Purpose: Exercise-induced muscle damage (EIMD) results in the generation of reactive oxygen species (ROS), but little is known about the temporal profile of change in ROS post-EIMD and how ROS levels relate to the onset of and recovery from EIMD. Our primary aim was to examine the effect of EIMD on the pattern of change in the blood level of thiol-oxidised albumin, a marker of oxidative stress. Methods: Seven male participants were subjected on separate days to eccentric muscle contraction to cause EIMD or a no-exercise condition. After each session, the participants collected daily dried blood spots to measure thiol-oxidised albumin and returned to the laboratory every 2 days for the assessment of indirect markers of EIMD, namely maximal voluntary contraction (MVC), delayed onset muscle soreness (DOMS), creatine kinase (CK), and myoglobin. Results: Eccentric exercise resulted in a significant decrease in MVC and increase in DOMS, CK, myoglobin, and thiol-oxidised albumin with the latter reaching above baseline level within 24–48 h post-exercise. All the markers of EIMD returned to baseline level within 6 days post-exercise, but not the level of thiol-oxidised albumin which remained elevated for 10 days after exercise. There was a moderate correlation between changes in thiol-oxidised albumin and DOMS, but no significant relationship between any other markers of muscle damage. Conclusion: The levels of thiol-oxidised albumin increase in response to EIMD and remain elevated for several days post-exercise. The temporal pattern of change in the level of thiol-oxidised albumin suggests that this may be a useful biomarker of muscle repair post-EIMD.

Inflammation and neonatal hypoxia-ischemia (HI) are important etiological factors of perinatal brain injury. However, underlying mechanisms remain unclear. Sirtuins are a family of nicotinamide adenine dinucleotide (NAD)+-dependent histone deacetylases. Sirtuin-6 is thought to regulate inflammatory and oxidative pathways, such as the extracellular release of the alarmin high mobility group box-1 (HMGB1). The expression and role of sirtuin-6 in neonatal brain injury are unknown. In a well-established model of neonatal brain injury, which encompasses inflammation (lipopolysaccharide, LPS) and hypoxia-ischemia (LPS+HI), we investigated the protein expression of sirtuin-6 and HMGB1, as well as thiol oxidation. Furthermore, we assessed the effect of the antioxidant N-acetyl cysteine (NAC) on sirtuin-6 expression, nuclear to cytoplasmic translocation, and release of HMGB1 in the brain and blood thiol oxidation after LPS+HI. We demonstrate reduced expression of sirtuin-6 and increased release of HMGB1 in injured hippocampus after LPS+HI. NAC treatment restored sirtuin-6 protein levels, which was associated with reduced extracellular HMGB1 release and reduced thiol oxidation in the blood. The study suggests that early reduction in sirtuin-6 is associated with HMGB1 release, which may contribute to neonatal brain injury, and that antioxidant treatment is beneficial for the alleviation of these injurious mechanisms.

Exercise‐induced muscle damage (EIMD) can affect athlete performance and is a risk factor for major muscle injury. The temporal profile of thiol‐oxidized albumin, a marker of oxidative stress, has shown potential in assessing recovery from EIMD in non‐athletically trained participants but not yet in trained participants. Our primary aim was to assess whether there are changes in the level of thiol‐oxidized albumin after a marathon in athletically trained participants. Twenty participants completed a marathon and collected daily dried blood spots from 3 days prior to and 7 days after the marathon to measure thiol‐oxidized albumin using a novel methodology (OxiDx). Participants were also assessed for indirect markers of EIMD prior to and on days 2 and 5 post‐marathon. The level of thiol‐oxidized albumin peaked at 2 days and remained elevated until 5 days after the marathon and correlated with indirect measures of EIMD. Furthermore, time of recovery for thiol‐oxidized albumin varied between participants, some recovered at 3 days post‐marathon whereas others extended beyond 7 days post marathon. Tracking temporal changes in the level of thiol‐oxidized albumin has potential to be useful in managing recovery from EIMD in athletes, particularly considering the ease of the OxiDx methodology.

