4. Discussion
PD, TNF-α, neurotoxic
INFLAMMATION, INFLAMMATION, RECRUITMENT
Recently, we reported that a 12-week BMI-based vitamin DThe activation of KP is primarily driven by the liver, and the majority of its metabolites originate from peripheral tissues. However, under specific physiological conditions such as aging or certain pathological conditions such as blood–brain barrier (BBB) damage, these metabolites have the potential to cross the BBB and affect the central nervous system. Moreover, it is also known that the KP is often disturbed in PD. Substances from KP such as 3-HK and XANA are known to be neurotoxic, whereas KYNA and PA are usually characterized as neuroprotective. In the literature, it was reported that during states of elevated inflammation, there is a diversion of tryptophan away from serotonin production toward the KP [Inflammation that is connected with age may stimulate the activation of KP. Moreover, the expression of IDO, which is the first enzyme of KP, can be influenced by inflammatory cytokines such as IL-6 and TNF-α [The study has some limitations. Firstly, the sample size is small because the recruitment of PD patients during the pandemic was impeded. Secondly, we did not measure the tryptophan concentrations but the kynurenine pathway is described as the main catabolism pathway (>95%) of tryptophan [