Diabetes Antibody Standardization Program: evaluation of assays for insulin autoantibodies

AIMS/HYPOTHESIS

Insulin autoantibodies (IAA) are important in type 1 diabetes risk assessment. However, their determination varies more between laboratories than other diabetes autoantibodies. The Diabetes Antibody Standardization Program (DASP) aims to improve and standardise measurement of autoantibodies associated with type 1 diabetes. We report the results of measurement of IAA from DASP workshops in 2002, 2003 and 2005.

METHODS

Up to 32 laboratories in 14 countries participated in each workshop. Aliquots of coded sera from 50 patients with newly diagnosed type 1 diabetes and 100 blood donor controls were circulated to participating laboratories. Reported results were analysed using receiver operator characteristic (ROC) curves. We compared concordance of antibody levels by ranking, IAA and insulin antibody (IA) indices and units derived from an IA standard curve.

RESULTS

In all three workshops IAA assay performance had improved compared with DASP 2000. The median area under the ROC curve was 0.73 in DASP 2002, 0.78 in 2003 and 0.80 in 2005 (p = 0.0012), and median laboratory-assigned sensitivity was 26% in 2002, 36% in 2003 and 45% in 2005 (p < 0.0001). There was, however, marked variation between assays. The range of AUC was 0.36-0.91 and that of laboratory-assigned sensitivity was 22-57%. Concordance of ranking of patient serum samples was related to AUC (p < 0.001). Using an index related to common IAA and IA-positive or -negative control sera improved the concordance between assays (p < 0.0001).

CONCLUSIONS/INTERPRETATION

The overall performance of IAA assays has improved but there is still wide variation between laboratories. Concordance between assays would be improved by the use of a common reference reagent.

German new onset diabetes in the young incident cohort study: DiMelli study design and first-year results

BACKGROUND

Diabetes incidence in childhood and youth is increasing worldwide, including autoimmune and non-autoimmune cases. Recent findings suggest that there is a larger than expected proportion of type 2 diabetes in youth, and potential cases of intermediate diabetes phenotypes. Most pediatric diabetes registries focus on type 1 diabetes. Also, there is an absence of reliable data on type 2 diabetes incidence in youth.

AIMS

The DiMelli study aims to establish a diabetes incidence cohort registry of patients in Germany, diagnosed with diabetes mellitus before age 20 years. It will be used to characterize diabetes phenotypes by immunologic, metabolic, and genetic markers. DiMelli will assess the contribution of obesity and socio-demographic factors to the development of diabetes in childhood and youth.

METHODS

Recruitment of patients started in 2009, and is expected to continue at a rate of 250 patients per year.

RESULTS

84% of the 216 patients recruited within the first year were positive for multiple islet autoantibodies, 12% for one islet autoantibody, and 4% were islet autoantibody-negative. Patients with multiple islet autoantibodies were younger and had lower fasting C-peptide levels, compared to islet autoantibody-negative patients (median age 10.0 vs. 14.1 years, p < 0.01).

CONCLUSIONS

Results from the first year of the study show that DiMelli will help to reveal new knowledge on the etiology of diabetes, and the contribution of genetic predisposition and environmental risk factors to the different types of diabetes.

Advances in the prediction and natural history of type 1 diabetes

Type 1 diabetes (T1D) has the hallmark characteristics of autoimmunity superimposed on genetic susceptibility. Both genes (HLA) and immune markers (autoantibodies) have been validated as predictive markers of the subsequent development of the disease in higher-risk relatives and the lower-risk general population. Over the last three decades, using a combination of genes, immune, and metabolic markers, clinicians are now able to quantify an individual's disease risk from 1 in 100,000 to more than 1 in 2. This article reviews these biomarkers and T1D prediction strategies, and discusses potential implications of prediction and natural history for the pathogenesis of T1D.

BMI at age 8 years is influenced by the type 2 diabetes susceptibility genes HHEX-IDE and CDKAL1

OBJECTIVE

To determine whether HHEX-IDE and CDKAL1 genes, which are associated with birth weight and susceptibility to type 2 diabetes, continue to influence growth during childhood.

