Gut-adipose tissue crosstalk: A bridge to novel therapeutic targets in metabolic syndrome?

Inter-organ crosstalk during development and progression of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterized by tissue-specific insulin resistance and pancreatic β-cell dysfunction, which result from the interplay of local abnormalities within different tissues and systemic dysregulation of tissue crosstalk. The main local mechanisms comprise metabolic (lipid) signalling, altered mitochondrial metabolism with oxidative stress, endoplasmic reticulum stress and local inflammation. While the role of endocrine dysregulation in T2DM pathogenesis is well established, other forms of inter-organ crosstalk deserve closer investigation to better understand the multifactorial transition from normoglycaemia to hyperglycaemia. This narrative Review addresses the impact of certain tissue-specific messenger systems, such as metabolites, peptides and proteins and microRNAs, their secretion patterns and possible alternative transport mechanisms, such as extracellular vesicles (exosomes). The focus is on the effects of these messengers on distant organs during the development of T2DM and progression to its complications. Starting from the adipose tissue as a major organ relevant to T2DM pathophysiology, the discussion is expanded to other key tissues, such as skeletal muscle, liver, the endocrine pancreas and the intestine. Subsequently, this Review also sheds light on the potential of multimarker panels derived from these biomarkers and related multi-omics for the prediction of risk and progression of T2DM, novel diabetes mellitus subtypes and/or endotypes and T2DM-related complications.

Are gut dysbiosis, barrier disruption, and endotoxemia related to adipose tissue dysfunction in metabolic disorders? Overview of the mechanisms involved

Recently, compelling evidence points to dysbiosis and disruption of the epithelial intestinal barrier as major players in the pathophysiology of metabolic disorders, such as obesity. Upon the intestinal barrier disruption, components from bacterial metabolism and bacteria itself can reach peripheral tissues through circulation. This has been associated with the low-grade inflammation that characterizes obesity and other metabolic diseases. While circulating bacterial DNA has been postulated as a common feature of obesity and even type 2 diabetes, almost no focus has been given to the existence and effects of bacteria in peripheral tissues, namely the adipose tissue. As a symbiont population, it is expected that gut microbiota modulate the immunometabolism of the host, thus influencing energy balance mechanisms and inflammation. Gut inflammatory signals cause direct deleterious inflammatory responses in adipose tissue and may also affect key gut neuroendocrine mechanisms governing nutrient sensing and energy balance, like incretins and ghrelin, which play a role in the gut-brain-adipose tissue axis. Thus, it is of major importance to disclose how gut microbiota and derived signals modulate neuroendocrine and inflammatory pathways, which contribute to the dysfunction of adipose tissue and to the metabolic sequelae of obesity and related disorders. This review summarizes the current knowledge regarding these topics and identifies new perspectives in this field of research, highlighting new pathways toward the reduction of the inflammatory burden of metabolic diseases.

The role of Th17 cells in endocrine organs: Involvement of the gut, adipose tissue, liver and bone

T Helper 17 (Th17) cells are adaptive immune cells that play myriad roles in the body. Immune-endocrine interactions are vital in endocrine organs during pathological states. Th17 cells are known to take part in multiple autoimmune diseases over the years. Current evidence has moved from minimal to substantial that Th17 cells are closely related to endocrine organs. Diverse tissue Th17 cells have been discovered within endocrine organs, including gut, adipose tissue, liver and bone, and these cells are modulated by various secretions from endocrine organs. Th17 cells in these endocrine organs are key players in the process of an array of metabolic disorders and inflammatory conditions, including obesity, insulin resistance, nonalcoholic fatty liver disease (NAFLD), primary sclerosing cholangitis (PSC), osteoporosis and inflammatory bowel disease (IBD). We reviewed the pathogenetic or protective functions played by Th17 cells in various endocrine tissues and identified potential regulators for plasticity of it. Furthermore, we discussed the roles of Th17 cells in crosstalk of gut-organs axis.

Can Fasting Curb the Metabolic Syndrome Epidemic?

Metabolic syndrome (MetS) represents a cluster of metabolic abnormalities that includes hypertension, central obesity, insulin resistance, and atherogenic dyslipidemia. Due to the high prevalence (around 1/3 of the world population) economic burden of MetS, there is a need for new dietary, lifestyle, and therapeutic options. Recently, fasting emerged as a dietary method proposed for controlling metabolic risk factors. Intermittent fasting (IF), or time-restricted feeding (TRF), describes an array of feeding patterns in which calorie intake is restricted to a specific time period. Hence, this review aimed to elucidate the latest data on MetS and explore the viability of simple management options, such as IF and TRF. Preclinical studies have shown how IF/TRF exerts beneficial effects on the gut microbiota, glucose and insulin metabolism, weight and visceral fat, and lipid metabolism. However, the results obtained from human studies are somewhat conflicting, as weight loss was achieved in all studies, whereas in some studies, there was no significant effect on insulin resistance, cholesterol/lipid metabolism, or blood pressure. Nevertheless, as only very few human studies were performed, there is a need for more randomized control trials on larger cohorts of patients with MetS to gather higher-yield evidence to clarify whether IF/TRF are suitable dietary patterns for this population.

Free fatty acid receptors in the endocrine regulation of glucose metabolism: Insight from gastrointestinal-pancreatic-adipose interactions

Glucose metabolism is primarily controlled by pancreatic hormones, with the coordinated assistance of the hormones from gastrointestine and adipose tissue. Studies have unfolded a sophisticated hormonal gastrointestinal-pancreatic-adipose interaction network, which essentially maintains glucose homeostasis in response to the changes in substrates and nutrients. Free fatty acids (FFAs) are the important substrates that are involved in glucose metabolism. FFAs are able to activate the G-protein coupled membrane receptors including GPR40, GPR120, GPR41 and GPR43, which are specifically expressed in pancreatic islet cells, enteroendocrine cells as well as adipocytes. The activation of FFA receptors regulates the secretion of hormones from pancreas, gastrointestine and adipose tissue to influence glucose metabolism. This review presents the effects of the FFA receptors on glucose metabolism via the hormonal gastrointestinal-pancreatic-adipose interactions and the underlying intracellular mechanisms. Furthermore, the development of therapeutic drugs targeting FFA receptors for the treatment of abnormal glucose metabolism such as type 2 diabetes mellitus is summarized.

Modulatory effect of filarial infection on the systemic hormone levels in subjects with metabolic syndrome (DM-LF5)

AIM

Metabolic syndrome (MS) refers to a group of co-morbidities which include central obesity, hypertension, hyperglycemia and dyslipidemia. Previously, we reported that childhood lymphatic filariasis (LF) confers significant protection against type-1 and type-2 forms of diabetes, by means of immunomodulation. In the present study, we studied the effect of LF on endocrine dysfunction in MS and Non-MS patients in baseline and after 10 years of follow-up.

METHODS

We quantified the serum levels of pancreatic hormones (insulin and glucagon), incretins (Ghrelin, GIP and GLP-1) and adipokines (leptin, adiponectin, adipsin, visfatin, PAI-1 and resistin) by multiplex bead array system.

RESULTS

MS (both LF- and LF+) subjects had increased insulin levels compared to NMS (both LF- and LF+) subjects. MS-LF+ subjects had significantly increased levels of glucagon, ghrelin, GIP and GLP-1 and decreased levels of adipsin, compared to MS-LF- subjects. Interestingly this effect was short-lived and was not seen in the follow-up samples.

CONCLUSION

Overall, LF infection might confer limited short-term beneficial effects against MS, by means of modulating the incretin levels,either directly or indirectly.