Susanna M. Hofmann

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.

Unimolecular Dual Incretins Maximize Metabolic Benefits in Rodents, Monkeys, and Humans

Compared to best-in-class GLP-1 mono-agonists, unimolecular co-agonists of GLP-1 and GIP with optimized pharmacokinetics enhance glycemic and metabolic benefits in mammals. “Twincretins”: Two Is Better than One Despite obesity-linked diabetes approaching worldwide epidemic proportions and the growing recognition of it as a global health challenge, safe and effective medicines have remained largely elusive. Pharmacological options targeting multiple obesity and diabetes signaling pathways offer greater therapeutic potential compared to molecules targeting a single pathway. Finan et al. now report the discovery, characterization, and translational efficacy of a single molecule that acts equally on the receptors for the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). In rodent models of obesity and diabetes, this dual incretin co-agonist more effectively lowered body fat and corrected hyperglycemia than selective mono-agonists for the GLP-1 and GIP receptors. An enhanced insulinotropic effect translated from rodents to monkeys and humans, with substantially improved levels of glycosylated hemoglobin A1c (HbA1c) in humans with type 2 diabetes. The dual incretin was engineered with selective chemical modifications to enhance pharmacokinetics. This, in combination with its inherent mixed agonism, lowered the drug dose and ameliorated the dose-limiting nausea that has plagued selective GLP-1 therapies. These dual incretin co-agonists signify a new direction for unimolecular combination therapy and represent a new class of drug candidates for the treatment of metabolic diseases. We report the discovery and translational therapeutic efficacy of a peptide with potent, balanced co-agonism at both of the receptors for the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). This unimolecular dual incretin is derived from an intermixed sequence of GLP-1 and GIP, and demonstrated enhanced antihyperglycemic and insulinotropic efficacy relative to selective GLP-1 agonists. Notably, this superior efficacy translated across rodent models of obesity and diabetes, including db/db mice and ZDF rats, to primates (cynomolgus monkeys and humans). Furthermore, this co-agonist exhibited synergism in reducing fat mass in obese rodents, whereas a selective GIP agonist demonstrated negligible weight-lowering efficacy. The unimolecular dual incretins corrected two causal mechanisms of diabesity, adiposity-induced insulin resistance and pancreatic insulin deficiency, more effectively than did selective mono-agonists. The duration of action of the unimolecular dual incretins was refined through site-specific lipidation or PEGylation to support less frequent administration. These peptides provide comparable pharmacology to the native peptides and enhanced efficacy relative to similarly modified selective GLP-1 agonists. The pharmacokinetic enhancement lessened peak drug exposure and, in combination with less dependence on GLP-1–mediated pharmacology, avoided the adverse gastrointestinal effects that typify selective GLP-1–based agonists. This discovery and validation of a balanced and high-potency dual incretin agonist enables a more physiological approach to management of diseases associated with impaired glucose tolerance.

GLP-1/Glucagon Coagonism Restores Leptin Responsiveness in Obese Mice Chronically Maintained on an Obesogenic Diet

We recently reported restoration of leptin responsiveness in diet-induced obese (DIO) mice using a pharmacologically optimized, polyethylene-glycolated (PEG)-leptin analog in combination with exendin-4 or FGF21. However, the return of leptin action required discontinuation of high-fat diet (HFD) exposure. Here we assess whether a single peptide possessing balanced coagonism at the glucagon-like peptide 1 (GLP-1) and glucagon receptors can restore leptin responsiveness in DIO mice maintained on a HFD. DIO mice were treated with PEG-GLP-1/glucagon (30 nmol/kg every fourth day) to induce an ∼15% body weight loss, upon which they were randomized to continue PEG-GLP-1/glucagon therapy or reassigned to receive supplemental daily PEG-leptin (185 nmol/kg/day). The addition of PEG-leptin to PEG-GLP-1/glucagon resulted in an ∼18% greater weight loss as compared with PEG-GLP-1/glucagon alone and was accompanied by further decreases in food intake and improved glucose and lipid metabolism. The beneficial effect of PEG-leptin supplementation occurred after an initial body weight loss similar to what we previously reported following reduced dietary fat along with PEG-leptin and exendin-4 or FGF21 cotreatment. In summary, we report that GLP-1/glucagon coagonism restores leptin responsiveness in mice maintained on a HFD, thus emphasizing the translational value of this polypharmacotherapy for the treatment of obesity and diabetes.

