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D C Robbins

Publications and source records attributed to D C Robbins.

At least 55 records · Page 3Linked to original sources
PubMed1989

A bill of rights.

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Diabetes Mellitus↗
PubMed1988

High-molecular-weight aggregates of therapeutic insulin. In vitro measurements of receptor binding and bioactivity.

On the basis of a monomeric insulin standard, approximately 28% of total circulating immunoreactive insulin in insulin-dependent diabetes mellitus (IDDM) is a covalent aggregate of insulin. This aggregate probably originates in therapeutic insulin preparations. In this study, the activity of these aggregates was compared with that of monomeric insulin with regard to behavior in the radioimmunoassay, binding to insulin receptors, and biologic activity in isolated rat adipose cells. Molar activity of the aggregate in the insulin radioimmunoassay was approximately twice (240%) that of monomeric insulin, whereas the log-logit slope produced by the aggregate was indistinguishable from that of monomeric insulin. Insulin-receptor binding was determined by displacement of 125I-labeled A14-insulin by insulin or insulin aggregate (10(-10)-10(-5) M). The free-insulin and aggregate concentrations required for half-maximal displacement of 125I-insulin were 4.0 x 10(-10) and 2.25 x 10(-9) M, respectively. [1-14C]glucose incorporation into 14CO2, glyceride-glycerol, and fatty acids was measured over a wide range of insulin monomer and aggregate concentrations (0-8 nM). In the bioassay, the maximal rates of glucose metabolism were equal (normal responsiveness). However, the concentration of insulin aggregates producing half-maximal stimulation of glucose metabolism was threefold greater than that of insulin (140 vs. 46 pM, respectively), indicating decreased sensitivity of the adipose cells to the aggregates. This was associated with a sixfold decrease in the Kd for binding of aggregates to adipose cell insulin receptors compared with binding of monomeric insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1988

Pharmacokinetic model of circulating covalent aggregates of insulin.

Covalent aggregates of insulin in blood of insulin-treated diabetic patients account for as much as 70% (mean 28 +/- 3.6%) of serum insulin immunoreactivity. These aggregates may originate in therapeutic insulin, because similar substances account for 0.1-3% of these preparations. Larger amounts in blood imply that aggregates accumulate as a result of delayed clearance. To test and quantify this speculation, we calculated the plasma kinetics of this material in four normal volunteers who received large intravenous doses (30 mU.kg-1.min-1) of beef-pork crystalline zinc insulin for 120 min. Insulin aggregate and monomer concentrations were measured in blood samples obtained at regular intervals throughout the infusion and during 4 h after discontinuation of insulin. Pharmacokinetic parameters were calculated from the data. Insulin aggregate and monomer serum t 1/2 were 63.6 +/- 6.9 and 34.3 +/- 2.8 min, respectively, and clearances were 101 +/- 10 and 232 +/- 47 ml/min. Volume of distribution (V beta) and volume at steady state (Vss) were 9.1 +/- 1.8 and 8.2 +/- 2.2 L for insulin aggregate and 11.6 +/- 2.8 and 12.2 +/- 3.6 L for insulin monomer, respectively. Mean residency time was 141 +/- 14 and 114 +/- 10 min for insulin aggregate and monomer, respectively [P less than .01 for all parameters except V beta (.014) and Vss (.012), aggregate vs. monomer]. Thus, in relation to insulin monomer, calculated pharmacokinetic parameters of the aggregate predict accumulation after insulin injection. Plasma t 1/2 of the aggregate was almost double that of monomeric insulin; total-body clearance and the corresponding volumes of distribution were smaller.

Adult↗
PubMed1988

Pointing fingers.

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Diabetes Complications↗
PubMed1987

Loss of early phase of insulin release in humans impairs glucose tolerance and blunts thermic effect of glucose.

