In situ determination of different dehydrogenase activity profiles in the linings of odontogenic keratocysts and radicular cysts.

The levels of succinate, lactate, glutamate, glycerophosphate and glucose-6-phosphate dehydrogenases within the linings of keratinizing and non-keratinizing odontogenic cysts were investigated using static end-point and continuously monitored Nitroblue Tetrazolium-based histochemical methods. The use of TV image analysis for quantification of formazan final reaction products was validated by demonstrating significant relationships between the integrated absorbance at 585 nm and the amount of formazan in, and thickness of, gelatin films containing reduced tetrazolium salt (r = 1.0, p < 0.001). Absorbance readings of stained sections gave mean coefficients of variation of 1.8 +/- 0.9% between day of measurement, and of 5.65 +/- 1.32% between serial sections. End-point assays indicated that the linings of odontogenic keratocysts contained higher levels of glucose-6-phosphate dehydrogenases (p < 0.0002) and lower levels of lactate dehydrogenase (p < 0.002) than those of radicular cysts. Succinate, glutamate and glycerophosphate dehydrogenase activities were similar in both cyst types. Results from continuously monitored assays, performed for glucose-6-phosphate and succinate dehydrogenases, demonstrated linear reaction rates over the first 2.75 min of reaction. The calculated enzyme activities from continuous assays were between 1.49 and 3.49 times higher than those determined from end-point assays and confirmed that levels of glucose-6-phosphate dehydrogenase were significantly higher in the linings of odontogenic keratocysts than those of radicular cysts (p < 0.004). By contrast, succinate dehydrogenase activity was significantly higher in radicular cyst linings (p < 0.03). These results highlight the benefits of an approach to in situ determination of enzyme activity using image analysis and continuous monitoring methodologies. Overall, the high level of glucose-6-phosphate dehydrogenase found in keratocyst linings is consistent with their clinical behaviour and higher level of proliferation and synthetic activity whereas the level of lactate dehydrogenase in radicular cysts probably reflects the presence of local tissue damage within these inflammatory lesions.