Gamma-aminobutyric acid (Gaba) is a non-proteinogenic amino acid that is widely present in microorganisms, plants, and vertebrates. So far, Gaba is well known as a main inhibitory neurotransmitter in the central nervous system. Its physiological roles are related to the modulation of synaptic transmission, the promotion of neuronal development and relaxation, and the prevention of sleeplessness and depression. Besides, various pharmaceutical properties of Gaba on non-neuronal peripheral tissues and organs were also reported due to anti-hypertension, anti-diabetes, anti-cancer, antioxidant, anti-inflammation, anti-microbial, anti-allergy, hepato-protection, reno-protection, and intestinal protection. Therefore, Gaba may be considered as potential alternative therapeutics for prevention and treatment of various diseases. Accordingly, this updated review was mainly focused to describe the pharmaceutical properties of Gaba as well as emphasize its important role regarding human health.

An Updated Review on Pharmaceutical Properties of Gamma-Aminobutyric Acid.

Brown rice, unmilled or partly milled, contains more nutritional components than ordinary white rice. Despite its elevated content of bioactive components, brown rice is rarely consumed as a staple food for its dark appearance and hard texture. The germination of brown rice can be used to improve its taste and further enhance its nutritional value and health functions. Germinated brown rice is considered healthier than white rice, as it is not only richer in the basic nutritional components such as vitamins, minerals, dietary fibers, and essential amino acids, but also contains more bioactive components, such as ferulic acid, γ-oryzanol, and gamma aminobutyric acid. Moreover, germinated brown rice has been reported to exhibit many physiological effects, including antihyperlipidemia, antihypertension, and the reduction in the risk of some chronic diseases, such as cancer, diabetes, cardiovascular disease, and Alzheimer's disease. Therefore, it is likely that germinated brown rice will become a popular health food.

Germinated brown rice and its role in human health.

Diet is an important variable in the course of type 2 diabetes, which has generated interest in dietary options like germinated brown rice (GBR) for effective management of the disease among rice-consuming populations. In vitro data and animal experiments show that GBR has potentials as a functional diet for managing this disease, and short-term clinical studies indicate encouraging results. Mechanisms for antidiabetic effects of GBR due to bioactive compounds like γ-aminobutyric acid (GABA), γ-oryzanol, dietary fibre, phenolics, vitamins, acylated steryl β-glucoside, and minerals include antihyperglycemia, low insulin index, antioxidative effect, antithrombosis, antihypertensive effect, hypocholesterolemia, and neuroprotective effects. The evidence so far suggests that there may be enormous benefits for diabetics in rice-consuming populations if white rice is replaced with GBR. However, long-term clinical studies are still needed to verify these findings on antidiabetic effects of GBR. Thus, we present a review on the antidiabetic properties of GBR from relevant preclinical and clinical studies, in order to provide detailed information on this subject for researchers to review the potential of GBR in combating this disease.

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Antidiabetic Properties of Germinated Brown Rice: A Systematic Review

Whole grain foods have been promoted to be included as one of the important components of a healthy diet because of the relationship between the regular consumption of whole-grain foods and reduced risk of chronic diseases. Rice is a staple food, which has been widely consumed for centuries by many Asian countries. Studies have suggested that brown rice is associated with a wide spectrum of nutrigenomic implications such as anti-diabetic, anti-cholesterol, cardioprotective and antioxidant. This is because of the presence of various phytochemicals that are mainly located in bran layers of brown rice. Therefore, this paper is a review of publications that focuses on the bioactive compounds and nutrigenomic implications of brown rice. Although current evidence supports the fact that the consumption of brown rice is beneficial for health, these studies are heterogeneous in terms of their brown rice samples used and population groups, which cause the evaluation to be difficult. Future clinical studies should focus on the screening of individual bioactive compounds in brown rice with reference to their nutrigenomic implications.

Phytochemical Profile of Brown Rice and Its Nutrigenomic Implications

To uncover the molecular mechanisms underlying GABA accumulation in giant embryo rice seeds, we analyzed the expression levels of GABA metabolism genes and contents of GABA and GABA metabolic intermediates in developing grains and germinated brown rice of giant embryo rice ‘Shangshida No. 5’ and normal embryo rice ‘Chao2-10’ respectively. In developing grains, the higher GABA contents in ‘Shangshida No. 5’ were accompanied with upregulation of gene transcripts and intermediate contents in the polyamine pathway and downregulation of GABA catabolic gene transcripts, as compared with those in ‘Chao2-10’. In germinated brown rice, the higher GABA contents in ‘Shangshida No. 5’ were parallel with upregulation of OsGAD and polyamine pathway gene transcripts and Glu and polyamine pathway intermediate contents and downregulation of GABA catabolic gene transcripts. These results are the first to indicate that polyamine pathway and GABA catabolic genes play a crucial role in GABA accumulation in giant embryo rice s...

Molecular Mechanisms Underlying γ-Aminobutyric Acid (GABA) Accumulation in Giant Embryo Rice Seeds.

We examined the effects of pre-germinated brown rice on hypertension and biochemical analysis of blood in spontaneously hypertensive rats (SHRs) fed a diet including 40% pre-germinated brown rice. A significant antihypertensive effect (p <0.01) was found from day 10 of food intake, compared to controls. At completion of the test period (8 weeks), SBP in the control and test groups were 207.4 ± 5.3 and 151.6 ± 4.5 mmHg, respectively, showing a significant (p <0.001) and strong antihypertensive effect of pre-germinated brown rice. The cholesterol levels in the control and test groups were 45.3 ± 5.4 and 37.5 ± 3.9 mg/dL, respectively, which also showed a significant difference (p < 0.01). Taken together, pre-germinated brown rice has an antihypertensive effect and decreases serum cholesterol in SHRs. These effects may be due to complex actions of various components abundantly found in the rice, including γ-aminobutyric acid, dietary fiber, phytic acid and ferulic acid.

Mika Ihara

Papers

Antihypertensive Effect of Pre-germinated Brown Rice in Spontaneously Hypertensive Rats

Effects of pre-germinated brown rice diet on skin condition in female university students