Functionally selective signaling and broad metabolic benefits by novel insulin receptor partial agonists.

Insulin analogs have been developed to treat diabetes with focus primarily on improving the time action profile without affecting ligand-receptor interaction or functional selectivity. As a result, inherent liabilities (e.g. hypoglycemia) of injectable insulin continue to limit the true therapeutic potential of related agents. Insulin dimers were synthesized to investigate whether partial agonism of the insulin receptor (IR) tyrosine kinase is achievable, and to explore the potential for tissue-selective systemic insulin pharmacology. The insulin dimers induced distinct IR conformational changes compared to native monomeric insulin and substrate phosphorylation assays demonstrated partial agonism. Structurally distinct dimers with differences in conjugation sites and linkers were prepared to deliver desirable IR partial agonist (IRPA). Systemic infusions of a B29-B29 dimer in vivo revealed sharp differences compared to native insulin. Suppression of hepatic glucose production and lipolysis were like that attained with regular insulin, albeit with a distinctly shallower dose-response. In contrast, there was highly attenuated stimulation of glucose uptake into muscle. Mechanistic studies indicated that IRPAs exploit tissue differences in receptor density and have additional distinctions pertaining to drug clearance and distribution. The hepato-adipose selective action of IRPAs is a potentially safer approach for treatment of diabetes.

Insulin replacement prevents the acquisition but not the expression of morphine-induced conditioned place preference in streptozotocin-induced diabetic rats

Abstract Insulin receptors have distributed in all brain regions, including the nucleus Accumbens (NAc), and where is implicated in the reward properties of drugs. It is well known that insulin signaling can regulate dopamine release. Therefore, in the present study, we tried to examine the effect of insulin replacement on the acquisition and expression of morphine-induced conditioned place preference (CPP) in diabetic rats. Forty-eight male Wistar rats were divided into two non-diabetic (Naïve) and diabetic groups rendered by a single injection of streptozotocin (STZ). These groups separately received insulin (10U/kg) or saline (1 ml/kg) one hour prior to morphine administration (5mg/kg;s.c.) during conditioning days (acquisition phase) or post-conditioning day (expression phase) in the CPP paradigm. In this paradigm, conditioning score (CS) and locomotion activity were recorded by Ethovision. The STZ-induced diabetic rats displayed higher CS compared to naïve rats (P<0.05). This effect was abolished in all diabetic rats that received insulin during conditioning days but not the expression phase. This study has provided evidence that insulin plays a modulatory role in morphine-induced CPP, and insulin replacement during the acquisition phase could reduce the rewarding properties of morphine in diabetes conditions through a possible modulating effect on dopamine release in the NAc region

Effects of tauroursodeoxycholic acid on glucose homeostasis: Potential binding of this bile acid with the insulin receptor.

AIMS: The bile acid (BA), tauroursodeoxycholic acid (TUDCA) regulates glucose homeostasis; however, it is not clear whether its effects on insulin signaling are due to its direct interaction with the insulin receptor (IR) or through activation of the G-coupled BA receptor, TGR5. We, herein, investigated whether the actions of TUDCA on glucose homeostasis occur via IR or TGR5 activation. MAIN METHODS: Glucose homeostasis was evaluated in high-fat diet (HFD)-obese or control (CTL) mice, after 30 days or one intraperitoneal (ip) injection of 300 mg/kg TUDCA, respectively. Molecular docking was performed to investigate the potential binding of TUDCA on the IR and TGR5. KEY FINDINGS: After 30 days of TUDCA treatment, HFD mice exhibited improvements in glucose tolerance and insulin sensitivity, which were abolished when these rodents received the IR antagonist, S961. Molecular docking experiments showed that TUDCA demonstrates high binding affinity for TGR5 and IR and strongly interacts with the insulin binding sites 1 and 2 of the IR. Consistent with this potential agonist activity of TUDCA on IR, CTL mice displayed increased hepatic phosphorylation of AKT after an ip injection of TUDCA. This effect was not associated with altered glycemia in CTL mice and was dependent on IR activation, as S961 prevented hepatic AKT activation by TUDCA. Furthermore, TUDCA activated the hepatic protein kinase A (PKA) and cAMP response element-binding protein (CREB) pathway in CTL mice, even after the administration of S961. SIGNIFICANCE: We provide novel evidence that TUDCA may be an agonist of the IR, in turn activating AKT and contributing, at least in part, to its beneficial effects upon glucose homeostasis.

