Isolation by anion-exchange of immunologically and enzymatically active human islet glutamic acid decarboxylase 65 overexpressed in Sf9 insect cells.

The enzyme L-glutamic acid decarboxylase is a major autoantigen of the beta cell. Autoantibodies against this enzyme are observed before the onset of insulin-dependent diabetes mellitus (IDDM) in man and may be of predictive value. There is evidence that this enzyme is involved in the development of autoimmune diabetes in animals. In order to facilitate the investigation of the role of L-glutamine acid decarboxylase in IDDM, we expressed the 65 kDa isoform of human islet L-glutamic acid decarboxylase in insect cells using a baculovirus-based vector. The material was expressed at high levels (up to 50 mg/l of cells). Partially purified metabolically labelled L-glutamic acid decarboxylase bound to immunoglobulins in the sera from 20 of 49 subjects with newly-diagnosed IDDM. The enzyme was isolated in high yields (up to 26 mg/l cell culture) with fully maintained enzymatic activity by either ion-exchange chromatography or immunoaffinity chromatography. Purified L-glutamic acid decarboxylase inhibited the binding of radioactive L-glutamic acid decarboxylase, prepared by in vitro translation of mRNA, to immunoglobulins in the sera of subjects with IDDM. Recombinant human islet L-glutamic acid decarboxylase, isolated from Sf9 cells, is a suitable material for the large scale investigation of the utility of this enzyme in the prediction and prevention of autoimmune diabetes.

Sulphatide in islets of Langerhans and in organs affected in diabetic late complications: a study in human and animal tissue.

Sulphatide has been found in rat islets of Langerhans and anti-sulphatide antibodies have been demonstrated in patients with insulin-dependent diabetes mellitus. Using a specific monoclonal antibody, Sulph I, directed against sulphatide, we investigated the in situ distribution of this glycolipid immunohistochemically; furthermore, the sulphatide concentration was determined in several organs and cells by thin-layer chromatography. The islets of Langerhans in all species examined, mouse, rat, pig, and monkey were intensively stained but exocrine tissue remained unlabelled. The sulphatide concentration in human islets was 150 +/- 46 pmol/100 islets. The only glycolipid-antigen detected was sulphatide. Regarding other tissues, sulphatide was found to be located in distal tubules in the kidney, peripheral nerves, distinct scattered spot-like structures in the choreoid layer of the eye, the ovum, and peripheral granulocytes. Sulph I injection in mice showed homing to kidney tubules, Lung, heart, liver, adrenal, spleen, lymph node and thymus were not stained by Sulph I. Thus, the distribution of sulphatide shows an association with organs known to be affected in diabetes, either initially or in late complications.

Contribution of glutamate decarboxylase antibodies to the reactivity of islet cell cytoplasmic antibodies.

The contribution of glutamate decarboxylase (Mr 65000) antibodies to the reactivity of islet cell cytoplasmic antibodies with the 'whole' islet staining pattern from patients with newly diagnosed Type I diabetes was investigated. Diluted sera (n = 10) were preincubated with increasing concentrations of purified recombinant human islet glutamate decarboxylase (Mr 65000) and the change in islet cell cytoplasmic antibody binding was evaluated by quantitative immunocytochemistry. Binding to islet cells was partially blocked by glutamate decarboxylase in 9/10 diluted sera; the maximum blocking obtained at high concentrations of glutamate decarboxylase (5 micrograms/ml) was 36% (median, range 24-61%). In contrast, binding to islet cells in three diluted sera (two polyendocrine patients without Type I diabetes and one patient with newly diagnosed Type I diabetes) with the 'selective' islet staining pattern was totally blocked by glutamate decarboxylase. The concentration of glutamate decarboxylase required to achieve maximum blocking was less for the 'whole' islet (0.4-8.0 micrograms/microliters undiluted serum) compared to the 'selective' islet (20-645 micrograms/microliters undiluted serum) positive sera. All sera were positive for glutamate decarboxylase antibodies in an immunoprecipitation assay using 35S-methionine labelled extract of baby hamster kidney cells transfected with glutamate decarboxylase. However, the binding activity of these antibodies was less in the sera positive for the 'whole' islet compared to the 'selective' islet staining pattern. In conclusion, glutamate decarboxylase antibodies contribute partially to the reactivity of islet cell cytoplasmic antibodies of the 'whole' islet staining pattern in the sera of newly diagnosed patients with Type I diabetes, and totally to reactivity of the 'selective' islet staining pattern. The antigens recognized by the other antibodies contributing to the 'whole' islet reactivity remain to be defined.

