Palmitic Acid-induced Lipotoxicity Research Articles

Tamoxifen upregulates the peroxisomal β-oxidation enzyme Enoyl CoA hydratase and 3-hydroxyacyl CoA hydratase ameliorating hepatic lipid accumulation in mice

Tamoxifen is an estrogen receptor modulator that has been reported to alleviate hepatic lipid accumulation in mice, but the mechanism is still unclear. Peroxisome fatty acid β-oxidation is the main metabolic pathway for the overload of long-chain fatty acids. As long-chain fatty acids are a cause of hepatic lipid accumulation, the activation of peroxisome fatty acid β-oxidation might be a novel therapeutic strategy for metabolic associated fatty liver disease. In this study, we investigated the mechanism of tamoxifen against hepatic lipid accumulation based on the activation of peroxisome fatty acid β-oxidation. Tamoxifen reduced liver long-chain fatty acids and relieved hepatic lipid accumulation in high fat diet mice without sex difference. In vitro, tamoxifen protected primary hepatocytes against palmitic acid-induced lipotoxicity. Mechanistically, the RNA-sequence of hepatocytes isolated from the liver revealed that peroxisome fatty acid β-oxidation was activated by tamoxifen. Protein and mRNA expression of enoyl CoA hydratase and 3-hydroxyacyl CoA hydratase were significantly increased in vivo and in vitro. Small interfering RNA enoyl CoA hydratase and 3-hydroxyacyl CoA hydratase in primary hepatocytes abolished the therapeutic effects of tamoxifen in lipid accumulation. In conclusion, our results indicated that tamoxifen could relieve hepatic lipid accumulation in high fat diet mice based on the activation of enoyl CoA hydratase and 3-hydroxyacyl CoA hydratase-mediated peroxisome fatty acids β-oxidation.

Hesperidin Protects Against High-Fat Diet-Induced Lipotoxicity in Rats by Inhibiting Pyroptosis.

It is currently thought that excess fatty acid-induced lipotoxicity in hepatocytes is a critical initiator in the development of nonalcoholic fatty liver disease (NAFLD). Lipotoxicity can induce hepatocyte death; thus, reducing lipotoxicity is one of the most effective therapeutic methods to combat NAFLD. Abundant evidence has shown that hesperidin (HSP), a type of flavanone mainly found in citrus fruits, is able to ameliorate NAFLD, but the molecular mechanisms are unclear. We previously reported that pyroptosis contributed to NAFLD development and that inhibiting pyroptosis contributed to blunting the progression of NAFLD in rat models. Therefore, we questioned whether HSP could contribute to ameliorating NAFLD by modulating pyroptosis. In this study, a high-fat diet (HFD) induced dyslipidemia and hepatic lipotoxicity in rats, and HSP supplementation ameliorated dyslipidemia and insulin resistance. In addition, the HFD also caused pyroptosis in the liver and pancreas, while HSP supplementation ameliorated pyroptosis. In vitro, we found that HSP ameliorated palmitic acid-induced lipotoxicity and pyroptosis in HepG2 and INS-1E cells. In conclusion, we showed for the first time that HSP has a protective effect against liver and pancreas damage in terms of pyroptosis and provides a novel mechanism for the protective effects of HSP on NAFLD.

Pharmacological effects of mTORC1/C2 inhibitor in a preclinical model of NASH progression

Knowledge of the benefits of mTOR inhibition concerning adipogenesis and inflammation has recently encouraged the investigation of a new generation of mTOR inhibitors for non-alcoholic steatohepatitis (NASH). We investigated whether treatment with a specific mTORC1/C2 inhibitor (Ku-0063794; KU) exerted any beneficial impacts on experimentally-induced NASH in vitro and in vivo. The results indicated that KU decreases palmitic acid-induced lipotoxicity in cultivated primary hepatocytes, thus emerging as a successful candidate for testing in an in vivo NASH dietary model, which adopted the intraperitoneal KU dosing route rather than oral application due to its significantly greater bioavailability in mice. The pharmacodynamics experiments commenced with the feeding of male C57BL/6 mice with a high-fat atherogenic western-type diet (WD) for differing intervals over several weeks aimed at inducing various phases of NASH. In addition to the WD, the mice were treated with KU for 3 weeks or 4 months. Acute and chronic KU treatments were observed to be safe at the given concentrations with no toxicity indications in the mice. KU was found to alleviate NASH-related hepatotoxicity, mitochondrial and oxidative stress, and decrease the liver triglyceride content and TNF-α mRNA in at least one set of in vivo experiments. The KU modulated liver expression of selected metabolic and oxidative stress-related genes depended upon the length and severity of the disease. Although KU failed to completely reverse the histological progression of NASH in the mice, we demonstrated the complexity of mTORC1/C2 signaling regulation and suggest a stratified therapeutic management approach throughout the disease course.

