Appetite control and obesity

Oleanolic acid inhibits appetite through the TGR5/cAMP signaling pathway

Inhibition of appetite is an effective approach to fight obesity. Recently, bile acids have been reported to suppress appetite and alleviate obesity via the Takeda G protein-coupled receptor 5 (TGR5). However, whether the downstream signaling molecule cyclic adenosine monophosphate (cAMP) of TGR5 is involved in this process remains unclear. Oleanolic acid (OA) is a plant analogue of bile acids. The study aimed to explore the effect of dietary OA supplementation on appetite and to examine the role of TGR5/cAMP signaling in this process. In our study, mice were divided into four treatment groups: basal diet, 50mg/kg OA-supplemented diet, 100mg/kg OA-supplemented diet, and 30mg/kg tauroursodeoxycholic acid (TUDCA)-supplemented diet. Our results showed that dietary supplementation of OA and TUDCA both suppressed appetite. Additionally, OA and TUDCA downregulated the expression of appetite-stimulating factors while upregulating appetite-suppressing factors in the hypothalamus. Furthermore, OA was found to activate TGR5 signaling in the hypothalamus. Mechanistic studies using N38 cells revealed that OA reduced the expression and secretion of agouti-related peptide (AgRP), while inhibition of TGR5 and cAMP attenuated this effect of OA. In conclusion, our findings suggest that OA may suppress appetite through activation of the TGR5/cAMP signaling pathway in the hypothalamus.

Recent Advances in the Anti-Obesity Benefits of Phytoconstituents: From Phytochemistry to Targeting Novel-Systems

Obesity is a metabolic disorder that has become a global health concern. The existing pharmaceutical drugs for treating obesity have some side effects. Compounds from natural sources are prospective substitutes for treating chronic diseases such as obesity, with the added advantages of being safe and cost-effective. However, due to factors such as poor solubility, low bioavailability, and instability in the physiological environment, the therapeutic efficacy of phytoconstituents is limited. Nowadays, developing nanoscaled systems has emerged as a vital strategy for enhancing the delivery and therapeutic effect of phytoconstituents. The present study discusses and categorizes phytoconstituents with anti-obesity effects and concludes the main mechanisms underlying their effects. Importantly, strategies used to develop phytoconstituent-based nano-drug delivery systems (NDDS) for obesity treatment that show improved efficacy relative to traditional administration routes are reviewed. Finally, the progress of research on phytoconstituent-based NDDS for obesity treatment is summarized to provide a reference for the development of safe and effective treatment strategies for obesity.

A flavonoid-rich Smilax china L. extract prevents obesity by upregulating the adiponectin-receptor/AMPK signalling pathway and modulating the gut microbiota in mice

The aim of this study was to investigate the effects of Smilax china L. flavonoid (SCF) on obesity and changes in gut microbiota high-fat/high-sucrose (HFHS)-fed mice. Male C57BL/6 mice fed either a normal-chow (NC) or a HFHS diet were treated with SCF for 12 weeks. The effect of SCF on the composition of gut microbiota was assessed by 16S rDNA sequencing. SCFA levels in the caecum were quantified by GC-MS. SCF supplementation alleviated the body weight gain, fat accumulation, serum lipid parameters, and hepatic steatosis and improved glucose homeostasis. SCF significantly increased plasma adiponectin level, adiponectin-receptor-gene (AdipoR1 and AdipoR2) expression in the liver, activated AMPKα, downregulated the expression of SREBP1-c, FAS, and ACCα, and upregulated the expression of PPARα, CPT-1α, and UCP-1. The anti-obesity effects of SCF might be through upregulation of adiponectin-receptor/AMPK signalling to improve lipid metabolism. SCF reversed HFHS-induced dysbiosis of gut microbiota and decreased SCFA production in the caecum, thus reducing energy absorption and leading to loss of body weight. Spearman's correlation analysis revealed significant correlations between obesity phenotypes, SCFA levels, and changes in gut microbiota. The results showed that SCF may be an effective dietary supplement that is useful for suppressing the development of obesity and associated disorders.

