Insulin analogues differently activate insulin receptor isoforms and post-receptor signalling

Insulin receptor alternative splicing in breast and prostate cancer

Cancer etiology represents an intricate, multifactorial orchestration where metabolically associated insulin-like growth factors (IGFs) and insulin foster cellular proliferation and growth throughout tumorigenesis. The insulin receptor (IR) exhibits two splice variants arising from alternative mRNA processing, namely IR-A, and IR-B, with remarkable distribution and biological effects disparities. This insightful review elucidates the structural intricacies, widespread distribution, and functional significance of IR-A and IR-B. Additionally, it explores the regulatory mechanisms governing alternative splicing processes, intricate signal transduction pathways, and the intricate association linking IR-A and IR-B splicing variants to breast and prostate cancer tumorigenesis. Breast cancer and prostate cancer are the most common malignant tumors with the highest incidence rates among women and men, respectively. These findings provide a promising theoretical framework for advancing preventive strategies, diagnostic modalities, and therapeutic interventions targeting breast and prostate cancer.

Insulin-Dendrimer Nanocomplex for Multi-Day Glucose-Responsive Therapy in Mice and Swine

The management of diabetes in a manner offering autonomous insulin therapy responsive to glucose-directed need, and moreover with a dosing schedule amenable to facile administration, remains an ongoing goal to improve the standard of care. While basal insulins with reduced dosing frequency, even once-weekly administration, are on the horizon, there is still no approved therapy that offers glucose-responsive insulin function. Herein, a nanoscale complex combining both electrostatic- and dynamic-covalent interactions between a synthetic dendrimer carrier and an insulin analogue modified with a high-affinity glucose-binding motif yields an injectable insulin depot affording both glucose-directed and long-lasting insulin availability. Following a single injection, it is even possible to control blood glucose for at least one week in diabetic swine subjected to daily oral glucose challenges. Measurements of serum insulin concentration in response to challenge show increases in insulin corresponding to elevated blood glucose levels, an uncommon finding even in preclinical work on glucose-responsive insulin. Accordingly, the subcutaneous nanocomplex that results from combining electrostatic- and dynamic-covalent interactions between a modified insulin and a synthetic dendrimer carrier affords a glucose-responsive insulin depot for week-long control following a single routine injection.

Drug repositioning in thyroid cancer treatment: the intriguing case of anti-diabetic drugs

Cancer represents the main cause of death worldwide. Thyroid cancer (TC) shows an overall good rate of survival, however there is a percentage of patients that do not respond or are refractory to common therapies. Thus new therapeutics strategies are required. In the past decade, drug repositioning become very important in the field of cancer therapy. This approach shows several advantages including the saving of: i) time, ii) costs, iii) de novo studies regarding the safety (just characterized) of a drug. Regarding TC, few studies considered the potential repositioning of drugs. On the other hand, certain anti-diabetic drugs, were the focus of interesting studies on TC therapy, in view of the fact that they exhibited potential anti-tumor effects. Among these anti-diabetic compounds, not all were judjed as appropriate for repositioning, in view of well documented side effects. However, just to give few examples biguanides, DPP-4-inhibitors and Thiazolidinediones were found to exert strong anti-cancer effects in TC. Indeed, their effects spaced from induction of citotoxicity and inhibition of metastatic spread, to induction of de-differentiation of TC cells and modulation of TC microenvironment. Thus, the multifacial anti-cancer effect of these compounds would make the basis also for combinatory strategies. The present review is aimed at discuss data from studies regarding the anti-cancer effects of several anti-diabetic drugs recently showed in TC in view of their potential repositioning. Specific examples of anti-diabetic repositionable drugs for TC treatment will also be provided.

Insulin-like peptides and ovary ecdysteroidogenic hormone differentially stimulate physiological processes regulating egg formation in the mosquito Aedes aegypti

Mosquitoes including Aedes aegypti are human disease vectors because females must blood feed to produce and lay eggs. Blood feeding triggers insulin-insulin growth factor signaling (IIS) which regulates several physiological processes required for egg development. A. aegypti encodes 8 insulin-like peptides (ILPs) and one insulin-like receptor (IR) plus ovary ecdysteroidogenic hormone (OEH) that also activates IIS through the OEH receptor (OEHR). In this study, we assessed the expression of A. aegypti ILPs and OEH during a gonadotrophic cycle and produced each that were functionally characterized to further understand their roles in regulating egg formation. All A. aegypti ILPs and OEH were expressed during a gonadotrophic cycle. Five ILPs (1, 3, 4, 7, 8) and OEH were specifically expressed in the head, while antibodies to ILP3 and OEH indicated each was released after blood feeding from ventricular axons that terminate on the anterior midgut. A subset of ILP family members and OEH stimulated nutrient storage in previtellogenic females before blood feeding, whereas most IIS-dependent processes after blood feeding were activated by one or more of the brain-specific ILPs and/or OEH. ILPs and OEH with different biological activities also exhibited differences in IIS as measured by phosphorylation of the IR, phosphoinositide 3-kinase/Akt kinase (AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK). Altogether, our results provide the first results that compare the functional activities of all ILP family members and OEH produced by an insect.

Insulin receptor Arg717 and IGF-1 receptor Arg704 play a key role in ligand binding and in receptor activation

The insulin receptor (IR, with its isoforms IR-A and IR-B) and the insulin-like growth factor 1 receptor (IGF-1R) are related tyrosine kinase receptors. Recently, the portfolio of solved hormone-receptor structures has grown extensively thanks to advancements in cryo-electron microscopy. However, the dynamics of how these receptors transition between their inactive and active state are yet to be fully understood. The C-terminal part of the alpha subunit (αCT) of the receptors is indispensable for the formation of the hormone-binding site. We mutated the αCT residues Arg717 and His710 of IR-A and Arg704 and His697 of IGF-1R. We then measured the saturation binding curves of ligands on the mutated receptors and their ability to become activated. Mutations of Arg704 and His697 to Ala in IGF-1R decreased the binding of IGF-1. Moreover, the number of binding sites for IGF-1 on the His697 IGF-1R mutant was reduced to one-half, demonstrating the presence of two binding sites. Both mutations of Arg717 and His710 to Ala in IR-A inactivated the receptor. We have proved that Arg717 is important for the binding of insulin to its receptor, which suggests that Arg717 is a key residue for the transition to the active conformation.

Insulin signaling in development

Nutrient intake is obligatory for animal growth and development, but nutrients alone are not sufficient. Indeed, insulin and homologous hormones are required for normal growth even in the presence of nutrients. These hormones communicate nutrient status between organs, allowing animals to coordinate growth and metabolism with nutrient supply. Insulin and related hormones, such as insulin-like growth factors and insulin-like peptides, play important roles in development and metabolism, with defects in insulin production and signaling leading to hyperglycemia and diabetes. Here, we describe the insulin hormone family and the signal transduction pathways activated by these hormones. We highlight the roles of insulin signaling in coordinating maternal and fetal metabolism and growth during pregnancy, and we describe how secretion of insulin is regulated at different life stages. Additionally, we discuss the roles of insulin signaling in cell growth, stem cell proliferation and cell differentiation. We provide examples of the role of insulin in development across multiple model organisms: Caenorhabditis elegans, Drosophila, zebrafish, mouse and human.

