Piperonal attenuates visceral adiposity in mice fed a high-fat diet: potential involvement of the adenylate cyclase-protein kinase A dependent pathway

Targeting Odorant Receptors in Adipose Tissue with Food-Derived Odorants: A Novel Approach to Obesity Treatment

Odorant receptors (ORs) have long been thought to serve as chemosensors located on the cilia of olfactory sensory neurons (OSNs) in the olfactory epithelium, where they recognize odorant molecules and comprise the largest family of seven transmembrane-domain G protein-coupled receptors (GPCRs). Over the last three decades, accumulating evidence has suggested that ORs are distributed in a variety of peripheral tissues beyond their supposed typical tissue expression in the olfactory epithelium. These ectopic ORs play a role in regulating various cellular, physiological, and pathophysiological phenomena in the body, such as regulation of hypertension, hepatic glucose production, cancer development, and chronic skin disease. Adipose tissue, the key organ in regulating obesity and energy metabolism, has been reported to take advantage of ectopic OR-mediated signaling. In this review, we summarize and provide an in-depth analysis of the current research on the key biological functions of adipose tissue ORs in response to food-derived odorants, as well as the molecular mechanisms underlying their activity.

Ilex paraguariensis A.St.-Hil. improves lipid metabolism in high-fat diet-fed obese rats and suppresses intracellular lipid accumulation in 3T3-L1 adipocytes via the AMPK-dependent and insulin signaling pathways

Background

Obesity is closely associated with several chronic diseases, and adipose tissue plays a major role in modulating energy metabolism.

Objective

This study aimed to determine whether Mate, derived from I. paraguariensis A.St.-Hil., ameliorates lipid metabolism in 3T3-L1 adipocytes and high-fat diet (HFD)-fed obese Sprague-Dawley (SD) rats.

Design

3T3-L1 adipocytes were cultured for 7 days, following which intracellular lipid accumulation and expression levels of lipid metabolism-related factors were examined. Dorsomorphin was used to investigate the potential pathways involved, particularly the adenosine monophosphate-activated protein kinase (AMPK)- dependent pathway. Mate was administered to rat HFD-fed obese SD models for 8 consecutive weeks. The expression of lipid metabolism-related factors in the organs and tissues collected from dissected SD rats was evaluated.

Results

Mate suppressed intracellular lipid accumulation in 3T3-L1 adipocytes, increased the protein and gene expression levels of AMPK, hormone sensitive lipase (HSL), calmodulin kinase kinase (CaMKK), liver kinase B1 (LKB1), protein kinase A (PKA), CCAAT/enhancer binding protein β (C/EBPβ), insulin receptor b (IRβ), and insulin receptor substrate 1 (IRS1) (Tyr465), and decreased those of sterol regulatory element binding protein 1C (Srebp1c), fatty acid synthase (FAS), peroxisome-activated receptor γ (PPARγ), and IRS1 (Ser1101). Furthermore, an AMPK inhibitor abolished the effects exerted by Mate on intracellular lipid accumulation and HSL and FAS expression levels. Mate treatment suppressed body weight gain and improved serum cholesterol levels in HFD-fed obese SD rats. Treatment with Mate increased the protein and gene expression levels of AMPK, PKA, Erk1/Erk2 (p44/p42), and uncoupling protein 1 and reduced those of mammalian target of rapamycin, S6 kinase, Srebp1c, ap2, FAS, Il6, Adiponectin, Leptin, and Fabp4 in rat HFD-fed obese SD models.

Discussion and conclusions

Mate suppressed intracellular lipid accumulation in 3T3-L1 adipocytes and improved lipid metabolism in the epididymal adipose tissue of HFD-fed obese SD rats via the activation of AMPK-dependent and insulin signaling pathways.

The Novel Inhibitory Effect of YM976 on Adipocyte Differentiation

The pyrimidine derivative YM976 (4-(3-chlorophenyl)-1,7-diethylpyrido(2,3-d)-pyrimidin-2(1H)-one) exerts anti-inflammatory and anti-asthmatic effects. Considering that accumulation of lipids in adipose tissue is accompanied by inflammation, we investigated whether YM976 affects adipocyte differentiation. We found that YM976 significantly decreased lipid accumulation without cytotoxicity and reduced the expression levels of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα) as well as their lipogenic regulators including fatty acid synthase (FASN) and fatty acid-binding protein 4 (FABP4) in 3T3-L1 cells induced for differentiation. YM976 mainly inhibited the early stage of adipocyte differentiation. Furthermore, intracellular cAMP level was elevated by YM976 resulting in increased phosphorylation of adenosine monophosphate-activated protein kinase (AMPK). Conversely, decreasing the levels of AMPK or treatment with Compound C, an AMPK inhibitor, lessened the suppressive effects of YM976 on PPARγ transcriptional activity and adipogenesis. Thus, our results suggest YM976 as a novel potential compound for controlling lipid accumulation and formation of adipocytes in obesity.

Novel anti-adipogenic effect of CF3-allylated indole in 3T3-L1 cells

Indole derivatives from various plants are known to have health benefits because of their anti-cancer, anti-oxidant, anti-inflammatory, and anti-tubercular effects. However, their effects on adipogenesis have not been fully elucidated yet. Herein, we show that a newly synthesized indole derivative, CF₃-allylated indole, [(E)-1-(pyrimidin- 2-yl)-2-(4,4,4- trifluorobut-2-enyl)-1H-indole], effectively inhibits adipogenesis. We found that CF₃-allylated indole inhibited lipid accumulation and suppressed the expression of CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator activated receptor γ (PPARγ) in 3T3-L1 cells. The inhibitory effect of CF₃-allylated indole primarily occurred at the early phase of adipocyte differentiation by increasing intracellular cyclic adenosine monophosphate (cAMP) levels and enhancing protein kinase A (PKA) and adenosine monophosphate-activated protein kinase (AMPK) signaling. Conversely, depletion of PKA or treatment with a protein kinase A inhibitor (H89) reversed such inhibitory effects of CF₃-allylated indole on adipogenesis and PPARγ expression. These results suggest that CF₃-allylated indole inhibits early stages of adipogenesis by increasing phosphorylation of PKA/AMPK, leading to decreased expression of adipogenic genes in 3T3-L1 cells. These results indicate that CF₃-allylated indole has potential for controlling initial adipocyte differentiation in metabolic disorders such as obesity.

