Darryl Craig Zeldin

Work from our laboratory has demonstrated that the cytochromes P450 metabolize arachidonic acid to a novel group of fatty acid epoxides called epoxyeicosatrienoic acids (EETs). These compounds have been shown to possess potent biological activities including effects on vascular and airway smooth muscle, stimulation of peptide hormone release, and modulation of ion transport. We hypothesize that the EETs and their hydration products, the dihydroxyeicosatrienoic acids (DHETs), play important roles in cell and organ physiology and that aberrant expression of the P450 epoxygenase genes leads to cell and organ dysfunction. Current research in the Clinical Studies Group involves: (1) characterization of the human cytochrome P450 arachidonic acid epoxygenases at the biochemical and molecular levels; (2) evaluation of the roles that the EETs and DHETs play in cell and organ physiology; and (3) examination of this enzymatic pathway in selected human diseases.

Recently, our laboratory has been successful in cloning a full length cDNA coding for a novel human cytochrome P450 arachidonic acid epoxygenase (designated CYP2J2). This 57 kilodalton protein catalyzed the NADPH-dependent, regio- and stereoselective metabolism of arachidonic acid to the biologically active EETs. Nucleic acid blot hybridization analysis and protein immunoblotting demonstrated that CYP2J2 was primarily expressed in the heart. Immunolocalization studies demonstrated that CYP2J2 is present mainly in cardiac myocytes. The in vivo significance of CYP2J2 was confirmed by demonstrating, for the first time, the presence of EETs in human heart using HPLC/GC/MS techniques. Importantly, we have shown that the EETs improve cardiac contractility following global cardiac ischemia suggesting that these endogenous lipid mediators are cardioprotective. Current research efforts are focused on: (a) elucidation of the mechanism(s) responsible for the cardioprotective effects of the EETs during ischemia; and (b) evaluation of the effects of hyperexpression and knock-out of epoxygenase genes on susceptibility of the heart to ischemia.

In a related project, we have identified EETs in human lung and bronchoalveolar lavage fluid, thus providing direct evidence for the in vivo pulmonary cytochrome P450 epoxidation of arachidonic acid. EETs were shown to be active in relaxing histamine-contracted airways in vitro indicating that these lipids may play an important role in controlling bronchial smooth muscle tone. Recently, we have used intact excised rat airways and cultured rat and human bronchial epithelial cells to demonstrate that both EETs and DHETs modulate fluid/electrolyte transport in the lung. Current efforts are focused on the following: (a) cloning, expression, and enzymatic characterization of the human lung cytochrome P450 arachidonic acid epoxygenase(s); (b) characterization of the mechanisms by which EETs and DHETs modulate ion flux in the airway; and (c) studying the role that epoxygenases play in lung disease using several well characterized rodent lung injury models.