Novel role of TLR4 in NAFLD development: Modulation of metabolic enzymes expression

Chinese herbal medicines: The modulator of nonalcoholic fatty liver disease targeting oxidative stress

ETHNOPHARMACOLOGICAL RELEVANCE

Plants are a natural treasure trove; their secondary metabolites participate in several pharmacological processes, making them a crucial component in the synthesis of novel pharmaceuticals and serving as a reserve resource foundation in this process. Nonalcoholic fatty liver disease (NAFLD) is associated with the risk of progression to hepatitis and liver cancer. The "Treatise on Febrile Diseases," "Compendium of Materia Medica," and "Thousand Golden Prescriptions" have listed herbal remedies to treat liver diseases.

AIM OF THE REVIEW

Chinese herbal medicines have been widely used for the prevention and treatment of NAFLD owing to their efficacy and low side effects. The production of reactive oxygen species (ROS) during NAFLD, and the impact and potential mechanism of ROS on the pathogenesis of NAFLD are discussed in this review. Furthermore, common foods and herbs that can be used to prevent NAFLD, as well as the structure-activity relationships and potential mechanisms, are discussed.

METHODS

Web of Science, PubMed, CNKI database, Google Scholar, and WanFang database were searched for natural products that have been used to treat or prevent NAFLD in the past five years. The primary search was performed using the following keywords in different combinations in full articles: NAFLD, herb, natural products, medicine, and ROS. More than 400 research papers and review articles were found and analyzed in this review.

RESULTS

By classifying and discussing the literature, we obtained 86 herbaceous plants, 28 of which were derived from food and 58 from Chinese herbal medicines. The mechanism of NAFLD was proposed through experimental studies on thirteen natural compounds (quercetin, hesperidin, rutin, curcumin, resveratrol, epigallocatechin-3-gallate, salvianolic acid B, paeoniflorin, ginsenoside Rg1, ursolic acid, berberine, honokiol, emodin). The occurrence and progression of NAFLD could be prevented by natural antioxidants through several pathways to prevent ROS accumulation and reduce hepatic cell injuries caused by excessive ROS.

CONCLUSION

This review summarizes the natural products and routinely used herbs (prescription) in the prevention and treatment of NAFLD. Firstly, the mechanisms by which natural products improve NAFLD through antioxidant pathways are elucidated. Secondly, the potential of traditional Chinese medicine theory in improving NAFLD is discussed, highlighting the safety of food-medicine homology and the broader clinical potential of multi-component formulations in improving NAFLD. Aiming to provide theoretical basis for the prevention and treatment of NAFLD.

Breaking the barriers: the role of gut homeostasis in Metabolic-Associated Steatotic Liver Disease (MASLD)

Obesity, insulin resistance (IR), and the gut microbiome intricately interplay in Metabolic-associated Steatotic Liver Disease (MASLD), previously known as Non-Alcoholic Fatty Liver Disease (NAFLD), a growing health concern. The complex progression of MASLD extends beyond the liver, driven by "gut-liver axis," where diet, genetics, and gut-liver interactions influence disease development. The pathophysiology of MASLD involves excessive liver fat accumulation, hepatocyte dysfunction, inflammation, and fibrosis, with subsequent risk of hepatocellular carcinoma (HCC). The gut, a tripartite barrier, with mechanical, immune, and microbial components, engages in a constant communication with the liver. Recent evidence links dysbiosis and disrupted barriers to systemic inflammation and disease progression. Toll-like receptors (TLRs) mediate immunological crosstalk between the gut and liver, recognizing microbial structures and triggering immune responses. The "multiple hit model" of MASLD development involves factors like fat accumulation, insulin resistance, gut dysbiosis, and genetics/environmental elements disrupting the gut-liver axis, leading to impaired intestinal barrier function and increased gut permeability. Clinical management strategies encompass dietary interventions, physical exercise, pharmacotherapy targeting bile acid (BA) metabolism, and microbiome modulation approaches through prebiotics, probiotics, symbiotics, and fecal microbiota transplantation (FMT). This review underscores the complex interactions between diet, metabolism, microbiome, and their impact on MASLD pathophysiology and therapeutic prospects.

GPR40 deficiency worsens metabolic syndrome-associated periodontitis in mice

BACKGROUND AND OBJECTIVE

G protein-coupled receptor 40 (GPR40) is a receptor for medium- and long-chain free fatty acids (FFAs). GPR40 activation improves type 2 diabetes mellitus (T2DM), metabolic syndrome (MetS), and the complications of T2DM and MetS. Periodontitis, a common oral inflammatory disease initiated by periodontal pathogens, is another complication of T2DM and MetS. Since FFAs play a key role in the pathogenesis of MetS which exacerbates periodontal inflammation and GPR40 is a FFA receptor with anti-inflammatory properties, it is important to define the role of GPR40 in MetS-associated periodontitis.

