Impact of the acute local inhibition of soluble epoxide hydrolase on diabetic skin microcirculatory dysfunction

Abstract

The impact of the local inhibition of soluble epoxide hydrolase, which metabolizes vasodilator and anti-inflammatory epoxyeicosanoids, on diabetic skin microvascular dysfunction was assessed. In diabetic db/db mice, basal skin blood flow assessed using laser Doppler imaging was similar to that of control mice, but thermal hyperemia was markedly reduced. At 2 h after the topical administration of an aqueous gel containing the soluble epoxide hydrolase inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB: 400 mg/L), the peak concentration of t-AUCB was detected in the skin of diabetic mice, which quickly decreased thereafter. In parallel, 2 h after application of t-AUCB treatment, thermal hyperemia was increased compared to the control gel. Quantification of t-AUCB in plasma of treated animals showed no or low systemic diffusion. Furthermore, haematoxylin and eosin histological staining of skin biopsies showed that skin integrity was preserved in t-AUCB-treated mice. Finally, for pig ear skin, a surrogate for human skin, using Franz diffusion cells, we observed a continuous diffusion of t-AUCB from 2 h after application to beyond 24 h. A single topical administration of a soluble epoxide hydrolase inhibitor improves microcirculatory function in the skin of db/db mice and might represent a new therapeutic approach for preventing the development of skin complications in diabetic patients.

Keywords: Diabetes; skin microvascular dysfunction; soluble epoxide hydrolase; topical form.

Figure 1.

Basal skin blood flow (A) and thermal hyperemia (B) measured by laser Doppler imaging in control (n=7) and db/db mice (n=31). A.P.U.: arbitrary perfusion unit.

Figure 2.

Basal skin blood flow (A) and thermal hyperemia (B) measured by laser Doppler imaging before and after a 2-hour topical application of the t-AUCB-containing gel (20 μL at 400 mg/L) and the vehicle control gel on the dorsal skin of db/db mice (n=13). *P<0.05 vs. before topical application, ^†P<0.05 vs. vehicle control gel. A.P.U.: arbitrary perfusion unit.

Figure 3.

A, Skin levels of t-AUCB, quantified by liquid chromatography coupled to tandem mass spectrometry, 2 (n=5) and 24 hours (n=6) after topical application of the t-AUCB-containing gel (20 μL at 400 mg/L) on the dorsal skin of db/db mice. B, Thermal hyperemia measured by laser Doppler imaging before (n=19), 2 (n=13) and 24 hours (n=6) after the topical application of the t-AUCB-containing gel on the dorsal skin of db/db mice. *P<0.05 vs. before topical application. A.P.U.: arbitrary perfusion unit.

Figure 4.

Representative images of hematoxylin & eosin staining of mouse skin 8 and 24 hours after topical application of t-AUCB-containing gel (20 μL at 400 mg/L) on the dorsal skin of db/db mice.

Figure 5.

Evolution of t-AUCB level, quantified by liquid chromatography coupled to tandem mass spectrometry, in the receptor compartment of Frantz cells from 0 to 24 hours after gel application (20 μL at 400 mg/L) to pig-ear skin (n=3 per time point).