Selenium status, its interaction with selected essential and toxic elements, and a possible sex-dependent response in utero, in a South African birth cohort

Selenium (Se) is an essential trace element and its deficiency in utero may affect fetus development and birth outcomes. The current study aimed to assess serum Se status at delivery and examine the possible association between Se levels and birth outcomes. The interaction of Se with selected essential and toxic elements as well as possible sex-dependent responses in utero were also evaluated. The negative association between Se levels and head circumference of neonates was evident in the total cohort (β = −0.164; p < 0.001) as well as in the pre-term and full-term cohorts. Sig-nificant positive correlations were found between maternal serum Se concentrations and zinc (Zn) and copper (Cu) in the total and regional cohorts. In the total cohort, the toxic elements lead (Pb) and arsenic (As) showed a negative correlation with Se levels, while mercury (Hg), aluminum (Al) and cadmium (Cd) showed a positive correlation. The study found a sex-dependent response in utero for Zn, Cu, Pb, Hg, and Al. The findings of the current study may inform reproductive health policy on Se status in South Africa and highlight the need for sensitive methods to measure Se intake during pregnancy and its complex interactions with other micronutrients and environmental pol-lutants.

In total, five study sites were chosen along coastal regions of South Africa (three study sites at the Indian Ocean coast of the KwaZulu-Natal (KZN) province, and two sites at the Atlantic Ocean coast of the Western Cape province) (Figure 1). All sites were rural, except for the urban study site of the city of Cape Town, in the Western Cape province. In the statistical analyses, we report the results for total cohort, Indian Ocean region, and Atlantic Ocean region, which differ by environmental pollution and socioeconomic status. Women admitted for delivery at the maternity sections of public hospitals in the study regions were informed of the study objectives by the medical personnel on duty and a research assistant and invited to participate in the investigation. They were also given a detailed information pamphlet about the study. In total, 650 women agreed to take part in the study, signed informed consent forms, and agreed to donate a blood sample before delivery. Furthermore, all study participants agreed to answer a socio-demographic questionnaire by interview, which included questions on the frequency of intake of various basic foods before and during pregnancy, lifestyle, and self-reported health status. All study participants agreed to allow researchers access to the hospital birth outcome data and understood that participation was voluntary and confidential and that they had the option of withdrawing from the study at any time. Study sites: Sites 1, 2, 3—Indian Ocean; sites 4 and 5—Atlantic Ocean. Figure is identical but site locations have been added, and is therefore for representative purposes only. https://www.cia.gov/library/publications/resources/cia-maps-publications/South%20Africa.html. (accessed on 6 March 2017). A sterile Venoject system and Becton, Dickinson & Company (BD, Franklin Lakes, NJ, USA) collection tubes were used for all blood collections. Each study participant donated 10 mL of venous blood into a non-additive tube to obtain serum fractions for the analyses of Se, copper (Cu), zinc (Zn), and aluminum (Al). The serum tubes were centrifuged and the serum was transferred to acid-washed polypropylene tubes using acid-washed plastic pipettes. For the analyses of toxic elements such as Hg, lead (Pb), manganese (Mn), Cd, and As in maternal whole blood, 10 mL of venous blood was collected into tubes containing ethylene diamine tetra acetic acid (EDTA). Samples of serum (post-centrifugation) and whole blood samples were stored at −20 °C and couriered in a frozen state to the National Institute for Occupational Health (NIOH) laboratory, Johannesburg, South Africa. All precautions to eliminate and prevent contamination at collection and during the preparation of samples were applied throughout. All samples were analyzed using an Agilent Inductively Coupled Plasma Mass Spectrometer (ICP-MS) 7900 with an Octopole Reaction System. The serum samples were analyzed at Lancet Laboratories, Johannesburg, and whole blood samples were analyzed at the NIOH laboratory, Johannesburg, South Africa. Both laboratories participate in a proficiency testing scheme for biological samples. For the measurement of