Polymorphonuclear cell apoptosis in exudates generated by polymers

Flow cytometry was used to quantify apoptotic and necrotic polymorphonuclea r (PMN) cells in an exudate generated by biomaterials, and the results were compared with determinations of spontaneous apoptosis and necrosis in PMN cells from the bloodstream. The exudate formed inside cylindrical tubes sub cutaneously implanted in the dorsal region of rats was collected over a 1-w eek period. A rapid and simple staining procedure based on the spectral pro perties of the bisbenzemide Hoechst 33342 was used to identify apoptotic PM N cells. Quantification of permeabilized PMN cells stained by propidium iod ide was possible in the same unfixed specimens. The percentages of apoptoti c and permeabilized PMN cells in peripheral rat blood were low (1.8 +/- 0.5 % and 1.7 +/- 0.7%, respectively), similar to results found in humans. In e xudates generated by polyvinyl chloride (PVC), the percentages of apoptotic and permeabilized PMN cells were higher than in the blood. The percentage of PMN cells undergoing apoptosis progressively increased with time and rea ched a maximum at day 2 (27% +/- 6%). The percentage of permeabilized cells progressively increased with time and was much higher than the percentage of apoptotic cells on days 4 and 8. Apoptosis and necrosis of PMN cells at day 2 were inhibited when tubes were filled with 10% serum. Selective inhib ition of apoptosis with a caspase inhibitor ill vivo indicated that apoptos is and necrosis are two separate pathways leading to the death of PMN cells in the exudate. At day 2, polyurethane (PU) was associated with a lower ra te of apoptosis than PVC or a random copolymer of trimethylene carbonate (T MC) and epsilon caprolactone (ECL). Apoptosis was interpreted as an organiz ed cell removal process that limits inflammation. Apoptosis was the natural route of PMN cell death at the early stage of inflammation. (C) 1999 John Wiley & Sons, Inc.