Antioxidant Activity of Piperlactam S: Prevention of Copper-Induced LDL Peroxidation and Amelioration of Free Radical-Induced Oxidative Stress of Endothelial Cells

Abstract

The protective effects of piperlactam S, an alkaloid isolated from Piper kadsura (Choisy) Ohwi, on lipid peroxidation and free radical-mediated cell injuries were investigated. Piperlactam S (1 to 20 μM) concentration-dependently prevented the copper-catalyzed oxidative modification of human low-density lipoproteins (LDL) measured through (i) the lag period, (ii) the slope of the propagation phase, (iii) the total amount of conjugated dienes formed, and (iv) the electrophoretic mobility of LDL. Fe²⁺-induced oxidative modification of cell membrane was also significantly attenuated by piperlactam S as measured by thiobarbituric acid-reactive substances (TBARS). Furthermore, piperlactam S effectively minimized the loss of cell viability induced by Fenton’s reagent (H₂O₂/FeSO₄) in cultured endothelial cells and significantly reversed H₂O₂/FeSO₄-induced impairment of endothelium-dependent relaxation to acetylcholine in rat aorta. Since the oxidative modification of LDL plays an important role in the genesis of atherosclerosis, piperlactam S may help to reduce the risk of atherosclerosis, not only by protecting LDL and membrane lipids from oxidative modification but also by reducing free radical-induced endothelial injury and/or dysfunction.

Abbreviations

LDL:low-density lipoprotein

MDA:malondialdehyde

PAECs:pulmonary artery endothelial cells

PE:phenylephrine

REM:relative electrophoretic mobility

TBARS:thiobarbituric acid-reactive substances

Key words

Piper kadsura (Choisy) Ohwi - Piperaceae - piperlactam S - low-density lipoprotein - TBARS - endothelial cells - free radicals - cytotoxicity

References

• 1 Prasad K, Debnath D, Kalra J, Lee P. Effects of dimethylthiourea on the cardiac function and oxyradicals status in ischemia reperfusion injury.  Ann NY Acad Sci. 2000;  723 375-9
• 2 Prasad K, Kalra J. Oxygen free radicals and hypercholesterolemic atherosclerosis: Effects of vitamin E.  Am Heart J. 1993;  125 958-73
• 3 Rubanyi G M, Vanhoutte P M. Superoxide anions and hyperoxia inactivate endothelium-derived relaxing factor.  Am J Physiol. 1986;  250 H822-7
• 4 Steinberg D S. Oxidative modification of LDL and atherogenesis.  Circulation. 1997;  95 1062-71
• 5 Frankel E N, Kanner J, German J B, Parks E, Kinsella J E. Inhibition of oxidation of human low-density lipoprotein by phenolic substances in red wine.  Lancet. 1993;  341 454-7
• 6 Han G Q, Dai P, Xu L, Ma J, Ki C L, Zheng Q T. PAF inhibitors: Neolignans from Piper kadsura .  Planta Med. 1990;  56 583-4
• 7 Kuo Y C, Yang N S, Chou C J, Lin L C, Tsai W J. Regulation of cell proliferation, gene expression, production of cytokines, and cell cycle progression in primary human T lymphocytes by piperlactam S isolated from Piper kadsura .  Mol Pharmacol. 2000;  58 1057-66
• 8 Puhl H, Wäg G, Esterbauer H. Methods to determine oxidation of low-density lipoproteins.  Methods Enzymol. 1994;  233 425-41
• 9 Areias F M, Rego A C, Oliveira C R, Seabra R M. Antioxidant effect of flavonoids after ascorbate/Fe²⁺-induced oxidative stress in cultured retinal cells.  Biochem Pharmacol. 2000;  62 111-8
• 10 Walling C. Fenton’s reagent revisited.  Acc Chem Res. 1975;  8 125-31
• 11 Chiou W F, Lin J J, Chen C F. Andrographolide suppresses the expression of inducible nitric oxide synthase in macrophage and restores the vasoconstriction in rat aorta treated with LPS.  Br J Pharmacol. 1998;  125 327-34
• 12 Shahidi F, Wanasundara P K. Phenolic antioxidants.  Crit Rev Food Sci Nutr. 1992;  32 67-103
• 13 Priyadarsini K I, Devasagayam T PA, Rao M NA, Guha S N. Properties of phenoxyl radical of dehydrozingerone, a probable antioxidant.  Rad Physics Chem. 1999;  54 551-8
• 14 Kajiyama T, Ohkatsu Y. Effect of para-substituents of phenolic antioxidants.  Polymer Degrad Stabil. 2001;  71 445-51
• 15 Priyadarsini K I, Guha S N, Rao M NA. Physico-chemical properties and antioxidant activities of methoxyphenols.  Free Radic Biol Med. 1998;  24 933-41
• 16 Van Acker S ABE, van den Berg D J, Tromp M NJL, Griffioen D H, van Bennekom W P, van der Vijgh W JF, Bast A. Structural aspects of antioxidant activity of flavonoids.  Free Radic Bio Med. 1996;  20 331-42
• 17 Patel R P, Svistunenko D, Wilson M T, Darley-Usmar V M. Reduction of Cu(II) by lipid hydroperoxides: Implications for the copper-dependent oxidation of low-density lipoprotein.  Biochem J. 1997;  322 425-33
• 18 Jessup W, Rankin S M, De Whalley C V, Honlt J RS, Scott J, Leak D S. α-Tocopherol consumption during low-density lipoprotein oxidation.  Biochem J. 1990;  265 399-405
• 19 Shen C. Study on antioxidant activities of lignans, kadsurenone and burchllin.  Beijing Med Acad J. 1995;  27 62-4
• 20 Shi L, Chen H. The role of neutrophils in hepatic ischemia-reperfusion injury and the protective effect of kadsurenone.  Nan-Jing-Tie-Daw Med Acad J. 1996;  15 83-6