Study on cytotoxicity anti-radiation activity and neuroprotective effects of melanin derivatives prepared from microbial melains

Abstract

Fungal melanin has several advantages such as lower cost, and easier for purification and production at a larger scale. Thus, fungi are excellent sources of natural melanin. Despite of having many significant bioactivities, one of the most challenging aspects of melanins is that they are insoluble in water. Previous studies proved that in vitro melanin modified with arginine would improve the water solubility, which could enhance their biological activities. Therefore, the objectives of the research were to evaluate cytotoxicity, anti-radiation activity and neuroprotective effects of argininemodified melanin prepared from Calvatia craniiformis and Xylaria sp. Consequently, the extraction and purification procedures involved the use of alkaline solution, then modification was the next step. Arginine modification with 1:1 mass ratio were choosen for futher use due to the highest absorbance value and the darkest color observation. FTIR spectra analysis were carried out to confirm product received from modification and it was found to be a typical melanin with arginine has been binding successfully. In cytotoxicity activity, SRB method was used to evaluated that melanin derivatives. At the concentration of 100 µg/mL, arginine modified melanin extracted from Calvatia craniiformis and Xylaria sp. inhibited -2.99% and -3.16% cell growth, respectively, which were not toxic to HepG2 cells. In anti-radiation experiment, arginine-modified melanins displayed anti-radiation activity in Staphylococcus aureus when the bacteria were expose to 254nm UV light within 20 minutes. This showed melanin derivatives had biological activities in vitro and could play as promising radiation protection agent. Additionally, in vitro neuroprotective effects, the toxicity of H2O2 and MPTP toward SH-SY5Y cells was proven as dependent of concentration. 1mM H2O2 and 0.5mM could inhibit approximately 50% cellviability. Both arginine-modified C. craniiformis and Xylaria sp. melanin (10-100 µg/mL) had no toxic to SH-SY5Y cells and they could protect the neuroblastoma cells from H2O2 toxicity. Specifically, at the concentration of 100 µg/mL, C. craniiformis and Xylaria sp. melanin derivatives could enhance up to 20% cell viability of SH-SY5Y cells when treated with H2O2, which is comparable with the positive control (20µM Resveratrol) with the viability of 35.5%. In contrast, modified melanin of C. craniiformis at the concentration from (10-100 µg/mL) could not protect neuron cells from damage while modified Xylaria sp. melanin could protect human neuroblastoma cells from neurotoxin at the concentration higher than 50 µg/mL. The results suggested arginine-modified melanin was a promising candidate agent to treat oxidative injury of neurocytes, which is worth further investigation.