Impaired glucose transport in inguinal adipocytes after short-term high-sucrose feeding in mice

Apple polyphenol extract ameliorates sugary-diet-induced depression-like behaviors in male C57BL/6 mice by inhibiting the inflammation of the gut-brain axis

To explore whether apple polyphenol extract (APE) ameliorates sugary-diet-induced depression-like behaviors, thirty male C57BL/6 mice (3-4 weeks old) were assigned to three groups randomly to receive different treatments for 8 consecutive weeks: (1) control group (CON), (2) S-HSD group (60% high sucrose diet feeding with 0.1 mg mL-1 sucralose solution as drinking water), and (3) S-APE group (S-HSD feeding with 500 mg per (kg bw day) APE solution gavage). The S-HSD group showed significant depression-like behaviors compared with the CON group, which was manifested by an increased number of buried marbles in the marble burying test, prolonged immobility time in both the tail suspension test and forced swimming test, and cognitive impairment based on the Morris water maze test. However, APE intervention significantly improved the depression-like behaviors by reducing serum levels of corticosterone and adrenocorticotropic hormone, and increasing the serum level of IL-10. Moreover, APE intervention inhibited the activation of the NF-κB inflammatory pathway, elevated colonic MUC-2 protein expression, and elevated the colonic and hippocampal tight junction proteins of occludin and ZO-1. Furthermore, APE intervention increased the richness and diversity of gut microbiota by regulating the composition of microbiota, with increased relative abundance of Firmicutes and Bacteroidota, decreased relative abundance of Verrucomicrobiota at the phylum level, significantly lowered relative abundance of Akkermansia at the genus level, and rebalanced abnormal relative abundance of Muribaculaceae_unclassified, Coriobacteriaceae_UCG-002, and Lachnoclostridium induced by S-HSD feeding. Thus, our study supports the potential application of APE as a dietary intervention for ameliorating depression-like behavioral disorders.

Skeletal muscle insulin resistance and adipose tissue hypertrophy persist beyond the reshaping of gut microbiota in young rats fed a fructose-rich diet

To investigate whether short term fructose-rich diet induces changes in the gut microbiota as well as in skeletal muscle and adipose tissue physiology and verify whether they persist even after fructose withdrawal, young rats of 30 d of age were fed for 3 weeks a fructose-rich or control diet. At the end of the 3-weeks period, half of the rats from each group were maintained for further 3 weeks on a control diet. Metagenomic analysis of gut microbiota and short chain fatty acids levels (faeces and plasma) were investigated. Insulin response was evaluated at the whole-body level and both in skeletal muscle and epididymal adipose tissue, together with skeletal muscle mitochondrial function, oxidative stress, and lipid composition. In parallel, morphology and physiological status of epididymal adipose tissue was also evaluated. Reshaping of gut microbiota and increased content of short chain fatty acids was elicited by the fructose diet and abolished by switching back to control diet. On the other hand, most metabolic changes elicited by fructose-rich diet in skeletal muscle and epididymal adipose tissue persisted after switching to control diet. Increased dietary fructose intake even on a short-time basis elicits persistent changes in the physiology of metabolically relevant tissues, such as adipose tissue and skeletal muscle, through mechanisms that go well beyond the reshaping of gut microbiota. This picture delineates a harmful situation, in particular for the young populations, posed at risk of metabolic modifications that may persist in their adulthood.

