Establishment of a microspheres-based homogeneous fluorescence immunoassay for the rapid detection of cardiac troponin I

Myocardial infarction occurs rapidly, and thus the rapid detection of cTnI levels is the key to its diagnosis. Most current assays take 10-30 min. In this study, we developed a method for accurately measuring cardiac troponin I (cTnI) levels in human sera with amplified luminescence neighborhood homogeneous assay (AlphaLISA). The method involves coupling two cTnI antibodies targeting different epitopes to the surface of carboxylated donor and acceptor beads. The final signal values were detected by the double-antibody sandwich method, and the best reaction conditions were obtained by optimizing the experimental conditions. The sensitivity, specificity, accuracy, and precision of the method were evaluated. Results showed that the method requires only 3 min to produce the results, the detection sensitivity is 27.06 ng L-1, and the measurement range is 34.56-62 500 ng L-1. cTnI-AlphaLISA has an intra-assay precision of 2.18-4.57% (<10%) and an inter-assay precision of 5.60-6.95% (<10%). The relative recovery rates are within reasonable limits. In addition, the serum assay results of the method were compared with chemiluminescence immunoassay, and the results are in agreement with one another (ρ = 0.8803; P < 0.0001). The method is expected to be developed as a routine method, but further studies and evaluations are needed.

Portable microfluidic plasmonic chip for fast real-time cardiac troponin I biomarker thermoplasmonic detection

Acute myocardial infarction is one of the most serious cardiovascular pathologies, impacting patients' long-term outcomes and health systems worldwide. Significant effort is directed toward the development of biosensing technologies, which are able to efficiently and accurately detect an early rise of cardiac troponin levels, the gold standard in detecting myocardial injury. In this context, this work aims to develop a microfluidic plasmonic chip for the fast and accurate real-time detection of the cardiac troponin I biomarker (cTnI) via three complementary detection techniques using portable equipment. Furthermore, the study focuses on providing a better understanding of the thermoplasmonic biosensing mechanism taking advantage of the intrinsic photothermal properties of gold nanoparticles. Specifically, a plasmonic nanoplatform based on immobilized gold nanobipyramids was fabricated, exhibiting optical and thermoplasmonic properties that promote, based on a sandwich-like immunoassay, the "proof-of-concept" multimodal detection of cTnI via localized surface plasmon resonance, surface enhanced Raman spectroscopy and thermoplasmonic effects under simulated conditions. Furthermore, after the integration of the plasmonic nanoplatform in a microfluidic channel, the determination of cTnI in 16 real plasma samples was successfully realized via thermoplasmonic detection. The results are compared with a conventional high-sensitivity enzyme-linked immunosorbent clinical assay (ELISA), showing high sensitivity (75%) and specificity (100%) as well as fast response features (5 minutes). Thus, the proposed portable and miniaturized microfluidic plasmonic chip is successfully validated for clinical applications and transferred to clinical settings for the early diagnosis of cardiac diseases, leading towards the progress of personalized medicine.

Utility of Cardiac Troponins in Patients With Chronic Kidney Disease

Cardiovascular disease is a major cause of death worldwide especially in patients with chronic kidney disease (CKD). Troponin T and troponin I are cardiac biomarkers used not only to diagnose acute myocardial infarction (AMI) but also to prognosticate cardiovascular and all-cause mortality. The diagnosis of AMI in the CKD population is challenging because of their elevated troponins at baseline. The development of high-sensitivity cardiac troponins shortens the time needed to rule in and rule out AMI in patients with normal renal function. While the sensitivity of high-sensitivity cardiac troponins is preserved in the CKD population, the specificity of these tests is compromised. Hence, diagnosing AMI in CKD remains problematic even with the introduction of high-sensitivity assays. The prognostic significance of troponins did not differ whether it is detected with standard or high-sensitivity assays. The elevation of both troponin T and troponin I in CKD patients remains strongly correlated with adverse cardiovascular and all-cause mortality, and the prognosis becomes poorer with advanced CKD stages. Interestingly, the degree of troponin elevation appears to be predictive of the rate of renal decline via unclear mechanisms though activation of the renin-angiotensin and other hormonal/oxidative stress systems remain suspect. In this review, we present the latest evidence of the use of cardiac troponins in both the diagnosis of AMI and the prognosis of cardiovascular and all-cause mortality. We also suggest strategies to improve on the diagnostic capability of these troponins in the CKD/end-stage kidney disease population.

Cardiac troponins: Mechanisms of release and role in healthy and diseased subjects

The cardiac troponins (cTns), cardiac troponin C (cTnC), cTnT, and cTnI are key elements of myocardial apparatus, fixed as protein complex on the thin filament of sarcomere and are involved in the regulation of excitation-contraction coupling of cardiomyocytes in the presence of Ca²⁺ . Circulating cTnT and cTnI (cTns) increase following cardiac tissue necrosis, and they are consolidated biomarkers of acute myocardial infarction (AMI). However, the use of high sensitivity (hs)-immunoassay tests for cTnT and cTnI has made it possible to identify a multitude of other clinical conditions associated with increased circulating levels of cTns. cTns can be measured also in the peripheral circulation of healthy subjects or athletes, suggesting that different mechanisms are involved in the release of cTns in the blood independently of cardiac cell necrosis. In this review, the molecular/cellular mechanisms involved in cTns release in blood and the exploitation of cTnI and cTnT as biomarkers of cardiac adverse events, in addition to cardiac necrosis, are discussed.

