Fullerene derivatives induce premature senescence: a new toxicity paradigm or novel biomedical applications.

Engineered fullerenes (C(60)) are extensively used for commercial and clinical applications based on their unique physicochemical properties. Such materials have also been recognized as byproducts of many industrial activities. Functionalization of C(60) may significantly influence the nature of its interactions with biological systems, impacting its applications and raising uncertainties about its health effects. In the present study, we compared the bioimpact of two chemically modified fullerene derivatives, hexa carboxyl fullerene adduct (Hexa-C(60)) and tris carboxyl fullerene adduct (tris-C(60)) to pristine fullerene C(60) encapsulated with gamma (gamma)-cyclodextrin C(60) (CD-C(60)), using human cutaneous epithelial cells (HEK) to simulate possible applications and occupational dermal exposure route. We report, for the first time, the discovery of premature senescence as a potential endpoint of nanomaterial elicited biological effects, providing a new paradigm for nanoparticle-induced toxicity in human cells. Moreover, this response appeared to be functionalization specific, in that, only tris-C(60) induced senescence. We investigated key biological responses, such as cellular viability, intracellular ROS generation, cell proliferation and cell cycle responses. Our results indicate that the often observed 'anti-apoptotic' function of fullerene derivatives may be independent of their 'ROS scavenging' role as previously reported. We discovered that the tris-C(60)-induced responses were associated with G(0)/G(1) cell cycle arrest and cellular senescence. On further evaluation of the molecular mechanisms underlying the senescent response, a significant decrease in the expression levels of HERC5 was noted. HERC5 is a ubiquitin ligase of the HERC family and is implicated to be involved in innate immune responses to viral and bacterial infections.