Table 1.

Summary of individual KP metabolites with known receptor targets, key biological functions, negative effects, and effects associated with AD (debated^∗).

Metabolite	Receptors	Biological functions	Negative effects	Effects associated with AD	Ref.
KYN	AHR	Immunomodulation, anticancer, oxidative stress regulation, neuroprotection∗, anti-inflammatory	Unknown	Antineuroinflammatory	[78–80, 95, 99, 100, 119, 120]
3-HK	Unknown	Oxidative stress regulation	Neurotoxicity	Neurotoxicity	[96, 110, 125]
3-HANA	Unknown	Anti-inflammatory, oxidative stress regulation, lipid-decreasing, immunomodulation	Unknown	Antineuroinflammatory	[127, 129–135]
QA	NMDAR	Proconvulsant, prooxidant	Neurotoxicity, proneuroinflammatory prodepression	Formation of Aβ and p-tau, proneuroinflammatory neurotoxicity	[7–9, 15–23]
KYNA	AHR, NMDAR, α7nAChR	Antioxidant, immunomodulation, anticonvulsant, antineurotoxicity	Unknown	Cognitive disorder	[23, 153–159, 163]
XA	mGLUR2/3∗	Antioxidant	Unknown	Unknown	[129, 165]
PA	Unknown	Anticonvulsant, antimicrobial, immunomodulation	Neurotoxicity	Neurotoxicity	[12, 167–169]
CA	AHR, mGLUR4	Immunomodulation, antineuroinflammatory	Proapoptosis	Antineuroinflammatory	[10, 11, 166]