Orientation of capture antibodies on gold nanoparticles to improve the sensitivity of ELISA-based medical devices.

The sensitivity of ELISA-based devices strongly depends on the right orientation of antibodies on the sensor surface. The aim of this work was to increase the analytical performance of a commercial ELISA-based medical device (VIDAS®), thanks to the specific orientation of antibodies on gold nanostructured disposables. For this purpose, fPSA VIDAS® assay was used as model and the disposable providing the antigen binding surface (SPR®) was functionalized with gold nanostructures coated with monovalent half-fragment antibodies (reduced IgG, rIgG). The functionalization of polystyrene SPRs® with gold nanostructures was achieved through a one-step incubation of gold dispersions in a mixture of non-toxic solvents. Five different concentrations of gold nanoparticles (NPs) were tested with a maximum fluorescence enhancement for NPs density around 3-8 *103 NPs/µm2 (752 ± 11 RFV vs 316 ± 5 RFV of bare SPRs®). The comparison of the dose-response curve obtained with commercial and gold coated-SPRs® revealed a significant improvement (p < 0.0001) of the analytical sensitivity of the VIDAS® system using nanostructured disposables. This improved version of SPRs® allows to distinguish small variations of fPSA concentrations opening the way to the application of this biomarker to other kinds of cancer as recently described in the literature.

Sensing of Catecholamine in Human Urine Using a Simple Colorimetric Assay Based on Direct Melanochrome and Indolequinone Formation.

We used the first enzyme-free synthesis and stabilization of soluble melanochrome (MC) and 5,6-indolequinone (IQ) derived from levodopa (LD), dopamine (DA), and norepinephrine (NE) oxidation to develop a simple colorimetric assay for catecholamine detection in human urine, also elucidating the time-dependent formation and molecular weight of MC and IQ using UV-Vis spectroscopy and mass spectrometry. The quantitative detection of LD and DA was achieved in human urine using MC as a selective colorimetric reporter to demonstrate the potential assay applicability in a matrix of interest in therapeutic drug monitoring (TDM) and in clinical chemistry. The assay showed a linear dynamic range between 5.0 mg L-1 and 50.0 mg L-1, covering the concentration range of DA and LD found in urine samples from, e.g., Parkinson's patients undergoing LD-based pharmacological therapy. The data reproducibility in the real matrix was very good within this concentration range (RSDav% 3.7% and 6.1% for DA and LD, respectively), also showing very good analytical performances with the limits of detection of 3.69 ± 0.17 mg L-1 and 2.51 ± 0.08 mg L-1 for DA and LD, respectively, thus paving the way for the effective and non-invasive monitoring of dopamine and levodopa in urine from patients during TDM in Parkinson's disease.

Serotonin-Derived Fluorophore: A Novel Fluorescent Biomaterial for Copper Detection in Urine.

We took advantage of the fluorescent features of a serotonin-derived fluorophore to develop a simple and low-cost assay for copper in urine. The quenching-based fluorescence assay linearly responds within the concentration range of clinical interest in buffer and in artificial urine, showing very good reproducibility (CVav% = 4% and 3%) and low detection limits (16 ± 1 µg L-1 and 23 ± 1 µg L-1). The Cu2+ content was also estimated in human urine samples, showing excellent analytical performances (CVav% = 1%), with a limit of detection of 59 ± 3 µg L-1 and a limit of quantification of 97 ± 11 µg L-1, which are below the reference value for a pathological Cu2+ concentration. The assay was successfully validated through mass spectrometry measurements. To the best of our knowledge, this is the first example of copper ion detection exploiting the fluorescence quenching of a biopolymer, offering a potential diagnostic tool for copper-dependent diseases.

A method to obtain purified free light chain monomers and dimers from urine samples of patients with multiple myeloma.

