The Journal of Maternal-Fetal and Neonatal Medicine, 2009; Early Online, 1–4
Consequences of methemoglobinemia in pregnancy in newborns, children, and adults: issues raised by new findings on methemoglobin catabolism
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by MD,PhD Lucijan Mohorovic For personal use only.
LUCIJAN MOHOROVIC1, ERIS MATERLJAN2, & GORDANA BRUMINI3 1
Department of Environmental Medicine, 2Department of Family Medicine, and 3Department of Medical Informatics, University of Rijeka School of Medicine, Rijeka, Croatia (Received 31 July 2009; revised 2 October 2009; accepted 13 October 2009)
Abstract Objective. The aim of this review is to warn about the effects of methemoglobin and its catabolic products and the toxic effects caused by environmental oxidants that cause high-risk pregnancy and may later impair the health of newborns, children and adolescents. Methods. In our study of pregnant women (n ¼ 36) whose methemoglobin level was 41.5 g/l, we took blood samples from their newborns to determine the frequency of sister chromatid exchange (SCE) by cultivating lymphocytes. The research took place at the Department of Biology and Medical Genetics of the School of Medicine in Rijeka (Croatia). Results. The results have shown that no deviation in the SCE frequency was found in either case (1990). We examined data on the health of newborns collected at perinatal hospital departments in Rijeka (Croatia), the preschool office and school service at the Labin Health Center and continued until they were 18 years of age (2008). The statistics obtained by applying the chi-square test show that the incidences of neonatal jaundice (p ¼ 0.034), heart murmur at a later age (p ¼ 0.011) and dyslalia and learning/memory impairments (p ¼ 0.002) were significantly higher than in children of control mothers (n ¼ 19). Conclusion. Depending on the mother’s exposure to environmental oxidants, during its development the fetus is more likely to be affected by methemoglobin and hemolysis. Oxidants affect the vascular endothelium of kidneys, brain and other vital organs, because they have the capacity to cross the damaged fetomaternal placental barrier. ‘Fetal preeclampsia’ is an expected manifestation of the condition. Our research proves our thesis on the pathophysiological relationship between methemoglobinemia and unexplained jaundice and hyperbilirubinemia, heart murmur at a later age, dyslalia and learning and memory impairments that have not exactly been demonstrated yet.
Keywords: High-risk pregnancy, environmental oxidants, methemoglobin level, ‘fetal preeclampsia’, impaired health, newborns, children, adolescents
Introduction The primary objective of this epidemiological study was to check the health of neonates up to 18 years of age whose mothers had elevated methemoglobin levels during pregnancy (41.5%). As I have found no evidence of the effect of mother’s methemoglobinemia on the fetus, the second objective was to focus on methemoglobin as an early biomarker of the environmental toxic that induces oxidative stress, causing high-risk pregnancy and may later impair the
health of newborns, children and adolescents. Under normal conditions, the level of methemoglobin is lower than 1% of the total hemoglobin [1], and it may increase when erythrocytes are affected by a variety of genetic, dietary, idiopathic, toxic, xenobiotic pharmaceutical and environmental compounds [2]. As the level of methemoglobin in blood rises, adults show signs of hypoxia which can potentially lead to coma and death if methemoglobin in blood reaches 70%. The symptoms of increased levels of methemoglobin in mothers include headaches, dyspnea,
Correspondence: Lucijan Mohorovic, School of Medicine Rijeka, Department of Environmental Medicine, Rijeka, Croatia. E-mail:
[email protected] ISSN 1476-7058 print/ISSN 1476-4954 online Ó 2009 Informa UK Ltd. DOI: 10.3109/14767050903410656
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by MD,PhD Lucijan Mohorovic For personal use only.
