Protection by different classes of dietary polyphenols against palmitic acid-induced steatosis, nitro-oxidative stress and endoplasmic reticulum stress in HepG2 hepatocytes

Development of a novel human triculture model of non-alcoholic fatty liver disease and identification of berberine as ameliorating steatosis, oxidative stress and fibrosis

Objectives: Non-alcoholic fatty liver disease (NAFLD) and its progression to non-alcoholic steatohepatitis (NASH) and hepatocarcinoma is a serious and growing problem. However, the development of new therapies is severely hindered by a lack of high-throughput assays for drug testing. Methods: We have developed a simple transwell assay comprised of HepG2 hepatocytes, hepatic LX-2 stellate cells, and differentiated THP-1 cells. The cells were incubated with an activating mixture containing the NASH-associated risk factors, glucose, insulin, free fatty acids (FFAs), and lipopolysaccharide (LPS) for 72 h. We compared different combinations of culture conditions to obtain a model system that recapitulates the main features of NAFLD/NASH, i.e., increased steatosis, reactive oxygen species (ROS), secretion of pro-inflammatory cytokines/chemokines, and presence of fibrosis. To confirm the usefulness of the optimized model system, we screened for compounds that inhibit steatosis in the hepatocytes and evaluated the most effective compound in the triculture model system. Results: The activating mixture stimulated HepG2 cells in this triculture to accumulate more fat and produce higher levels of reactive oxygen species (ROS) than HepG2 cells in monocultures. As well, higher levels of inflammatory cytokines and chemokines (IL-8, IL-6, MIP-1α, etc.) were produced in this triculture compared to monocultures. In addition, in all LX-2 monocultures and cocultures, exposure to the activating mixture increased markers of fibrosis. A major strength of our triculture system is that it makes possible the simultaneous monitoring of 4 main features of NASH, i.e., steatosis, oxidative stress, inflammation and fibrosis. Screening potential modulators that may reduce steatosis in HepG2 cells revealed the protective effects of the isoalkaloid, berberine. Tested using this novel triculture assay, treatment with 5 µM berberine decreased steatosis and ROS in HepG2 hepatocytes, reduced inflammatory cytokine production and inhibited collagen production from LX-2 cells. Conclusion: This simple triculture model recapitulates the main features of NAFLD/NASH and should be useful for high-throughput preclinical drug discovery. In this model, berberine showed promising results in decreasing steatosis and ROS and protection against fibrosis.

Advanced effect of curcumin and resveratrol on mitigating hepatic steatosis in metabolic associated fatty liver disease via the PI3K/AKT/mTOR and HIF-1/VEGF cascade

Metabolic associated fatty liver disease (MAFLD) is the most common chronic liver disease that has no viable treatment. Curcumin (Cur) and resveratrol (Res) are two natural products that have been studied for their potential to ameliorate MAFLD. However, while these compounds have been investigated individually, their combined use and the potential for a synergistic or augmented effect remain unexplored. This study aims to investigate the effect of curcumin (Cur) and resveratrol (Res) as a potential combination therapy on MAFLD. Cur, Res and Cur+Res were tested in palmitic acid (PA)-induced-HepG2 cells. MAFLD model was established using Goto-Kakizaki rats. The animals were treated with vehicle control (model group), Cur (150 mg/kg), Res (150 mg/kg), Cur+Res (150 mg/kg, 8:2, w/w), or metformin (Met, positive control, 400 mg/kg/day) via oral gavage for 4 weeks. Wistar rats were used as the control group. Network pharmacology was conducted to elucidate the molecular actions of Cur and Res, followed by q-PCR and immunoblotting in vivo. Cur+Res exhibited synergistic effects in reducing triglyceride, total cholesterol and lipid accumulation in PA-induced HepG2 cells. The combination also markedly attenuated hepatic steatosis in the MAFLD rats. Network pharmacology illustrated that the interaction of Cur and Res was associated with the modulation of multiple molecular targets associated with the PI3K/AKT/mTOR and HIF-1 signaling pathways. Experimental results confirmed that Cur+Res nomalised the gene targets and protein expressions in the PI3K/AKT/mTOR and HIF-1 signaling pathways, including PI3K, mTOR, STAT-3, HIF-1α, and VEGF. The present study demonstrated an advanced effect of Cur and Res in combination to attenuate MAFLD, and the mechanism is at least partly associated with the modulation of the PI3K/AKT/mTOR and HIF-1 signaling pathways.

