Original Clinical 207 Serin O et al. Glucose Tolerance and Oxidative Stress … Horm Metab Res 2007; 39: 207–211 received 29. 6. 2006 accepted after second revision 23. 10. 2006 Bibiliography DOI 10.1055/s-2007-970419 Horm Metab Res 2007; 39: 207–211 © Georg Thieme Verlag KG Stuttgart · New York · ISSN 0018-5043 Correspondence O. Serin Fatih Sitesi · B-4 Blok · Daire 5 Silivrikapi · Fatih · Istanbul · Turkey Tel.: 902/12/252 4300/2002 Fax: 902/12/252 6300 dkonuk@istanbul.edu.tr Key words   oxidized low density lipoprotein   paraoxonase 1   oral glucose tolerance test   impaired glucose tolerance Serum Oxidized Low Density Lipoprotein, Paraoxonase 1 and Lipid Peroxidation Levels during Oral Glucose Tolerance Test studies have reported that HDL had a protective effect against oxidative modification of LDL [11, 12] and it has been previously shown that the antioxidant activity of HDL may relate, at least in part to the enzymes associated with HDL [13]. Among them, human serum paraoxonase (PON1) has raised special interest, which is believed to be important in the protection against LDL oxida- tion [14, 15]. Studies have shown that serum PON1 activity is reduced in diabetic subjects [16, 17]. Some of the studies reported so far lack either postchallenge plasma glucose or fasting plasma glucose in relation to atherosclerosis [18]. Taking into account the marked postprandial/ postchallenge rise in blood glucose and its pos- sible contribution to atherosclerosis due to oxidative stress, the aim of our study is to inves- tigate the effects of glycemia on the serum oxLDL and PON1 concentrations at baseline and post challenge 2 hours’ during oral glucose tolerance test (OGTT), and to see whether we can relate Introduction & Diabetes is associated with accelerated athero- sclerosis and subsequent cardiovascular disease [1]. The mechanisms underlying diabetes accel- erated atherosclerosis are poorly understood. One of the proposed mechanisms, oxidative stress has been demonstrated to be increased in vivo in the diabetic state [2, 3], which may con- tribute to the higher incidence of vascular dis- ease in this population. Under oxidative stress, low density lipoprotein (LDL) and other serum lipoproteins including high density lipoprotein (HDL), are prone to lipid peroxidation [4]. Previ- ous studies have shown that intra-arterial LDL oxidation is relevant to atherosclerosis [5, 6] and oxidatively modified LDL (oxLDL) is believed to be one of the critical factors in atherogenesis [7]. The serum concentration of HDL has long been known to have an inverse correlation with the development of atherosclerosis [8–10]. Several Authors O. Serin 1 , D. Konukoglu 2 , S. Firtina 2 , O. Mavis 3 Affiliations 1 Taksim Education and Research Hospital, Department of Biochemistry, Istanbul, Turkey 2 Istanbul University, Cerrahpasa Faculty of Medicine, Department of Biochemistry, Istanbul, Turkey 3 Taksim Education and Research Hospital, Department of Internal Medicine, Istanbul, Turkey Abstract & Increasing evidence suggests that the postpran- dial state is a contributing factor to the develop- ment of atherosclerosis. To evaluate the effects of acute hyperglycemia on the oxidative stress, concentrations of serum-oxidized low density lipoprotein (oxLDL), paraoxonase 1 (PON1), and thiobarbituric acid reactive substances (TBARS) were measured in subjects with normal glucose tolerance (NGT) (n = 35), impaired glucose toler- ance (IGT) (n = 25), and diabetic glucose tolerance (DGT) (n = 20). In NGT group, the 2 hours’ TBARS and oxLDL levels were not statistically different when compared to baseline, and 2 hours’ PON1 activities were higher when compared to baseline (p < 0.01). Subjects with IGT and DGT have higher 2 hours’ serum TBARS and oxLDL levels than their baseline levels (p < 0.01, for each). Baseline oxLDL levels of both IGT and DGT groups were higher than NGT group (p < 0.01 and p < 0.01, respectively). While there were not any signifi- cant differences in 2 hours’ versus baseline PON1 activities in the IGT group, the 2 hours’ versus baseline PON1 activities in the DGT group were significantly lower (p < 0.01). The postchallenge 2 hours’ PON1 activities of both IGT and DGT groups were lower than NGT group (p < 0.01 and p < 0.01, respectively). Baseline oxLDL was posi- tively correlated with 2 hours’ glucose (r = 0.613, p < 0.01) in IGT and DGT groups. PON1 activities were correlated with HDL-cholesterol, total cho- lesterol, and fasting glucose (r = 0.680, r = 0.698 and r = 0.431, respectively, for each p < 0.01) in NGT. In conclusion, oxidative stress occurs at an early stage in diabetes, and protective effects of HDL against atherosclerosis may be dependent on the PON1 activities. Downloaded by: Istanbul University. Copyrighted material.