Insulin and its analogs: actions via insulin and IGF receptors

Sensitive and label-free SPR biosensing platforms for high-throughput screening of plasma membrane receptors interactions with insulin-like targets of hypoglycaemic activity

Progress in medical sciences aims for tailored therapy of civilization diseases like diabetes. Preclinical screening of new medicines superior to insulin should include the verification of their affinity to the membrane receptors naturally stimulated by this hormone: insulin receptor isoforms A and B and insulin-like growth factor receptor. Considering that the affinity constants obtained using different experimental conditions are incomparable, it is essential to develop a robust and reliable method to analyze these interactions. The versatile SPR platform developed in this study enables the evaluation of the bioactivity of hypoglycaemic molecules. Thanks to the comprehensive characterization of miscellaneous aspects of the analytical platform, including the design of the SPR biosensor receptor layer, ensuring interaction specificity, as well as the quality control of the standards used (human insulin, HI; long-acting insulin analog: glargine, Gla), the feasibility of the method of equilibrium and kinetic constants determination for insulin-like targets was confirmed. SPR assays constructed in the direct format using IR-A, IR-B, and IGF1-R receptor proteins show high sensitivities and low detection limits towards insulin and glargine detection in the range of 18.3-53.3 nM with no signs of mass transport limitations. The improved analytical performance and stability of SPR biosensors favor the acquisition of good-quality kinetic data, while preservation of receptors activity after binding to long-chain carboxymethyldextran, combined with spontaneous regeneration, results in stability and long shelf life of the biosensor, which makes it useful for label-free insulin analogs biosensing and thus extensive screening in diabetic drugs discovery.

Insulin-like growth factor family and prostate cancer: new insights and emerging opportunities

Prostate cancer is the second most commonly diagnosed cancer in men. The mammalian insulin-like growth factor (IGF) family is made up of three ligands (IGF-I, IGF-II, and insulin), three receptors (IGF-I receptor (IGF-1R), insulin receptor (IR), and IGF-II receptor (IGF-2R)), and six IGF-binding proteins (IGFBPs). IGF-I and IGF-II were identified as potent mitogens and were previously associated with an increased risk of cancer development including prostate cancer. Several reports showed controversy about the expression of the IGF family and their connection to prostate cancer risk due to the high degree of heterogeneity among prostate tumors, sampling bias, and evaluation techniques. Despite that, it is clear that several IGF family members play a role in prostate cancer development, metastasis, and androgen-independent progression. In this review, we aim to expand our understanding of prostate tumorigenesis and regulation through the IGF system. Further understanding of the role of IGF signaling in PCa shows promise and needs to be considered in the context of a comprehensive treatment strategy.

Actions and Consequences of Insulin in the Striatum

Insulin crosses the blood–brain barrier to enter the brain from the periphery. In the brain, insulin has well-established actions in the hypothalamus, as well as at the level of mesolimbic dopamine neurons in the midbrain. Notably, insulin also acts in the striatum, which shows abundant expression of insulin receptors (InsRs) throughout. These receptors are found on interneurons and striatal projections neurons, as well as on glial cells and dopamine axons. A striking functional consequence of insulin elevation in the striatum is promoting an increase in stimulated dopamine release. This boosting of dopamine release involves InsRs on cholinergic interneurons, and requires activation of nicotinic acetylcholine receptors on dopamine axons. Opposing this dopamine-enhancing effect, insulin also increases dopamine uptake through the action of insulin at InsRs on dopamine axons. Insulin acts on other striatal cells as well, including striatal projection neurons and astrocytes that also influence dopaminergic transmission and striatal function. Linking these cellular findings to behavior, striatal insulin signaling is required for the development of flavor–nutrient learning, implicating insulin as a reward signal in the brain. In this review, we discuss these and other actions of insulin in the striatum, including how they are influenced by diet and other physio-logical states.

Molecular Modeling and Bioinformatics Analysis of Drug-Receptor Interactions in the System Formed by Glargine, Its Metabolite M1, the Insulin Receptor, and the IGF1 Receptor

Introduction

Insulin and insulin-like growth factor type 1 (IGF1) regulate multiple physiological functions by acting on the insulin receptor (IR) and insulin-like growth factor type 1 receptor (IGF1R). The insulin analog glargine differs from insulin in three residues (Gly^A21, Arg^B31, Arg^B32), and it is converted to metabolite M1 (lacks residues Arg^B31 and Arg^B32) by in vivo processing. It is known that activation of these receptors modulates pathways related to metabolism, cell division, and growth. Though, the structures and structural basis of the glargine interaction with these receptors are not known.

Aim

To generate predictive structural models, and to analyze the drug/receptor interactions in the system formed by glargine, its metabolite M1, IR, and IGF1R by using bioinformatics tools.

Methods

Ligand/receptor models were built by homology modeling using SWISSMODEL, and surface interactions were analyzed using Discovery Studio® Visualizer. Target and hetero target sequences and appropriate template structures were used for modeling.

Results

Our glargine/IR and metabolite M1/IR models showed an overall symmetric T-shaped conformation and full occupancy with four ligand molecules. The glargine/IR model revealed that the glargine residues Arg^B31 and Arg^B32 fit in a hydrophilic region formed by the α-chain C-terminal helix (αCT) and the cysteine-rich region (CR) domain of this receptor, close to the CR residues Arg270-Arg271-Gln272 and αCT residue Arg717. Regarding IGF1R, homologous ligand/receptor models were further built assuming that the receptor is in a symmetrical T-shaped conformation and is fully occupied with four ligand molecules, similar to what we described for IR. Our glargine/IGF1R model showed the interaction of the glargine residues Arg^B31 and Arg^B32 with Glu264 and Glu305 in the CR domain of IGF1R.

Conclusion

Using bioinformatics tools and predictive modeling, our study provides a better understanding of the glargine/receptor interactions.

