Microglia-mediated neuroinflammation is a key driver of Alzheimer’s disease (AD). In AD, microglia are activated and trigger an increased secretion of pro-inflammatory factors. Rhein, an anthraquinone compound extracted from rhubarb, has been shown to reduce the secretion of pro-inflammatory cytokines including TNF-α and IL-1β in activated microglia. However, the mechanism of rhein on microglia-mediated neuroinflammation and neuronal damage in AD remains unclear. In this study, we found that rhein improved behavioral abnormalities in AD rats and reduced the levels of inflammatory factors such as IL-1β, iNOS, and NO in the brain of AD rats. In the LPS-induced microglial model, rhein significantly reduced the levels of inflammatory factors to improve neuroinflammation. Untargeted metabolomics showed that the reprogramming of glutamine metabolism occurred in M1 microglia. Targeted metabolomics and ¹³C, ¹⁵N isotope tracing experiments demonstrated that rhein regulated the metabolite levels in the glutamine–aspartate–arginine metabolic pathway. Meanwhile, the upregulated expression of proteins such as GLS1 and GOT1 within this pathway was reversed by rhein. Furthermore, we found that the glutamine–aspartate–arginine metabolic pathway regulates the production of nitric oxide (NO, a neuroinflammatory mediator). Rhein alleviates neuronal damage by inhibiting the glutamine–aspartate–arginine–NO metabolic pathway. In conclusion, our study shows that rhein may inhibits NO production by regulating the glutamine–aspartate–arginine metabolic pathway in activated microglia, thereby inhibiting the neuroinflammation and neuronal damage in AD.

Cydonia Oblonga Mill. is widely distributed in Turkey, Uzbekistan and China and commonly used by the food industry to produce jam, jelly and candies. The aim of this study was to investigate the in vitro antidiabetic activity and anti-diabetic mechanism of Cydonia Oblonga Mill. fruit (COMF). The chemical compositions were further characterized in COMF by UPLC-Q-Orbitrap/MS and 65 components including 22 flavonoids, 16 organic acids, 11 polyphenols, 5 amino acids, 3 pentacyclic triterpenoids and 8 other compounds were identified. The antioxidant activity by DPPH scavenging method and α-glucosidase inhibitory activity were tested. Furthermore, we detected the effects of COMF extract on the proliferation activity of HUVECs, cell viability of HUVECs under H₂O₂-induced oxidative stress, and NO production. Then, molecular docking activity and α-glucosidase inhibitory activity of seven key flavonoid components selected by bioinformatics analysis and literature in the COMF were studied. Among them, quercetin showed potent inhibitory activity, kaempferol, isorhamnetin, luteolin and apigenin demonstrated moderate inhibitory activity, while rutin and epicatechin exhibited poor inhibitory activity. Subsequently, the effects of quercetin, kaempferol, isorhamnetin, leteolin and apigenin on the gene expression levels of AKT1, IL-6 and VEGFA were verified by real-time fluorescence quantification (RT-qPCR). Molecular biology result showed that different active ingredients can significantly recover the levels of AKT1, IL-6 and VEGFA in HUVECs injured by high glucose.