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PubMed1976

The mobile receptor hypothesis and "cooperativity" of hormone binding. Application to insulin.

The mobile receptor hypothesis has been proposed to describe the process by which hormone receptor binding initiates a biological response; it states that receptors, which can diffuse independently in the plane of the membrane, reversibly associate with effectors to regulate their activity. The affinity for effector is greater when the receptor is occupied by hormone. A mathematical expression of the mobile receptor hypothesis is used to show that: (1) The predicted kinetics of hormone receptor binding may be indistinguishable from "negative cooperativity." (2) Receptor occupancy and biological response may be coupled in a non-linear fashion. By choosing specific parameters, most of the existing data on insulin binding and biological responses can be explained in terms of the mobile receptor hypothesis. Thus, the following are easily explained: (1) A single homogeneous receptor may appear kinetically to be composed of two classes (of high and low affinity) of receptors. (2) Occupancy of the apparent class of high affinity receptors is related linearly to the biological response. (3) The same receptor in different tissues may appear to have different affinity. (4) The binding of different biologically active insulin analogues may exhibit different degrees of "cooperativity." These considerations may also be pertinent to interpretations of other hormone-receptor systems and of various ligand-macromolecule interactions.

Binding Sites↗
PubMed1979

Isolation of a crystalline A14-(N-methylpyridinium) derivative of bovine insulin.

Reaction of insulin with 2-chloro- or 2-iodo-N-methylpyridinium iodide affords, amongst others, an insulin analogue modified at tha A14-tyrosine residue. Degradative procedures which pinpoint the exact position of modification are described. Highest yields of the derivative are obtained using the 2-iodo-N-methylpyridinium iodide as reagent. In the mouse convulsion assay this derivative retains 72% of its activity.

Amino Acids↗
PubMed1979

Effect of a 5'-substituted adenosine analogue (744c96) on insulin and glucagon release in isolated rat islets of Langerhans.

The effect of adenosine-5'-(N-ethylcarboxamide) (744-96), a highly vasoactive adenosine analogue, was investigated on insulin and glucagon release from isolated rat islets of Langerhans. The compound inhibited glucose-induced insulin release in a dose-dependent manner (concentration range 10(-8) to 10(-5 M). No effect of 744-96 was observed on basal or on arginine-induced glucagon release. By contrast, 744-96 (5 microgram/kg i.v.) produced a significant increase in plasma glucagon and glucose levels in normal as well as in reserpinized rats. The observed failure to promote glucagon release from isolated islets may be attributable to the isolation procedure, to a release of glucagon in vivo from non-pancreatic stores, or to a non-specific effect of 744-96 on glucagon secretion.

Adenosine↗
PubMed1977

Studies on the mechanism of somatostatin action on insulin release. V. Effect of somatostatin analogues on arginine induced release of insulin and glucagon from the perfused rat pancreas.

Eighteen analogues of somatostatin have been used in order to elucidate the structure-activity relationship of the peptide on the release of insulin and glucagon from the isolated perfused rat pancreas. Neither the amino terminal nor a free carboxyl terminal seemed to be essential for the activity of the cyclic peptide. Addition of amino acids to the amino terminal did not decrease the activity. On the other hand, minor changes in the structure of linear somatostatin, which lead to the loss of ability to form a cyclic peptide, impaired the activity. Deletion of Asn5 was accompanied by decreased action on glucagon but not on insulin release. It seems that the major actions of somatostatin on the pancreas are bound to the amino acid sequence 4-13 in the molecule and to the ability of the molecule to cyclize.

Amino Acid Sequence↗
PubMed1979

Effect of a long acting glucagon selective somatostatin analogue on plasma glucose, insulin and glucagon levels in the anaesthetized rat during arginine infusion.

