Background Exposure of joint cartilage to blood can occur after joint trauma, major joint surgery, or due to haemophilia. This ultimately leads to joint damage, having both the inflammatory characteristics of rheumatoid arthritis and the degenerative characteristics of osteoarthritis. Interleukin (IL)-4 and IL-10 are reported to limit blood-induced cartilage damage, potentially by reducing the production of pro-inflammatory cytokines like IL-1β and TNF-α.
Objectives To unravel further the precise role of IL-1β or TNF-α we investigated whether blocking of these cytokines prevents blood-induced cartilage damage in vitro, and whether this is still beneficial after onset of a bleed.
Methods Healthy human cartilage explants were cultured for 4 days in presence/absence of 50% whole blood. IL-1β monoclonal antibody (mAb) (1-100ng/mL, n=8), IL-1 receptor antagonist (RA) (10-1000ng/mL, n=7) or TNF-αmAb (10mg/mL, n=5) was added during blood exposure. Furthermore, IL-1βmAb (100ng/mL) or IL-1RA (1000ng/mL) was administered directly or after a delay of several hours up to 2 days (n=7). Proteoglycan turnover was determined after a recovery period of 12 days.
As the TNF-αmAb was unable to affect blood-induced cartilage damage, its efficacy was investigated by culturing cartilage explants for 4 days in the presence of TNF-a with/without TNF-αmAb (n=5). Moreover, in 4-day whole blood cultures (n=6) the effects of IL-1βmAb (100 ng/mL) and IL-1RA (1000 ng/mL) on the levels of IL-1β, IL-6, and TNF-α were determined.
Results Addition of an IL-1βmAb (see figure) or IL-1RA resulted in a dose- and time-dependent protection of cartilage from blood-induced damage. In higher concentrations, almost complete normalisation of proteoglycan turnover was achieved. This was accompanied by a reduction in IL-1β (74 pg/mL in whole blood culture versus undetectable after addition of IL-1RA, p=0.028) and IL-6 production (21347 pg/mL in whole blood culture versus 27 pg/mL and 289 pg/mL after addition of IL-1RA and IL-1βmAb (both p=0.028)) in whole blood cultures, while TNF-α levels were unaffected (35 pg/mL in whole blood culture versus 37 pg/mL after addition of IL-1RA or IL-1bmAb (both p=0.753)).
Addition of a TNF-αmAb, although completely inhibiting the direct effects of 1 and 5ng/mL TNF-α on cartilage, exhibited no effect on blood-induced cartilage damage.
Conclusions This study demonstrates that IL-1β is a crucial factor in the development of blood-induced cartilage damage in vitro, whereas TNF-α is indicated not to be elementary. Targeting IL-1β may protect cartilage after a joint bleed with early administration after blood-exposure being most beneficial. The key role of IL-1β results at least partly from regulating the production of other pro-inflammatory cytokines, including IL-1β itself and IL-6. As therapeutic agents opposing the activity of IL-1β are readily available, further research is warranted to investigate its in vivo capacity in prevention and treatment of joint damage upon joint bleeding.
Disclosure of Interest None declared