Objective: The proteasome is a multicatalytic proteinase complex regulating the intracellular breakdown of many proteins, including those mediating the activation of pro-inflammatory signaling pathways (e.g. NFkappaB), cell proliferation and survival. Conceptually, proteasome inhibitors may therefore elicit potential anti-inflammatory properties by inhibiting these processes and thereby impair the cellular release of pro-inflammatory cytokines such as Tumor Necrosis Factor-alpha (TNF-alpha) in RA patients.
Methods: Whole-blood from 19 RA patients (including methotrexate-responsive and non-responsive patients) and 7 healthy volunteers was incubated ex-vivo with the proteasome inhibitor bortezomib after T-cell stimulation with alphaCD3/CD28. Inhibition of cytokine production by bortezomib was measured after 24 and 72 hours by ELISA. Effects of bortezomib on apoptosis and T-cell activation (CD25 expression) were measured by FACS-analysis.
Results: Bortezomib proved to be a rapid (<24 hour) and potent inhibitor of the release of several NFkappaB-inducible cytokines (including TNF-alpha, IL-1Beta, IL-6 and IL-10) by activated T-cells from healthy volunteers and RA patients, regardless of their clinical responsiveness to methotrexate. Median concentrations of bortezomib required to inhibit TNF-alpha production by 50% (mIC-50) were 12 nM (range: 8-50 nM) for healthy volunteers and 46 nM (range: 18-60 nM) for RA patients. A reduction of T cell activation and a marked induction of T-cell apoptosis were revealed as late effects after bortezomib incubations beyond 24 hours.
Conclusion: Proteasome inhibitors represented by bortezomib may elicit potential anti-inflammatory properties that deserve further exploration in experimental therapies for RA.