Incidentally Raised Cardiac Troponin I Has a Worse Prognosis in Older Patients Compared to Those with Normal Cardiac Troponin I and Patients with Acute Coronary Syndrome : A Cohort Study

Acknowledgement J.H.B.-S. was supported by the Norfolk and Norwich University Hospital (NNUH) Research and Development (R&D) research capability funds between July 2013 and December 2014.

Troponin I and cardiovascular risk prediction in the general population: the BiomarCaRE consortium

AIMS: Our aims were to evaluate the distribution of troponin I concentrations in population cohorts across Europe, to characterize the association with cardiovascular outcomes, to determine the predictive value beyond the variables used in the ESC SCORE, to test a potentially clinically relevant cut-off value, and to evaluate the improved eligibility for statin therapy based on elevated troponin I concentrations retrospectively.

METHODS AND RESULTS: Based on the Biomarkers for Cardiovascular Risk Assessment in Europe (BiomarCaRE) project, we analysed individual level data from 10 prospective population-based studies including 74 738 participants. We investigated the value of adding troponin I levels to conventional risk factors for prediction of cardiovascular disease by calculating measures of discrimination (C-index) and net reclassification improvement (NRI). We further tested the clinical implication of statin therapy based on troponin concentration in 12 956 individuals free of cardiovascular disease in the JUPITER study. Troponin I remained an independent predictor with a hazard ratio of 1.37 for cardiovascular mortality, 1.23 for cardiovascular disease, and 1.24 for total mortality. The addition of troponin I information to a prognostic model for cardiovascular death constructed of ESC SCORE variables increased the C-index discrimination measure by 0.007 and yielded an NRI of 0.048, whereas the addition to prognostic models for cardiovascular disease and total mortality led to lesser C-index discrimination and NRI increment. In individuals above 6 ng/L of troponin I, a concentration near the upper quintile in BiomarCaRE (5.9 ng/L) and JUPITER (5.8 ng/L), rosuvastatin therapy resulted in higher absolute risk reduction compared with individuals <6 ng/L of troponin I, whereas the relative risk reduction was similar.

CONCLUSION: In individuals free of cardiovascular disease, the addition of troponin I to variables of established risk score improves prediction of cardiovascular death and cardiovascular disease.

Roles of the troponin isoforms during indirect flight muscle development in Drosophila

Troponin proteins in cooperative interaction with tropomyosin are responsible for controlling the contraction of the striated muscles in response to changes in the intracellular calcium concentration. Contractility of the muscle is determined by the constituent protein isoforms, and the isoforms can switch over from one form to another depending on physiological demands and pathological conditions. In Drosophila, a majority of the myofibrillar proteins in the indirect flight muscles (IFMs) undergo post-transcriptional and post-translational isoform changes during pupal to adult metamorphosis to meet the high energy and mechanical demands of flight. Using a newly generated Gal4 strain (UH3-Gal4) which is expressed exclusively in the IFMs, during later stages of development, we have looked at the developmental and functional importance of each of the troponin subunits (troponin-I, troponin-T and troponin-C) and their isoforms. We show that all the troponin subunits are required for normal myofibril assembly and flight, except for the troponin-C isoform 1 (TnC1). Moreover, rescue experiments conducted with troponin-I embryonic isoform in the IFMs, where flies were rendered flightless, show developmental and functional differences of TnI isoforms and importance of maintaining the right isoform.

