Insulin receptor and IGF-I receptor Bioactivity in Health and Disease

Insulin was discovered in 1921 by Banting and Best and its structure elucidated in 1955. The first insulin bioassays appeared in the 1940s. First, rats were injected with a range of known concentrations of purified commercial or ‘standard’ insulin and the subsequent fall in blood glucose levels was measured. Then an unknown sample of human plasma was administered to a rat and its insulin concentration was assumed to be identical to the standard dilution that caused the same fall in glucose levels. Due to poor correlations between measured blood glucose levels and calculated insulin levels, these bioassays were replaced by in vitro bioassays. Metabolic parameters, such as rate of glucose uptake in response to dose-response curves of known insulin concentrations were measured using isolated tissues, such as the hemidiaphragm or epididymal fat pad from the rat. Also these in vitro bioassays for plasma insulin were not very successful due to high inter-assay variability, their laborious nature and due to a growing doubt that they were not specific for insulin. Maybe even more importantly, in 1959 Leonards described a substance in normal human fasting serum that, like insulin, stimulated glucose oxidation and triglyceride synthesis in adipose tissue but that, unlike insulin, could not be extracted from plasma into acid-ethanol. In 1963, Froesch et. al. found that serum from guinea pigs immunized against insulin, suppressed insulin action in fat tissue, but it had no effect on Leonards’s insulin-like substance and so the term nonsuppressible insulin like activity (NSILA) was born

The insulin-like growth factor-I receptor stimulating activity (IRSA) in health and disease

Determination of true IGF-I bioactivity in serum and other biological fluids is still a substantial challenge. The IGF-IR Kinase Receptor Activation assay (IGF-IR KIRA assay) is a novel tool to asses IGF-IR stimulating activity (IRSA) and has opened a new era in studying the IGF system. In this paper we discuss many studies showing that measuring IRSA by the IGF-IR KIRA assay often provides fundamentally different information about the IGF system than the commonly used total IGF-I immunoassays. With the IGF-IR KIRA assay phosphorylation of tyrosine residues of the IGF-IR is used as read out to quantify IRSA in unknown (serum) samples. The IGF-IR KIRA assay gives information about net overall effects of circulating IGF-I, IGF-II, IGFBPs and IGFBP-proteases on IGF-IR activation and seems especially superior to immunoreactive total IGF-I in monitoring therapeutic interventions. Although the IRSA as measured by the IGF-IR KIRA assay probably more closely reflects true bioactive IGF-I than measurements of total IGF-I in serum, the IGF-IR KIRA assay in its current form does not give information about all the post-receptor intracellular events mediated by the IGF-IR. Interestingly, in several conditions in health and disease IRSA measured by the IGF-IR KIRA assay is considerably higher in interstitial fluid and ascites than in serum. This suggests that both the paracrine (local) and endocrine (circulating) IRSA should be measured to get a complete picture about the role of the IGF system in health and disease

In active acromegaly, IGF1 bioactivity is related to soluble Klotho levels and quality of life

The value of measuring IGF1 bioactivity in active acromegaly is unknown. Soluble Klotho (S-Klotho) level is elevated in active acromegaly and it has been suggested that S-Klotho can inhibit activation of the IGF1 receptor (IGF1R). A cross-sectional study was carried out in 15 patients with active acromegaly based on clinical presentation, unsuppressed GH during an oral glucose tolerance test, and elevated total IGF1 levels (>+2 s.d.). Total IGF1 was measured by immunoassay, IGF1 bioactivity by the IGF1R kinase receptor activation assay and S-Klotho by an ELISA. Quality of Life (QoL) was assessed by Acromegaly QoL (AcroQoL) Questionnaire and Short-Form-36 Health Survey Questionnaire (SF-36). Out of 15 patients, nine had IGF1 bioactivity values within the reference range. S-Klotho was higher in active acromegaly compared with controls. Age-adjusted S-Klotho was significantly related to IGF1 bioactivity (r=0.75, P=0.002) and to total IGF1 (r=0.62, P=0.02). IGF1 bioactivity and total IGF1 were inversely related to the physical component summary of the SF-36 (r=−0.78, P=0.002 vs r=−0.60, P=0.03). Moreover, IGF1 bioactivity, but not total IGF1, was significantly inversely related to the physical dimension of the AcroQoL Questionnaire (r=−0.60, P=0.02 vs r=−0.37, P=0.19). In contrast to total IGF1, IGF1 bioactivity was within the reference range in a considerable number of subjects with active acromegaly. Elevated S-Klotho levels may have reduced IGF1 bioactivity. Moreover, IGF1 bioactivity was more strongly related to physical measures of QoL than total IGF1, suggesting that IGF1 bioactivity may better reflect physical limitations perceived in active acromegaly

