Simultaneous Measurement of Plasma Concentrations of Proinsulin and C-Peptide and Their Ratio with a Trefoil-Type Time-Resolved Fluorescence Immunoassay

Baseline plasma proinsulin response to glucose for predicting therapeutic response to otelixizumab in recent-onset type 1 diabetes

AIMS

In recent-onset type 1 diabetes, clamp-derived C-peptide predicts good response to anti-CD3. Elevated proinsulin and proinsulin/C-peptide ratio (PI/CP) suggest increased metabolic/inflammatory beta cell burden. We reanalyzed trial data to compare the ability of baseline acutely glucose-stimulated proinsulin, C-peptide and PI/CP to predict functional outcome.

METHODS

Eighty recent-onset type 1 diabetes patients participated in the placebo-controlled otelixizumab (GSK; NCT00627146) trial. Hyperglycemic clamps were performed at baseline, 6, 12 and 18 months, involving 3 h of induced euglycemia, followed by acutely raising and maintaining glycemia to ≥ 10 mmol/l for 140 min. Plasma proinsulin, C-peptide and PI/CP were determined after acute (minute 0 at 10 mmol/l; PI0, CP0, PI/CP0) and sustained glucose stimulation (AUC between minutes 60-140). Outcome was assessed as change in AUC60-140 C-peptide from baseline.

RESULTS

In multiple linear regression, higher baseline (≥median [P50]) PI0 independently predicted preservation of beta cell function in response to anti-CD3 and interacted significantly with IAA. During follow-up, anti-CD3 tempered a further increase in PI/CP0, but not in PI0. CP0 outperformed PI0 and PI/CP0 for post-treatment monitoring.

CONCLUSIONS

In recent-onset type 1 diabetes, elevated acutely glucose-stimulated proinsulin may complement or replace acutely or sustainedly stimulated C-peptide release for identifying good responders to anti-CD3, but not as outcome measure.

A composite immune signature parallels disease progression across T1D subjects

At diagnosis, most people with type 1 diabetes (T1D) produce measurable levels of endogenous insulin, but the rate at which insulin secretion declines is heterogeneous. To explain this heterogeneity, we sought to identify a composite signature predictive of insulin secretion, using a collaborative assay evaluation and analysis pipeline that incorporated multiple cellular and serum measures reflecting β cell health and immune system activity. The ability to predict decline in insulin secretion would be useful for patient stratification for clinical trial enrollment or therapeutic selection. Analytes from 12 qualified assays were measured in shared samples from subjects newly diagnosed with T1D. We developed a computational tool (DIFAcTO, Data Integration Flexible to Account for different Types of data and Outcomes) to identify a composite panel associated with decline in insulin secretion over 2 years following diagnosis. DIFAcTO uses multiple filtering steps to reduce data dimensionality, incorporates error estimation techniques including cross-validation and sensitivity analysis, and is flexible to assay type, clinical outcome, and disease setting. Using this novel analytical tool, we identified a panel of immune markers that, in combination, are highly associated with loss of insulin secretion. The methods used here represent a potentially novel process for identifying combined immune signatures that predict outcomes relevant for complex and heterogeneous diseases like T1D.

Cell Mass Increase Associated with Formation of Glucose-Controlling β-Cell Mass in Device-Encapsulated Implants of hiPS-Derived Pancreatic Endoderm

Device-encapsulated human stem cell-derived pancreatic endoderm (PE) can generate functional β-cell implants in the subcutis of mice, which has led to the start of clinical studies in type 1 diabetes. Assessment of the formed functional β-cell mass (FBM) and its correlation with in vivo metabolic markers can guide clinical translation. We recently reported ex vivo characteristics of device-encapsulated human embryonic stem cell-derived (hES)-PE implants in mice that had established a metabolically adequate FBM during 50-week follow-up. Cell suspensions from retrieved implants indicated a correlation with the number of formed β cells and their maturation to a functional state comparable to human pancreatic β cells. Variability in metabolic outcome was attributed to differences in number of PE-generated β cells. This variability hinders studies on processes involved in FBM-formation. This study reports modifications that reduce variability. It is undertaken with device-encapsulated human induced pluripotent stem cell-derived-PE subcutaneously implanted in mice. Cell mass of each cell type was determined on intact tissue inside the device to obtain more precise data than following isolation and dispersion. Implants in a preformed pouch generated a glucose-controlling β-cell mass within 20 weeks in over 60% of recipients versus less than 20% in the absence of a pouch, whether the same or threefold higher cell dose had been inserted. In situ analysis of implants indicated a role for pancreatic progenitor cell expansion and endocrine differentiation in achieving the size of β- and α-cell mass that correlated with in vivo markers of metabolic control. Stem Cells Translational Medicine 2019;8:1296&1305.

