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No description available.

No description available.

No description available.

No description available.

Stearoyl-CoA desaturase (SCD) catalyses the rate-limiting step in the biosynthesis of monounsaturated fatty acids by the insertion of a a ^9-cis double bond into acyl-CoA substrates in the presence of NADH and molecular oxygen. Recent work with animals in which expression of the enzyme has been eliminated, suggests a critical role for this enzyme in regulating lipid metabolism and obesity.

Regulation of polyunsaturated fatty acid (PUFA) biosynthesis in proliferating and NGF-differentiated PC12 pheochromocytoma cells deficient in n-3 docosahexaenoic acid (DHA, 22:6n- 3) was studied. A dose- and time dependent increase in eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid (DPA, 22:5n-3) and DHA in phosphatidylethanolamine (EPG) and phosphatidylserine (SPG) glycerophospholipids (GPL) via the elongation/desaturation pathway following alpha-linolenic acid (ALA, 18:3n-3) supplements was observed.That was accompanied by a marked reduction of eicosatrienoic acid (Mead acid, 20:3n-9), an index of PUFA deficiency. EPA supplements were similarly converted to 22:5n-3 and 22:6n-3. On the other hand, supplements of linoleic acid (LA, 18:2n-6) were not effectively converted into higher n-6 PUFA intermediates nor did they impair elongation/desaturation of ALA. A marked decrease in the newly synthesized 22:5n-3 and 22:6n-3 following ALA or EPA supplements was observed after nerve growth factor (NGF)-induced differentiation. NGF also inhibited the last step in 22:5n-6 formation from LA. NGF alters differently the expression of several genes involved in the FA metabolism; ElovJ5, EJovJ2, Fads2 and Ppara genes encoding, respectively, for ELOVL5 elongase, ELOVL2 elongase, Delta6 desaturase (D6D) and the nuclear transcription factor PPARa. LA up-regulates the expression of the above genes, whereas ALA specifically up-regUlates the mRNA levels of Fads2 and Elovl5. The results found in this thesis emphasise the importance of overcoming n-3 PUFA deficiency, and raise the possibility that growth factor regulation of the last step in PUFA biosynthesis may constitute an important feature of neuronal phenotype acquisition.

Epidemiological studies- indicate an association between the consumption of a 'diet rich in polyphenols and several health benefits. As diabetes and other lipid associated diseases are now reaching menacing proportions worldwide, the need for the development of cost-efficient prevention strategies effective at the population level becomes more essential than ever. Studies in the biological effects of polyphenols are now starting to include their hypoglycaemic and hypolipidemic properties and to investigate potential mechanisms through which they may exert their actions. The focus of the present study was to examine the action of various flavonoids and phenolic acids in pathways of energy metabolism and how they may affect the gene expression of critical enzymes involved in lipid and glucose metabolism. Studied flavonols (quercetin, kaempferol, galangin), and coffee phenolic acids and their metabolites (caffeic acid, dihydroferulic acid, protocatechuic acid) were identified as novel regulators of CPTIA, while quercetin was found to importantly upregulate CPTIA & PDK4 gene expression, to restrict glucose uptake and citrate synthase activity, and therefore was shown to potentially modulate energy metabolism in HepG2 cells. Dihydroferulic acid, the main microbial metabolite of chlorogenic acids from coffee was found to significantly increase PDK4 mRNA levels and enhance citrate synthase activity while it increased glucose uptake. On the other hand, a mixture of flavonols at in vivo relevant concentrations was able to produce a synergistic upregulating effect on CPTIA & PDK4, similar to that observed with quercetin, but an increase in glucose uptake. Further studies showed that the induction of CPTIA and PDK4 by quercetin was mediated by more than one transcription factors, with AMPK to have a pivotal role but Nrf2 driven antioxidant mechanisms not to be involved. From our data we hypothesised for quercetin that it sets the cell under a similar with mild starvation state as in between meals. Phenolic acids were further studied for their role in p-oxidation processes and it was demonstrated for the first time that they may form intermediates of p-oxidation as part of their metabolism in HepG2 cells. Our data suggest a novel but distinct role between flavonols and phenolic acids in lipid metabolism. Their action is defined both by direct interactions with enzymes involved in p-oxidation as well as by indirect actions on the transcriptional level. The biological importance of these findings requires further studies with additional models, which will expand our knowledge with regards to the role of polyphenols in lipid metabolism and any possible beneficial in vivo effects. III

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Increasing the amount of energy derived from fat is likely to have important health and performance applications. This thesis applied contemporary knowledge in order to investigate strategies for optimising whole-body fat oxidation, in male subjects. Study 1 investigated the efficacy of Xenadrine EFXTM (Gx), a weight-loss supplement containing bitter orange, green tea, and guarana, in promoting fat metabolism during 6 h rest. The ingredients in Gx are purported to increase lipolysis and fat oxidation. Indeed, a metabolic effect of Gx was evident. However, carbohydrate oxidation was increased by 15.5 ± 5.6 g over the 6 h period with a concomitant decrease in fat oxidation of -5.9 ± 3.1 g, while the metabolic rate remained unchanged. Study 2 extended the work from the first experimental study, by examining the acute effects of GX during 60 min sub-maximal treadmill walking. Although the onset of the walking exercise resulted in an approximately five-fold increase in the rate of fat oxidation, a reduction in the energy derived from fat, and increase in the energy derived from carbohydrate, was again evident with Gx. In Study 3 the intensity of exercise was manipulated, during treadmill running, in order to determine the exercise intensity eliciting the highest rate of fat oxidation (Fatmax). There was a large variation in the rate of fat oxidation across the range of exercise intensities investigated, with Fatmax occurring at 65.9 ± 1.0 % V02max, while individual peak rates of fat oxidation were 0.54 ± 0.04 g·min-1. This study highlighted the need for careful consideration of the intensity of exercise in order to optimise fat oxidation. Study 4 identified a relationship between Fatmax and the lactate threshold, during treadmill exercise. Analysis of plasma glycerol and NEF A concentrations indicated that the reduced rates of fat oxidation at high exercise intensities were not mediated by reduced lipolysis or plasma FA availability. These finding's were interpreted as supporting either depletion of the free carnitine pool, or inhibition of CPTI by a reduction in intra-cellular pH, as mediating the reduction in fat oxidation at exercise intensities in excess of Fatmax. Based upon the hypothesis that a reduction in intra-cellular pH might contribute to the reduced rates of fat oxidation at high exercise intensities, Study 5 sought to increase intra-cellular H+ buffering capacity. Four weeks supplementation with ~-alanine resulted in a significant increase in the muscle concentration of carnosine, an imidazole dipeptide contributing to intra-cellular physico-chemical H+ buffering. Despite the augmented carnosine concentration there were no changes in substrate utilisation across the range of exercise intensities studied, whilst Fatmax remained unchanged. This data suggests that a reduction in intra-cellular pH does not mediate reduction in fat oxidation during intense exercise. Taken together, the findings of this thesis demonstrate the importance of exercise as an intervention for facilitating fat metabolism, and highlight the primacy of carbohydrate metabolism within the fat-carbohydrate interaction.