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.

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

There is a clinical need for plasma tests to detect and quantify the in vivo destruction of pancreatic β-cells in type 1 diabetes. We previously developed a time-resolved fluorescence immunoassay (TRFIA) to glutamate decarboxylase 65 kDa (GAD65) (GAD65-TRFIA) that was able to detect the synchronous necrotic destruction of transplanted β-cells in the hours after their infusion in the liver. This GAD65-TRFIA, however, lacked sensitivity to detect continued β-cell rejection beyond this acute phase. The aim of present study was to gain at least an order of magnitude in analytical sensitivity by switching to Becton Dickinson cytometric bead array (CBA) (GAD65-CBA) enhanced sensitivity format, using the same couple of monoclonal antibodies. We compared the performances of GAD65-CBA and GAD65-TRFIA using Clinical and Laboratory Standards Institute protocols for linearity, imprecision, specificity, limit of detection, and functional sensitivity. We conducted a method comparison and assessed the biologic potential on samples from human recipients of islet grafts. The GAD65-CBA showed acceptable linearity and imprecision. Switching from TRFIA to CBA lowered functional sensitivity by a factor 35 and lowered limit of detection by a factor 11 with minimal need for method optimization. The enhanced sensitivity greatly expands the application domain of our biomarker and allowed for the first time to detect ongoing β-cell destruction up to at least 1 day after islet transplantation. We conclude that the GAD65-CBA is suitable for biological and clinical assessment of the real-time destruction of β-cells in intraportal transplantation.

Dynamics of bone loss in experimental periodontitis

A dynamic histomorphometric study of bone loss in periodontitis induced by inserting a thread ligature around the neck of the lower first molar of Wistar rats weighing 300 g. was performed. Bone formation fronts were labelled twice by tetracycline injection (day 1 and day 14). On day 16 the animals were divided into 4 groups: Two experimental (ligature in place) and two controls (no ligature). Animals in one experimental and one control groups were killed 72 hours post insertion, and the other two groups 96 hours post-insertion. Grinding sections of the first molar were obtained to perform histomorphometric studies on microphotographs taken under fluorescence microscopy. At 72 hours results showed total loss of the double labeling in the mesial wall, partial loss in the top of the crest and no loss in the distal wall. At 96 hours, loss of the double labeling at the top of the crest was greater, while only one label (the first) could be observed in the distal wall. These results show that in this periodontitis experimental model, bone loss is initiated and is more rapid in the bone remodeling (mesial) wall than in the modeling (distal) wall. This understanding of bone loss dynamics enables the characterization of the model employed herein, contributing to further studies on the course of periodontal disease under different experimental conditions.

Early steps in bone resorption in experimental periodontitis: a histomorphometric study

A histomorphometric study of the initial steps in the process of bone resorption of inflammatory origin is presented. The study was performed in a model of experimental periodontitis, in which plaque formation is induced by means of a cotton thread ligature placed around the neck of the first molar of Wistar rats. The treated animals were killed in groups after 24, 48, 72 and 96 hours. An equivalent number of untreated rats were employed as controls. After routine histologic processing mesiodistal sections were obtained. The histologic studies showed the sequence of events of the inflammatory process and bone resorption. The histomorphometric studies showed the concomitant increase in erosive areas and number of osteoclasts with the highest values at 72 hours. At 96 hours both parameters decreased. The results are discussed in the light of those afforded by other experimental models, in which bone resorption is induced by orthodontic forces. In these models the increase in the resorptive areas precedes the increase in the number of osteoclasts. The existence of two different mechanisms for the initiation of bone resorption, one which involves the action of an inflammatory environment and the other which results from the action of mechanical forces, is proposed.

Role of crevice in the occurrence of hemoglobin in saliva

The aim of the present study was to analyze the role of the gingival-periodontal component in the presence of blood in saliva. We studied a population of 184 adult patients composed of 101 totally edentulous patients with no oral mucosa lesions and 83 dentulous patients with clinically healthy gums. Saliva samples obtained by spontaneous salivation were collected in sterile containers. Qualitative and quantitative evaluation of each of the samples was performed. 67% of the dentulous patients tested positive for hemoglobin in saliva. None of the patients in the totally edentulous group exhibited hemoglobin in saliva. These data suggest that the periodontal condition is an essential factor for the presence of hemoglobin in saliva.

Use of Zircalloy to induce bone regeneration. A 2-year follow-up study

In a previous study we analyzed the behaviour of Zircalloy 4 particles employed in patients with significant loss of periodontal bone support which threatened the permanence in situ of the tooth. We herein present the results obtained after regular examination over a 2-year period of 6 patients submitted to this treatment. Our results reveal that all patients exhibited excellent gingivo-periodontal health with an increase in clinical insertion of 7 mm +/- 1 and a marked reduction in motility from 3 to 1. None of the cases featured added inflammation or expulsion of the implant material. In one of the cases it was possible to study the histology of the area by punch biopsy with a disposable needle (Sherwood-Medical). Analysis of the sample revealed the presence of bone tissue in intimate contact with implanted metallic particles of Zircalloy 4, producing osseointegration. This osseointegration would lead to filling of the periodontal bone defect. Macrophages loaded with metallic particles were found in the vicinity of particles which were not osseointegrated. These features may correspond to superficial areas related with soft tissue as observed in our study on alveolar filling in rats with the same type of particles.