HIF-1-regulated vasoactive systems are differentially involved in acute hypoxic stress responses of the developing brain of newborn mice and are not affected by levetiracetam.

ABSTRACT

Hypoxia-inducible transcription factor-1 (HIF-1) is critically involved in adaptive endogenous mechanisms to hypoxic brain injury by transcriptional activation of specific target genes that restore oxygen supply. Exogenously, neuroprotective properties of levetiracetam (LEV) have been suggested in experimental cerebral ischemia and epilepsy. We aimed to elucidate 1) effects of acute hypoxic distress on HIF-1 and vasoactive target genes, and 2) effects of LEV on HIF-1-regulated mechanisms in the brain at early developmental stages. To this end, we studied the impact of hypoxia in the presence or absence of LEV on the O2-dependent HIF-1alpha subunit as well as on VEGF and iNOS in the developing brain of normoxic and hypoxic mice. C57BL/6 mice (P0, P7) were treated with saline or LEV (i.p.; 50 mg/kg) 1 h before exposure to either normoxia (21% O2; N) or hypoxia (8% O2 of 6 h; H) without reoxygenation. HIF-1alpha was analyzed by Western blot and immunohistochemistry and mRNA levels were quantified by TaqMan RT-PCR. Hypoxia led to prominent accumulation of cerebral HIF-1alpha protein in cortical neurons and glial cells and significant up-regulation of VEGF mRNA at P0 (N, 0.018+/-0.002, vs. H, 0.031+/-0.003, n=6; p<0.05) and P7 (N, 0.096+/-0.032, vs. H, 0.873+/-0.069, n=7; p<0.001). Interestingly, we detected a significant decrease of iNOS mRNA levels in hypoxic brains. LEV treatment did not alter HIF-1alpha accumulation either in normoxic or hypoxic brains (P0, P7). Moreover, significant changes of VEGF and NOS mRNA levels did not occur with the exception that hypoxia-induced decreased iNOS levels were not observed in P0 brains. We conclude that acute systemic hypoxia differentially affects expression of HIF-1-regulated vasoactive factors in the newborn mouse brain. Of clinical importance, LEV treatment did not alter crucial HIF-1-regulated neuroprotective mechanisms.