Insulin Receptor Isoforms and Insulin Growth Factor-like Receptors: Implications in Cell Signaling, Carcinogenesis, and Chemoresistance

This comprehensive review thoroughly explores the intricate involvement of insulin receptor (IR) isoforms and insulin-like growth factor receptors (IGFRs) in the context of the insulin and insulin-like growth factor (IGF) signaling (IIS) pathway. This elaborate system encompasses ligands, receptors, and binding proteins, giving rise to a wide array of functions, including aspects such as carcinogenesis and chemoresistance. Detailed genetic analysis of IR and IGFR structures highlights their distinct isoforms, which arise from alternative splicing and exhibit diverse affinities for ligands. Notably, the overexpression of the IR-A isoform is linked to cancer stemness, tumor development, and resistance to targeted therapies. Similarly, elevated IGFR expression accelerates tumor progression and fosters chemoresistance. The review underscores the intricate interplay between IRs and IGFRs, contributing to resistance against anti-IGFR drugs. Consequently, the dual targeting of both receptors could present a more effective strategy for surmounting chemoresistance. To conclude, this review brings to light the pivotal roles played by IRs and IGFRs in cellular signaling, carcinogenesis, and therapy resistance. By precisely modulating these receptors and their complex signaling pathways, the potential emerges for developing enhanced anti-cancer interventions, ultimately leading to improved patient outcomes.

The insulin receptor endocytosis

Insulin signaling controls multiple aspects of animal physiology. At the cell surface, insulin binds and activates the insulin receptor (IR), a receptor tyrosine kinase. Insulin promotes a large conformational change of IR and stabilizes the active conformation. The insulin-activated IR triggers signaling cascades, thus controlling metabolism, growth, and proliferation. The activated IR undergoes internalization by clathrin- or caveolae-mediated endocytosis. The IR endocytosis plays important roles in insulin clearance from blood, and distribution and termination of the insulin signaling. Despite decades of extensive studies, the mechanism and regulation of IR endocytosis and its contribution to pathophysiology remain incompletely understood. Here we discuss recent findings that provide insights into the molecular mechanisms and regulatory pathways that mediate the IR endocytosis.

Interaction of a viral insulin-like peptide with the IGF-1 receptor produces a natural antagonist

Lymphocystis disease virus-1 (LCDV-1) and several other Iridoviridae encode viral insulin/IGF-1 like peptides (VILPs) with high homology to human insulin and IGFs. Here we show that while single-chain (sc) and double-chain (dc) LCDV1-VILPs have very low affinity for the insulin receptor, scLCDV1-VILP has high affinity for IGF1R where it can antagonize human IGF-1 signaling, without altering insulin signaling. Consequently, scLCDV1-VILP inhibits IGF-1 induced cell proliferation and growth hormone/IGF-1 induced growth of mice in vivo. Cryo-electron microscopy reveals that scLCDV1-VILP engages IGF1R in a unique manner, inducing changes in IGF1R conformation that led to separation, rather than juxtaposition, of the transmembrane segments and hence inactivation of the receptor. Thus, scLCDV1-VILP is a natural peptide with specific antagonist properties on IGF1R signaling and may provide a new tool to guide development of hormonal analogues to treat cancers or metabolic disorders sensitive to IGF-1 without affecting glucose metabolism.

Maternal and neonatal outcomes with the use of long acting, compared to intermediate acting basal insulin (NPH) for managing diabetes during pregnancy: a systematic review and meta-analysis

BACKGROUND

To assess the impact of long-acting insulin analogues, compared to intermediate acting neutral protamine Hagedron (NPH), on maternal, perinatal and neonatal outcomes.

METHODS

Studies for inclusion in the review were identified using a structured search strategy in PubMed, Scopus and Cochrane Central Register of Controlled Trials (CENTRAL) database. Studies that were randomized controlled trials or observational in design were considered for inclusion. Eligible studies should have compared the maternal, perinatal and neonatal outcomes between pregnant women with gestational diabetes mellitus (GDM) managed by intermediate acting (NPH) and by long-acting insulin analogues. Statistical analysis was performed using STATA software.

RESULTS

We found 17 studies to be eligible for inclusion. The mean gestational weight gain and risk of maternal hypoglycaemia, hypertensive disorder, caesarean delivery, spontaneous abortion, endometritis and wound infection or dehiscence were similar among pregnant women with GDM managed using long-acting insulin analogues and NPH. Those receiving long-acting insulin analogues had significantly lower HbA1c values in the second (WMD - .09, 95% CI 0.12, - 0.06; N = 4) and third trimester (WMD - 0.08, 95% CI - 0.14, - 0.02; N = 12). The mean gestational age and birth weight and risk of perinatal mortality, prematurity, large for gestational age, small for gestational age, shoulder dystocia and congenital abnormalities was similar among babies in both groups. No statistically significant differences in risk of admission to neonatal intensive care unit, respiratory distress, neonatal hypoglycaemia, 5 min APGAR score of < 7, neonatal hyperbilirubinemia and sepsis was observed. The quality of pooled evidence, as per GRADE criteria, was judged to be "very low" for all the maternal and neonatal outcomes considered.

CONCLUSIONS

Findings suggest no significant differences in the maternal, perinatal and neonatal outcomes between intermediate and long-acting insulin analogues. The results provide support for use of long-acting insulin analogues in women with GDM. However, evidence is still needed from high quality randomized controlled trials to arrive at a recommendation for inclusion in routine clinical care.

Impact of Insulin Therapies on Cancer Incidence in Type 1 and Type 2 Diabetes: A Population-Based Cohort Study in Reggio Emilia, Italy

Simple Summary

The aim of this population-based study was to assess the impact of insulin treatment on cancer incidence in subjects with type 1 or type 2 diabetes in Italy. We found that insulin use was associated with a 20% excess for all sites cancer incidence among people with type 2 diabetes, while people with type 1 diabetes did not show any excess. Liver, pancreatic, bladder, and neuroendocrine cancers seem to be the sites with strongest association.

Abstract

Objective: To assess the effect of insulin on cancer incidence in type 1 (T1DM) and type 2 diabetes (T2DM). Methods: The cohort included all 401,172 resident population aged 20–84 in December 2009 and still alive on December 2011, classified for DM status. Drug exposure was assessed for 2009–2011 and follow up was conducted from 2012 to 2016 through the cancer registry. Incidence rate ratios (IRRs) were computed for all sites and for the most frequent cancer sites. Results: among residents, 21,190 people had diabetes, 2282 of whom were taking insulin; 1689 cancers occurred, 180 among insulin users. The risk for all site was slightly higher in people with T2DM compared to people without DM (IRR 1.21, 95% CI 1.14–1.27), with no excess for T1DM (IRR 0.73, 95% CI 0.45–1.19). The excess in T2DM remained when comparing with diet-only treatment. In T2DM, excess incidence was observed for liver and pancreas and for NETs: 1.76 (95% CI 1.44–2.17) and 1.37 (95% CI 0.99–1.73), respectively. For bladder, there was an excess both in T1DM (IRR 3.00, 95% CI 1.12, 8.02) and in T2DM (IRR1.27, 95% CI 1.07–1.50). Conclusions: Insulin was associated with a 20% increase in cancer incidence. The risk was higher for liver, pancreatic, bladder and neuroendocrine tumours.

Dysmetabolism and Neurodegeneration: Trick or Treat?

Accumulating evidence suggests the existence of a strong link between metabolic syndrome and neurodegeneration. Indeed, epidemiologic studies have described solid associations between metabolic syndrome and neurodegeneration, whereas animal models contributed for the clarification of the mechanistic underlying the complex relationships between these conditions, having the development of an insulin resistance state a pivotal role in this relationship. Herein, we review in a concise manner the association between metabolic syndrome and neurodegeneration. We start by providing concepts regarding the role of insulin and insulin signaling pathways as well as the pathophysiological mechanisms that are in the genesis of metabolic diseases. Then, we focus on the role of insulin in the brain, with special attention to its function in the regulation of brain glucose metabolism, feeding, and cognition. Moreover, we extensively report on the association between neurodegeneration and metabolic diseases, with a particular emphasis on the evidence observed in animal models of dysmetabolism induced by hypercaloric diets. We also debate on strategies to prevent and/or delay neurodegeneration through the normalization of whole-body glucose homeostasis, particularly via the modulation of the carotid bodies, organs known to be key in connecting the periphery with the brain.

