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2-Oxo-Imidazole-Containing Dipeptides Play a Key Role in the Antioxidant Capacity of Imidazole-Containing Dipeptides.

ABSTRACT: 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.

SUBMITTER: Kasamatsu S

PROVIDER: S-EPMC8466808 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The role of extracellular ?-synuclein (?-syn) in the initiation and the spreading of neurodegeneration in Parkinson's disease (PD) has been studied extensively over the past 10 years. However, the nature of the ?-syn toxic species and the molecular mechanisms by which they may contribute to neuronal cell loss remain controversial. In this study, we show that fully characterized recombinant monomeric, fibrillar or stabilized forms of oligomeric ?-syn do not trigger significant cell death when added individually to neuroblastoma cell lines. However, a mixture of preformed fibrils (PFFs) with monomeric ?-syn becomes toxic under conditions that promote their growth and amyloid formation. In hippocampal primary neurons and ex vivo hippocampal slice cultures, ?-syn PFFs are capable of inducing a moderate toxicity over time that is greatly exacerbated upon promoting fibril growth by addition of monomeric ?-syn. The causal relationship between ?-syn aggregation and cellular toxicity was further investigated by assessing the effect of inhibiting fibrillization on ?-syn-induced cell death. Remarkably, our data show that blocking fibril growth by treatment with known pharmacological inhibitor of ?-syn fibrillization (Tolcapone) or replacing monomeric ?-syn by monomeric ?-synuclein in ?-syn mixture composition prevent ?-syn-induced toxicity in both neuroblastoma cell lines and hippocampal primary neurons. We demonstrate that exogenously added ?-syn fibrils bind to the plasma membrane and serve as nucleation sites for the formation of ?-syn fibrils and promote the accumulation and internalization of these aggregates that in turn activate both the extrinsic and intrinsic apoptotic cell death pathways in our cellular models. Our results support the hypothesis that ongoing aggregation and fibrillization of extracellular ?-syn play central roles in ?-syn extracellular toxicity, and suggest that inhibiting fibril growth and seeding capacity constitute a viable strategy for protecting against ?-syn-induced toxicity and slowing the progression of neurodegeneration in PD and other synucleinopathies.

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2-Oxo-Imidazole-Containing Dipeptides Play a Key Role in the Antioxidant Capacity of Imidazole-Containing Dipeptides.

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