ORIGINAL ARTICLE Asymmetric dimethylarginine, arginine and homoarginine at 11--13 weeks’ gestation and preeclampsia: a case--control study AA Khalil 1 , D Tsikas 2 , R Akolekar 3 , J Jordan 2 and KH Nicolaides 1,3 The aim of this study was to investigate whether the nitric oxide (NO) pathway is altered in pregnancies that develop preeclampsia (PE). This was a nested case--control study of screening for PE, in which plasma asymmetric dimethylarginine (ADMA), L-arginine and L-homoarginine were measured at 11 þ 0 -- 13 þ 6 weeks. In all, 75 pregnancies that developed PE, including 25 requiring delivery before 34 weeks (early PE), and 300 unaffected controls were included. L-arginine and L-homoarginine were measured by gas chromatography-mass spectrometry, whereas ADMA was measured by gas chromatography-tandem mass spectrometry. Multiple regression analysis was used to determine if any maternal characteristics or gestation were significant predictors. In the early-PE group, both L-arginine and L-homoarginine expected medians (MoMs) were significantly reduced (median, IQR: 0.85, 0.76--1.04 vs 0.98, 0.88--1.16, P ¼ 0.021 and 0.78, 0.65--0.96 vs 0.99, 0.77--1.31, P ¼ 0.006, respectively) but ADMA MoMs were not significantly different (P ¼ 0.599). In early PE, compared with controls, the ratios of ADMA to L-arginine MoMs and ADMA to L-homoarginine MoMs were increased (median, IQR: 1.19, 0.94--1.33 vs 1.01, 0.75--1.31, P ¼ 0.003 and 1.21, 0.93--1.61 vs 0.99, 0.87--1.16, P ¼ 0.012, respectively). There were no significant differences between late PE and controls in ADMA, L-arginine, L-homoarginine or their ratios. In conclusion, development of early PE is associated with altered NO metabolism and/or synthesis apparent from the first trimester. Journal of Human Hypertension (2013) 27, 38--43; doi:10.1038/jhh.2011.109; published online 8 December 2011 Keywords: asymmetric dimethylarginine; first trimester; L-arginine; L-homoarginine; preeclampsia INTRODUCTION Normal pregnancy is associated with widespread vasodilatation, which is thought to be mediated by nitric oxide (NO). 1 NO is present in syncytiotrophoblast and in the fetoplacental vascular endothelium where it contributes to low fetoplacental vascular resistance. It is also an important regulator of trophoblast functions, such as implantation, differentiation, motility, invasion and apoptosis. 2-5 L-arginine is the substrate for the enzyme NO synthase (NOS) and asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of this enzyme. 6,7 L-homoarginine can replace L-arginine as a substrate for the biosynthesis of NO. 8,9 Studies have demonstrated a significant association between elevated ADMA levels and cardiovascular disease. 10,11 Infusion of ADMA is associated with endothelial dysfunction. 12 The ratio of L-arginine to ADMA is associated with altered NOS activity 13 and is a useful index for evaluating the effects of ADMA. 7,14 NO, along with its substrates and inhibitors, is thought to have an important role in the pathophysiology of preeclampsia (PE), which is characterized by widespread vasoconstriction. Several studies have reported that in PE the maternal plasma concentra- tion of ADMA is increased, whereas the concentration of L-arginine is decreased, increased or normal. 15 - 24 There is some evidence that altered maternal concentration of these metabolites may precede the clinical onset of the disease. 21,25 L-homoarginine levels are increased in normal pregnancy, but we were unable to locate any studies examining its levels in pathological pregnancies. 26 The aim of this study was to investigate further the possible role of NO in the pathogenesis of PE by comparing maternal plasma levels of ADMA, L-arginine and L-homoarginine at 11--13 weeks’ gestation in women who subsequently developed PE with unaffected controls. MATERIALS AND METHODS Study population This was an observational case - control study (between March 2006 and June 2009) drawn from a large prospective screening study on early prediction of complications of pregnancy in women attending for their routine first hospital visit at King’s College Hospital, London, UK. At this visit, which is held at 11 þ 0 -- 13 þ 6 weeks of gestation, we perform combined screening for aneuploidies from the ultrasound measurements of fetal crown-rump length and nuchal translucency thickness, and the maternal serum concentrations of pregnancy associated plasma protein-A and free b-human chorionic gonadotropin (b-hCG) (Delfia Xpress Analyzer, Perkin Elmer Life and Analytical Sciences, Waltham, MA, USA). 27,28 In addition, we record maternal characteristics and medical history, measure the maternal weight and height, and store maternal serum and plasma samples collected in EDTA tubes at 80 1C for subsequent biochemical analysis. Written informed consent is obtained from all women agreeing to participate in the study, which was approved by King’s College Hospital Ethics Committee. Maternal plasma ADMA, L-arginine and L-homoarginine were measured in singleton pregnancies delivering phenotypically normal neonates, 25 cases that later developed PE and required delivery before 34 weeks (early PE), 50 cases of PE delivering at or after 34 weeks (late PE) and 300 unaffected controls. Each case of PE was matched with four controls, which Received 21 April 2011; revised 12 September 2011; accepted 26 September 2011; published online 8 December 2011 1 Department of Fetal Medicine, Institute for Women’s Health, University College London Hospitals, London, UK; 2 Institute of Clinical Pharmacology, Hannover Medical School, Hannover, Germany and 3 Department of Fetal Medicine, Harris Birthright Research Centre for Fetal Medicine, King’s College Hospital, London, UK. Correspondence: Professor KH Nicolaides, Department of Fetal Medicine, Harris Birthright Research Centre for Fetal Medicine, King’s College Hospital, Denmark Hill, London SE5 9RS, UK. E-mail: kypros@fetalmedicine.com Journal of Human Hypertension (2013) 27, 38 - 43 & 2013 Macmillan Publishers Limited All rights reserved 0950-9240/13 www.nature.com/jhh