Ameliorative potential of standardized fruit extract of Pterodon pubescens Benth on neuropathic pain in mice: Evidence for the mechanisms of action

Plant-derived natural products targeting ion channels for pain

Chronic pain affects approximately one-fifth of people worldwide and reduces quality of life and in some cases, working ability. Ion channels expressed along nociceptive pathways affect neuronal excitability and as a result modulate pain experience. Several ion channels have been identified and investigated as potential targets for new medicines for the treatment of a variety of human diseases, including chronic pain. Voltage-gated channels Na⁺ and Ca²⁺ channels, K⁺ channels, transient receptor potential channels (TRP), purinergic (P2X) channels and acid-sensing ion channels (ASICs) are some examples of ion channels exhibiting altered function or expression in different chronic pain states. Pharmacological approaches are being developed to mitigate dysregulation of these channels as potential treatment options. Since natural compounds of plant origin exert promising biological and pharmacological properties and are believed to possess less adverse effects compared to synthetic drugs, they have been widely studied as treatments for chronic pain for their ability to alter the functional activity of ion channels. A literature review was conducted using Medline, Google Scholar and PubMed, resulted in listing 79 natural compounds/extracts that are reported to interact with ion channels as part of their analgesic mechanism of action. Most in vitro studies utilized electrophysiological techniques to study the effect of natural compounds on ion channels using primary cultures of dorsal root ganglia (DRG) neurons. In vivo studies concentrated on different pain models and were conducted mainly in mice and rats. Proceeding into clinical trials will require further study to develop new, potent and specific ion channel modulators of plant origin.

Antiproliferative Effects of Pterodon pubescens Extract and Isolated Diterpenes in HaCaT Cells

Pterodon pubescens fruits are popularly used because of their analgesic and anti-inflammatory actions, which are attributed to the isolated compounds with a vouacapan skeleton. This work aimed to evaluate the antiproliferative and anti-inflammatory effects of a P. pubescens fruit dichloromethane extract and the vouacapan diterpene furan isomer's mixture (1 : 1) (6α-hydroxy-7β-acetoxy-vouacapan-17β-oate methyl ester and 6α-acetoxy-7β-hydroxy-vouacapan-17β-oate methyl ester isomers) in HaCaT cells using the cell migration and the BrDU incorporation assay. Levels of IL-8 were measured by ELISA after TNF-α stimulation. HPLC/DAD analysis of the extract revealed the expressive presence of vouacapan diterpene furan isomer's mixture. P. pubescens extract (1.5625 - 25 µg/mL) and vouacapan diterpene furan isomer's mixture (3.125 - 50 µM) inhibited cell proliferation as indicated by a decreased BrdU-incorporation. For the evaluation of cell migration, time-lapse microscopy was used. P. pubescens presented inhibition on cell migration at all concentrations tested (3.125 - 12.5 µg/mL), whereas for the VDFI mixture, the inhibition was only observed at the highest concentrations (12.5 and 25 µM) tested. Furthermore P. pubescens extract and vouacapan diterpene furan isomer's mixture significantly decreased IL-8 levels. Our results showed antiproliferative and anti-inflammatory effects on HaCaT cells treated with the extract and the vouacapan isomer's mixture, without affecting cell viability. These activities could be attributed to the voucapan molecular structures. In conclusion, topical products developed of P. pubescens extract or the voucapan isomer's mixture should be further studied as a potential product for local treatment against hyperproliferative lesions as in psoriasis vulgaris, representing an alternative treatment approach.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Analgesic Effect of 5-(3,4-Dihydroxyphenyl)-3-hydroxy-1-(2-hydroxyphenyl)penta-2,4-dien-1-one in Experimental Animal Models of Nociception

