Our data show that the position of dietary PA in sn-2 of TAGs results in a better incorporation of PA in intestine, adipose tissue and liver PLs. Interestingly, the increase of PA was associated to an increase of PEA and decrease of AEA in adipose tissue, while higher levels of OEA were found in all other tissues tested. It seems therefore that PA increase in PLs is able to modify NAEs profile in different tissues. PEA and AEA have different activities in different tissues and experimental conditions. For instance, in visceral adipose tissue PEA has been shown to possess antiinflammatory properties [33], while AEA, acting as CB1 and PPAR gamma ligand, promotes adipogenesis [34]. Therefore, higher production of PEA and lower of AEA in visceral adipose tissue, as found in rats fed Hsn-2 PA diet, may reduce inflammatory state and adipogenesis. The lower deposition of fat in visceral adipose tissue, might favor fat accumulation in subcutaneous adipose tissue. Interestingly, pig fat is characterized by a high portion of PA in sn-2 of the TAG backbone, and it has been shown that subcutaneous porcine preadipocytes proliferated more actively and showed more rapid accumulation of TAG than visceral derived adipocytes [35]. Similarly, human milk contains most of PA in sn-2 position, and babies accumulate fat mainly in the subcutanoeus compartments [36]. It is well known that accumulation in subcutaneous adipose tissue does not lead to dismetabolism and insulin resistance as opposite to an excess accumulation in visceral adipose tissue, which leads to visceral obesity [37]. Interestingly, several studies demonstrated the protective effect of breastfeeding against obesity in childhood [38, 39] and adulthood [40–43]. Future studies will aim at verifying whether Hsn-2 PA may be a nutritional tool to significantly affect body fat distribution and thereby to protect from visceral obesity.

The increase of PEA in adipose tissue was associated to a reduction of plasma TNF alpha after treatment with LPS, while other pro-inflammatory cytokines such as IL-1 and IL-6 did not change significantly. Whether the effect of Hsn-2 PA is limited to TNF alpha, as it has been shown for PEA [13], or the anti-inflammatory activity is not sufficiently strong to also influence IL-1 and IL-6 levels, remains to be elucidated.

Peculiarly, in the other tissues we found increased levels of OEA and not PEA as one could expect. We may hypothesized that in the liver PA may undergo elongation and delta 9 desaturation to form OA and thereby OEA. However, we did not find any change in OA, only in muscle we found a significant higher level of OA in the NEFA fraction. Interestingly, recently it has been shown that dietary Hsn-2 PA increases non esterified plasma 18:0 in term infants [44], which may enter into muscle and, after delta 9 desaturation, form OA.

On the other hand, the no changes of OA found in other lipid fraction, is likely due to the abundant level of oleic acid in all tissues. In addition, in vitro studies in rat horizontal slices containing the midbrain, incubated for 1h with PA [45], we found increased levels of OEA but not of PEA and no change in PA concentration.

The global increase of OEA in different tissues may have important implications in terms of energy metabolism and body composition. In fact, OEA has been demonstrated to be a strong ligand of PPAR alpha, which regulates fatty acid metabolism in liver and muscle [46] and modulate several functions in the CNS [45]. Recently, it has been shown that OEA, is able to regulate dopamine homeostasis [47], consolidate memory [18], and may also influence hunger/satiety circuitry [48].

This could also explain the lower food intake, albeit not significant, recorded in Hsn-2 PA fed rats even though did not result in changes in weight gain but in an improved feed efficiency. Interestingly, breast fed babies has been shown to have lower food intake with respect to those fed infant formula [49], while whether they have similar growth is still debated [50]. Targeted experiments should be carried out in order to evaluate the possible effect of Hsn-2 PA in favoring a physiological growth.

To our knowledge, this the first report showing an influence of the dietary fatty acid position in the TAG backbone on endocannabinoid and congeners biosynthesis. Based on our data, the fatty acid in sn-2 position from the diet is preferentially incorporated into tissue PLs. Recently, it has been shown that dietary Hsn-2 PA increases PA in sn-2 TAG in term infants plasma [44]. Whether the preferential incorporation of PA into sn-2 plasma TAG favors tissue incorporation of PA into PLs should be further investigated.

There is at least one more example on the influence of the different properties of dietary fatty acids based on their form, on endocannabinoid biosynthesis. It has been shown that dietary EPA and DHA in PL form down-regulate endocannabinoid biosynthesis more efficiently than in the dietary TAG form, in experimental animals [32] and humans [51].

Overall our data demonstrate that Hsn-2 PA by increasing PA in tissue PLs modulate NAEs biosynthesis in different tissues resulting in a lower susceptibility to inflammation, improved feed efficiency, and opens to possible activities in the regulation of fat deposition and brain function.