Black phosphorus nanosheets induce autophagy dysfunction by a size- and surface modification-related impairment of lysosomes in macrophages

The widespread application of black phosphorus nanosheets (BPNSs) raises concerns about their potential impact on human health. Although that the autophagy-inducing properties of BPNSs in cancer cells are documented, their effects on macrophages-key components of the immune system and the mechanisms involved remain obscure, especially in terms of the influences of BPNS the size and surface modifications on the autophagic process. This study investigated the effects of bare BPNSs and PEGylated BPNSs (BP-PEG) on macrophage autophagy and its underlying mechanisms by comprehensive biochemical analyses. The results indicated that both BPNSs and BP-PEG are internalized by RAW264.7 cells through phagocytosis and caveolin-dependent endocytosis, leading to lysosomal accumulation. The internalized BPNSs induced mitochondrial dysfunction, which subsequently elevated the NAD⁺/NADH ratio and activated the SIRT-1 pathway, initiating autophagy. However, BPNSs disrupted the autophagic flux by impairing autolysosome formation, leading to apoptosis in a size-dependent manner. In contrast, BP-PEG preserved lysosomal integrity, maintaining autophagic activity and cell viability. These findings deepen our understanding of the influence of nanosheet size and surface modifications on macrophage autophagy, contributing to the formulation of regulatory guidelines to minimize the potential adverse effects and health risks associated with BPNS utilization in various applications.