Diabetes mellitus in rabbits immunized with insulin

Variants in the BACH2 and CLEC16A gene might be associated with susceptibility to insulin-triggered type 1 diabetes

AIM/INTRODUCTION

Insulin administration was found to trigger type 1 diabetes in six Japanese type 2 diabetes patients with type 1 diabetes high-risk human leukocyte antigen class II and the class I allele of the insulin gene variable number tandem repeat genotype. The objective of the present study was to assess the contribution of non-human leukocyte antigen single-nucleotide polymorphisms (SNPs) to the risk of developing insulin-triggered type 1 diabetes.

MATERIALS AND METHODS

We genotyped 13 type 1 diabetes susceptible SNPs in six patients and compared them with those in Japanese controls (Hap Map3-JPT). The SNPs that showed statistically significant results were further analyzed using non-diabetic control participants and participants with type 2 diabetes at the Ehime University Hospital.

RESULTS

The risk allele frequency of BACH2 rs3757247 in the six patients was significantly more frequent than that in 86 Japanese controls (P = 0.038). No significant difference in the allele frequency was observed in the other SNPs. This result was confirmed by the findings that the risk allele frequency of BACH2 in the six patients was significantly higher than that in the non-diabetic control participants (n = 179) and type 2 diabetes with or without insulin treatment (n = 154 or n = 152; P = 0.035, 0.034 or 0.037, respectively). Despite being statistically not significant, the six patients were all homozygous for the CLEC16A rs12708716 risk allele and five were homozygous for the CLEC16A rs2903692 risk allele.

CONCLUSIONS

In addition to type 1 diabetes high-risk human leukocyte antigen class II and the class I allele of the insulin gene variable number tandem repeat genotype, the possibility that the risk variants of BACH2 and CLEC16A could contribute to the development of insulin-triggered type 1 diabetes cannot be excluded.

Coxsackievirus B4 and type 1 diabetes pathogenesis: contribution of animal models

The role of enteroviruses, in particular type B coxsackieviruses (CV-B), in type 1 diabetes (T1D) pathogenesis is supported by epidemiological, clinical and experimental observations.The investigation of T1D pathogenesis benefits from the contribution of animal models called spontaneously diabetic. Among these animals the non-obese diabetic (NOD) mouse and the bio-breeding diabetes-prone (BBDP) rat present a genetic susceptibility manifested by the expression of an autoimmune diabetes similar to the pathology observed in human beings. Other models whose genetic predisposition is less known are of considerable contribution as well. Numerous major observations relative to several aspects of T1D pathogenesis in the context of CV-B infections, such as susceptibility, diabetogenicity, pancreatotropism, mechanisms of beta cells destruction and others, have been deduced thanks to investigations with animal models. Despite their limits, these models are necessary in improving our knowledge of the role of enteroviruses, like CV-B4, in the pathogenesis of T1D, and the recent advances ensuing from their contribution may have important therapeutic and preventive spin-offs.

Insulin administration may trigger pancreatic beta-cell destruction in patients with type 2 diabetes

Insulin administration causes various types of immune response to insulin. However, there have been no reports that insulin administration triggers pancreatic beta-cell destruction in diabetic patients. We evaluated three patients who had suffered from type 2 diabetes or impaired glucose tolerance for 5-30 years. After an episode of diabetic mononeuropathy or poor glycemic control, they started human insulin therapy. All the patients' serum or urinary C-peptide levels were preserved before insulin therapy, whereas within a few months they rapidly declined to below detection limits. A high titer of insulin antibody was detected at or after the development of insulin deficiency. Shortly after the initiation of insulin therapy, two of the patients developed an insulin allergy. Autoantibodies to GAD65 or IA-2 were negative throughout the clinical course in two cases, but transiently positive in one case. In a histological examination of pancreas tissue obtained by a pancreatic biopsy in one case, mononuclear cell infiltration into the islets was observed. They all had a type 1 diabetes high-risk HLA class II haplotype in Japanese, and class I alleles of the insulin gene VNTR. The above findings suggest that insulin administration may have triggered pancreatic beta-cell destruction in these patients.

