The response of peritoneal macrophages after implantation of several ceramics as measured by the change of ectoenzyme activity

Abstract

The bioactive calcium phosphate ceramics with various calcium : phosphorus ratios: Ca/P=1.67 (hydroxyapatite, HA), Ca/P=1.6 and Ca/P=1.5 (tricalcium phosphate, β-TCP), the bioinert aluminium oxide ceramic (Al 2O 3) and the toxic calcium oxide ceramic (CaO) have been investigated with respect to their ability to activate peritoneal macrophages of NMRI-mice and with respect to their influence on the extracellular nucleotide degradation of these macrophages. Two weeks after the intraperitoneal injection of a suspension of ceramic particles in an isotone salt solution (phosphate-buffered saline=PBS), we observed that the peritoneal macrophages were only slightly activated into the responsive state, independent of the type of ceramic. 5′Nucleotidase (5′N) ectoenzyme hydrolyses adenosine monophosphate (AMP) and a decrease of its activity is a general biochemical marker of activated macrophages. This ectoenzyme activity was slightly reduced after ceramic implantation. The lacking rise of the extracellular diadenosine tetraphosphate (Ap 4A)-catabolism by the macrophage ectoenzyme alkaline phosphodiesterase I (APD) demonstrated that the peritoneal macrophages did not completely reach the responsive state. After the implantation of calcium phosphate ceramics the extracellular adenosine triphosphate (ATP)-reduction was slightly diminished. After the implantation of tricalcium phosphate ceramic about 30% more peritoneal exsudate cells (PEC) were obtained from the peritoneal cavity than after injections of pure PBS (used as non-inflammatory control). Similar to the phenomena following the injection of thioglycollate (Tg, inflammation producing control agent) a slightly but not significantly increased proportion of pseudopodia-building cells was observed after the implantation of the ceramic with Ca/P=1.6.