Predicting mutant outcome by combining deep mutational scanning and machine learning

Deep mutational scanning provides unprecedented wealth of quantitative data regarding the functional outcome of mutations in proteins. A single experiment may measure properties (eg, structural stability) of numerous protein variants. Leveraging the experimental data to gain insights about unexplored regions of the mutational landscape is a major computational challenge. Such insights may facilitate further experimental work and accelerate the development of novel protein variants with beneficial therapeutic or industrially relevant properties. Here we present a novel, machine learning approach for the prediction of functional mutation outcome in the context of deep mutational screens. Using sequence (one-hot) features of variants with known properties, as well as structural features derived from models thereof, we train predictive statistical models to estimate the unknown properties of other variants. The utility of the new computational scheme is demonstrated using five sets of mutational scanning data, denoted "targets": (a) protease specificity of APPI (amyloid precursor protein inhibitor) variants; (b-d) three stability related properties of IGBPG (immunoglobulin G-binding β1 domain of streptococcal protein G) variants; and (e) fluorescence of GFP (green fluorescent protein) variants. Performance is measured by the overall correlation of the predicted and observed properties, and enrichment-the ability to predict the most potent variants and presumably guide further experiments. Despite the diversity of the targets the statistical models can generalize variant examples thereof and predict the properties of test variants with both single and multiple mutations.

Insulin therapy; a valuable legacy and its future perspective

Proteins and peptides are widely used in various areas including pharmaceutical, health, food, textile and biofuel industries. At present, pharmaceutical proteins and peptides have attracted the attention of many researchers. These types of drugs are superior to chemical drugs in many ways so that every year the number of drugs with a protein or peptide moiety is increasing. Due to high performance and low side effects, the demand for these drugs has increased year by year. The beginning of the protein and peptide drug industry dates back to 1982 with the introduction of the protein hormone insulin into the field of treatment. From this year onwards, a new number of protein and peptide drugs have entered the field of treatment every year. In this article, we focus on human therapeutic insulin. First, the history of the hormone will be introduced, then-current methods for insulin therapy will be discussed and finally, the treatments by this hormone in the future will be pointed. Reading this article would be very helpful for nano researchers, biochemists, organic chemists, material scientists and other people who are interested in soft and hard matters interfaces.

Insulin Bidirectionally Alters NAc Glutamatergic Transmission: Interactions between Insulin Receptor Activation, Endogenous Opioids, and Glutamate Release

Human fMRI studies show that insulin influences brain activity in regions that mediate reward and motivation, including the nucleus accumbens (NAc). Insulin receptors are expressed by NAc medium spiny neurons (MSNs), and studies of cultured cortical and hippocampal neurons suggest that insulin influences excitatory transmission via presynaptic and postsynaptic mechanisms. However, nothing is known about how insulin influences excitatory transmission in the NAc.

Human fMRI studies show that insulin influences brain activity in regions that mediate reward and motivation, including the nucleus accumbens (NAc). Insulin receptors are expressed by NAc medium spiny neurons (MSNs), and studies of cultured cortical and hippocampal neurons suggest that insulin influences excitatory transmission via presynaptic and postsynaptic mechanisms. However, nothing is known about how insulin influences excitatory transmission in the NAc. Furthermore, insulin dysregulation accompanying obesity is linked to cognitive decline, depression, anxiety, and altered motivation that rely on NAc excitatory transmission. Using whole-cell patch-clamp and biochemical approaches, we determined how insulin affects NAc glutamatergic transmission in nonobese and obese male rats and the underlying mechanisms. We find that there are concentration-dependent, bidirectional effects of insulin on excitatory transmission, with insulin receptor activation increasing and IGF receptor activation decreasing NAc excitatory transmission. Increases in excitatory transmission were mediated by activation of postsynaptic insulin receptors located on MSNs. However, this effect was due to an increase in presynaptic glutamate release. This suggested feedback from MSNs to presynaptic terminals. In additional experiments, we found that insulin-induced increases in presynaptic glutamate release are mediated by opioid receptor-dependent disinhibition. Furthermore, obesity resulted in a loss of insulin receptor-mediated increases in excitatory transmission and a reduction in NAc insulin receptor surface expression, while preserving reductions in transmission mediated by IGF receptors. These results provide the first insights into how insulin influences excitatory transmission in the adult brain, and evidence for a previously unidentified form of opioid receptor-dependent disinhibition of NAc glutamatergic transmission.

SIGNIFICANCE STATEMENT Data here provide the first insights into how insulin influences excitatory transmission in the adult brain, and identify previously unknown interactions between insulin receptor activation, opioids, and glutamatergic transmission. These data contribute to our fundamental understanding of insulin's influence on brain motivational systems and have implications for the use of insulin as a cognitive enhancer and for targeting of insulin receptors and IGF receptors to alter motivation.

Effects of insulin on IGF-1 receptors in equine lamellar tissue in vitro

Although it is understood that equine endocrinopathic laminitis can be triggered by high concentrations of insulin, it is unclear whether this represents a direct action on lamellar tissue via insulin receptors (InsR), an interaction with IGF-1 receptors (IGF-1R), or some other, indirect action. This uncertainty is because of the reported scarcity of InsR in lamellar tissue and the low affinity of insulin for equine IGF-1R. In the present study, the effects of insulin and IGF-1 (as a positive control) were examined using lamellar explants isolated from the hooves of healthy horses and incubated in cell culture medium for between 2 min and 48 h. In this system, a low physiological concentration of IGF-1 (10 nM; 1.31 ng/mL) caused a marked increase in the appearance of phosphorylated IGF-1R after 5 min (P < 0.05), and this effect was blocked by a human anti-IGF-1R monoclonal antibody (mAb). However, a high concentration of insulin (10 nM; 1,430 μIU/mL) appeared to cause dephosphorylation of the IGF-1R after 5 min (P < 0.01), 15 min, and 30 min (P < 0.001). Using ³H-thymidine as a marker, it was also demonstrated that insulin and IGF-1-stimulated cell proliferation in lamellar explants over the same concentration range as each other (1-100 nM), implying that each peptide acts via its own receptor (P < 0.001). Conversely, the effect of both peptides could be blocked using a selective anti-IGF-1R mAb (P < 0.001), implying that insulin acts via IGF1-R (either directly or indirectly). Notwithstanding this conundrum, the results demonstrate that insulin acts directly on lamellar tissue and suggest that a therapeutic anti-IGF-1R mAb could be useful in treating or preventing endocrinopathic laminitis.

