Oxyntomodulin (OXM) is a peptide secreted from the L cells of the gut following nutrient ingestion. OXM is a dual agonist of the glucagon-like peptide-1 receptor (GLP1R) and the glucagon receptor (GCGR) combining the effects of GLP1 and glucagon to act as a potentially more effective treatment for obesity than GLP1R agonists. Injections of OXM in humans cause a significant reduction in weight and appetite, as well as an increase in energy expenditure. Activation of GCGR is classically associated with an elevation in glucose levels, which would be deleterious in patients with T2DM, but the antidiabetic properties of GLP1R agonism would be expected to counteract this effect. Indeed, OXM administration improved glucose tolerance in diet-induced obese mice. Thus, dual agonists of the GCGR and GLP1R represent a new therapeutic approach for diabetes and obesity with the potential for enhanced weight loss and improvement in glycemic control beyond those of GLP1R agonists.
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- Abstract: Diabetes x
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S J Brandt, M Kleinert, M H Tschöp, and T D Müller
Obesity is a worldwide pandemic, which can be fatal for the most extremely affected individuals. Lifestyle interventions such as diet and exercise are largely ineffective and current anti-obesity medications offer little in the way of significant or sustained weight loss. Bariatric surgery is effective, but largely restricted to only a small subset of extremely obese patients. While the hormonal factors mediating sustained weight loss and remission of diabetes by bariatric surgery remain elusive, a new class of polypharmacological drugs shows potential to shrink the gap in efficacy between a surgery and pharmacology. In essence, this new class of drugs combines the beneficial effects of several independent hormones into a single entity, thereby combining their metabolic efficacy to improve systems metabolism. Such unimolecular drugs include single molecules with agonism at the receptors for glucagon, glucagon-like peptide 1 and the glucose-dependent insulinotropic polypeptide. In preclinical studies, these specially tailored multiagonists outperform both their mono-agonist components and current best in class anti-obesity medications. While clinical trials and vigorous safety analyses are ongoing, these drugs are poised to have a transformative effect in anti-obesity therapy and might hopefully lead the way to a new era in weight-loss pharmacology.
Michael J F Newson, Emma M Roberts, George R Pope, Stephen J Lolait, and Anne-Marie O'Carroll
The apelinergic system has a widespread expression in the central nervous system (CNS) including the paraventricular nucleus, supraoptic nucleus and median eminence, and isolated cells of the anterior lobe of the pituitary. This pattern of expression in hypothalamic nuclei known to contain corticotrophin-releasing factor (CRF) and vasopressin (AVP) and to co-ordinate endocrine responses to stress has generated interest in a role for apelin in the modulation of stress, perhaps via the regulation of hormone release from the pituitary. In this study, to determine whether apelin has a central role in the regulation of CRF and AVP neurones, we investigated the effect of i.c.v. administration of pGlu-apelin-13 on neuroendocrine function in male mice pre-treated with the CRF receptor antagonist, α-helical CRF9–41, and in mice-lacking functional AVP V1b receptors (V1bR KO). Administration of pGlu-apelin-13 (1 mg/kg i.c.v.) resulted in significant increases in plasma ACTH and corticosterone (CORT), which were significantly reduced by pre-treatment with α-helical CRF9–41, indicating the involvement of a CRF-dependent mechanism. Additionally, pGlu-apelin-13-mediated increases in both plasma ACTH and CORT were significantly attenuated in V1bR KO animals when compared with wild-type controls, indicating a role for the vasopressinergic system in the regulation of the effects of apelin on neuroendocrine function. Together, these data confirm that the in vivo effects of apelin on hypothalamic–pituitary–adrenal neuroendocrine function appear to be mediated through both CRF- and AVP-dependent mechanisms.
