Multiple sclerosis (MS) is a chronic autoimmune disease leading to the demyelination of nerve cells in the central nervous system. Nearly 3 million people worldwide suffer from this debilitating disease. Although there is no cure for MS, recent studies have shown that exercise regimens have a positive effect on both motor and cognitive function in people with MS.
The recent study published by Niklas Joisten et al. in Neurology Neuroimmunology & Neuroinflammation is a secondary analysis (Joisten et al, 2019) that assessed how aerobic exercise influences plasma levels of kynurenine pathway (KP) metabolites, neurofilament light chain (pNfL), and interleukin 6 (IL-6). Participants were randomly assigned to either the high-intensity interval training (HIIT) or the standard exercise training program (moderate continuous training (MCT) cohort for 3-weeks. Joisten et al. reported that pNfL levels decreased significantly following the HIIT exercise regimen. Decreases in pNfL could signify increased neuroprotection since other studies have shown higher levels correlate with inflammation and decreased motor function in people with MS. KP metabolite changes consisted of decreases in both tryptophan (TRP) and kynurenine (KYN) for both exercise programs. Importantly, there was a significant increase in plasma kynurenic acid levels resulting in a decrease in the quinolinic acid/kynurenic acid (QA/KA) ratio in the HIIT individuals. These changes in the KP are also indicative of neuroprotection, demonstrating the intensity-dependent effects of exercise on people with MS. Substantial research has demonstrated the link between inflammation and KP activation. Likewise, in the current study the activation of the kynurenine pathway correlated with IL-6 levels, specifically there were positive correlations between QA, KYN, and the KYN/TRP ratio with IL-6. This study (along with Joisten et al, 2020 and Zimmer et al, 2018) suggests that changing the therapeutic exercise program for people with MS from MCT to HIIT may improve and limit the disease progression. However, more research is warranted to determine whether these effects would be sustained following long-term HIIT intervention. Furthermore, it is tempting to speculate that therapeutic exercise may be alter KP metabolites in other disease states such as amyotrophic lateral sclerosis.