The effects of somatostatin and a long acting, glucagon selective somatostatin analog (des-Ala1Gly2[His4,5-D-TrP8]-somatostatin) used studied during arginine tolerance tests in normal anaesthetized rats. Arginine infusion in control animals resulted in a rapid increase in plasma insulin and glucagon, and an increase of 15 +/- 5 mg/dl in plasma glucose. Somatostatin infusion (1 mg/kg/h) resulted in suppression of basal insulin secretion and a decrease in arginine-induced insulin and glucagon release. Glucose levels increased rapidly during the combined arginine-somatostatin infusion reaching a peak of 72 +/- 10 mg/dl above basal levels. Similar results were obtained when somatostatin was injected SC (1 mg/kg) at times 0, 15, 30, and 45 minutes (arginine infused from 30-60 minutes). A single injection (1 mg/kg) of the long-acting somatostatin analogue resulted in significant inhibition of basal insulin and glucagon release; during arginine infusion glucagon levels rose only slightly, the insulin response was, however, nearly normal, and only a small arginine-induced increase in glucose levels was observed. Carbohydrate absorption was not influenced by either somatostatin or the analogue.

Animals↗
PubMed1978

Direct visualization of binding, aggregation, and internalization of insulin and epidermal growth factor on living fibroblastic cells.

We have studied in detail the binding of fluorescent derivatives of insulin and epidermal growth factor to 3T3 fibroblasts. We have used two types of fluorescent analogues of insulin and epidermal growth factor: highly fluorescent derivatives which have seven to eight rhodamine molecules or fluorescent derivatives which have a single rhodamine molecule per one molecule of insulin or epidermal growth factor. Both types of analogue retained substantial binding affinity as determined by radioreceptor assays and biological activity. The cells labeled with the fluorescent analogues were visualized with a sensitive video intensification microscopic system that enabled us to directly observe the location of the fluorescent hormone on the surface and within the living fibroblasts. We found that both insulin and epidermal growth factor initially bound diffusely to the cell surface and, at 4 degrees , remained dispersed. Within a few minutes at 23 degrees or 37 degrees the hormone-receptor complexes aggregated into patches that could be readily removed by trypsin but not by excess native hormone. The hormone-receptor complexes, which were initially mobile in the plane of the membrane, become immobilized later as the consequence of the receptor aggregation or internalization. Within approximately 30 min at 37 degrees , much of the labeled hormone was found within the cell in endocytic vesicles that moved about in the cytoplasm in a saltatory manner. The aggregation and immobilization of the hormone-receptor complexes could be due to either hormone-hormone interactions on the cell membrane or a hormone-induced conformational change in the hormone-receptor complex. Aggregation and internalization of hormone-receptor complexes could be associated with certain aspects of hormone action, hormone degradation, down regulation of receptors, or negative cooperativity of hormone binding.

Cell Line↗
PubMed2026

A New Highly Concentrated Insulin Aspart AT278 (500 U/mL) Demonstrates Ultra-Rapid Pharmacokinetic and Pharmacodynamic Properties in Type 2 Diabetes Regardless of BMI.

AIMS: To evaluate the pharmacokinetics, pharmacodynamics, and safety of a novel U500 insulin aspart formulation (AT278 [500&#x2009;U/mL]; AT278-U500) compared with standard concentration insulin aspart (InsAsp [100&#x2009;U/mL]; InsAsp-U100) and U500 human regular insulin (HumIns [500&#x2009;IU/mL]; HumIns-U500). MATERIALS AND METHODS: This single-centre, randomised, double-blind crossover 12-h euglycaemic clamp study was conducted in 41 overweight and obese people with type 2 diabetes (BMI 25.0-38.7&#x2009;kg/m2) receiving a single subcutaneous dose (0.5&#x2009;U/kg) of AT278-U500 and InsAsp-U100. HumIns-U500 was consecutively studied open label in a 24-h clamp. RESULTS: AT278-U500 exhibited a significantly faster insulin absorption than InsAsp-U100 and HumIns-U500 (t Early50%Cmax: 9&#x2009;min vs. 35&#x2009;min vs. 55&#x2009;min), leading to a significantly higher glucose-lowering effect within the first hour (AUCGIR,0-60min) compared with both InsAsp-U100 (treatment ratio 2.02 [95% CI 1.64; 2.50]) and HumIns-U500 (3.91 [2.89; 5.27]). When divided by median BMI (29.7&#x2009;kg/m2), AUCGIR,0-60min was significantly higher with AT278-U500 in both the low-BMI and high-BMI subgroup compared to InsAsp-U100. Linear regression showed a significant inverse relationship between BMI and AUCGIR,0-60min for InsAsp-U100 (slope -0.142, p&#x2009;<&#x2009;0.0001), whereas AT278-U500 showed no such relationship. Overall insulin exposure was similar for AT278-U500 and InsAsp-U100, while overall glucose-lowering effect was comparable across all three treatments. CONCLUSIONS: AT278-U500 maintains its ultra-rapid onset characteristics independent of BMI, representing the first ultra-rapid U500 option for prandial dosing in insulin-resistant people with type 2 diabetes requiring high-dose therapy. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT05754424.

