Fe/Ascorbic Acid-Induced Oxidative Modifications and Phosphatidylserine Exposure in Human Platelets are Reduced by Melatonin

Received June 24, 2008. Accepted January 28, 2009. Corresponding author: Azize Sener, Department of Biochemistry, Faculty of Pharmacy, Marmara University, Tibbiye Cad., No: 49, 34668, Haydarpasa-Istanbul, Turkey. Phone: +90 216 414 29 62; e-mail: [email protected] Abbreviations: apoB100 – apolipoprotein B100, apoER2 – apolipoprotein E receptor 2, FITC – fluorescein isothiocyanate, GpIIb/ IIIa – glycoprotein IIb/IIIa, GSH – glutathione, GSH-Px – glutathione peroxidase, GSSGRd – glutathione reductase, LOX-1 – lectin-like oxidized low-density lipoprotein receptor 1, LPA – lysophosphatidic acid, MDA – malondialdehyde, ox-LDL – oxidized low-density lipoprotein, PBS – phosphate-buffered saline, PCO – protein carbonyl, PRP – platelet-rich plasma, PS – phosphatidylserine, RNS – reactive nitrogen species, ROS – reactive oxygen species, SOD – superoxide dismutase. Abstract. Low-density lipoprotein (LDL) modifications and platelet activation are major risk factors for cardiovascular diseases. When platelets are exposed to oxidative stress, they become activated. Oxidized LDL (ox-LDL) and metal-catalysed oxidation systems such as Fe/ascorbic acid increase free radical production. We wanted to verify whether melatonin has a protective effect against oxidative modifications and phosphatidylserine externalization in platelets induced by ox-LDL and Fe/ascorbic acid. For in vitro effects of melatonin on platelets, ADPactivated platelets were incubated with ox-LDL or Fe/ascorbic acid for 1 h at 37 oC with or without melatonin. Then platelet malondialdehyde, protein carbonyl and glutathione levels were measured. Platelet phosphatidylserine exposure was measured with annexin-V using flow cytometry. Malondialdehyde, protein carbonyl and phosphatidylserine levels of platelets treated with Fe/ascorbic acid significantly increased compared to the control group. Glutathione contents of Fe/ascorbic acid-treated platelets significantly decreased. Melatonin pre-treatment of Fe/ascorbic acid-treated platelets caused a mar ked reduction in malondialdehyde and phosphatidylserine levels and a marked increase in glutathione levels. Melatonin also caused non-significant reduction in protein carbonyl contents of Fe/ascorbic acid-treated platelets. Malondialdehyde, protein carbonyl and phosphatidylserine levels of platelets treated with ox-LDL also significantly increased compared to the control group. Platelet glutathione levels non-significantly decreased with ox-LDL. With addition of melatonin, malondialdehyde, protein carbonyl and phosphatidylserine levels of platelets treated with ox-LDL significantly decreased. These data suggest that melatonin may protect platelets from iron overload-induced and ox-LDL-induced oxidative modifications and also from the triggering signals of apoptosis activation, possibly due to its scavenger effect on toxic free radicals.