Chemical Hybridization of Glucagon and Thyroid Hormone Optimizes Therapeutic Impact for Metabolic Disease.

Glucagon and thyroid hormone (T3) exhibit therapeutic potential for metabolic disease but also exhibit undesired effects. We achieved synergistic effects of these two hormones and mitigation of their adverse effects by engineering chemical conjugates enabling delivery of both activities within one precisely targeted molecule. Coordinated glucagon and T3 actions synergize to correct hyperlipidemia, steatohepatitis, atherosclerosis, glucose intolerance, and obesity in metabolically compromised mice. We demonstrate that each hormonal constituent mutually enriches cellular processes in hepatocytes and adipocytes via enhanced hepatic cholesterol metabolism and white fat browning. Synchronized signaling driven by glucagon and T3 reciprocally minimizes the inherent harmful effects of each hormone. Liver-directed T3 action offsets the diabetogenic liability of glucagon, and glucagon-mediated delivery spares the cardiovascular system from adverse T3 action. Our findings support the therapeutic utility of integrating these hormones into a single molecular entity that offers unique potential for treatment of obesity, type 2 diabetes, and cardiovascular disease.

Influence of Nutritional Status and Leptin Action on Agrp and Pomc Co-Expression in Hypothalamic Melanocortin System Neurons.

OBJECTIVES: The control of energy balance relies on the counterbalancing release of neuropeptides encoded by the pro-opiomelanocortin (Pomc) and agouti-related protein (Agrp) genes, expressed by 2 distinct neuronal populations of the arcuate (ARC) nucleus of the hypothalamus. Although largely segregated, single-cell resolution techniques demonstrate some degree of co-expression. We studied whether challenges to the control of energy balance influence the degree of Agrp and Pomc co-expression in ARC melanocortin neurons. METHODS: We used fluorescence-activated cell sorting followed by quantitative polymerase chain reaction and fluorescent in situ hybridization to measure Pomc and Agrp gene co-expression in POMC or AGRP neurons in response to (1) acute or chronic calorie restriction, or (2) obesity due to loss of leptin receptor expression or chronic high-fat diet feeding in male mice. RESULTS: Melanocortin ARC neurons of fed mice exhibited low, yet detectable, levels of Pomc and Agrp gene co-expression. Calorie restriction significantly increased and decreased total Agrp and Pomc expression, respectively, and reduced the expression of Pomc relative to Agrp in AGRP neurons. Leptin-deficient db/db mice showed increased total Agrp levels and decreased Pomc expression, as well as significantly increased Agrp expression relative to Pomc in POMC neurons. Expression or co-expression levels did not differ between diet-induced obese mice and lean controls. CONCLUSIONS: Changes in Agrp and Pomc co-expression within POMC and AGRP neurons following chronic calorie restriction or in db/db mice suggest an additional mechanism to further suppress the melanocortin signaling during conditions of severely reduced leptin action.

Contribution of brown adipose tissue activity to the control of energy balance by GLP-1 receptor signalling in mice.

AIMS/HYPOTHESIS: We assessed the contribution of glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) signalling to thermogenesis induced by high-fat diet (HFD) consumption. Furthermore, we determined whether brown adipose tissue (BAT) activity contributes to weight loss induced by chronic subcutaneous treatment with the GLP-1R agonist, liraglutide, in a model of diet-induced obesity. METHODS: Metabolic phenotyping was performed using indirect calorimetry in wild-type (WT) and Glp1r-knockout (KO) mice during chow and HFD feeding at room temperature and at thermoneutrality. In a separate study, we investigated the contribution of BAT thermogenic capacity to the weight lowering effect induced by GLP-1 mimetics by administering liraglutide (10 or 30 nmol kg(-1) day(-1) s.c.) to diet-induced obese (DIO) mice for 6 or 4 weeks, respectively. In both studies, animals were subjected to a noradrenaline (norepinephrine)-stimulated oxygen consumption [Formula: see text] test. RESULTS: At thermoneutrality, HFD-fed Glp1r-KO mice had similar energy expenditure (EE) compared with HFD-fed WT controls. However, HFD-fed Glp1r-KO mice exhibited relatively less EE when housed at a cooler standard room temperature, and had relatively lower [Formula: see text] in response to a noradrenaline challenge, which is consistent with impaired BAT thermogenic capacity. In contrast to the loss of function model, chronic peripheral liraglutide treatment did not increase BAT activity as determined by noradrenaline-stimulated [Formula: see text] and BAT gene expression. CONCLUSIONS/INTERPRETATION: These data suggest that although endogenous GLP-1R signalling contributes to increased BAT thermogenesis, this mechanism does not play a significant role in the food intake-independent body weight lowering effect of the GLP-1 mimetic liraglutide in DIO mice.

