Quinolinic acid is a neurotoxic substance produced by our own bodies and a metabolite of tryptophan.

Tryptophan and its different pathways:

The management of tryptophan converting to serotonin within the brain has some complex moving parts. Tryptophan gets converted into serotonin. High levels of stress of any type and acute/chronic infections can change this process by provoking an immune system response. Instead of serotonin being made from tryptophan in this process, two other compounds are eventually made: They are kynurenic acid which is neuroprotective and quinolinic acid which is neurodegenerative.The quinolinic acid is a NMDA-agonist, i.e. quinolinic acid, NMDA, and inflammation are best friends and like to wreak havoc when kynurenic acid is lacking. Recent research showed that patients suffering from severe depression and suicidality were found to have very high levels of inflammation and elevated NMDA activity as a result of long-term dysregulation of this pathway. The researchers’ recommended goal was to find ways to dampen the NMDA receptors and quinolinic acid in the brain.

Treatment:

The cause of inflammation needs to be treated. Simply taking SSRI drugs (Selective serotonin reuptake inhibitors) to make more serotonin further downstream is not going to work. The drug use and application generally fails to address the inflammation. The drugs simply try to increase the amount of serotonin within the system at the synapses, but the underlying damaging inflammation is still ongoing. This process also affects cognitive health, which has great implications for all neurodegenerative concerns. When the brain is on fire with inflammation leading to depression, anxiety, sleep problems, cognitive changes, it has to be thoroughly addressed. SSRIs miss this inflammatory aspect.

Resources:

- NMDA receptor function, memory, and brain aging (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181613/)

- A mechanism of quinolinic acid formation by brain in inflammatory neurological disease. Attenuation of synthesis from L-tryptophan by 6-chlorotryptophan and 4-chloro-3-hydroxyanthranilate. (https://www.ncbi.nlm.nih.gov/pubmed/8293279)

- Sulforaphane reduces the alterations induced by quinolinic acid: Modulation of glutathione levels (https://www.researchgate.net/publication/262569040_Sulforaphane_reduces_the_alterations_induced_by_quinolinic_acid_Modulation_of_glutathione_levels)

- Protective effects of the antioxidant selenium on quinolinic acid-induced neurotoxicity in rats: in vitro and in vivo studies. (https://www.ncbi.nlm.nih.gov/pubmed/12871589)

- Melatonin neutralizes neurotoxicity induced by quinolinic acid in brain tissue culture. (https://www.ncbi.nlm.nih.gov/pubmed/16150107)

- Neuroprotective potential of L-theanine against excitotoxic neuronal death induced by quinolinic acid: Possible neurotransmitters and nitric oxide modulation mechanism (http://www.mdsabstracts.org/abstract/neuroprotective-potential-of-l-theanine-against-excitotoxic-neuronal-death-induced-by-quinolinic-acid-possible-neurotransmitters-and-nitric-oxide-modulation-mechanism/)

- Green Tea Polyphenols Decrease Enzyme Activity of Nitric Oxide Synthase, https://www.fasebj.org/doi/abs/10.1096/fasebj.27.1_supplement.790.14

- Neuroprotective Activity of Curcumin in Combination with Piperine against Quinolinic Acid Induced Neurodegeneration in Rats (https://www.karger.com/Article/PDF/443896)