Revising Endosomal Trafficking under Insulin Receptor Activation.

The endocytosis of ligand-bound receptors and their eventual recycling to the plasma membrane (PM) are processes that have an influence on signalling activity and therefore on many cell functions, including migration and proliferation. Like other tyrosine kinase receptors (TKR), the insulin receptor (INSR) has been shown to be endocytosed by clathrin-dependent and -independent mechanisms. Once at the early endosome (EE), the sorting of the receptor, either to the late endosome (LE) for degradation or back to the PM through slow or fast recycling pathways, will determine the intensity and duration of insulin effects. Both the endocytic and the endosomic pathways are regulated by many proteins, the Arf and Rab families of small GTPases being some of the most relevant. Here, we argue for a specific role for the slow recycling route, whilst we review the main molecular mechanisms involved in INSR endocytosis, sorting and recycling, as well as their possible role in cell functions.

Immediate-early transcriptional response to insulin receptor stimulation.

Insulin binding to the insulin receptor triggers intracellular signaling cascades involving the activation of protein and lipid kinases. As a result, multiple biological functions of the cells are changed. Here, we analyzed the regulation and signaling cascades leading to insulin-induced activation of the stimulus-responsive transcription factors. For the analyses, we used chromatin-embedded reporter genes having a cellular nucleosomal organisation, and fibroblasts expressing human insulin receptors (HIRcB cells). The results show that stimulation of the insulin receptor induced the expression of the transcription factor Egr-1. Attenuation of Egr-1 promoter activation was observed following expression of a dominant-negative mutant of the ternary complex factor Elk-1. These data were corroborated by experiments showing that insulin receptor stimulation increased the transcriptional activation potential of Elk-1. In addition, the transcriptional activity of AP-1 was significantly elevated in insulin-stimulated HIRcB cells. Expression of the dominant-negative mutant of Elk-1 reduced insulin-induced activation of AP-1, indicating that Elk-1 controls both serum response element and AP-1-regulated transcription. Moreover, we show that stimulation of the insulin receptor activates cyclic AMP response element (CRE)-controlled transcription, involving the transcription factor CREB. Insulin-induced transcription of Elk-1 and CREB-controlled reporter genes was attenuated by overexpression of MAP kinase phosphatase-1 or a constitutively active mutant of calcineurin A, indicating that both phosphatases are part of a negative feedback loop for reducing insulin-mediated gene transcription. Finally, we show that expression of the adenoviral protein E1A selectively reduced CRE-mediated transcription following stimulation of the insulin receptor. These data indicate that insulin-regulated transcription of CRE-containing genes is under epigenetic control.

Arsenic disrupts neuronal insulin signaling through increasing free PI3K-p85 and decreasing PI3K activity.

Previously, we reported that prolonged arsenic exposure impaired neuronal insulin signaling. Here we have further identified novel molecular mechanisms underlying neuronal insulin signaling impairment by arsenic. Arsenic treatment altered insulin dose-response curve and reduced maximum insulin response in differentiated human neuroblastoma SH-SY5Y cells, suggesting that arsenic hindered neuronal insulin signaling in a non-competitive like manner. Mechanistically, arsenic suppressed insulin receptor (IR) kinase activity, as witnessed by a decreased insulin-activated autophosphorylation of IR at Y1150/1151. Arsenic decreased the level of insulin receptor substrate 1 (IRS1) but increased the protein ratio between PI3K regulatory subunit, p85, and PI3K catalytic subunit, p110. Interestingly, co-immunoprecipitation demonstrated that arsenic did not alter a level of PI3K-p110/PI3K-p85 complex while increased PI3K-p85 levels in a PI3K-p110 depletion supernatant resulted from PI3K-p110 immunoprecipitation. These results indicated that arsenic increased PI3K-p85 which was free from PI3K-p110 binding. In addition, arsenic significantly increased interaction between IRS1 and PI3K-p85 but not PI3K-p110, suggesting that there may be a fraction of free PI3K-p85 interacting with IRS1. In vitro PI3K activity demonstrated that arsenic lowered PI3K activity in both basal and insulin-stimulated conditions. These results suggested that the increase in free PI3K-p85 by arsenic might compete with PI3K heterodimer for the same IRS1 binding site, in turn blocking the activation of its catalytic subunit, PI3K-p110. Taken together, our results provide additional insights into mechanisms underlying the impairment of neuronal insulin signaling by arsenic through the reduction of IR autophosphorylation, the increase in free PI3K-p85, and the impeding of PI3K activity.

