Conjugated linoleic acid (CLA): elaboration of enriched fermented milk and evaluation of CLA-isomers effects on neuroinflammatory disease in vitro model

Abstract

Conjugated linoleic acid (CLA) is a mixture of geometric and positional conjugated isomers of linoleic acid (LA). CLA isomers are naturally present in foods, however, generally in small concentrations. Therefore, their intake values through natural sources are below of level recommended for achieving health beneficial effects. Thus, to increase the CLA content in foods is a technological challenge. Currently, the milk fermentation with CLA-producing bacteria is one of main technologies strategies studied with this objective. Nevertheless, the previous screening of lactic acid bacteria (LAB) by ability to produce CLA from LA in esterified way, similar those found in milk fat, still is a bottleneck in literature. Regard to bioactive effect of CLA, although CLA can freely get through the blood-brain barrier, it being metabolized in the brain, reports on CLA effects in the central nervous system are still scarce. Studies revealed CLA as potent anti-inflammatory modulator of immune response of peripheral macrophages and these effects of CLA are thought to be mainly via inhibition of NF-κB pathway in human in vivo models. Recently, microglial NF-κB was proposed as a pivotal therapeutic target in neurodegenerative disorders as Parkinson´s disease. CLA also primes macrophage M2 polarization in human in vitro models, and this would allow the targeting microglia polarization by CLA as a therapeutic avenue in neurodegenerative diseases. However, the effects of CLA on microglia are still unknown. In this context, the original hypothesis of first step of this work was that previous screen of LAB by ability to produce CLA from sterified lipid produces CLA-enriched fermented milk. In the second step of work, the major hypothesis was that CLA has antiinflammatory effect on microglial activation inhibiting the NF-κB pathway. The results of the first step of the present work showed that the previous selection of probiotic LAB strain by the ability to produce CLA from sunflower oil was a differential step to produce CLA-enriched fermented milk. Therefore, the probiotic Lactococcus lactis ssp. cremoris MRS 47 strain isolated from Brazilian kefir grains can increase the CLA content in the fermented milk. In the second step, CLA mitigated the mice primary microglia activation by LPS to reduce NO secretion. CLA completely prevented the suppression of arginase activity by LPS in primary microglia, driven it from M1 to M2 phenotype. This polarization was isomer-specific and, at least in part, due to inhibition of NF- κB and iNOS pathways through expression of IκBα inhibitor. Finally, co-treatment with CLA and LPS completely prevented cortical neuronal death induced by the endotoxin, being this neuroprotection also isomer-specific. Thus, CLA has potential as anti-inflammatory and neuroprotective agents against microglia-mediated neuroinflammatory disorders, in what seems to have isomer-specific particularities.