Al, Cu, Zn, and Se in serum, samples were diluted 20-fold with a diluent [ammonia 2.5 mL; butanol 6 mL, 0.1% triton-X 50 µL, and EDTA (50 µg) in 500 mL deionized water]. Ammonia, butanol, and EDTA were purchased from Merck Chemicals (PTY) Ltd., South Africa: Triton-X, calibration standards and internal standards were purchased from Industrial Analytical, South Africa. The following internal standards were also added to the diluent, indium (In, 25 µL), germanium (Ge, 25 µL), scandium (Sc, 25 µL), rhodium (Rh, 250 µL), and iridium (Ir, 250 µL). The ICP-MS instrument was calibrated with calibration standards prepared in a diluent using a multi-element custom standard (SPECTRASCAN–SS028226). The concentrations of the standards for Se, Cu, and Zn ranged from 0.1 to 100 µg/L, and for Al, the range was 0.1 to 50 µg/L. The internal standards used were Sc, Ge, Ge, and Ir for Al, Cu, Zn, and Se, respectively. The instrument was run in general purpose mode using helium gas. Two certified reference controls, Seronorm™ Trace Elements Serum (Sero Ltd., Billingstad, Norway) were analyzed with every analytical run in intervals of 10 samples for quality assurance of all element measurements. The percentage recovery for Cu, Zn, and Se was 88–104%, and 91–114% for Al. The coefficient of variation was 8.76%, 4.56%, 4.87%, and 6.88% for Al, Cu, Zn, and Se, respectively. The limits of quantitation (LoQ) for Al, Cu, Zn, and Se were 0.15, 0.06, 0.31, and 0.17 µg/L, respectively. The collection and analyses of samples for the selected elements manganese (Mn), Hg, Pb, Cd, and As in maternal whole blood have been described previously [40,41,42,43,44]. In short, analyses for the whole blood samples were performed on an ICP-MS, following digestion in nitric acid. Two blood certified reference controls, Seronorm ™ Trace Elements (Sero Ltd., Billingstad, Norway), were used. The percentage recovery of the Seronorm controls for the metals measured in blood ranged from 83–108%. The detection limits for Mn, Hg, Pb, Cd, and As were 0.07, 0.08, 0.04, 0.03, and 0.13 µg/L, respectively. Information on covariates was obtained from interviewer-administered questionnaires and hospital medical birth records of the neonates. Demographic and socio-economic status questions such as age, race/ethnicity, marital status, educational status, employment status, housing type, and source of water supply as well as self-evaluated health status were included in the questionnaire. Questions on nutrition of the mothers before and during pregnancy were also asked; these included the consumption of meat and fish, dairy products, and fruits. Additionally, the types of fuel used for the purpose of either cooking or heating were included in the questionnaire, as were smoking habits. Birth weight (g), birth length (cm), head circumference (cm), gestational age (weeks), Apgar score at 1 and 5 min, and placenta weight (g) were obtained from the medical records of the neonates. Data analyses were carried out using STATA version 12 [39]. The Chi-square test was used to determine if the socio-demographic and economic variables were significantly different between the two coastal regions. Bivariate analyses were carried out between Se exposure and covariates using Spearman’s correlation. All the continuous variables including maternal serum Se were found to be not normally distributed and had a skewed distribution, therefore, their median and geometric mean values were calculated rather that their arithmetic means. The Wilcoxon rank-sum test was used to compare the medians of continuous variables between the two geographical populations. For the categorical variables, missing values were treated as a separate category. Multi-variable adjusted quantile regression analysis was used to explore the risk factors associated with high Se levels in maternal serum using a backward deletion approach, starting with a full model of factors significantly associated with maternal serum Se in the univariate analysis. Statistical significance was set at p < 0.05 for all models. The study protocol was approved by the Human Research Ethics Committee of the University of Witwatersrand in Johannesburg (Protocol no. {"type":"entrez-nucleotide","attrs":{"text":"M10742","term_id":"147973"}}M10742), and by the Departments of Health of the different provinces. Personal data confidentiality and sample collection were carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki). Confidentiality was maintained by assigning identification numbers to all study participants.

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