Ternary BiOI/Bi2S3/Au Nanosheet Arrays as a Photoelectrochemical Signal Converter for the Detection of Cardiac Troponin I

Nanosheet arrays with stable signal output have become promising photoactive materials for photoelectrochemical (PEC) immunosensors. However, an essential concern is the facile recombination of carriers in one-component nanoarrays, which cannot be readily prevented, ultimately resulting in weak photocurrent signals. In this study, an immunosensor using gold nanoparticle-anchored BiOI/Bi2S3 nanosheet arrays (BiOI/Bi2S3/Au) as a signal converter was fabricated for sensitive detection of cardiac troponin I (cTnI). The ternary nanosheet arrays were prepared by a simple method in which Bi2S3 was well-coated on the BiOI surface by in situ growth, whereas the addition of Au further improved the photoelectric conversion efficiency and could link more antibodies. The three-dimensional (3D) ordered sheet-like network array structure and BiOI/Bi2S3/Au ternary nanosheet arrays showed stable and high photoelectric signal output and no significant difference in signals across different batches under visible light excitation. The fabricated immunosensor has a sensitive response to the target detection marker cTnI in a wide linear range of 500 fg/mL to 50 ng/mL, and the detection limit was 32 fg/mL, demonstrating good stability and selectivity. This work not only shows the great application potential of ternary heterojunction arrays in the field of PEC immunosensors but also provides a useful exploration for improving the stability of immunosensors.

Sensitive detection of cardiac troponin-I protein using fabricated piezoresistive microcantilevers by a novel method of asymmetric biofunctionalization

Microcantilever-based sensor platform has attracted a lot of attention over the time in detection of a variety of molecules due to their miniaturized dimensions. Sensitivity enhancement is an important aspect of such sensors, especially when used for point-of-care diagnostic purpose. However, the major concern while operating these sensors in deflection mode is their sensitivity which mainly relies on selective chemical modification protocols employed on these sensor surfaces. One of the ways of getting better sensitivity is through asymmetric (one side) biofunctionalization of the sensor surface. In the presented work here, we have demonstrated a novel approach of asymmetric biofunctionalization of proteins in overall sensitivity enhancement of piezoresistive silicon nitride-oxide microcantilever sensor platform inside a flow chamber. Herein, using our developed surface chemistry, asymmetrically biofunctionalized microcantilevers first exhibited a greater electrical response in terms of piezoresistance change than their symmetric counterpart in the detection of human immunoglobulins (HIgGs) protein. Finally, these microcantilevers were employed to exhibit the enhanced sensitivity towards the detection of a crucial cardiac marker protein, i.e. Troponin-I (cTnI) down to 250 ng ml^-1 using asymmetric biofunctionalization process. This study shows that the developed asymmetric biofunctionalization methodology may be used as a general protocol to detect other important biomarkers of clinical applications with improved sensitivity.

Paper-based cascade cationic isotachophoresis: Multiplex detection of cardiac markers

Paper-based analytical devices (PADs) are widely used in point-of-care testing (POCT) as they are cost-effective, simple and straightforward. However, poor sensitivity hinders their use in detecting diseases with low abundance biomarkers. The poor detection limit of PADs is mainly attributed to the low concentration of analytes, and the complexity of biological fluid, leading to insufficient interactions between analytes and capture antibodies. This study aims to overcome these difficulties by developing a paper-based cationic isotachophoresis (ITP) approach for simultaneously detecting pico-molar levels of two essential cardiac protein markers: acidic troponin T (cTnT) and basic troponin I (cTnI) spiked into human serum samples. The approach utilizes 3-aminopropyltrimethoxysilane (APTMS) treated glass fiber papers with decreasing cross-sectional area assembled on a 3D printed cartridge device. Our results showed that in the presence of cTnT monoclonal antibody (mAb), fluorescently labeled cTnI and cTnT could be effectively enriched in cationic ITP. Each individual target was captured subsequently by a test line in the detection zone where the capture mAb was immobilized. Detailed analysis suggests that the technology is capable of simultaneous on-board depletion of abundant plasma proteins and enrichment of cTnI/cTnT by ~1300-fold with a sensitivity of 0.6 pmol/L for cTnT and a sensitivity of 1.5 pmol/L for cTnI in less than 6 min. The results demonstrate the potential of this technology for rapid, ultra-sensitive and cost-effective analysis of multiplex protein markers in clinical serum samples at point of care.

Smartphone-app based point-of-care testing for myocardial infarction biomarker cTnI using an autonomous capillary microfluidic chip with self-aligned on-chip focusing (SOF) lenses

Cardiovascular disease is one of the most common causes of mortality in the world. Most of the diagnostic processes usually require bulky instruments and trained professionals, which cannot meet the demand for fast, early and regular bedside diagnosis. In this paper, a bespoke app on a smartphone and an autonomous capillary microfluidic chip (ACMC) are combined to realize the point-of-care testing of cardiac troponin I (cTnI). The smartphone-app-ACMC platform was based on the sandwich immunofluorescence principle and featured self-aligned on-chip focusing (SOF) lenses which can avoid the complex optical coupling process. The operator only needs to introduce 100 μl sample into the ACMC, where the priming, time-delaying, mixing and washing steps for the assay can be accomplished automatically. With the help of the bespoke app and a palm-sized optical attachment, the smartphone can capture fluorescence images, process fluorescence intensity information, output detection results and save the results for long-term monitoring. Our results showed that within 12 min, the detection limit of 78 pg ml-1 and 94 pg ml-1 for cTnI was attained in buffer and spiked human serum, respectively. Our proposed platform has the potential to be applied in the POCT field especially for some resource-limited settings.

Antibody-Oriented Strategy and Mechanism for the Preparation of Fluorescent Nanoprobes for Fast and Sensitive Immunodetection

Nanoprobes have been widely used in biomedical engineering. However, antibodies are generally conjugated onto nanoparticles disorderly, which reduces their antigen recognition ability. The existing antibody orientation approaches are usually complex. Here, we developed and demonstrated a simple antibody-oriented strategy for the lateral flow immunoassay of cardiac troponin I by conjugating antibodies onto polystyrene nanospheres at the optimal pH. The binding amount and orientation of antibodies as well as the detection sensitivity were significantly improved. Although pH regulation is commonly used to optimize antibody conjugation, this paper illustrates the mechanism of its antibody orientation enhancement ability for the first time and reveals the important influences of the density, the charge distribution and hydrophilicity of the antibody, the control of the velocities of physical adsorption and chemical coupling, and other factors on antibody orientation. It is of great significance to understand and regulate antibody conjugation on the surface of micro- or nanospheres to construct high-performance probes for in vitro diagnosis applications.

Chimeric recombinant antibody fragments in cardiac troponin I immunoassay

OBJECTIVES

To introduce a novel nanoparticle-based immunoassay for cardiac troponin I (cTnI) utilizing chimeric antibody fragments and to demonstrate that removal of antibody Fc-part and antibody chimerization decrease matrix related interferences.

DESIGN AND METHODS

A sandwich-type immunoassay for cTnI based on recombinant chimeric (mouse variable/human constant) antigen binding (cFab) antibodies and intrinsically fluorescent nanoparticles was developed. To test whether using chimeric antibody fragments helps to avoid matrix related interferences, samples (n=39) with known amounts of triglycerides, bilirubin, rheumatoid factor (RF) or human anti-mouse antibodies (HAMAs) were measured with the novel assay, along with a previously published nanoparticle-based research assay with the same antibody epitopes.

