main cause of simple steatosis formation and progression to NASH. Recently, administration of lactoferrin (LF), a glycoprotein present in milk, was suggested to prevent NAFLD development. However, the effect of LF on the contribution of FA to NAFLD development remains unclear. In this study, the effects of LF on FA mixture (FAm)-induced lipotoxicity using human hepatocarcinoma G2 cells were assessed. FAm significantly decreased cell viability and increased intracellular lipid accumulation, whereas LF significantly recovered cell viability without affecting lipid accumulation. FAm-induced lactic dehydrogenase (LDH) and caspase-3/7 activities were significantly decreased by LF and SP600125, a c-Jun N-terminal kinase (JNK) specific inhibitor. We also found that LF added to FAm-treated cells induced Akt phosphorylation, which contributed to inhibition of JNK signaling pathway-dependent apoptosis. Akt inhibitor VIII, an allosteric Akt inhibitor, significantly attenuated the effect of LF on LDH activity and abrogated the ones on cell viability and caspase-3/7 activity. In summary, the present study has revealed that LF has a protective effect on FAm-induced lipotoxicity in a HepG2 model of NAFLD and identified the activation of the Akt signaling pathway as a possibly major mechanism.

Saturated free fatty acids induce cholangiocyte lipoapoptosis.

UNLABELLED: Recent studies have identified a cholestatic variant of nonalcoholic fatty liver disease (NAFLD) with portal inflammation and ductular reaction. Based on reports of biliary damage, as well as increased circulating free fatty acids (FFAs) in NAFLD, we hypothesized the involvement of cholangiocyte lipoapoptosis as a mechanism of cellular injury. Here, we demonstrate that the saturated FFAs palmitate and stearate induced robust and rapid cell death in cholangiocytes. Palmitate and stearate induced cholangiocyte lipoapoptosis in a concentration-dependent manner in multiple cholangiocyte-derived cell lines. The mechanism of lipoapoptosis relied on the activation of caspase 3/7 activity. There was also a significant up-regulation of the proapoptotic BH3-containing protein, PUMA. In addition, palmitate-induced cholangiocyte lipoapoptosis involved a time-dependent increase in the nuclear localization of forkhead family of transcription factor 3 (FoxO3). We show evidence for posttranslational modification of FoxO3, including early (6 hours) deacetylation and dephosphorylation that coincide with localization of FoxO3 in the nuclear compartment. By 16 hours, nuclear FoxO3 is both phosphorylated and acetylated. Knockdown studies confirmed that FoxO3 and its downstream target, PUMA, were critical for palmitate- and stearate-induced cholangiocyte lipoapoptosis. Interestingly, cultured cholangiocyte-derived cells did not accumulate appreciable amounts of neutral lipid upon FFA treatment. CONCLUSION: Our data show that the saturated FFAs palmitate and stearate induced cholangiocyte lipoapoptosis by way of caspase activation, nuclear translocation of FoxO3, and increased proapoptotic PUMA expression. These results suggest that cholangiocyte injury may occur through lipoapoptosis in NAFLD and nonalcoholic steatohepatitis patients.

PPAR agonists reduce steatosis in oleic acid-overloaded HepaRG cells.

UNLABELLED: Although non-alcoholic fatty liver disease (NAFLD) is currently the most common form of chronic liver disease there is no pharmacological agent approved for its treatment. Since peroxisome proliferator-activated receptors (PPARs) are closely associated with hepatic lipid metabolism, they seem to play important roles in NAFLD. However, the effects of PPAR agonists on steatosis that is a common pathology associated with NAFLD, remain largely controversial. In this study, the effects of various PPAR agonists, i.e. fenofibrate, bezafibrate, troglitazone, rosiglitazone, muraglitazar and tesaglitazar on oleic acid-induced steatotic HepaRG cells were investigated after a single 24-hour or 2-week repeat treatment. Lipid vesicles stained by Oil-Red O and triglycerides accumulation caused by oleic acid overload, were decreased, by up to 50%, while fatty acid oxidation was induced after 2-week co-treatment with PPAR agonists. The greatest effects on reduction of steatosis were obtained with the dual PPARα/γ agonist muraglitazar. Such improvement of steatosis was associated with up-regulation of genes related to fatty acid oxidation activity and down-regulation of many genes involved in lipogenesis. Moreover, modulation of expression of some nuclear receptor genes, such as FXR, LXRα and CAR, which are potent actors in the control of lipogenesis, was observed and might explain repression of de novo lipogenesis. CONCLUSION: Altogether, our in vitro data on steatotic HepaRG cells treated with PPAR agonists correlated well with clinical investigations, bringing a proof of concept that drug-induced reversal of steatosis in human can be evaluated in in vitro before conducting long-term and costly in vivo studies in animals and patients.

