Cyto and genotoxicities of graphene oxide and reduced graphene oxide sheets on spermatozoa

Concentration-dependent cyto and genotoxicities of graphene oxide (GO) and reduced GO (rGO) sheets on spermatozoa were studied. rGO sheets with various surface chemical states were achieved using hydrazine (N2H4) hydrothermal (HT) reactions and green tea polyphenols (GTPs). Although 0.1 mu g mL(-1) graphene could not change sperm viability and kinetic parameters, <40% and 20% of spermatozoa were viable and progressively motile, after 2 h incubation with 400 mu g mL(-1) GO or rGO, respectively. All the graphene nanomaterials induced concentration-dependent reductions of adenosine triphosphate and NAD(+)/NADH produced by spermatozoa for motility and metabolic activity. While GO, N2H4-rGO, and HT-rGO sheets caused increasing reactive oxygen species and sperm nitric oxide production, GO sheets reduced by antioxidant GTPs decreased them. Hence, physical trapping of spermatozoa by graphene (particularly GTP-rGO) is one of the important mechanisms describing the cytotoxicity, in addition to the other reactions, resulting in the inactivation and/or death of spermatozoa. Graphene genotoxicity was initiated by 1.0 mu g mL(-1) of N2H4-rGO and HT-rGO and 10 mu g mL(-1) of GO and GTP-rGO sheets. The extremely sharp edge and/or high mobility of N2H4-rGO provided easy penetration of the sheets into spermatozoa to interact with cell nuclei. In contrast, the steric effect induced by GTPs attached on rGO caused a lower genotoxicity.