Isoamylases: Detection (by Immunoassay) and Metabolism

Rosenblum, Jerry

Abstract

Pancreatitis is a common disease, but difficult to diagnose with certainty. Although many of the signs and symptoms observed in patients with pancreatitis are non-specific, the diagnosis is most commonly based on a combination of clinical presentation and documentation of hyperamylasemia. An elevation in total serum amylase activity can be seen in many other pathologic conditions, however, and in certain clinical settings, its presence may contribute to misdiagnosis. We propose to develop quantitative immunoassays of pancreatic and salivary isoamylases in human serum using monoclonal antibodies. The development of rapid and simple immunoassays for serum isoamylases should help in the diagnosis of pancreatitis by identifying organ-specific isoamylase elevations in serum. By using hybridoma techniques, the immunoassays will be widely available due to a limitless supply of antibody with constant affinity, titer and specificity. Although quantitative immunoassays will permit detection of the major isoamylase contributing to hyperamylasemia, very little is known about the mechanisms that lead to elevated serum amylase activity in different pathological conditions. Since total amylase activity in serum is normally maintained within a well-defined range, hyperamylasemia must therefore result from a net increase in the rates of release of isoamylases into the circulation or a net decrease in their rates of clearance. We, therefore, propose to study the plasma clearance, urinary excretion and organ uptake following intravenous injection of iodinated human isoamylases into the conscious rabbit. Because available data suggests that the kidney and liver may play a role in the metabolism of isoamylases, we will study degradation of human isoamylases in the isolated, perfused rabbit kidney and in isolated rat hepatocytes. Although these studies do not investigate rates of circulatory isoamylase release, we may assume in the absence of altered clearance or excretion, that an increase in their net rate of circulatory release leads to hyperamylasemia. Studies of the factors regulating isoamylase release have not been carefully studied, and may represent an interesting area for future research.