2
L. Mohorovic et al.
pallor, cyanosis, palpitations, chest pain and confusion, delirium potentially leading to tonic-clonic convulsions, coma and death. The author has personally observed that these symptoms are also common in patients with severe anemia, preeclampsia and eclampsia, suggesting that methemoglobinemia may also be a precursor of those conditions. When high levels of methemoglobin as an oxidant become irreversible, the deficiency of antioxidants persists and oxidative stress continues, affecting the vascular endothelium of kidneys, brain and other vital organs and tissues of the mother. This can result in ‘maternal preeclampsia’ and its final form, eclampsia, potentially leading to death. As oxidants have the ability to cross the damaged fetomaternal placental barrier, ‘fetal preeclampsia’ is an expected manifestation of the condition. We use the term ‘fetal preeclampsia’ because, along with excessive maternal exposure to environmental oxidants, the fetus, in its more susceptible pathophysiological phase, is also involved. Methods For lack of evidence on fetal methemoglobin, we used the findings of applicable former studies of mother methemoglobinemia in human pregnancy, where during the ‘control’ and ‘exposure period’ blood samples were tested three times with a 1-month period between each test, using linear correlation statistical tests [3]. To prove the connection to the adverse effects of inhaled environmental toxics, our sample was the population of pregnant women living near the thermal power plant TE Plomin 1. This coal-fired power plant in the district of Labin (about 25,500 residents), in Istra, Croatia, is a single major air polluter. During each hour of operation the plant emits 8.5 tons (18,080 mg/m3 or 6900.8 ppm) of sulfur dioxide as well as nitrogen oxides, carbon dioxide, carbon monoxide, total suspended particulates and other products of coal combustion. The coal from this area has high sulfur content (9–11%) and a high level of radioactivity. Because the plant was closed from 19 February 1989 to 6 September 1989, it was possible to measure the frequency of reproductive loss (spontaneous abortion, premature and stillbirths) in two separate periods: the ‘control’ period from April to July 1989 and the ‘exposure’ period from December 1989 to March 1990. Results The level of methemoglobin in the bloodstream was determined in the laboratory by spectrophotometry on the basis of these samples on three separate occasions, with a 1-month period between each test,
for each pregnant woman (N ¼ 122) in the exposure period when the power plant was in operation as well as for each pregnant woman in the control period when the power plant was closed (N ¼ 138). The research has shown the presence of a significant positive correlation between the level of methemoglobin (as a product of inhaled nitrogen compounds resulting from coal combustion) and sulfhemoglobin in the bloodstream of pregnant women and the daily ground-level concentration of SO2 (r ¼ 0.72, p 5 0.01) resulting from coal combustion [3]. In our study of pregnant women (n ¼ 36) whose methemoglobin level was 41.5 g/l, we took blood samples from newborns to determine the sister chromatid exchange (SCE) frequency and tested them at the Department of Biology and Medical Genetics of the School of Medicine in Rijeka (1990). Basically, the SCE test detects reciprocal exchanges of DNA segments between sister chromatids of the metaphase chromosome, caused by the genotoxic influence of different, primarily chemical, agents. Chromosome slides were obtained by cultivating lymphocytes from peripheral blood with the constant presence of 5-bromodeoxyuridine (20 mgBUdR/ml), during 72 h at 378C. In each of the examinees, 25 metaphases were analysed, and the mean value of SCE per cell was calculated. We examined data on the health of newborns collected at perinatal hospital departments in Rijeka (Croatia), the preschool office and school service at the Labin Health Center and continued until they were 18 years of age (2008). The results have shown that there was no deviation in the SCE (sister chromatid exchange) frequency in either case. We examined data on the health of newborns collected at perinatal hospital departments in Rijeka (Croatia), the preschool office and school service at the Labin Health Center and continued until they were eighteen years of age and obtained statistical data by applying the chi-square test. The results have shown that the incidences of neonatal jaundice (p ¼ 0.034), heart murmur at a later age (p ¼ 0.011) and dyslalia and learning/memory impairments (p ¼ 0.002) were significantly higher than in children given birth to by control mothers (n ¼ 19). Discussion Balla et al. [4] posited that methemoglobin (ferricompound, Fe(III)), but not hemoglobin (ferrocompound, Fe(II)), released the hemes that were incorporated into endothelial cells and rapidly increased their heme oxygenase. Ferritin production was also markedly increased. These important research results support our supposition that methemoglobin has a relevant role as a marker but also as
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by MD,PhD Lucijan Mohorovic For personal use only.