MATERIALS AND METHODS

We induced MetS and periodontitis by high-fat diet and periodontal injection of lipopolysaccharide (LPS), respectively, in wild-type and GPR40-deficient mice and determined alveolar bone loss and periodontal inflammation using micro-computed tomography, histology, and osteoclast staining. We also performed in vitro study to determine the role of GPR40 in the expression of proinflammatory genes.

RESULTS

The primary outcome of the study is that GPR40 deficiency increased alveolar bone loss and enhanced osteoclastogenesis in control mice and the mice with both MetS and periodontitis. GPR40 deficiency also augmented periodontal inflammation in control mice and the mice with both MetS and periodontitis. Furthermore, GPR40 deficiency led to increased plasma lipids and insulin resistance in control mice but had no effect on the metabolic parameters in mice with MetS alone. For mice with both MetS and periodontitis, GPR40 deficiency increased insulin resistance. Finally, in vitro studies with macrophages showed that deficiency or inhibition of GPR40 upregulated proinflammatory genes while activation of GPR40 downregulated proinflammatory gene expression stimulated synergistically by LPS and palmitic acid.

CONCLUSION

GPR40 deficiency worsens alveolar bone loss and periodontal inflammation in mice with both periodontitis and MetS, suggesting that GPR40 plays a favorable role in MetS-associated periodontitis. Furthermore, GPR40 deficiency or inhibition in macrophages further upregulated proinflammatory and pro-osteoclastogenic genes induced by LPS and palmitic acid, suggesting that GPR40 has anti-inflammatory and anti-osteoclastogenic properties.

Involvement of eNAMPT/TLR4 inflammatory signaling in progression of non-alcoholic fatty liver disease, steatohepatitis, and fibrosis

Although the progression of non-alcoholic fatty liver disease (NAFLD) from steatosis to steatohepatitis (NASH) and cirrhosis remains poorly understood, a critical role for dysregulated innate immunity has emerged. We examined the utility of ALT-100, a monoclonal antibody (mAb), in reducing NAFLD severity and progression to NASH/hepatic fibrosis. ALT-100 neutralizes eNAMPT (extracellular nicotinamide phosphoribosyltransferase), a novel damage-associated molecular pattern protein (DAMP) and Toll-like receptor 4 (TLR4) ligand. Histologic and biochemical markers were measured in liver tissues and plasma from human NAFLD subjects and NAFLD mice (streptozotocin/high-fat diet-STZ/HFD, 12 weeks). Human NAFLD subjects (n = 5) exhibited significantly increased NAMPT hepatic expression and significantly elevated plasma levels of eNAMPT, IL-6, Ang-2, and IL-1RA compared to healthy controls, with IL-6 and Ang-2 levels significantly increased in NASH non-survivors. Untreated STZ/HFD-exposed mice displayed significant increases in NAFLD activity scores, liver triglycerides, NAMPT hepatic expression, plasma cytokine levels (eNAMPT, IL-6, and TNFα), and histologic evidence of hepatocyte ballooning and hepatic fibrosis. Mice receiving the eNAMPT-neutralizing ALT-100 mAb (0.4 mg/kg/week, IP, weeks 9 to 12) exhibited marked attenuation of each index of NASH progression/severity. Thus, activation of the eNAMPT/TLR4 inflammatory pathway contributes to NAFLD severity and NASH/hepatic fibrosis. ALT-100 is potentially an effective therapeutic approach to address this unmet NAFLD need.

Microbiome Dysbiosis: A Pathological Mechanism at the Intersection of Obesity and Glaucoma

The rate at which obesity is becoming an epidemic in many countries is alarming. Obese individuals have a high risk of developing elevated intraocular pressure and glaucoma. Additionally, glaucoma is a disease of epidemic proportions. It is characterized by neurodegeneration and neuroinflammation with optic neuropathy and the death of retinal ganglion cells (RGC). On the other hand, there is growing interest in microbiome dysbiosis, particularly in the gut, which has been widely acknowledged to play a prominent role in the etiology of metabolic illnesses such as obesity. Recently, studies have begun to highlight the fact that microbiome dysbiosis could play a critical role in the onset and progression of several neurodegenerative diseases, as well as in the development and progression of several ocular disorders. In obese individuals, gut microbiome dysbiosis can induce endotoxemia and systemic inflammation by causing intestinal barrier malfunction. As a result, bacteria and their metabolites could be delivered via the bloodstream or mesenteric lymphatic vessels to ocular regions at the level of the retina and optic nerve, causing tissue degeneration and neuroinflammation. Nowadays, there is preliminary evidence for the existence of brain and intraocular microbiomes. The altered microbiome of the gut could perturb the resident brain-ocular microbiome ecosystem which, in turn, could exacerbate the local inflammation. All these processes, finally, could lead to the death of RGC and neurodegeneration. The purpose of this literature review is to explore the recent evidence on the role of gut microbiome dysbiosis and related inflammation as common mechanisms underlying obesity and glaucoma.

