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Biomedical subjects

H Keilacker

Publications and source records attributed to H Keilacker.

At least 37 records · Page 2Linked to original sources
PubMed1987

The effect of prehepatic insulin administration on alanine flux rates in diabetic dogs.

The in vivo flux rates of glucose (6-3H-glucose) and of alanine (U-14C-alanine) were measured in insulin-dependent chronically diabetic dogs which were infused with insulin employing a bedside-type artificial B cell and either the peripheral or the portal venous route. In comparison with non-diabetic control animals the diabetic dogs had near-normal patterns of glucose metabolism and pancreatic glucagon regardless of the route of insulin administration. They also showed reduced basal portal but moderately elevated peripheral insulin levels on peripheral and near-normal peripheral values on portal insulin infusion. Both concentration and production rates of alanine were reduced on peripheral (0.142 +/- 0.016 mmol/l, 4.73 +/- 0.49 mumol.kg-1.min-1, p less than 0.05) but normal on portal insulin (0.206 +/- 0.030 mmol/l, 6.33 +/- 0.63 mumol.kg-1.min-1). The alanine clearance was slightly elevated or normal in the diabetic dogs, and the glucose production from alanine showed a strongly delayed response to an exogenous glucose load on either route of insulin administration. It is concluded that the peripheral hyperinsulinism during posthepatic insulin administration stimulates glucose utilisation to a normal extent, but inhibits the provision of amino groups in resting muscle. Alanine synthesis is thereby reduced, and the carbon moieties are shunted from glucose into circulating lactate. Long-term studies are needed to elucidate the role of the liver under these conditions.

Alanine↗
PubMed1987

5-year follow-up study of C-peptide secretion in newly diagnosed type I diabetics: relations to HLA-phenotype, insulin requirement and metabolic control.

50 HLA-typed insulin-dependent diabetics were studied at the time of diabetes onset and after 1, 2, 3 and 5 years with regard to C-peptide secretion after combined stimulation with glucose and glucagon, insulin requirement and glycaemic control index. The mean decrease of the residual B-cell reserve was observed within two years. C-peptide secretion was correlated with better metabolic control and lower insulin requirement after more than one year of diabetes duration, but had no influence on this at the time of diabetes onset. The C-peptide response sometimes varied between non response and high response in one individual from one investigation to the next. There was no prognostic value of C-peptide secretion at diabetes onset for the further development of B-cell function. We found a significantly longer persistence of B-cell function in patients who were older and in those with mild symptoms at diabetes onset. The presence of HLA B8, DR3 antigens was correlated with severe ketoacidosis at manifestation and a more pronounced destruction of B-cell function.

Adolescent↗
PubMed1987

Measurement of insulin in human sera using a new RIA kit. 1. Insulin determination in the absence of insulin antibodies--conventional assay and micro modification.

A sensitive and versatile radioimmunoassay (RIA) for insulin was established using human insulin standard, a specific guinea pig anti-insulin antiserum and rabbit anti-guinea pig serum. Radioiodination was performed according to a modified chloramine T method. Tracer preparations were used for as long as 6 weeks after iodination. The standard curve ranges from 0.044 to 1.2 nmol/l. The intra-assay coefficient of variation (CV) was 3-5% and the inter-assay CV was 6-9% in the optimal range between 0.4 and 0.9 nmol/l. The average recovery of human insulin added to plasma or serum samples was 100.2 +/- 2.0% (n = 38) and 100.1 +/- 1.9% (n = 42), respectively. In addition to human insulin, porcine, canine, rabbit and bovine insulin can also be determined but not rat or mouse insulin. The cross-reactivity of the antiserum with porcine proinsulin was found to be 40% on the molar basis. The range of mean fasting plasma insulin concentrations in healthy subjects and under various pathological conditions were estimated.

Humans↗
PubMed1987

Measurement of insulin in human sera using a new RIA kit. 2. Determination of free and total insulin--correlations to insulin antibody levels.

Using the micro-scale modification of a newly developed RIA kit for insulin, we established methods for the determination of free and total insulin in serum of insulin-treated diabetics. Precipitation with polyethylene glycol 6000 or acid alcohol extraction of sera was carried out to remove or to dissociate antibody-bound insulin. Both assays permit precise and accurate measurement of either serum insulin fraction. In 50 diabetic sera with tracer insulin binding of 0-97%, free (after equilibration of the sera at 37 degrees C) and total insulin levels as well as insulin antibody binding parameters were determined. There was a good correlation of free to total insulin levels with maximally 10-fold higher values of total insulin. Both free and total insulin were found to be correlated with the ability of the serum to bind insulin. In detail, binding affinities (i.e. the reciprocal of equilibrium dissociation constants) and binding site concentrations were evaluated which were shown to be positively correlated with free and total insulin levels as well. From these data we conclude that insulin antibodies in the serum may accumulate therapeutic insulin and function as a depot for delivering insulin in insulinopenic episodes (Keilacker et al., 1982 and 1986).