Loss of the early phase of insulin release has been documented in both type I (insulin-dependent) and type II (non-insulin-dependent) diabetes; however, the physiological importance of this loss is unsettled. We created a model of loss of the early phase of insulin release in normal volunteers. Somatostatin (SRIF) was briefly infused (from -5 to 15 min) during intravenous (IVGTT) and oral (OGTT) glucose tolerance tests. The thermic response to oral glucose was determined under these conditions by indirect calorimetry. Early insulin release was totally blocked during IVGTT and OGTT by SRIF infusion. During the IVGTT, glucose tolerance was deteriorated in association with loss of the early phase of insulin release as indicated by a decrease in the K value (control 1.9 +/- 0.36 vs. SRIF 1.1 +/- 0.27, P less than .001). Higher plasma glucose concentrations were observed during SRIF tests in the OGTT at 60, 90, 120, 150, and 180 min; total glycemic excursion was larger during the SRIF test (9473 +/- 3089 mg X dl-1 X 5 h-1) when compared with the control condition (6583 +/- 2329 mg X dl-1 X 5 h-1). During the OGTT the total amount of glucose oxidized (control 56 +/- 4.2 vs. SRIF 55 +/- 3.4 g/5 h) was similar in both conditions, suggesting that nonoxidative pathways of glucose disposal were responsible for the deterioration in glucose tolerance. Surprisingly, we found that glucose-induced thermogenesis was reduced in association with loss of the early phase of insulin release (control 102 +/- 21.3 vs. SRIF 72 +/- 27.8 J/5 h, P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1987

Free covalent aggregates of therapeutic insulin in blood of insulin-dependent diabetics.

Immunoreactive insulin (IRI) in the circulation of diabetics using insulin includes a 12,000-Mr covalent aggregate of insulin. In this study, both free and bound IRI were measured in nine type I diabetics who were treated sequentially for 3 wk with constant doses of conventional beef-pork, biosynthetic human, and beef-pork insulins (phases 1, 2, and 3, respectively). The aggregate accounted for 19 +/- 5.7, 38 +/- 7.7, and 26 +/- 7% of bound IRI, and 19 +/- 8.3, 35 +/- 7.3, and 31 +/- 5.0% of free IRI during phases 1, 2, and 3, respectively. Taken as concentrations (microU/ml), the absolute amounts of aggregate in the bound fraction were significantly (P less than .001) greater than those that were free, whereas the ratios of aggregate to monomer within each pool were similar (P greater than .1). The relative and absolute amounts of the insulin aggregate during each of the three treatment phases (compared by analysis of variance) were indistinguishable (P greater than 0.5). However, the aggregate was overestimated by a factor of approximately 2 when measurements were made on the basis of an insulin-monomer standard. We conclude that both the bound and free fractions of IRI contain insulin aggregate. Overreactivity of the aggregate in the radioimmunoassay contributes to the so-called hyperinsulinism of type I diabetes. As with insulin monomer, most of the 12,000-Mr aggregate is bound to antibodies. Because some of the aggregate is free, its biologic consequences must be assessed.

Adult↗
PubMed1987

Antibodies to covalent aggregates of insulin in blood of insulin-using diabetic patients.

A covalent aggregate twice the size of insulin accounts for approximately 28% of total circulating insulin immunoreactivity in type I diabetic patients. These aggregates are probably covalent dimers of insulin and should contain unique epitopes distinct from the parent molecule. Therapeutic insulin contains a similar material and is the source of the circulating aggregate. Anti-aggregate antibodies were detected by binding-inhibition techniques in 9 of 29 long-term diabetic patients. These antibodies were directed against structures distinct from those of the parent molecule insulin monomer. All antibody-positive patients were men whose blood also contained antibodies to insulin monomer. We conclude that the blood of approximately 30% of insulin-using diabetic patients contains antibodies directed against epitopes unique to the insulin aggregates. Because insulin monomer and aggregates probably share a common primary amino acid sequence, the anti-aggregate antibodies are probably directed against conformational determinants. Further work is needed to determine whether such aggregates promote or accentuate the development of anti-insulin antibodies in certain genetically predisposed individuals.