Humans↗
PubMed1978

The effect of solubilization on the properties of the insulin receptor of human placental membranes.

The insulin receptor for human placental membranes has been solubilized in Triton X-100 and its properties have been examined in detail. Binding of [125 I]iodoinsulin to the soluble receptor is markedly inhibited by increas-ng concentrations of Triton X-100, due to a fall in receptor affinity. In 0.02--0.10% Triton X-100, the soluble receptor exhibits all the essential characteristics of the intact or particulate receptor. These include strict specificity for insulin and its analogues, increase in steady state binding with decrease in temperature, a pH optimum at 7.8--8.0, and negatively cooperative site-site interactions. The initial association rate of [125 I]iodoinsulin and the soluble receptor is a direct function of temperature, but the level of steady-state binding is lower at higher temperatures due to a marked increase in dissociation rate. Scatchard binding plots are curvilinear and show a large increase in affinity at 4 C with no change in total binding capacity (R0); increased binding to the particulate placental membrane at 4 C is due chiefly to an increase in R3. Negative cooperatively in the soluble receptor has been confirmed by kinetic experiments; thus, the dissociation of [125I]iodoinsulin from the receptor in the presence of "infinite" dilution is accelerated in the presence of 10(-8) M unlabeled insulin. The apparent molecular weight of the placental receptor, determined by gel filtration on 6% agarose, is approximately 300,000. These studies show that the basic properties of the insulin receptor do not depend on it being an integral conponent of the cell membrane.

Female↗
PubMed1979

Differential effects of somatostatin analogues on alpha- and beta-cells of the pancreas.

We examined the effect of somatostatin (SS) and its analogues on basal insulin and glucagon output from the right lobe of the in situ canine pancreas. Somatostatin (0.17 and 1.7 microgram/min, iv) significantly inhibited insulin (delta = -48 +/- 9% and delta = -88 +/- 3%) and glucagon (delta = -13 +/- 16%, P = NS and delta = -55 +/- 8%). Des-Asn5-SS Significantly inhibited insulin (delta = -40 +/- 9% and delta = -92 +/- 3%) but not glucagon (delta = +35 +/- 18% and delta = +4 +/- 12%). Likewise, [D-Ser13]-SS significantly inhibited insulin (delta = -40 +/- 14% and delta = -71 +/- 8%) with only slight inhibition of glucagon (delta = +26 +/- 15%, P = NS and delta = -16 +/- 6%, P less than 0.05). In contrast, [D-Cys14]-SS significantly inhibited both inhibited both insulin and glucagon. We conclude that structural changes of cyclic somatostatin can dissociate its ability to inhibit pancreatic insulin and glucagon secretion. Because the putative receptors on the pancreatic alpha- and beta-cell appear to recognize different configurations of the somatostatin molecule, it is suggested that the receptors themselves are different.

Animals↗
PubMed1979

The effect of insulin and guanosine nucleotides on protein phosphorylations by sarcolemma membranes from skeletal muscle.

