title: Niacin decreases leukocyte myeloperoxidase: mechanistic role of redox agents and Src/p38MAP kinase.
abstract: OBJECTIVE
  Leukocyte myeloperoxidase (MPO) is a major player in the pathogenesis of various chronic diseases including atherosclerosis. This study proposes the novel concept that niacin, through reactive oxygen species (ROS)-mediated signaling, decreases neutrophil MPO release and its activity, protects apolipoprotein-AI (apo-AI) modification and improves HDL function.
  
  
  METHODS
  Human blood leukocytes and leukocytic cell line HL-60 cells were treated with niacin, and stimulated with phorbol myristate acetate (PMA). Cellular and released MPO activity in the medium was measured by assessing chlorination of MPO-specific substrate. MPO protein release in the medium and apo-AI degradation was measured by Western blot analysis. Monocyte adhesion to human aortic primary endothelial cells was measured to assess biological function of HDL/apo-AI.
  
  
  RESULTS
  PMA significantly increased leukocyte MPO activity in both intracellular extract and medium. Niacin (0.25-0.5 mM) decreased PMA-induced MPO activity (cellular and released in the media). Niacin also decreased MPO protein mass in the medium without affecting its mRNA expression. Increased NADPH oxidase and ROS production by PMA were also significantly inhibited by niacin. Studies with specific inhibitors suggest that ROS-dependent Src and p38MAP kinase mediate decreased MPO activity by niacin. Niacin blocked apo-AI degradation, and apo-AI from niacin treated cells decreased monocyte adhesion to aortic endothelial cells.
  
  
  CONCLUSIONS
  These findings identify niacin as a potent inhibitor of leukocyte MPO release and MPO-mediated formation of dysfunctional HDL. Niacin and niacin-related chemical entities may form important therapeutic agents for MPO-mediated inflammatory diseases.
authors: Atherosclerosis Research Center, Department of Veterans Affairs Healthcare System, Long Beach, CA, USA; The University of California, Irvine, CA, USA.
authors: Shobha H
authors: SH
authors: Ganji
authors: Atherosclerosis Research Center, Department of Veterans Affairs Healthcare System, Long Beach, CA, USA; The University of California, Irvine, CA, USA. Electronic address: vaijinath.kamanna@va.gov.
authors: Vaijinath S
authors: VS
authors: Kamanna
authors: Atherosclerosis Research Center, Department of Veterans Affairs Healthcare System, Long Beach, CA, USA; The University of California, Irvine, CA, USA. Electronic address: Moti.Kashyap@va.gov.
authors: Moti L
authors: ML
authors: Kashyap
mesh_terms: D016632:Apolipoprotein A-I / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D007962:Leukocytes / Q000187:drug effects / Q000201:enzymology; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors; D009525:Niacin / Q000494:pharmacology*; D009195:Peroxidase / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D016632:Apolipoprotein A-I; D017382:Reactive Oxygen Species; D009525:Niacin; D009195:Peroxidase; D019255:NADPH Oxidases; D019061:src-Family Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate
keywords: Apolipoprotein AI; Atherosclerosis; High density lipoproteins; Myeloperoxidase; Niacin