Inhibitory Effect of Lutein and Pycnogenol on Lipid Peroxidation in Porcine Retinal Homogenate

Abstract

This study aimed to investigate the antioxidant effect of lutein, human macula pigment, and pycnogenol, which contains several flavonoids, on lipid peroxidation induced in 10% porcine retinal homogenate by the addition of 1 mM Ferric chloride (FeCl₃), 50 mM 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH), or 25 mM 2,2'-azobis (2,4-dimethyl-valeronitrile) (AMVN). Lipid hydroperoxide concentration was determined from the amount of thiobarbituric acid reactive substances (TBARS) in the sample following treatment. After 60 min of oxidation with FeCl₃, AAPH and AMVN, the TBARS content in the retinal homogenates increased from 28.6 ± 1.6 to 85.4 ± 0.9, from 27.9 ± 1.2 to 57.2 ± 1.1, and from 26.0 ± 1.0 to 77.5 ± 2.0 nmol MDA/mg protein, respectively. Lutein did not show remarkable antioxidant activity in this experimental system. However, IC₅₀ of pycnogenol for TBARS formation was decreased by combining 10 μM lutein in each initiator; from 12 to 5 μg/mL in FeCl₃, from 2.8 to 0.5 μg/mL in AAPH, from 465 to 110 μg/mL in AMVN. These results suggested that a combination treatment of lutein and pycnogenol is more effective for inhibiting lipid peroxidation in porcine retinal homogenate. This synergy might be due to efficient functional antioxidants acting in both hydrophilic and lipophilic cellular environments.