GPR120: a critical role in adipogenesis, inflammation, and energy metabolism in adipose tissue

Loureirin B Reduces Insulin Resistance and Chronic Inflammation in a Rat Model of Polycystic Ovary Syndrome by Upregulating GPR120 and Activating the LKB1/AMPK Signaling Pathway

Polycystic ovary yndrome (PCOS) is a common metabolic disorder in women, which is usually associated with insulin resistance (IR) and chronic inflammation. Loureirin B (LrB) can effectively improve insulin resistance and alleviate chronic inflammation, and in order to investigate the therapeutic effect of LrB on polycystic ovary syndrome with insulin resistance (PCOS-IR), we conducted animal experiments. A PCOS-IR rat model was established by feeding a high-fat diet combined with letrozole (1 mg/kg·d for 21 days). The rats were treated with the GPR120 agonists TUG-891 and LrB for 4 weeks. Biochemical parameters (fasting blood glucose, total cholesterol, triglycerides, high- and low-density lipoprotein), hormone levels (serum insulin, E2, T, LH, and FSH), and inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-18) were analyzed. Histopathological analyses of ovaries were performed using hematoxylin/eosin (H&E) staining. Real-time PCR and western blotting were used to assess GPR120, NLRP3, and caspase-1 expression in ovaries, and immunohistochemistry was used to evaluate LKB1 and AMPK protein expression. LrB reduced body weight, Lee's index, ovarian index, ovarian area, and volume in PCOS-IR rats. It lowered fasting blood glucose, serum insulin, and HOMA-IR. LrB decreased total serum cholesterol, triglyceride, and LDL levels and increased HDL levels. It reduced serum T, LH, and LH/FSH and raised serum E2 and FSH levels. LrB downregulated the mRNA and protein expression levels of NLRP3 and Caspase-1, increased the protein and mRNA expression levels of GPR120 in rat ovaries, and increased LKB1 and AMPK protein expression in ovaries, ameliorating ovarian histopathological changes in PCOS-IR rats. Taken together, LrB upregulated GPR120, LKB1, and AMPK protein expression, downregulated NLRP3 and Caspase-1 protein expression, reduced insulin resistance and chronic inflammation, and ameliorated histopathological changes in ovarian tissues in PCOS rats, suggesting its potential as a treatment for PCOS.

Key questions and gaps in understanding adipose tissue macrophages and early-life metabolic programming

The global obesity epidemic, with its associated comorbidities and increased risk of early mortality, underscores the urgent need for enhancing our understanding of the origins of this complex disease. It is increasingly clear that metabolism is programmed early in life and that metabolic programming can have life-long health consequences. As a critical metabolic organ sensitive to early-life stimuli, proper development of adipose tissue (AT) is crucial for life-long energy homeostasis. Early-life nutrients, especially fatty acids (FAs), significantly influence the programming of AT and shape its function and metabolism. Of growing interest are the dynamic responses during pre- and postnatal development to proinflammatory omega-6 (n6) and anti-inflammatory omega-3 (n3) FA exposures in AT. In the US maternal diet, the ratio of "pro-inflammatory" n6- to "anti-inflammatory" n3-FAs has grown dramatically due to the greater prevalence of n6-FAs. Notably, AT macrophages (ATMs) form a significant population within adipose stromal cells, playing not only an instrumental role in AT formation and maintenance but also acting as key mediators of cell-to-cell lipid and cytokine signaling. Despite rapid advances in ATM and immunometabolism fields, research has focused on responses to obesogenic diets and during adulthood. Consequently, there is a significant gap in identifying the mechanisms contributing metabolic health, especially regarding lipid exposures during the establishment of ATM physiology. Our review highlights the current understanding of ATM diversity, their critical role in AT, their potential role in early-life metabolic programming, and the broader implications for metabolism and health.

G-Protein-Coupled Receptor 120 Agonist Mitigates Steatotic and Fibrotic Features Triggered in Obese Mice by the Administration of a High-Fat and High-Carbohydrate Diet

Nonalcoholic fatty liver disease (NALFD) represents a complex condition ranging from simple steatosis (nonalcoholic fatty liver, NAFL) to inflammation, and fibrosis is one of the main features of nonalcoholic steatohepatitis (NASH). The pathogenesis of NAFLD is not well established but involves several factors (i.e., predisposition of genetic variants, obesity, and unhealthy lifestyle as unbalanced diets) that lead to an alteration of lipid homeostasis and consequently to an abnormal accumulation of triglycerides and other lipids in the liver parenchyma. Currently, no resolutive pharmacological treatment for NAFLD is available, and the only therapeutic approach is a healthy diet and physical exercise. In this study, we investigated the potential beneficial effect of GprA, a new synthetic agonist of G-protein-coupled receptor 120/free fatty acid receptor 4 (GPR120/FFAR4), in the progression of NAFL/NASH in mice fed for different periods (26 weeks and 30 weeks), with a high-fat (40% kcal) and high-carbohydrate diet, also called a Western-style diet (WSD). In our experimental model, the histological, protein, and transcriptomic analyses highlighted that the GprA can reduce signs of steatosis in WSD-fed mice. Furthermore, in 30 week-treated mice, GprA is also effective in the reduction of collagen deposition and fibrosis development. Altogether, our data validate the central role of FFAR4 in the context of NAFL/NASH onset and progression and reveal that GprA could represent an interesting candidate for the development of a new therapeutic approach in NAFLD treatment.

