Role of physical exercise on hepatic insulin, glucocorticoid and inflammatory signaling pathways in an animal model of non-alcoholic steatohepatitis

Mechanisms underpinning the effect of exercise on the non-alcoholic fatty liver disease: review

Non-alcoholic Fatty Liver Disease (NAFLD) - whose terminology was recently replaced by metabolic liver disease (MAFLD) - is an accumulation of triglycerides in the liver of >5 % of its weight. Epidemiological studies indicated an association between NAFLD and reduced physical activity. In addition, exercise has been shown to improve NAFLD independently of weight loss. In this paper, we aim to systematically review molecular changes in sedentary experimental NAFLD models vs. those subjected to exercise. We utilized the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist and standard review techniques. Studies were considered for inclusion if they addressed the primary question: the mechanisms by which exercise influenced NAFLD. This review summarized experimental evidence of improvements in NAFLD with exercise in the absence of weight loss. The pathways involved appeared to have AMPK as a common denominator. See also the graphical abstract(Fig. 1).

Prenatal stress induces sex- and tissue-specific alterations in insulin pathway of Wistar rats offspring

BACKGROUND AND AIMS

Prenatal stress may lead to tissue and sex-specific cardiometabolic disorders in the offspring through imbalances in the insulin signaling pathway. Therefore, we aimed to determine the sex-specific adaptations of prenatal stress on the insulin signaling pathway of cardiac and hepatic tissue of adult offspring Wistar rats.

METHODS

Wistar pregnant rats were divided into control and stress groups. Unpredictable stress protocol was performed from the 14th to the 21st day of pregnancy. After lactation, the dams were euthanized and blood was collected for corticosterone measurement and the offspring were separated into four groups according to sex and intervention (n=8/group). At 90 days old, the offspring were submitted to an oral glucose tolerance test (OGTT) and an insulin tolerance test (ITT). After euthanasia blood collection was used for biochemical analysis and the left ventricle and liver were used for protein expression and histological analysis.

RESULTS

Stress increased maternal corticosterone levels, and in the offspring, decreased glucose concentration in both OGTT and ITT, reduced insulin receptor (Irβ) and insulin receptor substrate-1 (IRS1) activation and reduced insulin receptor inhibition (PTP1B) in the liver of male offspring at 90 days old, without repercussions in cardiac tissue. Moreover, female offspring submitted to prenatal stress exhibited reduced fatty acid uptake, with lower hepatic CD36 expression, reduced high density lipoprotein (cHDL) and increased Castelli risk indexes I and II.

CONCLUSIONS

Unpredictable prenatal stress evoked reduced insulin sensitivity and liver-specific impairment in insulin signaling activation in male while increasing markers of cardiovascular risk in females.

Association between composite dietary antioxidant index and metabolic dysfunction associated steatotic liver disease: result from NHANES, 2017-2020

Background

The development of metabolic dysfunction associated steatotic liver disease (MASLD) has been associated with lipid accumulation, oxidative stress, endoplasmic reticulum stress, and lipotoxicity. The Composite Dietary Antioxidant Index (CDAI) is a comprehensive score representing an individual intake of various dietary antioxidants, including vitamin A, vitamin C, vitamin E, selenium, zinc, and carotenoids. This study investigated the association between CDAI and MASLD.

Materials and methods

Clinical and demographic data, as well as ultrasound transient elastography measurements at baseline, were collected from the National Health and Nutrition Examination Survey 2017-2020 (NHANES 2017-2020). The controlled attenuation parameter was utilized to diagnose the presence of hepatic steatosis and to categorize individuals into those with and without MASLD. Liver stiffness was measured by ultrasound transient elastography, and subjects were classified as those with and without advanced liver fibrosis.

Results

This study included 5,884 adults, of whom 3,433 were diagnosed with MASLD, resulting in a weighted prevalence of 57.3%. After adjusting for covariates, the odds ratios for MASLD were 0.96 (95% CI: 0.82, 1.12) in the second quartile, 0.80 (95% CI: 0.68, 0.95) in the third quartile and 0.60 (95% CI: 0.49, 0.73) in the fourth quartile, respectively. CDAI, however, was not significantly associated with advanced liver fibrosis.

