published_or_final_version / abstract / Surgery / Master / Master of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Thesis advisor: Steven D. Bruner / Complex and unique enzymology is often behind the biosynthesis of natural products. This thesis is focused on how non-proteinogenic amino acids are biosynthesized and then incorporated into natural products. Chapters two, three and four deal with a unique dioxygenase found in vancomycin biosynthesis. Chapter five elaborates on the biochemical characterization along with efforts toward structural characterization of a terminal non-ribosomal peptide synthetase module. The vancomycin biosynthetic enzyme DpgC belongs to a small class of oxygenation enzymes that are not dependent on an accessory cofactor or metal ion. The detailed mechanism of cofactor-independent oxygenases has not been established. We have solved the first structure of an enzyme of this oxygenase class complexed with a bound substrate mimic. The use of a designed, synthetic substrate analog allows unique insights into the chemistry of oxygen activation. The structure confirms the absence of cofactors, and electron density consistent with molecular oxygen is present adjacent to the site of oxidation on the substrate. Molecular oxygen is bound in a small hydrophobic pocket and the substrate provides the reducing power to activate oxygen for downstream chemical steps. Our results resolve the unique and complex chemistry of DpgC, a key enzyme in the biosynthetic pathway of an important class of antibiotics. Mechanistic parallels exist between DpgC and cofactor-dependent flavoenzymes, providing information regarding the general mechanism of enzymatic oxygen activation. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis (M. Med. Sc.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 46-57)

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Abstract Lysyl hydroxylase (EC 1.14.11.4, procollagen-lysine 2-oxoglutarate 5-dioxygenase, PLOD) catalyzes the hydroxylation of lysine residues in collagens and other proteins. It occurs as a post-translational event. The hydroxylysine residues participate in the formation of covalent cross-links to stabilize the collagenous structure in tissues. The hydroxylysine residues can be glycosylated to galactosyl- or glucosylgalactosylhydroxylysine residues. Novel human lysyl hydroxylases, 2a, 2b and 3 isoforms, were characterized in this study. Lysyl hydroxylases 2a and 2b are alternatively spliced forms of lysyl hydroxylase 2. Lysyl hydroxylase 2b contains an additional exon of 63 nucleotides. The polypeptide size of lysyl hydroxylase 2a is 737 amino acids, lysyl hydroxylase 2b is 758 amino acids and lysyl hydroxylase 3 is 738 amino acids. The putative signal peptide is 25 amino acids in lysyl hydroxylases 2a and 2band 24 amino acids in lysyl hydroxylase 3. Lysyl hydroxylases 2aand 2b contain 7 possible N-glycosylation sites and lysyl hydroxylase3 contains 2 sites. Tissue distribution of novel isoforms were studied on Northern blots. The expression of lysyl hydroxylases 2a, 2b and 3 differ from the expression of previously characterized lysyl hydroxylase 1. Lysyl hydroxylase 1 is expressed constitutively in all tissues whereas the expression of novel isoforms is more strictly regulated. Lysyl hydroxylase 2 is highly expressed in heart, placenta, liver and pancreas. Lysyl hydroxylase 2b expression is highest in heart and skeletal muscle and lysyl hydroxylase 3 expression is highest in heart, placenta and pancreas. Brain, lung and kidney contain the lowest amounts of these isoforms. Novel isoforms were expressed as recombinant proteins in baculovirus expression system in vitro. All these novel isoforms were able to hydroxylate lysine residues in short collagenous peptides. A more detailed kinetic analysis was performed on lysyl hydroxylase 2a and 2b in order to find out if they differed from each other. The binding affinity of ascorbate and peptide substrate is different in lysyl hydroxylase 2a from 2b. Chromosomal assignments were carried out on human lysyl hydroxylases 2 and 3. Lysyl hydroxylase 2 was localized to chromosome 3q23–q24 and lysyl hydroxylase 3 to chromosome 7q36.

No description available.

