Steatosis in the liver

Eplerenone, a mineralocorticoid receptor inhibitor, reduces cirrhosis associated changes of hepatocyte glucose and lipid metabolism

BACKGROUND

Recent studies suggest a contribution of intrahepatic mineralocorticoid receptor (MR) activation to the development of cirrhosis. As MR blockade abrogates the development of cirrhosis and hypoxia, common during the development of cirrhosis, can activate MR in hepatocytes. But, the impact of non-physiological hepatic MR activation is unknown. In this study, we investigate the impact of hypoxia-induced hepatocyte MR activation as a relevant factor in cirrhosis.

METHODS

RNA sequencing followed by gene ontology term enrichment analysis was performed on liver samples from rats treated for 12 weeks with or without CCl4 and for the last four weeks with or without eplerenone (MR antagonist). We investigated if these changes can be mimicked by hypoxia in a human hepatocyte cell line (HepG2 cells) and in primary rat hepatocytes (pRH). In order to evaluate the functional cellular importance, hepatocyte lipid accumulation, glucose consumption, lactate production and mitochondrial function were analyzed.

RESULTS

In cirrhotic liver tissue genes annotated to the GOterm "Monocarboxylic acid metabolic process" (PPARα, PDK4, AMACR, ABCC2, Lipin1) are downregulated. This effect is reversed by the MR antagonist eplerenone in vivo. The alterations are partially mimicked by hypoxia in rat and human hepatocytes in tissue culture. Furthermore, the reduction of mRNA and protein expression of PPARα, PDK4, AMACR, ABCC2 and Lipin1 during hypoxia is prevented by eplerenone in rat and human hepatocytes. Aldosterone, the endogenous MR agonist, did not affect the expression of those proteins in hepatocytes. As those proteins are key regulators of hepatocyte energy homeostasis, we analyzed if hypoxia affected glucose consumption, lactate production and lipid accumulation in HepG2 cells in a MR-mediated manner. All three parameters were affected by hypoxia and were partially normalized by eplerenone.

CONCLUSION

Our findings suggest that non-physiological MR activation plays a role in the dysregulation of glucose and lipid metabolism in hepatocytes. This leads to an increase in apoptosis, probably resulting in a proinflammatory micromilieu of the hepatic tissue. The enhanced deposition of extracellular matrix contributes to the development of cirrhosis. Therefore, MR antagonists may have therapeutic potential in the treatment of early stages of liver disease due to their direct action in the liver.

Characterization of an in vitro steatosis model simulating activated de novo lipogenesis in MAFLD patients

Activated de novo lipogenesis (DNL) is the critical pathway involved in the progression of metabolic-associated fatty liver disease (MAFLD). We present an in vitro steatosis model for MAFLD that induces steatosis through activated DNL. This model utilizes insulin and LXR receptor ligand T0901317, eliminating the need for fatty acid treatment. Significant increases in triglycerides (TAGs) and expression of DNL-related transcription factors were observed. Transcriptomic analysis revealed distinct gene expression profiles between the DNL and conventional oleic acid (OA)-induced steatosis model. DNL steatosis model exhibited elevated pathways related to glycolysis, cholesterol homeostasis, and bile acid metabolism, reflecting its clinical relevance to MAFLD. Moreover, C75 and JNK-IN-5A compounds effectively reduced TAG accumulation and steatosis-related protein expression in the DNL model, whereas they had no significant impact on TAG accumulation in the OA model. In conclusion, we introduce an ideal model for steatosis study, which could help in understanding the MAFLD mechanisms.

Gender and Liver Steatosis Discriminate Different Physiological Patterns in Obese Patients Undergoing Bariatric Surgery: Obesity Center Cohort

BACKGROUND

Obesity is a major public health problem worldwide. Bariatric surgery can reduce body weight, and it is one of the better ways to improve metabolic disease and lifestyle. The aim of this study was to explore a new cohort of patients with obesity and evaluate the gender differences and the steatosis status within the gender group.

METHODS

A cohort of 250 adult obese patients with BMI ≥ 30 and age >18 years, eligible for gastric bariatric surgery at Pineta Grande Hospital, Castel Volturno (Italy) was studied.

RESULTS

The prevalence in women was higher (72.40%) than men (27.60%). Overall, results indicated many statistically significant gender differences in hematological and clinical parameters. Analysis of the subcohorts based on the severity of steatosis revealed differences of this condition between the genders. Steatosis was more prevalent in the male subcohort, but female patients revealed greater within-group differences.

CONCLUSIONS

Many differences were found not only in the total cohort but also between the gender subcohorts, both in the presence and absence of steatosis. We can conclude that the pathophysiological, genetic, and hormonal patterns affecting these patients delineate different individual profiles.

