Potentiation of insulin-mediated glucose lowering without elevated hypoglycemia risk by a small molecule insulin receptor modulator

The Insulin Receptor: An Important Target for the Development of Novel Medicines and Pesticides

The insulin receptor (IR) is a transmembrane protein that is activated by ligands in insulin signaling pathways. The IR has been considered as a novel therapeutic target for clinical intervention, considering the overexpression of its protein and A-isoform in multiple cancers, Alzheimer’s disease, and Type 2 diabetes mellitus in humans. Meanwhile, it may also serve as a potential target in pest management due to its multiple physiological influences in insects. In this review, we provide an overview of the structural and molecular biology of the IR, functions of IRs in humans and insects, physiological and nonpeptide small molecule modulators of the IR, and the regulating mechanisms of the IR. Xenobiotic compounds and the corresponding insecticidal chemicals functioning on the IR are also discussed. This review is expected to provide useful information for a better understanding of human IR-related diseases, as well as to facilitate the development of novel small-molecule activators and inhibitors of the IR for use as medicines or pesticides.

2'-O-Methylperlatolic Acid Enhances Insulin-Regulated Blood Glucose-Lowering Effect through Insulin Receptor Signaling Pathway

PURPOSE

Insulin receptor (InsR) sensitizers represent a new type of therapeutic agent for the treatment of diabetes, with 2'-O-methylperlatolic acid (2-O-M) being a potential InsR targeting drug. The purpose of this study was to determine whether 2-O-M functions as an activator of the insulin signaling pathway, regulating glucose hemostasis through the InsR and exerting a glucose-lowering effect in an animal model of diabetes.

METHODS

SPR-based analyses were used to detect the binding of different concentrations of 2-O-M to the InsR. The protein levels of IR-β, p-IR, AKT, and p-AKT in Hepa and C2C12 cell lines and liver and muscle tissues were determined by western blotting. Glucose uptake capacity was determined in C2C12 cells. Streptozotocin-induced diabetic mice were randomly divided into four groups: the control, insulin treated, 2-O-M treated, and combined insulin and 2-O-M treated. Mice were injected with 2-O-M or normal saline and the average blood glucose concentration after 120 min, and the serum levels of insulin, glucagon, and C-peptide were measured. Next, qRT-PCR was performed to detect the mRNA expression of genes involved in lipid and glucose metabolism in the liver and muscle tissues.

RESULTS

2-O-M binds to the extracellular domain of the InsR. Moreover, combination treatment with 2-O-M and insulin resulted in significant activation of the insulin signaling pathway in vitro and significant stimulation of the glucose uptake capacity of C2C12 myotubes. In mice with streptozotocin-induced diabetes, 2-O-M significantly prolonged the blood glucose-lowering effect of insulin, significantly reduced the secretion of exogenous insulin, and reduced the blood glucose concentration in vivo. In addition, treatment with 2-O-M alone significantly enhanced the phosphorylation of AKT in muscle tissue, which enhanced glucose uptake in C2C12 myotubes. Further, 2-O-M significantly increased glucagon secretion and enhanced liver gluconeogenesis to prevent hypoglycemia.

CONCLUSION

2-O-M enhances the hypoglycemic effect of insulin through the insulin signaling pathway and can be used as a complement to insulin. This synergetic effect may lower the required dose of insulin and protect β cells.

Anti-Insulin Receptor Antibodies in the Pathology and Therapy of Diabetes Mellitus

Diabetes mellitus (DM) is recognized as the most common and the world's fastest-growing chronic disease with severe complications leading to increased mortality. Many strategies exist for the management of DM and its control, including treatment with insulin and insulin analogs, oral hypoglycemic therapy such as insulin secretion stimulators and insulin sensitizers, and diet and physical training. Over the years, many types of drugs and molecules with an interesting pharmacological diversity have been developed and proposed for their anti-diabetic potential. Such molecules target diverse key receptors, enzymes, and regulatory/signaling proteins known to be directly or indirectly involved in the pathophysiology of DM. Among them, insulin receptor (IR) is undoubtedly the target of choice for its central role in insulin-mediated glucose homeostasis and its utilization by the major insulin-sensitive tissues such as skeletal muscles, adipose tissue, and the liver. In this review, we focus on the implication of antibodies targeting IR in the pathology of DM as well as the recent advances in the development of IR antibodies as promising anti-diabetic drugs. The challenge still entails development of more powerful, highly selective, and safer anti-diabetic drugs.

