Yoshitaka Nii

Determination of Antihypertensive Peptides from an Izumi Shrimp Hydrolysate

The izumi shrimp (Plesionika izumiae Omori, 1971) is an unused resource which can be caught off the southern coast of Tokushima Prefecture. We have previously found that an izumi shrimp hydrolysate significantly inhibited the age-associated spontaneous increase in blood pressure in stroke-prone spontaneously hypertensive rats. In this present study, two angiotensin I-converting enzyme inhibitory peptides were isolated from an izumi shrimp hydrolysate by using high-performance liquid chromatography, and their amino acid sequences were determined to be Val-Trp-Tyr-His-Thr and Val-Trp. A single oral administration of synthetic Val-Trp-Tyr-His-Thr or Val-Trp significantly decreased the blood pressure in stroke-prone spontaneously hypertensive rats. The antigenicity and allergenicity of the izumi shrimp hydrolysate against BALB/c mice were very low. These results demonstrate that the angiotensin I-converting enzyme inhibitory peptides isolated from the izumi shrimp hydrolysate had an anti-hypertensive effect on rats.

Vitamin A Deficiency Impairs Induction of Oral Tolerance in Mice

Oral tolerance is a phenomenon of induction of systemic unresponsiveness to antigens ingested by the oral route and loss of immune response. Studies have shown the importance of vitamin A in oral tolerance in vitro but not in an in vivo experimental model. Therefore, we carried out experiments to determine how vitamin A deficiency affects tolerance induction and the ability of mesenteric lymph node (MLN) CD11c(+) cells to induce regulatory T cells (Tregs). Immunological tolerance was induced by oral ovalbumin (OVA) administration in vitamin A-sufficient mice. OVA-specific antibody and cytokine production were significantly reduced. On the other hand, in vitamin A-deficient mice, both OVA-specific antibody and cytokine production were not suppressed by oral OVA administration. Regarding induction of Tregs, the conversion rate of Foxp3(+) cells from naïve CD4(+) cell by CD11c(+) cells was decreased in vitamin A-deficient mice. Our study indicates that vitamin A deficiency causes the breakdown of oral tolerance in vivo.

Extracts of citrus Sudachi peel attenuate body weight gain in C57BL/6 mice fed a high-fat diet

Citrus Sudachi is the special local product of Tokushima Prefecture, and over 98% of Sudachi consumed in Japan every year is produced in Tokushima Prefecture. In this study, we evaluated the function of sudachi peel extract (SPE) using an animal model of obesity. C57BL/6 mice were fed a high-fat diet containing 1% SPE powder. Treatment with SPE significantly decreased body weight compared to that of mice fed a high-fat diet. A significant difference in body weight was observed between the control and SPE groups from 7 weeks after the start of the experiment, the significant difference continued until the end of the 14-week experiment. Reduction of blood glucose levels following insulin administration in SPE-treated mice was grater than that in control mice. