Differential effects of angiostatic steroids and dexamethasone on angiogenesis and cytokine levels in rat sponge implants

Abstract

1. Subcutaneous implantation of sterile polyether sponges elicited a reproducible neovascular response in rats, as determined by blood flow measurement with a 133Xe clearance technique and confirmed histologically. This model was used to monitor the levels of two cytokines during angiogenesis and to compare the activities of angiostatic steroids and anti-inflammatory steroids. 2. Initial experiments followed the neovascular development over a 20-day period. Daily local injection of hydrocortisone caused a dose-dependent (0.5, 5 and 50 μg per sponge) inhibition of the basal sponge-induced angiogenesis. However, daily systemic treatment of hydrocortisone (2, 10 and 50 mg kg-1, s.c.) was less effective at inhibiting angiogenesis, and this inhibition was not sustained by day 20 after sponge implantation. 3. To investigate the involvement of cytokines during the course of angiogenesis, we measured the endogenous levels of tumour necrosis factor-α (TNF-α) and interleukin 6 (IL-6) in sponge implants. Levels of IL-6 and TNF-α peaked at day 7 and day 11 after implantation, respectively. These cytokine levels subsided through the completion of angiogenesis by day 20. 4. Subsequent experiments were carried out over a 14-day period. Among the three angiostatic steroids tested, U-24067 (6α-fluoro-17,21-dihydroxy-16α-methylpregna-4,9(11)-diene-3,20-dione-21 -acetate) showed a dose-dependent inhibition (0.5, 5 and 50 μg per sponge per day) of sponge-induced angiogenesis. Tetrahydro-S was also effective at 5 μg doses, but medroxyprogesterone failed to affect the angiogenic response. None of these steroids caused atrophies of the spleen and thymus. 5. Daily local injection of dexamethasone (0.5 μg per sponge) inhibited the basal sponge-induced angiogenesis almost completely. Although higher doses of dexamethasone (5 and 50 μg per sponge) did not produce further inhibition of angiogenesis, they caused severe spleen and thymus weight losses, indicative of immunosuppression. 6. At the daily dose of 5 μg per sponge, dexamethasone inhibited angiogenesis and produced a marked reduction in the levels of TNF-α and IL-6 at day 14. In contrast, hydrocortisone, U-24067 and tetrahydro-S did not influence the levels of TNF-α and IL-6. 7. We concluded that the anti-angiogenic activity of angiostatic steroids and anti-inflammatory steroids in the rat sponge model is independent of their ability to reduce the production of TNF-α and IL-6. The differential effects of angiostatic and anti-inflammatory steroids suggest that U-24067 and its derivatives may have therapeutic potential in the management of angiogenic diseases such as rheumatoid arthritis.