Insulin therapy and biliary tract cancer: insights from real-world data

OBJECTIVE

The association between insulin therapy and the risk of biliary tract cancer (BTC) is uncertain. We aimed to assess this risk in type 2 diabetic patients.

METHODS

Using electronic medical data from the Shanghai Hospital Link database, 202,557 patients with type 2 diabetes (164,997 insulin never-users and 37,560 insulin ever-users) were identified in this study between January 1, 2013, and December 31, 2016, with follow-up until December 31, 2019. By propensity score matching, an ever-user was matched with a never-user. Cox proportional hazards regression analysis was used to estimate risk ratios (HRs) and 95% CIs for three subtypes of BTC (intrahepatic cholangiocarcinoma (ICC), extrahepatic cholangiocarcinoma (ECC), and gallbladder cancer (GBC)).

RESULTS

At a mean follow-up of 5.33 years, 143 cases of BTC were observed. The crude incidence rates (per 100,000 person-years) of ECC, ICC, and GBC in ever-users:never-users were 10.22:3.63, 2.04:2.04, and 8.17:6.01, respectively. Insulin therapy was associated with an increased risk of ECC (HR, 4.10; 95% CI, 1.54-10.92; P = 0.005) compared to patients who never used insulin. No statistically significant results were observed for insulin and ICC/GBC. Consistent results were also found in the original cohort.

CONCLUSIONS

The relationship between insulin therapy and BTC is type-specific. Further studies are warranted to provide evidence on the identification of ECC risk groups among type 2 diabetic patients.

The Relationship Between Diabetes Mellitus and Cancers and Its Underlying Mechanisms

Epidemiological studies suggest associations between diabetes mellitus and some cancers. The risk of a number of cancers appears to be increased in diabetes mellitus. On the other hand, some cancer and cancer therapies could lead to diabetes mellitus. Genetic factors, obesity, inflammation, oxidative stress, hyperglycemia, hyperinsulinemia, cancer therapies, insulin and some oral hypoglycemic drugs appear to play a role in the crosstalk between diabetes mellitus and cancers. This review summarized the associations between various types of diabetes and cancers and updated available evidence of underlying mechanisms between diabetes and cancers.

Minimizing Mitogenic Potency of Insulin Analogues Through Modification of a Disulfide Bond

The mechanisms by which insulin activates the insulin receptor to promote metabolic processes and cellular growth are still not clear. Significant advances have been gained from recent structural studies in understanding how insulin binds to its receptor. However, the way in which specific interactions lead to either metabolic or mitogenic signalling remains unknown. Currently there are only a few examples of insulin receptor agonists that have biased signalling properties. Here we use novel insulin analogues that differ only in the chemical composition at the A6-A11 bond, as it has been changed to a rigid, non-reducible C=C linkage (dicarba bond), to reveal mechanisms underlying signaling bias. We show that introduction of an A6-A11 cis-dicarba bond into either native insulin or the basal/long acting insulin glargine results in biased signalling analogues with low mitogenic potency. This can be attributed to reduced insulin receptor activation that prevents effective receptor internalization and mitogenic signalling. Insight gained into the receptor interactions affected by insertion of an A6-A11 cis-dicarba bond will ultimately assist in the development of new insulin analogues for the treatment of diabetes that confer low mitogenic activity and therefore pose minimal risk of promoting cancer with long term use.

Gestational Diabetes Mellitus Among Asians - A Systematic Review From a Population Health Perspective

OBJECTIVE

Since Asians are particularly vulnerable to the risk of gestational diabetes mellitus (GDM), the lifecourse health implications of which are far beyond pregnancy, we aimed to summarize the literature to understand the research gaps on current GDM research among Asians.

METHODS

We systematically searched the articles in PubMed, Web of Science, Embase, and Scopus by 30 June 2021 with keywords applied on three topics, namely "GDM prevalence in Asians", "GDM and maternal health outcomes in Asians", and "GDM and offspring health outcomes in Asians".

RESULTS

We observed that Asian women (natives and immigrants) are at the highest risk of developing GDM and subsequent progression to type 2 diabetes among all populations. Children born to GDM-complicated pregnancies had a higher risk of macrosomia and congenital anomalies (i.e. heart, kidney and urinary tract) at birth and greater adiposity later in life.

CONCLUSION

This review summarized various determinants underlying the conversion between GDM and long-term health outcomes in Asian women, and it might shed light on efforts to prevent GDM and improve the lifecourse health in Asians from a public health perspective.

SYSTEMATIC REVIEW REGISTRATION

Prospero, CRD42021286075.

New Intracellular Peptide Derived from Hemoglobin Alpha Chain Induces Glucose Uptake and Reduces Blood Glycemia

Intracellular peptides were shown to derive from proteasomal degradation of proteins from mammalian and yeast cells, being suggested to play distinctive roles both inside and outside these cells. Here, the role of intracellular peptides previously identified from skeletal muscle and adipose tissues of C57BL6/N wild type (WT) and neurolysin knockout mice were investigated. In differentiated C2C12 mouse skeletal muscle cells, some of these intracellular peptides like insulin activated the expression of several genes related to muscle contraction and gluconeogenesis. One of these peptides, LASVSTVLTSKYR (Ric4; 600 µg/kg), administrated either intraperitoneally or orally in WT mice, decreased glycemia. Neither insulin (10 nM) nor Ric4 (100 µM) induced glucose uptake in adipose tissue explants obtained from conditional knockout mice depleted of insulin receptor. Ric4 (100 µM) similarly to insulin (100 nM) induced Glut4 translocation to the plasma membrane of C2C12 differentiated cells, and increased GLUT4 mRNA levels in epididymal adipose tissue of WT mice. Ric4 (100 µM) increased both Erk and Akt phosphorylation in C2C12, as well as in epididymal adipose tissue from WT mice; Erk, but not Akt phosphorylation was activated by Ric4 in tibial skeletal muscle from WT mice. Ric4 is rapidly degraded in vitro by WT liver and kidney crude extracts, such a response that is largely reduced by structural modifications such as N-terminal acetylation, C-terminal amidation, and substitution of Leu8 for DLeu8 (Ac-LASVSTV[DLeu]TSKYR-NH2; Ric4-16). Ric4-16, among several Ric4 derivatives, efficiently induced glucose uptake in differentiated C2C12 cells. Among six Ric4-derivatives evaluated in vivo, Ac-LASVSTVLTSKYR-NH2 (Ric4-2; 600 µg/kg) and Ac-LASVSTV[DLeu]TSKYR (Ric4-15; 600 µg/kg) administrated orally efficiently reduced glycemia in a glucose tolerance test in WT mice. The potential clinical application of Ric4 and Ric4-derivatives deserves further attention.

