Protective Effects on Keratinocytes by Extracts Enriched in Polysaccharides from Limnospira platensis Grown Under Autotrophic and Mixotrophic Conditions

Background/Objectives: Natural polysaccharides have many bio-pharmacological effects, which make them compounds with potential in healthcare. Limnospira platensis (Spirulina), a well-known blue–green cyanobacterium with relevance in the market of nutraceuticals, produces polysaccharides with recognized antioxidant and anti-inflammatory activities. Noteworthy, the growth of the cyanobacterium biomass may be obtained in a more sustainable manner under mixotrophic conditions. In the present study, we compared the antioxidant and anti-inflammatory effects of polysaccharide-enriched extracts from the cyanobacterium cultured under autotrophism (Auto−P extract) or mixotrophism (Mixo−P extract); this latter was realized using medium added with brewery wastewater (BWW). Methods and Results: Non-cellular investigation showed a better antioxidant profile for Mixo−P extract in the OH radical scavenging assay and a similar activity between the extracts in ABTS and ferrous chelation assays. The antioxidant protective activity of L. platensis extracts investigated on HaCat cells in the range of 0.3–10 μg/mL (not cytotoxic concentrations), against hydrogen peroxide (H2O2, 600 μM)-induced damage, revealed a similar activity by the two extracts. When tested against the inflammatory stimuli with lipopolysaccharide (LPS, 10 μg/mL) or tumor necrosis factor-α (TNF-α, 10 ng/mL), both Auto−P and Mixo−P showed an ability to prevent the effects of the inflammatory agents on cell viability and on interleukin-1β (IL-1β) and interleukin-6 (IL-6) release, with a slightly greater potency by Mixo−P extract. Conclusions: In conclusion, our data suggest the possible use of L. platensis polysaccharide-enriched extracts in biological-made pharmaceuticals for skin disorders or in cosmeceuticals. In addition, this study demonstrates that mixotrophic cultivation of L. platensis may be an alternative and sustainable way for biotechnological applications of the cyanobacterium biomass.