|Abstract: ||The nutritional role of dietary fatty acids is quite controversial and often the object of mediatic campaigns either as panacea against all diseases or detrimental for human health. The most recent data are instead showing that it should be considered, in an optimal dietary regimen, the balance among all dietary fatty acids based on the current physiological needs, applying what it is currently known as personalised nutrition. It has been paid particular attention to the ratio between highly polyunsaturated fatty acids (HPUFAs) n-6, mainly arachidonic acid (ARA, 20:4n-6;) and n-3 HPUFAs, mainly eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) in tissues, since an inverse correlation between circulating n-3 HPUFAs and several chronic pathological states has been observed, possibly mediated by modulation of the endocannabinoid system (ECS). However, to assess this balance and controlling it by dietary means remains a great challenge for nutritionists. In addition, other nutritional factors may influence their tissue concentration. It is therefore compelling to individuate the mechanism(s) of action and what are the most efficient nutritional conditions to maximize n-3 HPUFAs health-related beneficial activities.
The aim of this thesis was to evaluate the effects of some nutritional factors, such as conjugated linoleic acid (CLA), naturally occurring in the diet or produced by the probiotic Bifidobacterium breve (B. breve), in influencing n-3 PUFA metabolism to optimize the n-3 HUFA score (a biomarker of n-3 status in tissues) and possible interactions with the ECS in rodents and humans.
We evaluated whether CLA, from different dietary sources, was able to enhance DHA biosynthesis, from its precursor alpha linolenic (ALA), in experimental models and humans. We found that different dietary ALA/CLA ratios affected n-3 PUFA and EC profile with a graded decrease of ALA and EPA and corresponding increase of DHA, while the EC arachidonoylethanolamine (AEA) decreased parallel to ratio ALA/CLA, whereas dietary ALA, in absence of CLA, was not able to increase significantly circulating DHA levels. We also evaluated whether supplementation with B. Breve as probiotic, along with ALA, in mice, as a nutritional factor that may increase dietary CLA, modulated n-3 fatty acid metabolism. We found that dietary probiotics increased DHA biosynthesis in liver and epididymal adipose tissue. Actually, we showed an increased of DHA biosynthesis in liver, but not an increase of CLA, while the ratio CD 16:2/CLA, a biomarker of peroxisomal beta oxidation, increased significantly but not associated to a higher PPAR α gene expression. The observed parameters suggested that these effects may be related to a pro-inflammatory event possibly triggered by the activation of toll like receptors by B. breve. In fact, in an ancillary experiment on rats challenged with LPS, we obtained similar results on fatty acid metabolism. In addition, dietary probiotics decreased AEA and its congener palmitoylethanolamine (PEA) levels in liver, while in adipose tissue we found a significant increased levels of AEA, PEA and the other AEA congener oleoylethanolamide (OEA).
Our studies strongly suggest that background diet may play an important role in modulating fatty acid metabolism and in particular in modulating n-3/n-6 fatty acid balance, thereby differently affecting the ECS. Therefore, the synergistic effects of different nutritional factors, as it occurs in daily life in humans are somewhat difficult to predict and may explain the contradictory results in the literature on the effects of dietary fatty acids, in particular when they are singularly considered without taking into account the whole dietary regimen. The discover that gut microbiota may directly interfere and modify fatty acid metabolism opens to novel nutritional strategies in shaping the optimal milieu for contrasting several metabolic disorders by modulating the ECS.
Future studies in humans will be focus on evaluating possible synergistic effects of CLA-enriched products with B. breve in maintaining and/or re-equilibrating energy and lipid metabolism, by modulating EC and congeners tissue profile, acting on energy metabolism and EPA and DHA related molecules, and also to assess if there is an optimal level of dietary EPA and DHA to allow a synergistic activity in different physio-pathological conditions.|