Physical exercise modulates plasma irisin levels in endurance athletes: Implications for Parkinson's disease

Physical exercise (PE) improves clinical outcomes in individuals with Parkinson's disease (PD) through unclear mechanisms. Irisin, a neuroprotective protein released by myocytes during PE, may play a role, but in vivo data in PD are limited. We investigated plasma irisin in a unique PD population engaged in chronic, intense PE. Ninety-three participants were classified based on both disease status (PD versus healthy controls, HC), and PE level (sedentary versus endurance athletes). Endurance athletes included subjects regularly participating in endurance sports (triathlon/long-distance marathon/cycling) for at least 5 years, with an average training duration of 1.5 h/day, 6 days/week. Four groups were generated: PD-Sedentary (PD-SD, n = 30), PD-Endurance Athletes (PD-EA, n = 15), HC-Sedentary (HC-SD, n = 30), and HC-Endurance Athletes (HC-EA, n = 18). Clinical and demographic features were collected. Plasma irisin was dosed in all groups. PD-EA had a longer disease duration compared to PD-SD (p = 0.005) but scored better on both MDS-UPDRS-part III (p = 0.029) and MMSE (p = 0.016). Plasma irisin was lower in endurance athletes versus sedentary participants regardless of disease status (PD-EA vs PD-SD, p = 0.002; PD-EA vs HC-SD, p = 0.003; HC-EA vs HC-SD, p = 0.046; HC-EA vs PD-SD, p = 0.029). In PD-SD plasma irisin positively correlated with MDS-UPDRS-part III (r = 0.395, p = 0.034), HY (r = 0.386, p = 0.042), and LEDD (r = 0.385, p = 0.043). Lower plasma irisin levels were associated with male sex (p < 0.001). Our findings suggest that chronic, intense PE ameliorates the neurological symptoms in individuals with PD, while differently modulating plasma irisin in a sex-dependent fashion. Irisin might mediate the beneficial clinical effects of PE, though further investigation is warranted.