Infection with a gram-negative organism stimulates gingival collagenase production in non-diabetic and diabetic germfree rats.

Experimental diabetes in the rat rapidly produces a shift in the gingival crevicular microflora which is followed, within weeks, by increased production of collagenase by the gingival tissues. To assess the contribution of endogenous (hormonal or metabolic) and exogenous (altered crevicular microflora) factors on this diabetes-induced abnormality in collagenase production, the following series of experiments was undertaken: In each experiment, the germfree rats were housed in two isolators. Half of the animals in both isolators were rendered diabetic (D) with streptozotocin while the remainder were left untreated (non-diabetic (ND) controls). All of the germfree ND and D rats in one isolator of the pair were then infected with either a Gram-positive (S. mitis or A. odontolyticus) or a Gram-negative (Capnocytophaga, A. aclmomycetemcomitans or B. gingivalis) organism. In the other isolator, the ND and D rats were maintained in their germfree state. After 3 wk, the germfree and monoinfected rats were killed and the gingiva (and in one experiment, skin) were dissected. Collagenase activity produced by gingiva in culture (or extracted from gingiva or from skin) was measured using 14C-collagen fibrils (or [3Hmethyl] collagen molecules) as the substrate. Diabetes increased the collagenolytic activity in the gingiva and skin of the germfree rats. Infecting the germfree rats with a Gram-positive organism had no effect on collagenase activity generated by the gingival explants in the tissue culture system. In contrast, infection with any of the Gram-negative organisms dramatically increased the collagenase activity in the gingival tissues of the ND rats in culture, an effect not seen in the D group of rats using this system. However, monoinfection with B. gingivalis did increase collagenase activity in the extracts of gingiva (but not in skin) from both ND and D rats, with the latter group showing the highest level of enzyme activity. We suggest (i) that experimental diabetes stimulates collagenase production in gingiva by both endogenous (hormonal) and exogenous (bacterial) mechanisms, and (ii) that crevicular Gram-negative organisms stimulate collagenolysis in the adjacent gingival tissues by releasing bacterial products (e.g. endotoxins) which penetrate into the connective tissue and enhance host cell collagenase production.