Roles of vascular endothelial and smooth muscle cells in the vasculoprotective effect of insulin in a mouse model of restenosis.

BACKGROUND: Insulin exerts vasculoprotective effects on endothelial cells (ECs) and growth-promoting effects on vascular smooth muscle cells (SMCs) in vitro, and suppresses neointimal growth in vivo. Here we determined the role of ECs and SMCs in the effect of insulin on neointimal growth. METHODS: Mice with transgene CreERT2 under the control of EC-specific Tie2 (Tie2-Cre) or SMC-specific smooth muscle myosin heavy chain promoter/enhancer (SMMHC-Cre) or littermate controls were crossbred with mice carrying a loxP-flanked insulin receptor (IR) gene. After CreERT2-loxP-mediated recombination was induced by tamoxifen injection, mice received insulin pellet or sham (control) implantation, and underwent femoral artery wire injury. Femoral arteries were collected for morphological analysis 28 days after wire injury. RESULTS: Tamoxifen-treated Tie2-Cre+ mice showed lower IR expression in ECs, but not in SMCs, than Tie2-Cre- mice. Insulin treatment reduced neointimal area after arterial injury in Tie2-Cre- mice, but had no effect in Tie2-Cre+ mice. Tamoxifen-treated SMMHC-Cre+ mice showed lower IR expression in SMCs, but not in ECs, than SMMHC-Cre- mice. Insulin treatment reduced neointimal area in SMMHC-Cre- mice, whereas unexpectedly, it failed to inhibit neointima formation in SMMHC-Cre+ mice. CONCLUSION: Insulin action in both ECs and SMCs is required for the "anti-restenotic" effect of insulin in vivo.

AKT2 maintains brain endothelial claudin-5 expression and selective activation of IR/AKT2/FOXO1-signaling reverses barrier dysfunction.

Inflammation-induced blood-brain barrier (BBB) dysfunction and microvascular leakage are associated with a host of neurological disorders. The tight junction protein claudin-5 (CLDN5) is a crucial protein necessary for BBB integrity and maintenance. CLDN5 is negatively regulated by the transcriptional repressor FOXO1, whose activity increases during impaired insulin/AKT signaling. Owing to an incomplete understanding of the mechanisms that regulate CLDN5 expression in BBB maintenance and dysfunction, therapeutic interventions remain underdeveloped. Here, we show a novel isoform-specific function for AKT2 in maintenance of BBB integrity. We identified that AKT2 during homeostasis specifically regulates CLDN5-dependent barrier integrity in brain microvascular endothelial cells (BMVECs) and that intervention with a selective insulin-receptor (IR) agonist, demethylasterriquinone B1 (DMAQ-B1), rescued IL-1ß-induced AKT2 inactivation, FOXO1 nuclear accumulation, and loss of CLDN5-dependent barrier integrity. Moreover, DMAQ-B1 attenuated preclinical CLDN5-dependent BBB dysfunction in mice subjected to experimental autoimmune encephalomyelitis. Taken together, the data suggest a regulatory role for IR/AKT2/FOXO1-signaling in CLDN5 expression and BBB integrity during neuroinflammation.

Fish-hunting cone snail venoms are a rich source of minimized ligands of the vertebrate insulin receptor.