Cardiac troponins - a paradigm for diagnostic biomarker identification and development

The introduction of cardiac troponins into clinical diagnostics has not only improved diagnostic pathways for myocardial infarction but also profoundly influenced the definition of myocardial infarction. The term troponin appeared in the literature almost 60 years ago, i.e. shortly after this journal was founded. The development of cardiac troponins from proteins involved in muscle contraction, which were in the focus of few specialized research groups from physiology and biochemistry, to one of the most frequently measured protein biomarkers in medicine is a paradigmatic success story which is also reflected in almost 300 publications on the topic in this journal. From the viewpoint of biomarker development the critical success factors were medical need, timely generation of medical evidence, and the rapid development of robust and precise laboratory assays.

Astaxanthin extenuates the inhibition of aldehyde dehydrogenase and Klotho protein expression in cyclophosphamide-induced acute cardiomyopathic rat model

This study evaluated the mechanistic sequel of aldehyde dehyrogenase (ALDH2) and Klotho protein in cyclophosphamide (CP)-induced cardiotoxicity in rats and the protective effect of astaxanthin (AST) against that sequel. A total of 40 male Wistar albino rats were divided into four groups of 10 animals each: Group 1 was injected intraperitoneally (i.p.) with normal saline for 10 successive days. Group 2 was injected with normal saline for 5 days before and after a single dose of CP (200 mg/kg, i.p.). Group 3 received AST (50 mg/kg/day, i.p.) for 10 days. Group 4 received CP as group 2 and AST as group 3. After the last dose of the treatment protocol, serum was separated to measure cardiotoxicity indices and the left ventricle was then dissected for mRNA and protein expression studies and histopathological examinations. Treatment with CP significantly increased serum lactate dehydrogenase (LDH), creatine kinase isoenzyme MB (CK-MB), and troponin, while significantly decreased soluble α Klotho protein and caused histopathological lesions in cardiac tissues. In cardiac tissues, CP significantly decreased gene expression of ALDH2, Klotho protein, mTOR, IGF, AKT, AMPK, BCL2, but significantly increased expression of BAX and caspase-8. Interestingly, administration of AST in combination with CP completely reversed all the biochemical, histopathological and gene expression changes induced by CP to the control values. The current study suggests that inhibition of ALDH2, Klotho protein, mTOR, and AMPK signals in cardiac tissues may contribute to CP-induced acute cardiomyopathy. AST supplementation attenuates CP-induced cardiotoxicity by modulating ALDH2 and Klotho protein expression in heart tissues, along with its downstream apoptosis effector markers.

Implications of the complex biology and micro-environment of cardiac sarcomeres in the use of high affinity troponin antibodies as serum biomarkers for cardiac disorders

Cardiac troponin I (cTnI), the inhibitory-unit, and cardiac troponin T (cTnT), the tropomyosin-binding unit together with the Ca-binding unit (cTnC) of the hetero-trimeric troponin complex signal activation of the sarcomeres of the adult cardiac myocyte. The unique structure and heart myocyte restricted expression of cTnI and cTnT led to their worldwide use as biomarkers for acute myocardial infarction (AMI) beginning more than 30 years ago. Over these years, high sensitivity antibodies (hs-cTnI and hs-cTnT) have been developed. Together with careful determination of history, physical examination, and EKG, determination of serum levels using hs-cTnI and hs-cTnT permits risk stratification of patients presenting in the Emergency Department (ED) with chest pain. With the ability to determine serum levels of these troponins with high sensitivity came the question of whether such measurements may be of diagnostic and prognostic value in conditions beyond AMI. Moreover, the finding of elevated serum troponins in physiological states such as exercise and pathological states where cardiac myocytes may be affected requires understanding of how troponins may be released into the blood and whether such release may be benign. We consider these questions by relating membrane stability to the complex biology of troponin with emphasis on its sensitivity to the chemo-mechanical and micro-environment of the cardiac myocyte. We also consider the role determinations of serum troponins play in the precise phenotyping in personalized and precision medicine approaches to promote cardiac health.

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Serum levels of cardiac TnI and cardiac TnT permit stratification of patients with chest pain.

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Release of troponins into blood involves not only frank necrosis but also programmed necroptosis.

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Genome wide analysis of serum troponin levels in the general population may be prognostic about cardiovascular health.

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Significant levels of serum troponins with exhaustive exercise may not be benign.

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Troponin in serum can lead to important data related to personalized and precision medicine.