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 IGFI 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

双方向グラフの最大重み最小帰還辺集合問題について

Centenarians' offspring represent a suitable model to study age-dependent variables (e.g. IGF-I) potentially involved in the modulation of the lifespan. The aim of the present study was to investigate the role of the IGF-I in human longevity. We evaluated circulating IGF-I bioactivity measured by an innovative IGF-I Kinase Receptor Activation (KIRA) Assay, total IGF-I, IGFBP-3, total IGF-II, insulin, glucose, HOMA2-B% and HOMA2-S% in 192 centenarians' offspring and 80 offspring-controls of which both parents died relatively young. Both groups were well-matched for age, gender and BMI with the centenarians' offspring. IGF-I bioactivity (p\u30080.01), total IGF-I (p\u30080.01) and the IGF-I/IGFBP-3 molar ratio (p\u30080.001) were significantly lower in centenarians' offspring compared to offspring matched-controls. Serum insulin, glucose, HOMA2-B% and HOMA2-S% values were similar between both groups. In centenarians' offspring IGF-I bioactivity was inversely associated to insulin sensitivity. In conclusion: 1) centenarians' offspring had relatively lower circulating IGF-I bioactivity compared to offspring matched-controls; 2) IGF-I bioactivity in centenarians' offspring was inversely related to insulin sensitivity. These data support a role of the IGF-I/insulin system in the modulation of human aging process

Molecular Characterisation of Long-Acting Insulin Analogues in Comparison with Human Insulin, IGF-1 and Insulin X10

AIMS/HYPOTHESIS: There is controversy with respect to molecular characteristics of insulin analogues. We report a series of experiments forming a comprehensive characterisation of the long acting insulin analogues, glargine and detemir, in comparison with human insulin, IGF-1, and the super-mitogenic insulin, X10. METHODS: We measured binding of ligands to membrane-bound and solubilised receptors, receptor activation and mitogenicity in a number of cell types. RESULTS: Detemir and glargine each displayed a balanced affinity for insulin receptor (IR) isoforms A and B. This was also true for X10, whereas IGF-1 had a higher affinity for IR-A than IR-B. X10 and glargine both exhibited a higher relative IGF-1R than IR binding affinity, whereas detemir displayed an IGF-1R:IR binding ratio of ≤ 1. Ligands with high relative IGF-1R affinity also had high affinity for IR/IGF-1R hybrid receptors. In general, the relative binding affinities of the analogues were reflected in their ability to phosphorylate the IR and IGF-1R. Detailed analysis revealed that X10, in contrast to the other ligands, seemed to evoke a preferential phosphorylation of juxtamembrane and kinase domain phosphorylation sites of the IR. Sustained phosphorylation was only observed from the IR after stimulation with X10, and after stimulation with IGF-1 from the IGF-1R. Both X10 and glargine showed an increased mitogenic potency compared to human insulin in cells expressing many IGF-1Rs, whereas only X10 showed increased mitogenicity in cells expressing many IRs. CONCLUSIONS: Detailed analysis of receptor binding, activation and in vitro mitogenicity indicated no molecular safety concern with detemir

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

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

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