Insulin and its analogues and their affinities for the IGF1 receptor

Implications of Insulin-like Growth Factor 1 Receptor Activation in Lung Cancer

Insulin-like growth factor 1 receptor (IGF1R) has been intensively investigated in many preclinical studies using cell lines and animal models, and the results have provided important knowledge to help improve the understanding of cancer biology. IGF1R is highly expressed in patients with lung cancer, and high levels of circulating insulin-like growth factor 1 (IGF1), the main ligand for IGF1R, increases the risk of developing lung malignancy in the future. Several phase I clinical trials have supported the potential use of an IGF1R-targeted strategy for cancer, including lung cancer. However, the negative results from phase III studies need further attention, especially in selecting patients with specific molecular signatures, who will gain benefits from IGF1R inhibitors with minimal side effects. This review will discuss the basic concept of IGF1R in lung cancer biology, such as epithelial-mesenchymal transition (EMT) induction and cancer stem cell (CSC) maintenance, and also the clinical implications of IGF1R for lung cancer patients, such as prognostic value and cancer therapy resistance.

Potency of Full-Length MGF to Induce Maximal Activation of the IGF-I R Is Similar to Recombinant Human IGF-I at High Equimolar Concentrations

AIMS

To compare full-length mechano growth factor (full-length MGF) with human recombinant insulin-like growth factor-I (IGF-I) and human recombinant insulin (HI) in their ability to activate the human IGF-I receptor (IGF-IR), the human insulin receptor (IR-A) and the human insulin receptor-B (IR-B), respectively. In addition, we tested the stimulatory activity of human MGF and its stabilized analog Goldspink-MGF on the IGF-IR.

METHODS

The effects of full-length MGF, IGF-I, human mechano growth factor (MGF), Goldspink-MGF and HI were compared using kinase specific receptor activation (KIRA) bioassays specific for IGF-I, IR-A or IR-B, respectively. These assays quantify activity by measuring auto-phosphorylation of the receptor upon ligand binding.

RESULTS

IGF-IR: At high equimolar concentrations maximal IGF-IR stimulating effects generated by full-length MGF were similar to that of IGF-I (89-fold vs. 77-fold, respectively). However, EC50 values of IGF-I and full-length MGF for the IGF-I receptor were 0.86 nmol/L (95% CI 0.69-1.07) and 7.83 nmol/L (95% CI: 4.87-12.58), respectively. No IGF-IR activation was observed by human MGF and Goldspink-MGF, respectively. IR-A/IR-B: At high equimolar concentrations similar maximal IR-A stimulating effects were observed for full -length MGF and HI, but maximal IR-B stimulation achieved by full -length MGF was stronger than that by HI (292-fold vs. 98-fold). EC50 values of HI and full-length MGF for the IR-A were 1.13 nmol/L (95% CI 0.69-1.84) and 73.11 nmol/L (42.87-124.69), respectively; for IR-B these values were 1.28 nmol/L (95% CI 0.64-2.57) and 35.10 nmol/L (95% 17.52-70.33), respectively.

CONCLUSIONS

Full-length MGF directly stimulates the IGF-IR. Despite a higher EC50 concentration, at high equimolar concentrations full-length MGF showed a similar maximal potency to activate the IGF-IR as compared to IGF-I. Further research is needed to understand the actions of full-length MGF in vivo and to define the physiological relevance of our in vitro findings.

Looking at the carcinogenicity of human insulin analogues via the intrinsic disorder prism

Therapeutic insulin, in its native and biosynthetic forms as well as several currently available insulin analogues, continues to be the protein of most interest to researchers. From the time of its discovery to the development of modern insulin analogues, this important therapeutic protein has passed through several stages and product generations. Beside the well-known link between diabetes and cancer risk, the currently used therapeutic insulin analogues raised serious concerns due to their potential roles in cancer initiation and/or progression. It is possible that structural variations in some of the insulin analogues are responsible for the appearance of new oncogenic species with high binding affinity to the insulin-like growth factor 1 (IGF1) receptor. The question we are trying to answer in this work is: are there any specific features of the distribution of intrinsic disorder propensity within the amino acid sequences of insulin analogues that may provide an explanation for the carcinogenicity of the altered insulin protein?

