It has been believed that the increased release of free oxygen radicals(O₂^-, H₂O₂ and OH^-) might be one of important factors in the pathogenesis of periodontal diseases.

Polymorphonuclear leukocytes(PMNs) constitute the primary host resistance factor against infection. They are prominent cells in both the gingival tissue and gingival sulcus in most forms of periodontal disease. In response to invading microorganisms, the activated PMNs and macrophages generate free oxygen radicals, which play an important role in bacterial killing. The normal production of these free oxygen radicals is vital for the successful resistance of individuals to bacterial infection. However, the enhanced production of reactive oxygen species by accumulating PMNs may be detrimental to the host in certain disease states.

This study was performed to evaluate the effect of Tetracycline-HCl(Tc-HCl) on generation of superoxide anion by PMNs.

For the present study, 60ml of peripheral venous blood were obtained from systemically healthy subjects by venipuncture in median cubital vein and PMNs were separated by a one-step Ficoll-Hypaque gradient centrifugation method. PMNs were incubated with 1µg/ml P.gingivalis strain A7436 LPS, 5% serum and Tc-HCl(5, 10, 50 and 100µg/ml). The superoxide anion analysis was carried out by superoxide dismutase-inhibitable cytochrome C reduction method using Microplate autoreader(BIO-TEK™ Instrument Inc.).

The difference of superoxide anion generation between control group and Tc-HCl group was statistically analyzed by paired t -test. The superoxide anion generation in the course of time after treatment with Tc-HCl was analyzed by ANOVA, and the superoxide anion generation in the course of time after treatment with various concentrations of Tc-HCl was analyzed by Repeated Measurement test.

The results were as follows:

1. Superoxide anion generation by PMNs was significantly decreased by Tc-HCl(p<0.05).

2. There was no statistical significance in the inhibition of superoxide anion generation in the course of time after treatment with various concentrations of Tc-HCl(p>0.05).

3. Superoxide anion generation by PMNs was significantly decreased in the course of incubation time after treatment with Tc-HCl(p<0.05).

The results demonstrate that the Tc-HCl inhibit superoxide anion generation by PMNs and the inhibitory effects depend on the exposure time rather than the concentration of Tc-HCl.