RESULTS

The limit of detection (LoD) was 3.30ng/L. Within-laboratory precision for 29ng/L and 2819ng/L cTnI were 13.7% and 15.9%, respectively. Regression analysis with Siemens ADVIA Centaur® yielded a slope (95% confidence intervals) of 0.18 (0.17-1.19) and a y-intercept of 1.94 (-1.28-3.91) ng/L. When compared to a previously published nanoparticle-based assay, the novel assay showed substantially reduced interference in the tested interference prone samples, 15.4 vs. 51.3%. A rheumatoid factor containing sample was decreased from 241ng/L to <LoD.

CONCLUSIONS

Utilization of cFab-fragments enabled the development of a sensitive (LoD=3.3ng/L) immunoassay for the detection of cTnI and decreased matrix related interferences, thus resulting in a lower number of falsely elevated cTnI-values.

[Protective effect and mechanism of IL-17 monoclonal antibody on mice with viral myocarditis]

OBJECTIVE

To explore the protective effects of interleukin-17 monoclonal antibody (IL-17 mAb) on viral myocarditis (VMC) mice and its possible molecular mechanisms.

METHODS

Ninety BALB/c mice were randomly divided into 4 groups: normal control group (n=15), model group (n=25), isotype control group (n=25) and IL-17 mAb group (n=25). Mice in model, isotype control and IL-17 mAb groups were inoculated with 0.1 mL Eagle's solution containing Coxsackievirus B3 (CVB3) intraperitoneally; and those in normal control group were treated with 0.1 mL Eagle's solution without CVB3. On the day 3 and 5 after inoculation, mice in isotype control and IL-17 mAb groups received intragastric administration of 100 μg non-specific IgG antibody and IL-17 mAb, respectively. On day 7 postinoculation, 5 mice were killed in each group, and the hearts were removed. Virus titer was detected using Reed-Muench method, and CVB3 mRNA copy number was measured by real-time quantitative PCR. All mice were killed on day 14 after weighing body mass (BM). The mortality was compared among groups. Serum was separated and serum cardiac troponin I (cTnI) concentration was detected using ELISA. The heart was removed and weighed to calculate heart index (HM/BM). Histological sections of heart were stained with hematoxylin-eosin and myocardial histopathologic scores were counted under optical microscope. The expression of nuclear factor-κB (NF-κB) p65 was examined by Western blotting. Myocardial interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) levels were detected by ELISA.

RESULTS

The HM/BM, serum cTnI concentration, NF-κB p65 expression level and myocardial IL-6 and TNF-α contents in model group were higher than those in normal control group (P<0.01). In comparison with model and isotype control groups, mortality, HM/BM, serum cTnI concentration, myocardial histopathologic scores, virus titer, CVB3 mRNA copy number, NF-κB p65 expression level, and myocardial IL-6 and TNF-α contents in IL-17 mAb group were significantly reduced (P<0.05 or 0.01). There was no difference in the above indicators between isotype control group and model group(P>0.05).

CONCLUSION

IL-17 mAb can improve myocardial injury in VMC mice, and the mechanisms are associated with the inhibition of viral replication and NF-κB activation.

Immunopathologic characterization of naturally acquired Trypanosoma cruzi infection and cardiac sequalae in cynomolgus macaques (Macaca fascicularis)

Trypanosoma cruzi, the causative agent of Chagas disease, is endemic in south Texas due to the abundant vector and wild small mammalian reservoir populations. This situation predisposes nonhuman primate colonies exposed to outdoor housing to infection from ingestion or bite of triatomid insects. Using a T. cruzi-specific real-time PCR and Trypanosome spp.-specific ELISA, we revealed a prevalence rate of 8.5% in a colony of outdoor-housed cynomolgus macaques. By using a discriminating kinetoplastid minicircle PCR, we eliminated the possibility of mixed prevalence with nonpathogenic trypanosomes and showed the ELISA results were specific for T. cruzi. In this study, we found an inverse relationship between antibody titers and circulating parasite load. Also, 23% of T. cruzi IgG ELISA-positive macaques were negative by real-time PCR. Furthermore, in a subset of infected macaques, cardiac tissue was infiltrated by inflammatory mononuclear cells and contained T. cruzi genomic and kinetoplast DNA despite lacking microscopic evidence of discrete parasite stages. In addition, 19% of the infected macaques had titers for cardiac troponin I autoantibody, which could contribute to autoimmune myocarditis or interfere with circulating troponin I measurements. These findings indicate the possibility of T. cruzi to interfere with the assessment of cardiac safety signals in preclinical toxicology and safety pharmacology studies and the necessity for prestudy screening for T. cruzi in outdoor-housed nonhuman primates from endemic areas.

Development of autoimmune hair loss disease alopecia areata is associated with cardiac dysfunction in C3H/HeJ mice

Alopecia areata (AA) is a chronic autoimmune hair loss disease that affects several million men, women and children worldwide. Previous studies have suggested a link between autoimmunity, stress hormones, and increased cardiovascular disease risk. In the current study, histology, immunohistology, quantitative PCR (qPCR) and ELISAs were used to assess heart health in the C3H/HeJ mouse model for AA and heart tissue response to adrenocorticotropic hormone (ACTH) exposure. Mice with AA exhibited both atrial and ventricular hypertrophy, and increased collagen deposition compared to normal-haired littermates. QPCR revealed significant increases in Il18 (4.6-fold), IL18 receptor-1 (Il18r1; 2.8-fold) and IL18 binding protein (Il18bp; 5.2-fold) in AA hearts. Time course studies revealed a trend towards decreased Il18 in acute AA compared to controls while Il18r1, Il18bp and Casp1 showed similar trends to those of chronic AA affected mice. Immunohistochemistry showed localization of IL18 in chronic AA mouse atria. ELISA indicated cardiac troponin-I (cTnI) was elevated in the serum and significantly increased in AA heart tissue. Cultures of heart atria revealed differential gene expression between AA and control mice in response to ACTH. ACTH treatment induced significant increase in cTnI release into the culture medium in a dose-dependent manner for both AA and control mice. In conclusion, murine AA is associated with structural, biochemical, and gene expression changes consistent with cardiac hypertrophy in response to ACTH exposure.

Are troponin assays occasionally deceiving us?

Troponin (I or T) is the principal marker of myocardial injury used in clinical practice. Although immune-based methods to determine troponin I levels are generally reliable, the presence of human antibodies interfering with the assays components could lead to erroneous results. In this report, we will discuss the case of a patient with misleadingly elevated troponin I due to high rheumatoid factor titer and provide an insight into the responsible molecular mechanisms.

