The influence of dietary supplementation with Tetraselmis chuii on gene expression and exercise tolerance in healthy adults

It is now recognised that reactive species, when present at physiological concentrations, are important signalling molecules and a key component of the complex biological processes that sustain life and normal functioning. Traditionally, however, it was considered that reactive species were associated with damage to cellular biomolecules. This stigma has fuelled the widespread consumption of redox-active dietary supplements in an attempt to protect against such deleterious effects and promote favourable outcomes on human health and function. Conversely, however, the existing empirical evidence suggests that the consumption of redox-active dietary supplements is largely ineffective unless there is a deficiency in endogenous antioxidants to preserve oxidative eustress. Microalgae represent an emerging, and sustainable, source of dietary nutrients and redox-active biomolecules, and may have the potential to regulate endogenous redox signalling and elicit adaptive changes in humans. Whilst this generated substantial recent scientific interest in the use of microalga-derived dietary supplements for health and athletic performance, further research was required to investigate the effects of such supplements on human redox signalling, health and function. Accordingly, this thesis presents data from three original experimental chapters that explored the efficacy of a select microalgae species, Tetraselmis chuii, as a purported redox-active dietary supplement to regulate transcriptional redox signalling in human skeletal muscle in vitro and in vivo and exercise capacity.

In the first experimental chapter, gene expression was measured in human primary skeletal muscle myoblasts following incubation for 24 h in vitro with a Tetraselmis chuii extract compared to a control, and data were available for 89 pre-selected targets. Gene expression was significantly up-regulated for 7 genes [CAT (1.35 ± 1.34, dz = -1.9), GSTK1 (1.15 ± 1.45, dz = -2.0), MAF (2.06 ± 1.10, dz = -2.4), NQO2 (1.27 ± 1.09, dz = -2.9), PLA2G4C (1.85 ± 1.46, dz = -2.2), PRDX2 (1.22 ± 1.18, dz = -2.0) and SOD2 (5.08 ± 1.23, dz = -1.7)] and down-regulated for 4 genes [ATF1 (0.72 ± 1.24, dz = 3.4), ATF4 (0.47 ± 1.35, dz = 2.6), BAK1 (0.73 ± 1.10, dz = 3.3) and PRDX4 (0.81 ± 1.34, dz = 3.2)] with large effect sizes following incubation with Tetraselmis chuii (p < 0.05). Additionally, strong statistically significant negative correlations were observed between the magnitude of change in gene expression with Tetraselmis chuii and basal gene expression for 8 genes. In the second experimental chapter, gene expression was measured in resting human skeletal muscle tissue following dietary supplementation for 2 weeks with Tetraselmis chuii compared to a placebo, and data were available for 95 pre-selected targets. Gene expression was significantly up-regulated for 15 genes [CASP10 (1.34 ± 1.59, dz = -0.6), CCL2 (1.39 ± 1.39, dz = -1.0), CUL3 (1.77 ± 2.49, dz = -0.6), ERK3 (MAPK6) (1.92 ± 2.42, dz = -0.7), GPX7 (1.26 ± 1.37, dz = -0.7), GSR (1.22 ± 1.41, dz = -0.6), GSTM3 (1.34 ± 1.49, dz = -0.7), JUN (1.53 ± 1.89, dz = -0.7), LOXHD1 (1.38 ± 1.62, dz = -0.7), NRF2 (1.62 ± 2.16, dz = -0.6), p38a (MAPK14) (1.33 ± 1.58, dz = -0.6), PLA2G12A (1.63 ± 2.05, dz = -0.7), PLA2G16 (1.36 ± 1.42, dz = -0.9), PRDX6 (1.36 ± 1.57, dz = -0.7) and SIRT1 (1.73 ± 2.25, dz = -0.7)] with medium to large effect sizes following dietary supplementation with Tetraselmis chuii. Additionally, moderate or strong statistically significant negative correlations were observed between the magnitude of change in gene expression with Tetraselmis chuii and basal gene expression for 54 genes. In the third experimental chapter, exercise physiology parameters were measured during severe-intensity cycling and with dietary supplementation for 2 weeks with Tetraselmis chuii and a placebo. End-exercise pulmonary O2 uptake (V̇O2) was greater following dietary supplementation with Tetraselmis chuii compared to pre-supplementation baseline (4.1 ± 0.4 vs. 3.9 ± 0.3 L/min; p < 0.05; dz = -0.8), and was unchanged with placebo (p = 0.66; dz = 0.1). End-exercise rating of perceived exertion (RPE) (p = 0.34; w = 0.1), end-exercise blood lactate concentration (B[La]) (p = 0.87; np2 = 0.0) and exercise tolerance (p = 0.42; np2 = 0.1) were unchanged with Tetraselmis chuii.

The principal novel findings are: 1) gene expression of redox-relevant targets was altered in both human primary skeletal muscle myoblasts following incubation for 24 h in vitro with a Tetraselmis chuii extract and in resting human skeletal muscle tissue following dietary supplementation for 2 weeks with Tetraselmis chuii; 2) the magnitude of change in gene expression with Tetraselmis chuii was negatively correlated with basal gene expression in both models; and 3) end-exercise V̇O2 was improved, with no change in end-exercise RPE, end-exercise B[La] and exercise tolerance, during severe-intensity cycling and with dietary supplementation for 2 weeks with Tetraselmis chuii. Collectively, these original findings enhance understanding of the efficacy of Tetraselmis chuii as a redox-active dietary supplement in vitro and in vivo and its effect on exercise capacity.