Mycotoxin contamination in food commodities is an age-old problem. Due to the detrimental impact of mycotoxins on human health, exposure to mycotoxins and their health implications have been increasingly recognized. Ochratoxin A (OTA), one of the mycotoxins, has been found to cause diverse toxicities in animals, with potential impact on human health. OTA has been reported to be teratogenic and interfere with steroidogenesis in vivo. Chronic exposure of pregnant women to OTA may be hazardous for the human foetus, especially when endocrine and developmental toxicities are taken into consideration. Accordingly, in the first part of this project, I hypothesized that OTA may interfere with enzymes involved in human placental steroidogenesis. By evaluation of human placental 3β–hydroxysteroid dehydrogenase/isomerase (3β-HSD) at both mRNA and protein (hormonal) levels, my results showed that OTA could up-regulate 3β-HSD1 expression in human placental cells with concentration relevant to human exposure. This study is the first to report the endocrine disruption potential of OTA in human placental cells. As several mycotoxins have been demonstrated previously to cross human placental barrier and OTA has been associated with developmental toxicity in vivo, I further hypothesized that OTA may be transferred through human placenta and accumulate in foetal compartment. In the second part of this project, human perfused placenta was used to investigate the placental toxicokinetics of OTA using concentrations found in serum of pregnant women. Findings from this study clearly showed that the transfer of OTA through term human placenta was minimal, contradicting the existing epidemiological studies reporting higher foetal OTA levels than maternal. This is the first study where transplacental kinetics of OTA has been studied in human perfused placenta. To assess the relevance of the study findings, it is very important to provide information on maternal OTA exposure during pregnancy. Currently there is limited information regarding OTA exposure of pregnant women. The third part of this project aimed at evaluating the frequency and level of exposure to OTA in pregnant women from Egypt, where exposure to dietary mycotoxins is common due to the environmental conditions. Biomonitoring of both serum and urinary OTA levels showed that more than 70% of pregnant women were exposed to OTA with a geometric mean of 0.27 ng/ml in serum and 37.21 pg/mg creatinine in urine indicating frequent exposure of this subpopulation. As an ultimate aim, maternal-foetal risk assessment served as a conclusive part of this project to predict and evaluate both maternal and foetal risk of exposure to OTA during pregnancy. Data from the exposure of pregnant women in Egypt to OTA were further ultilized to conduct maternal-foetal risk assessment in relation to OTA exposure. Based on the refined Klaassen equation for exposure estimation during pregnancy and the benchmark dose approach for risk assessment, this subpopulation of pregnant women generally was not exposed to OTA in a high-risk manner. However, considering the suspected chronic exposure beginning from early pregnancy with high foetal susceptibility and diverse toxic effects, and in particular the potential endocrine disruption of OTA, keeping OTA exposure to a minimum is recommended. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Kwan Pui-Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 140-155). / Abstracts in English and Chinese. / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Iron homeostasis --- p.5 / Chapter 1.3 --- Natural Resistance Associated Marcophage Protein (Nramp) Family --- p.15 / Chapter 1.4 --- Divalent Metal Transporter 1 (DMT1) --- p.18 / Chapter 1.5 --- Iron Responsive Element (IRE) and Iron Regulatory Protein (IRP) --- p.23 / Chapter 1.6 --- Expression and localization of DMT-1 in human --- p.27 / Chapter 1.7 --- Iron and the developing feus --- p.31 / Chapter 1.8 --- Objectives of the study --- p.36 / Chapter Chapter 2 --- Materials and Method / Chapter 2.1 --- Study population --- p.37 / Chapter 2.2 --- Procedure of surgical termination of pregnancy --- p.38 / Chapter 2.3 --- Tissues collection and preparation --- p.39 / Chapter 2.4 --- Semi-quantitative Reverse Transcription-Polymerase Chain Reaction --- p.44 / Chapter 2.5 --- Immunohistochemistry --- p.49 / Chapter 2.6 --- Statistical analysis --- p.55 / Chapter Chapter 3 --- Results / Chapter 3.1 --- Description of subjects --- p.56 / Chapter 3.2 --- Existence of human DMT-1 isoforms at early pregnancy --- p.58 / Chapter 3.3 --- Relative expression of DMT-1 isoforms to β -actin mRNA expression at different week gestation --- p.67 / Chapter 3.4 --- Cellular localization of DMT-1 isoforms at early pregnancy --- p.91 / Chapter 3.5 --- Relative expression of DMT-1 proteins at early pregnancy --- p.101 / Chapter Chapter 4 --- Discussion / Chapter 4.1 --- Existence of DMT-1 at early pregnancy --- p.116 / Chapter 4.2 --- Expression of DMT-1 isoforms at early pregnancy at gene level --- p.118 / Chapter 4.3 --- Expression of DMT-1 isoforms at early pregnancy at protein level --- p.120 / Chapter 4.4 --- "Comparison expression of DMT-1 between human fetus, human adult and animal studies" --- p.121 / Chapter 4.5 --- Functional importance of DMT-1 at developing fetus at early pregnancy --- p.130 / Chapter 4.6 --- Conclusion --- p.138 / Chapter 4.7 --- Further study --- p.139 / Chapter Chapter 5 --- Reference --- p.140 / Appendix I: Calculation of EM --- p.156