Concerns about global warming have resulted in a surge of research into alternatives to fossil fuels. In recent years, biofuels have gained traction due to their low environmental impact. Biofuel production most commonly employs microorganisms to convert biomass to fuel for industrial and transportation applications. Compounds made in biofuel production, however, are toxic to cell membranes and disrupt their integrity, harming the microorganisms and limiting biofuel yield. A key to overcoming this challenge is understanding how fuels interact with microorganisms’ cell membranes, which perform a host of functions, including transport, cell recognition, transduction, and movement. Phospholipids are the cell membrane’s building blocks and provide the critical matrix to support these vital functions. This research sought to make in-vitro membrane phospholipid models of the bacterium Bacillus subtilis (a biofuel producer candidate), subject them to fuel stress and employ fluorescence techniques to understand how fuels affect membrane integrity.

Trimethylamine-N-oxide (TMAO) is an important biomarker of atherosclerosis. TMAO is the product of a hepatic conversion of trimethylamine (TMA). Releasing of TMA moieties is dependent on the adaptation of the gut microbiota to dietary TMA containing substrates such as phosphatidylcholine (PC), choline, and L-carnitine. A high-fat diet is an environmental risk factor that may increase TMAO production. However, it isn’t clear if the high dietary intake of TMA is sufficient to promote increased plasma TMAO or if a high-fat intake is also required. We hypothesized that TMAO would be increased after consuming a high-fat diet and a high PC diet independently, with greater increases when consumed together. Four groups of twelve mice each were maintained on different treatments that were either low or high-fat with or without PC over two weeks. Then, a meal containing 9.99 g of corn oil and 0.75 g soybean L-α-Lecithin per 1 kg body weight was provided to all mice to indirectly observe the adaptation of the microbiota to the altered diet. The results of circulating TMAO levels showed that fat appeared to suppress TMAO production, which is against previous evidence. The microbial adaptation to the different treatments wasn’t observed in the measurement of fecal TMA levels. As a result, our hypothesis was rejected. Future work addressing the impact of gene expressions of enzymes on the gut and the liver is needed. The use of another high TMA containing substrates such as choline and rats is recommended. / Master of Science in Life Sciences / Cardiovascular disease (CVD) is heart and blood vessel diseases - many of which are caused by atherosclerosis, a condition wherein fatty materials accumulate in the artery wall, reducing blood flow. The compound trimethylamine-N-oxide (TMAO) was found to be an important biomarker of atherosclerosis. TMAO levels increase in the body when gut microbiota releases trimethylamine (TMA) moieties from dietary phosphatidylcholine (PC), choline, and L-carnitine such as eggs and meat. A high-fat intake was believed to have an impact on increased levels of TMAO. However, it wasn’t clear if the dietary intake of high TMA containing substrates such as PC, is sufficient to promote TMAO formation or if a high-fat content is also required. We hypothesized that TMAO would be increased after consuming a high-fat diet and a high PC diet independently, with greater increases when consumed together. The results would suggest new dietary strategies to avoid CVD. Four groups of twelve mice each were maintained on different treatments that were either low or high-fat with or without PC over two weeks. Then, a meal containing corn oil and PC was provided to all mice to observe the adaptation of the microbiota to the altered diet. The results showed that fat reduces circulating TMAO production, which is against previous evidence. Fecal TMA levels showed that microbiota activities weren’t observed in the colon. As a results, no significant levels of TMA and its precursors were observed in feces.