High-Density Lipoprotein Maintains Skeletal Muscle Function by Modulating Cellular Respiration in Mice

Background— Abnormal glucose metabolism is a central feature of disorders with increased rates of cardiovascular disease. Low levels of high-density lipoprotein (HDL) are a key predictor for cardiovascular disease. We used genetic mouse models with increased HDL levels (apolipoprotein A-I transgenic [apoA-I tg]) and reduced HDL levels (apoA-I–deficient [apoA-I ko]) to investigate whether HDL modulates mitochondrial bioenergetics in skeletal muscle. Methods and Results— ApoA-I ko mice exhibited fasting hyperglycemia and impaired glucose tolerance test compared with wild-type mice. Mitochondria isolated from gastrocnemius muscle of apoA-I ko mice displayed markedly blunted ATP synthesis. Endurance capacity during exercise exhaustion test was impaired in apoA-I ko mice. HDL directly enhanced glucose oxidation by increasing glycolysis and mitochondrial respiration rate in C2C12 muscle cells. ApoA-I tg mice exhibited lower fasting glucose levels, improved glucose tolerance test, increased lactate levels, reduced fat mass, associated with protection against age-induced decline of endurance capacity compared with wild-type mice. Circulating levels of fibroblast growth factor 21, a novel biomarker for mitochondrial respiratory chain deficiencies and inhibitor of white adipose lipolysis, were significantly reduced in apoA-I tg mice. Consistent with an increase in glucose utilization of skeletal muscle, genetically increased HDL and apoA-I levels in mice prevented high-fat diet–induced impairment of glucose homeostasis. Conclusions— In view of impaired mitochondrial function and decreased HDL levels in type 2 diabetes mellitus, our findings indicate that HDL-raising therapies may preserve muscle mitochondrial function and address key aspects of type 2 diabetes mellitus beyond cardiovascular disease.

Animal models of obesity and diabetes mellitus

More than one-third of the worldwide population is overweight or obese and therefore at risk of developing type 2 diabetes mellitus. In order to mitigate this pandemic, safer and more potent therapeutics are urgently required. This necessitates the continued use of animal models to discover, validate and optimize novel therapeutics for their safe use in humans. In order to improve the transition from bench to bedside, researchers must not only carefully select the appropriate model but also draw the right conclusions. In this Review, we consolidate the key information on the currently available animal models of obesity and diabetes and highlight the advantages, limitations and important caveats of each of these models.

Role of adipose and hepatic atypical protein kinase C lambda (PKCλ) in the development of obesity and glucose intolerance

PKCλ, an atypical member of the multifunctional protein kinase C family, has been implicated in the regulation of insulin-stimulated glucose transport and of the intracellular immune response. To further elucidate the role of this cellular regulator in diet-induced obesity and insulin resistance, we generated both liver (PKC-Alb) and adipose tissue (PKC-Ap2) specific knockout mice. Body weight, fat mass, food intake, glucose homeostasis and energy expenditure were evaluated in mice maintained on either chow or high fat diet (HFD). Ablation of PKCλ from the adipose tissue resulted in mice that were indistinguishable from their wild-type littermates. However, PKC-Alb mice were resistant to diet-induced obesity (DIO). Surprisingly this DIO resistance was not associated with either a reduction in caloric intake or an increase in energy expenditure as compared with their wild-type littermates. Furthermore, these mice displayed an improvement in glucose tolerance. When maintained on chow diet, these mice were similar to wild types in respect to body weight and fat mass, yet insulin sensitivity was impaired compared with wt littermates. Taken together these data suggest that hepatic PKCλ is modulating insulin-mediated glucose turnover and response to high fat diet feeding, thus offering a deeper understanding of an important target for anti-obesity therapeutics.