Wang, Ruizhi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 109-134). / Abstracts in English and Chinese. / Acknowledgement --- p.i / Publications --- p.ii / Abstract --- p.iv / 中文摘要 --- p.viii / Abbreviations --- p.xi / List of tables --- p.xiv / List of figures --- p.xv / Contents --- p.xvii / Chapter Chapter One: --- Introduction --- p.1 / Chapter 1.1 --- Epidemiology of gastric cancer --- p.2 / Chapter 1.2 --- Risk factors of gastric cancer --- p.3 / Chapter 1.3 --- Treatment of gastric cancer --- p.4 / Chapter 1.3.1 --- Surgical treatment --- p.4 / Chapter 1.3.2 --- Chemotherapy --- p.4 / Chapter 1.3.3 --- Targeted therapy --- p.5 / Chapter 1.4 --- "Phenotypes of cell death: apoptosis, oncosis and autophagy" --- p.9 / Chapter 1.4.1 --- Cell death --- p.9 / Chapter 1.4.2 --- Apoptosis --- p.10 / Chapter 1.4.2 --- Oncosis --- p.11 / Chapter 1.4.3 --- Autophagy --- p.12 / Chapter 1.4.4 --- p53 --- p.13 / Chapter 1.5 --- Heme oxygenase-1 --- p.14 / Chapter 1.5.1 --- General introduction of Heme oxygenase --- p.14 / Chapter 1.5.2 --- Anti-oxidant function of HO-1 --- p.15 / Chapter 1.5.3 --- Anti-inflammation function of HO-1 --- p.17 / Chapter 1.5.4 --- Pro-angiogenesis role of HO-1 --- p.18 / Chapter 1.5.5 --- HO-1 and cell proliferation --- p.19 / Chapter 1.5.6 --- HO-1 as a therapeutic target for tumors --- p.20 / Chapter 1.6 --- Objectives of study --- p.22 / Chapter Chapter Two: --- Methods and materials --- p.26 / Chapter 2.1 --- Gastric cancer cell lines --- p.27 / Chapter 2.2 --- Cell proliferation detection --- p.27 / Chapter 2.2.1 --- "MTT(3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)assay" --- p.27 / Chapter 2.2.1.1 --- Introduction of MTT assay --- p.27 / Chapter 2.2.1.2 --- Processes of MTT assay --- p.27 / Chapter 2.2.1.3 --- Cell proliferation and cytotoxicity of drugs --- p.28 / Chapter 2.2.2 --- Detection of apoptosis by TUNEL assay --- p.29 / Chapter 2.2.2.1 --- TUNEL (Terminal uridine deoxynucleotidyl transferase dUTP nick end labeling) --- p.29 / Chapter 2.2.2.2 --- Sample preparation --- p.29 / Chapter 2.3 --- Detection of cell cycle by flow cytometry --- p.32 / Chapter 2.3.1 --- Cell cycle --- p.32 / Chapter 2.3.2 --- Sample preparation --- p.33 / Chapter 2.3.3 --- Flow cytometry analysis --- p.34 / Chapter 2.4 --- Detection of mitochondrial membrane potential(ΔΨm) --- p.35 / Chapter 2.4.1 --- Sample preparation --- p.35 / Chapter 2.4.2 --- Mitochondrial membrane potential(ΔΨm) analysis by flow cytometry --- p.36 / Chapter 2.5 --- Detection of proteins investigated in the project --- p.37 / Chapter 2.5.1 --- Antibodies --- p.37 / Chapter 2.5.2 --- Sample Preparation --- p.39 / Chapter 2.5.2.1 --- Cell culture --- p.39 / Chapter 2.5.2.2 --- Protein extraction --- p.39 / Chapter 2.5.2.3 --- Protein assay --- p.41 / Chapter 2.5.2.4 --- Final loading protein --- p.42 / Chapter 2.5.3 --- Western blotting --- p.43 / Chapter 2.6 --- Statistical analysis --- p.45 / Chapter Chapter three: --- Roles of HO-1 in 5-FU treatment for gastric cancer cell lines --- p.47 / Chapter 3.1 --- Cell proliferations with drug treatments --- p.48 / Chapter 3.1.1 --- MTT assay --- p.48 / Chapter 3.1.1.1 --- Introduction --- p.48 / Chapter 3.1.1.2 --- Method and results --- p.49 / Chapter 3.1.2 --- TUNEL assay --- p.58 / Chapter 3.1.2.1 --- Introduction --- p.58 / Chapter 3.1.2.2 --- Method and results --- p.59 / Chapter 3.2 --- HO-1 expression with drug treatments --- p.63 / Chapter 3.2.1 --- Introduction --- p.63 / Chapter 3.2.2 --- Method and results --- p.64 / Chapter 3.3 --- Discussion --- p.72 / Chapter Chapter Four: --- Mechanism responsible for the additive effect of 5-FU and ZnPP --- p.77 / Chapter 4.1 --- Cell cycle arrest after drug treatments --- p.78 / Chapter 4.1.1 --- Introduction --- p.78 / Chapter 4.1.2 --- Method and results --- p.79 / Chapter 4.2 --- Mitochondrial dependent and independent pathway --- p.85 / Chapter 4.2.1 --- Introduction --- p.85 / Chapter 4.2.2 --- Method and results --- p.87 / Chapter 4.3 --- Alteration of apoptotic proteins in gastric cancer cell death after drug treatments --- p.91 / Chapter 4.3.1 --- Introduction --- p.91 / Chapter 4.3.2 --- Method and results --- p.94 / Chapter 4.4 --- Discussion --- p.101 / Chapter Chapter Five: --- Summary and future prospects --- p.107 / Chapter 5.1 --- Summary --- p.108 / Chapter 5.1.1. --- The inhibition of HO-1 enhances the sensitivity of gastric cancer cells to 5-FU --- p.108 / Chapter 5.1.2 --- Apoptosis induced by 5-FU plus HO-1 inhibitor ZnPP is through a mitochondrial-related pathway in MKN28 and MKN45 --- p.109 / Chapter 5.1.3 --- 5-FU plus ZnPP induces apoptosis in a caspase-dependent pathway in MKN45 while in both caspase-dependent and caspase-independent pathway in MKN28 --- p.110 / Chapter 5.2 --- Future prospects --- p.111 / References --- p.113

Essential hypertension (EH) is a risk factor for many cardiovascular disorders. Treatment of established EH, especially for prolonged control of this pathogenic process, represents a great challenge. Moreover, hypertension is considered an important risk factor for the development of many other diseases, e.g. erectile dysfunction. <p> Hemin and other heme derivatives, e.g. heme-L-lysinate (HLL) and heme-L-arginate, have been used extensively to upregulate expression of heme oxygenase (HO) and production of endogenous carbon monoxide (CO). Short-term hemin administration for 4-5 days has been shown to markedly decrease high blood pressure (BP) in spontaneously hypertensive rats (SHR), but not in normotensive Wistar-Kyoto (WKY) or Sprague Dawley (SD) rats. This short-term therapy was effective in treating young, but not adult SHR. In the present study, hemin (15 mg/kg/day) was administered to 12-week old adult SHR through subcutaneously implanted osmotic minipumps for 3 consecutive weeks (the hemin protocol). Into the second week of the hemin protocol, BP of SHR was normalized from 203.2 ± 2.5 to 123.4 ±1.9 mmHg (n=20, p<0.001). There was no further decrease of BP in the remaining days of the hemin protocol. Normalization of BP in these treated SHR was maintained for 9 months after the removal of hemin pumps. <p>To further investigate the metabolic characteristics of hemin during hemin protocol administration, we attempted to monitor circulatory heme levels. A valid standard calibration curve was established using hemin or HLL in <i>in vitro</i> experiments. It was established that the basal serum level of heme was negligible in all rat strains prior to hemin protocol initiation. During the hemin protocol, serum heme level of all rats was significantly elevated; however, it quickly dropped to basal levels thereafter. <p>At the end of the 3-week hemin protocol, HO-1 expression, HO activity, soluble