Antibody light chains are synthesized in excess by plasma cells, and this excess can be secreted into biological fluids as dimers or monomers in various proportions. Structural differences between monomers or dimers of free light chains (FLC) can affect their biological functions and possibly their pathogenicity. They also may exhibit differential immune reactivity, perhaps explaining discrepant quantifications when measured by different immunoreagents. Having purified FLC monomers and dimers available can be useful for studying their properties. Here we propose a simple preparatory procedure to purify FLC monomers and dimers from urine samples of patients with plasma cell disorders. Two representative urine samples containing lambda or kappa FLC were loaded into a nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The gel strips containing separate monomers and dimers were excised, electroeluted, and the FLC recovered. The FLC were recovered from SDS-PAGE gel in sufficient amounts to be quantified by UV and two automated nephelometric assays immunochemical. The procedure was found to be simple, reproducible, and with a high yield, thus offering the opportunity to compare different assays. Not all urine samples are suitable for this procedure, but this approach allows for the purification of FLC monomers and dimers from many selected urine samples which maintain their oligomeric organization.

The Journey of Human Transthyretin: Synthesis, Structure Stability, and Catabolism.

Transthyretin (TTR) is a homotetrameric protein mainly synthesised by the liver and the choroid plexus whose function is to carry the thyroid hormone thyroxine and the retinol-binding protein bound to retinol in plasma and cerebrospinal fluid. When the stability of the tetrameric structure is lost, it breaks down, paving the way for the aggregation of TTR monomers into insoluble fibrils leading to transthyretin (ATTR) amyloidosis, a progressive disorder mainly affecting the heart and nervous system. Several TTR gene mutations have been characterised as destabilisers of TTR structure and are associated with hereditary forms of ATTR amyloidosis. The reason why also the wild-type TTR is intrinsically amyloidogenic in some subjects is largely unknown. The aim of the review is to give an overview of the TTR biological life cycle which is largely unknown. For this purpose, the current knowledge on TTR physiological metabolism, from its synthesis to its catabolism, is described. Furthermore, a large section of the review is dedicated to examining in depth the role of mutations and physiological ligands on the stability of TTR tetramers.

A biomimetic enzyme-linked immunosorbent assay (BELISA) for the analysis of gonadorelin by using molecularly imprinted polymer-coated microplates.

An original biomimetic enzyme-linked immunoassay (BELISA) to target the small peptide hormone gonadorelin is presented. This peptide has been recently listed among the substances banned in sports by the World Antidoping Agency (WADA) since its misuse by male athletes triggers testosterone increase. Hence, in response to this emerging issue in anti-doping controls, we proposed BELISA which involves the growth of a polynorepinephrine (PNE)-based molecularly imprinted polymer (MIP) directly on microwells. PNE, a polydopamine (PDA) analog, has recently displayed impressive performances when it was exploited for MIP preparation, giving even better results than PDA. Gonadorelin quantification was accomplished via a colorimetric indirect competitive bioassay involving the competition between biotinylated gonadorelin linked to the signal reporter and the unlabeled analyte. These compete for the same MIP binding sites resulting in an inverse correlation between gonadorelin concentration and the output color signal (λ = 450 nm). A detection limit of 277 pmol L-1 was achieved with very good reproducibility in standard solutions (avCV% = 4.07%) and in urine samples (avCV% = 5.24%). The selectivity of the assay resulted adequate for biological specimens and non-specific control peptides. In addition, the analytical figures of merit were successfully validated by mass spectrometry, the reference anti-doping benchtop platform for the analyte. BELISA was aimed to open real perspectives for PNE-based MIPs as alternatives to antibodies, especially when the target analyte is a poorly or non-immunogenic small molecule, such as gonadorelin. Biomimetic enzyme-linked immunosorbent assay (BELISA).

Signal Enhancement in Oriented Immunosorbent Assays: A Balance between Accessibility of Antigen Binding Sites and Avidity.