In a previous report we have shown that insulin increases the phosphorylation of an endogenous protein of mol. wt. 16 000 daltons in sarcolemma membranes. In the present work we have demonstrated that phosphorylations of exogenous histones by the sarcolemma membranes are also increased by insulin. These results indicate that insulin activates a cyclic-AMP-independent protein kinase in sarcolemma membranes. The stimulatory effect of insulin on protein phosphorylations is increased by GTP and its analogue GMP-P(NH)P. The insulin effect was increased 3--4-fold by micromolar concentrations of GTP. The effect by the analogue GMP-P(NH)P was somewhat less. In the absence of insulin guanosine nucleotides had no effect on phosphorylation of the proteins. The results suggest that GTP is a modulator in the activation of a sarcolemma membrane protein kinase by insulin.

Animals↗
PubMed2026

Efficacy and Safety of iGlarLixi Versus IDegAsp by Baseline Age, Disease Duration and HbA1c in Chinese People With Type 2 Diabetes: Post Hoc Analyses of the Soli-D Study.

AIMS: To compare the efficacy and safety of insulin glargine 100&#x2009;U/mL plus lixisenatide (iGlarLixi) with insulin degludec plus insulin aspart (IDegAsp) by baseline age, Type 2 diabetes (T2D) duration and glycated haemoglobin (HbA1c) in the Soli-D study. MATERIALS AND METHODS: In Soli-D, Chinese adults with T2D suboptimally controlled on oral antidiabetic drugs (OADs) were randomized to iGlarLixi or IDegAsp for 24&#x2009;weeks. These post hoc analyses evaluated glycaemic efficacy, insulin dose, body weight and hypoglycaemia outcomes in subgroups defined by baseline age (<&#x2009;65, &#x2265;&#x2009;65&#x2009;years), T2D duration (<&#x2009;10, &#x2265;&#x2009;10&#x2009;years) and HbA1c (&#x2265;&#x2009;7% to &#x2264;&#x2009;8% [&#x2265;&#x2009;53 to &#x2264;&#x2009;64&#x2009;mmol/mol], >&#x2009;8% to &#x2264;&#x2009;9% [>&#x2009;64 to &#x2264;&#x2009;75&#x2009;mmol/mol], >&#x2009;9% [>&#x2009;75&#x2009;mmol/mol]). RESULTS: Among 582 participants (iGlarLixi n&#x2009;=&#x2009;291; IDegAsp n&#x2009;=&#x2009;291), baseline age was <&#x2009;65&#x2009;years in 442 and &#x2265;&#x2009;65&#x2009;years in 140; T2D duration was <&#x2009;10&#x2009;years in 366 and &#x2265;&#x2009;10&#x2009;years in 216; and HbA1c was &#x2265;&#x2009;7% to &#x2264;&#x2009;8% in 205, >&#x2009;8% to &#x2264;&#x2009;9% in 209 and >&#x2009;9% in 168. At Week 24, HbA1c reductions were greater with iGlarLixi versus IDegAsp, with no treatment-by-subgroup interactions for baseline age, T2D duration or HbA1c. Change in other glycaemic outcomes, insulin dose and body weight generally showed no interaction across subgroups. Total insulin daily doses during treatment and hypoglycaemia event rates were consistently lower with iGlarLixi versus IDegAsp in all subgroups. CONCLUSIONS: iGlarLixi provides improved glycaemic control at lower insulin doses with reduced risk of hypoglycaemia in Chinese adults with suboptimally controlled T2D on OADs, regardless of baseline age, disease duration or HbA1c.

Humans↗
PubMed1977

Studies on the relationship between the molecular structure and the catabolism of insulin.

The catabolism of insulins modified at the A1, B1 or B29 positions or containing a synthetic crosslink between the A1 and B29 positions has been studied in vivo and in vitro. The metabolic clearance rates (MCR) of insulin, proinsulin and chemically modified insulins have been measured by a priming-dose constant infusion technique in greyhounds. Insulins modified at A1 and B29, particularly the crosslinked materials, had markedly lowered MCR's whilst B1 analogues did not differ from insulin. Proinsulin and the A1-B29 crosslinked materials showed a markedly lowered degradability by glutathione-insulin transhydrogenase.

Animals↗
PubMed1978

The effect of sugars on (pro)insulin biosynthesis.

