The effect of alpha-tocopherol on the nitration of gamma-tocopherol by peroxynitrite

Arch Biochem Biophys. 1999 Mar 15;363(2):333-40. doi: 10.1006/abbi.1998.1094.

Abstract

It has been proposed (S. Christen et al. Proc. Natl. Acad. Sci. USA 94, 3217-3222, 1997) that although alpha-tocopherol (alpha-TH) is an efficient antioxidant, the presence of gamma-tocopherol (gamma-TH) may be required to scavenge peroxynitrite-derived reactive nitrogen species. To investigate the reactions between alpha-TH, gamma-TH, and peroxynitrite, endogenous levels of both alpha-TH and gamma-TH were monitored when low-density lipoprotein was oxidized in the presence of the peroxynitrite generator 5-amino-3-(4-morpholinyl)-1, 2,3-oxadiazolium (SIN-1). SIN-1 oxidized alpha-TH while gamma-TH levels remained constant. The sparing of gamma-TH was also demonstrated when 1,2-dilauroyl-sn-glycero-3-phosphocholine liposomes containing alpha-TH and gamma-TH were incubated with either SIN-1 or peroxynitrite. Our data show that alpha-TH inhibits peroxynitrite-mediated gamma-TH nitration, i.e., 5-NO2-gamma-tocopherol formation. The rate constants for the reactions between both alpha-TH and gamma-TH with peroxynitrite suggest that the sparing of gamma-TH by alpha-TH does not occur by competitive scavenging, but may be due to the formation of a transient gamma-TH intermediate. Nitration of gamma-TH becomes significant only after alpha-TH levels have been depleted. We conclude alpha-TH alone is sufficient to remove any peroxynitrite-derived reactive nitrogen species, as the presence of alpha-TH attenuates nitration of both gamma-TH and tyrosine. The present results also indicate that a bolus addition of peroxynitrite or SIN-1 to liposomes containing gamma-TH forms 5-NO2-gamma-tocopherol in similar yields. This is in contrast to their reaction profile with tyrosine in aqueous solution. Under these conditions, SIN-1 does not form nitrotyrosine at detectable yields.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Chelating Agents / metabolism
  • Dose-Response Relationship, Drug
  • Enzyme Inhibitors / metabolism
  • Liposomes
  • Molsidomine / analogs & derivatives
  • Molsidomine / metabolism
  • Nitrates / antagonists & inhibitors*
  • Nitrates / metabolism*
  • Nitrates / pharmacology*
  • Oxidants / antagonists & inhibitors*
  • Oxidants / metabolism
  • Oxidants / pharmacology*
  • Pentetic Acid / metabolism
  • Stereoisomerism
  • Tyrosine / metabolism
  • Vitamin E / metabolism*
  • Vitamin E / pharmacology*

Substances

  • Chelating Agents
  • Enzyme Inhibitors
  • Liposomes
  • Nitrates
  • Oxidants
  • Vitamin E
  • peroxynitric acid
  • Tyrosine
  • linsidomine
  • Pentetic Acid
  • Molsidomine