Dysregulated hepatic lipid metabolism and gut microbiota associated with early-stage NAFLD in ASPP2-deficiency mice

BACKGROUND

Growing evidence indicates that lipid metabolism disorders and gut microbiota dysbiosis were related to the progression of non-alcoholic fatty liver disease (NAFLD). Apoptosis-stimulating p53 protein 2 (ASPP2) has been reported to protect against hepatocyte injury by regulating the lipid metabolism, but the mechanisms remain largely unknown. In this study, we investigate the effect of ASPP2 deficiency on NAFLD, lipid metabolism and gut microbiota using ASPP2 globally heterozygous knockout (ASPP2+/-) mice.

METHODS

ASPP2+/- Balb/c mice were fed with methionine and choline deficient diet for 3, 10 and 40 day to induce an early and later-stage of NAFLD, respectively. Fresh fecal samples were collected and followed by 16S rRNA sequencing. HPLC-MRM relative quantification analysis was used to identify changes in hepatic lipid profiles. The expression level of innate immunity-, lipid metabolism- and intestinal permeability-related genes were determined. A spearman's rank correlation analysis was performed to identify possible correlation between hepatic medium and long-chain fatty acid and gut microbiota in ASPP2-deficiency mice.

RESULTS

Compared with the WT control, ASPP2-deficiency mice developed moderate steatosis at day 10 and severe steatosis at day 40. The levels of hepatic long chain omega-3 fatty acid, eicosapentaenoic (EPA, 20:5 n-3) and docosahexaenoic (DHA, 22:6 n-3), were decreased at day 10 and increased at day 40 in ASPP+/- mice. Fecal microbiota analysis showed significantly increased alpha and beta diversity, as well as the composition of gut microbiota at the phylum, class, order, family, genus, species levels in ASPP2+/- mice. Moreover, ASPP-deficiency mice exhibited impaired intestinal barrier function, reduced expression of genes associated with chemical barrier (REG3B, REG3G, Lysozyme and IAP), and increased expression of innate immune components (TLR4 and TLR2). Furthermore, correlation analysis between gut microbiota and fatty acids revealed that EPA was significantly negatively correlated with Bifidobacterium family.

CONCLUSION

Our findings suggested that ASPP2-deficiency promotes the progression of NAFLD, alterations in fatty acid metabolism and gut microbiota dysbiosis. The long chain fatty acid EPA was significantly negatively correlated with Bifidobacterial abundance, which is a specific feature of NAFLD in ASPP2-deficiency mice. Totally, the results provide evidence for a mechanism of ASPP2 on dysregulation of fatty acid metabolism and gut microbiota dysbiosis.

Dietary Fructose and Fructose-Induced Pathologies

The consumption of fructose as sugar and high-fructose corn syrup has markedly increased during the past several decades. This trend coincides with the exponential rise of metabolic diseases, including obesity, nonalcoholic fatty liver disease, cardiovascular disease, and diabetes. While the biochemical pathways of fructose metabolism were elucidated in the early 1990s, organismal-level fructose metabolism and its whole-body pathophysiological impacts have been only recently investigated. In this review, we discuss the history of fructose consumption, biochemical and molecular pathways involved in fructose metabolism in different organs and gut microbiota, the role of fructose in the pathogenesis of metabolic diseases, and the remaining questions to treat such diseases.

New Insights of OLFM2 and OLFM4 in Gut-Liver Axis and Their Potential Involvement in Nonalcoholic Fatty Liver Disease

Olfactomedins (OLFMs) are a family of glycoproteins that play a relevant role in embryonic development and in some pathological processes. Although OLFM2 is involved in the regulation of the energy metabolism and OLFM4 is an important player in inflammation, innate immunity and cancer, the role of OLFMs in NAFLD-related intestinal dysbiosis remains unknown. In this study, we analysed the hepatic mRNA expression of OLFM2 and the jejunal expression of OLFM4 in a well-established cohort of women with morbid obesity (MO), classified according to their hepatic histology into normal liver (n = 27), simple steatosis (n = 26) and nonalcoholic steatohepatitis (NASH, n = 16). Our results showed that OLFM2 hepatic mRNA was higher in NASH, in advanced degrees of steatosis and in the presence of lobular inflammation. Additionally, we obtained positive correlations between hepatic OLFM2 and glucose, cholesterol, trimethylamine N-oxide and deoxycholic acid levels and hepatic fatty acid synthase, and negative associations with weight and jejunal Toll-like receptors (TLR4) and TLR5 expression. Regarding jejunal OLFM4, we observed positive correlations with circulating interleukin (IL)-8, IL-10, IL-17 and jejunal TLR9. In conclusion, OLFM2 in the liver seems to play a relevant role in NAFLD progression, while OLFM4 in the jejunum could be involved in gut dysbiosis-related inflammatory events.

