Antiarthritic Effects of a Root Extract from Harpagophytum procumbens DC: Novel Insights into the Molecular Mechanisms and Possible Bioactive Phytochemicals

Harpagophytum procumbens (Burch.) DC. ex Meisn. is a traditional remedy for osteoarticular diseases, including osteoarthritis (OA), although the bioactive constituents and mechanisms involved are yet to be clarified. In the present study, an aqueous H. procumbens root extract (HPE; containing 1.2% harpagoside) was characterized for its effects on synoviocytes from OA patients and phytochemical composition in polyphenols, and volatile compounds were detected. HPE powder was dissolved in different solvents, including deionized water (HPE(H2O)), DMSO (HPE(DMSO)), 100% v/v ethanol (HPE(EtOH100)), and 50% v/v ethanol (HPE(EtOH50)). The highest polyphenol levels were found in HPE(DMSO) and HPE(EtOH50), whereas different volatile compounds, mainly β-caryophyllene and eugenol, were detected in all the extracts except for HPE(H2O). HPE(H2O) and HPE(DMSO) were able to enhance CB2 receptor expression and to downregulate PI-PLC β2 in synovial membranes; moreover, all the extracts inhibited FAAH activity. The present results highlight for the first time a multitarget modulation of the endocannabinoid system by HPE, likely ascribable to its hydrosoluble compounds, along with the presence of volatile compounds in H. procumbens root. Although hydrosoluble compounds seem to be mainly responsible for endocannabinoid modulation by HPE, a possible contribution of volatile compounds can be suggested, strengthening the hypothesis that the entire phytocomplex can contribute to the H. procumbens healing properties.