Soy Isoflavones Improve Spatial Delayed Matching-to-Place Performance and Reduce Cholinergic Neuron Loss in Elderly Male Rats

Abstract

To investigate the protective activity of soy isoflavones on neurons, the effects of isoflavones on cholinergic enzyme activity, immunoreactivities of cholinergic enzyme, and delayed matching-to-place (DMP) performance were measured in normal elderly rats. Male Sprague-Dawley rats (n = 48; 10 mo old) were assigned to 3 groups: CD (control diet), ISO 0.3 (0.3 g/kg soy isoflavones diet), and ISO 1.2 (1.2 g/kg soy isoflavones diet). After 16 wk of consuming these diets, choline acetyltransferase (ChAT) activity in the ISO 0.3 group was greater in cortex and basal forebrain (BF; P < 0.05) than in controls. In BF, ChAT activity was also significantly greater in the ISO 1.2 group than in control rats. Acetylcholine esterase (AChE) activity in the ISO 0.3 group was significantly inhibited in cortex, BF, and hippocampus and in the ISO 1.2 group in cortex and hippocampus. Choline acetyltransferase immunoreactivity (ChAT-IR) in the ISO 1.2 group was significantly greater than in controls in the medial septum area. ChAT-IR in the ISO 0.3 and ISO 1.2 groups was significantly higher than in the CD group in the hippocampus CA1 area. Spatial DMP performance by the ISO 0.3 group showed significantly shorter swimming time than by the CD group. These findings show that soy isoflavones can influence the brain cholinergic system and reduce age-related neuron loss and cognition decline in male rats.

Adaptive Cellular Stress Pathways as Therapeutic Targets of Dietary Phytochemicals: Focus on the Nervous System

“…However, at higher concentrations, genistein inhibits tyrosine kinases (Akiyama et al, 1987), some of which are involved in long-term potentiation and cognitive function. Studies of the effects of soy isoflavones on cognitive function in men are as yet inconclusive (Lund et al, 2001;Lee et al, 2004). Therefore, it can be postulated that soy phytoestrogens may enhance cognitive function at low doses, but impair cognitive function when ingested in higher amounts.…”

The neuroprotective potential of flavonoids: a multiplicity of effects

“…Isoflavone supplementation has been observed to have a favourable effect on cognitive function [13], particularly verbal memory, in postmenopausal women [51] and a 6 and 12-week supplementation was observed to have a positive effect of frontal lobe function [27]. Furthermore, animal studies have also indicated that isoflavones are capable of improving cognitive function [58,64,77]. However, there is still uncertainty regarding their effects as some large intervention trials have reported that isoflavone supplementation does not lead to cognitive improvements [30].…”

Soy isoflavone: The multipurpose phytochemical (Review)

“…Dietary soy-derived phytoestrogens may affect learning and memory and alter the expression of proteins involved in neural protection and inflammation in rats (27). Soy isoflavones may also affect the cholinergic system of the brain and reduce age-related neuronal loss and cognition decline in male rats (28). There are proposed mechanisms for the neuroprotective effects of isoflavones.…”