The status of research into resistance to diet-induced obesity

Variation in body weight, glucose/insulin tolerances, blood lipids and liver enzymes in mice in response to a high-fat-diet from lard

It raises questions about the impact of lard on the health and the differences in individual responses. Therefore, we developed a model of mice fed with high fat (HF) from lard in 130 days. The weight of the mice was measured every two days. Glucose tolerance test and insulin tolerance tests were performed at 70 days and 130 days of experiment. At the end of the study, the fat tissue was collected to check the weight, and a blood sample was collected to check the blood lipids and liver enzymes. Surprisingly, mice responded variously to the HF by being classified into two groups, one group had significantly high gained weight (HG_HF) versus the mice fed a standard diet (STD) (p < 0.001), and another group (LG_HF) has not difference in body weight compared to the STD groups. This phenomenon in body weight is directly reflected by the white fat accumulation, but not by brown fat. Eating HF from lard for a long time can disrupt glucose tolerance and cause dyslipidemia in mice, even in the LG_HF group, but can not disrupt insulin tolerance and cause liver enzyme disorders. In summary, our findings are a wake-up call for many cases where eating HF from lard does not gain weight and not increase the white fat storage, but still has the potential to cause adverse health effects. Further studies are encouraged to understand the molecular mechanisms that causes the body to regulate its weight and responses when eating HF from lard, especially in the LG_HF group.

How hypoxia affects microbiota metabolism in mice

Objective

To investigate the relationship between gut microbiota and the fecal metabolites of hypoxic environments in mice.

Methods

High-fat diet-induced obese mice (n = 20) and normal diet-fed mice (n = 20) were randomly divided into four groups: high altitude obese group (HOB), high altitude normal weight group (HN), low altitude obese group LOB (LOB), and low altitude normal weight group (LN). Fecal samples from each group were 16S rRNA gene sequenced, and five samples from each of the four groups above were selected for non-targeted fecal metabolomics analysis using liquid chromatography-mass spectrometry. The relationship between gut microbiota and fecal metabolites was analyzed using SIMCA 14.1, MetaboAnalyst 5.0 and R 4.1.11.

Results

(A) Body weight was significantly lower in the hypoxic obesity group than in the normoxic obesity group. (B) Differences in α-diversity and β-diversity were found in the fecal gut microbiota of mice of different body weights and altitude, and the diversity of gut microbiota was higher in the normal group than in the obese group; the results of the comparison between the two groups showed that Faecalibaculum, Romboutsia, Lactobacillus, and A2 were associated with obesity; Romboutsia was associated with hypoxia. (C) The metabolic profiles of fecal metabolites differed between groups: gut microbiota were associated with nucleotide and amino acid metabolism in the same body groups, while gut microbiota were associated with lipid and amino acid metabolism in the same oxygen concentration groups.

Conclusion

(a) Gut microbiota diversity was reduced in obese groups. Romboutsia was the dominant microbiota in the hypoxia group. (b) Gut microbiota were associated with nucleotide and amino acid metabolism in the same body weight groups, while they were associated with lipid and amino acid metabolism in the same altitude groups.

Obesity, but not high-fat diet, is associated with bone loss that is reversed via CD4+CD25+Foxp3+ Tregs-mediated gut microbiome of non-obese mice

Osteoporosis is characterized by decreased bone mass, microarchitectural deterioration, and increased bone fragility. High-fat diet (HFD)-induced obesity also results in bone loss, which is associated with an imbalanced gut microbiome. However, whether HFD-induced obesity or HFD itself promotes osteoclastogenesis and consequent bone loss remains unclear. In this study, we developed HFD-induced obesity (HIO) and non-obesity (NO) mouse models to evaluate the effect of HFD on bone loss. NO mice were defined as body weight within 5% of higher or lower than that of chow diet fed mice after 10 weeks HFD feeding. NO was protected from HIO-induced bone loss by the RANKL /OPG system, with associated increases in the tibia tenacity, cortical bone mean density, bone volume of cancellous bone, and trabecular number. This led to increased bone strength and improved bone microstructure via the microbiome-short-chain fatty acids (SCFAs) regulation. Additionally, endogenous gut-SCFAs produced by the NO mice activated free fatty acid receptor 2 and inhibited histone deacetylases, resulting in the promotion of Treg cell proliferation in the HFD-fed NO mice; thereby, inhibiting osteoclastogenesis, which can be transplanted by fecal microbiome. Furthermore, T cells from NO mice retain differentiation of osteoclast precursors of RAW 264.7 macrophages ex vivo. Our data reveal that HFD is not a deleterious diet; however, the induction of obesity serves as a key trigger of bone loss that can be blocked by a NO mouse-specific gut microbiome.

