Loss of GIPR in LEPR cells impairs glucose control by GIP and GIP:GLP-1 co-agonism without affecting body weight and food intake in mice

OBJECTIVE

The glucose-dependent insulinotropic polypeptide (GIP) decreases body weight via central GIP receptor (GIPR) signaling, but the underlying mechanisms remain largely unknown. Here, we assessed whether GIP regulates body weight and glucose control via GIPR signaling in cells that express the leptin receptor (Lepr).

METHODS

Hypothalamic, hindbrain, and pancreatic co-expression of Gipr and Lepr was assessed using single cell RNAseq analysis. Mice with deletion of Gipr in Lepr cells were generated and metabolically characterized for alterations in diet-induced obesity (DIO), glucose control and leptin sensitivity. Long-acting single- and dual-agonists at GIPR and GLP-1R were further used to assess drug effects on energy and glucose metabolism in DIO wildtype (WT) and Lepr-Gipr knock-out (KO) mice.

RESULTS

Gipr and Lepr show strong co-expression in the pancreas, but not in the hypothalamus and hindbrain. DIO Lepr-Gipr KO mice are indistinguishable from WT controls related to body weight, food intake and diet-induced leptin resistance. Acyl-GIP and the GIPR:GLP-1R co-agonist MAR709 remain fully efficacious to decrease body weight and food intake in DIO Lepr-Gipr KO mice. Consistent with the demonstration that Gipr and Lepr highly co-localize in the endocrine pancreas, including the β-cells, we find the superior glycemic effect of GIPR:GLP-1R co-agonism over single GLP-1R agonism to vanish in Lepr-Gipr KO mice.

CONCLUSIONS

GIPR signaling in cells/neurons that express the leptin receptor is not implicated in the control of body weight or food intake, but is of crucial importance for the superior glycemic effects of GIPR:GLP-1R co-agonism relative to single GLP-1R agonism.

A viral insulin-like peptide inhibits IGF-1 receptor phosphorylation and regulates IGF1R gene expression

OBJECTIVE

The insulin/IGF superfamily is conserved across vertebrates and invertebrates. Our team has identified five viruses containing genes encoding viral insulin/IGF-1 like peptides (VILPs) closely resembling human insulin and IGF-1. This study aims to characterize the impact of Mandarin fish ranavirus (MFRV) and Lymphocystis disease virus-Sa (LCDV-Sa) VILPs on the insulin/IGF system for the first time.

METHODS

We chemically synthesized single chain (sc, IGF-1 like) and double chain (dc, insulin like) forms of MFRV and LCDV-Sa VILPs. Using cell lines overexpressing either human insulin receptor isoform A (IR-A), isoform B (IR-B) or IGF-1 receptor (IGF1R), and AML12 murine hepatocytes, we characterized receptor binding, insulin/IGF signaling. We further characterized the VILPs' effects of proliferation and IGF1R and IR gene expression, and compared them to native ligands. Additionally, we performed insulin tolerance test in CB57BL/6 J mice to examine in vivo effects of VILPs on blood glucose levels. Finally, we employed cryo-electron microscopy (cryoEM) to analyze the structure of scMFRV-VILP in complex with the IGF1R ectodomain.

RESULTS

VILPs can bind to human IR and IGF1R, stimulate receptor autophosphorylation and downstream signaling pathways. Notably, scMFRV-VILP exhibited a particularly strong affinity for IGF1R, with a mere 10-fold decrease compared to human IGF-1. At high concentrations, scMFRV-VILP selectively reduced IGF-1 stimulated IGF1R autophosphorylation and Erk phosphorylation (Ras/MAPK pathway), while leaving Akt phosphorylation (PI3K/Akt pathway) unaffected, indicating a potential biased inhibitory function. Prolonged exposure to MFRV-VILP led to a significant decrease in IGF1R gene expression in IGF1R overexpressing cells and AML12 hepatocytes. Furthermore, insulin tolerance test revealed scMFRV-VILP's sustained glucose-lowering effect compared to insulin and IGF-1. Finally, cryo-EM analysis revealed that scMFRV-VILP engages with IGF1R in a manner closely resembling IGF-1 binding, resulting in a highly analogous structure.

CONCLUSIONS

This study introduces MFRV and LCDV-Sa VILPs as novel members of the insulin/IGF superfamily. Particularly, scMFRV-VILP exhibits a biased inhibitory effect on IGF1R signaling at high concentrations, selectively inhibiting IGF-1 stimulated IGF1R autophosphorylation and Erk phosphorylation, without affecting Akt phosphorylation. In addition, MFRV-VILP specifically regulates IGF-1R gene expression and IGF1R protein levels without affecting IR. CryoEM analysis confirms that scMFRV-VILP' binding to IGF1R is mirroring the interaction pattern observed with IGF-1. These findings offer valuable insights into IGF1R action and inhibition, suggesting potential applications in development of IGF1R specific inhibitors and advancing long-lasting insulins.

Hepatic mTORC2 Signaling Facilitates Acute Glucagon Receptor Enhancement of Insulin-Stimulated Glucose Homeostasis in Mice

Long-term glucagon receptor (GCGR) agonism is associated with hyperglycemia and glucose intolerance, while acute GCGR agonism enhances whole-body insulin sensitivity and hepatic AKTSer473 phosphorylation. These divergent effects establish a critical gap in knowledge surrounding GCGR action. mTOR complex 2 (mTORC2) is composed of seven proteins, including RICTOR, which dictates substrate binding and allows for targeting of AKTSer473. We used a liver-specific Rictor knockout mouse (RictorΔLiver) to investigate whether mTORC2 is necessary for insulin receptor (INSR) and GCGR cross talk. RictorΔLiver mice were characterized by impaired AKT signaling and glucose intolerance. Intriguingly, RictorΔLiver mice were also resistant to GCGR-stimulated hyperglycemia. Consistent with our prior report, GCGR agonism increased glucose infusion rate and suppressed hepatic glucose production during hyperinsulinemic-euglycemic clamp of control animals. However, these benefits to insulin sensitivity were ablated in RictorΔLiver mice. We observed diminished AKTSer473 and GSK3α/βSer21/9 phosphorylation in RictorΔLiver mice, whereas phosphorylation of AKTThr308 was unaltered in livers from clamped mice. These signaling effects were replicated in primary hepatocytes isolated from RictorΔLiver and littermate control mice, confirming cell-autonomous cross talk between GCGR and INSR pathways. In summary, our study reveals the necessity of RICTOR, and thus mTORC2, in GCGR-mediated enhancement of liver and whole-body insulin action.

Glucagon receptor signaling regulates weight loss via central KLB receptor complexes

Glucagon regulates glucose and lipid metabolism and promotes weight loss. Thus, therapeutics stimulating glucagon receptor (GCGR) signaling are promising for obesity treatment; however, the underlying mechanism(s) have yet to be fully elucidated. We previously identified that hepatic GCGR signaling increases circulating fibroblast growth factor 21 (FGF21), a potent regulator of energy balance. We reported that mice deficient for liver Fgf21 are partially resistant to GCGR-mediated weight loss, implicating FGF21 as a regulator of glucagon’s weight loss effects. FGF21 signaling requires an obligate coreceptor (β-Klotho, KLB), with expression limited to adipose tissue, liver, pancreas, and brain. We hypothesized that the GCGR-FGF21 system mediates weight loss through a central mechanism. Mice deficient for neuronal Klb exhibited a partial reduction in body weight with chronic GCGR agonism (via IUB288) compared with controls, supporting a role for central FGF21 signaling in GCGR-mediated weight loss. Substantiating these results, mice with central KLB inhibition via a pharmacological KLB antagonist, 1153, also displayed partial weight loss. Central KLB, however, is dispensable for GCGR-mediated improvements in plasma cholesterol and liver triglycerides. Together, these data suggest GCGR agonism mediates part of its weight loss properties through central KLB and has implications for future treatments of obesity and metabolic syndrome.

