d-Amino acids differentially trigger an inflammatory environment in vitro

• Main Authors: Yap, Siew Hwei, Lee, Cheng Siang, Zulkifli, Nur Diyana, Suresh, Darshinie, Hamase, Kenji, Das, Kumitaa Theva, Rajasuriar, Reena, Leong, Kok Hoong
• Format: Article
• Published: Springer Wien 2024
• Subjects: R Medicine (General); RM Therapeutics. Pharmacology
• Online Access: http://eprints.um.edu.my/45663/; https://doi.org/10.1007/s00726-023-03360-8

Studies in vivo have demonstrated that the accumulation of D-amino acids (D-AAs) is associated with age-related diseases and increased immune activation. However, the underlying mechanism(s) of these observations are not well defined. The metabolism of D-AAs by D-amino oxidase (DAO) produces hydrogen peroxide (H2O2), a reactive oxygen species involved in several physiological processes including immune response, cell differentiation, and proliferation. Excessive levels of H2O2 contribute to oxidative stress and eventual cell death, a characteristic of age-related pathology. Here, we explored the molecular mechanisms of D-serine (D-Ser) and D-alanine (D-Ala) in human liver cancer cells, HepG2, with a focus on the production of H2O2 the downstream secretion of pro-inflammatory cytokine and chemokine, and subsequent cell death. In HepG2 cells, we demonstrated that D-Ser decreased H2O2 production and induced concentration-dependent depolarization of mitochondrial membrane potential (MMP). This was associated with the upregulation of activated NF-& kcy;B, pro-inflammatory cytokine, TNF-alpha, and chemokine, IL-8 secretion, and subsequent apoptosis. Conversely, D-Ala-treated cells induced H2O2 production, and were also accompanied by the upregulation of activated NF-& kcy;B, TNF-alpha, and IL-8, but did not cause significant apoptosis. The present study confirms the role of both D-Ser and D-Ala in inducing inflammatory responses, but each via unique activation pathways. This response was associated with apoptotic cell death only with D-Ser. Further research is required to gain a better understanding of the mechanisms underlying D-AA-induced inflammation and its downstream consequences, especially in the context of aging given the wide detection of these entities in systemic circulation.