Cy3 RNA Several observations about structure activity
Several observations about structure–activity relationships can be made from this series, including that: (1) all lead compounds are NSAIDs of the 2-arylpropionic Cy3 RNA class, (2) analogues with -oriented aryl substituents showed the best inhibition of FAAH, and (3) replacing the ether linkage of fenoprofen with a ketone (in ketoprofen) significantly reduced TRPV1 inhibition. Furthermore, an amide linker, rather than a carbamate or urea, was present in all analogues, consistent with the observation that amide linkers are better suited to provide dual inhibition of FAAH and TRPV1.
There was greater inhibition of FAAH by the NSAID analogues and AA-5-HT in the IC assays using ethanol as a stock solvent than there was in initial screens where the analogues were delivered in DMSO (). The use of ethanol allowed AA-5-HT to be aliquoted on ice without freezing the solvent and the effect on inhibition may be due to improved solubility or dispersal of the compounds in buffer when delivered in ethanol. In the IC assays, AA-5-HT was aliquoted on ice and flushed with argon to minimize loss of inhibitory activity, presumably due to oxidation of its unsaturated fatty acid chain. The NSAID-5-HT analogues, which did not require aliquoting on ice or the use of an inert gas during handling, are likely to have better drug properties than AA-5-HT in regard to stability and oral bioavailability.
Hyperthermia has been a hindrance to the development of TRPV1 antagonists. This side-effect has been hypothesized to be due to inhibition of TRPV1 by molecules that bind the proton binding site, as opposed to the capsaicin binding site, since hyperthermia seems to be associated only with antagonists that inhibit activation of TRPV1 by acidic pH. The effect of NSAID-5-HT analogues on body temperature has not been determined. However, systemic administration of AA-5-HT did not cause hyperthermia in mice.
Introduction Toll-like receptors (TLRs) are key players in host defense, homeostasis and response to injury. However, uncontrolled and aberrant TLR activation has been proposed to trigger the onset of certain psychiatric and neurodegenerative disorders and elicit detrimental effects on the progression and outcome of established disease [for reviews see (Arroyo et al., 2011, Bergink et al., 2014, Deleidi and Isacson, 2012, Reus et al., 2015)]. Furthermore, TLR-induced neuroinflammation results in a constellation of behavioural changes which include altered appetite, reduced mood, cognitive changes, anxiety and anhedonia. Accumulating evidence demonstrates potent immunoregulatory effects of the endogenous cannabinoid (endocannabinoid) system, suggesting that this system may represent an important therapeutic target in disorders with a neuroinflammatory component [for reviews see (Downer, 2011, Fitzgibbon et al., 2015, Henry et al., 2016)]. The most widely studied endocannabinoid, N-arachidonoyl ethanolamine (AEA, also referred to as anandamide), has been shown to modulate neuroimmune responses, including those induced following TLR activation, although the effects depend on conditions under investigation. For example, several in vitro studies have demonstrated that increasing AEA tone, directly or via inhibition of the primary enzyme responsible for its metabolism, the serine hydrolase fatty acid amide hydrolase (FAAH), is associated with attenuation of TLR4-induced production of pro-inflammatory cytokines and mediators such as TNFα, IL-1β, prostaglandins and nitric oxide (Facchinetti et al., 2003, Molina-Holgado et al., 1997, Ortega-Gutierrez et al., 2005, Puffenbarger et al., 2000, Tham et al., 2007), while concurrently increasing anti-inflammatory mediators such as IL-10 (Correa et al., 2010, Krishnan and Chatterjee, 2012). However, data also demonstrate an augmentation of TLR4-induced pro-inflammatory mediators such as IL-6 by AEA (Molina-Holgado et al., 1998, Ortega-Gutierrez et al., 2005). While some studies have demonstrated anti-inflammatory effects of AEA on TLR4-induced inflammatory responses to be mediated by cannabinoid CB1 and/or CB2 receptor activation and consequential regulation of NFκB and MAPK activation (Correa et al., 2009, Correa et al., 2010, Krishnan and Chatterjee, 2012, Ortega-Gutierrez et al., 2005), non-CB1/CB2 receptor mediated effects of AEA on inflammatory processes in vitro have also been reported (Correa et al., 2008, Tham et al., 2007). AEA also has affinity for and activity at additional receptor targets to CB1 and CB2 receptors, namely the peroxisome proliferator-activated receptors (PPARs), the transient receptor potential cation channel, subfamily V, member 1 (TRPV1) and also the novel cannabinoid receptor, G-protein coupled receptor (GPR)55 [for reviews see (Alexander and Kendall, 2007, Di Marzo et al., 2001, Madasu et al., 2015, O'Sullivan and Kendall, 2010)], activity at which may account for the variability in the effects of AEA on neuroinflammatory responses following TLR activation.