Troponin and anti-troponin autoantibody levels in patients with ventricular noncompaction

Ventricular hypertrabeculation/noncompaction is a morphologic and functional anomaly of myocardium characterized by prominent trabeculae accompanied by deep recessus. Dilated cardiomyopathy with left ventricular failure is observed in these patients, while the cause or pathophysiologic nature of this complication is not known. Anti-troponin antibodies are formed against circulating cardiac troponins after an acute coronary event or conditions associated with chronic myocyte necrosis, such as dilated cardiomyopathy. In present study, we aimed to investigate cardiac troponins and anti troponin autoantibodies in ventricular noncompaction/hypertrabeculation patients with/without reduced ejection fraction. A total of 50 patients with ventricular noncompaction and 23 healthy volunteers were included in this study. Noncompaction/hypertrabeculation was diagnosed with two-dimensional echocardiography using appropriate criteria. Depending on ejection fraction, patients were grouped into noncompaction with preserved EF (LVEF >50%, n = 24) and noncompaction with reduced EF (LVEF <35%, n = 26) groups. Troponin I, troponin T, anti-troponin I IgM and anti-troponin T IgM were measured with sandwich immunoassay method using a commercially available kit. Patients with noncompaction had significantly higher troponin I (28.98±9.21 ng/ml in NCNE group and 28.11±10.42 ng/ml in NCLE group), troponin T (22.17±6.97 pg/ml in NCNE group and 22.78±7.76 pg/ml in NCLE group) and antitroponin I IgM (1.92±0.43 µg/ml in NCNE group and 1.79±0.36 µg/ml in NCLE group) levels compared to control group, while antitroponin T IgM and IgG were only elevated in patients with noncompaction and reduced EF (15.81±6.52 µg/ml for IgM and 16.46±6.25 µg/ml for IgG). Elevated cardiac troponins and anti-troponin I autoantibodies were observed in patients with noncompaction preceding the decline in systolic function and could indicate ongoing myocardial damage in these patients.

Fabrication of anionic sulfate-functionalized nanoparticles as an immunosensor by protein immobilization

Anionic sulfate (SO(4)(-))-functionalized polystyrene (PS) nanoparticles were prepared by the thermal decomposition of potassium persulfate (KPS) in the presence of sodium tetraborate via emulsion polymerization. The presence of a SO(4)(-) group at a solid/liquid interface of a particle surface was confirmed by a zeta potential value of -40.6 mV as well as the shifting of S 2p spectra toward a lower-binding-energy region around 162.7 eV (2p(3/2)) and 164.4 eV (2p(1/2)) in X-ray photoelectron spectroscopy (XPS) analysis. The electrostatic attraction between positively charged antibodies of human immunoglobulin G (hIgG) and cardiac troponin I (cTnI) and negatively charged particle surfaces was accomplished. The atomic force microscopy (AFM) measurement and bicinchoninic acid (BCA) assay results show binding structure between hIgG and antibodies of hIgG (anti-hIgG) with a gradual increase in particle diameter to 152.6 nm (bare), 170.2 nm (hIgG), and 178.9 nm (hIgG/anti-hIgG). Surface coverage densities of 331.4 ng/cm(2) (hIgG) and 320.3 ng/cm(2) (cTnI) and the binding capacity of hIgG to HyLite-750-labeled Fab-specific anti-hIgG (approximately 81.2%) indicate that the majority of hIgG was immobilized with a Y-shaped orientation. The sandwich immunoassay results provide the evidence that the immunological activity of cTnI on the PS nanoparticle surface was retained because the binding activity of the cTnI-PS nanoparticle/cTnI (antigen)/detection cTnI-antibody reaction showed a 5-fold higher activity than that of the cTnI-PS nanoparticle/human serum albumin (HSA)/detection cTnI antibody used as a negative control.

Bioconjugation and characterisation of gold colloid-labelled proteins

Colloidal metal particles, in particular gold, have found many biological applications often as probes in light and electron microscopy, and more recently since the 1980s in membrane-based rapid immunoaffinity tests. The surface plasmon resonance absorbance properties in the visible spectroscopy region of gold colloids make them useful tools in medical devices, as the colloids are directly visible to the naked eye. Despite the relative ease with which gold-protein conjugates can be prepared a major issue is the manufacture of poor-quality and poorly characterised bioconjugates that can result in the under performance of subsequent diagnostic tests. This paper describes the preparation of good-quality conjugates for use in immunoassays by optimising the adsorption of antibodies onto the surface of gold colloids, followed by their subsequent characterisation. The conjugates were characterized for size, aggregation and quality using a range of techniques: UV-visible (UV/Vis) absorption spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The biological activities of the conjugated products were also assessed using an immunoassay format and electrochemical measurements. By utilising a number of measurement techniques we aimed to gain a better understanding of the extent of particle aggregation, and the resulting stability and activity of the biological molecule on the surfaces of nanoparticles. The tools developed will enable researchers and companies to ensure the sensitivity, quality and reproducibility of batches of nanoparticle bio-conjugates.

Multiple inflammatory prognostic factors in acute coronary syndromes: a prospective inception cohort study

Inflammatory basis in pathopoiesis of coronary artery disease (CAD) have been demonstrated in recent decades. Elevated C-Reactive Protein (CRP) and leukocytosis were associated with an elevated risk for acute coronary syndrome (ACS). To evaluate the relationship between quantitative CRP and cardiac troponin I in conjunction with white blood cell (WBC) count and 30 days outcomes and treatment planning in patients with ACS. A concurrent inception cohort study was designed involving 200 patients as exposed and 200 patients as non exposed groups. We evaluated the relationship between baseline CRP and WBC count and cardiac troponin I , other risk factors and biomarkers, angiographic and other para-clinical tests and clinical outcomes with ACS. Higher CRP and WBC count were associated with additional coronary care unite (CCU) admission days (P = 0.002), hospitalization days (P = 0.007), arrhythmia type (P = 0.007), receiving streptokinase (P = 0.001), angiographic findings (P = 0.003), final myocardial infarction versus unstable angina (P = 0.001), date of complication (P = 0.001) and the date of cardiopulmonary resuscitation (if incident) (P = 0.015). In a multivariate Cox proportional hazard model high CRP and WBC count remained strong predictor of mortality (P = 0.028), angiography findings (three Vessel disease (3VD) and left main (LM) disease) (P = 0.001), and readmission in CCU (P = 0.002). A cardiac troponin I above 0.1 microg/lit was considered elevated. Elevated troponin level, demonstrated a significant relationship with MI incidence between two groups (P = 0.001) (89% in troponin positive group versus 11% in troponin less than 0.1 microg/lit). Inflammatory markers including, CRP and WBC count can be used to predict mortality, readmission, 3VD and LM disease in patients with ACS. In a Cox Proportional Hazard Model cardiac troponin above 0.1 microg/lit was significant predictors of MI (P = 0.003) and CPR (P = 0.044) at 30 days follow up period.

Circulating autoantibodies to troponin I in Emery-Dreifuss muscular dystrophy

The pathogenesis of dilated cardiomyopathy in Emery- Dreifuss muscular dystrophy (EDMD) is still unknown. Autoimmune mechanisms have recently been taken into account. The aim of this investigation was to determine whether the level of circulating antibodies to heart proteins which were previously detected, correlates with disease progression. Troponin I was chosen as the target. Ten patients with EDMD and 10 age-matched normal controls were tested. An enzyme linked immunoassay (ELISA) technique was used to determine the possible relation between the level of anti-troponin I antibodies at diagnosis and at followup. Autoantibodies against troponin I were detected in all EDMD patients. At diagnosis the level was higher in the X-linked EDMD form (X-EDMD), as compared to the autosomal dominant form (AD-EDMD). At follow-up the elevated level of the autoantibodies persisted in all the EDMD cases. However, in the AD-EDMD form, the level was found to be significantly rising with disease progression, in the X-EDMD form, on the other hand, it was declining. No clear-cut relationship between the level of the circulating antibodies and cardiac symptomatology was present. Detection of anti-troponin I antibodies may provide a non-invasive marker of early stages of dilated cardiomyopathy in EDMD.