Eu3+ /Sm3+ dual-label time-resolved fluoroimmunoassay for measurement of hepatitis C virus antibodies

AIM

To develop a new immunoassay based on the time-resolved fluorescence immunoassay (TRFIA) system for the simultaneous measurement of IgM and IgG antibodies to HCV.

METHODS

Coated recombinant HCV antigens and Eu³⁺ -labeled IgM and Sm³⁺ -labeled IgG antibodies were prepared. HCV-IgM/IgG TRFIA was established and optimized, followed by a methodological assessment. Data were expressed as x ¯ +SD and analyzed using the SPSS 13.0 software. The percentile method was used to calculate cutoff values.

RESULTS

The detection sensitivities of HCV-IgM and HCV-IgG were 0.06 S/CO and 0.15 S/CO, respectively. There was a good linear response from 1:40 to 1:40 960 for HCV-IgM and 1:20 to 1:40 960 for HCV-IgG, when samples strongly positive for HCV-IgM and HCV-IgG were serially diluted from 1:10 to 1:81 920. The average intra-assay coefficients of variation (CV) for HCV-IgM and -IgG were 3.45% and 3.71% and the inter-assay coefficients of variation (CV) were 6.49% and 6.79%, respectively. When HCV-negative/positive sera were tested by ELISA and using established kits, the negative, positive, and total conformity rates for HCV-IgM were 93.3% (28/30), 100% (25/25), and 96.4% (53/55), and those for HCV-IgG were 93.3% (28/30), 100% (35/35), and 96.9% (63/65), respectively. Additionally, the established kit exhibited good stability, with declines in fluorescence values to 11.1% and 9.5%, respectively, after storage at 37°C for 7 days.

CONCLUSION

We established a dual-label HCV-IgM/IgG TRFIA assay with a wide detection range, high specificity, high sensitivity, good stability, and good clinical value for the simultaneous measurement of HCV-IgM and HCV-IgG titers in a single test.

SLC30A8 polymorphism and BMI complement HLA-A*24 as risk factors for poor graft function in islet allograft recipients

AIMS/HYPOTHESIS

HLA-A*24 carriership hampers achievement of insulin independence in islet allograft recipients. However, less than half of those who fail to achieve insulin independence carry the allele. We investigated whether genetic polymorphism at the recipients' zinc transporter 8-encoding SLC30A8 gene (rs13266634) could complement their HLA-A*24 status in predicting functional graft outcome.

METHODS

We retrospectively analysed data of a hospital-based patient cohort followed for 18 months post transplantation. Forty C-peptide-negative type 1 diabetic individuals who received >2 million beta cells (>4000 islet equivalents) per kg body weight in one or two intraportal implantations under similar immunosuppression were genotyped for SLC30A8. Outcome measurements included achievement and maintenance of graft function. Metabolic benefit was defined as <25% CV of fasting glycaemia in the presence of >331 pmol/l C-peptide, in addition to achievement of insulin independence and maintenance of C-peptide positivity.

RESULTS

In multivariate analysis, HLA-A*24 positivity, presence of SLC30A8 CT or TT genotypes and BMI more than or equal to the group median (23.9 kg/m²) were independently associated with failure to achieve insulin independence (p = 0.015-0.046). The risk increased with the number of factors present (p < 0.001). High BMI interacted with SLC30A8 T allele carriership to independently predict difficulty in achieving graft function with metabolic benefit (p = 0.015). Maintenance of C-peptide positivity was mainly associated with older age at the time of implantation. Only HLA-A*24 carriership independently predicted failure to maintain acceptable graft function once achieved (p = 0.012).

CONCLUSIONS/INTERPRETATION

HLA-A*24, the SLC30A8 T allele and high BMI are associated with poor graft outcome and should be considered in the interpretation of future transplantation trials.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00798785 and NCT00623610.

Functional Beta Cell Mass from Device-Encapsulated hESC-Derived Pancreatic Endoderm Achieving Metabolic Control

Human stem cells represent a potential source for implants that replace the depleted functional beta cell mass (FBM) in diabetes patients. Human embryonic stem cell-derived pancreatic endoderm (hES-PE) can generate implants with glucose-responsive beta cells capable of reducing hyperglycemia in mice. This study with device-encapsulated hES-PE (4 × 10⁶ cells/mouse) determines the biologic characteristics at which implants establish metabolic control during a 50-week follow-up. A metabolically adequate FBM was achieved by (1) formation of a sufficient beta cell number (>0.3 × 10⁶/mouse) at >50% endocrine purity and (2) their maturation to a functional state comparable with human pancreatic beta cells, as judged by their secretory responses during perifusion, their content in typical secretory vesicles, and their nuclear NKX6.1-PDX1-MAFA co-expression. Assessment of FBM in implants and its correlation with in vivo metabolic markers will guide clinical translation of stem cell-derived grafts in diabetes.

