The etiology and pathogenesis of preeclampsia remain poorly understood. Recent reports suggest that free radical–induced endothelial cell injury might be an etiologic factor in the pathogenesis of preeclampsia.1,2 Such cell injury might, in turn, cause uncontrolled lipid peroxidation, which is counteracted by the action of several antioxidants.3,4 Many natural dietary carotenoids have antioxidant properties that can protect against free radical–induced endothelial cell damage.5,6 Previous reports of plasma carotenoids in preeclamptic women have been limited to β-carotene.7,8 Lycopene and canthaxanthin are prominent carotenoids, commonly present in human diet, and both are potent antioxidants that have been studied for their ability to prevent chronic diseases by protecting against free radical damage.9,10 We reported that plasma levels of β-carotene, α-tocopherol, and ascorbic acids are lower in women with preeclampsia.7 The purpose of this preliminary study was to compare the levels of lipid-soluble provitamin A (α-carotene and β-carotene) and non-provitamin A (lycopene and canthaxanthin) carotenoids in maternal serum, umbilical cord blood, and placental tissue samples at delivery from normal pregnant women and women with preeclampsia.
MATERIALS AND METHODS
In this cross-sectional study, a total of 58 pregnant women seen for their prenatal care at Bronx Municipal Hospital Center, Bronx, New York, were interviewed for study participation. Of these 58, 41 (70%) women were recruited after they gave informed consent, and 17 (30%) refused to participate because of personal reasons. The Institutional Review Board approved the study protocol. The study period was 12 months, and a single investigator collected all samples while on call at Labor and Delivery. All subjects came from the same catchment area and had similar socioeconomic backgrounds. Most women in the study population were Hispanic (52%) or black (38%), and most subjects were representative of an inner-city underserved population. Recruitment criteria included age 15–35 years, gestational age 30–42 weeks, singleton pregnancy, intact membranes, absence of labor contractions, and absence of any other medical complication concurrent with preeclampsia. The diagnosis of preeclampsia was established in accordance with the definitions of the ACOG.11 Preeclampsia was classified as mild unless one or more of the following signs or symptoms was present, in which case the preeclampsia was classified as severe: (1) systolic blood pressure at least 160 mmHg or 105 mmHg diastolic if sustained, (2) oliguria (24-hour urinary output less than 500 mL), (3) pulmonary edema or cyanosis, or (4) impaired liver function of unknown cause.
Maternal and cord venous blood samples and placental tissue specimens were collected from normal and preeclamptic women shortly after delivery. Placental tissue samples were full thickness excluding amniotic membranes. All samples were coded so that laboratory personnel were blinded to sample source. Tissue samples (200 mg wet weight full thickness) were washed free of blood with ice-cold saline until the final wash was colorless. Samples were frozen in liquid nitrogen and stored at −80°C until assayed. The levels of α-carotene, β-carotene, lycopene, and canthaxanthin were measured by high-pressure liquid chromatography in placental tissue and maternal and umbilical cord venous serum samples.
Samples were processed under subdued or gold light. The extraction procedures for carotenoids from tissue samples were described previously.12 Serum α-carotene, β-carotene, lycopene, and canthaxanthin were extracted as previously described.13 The levels of all four carotenoids in placental tissue specimens and serum samples were measured by high-pressure liquid chromatography attached to a Waters 490E multiwavelength ultraviolet detector (Waters Associates, Division of Millipore, Milford, MA). Results were calculated using the ratio of peak area of the compound over the peak area of the internal standard. Using a sensitive high-pressure liquid chromatography system, all four carotenoids at a level of 20 ng or more could be measured in biologic samples. The recovery rate after three-time hexane extractions was 94%, and the coefficient variation in all cases was less than 10%. The high-pressure liquid chromatography system with a four-channel detector allows the separation of several carotenoids in the same run without any interference from lutein or zeaxanthin.
During the study period, not all four carotenoids were measured in some of the tissue and serum samples, because standardization of the high-pressure liquid chromatography technique for α-carotene and canthaxanthin was still being developed. Because group-specific sample size was limited and many of the carotenoid levels were skewed, the statistical analyses were performed by the Mann-Whitney test for nonparametric data to determine the differences between the two groups. Student t test was also applied when two groups were being compared.
After completion of the carotenoid assays, the sample codes were broken and clinical diagnoses were retrieved and correlated with tissue and serum carotenoid levels. Twenty-two of 41 women (54%) had normal pregnancies and 19 (46%) had preeclampsia (16 mild and three severe). Table 1 shows the mean maternal age, gestational age, birth weight, blood pressure, smoking status, and clinical data of the study population.
