by Cheng Sau-kwan. / Thesis (M.Sc.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 98-106). / LIST OF TABLES / LIST OF FIGURES / ACKNOWLEDGEMENTS / ABSTRACT --- p.1 / Chapter CHAPTER ONE --- p.3 / Chapter 1.1 --- Introduction --- p.3 / Chapter 1.1.1 --- Sources of homocysteine and origins of deficiency or excess in the human body --- p.3 / Chapter 1.1.2 --- Homocysteine metabolism --- p.4 / Chapter 1.2 --- Causes of and clinical syndromes in homocysteinaemia --- p.12 / Chapter 1.2.1 --- Deficiency of cystathionine β-synthase --- p.12 / Chapter 1.2.1.1a --- Homozygous homocysteinaemia --- p.13 / Chapter 1.2.1.1b --- Heterozygous hyperhomocysteinaemia --- p.17 / Chapter 1.2.2 --- "Deficiency of 5, 10 methylenetetrahydrofolate reductase" --- p.20 / Chapter 1.2.3 --- Defects of cobalamin synthesis --- p.21 / Chapter 1.3 --- Standardised oral methionine load test --- p.23 / Chapter 1.4 --- Treatment and prospects for homocysteinaemia --- p.25 / Chapter 1.4.1 --- Homozygous homocysteinaemia --- p.25 / Chapter 1.4.2 --- Heterozygous homocysteinaemia --- p.27 / Chapter 1.5 --- Pathogenesis of vascular disease in homocystinuria --- p.28 / Chapter 1.6 --- Aim of the study --- p.30 / Chapter CHAPTER TWO --- p.31 / Chapter 2.1 --- Patient's criteria --- p.31 / Chapter 2.2 --- Control' s criteria --- p.32 / Chapter 2.3 --- Exclusion criteria for patients and controls --- p.32 / Chapter 2.4 --- The methionine loading test and additional investigations carried out --- p.33 / Chapter 2.5 --- Statistics used for data analyses --- p.35 / Chapter CHAPTER THREE --- p.38 / Chapter 3.1 --- Sample collection --- p.38 / Chapter 3.2 --- Analytical methods for homocysteine determination --- p.39 / Chapter 3.2.1 --- Cyanide nitroprusside test --- p.39 / Chapter 3.2.2 --- Radioenzymic Assays --- p.40 / Chapter 3.2.3 --- Gas chromatography - Mass spectrometry --- p.41 / Chapter 3.2.4 --- HPLC with Electrochemical detection --- p.42 / Chapter 3.2.5 --- HPLC and postcolumn derivatization --- p.43 / Chapter 3.2.6 --- "Precolumn derivatization, HPLC and fluorescence detection" --- p.44 / Chapter 3.3 --- The method used in this study --- p.47 / Chapter 3.3.1 --- Materials --- p.48 / Chapter 3.3.2 --- Reagents --- p.49 / Chapter 3.3.3 --- Instrumentation --- p.49 / Chapter 3.3.4 --- Sample preparation --- p.50 / Chapter 3.3.4.1 --- Reduction --- p.50 / Chapter 3.3.4.2 --- Derivatization --- p.50 / Chapter 3.3.5 --- Chromatographic conditions --- p.51 / Chapter 3.3.6 --- Standard preparation --- p.51 / Chapter 3.4 --- Method Optimization --- p.52 / Chapter 3.4.1 --- Choice of reducing agent --- p.52 / Chapter 3.4.1.1 --- Dithiotreitol (DTT) --- p.52 / Chapter 3.4.1.2 --- Sodium borohydride --- p.53 / Chapter 3.4.2 --- Choice of precipitating reagent --- p.56 / Chapter 3.4.3 --- Optimization of chromatographic conditions --- p.56 / Chapter 3.4.3.1 --- "Flow rate, temperature and organic composition of mobile phase" --- p.56 / Chapter 3.4.3.2 --- pH of the mobile phase --- p.59 / Chapter 3.4.4 --- Confirmation of homocysteine peak --- p.60 / Chapter 3.5 --- Analysis of results --- p.60 / Chapter 3.6 --- Method validation --- p.60 / Chapter 3.6.1 --- Linearity --- p.60 / Chapter 3.6.2 --- Precision --- p.63 / Chapter 3.6.3 --- Recovery --- p.64 / Chapter CHAPTER FOUR --- RESULTS --- p.66 / Chapter 4.1 --- The pre- and post-methionine loading plasma homocysteine concentrations in patients and controls --- p.66 / Chapter 4.2 --- The frequency distributions of hyperhomocysteinaemia in patients and controls --- p.68 / Chapter 4.2.1 --- The distributions of homocysteinaemia in patients and controls --- p.68 / Chapter 4.2.2 --- The frequency distributions of fasting hyper-homocysteinaemia in patients and controls --- p.68 / Chapter 4.2.3 --- The frequency distributions of post-methionine hyperhomocysteinaemia in patients and controls --- p.73 / Chapter 4.2.4 --- The frequency distributions of the abnormal methionine tolerance in patients and controls --- p.75 / Chapter 4.3 --- "The frequency distributions of hypertension and hyperlipidaemia in controls and, including smoking,in patients without and with hyperhomocysteinaemia" --- p.77 / Chapter 4.3.1 --- The frequency distribution of hypertension and hyperlipidaemia in patients and controls --- p.77 / Chapter 4.3.2 --- "The frequency distributions of hyper-lipidaemia, hypertension, smoking and gender in patients with vascular disease with and without hyperhomocysteinaemia" --- p.79 / Chapter 4.4 --- "The comparison of the age, haematological and biochemical indices and the blood pressure between the patients and controls" --- p.81 / Chapter 4.4.1 --- The comparison of the patients' age at presentation and plasma lipids following recovery from the acute episode with those in controls at the time of methionine loading --- p.81 / Chapter 4.4.2 --- The comparison of the age at presentation and the plasma lipids in patients with and without hyperhomocysteinaemia --- p.83 / Chapter 4.4.3 --- "The comparison of the B12, serum folate and RBC folate in patients and controls at the time of presentation" --- p.84 / Chapter 4.4.4 --- "The comparison of the B12, serum folate and RBC folate levels in patients with and without hyperhomocysteinaemia and in controls" --- p.85 / Chapter CHAPTER FIVE --- DISCUSSION --- p.87 / REFERENCES --- p.98