Molecular pincers: antibody-based homogeneous protein sensors

We describe here a new homogeneous antibody-based protein sensor design (molecular pincers) that allows rapid and sensitive detection of a specific protein in solution. In the presence of the target protein these sensors produce fluorescence signal derived from target-dependent annealing of short complementary fluorochrome-labeled oligonucleotides attached to a pair of target-specific antibodies via nanometer-scale flexible linkers. The sensors allow near-instantaneous detection of the target with sensitivity and specificity approaching that of enzyme-linked immunosorbent assay (ELISA) but requiring no sample manipulation other then the addition of the sample to the sensor mix. We used cardiac troponin I and C-reactive protein as the targets to validate these desirable properties of the sensors. Due to the availability of antibodies to thousands of interesting targets and the straightforward design blueprint of the sensors we expect their wide-ranging applications in research and medical diagnosis, especially when simplicity, high throughput, and short detection time are essential.

Earlier detection of myocardial infarction by an improved cardiac TnI assay

OBJECTIVES

The aim of this study was to establish the diagnostic sensitivity of combinations of well-selected monoclonal antibodies (mAbs) against cardiac troponin I (cTnI) to allow an earlier rule-in of acute coronary syndrome (ACS) patients.

DESIGN AND METHODS

Using several combinations of mAbs, four new experimental cTnI immunoassays were evaluated to analyze plasma samples from 62 patients suffering from angina (16/62), patients having a chest pain of extracardiovascular origin (19/62) and ACS without ST elevation (NSTE-ACS) (27/62).

RESULTS

Assay 2, which relies on a capture mAb directed against the central part of cTnI and two conjugated mAbs directed against the N-ter region, provided the best clinical sensitivity. In 11 out of 27 patients with NSTE-ACS, it detected an early rise of cTnI within 0 and 1 h upon admission, contributing to the detection of 53% of samples found to be negative by the reference AccuTnI Assay upon admission (Beckman Coulter), thereby reducing the delay in diagnosis.

CONCLUSIONS

Assay 2 can identify early cTnI elevation in NSTE-ACS, possibly facilitating the rule-in procedure for these patients once the assay is automated.

Falsely elevated cardiac troponin I levels

The measurement of cardiac troponins (cTn) is of considerable usefulness in the diagnosis of acute coronary syndrome. Abnormal levels of serum cTn are occasionally found in patients who are not suffering a myocardial infarction. This may be observed in several well-known situations including pulmonary embolism, pericarditis, myocarditis, coronary vasospasm, sepsis, congestive heart failure, supraventricular tachycardia with hemodynamic compromise, re-nal insufficiency, and prolonged strenuous endurance exercise. Endogenous antibodies such as heterophile antibodies, rheumatoid factor, and other autoantibodies are known to interfere with the immunoassay measurements of many different analytes, including the widely used Abbot AxSYM cTnI analyzer. Other sources of circulating antibodies include immunotherapies, vaccinations, or blood transfusions that may interfere with these immunoassays as well. We examine the case of a 48-year-old man with a history of hypercholesterolemia and obesity who presented with chest pain and was found to have elevated Tn I levels on two separate occasions. Further work-up revealed that the Tn I levels were spuriously elevated because the patient's blood revealed a normal cTnI level when mixed with polyethylene glycol to inactivate any antibodies interfering with the cTnI assay.

Autoantibodies to cardiac troponin I in patients with idiopathic dilated and ischemic cardiomyopathy

BACKGROUND

Progressive dilatation and functional compromise of heart function is attributed to a variety of pathogenic mechanisms. Experimental data suggests that autoantibodies could promote myocardial damage by inducing either inflammation or alternatively, augmentation of Ca2+ currents or activation of surface receptors on cardiomyocytes. Cardiac troponin I (cTpnI) is an essential protein component of the contractile heart. Herein, we studied the presence and functional properties of autoantibodies to cTpnI in patients with idiopathic dilated cardiomyopathy (DCM) and ischemic cardiomyopathy (ICM).

METHODS AND RESULTS

Anti-cTpnI antibody ELISA was established for assessment of sera obtained from 33 patients with ICM, 32 with DCM and 42 healthy subjects. Binding specificity of purified cTpnI-reactive IgG fractions from patients with ICM and DCM was confirmed by competitive inhibition studies employing fluid-phase cTpnI. The effect of IgG preparations on intracellular Ca2+ ([Ca2+]i) transients was tested in cultured neonatal rat ventricular myocytes (NRVM). Six of the 33 ICM patients (18.2%) and 5 of the 32 DCM patients (15.6%) had positive anti-cTpnI antibody titer as compared to none in the healthy subjects. Purified IgG from positive patients appeared specific to cTpnI. IgG preparations reactive with cTpnI did not exhibit measurable effects on [Ca2+]i transients in cultured NRVM nor did they bind the respective cells by direct immunofluorescence.

CONCLUSION

IgG antibodies to TpnI are increased in a significant number of patients with both ICM and idiopathic DCM, yet it appears that these autoantibodies cannot bind heart muscle cells or influence [Ca2+]i transients.

Preparation of anti-human cardiac troponin I immunomagnetic nanoparticles and biological activity assays

Maghemite nanoparticles (MNPs) were synthesized by chemical coprecipitation and coated with meso-2,3-dimercaptosuccinic acid (HOOC-CH(SH)-CH(SH)-COOH or DMSA). The morphology and properties of the nanoparticles were characterized by TEM, XRD, Zeta Potential Analyzer and VSM. Subsequentially, the anti-human cardiac troponin I (cTnI) immunomagnetic nanoparticles (IMNPs) were prepared by grafting anti-human cTnI antibodies on the surface of DMSA-coated MNPs using the linker of EDC (1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride). The conjugation amount of the antibodies and the activity of IMNPs was evaluated by enzyme linked immunosorbent assay (ELISA) and Western blotting. The results show that the physical and chemical adsorption occurred at the same time, but the former was unstable and apt to desorb, and the maximum conjugation amount of antibody was about 96 microg on the 0.1 mg MNPs by covalent bond. The stability was also investigated, and after 300 days the antibodies on the IMNPs remained the biological activity.

Tissue-specific interactions of TNI isoforms with other TN subunits and tropomyosins in C. elegans: the role of the C- and N-terminal extensions

The aim of this study is to investigate the function of the C-terminal extension of three troponin I isoforms, that are unique to the body wall muscles of Caenorhabditis elegans and to understand the molecular interactions within the TN complex between troponin I with troponin C/T, and tropomyosin. We constructed several expression vectors to generate recombinant proteins of three body wall and one pharyngeal troponin I isoforms in Escherichia coli. Protein overlay assays and Western blot analyses were performed using antibodies. We demonstrated that pharyngeal TNI-4 interacted with only the pharyngeal isoforms of troponin C/T and tropomyosin. In contrast, the body wall TNI-2 bound both the body wall and pharyngeal isoforms of these components. Similar to other invertebrates, the N-terminus of troponin I contributes to interactions with troponin C. Full-length troponin I was essential for interactions with tropomyosin isoforms. Deletion of the C-terminal extension had no direct effect on the binding of the body wall troponin I to other muscle thin filament troponin C/T and tropomyosin isoforms.

