Citrulline supplementation attenuates the development of non-alcoholic steatohepatitis in female mice through mechanisms involving intestinal arginase

Honokiol, a Neolignan from Magnolia officinalis, Attenuated Fructose-Induced Hepatic Fat Accumulation by Improving Intestinal Barrier Function in Mice

BACKGROUND

Fructose (Fru) consumption has been suggested to contribute to metabolic diseases including metabolic dysfunction-associated steatotic liver disease (MASLD), at least in part, by disturbing intestinal barrier function and intestinal nitric oxide (NO) homeostasis. Honokiol (Hon), a neolignan found in Magnolia officinalis, has been suggested to affect intestinal integrity and barrier function.

OBJECTIVES

We assessed whether Hon affects Fru-induced small intestinal permeability in settings of early MASLD.

METHODS

Female 8-10-wk-old C57BL/6J mice (n = 7/group) received either a 30% Fru solution + vehicle or plain drinking water + vehicle ± Hon (10 mg/kg bw/d) for 4 wk. Liver damage [e.g. nonalcoholic fatty liver disease activity score (NAS), number of neutrophils, interleukin-6 (IL-6) protein concentration], markers of intestinal permeability (bacterial endotoxin, tight junction proteins), and NO homeostasis in the small intestine were determined in vivo as well as ex vivo in an everted sac model and in Caco-2 cells. One-way and 2-way analysis of variance were performed, respectively.

RESULTS

Hon diminished the development of MASLD, which was associated with a significant lower NAS (-38%), number of neutrophils (-48%), and IL-6 protein concentrations (-38%) in livers of Fru-fed mice. Hon also attenuated Fru-induced alterations of markers of intestinal barrier function with Fru+Hon-fed mice showing lower bacterial toxin levels in portal plasma (-29%, P = 0.075), higher tight junction protein concentrations (+2.4-fold, P < 0.05), and lower NOx concentration (-44%, P < 0.05) as well as NO synthase activity (-35%) in the small intestine compared with Fru+vehicle-fed mice. Moreover, the decrease in AMP-activated protein kinase phosphorylation found in the small intestine of Fru-fed mice was significantly attenuated (+5.3-fold) by the concomitant treatment with Hon in Fru-fed mice. In support of the in vivo findings, Hon significantly attenuated Fru-induced intestinal permeability ex vivo and in Caco-2 cells.

CONCLUSIONS

Our data suggest that Hon diminished the development of Fru-induced early MASLD by alleviating impairments in intestinal barrier function.

Oral supplementation of choline attenuates the development of alcohol-related liver disease (ALD)

BACKGROUND

Chronic alcohol intake is associated with alterations of choline metabolism in various tissues. Here, we assessed if an oral choline supplementation attenuated the development of alcohol-related liver disease (ALD) in mice.

METHODS

Female C57BL/6 J mice (n = 8/group) were either pair-fed a liquid control diet, or a Lieber DeCarli liquid diet (5% ethanol) ± 2.7 g choline/kg diet for 29 days. Liver damage, markers of intestinal permeability and intestinal microbiota composition were determined. Moreover, the effects of choline on ethanol-induced intestinal permeability were assessed in an ex vivo model.

RESULTS

ALD development as determined by liver histology and assessing markers of inflammation (e.g., nitric oxide, interleukin 6 and 4-hydroxynonenal protein adducts) was attenuated by the supplementation of choline. Intestinal permeability in small intestine being significantly higher in ethanol-fed mice was at the level of controls in ethanol-fed mice receiving choline. In contrast, no effects of the choline supplementation were found on intestinal microbiota composition. Choline also significantly attenuated the ethanol-induced intestinal barrier dysfunction in small intestinal tissue ex vivo, an effect almost entirely abolished by the choline oxidase inhibitor dimbunol.

CONCLUSION

Our results suggest that an oral choline supplementation attenuates the development of ALD in mice and is related to a protection from intestinal barrier dysfunction.