Positive interplay between FFAR4/GPR120, DPP-IV inhibition and GLP-1 in beta cell proliferation and glucose homeostasis in obese high fat fed mice

G-protein coupled receptor-120 (GPR120; FFAR4) is a free fatty acid receptor, widely researched for its glucoregulatory and insulin release activities. This study aimed to investigate the metabolic advantage of FFAR4/GPR120 activation using combination therapy. C57BL/6 mice, fed a High Fat Diet (HFD) for 120 days to induce obesity-diabetes, were subsequently treated with a single daily oral dose of FFAR4/GPR120 agonist Compound A (CpdA) (0.1μmol/kg) alone or in combination with sitagliptin (50 mg/kg) for 21 days. After 21-days, glucose homeostasis, islet morphology, plasma hormones and lipids, tissue genes (qPCR) and protein expression (immunocytochemistry) were assessed. Oral administration of CpdA improved glucose tolerance (34% p<0.001) and increased circulating insulin (38% p<0.001). Addition of CpdA with the dipeptidyl peptidase-IV (DPP-IV) inhibitor, sitagliptin, further improved insulin release (44%) compared to sitagliptin alone and reduced fat mass (p<0.05). CpdA alone (50%) and in combination with sitagliptin (89%) induced marked reductions in LDL-cholesterol, with greater effects in combination (p<0.05). All treatment regimens restored pancreatic islet and beta-cell area and mass, complemented with significantly elevated beta-cell proliferation rates. A marked increase in circulating GLP-1 (53%) was observed, with further increases in combination (38%). With treatment, mice presented with increased Gcg (proglucagon) gene expression in the jejunum (130% increase) and ileum (120% increase), indicative of GLP-1 synthesis and secretion. These data highlight the therapeutic promise of FFAR4/GPR120 activation and the potential for combined benefit with incretin enhancing DPP-IV inhibitors in the regulation of beta cell proliferation and diabetes.

Cryo-electron microscopy for GPCR research and drug discovery in endocrinology and metabolism

G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors, with many GPCRs having crucial roles in endocrinology and metabolism. Cryogenic electron microscopy (cryo-EM) has revolutionized the field of structural biology, particularly regarding GPCRs, over the past decade. Since the first pair of GPCR structures resolved by cryo-EM were published in 2017, the number of GPCR structures resolved by cryo-EM has surpassed the number resolved by X-ray crystallography by 30%, reaching >650, and the number has doubled every ~0.63 years for the past 6 years. At this pace, it is predicted that the structure of 90% of all human GPCRs will be completed within the next 5-7 years. This Review highlights the general structural features and principles that guide GPCR ligand recognition, receptor activation, G protein coupling, arrestin recruitment and regulation by GPCR kinases. The Review also highlights the diversity of GPCR allosteric binding sites and how allosteric ligands could dictate biased signalling that is selective for a G protein pathway or an arrestin pathway. Finally, the authors use the examples of glycoprotein hormone receptors and glucagon-like peptide 1 receptor to illustrate the effect of cryo-EM on understanding GPCR biology in endocrinology and metabolism, as well as on GPCR-related endocrine diseases and drug discovery.

Mechanism of NLRP3 Inflammasome in Epilepsy and Related Therapeutic Agents

Epilepsy is one of the most widespread and complex diseases in the central nervous system (CNS), affecting approximately 65 million people globally, an important factor resulting in neurological disability-adjusted life year (DALY) and progressive cognitive dysfunction. Medication is the most essential treatment. The currently used drugs have shown drug resistance in some patients and only control symptoms; the development of novel and more efficacious pharmacotherapy is imminent. Increasing evidence suggests neuroinflammation is involved in the occurrence and development of epilepsy, and high expression of NLRP3 inflammasome has been observed in the temporal lobe epilepsy (TLE) brain tissue of patients and animal models. The inflammasome is a crucial cause of neuroinflammation by activating IL-1β and IL-18. Many preclinical studies have confirmed that regulating NLRP3 inflammasome pathway can prevent the development of epilepsy, reduce the severity of epilepsy, and play a neuroprotective role. Therefore, regulating NLRP3 inflammasome could be a potential target for epilepsy treatment. In summary, this review describes the priming and activation of inflammasome and its biological function in the progression of epilepsy. In addition, we reviewes the current pharmacological researches for epilepsy based on the regulation of NLRP3 inflammasome, aiming to provide a basis and reference for developing novel antiepileptic drugs.

The Effect of Enteric-Derived Lipopolysaccharides on Obesity

Endotoxin is a general term for toxic substances in Gram-negative bacteria, whose damaging effects are mainly derived from the lipopolysaccharides (LPS) in the cell walls of Gram-negative bacteria, and is a strong pyrogen. Obesity is a chronic, low-grade inflammatory condition, and LPS are thought to trigger and exacerbate it. The gut flora is the largest source of LPS in the body, and it is increasingly believed that altered intestinal microorganisms can play an essential role in the pathology of different diseases. Today, the complex axis linking gut flora to inflammatory states and adiposity has not been well elucidated. This review summarises the evidence for an interconnection between LPS, obesity, and gut flora, further expanding our understanding of LPS as a mediator of low-grade inflammatory disease and contributing to lessening the effects of obesity and related metabolic disorders. As well as providing targets associated with LPS, obesity, and gut flora, it is hoped that interventions that combine targets with gut flora address the individual differences in gut flora treatment.

Bioconversion, Pharmacokinetics, and Therapeutic Mechanisms of Ginsenoside Compound K and Its Analogues for Treating Metabolic Diseases

Rare ginsenoside compound K (CK) is an intestinal microbial metabolite with a low natural abundance that is primarily produced by physicochemical processing, side chain modification, or metabolic transformation in the gut. Moreover, CK exhibits potent biological activity compared to primary ginsenosides, which has raised concerns in the field of ginseng research and development, as well as ginsenoside-related dietary supplements and natural products. Ginsenosides Rb1, Rb2, and Rc are generally used as a substrate to generate CK via several bioconversion processes. Current research shows that CK has a wide range of pharmacological actions, including boosting osteogenesis, lipid and glucose metabolism, lipid oxidation, insulin resistance, and anti-inflammatory and anti-apoptosis properties. Further research on the bioavailability and toxicology of CK can advance its medicinal application. The purpose of this review is to lay the groundwork for future clinical studies and the development of CK as a therapy for metabolic disorders. Furthermore, the toxicology and pharmacology of CK are investigated as well in this review. The findings indicate that CK primarily modulates signaling pathways associated with AMPK, SIRT1, PPARs, WNTs, and NF-kB. It also demonstrates a positive therapeutic effect of CK on non-alcoholic fatty liver disease (NAFLD), obesity, hyperlipidemia, diabetes, and its complications, as well as osteoporosis. Additionally, the analogues of CK showed more bioavailability, less toxicity, and more efficacy against disease states. Enhancing bioavailability and regulating hazardous variables are crucial for its use in clinical trials.

