Reciprocal protection of LDL and HDL oxidised by ^⋅OH free radicals in the presence of oxygen

Abstract

The aim of this work was to compare the behaviour of HDL oxidised by "OH or 'OH/0' 2~ free radicals produced by gamma radiolysis in the absence or in the presence of LDL at the same concentration of 3 g-1 -1 , in order to specify the possibility of reciprocal protection of HDL and LDL towards lipid peroxidation. This oxidation was quantitatively evaluated by the decrease of endogenous a-tocopherol and the formation of oxidation products (thiobarbituric acid-reactive substances and conjugated dienes) and by the determination of initial radiation yields. Our results demonstrated that HDL could be protected by LDL against in vitro radical oxidation only in the presence of oxygen (action of *OH/0' 2 free radicals). This observation addresses new questions about the interaction between HDL and LDL, especially the possibility of a reciprocal protection.

High Density Lipoproteins (HDL) and the Oxidative Hypothesis of Atherosclerosis

“…Thus, Tribble et al . Similarly, we obtained evidence that HDL could be protected by LDL against radical-induced oxidation in the presence of oxygen (action of • OH/O 2 •free radicals generated by γ-radiolysis) (56). These authors showed that HDL inhibited both Cu 2+ and Fe 3+ -induced peroxidation of LDL-associated lipids, which was consistent with a direct antioxidant effect of HDL.…”

“…Indeed, others (55,56) suggested the existence of a reciprocal protection of HDL and LDL, which should involve other mechanisms. Indeed, others (55,56) suggested the existence of a reciprocal protection of HDL and LDL, which should involve other mechanisms.…”

“…However, when native HDL are exposed in vitro to a cellular (12), chemical (65) or physical (66,67) oxidative stress, they undergo chemical changes which are very similar to those observed in oxidized LDL. Moreover, when LDL and HDL are simultaneously exposed to an oxidative stress, both lipoproteins undergo lipid peroxidation (56). Moreover, when LDL and HDL are simultaneously exposed to an oxidative stress, both lipoproteins undergo lipid peroxidation (56).…”

Age‐related increased susceptibility of high‐density lipoproteins (HDL) to in vitro oxidation induced by γ‐radiolysis of water

“…Human HDL are well known for their protective effect against the development of the atherosclerotic process, because of their ability to promote cholesterol efflux from cells [11, 12, 46]and to inhibit oxidative modification of LDL [2, 38, 47, 48]. However, compared to LDL, less is known about the peroxidation of HDL and their susceptibility to oxidation in different pathologies.…”

“…Hence, these results strongly suggest that the number of targets on HDL decreases with aging. In the oxidative theory of atherosclerosis based on the reciprocal protection of LDL and HDL [47], reduction in the number of potentially oxidizable targets on the HDL may direct radical attacks onto LDL, thus contributing indirectly to LDL oxidation and in turn to the enhancement of the incidence of cardiovascular diseases with aging.…”