Detection of GAD65 antibodies in diabetes and other autoimmune diseases using a simple radioligand assay.

Autoantibodies to glutamic acid decarboxylase (GAD) are frequent at or before the onset of insulin-dependent diabetes mellitus (IDDM). We have developed a simple, reproducible, and quantitative immunoprecipitation radioligand assay using as antigen in vitro transcribed and translated [35S]methionine-labeled human islet GAD65. By using this assay, 77% (77 of 100) of serum samples from recent-onset IDDM patients were positive for GAD65 antibodies compared with 4% (4 of 100) of serum samples from healthy control subjects. In competition analysis with unlabeled purified recombinant human islet GAD65, binding to tracer was inhibited in 74% (74 of 100) of the GAD65-positive IDDM serum samples compared with 2% of the control samples. The levels of GAD antibodies expressed as an index value relative to a standard serum, analyzed with or without competition, were almost identical (r = 0.991). The intra- and interassay variations of a positive control serum sample were 2.9 and 7.6%, respectively (n = 4). The frequency of GAD antibodies was significantly higher with IDDM onset before the age of 30 (80%, 59 of 74) than after the age of 30 (48%, 10 of 21) (P < 0.01). The prevalence of islet cell antibodies showed a similar pattern relative to age at onset. Because simultaneous occurrences of multiple autoimmune phenomena are common, we analyzed sera from patients with other autoimmune diseases. The frequency of GAD antibodies in sera positive for DNA autoantibodies (8% [2 of 25] and 4% [1 of 25] in competition analysis) or rheuma factor autoantibodies [12% (4 of 35) and 3% (1 of 35) in competition analysis] was not different from that in control samples. In contrast, in sera positive for ribonucleoprotein antibodies the frequency of GAD antibodies was significantly increased (73% [51 of 70] and 10% [7 of 70] in competition analysis [P < 0.025]). In conclusion, even large numbers of serum samples can now be tested for GAD65 antibodies in a relatively short time, allowing screening of individuals without a family history of IDDM for the presence of this marker.

Transfer of type 1 (insulin-dependent) diabetes mellitus associated autoimmunity to mice with severe combined immunodeficiency (SCID).

Pancreatic beta-cell destruction and development of Type 1 (insulin-dependent) diabetes mellitus are associated with circulating islet cell antibodies. Mice with severe combined immunodeficiency (SCID mice) were reconstituted with peripheral blood mononuclear cells from Type 1 diabetic patients, one who was antibody positive and one antibody negative, and from healthy individuals. Reconstituted mice were subsequently immunized with rat islets in incomplete Freunds adjuvant or adjuvant alone. Seventeen mice received peripheral blood mononuclear cells obtained at three different time points from the islet cell antibody positive patient. Before immunization with rat islets two mice developed antibodies to glutamic acid decarboxylase, a major target for antibodies in Type 1 diabetes, whereas none were positive for cytoplasmic islet cell antibodies. Following immunization with rat islets, glutamic acid decarboxylase antibodies were detected by immunoprecipitation in three additional mice, two of which also became positive for cytoplasmic islet cell antibodies. Of 22 mice which received peripheral blood mononuclear cells from either the islet cell antibody negative patient (n = 5) or from two healthy individuals (n = 17), none were positive for islet cell autoantibodies before or after immunization. None of the islet cell antibody positive mice became hyperglycaemic, showed impaired glucose tolerance or islet cell damage when studied 40 days after immunization (i.e. 100 days after reconstitution). In conclusion these results show that human B lymphocytes producing diabetes-associated autoantibodies can be transferred to SCID mice and remain antigen sensitive, but also that autoantibodies alone are not sufficient to induce beta-cell destruction.

Differential expression of glutamic acid decarboxylase in rat and human islets.