Are There Shared Mechanisms in the Pathophysiology of Different Clinical Forms of Laminitis and What Are the Implications for Prevention and Treatment?

Laminitis is a consequence of primary disease processes elsewhere in the body. The key pathophysiologic events are insulin dysregulation in endocrinopathic laminitis, ischemia in supporting limb laminitis, and inflammation in sepsis-related laminitis. These apparently disparate mechanisms converge to cause lamellar attachment failure through epithelial cell adhesion loss and stretch, possibly mediated by common growth factor signaling pathways. Tissue damage through mechanical distraction, inflammation, pain, and a proliferative epithelial healing response are features of acute laminitis regardless of the cause. Preventive and treatment strategies based on knowledge of these unique and common mechanistic events are likely to improve clinical outcomes.

Insulin in the ventral tegmental area reduces cocaine-evoked dopamine in the nucleus accumbens in vivo

Mesolimbic dopamine circuits, implicated in incentive motivation, are sensitive to changes in metabolic state such as weight loss and diet-induced obesity. These neurons are important targets for metabolic hormones such as leptin, glucagon-like peptide-1, ghrelin and insulin. Insulin receptors are located on dopamine neurons in the ventral tegmental area (VTA) and we have previously demonstrated that insulin induces long-term depression of excitatory synapses onto VTA dopamine neurons. While insulin can decrease dopamine concentration in somatodendritic regions, it can increase dopamine in striatal slices. Whether insulin directly targets the VTA to alter dopamine release in projection areas, such as the nucleus accumbens (NAc), remains unknown. The main goal of the present experiments was to examine NAc dopamine concentration following VTA administration of insulin. Using in vivo FSCV to detect rapid fluctuations in dopamine concentration, we showed that intra-VTA insulin via action at insulin receptors reduced pedunculopontine nucleus-evoked dopamine release in the NAc. Furthermore, intra-VTA insulin reduced cocaine-potentiated NAc dopamine. Finally, intra-VTA or intranasal insulin decreased locomotor responses to cocaine, an effect blocked by an intra-VTA administered insulin receptor antagonist. Together, these data demonstrate that mesolimbic dopaminergic projections are important targets of the metabolic hormone, insulin.

The effect of insulin on equine lamellar basal epithelial cells mediated by the insulin-like growth factor-1 receptor

Background

In horses and ponies, insulin dysregulation leading to hyperinsulinemia may be associated with increased risk of laminitis, and prolonged infusion of insulin can induce the condition. It is unclear whether insulin may have a direct or indirect effect on the lamellar tissues. Insulin is structurally related to insulin-like growth factor (IGF-1), and can bind the IGF-1 receptor, albeit at a lower affinity than IGF-1.

Methods

Immunohistochemistry was performed on formalin-fixed lamellar tissue sections from six normal horses, euthanised for non-research purposes, using an anti-IGF-1 receptor antibody. In further studies, lamellar epithelial cells were obtained by collagenase digestion from the hooves of 18 normal horses, also euthanised for non-research purposes, and incubated for 48 h in the presence of insulin (0–2,000 m IU/ml). The increase in cell numbers was determined using a cell proliferation assay, and compared to the effect of zero insulin using one-way ANOVA.

Results

Immunohistochemistry demonstrated IGF-1 receptors on lamellar epidermal epithelial cells. With cultured cells, insulin caused a concentration-dependent increase in cell proliferation compared to untreated cells (maximal effect 63.3 ± 12.8% more cells after 48 h with 1,000 m IU/ml insulin; P < 0.01). Co-incubation with a blocking antibody against the IGF-1 receptor significantly inhibited the proliferative effect of insulin (P < 0.01).

Discussion

These results demonstrate that IGF-1 receptors are present on lamellar epithelial cells. At high physiological concentrations, insulin may activate these cells, by a mechanism involving IGF-1 receptors, resulting in a proliferative effect. This mechanism could help to explain the link between hyperinsulinemia and laminitis.

Association between hyperinsulinaemia and laminitis severity at the time of pituitary pars intermedia dysfunction diagnosis

BACKGROUND

Hyperinsulinaemia is the suspected component of insulin dysregulation having the strongest association with laminitis and occurs variably in equids with pituitary pars intermedia dysfunction (PPID).

OBJECTIVES

We hypothesised that magnitude of hyperinsulinaemia correlates with laminitis severity in PPID-affected equids. Furthermore, we hypothesised that owners can be unaware of chronic endocrinopathic laminitis.

STUDY DESIGN

Cross-sectional study.

METHODS

Serum insulin concentrations, owner-reported laminitis history and radiographic evidence of laminitis were determined in 38 client-owned horses and ponies with confirmed PPID. Laminitis severity was classified into four categories (normal [nonlaminitic], mild, moderate or severe laminitis) based on degree of distal phalangeal rotation. Animals were also categorised as normoinsulinaemic (<20 μU/ml), mildly hyperinsulinaemic (20-50 μU/ml) and severely hyperinsulinaemic (>50 μU/ml). One-way ANOVA, t tests and Fisher's exact tests were performed.

RESULTS

While owners reported laminitis in 37% of animals, 76% were laminitic based on study criteria (P = 0.01). Owners reported laminitis more frequently in hyperinsulinaemic vs. normoinsulinaemic animals; recognition increased with severity of hyperinsulinaemia (P = 0.03). Mean insulin concentrations were higher in equids with moderate to severe radiographic laminitis (geometric mean 74.1, 95% confidence interval (CI) 38.4-143.1 uU/ml) vs. those classified radiographically as normal to mild (31.9, 95% CI 21.1-48.1 uU/ml P = 0.03).

MAIN LIMITATIONS

Dynamic insulin testing was not performed; some normoinsulinaemic animals might have had subtle insulin dysregulation.

CONCLUSIONS

Although radiographic abnormalities were present in most animals at the time of PPID diagnosis, chronic laminitis remained unrecognised by many owners. Owner awareness of laminitis increased with severity of hyperinsulinaemia and higher insulin concentrations were detected in association with more severe radiographic changes. The Summary is available in Chinese - See Supporting Information.