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Human stem cell-derived pancreatic precursors generate functional beta cell mass

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Cellular markers identify metabolically adequate human stem cell-generated implants

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Significance of determining beta cell number and maturation in implants

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Functional implants differ in endocrine composition from endocrine pancreas

Prediction of Impending Type 1 Diabetes through Automated Dual-Label Measurement of Proinsulin:C-Peptide Ratio

BACKGROUND

The hyperglycemic clamp test, the gold standard of beta cell function, predicts impending type 1 diabetes in islet autoantibody-positive individuals, but the latter may benefit from less invasive function tests such as the proinsulin:C-peptide ratio (PI:C). The present study aims to optimize precision of PI:C measurements by automating a dual-label trefoil-type time-resolved fluorescence immunoassay (TT-TRFIA), and to compare its diagnostic performance for predicting type 1 diabetes with that of clamp-derived C-peptide release.

METHODS

Between-day imprecision (n = 20) and split-sample analysis (n = 95) were used to compare TT-TRFIA (AutoDelfia, Perkin-Elmer) with separate methods for proinsulin (in-house TRFIA) and C-peptide (Elecsys, Roche). High-risk multiple autoantibody-positive first-degree relatives (n = 49; age 5-39) were tested for fasting PI:C, HOMA2-IR and hyperglycemic clamp and followed for 20-57 months (interquartile range).

RESULTS

TT-TRFIA values for proinsulin, C-peptide and PI:C correlated significantly (r2 = 0.96-0.99; P<0.001) with results obtained with separate methods. TT-TRFIA achieved better between-day %CV for PI:C at three different levels (4.5-7.1 vs 6.7-9.5 for separate methods). In high-risk relatives fasting PI:C was significantly and inversely correlated (rs = -0.596; P<0.001) with first-phase C-peptide release during clamp (also with second phase release, only available for age 12-39 years; n = 31), but only after normalization for HOMA2-IR. In ROC- and Cox regression analysis, HOMA2-IR-corrected PI:C predicted 2-year progression to diabetes equally well as clamp-derived C-peptide release.

CONCLUSIONS

The reproducibility of PI:C benefits from the automated simultaneous determination of both hormones. HOMA2-IR-corrected PI:C may serve as a minimally invasive alternative to the more tedious hyperglycemic clamp test.

HLA-A*24 Carrier Status and Autoantibody Surges Posttransplantation Associate With Poor Functional Outcome in Recipients of an Islet Allograft

OBJECTIVE

We investigated whether changes in islet autoantibody profile and presence of HLA risk markers, reported to predict rapid β-cell loss in pre-type 1 diabetes, associate with poor functional outcome in islet allograft recipients.

RESEARCH DESIGN AND METHODS

Forty-one patients received ≥2.3 million β-cells/kg body wt in one to two intraportal implantations. Outcome after 6-18 months was assessed by C-peptide (random and stimulated), insulin dose, and HbA1c.

RESULTS

Patients carrying HLA-A*24-positive or experiencing a significant autoantibody surge within 6 months after the first transplantation (n = 19) had lower C-peptide levels (P ≤ 0.003) and higher insulin needs (P < 0.001) despite higher HbA1c levels (P ≤ 0.018). They became less often insulin independent (16% vs. 68%, P = 0.002) and remained less often C-peptide positive (47% vs. 100%, P < 0.001) than recipients lacking both risk factors. HLA-A*24 positivity or an autoantibody surge predicted insulin dependence (P = 0.007).

CONCLUSIONS

HLA-A*24 and early autoantibody surge after islet implantation associate with poor functional graft outcome.

Hyperglycemic clamp and oral glucose tolerance test for 3-year prediction of clinical onset in persistently autoantibody-positive offspring and siblings of type 1 diabetic patients

CONTEXT AND OBJECTIVE

In preparation of future prevention trials, we aimed to identify predictors of 3-year diabetes onset among oral glucose tolerance test (OGTT)- and hyperglycemic clamp-derived metabolic markers in persistently islet autoantibody positive (autoAb(+)) offspring and siblings of patients with type 1 diabetes (T1D).