Diabetes Mellitus, Type 1↗
PubMed1986

The role of insulin antibodies in insulin treatment of type I diabetes.

We investigated equilibrium plasma binding patterns of insulin in 45 juvenile diabetics treated with conventional insulin preparations. Insulin binding parameters were evaluated by Scatchard analysis of the binding data. Stable diabetics had significantly lower equilibrium dissociation constants than labile, thus suggesting an enhanced insulin depot effect due to stronger insulin binding. Correlation of insulin binding data with a glycemic control index yielded a positive relationship between insulin antibody binding and the degree of glycemic control. Insulin neutralization as detected by a relationship between maximum binding capacity of high affinity antibodies and insulin requirement could only be found if patients with poor diabetes control were excluded. Similarly, the well-known promoting influence of residual beta-cell functional capacity (assessed by C-peptide levels) on diabetic stability was observed only after exclusion of patients with higher insulin antibody binding. These data suggest that insulin antibodies are influencing insulin treatment of diabetics in a dual way. They may neutralize therapeutic insulin but at the same time they exert an insulin-sparing action by improvement of diabetes control. Occasionally the latter effect may abolish the correlation between diabetes control and beta-cell functional capacity.

Adolescent↗
PubMed1986

Differences in the content of glucagon-like immunoreactivity in rat submaxillary glands.

Two different antisera which specifically reacted with either the C- or N-terminal region of pancreas glucagon were employed to determine the concentration of glucagon and glucagon-like immunoreactivity in extracts from submaxillary glands of rats. The content of glucagon and glucagon-like immunoreactivity increased with age and was found to be higher in adult males than in females. Pancreas glucagon immunoreactivity constituted only a small proportion of the total glucagon-like immunoreactivity. The role that glucagon-like peptides present in the submaxillary gland of rats might play in the glucose homeostasis remains still unknown.

Age Factors↗
PubMed1986

Measurement of insulin during isolation and purification from animal pancreas. A comparison of radioimmunoassay, radioreceptor assay and in-vivo bioassay.

For the purpose of monitoring the yield of the insulin extraction procedure from animal pancreas three methods of insulin determination were compared, i.e. the mouse convulsion test, a radioreceptor assay (RRA) on rat fat cells and a radioimmunoassay (RIA) which was especially laid out for high insulin concentrations. In samples containing actually insulin in general all three methods provided comparable results. Notable differences were only found in proinsulin-containing material. Because of its simplicity and high reproducibility as well as the good agreement of its results with those obtained with the other assays, the RIA turned out to be the most suitable assay. On the other hand, the RRA should be useful in detecting molecular differences between the investigated insulin-like preparations and standard insulin.

Animals↗
PubMed1986

Kinetic properties of monoclonal insulin antibodies.

We investigated four insulin-specific hybridoma antibodies with respect to their kinetic properties as well as the binding behaviour of some combinations of them. From equilibrium binding data all but one antibodies were shown to bear homogeneous binding sites. They revealed homogeneity of binding sites also by kinetic experiments, thus with high probability being monoclonal. At 0 degree C, two of them showed discrepancies between kinetic and steady state binding data in as much as, at steady state, the measured bound-to-free ratio of tracer insulin was 3-4 times lower than calculated from kinetic data. Thus a simple bimolecular reaction mechanism could possibly not be applicable. Mixing two monoclonal insulin antibodies, neither cooperative nor additive binding to the insulin molecule could be observed but only competitive effects. Especially, no positive cooperativity between two or more antibodies could be detected, which would be able to account for the higher affinity usually observed for polyclonal vs. monoclonal antibodies.

Animals↗
PubMed1986

Polyacrylamide gel electrophoretic preparation of labeled and non-labeled peptides for radioimmunoassay.

Radioiodinated polypeptide hormones, such as insulin, glucagon, human growth hormone, and human C-peptide are employed for radioimmunoassays for investigations of hormonal alterations in states of disturbed carbohydrate metabolism. Iodination was performed using chloramine T. Iodination products of these polypeptide hormones and, for preparation of standard material, native human C-peptide from cadaver pancreases were fractionated by polyacrylamide gel electrophoresis at pH 8.9. Disc electrophoresis in 24 cm-long gel rods resulted in stable tracers with high specific activity as well as homogeneous standard material being highly suitable for radioimmunoassays.