Dietary Bioactive Ingredients Modulating the cAMP Signaling in Diabetes Treatment

As the prevalence of diabetes increases progressively, research to develop new therapeutic approaches and the search for more bioactive compounds are attracting more attention. Over the past decades, studies have suggested that cyclic adenosine monophosphate (cAMP), the important intracellular second messenger, is a key regulator of metabolism and glucose homeostasis in diverse physiopathological states in multiple organs including the pancreas, liver, gut, skeletal muscle, adipose tissues, brain, and kidney. The multiple characteristics of dietary compounds and their favorable influence on diabetes pathogenesis, as well as their intersections with the cAMP signaling pathway, indicate that these compounds have a beneficial effect on the regulation of glucose homeostasis. In this review, we outline the current understanding of the diverse functions of cAMP in different organs involved in glucose homeostasis and show that a diversity of bioactive ingredients from foods activate or inhibit cAMP signaling, resulting in the improvement of the diabetic pathophysiological process. It aims to highlight the diabetes-preventative or -therapeutic potential of dietary bioactive ingredients targeting cAMP signaling.

Non-shivering Thermogenesis Signalling Regulation and Potential Therapeutic Applications of Brown Adipose Tissue

In mammals, thermogenic organs exist in the body that increase heat production and enhance energy regulation. Because brown adipose tissue (BAT) consumes energy and generates heat, increasing energy expenditure via BAT might be a potential strategy for new treatments for obesity and obesity-related diseases. Thermogenic differentiation affects normal adipose tissue generation, emphasizing the critical role that common transcriptional regulation factors might play in common characteristics and sources. An understanding of thermogenic differentiation and related factors could help in developing ways to improve obesity indirectly or directly through targeting of specific signalling pathways. Many studies have shown that the active components of various natural products promote thermogenesis through various signalling pathways. This article reviews recent major advances in this field, including those in the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA), cyclic guanosine monophosphate-GMP-dependent protein kinase G (cGMP-AKT), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), transforming growth factor-β/bone morphogenic protein (TGF-β/BMP), transient receptor potential (TRP), Wnt, nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κΒ), Notch and Hedgehog (Hh) signalling pathways in brown and brown-like adipose tissue. To provide effective information for future research on weight-loss nutraceuticals or drugs, this review also highlights the natural products and their active ingredients that have been reported in recent years to affect thermogenesis and thus contribute to weight loss via the above signalling pathways.

Transcriptome Analysis Reveals Genes Involved in Thermogenesis in Two Cold-Exposed Sheep Breeds

Thermogenesis plays an important role in the survival of sheep exposed to low temperatures; however, little is known about the genetic mechanisms underlying cold adaptation in sheep. We examined 6 Altay (A) and 6 Hu (H) six-month-old ewe lambs. Altay sheep are raised in northern China and are adapted to dry, cold climates, while Hu sheep are raised in southern China and are adapted to warm, humid climates. Each breed was divided into two groups: chronic cold sheep, exposed to -5 °C for 25 days (3 A^c; 3 H^c), and thermo-neutral sheep, maintained at 20 °C (3 A^w; 3 H^w). The transcriptome profiles of hypothalamus, tail-fat and perirenal fat tissues from these four groups were determined using paired-end sequencing for RNA expression analysis. There are differences in cold tolerance between Hu and Altay sheep. Under cold exposure of the lambs: (1) UCP1-dependent thermogenesis and calcium- and cAMP-signaling pathways were activated; and (2) different fat tissues were activated in Hu and Altay lambs. Several candidate genes involved in thermogenesis including UCP1, ADRB3, ADORA2A, ATP2A1, RYR1 and IP6K1 were identified. Molecular mechanisms of thermogenesis in the sheep are discussed and new avenues for research are suggested.

Sesamol Alleviates Obesity-Related Hepatic Steatosis via Activating Hepatic PKA Pathway

This study aimed to investigate the effect of sesamol (SEM) on the protein kinase A (PKA) pathway in obesity-related hepatic steatosis treatment by using high-fat diet (HFD)-induced obese mice and a palmitic acid (PA)-treated HepG2 cell line. SEM reduced the body weight gain of obese mice and alleviated related metabolic disorders such as insulin resistance, hyperlipidemia, and systemic inflammation. Furthermore, lipid accumulation in the liver and HepG2 cells was reduced by SEM. SEM downregulated the gene and protein levels of lipogenic regulator factors, and upregulated the gene and protein levels of the regulator factors responsible for lipolysis and fatty acid β-oxidation. Meanwhile, SEM activated AMP-activated protein kinase (AMPK), which might explain the regulatory effect of SEM on fatty acid β-oxidation and lipogenesis. Additionally, the PKA-C and phospho-PKA substrate levels were higher after SEM treatment. Further research found that after pretreatment with the PKA inhibitor, H89, lipid accumulation was increased even with SEM administration in HepG2 cells, and the effect of SEM on lipid metabolism-related regulator factors was abolished by H89. In conclusion, SEM has a positive therapeutic effect on obesity and obesity-related hepatic steatosis by regulating the hepatic lipid metabolism mediated by the PKA pathway.