High glucose-induced endothelial STING activation inhibits diabetic wound healing through impairment of angiogenesis

Chronic hyperglycemia-induced impairment of angiogenesis is important in diabetic foot ulcer (DFU). Additionally, the stimulator of interferon gene (STING), which is a key protein in innate immunity, mediates palmitic acid-induced lipotoxicity in metabolic diseases through oxidative stress-induced STING activation. However, the role of STING in DFU is unknown. In this study, we established a DFU mouse model with streptozotocin (STZ) injection and found that the expression of STING was significantly increased in the vascular endothelial cells of wound tissues from diabetic patients and in the STZ-induced diabetic mouse model. We further established high glucose (HG)-induced endothelial dysfunction with rat vascular endothelial cells and found that the expression of STING was also increased by high-glucose treatment. Moreover, the STING inhibitor, C176, promoted diabetic wound healing, whereas the STING activator, DMXAA, inhibited diabetic wound healing. Consistently, STING inhibition reversed the HG-induced reduction of CD31 and vascular endothelial growth factor (VEGF), inhibited apoptosis, and promoted migration of endothelial cells. Notably, DMXAA treatment alone was sufficient to induce endothelial cell dysfunction as a high-glucose treatment. Mechanistically, STING mediated HG-induced vascular endothelial cell dysfunction by activating the interferon regulatory factor 3/nuclear factor kappa B pathway. In conclusion, our study reveals an endothelial STING activation-mediated molecular mechanism in the pathogenesis of DFU and identifies STING as a novel potential therapeutic target for DFU.

Ameliorative effect of Fructus Gardeniae against lipotoxicity associated hepatocytes injury through activating Nrf2 signaling pathway

Fructus Gardeniae (FG) is the dried ripe fruit of Gardenia jasminoides Ellis, having beneficial effects for human health. In this study, we discovered that the most relevant pathway influenced by Fructus Gardeniae extract (FGE) is lipid metabolism according to the analysis of network pharmacology. Furthermore, the protective effect of FGE against palmitic acid-induced lipotoxicity was investigated. In L02 cells, FGE significantly promoted cellular proliferation after being treated with palmitic acid, and reduced the accumulation of lipid droplets and triglyceride level. Palmitic acid led to an increase of ROS content, which was reduced by FGE. Additionally, FGE could facilitate Nrf2 localized to nuclear and followed by activating its downstream targets. ML385 (a Nrf2 inhibitor) treatment further proved that FGE attenuated lipotoxicity through regulating Nrf2/ARE pathway. Consequently, we demonstrated for the first time FGE could be regarded as potential functional food materials for hepatic protection.

Tranilast protects pancreatic β-cells from palmitic acid-induced lipotoxicity via FoxO-1 inhibition

Tranilast, an anti-allergic drug used in the treatment of bronchial asthma, was identified as an inhibitor of the transcription factor Forkhead box O-1 (FoxO-1) by high throughput chemical library screening in the present study. Based on FoxO-1’s role in apoptotic cell death and differentiation, we examined the effect of tranilast on palmitic acid (PA)-induced cell damage in INS-1 cells. Tranilast substantially inhibited lipoapoptosis and restored glucose-stimulated insulin secretion under high PA exposure. Moreover, PA-mediated downregulation of PDX-1, MafA, and insulin expression was attenuated by tranilast. PA-induced oxidative and ER stress were also reduced in the presence of tranilast. These protective effects were accompanied by increased phosphorylation and decreased nuclear translocation of FoxO-1. Conversely, the effects of tranilast were diminished when treated in transfected cells with FoxO-1 phosphorylation mutant (S256A), suggesting that the tranilast-mediated effects are associated with inactivation of FoxO-1. Examination of the in vivo effects of tranilast using wild type and diabetic db/db mice showed improved glucose tolerance along with FoxO-1 inactivation in the pancreas of the tranilast-treated groups. Thus, we report here that tranilast has protective effects against PA-induced lipotoxic stress in INS-1 cells, at least partly, via FoxO-1 inactivation, which results in improved glucose tolerance in vivo.