Time course of degradation of cardiac troponin I in patients with acute ST-elevation myocardial infarction: the ASSENT-2 troponin substudy

Although measurement of troponin is widely used for diagnosing acute myocardial infarction (AMI), its diagnostic potential may be increased by a more complete characterization of its molecular appearance and degradation in the blood. The aim of this study was to define the time course of cardiac troponin I (cTnI) degradation in patients with acute ST-elevation myocardial infarction (STEMI). In the ASSENT-2 substudy, 26 males hospitalized with STEMI were randomized to 2 different thrombolytic drugs within 6 hours after onset of symptoms. Blood samples were obtained just before initiation of thrombolysis and at 30 minutes intervals (7 samples per patient). Western blot analysis was performed using anti-cTnI antibodies and compared with serum concentrations of cTnI. All patients exceeded the cTnI cutoff for AMI during the sampling period; at initiation of therapy, 23 had elevated cTnI values. All patients demonstrated 2 bands on immunoblot: intact cTnI and a single degradation product as early as 90 minutes after onset of symptoms. On subsequent samples, 15 of 26 patients showed multiple degradation products with up to 7 degradation bands. The appearance of fragments was correlated with higher levels of cTnI (P<0.001) and time to initiation of treatment (P=0.058). This study defines for the first time the initial time course of cTnI degradation in STEMI. Intact cTnI and a single degradation product were detectable on immunoblot as early as 90 minutes after onset of symptoms with further degradation after 165 minutes. Infarct size and time to initiation of treatment was the major determinant for degradation.

Cardiac troponin I but not cardiac troponin T induces severe autoimmune inflammation in the myocardium

BACKGROUND

Cardiac troponins in blood are the most preferred markers of myocardial damage. The fact that they are normally not found in the circulation provides a high level of clinical sensitivity and specificity even when cardiac lesions are small. After myocardial injury, the troponins enter the circulation, where they can be used for diagnosis of acute coronary syndromes. Thus, the cardiac troponins are paramount for disease classification and risk stratification. However, little is known about the long-term effects of the released troponins on cardiac function.

METHODS AND RESULTS

In this study we prepared recombinant murine cardiac troponin I (mc-TnI) and murine cardiac troponin T and used them to immunize mice. We report that A/J mice immunized with mc-TnI developed severe inflammation of the myocardium with increased expression of inflammatory chemokines RANTES (regulated on activation normal T cell expressed and secreted), monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, MIP-2, T-cell activation gene 3, and eotaxin and chemokine receptors CCR1, CCR2, and CCR5. The inflammation was followed by cardiomegaly, fibrosis, reduced fractional shortening, and 30% mortality over 270 days. In contrast, mice immunized with murine cardiac troponin T or with the control buffer showed little or no inflammation and no death. Furthermore, we demonstrate that mice preimmunized with mc-TnI before left anterior descending coronary artery ligation showed greater infarct size, more fibrosis, higher inflammation score, and reduced fractional shortening.

CONCLUSIONS

Overall, our results show for the first time that provocation of an autoimmune response to mc-TnI induces severe inflammation in the myocardium followed by fibrosis and heart failure with increased mortality in mice.

The Antibody Configurations of Cardiac Troponin I Assays May Determine Their Clinical Performance

Background: Previous studies have shown superior clinical performance of the cardiac troponin I (cTnI) assay from Beckman-Coulter Diagnostics. This assay had a unique combination of monoclonal antibodies with 2 monoclonal antibodies directed against epitopes near the NH2 terminus of the heart-specific region of troponin I. The approach has been adopted by the new cTnI assay from Abbott Diagnostics. The aim of our study was to investigate whether this approach affects the clinical performance of cTnI assays.

Methods: Cardiac troponin concentrations were measured in a random sample of patients with unstable coronary artery disease included in the GUSTO IV trial (n = 696) by the AccuTnI (Beckman-Coulter Diagnostics), Architect cTnI (Abbott Diagnostics), Immulite 2500 cTnI (Diagnostics Products Corporation), and Elecsys 2010 cTnT (Roche Diagnostics) assays and related to the 1-year mortality. The primary cutoff concentrations were based on the 99th percentile upper reference limits and an imprecision (CV) ≤10%.

Results: The sensitivities of the AccuTnI and Architect cTnI assays in identifying patients who died within 1 year were equal and were significantly higher (P &lt;0.05) than those of the Immulite 2500 cTnI and the Elecsys cTnT assays. The concordance between the AccuTnI and Architect cTnI assays was 97%, but concordances between the Architect cTnI and the Elecsys cTnT assays were 89%–92% with more at-risk patients (P &lt;0.01 to P &lt;0.001) identified by the Architect cTnI assay.

Conclusions: The Architect cTnI assay has clinical performance similar to that of the AccuTnI, probably as a result of the inclusion of a monoclonal antibody against troponin I epitope 41–49 in the assay.

Determination of cardiac troponin I for the auxiliary diagnosis of acute myocardial infarction by anodic stripping voltammetry at a carbon paste electrode

An electrochemical immunoassay for cardiac troponin I (cTnI) combining the concepts of the dual monoclonal antibody "sandwich" principle, the silver enhancement on the nano-gold particle, and the anodic stripping voltammetry is described. Four main steps were carried out to obtain the analytical signal, i.e., electrode preparation, immunoreaction, silver enhancement, and anodic stripping voltammetric detection. A linear relationship between the anodic stripping peak current and concentration of cTnl from 1 to 20 ng/ml and a limit of detection of 0.8 ng/ml were obtained. The established method was tested by determining cTnI in acute myocardial infarction (AMI) samples using enzyme-linked immunoadsorbent assay (ELISA) for comparison analysis, and good results were obtained.

[Prokaryotic expression of human cTnI and preparation of rabbit anti-hcTnI antibody]

AIM

To construct the prokaryotic expression vector pET-21a(+)-hcTnI and prepare the rabbit anti-hcTnI antibody using hcTnI expressed in E.coli as immunogen.

METHODS

The full-length gene encoding human cardiac troponin I (hcTnI) was synthesized chemically and inserted into expression plasmid pET-21a(+) to construct recombinant plasmid pET-21a(+)-hcTnI. The recombinant plasmid was transformed into E.coli BL21 (DE3) plysS which then expressed hcTnI under IPTG induction. The immunological activity of the expressed hcTnI was analyzed by Western blot. A rabbit was immunized with purified hcTnI to prepare anti-hcTnI antibody and the Ab's properties were identified.

RESULTS

Human cTnI gene was synthesized and confirmed by DNA sequencing. Positive recombinant clones were identified by restriction enzyme digestion analysis and DNA sequencing. After induction with IPTG, hcTnI with M(r) being 24 000 was expressed in E.coli BL21 (DE3) plysS, and the expressed hcTnI accounted for 28% of total bacterial protein. Western blot analysis showed that the hcTnI protein could be recognized by an anti-hcTnI antibody. Rabbit polyclonal antibody with a good specificity was obtained. The titer of the polyclonal antibody was 3x10(-4).

CONCLUSION

The recombinant expression plasmid of hcTnI was constructed successfully and expressed in E.coli. The prepared rabbit anti-hcTnI antibody had a high titer and specificity.