Conclusion

These findings suggested that scores on the CDAI were linearly and negatively associated with the prevalence of MASLD in the United States adults.

Voluntary exercise fails to prevent metabolic dysfunction-associated steatotic liver disease progression in male rats fed a high-fat high-cholesterol diet

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major public health issue with a worldwide prevalence of 30%-32%. In animal models, voluntary exercise may be an alternative to forced physical activity, avoiding stress, potential injuries, and being logistically simpler. Here, we assessed voluntary exercise (Vex) in Sprague-Dawley rats fed a high-fat, high-cholesterol diet for 18 weeks to induce MASLD. We quantified workload (speed and distance) using exercise wheels and evaluated energy expenditure using calorimetric cages. MASLD progression was assessed using circulating and hepatic biochemical and gene markers of steatosis, inflammation, and fibrosis. The animals ran an average of 301 km during the study period, with the average daily distance peaking at 4937 m/day during Weeks 3-4 before decreasing to 757 m/day by the end of the study. Rats exposed to Vex showed no improvement in any of the MASLD-associated features, such as steatosis, inflammation, or fibrosis. Rats exposed to Vex exhibited a higher total energy expenditure during the night phase (+0.35 kcal/h; p = 0.003) without resulting in any effect on body composition. We conclude that, in our experimental conditions, Vex failed to prevent MASLD progression in male Sprague-Dawley rats exposed to a high-fat high-cholesterol diet for 18 weeks.

EXERCISE IMPROVES ALVEOLAR BONE LOSS AND THE INFLAMMATORY PROFILE OF PERIODONTAL DISEASE

ABSTRACT Periodontal disease (PD) is an inflammatory oral disease and alveolar bone loss is the most important sign of PD. However, the effects of exercise on inflammatory factors and alveolar bone loss in individuals with PD have been little studied. This meta-analysis assesses the effect of physical exercise on alveolar bone loss (ABL) and the inflammatory profile of PD in animal models. Relevant studies published through July 2020 in PubMed, Medline, Embase and Web of Science were searched after developing a PICOS statement. Quality assessment and risk of bias were analyzed according to the SYRCLE protocol. A total of 52 references were retrieved, 4 of which were considered eligible for inclusion. A total of thirty-four male Wistar rats from the included studies were evaluated for alveolar bone loss and assessed for inflammatory profile. The results indicated that physical exercise could reduce alveolar bone loss (95% CI -2.85 to -0.82, p = 0.002) and the pro-inflammatory tumor necrosis factor–α (TNF-α) in serum or gingival tissue (95% CI -0.45 to -0.24, p < 0.00001). Inversely, exercise increased anti-inflammatory interleukin–10 (IL-10) in serum or gingival tissue (95% CI 0.28 to 0.69, p < 0.00001). However, one study reported a negative result in the expression of TNF-α and IL-10. Current evidence indicates that physical exercise contributes to ameliorate PD by reducing alveolar bone loss and inflammation in animal PD models, which suggests that moderate exercise can be implemented in clinical practice to maintain periodontal health. Level of Evidence I; Systematic Review and Meta-analysis

Effect of training and crocin supplementation on mitochondrial biogenesis and redox-sensitive transcription factors in liver tissue of type 2 diabetic rats

Present study investigated the effect of continued training (CT) and interval training (IT) with crocin (C) supplementation on mitochondrial biogenesis and redox-sensitive transcription factors in liver tissue of type 2 diabetes (T2D) rats. Forty-eight high fat diet and streptozotocin- induced diabetic rats (mean age: 20 weeks, mean weight: 360.12 ± 12.11 g) were randomly divided into six groups including: (1) sham (Sh), (2) CT, (3) IT, (4) C (25 mg/kg/day), (5) CT + C, and (6) IT + C. IT and CT were performed 8 weeks for five sessions per week on treadmill with 80-85% and 50-55% of maximum speed running respectively. IT, CT and C decreased AP1 and increased LCAD (p ≤ .05); C increased SIRT1 (p ≤ .05); IT + C and CT + C decreased AP1 as well as increased NF-κB and LCAD (p ≤ .05); IT + C increased SIRT1, SIRST3 and PGC1-α (p ≤ .05). It appears that IT along with C compared to CT and C have favourable effect on mitochondrial biogenesis factors.

