038P University of Nottingham
Focused Meeting Cannabinoid Research April 2007

Effects of inhibition of FAAH on levels of endocannabinoids in the hindpaw and spinal cord of rats with a carrageenan-induced inflamed hindpaw

Denise Richardson, Maulik Jhaveri, David Kendall, David Barrett, Victoria Chapman. University of Nottingham, Nottingham, United Kingdom.

The endocannabinoid (EC) system has been implicated in the pathogenesis of inflammatory pain. The EC anandamide (AEA) reduces carrageenan-induced inflammation and hyperalgesia in an animal model of inflammatory pain, via a peripheral mechanism (Richardson et al., 1998). One method to increase levels of ECs, such as AEA, is to inhibit their metabolism by the predominant hydrolytic enzyme; fatty acid amide hydrolase (FAAH). URB597 (cyclohexyl carbamic acid 3’-carbamoyl-biphenyl-3-yl ester) is a FAAH inhibitor which has been shown to increase levels of ECs and be anti-nociceptive in vivo. The aim of this study was to determine the effects of peripheral inhibition of FAAH on levels of ECs in the hindpaw of carrageenan-treated rats.

Male Sprague-Dawley rats (200-260 g) received an intraplantar injection of URB597 (25 μg / 100 μg in 50 μl) or vehicle (3% Tween 80 in saline) 30 minutes prior to intraplantar injection of carrageenan (2 mg in 100 μl) or vehicle (saline). 3 hours after injection of carrageenan or vehicle, rats were killed by stunning and decapitation and the hindpaw tissue was dissected rapidly onto dry ice. Samples were stored at -80oC until analysis. The ECs AEA and 2-arachidonyl glycerol (2-AG) were extracted and levels were quantified using a targeted liquid chromatography- tandem mass-spectrometry approach, based on a published method (Richardson et al., 2007).

Table 1. Effects of URB597 (URB, 25 μg and 100 μg in 50 μl) or vehicle on levels of AEA and 2-AG in the ipsilateral (ipsi) hindpaw of saline and carrageenan treated rats. Data were analysed using Kruskal-Wallis test (effect of URB vs vehicle comparisons), and are expressed as mean ± SEM. φφφ P < 0.001 vs ipsi vehicle-saline and † P < 0.05, †† P < 0.01, ††† P < 0.001 vs ipsi value of appropriate vehicle group.
AEA (pmol/g) 2-AG (nmol/g)
Vehicle-Saline 30±3 1.9±0.4
URB-Saline (25 μg) 44±8 2.6±0.4
URB-Saline (100 μg) 9.7±2 † 15±2 ††
Vehicle-Carrageenan 6.8±2 φφφ 1.9±0.5
URB-Carrageenan (25 μg) 21±5 † 4.3±1
URB-Carrageenan (100μg) 24±2 ††† 18±5 ††

These data show that intraplantar injection of carrageenan decreases levels of AEA in the ipsilateral (injected) hindpaw compared to saline-treated controls and the contralateral hindpaw (data not shown). Both doses of URB597 increased levels of AEA in the ipsilateral hindpaw of carrageenan-treated rats, compared to vehicle-carrageenan rats. By contrast, only the higher dose of URB597 increased levels of 2-AG in the ipsilateral hindpaw of both saline- and carrageenan-treated rats. This suggests an altered role of FAAH in carrageenan-treated rats compared to vehicle-treated rats.

Richardson, D. et al. (2007) Anal Biochem 360(2): 216-26

Richardson, J. et al. (1998) Pain 75(1): 111-9

This study was supported by the BBSRC.