Is It Dietary Insulin?

In humans the primary trigger of insulin-specific immunity is a modified self-antigen, that is, dietary bovine insulin, which breaks neonatal tolerance to self-insulin. The immune response induced by bovine insulin spreads to react with human insulin. This primary immune response induced in the gut immune system is regulated by the mechanisms of oral tolerance. Genetic factors and environmental factors, such as the gut microflora, breast milk-derived factors, and enteral infections, control the development of oral tolerance. The age of host modifies the immune response to oral antigens because the permeability of the gut decreases with age and mucosal immune response, such as IgA response, develops with age. The factors that control the function of the gut immune system may either be protective from autoimmunity by supporting tolerance, or they may induce autoimmunity by abating tolerance to dietary insulin. There is accumulating evidence that the intestinal immune system is aberrant in children with type 1 diabetes (T1D). Intestinal immune activation and increased gut permeability are associated with T1D. These aberrancies may be responsible for the impaired control of tolerance to dietary insulin. Later in life, factors that activate insulin-specific immune cells derived from the gut may switch the response toward cytotoxic immunity. Viruses, which infect beta cells, may release autoantigens and potentiate their presentation by an infection-associated "danger signal." This kind of secondary immunization may cause functional changes in the dietary insulin primed immune cells, and lead to the infiltration of insulin-reactive T cells to the pancreatic islets.

Induction and acceleration of insulitis/diabetes in mice with a viral mimic (polyinosinic-polycytidylic acid) and an insulin self-peptide

Polyinosinic-polycytidylic acid (PolyIC), a "mimic" of double-stranded viral RNA, can induce diabetes when administered to rats with RT1(u), and immunization of normal H-2(d) mice (e.g., BALB/c) with insulin B:9-23 peptide (but not H-2(b)) results in the rapid induction of insulin autoantibodies. Because a mouse model of PolyIC/antigen-induced diabetes is lacking, we sought to produce insulitis and diabetes with either PolyIC and/or B:9-23 peptide immunization. Simultaneous administration of PolyIC and B:9-23 peptide to BALB/c mice (but with neither alone) induced insulitis. CD4 T lymphocytes predominated within islets, and the mice did not progress to hyperglycemia. Islets with transgene-induced expression of the costimulatory B7-1 molecule have enhanced diabetes susceptibility. Diabetes was frequently induced in B7-1 transgenic mice with H-2(d) in contrast to H-2(b) mice after PolyIC administration. Disease induction was accelerated by adding B:9-23 immunization to PolyIC. These studies demonstrate that "normal" mice have autoreactive T lymphocytes able to rapidly target islets and insulin given appropriate MHC alleles and that a peripherally administered insulin peptide (an altered peptide ligand of which is in clinical trials) can enhance specific anti-islet autoimmunity. These first PolyIC/insulin-induced murine models should provide an important tool to study the pathogenesis of type 1 diabetes with experimental autoimmune diabetes.

Insulin-specific tolerance in diabetes

At present it is possible to predict the development of type 1A diabetes (immune-mediated diabetes) in man and prevent the disorder in animals. Studies of immunity to insulin play a prominent role in both disease prediction and disease prevention. For both man and the NOD mouse, insulin autoantibodies usually precede the development of diabetes and can be utilized to assist in disease prediction. T cells clones recognizing insulin, both CD4 and CD8, can transfer disease to young mice or immunodeficient animals. Specific insulin peptides reacting with these clones have been identified, their crystal structure when bound to a human "diabetogenic" MHC allele has been determined, and specific peptides can be used either to induce or to prevent disease. Clinical trials of both insulin and an altered peptide ligand of insulin to prevent islet beta-cell destruction are underway. Insulin is one of a number of islet autoantigens, but it is likely that immune responses to insulin will be central to both pathogenesis and immunologic protection.

