Size-dependent toxicity of nano-C₆₀ aggregates: More sensitive indication by apoptosis-related bax translocation in cultured human cells

The toxicity of NPs is not well characterized in terms of their size. In particular, the size-based toxicity of fullerene (C₆₀) remains an issue because of a lack of C₆₀ NPs with a well-controlled size. In this work, six fractions of the nano-C₆₀ aggregates (nC₆₀) with different size distribution were prepared by a simple differential centrifugation. By using these nC₆₀ fractions, we demonstrate the size-dependent inhibition of DNA polymerase and reduced-size enhanced cytotoxicity. Above all, we found that nC₆₀ NPs with smaller size may have higher toxicity potency. These size-dependent effects were observed at the high exposure doses (4-6 mg/L). Interestingly, at 20-times lower and noncytotoxic doses, the size-dependent effect can be indicated by apoptosis-related fluorescent protein fused Bax translocation. Considering the toxicity of NPs is often ignored in the traditional end-point analysis for cytotoxicity when the exposure dose is low, the findings presented here will assist in the evaluation of the size-dependent cytotoxicity and dose-response relationships of toxicity mediated by nC₆₀ NPs at low doses.