Managing feline diabetes: current perspectives

Diabetes mellitus is a common endocrine disease in cats. While type 2 diabetes is the most common form seen in cats, other underlying causes may contribute to insulin resistance. Guidelines for diagnosis vary and often do not take into account prediabetic cats. The goals of treatment are to maximize the chance of remission, while minimizing the risks of hypoglycemia. This article presents a further overview of current treatment and monitoring recommendations for diabetic cats.

Quantitative Missense Variant Effect Prediction Using Large-Scale Mutagenesis Data

Large datasets describing the quantitative effects of mutations on protein function are becoming increasingly available. Here, we leverage these datasets to develop Envision, which predicts the magnitude of a missense variant's molecular effect. Envision combines 21,026 variant effect measurements from nine large-scale experimental mutagenesis datasets, a hitherto untapped training resource, with a supervised, stochastic gradient boosting learning algorithm. Envision outperforms other missense variant effect predictors both on large-scale mutagenesis data and on an independent test dataset comprising 2,312 TP53 variants whose effects were measured using a low-throughput approach. This dataset was never used for hyperparameter tuning or model training and thus serves as an independent validation set. Envision prediction accuracy is also more consistent across amino acids than other predictors. Finally, we demonstrate that Envision's performance improves as more large-scale mutagenesis data are incorporated. We precompute Envision predictions for every possible single amino acid variant in human, mouse, frog, zebrafish, fruit fly, worm, and yeast proteomes (https://envision.gs.washington.edu/).

Insulin-mediated synaptic plasticity in the CNS: Anatomical, functional and temporal contexts

For decades the brain was erroneously considered an insulin insensitive organ. Although gaps in our knowledge base remain, conceptual frameworks are starting to emerge to provide insight into the mechanisms through which insulin facilitates critical brain functions like metabolism, cognition, and motivated behaviors. These diverse physiological and behavioral activities highlight the region-specific activities of insulin in the CNS; that is, there is an anatomical context to the activities of insulin in the CNS. Similarly, there is also a temporal context to the activities of insulin in the CNS. Indeed, brain insulin receptor activity can be conceptualized as a continuum in which insulin promotes neuroplasticity from development into adulthood where it is an integral part of healthy brain function. Unfortunately, brain insulin resistance likely contributes to neuroplasticity deficits in obesity and type 2 diabetes mellitus (T2DM). This neuroplasticity continuum can be conceptualized by the mechanisms through which insulin promotes cognitive function through its actions in brain regions like the hippocampus, as well as the ability of insulin to modulate motivated behaviors through actions in brain regions like the nucleus accumbens and the ventral tegmental area. Thus, the goals of this review are to highlight these anatomical, temporal, and functional contexts of insulin activity in these brain regions, and to identify potentially critical time points along this continuum where the transition from enhancement of neuroplasticity to impairment may take place.

Bioanalytical approaches to assess the proteolytic stability of therapeutic fusion proteins

Therapeutic fusion proteins (TFPs) are designed to improve the therapeutic profile of an endogenous protein or protein fragment with a limited dose frequency providing the desired pharmacological activity in vivo. Fusion of a therapeutic protein to a half-life extension or targeting domain can improve the disposition of the molecule or introduce a novel mechanism of action. Prolonged exposure and altered biodistribution of an endogenous protein through fusion technology increases the potential for local protein unfolding during circulation increasing the chance for partial proteolysis of the therapeutic domain. Characterizing the proteolytic liabilities of a TFP can guide engineering efforts to inhibit or hinder partial proteolysis. This review focuses on considerations and techniques for evaluating the stability of a TFP both in vivo and in vitro.

Non-small cell lung cancer cell survival crucially depends on functional insulin receptors

Insulin plays an important role as a growth factor and its contribution to tumor proliferation is intensely discussed. It acts via the cognate insulin receptor (IR) but can also activate the IGF1 receptor (IGF1R). Apart from increasing proliferation, insulin might have additional effects in lung cancer. Therefore, we investigated insulin action and effects of IR knockdown (KD) in three (NCI-H292, NCI-H226 and NCI-H460) independent non-small cell lung cancer (NSCLC) cell lines. All lung cancer lines studied were found to express IR, albeit with marked differences in the ratio of the two variants IR-A and IR-B. Insulin activated the classical signaling pathway with IR autophosphorylation and Akt phosphorylation. Moreover, activation of MAPK was observed in H292 cells, accompanied by enhanced proliferation. Lentiviral shRNA IR KD caused strong decrease in survival of all three lines, indicating that the effects of insulin in lung cancer go beyond enhancing proliferation. Unspecific effects were ruled out by employing further shRNAs and different insulin-responsive cells (human pre-adipocytes) for comparison. Caspase assays demonstrated that IR KD strongly induced apoptosis in these lung cancer cells, providing the physiological basis of the rapid cell loss. In search for the underlying mechanism, we analyzed alterations in the gene expression profile in response to IR KD. A strong induction of certain cytokines (e.g. IL20 and tumour necrosis factor) became obvious and it turned out that these cytokines trigger apoptosis in the NSCLC cells tested. This indicates a novel role of IR in tumor cell survival via suppression of pro-apoptotic cytokines.

The advent of biosimilars for the treatment of diabetes: current status and future directions

Biosimilar insulins are likely to enter the market of diabetes therapies as patents for major branded insulin products start to expire in the next few years (on June 2014, the European Medicines Agency authorized the first biosimilar of insulin glargine, Abasria, 100 Units/ml, for the treatment of diabetes mellitus). This would allow providing comparable clinical benefits of the current available insulins at a significantly lower cost, thus increasing the affordability and access of insulin treatment for patients with diabetes. Biosimilars are approved via a stringent regulatory pathway demonstrating quality, safety, and efficacy comparable to the reference product. However, the production complexities of such products raise important considerations for treatment efficacy and patient safety, including naming and product tracking, substitution practices, and pharmacovigilance. Additionally, as practitioners' knowledge regarding the differences about pharmacological, clinical, and regulatory aspects between biosimilars and generic small molecules is often suboptimal, specific education on biosimilar prescribing, dispensing, and administering is critical for ensuring patients' benefit and safety. This article discusses all the issues concerning biosimilar, especially biosimilar insulins.

