The University of the Ryukyus finds component in brown rice that improves cognitive function: Neurogenesis promotion shown in mice

On May 30, a research group led by Assistant Professor Shiki Okamoto and Professor Hiroaki Masuzaki of the Graduate School of Medicine at the University of the Ryukyus announced their research results demonstrating that "γ-oryzanol," a functional component specifically and abundantly found in brown rice, is effective in improving cognitive function in mice. Treatment with γ-oryzanol quenched inflammation in the hippocampus, which is involved in memory, and accelerated neurogenesis in old, cognitively impaired model mice fed on a diet containing high-level animal fat. Cognitive impairment was confirmed to improve markedly. The patent was granted this year. In collaboration with SENTAN Pharma, the research group also succeeded in developing a dietary supplement in which γ-oryzanol was encapsulated in biocompatible nanoparticles. Oral administration of this γ-oryzanol preparation to mice was confirmed to show a cognitive improvement effect comparable to the conventional preparation despite the shorter administration period and smaller dose. The findings are expected to contribute to developing products for healthy longevity.

In Japan, the population is super-aging, and age-related dementia has become a major problem. Recovery from neurological diseases at advanced stages is difficult, and it is considered important to stop aggravation while the disease is at a mild stage. In the experiment, 50-week-old laboratory mice, equivalent to humans in their late 50s, were divided into the following three groups: the normal diet group, the high-calorie high-fat diet group (fed mainly on lard), and the high-fat diet plus 1% γ-oryzanol group. After the mice of each group were fed on the assigned diet for 4 months, they underwent a Y-maze test to evaluate short-term memory performance. The results showed that the spatial working memory rate, a measure of short-term memory performance, in the lard-based, high-calorie, high-fat diet group decreased significantly more than that in the normal diet group.

On the other hand, the rate in the high-fat diet plus 1% γ-oryzanol group recovered significantly better than that in the lard-based, high-calorie, high-fat diet group. The rate of the former group recovered to a level comparable to that in the normal diet group. Comparisons of expression levels of various mRNA measured in the hippocampal area among the three groups of mice showed that inflammatory markers were significantly increased in the central nervous system in the lard-based, high-calorie, high-fat diet group. In contrast, the high-fat diet plus 1% γ-oryzanol group showed no such increase in inflammatory markers and a 1.5-fold increase in neurogenic markers.

These experiments indicate that oral intake of γ-oryzanol over a certain period may suppress inflammation in the hippocampus associated with aging and a high-fat diet and promote neurogenesis, leading to the prevention of cognitive decline. Administration of the developed supplement showed promotion of neurogenesis in the hippocampus and amelioration of cognitive impairment in a shorter period.