Gryllus bimaculatus De Geer hydrolysates alleviate lipid accumulation, inflammation, and endoplasmic reticulum stress in palmitic acid-treated human hepatoma G2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Nonalcoholic fatty liver disease (NAFLD) is one of the most common hepatic diseases closely intertwined with saturated fatty acids intake. Therefore, various studies are being conducted to find natural substances to prevent either the onset or progression of NAFLD. According to traditional medicinal literature, it has been reported that Gryllus bimaculatus De Geer (GB) has systemic detoxifying activity; however, the preventive effects of GB on NAFLD have not been elucidated to date.

AIM OF STUDY

To evaluate the potential of GB as a material for the mitigation of NAFLD, we investigated the effects of GB hydrolysates on the hepatic lipid accumulation, inflammation, and endoplasmic reticulum (ER) stress in human hepatoma G2 (Hep G2) cells treated with palmitic acid (PA).

METHODS

Steamed and dried GB was defatted, pulverized, and then lyophilized following hydrolyzation using Neutrase® (GB-N) or Flavourzyme® (GB-F). Hep G2 cells were incubated with GB-N or GB-F at various concentrations (0, 0.25, 0.5, and 1 mg/mL) for 24 h, and then PA was treated for another 24 h.

RESULTS

The GB-N and GB-F significantly prevented the PA-induced intracellular lipid accumulation in the human liver cells (p < 0.05). Moreover, the GB-N and GB-F increased the hepatic cellular viability against the PA-treatment (p < 0.05). In addition, the GB-N and GB-F significantly ameliorated the PA-inducible proinflammatory cytokines mRNA expression, such as tumor necrosis factor-α and interleukin-1β, compared to the PA-treated hepatic cells (p < 0.05). Furthermore, the GB-N and GB-F inhibited the PA-inducible lipogenic mRNA expression, such as fatty acid synthase, sterol regulatory element-binding protein 1c, and peroxisome proliferator-activated receptor-γ (p < 0.05). Moreover, the GB-N and GB-F alleviated the ER stress-related mRNA expression, such as glucose regulatory protein 78 and X-box binding protein increased in PA-treated cells (p < 0.05).

CONCLUSIONS

These results indicate that GB-N and GB-F could be used as materials to prevent the NAFLD onset or progression with alleviating hepatic lipid accumulation, inflammation, and ER stress.

Phytochemicals from the Cocoa Shell Modulate Mitochondrial Function, Lipid and Glucose Metabolism in Hepatocytes via Activation of FGF21/ERK, AKT, and mTOR Pathways

The cocoa shell is a by-product that may be revalorized as a source of bioactive compounds to prevent chronic cardiometabolic diseases. This study aimed to investigate the phytochemicals from the cocoa shell as targeted compounds for activating fibroblast growth factor 21 (FGF21) signaling and regulating non-alcoholic fatty liver disease (NAFLD)-related biomarkers linked to oxidative stress, mitochondrial function, and metabolism in hepatocytes. HepG2 cells treated with palmitic acid (PA, 500 µmol L⁻¹) were used in an NAFLD cell model. Phytochemicals from the cocoa shell (50 µmol L⁻¹) and an aqueous extract (CAE, 100 µg mL⁻¹) enhanced ERK1/2 phosphorylation (1.7- to 3.3-fold) and FGF21 release (1.4- to 3.4-fold) via PPARα activation. Oxidative stress markers were reduced though Nrf-2 regulation. Mitochondrial function (mitochondrial respiration and ATP production) was protected by the PGC-1α pathway modulation. Cocoa shell phytochemicals reduced lipid accumulation (53–115%) and fatty acid synthase activity (59–93%) and prompted CPT-1 activity. Glucose uptake and glucokinase activity were enhanced, whereas glucose production and phosphoenolpyruvate carboxykinase activity were diminished. The increase in the phosphorylation of the insulin receptor, AKT, AMPKα, mTOR, and ERK1/2 conduced to the regulation of hepatic mitochondrial function and energy metabolism. For the first time, the cocoa shell phytochemicals are proved to modulate FGF21 signaling. Results demonstrate the in vitro preventive effect of the phytochemicals from the cocoa shell on NAFLD.