Mechanism of GLP-1 Receptor Agonists-Mediated Attenuation of Palmitic Acid-Induced Lipotoxicity in L6 Myoblasts.

Cells were divided into 5 groups-control, high-fat, 10 nmol/L LR + 0.6 mmol/L palmitic acid (PA) (10LR), 100 nmol/L LR + 0.6 mmol/L PA (100LR), and 1000 nmol/L LR + 0.6 mmol/L PA (1000LR). CCK-8 method to detect cell viability, GPO-PAP enzymatic method to detect intracellular triglyceride content, and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and western blotting methods to detect fatty acid translocase CD36 (FAT/CD36) and fatty acid binding protein 4 (FABP4) in L6 cells, glucose-regulated protein 78 (GRP78), glucose transporter 4 (GLUT4) expression at the mRNA and protein levels, respectively, were performed. We found that after PA intervention for 24 h, the cell viability decreased significantly; the cell viability of the LR group was higher than that of the high-fat group (P < 0.01). After PA intervention, compared with those in the high-fat group, GRP-78, FAT/CD36, FABP4 mRNA ((4.36 ± 0.32 vs. 8.15 ± 0.35); (1.00 ± 0.04 vs. 2.46 ± 0.08); (2.88 ± 0.55 vs. 8.29 ± 0.52), P < 0.01) and protein ((3338.13 ± 333.15 vs. 4963.98 ± 277.29); (1978.85 ± 124.24 vs. 2676.07 ± 100.64); (3372.00 ± 219.84 vs. 6083.20 ± 284.70), both P < 0.01) expression decreased in the LR group. The expression levels of GLUT4 mRNA ((0.75 ± 0.04 vs. 0.34 ± 0.03), P < 0.01) and protein ((3443.71 ± 191.89 vs. 2137.79 ± 118.75), P < 0.01) increased. Therefore, we conclude that LR can reverse PA-induced cell inactivation and lipid deposition, which may be related to the change in GRP-78, FAT/CD36, FABP4, GLUT4, and other factors.

Tibolone Pre-Treatment Ameliorates the Dysregulation of Protein Translation and Transport Generated by Palmitic Acid-Induced Lipotoxicity in Human Astrocytes: A Label-Free MS-Based Proteomics and Network Analysis.

Excessive accumulation and release of fatty acids (FAs) in adipose and non-adipose tissue are characteristic of obesity and are associated with the leading causes of death worldwide. Chronic exposure to high concentrations of FAs such as palmitic acid (pal) is a risk factor for developing different neurodegenerative diseases (NDs) through several mechanisms. In the brain, astrocytic dysregulation plays an essential role in detrimental processes like metabolic inflammatory state, oxidative stress, endoplasmic reticulum stress, and autophagy impairment. Evidence shows that tibolone, a synthetic steroid, induces neuroprotective effects, but its molecular mechanisms upon exposure to pal remain largely unknown. Due to the capacity of identifying changes in the whole data-set of proteins and their interaction allowing a deeper understanding, we used a proteomic approach on normal human astrocytes under supraphysiological levels of pal as a model to induce cytotoxicity, finding changes of expression in proteins related to translation, transport, autophagy, and apoptosis. Additionally, tibolone pre-treatment showed protective effects by restoring those same pal-altered processes and increasing the expression of proteins from cell survival processes. Interestingly, ARF3 and IPO7 were identified as relevant proteins, presenting a high weight in the protein-protein interaction network and significant differences in expression levels. These proteins are related to transport and translation processes, and their expression was restored by tibolone. This work suggests that the damage caused by pal in astrocytes simultaneously involves different mechanisms that the tibolone can partially revert, making tibolone interesting for further research to understand how to modulate these damages.

