C. Binder

Pharmacokinetics of Continuous Subcutaneous Insulin Infusion

SummaryOne of the reasons for the variability of blood glucose regulation in Type 1 (insulin-dependent) diabetic patients is the huge variation in subcutaneous absorption of intermediate-acting insulin. We have investigated the variation in insulin absorption during continuous subcutaneous insulin infusion in eight such patients. The content of insulin in the subcutaneous tissue was measured using 125I-labelled insulin. The concentration of free serum insulin and blood glucose was followed from 1 h before and from 7 h after breakfast on two consecutive days. The amount of insulin absorbed during 24 h differed in all cases by less than 3% from the daily insulin dose given by the pumps. Mean insulin absorption rates and mean free insulin concentration showed peak values 30–90 min after meal bolus injections; this was sufficient to maintain near-normal blood glucose. Mean free serum insulin correlated strongly with disappearance of insulin from the subcutaneous tissue (r=0.98). From the insulin absorption rates and free insulin concentrations during basal constant insulin infusion, the half-time of serum insulin was calculated as 6 min. Compared with the known large variability in the absorption of intermediate-acting insulin, continuous subcutaneous insulin infusion offers a precise and reproducible way of insulin administration resulting in post-prandial serum insulin peaks sufficient to maintain near-normal blood glucose levels. The half-time of serum insulin during subcutaneous infusion corresponds to values for intravenous infusion given in the literature, indicating that local degradation of insulin in subcutaneous tissue is of minor importance.

Modeling absorption kinetics of subcutaneous injected soluble insulin

Absorption of subcutaneously injected soluble insulin deviates markedly from simple first-order kinetics and depends both on the volume and concentration of the injected solution. This paper presents a model of the absorption process in which insulin is presumed to be present in subcutis in a low molecular weight form, a high molecular weight form, and an immobile form where the molecules are bound to the tissue. The model describes how diffusion and absorption gradually reduce the insulin concentrations in the subcutaneous depot and thereby shift the balance between the three forms in accordance with usual laws of chemical kinetics. By presuming that primarily low molecular weight insulin penetrates the capillary walls, the model can account for experimentally observed variations in the absorption rate over a wide range of volumes and of concentrations. The model is used to determine the effective diffusion constant D for insulin in subcutis, the absorption rate constant B for low molecular weight insulin, the equilibrium constant Q between high and low molecular weight insulin, the binding capacity C for insulin in the tissue, and the average life time T for insulin in its bound state. Typical values for a bolus injection in the thigh of fasting type I diabetic patients are D=0.9 × 10−4 cm2/min, B=1.3 × 10−2/min, and Q=0.13 (ml/IU)2. Binding of insulin in the tissue is significant only at small concentrations. The binding capacity is of the order of C=0.05 IU/cm3 with a typical average life time in the bound state of T=800 min. Combined with a simplified model for distribution and degradation of insulin in the body, the absorption model is used to simulate variations in plasma free insulin concentrations with different delivery schedules, i.e., bolus injection and dosage by means of an infusion pump. The simulations show that a pump repetition frequency of 1–2 per hr is sufficient to secure an almost constant plasma insulin concentration.

Variation in125i-insulin absorption and blood glucose concentration

SummaryThe absorption of monocomponent porcine125I-insulin Monotard and Isophane was studied in six insulin dependent diabetic patients over a period of 12 days. The absorption of insulin was measured as the disappearance of radioactivity from sites of injection. The daily125I-insulin doses ranged from 20 to 48 IU between patients. The insulin absorbed varied considerably within and between patients. The range of individual daily absorbed insulin varied from 19 to 104 per cent of the125I-insulin dose. A significant correlation (p<0.05) was found between insulin absorption and blood glucose concentration. Insulin absorption rates were relatively high before all hypoglycaemic episodes and reactive hyperglycaemia was only observed when relatively low insulin absorption rates followed the hypoglycaemic attack. The results show that lability in some insulin dependent diabetics is explained by variation in insulin absorption.

Remission in IDDM: Prospective Study of Basal C-Peptide and Insulin Dose in 268 Consecutive Patients

To elucidate β-cell function, insulin requirement, and remission period in insulin-dependent diabetes mellitus (IDDM), a study was undertaken comprising 268 patients consecutively admitted to Steno Memorial Hospital with newly diagnosed IDDM. The patients were characterized by sex, age, and seasonal variation at onset of diabetes mellitus. Duringthe first 36 mo of the disease, an evaluation was performed for basal C-peptide, HbA1c, and insulin dose per kilogram. Total remission was interpreted as complete discontinuation of insulin therapy for at least 1 wk while still metabolically well controlled, and partial remission was interpreted as an insulin need that was <50% of the insulin dose at discharge from the hospital. During the first 18 mo of the disease, 12.3% of the patients entered total remission (median 6 mo), and 18.3% of the patients entered partial remission (median 6 mo). Patients entering remission had significantly higher basal C-peptide levels than those who did not. Sex, age, and initial HbA1c levels did not influence the frequency of remission.