Oxidized Lipids: Common Immunogenic Drivers of Non-Alcoholic Fatty Liver Disease and Atherosclerosis

The prevalence of non-alcoholic fatty liver disease (NAFLD), ranging from simple steatosis to inflammatory steatohepatitis (NASH) and cirrhosis, continues to rise, making it one of the major chronic liver diseases and indications for liver transplantation worldwide. The pathological processes underlying NAFLD not only affect the liver but are also likely to have systemic effects. In fact, growing evidence indicates that patients with NAFLD are at increased risk for developing atherosclerosis. Indeed, cardiovascular complications are the leading cause of mortality in NAFLD patients. Here, we aim to address common pathophysiological molecular pathways involved in chronic fatty liver disease and atherosclerosis. In particular, we focus on the role of oxidized lipids and the formation of oxidation-specific epitopes, which are important targets of host immunity. Acting as metabolic danger signals, they drive pro-inflammatory processes and thus contribute to disease progression. Finally, we summarize encouraging studies indicating that oxidized lipids are promising immunological targets to improve intervention strategies for NAFLD and potentially limit the risk of developing atherosclerosis.

Non-Alcoholic Fatty Liver Disease in HIV/HBV Patients - a Metabolic Imbalance Aggravated by Antiretroviral Therapy and Perpetuated by the Hepatokine/Adipokine Axis Breakdown

Non-alcoholic fatty liver disease (NAFLD) is strongly associated with the metabolic syndrome and is one of the most prevalent comorbidities in HIV and HBV infected patients. HIV plays an early and direct role in the development of metabolic syndrome by disrupting the mechanism of adipogenesis and synthesis of adipokines. Adipokines, molecules that regulate the lipid metabolism, also contribute to the progression of NAFLD either directly or via hepatic organokines (hepatokines). Most hepatokines play a direct role in lipid homeostasis and liver inflammation but their role in the evolution of NAFLD is not well defined. The role of HBV in the pathogenesis of NAFLD is controversial. HBV has been previously associated with a decreased level of triglycerides and with a protective role against the development of steatosis and metabolic syndrome. At the same time HBV displays a high fibrogenetic and oncogenetic potential. In the HIV/HBV co-infection, the metabolic changes are initiated by mitochondrial dysfunction as well as by the fatty overload of the liver, two interconnected mechanisms. The evolution of NAFLD is further perpetuated by the inflammatory response to these viral agents and by the variable toxicity of the antiretroviral therapy. The current article discusses the pathogenic changes and the contribution of the hepatokine/adipokine axis in the development of NAFLD as well as the implications of HIV and HBV infection in the breakdown of the hepatokine/adipokine axis and NAFLD progression.

Epigenetics in NAFLD/NASH: Targets and therapy

Recently non-alcoholic fatty liver disease (NAFLD) has grabbed considerable scientific attention, owing to its rapid increase in prevalence worldwide and growing burden on end-stage liver diseases. Metabolic syndrome including obesity, diabetes, and hypertension poses a grave risk to NAFLD etiology and progression. With no drugs available, the mainstay of NAFLD management remains lifestyle changes with exercise and dietary modifications. Nonselective drugs such as metformin, thiazolidinediones (TZDs), ursodeoxycholic acid (UDCA), silymarin, etc., are also being used to target the interrelated pathways for treating NAFLD. Considering the enormous disease burden and the unmet need for drugs, fresh insights into pathogenesis and drug discovery are required. The emergence of the field of epigenetics offers a convincing explanation for the basis of lifestyle, environmental, and other risk factors to influence NAFLD pathogenesis. Therefore, understanding these epigenetic modifications to target the primary cause of the disease might prove a rational strategy to prevent the disease and develop novel therapeutic interventions. Apart from describing the role of epigenetics in the pathogenesis of NAFLD as in other reviews, this review additionally provides an elaborate discussion on exploiting the high plasticity of epigenetic modifications in response to environmental cues, for developing novel therapeutics for NAFLD. Besides, this extensive review provides evidence for epigenetic mechanisms utilized by several potential drugs for NAFLD.

Anti-inflammatory and antidiabetic effects of grape-derived stilbene concentrate in the experimental metabolic syndrome

AIMS

This study aimed to investigate the carbohydrate and lipid dynamics, associated inflammation markers and the effectiveness of a grape-derived stilbene concentrate (GDSC) treatment in experimental metabolic syndrome (MetS).

METHODS

The study was carried out on 40 male 12-weeks of age Wistar rats. The MetS was induced using the fructose model (feeding with 60%-solid fructose diet for 24 weeks). Rats with induced MetS were treated with polyphenolic GDSC, which was obtained by water-alcohol extraction of Vitis vinifera grapevine (Ressfood LLC, Russia).