Rates of incorporation of [4,5-(3)H]leucine into insulin plus proinsulin, designated ;(pro)insulin', and total protein in rat pancreatic islets were measured. Glucose stimulates rates of total protein and (pro)insulin biosynthesis, but (pro)insulin biosynthesis is stimulated preferentially. Mannose and N-acetylglucosamine also stimulate (pro)insulin and total protein biosynthesis; inosine and dihydroxyacetone stimulate (pro)insulin biosynthesis specifically. Fructose does not stimulate (pro)insulin biosynthesis when tested alone, but does so in the presence of low concentrations of glucose, mannose or N-acetylglucosamine. Many glucose analogues do not stimulate (pro)insulin biosynthesis. Mannoheptulose inhibits synthesis of (pro)insulin and total protein stimulated by glucose or mannose but not by dihydroxyacetone, inosine or N-acetylglucosamine; phloretin (9mum) inhibits N-acetylglucosamine-stimulated (pro)insulin biosynthesis preferentially. The data are in agreement with the view that the same glucose-sensor mechanism may control both insulin release and biosynthesis, and ;substrate-site' model is suggested. The threshold for stimulation of biosynthesis of (pro)insulin and total protein is lower than that found for glucose-stimulated insulin release; moreover the biosynthetic response to an elevation of glucose concentration is slower than that found for insulin release. The physiological implication of these findings is discussed. Caffeine and isobutylmethylxanthine, at concentrations known to increase islet 3':5'-cyclic AMP and potentiate glucose-induced insulin release, were without effect on rates of glucose-stimulated (pro)insulin biosynthesis.

Adenosine↗
PubMed1978

Structure-activity relationships of eighteen somatostatin analogues on gastric secretion.

1. The effect of somatostatin and eighteen somatostatin analogues on pentagastrin-stimulated gastric acid and pepsin secretion was investigated in the conscious vagotomized cat prepared with chronic gastric fistulae. The majority of the analogues are peptides where D-amino acids are incorporated into the molecule instead of the natural L-isomers. 2. The ID50 for cyclic-somatostatin inhibition of near-maximal gastric acid secretion stimulated by pentagastrin 8 microgram kg-1 hr-1 was found to be 1.29 +/- 0.13 n-mole kg-1 hr-1. Pentagastrin-stimulated pepsin secretion had a lower threshold to somatostatin inhibition than did acid secretion. 3. D-Phe6, D-Phe7, D-Thr10, D-Thr12 and D-Phe6-D-Trp8 analogues all show low biological activity against the secretion of gastric acid and pepsin, growth hormone, insulin and glucagon. None of these analogues are antagonists of the cyclic-somatostatin inhibition of gastric secretion, suggesting that they have low affinity for this somatostatin receptor. 4. The analogues under investigation show parallel changes in activity against gastric and growth hormone secretion, suggesting a similarity between the gastric and growth hormone receptors for somatostatin. 5. D-Cys14 analogues are equipotent with or have a greater potency than cyclic-simatostatin in inhibiting the secretion of gastric acid, growth hormone and glucagon but show low insulin inhibiting activity.

Animals↗
PubMed1979

Non-selective inhibition of basal glucagon release by [D-Cys14]-analogues of somatostatin in the rat.

The effects of two [D-Cys14]-analogues of somatostatin on basal plasma levels of glucagon, insulin and glucose were determined in unanaesthetized rats to re-examine a glucagon-selective action of these peptides which has been claimed by others. Somatostatin, [D-Cys14]-somatostatin and [D-Trp8, D-Cys14]-somatostatin caused a short-lasting, dose-dependent decrease of plasma glucagon and insulin but they had no significant influence on plasma glucose. Glucagon and insulin reached the nadir 2 min after intravenous injection of the peptides (dose range 1--10 micrograms/kg) or 5 min after subcutaneous administration (30 and 300 micrograms/kg). At the nadir, insulin was decreased to a greater extent than glucagon and the effecer the nadir and at high doses, the time-course of some effects of the analogues on either glucagon or insulin differed from that of somatostatin. Thus, these [D-Cys14]-analogues may show partial kinetic dissociation of effects on glucagon and insulin but they are not truly selective inhibitors of glucagon release.

Animals↗