Effect of racing on cardiac troponin I concentration and associations with cardiac rhythm disturbances in Standardbred racehorses.

INTRODUCTION/OBJECTIVES: Accumulating evidence indicates intense exercise can be associated with myocardial damage. Investigating the impact of maximal effort on myocardium and exploring possible association of injury with rhythm disturbance requires a high-sensitivity cardiac troponin assay. The objectives of this study were: (1) to determine the effect of racing on serum cardiac troponin I (cTnI) in Standardbred horses using a high-sensitivity assay; (2) to determine the 99th percentile of cTnI in healthy horses and investigate the effect of demographic variables on cTnI prevailing pre-race in Standardbred horses using a validated high-sensitivity assay and a contemporary assay, and; (3) to explore associations between exercise-associated arrhythmia and cTnI concentration. ANIMALS: Racehorses (n = 145). MATERIALS AND METHODS: ≤ 2 h pre-race, cTnI concentrations were measured in 158 race starts. Electrocardiogram (ECG) monitoring was applied during racing and race recovery and screened for complex ventricular arrhythmia. Associations between cTnI prevailing before racing concentration, age, sex, and gait were investigated. Demographic and performance variables were evaluated for associations with cTnI concentration post-race and rhythm disturbance. RESULTS: Incidence of arrhythmia was 11.6% (16 horses). A significant increase in median (interquartile range) cTnI concentration of 1.36 (0.49-2.81) ng/L was found post-race (p < 0.0001). Serum cardiac troponin I (cTnI) concentration prevailing pre-race was positively associated with increasing age, and gait. Serum cardiac troponin I prevailing post-race was positively associated with concentration prevailing pre-race. Interaction between arrhythmia and finishing distanced revealed horses finishing distanced and experiencing arrhythmia displayed higher cTnI release than with the presence of either alone. CONCLUSIONS: Racing increased cTnI concentration. Horses finishing distanced and also exhibiting arrhythmia may be experiencing myocardial compromise.

MEDiastinal Irradiation and CArdio-Toxic Effects (MEDICATE): Exploring the Relationship between Cardiac Irradiation and High Sensitivity Troponins.

AIMS: Radiation-induced heart disease is a late effect of cardiac irradiation and has been shown in patients with lymphoma and thoracic cancers. There is no established measurement tool to detect acute cardiac damage. However, high sensitivity troponin I and T (HsTnI and HsTnT) and echocardiograms have shown promise in some studies. A pilot trial was conducted to characterise whether these instruments may detect subclinical radiotherapy-induced cardiac damage. MATERIALS AND METHODS: Eligible patients received high cardiac doses defined by either at least 30 Gy to 5% of cardiac volume or a mean dose of 4 Gy. HsTnI and HsTnT were measured before radiotherapy and after 2 and 4 weeks of radiotherapy; three-dimensional echocardiograms were completed before and 1 year after radiotherapy. RESULTS: Of 19 patients, the median 'mean left ventricular dose' was 3.1 Gy and the 'mean cardiac dose' was 8.6 Gy. Significant positive associations between HsTnI and HsTnT were observed at all time points, but there was no significant association with cardiac dose. The mean left ventricular dose and the maximum left ventricular dose were, however, associated with a decrease in ejection fraction (P = 0.054, 0.043) as well as an increase in left ventricular strain (P = 0.058). CONCLUSION: This study suggests that HsTnI and HsTnT are intimately related, but detection of acute cardiac damage was not shown, potentially due to limitations of these markers or low radiotherapy doses using conformal techniques. Our results also suggest subacute damage at 1 year may depend on the dose to the left ventricle. Further studies are needed, as identification of early damage could facilitate the ability to closely monitor and intervene in patients at risk for radiation-induced heart disease.

Post-exercise cardiac troponin I release and clearance in normal Standardbred racehorses.

BACKGROUND: There are currently no studies detailing cardiac troponin I (cTnI) release in normal horses post-exercise using an analytically validated assay. These data are essential for selecting appropriate sampling times in equine athletes with suspected myocardial injury. OBJECTIVE: To plot the magnitude and time course of cTnI release after maximal effort, using validated cTnI assays. STUDY DESIGN: Descriptive longitudinal study. METHODS: Five clinically normal Standardbred racehorses in race training were included in the study. Horses were exercised in harness at near-race intensity. Blood samples were taken immediately pre- and post-exercise and then hourly for 24 h. Samples were analysed using the validated high-sensitivity cTnI assay and a contemporary sensitivity cTnI assay. RESULTS: Mean resting cTnI was 1.33 ± 0.6 s.d. ng/L (range, 0.82-2.33 ng/L) using assay A. All horses were below the detection limit at rest using assay B. Peak elevation occurred 2-6 h post-exercise with both assays (mean, 4.6 ± 1.7 and 4.0 ± 2 h, respectively). Mean peak increase in cTnI was 11.96 ± 9.41 ng/L (range, 1.72-23.76 ng/L) using assay A. Peak concentrations were detectable in three of the horses using assay B and were between 0.039 and 0.051 µg/L (mean: 0.043 ± 0.006 µg/L). All horses returned to baseline within 24 h. MAIN LIMITATIONS: A small (n = 5) convenience sample was used as random sampling was not logistically possible. CONCLUSIONS: All horses experienced an increase in cTnI post-exercise, with peak occurring 2-6 h post-exercise. Cardiac troponin I elevation was detected earlier using the high-sensitivity assay, which may convey a diagnostic advantage. Targeted studies are needed to determine the significance of these increases.

Combining presentation high-sensitivity cardiac troponin I and glucose measurements to rule-out an acute myocardial infarction in patients presenting to emergency department with chest pain.

