Measurement of the total antioxidant response in preeclampsia with a novel automated method

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Abstract

Objectives: Preeclampsia is one of the most serious complications of pregnancy. Free radical damage has been implicated in the pathophysiology of this condition. In this study, we aimed to measure the antioxidant capacity in plasma samples from normotensive and preeclamptic pregnant women to evaluate their antioxidant status using a more recently developed automated measurement method. Study design: Our study group contained 42 women, 24 of whom had preeclampsia, while 18 had normotensive pregnancies. We measured the total plasma antioxidant capacity for all patients, as well as the levels of four major individual plasma antioxidant components; albumin, uric acid, ascorbic acid and bilirubin, and as a reciprocal measure, their total plasma peroxide levels. Results: Statistically significant differences (determined using Student’s t-test) were noted between the normotensive and the preeclamptic groups for their total antioxidant responses and their vitamin C levels (1.31±0.12 mmol versus 1.06±0.41 mmol Trolox eq./L; 30.2±17.83 μmol/L versus 18.1±11.37 μmol/L, respectively), which were both considerably reduced in the preeclamptic patients. In contrast, the total plasma peroxide levels were significantly elevated in this group (49.8±14.3 μmol/L versus 38.8±9.6 μmol/L). Conclusions: We found a decreased total antioxidant response in preeclamptic patients using a simple, rapid and reliable automated colorimetric assay, which may suitable for use in any routine clinical biochemistry laboratory, and considerably facilitates the assessment of this useful clinical parameter. We suggest that this novel method may be used as a routine test to evaluate and follow up of the levels of oxidative stress in preeclampsia.

Introduction

Reactive oxygen species (ROS) are produced during many metabolic and physiological processes. All organisms possess a range of enzymatic and non-enzymatic antioxidant systems which serve to protect them against the harmful oxidative reactions that occur as a consequence of this endogenous ROS production. Under certain conditions, increases in oxidants and decreases in antioxidants cannot be prevented, and the oxidant/antioxidant balance shifts towards the oxidative state. Consequently, oxidative stress, which has been implicated in over a hundred disorders, including preeclampsia, develops [1].

There is increasing evidence that oxidative stress is an important contributing factor in the pathogenesis of preeclampsia. Lipid peroxidation has been implicated in the vascular dysfunction that underlies this disorder, and a number of studies have reported increased serum levels of lipid peroxidation products together with a reduction in the levels of the serum antioxidant components [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Antioxidant supplementation in women at risk of preeclampsia has been associated with an improvement in biochemical indices of the disease, and supplementation with antioxidants may have a beneficial effect in the prevention of this condition [13], [14].

Knowledge of the total responses of the serum antioxidant systems in pre-eclampsia is limited [12]. Radical-scavenging antioxidants are consumed by the increased free radical activity associated with this condition, and the total antioxidant status has been used to indirectly assess free-radical activity [10], [11], [15]. There are conflicting results concerning this topic. Kharb [10], [11] found significantly higher TARs in women with preeclampsia, while Shaarawy et al. [12] found significantly lower TAR values in preeclamptic patients than had been reported in other studies.

Various methods have been developed for the measurement of total antioxidant status. However, there is not yet an accepted “gold standard” reference method [2], and decisions concerning standardisation, and the terms and units used for the measurement of TAR have not yet been made [16]. This implies that this topic needs to be studied further [17]. The most widely used methods for TAR measurement are colorimetric, or involve either fluorescence or chemiluminescence [18], [19], [20]. The fluorescence and chemiluminescence methods require sophisticated techniques, and these improved systems are not present in many routine clinical biochemistry laboratories. On the other hand, even when these techologies are available, their routine use is limited [16].

In this study, we aimed to measure both the levels of individual antioxidant components and the TAR values in plasma samples from pregnant women to evaluate their antioxidant status using a novel automated method [17]. As a reciprocal measure, the total peroxide levels of the same plasma samples were also measured. The percent ratio of the total plasma peroxide level to the plasma TAR level was regarded as the oxidative stress index (OSI) [21].

Section snippets

Subjects

The study population, treated in our department, consisted of 24 women with preeclampsia and 18 women with normal, normotensive pregnancies. The diagnosis of preeclampsia was established in accordance with the American College of Obstetrics and Gynecology definition [22]. All women gave informed consent to participate in the study, which had been approved by the local Ethics Committee. None of the patients had pre-existing hypertensive disorders or any renal, hepatic, or hematologic diseases,

Results

The demographic and clinical data of the subjects are shown in Table 1. As expected, the women affected by preeclampsia demonstrated significantly higher systolic (P<0.001) and diastolic blood pressures (P<0.001) than women with normal pregnancies. Furthermore, the women with preeclampsia had a significantly higher mean body weight (P<0.001) and gave birth to babies with significantly lower birth weights (P<0.001). The maternal age, gestational age, gravidity, parity, and placental weight also

Comment

It is well known that oxidative stress increases during normal pregnancy. In healthy pregnancy it has been reported that plasma lipid hydroperoxide levels are increased, and the total antioxidant capacity decreased [26], while the activity of the antioxidant enzyme erythrocyte glutathione peroxidase is decreased, along with the levels of its cofactor selenium [4]. However, the nature of this mechanism is not yet known.

Preeclampsia remains one of the most serious complications of pregnancy. The

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