S. Banni et al., A NOVEL-APPROACH TO STUDY LINOLEIC-ACID AUTOXIDATION - IMPORTANCE OF SIMULTANEOUS DETECTION OF THE SUBSTRATE AND ITS DERIVATIVE OXIDATION-PRODUCTS, Free radical research, 25(1), 1996, pp. 43-53
In this paper we have proposed a novel approach for studying the react
ion of lipid oxidation by using the simplest chemical system available
. Neat linoleic acid was incubated for 24 hours at 37 degrees C in the
air. The course of lipid oxidation was followed by measuring simultan
eously by HPLC with a diode array detector 1) linoleic acid decrease,
2) the products formed by radical attack, namely four hydroperoxy-octa
decadienoic acid (HPODE) isomers, two c,t (c,t) and two trans, trans (
t,t). 3) the byproducts formed by HPODE degradations, the four oxo-oct
adeca-dienoic acid (oxo-ODE) isomers. In HPODEs the presence of conjug
ated diene chromophore was confirmed by second derivative spectrophoto
metry. c,t HPODEs were also identified for their positional isomerism,
while for t,t molecules the lack of suitable reference compound makes
unfeasible the identification of their positional isomerism. As in th
e case of the latter two c,t and two t,t oxo-ODE isomers were characte
rized. This simple system appears to be useful for studying the activi
ty exherted by lipophilic molecules that, like alpha-tocopherol, may a
ct as antioxidants and/or as hydrogen atom donating molecules. The pre
sence of alpha-tocopherol in different concentration for 24 hours in t
he reaction environment, shifts the reaction of linoleic acid autoxida
tion towards different byproduct formations. From the results obtained
it is evident that alpha-tocopherol acts as hydrogen atom donor at al
l concentration tested, shifting the reaction toward a prevalent forma
tion of c.t isomer of both HPODEs and oxo-ODEs. At concentration lower
than 40 nmoles, when the ratio between alpha-tocopherol and linoleic
acid was 1:100, the reaction of autoxidation is strongly inhibited, wh
ile at higher concentration alpha-tocopherol acted as a prooxidant. In
these experimental conditions, alpha-tocopherylquinone was spectropho
tometrically identified as the predominant oxidation product of alpha-
tocopherol.