Cytokine-mediated inflammatory hyperalgesia limited by interleukin-1 receptor antagonist

Abstract

1. The effect of IL-1ra on response to intraplantar (i.pl.) injection of LPS, carrageenin, bradykinin, TNFalpha, IL-1beta, IL-8, PGE(2) and dopamine was investigated in a model of mechanical hyperalgesia in rats. 2. IL-1ra inhibited hyperalgesic response to LPS, carrageenin, bradykinin, TNFalpha, and IL-1beta, but not responses to IL-8, PGE(2) and dopamine. 3. A sheep anti-rat IL-1ra serum potentiated response to LPS, carrageenin, bradykinin, TNFalpha and IL-1beta but not IL-8. 4. Carrageenin and LPS stimulated and production of immunoreactive TNFalpha, IL-1beta and IL-1ra in the skin of injected paws. 5. The inhibition by IL-1ra of the hyperalgesic response to carrageenin was not affected by antibodies neutralizing IL-4 and IL-10. 6. In mice, IL-1ra inhibited the nociceptive response to i.p. injection of acetic acid. 7. These data suggest that IL-1ra, released at sites of inflammation, limits inflammatory hyperalgesia. This effect is independent of (IL-1ra-induced) IL-4 and IL-10 and appears to be the result of antagonism by IL-1ra of IL-1beta-stimulated eicosanoid production.

Figure 1

Antagonism by IL-1ra (30, 100 and 300 pg, 100 μl⁻¹, i.pl.) of the hyperalgesic responses to IL-1β (IL-1β, 0.5 pg 100 μg⁻¹, i.pl.). Saline (0) or IL-1ra was injected into paws to be injected with IL-1β, 30 min before the cytokine injection. The intensity of hyperalgesia was measured 3 h after injection of IL-1β. Results are expressed as means±s.e.mean in groups of five rats.

Figure 2

Effect of saline or IL-1ra (100 pg 100 μg⁻¹, i.pl.) on hyperalgesic responses to injections (in 100 μl, i.pl.) or LPS (1 μg), carrageenin (Cg, 100 μg), bradykinin (BK, 500 ng), TNF-α (2.5 pg), IL-8 (100 pg), PGE₂ (100 ng) and dopamine (10 μg). IL-1ra was injected into paws to be injected with one of the hyperalgesic agents, 30 min before the hyperalgesic agent. Hyperalgesia was measured 3 h after injection of hyperalgesic agents. Results are expressed as mean±s.e.mean in groups of five rats.

Figure 3

Effect of anti-rat IL-1ra serum (50 μl, i.pl.), and pre-immune serum on hyperalgesic responses to LPS (0.1 μg), carrageenin (Cg, 10 μg), BK (50 ng), TNFα (0.25 pg), IL-1β (0.05 pg), IL-8 (10 pg). The sera were injected into paws to be injected with one of the hyperalgesic agents, 30 min before the hyperalgesic agent. The intensity of hyperalgesia was measured 1 h after injection of the hyperalgesic agents. Results are expressed as means±s.e.mean in groups of five rats.

Figure 4

Concentrations of TNFα (A, B), IL-1β (C, D) and IL-1ra (E, F) in rat paws injected with carrageenin (Cg, filled columns, A, C, E) or LPS (B, D, F). Paws were injected (100 μl) with saline, carrageenin (Cg, 100 μg), or LPS (1 μg). At times after injection of 30 min, 1, 2, 3 and 6 h rats were killed and paw skin samples were extracted for cytokines, which were measured by ELISA. The results are reported as means±s.e.mean of three rats.

Figure 5

Effect of antibodies neutralizing IL-4 and IL-10 on the anti-hyperalgesic effect of IL-1ra. Rats were injected i.pl. with 50 μg (in 50 μl) of antibody to IL-4 (IL-4Ab, BVDG), IL-10 (IL-10Ab, JEA-5), or with (control) antibody to ovalbumin. Fifteen min later, one of the following was injected (in 50 μl) into the same paws: saline (50 μl), IL-1ra (100 pg, A), IL-4 (10 ng, B) or IL-10 (100 ng, B). After a further 15 min, carrageenin (Cg, 100 μg (in 100 μl)) was injected and the hyperalgesia measured 3 h after this final injection. Results are expressed as means±s.e.mean in groups of five rats.

Figure 6

The anti-hyperalgesic effect of IL-1ra. Mice were injected into the peritoneal cavities (i.p.) with acetic acid (0.8% w v⁻¹, 0.1 ml 10 g⁻¹) and the cumulative abdominal constrictions counted between 0 and 20 min after the injection of the acetic acid. IL-1ra (0.1 ng, open circles; 0.3 ng, open triangles; 0.6 ng, filled triangles; 0.9 ng, open squares, 1.2 ng, filled circles; 0.2 ml, i.p.) or saline was given 30 min before the acetic acid. Results are expressed as means±s.e.mean in groups of at last six mice.