Coenzyme Q9 (CoQ9) is a normal constituent of human plasma.?CoQ9 in human plasma may originate as a product of incomplete CoQ10 biosynthesis or from the diet.

4-Hydroxyphenylpyruvic acid is an enzyme inhibitor.4-Hydroxyphenylpyruvic acid (4-HPPA) is a keto acid that is involved in the tyrosine catabolism pathway.

1-Methylhistamine dihydrochloride is a major metabolite of histamine by histamine N-methyltransferase in the pathway of histidine metabolism.?It has been used as a biomarker of histaminergic system activity in the brains of Alzheimer's disease patients as well as those with hypersomnia and other neurological conditions.