title: Ammonia increases nitric oxide, free Zn(2+), and metallothionein mRNA expression in cultured rat astrocytes.
abstract: Ammonia is a major player in the pathogenesis of hepatic encephalopathy (HE) and affects astrocyte function by triggering a self-amplifying cycle between osmotic and oxidative stress. We recently demonstrated that hypoosmotic astrocyte swelling rapidly stimulates nitric oxide (NO) production and increases intracellular free Zn(2+) concentration ([Zn(2+)](i)). Here we report effects of ammonia on [Zn(2+)](i) homeostasis and NO synthesis. In cultured rat astrocytes, NH(4)Cl (5 mm) increased within 6 h both cytosolic and mitochondrial [Zn(2+)]. The [Zn(2+)](i) increase was transient and was mimicked by the nonmetabolizable CH(3)NH(3)Cl, and it was dependent on NO formation, as evidenced by the sensitivity toward the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine. The NH(4)Cl-induced NO formation was sensitive to the Ca(2+) chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester and increases in both NO and [Zn(2+)](i) were blocked by the N-methyl-d-aspartate receptor antagonist MK-801. The NH(4)Cl-triggered increase in [Zn(2+)](i) was followed by a Zn(2+)-dependent nuclear appearance of the metal response element-binding transcription factor and metallothionein messenger RNA (mRNA) induction. Metallothionein mRNA was also increased in vivo in rat cerebral cortex 6 h after an NH(4)Ac challenge. NH(4)Cl increased peripheral-type benzodiazepine receptor (PBR) protein expression, whereas PBR mRNA levels were decreased in a Zn(2+)-independent manner. The Zn(2+)-dependent upregulation of metallothionein following ammonia intoxication may reflect a cytoprotective response, whereas the increase in PBR expression may augment HE development.
authors: University Clinic of Düsseldorf, Clinic for Gastroenterology, Hepatology and Infectiology, Moorenstrasse 5, 40225 Düsseldorf, Germany.
authors: Carolin
authors: C
authors: Kruczek
authors: Boris
authors: B
authors: Görg
authors: Verena
authors: V
authors: Keitel
authors: Hans J
authors: HJ
authors: Bidmon
authors: Freimut
authors: F
authors: Schliess
authors: Dieter
authors: D
authors: Häussinger
mesh_terms: D000641:Ammonia / Q000494:pharmacology*; D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D008297:Male; D008668:Metallothionein / Q000235:genetics*; D009569:Nitric Oxide / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D015854:Up-Regulation / Q000187:drug effects*; D015032:Zinc / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D009569:Nitric Oxide; D000641:Ammonia; D008668:Metallothionein; D015032:Zinc