guanylyl cyclase (sGC) expression, and cyclic guanosine monophosphate (cGMP) content were all increased, but phosphodiesterase-5 (PDE-5) expression was down-regulated in the mesenteric arteries. The hemin protocol also reversed SHRs decreased arterial lumen size, and increased expression levels of vascular endothelial growth factor. These changes lasted 9 months after the hemin protocol. The hemin protocol did not cause hepatic or renal toxicity. Our study thus unmasks a novel hemin protocol that will not only normalize BP in SHR with established hypertension but, more importantly, also provide long-lasting anti-hypertension protection. Sustained upregulation of the HO-regulated signaling pathways and reversal of vascular remodeling in small peripheral vessels in treated SHR are among potential underlying mechanisms for the anti-hypertensive effect of the hemin protocol.<p>We further studied if the beneficial effects of hemin protocol on BP of SHR could be extended to improvement of their penile erection. Intracavernosal pressure changes after electrical stimulation of the cavernous nerve (CN) were monitored in adult SHR and age-matched normotensive SD rats after administration of either hemin or hydralazine. Expression levels of HO-1, HO-2, sGC, and PDE-5 in penile tissues were also examined. Frequency-dependent intracavernosal pressure (ICP) changes were reduced in adult SHR. Three weeks after hemin treatment, ICP responses to CN stimulations were significantly increased to the level of normotensive rats, which was linked to normalization of BP of hemin-treated SHR. Hydralazine-treated SHR experienced normalization of BP but not ICP after 3 weeks of treatment. Expression of HO-1 and sGC was upregulated and that of PDE-5 downregulated in hemin-treated SHR. Decreased ICP response in adult SHR can be improved through chronic hemin treatment of SHR. Prolonged upregulation of HO-1 and sGC as well as lowered expression of PDE-5 may account for normalization of erectile dysfunction in SHR subsequent to hemin treatment. <p>This thesis reports for the first time that 21-day hemin administration led to a 9-month normalization of high BP of adult SHR. These effects were mediated through sustained stimulation of the HO/CO system and its downstream effectors targets. Increased activity of HO-1 led to normalization of the abnormally high expression level of VEGF in peripheral mesenteric arteries of adult SHR. Subsequently, this resulted in reversal of the eutrophic remodeling of these arteries, which seems to be the priniciple determinant of the long-term normalization of BP observed for 9 months after stoppage of hemin treatment. The invention of hemin protocol offers a new therapeutic approach for the clinical management of established hypertension for a long duration.<p>Our study, for the first time, correlated changes in serum heme levels with BP levels after injection of hemin or HLL in normotensive and hypertensive rats. Application of this heme monitoring technology will also pave the way for clinical application of hemin therapy in treatment of EH.<p> Another intriguing finding in this thesis is that upregulation of HO-1, through the hemin protocol, led to improvement of abnormally low ICP encountered in adult SHR. Upregulation of HO-1 may represent a novel therapeutic approach to treat hypertension-related erectile dysfunction.