DISAPPEARANCE AND REAPPEARANCE OF ISLET CELL CYTOPLASMIC ANTIBODIES IN CYCLOSPORIN-TREATED INSULIN-DEPENDENT DIABETICS

In 68 newly diagnosed patients with insulin-dependent diabetes mellitus (IDDM) whose treatment included cyclosporin (CyA) the prevalence and mean titre of islet cell cytoplasmic antibodies (ICA) fell faster than they did in the 56 who received only insulin. However, in the CyA-treated patients the prevalence or titre of ICA at diagnosis did not correlate with beta-cell function as measured by glucagon-stimulated C-peptide levels; improvement and recovery of beta-cell function after 30 days of CyA therapy occurred despite the continued presence of ICA; and CyA-induced remission of IDDM (ie, glucagon stimulated plasma C-peptide levels greater than 0.6 pmol/ml) was not predicted by nor coincident with disappearance of ICA. Therefore, although CyA therapy was associated with a higher than expected frequency of remission and faster disappearance of ICA, the two observations were not temporally and may not be causally related. ICA should not be used to identify the target population for or to predict response to immunosuppressive therapy. The contribution of ICA to the pathogenesis of beta-cell destruction in IDDM needs serious re-examination.

ELISA for human proinsulin

A micro enzyme-linked-immunosorbent-assay (ELISA) for monitoring circulating human proinsulin (hPI) was developed. A micro test plate was coated with guinea pig anti-insulin antibody. As labelling system peroxidase-labelled F(ab1)2-fragments of a guinea pig anti-human-C-peptide was used. The detection limit in buffer (95% level) was 0.6 pmol/l corresponding to 0.06 fmol/incubation well and to 1.2 pmol/l in serum, since samples were diluted 50%. Standard operating range was from 0-160 pmol/l. Interassay variation was 9% estimated from two human control materials (assayed within the range 6-9 pmol/l and 9-14 pmol/l, respectively). Insulin in samples did not interfere in concentrations below 400 pmol/l. Human C-peptide, porcine, and bovine proinsulins did not cross-react even at 10 000 pmol/l. In 38 healthy fasting subjects a reference range less than 1.2-13 pmol/l with a median of 4.1 pmol/l was found. Serum from total pancreatectomised patients showed values below the detection limit. The value from a patient with an insulinoma was 263 pmol/l. When stored at -20 degrees C human proinsulin appeared stable in serum or plasma for at least 9 mth. This ELISA, although among the most sensitive immunoassays for human proinsulin, is still not sensitive enough to measure the concentrations expected in samples from IDDM patients in the fasting state. In spite of this the method is useful in characterising beta-cell function in stimulated situations, as well as in the diagnosis of insulinoma.

IMPORTANCE OF INSULIN ABSORPTION, SUBCUTANEOUS BLOOD FLOW, AND RESIDUAL BETA-CELL FUNCTION IN INSULIN THERAPY

Abstract. Lauritzen, T., Binder, C. and Faber, O. K. (Steno Memorial Hospital, Gentofte, Denmark). Importance of insulin absorption, subcutaneous blood flow, and residual beta‐cell function in insulin therapy. Acta Paediatr Scand, Suppl. 283: 81, 1980.—The interaction between variation in insulin absorption and beta‐cell function was studied as well as the possible relation between subcutaneous blood flow through the region of injection and the variability in insulin absorption. The results indicate that the dose of insulin, the type of insulin preparation and the local blood flow influence the insulin absorption. Residual endogenous insulin secretion, governed by the blood glucose values, serves as a modulator.

Proinsulin and C-peptide at onset and during 12 months cyclosporin treatment of type 1 (insulin-dependent) diabetes mellitus.

