Metabolic Damage Presents Differently in Young and Early-Aged C57BL/6 Mice Fed a High-Fat Diet

Obesity and lifespan, a complex tango

Obesity and aging share comorbidities, phenotypes, and deleterious effects on health that are associated with chronic diseases. However, distinct features set them apart, with underlying biology that should be explored and exploited, especially given the demographic shifts and the obesity epidemic that the world is facing.

Ameliorative effects of zinc supplementation on cognitive function and hippocampal leptin signaling pathway in obese male and female rats

Obesity has been associated with cognitive impairments, increasing the probability of developing dementia. Recently, zinc (Zn) supplementation has attracted an increasing attention as a therapeutic agent for cognitive disorders. Here, we investigated the potential effects of low and high doses of Zn supplementation on cognitive biomarkers and leptin signaling pathway in the hippocampus of high fat diet (HFD)-fed rats. We also explored the impact of sex difference on the response to treatment. Our results revealed a significant increase in body weight, glucose, triglycerides (TG), total cholesterol (TC), total lipids and leptin levels in obese rats as compared to controls. HFD feeding also reduced brain-derived neurotrophic factor (BDNF) levels and increased acetylcholinesterase (AChE) activity in the hippocampus of both sexes. The low and high doses of Zn supplementation improved glucose, TG, leptin, BDNF levels and AChE activity in both male and female obese rats compared to untreated ones. Additionally, downregulated expression of leptin receptor (LepR) gene and increased levels of activated signal transducer and activator of transcription 3 (p-STAT3) that observed in hippocampal tissues of obese rats were successfully normalized by both doses of Zn. In this study, the male rats were more vulnerable to HFD-induced weight gain, most of the metabolic alterations and cognition deficits than females, whereas the female obese rats were more responsive to Zn treatment. In conclusion, we suggest that Zn treatment may be effective in ameliorating obesity-related metabolic dysfunction, central leptin resistance and cognitive deficits. In addition, our findings provide evidence that males and females might differ in their response to Zn treatment.

The Influence of Ambient Temperature on Adipose Tissue Homeostasis, Metabolic Diseases and Cancers

Adipose tissue is a recognized energy storage organ during excessive energy intake and an endocrine and thermoregulator, which interacts with other tissues to regulate systemic metabolism. Adipose tissue dysfunction is observed in most obese mouse models and humans. However, most studies using mouse models were conducted at room temperature (RT), where mice were chronically exposed to mild cold. In this condition, energy use is prioritized for thermogenesis to maintain body temperature in mice. It also leads to the activation of the sympathetic nervous system, followed by the activation of β-adrenergic signaling. As humans live primarily in their thermoneutral (TN) zone, RT housing for mice limits the interpretation of disease studies from mouse models to humans. Therefore, housing mice in their TN zone (~28–30 °C) can be considered to mimic humans physiologically. However, factors such as temperature ranges and TN pre-acclimatization periods should be examined to obtain reliable results. In this review, we discuss how adipose tissue responds to housing temperature and the outcomes of the TN zone in metabolic disease studies. This review highlights the critical role of TN housing in mouse models for studying adipose tissue function and human metabolic diseases.

Obesity-induced oxidative stress and mitochondrial dysfunction negatively affect sperm quality

Obesity is a systemic metabolic disease that can induce male infertility or subfertility through oxidative stress. The aim of this study was to determine how obesity impairs sperm mitochondrial structural integrity and function, and reduces sperm quality in both overweight/obese men and mice on a high-fat diet (HFD). Mice fed the HFD demonstrated higher body weight and increased abdominal fat content than those fed the control diet. Such effects accompanied the decline in antioxidant enzymes, such as glutathione peroxidase (GPX) and catalase and superoxide dismutase (SOD) in testicular and epidydimal tissues. Moreover, malondialdehyde (MDA) content significantly increased in sera. Mature sperm in HFD mice demonstrated higher oxidative stress, including increased mitochondrial reactive oxygen species (ROS) levels and decreased protein expression of GPX1, which may impair mitochondrial structural integrity and reduce mitochondrial membrane potential (MMP) and ATP production. Moreover, cyclic AMPK phosphorylation status increased, whereas sperm motility declined in the HFD mice. Clinical studies demonstrated that being overweight/obese reduced SOD enzyme activity in the seminal plasma and increased ROS in sperm, accompanied by lower MMP and low-quality sperm. Furthermore, ATP content in the sperm was negatively correlated with increases in the BMI of all clinical subjects. In conclusion, our results suggest that excessive fat intake had similar disruptive effects on sperm mitochondrial structure and function, as well as oxidative stress levels in humans and mice, which in turn induced lower sperm motility. This agreement strengthens the notion that fat-induced increases in ROS and impaired mitochondrial function contribute to male subfertility.