Duodenal nutrient exclusion improves metabolic syndrome and stimulates villus hyperplasia.

OBJECTIVE: Surgical interventions that prevent nutrient exposure to the duodenum are among the most successful treatments for obesity and diabetes. However, these interventions are highly invasive, irreversible and often carry significant risk. The duodenal-endoluminal sleeve (DES) is a flexible tube that acts as a barrier to nutrient-tissue interaction along the duodenum. We implanted this device in Zucker Diabetic Fatty (ZDF) rats to gain greater understanding of duodenal nutrient exclusion on glucose homeostasis. DESIGN: ZDF rats were randomised to four groups: Naive, sham ad libitum, sham pair-fed, and DES implanted. Food intake, body weight (BW) and body composition were measured for 28 days postoperatively. Glucose, lipid and bile acid metabolism were evaluated, as well as histological assessment of the upper intestine. RESULTS: DES implantation induced a sustained decrease in BW throughout the study that was matched by pair-fed sham animals. Decreased BW resulted from loss of fat, but not lean mass. DES rats were also found to be more glucose tolerant than either ad libitum-fed or pair-fed sham controls, suggesting fat mass independent metabolic benefits. DES also reduced circulating triglyceride and glycerol levels while increasing circulating bile acids. Interestingly, DES stimulated a considerable increase in villus length throughout the upper intestine, which may contribute to metabolic improvements. CONCLUSIONS: Our preclinical results validate DES as a promising therapeutic approach to diabetes and obesity, which offers reversibility, low risk, low invasiveness and triple benefits including fat mass loss, glucose and lipid metabolism improvement which mechanistically may involve increased villus growth in the upper gut.

Hormones and diet, but not body weight, control hypothalamic microglial activity.

The arcuate nucleus (ARC) of the hypothalamus plays a key role in sensing metabolic feedback and regulating energy homeostasis. Recent studies revealed activation of microglia in mice with high-fat diet (HFD)-induced obesity (DIO), suggesting a potential pathophysiological role for inflammatory processes within the hypothalamus. To further investigate the metabolic causes and molecular underpinnings of such glial activation, we analyzed the microglial activity in wild-type (WT), monogenic obese ob/ob (leptin deficient), db/db (leptin-receptor mutation), and Type-4 melanocortin receptor knockout (MC4R KO) mice on either a HFD or on standardized chow (SC) diet. Following HFD exposure, we observed a significant increase in the total number of ARC microglia, immunoreactivity of ionized calcium binding adaptor molecule 1 (iba1-ir), cluster of differentiation 68 (CD68-ir), and ramification of microglial processes. The ob/ob mice had significantly less iba1-ir and ramifications. Leptin replacement rescued these phenomena. The db/db mice had similar iba1-ir comparable with WT mice but had significantly lower CD68-ir and more ramifications than WT mice. After 2 weeks of HFD, ob/ob mice showed an increase of iba1-ir, and db/db mice showed increase of CD68-ir. Obese MC4R KO mice fed a SC diet had comparable iba1-ir and CD68-ir with WT mice but had significantly more ramifications than WT mice. Intriguingly, treatment of DIO mice with glucagon-like peptide-1 receptor agonists reduced microglial activation independent of body weight. Our results show that diet type, adipokines, and gut signals, but not body weight, affect the presence and activity levels of hypothalamic microglia in obesity.