SummaryAn increased proinsulin to C-peptide molar ratio at the onset of Type 1 (insulin-dependent) diabetes mellitus has been suggested. We studied fasting proinsulin levels and proinsulin/C-peptide ratios in the newly diagnosed diabetic subjects participating in the Canadian/European placebo controlled cyclosporin study at entry, during the one year treatment period and six months of follow-up. Available entry data from 176 out of the 188 allocated patients were compared to 60 age and weight matched control subjects. Fasting proinsulin was significantly elevated in male patients compared to male control subjects (p<0.01), whereas the levels only tended to be elevated in female patients. The proinsulin/C-peptide ratio was three to fourfold elevated in the diabetic groups of both sexes, (p<0.001). Further, proinsulin and C-peptide were studied in 83 cyclosporin and 86 placebo-treated subjects during the trial and follow-up. An additional increase of proinsulin/C-peptide ratio was observed during the first three months of placebo treatment. It remained constantly high for nine months and then declined to entry level. This pattern was not seen in the cyclosporintreated group, where the ratio was unchanged during the 12 months trial and follow-up. The effect of cyclosporin on the induction of non-insulin requiring remission was unrelated to fasting and glucagon stimulated C-peptide levels at entry, whereas 64% of the cyclosporin-treated against 28% of the placebo-treated subjects (p<0.01) went into remission if the proinsulin/C-peptide ratio at entry was above 0.024. If the ratio was below 0.024 at entry, 42% and 33% went into non-insulin requiring remission, respectively (NS). We conclude that fasting proinsulin to C-peptide molar ratio is elevated at the onset of Type 1 diabetes mellitus. A further plateaushape elevation lasting nine months was seen during the remission period. Cyclosporin seems to inhibit or delay this development. The proinsulin/C-peptide ratio at diagnosis may show to be of value in the prediction of remission during cyclosporin treatment.

The relationship between symptomatic and biochemical hypoglycaemia in insulin‐dependent diabetic patients

Abstract. The relationship between symptomatic (subjective feelings) and biochemical (blood glucose concentration < 3 mmol I−1) hypoglycaemia was studied in 66 randomly selected insulin‐dependent diabetic out‐patients under normal conditions of daily life with conventional insulin injection regimens. The patients (a) collected 7‐point diurnal blood glucose profiles at home on three consecutive days and then once weekly for 3 weeks, (b) indicated whether they felt hypoglycaemic at sampling times, and (c) collected extra samples if they felt hypoglycaemic at any time during the study period. The weekly frequencies of symptomatic and biochemical hypoglycaemia were 0.99 and 1.75 per patient, respectively. Biochemical hypoglycaemia was present in 29% of the symptomatic episodes, and symptomatic hypoglycaemia accompanied 16% of the biochemical episodes. Symptomatic hypoglycaemia was experienced at a median blood glucose concentration of 3.4 mmol I−1 (range 1.4‐14.9 mmol I−1). Fifty per cent of both symptomatic and biochemical episodes occurred before lunch, while the remainder were evenly distributed throughout the day. The occurrence of biochemical hypoglycaemia, but not of symptomatic hypoglycaemia, was inversely correlated with HbA1c and median blood glucose concentration. Thus symptomatic hypoglycaemia is an unreliable indicator of biochemical hypoglycaemia and of the degree of glycaemic control. Blood glucose measurements are a prerequisite for the diagnosis of hypoglycaemia.

Insulin autoantibodies are associated with islet cell antibodies; their relation to insulin antibodies and B-cell function in diabetic children.

SummaryBlood was drawn from 74 children, 3–16 years old, at diagnosis of Type 1 (insulin-dependent) diabetes and before the first insulin injection. Insulin autoantibodies were detected with a polyethylen-glycol-method in 27/74 (36.4%) and with an immuno-electrophoretic method in 6/74 (8.1%). Islet cell cytoplasmic antibodies detected by indirect immuno-fluorescence were found in 49/74 patients (66.2%), who included as many as 23 of the 27 patients with insulin autoantibodies determined with the polyethylen-glycol-method (p<0.01). The proportion of insulin autoantibody-positive patients who developed insulin antibodies during the first 9 months of insulin treatment was not significantly greater (51.8%) than that of insulin autoantibody-negative patients (44.6%), but patients with both islet cell antibodies and insulin autoantibodies at diagnosis produced more insulin antibodies during the first 9 months (p<0.05). There was no difference in fasting or meal stimulated serum C-peptide after 3, 9 or 18 months as related to occurrence of insulin autoantibodies and/or islet cell antibodies. The correlation between insulin autoantibodies and islet cell antibodies indicates that both types of autoantibodies reflect the same immunological process, although the lack of correlation to C-peptide may indicate that they play a minor causal role. In addition, the results show that patients with an active autoimmune process evidently tend to produce more insulin antibodies during the first months of insulin treatment, but the islet cell antibodies and insulin autoantibodies-positive patients had at least as good residual B-cell function as patients without autoantibodies at diagnosis. If insulin antibodies produced as a response to exogenous insulin do have a negative effect on B-cell function our present results suggest that such mechanisms are of minor importance.