Modified Signaling of Membrane Formyl Peptide Receptors in NADPH-Oxidase Regulation in Obesity-Resistant Mice

The signaling of membrane receptors is modified in obesity characterized by low-grade inflammation. The obesity-resistant state of organisms is poorly understood. We analyzed the generation of reactive oxygen species (ROS) initiated though membrane formyl peptide receptors (Fpr1, Fpr2) in bone-marrow granulocytes of obesity-resistant mice (ORM). A chemiluminescence assay was used to assess NADPH-oxidase-related intensity of ROS generation. ORM were chosen from animals that received high-fat diets and had metric body parameters as controls (standard diet). High spontaneous ROS production was observed in ORM cells. The EC50 for responses to bacterial or mitochondrial peptide N-formyl-MLF was higher in ORM with and without inflammation vs. the same control groups, indicating an insignificant role of high-affinity Fpr1. Increased responses to synthetic peptide WKYMVM (Fpr2 agonist) were observed in controls with acute inflammation, but they were similar in other groups. Fpr2 was possibly partially inactivated in ORM owing to the inflammatory state. Weakened Fpr1 and Fpr2 signaling via MAPKs was revealed in ORM using specific inhibitors for p38, ERK1/2, and JNK. P38 signaling via Fpr2 was lower in ORM with inflammation. Thus, a high-fat diet modified FPRs' role and suppressed MAPK signaling in NADPH-oxidase regulation in ORM. This result can be useful to understand the immunological features of obesity resistance.

Diet-induced rodent models of obesity-related metabolic disorders-A guide to a translational perspective

Diet is a critical element determining human health and diseases, and unbalanced food habits are major risk factors for the development of obesity and related metabolic disorders. Despite technological and pharmacological advances, as well as intensification of awareness campaigns, the prevalence of metabolic disorders worldwide is still increasing. Thus, novel therapeutic approaches with increased efficacy are urgently required, which often depends on cellular and molecular investigations using robust animal models. In the absence of perfect rodent models, those induced by excessive consumption of fat and sugars better replicate the key aspects that are the root causes of human metabolic diseases. However, the results obtained using these models cannot be directly compared, particularly because of the use of different dietary protocols, and animal species and strains, among other confounding factors. This review article revisits diet-induced models of obesity and related metabolic disorders, namely, metabolic syndrome, prediabetes, diabetes and nonalcoholic fatty liver disease. A critical analysis focused on the main pathophysiological features of rodent models, as opposed to the criteria defined for humans, is provided as a practical guide with a translational perspective for the establishment of animal models of obesity-related metabolic diseases.

An Overview of Murine High Fat Diet as a Model for Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a worldwide epidemic, which by all predictions will only increase. To help in combating the devastating array of phenotypes associated with T2DM a highly reproducible and human disease-similar mouse model is required for researchers. The current options are genetic manipulations to cause T2DM symptoms or diet induced obesity and T2DM symptoms. These methods to model human T2DM have their benefits and their detractions. As far as modeling the majority of T2DM cases, HFD establishes the proper etiological, pathological, and treatment options. A limitation of HFD is that it requires months of feeding to achieve the full spectrum of T2DM symptoms and no standard protocol has been established. This paper will attempt to rectify the last limitation and argue for a standard group of HFD protocols and standard analysis procedures.

Impaired GLP-1 signaling contributes to reduced sensitivity to duodenal nutrients in obesity-prone rats during high-fat feeding

OBJECTIVE

Increased consumption of a high-fat (HF) diet is a salient contributor to obesity; however, how diminished satiation signaling contributes to overconsumption and obesity development remains poorly understood.

METHODS

Using obese-prone (OP) and obese-resistant (OR) rats, we tested feeding responses to intragastric liquid meal replacement, prior and after HF feeding. Next, chow- and HF-fed OP and OR rats were tested for sensitivity to intraduodenal glucose, intralipid, and meal replacement loads. To examine the role of glucagon-like peptide-1 (GLP-1) and vagal signaling, animals were treated with exendin-9, GLP-1 receptor antagonist, prior to meal replacement infusion, and Fos-like immunoreactivity (Fos-Li) in the dorsal hindbrain was examined after infusion.

RESULTS

OP and OR rats reduced chow intake equally following gastric liquid meal; however, after 2 weeks of HF feeding, intragastric meal replacement reduced food intake less in OP than OR. Similarly, HF feeding, but not chow, diminished the suppressive effects of intraduodenal meal replacement, glucose, and intralipid in OP compared to OR. This effect was associated with lower Fos-Li expression in the dorsal hindbrain of OP rats. Finally, exendin-9 failed to attenuate reduction of food intake by meal replacement in OP rats during HF feeding.

CONCLUSIONS

Susceptibility to obesity coupled with HF feeding results in rapid impairments in nutrient-induced satiation through blunted responses in endogenous GLP-1 and hindbrain vagal afferent signaling.