Irisin/FNDC5 influences myogenic markers on skeletal muscle following high and moderate-intensity exercise training in STZ-diabetic rats

In the present study, we investigated the effects of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) on irisin and expression of myogenic markers (paired box 7 (Pax7), myogenic differentiation 1 (MyoD), myogenin) in skeletal muscle of diabetic rats. Eighty-four male Wistar rats (6 weeks of age) were randomly divided into seven groups (n = 12): basic control (Co Basic), 8 weeks control (Co 8w), diabetes mellitus (DM), HIIT, DM + HIIT, MICT, and DM + MICT groups. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ). TheV ˙ o 2 max protocol was characterized by running on a rodent treadmill with moderate intensity (60-70%V ˙ o 2 max ), 60 min per session, 5 days/week, for 6 weeks. HIIT consisted of six 3-min runs at a high intensity (80-90%V ˙ o 2 max ) alternated with 2-min running at low intensity (50%V ˙ o 2 max ), 30 min per session, 5 days/week, for 6 weeks. Results showed that DM decreased myoblast markers compared to Co Basic and Co 8w groups. Fibronectin type III domain-containing protein 5 (FNDC5) mRNA decrease was correlated with myoblast markers (Pax7 r = 0.632, p = 0.027; MyoD r = 0.999, p = 0.001; myogenin r = 1.000, p = 0.001) in DM group. DM + MICT significantly increased gene expression of MyoD, myogenin, and FNDC5 compared to DM and DM + HIIT. The results also showed that the intensity and duration of exercise on the treadmill were effective in stimulating irisin and myogenic markers after DM.

Physical exercise positively modulates nonalcoholic steatohepatitis-related hepatic endoplasmic reticulum stress

Obesity is a predictive factor for the development of nonalcoholic steatohepatitis (NASH). Although some of the mechanisms associated with NASH development are still elusive, its pathogenesis relies on a complex broad spectrum of (interconnected) metabolic-based disorders. We analyzed the effects of voluntary physical activity (VPA) and endurance training (ET), as preventive and therapeutic nonpharmacological strategies, respectively, against hepatic endoplasmic reticulum (ER) stress, ER-related proapoptotic signaling, and oxidative stress in an animal model of high-fat diet (HFD)-induced NASH. Adult male Sprague-Dawley rats were divided into standard control liquid diet (SCLD) or HFD groups, with sedentary, VPA, and ET subgroups in both (sedentary animals with access to SCLD [SS], voluntarily physically active animals with access to SCLD [SV], and endurance-trained animals with access to SCLD [ST] in the former and sedentary animals with access to liquid HFD [HS], voluntarily physically active animals with access to liquid HFD [HV], and endurance-trained animals with access to liquid HFD [HT] in the latter, respectively). Hepatic ER stress and ER-related proapoptotic signaling were evaluated by Western blot and reverse transcriptase-polymerase chain reaction; redox status was evaluated through quantification of lipid peroxidation, protein carbonyls groups, and glutathione levels as well as antioxidant enzymes activity. In SCLD-treated animals, VPA significantly decreased eukaryotic initiation factor-2 alpha (eIF2α). In HFD-treated animals, VPA significantly decreased eIF2α and phospho-inositol requiring enzyme-1 alpha (IRE1α) but ET significantly decreased eIF2α and significantly increased both spliced X-box binding protein 1 (sXBP1) and unspliced X-box binding protein 1; a significant increase of phosphorylated-eIF2α (p-eIF2α) to eIF2α ratio occurred in ET versus VPA. HS compared to SS disclosed a significant increase of total and reduced glutathione, HV compared to SV a significant increase of oxidized glutathione, HT compared to ST a significant increase of p-eIF2α to eIF2α ratio and sXBP1. Physical exercise counteracts NASH-related ER stress and its associated deleterious consequences through a positive and dynamical modulation of the hepatic IRE1α-X-box binding protein 1 pathway.

