Dexamethasone delays ulcer healing by inhibition of angiogenesis in rat stomachs

Abstract

Using the non-ulcerogenic doses of dexamethasone, we explored the action of glucocorticoids on ulcer healing and its relationship with angiogenic factors in the gastric mucosa. We applied dexamethasone (0.1 or 0.2 mg/kg/day) intragastrically in rats with acetic acid-induced gastric ulcer. The mucosal prostaglandin E₂ level and protein expressions of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) at the ulcer margin were determined. Ulcer induction significantly increased protein expressions of bFGF, VEGF, and prostaglandin E₂ level at the ulcer margin together with angiogenesis at the ulcer margin and base. The non-ulcerogenic doses of dexamethasone inhibited angiogenesis at the ulcer margin and ulcer base and delayed ulcer healing. These were associated with a significant decrease of prostaglandin E₂ level and VEGF expression, but not the bFGF expression. Supplementation with prostaglandin E₂ attenuated the inhibitory action of dexamethasone on VEGF expression and reversed the adverse effects of dexamethasone on angiogenesis and ulcer healing, without influencing bFGF expression. We concluded that dexamethasone given at non-ulcerogenic doses could decrease angiogenesis and delay acetic acid-induced ulcer healing; these actions were at least, in part, due to depletion of prostaglandin E₂ level followed by down-regulation of VEGF at the ulcer margin of the stomach.

Introduction

Glucocorticoids are reported to be ulcerogenic in the stomach Nobuhara et al., 1985, Wallace, 1987, Filep et al., 1992 and delay gastric ulcer healing Kuwayama et al., 1991, Carpani de Kaski et al., 1995. Both actions could be interrelated and cannot be differentiated if ulcerogenic doses of glucocorticoids are given. It is hard to define whether this type of drug indeed can delay ulcer healing in the stomach. It is therefore necessary to delineate such action using a non-ulcerogenic dose of corticosteroid. With this approach, we can elucidate not only the adverse action of corticosteroids but also the mechanisms for ulcer repair in the stomach.

Following acute gastric mucosal necrosis such as erosions or ulcers, most of the mucosal components, including microvessels, are destroyed within the focal lesion area. Healing of such lesions requires a reconstruction of the surface epithelium, glandular epithelial structures, restoration of the lamina propria, and, most importantly, reconstruction of the microvascular network essential for delivery of oxygen and nutrients to the healing site. Angiogenesis within granulation tissue is considered to be one of the most important processes in ulcer healing. The growth of new microvessels through angiogenesis is promoted by angiogenic growth factors such as basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), platelet-derived growth factor, and angiopoietin (Tarnawski, 2002).

The two heparin-binding angiogenic factors, bFGF and VEGF, which are the important angiogenic mediators, are examined in this study. bFGF is a direct mitogen for vascular endothelial cells, fibroblast, and smooth muscle cells Shing et al., 1984, Folkman et al., 1988. bFGF expression is up-regulated in the submucosa during the early ulcer healing stage (Pohle et al., 1999) and its effect in ulcer healing via stimulating angiogenesis has been well established Folkman et al., 1991, Szabo et al., 1994. VEGF expression was elevated during granulation tissue formation in a skin wound repairing model (Frank et al., 1995). This growth factor acts specifically on vascular endothelial cells to increase vascular permeability, and stimulates endothelial cell proliferation, migration and tube formation (Szabo et al., 2000). VEGF significantly accelerates gastric ulcer healing by enhancing angiogenesis at the ulcer site (Jones et al., 2001).

It has been shown that corticosteroids affect prostaglandin synthesis in tissues Flower, 1998, Izhar et al., 1992 and its analog prostaglandin E₂ causes vasodilatation and stimulates angiogenesis Form and Auerbach, 1983, Diaz-Flores et al., 1994. It is therefore suggested that depletion of prostaglandins could be the major detrimental factor contributing to the adverse action of corticosteroids on ulcer repair through the suppression of angiogenesis at the ulcer site. This action could act in line with the expression of the abovementioned growth factors in the course of ulcer healing process. Studying the interrelationship between prostaglandin E₂ and other angiogenic factors including bFGF and VEGF in the induction of angiogenesis and ulcer healing is interesting and should be important to understand the mechanisms for tissue repair in the stomach.

In this study, we would like to apply the non-ulcerogenic doses of dexamethasone, a potent corticosteroid, to explore its action on angiogenesis and further on ulcer healing in connection with prostaglandin E₂ and the angiogenic factors bFGF and VEGF in rat stomachs.