RESULTS

The experimentally induced MetS development leads to classic MetS signs, including abdominal obesity, hyperglycemia, high lipid levels and heart damage. The expression of glucose transporter type 4 (GLUT4) and peroxisome proliferator-activated receptor-γ (PPAR-γ) had greater dynamics than biochemical measurements. The development of the associated inflammatory reactions was confirmed by the increased level of Toll-like receptor type 4 (TLR4) and C-reactive protein (CRP) compared to control levels. The use of the GDSC had positive dynamics in carbohydrate and lipid levels, inflammatory marker, also prevented associated inflammation and heart damage.

Organismal Fructose Metabolism in Health and Non-Alcoholic Fatty Liver Disease

NAFLD has alarmingly increased, yet FDA-approved drugs are still lacking. An excessive intake of fructose, especially in liquid form, is a dietary risk factor of NAFLD. While fructose metabolism has been studied for decades, it is still controversial how fructose intake can cause NAFLD. It has long been believed that fructose metabolism solely happens in the liver and accordingly, numerous studies have investigated liver fructose metabolism using primary hepatocytes or liver cell lines in culture. While cultured cells are useful for studying detailed signaling pathways and metabolism in a cell-autonomous manner, it is equally important to understand fructose metabolism at the whole-body level in live organisms. In this regard, recent in vivo studies using genetically modified mice and stable isotope tracing have tremendously expanded our understanding of the complex interaction between fructose-catabolizing organs and gut microbiota. Here, we discuss how the aberrant distribution of fructose metabolism between organs and gut microbiota can contribute to NAFLD. We also address potential therapeutic interventions of fructose-elicited NAFLD.

Unraveling Host-Gut Microbiota Dialogue and Its Impact on Cholesterol Levels

Disruption in cholesterol metabolism, particularly hypercholesterolemia, is a significant cause of atherosclerotic cardiovascular disease. Large interindividual variations in plasma cholesterol levels are traditionally related to genetic factors, and the remaining portion of their variance is accredited to environmental factors. In recent years, the essential role played by intestinal microbiota in human health and diseases has emerged. The gut microbiota is currently viewed as a fundamental regulator of host metabolism and of innate and adaptive immunity. Its bacterial composition but also the synthesis of multiple molecules resulting from bacterial metabolism vary according to diet, antibiotics, drugs used, and exposure to pollutants and infectious agents. Microbiota modifications induced by recent changes in the human environment thus seem to be a major factor in the current epidemic of metabolic/inflammatory diseases (diabetes mellitus, liver diseases, inflammatory bowel disease, obesity, and dyslipidemia). Epidemiological and preclinical studies report associations between bacterial communities and cholesterolemia. However, such an association remains poorly investigated and characterized. The objectives of this review are to present the current knowledge on and potential mechanisms underlying the host-microbiota dialogue for a better understanding of the contribution of microbial communities to the regulation of cholesterol homeostasis.

Oxidation-Specific Epitopes in Non-Alcoholic Fatty Liver Disease

An improper balance between the production and elimination of intracellular reactive oxygen species causes increased oxidative stress. Consequently, DNA, RNA, proteins, and lipids are irreversibly damaged, leading to molecular modifications that disrupt normal function. In particular, the peroxidation of lipids in membranes or lipoproteins alters lipid function and promotes formation of neo-epitopes, such as oxidation-specific epitopes (OSEs), which are found to be present on (lipo)proteins, dying cells, and extracellular vesicles. Accumulation of OSEs and recognition of OSEs by designated pattern recognition receptors on immune cells or soluble effectors can contribute to the development of chronic inflammatory diseases. In line, recent studies highlight the involvement of modified lipids and OSEs in different stages of the spectrum of non-alcoholic fatty liver disease (NAFLD), including inflammatory non-alcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma. Targeting lipid peroxidation products shows high potential in the search for novel, better therapeutic strategies for NASH.

The Role of Probiotics in Nonalcoholic Fatty Liver Disease: A New Insight into Therapeutic Strategies

Nonalcoholic fatty liver disease (NAFLD) encompasses a broad spectrum of pathological hepatic conditions ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), which may predispose to liver cirrhosis and hepatocellular carcinoma (HCC). Due to the epidemic obesity, NAFLD is representing a global health issue and the leading cause of liver damage worldwide. The pathogenesis of NAFLD is closely related to insulin resistance (IR), adiposity and physical inactivity as well as genetic and epigenetic factors corroborate to the development and progression of hepatic steatosis and liver injury. Emerging evidence has outlined the implication of gut microbiota and gut-derived endotoxins as actively contributors to NAFLD pathophysiology probably due to the tight anatomo-functional crosstalk between the gut and the liver. Obesity, nutrition and environmental factors might alter intestinal permeability producing a favorable micro-environment for bacterial overgrowth, mucosal inflammation and translocation of both invasive pathogens and harmful byproducts, which, in turn, influence hepatic fat composition and exacerbated pro-inflammatory and fibrotic processes. To date, no therapeutic interventions are available for NAFLD prevention and management, except for modifications in lifestyle, diet and physical exercise even though they show discouraging results due to the poor compliance of patients. The premise of this review is to discuss the role of gut–liver axis in NAFLD and emphasize the beneficial effects of probiotics on gut microbiota composition as a novel attractive therapeutic strategy to introduce in clinical practice.

