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  • 1
    ISSN: 1432-0428
    Keywords: Insulin structure-function ; chemically modified insulin ; proinsulin ; bioactivity of insulin analogues
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Beef insulin, pork proinsulin and four derivatives of beef insulin modified at the A1-B29 site on the molecular surface have been studied. Three derivatives had a synthetic crosslink between the A and B chains. Previous studies with these materials [2, 3 and 5] had demonstrated in vivo bioactivities which were much higher than those displayed in vitro. This paper reports experiments which explain this discrepancy. The analogues were administered at equimolar rates to anaesthetised greyhounds by a priming-dose constant infusion technique and the plasma concentrations achieved were estimated by radioimmunoassay. Proinsulin and the modified insulins were metabolised more slowly than insulin. Biopotency values, which related fall in plasma glucose concentration to the total administered dose of analogue, agreed broadly with published results of conventional in vivo bioassays. On the other hand, calculation of potency in relation to the serum concentration of analogue actually achieved, yielded results which agreed more closely with in vitro assay data. We conclude that for these analogues, reported discrepancies between in vitro and in vivo biopotencies can be largely explained by the different rates at which these materials are metabolised.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Insulin ; insulin receptors ; mouse skeletal muscle ; rat hepatocytes ; human lymphocytes ; photoaffinity labelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Using the photoreactive, biologically active insulin analogue, B2-(2 nitro, 4-azidophenylacetyl)des-PheB1 insulin, which can be covalently bound to receptor molecules upon photolysis, the insulin receptor has been studied in three different types of cells or tissues: isolated rat hepatocytes, intact murine soleus muscle and cultured human lymphocytes. When compared with native insulin, this analogue displayed a slightly reduced binding affinity. Accordingly, the biological potency of the photoreactive analogue was decreased by approximately 30% compared with native insulin when tested for its ability to stimulate amino acid transport in hepatocytes, and deoxyglucose uptake in soleus muscles. It was as effective as insulin, however, at maximally stimulating concentrations and therefore is a full insulin agonist. This photoprobe was used to specifically label the insulin receptor in the three tissues: after ultra-violet irradiation, sodium dodecyl sulphatepolyacrylamide gel analysis of extracts under reducing conditions revealed that most of the radioactivity was associated with a 130,000 dalton band. In isolated hepatocytes, two bands at 125,000 and 23,000 daltons were also specifically labelled. In three different cell types from three different animal species, the 130,000 dalton band appeared to be the major subunit of the insulin receptor.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Insulin receptor ; ontogenesis ; photoreactive labelling ; tyrosine kinase ; anti-receptor antibodies ; rabbit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The domain structure of the insulin receptor was investigated in liver and brown adipose tissue of developing rabbits. The structure of the binding domain (α-subunit) was analysed after covalent labelling with a 125I photo-reactive insulin analogue. The structure of the tyrosine kinase domain (β-subunit) and the transmission of the hormonal signal from the α-to the β-subunit were analysed by stimulating with insulin the autophosphorylation of the β-subunit. Finally, the immunoreactivity of the receptor in developing tissues was assessed with anti-receptor antibodies. The results show that a functional insulin receptor can be detected at the early stages of fetal development in both tissues and is conserved throughout ontogenesis to adulthood.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 18 (1980), S. 59-63 
    ISSN: 1432-0428
    Keywords: Radioimmunoassay ; chemically modified insulins ; insulin antiserum specificity ; in vivo biological activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The reactions between four insulin antisera and eighteen insulin derivatives with modifications at the A1, B1 and B29 positions have been studied using a standard double-antibody radioimmunoassay procedure. The derivatives studied had: a) single modifications at A1, B1 or B29; b) modifications at two sites with or without a crosslink between them; c) modifications at all three sites with or without a crosslink. Analysis of the results showed a clear difference in the reactivity of the antisera. One antiserum (GP 5) was highly sensitive to modifications of the B1 residue and another (Ab 1) was sensitive to A1 and B29 modifications. Thus, immunological potencies of insulin analogues derived on the basis of these reactions with the antisera give widely varying results. These antisera were used in discriminatory radioimmunoassays of chemically modified insulins in biological fluids for estimation of in vivo hypoglycaemic potencies by an infusion technique, where the knowledge of the specificity of the antisera was useful in assessing the immunological identity of immunoreactive material in plasma with the analogue infused.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0428