Emma Castrique, Marta Fernandez-Fuente, Paul Le Tissier, Andy Herman, and Andy Levy
In rats, a shift from somatotroph dominance to lactotroph dominance during pregnancy and lactation is well reported. Somatotroph to lactotroph transdifferentiation and increased lactotroph mitotic activity are believed to account for this and associated pituitary hypertrophy. A combination of cell death and transdifferentiation away from the lactotroph phenotype has been reported to restore non-pregnant pituitary proportions after weaning. To attempt to confirm that a similar process occurs in mice, we generated and used a transgenic reporter mouse model (prolactin (PRL)-Cre/ROSA26-expression of yellow fluorescent protein (EYFP)) in which PRL promoter activity at any time resulted in permanent, stable, and highly specific EYFP. Triple immunochemistry for GH, PRL, and EYFP was used to quantify EYFP+ve, PRL−ve, and GH+ve cell populations during pregnancy and lactation, and for up to 3 weeks after weaning, and concurrent changes in cell size were estimated. At all stages, the EYFP reporter was expressed in 80% of the lactotrophs, but in fewer than 1% of other pituitary cell types, indicating that transdifferentiation from those lactotrophs where reporter expression was activated is extremely rare. Contrary to expectations, no increase in the lactotroph/somatotroph ratio was seen during pregnancy and lactation, whether assessed by immunochemistry for the reporter or PRL: findings confirmed by PRL immunochemistry in non-transgenic mice. Mammosomatotrophs were rarely encountered at the age group studied. Individual EYFP+ve cell volumes increased significantly by mid-lactation compared with virgin animals. This, in combination with a modest and non-cell type-specific estrogen-induced increase in mitotic activity, could account for pregnancy-induced changes in overall pituitary size.
Eun Young Lee, Shuji Kaneko, Promsuk Jutabha, Xilin Zhang, Susumu Seino, Takahito Jomori, Naohiko Anzai, and Takashi Miki
Oral ingestion of carbohydrate triggers glucagon-like peptide 1 (GLP1) secretion, but the molecular mechanism remains elusive. By measuring GLP1 concentrations in murine portal vein, we found that the ATP-sensitive K+ (KATP) channel is not essential for glucose-induced GLP1 secretion from enteroendocrine L cells, while the sodium-glucose co-transporter 1 (SGLT1) is required, at least in the early phase (5 min) of secretion. By contrast, co-administration of the α-glucosidase inhibitor (α-GI) miglitol plus maltose evoked late-phase secretion in a glucose transporter 2-dependent manner. We found that GLP1 secretion induced by miglitol plus maltose was significantly higher than that by another α-GI, acarbose, plus maltose, despite the fact that acarbose inhibits maltase more potently than miglitol. As miglitol activates SGLT3, we compared the effects of miglitol on GLP1 secretion with those of acarbose, which failed to depolarize the Xenopus laevis oocytes expressing human SGLT3. Oral administration of miglitol activated duodenal enterochromaffin (EC) cells as assessed by immunostaining of phosphorylated calcium–calmodulin kinase 2 (phospho-CaMK2). In contrast, acarbose activated much fewer enteroendocrine cells, having only modest phospho-CaMK2 immunoreactivity. Single administration of miglitol triggered no GLP1 secretion, and GLP1 secretion by miglitol plus maltose was significantly attenuated by atropine pretreatment, suggesting regulation via vagal nerve. Thus, while α-GIs generally delay carbohydrate absorption and potentiate GLP1 secretion, miglitol also activates duodenal EC cells, possibly via SGLT3, and potentiates GLP1 secretion through the parasympathetic nervous system.