Impaired Function of Solute Carrier Family 19 Leads to Low Folate Levels and Lipid Droplet Accumulation in Hepatocytes

Low serum folate levels are inversely related to metabolic associated fatty liver disease (MAFLD). The role of the folate transporter gene (SLC19A1) was assessed to clarify its involvement in lipid accumulation during the onset of MAFLD in humans and in liver cells by genomic, transcriptomic, and metabolomic techniques. Genotypes of 3 SNPs in a case-control cohort were initially correlated to clinical and serum MAFLD markers. Subsequently, the expression of 84 key genes in response to the loss of SLC19A1 was evaluated with the aid of an RT² profiler-array. After shRNA-silencing of SLC19A1 in THLE2 cells, folate and lipid levels were measured by ELISA and staining techniques, respectively. In addition, up to 482 amino acids and lipid metabolites were semi-quantified in SLC19A1-knockdown (KD) cells through ultra-high-performance liquid chromatography coupled with mass spectrometry. SNPs, rs1051266 and rs3788200, were significantly associated with the development of fatty liver for the single-marker allelic test. The minor alleles of these SNPs were associated with a 0.6/-1.67-fold decreased risk of developing MAFLD. When SLC19A1 was KD in THLE2 cells, intracellular folate content was four times lower than in wild-type cells. The lack of functional SLC19A1 provoked significant changes in the regulation of genes associated with lipid droplet accumulation within the cell and the onset of NAFLD. Metabolomic analyses showed a highly altered profile, where most of the species that accumulated in SLC19A1-KD-cells belong to the chemical groups of triacylglycerols, diacylglycerols, polyunsaturated fatty acids, and long chain, highly unsaturated cholesterol esters. In conclusion, the lack of SLC19A1 gene expression in hepatocytes affects the regulation of key genes for normal liver function, reduces intracellular folate levels, and impairs lipid metabolism, which entails lipid droplet accumulation in hepatocytes.

Sweet potato extract alleviates high-fat-diet-induced obesity in C57BL/6J mice, but not by inhibiting pancreatic lipases

Scope and aim

Sweet potato is widely consumed as a healthy and nutritive vegetable containing bioactive constituents for health promotion. This study investigated the beneficial impact of white-fleshed sweet potato extract (SPE) on high fat diet (HFD)-induced obese mice.

Methods and results

First, SPE, in which resin glycoside was found as the dominant constituent, was suggested as a potential anti-obesity agent, because 20-70% pancreatic lipase (PL) inhibition was measured with SPE by in vitro turbidity assay and pNPP assay. Hence, next, the effect of SPE on obese mice was detected by oral administration of HFD supplemented with 6% SPE on C57BL/6J mice for 9 weeks. Surprisingly, being the opposite of what was typically observed from a lipase inhibitor such as orlistat, the fecal fat content in SPE-fed obese mice was decreased (p < 0.01). Meanwhile, 6% SPE supplement indeed significantly ameliorated HFD-induced obesity in mice, including body weight gain, fat accumulation, adipocyte enlargement, insulin resistance, and hepatic steatosis (p < 0.05). The improved liver steatosis was found associated with a down-regulating action of SPE on nuclear factor kappa B activation in HFD-fed mice. The anti-obesity influence of SPE was also confirmed on the HepG2 cell model for non-alcoholic fatty liver disease (NAFLD).

Conclusion

These results indicate that SPE, as a dietary supplement, has the great potential for weight control and treating hepatic steatosis, possibly through a different action mechanism from that of orlistat.

Exploring the Protective Effects and Mechanism of Huaji Jianpi Decoction against Nonalcoholic Fatty Liver Disease by Network Pharmacology and Experimental Validation

This paper was designed to predict the mechanisms of the active components of Huaji Jianpi Decoction (HJJPD) against nonalcoholic fatty liver disease (NAFLD) based on network pharmacology-combined animal experiments. The candidate compounds of HJJPD and its relative targets were obtained from TCMSP and PharmMapper web server, and the intersection genes for NAFLD were discerned using OMIM, GeneCards, and DisGeNET. Then, the target protein-protein interaction (PPI) and component-target-pathway networks were constructed. Moreover, gene function annotation (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to study the potential signaling pathways associated with HJJPD’s effect on NAFLD. Molecular docking simulation was preformed to validate the binding affinity between potential core components and key targets. Eventually, the candidate targets, the possible pathway, and the mechanism of HJJPD were predicted by the network pharmacology-based strategy, followed by experimental validation in the NAFLD mice model treated with HJJPD. A total of 55 candidate compounds and 36 corresponding genes were identified from HJJPD that are associated with activity against NAFLD, and then the network of them was constructed. Inflammatory response and lipid metabolism-related signaling pathways were identified as the critical signaling pathways mediating the therapeutic effect of the active bioactive ingredients on NAFLD. Compared with the model group, the liver wet weight, liver/body ratio, the levels of total cholesterol (TC), triglyceride (TG), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and high-density lipoprotein (HDL) in serum in the HJJPD low-dose (17.52 g/kg·d), medium-dose (35.04 g/kg·d), and high-dose (70.07 g/kg·d) groups significantly decreased ( $P<0.05$ ). Light microscope observation shows that HJJPD could control the degree of lipid denaturation of the mouse liver tissue to a great extent. RT-qPCR results show that the mRNA expression levels of peroxisome proliferative activated receptor gamma (PPARG), tumor necrosis factor-α (TNF-α), antiserine/threonine protein kinase 1 (AKT1), and prostaglandin-endoperoxide synthase (PTGS2) in the liver tissues of the three HJJPD groups (17.52 g/kg·d, 35.04 g/kg·d, and 70.07 g/kg·d) were significantly lower than those in the model group ( $P<0.05$ ). HJJPD can exert its effect by inhibiting hepatic steatosis and related mRNA expression and decreasing the levels of other liver-related indexes. This study suggested that HJJPD exerted its effect on NAFLD by modulating multitargets with multicompounds through multipathways. It also demonstrated that the network pharmacology-based approach might provide insights for understanding the interrelationship between complex diseases and interventions of HJJPD.

