Management of the patient with chronic pain

Anti-hypersensitivity effects of the phthalimide derivative N-(4methyl-phenyl)-4-methylphthalimide in different pain models in mice

The treatment of chronic pain remains a challenge for clinicians worldwide, independent of its pathogenesis. It motivates several studies attempting to discover strategies to treat the disease. The in silico analysis using molecular docking approach demonstrated that the phthalimide N-(4methyl-phenyl)-4-methylphthalimide (MPMPH-1) presented high affinity to adenylyl-cyclase enzyme (AC). It also prominently reduced the mechanical hypersensitivity of mice challenged by Forskolin, an AC activator. This effect lasted for up to 48h after Forskolin injection, presenting activity longer than MDL-12330A (AC inhibitor). MPMPH-1 was also effective in reducing the hypersensitivity induced by IL-1β, bradykinin, prostaglandin E₂ or epinephrine, chemical mediators that have, among others, AC as pivotal protein in their signalling cascade to induce mechanical-pain behaviour. The compound presented marked inhibition in inflammatory-pain models induced by carrageenan, lipopolysaccharide or complete Freund's adjuvant, including neutrophil migration inhibition. Furthermore, it also seems to act in both peripheral and pain central-control pathways, being also effective in reducing the persistent cancer-pain behaviour induced by melanoma cells in mice. MPMPH-1 could represent a promising pharmacological tool to treat acute and chronic painful diseases, with good bioavailability, local activity, and lack of locomotor-activity interference. Further studies are necessary to determine the exact mechanism of action but it seems to involve AC enzyme as possible target.

Chrysophyllum cainito leaves are effective against pre-clinical chronic pain models: Analysis of crude extract, fraction and isolated compounds in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Chrysophyllum cainito L. (Sapotaceae), commonly known as caimito or star apple, is a neotropical tree valued for its ornamental quality and edible fruits. Besides its culinary use, the leaves are also popularly used to treat diabetes mellitus and several inflammatory diseases.

AIM OF THIS STUDY

This study aimed to complement previous data obtained about the anti-hypersensitivity effects of the crude methanol extract (CME), CHCl3 fraction and isolated compounds obtained from C. cainito.

MATERIALS AND METHODS

The CME, CHCl3 fraction and two isolated triterpenes identified as 3β-Lup-20(29)-en-3-yl acetate (1) and Lup-20(29)-en-3β-O-hexanoate (2) were evaluated regarding their effects using clinical pain models, such as post-operative, inflammatory and neuropathic pain. Acute inflammatory pain models induced by PGE2, epinephrine, LPS and CFA were also used to improve the knowledge about the mechanism of action.

RESULTS

The animals treated with the CME and submitted to PGE2, epinephrine, LPS or CFA had the mechanical hypersensitivity significantly reduced. When repeatedly administered, the CME enhanced the mechanical withdrawal threshold of mice submitted to post-operative pain model, CFA-induced chronic inflammatory pain and two different models of neuropathic pain. In turn, the CHCl3 fraction presented anti-hypersensitivity effect against epinephrine- or LPS-induced hypersensitivity, with a more prominent activity in both the neuropathic pain models. The compound 1 seems to present the same profile of the CHCl3, whereas compound 2 exhibited activity similar to the CME.

CONCLUSIONS

This data suggests that the CME effect involves interference in the production, release or action of some chemical mediators, such as PGE2, sympathetic amines, cytokines, etc. Part of these effects was observed with the CHCl3 fraction, emphasizing the prominent inhibition of neuropathic pain. The results also demonstrated that part of the CME effects are due to the presence of the triterpenes 1 and 2, but it is important to mention that we cannot discard the effects of countless other compounds presented in the crude extract, acting in a synergic way.