Theoretical studies of the interaction between silver and lipids present in HepG2 cells

We performed DFT and TDDFT calculations to determine interactions between silver atom and model cell membrane of human hepatocellular carcinoma (HepG2) cells or human liver cells. Specifically, we chose the two major lipid constituents of HepG2 cells which are 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyI-sn-glycero-3-phosphoethanolamine (POPE) to represent HepG2 cell membrane. Silver atom (Ag0) and silver ion (Ag+) are used as silver models to represent possible point-to-point interaction and the effect of silver ion (Ag+) leakage. The results show that exposure of POPC to silver ion (Ag+) at a high concentration can cause structural conformational changes from being originally bent to straight conformation. In addition, the interaction between silver ion (Ag+) and the lipids can cause significant amount of charge transfer that ranges from 0.14 to 0.16 for POPC and 0.12 to 0.14 for POPE. Moreover, though silver ion (Ag+) binds three to five times stronger to the lipids than silver atom (Ag0), both interactions are Van der Waals interaction. Finally, the presence of silver atom (Ag0) in the lipids can be detected using UV-Vis spectrophotometer by occurrence of a red shift which is seen at 376 nm and 372 nm for POPC and POPE respectively. However, detecting silver ion (Ag+) using this method is not feasible as no apparent shifts are shown.