Long-term hepatic damage in high-fructose-fed C57BL/6 mice: hepatic fibrogenesis, endoplasmic reticulum stress markers, and fibrosis.

The rising fructose intake in sugar-sweetened beverages and ultra-processed foods relates to the high incidence of nonalcoholic fatty liver disease. This study aimed to examine the effects of long-term high-fructose diet intake (for 16 or 20 weeks) on progressive hepatic damage, focusing on the endoplasmic reticulum stress markers and fibrogenesis as possible triggers of liver fibrosis. Forty 3-month-old male C57BL/6J mice were randomly divided into four nutritional groups: C16 (control diet for 16 weeks), C20 (control diet for 20 weeks), HFRU16 (high-fructose diet for 16 weeks), and HFRU20 (high-fructose diet for 20 weeks). Both HFRU groups showed oral glucose intolerance and insulin resistance, but only the HFRU20 group exhibited increased inflammation. The increased lipogenic and endoplasmic reticulum stress markers triggered hepatic fibrogenesis. Hence, time-dependent perivascular fibrosis with positive immunostaining for alpha-smooth muscle actin and reelin in HFRU mice was observed, ensuring fibrosis development in this mouse model. Our study showed time-dependent and progressive damage on hepatic cytoarchitecture, with maximization of hepatic steatosis without overweight in HFRU20 mice. ER stress and liver inflammation could mediate hepatic stellate cell activation and fibrogenesis, emerging as targets to prevent NAFLD progression and fibrosis onset in this dietary model.

Endoplasmic reticulum stress as the basis of obesity and metabolic diseases: focus on adipose tissue, liver, and pancreas.

Obesity challenges lipid and carbohydrate metabolism. The resulting glucolipotoxicity  causes endoplasmic reticulum (ER) dysfunction, provoking the accumulation of immature proteins, which triggers the unfolded protein reaction (UPR) as an attempt to reestablish ER homeostasis. When the three branches of UPR fail to correct the unfolded/misfolded proteins, ER stress happens. Excessive dietary saturated fatty acids or fructose exhibit the same impact on the ER stress, induced by excessive ectopic fat accumulation or rising blood glucose levels, and meta-inflammation. These metabolic abnormalities can alleviate through dietary interventions. Many pathways are disrupted in adipose tissue, liver, and pancreas during ER stress, compromising browning and thermogenesis, favoring hepatic lipogenesis, and impairing glucose-stimulated insulin secretion within pancreatic beta cells. As a result, ER stress takes part in obesity, hepatic steatosis, and diabetes pathogenesis, arising as a potential target to treat or even prevent metabolic diseases. The scientific community seeks strategies to alleviate ER stress by avoiding inflammation, apoptosis, lipogenesis suppression, and insulin sensitivity augmentation through pharmacological and non-pharmacological interventions. This comprehensive review aimed to describe the contribution of excessive dietary fat or sugar to ER stress and the impact of this adverse cellular environment on adipose tissue, liver, and pancreas function.

Revisiting pancreatic islet isolation in murine models: A practical and effective technical protocol.

The endocrine pancreas is composed of clusters of cell groups called pancreatic islets. These cells are responsible for the synthesis and secretion of hormones crucial for glycemic homeostasis, such as insulin and glucagon. Therefore, these cells were the targets of many studies. One method to study and/or understand endocrine pancreatic physiology is the isolation of these islets and stimulation of hormone production using different concentrations of glucose, agonists, and/or antagonists of specific secretagogues and mimicking the stimulation of hormonal synthesis and secretion. Many researchers studied pancreatic physiology in murine models due to their ease of maintenance and rapid development. However, the isolation of pancreatic islets involves meticulous processes that may vary between rodent species. The present study describes a simple and effective technical protocol for isolating intact islets from mice and rats for use as a practical guide for researchers. The method involves digestion of the acinar parenchyma by intraductal collagenase. Isolated islets are suitable for in vitro endocrine secretion analyses, microscopy techniques, and biochemical analyses.

Anti-steatotic effects of PPAR-alpha and gamma involve gut-liver axis modulation in high-fat diet-fed mice.