Is insulin resistance tissue-dependent and substrate-specific? The role of white adipose tissue and skeletal muscle

Insulin resistance (IR) refers to a reduction in the ability of insulin to exert its metabolic effects in organs such as adipose tissue (AT) and skeletal muscle (SM), leading to chronic diseases such as type 2 diabetes, hepatic steatosis, and cardiovascular diseases. Obesity is the main cause of IR, however not all subjects with obesity develop clinical insulin resistance, and not all clinically insulin-resistant people have obesity. Recent evidence implies that IR onset is tissue-dependent (AT or SM) and/or substrate-specific (glucometabolic or lipometabolic). Therefore, the aims of the present review are 1) to describe the glucometabolic and lipometabolic activities of insulin in AT and SM in the maintenance of whole-body metabolic homeostasis, 2) to discuss the pathophysiology of substrate-specific IR in AT and SM, and 3) to highlight novel validated tests to assess tissue and substrate-specific IR that are easy to perform in clinical practice. In AT, glucometabolic IR reduces glucose availability for glycerol and fatty acid synthesis, thus decreasing the esterification and synthesis of signaling bioactive lipids. Lipometabolic IR in AT impairs the antilipolytic effect of insulin and lipogenesis, leading to an increase in circulating FFAs and generating lipotoxicity in peripheral tissues. In SM, glucometabolic IR reduces glucose uptake, whereas lipometabolic IR impairs mitochondrial lipid oxidation, increasing oxidative stress and inflammation, all of which lead to metabolic inflexibility. Understanding tissue-dependent and substrate-specific IR is of paramount importance for early detection before clinical manifestations and for the development of more specific treatments or direct interventions to prevent chronic life-threatening diseases.

Research progress of extracellular vesicles in type 2 diabetes and its complications

Type 2 diabetes is one of the most common chronic diseases in modern society. However, there is still insufficient research on the pathogenesis, diagnosis and treatment of type 2 diabetes and its complications. Extracellular vesicles are small bilayer vesicles secreted by cells. In recent years, the effect of extracellular vesicles in type 2 diabetes and its complications has aroused extensive attention. The research on the influence of protein and nucleic acids carried by extracellular vesicles secreted by stem cells and inflammatory cells on the pathogenesis of type 2 diabetes and its complications provides new ideas for its diagnosis and treatment. This review focuses on the influence of extracellular vesicles on insulin resistance by regulating inflammation and glucose transporter 4 expression. The second part mainly discusses the research progress and limitations of extracellular vesicles use in treating and diagnosing type 2 diabetes and its complications. This review introduces the current research status of type 2 diabetes and its complications, illustrates the biogenesis of extracellular vesicles, their effect on type 2 diabetes pathogenesis and its complications and their potential as therapeutic tools and diagnostic markers in type 2 diabetes and its complications.

The compound enzymatic hydrolysate of Neoporphyra haitanensis improved hyperglycemia and regulated the gut microbiome in high-fat diet-fed mice

We previously found that the combination of protease and a novel β-porphyranase Por16A_Wf may contribute to the deep-processing of laver. The purpose of the present study is to assess the hypoglycemic effect of the compound enzymatic hydrolysate (CEH) of Neoporphyra haitanensis. Thus, biochemical indexes related to diet-induced hyperglycemia were mainly detected using hematoxylin and eosin (H&E) staining, fluorescence quantitative PCR, and ultrahigh performance liquid chromatography-mass spectrometry (UPLC-MS). Then 16s rRNA gene sequencing was performed to analyze the effects of CEH on the gut microbiome in high-fat diet (HFD)-fed mice. The results suggested that CEH reduced the blood glucose level and alleviated insulin resistance. Possibly because CEH repressed intestinal α-glucosidase activity, inhibiting key enzymes (G6Pase and PEPCK) related to hepatic gluconeogenesis, and increased the expression of the enzyme (GLUT4) involved in peripheral glucose uptake. As potential indicators of hyperglycemia, total bile acids in the feces were reversed to the control levels after CEH intervention. Particularly, CEH decreased the content of tauro-α-muricholic acid (TαMCA) and ω-muricholic acid (ωMCA). Furthermore, CEH promoted the proliferation of beneficial bacteria (e.g. Parabacteroides), which may play a role in glycemic control. CEH also regulated the KEGG pathways associated with glycometabolism, such as "fructose and mannose metabolism". In summary, CEH supplementation has favorable effects on improving glucose metabolism and regulating the gut microbiome in HFD-fed mice. CEH has potential to be applied in the development of functional foods.

