Abstracts

Rationale: Selected D-amino acids (e.g., D-serine) have biological activity. D-leucine may account for up to 0.5% of commercial L-leucine preparations. Thus, modest protection of L-leucine against seizures may be due to either isomer. We investigated whether D-leucine protected against kainic acid- and 6 Hz-induced seizures.Methods: NIH Swiss male mice (5 weeks) were injected intraperitoneally with D-leucine (high dose, 300 mg/kg; low dose, 3 mg/kg) or H2O 3 hours before seizure tests (kainic acid & 6 Hz tests). D-leucine also was administered in drinking water (1.5% w/v) for 13 days prior to the 6 Hz test. Blood glucose and beta-hydroxybutyrate levels were measured prior to seizure testing.Results: In the kainic acid test, D-leucine treatment at both doses led to lower mean maximum seizure scores (P<0.005, one-way ANOVA; P<0.01 H2O vs high-dose D-leu, P<0.05 H2O vs low-dose D-leu, Tukey) and number of epochs spent in seizure stage 2 (P<0.0001, one-way ANOVA; P<0.001 H2O vs either dose of D-leu, Tukey). Treatment only at the high dose led to longer latency of onset to seizure stage 2 (P=0.003, one-way ANOVA; P<0.01 H2O vs high-dose D-leu, Tukey). There was no difference between groups in the maximum seizure score (P=0.2). In the 6 Hz test, mice treated with D-leucine in drinking water had a higher CC50 (i.e., current where half of mice had a convulsion) than mice drinking plain water (P = 0.02, probit analysis). In contrast, when injected 3 h prior to testing, there was no difference between H2O and low-dose D-Leu in the 6 Hz test. In both treatment paradigms, there was no difference between groups in seizure duration or maximum seizure score. Blood glucose levels after a 3 h pretreatment with low-dose D-leucine were lower than controls (P=0.008) but no differences were noted in blood glucose or beta-hydroxybutyrate after a 13 d treatment.Conclusions: D-leucine exerts antiseizure properties when administered prior to seizure testing. Protection at a low dose suggests that D-leucine may act as a signaling molecule. Lower blood glucose levels after a short D-leucine exposure suggest the antiseizure effect may be due to cellular responses to mild hypoglycemia (i.e., as seen with the glycolysis inhibitor 2-deoxy-D-glucose), which also protects against seizures. Compared to prior work on L-leucine, these data suggest that D-leucine may account for much of the antiseizure effect of commercially-prepared L-leucine.