Turbinate Osteoporosis in Pigs Following Intranasal Inoculation of Purified Pasteurella Toxin: Histomorphometric and Ultrastructural Studies

Turbinate osteoporosis, induced by intranasal inoculation of purified toxin isolated from serotype D Pasteurella multocida, was investigated in 3- to 5-week-old, caesarean-derived, colostrum-deprived, isolation- reared pigs. Marked bilateral reduction in relative volume of trabecular bone occurred in osseous cores of turbinates of toxin-treated pigs relative to control pigs on post-inoculation day (pid.) 3, 6, 9, 12, and 15. The fractional resorptive surface along turbinate bone was greater in toxin-treated pigs when compared to controls on p.i.d. 3 and 6. A significant decrease in resorptive surface occurred over time in toxin-treated pigs, whereas the fractional resorptive surface was constant over time in control pigs. Osteoclasts in medullary spaces separating bony trabeculae of turbinates were abundant in toxin-treated pigs and scant in controls on p.i.d. 3, 6, and 9. Degeneration and necrosis of bone forming cells, principally osteoblasts, were progressively more extensive with time and were associated with decreased mineralization and reduced thickness of osteoid and woven bone matrix. Osteoclasts along resorptive surfaces of turbinate bone in toxin-treated pigs had more abundant, more highly vacuolated cytoplasm, a more prominent microvillous border, and a greater number of nuclei per cell than osteoclasts from control pigs on p.i.d. 3 and 6. We conclude that this Pasteurella toxin stimulates osteoclastic osteolysis and inhibits osteogenesis in turbinates by causing degeneration and death of osteoblasts. Most studies of the effects of bacterial products on osteogenesis and osteolysis have been prompted by the association of alveolar bone loss with bacterial plaque formation in periodontal di~ease.~~,~~ Endotoxin was the first bacterial product shown to stimulate bone resorption in organ culture.22 Increased bone resorp- tion has also been demonstrated in bone organ cultures treated with lipopolysaccharide (LPS),23,38,41 muramyl di~eptide,~~ lipid A,21 lipoteichoic a~id,~',~~ and strep- tococcal cell wall component^.^^ In vivo activation of bone resorption by bacterial products has been poorly documented. Gnotobiotic rats inoculated with a human oral strain of Actino- myces naeslundii readily develop plaque and concur- rent alveolar bone However, differentiation of direct and indirect effects of bacterial products on bone cell function in vivo is difficult, since accelerated bone resorption and formation may occur simultaneously as nonspecific sequelae to inflammation incited by bac- teria or their product^.^ For example, intragingival in- jection of rats with lipoteichoic acid isolated from Streptococcus mutans results in localized abscessation, granulation, new bone formation, and increased bone resorption.2 In pigs, atrophic rhinitis occurs as an upper respi- ratory disease caused principally by Bordetella bron- chiseptica and toxigenic strains of Pasteurella multo- cida. 28 Clinical disease is marked by variable turbinate osteoporosis, with severe cases manifested by complete chonchal atrophy, nasal septa1 deviation, and reactive changes in bone surrounding the nasal cavity. Turbi- nate osteoporosis of atrophic rhinitis results, in part, from effects of a protein toxin produced by toxigenic strains of serotype D Pasteurella multocida. 103J2 This study characterizes ultrastructural changes in turbinate bone associated with Pasteurella toxin and ascertains, by morphometric analysis, the effects of toxin on os- teoclastic activity. We provide experimental evidence of induction of turbinate osteoporosis by inhibition of osteogenesis and stimulation of osteoclastic osteolysis in the absence of significant inflammation, after in- tranasal inoculation of toxin isolated from Pasteurella multocida.