DHA supplementation prevent the progression of NASH via GPR120 signaling

Therapeutic potential of traditional Chinese medicine in the prevention and treatment of digestive inflammatory cancer transformation: Portulaca oleracea L. as a promising drug

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) has been used for centuries to treat various types of inflammation and tumors of the digestive system. Portulaca oleracea L. (POL), has been used in TCM for thousands of years. The chemical composition of POL is variable and includes flavonoids, alkaloids, terpenoids and organic acids and other classes of natural compounds. Many of these compounds exhibit powerful anti-inflammatory and anti-cancer-transforming effects in the digestive system.

AIM OF STUDY

In this review, we focus on the potential therapeutic role of POL in NASH, gastritis and colitis and their associated cancers, with a focus on the pharmacological properties and potential mechanisms of action of the main natural active compounds in POL.

METHODS

The information and data on Portulaca oleracea L. and its main active ingredients were collated from various resources like ethnobotanical textbooks and literature databases such as CNKI, VIP (Chinese literature), PubMed, Science Direct, Elsevier and Google Scholar (English literatures), Wiley, Springer, Tailor and Francis, Scopus, Inflibnet.

RESULTS

Kaempferol, luteolin, myricetin, quercetin, genistein, EPA, DHA, and melatonin were found to improve NASH and NASH-HCC, while kaempferol, apigenin, luteolin, and quercetin played a therapeutic role in gastritis and gastric cancer. Apigenin, luteolin, myricetin, quercetin, genistein, lupeol, vitamin C and melatonin were found to have therapeutic effects in the treatment of colitis and its associated cancers. The discovery of the beneficial effects of these natural active compounds in POL supports the idea that POL could be a promising novel candidate for the treatment and prevention of inflammation-related cancers of the digestive system.

CONCLUSION

The discovery of the beneficial effects of these natural active compounds in POL supports the idea that POL could be a promising novel candidate for the treatment and prevention of inflammation-related cancers of the digestive system. However, clinical data describing the mode of action of the naturally active compounds of POL are still lacking. In addition, pharmacokinetic data for POL compounds, such as changes in drug dose and absorption rates, cannot be extrapolated from animal models and need to be measured in patients in clinical trials. On the one hand, a systematic meta-analysis of the existing publications on TCM containing POL still needs to be carried out. On the other hand, studies on the hepatic and renal toxicity of POL are also needed. Additionally, well-designed preclinical and clinical studies to validate the therapeutic effects of TCM need to be performed, thus hopefully providing a basis for the validation of the clinical benefits of POL.

Structural basis for the ligand recognition and signaling of free fatty acid receptors

Free fatty acid receptors 1-4 (FFA1-4) are class A G protein-coupled receptors (GPCRs). FFA1-3 share substantial sequence similarity whereas FFA4 is unrelated. Despite this FFA1 and FFA4 are activated by the same range of long chain fatty acids (LCFAs) whilst FFA2 and FFA3 are instead activated by short chain fatty acids (SCFAs) generated by the intestinal microbiota. Each of FFA1, 2 and 4 are promising targets for novel drug development in metabolic and inflammatory conditions. To gain insights into the basis of ligand interactions with, and molecular mechanisms underlying activation of, FFAs by LCFAs and SCFAs, we determined the active structures of FFA1 and FFA4 bound to the polyunsaturated LCFA docosahexaenoic acid (DHA), FFA4 bound to the synthetic agonist TUG-891, as well as SCFA butyrate-bound FFA2, each complexed with an engineered heterotrimeric Gq protein (miniGq), by cryo-electron microscopy. Together with computational simulations and mutagenesis studies, we elucidated the similarities and differences in the binding modes of fatty acid ligands with varying chain lengths to their respective GPCRs. Our findings unveil distinct mechanisms of receptor activation and G protein coupling. We anticipate that these outcomes will facilitate structure-based drug development and underpin future research to understand allosteric modulation and biased signaling of this group of GPCRs.

Metabolite-sensing GPCRs controlling interactions between adipose tissue and inflammation

Metabolic disorders including obesity, diabetes and non-alcoholic steatohepatitis are a group of conditions characterised by chronic low-grade inflammation of metabolic tissues. There is now a growing appreciation that various metabolites released from adipose tissue serve as key signalling mediators, influencing this interaction with inflammation. G protein-coupled receptors (GPCRs) are the largest family of signal transduction proteins and most historically successful drug targets. The signalling pathways for several key adipose metabolites are mediated through GPCRs expressed both on the adipocytes themselves and on infiltrating macrophages. These include three main groups of GPCRs: the FFA4 receptor, which is activated by long chain free fatty acids; the HCA₂ and HCA₃ receptors, activated by hydroxy carboxylic acids; and the succinate receptor. Understanding the roles these metabolites and their receptors play in metabolic-immune interactions is critical to establishing how these GPCRs may be exploited for the treatment of metabolic disorders.