Insulin Receptor Isoforms Differently Regulate Cell Proliferation and Apoptosis in the Ligand-Occupied and Unoccupied State

The insulin receptor (IR) presents two isoforms (IR-A and IR-B) that differ for the α-subunit C-terminal. Both isoforms are expressed in all human cells albeit in different proportions, yet their functional properties-when bound or unbound to insulin-are not well characterized. From a cell model deprived of the Insulin-like Growth Factor 1 Receptor (IGF1-R) we therefore generated cells exhibiting no IR (R-shIR cells), or only human IR-A (R-shIR-A), or exclusively human IR-B (R-shIR-B) and we studied the specific effect of the two isoforms on cell proliferation and cell apoptosis. In the absence of insulin both IR-A and IR-B similarly inhibited proliferation but IR-B was 2–3 fold more effective than IR-A in reducing resistance to etoposide-induced DNA damage. In the presence of insulin, IR-A and IR-B promoted proliferation with the former significantly more effective than the latter at increasing insulin concentrations. Moreover, only insulin-bound IR-A, but not IR-B, protected cells from etoposide-induced cytotoxicity. In conclusion, IR isoforms have different effects on cell proliferation and survival. When unoccupied, IR-A, which is predominantly expressed in undifferentiated and neoplastic cells, is less effective than IR-B in protecting cells from DNA damage. In the presence of insulin, particularly when present at high levels, IR-A provides a selective growth advantage.

Gestational diabesity and foetoplacental vascular dysfunction

Gestational diabetes mellitus (GDM) shows a deficiency in the metabolism of D-glucose and other nutrients, thereby negatively affecting the foetoplacental vascular endothelium. Maternal hyperglycaemia and hyperinsulinemia play an important role in the aetiology of GDM. A combination of these and other factors predisposes women to developing GDM with pre-pregnancy normal weight, viz. classic GDM. However, women with GDM and prepregnancy obesity (gestational diabesity, GDty) or overweight (GDMow) show a different metabolic status than women with classic GDM. GDty and GDMow are associated with altered l-arginine/nitric oxide and insulin/adenosine axis signalling in the human foetoplacental microvascular and macrovascular endothelium. These alterations differ from those observed in classic GDM. Here, we have reviewed the consequences of GDty and GDMow in the modulation of foetoplacental endothelial cell function, highlighting studies describing the modulation of intracellular pH homeostasis and the potential implications of NO generation and adenosine signalling in GDty-associated foetal vascular insulin resistance. Moreover, with an increase in the rate of obesity in women of childbearing age worldwide, the prevalence of GDty is expected to increase in the next decades. Therefore, we emphasize that women with GDty and GDMow should be characterized with a different metabolic state from that of women with classic GDM to develop a more specific therapeutic approach for protecting the mother and foetus.

The brain as an insulin-sensitive metabolic organ

Background

The brain was once thought of as an insulin-insensitive organ. We now know that the insulin receptor is present throughout the brain and serves important functions in whole-body metabolism and brain function. Brain insulin signaling is involved not only in brain homeostatic processes but also neuropathological processes such as cognitive decline and Alzheimer's disease.

Scope of review

In this review, we provide an overview of insulin signaling within the brain and the metabolic impact of brain insulin resistance and discuss Alzheimer's disease, one of the neurologic diseases most closely associated with brain insulin resistance.

Major conclusions

While brain insulin signaling plays only a small role in central nervous system glucose regulation, it has a significant impact on the brain's metabolic health. Normal insulin signaling is important for mitochondrial functioning and normal food intake. Brain insulin resistance contributes to obesity and may also play an important role in neurodegeneration.

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Insulin is an important regulator of brain metabolism.

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Brain insulin signaling helps regulate whole body metabolism.

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Brain insulin signaling may play an important role in the pathogenesis of Alzheimer's disease.

The biophysical basis of receptor tyrosine kinase ligand functional selectivity: Trk-B case study

Tropomyosin receptor kinase B (Trk-B) belongs to the second largest family of membrane receptors, Receptor Tyrosine Kinases (RTKs). Trk-B is known to interact with three different neurotrophins: Brain-Derived Neurotrophic Factor (BDNF), Neurotrophin-4 (NT-4), and Neurotrophin-3 (NT-3). All three neurotrophins are involved in survival and proliferation of neuronal cells, but each induces distinct signaling through Trk-B. We hypothesize that the different biological effects correlate with differences in the interactions between the Trk-B receptors, when bound to different ligands, in the plasma membrane. To test this hypothesis, we use quantitative FRET to characterize Trk-B dimerization in response to NT-3 and NT-4 in live cells, and compare it to the previously published data for Trk-B in the absence and presence of BDNF. Our study reveals that the distinct Trk-B signaling outcomes are underpinned by both different configurations and different stabilities of the three ligand-bound Trk-B dimers in the plasma membrane.

Regulation of ecdysone production in Drosophila by neuropeptides and peptide hormones

In both mammals and insects, steroid hormones play a major role in directing the animal's progression through developmental stages. To maximize fitness outcomes, steroid hormone production is regulated by the environmental conditions experienced by the animal. In insects, the steroid hormone ecdysone mediates transitions between developmental stages and is regulated in response to environmental factors such as nutrition. These environmental signals are communicated to the ecdysone-producing gland via the action of neuropeptide and peptide hormone signalling pathways. While some of these pathways have been well characterized, there is evidence to suggest more signalling pathways than has previously been thought function to control ecdysone production, potentially in response to a greater range of environmental conditions. Here, we review the neuropeptide and peptide hormone signalling pathways known to regulate the production of ecdysone in the model genetic insect Drosophila melanogaster, as well as what is known regarding the environmental signals that trigger these pathways. Areas for future research are highlighted that can further contribute to our overall understanding of the complex orchestration of environmental, physiological and developmental cues that together produce a functioning adult organism.

Ligand bias in receptor tyrosine kinase signaling

Ligand bias is the ability of ligands to differentially activate certain receptor signaling responses compared with others. It reflects differences in the responses of a receptor to specific ligands and has implications for the development of highly specific therapeutics. Whereas ligand bias has been studied primarily for G protein-coupled receptors (GPCRs), there are also reports of ligand bias for receptor tyrosine kinases (RTKs). However, the understanding of RTK ligand bias is lagging behind the knowledge of GPCR ligand bias. In this review, we highlight how protocols that were developed to study GPCR signaling can be used to identify and quantify RTK ligand bias. We also introduce an operational model that can provide insights into the biophysical basis of RTK activation and ligand bias. Finally, we discuss possible mechanisms underpinning RTK ligand bias. Thus, this review serves as a primer for researchers interested in investigating ligand bias in RTK signaling.

Oleanane Triterpenoids from the Leaves of Gymnema inodorum and Their Insulin Mimetic Activities

During an effort to find insulin mimetic compounds, the leaves of Gymnema inodorum were shown to have a stimulatory effect on glucose uptake in 3T3-L1 adipocyte cells. Bioassay-guided fractionation on a 70% ethanol extract of G. inodorum was applied to yield two new (1 and 2) and two known (8 and 9) oleanane triterpenoids with a methyl anthranilate moiety together with five further new oleanane triterpenoids (3-7). The chemical structures of all isolates were determined based on their spectroscopic data, including IR, UV, NMR, and mass spectrometric analysis. The isolated compounds (1-9) were determined for their stimulatory activities on glucose uptake in differentiated 3T3-L1 adipocyte cells using 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-d-glucose (2-NBDG) as a fluorescent-tagged glucose probe. Three compounds (3, 5, and 9) showed stimulatory effects on the uptake of 2-NBDG in 3T3-L1 adipocyte cells. Chemicals with a methyl anthranilate moiety have been considered as crucial contributors of flavor odor in foods, and quantitative analysis showed the content of compound 8 to be 0.90 ± 0.01 mg/g of the total extract. These results suggest that the leaves of G. inodorum have the potential to be used as an antidiabetic functional food or tea.