Troponina I y factores de riesgo como predictores enfermedad ateroesclerótica coronaria en pacientes con IAM sin elevación del ST en Bogotá 2010-2013

RESUMEN Introducción: La enfermedad cardiovascular es una de las principales causas de morbilidad y mortalidad tanto en hombres como en mujeres a nivel mundial (1). En Colombia para el 2010, se presentaron 26.334 muertes por infarto agudo de miocardio, siendo la primera causa de defunción a nivel nacional (2). Objetivo: Determinar factores de riesgo asociados a troponina I de alta sensibilidad como predictores de enfermedad coronaria ateroesclerótica en pacientes con infarto agudo de miocardio sin elevación del ST, con alteración vascular coronaria ateroesclerótica demostrada por coronoangiografía en una población de pacientes ingresados a la unidad coronaria de una clínica privada de III nivel de la ciudad de Bogotá durante los años 2010 al 2013. Metodología: Se propuso un estudio retrospectivo observacional analítico, tipo casos y controles, en una población con diagnóstico de infarto agudo de miocardio sin elevación ST que consultó a un servicio de urgencias de una clínica privada de Bogotá, en la cual se quiso evaluar la predictividad de la troponina I ultrasensible para el diagnóstico de enfermedad coronaria ateroesclerótica comprobada por coronoangiografía, y los factores de riesgo asociados que pudieran aumentar dicha predictividad. Resultados: De los 918 pacientes diagnosticados con infarto agudo de miocardio sin elevación del ST, estratificados según presencia de enfermedad coronaria ateroesclerótica comprobada por coronoangiografía, se encontró que la troponina I presentó una sensibilidad de 89% y una especificidad de 18% para el diagnóstico de enfermedad coronaria sin elevación del ST al ingreso a urgencias en un paciente diagnosticado clínicamente con IAM sin elevación del ST. En cuanto al valor predictivo positivo este fue de 77% y el valor predictivo negativo fue de 35%. En el modelo propuesto, si un paciente presentara edad avanzada (65 años), troponina I ultrasensible positiva, diabetes mellitus, dislipidemia, tabaquismo, enfermedad coronaria previa, enfermedad artero-oclusiva, historia de stent previo, revascularización previa, este paciente presentaría un riesgo de tener enfermedad ateroesclerótica coronaria de 99.83%; mientras que si un paciente presentara edad avanzada (65 años), troponina I ultrasensible positiva, diabetes mellitus, dislipidemia, tabaquismo, enfermedad artero-oclusiva, este paciente presentaría un riesgo de tener enfermedad ateroesclerótica coronaria de 96.81%. Adicionalmente, el modelo propuesto presenta una probabilidad pronostica de 0,828, evaluado por curva ROC. Conclusión: La predictividad de la troponina I para enfermedad coronaria ateroesclerótica fue aceptable. Sin embargo esta aumenta cuando se suma a factores de riesgo como ser hombre, edad avanzada, diabetes, tabaquismo, enfermedad coronaria previa, enfermedad arterial oclusiva previa, STENT previo, PCI previo y revascularización previa.

Malondialdeído e troponina I cardíaca em equinos da raça Puro Sangue Árabe submetidos ao exercício e à suplementação com vitamina E

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The Effects of N Helix Deletion and Mutant F29W on the Ca2+ Binding and Functional Properties of Chicken Skeletal Muscle Troponin C

To assess the structural and functional significance of the N helix (residues 3-13) of avian recombinant troponin C (rTnC), we have constructed NHdel, in which residues 1-11 have been deleted, both in rTnC and in the spectral probe mutant F29W (Pearlstone, J. R., Borgford, T., Chandra, M., Oikawa, K., Kay, C. M., Herzberg, O., Moult, J., Herklotz, A., Reinach, F. C., and Smillie, L.B. (1992) Biochemistry 31, 6545-6553). Comparison of the far- and near-UV CD spectra (±Ca2+) of F29W and F29W/ NHdel and titration of the Ca2+-induced ellipticity and fluorescence changes indicates that the deletion has little effect on the global fold of the molecule but reduces the Ca2+ affinity of the N domain, but not the C domain, by 1.6-1.8-fold. Comparisons of the mutants NHdel, F29W, and F29W/NHdel with rTnC have been made using several functional assays. In reconstituted troponin-tropomyosin actomyosin subfragment 1 and myofibrillar ATPase systems, both F29W and NHdel have significantly reduced Ca2+-activated enzymic activities. These effects are cumulative in the double mutant F29W/ NHdel. On the other hand, maximal isometric tension development in Ca2+-activated reconstituted skinned fibers is not affected with F29W and NHdel, although the Ca2+ sensitivity of NHdel in this system is markedly reduced. We conclude that both mutations, NHdel and F29W, are functionally deleterious, possibly affecting interactions of the N domain with troponin I and/or T.