The relevance of intestinal barrier dysfunction, antimicrobial proteins and bacterial endotoxin in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a leading cause of end-stage liver disease associated with increased mortality and cardiovascular disease. Obesity and diabetes are the most important risk factors of MASLD. It is well-established that obesity-associated insulin resistance leads to a situation of tissue lipotoxicity characterized by an accumulation of excess fat in non-fat tissues such as the liver, promoting the development of MASLD, and its progression into metabolic dysfunction-associated steatohepatitis.

METHODS

Here, we aimed to review the impact of disrupted intestinal permeability, antimicrobial proteins and bacterial endotoxin in the development and progression of MASLD.

RESULTS AND CONCLUSION

Recent studies demonstrated that obesity- and obesogenic diets-associated alterations of intestinal microbiota along with the disruption of intestinal barrier integrity, the alteration in antimicrobial proteins and, in consequence, an enhanced translocation of bacterial endotoxin into bloodstream might contribute to this pathological process through to impacting liver metabolism and inflammation.

Circulating metabolites are associated with persistent elevations of ALT in patients with chronic hepatitis B with complete viral suppression

Hepatitis B virus (HBV) can be completely suppressed after antiviral treatment; however, some patients with chronic hepatitis B (CHB) exhibit elevated alanine aminotransferase (ALT) levels and sustained disease progression. This study provides novel insights into the mechanism and potential predictive biomarkers of persistently elevated ALT (PeALT) in patients with CHB after complete viral inhibition. Patients having CHB with undetectable HBV DNA at least 12 months after antiviral treatment were enrolled from a prospective, observational cohort. Patients with PeALT and persistently normal ALT (PnALT) were matched 1:1 using propensity score matching. Correlations between plasma metabolites and the risk of elevated ALT were examined using multivariate logistic regression. A mouse model of carbon tetrachloride-induced liver injury was established to validate the effect of key differential metabolites on liver injury. Of the 1238 patients with CHB who achieved complete viral suppression, 40 (3.23%) had PeALT levels during follow-up (median follow-up: 2.42 years). Additionally, 40 patients with PnALT levels were matched as controls. Ser-Phe-Ala, Lys-Ala-Leu-Glu, 3-methylhippuric acid, 3-methylxanthine, and 7-methylxanthine were identified as critical differential metabolites between the two groups and independently associated with PeALT risk. Ser-Phe-Ala and Lys-Ala-Leu-Glu levels could be used to discriminate patients with PeALT from those with PnALT. Furthermore, N-acetyl- l-methionine (NALM) demonstrated the strongest negative correlation with ALT levels. NALM supplementation alleviated liver injury and hepatic necrosis induced by carbon tetrachloride in mice. Changes in circulating metabolites may contribute to PeALT levels in patients with CHB who have achieved complete viral suppression after antiviral treatment.

MASLD is related to impaired alcohol dehydrogenase (ADH) activity and elevated blood ethanol levels: Role of TNFα and JNK

Elevated fasting ethanol levels in peripheral blood frequently found in metabolic dysfunction-associated steatohepatitis (MASLD) patients even in the absence of alcohol consumption are discussed to contribute to disease development. To test the hypothesis that besides an enhanced gastrointestinal synthesis a diminished alcohol elimination through alcohol dehydrogenase (ADH) may also be critical herein, we determined fasting ethanol levels and ADH activity in livers and blood of MASLD patients and in wild-type ± anti-TNFα antibody (infliximab) treated and TNFα-/- mice fed a MASLD-inducing diet. Blood ethanol levels were significantly higher in patients and wild-type mice with MASLD while relative ADH activity in blood and liver tissue was significantly lower compared to controls. Both alterations were significantly attenuated in MASLD diet-fed TNFα-/- mice and wild-type mice treated with infliximab. Moreover, alcohol elimination was significantly impaired in mice with MASLD. In in vitro models, TNFα but not IL-1β or IL-6 significantly decreased ADH activity. Our data suggest that elevated ethanol levels in MASLD patients are related to TNFα-dependent impairments of ADH activity.