Spatiotemporal GLP-1 and GIP receptor signaling and trafficking/recycling dynamics induced by selected receptor mono- and dual-agonists

Objective

We assessed the spatiotemporal GLP-1 and GIP receptor signaling, trafficking, and recycling dynamics of GIPR mono-agonists, GLP-1R mono-agonists including semaglutide, and GLP-1/GIP dual-agonists MAR709 and tirzepatide.

Methods

Receptor G protein recruitment and internalization/trafficking dynamics were assessed using bioluminescence resonance energy transfer (BRET)-based technology and live-cell HILO microscopy.

Results

Relative to native and acylated GLP-1 agonists, MAR709 and tirzepatide showed preserved maximal cAMP production despite partial Gα_s recruitment paralleled by diminished ligand-induced receptor internalization at both target receptors. Despite MAR709's lower internalization rate, GLP-1R co-localization with Rab11-associated recycling endosomes was not different between MAR709 and GLP-1R specific mono-agonists.

Conclusions

Our data indicated that MAR709 and tirzepatide induce unique spatiotemporal GLP-1 and GIP receptor signaling, trafficking, and recycling dynamics relative to native peptides, semaglutide, and matched mono-agonist controls. These findings support the hypothesis that the structure of GLP-1/GIP dual-agonists confer a biased agonism that, in addition to its influence on intracellular signaling, uniquely modulates receptor trafficking.

•

GLP-1/GIP dual-agonists, MAR709 and tirzepatide, are partial effectors at multiple GLP-1R pathways, yet retain full cAMP agonism.

•

MAR709 elicits comparable GLP-1R incorporation into Rab11⁺ recycling endosomes relative to the native peptides and acyl-GLP-1.

•

At the GIPR, both dual-agonists exhibit full-agonism properties with limited receptor internalization/trafficking properties.

MS-275, a class 1 histone deacetylase inhibitor augments glucagon-like peptide-1 receptor agonism to improve glycemic control and reduce obesity in diet-induced obese mice

Given its glycemic efficacy and ability to reduce the body weight, glucagon-like peptide 1 receptor (GLP-1R) agonism has emerged as a preferred treatment for diabetes associated with obesity. We here report that a small-molecule Class 1 histone deacetylase (HDAC) inhibitor Entinostat (MS-275) enhances GLP-1R agonism to potentiate glucose-stimulated insulin secretion and decrease body weight in diet-induced obese (DIO) mice. MS-275 is not an agonist or allosteric activator of GLP-1R but enhances the sustained receptor-mediated signaling through the modulation of the expression of proteins involved in the signaling pathway. MS-275 and liraglutide combined therapy improved fasting glycemia upon short-term treatment and a chronic administration causes a reduction of obesity in DIO mice. Overall, our results emphasize the therapeutic potential of MS-275 as an adjunct to GLP-1R therapy in the treatment of diabetes and obesity.

Glucagon-Receptor Signaling Reverses Hepatic Steatosis Independent of Leptin Receptor Expression

Glucagon (GCG) is an essential regulator of glucose and lipid metabolism that also promotes weight loss. We have shown that glucagon-receptor (GCGR) signaling increases fatty acid oxidation (FAOx) in primary hepatocytes and reduces liver triglycerides in diet-induced obese (DIO) mice; however, the mechanisms underlying this aspect of GCG biology remains unclear. Investigation of hepatic GCGR targets elucidated a potent and previously unknown induction of leptin receptor (Lepr) expression. Liver leptin signaling is known to increase FAOx and decrease liver triglycerides, similar to glucagon action. Therefore, we hypothesized that glucagon increases hepatic LEPR, which is necessary for glucagon-mediated reversal of hepatic steatosis. Eight-week-old control and liver-specific LEPR-deficient mice (LeprΔliver) were placed on a high-fat diet for 12 weeks and then treated with a selective GCGR agonist (IUB288) for 14 days. Liver triglycerides and gene expression were assessed in liver tissue homogenates. Administration of IUB288 in both lean and DIO mice increased hepatic Lepr isoforms a-e in acute (4 hours) and chronic (72 hours,16 days) (P < 0.05) settings. LeprΔliver mice displayed increased hepatic triglycerides on a chow diet alone (P < 0.05), which persisted in a DIO state (P < 0.001), with no differences in body weight or composition. Surprisingly, chronic administration of IUB288 in DIO control and LeprΔliver mice reduced liver triglycerides regardless of genotype (P < 0.05). Together, these data suggest that GCGR activation induces hepatic Lepr expression and, although hepatic glucagon and leptin signaling have similar liver lipid targets, these appear to be 2 distinct pathways.

Gut Peptide Agonism in the Treatment of Obesity and Diabetes

Obesity is a global healthcare challenge that gives rise to devastating diseases such as the metabolic syndrome, type-2 diabetes (T2D), and a variety of cardiovascular diseases. The escalating prevalence of obesity has led to an increased interest in pharmacological options to counteract excess weight gain. Gastrointestinal hormones such as glucagon, amylin, and glucagon-like peptide-1 (GLP-1) are well recognized for influencing food intake and satiety, but the therapeutic potential of these native peptides is overall limited by a short half-life and an often dose-dependent appearance of unwanted effects. Recent clinical success of chemically optimized GLP-1 mimetics with improved pharmacokinetics and sustained action has propelled pharmacological interest in using bioengineered gut hormones to treat obesity and diabetes. In this article, we summarize the basic biology and signaling mechanisms of selected gut peptides and discuss how they regulate systemic energy and glucose metabolism. Subsequently, we focus on the design and evaluation of unimolecular drugs that combine the beneficial effects of selected gut hormones into a single entity to optimize the beneficial impact on systems metabolism. © 2020 American Physiological Society. Compr Physiol 10:99-124, 2020.

OR28-5 Bile Acid Sequestration Accelerates Glucagon Receptor-Mediated Body Weight Loss in Obese Mice

Glucagon, an essential regulator of glucose and lipid metabolism, also promotes weight loss. Previously, we reported that chronic glucagon receptor (GCGR) activation increased energy expenditure and plasma bile acid (BA) levels. Hepatic Farnesoid X Receptor (FXR) has been associated with this GCGR-BA pathway, and liver-specific FXR-deficient mice showed diminished response to the anti-obesity effects of GCGR agonism as compared to WT mice (Diabetes 2018 PMID: 29925501). In this study we hypothesized that BAs play an important role in GCGR-mediated weight loss. To test this, we utilized an anion-exchange BA-binding resin (BABR, cholestyramine or Questran, SANDOZ Inc.) known to reduce plasma total cholesterol, LDL, and BAs. Diet-induced obese C57BL6 mice were weight stable during the 10 d Cholestyramine pretreatment (1.5% in high fat diet 58 kcal%). Daily administration of GCGR agonist, IUB288 (10 nmol/kg, s.c.), for 14 d reduced body weight by 15%; whereas IUB288+Cholestyramine doubled this effect (30%, 2-way ANOVA Time p<0.0001; Drug p=0.019; Time x Drug interaction p<0.0001). As expected, plasma cholesterol was reduced by BABR. However, unexpectedly total BA levels were increased in plasma and feces. Thus, suggesting that cholesterol and BA excretion to feces stimulated BA synthesis and increased whole body energy expenditure. With cholestyramine treatment was increased to 3%, cholestyramine-dependent body weight loss was observed (p<0.05). Combined with daily IUB288 treatment, body weight was further reduced (Time p<0.0001; Drug p=0.0009; Time x Drug interaction p<0.0001). Together, these studies suggest a combination of BABR and GCGR agonism as a novel therapeutic approach for obesity. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