Advances in the pharmacological effects and molecular mechanisms of emodin in the treatment of metabolic diseases

Rhubarb palmatum L., Polygonum multijiorum Thunb., and Polygonum cuspidatum Sieb. Et Zucc. are traditional Chinese medicines that have been used for thousands of years. They are formulated into various preparations and are widely used. Emodin is a traditional Chinese medicine monomer and the main active ingredient in Rhubarb palmatum L., Polygonum multijiorum Thunb., and Polygonum cuspidatum Sieb. Et Zucc. Modern research shows that it has a variety of pharmacological effects, including promoting lipid and glucose metabolism, osteogenesis, and anti-inflammatory and anti-autophagy effects. Research on the toxicity and pharmacokinetics of emodin can promote its clinical application. This review aims to provide a basis for further development and clinical research of emodin in the treatment of metabolic diseases. We performed a comprehensive summary of the pharmacology and molecular mechanisms of emodin in treating metabolic diseases by searching databases such as Web of Science, PubMed, ScienceDirect, and CNKI up to 2023. In addition, this review also analyzes the toxicity and pharmacokinetics of emodin. The results show that emodin mainly regulates AMPK, PPAR, and inflammation-related signaling pathways, and has a good therapeutic effect on obesity, hyperlipidemia, non-alcoholic fatty liver disease, diabetes and its complications, and osteoporosis. In addition, controlling toxic factors and improving bioavailability are of great significance for its clinical application.

Cardiac-to-adipose axis in metabolic homeostasis and diseases: special instructions from the heart

Adipose tissue is essential for maintaining systemic metabolic homeostasis through traditional metabolic regulation, endocrine crosstalk, and extracellular vesicle production. Adipose dysfunction is a risk factor for cardiovascular diseases. The heart is a traditional pump organ. However, it has recently been recognized to coordinate interorgan cross-talk by providing peripheral signals known as cardiokines. These molecules include specific peptides, proteins, microRNAs and novel extracellular vesicle-carried cargoes. Current studies have shown that generalized cardiokine-mediated adipose regulation affects systemic metabolism. Cardiokines regulate lipolysis, adipogenesis, energy expenditure, thermogenesis during cold exposure and adipokine production. Moreover, cardiokines participate in pathological processes such as obesity, diabetes and ischemic heart injury. The underlying mechanisms of the cardiac-to-adipose axis mediated by cardiokines will be further discussed to provide potential therapeutic targets for metabolic diseases and support a new perspective on the need to correct adipose dysfunction after ischemic heart injury.

DHA-Provoked Reduction in Adipogenesis and Glucose Uptake Could Be Mediated by Gps2 Upregulation in Immature 3T3-L1 Cells

The signaling pathway of fatty acids in the context of obesity is an extensively explored topic, yet their primary mechanism of action remains incompletely understood. This study aims to examine the effect of docosahexaenoic acid (DHA) on some crucial aspects of adipogenesis in differentiating 3T3-L1 cells, using palmitic acid-treated (PA), standard differentiated, and undifferentiated adipocytes as controls. Employing 60 µM DHA or PA, 3T3-L1 preadipocytes were treated from the onset of adipogenesis, with negative and positive controls included. After eight days, we performed microscopic observations, cell viability assays, the determination of adiponectin concentration, intracellular lipid accumulation, and gene expression analysis. Our findings demonstrated that DHA inhibits adipogenesis, lipolysis, and glucose uptake by suppressing peroxisome proliferator-activated receptor gamma (Pparg) and G-protein coupled receptor 120 (Gpr120) gene expression. Cell cytotoxicity was ruled out as a causative factor, and β-oxidation involvement was suspected. These results challenge the conventional belief that omega-3 fatty acids, acting as Pparg and Gpr120 agonists, promote adipogenesis and enhance insulin-dependent glucose cell flux. Moreover, we propose a novel hypothesis suggesting the key role of the co-repressor G protein pathway suppressor 2 in mediating this process. Additional investigations are required to elucidate the molecular mechanisms driving DHA's anti-adipogenic effect and its broader health implications.

Effect of oral cannabis administration on the fat depots of obese and streptozotocin-induced diabetic rats

The prevalence of obesity and insulin-resistance is on the rise, globally. Cannabis have been shown to have anti-diabetic/obesity properties, however, the effect mediated at various fat depots remains to be clarified. The aim of this study was to (1) investigate the anti-diabetic property of an oral cannabis administration in an obese and streptozotocin-induced diabetic rat model and (2) to determine and compare the effect mediated at the peritoneal and intramuscular fat level. Cannabis concentration of 1.25 mg/kg body weight (relative to THC content) was effective in reversing insulin-resistance in the rat model, unlike the other higher cannabinoid concentrations. At the peritoneal fat level, gene expression of fat beigeing markers, namely Cidea and UCP1, were significantly increased compared to the untreated control. At the intramuscular fat level, on the other hand, CE1.25 treatment did not promote fat beigeing but instead significantly increased mitochondrial activity, relative to the untreated control. Therefore, these findings indicate that the mechanism of action of oral cannabis administration, where glucose and lipid homeostasis is restored, is not only dependent on the dosage but also on the type of fat depot investigated.

GPCR in Adipose Tissue Function-Focus on Lipolysis

Adipose tissue can be divided anatomically, histologically, and functionally into two major entities white and brown adipose tissues (WAT and BAT, respectively). WAT is the primary energy depot, storing most of the bioavailable triacylglycerol molecules of the body, whereas BAT is designed for dissipating energy in the form of heat, a process also known as non-shivering thermogenesis as a defense against a cold environment. Importantly, BAT-dependent energy dissipation directly correlates with cardiometabolic health and has been postulated as an intriguing target for anti-obesity therapies. In general, adipose tissue (AT) lipid content is defined by lipid uptake and lipogenesis on one side, and, on the other side, it is defined by the breakdown of lipids and the release of fatty acids by lipolysis. The equilibrium between lipogenesis and lipolysis is important for adipocyte and general metabolic homeostasis. Overloading adipocytes with lipids causes cell stress, leading to the recruitment of immune cells and adipose tissue inflammation, which can affect the whole organism (metaflammation). The most important consequence of energy and lipid overload is obesity and associated pathophysiologies, including insulin resistance, type 2 diabetes, and cardiovascular disease. The fate of lipolysis products (fatty acids and glycerol) largely differs between AT: WAT releases fatty acids into the blood to deliver energy to other tissues (e.g., muscle). Activation of BAT, instead, liberates fatty acids that are used within brown adipocyte mitochondria for thermogenesis. The enzymes involved in lipolysis are tightly regulated by the second messenger cyclic adenosine monophosphate (cAMP), which is activated or inhibited by G protein-coupled receptors (GPCRs) that interact with heterotrimeric G proteins (G proteins). Thus, GPCRs are the upstream regulators of the equilibrium between lipogenesis and lipolysis. Moreover, GPCRs are of special pharmacological interest because about one third of the approved drugs target GPCRs. Here, we will discuss the effects of some of most studied as well as "novel" GPCRs and their ligands. We will review different facets of in vitro, ex vivo, and in vivo studies, obtained with both pharmacological and genetic approaches. Finally, we will report some possible therapeutic strategies to treat obesity employing GPCRs as primary target.

