title: Overendocytosis of gold nanoparticles increases autophagy and apoptosis in hypoxic human renal proximal tubular cells.
abstract: BACKGROUND
  Gold nanoparticles (GNPs) can potentially be used in biomedical fields ranging from therapeutics to diagnostics, and their use will result in increased human exposure. Many studies have demonstrated that GNPs can be deposited in the kidneys, particularly in renal tubular epithelial cells. Chronic hypoxic is inevitable in chronic kidney diseases, and it results in renal tubular epithelial cells that are susceptible to different types of injuries. However, the understanding of the interactions between GNPs and hypoxic renal tubular epithelial cells is still rudimentary. In the present study, we characterized the cytotoxic effects of GNPs in hypoxic renal tubular epithelial cells.
  
  
  RESULTS
  Both 5 nm and 13 nm GNPs were synthesized and characterized using various biophysical methods, including transmission electron microscopy, dynamic light scattering, and ultraviolet-visible spectrophotometry. We detected the cytotoxicity of 5 and 13 nm GNPs (0, 1, 25, and 50 nM) to human renal proximal tubular cells (HK-2) by Cell Counting Kit-8 assay and lactate dehydrogenase release assay, but we just found the toxic effect in the 5 nm GNP-treated cells at 50 nM dose under hypoxic condition. Furthermore, the transmission electron microscopy images revealed that GNPs were either localized in vesicles or free in the lysosomes in 5 nm GNPs-treated HK-2 cells, and the cellular uptake of the GNPs in the hypoxic cells was significantly higher than that in normoxic cells. In normoxic HK-2 cells, 5 nm GNPs (50 nM) treatment could cause autophagy and cell survival. However, in hypoxic conditions, the GNP exposure at the same condition led to the production of reactive oxygen species, the loss of mitochondrial membrane potential (ΔΨM), and an increase in apoptosis and autophagic cell death.
  
  
  CONCLUSIONS
  Our results demonstrate that renal tubular epithelial cells presented different responses under normoxic and hypoxic environments, which provide an important basis for understanding the risks associated with GNP use-especially for the potential GNP-related therapies in chronic kidney disease patients.
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China.
authors.forename: Fengan
authors.initials: F
authors.lastname: Ding
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Li
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Liu
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China.
authors.forename: Wenmin
authors.initials: W
authors.lastname: Yu
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Institute of Nephrology, The Affiliated Zhongda Hospital, Southeast University, Nanjing, People's Republic of China.
authors.forename: Haifeng
authors.initials: H
authors.lastname: Ni
authors.affiliation: Institute of Nephrology, The Affiliated Zhongda Hospital, Southeast University, Nanjing, People's Republic of China.
authors.forename: Bicheng
authors.initials: B
authors.lastname: Liu
authors.affiliation: School of Medicine, Southeast University, Nanjing, People's Republic of China ; Institute of Nephrology, The Affiliated Zhongda Hospital, Southeast University, Nanjing, People's Republic of China.
authors.forename: Pingsheng
authors.initials: P
authors.lastname: Chen
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D015687:Cell Hypoxia; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004705:Endocytosis; D006046:Gold / Q000737:chemistry / Q000493:pharmacokinetics* / Q000633:toxicity*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects*; D010316:Particle Size; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D006046:Gold
keywords: apoptosis; autophagy; gold nanoparticles (GNPs); toxicity