Oral Supplementation of Phosphatidylcholine Attenuates the Onset of a Diet-Induced Metabolic Dysfunction-Associated Steatohepatitis in Female C57BL/6J Mice

BACKGROUND & AIMS

Changes in phosphatidylcholine levels in the liver have been associated with the development of metabolic dysfunction-associated steatotic liver disease. Here, the effects of supplementing phosphatidylcholine on the development of early signs of metabolic dysfunction-associated steatohepatitis were assessed.

METHODS

Male and female C57BL/6J mice were fed a liquid control or a fructose-, fat-, and/or cholesterol-rich diet for 7 or 8 weeks. The diets of female mice were fortified ± phosphatidylcholine (12.5 mg/g diet). In liver tissue and portal blood, indices of liver damage, inflammation, and bacterial endotoxemia were measured. J774A.1 cells and human monocytes preincubated with phosphatidylcholine (0.38 mmol/L) were challenged with lipopolysaccharide (50-100 ng/mL) ± the peroxisome proliferator-activated receptor γ (PPARγ) activator pioglitazone (10 μmol/L) or ± a liver receptor homolog 1 (LRH-1) antagonist 1-(3'-[1-(2-[4-morpholinyl]ethyl)-1H-pyrazol-3-yl]-3-biphenylyl)ethanon (1-10 μmol/L).

RESULTS

In fructose-, fat-, and/or cholesterol-rich diet-fed mice the development of fatty liver and the beginning of inflammation were associated with significantly lower hepatic phosphatidylcholine levels when compared with controls. Supplementing phosphatidylcholine significantly attenuated the development of fatty liver and inflammation, being associated with protection against the induction of PPARγ2, and activation of nuclear factor of κ light polypeptide gene enhancer in B-cell inhibitor α whereas Lrh1 expression was unchanged. The protective effects of phosphatidylcholine on the lipopolysaccharide-induced activation of J774A.1 cells and human monocytes were attenuated significantly by the PPARγ activator pioglitazone and the LRH-1 antagonist.

CONCLUSIONS

Our data suggest that phosphatidylcholine levels in the liver are lower in early metabolic dysfunction-associated steatohepatitis in mice and that supplementation of phosphatidylcholine can diminish the development of metabolic dysfunction-associated steatotic liver disease through mechanisms involving LRH-1/PPARγ2/ nuclear factor κ-light-chain enhancer of activated B-cell signaling.

Mechanical study of alisol B 23-acetate on methionine and choline deficient diet-induced nonalcoholic steatohepatitis based on untargeted metabolomics

Alisol B 23-acetate (AB23A) has been demonstrated to have beneficial effects on nonalcoholic steatohepatitis (NASH). However, the mechanisms of AB23A on NASH remain unclear. This study aimed to investigate the mechanisms underlying the metabolic regulatory effects of AB23A on NASH. We used AB23A to treat mice with NASH, which was induced by a methionine and choline deficient (MCD) diet. We initially investigated therapeutic effect and resistance to oxidation and inflammation of AB23A on NASH. Subsequently, we performed untargeted metabolomic analyses and relative validation assessments to evaluate the metabolic regulatory effects of AB23A. AB23A reduced lipid accumulation, ameliorated oxidative stress and decreased pro-inflammatory cytokines in the liver. Untargeted metabolomic analysis found that AB23A altered the metabolites of liver. A total of 55 differential metabolites and three common changed pathways were screened among the control, model and AB23A treatment groups. Further tests validated the effects of AB23A on modulating common changed pathway-involved factors. AB23A treatment can ameliorate NASH by inhibiting oxidative stress and inflammation. The mechanism of AB23A on NASH may be related to the regulation of alanine, aspartate and glutamate metabolism, d-glutamine and d-glutamate metabolism, and arginine biosynthesis pathways.