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

Blood 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 less than 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 less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Instability of fasting blood glucose values in noninsulin-dependent diabetic patients with long-term insulin treatment

We studied serum free C-peptide immunoreactivity (CPR) and the coefficient of variation (CV) of fasting blood glucose values (FBG) in 26 insulin-treated patients with non-insulin-dependent diabetes mellitus (NIDDM) in relation to the duration of insulin treatment. Serum free CPR responses during 100 g oral glucose tolerance test (OGTT) were significantly lower in patients with insulin treatment for five years or more than in those with insulin treatment for less than five years although their previous immunoreactive insulin (IRI) responses during OGTT before insulin treatment showed no significant difference. CV of FBG was found to be significantly higher at the time of this study (20.6 +/- 7.8%, mean +/- SD) than at the second year of insulin treatment (15.3 +/- 7.7%, P less than 0.05) in the patients with insulin treatment for five or more years but did not show any significant difference in patients with insulin treatment for less than five years at the corresponding times. Thus we measured CV of the FBG in NIDDM patients at various intervals during the long-term insulin or oral hypoglycemic agent treatment in another study. In 20 patients with insulin treatment, CV of FBG was found to be significantly different among the various intervals during insulin treatment (P less than 0.0025). It was significantly higher at the eight year (22.2 +/- 8.6%) and 12th year (21.9 +/- 9.1%) than at the second year (14.9 +/- 6.1%) and fifth year (15.0 +/- 6.7%) of insulin treatment (P less than 0.025, P less than 0.025; P less than 0.05, P less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal proinsulin/C-peptide ratio in juvenile diabetes

B-cell function was studied in 20 diabetic children, with an age at onset of diabetes between 1.16 years (8.8 +/- 4.0). Serum samples were taken before the first insulin injection and after 1, 3, 6, 9 and in a few patients after 18 months. At 3, 9, and 18 months the patients were also given a standardized breakfast load. Serum proinsulin, C-peptide, IRI and insulin antibodies (IgG) were determined. At onset 19 patients had measurable C-peptide (0.22 +/- 0.17 pmol/ml; range 0.05-0.58). Proinsulin varied between 0.000-0.25 pmol/ml (0.069 +/- 0.071) and at onset amounted to 31.3 +/- 29.4 (0.100)% of C-peptide as compared to 3.3 +/- 1.1 (1.7-6.6) in non-diabetics. A long partial remission was significantly correlated to a low proinsulin/C-peptide ratio at onset. In patients with low fasting proinsulin and no insulin antibodies, breakfast stimulation was accompanied by an increased proinsulin release at 3 and 9 months. The results suggest that abnormal proinsulin secretion is a feature of the 'B-cell exhaustion' complex in juvenile-onset diabetes.

Renovascular hypertension in rats immunized with angiotensin II

The experimental design which most closely reproduces clinical renovascular hypertension is constriction of one renal artery, with the other renal artery and kidney left intact. To test the role of renin and angiotensin in the pathogenesis of renovascular hypertension, attempts were made to induce such hypertension in rats previously immunized with angiotensin. In 29 highly immunized and 33 control rats, one renal artery was partially constricted and the other kidney and renal artery left intact. Preoperative blood pressures were equal in all rats (means: immunized, 118 ± SE 0.95; controls, 117 ± 0.70 mm Hg). Both groups developed hypertension during the 13 days following operation (means: immunized, 173 ± 3.42; controls, 169 ± 4.65 mm Hg). The high blood pressures persisted throughout the observation period (56 days). Immune sera completely inactivated large amounts of angiotensin (mean, 1130 ± SD 887 ng/ml antiserum; range 200-4000), and high intravenous doses of renin and angiotensin had no effect on the blood pressure of immunized rats. These data provide strong evidence that the direct pressor effect of circulating angiotensin is not essential for the development of hypertension evoked by constricting one renal artery in the rat.