Kynurenine, plasma

He isoleucine, Kyn kynurenine, Leu leucine, Lys lysine, Met methionine, MTHFR 5,10-methylene tetrahydrofolate reductase, Orn ornithine, p plasma, P5C pyrroline-5-carboxylic acid, PEA phosphoethanolamine, Phe phenylalanine, P-Hyl O-phosphohydroxylysine, Pip pipecolic acid, Pro proline, Sacch saccharopine, Sar sarcosine, Ser serine,... 

Vitamin Bg status can be evaluated by direct measurement of plasma pyridoxine or pyridoxal phosphate by microbiological, enzymatic, radioimmunological, or chemical methods. Measurement of urinary xanthurenic acid or other intermediates of the kynurenine pathway (Chapter 17) are used to assess indirectly the adequacy of vitamin Bg for metabolic needs. 

S. L., Increased plasma kynurenine and its relationship to neopterin and tryptophan in Tourette s syndrome, Psychol. Med., 26, 857, 1996. 

Silver et al.58 have reported that during the active phase of EMS tryptophan metabolism via the kynurenine pathway was accentuated, probably secondary to induction of the enzyme indoleamine-2,3-dioxygenase. Indeed, patients with EMS generally have low plasma L-tryptophan and high plasma L-kynurenine and quinolinic acid levels. 

Figure 9. Effects of LPS treatment on plasma kynurenine level (upper) and the activity of indolcamine 2,3-dioxygcnase in the lung (lower).

The increased plasma kynuremne pool and the induced xanthurenic acid urinary excretion have several implications in the assessment of diazinon noncholinergic toxicity. An increase in xanthurenic acid formation may alter glucose metabolism. Xanthurenic acid has been reported to form a complex with insulin and damage pancreatic P cells. Elevated plasma kynurenin may alter kynurenin transport into the brain. Since more than 40% of brain kynurenin originates from the systemic circulation, cerebral biosynthesis of neuroactive kynurenin metabolites such as quinolinic acid and kynurenic acid may change. Finally, the availability of L-iryptophan for other L-lryptophan-dependent processes may be reduced. Tryptophan is the metabolic precursor for. serotonin and nicotinic adenine dinucleotidc. Diabetes, bladder cancer, and neurological disorders may be the toxic consequences of diazinon-altered L-tryptophan metaboli.sm (Seifert and Pewnim, 1992 Pewnim and Seifert, 1993). 

Mitsuhashi, S. Fukushima, T. Arai, K. Tomiya, M. Santa, T. Imai, K. Toyo oka, T. Development of a columnswitching high-performance liquid chromatography for kynurenine enantiomers and its application to a pharmacokinetic study in rat plasma. Anal. Chim. Acta. 2007, 587, 60-66. 

The neutral amino acids alanine, serine, threonine, asparagine, glutamine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, histidine and citrulline share a common transporter at the luminal border of the epithelial cells in the renal tubuli and the epithelial cells in the small intestine [16]. In Hartnup disorder an impairment of this transporter leads to hyperexcretion of these neutral amino acids and to intestinal malabsorption. Excretion of tryptophan metabolites kynurenine and N-methyl-nico-tinamide is reduced. Plasma concentrations of the affected amino acids may be low normal or reduced. The inheritance is autosomal recessive. The hph2-deficient mouse has been postulated as a model for Hartnup disorder [17]. Affected persons may be asymptomatic, while some demonstrate pellagra-like photodermatitis or cerebellar ataxia due to a nicotinamide deficiency and respond well to the administration of nicotinamide [16]. 

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