Accumulating evidence from diverse experiments, including heterochronic parabiosis-the surgical joining of two animals of different ages-has highlighted the importance of systemic factors in the progressive functional decline of various organs and tissues during aging. The major metabolic pathway of tryptophan, an essential amino acid in humans, is the kynurenine pathway (KP) in which indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) catalyze the conversion of tryptophan into kynurenine. Importantly, circulating kynurenine produced by this enzymatic breakdown, as a primary driver of the aging process, has been linked to higher mortality in humans. This review discusses the potential roles of tryptophan derivatives as biomarkers for the risk of frailty in the elderly, based on human observational studies as well as the KP as a therapeutic target for age-related diseases.

中文翻译：

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年龄相关疾病中犬尿氨酸途径的临床见解。

来自包括异时共生生物（两种不同年龄的动物的手术连接）在内的各种实验的越来越多的证据，突显了系统性因素在衰老过程中各种器官和组织的逐渐功能衰退中的重要性。色氨酸（人类必需的氨基酸）的主要代谢途径是犬尿氨酸途径（KP），其中吲哚胺2,3-二加氧酶（IDO）和色氨酸2,3-二加氧酶（TDO）催化色氨酸转化为犬尿氨酸。重要的是，由这种酶促分解产生的犬尿氨酸循环作为衰老过程的主要驱动力，已与人类较高的死亡率有关。这篇评论讨论了色氨酸衍生物作为老年人衰老风险生物标志物的潜在作用，