Novel Invasive and Noninvasive Cardiac-Specific Biomarkers in Obesity and Cardiovascular Diseases

Cardiovascular disease (CVD) is the leading cause of fatality and disability worldwide regardless of gender. Obesity has reached epidemic proportions in population across different regions. According to epidemiological studies, CVD risk markers in childhood obesity are one of the significant risk factors for adulthood CVD, but have received disproportionally little attention. This review has examined the evidence for the presence of traditional cardiac biomarkers (nonspecific; lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase, creatine kinase, myoglobulin, glycogen phosphorylase isoenzyme BB, myosin light chains, ST2, and ischemia-modified albumin) and novel emerging cardiac-specific biomarkers (cardiac troponins, natriuretic peptides, heart-type fatty acid-binding protein, and miRNAs). Besides, noninvasive anatomical and electrophysiological markers (carotid intima-media thickness, coronary artery calcification, and heart rate variability) in CVDs and obesity are also discussed. Modifiable and nonmodifiable risk factors associated with metabolic syndrome in the progression of CVD, such as obesity, diabetes, hypertension, dyslipidemia, oxidative stress, inflammation, and adipocytokines are also outlined. These underlying prognostic risk factors predict the onset of future microvascular and macrovascular complications. The understanding of invasive and noninvasive cardiac-specific biomarkers and the risk factors may yield valuable insights into the pathophysiology and prevention of CVD in a high-risk obese population at an early stage.

Electrochemiluminescence Immunosensor Based on Au Nanocluster and Hybridization Chain Reaction Signal Amplification for Ultrasensitive Detection of Cardiac Troponin I

Measurement of cardiac troponin I in the blood is crucial for the early diagnosis of acute myocardial infarction. Herein, a novel and ultrasensitive electrochemiluminescence (ECL) immunosensor has been developed for determination of cardiac troponin I (cTnI) by using Au nanoclusters and hybridization chain reaction (HCR) signal amplification. In this ECL immunosensor, Au nanoclusters were dual-labeled at each end of hairpin DNA (H₁ and H₂) and acted as the luminophore. DNA initiator strands (T₁) and secondary antibody (Ab₂) were conjugated on Au nanoparticles (AuNPs) to obtain a smart probe (Ab₂-AuNP-T₁). In the presence of target cTnI, the sandwiched immunocomplex composed of cTnI, Ab₁, and Ab₂-AuNP-T₁ was formed. Then the initiator strands T₁ of Ab₂-AuNP-T₁ opened the hairpin DNA structures and triggered a cascade of hybridization events. Consequently, a large number of Au NCs were indirectly modified on the surface of the electrode, which could react with the coreactant (K₂S₂O₈) and emit a strong ECL signal. Under the optimal conditions, the immunosensor exhibited a wide detection range for cTnI from 5 fg/mL to 50 ng/mL and a low detection limit of 1.01 fg/mL (S/N = 3). Because of the excellent specificity, stability, and reproducibility of the proposed ECL-HCR sensor, it has a great application prospect for cTnI detection in clinical diagnosis.

A paper microfluidics-based fluorescent lateral flow immunoassay for point-of-care diagnostics of non-communicable diseases

In the emergency diagnosis of patients, acute myocardial infarction (AMI) is always time-consuming to diagnose, and the process requires multiple laboratory procedures, expensive equipment and skilled workers. Herein, we developed an easy-to-use, low-cost and portable fluorescent lateral flow immunoassay based on paper microfluidics for the point-of-care diagnostics of non-communicable diseases. The fluorescent lateral flow immunoassay can produce results in less than 10 minutes, and the limit of detection (LOD) is 0.019 ng ml^-1. The slope was linear from 0 to 100 ng ml^-1; the equation is y = 0.0342e^2.1181x and R² = 0.9618, which are distinctive features that ensure maximum amplification of the signal and recording of quantitative values by an analyser. The detection sensitivity showed an exceptional increase to 0.01 ng ml^-1. Compared with conventional bioassay readers, our analyser shows some advantages to easily, clearly and effectively read data. The present point-of-care test for cardiac troponin I decreases the turnaround time and has a high coefficient of variation even at lower concentrations of troponin. So, the development of lateral flow assay-based point-of-care assays with higher analytical performance for real world samples can decrease the rule-out time for AMI in emergency departments and other fields.

Multiplexed chemiluminescence determination of three acute myocardial infarction biomarkers based on microfluidic paper-based immunodevice dual amplified by multifunctionalized gold nanoparticles