Diabetes and Cancer: Cancer Should Be Screened in Routine Diabetes Assessment

Cancer incidence appears to be increased in both type 1 and type 2 diabetes mellitus (DM). DM represents a risk factor for cancer, particularly hepatocellular, hepatobiliary, pancreas, breast, ovarian, endometrial, and gastrointestinal cancers. In addition, there is evidence showing that DM is associated with increased cancer mortality. Common risk factors such as age, obesity, physical inactivity and smoking may contribute to increased cancer risk in patients with DM. Although the mechanistic process that may link diabetes to cancer is not completely understood yet, biological mechanisms linking DM and cancer are hyperglycemia, hyperinsulinemia, increased bioactivity of insulin-like growth factor 1, oxidative stress, dysregulations of sex hormones, and chronic inflammation. However, cancer screening rate is significantly lower in people with DM than that in people without diabetes. Evidence from previous studies suggests that some medications used to treat DM are associated with either increased or reduced risk of cancer. However, there is no strong evidence supporting the association between the use of anti-hyperglycemic medication and specific cancer. In conclusion, all patients with DM should be undergo recommended age- and sex appropriate cancer screenings to promote primary prevention and early detection. Furthermore, cancer should be screened in routine diabetes assessment.

Insulin Therapy and Diabetic Pregnancy

BACKGROUND

A good metabolic control before conception and throughout pregnancy with diabetes decreases the risk of short- and long-term adverse outcomes of the mothers and their offsprings. Insulin treatment remains the gold standard treatment recommended for any type of diabetes. New technologies including new insulins and insulin analogues, continuous subcutaneous insulin infusion without and with sensors, the low-glucose predictive suspension function, and closed-loop systems that persistently and automatically self-adjust according to patients' continuous glucose monitoring readings have expanded the offer to clinicians for achieving tight glucose control.

AREAS OF UNCERTAINTY

Unsafe effects of insulin and insulin analogues in pregnancy with diabetes could be linked with changes in insulin immunogenicity, teratogenicity, and mitogenicity. Second-generation insulin analogues need to be tested and proven. Effectiveness and safety of new insulin delivery systems in real life of diabetic women in pregnancy need further confirmations.

SOURCES

MEDLINE, EMBASE, Web of Science, Cochrane Library, randomized controlled trials, systematic review and meta-analysis, observational prospective and retrospective studies, case series reports for the most recent insulin analogues, published in English impacted journals, and consensus statements from scientific societies I excluded 60 from 221 papers as not suitable for the purpose of the subject.

RESULTS

Subcutaneous insulin infusion can be safely used during pregnancy and delivery of well-trained women. Sensors are increasingly accurate tools that improve the efficacy and safety of integrated systems' functioning. Continuous glucose monitoring provides metrics ("time in range" time in "hypoglycemia" and in "hyperglycemia," glucose variability, average glucose levels in different time intervals) used as a guide to diabetes management; these new metrics are object of discussion in special populations. Randomized controlled trials have shown that sensor-augmented pump therapy improves pregnancy outcomes in women with type 1 diabetes. Closed-loop insulin delivery provides better glycemic control than sensor-augmented pump therapy during pregnancy, before, and after delivery.

CONCLUSION

Second-generation insulin analogues and newer insulin infusion systems that automatically self-adjust according to patients continuous glucose monitor readings are important tools improving the treatment and quality of life of these women. Multi-institutional and disciplinary teams are working to develop and evaluate a pregnancy-specific artificial pancreas.

Lipid mediators of insulin signaling in diabetic kidney disease

Diabetic kidney disease (DKD) affects ∼40% of patients with diabetes and is associated with high mortality rates. Among different cellular targets in DKD, podocytes, highly specialized epithelial cells of the glomerular filtration barrier, are injured in the early stages of DKD. Both clinical and experimental data support the role of preserved insulin signaling as a major contributor to podocyte function and survival. However, little is known about the key modulators of podocyte insulin signaling. This review summarizes the novel knowledge that intracellular lipids such as cholesterol and sphingolipids are major determinants of podocyte insulin signaling. In particular, the implications of these lipids on DKD development, progression, and treatment will be addressed.

Insulin/IGF signaling and discoidin domain receptors: An emerging functional connection

The insulin/insulin-like growth factor system (IIGFs) plays a fundamental role in the regulation of prenatal and postnatal growth, metabolism and homeostasis. As a consequence, dysregulation of this axis is associated with growth disturbance, type 2 diabetes, chronic inflammation and tumor progression. A functional crosstalk between IIGFs and discoidin domain receptors (DDRs) has been recently discovered. DDRs are non-integrin collagen receptors that canonically undergo slow and long-lasting autophosphorylation after binding to fibrillar collagen. While both DDR1 and DDR2 functionally interact with IIGFs, the crosstalk with DDR1 is so far better characterized. Notably, the IIGFs-DDR1 crosstalk presents a feed-forward mechanism, which does not require collagen binding, thus identifying novel non-canonical action of DDR1. Further studies are needed to fully explore the role of this IIGFs-DDRs functional loop as potential target in the treatment of inflammatory and neoplastic disorders.

Insulin and Insulin Receptors in Adipose Tissue Development

Insulin is a major endocrine hormone also involved in the regulation of energy and lipid metabolism via the activation of an intracellular signaling cascade involving the insulin receptor (INSR), insulin receptor substrate (IRS) proteins, phosphoinositol 3-kinase (PI3K) and protein kinase B (AKT). Specifically, insulin regulates several aspects of the development and function of adipose tissue and stimulates the differentiation program of adipose cells. Insulin can activate its responses in adipose tissue through two INSR splicing variants: INSR-A, which is predominantly expressed in mesenchymal and less-differentiated cells and mainly linked to cell proliferation, and INSR-B, which is more expressed in terminally differentiated cells and coupled to metabolic effects. Recent findings have revealed that different distributions of INSR and an altered INSR-A:INSR-B ratio may contribute to metabolic abnormalities during the onset of insulin resistance and the progression to type 2 diabetes. In this review, we discuss the role of insulin and the INSR in the development and endocrine activity of adipose tissue and the pharmacological implications for the management of obesity and type 2 diabetes.

Metabolic Syndrome and Skin Diseases

The increasing prevalence of Metabolic syndrome (MetS) is a worldwide health problem, and the association between MetS and skin diseases has recently attracted growing attention. In this review, we summarize the associations between MetS and skin diseases, such as psoriasis, acne vulgaris, hidradenitis suppurativa, androgenetic alopecia, acanthosis nigricans, and atopic dermatitis. To discuss the potential common mechanisms underlying MetS and skin diseases, we focus on insulin signaling and insulin resistance, as well as chronic inflammation including adipokines and proinflammatory cytokines related to molecular mechanisms. A better understanding of the relationship between MetS and skin diseases contributes to early diagnosis and prevention, as well as providing clues for developing novel therapeutic strategies.

Evaluation of the Association between Gestational Diabetes Mellitus at First Pregnancy and Cancer within 10 Years Postpartum Using National Health Insurance Data in South Korea

This study aims to evaluate the association between gestational diabetes mellitus (GDM) at first pregnancy and the incidence of cancer within 10 years postpartum. We used customized health information data from the National Health Insurance Corporation (NHIC). This retrospective cohort study included data from women who were not previously diagnosed with diabetes or any kind of malignancy in the National Health Screening Examination through the NHIC during 2002–2003, and only women who had their first delivery between 2004 and 2005 was included. Follow-up cancer diagnosis was carried out up until 2015. Among the 102,900 primiparous women, 4970 (4.83%) were diagnosed with GDM. During 10 year total follow-up period, 6569 (6.38%) cases of primary cancer were identified. The incidence of cancer was higher in women with GDM and the most common type of cancer was thyroid cancer, followed by breast cancer. On the basis of survival analysis, we adopted the Cox proportional hazards model and found that GDM was positively associated with cancer, particularly in thyroid cancer (HR: 1.27, 95% CI: 1.054–1.532, p = 0.012). However, the incidence of other malignancies (including ovarian and breast cancers) were not significantly associated with GDM, though they did show positive trends. Our findings suggest that GDM is associated with the incidence of cancer, particular thyroid cancer.

