title: Antiproliferative effects of lactic acid via the induction of apoptosis and cell cycle arrest in a human keratinocyte cell line (HaCaT).
abstract: BACKGROUND
  Alpha-hydroxy acids (AHAs) have been widely used in cosmetic industry. However, knowledge on cytotoxicity of AHAs in human keratinocytes is limited.
  
  
  OBJECTIVE
  Lactic acid (LA) is one of the most commonly used AHAs in skin care and peeling formulations. We investigated the antiproliferative effects of LA in a human keratinocyte cell line (HaCaT).
  
  
  METHODS
  HaCaT cells were treated with LA at 7.5 approximately 17.5mM for various time periods. The molecular mechanisms of anti-proliferation through cell cycle arrest and apoptosis were investigated by 4,6-diamidino-2-phenylindole dihydrochloride (DAPI) stain, flow cytometry, Western blot and confocal microscopy.
  
  
  RESULTS
  Viability of HaCaT cells decreased on exposure to LA. Flow cytometry showed apoptosis was closely related to the increase of reactive oxygen species (ROS) and calcium release, and to the decline of mitochondrial membrane potential (MMP). Western blotting showed an increase in the levels of P21, P27 and a decrease in the levels of Cyclin E, Cyclin A, and CDK 2, indicating cell cycle arrest at G1/S. The occurrence of apoptosis was proved by the increased expressions of Fas, Bax, caspase-3, -8, and -9, apoptosis-inducing factor (AIF), and endonuclease G (EndoG), and the declined expressions of Bcl-2 and Bcl-xL. In addition, the intracytosolic release of AIF, EndoG, and cytochrome c contributing to the occurrence of apoptosis was demonstrated by confocal microscopy.
  
  
  CONCLUSIONS
  We demonstrated that LA had antiproliferative effect in HaCaT cell through the inhibition of cell cycle progression at G1/S, and the induction of programmed cell death through caspase-dependent and caspase-independent pathways.
authors.affiliation: Department of Dermatology, Chung Shan Medical University Hospital, Taichung, Taiwan, ROC.
authors.forename: Yu-Ping
authors.initials: YP
authors.lastname: Hsiao
authors.forename: Hsin-Lien
authors.initials: HL
authors.lastname: Huang
authors.forename: Wan-Wen
authors.initials: WW
authors.lastname: Lai
authors.forename: Jing-Gung
authors.initials: JG
authors.lastname: Chung
authors.forename: Jen-Hung
authors.initials: JH
authors.lastname: Yang