Acute myocardial infarction (AMI) causes significant mortality and morbidity. The determination of multiple AMI biomarkers is very important for the timely diagnosis of AMI. In this work, simultaneous determination of three AMI biomarkers were achieved by virtue of a three-dimensional (3D) microfluidic paper-analytical device (μPAD) with temporally resolved chemiluminescence (CL) emissions for the first time. A dual-signal amplification strategy was introduced including by employing primary antibody functionalized gold nanoparticles (Ab₁-GNPs) immobilized on the detection zone as amplified capture probes, and Co(II) catalyst, secondary antibody, luminol multifunctionalized gold nanoparticles (Co(II)-Ab₂-luminol-GNPs) with excellent CL activity as amplified signal probes. CL immunoreactions were performed at three detection zone of the fabricated 3D μPAD by assembling Ab₁-GNPs, antigen, and Co(II)-Ab₂-luminol-GNPs to form sandwich-type immunocomplexes. Auto separated CL signals with temporal resolution were obtained by time delayed transport of H₂O₂ to different detection zones for multiplexed analysis. The CL signal obtained by using Co(II)-Ab₂-luminol-GNPs as signal probe (10576 a.u.) were about 20-fold higher than that by using conventional horseradish peroxidase labeled antibody modified luminol-GNPs as signal probe (531 a.u.). Finally, three AMI biomarkers including heart-type fatty acid-binding protein (H-FABP), cardiac troponin I (cTnI) and copeptin were quantitatively analyzed in one CL detection run by reading the CL intensity of the obtained three CL emission peaks. The detection range were ultra-wide ranged from 0.1 pg/mL to 1 μg/mL, 0.5 pg/mL to 1 μg/mL and 1 pg/mL to 1 mg/mL with the detection limits down to 0.06 pg/mL, 0.3 pg/mL and 0.4 pg/mL for H-FABP, cTnI and copeptin detection, respectively. The developed μPAD based immunoassay performing multiplexed analysis ability, high sensitivity, ultra-wide dynamic range, favorable selectivity, accessible accuracy and reproducibility, have great application potential for the early diagnosis of AMI.

DNA nanotetrahedron-assisted electrochemical aptasensor for cardiac troponin I detection based on the co-catalysis of hybrid nanozyme, natural enzyme and artificial DNAzyme

The sensitive and accurate detection of cardiac troponin I (cTnI) is critical for myocardial infarction diagnosis. In this work, a dual-aptamer-based electrochemical (EC) biosensor was designed for cTnI detection based on the DNA nanotetrahedron (NTH) capture probes and multifunctional hybrid nanoprobes. First, the NTH-based Tro4 aptamer probes were anchored on a screen printed gold electrode (SPGE) surface through the Au-S bond, providing an enhanced spatial dimension and accessibility for capturing cTnI. Then, the hybrid nanoprobes were fabricated by using magnetic Fe₃O₄ nanoparticles as nanocarriers to load a large amount of cTnI-specific Tro6 aptamer, natural horseradish peroxidase (HRP), HRP-mimicking Au@Pt nanozymes and G-quadruplex/hemin DNAzyme. This signaling nanoprobes are capable of specifically recognizing the target cTnI based on the Tro6 aptamer and amplifying the signals to improve the detection sensitivity via enzymatic processes. We found the remarkable enhanced effect of EC signal to be attributed to the co-catalysis effect of hybrid nanozymes, HRP and DNAzyme. The target cTnI was sandwiched between the two types of aptamers (Tro4 and Tro6) on the electrode interface. Finally, this EC aptasensing platform exhibited great analytical performance with a wide dynamic range of 0.01-100 ng mL^-1 and a low detection limit of 7.5 pg mL^-1 for cTnI. The high selectivity, sensitivity and reliability of EC aptasensor can provide great potential in the clinic disease diagnostics.

A graphene oxide/gold nanoparticle-based amplification method for SERS immunoassay of cardiac troponin I

A multiple signal amplification of a SERS biosensor was developed for sensitive detection of cTnI with the aid of GO/AuNP complexes.

Studies towards hcTnI Immunodetection Using Electrochemical Approaches Based on Magnetic Microbeads

Different electrochemical strategies based on the use of magnetic beads are described in this work for the detection of human cardiac troponin I (hcTnI). hcTnI is also known as the gold standard for acute myocardial infarction (AMI) diagnosis according to the different guidelines from the European Society of Cardiology (ESC) and the American College of Cardiology (ACC). Amperometric and voltamperometric sandwich magnetoimmunoassays were developed by biofunctionalization of paramagnetic beads with specific antibodies. These bioconjugates were combined with biotinylated antibodies as detection antibodies, with the aim of testing different electrochemical transduction principles. Streptavidin labeled with horseradish peroxidase was used for the amperometric magnetoimmunoassay, reaching a detectability of 0.005 ± 0.002 µg mL-1 in 30 min. Cadmium quantum dots-streptavidin bioconjugates were used in the case of the voltamperometric immunosensor reaching a detectability of 0.023 ± 0.014 µg mL-1.

Rapid and Sensitive Detection of Cardiac Troponin I for Point-of-Care Tests Based on Red Fluorescent Microspheres

A reliable lateral flow immunoassay (LFIA) based on a facile one-step synthesis of single microspheres in combining with immunochromatography technique was developed to establish a new point-of-care test (POCT) for the rapid and early detection of cardiac troponin I (cTnI), a kind of cardiac specific biomarker for acute myocardial infarction (AMI). The double layered microspheres with clear core-shell structures were produced using soap-free emulsion polymerization method with inexpensive compounds (styrene and acrylic acid). The synthetic process was simple, rapid and easy to control due to one-step synthesis without any complicated procedures. The microspheres are nanostructure with high surface area, which have numerous carboxyl groups on the out layer, resulting in high-efficiency coupling between the carrier and antibody via amide bond. Meanwhile, the red fluorescent dye, Nile-red (NR), was wrapped inside the microspheres to improve its stability, as well to reduce the background noise, because of its higher emission wavelength than interference from real plasma samples. The core-shell structures provided different functional areas to separate antibody and dyes, so the immunoassay has highly sensitive, wide working curves in the range of 0–40 ng/mL, low limits of detection (LOD) at 0.016 ng/mL, and limits of quantification (LOQ) at 0.087 ng/mL with coefficient of variations (CV) of 10%. This strategy suggested an outstanding platform for LFIA, with good reproducibility and stability to straightforwardly analyze the plasma samples without washing steps, thereby reducing the operating procedures for non-professionals and promoting detection efficiency. The whole detection process can be completed in less than 15 min. This novel immunoassay offers a reliable and favorable analytical result by detecting the real samples, indicating that it holds great potential as a new alternative for biomolecule detection in complex samples, for the early detection of cardiac specific biomarkers.