The sensitivity of immunoassays was reported to be increased by the orientation of antibodies. We investigated how the size and valence of antigens and orientation and valence of antibodies contribute to the analytical sensitivity of ELISA. Antigens differing in size and number of epitopes were compared using oriented and non-oriented ELISAs: the orientation of antibodies was obtained coating half-fragment antibodies on maleimide microplates, while, in non-oriented ELISA, whole antibodies were randomly physisorbed. The oriented assay performed better than the non-oriented one at each concentration (0.4-3.3 ng/mL) of a small monomeric antigen (cardiac Troponin I, 24 kDa, Rh 3 nm). No significant differences were observed with a large monovalent antigen (prostate-specific antigen-alpha(1) antichymotrypsin, 90 kDa, Rh > 3 nm), since its steric hindrance overcame the increased availability of antigen binding sites given by orientation. Large multivalent antigens (ferritin, 280 kDa, Rh 6 nm; α-fetoprotein, >70 kDa, Rh > 3.3 nm) performed better in non-oriented assays. In this case, the repeated epitopes on the surface of the antigens favored the engagement of both antigen binding sites of the whole IgG, thus suggesting that avidity represented the leading force in this experimental setting. In conclusion, the design of high-sensitivity ELISAs should consider the dimension and valency of antigens in addition to the affinity and avidity of antibodies.

C-C motive chemokine ligand 2 and thromboinflammation in COVID-19-associated pneumonia: A retrospective study.

PURPOSE: A derangement of the coagulation process and thromboinflammatory events has emerged as pathologic characteristics of severe COVID-19, characterized by severe respiratory failure. CC motive chemokine ligand 2 (CCL2), a chemokine originally described as a chemotactic agent for monocytes, is involved in inflammation, coagulation activation and neoangiogenesis. We investigated the association of CCL2 levels with coagulation derangement and respiratory impairment in patients with COVID-19. METHODS: We retrospectively evaluated 281 patients admitted to two hospitals in Italy with COVID-19. Among them, CCL2 values were compared in different groups (identified according to D-dimer levels and the lowest PaO2/FiO2 recorded during hospital stay, P/Fnadir) by Jonckheere-Terpstra tests; linear regression analysis was used to analyse the relationship between CCL2 and P/Fnadir. We performed Mann-Whitney test and Kaplan-Meier curves to investigate the role of CCL2 according to different clinical outcomes (survival and endotracheal intubation [ETI]). RESULTS: CCL2 levels were progressively higher in patients with increasing D-dimer levels and with worse gas exchange impairment; there was a statistically significant linear correlation between log CCL2 and log P/Fnadir. CCL2 levels were significantly higher in patients with unfavourable clinical outcomes; Kaplan-Meier curves for the composite outcome death and/or need for ETI showed a significantly worse prognosis for patients with higher (> median) CCL2 levels. CONCLUSIONS: CCL2 correlates with both indices of activation of the coagulation cascade and respiratory impairment severity, which are likely closely related in COVID-19 pathology, thus suggesting that CCL2 could be involved in the thromboinflammatory events characterizing this disease.

Data about performances of whole and monovalent half-fragments antibodies in immunosorbent assays.

The data here presented are related to the research article entitled "Sensitivity and reproducibility enhancement in enzyme immunosorbent assays based on half fragment antibodies" [1] aimed to compare the performance in ELISA of whole antibodies and their corresponding monovalent half-fragments obtained by reduction. Half-fragment antibodies represent an interesting method to orient antibodies in high-sensitive immunoassays taking advantage of the free sulfhydryl groups of the hinge region [2], [3], [4] that allow their oriented binding on maleimide functionalized microplates. Data here presented describe the contribution of both chemical reduction and orientation on the antigen binding capacity of whole and half-fragments antibodies. For this purpose, monoclonal anti-horseradish peroxidase (anti-HRP) or monoclonal anti-fPSA antibodies, and their respective half-fragments, were coated on polystyrene or maleimide functionalized microplates. The antigen binding capability was analyzed by in-house enzyme linked immunosorbent assays. These data would be used for further studies on the development of oriented immunoassays based on half fragment antibodies.

Sensitivity and reproducibility enhancement in enzyme immunosorbent assays based on half fragment antibodies.