Treatment of liver fibrosis: Past, current, and future

Liver fibrosis accompanies the progression of chronic liver diseases independent of etiologies, such as hepatitis viral infection, alcohol consumption, and metabolic-associated fatty liver disease. It is commonly associated with liver injury, inflammation, and cell death. Liver fibrosis is characterized by abnormal accumulation of extracellular matrix components that are expressed by liver myofibroblasts such as collagens and alpha-smooth actin proteins. Activated hepatic stellate cells contribute to the major population of myofibroblasts. Many treatments for liver fibrosis have been investigated in clinical trials, including dietary supplementation (e.g., vitamin C), biological treatment (e.g., simtuzumab), drug (e.g., pegbelfermin and natural herbs), genetic regulation (e.g., non-coding RNAs), and transplantation of stem cells (e.g., hematopoietic stem cells). However, none of these treatments has been approved by Food and Drug Administration. The treatment efficacy can be evaluated by histological staining methods, imaging methods, and serum biomarkers, as well as fibrosis scoring systems, such as fibrosis-4 index, aspartate aminotransferase to platelet ratio, and non-alcoholic fatty liver disease fibrosis score. Furthermore, the reverse of liver fibrosis is slowly and frequently impossible for advanced fibrosis or cirrhosis. To avoid the life-threatening stage of liver fibrosis, anti-fibrotic treatments, especially for combined behavior prevention, biological treatment, drugs or herb medicines, and dietary regulation are needed. This review summarizes the past studies and current and future treatments for liver fibrosis.

FFAR4 regulates cardiac oxylipin balance to promote inflammation resolution in HFpEF secondary to metabolic syndrome

Heart failure with preserved ejection fraction (HFpEF) is a complex clinical syndrome, but a predominant subset of HFpEF patients has metabolic syndrome (MetS). Mechanistically, systemic, nonresolving inflammation associated with MetS might drive HFpEF remodeling. Free fatty acid receptor 4 (Ffar4) is a GPCR for long-chain fatty acids that attenuates metabolic dysfunction and resolves inflammation. Therefore, we hypothesized that Ffar4 would attenuate remodeling in HFpEF secondary to MetS (HFpEF-MetS). To test this hypothesis, mice with systemic deletion of Ffar4 (Ffar4KO) were fed a high-fat/high-sucrose diet with L-NAME in their water to induce HFpEF-MetS. In male Ffar4KO mice, this HFpEF-MetS diet induced similar metabolic deficits but worsened diastolic function and microvascular rarefaction relative to WT mice. Conversely, in female Ffar4KO mice, the diet produced greater obesity but no worsened ventricular remodeling relative to WT mice. In Ffar4KO males, MetS altered the balance of inflammatory oxylipins systemically in HDL and in the heart, decreasing the eicosapentaenoic acid-derived, proresolving oxylipin 18-hydroxyeicosapentaenoic acid (18-HEPE), while increasing the arachidonic acid-derived, proinflammatory oxylipin 12-hydroxyeicosatetraenoic acid (12-HETE). This increased 12-HETE/18-HEPE ratio reflected a more proinflammatory state both systemically and in the heart in male Ffar4KO mice and was associated with increased macrophage numbers in the heart, which in turn correlated with worsened ventricular remodeling. In summary, our data suggest that Ffar4 controls the proinflammatory/proresolving oxylipin balance systemically and in the heart to resolve inflammation and attenuate HFpEF remodeling.

Enzymatically-epoxidized docosahexaenoic acid, 19,20-EpDPE, suppresses hepatic crown-like structure formation and nonalcoholic steatohepatitis fibrosis through GPR120

A hepatic crown-like structure (hCLS) formed by macrophages accumulating around lipid droplets and dead cells in the liver is a unique feature of nonalcoholic steatohepatitis (NASH) that triggers progression of liver fibrosis. As hCLS plays a key role in the progression of NASH fibrosis, hCLS formation has emerged as a potential therapeutic target. n-3 polyunsaturated fatty acids (n-3 PUFAs) have potential suppressive effects on NASH fibrosis; however, the mechanisms underlying this effect are poorly understood. Here, we report that n-3 PUFA-enriched Fat-1 transgenic mice are resistant to hCLS formation and liver fibrosis in a NASH model induced by a combination of high-fat diet, CCl4 and a Liver X receptor (LXR) agonist. Liquid chromatography-tandem mass spectrometry-based mediator lipidomics revealed that the amount of endogenous n-3 PUFA-derived metabolites, such as 17,18-dihydroxyeicosatetraenoic acid (17,18-diHETE), and 19,20-epoxy docosapentaenoic acid (19,20-EpDPE), was significantly elevated in Fat-1 mice, along with hCLS formation. In particular, DHA-derived 19,20-EpDPE produced by Cyp4f18 attenuated the hCLS formation and liver fibrosis in a G protein-coupled receptor 120 (GPR120)-dependent manner. These results indicated that 19,20-EpDPE is an endogenous active metabolite that mediates the preventive effect of n-3 PUFAs against NASH fibrosis.