The fish-hunting marine cone snail Conus geographus uses a specialized venom insulin to induce hypoglycemic shock in its prey. We recently showed that this venom insulin, Con-Ins G1, has unique characteristics relevant to the design of new insulin therapeutics. Here, we show that fish-hunting cone snails provide a rich source of minimized ligands of the vertebrate insulin receptor. Insulins from C. geographus, Conus tulipa and Conus kinoshitai exhibit diverse sequences, yet all bind to and activate the human insulin receptor. Molecular dynamics reveal unique modes of action that are distinct from any other insulins known in nature. When tested in zebrafish and mice, venom insulins significantly lower blood glucose in the streptozotocin-induced model of diabetes. Our findings suggest that cone snails have evolved diverse strategies to activate the vertebrate insulin receptor and provide unique insight into the design of novel drugs for the treatment of diabetes.

Insulin is a hormone critical for maintaining healthy blood sugar levels in humans. When the insulin system becomes faulty, blood sugar levels become too high, which can lead to diabetes. At the moment, the only effective treatment for one of the major types of diabetes are daily insulin injections. However, designing fast-acting insulin drugs has remained a challenge. Insulin molecules form clusters (so-called hexamers) that first have to dissolve in the body to activate the insulin receptor, which plays a key role in regulating the blood sugar levels throughout the body. This can take time and can therefore delay the blood-sugar control. In 2015, researchers discovered that the fish-hunting cone snail Conus geographus uses a specific type of insulin to capture its prey ­ fish. The cone snail releases insulin into the surrounding water and then engulfs its victim with its mouth. This induces dangerously low blood sugar levels in the fish and so makes them an easy target. Unlike the human version, the snail insulin does not cluster, and despite structural differences, can bind to the human insulin receptor. Now, Ahorukomeye, Disotuar et al. ­ including some of the authors involved in the previous study ­ wanted to find out whether other fish-hunting cone snails also make insulins and if they differed from the one previously discovered in C. geographus. The insulin molecules were extracted and analyzed, and the results showed that the three cone snail species had different versions of insulin ­ but none of them formed clusters. Ahorukomeye, Disotuar et al. further revealed that the snail insulins could bind to the human insulin receptors and could also reverse high blood sugar levels in fish and mouse models of the disease. This research may help guide future studies looking into developing fast-acting insulin drugs for diabetic patients. A next step will be to fully understand how snail insulins can be active at the human receptor without forming clusters. Cone snails solved this problem millions of years ago and by understanding how they have done this, researchers are hoping to redesign current diabetic therapeutics. Since the snail insulins do not form clusters and should act faster than currently available insulin drugs, they may lead to better or new diabetes treatments.

Insulin receptor in the brain: Mechanisms of activation and the role in the CNS pathology and treatment.

While the insulin receptor (IR) was found in the CNS decades ago, the brain was long considered to be an insulin-insensitive organ. This view is currently revisited, given emerging evidence of critical roles of IR-mediated signaling in development, neuroprotection, metabolism, and plasticity in the brain. These diverse cellular and physiological IR activities are distinct from metabolic IR functions in peripheral tissues, thus highlighting region specificity of IR properties. This particularly concerns the fact that two IR isoforms, A and B, are predominantly expressed in either the brain or peripheral tissues, respectively, and neurons express exclusively IR-A. Intriguingly, in comparison with IR-B, IR-A displays high binding affinity and is also activated by low concentrations of insulin-like growth factor-2 (IGF-2), a regulator of neuronal plasticity, whose dysregulation is associated with neuropathologic processes. Deficiencies in IR activation, insulin availability, and downstream IR-related mechanisms may result in aberrant IR-mediated functions and, subsequently, a broad range of brain disorders, including neurodevelopmental syndromes, neoplasms, neurodegenerative conditions, and depression. Here, we discuss findings on the brain-specific features of IR-mediated signaling with focus on mechanisms of primary receptor activation and their roles in the neuropathology. We aimed to uncover the remaining gaps in current knowledge on IR physiology and highlight new therapies targeting IR, such as IR sensitizers.

Evaluation of anti-insulin receptor antibodies as potential novel therapies for human insulin receptoropathy using cell culture models.