Curcuminoids derived from turmeric rhizome have been reported to exhibit antinociceptive, antioxidant and anti-inflammatory activities. We evaluated the peripheral and central antinociceptive activities of 5-(3,4-dihydroxyphenyl)-3-hydroxy-1-(2-hydroxyphenyl)penta-2,4-dien-1-one (DHHPD), a novel synthetic curcuminoid analogue at 0.1, 0.3, 1 and 3 mg/kg (intraperitoneal), through chemical and thermal models of nociception. The effects of DHHPD on the vanilloid and glutamatergic systems were evaluated through the capsaicin- and glutamate-induced paw licking tests. Results showed that DHHPD significantly (p < 0.05) attenuated the writhing response produced by the 0.8% acetic acid injection. In addition, 1 and 3 mg/kg of DHHPD significantly (p < 0.05) reduced the licking time spent by each mouse in both phases of the 2.5% formalin test and increased the response latency of mice on the hot-plate. However, the effect produced in the latter was not reversed by naloxone, a non-selective opioid receptor antagonist. Despite this, DHHPD decreased the licking latency of mice in the capsaicin- and glutamate-induced paw licking tests in a dose response manner. In conclusion, DHHPD showed excellent peripheral and central antinociceptive activities possibly by attenuation of the synthesis and/or release of pro-inflammatory mediators in addition to modulation of the vanilloid and glutamatergic systems without an apparent effect on the opioidergic system.

Oil from the fruits of Pterodon emarginatus Vog.: A traditional anti-inflammatory. Study combining in vivo and in silico

ETHNOBOTANICAL RELEVANCE

The oil obtained from the fruits of Pterodon emarginatus Vog. (OPe) is used orally and topically, in traditional medicine for some purposes, such as acute and chronic inflammatory states as rheumatoid arthritis.

MATERIALS AND METHODS

In this work, the anti-inflammatory activity of the OPe was demonstrated based on several animal models and presented an in silico study based on the 6α,7β-dihydroxy-vouacapan-17β-oic acid (DHVA) majority compound of the OPe to evaluate the interaction this compound, with cyclooxygenase-2 (COX-2) in 4COX (Mus musculus) and 5KIR (Homo sapiens) and molecular dynamics simulation.

RESULTS

The OPe (498 mg/kg, p.o) significantly inhibited (p < 0.05, Student t-test) the primary and secondary reactions of arthritis by Freund's Complete Adjuvant (FCA) and in dermatitis induced by croton oil in mice, OPe inhibited peak of edema. In vascular permeability test in rats, the treatment with OPe was able to block the response to PGE₂, serotonin, and bradykinin (p < 0.05, Student t-test). In the writhing test in mice, the OPe at doses of 498 and 980 mg/kg (p.o) produced inhibition of 73% and 92%, respectively, and was not significantly effective in the hot plate test. In the evaluation of the potency in relation to gastric injury (gastric ulcer induced by stress) and combined assay in the assessment of anti-inflammatory potency and gastric damage, it was observed that indomethacin (10 mg/kg, p.o.) inhibited carrageenan edema by 51% and produced a higher number of gastric lesions when compared to the group treated with OPe, where only areas of hyperemia were observed, without the occurrence of ulcerative lesion, and which inhibited the edema by 47%. In the in silico study, it was found that the DHVA is capable of binding to two organisms (4COX - Mus musculus and 5KIR - Homo sapiens), however, with higher binding affinity to the organism Homo sapiens.

CONCLUSIONS

As expected, all tested ligands were capable of forming hydrogen interactions with residues at their respective binding sites, but the DHVA ligand was capable of creating slightly more hydrogen bonds when docked to either 4COX or 5KIR than the other tested ligands, thus demonstrating the participation of this compound in the anti-inflammatory and antialgic responses observed in the in vivo assays as a COX-2 inhibitor. Therefore, the results obtained support the traditional use of OPe for inflammatory and gastric problems.

Ethnobotanical study of medicinal plants used by Ribeirinhos in the North Araguaia microregion, Mato Grosso, Brazil

ETHNOPHARMACOLOGICAL IMPORTANCE

Currently, in many traditional communities, such as the riverine community in the North Araguaia microregion (Mato Grosso, Brazil), plant knowledge and use represent the main, if not the only, therapeutic resource for the maintenance of health and/or treatment of diseases. This study aimed to identify and document species of medicinal plants used by local experts from riverine communities in the North Araguaia microregion in Mato Grosso State, and to further chemical and pharmacological studies on species selected based on searches in the relevant literature.

MATERIALS AND METHODS

This is a cross-sectional ethnobotanical study, with non-probabilistic sampling (n =60), that applied the snowball method to select local riverine experts who understand medicinal plant use. Socio-demographic, ethnobotanical and ethnopharmacological data (vernacular name, uses, geographical origin, habit, method of preparation and part used) on medicinal plants were collected during semi-structured interviews. The results were analyzed by descriptive and quantitative means: indices of use-report (UR) were used to select plant species with therapeutic potential.

