Fluorescence nanoparticles from instant coffee accumulated in lysosome and induced lysosome-dependent cell death via necroptosis-like pathway

Fluorescence nanoparticles (FNs) are a type of nano-dots generated during baking process, and their safety on organism is unclear and little is known to their cytotoxicity. In this study, the FNs from instant coffee were purified and characterized. The FNs with an average size about 2.08 nm emitted bright blue fluorescence with lifetime about 2.74 ns. The element and functional groups were analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, respectively. The results indicated that these FNs were internalized in lysosomes and induced apoptosis of normal rat kidney (NRK) and Caco-2 cells. While, the pan-caspase inhibitor, Z-VAD-FMK didn?t decrease the rate of apoptosis and cell death of the FNs-treated NRK and Caco-2 cells. These internalized FNs enlarged lysosomes, decreased lysosomal enzyme degradation activity and increased lysosomal pH value. Partial co-localization of receptor-interacting serine-threonine kinase 3 (RIPK3) to lysosomes in FNs-treated cells was observed, and the amount of RIPK1 and RIPK3 increased after treatment with FNs. The results demonstrated that the FNs from instant coffee induced lysosomal membrane permeabilization and initiated necroptosis.