The islet-expressed Lhx1 transcription factor interacts with Islet-1 and contributes to glucose homeostasis

The LIM-homeodomain (LIM-HD) transcription factor Islet-1 (Isl1) interacts with the LIM domain-binding protein 1 (Ldb1) coregulator to control expression of key pancreatic β-cell genes. However, Ldb1 also has Isl1-independent effects, supporting that another LIM-HD factor interacts with Ldb1 to impact β-cell development and/or function. LIM homeobox 1 (Lhx1) is an Isl1-related LIM-HD transcription factor that appears to be expressed in the developing mouse pancreas and in adult islets. However, roles for this factor in the pancreas are unknown. This study aimed to determine Lhx1 interactions and elucidate gene regulatory and physiological roles in the pancreas. Co-immunoprecipitation using β-cell extracts demonstrated an interaction between Lhx1 and Isl1, and thus we hypothesized that Lhx1 and Isl1 regulate similar target genes. To test this, we employed siRNA-mediated Lhx1 knockdown in β-cell lines and discovered reduced Glp1R mRNA. Chromatin immunoprecipitation revealed Lhx1 occupancy at a domain also known to be occupied by Isl1 and Ldb1. Through development of a pancreas-wide knockout mouse model ( Lhx1^∆Panc), we demonstrate that aged Lhx1^∆Panc mice have elevated fasting blood glucose levels, altered intraperitoneal and oral glucose tolerance, and significantly upregulated glucagon, somatostatin, pancreatic polypeptide, MafB, and Arx islet mRNAs. Additionally, Lhx1^∆Panc mice exhibit significantly reduced Glp1R, an mRNA encoding the insulinotropic receptor for glucagon-like peptide 1 along with a concomitant dampened Glp1 response and mild glucose intolerance in mice challenged with oral glucose. These data are the first to reveal that the Lhx1 transcription factor contributes to normal glucose homeostasis and Glp1 responses.

Hepatic Glucagon Receptor Signaling Enhances Insulin-Stimulated Glucose Disposal in Rodents

Glucagon receptor (GCGR) agonists cause hyperglycemia but also weight loss. However, GCG-like peptide 1 receptor (GLP1R)/GCGR mixed agonists do not exhibit the diabetogenic effects often attributed to GCGR activity. Thus, we sought to investigate the effect of glucagon agonism on insulin action and glucose homeostasis. Acute GCGR agonism induced immediate hyperglycemia, followed by improved glucose tolerance and enhanced glucose-stimulated insulin secretion. Moreover, acute GCGR agonism improved insulin tolerance in a dose-dependent manner in both lean and obese mice. Improved insulin tolerance was independent of GLP1R, FGF21, and hepatic glycogenolysis. Moreover, we observed increased glucose infusion rate, disposal, uptake, and suppressed endogenous glucose production during euglycemic clamps. Mice treated with insulin and GCGR agonist had enhanced phosphorylation of hepatic AKT at Ser473; this effect was reproduced in isolated mouse primary hepatocytes and resulted in increased AKT kinase activity. These data reveal that GCGR agonism enhances glucose tolerance, in part, by augmenting insulin action, with implications for the use of GCGR agonism in therapeutic strategies for diabetes.

Metabolic syndrome and extensive adipose tissue inflammation in morbidly obese Göttingen minipigs

OBJECTIVE

The worldwide prevalence of obesity has increased to 10% in men and 15% in women and is associated with severe comorbidities such as diabetes, cancer, and cardiovascular disease. Animal models of obesity are central to experimental studies of disease mechanisms and therapeutic strategies. Diet-induced obesity (DIO) models in rodents have provided important insights into the pathophysiology of obesity and, in most instances, are the first in line for exploratory pharmacology studies. To deepen the relevance towards translation to human patients, we established a corresponding DIO model in Göttingen minipigs (GM).

METHODS

Young adult female ovariectomized GM were fed a high-fat/high-energy diet for a period of 70 weeks. The ration was calculated to meet the requirements and maintain body weight (BW) of lean adult minipigs (L-GM group) or increased stepwise to achieve an obese state (DIO-GM group). Body composition, blood parameters and intravenous glucose tolerance were determined at regular intervals. A pilot chronic treatment trial with a GLP1 receptor agonist was conducted in DIO-GM. At the end of the study, the animals were necropsied and a biobank of selected tissues was established.

RESULTS

DIO-GM developed severe subcutaneous and visceral adiposity (body fat >50% of body mass vs. 22% in L-GM), increased plasma cholesterol, triglyceride, and free fatty acid levels, insulin resistance (HOMA-IR >5 vs. 2 in L-GM), impaired glucose tolerance and increased heart rate when resting and active. However, fasting glucose concentrations stayed within normal range throughout the study. Treatment with a long-acting GLP1 receptor agonist revealed substantial reduction of food intake and body weight within four weeks, with increased drug sensitivity relative to observations in other DIO animal models. Extensive adipose tissue inflammation and adipocyte necrosis was observed in visceral, but not subcutaneous, adipose tissue of DIO-GM.

CONCLUSIONS

The Munich DIO-GM model resembles hallmarks of the human metabolic syndrome with extensive adipose tissue inflammation and adipocyte necrosis reported for the first time. DIO-GM may be used for evaluating novel treatments of obesity and associated comorbidities. They may help to identify triggers and mechanisms of fat tissue inflammation and mechanisms preventing complete metabolic decompensation despite morbid obesity.

Glucagon Receptor Signaling Regulates Energy Metabolism via Hepatic Farnesoid X Receptor and Fibroblast Growth Factor 21

Glucagon, an essential regulator of glucose and lipid metabolism, also promotes weight loss, in part through potentiation of fibroblast growth factor 21 (FGF21) secretion. However, FGF21 is only a partial mediator of metabolic actions ensuing from glucagon receptor (GCGR) activation, prompting us to search for additional pathways. Intriguingly, chronic GCGR agonism increases plasma bile acid levels. We hypothesized that GCGR agonism regulates energy metabolism, at least in part, through farnesoid X receptor (FXR). To test this hypothesis, we studied whole-body and liver-specific FXR-knockout (Fxr∆liver) mice. Chronic GCGR agonist (IUB288) administration in diet-induced obese (DIO) Gcgr, Fgf21, and Fxr whole-body or liver-specific knockout (∆liver) mice failed to reduce body weight when compared with wild-type (WT) mice. IUB288 increased energy expenditure and respiration in DIO WT mice, but not Fxr∆liver mice. GCGR agonism increased [14C]palmitate oxidation in hepatocytes isolated from WT mice in a dose-dependent manner, an effect blunted in hepatocytes from Fxr∆liver mice. Our data clearly demonstrate that control of whole-body energy expenditure by GCGR agonism requires intact FXR signaling in the liver. This heretofore-unappreciated aspect of glucagon biology has implications for the use of GCGR agonism in the therapy of metabolic disorders.

Pharmacodynamics, pharmacokinetics, safety and tolerability of the novel dual glucose-dependent insulinotropic polypeptide/glucagon-like peptide-1 agonist RG7697 after single subcutaneous administration in healthy subjects

AIMS

To evaluate the pharmacodynamics, pharmacokinetics and safety of single subcutaneous (s.c.) injection of ascending doses of RG7697, a dual glucose-dependent insulinotropic polypeptide/glucagon-like peptide-1 agonist, in healthy subjects.