RESEARCH DESIGN AND METHODS

BMI, weight, and height at age 8 years expressed as age- and sex-corrected standard deviation scores (SDS) against national reference data and single-nucleotide polymorphism genotyping of HHEX-IDE and CDKAL1 loci were analyzed in 646 prospectively followed children in the German BABYDIAB cohort. All children were singleton full-term births; 386 had mothers with type 1 diabetes, and 260 had fathers with type 1 diabetes and a nondiabetic mother.

RESULTS

Type 2 diabetes risk alleles at the HHEX-IDE locus were associated with reduced BMI-SDS at age 8 years (0.17 SDS per allele; P = 0.004). After stratification for birth weight, both HHEX-IDE and CDKAL1 risk alleles were associated with reduced BMI-SDS (0.45 SDS, P = 0.0002; 0.52 SDS, P = 0.0001) and weight-SDS (0.22 SDS, P = 0.04; 0.56 SDS, P = 0.0002) in children born large for gestational age (>90th percentile) but not children born small or appropriate for gestational age. Within children born large for gestational age, BMI and weight decreased with each additional type 2 diabetes risk allele ( approximately -2 kg per allele; >8 kg overall). Findings were consistent in children of mothers with type 1 diabetes (P < 0.0001) and children of nondiabetic mothers (P = 0.008).

CONCLUSIONS

The type 2 diabetes susceptibility alleles at HHEX-IDE and CDKAL1 loci are associated with low BMI at age 8 years in children who were born large for gestational age.

Harmonization of glutamic acid decarboxylase and islet antigen-2 autoantibody assays for national institute of diabetes and digestive and kidney diseases consortia

BACKGROUND/RATIONALE

Autoantibodies to islet antigen-2 (IA-2A) and glutamic acid decarboxylase (GADA) are markers for diagnosis, screening, and measuring outcomes in National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) consortia studies. A harmonization program was established to increase comparability of results within and among these studies.

METHODS

Large volumes of six working calibrators were prepared from pooled sera with GADA 4.8-493 World Health Organization (WHO) units/ml and IA-2A 2-235 WHO units/ml. Harmonized assay protocols for IA-2A and GADA using (35)S-methionine-labelled in vitro transcribed and translated antigens were developed based on methods in use in three NIDDK laboratories. Antibody thresholds were defined using sera from patients with recent onset type 1 diabetes and healthy controls. To evaluate the impact of the harmonized assay protocol on concordance of IA-2A and GADA results, two laboratories retested stored TEDDY study sera using the harmonized assays.

RESULTS

The harmonized assays gave comparable but not identical results in the three laboratories. For IA-2A, using a common threshold of 5 DK units/ml, 549 of 550 control and patient samples were concordantly scored as positive or negative, specificity was greater than 99% with sensitivity 64% in all laboratories. For GADA, using thresholds equivalent to the 97th percentile of 974 control samples in each laboratory, 1051 (97.9%) of 1074 samples were concordant. On the retested TEDDY samples, discordance decreased from 4 to 1.8% for IA-2A (n = 604 samples; P = 0.02) and from 15.4 to 2.7% for GADA (n = 515 samples; P < 0.0001).

CONCLUSION

Harmonization of GADA and IA-2A is feasible using large volume working calibrators and common protocols and is an effective approach to ensure consistency in autoantibody measurements.

No effect of the 1alpha,25-dihydroxyvitamin D3 on beta-cell residual function and insulin requirement in adults with new-onset type 1 diabetes

OBJECTIVE

To determine whether daily intake of 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] is safe and improves beta-cell function in patients with recently diagnosed type 1 diabetes.

RESEARCH DESIGN AND METHODS

Safety was assessed in an open study of 25 patients aged 18-39 years with recent-onset type 1 diabetes who received 0.25 microg 1,25(OH)(2)D(3) daily for 9 months. An additional 40 patients were randomly assigned to 0.25 microg 1,25(OH)(2)D(3) or placebo daily for 9 months and followed for a total of 18 months for safety, beta-cell function, insulin requirement, and glycemic control.