Effects of the Water Extract of Fermented Rice Bran on Liver Damage and Intestinal Injury in Aged Rats with High-Fat Diet Feeding

The purpose of this study was to investigate the protective effects of the water extract of fermented rice bran (FRB) on liver damage and intestinal injury in old rats fed a high-fat (HF) diet. Rice bran (RB) was fermented with Aspergillus kawachii, and FRB was produced based on a previous study. Male Sprague Dawley rats at 36 weeks of age were allowed free access to a standard rodent diet and water for 8 weeks of acclimation then randomly divided into four groups (six rats/group), including a normal control (NC) group (normal diet), HF group (HF diet; 60% of total calories from fat), HF + 1% FRB group (HF diet + 1% FRB w/w), and HF + 5% FRB group (HF diet + 5% FRB w/w). It was found that the antioxidant ability of FRB was significantly increased when compared to RB. After 8 weeks of feeding, the HF group exhibited liver damage including an increased non-alcoholic fatty liver disease score (hepatic steatosis and inflammation) and higher interleukin (IL)-1β levels, while these were attenuated in the FRB-treated groups. Elevated plasma leptin levels were also found in the HF group, but the level was down-regulated by FRB treatment. An altered gut microbiotic composition was observed in the HF group, while beneficial bacteria including of the Lactobacillaceae and Lachnospiraceae had increased after FRB supplementation. In conclusion, it was found that FRB had higher anti-oxidative ability and showed the potential for preventing liver damage induced by a HF diet, which might be achieved through regulating imbalanced adipokines and maintaining a healthier microbiotic composition.

Distinct Effects of a High Fat Diet on Bone in Skeletally Mature and Developing Male C57BL/6J Mice

Increased risks of skeletal fractures are common in patients with impaired glucose handling and type 2 diabetes mellitus (T2DM). The pathogenesis of skeletal fragility in these patients remains ill-defined as patients present with normal to high bone mineral density. With increasing cases of glucose intolerance and T2DM it is imperative that we develop an accurate rodent model for further investigation. We hypothesized that a high fat diet (60%) administered to developing male C57BL/6J mice that had not reached skeletal maturity would over represent bone microarchitectural implications, and that skeletally mature mice would better represent adult-onset glucose intolerance and the pre-diabetes phenotype. Two groups of developing (8 week) and mature (12 week) male C57BL/6J mice were placed onto either a normal chow (NC) or high fat diet (HFD) for 10 weeks. Oral glucose tolerance tests were performed throughout the study period. Long bones were excised and analysed for ex vivo biomechanical testing, micro-computed tomography, 2D histomorphometry and gene/protein expression analyses. The HFD increased fasting blood glucose and significantly reduced glucose tolerance in both age groups by week 7 of the diets. The HFD reduced biomechanical strength, both cortical and trabecular indices in the developing mice, but only affected cortical outcomes in the mature mice. Similar results were reflected in the 2D histomorphometry. Tibial gene expression revealed decreased bone formation in the HFD mice of both age groups, i.e., decreased osteocalcin expression and increased sclerostin RNA expression. In the mature mice only, while the HFD led to a non-significant reduction in runt-related transcription factor 2 (Runx2) RNA expression, this decrease became significant at the protein level in the femora. Our mature HFD mouse model more accurately represents late-onset impaired glucose tolerance/pre-T2DM cases in humans and can be used to uncover potential insights into reduced bone formation as a mechanism of skeletal fragility in these patients.

