Linoleic acid peroxidation vs. isomerization: a biomimetic model of free radical reactivity in the presence of thiols

Abstract

Biomimetic models of free radical-induced transformation of polyunsaturated fatty acids, such as micelles and liposomes, have been used for the study of lipid peroxidation and lipid isomerization. Free radical reactivity of thiol compounds is the common link between the two processes, since lipid peroxidation is inhibited by thiols, due to their H-donation ability, whereas lipid isomerization is catalysed by S-centered radicals. In this paper the two processes are compared for the first time, in solution and under biomimetic conditions, demonstrating that hydroperoxides and trans lipids are formed to comparable extents as a result of oxidative free radical conditions. The biomimetic model of micelles of linoleic acid, prepared by addition of a non-ionic surfactant (TWEEN(®)-20) and 2-mercaptoethanol as the amphiphilic thiol, was irradiated by ionizing radiation up to 400 Gy under various conditions. In air-equilibrated solutions, the cis-trans isomerization process was observed with a catalytic cycle of 370 together with a substantial amount of hydroperoxides (LOOH). The effect of micelle size was also studied in order to envisage the effect of the supramolecular organization on the outcome of the two processes, and in particular, for the positional preference of the double bond isomerization.

F2-isoprostanes are correlated with trans fatty acids in the plasma of pregnant women

“…This was also in agreement with an in vitro study that investigated the competition between lipid peroxidation and isomerization. Indeed, the major trans isomer of 9c,12c-18:2 formed in liposomes was 9t,12c-18:2 [12]. We detected only this specific isomer in our cohorts but not the 9t,12t-18:2 or 9c,12t-18:2.…”

“…Beside, the thiyl radical, it has also been demonstrated that some isomers of trans-arachidonic acid may originate from the NO 2 -mediated AA isomerization in human [14]. An in vitro study has shown the competition between lipid peroxidation and isomerization [12]. This competition could explain, at least in part, why correlations are observed between F 2 -isoPs and 9t-18:1 generated from the high level 9c-18:1 but not with 11t-18:1 derived from the low level 11c-18:1.…”

“…Beside ingested TFA, there is also a possibility for TFA to be generated indirectly from oxidative stress as shown by liposomes exposed to γ-radiation or UV photolysis [12,13]. The mechanism proposed for cis-trans isomerisation is the action of either the thiyl or the nitrogen dioxide radicals on cis fatty acids [14][15][16].…”

Evaluation of a model system for the selective study of the lipid peroxidation process

“…The effect of TWEEN®‐20 concentrations on LA oxidation was determined under the conditions of constant LA and varying TWEEN®‐20 concentrations (Table 2). It should be pointed out that Tween®‐20 alone did not induce lipid peroxidation process in the solutions of LA 23. The solutions were prepared by diluting the original solution with aqueous surfactant solutions in 5.0 mM MES.…”

The influence of antioxidants in the thiyl radical induced lipid peroxidation and geometrical isomerization in micelles of linoleic acid

“…One of them is lipid peroxidation [1][2][3] and the second one is the process of geometrical isomerization of naturally occurring cis unsaturated lipids which can be catalyzed by thiyl radicals (RS ) [4][5][6]. It has been shown that one process can be parallel with the occurrence of the other and both lipid hydroperoxides and trans lipids are the resulting products of oxidative free radical conditions [7] (Scheme 1). Investigations of peroxidation and isomerization processes in liposome models were shown to occur by chemical agents, such as the antitumor drug bleomycin, known to form metal complexes, thus producing oxidative stress conditions [8].…”