Multi-Omics Integrative Analysis Coupled to Control Theory and Computational Simulation of a Genome-Scale metabolic Model Reveal Controlling Biological Switches in Human Astrocytes Under Palmitic Acid-Induced Lipotoxicity

Astrocytes play an important role in various processes in the brain, including pathological conditions such as neurodegenerative diseases. Recent studies have shown that the increase in saturated fatty acids such as palmitic acid (PA) triggers pro-inflammatory pathways in the brain. The use of synthetic neurosteroids such as tibolone has demonstrated neuro-protective mechanisms. However, broad studies, with a systemic point of view on the neurodegenerative role of PA and the neuro-protective mechanisms of tibolone are lacking. In this study, we performed the integration of multi-omic data (transcriptome and proteome) into a human astrocyte genomic scale metabolic model to study the astrocytic response during palmitate treatment. We evaluated metabolic fluxes in three scenarios (healthy, induced inflammation by PA, and tibolone treatment under PA inflammation). We also applied a control theory approach to identify those reactions that exert more control in the astrocytic system. Our results suggest that PA generates a modulation of central and secondary metabolism, showing a switch in energy source use through inhibition of folate cycle and fatty acid β-oxidation and upregulation of ketone bodies formation. We found 25 metabolic switches under PA-mediated cellular regulation, 9 of which were critical only in the inflammatory scenario but not in the protective tibolone one. Within these reactions, inhibitory, total, and directional coupling profiles were key findings, playing a fundamental role in the (de)regulation in metabolic pathways that may increase neurotoxicity and represent potential treatment targets. Finally, the overall framework of our approach facilitates the understanding of complex metabolic regulation, and it can be used for in silico exploration of the mechanisms of astrocytic cell regulation, directing a more complex future experimental work in neurodegenerative diseases.

Astragalin Inhibits Insulin Resistance and Oxidative Stress in Palmitic Acid-Induced HEPG2 Cells

Insulin resistance is an element of metabolic syndrome, manifested as a decrease in glucose uptake, which often leads to a variety of complications, including type 2 diabetes. Astragalin is a natural flavonoid, isolated from traditional medicinal plants, such as Cuscuta chinensis, that has been shown to exhibit a variety of pharmacological activities with anti-inflammatory, antioxidant, neuroprotective, cardioprotective, antiobesity, antiosteoporotic, anticancer, antiulcer, and antidiabetic properties. However, the mechanism of astragalin on insulin resistance has not yet been elucidated. To this end, we examined the effect of astragalin on palmitic acid-induced insulin resistance in HepG2 cells. The effects of the co-incubation of PA and astragalin on the cell viability, superoxide dismutase, fat content, and markers of oxidative stress in HepG2 cells were measured. The results show that astragalin restored the cell viability, reduced oxidative stress, and insulin resistance in palmitic acid treated HepG2 cells. The protective effect of astragalin on palmitic acid-induced lipotoxicity in HepG2 cells was through inhibition of NF-was through inhibition of NF-κ and JNK signaling pathways.

Empagliflozin-Enhanced Antioxidant Defense Attenuates Lipotoxicity and Protects Hepatocytes by Promoting FoxO3a- and Nrf2-Mediated Nuclear Translocation via the CAMKK2/AMPK Pathway.

Lipotoxicity is an important factor in the development and progression of nonalcoholic steatohepatitis. Excessive accumulation of saturated fatty acids can increase the substrates of the mitochondrial electron transport chain in hepatocytes and cause the generation of reactive oxygen species, resulting in oxidative stress, mitochondrial dysfunction, loss of mitochondrial membrane potential, impaired triphosphate (ATP) production, and fracture and fragmentation of mitochondria, which ultimately leads to hepatocellular inflammatory injuries, apoptosis, and necrosis. In this study, we systematically investigated the effects and molecular mechanisms of empagliflozin on lipotoxicity in palmitic acid-treated LO2 cell lines. We found that empagliflozin protected hepatocytes and inhibited palmitic acid-induced lipotoxicity by reducing oxidative stress, improving mitochondrial functions, and attenuating apoptosis and inflammation responses. The mechanistic study indicated that empagliflozin significantly activated adenosine 5’-monophosphate (AMP)-activated protein kinase alpha (AMPKα) through Calcium/Calmodulin dependent protein kinase kinase beta (CAMKK2) instead of liver kinase B1 (LKB1) or TGF-beta activated kinase (TAK1). The activation of empagliflozin on AMPKα not only promoted FoxO3a phosphorylation and thus forkhead box O 3a (FoxO3a) nuclear translocation, but also promoted Nrf2 nuclear translocation. Furthermore, empagliflozin significantly upregulated the expressions of antioxidant enzymes superoxide dismutase (SOD) and HO-1. In addition, empagliflozin did not attenuate lipid accumulation at all. These results indicated that empagliflozin mitigated lipotoxicity in saturated fatty acid-induced hepatocytes, likely by promoting antioxidant defense instead of attenuating lipid accumulation through enhanced FoxO3a and Nrf2 nuclear translocation dependent on the CAMKK2/AMPKα pathway. The CAMKK2/AMPKα pathway might serve as a promising target in treatment of lipotoxicity in nonalcoholic steatohepatitis.