AIMS/HYPOTHESIS: Bi-allelic loss-of-function mutations in the INSR gene (encoding the insulin receptor [INSR]) commonly cause extreme insulin resistance and early mortality. Therapeutic options are limited, but anti-INSR antibodies have been shown to activate two mutant receptors, S323L and F382V. This study evaluates four well-characterised murine anti-INSR monoclonal antibodies recognising distinct epitopes (83-7, 83-14, 18-44, 18-146) as surrogate agonists for potential targeted treatment of severe insulin resistance arising from insulin receptoropathies. METHODS: Ten naturally occurring mutant human INSRs with defects affecting different aspects of receptor function were modelled and assessed for response to insulin and anti-INSR antibodies. A novel 3T3-L1 adipocyte model of insulin receptoropathy was generated, permitting conditional knockdown of endogenous mouse Insr by lentiviral expression of species-specific short hairpin (sh)RNAs with simultaneous expression of human mutant INSR transgenes. RESULTS: All expressed mutant INSR bound to all antibodies tested. Eight mutants showed antibody-induced autophosphorylation, while co-treatment with antibody and insulin increased maximal phosphorylation compared with insulin alone. After knockdown of mouse Insr and expression of mutant INSR in 3T3-L1 adipocytes, two antibodies (83-7 and 83-14) activated signalling via protein kinase B (Akt) preferentially over signalling via extracellular signal-regulated kinase 1/2 (ERK1/2) for seven mutants. These antibodies stimulated glucose uptake via P193L, S323L, F382V and D707A mutant INSRs, with antibody response greater than insulin response for D707A. CONCLUSIONS/INTERPRETATION: Anti-INSR monoclonal antibodies can activate selected naturally occurring mutant human insulin receptors, bringing closer the prospect of novel therapy for severe insulin resistance caused by recessive mutations.

Unique pharmacology of a novel allosteric agonist/sensitizer insulin receptor monoclonal antibody.

OBJECTIVE: Insulin resistance is a key feature of Type 2 Diabetes (T2D), and improving insulin sensitivity is important for disease management. Allosteric modulation of the insulin receptor (IR) with monoclonal antibodies (mAbs) can enhance insulin sensitivity and restore glycemic control in animal models of T2D. METHODS: A novel human mAb, IRAB-A, was identified by phage screening using competition binding and surface plasmon resonance assays with the IR extracellular domain. Cell based assays demonstrated agonist and sensitizer effects of IRAB-A on IR and Akt phosphorylation, as well as glucose uptake. Lean and diet-induced obese mice were used to characterize single-dose in vivo pharmacological effects of IRAB-A; multiple-dose IRAB-A effects were tested in obese mice. RESULTS: In vitro studies indicate that IRAB-A exhibits sensitizer and agonist properties distinct from insulin on the IR and is translated to downstream signaling and function; IRAB-A bound specifically and allosterically to the IR and stabilized insulin binding. A single dose of IRAB-A given to lean mice rapidly reduced fed blood glucose for approximately 2 weeks, with concomitant reduced insulin levels suggesting improved insulin sensitivity. Phosphorylated IR (pIR) from skeletal muscle and liver were increased by IRAB-A; however, phosphorylated Akt (pAkt) levels were only elevated in skeletal muscle and not liver vs. control; immunochemistry analysis (IHC) confirmed the long-lived persistence of IRAB-A in skeletal muscle and liver. Studies in diet-induced obese (DIO) mice with IRAB-A reduced fed blood glucose and insulinemia yet impaired glucose tolerance and led to protracted insulinemia during a meal challenge. CONCLUSION: Collectively, the data suggest IRAB-A acts allosterically on the insulin receptor acting non-competitively with insulin to both activate the receptor and enhance insulin signaling. While IRAB-A produced a decrease in blood glucose in lean mice, the data in DIO mice indicated an exacerbation of insulin resistance; these data were unexpected and suggested the interplay of complex unknown pharmacology. Taken together, this work suggests that IRAB-A may be an important tool to explore insulin receptor signaling and pharmacology.