RESULTS

Safety assessment showed values in the normal range in nearly all patients, regardless of whether they received 1,25(OH)(2)D(3) or placebo. No differences in AUC C-peptide, peak C-peptide, and fasting C-peptide after a mixed-meal tolerance test between the treatment and placebo groups were observed at 9 and 18 months after study entry, with approximately 40% loss for each parameter over the 18-month period. A1C and daily insulin requirement were similar between treatment and placebo groups throughout the study follow-up period.

CONCLUSIONS

Treatment with 1,25(OH)(2)D(3) at a daily dose of 0.25 microg was safe but did not reduce loss of beta-cell function.

Role of CCL2/MCP-1 in islet transplantation

High levels of donor-derived CCL2 have been associated with poor islet allograft outcome in patients with type 1 diabetes. The aim of our work was to determine whether CCL2 secreted by the islet has independent proinflammatory effects that influence engraftment and graft acceptance. Both in mice and humans CCL2 is significantly positively associated with other cytokines/chemokines, in particular with the highly released "proinflammatory" IL-6 and CXCL8 or CXCL1. Transplantation of CCL2-/- islets into syngenic recipients did not improve the transplant function. Transplantation of islets into CCL2-/- syngenic recipients led to a significant improvement of transplant function and partial abrogation of local hepatic inflammation. When evaluated in human islets CCL2 release was strongly related to the immediate local inflammatory response in the liver and impacted short-term human islet function dependently by the induced inflammatory response and independently by the immunosuppressive therapy. The data showed that islet CCL2 release is a sign of "inflamed" islets without having a direct role in graft failure. On the other hand, a causal effect for developing detrimental proinflammatory conditions after transplant was proved for recipient CCL2. Strategies to selectively decrease recipient, but not donor, CCL2 release may increase the success of islet transplantation.

Co-graft of allogeneic immune regulatory neural stem cells (NPC) and pancreatic islets mediates tolerance, while inducing NPC-derived tumors in mice

BACKGROUND

Data available on the immunomodulatory properties of neural stem/precursor cells (NPC) support their possible use as modulators for immune-mediated process. The aim of this study was to define whether NPC administered in combination with pancreatic islets prevents rejection in a fully mismatched allograft model.

METHODOLOGY/PRINCIPAL FINDING

Diabetic Balb/c mice were co-transplanted under the kidney capsule with pancreatic islets and GFP(+) NPC from fully mismatched C57BL/6 mice. The following 4 groups of recipients were used: mice receiving islets alone; mice receiving islets alone and treated with standard immunosuppression (IL-2Ralpha chain mAbs + FK506 + Rapamycin); mice receiving a mixed islet/NPC graft under the same kidney capsule (Co-NPC-Tx); mice receiving the islet graft under the left kidney capsule and the NPC graft under the right kidney capsule (NPC-Tx). Our results demonstrate that only the co-transplantation and co-localization of NPC and islets (Co-NPC-Tx) induce stable long-term graft function in the absence of immunosuppression. This condition is associated with an expansion of CD4(+)CD25(+)FoxP3(+) T regulatory cells in the spleen. Unfortunately, stable graft function was accompanied by constant and reproducible development of NPC-derived cancer mainly sustained by insulin secretion.

CONCLUSION

These data demonstrate that the use of NPC in combination with islets prevents graft rejection in a fully mismatched model. However, the development of NPC-derived cancer raises serious doubts about the safety of using adult stem cells in combination with insulin-producing cells outside the original microenvironment.

Mesenchymal cells appearing in pancreatic tissue culture are bone marrow-derived stem cells with the capacity to improve transplanted islet function

Adherent fibroblast-like cells have been reported to appear in cultures of human endocrine or exocrine pancreatic tissue during attempts to differentiate human beta cells from pancreatic precursors. A thorough characterization of these mesenchymal cells has not yet been completed, and there are no conclusive data about their origin.We demonstrated that the human mesenchymal cells outgrowing from cultured human pancreatic endocrine or exocrine tissue are pancreatic mesenchymal stem cells (pMSC) that propagate from contaminating pMSC. The origin of pMSC is partly extrapancreatic both in humans and mice, and by using green fluorescent protein (GFP(+)) bone marrow transplantation in the mouse model, we were able to demonstrate that these cells derive from the CD45(+) component of bone marrow. The pMSC express negligible levels of islet-specific genes both in basal conditions and after serum deprivation or exogenous growth factor exposure, and might not represent optimal candidates for generation of physiologically competent beta-cells. On the other hand, when cotransplanted with a minimal pancreatic islet mass, pMSC facilitate the restoration of normoglycemia and the neovascularization of the graft. These results suggest that pMSCs could exert an indirect role of "helper" cells in tissue repair processes.