Ultrasensitive label-free optical microfiber coupler biosensor for detection of cardiac troponin I based on interference turning point effect

Sensitive detection of cardiac biomarkers is critical for clinical diagnostics of myocardial infarction (MI) while such detection is quite challenging due to the ultra-low concentration of cardiac biomarkers. In this work, a label-free immunosensor based on optical microfiber coupler (OMC) has been developed for the ultrasensitive detection of cardiac troponin I (cTnI), a selective and highly sensitive biomarker of acute myocardial infarction (AMI). CTnI monoclonal antibodies were immobilized on the surface of the fiber through polyelectrolyte layer using layer-by-layer deposition technique. For refractive index sensing characterization, an ultra-high sensitivity of 91777.9 nm/RIU was achieved when the OMC works around the dispersion turning point, which is the highest experimental demonstration in the field of fiber-optic evanescent biosensors. For biosensing, the immunosensor with good specificity showed a linear wavelength shift in the range of 2-10 fg/mL and an ultra-low detection limit of 2 fg/mL. Such immunosensors have huge application potential for the detection of cardiac biomarkers of myocardial infarction due to simple detection scheme, quick response time, ease of handling and miniaturation.

Cardiac troponins: 25 years on the stage and still improving their clinical value

Twenty-five years ago, non-isotopic immunoassays for measuring the cardiac specific isoforms of troponin I (cTnI) and T (cTnT) were developed. Both biomarkers radically changed the diagnosis, prognosis, and therapy indication of acute coronary syndromes (ACS) and, particularly, of myocardial infarction (MI). However, cardiac troponins (cTn) rapidly demonstrated their usefulness in other cardiac and non-cardiac conditions, a part of the ischemic coronary diseases. Consequently, the number of patients to be tested for cTn and the number of tests requested to clinical laboratories sharply increased. Though the manufacturers continuously improved the analytical characteristics of the first cTn assays and produced different cTn assay "generations", the universal definition of myocardial infarction required less-than-available analytical imprecision at the cTn concentration used to assess MI (i.e. the 99th reference percentile). To address the clinical requirements, manufacturers developed the high-sensitivity cTn (hs-cTn) assays that allow to measure the 99th reference percentile with adequate precision, to detect cTn in many healthy subjects and, hence, to calculate the hs-cTn biological variation and especially to observe in very short time intervals serial differences in hs-cTn attributable to cardiac ischemia. Since the number of patients attending the emergency departments (ED) for a suspected ACS or MI is increasing, the improved properties of hs-cTn assays, allowing faster and safer patient assessment, will help to alleviate the sometimes overcrowded EDs. However, there are many biological, analytical, and clinical factors that can influence the true hs-cTn values of a patient. Clinicians and laboratory professionals should know about them for the best interpretation of the otherwise largely useful hs-cTn measurements. In conclusion, 25 years after their introduction for clinical use, "cTn are still on the stage and improving their clinical value".

Analytical validation of cardiac troponin I assays in horses

Human cardiac troponin I (cTnI) assays have been used in equine medicine, often without prior analytical validation for equine use. In the absence of appropriate validation, the clinical significance of assay results is uncertain and can lead to misdiagnosis. We followed the American Society for Veterinary Clinical Pathology guidelines and investigated linearity, precision, limit of quantification (LoQ), and comparative recovery for 6 commercial cTnI assays developed for use in human medicine. Clinically acceptable linearity was observed in assays A-D, whereas assay E did not detect equine cTnI in any sample. Comparative recovery revealed 1-3-fold differences between assay results, and low analyte recoveries (2.2-3.4%) were observed in assay F. Precision was investigated in assays A and B, and found to be within acceptable limits. The LoQ was 1.53 ng/L for assay A, and 0.031 µg/L for assay B. Assays A and B performed within clinically acceptable limits and were deemed suitable for use in equine medicine. Assays C and D did not undergo full validation but had acceptable linearity, which demonstrates their potential for use in equine medicine. Assays E and F are unsuitable for use in horses given issues with detection of equine cTnI. The variability in results between assays indicates that reference intervals and cutoffs for diagnostic decision-making are assay specific and should be established prior to adoption by diagnostic laboratories.