C-Peptide↗
PubMed1985

Effect of antibody-mediated crosslinking of insulin on its bioactivity and receptor binding.

Precipitating anti-insulin antibodies or anti-insulin IgG/anti-IgG complexes bind insulin in a highly aggregated form and thus should preferably be capable of inducing receptor aggregation, which has recently been suggested to be a precondition for insulin bioactivity. We, therefore, studied the influence of antibody-mediated crosslinking of insulin on the glucose conversion into CO2 in rat fat cells and glycogen synthesis in rat liver cells. As far as possible receptor-bound insulin was measured in parallel. Insulin bound to antibodies with low insulin precipitating capacity had no or little bioactivity and receptor reactivity on fat cells. The bioactivity, however, could be restored in part by addition of a second antibody. On liver cells, second antibody-mediated crosslinking of insulin-antibody complexes resulted in an enhancement of receptor reactivity, and insulin bioactivity of such crosslinked immune complexes was demonstrable. An insulin-precipitating antiserum was shown to form insulin-antibody complexes with significant bioactivity in fat cells which correlated with their receptor binding. In each case antibodies had no or little effect in the absence of insulin. Our data suggest that insulin neutralization by antibodies can be compensated by crosslinking the insulin-antibody complexes or by formation of big complexes precipitating by themselves. This is probably due to the induction of receptor aggregation.

Adipose Tissue↗
PubMed1985

Metabolic, hormonal, and immunological alterations in subjects with antecedent mumps infection.

Since mumps virus seems to be one of the most likely candidates in viral etiology of insulin-dependent diabetes (IDDM) we studied the possible relationship of glucose tolerance (75 g oGTT), beta cell function, diabetes associated HLA antigens, haptoglobin phenotype, islet cell antibodies (ICA) and islet cell surface antibodies (ICSA) in 125 subjects with antecedent mumps infection. Impaired glucose tolerance (IGT) was diagnosed in 3.2% (n = 4) but onset of diabetes did not appear within 14 months after mumps infection. There was no relationship between glucose tolerance and complications of antecedent mumps infection (e.g. pancreatitis, meningitis, orchitis). The prevalence rate of ICA was 76%. ICSA were detectable in about 36% of children and 62% of the adults tested (p less than 0.01). There was no relationship between ICA/ICSA and diabetes-associated HLA antigens, haptoglobin phenotype or beta cell function (fasting C-peptide and insulin response to 75 g oGTT). However, adults with circulating ICA were characterized by a significantly lower insulin response to glucose. Fifty two "risk" subjects characterized by IGT, diabetes associated HLA antigen(s), ICA or ICSA either alone or combined were studied again 26 months after mumps infection. No symptomatic diabetes appeared and IGT was diagnosed in one case only. ICA and ICSA persisted in more than 50% of subjects in whom ICA or ICSA were present 14 months after mumps infection. Since the used immunological techniques do not clearly distinguish organ-specific from non-organ-specific antibodies the results must be interpreted with caution. To summarize, the preliminary results do not support a close temporal relationship between mumps infection and the onset of IDDM. The pathogenetic role of mumps virus and ICA/ICSA and their possible relation to a slow progressive beta cell destruction has still to be determined.

Adult↗
PubMed1984

Does insulin down-regulate its own receptor on erythrocytes in vitro?

The purpose of this study was to examine the in vitro effect of insulin on its own receptors on erythrocytes. Whole blood from 6 fasting normal and 6 diabetic (type II) subjects was incubated without or with exogenous insulin for 5 hours. The insulin binding to erythrocytes was then evaluated. At a tracer concentration, the percent 125I-insulin specifically bound amounted to 8.6 +/- 0.59% and 8.1 +/- 0.41% in fasting normal subjects and type II-diabetics, respectively. In contrast to in vivo studies, supraphysiologic insulin concentrations in the incubation medium did not alter significantly the insulin binding process. Thus, in vitro we could not demonstrate a down regulation of insulin receptor binding. It is likely that factors other than insulin are involved in the short-term regulation of insulin receptor affinity in man.

Erythrocytes↗
PubMed1984

Islet cell antibodies in individuals at increased risk for IDDM.