Adult↗
PubMed1986

The source of the circulating aggregate of insulin in type I diabetic patients is therapeutic insulin.

Circulating insulin immunoreactivity (IRI) in type I diabetic patients (insulin-dependent diabetes mellitus [IDDM]) includes a covalent aggregate about twice the size of insulin. These studies were designed to determine the source and conditions promoting the accumulation of this material. Among 31 IDDMs, the aggregate made up 28 +/- 3.6% of the mean fasting plasma IRI. Five of these patients were restudied after 5 d of treatment with equidose intravenous insulin. The relative amount of the aggregate during subcutaneous treatment (40 +/- 8.0%) was indistinguishable (P greater than 0.7) from that at the termination of intravenous treatment (41 +/- 6.8%). To determine whether previous exposure to therapeutic insulin influenced the appearance and accumulation of the aggregate, we intravenously or subcutaneously infused insulin for 5 h in nine healthy volunteers (euglycemic clamp). At the termination of the high-dose intravenous infusion (10 mU X kg-1 X min-1), the concentration of the aggregate was 81 +/- 18 microU/ml, and it accounted for 2.9% of total IRI. At the conclusion of the other infusion protocols, the absolute amounts of aggregate were somewhat less, but they accounted for similar percentages. On polyacrylamide gel electrophoresis, the circulating aggregate was indistinguishable from a material of similar molecular weight contaminating commercial insulin. We conclude that the insulin aggregate found in the blood of IDDMs originates in commercial insulin. Its appearance is independent of the route of insulin administration. Prolonged and continuous use of insulin may increase its concentration but is not necessary for its appearance. The potential biologic and immunologic consequences of the aggregate are important matters that need to be addressed.

Chromatography, Gel↗
PubMed1985

The thermic effect of carbohydrate versus fat feeding in man.

Metabolic rate increases and heat is produced after eating a meal. This response has been termed the thermic effect of feeding. While some studies have found this response to be defective in obese subjects others have not. It is also unclear how dietary composition affects the thermic response to a meal. In this study, we evaluated the thermic response to both a high carbohydrate meal and a high fat meal in normal and obese subjects. Using the ventilated hood technique, metabolic rate was measured in seated subjects before and for 6 hours following a meal. Blood samples for insulin, glucose, and catecholamines were withdrawn each half hour to evaluate their possible role in regulating the thermic response. The overall response to the high carbohydrate meal was greater than to high fat (0.26 +/- .07 v 0.18 +/- 0.11 kcal/min; P less than .01). The thermic response to the high fat meal, however, was similar in the normal and obese groups. Although the 6-hour response to the high carbohydrate diet was not statistically different between the subject groups, there was a trend toward a diminished response in the obese relative to the normal group during the first 3 hours following the meal (0.30 +/- .06 v .22 +/- .09; P = .06). In our seated subjects, the thermic response to a meal accounted for 8%-13% of the total calories ingested, with the highest value found in the normal weight subjects after a high carbohydrate meal. No significant thermic response was noted when subjects were fed a noncaloric meal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Metabolic response to three years of continuous, basal rate intravenous insulin infusion in type II diabetic patients.

We studied two obese type II diabetic patients before, during, and after 3 yr of continuous iv insulin infusion, delivered by means of totally implanted insulin infusion pumps. Tolerance of the devices was excellent, and no side-effects or episodes of significant hypoglycemia occurred. Glycosuria was eliminated, and mean 24-h plasma glucose and hemoglobin A1c levels decreased in both patients and remained in or near the normal range for 3 yr. Improvements were also noted in serum triglyceride concentrations and vitreous fluorescein concentrations after iv fluorescein injection. Euglycemic insulin clamp studies showed that no significant change in glucose disposal rate occurred after 6 and 12 months of treatment. However, some improvement in insulin secretion during hyperglycemic insulin clamp studies occurred in both patients after 6 months of insulin infusion. Evaluation of the insulin-glycerol mixture used in the pump revealed that moderate degradation of insulin occurred in the pump during the 21-day flow cycle, resulting in 6-12% increases in fasting blood glucose levels; in addition, higher mol wt species of immunoreactive insulin were present in the patients' serum. We conclude that long term continuous iv infusion of insulin using a totally implantable infusion pump is practical in type II diabetic patients, is acceptable to patients, and is capable of providing near-normal glycemic control.