Advances in Cardiac Biomarkers of Acute Coronary Syndrome

Acute coronary syndrome (ACS) encompasses a pathophysiological spectrum of cardiovascular diseases, all of which have significant morbidity and mortality. ACS was once considered an acute condition; however, new treatment strategies and improvements in biomarker assays have led to ACS being an acute and chronic disease. Cardiac troponin is the preferred biomarker for the diagnosis of myocardial infarction, and there is considerable interest and efforts toward development and implementation of high-sensitivity cardiac troponin (hs-cTn) assays worldwide. Analytical and clinical performance characteristics of hs-cTn assays as well as testing limitations are important for laboratorians and clinicians to understand in order to utilize testing appropriately. Furthermore, expanding the clinical utility of hs-cTn into other cohorts such as asymptomatic community dwelling populations, heart failure, and chronic kidney disease populations supports novel opportunities for improved short- and long-term prognosis.

Using anti-poly(ethylene glycol) bioparticles for the quantitation of PEGylated nanoparticles

Attachment of polyethylene glycol (PEG) molecules to nanoparticles (PEGylation) is a widely-used method to improve the stability, biocompatibility and half-life of nanomedicines. However, the evaluation of the PEGylated nanomedicine pharmacokinetics (PK) requires the decomposition of particles and purification of lead compounds before analysis by high performance liquid chromatography (HPLC), mass spectrometry, etc. Therefore, a method to directly quantify un-decomposed PEGylated nanoparticles is needed. In this study, we developed anti-PEG bioparticles and combined them with anti-PEG antibodies to generate a quantitative enzyme-linked immunosorbent assay (ELISA) for direct measurement of PEGylated nanoparticles without compound purification. The anti-PEG bioparticles quantitative ELISA directly quantify PEG-quantum dots (PEG-QD), PEG-stabilizing super-paramagnetic iron oxide (PEG-SPIO), Lipo-Dox and PEGASYS and the detection limits were 0.01 nM, 0.1 nM, 15.63 ng/mL and 0.48 ng/mL, respectively. Furthermore, this anti-PEG bioparticle-based ELISA tolerated samples containing up to 10% mouse or human serum. There was no significant difference in pharmacokinetic studies of radiolabeled PEG-nanoparticles (Nano-X-¹¹¹In) through anti-PEG bioparticle-based ELISA and a traditional gamma counter. These results suggest that the anti-PEG bioparticle-based ELISA may provide a direct and effective method for the quantitation of any whole PEGylated nanoparticles without sample preparation.

Flexible Molybdenum Electrodes towards Designing Affinity Based Protein Biosensors

Molybdenum electrode based flexible biosensor on porous polyamide substrates has been fabricated and tested for its functionality as a protein affinity based biosensor. The biosensor performance was evaluated using a key cardiac biomarker; cardiac Troponin-I (cTnI). Molybdenum is a transition metal and demonstrates electrochemical behavior upon interaction with an electrolyte. We have leveraged this property of molybdenum for designing an affinity based biosensor using electrochemical impedance spectroscopy. We have evaluated the feasibility of detection of cTnI in phosphate-buffered saline (PBS) and human serum (HS) by measuring impedance changes over a frequency window from 100 mHz to 1 MHz. Increasing changes to the measured impedance was correlated to the increased dose of cTnI molecules binding to the cTnI antibody functionalized molybdenum surface. We achieved cTnI detection limit of 10 pg/mL in PBS and 1 ng/mL in HS medium. The use of flexible substrates for designing the biosensor demonstrates promise for integration with a large-scale batch manufacturing process.

Cardiac Troponin I Concentrations during On-Pump Coronary Artery Surgery

Perioperative myocardial infarction remains a frequent complication after coronary artery bypass grafting, and is associated with a poor prognosis. This retrospective study compared cardiac troponin I concentrations after on-pump bypass grafting in 2 groups of patients: 100 operated on using a single-clamp technique to perform anastomoses, and 80 operated on using a double-clamp technique. Postoperative cardiac troponin I levels were not significantly different between groups. It was concluded that the double-clamp technique did not reduce the incidence of myocardial infarction after elective on-pump coronary artery bypass grafting, and use of a single clamp is safe with no adverse effect on postoperative outcome.

A High-Performance Fluorescence Immunoassay Based on the Relaxation of Quenching, Exemplified by Detection of Cardiac Troponin I

The intramolecular fluorescence self-quenching phenomenon is a major drawback in developing high-performance fluorometric biosensors which use common fluorophores as signal generators. We propose two strategies involving liberation of the fluorescent molecules by means of enzymatic fragmentation of protein or dehybridization of double-stranded DNA. In the former, bovine serum albumin (BSA) was coupled with the fluorescent BODIPY dye (Red BSA), and then immobilized on a solid surface. When the insolubilized Red BSA was treated with proteinase K (10 units/mL) for 30 min, the fluorescent signal was significantly increased (3.5-fold) compared to the untreated control. In the second case, fluorophore-tagged DNA probes were linked to gold nanoparticles by hybridization with capture DNA strands densely immobilized on the surface. The quenched fluorescence signal was recovered (3.7-fold) by thermal dehybridization, which was induced with light of a specific wavelength (e.g., 530 nm) for less than 1 min. We next applied the Red BSA self-quenching relaxation technique employing enzymatic fragmentation to a high-performance immunoassay of cardiac troponin I (cTnI) in a microtiter plate format. The detection limit was 0.19 ng/mL cTnI, and the fluorescent signal was enhanced approximately 4.1-fold compared with the conventional method of direct measurement of the fluorescent signal from a non-fragmented fluorophore-labeled antibody.