David E Maridas, Victoria E DeMambro, Phuong T Le, Kenichi Nagano, Roland Baron, Subburaman Mohan, and Clifford J Rosen
Insulin-like growth factor-1 (IGF-1) and its binding proteins are critical mediators of skeletal growth. Insulin-like growth factor-binding protein 4 (IGFBP-4) is highly expressed in osteoblasts and inhibits IGF-1 actions in vitro. Yet, in vivo studies suggest that it could potentiate IGF-1 and IGF-2 actions. In this study, we hypothesized that IGFBP-4 might potentiate the actions of IGF-1 on the skeleton. To test this, we comprehensively studied 8- and 16-week-old Igfbp4−/− mice. Both male and female adult Igfbp4−/− mice had marked growth retardation with reductions in body weight, body and femur lengths, fat proportion and lean mass at 8 and 16 weeks. Marked reductions in aBMD and aBMC were observed in 16-week-old Igfbp4−/− females, but not in males. Femoral trabecular BV/TV and thickness, cortical fraction and thickness in 16-week-old Igfbp4−/− females were significantly reduced. However, surprisingly, males had significantly more trabeculae with higher connectivity density than controls. Concordantly, histomorphometry revealed higher bone resorption and lower bone formation in Igfbp4−/− females. In contrast, Igfbp4−/− males had lower mineralized surface/bone surface. Femoral expression of Sost and circulating levels of sclerostin were reduced but only in Igfbp4−/− males. Bone marrow stromal cultures from mutants showed increased osteogenesis, whereas osteoclastogenesis was markedly increased in cells from Igfbp4−/− females but decreased in males. In sum, our results indicate that loss of Igfbp4 affects mesenchymal stromal cell differentiation, regulates osteoclastogenesis and influences both skeletal development and adult bone maintenance. Thus, IGFBP-4 modulates the skeleton in a gender-specific manner, acting as both a cell autonomous and cell non-autonomous factor.
Shuang-Xia Zhao, Shanli Tsui, Anthony Cheung, Raymond S Douglas, Terry J Smith, and J Paul Banga
The TSH receptor (TSHR) is the critical target for antibody production in Graves' disease (GD). Insulin-like growth factor 1 receptor (IGF1R) has been proposed as a second autoantigen in complications of GD such as orbitopathy. We attempted to induce orbital tissue remodeling in mice undergoing immunizations with plasmids encoding TSHR and IGF1R delivered by in vivo skeletal muscle electroporation, a procedure known to give a sustained, long-term antibody response. Female BALB/c mice were challenged with TSHR A-subunit or IGF1Rα subunit plasmid by injection and electroporation. Mice challenged with TSHR A-subunit plasmid resulted in high frequency (75%) of hyperthyroidism and thyroid-stimulating antibodies. But strikingly, immunization with TSHR A-subunit plasmid also elicited antibody to IGF1Rα subunit. Mice challenged in the same manner with IGF1Rα subunit plasmid produced strong antibody responses to IGF1R, but did not undergo any changes in phenotype. Simultaneous challenge by double antigen immunization with the two plasmids in distant anatomical sites reduced the incidence of hyperthyroidism, potentially as a consequence of antigenic competition. Thyroid glands from the TSHR A-subunit plasmid-challenged group were enlarged with patchy microscopic infiltrates. Histological analysis of the orbital tissues demonstrated moderate connective tissue fibrosis and deposition of Masson's trichrome staining material. Our findings imply that immunization with TSHR A-subunit plasmid leads to generation of IGF1R antibodies, which together with thyroid-stimulating antibodies may precipitate remodeling of orbital tissue, raising our understanding of its close association with GD.
Gisela Helfer and Qing-Feng Wu
Metabolic syndrome is a global public health problem and predisposes individuals to obesity, diabetes and cardiovascular disease. Although the underlying mechanisms remain to be elucidated, accumulating evidence has uncovered a critical role of adipokines. Chemerin, encoded by the gene Rarres2, is a newly discovered adipokine involved in inflammation, adipogenesis, angiogenesis and energy metabolism. In humans, local and circulating levels of chemerin are positively correlated with BMI and obesity-related biomarkers. In this review, we discuss both peripheral and central roles of chemerin in regulating body metabolism. In general, chemerin is upregulated in obese and diabetic animals. Previous studies by gain or loss of function show an association of chemerin with adipogenesis, glucose homeostasis, food intake and body weight. In the brain, the hypothalamus integrates peripheral afferent signals including adipokines to regulate appetite and energy homeostasis. Chemerin increases food intake in seasonal animals by acting on hypothalamic stem cells, the tanycytes. In peripheral tissues, chemerin increases cell expansion, inflammation and angiogenesis in adipose tissue, collectively resulting in adiposity. While chemerin signalling enhances insulin secretion from pancreatic islets, contradictory results have been reported on how chemerin links to obesity and insulin resistance. Given the association of chemerin with obesity comorbidities in humans, advances in translational research targeting chemerin are expected to mitigate metabolic disorders. Together, the exciting findings gathered in the last decade clearly indicate a crucial multifaceted role for chemerin in the regulation of energy balance, making it a promising candidate for urgently needed pharmacological treatment strategies for obesity.