Building the Case for Insulin-Like Growth Factor Receptor-I Involvement in Thyroid-Associated Ophthalmopathy

The pathogenesis of orbital Graves' disease (GD), a process known as thyroid-associated ophthalmopathy (TAO), remains incompletely understood. The thyrotropin receptor (TSHR) represents the central autoantigen involved in GD and has been proposed as the thyroid antigen shared with the orbit that could explain the infiltration of immune cells into tissues surrounding the eye. Another cell surface protein, insulin-like growth factor-I receptor (IGF-IR), has recently been proposed as a second antigen that participates in TAO by virtue of its interactions with anti-IGF-IR antibodies generated in GD, its apparent physical and functional complex formation with TSHR, and its necessary involvement in TSHR post-receptor signaling. The proposal that IGF-IR is involved in TAO has provoked substantial debate. Furthermore, several studies from different laboratory groups, each using different experimental models, have yielded conflicting results. In this article, we attempt to summarize the biological characteristics of IGF-IR and TSHR. We also review the evidence supporting and refuting the postulate that IGF-IR is a self-antigen in GD and that it plays a potentially important role in TAO. The putative involvement of IGF-IR in disease pathogenesis carries substantial clinical implications. Specifically, blocking this receptor with monoclonal antibodies can dramatically attenuate the induction by TSH and pathogenic antibodies generated in GD of proinflammatory genes in cultured orbital fibroblasts and fibrocytes. These cell types appear critical to the development of TAO. These observations have led to the conduct of a now-completed multicenter therapeutic trial of a fully human monoclonal anti-IGF-IR blocking antibody in moderate to severe, active TAO.

A framework for the in vitro evaluation of cancer-relevant molecular characteristics and mitogenic potency of insulin analogues

Clinically prescribed insulin analogues are putatively linked with increased cancer risk. We developed a framework for the mandated regulatory in vitro evaluation of cancer-relevant bioassays for comparisons of insulin analogues, and showed that the cell-specific IGF-IR/IR ratio is crucial for interpretation.

Epidemiological and laboratory studies raise the possibility of a link between clinically prescribed insulin analogues and increased cancer risk. Accordingly, there is a regulatory mandate for cancer-related pre-clinical safety evaluation during insulin analogue development, but currently, there is no standardized framework for such in vitro evaluation. We tested human insulin; the super-mitogenic insulin, X10 and insulin-like growth factor I, in four cancer cell lines with a range of insulin-like growth factor-I receptor (IGF-IR)/IR (insulin receptor) ratios (HCT 116, HT-29, COLO 205 and MCF7) and related these to IGF-IR and IR expression in 17 human adenocarcinomas. All cell types were IR-A isoform dominant. We determined IGF-IR/IR signalling pathway endpoints in dose- and time-varying experiments, and performed mitogenic dose–response equivalent assays to derive EC₅₀ values, and correlated these with IGF-IR/IR ratios. We superimposed relative EC₅₀ values onto data from the literature in a meta-analysis. The IGF-IR/IR ratios varied from <1 to 12 in the selected cell lines; similar pattern ranges were observed in human adenocarcinomas. The three ligands demonstrated differential IR/IGF-IR and Akt phosphorylation, which correlated with cell-specific IGF-IR/IR ratios. Mitogenic profiles of X10 mimicked those for insulin-like growth factor I (IGF-I) and correlated with IGF-IR/IR ratios. The meta-analysis, adding data from five additional studies, supported the hypothesis that ligand mitogenic potency, relative to human insulin, increases with increasing cell-specific IGF-IR/IR ratio. This study established a framework for the in vitro evaluation of cancer-relevant bioassays for comparisons of insulin analogues, and specifically consolidated earlier studies that determination of the cell-specific IGF-IR/IR ratio is crucial for the interpretation of ranking relative biological activities.

