The biotransformation of graphene oxide in lung fluids significantly alters its inherent properties and bioactivities toward immune cells

Engineered nanomaterials (such as graphene oxide, GO) have shown great potential in biomedical applications as therapeutic and imaging agents. However, little is known about their potential transformations in biological settings, which may alter their physicochemical properties and consequently hinder their biomedical applications. Here, we show that GO undergoes a significant physicochemical transformation in two simulated human lung fluids–Gamble’s solution and artificial lysosomal fluid (ALF), as the organic acids (e.g., citrate and acetate) in the lung fluids cause the reduction of GO, which is mainly due to the conversion of epoxy and carbonyl groups to phenolic groups. This biotransformation markedly inhibits the endocytosis of GO by scavenging macrophages. Notably, the alterations that occur in Gamble’s solution enhance the layer-by-layer aggregation of GO, resulting in the precipitation of GO and a reduction in its interaction with cells, whereas the changes that occur in ALF lead to edge-to-edge aggregation of GO, thereby enhancing the adhesion of large sheet-like GO aggregates on the plasma membrane without cellular uptake. The varied interaction mechanisms with macrophages eventually induce different proinflammatory reactions. Experiments conducted in mice corroborated the morphological alterations of GO in a realistic lung microenvironment. Overall, the findings suggest that the biotransformation of nanomaterials may significantly alter their inherent properties and therefore affect their biosafety, such as the clearance of “worn-out” nanomaterials by immune cells, giving rise to potentially long-term side effects at the accumulation sites. Graphene-oxide particles inserted into the body for biomedical applications such as drug delivery or enhanced imaging can form aggregates over time with possible adverse effects on health, and show researchers in China. After the medical objectives have been achieved, the nanoparticles often remain inside the human body, but it is unclear what happens to them after long time periods in a biological environment. Sijin Liu from the Chinese Academy of Sciences in Beijing, Wei Chen from Nankai University in Tianjin, and their colleagues show that graphene-oxide nanoparticles undergo a physicochemical transformation in simulated human lung fluids, aggregating to form larger particles. This reduces their interaction with cells and inhibits cellular uptake, and can induce proinflammatory reactions. The results highlight the need to consider the biosafety of nanomaterials and their potential long-term side effects. GO can undergo significant physicochemical transformation in two simulated lung fluids–Gamble’s solution and artificial lysosomal fluid (ALF), as the organic acids in lung fluids cause reduction of GO. Biotransformation markedly inhibits the endocytosis of GO by scavenging macrophages. Notably, alterations in Gamble’s solution enhance the aggregation of GO in a layer-to-layer manner, resulting in GO precipitation and reduced interaction with cells, whereas changes in ALF lead to edge-to-edge aggregation of GO, enhancing the adhesion of large sheet-like GO aggregates on plasma membrane without cellular uptake.