Secretin-Activated Brown Fat Mediates Prandial Thermogenesis to Induce Satiation.

The molecular mediator and functional significance of meal-associated brown fat (BAT) thermogenesis remains elusive. Here, we identified the gut hormone secretin as a non-sympathetic BAT activator mediating prandial thermogenesis, which consequentially induces satiation, thereby establishing a gut-secretin-BAT-brain axis in mammals with a physiological role of prandial thermogenesis in the control of satiation. Mechanistically, meal-associated rise in circulating secretin activates BAT thermogenesis by stimulating lipolysis upon binding to secretin receptors in brown adipocytes, which is sensed in the brain and promotes satiation. Chronic infusion of a modified human secretin transiently elevates energy expenditure in diet-induced obese mice. Clinical trials with human subjects showed that thermogenesis after a single-meal ingestion correlated with postprandial secretin levels and that secretin infusions increased glucose uptake in BAT. Collectively, our findings highlight the largely unappreciated function of BAT in the control of satiation and qualify BAT as an even more attractive target for treating obesity.

GIPR Agonism Enhances TZD-Induced Insulin Sensitivity in Obese IR Mice.

Recent studies have found that glucose-dependent insulinotropic polypeptide receptor (GIPR) agonism can enhance the metabolic efficacy of glucagon-like peptide-1 receptor agonist treatment by promoting both weight-dependent and -independent improvements on systemic insulin sensitivity. These findings have prompted new investigations aimed at better understanding the broad metabolic benefit of GIPR activation. Herein, we determined whether GIPR agonism favorably influenced the pharmacologic efficacy of the insulin-sensitizing thiazolidinedione (TZD) rosiglitazone in obese insulin-resistant (IR) mice. Genetic and pharmacological approaches were used to examine the role of GIPR signaling on rosiglitazone-induced weight gain, hyperphagia, and glycemic control. RNA sequencing was conducted to uncover potential mechanisms by which GIPR activation influences energy balance and insulin sensitivity. In line with previous findings, treatment with rosiglitazone induced the mRNA expression of the GIPR in white and brown fat. However, obese GIPR-null mice dosed with rosiglitazone had equivalent weight gain to that of wild-type (WT) animals. Strikingly, chronic treatment of obese IR WT animals with a long-acting GIPR agonist prevented rosiglitazone-induced weight-gain and hyperphagia, and it enhanced the insulin-sensitivity effect of this TZD. The systemic insulin sensitization was accompanied by increased glucose disposal in brown adipose tissue, which was underlined by the recruitment of metabolic and thermogenic genes. These findings suggest that GIPR agonism can counter the negative consequences of rosiglitazone treatment on body weight and adiposity, while improving its insulin-sensitizing efficacy at the same time.

Tirzepatide modulates the regulation of adipocyte nutrient metabolism through long-acting activation of the GIP receptor.

Tirzepatide, a glucose-dependent insulinotropic polypeptide/glucagon-like peptide 1 receptor (GIPR/GLP-1R) agonist, has, in clinical trials, demonstrated greater reductions in glucose, body weight, and triglyceride levels compared with selective GLP-1R agonists in people with type 2 diabetes (T2D). However, cellular mechanisms by which GIPR agonism may contribute to these improved efficacy outcomes have not been fully defined. Using human adipocyte and mouse models, we investigated how long-acting GIPR agonists regulate fasted and fed adipocyte functions. In functional assays, GIPR agonism enhanced insulin signaling, augmented glucose uptake, and increased the conversion of glucose to glycerol in a cooperative manner with insulin; however, in the absence of insulin, GIPR agonists increased lipolysis. In diet-induced obese mice treated with a long-acting GIPR agonist, circulating triglyceride levels were reduced during oral lipid challenge, and lipoprotein-derived fatty acid uptake into adipose tissue was increased. Our findings support a model for long-acting GIPR agonists to modulate both fasted and fed adipose tissue function differentially by cooperating with insulin to augment glucose and lipid clearance in the fed state while enhancing lipid release when insulin levels are reduced in the fasted state.

LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept.

With an increasing prevalence of obesity, there is a need for new therapies to improve body weight management and metabolic health. Multireceptor agonists in development may provide approaches to fulfill this unmet medical need. LY3437943 is a novel triple agonist peptide at the glucagon receptor (GCGR), glucose-dependent insulinotropic polypeptide receptor (GIPR), and glucagon-like peptide-1 receptor (GLP-1R). In vitro, LY3437943 shows balanced GCGR and GLP-1R activity but more GIPR activity. In obese mice, administration of LY3437943 decreased body weight and improved glycemic control. Body weight loss was augmented by the addition of GCGR-mediated increases in energy expenditure to GIPR- and GLP-1R-driven calorie intake reduction. In a phase 1 single ascending dose study, LY3437943 showed a safety and tolerability profile similar to other incretins. Its pharmacokinetic profile supported once-weekly dosing, and a reduction in body weight persisted up to day 43 after a single dose. These findings warrant further clinical assessment of LY3437943.

GIPR agonism mediates weight-independent insulin sensitization by tirzepatide in obese mice.

Tirzepatide (LY3298176), a dual GIP and GLP-1 receptor (GLP-1R) agonist, delivered superior glycemic control and weight loss compared with GLP-1R agonism in patients with type 2 diabetes. However, the mechanism by which tirzepatide improves efficacy and how GIP receptor (GIPR) agonism contributes is not fully understood. Here, we show that tirzepatide is an effective insulin sensitizer, improving insulin sensitivity in obese mice to a greater extent than GLP-1R agonism. To determine whether GIPR agonism contributes, we compared the effect of tirzepatide in obese WT and Glp-1r-null mice. In the absence of GLP-1R-induced weight loss, tirzepatide improved insulin sensitivity by enhancing glucose disposal in white adipose tissue (WAT). In support of this, a long-acting GIPR agonist (LAGIPRA) was found to enhance insulin sensitivity by augmenting glucose disposal in WAT. Interestingly, the effect of tirzepatide and LAGIPRA on insulin sensitivity was associated with reduced branched-chain amino acids (BCAAs) and ketoacids in the circulation. Insulin sensitization was associated with upregulation of genes associated with the catabolism of glucose, lipid, and BCAAs in brown adipose tissue. Together, our studies show that tirzepatide improved insulin sensitivity in a weight-dependent and -independent manner. These results highlight how GIPR agonism contributes to the therapeutic profile of dual-receptor agonism, offering mechanistic insights into the clinical efficacy of tirzepatide.

The anti-obesity effect of FGF19 does not require UCP1-dependent thermogenesis.

OBJECTIVE: Fibroblast growth factor 19 (FGF19) is a postprandial hormone which plays diverse roles in the regulation of bile acid, glucose, and lipid metabolism. Administration of FGF19 to obese/diabetic mice lowers body weight, improves insulin sensitivity, and enhances glycemic control. The primary target organ of FGF19 is the liver, where it regulates bile acid homeostasis in response to nutrient absorption. In contrast, the broader pharmacologic actions of FGF19 are proposed to be driven, in part, by the recruitment of the thermogenic protein uncoupling protein 1 (UCP1) in white and brown adipose tissue. However, the precise contribution of UCP1-dependent thermogenesis to the therapeutic actions of FGF19 has not been critically evaluated. METHODS: Using WT and germline UCP1 knockout mice, the primary objective of the current investigation was to determine the in vivo pharmacology of FGF19, focusing on its thermogenic and anti-obesity activity. RESULTS: We report that FGF19 induced mRNA expression of UCP1 in adipose tissue and show that this effect is required for FGF19 to increase caloric expenditure. However, we demonstrate that neither UCP1 induction nor an elevation in caloric expenditure are necessary for FGF19 to induce weight loss in obese mice. In contrast, the anti-obesity action of FGF19 appeared to be associated with its known physiological role. In mice treated with FGF19, there was a significant reduction in the mRNA expression of genes associated with hepatic bile acid synthesis enzymes, lowered levels of hepatic bile acid species, and a significant increase in fecal energy content, all indicative of reduced lipid absorption in animals treated with FGF19. CONCLUSION: Taken together, we report that the anti-obesity effect of FGF19 occurs in the absence of UCP1. Our data suggest that the primary way in which exogenous FGF19 lowers body weight in mice may be through the inhibition of bile acid synthesis and subsequently a reduction of dietary lipid absorption.