Beneficial Effects of Carvacrol on In Vitro Models of Metabolically-Associated Liver Steatosis and Endothelial Dysfunction: A Role for Fatty Acids in Interfering with Carvacrol Binding to Serum Albumin

BACKGROUND

Carvacrol, a plant phenolic monoterpene, is largely employed as food additive and phytochemical.

OBJECTIVE

We aimed to assess the lipid lowering and protective effects of carvacrol in vitro using cellular models of hepatic steatosis and endothelial dysfunction. We also investigated if and how the binding of carvacrol to albumin, the physiological transporter for small compounds in the blood, might be altered by the presence of high levels of fatty acids (FAs).

METHODS

Hepatic FaO cells treated with exogenous FAs mimic hepatosteatosis; endothelial HECV cells exposed to hydrogen peroxide are a model of endothelial dysfunction. In these models, we measured spectrophotometrically lipid accumulation and release, lipoperoxidation, free radical production, and nitric oxide release before and after treatment with carvacrol. The carvacrol binding to albumin in the presence or absence of high levels of FAs was assessed by absorption and emission spectroscopies.

RESULTS

Carvacrol counteracted lipid accumulation and oxidative stress in hepatocytes and protected endothelial cells from oxidative stress and dysfunction. Moreover, high levels of FAs reduced the binding of carvacrol to albumin.

CONCLUSION

The results suggest the good potential of carvacrol in ameliorating dysfunction of hepatic and endothelial cells in vitro. High levels of circulating FAs might compete with carvacrol for binding to albumin thus influencing its transport and bio-distribution.

Fowl Adenovirus Serotype 4 Induces Hepatic Steatosis via Activation of Liver X Receptor-α

Fowl adenovirus serotype 4 (FAdV-4) is a hepatotropic virus that causes severe hepatic damage characterized by basophilic intranuclear inclusion bodies, vacuolar degeneration, and multifocal necrosis in hepatocytes. Many aspects of FAdV-4 infection and pathogenesis, however, remain unknown. Here, we found that FAdV-4-induced hepatic injury is accompanied by the accumulation of oil droplets (triglycerides) in the cytoplasm of hepatocytes, a typical indicator of steatosis, in FAdV-4-infected chickens. Significant upregulation of adipose synthesis-related genes, such as liver X receptor-α (LXR-α), peroxisome proliferator-activated receptor gamma (PPAR-γ), and sterol regulatory element-binding protein-1c (SREBP-1c), and significant downregulation of low-density lipoprotein secretion-related genes and lipid oxidation- and lipid decomposition-related genes were observed in the infected chickens. FAdV-4 infection in cultured leghorn male hepatoma (LMH) cells caused similar signs of steatosis, with alterations in various lipogenesis-related genes. We eliminated the effect of LXR-α activation on FAdV-4-induced steatosis and found that treatment with an LXR-α antagonist (SR9243) and RNA interference (small interfering RNA targeting LXR-α [Si-LXR-α]) decreased the number of oil droplets and the accumulation of lipogenic genes, but treatment with an LXR-α agonist (T0901317) increased the number of oil droplets and the accumulation of lipogenic genes in the cells. Additionally, SR9243 treatment or Si-LXR-α transfection led to significant reductions in viral DNA level, protein expression, and virus production, whereas T0901317 treatment caused significant increases in viral DNA level, protein expression, and virus production. However, inhibition of SREBP-1c activity had no significant effect on virus production. Collectively, these results indicated that FAdV-4-induced steatosis involves activation of the LXR-α signaling pathway, which might be a molecular mechanism underlying the hepatic injury associated with FAdV-4 infection.IMPORTANCE Fowl adenovirus serotype 4 (FAdV-4) is an important hepatotropic adenovirus in chicken, but the underlying mechanism of FAdV-4-induced hepatic injury remains unclear. We report here that infection with FAdV-4 induced the accumulation of oil droplets (triglycerides) in the cytoplasm of hepatocytes, a typical indicator of steatosis, in the livers of chickens. FAdV-4-induced steatosis might be caused by a disrupted balance of fat metabolism, as evidenced by differential regulation of various lipase genes. The significant upregulation of liver X receptor-α (LXR-α) prompted us to investigate the interplay between LXR-α activation and FAdV-4-induced steatosis. Treatment with an agonist, an antagonist, or RNA interference targeting LXR-α in cultured leghorn male hepatoma (LMH) cells indicated that FAdV-4-induced steatosis was dependent upon LXR-α activation, which contributed to virus replication. These results provide important mechanistic insights, revealing that FAdV-4 induces hepatic steatosis by activating the LXR-α signaling pathway and highlighting the therapeutic potential of strategies targeting the LXR-α pathway for the treatment of FAdV-4 infection.

Lipids Composition in Plant Membranes

The paper focuses on the selected plant lipid issues. Classification, nomenclature, and abundance of fatty acids was discussed. Then, classification, composition, role, and organization of lipids were displayed. The involvement of lipids in xantophyll cycle and glycerolipids synthesis (as the most abundant of all lipid classes) were also discussed. Moreover, in order to better understand the biomembranes remodeling, the model (artificial) membranes, mimicking the naturally occurring membranes are employed and the survey on their composition and application in different kind of research was performed. High level of lipids remodeling in the plant membranes under different environmental conditions, e.g., nutrient deficiency, temperature stress, salinity or drought was proved. The key advantage of lipid research was the conclusion that lipids could serve as the markers of plant physiological condition and the detailed knowledge on lipids chemistry will allow to modify their composition for industrial needs.