Islet cell cytoplasmic antibodies (ICA), islet cell surface ( ICSA ) antibodies, HLA phenotypes, glucose tolerance, insulin secretion, and insulin sensitivity were studied in 16 twins of insulin-dependent diabetics as well as in 21 subjects with impaired glucose tolerance (IGT). 60% of the identical twins and 40% of the non-identical twins were ICSA -positive. The prevalence of ICSA in control persons was only 5%. ICA were found in all identical twins and in half of the non-identical twins. However, ICSA and ICA results were concordant in only 46% of the whole group of twins. There was no correlation between ICSA and either insulin secretion or insulin sensitivity. In the IGT subjects exhibiting low and normal insulin responses ICSA were observed in 67% and 23%, respectively. A high proportion of twins, but not of IGT subjects, had HLA DR3 or DR4 antigens which seem to confer genetic susceptibility to the development of IDDM. In the majority of DR3/DR4 twins, ICSA were also present. This might support the hypothesis of genetically-based autoimmunity, although the precise relationship between HLA and islet cell antibodies has to be clarified in a prospective study.

Adolescent↗
PubMed1984

Prevalence of islet cell antibodies (ICA) and islet cell surface antibodies (ICSA) in children and adolescents with antecedent mumps infection).

There is good evidence that viruses may play a role in some animal models of diabetes. Since mumps virus seems to be the most likely candidate, we studied the possible relationship of islet cell antibodies, islet cell surface antibodies and glucose tolerance in 86 children and adolescents in whom mumps infection had occurred 14 months previously. Impaired glucose tolerance was diagnosed in 3.5% (n = 3) but symptomatic diabetes did not appear. No relationship existed between complications of antecedent mumps infection (pancreatitis, orchitis, meningitis) and glucose tolerance. The prevalence of ICA and ICSA was 78% and 36%, respectively. The simultaneous prevalence of ICA and ICSA was 33%. The pathogenetic role of mumps infection and ICA/ ICSA and their possible relation to slow progressive beta cell destruction remains to be elucidated.

Adolescent↗
PubMed1984

Is there a relationship between genetically determined haptoglobin phenotype and insulin-dependent diabetes mellitus (IDDM)?

The possible relationship between genetically determined haptoglobin phenotype and insulin-dependent diabetes (IDDM), circulating insulin antibodies and the occurrence of microangiopathy was studied in 144 IDDM. There were no differences regarding the distribution of Hp-phenotypes in 144 patients in comparison with a control population (n = 1726). Irrespective of the Hp-phenotype, the degree and severity of diabetic complications (retinopathy and/or nephropathy) significantly increased with the duration of diabetes. There was no relationship between Hp-phenotype and diabetic microangiopathy (retinopathy, nephropathy). No association existed between Hp-phenotype and the percentage of insulin antibody binding. Regardless of the Hp-phenotype, the insulin antibody concentration decreased with increasing duration of diabetes. Insulin binding parameters (maximum binding capacity and equilibrium dissociation constant) were found to vary considerably with the Hp-phenotypes among IDDM. For a given duration of diabetes the equilibrium dissociation constant increased significantly in the range from Hp 1-1, Hp 2-1 to Hp 2-2 phenotype. There was a direct relationship between the logarithm of the equilibrium dissociation constant and the degree of metabolic control, i.e. the lower the dissociation constant the better the metabolic balance. In conclusion, the results do not provide support for a putative relationship between Hp-phenotype and IDDM. However, differences between insulin binding parameters, in dependence on the Hp-phenotype may be of clinical importance.

Adolescent↗
PubMed1984

Islet cell cytoplasmic and surface antibodies' prevalence and beta cell specificity of islet cell surface antibodies in some subjects with putative islet cell autoimmunity.

In human sera two methods of islet cell cytoplasmic antibody (ICA) detection (on Bouin-fixed or cryostate sections of human pancreas) and the islet cell surface antibody (ICSA) method on isolated rat islet cells were compared. The ICA detection on Bouin-fixed sections was more sensitive than that on cryostate sections. In two groups of subjects with putative islet cell autoimmunity ICA prevalence was higher than ICSA prevalence. However, a weak correlation between both types of antibodies was established. In one group of healthy subjects with cytotoxic serum against rat beta cells a high prevalence of ICSA was found, whereas none of them had ICA. Defined on the basis of a positive immunofluorescence on rat islet cells, ICSA positive sera of newly diagnosed IDDM patients reacted to a significantly higher percentage with beta cells than did normal controls. In conclusion, of all methods compared ICA detection on Bouin-fixed pancreas sections seems to be the most suitable method for the detection of an islet cell autoimmunity.

Acetates↗