Proliferative and signaling activities of insulin analogues in endometrial cancer cells

Insulin analogues have been developed to achieve further improvement in the therapy of diabetes. However, modifications introduced into the insulin molecule may enhance their affinity for the insulin-like growth factor-1 receptor (IGF1R). Hyperinsulinemia has been identified as a risk factor for endometrial cancer. We hypothesized that insulin analogues may elicit atypical proliferative and signaling activities in endometrial cancer cells. Our results demonstrate that glargine, but not detemir, stimulated cell proliferation, displayed an anti-apoptotic effect, and had a positive effect on cell cycle progression in endometrial cancer cell lines ECC-1 and USPC-1. In addition, we showed that glargine and detemir induced dual activation of the insulin receptor (INSR) and IGF1R in both cell types. Furthermore, we showed that glargine elicited signaling events that are markedly different from those induced by insulin. In conclusion, our data support the concept that, although insulin analogues were designed to display insulin-like metabolic effects, glargine and, possibly, additional analogues exhibit IGF1-like activities and, accordingly, may function as IGF1 analogues.

Loss of the insulin receptor in murine megakaryocytes/platelets causes thrombocytosis and alterations in IGF signalling

Aims

Patients with conditions that are associated with insulin resistance such as obesity, type 2 diabetes mellitus, and polycystic ovary syndrome have an increased risk of thrombosis and a concurrent hyperactive platelet phenotype. Our aim was to determine whether insulin resistance of megakaryocytes/platelets promotes platelet hyperactivation.

Methods and results

We generated a conditional mouse model where the insulin receptor (IR) was specifically knocked out in megakaryocytes/platelets and performed ex vivo platelet activation studies in wild-type (WT) and IR-deficient platelets by measuring aggregation, integrin α_IIbβ₃ activation, and dense and α-granule secretion. Deletion of IR resulted in an increase in platelet count and volume, and blocked the action of insulin on platelet signalling and function. Platelet aggregation, granule secretion, and integrin α_IIbβ₃ activation in response to the glycoprotein VI (GPVI) agonist collagen-related peptide (CRP) were significantly reduced in platelets lacking IR. This was accompanied by a reduction in the phosphorylation of effectors downstream of GPVI. Interestingly, loss of IR also resulted in a reduction in insulin-like growth factor-1 (IGF-1)- and insulin-like growth factor-2 (IGF-2)-mediated phosphorylation of IRS-1, Akt, and GSK3β and priming of CRP-mediated platelet activation. Pharmacological inhibition of IR and the IGF-1 receptor in WT platelets recapitulated the platelet phenotype of IR-deficient platelets.

Conclusions

Deletion of IR (i) increases platelet count and volume, (ii) does not cause platelet hyperactivity, and (iii) reduces GPVI-mediated platelet function and platelet priming by IGF-1 and IGF-2.

Insulin analogues display atypical differentiative activities in skin keratinocytes

BACKGROUND

We have previously shown that both insulin and IGF1 lead to increased proliferation of keratinocytes. However, whereas insulin supports keratinocytes differentiation, IGF1 inhibits this process. The aim of the present study was to examine the proliferative and differentiative effects of insulin analogues (glargine, detemir, lispro and aspart) in primary keratinocytes in comparison with insulin and IGF1.

METHODS

Primary keratinocytes cultures were produced from newborn BALB/c mice skin. Proliferation rates were assessed by [(3)H]-thymidine incorporation and XTT assays and differentiation was evaluated by Western blots analysis. Insulin receptor and IGF1 receptor phosphorylation was assessed by immunoprecipitation assays.

RESULTS

Treatment with glargine or detemir resulted in an insulin-like effect on the differentiation process whereas lispro and aspart treatment led to an IGF1-like effect. In addition, treatment of keratinocytes with aspart led to a rapid phosphorylation of the IGF1 receptor.

CONCLUSIONS

Our study provides evidence that insulin analogues elicit atypical actions in the skin.

Probing the stability of insulin oligomers using electrospray ionization ion mobility mass spectrometry

