title: An in vitro evaluation of the cytotoxicity of varying concentrations of sodium hypochlorite on human mesenchymal stem cells.
abstract: OBJECTIVE
  To evaluate and compare the cytotoxicity of various concentrations of sodium hypochlorite on immortalized human bone marrow mesenchymal stem cells (MSCs).
  
  
  METHODS
  The 5.25 percent sodium hypochlo-rite (NaOCl) at concentrations of 0.5, 0.1, 0.025, 0.0125, and 0.005 mg/ml were used to assess the cytotoxic effect on MSCs. Immortalized human bone marrow mesenchymal stem cells (hTERT-MSCs) were exposed to NaOCl at 5 different concentrations. Cell viability was assessed by 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and alamarBlue assays. The cell morphology changes were assessed with scanning electron microscopy (SEM) after exposure to 2, 4, and 24 hour incubation. The ethidium bromide/acridine orange (EB/ AO) fuorescent stain was applied to the cells in the 8-chamber slides after they were incubated with the testing agents for 2 and 4 hours to detect live and dead cells. The observations were quantitatively and qualitatively analyzed.
  
  
  RESULTS
  The cell viability study using MTT assay and AB assay showed significant reduction with varying concentration at 2 and 4 hours incubation period. The cell viability decreased with the higher percentage of NaOCl. The exposure time also revealed an inverse relation to the cell viability. The SEM analysis showed reduction in the number of cells and morphological alterations with 0.5 mg/ml at 2 and 4 hours compared to 0.025 mg/ml NaOCl. Destruction of the cells with structural alterations and lysis was evident under fuorescence microscope when the cells were exposed to 0.5 mg/ml NaOCl.
  
  
  CONCLUSIONS
  Within the limitations of this in vitro study it can be concluded that NaOCl is toxic to the human bone marrow MSCs. The cell lysis was evident with higher concentration of sodium hypochlorite. From the observations, it can be concluded that a lower concentration of NaOCl may be used as endodontic irrigant due to its cytotoxic properties. Further studies are mandatory to evolve a consensus on the optimal concentration of sodium hypochlorite to be used as endodontic irrigant.
authors.affiliation: Associate Professor, Department of Restorative Dental Sciences, College of Dentistry, King Saud University, Riyadh, Kingdom of Saudi Arabia, e-mail: ksucod@gmail.com.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Alkahtani
authors.affiliation: Lecturer, Department of Restorative Dental Sciences, College of Dentistry, King Saud University, Riyadh, Kingdom of Saudi Arabia.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Alkahtany
authors.affiliation: Professor, Department of Periodontics and Community Dentistry, College of Dentistry, King Saud University, Riyadh, Kingdom of Saudi Arabia.
authors.forename: Sukumaran
authors.initials: S
authors.lastname: Anil
mesh_terms: D000165:Acridine Orange; D018929:Cell Culture Techniques; D016923:Cell Death; D002460:Cell Line; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004396:Coloring Agents; D004996:Ethidium; D005456:Fluorescent Dyes; D006801:Humans; D007202:Indicators and Reagents; D008422:Materials Testing; D059630:Mesenchymal Stem Cells / Q000187:drug effects*; D008855:Microscopy, Electron, Scanning; D010078:Oxazines; D012388:Root Canal Irrigants / Q000008:administration & dosage / Q000633:toxicity*; D012973:Sodium Hypochlorite / Q000008:administration & dosage / Q000633:toxicity*; D013778:Tetrazolium Salts; D013844:Thiazoles; D013997:Time Factors; D014966:Xanthenes
chemical_list: D004396:Coloring Agents; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D010078:Oxazines; D012388:Root Canal Irrigants; D013778:Tetrazolium Salts; D013844:Thiazoles; D014966:Xanthenes; C005843:resazurin; D012973:Sodium Hypochlorite; D004996:Ethidium; C022616:thiazolyl blue; D000165:Acridine Orange