Precipitin reactions between insulin,proinsulin, insulin chains and insulin antibody

Summary Insulin antibody was produced in guinea pigs and the precipitins tested by double diffusion in agarose gel. Pork, beef and monocomponent insulin produced precipitin lines. Proinsulin also produced a precipitin line with these antisera but no lines appeared with either the A-chain or the B-chain of insulin. There was good correlation between the precipitin titre and the radioimmunoassay titre.     

ATP sensitizes the insulin receptor to insulin

Insulin receptor with high insulin binding and tyrosine kinase activities has been prepared from human placenta. Based on a molecular mass of 306 kDa for the receptor (the value obtained from the sum of the amino acid residues), this preparation is capable of binding 1.48 mol of insulin per mol of receptor. The receptor is free from phosphatase and ATPase activity and is not stimulated by sodium vanadate. Autophosphorylation is linear with respect to receptor concentration, and the 32P incorporated is stable even in the presence of a 100-fold excess of unlabeled ATP. The Km for ATP is 208 microM. N-Ethylmaleimide inhibits autophosphorylation. Alkylation with 3H-labeled N-ethylmaleimide results in the incorporation of 1.13 +/- 0.37 mol of N-ethylmaleimide per mol of insulin binding activity exclusively into the beta subunit of the receptor. The nonhydrolyzable ATP analog adenosine 5'-[beta,gamma-imido]triphosphate stimulates autophosphorylation of the receptor, an effect that is evident at ATP concentrations below 1 mM. The stimulatory effect of adenosine 5'-[beta,gamma-imido]triphosphate is the result of increasing the binding of insulin to the alpha subunit, and this reflects itself in a shift to the left of the insulin dose-response curve for autophosphorylation. The same is true for ATP. As a consequence, it is now possible to reconcile the concentration of insulin necessary for stimulating the autophosphorylation reaction with physiological levels and with the levels of insulin required for its classical biological 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.     

Measurement of insulin absorption and insulin action

For the practical implementation of every type of insulin therapy it is necessary to know both the time course of action of therapeutically used short- and long-acting insulin preparations and the factors influencing such time-action profiles. The only reliable way to obtain the required quantitative information about the pharmacokinetic and glucodynamic properties of insulin preparations has been the use of the euglycemic glucose clamp technique. The first studies with each new insulin formulation or insulin application technique should be performed with healthy subjects in order to have the most comparable study conditions. Thereafter, results from such clinical-experimental studies should be verified in similar studies with patients with diabetes. Earlier investigational approaches, which either had been limited to the determination of the pharmacokinetic properties of insulin preparations or had used the quantitative decrease of the blood glucose level as a measure of the pharmacodynamic properties, do not provide valid quantitative results. The proposed glucose clamp technique makes possible the quantitative study of the pharmacokinetic and pharmacodynamic properties of insulin preparations under comparative and reproducible conditions.     

Relationship between insulin resistance, insulin secretion and insulin metabolism in simple obesity

The study was designed to evaluate whether the correlation occurring in simple obesity between insulin resistance and peripheral hyperinsulinemia corresponds to a relationship between insulin resistance and insulin overproduction by the pancreas. In addition, the study investigated the relation existing in simple obesity between insulin resistance and insulin metabolism. For these purposes, we measured and correlated: (1) insulin sensitivity, estimated by glucose disappearance rate from plasma after intravenous insulin injection; (2) insulin secretion by the pancreas, estimated by fasting C-peptide levels in peripheral blood; (3) insulin metabolism, estimated by means of C-peptide: insulin molar ratio in peripheral blood. Twenty-five subjects (20 females, five males) aged 21 to 59 years were studied. All were obese and had a normal glucose tolerance. Glucose disappearance rate from plasma after i.v. insulin injection averaged 3.65 +/- 0.42 mg/dl/min (mean +/- s.e.m.). Fasting C-peptide was 0.90 +/- 0.09 nmol/l. Fasting C-peptide: insulin molar ratio averaged 5.94 +/- 0.48. Negative correlations were found between glucose disappearance rates after i.v. insulin injection, ie, insulin sensitivity, and fasting concentrations of both insulin (r = -0.806, P less than 0.001) and C-peptide (r = -0.525, P less than 0.01). A positive relationship was found between glucose disappearance rate from plasma after i.v. insulin injection and fasting C-peptide: insulin molar ratio, ie, insulin metabolism (r = 0.707, P less than 0.001). We conclude that in simple obesity insulin overproduction by the pancreas is negatively related to insulin resistance, and insulin resistance and impaired insulin metabolism are strictly related phenomena.     

