Abstracts

Rationale: Leucine is a ketogenic amino acid that protects against picrotoxin- and pentylenetetrazol-induced seizures in rats (Skeie, Pharmacol Biochem Behav 1994; Dufour, Brain Res 1999) but not against hexafluorodiethyl ether seizures (Gallagher, J Neurochem 1969). Similar to rapamycin (which suppresses seizures), leucine depletion suppresses mTOR activity in cell culture (Zeng, J Neurosci 2009; Laplante, J Cell Sci 2009). Leucine also decreases synaptic glutamate concentration (Yudkoff, Prostaglandins Leukot Essent Fatty Acids 2004). It is unknown whether leucine has an anticonvulsant mechanism similar to treatments that affect metabolism, including the ketogenic diet or rapamycin. We investigated the anticonvulsant effects of leucine using acute seizure tests in normal mice. Methods: In Cohort #1, NIH Swiss mice aged 3 weeks received leucine via drinking water (1.5% w/v) for 12 days (control mice received water without leucine). Seizures were induced using the 6 Hz, pentylenetretrazol, maximal electroshock, and kainic acid tests. Blood ketones were measured prior to seizure testing. In Cohort #2, mice aged 5 weeks were injected intraperitoneally with leucine (300 mg/kg in PBS) either 3 hours before or 15 minutes after kainic acid injection. Results: In Cohort #1, leucine-treated mice were protected against 6 Hz-induced seizures (P = 0.02). In the pentylenetetrazol test, mice treated with leucine had a prolonged latency to the first tail twitch (P = 0.04) but did not differ in other parameters. In the kainic acid test, leucine-treated mice had lower overall seizure scores than control mice (P = 0.0009). There was no difference in the maximal electroshock threshold test. Blood ketone levels were similar between leucine-treated and control mice. In Cohort #2, mice treated with leucine 3 hours prior to kainic acid had significantly lower overall seizure scores (P = 0.0002) and a shorter duration of convulsions (P = 0.03). Mice treated with leucine 15 min after kainic acid treatment had lower maximum seizure scores (P = 0.01) and a borderline longer latency to onset of overt convulsions (P = 0.049) but no differences in other parameters. Conclusions: Leucine is protective in acute seizure tests. Leucine has an acute seizure test profile that is distinct from anticonvulsants currently used in the clinic and other metabolism-based antiseizure treatments, including the ketogenic diet and rapamycin. Anticonvulsant effects could not be attributed to differences in blood ketone levels.