Electrochemical aptasensor of cardiac troponin I for the early diagnosis of acute myocardial infarction

Cardiac troponin I (cTnI) is well-known as a promising biomarker for the early diagnosis of acute myocardial infarction (AMI). In this work, single-stranded DNA aptamers against cTnI were identified by the Systematic Evolution of Ligands by Exponential enrichment (SELEX) method. The aptamer candidates exhibited a high selectivity and sensitivity toward both cTnI and the cardiac Troponin complex. The binding affinities of each aptamer were evaluated based on their dissociation constants (Kd) by surface plasma resonance. The Tro4 aptamer that had the highest binding capacity to cTnI showed a very low Kd value (270 pM) compared with that of a cTnI antibody (20.8 nM). Furthermore, we designed a new electrochemical aptasensor based on square wave voltammetry using ferrocene-modified silica nanoparticles. The developed aptasensor demonstrated an excellent analytical performance for cTnI with a wide linear range of 1-10 000 pM in a buffer and a detection limit of 1.0 pM (24 pg/mL; S/N = 3), which was noticeably lower than the cutoff values (70-400 pg/mL). The specificity of the aptamers was also examined using nontarget proteins, demonstrating that the proposed sensor responded to only cTnI. In addition, cTnI was successfully detected in a human serum albumin solution. On the basis of the calibration curve that was constructed, the concentrations of cTnI in a solution supplemented with human serum were effectively measured. The calculated values correlated well with the actual concentrations of cTnI. It is anticipated that the highly sensitive and selective aptasensor for cTnI could be readily applicable for the accurate diagnosis of AMI.

The effect of elapsed time on cardiac troponin-T (cTnT) degradation and its relation to postmortem interval in cases of electrocution

BACKGROUND

The estimation of postmortem interval (PMI) is of paramount importance for the police in their investigation when arriving at the scene of a questionable death. The aim of present study is to evaluate the effect of elapsed time on cardiac Troponin-T degradation and its association with PMI in cases of death due to electrocution.

METHODS

Cardiac tissue samples were collected from medico-legal autopsies, after informed consent from the relatives. The cases included were the subjects of electrocution without any prior history of disease who died in the hospital and their exact time of death was known. The analysis involves extraction of the protein at room temperature for different time periods (∼5, 26, 50, 84, 132, 157, 180, 205 and 230 Hrs), separation by SDS-PAGE and visualization by Western blot using cTnT specific monoclonal antibodies.

RESULTS

The results specify a characteristic banding pattern amongst human cadavers (n = 5), a pseudo-linear relationship between percent cTnT degraded and the time since death (R(2) = 0.87, p = 0.0001) was observed. The area of the bands within a lane was quantified by scanning and digitizing the image using Gel Doc (Universal Hood II).

CONCLUSIONS

The post-mortem Troponin-T fragmentation observed in this study reveals a sequential, time-dependent process with the potential for use as a predictor of PMI in cases of electrocution.

Diagnostics on acute myocardial infarction: Cardiac troponin biomarkers

Acute myocardial infarction or myocardial infarction (MI) is a major health problem, due to diminished flow of blood to the heart, leads to higher rates of mortality and morbidity. Data from World Health Organization (WHO) accounted 30% of global death annually and expected more than 23 million die annually by 2030. This fatal effects trigger the need of appropriate biomarkers for early diagnosis, thus countermeasure can be taken. At the moment, the most specific markers for cardiac injury are cardiac troponin I (cTnI) and cardiac troponin T (cTnT) which have been considered as 'gold standard'. Due to higher specificity, determination of the level of cardiac troponins became a predominant indicator for MI. Several ways of diagnostics have been formulated, which include enzyme-linked immunosorbent assay, chemiluminescent, fluoro-immunoassays, electrical detections, surface plasmon resonance, and colorimetric protein assay. This review represents and elucidates the strategies, methods and detection levels involved in these diagnostics on cardiac superior biomarkers. The advancement, sensitivity, and limitations of each method are also discussed. In addition, it concludes with a discussion on the point-of care (POC) assay for a fast, accurate and ability of handling small sample measurement of cardiac biomarker.

Diagnostic value of cardiac troponin I in postmortem diagnosis of myocardial infarction

Troponin I (cTnI) is a very sensitive biochemical marker for the diagnosis of myocardial infarction (MI). Cardiac troponin (cTnI or cTnT) has nearly absolute myocardial tissue specificity, thereby reflecting even microscopic zones of myocardial necrosis. The aim of this study is to evaluate the pericardial fluid levels of cTnI in medicolegal autopsy cases where patients died of MI and compare them with cases where patients died of other causes. This study included 89 cases selected during a 1-year period from medicolegal autopsies. These were classified into 4 groups: (A) myocardial infarction (n = 28), (B) salt water drowning (n = 20), (C) death resulting from injury in the respiratory system (n = 16), and (D) other causes of death (n = 25), excluding MI. The mean concentrations of cTnI were 1067.03 mg/dL for group A, 546.98 mg/dL for group B, 398.75 mg/dL for group C, and 577.47 mg/dL for group D. In cases with MI (group A), there was a significant difference in the levels of cTnI compared with the other cases. More research needs to be done in order for a cutoff level to be determined.