Impaired insulin turnover in islets from type 2 diabetic patients

Failure of pancreatic β-cells contributes to the development of type 2 diabetes. Besides evidence of reduced glucose-stimulated insulin secretion and β-cell mass, little information is available about the molecular deficits of human diabetic islets. Islets were isolated from macroscopically normal pancreatic tissue from 8 patients with type 2 diabetes and 17 matched non-diabetic patients who underwent pancreatic surgery. Insulin content and insulin secretion were measured before and after islet stimulation with 25 mM glucose for 2 hours. In parallel, we also investigated the subcellular localization of polypyrimidine tract-binding protein 1 (PTBP1), whose nucleocytoplasmic translocation is involved in the rapid posttranscriptional up-regulation of insulin biosynthesis following islet stimulation with glucose and GLP-1. Glucose stimulated insulin secretion was decreased, albeit not significantly, in type 2 diabetic islets compared to non-diabetic islets. Stimulation increased the total amount of insulin (islet insulin content + secreted insulin) in islet preparation from non-diabetic patients, but not from type 2 diabetic subjects. Furthermore, the nuclear levels of PTBP1 were decreased in stimulated non-diabetic islets, but not in type 2 diabetic islets. These results suggest that impairment of rapid insulin increase in response to glucose is a specific trait of type 2 diabetic islets. Nuclear retention of PTBP1 is likely to play a role in this deficit, which in turn can contribute to impaired insulin secretion in type 2 diabetes. Overall, these data highlight the importance of investigating mechanisms of insulin biosynthesis and degradation to gain insight into the pathogenesis of type 2 diabetes.

Zinc transporter 8 antibodies complement GAD and IA-2 antibodies in the identification and characterization of adult-onset autoimmune diabetes: Non Insulin Requiring Autoimmune Diabetes (NIRAD) 4

OBJECTIVE

Zinc transporter 8 (ZnT8) is an islet beta-cell secretory granule membrane protein recently identified as an autoantibody antigen in type 1 diabetes. The aim of this study was to determine the prevalence and role of antibodies to ZnT8 (ZnT8As) in adult-onset diabetes.

RESEARCH DESIGN AND METHODS

ZnT8As were measured by a radioimmunoprecipitation assay using recombinant ZnT8 COOH-terminal or NH(2)-terminal proteins in 193 patients with adult-onset autoimmune diabetes having antibodies to either GAD (GADAs) or IA-2 (IA-2As) and in 1,056 antibody-negative patients with type 2 diabetes from the Non Insulin Requiring Autoimmune Diabetes (NIRAD) study.

RESULTS

ZnT8As-COOH were detected in 18.6% patients with autoimmune diabetes and 1.4% with type 2 diabetes. ZnT8As-NH(2) were rare. ZnT8As were associated with younger age and a high GADA titer. The use of GADAs, IA-2As, and ZnT8As in combination allowed a stratification of clinical phenotype, with younger age of onset of diabetes and characteristics of more severe insulin deficiency (higher fasting glucose and A1C, lower BMI, total cholesterol, and triglycerides) in patients with all three markers, with progressive attenuation in patients with two, one, and no antibodies (all P(trend) < 0.001). Autoantibody titers, association with high-risk HLA genotypes, and prevalence of thyroid peroxidase antibodies followed the same trend (all P < 0.001).

CONCLUSIONS

ZnT8As are detectable in a proportion of patients with adult-onset autoimmune diabetes and seem to be a valuable marker to differentiate clinical phenotypes.