A long-acting LEAP2 analog reduces hepatic steatosis and inflammation and causes marked weight loss in mice.

OBJECTIVE: The number of individuals affected by metabolic dysfunction associated fatty liver disease [1] is on the rise, yet hormonal contributors to the condition remain incompletely described and only a single FDA-approved treatment is available. Some studies suggest that the hormones ghrelin and LEAP2, which act as agonist and antagonist/inverse agonist, respectively, for the G protein coupled receptor GHSR, may influence the development of MAFLD. For instance, ghrelin increases hepatic fat whereas synthetic GHSR antagonists do the opposite. Also, hepatic steatosis is less prominent in standard chow-fed ghrelin-KO mice but more prominent in 42% high-fat diet-fed female LEAP2-KO mice. METHODS: Here, we sought to determine the therapeutic potential of a long-acting LEAP2 analog (LA-LEAP2) to treat MAFLD in mice. LEAP2-KO and wild-type littermate mice were fed a Gubra-Amylin-NASH (GAN) diet for 10 or 40 wks, with some randomized to an additional 28 or 10 days of GAN diet, respectively, while treated with LA-LEAP2 vs Vehicle. Various metabolic parameters were followed and biochemical and histological assessments of MAFLD were made. RESULTS: Among the most notable metabolic effects, daily LA-LEAP2 administration to both LEAP2-KO and wild-type littermates during the final 4 wks of a 14 wk-long GAN diet challenge markedly reduced liver weight, hepatic triglycerides, plasma ALT, hepatic microvesicular steatosis, hepatic lobular inflammation, NASH activity scores, and prevalence of higher-grade fibrosis. These changes were accompanied by prominent reductions in body weight, without effects on food intake, and reduced plasma total cholesterol. Daily LA-LEAP2 administration during the final 10 d of a 41.5 wk-long GAN diet challenge also reduced body weight, plasma ALT, and plasma total cholesterol in LEAP2-KO and wild-type littermates and prevalence of higher grade fibrosis in LEAP2-KO mice. CONCLUSIONS: Administration of LA-LEAP2 to mice fed a MAFLD-prone diet markedly improves several facets of MAFLD, including hepatic steatosis, hepatic lobular inflammation, higher-grade hepatic fibrosis, and transaminitis. These changes are accompanied by prominent reductions in body weight and lowered plasma total cholesterol. Taken together, these data suggest that LEAP2 analogs such as LA-LEAP2 hold promise for the treatment of MAFLD and obesity.

Characterization of genetic variants of GIPR reveals a contribution of ß-arrestin to metabolic phenotypes.

Incretin-based therapies are highly successful in combatting obesity and type 2 diabetes1. Yet both activation and inhibition of the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) in combination with glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) activation have resulted in similar clinical outcomes, as demonstrated by the GIPR-GLP-1R co-agonist tirzepatide2 and AMG-133 (ref. 3) combining GIPR antagonism with GLP-1R agonism. This underlines the importance of a better understanding of the GIP system. Here we show the necessity of ß-arrestin recruitment for GIPR function, by combining in vitro pharmacological characterization of 47 GIPR variants with burden testing of clinical phenotypes and in vivo studies. Burden testing of variants with distinct ligand-binding capacity, Gs activation (cyclic adenosine monophosphate production) and ß-arrestin 2 recruitment and internalization shows that unlike variants solely impaired in Gs signalling, variants impaired in both Gs and ß-arrestin 2 recruitment contribute to lower adiposity-related traits. Endosomal Gs-mediated signalling of the variants shows a ß-arrestin dependency and genetic ablation of ß-arrestin 2 impairs cyclic adenosine monophosphate production and decreases GIP efficacy on glucose control in male mice. This study highlights a crucial impact of ß-arrestins in regulating GIPR signalling and overall preservation of biological activity that may facilitate new developments in therapeutic targeting of the GIPR system.

MLK3 promotes metabolic dysfunction induced by saturated fatty acid-enriched diet.