Relationship between Changes in Microbiota and Liver Steatosis Induced by High-Fat Feeding-A Review of Rodent Models

Several studies have observed that gut microbiota can play a critical role in nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) development. The gut microbiota is influenced by different environmental factors, which include diet. The aim of the present review is to summarize the information provided in the literature concerning the impact of changes in gut microbiota on the effects which dietary fat has on liver steatosis in rodent models. Most studies in which high-fat feeding has induced steatosis have reported reduced microbiota diversity, regardless of the percentage of energy provided by fat. At the phylum level, an increase in Firmicutes and a reduction in Bacteroidetes is commonly found, although widely diverging results have been described at class, order, family, and genus levels, likely due to differences in experimental design. Unfortunately, this fact makes it difficult to reach clear conclusions concerning the specific microbiota patterns associated with this feeding pattern. With regard to the relationship between high-fat feeding-induced changes in liver and microbiota composition, although several mechanisms such as alteration of gut integrity and increased permeability, inflammation, and metabolite production have been proposed, more scientific evidence is needed to address this issue and thus further studies are needed.

Pattern Recognition Receptor-Mediated Chronic Inflammation in the Development and Progression of Obesity-Related Metabolic Diseases

Obesity-induced chronic inflammation is known to promote the development of many metabolic diseases, especially insulin resistance, type 2 diabetes mellitus, nonalcoholic fatty liver disease, and atherosclerosis. Pattern recognition receptor-mediated inflammation is an important determinant for the initiation and progression of these metabolic diseases. Here, we review the major features of the current understanding with respect to obesity-related chronic inflammation in metabolic tissues, focus on Toll-like receptors and nucleotide-binding oligomerization domain-like receptors with an emphasis on how these receptors determine metabolic disease progression, and provide a summary on the development and progress of PRR antagonists for therapeutic intervention.

Telmisartan and/or chlorogenic acid attenuates fructose-induced non-alcoholic fatty liver disease in rats: Implications of cross-talk between angiotensin, the sphingosine kinase/sphingoine-1-phosphate pathway, and TLR4 receptors

Renin-angiotensin-aldosterone system (RAS) has been implicated in non-alcoholic fatty liver disease (NAFLD); the most common cause of chronic liver diseases. There is accumulating evidence that altered TLR4 and Sphingosine kinase 1(SphK1)/sphingosine1phosphate (S1P) signaling pathways are key players in the pathogenesis of NAFLD. Cross talk of the sphingosine signaling pathway, toll-4 (TLR4) receptors, and angiotensin II was reported in various tissues. Therefore, the aim of this study was to define the contribution of these two pathways to the hepatoprotective effects of telmisartan and/or chlorogenic acid (CGA) in NAFLD. CGA is a strong antioxidant that was previously reported to inhibit angiotensin converting enzyme. Male Wistar rats were treated with either high-fructose, with or without telmisartan, CGA, telmisartan + CGA for 8 weeks. Untreated NAFL rats showed characteristics of NAFLD, as evidenced by significant increase in the body weight, insulin resistance, and serum hepatotoxicity markers (Alanine and Aspartate transaminases) and lipids as compared to the negative control group, in addition to characteristic histopathological alterations. Treatment with either telmisartan and/or CGA improved aforementioned parameters, in addition to upregulation of antioxidant enzymes (Superoxide dismutase and Glutathione peroxidase). Effect of inhibiting RAS on both sphingosine pathway and TLR4 was evident by the suppressing effect of telmisartan and/or CGA on high fructose-induced upregulation of hepatic SPK1 and S1P, in addition to concomitant up-regulation of Sphingosine-1-Phosphate receptor (S1PR)3 protein level and increased expression of S1PR1 and TLR4. As TLR4 and SPK/S1P signaling pathways play important roles in the progression of liver inflammation, the effect on sphingosine pathway and TLR4 was associated with decreased concentrations of inflammatory markers, enzyme kB kinase (IKK), nuclear factor-kB and tumor necrosis factor-α as compared to untreated NAFL group. In conclusion, the present data strongly suggests the cross-talk between angiotensin, the Sphingosine SPK/S1P Axis and TLR4 Receptors, and their role in the pathogenesis of fructose-induced NAFLD, and the protection afforded by drugs inhibiting RAS.