Pathogenic roles of cardiac autoantibodies in dilated cardiomyopathy

Whether autoimmunity could cause dilated cardiomyopathy (DCM) was disputed for more than half a century. Autoantibodies against various cardiac antigens have been found in the sera of patients with DCM but none of these autoantibodies has been shown to have a substantial role in the development of DCM. It was recently reported that the injection of autoantibodies against cardiac troponin I (cTnI) can induce DCM in normal mice. This observation showed that autoantibodies can cause DCM and put an end to the controversy. Clinical trials of immunoglobulin-adsorption therapy for DCM have already started in Germany and the results seem promising. Here, we discuss the recent findings and possibilities of immunoglobulin-adsorption therapy for this deadly disease.

[Study of CTnI immunohistochemistry on acute myocardial infarction in rabbits]

OBJECTIVE

To investigate the signification of CTnI in acute myocardial infarction.

METHODS

The model of myocardial infarction was established by ligating the left ventricle branch. Immunohistochemistry and image analysis were used to detect the change of CTnI in the model, and The sensitivity of immunohistochemistry and HE coloration were also compared.

RESULTS

The acute myocardial infarction tissue showed obvious depletion of CTnI, there was no characterization of myocardial infarction in HE coloration.

CONCLUSION

CTnI is sensitive to diagnosis of acute myocardial infarction.

Comparison of Cardiac Troponin I Immunoassays Variably Affected by Circulating Autoantibodies

Background: We recently provided evidence that circulating autoantibodies against cardiac troponin I (cTnI) or the troponin complex cause negative interference in cTnI immunoassays. By comparing three cTnI immunoassays, we further explored the phenomenon of circulating autoantibodies and their consequences in patient samples.

Methods: We developed a cTnI immunoassay with a novel assay design using three antibodies, two of which bind epitopes outside the stable, central part of cTnI. Samples from 541 chest pain patients were measured with the new cTnI assay and with a first-generation cTnI assay (Innotrac Aio cTnI) using a conventional midfragment assay design. Using another sample cohort, we also compared the new assay with a second-generation cTnI assay (Access AccuTnI).

Results: The analytical detection limit of the new cTnI assay was 0.012 μg/L, and the lowest concentration giving a total imprecision (CV) of 10% was 0.060 μg/L. The mean difference (95% limits of agreement) between the new cTnI and Aio cTnI assays was larger in admission samples (21.0%; −107.8% to 149.7%) than in samples taken 6–12 h (12.8%; −61.5% to 87.2%) and 24 h after admission (3.0%; −71.3% to 77.4%; P &lt;0.001). With the lowest concentrations giving 10% CV (0.22 μg/L for Aio cTnI) used as cutoffs, 14.3% (n = 76) of admission samples were positive only with the new assay, whereas 13.5% (n = 72) were positive with both assays. Of samples taken at 6–12 and 24 h, 10.2% (n = 31) and 8.3% (n = 29) were positive only with the new assay. ROC curve analysis of admission samples showed a significantly higher area under the curve for the new cTnI assay (0.940) than for the Aio cTnI assay (0.846; P &lt;0.001). The new cTnI assay gave generally lower results than the AccuTnI assay; the mean (95% limits of agreement) differences were −58.9% (−151.8% to 34.0%) in admission samples. In samples with severe interference from autoantibodies, median ratios between the new assay and AccuTnI were higher than in samples with no apparent troponin autoantibodies (0.875 vs 0.481; P&lt;0.001).

Conclusions: The new cTnI assay, which is based on a novel antibody combination different from the conventional midfragment antibody approach, offers improved detection of cTnI in samples containing troponin autoantibodies.

Negative Interference in Cardiac Troponin I Immunoassays by Circulating Troponin Autoantibodies

Background: There are numerous potential sources of interference in immunoassays. Our aim was to identify the blood component that causes negative interference in cardiac troponin I (cTnI) immunoassays based on antibodies against the central part of cTnI.

Methods: We isolated an interfering factor (IF) from a sample with low recovery of added cTnI, using several consecutive purification steps: caprylic acid precipitation, ammonium sulfate precipitation, and purification on Cibacron Blue gel and protein G columns. Purified IF was identified by gel electrophoresis and mass spectrometric analysis of protein bands. For the direct detection of human antibodies to cardiac troponin in serum samples, we developed immunoassays using three different anti-human immunoglobulin antibodies and measured troponin antibodies in samples with low and normal cTnI recovery.

Results: Treatment with caprylic acid did not precipitate IF, but IF precipitated at 40% ammonium sulfate saturation. IF bound to a Cibacron Blue gel column, from which it was eluted with a linear salt gradient; it also bound to protein G. Gel electrophoresis of purified IF showed two major bands with molecular masses corresponding to the heavy (∼50 kDa) and light chains (∼25 kDa) of immunoglobulin, and their identities were confirmed by mass spectrometry. The presence of troponin-specific autoantibodies was confirmed in samples with low recoveries of cTnI by three different immunoassays. The median signals were significantly higher in 10 samples with low recovery than in 10 samples with normal recovery of cTnI (P ≤ 0.007).

Conclusions: Circulating autoantibodies to cTnI or other proteins of the troponin complex can be a source of negative interference in cTnI immunoassays.

The incremental value of troponin-I testing in patients with intermediate risk unstable angina

BACKGROUND

Classification of patients with unstable angina (UA) by Agency for Health Care Policy and Research (AHCPR) guidelines in the emergency department reliably stratifies risk of death or myocardial infarction (MI) for triage to outpatient evaluation (low-risk), hospitalization (high-risk), or additional testing (intermediate-risk). Cardiac troponin-I elevation may identify patients at higher risk, but the incremental value may vary with AHCPR clinical risk.

HYPOTHESIS

The objective of this study was to determine whether cardiac troponin-I had any additional value beyond triage based upon history, physical examination, and electrocardiogram, in the evaluation of patients with UA.

METHODS

In all, 212 consecutive patients with UA and normal serum creatine kinase (CK)-MB levels and elevated troponin-I were risk stratified by AHCPR guidelines to evaluate the incremental value of adding routine troponin-I measurements to our current model for risk stratification.

RESULTS

Primary events (death/nonfatal MI) occurred in 35% of high-risk, 15% of intermediate-risk, and 0% of low-risk patients (p < 0.001 by chi-square for trend). High troponin-I (> or =2.0 ng/dl) occurred in 48% of high-risk, 21% of intermediate-risk, and 19% of low-risk patients. The remaining patients in each risk group had indeterminate troponin-I levels (> or =0.4 < 2 ng/dl). Of those with high troponin-I, a primary event occurred in 36, 42, and 0% in the respective high-, intermediate-, and low-risk groups (p < 0.001). High troponin-I levels corresponded with a statistically significant increased rate of primary events only in patients at AHCPR intermediate risk: 42.4 vs. 7.3%, p < 0.001.

CONCLUSION

The AHCPR guidelines risk stratify patients with UA. High troponin-I adds significant (p < 0.001) prognostic value in the patients at AHCPR intermediate risk and should be evaluated further in larger trials of such patients.

An interfering component in cardiac troponin I immunoassays—Its nature and inhibiting effect on the binding of antibodies against different epitopes

OBJECTIVES

We recently reported on the occurrence of a common interfering factor (IF) that negatively affects determinations of cardiac troponin I (cTnI). The aim of the present investigation was to extend our initial finding by a detailed epitope-based determination of the location of IF and to reveal the approximate size and characteristics of IF.

