Effects of Reference Analgesics and Psychoactive Drugs on the Noxious Heat Threshold of Mice Measured by an Increasing-Temperature Water Bath

Anti-Inflammatory and Analgesic Effect of Arachic Acid Ethyl Ester Isolated from Propolis

Inflammatory diseases are a real public health problem worldwide. Many synthetic drugs used in the treatment of inflammatory diseases such as steroidal anti-inflammatory drugs, nonsteroidal anti-inflammatory drugs (NSAIDs) and immunosuppressive drugs have harmful side effects. However, there are natural products like propolis, which is traditionally used in the treatment of pain. The objective of this work was to evaluate the anti-inflammatory and analgesic activities of the ethyl ester of arachic acid, a compound isolated from Cameroonian propolis. The ethyl ester of arachic acid was isolated by chromatography of the ethanolic extract of propolis harvested at Tala-Mokolo (Far North Region of Cameroon) and identified by nuclear magnetic resonance (NMR) spectra and the ¹H-¹H correlated spectroscopy. The anti-inflammatory and analgesic properties of oral administration of arachic acid ethyl ester (12.5, 25.0, and 50.0 mg/kg bw) were evaluated using carrageenan-induced paw edema, xylene-induced ear edema, cotton pellets-induced granuloma formation, and hot plate test in rat. Arachic acid ethyl ester produced maximum inhibition at 50.0 mg/kg for carrageenan-induced paw edema (62.5%), xylene-induced ear edema (54.5%), cotton pellet-induced granuloma (47.4%), and increased mean latency for hot plate test in rats. These results show clearly that the arachic acid ethyl ester has acute and chronic anti-inflammatory properties as well as central analgesic properties. This justifies the use of propolis in the treatment of pain in traditional medicine.

Could Mycolactone Inspire New Potent Analgesics? Perspectives and Pitfalls

Pain currently represents the most common symptom for which medical attention is sought by patients. The available treatments have limited effectiveness and significant side-effects. In addition, most often, the duration of analgesia is short. Today, the handling of pain remains a major challenge. One promising alternative for the discovery of novel potent analgesics is to take inspiration from Mother Nature; in this context, the detailed investigation of the intriguing analgesia implemented in Buruli ulcer, an infectious disease caused by the bacterium Mycobacterium ulcerans and characterized by painless ulcerative lesions, seems particularly promising. More precisely, in this disease, the painless skin ulcers are caused by mycolactone, a polyketide lactone exotoxin. In fact, mycolactone exerts a wide range of effects on the host, besides being responsible for analgesia, as it has been shown notably to modulate the immune response or to provoke apoptosis. Several cellular mechanisms and different targets have been proposed to account for the analgesic effect of the toxin, such as nerve degeneration, the inhibition of inflammatory mediators and the activation of angiotensin II receptor 2. In this review, we discuss the current knowledge in the field, highlighting possible controversies. We first discuss the different pain-mimicking experimental models that were used to study the effect of mycolactone. We then detail the different variants of mycolactone that were used in such models. Overall, based on the results and the discussions, we conclude that the development of mycolactone-derived molecules can represent very promising perspectives for new analgesic drugs, which could be effective for specific pain indications.