The free sulfhydryl groups of the hinge region of monovalent antibody fragments (rIgG) allow the orientation of rIgG on functionalized surfaces in immunosensors. To evaluate the contribution of reduction and orientation on signal enhancement we compared the performance of whole antibodies and their rIgG in ELISA performed on polystyrene or maleimide-functionalized microplates. Monoclonal anti-horseradish peroxidase (anti-HRP) and monoclonal anti-fPSA antibodies (1 mg/mL) were reduced with 2-mercaptoethylamine (53 mM). Western blot confirmed the presence of rIgG as a band at 75 kDa, detectable only by anti-heavy chain but not by anti-light chain antibodies, suggesting a possible folding rearrangement. Using anti-HRP we confirmed the retention of the antigen binding capacity of rIgG. Moreover, we observed a signal enhancement for rIgG even if randomly absorbed on polystyrene [linear regression slope (95%CI): rIgG 0.524 (0.434-0.614), IgG 0.370 (0.430-0.399); P = 0.0016] suggesting that chemical reduction might affect the antigen binding capacity of antibodies. ELISA with anti-fPSA rIgG coated on polystyrene confirmed these observations. Oriented anti-fPSA rIgG on a maleimide surface showed comparable signals to the assay performed on polystyrene for each analyzed concentration of antigen (PANOVA = 0.1980), anyway, with a significant improvement of the repeatability likely providing a more homogeneous capturing surface (SD rIgGmaleimide-rIgGpolystirene: fPSA 0.725 ng/mL:0.74-2.89; 1.45 ng/mL:1.56-8.69; 3.625 ng/mL:3.52-15.03; 7.25 ng/mL:7.78-18.44).

Free light chain UV quantification compared with immunochemical measurement: How dimers and monomers may influence the results.

Serum κ and λ free light chain (FLC) levels are important for the management of plasma cell disorders. Immunochemical measurements on automated platforms with different reagents occasionally return different results that make them not interchangeable. The reasons for this behaviour are not clear and it is not known which result is the most accurate. The aim of the study is to quantify naturally occurring FLCs with a reference method (UV absorbance) in a sample devoid of other sources of UV absorbance. This was possible on a particular urine sample containing only lambda FLC proteins, dialyzed to clear it from low molecular weight UV absorbing compounds. The sample was submitted to Fast Protein Liquid Chromatography separation with a size-exclusion column in order to separate the FLC monomers and dimers. FLCs were also measured with the Freelite and N Latex FLC methods and the results were compared. The results demonstrated that the amount of FLC calculated on the basis of UV absorbance was overestimated by both immunochemical methods, and that the amount measured by the two reagents was affected by the different proportions of dimers or monomers. The present findings may be useful for the comprehension of the immunochemical measurement of FLC.

Inter-assay variability in automated serum free light chain assays and their use in the clinical laboratory.

Serum κ and λ free light chain levels are markers of plasma cell proliferation, and their measurements have been included in recent guidelines by the International Myeloma Working Group for the management of patients with plasma cellular dyscrasias. Five in vitro diagnostic methods for the immunochemical quantification of serum free light chains (FLC) are available, three based on polyclonal antibodies (Freelite®, The Binding Site; FLC ELISA κ and λ, Sebia; human κ and λ FLC, Diazyme Laboratories) and two on monoclonal antibodies (N Latex FLC, Siemens Healthineers; Seralite®, Sebia). Several studies have shown that these methods cannot be used interchangeably for the follow-up of patients because measured κ and λ FLC concentrations may differ significantly, especially at high levels. Because no international reference material for the measurement of FLC is available, it is not possible to establish which method is the most accurate. For this reason, knowledge about the analytical and diagnostic performances of the assays used is important. The aim of this review is to describe the main analytical features of the κ and λ FLC assays and how they may influence the clinical use of these parameters.

Dabrafenib and Trametinib prolong coagulation through the inhibition of tissue factor in BRAFv600e mutated melanoma cells in vitro.