Reduced Free Fatty Acid Receptor 4 Gene Expression is Associated With Extreme Obesity and Insulin Resistance in Children

OBJECTIVES

Free fatty acid receptor 4 (FFAR4) is a G-protein-coupled membrane receptor highly expressed in macrophages that triggers anti-inflammatory effects and promotes insulin sensitization. We have previously found significant associations between the FFAR4 rs11187533 single nucleotide polymorphism (SNP) and various obesity comorbidity parameters. We aimed to verify the FFAR4 expression levels in children with obesity and the associated comorbidities.

METHODS

Thirty-eight children with obesity were studied. Clinical and anthropometric evaluation was performed. A venous sample under fasting conditions was obtained. Biochemical study included parameters of metabolic risk. DNA was extracted and genotyped for the rs11187533 FFAR4 SNP. Real-time PCR technique was performed to investigate the gene expression. Relative FFAR4 mRNA levels were determined according to the 2-ΔΔCt method.

RESULTS

Significant differences in FFAR4 expression levels between the CC and CT-TT genotypes of the rs11187533 FFAR4 SNP were observed (P = 0.034). The minor allele T presented higher levels of FFAR4 expression. We found that a loss of FFAR4 expression was associated with extreme obesity (P = 0.032). The lowest FFAR4 expression levels were observed in children who had higher insulin (P = 0.008) and homeostasis model assessment insulin resistance values (P = 0.012) and lower quantitative insulin-sensitivity check index (P = 0.033).

CONCLUSIONS

The underexpression of FFAR4 was associated with extreme obesity and parameters indicative of obesity comorbidities in children. This under expression could be partially influenced by the presence of the C allele rs11187533 FFAR4 SNP.

Docosahexaenoic Acid Attenuates the Progression of Nonalcoholic Steatohepatitis by Suppressing the Adipocyte Inflammation via the G Protein-Coupled Receptor 120/Free Fatty Acid Receptor 4 Pathway

INTRODUCTION

Our previous study demonstrated that docosahexaenoic acid (DHA), an endogenous G protein-coupled receptor 120 (GPR120)/free fatty acid receptor (FFAR) 4 agonist, attenuated the liver inflammation in nonalcoholic steatohepatitis (NASH), while exacerbated liver inflammation was observed in the GPR120/FFAR4 knockout (GPR120/FFAR4KO) mice. Recently, abdominal adiposity has been reported to correlate with the severity of inflammation and fibrosis in patients with NASH. In this study, we investigated whether the activation of GPR120/FFAR4 suppressed the inflammation of the adipose tissue and whether these suppressive effects attenuated the development of NASH.

METHODS

A choline-deficient and 0.1% methionine-containing high-fat (CDAHF) diet was used to create a mouse model of NASH. DHA was orally administered to the mice for 1 week. Epididymal fat pads which collected from the control-fed wild-type (WT) or GPR120/FFAR4KO mice were used as ex vivo white adipose tissue (WAT) culture systems.

RESULTS

The mice fed a CDAHF diet for 2 weeks showed NASH-like liver diseases. In the WAT of mice fed with the CDAHF diet, inflammation and fibrosis were significantly increased, and the administration of DHA suppressed these phenomena. In an ex vivo adipocyte culture study, DHA dose-dependently suppressed the lipopolysaccharide-induced inflammation in the adipocyte tissue of WT mice, which was reversed by pretreatment with AH7614, a GPR120/FFAR4 antagonist, but not GPR40 or peroxisome proliferator-activated receptor γ antagonist.

CONCLUSIONS

These findings suggest that the activation of GPR120/FFAR4 may suppress the inflammation of adipocytes, which could be a key pathway to prevent the development of NASH.