Essential hypertension (EH) is a risk factor for many cardiovascular disorders. Treatment of established EH, especially for prolonged control of this pathogenic process, represents a great challenge. Moreover, hypertension is considered an important risk factor for the development of many other diseases, e.g. erectile dysfunction. <p> Hemin and other heme derivatives, e.g. heme-L-lysinate (HLL) and heme-L-arginate, have been used extensively to upregulate expression of heme oxygenase (HO) and production of endogenous carbon monoxide (CO). Short-term hemin administration for 4-5 days has been shown to markedly decrease high blood pressure (BP) in spontaneously hypertensive rats (SHR), but not in normotensive Wistar-Kyoto (WKY) or Sprague Dawley (SD) rats. This short-term therapy was effective in treating young, but not adult SHR. In the present study, hemin (15 mg/kg/day) was administered to 12-week old adult SHR through subcutaneously implanted osmotic minipumps for 3 consecutive weeks (the hemin protocol). Into the second week of the hemin protocol, BP of SHR was normalized from 203.2 ± 2.5 to 123.4 ±1.9 mmHg (n=20, p<0.001). There was no further decrease of BP in the remaining days of the hemin protocol. Normalization of BP in these treated SHR was maintained for 9 months after the removal of hemin pumps. <p>To further investigate the metabolic characteristics of hemin during hemin protocol administration, we attempted to monitor circulatory heme levels. A valid standard calibration curve was established using hemin or HLL in <i>in vitro</i> experiments. It was established that the basal serum level of heme was negligible in all rat strains prior to hemin protocol initiation. During the hemin protocol, serum heme level of all rats was significantly elevated; however, it quickly dropped to basal levels thereafter. <p>At the end of the 3-week hemin protocol, HO-1 expression, HO activity, soluble guanylyl cyclase (sGC) expression, and cyclic guanosine monophosphate (cGMP) content were all increased, but phosphodiesterase-5 (PDE-5) expression was down-regulated in the mesenteric arteries. The hemin protocol also reversed SHRs decreased arterial lumen size, and increased expression levels of vascular endothelial growth factor. These changes lasted 9 months after the hemin protocol. The hemin protocol did not cause hepatic or renal toxicity. Our study thus unmasks a novel hemin protocol that will not only normalize BP in SHR with established hypertension but, more importantly, also provide long-lasting anti-hypertension protection. Sustained upregulation of the HO-regulated signaling pathways and reversal of vascular remodeling in small peripheral vessels in treated SHR are among potential underlying mechanisms for the anti-hypertensive effect of the hemin protocol.<p>We further studied if the beneficial effects of hemin protocol on BP of SHR could be extended to improvement of their penile erection. Intracavernosal pressure changes after electrical stimulation of the cavernous nerve (CN) were monitored in adult SHR and age-matched normotensive SD rats after administration of either hemin or hydralazine. Expression levels of HO-1, HO-2, sGC, and PDE-5 in penile tissues were also examined. Frequency-dependent intracavernosal pressure (ICP) changes were reduced in adult SHR. Three weeks after hemin treatment, ICP responses to CN stimulations were significantly increased to the level of normotensive rats, which was linked to normalization of BP of hemin-treated SHR. Hydralazine-treated SHR experienced normalization of BP but not ICP after 3 weeks of treatment. Expression of HO-1 and sGC was upregulated and that of PDE-5 downregulated in hemin-treated SHR. Decreased ICP response in adult SHR can be improved through chronic hemin treatment of SHR. Prolonged upregulation of HO-1 and sGC as well as lowered expression of PDE-5 may account for normalization of erectile dysfunction in SHR subsequent to hemin treatment. <p>This thesis reports for the first time that 21-day hemin administration led to a 9-month normalization of high BP of adult SHR. These effects were mediated through sustained stimulation of the HO/CO system and its downstream effectors targets. Increased activity of HO-1 led to normalization of the abnormally high expression level of VEGF in peripheral mesenteric arteries of adult SHR. Subsequently, this resulted in reversal of the eutrophic remodeling of these arteries, which seems to be the priniciple determinant of the long-term normalization of BP observed for 9 months after stoppage of hemin treatment. The invention of hemin protocol offers a new therapeutic approach for the clinical management of established hypertension for a long duration.<p>Our study, for the first time, correlated changes in serum heme levels with BP levels after injection of hemin or HLL in normotensive and hypertensive rats. Application of this heme monitoring technology will also pave the way for clinical application of hemin therapy in treatment of EH.<p> Another intriguing finding in this thesis is that upregulation of HO-1, through the hemin protocol, led to improvement of abnormally low ICP encountered in adult SHR. Upregulation of HO-1 may represent a novel therapeutic approach to treat hypertension-related erectile dysfunction.