Defensive Effects of a Unique Polysaccharide, Sacran, to Protect Keratinocytes against Extracellular Stimuli and Its Possible Mechanism of Action.

Sacran, a polysaccharide isolated from the alga Aphanothece sacrum (Suizenji-nori), has unique physical and physiological characteristics. In a previous study, we reported that sacran improves skin conditions in individuals who suffer from atopic dermatitis (AD), focusing on its trapping function against extrinsic stimuli compared with hyaluronic acid (HA). First, we examined the penetration of sacran through stratum corneum (SC) with an impaired barrier function using immature reconstructed human epidermal equivalents. Sacran penetrates the SC to living cell layers of the epidermis, which suggested that sacran would attenuate adverse influences in keratinocytes caused by extracellular factors such as irritants or proinflammatory cytokines such as interleukin 1α (IL-1α). Sacran markedly reduced the cell damage induced by a nonionic detergent, sodium lauryl sulfate (SLS). Moreover, sacran restored the elevation of intracellular reactive oxygen species (ROS) levels stimulated by SLS and by IL-1α. These effects of sacran were superior to those of HA. In order to investigate the restoration effects of sacran, the influence of sacran on the physical properties of lipid bilayers was evaluated by measuring the order parameter using the ESR spin-labeling method. Because sacran failed to cause changes in the order parameters of liposomes and HaCaT keratinocytes, these results indicate that sacran does not interact with lipid bilayers although it restored changes in the order parameter caused by SLS. The sum of these results demonstrates that sacran reduces the influence of extracellular stimuli by its trapping effects. We conclude that the improving action of sacran is based on its trapping effect.