Integrating the effects of sucrose intake on the brain and white adipose tissue: Could autophagy be a possible link?

Excess dietary sucrose is associated with obesity and metabolic diseases. This relationship is driven by the malfunction of several cell types and tissues critical for the regulation of energy balance, including hypothalamic neurons and white adipose tissue (WAT). However, the mechanisms behind these effects of dietary sucrose are still unclear and might be independent of increased adiposity. Accumulating evidence has indicated that dysregulation of autophagy, a fundamental process for maintenance of cellular homeostasis, alters energy metabolism in hypothalamic neurons and WAT, but whether autophagy could mediate the detrimental effects of dietary sucrose on hypothalamic neurons and WAT that contribute to weight gain is a matter of debate. In this review, we examine the hypothesis that dysregulated autophagy in hypothalamic neurons and WAT is an adiposity-independent effect of sucrose that contributes to increased body weight gain. We propose that excess dietary sucrose leads to autophagy unbalance in hypothalamic neurons and WAT, which increases caloric intake and body weight, favoring the emergence of obesity and metabolic diseases.

No evidence for change in expression of TBC1D1 and TBC1D4 genes in cultured human adipocytes stimulated by myokines and adipokines

TBC1D1 and TBC1D4 proteins play analogous, but not identical role in governing insulin-signalling pathway. Little is known about changes in expression levels of TBC1D1 and TBC1D4 genes in mammals, including humans. Number of factors were studied, but data remain controversial. The aim of this study was to evaluate the effect of selected cytokines, adipokines and myokines with known or putative insulin sensitivity regulation activity (adiponectin, irisin, omentin, interleukin 6, leptin, resistin, and tumour necrosis factor) on TBC1D1 and TBC1D4 expression levels in cultured differentiated human adipocytes. No significant differences were found between the adipocytes treated with different stimuli and this effect was determined not dose dependent. It is reasonable to conclude that relative shortage of data showing no change in TBC1D1 and TBC1D4 from literature results from publication bias; therefore, our finding provides additional insight into the role of both genes.

Adipose tissue and insulin resistance in obese

Currently, obesity has become a global health issue and is referred to as an epidemic. Dysfunctional obese adipose tissue plays a pivotal role in the development of insulin resistance. However, the mechanism of how dysfunctional obese-adipose tissue develops insulin-resistant circumstances remains poorly understood. Therefore, this review attempts to highlight the potential mechanisms behind obesity-associated insulin resistance. Multiple risk factors are directly or indirectly associated with the increased risk of obesity; among them, environmental factors, genetics, aging, gut microbiota, and diets are prominent. Once an individual becomes obese, adipocytes increase in their size; therefore, adipose tissues become larger and dysfunctional, recruit macrophages, and then these polarize to pro-inflammatory states. Enlarged adipose tissues release excess free fatty acids (FFAs), reactive oxygen species (ROS), and pro-inflammatory cytokines. Excess systemic FFAs and dietary lipids enter inside the cells of non-adipose organs such as the liver, muscle, and pancreas, and are deposited as ectopic fat, generating lipotoxicity. Toxic lipids dysregulate cellular organelles, e.g., mitochondria, endoplasmic reticulum, and lysosomes. Dysregulated organelles release excess ROS and pro-inflammation, resulting in systemic inflammation. Long term low-grade systemic inflammation prevents insulin from its action in the insulin signaling pathway, disrupts glucose homeostasis, and results in systemic dysregulation. Overall, long-term obesity and overnutrition develop into insulin resistance and chronic low-grade systemic inflammation through lipotoxicity, creating the circumstances to develop clinical conditions. This review also shows that the liver is the most sensitive organ undergoing insulin impairment faster than other organs, and thus, hepatic insulin resistance is the primary event that leads to the subsequent development of peripheral tissue insulin resistance.