The Biased G-Protein-Coupled Receptor Agonism Bridges the Gap between the Insulin Receptor and the Metabolic Syndrome.

Insulin signaling, as mediated through the insulin receptor (IR), plays a critical role in metabolism. Aberrations in this signaling cascade lead to several pathologies, the majority of which are classified under the umbrella term "metabolic syndrome". Although many of these pathologies are associated with insulin resistance, the exact mechanisms are not well understood. One area of current interest is the possibility of G-protein-coupled receptors (GPCRs) influencing or regulating IR signaling. This concept is particularly significant, because GPCRs have been shown to participate in cross-talk with the IR. More importantly, GPCR signaling has also been shown to preferentially regulate specific downstream signaling targets through GPCR agonist bias. A novel study recently demonstrated that this GPCR-biased agonism influences the activity of the IR without the presence of insulin. Although GPCR-IR cross-talk has previously been established, the notion that GPCRs can regulate the activation of the IR is particularly significant in relation to metabolic syndrome and other pathologies that develop as a result of alterations in IR signaling. As such, we aim to provide an overview of the physiological and pathophysiological roles of the IR within metabolic syndrome and its related pathologies, including cardiovascular health, gut microflora composition, gastrointestinal tract functioning, polycystic ovarian syndrome, pancreatic cancer, and neurodegenerative disorders. Furthermore, we propose that the GPCR-biased agonism may perhaps mediate some of the downstream signaling effects that further exacerbate these diseases for which the mechanisms are currently not well understood.

A Novel Strategy to Prevent Advanced Atherosclerosis and Lower Blood Glucose in a Mouse Model of Metabolic Syndrome.

Cardiovascular disease caused by atherosclerosis is the leading cause of mortality associated with type 2 diabetes and metabolic syndrome. Insulin therapy is often needed to improve glycemic control, but it does not clearly prevent atherosclerosis. Upon binding to the insulin receptor (IR), insulin activates distinct arms of downstream signaling. The IR-Akt arm is associated with blood glucose lowering and beneficial effects, whereas the IR-Erk arm might exert less desirable effects. We investigated whether selective activation of the IR-Akt arm, leaving the IR-Erk arm largely inactive, would result in protection from atherosclerosis in a mouse model of metabolic syndrome. The insulin mimetic peptide S597 lowered blood glucose and activated Akt in insulin target tissues, mimicking insulin's effects, but only weakly activated Erk and even prevented insulin-induced Erk activation. Strikingly, S597 retarded atherosclerotic lesion progression through a process associated with protection from leukocytosis, thereby reducing lesional accumulation of inflammatory Ly6Chi monocytes. S597-mediated protection from leukocytosis was accompanied by reduced numbers of the earliest bone marrow hematopoietic stem cells and reduced IR-Erk activity in hematopoietic stem cells. This study provides a conceptually novel treatment strategy for advanced atherosclerosis associated with metabolic syndrome and type 2 diabetes.

Controlled dimerization of insulin-like growth factor-1 and insulin receptors reveals shared and distinct activities of holo and hybrid receptors.

Breast cancer development and progression are influenced by insulin-like growth factor receptor 1 (IGF1R) and insulin receptor (InsR) signaling, which drive cancer phenotypes such as cell growth, proliferation, and migration. IGF1R and InsR form IGF1R/InsR hybrid receptors (HybRs) consisting of one molecule of IGF1R and one molecule of InsR. The specific signaling and functions of HybR are largely unknown, as HybR is activated by both IGF1 and insulin, and no cellular system expresses HybR in the absence of holo-IGF1R or holo-InsR. Here we studied the role of HybR by constructing inducible chimeric receptors and compared HybR signaling with that of holo-IGF1R and holo-InsR. We cloned chemically inducible chimeric IGF1R and InsR constructs consisting of the extracellular domains of the p75 nerve growth factor receptor fused to the intracellular ß subunit of IGF1R or InsR and a dimerization domain. Dimerization with the drugs AP20187 or AP21967 allowed specific and independent activation of holo-IGF1R, holo-InsR, or HybR, resulting in activation of the PI3K pathway. Holo-IGF1R and HybR both promoted cell proliferation and glucose uptake, whereas holo-InsR only promoted glucose uptake, and only holo-IGF1R showed anti-apoptotic effects. We also found that the three receptors differentially regulated gene expression: holo-IGF1R and HybR up-regulated EGR3; holo-InsR specifically down-regulated JUN and BCL2L1; holo-InsR down-regulated but HybR up-regulated HK2; and HybR specifically up-regulated FHL2, ITGA6, and PCK2. Our findings suggest that, when expressed and activated in mammary epithelial cells, HybR acts in a manner similar to IGF1R and support further investigation of the role of HybR in breast cancer.

