Relationship between cathepsin B and thrombin in rheumatoid arthritis.
OBJECTIVE
To investigate the pathophysiological significance of cathepsin B and thrombin in synovial fluid (SF) from patients with rheumatoid arthritis (RA).


METHODS
Thrombin and cathepsin B activities of samples from patients with RA and osteoarthritis (OA) were measured using fluorogenic synthetic substrates. The concentration of interleukin 8 (IL-8) in SF was measured by ELISA. The effect of thrombin on the proliferation of synovial fibroblast-like cells (SFC) was examined by measuring 3H-thymidine incorporation. The effect of thrombin on the release of IL-8 and cathepsin B from SFC was investigated. The expression of IL-8 mRNA in SFC after stimulation with thrombin was evaluated using real-time quantitative RT-PCR. The effect of recombinant IL-8 on the activation of cathepsin B was examined using the knee joints of rabbits.


RESULTS
In SF supernatants, cathepsin B and thrombin-like activity was significantly higher in RA than in OA, and there was a significant correlation between them. Cathepsin B activity was also significantly higher in SF cells and synovial tissue extracts from RA patients than in those from OA patients. There was a significant correlation between cathepsin B activity and the concentration of IL-8 in RA SF. Thrombin enhanced the proliferation of SFC in a dose-dependent manner. Thrombin significantly enhanced the release of IL-8 from SFC as well as the expression of IL-8 mRNA in SFC. IL-8 induced activation of cathepsin B in the knee joints of rabbits. However, thrombin did not directly increase cathepsin B activity in SFC.


CONCLUSIONS
In RA, thrombin was found to be related to the enhanced growth of SFC and the release of IL-8 from these cells; thus thrombin is probably related to worsening of inflammation through the recruitment of leukocytes (neutrophils), which release cathepsin B into the SF. Thrombin can induce activation of cathepsin B in SFC via increased expression of IL-8.
Mishiro
Takuya
T
Department of Orthopedics, School of Medicine, The University of Tokushima, 3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan.
Nakano
Shunji
S
Takahara
Shigeyuki
S
Miki
Mari
M
Nakamura
Yoichi
Y
Yasuoka
Susumu
S
Nikawa
Takeshi
T
Yasui
Natsuo
N
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000503:physiopathology; D002401:Cathepsin B / Q000096:biosynthesis / Q000276:immunology*; D005260:Female; D005347:Fibroblasts / Q000276:immunology; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis / Q000276:immunology; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000276:immunology / Q000503:physiopathology; D011817:Rabbits; D013582:Synovial Fluid / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology*; D013917:Thrombin / Q000276:immunology*
D016209:Interleukin-8; D013917:Thrombin; D002401:Cathepsin B