LHP increases the transcription factor AP-1 which in turn may regulate retinal MMP-9 synthesis during neovascularization.

Background: It is possible that oxidative stress causes several retinal diseases. However, the natural biogenic role of antioxidants in the retina is not clear. Purpose: This study investigates the change in concentration of vitamin E (VE), ascorbate and glutathione (GSH) in the retina following vitreous injection of 600 µg 18:2 linoleic acid hydroperoxide (LHP) in male New Zealand rabbits. Method: LHP was injected above the retinal surface. The animals were sacrificed and the eyes enucleated before LHP injection, 1, 3, 6, 12, 24 h and 4 and 7 days after LHP injection. Retinas were removed, VE and ascorbate measured by HPLC, and GSH determined by a fluorometric method. Results: The concentration of VE in the retina decreased from pretreatment levels of 154.6 ± 29.7 nmol/g wet weight (n = 7) and was lowest at 6 h (61.1 ± 18.1 nmol/g wet weight, n = 4, p < 0.05), then increased gradually, returning slowly to pre-LHP levels by 7 days. The concentration of ascorbate in control retinas decreased at 6 h from pretreatment levels of 7.33 ± 0.93 µmol/g wet weight (n = 7) to 2.74 ± 0.16 µmol/g wet weight (n = 4, p < 0.05) and returned to pretreatment levels rapidly by 24 h after injection. The concentration of GSH in retinas decreased from baseline levels of 109.53 ± 8.19 µg/g wet weight (n = 9), was lowest at 12 h (72.40 ± 11.17 µg/g wet weight, n = 5, p < 0.05) and returned to pretreatment levels by 7 days. Conclusion: The results suggest that intravitreous LHP injection is a contributor to oxidative stress in the rabbit retina by causing a reduction in antioxidant capacity.

Summary 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-dimethylvaleronitrile) (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.