BACKGROUND: Neoplastic cells promote a hypercoagulable state by the expression of cell surface proteins, such as tissue factor. In BRAFv600 mutated melanoma patients upon BRAF inhibitors, a hypercoagulable state correlates with prognosis, while a down-regulation of the hemostatic parameters is observed in patients responders as compared to non responders. The present study was intended to better clarify the strict relationship between coagulation mediators and target therapy in melanoma. METHODS: The expression of tissue factor was investigated after the treatment with the BRAF inhibitor Dabrafenib and the MEK inhibitor Trametinib in the BRAFv600e mutated melanoma cell lines A-375 and SK-MEL-28, together with its ability to activate the coagulation cascade. RESULTS: Dabrafenib and Trametinib caused the down-regulation of TF in both cell lines A-375 and SK-MEL-28. For the cell line A-375 the effect was evident both at RNA and procoagulant activity; for the cell line SK-MEL-28 only at RNA level without any variation of the protein. Interestingly, when in contact with plasma deficient of factor VII, both cell lines were not able to activate the coagulation cascade. CONCLUSIONS: The present study provides the first in vitro observation that tissue factor expressed in melanoma cells may contribute to the modulation of the coagulation state of patients in the treatment with BRAF inhibitors.

Different immunoreactivity of monomers and dimers makes automated free light chains assays not equivalent.

Background The automated immunochemical serum free light chains (FLC) assays, Freelite (a polyclonal antiserum) and N Latex FLC (a mixture of monoclonal antibodies), are not interchangeable, as they may provide different results on a same sample. This study was aimed to establish if the calibrators contain FLC oligomers, and if different reactivity against monomers and dimers contributes to the discrepancy. Methods Gel filtration chromatography fractions of the calibrators were subjected to a Western blot (WB) and analyzed by each reagent. The procedure was repeated after pretreating the N Latex FLC calibrator with the reducing agent dithiothreitol (DTT). Results Both calibrators contain FLC dimers and monomers. Both reagents detect (with different sensitivity) FLC kappa monomers and dimers; instead, Freelite detects only FLC lambda dimers, while N Latex FLC detects only FLC monomers. After DTT treatment, only the N Latex lambda still detects FLC with reduced protein thiols, while the reactivity of all other reagents is abolished. Conclusions Due to their different reactivity against FLC monomers and oligomers, the Freelite and N Latex FLC are calibrated against different components of their own calibrators, making the two reagents not equivalent. The redox status of FLC determines the immunoreactivity not only of FLC dimers, but also of the monomers.

γ-Glutamyltransferase Fractions in Obese Subjects with Type 2 Diabetes: Relation to Insulin Sensitivity and Effects of Bariatric Surgery.

BACKGROUND/OBJECTIVES: Gamma-glutamyltranspeptidase (GGT) levels are an independent risk marker for the development of type 2 diabetes (T2DM). We investigated the relationship between the newly identified serum GGT fractions and glucose metabolism in obese subjects before and after bariatric surgery. SUBJECTS/METHODS: Twenty-nine T2DM subjects, wait-listed for Roux-en-Y gastric bypass (RYGB; n = 21) or laparoscopic sleeve gastrectomy (LSG; n = 8), received a 5-h mixed meal test before (T0), 15 days (T15), and 1 year after surgery (T365). Insulin sensitivity was assessed by the OGIS index and ß-cell function by C-peptide analysis; fractional GGT (b-, s-, m-, and f-GGT) analysis was performed by gel-filtration chromatography. RESULTS: At T15, total GGT activity decreased by 40% after LSG (p = 0.007) but remained unchanged after RYGB. At T365, all patients showed a reduction in total GGT, in particular b-GGT (≥ 60%) and m-GGT (≥ 50%). In patients with biopsy-proven steatohepatitis (n = 10), total, b-, s-, and m-GGT fractions at T0 were significantly higher than in patients with low-grade steatosis (p = 0.016, 0.0003, and 0.005, respectively); at T365, there was a significant fall in total GGT as well as in each fraction in both groups. In a multiple regression model, b-GGT was the only fraction related to insulin sensitivity (p = 0.016; ß coeff. = - 14.0) independently of BMI, fasting glucose, and triglycerides. CONCLUSIONS: While GGT activity is generally associated with impaired glucose metabolism, fractional GGT analysis showed that the b-GGT fraction specifically and independently tracks with insulin resistance.

ß-trace protein is highly removed during haemodialysis with high-flux and super high-flux membranes.

