Anti-nociceptive effect of Arbutus andrachne L. methanolic leaf extract mediated by CB1, TRPV1 and PPARs in mouse pain models

Natural Active Ingredients and TRPV1 Modulation: Focus on Key Chemical Moieties Involved in Ligand-Target Interaction

Diseases such as cancer, neurological pathologies and chronic pain represent currently unmet needs. The existing pharmacotherapeutic options available for treating these conditions are limited by lack of efficiency and/or side effects. Transient receptor potential vanilloid 1 ion channel emerged as an attractive therapeutic target for developing new analgesic, anti-cancer and antiepileptic agents. Furthermore, various natural ingredients were shown to have affinity for this receptor. The aim of this narrative review was to summarize the diverse natural scaffolds of TRPV1 modulators based on their agonistic/antagonistic properties and to analyze the structure-activity relationships between the ligands and molecular targets based on the results of the existing molecular docking, mutagenesis and in vitro studies. We present here an exhaustive collection of TRPV1 modulators grouped by relevant chemical features: vanilloids, guaiacols, phenols, alkylbenzenes, monoterpenes, sesquiterpenoids, alkaloids, etc. The information herein is useful for understanding the key structural elements mediating the interaction with TRPV1 and how their structural variation impacts the interaction between the ligand and receptor. We hope this data will contribute to the design of novel effective and safe TRPV1 modulators, to help overcome the lack of effective therapeutic agents against pathologies with high morbidity and mortality.

Antinociceptive and Anti-inflammatory Effect of Corynoline in Different Nociceptive and Inflammatory Experimental Models

Pain is growing to be a massive health issue across the globe. It is reported that one in every five adults tends to suffer from pain worldwide each year, regardless of age and gender. Inflammation caused by tissue damage, chemical stimulus, and foreign substances is commonly associated with pain. Inflammatory pain is mainly caused by the direct effect of inflammatory mediators on particular classes of nociceptive neurons. In the current investigation, the antinociceptive and anti-inflammatory effect of corynoline, a phytochemical compound isolated from Corydalis bungeana Turcz., has been evaluated in experimental mice. The experimental mice were divided into 5 groups of 6 animals each. The first control group was fed with water. The second, third, and fourth groups received different doses of corynoline and the fifth group of mice received positive controls. Nociception was induced with the help of acetic acid, formalin, glutamate, capsaicin, hot plate, and tail immersion in mice whereas carrageenan was used to induce inflammation. The peritoneal cavity leukocyte infiltration and pro-inflammatory mediator generation were also analyzed to confirm the anti-inflammatory effect and the natural locomotor activity was determined using an open field test. Corynoline treatment significantly suppressed the paw licking, writhing in the abdominal region, and displayed high nociceptive inhibitory reaction in a dose-related manner. Additionally, corynoline significantly reduced the carrageenan-triggered paw edema and also reduced the levels of pro-inflammatory cytokines. Thus, the antinociceptive and anti-inflammatory activity of corynoline has been successfully established.

KCNQ and KCNE Isoform-Dependent Pharmacology Rationalizes Native American Dual Use of Specific Plants as Both Analgesics and Gastrointestinal Therapeutics

Indigenous peoples of the Americas are proficient in botanical medicine. KCNQ family voltage-gated potassium (Kv) channels are sensitive to a variety of ligands, including plant metabolites. Here, we screened methanolic extracts prepared from 40 Californian coastal redwood forest plants for effects on Kv current and membrane potential in Xenopus oocytes heterologously expressing KCNQ2/3, which regulates excitability of neurons, including those that sense pain. Extracts from 9 of the 40 plant species increased KCNQ2/3 current at –60 mV by ≥threefold (maximally, 15-fold by Urtica dioica) and/or hyperpolarized membrane potential by ≥-3 mV (maximally, –11 mV by Arctostaphylos glandulosa). All nine plants have traditionally been used as both analgesics and gastrointestinal therapeutics. Of two extracts tested, both acted as KCNQ-dependent analgesics in mice. KCNQ2/3 activation at physiologically relevant, subthreshold membrane potentials by tannic acid, gallic acid and quercetin provided molecular correlates for analgesic action of several of the plants. While tannic acid also activated KCNQ1 and KCNQ1-KCNE1 at hyperpolarized, negative membrane potentials, it inhibited KCNQ1-KCNE3 at both negative and positive membrane potentials, mechanistically rationalizing historical use of tannic acid-containing plants as gastrointestinal therapeutics. KCNE dependence of KCNQ channel modulation by plant metabolites therefore provides a molecular mechanistic basis for Native American use of specific plants as both analgesics and gastrointestinal aids.