METHODS

A total of 51 healthy volunteers were enrolled in this double-blind, placebo-controlled study investigating RG7697 doses ranging from 0.03 to 5 mg. Adverse events (AEs) were monitored and drug concentrations, fasting glycaemic variables, vital signs, ECG, antibody formation and routine laboratory variables were assessed. A meal tolerance test (MTT) was performed at the same time on day -1 (baseline) and day 1.

RESULTS

RG7697 was generally well tolerated in healthy participants after s.c. injections up to 3.6 mg. Tolerability was limited by gastrointestinal AEs (nausea and vomiting) at the highest dose. There was a small dose-dependent increase in heart rate. No episodes of hypoglycaemia occurred. RG7697 concentrations peaked at 2 to 4 hours post-dose with a half-life of 19 to 25 hours. During MTT, RG7697 at doses ≥1.8 mg, reduced glucose maximum plasma concentration (C_max ; -46%) without affecting overall glucose area under the curve (AUC). Its effect on insulin was more pronounced, with reductions in both C_max (-64%) and AUC (-51%). Pharmacodynamic variables were well correlated to RG7697 average plasma concentration during MTT, with IC₅₀ (average concentration required for 50% reduction) values of 49 and 24.5 ng/mL for glucose and insulin, respectively.

CONCLUSION

Single s.c. injections of RG7697 up to 3.6 mg were generally well tolerated. Evidence of glycaemic effect and pharmacokinetic profiles consistent with once-daily dosing render this drug candidate suitable to be further tested in multiple-dose clinical trials in patients with type 2 diabetes.

Pharmacodynamics, pharmacokinetics and safety of multiple ascending doses of the novel dual glucose-dependent insulinotropic polypeptide/glucagon-like peptide-1 agonist RG7697 in people with type 2 diabetes mellitus

AIMS

To investigate the pharmacodynamics, pharmacokinetics and safety of multiple ascending doses of RG7697, a dual glucose-dependent insulinotropic polypeptide/glucagon-like peptide-1 agonist, in patients with type 2 diabetes mellitus (T2D).

METHODS

A total of 56 patients with T2D received once-daily subcutaneous (s.c.) injection of RG7697 (0.25-2.5 mg) or placebo for 14 days in a randomized, double-blind, dose-escalation study. Adverse events (AEs), vital signs, ECGs and routine laboratory variables were intensively monitored. Drug concentrations, fasting glycaemic variables, 24-hour glucose profiles, glycated haemoglobin (HbA1c) and antibody formation were measured. Several meal tolerance and gastric emptying tests were performed during the study.

RESULTS

Daily s.c. injections of RG7697 were well tolerated by the majority of participants with T2D. The most frequently reported AEs with RG7697 were diarrhoea, nausea and decreased appetite. Asymptomatic events of hypoglycaemia were relatively uniformly distributed across dose groups including placebo. Pharmacokinetic steady-state was achieved within 1 week. Meaningful reductions in fasting, postprandial and 24-hour plasma glucose profile were observed at doses ≥0.75 mg, and were associated with numerical decreases in HbA1c (-0.67% [2.5-mg dose] vs -0.21% [placebo]). Decrease in postprandial insulin at doses ≥1.1 mg suggested improvement in insulin sensitivity. Minimum delay in gastric emptying and body weight reductions numerically greater than placebo (- 3.0 kg vs -0.9 kg) were seen at the highest dose of 2.5 mg.

CONCLUSIONS

Daily doses of RG7697 for 2 weeks were well tolerated by the majority of patients with T2D. Pharmacokinetic data supported once-daily dosing and pharmacodynamic effect displayed dose-dependent reductions in fasting and postprandial plasma glucose, without increasing the risk of hypoglycaemia.

Synthetic Advances in Insulin-like Peptides Enable Novel Bioactivity

Insulin is a miraculous hormone that has served a seminal role in the treatment of insulin-dependent diabetes for nearly a century. Insulin resides within in a superfamily of structurally related peptides that are distinguished by three invariant disulfide bonds that anchor the three-dimensional conformation of the hormone. The additional family members include the insulin-like growth factors (IGF) and the relaxin-related set of peptides that includes the so-called insulin-like peptides. Advances in peptide chemistry and rDNA-based synthesis have enabled the preparation of multiple insulin analogues. The translation of these methods from insulin to related peptides has presented unique challenges that pertain to differing biophysical properties and unique amino acid compositions. This Account presents a historical context for the advances in the chemical synthesis of insulin and the related peptides, with division into two general categories where disulfide bond formation is facilitated by native conformational folding or alternatively orthogonal chemical reactivity. The inherent differences in biophysical properties of insulin-like peptides, and in particular within synthetic intermediates, have constituted a central limitation to achieving high yield synthesis of properly folded peptides. Various synthetic approaches have been advanced in the past decade to successfully address this challenge. The use of chemical ligation and metastable amide bond surrogates are two of the more important synthetic advances in the preparation of high quality synthetic precursors to high potency peptides. The discovery and application of biomimetic connecting peptides simplifies proper disulfide formation and the subsequent traceless removal by chemical methods dramatically simplifies the total synthesis of virtually any two-chain insulin-like peptide. We report the application of these higher synthetic yield methodologies to the preparation of insulin-like peptides in support of exploratory in vivo studies requiring a large quantity of peptide. Tangentially, we demonstrate the use of these methods to study the relative importance of the IGF-1 connecting peptide to its biological activity. We report the translation of these finding in search of an insulin analog that might be comparably enhanced by a suitable connecting peptide for interaction with the insulin receptor, as occurs with IGF-1 and its receptor. The results identify a unique receptor site in the IGF-1 receptor from which this enhancement derives. The selective substitution of this specific IGF-1 receptor sequence into the homologous site in the insulin receptor generated a chimeric receptor that was equally capable of signaling with insulin or IGF-1. This novel receptor proved to enhance the potency of lower affinity insulin ligands when they were supplemented with the IGF-1 connecting peptide that similarly enhanced IGF-1 activity at its receptor. The chimeric insulin receptor demonstrated no further enhancement of potency for native insulin when it was similarly prepared as a single-chain analogue with a native IGF-1 connecting peptide. These results suggest a more highly evolved insulin receptor structure where the requirement for an additional structural element to achieve high potency interaction as demonstrated for IGF-1 is no longer required.

Fibroblast growth factor 21 night watch: advances and uncertainties in the field

Fibroblast growth factor (FGF) 21 belongs to a hormone-like subgroup within the FGF superfamily. The members of this subfamily, FGF19, FGF21 and FGF23, are characterized by their reduced binding affinity for heparin that enables them to be transported in the circulation and function in an endocrine manner. It is likely that FGF21 also acts in an autocrine and paracrine fashion, as multiple organs can produce this protein and its plasma concentration seems to be below the level necessary to induce a pharmacological effect. FGF21 signals via FGF receptors, but for efficient receptor engagement it requires a cofactor, membrane-spanning βKlotho (KLB). The regulation of glucose uptake in adipocytes was the initial biological activity ascribed to FGF21, but this hormone is now recognized to stimulate many other pathways in vitro and display multiple pharmacological effects in metabolically compromised animals and humans. Understanding of the precise physiology of FGF21 and its potential medicinal role has evolved exponentially over the last decade, yet numerous aspects remain to be defined and others are a source of debate. Here we provide a historical overview of the advances in FGF21 biology focusing on the uncertainties in the mechanism of action as well as the differing viewpoints relating to this intriguing protein.

