title: Inhibition of biliverdin reductase increases ANG II-dependent superoxide levels in cultured renal tubular epithelial cells.
abstract: Induction of heme oxygenase-1 (HO-1) in the renal medulla increases carbon monoxide and bilirubin production and decreases ANG II-mediated superoxide production. The goal of this study was to determine the importance of increases in bilirubin to the antioxidant effects of HO-1 induction in cultured mouse thick ascending loop of Henle (TALH) and inner medullary collecting duct (IMCD3) cells. Bilirubin levels were decreased by using small interfering RNAs (siRNAs) targeted to biliverdin reductase (BVR), which is the cellular enzyme responsible for the conversion of biliverdin to bilirubin. Treatment of cultured TALH or IMCD-3 cells with BVR siRNA (50 or 100 nM) resulted in an 80% decrease in the level of BVR protein and decreased cellular bilirubin levels from 46 +/- 5 to 23 +/- 4 nM (n = 4). We then determined the effects of inhibition of BVR on ANG II-mediated superoxide production. Superoxide production induced by ANG II (10(-9) M) significantly increased in both TALH and IMCD-3 cells. Treatment of TALH cells with BVR siRNA resulted in a significant increase in ouabain-sensitive rubidium uptake from 95 +/- 6 to 122 +/- 5% control (n = 4, P < 0.05). Lastly, inhibition of BVR with siRNA did not prevent the decrease in superoxide levels observed in cells pretreated with the HO-1 inducer, hemin. We conclude that decreased levels of cellular bilirubin increase ANG II-mediated superoxide production and sodium transport; however, increases in bilirubin are not necessary for HO-1 induction to attenuate ANG II-mediated superoxide production.
authors.affiliation: Department of Physiology and Biophysics, Center for Excellence in Cardiovascular-Renal Research, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA.
authors.forename: Shelby C
authors.initials: SC
authors.lastname: Young
authors.forename: Megan V
authors.initials: MV
authors.lastname: Storm
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Speed
authors.forename: Silvia
authors.initials: S
authors.lastname: Kelsen
authors.forename: Chelsea V
authors.initials: CV
authors.lastname: Tiller
authors.forename: Trinity
authors.initials: T
authors.lastname: Vera
authors.forename: Heather A
authors.initials: HA
authors.lastname: Drummond
authors.forename: David E
authors.initials: DE
authors.lastname: Stec
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D001663:Bilirubin / Q000378:metabolism; D001664:Biliverdine / Q000494:pharmacology; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051547:Heme Oxygenase-1 / Q000378:metabolism; D006427:Hemin / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007686:Kidney Tubules, Distal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; D013481:Superoxides; D000804:Angiotensin II; D006427:Hemin; D051547:Heme Oxygenase-1; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D001664:Biliverdine; D001663:Bilirubin