The peptide hormone insulin is central to regulating carbohydrate and fat metabolism in the body by controlling blood sugar levels. Insulin's most active form is the monomer and the extent of insulin oligomerization is related to insulin's activity of controlling blood sugar levels. Electrospray ionization (ESI) of human insulin produced a series of oligomers from the monomer to the undecamer identified using quadrupole ion mobility time-of-flight mass spectrometry. Previous research suggested that only the monomer, dimer and hexamer are native forms of insulin in solution and the range of oligomers observed in the gas-phase are ESI artifacts. Here the properties of three distinct oligomer bands I, II and III, where both the charge state and number of insulin units of the oligomer increase incrementally, were investigated. When Zn(ii) was added to the insulin sample the same oligomers were observed but with 0-6 Zn(ii) ions bound to each of the oligomers. The oligomers of bands I, II and III were characterized by comparing their drift times, collision cross- sections, relative intensities, collision-induced dissociation (CID) patterns and relative breakdown energies. Insulin oligomers of band I dissociated primarily by releasing either the 2+ or 3+ monomer accompanied by an oligomer that conserved the mass, charge and Zn(ii) of the precursor. Insulin oligomers of bands II and III dissociated primarily by releasing the 2+ monomer accompanied by an oligomer which conserved the mass, charge and Zn(ii) of the precursor. Comparison of CID patterns and breakdown energies showed all the oligomers in band II required higher collision energies to dissociate than the oligomers in band I, and the oligomers of band III required higher energies to dissociate than oligomers of band II. These results show that the amount of excess charge on the oligomer in respect to the number of insulin monomers in the oligomer affects their stability.

Targeting the insulin-like growth factor pathway in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide. Only 30%-40% of the patients with HCC are eligible for curative treatments, which include surgical resection as the first option, liver transplantation and percutaneous ablation. Unfortunately, there is a high frequency of tumor recurrence after surgical resection and most HCC seem resistant to conventional chemotherapy and radiotherapy. Sorafenib, a multi-tyrosine kinase inhibitor, is the only chemotherapeutic option for patients with advanced hepatocellular carcinoma. Patients treated with Sorafenib have a significant increase in overall survival of about three months. Therefore, there is an urgent need to develop alternative treatments. Due to its role in cell growth and development, the insulin-like growth factor system is commonly deregulated in many cancers. Indeed, the insulin-like growth factor (IGF) axis has recently emerged as a potential target for hepatocellular carcinoma treatment. To this aim, several inhibitors of the pathway have been developed such as monoclonal antibodies, small molecules, antisense oligonucleotides or small interfering RNAs. However recent studies suggest that, unlike most tumors, HCC development requires increased signaling through insulin growth factor II rather than insulin growth factor I. This may have great implications in the future treatment of HCC. This review summarizes the role of the IGF axis in liver carcinogenesis and the current status of the strategies designed to target the IGF-I signaling pathway for hepatocellular carcinoma treatment.

Synthesis, cloning and expression of a novel pre-miniproinsulin analogue gene in Escherichia coli

In the present study, a novel pre-miniproinsulin analogue was designed to have a short 9 residue sequence replacing the 35 residue C-chain, one lysine and one arginine added to the C-terminus of the B-chain in combination with glycine and arginine substitution at A21 and B29, respectively, and a 16-residue fusion partner comprising the pentapeptide sequence (PSDKP) of the N-terminus of human tumor necrosis factor-α (TNF-α), 6 histidine residues for Ni²⁺ chelated affinity purification and a pentapeptide ending with methionine for ease of chemical cleavage fused at the N-terminus. Homology modeling of the designed protein against miniproinsulin (protein databank file 1 efeA) as a template showed that the distance between the α-carbons of the C-terminus of the B-chain and the N-terminus of the A-chain did not change; the root-mean-square deviation of the backbone atoms between the structures of modeled miniproinsulin and miniproinsulin template was 0.000 Å. DNA sequencing of the synthesized gene showed 100% identity with theoretical sequence. The gene was constructed taking into account the codon preference of Escherichia coli (CAI value 0.99) in order to increase the expression rate of the DNA in the host strain. The designed gene was synthesized using DNA synthesis technology and then cloned into the expression plasmid pET-24a(+) and propagated in E. coli strain JM109. Gene expression was successful in two E. coli strains: namely JM109(DE3) and BL21(DE3)pLysS. SDS–PAGE analysis was carried out to check protein size and to check and optimize expression. Rapid screening and purification of the resulting protein was carried out by Ni–NTA technology. The identity of the expressed protein was verified by immunological detection method of western blot using polyclonal rabbit antibody against insulin.

