Genetic variation may explain the heterogeneity in the lipid response to dietary change. A systematic literature review found 79 articles on dietary intervention studies, 14 articles on observational studies, and 22 reviews on diet-gene interactions. The evidence suggests that variation within the genes for apolipoprotein (apo) AI, AIV, B and E may influence the lipid response to dietary change. This study assessed the influence of six polymorphisms within the genes for apo B, apo E and lipoprotein lipase (LPL) on the association between habitual diet and lipid levels in 239 healthy men and women (91 men and 148 women) aged 18-54 years, including 110 twin pairs, who were recruited for a population-based study of coronary heart disease (CHD) risk factors. Diet was assessed by a food frequency questionnaire, which was compared with 4-day weighed records in 41 men and 40 women aged 19-58 years. The nutrients of interest had either a correlation coefficient ≥0.5, ≥50/≤10% in the same/opposite third, a KW30.04. Genotypes were determined by the polymerase chain reaction and digestion with the appropriate enzyme. Significant diet-gene interactions were observed at each of the polymorphic sites, suggesting that genetic variation contributes to the framework within which diet, especially n-3 PUFAs, the P:S ratio and NSP can influence lipid levels. In particular, individuals with the apo B XbaI X+ allele, the apo B signal peptide insertion/deletion D allele, the apo &egr;4 allele, the LPL PvuII P- allele and the LPL S447X X allele may be at greater risk of developing CHD due to their poorer lipid profiles and/or poorer response to diet. At present, it is premature to recommend the use of genotyping in the design of therapeutic diets, however investigating diet-gene interactions will increase our knowledge of the mechanisms involved in the role of diet in reducing CHD risk.

The objective of this thesis was to assess the impact of altering macronutrient intakes on hepatic lipid metabolism. Two separate studies were performed, with liver triglyceride content being the principal outcome of both. In the first study 32 healthy and centrally overweight males were randomised to 2 periods, each of 2 weeks, of either a high fructose or glucose intake in a non-crossover fashion. Isoenergetic status was maintained by providing foodstuffs during the first period, followed by a 6 week washout and then a second period of ad libitum overfeeding. In the second study 55 patients with biopsy proven non-alcoholic fatty liver disease were randomised to 3 months 5g a day of capsules containing either n-3 polyunsaturated fatty acid or oleic enriched sunflower oil. The main findings are summarised. High intakes of fructose and glucose in the isoenergetic period resulted in a stable weight, and no change in hepatic, serum and ectopic triglyceride content. There was a raised serum uric acid with fructose. During the hyperenergetic period there was a tendency for greater uric acid with fructose, whilst both groups had a matched weight gain, elevation of liver biochemistry and an increase in hepatic, serum and muscle triglycerides. Changes in liver biochemistry and triglycerides were associated with changes in weight. During both periods there was calorimetric evidence for a shift in whole body metabolism towards that reflective of a high carbohydrate intake. There was no alteration in renal function or cardiovascular haemodynamic parameters or consistent change in insulin resistance. The n-3 polyunsaturated versus oleic acid study resulted in significant alterations of serum fatty acid profiles between the groups, which were in line with the capsules’ contents. These changes however failed to translate, in the whole group, to any detected metabolic or hepatic changes beyond a reduction in serum triglyceride with n-3 polyunsaturated fatty acids. Only 43 of the 55 patients had elevated liver triglycerides on baseline MRI. Amongst this 43 there was a reduction in liver triglyceride with n-3 polyunsaturated fatty acids, but no other associated metabolic changes. The uric acid findings support the notion of fructose and glucose differing in their pre triose metabolism. There was however no differing outcomes in terms of lipid synthesis or storage. There was a suggestion of reduced liver triglycerides with n-3 polyunsaturated fatty acids though this was an isolated result only found amongst those with a steatotic liver at baseline. Ultimately the exquisite sensitivity of the liver to nutrient intakes was highlighted by the 0.8% gain in weight in the fructose / glucose study resulting in a 24% increase in liver lipid. This affirms the notion that dietary energy intakes have a profound influence on hepatic metabolism, but there is no evidence from this thesis that this influence is macronutrient specific. In the future macronutrient comparisons need to be made.