Fucoidan and Fucoxanthin Attenuate Hepatic Steatosis and Inflammation of NAFLD through Modulation of Leptin/Adiponectin Axis.

Non-alcoholic fatty liver disease (NAFLD) is the emerging cause of chronic liver disease globally and lack of approved therapies. Here, we investigated the feasibility of combinatorial effects of low molecular weight fucoidan and high stability fucoxanthin (LMF-HSFx) as a therapeutic approach against NAFLD. We evaluated the inhibitory effects of LMF-HSFx or placebo in 42 NAFLD patients for 24 weeks and related mechanism in high fat diet (HFD) mice model and HepaRGTM cell line. We found that LMF-HSFx reduces the relative values of alanine aminotransferase, aspartate aminotransferase, total cholesterol, triglyceride, fasting blood glucose and hemoglobin A1c in NAFLD patients. For lipid metabolism, LMF-HSFx reduces the scores of controlled attenuation parameter (CAP) and increases adiponectin and leptin expression. Interestingly, it reduces liver fibrosis in NAFLD patients, either. The proinflammatory cytokines interleukin (IL)-6 and interferon-γ are reduced in LMF-HSFx group. In HFD mice, LMF-HSFx attenuates hepatic lipotoxicity and modulates adipogenesis. Additionally, LMF-HSFx modulates SIRI-PGC-1 pathway in HepaRG cells under palmitic acid-induced lipotoxicity environment. Here, we describe that LMF-HSFx ameliorated hepatic steatosis, inflammation, fibrosis and insulin resistance in NAFLD patients. LMF-HSFx may modulate leptin-adiponectin axis in adipocytes and hepatocytes, then regulate lipid and glycogen metabolism, decrease insulin resistance and is against NAFLD.

Novel FoxO1 inhibitor, JY-2, ameliorates palmitic acid-induced lipotoxicity and gluconeogenesis in a murine model

Forkhead transcription factor forkhead box O1 (FoxO1) plays an important role in glucose and lipid metabolism, contributing to the pathogenesis of metabolic disorders. This study aimed to discover a novel FoxO1 inhibitor as a potential new anti-diabetic drug candidate, and describes the biological effects of JY-2, 5-(2,4-dichlorophenyl)-3-(pyridin-2-yl)-1,2,4-oxadiazole in vitro and in vivo. JY-2 inhibited FoxO1 transcriptional activity in a concentration-dependent manner, with an IC50 value of 22 μM. The inhibitory effects of JY-2 on FoxO3a and FoxO4 appeared to be weaker than that on FoxO1. Consistent with its inhibitory effect on FoxO1, JY-2 reduced the palmitic acid (PA)-stimulated mRNA expression of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), two key enzymes involved in gluconeogenesis in HepG2 cells. In association with the reduced expression of lipid metabolism genes, triglyceride accumulation was also reduced by JY-2, as determined by Oil Red O staining. In addition, JY-2 restored PA-impaired glucose-stimulated insulin secretion (GSIS), in conjunction with an increased mRNA expression of PDX1, MafA, and insulin in INS-1 cells. The in vivo efficacy of JY-2 was examined using C57BL/6J, db/db, and high fat-diet induced obese and diabetic (DIO) mice models, and showed that JY-2 improved glucose tolerance, in parallel with a reduced mRNA expression of gluconeogenic genes. Pharmacokinetic analysis revealed that JY-2 exhibited excellent oral bioavailability (98%), with little adverse effects. These results demonstrated that the novel FoxO1 inhibitor, JY-2, may exert beneficial anti-diabetic effects and that it warrants further investigation as a novel anti-diabetic drug candidate.

Plants of the Spontaneous Flora with Beneficial Action in the Management of Diabetes, Hepatic Disorders, and Cardiovascular Disease.