The GABA synthesizing enzyme GAD is a prominent islet cell autoantigen in type I diabetes. The two forms of GAD (GAD64 and GAD67) are encoded by different genes in both rats and humans. By in situ hybridization analysis of rat and human pancreases, expression of both genes was detected in rat islets, whereas only GAD64 mRNA was detected in human islets. Immunocytochemical analysis of rat and human pancreatic sections or isolated islets with antibodies to GAD64 and GAD67 in combination with antibodies to insulin, glucagon, or SRIF confirmed that a GAD64 and GAD67 expression were beta-cell specific in rat islets. In contrast, only GAD64 was detected in human islets and was, in addition to beta-cells, also surprisingly localized to some alpha-cells, delta-cells, and PP-cells. In long-term (4 wk) monolayer cultures of newborn rat islet cells, GAD64 expression remained beta-cell specific as observed in vivo, whereas GAD67 was localized not only to the beta-cells but also in the alpha-cells and delta-cells. A small but distinct fraction of GAD positive cells in these monolayer cultures did not accumulate GABA immunoreactivity, which may indicate cellular heterogeneity with respect to GABA catabolism or GAD enzyme activity. In a rat insulinoma cell line (NHI-6F) producing both glucagon and insulin depending on the culture conditions, GAD64 expression was detected only in cultures in which the insulin producing phenotype dominated. In conclusion, these data demonstrate that the two GAD isoforms are differentially expressed in rat and human islets but also that the expression differs according to culture conditions. These findings emphasize the need to consider both the species and culture conditions of islets.

Pancreatic beta-cells express a low affinity glucose transporter: functional consequences in normal and diabetic states.

The application of molecular biology to the study of membrane transport proteins has led to a rapid advance in our understanding of the mechanisms behind the regulation of blood glucose levels. Moreover the demonstration of lesions in the expression of GLUT2 in the islets from diabetic models has provided a focus for research efforts aimed at addressing the defects responsible for the development and onset of both type I and perhaps type II diabetes. The recent demonstration that an 'artificial beta-cell' can be engineered from anterior pituitary-derived cell lines by transfection with both the insulin cDNA and the cDNA encoding GLUT2 represents a significant advance in the development of potential therapies for type I diabetes [24].

Diabetes mellitus in cystic fibrosis: genetic and immunological markers.

Family history, as well as genetic and immunological markers of diabetes mellitus, were studied in cystic fibrosis (CF) patients with and without diabetes mellitus. Positive family history of diabetes mellitus in first-degree relatives was found in only 6 of 210 (3%) CF patients, with no difference between non-diabetic and diabetic patients. The frequency distributions of the HLA types DR3, DR4 and DR3/4, which normally confer susceptibility to insulin-dependent diabetes mellitus and of HLA-DR2, which normally confers resistance to insulin-dependent diabetes mellitus, were not different in non-diabetic CF patients, diabetic CF patients and normal subjects. The genotypic frequencies of tumor necrosis factor-beta and of heat shock protein 70, located within the HLA region on chromosome 6, in CF patients with diabetes were not different from those in patients with insulin-dependent diabetes mellitus, while non-diabetic CF patients and normal subjects shared other patterns. The frequencies of the interleukin-1 beta alleles, located on chromosome 2, were not different in non-diabetic and diabetic CF patients, insulin-dependent diabetic patients and normal subjects. Islet cell cytoplasmic antibodies, measured before, at and after the diagnosis of diabetes in 33 diabetic CF patients and in 32 matched non-diabetic CF patients, were detected in only 2 of 236 (0.8%) serum samples: in a pre-diabetic patient and in a non-diabetic control patient. Birth weights were not different in diabetic and non-diabetic CF patients, arguing against the importance of the intrauterine environment as a determinant in the transmission of diabetes mellitus in CF patients.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative immunocytochemical method for the measurement of islet cell cytoplasmic antibodies.

A quantitative immunocytochemical method for the measurement of islet cell cytoplasmic antibodies has been developed. The method employs human or rat pancreas, a protein A-peroxidase/diaminobenzidine secondary antibody system and an independent measurement of islet total and exocrine mean integrated absorbance by scanning microdensitometry. Specific islet cell cytoplasmic antibody binding (islet total-exocrine mean integrated absorbance) was dependent on serum dilution and substrate reaction time. The detection limit was approximately 5 JDF units. Specific islet cell cytoplasmic antibody binding values with human and rat pancreas were similar. Specific islet cell cytoplasmic antibody binding (human pancreas) was greater (p less than 0.001) in sera from patients with newly diagnosed insulin dependent diabetes mellitus (0.119 +/- 0.086, n = 29) compared to normal sera (0.003 +/- 0.008, n = 29). Thus, the method has been validated and may be useful for measuring the blocking effect of potential antigens on specific islet cell cytoplasmic antibody.