Fatty Acid Transport and Signaling: Mechanisms and Physiological Implications

Long-chain fatty acids (FAs) are components of plasma membranes and an efficient fuel source and also serve as metabolic regulators through FA signaling mediated by membrane FA receptors. Impaired tissue FA uptake has been linked to major complications of obesity, including insulin resistance, cardiovascular disease, and type 2 diabetes. Fatty acid interactions with a membrane receptor and the initiation of signaling can modify pathways related to nutrient uptake and processing, cell proliferation or differentiation, and secretion of bioactive factors. Here, we review the major membrane receptors involved in FA uptake and FA signaling. We focus on two types of membrane receptors for long-chain FAs: CD36 and the G protein-coupled FA receptors FFAR1 and FFAR4. We describe key signaling pathways and metabolic outcomes for CD36, FFAR1, and FFAR4 and highlight the parallels that provide insight into FA regulation of cell function.

Lorcaserin and phentermine exert anti-obesity effects with modulation of the gut microbiota

Although drugs have been reported to modulate the gut microbiota, the effects of anti-obesity drugs on the gut microbiota remain unclear. Lorcaserin (LS) and phentermine (PT) are commonly used anti-obesity drugs. However, to our best knowledge, no studies have simultaneously assessed the effects of LS and PT on obesity and gut microbiota. This study aimed to explore the relationship between the anti-obesity effects of LS and PT and re-modulation of host gut microbiota. To test hypothesis, we fed C57BL/6J mice with a high-fat diet supplemented with LS and PT via oral gavage for 8 weeks. After sacrifice, body weight, fat accumulation, and serum biomarkers were measured, and the gut microbial composition was analyzed using 16 s rRNA amplicon sequencing. LS and PT were observed to modulate the gut microbial composition and restore gut microbial dysbiosis, as indicated by an increased Firmicutes/Bacteroidetes ratio. Significantly modulated genera by LS and PT treatment were strongly correlated with obesity-related markers. Additionally, LS and PT increased the mRNA level of G protein-coupled receptor 120 (GPR120) in the colon tissue. ASV3566, which corresponds to Eubacterium coprostanoligenes, was correlated with GPR120 and obesity-related markers such as glutamic pyruvic transaminase (GPT) and serum triglyceride (TG). In conclusion, LS and PT can modulate the gut microbiota dysbiosis and the gut microbiota plays a role in mediating the anti-obesity effect of drugs.

How Arrestins and GRKs Regulate the Function of Long Chain Fatty Acid Receptors

FFA1 and FFA4, two G protein-coupled receptors that are activated by long chain fatty acids, play crucial roles in mediating many biological functions in the body. As a result, these fatty acid receptors have gained considerable attention due to their potential to be targeted for the treatment of type-2 diabetes. However, the relative contribution of canonical G protein-mediated signalling versus the effects of agonist-induced phosphorylation and interactions with β-arrestins have yet to be fully defined. Recently, several reports have highlighted the ability of β-arrestins and GRKs to interact with and modulate different functions of both FFA1 and FFA4, suggesting that it is indeed important to consider these interactions when studying the roles of FFA1 and FFA4 in both normal physiology and in different disease settings. Here, we discuss what is currently known and show the importance of understanding fully how β-arrestins and GRKs regulate the function of long chain fatty acid receptors.

Free Fatty Acid Receptors (FFARs) in Adipose: Physiological Role and Therapeutic Outlook

Fatty acids (FFAs) are important biological molecules that serve as a major energy source and are key components of biological membranes. In addition, FFAs play important roles in metabolic regulation and contribute to the development and progression of metabolic disorders like diabetes. Recent studies have shown that FFAs can act as important ligands of G-protein-coupled receptors (GPCRs) on the surface of cells and impact key physiological processes. Free fatty acid-activated receptors include FFAR1 (GPR40), FFAR2 (GPR43), FFAR3 (GPR41), and FFAR4 (GPR120). FFAR2 and FFAR3 are activated by short-chain fatty acids like acetate, propionate, and butyrate, whereas FFAR1 and FFAR4 are activated by medium- and long-chain fatty acids like palmitate, oleate, linoleate, and others. FFARs have attracted considerable attention over the last few years and have become attractive pharmacological targets in the treatment of type 2 diabetes and metabolic syndrome. Several lines of evidence point to their importance in the regulation of whole-body metabolic homeostasis including adipose metabolism. Here, we summarize our current understanding of the physiological functions of FFAR isoforms in adipose biology and explore the prospect of FFAR-based therapies to treat patients with obesity and Type 2 diabetes.

GPR120 agonist ameliorated insulin resistance and improved ovarian function

GPR120 is implicated in the regulation of glucose and lipid metabolism, and insulin resistance. In the current study, we aimed to investigate the role of GPR120 in polycystic ovary syndrome (PCOS). With the adoption of dehydroepiandrosterone, a rat model was established to simulate PCOS in vitro. mRNA and protein expression levels of GPR120 were measured using RT-qPCR and western blot, respectively. In addition, expression levels of testosterone, estradiol, luteinizing hormone and follicle-stimulating hormone, serum total cholesterol and triglyceride were assessed using the corresponding kits. Moreover, haematoxylin and eosin staining was used to detect pathological changes in ovary or liver and oil red staining was utilized to evaluate lipid accumulation. In the present study, GPR120 was downregulated in plasma, liver and ovary in the PCOS rat model. In addition, the GPR120 agonist regulated lipid metabolism in the liver and weight in the PCOS rat model. Furthermore, the GPR120 agonist decreased insulin resistance in the PCOS rat model but improved the ovarian function. It is suggested that GPR120 plays a vital role in suppressing insulin resistance, regulating ovary function and decreasing lipid accumulation in the liver, demonstrating that targeting GPR120 could be an effective method for the improvement of PCOS.

