Kynurenic acid (KYNA) is an antioxidant degradation product of tryptophan that has been shown to have a variety of cytoprotective, neuroprotective and neuronal signalling properties. However, mammalian transporters and receptors display micromolar binding constants; these are consistent with its typically micromolar tissue concentrations but far above its serum/plasma concentration (normally tens of nanomolar), suggesting large gaps in our knowledge of its transport and mechanisms of action, in that the main influx transporters characterized to date are equilibrative, not concentrative. In addition, it is a substrate of a known anion efflux pump (ABCC4), whose in vivo activity is largely unknown. Exogeneous addition of L-tryptophan or L-kynurenine leads to the production of KYNA but also to that of many other co-metabolites (including some such as 3-hydroxy-L-kynurenine and quinolinic acid that may be toxic). With the exception of chestnut honey, KYNA exists at relatively low levels in natural foodstuffs. However, its bioavailability is reasonable, and as the terminal element of an irreversible reaction of most tryptophan degradation pathways, it might be added exogenously without disturbing upstream metabolism significantly. Many examples, which we review, show that it has valuable bioactivity. Given the above, we review its potential utility as a nutraceutical, finding it significantly worthy of further study and development.

Keywords: ABCC4; SLC22A6; SLC22A8; cytoprotectant; kynurenic acid; nutraceutical; oxidative stress.

犬尿酸（KYNA）是色氨酸的抗氧化分解产物，已被证明具有多种细胞保护、神经保护和神经信号传导特性。然而，哺乳动物转运蛋白和受体表现出微摩尔结合常数；这些常数与通常的组织浓度一致，但远高于其血清/血浆浓度（通常是数十纳摩尔），这表明我们对其运输机制和作用方式的理解存在很大差距，因为在已知的主要流入转运蛋白中，大多数是平衡型而非集中型。此外，它是已知阴离子外排泵（ABCC4）的底物，但其体内活性在很大程度上尚不清楚。添加L-色氨酸或L-犬尿素会导致犬尿酸和其他许多共代谢产物（包括一些可能具有毒性的代谢产物，如3-羟基-L-犬尿素和喹啉酸）的产生。除了栗子蜂蜜外，KYNA在天然食品中的含量相对较低。然而，它的生物利用度是合理的，并且作为大多数色氨酸分解途径的终末步骤，它可以外源添加而不会显著干扰上游代谢。我们回顾了许多显示其具有宝贵生物活性的例子。鉴于以上所述，我们对其作为保健品的潜在效用进行了评估，认为它值得进一步研究和发展。

关键词：ABCC4；SLC22A6；SLC22A8；细胞保护剂；犬尿酸；保健品；氧化应激。