Blood Glucose↗
PubMed1985

Products of therapeutic insulins in the blood of insulin-dependent (type I) diabetic patients.

The tendency of insulin in high concentrations to self-associate and the widespread presence of insulin-degrading enzymes suggest that fragments and/or aggregates of insulin may circulate in normal and insulin-dependent diabetic (IDDM) individuals. To examine this possibility, we have analyzed, by sensitive physicochemical methods, immunoreactive insulin (IRI) taken from the blood of 9 healthy volunteers and 12 insulin-dependent diabetic patients. IRI from the blood of the normal volunteers was composed of 6000 (91.0 +/- 1.4%) and 9000 (9.0 +/- 1.4%) molecular weight (mol wt) material. By 10% polyacrylamide disc gel electrophoresis (PAGE) and reverse-phase, high-performance liquid chromatography (HPLC), the 6000 mol wt material was indistinguishable from human insulin standards and insulin fragments were not found. C-peptide reactivity in the 9000 mol wt material confirmed the expected presence of proinsulin and intermediates of proinsulin conversion. IRI harvested from the blood of 12 C-peptide-negative IDDMs, using a variety of insulin preparations, also separated into 6000 (80.5 +/- 3.9%) and 9000-12,000 (19.5 +/- 3.9%) mol wt material. By HPLC, 6000 mol wt IRI was either pork insulin (in volunteers using pure pork insulin) or a mixture of beef (approximately 90%), pork (approximately 10%) and deamidated beef (trace) insulin in those using a beef-pork mixture. However, the 9000-12,000 mol wt material had characteristics entirely distinct from proinsulin of either human or animal origin: C-peptide reactivity was undetectable using any of three sensitive radioimmunoassay systems, on PAGE it migrated more rapidly than proinsulin-like material, and in contrast to proinsulin, it was unaffected by proteolytic degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Affinity↗
PubMed1984

Characterization of immunoreactive insulin in human saliva: evidence against production in situ.

The presence of insulin immunoreactivity in extra-pancreatic tissues and fluids suggests multiple sites of insulin production. Immunoreactive insulin occurs in human saliva and concentrations increase after oral glucose ingestion. The goal of these experiments was to determine whether the presence of immunoreactive insulin in this extra-pancreatic site is independent of pancreatic production or merely represents the accumulation of circulating pancreatic insulin. The mean +/- SEM concentration of extracted salivary immunoreactive insulin in five normal volunteers increased during an oral glucose tolerance test from basal values of 36 +/- 3.0 to 291 +/- 40 pmol/l; however, the peak occurred 45-90 min later than in serum. On this basis, it was not possible to distinguish between the stimulation (by increased blood glucose concentrations) of insulin synthesis in the saliva glands from the accumulation of blood insulin. Therefore, we studied a group of five volunteers during intravenous infusion of insulin (1 and 10 mU X kg-1 X min-1, sequentially) and glucose (euglycaemic clamp). Under these conditions, salivary immunoreactive insulin concentrations increased significantly from 254 +/- 100 to 1919 +/- 437 pmol/l (p less than 0.05), while simultaneous mean plasma C-peptide concentrations were unchanged. Thus, the concentration of salivary immunoreactive insulin was clearly related to the amount of insulin in the blood and not to the plasma glucose concentration. Physico-chemical and immunological characterization of salivary immunoreactive insulin by dilution in radioimmunoassay, gel filtration and polyacrylamide disc gel electrophoresis demonstrated that the majority of it was indistinguishable from insulin standards.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