Species differences in regulation of renal proximal tubule transport by certain molecules

Renal proximal tubules (PTs) play important roles in the regulation of acid/base, plasma volume and blood pressure. Recent studies suggest that there are substantial species differences in the regulation of PT transport. For example, thiazolidinediones (TZDs) are widely used for the treatment of type 2 diabetes mellitus, but the use of TZDs is associated with fluid overload. In addition to the transcriptional enhancement of sodium transport in distal nephrons, TZDs rapidly stimulate PT sodium transport via a non-genomic mechanism depending on peroxisome proliferator activated receptor γ/Src/epidermal growth factor receptor (EGFR)/MEK/ERK. In mouse PTs, however, TZDs fail to stimulate PT transport probably due to constitutive activation of Src/EGFR/ERK pathway. This unique activation of Src/ERK may also affect the effect of high concentrations of insulin on mouse PT transport. On the other hand, the effect of angiotensin II (Ang II) on PT transport is known to be biphasic in rabbits, rats, and mice. However, Ang II induces a concentration-dependent, monophasic transport stimulation in human PTs. The contrasting responses to nitric oxide/guanosine 3’,5’-cyclic monophosphate pathway may largely explain these different effects of Ang II on PT transport. In this review, we focus on the recent findings on the species differences in the regulation of PT transport, which may help understand the species-specific mechanisms underlying edema formation and/or hypertension occurrence.

Diabetes mellitus as a novel risk factor for gastrointestinal malignancies

Evidence of an emerging etiologic link between diabetes mellitus and several gastrointestinal malignancies is presented. Although a correlation between pancreatic cancer and diabetes mellitus has long been suspected, the potential role diabetes mellitus plays in the pathogenicity of both hepatocellular carcinoma and colon cancer is becoming increasingly well defined. Further supporting the prospect of etiologic linkage, the association of diabetes mellitus with colon cancer is consistently demonstrated to be independent of obesity. An increasing incidence of diabetes and obesity in the United States has led to a recent surge in incidence of hepatocellular cancer on the background of nonalcoholic fatty liver disease, and this disease is expected to commensurately grow in incidence. Widespread recognition of this emerging risk factor may lead to a change in screening practices. Although the mechanisms underlying the correlation are still under investigation, the role of insulin, the insulin-like growth factor-I, and related binding and signaling pathways as regulators of cell growth and cell proliferation are implicated in carcinogenesis and tumor growth. The potential role of metformin and other medications for diabetes mellitus in the chemoprevention, carcinogenesis, and treatment of gastrointestinal malignancies is also presented.

Basal insulin analogues in the management of diabetes mellitus: What progress have we made?

Insulin remains the most effective and consistent means of controlling blood glucose levels in diabetes. Since 1946, neutral protamine Hagedorn (NPH) has been the predominant basal insulin in clinical use. However, absorption is variable due to the need for resuspension and the time-action profile (peak activity 4-6 h after subcutaneous administration) confers an increased propensity for between-meal and nocturnal hypoglycaemia. In the 1980s, recombinant DNA technology enabled modifications to the insulin molecule resulting in the soluble long-acting insulin analogues, glargine and detemir. Both exhibit a lower risk of hypoglycaemia compared with neutral protamine Hagedorn due to improved time-action profiles and reduced day-to-day glucose variability. Glargine is indicated for administration once daily and detemir once or twice daily. Degludec is the latest prolonged-acting insulin which forms long subcutaneous multi-hexamers that delay absorption. Recent phase III trials in type 1 and type 2 diabetes show that degludec was non-inferior to comparators (predominantly glargine) with a minimal although inconsistent reduction in overall hypoglycaemia and a small absolute difference in nocturnal hypoglycaemia. Newer developmental agents include LY2605541 and glargine U300. LY2605541 comprises insulin lispro combined with polyethylene glycol, thereby increasing its hydrodynamic size and retarding absorption from the subcutaneous tissue. Glargine U300 is a new formulation of glargine resulting in a flatter and more prolonged time-action profile than its predecessor. This article reviews recent advances in basal insulin analogues, including a critical appraisal of the degludec trials.

Insulin analogs and cancer: a note of caution

In view of the lifelong exposure and large patient populations involved, insulin analogs with an increased mitogenic effect in comparison to human insulin may potentially constitute a major health problem, since these analogs may possibly induce the growth of pre-existing neoplasms. At present, the available data suggest that insulin analogs are safe. In line with these findings, we observed that serum of diabetic patients treated with insulin analogs, compared to that of diabetic patients treated with human insulin, did not induce an increased phosphorylation of tyrosine residues of the insulin-like growth factor-I receptor (IGF-IR). However, the classical model of the IGF-IR signaling may be insufficient to explain (all) mitogenic effects of insulin analogs since also non-canonical signaling pathways of the IGF-IR may play a major role in this respect. Although phosphorylation of tyrosine residues of the IGF-IR is generally considered to be the initial activation step within the intracellular IGF-IR signaling pathway, it has been found that cells undergo a signaling switch under hyperglycemic conditions. After this switch, a completely different mechanism is utilized to activate the mitogenic (mitogen-activated protein kinase) pathways of the IGF-IR that is independent from tyrosine phosphorylation of the IGF-IR. At present it is unknown whether activation of this alternative intracellular pathway of the IGF-IR occurs during hyperglycemia in vivo and whether it is stronger in patients treated with (some) insulin analogs than in patients treated with human insulin. In addition, it is unknown whether the insulin receptors (IRs) also undergo a signaling switch during hyperglycemia. This should be investigated in future studies. Finally, relative overexpression of IR isoform A (IR-A) in (pre) cancer tissues may play a key role in the development and progression of human cancers during treatment with insulin (analogs). Further studies are required to unravel whether the IR-A is involved in the development of cancers and whether, in this respect (some) insulin analogs differ from human insulin.

Six cases with severe insulin resistance (SIR) associated with mutations of insulin receptor: Is a Bartter-like syndrome a feature of congenital SIR?