Childhood obesity, cardiovascular and liver health: a growing epidemic with age

BACKGROUND

The frequency of childhood obesity has increased over the last 3 decades, and the trend constitutes a worrisome epidemic worldwide. With the raising obesity risk, key aspects to consider are accurate body mass index classification, as well as metabolic and cardiovascular, and hepatic consequences.

DATA SOURCES

The authors performed a systematic literature search in PubMed and EMBASE, using selected key words (obesity, childhood, cardiovascular, liver health). In particular, they focused their search on papers evaluating the impact of obesity on cardiovascular and liver health.

RESULTS

We evaluated the current literature dealing with the impact of excessive body fat accumulation in childhood and across adulthood, as a predisposing factor to cardiovascular and hepatic alterations. We also evaluated the impact of physical and dietary behaviors starting from childhood on cardio-metabolic consequences.

CONCLUSIONS

The epidemic of obesity and obesity-related comorbidities worldwide raises concerns about the impact of early abnormalities during childhood and adolescence. Two key abnormalities in this context include cardiovascular diseases, and nonalcoholic fatty liver disease. Appropriate metabolic screenings and associated comorbidities should start as early as possible in obese children and adolescents. Nevertheless, improving dietary intake and increasing physical activity performance are to date the best therapeutic tools in children to weaken the onset of obesity, cardiovascular diseases, and diabetes risk during adulthood.

Effects of epoxy stearic acid on lipid metabolism in HepG2 cells

In the present study, effects of cis-9,10-epoxystearic acid (ESA) generated by the thermal oxidation of oleic acid on HepG2 cells, including intracellular lipid accumulation, fatty acid composition, and lipid metabolism, were investigated. Our results revealed that ESA increased the number and size of cellular lipid droplets. Intracellular triacylglycerol and total cholesterol content demonstrated that ESA induced lipid accumulation in HepG2 cells in a dose- and time-dependent manner. Results of fatty acid composition further indicated that ESA could lead to intracellular lipid accumulation. Our results also revealed that ESA may suppress the fatty acid oxidation in peroxisomes and mitochondria, including PPARα, Cpt1α, and Acox1, whereas the expression of genes involved in lipid synthesis, including Srebp-1c and Scd1, was enhanced. These findings provide critical information on the effects of ESA on HepG2 cells, particularly lipid accumulation and metabolism, which is important for evaluating the biosafety of the oxidative product of oleic acid. PRACTICAL APPLICATION: The administration of cis-9,10-epoxystearic acid to HepG2 cells could lead to disorder of lipid metabolism of cells by enhancing the intracellular lipid content, as well as suppressing the fatty acid oxidation in peroxisomes and mitochondria. These findings could provide information for the evaluation of the biosafety of the oxidative product of oleic acid.

Activation of SIK1 by phanginin A inhibits hepatic gluconeogenesis by increasing PDE4 activity and suppressing the cAMP signaling pathway

Objective

Salt-induced kinase 1 (SIK1) acts as a key modulator in many physiological processes. However, the effects of SIK1 on gluconeogenesis and the underlying mechanisms have not been fully elucidated. In this study, we found that a natural compound phanginin A could activate SIK1 and further inhibit gluconeogenesis. The mechanisms by which phanginin A activates SIK1 and inhibits gluconeogenesis were explored in primary mouse hepatocytes, and the effects of phanginin A on glucose homeostasis were investigated in ob/ob mice.

Methods

The effects of phanginin A on gluconeogenesis and SIK1 phosphorylation were examined in primary mouse hepatocytes. Pan-SIK inhibitor and siRNA-mediated knockdown were used to elucidate the involvement of SIK1 activation in phanginin A-reduced gluconeogenesis. LKB1 knockdown was used to explore how phanginin A activated SIK1. SIK1 overexpression was used to evaluate its effect on gluconeogenesis, PDE4 activity, and the cAMP pathway. The acute and chronic effects of phanginin A on metabolic abnormalities were observed in ob/ob mice.

Results

Phanginin A significantly increased SIK1 phosphorylation through LKB1 and further suppressed gluconeogenesis by increasing PDE4 activity and inhibiting the cAMP/PKA/CREB pathway in primary mouse hepatocytes, and this effect was blocked by pan-SIK inhibitor HG-9-91-01 or siRNA-mediated knockdown of SIK1. Overexpression of SIK1 in hepatocytes increased PDE4 activity, reduced cAMP accumulation, and thereby inhibited gluconeogenesis. Acute treatment with phanginin A reduced gluconeogenesis in vivo, accompanied by increased SIK1 phosphorylation and PDE4 activity in the liver. Long-term treatment of phanginin A profoundly reduced blood glucose levels and improved glucose tolerance and dyslipidemia in ob/ob mice.

Conclusion

We discovered an unrecognized effect of phanginin A in suppressing hepatic gluconeogenesis and revealed a novel mechanism that activation of SIK1 by phanginin A could inhibit gluconeogenesis by increasing PDE4 activity and suppressing the cAMP/PKA/CREB pathway in the liver. We also highlighted the potential value of phanginin A as a lead compound for treating type 2 diabetes.

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Phanginin A inhibits gluconeogenesis in primary mouse hepatocytes.

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Phanginin A increases hepatic SIK1 phosphorylation both in vitro and in vivo.

