The effect of Am-80, one of retinoids derivatives on experimental allergic encephalomyelitis in rats.

Experimental allergic encephalomyelitis (EAE) is an autoimmune model with inflammation and demyelination in the central nervous system, which resembles the human demyelinating disorder, multiple sclerosis (MS). In this study, we investigated the effect of Am-80, a synthetic retinoid, on EAE in DA rats. DA rats immunized with complete Freund's adjuvant (CFA) supplemented with myelin basic protein (MBP) developed severe EAE which reached the peak 12 to 14 days after immunization. Am-80 and prednisolone administered orally for 12 days after immunization diminished the clinical symptoms and infiltration of inflammatory cells in a dose dependent manner. However, after stopping administration, EAE recurred in DA rats treated with Am-80, but not with prednisolone. The different responses between Am-80 and prednisolone were not due to the difference in the tolerability to the MBP because both inhibited the delayed-type hypersensitivity response to MBP only during administration. To investigate the mechanism how Am-80 alone delayed the response, the expressional levels of mRNA for interleukin-6 (IL-6), interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in spinal cord were examined. Transcriptional levels of IL-6, IFN-gamma and TNF-alpha were parallel with the clinical symptoms of the disease in Am-80-treated rats, that is, expressional levels of their mRNA were diminished during the administration of Am-80, which then increased as soon as the administration was stopped. Among them, the expression of IL-6 mRNA was more rapidly and highly relapsed than that of the other two cytokines mRNA. However, prednisolone attenuated transcriptions of all these cytokines throughout the experiment. Therefore, these findings suggested that the inhibition of EAE is, in part, related to the inhibition of IL-6 production. However, there are many possible mechanism in the suppression of EAE by Am-80, further experiments will be necessary.

Effect of selective IL-6 inhibitor Am-80 on experimental autoimmune encephalomyelitis in DA rats.

AIM: To observe the role of interleukin (IL)-6 in the development of experimental autoimmune encephalomyelitis (EAE). METHODS: DA rats were immunized by injecting bovine myelin basic protein (MBP). mRNA of cytokines, such as IL-6, IL-10, TNF-alpha, TGF-beta 1, IFN-gamma, and iNOS, were detected by RT-PCR. MBP was injected into ear to induce delayed type cutaneous hypersensitivity response (DTH). Histological studies were performed on the spinal cord with HE staining. Nitric oxide (NO) production from cultured murine macrophage clones was stimulated with LPS plus IFN-gamma. RESULTS: DA rats developed EAE disease with a peak of severity on d 13 and d 14. Am-80 (1.0, 3.0 mg/kg), a selective IL-6 inhibitor, inhibited the symptoms in terms of deterioration as observed by the clinical score, body weight and histological findings, in a dose-related manner. A high dose of Am-80 (3.0 mg/kg for 12 d) did not completely inhibit the disease, but delayed the symptoms and enhanced the delayed response. By prolonging the duration of treatment (18 d), Am-80 inhibited the onset of EAE during administration, but the symptoms of EAE appeared after the administration was stopped. Am-80 administerd for 12 d inhibited the DTH response on d 11 but not on d 22. RT-PCR studies demonstrated a strong expression of IFN-gamma, IL-6, IL-10, TGF-beta 1, TNF-alpha, and iNOS mRNA in spinal cord 13 d after immunization. However IFN-gamma, IL-10, TNF-alpha, and iNOS mRNA expression (on d 13) was suppressed by Am-80, except in the case of IL-6, hence the effect of Am-80 on the expression of IL-6 mRNA was examined in additional experiments. After Am-80 was administered for 12 d or 18 d, the expression of IL-6 mRNA was inhibited on d 12 or d 18, but increased on d 13 or d 19, respectively. CONCLUSION: These findings suggest that inhibition of EAE by Am-80 is initiated by inhibition of IL-6 production.

Effect of Am-80, a synthetic derivative of retinoid, on experimental arthritis in mice.

Am-80 is a newly snythesized retinoid with the structure of one aromatic amide among retinobenzoic acids. It exhibits specific biological activities of retinoic acid such as the activation of cellular differentiation and proliferation. We investigated the effect of Am-80 on collagen-induced arthritis (CIA) in mice and the immunopharmacological action on the production of several cytokines in the in vitro and in vivo models. Am-80, at doses of 0.3, 1 and 3 mg/kg, significantly inhibited the severity and development of the arthritis index, progression of foot pad swelling, bone damage and histopathological alterations. Am-80 also inhibited the production of anti-type II collagen (CII) IgG antibody, but did not affect the delayed-type hypersensitivity (DTH) response in arthritic mice. To determine the inhibitory mechanism of Am-80, we studied the effect of Am-80 on the production of cytokines. Am-80 did not affect the production of IFN-gamma by Th1 cells (1E10.H2 cells) and IL-4 by Th2 cells (D10.G4.1 cells), respectively. Am-80 selectively inhibited bacterial lipopolysaccharide (LPS)-induced IL-6, but not TNF-alpha and IL-1beta, production in mice. Moreover Am-80 inhibited IL-1beta induced IL-6 production and IL-6 mRNA expression in human osteoblast-like cells (MG-63). The inhibition of IL-6 production by Am-80 was due to downregulation of the pretranscription or the transcription of IL-6 in MG 63 cells. These findings suggest that the inhibitory effect of Am-80 on CIA is partially by modulating the production of the proinflammatory cytokine, IL-6.