Table 2 shows that placental tissue levels of β-carotene, lycopene, and canthaxanthin were significantly lower in preeclamptic women than mean values obtained from normal women. Table 3 compares carotenoid levels in maternal serum and umbilical cord venous blood of normal and preeclamptic pregnancies. Venous blood levels of all four carotenoids in umbilical cord samples were comparable in both groups, with no statistically significant differences. In contrast, maternal serum β-carotene and lycopene levels were significantly lower in the preeclampsia group compared with the normal group. Cord serum levels of retinol and α-tocopherol were comparable in both groups (data not shown).
A MEDLINE search for the period 1966 to 2000, using the terms “placenta” and “carotenoids” found no other reports of placental carotenoid levels in women with preeclampsia. The present study found detectable, variable levels of four lipid-soluble antioxidant carotenoids, namely, α-carotene, β-carotene, lycopene, and canthaxanthin in human placental tissue samples and in maternal serum and umbilical cord venous blood at delivery as well as decreased carotenoid concentrations in placental tissue and maternal serum samples in women with preeclampsia.
Exogenous and endogenous factors contribute to the production of highly reactive free radicals in the human body.2 There is a delicate balance between free radical production and natural antioxidant body defenses.2,14 A cellular redox imbalance leads to oxidative stress and tissue injury.15 Human defense against oxidative stress and free radical–induced damage primarily consists of antioxidant enzymes and antioxidant nutrients, including carotenoids, α-tocopherol, and thiols.2,14 Endothelial cell injury in preeclampsia can be caused by free radical–induced uncontrolled lipid peroxidation.1,3 Lipid peroxidation of the endothelial cell membrane could lead to membrane damage, inhibition of the prostacyclin synthetase enzyme, and inactivation of endothelium-derived relaxing factors.2,16 Antioxidants, by their quenching abilities, have been postulated to protect the endothelial cell membrane against free radical damage.6,14 Placental concentrations of β-carotene, lycopene, and canthaxanthin were significantly lower in preeclamptic women compared with normal controls. Serum concentrations of these carotenoids in cord blood samples did not show any significant differences between normal pregnancies and preeclampsia, whereas maternal levels of β-carotene and lycopene were significantly lower in preeclampsia. Our current findings of reduced levels of placental β-carotene in preeclampsia are in agreement with our previous report of decreased plasma lipid-soluble antioxidant levels in women with preeclampsia.7
Decreased placental antioxidant carotenoid levels in preeclampsia might result in increased lipid peroxidation as a response to cumulative oxidative stress. Several antioxidant mechanisms control lipid peroxidation.3,6,15 Under certain conditions, the protective mechanisms could be compromised, leading to increased concentrations of lipid peroxidation products and decreased levels of antioxidant carotenoids.5,6 Hypothetically in preeclampsia, an imbalance between formation of lipid peroxidation and antioxidant defenses could result in free radical–mediated endothelial cell damage and related metabolic endothelial dysfunction. This findings of this study indirectly support the concept that free radical–mediated lipid peroxidation and increased endogenous antioxidant consumption might be involved in the pathophysiology of preeclampsia. The exact etiology of preeclampsia, however, remains unknown.
In humans, antioxidant carotenoid levels can be manipulated easily by increasing dietary intake of carotenoid-rich fruits and vegetables or by pharmacologic supplementation.17 Of approximately 600 carotenoids found in nature, about 40 are present in a typical human diet. There are no reports of toxicity of these dietary carotenoids.18 α-Carotene and β-carotene are found in abundance in carrots and sweet potatoes, lycopene in tomatoes, and canthaxanthin in mushrooms and fish. The human body does not synthesize these carotenoids, and daily dietary intake of green and yellow fruits and vegetables could enhance antioxidant defenses against oxidative stress and protect against free radical–induced cellular damage.2,6 Several epidemiologic studies showed an association between high carotenoid intake and lower incidence of several chronic diseases.19,20 Further research is needed to confirm the present preliminary findings in a larger population sample. Future studies should include a double-blind, placebo-controlled nutritional intervention trial, using various antioxidants as potential preventive agents against the development of preeclampsia. Research advances in pregnancy-induced hypertensive disorders have facilitated a better understanding of the pathophysiologic processes associated with this disease. Strategies of prevention, early diagnostic recognition, and novel therapies have contributed to a more favorable outcome for preeclampsia. Further challenges in this area include focused efforts to elucidate mechanism(s) involved in free radical–mediated endothelial cell damage and the potential therapeutic role of dietary antioxidant protection.
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© 2001 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
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