Lactate balance in perfused rat liver: effects of glucose concentration, flow and low pH on glucose to lactate flux.

The effects of medium glucose concentration (0-20 mmol l-1), pH (7.4 and 6.8) and flow (100 to 33% normal) on lactate uptake and glycolytic flux from 6-3H glucose were studied in perfused livers from 48-h starved rats. At both pH values, the glycolytic flux increased proportionally with the medium glucose concentration. Maximum glycolytic flux at 20 mmol l-1 glucose in the medium was 0.5 mumol min-1 g-1 liver (C6-units) at pH 7.4. At pH 7.4 and 20 mmol l-1 glucose the glycolytic flux decreased approximately proportional with flow. At pH 6.8 the glycolytic flux was extremely low and independent of flow. At flow 33% normal and pH 7.4 a net lactate production was accounted for by glycolysis from medium glucose concentration, indicating virtually no simultaneous lactate uptake. In contrast, at pH 6.8 net lactate production accounted for only half the glycolytic rate, indicating that lactate uptake occurred simultaneously with glycolysis. Thus, glucose-to-lactate flux in liver (as in muscle and brain) is subject to inhibition by low pH, and lactate uptake is enhanced by low pH.

Development of insulin antibodies, metabolic control and B-cell function in newly diagnosed insulin dependent diabetic children treated with monocomponent human insulin or monocomponent porcine insulin.

One hundred and thirty eight patients participated in a two-year randomized, double-blind multicentre trial to compare monocomponent human insulin and porcine insulin in the treatment of newly diagnosed insulin dependent diabetic children with respect to development of insulin antibodies, metabolic control and B-cell function. There was no difference between the two patient groups throughout treatment either in the level of IgG insulin binding or the percentage of patients with insulin antibodies (IgG-insulin greater than 0.012 U/l). However, the estimated mean of log insulin binding values in the antibody positive patients alone was significantly lower (p less than 0.05) in the human insulin treated group at all times apart from 1 and 18 months (e.g., human insulin group at one and two years: 0.104 and 0.152 U/l, porcine insulin group at one and two years: 0.162 and 0.212 U/l). The insulin antibodies in both patient groups bound equivalent amounts of human and porcine insulin tracer. Metabolic control, insulin dosage and B-cell function in the two treatment groups were similar throughout the treatment period. It is concluded that in newly diagnosed insulin dependent diabetic children monocomponent human insulin is slightly less immunogenic than monocomponent porcine insulin, and equally effective in overall metabolic control.

Mumps with laboratory signs of subclinical pancreatitis may cause a disturbed beta-cell function.

Mumps epidemics are followed by sporadic cases of insulin dependent diabetes mellitus (IDDM). We have studied beta-cell function in 11 subjects who had had a mumps infection. They had no clinical pancreatitis but were selected as they had abnormal pancreas iso-amylase values and/or glucosuria during the mumps virus infection. At the follow-up some years later the subjects were healthy. A few HbA1-values were noted in the upper part of the normal range. Total serum insulin values were normal, but the C-peptide values were low at first follow-up 1-3 years after infection in all but two patients. These values increased in 4/7 patients during the follow-up period but were subnormal in five subjects still 3-6 years after the infection. All five patients had HLA-DR 3 and/or 4. In 7 out of 11 patients islet cell surface antibodies could be demonstrated. Our results indicate that subclinical mumps pancreatitis may initiate a reaction towards the beta-cells recognized as subnormal C-peptide levels several years later in certain patients. This might contribute to manifest IDDM many years after infection.

Regulation of lactate uptake and lactate production in liver from 48-h-starved rats: effects of pH, flow and glucose concentration.

1. The effects of medium glucose concentration (0-20 mmol/l) and flow (100-33% of normal) on lactate uptake at low lactate concentration were studied in perfused livers from 48-h-starved rats with perfusate pH values of 7.4 and 6.8. 2. Lactate uptake was independent of glucose concentration in the range 5-10 mmol/l, but was slightly inhibited with time at 20 mmol/l glucose. This pattern was independent of perfusate pH. 3. At both pH values lactate uptake decreased proportionally with flow, and at low flow lactate was produced by the livers. The effect of flow was greatest at pH 7.4 where a net lactate production was found at 48% of normal flow, whereas at pH 6.8 lactate production was not seen until the flow was reduced to 33% of normal. 4. When glucose was omitted from the perfusate lactate production ceased at both pH values. 5. The effect of low pH on lactate uptake and production in liver probably reflects inhibition of glycolysis by low pH.