Chronic treatment with acetaminophen protects against liver aging by targeting inflammation and oxidative stress

The liver exhibits a variety of functions that are well-preserved during aging. However, the cellular hallmarks of aging increase the risk of hepatic alterations and development of chronic liver diseases. Acetaminophen (APAP) is a first choice for relieving mild-to-moderate pain. Most of the knowledge about APAP-mediated hepatotoxicity arises from acute overdose studies due to massive oxidative stress and inflammation, but little is known about its effect in age-related liver inflammation after chronic exposure. Our results show that chronic treatment of wild-type mice on the B6D2JRcc/Hsd genetic background with APAP at an infratherapeutic dose reduces liver alterations during aging without affecting body weight. This intervention attenuates age-induced mild oxidative stress by increasing HO-1, MnSOD and NQO1 protein levels and reducing ERK1/2 and p38 MAPK phosphorylation. More importantly, APAP treatment counteracts the increase in Cd8⁺ and the reduction in Cd4⁺ T lymphocytes observed in the liver with age. This response was also found in peripheral blood mononuclear cells. In conclusion, chronic infratherapeutic APAP treatment protects mice from age-related liver alterations by attenuating oxidative stress and inflammation.

Modeling Diet-Induced Metabolic Syndrome in Rodents

Standardized animal models represent one of the most valuable tools available to understand the mechanism underlying the metabolic syndrome (MetS) and to seek for new therapeutic strategies. However, there is considerable variability in the studies conducted with this essential purpose. This review presents an updated discussion of the most recent studies using diverse experimental conditions to induce MetS in rodents with unbalanced diets, discusses the key findings in metabolic outcomes, and critically evaluates what we have been learned from them and how to advance in the field. The study includes scientific reports sourced from the Web of Science and PubMed databases, published between January 2013 and June 2020, which used hypercaloric diets to induce metabolic disorders, and address the impact of the diet on metabolic parameters. The collected data are used as support to discuss variables such as sex, species, and age of the animals, the most favorable type of diet, and the ideal diet length to generate metabolic changes. The experimental characteristics propose herein improve the performance of a preclinical model that resembles the human MetS and will guide researchers to investigate new therapeutic alternatives with confidence and higher translational validity.

Advances in the Involvement of Gut Microbiota in Pathophysiology of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis and progresses to non-steatohepatitis (NASH) when the liver displays overt inflammatory damage. Increasing evidence has implicated critical roles for dysbiosis and microbiota-host interactions in NAFLD pathophysiology. In particular, microbiota alter intestine absorption of nutrients and intestine permeability, whose dysregulation enhances the delivery of nutrients, endotoxin, and microbiota metabolites to the liver and exacerbates hepatic fat deposition and inflammation. While how altered composition of gut microbiota attributes to NAFLD remains to be elucidated, microbiota metabolites are shown to be involved in the regulation of hepatocyte fat metabolism and liver inflammatory responses. In addition, intestinal microbes and circadian coordinately adjust metabolic regulation in different stages of life. During aging, altered composition of gut microbiota, along with circadian clock dysregulation, appears to contribute to increased incidence and/or severity of NAFLD.

The Vascular Consequences of Metabolic Syndrome: Rodent Models, Endothelial Dysfunction, and Current Therapies

Metabolic syndrome is characterized by visceral obesity, dyslipidemia, hyperglycemia and hypertension, and affects over one billion people. Independently, the components of metabolic syndrome each have the potential to affect the endothelium to cause vascular dysfunction and disrupt vascular homeostasis. Rodent models of metabolic syndrome have significantly advanced our understanding of this multifactorial condition. In this mini-review we compare the currently available rodent models of metabolic syndrome and consider their limitations. We also discuss the numerous mechanisms by which metabolic abnormalities cause endothelial dysfunction and highlight some common pathophysiologies including reduced nitric oxide production, increased reactive oxygen species and increased production of vasoconstrictors. Additionally, we explore some of the current therapeutics for the comorbidities of metabolic syndrome and consider how these benefit the vasculature.