Chronic intake of moderate fat-enriched diet induces fatty liver and low-grade inflammation without obesity in rabbits

Non-Alcoholic Fatty Liver Disease (NAFLD) is the cause of chronic liver disease. Even though NAFLD is strongly associated with obesity and metabolic syndrome, there is a proportion of patients who develop this condition in the absence of obesity and the underlying mechanisms are poorly understood. We investigated early events in the pathogenesis of non-obese NAFLD, analyzing the impact of the chronic intake of a moderate fat-enriched diet on hepatic lipid accumulation and their relationship with inflammation. Rabbits fed with a moderate Fatty-Acid- Enriched Diet 3% palmitic acid (FAED), were evaluated for body weight, biochemical parameters, and liver function. Liver samples were analyzed by histology and RT-qPCR to measure lipid accumulation, the expression of inflammation-related genes IL-1β, IL-6, IL-10, IL-13, IL-18, COX-2, TNF-α, and TLR-4. Chronic consumption by 6-months of FAED did not generate metabolic changes, but it induced fatty liver. We also observed the development of low-grade inflammation characterized by the up regulation of TNF-α, IL-13 and IL-18. The consumption by 12-months of FAED caused the overexpression of IL-6, IL-10, IL-13, COX-2, and TLR-4. We show that hepatic steatosis is an early consequence of fat-enriched diets, and that it is accompanied by an immune response that exerts protective effects that prevent the development of metabolic disorders, such as overweight/obesity and metabolic syndrome. However, the excessive intake of fatty acids renders these mechanisms less efficient for delaying the start of metabolic alterations. Rabbits fed with FAED can be used as a model of NAFLD in non-obese and obese groups, especially at early stages of the disease.

Intestinal Microbiota Modulation in Obesity-Related Non-alcoholic Fatty Liver Disease

Obesity and associated comorbidities, including non-alcoholic fatty liver disease (NAFLD), are a major concern to public well-being worldwide due to their high prevalence among the population, and its tendency on the rise point to as important threats in the future. Therapeutic approaches for obesity-associated disorders have been circumscribed to lifestyle modifications and pharmacological therapies have demonstrated limited efficacy. Over the last few years, different studies have shown a significant role of intestinal microbiota (IM) on obesity establishment and NAFLD development. Therefore, modulation of IM emerges as a promising therapeutic strategy for obesity-associated diseases. Administration of prebiotic and probiotic compounds, fecal microbiota transplantation (FMT) and exercise protocols have shown a modulatory action over the IM. In this review we provide an overview of current approaches targeting IM which have shown their capacity to counteract NAFLD and metabolic syndrome features in human patients and animal models.

Phenylmethimazole abrogates diet-induced inflammation, glucose intolerance and NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of both metabolic and inflammatory diseases and has become the leading chronic liver disease worldwide. High-fat (HF) diets promote an increased uptake and storage of free fatty acids (FFAs) and triglycerides (TGs) in hepatocytes, which initiates steatosis and induces lipotoxicity, inflammation and insulin resistance. Activation and signaling of Toll-like receptor 4 (TLR4) by FFAs induces inflammation evident in NAFLD and insulin resistance. Currently, there are no effective treatments to specifically target inflammation associated with this disease. We have established the efficacy of phenylmethimazole (C10) to prevent lipopolysaccharide and palmitate-induced TLR4 signaling. Because TLR4 is a key mediator in pro-inflammatory responses, it is a potential therapeutic target for NAFLD. Here, we show that treatment with C10 inhibits HF diet-induced inflammation in both liver and mesenteric adipose tissue measured by a decrease in mRNA levels of pro-inflammatory cytokines. Additionally, C10 treatment improves glucose tolerance and hepatic steatosis despite the development of obesity due to HF diet feeding. Administration of C10 after 16 weeks of HF diet feeding reversed glucose intolerance, hepatic inflammation, and improved hepatic steatosis. Thus, our findings establish C10 as a potential therapeutic for the treatment of NAFLD.