Engineering Glucose Responsiveness Into Insulin.

Insulin has a narrow therapeutic index, reflected in a small margin between a dose that achieves good glycemic control and one that causes hypoglycemia. Once injected, the clearance of exogenous insulin is invariant regardless of blood glucose, aggravating the potential to cause hypoglycemia. We sought to create a "smart" insulin, one that can alter insulin clearance and hence insulin action in response to blood glucose, mitigating risk for hypoglycemia. The approach added saccharide units to insulin to create insulin analogs with affinity for both the insulin receptor (IR) and mannose receptor C-type 1 (MR), which functions to clear endogenous mannosylated proteins, a principle used to endow insulin analogs with glucose responsivity. Iteration of these efforts culminated in the discovery of MK-2640, and its in vitro and in vivo preclinical properties are detailed in this report. In glucose clamp experiments conducted in healthy dogs, as plasma glucose was lowered stepwise from 280 mg/dL to 80 mg/dL, progressively more MK-2640 was cleared via MR, reducing by ∼30% its availability for binding to the IR. In dose escalations studies in diabetic minipigs, a higher therapeutic index for MK-2640 (threefold) was observed versus regular insulin (1.3-fold).

[Sar1, Ile4, Ile8]-angiotensin II Potentiates Insulin Receptor Signalling and Glycogen Synthesis in Hepatocytes.

The angiotensin II type I receptor (AT1R) is involved in the regulation of cardiovascular function. Excessive activation of AT1R by angiotensin II (Ang II) leads to cardiovascular disease and may be involved in the development of insulin resistance and diabetes. Functionally selective Ang II analogues, such as the [Sar1, Ile4, Ile8]-angiotensin II (SII Ang II) analogue, that only activate a subset of signalling networks have been demonstrated to have beneficial effects on cardiovascular function in certain settings, including lowering blood pressure and increasing cardiac performance. Here, we studied the effect of SII Ang II on insulin receptor (IR) signalling and glucose metabolism in primary rat hepatocytes. We show that long-term pre-treatment of hepatocytes with SII Ang II increased insulin-stimulated glycogen synthesis, while Ang II and the AT1R antagonist losartan had no effect. Insulin-stimulated suppression of hepatic glucose output was not affected by Ang II or SII Ang II. It is well known that insulin regulates glycogen synthesis and glucose output through Akt-mediated phosphorylation of glycogen synthase kinase α/ß (GSK3α/ß) and forkhead box protein O1 (FOXO1), respectively. In line with this, we show that SII Ang II potentiated insulin-stimulated phosphorylation of Akt and GSK3α/ß, but not FOXO1. Furthermore, we demonstrate that the effect of SII Ang II on insulin-stimulated signalling and glycogen synthesis was dependent on Src and Gαq, as inhibitors of these proteins abolished the potentiating effect of SII Ang II. Thus, our results demonstrate that SII Ang II may have a positive effect on IR signalling and glucose metabolism in hepatocytes.

Hemin Improves Insulin Sensitivity and Lipid Metabolism in Cultured Hepatocytes and Mice Fed a High-Fat Diet.