Antibiotics attenuate diet-induced nonalcoholic fatty liver disease without altering intestinal barrier dysfunction

To date the role of the alterations of intestinal microbiota in the development of intestinal barrier dysfunction in settings of nonalcoholic fatty liver disease (NAFLD) has not been fully understood. Here, we assessed the effect of antibiotics on development of NAFLD and their impact on intestinal barrier dysfunction. Male C57BL/6J mice were either pair-fed a liquid control diet (C) or fat- and fructose-rich diet (FFr) +/- antibiotics (AB, ampicillin/vancomycin/metronidazole/gentamycin) for 7 weeks. Fasting blood glucose was determined and markers of liver damage, inflammation, intestinal barrier function, and microbiota composition were assessed. The development of hepatic steatosis with early signs of inflammation found in FFr-fed mice was significantly abolished in FFr+AB-fed mice. Also, while prevalence of bacteria in feces was not detectable and TLR4 ligand levels in portal plasma were at the level of controls in FFr+AB-fed mice, impairments of intestinal barrier function like an increased permeation of xylose and iNOS protein levels persisted to a similar extent in both FFr-fed groups irrespective of AB use. Exposure of everted small intestinal tissue sacs of naïve mice to fructose resulted in a significant increase in tissue permeability and loss of tight junction proteins, being not affected by the presence of AB, whereas the concomitant treatment of tissue sacs with the NOS inhibitor aminoguanidine attenuated these alterations. Taken together, our data suggest that intestinal barrier dysfunction in diet-induced NAFLD in mice may not be predominantly dependent on changes in intestinal microbiota but rather that fructose-induced alterations of intestinal NO-homeostasis might be critically involved.

Fructose: a modulator of intestinal barrier function and hepatic health?

PURPOSE

Consumption of fructose has repeatedly been discussed to be a key factor in the development of health disturbances such as hypertension, diabetes type 2, and non-alcoholic fatty liver disease. Despite intense research efforts, the question if and how high dietary fructose intake interferes with human health has not yet been fully answered.

RESULTS

Studies suggest that besides its insulin-independent metabolism dietary fructose may also impact intestinal homeostasis and barrier function. Indeed, it has been suggested by the results of human and animal as well as in vitro studies that fructose enriched diets may alter intestinal microbiota composition. Furthermore, studies have also shown that both acute and chronic intake of fructose may lead to an increased formation of nitric oxide and a loss of tight junction proteins in small intestinal tissue. These alterations have been related to an increased translocation of pathogen-associated molecular patterns (PAMPs) like bacterial endotoxin and an induction of dependent signaling cascades in the liver but also other tissues.

CONCLUSION

In the present narrative review, results of studies assessing the effects of fructose on intestinal barrier function and their impact on the development of health disturbances with a particular focus on the liver are summarized and discussed.

Supplementing L-Citrulline Can Extend Lifespan in C. elegans and Attenuate the Development of Aging-Related Impairments of Glucose Tolerance and Intestinal Barrier in Mice

L-Citrulline (L-Cit) is discussed to possess a protective effect on intestinal barrier dysfunction but also to diminish aging-associated degenerative processes. Here, the effects of L-Cit on lifespan were assessed in C. elegans, while the effects of L-Cit on aging-associated decline were determined in C57BL/6J mice. For lifespan analysis, C. elegans were treated with ±5 mM L-Cit. Twelve-month-old male C57BL/6J mice (n = 8-10/group) fed a standard chow diet received drinking water ± 2.5 g/kg/d L-Cit or 5 g/kg/d hydrolyzed soy protein (Iso-N-control) for 16 or 32 weeks. Additionally, 4-month-old C57BL/6J mice were treated accordingly for 8 weeks. Markers of senescence, glucose tolerance, intestinal barrier function, and intestinal microbiota composition were analyzed in mice. L-Cit treatment significantly extended the lifespan of C. elegans. The significant increase in markers of senescence and signs of impaired glucose tolerance found in 16- and 20-month-old control mice was attenuated in L-Cit-fed mice, which was associated with protection from intestinal barrier dysfunction and a decrease in NO2- levels in the small intestine, while no marked differences in intestinal microbiota composition were found when comparing age-matched groups. Our results suggest that pharmacological doses of L-Cit may have beneficial effects on lifespan in C. elegans and aging-associated decline in mice.

