Fetal Diagn Ther 2007;22:254–258 DOI: 10.1159/000100785
Received: November 16, 2005 Accepted after revision: June 2, 2006 Published online: March 16, 2007
Plasma Cysteine Concentrations in Uncomplicated Pregnancies H. Viskova a K. Vesela b B. Janosikova b J. Krijt b J.A. Visek c P. Calda a a Department of Obstetrics and Gynaecology, b Institute of Inherited Metabolic Disorders, 1st Faculty of Medicine, and c Faculty of Social Sciences, Charles University, Prague, Czech Republic
Key Words Plasma total cysteine Pre-eclampsia
Abstract Objective: To measure levels of total plasma cysteine, homocysteine, cysteinylglycine and glutathione of normotensive primiparous pregnant women in the second and the third trimester. Methods: Two consecutive blood samples were taken from 65 healthy primiparous women in the 19th to 21st weeks of pregnancy and then in the 30th to 32nd weeks. Plasma total cysteine, homocysteine, cysteinylglycine and glutathione were determined by HPLC method. Women were followed until delivery. Sixty-two pregnant women were normotensive throughout the pregnancy and 3 developed pre-eclampsia. Median levels of thiols in the second and the third trimesters were compared using paired t test. Results: Levels (median [range], mol/l) of plasma total cysteine in normotensive pregnant women were significantly lower in the third than in the mid-trimester (176.1 [163.0, 189.4] vs. 187.4 [178.7, 205.2], p ! 0.001). Concentrations of total homocysteine, cysteinylglycine and glutathione were not different. Conclusion: Plasma total cysteine (t-Cys) is significantly lower in the third compared to the second trimester. Urinary excretion of t-Cys does not differ in the second compared to the third trimester. The decrease of t-Cys might indicate that cysteine is essential for the fetus. Copyright © 2007 S. Karger AG, Basel
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Introduction
Methionine, the only essential sulphur amino acid in the mammalian diet [1], is important to intermediate metabolism. The most important metabolic roles of methionine include synthesis of S-adenosylmethionine, the primary biological donor of methyl groups, and synthesis of homocysteine. Homocysteine is either remethylated back to methionine in the remethylation pathway or directed to the transsulphuration pathway in which homocysteine is irreversibly converted to cysteine. Cysteine is an intermediary product of methionine metabolism (fig. 1), one of three amino acids contained in glutathione, which plays an important role in detoxification processes and in scavenging free radicals. Methionine metabolism is closely related to the folate cycle. Hundreds of studies have been published about homocysteine in pregnancy, but less is known about cysteine. Maternal plasma total homocysteine (t-Hcy) is significantly decreased in normal pregnancy compared to the non-pregnant state [2]. On the other hand, published studies demonstrate an association between increased plasma levels of homocysteine and several obstetric complications such as pre-eclampsia [3–7], intrauterine growth retardation (IUGR), placental abruption [8], spontaneous miscarriage, neural tube defects (NTD) [9] and other pregnancy complications [10]. Published studies also demonstrate lower plasma total cysteine (t-Cys) in pregnant than in nonpregnant women and higher plas-
Hana Viskova, MD Department of Obstetrics and Gynaecology, 1st Faculty of Medicine Charles University and the General Faculty Hospital Apolinarska 18, Prague 2, 120 00 (Czech Republic) Tel. +420 2 2496 7273, Fax +420 2 2491 5886, E-Mail
[email protected]
Table 1. Clinical characteristics of 62 healthy pregnant women FH4
Met
AdoMet Folate cycle
CH3–FH4
Methionine cycle
AdoHcy
Remethylation pathway
Age, years BMI preconceptionally Hematocrit 19–21 weeks Hematocrit 30–32 weeks Supplementeda, % Normotension, %
27 (17–35) 22.35 (18.1–32.9) 0.348 (0.287–0.475) 0.342 (0.296–0.465) 80 100
Data are given as median (range). a Supplementation with folates.
