MULTINUCLEATED GIANT-CELLS ELICITED AROUND HYDROXYAPATITE PARTICLES IMPLANTED IN CRANIOTOMY DEFECTS ARE NOT OSTEOCLASTS

Background: The nature of the multinucleated giant cells (MNGC) elicit ed in contact with implantable biomaterials is still indecisive. Metho d: In Wistar rats the MNGC recruited after the implantation of hydroxy apatite (HA) particles in standardized skull defects were examined mor phologically (at both the light and electron microscope levels), enzym atically (tartrate-resistant acid phosphatase and non-specific esteras e), and after a challenge with salmon calcitonin. Results: The MNGC we re of great size and contained abundant mitochondria, vacuoles, and ve sicles throughout the cytoplasm; they were either tightly apposed to t he HA surface or had long and thin processes penetrating the material. When processed for tartrate-resistant acid phosphatase, only a few ce lls were weakly stained. The staining was totally suppressed when samp les were pretreated with cyanuric chloride in the MNGC but not in the host osteoclasts. Calcitonin induced the withdrawal of the host osteoc lasts from the bone surface while the MNGC remained in contact with th e HA material. Conclusion: The MNGC recruited to HA particles did not exhibit the morphologic, enzymatic and functional characteristics of t he osteoclasts, and consequently must be regarded as macrophage polyka ryons. (C) 1995 Wiley-Liss, Inc.