Yarrowia lipolytica appartient à un groupe de levures qui a divergé très tôt dans l'arbre des hémiascomycètes. Cette levure est capable d'utiliser, comme seule source de carbone, des substrats hydrophobes très variés et est capable de synthétiser de nouveaux acides gras libres à partir de composés non hydrophobes. Ces caractéristiques font de Y. lipolytica un modèle de levure hémiascomycète pour l'étude du métabolisme des lipides. Sa capacité oléagineuse est facilitée par l'expansion de familles de protéines ayant eu lieu au cours de l'évolution après la divergence du clade Yarrowia. En effet, parmi les 204 gènes impliqués dans le métabolisme des lipides dans Y. lipolytica, plus de 67% sont regroupés dans 30 familles multigéniques avec un maximum de 16 membres pour la famille de la lipase. Le récent séquençage de génomes 5 dans le clade Yarrowia a permis de comparer leur contenu génétique. L'étude des familles de gènes du métabolisme des lipides a permis de mettre en évidence les mécanismes impliqués dans l'évolution de ce clade. Toutes les fonctions nécessaires pour le métabolisme des lipides sont présentes dans toutes les espèces étudiées, avec au moins un gène par famille, même pour les espèces qui ont de 500 à 1000 moins de gènes que Y. lipolytica. Ces espèces se sont d'ailleurs révélées être toutes oléagineuses, grâce à des études physiologiques. Les familles de gènes observées proviennent de multiples duplications de gènes dont chaque exemplaire évolue indépendamment par différents processus de sub- ou neofonctionalisations, fixations, pseudogénisations ou pertes. Les contractions et expansions de familles de protéines, l'expression des gènes, la synténie et la localisation relative des gènes dans le génome ont été étudiés. Plus particulièrement, la pression de sélection agissant sur ces familles de gènes a été comparée à celles agissant sur le reste du génome. La combinaison de ces approches, physiologie, génomique et transcriptomique, a permis d'améliorer la compréhension du métabolisme lipidique, de son évolution et de la régulation des gènes dans un clade des levures oléagineuses. / Yarrowia lipolytica belongs to a group of yeasts that have diverged very early from most other hemiascomycetous yeasts. This yeast is able to use various hydrophobic substrates as unique carbon source and to synthesize new free fatty acid from non hydrophobic compounds. These characteristics make Y. lipolytica a known oleaginous model for the lipid metabolism survey of yeasts. Its oleaginous capacity is facilitated by protein family expansions that occurred across evolution after the divergence of the Yarrowia clade. Indeed, among 190 genes involved in the lipid metabolism in Y. lipolytica, more than 67% are grouped into 30 multigenic families with up to 16 members in the lipase family. The recent sequencing of 5 genomes within the Yarrowia clade enabled to compare their gene content. The study of gene families of the lipid metabolism allowed to highlight the evolutionary mechanisms involved in this clade. All the functions necessary to lipid metabolism are present in all species studied with at least one gene per family even for species that have 500 to 1,000 fewer genes than Y. lipolytica. These species are also found to be all oleaginous through physiological studies. The observed gene families derive from multiple gene duplications of which each copy evolves independently by different processes of sub- or neofunctionalisation, fixation, pseudogenization or loss. Contractions and expansions of protein families, gene expression, synteny and relative localisation of genes in the genome were investigated. More particularly, the selection pressure acting on these gene families was compared with those acting on the rest of the genome. The combination of these approaches, physiology, genomics and transcriptomics, has improved the comprehension of the lipid metabolism, its evolution and gene regulation within a clade of oleaginous yeasts.