Atypical Antipsychotics and Metabolic Syndrome: From Molecular Mechanisms to Clinical Differences

Atypical antipsychotics (AAPs) are commonly prescribed medications to treat schizophrenia, bipolar disorders and other psychotic disorders. However, they might cause metabolic syndrome (MetS) in terms of weight gain, dyslipidemia, type 2 diabetes (T2D), and high blood pressure, which are responsible for reduced life expectancy and poor adherence. Importantly, there is clear evidence that early metabolic disturbances can precede weight gain, even if the latter still remains the hallmark of AAPs use. In fact, AAPs interfere profoundly with glucose and lipid homeostasis acting mostly on hypothalamus, liver, pancreatic β-cells, adipose tissue, and skeletal muscle. Their actions on hypothalamic centers via dopamine, serotonin, acetylcholine, and histamine receptors affect neuropeptides and 5'AMP-activated protein kinase (AMPK) activity, thus producing a supraphysiological sympathetic outflow augmenting levels of glucagon and hepatic glucose production. In addition, altered insulin secretion, dyslipidemia, fat deposition in the liver and adipose tissues, and insulin resistance become aggravating factors for MetS. In clinical practice, among AAPs, olanzapine and clozapine are associated with the highest risk of MetS, whereas quetiapine, risperidone, asenapine and amisulpride cause moderate alterations. The new AAPs such as ziprasidone, lurasidone and the partial agonist aripiprazole seem more tolerable on the metabolic profile. However, these aspects must be considered together with the differences among AAPs in terms of their efficacy, where clozapine still remains the most effective. Intriguingly, there seems to be a correlation between AAP's higher clinical efficacy and increase risk of metabolic alterations. Finally, a multidisciplinary approach combining psychoeducation and therapeutic drug monitoring (TDM) is proposed as a first-line strategy to avoid the MetS. In addition, pharmacological treatments are discussed as well.

The Endocannabinoid System and PPARs: Focus on Their Signalling Crosstalk, Action and Transcriptional Regulation

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors including PPARα, PPARγ, and PPARβ/δ, acting as transcription factors to regulate the expression of a plethora of target genes involved in metabolism, immune reaction, cell differentiation, and a variety of other cellular changes and adaptive responses. PPARs are activated by a large number of both endogenous and exogenous lipid molecules, including phyto- and endo-cannabinoids, as well as endocannabinoid-like compounds. In this view, they can be considered an extension of the endocannabinoid system. Besides being directly activated by cannabinoids, PPARs are also indirectly modulated by receptors and enzymes regulating the activity and metabolism of endocannabinoids, and, vice versa, the expression of these receptors and enzymes may be regulated by PPARs. In this review, we provide an overview of the crosstalk between cannabinoids and PPARs, and the importance of their reciprocal regulation and modulation by common ligands, including those belonging to the extended endocannabinoid system (or "endocannabinoidome") in the control of major physiological and pathophysiological functions.

Omega 3 fatty acids stimulate thermogenesis during torpor in the Arctic Ground Squirrel

Omega 3 polyunsaturated fatty acids (PUFAs) influence metabolism and thermogenesis in non-hibernators. How omega 3 PUFAs influence Arctic Ground Squirrels (AGS) during hibernation is unknown. Prior to hibernation we fed AGS chow composed of an omega 6:3 ratio approximately 1:1 (high in omega 3 PUFA, termed Balanced Diet), or an omega 6:3 ratio of 5:1 (Standard Rodent Chow), and measured the influence of diet on core body temperature (T_b), brown adipose tissue (BAT) mass, fatty acid profiles of BAT, white adipose tissue (WAT) and plasma as well as hypothalamic endocannabinoid and endocannabinoid-like bioactive fatty acid amides during hibernation. Results show feeding a diet high in omega 3 PUFAs, with a more balanced omega 6:3 ratio, increases AGS T_b in torpor. We found the diet-induced increase in T_b during torpor is most easily explained by an increase in the mass of BAT deposits of Balanced Diet AGS. The increase in BAT mass is associated with elevated levels of metabolites DHA and EPA in tissue and plasma suggesting that these omega 3 PUFAs may play a role in thermogenesis during torpor. While we did not observe diet-induced change in endocannabinoids, we do report altered hypothalamic levels of some endocannabinoids, and endocannabinoid-like compounds, during hibernation.

Anti-obesity effects of DHA and EPA in high fat-induced insulin resistant mice

Docosahexaenoic acid (DHA, 22:6) and eicosapentaenoic acid (EPA, 20:5) exert their anti-obesity effect by mechanisms dependent or independent of PPARγ and GPR120 signaling in insulin resistant mice.

Diversity of energy metabolism in immune responses regulated by micro-organisms and dietary nutrition

Immune metabolism has been recognized as a new paradigm in the regulation of host immunity. In the environment, there are many micro-organisms including pathogenic and non-pathogenic and/or beneficial ones. Immune cells exhibit various responses against different types of microbes, which seem to be associated with changes in energy metabolism. In addition, dietary nutrition influences host metabolism and consequent responses by immune cells. In this review, we describe the complex network of immune metabolism from the perspectives of nutrition, micro-organisms and host immunity for the control of immunologic health and diseases.

Investigating the effects of differently produced synthetic amorphous silica (E 551) on the integrity and functionality of the human intestinal barrier using an advanced in vitro co-culture model

E 551, also known as synthetic amorphous silica (SAS), is the second most produced food additive. However, according to the re-evaluation of E 551 by the European Food Safety Authority (EFSA) in 2018, the amount of available data on the oral toxicity of food grade E 551 is still insufficient for reliable risk assessment. To close this gap, this study aimed to investigate six food-grade SAS with distinct physicochemical properties on their interaction with the intestinal barrier using advanced in vitro intestinal co-cultures and to identify potential structure-activity relationships. A mucus-secreting Caco-2/HT-29/Raji co-culture model was treated with up to 50 µg/ml SAS for 48 h, which represents a dose range relevant to dietary exposure. No effects on cell viability, barrier integrity, microvilli function or the release of inflammatory cytokine were detected after acute exposure. Slight biological responses were observed for few SAS materials on iron uptake and gene expression levels of mucin 1 and G-protein coupled receptor 120 (GPR120). There was no clear correlation between SAS properties (single or combined) and the observed biological responses. Overall, this study provides novel insights into the short-term impact of food-relevant SAS with distinct characteristics on the intestinal epithelium including a range of intestine-specific functional endpoints. In addition, it highlights the importance of using advanced intestinal co-cultures embracing relevant cell types as well as a protective mucus barrier to achieve a comprehensive understanding of the biological response of food additives at the intestinal barrier in vitro.

