Soy isoflavones modulate the expression of BAD and neuron-specific beta III tubulin in male rat brain.

Isoflavones, the most abundant phytoestrogens in soy foods, are structurally similar to 17beta-estradiol. There is evidence that soy isoflavones influence neuronal apoptosis or proliferation in vitro and in vivo. However, little research has been done to investigate the effects of soy isoflavones on markers of neuronal apoptosis and survival in vivo. We examined brain BAD (a proapoptotic member of Bcl-2 protein family) and neuron-specific beta III tubulin (an early marker of neuronal differentiation/survival) levels in male rats fed either a standard chow rich of soy isoflavones (Phyto-600) or one free of soy isoflavones (Phyto-free) life-long (from conception until time tissue collected). Among five brain regions, the expression of BAD was highest in medial basal hypothalamus (MBH); the next highest in hippocampus; moderate in amygdala and frontal cortex; and lowest in cerebellum in Phyto-free fed animals. In animals on Phyto-600 diet, the levels of BAD were significantly decreased in frontal cortex and MBH; but significantly increased in the amygdala. The expression of beta III tubulin was highest in frontal cortex; moderate in amygdala, hippocampus and MBH; and lowest in cerebellum in the Phyto-free group. In rats fed with the Phyto-600 diet, levels of beta III tubulin were significantly increased in amygdala, frontal cortex, hippocampus and MBH compared to Phyto-free values. In summary, these findings provide evidence for the neuroprotective potential of soy isoflavones in the amygdala, frontal cortex, hippocampus and MBH. This implies that consumption of soy isoflavones may be beneficial on learning and memory, anxiety-related behaviors, and recovery from trauma.