The non-thiol angiotensin-converting enzyme inhibitor quinapril suppresses inflammatory arthritis

Objectives. In addition to its vasoactive effects, angiotensin II has proinflammatory properties. Angiotensin-converting enzyme (ACE) inhibitors reduce the production of angiotensin II and could therefore act as anti-inflammatory agents. Here we investigated the capacity of the ACE inhibitor quinapril to modulate inflammatory arthritis. Methods. We studied the effect of quinapril on disease activity in mice with collagen-induced arthritis (CIA). Mice received oral quinapril (10 mg/kg/day) at the time of arthritis induction (prophylaxis protocol) or at the onset of mild arthritis (therapy protocol). Concentrations of immunoglobulin G (IgG) subtypes specific for bovine Type II collagen and TNF-alpha were measured by enzyme-linked immunoassay. Results. Quinapril significantly diminished the activity of CIA when given as prophylaxis or therapy (prophylaxis protocol, P<0.001; therapy protocol P = 0.002). Antigen-specific IgG2a antibodies were reduced by 52% (P = 0.02) in the quinapril prophylaxis protocol. Suppression of arthritis by quinapril was associated with reduced articular expression of TNF-alpha by 68% (P = 0.01) in the prophylaxis protocol and 27% (P = 0.06) in the therapy protocol. Quinapril therapy also inhibited expression of splenocyte TNF-alpha production following lipopolysaccharide (LPS) in vitro stimulation by 59% (P = 0.02). In parallel human in vitro experiments, ACE inhibition suppressed LPS-stimulated production of TNF-alpha by monocytes. In order to confirm that the action of quinapril occurred predominantly through suppression of angiotensin II, parallel experiments with the angiotensin receptor antagonist candesartan cilexetil demonstrated that this agent also inhibited disease activity in CIA. Conclusions. These data suggest that angiotensin II is a mediator of chronic inflammation and that ACE inhibition may have therapeutic effects in human inflammatory arthritis.