    Keywords: Radioimmune assay ; enzyme linked immunosorbent assay ; insulin antibodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Human sera were tested for insulin antibodies by fluid and solid phase assays. Radioimmune titres determined with 125-I Tyr A14 insulin were not correlated with those obtained using insulin coated microplates and enzyme linked immunodetection (n=60). Several reasons for this lack of correlation were found. Iodine substitution on the A14 residue of insulin may significantly alter the avidity of some insulin antibodies for their ligand; hence, disclosing a heretofore unsuspected pitfall for antibody determination by radio-immunoassay. Specificity for bovine insulin was easily demonstrable in fluid phase by comparing the binding of monoiodinated bovine, porcine and human insulin. By contrast, in solid phase assay, titres obtained with microplates coated with bovine or human insulin were almost equal, regardless of the serum specificity for bovine insulin. This lack of specificity of the solid phase assay is not due to denaturation or unavailability of the bovine specific epitope because: bovine specificity could be demonstrated by competitive assay, after preincubation of the serum with insulin of the different species; and, coating with crosslinked insulin dimers or oligomers instead of monomers did not unmask bovine specificity. It is concluded that radioimmune methods are best suited to study specificity but may be biased by the presence of the radioiodine label whereas solid phase assay detects low avidity antibodies with great efficiency but is less appropriate to study specificity.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0428
    Keywords: Insulin ; insulin analogues ; glucose metabolism ; euglycaemic clamp ; insulin action ; hepatoselectivity ; glucose production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin analogues with relatively greater effect on hepatic glucose production than peripheral glucose disposal could offer a more physiological approach to the treatment of diabetes mellitus. The fact that proinsulin exhibits this property to a minor degree may suggest that analogues with increased molecular size may be less able than insulin to obtain access to peripheral receptor sites. Covalent insulin dimers have previously been shown to possess lower hypoglycaemic potencies than predicted by their in vivo receptor binding affinities. Reduced rates of diffusion to peripheral target tissues-might be an explanation for the lower in vivo potency compared to insulin. To test the relative hepatic and peripheral effects of covalent insulin dimers, glucose clamp procedures with D-[3-3H] glucose tracer infusions were used in anaesthetised greyhounds to establish dose-response curves for rates of hepatic glucose production and glucose disposal with insulin, NαB1, NαB′ 1,-suberoyl-insulin dimer, and NεB29, NεB′ 29,-suberoyl-insulin dimer. With NαB1, NαB′ 1,-suberoyl-insulin dimer molar potencies relative to insulin were 68%, (34–133) (mean and 95% fiducial limits), for inhibition of hepatic glucose production and 14.7%, (10.3–20.9) for glucose disposal. With NεB29,NεB′ 29,-suberoyl-insulin dimer potencies were 75%, (31–184) and 2.5%, (1.5–4.3), for inhibition of hepatic glucose production and for glucose disposal, respectively. The demonstration that both dimers exhibit a significantly greater effect on glucose production than on glucose disposal supports the suggestion that analogues with increased molecular size may exhibit reduced ability to gain access to peripheral target cells.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 9 (1973), S. 53-55 
    ISSN: 1432-0428
    Keywords: insulin ; peroxidase ; enzyme marker ; immunologic activity ; modified insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary By coupling purified horseradish peroxidase with glutaraldehyde and subsequent reaction with insulin, conjugates were obtained. These were partially purified by ion exchange chromatography on DEAE-cellulose. A fraction with an average molar ratio of peroxidase to insulin 1:0.37 was analysed by electrophoresis and gel filtration. The peroxidase activity of this fraction was found to be 19% of normal and the immunological reactivity 0.6% as compared with that of insulin.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-0428