DESIGN AND METHODS

Two-site immunoassays using combinations of 16 monoclonal and 2 polyclonal cTnI antibodies and 1 monoclonal troponin C (TnC) antibody were used to measure the analytical recovery of cTnI or cTnI-TnC in serum samples. Gel filtration of serum samples containing IF was performed and the analytical recovery of cTnI in the fractions was determined. EDTA-plasma samples to which cTnI had been added and serum samples containing endogenous cTnI were also separated by gel filtration.

RESULTS

The mean analytical recoveries of cTnI were 28.3% (range 7.5-55.1%) and of cTnI-TnC were 23.5% (range 8.7-51.8%) in samples containing IF when antibodies against midfragment epitopes of cTnI were used. The mean recovery of cTnI was 65.1% and 73.3% for antibodies with N- and C-terminal epitopes. Gel filtration of samples with low recovery of cTnI showed that the approximate molecular mass of IF was 50-200 kDa and that the cTnI elution profiles of samples containing IF were shifted towards higher molecular mass compared with samples with less IF.

CONCLUSIONS

Antibodies against midfragment epitopes of cTnI are affected by IF to a considerable but variable extent, and the presence of IF can be demonstrated by gel filtration.

Monoclonal antibody-based sandwich enzyme-linked immunosorbent assay for sensitive detection of prohibited ruminant proteins in feedstuffs

Regulations aimed to control the epidemic of bovine spongiform encephalopathy have banned the use of certain animal products, i.e., ruminant meat and bone meals, in ruminant animal feeds. A sensitive enzyme-linked immunosorbent assay has been developed to detect prohibited bovine and ovine muscles in feedstuffs. The assay utilizes a pair of monoclonal antibodies (MAbs) against skeletal troponin I (TnI). MAb 5G9, specific to bovine and ovine TnI, was used as the capture antibody and the biotin-conjugated MAb 2G3, reacting to all heterologous TnI, was used as the detection antibody. Quantitative procedures were applied to samples containing 5, 0.5, and 0.05% (wt/wt) of heat-treated (132 degrees C/2 bar, 2 h) bovine and ovine meat meals in three different feeds, coexisting with porcine, chicken, or turkey meat meal. The presence of these nonprohibited species did not affect the detection of bovine and ovine meat meals in the feed samples (P > 0.05). Quantitative determinations of extractable bovine and ovine TnI, with a detection limit of 5.0 and 4.0 ng/ml, respectively, were achieved when the matching feed matrixes were used in the calibration curves. This new assay provides a rapid and reliable way to detect animal protein products containing a trace amount of bovine or ovine muscle tissue in feedstuffs.

Autoantibodies against cardiac troponin I are responsible for dilated cardiomyopathy in PD-1-deficient mice

We recently reported that mice deficient in the programmed cell death-1 (PD-1) immunoinhibitory coreceptor develop autoimmune dilated cardiomyopathy (DCM), with production of high-titer autoantibodies against a heart-specific, 30-kDa protein. In this study, we purified the 30-kDa protein from heart extract and identified it as cardiac troponin I (cTnI), encoded by a gene in which mutations can cause familial hypertrophic cardiomyopathy (HCM). Administration of monoclonal antibodies to cTnI induced dilatation and dysfunction of hearts in wild-type mice. Monoclonal antibodies to cTnI stained the surface of cardiomyocytes and augmented the voltage-dependent L-type Ca2+ current of normal cardiomyocytes. These findings suggest that antibodies to cTnI induce heart dysfunction and dilatation by chronic stimulation of Ca2+ influx in cardiomyocytes.

Negative interference in cardiac troponin I immunoassays from a frequently occurring serum and plasma component

BACKGROUND

Cardiac troponin I (cTnI) is a sensitive marker of cardiac injury, but cTnI assays, like other immunoassays, are susceptible to interferences. We evaluated the presence of interfering substances by measuring the recovery of cTnI added to samples from volunteers and from patients with acute coronary syndromes (ACS).

METHODS

We added a ternary complex of human cardiac troponin (30-500 microg/L) or cTnI from serum to samples from healthy volunteers and ACS patients. We measured cTnI with a two-site sandwich time-resolved immunofluorometric assay using two antibodies against epitopes in the central stable part of cTnI. We also analyzed 108 heparin-plasma samples from 16 ACS patients with this assay, with an assay based on four antibodies, and with two commercial cTnI assays, AxSYM and ACS:180.

RESULTS

In samples from both healthy persons and ACS patients, recoveries for our assay were 1-167% (range). Recoveries were increased by addition of an antibody with an epitope in the N-terminal region of cTnI to the solid phase and an antibody with an epitope in the C-terminal region as a second detection antibody. In 2 of 16 patients with ACS, normal cTnI concentrations found when measured with the original assay demonstrated clinically abnormal (up to 10-fold higher) results with the additional N- and C-terminal antibodies in the early phase of infarction. Both commercial cTnI assays also demonstrated clinically misleading, falsely low cTnI concentrations.

CONCLUSIONS

Some yet unidentified, variable component, present in the blood from healthy volunteers and ACS patients, interferes with the binding of antibodies against epitopes in the central part of cTnI used in two commercial assays. Our approach to supplement the mid-fragment cTnI antibodies with antibodies in the N- and C-terminal parts of the molecule in an experimental assay represents a step in resolving this interferent.

Measurement of cardiac troponin I in striated muscle using three experimental methods

BACKGROUND

Qualitative and quantitative measures of cardiac troponin I (cTnI) in striated muscle have been reported as part of diverse investigations. However, there is disparity in the literature regarding the findings of these analyses. The cTnI molecule can exist in phosphorylated, non-phosphorylated, reduced, non-reduced, complexed or non-complexed forms. Each of these forms can change the antigenicity of cTnI, resulting in different antibody-antigen interactions in different experimental formats, thereby giving rise to the disparities in the literature.

METHODS

cTnI in heart and skeletal muscles were investigated by three techniques employing the same specific cTnI antibodies: the recently revised Dade-Behring Dimension RXL assay, immunoblotting and immunohistochemistry.

RESULTS

cTnI was detected in heart muscle but not skeletal muscle using the quantitative assay and immunoblotting. Unexpectedly, using the same antibodies, cTnI was not immunolocalized to either heart or skeletal muscle.

CONCLUSION

The antibody-cTnI interaction might be impeded on fixed immunohistochemistry sections. Our findings reflect those of a previous study, showing that cTnI was not detected in skeletal muscle extracts using a quantitative assay. The behaviour of cTnI antibodies varies depending on experimental design. Conclusions drawn from experiments using qualitative methods cannot necessarily be extrapolated to the quantitative assay and vice versa.

Determination of affinities and antigenic epitopes of bovine cardiac troponin I (cTnI) with monoclonal antibodies by surface plasmon resonance biosensor

A surface plasmon resonance (SPR) biosensor based on wavelength modulation was used for real-time detection of the interaction of three monoclonal antibodies and antigens of bovine cardiac troponin I (cTnI). In order to recognize antigenic epitopes of bovine cTnI, two experimental modes were applied. In the first experimental mode, three monoclonal antibodies were divided into three groups and three experiments were performed on biosensor surfaces prepared with protein A. In the second experimental mode, antigen was immobilized on the biosensor surface prepared by the amine-coupling method and three monoclonal antibodies were detected in turn. The results obtained by the two modes are consistent. In addition, the affinities of the monoclonal antibodies for the antigen were also determined by the association rate and the disassociation rate in real-time. These results validate the biosensor technology and illustrate how biosensors based on wavelength modulation can be used to study the interaction of monoclonal antibodies and antigens in real time.

