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Abstract: Hypertension affects one third of the population worldwide. It is a multifactorial, polygenic disorder which involves the interplay among various risk factors. A number of scientific studies have demonstrated that renin-angiotensin system (RAS), oxidative stress and inflammation interact with each other in regulating the hypertensive response and targeted organ injury. Inhibiting angiotensin I-converting enzyme (ACE) is the key target for controlling high blood pressure. Due to the inevitable adverse side effects of antihypertensive drugs, food-derived compounds, especially food protein-derived peptides have emerged as an alternative strategy in the prevention and management of hypertension. The objectives of this thesis were to 1) identify potent ACE inhibitory peptides from various food proteins by in silico digestion and quantitative structure-activity relationship (QSAR) modeling and to 2) explore their additional antioxidative and anti-inflammatory activities in endothelial cells. A systematic evaluation was performed on 15 food commodities as potential sources of ACE inhibitory peptides. In silico digestion of proteins by thermolysin generated 5709 peptides containing 2 to 6 amino acid residues, and their ACE inhibitory activity was predicted using QSAR modeling. Meat proteins from pork, beef and chicken contain the largest number of potent peptides (IC50 < 10 μM), followed by proteins from milk, egg, soybean and canola, whereas proteins from fish (with the exception of salmon) and cereals (oat and barley) contain the least number of potent peptides. This study has demonstrated that proteins from livestock meat, milk, egg, soybean and canola are good sources of ACE inhibitory peptides. Soybean, bovine latoferrin and spent hen were then selected to validate the prediction. Three tripeptides, LSW (IC50=2.7 µM), IVF (IC50=63.3 µM) and LLF (IC50=63.8 µM) with potent ACE inhibitory activity were characterized from soybean hydrolysates, while LRP (IC50=1.2 ± 0.05 µM) and IWHHT (IC50=9.93 ± 0.65 µM) were characterized from bovine lactoferrin and spent hen, respectively. IWHHT was not resistant to simulated gastrointestinal digestion and produced a mixture of IW, IWH, HHT and HT. IW showed a more potent ACE inhibitory activity (IC50=2.0 ± 0.06 µM). LSW, LRP and IWHHT were all predicted to be released from corresponding food proteins in the computational study. LRP significantly inhibited tumor necrosis factor-alpha (TNF-α) induced vascular inflammation by reducing the expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) at 50 µM in endothelial cells. LRP, IWHHT, IWH and IW all significantly reduced the level of superoxide when the cells were subject to serum withdrawal to induce oxidative stress. While IWHHT and IWH significantly reduced the expression of VCAM-1 only in TNF-α induced inflammation. This thesis demonstrated the potential of various food proteins as sources of ACE inhibitory peptides. The ACE inhibitory peptides, with additional antioxidative and anti-inflammatory activities identified in the thesis may enhance their antihypertensive effects by interacting with different elements essential in the pathogenesis of hypertension.

In the absence of a clear understanding of the aetiology of diseases and measurable parameters for the attributes of drugs described in the traditional systems of medicine, an approach encompassing a broad spectrum of biological activities on the whole body that may be ascribable to the attributes of the drugs and aetiology of a disease described in the traditional medical systems such as Ayurveda, taken to investigate putative anticancer plants, is presented. Extracts of the putative anticancer plants, Euphorbia peplus L. (petty spurge) and Viola odorata L. (sweet violet), which grow in Australia, were investigated for in vitro anticancer activity using DPPH free radical scavenging, Fe-(III)-TPTZ reducing (FRAP) and linoleic peroxidation inhibitory (TBARS and FTC) antioxidant activities; human complement inhibitory (CP and AP), anti-platelet aggregating (impedance method), COX-2 inhibitory immunomodulatory activities as well as the conventional in vitro anticancer activities using CEM (3H] thymidine uptake, MTS and US-NCI's sulforhodamine B assay using 60 cell line humour tumour screen. Results were compared with relevant standards. Isolation of active extracts and chemical studies were carried out using HPLC-PDA, UV-VIS, TLC, GC-MS, ESI-MS, and AAS. Although the two plants have failed in the NCI's conventional in vitro anticancer screen, our results showed that the extracts of both plants indicated a combination of biological activities. These results raise the possibility that broad-spectrum approach comprising a number of different biological systems may help to explain the purported in vivo anticancer activity of Euphorbia peplus L. and Viola odorata L. Preliminary chemical studies showed the presence of the flavonoid, quercetin among other compounds, in the antioxidant extracts of both plants. The ESI-MS and GC-MS profiles may be used to characterise the active extracts. Presented results may be used to design further in vivo studies towards utilising natural resources as anticancer agents.