Blood cardiac troponin in toxic myocardial injury: archetype of a translational safety biomarker

A translational safety biomarker for toxic myocardial injury is needed in drug discovery and development. This need reflects the increasing recognition of occurrence of cardiotoxicities, prior lack of preclinical blood biomarkers for toxic cardiac injury, introduction of troponin as a biomarker, and regulatory and industry drivers. Cardiac troponin is considered the gold-standard biomarker in humans for cardiac injury due to ischemic injury and drug toxicity. It has been demonstrated to correlate highly with histopathological extent of injury, degree of impairment of cardiac function, and prognosis. Numerous studies have now clearly demonstrated that both cardiac troponin T and cardiac troponin I are sensitive and specific biomarkers of cardiac injury in laboratory animals. Their use is highly recommended for incorporation into preclinical drug-safety studies, especially whenever there is any history of cardiac effect in prior studies with a compound of the same or similar chemical or pharmacological class. The main caveats with respect to cross-species use of specific cardiac troponin assays are the need for species-specific validation, definition of cut-offs based on relevant assessments of imprecision and reference ranges or concurrent controls, and knowledge of the species-dependent kinetics of release into, and clearance from, the blood. Future development of high-sensitivity assays should determine whether minimal increases below a threshold concentration of troponin might reflect reversible myocardial effects.

Electrochemiluminescence immunosensor using poly(l-histidine)-protected glucose dehydrogenase on Pt/Au bimetallic nanoparticles to generate an in situ co-reactant

A new ECL immunosensor based on poly(l-histidine)-protected glucose dehydrogenase on Pt/Au bimetallic nanoparticles to generate co-reactantin situ.

The influence of age on serum concentrations of cardiac troponin I: results in rats, monkeys, and commercial sera

Cardiac troponins serve as serum biomarkers of myocardial injury. The current study examined the influence of age on serum concentrations of cardiac troponin I (cTnI). An ultrasensitive immunoassay was used to monitor cTnI concentrations in Sprague-Dawley (SD) rats and Erythrocebus patas monkeys of different ages. The mean cTnI concentrations were highest in 10-day-old rats compared to 25-, 40-, and 80-day-old SD rats. Cardiomyocyte remodeling was apparent in hearts from 10-day-old SD rats as evident by hypercellularity, irregularly shaped nuclei, and moderate numbers of myocytes undergoing mitosis and apoptosis. The mean concentration of cTnI in 5 newborn monkeys was considerably higher than that of three 1-year-old monkeys. Evidence of cardiomyocyte remodeling was also observed in these newborn hearts (loss of myofibrils and cytoplasmic vacuolation). Commercial animal serum samples were also analyzed. The concentrations of cTnI detected in fetal equine and porcine serum were considerably higher than that found in adult equine and porcine serum samples Likewise, fetal bovine serum had higher cTnI concentrations (>2,400 pg/ml) than did adult caprine and laprine samples (2.5-2.7 pg/ml). The present study found age-related differences in cTnI concentrations, with higher levels occurring at younger ages. This effect was consistent across several animal species.

Circulating microRNAs as novel biomarkers for the early diagnosis of acute coronary syndrome

Small non-coding microRNAs (miRNAs) are important physiological regulators of post-transcriptional gene expression. miRNAs not only reside in the cytoplasm but are also stably present in several extracellular compartments, including the circulation. For that reason, miRNAs are proposed as diagnostic biomarkers for various diseases. Early diagnosis of acute coronary syndrome (ACS), especially non-ST elevated myocardial infarction and unstable angina pectoris, is essential for optimal treatment outcome, and due to the ongoing need for additional identifiers, miRNAs are of special interest as biomarkers for ACS. This review highlights the nature and cellular release mechanisms of circulating miRNAs and therefore their potential role in the diagnosis of myocardial infarction. We will give an update of clinical studies addressing the role of circulating miRNA expression after myocardial infarction and explore the diagnostic value of this potential biomarker.

Cardiac troponins I and T: molecular markers for early diagnosis, prognosis, and accurate triaging of patients with acute myocardial infarction

Acute myocardial infarction (AMI) is the leading cause of death worldwide, with early diagnosis still being difficult. Promising new cardiac biomarkers such as troponins and creatine kinase (CK) isoforms are being studied and integrated into clinical practice for early diagnosis of AMI. The cardiac-specific troponins I and T (cTnI and cTnT) have good sensitivity and specificity as indicators of myocardial necrosis and are superior to CK and its MB isoenzyme (CK-MB) in this regard. Besides being potential biologic markers, cardiac troponins also provide significant prognostic information. The introduction of novel high-sensitivity troponin assays has enabled more sensitive and timely diagnosis or exclusion of acute coronary syndromes. This review summarizes the available information on the potential of troponins and other cardiac markers in early diagnosis and prognosis of AMI, and provides perspectives on future diagnostic approaches to AMI.