Saturated fatty acids activate the c-Jun NH2-terminal kinase (JNK) pathway, resulting in chronic low-grade inflammation and the development of insulin resistance. Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that mediates JNK activation in response to saturated fatty acids in vitro; however, the exact mechanism for diet-induced JNK activation in vivo is not known. Here, we have used MLK3-deficient mice to examine the role of MLK3 in a saturated-fat diet model of obesity. MLK3-KO mice fed a high-fat diet enriched in medium-chain saturated fatty acids for 16 wk had decreased body fat compared with wild-type (WT) mice due to increased energy expenditure independently of food consumption and physical activity. Moreover, MLK3 deficiency attenuated palmitate-induced JNK activation and M1 polarization in bone marrow-derived macrophages in vitro, and obesity induced JNK activation, macrophage infiltration into adipose tissue, and expression of proinflammatory cytokines in vivo. In addition, loss of MLK3 improved insulin resistance and decreased hepatic steatosis. Together, these data demonstrate that MLK3 promotes saturated fatty acid-induced JNK activation in vivo and diet-induced metabolic dysfunction.

Synaptic input organization of the melanocortin system predicts diet-induced hypothalamic reactive gliosis and obesity.

The neuronal circuits involved in the regulation of feeding behavior and energy expenditure are soft-wired, reflecting the relative activity of the postsynaptic neuronal system, including the anorexigenic proopiomelanocortin (POMC)-expressing cells of the arcuate nucleus. We analyzed the synaptic input organization of the melanocortin system in lean rats that were vulnerable (DIO) or resistant (DR) to diet-induced obesity. We found a distinct difference in the quantitative and qualitative synaptology of POMC cells between DIO and DR animals, with a significantly greater number of inhibitory inputs in the POMC neurons in DIO rats compared with DR rats. When exposed to a high-fat diet (HFD), the POMC cells of DIO animals lost synapses, whereas those of DR rats recruited connections. In both DIO rats and mice, the HFD-triggered loss of synapses on POMC neurons was associated with increased glial ensheathment of the POMC perikarya. The altered synaptic organization of HFD-fed animals promoted increased POMC tone and a decrease in the stimulatory connections onto the neighboring neuropeptide Y (NPY) cells. Exposure to HFD was associated with reactive gliosis, and this affected the structure of the blood-brain barrier such that the POMC and NPY cell bodies and dendrites became less accessible to blood vessels. Taken together, these data suggest that consumption of an HFD has a major impact on the cytoarchitecture of the arcuate nucleus in vulnerable subjects, with changes that might be irreversible due to reactive gliosis.

The incretin co-agonist tirzepatide requires GIPR for hormone secretion from human islets.

The incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) mediate insulin responses that are proportionate to nutrient intake to facilitate glucose tolerance1. The GLP-1 receptor (GLP-1R) is an established drug target for the treatment of diabetes and obesity2, whereas the therapeutic potential of the GIP receptor (GIPR) is a subject of debate. Tirzepatide is an agonist at both the GIPR and GLP-1R and is a highly effective treatment for type 2 diabetes and obesity3,4. However, although tirzepatide activates GIPR in cell lines and mouse models, it is not clear whether or how dual agonism contributes to its therapeutic benefit. Islet beta cells express both the GLP-1R and the GIPR, and insulin secretion is an established mechanism by which incretin agonists improve glycemic control5. Here, we show that in mouse islets, tirzepatide stimulates insulin secretion predominantly through the GLP-1R, owing to reduced potency at the mouse GIPR. However, in human islets, antagonizing GIPR activity consistently decreases the insulin response to tirzepatide. Moreover, tirzepatide enhances glucagon secretion and somatostatin secretion in human islets. These data demonstrate that tirzepatide stimulates islet hormone secretion from human islets through both incretin receptors.

Ghrelin-induced adiposity is independent of orexigenic effects.