BACKGROUND: Serum ß-trace protein (ßTP, MW 23-29 kDa) is a marker of GFR impairment in renal patients. Recent papers propose to predict residual renal function (RRF) in maintenance haemodialysis (MHD) patients from serum concentrations of ßTP and other small proteins, avoiding the collection of urine. Few data are available on the removal of ßTP in patients treated with dialysis membranes with different flux characteristics. The aim of this study was to evaluate the effects of haemodialysis with low-flux, high-flux and super high-flux membranes on serum concentrations of ßTP in MHD patients with null RRF. METHODS: Serum ßTP concentrations were measured before and after the first dialysis of the week in 51 MDH patients treated by low-flux (n = 24), high-flux (n = 17), or super high-flux (n = 10) membranes. The removal of ß2-microglobulin (ß2M, MW 11.8), cystatin C (Cys, MW 13.3), urea and creatinine was also analyzed. RESULTS: Low-flux membranes did not remove ßTP, ß2M and Cys whose concentration increased at the end of dialysis. High-flux membrane removed more efficiently ß2M and Cys than ßTP. Super high-flux membrane had the highest efficiency to remove ßTP: mean reduction ratio (RR) 53.4%, similar to ß2M (59.5%), and Cys (62.0%). CONCLUSIONS: In conclusion, the plasma clearance of small proteins and particularly of ßTP is dependent from the permeability of the dialysis membranes Therefore, the reliability of the formulas proposed to predict RRF from serum ßTP and other LMWP may be affected by the different permeability of the dialysis membranes.

Serological screening for Celiac Disease in 382 pre-schoolers with Autism Spectrum Disorder.

BACKGROUND: Recent investigations suggest a possible common genetic background between Autism Spectrum Disorders (ASD) and Celiac Disease (CD). However, studies regarding this association are scarce and often limited by the small sample sizes and/or large heterogeneity among ASD groups in terms of demographic and clinical features. The present study aims to investigate the overall CD prevalence (biopsy proven-CD patients plus screening detected tTG and EMA positive cases) in a large population of pre-schoolers with ASD referred to a tertiary care University Hospital. METHODS: We retrospectively collected data about 382 children (mean age: 46.97 ± 13.55 months; age-range: 18-72 months) consecutively diagnosed as ASD (according to the Diagnostic and Statistical Manual of Mental Disorders 4th edition criteria) over the period 2010-2013, and who performed a serological CD screening. RESULTS: The overall CD prevalence was 2.62%, which is statistically significant higher to that reported in the Italian paediatric population (p = 0.0246). Half of these children had no symptoms or risk factors related to CD when they performed the serological screening. CONCLUSIONS: If replicated, these data suggest the importance of regular screening for CD in young patients with ASD, and are of relevance for clinical and public health.

C-type natriuretic peptide is closely associated to obesity in Caucasian adolescents.

CNP is a natural regulator of adipogenesis playing a role in the development of obesity in childhood. Aim of the study was to evaluate CNP plasma levels in normal-weight (N), overweight (OW) and obese adolescents (O). Eighty two subjects (age:12.8±2.4, years) without cardiac dysfunction were enrolled and CNP plasma levels were measured by RIA. NT-proBNP, MR-proANP, AGEs, reactive hyperemia index (RHI) and standard clinical chemistry parameters were also measured. O and OW adolescents had higher values of BMI and fat mass than N. CNP levels were significantly lower in OW:4.79[3.29-21.15] and O:3.81[1.55-13.4] than in N:13.21[7.6-37.8]; p<0.0001N vs O, p=0.0003N vs OW). LogCNP values correlated significantly and inversely with BMI z-score, FM%, TF% and circulating levels of CRP, insulin, total cholesterol, LDL, and triglycerides, in addition to an inverse relationship with skin AGEs and a direct correlation with RHI. LogCNP was also inversely associated with LogNT-proBNP and LogMR-proANP values. Using ROC analysis the risk of obesity resulted significantly (p≪0.0001) associated with CNP values (AUC=0.9724). These results suggest that CNP may play a more important role than BNP and ANP related peptides, as risk marker of obesity, in addition to its involvement in adipogenesis and endothelial dysfunction.