Background: The extent to which muscle strain or tears are affecting race performance in horses is unknown because it is difficult to objectively identify muscle damage. One approach includes the use of physiological markers in blood. Recently, we linked the level of plasma thiol‐oxidised albumin, an oxidative stress biomarker, to muscle damage in humans. Objectives: This aim of this work was to investigate whether the level of plasma thiol‐oxidised albumin was elevated in the days following a thoroughbred horse race. Study design: ‘In vivo’ experiments. Methods: Blood collection was performed by each trainer at their respective stable. Dried blood samples were collected for the level of thiol‐oxidised albumin before and each day for 7 days post‐race. Liquid blood samples were collected for analysis of the muscle enzymes creatine kinase (CK) and aspartate amino transferase (AST) before and on Day 2 and 5 post‐race and were analysed by external pathology centre. Results: The level of thiol‐oxidised albumin peaked at 2 days post‐race, increasing by 3.9 ± 0.7% ( p < 0.0001) and returned to pre‐race levels by Day 5. Thiol‐oxidised albumin also correlated with the activity of AST ( R ² = 0.2, p = 0.01). The time of recovery for thiol‐oxidised albumin varied between individual horses, some recovered at Day 3 post‐race whereas others extended beyond 7 days post‐race. Main limitations: No histological or imaging diagnosis was conducted to confirm that horses with elevated levels of thiol‐oxidised albumin also had definitive evidence of muscle damage. The activity of CK and AST was not measured daily, as was the case for the level of thiol‐oxidised albumin. Conclusions: The level of thiol‐oxidised albumin has the potential to be useful in managing recovery and return to training or competition in horse following a bout of damaging exercise, particularly given the ease of collecting small serial small blood samples.

Background: The extent to which muscle strain or tears are affecting race performance in horses is unknown because it is difficult to objectively identify muscle damage. One approach includes the use of physiological markers in blood. Recently, we linked the level of plasma thiol-oxidised albumin, an oxidative stress biomarker, to muscle damage in humans. Objectives: This aim of this work was to investigate whether the level of plasma thiol-oxidised albumin was elevated in the days following a thoroughbred horse race. Study design: “In vivo” experiments Methods: Blood collection was performed by each trainer at their respective stable. Dried blood samples were collected for the level of thiol-oxidised albumin before and each day for 7 days post-race. Liquid blood samples were collected for analysis of the muscle enzymes Creatine Kinase (CK) and Aspartate Amino Transferase (AST) before and on day 2 and 5 post race and were analysed by external pathology center. Results: The level of thiol-oxidised albumin peaked at 2 days post-race, increasing by 3.9% ± 0.7% (p<0.0001) and returned to pre-race levels by day 5. Thiol-oxidised albumin also correlated with the activity of AST (R ² =0.2, p=0.01). The time of recovery for thiol-oxidised albumin varied between individual horses, some recovered at day 3 post-race whereas others extended beyond 7 days post-race. Main limitations: No histological or imaging diagnosis was conducted to confirm that horses with elevated levels of thiol-oxidised albumin also had definitive evidence of muscle damage. The activity of CK and AST was not measured daily, as was the case for the level of thiol oxidised albumin. Conclusions: The level of thiol-oxidised albumin has the potential to be useful in managing recovery and return to training or competition in horse following a bout of damaging exercise, particularly given the ease of collecting small serial small blood samples.

Thoroughbred race performance is influenced by genetics, training, recovery, and management, but decisions about race readiness are often subjective and lack validated physiological markers. This study evaluated thiol-oxidised albumin, a blood-based indicator of oxidative stress, as a potential biomarker of pre-race fitness in Australian Thoroughbreds. Seventy-five clinically healthy racehorses from seven stables were monitored across 216 competitive events (150 races, 66 trials). Blood samples were collected from the jugular at baseline, 48 h pre-race, and for each day up to 8 days post-race to examine levels of thiol-oxidised using the OxiDx test. At baseline, thiol-oxidised albumin levels were stable, but 24% of horses exhibited oxidative stress before racing, rising to 53% after three consecutive races. Thiol-oxidised albumin levels also remained increased for at least 8 days post-race. Statistical analyses were conducted in GraphPad Prism 10.6 using paired t-tests or repeated-measures one-way ANOVA with Dunnett’s post hoc test, alongside a generalised estimating equation model to assess associations with ordinal variables; significance was set at p < 0.05. Reference change values were calculated to determine thresholds for biologically meaningful changes in thiol-oxidised albumin levels. Increased pre-race oxidative stress was significantly associated with poorer finishing positions and lower trainer-perceived performance but was unrelated to horse age or sex. Horses without oxidative stress were more likely to finish in the top three. These findings demonstrate that oxidative stress prior to racing is common and adversely affects performance. Thiol-oxidised albumin represents a promising objective biomarker to guide training and racing strategies, with implications for both performance and equine welfare.