Development of an Enhanced Sensitivity Bead-Based Immunoassay for Real-Time In Vivo Detection of Pancreatic β-Cell Death

The early detection of type 1 diabetes mellitus and latent autoimmune diabetes in adults (LADA) through rapid test reverse-flow immunochromatography for glutamic acid decarboxylase 65 kDa (GAD65)

Background

Diabetes mellitus (DM) is a chronic and costly disease that has become a primary concern worldwide. Type 1 diabetes mellitus is categorized as an autoimmune disease, which results in islet cell apoptosis and insulin-dependent. GAD₆₅ is known as a potential marker of impaired pancreatic β cell function that appears in the initial phase of type 1 DM and latent autoimmune diabetes in adults (LADA). This study aimed to develop a novel rapid test of anti-GAD₆₅ autoantibodies in human serum samples.

Methods

We have developed a rapid test for anti-GAD65 autoantibodies in this assay based on the reverse-flow immunochromatography method. Human recombinant-protein antigen for GAD₆₅ was attached as the control line over the nitrocellulose membrane. On the other side, the goat anti-mouse immunoglobulin G (IgG) was coated on the same membrane as a control line. The positive result for GAD₆₅ was confirmed by a colloidal gold signal on the strip. Our novel assay analyzed 276 healthy subjects and 51 type 1 diabetes individuals serum samples from several ethnicities in Indonesia for this study.

Results

Among the 276 healthy samples, 225 samples were identified as positive for anti-GAD₆₅ autoantibodies, while 51 samples were negative. Interestingly, the positive results for anti-GAD₆₅ autoantibodies were linear to the decreasing of high-density lipoprotein (HDL) levels and inversely associated with triglyceride levels. A significant correlation with age was observed in all groups. The sensitivity and specificity test proved that this kit has higher accuracy (AUC value = 0.960).

Conclusion

The significant advantages of our rapid test for anti-GAD₆₅ autoantibodies provide higher sensitivity, specificity, and stability compared to previous commercial kits. Therefore, it could be proposed as the future clinical diagnostic kit for patient management of type 1 DM.

The MicroRNA Landscape of Acute Beta Cell Destruction in Type 1 Diabetic Recipients of Intraportal Islet Grafts

Ongoing beta cell death in type 1 diabetes (T1D) can be detected using biomarkers selectively discharged by dying beta cells into plasma. microRNA-375 (miR-375) ranks among the top biomarkers based on studies in animal models and human islet transplantation. Our objective was to identify additional microRNAs that are co-released with miR-375 proportionate to the amount of beta cell destruction. RT-PCR profiling of 733 microRNAs in a discovery cohort of T1D patients 1 h before/after islet transplantation indicated increased plasma levels of 22 microRNAs. Sub-selection for beta cell selectivity resulted in 15 microRNAs that were subjected to double-blinded multicenter analysis. This led to the identification of eight microRNAs that were consistently increased during early graft destruction: besides miR-375, these included miR-132/204/410/200a/429/125b, microRNAs with known function and enrichment in beta cells. Their potential clinical translation was investigated in a third independent cohort of 46 transplant patients by correlating post-transplant microRNA levels to C-peptide levels 2 months later. Only miR-375 and miR-132 had prognostic potential for graft outcome, and none of the newly identified microRNAs outperformed miR-375 in multiple regression. In conclusion, this study reveals multiple beta cell-enriched microRNAs that are co-released with miR-375 and can be used as complementary biomarkers of beta cell death.

The role of beta-cell dysfunction in early type 1 diabetes

PURPOSE OF REVIEW

Emerging data have suggested that β-cell dysfunction may exacerbate the development and progression of type 1 diabetes (T1D). In this review, we highlight clinical and preclinical studies suggesting a role for β-cell dysfunction during the evolution of T1D and suggest agents that may promote β-cell health in T1D.

RECENT FINDINGS

Metabolic abnormalities exist years before development of hyperglycemia and exhibit a reproducible pattern reflecting progressive deterioration of β-cell function and increases in β-cell stress and death. Preclinical studies indicate that T1D may be prevented by modification of pathways impacting intrinsic β-cell stress and antigen presentation. Recent findings suggest that differences in metabolic phenotypes and β-cell stress may reflect differing endotypes of T1D. Multiple pathways representing potential drug targets have been identified, but most remain to be tested in human populations with preclinical disease.

SUMMARY

This cumulative body of work shows clear evidence that β-cell stress, dysfunction, and death are harbingers of impending T1D and likely contribute to progression of disease and insulin deficiency. Treatment with agents targeting β-cell health could augment interventions with immunomodulatory therapies but will need to be tested in intervention studies with endpoints carefully designed to capture changes in β-cell function and health.

Combined Analysis of GAD65, miR-375, and Unmethylated Insulin DNA Following Islet Transplantation in Patients With T1D

AIM

Several biomarkers have been proposed to detect pancreatic β cell destruction in vivo but so far have not been compared for sensitivity and significance.

METHODS

We used islet transplantation as a model to compare plasma concentrations of miR-375, 65-kDa subunit of glutamate decarboxylase (GAD65), and unmethylated insulin DNA, measured at subpicomolar sensitivity, and study their discharge kinetics, power for outcome prediction, and detection of graft loss during follow-up.

