There is substantial evidence for the antioxidant functions of imidazole-containing dipeptides (IDPs), including carnosine and anserine, under physiological and pathological conditions in vivo. However, the detailed mechanism underlying the antioxidant functions is still poorly understood. Recently, we discovered the endogenous production of 2-oxo-imidazole-containing dipeptides (2-oxo-IDPs), such as 2-oxo-carnosine and 2-oxo-anserine, as novel derivatives of IDPs in mouse tissues and revealed that the antioxidant capacity of 2-oxo-carnosine was much greater than that of carnosine. However, the antioxidant capacity of 2-oxo-IDPs still remains unclear. In this study, we evaluated 2-oxo-carnosine and 2-oxo-anserine by multiple in vitro assays, such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, ferric reducing/antioxidant power, and oxygen radical absorbance capacity assays in comparison with the corresponding IDPs, carnosine and anserine. All the assays employed herein demonstrated that 2-oxo-carnosine and 2-oxo-anserine exhibited a greater antioxidant capacity than that of the corresponding IDPs. Quantitative high-performance liquid chromatography tandem mass spectrometry revealed that commercial IDPs standards were contaminated with a certain amount of 2-oxo-IDPs, which was correlated with the antioxidant capacity. DPPH radical scavenging assay revealed that the elimination of contaminated 2-oxo-IDPs from the IDPs standards caused a significant decrease in the antioxidant capacity compared to the original IDPs standards. These results suggest that the main driver of the antioxidant capacity of IDPs is 2-oxo-IDPs; accordingly, the conversion of IDPs to 2-oxo-IDPs may be a critical step in the antioxidant functions.

中文翻译：

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含 2-氧代-咪唑二肽在含咪唑二肽的抗氧化能力中起关键作用

有大量证据表明，在体内生理和病理条件下，含咪唑的二肽 (IDP)（包括肌肽和鹅肌肽）具有抗氧化功能。然而，抗氧化功能的详细机制仍然知之甚少。最近，我们发现内源性产生含有 2-oxo-imidazole 的二肽（2-oxo-IDPs），例如 2-oxo-carnosine 和 2-oxo-anserine，作为 IDPs 在小鼠组织中的新型衍生物，并揭示了2-氧代肌肽的抗氧化能力远大于肌肽。然而，2-oxo-IDPs 的抗氧化能力仍不清楚。在这项研究中，我们通过多种体外测定评估了 2-氧代肌肽和 2-氧代鹅肌肽，例如 2,2-二苯基-1-苦基肼 (DPPH) 自由基清除、铁还原/抗氧化能力、和氧自由基吸收能力测定与相应的 IDP、肌肽和鹅肌肽进行比较。此处采用的所有测定表明，2-氧代-肌肽和2-氧代-鹅肌肽比相应的IDP 具有更大的抗氧化能力。定量高效液相色谱串联质谱显示商业 IDP 标准品被一定量的 2-oxo-IDPs 污染，这与抗氧化能力相关。DPPH 自由基清除试验表明，与原始 IDP 标准相比，从 IDP 标准中消除受污染的 2-氧代-IDP 导致抗氧化能力显着降低。这些结果表明，IDPs 抗氧化能力的主要驱动因素是 2-oxo-IDPs；因此，