Calycosin suppresses breast cancer cell growth via ERβ-dependent regulation of IGF-1R, p38 MAPK and PI3K/Akt pathways

We previously reported that calycosin, a natural phytoestrogen structurally similar to estrogen, successfully triggered apoptosis of estrogen receptor (ER)-positive breast cancer cell line, MCF-7. To better understand the antitumor activities of calycosin against breast cancer, besides MCF-7 cells, another ER-positive cell line T-47D was analyzed here, with ER-negative cell lines (MDA-231, MDA-435) as control. Notably, calycosin led to inhibited cell proliferation and apoptosis only in ER-positive cells, particularly in MCF-7 cells, whereas no such effect was observed in ER-negative cells. Then we investigated whether regulation of ERβ, a subtype of ER, contributed to calycosin-induced apoptosis in breast cancer cells. The results showed that incubation of calycosin resulted in enhanced expression ERβ in MCF-7 and T-47D cells, rather than MDA-231 and MDA-435 cells. Moreover, with the upregulation of ERβ, successive changes in downstream signaling pathways were found, including inactivation of insulin-like growth factor 1 receptor (IGF-1R), then stimulation of p38 MAPK and suppression of the serine/threonine kinase (Akt), and finally poly(ADP-ribose) polymerase 1 (PARP-1) cleavage. However, the other two members of the mitogen-activated protein kinase (MAPK) family, extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK), were not consequently regulated by downregulated IGF-1R, indicating ERK 1/2 and JNK pathways were not necessary to allow proliferation inhibition by calycosin. Taken together, our results indicate that calycosin tends to inhibit growth and induce apoptosis in ER-positive breast cancer cells, which is mediated by ERβ-induced inhibition of IGF-1R, along with the selective regulation of MAPK and phosphatidylinositol 3-kinase (PI3K)/Akt pathways.

IGF-IR Targeted Therapy: Past, Present and Future

The IGF-I receptor (IGF-IR) has been studied as an anti-cancer target. However, monotherapy trials with IGF-IR targeted antibodies or with IGF-IR specific tyrosine kinase inhibitors have, overall, been very disappointing in the clinical setting. This review discusses potential reasons why IGF-I R targeted therapy fails to inhibit growth of human cancers. It has become clear that intracellular signaling pathways are highly interconnected and complex instead of being linear and simple. One of the most potent candidates for failure of IGF-IR targeted therapy is the insulin receptor isoform A (IR-A). Activation of the IR-A by insulin-like growth factor-II (IGF-II) bypasses the IGF-IR and its inhibition. Another factor may be that anti-cancer treatment may reduce IGF-IR expression. IGF-IR blocking drugs may also induce hyperglycemia and hyperinsulinemia, which may further stimulate cell growth. In addition, circulating IGF-IRs may reduce therapeutic effects of IGF-IR targeted therapy. Nevertheless, it is still possible that the IGF-IR may be a useful adjuvant or secondary target for the treatment of human cancers. Development of functional inhibitors that affect the IGF-IR and IR-A may be necessary to overcome resistance and to make IGF-IR targeted therapy successful. Drugs that modify alternative downstream effects of the IGF-IR, so called "biasing agonists," should also be considered.

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.

Insulin suppresses IKs (KCNQ1/KCNE1) currents, which require β-subunit KCNE1

Abnormal QT prolongation in diabetic patients has become a clinical problem because it increases the risk of lethal ventricular arrhythmia. In an animal model of type 1 diabetes mellitus, several ion currents, including the slowly activating delayed rectifier potassium current (IKs), are altered. The IKs channel is composed of KCNQ1 and KCNE1 subunits, whose genetic mutations are well known to cause long QT syndrome. Although insulin is known to affect many physiological and pathophysiological events in the heart, acute effects of insulin on cardiac ion channels are poorly understood at present. This study was designed to investigate direct electrophysiological effects of insulin on IKs (KCNQ1/KCNE1) currents. KCNQ1 and KCNE1 were co-expressed in Xenopus oocytes, and whole cell currents were measured by a two-microelectrode voltage-clamp method. Acute application of insulin suppressed the KCNQ1/KCNE1 currents and phosphorylated Akt and extracellular signal-regulated kinase (ERK), the two major downstream effectors, in a concentration-dependent manner. Wortmannin (10(-6) M), a phosphoinositide 3-kinase (PI3K) inhibitor, attenuated the suppression of the currents and phosphorylation of Akt by insulin, whereas U0126 (10(-5) M), a mitogen-activated protein kinase kinase (MEK) inhibitor, had no effect on insulin-induced suppression of the currents. In addition, insulin had little effect on KCNQ1 currents without KCNE1, which indicated an essential role of KCNE1 in the acute suppressive effects of insulin. Mutagenesis studies revealed amino acid residues 111-118 within the distal third C-terminus of KCNE1 as an important region. Insulin has direct electrophysiological effects on IKs currents, which may affect cardiac excitability.

