Nanoparticles cellular uptake, trafficking, activation, toxicity and in vitro evaluation

Nanoparticles (NPs) physicochemical properties, such as size, shape, surface chemistry, charge, etc., play a critical role in biological systems interactions, which include NPs' cellular uptake, trafficking, activation, and toxicity. Although nano-bio interactions are multifaceted and complex, their assessment is essential for future therapeutic and diagnostic use since being carriers that deliver specific molecules (i.e., active pharmaceutical ingredients and imaging agents) in intracellular sites. The journey of NPs begins by reaching the plasma membrane and entering the cell mainly through endocytosis. After vesicles pinch off the cell membrane, the intracellular trafficking is mediated by a network of cellular endosomes which direct NPs to the different cellular components. Otherwise, NPs or their contents are released into the cytoplasm. In both cases, NPs can pass undetected or be recognized by the cell leading to a pro or anti-inflammatory response. Indeed, the cell response mostly depends on cell type and NPs physicochemical properties. The principal mechanism by which NPs activate the cell response is RONS production. Other mechanism includes signaling pathways modulation related to metabolic and enzymatic reactions, cell transduction, and immune modulation. Hence, the underlying mechanisms of cellular and subcellular interactions in vitro should be performed to provide insights into NPs' effect. This information helps us to improve their synthesis and design to maximize the clinical benefits while minimizing side effects. Most in vitro tests to evaluate NPs' effect in cells were developed focusing on cell dysfunctions, cytotoxicity, genotoxicity, immunogenicity, and cell death.