Uncovering a photoprotective polysaccharide from Gentiana dahurica via systematic fractionation

Gentiana dahurica Fisch. (G. dahurica) is a plant native to high-altitude plateaus that has developed unique biochemical adaptations to intense UV radiation. This study aimed to discover novel polysaccharides from G. dahurica (GDP) with prominent activity against UV-induced photoaging. Three methods were used to extract GDP: hot water (GDP-W), alkaline (GDP-A), and cellulase-assisted methods (GDP-E), with yields of 2.30%, 0.10%, and 0.46%, respectively. GDP-W and GDP-E mainly contained arabinose and galacturonic acid, while GDP-A was mainly composed of arabinose and mannose. Among the three polysaccharides, GDP-A contained a higher proportion of high-molecular-weight fractions. In vitro assays revealed that all GDPs exhibited concentration-dependent antioxidant activity, effectively scavenging DPPH, ABTS, and hydroxyl radicals. GDP-A exhibited the strongest effects. In UVB-irradiated HaCaT cells, all GDPs effectively alleviated the reduction in cell viability and proliferation. They increased the levels of antioxidant enzymes, reduced the levels of inflammatory factors, decreased intracellular ROS accumulation, and inhibited apoptosis. In the zebrafish photoaging model, GDPs significantly reduced the UVA-induced increase in ROS levels. GDP-A exhibited greater efficacy in both antioxidation and inhibiting apoptosis. Furthermore, in a mouse model of skin photoaging, GDP-A ameliorated UVB-induced skin damage. It increased antioxidant enzyme levels, decreased pro-inflammatory cytokines, and suppressed matrix metalloproteinase-3 expression in the epidermis. These changes resulted in higher collagen content and improved therapeutic outcomes. The results indicated the potential use of GDP-A in pharmaceutical and cosmetic applications and provided new insights into the impact of isolation methods on discovering bioactive polysaccharides.