Disengaging the IL-2 receptor with daclizumab enhances IL-7-mediated proliferation of CD4(+) and CD8(+) T cells

Allograft rejection is mainly driven by the production of IL-2, which expands T cells by linking the IL-2 receptor (IL-2R) composed of three subunits: CD25, CD122 and CD132. Daclizumab, widely used in immunosuppression, is a humanized anti-CD25 antibody that disrupts IL-2 signaling by binding to CD25 and preventing the assembly of the high-affinity IL-2R. Here we show that Daclizumab, while blocking the T-cell response to IL-2, increases CD4(+) and CD8(+) T-cell proliferative response to the homeostatic cytokine IL-7. The IL-7R shares CD132 with the IL-2R and blocking of CD25 by Daclizumab results in the enhanced formation of the IL-7R that in turn allows IL-7 to bind more efficiently on the cell surface. The consequently increased IL-7R signaling boosts intracellular phosphorylated STAT5 and T-cell proliferation. In addition, treatment with Daclizumab delays the internalization of CD127 upon IL-7 treatment, retaining T-cell sensitivity to IL-7 for a prolonged time. This effect of Daclizumab highlights the redundancy of the cytokine system, which may influence T-cell proliferation in transplanted patients, and provides information to improve future immunosuppressive strategies.

Azide and Tween-20 reduce binding to autoantibody epitopes of islet antigen-2; implications for assay performance and reproducibility

Autoantibodies to islet antigen 2 (IA-2A) are important markers for predicting diabetes in children and young adults. Harmonization of IA-2A assay measurement is essential if results from different laboratories are to be compared. We investigated whether sodium azide, a bacteriostatic agent added to some assays, could affect IA-2A binding and thereby contribute to differences in IA-2A measurement between laboratories. Addition of 0.1% azide to assay buffer was found to reduce median IA-2A binding of 18 selected sera from IA-2A positive patients with type 1 diabetes and their relatives by 41% (range, 78 to -33%, p<0.001). The effect on binding was epitope specific; median IA-2A binding by 14 sera with antibodies to the protein tyrosine phosphatase region of IA-2 was reduced by 48% (range, 11 to 78%, p<0.001), while binding by 4 sera with antibodies specific to only the juxtamembrane region of IA-2 showed no change (median increase 16% (range 6 to 33%, p=0.125). When the Tween-20 concentration was reduced from 1% to 0.15% the median reduction in IA-2A binding with azide by the 18 sera was only 10% (range, -12 to 41%, p<0.001). Tween-20 also exerted an independent effect, since median IA-2A binding increased by 23% (range 3% to 86%, p<0.001) when Tween-20 concentration was reduced from 1% to 0.15% in the absence of azide. We conclude that common assay reagents such as azide and Tween-20 can strongly influence IA-2A binding in an epitope-related manner, and their use may explain some of the differences between laboratories in IA-2A measurement.

HHEX-IDE polymorphism is associated with low birth weight in offspring with a family history of type 1 diabetes

CONTEXT

The fetal insulin hypothesis proposes that common genetic variants that reduce insulin secretion also reduce birth weight, and an association of low birth weight and the type 2 diabetes risk alleles at the HHEX-IDE and CDKAL1 loci were recently reported.

OBJECTIVE

Here, we examined the relationship between type 2 diabetes risk alleles and birth weight in a diabetic environment presented in children of mothers with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Birth weight and genotyping of single nucleotide polymorphisms (SNPs) at the CDKAL1, HHEX-IDE, and SLC30A8 loci was obtained and analyzed in 729 singleton full-term children of mothers with type 1 diabetes born in Germany.

RESULTS

The fetal risk alleles of HHEX-IDE SNP rs5015480 and SNP rs10882102 were associated with reduced birth weight: 81g (95% confidence interval, 20-140 g; P = 0.009) and 85 g (95% confidence interval, 25-145 g; P = 0.005) lower birth weight per risk allele, respectively. The association remained significant after adjusting for maternal pregnancy-glycosylated hemoglobin. Fetal genotypes at the CDKAL1 and SLC30A8 loci were not associated with birth weight in this cohort.

