## 4 Discussion
Preliminarily, the expression of CB2 receptors was checked in synovial membranes from OA and non-OA joints, and we found that it was expressed only in non-OA joints and was completely absent in OA. This finding agrees with the observations of [PERSON] and coworkers, who found that CB2 receptors are expressed in rheumatoid arthritis (RA) synovial membranes and not in OA synovial membranes [46]. Moreover, they showed that CB2 plays an anti-inflammatory role in RA, and the treatment of RA synoviocytes with an agonist of CB2 blocked the production of proinflammatory mediators, through the inhibition of adenylyl cyclase, which, in turn, did not produce cAMP. Thus, protein kinase A was not activated,finally leading to failure of the activation of NF-kB [46]. Accordingly, the absence of CB2 in OA synovial membranes, which has been observed in our samples, can be associated with the activated inflammatory pathways present in joints of OA patients. Several studies showed the activation of NF-kB in OA joints [34; 47]; thus, the activation of pathways or molecules that can downregulate NF-kB activity is very desirable [48; 49]. Moreover, [PERSON] and coworkers showed that CB2\({}^{\prime\prime}\)- mice had a greater susceptibility to OA [4]. The phosphoinositide (PI)-dependent signal plays important roles in many cellular processes, among them proinflammatory pathways, the alteration of which is involved in the onset and progression of several diseases [50]. The PI-phospholipase C (PI-PLC) \(\beta\)1 isoform has been described as differently modulated in osteoblasts from OA and RA patients [51]. We analyzed the synovial membranes from OA and non-OA patients for the presence of PI-PLC \(\beta\)1-\(\beta\)4, finding that \(\beta\)1 and \(\beta\)4 were almost unexpressed both in OA and non-OA tissues, whereas \(\beta\)3 was equally expressed in both tissues. Interestingly, \(\beta\)2 was highly expressed in OA and poorly expressed in non-OA, suggesting that only \(\beta\)2 is related to injured OA tissue. These findings prompted us to evaluate whether the _H. procumbens_ extracts were able to modulate both CB2 and PI-PLC \(\beta\)2 in isolated human primary FLSs, finding that \(\text{HPE}_{\text{H2O}}\) and \(\text{HPE}_{\text{DMSO}}\) stimulated the expression of CB2 receptors and decreased the expression of PI-PLC \(\beta\)2, whereas the \(\text{HPE}_{\text{EOH50}}\) had a weak effect and \(\text{HPE}_{\text{EOH100}}\) was completely ineffective on the expression of these two molecules. Thus, the ability of \(\text{HPE}_{\text{H2O}}\) and \(\text{HPE}_{\text{DMSO}}\) to increase the expression of CB2 receptors may explain the anti-inflammatory and antinociceptive activity of this plant. The role of PI-PLC \(\beta\)2 in inflammatory pathways has not been described so far; for this reason, the inhibition of its expression needs to be explored more in depth. We suppose that its expression in OA tissue could be associated with stimulation of the proinflammatory pathway through the activation of protein kinase C.  
Moreover, further anti-inflammatory mechanisms are affected, as shown by the inhibition of FAAH in all the analyzed HPE extracts. The best inhibition was shown by \(\text{HPE}_{\text{EOH100}}\) and \(\text{HPE}_{\text{EOH50}}\), so we can hypothesize that volatile compounds, such as \(\beta\)-caryophyllene, eugenol, and \(\alpha\)-humulene, can be involved in these HPE effects.