A dipeptidyl peptidase IV inhibitory peptide relieves palmitic acid-induced endoplasmic reticulum stress in HepG2 cells independent of inhibiting dipeptidyl peptidase IV activity

The peptide VLATSGPG (VLA) is known to inhibit dipeptidyl peptidase IV (DPP-IV), although its mechanism in relieving endoplasmic reticulum (ER) stress is unclear. In this study, we found that treating HepG2 cells with 1.0 mM VLA reduced DPP-IV activity by 73.7 ± 4.8% without changing the DPP-IV mRNA expression level. In addition, 1.0 and 0.5 mM VLA alleviated palmitic acid (PA)-induced cell death and intracellular calcium imbalances. The levels of apoptosis-related proteins (caspase-3, caspase-9, and CHOP) were reduced by VLA treatment, which was presumed to be related to ER stress. Further studies confirmed that VLA alleviated PA-induced morphological damage to the ER and reduced the levels of the ER stress marker proteins (BIP, p-PERK, and p-IRE1α). VLA alleviated PA-induced ER stress in HepG2 cells independent of DPP-IV enzymatic activity inhibition. These findings have implications for developing novel treatment approaches for liver diseases caused by ER stress.

Quercetin and its role in modulating endoplasmic reticulum stress: A review

The endoplasmic reticulum (ER) is the place where proteins and lipids are biosynthesized and where transmembrane proteins are folded. Both pathological and physiological situations may disturb the function of the ER, resulting in ER stress. Under stress conditions, the cells initiate a defensive procedure known as the unfolded protein response (UPR). Cases of severe stress lead to autophagy and/or the induction of cell apoptosis. Many studies implicate ER stress as a major factor contributing to many diseases. Therefore, the modulation of ER stress pathways has become an attractive therapeutic target. Quercetin is a plant-derived metabolite belonging to the flavonoids class which presents a range of beneficial effects including anti-inflammatory, cardioprotective, anti-oxidant, anti-obesity, anti-carcinogenic, anti-atherosclerotic, anti-diabetic, anti-hypercholesterolemic, and anti-apoptotic activities. Quercetin also has anti-cancer activity, and can be used as an adjuvant to decrease resistance to cancer chemotherapy. Furthermore, the effect of quercetin can be increased with the help of nanotechnology. This review discusses the role of quercetin in the modulation of ER stress (and related diseases) and provides novel evidence for the beneficial use of quercetin in therapy.

Regulatory mechanisms of energy metabolism and inflammation in oleic acid-treated HepG2 cells from Lactobacillus acidophilus NX2-6 extract

In this study, the cell-free extracts (CFE) of Lactobacillus acidophilus NX2-6 were utilized to treat oleic acid (OA)-induced hepatic steatosis. It was found that CFE treatment improved lipid metabolism in OA-induced hepatic steatosis model by downregulating several lipogenic genes but increasing expression levels of lipolysis-related genes. In addition, gene expression analysis revealed that CFE treatment promoted mitochondrial biogenesis and fission by upregulating the mRNA levels of PGC-1α, PGC-1β, Sirt1, NRF1, and Fis1. CFE treatment also increased protein expression of p-AMPKα, PGC-1α, ACOX1, and Sirt1 in OA-treated cells, suggesting that CFE possessed ability to improve energy metabolism. Furthermore, CFE treatment also reversed OA-induced oxidative stress by increasing CAT activity and protein level of Nrf-2 as well as reducing protein expression of ATF6, XBP1, GRP78, p50, and p-ERK, indicating that CFE could inhibit endoplasmic reticulum stress and sterile inflammation. Thus, L. acidophilus NX2-6 had potential to fight against NAFLD. PRACTICAL APPLICATIONS: Diet-induced hepatic steatosis is one of major public health concerns all over the world. Hepatic steatosis is accompanied by disregulation of lipid metabolism and energy metabolism, endoplasmic reticulum stress, oxidative stress as well as chronic inflammation. It is reported that probiotics are considered as emerging therapeutic strategy to alleviate hepatic steatosis. This study indicated potential applications of dead probiotics in the prevention of hepatic steatosis and development of functional foods.

Lily bulbs' polyphenols extract ameliorates oxidative stress and lipid accumulation in vitro and in vivo

BACKGROUND

Polyphenols have the potential to reduce the risk of many metabolic disorders. Lily bulbs are rich in polyphenols; however, their effects on lipid metabolism remain unclear. This study aimed to explore the effects of lily bulbs' polyphenols (LBPs) on oxidative stress and lipid metabolism.

