published_or_final_version / abstract / Pathology / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / abstract / toc / Pathology / Doctoral / Doctor of Philosophy

published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

No description available.

A large and varied array of xenobiotics (foreign chemicals) enters into our bodies every day. In order to prevent toxicity resulting from xenobiotic accumulation, the body has developed a complex and integrated network of enzymes and transporters to promote and control the metabolism and excretion of drugs and other compounds. Drug metabolizing enzymes are classified as oxidative (Phase I) or conjugative (Phase II), and generally result in increased hydrophilicity of their substrates. Drug transporters actively route xenobiotics into (Phase 0) or out of (Phase III) the cells. The expression of the proteins involved in drug metabolism and transport are coordinately regulated by xenosensing transcription factors, including the constitutive androstane receptor, the pregnane X receptor, the aryl hydrocarbon receptor, and Nrf2. Through the activation of these xenosensors, chemical exposure itself induces the processes which help to remove the xenobiotics from the body. The liver is the major organ of drug metabolism in the body. Chronic hepatic diseases impact the activity of xenosensors and the expression of their enzyme and transporter gene targets. Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease in the United States, affecting 20-30% of the populations. This profoundly underdiagnosed disease has significant effects on hepatic gene expression and may increase the risk of adverse drug reactions and xenobiotic toxicity in affected patients. This manuscript presents original research which contributes to our understanding of xenosensor function in the contexts of chemical exposure and liver disease. Manuscripts in this dissertation investigate 1) the induction profile and mechanisms of the experimental therapeutic agent oltipraz, 2) the xenosensor-regulated mechanisms of induction of the drug transporter ABCC3, 3) the impact of NAFLD on the expression of major drug metabolizing enzymes, and 4) the utility of altered drug disposition as a biomarker for NAFLD progression. The findings of these studies highlight the clinical importance of xenosensor activation and the potential pharmacological and toxicological consequences of hepatic disease.

No description available.

No description available.

It has been demonstrated that 1,25 dihydroxy vitamin D3 (1,25 (OH)2VD3) can inhibit the proliferation of cancer cells including colorectal and hepatocellular cells which are mainly responsible for liver cancer. However, the use of 1, 25 (OH)2VD3 is hampered due to the development of hypercalcaemia. Current treatment using hepatic arterial delivery of drug solution is inconvenient since repetitive invasive treatments are required. This work aims to tackle this problem by utilizing crosslinked microspheres prepared by suspension polymerization as a carrier to control the release of 1, 25 (OH)2VD3 or hydrophobic drug in general at targeted sites over a long period. Poly(vinyl neodecanoate crosslinked ethyleneglycol dimethacrylate) microspheres in the size range of 35 m were prepared via suspension polymerization. Different parameters in suspension polymerization such as temperature, concentration and crosslinker percentage were studied in details. The effect of stabilizer on the formation of spheres was carefully investigated by using RAFT polymerization to produce various structures of the stabilizer, poly (vinyl pyrrolidone). Core- shell microspheres were also produced to enhance the hydrophilicity of the surface of microspheres. Hydrophobic drugs were loaded to these microspheres after reaction by the evaporation method. These microspheres were then used for drug loading and drug release study. Release study has shown that up to 10% of drug was released after 40 days. Cytotoxicity test reveals the suitability of this polymer for application in biomedical field. The MTT assay of Clofazimine loaded microspheres on the colorectal cancer cell lines HT29 has shown that the cell number was decreased about 50% after drug treatment.

Obesity and type 2 diabetes are the most prevalent metabolic diseases in the western world and affect over 50% of the world’s population. During obesity non-adipose tissues such as the liver and skeletal muscle take up and store excess fatty acids (FA) as lipids such as triacylglycerols (TAG) and diacylglycerols (DAG). Excessive lipid storage in non-adipose tissues can result in the dysfunction of cellular processes and lead to programmed cell death (apoptosis). Lipid-induced apoptosis was investigated in the key glucoregulatory tissues, the liver and skeletal muscle. Lipid-induced apoptosis was detected in vitro in both hepatocytes and myotubes but was not detected in the livers or skeletal muscles of genetically obese mice or high-fat fed mice. Further investigation discovered despite exacerbated TAG accumulation, endoplasmic reticulum stress (ER) was not activated in the liver and pathways of cellular remodelling (proteolysis and autophagy) were not initiated in skeletal muscle. These studies demonstrated that the liver and skeletal muscle are adaptable to increased lipid storage in physiological models but not isolated cell culture systems. In vitro experiments demonstrated unsaturated FAs could protect hepatocytes from lipoapoptosis and it has been suggested this is due to driving FA accumulation into TAG lipid droplets. Adipose triglyceride lipase (ATGL) is one of the primary TAG lipases. To explore TAG metabolism in the liver, primary hepatocytes were derived from ATGL null mice and ATGL was over-expressed in the livers of chronically obese mice. / It was found that cellular FA uptake and TAG esterification was increased and TAG lipolysis and FA oxidation were decreased in the ATGL null hepatocytes. This resulted in exacerbated TAG and diacylglycerol (DAG) storage. The gene expression of metabolic regulators such as cytochrome c oxidase subunit 2 (COX2), medium chain acyl Co-A dehydrogenase (MCAD), peroxisome proliferators-activated receptor co-activator 1! (PGC1!), nuclear respiratory factor 1 (NRF1) and FA translocase/cluster of differentiation 36 (FAT/CD36) were increased in ATGL null hepatocytes compared with wild type hepatocytes, suggesting that the reduction in FA oxidation in the ATGL null hepatocytes was probably due to limited FA substrate availability. Interestingly, despite increased TAG and DAG, the hepatocytes remained insulin sensitive. To investigate hepatic ATGL over-expression an adenovirus containing an ATGL insert was injected into chronic high fat fed mice. Hepatic ATGL over-expression in the iii chronically obese mice reduced TAG, DAG and ceramide content in the liver. This resulted in improved hepatic insulin signalling and whole body insulin sensitivity. In summary, studies from this thesis suggested the use of in vitro systems are not a substitute for in vivo models when assessing the toxic effects of lipid oversupply, TAG accumulation may be a protective mechanism against cellular remodelling and programmed cell death, and increased ATGL expression in the liver can reduce hepatic steatosis and enhance whole body insulin sensitivity. Therefore, increasing hepatic ATGL expression could be a therapeutic approach to treat obesity and type 2 diabetes.