CONCLUSIONS

The association of low birth weight and type 2 diabetes risk alleles of the HHEX-IDE locus is confirmed in children of mothers with type 1 diabetes.

Is islet autoimmunity related to insulin sensitivity or body weight in children of parents with type 1 diabetes?

AIMS/HYPOTHESIS

It has been suggested that metabolic demand and insulin resistance play a role in the development of type 1 diabetes, including the onset of autoimmunity. The aim of the present study was to determine whether insulin demand is increased in children with islet autoantibodies.

METHODS

BMI standard deviation score (BMI-SDS) was measured from 2 years of age in 1,650 prospectively followed children of mothers or fathers with type 1 diabetes, including 135 who developed persistent islet autoantibodies. HOMA of insulin resistance (HOMA-IR) was determined using fasting samples from 777 of the children starting from age 5 years.

RESULTS

An increased HOMA-IR was associated with female sex (p = 0.0004), older age (p < 0.0001) and increased BMI-SDS (p < 0.0001). Children with islet autoantibodies did not have an increased HOMA-IR compared with age-matched islet autoantibody-negative children (age 8 years: mean 0.61 vs mean 0.72, respectively, p = 0.21; age 11 years: mean 0.96 vs mean 1.21, respectively, p = 0.07). Furthermore, after correction for age and sex, autoantibody positivity was associated with decreased HOMA-IR values (p = 0.01). BMI-SDS was similar between islet autoantibody-positive and -negative children at age 2 (mean 0.07 vs mean 0.16, respectively), 5 (mean 0.06 vs 0.08, respectively), 8 (mean - 0.09 vs mean 0.02, respectively), and 11 years (mean 0.22 vs mean 0.16, respectively) and similar to that of national reference values.

CONCLUSIONS/INTERPRETATION

Islet autoantibody-positive children in the BABYDIAB cohort are not insulin resistant and do not have an increased BMI around and early after islet autoantibody seroconversion. These findings are inconsistent with the notion that insulin resistance is a risk factor for islet autoimmunity.

Autoantibodies to zinc transporter 8 and SLC30A8 genotype stratify type 1 diabetes risk

AIMS/HYPOTHESIS

Our aim was to determine the relationships between autoantibodies to zinc transporter 8 (ZnT8), genotypes of the ZnT8-encoding gene SLC30A8 and type 1 diabetes risk.

METHODS

ZnT8 autoantibodies (ZnT8A) were measured in sera of 1,633 children with a first-degree family history of type 1 diabetes and who were prospectively followed from birth. Antibodies were measured by Protein A-based radiobinding assays and COOH-terminal (R325, W325 or Q325 variants) or NH(2)-terminal constructs of human ZnT8. SLC30A8 genotyping at single-nucleotide polymorphism (SNP) rs13266634 was performed on 1,170 children.

RESULTS

Antibodies against COOH-terminal ZnT8 constructs (ZnT8A-COOH) developed in 58 children as early as 9 months of age (median 3 years). They were detected in 55 of 128 (43%) children with autoantibodies to insulin, GAD and/or insulinoma-associated protein 2 and 34 of 42 (81%) who progressed to diabetes. The additional presence of ZnT8A-COOH stratified diabetes risk in islet autoantibody-positive children (p < 0.0001). SLC30A8 genotype strongly influenced ZnT8A type and diabetes risk in ZnT8A-COOH-positive children. Antibody binding against the ZnT8 R325 variant was strictly correlated with the number of the corresponding SLC30A8 R325-encoding alleles, whereas binding against the W325 variant was highest in children who had SLC30A8 W325-encoding alleles (p = 0.001). Moreover, ZnT8A-COOH-positive children who carried homozygous SLC30A8 SNP rs13266634 genotypes progressed faster to diabetes than those who were heterozygous (59% [95% CI 42.3-75.7%] vs 22% [95% CI 0-44.3%] within 5 years; p = 0.01).

CONCLUSIONS/INTERPRETATION

Autoimmunity against the COOH-terminal region of ZnT8 is a highly relevant prognostic feature in childhood type 1 diabetes. Risk stratification in ZnT8A-COOH-positive children is further improved by SLC30A8 genotyping.