False-positive AxSYM cardiac troponin I results in a 53-year-old woman

A number of classes of endogenous antibodies, including heterophile, rheumatoid factor, and autoantibodies, can interfere with immunoassay measurements of many different analytes. Heterophile and rheumatoid factor antibody interferences have been described previously for the AxSYM cardiac troponin I assay. Several commercial products have been developed to neutralize heterophile antibody interferences. We describe a patient with multiple apparently falsely elevated cardiac troponin I results that were unique to the AxSYM analyzer. These cardiac troponin I results diluted linearly. When treated with 2 different heterophile-blocking reagents, the magnitudes of the falsely elevated results increased 17- and 26-fold, and these results also demonstrated dilution linearity. This interfering substance could be removed by passage through an immobilized protein A column and by polyethylene glycol precipitation. It does not appear to be a classic heterophile antibody, nor is it a paraprotein. Laboratorians must remain constantly vigilant for immunoassay interferences that lead to clinically significant inaccurate results and must recognize that accepted methods for detecting and neutralizing the interference may be ineffective.

The neuropeptide proctolin induces phosphorylation of a 30 kDa protein associated with the thin filament in crustacean muscle

In the isopod Idotea emarginata, the neuropeptide proctolin is contained in a single pair of motoneurones located in pereion ganglion 4. The two neurones supply dorsal extensor muscle fibres of all segments. Proctolin (1μmoll−1) potentiates the amplitude of contractures of single extensor muscle fibres elicited by 10mmoll−1 caffeine. In western blots of myofibrillar proteins isolated from single muscle fibres and treated with an anti-phosphoserine antibody, a protein with an apparent molecular mass of 30kDa was consistently found. The phosphorylation of this protein was significantly increased by treating the fibres with proctolin. After separation of myofibrillar filaments, a 30kDa protein was found only in the thin filament fraction. This protein is phosphorylated and detected by an antiserum against crustacean troponin I.

Biochemical and immunological properties of human cardiac troponin I fragments

Cardiac troponin I (cTnI) is the inhibitory subunit of the troponin complex and is a biochemical marker for myocardial infarction (MI). It is found in human serum within 4-6 h following MI. One of us has shown [Morjana (1998) Biotechnol. Appl. Biochem. 28, 105-111] that MI patient serum TnI is cleaved at the N- and C-terminals and that the TnI fragments exist as a complex with tropinin C (TnC) and troponin T (TnT). In the present study, we have generated C-terminal truncated TnI fragments and studied their immunological and biochemical properties. Human recombinant TnI (rTnI) expressed in Escherichia coli is cleaved into a major fragment with a molecular mass of 17500 Da using CNBr. The major CNBr fragment contains the first 153 amino acids of human cTnI (TnI153). Cleavage of the rTnI with the endoproteinase Asp-N generates a smaller TnI fragment (TnI88, residues 6-96). TnI153 has higher immunological activity than that of rTnI and lower activity than that of TnI88, as judged by the Stratus II TnI Immunoassay. TnI153 exhibits biochemical and immunological properties similar to those of intact TnI. It binds TnC at a molar ratio of 1:1 and forms a ternary complex with TnC and TnT. TnC enhances the immunological activity of TnI153, but has little effect on the activity of TnI88. The TnI153-TnC complex exhibits higher immunological activity than rTnI-TnC and TnI88-TnC, and much higher activity than free rTnI, TnI153 and TnI88. The presence of TnT has no effect on the immunological activity of the TnI153-TnC complex, suggesting that the addition of TnT does not interfere with TnI153 recognition by TnI monoclonal antibodies. Free TnI153 and TnI88 degrade rapidly in human serum. TnC protects TnI153 from proteolytic degradation, but offers less protection for TnI88. The TnI88-TnC complex lost 80% of its immunological activity after incubation for 2 days in human serum at 37 degrees C. However, there was no loss in the immunological activity of the TnI153-TnC complex under the same conditions. A cTnI fragment (TnI80, residues 1-80), expressed in E. coli as a fusion protein, exhibits immunological activity and stability similar to that of TnI88.

The highly conserved COOH terminus of troponin I forms a Ca2+-modulated allosteric domain in the troponin complex

The primary structure of the COOH-terminal region of troponin I (TnI) is highly conserved among the cardiac, slow, and fast skeletal muscle TnI isoforms and across species. Although no binding site for the other thin filament proteins is found at the COOH terminus of TnI, truncations of the last 19-23 amino acid residues reduce the activity of TnI in the inhibition of actomyosin ATPase and result in cardiac muscle malfunction. We have developed a specific monoclonal antibody (mAb), TnI-1, against the conserved COOH terminus of TnI. Using this mAb, isolation of the troponin complex by immunoaffinity chromatography from muscle homogenate and immunofluorescence microscopic staining of myofibrils indicate that the COOH terminus of TnI forms an exposed structure in the muscle thin filament. Binding of this mAb to the COOH terminus of cardiac TnI induced extensive conformational changes in the protein, suggesting an allosteric role of this region in the functional integrity of troponin. In the absence of Ca2+, the binding of troponin C and troponin T to TnI had very little effect on the conformation of the COOH terminus of TnI as indicated by the unaffected mAb affinity for the TnI-1 epitope. However, Ca2+ significantly increased the accessibility of the TnI-1 epitope on TnI in the presence of troponin C and troponin T. The results provide evidence that the COOH terminus is an essential structure in TnI and participates in the allosteric switch during Ca2+ activation of contraction.

Myocardial fixation of anticardiac troponin I antibody and cardiac troponin I release

BACKGROUND

The threefold aim of this experimental study was to test the correlation of cardiac troponin I released to myocardial infarction size and myocardial fixation of anticardiac troponin I antibody and to determine how long after myocardial infarction the measure of cardiac troponin I concentration can evaluate myocardial infarction size.

METHODS

Forty rabbits were assigned either to a control group or to an experimental preconditioned group. Infarction was obtained by tightening a snare around the left anterior descending artery. Serial venous blood samples were drawn for measurement of cardiac troponin I. The rabbits were sacrificed at 72 hours and a histological study was performed to determine the infarct size and the size of the area void of fixation of anticardiac troponin I antibody.

RESULTS

There was a linear correlation between the total amount of CTn I released and both infarct size (r=0.45, p<0.02) and the size of the area void of anti-cardiac troponin I antibody (r=0.47, p<0.02). These two sizes were strongly correlated (r=0.95, p<0.02). The hour 9 CTn I sample was the best correlated with both the infarct size (r=0.47, p<0.02) and the size of area void of anticardiac troponin I antibody (r=0.45, p<0.02).

CONCLUSIONS

Our study shows that: 1) cardiac troponin I release is correlated to both myocardial infarction size and the size of area void of fixation of anticardiac troponin I antibody, 2) the area void of anticardiac troponin I antibody fixation includes the whole ischemic area, and 3) evaluation of myocardial infarction size can be obtained by CTn I concentration as early as the ninth hour.