Impaired hippocampal glucose metabolism during and after flurothyl-induced seizures in mice: Reduced phosphorylation coincides with reduced activity of pyruvate dehydrogenase

Summary

Objective

To determine changes in glucose metabolism and the enzymes involved in the hippocampus ictally and postictally in the acute mouse flurothyl seizure model.

Methods

[U-¹³C]-Glucose was injected (i.p.) prior to, or following a 5 min flurothyl-induced seizure. Fifteen minutes later, mice were killed and the total metabolite levels and % ¹³C enrichment were analyzed in the hippocampal formation using gas chromatography–mass spectrometry. Activities of key metabolic and antioxidant enzymes and the phosphorylation status of pyruvate dehydrogenase were measured, along with lipid peroxidation.

Results

During seizures, total lactate levels increased 1.7-fold; however, [M + 3] enrichment of both lactate and alanine were reduced by 30% and 43%, respectively, along with a 28% decrease in phosphofructokinase activity. Postictally the % ¹³C enrichments of all measured tricarboxylic acid (TCA) cycle intermediates and the amino acids were reduced by 46–93%. At this time, pyruvate dehydrogenase (PDH) activity was 56% of that measured in controls, and there was a 1.9-fold increase in the phosphorylation of PDH at ser232. Phosphorylation of PDH is known to decrease its activity.

Significance

Here, we show that the increase of lactate levels during flurothyl seizures is from a source other than [U-¹³C]-glucose, such as glycogen. Surprisingly, although we saw a reduction in phosphofructokinase activity during the seizure, metabolism of [U-¹³C]-glucose into the TCA cycle seemed unaffected. Similar to our recent findings in the chronic phase of the pilocarpine model, postictally the metabolism of glucose by glycolysis and the TCA cycle was impaired along with reduced PDH activity. Although this decrease in activity may be a protective mechanism to reduce oxidative stress, which is observed in the flurothyl model, ATP is critical to the recovery of ion and neurotransmitter balance and return to normal brain function. Thus we identified promising novel strategies to enhance energy metabolism and recovery from seizures.

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