Human neutrophil priming: chemiluminescence modified by hydroxyapatite and three bisphosphonates in vitro

Activated inflammatory cells, particularly neutrophil granulocytes, are thought to play an important role in the tissue damage associated with several chronic inflammatory diseases including rheumatoid arthritis. Of importance to pathogenesis may be the interaction of cells and hydroxyapatite (HA) crystals, both present in synovial fluid, and to therapy, the ameliorating influence of many groups of drugs, including the bisphosphonates. The aim of this in vitro study was to verify the priming effect of serum-coated HA particles on human neutrophils, and investigate possible modification by three bisphosphonates in current clinical use; clodronate, etidronate, and pamidronate. After incubation of neutrophils with drugs alone, HA or drug/HA combinations over a bisphosphonate concentration range of 1.10(-5) to 1.10(5) micrograms/ml, for 60 or 270 min, resultant luminol-dependent chemiluminescence (CL) was monitored as millivoltage after further challenge with serum-treated zymosan. As previously shown, HA produced a profound priming to the second challenge and this was not appreciably altered by the drugs bound to HA, except at the highest concentrations. Pamidronate, in particular, appeared to sustain the cell activity even at these high concentrations, well beyond the tissue levels achieved in clinical therapeutics. Only at highest concentrations of 1.10(3) and 1.10(5) micrograms/ml did the drugs alone inhibit cellular activity, when challenged with zymosan. This study therefore, confirmed the ability of HA particles to strongly prime human neutrophils and the low toxicity of the three bisphosphonates tested within this cell model.