Ghrelin is a hormone produced predominantly by the stomach that targets a number of specific areas in the central nervous system to promote a positive energy balance by increasing food intake and energy storage. In that respect, similarities exist with the effects of consuming a high-fat diet (HFD), which also increases caloric intake and the amount of stored calories. We determined whether the effects of ghrelin on feeding and adiposity are influenced by the exposure to an HFD. Chronic intracerebroventricular ghrelin (2.5 nmol/d) increased feeding in lean rats fed a low-fat control diet (CD) [192 ± 5 g (ghrelin+CD) vs. 152 ± 5 g (control i.c.v. saline+CD), P<0.001], but the combination of ghrelin plus HFD did not result in significantly greater hyperphagia [150 ± 7 g (ghrelin+HFD) vs. 136 ± 4 g (saline+HFD)]. Despite failing to increase food intake in rats fed the HFD, ghrelin nonetheless increased adiposity [fat mass increase of 14 ± 2 g (ghrelin+HFD) vs. 1 ± 1 g (saline+HFD), P<0.001] up-regulating the gene expression of lipogenic enzymes in white adipose tissue. Our findings demonstrate that factors associated with high-fat feeding functionally interact with pathways regulating the effect of ghrelin on food intake. We conclude that ghrelin's central effects on nutrient intake and nutrient partitioning can be separated and suggest an opportunity to identify respective independent neuronal pathways.

Restoration of leptin responsiveness in diet-induced obese mice using an optimized leptin analog in combination with exendin-4 or FGF21.

The identification of leptin as a mediator of body weight regulation provided much initial excitement for the treatment of obesity. Unfortunately, leptin monotherapy is insufficient in reversing obesity in rodents or humans. Recent findings suggest that amylin is able to restore leptin sensitivity and when used in combination with leptin enhances body weight loss in obese rodents and humans. However, as the uniqueness of this combination therapy remains unclear, we assessed whether co-administration of leptin with other weight loss-inducing hormones equally restores leptin responsiveness in diet-induced obese (DIO) mice. Accordingly, we report here the design and characterization of a series of site-specifically enhanced leptin analogs of high potency and sustained action that, when administered in combination with exendin-4 or fibroblast growth factor 21 (FGF21), restores leptin responsiveness in DIO mice after an initial body weight loss of 30%. Using either combination, body weight loss was enhanced compared with either exendin-4 or FGF21 monotherapy, and leptin alone was sufficient to maintain the reduced body weight. In contrast, leptin monotherapy proved ineffective when identical weight loss was induced by caloric restriction alone over a comparable time. Accordingly, we find that a hypothalamic counter-regulatory response to weight loss, assessed using changes in hypothalamic agouti related peptide (AgRP) levels, is triggered by caloric restriction, but blunted by treatment with exendin-4. We conclude that leptin re-sensitization requires pharmacotherapy but does not appear to be restricted to a unique signaling pathway. Our findings provide preclinical evidence that high activity, long-acting leptin analogs are additively efficacious when used in combination with other weight-lowering agents.

Neural regulation of cholesterol metabolism.

PURPOSE OF REVIEW: The increasing incidence of obesity and diabetes worldwide are critical risk factors for the development of cardiovascular disease. Although the role of the central nervous system (CNS) in the control of fat mass and glucose metabolism has been studied in detail, less is known about the contribution of neural-derived signals in the development of systemic dyslipidemia. In this review we summarize and analyze evidence suggesting a specific role of the CNS in the control of systemic cholesterol metabolism and circulating plasma lipids levels. RECENT FINDINGS: Although early reports based in lesions or electrical stimulation suggested a role for CNS-derived signals in the development of dyslipidemia, more recent findings have confirmed the involvement of specific neural pathways critical for the neuroendocrine control of cholesterol metabolism and plasma lipid levels. SUMMARY: The identification of the pathways targeted by the CNS to control plasma lipid levels could offer alternative targets to create efficient novel therapies for the treatment of several metabolic syndrome components including dyslipidemia.

Discovery of a potent GIPR peptide antagonist that is effective in rodent and human systems.