The current pharmacological agents advised for the management of diabetes as well as cardiovascular and hepatic diseases are subject to numerous studies for safety and efficacy. Therefore, it is worth looking into alternative therapeutic aids such as natural products of medicinal plants. By a broad review of in vitro and in vivo studies on the various dandelion, chicory, and mulberry extracts, this work highlights their bioactive compounds and therapeutic action when used as a prevention and management aid in public health such as diabetes, cardiovascular disease, and hepatic disorders like non-alcoholic steatohepatitis. Natural products of dandelion leaves and root extracts can suppress the development of liver cancer, decrease insulin resistance, and suppress total triglyceride and cholesterol levels. Recent studies on mulberry leaves extracts indicated that they could decrease palmitic acid-induced lipotoxicity, increase total cholesterol and bile acid excretion, improve superoxide dismutase expression, and improve insulin resistance. Chicory root extracts boost satiety, reverse insulin resistance, and augment lipid metabolism thanks to their contents in chicoric acid, chlorogenic acid, and polysaccharides. Taraxacum officinale L., Morus nigra L., and Cichorium intybus L. present hepatoprotective, anti-inflammatory, antioxidant, hypolipidemic, and hypoglycemic activities and are shown to be advantageous in the management of obesity, dyslipidemia, Type 2 diabetes, and non-alcoholic fatty liver diseases. These plants are commonly available in the European spontaneous flora and more attention could be paid to their natural products.

Activation of the AMPK-SIRT1 pathway contributes to protective effects of Salvianolic acid A against lipotoxicity in hepatocytes and NAFLD in mice.

Background: Salvianolic acid A (Sal A), a natural polyphenol compound extracted from Radix Salvia miltiorrhiza (known as Danshen in China), possesses a variety of potential pharmacological activities. The aim of this study is to determine mechanisms of hepatoprotective effects of Sal A against lipotoxicity both in cultured hepatocytes and in a mouse model of fatty liver disease. Methods: High-fat and high-carbohydrate diet (HFCD)-fed C57BL/6J mice were employed to establish hepatic lipotoxicity in a mouse model. Two doses of Sal A were administered every other day via intraperitoneal injection (20 and 40 mg/kg BW, respectively). After a 10-week intervention, liver injury was detected by immunohistochemical and biochemical analyses. For in vitro studies, we used HepG2, a human hepatoma cell line, and exposed them to palmitic acid to induce lipotoxicity. The protective effects of Sal A on palmitic acid-induced lipotoxicity were examined in Sal A-pretreated HepG2 cells. Results: Sal A treatments attenuated body weight gain, liver injury, and hepatic steatosis in mice exposed to HFCD. Sal A pretreatments ameliorated palmitic acid-induced cell death but did not reverse effects of HFCD- or palmitate-induced activations of JNK, ERK1/2, and PKA. Induction of p38 phosphorylation was significantly reversed by Sal A in HFCD-fed mice but not in palmitate-treated HepG2 cells. However, Sal A rescued hepatic AMP-activated protein kinase (AMPK) suppression and sirtuin 1 (SIRT1) downregulation by both HFCD feeding in mice and exposure to palmitate in HepG2 cells. Sal A dose-dependently up-regulated p-AMPK and SIRT1 protein levels. Importantly, siRNA silencing of either AMPK or SIRT1 gene expression abolished the protective effects of Sal A on lipotoxicity. Moreover, while AMPK silencing blocked Sal A-induced SIRT1, silencing of SIRT1 had no effect on Sal A-triggered AMPK activation, suggesting SIRT1 upregulation by Sal A is mediated by AMPK activation. Conclusion: Our data uncover a novel mechanism for hepatoprotective effects of Sal A against lipotoxicity both in livers from HFCD-fed mice and palmitic acid-treated hepatocytes.

Emerging roles for non-selenium containing ER-resident glutathione peroxidases in cell signaling and disease

Maintenance of cellular redox control is pivotal for normal cellular functions and cell fate decisions including cell death. Among the key cellular redox systems in mammals, the glutathione peroxidase (GPX) family of proteins is the largest conferring multifaceted functions and affecting virtually all cellular processes. The endoplasmic reticulum (ER)-resident GPXs, designated as GPX7 and GPX8, are the most recently added members of this family of enzymes. Recent studies have provided exciting insights how both enzymes support critical processes of the ER including oxidative protein folding, maintenance of ER redox control by eliminating H2O2, and preventing palmitic acid-induced lipotoxicity. Consequently, numerous pathological conditions, such as neurodegeneration, cancer and metabolic diseases have been linked with altered GPX7 and GPX8 expression. Studies in mice have demonstrated that loss of GPX7 leads to increased differentiation of preadipocytes, increased tumorigenesis and shortened lifespan. By contrast, GPX8 deficiency in mice results in enhanced caspase-4/11 activation and increased endotoxic shock in colitis model. With the increasing recognition that both types of enzymes are dysregulated in various tumor entities in man, we deem a review of the emerging roles played by GPX7 and GPX8 in health and disease development timely and appropriate.