Building better drugs: developing and regulating engineered therapeutic proteins

Most native proteins do not make optimal drugs and thus a second- and third-generation of therapeutic proteins, which have been engineered to improve product attributes or to enhance process characteristics, are rapidly becoming the norm. There has been unprecedented progress, during the past decade, in the development of platform technologies that further these ends. Although the advantages of engineered therapeutic proteins are considerable, the alterations can affect the safety and efficacy of the drugs. We discuss both the key technological innovations with respect to engineered therapeutic proteins and advancements in the underlying basic science. The latter would permit the design of science-based criteria for the prediction and assessment of potential risks and the development of appropriate risk management plans. This in turn holds promise for more predictable criteria for the licensure of a class of products that are extremely challenging to develop but represent an increasingly important component of modern medical practice.

Insulin analogues may accelerate progression of diabetic retinopathy after impairment of inner blood-retinal barrier

Diabetic retinopathy regresses after spontaneous infarction or surgical ablation of pituitary gland. Growth hormone deficiency seems to be a protective factor for development of diabetic retinopathy in dwarfs. Despite the same glycemic control, development of diabetic retinopathy is significantly higher in pubertal subjects than pre-pubertal subjects. These evidences indicate a strong relationship between growth hormone and progression of diabetic retinopathy. Insulin like growth factor-1 (IGF-1) is the most important mediator of effects of growth hormone (GH). It stimulates IGF-1 receptor. Insulin analogues also stimulate IGF-1 receptor. Therefore insulin analogues may show similar effects like growth hormone and deteriorate diabetic retinopathy. However we suggest that impairment degree of inner blood-retinal barrier should be considered for this claim. We hypothesize that insulin analogues have dual effects (beneficial and worsening) depending on stage of impairment of inner blood-retinal barrier. Insulin analogues protect pericytes and blood-retinal barrier by decreasing blood glucose level. Analogues may pass into the retinal tissue in very low amounts when inner blood-retinal barrier is intact. Therefore, insulin analogues may not deteriorate diabetic retinopathy but also have beneficial effect by protecting blood-retinal barrier at this stage. However, they may pass into the retinal tissue in much more amounts when inner blood-retinal barrier impairs. Analogues may deteriorate cellular composition of retina through stimulation of IGF-1 receptors. A number of different cell types, including glia, retinal pigment epithelial cells and fibroblast-like cells have been identified in diabetic epiretinal tissues. Insulin analogues may cause proliferation in these cells. A type of glial cell named Non-astrocytic Inner Retinal Glia-like (NIRG) cell was identified to be stimulated and proliferate by IGF-1. IGF has been reported to generate traction force in retinal pigment epitelium (RPE) and mullerian cells. Mullerian cells also support inner blood-retinal barrier. Insulin analogues may cause proliferation in glial cells and generate traction force in RPE and mullerian cells by stimulating IGF-1 receptor. These effects of analogues may increase after deterioration of inner blood-retinal barrier and cause structural changes in retinal tissue. Deterioration of cellular structure may contribute to impairment of inner blood-retinal barrier, facilitate anjiogenesis and influence vitreoretinal interface. Therefore we suggest that insulin analogues should be used carefully after impairment of inner blood-retinal barrier. Analogues that bind with lesser affinity to IGF-1 receptor should be chosen after impairment. Pharmacologic agents may be developed to antagonize effect of insulin analogues on IGF-1 receptors.

