title: Protective effect of nicotinamide against poly(ADP-ribose) polymerase-1-mediated astrocyte death depends on its transporter-mediated uptake.
abstract: OBJECTIVE
  Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA repair enzyme, and its excessive activation, following ischemia, trauma, etc., depletes cellular nicotinamide adenine dinucleotide (NAD(+)) as a substrate and eventually leads to brain cell death. Nicotinamide, an NAD(+) precursor and a PARP-1 inhibitor, is known to prevent PARP-1-triggered cell death, but there is no available information on the mechanisms involved in its transport. Here we clarified the transport characteristics of nicotinamide in primary cultured mouse astrocytes.
  
  
  METHODS
  Uptake characteristics of [(14)C]nicotinamide were assessed by a conventional method with primary cultured mouse astrocytes. Cell viability and PARP-1 activity were determined with intracellular LDH activity and immunocytochemical detection of PAR accumulation, respectively.
  
  
  RESULTS
  PARP-1 activation was induced by treatment of astrocytes with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), an alkylating agent. MNNG-triggered astrocyte death and PAR accumulation were completely inhibited by treatment with nicotinamide as with DPQ (3,4-dihydro-5-(4-(1-piperidinyl)butoxy)-1(2H)-isoquinolinone), a second generation PARP inhibitor. The uptake of [(14)C]nicotinamide was time-, temperature-, concentration- and pH-dependent, and was inhibited and stimulated by co- and pre-treatment with N-methylnicotinamide, a representative substrate of an organic cation transport system, respectively. Co-treatment of astrocytes with nicotinamide and N-methylnicotinamide resulted in a decrease in PAR accumulation and absolute prevention of cell death.
  
  
  CONCLUSIONS
  These findings suggest that nicotinamide has a protective effect against PARP-1-induced astrocyte death and that its transporter-mediated uptake, which is extracellular pH-sensitive and common to N-methylnicotinamide, is critical for prevention of PARP-1-triggered cell death.
authors.affiliation: Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Suzuki
authors.forename: Hiroto
authors.initials: H
authors.lastname: Okuda
authors.forename: Kentaro
authors.initials: K
authors.lastname: Nishida
authors.forename: Sadaki
authors.initials: S
authors.lastname: Fujimoto
authors.forename: Kazuki
authors.initials: K
authors.lastname: Nagasawa
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D001692:Biological Transport; D016923:Cell Death / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D051379:Mice; D009536:Niacinamide / Q000031:analogs & derivatives / Q000493:pharmacokinetics / Q000494:pharmacology*; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D014803:Vitamin B Complex / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D014803:Vitamin B Complex; D009536:Niacinamide; C499321:Parp1 protein, mouse; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C008472:N-methylnicotinamide