Co-purification of gastric mucoproteins with DNA: An explanation for the reported ‘interaction’ of omeprazole with DNA in rat tissues

Abstract Recently, Phillips et al. reported that small amounts of radioactivity derived from [ 14 C]omeprazole were ‘associated’ with DNA purified from gastrointestinal tissues of treated rats (Mutagenesis 7, 277–283, 1992). We hypothesized that this radioactivity arose from omeprazole bound to contaminating protein in the DNA fraction (Mutagenesis 7, 395–396, 1992). Using rats injected with 35 S-labeled amino acids, we found significant protein contamination (0.06 mu;g of protein per mu;g of DNA) in DNA purified from gastrointestinal tissues. Gastric mucous proteins represent likely candidates for binding of omeprazole in the rat model used by Phillips et al. To investigate this, we partially purified proteins from gastric mucus, incubated them with [ 14 C]omeprazole, and then added these radiolabeled mucoproteins to homogenates of rat colon and duodenum before starting the DNA purification. Detectable amounts of the added mucoproteins remained in the DNA fraction, but none of the control protein, bovine serum albumin, remained with the DNA. Further characterization of the mucoproteins by hydroxyapatite chromatography indicated that a certain population of these proteins survived the DNA purification procedures. These data indicate that the association of omeprazole with DNA reported by Phillips et al. most probably is explained by binding of omeprazole to mucous glycoproteins (or other proteins present in the GI tract) that selectively survive DNA purification protocols.