Ursodesoxycholic acid is an FFA4 agonist and reduces hepatic steatosis via FFA4 signaling

Ursodeoxycholic acid (UDCA) is a safe bile acid effective in reducing hepatic steatosis in non-alcoholic fatty liver disease (NAFLD). However, the mechanism of action linked to this effect is poorly defined. In the present study, we identified that UDCA acted as a free fatty acid receptor 4 (FFA4) agonist with EC50 of 10.4 ± 0.7 μM, and its activity was determined by dynamic mass redistribution, fluorometric imaging plate reader, inositol monophosphate and bioluminescence resonance energy transfer assays. Moreover, UDCA showed FFA4 selectivity over eleven other G protein-coupled receptors. Real-Time PCR and immunocytochemistry analyses showed that FFA4 was abundantly expressed in human hepatocytes HuH-7 cells. In an in vitro model of NAFLD induced by oleic acid (OA), UDCA downregulated lipid accumulation in HuH-7 cells and suppressed sterol-regulatory element binding protein-1c (SREBP-1c) mRNA expression. This suppression of SREBP-1c was restored when FFA4 expression was knocked down in siRNA assay. In a mouse model of hepatic steatosis, db/db mice were exposed to a high-fat diet (HFD), and treatment of UDCA or docosahexaenoic acid (DHA, an endogenous FFA4 agonist) effectively prevented body weight gain and hepatic fat deposition and reduced triglyceride (TG) levels in serum and liver. This study not only identified a new skeleton of FFA4 agonists, but also demonstrated that FFA4 signal was accounting for the protective effects of UDCA in the NAFLD treatment.

GPR120 induces regulatory dendritic cells by inhibiting HK2-dependent glycolysis to alleviate fulminant hepatic failure

Fulminant hepatic failure (FHF) is a potentially fatal liver disease that is associated with intrahepatic infiltration of inflammatory cells. As the receptor of polyunsaturated long chain fatty acids, GPR120 can regulate cell differentiation, proliferation, metabolism, and immune response. However, whether GPR120 is involved in FHF remains unknown. Using Propionibacterium acnes (P. acnes)-primed, LPS-induced FHF in mice, we found that interference with GPR120 activity using pharmacological agonist attenuated the severity of the liver injury and mortality of FHF in mice, while a lack of GPR120 exacerbated the disease. GPR120 activation potently alleviated FHF and led to decreased T helper (Th) 1 cell response and expansion of regulatory T cells (Tregs). Interestingly, GPR120 agonist didn't directly target T cells, but dramatically induced a distinct population of CD11c⁺MHC II^lowCD80^lowCD86^low regulatory DCs in the livers of FHF mice. GPR120 was found to restrict HIF-1α-dependent glycolysis. The augmented HIF-1α stabilization caused by GPR120 antagonism or deletion could be attenuated by the inhibition of ERK or by the activation of AMPK. Through the analysis of the clinical FHF, we further confirmed the activation of GPR120 was negatively associated with the severity in patients. Our findings indicated that GPR120 activation has therapeutic potential in FHF. Strategies to target GPR120 using agonists or free fatty acids (FFAs) may represent a novel approach to FHF treatment.

Immunomodulating effects of 13- and 16-hydroxylated docosahexaenoyl ethanolamide in LPS stimulated RAW264.7 macrophages

Docosahexaenoyl ethanolamide (DHEA), the ethanolamine conjugate of the n-3 long chain polyunsaturated fatty acid docosahexaenoic acid, is endogenously present in the human circulation and in tissues. Its immunomodulating properties have been (partly) attributed to an interaction with the cyclooxygenase-2 (COX-2) enzyme. Recently, we discovered that COX-2 converts DHEA into two oxygenated metabolites, 13- and 16-hydroxylated-DHEA (13- and 16-HDHEA, respectively). It remained unclear whether these oxygenated metabolites also display immunomodulating properties like their parent DHEA. In the current study we investigated the immunomodulating properties of 13- and 16-HDHEA in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. The compounds reduced production of tumor necrosis factor alpha (TNFα), interleukin (IL)-1β and IL-1Ra, but did not affect nitric oxide (NO) and IL-6 release. Transcriptome analysis showed that the compounds inhibited the LPS-mediated induction of pro-inflammatory genes (InhbA, Ifit1) and suggested potential inhibition of regulators such as toll-like receptor 4 (TLR4), MyD88, and interferon regulatory factor 3 (IRF3), whereas anti-inflammatory genes (SerpinB2) and potential regulators IL-10, sirtuin 1 (Sirt-1), fluticasone propionate were induced. Additionally, transcriptome analysis of 13-HDHEA suggests a potential anti-angiogenic role. In contrast to the known oxylipin-lowering effects of DHEA, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analyses revealed that 13- and 16-HDHEA did not affect oxylipin formation. Overall, the anti-inflammatory effects of 13-HDHEA and 16-HDHEA are less pronounced compared to their parent molecule DHEA. Therefore, we propose that COX-2 metabolism of DHEA acts as a regulatory mechanism to limit the anti-inflammatory properties of DHEA.

