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University of Macau / Institute of Chinese Medical Sciences

Indiana University-Purdue University Indianapolis (IUPUI) / Each biological cell is surrounded by a membrane that consists of many different kinds of lipids. The lipids are mainly composed of phospholipids, which form a fluid bilayer that serves as the platform for the function of membrane bound proteins regulating cellular activity. In the research described in this thesis we employed solid state 2H NMR, complemented by DSC (differential scanning calorimetry) and MD (molecular dynamics) simulations, to study the effect of PUFA (polyunsaturated fatty acids) and TFA (trans fatty acids) on molecular organization in protein-free model membranes of controlled composition. These two classes of unsaturated fatty acid incorporate into membrane lipids and have, respectively, a beneficial and harmful impact on health. The aim is to gain insight into the molecular origin of this behavior. DHA (docosahexaenoic acid), which with 6 "natural" cis double bonds is the most highly unsaturated PUFA found in fish oils, and EA (elaidic acid), which with only a single "unnatural" trans double bond is the simplest manmade TFA often found in commercially produced food, were the focus. 2H NMR spectra for [2H31]-N-palmitoylsphingomyelin ([2H31]16:0SM) in SM/16:0-22:6PE (1-palmitoyl-2-docosahexaenoylphosphatidylethanolamine)/cholesterol (1:1:1 mol) mixed membranes were recorded. This system served as our PUFA-containing model. The spectra are consistent with lateral separation into nano-sized (< 20 nm) domains that are SM-rich/cholesterol-rich (raft), characterized by higher chain order, and DHA-rich/cholesterol-poor (non-raft), characterized by lower chain order. The aversion cholesterol has for DHA, as opposed to the affinity cholesterol has for predominantly saturated SM, excludes the sterol from DHA-containing PE-rich domains and DHA from SM-rich/cholesterol-rich domains. It is the formation of highly disordered membrane domains that we hypothesize is responsible, in part, for the diverse health benefits associated with dietary consumption of DHA. 2H NMR spectra for 1-elaidoyl-2-[2H35]stearoylphosphatidylcholine (t18:1-[2H35]18:0PC) and 1-oleoyl-2-[2H35]stearoylphosphatidylcholine (c18:1-[2H35]18:0PC) were recorded to compare membranes with respect to a trans vs. cis ("natural") double bond. The spectra indicate that while a trans double bond produces a smaller deviation from linear conformation than a cis double bond, membrane order is decreased by a comparable amount because the energy barrier to rotation about the C-C single bonds either side of a <italic>trans</italic> or <italic>cis</italic> double bond is reduced. Although EA adopts a conformation somewhat resembling a saturated fatty acid, the TFA is almost as disordered as its <italic>cis</italic> counterpart oleic acid (OA). We speculate that EA could be mistaken for a saturated fatty acid and infiltrate lipid rafts to disrupt the high order therein that is necessary for the function of signaling proteins.

Call number: LD2668 .T4 1948 J3 / Master of Science

Call number: LD2668 .T4 1948 N49 / Master of Science

Call number: LD2668 .T4 1949 C49 / Master of Science

Ruminant products, meat and milk, were long ago discovered to contain a high content of saturated fat associated with various chronic diseases in human, including coronary heart disease. Increased consumption of n-3 fatty acids, linolenic (LNA; 18:3n-3), eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) by man has been linked with reduced incidences of these diseases. Therefore, in vitro experiments carried out in this thesis investigated the possibility that the dietary inclusion of essential oil compounds (EOC) might modify ruminal biohydrogenation of polyunsaturated fatty acids (PUFA), and thereby improve the fatty acid profiles of ruminant derived foods. In the first experiment, twenty EOC were screened, of which carvacrol, thymol, cis/trans-citral, geraniol, nerol, (+)-α-pinene, l-menthone, linalyl acetate and (R)-(+)-pulegone were most effective at protecting the PUFA from biohydrogenation. The reduced accumulation of stearic acid with concomitant increases in vaccenic acid following the addition of the EOC confirmed their capacity to inhibit biohydrogenation of both LA and LNA. However, the observed decreases in total volatile fatty acids concentrations suggested that the inclusion of these compounds at 300 mg l-1 also suppressed microbial fermentation. Of these EOC, carvacrol and thymol were the most potent inhibitors of fermentation as they decreased total VFA concentrations by ≥60% from those of the control. In the second experiment, selected EOC, namely linalyl acetate, l-menthone and (+)-α-pinene, were tested at lower doses. It was observed that these EOC when added at 100 and 200 mg l-1 also inhibited biohydrogenation with minimal effect on VFA concentration. In experiment 3, pure culture work was undertaken to assess the effects of EOC on three key Butyrivibrio spp., involved in the biohydrogenation process, namely B. fibrisolvens, B. hungatei and B. proteoclasticus. The EOC inhibited biohydrogenation through their bacteriostatic effects on these bacteria. In conclusion, these studies revealed that EOC have the potential to modify ruminal biohydrogenation to varying extents depending on the type of compound used and the dose applied. Consequently, they might be useful at improving the healthiness of ruminant products, however their effects have to be confirmed in vivo and ensure that they do not cause significant inhibition of fibre digestion.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy