H2O2 production by cells on titanium and polystyrene surfaces using an in vivo model of exudate and surface related cell function

Abstract

The determination of secreted levels of reactive oxygen species by implant-adherent cells in vivo is required for understanding of the role(s) of such reactive oxygen species for the tissue response around medical devices. A model with subcutaneous implants of c.p. titanium (Ti) or polystyrene (PS) (cell culture grade) inserted on the back of rats were used. Implants and associated cells were retrieved and assayed after 1, 3, 5, 7, 14, 21 and 28 days. Morphological analysis of exudate cells showed that polymorphonuclear leukocytes (PMN) predominated after one day whereas macrophages were predominant after three days. The number of implant-adherent cells, as reflected by measurement of DNA, decreased with time. Ultrastructural observations showed that macrophages were predominant cells in contact with the implant surface. Measurement of hydrogen peroxide (H(2)O(2)) secretion by implant-adherent cells during 40 min incubation ex vivo revealed a constitutive generation of 40-400 pmol H(2)O(2)/microg DNA, depending on implantation time. Stimulation with protein kinase C agonist phorbol myristate acetate (PMA) caused an increased H(2)O(2) generation by adherent cells at early (up to five days) but not later (7-28 days) time periods. No major differences between Ti and PS were observed. Taken together, these findings show that Ti and PS implant-adherent cells secrete H(2)O(2) under in vivo conditions. Further, a reduced capacity to mount an enhanced H(2)O(2) secretion upon stimulation was demonstrated at late time periods. The role of this mediator for biocompatibility remains to be established.