DHA Protects Hepatocytes from Oxidative Injury through GPR120/ERK-Mediated Mitophagy

Oxidative stress occurs in a variety of clinical liver diseases and causes cellular damage and mitochondrial dysfunction. The clearance of damaged mitochondria by mitophagy may facilitate mitochondrial biogenesis and enhance cell survival. Although the supplementation of docosahexaenoic acid (DHA) has been recognized to relieve the symptoms of various liver diseases, the antioxidant effect of DHA in liver disease is still unclear. The purpose of our research was to investigate the antioxidant effect of DHA in the liver and the possible role of mitophagy in this. In vitro, H₂O₂-induced injury was caused in AML12 cells. The results showed that DHA repressed the level of reactive oxygen species (ROS) induced by H₂O₂ and stimulated the cellular antioxidation response. Most notably, DHA restored oxidative stress-impaired autophagic flux and promoted protective autophagy. In addition, PINK/Parkin-mediated mitophagy was activated by DHA in AML12 cells and alleviated mitochondrial dysfunction. The ERK1/2 signaling pathway was inhibited during oxidative stress but reactivated by DHA treatment. It was proven that the expression of ERK1/2 was involved in the regulation of mitophagy by the ERK1/2 inhibitor. We further proved these results in vivo. DHA effectively alleviated the liver oxidative damage caused by CCl₄ and enhanced antioxidation capacity; intriguingly, autophagy was also activated. In summary, our data demonstrated that DHA protected hepatocytes from oxidative damage through GPR120/ERK-mediated mitophagy.

Anti-Atherosclerotic Potential of Free Fatty Acid Receptor 4 (FFAR4)

Fatty acids (FAs) are considered not only as a basic nutrient, but are also recognized as signaling molecules acting on various types of receptors. The receptors activated by FAs include the family of rhodopsin-like receptors: GPR40 (FFAR1), GPR41 (FFAR3), GPR43 (FFAR2), GPR120 (FFAR4), and several other, less characterized G-protein coupled receptors (GPR84, GPR109A, GPR170, GPR31, GPR132, GPR119, and Olfr78). The ubiquitously distributed FFAR4 can be activated by saturated and unsaturated medium- and long-chain fatty acids (MCFAs and LCFAs), as well as by several synthetic agonists (e.g., TUG-891). The stimulation of FFAR4 using selective synthetic agonists proved to be promising strategy of reduction of inflammatory reactions in various tissues. In this paper, we summarize the evidence showing the mechanisms of the potential beneficial effects of FFAR4 stimulation in atherosclerosis. Based partly on our own results, we also suggest that an important mechanism of such activity may be the modulatory influence of FFAR4 on the phenotype of macrophage involved in atherogenesis.

GPR120/FFAR4 Pharmacology: Focus on Agonists in Type 2 Diabetes Mellitus Drug Discovery

The G-protein coupled receptors (GPCRs) activated by free fatty acids (FFAs) have emerged as new and exciting drug targets, due to their plausible translation from pharmacology to medicines. This perspective aims to report recent research about GPR120/FFAR4 and its involvement in several diseases, including cancer, inflammatory conditions, and central nervous system disorders. The focus is to highlight the importance of GPR120 in Type 2 diabetes mellitus (T2DM). GPR120 agonists, useful in T2DM drug discovery, have been widely explored from a structure–activity relationship point of view. Since the identification of the first reported synthetic agonist TUG-891, the research has paved the way for the development of TUG-based molecules as well as new and different chemical entities. These molecules might represent the starting point for the future discovery of GPR120 agonists as antidiabetic drugs.

Free Fatty Acid Receptors as Mediators and Therapeutic Targets in Liver Disease

Free fatty acid receptors (FFARs) are a class of G protein-coupled receptors (GPCRs) that have wide-ranging effects on human physiology. The four well-characterized FFARs are FFAR1/GPR40, FFAR2/GPR43, FFAR3/GPR41, and FFAR4/GPR120. Short-chain (<6 carbon) fatty acids target FFAR2/GPR43 and FFAR3/GPR41. Medium- and long-chain fatty acids (6-12 and 13-21 carbon, respectively) target both FFAR1/GPR40 and FFAR4/GPR120. Signaling through FFARs has been implicated in non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), intestinal failure-associated liver disease (IFALD), and a variety of other liver disorders. FFARs are now regarded as targets for therapeutic intervention for liver disease, diabetes, obesity, hyperlipidemia, and metabolic syndrome. In this review, we provide an in-depth, focused summary of the role FFARs play in liver health and disease.

