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BackgroundThe innate immune response is the first line of defence against invading microorganisms and it is also activated in different neurologic/neurodegenerative pathological scenarios. As a result, the family of the innate immune toll-like receptors (TLRs) and, in particular, the genetic/pharmacological manipulation of the TLR-4 signalling pathway emerges as a potential therapeutic strategy. Growing evidence relates stress exposure with altered immune responses, but the precise role of TLR-4 remains partly unknown.MethodsThe present study aimed to elucidate whether the elements of the TLR-4 signalling pathway are activated after acute stress exposure in rat brain frontal cortex and its role in the regulation of the stress-induced neuroinflammatory response, by means of its pharmacological modulation with the intravenous administration of the TLR-4 specific inhibitor TAK-242. Considering that TLR-4 responds predominantly to lipopolysaccharide from gram-negative bacteria, we checked whether increased intestinal permeability and a resultant bacterial translocation is a potential regulatory mechanism of stress-induced TLR-4 activation.ResultsAcute restraint stress exposure upregulates TLR-4 expression both at the mRNA and protein level. Stress-induced TLR-4 upregulation is prevented by the protocol of antibiotic intestinal decontamination made to reduce indigenous gastrointestinal microflora, suggesting a role for bacterial translocation on TLR-4 signalling pathway activation. TAK-242 pre-stress administration prevents the accumulation of potentially deleterious inflammatory and oxidative/nitrosative mediators in the brain frontal cortex of rats.ConclusionsThe use of TAK-242 or other TLR-4 signalling pathway inhibitory compounds could be considered as a potential therapeutic adjuvant strategy to constrain the inflammatory process taking place after stress exposure and in stress-related neuropsychiatric diseases.

Stress is known to be one of the risk factors of stroke, but only a few experimental studies have examined the possible mechanisms by which prior stress may affect stroke outcome. In stroke patients, infections impede neurological recovery and increase morbidity as well as mortality. We previously reported that stress induces a bacterial translocation and that prior immobilization stress worsens experimental stroke outcome through mechanisms that involve inflammatory mediators such as release of proinflammatory cytokines and enzyme activation. We now investigate whether bacterial translocation from the intestinal flora of rats with stress before experimental ischemia is involved in stroke outcome. We used an experimental paradigm consisting of exposure of Fischer rats to repeated immobilization sessions before permanent middle cerebral artery occlusion (MCAO). The presence of bacteria and the levels and expression of different mediators involved in the bacterial translocation were analyzed. Our results indicate that stress before stroke is related to the presence of bacteria in different organs (mesenteric nodes, spleen, liver, and lung) after MCAO and increases inflammatory colonic parameters (such as cyclooxygenase-2, inducible nitric oxide synthase, and myeloperoxidase), but decreases colonic immunoglobulin A, and these results are correlated with colonic inflammation and bacterial translocation. Understanding the implication of bacterial translocation during stress-induced stroke worsening is of great potential clinical relevance, given the high incidence of infections after severe stroke and their main role in mortality and morbidity in stroke patients.

Although alterations in the gut microbiota have been linked to the pathophysiology of major depressive disorder (MDD), including through effects on the immune response, our understanding is deficient about the straight connection patterns among microbiota and MDD in patients. Male and female MDD patients were recruited: 46 patients with a current active MDD (a-MDD) and 22 in remission or with only mild symptoms (r-MDD). Forty-five healthy controls (HC) were also recruited. Psychopathological states were assessed, and fecal and blood samples were collected. Results indicated that the inducible nitric oxide synthase expression was higher in MDD patients compared with HC and the oxidative stress levels were greater in the a-MDD group. Furthermore, the lipopolysaccharide (an indirect marker of bacterial translocation) was higher in a-MDD patients compared with the other groups. Fecal samples did not cluster according to the presence or the absence of MDD. There were bacterial genera whose relative abundance was altered in MDD: Bilophila (2-fold) and Alistipes (1.5-fold) were higher, while Anaerostipes (1.5-fold) and Dialister (15-fold) were lower in MDD patients compared with HC. Patients with a-MDD presented higher relative abundance of Alistipes and Anaerostipes (1.5-fold) and a complete depletion of Dialister compared with HC. Patients with r-MDD presented higher abundance of Bilophila (2.5-fold) compared with HC. Thus, the abundance of bacterial genera and some immune pathways, both with potential implications in the pathophysiology of depression, appear to be altered in MDD, with the most noticeable changes occurring in patients with the worse clinical condition, the a-MDD group.