Soluble epoxide hydrolase inhibition reveals novel biological functions of epoxyeicosatrienoic acids (EETs)

Abstract

Early on, intriguing biological activities were found associated with the EETs using in vitro systems. Although the EETs other than the 5,6-isomer, are quite stable chemically, they are quickly degraded enzymatically with the sEH accounting in many cases for much of the metabolism. This rapid degradation often made it difficult to associate biological effects with the administration of EETs and other lipid epoxides particularly in vivo. Thus, it is the power to inhibit the sEH that has facilitated the demonstration of many physiological processes associated with EETs and possibly other epoxy fatty acids. In the last few years it has become clear that major roles of the EETs include modulation of blood pressure and modulation of inflammatory cascades. There are a number of other physiological functions now associated with the EETs including angiogenesis, neurohormone release, cell proliferation, G protein signaling, modulation of ion channel activity, and a variety of effects associated with modulation of NFkappaB. More recently we observed a role of the EETs as modulated by sEHI in reducing non-neuropathic pain. The array of biological effects observed with sEHI illustrates the power of modulating the degradation of chemical mediators in addition to the modulation of their biosynthesis, receptor binding and signal transduction. Many of these biological effects can be modulated by sEHIs but also by the natural eicosanoids and their mimics all of which offer therapeutic potential.

Fig. 1

The sEHI AUDA-be blocks carrageenan (CAR) induced local thermal hyperalgesia effectively. Male rats (n = 8) were administered 100 μl (2%) of CAR in saline by subplantar injections. CAR was injected immediately following baseline measurement of thermal hind paw withdrawal latency (PWL). AUDA-be was formulated in a neutral cream (Vanicream^™) and applied topically to the treated paw (100 mg/kg) 20 h post-CAR injection. PWL for the contralateral and ipsilateral (treated) paws were measured at each time point. Therefore AUDA-be had not only a prophylactic effect in reversing thermal hyperalgesia (data not shown), but it was also effective therapeutically.

Fig. 2

Synergistic reduction of PGE₂ plasma levels by combined treatment of COX and sEHI. Co-administration AUDA-be and NSAIDs produce a synergistic decrease in prostaglandin PGE₂ (black bars) and increase in EpETrEs (EETs grey bars), 6 h after LPS exposure. The data indicate that using a prophylactic dose of AUDA-be with a non-optimal therapeutic dose of COX inhibitor can further reduce PGE₂. The data represent an average ± S.D. (n = 4) and are depicted as percent of control mice receiving vehicle without LPS. *Significantly different from NSAID alone (p < 0.05) as determined by analysis of variance followed by Tukey’s test.

Fig. 3

A prophylactic dose of AUDA-be reduces hepatic COX-2 protein expression 6 h after LPS exposure relative to mice receiving LPS only. Results from individual inhibitors at various doses are in dark grey bars. Co-administration of the sEHI and rofecoxib is depicted as a light grey bar, indicating that a prophylactic dose of AUDA-be used in conjunction with a non-optimal therapeutic dose of rofecoxib (10 mg/kg) can further decrease COX-2 induction. Data represent the COX-2 protein levels ± S.D. (n = 3) in murine liver after exposure to LPS as determined by independent western blots. *Significantly different from vehicle (p < 0.05) as determined by analysis of variance followed by Tukey’s test. ^#Significantly different from AUDA-be alone (p < 0.05) as determined by analysis of variance followed by Tukey’s test.