Fortifying Butterfat with Soybean Oil Attenuates the Onset of Diet-Induced Non-Alcoholic Steatohepatitis and Glucose Intolerance

The addition of plant oils such as soybean oil (S) to a diet rich in saturated fatty acids is discussed as a possible route to prevent or diminish the development of metabolic disease. Here, we assessed whether a butterfat-rich diet fortified with S affects the development of early non-alcoholic steatohepatitis (NASH) and glucose intolerance. Female C57BL/6J mice were fed a standard-control diet (C); a fat-, fructose-, and cholesterol-rich diet (FFC, 25E% butterfat, 50% (wt./wt.) fructose, 0.16% (wt./wt.) cholesterol); or FFC supplemented with S (FFC + S, 21E% butterfat + 4E% S) for 13 weeks. Indicators of liver damage, inflammation, intestinal barrier function, and glucose metabolism were measured. Lipopolysaccharide (LPS)-challenged J774A.1 cells were incubated with linolenic and linoleic acids (ratio 1:7.1, equivalent to S). The development of early NASH and glucose intolerance was significantly attenuated in FFC + S–fed mice compared to FFC-fed mice associated with lower hepatic toll-like receptor-4 mRNA expression, while markers of intestinal barrier function were significantly higher than in C-fed mice. Linolenic and linoleic acid significantly attenuated LPS-induced formation of reactive nitrogen species and interleukin-1 beta mRNA expression in J774A.1 cells. Our results indicate that fortifying butterfat with S may attenuate the development of NASH and glucose intolerance in mice.

Effects of Long-Term DHA Supplementation and Physical Exercise on Non-Alcoholic Fatty Liver Development in Obese Aged Female Mice

Obesity and aging are associated to non-alcoholic fatty liver disease (NAFLD) development. Here, we investigate whether long-term feeding with a docosahexaenoic acid (DHA)-enriched diet and aerobic exercise, alone or in combination, are effective in ameliorating NAFLD in aged obese mice. Two-month-old female C57BL/6J mice received control or high fat diet (HFD) for 4 months. Then, the diet-induced obese (DIO) mice were distributed into four groups: DIO, DIO + DHA (15% dietary lipids replaced by a DHA-rich concentrate), DIO + EX (treadmill running), and DIO + DHA + EX up to 18 months. The DHA-rich diet reduced liver steatosis in DIO mice, decreasing lipogenic genes (Dgat2, Scd1, Srebp1c), and upregulated lipid catabolism genes (Hsl/Acox) expression. A similar pattern was observed in the DIO + EX group. The combination of DHA + exercise potentiated an increase in Cpt1a and Ppara genes, and AMPK activation, key regulators of fatty acid oxidation. Exercise, alone or in combination with DHA, significantly reversed the induction of proinflammatory genes (Mcp1, Il6, Tnfα, Tlr4) in DIO mice. DHA supplementation was effective in preventing the alterations induced by the HFD in endoplasmic reticulum stress-related genes (Ern1/Xbp1) and autophagy markers (LC3II/I ratio, p62, Atg7). In summary, long-term DHA supplementation and/or exercise could be helpful to delay NAFLD progression during aging in obesity.

Pinocembrin and its linolenoyl ester derivative induce wound healing activity in HaCaT cell line potentially involving a GPR120/FFA4 mediated pathway

Wound healing represents an urgent need from the clinical point of view. Several diseases result in wound conditions which are difficult to treat, such as in the case of diabetic foot ulcer. Starting from there, the medicinal research has focused on various targets over the years, including GPCRs as new wound healing drug targets. In line with this, GPR120, known to be an attractive target in type 2 diabetes drug discovery, was studied to finalize the development of new wound healing agents. Pinocembrin (HW0) was evaluated as a suitable compound for interacting with GPR120, and was hybridized with fatty acids, which are known endogenous GPR120 ligands, to enhance the wound healing potential and GPR120 interactions. HW0 and its 7-linolenoyl derivative (HW3) were found to be innovative wound healing agents. Immunofluorescence and functional assays suggested that their activity was mediated by GPR120, and docking simulations showed that the compounds could share the same pocket occupied by the known GPR120 agonist, TUG-891.

DHA/AA alleviates LPS-induced Kupffer cells pyroptosis via GPR120 interaction with NLRP3 to inhibit inflammasome complexes assembly