RESULTS

A total of 14 polyphenolic compounds in LBPs were identified by high-performance liquid chromatography equipped with diode-array detection mass spectrometry. Total phenolic compound in LBPs was 53.76 ± 1.12 g kg^-1 dry weight. In cellular experiments, LBPs attenuated the disruption of mitochondrial membrane potential, impeded reactive oxygen species production, alleviated oxidative stress, and reduced lipid accumulation in oleic acid induced HepG2 cells. In in vivo studies, LBPs significantly inhibited body weight gain, reduced lipid levels in serum and liver, and improved oxidative damage in a dose-dependent manner in mice fed a high-fat diet. Moreover, LBPs ameliorated hepatic steatosis and suppressed the expression of hepatic-lipogenesis-related genes (SREBP-1c, FAS, ACC1, and SCD-1) and promoted lipolysis genes (SRB1 and HL) and lipid oxidation genes (PPARα and CPT-1) in mice fed a high-fat diet.

CONCLUSION

It was concluded that LBPs are a potential complementary therapeutic alternative in the development of functional foods to curb obesity and obesity-related diseases, such as metabolic syndrome. © 2021 Society of Chemical Industry.

Combined effects of arsenic and palmitic acid on oxidative stress and lipid metabolism disorder in human hepatoma HepG2 cells

The toxicity of arsenic (As) can be influenced by many nutrients in food. However, the combined effects and underlying mechanisms of As and palmitic acid (PA) are still unclear. Here, cell viability, oxidative stress, lipids accumulation, gene expression profiles, and metabolome profiles of human hepatoma HepG2 cells exposed to As, PA, and As + PA were analyzed and compared. Results showed that co-exposure of 100 μM PA and 2 μM As induced lower cell viability, higher intracellular reactive oxygen species level, more lipid droplet accumulation, and more intracellular triglyceride contents than As alone or PA alone exposure. High-throughput quantitative PCR and ¹H NMR-based metabolomics analysis showed that co-exposure of As and PA caused all toxic effects on gene expression and metabolome profiles induced by As alone or PA alone exposure, and showed higher toxicities. Gene expression profiles in the As + PA group had higher similarity with those in the As group than the PA group. However, PA played a more important role in metabolism disorder than As in their interactive effects. Oxidative stress and lipid metabolism disorder were found to be the main toxic effects in the As + PA group. Several differentially expressed genes (such as OXR1, OXSR1, INSR, and PPARA) and changed metabolites (such as pyruvate, acetate, and L-phenylalanine) were involved in the combined toxicity of As and PA. This study provides basic information on the interactive effects of As and PA, which is useful for the health risk assessment of As and FFA.

Erica multiflora extract rich in quercetin-3-O-glucoside and kaempferol-3-O-glucoside alleviates high fat and fructose diet-induced fatty liver disease by modulating metabolic and inflammatory pathways in Wistar rats

The wide morbidity of obesity has heightened interest in providing natural and safe compounds to maintain optimal health. The present study was designed to determine the chemical constituents and the effects of methanol leaf extract from Erica multiflora (M-EML) on mitigating high-fat and high-fructose diet (HFFD)-induced metabolic syndrome (MS). LC-MS/MS characterization of M-EML allowed the identification of 14 secondary metabolites and showed that quercetin-3-O-glucoside and kaempferol-3-O-glucoside were the main compounds of our extract. In the in vivo study, the oral administration of M-EML (250 mg/kg) during the last 4 weeks of the experimentation alleviated HFFD-induced obesity, insulin resistance (IR) and cardiovascular diseases. Thus, M-EML treatment significantly normalized body and liver weight, allowed to a sharp decline in plasma levels of TC, TG and LDL-c by 32%, 35% and 66%, respectively. Moreover, hepatic enzymes, total and direct bilirubin, lipase and uric acid levels have been diminished in treated group. Histopathology of the liver confirmed the changes induced by HFFD and the hepatoprotective effect of M-EML. The supply of M-EML reduced NO production and cellular lysosomal enzyme activity by 44% and 60%, respectively compared to HFFD. Besides, M-EML showed decreased pro-inflammatory cytokines levels (259.5±47.35 pg/ml and 56.08±1.56 pg/ml) of TNF-α and IL-6, respectively. In addition, M-EML reduced liver malondialdehyde (MDA) content and enhanced superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activities. In contrast, these enzymatic activities have been disrupted in HFFD rats. Overall, M-EML prevented obesity through the modulation of metabolic syndrome, reducing inflammation and promoting antioxidant enzymes activities.

