Doctor of Philosophy / Department of Diagnostic Medicine/Pathobiology / Deon van der Merwe / 1,4-Dioxane is a potentially carcinogenic solvent. It is a problematic groundwater contaminant because of its unique physical-chemical properties. It is found in a wide range of consumer products as a by-product contaminant. This research aimed to investigate contaminant properties and behavior of dioxane in the environment and also in the human body. The dioxane ability to decontamination by adsorption processes was evaluated with four adsorbents. The adsorption efficiencies of activated carbon (AC), metal oxide nanomaterials (TiO[subscript]2 and MgO), and diatomaceous earth (DE) were assessed in aqueous and vapor phases using infrared spectroscopy. AC showed the highest adsorptive capacity for dioxane at equilibrium in both phases. The rate and extent of dermal absorption are important in the analysis of risk from dermal exposure to dioxane. For this purpose, a new flow through diffusion system (FTDS) was developed by modifying a Bronaugh flow through diffusion cell with flow capacity in both the donor and receptor compartments and using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) as the analytical technique. FTDS can provide ‘real time’ quantitative high-density permeation data over time and is characterized by the simplicity of its use and the low cost of test samples. The in vitro dermal absorption study of dioxane across human skin showed that the absorption parameters of dioxane were 1.16 ± 0.22 hr, 5.7 X 10[superscript]-4 ± (0.62) cm/hr, 0.286 ± 0.035 mg/cm2/hr, 4.8 X 10-5 (± 0.32) cm[superscript]2/hr, and 1.99 ± 0.086 mg for lag time, permeability, steady-state flux, diffusivity, and total amount absorbed over 8 hr, respectively. The study of the effect of the surfactant sodium lauryl sulphate and solvent systems water, ethanol, propylene glycol, and ethyl acetate on permeation profiles revealed that these solvents and surfactants increased the permeation of dioxane significantly. The FT-IR spectra of stratum corneum treated with solvents showed that there was broadening of the CH[subscript]2 asymmetric stretching vibration of the CH[subscript]2 peak near 2920 cm[superscript]-1 only in samples treated with ethanol. The lipid extract precipitates were detected and were mostly composed of the stratum corneum lipid part.

Gestational diabetes, a common medical complication in pregnancy, may lead to severe fetal consequences if left untreated. A major concern with the use of antidiabetic drugs in pregnancy is the potential for placental transfer and fetal toxicity. The presence of endocytic pathways and several ABC transporter proteins has been demonstrated in the human placenta and are believed to play an important role in determining fetal exposure to drugs used in pregnancy. The objective of this thesis is to investigate the safety and transfer of the oral hypoglycemic agent, glyburide, and the new long acting insulin analog, insulin glargine, across the human placenta. The oral antidiabetic, glyburide, has been shown to be actively effluxed across the placenta in the fetal to maternal direction. The transport of glyburide in the presence of a breast cancer resistance protein (BCRP) inhibitor was investigated in the dually perfused human placenta model. The results of the perfusion studies indicate that BCRP plays a role in protecting the fetus from the accumulation of glyburide. Subsequently, cellular studies were carried out to determine the effect of the naturally occurring single nucleotide polymorphism within the coding region of BCRP (C421A/Q141K) on glyburide transport. Results suggest that glyburide transport may be reduced in the presence of the Q141K polymorphism. While insulin remains as the gold standard, the potential for maternal hypoglycemia with insulin injection has resulted in the development of insulin analogs. Insulin glargine, a human insulin analog, has a long half life with no pronounced peak when compared to currently used NPH insulin. Human placental perfusion experiments examining the extent and rate of transfer of insulin glargine across the placenta demonstrated that, at therapeutic concentrations, insulin glargine does not cross the placenta to a measurable extent. To further determine the fetal safety of insulin glargine therapy compared with NPH insulin, a systematic review and meta-analysis were performed. No evidence was identified for increased adverse fetal outcomes with the use of insulin glargine during pregnancy. Overall, the results of this research serve to provide improved treatment options for women with diabetes in pregnancy.

Clinical characteristics of idiosyncratic drug reactions (IDRs) suggest that they are immune mediated. Penicillamine-induced autoimmunity in Brown Norway rats was used as a tool for mechanistic studies of this type of IDR. It has been shown that T helper 17 (Th17) cells play a central role in many types of autoimmune diseases. This study was designed to test whether Th17 cells are involved in the pathogenesis of penicillamine-induced autoimmunity. In sick animals, interleukin (IL) 6 and transforming growth factor-β1, known to be driving forces of Th17 differentiation, were consistently increased following penicillamine treatment. IL-17 and IL-22, characteristic cytokines produced by Th17 cells, were increased in sick animals. Furthermore, the percentage of IL-17-producing CD4 T cells was significantly increased, but only in sick animals. Retinoic acid, which has been reported to inhibit Th17 cell development, made the autoimmunity worse, increased IL-6 production, and did not decrease the number of Th17 cells. An infiltration of CD8 cytotoxic T cells in the liver suggests that they may be the key player in causing liver toxicity induced by D-penicillamine. Drug-induced liver injury (DILI) is one of the major causes of morbidity, mortality, and drug candidate failure. Recently, it has been suggested that Th17 cells may play an active role in inflammatory human liver diseases. In a study of patients being treated with isoniazid, some patients developed mild liver injury. The percentage of Th17 cells in the blood of these patients significantly increased when the ALT increased, and this suggests that they play a role in the mechanism of this liver injury. Furthermore, IL-10-producing T cells also increased and this may have prevented the development of severe liver injury. In another study, two hours after treatment of mice with acetaminophen there was a significant increase in Th17 cells in the liver. This rapid response suggests that Th17 cells can be part of the innate immune response to liver injury. Our data provided evidence that Th17 cells are involved in both “toxic” and idiosyncratic liver toxicity. This pathway could be a new target for the therapeutic interventions to treat DILI.

