Metabolomic insights of macrophage responses to graphene nanoplatelets: Role of scavenger receptor CD36

Graphene nanoplatelets (GNPs) are novel two-dimensional engineered nanomaterials consisting of planar stacks of graphene. Although human exposures are increasing, our knowledge is lacking regarding immune-specific responses to GNPs and mechanisms of interactions. Our current study utilizes a metabolite profiling approach to evaluate macrophage responses to GNPs. Furthermore, we assessed the role of the scavenger receptor CD36 in mediating these GNP-induced responses. GNPs were purchased with dimensions of 2 μm × 2 μm × 12 nm. Macrophages were exposed to GNPs at different concentrations of 0, 25, 50, or 100 μg/ml for 1, 3, or 6 h. Following exposure, no cytotoxicity was observed, while GNPs readily associated with macrophages in a concentration-dependent manner. After the 1h-pretreatment of either a CD36 competitive ligand sulfo-N-succinimidyl oleate (SSO) or a CD36 specific antibody, the cellular association of GNPs by macrophages was significantly reduced. GNP exposure was determined to alter mitochondrial membrane potential while the pretreatment with a CD36 antibody inhibited these changes. In a separate exposure, macrophages were exposed to GNPs at concentrations of 0, 50, or 100 μg/mL for 1 or 3h or 100 μM SSO (a CD36 specific ligand) for 1h and collected for metabolite profiling. Principal component analysis of identified compounds determined differential grouping based on exposure conditions. The number of compounds changed following exposure was determined to be both concentration- and time-dependent. Identified metabolites were determined to relate to several metabolism pathways such as glutathione metabolism, Pantothenate and CoA biosynthesis, Sphingolipid metabolism, Purine metabolism, arachidonic acid metabolism and others. Lastly, a number of metabolites were found in common between cells exposed to the CD36 receptor ligand, SSO, and GNPs suggesting both CD36-dependent and independent responses to GNP exposure. Together our data demonstrates GNP-macrophage interactions, the role of CD36 in the cellular response, and metabolic pathways disrupted due to exposure.