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Activation of SIK1 increases PDE4 activity and suppresses the cAMP signaling pathway.

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Activation of SIK1 inhibits gluconeogenesis by regulating the PDE4/cAMP/PKA/CREB pathway.

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Phanginin A improves metabolic disorders in ob/ob mice.

Pro-inflammatory signalling and gut-liver axis in non-alcoholic and alcoholic steatohepatitis: Differences and similarities along the path

Non-alcoholic fatty liver disease (NAFLD) and alcohol-associated liver disease (ALD) represent a spectrum of injury, ranging from simple steatosis to steatohepatitis and cirrhosis. In humans, in fact, fatty changes in the liver, possibly leading to end-stage disease, were observed after chronic alcohol intake or in conditions of metabolic impairment. In this article, we examined the features and the pro-inflammatory pathways leading to non-alcoholic and alcoholic steatohepatitis. The involvement of several events (hits) and multiple inter-related pathways in the pathogenesis of these diseases suggest that a single therapeutic agent is unlikely to be an effective treatment strategy. Hence, a combination treatment towards multiple pro-inflammatory targets would eventually be required. Gut-liver crosstalk is involved not only in the impairment of lipid and glucose homoeostasis leading to steatogenesis, but also in the initiation of inflammation and fibrogenesis in both NAFLD and ALD. Modulation of the gut-liver axis has been suggested as a possible therapeutic approach since gut-derived components are likely to be involved in both the onset and the progression of liver damage. This review summarizes the translational mechanisms underlying pro-inflammatory signalling and gut-liver axis in non-alcoholic and alcoholic steatohepatitis. With a multitude of people being affected by liver diseases, identification of possible treatments and the elucidation of pathogenic mechanisms are elements of paramount importance.

Novel insights in health-promoting properties of sweet cherries

Sweet cherry (Prunus avium L.) is one of the most popular and appreciated temperate fruit not only for its sensory and nutritional properties, but also for its content in bioactive compounds. Consumption of sweet cherries brings beneficial effects on to health, which include prevention and modulatory effects in several chronic diseases such as (diabetes mellitus, cancer, cardiovascular and other inflammatory diseases). The presence of natural polyphenolic compounds with high antioxidant potential might drive and partly explain such beneficial effects, but more translational and clinical studies should address this topic. Here, we review the health-promoting properties of cherries and their bioactive compounds against human diseases.

Novel Insights into the Pathogenesis and Management of the Metabolic Syndrome

The metabolic syndrome, by definition, is not a disease but is a clustering of individual metabolic risk factors including abdominal obesity, hyperglycemia, hypertriglyceridemia, hypertension, and low high-density lipoprotein cholesterol levels. These risk factors could dramatically increase the prevalence of type 2 diabetes and cardiovascular disease. The reported prevalence of the metabolic syndrome varies, greatly depending on the definition used, gender, age, socioeconomic status, and the ethnic background of study cohorts. Clinical and epidemiological studies have clearly demonstrated that the metabolic syndrome starts with central obesity. Because the prevalence of obesity has doubly increased worldwide over the past 30 years, the prevalence of the metabolic syndrome has markedly boosted in parallel. Therefore, obesity has been recognized as the leading cause for the metabolic syndrome since it is strongly associated with all metabolic risk factors. High prevalence of the metabolic syndrome is not unique to the USA and Europe and it is also increasing in most Asian countries. Insulin resistance has elucidated most, if not all, of the pathophysiology of the metabolic syndrome because it contributes to hyperglycemia. Furthermore, a major contributor to the development of insulin resistance is an overabundance of circulating fatty acids. Plasma fatty acids are derived mainly from the triglycerides stored in adipose tissues, which are released through the action of the cyclic AMP-dependent enzyme, hormone sensitive lipase. This review summarizes the latest concepts in the definition, pathogenesis, pathophysiology, and diagnosis of the metabolic syndrome, as well as its preventive measures and therapeutic strategies in children and adolescents.

Short-term Dietary Interventions for the Management of Nonalcoholic Fatty Liver

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) affects millions of individuals on a global scale and currently no gold standard treatment exists. The risk of developing NAFLD is considerably higher with increasing body mass index. Consequently, weight loss should be recommended to all overweight patients with fatty liver. However, lifestyle interventions, irrespective of weight status, may also influence the condition. The aim herein is to present examples of short-term interventions which assess direct effects of dietary-related components on hepatic steatosis.

METHODS

This review includes studies with short-term dietary-related interventions of up to 16 weeks that evaluate their efficacy in reducing intrahepatic lipid contents (hepatic steatosis). This review primarily focuses on the three main macronutrients: dietary carbohydrates, fats and proteins.

RESULTS

High saturated fat intake and high consumption of carbohydrates, particularly from simple sugars such as fructose are reported as risk factors for hepatic steatosis. Overall, shortterm hypocaloric diets have shown beneficial effects in reducing intrahepatic lipid contents. Macronutrient manipulations such as carbohydrate restriction as well as the consumption of unsaturated fatty acids are also reported to have efficacious effects.

CONCLUSION

This review highlights the different dietary interventions that can influence hepatic steatosis in the short term, illustrating both pro and anti-steatotic effects.

Dietary Patterns and Components in Nonalcoholic Fatty Liver Disease (NAFLD): What Key Messages Can Health Care Providers Offer?