Treatment of Diabetes and Obesity by Rationally Designed Peptide Agonists Functioning at Multiple Metabolic Receptors

Obesity and its comorbidities such as type 2 diabetes constitute major worldwide health threats, and the identification of an effective medical intervention has emerged as a global priority. The limited effectiveness of historical, anti-obesity treatments is commonly attributed to the complexity of the disease and the redundancy of metabolic regulatory mechanisms that sustain body weight. At the forefront of obesity research is the development of combinational drug therapies that simultaneously target multiple regulatory pathways, which promote dysfunctional metabolism. Recently, molecularly crafted unimolecular "multi-agonism" of balanced activity at 3 key receptors involved in metabolism and specifically the glucagon-like peptide (GLP)-1 receptor, glucose-dependent insulinotropic polypeptide (GIP) receptor and glucagon receptor was reported as superior to conventional monoagonist therapy. These mixed peptide agonists are designed to pharmacologically integrate the insulinotropic and anorexigenic effects of GLP-1, the thermogenic and lipolytic activities of glucagon, and the insulinotropic and insulin sensitizing properties of GIP. The molecular mechanism of these purposefully promiscuous ligands is not completely understood, however, recent studies in pancreatic beta cells point to the prospect of a complex signaling network that can magnify the signaling of multi-agonist ligands. The activation of this signalosome might explain the additional therapeutic benefit inherent to simultaneous cellular activation through multiple metabolic receptors.

FGF21 Revolutions: Recent Advances Illuminating FGF21 Biology and Medicinal Properties

The biology of fibroblast growth factor 21 (FGF21) has evolved through its first decade at a revolutionary pace with dramatic refinements in this relatively short span of time. This field is poised now with a deeper understanding of its specific physiological role, pathological ramifications for its inappropriate function, and a much-enriched context of the complex hormonal network in which it serves to regulate metabolism. As a derivative of these discoveries, the application of FGF21 as a medicinal agent has emerged with structurally optimized protein-based analogs being preclinically explored in multiple species, and, more recently, through clinical studies. These novel findings set a foundation for ongoing inquiries that structure future research into this intriguing protein.

Effect of targeted estrogen delivery using glucagon-like peptide-1 on insulin secretion, insulin sensitivity and glucose homeostasis

The female estrogen 17β-estradiol (E2) enhances pancreatic β-cell function via estrogen receptors (ERs). However, the risk of hormone dependent cancer precludes the use of general estrogen therapy as a chronic treatment for diabetes. To target E2 to β-cells without the undesirable effects of general estrogen therapy, we created fusion peptides combining active or inactive glucagon-like peptide-1 (GLP-1) and E2 in a single molecule (aGLP1-E2 and iGLP1-E2 respectively). By combining the activities of GLP-1 and E2, we envisioned synergistic insulinotropic activities of these molecules on β-cells. In cultured human islets and in C57BL/6 mice, both aGLP1 and aGLP1-E2 enhanced glucose-stimulated insulin secretion (GSIS) compared to vehicle and iGLP1-E2 without superior efficacy of aGLP1-E2 compared to GLP-1 alone. However, aGLP1-E2 decreased fasting and fed blood glucose to a greater extent than aGLP1 and iGLP1-E2 alone. Further, aGLP1-E2 exhibited improved insulin sensitivity compared to aGLP1 and iGLP1-E2 alone (HOMA-IR and insulin tolerance test). In conclusion, targeted estrogen delivery to non-diabetic islets in the presence of GLP-1 does not enhance GSIS. However, combining GLP-1 to estrogen delivers additional efficacy relative to GLP-1 alone on insulin sensitivity and glucose homeostasis in non-diabetic mice.

Current and Emerging Treatment Options in Diabetes Care

Diabetes constitutes an increasing threat to human health, particularly in newly industrialized and densely populated countries. Type 1 and type 2 diabetes arise from different etiologies but lead to similar metabolic derangements constituted by an absolute or relative lack of insulin that results in elevated plasma glucose. In the last three decades, a set of new medicines built upon a deeper understanding of physiology and diabetic pathology have emerged to enhance the clinical management of the disease and related disorders. Recent insights into insulin-dependent and insulin-independent molecular events have accelerated the generation of a series of novel medicinal agents, which hold the promise for further advances in the management of diabetes. In this chapter, we provide a historical context for what has been accomplished to provide perspective for future research and novel emerging treatment options.

Break on through to the other 1

Although discovered in 1974, FGF1 was previously unrealized to have a role in metabolism. Suh et al. (2014) now report impressive pharmacological outcomes of FGF1 therapy in mice that imply this protein is an important metabolic regulator with therapeutic potential in the treatment of insulin resistance and type 2 diabetes.

Estrogens stimulate serotonin neurons to inhibit binge-like eating in mice

Binge eating afflicts approximately 5% of US adults, though effective treatments are limited. Here, we showed that estrogen replacement substantially suppresses binge-like eating behavior in ovariectomized female mice. Estrogen-dependent inhibition of binge-like eating was blocked in female mice specifically lacking estrogen receptor-α (ERα) in serotonin (5-HT) neurons in the dorsal raphe nuclei (DRN). Administration of a recently developed glucagon-like peptide-1-estrogen (GLP-1-estrogen) conjugate designed to deliver estrogen to GLP1 receptor-enhanced regions effectively targeted bioactive estrogens to the DRN and substantially suppressed binge-like eating in ovariectomized female mice. Administration of GLP-1 alone reduced binge-like eating, but not to the same extent as the GLP-1-estrogen conjugate. Administration of ERα-selective agonist propylpyrazole triol (PPT) to murine DRN 5-HT neurons activated these neurons in an ERα-dependent manner. PPT also inhibited a small conductance Ca2+-activated K+ (SK) current; blockade of the SK current prevented PPT-induced activation of DRN 5-HT neurons. Furthermore, local inhibition of the SK current in the DRN markedly suppressed binge-like eating in female mice. Together, our data indicate that estrogens act upon ERα to inhibit the SK current in DRN 5-HT neurons, thereby activating these neurons to suppress binge-like eating behavior and suggest ERα and/or SK current in DRN 5-HT neurons as potential targets for anti-binge therapies.

Optimization of co-agonism at GLP-1 and glucagon receptors to safely maximize weight reduction in DIO-rodents

The ratio of GLP-1/glucagon receptor (GLP1R/GCGR) co-agonism that achieves maximal weight loss without evidence of hyperglycemia was determined in diet-induced obese (DIO) mice chronically treated with GLP1R/GCGR co-agonist peptides differing in their relative receptor agonism. Using glucagon-based peptides, a spectrum of receptor selectivity was achieved by a combination of selective incorporation of GLP-1 sequences, C-terminal modification, backbone lactam stapling to stabilize helical structure, and unnatural amino acid substitutions at the N-terminal dipeptide. In addition to α-amino-isobutyric acid (Aib) substitution at position two, we show that α,α'-dimethyl imidazole acetic acid (Dmia) can serve as a potent replacement for the highly conserved histidine at position one. Selective site-specific pegylation was used to further minimize enzymatic degradation and provide uniform, extended in vivo duration of action. Maximal weight loss devoid of any sign of hyperglycemia was achieved with a co-agonist comparably balanced for in vitro potency at murine GLP1R and GCGR. This peptide exhibited superior weight loss and glucose lowering compared to a structurally matched pure GLP1R agonist, and to co-agonists of relatively reduced GCGR tone. Any further enhancement of the relative GCGR agonist potency yielded increased weight loss but at the expense of elevated blood glucose. We conclude that GCGR agonism concomitant with GLP1R agonism constitutes a promising approach to treatment of the metabolic syndrome. However, the relative ratio of GLP1R/GCGR co-agonism needs to be carefully chosen for each species to maximize weight loss efficacy and minimize hyperglycemia.