RESULTS

In total, 309 plant species belonging to 86 botanical families were cited; 73% were native to Brazil, and Fabaceae was the most representative family (11.3%). Arboreal was the predominant life form (37.2%). The leaf was the most used part (28.9%). Infusion was the most commonly reported method of preparation (31.3%). The plants reported in the survey were indicated for 18 of the 22 ICD-10 disease categories. The disease categories most commonly cited were the infectious and parasitic diseases (IPD, 718 UR), digestive system diseases (DSD, 565 UR) and respiratory system diseases (RSD, 504 UR), representing 16.6%, 13.1% and 11.7%, respectively of the total UR. Dysphania ambrosioides L. was the most sighted in the IPD category 50 UR. Copaifera langsdorffii Desf. (133), Lafoensia pacari A. St.-Hil. (131), and Cecropia pachystachya Trécul (126) were the species with the highest UR. Bidens pilosa L., Vernonia ferruginea Less, and L. pacari, respectively, were the most cited native plants used to treat such diseases. Of the 8 investigated native plants, C. langsdorffii, and Brosimum gaudichaudii are the most prominent: in addition to having been widely studied, in terms of phytochemical and pharmacological, these species have been marketed as pharmaceutical products, with associated patent deposits.

CONCLUSIONS

Local riverine experts from the North Araguaia microregion use a wide variety of medicinal plants in self-care health, especially those species used to treat IPD. The therapeutic potential of some of these plants has been scientifically validated; however, there are other species whose pharmacological effects and safety remain to be properly investigated. Thus, the present study, aside from being a basis for future chemical, pharmacological and agronomic bioprospecting studies, may contribute to the development of the management, conservation and sustainable use of medicinal flora in the microregion studied.

Antinociceptive effect of hydroalcoholic extract and isoflavone isolated from Polygala molluginifolia in mice: evidence for the involvement of opioid receptors and TRPV1 and TRPA1 channels

PURPOSE

The plants of the genus Polygala (Polygalaceae) have been used for a long time in folk medicine to treat pain and inflammation. The species Polygala molluginifolia is native to southern Brazil and is popularly known as "cânfora". The presented study analyzes the antinociceptive effect of hydroalcoholic extract from Polygala molluginifolia (HEPm) and an isoflavone (ISO) isolated from the extract, in behavioral models of pain in mice, as well as the mechanism underlying this effect.

MATERIALS AND METHODS

The phytochemical analysis of HEPm was performed through a capillary electrophoresis analysis and colorimetric test. The antinociceptive effects of HEPm and ISO (10-1000 mg/kg, i.g.) were evaluated by applying the formalin test; mechanical and thermal hyperalgesia to postoperative pain in mice. The possible involvement of opioid receptors, TRPV1 and TRPA1 channels in the antinociceptive effect of HEPm and ISO were also evaluated. Finally, the nonspecific effects of HEPm and ISO were evaluated by measuring locomotor activity (Open-field Test) and corporal temperature.

RESULTS

The 5,3',4'-trihydroxy-6″,6″-dimethylpyrano[2″,3″:7,6] isoflavone (ISO) was identified in HEPm by capillary electrophoresis analysis and selected for the experimental tests. The oral administration of HEPm or of ISO significantly inhibited the neurogenic and inflammatory phases of formalin-induced pain, edema formation and local hyperemia, without causing any change to locomotor activity. Acute and repeated treatment of animals with HEPm reduced mechanical and thermal (heat and cold) hyperalgesia in the postoperative pain. In addition, administering HEPm or ISO markedly reduced nociceptive behavior induced by the peripheral and central injection of TRPV1 and TRPA1 channels activators. Finally, the antinociception provided by the administration of HEPm or ISO was reversed by the preadministration of naloxone.

CONCLUSIONS

Taken together, these results provide the first experimental evidence of the significant antinociceptive effect of HEPm and ISO in animal models of acute pain without causing sedation or locomotor dysfunction. This effect appears to be mediated, at least in part, by the activation of opioid receptors and/or by the inhibition of TRPV1 and TRPA1 channels. Moreover, this study adds new scientific evidence and highlights the therapeutic potential of the medicinal plant Polygala molluginifolia in the development of phytomedicines with analgesic properties.