DESIGN

The design is a registry-based study.

SETTING

Functional tests were performed in a hospital setting.

PARTICIPANTS

Persistently autoAb(+) first-degree relatives of patients with T1D (n = 81; age 5-39 years).

MAIN OUTCOME MEASURES

We assessed 3-year predictive ability of OGTT- and clamp-derived markers using receiver operating characteristics (ROC) and Cox regression analysis. Area under the curve of clamp-derived first-phase C-peptide release (AUC(5-10 min); min 5-10) was determined in all relatives and second-phase release (AUC(120-150 min); min 120-150) in those aged 12-39 years (n = 62).

RESULTS

Overall, the predictive ability of AUC(5-10 min) was better than that of peak C-peptide, the best predictor among OGTT-derived parameters (ROC-AUC [95%CI]: 0.89 [0.80-0.98] vs 0.81 [0.70-0.93]). Fasting blood glucose (FBG) and AUC(5-10 min) provided the best combination of markers for prediction of diabetes within 3 years; (ROC-AUC [95%CI]: 0.92 [0.84-1.00]). In multivariate Cox regression analysis, AUC(5-10 min)) (P = .001) was the strongest independent predictor and interacted significantly with all tested OGTT-derived parameters. AUC(5-10 min) below percentile 10 of controls was associated with 50-70% progression to T1D regardless of age. Similar results were obtained for AUC(120-150 min).

CONCLUSIONS

Clamp-derived first-phase C-peptide release can be used as an efficient and simple screening strategy in persistently autoAb(+) offspring and siblings of T1D patients to predict impending diabetes.

Composition and function of macroencapsulated human embryonic stem cell-derived implants: comparison with clinical human islet cell grafts

β-Cells generated from large-scale sources can overcome current shortages in clinical islet cell grafts provided that they adequately respond to metabolic variations. Pancreatic (non)endocrine cells can develop from human embryonic stem (huES) cells following in vitro derivation to pancreatic endoderm (PE) that is subsequently implanted in immune-incompetent mice for further differentiation. Encapsulation of PE increases the proportion of endocrine cells in subcutaneous implants, with enrichment in β-cells when they are placed in TheraCyte-macrodevices and predominantly α-cells when they are alginate-microencapsulated. At posttransplant (PT) weeks 20-30, macroencapsulated huES implants presented higher glucose-responsive plasma C-peptide levels and a lower proinsulin-over-C-peptide ratio than human islet cell implants under the kidney capsule. Their ex vivo analysis showed the presence of single-hormone-positive α- and β-cells that exhibited rapid secretory responses to increasing and decreasing glucose concentrations, similar to isolated human islet cells. However, their insulin secretory amplitude was lower, which was attributed in part to a lower cellular hormone content; it was associated with a lower glucose-induced insulin biosynthesis, but not with lower glucagon-induced stimulation, which together is compatible with an immature functional state of the huES-derived β-cells at PT weeks 20-30. These data support the therapeutic potential of macroencapsulated huES implants but indicate the need for further functional analysis. Their comparison with clinical-grade human islet cell grafts sets references for future development and clinical translation.

Detection of Hepatitis B Virus Large Surface Protein Using a Time-Resolved Immunofluorometric Assay

BACKGROUND

To establish a novel method based on time-resolved immunofluorometric assay (TR-IFMA) with higher sensitivity and a broader detection range for detecting serum hepatitis B virus large surface protein (L protein).

METHODS

The precision, sensitivity, specificity, coefficient of recovery, and stability of the assay were evaluated and comparison with the classical enzyme-linked immunosorbent assay (ELISA) was also executed.

RESULTS

The precision, specificity, and sensitivity of the TR-IFMA were clearly better than ELISA. Particularly, the sensitivity was 0.1 ng/ml; moreover, the specificity was 100%, 96%, 92.5%, 96.9%, 97.8%, and 100% in the sera of healthy blood donors, systemic lupus erythematosus (SLE) patients, rheumatoid arthritis (RA) patients, hepatitis C virus (HCV) patients, cytomegalovirus (CMV) infection patients, and pregnant patients, respectively. Meanwhile, we observed that the established TR-IFMA kit has a wider acceptable linear range of 0.63-10,367 ng/ml rather than the regular commercial ELISA kit having range of only 10.12-1095.9 ng/ml. Subsequently, correlation coefficient between the TR-IFMA and ELISA was 0.8009. The intra- and interassay precision rates were less than 5% for three different concentrations. The average recovery rate for L protein was 101.17%. In sum, the established assay kit performed better in terms of stability than the commercial ELISA kit.

