Porphyromonas gingivalis is a major etiological pathogen of adult periodontitis characterized by alveolar bone resorption. Vascular endothelial cells supply many inflammatory cytokines into periodontal tissue. However, whether the cells contribute to bone metabolism in periodontitis remains unknown. In this study, we investigated the effect of P. gingivalis on osteoprotegerin (OPG) and receptor activator of NF-kappaB ligand (RANKL) production, both of which are key regulators of bone metabolism, in human microvascular endothelial cells (HMVECs). We showed that P. gingivalis upregulated expression of OPG but not RANKL mRNA in HMVEC. P. gingivalis induced NF-kappaB activation, and the induction of OPG in HMVEC by the pathogen was blocked by the inhibitors of NF-kappaB. In addition, incubation of OPG with P. gingivalis supernatant resulted in loss of the protein. These results indicate that P. gingivalis-stimulated HMVEC secrete OPG via a NF-kappaB-dependent pathway, while the OPG is partly degraded by the bacteria. Thus, microvascular endothelial cells can act as a source of OPG and thereby may play an important role in regulating bone metabolism in periodontitis. (C) 2004 Elsevier Inc. All rights reserved.