Both acyl and des-acyl ghrelin regulate adiposity and glucose metabolism via central nervous system ghrelin receptors

Growth hormone secretagogue receptors (GHSRs) in the central nervous system (CNS) mediate hyperphagia and adiposity induced by acyl ghrelin (AG). Evidence suggests that des-AG (dAG) has biological activity through GHSR-independent mechanisms. We combined in vitro and in vivo approaches to test possible GHSR-mediated biological activity of dAG. Both AG (100 nmol/L) and dAG (100 nmol/L) significantly increased inositol triphosphate formation in human embryonic kidney-293 cells transfected with human GHSR. As expected, intracerebroventricular infusion of AG in mice increased fat mass (FM), in comparison with the saline-infused controls. Intracerebroventricular dAG also increased FM at the highest dose tested (5 nmol/day). Chronic intracerebroventricular infusion of AG or dAG increased glucose-stimulated insulin secretion (GSIS). Subcutaneously infused AG regulated FM and GSIS in comparison with saline-infused control mice, whereas dAG failed to regulate these parameters even with doses that were efficacious when delivered intracerebroventricularly. Furthermore, intracerebroventricular dAG failed to regulate FM and induce hyperinsulinemia in GHSR-deficient (Ghsr(-/-)) mice. In addition, a hyperinsulinemic-euglycemic clamp suggests that intracerebroventricular dAG impairs glucose clearance without affecting endogenous glucose production. Together, these data demonstrate that dAG is an agonist of GHSR and regulates body adiposity and peripheral glucose metabolism through a CNS GHSR-dependent mechanism.

Direct control of brown adipose tissue thermogenesis by central nervous system glucagon-like peptide-1 receptor signaling

We studied interscapular brown adipose tissue (iBAT) activity in wild-type (WT) and glucagon-like peptide 1 receptor (GLP-1R)-deficient mice after the administration of the proglucagon-derived peptides (PGDPs) glucagon-like peptide (GLP-1), glucagon (GCG), and oxyntomodulin (OXM) directly into the brain. Intracerebroventricular injection of PGDPs reduces body weight and increases iBAT thermogenesis. This was independent of changes in feeding and insulin responsiveness but correlated with increased activity of sympathetic fibers innervating brown adipose tissue (BAT). Despite being a GCG receptor agonist, OXM requires GLP-1R activation to induce iBAT thermogenesis. The increase in thermogenesis in WT mice correlates with increased expression of genes upregulated by adrenergic signaling and required for iBAT thermogenesis, including PGC1a and UCP-1. In spite of the increase in iBAT thermogenesis induced by GLP-1R activation in WT mice, Glp1r(-/-) mice exhibit a normal response to cold exposure, demonstrating that endogenous GLP-1R signaling is not essential for appropriate thermogenic response after cold exposure. Our data suggest that the increase in BAT thermogenesis may be an additional mechanism whereby pharmacological GLP-1R activation controls energy balance.

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.

The metabolic actions of glucagon revisited

The initial identification of glucagon as a counter-regulatory hormone to insulin revealed this hormone to be of largely singular physiological and pharmacological purpose. Glucagon agonism, however, has also been shown to exert effects on lipid metabolism, energy balance, body adipose tissue mass and food intake. The ability of glucagon to stimulate energy expenditure, along with its hypolipidemic and satiating effects, in particular, make this hormone an attractive pharmaceutical agent for the treatment of dyslipidemia and obesity. Studies that describe novel preclinical applications of glucagon, alone and in concert with glucagon-like peptide 1 agonism, have revealed potential benefits of glucagon agonism in the treatment of the metabolic syndrome. Collectively, these observations challenge us to thoroughly investigate the physiology and therapeutic potential of insulin's long-known opponent.

Effects of obestatin on energy balance and growth hormone secretion in rodents

Ghrelin stimulates food intake and adiposity and thereby increases body weight (BW) in rodents after central as well as peripheral administration. Recently, it was discovered that the gene precursor of ghrelin encoded another secreted and bioactive peptide named obestatin. First reports appeared to demonstrate that this peptide requires an amidation for its biological activity and acts through the orphan receptor, GPR-39. Obestatin was shown to have actions opposite to ghrelin on food intake, BW, and gastric emptying. In the present study, we failed to observe any effect of obestatin on food intake, BW, body composition, energy expenditure, locomotor activity, respiratory quotient, or hypothalamic neuropeptides involved in energy balance regulation. In agreement with the first report, we were unable to find any effect of obestatin on GH secretion in vivo. Moreover, we were unable to find mRNA expression of GPR-39, the putative obestatin receptor, in the hypothalamus of rats. Therefore, the results presented here do not support a role of the obestatin/GPR-39 system in the regulation of energy balance.

Basal activity profiles of NPH and [Nepsilon-palmitoyl Lys (B29)] human insulins in subjects with IDDM

[Nepsilon-palmitoyl Lys (B29)] human insulin is a fatty acid-acylated derivative of insulin with extended action compared to unmodified insulin when infused intravenously (i.v.) secondary to its binding to circulating albumin. The duration and activity profile of the acylated (A) and NPH (B) insulins were assessed following subcutaneous (s.c.) doses of (A) 6 nmol/kg and (B) 1.2 nmol/kg (equivalent to 0.2 U/kg) in 9 subjects with IDDM. After overnight i.v. infusion of regular human insulin, morning glucose was (A) 6.9 +/- 0.1 and (B) 6.8 +/- 0.1 mmol/l. After the s.c. injection, i.v. human insulin or glucose was infused to maintain near-basal glycaemia and tracer glucose to assess hepatic glucose production (HGP). An activity profile was deduced for each study by expressing the glucose infusion rate at each time point, as a fraction (%) of the basal (measured) HGP, and the i.v. insulin infusion rate as a fraction (%) of the basal requirement. The two fractions are combined by adding the fractional glucose infusion rate and subtracting the fractional insulin infusion rate. Infusion rates of i.v. insulin in the morning were (A) 0.96 +/- 0.096 and (B) 1.22 +/- 0.09 pmol x kg(-1) x min(-1). After insulin injection, i.v. insulin requirements decreased and were below 10% of basal between 100 and 150 min. A constant activity profile of 0% represents a perfect substitution of the basal i.v. insulin infusion by the s.c. dose. The actual profile is defined by deviations from this (above) and was -17 +/- 11, 7 +/- 10, -9 +/- 6 and -18 +/- 18% for [Nepsilon-palmitoyl Lys (B29)] human insulin and 17 +/- 12, 5 +/- 6, -9 +/- 15, 22 +/- 18% for NPH insulin at 3, 6, 9 and 12 h after s.c. injection. HGP was similar for the two insulins, demonstrating similar metabolic actions and profiles both peripherally and at the liver.

Mealtime treatment with insulin analog improves postprandial hyperglycemia and hypoglycemia in patients with non-insulin-dependent diabetes mellitus. Multicenter Insulin Lispro Study Group

BACKGROUND

Insulin lispro is an insulin analog that was recently developed particularly for a mealtime therapy. It has a fast absorption rate and short duration of action. The efficacy of insulin lispro in the clinical therapy of patients with non-insulin-dependent diabetes mellitus (NIDDM) has not been tested.

OBJECTIVES

To compare insulin lispro and human regular insulin in the mealtime treatment of patients with NIDDM.

METHODS

A 6-month, randomized, multinational (16 countries), multicenter (80 sites) clinical trial with an open-label, crossover design was performed in 722 patients with NIDDM. Insulin lispro was injected immediately before and human regular insulin 30 to 45 minutes before the meal.