Biallelic insulin receptor (INSR) gene mutations cause congenital syndromes of severe insulin resistance (SIR) known as Donohue syndrome (DS) and Rabson-Mendenhall syndrome (RMS). At presentation, DS and RMS are difficult to differentiate since they share many clinical features; however, while patients with DS usually die within 1 year of birth, individuals classified as RMS can reach adult age. INSR mutations can be also found in pubertal females with hyperinsulinism, hyperandrogenism, and acanthosis nigricans (type A SIR). We studied the INSR gene in five subjects with congenital SIR and in a patient with type A SIR. Nine biallelic INSR gene mutations (eight novels, including an in-frame deletion of INSR signal peptide) were identified in patients with congenital SIR; a heterozygous, spontaneous INSR mutation was detected in the patient with type A SIR. Two probands, presenting severe hirsutism at birth, died at the age of 3 months and were classified as DS, while other 2, currently 2 and 3 years old, were diagnosed with RMS (patients 3 and 4). The fifth patient with congenital SIR died when 14 months old. Nephrocalcinosis, hyperaldosteronism, hyperreninemia, and hypokalemia, in the absence of hypertension, were discovered in patients 3 and 5 when 24 and 4 months old, respectively. Patient 3, now 3 years/3 months old, still shows hyperreninemic hyperaldosteronism requiring potassium supplementation. We conclude that renal abnormalities resembling antenatal Bartter's syndrome type II, recently reported also by others, is a common observation in patients with congenital SIR.

Comparison of human insulin and insulin analogues on hypoglycaemia and metabolic variability in type 1 diabetes using standardized measurements (HYPO score and Lability Index)

To evaluate whether treatment with insulin analogues is associated with a lower risk of hypoglycaemia (HYPO score) and less glycaemic variability (Lability Index) than treatment with human insulin in patients with type 1 diabetes. In a 6-month prospective, open-labelled trial, we randomized 47 patients treated with human insulin to receive treatment with human insulin (n = 21) or insulin analogues (n = 26). HYPO score, Lability Index (LI), and hypoglycaemic episode characteristics were assessed at baseline and at the end of follow-up. A 72-h, continuous glucose monitoring was performed at the end in a subgroup of patients. Groups were compared with nonparametric tests. Significance was defined as P < 0.05. HYPO score (71.5 [36.0-162] vs. 260 [52.0-676], P < 0.05), nocturnal hypoglycaemia (0.4 vs. 1.4 events/patient/4-week, P < 0.05), and <2.5 mmol/l hypoglycaemic events were lower in insulin analogue group after 6 months. There was a trend towards a lower LI in insulin analogue group (74.3 [51.3-133] vs. 123 [76.4-171] mmol/l(2)/h week(-1), P = 0.064). HbA1c and insulin dose were comparable between groups. In type 1 diabetes, insulin analogues were associated with a lower hypoglycaemic risk and a trend towards reduced glycaemic variability compared with human insulin. These effects occurred despite comparable metabolic control.

Regulation of ENaC in mice lacking renal insulin receptors in the collecting duct

The epithelial sodium channel (ENaC) is one of the central effectors involved in regulation of salt and water homeostasis in the kidney. To study mechanisms of ENaC regulation, we generated knockout mice lacking the insulin receptor (InsR KO) specifically in the collecting duct principal cells. Single-channel analysis in freshly isolated split-open tubules demonstrated that the InsR-KO mice have significantly lower ENaC activity compared to their wild-type (C57BL/6J) littermates when animals were fed either normal or sodium-deficient diets. Immunohistochemical and Western blot assays demonstrated no significant changes in expression of ENaC subunits in InsR-KO mice compared to wild-type littermates. Insulin treatment caused greater ENaC activity in split-open tubules isolated from wild-type mice but did not have this effect in the InsR-KO mice. Thus, these results suggest that insulin increases ENaC activity via its own receptor affecting the channel open probability. To further determine the mechanism of the action of insulin on ENaC, we used mouse mpkCCDc14 principal cells. Insulin significantly augmented amiloride-sensitive transepithelial flux in these cells. Pretreatment of the mpkCCDc14 cells with phosphatidylinositol 3-kinase (LY294002; 10 μM) or mTOR (PP242; 100 nM) inhibitors precluded this effect. This study provides new information about the importance of insulin receptors expressed in collecting duct principal cells for ENaC activity.

Glargine safety, diabetes and cancer

INTRODUCTION

In 2009, several epidemiological studies suggested a higher frequency of malignancy in insulin glargine -treated patients. A number of follow-up epidemiological population studies as well as two randomized, controlled clinical studies, one a 5000-patient retinopathy study and the other a 12,000-patient cardiovascular outcomes trial (ORIGIN), found no higher frequency of malignancy in glargine-treated patients.

AREAS COVERED

We reviewed the existing literature as well as U.S. FDA records to investigate the association of cancer, diabetes, and insulin. There is a 20 - 40% higher incidence of malignancy in type 2 diabetes patients. Certain cancers are more common, including hepatocellular and pancreatic carcinoma, colorectal cancer, renal cancer, and breast and endometrial cancer, and non-Hodgkin's lymphoma. There are numerous inter-related factors which may promote both diabetes and malignancy, including dietary patterns, obesity, insulin resistance, and alcoholism. Patients who receive insulin treatment are typically older and "sicker" than those who receive oral agents.

EXPERT OPINION

It is very difficult to prove causal associations between diabetes and cancer due to the host of confounding factors. The hypothesis that hyperinsulinemia and IGF-1 receptor activation promote cancer is strong, but confounded by the association of hyperinsulinemia with obesity, which separately promotes malignancy. Although statistical techniques to adjust for confounding variables can improve epidemiological comparisons, the lesson of the glargine cancer controversy is that controlled clinical trials are the only means to definitely prove hypotheses.

The metabolic and mitogenic properties of basal insulin analogues

CONTEXT

Retrospective, observational studies have reported an association between diabetes treatment with insulin and a higher incidence of cancer.

OBJECTIVE

Overview the literature for in vitro and in vivo studies of the metabolic and mitogenic properties of basal insulin analogues and assess the implications for clinical use.

METHODS

Relevant studies were identified through PubMed and congress abstract database searches; data on metabolic and mitogenic signalling in relation to insulin treatment of diabetes are included in this review.

