Abstract
The work reported herein deals with the evaluation of the antioxidant properties of bitailed amphiphilic ␣-phenyl-N-tert-butylnitrone derivatives (BPBNs) towards oxidation of an unsaturated lipid, the 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLoPC). Oxidation was induced either by UV light irradiation or radical initiators, i.e. the water soluble AAPH and the Fenton reaction, and the antioxidant evaluation was carried out using two biomimetic systems, namely Langmuir monolayers and large unilamellar vesicles. Measurement of the molecular area and the membrane fluidity of pure nitrone monolayers before and after UV-irradiation demonstrated the better stability and antioxidant properties of B 17 PBN, the derivative with two C 17 H 35 alkyl chains, compared to its analogue B 11 PBN with two C 11 H 23 alkyl chains. At only 5% molar ratio of nitrone in mixed DLoPC/nitrone monolayers, a complete inhibition of the molecular area decrease was observed for B 17 PBN whereas B 11 PBN showed lower protection. The oxidation of mixed DLoPC/nitrones large unilamellar vesicles in the presence of free radicals arising from AAPH decomposition or Fenton reaction was assessed by measuring lipid conjugated dienes and thiobarbituric acid reactive substances on the whole series of nitrone, i.e. C 11-, C 13-, C 15-and C 17-based compounds. Compared to the saturated 1,2-dimyristoyl-sn-glycero-3-phosphocholine, all bitailed amphiphilic nitrones were able to decrease conjugated dienes and TBARS in both oxidative paradigms, demonstrating therefore antioxidant property. The inhibition of phospholipids oxidation was increased when increasing the concentration of nitrone with the two B 11 PBN and B 13 PBN derivatives exhibiting higher potency. This study underlines the importance in the choice of a model membrane system when evaluating the potency of antioxidants against lipid oxidation.