Insulin Receptor Isoforms in Cancer

The insulin receptor (IR) mediates both metabolic and mitogenic effects especially when overexpressed or in clinical conditions with compensatory hyperinsulinemia, due to the metabolic pathway resistance, as obesity diabetes. In many cancers, IR is overexpressed preferentially as IR-A isoform, derived by alternative splicing of exon 11. The IR-A overexpression, and the increased IR-A:IR-B ratio, are mechanisms that promote the mitogenic response of cancer cells to insulin and IGF-2, which is produced locally by both epithelial and stromal cancer cells. In cancer IR-A, isoform predominance may occur for dysregulation at both mRNA transcription and post-transcription levels, including splicing factors, non-coding RNAs and protein degradation. The mechanisms that regulate IR isoform expression are complex and not fully understood. The IR isoform overexpression may play a role in cancer cell stemness, in tumor progression and in resistance to target therapies. From a clinical point of view, the IR-A overexpression in cancer may be a determinant factor for the resistance to IGF-1R target therapies for this issue. IR isoform expression in cancers may have the meaning of a predictive biomarker and co-targeting IGF-1R and IR-A may represent a new more efficacious treatment strategy.

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.

Diabetes and cancer: Pathophysiological fundamentals of a 'dangerous affair'

Diabetes and cancer are worldwide chronic diseases with a major impact on the quality and expectancy of life. Metabolic abnormalities observed during the onset and progression of diabetes may have a critical role on the initiation and progression of carcinogenesis. To date, there are no conclusive data on the mechanisms underlying the relationship between diabetes and any type of human cancer. However, recent evidence suggests that both hyperglycemia and hyperinsulinemia in diabetes could elicit cell damage responses, such as glucotoxicity, lipotoxicity and oxidative stress, which participate in the cell transformation process raising the risk of cancer development. In addition, clinical trials have revealed that several anti-diabetes therapies may potentially affect the risk of cancer though largely undefined mechanisms. In this review, we highlight epidemiological and pathophysiological aspects of diabetes, which may influence cancer initiation and progression.

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.

Evaluation of the innate immunostimulatory potential of originator and non-originator copies of insulin glargine in an in vitro human immune model

BACKGROUND

The manufacture of insulin analogs requires sophisticated production procedures which can lead to differences in the structure, purity, and/or other physiochemical properties of resultant products that can affect their biologic activity. Here, we sought to compare originator and non-originator copies of insulin glargine for innate immune activity and mechanisms leading to differences in these response profiles in an in vitro model of human immunity.

METHODS

An endothelial/dendritic cell-based innate immune model was used to study antigen-presenting cell activation, cytokine secretion, and insulin receptor signalling pathways induced by originator and non-originator insulin glargine products. Mechanistic studies included signalling pathway blockade with specific inhibitors, analysis of the products in a Toll-like receptor reporter cell line assay, and natural insulin removal from the products by immunopurification.

FINDINGS

All insulin glargine products elicited at least a minor innate immune response comparable to natural human insulin, but some lots of a non-originator copy product induced the elevated secretion of the cytokines, IL-8 and IL-6. In studies aimed at addressing the mechanisms leading to differential cytokine production by these products, we found (1) the inflammatory response was not mediated by bacterial contaminants, (2) the innate response was driven by the native insulin receptor through the MAPK pathway, and (3) the removal of insulin glargine significantly reduced their capacity to induce innate activity. No evidence of product aggregates was detected, though the presence of some high molecular weight proteins argues for the presence of insulin glargine dimers or others contaminants in these products.

CONCLUSION

The data presented here suggests some non-originator insulin glargine product lots drive heightened in vitro human innate activity and provides preliminary evidence that changes in the biochemical composition of non-originator insulin glargine products (dimers, impurities) might be responsible for their greater immunostimulatory potential.

Long-acting insulin analogs and cancer

AIMS

Hyperinsulinemia is a recognized risk factor for cancer and plays a major role for the increased cancer incidence in diabetic patients. Whether insulin analogs, and particularly long-acting analogs, worsen the pro-cancer effect of excess insulin is still controversial.

DATA SYNTHESIS

In this paper we summarize the biological bases for the potential detrimental effect of long-acting analogs on cancer cells and review the in vitro and in vivo evidence on this issue. Because of their different molecular structure relative to native insulin, insulin analogs may activate the insulin receptor (IR) and the post receptor pathways differently. Most, but not all, in vitro evidence indicate that long-acting analogs may have a stronger mitogenic potency than insulin on cancer cells. Notably insulin glargine, the most studied long-acting analog, also has a higher affinity for the insulin-like growth factor (IGF)-1 receptor, a potent growth mediator. In vitro observations, however, may not reflect what occurs in vivo when analogs are metabolized to derivatives with a different mitogenic activity. Clinical studies, mostly retrospective and predominantly concerning glargine, provide contrasting results. The only perspective trial found no cancer increase in patients treated with glargine. All these studies, however, have severe weaknesses because of the insufficient evaluation of important factors such as dose administered, length of exposure, patient follow-up duration and site-specific cancer investigation. Moreover, whether cancer promotion is a long-acting analog class characteristic or a specific effect of a single agent is not clear.

CONCLUSIONS

In conclusion the carcinogenic risk of long-acting analogs, and specifically glargine, can be neither confirmed nor excluded. A personalized and shared decision, considering all the individual risk factors (metabolic and non-metabolic), is the suggestion for the clinician.

Effects of Regular and Long-Acting Insulin on Cognition and Alzheimer's Disease Biomarkers: A Pilot Clinical Trial

Background: Long acting insulin detemir administered intranasally for three weeks enhanced memory for adults with Alzheimer’s disease dementia (AD) or amnestic mild cognitive impairment (MCI). The investigation of longer-term administration is necessary to determine whether benefits persist, whether they are similar to benefits provided by regular insulin, and whether either form of insulin therapy affects AD biomarkers.

Objective: The present study aimed to determine whether four months of treatment with intranasal insulin detemir or regular insulin improves cognition, daily functioning, and AD biomarkers for adults with MCI or AD.

Methods: This randomized, double-blind, placebo-controlled trial included an intent-to-treat sample consisting of 36 adults diagnosed with MCI or mild to moderate AD. Participants received placebo (n = 12), 40 IU of insulin detemir (n = 12), or 40 IU of regular insulin (n = 12) daily for four months, administered with a nasal delivery device. A cognitive battery was administered at baseline and after two and four months of treatment. MRI was administered for all participants and lumbar puncture for a subset (n = 20) at baseline and four months. The primary outcome was change from baseline to four months on a memory composite (sum of Z scores for delayed list and story recall). Secondary outcomes included: global cognition (Alzheimer’s Disease Assessment Scale-Cognition), daily functioning (Dementia Severity Rating Scale), MRI volume changes in AD-related regions of interest, and cerebrospinal fluid AD markers.

Results: The regular insulin treated group had better memory after two and four months compared with placebo (p < 0.03). No significant effects were observed for the detemir-assigned group compared with the placebo group, or for daily functioning for either group. Regular insulin treatment was associated with preserved volume on MRI. Regular insulin treatment was also associated with reduction in the tau-P181/Aβ₄₂ ratio.