RESULTS

The balance of evidence shows that although some analogues have demonstrated mitogenic potency in some in vitro studies in cancer cell lines, these findings do not translate to the in vivo setting in animals or to the clinical setting in humans.

CONCLUSIONS

The current consensus is that there is no clinical or in vivo evidence to indicate that any commercially available insulin analogue has carcinogenic effects. Large-scale, prospective clinical and observational studies will further establish any potential link.

Insulin induces long-term depression of ventral tegmental area dopamine neurons via endocannabinoids

The prevalence of obesity has drastically increased over the last few decades. Exploration into how hunger and satiety signals influence the reward system can help us to understand non-homeostatic mechanisms of feeding. Evidence suggests that insulin may act in the ventral tegmental area (VTA), a critical site for reward-seeking behavior, to suppress feeding. However, the neural mechanisms underlying insulin effects in the VTA remain unknown. We demonstrate that insulin, a circulating catabolic peptide that inhibits feeding, can induce a long-term depression (LTD) of excitatory synapses onto VTA dopamine neurons. This effect requires endocannabinoid-mediated presynaptic inhibition of glutamate release. Furthermore, after a sweetened high fat meal, which elevates endogenous insulin levels, insulin-induced LTD is occluded. Finally, insulin in the VTA reduces food anticipatory behavior and conditioned place preference for food. Taken together, these results suggest that insulin in the VTA suppresses excitatory synaptic transmission and reduces salience of food-related cues.

Insulin and its analogues and their affinities for the IGF1 receptor

Insulin analogues have been developed in an attempt to achieve a more physiological replacement of insulin and thereby a better glycaemic control. However, structural modification of the insulin molecule may result in altered binding affinities and activities to the IGF1 receptor (IGF1R). As a consequence, insulin analogues may theoretically have an increased mitogenic action compared to human insulin. In view of the lifelong exposure and large patient populations involved, insulin analogues with an increased mitogenic effect in comparison to human insulin may potentially constitute a major health problem, since these analogues may possibly induce the growth of pre-existing neoplasms. This hypothesis has been evaluated extensively in vitro and also in vivo by using animal models. In vitro, all at present commercially available insulin analogues have lower affinities for the insulin receptor (IR). Although it has been suggested that especially insulin analogues with an increased affinity for the IGF1R (such as insulin glargine) are more mitogenic when tested in vitro in cells expressing a high proportion of IGF1R, the question remains whether this has any clinical consequences. At present, there are several uncertainties which make it very difficult to answer this question decisively. In addition, recent data suggest that insulin (or insulin analogues)-mediated stimulation of IRs may play a key role in the progression of human cancer. More detailed information is required to elucidate the exact mechanisms as to how insulin analogues may activate the IR and IGF1R and how this activation may be linked to mitogenesis.

Evaluation of detemir in diabetic cats managed with a protocol for intensive blood glucose control

The aim of this study was to report outcomes using detemir and a protocol aimed at intensive blood glucose control with home monitoring in diabetic cats, and to compare the results with a previous study using the same protocol with glargine. Eighteen cats diagnosed with diabetes and previously treated with other insulins were included in the study. Data was provided by owners who joined the online German Diabetes-Katzen Forum. The overall remission rate was 67%. For cats that began the protocol before or after 6 months of diagnosis, remission rates were 81% and 42%, respectively (P = 0.14). No significant differences were identified between the outcomes for the glargine and detemir studies, with the exception of three possibly interrelated factors: a slightly older median age of the detemir cohort at diabetes diagnosis, a higher rate of chronic renal disease in the detemir cohort and lower maximal dose for insulin detemir.

Insulin degludec as an ultralong-acting basal insulin once a day: a systematic review

BACKGROUND

Insulin degludec (IDeg) is a neutral, ultralong-acting new generation basal insulin analog developed by NovoNordisk currently in Phase III clinical development. IDeg offers a duration of action of more than 42 hours in adults, much longer than current basal insulin formulations.

OBJECTIVE

The aim of this review is to assess the efficacy and safety data of IDeg in the treatment of type 1 and type 2 diabetes mellitus.

METHODS

Relevant English language articles from 2010 to 2012 were identified through MEDLINE, PubMed, EMBASE, Scopus, BIOSIS, and Google Scholar. Online conference proceedings of the 71st ADA Scientific Sessions and the 47th EASD Annual Meeting were reviewed. Studies were compared in terms of their study designs, primary and secondary efficacy parameters, and tolerability data.

RESULTS

There are a total of nine published trials investigating the clinical efficacy and safety of IDeg in over 3000 subjects with type 1 and 2 diabetes. Only three trials were published in full. All were open-label, randomized multicenter trials with durations of 16 to 52 weeks. IDeg and coformulations of IDeg with insulin aspart (IAsp) were compared to insulin glargine (IGlar), detemir, and biphasic IAsp 30 (BIAsp 30).

CONCLUSION

Based upon the available evidence, there appear to be no reported differences between IDeg and IGlar, detemir, or BIAsp 30 in the reduction of the primary efficacy end-points of HbA(1c) and mean fasting plasma glucose (FPG) concentrations. Only flexible dosing of IDeg provided a significant reduction in FPG compared to IGlar. IDeg demonstrated a significant reduction in nocturnal hypoglycemia in type 1 diabetes. In type 2 diabetes, IDeg reduced the incidence of hypoglycemia by 18% and 58% compared to IGlar and BIAsp 30, respectively.

Optimizing treatment strategies with insulin glargine in Type 2 diabetes

Advances in insulin therapy have made a positive contribution to improving disease management in both Type 1 and Type 2 diabetes. The development of insulin analogs with time-action characteristics has made it easier to mimic physiological insulin secretion. The parallel improvement in delivery devices has also made insulin therapy more convenient, flexible and acceptable. The inevitable progression of Type 2 diabetes means that the majority of those people will also require insulin therapy at some point in their disease course. Current treatment options are many; when to initiate insulin and which regimen to choose are among the major questions confronting physicians in today's rapidly evolving environment. This article summarizes the current strategies for initiating and optimizing the use of the basal insulin analog, insulin glargine, in Type 2 diabetes, leading to the intermediate stage of insulin therapy with the introduction of meal-related, rapid-acting insulin analogs in a stepwise manner prior to a full replacement basal-bolus regimen.