BACKGROUND AND AIMS: The use of high sensitivity troponin (hs-Tn) may enable early rule out of acute myocardial infarction (AMI) for patients presenting to the emergency department (ED) with chest pain. This study evaluated two approaches to the early rule out of AMI; a combination of a presentation hs-Tn <4ng/L and normal glucose at presentation (dual testing) and a presentation hs-Tn troponin below the limit of detection (LoD). METHODS: We utilised prospectively collected data on adult patients presenting with suspected ACS in two EDs in Australia and New Zealand. Blood samples were taken on presentation and tested for glucose and high sensitivity troponin I. The primary endpoint was index AMI and the secondary endpoint was 30-day acute coronary syndrome (ACS). Sensitivity, specificity, positive and negative predictive values were used to assess the diagnostic accuracy of the dual testing and LoD approaches. RESULTS: Of the 1412 participants, 182 (12.9%) had index AMI. The LoD and the dual testing approach were 100% sensitive for index AMI. The specificity of the dual testing approach (25.2%) was slightly higher than that of the LoD (20.4%). Sensitivity for ACS was similar for the two approaches (96.5% for dual testing and 98.1% for the LoD). CONCLUSIONS: The dual testing and LoD approach identified all patients with index AMI and could be used to reduce the proportion of patients requiring lengthy assessment and inpatient admission. Further investigation is still required to rule out unstable angina pectoris in patients identified as low risk.

Use of an interferon-gamma based assay to assess bladder cancer patients treated with intravesical BCG and exposed to tuberculosis.

OBJECTIVE: Compare the QuantiFERON-TB Gold In-Tube (QFT) assay and the tuberculin skin test (TST) in bladder cancer patients receiving high dose BCG therapy (BCG patients). DESIGN AND METHODS: BCG patients and healthy visitors, both exposed to tuberculosis, were screened with a TST and QFT. RESULTS: QFT-TST correlation was excellent in visitors, but poor in BCG patients. BCG therapy predicted a positive TST (p<0.001) but not a positive QFT (p=0.35). DISCUSSION: The management of BCG patients was impacted, by measuring the QFT.

TGF-beta induces assembly of a Smad2-Smurf2 ubiquitin ligase complex that targets SnoN for degradation.

The receptor-regulated Smad proteins are essential intracellular mediators of signal transduction by the transforming growth factor-beta (TGF-beta) superfamily of growth factors and are also important as regulators of gene transcription. Here we describe a new role for TGF-beta-regulated Smad2 and Smad3 as components of a ubiquitin ligase complex. We show that in the presence of TGF-beta signalling, Smad2 interacts through its proline-rich PPXY motif with the tryptophan-rich WW domains of Smurf2, a recently identified E3 ubiquitin ligases. TGF-beta also induces the association of Smurf2 with the transcriptional co-repressor SnoN and we show that Smad2 can function to mediate this interaction. This allows Smurf2 HECT domain to target SnoN for ubiquitin-mediated degradation by the proteasome. Thus, stimulation by TGF-beta can induce the assembly of a Smad2-Smurf2 ubiquitin ligase complex that functions to target substrates for degradation.

Smad7 binds to Smurf2 to form an E3 ubiquitin ligase that targets the TGF beta receptor for degradation.

Ubiquitin-mediated proteolysis regulates the activity of diverse receptor systems. Here, we identify Smurf2, a C2-WW-HECT domain ubiquitin ligase and show that Smurf2 associates constitutively with Smad7. Smurf2 is nuclear, but binding to Smad7 induces export and recruitment to the activated TGF beta receptor, where it causes degradation of receptors and Smad7 via proteasomal and lysosomal pathways. IFN gamma, which stimulates expression of Smad7, induces Smad7-Smurf2 complex formation and increases TGF beta receptor turnover, which is stabilized by blocking Smad7 or Smurf2 expression. Furthermore, Smad7 mutants that interfere with recruitment of Smurf2 to the receptors are compromised in their inhibitory activity. These studies thus define Smad7 as an adaptor in an E3 ubiquitin-ligase complex that targets the TGF beta receptor for degradation.

A SMAD ubiquitin ligase targets the BMP pathway and affects embryonic pattern formation.

The TGF-beta superfamily of proteins regulates many different biological processes, including cell growth, differentiation and embryonic pattern formation. TGF-beta-like factors signal across cell membranes through complexes of transmembrane receptors known as type I and type II serine/threonine-kinase receptors, which in turn activate the SMAD signalling pathway. On the inside of the cell membrane, a receptor-regulated class of SMADs are phosphorylated by the type-I-receptor kinase. In this way, receptors for different factors are able to pass on specific signals along the pathway: for example, receptors for bone morphogenetic protein (BMP) target SMADs 1, 5 and 8, whereas receptors for activin and TGF-beta target SMADs 2 and 3. Phosphorylation of receptor-regulated SMADs induces their association with Smad4, the 'common-partner' SMAD, and stimulates accumulation of this complex in the nucleus, where it regulates transcriptional responses. Here we describe Smurf1, a new member of the Hect family of E3 ubiquitin ligases. Smurf1 selectively interacts with receptor-regulated SMADs specific for the BMP pathway in order to trigger their ubiquitination and degradation, and hence their inactivation. In the amphibian Xenopus laevis, Smurf1 messenger RNA is localized to the animal pole of the egg; in Xenopus embryos, ectopic Smurf1 inhibits the transmission of BMP signals and thereby affects pattern formation. Smurf1 also enhances cellular responsiveness to the Smad2 (activin/TGF-beta) pathway. Thus, targeted ubiquitination of SMADs may serve to control both embryonic development and a wide variety of cellular responses to TGF-beta signals.