TNFα is a key trigger of inflammation in diet-induced non-obese MASLD in mice

Tumor necrosis factor alpha (TNFα) is thought to be a critical factor in the development of metabolic dysfunction-associated steatotic liver disease (MASLD). Here, we determined the effects of a treatment with the anti-TNFα antibody infliximab and a genetic deletion of TNFα, respectively, in the development of non-obese diet-induced early metabolic dysfunction-associated steatohepatitis (MASH) in mice. The treatment with infliximab improved markers of liver damage in mice with pre-existing early MASH. In TNFα-/- mice, the development of early signs of MASH and insulin resistance was significantly attenuated compared to wild-type animals. While mRNA expression of proinflammatory cytokines like interleukin 1β (Il1b) and interleukin 6 (Il6) were significantly lower in livers of MASH-diet-fed TNFα-/- mice compared to wild-type mice with early MASH, markers of intestinal barrier function were similarly impaired in both MASH-diet-fed groups compared to controls. Our data suggest that TNFα is a key regulator of hepatic inflammation and insulin resistance associated with the development of early non-obese MASH.

Cognitive Alterations in Old Mice Are Associated with Intestinal Barrier Dysfunction and Induced Toll-like Receptor 2 and 4 Signaling in Different Brain Regions

Emerging evidence implicate the 'microbiota-gut-brain axis' in cognitive aging and neuroinflammation; however, underlying mechanisms still remain to be elucidated. Here, we assessed if potential alterations in intestinal barrier function and microbiota composition as well as levels of two key pattern-recognition receptors namely Toll-like receptor (TLR) 2 and TLR4, in blood and different brain regions, and depending signaling cascades are paralleling aging associated alterations of cognition in healthy aging mice. Cognitive function was assessed in the Y-maze and intestinal and brain tissue and blood were collected in young (4 months old) and old (24 months old) male C57BL/6 mice to determine intestinal microbiota composition by Illumina amplicon sequencing, the concentration of TLR2 and TLR4 ligands in plasma and brain tissue as well as to determine markers of intestinal barrier function, senescence and TLR2 and TLR4 signaling. Cognitive function was significantly impaired in old mice. Also, in old mice, intestinal microbiota composition was significantly altered, while the relative abundance of Gram-negative or Gram-positive bacteria in the small and large intestines at different ages was not altered. Moreover, intestinal barrier function was impaired in small intestine of old mice, and the levels of TLR2 and TLR4 ligands were also significantly higher in both portal and peripheral blood. Furthermore, levels of TLR2 and TLR4 ligands, and downstream markers of TLR signaling were higher in the hippocampal and prefrontal cortex of old mice compared to young animals. Taken together, our results suggest that even in 'healthy' aging, cognitive function is impaired in mice going along with an increased intestinal translocation of TLR ligands and alterations of TLR signaling in several brain regions.

Elafibranor modulates ileal macrophage polarization to restore intestinal integrity in NASH: Potential crosstalk between ileal IL-10/STAT3 and hepatic TLR4/NF-κB axes

