Ammonia induces RNA oxidation in cultured astrocytes and brain in vivo.
Oxidative stress plays a major role in cerebral ammonia toxicity and the pathogenesis of hepatic encephalopathy (HE). As shown in this study, ammonia induces a rapid RNA oxidation in cultured rat astrocytes, vital mouse brain slices, and rat brain in vivo. Ammonia-induced RNA oxidation in cultured astrocytes is reversible and sensitive to MK-801, 1,2-Bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, apocynin, epigallocatechin gallate, and polyphenon 60, suggesting the involvement of N-methyl-D-aspartic acid (NMDA) receptor activation, Ca(2+), nicotinamide adenine dinucleotide phosphate, and reduced form (NADPH) oxidase-dependent oxidative stress. Also, hypo-osmolarity, tumor necrosis factor alpha (TNF-alpha), and diazepam increase RNA oxidation in cultured astrocytes, suggesting that the action of different HE-precipitating factors converges at the level of RNA oxidation. Among the oxidized RNA species, 18S-rRNA and the messenger RNA (mRNA) coding for the glutamate/aspartate transporter (GLAST) were identified. Cerebral RNA oxidation in acutely ammonia-loaded rats in vivo is reversible and predominates in neuronal soma and perivascular astrocyte processes. In neuronal dendrites, oxidized RNA colocalizes with the RNA-binding splicing protein neurooncological ventral antigen (NOVA)-2 within putative RNA transport granules, which are also found in close vicinity to postsynaptic spines. This indicates that oxidized RNA species may participate in postsynaptic protein synthesis, which is a biochemical substrate for learning and memory consolidation. Neuronal and astroglial RNA oxidation increases also in vital mouse brain slices treated with ammonia and TNF-alpha, respectively.


CONCLUSIONS
Cerebral RNA oxidation is identified as a not yet recognized consequence of acute ammonia intoxication. RNA oxidation may affect gene expression and local protein synthesis and thereby provide another link between reactive oxygen species (ROS)/reactive nitrogen oxide species (RNOS) production and ammonia toxicity.
Görg
Boris
B
Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine University, Düsseldorf, Germany.
Qvartskhava
Natalia
N
Keitel
Verena
V
Bidmon
Hans J
HJ
Selbach
Oliver
O
Schliess
Freimut
F
Häussinger
Dieter
D
D027322:Amino Acid Transport System X-AG / Q000235:genetics; D000641:Ammonia / Q000494:pharmacology*; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D002478:Cells, Cultured; D003712:Dendrites / Q000378:metabolism; D003975:Diazepam / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000378:metabolism; D009994:Osmolar Concentration; D010084:Oxidation-Reduction / Q000187:drug effects; D012313:RNA / Q000378:metabolism*; D034443:RNA Transport; D012333:RNA, Messenger / Q000378:metabolism; D012337:RNA, Ribosomal, 18S / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014018:Tissue Distribution; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D027322:Amino Acid Transport System X-AG; D012333:RNA, Messenger; D012337:RNA, Ribosomal, 18S; D014409:Tumor Necrosis Factor-alpha; D012313:RNA; D000641:Ammonia; D003975:Diazepam