A starch from Spirulina subsalsa: structural characterization and anti-photoaging activity

Spirulina subsalsa is a filamentous cyanobacterium with great potential as a source of functional polysaccharides, but the structural characteristics of these polysaccharides and their potential role in skin photoaging protection remain largely unexplored. In this study three polysaccharide fractions (SPS-1, SPS-2, & SPS-3) were isolated from the aqueous extract of Spirulina subsalsa, among which SPS-1 was further investigated due to its structural homogeneity and superior yield. SPS-1 was a homogeneous neutral polysaccharide composed mainly of glucose (98.9%), with a molecular mass of 2.89 × 10⁵ g/mol and a relatively low polydispersity index (PDI = 2.22). NMR and methylation analyses confirmed that it had a semi-rigid starch structure, characterized by a backbone of repeating →4)-α-d-Glcp-(1 → residues with limited branching. In UVB-irradiated HaCaT cells, SPS-1 exhibited anti-photoaging effects by attenuating oxidative stress, suppressing inflammation, and restoring extracellular matrix homeostasis through inhibition of the MAPK/NF-κB pathways. In vivo evaluation demonstrated its efficacy in enhancing skin barrier function, with limited skin permeation promoting surface retention and sustained activity that improved hydration and reduced water loss. These results indicate that SPS-1 has potential natural anti-photoaging activity and provide a theoretical basis for the structure-function study and skincare application of Spirulina subsalsa polysaccharides.