Photoprotective and Heavy Metal-Detoxifying Melanin Fractions Isolated from Ophiocordyceps sinensis Fermentation...

Melanin is a natural biopolymer with broad biological activities, yet research on melanin from the medicinal fungus Ophiocordyceps sinensis remains insufficient. In this study, two melanin fractions, TZ-a and TZ-b, were isolated from its fermentation products and characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA) and Ultraviolet-Visible spectra (UV-Vis). Their protective effects against UVB-induced damage in keratinocytes and heavy metal (Cd²⁺, Pb²⁺, As³⁺, Hg²⁺) cytotoxicity were evaluated. Both fractions exhibited characteristic melanin peaks but showed structural differences. TZ-a displayed lamellar or needle-like crystals, whereas TZ-b formed block-like aggregates. Both demonstrated good thermal stability. UV-Vis spectra confirmed their typical melanin identity. At 200 μg/mL, TZ-a and TZ-b increased cell viability from ~50% (model) to 80.59% and 82.48%, respectively. Additionally, they elevated the proportion of viable cells within the apoptotic population from 59.11% to 86.08% and 84.79%. Both fractions concentration-dependently alleviated heavy metal-induced cytotoxicity, reduced malondialdehyde levels, and restored glutathione pools. In conclusion, the melanin fractions TZ-a and TZ-b from O. sinensis exhibited photoprotective effects and alleviated heavy metal toxicity.