Experimental and clinical evidence implicate disrupted gut barrier integrity in provoking innate immune responses, specifically macrophages, towards the progression of non-alcoholic steatohepatitis (NASH). Peroxisome proliferator-activated receptors (PPARs), a subset of the nuclear receptor superfamily, act to fine-tune several metabolic and inflammatory processes implicated in NASH. As such, the current study was carried out to decipher the potential role of dual PPAR α/δ activation using elafibranor (ELA) on ileal macrophage polarization (MP) and its likely impact on the liver in a NASH setting. To achieve this aim, an in vitro NASH model using fat-laden HepG2 cells was first used to validate the impact of ELA on hepatic fat accumulation. Afterwards, ELA was used in a combined model of dietary NASH and chronic colitis analogous to the clinical presentation of NASH parallel with intestinal barrier dysfunction. ELA mitigated fat accumulation in vitro as evidenced by Oil Red-O staining and curbed triglyceride levels. Additionally, ELA restored the expression of tight junctional proteins, claudin-1 and occludin, along with decreasing intestinal permeability and inflammation skewing ileal macrophages towards the M2 phenotype, as indicated by boosted arginase-1 (Arg1) and curtailed inducible nitric oxide synthase (iNOS) expression levels. These changes were aligned with a modulation in hepatic toll-like receptor-4 (TLR4)/nuclear factor kappa B (NF-κB) along with ileal interleukin-10 (IL-10)/signal transducer and activator of transcription-3 (STAT3) axes. Overall, the present findings suggest that the dual PPAR α/δ agonist, ELA, may drive MP in the ileum towards the M2 phenotype improving intestinal integrity towards alleviating NASH.

Maternal fructose boosts the effects of a Western-type diet increasing SARS-COV-2 cell entry factors in male offspring

Fructose-rich beverages and foods consumption correlates with the epidemic rise in cardiovascular disease, diabetes and obesity. Severity of COVID-19 has been related to these metabolic diseases. Fructose-rich foods could place people at an increased risk for severe COVID-19. We investigated whether maternal fructose intake in offspring affects hepatic and ileal gene expression of proteins that permit SARS-CoV2 entry to the cell. Carbohydrates were supplied to pregnant rats in drinking water. Adult and young male descendants subjected to water, liquid fructose alone or as a part of a Western diet, were studied. Maternal fructose reduced hepatic SARS-CoV2 entry factors expression in older offspring. On the contrary, maternal fructose boosted the Western diet-induced increase in viral entry factors expression in ileum of young descendants. Maternal fructose intake produced a fetal programming that increases hepatic viral protection and, in contrast, exacerbates fructose plus cholesterol-induced diminution in SARS-CoV2 protection in small intestine of progeny.

Impairments of intestinal arginine and NO metabolisms trigger aging-associated intestinal barrier dysfunction and 'inflammaging'

Aging is considered a state of low grade inflammation, occurring in the absence of any overt infection often referred to as 'inflammaging'. Maintaining intestinal homeostasis may be a target to extend a healthier status in older adults. Here, we report that even in healthy older men low grade bacterial endotoxemia is prevalent. In addition, employing multiple mouse models, we also show that while intestinal microbiota composition changes significantly during aging, fecal microbiota transplantation to old mice does not protect against aging-associated intestinal barrier dysfunction in small intestine. Rather, intestinal NO homeostasis and arginine metabolism mediated through arginase and NO synthesis is altered in small intestine of aging mice. Treatment with the arginase inhibitor norNOHA prevented aging-associated intestinal barrier dysfunction, low grade endotoxemia and delayed the onset of senescence in peripheral tissue e.g., liver. Intestinal arginine and NO metabolisms could be a target in the prevention of aging-associated intestinal barrier dysfunction and subsequently decline and 'inflammaging'.

Tianhuang formula reduces the oxidative stress response of NAFLD by regulating the gut microbiome in mice

Background

The gut microbiome affects the occurrence and development of NAFLD, but its mechanism has not yet been fully elucidated. Chinese medicine is a new treatment strategy to improve NAFLD by regulating the gut microbiome. Tianhuang formula (TH) has been proved to have a lipid-lowering effect in which constituents of ginsenoside Rb1, ginsenoside Rg1, ginsenoside Rb, ginsenoside Re, and ginsenoside R1 from Panax notoginseng and berberine, palmatine, and coptisine from Coptis chinensis have low drug permeability, which results in poor intestinal absorption into the human body, and are thus able to come into contact with the gut microflora for a longer time. Therefore, it might be able to influence the gut microbial ecosystem, but it still needs to be investigated.