Twenty-four Quarter horse weanlings (120 d +/- 10 d) were blocked by age into 4 groups (n = 6) for a 56 d trial to evaluate the influence of methionine on growth and nitrogen retention. Weanlings were housed by block and individually fed 1 of 4 concentrate diets twice daily at 1.5% BW (as fed). Weanlings were randomly assigned to 1 of 4 treatments: basal (0.20 MET), basal + 0.03% methionine (0.23 MET), basal + 0.07% methionine (0.27 MET), and basal + 0.11% methionine (0.31 MET). Diets were formulated to be isonitrogenous, isocaloric, and contain equal amounts of LYS and THR. Coastal bermudagrass hay was individually fed at 0.75% BW (as fed). Growth measurements, body weight, rump fat, and plasma were obtained every 7 d. The final 4 days consisted of total collection of urine and feces. Feed, fecal, and urine samples were analyzed for nitrogen content and nitrogen balance was calculated. Urine was analyzed for urea and ammonia concentration. Plasma was analyzed for urea concentration. Grain, hay, and fecal samples were analyzed for nutrient composition. Data were analyzed using the PROC MIX procedure of SAS. Linear, quadratic, and cubic effects were tested in the form of contrasts. There was no influence of treatment on growth measurements, nitrogen balance, or urinary urea or ammonia. Intake of LYS and THR (g/d) did not differ among treatments (P = 0.78 and P = 0.38 respectively). Plasma urea nitrogen (PUN) was influenced by treatment (P = 0.005) exhibiting quadratic (P = 0.04) and cubic (P = 0.002) effects. An unexpected peak in PUN was observed with 0.27 MET. Upon analysis, 0.20 MET contained more lysine than formulated, and 0.27 MET contained the least lysine. Treatments 0.20 MET and 0.31 MET contained more threonine compared to formulations. These differences may explain unexpected values of PUN concentration. Results suggest future studies that more closely isolate methionine as the only dietary variable are necessary to better explain the methionine requirements of weanling horses.