Activation of prostaglandin E receptor 4 triggers secretion of gut hormone peptides GLP-1, GLP-2, and PYY.

Prostaglandins E1 and E2 are synthesized in the intestine and mediate a range of gastrointestinal functions via activation of the prostanoid E type (EP) family of receptors. We examined the potential role of EP receptors in the regulation of gut hormone secretion from L cells. Analysis of mRNA expression in mouse enteroendocrine GLUTag cells demonstrated the abundant expression of EP4 receptor, whereas expression of other EP receptors was much lower. Prostaglandin E1 and E2, nonselective agonists for all EP receptor subtypes, triggered glucagon like peptide 1 (GLP-1) secretion from GLUTag cells, as did the EP4-selective agonists CAY10580 and TCS2510. The effect of EP4 agonists on GLP-1 secretion was blocked by incubation of cells with the EP4-selective antagonist L161,982 or by down-regulating EP4 expression with specific small interfering RNA. Regulation of gut hormone secretion with EP4 agonists was further studied in mice. Administration of EP4 agonists to mice produced a significant elevation of plasma levels of GLP-1, glucagon like peptide 2 (GLP-2) and peptide YY (PYY), whereas gastric inhibitory peptide (GIP) levels were not increased. Thus, our data demonstrate that activation of the EP4 receptor in enteroendocrine L cells triggers secretion of gut hormones.

Fibroblast growth factor 21 is not required for the antidiabetic actions of the thiazoladinediones.

Fibroblast growth factor 21 is an emerging metabolic regulator that was recently proposed to be a fed-state inducible factor in adipose tissue. As mice lacking FGF21 were refractory to treatment with rosiglitazone, FGF21 was suggested to underlie PPARγ-driven pharmacology and side effect profile (Dutchak et al., 2012 [12]). To evaluate FGF21/PPARγ cross-talk we conducted experiments in control and FGF21 null animals and found that rosiglitazone was equally efficacious in both strains. Specifically, diverse endpoints ranging from enhanced glycemic control, improved lipid homeostasis and side effects such as adipose accumulation were evident in both genotypes. Furthermore, the transcriptional signature and cytokine secretion profile of rosiglitazone action were maintained in our FGF21KO animals. Finally, we found that FGF21 in adipose was expressed at comparable levels in fasted and fed states. Thus, our data present a new viewpoint on the FGF21/PPARγ interplay whereby FGF21 is not necessary for the metabolic events downstream of PPARγ.

Combination of a Beta adrenoceptor modulator and a norepinephrine-serotonin uptake inhibitor for the treatment of obesity.

We report the novel combination of a selective beta adrenoceptor modulator and a norepinephrine-serotonin uptake inhibitor (sibutramine) with potential for the treatment of obesity. The synthesis and characterization of 6-[4-[2-[[(2S)-3-(9H-carbazol-4-yloxy)-2-hydroxypropyl]amino]-2-methylpropyl]phenoxy]pyridine-3-carboxamide (LY377604), a human ß3-adrenergic receptor agonist and ß1- and ß2-adrenergic receptor antagonist with no sympathomimetic activity at the ß1- and ß2-adrenergic receptors, is reported. Some in vivo data in both rats and humans is presented.