Adiponectin receptor 1 enhances fatty acid metabolism and cell survival in palmitate-treated HepG2 cells through the PI3 K/AKT pathway.

PURPOSES: Hepatic lipid overloading induces lipotoxicity which can cause hepatocyte damage, fibrosis, and eventually progress to cirrhosis, which is associated with nonalcoholic fatty liver disease. Adiponectin receptors play important roles in regulating lipid metabolism. In this study, we used a lentivirus system to overexpress the adiponectin receptor 1 (AdipoR1) in HepG2 cells to define the role of adiponectin and its receptor 1 in the development of fatty liver syndrome. METHODS AND RESULTS: Exposure of human hepatocytes, HepG2 cells, to palmitate (0.2 or 0.4 mM) for 16 h resulted in elevated apoptosis, whereas AdipoR1 decreased the palmitate-induced apoptosis. Transgene AdipoR1 increased the expression of FATP2, acyl-coA oxidase, and carnitine palmitoyltransferase I in palmitate-treated HepG2 cells. The transcript level of acetyl-CoA carboxylase and fatty acid synthase was upregulated by palmitate treatment, while AdipoR1 reversed the effect induced by palmitate. AdipoR1 increased the gene expression of cytochrome C oxidase, peroxisome proliferator-activated receptor α, and decreased the gene expression of PGC1α and AMPKα in HepG2 cells under palmitate treatment. Palmitate suppressed ATP production, while transgene AdipoR1 reversed the decreased ATP production by palmitate. Transgene AdipoR1 enhanced AKT phosphorylation in HepG2 cells both with and without palmitate treatment. When PI3 kinase inhibitor was applied, the protective effect of AdipoR1 was absent, such that palmitate again decreased ATP production while also reducing cell viability. CONCLUSION: AdipoR1 enhances fatty acid metabolism and cell viability in palmitate-treated HepG2 cells partially by activating AKT signaling. Therefore, AdipoR1 has therapeutic potential in the treatment of nonalcoholic fatty liver disease.

Fatty acid composition, physicochemical properties, antioxidant and cytotoxic activity of apple seed oil obtained from apple pomace.

BACKGROUND: Apple pomace is generated in huge quantities in juice-processing industries the world over and continuous efforts are being made for its inclusive utilization. In this study, apple seeds separated from industrial pomace were used for extraction of oil. The fatty acid composition, physicochemical and antioxidant as well as in vitro anticancer properties of extracted oil were studied to assess its suitability in food and therapeutic applications. RESULTS: The fatty acid composition of seed oil revealed the dominance of oleic (46.50%) and linoleic acid (43.81%). It had high iodine (121.8 g I 100 g⁻¹) and saponification value (184.91 mg KOH g⁻¹ oil). The acid value, refractive index and relative density were 4.28 mg KOH g⁻¹, 1.47 and 0.97 mg mL⁻¹, respectively. The antioxidant potential (IC50) of apple seed oil was 40.06 µg mL⁻¹. Cytotoxicity of apple seed oil against CHOK1, SiHa and A549 cancer cell lines ranged between 0.5 ± 0.06% and 88.6 ± 0.3%. CONCLUSION: The physicochemical properties of apple seed oil were comparable with edible food oil, indicating its better stability and broad application in the food and pharmaceutical industries. Apple seed oil could be a good source of natural antioxidants. Also, the in vitro cytotoxic activity against specific cell lines exhibited its potential as an anticancer agent.

[Study of synergistic effect of free fatty acid and iron on the establishment of nonalcoholic fatty liver disease model].

