Biphenyl-induced cytotoxicity is mediated by an increase in intracellular Zn2+

Biphenyl is found both in natural and anthropogenic sources and is used as a fungistat in the packaging of citrus fruits. Acute exposure to high levels of biphenyl has been observed to cause skin irritation and toxic effects on the liver and kidneys. However, the mechanisms of cytotoxicity induced by biphenyl are not yet well understood. In the present study, the cytotoxicity of biphenyl was studied by flow cytometry with fluorescent probes. Biphenyl at 100?μM significantly increased cell lethality after 3?h in rat thymocytes. In addition, biphenyl at 100?μM or more elevated intracellular Zn²⁺ levels. N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), an intracellular and extracellular Zn²⁺ chelator, but not diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA), a membrane-impermeable Zn²⁺ chelator, attenuated the biphenyl-induced increase in intracellular Zn²⁺ levels and cell death. These results suggested that biphenyl-induced cytotoxicity caused an increase in intracellular Zn²⁺ levels, which was dependent on internal Zn²⁺. Moreover, biphenyl led to an increase in sensitivity to oxidative stress, while TPEN inhibited this biphenyl-induced increase. Our findings revealed that biphenyl caused an increase in the intracellular free Zn²⁺ concentration, inducing cytotoxicity, cell death, and an increase in sensitivity to oxidative stress.