Method

The characteristics of the gut microbiome were represented by 16S rRNA sequencing, and the metabolites in intestinal contents and liver were discovered by non-targeted metabolomics. Correlation analysis and fermentation experiments revealed the relationship between the gut microbiome and metabolites. Blood biochemical indicators, liver function indicators, and oxidation-related indicators were assayed. H&E staining and Oil Red O staining were used to analyze the characteristics of hepatic steatosis. RT-qPCR and western blotting were used to detect the expression of genes and proteins in liver tissues, and fecal microbial transplantation (FMT) was performed to verify the role of the gut microbiome.

Results

Gut microbiome especially Lactobacillus reduced, metabolites such as 5-Methoxyindoleacetate (5-MIAA) significantly reduced in the liver and intestinal contents, the level of hepatic GSH and SOD reduced, MDA increased, and the protein expression of Nrf2 also reduced in NAFLD mice induced by high-fat diet (HFD). The normal diet mice transplanted with NAFLD mice feces showed oxidative liver injury, indicating that the NAFLD was closely related to the gut microbiome. TH and TH-treated mice feces both can reshape the gut microbiome, increase the abundance of Lactobacillus and the content of 5-MIAA in intestinal contents and liver, and improve oxidative liver injury. This indicated that the effect of TH improving NAFLD was related to the gut microbiome, especially Lactobacillus. 5-MIAA, produced by Lactobacillus, was proved with fermentation experiments in vitro. Further experiments proved that 5-MIAA activated the Nrf2 pathway to improve oxidative stress in NAFLD mice induced by HFD. TH reshaped the gut microbiome, increased the abundance of Lactobacillus and its metabolite 5-MIAA to alleviate oxidative stress, and improved NAFLD.

Conclusion

The study has demonstrated a mechanism by which the gut microbiome modulated oxidative stress in NAFLD mice induced by HFD. The traditional Chinese medicine TH improved NAFLD by regulating the gut microbiome, and its mechanism was related to the “Lactobacillus-5-MIAA-Nrf2” pathway. It provided a promising way for the intervention of NAFLD.

Inhibition of GCN2 alleviates hepatic steatosis and oxidative stress in obese mice: Involvement of NRF2 regulation

The development of nonalcoholic fatty liver disease (NAFLD) is associated with increased reactive oxygen species (ROS) production. Previous observations on the contradictory roles of general control nonderepressible 2 (GCN2) in regulating the hepatic redox state under different nutritional conditions prompted an investigation of the underlying mechanism by which GCN2 regulates ROS homeostasis. In the present study, GCN2 was found to interact with NRF2 and decrease NRF2 expression in a KEAP1-dependent manner. Activation of GCN2 by halofuginone treatment or leucine deprivation decreased NRF2 expression in hepatocytes by increasing GSK-3β activity. In response to oxidative stress, GCN2 repressed NRF2 transcriptional activity. Knockdown of hepatic GCN2 by tail vein injection of an AAV8-shGcn2 vector attenuated hepatic steatosis and oxidative stress in leptin-deficient (ob/ob) mice in an NRF2-dependent manner. Inhibition of GCN2 by GCN2iB also ameliorated hepatic steatosis and oxidative stress in both ob/ob mice and high fat diet-fed mice, which was associated with significant changes in lipid and amino acid metabolic pathways. Untargeted metabolomics analysis revealed that GCN2iB decreased fatty acid and sphingomyelin levels but increased aliphatic amino acid and phosphatidylcholine levels in fatty livers. Collectively, our results provided the first direct evidence that GCN2 is a novel regulator of NRF2 and that specific GCN2 inhibitors might be potential drugs for NAFLD therapy.