RESULTS

Throughout the study, the postprandial rise in serum glucose levels was significantly lower during insulin lispro than human regular insulin treatment. At end point the rise (mean +/- SEM) in serum glucose levels was 30% lower at 1 hour (2.6 +/- 0.1 mmol/L [46.8 +/- 1.8 mg/ dL] for lispro vs 3.7 +/- 0.1 mmol/L [66.6 +/- 1.8 mg/dL] for human regular insulin) and 53% lower 2 hours after the test meal (1.4 +/- 0.1 mmol/L [25.2 +/- 1.8 mg/dL] for lispro vs 3.0 +/- 0.1 mmol/L [54.0 +/- 1.8 mg/dL] for human regular insulin) with insulin lispro compared with human regular insulin therapy (P < .001 for both intervals). During insulin lispro therapy the rate of hypoglycemia overall (P = .01) and overnight (P < .001) was lower and the number of asymptomatic hypoglycemic episodes was smaller (P = .03) than during human regular insulin therapy. Associated with a similar 13% increase (P < .001) in the total daily insulin dose, the glycosylated hemoglobin level decreased (P < .001) equally in both treatment groups. Serum lipid and lipoprotein levels remained unchanged. There were no differences in the adverse events between the 2 treatment groups.

CONCLUSIONS

Compared with human regular insulin therapy, mealtime therapy with insulin lispro reduced postprandial hyperglycemia and may decrease the rate of mild hypoglycemic episodes in patients with NIDDM.

Reduction of postprandial hyperglycemia and frequency of hypoglycemia in IDDM patients on insulin-analog treatment. Multicenter Insulin Lispro Study Group

Insulin lispro, an insulin analog recently developed particularly for mealtime therapy, has a fast absorption rate and a short duration of action. We compared insulin lispro and regular human insulin in the mealtime treatment of 1,008 patients with IDDM. The study was a 6-month randomized multinational (17 countries) and multicenter (102 investigators) clinical trial performed with an open-label crossover design. Insulin lispro was injected immediately before the meal, and regular human insulin was injected 30-45 min before the meal. Throughout the study, the postprandial rise in serum glucose was significantly lower during insulin lispro therapy. At the endpoint, the postprandial rise in serum glucose was reduced at 1 h by 1.3 mmol/l and at 2 h by 2.0 mmol/l in patients treated with insulin lispro (P < 0.001). The rate of hypoglycemia was 12% less with insulin lispro (6.4 +/- 0.2 vs. 7.2 +/- 0.3 episodes/30 days, P < 0.001), independent of basal insulin regimen or HbA1c level. The reduction was observed equally in episodes with and without symptoms. When the total number of episodes for each patient was analyzed according to the time of occurrence, the number of hypoglycemic episodes was less with insulin lispro than with regular human insulin therapy during three of four quarters of the day (P < 0.001). The largest relative improvement was observed at night. In conclusion, insulin lispro improves postprandial control, reduces hypoglycemic episodes, and improves patient convenience, compared with regular human insulin, in IDDM patients.

Improved mealtime treatment of diabetes mellitus using an insulin analogue. Multicenter Insulin Lispro Study Group

The absorption of regular human insulin from subcutaneous injection sites is delayed due to the self-association of insulin to multimeric forms. The insulin analogue insulin lispro has a weak self-association and a fast absorption rate. We examined the safety and efficacy of insulin lispro in the premeal treatment of patients with diabetes mellitus. A 12-month study was performed in 336 patients with insulin-dependent diabetes mellitus (IDDM) and 295 patients with non-insulin-dependent diabetes mellitus (NIDDM). The patients were randomized to inject either regular human insulin 30 to 45 minutes before eating, or insulin lispro immediately before each meal, in addition to basal insulin. The postprandial rise in serum glucose was lower in patients receiving insulin lispro than in those receiving regular human insulin therapy. At end point the increment was significantly lower at 1 hour (35%) and at 2 hours (64%) after the meal in IDDM patients; in NIDDM patients, the increment was nonsignificantly lower at 1 hour (19%) and significantly lower at 2 hours (48%). IDDM patients receiving insulin lispro achieved significantly lower glycated hemoglobin (HbA1c) levels in patients receiving regular human insulin (8.1% vs 8.3%). In NIDDM patients, HbA1c levels decreased equally in both treatment groups. Due to its fast absorption rate, insulin lispro improves postprandial control in diabetes. Insulin lispro can be considered one step toward optimal insulin therapy and improved patient convenience.

Cross-reactive and serotype-specific antibodies against foot-and-mouth disease virus generated by different regions of the same synthetic peptide

Synthetic peptides based on the VP1 proteins of two serotypes of foot-and-mouth disease virus (FMDV) and having the general formula C-C-(200-213)-P-P-S-(141-158)-P-C-G induce heterologous as well as homologous protection against challenge. Substitution of the sequence consisting of residues 200 to 213 (200-213 sequence) with a second copy of the homologous 141-158 sequence (i.e., homodimers) resulted in failure of either serotype peptide to protect heterologously. The antiviral and antipeptide titers of sera from guinea pigs immunized with the homodimeric 141-158 peptides showed serotype specificity and, with the data from the heterodimeric peptide vaccines, suggested that the C-terminal 141-158 sequence was more effectively recognized by the immune system than the N-terminal sequence. Whereas heterologous antiviral titers as measured by enzyme-linked immunosorbent assay and virus neutralization tests have not been observed with sera from cross-protected animals, epitope-mapping studies established that there was heterologous recognition of an octapeptide within the 200-213 sequence. That the 200-213 sequence was required for the induction of heterologous protection was also confirmed with a number of peptides, including hybrids based on the 200-213 sequence of one virus and the 141-158 sequence of a second virus. Thus, peptides of the general formula given above induce serotype-specific and serotype-cross-reactive protective antibodies and are unique in their induction of significant levels of heterologous protection, a property which has never been reported for whole FMDV vaccines.

Modulation of T-cell reactivity to synthetic peptide analogues of foot-and-mouth disease virus in sheep by amino acid substitutions

The ability of synthetic peptide analogues of foot-and-mouth disease virus VP1 capsid protein to induce T-cell proliferation in vitro following immunization of sheep with the uncoupled peptides was assessed. Elevated T-cell responses were obtained to a 21-residue peptide containing VP1 residues 141-158, and a 40-residue peptide containing residues 200-213 and 141-158 linked via a diproline-serine spacer. In contrast, no significant T-cell response was obtained with a 19-residue peptide containing residues 200-213 alone. In an attempt to engineer T-cell reactivity to this peptide, a sequence motif found in many peptides recognized by human or mouse T-cells was introduced by amino acid substitution. Substitution of a glycine or an aspartic acid for an alanine at position 207 in the 19-residue peptide resulted in the introduction of two such motifs running consecutively. Immunization of sheep with these peptides resulted in significant T-cell proliferative responses and elevated antibody responses. Analysis of further sequence variants showed that T-cell responsiveness was maintained with peptides containing single amino acid changes within these motifs, provided position 207 was glycine. The results thus suggest that increased T-cell reactivity, might be engineered via sequence manipulation of the 200-213 component of the 40-residue synthetic peptide. Such an additional T-cell epitope in the 40-residue peptide could potentially result in superior neutralizing antibody responses directed against the major epitope in residues 141-160 of VP1.