Nonalcoholic fatty liver disease (NAFLD) is a rising epidemic worldwide and will be the leading cause of cirrhosis, hepatocellular carcinoma, and liver transplant within the next decade. NAFLD is considered as the hepatic manifestation of metabolic syndrome. Behaviors, such as a sedentary lifestyle and consuming a Western diet, have led to substantial challenges in managing NAFLD patients. With no curative pharmaceutical therapies, lifestyle modifications, including dietary changes and exercise, that ultimately lead to weight loss remain the only effective therapy for NAFLD. Multiple diets, including low-carbohydrate, low-fat, Dietary Approaches to Stop Hypertension (DASH), and Mediterranean (MD) diets, have been evaluated. NAFLD patients have shown better outcomes with a modified diet, such as the MD diet, where patients are encouraged to increase the consumption of fruits and vegetables, whole grains, and olive oil. It is increasingly clear that a personalized approach to managing NAFLD patients, based on their preferences and needs, should be implemented. In our review, we cover NAFLD management, with a specific focus on dietary patterns and their components. We emphasize the successful approaches highlighted in recent studies to provide recommendations that health care providers could apply in managing their NAFLD patients.

Quercetin alleviates ethanol-induced liver steatosis associated with improvement of lipophagy

Although emerging evidence demonstrated that quercetin could be explored as a potential candidate for the early intervention of alcoholic liver disease (ALD), the exact mechanisms against ethanol-induced hepatic steatosis haven't been fully elucidated. Herein, we investigated the effect of quercetin on liver steatosis caused by chronic-plus-single-binge ethanol feeding, focusing on lipophagy. Adult male mice were pair-fed with liquid diets containing ethanol (28% of total calories) and treated with quercetin for 12 weeks. Chronic-plus-binge ethanol consumption led to lipid droplets accumulation and liver damage as evidenced by histopathological changes, the increased content of triglyceride in serum and liver, and the elevated of serum ALT and AST level, which were greatly attenuated by quercetin. Moreover, quercetin blocked autophagy suppression by chronic-binge ethanol intake as manifested by the morphological improvement of mitochondrial characteristics, the increased number of autolysosome and restoration of autophagy-related protein expression. Furthermore, quercetin promoted lipophagy confirmed by the decreased perilipin 2 (PLIN2) level, activated AMPK activity and increased co-localization of liver LC3II and PLIN2 proteins. Collectively, these findings suggest that regular consumption of dietary quercetin has a role in preventing hepatic steatosis induced by chronic-plus-binge ethanol feeding, which mechanism may associate with the evident regulatory effect of quercetin on lipophagy.

Lipophagy and liver disease: New perspectives to better understanding and therapy

Intracellular lipid droplets (LDs) are remarkably dynamic and complex organelles that enact regulated storage and release of lipids to fulfil their fundamental roles in energy metabolism, membrane synthesis and provision of lipid-derived signaling molecules. The recent finding that LDs can be selectively degraded by the lysosomal pathway of autophagy through a process termed lipophagy has opened up a new understanding of how lipid metabolism regulates cellular physiology and pathophysiology. Many new functions for autophagic lipid metabolism have now been defined in various diseases including liver disease. Lipophagy was originally described in hepatocytes, where it is critical for maintaining cellular energy homeostasis in obesity and metabolic syndrome. In vitro and in vivo studies have demonstrated the selective uptake of LDs by autophagosomes, and inhibition of autophagy has been shown to reduce the β-oxidation of free fatty acids due to the increased accumulation of lipids and LDs. The identification of lipophagy as a new process dedicated to cellular lipid removal has mapped autophagy as an emerging player in cellular lipid metabolism. Pharmacological or genetic modulation of lipophagy might point to possible therapeutic strategies for combating a broad range of liver diseases. This review summarizes recent work focusing on lipophagy and liver disease as well as highlighting challenges and future directions of research. On the other hand, it also offers a glimpse into different strategies that have been used in experimental models to counteract excessive pathological lipophagy in the prevention and treatment of liver disease.

Inactivation of human DGAT2 by oxidative stress on cysteine residues

Diacylglycerol acyltransferases (DGATs) have a crucial role in the biosynthesis of triacylglycerol (TG), the major storage form of metabolic energy in eukaryotic organisms. Even though DGAT2, one of two distinct DGATs, has a vital role in TG biosynthesis, little is known about the regulation of DGAT2 activity. In this study, we examined the role of cysteine and its oxidation in the enzymatic activity of human DGAT2 in vitro. Human DGAT2 activity was considerably inhibited not only by thiol-modifying reagents (NEM and IA) but also by ROS-related chemicals (H₂O₂ and β-lapachone), while human DGAT1 and GPAT1 were little affected. Particularly, ROS-related chemicals concomitantly induced intermolecular disulfide crosslinking of human DGAT2. Both the oxidative inactivation and disulfide crosslinking were almost completely reversed by the treatment with DTT, a disulfide-reducing agent. These results clearly demonstrated the significant role of ROS-induced intermolecular crosslinking in the inactivation of human DGAT2 and also suggested DGAT2 as a redox-sensitive regulator in TG biosynthesis.