Consequences of methemoglobinemia the cause of early and late endothelial dysfunctions of a vital organ as the CNS. The formation of methemoglobin (ferric iron) from hemoglobin (ferrous iron) leads to hemolysis [5]. When high levels of methemoglobin become irreversible, affecting the vascular endothelium of kidneys, brain and other vital organs, crossing the damaged fetomaternal placental barrier, ‘fetal preeclampsia’ is an expected manifestation of the condition [6]. Nitric oxide and superoxide in fetal blood form the peroxynitrite (ONOO7) that reacts with hemoglobin causing heme loss and converts oxyhemoglobin (ferrous (II) iron) to methemoglobin (ferric (III) iron) and releases the heme from methemoglobin [7– 9], and the heme induces endothelial cytolysis [10]. Iron is essential for the normal functioning of cells but is also capable of generating toxic reactive oxygen species and may have a deleterious effect on the vascular endothelium [11]. The astrocytes distribute iron in the brain and possess transporters for transferrin, hemin and non-transferrin-bound iron [12]. Brain iron is a major contributor to magnetic resonance imaging (MRI) contrast in the normal gray matter. Non-heme brain iron is present mainly in the form of ferritin. The quantitation of non-heme brain ferric iron indicated by the MRI helps in the diagnosis and monitoring of different neurological diseases [13]. Most of the brain non-heme iron is believed to be present as a storage pool consisting of ferritin or hemosiderin and also as a product of methemoglobin catabolism [14]. However, the concentration of transferrin-bound iron is always far too small to affect the MRI. This fact suggests that the role of methemoglobin catabolism in pregnancy should be considered as the source of Ferric (Fe(III)) form concentrated in various brain regions. Hemoglobin is degraded daily to free heme as a pro-oxidant which, along with the enzyme heme oxygenase (HO) mediation, catalyses free heme producing biliverdin, carbon monoxide and the most dangerous product – redox-active iron [15]. Heme oxygenase-1 (HO-1) is a heme-degradation enzyme induced under various oxidative stress conditions [16]. Neonatal jaundice is the result of an imbalance between bilirubin production and elimination; however, increased heme catabolism is an important mechanism responsible for hyperbilirubinemia. The limited antioxidant protective capacity against the cytotoxic nitric oxide effects of free radicals may predispose them to increased oxidative stress hemolysis and hyperbilirubinemia [17]. The abnormal development of the brain during fetal life because of iron deposition or neurotoxicity of hyperbilirubinemia is now thought to contribute to the etiology of many neurological disorders that manifest throughout life. Studies have shown that the
3
timing, severity and the nature of specific insults are critical in determining the pattern of injury and thus the extent to which neurological function will be affected post-natally [18]. Our retrospective epidemiological study confirms the observation of Koger et al. [19] that the developmental, learning and behavioural disability presents a significant public health problem. The posited scientific researches confirm our thesis on the pathophysiological relationship between methemoglobinemia and unexplained jaundice and hyperbilirubinemia, dyslalia, learning and memory impairment, which has not exactly been demonstrated yet. Conclusion Our results point out the consequence of motherfetal methemoglobinemia caused by environmental oxidants, causing oxyhemoglobin and methemoglobin hemolysis, hyperbilirubinemia and toxic brain damage with the view to the role of methemoglobin catabolism in pregnancy as the source of ferric (Fe(III)) form concentrated in various brain regions. Under the gradual influence of free radicals on erythrocytes catabolism, we found significant incidences of neonatal bilirubinemia, heart murmur and dyslalia and learning/memory disturbances in children and teenagers, which have not exactly been demonstrated yet. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. References 1. Kinoshita A, Nakayama Y, Kitayama T, Tomita T, Tomita M. Simulation study of methemoglobin reduction in erythrocytes. Differential contributions of two pathways to tolerance to oxidative stress. FEBS J 2007;274:1449–1458. 2. Jaffe ER. Enzymopenic hereditary methemoglobinemia: a clinical-biochemical classification. Blood cells 1986;12:81–90. 3. Mohorovic L. The Level of maternal methemoglobin during pregnancy in an air-polluted environment. Environ Health Perspect 2003;111:1902–1905. 4. Balla J, Jacob HS, Balla G, Nath K, Eaton JW, Vercellotti GM. Endothelial-cell heme uptake from heme proteins: induction of sensitization to oxidant damage. Proc Natl Acad sci USA 1993;90:9285–9289. 5. Starodubtseva MN, Ignatenko VA, Cherenkevich SN. Damage to erythrocytes caused by the interaction of nitriteions with hemoglobin. Biofizika 1999;44:1068–1072. 6. Mohorovic L. The role of methemoglobinemia in early and late complicated pregnancy. Med Hypotheses 2007;68:1114– 1119. 7. Denicola A, Souza JM, Radi R. Diffusion of peroxynitrite across erythrocyte membranes. Proc Natl Acad Sci USA 1998;95:3566–3571. 8. Li DJ, Luo H, Wang LL, Zou GL. Potential of peroxynitrite to promote the conversion of oxyhemoglobin to methemoglobin. Acta Biochim Biophys Sin (Shanghai) 2004;36:87–92.
4
L. Mohorovic et al.
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by MD,PhD Lucijan Mohorovic For personal use only.
9. Umbreit J. Methemoglobin – it’s not just blue: a concise review. Am J Hematol 2007;82:134–144. 10. Jeney V, Balla J, Yachie A, Varga Z, Vercellotti GM, Eaton JW, Balla G. Pro-oxidant and cytotoxic effects of circulating heme. Blood 2002;100:879–887. 11. Rouault TA, Cooperman S. Brain iron metabolism. Semin Pediatr Neurol 2006;13:142–148. 12. Dringen R, Bishop GM, Koeppe M, Dang TN, Robinson SR. The pivotal role of astrocytes in the metabolism of iron in the brain. Neurochem Res 2007;32:1884–1890. 13. Vymazal J, Brooks RA, Patronas N, Hajek M, Bulte JW, Di Chiro G. Magnetic resonance imaging of brain iron in health and disease. Neurol Sci 1995;134(Suppl):1926. 14. Schenk JF, Zimmerman EA. High-field magnetic resonance imaging of brain iron: birth of a biomarker? NMR Biomed 2004;17:433–445.
15. Balla J, Vercellotti GM, Jeney V, Yachie A, Varga Z, Jacob HS, Eaton JW, Balla G. Heme, heme oxygenase, and ferritin: how the vascular endothelium survives (and dies) in iron-rich environment. Antioxid Redox Signal 2007;9:2119– 2137. 16. Maisels MJ, Kring E. The contribution of hemolysis to early jaundice in normal newborn. Pediatrics 2006;118:276–279. 17. Turgut M, Basaran O, Cekmen M, Karatas F, Kurt A, Aygun AD. Oxidant and antioxidant levels in preterm newborns with idiopathic hyperbilirubinemia. Pediatric Child Health 2004;40:633–637. 18. Rees S, Inder T. Fetal and neonatal origins of altered brain development. Early Hum Dev 2005;81:753–761. 19. Koger SM, Shettler T, Weiss B. Environmental toxicants and developmental disabilities: a challenge for psychologists. Am Psychol 2005;60:243–255.
