Variation diurne de la composition chimique et influence sur les propriétés antimicrobiennes de l’huile essentielle de Ocimum canum Sims cultivé au Bénin

L’huile essentielle de Ocimum canum Sims (Lamiaceae) obtenue par hydrodiffusion à différents moments de la journée a été analysée par GC/FID et GC/SM puis testée sur différentes bactéries par la microtechnique de dilution. Le rendement et la composition chimique de l’huile varient selon le temps et l’ensoleillement. Abondant le matin à 7 heures (1,71±0,01%), le rendement décroît progressivement avec l’augmentation des rayons solaires, jusqu’à son minimum à 13 heures (1,35±0,01%) quand le soleil est au zénith, avant de croître à nouveau à sa valeur la plus élevée (1,78±0,02% à 19 h) au couché du soleil. Plus de 54 composés représentant près de 98% des hydrodiffusats, ont été identifiés dans les différents échantillons. Les principaux sont : α-thujène (5,56 à 7,85%), β-myrcene (2 à 6,94%), δ-3-carène (3,07 à 4,84%), p-cymène (14,61 à 22,8%), g-terpinène (6,05 à 10,7%), carvacrol (7,94 à 30,8%), β-caryophyllène (0,15 à 18,86%) et β- sélinène (2,74 à 14,41%). Les taux de certains constituants comme β-caryophyllène et β-sélinène croissent avec l’ensoleillement contrairement à ceux du carvacrol, p-cymène. Cette variation diurne perturbe la synergie d’action des constituants de l’huile qui présentent une forte activité inhibitrice (0,38 à 7,19 mg/ml) sur Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25923, Acinetobacter baumannii ATCC 19609 et Staphylococcus aureus résistante 1199B NorA. Les huiles obtenues à 7 heures et 19 heures sont les plus efficaces à faible concentration (0,38 à 2,88 mg/ml). Pour la première fois, l'interaction est démontrée entre variation diurne de la composition chimique et propriétés antimicrobiennes de l'huile essentielle de Ocimum canum Sims du Bénin.Keywords: Ocimum americanum, composés volatils, Chémotype à carvacrol Variation diurne-Activité antibactérienn

The ε3 and ε4 Alleles of Human APOE Differentially Affect Tau Phosphorylation in Hyperinsulinemic and Pioglitazone Treated Mice

Impaired insulin signalling is increasingly thought to contribute to Alzheimer's disease (AD). The ε4 isoform of the APOE gene is the greatest genetic risk factor for sporadic, late onset AD, and is also associated with risk for type 2 diabetes mellitus (T2DM). Neuropathological studies reported the highest number of AD lesions in brain tissue of ε4 diabetic patients. However other studies assessing AD pathology amongst the diabetic population have produced conflicting reports and have failed to show an increase in AD-related pathology in diabetic brain. The thiazolidinediones (TZDs), peroxisome proliferator-activated receptor gamma agonists, are peripheral insulin sensitisers used to treat T2DM. The TZD, pioglitazone, improved memory and cognitive functions in mild to moderate AD patients. Since it is not yet clear how apoE isoforms influence the development of T2DM and its progression to AD, we investigated amyloid beta and tau pathology in APOE knockout mice, carrying human APOEε3 or ε4 transgenes after diet-induced insulin resistance with and without pioglitazone treatment.Male APOE knockout, APOEε3-transgenic and APOEε4-transgenic mice, together with background strain C57BL6 mice were kept on a high fat diet (HFD) or low fat diet (LFD) for 32 weeks, or were all fed HFD for 32 weeks and during the final 3 weeks animals were treated with pioglitazone or vehicle.All HFD animals developed hyperglycaemia with elevated plasma insulin. Tau phosphorylation was reduced at 3 epitopes (Ser396, Ser202/Thr205 and Thr231) in all HFD, compared to LFD, animals independent of APOE genotype. The introduction of pioglitazone to HFD animals led to a significant reduction in tau phosphorylation at the Ser202/Thr205 epitope in APOEε3 animals only. We found no changes in APP processing however the levels of soluble amyloid beta 40 was reduced in APOE knockout animals treated with pioglitazone