AIM: To evaluate the effects of PPARα and PPARγ activation (alone or in combination) on the gut-liver axis, emphasizing the integrity of the intestinal barrier and hepatic steatosis in mice fed a high saturated fat diet. METHODS: Male C57BL/6J were fed a control diet (C) or a high-fat diet (HF) for ten weeks. Then, a four-week treatment started: HF-α (WY14643), HF-γ (low-dose pioglitazone), and HF-αγ (combination). RESULTS: The HF caused overweight, insulin resistance, impaired gut-liver axis, and marked hepatic steatosis. Treatments reduced body mass, improved glucose homeostasis, and restored the gut microbiota diversity and intestinal barrier gene expression. Treatments also lowered the plasma lipopolysaccharide concentrations and favored beta-oxidation genes, reducing macrophage infiltration and steatosis in the liver. CONCLUSION: Treatment with PPAR agonists modulated the gut microbiota and rescued the integrity of the intestinal barrier, alleviating hepatic steatosis. These results show that these agonists can contribute to metabolic-associated fatty liver disease treatment.

Chronic Excessive Fructose Intake Maximizes Brown Adipocyte Whitening but Causes Similar White Adipocyte Hypertrophy Than a High-Fat Diet in C57BL/6 Mice.

Objective: This study aimed to evaluate the differential role of a high-fat diet (HF) or high-fructose diet (HFRU) on white adipose tissue and brown adipose tissue remodeling in C57BL/6 mice.Methods: The animals were randomly assigned to receive HF (50% of energy as lipids), HFRU (50% of energy as fructose), or a control diet (C, 10% of energy as lipids) for 12 weeks. Results: The HF group became overweight from the 7th week onwards, but both HF and HFRU groups showed hyperinsulinemia, oral glucose intolerance, and adverse adipose tissue remodeling. HF and HFRU groups showed interscapular brown adipose tissue whitening, tough the reduced QA [nuclei] suggested maximized brown adipocyte dysfunction due to the HFRU diet. In contrast, HF and HFRU diets exerted similar effects upon subcutaneous white adipocytes, with a similar average cross-sectional area. Immunohistochemistry confirmed the whitening enhancement with reduced UCP1 immunodensity in the HFRU group. Conclusion: In conclusion, HF and HFRU diets had indistinguishable effects upon white adipocyte morphology, but the HFRU diet provoked a more pronounced whitening than the HF diet after a 12-week protocol. These results point to the silent and harmful impact that excessive fructose has upon the metabolism of lean mice.

Peroxisome proliferator-activated receptors as targets to treat metabolic diseases: Focus on the adipose tissue, liver, and pancreas.

The world is experiencing reflections of the intersection of two pandemics: Obesity and coronavirus disease 2019. The prevalence of obesity has tripled since 1975 worldwide, representing substantial public health costs due to its comorbidities. The adipose tissue is the initial site of obesity impairments. During excessive energy intake, it undergoes hyperplasia and hypertrophy until overt inflammation and insulin resistance turn adipocytes into dysfunctional cells that send lipotoxic signals to other organs. The pancreas is one of the organs most affected by obesity. Once lipotoxicity becomes chronic, there is an increase in insulin secretion by pancreatic beta cells, a surrogate for type 2 diabetes mellitus (T2DM). These alterations threaten the survival of the pancreatic islets, which tend to become dysfunctional, reaching exhaustion in the long term. As for the liver, lipotoxicity favors lipogenesis and impairs beta-oxidation, resulting in hepatic steatosis. This silent disease affects around 30% of the worldwide population and can evolve into end-stage liver disease. Although therapy for hepatic steatosis remains to be defined, peroxisome proliferator-activated receptors (PPARs) activation copes with T2DM management. Peroxisome PPARs are transcription factors found at the intersection of several metabolic pathways, leading to insulin resistance relief, improved thermogenesis, and expressive hepatic steatosis mitigation by increasing mitochondrial beta-oxidation. This review aimed to update the potential of PPAR agonists as targets to treat metabolic diseases, focusing on adipose tissue plasticity and hepatic and pancreatic remodeling.

Exercise prevents obesity by reducing gut-derived inflammatory signals to brown adipocytes in mice.