Hemin is a breakdown product of hemoglobin. It has been reported that the injection of hemin improves lipid metabolism and insulin sensitivity in various genetic models. However, the effect of hemin supplementation in food on lipid metabolism and insulin sensitivity is still unclear, and whether hemin directly affects cellular insulin sensitivity is yet to be elucidated. Here we show that hemin enhances insulin-induced phosphorylation of insulin receptors, Akt, Gsk3ß, FoxO1 and cytoplasmic translocation of FoxO1 in cultured primary hepatocytes under insulin-resistant conditions. Furthermore, hemin diminishes the accumulation of triglyceride and increases in free fatty acid content in primary hepatocytes induced by palmitate. Oral administration of hemin decreases body weight, energy intake, blood glucose and triglyceride levels, and improves insulin and glucose tolerance as well as hepatic insulin signaling and hepatic steatosis in male mice fed a high-fat diet. In addition, hemin treatment decreases the mRNA and protein levels of some hepatic genes involved in lipogenic regulation, fatty acid synthesis and storage, and increases the mRNA level and enzyme activity of CPT1 involved in fatty acid oxidation. These data demonstrate that hemin can improve lipid metabolism and insulin sensitivity in both cultured hepatocytes and mice fed a high-fat diet, and show the potential beneficial effects of hemin from food on lipid and glucose metabolism.

LAPS Insulin115: A novel ultra-long-acting basal insulin with a unique action profile.

AIMS: To conduct a comprehensive pre-clinical study of the novel ultra-long acting insulin analogue LAPS Insulin115. METHODS: Pharmacokinetic/pharmacodynamic studies comparing LAPS Insulin115 with other basal insulins were conducted in genetically diabetic (db/db) mice. Insulin signalling in the major target organs was analysed using Western blot after single subcutaneous injection in wild-type male Wistar rats. Using in vitro assays we analysed transendothelial transport, insulin receptor (IR) interaction, and the mitogenic and metabolic properties of LAPS Insulin115. Furthermore, IR downregulation after long-term exposure to high concentrations of LAPS Insulin115 was analysed using an in vitro desensitization/resensitization model. RESULTS: The novel Fc-conjugated insulin derivative LAPS Insulin115 showed an extensively prolonged pharmacokinetic and pharmacodynamic profile in rodents. Despite its size of 59 kDa, LAPS Insulin115 passes the vascular endothelial barrier and induces insulin signalling in all major target tissues in rats. In vitro, LAPS Insulin115 showed a very slow onset of action because of its reduced IR affinity; however, after long-term stimulation it was equipotent in respect to its metabolic potency and showed no increased mitogenic action when compared with regular insulin. Remarkably, under conditions of chronic exposure, LAPS Insulin115 does not induce irreversible desensitization of target cells, which is probably attributable to much less prominent IR downregulation. CONCLUSION: Thus, LAPS Insulin115 exhibits a unique in vivo and in vitro profile and thereby represents an excellent candidate for a once-weekly insulin analogue.

Effect of Peroral Administration of Chromium on Insulin Signaling Pathway in Skeletal Muscle Tissue of Holstein Calves.

The objective of this study was to investigate the effects of peroral administration of chromium-enriched yeast on glucose tolerance in Holstein calves, assessed by insulin signaling pathway molecule determination and intravenous glucose tolerance test (IVGTT). Twenty-four Holstein calves, aged 1 month, were chosen for the study and divided into two groups: the PoCr group (n = 12) that perorally received 0.04 mg of Cr/kg of body mass daily, for 70 days, and the NCr group (n = 12) that received no chromium supplementation. Skeletal tissue samples from each calf were obtained on day 0 and day 70 of the experiment. Chromium supplementation increased protein content of the insulin ß-subunit receptor, phosphorylation of insulin receptor substrate 1 at Tyrosine 632, phosphorylation of Akt at Serine 473, glucose transporter-4, and AMP-activated protein kinase in skeletal muscle tissue, while phosphorylation of insulin receptor substrate 1 at Serine 307 was not affected by chromium treatment. Results obtained during IVGTT, which was conducted on days 0, 30, 50, and 70, suggested an increased insulin sensitivity and, consequently, a better utilization of glucose in the PoCr group. Lower basal concentrations of glucose and insulin in the PoCr group on days 30 and 70 were also obtained. Our results indicate that chromium supplementation improves glucose utilization in calves by enhancing insulin intracellular signaling in the skeletal muscle tissue.