A study of guanidinobenzoatase during development of mesothelioma induced in the rat by fibrous erionite.

Exposure to the fibrous mineral erionite is known to induce mesothelioma in man and laboratory animals. Previous studies demonstrated the presence of a trypsin-like protease associated with tumour cells. This protease could be demonstrated by the use of fluorescent probes which located cells possessing this enzyme. We have employed this fluorescent probe technique to follow the early events in the lungs of rats exposed to erionite. The evidence presented shows that the mesothelial cells initially lack this enzyme but the enzyme can be detected within hours of exposure of the rat to erionite. The number of mesothelial cells possessing the enzyme steadily increased after a single exposure to the mineral until the animal finally died with a massive pleural tumour. This is the first study of such fluorescent probes in the early stages of tumour induction.