Short-Term Strength Exercise Reduces Hepatic Insulin Resistance in Obese Mice by Reducing PTP1B Content, Regardless of Changes in Body Weight

Obesity is closely related to insulin resistance and type 2 diabetes genesis. The liver is a key organ to glucose homeostasis since insulin resistance in this organ increases hepatic glucose production (HGP) and fasting hyperglycemia. The protein-tyrosine phosphatase 1B (PTP1B) may dephosphorylate the IR and IRS, contributing to insulin resistance in this organ. Aerobic exercise is a great strategy to increase insulin action in the liver by reducing the PTP1B content. In contrast, no study has shown the direct effects of strength training on the hepatic metabolism of PTP1B. Therefore, this study aims to investigate the effects of short-term strength exercise (STSE) on hepatic insulin sensitivity and PTP1B content in obese mice, regardless of body weight change. To achieve this goal, obese Swiss mice were submitted to a strength exercise protocol lasting 15 days. The results showed that STSE increased Akt phosphorylation in the liver and enhanced the control of HGP during the pyruvate tolerance test. Furthermore, sedentary obese animals increased PTP1B content and decreased IRS-1/2 tyrosine phosphorylation; however, STSE was able to reverse this scenario. Therefore, we conclude that STSE is an important strategy to improve the hepatic insulin sensitivity and HGP by reducing the PTP1B content in the liver of obese mice, regardless of changes in body weight.

Elevation of hepatic autophagy and antioxidative capacity by endurance exercise is associated with suppression of apoptosis in mice

INTRODUCTION AND OBJECTIVES

Endurance exercise (EXE) has emerged as a potent inducer of autophagy essential in maintaining cellular homeostasis in various tissues; however, the functional significance and molecular mechanisms of EXE-induced autophagy in the liver remain unclear. Thus, the aim of this study is to examine the signaling nexus of hepatic autophagy pathways occurring during acute EXE and a potential crosstalk between autophagy and apoptosis.

MATERIALS AND METHODS

C57BL/6 male mice were randomly assigned to sedentary control group (CON, n=9) and endurance exercise (EXE, n=9). Mice assigned to EXE were gradually acclimated to treadmill running and ran for 60min per day for five consecutive days.

RESULTS

Our data showed that EXE promoted hepatic autophagy via activation of canonical autophagy signaling pathways via mediating microtubule-associated protein B-light chain 3 II (LC3-II), autophagy protein 7 (ATG7), phosphorylated adenosine mono phosphate-activated protein kinase (p-AMPK), CATHEPSIN L, lysosome-associated membrane protein 2 (LAMP2), and a reduction in p62. Interestingly, this autophagy promotion concurred with enhanced anabolic activation via AKT-mammalian target of rapamycin (mTOR)-p70^S6K signaling cascade and enhanced antioxidant capacity such as copper zinc superoxide dismutase (CuZnSOD), glutathione peroxidase (GPX), and peroxiredoxin 3 (PRX3), known to be as antagonists of autophagy. Moreover, exercise-induced autophagy was inversely related to apoptosis in the liver.

CONCLUSIONS

Our findings indicate that improved autophagy and antioxidant capacity, and potentiated anabolic signaling may be a potent non-pharmacological therapeutic strategy against diverse liver diseases.

Reduced Oxidative Stress and Enhanced FGF21 Formation in Livers of Endurance-Exercised Rats with Diet-Induced NASH

Non-alcoholic fatty liver diseases (NAFLD) including the severe form with steatohepatitis (NASH) are highly prevalent ailments to which no approved pharmacological treatment exists. Dietary intervention aiming at 10% weight reduction is efficient but fails due to low compliance. Increase in physical activity is an alternative that improved NAFLD even in the absence of weight reduction. The underlying mechanisms are unclear and cannot be studied in humans. Here, a rat NAFLD model was developed that reproduces many facets of the diet-induced NAFLD in humans. The impact of endurance exercise was studied in this model. Male Wistar rats received control chow or a NASH-inducing diet rich in fat, cholesterol, and fructose. Both diet groups were subdivided into a sedentary and an endurance exercise group. Animals receiving the NASH-inducing diet gained more body weight, got glucose intolerant and developed a liver pathology with steatosis, hepatocyte hypertrophy, inflammation and fibrosis typical of NAFLD or NASH. Contrary to expectations, endurance exercise did not improve the NASH activity score and even enhanced hepatic inflammation. However, endurance exercise attenuated the hepatic cholesterol overload and the ensuing severe oxidative stress. In addition, exercise improved glucose tolerance possibly in part by induction of hepatic FGF21 production.