Malondialdeído, troponina I cardíaca e eletrocardiografia em equinos da raça puro sangue árabe submetido ao exercício e à suplementação com vitamina E(dl-alfa-tocofenol)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Experimental dissection and characterization of the functional domains in cardiac troponin C

Contraction of vertebrate cardiac muscle is regulated by the binding of Ca$\sp{2+}$ to the troponin C (cTnC) subunit of the troponin complex. In this study, we have used site-directed mutagenesis and a variety of assay techniques to explore the functional roles of regions in cTnC, including Ca$\sp{2+}$/Mg$\sp{2+}$-binding sites III and IV, the functionally inactive site I, the N-terminal helix, the N-terminal hydrophobic pocket and the two cysteine residues with regard to their ability to form disulfide bonds. Conversion of the first Ca$\sp{2+}$ ligand from Asp to Ala inactivated sites III and IV and decreased the apparent affinity of cTnC for the thin filament. Conversion of the second ligand from Asn to Ala also inactivated these sites in the free protein but Ca$\sp{2+}$-binding was recovered upon association with troponin I and troponin T. The Ca$\sp{2+}$-concentrations required for tight thin filament-binding by proteins containing second-ligand mutations were significantly greater than that required for the wild-type protein. Mutation of site I such that the primary sequence was that of an active site with the first Ca$\sp{2+}$ ligand changed from Asp to Ala resulted in a 70% decrease in maximal Ca$\sp{2\sp+}$ dependent ATPase activity in both cardiac and fast skeletal myofibrils. Thus, the primary sequence of the inactive site I in cTnC is functionally important. Major changes in the sequence of the N-terminus had little effect on the ability of cTnC to recover maximal activity but deletion of the first nine residues resulted in a 60 to 80% decrease in maximal activity with only a minor decrease in the pCa$\sb{50}$ of activation, suggesting that the N-terminal helix must be present but that a specific sequence is not required. The formation of an inter- or intramolecular disulfide bonds caused the exposure of hydrophobic surfaces on cTnC and rendered the protein Ca$\sp{2+}$ independent. Finally, elution patterns from a hydrophobic interactions column suggest that cTnC undergoes a significant change in hydrophobicity upon Ca$\sp{2+}$ binding, the majority of which is caused by site II. These latter data show an interesting correlation between exposure of hydrophobic surfaces on and activation of cTnC. Overall, these results represent significant progress toward the elucidation of the functional roles of a variety of structural regions in cTnC. ^

Bepridil opens the regulatory N-terminal lobe of cardiac troponin C

Cardiac troponin C (cTnC) is the calcium-dependent switch for contraction in heart muscle and a potential target for drugs in the therapy of congestive heart failure. This calmodulin-like protein consists of two lobes connected by a central linker; each lobe contains two EF-hand domains. The regulatory N-terminal lobe of cTnC, unlike that of skeletal troponin C (sTnC), contains only one functional EF-hand and does not open fully upon the binding of Ca2+. We have determined the crystal structure of cTnC, with three bound Ca2+ ions, complexed with the calcium-sensitizer bepridil, to 2.15-Å resolution. In contrast to apo- and 3Ca2+-cTnC, the drug-bound complex displays a fully open N-terminal lobe similar to the N-terminal lobes of 4Ca2+-sTnC and cTnC bound to a C-terminal fragment of cardiac troponin I (residues 147–163). The closing of the lobe is sterically hindered by one of the three bound bepridils. Our results provide a structural basis for the Ca2+-sensitizing effect of bepridil and reveal the details of a distinctive two-stage mechanism for Ca2+ regulation by troponin C in cardiac muscle.