Conclusion: Future research is warranted to examine the mechanistic basis of treatment differences, and to further assess the efficacy and safety of intranasal insulin.

IGF1/MAPK/ERK signaling pathway-mediated programming alterations of adrenal cortex cell proliferation by prenatal caffeine exposure in male offspring rats

Our previous study proposed a glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis programming mechanism for prenatal caffeine exposure (PCE)-induced adrenal developmental dysfunction. Here, we focused on PCE-induced cell proliferation changes of the adrenal cortex in male offspring rats before and after birth and clarified the intrauterine programming mechanism. On gestational day (GD) 20, the PCE group had an elevated serum corticosterone level reduced fetal bodyweight, maximum adrenal sectional area, and elevated adrenal corticosterone and aldosterone contents. However, in postnatal week (PW) 6, the serum corticosterone level was decreased, and the bodyweight, with catch-up growth, adrenal cortex maximum cross-sectional area and aldosterone content were relatively increased, while the adrenal corticosterone content was lower. On GD20, the expression of adrenal IGF1, IGF1R and proliferating cell nuclear antigen (PCNA) were decreased, while the expression of these factors at PW6 were increased in the PCE group. Fetal adrenal gene chip analysis suggested that the mitogen-activated protein kinase/extracellular regulated protein kinase (MAPK/ERK) signal pathway was suppressed in the PCE group. Moreover, in the rat primary adrenal cells, corticosterone (rather than caffeine) was shown to significantly inhibit cell proliferation, IGF1 and PCNA expression, and ERK phosphorylation, which could be reversed by exogenous IGF1. Meanwhile, the effects of exogenous IGF1 were reversed by the ERK pathway inhibitor (PD184161). In conclusion, PCE could induce programming alterations in adrenal cortical cell proliferation before and after birth in male offspring rats. The underlying mechanism is associated with the inhibition of fetal adrenal IGF1-related MAPK/ERK signaling pathway caused by high glucocorticoid levels.

Drosophila Insulin-Like Peptides DILP2 and DILP5 Differentially Stimulate Cell Signaling and Glycogen Phosphorylase to Regulate Longevity

Insulin and IGF signaling (IIS) is a complex system that controls diverse processes including growth, development, metabolism, stress responses, and aging. Drosophila melanogaster IIS is propagated by eight Drosophila insulin-like peptides (DILPs), homologs of both mammalian insulin and IGFs, with various spatiotemporal expression patterns and functions. DILPs 1-7 are thought to act through a single Drosophila insulin/IGF receptor, InR, but it is unclear how the DILPs thereby mediate a range of physiological phenotypes. We determined the distinct cell signaling effects of DILP2 and DILP5 stimulation upon Drosophila S2 cells. DILP2 and DILP5 induced similar transcriptional patterns but differed in signal transduction kinetics. DILP5 induced sustained phosphorylation of Akt, while DILP2 produced acute, transient Akt phosphorylation. Accordingly, we used phosphoproteomic analysis to identify distinct patterns of non-genomic signaling induced by DILP2 and DILP5. Across all treatments and replicates, 5,250 unique phosphopeptides were identified, representing 1,575 proteins. Among these peptides, DILP2, but not DILP5, dephosphorylated Ser15 on glycogen phosphorylase (GlyP), and DILP2, but not DILP5, was subsequently shown to repress enzymatic GlyP activity in S2 cells. The functional consequences of this difference were evaluated in adult Drosophila dilp mutants: dilp2 null adults have elevated GlyP enzymatic activity relative to wild type, while dilp5 mutants have reduced GlyP activity. In flies with intact insulin genes, GlyP overexpression extended lifespan in a Ser15 phosphorylation-dependent manner. In dilp2 mutants, that are otherwise long-lived, longevity was repressed by expression of phosphonull GlyP that is enzymatically inactive. Overall, DILP2, unlike DILP5, signals to affect longevity in part through its control of phosphorylation to deactivate glycogen phosphorylase, a central modulator of glycogen storage and gluconeogenesis.

Association between insulin therapy and risk of liver cancer among diabetics: a meta-analysis of epidemiological studies

As the results of the association between insulin therapy and risk of liver cancer among diabetics have been inconsistent in epidemiological studies, we conducted a meta-analysis to quantify this issue. Data of relevant epidemiological studies were collected by searching articles in PubMed, Web of Science, and Embase till 29 June 2017. Random-effects models were employed to combine study-specific risks. Five cohort studies and nine case-control studies were included in our meta-analysis with 285 008 patients with diabetes mellitus and 4329 liver cancer cases. When we compared insulin-use group with noninsulin use group in patients with diabetes mellitus, we observed a statistically significant association between insulin therapy and liver cancer, with an overall relative risk of 1.90 (95% confidence interval: 1.44-2.50, I=76.1%). We did not find heterogeneity between subgroups stratified by study characteristics and adjusted confounders, except for subgroups related to 'follow-up years' of cohort studies. The combined estimate was robust across sensitivity analysis, and no publication bias was detected. Our results indicated that insulin therapy was associated with elevated incidence of liver cancer among diabetics. Given the high prevalence of diabetes, avoiding excess or unnecessary insulin use to control the blood glucose may offer a potential public health benefit in reducing liver cancer risk. Further studies are warranted to investigate the types, doses, and treatment duration of insulin use in large sample size or cohort of diabetic patients.

Insulin Receptor Isoforms in Physiology and Disease: An Updated View

The insulin receptor (IR) gene undergoes differential splicing that generates two IR isoforms, IR-A and IR-B. The physiological roles of IR isoforms are incompletely understood and appear to be determined by their different binding affinities for insulin-like growth factors (IGFs), particularly for IGF-2. Predominant roles of IR-A in prenatal growth and development and of IR-B in metabolic regulation are well established. However, emerging evidence indicates that the differential expression of IR isoforms may also help explain the diversification of insulin and IGF signaling and actions in various organs and tissues by involving not only different ligand-binding affinities but also different membrane partitioning and trafficking and possibly different abilities to interact with a variety of molecular partners. Of note, dysregulation of the IR-A/IR-B ratio is associated with insulin resistance, aging, and increased proliferative activity of normal and neoplastic tissues and appears to sustain detrimental effects. This review discusses novel information that has generated remarkable progress in our understanding of the physiology of IR isoforms and their role in disease. We also focus on novel IR ligands and modulators that should now be considered as an important strategy for better and safer treatment of diabetes and cancer and possibly other IR-related diseases.

Diabetes drugs and the incidence of solid cancers: a survey of the current evidence

INTRODUCTION

The evaluation of the relationship between the use of antidiabetic drug and the occurrence of cancer is extremely challenging, both from the clinical and pharmacoepidemiological standpoint. This narrative review described the current evidence supporting a relationship between the use of antidiabetic drugs and the incidence of solid cancers. Areas covered: Data from pharmacoepidemiological studies on cancer incidence were presented for the main antidiabetic drugs and drug classes, including human insulin and insulin analogues, metformin, sulfonylureas, glinides, alpha-glucosidase inhibitors, thiazolidinediones, incretin mimetics, and sodium glucose co-transporter 2 inhibitors. The relationship between the use of antidiabetics and the incidence of solid cancer was described in strata by any cancer and by organ-specific cancer and by drug and by drug classes. Information supporting biological evidence and putative mechanisms were also provided. Expert opinion: The history of exploration of the relationship between antidiabetic drugs and the risk of solid cancers has showed several issues. Unrecognized biases and misinterpretations of study results have had important consequences that delayed the identification of actual risk and benefits of the use of antidiabetic drugs associated with cancer occurrence or progression. The lesson learned from the past should address the future research in this area, since in the majority of cases findings are controversial and confirmatory studies are warranted.