Pyroptosis is a novel type of programmed cell death associated with the pathogenesis of many inflammatory diseases. Docosahexaenoic acid (DHA) and Arachidonic acid (AA) is widely involved in inflammatory pathological processes. However, the effect and mechanism of DHA and AA on pyroptosis in Kupffer cells are poorly understood. The present study demonstrated that DHA and AA ameliorated lipopolysaccharide (LPS)-induced Kupffer cells pyroptosis by reversing the increased expression of NLRP3 inflammasome complex, GSDMD, IL-1β, IL-18, and PI-stained positive rate. Next, the study revealed that GPR120 silencing eliminated the anti-pyroptosis of DHA and AA in LPS-induced Kupffer cells, suggesting that DHA and AA exerted their effect through GPR120 signaling. Importantly, GPR120 endocytose and binds to NLRP3 under LPS stimulation. Furthermore, co-immunoprecipitation showed that DHA and AA promoted the interaction between GPR120 and NLRP3 in LPS-exposed Kupffer cells, thus inhibiting the self-assembly of NLRP3 inflammasome complex. Finally, the study verified that DHA and AA alleviated hepatic injury through inhibiting Kupffer cells pyroptosis in vivo. The findings indicated that DHA and AA alleviated LPS-induced Kupffer cells pyroptosis via GPR120 interaction with NLRP3, it might become a potential therapeutic approach hepatic injury.

DHA substitution overcomes high-fat diet-induced disturbance in the circadian rhythm of lipid metabolism

Disruptions to circadian rhythm have been associated with an increased risk of nonalcoholic fatty liver disease (NAFLD). DHA has been found to affect both circadian rhythm and lipid metabolism. In this study, the relationship between DHA substitution and improvements in lipid metabolism and circadian clock regulation was studied. Male C57BL/6 mice were fed a control, a high fat or a DHA substituted diet for 12 weeks. Biochemical analysis and H&E staining showed that the high-fat diet (HFD) could induce NAFLD, and DHA substitution (AOH) could attenuate NAFLD. The qPCR results showed that the expressions of core clock genes Clock and Bmal1 were significantly higher at zeitgeber (ZT) 0 (7:00 am) than those at ZT12 (7:00 pm) in the control group, while this difference in day and night disappeared in the HFD group, but was observed in the AOH group. Western blotting results indicated that the expressions of rhythm output molecules (RORα and REV-ERBα) and their downstream protein INSIG2 all showed the corresponding circadian changes. SREBP-regulated proteins were significantly increased in the HFD group at both ZT0 and ZT12, but decreased in the AOH group accompanied by the corresponding changes in the protein expressions of HMGCR, LXR, CYP7A1 and CYP27A1. Altogether, HFD can decrease or disrupt circadian rhythm fluctuation by up-regulating the expression of core circadian rhythm genes Clock and Bmal1 at ZT12, and induce metabolic abnormalities through the INSIG2-SREBP pathway regulated by RORα and REV-ERBα. DHA substitution seems to restore circadian rhythm similar to the normal circadian rhythm of "night-high, day-low" through the metabolic pathway regulated by rhythmic nuclear receptors, improving the lipid metabolism rhythm and reducing liver fat.

[Involvement of the Free Fatty Acid Receptor GPR120/FFAR4 in the Development of Nonalcoholic Steatohepatitis]

Nonalcoholic fatty liver disease (NAFLD) is characterized by the pathological accumulation of fat in the liver in the absence of any other disease related to liver steatosis, which includes a wide spectrum ranging from mild asymptomatic fatty liver to nonalcoholic steatohepatitis (NASH) and cirrhosis. However, the pathogenesis of NASH has not been established. In this study, we investigated the involvement of the G-protein-coupled receptor 120/free fatty acid receptor 4 (GPR120/FFAR4) in the pathogenesis of NASH. Mice fed a 0.1% methionine- and choline-deficient l-amino acid-defined, high-fat (CDAHF) diet showed a significant increase in plasma aspartate aminotransferase and alanine aminotransferase levels, fatty deposition, inflammatory cell infiltration, and slight fibrosis. Docosahexanoic acid (DHA, a GPR120/FFAR4 agonist) suppressed the inflammatory cytokines in hepatic tissues and prevented liver fibrosis. On the other hand, GPR120/FFAR4-deficient CDAHF-fed mice showed increments in the number of hepatic crown-like structures and immunoreactivity to F4/80-positive cells compared with wild-type mice. Furthermore, the levels of hepatic TNF-α mRNA expression increased in GPR120-deficient mice. These findings suggest that the GPR120/FFAR4-mediating system could be a key signaling pathway to prevent the development of NASH. In this review, we describe our recent data showing that GPR120/FFAR4 could be a therapeutic target in NASH/NAFLD.

