Apoptosis and autoimmunity induced by clodronate in systemic lupus erythematosus mononuclear circulating cells

The aim of this study is to evaluate the effect of clodronate on apoptosis of human systemic lupus erythematosus circulating mononuclear cells and to analyze possible correlations with changes in autoantibody production in vitro. Lympho-monocytes from 20 SLE patients were isolated and incubated with or without addition of 1 microM clodronate for 72 hours. Apoptosis and release of genomic material was assessed by immunofluorescent detection of cleaved caspase-3 and by Cell-Death-Detection ELISAPLUS kit (Roche). Anti-Nucleosome IgG and anti-dsDNA IgM and IgG autoantibody levels were determined in supernatants by commercially available ELISA kits. Clodronate induced apoptosis in monocytes as confirmed by cleaved caspase-3 immunostaining and by quantification of cleaved nucleosome in the supernatants (treated 0.22+/-0.05 O.D. vs untreated 0.09+/-0.04 O.D.; P less than 0.001). This finding was coupled with a significant increasing in supernatants of IgG anti-Nucleosome (treated 6.5+/-1.1 vs untreated 5.5+/-0.6 IU/mL; p=0.001) and IgM (treated 3.0+/-1.3 vs 2.2+/-0.9 IU/mL; p=0.02) and IgG (treated 4.0+/-1.8 vs untreated 2.8+/-1.5 IU/mL; p=0.02) anti-dsDNA autoantibody levels. Our findings stressed the pro-apoptotic activity of clodronate, as well as its potential autoimmunity induction in SLE mononuclear circulating cells. Clinical studies could clarify the role of bisphosphonates on autoantibody production and worsening of disease activity.