La couche de nacre de la coquille de l'huître perlière Pinctada radiata des côtes tunisiennes est considérée comme un biomatériau ostéogénique prometteur. L’objectif de ce travail intitulé « Ostéogénie, intégration et qualité de la nacre d’un bivalve des côtes tunisiennes : Pinctada radiata (Leach, 1814) » consiste dans un premier temps à valoriser l’espèce P. radiata par sa qualité nutritionnelle par un suivi saisonnier de la composition de sa chair en lipides totaux et en phospholipides particulièrement les PC, PE, PS et PI. Les analyses effectuées ont montré que les lipides de P.radiata sont caractérisés par une richesse en acides gras polyinsaturés (AGPI) de la série n-3 qui dépasse 3 fois celle des AGPI de la série n-6. Ces AGPI de la série n-3 en particulier l’EPA (C20:5n-3) et le DHA (C22:6n-3), sont connus comme étant les AG les plus importants dans l’alimentation humaine puisqu’ils préviennent des maladies cardiovasculaires et des pathologies ostéo-articulaires. Par ailleurs, P. radiata de la région de Maharès présente la meilleure qualité de nacre en Tunisie. Les analyses biochimiques ont montré que cette région, constitue la meilleure localisation de cette espèce qui est loin des zones portuaires et des différentes origines de stress (pêche, exploitation, zone touristique etc…). En plus de cet aspect, la zone de Maharès renferme des pintadines présentant une bonne qualité en termes d’épaisseur de nacre. Nos résultats montrent que la composition, saisonnière, en acide gras des phospholipides et en particulier des glycérophospholipides (PE, PI, PS et PC) de la nacre est riche en acides gras saturés C14 :0, C16 :0 et C18 :0 particulièrement en hiver et dans un moindre degré au printemps. La nacre, substance ostéogénique, a été également caractérisée par un taux élevé de plusieurs AGPI de la série n-3 et n-6, particulièrement (18:3n-3, 18:4n-3, 20:5n-3, 22:5n-3, 22:6n-3 et le 20:4n-6). Pour démontrer les potentialités ostéogéniques des extraits de la nacre, nous avons utilisé un modèle "in vitro" utilisant 4 extraits lipidiques : l’extrait lipidique de la nacre de P.radiata (Ln), l’extrait lipidique de la chair de P.radiata (Lc), l’ESM (Ethanol soluble Matrix) de la nacre de P.radiata (Br) et l’ESM de la nacre de P.margaritifera (Bm). Nous avons comparé, in vitro, le pouvoir ostéogénique des extraits ESM des deux espèces P. radiata et P. margaritifera sur deux types de cellules les préchondrocytes ATDC5 et les préostéoblastes murins MC3T3. Les différents extraits (Ln, Lc, Br et Bm) induisent l’engagement des cellules MC3T3 vers le lignage ostéoblastique par l’activation des promoteurs des gènes spécifiques du tissu osseux, tels que: le collagène de type 1, l’ostéocalcine (OC), l’ostéopontine(OP) et le Runx2. Ces extraits induisent aussi l’engagement des cellules ATDC5 vers la différenciation endochondrale par l’activation des promoteurs des gènes spécifiques du tissu osseux, tels que: le collagène de type 1 alpha-1 (Col1a1), l’Aggrécane et le collagène de type X alpha-1 (ColXA1). De plus, nous remarquons que la fraction organique ou ESMr(Br) en comparaison avec celle de P.margaritifera (Bm) présente également les propriétés stimulantes de la nacre et la stimulation est même beaucoup plus importante. Ces résultats mettent en évidence, dans les modèles expérimentaux mis en oeuvre, l’intérêt des lipides. Ces derniers semblent jouer un rôle important dans cette stimulation. De plus, nous pouvons penser à la possibilité de l’association des molécules de nacre ou de biominéralisation avec les acides gras de la nacre et de la chair dans les défauts osseux à travers les sites actifs de l’os ou du cartilage humain présentant les différentes pathologies ostéarticulaires / The nacre layer of the shell of the pearl oyster Pinctada radiata of tunisian coast is considered a promising osteogenic biomaterial. The objective of this work entitled "Osteogenie, integration and quality of nacre of a tunisian coast bivalve: Pinctada radiata (Leach, 1814)" is a first step to enhance the species P.radiata its nutritional quality by seasonal monitoring of the composition of the flesh of total lipids and phospholipids in particular PC, PE, PS and PI. The analyzes showed that lipids of P.radiata are characterized by rich in polyunsaturated fatty acids (PUFAs) of the n-3 more than 3 times that of PUFAs n-6 series. These PUFAs of the n-3 series particularly EPA (C20: 5n-3) and DHA (C22: 6n-3) are known to be the most important AG in the food as prevent of the cardiovascular disease, and joint/ bone pathologies. Moreover, P. radiata of Mahares region has the best quality of nacre in Tunisia. Biochemical analyzes showed that this region is the best location of this species that is far from the port areas and different sources of stress (fishing, exploitation, tourist area etc ...). In addition to this aspect, the area contains pintadines having good quality in terms of thickness of nacre. Our results show that the seasonal composition of fatty acid of phospholipids in particular glycerophospholipids (PE, PI, PS and PC) nacre is rich in saturated fatty acids C14: 0, C16: 0 and C18: 0 especially in winter and spring in a lesser degree. Nacre, osteogenic substance, was also characterized by a high rate of PUFA of the n-3 and n-6 rate, especially (18: 3n-3, 18: 4n-3, 20: 5n-3, 22 5n-3, 22: 6n-3 and 20: 4n-6). To demonstrate the osteogenic potential of extracts of nacre, we have established an "in vitro" model using 4 lipid extracts: the lipid extract of nacre P.radiata (Ln); the lipid extract of the flesh of P.radiata (Lc), ESM (Ethanol soluble Matrix) of the mother-of P.radiata (Br) and ESM nacre of P. margaritifera (Bm). We compared “in vitro” osteogenic power ESM extracts of both species P. radiata and P. margaritifera on two types of cells the préchondrocytes ATDC5 and the murine preosteoblasts MC3T3. The different extracts (Ln, Lc, Br and Bm) induce engagement MC3T3 osteoblast lineage cells to the activation of the promoters of specific genes of bone tissue, such as collagen type 1, osteocalcin (OC), osteopontin (OP) and Runx2. These extracts also induce the commitment of ATDC5 cells to endochondral differentiation by activating specific genes promoters of bone tissue, such as collagen type 1 alpha 1 (COL1A1), the aggrecan and collagen type alpha 1-X (ColXA1). Moreover, we note that the organic fraction or ESMR (Br) compared with that of P. margaritifera (Bm) also has stimulant properties of nacre and the stimulation is even more important. These results demonstrate, in experimental models used, the interest of lipids. They seem to play an important role in this stimulation. Moreover, we can think about the possibility of the association of molecules or nacre biomineralization with the fatty acids of the nacre and flesh in bone defects through the active sites of bone or cartilage presenting the human osteoarticular different pathologies

This diploma thesis deals with the preparation and characterization of stealth liposomes and their combination with trimethylchitosan (TMC). This complex could find application in the field of inhalation administration. Stealth liposomes were prepared from neutral phophatidylcholine, negatively charged fosfatidic acid and polyethyleneglycol bounded to phosphatidylethanolamine. We have managed to prepare stealth liposomes with suitable properties that should guarantee passive targeting without evocation an immune response, despite the content of the negative component. We also found a suitable method of preparation for stealth liposome–TMC complex, where the change of size and zeta potential confirmed the non–covalent bound between two components despite the content of the polyethyleneglycol.