Certain medications for degenerative diseases (such as atherosclerosis and cardiac arrhythmias) associated with aging can cause serologic abnormalities characteristic of an autoimmune diathesis. Some of these patients may go on to develop symptoms of a lupus-like syndrome, necessitating discontinuation of therapy. The overall goals of this project are to determine the cause of this and other forms of chronic toxicity, and the basis for the variable sensitivity of the patient population. The premise of this proposal is that some forms of idiosyncratic drug toxicity are not directly due to the ingested parent compound but may be related to reactive drug metabolites, generated in vivo. Based on the precedent established with procainamide metabolism, it is proposed that activated neutrophils may be primary mediators in oxidizing certain drugs to reactive forms. Preliminary data suggest that this mechanism may, in fact, be applicable to metabolism of other drugs. Reactive products will be detected using a bioassay for cytotoxicity of cells in culture, chromatographically separated and identified by spectrophotometric and mass spectrometric analyses. These studies will determine the chemical prerequisites for drug susceptibility to neutrophil-mediated metabolic reactions. The mechanisms for these transformations will be determined by the use of specific inhibitors and competitors of the extracellular oxidative machinery of neutrophils, by using neutrophils from patients with well-defined genetic lesions in components of this pathway and a cell-free system which models the oxidative reactions. The cell-free system will also provide a convenient assay for screening new drugs for susceptibility to neutrophil-mediated transformations. Capacity of neutrophils to generate reactive drug metabolites will be evaluated in patients with a history of drug-induced autoimmunity, in asymptomatic drug users and in normal donors of various ages. These studies will identify functional polymorphisms in neutrophil oxidative machinery and determine if increasing age exacerbates drug metabolism by this mechanism. Mouse models will be developed in which the test drug is continuously infused from implanted osmotic pumps, creating a uniform and long-term exposure regimen at drug levels comparable to that of human subjects. This system is intended to facilitate identification of in vivo-generated metabolites recognized by drug-specific lymphocytes and allow further exploration of the pathogenesis of chronic drug toxicity.