Different Phenolic Extracts of Oil Palm Fruits and Caffeic Acid Prevent Palmitic Acid-Induced Lipotoxicity in HepG2 Cells via Improving Mitochondrial Function

Oil palm (Elaeis guineensis Jacq.) fruits are rich in antioxidative phenolic compounds, which exert various health improving effects. This study aimed to comparatively study the protective effects of different phenolic fractions from the fruits treated with or without ultrahigh pressure (UHP) and their most abundant phenolic substance, caffeic acid, against the palmitic acid-induced lipotoxicity in HepG2 cells and to clarify the potential mechanisms. Results showed that the TG accumulation, intracellular reactive oxygen species content, cell apoptosis, and mitochondrial membrane potential depolarization were relieved by the administration of those phenolic fractions and caffeic acid. The protection of insoluble-bound (IB) phenolic fraction was the best, and UHP treatment significantly enhanced its protective effect on lipotoxicity. The lipotoxicity preventive effect may be achieved by alleviating intracellular oxidative stress, downregulating the expression of P-P38, COX-2, and iNOS to relieve inflammation, and downregulating Bax and cytochrome C and upregulating Bcl-2 to suppress the mitochondrial-mediated apoptosis. Therefore, the oil palm fruits phenolic fractions, especially the IB phenolic fraction, might be utilized as dietary antioxidants to relieve the adverse effects of a high-fat diet on the body, and UHP treatment is a potential method to increase this bioactivity.

70 Trolox during invitro maturation of bovine oocytes protects developing embryos from palmitic acid-induced lipotoxicity

Maternal metabolic disorders are associated with elevated concentrations of palmitic acid (PA), which is known to jeopardize bovine oocyte and embryo development and quality. Analyses of PA-exposed bovine oocytes and embryos point toward oxidative stress (OS)-related pathways. Previous research has shown that the detrimental effects of PA exposure during oocyte IVM cannot be alleviated by antioxidant supplementation, e.g. Trolox (TR, water-soluble vitamin E), during IVM or invitro culture (IVC). In contrast, supplementing TR during IVM could protect developing zygotes from PA-induced lipotoxicity by increasing their development into 4-cell embryos and Day 8 blastocysts. In the present study, we examined the effects of TR during IVM or IVC on PA-exposed oocytes and embryos by evaluating OS and mitochondrial membrane potential (MMP) of the produced ≥2-cell Day 2 embryos (Table 1). Bovine cumulus-oocyte complexes (COCs) were matured, fertilised, and cultured in 2 experiments. In Experiment 1, COCs were exposed to pathophysiological follicular PA concentrations (150 µM), and subsequent embryos were cultured under solvent control (ethanol) conditions (PA-SC). The TR treatment was applied during IVM or IVC (100 µM; PATR-SC, PA-TR). In Experiment 2, COCs were matured under SC conditions, and subsequent embryos were exposed to pathophysiological oviductal PA concentrations (230 µM; SC-PA). The TR treatment was applied during IVM or IVC (100 µM; TR-PA, SC-PATR). In each experiment, a SC was included (SC-SC). A total of 126 and 137 Day 2 embryos were stained with JC-1 and CellRox Deep Red in Experiment 1 and Experiment 2 (3 repeats), respectively. The MMP was evaluated as active/total mitochondria and OS as OS/total mitochondria and analysed by one-way ANOVA. Exposure of oocytes and embryos to PA significantly increased OS and MMP in Day 2 embryos compared with controls. Regardless of the moment of PA exposure, TR treatment during IVM increased MMP even more. The increased MMP levels in PA-exposed oocytes and embryos were not influenced by TR treatment during IVC. Regardless of the antioxidant effect of TR, increased embryonic OS levels observed in PA-exposed oocytes and embryos could not be reversed to control levels by TR treatment during IVM or IVC. However, when OS levels were expressed on active mitochondria, we found that TR treatment before the PA insult (TR-PA) generated Day 2 embryos that displayed significantly lower OS/active mitochondria rates compared with SC-PA-treated embryos. Taken together, we conclude that the combination of relatively low OS levels with highly active mitochondria may be a mechanism implicated in the protective effect of TR before the PA insult on embryo developmental competence. Table 1.Effects of TR during IVM or IVC on PA-exposed oocytes and embryos in Experiments 1 and 2 Controls PA exposure TR during IVM TR during IVC SC-SC PA-SC PATR-SC PA-TR Exp. 1 MMP 0.39±0.02a 0.53±0.02b 0.65±0.02c 0.50±0.02b OS 0.55±0.04a 0.68±0.04b 0.78±0.03b 0.59±0.03ab SC-SC SC-PA TR-PA SC-PATR Exp. 2 MMP 0.39±0.02a 0.50±0.02b 0.65±0.02c 0.58±0.02b OS 0.55±0.04a 0.69±0.04b 0.70±0.03b 0.71±0.02b abcDifferent letters in the same row indicate significant differences (P&amp;lt;0.05).

