Ammonia-induced production of free radicals in primary cultures of rat astrocytes

C. R.K. Murthy, K. V. Rama Rao, Ge Bai, Michael D. Norenberg

Research output: Contribution to journalArticle

222 Scopus citations

Abstract

Elevated levels of ammonia in blood and brain result in derangement of cerebral function. Recently, lipid peroxidation and oxidative stress have been implicated in ammonia neurotoxicity. Because ammonia is primarily detoxified in astrocytes, we postulated that pathophysiological concentrations of ammonia might induce free radical formation in these cells. To test this hypothesis, we examined the extent of free radical production in primary cultures of astrocytes that had been preloaded with the fluorescent dye 5- (and 6-)carboxy-2′,7′-dichlorodihydrofluorescein diacetate (DCFDA). DCFDA fluorescence was found to be increased in a dose-dependent manner when astrocytes were exposed to 1, 5, and 10 mM NH4Cl. This phenomenon was transitory; it peaked at 2.5 min after exposure and declined subsequently. By 2 hr after treatment, DCFDA fluorescence was below control level. Addition of catalase or superoxide dismutase to 5 mM NH4Cl-treated astrocytes reduced free radical formation. Pretreatment with 3 mM methionine sulfoximine, an inhibitor of glutamine synthetase, also suppressed free radical formation by 5 mM NH4Cl. The results of this study suggest that elevated concentrations of ammonia induce the formation of free radicals in astrocytes and that this process is associated with the synthesis of glutamine. We propose that astrocyte-derived free radicals may be responsible for some of the pathophysiological changes associated with hyperammonemic conditions.

Original languageEnglish (US)
Pages (from-to)282-288
Number of pages7
JournalJournal of Neuroscience Research
Volume66
Issue number2
DOIs
StatePublished - Oct 15 2001

Keywords

  • Ammonia
  • Astrocytes
  • Free radicals
  • Glutamine
  • Hepatic encephalopathy

ASJC Scopus subject areas

  • Neuroscience(all)

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