Nonalcoholic Fatty Liver Disease Is Exacerbated in High-Fat Diet-Fed Gnotobiotic Mice by Colonization with the Gut Microbiota from Patients with Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a serious liver disorder associated with the accumulation of fat and inflammation. The objective of this study was to determine the gut microbiota composition that might influence the progression of NAFLD. Germ-free mice were inoculated with feces from patients with nonalcoholic steatohepatitis (NASH) or from healthy persons (HL) and then fed a standard diet (STD) or high-fat diet (HFD). We found that the epididymal fat weight, hepatic steatosis, multifocal necrosis, and inflammatory cell infiltration significantly increased in the NASH-HFD group. These findings were consistent with markedly elevated serum levels of alanine transaminase, aspartate transaminase, endotoxin, interleukin 6 (IL-6), monocyte chemotactic protein 1 (Mcp1), and hepatic triglycerides. In addition, the mRNA expression levels of Toll-like receptor 2 (Tlr2), Toll-like receptor 4 (Tlr4), tumor necrosis factor alpha (Tnf-α), Mcp1, and peroxisome proliferator-activated receptor gamma (Ppar-γ) significantly increased. Only abundant lipid accumulation and a few inflammatory reactions were observed in group HL-HFD. Relative abundance of Bacteroidetes and Firmicutes shifted in the HFD-fed mice. Furthermore, the relative abundance of Streptococcaceae was the highest in group NASH-HFD. Nevertheless, obesity-related Lactobacillaceae were significantly upregulated in HL-HFD mice. Our results revealed that the gut microbiota from NASH Patients aggravated hepatic steatosis and inflammation. These findings might partially explain the NAFLD progress distinctly was related to different compositions of gut microbiota.

Fat and carbohydrate content in the diet induces drastic changes in gene expression in young Göttingen minipigs

In human health, there is interest in developing specific diets to reduce body weight. These studies are mainly focused on phenotypic changes induced in blood measurements, i.e., triglycerides, HDL, LDL, and insulin, and on physical changes, i.e., body weight and BMI. To evaluate the biological impact of diet interventions, it is very important to investigate the molecular mechanisms driving the diet-induced phenotypic changes in relevant tissues. However, studying these effects in humans is difficult due to ethical concerns in doing interventions and obtaining tissue samples and good animal models are therefore needed. Göttingen minipigs, a small size obesity prone pig breed, have previously been shown to be a useful translational animal model for metabolic studies. In this study, 16 Göttingen minipig males (2-month old) were submitted to 13 weeks of differential diets to investigate the initial stages of diet-induced metabolic changes. Half of them were fed a high-fat/cholesterol, low-carbohydrate (HFLC) diet, and the other half were fed a low- fat/cholesterol, high-carbohydrate (LFHC) diet. After 13 weeks, the HFLC group weighted less and had dyslipidemia compared to the LFHC group. Liver, pancreas, and adipose tissues were collected at slaughter. Gene expression profiling of 83 metabolism-relevant genes was performed using high-throughput qPCR. In total, 41 genes were deregulated in at least one of the five tissues analyzed, with liver being the most drastically affected tissue. The new knowledge gained in this study could potentially be of value for considering direct modulation of gene expression by nutrient content in the diet.

Update on lipid species and paediatric nonalcoholic fatty liver disease

PURPOSE OF REVIEW

To describe the recent advances in our understanding of fatty acids and lipids in paediatric nonalcoholic fatty liver disease (NAFLD) and their future implications.

RECENT FINDINGS

Data have been accumulated to suggest that ceramides are the main drivers of hepatic insulin resistance in NAFLD, and inhibition of ceramide synthesis improves histology in mice.Saturated fatty acids formed by de novo lipogenesis generate increased lipotoxicity compared with dietary-derived saturated fatty acids.Hepatic lipogenesis and associated insulin resistance have been found to be influenced by several novel proteins, including E2F1, cyclic AMP response element binding protein transcriptional coactivator 2, Raptor, and eukaryotic initiation factor 6. There are encouraging data from animal models that modulation of these could be therapeutic targets.Human and animal metabolomics and lipidomics data have been used to generate a lipid signature for NAFLD and nonalcoholic steatohepatitis. Serum lipidomics appears to correlate with hepatic lipidomics.Therapeutic trials of polyunsaturated fatty acids in children have had mixed results, with some reductions in noninvasive biomarkers.

SUMMARY

Multiple new pathways for drug targets have been identified, and use of lipidomics is likely to become a noninvasive method for assessing disease. However, much of the data for paediatric NAFLD are extrapolated from adult or animal studies.

The role of bile acids in metabolic regulation

Bile acids (BA), long believed to only have lipid-digestive functions, have emerged as novel metabolic modulators. They have important endocrine effects through multiple cytoplasmic as well as nuclear receptors in various organs and tissues. BA affect multiple functions to control energy homeostasis, as well as glucose and lipid metabolism, predominantly by activating the nuclear farnesoid X receptor and the cytoplasmic G protein-coupled BA receptor TGR5 in a variety of tissues. However, BA also are aimed at many other cellular targets in a wide array of organs and cell compartments. Their role in the pathogenesis of diabetes, obesity and other 'diseases of civilization' becomes even more clear. They also interact with the gut microbiome, with important clinical implications, further extending the complexity of their biological functions. Therefore, it is not surprising that BA metabolism is substantially modulated by bariatric surgery, a phenomenon contributing favorably to the therapeutic effects of these surgical procedures. Based on these data, several therapeutic approaches to ameliorate obesity and diabetes have been proposed to affect the cellular targets of BA.