ADAR1 deficiency protects against high-fat diet-induced obesity and insulin resistance in mice

Obesity is an important independent risk factor for type 2 diabetes, cardiovascular diseases, and many other chronic diseases. The objective of this study was to determine the role of adenosine deaminase acting on RNA 1 (ADAR1) in the development of obesity and insulin resistance. Wild-type (WT) and heterozygous ADAR1-deficient (Adar1+/-) mice were fed normal chow or a high-fat diet (HFD) for 12 wk. Adar1+/- mice fed with HFD exhibited a lean phenotype with reduced fat mass compared with WT controls, although no difference was found under chow diet conditions. Blood biochemical analysis and insulin tolerance test showed that Adar1+/- improved HFD-induced dyslipidemia and insulin resistance. Metabolic studies showed that food intake was decreased in Adar1+/- mice compared with the WT mice under HFD conditions. Paired feeding studies further demonstrated that Adar1+/- protected mice from HFD-induced obesity through decreased food intake. Furthermore, Adar1+/- restored the increased ghrelin expression in the stomach and the decreased serum peptide YY levels under HFD conditions. These data indicate that ADAR1 may contribute to diet-induced obesity, at least partially, through modulating the ghrelin and peptide YY expression and secretion.NEW & NOTEWORTHY This study identifies adenosine deaminase acting on RNA 1 as a novel factor promoting high-fat diet-induced obesity, at least partially, through modulating appetite-related genes ghrelin and PYY.

Central chronic apelin infusion decreases energy expenditure and thermogenesis in mice

Apelin is a bioactive peptide involved in the control of energy metabolism. In the hypothalamus, chronic exposure to high levels of apelin is associated with an increase in hepatic glucose production, and then contributes to the onset of type 2 diabetes. However, the molecular mechanisms behind deleterious effects of chronic apelin in the brain and consequences on energy expenditure and thermogenesis are currently unknown. We aimed to evaluate the effects of chronic intracerebroventricular (icv) infusion of apelin in normal mice on hypothalamic inflammatory gene expression, energy expenditure, thermogenesis and brown adipose tissue functions. We have shown that chronic icv infusion of apelin increases the expression of pro-inflammatory factors in the hypothalamus associated with an increase in plasma interleukin-1 beta. In parallel, mice infused with icv apelin exhibit a significant lower energy expenditure coupled to a decrease in PGC1alpha, PRDM16 and UCP1 expression in brown adipose tissue which could explain the alteration of thermogenesis in these mice. These data provide compelling evidence that central apelin contributes to the development of type 2 diabetes by altering energy expenditure, thermogenesis and fat browning.

Functional foods as potential therapeutic options for metabolic syndrome

Obesity as part of metabolic syndrome is a major lifestyle disorder throughout the world. Current drug treatments for obesity produce small and usually unsustainable decreases in body weight with the risk of major adverse effects. Surgery has been the only treatment producing successful long-term weight loss. As a different but complementary approach, lifestyle modification including the use of functional foods could produce a reliable decrease in obesity with decreased comorbidities. Functional foods may include fruits such as berries, vegetables, fibre-enriched grains and beverages such as tea and coffee. Although health improvements continue to be reported for these functional foods in rodent studies, further evidence showing the translation of these results into humans is required. Thus, the concept that these fruits and vegetables will act as functional foods in humans to reduce obesity and thereby improve health remains intuitive and possible rather than proven.

Microbiome remodelling leads to inhibition of intestinal farnesoid X receptor signalling and decreased obesity

The antioxidant tempol reduces obesity in mice. Here we show that tempol alters the gut microbiome by preferentially reducing the genus Lactobacillus and its bile salt hydrolase (BSH) activity leading to the accumulation of intestinal tauro-β-muricholic acid (T-β-MCA). T-β-MCA is an farnesoid X receptor (FXR) nuclear receptor antagonist, which is involved in the regulation of bile acid, lipid and glucose metabolism. Its increased levels during tempol treatment inhibit FXR signalling in the intestine. High-fat diet-fed intestine-specific Fxr-null (Fxr(ΔIE)) mice show lower diet-induced obesity, similar to tempol-treated wild-type mice. Further, tempol treatment does not decrease weight gain in Fxr(ΔIE) mice, suggesting that the intestinal FXR mediates the anti-obesity effects of tempol. These studies demonstrate a biochemical link between the microbiome, nuclear receptor signalling and metabolic disorders, and suggest that inhibition of FXR in the intestine could be a target for anti-obesity drugs.