Immunological impact of graphene oxide sheets in the abdominal cavity is governed by surface reactivity

Graphene oxide (GO) is an oxidised form of graphene that has attractedcommercial interest in multiple applications, including inks, printedelectronics and spray coatings, which all raise health concerns due topotential creation of inhalable aerosols. Although a number of studies havediscussed the toxicity of GO sheets, the invivo impact of their lateral dimensions is still not clear. Here, we compared the effects of large GO sheets (l-GO, 1 µm– 20 µm) with those of small GO sheets (s-GO, < 1 µm) in terms of mesothelialdamage and peritoneal inflammation, after intraperitoneal (i.p.) injection inmice. To benchmark the outcomes, long and rigid multi-walled carbon nanotubes(MWCNTs) that were shown to be associated with asbestos-like pathogenicity onthe mesothelium were also tested. Our aim was to assess whether lateraldimensions can be a predictor of inflammogenicity for GO sheets as good aslength is for MWCNTs.   

While long MWCNTs dispersed in 0.5% BSA induced a granulomatous responseon the diaphragmatic mesothelium and immune cell recruitment to the peritonealcavity, GO sheets dispersed under similar conditions did not cause anyresponse, regardless of their lateral dimensions. We further interrogatedwhether tuning the surface reactivity of GO by testing different dispersions(5% dextrose instead of 0.5%BSA) may change the biological outcome. Although the change of dispersion didnot alter the impact of GO on the mesothelium (i.e. no granuloma), weobserved that, when dispersed in protein-free 5% dextrose solution, s-GOelicited a greater recruitment of monocytic cells to the peritoneal cavity thanl-GO, or when dispersed in protein containing solution. Such recruitmentcoincided with the greater ability of s-GO to interact in vivo withperitoneal macrophages and was associated with a greater surface reactivity incomparison to l-GO.

In conclusion, large dimension was not a determining factor of the immunological impact of GO sheets afteri.p. administration. For an equal dose, GO sheets with lateral dimensionssimilar to the length of long MWCNTs were less pathogenic than the MWCNTs. Onthe other hand, surface reactivity and the ability of some smaller GO sheets tointeract more readily with immune cells seem to be key parameters that can be tunedto improve the safety profile of GO. In particular, the choice of dispersionmodality, which affected these two parameters, was found to be of crucialimportance in the assessment of GO impact in this model. Overall, thesefindings are essential for a better understanding of the parameters governingGO toxicity and inflammation, and the rational design of safe GO-basedformulations for various applications, including biomedicine.