RESULTS

At 60 minutes after transplantation, GAD65 and miR-375 consistently showed near-equimolar and correlated increases proportional to the number of implanted β cells. GAD65 and miR-375 showed comparable power to predict poor graft outcome at 2 months, with areas under the curve of 0.833 and 0.771, respectively (P = 0.53). Using receiver operating characteristic analysis, we defined likelihood ratios (LRs) for rationally selected result intervals. In GADA-negative recipients (n = 28), GAD65 <4.5 pmol/L (LR = 0.15) and >12.2 pmol/L (LR = ∞) predicted good and poor outcomes, respectively. miR-375 could be used in all recipients irrespective of GAD65 autoantibody status (n = 46), with levels <1.4 pmol/L (LR = 0.14) or >7.6 pmol/L (LR = 9.53) as dual thresholds. The posttransplant surge of unmethylated insulin DNA was inconsistent and unrelated to outcome. Combined measurement of these three biomarkers was also tested as liquid biopsy for β cell death during 2-month follow-up; incidental surges of GAD65, miR-375, and (un)methylated insulin DNA, alone or combined, were confidently detected but could not be related to outcome.

CONCLUSIONS

GAD65 and miR-375 performed equally well in quantifying early graft destruction and predicting graft outcome, outperforming unmethylated insulin DNA.

A dual-label time-resolved fluorescence immunoassay for screening of osteoporosis based on simultaneous detection of C-terminal telopeptide (β-CTX) and aminoterminal propeptide (P1NP) of type I procollagen

Osteoporosis is a disease where increased bone weakness increases the risk of a broken bone. Until a broken bone occurs, there are typically no symptoms. Osteoporosis affects more than 75 million people in the United States, Europe and Japan. The diagnosis of osteoporosis is primarily determined by measuring bone mineral density using dual-energy X-ray absorptiometry, but for men under 50 years of age, premenopausal women should not be made on the basis of densitometric criteria alone. Bone biomarkers are a useful tool in detecting osteoporotic. A two-step dual-label time-resolved fluorescence immunoassay (TRFIA) was developed for the simultaneous detection of serum C-terminal telopeptide (β-CTX) and amino-terminal propeptide (P1NP) of Type I procollagen in a single run. The performance of this assay was first evaluated using clinical serum samples, and then compared with commercialized kits. The sensitivity of this assay for β-CTX was 1 ng/L (dynamic range, 0-1000 ng/L), and the sensitivity for P1NP detection was 1 μg/L (dynamic range, 1-1000 μg/L). High correlation coefficients (R) were obtained between the present dual-label TRFIA and commercially available kits (R = 0.99 for β-CTX and P1NP). The present dual-label TRFIA has high sensitivity, specificity and accuracy in clinical sample analysis. It is a good alternative to the single-label diagnostic methods.

Biomarkers of islet beta cell stress and death in type 1 diabetes

Recent work on the pathogenesis of type 1 diabetes has led to an evolving recognition of the heterogeneity of this disease, both with regards to clinical phenotype and responses to therapies to prevent or revert diabetes. This heterogeneity not only limits efforts to accurately predict clinical disease but also is reflected in differing responses to immunomodulatory therapeutics. Thus, there is a need for robust biomarkers of beta cell health, which could provide insight into pathophysiological differences in disease course, improve disease prediction, increase the understanding of therapeutic responses to immunomodulatory interventions and identify individuals most likely to benefit from these therapies. In this review, we outline current literature, limitations and future directions for promising circulating markers of beta cell stress and death in type 1 diabetes, including markers indicating abnormal prohormone processing, circulating RNAs and circulating DNAs.

Biomarkers in Islet Cell Transplantation for Type 1 Diabetes

PURPOSE OF REVIEW

Islet transplantation, an important approach to achieve insulin independence for individuals with type 1 diabetes, is limited by the lack of accurate biomarkers to track beta-cell death post islet infusion. In this review, we will discuss existing and recently described biomarkers.

RECENT FINDINGS

As beta cells are killed by the immune system, fragments of beta cell-specific cell-free DNA and proteins are released into the periphery. Several different strategies to identify these fragments have been described. Some circulating, non-coding microRNAs, particularly miRNA-375 are also showing potential to reflect the rate of beta cell loss post-clinical islet transplantation. Recent advances in identifying accurate beta cell-specific biomarkers such as differentially methylated insulin cell-free DNA and circulating miRNA-375 may help predict clinical outcomes. More studies are required to examine the robustness of these biomarkers to detect chronic beta-cell loss in islet transplantation recipients.

An analytical comparison of three immunoassay platforms for subpicomolar detection of protein biomarker GAD65

A disproportional increase of circulating GAD65 within hours from an intraportal islet allotransplantation has been validated as biomarker of beta cell loss and poor functional outcome. More sensitive assays are, however, needed to allow detection of episodes of subtle beta cell loss during late-stage graft rejection or in the peri-onset period of type 1 diabetes. We applied the same sandwich monoclonal antibody couple reactive towards the C- and N-terminus of GAD65 on three advanced immunoassay platforms—the Cytometric Bead Array (CBA, Becton, Dickinson and Company), ElectroChemiLuminescence ImmunoAssay (ECLIA, Meso Scale Discovery) and digital ELISA technology (Single Molecule Array—SIMOA, Quanterix. We then compared analytical performance (linearity, imprecision, limit of detection and functional sensitivity), correlation of results, and practicality. All evaluated techniques showed linearity up to at least 500 ng/dL (76.9 pmol/L). SIMOA achieved the lowest imprecision. The 3 platforms correlate well with each other and could all detect subpicomolar concentrations of GAD65 in plasma, but only SIMOA and CBA could quantify down to that range. SIMOA can achieve the highest sample throughput. The three methods tested allow sensitive detection of GAD65, but SIMOA appears best suited for automated quantification of subpicomolar concentrations.