Developing Insulin and BDNF Mimetics for Diabetes Therapy

Diabetes is a global public health concern nowadays. The majority of diabetes mellitus (DM) patients belong to type 2 diabetes mellitus (T2DM), which is highly associated with obesity. The general principle of current therapeutic strategies for patients with T2DM mainly focuses on restoring cellular insulin response by potentiating the insulin-induced signaling pathway. In late-stage T2DM, impaired insulin production requires the patients to receive insulin replacement therapy for maintaining their glucose homeostasis. T2DM patients also demonstrate a drop of brain-derived neurotrophic factor (BDNF) in their circulation, which suggests that replenishing BDNF or enhancing its downstream signaling pathway may be beneficial. Because of their protein nature, recombinant insulin or BDNF possess several limitations that hinder their clinical application in T2DM treatment. Thus, developing orally active "insulin pill" or "BDNF pill" is essential to provide a more convenient and effective therapy. This article reviews the current development of non-peptidyl chemicals that mimic insulin or BDNF and their potential as anti-diabetic agents.

Structure and dynamics of the insulin receptor: implications for receptor activation and drug discovery

Recently, major progress has been made in uncovering the mechanisms of how insulin engages its receptor and modulates downstream signal transduction. Here, we present in detail the current structural knowledge surrounding the individual components of the complex, binding sites, and dynamics during the activation process. A novel kinase triggering mechanism, the 'bow-arrow model', is proposed based on current knowledge and computational simulations of this system, in which insulin, after its initial interaction with binding site 1, engages with site 2 between the fibronectin type III (FnIII)-1 and -2 domains, which changes the conformation of FnIII-3 and eventually translates into structural changes across the membrane. This model provides a new perspective on the process of insulin binding to its receptor and, thus, could lead to future novel drug discovery efforts.

A computer model simulating human glucose absorption and metabolism in health and metabolic disease states

A computer model designed to simulate integrated glucose-dependent changes in splanchnic blood flow with small intestinal glucose absorption, hormonal and incretin circulation and hepatic and systemic metabolism in health and metabolic diseases e.g. non-alcoholic fatty liver disease, (NAFLD), non-alcoholic steatohepatitis, (NASH) and type 2 diabetes mellitus, (T2DM) demonstrates how when glucagon-like peptide-1, (GLP-1) is synchronously released into the splanchnic blood during intestinal glucose absorption, it stimulates superior mesenteric arterial (SMA) blood flow and by increasing passive intestinal glucose absorption, harmonizes absorption with its distribution and metabolism. GLP-1 also synergises insulin-dependent net hepatic glucose uptake (NHGU). When GLP-1 secretion is deficient post-prandial SMA blood flow is not increased and as NHGU is also reduced, hyperglycaemia follows. Portal venous glucose concentration is also raised, thereby retarding the passive component of intestinal glucose absorption.   Increased pre-hepatic sinusoidal resistance combined with portal hypertension leading to opening of intrahepatic portosystemic collateral vessels are NASH-related mechanical defects that alter the balance between splanchnic and systemic distributions of glucose, hormones and incretins.The model reveals the latent contribution of portosystemic shunting in development of metabolic disease. This diverts splanchnic blood content away from the hepatic sinuses to the systemic circulation, particularly during the glucose absorptive phase of digestion, resulting in inappropriate increases in insulin-dependent systemic glucose metabolism.  This hastens onset of hypoglycaemia and thence hyperglucagonaemia. The model reveals that low rates of GLP-1 secretion, frequently associated with T2DM and NASH, may be also be caused by splanchnic hypoglycaemia, rather than to intrinsic loss of incretin secretory capacity. These findings may have therapeutic implications on GLP-1 agonist or glucagon antagonist usage.

Effect of oxymatrine on insulin resistance in patients with type 2 diabetes mellitus

AIM: To observe the influence of oxymatrine on insulin resistance in patients with type 2 diabetes mellitus and the mechanism involved.

METHODS: This was a prospective randomized controlled clinical study. Patients with type 2 diabetes mellitus were divided into either an oxymatrine treatment group or an untreated group. Glucose oxidase method was used to detect serum fasting blood glucose (FBG) and fasting insulin (FINS). The homeostasis model assessment of insulin resistance (HOMA-IR) and homeostasis model assessment of insulin sensitivity index (HOMA-ISI) were also detected. ELISA was carried out to detect the serum levels of reactive oxygen species (ROS) and tumor necrosis factor-α (TNF-α). Western blot was used to detect the expression of protein kinase B (AKT), p-AKT, glycogen synthase kinase-3α/β (GSK3α/β), and p-GSK3α/β proteins.

RESULTS: FBG, FINS and HOMA-IR significantly decreased and HOMA-ISI increased in the oxymatrine treatment group compared with the untreated group (P < 0.05). Serum levels of ROS and TNF-α in the oxymatrine treatment group decreased significantly compared with the untreated group (P < 0.05). Western blot analysis showed that the total protein levels of AKT and GSK3α/β were unchanged (P > 0.05), but the expression of p-AKT and p-GSK3α/β significantly increased in the oxymatrine treatment group compared with the untreated group (P < 0.05).

CONCLUSION: Oxymatrine can reduce FBG and FINS, and improve insulin resistance by reducing the production of serum ROS and TNF-α and by influencing the photophosphorylation of key proteins (such as AKT and GSK3α/β) in the insulin resistance-related signaling pathways.