OBJECTIVE: Glucose-dependent insulinotropic polypeptide (GIP) is one of the two major incretin factors that regulate metabolic homeostasis. Genetic ablation of its receptor (GIPR) in mice confers protection against diet-induced obesity (DIO), while GIPR neutralizing antibodies produce additive weight reduction when combined with GLP-1R agonists in preclinical models and clinical trials. Conversely, GIPR agonists have been shown to promote weight loss in rodents, while dual GLP-1R/GIPR agonists have proven superior to GLP-1R monoagonists for weight reduction in clinical trials. We sought to develop a long-acting, specific GIPR peptide antagonist as a tool compound suitable for investigating GIPR pharmacology in both rodent and human systems. METHODS: We report a structure-activity relationship of GIPR peptide antagonists based on the human and mouse GIP sequences with fatty acid-based protraction. We assessed these compounds in vitro, in vivo in DIO mice, and ex vivo in islets from human donors. RESULTS: We report the discovery of a GIP(5-31) palmitoylated analogue, [Nα-Ac, L14, R18, E21] hGIP(5-31)-K11 (γE-C16), which potently inhibits in vitro GIP-mediated cAMP generation at both the hGIPR and mGIPR. In vivo, this peptide effectively blocks GIP-mediated reductions in glycemia in response to exogenous and endogenous GIP and displays a circulating pharmacokinetic profile amenable for once-daily dosing in rodents. Co-administration with the GLP-1R agonist semaglutide and this GIPR peptide antagonist potentiates weight loss compared to semaglutide alone. Finally, this antagonist inhibits GIP- but not GLP-1-stimulated insulin secretion in intact human islets. CONCLUSIONS: Our work demonstrates the discovery of a potent, specific, and long-acting GIPR peptide antagonist that effectively blocks GIP action in vitro, ex vivo in human islets, and in vivo in mice while producing additive weight-loss when combined with a GLP-1R agonist in DIO mice.

Next generation GLP-1/GIP/glucagon triple agonists normalize body weight in obese mice.

OBJECTIVE: Pharmacological strategies that engage multiple mechanisms-of-action have demonstrated synergistic benefits for metabolic disease in preclinical models. One approach, concurrent activation of the glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and glucagon (Gcg) receptors (i.e. triagonism), combines the anorectic and insulinotropic activities of GLP-1 and GIP with the energy expenditure effect of glucagon. While the efficacy of triagonism in preclinical models is known, the relative contribution of GcgR activation remains unassessed. This work aims to addresses that central question. METHODS: Herein, we detail the design of unimolecular peptide triagonists with an empirically optimized receptor potency ratio. These optimized peptide triagonists employ a protraction strategy permitting once-weekly human dosing. Additionally, we assess the effects of these peptides on weight-reduction, food intake, glucose control, and energy expenditure in an established DIO mouse model compared to clinically relevant GLP-1R agonists (e.g. semaglutide) and dual GLP-1R/GIPR agonists (e.g. tirzepatide). RESULTS: Optimized triagonists normalize body weight in DIO mice and enhance energy expenditure in a manner superior to that of GLP-1R mono-agonists and GLP-1R/GIPR co-agonists. CONCLUSIONS: These pre-clinical data suggest unimolecular poly-pharmacology as an effective means to target multiple mechanisms contributing to obesity and further implicate GcgR activation as the differentiating factor between incretin receptor mono- or dual-agonists and triagonists.

GLP-1-mediated delivery of tesaglitazar improves obesity and glucose metabolism in male mice.

Dual agonists activating the peroxisome proliferator-activated receptors alpha and gamma (PPARɑ/ɣ) have beneficial effects on glucose and lipid metabolism in patients with type 2 diabetes, but their development was discontinued due to potential adverse effects. Here we report the design and preclinical evaluation of a molecule that covalently links the PPARɑ/ɣ dual-agonist tesaglitazar to a GLP-1 receptor agonist (GLP-1RA) to allow for GLP-1R-dependent cellular delivery of tesaglitazar. GLP-1RA/tesaglitazar does not differ from the pharmacokinetically matched GLP-1RA in GLP-1R signalling, but shows GLP-1R-dependent PPARɣ-retinoic acid receptor heterodimerization and enhanced improvements of body weight, food intake and glucose metabolism relative to the GLP-1RA or tesaglitazar alone in obese male mice. The conjugate fails to affect body weight and glucose metabolism in GLP-1R knockout mice and shows preserved effects in obese mice at subthreshold doses for the GLP-1RA and tesaglitazar. Liquid chromatography-mass spectrometry-based proteomics identified PPAR regulated proteins in the hypothalamus that are acutely upregulated by GLP-1RA/tesaglitazar. Our data show that GLP-1RA/tesaglitazar improves glucose control with superior efficacy to the GLP-1RA or tesaglitazar alone and suggest that this conjugate might hold therapeutic value to acutely treat hyperglycaemia and insulin resistance.

