DIRECT EFFECTS OF METABOLIC PRODUCTS AND SONICATED EXTRACTS OF PORPHYROMONAS-GINGIVALIS-2561 ON OSTEOGENESIS IN-VITRO

It is well documented that oral microorganisms play a significant role in the initiation and progression of periodontal disease. By using va rious in vitro models, it has been shown that some bacteria considered periodontal pathogens or their products can Stimulate bone resorption and some other parameters of osteoblast-like cell activity. However, the effects of these organisms and their products on osteogenesis itse lf are not known. This study was undertaken to determine the direct ef fects of metabolic products and sonicated extracts of Porphyromonas gi ngivalis on bone formation in the chick periosteal osteogenesis model. Cultures of P. gingivalis 2561 were grown under standard anaerobic cu lture conditions. The spent medium was collected, and following centri fugation, sonicated bacterial extracts were prepared from the bacteria l pellet. These were added in various proportions to the chick periost eal osteogenesis cultures. Sonicated extracts were further fractionate d into five molecular-size ranges and similarly tested. Parameters of osteogenesis, including alkaline phosphatase activity, calcium and P-i accumulation, and collagen synthesis, were measured on 6-day-old cult ures. Compared with controls devoid of bacterial products, osteogenesi s was inhibited significantly in cultures treated with either conditio ned medium or extracts obtained from P. gingivalis. Various amounts of inhibitory activity were observed in the different ultrafiltration mo lecular-size fractions, with very profound inhibitory effects observed in the <5-kDa range. Histological observations indicated the presence of cells, some bone, and/or new fibrous connective tissue at all conc entrations, indicating that toxicity was not a factor. These results s uggest that periodontal pathogens such as P. gingivalis might contribu te to the bone loss in periodontal diseases not-only by stimulating re sorption but, possibly, by inhibiting bone formation directly.