Avaliação dos valores séricos de troponina cardíaca I (cTnI) e capacidade antioxidante total (TAC) em felídeos com doença renal crónica e seu valor de prognóstico : estudo preliminar

Dissertação de Mestrado Integrado em Medicina Veterinária

Biomarkers of exercise-induced myocardial stress in relation to inflammatory and oxidative stress

Increased concentrations of biomarkers reflecting myocardial stress such as cardiac troponin I and T and brain natriuretic peptide (BNP) have been observed following strenuous, long-lasting endurance exercise. The pathophysiological mechanisms are still not fully elucidated and the interpretations of increased post-exercise concentrations range from (i) evidence for exercise-induced myocardial damage to (ii) non-relevant spurious troponin elevations, presumably caused by assay imprecision or heterophilic antibodies. Several lines of evidence suggest that inflammatory processes or oxidative stress could be involved in the rise of NT-proBNP and Troponin observed in critically ill patients with sepsis or burn injury. We tested the hypothesis that inflammatory or oxidative stress is also responsible for exercise-induced cardiomyocyte strain in a large cohort of triathletes following an Ironman triathlon. However, the post-race increase in cardiac troponin T and NT-proBNP was not associated with several markers of exercise-induced inflammation, oxidative stress or antioxidant vitamins. Therefore, we clearly need more studies with other inflammatory markers and different designs to elucidate the scientific background for increases in myocardial stress markers following strenuous endurance events.

The profound effects of microcystin on cardiac antioxidant enzymes, mitochondrial function and cardiac toxicity in rat

Deaths from microcystin toxication have widely been attributed to hypovolemic shock due to hepatic interstitial hemorrhage, while some recent studies suggest that cardiogenic complication is also involved. So far, information on cardiotoxic effects of MC has been rare and the underlying mechanism is still puzzling. The present study examined toxic effects of microcystins on heart muscle of rats intravenously injected with extracted MC at two doses, 0.16LD(50) (14 mu g MC-LReq kg(-1) body weight) and 1LD(50) (87 mu g MC-LReq kg(-1) body weight). In the dead rats, both TTC staining and maximum elevations of troponin I levels confirmed myocardial infarction after MC exposure, besides a serious interstitial hemorrhage in liver. In the 1LD(50) dose group, the coincident falls in heart rate and blood pressure were related to mitochondria dysfunction in heart, while increases in creatine kinase and troponin I levels indicated cardiac cell injury. The corresponding pathological alterations were mainly characterized as loss of adherence between cardiac myocytes and swollen or ruptured mitochondria at the ultrastructural level. MC administration at a dose of 1LD(50) not only enhanced activities and up-regulated mRNA transcription levels of antioxidant enzymes, but also increased GSH content. At both doses, level of lipid peroxides increased obviously, suggesting serious oxidative stress in mitochondria. Simultaneously. complex I and III were significantly inhibited, indicating blocks in electron flow along the mitochondrial respiratory chain in heart. In conclusion, the findings of this study implicate a role for MC-induced cardiotoxicity as a potential factor that should be considered when evaluating the mechanisms of death associated with microcystin intoxication in Brazil. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

Expression of muscle-related genes and two MyoD genes during amphioxus notochord development