Maayan Vatarescu, Sapir Bechor, Yulia Haim, Tal Pecht, Tanya Tarnovscki, Noa Slutsky, Ori Nov, Hagit Shapiro, Avishai Shemesh, Angel Porgador, Nava Bashan, and Assaf Rudich
Adipose tissue inflammation and dysfunction are considered central in the pathogenesis of obesity-related dysmetabolism, but their role in the rapid metabolic recovery upon obesity reversal is less well defined. We hypothesized that changes in adipose tissue endocrine and paracrine mechanisms may support the rapid improvement of obesity-induced impairment in cellular lipid handling. C57Bl-6J mice were fed ad libitum either normal chow (NC) or high-fat diet (HFF) for 10 weeks. A dietary obesity reversal group was fed HFF for 8 weeks and then switched to NC for 2 weeks (HFF→NC). Whole-body glucose homeostasis rapidly nearly normalized in the HFF→NC mice (fasting glucose and insulin fully normalized, glucose and insulin tolerance tests reversed 82% to the NC group levels). During 2 weeks of the dietary reversal, the liver was significantly cleared from ectopic fat, and functionally, glucose production from pyruvate, alanine or fructose was normalized. In contrast, adipose tissue inflammation (macrophage infiltration and polarization) largely remained as in HFF, though obesity-induced adipose tissue macrophage lipid accumulation decreased by ~50%, and adipose tissue MAP kinase hyperactivation was reversed. Ex vivo, mild changes in adipose tissue adipocytokine secretion profile were noted. These corresponded to partial or full reversal of the excess cellular lipid droplet accumulation induced by HFF adipose tissue conditioned media in hepatoma or macrophage cells, respectively. We propose that early after initiating reversal of nutritional obesity, rapid metabolic normalization largely precedes resolution of adipose tissue inflammation. Nevertheless, we demonstrate a hitherto unrecognized contribution of adipose tissue to the rapid improvement in lipid handling by the liver and by macrophages.
Lisa Rice, Charlotte E Waters, Jennifer Eccles, Helen Garside, Paula Sommer, Paul Kay, Fiona H Blackhall, Leo Zeef, Brian Telfer, Ian Stratford, Rob Clarke, Dave Singh, Adam Stevens, Anne White, and David W Ray
Glucocorticoid (GC) receptors (GRs) have profound anti-survival effects on human small cell lung cancer (SCLC). To explore the basis of these effects, protein partners for GRs were sought using a yeast two-hybrid screen. We discovered a novel gene, FAM33A, subsequently identified as a SKA1 partner and involved in mitosis, and so renamed Ska2. We produced an anti-peptide antibody that specifically recognized full-length human SKA2 to measure expression in human cell lines and tissues. There was a wide variation in expression across multiple cell lines, but none was detected in the liver cell line HepG2. A xenograft model of human SCLC had intense staining and archival tissue revealed SKA2 in several human lung and breast tumours. SKA2 was found in the cytoplasm, where it co-localized with GR, but nuclear expression of SKA2 was seen in breast tumours. SKA2 overexpression increased GC transactivation in HepG2 cells while SKA2 knockdown in A549 human lung epithelial cells decreased transactivation and prevented dexamethasone inhibition of proliferation. GC treatment decreased SKA2 protein levels in A549 cells, as did Staurosporine, phorbol ester and trichostatin A; all agents that inhibit cell proliferation. Overexpression of SKA2 potentiated the proliferative response to IGF-I exposure, and knockdown with shRNA caused cells to arrest in mitosis. SKA2 has recently been identified in HeLa S3 cells as part of a complex, which is critical for spindle checkpoint silencing and exit from mitosis. Our new data show involvement in cell proliferation and GC signalling, with implications for understanding how GCs impact on cell fate.