Effect of outer membrane of <em>Treponema denticola</em> on bone resorption.

The effect of the outer membrane (outer sheath) of Treponema denticola on bone resorption was studied. Bone resorption was measured by the release of previously incorporated ⁴⁵Ca from the shafts of the radii and ulnae of 19-day fetal rats. A treated-over-control ratio (T/C ratio) significantly greater than 1 indicated the stimulation of bone resorption by the test substance. The addition of outer membrane of T. denticola increased the release of ⁴⁵Ca from the assay bones. The minimum concentrations required to yield significant ⁴⁵Ca release from the assay bones were 15, 22 and 75 μg protein/ml for serovars a, b and c, respectively. These protein values corresponded to estimated lipopolysaccharide contents of 0.6, 0.8 and 2.8 μg/ml, based on 3-deoxy-2-manno-octulosonate analysis. Heat treatment of outer membrane (60° for 30 min) did not change the effect on ⁴⁵Ca release. Parathyroid hormone or prostaglandin E₂, known to act synergistically with lipopolysaccharides in bone resorption, was also added to the assay system. Neither prostaglandin E₂ at 10^-7 M nor parathyroid hormone at 40 ng/ml, by itself, increased ⁴⁵Ca release. However, in the presence of 10 μg protein/ml of outer membrane of serovar b at 120 h, the T/C ratio was increased to 1.31 ± 0.07 and 1.58 ± 0.118, respectively. These results suggest that a lipopolysaccharide-like material is present in the outer membrane of T. denticola that may be responsible for bone resorption in the in vitro system. [ABSTRACT FROM AUTHOR]