Treatment of insulin lipoatrophy with monocomponent insulin

Summary A female diabetic with severe insulininduced lipoatrophy was successfully treated with a monocomponent (MC) Lente preparation. This patient was studied for over 6 years and, during periods of treatment with various insulins of different purity, a variety of reactions was observed in the adipose tissue. Evidence is presented that lipoatrophy may be caused by insulin impurities. Lipoatrophy occurring after treatment with recrystallized, mixed species Lente insulin was substantially reduced after treatment with 10 times recrystallized porcine Lente, but recurred on 4 times recrystallized beef Lente, also in areas where beef Lente was not injected. Beef insulin impurities seem more prone to produce lipoatrophy than pork insulin impurities. It is suggested that MC-insulin is the treatment of choice for this condition.     

Variability of insulin absorption and insulin action

Subcutaneous (s.c.) injections of identical insulin doses may lead to considerable intra- and inter-individual differences in the current metabolic control of patients with diabetes mellitus. This well-known variability of the metabolic effect of insulin hampers practical insulin therapy considerably. The aim of this review is to summarize the knowledge about this topic, with a special focus on the variability of insulin action after pulmonary administration of insulin. A number of studies have been published describing the variability of insulin absorption from the s.c. depot. Only in a few published studies has the variability of insulin action after s.c. administration been quantified. Under controlled experimental conditions s.c. injections of regular insulins result in an intra-individual coefficient of variation (CV) of 15-25% of certain pharmacodynamic summary measures--which characterize the metabolic effect of the applied insulin--in healthy subjects. The inter-individual variability was approximately 10% higher than the intra-individual variability. Subcutaneously injected intermediate- and long-acting insulin preparations were described to have an even greater variability (> 50%) than subcutaneously injected regular insulin. However, in a glucose clamp study s.c. application of NPH insulin led to an intra-individual CV in the range of 12-45% in healthy subjects. The reason for this discrepancy might be that the NPH insulin suspension was sufficiently shaken prior to drawing up the dose. Compared with conventional insulin formulations, rapid- and long-acting insulin analogues appear to have a similar variability, which means that, unfortunately, no considerable advantages in terms of variability were achieved by the invention of these novel insulin preparations. There are no appropriate studies available investigating the variability of the metabolic effect after s.c. insulin administration in patients with diabetes. The inhalation of insulin is a novel form of insulin administration that is currently under clinical development. The variability of the metabolic effect induced by the inhalation of insulin has up to now only been investigated in a small number of (published) studies. In a glucose-clamp study with healthy subjects the inhalation of an identical insulin dose on three study days led to an intra-individual variability that was comparable to that after s.c. injection of regular insulin. In a dose-response study with patients with type 1 diabetes the intra-individual CV was 34% for the area under the curve of the glucose infusion rate for 0-10 h. Studies with patients with type 2 diabetes have shown that the intra-individual CVs were within the range seen after s.c. insulin administration or even lower. In summary, the intra-individual variability of the metabolic effect observed after insulin application, be it subcutaneously injected or be it inhaled, is considerable and, therefore, hampers practical diabetes therapy. To date no means have been found that could lead to a clinically relevant reduction in the variable metabolic effect.     