Addition of insulin glargine or NPH insulin to metformin monotherapy in poorly controlled type 2 diabetic patients decreases IGF-I bioactivity similarly

AIMS/HYPOTHESIS

The aim of this study was to compare IGF-I bioactivity 36 weeks after the addition of insulin glargine (A21Gly,B31Arg,B32Arg human insulin) or NPH insulin to metformin therapy in type 2 diabetic patients who had poor glucose control under metformin monotherapy.

METHODS

In the Lantus plus Metformin (LANMET) study, 110 poorly controlled insulin-naive type 2 diabetic patients were randomised to receive metformin with either insulin glargine (G+MET) or NPH insulin (NPH+MET). In the present study, IGF-I bioactivity was measured, retrospectively, in 104 out of the 110 initially included LANMET participants before and after 36 weeks of insulin therapy. IGF-I bioactivity was measured using an IGF-I kinase receptor activation assay.

RESULTS

After 36 weeks of insulin therapy, insulin doses were comparable between the G+MET (68 ± 5.7 U/day) and NPH+MET (71 ± 6.2 U/day) groups (p = 0.68). Before insulin therapy, circulating IGF-I bioactivity was similar between the G+MET (134 ± 9 pmol/l) and NPH+MET (135 ± 10 pmol/l) groups (p = 0.83). After 36 weeks, IGF-I bioactivity had decreased significantly (p = 0.001) and did not differ between the G+MET (116 ± 9 pmol/l) and NPH+MET (117 ± 10 pmol/l) groups (p = 0.91). At baseline and after insulin therapy, total IGF-I concentrations were comparable in both groups (baseline: G+MET 13.3 ± 1.0 vs NPH+MET 13.3 ± 1.0 nmol/l, p = 0.97; and 36 weeks: 13.4 ± 1.0 vs 13.1 ± 0.9 nmol/l, p = 0.71). Total IGF-I concentration did not change during insulin therapy (13.3 ± 0.7 vs 13.3 ± 0.7 nmol/l, baseline vs 36 weeks, p = 0.86).

CONCLUSIONS/INTERPRETATION

Addition of insulin glargine or NPH insulin to metformin monotherapy in poorly controlled type 2 diabetic patients decreases serum IGF-I bioactivity in a similar manner.

Insulin-like growth factor-I receptor (IGF-IR) translocates to nucleus and autoregulates IGF-IR gene expression in breast cancer cells

The insulin-like growth factor (IGF) system plays an important role in mammary gland biology as well as in the etiology of breast cancer. The IGF-I receptor (IGF-IR), which mediates the biological actions of IGF-I and IGF-II, has emerged in recent years as a promising therapeutic target. The IGF and estrogen signaling pathways act in a synergistic manner in breast epithelial cells. The present study was aimed at investigating 1) the putative translocation of IGF-IR and the related insulin receptor (IR) to the nucleus in breast cancer cells, 2) the impact of IGF-IR and IR levels on IGF-IR biosynthesis in estrogen receptor (ER)-positive and ER-depleted breast cancer cells, and 3) the potential transcription factor role of IGF-IR in the specific context of IGF-IR gene regulation. We describe here a novel mechanism of autoregulation of IGF-IR gene expression by cellular IGF-IR, which is seemingly dependent on ER status. Regulation of the IGF-IR gene by IGF-IR protein is mediated at the level of transcription, as demonstrated by 1) binding assays (DNA affinity chromatography and ChIP) showing specific IGF-IR binding to IGF-IR promoter DNA and 2) transient transfection assays showing transactivation of the IGF-IR promoter by exogenous IGF-IR. The IR is also capable of translocating to the nucleus and binding the IGF-IR promoter in ER-depleted, but not in ER-positive, cells. However, transcription factors IGF-IR and IR display diametrically opposite activities in the context of IGF-IR gene regulation. Thus, whereas IGF-IR stimulated IGF-IR gene expression, IR inhibited IGF-IR promoter activity. In summary, we have identified a novel mechanism of IGF-IR gene autoregulation in breast cancer cells. The clinical implications of these findings and, in particular, the impact of IGF-IR/IR nuclear localization on targeted therapy require further investigation.

Differences in bioactivity between human insulin and insulin analogues approved for therapeutic use- compilation of reports from the past 20 years

In order to provide comprehensive information on the differences in bioactivity between human insulin and insulin analogues, published in vitro comparisons of human insulin and the rapid acting analogues insulin lispro (Humalog®), insulin aspart ( NovoRapid®), insulin glulisine (Apidra®), and the slow acting analogues insulin glargine (Lantus®), and insulin detemir (Levemir®) were gathered from the past 20 years (except for receptor binding studies). A total of 50 reports were retrieved, with great heterogeneity among study methodology. However, various differences in bioactivity compared to human insulin were obvious (e.g. differences in effects on metabolism, mitogenesis, apoptosis, intracellular signalling, thrombocyte function, protein degradation). Whether or not these differences have clinical bearings (and among which patient populations) remains to be determined.

Introduction to current and future protein therapeutics: a protein engineering perspective

Protein therapeutics and its enabling sister discipline, protein engineering, have emerged since the early 1980s. The first protein therapeutics were recombinant versions of natural proteins. Proteins purposefully modified to increase their clinical potential soon followed with enhancements derived from protein or glycoengineering, Fc fusion or conjugation to polyethylene glycol. Antibody-based drugs subsequently arose as the largest and fastest growing class of protein therapeutics. The rationale for developing better protein therapeutics with enhanced efficacy, greater safety, reduced immunogenicity or improved delivery comes from the convergence of clinical, scientific, technological and commercial drivers that have identified unmet needs and provided strategies to address them. Future protein drugs seem likely to be more extensively engineered to improve their performance, e.g., antibodies and Fc fusion proteins with enhanced effector functions or extended half-life. Two old concepts for improving antibodies, namely antibody-drug conjugates and bispecific antibodies, have advanced to the cusp of clinical success. As for newer protein therapeutic platform technologies, several engineered protein scaffolds are in early clinical development and offer differences and some potential advantages over antibodies.