    Keywords: Key words Insulin ; insulin analogues ; glucose metabolism ; euglycaemic clamp ; insulin action ; hepatoselectivity ; glucose production.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin analogues with relatively greater effect on hepatic glucose production than peripheral glucose disposal could offer a more physiological approach to the treatment of diabetes mellitus. The fact that proinsulin exhibits this property to a minor degree may suggest that analogues with increased molecular size may be less able than insulin to obtain access to peripheral receptor sites. Covalent insulin dimers have previously been shown to possess lower hypoglycaemic potencies than predicted by their in vivo receptor binding affinities. Reduced rates of diffusion to peripheral target tissues might be an explanation for the lower in vivo potency compared to insulin. To test the relative hepatic and peripheral effects of covalent insulin dimers, glucose clamp procedures with D-[3-3H]glucose tracer infusions were used in anaesthetised greyhounds to establish dose-response curves for rates of hepatic glucose production and glucose disposal with insulin, NαB1, NαB′ 1,-suberoyl-insulin dimer, and NɛB29, NɛB′ 29,-suberoyl-insulin dimer. With NαB1, NαB′ 1,-suberoyl-insulin dimer molar potencies relative to insulin were 68 %, (34–133) (mean and 95 % fiducial limits), for inhibition of hepatic glucose production and 14.7 %, (10.3–20.9) for glucose disposal. With NɛB29,NɛB′ 29,-suberoyl-insulin dimer potencies were 75 %, (31–184) and 2.5 %, (1.5–4.3), for inhibition of hepatic glucose production and for glucose disposal, respectively. The demonstration that both dimers exhibit a significantly greater effect on glucose production than on glucose disposal supports the suggestion that analogues with increased molecular size may exhibit reduced ability to gain access to peripheral target cells. [Diabetologia (1995) 38: 1007–1013]
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 10 (1974), S. 1-5 
    ISSN: 1432-0428
    Keywords: Receptor-binding assay of insulin ; insulin receptor ; plasma membrane ; insulin derivatives ; chemically modified insulins ; biological activity in vitro and in vivo ; insulin structure-function relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The binding affinity for the insulin receptor was determined with a variety of insulin derivatives and compared to the biological activity in vitro and in vivo and to the physical properties of the derivatives. The relative binding affinity of each derivative was measured in a specific insulin-receptor binding system using mono 125I-insulin and purified plasma membranes of rat liver. Twenty one chemically modified insulins were investigated, including acetylinsulins, crosslinked insulin dimer and insulin trimer, and insulins with an A1-B1 or A1-B29 intra-molecular crosslink. The relative binding affinity corresponded to the relative biological potency in vitro for all of the derivatives studied. There was a good agreement between the activity in vitro and the physical properties as measured by circular dichroism spectroscopy with the acetylinsulins and with the crosslinked insulin monomer, dimer and trimer. In contrast, with most of the derivatives possessing an intra-molecular crosslink, the very reduced binding affinity (0.2–5.9%) and the comparably reduced biological potency in vitro opposed the moderate changes in physical properties. Biological activity was consistently higher in vivo than in vitro.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Diabetologia 20 (1981), S. 94-101 
    ISSN: 1432-0428
    Keywords: Chemically modified insulins ; gluconeogenesis ; glucose turnover ; insulin structure-function ; proinsulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A [14C]-glucose tracer infusion method was used to compare the effects of insulin infusion on glucose metabolism with the effects of infusion of three semisynthetic modified insulins and of proinsulin. Insulin produced hypoglycaemia in the anaesthetised dog by decreasing hepatic glucose production and increasing peripheral glucose utilisation. Compensatory antihypoglycaemic mechanisms eventually modified these responses. A1 B29-Diacetyl insulin exerted an hypoglycaemic effect entirely by stimulation of peripheral glucose uptake. A1-B29 crosslinked insulins and proinsulin produced hypoglycaemia almost entirely by decreasing hepatic glucose production and had little effect on tissue uptake. These observations suggest that insulin analogues may have actions in vivo that are qualitatively different from those of native insulin and suggest that certain analogues have a predominant action on the liver. This has important therapeutic implications concerning the development of semisynthetic insulins for clinical use.
    Type of Medium: Electronic Resource
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