Insulin, insulin receptors, and cancer

Insulin is a major regulator of cell metabolism but, in addition, is also a growth factor. Insulin effects in target cells are mediated by the insulin receptor (IR), a transmembrane protein with enzymatic (tyrosine kinase) activity. The insulin receptor, however, is represented by a heterogeneous family of proteins, including two different IR isoforms and also hybrid receptors resulting from the IR hemireceptor combination with a hemireceptor of the cognate IGF-1 receptor. These different receptors may bind insulin and its analogs with different affinity and produce different biologic effects. Since many years, it is known that many cancer cells require insulin for optimal in vitro growth. Recent data indicate that: (1) insulin stimulates growth mainly via its own receptor and not the IGF-1 receptor; (2) in many cancer cells, the IR is overexpressed and the A isoform, which has a predominant mitogenic effect, is more represented than the B isoform. These characteristics provide a selective growth advantage to malignant cells when exposed to insulin. For this reason, all conditions of hyperinsulinemia, both endogenous (prediabetes, metabolic syndrome, obesity, type 2 diabetes before pancreas exhaustion and polycystic ovary syndrome) and exogenous (type 1 diabetes) will increase the risk of cancer. Cancer-related mortality is also increased in patients exposed to hyperinsulinemia but other factors, related to the different diseases, may also contribute. The complexity of the diseases associated with hyperinsulinemia and their therapies does not allow a precise evaluation of the cancer-promoting effect of hyperinsulinemia, but its detrimental effect on cancer incidence and mortality is well documented.

Insulin receptor isoforms: an integrated view focused on gestational diabetes mellitus

The human insulin receptor (IR) exists in two isoforms that differ by the absence (IR-A) or the presence (IR-B) of a 12-amino acid segment encoded by exon 11. Both isoforms are functionally distinct regarding their binding affinities and intracellular signalling. However, the underlying mechanisms related to their cellular functions in several tissues are only partially understood. In this review, we summarize the current knowledge in this field regarding the alternative splicing of IR isoform, tissue-specific distribution and signalling both in physiology and disease, with an emphasis on the human placenta in gestational diabetes mellitus (GDM). Furthermore, we discuss the clinical relevance of IR isoforms highlighted by findings that show altered insulin signalling due to differential IR-A and IR-B expression in human placental endothelium in GDM pregnancies. Future research and clinical studies focused on the role of IR isoform signalling might provide novel therapeutic targets for treating GDM to improve the adverse maternal and neonatal outcomes.

Long-acting insulin analog detemir displays reduced effects on adipocyte differentiation of human subcutaneous and visceral adipose stem cells

BACKGROUND AND AIMS

Since treatment with insulin detemir results in a lower weight gain compared to human insulin, we investigated whether detemir is associated with lower ability to promote adipogenesis and/or lipogenesis in human adipose stem cells (ASC).

METHODS AND RESULTS

Human ASC isolated from both the subcutaneous and visceral adipose tissues were differentiated for 30 days in the presence of human insulin or insulin detemir. Nile Red and Oil-Red-O staining were used to quantify the rate of ASC conversion to adipocytes and lipid accumulation, respectively. mRNA expression levels of early genes, including Fos and Cebpb, as well as of lipogenic and adipogenic genes, were measured at various phases of differentiation by qRT-PCR. Activation of insulin signaling was assessed by immunoblotting. ASC isolated from subcutaneous and visceral adipose tissue were less differentiated when exposed to insulin detemir compared to human insulin, showing lower rates of adipocyte conversion, reduced triglyceride accumulation, and impaired expression of late-phase adipocyte marker genes, such as Pparg2, Slc2a4, Adipoq, and Cidec. However, no differences in activation of insulin receptor, Akt and Erk and induction of the early genes Fos and Cebpb were observed between insulin detemir and human insulin.

CONCLUSION

Insulin detemir displays reduced induction of the Pparg2 adipocyte master gene and diminished effects on adipocyte differentiation and lipogenesis in human subcutaneous and visceral ASC, in spite of normal activation of proximal insulin signaling reactions. These characteristics of insulin detemir may be of potential relevance to its weight-sparing effects observed in the clinical setting.

Effect of insulin analogues on phosphatidyl inositol-3 kinase/Akt signalling in INS-1 rat pancreatic derived β-cells

CONTEXT

Insulin analogues are largely used for the treatment of diabetic patients, but concerns have been raised about their mitogenic/anti-apoptotic potential. It is therefore important to evaluate these analogues in different cell systems.

OBJECTIVE

The aim of this work was to establish the pharmacological profiles of insulin analogues towards PI-3 kinase/Akt pathway in INS-1 β-pancreatic cells.

METHODS

Bioluminescence Resonance Energy Transfer (BRET), in cell western and caspase 3/7 assays, was used to study the effects of ligands.

RESULTS

Among the five analogues evaluated, only glargine stimulated PI-3 kinase/Akt pathway with higher efficiency than insulin, whereas glargine's metabolite M1 was less efficient. However, glargine did not show higher anti-apoptotic efficiency than insulin.

CONCLUSION

Glargine was more efficient than insulin for the activation of PI-3 kinase/Akt pathway, but not for the inhibition of caspase 3/7 activity. Moreover, glargine's metabolite M1 displayed lower efficiency than insulin towards PI-3 kinase/Akt activation and caspase 3/7 inhibition.

Obesity and cancer, a case for insulin signaling

Obesity is a worldwide epidemic, with the number of overweight and obese individuals climbing from just over 500 million in 2008 to 1.9 billion in 2014. Type 2 diabetes (T2D), cardiovascular disease and non-alcoholic fatty liver disease have long been associated with the obese state, whereas cancer is quickly emerging as another pathological consequence of this disease. Globally, at least 2.8 million people die each year from being overweight or obese. It is estimated that by 2020 being overweight or obese will surpass the health burden of tobacco consumption. Increase in the body mass index (BMI) in overweight (BMI>25 kg/m²) and obese (BMI>30 kg/m²) individuals is a result of adipose tissue (AT) expansion, which can lead to fat comprising >50% of the body weight in the morbidly obese. Extensive research over the last several years has painted a very complex picture of AT biology. One clear link between AT expansion and etiology of diseases like T2D and cancer is the development of insulin resistance (IR) and hyperinsulinemia. This review focuses on defining the link between obesity, IR and cancer.

Metabolic, anabolic, and mitogenic insulin responses: A tissue-specific perspective for insulin receptor activators

Insulin acts as the major regulator of the fasting-to-fed metabolic transition by altering substrate metabolism, promoting energy storage, and helping activate protein synthesis. In addition to its glucoregulatory and other metabolic properties, insulin can also act as a growth factor. The metabolic and mitogenic responses to insulin are regulated by divergent post-receptor signaling mechanisms downstream from the activated insulin receptor (IR). However, the anabolic and growth-promoting properties of insulin require tissue-specific inter-relationships between the two pathways, and the nature and scope of insulin-regulated processes vary greatly across tissues. Understanding the nuances of this interplay between metabolic and growth-regulating properties of insulin would have important implications for development of novel insulin and IR modulator therapies that stimulate insulin receptor activation in both pathway- and tissue-specific manners. This review will provide a unique perspective focusing on the roles of "metabolic" and "mitogenic" actions of insulin signaling in various tissues, and how these networks should be considered when evaluating selective pharmacologic approaches to prevent or treat metabolic disease.