Inhibition of human periodontal prostaglandin E2 synthesis with selected agents

Considerable evidence has demonstrated the importance of PGE₂ synthesis in the pathogenesis of periodontal disease. Although various cyclooxygenase inhibitors have been known to block periodontal PGE₂ synthesis and prevent disease progression in animal models, there are few reports comparing relative efficacies of various inhibitors of arachidonic acid (ARA) metabolism. We have developed a sensitivein vitro assay to measure PGE₂ synthesis in periodontal tissues. The apparent IC₅₀ values (i.e. the concentration of drug which causes 50% inhibition of maximum PGE₂ synthesis) have been determined for a series of arachidonic acid analogues as well as competitive and non-competitive cyclooxygenase inhibitors. Periodontal tissue homogenates were incubated in the presence of³H-arachidonic acid for 45 min at 37°C. Inhibitors were tested at 10⁻¹⁰–10⁻⁴M and at zero concentration to measure conversion of³H-arachidonate to³H-PGE₂. Log or half log dilutions of inhibitors were tested in triplicate for each assay. Radiolabeled PGE₂ was extracted from homogenates, purified by reverse phase chromatography and quantitated by double antibody capture. RIA was performed on each homogenate to determine the amount of endogenous unlabeled PGE₂ present in the sample to correct for antibody capture recovery. The apparent IC₅₀ values were determined for each drug by averaging two or more replicate assays. Specific total enzymatic activity of periodontal tissue homogenates was typically 5–11 pg PGE₂/min/mg tissue. The following series of compounds were tested and are listed in order of increasing IC₅₀ values: α-tocopherol (3.3×10⁻⁹M), ketoprofen (5.4×10⁻⁹M), indomethacin (1.0×10⁻⁸M), flurbiprofen (1.5×10⁻⁸M), meclofenamate (1.5×10⁻⁶M), naproxen (2.5×10⁻⁶M), docosahexaenoic acid (1.0×10⁻⁵M), eicosapentaenoic acid (1.5×10⁻⁵M), and ibuprofen (1.5×10⁻⁵M). These data will enable the rational design of pharmacological formulations to inhibit periodontal tissue PGE₂ synthesis and resultant inflammation, attachment loss and bone resorption.