High density lipoprotein and metabolic disease: Potential benefits of restoring its functional properties.

Background High density lipoproteins (HDLs) are thought to be atheroprotective and to reduce the risk of cardiovascular disease (CVD). Besides their antioxidant, antithrombotic, anti-inflammatory, anti-apoptotic properties in the vasculature, HDLs also improve glucose metabolism in skeletal muscle. Scope of the review Herein, we review the functional role of HDLs to improve metabolic disorders, especially those involving insulin resistance and to induce regression of CVD with a particular focus on current pharmacological treatment options as well as lifestyle interventions, particularly exercise. Major conclusions Functional properties of HDLs continue to be considered important mediators to reverse metabolic dysfunction and to regress atherosclerotic cardiovascular disease. Lifestyle changes are often recommended to reduce the risk of CVD, with exercise being one of the most important of these. Understanding how exercise improves HDL function will likely lead to new approaches to battle the expanding burden of obesity and the metabolic syndrome.

Teneurin-2 (TENM2) deficiency induces UCP1 expression in differentiating human fat cells

Under certain conditions UCP1 expressing adipocytes arise in white adipose tissue depots of both mice and humans. It is still not fully understood whether these cells differentiate de novo from specific progenitor cells or if they transdifferentiate from mature white adipocytes. Performing expression pattern analysis comparing adipocyte progenitor cells from deep and subcutaneous neck adipose tissue, we recently identified teneurin-2 (TENM2) enriched in white adipocyte progenitor cells. Here we tested whether TENM2 deficiency in adipocyte progenitor cells would lead to a brown adipocyte phenotype. By targeting TENM2 in SGBS preadipocytes using siRNA, we demonstrate that TENM2 knockdown induces both UCP1 mRNA and protein expression upon adipogenic differentiation without affecting mitochondrial mass. Furthermore, TENM2 knockdown in human SGBS adipocytes resulted in increased basal and leak mitochondrial respiration. In line with our previous observation these data suggest that TENM2 deficiency in human adipocyte precursors leads to induction of brown adipocyte marker genes upon adipogenic differentiation.

Coordinated targeting of cold and nicotinic receptors synergistically improves obesity and type 2 diabetes

Pharmacological stimulation of brown adipose tissue (BAT) thermogenesis to increase energy expenditure is progressively being pursued as a viable anti-obesity strategy. Here, we report that pharmacological activation of the cold receptor transient receptor potential cation channel subfamily M member 8 (TRPM8) with agonist icilin mimics the metabolic benefits of cold exposure. In diet-induced obese (DIO) mice, treatment with icilin enhances energy expenditure, and decreases body weight, without affecting food intake. To further potentiate the thermogenic action profile of icilin and add complementary anorexigenic mechanisms, we set out to identify pharmacological partners next to icilin. To that end, we specifically targeted nicotinic acetylcholine receptor (nAChR) subtype alpha3beta4 (α3β4), which we had recognized as a potential regulator of energy homeostasis and glucose metabolism. Combinatorial targeting of TRPM8 and nAChR α3β4 by icilin and dimethylphenylpiperazinium (DMPP) orchestrates synergistic anorexic and thermogenic pathways to reverse diet-induced obesity, dyslipidemia, and glucose intolerance in DIO mice.Tobacco smoking and cold exposure are environmental modulators of human energy metabolism suppressing appetite and increasing energy expenditure, respectively. Here, the authors develop a novel pharmacological strategy in which they simultaneously mimic the metabolic benefits of both phenomena through small-molecule combination therapy, and show that this treatment improves metabolic health of obese mice.