The interaction of proinsulin with the insulin-like growth factor-I receptor in human liver, muscle, and adipose tissue

Because of the sequence homology and tertiary structure similarities between proinsulin (PI) and insulin-like growth factor-I (IGF-I), it is possible that PI interacts with the IGF-I receptor with higher affinity than insulin. To test this hypothesis in man, we have partially purified IGF-I receptors from liver, muscle, and adipose tissue and studied their interaction with PI, insulin, IGF-I, and IGF-II. With some tissue to tissue variation, [125I]insulin binding was 4- to 8-fold greater than IGF-I binding. Unlabeled IGF-I at about 1 x 10(-9 M, IGF-II at about 1 x 10(-8) M, and insulin at about 1 x 10(-6) M displace 50% the binding of [125I]IGF-I to its receptor, whereas PI at 1 x 10(-6) M displaces less than 20% of the binding of [125I]IGF-I to its receptor. We conclude that in human liver, muscle, and adipose tissue, PI does not interact with the IGF-I receptor at a higher affinity than insulin, and the affinity of IGF-I receptors is several-fold lower than that of insulin receptors. It is, therefore, unlikely that if PI were to be administered to man any of its biological effects would be by interacting with the IGF-I receptor.

IGF-I--stimulated glucose transport in human skeletal muscle and IGF-I resistance in obesity and NIDDM

Based on the observation that insulinlike growth factor I (IGF-I) can stimulate glucose utilization in nondiabetic subjects and that the action of the IGF-I receptor is normal in the skeletal muscle of patients with non-insulin-dependent diabetes mellitus (NIDDM), it seems possible that IGF-I might provide an effective acute treatment for the hyperglycemia of NIDDM. Using our recently developed in vitro human muscle preparation, we investigated the hypothesis that IGF-I might be an effective alternative to insulin in stimulating glucose transport in diabetic muscle. Abdominal muscle samples from nonobese nondiabetic, obese nondiabetic, and obese NIDDM patients were obtained during elective abdominal surgery. Plasma levels of IGF-I in diabetic patients were lower than those in either of the nondiabetic groups. Binding studies with wheat-germ-agglutinin-chromatography-purified receptors demonstrated the presence of IGF-I receptors in human muscle, with IGF-I binding being approximately 24% that of insulin. There was no change in IGF-I binding in muscle from obese or diabetic subjects, and the structural characteristics of the IGF-I receptor were not altered, as determined by electrophoretic mobility. IGF-I stimulated glucose transport approximately twofold in incubated muscle from control subjects, but there was no IGF-I stimulation of transport in muscle from obese subjects with or without NIDDM. These results confirm a previous report that human muscle contains receptors for IGF-I and demonstrate for the first time that IGF-I can stimulate glucose transport in human muscle. However, muscle from obese subjects with or without NIDDM is resistant to the action of IGF-I.

IGF-II receptors and IGF-II-stimulated glucose transport in human fat cells

Insulin-like growth factor II (IGF-II) receptors have been described in rat but not in human adipocytes. In both species, IGF-II has been reported to stimulate glucose transport by interacting with the insulin receptor. In this study, we have unequivocally demonstrated the presence of IGF-II receptors in human adipocytes. 125I-labeled IGF-II specifically binds to intact adipocytes, membranes, and lectin-purified detergent solubilized extracts. Through the use of 0.5 mM disuccinimidyl suberate, 125I-IGF-II is cross-linked to a 260-kDa protein that is identified as the IGF-II receptor by displacement experiments with unlabeled IGF-II, IGF-I, and insulin and either by immunoprecipitation or by Western blot analysis with mannose 6-phosphate receptor antibodies. The concentrations of IGF-II required for half-maximal and maximal stimulation of glucose transport in human adipocytes are 35 and 100 times more than that of insulin. The possibility of IGF-II stimulating glucose transport by interacting predominantly with the insulin receptor is suggested by the following: 1) the concentration of IGF-II that inhibits half of insulin binding is only 20 times more than that of insulin; 2) the lack of an additive effect of IGF-II and insulin for maximal stimulation of glucose transport; 3) the ability of monoclonal insulin receptor antibodies to decrease glucose transport stimulated by submaximal concentrations of both IGF-II and insulin; and 4) the ability of IGF-II to stimulate insulin receptor autophosphorylation albeit at a reduced potency when compared with insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of immune responses in the sheep to synthetic peptides of foot-and-mouth disease virus using ovine polyclonal and monoclonal antibodies

A 40-residue peptide incorporating residues 200-213 and 141-158 of foot-and-mouth disease virus VP1 capsid protein strain O1 Kaufbeuren was injected uncoupled into sheep, and the immune responses analysed. Direct-binding and inhibition experiments showed that the polyclonal antibody response was directed mainly against epitopes unique to the 40-residue peptide but absent from the constituent peptides containing residues 200-213 or 141-158, respectively. Further confirmation of the presence of unique epitopes on the 40-residue peptide was obtained from similar experiments performed with sheep monoclonal antibodies generated through the use of an aminopterin-sensitive sheep/mouse heterohybridoma cell line as a fusion partner. The sheep polyclonal antisera to the 40-residue peptide had high neutralization titres and were fully active in a mouse protection assay, whereas none of the sheep monoclonal antibodies conferred protection. The results suggest that the conformation of the 40-residue peptide is important for its ability to induce neutralizing antibodies.

Effect of insulin and insulin-like growth factors I and II on phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate breakdown in liver from humans with and without type II diabetes

We have characterized a plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2)-specific phospholipase C (PLC) and a cytosolic phosphatidylinositol (PI)-specific PLC in human liver. Epinephrine, 1 x 10(-5) M, and vasopressin, 1 x 10(-8) M, stimulated PIP2-PLC which was enhanced by guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). PI-PLC stimulation was not observed by these agents. Insulin and insulin-like growth factors (IGF-I and IGF-II) in the presence and absence of GTP gamma S did not stimulate PIP2-PLC or PI-PLC in plasma membranes and cytosol preparations nor phosphoinositide breakdown in isolated human hepatocytes. Furthermore, serendipitly we found that PIP2-PLC activity was increased in liver membranes from obese patients with type II diabetes when compared to obese and lean controls. We conclude that in human liver, insulin and IGFs are not members of the family of hormones generating inositol trisphosphate (IP3) as a second messenger. Furthermore, the increased PIP2-PLC in diabetic liver may result in: (a) increased intracellular concentrations of IP3 and thus increased Ca2+, which has been postulated to induce insulin resistance; and (b) increased diacylglycerol and thus increased protein kinase C which phosphorylates the insulin receptor at serine residues inactivating the insulin receptor kinase. While the mechanism of increased PIP2-PLC activity in diabetes is unknown, it may initiate a cascade of events that result in insulin resistance.

Immunization against foot-and-mouth disease with synthetic peptides representing the C-terminal region of VP1

Foot-and-mouth disease virus challenge experiments in guinea-pigs and immunoassays with a range of peptides equivalent to either or both of the sequences 141 to 158 and 200 to 213 of VP1 showed the most effective structure, in terms of protection, to be one in which both 'sites' were present with a minimum of additional amino acids. An 80 residue peptide comprising amino acids 134 to 213 was considerably less effective than 40 or 45 residue peptides. The major site for the induction of protection was deduced to be in the region 141 to 158. Thus, protection with the 40 or 45 residue peptide did not appear to be due to the presence of antibody directed solely to the 200 to 213 sequence. Finally, induction of antibody to the latter site appeared to be dependent on both the size of the peptide and the disposition of 'sites' within it.

Protection of cattle against foot-and-mouth disease by a synthetic peptide

A chemically synthesized peptide consisting essentially of two separate regions (residues 141 to 158 and 200 to 213) of a virus coat protein (VP1) from the O1 Kaufbeuren strain of foot-and-mouth disease virus was prepared free of any carrier protein. It elicited high levels of neutralizing antibody and protected cattle against intradermolingual challenge by inoculation with infectious virus. Comparative evaluation of this peptide with a single-site peptide (residues 141 to 158) in guinea pigs suggests the importance of the VP1 carboxyl terminal residues in enhancing the protective response.