Multi-Set Testing Strategies Show Good Behavior When Applied to Very Large Sets of Rare Variants

Gene-based tests of association (e.g., variance components and burden tests) are now common practice for analyses attempting to elucidate the contribution of rare genetic variants on common disease. As sequencing datasets continue to grow in size, the number of variants within each set (e.g., gene) being tested is also continuing to grow. Pathway-based methods have been used to allow for the initial aggregation of gene-based statistical evidence and then the subsequent aggregation of evidence across the pathway. This “multi-set” approach (first gene-based test, followed by pathway-based) lacks thorough exploration in regard to evaluating genotype–phenotype associations in the age of large, sequenced datasets. In particular, we wonder whether there are statistical and biological characteristics that make the multi-set approach optimal vs. simply doing all gene-based tests? In this paper, we provide an intuitive framework for evaluating these questions and use simulated data to affirm us this intuition. A real data application is provided demonstrating how our insights manifest themselves in practice. Ultimately, we find that when initial subsets are biologically informative (e.g., tending to aggregate causal genetic variants within one or more subsets, often genes), multi-set strategies can improve statistical power, with particular gains in cases where causal variants are aggregated in subsets with less variants overall (high proportion of causal variants in the subset). However, we find that there is little advantage when the sets are non-informative (similar proportion of causal variants in the subsets). Our application to real data further demonstrates this intuition. In practice, we recommend wider use of pathway-based methods and further exploration of optimal ways of aggregating variants into subsets based on emerging biological evidence of the genetic architecture of complex disease.

Novel Insights into Adipogenesis from the Perspective of Transcriptional and RNA N6-Methyladenosine-Mediated Post-Transcriptional Regulation

Obesity is a critical risk factor causing the development of metabolic diseases and cancers. Its increasing prevalence worldwide has aroused great concerns of the researchers on adipose development and metabolic function. During adipose expansion, adipogenesis is a way to store lipids as well as to avoid lipotoxicity in other tissues, and may be an approach to offset the negative metabolic effects of obesity. In this Review, the transcriptional regulation of adipogenesis is outlined to characterize numerous biological processes in research on the determination of adipocyte fate and regulation of adipogenic differentiation. Notably, one of the post-transcriptional modifications of mRNA, namely, N6-methyladenosine (m6A), has been recently found to play a role in adipogenesis. Here, the roles of m6A-related enzymes and proteins in adipogenesis, with a particular focus on how these m6A-related proteins function at different stages of adipogenesis, are mainly discussed. The Review also highlights the coordination role of the transcriptional and post-transcriptional (RNA m6A methylation) regulation in adipogenesis and related biological processes. In this context, a better understanding of adipogenesis at both the transcriptional and post-transcriptional levels may facilitate the development of novel strategies to improve metabolic health in obesity.

Protective Effects of Eicosapentaenoic Acid Plus Hydroxytyrosol Supplementation Against White Adipose Tissue Abnormalities in Mice Fed a High-Fat Diet

Objective: Obesity induced by high-fat diet (HFD) elicits white adipose tissue dysfunction. In this study, we have hypothesized that the metabolic modulator eicosapentaenoic acid (EPA) combined with the antioxidant hydroxytyrosol (HT) attenuates HFD-induced white adipose tissue (WAT) alterations. Methods: C57BL/6J mice were administered with a HFD (60% fat, 20% protein, 20% carbohydrates) or control diet (CD; 10% fat, 20% protein, 70% carbohydrates), with or without EPA (50 mg/kg/day), HT (5 mg/kg/day), or both for 12 weeks. Determinations in WAT include morphological parameters, EPA and docosahexaenoic acid content in phospholipids (gas chromatography), lipogenesis, oxidative stress (OS) and inflammation markers, and gene expression and activities of transcription factors, such as sterol regulatory element-binding protein-1c (SREBP-1c), peroxisome proliferator-activated receptor-gamma (PPAR-γ), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) (p65 subunit) and nuclear factor erythroid 2-related factor 2 (Nrf2) (quantitative polymerase chain reaction and enzyme linked immunosorbent assay). Results: HFD led to WAT hypertrophy in relation to PPAR-γ downregulation. WAT metabolic dysfunction was characterized by upregulation of lipogenic SREBP-1c system, mitochondrial energy metabolism depression, loss of the antioxidant Nrf2 signaling with OS enhancement, n-3 long-chain polyunsaturated fatty acids depletion and activation of the pro-inflammatory NF-κB system. EPA and HT co-supplementation diminished HFD-dependent effects additively, reaching values close or similar to controls. Conclusion: Data presented strengthen the importance of combined protocols such as EPA plus HT to attenuate metabolic-inflammatory states triggered by obesity.

Mechanisms underlying N3-PUFA regulation of white adipose tissue endocrine function

Omega-3 polyunsaturated fatty acids (N3-PUFA) are widely reported to improve obesity-associated metabolic impairments, in part, through the regulation of adipokine and cytokine secretion from white adipose tissue (WAT). However, the precise underlying molecular mechanisms by which N3-PUFA influence WAT endocrine function remain poorly described. Available evidence supports that N3-PUFA and related bioactive lipid mediators regulate several intracellular pathways that converge on two important transcription factors: PPAR-γ and NF-κB. Further, N3-PUFA signaling through GPR120 appears integral for the regulation of adipokine and cytokine production. This review collates insights from in vitro and in vivo studies using genetic and chemical inhibition of key signaling proteins to describe the pathways by which N3-PUFA regulate WAT endocrine function. Existing gaps in knowledge and opportunities to advance our understanding in this area are also highlighted.