Certains facteurs de risque, comme l’hyperlipidémie, l’hyper-agrégabilité des plaquettes sanguines et le stress oxydant favorisent la progression des maladies cardiovasculaires. L’objectif de ce travail est de comparer les effets des AGPI-LC issus de sources différentes (microalgue marine, huile d’argan et de poisson) sur l’installation du syndrome métabolique chez des rats soumis à un régime hyperlipidique. Les effets de l’huile d’argan sur la fonction plaquettaire et sur le bilan lipidique ont aussi été testés chez des patients dyslipidémiques. Une étude préliminaire sur des rats a été réalisée afin de rechercher la dose minimale de la microalgue (Odontella aurita) à incorporer dans le régime pour obtenir un effet positif sur les différents paramètres mesurés. Nous avons ensuite étudié l’effet du lyophilisat d’O. aurita sur les facteurs de risque cardiovasculaire induits par un régime hyperlipidique chez le rat. Les résultats ont montré, que l'apport d'O. aurita induit une diminution de la glycémie et des teneurs en lipides plasmatiques ainsi qu’une réduction de l'agrégation plaquettaire. Nous avons ensuite comparé les effets de cette microalgue avec l’huile de poisson. Pour cela une étude nutritionnelle a été réalisée chez des rats soumis à un régime hyperlipidique supplémenté ou non avec du lyophilisat d’O. aurita ou de l’huile de poisson. Il a ainsi été montré que la supplémentation en lyophilisat d’O. aurita et en huile de poisson diminue l’agrégation plaquettaire et le stress oxydatif. Nous avons par la suite comparé les effets de l’huile de poisson riche en oméga-3, et de l’huile d’argan riche en oméga-6 et oméga-9. Nos résultats montrent que les 2 sources diminuent l’agrégation plaquettaire et les facteurs de risque du syndrome métabolique mais leurs mécanismes d’action semblent être différent. En complément Nous avons sur l’huile d’argan, réalisé au Maroc une étude clinique pour rechercher l’effet antiagrégant et hypolipémiant chez des patients dyslipidémiques. Les résultats obtenus montrent une amélioration significative des lipides athérogènes chez les patients consommant de l'huile d’argan. Cette amélioration consiste en une baisse très significative des taux de cholestérol total et de LDL-cholestérol sériques auxquels s'ajoutent une diminution de l’agrégation plaquettaire et du stress oxydatif chez les patients consommant de l'huile d’argan. / Some risk factors, such as hyperlipidemia, hyperaggregability of blood platelets and oxidative stress promotes the progression of cardiovascular disease. The objective of this study was to compare the effects of LC-PUFA from different sources (marine microalgae, argan oil and fish oil) on installing the metabolic syndrome in rats fed high fat diet. The effects of argan oil on platelet function and lipid profiles were also tested in dyslipidemic patients. A preliminary study was conducted to find the minimum dose of microalgae (Odontella aurita) to be incorporated in the diet for a positive effect on the different parameters measured. We then studied the effect of lyophilized O. aurita on cardiovascular risk factors induced by a high fat diet in rats. The results showed that the addition of O. aurita induces a reduction in blood glucose and plasma lipid levels and a reduction in platelet aggregation. We then compare the effects of microalgae with fish oil. For this, a nutritional study was conducted in rats subjected to a high fat diet (HF) supplemented or not with the freeze-dried O. aurita (HFOA) or fish oil (HFFO). Supplementation lyophilized O. aurita and fish oil decreases platelet aggregation and oxidative stress.We subsequently compared the effects of fish oil rich in omega-3, and argan oil which is rich in omega-6 and omega-9. Our results show that 2 sources of LC-PUFA decrease platelet aggregation and the risk factors of metabolic syndrome, but their mechanism of action appears to be different.We have also conducted a clinical study in Morocco to investigate the antiplatelet and lipid lowering effect of argan oil in patients with dyslipidemia. The results show a significant improvement in atherogenic lipids in patients consuming argan oil for 3 weeks. This improvement consists in a very significant reduction in total cholesterol and serum LDL cholesterol, with a decreased platelet aggregation and oxidative stress in patients consuming argan oil.