The notochord is one of the diagnostic features of the phylum Chordata. Despite the similarities in the early morphogenetic patterns of the notochords of various chordates, they are strikingly distinct from one another at the histological level. The amphioxus notochord is one example of an evolutionary novelty because it is made up of muscle cells. Our previous expressed sequence tag analysis, targeting messenger RNAs expressed in the adult amphioxus notochord, demonstrated that many muscle-related genes are expressed there. To characterize amphioxus notochord cells and to gain insights into the myogenic program in the notochord, we determined the spatial and temporal expression patterns of these muscle-related genes during amphioxus development. We found that BbNA1 (notochord actin), Amphi-Trop I (troponin I), Amphi-TPmyosin (tropomyosin), Amphi-MHC2 (myosin heavy chain), Amphi-nMRLC (notochord-specific myosin regulatory light chain), AmphinTitin/MLCK (notochord-specific titin/myosin light chain kinase), Amphi-MLP/CRP3 (muscle LIM protein), and Amphi-nCalponin (notochord-specific calponin) are expressed with characteristic patterns in notochord cells, including the central cells, dorsally located cells, and ventrally located cells, suggesting that each notochord cell has a unique molecular architecture that may reflect its function. In addition, we characterized two MyoD genes (Amphi-MyoD1 and Amphi-MyoD2) to gain insight into the genetic circuitry governing the formation of the notochord muscle. One of the MyoD genes (Amphi-MyoD2) is expressed in the central notochord cells, and the coexistence of Amphi-MyoD2 transcripts along with the Amphi-MLP/CRP3 transcripts implies the participation of Amphi-MyoD2 in the myogenic program in the notochord muscle.

Characterization and mapping of expressed sequence tags isolated from a subtracted cDNA library of Litopenaeus vannamei injected with white spot syndrome virus

A large number of polymorphic simple sequence repeats (SSRs) or microsatellites are needed to develop a genetic map for shrimp. However, developing an SSR map is very time-consuming, expensive, and most SSRs are not specifically linked to gene loci of immediate interest. We report here on our strategy to develop polymorphic markers using expressed sequence tags (ESTs) by designing primers flanking single or multiple SSRs with three or more repeats. A subtracted cDNA library was prepared using RNA from specific pathogen-free (SPF) Litopenaeus vannamei juveniles (similar to 1 g) collected before (0) and after (48 h) inoculation with the China isolate of white spot syndrome virus (WSSV). A total of 224 clones were sequenced, 194 of which were useful for homology comparisons against annotated genes in NCBI nonredundant (nr) and protein databases, providing 179 sequences encoded by nuclear DNA, 4 mitochondrial DNA, and 11 were similar to portions of WSSV genome. The nuclear sequences clustered in 43 groups, 11 of which were homologous to various ESTs of unknown function, 4 had no homology to any sequence, and 28 showed similarities to known genes of invertebrates and vertebrates, representatives of cellular metabolic processes such as calcium ion balance, cytoskeleton mRNAs, and protein synthesis. A few sequences were homologous to immune system-related (allergens) genes and two were similar to motifs of the sex-lethal gene of Drosophila. A large number of EST sequences were similar to domains of the EF-hand superfamily (Ca2+ binding motif and FRQ protein domain of myosin light chains). Single or multiple SSRs with three or more repeats were found in approximately 61 % of the 179 nuclear sequences. Primer sets were designed from 28 sequences representing 19 known or putative genes and tested for polymorphism (EST-SSR marker) in a small test panel containing 16 individuals. Ten (53%) of the 19 putative or unknown function genes were polymorphic, 4 monomorphic, and 3 either failed to satisfactorily amplify genomic DNA or the allele amplification conditions need to be further optimized. Five polymorphic ESTs were genotyped with the entire reference mapping family, two of them (actin, accession #CX535973 and shrimp allergen arginine kinase, accession #CX535999) did not amplify with all offspring of the IRMF panel suggesting presence of null alleles, and three of them amplified in most of the IRM F offspring and were used for linkage analysis. EF-hand motif of myosin light chain (accession #CX535935) was placed in ShrimpMap's linkage group 7, whereas ribosomal protein S5 (accession #CX535957) and troponin I (accession #CX535976) remained unassigned. Results indicate that (a) a large number of ESTs isolated from this cDNA library are similar to cytoskeleton mRNAs and may reflect a normal pathway of the cellular response after im infection with WSSV, and (b) primers flanking single or multiple SSRs with three or more repeats from shrimp ESTs could be an efficient approach to develop polymorphic markers useful for linkage mapping. Work is underway to map additional SSR-containing ESTs from this and other cDNA libraries as a plausible strategy to increase marker density in ShrimpMap.