Cytotoxicity and Photo-cytotoxcity of Modified, Water- Soluble Carbon Nanotubes in Human Skin Keratinocytes

Water soluble carbon nanotubes have been found to be most promising in biological and biomedical based applications. However, there has been major concern placed on their ability to cause cellular and DNA structural damages upon exposure. Also, influence on natural occurrences such as sunlight, has ignited some apprehension of phototoxicity when exposing to light and carbon based nanomaterials to various cell lines. We hypothesize light absorbing raw carbon nanotubes may undergo photochemical reactions leading to toxicity and increase DNA damage, while purified and soluble carbon nanotubes will remain non-toxic can cause minimal to no DNA damage to the skin keratinocytes (HaCaT). In this work, we explore the toxicity influence on the HaCaT cells by four multi-walled carbon nanotubes (MWNT) produced by high pressure carbon monoxide (HiPCO). Effect of all MWNT were tested with the conventional MTT and the water-soluble tetrazolium (WST-1) assays for 24 hrs and 30 min exposure. Both exposures times showed that purified carbon nanotubes caused greater cytotoxicity than unpurified and soluble nanotubes. However, HaCaT cell viability for those exposed to purified nanotubes did not fall below 50%. Assessments of direct and oxidative DNA damage was determined by Comet assay and Formamidopyrimidine DNA glycosylase (FPG) modified Comet assay, respectively. Direct DNA damage results indicated that treatment with 1 mg/mL HiPCO processed, purified and modified carbon nanotubes alone did not cause significant DNA damage to HaCaT cells, but upon UV irradiation, it seemed to cause a slight increase in percent of DNA damage. Oxidative DNA damage studies revealed significant increase of DNA damage in HaCaT cells without UV radiation. An expected increase in percent DNA damage was seen in HaCaT cells treated with selective carbon nanotubes and UV radiation. Results suggest that all HiPCO processed carbon nanotubes, including the water soluble, may not render toxic results, but are capable of causing oxidative DNA damage to cells with and without environmental factors such as UV radiation.