Effects of Polar Compounds Generated from the Deep-Frying Process of Palm Oil on Lipid Metabolism and Glucose Tolerance in Kunming Mice

In the present study, effects of deep-fried palm oil, specifically polar compounds generated during the frying process, on animal health including lipid and glucose metabolism and liver functions were investigated. Kunming mice were fed a high-fat diet containing deep-fried palm oil or purified polar compounds for 12 weeks. Their effects on animal health including hepatic lipid profile, antioxidant enzyme activity, serum biochemistry, and glucose tolerance were analyzed. Our results revealed that the consumption of polar compounds was related to the change of lipid deposition in liver and adipose tissue, as well as glucose tolerance alteration in Kunming mice. Correspondingly, the transcription study of genes involved in lipid metabolism including PPARα, Acox1, and Cpt1α indicated that polar compounds probably facilitated the fatty acid oxidation on peroxisomes, whereas lipid oxidation in mitochondria was suppressed. Furthermore, glucose tolerance test (GTT) revealed that a high amount of polar compound intake impaired glucose tolerance, indicating its effect on glucose metabolism in vivo. Our results provide critical information on the effects of polar compounds generated from the deep-frying process of palm oil on animal health, particularly liver functions and lipid and glucose metabolism, which is important for the evaluation of the biosafety of frying oil.

Microarray analysis of gene expression in liver, adipose tissue and skeletal muscle in response to chronic dietary administration of NDGA to high-fructose fed dyslipidemic rats

Nordihydroguaiaretic acid (NDGA), the main metabolite of Creosote Bush, has been shown to have profound effects on the core components of metabolic syndrome, including lowering of blood glucose, free fatty acids and triglyceride levels, attenuating elevated blood pressure in several rodent models of dyslipidemia, and improving body weight, insulin resistance, diabetes and hypertension. In the present study, a high-fructose diet fed rat model of hypertriglyceridemia, dyslipidemia, insulin resistance and hepatic steatosis was employed to investigate the global transcriptional changes in the lipid metabolizing pathways in three insulin sensitive tissues: liver, skeletal muscle and adipose tissue in response to chronic dietary administration of NDGA. Sprague-Dawley male rats (SD) were fed a chow (control) diet, high-fructose diet (HFrD) or HFrD supplemented with NDGA (2.5 g/kg diet) for eight weeks. Dietary administration of NDGA decreased plasma levels of TG, glucose, and insulin, and attenuated hepatic TG accumulation. DNA microarray expression profiling indicated that dietary administration of NDGA upregulated the expression of certain genes involved in fatty acid oxidation and their transcription regulator, PPARα, decreased the expression of a number of lipogenic genes and relevant transcription factors, and differentially impacted the genes of fatty acid transporters, acetyl CoA synthetases, elongases, fatty acid desaturases and lipid clearance proteins in liver, skeletal muscle and adipose tissues. These findings suggest that NDGA ameliorates hypertriglyceridemia and steatosis primarily by inhibiting lipogenesis and enhancing fatty acid catabolism in three major insulin responsive tissues by altering the expression of key enzyme genes and transcription factors involved in de novo lipogenesis and fatty acid oxidation.

Getting the Skinny on CD4(+) T Cell Survival in Fatty Livers

Non-alcoholic fatty liver disease is associated with hepatocellular carcinoma. In the March 10 issue of Nature, Greten and colleagues report that this metabolic disruption affects tumor surveillance by depleting CD4+ T helper cells through lipotoxic mechanisms associated with NAFLD.

Thermogenic activation represses autophagy in brown adipose tissue

BACKGROUND

Brown adipose tissue (BAT) thermogenesis is an adaptive process, essential for energy expenditure and involved in the control of obesity. Obesity is associated with abnormally increased autophagy in white adipose tissue. Autophagy has been proposed as relevant for brown-vs-white adipocyte differentiation; however, its role in the response of BAT to thermogenic activation is unknown.

METHODS

The effects of thermogenic activation on autophagy in BAT were analyzed in vivo by exposing mice to 24 h cold condition. The effects of norepinephrine (NE), cAMP and modulators of lysosomal activity were determined in differentiated brown adipocytes in the primary culture. Transcript expression was quantified by real-time PCR, and specific proteins were determined by immunoblot. Transmission electron microscopy, as well as confocal microscopy analysis after incubation with specific antibodies or reagents coupled to fluorescent emission, were performed in BAT and cultured brown adipocytes, respectively.

RESULTS

Autophagy is repressed in association with cold-induced thermogenic activation of BAT in mice. This effect was mimicked by NE action in brown adipocytes, acting mainly through a cAMP-dependent protein kinase A pathway. Inhibition of autophagy in brown adipocytes leads to an increase in UCP1 protein and uncoupled respiration, suggesting a repressing role for autophagy in relation to the activity of BAT thermogenic machinery. Under basal conditions, brown adipocytes show signs of active lipophagy, which is suppressed by a cAMP-mediated thermogenic stimulus.

CONCLUSIONS

Our results show a noradrenergic-mediated inverse relationship between autophagy and thermogenic activity in BAT and point toward autophagy repression as a component of brown adipocyte adaptive mechanisms to activate thermogenesis.