Gut dysbiosis impairs nonshivering thermogenesis (NST) in obesity. The antiobesogenic effects of exercise training might involve the modulation of gut microbiota and its inflammatory signals to the brown adipose tissue (BAT). This study evaluated whether high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) prevent overweight through reduced gut-derived inflammatory signals to BAT in high-fat-fed mice. Sixty male C57BL/6 mice (3 months old) comprised six experimental groups: control (C) diet group, C diet + HIIT (C-HIIT) group, C diet + MICT (C-MICT) group, high-fat (HF) diet group, HF diet + HIIT (HF-HIIT) group, and HF diet + MICT (HF-MICT) group. The protocols lasted for 10 weeks. HIIT and MICT restored body mass, mitigated glucose intolerance, and prevented hyperinsulinemia in HF-trained groups. A chronic HF diet caused dysbiosis, but HIIT and MICT prevented gut dysbiosis and preserved tight junction (TJ) gene expression. HF-HIIT and HF-MICT groups exhibited a similar pattern of goblet cell distribution, agreeing with the decreased plasma lipopolysaccharide concentrations and interscapular BAT (iBAT) Lbp-Cd14-Tlr4 expression. The lowered Nlrp3 and Il1ß in the HF-HITT and HF-MICT groups complied with iBAT thermogenic capacity maintenance. This study shows reliable evidence that HIIT and MICT prevented overweight by restoring the diversity of the gut microbiota phyla and TJ gene expression, thereby reducing inflammatory signals to brown adipocytes with preserved thermogenic capacity. Both exercise modalities prevented overweight, but HIIT rescued Zo-1 and Jam-a gene expression, exerting more potent anti-inflammatory effects than MICT (reduced LPS concentrations), providing a sustained increase in thermogenesis with 78% less distance traveled.

Peroxisome proliferator-activated receptors-alpha and gamma synergism modulate the gut-adipose tissue axis and mitigate obesity.

AIM: To evaluate the effects of single PPARα or PPARγ activation, and their synergism (combined PPARα/γ activation) upon the gut-adipose tissue axis, focusing on the endotoxemia and upstream interscapular brown adipose tissue (iBAT) function in high-saturated fat-fed mice. METHODS: Male C57BL/6 mice received a control diet (C, 10% lipids) or a high-fat diet (HF, 50% lipids) for 12 weeks. Then, the HF group was divided to receive the treatments for four weeks: HFγ (pioglitazone, 10 mg/kg), HFα (WY-14643, 3.5 mg/kg), and HFα/γ (tesaglitazar, 4 mg/kg). RESULTS: The HF group exhibited overweight, oral glucose intolerance, gut dysbiosis, altered gut permeability, and endotoxemia, culminating in iBAT whitening. The downregulation of LPS-Tlr4 signaling underpinned reduced inflammation and improved lipid metabolism in iBAT in the HFα/γ group, the unique to show normalized body mass and increased energy expenditure. CONCLUSION: PPARα/γ synergism treated obesity by ameliorating the gut-adipose tissue axis, where restored gut microbiota and permeability controlled endotoxemia and rescued iBAT whitening through favored thermogenesis.

A PPAR-alpha agonist and DPP-4 inhibitor mitigate adipocyte dysfunction in obese mice.

Obesity causes white and brown adipocyte dysfunction, reducing browning and stimulating whitening. Drugs that tackle adipocyte dysfunction through thermogenesis stimulation could be used to treat obesity. This study sought to address whether a combination of the PPAR-alpha agonist (WY14643) and DPP4i (linagliptin) potentiates browning and mitigates adipose tissue dysfunction, emphasizing the pathways related to browning induction and the underlying thermogenesis in high-fat-fed mice. Adult male C57BL/6 mice were randomly assigned to receive a control diet (C, 10% lipids) or a high-fat diet (HF, 50% lipids) for 12 weeks. Experiment 1 aimed to evaluate whether 5 weeks of combined therapy was able to potentiate browning using a five-group design: C, HF, HFW (monotherapy with WY14643, 2.5 mg/kg body mass), HFL (monotherapy with linagliptin, 15 mg/kg body mass), and HFC (a combination of both drugs). Experiment 2 further addressed the pathways involved in browning maximization using a four-group study design: C, CC (C diet plus the drug combination), HF, and HFC (HF diet plus the drug combination). The HF group showed overweight, oral glucose intolerance, sWAT adipocyte hypertrophy, and reduced numerical density of nuclei per area of BAT confirming whitening. Only the combined treatment normalized these parameters in addition to body temperature increase, browning induction, and whitening rescue. The high expression of thermogenic marker genes parallel to reduced expression of inflammatory and endoplasmic reticulum stress genes mediated the beneficial findings. Hence, the PPAR-alpha agonist and DPP-4i combination is a promising target for obesity control by inducing functional brown adipocytes, browning of sWAT, and enhanced adaptive thermogenesis.