Maternal hyperglycemia leads to fetal cardiac hyperplasia and dysfunction in a rat model

Accelerated fetal myocardial growth with altered cardiac function is a well-documented complication of human diabetic pregnancy, but its pathophysiology is still largely unknown. Our aim was to explore the mechanisms of fetal cardiac remodeling and cardiovascular hemodynamics in a rat model of maternal pregestational streptozotocin-induced hyperglycemia. The hyperglycemic group comprised 107 fetuses (10 dams) and the control group 219 fetuses (20 dams). Fetal cardiac function was assessed serially by Doppler ultrasonography. Fetal cardiac to thoracic area ratio, newborn heart weight, myocardial cell proliferative and apoptotic activities, and cardiac gene expression patterns were determined. Maternal hyperglycemia was associated with increased cardiac size, proliferative, apoptotic and mitotic activities, upregulation of genes encoding A- and B-type natriuretic peptides, myosin heavy chain types 2 and 3, uncoupling proteins 2 and 3, and the angiogenetic tumor necrosis factor receptor superfamily member 12A. The genes encoding Kv channel-interacting protein 2, a regulator of electrical cardiac phenotype, and the insulin-regulated glucose transporter 4 were downregulated. The heart rate was lower in fetuses of hyperglycemic dams. At 13-14 gestational days, 98% of fetuses of hyperglycemic dams had holosystolic atrioventricular valve regurgitation and decreased outflow mean velocity, indicating diminished cardiac output. Maternal hyperglycemia may lead to accelerated fetal myocardial growth by cardiomyocyte hyperplasia. In fetuses of hyperglycemic dams, expression of key genes that control and regulate cardiomyocyte electrophysiological properties, contractility, and metabolism are altered and may lead to major functional and clinical implications on the fetal heart.

Insulin-mediated oxidative stress and DNA damage in LLC-PK1 pig kidney cell line, female rat primary kidney cells, and male ZDF rat kidneys in vivo

Hyperinsulinemia, a condition with excessively high insulin blood levels, is related to an increased cancer incidence. Diabetes mellitus is the most common of several diseases accompanied by hyperinsulinemia. Because an elevated kidney cancer risk was reported for diabetic patients, we investigated the induction of genomic damage by insulin in LLC-PK1 pig kidney cells, rat primary kidney cells, and ZDF rat kidneys. Insulin at a concentration of 5nM caused a significant increase in DNA damage in vitro. This was associated with the formation of reactive oxygen species (ROS). In the presence of antioxidants, blockers of the insulin, and IGF-I receptors, and a phosphatidylinositol 3-kinase inhibitor, the insulin-mediated DNA damage was reduced. Phosphorylation of protein kinase B (PKB or AKT) was increased and p53 accumulated. Inhibition of the mitochondrial and nicotinamide adenine dinucleotide phosphatase oxidase-related ROS production reduced the insulin-mediated damage. In primary rat cells, insulin also induced genomic damage. In kidneys from healthy, lean ZDF rats, which were infused with insulin to yield normal or high blood insulin levels, while keeping blood glucose levels constant, the amounts of ROS and the tumor protein (p53) were elevated in the high-insulin group compared with the control level group. ROS and p53 were also elevated in diabetic obese ZDF rats. Overall, insulin-induced oxidative stress resulted in genomic damage. If the same mechanisms are active in patients, hyperinsulinemia might cause genomic damage through the induction of ROS contributing to the increased cancer risk, against which the use of antioxidants and/or ROS production inhibitors might exert protective effects.

Clinical utility of insulin and insulin analogs

Diabetes is a pandemic disease characterized by autoimmune, genetic and metabolic abnormalities. While insulin deficiency manifested as hyperglycemia is a common sequel of both Type-1 and Type-2 diabetes (T1DM and T2DM), it does not result from a single genetic defect--rather insulin deficiency results from the functional loss of pancreatic β cells due to multifactorial mechanisms. Since pancreatic β cells of patients with T1DM are destroyed by autoimmune reaction, these patients require daily insulin injections. Insulin resistance followed by β cell dysfunction and β cell loss is the characteristics of T2DM. Therefore, most patients with T2DM will require insulin treatment due to eventual loss of insulin secretion. Despite the evidence of early insulin treatment lowering macrovascular (coronary artery disease, peripheral arterial disease and stroke) and microvascular (diabetic nephropathy, neuropathy and retinopathy) complications of T2DM, controversy exists among physicians on how to initiate and intensify insulin therapy. The slow acting nature of regular human insulin makes its use ineffective in counteracting postprandial hyperglycemia. Instead, recombinant insulin analogs have been generated with a variable degree of specificity and action. Due to the metabolic variability among individuals, optimum blood glucose management is a formidable task to accomplish despite the presence of novel insulin analogs. In this article, we present a recent update on insulin analog structure and function with an overview of the evidence on the various insulin regimens clinically used to treat diabetes.