Glutamine in the mechanism of ammonia-induced astrocyte swelling

A. R. Jayakumar, K. V Rama Rao, Ch R K Murthy, Michael D Norenberg

Research output: Contribution to journalArticle

84 Citations (Scopus)

Abstract

Brain edema and the subsequent increase in intracranial pressure are the major neurological complications in fulminant hepatic failure (FHF). Brain edema in FHF is predominantly "cytotoxic" due principally to astrocyte swelling. It is generally believed that ammonia plays a key role in this process, although the mechanism by which ammonia brings about such swelling is yet to be defined. It has been postulated that glutamine accumulation in astrocytes subsequent to ammonia detoxification results in increased osmotic forces leading to cell swelling. While the hypothesis is plausible and has gained support, it has never been critically tested. In this study, we examined whether a correlation exists between cellular glutamine levels and the degree of cell swelling in cultured astrocytes exposed to ammonia. Cultured astrocytes derived from rat brain cortices were exposed to ammonia (5 mM) for different time periods and cell swelling was measured. Cultures treated with ammonia for 1-3 days showed a progressive increase in astrocyte cell volume (59-127%). Parallel treatment of astrocyte cultures with ammonia showed a significant increase in cellular glutamine content (60-80%) only at 1-4 h, a time when swelling was absent, while glutamine levels were normal at 1-3 days, a time when peak cell swelling was observed. Thus no direct correlation between cell swelling and glutamine levels was detected. Additionally, acute increase in intracellular levels of glutamine by treatment with the glutaminase inhibitor 6-diazo-5-oxo-l-norleucine (DON) after ammonia exposure also did not result in swelling. On the contrary, DON treatment significantly blocked (66%) ammonia-induced astrocyte swelling at a later time point (24 h), suggesting that some process resulting from glutamine metabolism is responsible for astrocyte swelling. Additionally, ammonia-induced free radical production and induction of the mitochondrial permeability transition (MPT) were significantly blocked by treatment with DON, suggesting a key role of glutamine in the ammonia-induced free radical generation and the MPT. In summary, our findings indicate a lack of direct correlation between the extent of cell swelling and cellular levels of glutamine. While glutamine may not be acting as an osmolyte, we propose that glutamine-mediated oxidative stress and/or the MPT may be responsible for the astrocyte swelling by ammonia.

Original languageEnglish
Pages (from-to)623-628
Number of pages6
JournalNeurochemistry International
Volume48
Issue number6-7
DOIs
StatePublished - May 1 2006

Fingerprint

Glutamine
Ammonia
Astrocytes
Norleucine
Permeability
Acute Liver Failure
Brain Edema
Free Radicals
Diazooxonorleucine
Glutaminase
Intracranial Hypertension
Cell Size
Oxidative Stress

Keywords

  • Ammonia
  • Astrocyte swelling
  • Free radicals
  • Glutaminase
  • Glutamine
  • Mitochondrial permeability transition
  • Osmolyte

ASJC Scopus subject areas

  • Cell Biology
  • Molecular Biology
  • Cellular and Molecular Neuroscience

Cite this

Glutamine in the mechanism of ammonia-induced astrocyte swelling. / Jayakumar, A. R.; Rao, K. V Rama; Murthy, Ch R K; Norenberg, Michael D.

In: Neurochemistry International, Vol. 48, No. 6-7, 01.05.2006, p. 623-628.

Research output: Contribution to journalArticle

Jayakumar, A. R. ; Rao, K. V Rama ; Murthy, Ch R K ; Norenberg, Michael D. / Glutamine in the mechanism of ammonia-induced astrocyte swelling. In: Neurochemistry International. 2006 ; Vol. 48, No. 6-7. pp. 623-628.
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