[ACE: physiopathology and role in the diagnosis and prognosis of systemic granulomatosis, neoplasms and lung toxicity caused by antineoplastic agents].

Several studies have been performed in the last ten-years on the biochemical and physiopathologic properties of angiotensin-converting enzyme (ACE). Human lung and kidney are a rich source of ACE and the enzyme is bound to the plasma-membrane of vascular endothelial cells; however, the small intestine and the choroid plexus are also particularly rich in ACE, where it is concentrated on the surface of cuboidal epithelial cells facing the cerebrospinal fluid. The ACE is a glycoprotein with a molecular weight of 150,000 daltons and it cleaves C-terminal dipeptides of several oligo-peptides, including angiotensin I and bradykinin. It catalyzes conversion of angiotensin I to angiotensin II and induces inactivation of bradykinin. Synthetic acylated tripeptides such as radiolabelled hippuryl-histidyl-leucine and hippuryl-glycyl-glycine have been found to be the most suitable substrates for determining the activity of ACE with radiochemical assays. The mean-normal values for ACE activity is 25 U/ml; there are no significant differences in ACE activity between different sexes and races, but there is significant decrease in adults. The measurement of ACE activity in sarcoidosis suggests the following results: 1) There is a relationship between the increased SACE and LACE activity and active disease and between normal ACE activity and inactive disease. 2) Normal or decreased ACE activity is useful for therapeutic evaluation of sarcoidosis. 3) Increased SACE activity can be a sensitive parameter for predicting clinical relapse of the disease. An increased SACE activity is found in a wide variety of non-sarcoid granulomatous diseases and non-granulomatous systemic diseases. A decreased SACE and LACE activity is found in non-granulomatous pulmonary diseases such as "Adult Respiratory Distress Syndrome", lung cancer and lung toxicity caused by antineoplastic drugs. Moreover, a low preoperative SACE is associated with poor prognosis in lung cancer and its levels may be useful for predicting clinical relapse of this disorder after operation. Finally, a low SACE activity is found in malignant lymphomas, leukemia and multiple myeloma. A relationship is also found between decreased enzyme activity and a poor prognosis and clinical relapse of these diseases.