Palmitic acid-induced lipotoxicity promotes a novel interplay between Akt-mTOR, IRS-1, and FFAR1 signaling in pancreatic \u03b2-cells

BackgroundFree fatty acid receptor 1 (FFAR1) is G-protein coupled receptor predominantly expressed in pancreatic β-cells that is activated by a variety of free fatty acids (FFAs). Once activated, it promotes glucose-stimulated insulin secretion (GSIS). However, increased levels of FFAs lead to lipotoxicity, inducing loss of β-cell function. FFAR1 plays a key role in the development of type 2 diabetes (T2D), and previous studies have indicated the importance of developing anti-diabetic therapies against FFAR1, although its role in the regulation of β-cell function remains unclear. The present study investigated the role of FFAR1 under lipotoxic conditions using palmitic acid (PA). The rat insulinoma 1 clone 832/13 (INS-1 832/13) cell line was used as a model as it physiologically resembles native pancreatic β-cells. Key players of the insulin signaling pathway, such as mTOR, Akt, IRS-1, and the insulin receptor (INSR1β), were selected as candidates to be analyzed under lipotoxic conditions.ResultsWe revealed that PA-induced lipotoxicity affected GSIS in INS-1 cells and negatively modulated the activity of both IRS-1 and Akt. Reduced phosphorylation of both IRS-1 S636/639 and Akt S473 was observed, in addition to decreased expression of both INSR1β and FFAR1. Moreover, transient knockdown of FFAR1 led to a reduction in IRS-1 mRNA expression and an increase in INSR1β mRNA. Finally, PA affected localization of FFAR1 from the cytoplasm to the perinucleus.ConclusionsIn conclusion, our study suggests a novel regulatory involvement of FFAR1 in crosstalk with mTOR–Akt and IRS-1 signaling in β-cells under lipotoxic conditions.

High-density lipoprotein ameliorates palmitic acid-induced lipotoxicity and oxidative dysfunction in H9c2 cardiomyoblast cells via ROS suppression

BackgroundHigh levels circulating saturated fatty acids are associated with diabetes, obesity and hyperlipidemia. In heart, the accumulation of saturated fatty acids has been determined to play a role in the development of heart failure and diabetic cardiomyopathy. High-density lipoprotein (HDL) has been reported to possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, anti-oxidative and anti-inflammatory activities. However, the underlying mechanisms are still largely unknown. Therefore, the aim of the present study is to test whether HDL could protect palmitic acid (PA)-induced cardiomyocyte injury and explore the possible mechanisms.ResultsH9c2 cells were pretreated with HDL (50–100 μg/ml) for 2 h followed by PA (0.5 mM) for indicated time period. Our results showed that HDL inhibited PA-induced cell death in a dose-dependent manner. Moreover, HDL rescued PA-induced ROS generation and the phosphorylation of JNK which in turn activated NF-κB-mediated inflammatory proteins expressions. We also found that PA impaired the balance of BCL2 family proteins, destabilized mitochondrial membrane potential, and triggered subsequent cytochrome c release into the cytosol and activation of caspase 3. These detrimental effects were ameliorated by HDL treatment.ConclusionPA-induced ROS accumulation and results in cardiomyocyte apoptosis and inflammation. However, HDL attenuated PA-induced lipotoxicity and oxidative dysfunction via ROS suppression. These results may provide insight into a possible molecular mechanism underlying HDL suppression of the free fatty acid-induced cardiomyocyte apoptosis.