title: Intracellular oxidative stress and cadmium ions release induce cytotoxicity of unmodified cadmium sulfide quantum dots.
abstract: OBJECTIVE
  To fully understand the cytotoxicity of after-degradation QDs, we synthesized CdS QDs and investigated its toxicity mechanism.
  
  
  METHODS
  Biomimetic method was proposed to synthesize cadmium sulfide (CdS) QDs. Thereafter MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay was conducted to evaluate their cytotoxicity. To investigate the toxicity mechanism, we subsequently conducted intracellular reactive oxygen species (ROS) measurement with DCFH-DA, glutathione (GSH) measurement with DTNB, and cellular cadmium assay using atomic absorption spectrometer. Microsized CdS were simultaneously tested as a comparison.
  
  
  RESULTS
  MTT assay results indicated that CdS QDs are more toxic than microsized CdS especially at concentrations below 40 microg/ml. While microsized CdS did not trigger ROS elevation, CdS QDs increase ROS by 20-30% over control levels. However, they both deplete cellular GSH significantly at the medium concentration of 20 microg/ml. In the presence of NAC, cells are partially protected from CdS QDs, but not from microsized particles. Additionally, nearly 20% of cadmium was released from CdS nanoparticles within 24h, which also accounts for QDs' toxicity.
  
  
  CONCLUSIONS
  Intracellular ROS production, GSH depletion, and cadmium ions (Cd(2+)) release are possible mechanisms for CdS QDs' cytotoxicity. We also suggested that with QD concentration increasing, the principal toxicity mechanism changes from intracellular oxidative stress to Cd(2+) release.
authors.affiliation: College of Environmental Science and Engineering, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin 300071, PR China.
authors.forename: K G
authors.initials: KG
authors.lastname: Li
authors.forename: J T
authors.initials: JT
authors.lastname: Chen
authors.forename: S S
authors.initials: SS
authors.lastname: Bai
authors.forename: X
authors.initials: X
authors.lastname: Wen
authors.forename: S Y
authors.initials: SY
authors.lastname: Song
authors.forename: Q
authors.initials: Q
authors.lastname: Yu
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: Y Q
authors.initials: YQ
authors.lastname: Wang
mesh_terms: D000818:Animals; D032701:Biomimetics / Q000379:methods; D019187:Cadmium Compounds / Q000737:chemistry / Q000633:toxicity*; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D005978:Glutathione / Q000187:drug effects / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D053758:Nanoparticles; D018384:Oxidative Stress / Q000187:drug effects*; D045663:Quantum Dots; D017382:Reactive Oxygen Species / Q000378:metabolism; D013054:Spectrophotometry, Atomic; D013440:Sulfides / Q000737:chemistry / Q000633:toxicity*; D013778:Tetrazolium Salts; D013844:Thiazoles
chemical_list: D019187:Cadmium Compounds; D017382:Reactive Oxygen Species; D013440:Sulfides; D013778:Tetrazolium Salts; D013844:Thiazoles; C034939:cadmium sulfide; C022616:thiazolyl blue; D005978:Glutathione