OBJECTIVE: To establish nonalcoholic fatty liver disease (NAFLD) model induced by free fatty acid (FFA) and iron, and to explore the synergistic effect of FFA and Fe(2+) on the pathogenesis of NAFLD and mechanisms. METHODS: Human liver carcinoma cell HepG2 was respectively treated with 0.250, 0.500, 1.000 mmol/L oleic acid, 0.500 mmol/L oleic acid+0.125 mmol/L Fe(2+), 0.500 mmol/L oleic acid+0.250 mmol/L Fe(2+), and 0.500 mmol/L oleic acid+0.500 mmol/L Fe(2+). Human liver carcinoma cell HepG2 was normally cultured in the control group. Lipid accumulation of cells were observed by oil red O staining and the determination of the triglyceride (TG) contents by GPO-PAP, then the expression of key genes involved in fatty acid ß-oxidation (fatty acyl CoA synthetase-1 (ACSL-1), carnitine acyl transferase 1 (CPT-1a), fatty acid synthetase (FAS)) was determined using RT-PCR. The differences of TG content and ACSL-1, CPT-1a, FAS, mRNA relative value were analyzed among different groups. RESULTS: The results of oil red O staining indicated that the contents of lipid droplets were obviously elevated with the increase of Fe(2+) concentration in human liver carcinoma cell HepG2 treated with 0.500 mmol/L oleic acid and different concentrations of Fe(2+). The TG contents of HepG2 cell in control group, 0.250, 0.500, 1.000 mmol/L oleic acid groups, 0.500 mmol/L oleic acid+0.125 mmol/L Fe(2+) group, 0.500 mmol/L oleic acid+0.250 mmol/L Fe(2+) group, 0.500 mmol/L oleic acid+0.500 mmol/L Fe(2+) group respectively were (90.0 ± 1.6), (131.7 ± 5.4), (153.7 ± 3.0), (254.1 ± 4.0), (164.5 ± 6.0), (180.1 ± 7.7), (235.6 ± 4.5) nmol/mg (F = 396.00, P < 0.05). The expression levels of ACSL-1 mRNA in 0.500 mmol/L oleic acid group, 0.500 mmol/L oleic acid+0.125 mmol/L Fe(2+) group, 0.500 mmol/L oleic acid +0.250 mmol/L Fe(2+) group, 0.500 mmol/L oleic acid +0.500 mmol/L Fe(2+) group respectively were (0.94 ± 0.02), (0.89 ± 0.04), (0.85 ± 0.02), (0.74 ± 0.04) (F = 50.00, P < 0.05); the mRNA levels of CPT-1a were (0.89 ± 0.03), (0.79 ± 0.05), (0.67 ± 0.04), (0.51 ± 0.05) (F = 79.00, P < 0.05); the mRNA levels of FAS were (1.31 ± 0.05) , (1.44 ± 0.03), (1.51 ± 0.05), (1.56 ± 0.06 ) (F = 79.70, P < 0.05). CONCLUSION: The NAFLD liver cell model could be established by oleic acid and Fe(2+) in HepG2 cells. FFA and iron might be involved in the pathogenesis of NAFLD through the intervention of fatty acid ß-oxidation.

NADPH oxidase inhibition prevents beta cell dysfunction induced by prolonged elevation of oleate in rodents.

AIMS/HYPOTHESIS: The activation of NADPH oxidase has been implicated in NEFA-induced beta cell dysfunction. However, the causal role of this activation in vivo remains unclear. Here, using rodents, we investigated whether pharmacological or genetic inhibition of NADPH oxidase could prevent NEFA-induced beta cell dysfunction in vivo. METHODS: Normal rats were infused for 48 h with saline or oleate with or without the NADPH oxidase inhibitor apocynin. In addition, NADPH oxidase subunit p47(phox)-null mice and wild-type littermate controls were infused with saline or oleate for 48 h. This was followed by measurement of NADPH oxidase activity, reactive oxygen species (ROS) and superoxide imaging and assessment of beta cell function in isolated islets and hyperglycaemic clamps. RESULTS: Oleate infusion in rats increased NADPH oxidase activity, consistent with increased total but not mitochondrial superoxide in islets and impaired beta cell function in isolated islets and during hyperglycaemic clamps. Co-infusion of apocynin with oleate normalised NADPH oxidase activity and total superoxide levels and prevented beta cell dysfunction. Similarly, 48 h NEFA elevation in wild-type mice increased total but not mitochondrial superoxide and impaired beta cell function in isolated islets. p47(phox)-null mice were protected against these effects when subjected to 48 h oleate infusion. Finally, oleate increased the levels of total ROS, in both models, whereas inhibition of NADPH oxidase prevented this increase, suggesting that NADPH oxidase is the main source of ROS in this model. CONCLUSIONS/INTERPRETATION: These data show that NADPH-oxidase-derived cytosolic superoxide is increased in islets upon oleate infusion in vivo; and whole-body NADPH-oxidase inhibition decreases superoxide in concert with restoration of islet function.

