Abstract
PurposeDue to distinct immuno- and neuro-modulatory properties, growing research interest focuses on exercise-induced alterations of the kynurenine (KYN) pathway in healthy and clinical populations. To date, knowledge about the impact of different acute strength exercise modalities on the KYN pathway is scarce. Therefore, we investigated the acute effects of hypertrophic (HYP) compared to maximal (MAX) strength loadings on the KYN pathway regulation.MethodsBlood samples of twelve healthy males (mean age and weight: 23.5 ± 3.2 years; 77.5 ± 7.5 kg) were collected before (T0), immediately after (T1), and 1 h after completion (T2) of HYP (5 sets with 10 repetitions at 80% of 1RM) and MAX (15 sets with 1RM) loadings performed in a randomized cross-over design. Serum concentrations of tryptophan (TRP), KYN, kynurenic acid (KA), and quinolinic acid (QA) were assessed using high-performance liquid chromatography.ResultsThe KA/KYN ratio increased from T0 to T1 (p = 0.01) and decreased from T1 to T2 (p = 0.011) in HYP, while it was maintained within MAX. Compared to MAX, serum concentrations of KA were greater in HYP at T1 (p = 0.014). Moreover, the QA/KA ratio was significantly lower in HYP than in MAX at T1 (p = 0.002).ConclusionAcute HYP loading led to increases in the metabolic flux yielding KA, thereby possibly promoting immunosuppression and neuroprotection. Our findings emphasize the potential of acute HYP exercise as short-term modulator of KYN pathway downstream to KA in healthy males and need to be proven in other samples.
Highlights
The essential amino acid tryptophan (TRP) plays a crucial role as precursor of different physiological processes, such as protein or serotonin synthesis as well as the kynurenine (KYN) pathway, which is closely linked to immuno- and neuro-modulatory properties
This study shows that acute HYP but not MAX transiently enhances the metabolic flux of the KYN pathway towards kynurenic acid (KA), thereby potentially inducing peripheral KYN clearance and immunomodulatory effects
In line with our findings, future studies investigating the effects of strength exercise on KYN pathway alterations should focus on hypertrophic strength exercise modalities
Summary
The essential amino acid tryptophan (TRP) plays a crucial role as precursor of different physiological processes, such as protein or serotonin synthesis as well as the kynurenine (KYN) pathway, which is closely linked to immuno- and neuro-modulatory properties. The immunomodulatory effects along the KYN pathway are primarily associated with an IDO-mediated conversion to KYN as well as with levels of KA. Both metabolites can promote the differentiation of T-cell subsets to anti-inflammatory regulatory T-cells (Opitz et al.2011). An elevated peripheral degradation of circulating TRP and KYN levels to QA and/or KA might promote neuroprotection Both immunosuppressive and neuroprotective properties (illustrated in Fig. 1) have led to extended research interest in the understanding and modulation of the KYN pathway in healthy and clinical populations (e.g., Parkinson’s disease, multiple sclerosis, and cancer) (Lovelace et al 2017; Platten et al 2019)
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