In Situ Evaluation of Oxidative Stress in Rat Fatty Liver Induced by a Methionine- and Choline-Deficient Diet

Nonalcoholic fatty liver disease (NAFLD) is a serious health problem in developed countries. We documented the effects of feeding with a NAFLD-inducing, methionine- and choline-deficient (MCD) diet, for 1-4 weeks on rat liver oxidative stress, with respect to a control diet. Glycogen, neutral lipids, ROS, peroxidated proteins, and SOD2 were investigated using histochemical procedures; ATP, GSH, and TBARS concentrations were investigated by biochemical dosages, and SOD2 expression was investigated by Western Blotting. In the 4-week-diet period, glycogen stores decreased whereas lipid droplets, ROS, and peroxidated proteins expression (especially around lipid droplets of hepatocytes) increased. SOD2 immunostaining decreased in poorly steatotic hepatocytes but increased in the thin cytoplasm of macrosteatotic cells; a trend towards a quantitative decrease of SOD expression in homogenates occurred after 3 weeks. ATP and GSH values were significantly lower for rats fed with the MCD diet with respect to the controls. An increase of TBARS in the last period of the diet is in keeping with the high ROS production and low antioxidant defense; these TBARS may promote protein peroxidation around lipid droplets. Since these proteins play key roles in lipid mobilization, storage, and metabolism, this last information appears significant, as it points towards a previously misconsidered target of NAFLD-associated oxidative stress that might be responsible for lipid dysfunction.

Differential Impacts of Soybean and Fish Oils on Hepatocyte Lipid Droplet Accumulation and Endoplasmic Reticulum Stress in Primary Rabbit Hepatocytes

Parenteral nutrition-associated liver disease (PNALD) is a severe ailment associated with long-term parenteral nutrition. Soybean oil-based lipid emulsions (SOLE) are thought to promote PNALD development, whereas fish oil-based lipid emulsions (FOLE) are thought to protect against PNALD. This study aimed to investigate the effects of SOLE and FOLE on primary rabbit hepatocytes. The results reveal that SOLE caused significant endoplasmic reticulum (ER) and mitochondrial damage, ultimately resulting in lipid droplets accumulation and ER stress. While these deleterious events induce hepatocyte injury, FOLE at high doses cause only minor ER and mitochondrial damage, which has no effect on hepatic function. SOLE also significantly upregulated glucose-regulated protein 94 mRNA and protein expression. These data indicate that SOLE, but not FOLE, damage the ER and mitochondria, resulting in lipid droplets accumulation and ER stress and, finally, hepatocyte injury. This likely contributes to the differential impacts of SOLE and FOLE on PNALD development and progression.

Deciphering non-alcoholic fatty liver disease through metabolomics

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver disorders in industrialized countries. NAFLD develops in the absence of alcohol abuse and encompasses a wide spectrum of disorders ranging from benign fatty liver to non-alcoholic steatohepatitis (NASH). NASH often leads to fibrosis, cirrhosis and, finally, hepatocellular carcinoma (HCC). Therefore the earlier NAFLD is diagnosed, the better the patient's outlook. A tightly connected basic and applied research is essential to find the molecular mechanisms that accompany illness and to translate them into the clinic. From the simple starting point for triacylglycerol (TG) accumulation in the liver to the more complex implications of phospholipids in membrane biophysics, the influence of lipids may be the clue to understand NAFLD pathophysiology. Nowadays, it is achievable to diagnose non-invasively the initial symptoms to stop, revert or even prevent disease development. In this context, merging metabolomics with other techniques and the interpretation of the huge information obtained resembles the 'Rosetta stone' to decipher the pathological metabolic fluxes that must be targeted to find a cure. In the present review, we have tackled the application of metabolomics to find out the metabolic fluxes that underlie membrane integrity in NAFLD.

How Inflammation Impinges on NAFLD: A Role for Kupffer Cells

Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming the most prevalent cause of liver disease worldwide and afflicts adults and children as currently associated with obesity and insulin resistance. Even though lately some advances have been made to elucidate the mechanism and causes of the disease much remains unknown about NAFLD. The aim of this paper is to discuss the present knowledge regarding the pathogenesis of the disease aiming at the initial steps of NAFLD development, when inflammation impinges on fat liver deposition. At this stage, the Kupffer cells attain a prominent role. This knowledge becomes subsequently relevant for the development of future diagnostic, prevention, and therapeutic options for the management of NAFLD.

New insights into the molecular mechanism of intestinal fatty acid absorption

BACKGROUND

Dietary fat is one of the most important energy sources of all the nutrients. Fatty acids, stored as triacylglycerols (also called triglycerides) in the body, are an important reservoir of stored energy and derived primarily from animal fats and vegetable oils.

DESIGN

Although the molecular mechanisms for the transport of water-insoluble amphipathic fatty acids across cell membranes have been debated for many years, it is now believed that the dominant means for intestinal fatty acid uptake is via membrane-associated fatty acid-binding proteins, that is, fatty acid transporters on the apical membrane of enterocytes.

RESULTS

These findings indicate that intestinal fatty acid absorption is a multistep process that is regulated by multiple genes at the enterocyte level, and intestinal fatty acid absorption efficiency could be determined by factors influencing intraluminal fatty acid molecules across the brush border membrane of enterocytes. To facilitate research on intestinal, hepatic and plasma triacylglycerol metabolism, it is imperative to establish standard protocols for precisely and accurately measuring the efficiency of intestinal fatty acid absorption in humans and animal models. In this review, we will discuss the chemical structure and nomenclature of fatty acids and summarize recent progress in investigating the molecular mechanisms underlying the intestinal absorption of fatty acids, with a particular emphasis on the physical chemistry of intestinal lipids and the molecular physiology of intestinal fatty acid transporters.

CONCLUSIONS

A better understanding of the molecular mechanism of intestinal fatty acid absorption should lead to novel approaches to the treatment and the prevention of fatty acid-related metabolic diseases that are prevalent worldwide.