No description available.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 96-103). Also available in print.

No description available.

No description available.

Folate derivatives are required for nucleotide/DNA synthesis and DNA methylation. Methylenetetrahydrofolate reductase (MTHFR) converts 5,10-methylenctetrahydrofolate to 5-methyltetrahydrofolate, the folate derivative required for homocysteine remethylation to methionine, the precursor of S-adenosylmethionine. Approximately 45%--50% of the general population is heterozygous for a common substitution (677C &rarr; T, A to V) in MTHFR. Due to loss of heterozygosity (LOH) in cancer cells, individuals who are heterozygous for MTHFR in their constitutional DNA may contain only one of the above alleles in their tumor DNA. / Loss of heterozygosity of MTHFR was observed in 40% of ovarian carcinoma tumor samples and in 16% of colon carcinoma samples suggesting that the chromosomal location to which the MTHFR gene maps (1p36.3) undergoes frequent LOH. Examination of cell viability of human fibroblasts and of human colon carcinoma cell lines in minimum essential media (MEM) lacking methionine found both cell types to be extremely sensitive to the methionine deficiency. Replacing methionine with homocysteine and vitamin B12 restored the growth of normal fibroblast lines to levels that approached those of replete MEM, but the transformed lines increased proliferation only slightly under these conditions. These results support earlier reports regarding the increased methionine dependence of transformed lines. Targeting specific MTHFR variants with the antisense oligonucleotide resulted in &sim;50% decreased survival of two carcinoma cell lines (V/V genotype), possibly due to MTHFR's involvement in methionine synthesis. Allele-specific targeting of MTHFR could therefore provide an effective approach for cancer therapy. Furthermore, cancer patients with the V/V genotype may require less aggressive anti-folate chemotherapy since V/V carcinoma lines were highly sensitive to drug treatment (IC50 < 25 nM) whereas the A/A lines were more variable in response.

Amino acids (AA) are required for protein accretion and the need for a specific AA depends on the physiological status, breed, and the health of the pig. Inasmuch as the AA requirements for growing pigs are given in an ideal AA ratio for protein accretion, the utilization of all AA is beyond growth and at least 30% of the total dietary AA will be used by the splanchnic tissue. A ban in the use of antimicrobial growth promoters (AGP) in piglets’ diets is likely to increase incidences of disease occurrence and exert additional AA requirements. Immune challenge models were used to determine standardized ileal digestible (SID) Lys and sulfur amino acids (SAA):Lys requirements for piglets under an antibiotic-free feeding regime. The first objective was to establish the dietary Lys requirement for piglets raised under both clean and unclean sanitary conditions. The Lys requirement could not be determined in the first experiment. However, from the second and third experiments the dietary SID Lys content for optimal growth of 7 to 16 kg weaned piglets was estimated to be 1.32%. The objective of fourth experiment was to determine the optimum SID SAA:Lys ratio in piglets when reared under clean or unclean conditions. Based on performance parameters, the optimum SAA:Lys ratios were 58 and 61 for piglets raised under clean and unclean conditions, respectively. However, VH estimates were 60 and 66 SAA:Lys under clean and unclean sanitary conditions, respectively. The objective for the fifth experiment was to determine SID SAA:Lys ratio of piglets under an enterotoxigenic Escherichia coli challenge using genes for expression of key products in the Met metabolic pathway. Gene expressions of methionine adenosyltransferase 1 and 2-α, 5-methyltetrahydrofolate-homocysteine methyltransferase, and cystathionine γ-lyase was done for liver and ileal tissue. The gene expressions indicates that the dietary SAA:Lys ratio of 60 was enough to support piglet’s immune response and performance during an immune challenge. Therefore, under an antibiotic-free feeding regime, the Lys requirement recommended by NRC (2012) is sufficient, however, the SAA:Lys should be raised to 60 in diets of both healthy and immune challenged piglets.

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 96-105)

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 105-119). Also available via the Internet.