Hcy Transsulfiration pathway
Cysteine Tau
GSH
SO32–
Fig. 1. Metabolism of cysteine. Methionine (Met) is converted to S-adenosylmethionine (AdoMet), the donor of methyl groups and intermediate in synthesis of spermidine and spermine, and after demethylation to S-adenosylhomocysteine (AdoHcy) and hydrolysis homocysteine (Hcy) is produced. Homocysteine is then either catabolized into cystathionine and cysteine in the transsulphuration pathway, or converted back to methionine in the remethylation pathway, which is closely related to the folate cycle; methyltetrahydrofolate (CH3-FH4), tetrahydrofolate (FH4). Cysteine is either incorporated into gluthatione (GSH) or converted to taurine (Tau).
ma t-Cys in pre-eclamptic women than in those with normal pregnancies [4, 7]. Both those studies had cross-sectional designs and it is not known whether elevated t-Cys is the result of established pre-eclampsia or whether the elevation is already present before development of clinical and laboratory signs of pre-eclampsia. The aim of our study was to describe normal levels of plasma total cysteine and other aminothiols in the second and the third trimesters of physiologic pregnancy.
questionnaire (personal and family history, vitamin and folate supplementation, consumption of alcohol, smoking). Inclusion criteria were: primigravida, with singleton pregnancy. Exclusion criteria were: primary or pregnancy-induced hypertension, diabetes mellitus, renal disease, abnormal anomaly scan and family history of pre-eclampsia. Patients referred to our center for any reason were excluded as well. A nonfasting blood sample was taken and the woman was asked to return in the 30th to 32nd weeks of pregnancy for the second scan and blood sampling. Sixty-five consecutively presenting pregnant women met the inclusion criteria and had both blood samplings between January 2002 and September 2003. Women were followed up until labor. Sixty-two pregnant women were normotensive throughout the pregnancy and 3 developed pre-eclampsia. The clinical characteristics of 62 healthy pregnant women are shown in table 1. Pre-eclampsia was defined, according to the standards of the International Society for the study of Hypertension in Pregnancy, as hypertension developing in the second half of pregnancy (diastolic blood pressure above 90 on at least two consecutive occasions, each more than 4 h apart) with proteinuria. The study was approved by Ethics Committee of the 1st Faculty of Medicine, Charles University, Prague, Czech Republic. All subjects gave their written informed consent. Laboratory Analyses Blood was drawn by standard venipuncture using EDTA tubes. The blood sample for aminothiol analysis was chilled immediately in an ice water bath. Plasma was obtained by centrifugation at 2,000 g for 15 min at 4 ° C within 15 min after sampling. All plasma samples were immediately frozen at –80 ° C prior to the analysis. Concentrations of plasma total cysteine (t-Cys), homocysteine (t-Hcy), cysteinylglycine (t-Cys-Gly) and glutathione (GSH) were determined by the HPLC method using Tris(2-carboxyl-ethyl)phosphine as a reductant of disulphide bonds, and ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate as a fluorescent derivatization agent as previously described [11].
Subjects and Methods Study Design This study was designed as prospective and observational. Study subjects were pregnant women coming for screening anomaly scan in the 19th to 21st weeks of pregnancy to the Department of Obstetrics and Gynecology of the 1st Faculty of Medicine of Charles University, Prague. History was taken by structured
Plasma Cysteine Concentrations in Uncomplicated Pregnancies
Statistics The data were analyzed using STATISTICA (99 edition) software. For analyses of aminothiol levels in pregnant women in the 20th versus the 30th week of pregnancy the t test for dependent samples with separate variance estimate was used. Analysis of correlation of t-Cys and hematocrit was done by correlation matrix. The statistical significance level was set to 0.05.
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Table 2. Values of plasma total cysteine,
homocysteine, cysteinylglycine, and glutathione in 62 prospectively studied uncomplicated pregnancies
Cysteine Homocysteine Cysteinylglycine Glutathione
19–21 weeks
30–32 weeks
p value
187.4 (178.7, 205.2) 4.9 (4.1, 5.7) 30.2 (27.4, 33.7) 8.1 (7.5, 9.2)
176.1 (163.0, 189.4) 4.6 (3.9, 5.6) 31.6 (28.1, 34.8) 7.9 (6.9, 8.7)