CONCLUSION

The TR-IFMA that we developed for L protein presented a higher sensitivity and wider detecting range than regular commercial ELISA. Therefore, this TR-IFMA has promising value both in the screening of HBV and monitoring of antiviral therapy.

Simultaneous determination of the cytokeratin 19 fragment and carcinoembryonic antigen in human serum by magnetic nanoparticle-based dual-label time-resolved fluoroimmunoassay

A magnetic nanoparticle-based dual-label TRFIA employing europium and samarium chelate labels for simultaneous determination of CYFRA 21-1 and CEA.

Validation of an enzyme-linked immunosorbent assay for C-peptide analysis in Cameroon

AIMS

To validate an ELISA method for C-peptide analysis in Cameroon.

METHODS

We evaluated the linearity, detection limit, functional sensitivity, precision and accuracy, and further investigated for cross-reactivity by proinsulin, and interferences by lipids, bilirubin and hemoglobin. This method was compared with the Roche electrochemiluminescence immunoassay. C-peptide stability was assessed following a series of freeze-thaw cycles, and after storage at room temperature. The C-peptide reference range was determined by analyzing fifty plasma samples of Cameroonians without diabetes.

RESULTS

The ELISA was linear at least up to 7.09 μg/L, and had a detection limit of 0.09 μg/L, and a functional sensitivity of 0.32 μg/L. The inter- and intraassay %CV were 2.9-9.9%, and 5.2-9.4%, respectively. Recoveries were 81-94% in serum, and 93-98% in buffer. Comparison with the ECLIA yielded a good correlation coefficient (R(2)=0.98). There was no cross-reactivity with proinsulin, and no interference with lipids, bilirubin and hemoglobin. C-peptide was stable at room temperature for 24 h and up to 7 freeze-thaw cycles for medium (1-6 μg/L) and high (>6 μg/L) levels (<-15°C and <-70°C). The reference range for C-peptide was 0.38-3.63 μg/L.

CONCLUSIONS

This method is suitable for C-peptide analysis in low-income countries like Cameroon.

Detection of anticardiolipin antibody IgG by time-resolved fluoroimmunoassay

In an effort to improve the quantitative detection of anticardiolipin antibodies (aCL) IgG so as to classify patients correctly as antiphospholipid syndrome (APS) positive, we developed a new immunoassay based on a sandwich time-resolved fluoroimmunoassay (TRFIA) using the complex of cardiolipin plus bovine β(2)GPI as antigen and Eu(3+)-labeled rabbit antihuman IgG as conjugate. The precision, sensitivity, specificity, and stability of the assay were evaluated, and comparison with the classical ELISA was also made. The aCL IgG TRFIA kit we established had a wider detectable range than three commercial ELISA ones from different manufacturers when a specimen was diluted, with strong positive result from 1:12.5 to 1:204,800. The average intra-assay and inter-assay CVs detected by the aCL IgG TRFIA was 3.14 and 3.70 %, respectively. The sensitivity was 0.1 GPL U/ml, and the clinical diagnostic specificity was 98 %. The established assay kit also behaved better in stability than the commercial ELISA ones. Additionally, the immunoassay we established correlated well with the ELISA, and the correlation coefficient was 0.975. We thus conclude that the TRFIA we developed for aCL IgG detection gives promise to a more sensitive and reliable diagnosis of APS and has potential value for large-scale screening programs.

Application of size-exclusion chromatography in the investigation of the in vitro stability of proinsulin and its cleaved metabolites in human serum and plasma

To help ensure reliability of proinsulin measurements and define the optimal matrix for conducting routine bioanalysis of this prognostic biomarker, we undertook a systematic evaluation of its in vitro stability. For this study, we subjected mono-radioiodinated forms of hPI and its cleaved metabolites to size-exclusion chromatography (FPLC-SEC employing a Superdex-75 10/30 HR column) to characterize their elution profiles following incubation in human serum and plasma. We determined that intact hPI is a substrate for serine-like protease(s) that are present in human serum. Furthermore, RIA analysis of the elution profile of unlabeled peptide demonstrated that the B-C junction is cleaved preferentially. Thus, in vitro degradation of hPI represents a potential pathway for the formation of cleaved metabolites. Our findings confirmed that EDTA plasma is the preferred matrix for quantitative determination of intact hPI and its cleaved metabolites. We concluded the SEC strategy employed in this study is broadly applicable to evaluating the in vitro stability of other peptides/proteins of diagnostic or therapeutic interest.