The role of n-3 PUFA-derived fatty acid derivatives and their oxygenated metabolites in the modulation of inflammation

Notwithstanding the ongoing debate on their full potential in health and disease, there is general consensus that n-3 PUFAs play important physiological roles. Increasing dietary n-3 PUFA intake results in increased DHA and EPA content in cell membranes as well as an increase in n-3 derived oxylipin and -endocannabinoid concentrations, like fatty acid amides and glycerol-esters. These shifts are believed to (partly) explain the pharmacological and anti-inflammatory effects of n-3 PUFAs. Recent studies discovered that n-3 PUFA-derived endocannabinoids can be further metabolized by the oxidative enzymes CYP-450, LOX and COX, similar to the n-6 derived endocannabinoids. Interestingly, these oxidized n-3 PUFA derived endocannabinoids of eicosapentaenoyl ethanolamide (EPEA) and docosahexaenoyl ethanolamide (DHEA) have higher anti-inflammatory and anti-proliferative potential than their precursors. In this review, an overview of recently discovered n-3 PUFA derived endocannabinoids and their metabolites is provided. In addition, the use of chemical probes will be presented as a promising technique to study the n-3 PUFA and n-3 PUFA metabolism within the field of lipid biochemistry.

Fish oil protects the liver from parenteral nutrition-induced injury via GPR120-mediated PPARγ signaling

Intravenous fish oil lipid emulsions (FOLE) can prevent parenteral nutrition (PN)-induced liver injury in murine models and reverse PN-induced cholestasis in pediatric patients. However, the mechanisms by which fish oil protects the liver are incompletely characterized. Fish oil is rich in omega-3 fatty acids, which are ligands for the G-protein coupled receptor 120 (GPR120), expressed on hepatic Kupffer cells. This study tested the hypothesis that FOLE protects the liver from PN-induced injury through GPR120 signaling. Utilizing a previously described murine model of PN-induced liver injury in which mice develop steatosis in response to an oral parenteral nutrition diet, FOLE was able to preserve normal hepatic architecture in wild type mice, but not in congenic GPR120 knockout (gpr120-/-) mice. To further characterize the requirement of intact GPR120 for FOLE-mediated hepatic protection, gene expression profiles of key regulators of fat metabolism were measured. PPARγ was identified as a gene that is up-regulated by the PN diet and normalized with the addition of FOLE in wild type, but not in gpr120-/- mice. This was confirmed at the protein expression level. A PPARγ expression array further identified CD36 and SCD1, both down-stream effectors of PPARγ, to be up-regulated in PN-fed wild type mice yet normalized upon FOLE administration in wild type but not in gpr120-/- mice. Together, these results suggest that FOLE protects the liver, in part, through activation of GPR120 and the downstream effectors PPARγ and CD36. Identification of key genetic determinants of FOLE-mediated hepatic protection may provide targets for small molecule-based hepatic protection strategies.

Label-free cell phenotypic study of FFA4 and FFA1 and discovery of novel agonists of FFA4 from natural products

In this article, pharmacological studies of the free fatty acid receptor (FFA) 4 and FFA1 were conducted in transfected CHO cells (FFA4&FFA1) and HT29 cells with application of a label-free dynamic mass redistribution (DMR) assay. Commercially available compounds including α-linolenic acid (ALA), GW9508, TUG891, GSK137647A, TAK875, MEDICA16, AH7614 and GW1100, were used to validate the assay; real-time tracing of ligand-induced cell responses elucidated pharmacological properties of ligand–receptor interactions. A pool of 140 natural compounds was screened using the CHO-FFA4 cells. Three new FFA4 agonists with novel skeletons were discovered and they were dihydrotanshinone, emodin and acetylshikonin (EC₅₀ values were 32.88, 38.18 and 10.17 μM, respectively). Ligand selectivity was compared between FFA4 and FFA1; dihydrotanshinone and emodin displayed FFA4 selectivity, while acetylshikonin shared FFA1 and FFA4 agonist activities with EC₅₀ values comparable to the endogenous ligand ALA. The three novel FFA4 agonists provide a promising chemical starting point for identification and optimization of drugs used for treating metabolic and inflammatory diseases. Besides, this work will help to explain the mechanism of actions of natural products.

Pharmacological studies of the FFA4 and FFA1 and discovery of three novel agonists was conducted using a label-free DMR assay.

Dissecting the Physiology and Pathophysiology of Glucagon-Like Peptide-1

An aging world population exposed to a sedentary life style is currently plagued by chronic metabolic diseases, such as type-2 diabetes, that are spreading worldwide at an unprecedented rate. One of the most promising pharmacological approaches for the management of type 2 diabetes takes advantage of the peptide hormone glucagon-like peptide-1 (GLP-1) under the form of protease resistant mimetics, and DPP-IV inhibitors. Despite the improved quality of life, long-term treatments with these new classes of drugs are riddled with serious and life-threatening side-effects, with no overall cure of the disease. New evidence is shedding more light over the complex physiology of GLP-1 in health and metabolic diseases. Herein, we discuss the most recent advancements in the biology of gut receptors known to induce the secretion of GLP-1, to bridge the multiple gaps into our understanding of its physiology and pathology.