Fatty liver, oxidative stress, and mitochondrial dysfunction are key pathophysiological features of insulin resistance and obesity. Butyrate, produced by fermentation in the large intestine by gut microbiota, and its synthetic derivative, the N-(1-carbamoyl-2-phenyl-ethyl) butyramide, FBA, have been demonstrated to be protective against insulin resistance and fatty liver. Here, hepatic mitochondria were identified as the main target of the beneficial effect of both butyrate-based compounds in reverting insulin resistance and fat accumulation in diet-induced obese mice. In particular, butyrate and FBA improved respiratory capacity and fatty acid oxidation, activated the AMPK-acetyl-CoA carboxylase pathway, and promoted inefficient metabolism, as shown by the increase in proton leak. Both treatments consistently increased utilization of substrates, especially fatty acids, leading to the reduction of intracellular lipid accumulation and oxidative stress. Finally, the shift of the mitochondrial dynamic toward fusion by butyrate and FBA resulted in the improvement not only of mitochondrial cell energy metabolism but also of glucose homeostasis. In conclusion, butyrate and its more palatable synthetic derivative, FBA, modulating mitochondrial function, efficiency, and dynamics, can be considered a new therapeutic strategy to counteract obesity and insulin resistance.

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Microglia respond rapidly to injury, increasing their synthesis and release of inflammatory mediators, many of which contribute to the maintenance of persistent pain following CNS or PNS injury. We have recently shown that the lysosomal cysteine protease Cathepsin S (CatS) expressed by spinal microglia is vital for the full expression of neuropathic pain. Here we evaluated the mechanisms by which CatS release occurs from primary microglia in culture. Stimulation of microglia with lipopolysaccharide (LPS) or adenosine tri-phosphate (ATP) alone was insufficient to induce release of enzymatically active CatS in extracellular media. However, following priming with LPS, ATP at 1 mM but not 50 μM resulted in significant release of CatS in the media and maturation of CatS protein in cell extracts. The enzymatic activity measured in media at neutral pH was specific for CatS as it was completely prevented by the CatS inhibitor LHVS. ATP-induced release of CatS required potassium efflux and both extracellular calcium influx and mobilization of intracellular calcium. Pharmacological modulation of ATP-induced release of CatS enzymatic activity revealed that this was dependent on activation of the P2X7 receptor and intracellular phospholipase C and phospholipase A(2). In addition, ATP-induced CatS release involved p38 mitogen activated protein kinase (MAPK) phosphorylation, but not ERK and PI3K signalling pathways. Thus, as high concentration of extracellular ATP promotes release of active CatS from microglia via P2X7 receptor activation, we suggest that the inhibition of CatS release is one of the mechanisms responsible for P2X7 antagonist efficacy in neuropathic pain.

BackgroundEnhanced supraspinal glutamate levels following nerve injury are associated with pathophysiological mechanisms responsible for neuropathic pain. Chronic pain can interfere with specific brain areas involved in glutamate-dependent neuropsychological processes, such as cognition, memory, and decision-making. The medial prefrontal cortex (mPFC) is thought to play a critical role in pain-related depression and anxiety, which are frequent co-morbidities of chronic pain. Using an animal model of spared nerve injury (SNI) of the sciatic nerve, we assess bio-molecular modifications in glutamatergic synapses in the mPFC that underlie neuropathic pain-induced plastic changes at 30 days post-surgery. Moreover, we examine the effects of palmitoylethanolamide (PEA) administration on pain-related behaviours, as well as the cortical biochemical and morphological changes that occur in SNI animals.ResultsAt 1 month, SNI was associated with mechanical and thermal hypersensitivity, as well as depression-like behaviour, cognitive impairments, and obsessive-compulsive activities. Moreover, we observed an overall glutamate synapse modification in the mPFC, characterized by changes in synaptic density proteins and amino acid levels. Finally, with regard to the resolution of pain and depressive-like syndrome in SNI mice, PEA restored the glutamatergic synapse proteins and changes in amino acid release.ConclusionsGiven the potential role of the mPFC in pain mechanisms, our findings may provide novel insights into neuropathic pain forebrain processes and indicate PEA as a new pharmacological tool to treat neuropathic pain and the related negative affective states.Graphical AbstractPalmitoylethanolamide: a new pharmacological tool to treat neuropathic pain and the related negative affective states.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-015-0139-5) contains supplementary material, which is available to authorized users.

The endogenous fatty acid amide palmitoylethanolamide (PEA) has been shown to exert anti-inflammatory actions mainly through inhibition of the release of pro-inflammatory molecules from mast cells, monocytes and macrophages. Indirect activation of the endocannabinoid (eCB) system is among the several mechanisms of action that have been proposed to underlie the different effects of PEA in vivo. In this study, we used cultured rat microglia and human macrophages to evaluate whether PEA affects eCB signaling. PEA was found to increase CB2 mRNA and protein expression through peroxisome proliferator-activated receptor-α (PPAR-α) activation. This novel gene regulation mechanism was demonstrated through: (i) pharmacological PPAR-α manipulation, (ii) PPAR-α mRNA silencing, (iii) chromatin immunoprecipitation. Moreover, exposure to PEA induced morphological changes associated with a reactive microglial phenotype, including increased phagocytosis and migratory activity. Our findings suggest indirect regulation of microglial CB2R expression as a new possible mechanism underlying the effects of PEA. PEA can be explored as a useful tool for preventing/treating the symptoms associated with neuroinflammation in CNS disorders.