Assessment of UVB-photoprotective and antioxidative activities of carrageenan in keratinocytes

Ultraviolet B (UVB) (290–320 nm) is the foremost cause of photoaging, sunburn, wrinkles and skin cancer. Photoprotection against harmful UVB radiation is essential through various means including the use of skincare products. The seaweed polysaccharide carrageenan is widely used as an excipient in cosmetics and skincare products. However, its effects on normal skin keratinocytes or potential use as a photoprotective agent have yet to be established. The primary aim of this study was to assess the cytotoxic, photoprotective and antioxdative effects of carrageenan in UVB-induced immortalised normal human keratinocytes (HaCaT cells). Results showed that the percentage of cell viability decreased linearly with increasing UVB doses from 10, 50, 100, 222 to 1,000 mJ cm^?2. Four isomers of carrageenan, namely iota 2 [ι (??)], iota 5 [ι (V)], lambda (λ) and kappa (κ) carrageenan were used in this study. Vitamin E was used as a positive control. In terms of cytotoxicity, the CD₅₀ of kappa carrageenan was ~200 μg mL^?1 while for the other isomers, the values ranged from 122 to 162 μg mL^?1. Carrageenan showed significant protection against detrimental effects of UVB-induced cell killing and reactive oxygen species (ROS) release based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and 2′,7′-dichlorfluorescein-diacetate (DCFH-DA) assays, respectively. Carrageenan was also able to quench 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals. The ability to protect against UVB suggests that carrageenan has potential application as a photoprotective agent in addition to just being used as an excipient.