Abstract: This study aimed to investigate the protective effects and mechanisms of extracts from differently processed forms of Rehmannia glutinosa roots (fresh, dried, and prepared) on D-galactose-induced aging in mice. The chemical constituents and in vitro antioxidant activity of the three extracts were determined. Their effects on antioxidant capacity and the gut microbiota in D-galactose-induced aging mice were compared. The results indicated that the extract from fresh R. glutinosa root was rich in catalpol and total phenols, while the total sugar and polysaccharide contents of the extract from prepared R. glutinosa root were significantly increased. In vitro assays showed that all extracts from R. glutinosa had antioxidant activity, with the extracts from dried and prepared R. glutinosa roots exerting stronger activity. In animal experiments, the three extracts exerted anti-aging effects by significantly enhancing total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity in mouse tissues and serum, inhibiting the production of malondialdehyde (MDA), reducing the levels of the pro-inflammatory factors tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), and increasing the levels of the anti-inflammatory factor interleukin-10 (IL-10). Additionally, they improved liver function markers, including alanine aminotransferase (ALT) and aspartate aminotransferase (AST) concentrations. The antioxidant and anti-inflammatory effects of the extract from dried R. glutinosa root were superior to those of the extract from fresh and prepared R. glutinosa roots. Molecular mechanism studies indicated that intervention with each of these R. glutinosa root extracts upregulated the mRNA and protein expression of Nrf2, HO-1, and NQO1 in the liver, thereby activating the Nrf2-mediated oxidative stress response pathway. 16S rRNA sequencing indicated that R. glutinosa root could ameliorate gut microbiota dysbiosis in aging mice, as evidenced by enhanced microbial α-diversity, modulated Firmicutes/Bacteroides abundance ratio, and increased relative abundance of beneficial bacteria such as Lactobacillus and Adlerocroccus. In summary, the extracts from all three forms of R. glutinosa root exhibited anti-aging effects, with the extract from dried R. glutinosa root demonstrating the most potent activity. The underlying mechanism may be associated with the activation of the Nrf2 signaling pathway, the regulation of oxidative stress and inflammatory responses, and the restoration of gut microbiota homeostasis.

Key words: Rehmannia glutinosa root extracts; aging; antioxidant; anti-inflammatory; gut microbiota