Neutrophil depletion improves diet-induced non-alcoholic fatty liver disease in mice

PURPOSE

Non-alcoholic fatty liver disease is highly associated with morbidity and mortality in population. Although studies have already demonstrated that the immune response plays a pivotal role in the development of non-alcoholic fatty liver disease, the comprehensive regulation is unclear. Therefore, present study was carried out to investigate the non-alcoholic fatty liver disease development under neutrophil depletion.

METHODS

To achieve the aim of the study, C57BL/6 J mice were fed with high fat diet for 6 weeks before treated with neutrophil deplete antibody 1A8 or isotype control (200 μg/ mouse every week) for another 4 weeks.

RESULTS

Treated with 1A8 antibody, obese mice exhibited better whole body metabolic parameters, including reduction of body weight gain and fasting blood glucose levels. Neutrophil depletion also effectively reduced hepatic structural disorders, dysfunction and lipid accumulation. Lipid β-oxidative markers, phosphorylated-AMP-activated protein kinase α and phosphorylated-acetyl-CoA carboxylase levels were increased in 1A8 antibody-treated obese mouse group. The mitochondrial number and function were also reversed after 1A8 antibody treatment, including increased mitochondrial number, reduced lipid oxidative damage and enhanced mitochondrial activity. Furthermore, the expression of inflammatory cytokines, tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein-1 were obviously reduced after neutrophil depletion, accompanied with decreased F4/80 mRNA level and macrophage percentage in liver. The decreased NF-κB signaling activity was also involved in the beneficial effect of neutrophil depletion.

CONCLUSION

Taken together, neutrophil depletion could attenuate metabolic syndromes and hepatic dysfunction.

Oxidative stress and inflammation: liver responses and adaptations to acute and regular exercise

The liver is remarkably important during exercise outcomes due to its contribution to detoxification, synthesis, and release of biomolecules, and energy supply to the exercising muscles. Recently, liver has been also shown to play an important role in redox status and inflammatory modulation during exercise. However, while several studies have described the adaptations of skeletal muscles to acute and chronic exercise, hepatic changes are still scarcely investigated. Indeed, acute intense exercise challenges the liver with increased reactive oxygen species (ROS) and inflammation onset, whereas regular training induces hepatic antioxidant and anti-inflammatory improvements. Acute and regular exercise protocols in combination with antioxidant and anti-inflammatory supplementation have been also tested to verify hepatic adaptations to exercise. Although positive results have been reported in some acute models, several studies have shown an increased exercise-related stress upon liver. A similar trend has been observed during training: while synergistic effects of training and antioxidant/anti-inflammatory supplementations have been occasionally found, others reported a blunting of relevant adaptations to exercise, following the patterns described in skeletal muscles. This review discusses current data regarding liver responses and adaptation to acute and regular exercise protocols alone or combined with antioxidant and anti-inflammatory supplementation. The understanding of the mechanisms behind these modulations is of interest for both exercise-related health and performance outcomes.

Association Between Aerobic Exercise and Rosiglitazone Avoided the NAFLD and Liver Inflammation Exacerbated in PPAR-α Knockout Mice

Nonalcoholic fatty liver disease (NAFLD) is one of the main liver diseases today, and may progress to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Some studies have shown the beneficial effects of aerobic exercise on reversing NAFLD. To verify whether chronic aerobic exercise improves the insulin resistance, liver inflammation, and steatohepatitis caused by a high fat diet (HF) and whether PPARα is involved in these actions. C57BL6 wild type (WT) and PPAR-α knockout (KO) mice were fed with a standard diet (SD) or HF during 12 weeks; the HF mice were trained on a treadmill during the last 8 weeks. Serum glucose and insulin tolerances, serum levels of aspartate aminotransferase, hepatic content of triacylglycerol, cytokines, gene expression, and protein expression were evaluated in all animals. Chronic exposure to HF diet increased triacylglycerol accumulation in the liver, leading to NAFLD, increased aminotransferase in the serum, increased peripheral insulin resistance, and higher adiposity index. Exercise reduced all these parameters in both animal genotypes. The liver lipid accumulation was not associated with inflammation; trained KO mice, however, presented a huge inflammatory response that was probably caused by a decrease in PPAR-γ expression. We conclude that exercise improved the damage caused by a HF independently of PPARα, apparently by a peripheral fatty acid oxidation in the skeletal muscle. We also found that the absence of PPARα together with exercise leads to a decrease in PPAR-γ and a huge inflammatory response. J. Cell. Physiol. 232: 1008-1019, 2017. © 2016 Wiley Periodicals, Inc.

