Table 2.

Studies of biomarkers in biofluids and their association with KP metabolites in AD.

Biofluid biomarker	Metabolites	Observation	Ref.
Serum	17 metabolites	Decreased concentration of L-TRP, KYN, and KYNA	[179]
	L-TRP, KYN, and 5-HT	Increased concentration of K/T	[181]
Plasma	17 metabolites	Decreased concentration of KYN, 3-HANA, XA, QA, and L-TRP	[109]
	6 metabolites	Decreased concentration of L-TRP and KYNA; increased concentration of QA	[182]
Urine	8 metabolites	Decreased concentration of KYNA, L-TRP, and K/T	[179]
CSF	L-TRP	Increased concentration of KYNA	[13, 107, 180]
	L-TRP	Increased concentration of KYNA and QA	[13]
CSF and serum	L-TRP, KYN, and 5-HT	Increased concentration of KYN	[181]