The GPR120 Agonist TUG-891 Inhibits the Motility and Phagocytosis of Mouse Alveolar Macrophages

Movement and phagocytosis characterize the fundamental actions of macrophages. Although it is known that the free fatty acid receptor GPR120 is expressed in macrophages and regulates cytokine expression to exert anti-inflammatory activities, the effects of GPR120 activation on the motility and phagocytosis of macrophages are not clear. In this study, mouse alveolar macrophages (AM) were stimulated with the GPR120 agonist TUG-891, and the changes in cell motility, intracellular Ca²⁺ concentration ([Ca²⁺]i), and the ability of phagocytosis were measured. Mouse AM in controls exhibited active movement in vitro, and TUG-891 significantly restrained AM movement. Meanwhile, TUG-891 stimulated a quick increase in [Ca²⁺]i in AM, which was blocked separately by the Gq protein inhibitor YM-254890, the phospholipase C (PLC) inhibitor U73122, or depletion of endoplasmic reticulum (ER) Ca²⁺ store by thapsigargin. The inhibition of AM movement by TUG-891 was eliminated by YM-254890, U73122, thapsigargin, and chelation of cytosolic Ca²⁺ by BAPTA. Moreover, TUG-891 inhibited AM phagocytosis of fluorescent microspheres, which was also blocked by YM-254890, U73122, thapsigargin, and BAPTA. In conclusion, GPR120 activation in mouse AM increases [Ca²⁺]i but inhibits the motility and phagocytosis via Gq protein/PLC-mediated Ca²⁺ release from ER Ca²⁺ store.

Free Fatty Acid Receptors in Health and Disease

Fatty acids are metabolized and synthesized as energy substrates during biological responses. Long- and medium-chain fatty acids derived mainly from dietary triglycerides, and short-chain fatty acids (SCFAs) produced by gut microbial fermentation of the otherwise indigestible dietary fiber, constitute the major sources of free fatty acids (FFAs) in the metabolic network. Recently, increasing evidence indicates that FFAs serve not only as energy sources but also as natural ligands for a group of orphan G protein-coupled receptors (GPCRs) termed free fatty acid receptors (FFARs), essentially intertwining metabolism and immunity in multiple ways, such as via inflammation regulation and secretion of peptide hormones. To date, several FFARs that are activated by the FFAs of various chain lengths have been identified and characterized. In particular, FFAR1 (GPR40) and FFAR4 (GPR120) are activated by long-chain saturated and unsaturated fatty acids, while FFAR3 (GPR41) and FFAR2 (GPR43) are activated by SCFAs, mainly acetate, butyrate, and propionate. In this review, we discuss the recent reports on the key physiological functions of the FFAR-mediated signaling transduction pathways in the regulation of metabolism and immune responses. We also attempt to reveal future research opportunities for developing therapeutics for metabolic and immune disorders.

Fatty Acid Signaling Mechanisms in Neural Cells: Fatty Acid Receptors

Fatty acids (FAs) are typically associated with structural and metabolic roles, as they can be stored as triglycerides, degraded by β-oxidation or used in phospholipids’ synthesis, the main components of biological membranes. It has been shown that these lipids exhibit also regulatory functions in different cell types. FAs can serve as secondary messengers, as well as modulators of enzymatic activities and substrates for cytokines synthesis. More recently, it has been documented a direct activity of free FAs as ligands of membrane, cytosolic, and nuclear receptors, and cumulative evidence has emerged, demonstrating its participation in a wide range of physiological and pathological conditions. It has been long known that the central nervous system is enriched with poly-unsaturated FAs, such as arachidonic (C20:4ω-6) or docosohexaenoic (C22:6ω-3) acids. These lipids participate in the regulation of membrane fluidity, axonal growth, development, memory, and inflammatory response. Furthermore, a whole family of low molecular weight compounds derived from FAs has also gained special attention as the natural ligands for cannabinoid receptors or key cytokines involved in inflammation, largely expanding the role of FAs as precursors of signaling molecules. Nutritional deficiencies, and alterations in lipid metabolism and lipid signaling have been associated with developmental and cognitive problems, as well as with neurodegenerative diseases. The molecular mechanism behind these effects still remains elusive. But in the last two decades, different families of proteins have been characterized as receptors mediating FAs signaling. This review focuses on different receptors sensing and transducing free FAs signals in neural cells: (1) membrane receptors of the family of G Protein Coupled Receptors known as Free Fatty Acid Receptors (FFARs); (2) cytosolic transport Fatty Acid-Binding Proteins (FABPs); and (3) transcription factors Peroxisome Proliferator-Activated Receptors (PPARs). We discuss how these proteins modulate and mediate direct regulatory functions of free FAs in neural cells. Finally, we briefly discuss the advantages of evaluating them as potential targets for drug design in order to manipulate lipid signaling. A thorough characterization of lipid receptors of the nervous system could provide a framework for a better understanding of their roles in neurophysiology and, potentially, help for the development of novel drugs against aging and neurodegenerative processes.

Increased GPR120 level is associated with gestational diabetes mellitus

G-protein coupled receptor 120 (GPR120 or FFAR4) functions as a receptor for free fatty acids and plays a critical role in lipid metabolism. Studies have shown a close relationship between GDM and lipid metabolism disorders, whether GPR120 participates in the metabolic regulation of GDM remains unclear. In this study, 29 women with GDM and 33 normal pregnant women were enrolled. Lipid profiles were determined by lipidomics, expression of GPR120 and FGF21 was measured in the white blood cells, and regulation of FGF21 by GPR120 was investigated in THP-1 cells as well as human peripheral blood monocytes. Lipidomics reveal altered lipid metabolism in patients with GDM. The expression of both GPR120 and FGF21 is significantly higher in the GDM than in the control at the 32nd and 37th weeks of pregnancy, but the differences disappear by the 2nd day post-delivery. Generally positive correlations are found between the total amount of lipids and expression levels of GPR120 and FGF21 in GDM patients. FGF21 expression is induced by GPR120 activation in THP-1 cells and WBCs. GPR120 may act as a metabolic regulator, through the induction of FGF21, to control lipid metabolism, and GDM patients may manifest a GPR120 insensitivity.