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.

Phenolic Breakdown Products of Cyanidin and Quercetin Contribute to Protection against Mitochondrial Impairment and Reactive Oxygen Species Generation in an In Vitro Model of Hepatocyte Steatosis

A question in cell culture and dietary studies on protection by flavonoids against conditions such as hepatocyte steatosis is whether effects might be due to phenolic breakdown/digestion products. In HepG2 hepatocytes, treatment with quercetin, cyanidin, or their phenolic breakdown/digestion products (protocatechuic acid, 2,4,6-trihydroxybenzaldehyde, and caffeic acid), starting 2 h prior to oleic acid for 24 h, protected similarly against increases in intracellular lipid and reactive oxygen species and decreased mitochondrial membrane potential. Cyanidin or the phenolic products also protected against decreased mitochondrial content. After preincubation for only 1 h (to limit spontaneous degradation) and removal prior to oleic acid, only the phenolic products protected against decreased mitochondrial content, and without adding oleic acid, only protocatechuic acid and caffeic acid, and less so cyanidin, induced mitochondrial content. The results suggest that phenolic breakdown/digestion products of cyanidin and quercetin contribute to the protective effects in vitro, and perhaps in vivo.

Dietary Polyphenols Protect Against Oleic Acid-Induced Steatosis in an in Vitro Model of NAFLD by Modulating Lipid Metabolism and Improving Mitochondrial Function

In this study, we aimed to determine the relative effectiveness of common dietary polyphenols or the isoquinoline alkaloid berberine in protecting against molecular mechanisms underlying non-alcoholic fatty liver disease (NAFLD) involving changes to cellular lipid metabolism and bioenergetics. In a model of steatosis using HepG2 hepatocytes, exposure of the cells to 1.5 mM oleic acid (OA) for 24 h caused steatosis and distorted cell morphology, induced the expression of mRNA for enzymes that are involved in lipogenesis and fatty acid oxidation (FAS and CPT1A), and impaired indices of aerobic energy metabolism (PPARγ mRNA expression, mitochondrial membrane potential (MMP), and galactose-supported ATP production). Co-treatment with 10 µM of selected polyphenols all strongly protected against the steatosis and changes in cell morphology. All polyphenols, except cyanidin, inhibited the effects on FAS and PPARγ and further increased CPT1A1 expression, suggesting a shift toward increased β-oxidation. Resveratrol, quercetin, catechin, and cyanidin, however not kuromanin or berberine, ameliorated the decreases in MMP and galactose-derived ATP. Berberine was unique in worsening the decrease in galactose-derived ATP. In further investigations of the mechanisms involved, resveratrol, catechin, and berberine increased SIRT1 enzyme activity and p-AMPKα^Thr172 protein, which are involved in mitochondrial biogenesis. In conclusion, selected polyphenols all protected against steatosis with similar effectiveness, however through different mechanisms that increased aerobic lipid metabolism and mitochondrial function.

Comparison of Phenols Content and Antioxidant Activity of Fruits from Different Maturity Stages of Ribes stenocarpum Maxim

Differences in the content of nine phenols and the antioxidant capacity of Ribes stenocarpum Maxim (RSM) fruits at different stages of maturity were investigated, and the extraction process of polyphenols from RSM was also optimized using Box-Behnken design method. Results showed that the content of the nine phenols varied considerably at different ripening stages; catechin, chlorogenic acid, coumaric acid, and ferulic acid were abundant in immature fruits but decreased with fruit ripening, whereas the levels of rosemary acid and querctin acid were low in immature fruits and increased with time, reaching the highest value after the fruit was completely mature. The phenols extracted from RSM fruits possessed good antioxidant activities for effective and rapid scavenging of DPPH and ABTS free radicals, as well as intracellular ROS. Analysis of the phenols content at different maturity stages indicated that the unripe fruits had significantly higher polyphenols content than mature fruits. Consequently, unripe fruits possessed higher antioxidant activities. According to the overall results of the extraction process optimization, the selected optimal conditions for extracting polyphenols from RSM were as follows: extraction time, 95 min; solvent concentration, 60%; ratio of sample to solvent, 1:25.