Transient Receptor Potential Cation Channel Subfamily M Member 8 channels mediate the anti-inflammatory effects of eucalyptol.

BACKGROUND AND PURPOSE: Eucalyptol (1,8-cineol), the major ingredient in the essential oil of eucalyptus leaves and other medicinal plants, has long been known for its anti-inflammatory properties. Eucalyptol interacts with the TRP cation channels among other targets, but it is unclear which of these mediates its anti-inflammatory effects. EXPERIMENTAL APPROACH: Effects of eucalyptol were compared in wild-type and TRPM8 channel-deficient mice in two different models: footpad inflammation elicited by complete Freund's adjuvant (CFA) and pulmonary inflammation following administration of LPS. Oedema formation, behavioural inflammatory pain responses, leukocyte infiltration, enzyme activities and cytokine and chemokine levels were measured. KEY RESULTS: In the CFA model, eucalyptol strongly attenuated oedema and mechanical allodynia and reduced levels of inflammatory cytokines (IL-1ß, TNF-α and IL-6), effects comparable with those of ibuprofen. In the LPS model of pulmonary inflammation, eucalyptol treatment diminished leukocyte infiltration, myeloperoxidase activity and production of TNF-α, IL-1ß, IFN-γ and IL-6. Genetic deletion of TRPM8 channels abolished the anti-inflammatory effects of eucalyptol in both models. Eucalyptol was at least sixfold more potent on human, than on mouse TRPM8 channels. A metabolite of eucalyptol, 2-hydroxy-1,8-cineol, also activated human TRPM8 channels. CONCLUSION AND IMPLICATIONS: Among the pharmacological targets of eucalyptol, TRPM8 channels were essential for its anti-inflammatory effects in mice. Human TRPM8 channels are more sensitive to eucalyptol than rodent TRPM8 channels explaining the higher potency of eucalyptol in humans. Metabolites of eucalyptol could contribute to its anti-inflammatory effects. The development of more potent and selective TRPM8 agonists may yield novel anti-inflammatory agents.

Comparison of Glucosamine Absorption After Administration of Oral Liquid, Chewable, and Tablet Formulations to Dogs.

Glucosamine (GS) is commonly administered as a nutritional supplement to support joint function. Although many supplements are available, the effect of formulation on oral absorption in dogs is unknown. The purpose of this study was to determine the relative bioavailability of GS for liquid, chewable, and tablet formulations containing GS sulfate or hydrochloride and chondroitin sulfate. In a randomized cross-over design, supplements were administered daily for 8 days with a 1 wk washout period between treatments. Liquid or Tablet A was administered to four dogs, whereas Liquid or Tablet B was administered to four additional dogs. When nutraceutical exposure was normalized to the administered dose of GS free base, similar relative bioavailabilities were determined for all three formulations. However, the dose-normalized maximum plasma GS concentration was higher for the liquid supplement (5.5 ± 0.5 µg/mL) than for the two tablets (3.1 ± 0.6 and 2.1 ± 0.6 µg/mL, P < 0.001). Similarly, the time at which maximal plasma GS concentrations occurred was shorter for the liquid formulation (0.7 ± 0.5 hr) than for the two tablets (4.2 ± 0.6 and 5.0 ± 0.6 hr, P < 0.001). These data show that the formulation of joint supplements affects the oral absorption of GS in dogs.