Mercury is an environmental contaminant of global concern. The distribution of mercury in freshwater systems is poorly characterized in Mexico, despite widespread contamination from industrial and urban effluents. The land use, geology, and hydrology of the Lake Zapotlán basin, Mexico are conducive to the delivery of elevated mercury in water to the lake due to untreated wastewater discharge, deforestation, and local volcanic history. To assess a mercury exposure risk to fish consumers, the concentrations of total Hg (THg) in water inputs, surface waters, sediments, and the commercial catch of tilapia and carp were investigated. Results indicate that despite high particle-bound inputs of THg to the lake in runoff and wastewater, THg in sediments and surface waters were low. Dense Typha latifolia dominated wetlands are believed to retain THg inflow from water inputs. Concentrations of THg in tilapia and carp were low, suggesting low mercury bioavailability in this system.

An animal model of nevirapine (NVP)-induced skin rash was used to test the hypothesis that sulfonation of 12-OH NVP, a metabolite of NVP proven essential for rash development, is the link between 12-OH NVP and the skin rash. Female Brown Norway (BN) rats were co-treated with NVP or 12-OH NVP and sulfation inhibitors dehydroepiandrosterone (DHEA) and salicylamide. Co-treatment with salicylamide markedly decreased formation of the sulfate conjugate but did not prevent development of the rash suggesting that the sulfate is not involved. However, it is not known whether the sulfate formation in the skin was affected. Co-treatments with DHEA decreased the sulfate formation and prevented the rash but also had other effects on NVP metabolism. This implies that the sulfate metabolite is responsible for the rash. Additional studies will be required to resolve these conflicting results.

An animal model of nevirapine (NVP)-induced skin rash was used to test the hypothesis that sulfonation of 12-OH NVP, a metabolite of NVP proven essential for rash development, is the link between 12-OH NVP and the skin rash. Female Brown Norway (BN) rats were co-treated with NVP or 12-OH NVP and sulfation inhibitors dehydroepiandrosterone (DHEA) and salicylamide. Co-treatment with salicylamide markedly decreased formation of the sulfate conjugate but did not prevent development of the rash suggesting that the sulfate is not involved. However, it is not known whether the sulfate formation in the skin was affected. Co-treatments with DHEA decreased the sulfate formation and prevented the rash but also had other effects on NVP metabolism. This implies that the sulfate metabolite is responsible for the rash. Additional studies will be required to resolve these conflicting results.

Recent epidemiological evidence suggests that many chronic health disorders in the developed world are associated with endogenous toxins formed from the Western diet. The Western diet, which encompasses calorie dense foods, processed foods and increased quantities of red meat, can cause intracellular oxidative stress through increased formation of reactive oxygen species(ROS) and reactive carbonyl species (RCS). A number of micronutrients have been investigated for their protective capacity in in vitro and in vivo models of oxidative stress. This thesis investigated the cytotoxic targets of Fenton-mediated ROS and RCS and the subsequent protective mechanisms of vitamins B1 (thiamin) or B6 (pyridoxal, pyridoxamine or pyridoxine) in an isolated rat hepatocyte model. The approach was to use an “accelerated cytotoxicity mechanism screening” technique (ACMS) to develop an in vitro cell system that mimicked in vivo tissue cytotoxicity. Using this technique, we investigated the protective mechanisms of vitamins B1 and/or B6 against the cytotoxic effects of two endogenous toxins associated with the Western diet: 1) RCS, as exemplified by glyoxal, a glucose/fructose autoxidation product and 2) biological ROS induced by exogenous iron. Firstly, we developed an understanding of the sequence of events contributing to glyoxal-induced oxidative stress, with a focus on protein carbonylation. Next, we determined the mechanisms by which carbonyl scavenging drugs (vitamin B6 included) protected against the intracellular targets of glyoxal-induced toxicity. Our results suggested that the agents used were cytoprotective by multiple mechanisms and glyoxal trapping was only observed when the agents were administered at concentrations equal to glyoxal. We also evaluated the protective capacity of vitamins B1 and B6 against iron-catalyzed cytotoxicity and found that hepatocytes could be rescued from protein and DNA damage when vitamins B1 or B6 were added up to one hour after treatment with iron. The vitamins also varied in their primary mechanisms of protection. Our improved understanding of Western diet-derived endogenous toxins enabled us to identify and prioritize the specific inhibitory mechanisms of vitamins B1 or B6. The ability to delay, inhibit or reverse toxicity using multi-functional B1 or B6 vitamins could prove useful as therapy to minimize oxidative stress in diet-induced chronic conditions.