Serum insulin,insulin antibodies and insulin requirement in the first period of insulin treatment in non-insulin resistant diabetics

Summary Twelve insulin-sensitive diabetics were studied for 200 days after the initiation of mixed beef-pork NPH insulin. Normalization of the fasting blood glucose was not accompanied by any elevation in the pre-treatment fasting immunoreactive insulin level. Insulin antibodies appeared in 2 patients on the second week of insulin treatment, in 6 others within 87 days. In 4 patients no antibodies were found 200 days after the start of insulin. The appearance of antibodies was accompanied in two patients by a decrease in insulin requirement, in others there was no change. When antibodies were present, the total maximum insulin binding capacity was 4 to 12 U/1, but the total insulin constituted only 3 to 36% of the binding capacity. Insulin wastage caused by the destruction of the immune complexes was calculated to be 0.35 to 5.6 U/die only, and this explains the negligible effect of insulin antibodies on insulin requirement in non-resistant patients. Presented at the 10th Annual Meeting of the European Association for the Study of Diabetes in Jerusalem, September 11–13, 1974.     

The renal metabolism of insulin: urinary insulin excretion in patients with mutant insulin syndrome (insulin Wakayama)

Many studies have shown that the kidney plays an important role in the metabolism of many proteins and small peptides. To understand insulin handling in the kidney, we examined urinary insulin excretion under several conditions in patients with mutant insulin syndrome (MIS; insulin Wakayama). Urinary excretion of insulin was studied using high-performance liquid chromatography analysis in patients with MIS. In these patients, most of the insulin extracted from a 24-hour urine collection and from urine collected after stimulation of insulin secretion by glucose or glucagon was normal insulin, whereas 90% of serum insulin is structurally abnormal (Leu-A3 insulin). On the other hand, arginine, which is known as an inhibitor of renal tubular reabsorption, increased urinary excretion of Leu-A3 insulin. The ratio of Leu-A3 and normal insulin in urine after arginine was similar to that in serum. A large amount of Leu-A3 insulin is excreted in urine when reabsorption of insulin at renal tubules is inhibited by arginine. These data indicate that normal and Leu-A3 insulin are filtered through the glomerulus with relatively little restriction. Using the fact that basal urine has a high concentration of normal insulin and an extremely low concentration of Leu-A3 insulin, which has less receptor-binding affinity, we speculated some possibilities. One possibility is that both forms of insulin are reabsorbed by the tubular cells, but with different efficiencies. Leu-A3 insulin absorption in more complete, and this suggests differences in the uptake pathways that may account for the differences in response to arginine infusions. Another possibility is that only normal insulin is secreted from tubules into urine which is mediated by receptors. Our results provide new insight into renal metabolism of insulin and showed that MIS is a useful model for studying it.     

免疫原性与特异性胰岛素检测对胰岛β细胞功能评估的比较

在不同糖耐量者同时检测免疫原性胰岛素(IRI)与特异性胰岛素,发现虽然数值不同,但两种测定方法对于评估不同糖耐量者胰岛β细胞分泌功能及胰岛素敏感性的效果是一致的,提示测定IRI仍有临床实用价值.     

Allergy reactions to insulin: effects of continuous subcutaneous insulin infusion and insulin analogues

The purification of animal insulin preparations and the use of human recombinant insulin have markedly reduced the incidence but not completely suppressed the occurrence of insulin allergy manifestations. Advances in technologies concerning the mode of delivery of insulin, i.e. continuous subcutaneous insulin infusion (CSII), and the use of insulin analogues, resulting from the alteration in the amino acid sequence of the native insulin molecule, may influence the immunogenicity and antigenicity of native insulin. Instead of increasing allergy reactions, CSII has been reported to represent a successful alternative treatment in diabetic patients presenting local or generalized allergy to insulin or other components (zinc, protamine) of conventional treatment. Most recent reports concern CSII-treated patients using short-acting insulin analogues (essentially insulin lispro), although the precise role of these insulin analogues remains unclear as allergy to them has also been described. Finally, data on antigenicity and immunogenicity of long-acting insulin analogues (glargine, detemir), which may mimic the basal insulin delivery with CSII, remain scarce at present.