Alterations of nitric oxide homeostasis as trigger of intestinal barrier dysfunction in non-alcoholic fatty liver disease

Changes in intestinal nitric oxide metabolism are discussed to contribute for the development of intestinal barrier dysfunction in non‐alcoholic fatty liver disease (NAFLD). To induce steatosis, female C57BL/6J mice were pair‐fed with a liquid control diet (C) or a fat‐, fructose‐ and cholesterol‐rich diet (FFC) for 8 weeks. Mice received the diets ± 2.49 g L‐arginine/kg bw/day for additional 5 weeks. Furthermore, mice fed C or FFC ± L‐arginine/kg bw/day for 8 weeks were concomitantly treated with the arginase inhibitor N^ω‐hydroxy‐nor‐L‐arginine (nor‐NOHA, 0.01 g/kg bw). Liver damage, intestinal barrier function, nitric oxide levels and arginase activity in small intestine were assessed. Also, arginase activity was measured in serum from 13 patients with steatosis (NAFL) and 14 controls. The development of steatosis with beginning inflammation was associated with impaired intestinal barrier function, increased nitric oxide levels and a loss of arginase activity in small intestine in mice. L‐arginine supplementation abolished the latter along with an improvement of intestinal barrier dysfunction; nor‐NOHA attenuated these effects. In patients with NAFL, arginase activity in serum was significantly lower than in healthy controls. Our data suggest that increased formation of nitric oxide and a loss of intestinal arginase activity is critical in NAFLD‐associated intestinal barrier dysfunction.

Potential Implications of Citrulline and Quercetin on Gut Functioning of Monogastric Animals and Humans: A Comprehensive Review

The importance of gut health in animal welfare and wellbeing is undisputable. The intestinal microbiota plays an essential role in the metabolic, nutritional, physiological, and immunological processes of animals. Therefore, the rapid development of dietary supplements to improve gut functions and homeostasis is imminent. Recent studies have uncovered the beneficial effects of dietary supplements on the immune response, microbiota, gut homeostasis, and intestinal health. The application of citrulline (a functional gut biomarker) and quercetin (a known potent flavonoid) to promote gut functions has gained considerable interest as both bioactive substances possess anti-inflammatory, anti-oxidative, and immunomodulatory properties. Research has demonstrated that both citrulline and quercetin can mediate gut activities by combating disruptions to the intestinal integrity and alterations to the gut microbiota. In addition, citrulline and quercetin play crucial roles in maintaining intestinal immune tolerance and gut health. However, the synergistic benefits which these dietary supplements (citrulline and quercetin) may afford to simultaneously promote gut functions remain to be explored. Therefore, this review summarizes the modulatory effects of citrulline and quercetin on the intestinal integrity and gut microbiota, and further expounds on their potential synergistic roles to attenuate intestinal inflammation and promote gut health.

NO, way to go: critical amino acids to replenish nitric oxide production in treating mucositis

PURPOSE OF REVIEW

There is still an unmet need for preventive and treatment strategies for chemotherapy-induced and radiotherapy-induced mucositis and its associated systemic inflammatory response (SIR) in cancer patients. Because of citrulline depletion due to cytotoxic therapy, nitric oxide (NO) production can be reduced, limiting its effect in many physiological processes. Restoring NO production could relieve mucositis severity by supporting host damage control mechanisms. Amino acids glutamine, arginine and citrulline are involved in NO production. This review including recent literature of preclinical and clinical studies will discuss the potential benefits of glutamine, arginine and citrulline on mucositis development with focus on NO production.

RECENT FINDINGS

Mucositis severity is more defined by host response to DNA damage than by DMA damage itself. Citrulline depletion because of afunctional enterocytes could be responsible for NO depletion during cytotoxic therapy. Restoring NO production during cytotoxic therapy could have a beneficial effect on mucositis development. Citrulline seems a more promising NO donor than glutamine or arginine during cytotoxic therapy, although clinical studies in mucositis patients are currently lacking.

SUMMARY

Glutamine, arginine and citrulline show in-vitro beneficial effects on inflammatory processes involved in mucositis. Translation to the clinic is difficult as demonstrated with use of glutamine and arginine. Citrulline, being the most potent NO donor with excellent oral bio-availability, is very promising as treatment choice for mucositis and its use deserves to be investigated in clinical trials with mucositis patients.