Regular exposure to non-burning ultraviolet radiation reduces signs of non-alcoholic fatty liver disease in mature adult mice fed a high fat diet: results of a pilot study

Objective

Obesity often emerges in middle age, increasing risk for metabolic disorders. Our previous preclinical experiments identified that chronic exposure to non-burning ultraviolet radiation, like that achieved through sun exposure, prevented weight gain and signs of metabolic dysfunction in young adult mice fed a high fat diet. Our objective was to perform a pilot study to estimate the effect size of ongoing exposure to sub-erythemal (non-burning, low dose) UVB (1 kJ/m²) radiation on measures of adiposity, food intake and physical activity in ‘mature’ adult C57Bl/6J male mice fed a high fat diet for 12 weeks.

Results

The severity of liver steatosis, fibrosis and inflammation were reduced in older adult mice exposed twice a week to ultraviolet radiation (from 29 weeks of age), compared to mock-irradiated mice, with some evidence for reduced hepatic mRNAs for tnf and tgfß1 (not fatp2 nor fasN). Power analyses suggested that up to 24 mice per treatment would be required in future experiments to detect a significant effect on some markers of adiposity such as body weight gain. Our studies suggest frequent exposure to low levels of sunlight may reduce the severity of hepatic steatosis induced in older adults living in environments of high caloric intake.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4112-8) contains supplementary material, which is available to authorized users.

Comparison between red wine and isolated trans-resveratrol on the prevention and regression of atherosclerosis in LDLr (-/-) mice

Moderate consumption of red wine has been widely associated with reduced cardiovascular risk, mainly due to its composition in phenolic compounds with antioxidant activity, such as resveratrol. The objective of this study was to compare the effect of red wine vs. trans-resveratrol consumption on the prevention and regression of atherosclerosis in LDLr ^(-/-) mice. This study consisted of two protocols: "Prevention" (PREV) and "Regression" (REGR). Both protocols included four groups: red wine (WINE), dealcoholized red wine (EXT), trans-resveratrol (RESV), and control (CONT). In PREV protocol, animals received a regular diet for 8 weeks and then switched to an atherogenic diet for the following 8 weeks, while the opposite was performed in REGR. Animals that received atherogenic diet after an initial period of standard diet (PREV) gained more body weight (39.25±2.30%) than the opposite (29.27±1.91%, P=.0013), suggesting an interaction between age and weight gain. Trans-resveratrol showed the highest hypocholesterolemic effect during PREV, reducing total cholesterol, LDL-C, VLDL-C and HDL-C. Supplementation with trans-resveratrol and dealcoholized red wine changed the fatty acids profile in the liver in both protocols, leading to an increase of MDA concentrations and SOD activity in the PREV protocol. In conclusion, supplementation with trans-resveratrol, red wine and the same wine without alcohol altered biomarkers of oxidative stress and lipidemia but had no effect on the prevention or regression of fatty streaks. These data suggest that cardiovascular protection associated with the "French Paradox" may be a result of synergistic effects between wine and the Mediterranean diet.

A Population-Based Cross-Sectional Study of the Association between Liver Enzymes and Lipid Levels

BACKGROUND

To examine the association between low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels and liver enzyme functions.

METHODS

The National Health and Nutrition Examination Survey (NHANES) data from 1999 to 2012 was used to examine the association between liver enzymes and lipid levels amongst adults in the United States.

RESULTS

Sixteen percent adults had ALT > 40 U/L, 11% had AST > 40 U/L, and 96% had ALP > 120 U/L. Age, gender, and race/ethnicity showed significant association with LDL, HDL, and triglycerides levels. LDL greater than borderline high was associated with little over two times higher odds of elevated ALT (OR: 2.33, 95% CI: 2.17, 2.53, p ≤ 0.001) and AST (OR: 2.79, 95% CI: 2.55, 3.06, p ≤ 0.001). High HDL was associated with 50% higher odds for elevated ALT (OR: 1.51, 95% CI: 1.39, 1.64, p ≤ 0.001) and over two-and-half fold elevated AST (OR: 2.77, 95% CI: 2.47, 3.11, p ≤ 0.001). LDL-C, HDL-C, and triglycerides were found to be good predictor of elevated ALT, AST, and ALP levels. Similarly, old age and female gender were significant predictor of elevated ALT and AST (p ≤ 0.001).

CONCLUSIONS

Underlying hepatic pathophysiology from dyslipidemia deserves further exploration due to its potential effects on hepatic drug metabolism/detoxification.