Dihydropyridine calcium channel blockers inhibit non-esterified-fatty-acid-induced endothelial and rheological dysfunction.

Circulating NEFAs (non-esterified fatty acids) from adipose tissue lipolysis lead to endothelial dysfunction and insulin resistance in patients with the metabolic syndrome or Type 2 diabetes mellitus. The aim of the present study was to test the hypothesis that DHP (dihydropyridine) CCBs (calcium channel blockers) prevent NEFA-induced endothelial and haemorheological dysfunction independently of their antihypertensive properties. Using a double-blind cross-over study design, nifedipine, amlodipine, diltiazem or placebo were administered to eight healthy subjects for 2 days before each study day. On the study days, the following were assessed before and after the infusion of lipid and heparin to raise serum NEFAs: endothelial function, by measuring FBF (forearm blood flow) responses to ACh (acetylcholine); leucocyte activation, by ex vivo measurement of plasma MPO (myeloperoxidase) levels, adherent leucocyte numbers and whole blood transit time through microchannels; and oxidative stress, by determining plasma levels of d-ROMs (derivatives of reactive oxygen metabolites). Effects of the CCBs on NF-κB (nuclear factor κB) p65 phospholylation stimulated by NEFAs were assessed in cultured monocytic cells in vitro. Elevated NEFAs reduced the responses to ACh and significantly increased whole blood transit time, adherent leucocyte numbers and d-ROMs. Nifedipine and amlodipine, but not diltiazem, prevented NEFA-induced endothelial dysfunction, leucocyte activation and enhancement of oxidative stress without affecting BP (blood pressure), whereas all these drugs prevented NEFA-induced p65 activation in vitro. These results suggest that DHP CCBs, independent of their antihypertensive properties in humans, prevent NEFA-induced endothelial and haemorheological dysfunction through inhibition of NEFA-induced leucocyte activation, although the sensitivity to drugs of leucocyte Ca2+ channels may differ among cells.

Examining acute and chronic effects of short- and long-chain fatty acids on peptide YY (PYY) gene expression, cellular storage and secretion in STC-1 cells.

PURPOSE: Peptide YY (PYY) is a gastrointestinal hormone with physiological actions regulating appetite and energy homoeostasis. The cellular mechanisms by which nutrients stimulate PYY secretion from intestinal enteroendocrine cells are still being elucidated. METHODS: This study comprehensively evaluated the suitability of intestinal STC-1 cells as an in vitro model of PYY secretion. PYY concentrations (both intracellular and in culture media) with other intestinal peptides (CCK, GLP-1 and GIP) demonstrated that PYY is a prominent product of STC-1 cells. Furthermore, acute and chronic PYY responses to 15 short (SCFAs)- and long-chain (LCFAs) dietary fatty acids were measured alongside parameters for DNA synthesis, cell viability and cytotoxicity. RESULTS: We found STC-1 cells to be reliable secretors of PYY constitutively releasing PYY into cell culture media (but not into non-stimulatory buffer). We demonstrate for the first time that STC-1 cells produce PYY mRNA transcripts; that STC-1 cells produce specific time- and concentration-dependent PYY secretory responses to valeric acid; that linoleic acid and conjugated linoleic acid 9,11 (CLA 9,11) are potent PYY secretagogues; and that chronic exposure of SCFAs and LCFAs can be detrimental to STC-1 cells. CONCLUSIONS: Our studies demonstrate the potential usefulness of STC-1 cells as an in vitro model for investigating nutrient-stimulated PYY secretion in an acute setting. Furthermore, our discovery that CLA directly stimulates L-cells to secrete PYY indicates another possible mechanism contributing to the observed effects of dietary CLA on weight loss.