Influence of Acute and Chronic Exercise on Glucose Uptake

Insulin resistance plays a key role in the development of type 2 diabetes. It arises from a combination of genetic predisposition and environmental and lifestyle factors including lack of physical exercise and poor nutrition habits. The increased risk of type 2 diabetes is molecularly based on defects in insulin signaling, insulin secretion, and inflammation. The present review aims to give an overview on the molecular mechanisms underlying the uptake of glucose and related signaling pathways after acute and chronic exercise. Physical exercise, as crucial part in the prevention and treatment of diabetes, has marked acute and chronic effects on glucose disposal and related inflammatory signaling pathways. Exercise can stimulate molecular signaling pathways leading to glucose transport into the cell. Furthermore, physical exercise has the potential to modulate inflammatory processes by affecting specific inflammatory signaling pathways which can interfere with signaling pathways of the glucose uptake. The intensity of physical training appears to be the primary determinant of the degree of metabolic improvement modulating the molecular signaling pathways in a dose-response pattern, whereas training modality seems to have a secondary role.

Effect of Regular Exercise on Inflammation Induced by Drug-resistant Staphylococcus aureus 3089 in ICR mice

Obesity is often associated with irregular dietary habits and reduced physical activity. Regular exercise induces a metabolic response that includes increased expression of various cytokines, signaling proteins and hormones, and reduced adipocyte size. In this study, mice performed a swimming exercise for 10 min/day, 5 days/week for 3 weeks. We then investigated the effect of this exercise regimen on inflammation induced by infection with drug-resistant Staphylococcus aureus strain 3089 (DRSA). In humans, DRSA causes dermatitis and pneumonitis. Similarly, DRSA induced inflammatory pneumonitis in both no-exercise (No-EX) and swim-trained (SW-EX) ICR mice. Regular exercise increased levels of the pro-inflammatory cytokines TNF-α and IL-1β and nitric oxide in both serum and whole lung tissue in SW-EX, as compared to No-EX control mice. Moreover, levels of the antimicrobial peptide cathelicidin were significantly increased in visceral adipose tissue and whole lung tissue in the SW-EX group, and this was accompanied by a reduction in the size of visceral adipocytes. In addition, levels of the inflammation marker peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) were not increased in the lung tissue of SW-EX mice. These findings suggest that in these model mice, regular exercise strengthens immune system responses, potentially preventing or mitigating infectious disease.

Endoplasmic Reticulum Stress Response in Non-alcoholic Steatohepatitis: The Possible Role of Physical Exercise

Sedentary lifestyle coupled with excessive consumption of high caloric food has been related to the epidemic increase of non-alcoholic fatty liver disease, which can progress from simple steatosis to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis and, eventually, may culminate in hepatocellular carcinoma. Although the precise mechanisms underlying the progression of NASH are not completely understood, endoplasmic reticulum (ER) dysfunction seems to play a key role in the process. Hepatic ER stress has been associated to hepatic steatosis, insulin resistance, inflammation, oxidative stress and hepatocyte death, contributing to liver dysfunction. Physical exercise seems to be the most effective preventive and therapeutic non-pharmacological strategy to mitigate several features related to NASH, possibly targeting most of the referred mechanisms associated with the pathophysiology of ER-related NASH. Nevertheless, little is known about the impact of physical exercise on NASH-related ER stress. In this review, we will discuss the ER stress associated to NASH conditions and highlight the possible benefits of physical exercise in the attenuation and/or reversion of NASH-related ER stress.