Mechanisms Underlying Insulin Deficiency-Induced Acceleration of β-Amyloidosis in a Mouse Model of Alzheimer's Disease

Although evidence is accumulating that diabetes mellitus is an important risk factor for sporadic Alzheimer's disease (AD), the mechanisms by which defects in insulin signaling may lead to the acceleration of AD progression remain unclear. In this study, we applied streptozotocin (STZ) to induce experimental diabetes in AD transgenic mice (5XFAD model) and investigated how insulin deficiency affects the β-amyloidogenic processing of amyloid precursor protein (APP). Two and half months after 5XFAD mice were treated with STZ (90 mg/kg, i.p., once daily for two consecutive days), they showed significant reductions in brain insulin levels without changes in insulin receptor expression. Concentrations of cerebral amyloid-β peptides (Aβ40 and Aβ42) were significantly increased in STZ-treated 5XFAD mice as compared with vehicle-treated 5XFAD controls. Importantly, STZ-induced insulin deficiency upregulated levels of both β-site APP cleaving enzyme 1 (BACE1) and full-length APP in 5XFAD mouse brains, which was accompanied by dramatic elevations in the β-cleaved C-terminal fragment (C99). Interestingly, BACE1 mRNA levels were not affected, whereas phosphorylation of the translation initiation factor eIF2α, a mechanism proposed to mediate the post-transcriptional upregulation of BACE1, was significantly elevated in STZ-treated 5XFAD mice. Meanwhile, levels of GGA3, an adapter protein responsible for sorting BACE1 to lysosomal degradation, are indistinguishable between STZ- and vehicle-treated 5XFAD mice. Moreover, STZ treatments did not affect levels of Aβ-degrading enzymes such as neprilysin and insulin-degrading enzyme (IDE) in 5XFAD brains. Taken together, our findings provide a mechanistic foundation for a link between diabetes and AD by demonstrating that insulin deficiency may change APP processing to favor β-amyloidogenesis via the translational upregulation of BACE1 in combination with elevations in its substrate, APP

Oxidation of laccase for improved cathode biofuel cell performances

Graphite rodswere modified by substituted aryldiazoniumsalts allowing subsequent laccase immobilisation and direct electron transfer at the cathode. Two covalent enzyme immobilisation methods were performed with carboxy and amino substituted grafted groups, either via the formation of an amide bond or a Schiff base between the glycosidic groups of the enzyme and the amino groups on the electrode surface, respectively. Laccase adsorption efficiency was consistently compared to the covalent attachment method on the same carbon surface, showing that the latter method led to a higher immobilisation yield when the electrode surface was functionalised with carboxylic groups, as shown fromboth laccase activitymeasurement towards an organic reducing substrate, ABTS, and quantitative XPS analysis. Both analytical methods led to similar laccase surface coverage estimations. From activity measurements, when laccase was covalently immobilised on the electrode functionalised with carboxylic groups, the surface coverage was found to be 43 ± 2% whereas it was only 10 ± 3% when laccase was adsorbed. Biocatalysed dioxygen reduction current was also higher in the case of covalent immobilisation. For the first time, oxidised laccase performances were compared to unmodified laccase, showing significant improved efficiencywhen using oxidised laccase: the current obtainedwith oxidised laccasewas 141±37 μAcm-2 compared to 28 ± 6 μA cm-2 for unmodified laccase after covalent immobilisation of the enzyme on a graphite electrode functionalised with carboxylic groups. © 2015 Elsevier B.V

Shifting the optimal pH of activity for a laccase by structure-based mutagenesis at the reducing substrate Cu binding site

Shifting the optimal pH of activity for a laccase by structure-based mutagenesis at the reducing substrate Cu binding site. 3rd European Meeting in Oxizyme