Omega-3 Fatty Acids as Druggable Therapeutics for Neurodegenerative Disorders

Neurodegenerative disorders are commonly associated with a complex pattern of pathophysiological hallmarks, including increased oxidative stress and neuroinflammation, which makes their treatment challenging. Omega-3 Fatty Acids (O3FA) are natural products with reported neuroprotective, anti-inflammatory, and antioxidant effects. These effects have been attributed to their incorporation into neuronal membranes or through the activation of intracellular or recently discovered cell-surface receptors (i.e., Free-Fatty Acid Receptors; FFAR). Molecular docking studies have investigated the roles of O3FA as agonists of FFAR and have led to the development of receptor-specific targeted agonists for therapeutic purposes. Moreover, novel formulation strategies for targeted delivery of O3FA to the brain have supported their development as therapeutics for neurodegenerative disorders. Despite the compelling evidence of the beneficial effects of O3FA for several neuroprotective functions, they are currently only available as unregulated dietary supplements, with only a single FDA-approved prescription product, indicated for triglyceride reduction. This review highlights the relative safety and efficacy of O3FA, their drug-like properties, and their capacity to be formulated in clinically viable drug delivery systems. Interestingly, the presence of cardiac conditions such as hypertriglyceridemia is associated with brain pathophysiological hallmarks of neurodegeneration, such as neuroinflammation, thereby further suggesting potential therapeutic roles of O3FA for neurodegenerative disorders. Taken together, this review article summarizes and integrates the compelling evidence regarding the feasibility of developing O3FA and their synthetic derivatives as potential drugs for neurodegenerative disorders.

Science behind the cardio-metabolic benefits of omega-3 polyunsaturated fatty acids: biochemical effects vs. clinical outcomes

Lower incidence of cardiovascular disease (CVD) in the Greenland Inuit, Northern Canada and Japan has been attributed to their consumption of seafood rich in long chain omega-3 polyunsaturated fatty acids (LCn-3PUFA). While a large majority of pre-clinical and intervention trials have demonstrated heart health benefits of LCn-3PUFA, some studies have shown no effects or even negative effects. LCn-3PUFA have been shown to favourably modulate blood lipid levels, particularly a reduction in circulating levels of triglycerides. High density lipoprotein-cholesterol (HDL-C) levels are elevated following dietary supplementation with LCn-3PUFA. Although LCn-3PUFA have been shown to increase low-density lipoprotein-cholesterol (LDL-C) levels, the increase is primarily in the large-buoyant particles that are less atherogenic than small-dense LDL particles. The anti-inflammatory effects of LCn-3PUFA have been clearly outlined with inhibition of NFkB mediated cytokine production being the main mechanism. In addition, reduction in adhesion molecules (intercellular adhesion molecule, ICAM and vascular cell adhesion molecule 1, VCAM-1) and leukotriene production have also been demonstrated following LCn-3PUFA supplementation. Anti-aggregatory effects of LCn-3PUFA have been a subject of controversy, however, recent studies showing sex-specific effects on platelet aggregation have helped resolve the effects on hyperactive platelets. Improvements in endothelium function, blood flow and blood pressure after LCn-3PUFA supplementation add to the mechanistic explanation on their cardio-protective effects. Modulation of adipose tissue secretions including pro-inflammatory mediators and adipokines by LCn-3PUFA has re-ignited interest in their cardiovascular health benefits. The aim of this narrative review is to filter out the reasons for possible disparity between cohort, mechanistic, pre-clinical and clinical studies. The focus of the article is to provide possible explanation for the observed controversies surrounding heart health benefits of LCn-3PUFA.

Fatty and hydroxycarboxylic acid receptors: The missing link of immune response and metabolism in cattle

Fatty and hydroxycarboxylic acids are one of the main intermediates of energy metabolism in ruminants and critical in the milk production of cattle. High production demands on a dairy farm can induce nutritional imbalances and metabolism disorders, which have been widely associated with the onset of sterile inflammatory processes and increased susceptibility to infections. The literature suggests that short-chain fatty acids (SCFA), long-chain fatty acids (LCFA) and hydroxycarboxylic acids are relevant modulators of the host innate inflammatory response. For instance, increased SCFA and lactate levels are associated with subacute ruminal acidosis (SARA) and the activation of pro-inflammatory processes mediated by diverse leukocyte and vascular endothelial cells. As such, free LCFA and the ketone body β-hydroxybutyrate are significantly increased in the plasma 1-2 weeks postpartum, coinciding with the time period in which cows are more susceptible to acquiring infectious diseases that the host innate immune system should actively oppose. Today, many of these pro-inflammatory responses can be related to the activation of specific G protein-coupled receptors, including GPR41/FFA3 and GPR43/FFA2 for SCFA; GPR40/FFA1 and GPR120/FFA4 for LCFA, GPR109A/HCA2 for ketone body β-hydroxybutyrate, and GPR81/HCA₁ for lactate, all expressed in different bovine tissues. The activation of these receptors modulates the release of intracellular granules [e.g., metalloproteinase-9 (MMP-9) and lactoferrin], radical oxygen species (ROS) production, chemotaxis, and the production of relevant pro-inflammatory mediators. The article aimed to review the role of natural ligands and receptors and the resulting impact on the host innate immune reaction of cattle and, further, to address the most recent evidence supporting a potential connection to metabolic disorders.

Adaptive thermogenesis by dietary n-3 polyunsaturated fatty acids: Emerging evidence and mechanisms

Brown/beige fat plays a crucial role in maintaining energy homeostasis through non-shivering thermogenesis in response to cold temperature and excess nutrition (adaptive thermogenesis). Although numerous molecular and genetic regulators have been identified, relatively little information is available regarding thermogenic dietary molecules. Recently, a growing body of evidence suggests that high consumption of n-3 polyunsaturated fatty acids (PUFA) or activation of GPR120, a membrane receptor of n-3 PUFA, stimulate adaptive thermogenesis. In this review, we summarize the emerging evidence that n-3 PUFA promote brown/beige fat formation and highlight the potential mechanisms whereby n-3 PUFA require GPR120 as a signaling platform or act independently. Human clinical trials are revisited in the context of energy expenditure. Additionally, we explore some future perspective that n-3 PUFA intake might be a useful strategy to boost or sustain metabolic activities of brown/beige fat at different lifecycle stages of pregnancy and senescence. Given that a high ratio of n-6/n-3 PUFA intake is associated with the development of obesity and type 2 diabetes, understanding the impact of n-6/n-3 ratio on energy expenditure and adaptive thermogenesis will inform the implementation of a novel nutritional strategy for preventing obesity.