Hepatic lactate uptake is enhanced by low pH at low lactate concentrations in perfused rat liver.

The effect of pH on lactate uptake was studied in perfused liver of rats starved for 48 h. At both low pH (6.8) and normal pH (7.4) lactate uptake was a linear function of lactate concentration in input medium in the range 0.4-1.5 mmol/l. In the lower concentration range (0.4-0.8 mmol/l) the rate of lactate uptake was 30% higher at pH 6.8 than at pH 7.4. At pH 6.8 lactate uptake was independent of whether PCO2 was 2.7 or 5.3 kPa. We suggest the increased rate of lactate uptake at low pH and concentrations lower than 0.8 mmol/l was due to the stimulatory effect of H+ on the lactate carrier.

Immunogenicity of monocomponent human and porcine insulin in newly diagnosed type 1 (insulin-dependent) diabetic children.

The aim of the present study was to compare the immunogenicity of monocomponent human insulin with that of monocomponent porcine insulin in newly diagnosed Type 1 (insulin-dependent) diabetic children. One hundred and thirty-five patients at diagnosis of diabetes (age 1-18 years, mean age 9.3 years) were randomly allocated to treatment with either Monotard MC + Actrapid MC or Monotard HM + Actrapid HM in a double-blind trial conducted in Sweden, Finland, Norway and Denmark. The human and porcine insulin groups were identical at diagnosis with respect to age, sex and measures of metabolic control. At all times the mean insulin antibody levels and the percentage of antibody-positive patients were lower in the human group compared with the porcine group. At 3 and 12 months, the insulin antibody values were significantly lower in the human group than in the porcine group (p less than 0.05, Wilcoxon's rank sum test). At 12 months, antibody values in the human group ranged from 0 to 1.2 U/l (mean 0.14 U/l) and in the porcine insulin group from 0-5.2 U/l (mean 0.63 U/l). It is therefore concluded that human monocomponent insulin has a lower immunogenicity than porcine insulin of the same purity in newly diagnosed diabetic children during the first year of insulin treatment.

Acid-base balance in diabetic ketoacidosis.

Acid-base balance during development of diabetic ketoacidosis was reappraised on the basis of old studies on urinary excretion of ions. Circulatory collapse with impaired urinary excretion of acids is a prominent feature of the late phase of diabetic ketoacidosis, in which pathophysiological measurements are difficult to make. To elucidate the balance between hepatic uptake of carboxylic acids (free fatty acids and lactate plus pyruvate) and hepatic release of carboxylic acids (ketone bodies and lactate plus pyruvate) during the late phase of diabetic ketoacidosis, perfused livers from normal and streptozotocine-diabetic rats, fasted for 48 h, were subjected to high perfusate glucose concentrations, low perfusate pH and low perfusate flow rates. Provided that flow was kept normal, there was always a net uptake of carboxylic acids. At normal flow, a low pH and a high glucose concentration in the perfusate did not affect the hepatic uptake of lactate plus pyruvate or the flux of carbon from lactate to glucose. Reduction of the perfusate flow rate by two-thirds invariably turned the liver into a state of net carboxylic acid production. The net uptake of lactate plus pyruvate was greatly reduced, mainly due to initiation of a glycolytic flux.

Self-monitoring of blood glucose without a meter.

We studied the reliability of the Chemstrip system in the self-monitoring of blood glucose by diabetic patients. A total of 453 blood glucose values obtained by 38 diabetic patients using Chemstrip were compared with the glucose values of the same blood samples measured with a conventional laboratory method. We found a definite tendency at concentrations less than 320 mg/dl for patient-read Chemstrip values to be too low. Also, we found a wide range in laboratory values corresponding to a given patient-read Chemstrip value. However, a better agreement between Chemstrip and laboratory values was obtained when the Chemstrips were read by trained staff. We recommend, therefore, that the use of Chemstrip in the self-monitoring of blood glucose can be restricted to patients who have shown competence in the use of Chemstrip during prior testing.