Amelioration of experimental arthritis by a calpain-inhibitory compound: regulation of cytokine production by E-64-d in vivo and in vitro.

Calpain, a calcium-dependent cysteine proteinase, has been reported to participate in the pathophysiology of rheumatoid arthritis (RA). The aim of this study is to investigate the therapeutic efficacy of calpain-inhibitory compounds in an animal model of RA and to clarify the underlying mechanisms in vivo and in vitro. Arthritis was induced in BALB/c mice with anti-type II collagen mAbs and LPS, and the mice were treated intra-peritoneally with a high dose (9 mg kg(-1) per day) or low dose (3 mg kg(-1) per day) of E-64-d (a membrane-permeable cysteine proteinase inhibitor) or control diluent. As a result, a high dose of E-64-d significantly alleviated the clinical arthritis and the histopathological findings, compared with the control diluent, although a low dose of E-64-d did not have a significant effect. Next, we evaluated the effects of E-64-d on cytokine mRNA expression at the inflamed joints by quantitative reverse transcription-PCR. High dose of E-64-d significantly decreased IL-6 and IL-1beta mRNA levels at the inflamed joints. The regulatory effects of E-64-d on cytokine production were also confirmed in vitro, using a synovial cell line (E11) and crude synoviocytes derived from RA patients. These results suggest the key roles of calpain in the pathophysiology of arthritis and that calpain-inhibitory compounds might be applicable to the treatment of arthritic diseases such as RA.