Selectivity and sensitivity in the measurement of reactive oxygen species (ROS) using chemiluminescent microspheres prepared by the binding of acridinium ester or ABEI to polymer microspheres

Two kinds of chemiluminescent microspheres were prepared as tools for measuring reactive oxygen species (ROS) released into phagosomes in phagocytizing cells, by chemically binding acridinium ester or ABEI (isoluminol derivative) to polymer microspheres, and were examined from the viewpoint of specificity and sensitivity to ROS. Acridinium ester-bound microspheres (AE-ms) were found to be a sensitive probe to superoxide anion and hydrogen peroxide under a neutral condition (pH 7.2). AE-ms emitted strong chemiluminescence (CL) by hypoxanthine (HPX)/xanthine oxidase (XOD) or hydrogen peroxide. The CL by HPX/XOD was initially inhibited by superoxide dismutase. At pH 5.6, the CL intensity from AE-ms in the presence of HPX/XOD was reduced to about one-eighth of that at pH 7.2. ABEI-bound microspheres (ABEI-ms) were found to be a selective probe for singlet oxygen although not highly sensitive. ABEI-ms emitted CL of moderate intensity with hydrogen peroxide/myeloperoxidase (MPO), but not with hydrogen peroxide alone or with hypochlorite/MPO at pH 5.6. The CL from ABEI-ms with hydrogen peroxide/MPO was completely inhibited by azide. ABEI-ms did not emit CL in the presence of HPX/XOD or by potassium superoxide at pH 5.6. The result of supplemental experiments using dissolved chemiluminescent probes and non-enzymatically generated ROS supported the above-described selectivity and sensitivity of chemiluminescent microspheres.