Kynurenine (kyn) and kynurenic acid (kyna) are well-defined metabolites of tryptophan catabolism collectively known as “kynurenines”, which exert regulatory functions in host-microbiome signaling, immune cell response, and neuronal excitability. Kynurenine containing peptides endowed with opioid receptor activity have been isolated from natural organisms; thus, in this work, novel opioid peptide analogs incorporating L-kynurenine (L-kyn) and kynurenic acid (kyna) in place of native amino acids have been designed and synthesized with the aim to investigate the biological effect of these modifications. The kyna-containing peptide (KA1) binds selectively the μ-opioid receptor with a Ki = 1.08 ± 0.26 (selectivity ratio μ/δ/κ = 1:514:10,000), while the L-kyn-containing peptide (K6) shows a mixed binding affinity for μ, δ, and κ-opioid receptors, with efficacy and potency (Emax = 209.7 + 3.4%; LogEC50 = −5.984 + 0.054) higher than those of the reference compound DAMGO. This novel oligopeptide exhibits a strong antinociceptive effect after i.c.v. and s.c. administrations in in vivo tests, according to good stability in human plasma (t1/2 = 47 min).
Kynurenine(Kyn)和犬尿酸(Kyna)是色氨酸代谢中明确定义的代谢产物,共同称为“酪氨酸酮”,在宿主-微生物组信号传导、免疫细胞反应和神经兴奋性中发挥调节功能。含有阿片受体活性的酪氨酸酮肽已从天然生物中分离出来;因此,在这项工作中,设计并合成了新型阿片肽类似物,其中包含L-酪氨酸(L-kyn)和犬尿酸(Kyna),以取代天然氨基酸,目的是研究这些修饰的生物效应。含有犬尿酸的肽(KA1)选择性地结合μ-阿片受体,Ki = 1.08 ± 0.26(选择比μ/δ/κ = 1:514:10,000),而含有L-酪氨酸的肽(K6)对μ、δ和κ-阿片受体显示混合结合亲和力,效力和效能(Emax = 209.7 + 3.4%; LogEC50 = −5.984 + 0.054)高于参考化合物DAMGO。这种新型寡肽在体内试验中经i.c.v.和s.c.给药后表现出强抗痛效应,根据其在人类血浆中的良好稳定性(t1/2 = 47分钟)。