Light-Induced Mutagenicity in Salmonella TA102 and Genotoxicity/Cytotoxicity in Human T-cells by 33’-Dichlorobenzidine: A Chemical Used in the Manufacture of Dyes and Pigments and in Tattoo Inks

摘要

3,3’-Dichlorobenzidine (DCB) is used primarily as an intermediate in the manufacture of diarylide yellow or azo red pigments for printing inks, textiles, paints, and plastics. It is also used in tattoo inks. In this article, we investigate light-induced toxicity of DCB in both bacteria and human Jurkat T-cells. DCB itself is not toxic or mutagenic to Salmonella typhimurium TA102, but is photomutagenic at concentrations as low as 2 µM and phototoxic at concentrations >100 µM when the bacteria is exposed to DCB and light at the same time (1.2 J/cm² of UVA and 2.1 J/cm² of visible light). Furthermore, DCB is both photocytotoxic and photogenotoxic to human Jurkat T-cells. Under a constant light irradiation dose of 2.3 J/cm² of UVA and 4.2 J/cm² of visible light, it causes the Jurkat T-cells to become non-viable in a DCB dose-dependent manner and only 40% viable cells remaining at DCB concentrations higher than 50 µM. At the same time, DNA fragmentation is observed for the cells exposed to both DCB and light, determined by single cell gel electrophoresis (Comet assay). As much as 8 % of the cellular DNA is fragmented when exposed to 200 µM DCB and light irradiation. This suggests that DCB can penetrate the cell membrane and enter the cell. Upon light activation, DCB in the cells can cause various cellular damages, including DNA fragmentation, leading to non-viable Jurkat T-cells. It appears, though, non-viable cells may not be caused solely by fragmentation of cellular DNA, but other damages such as to proteins and cell membranes, or other forms of DNA damage such as alkylation that does not cause DNA to fragment, may also be involved. Therefore, persons exposed to DCB through environmental contamination or through tattoo piercing using DCB-contaminated inks must not only concern about its toxicity without exposing to light, but also about its phototoxicity.