CNS leptin action modulates immune response and survival in sepsis.

Sepsis describes a complex clinical syndrome that results from an infection, setting off a cascade of systemic inflammatory responses that can lead to multiple organ failure and death. Leptin is a 16 kDa adipokine that, among its multiple known effects, is involved in regulating immune function. Here we demonstrate that leptin deficiency in ob/ob mice leads to higher mortality and more severe organ damage in a standard model of sepsis in mice [cecal ligation and puncture (CLP)]. Moreover, systemic leptin replacement improved the immune response to CLP. Based on the molecular mechanisms of leptin regulation of energy metabolism and reproductive function, we hypothesized that leptin acts in the CNS to efficiently coordinate peripheral immune defense in sepsis. We now report that leptin signaling in the brain increases survival during sepsis in leptin-deficient as well as in wild-type mice and that endogenous CNS leptin action is required for an adequate systemic immune response. These findings reveal the existence of a relevant neuroendocrine control of systemic immune defense and suggest a possible therapeutic potential for leptin analogs in infectious disease.

Sleeve gastrectomy induces loss of weight and fat mass in obese rats, but does not affect leptin sensitivity.

BACKGROUND & AIMS: Surgical intervention produces sustainable weight loss and metabolic improvement in obese individuals. Vertical sleeve gastrectomy (VSG) produces dramatic, sustained weight loss; we investigated whether these changes result from improved sensitivity to leptin. METHODS: VSG was performed in Long-Evans rats with diet-induced obesity. Naïve or sham-operated rats, fed either ad libitum or pair-fed with the VSG group, were used as controls. Following surgery, body weights and food intake were monitored. We investigated energy expenditure, meal patterns, leptin sensitivity, and expression of pro-opiomelanocortin/agouti-related peptide/neuropeptide Y in the hypothalamus of the rats. RESULTS: We observed sustained losses in weight and body fat in male and female rats after VSG. Weight loss persisted after the disappearance of a transient, postsurgical food intake reduction. Resting energy expenditure was similar between control and VSG rats. VSG rats maintained their reduced body weights. However, they responded to a chronic food restriction challenge by overeating, which resulted in prerestriction, rather than pre-VSG, body weights. Consistent with lower adiposity, VSG decreased plasma leptin levels. Although VSG slightly improved leptin's anorectic action, the response was comparable to that observed in controls matched for adiposity by caloric restriction. Changes in hypothalamic neuropeptide expression were consistent with the lower body weight and lower leptin levels but cannot account for the sustained weight loss. CONCLUSIONS: VSG causes sustained reduction in body weight, which results from loss of fat mass. The maintenance of weight loss observed did not result from changes in sensitivity to leptin.

A new glucagon and GLP-1 co-agonist eliminates obesity in rodents.

We report the efficacy of a new peptide with agonism at the glucagon and GLP-1 receptors that has potent, sustained satiation-inducing and lipolytic effects. Selective chemical modification to glucagon resulted in a loss of specificity, with minimal change to inherent activity. The structural basis for the co-agonism appears to be a combination of local positional interactions and a change in secondary structure. Two co-agonist peptides differing from each other only in their level of glucagon receptor agonism were studied in rodent obesity models. Administration of PEGylated peptides once per week normalized adiposity and glucose tolerance in diet-induced obese mice. Reduction of body weight was achieved by a loss of body fat resulting from decreased food intake and increased energy expenditure. These preclinical studies indicate that when full GLP-1 agonism is augmented with an appropriate degree of glucagon receptor activation, body fat reduction can be substantially enhanced without any overt adverse effects.