Mercury is an environmental contaminant of global concern. The distribution of mercury in freshwater systems is poorly characterized in Mexico, despite widespread contamination from industrial and urban effluents. The land use, geology, and hydrology of the Lake Zapotlán basin, Mexico are conducive to the delivery of elevated mercury in water to the lake due to untreated wastewater discharge, deforestation, and local volcanic history. To assess a mercury exposure risk to fish consumers, the concentrations of total Hg (THg) in water inputs, surface waters, sediments, and the commercial catch of tilapia and carp were investigated. Results indicate that despite high particle-bound inputs of THg to the lake in runoff and wastewater, THg in sediments and surface waters were low. Dense Typha latifolia dominated wetlands are believed to retain THg inflow from water inputs. Concentrations of THg in tilapia and carp were low, suggesting low mercury bioavailability in this system.

Gestational diabetes, a common medical complication in pregnancy, may lead to severe fetal consequences if left untreated. A major concern with the use of antidiabetic drugs in pregnancy is the potential for placental transfer and fetal toxicity. The presence of endocytic pathways and several ABC transporter proteins has been demonstrated in the human placenta and are believed to play an important role in determining fetal exposure to drugs used in pregnancy. The objective of this thesis is to investigate the safety and transfer of the oral hypoglycemic agent, glyburide, and the new long acting insulin analog, insulin glargine, across the human placenta. The oral antidiabetic, glyburide, has been shown to be actively effluxed across the placenta in the fetal to maternal direction. The transport of glyburide in the presence of a breast cancer resistance protein (BCRP) inhibitor was investigated in the dually perfused human placenta model. The results of the perfusion studies indicate that BCRP plays a role in protecting the fetus from the accumulation of glyburide. Subsequently, cellular studies were carried out to determine the effect of the naturally occurring single nucleotide polymorphism within the coding region of BCRP (C421A/Q141K) on glyburide transport. Results suggest that glyburide transport may be reduced in the presence of the Q141K polymorphism. While insulin remains as the gold standard, the potential for maternal hypoglycemia with insulin injection has resulted in the development of insulin analogs. Insulin glargine, a human insulin analog, has a long half life with no pronounced peak when compared to currently used NPH insulin. Human placental perfusion experiments examining the extent and rate of transfer of insulin glargine across the placenta demonstrated that, at therapeutic concentrations, insulin glargine does not cross the placenta to a measurable extent. To further determine the fetal safety of insulin glargine therapy compared with NPH insulin, a systematic review and meta-analysis were performed. No evidence was identified for increased adverse fetal outcomes with the use of insulin glargine during pregnancy. Overall, the results of this research serve to provide improved treatment options for women with diabetes in pregnancy.

Recent epidemiological evidence suggests that many chronic health disorders in the developed world are associated with endogenous toxins formed from the Western diet. The Western diet, which encompasses calorie dense foods, processed foods and increased quantities of red meat, can cause intracellular oxidative stress through increased formation of reactive oxygen species(ROS) and reactive carbonyl species (RCS). A number of micronutrients have been investigated for their protective capacity in in vitro and in vivo models of oxidative stress. This thesis investigated the cytotoxic targets of Fenton-mediated ROS and RCS and the subsequent protective mechanisms of vitamins B1 (thiamin) or B6 (pyridoxal, pyridoxamine or pyridoxine) in an isolated rat hepatocyte model. The approach was to use an “accelerated cytotoxicity mechanism screening” technique (ACMS) to develop an in vitro cell system that mimicked in vivo tissue cytotoxicity. Using this technique, we investigated the protective mechanisms of vitamins B1 and/or B6 against the cytotoxic effects of two endogenous toxins associated with the Western diet: 1) RCS, as exemplified by glyoxal, a glucose/fructose autoxidation product and 2) biological ROS induced by exogenous iron. Firstly, we developed an understanding of the sequence of events contributing to glyoxal-induced oxidative stress, with a focus on protein carbonylation. Next, we determined the mechanisms by which carbonyl scavenging drugs (vitamin B6 included) protected against the intracellular targets of glyoxal-induced toxicity. Our results suggested that the agents used were cytoprotective by multiple mechanisms and glyoxal trapping was only observed when the agents were administered at concentrations equal to glyoxal. We also evaluated the protective capacity of vitamins B1 and B6 against iron-catalyzed cytotoxicity and found that hepatocytes could be rescued from protein and DNA damage when vitamins B1 or B6 were added up to one hour after treatment with iron. The vitamins also varied in their primary mechanisms of protection. Our improved understanding of Western diet-derived endogenous toxins enabled us to identify and prioritize the specific inhibitory mechanisms of vitamins B1 or B6. The ability to delay, inhibit or reverse toxicity using multi-functional B1 or B6 vitamins could prove useful as therapy to minimize oxidative stress in diet-induced chronic conditions.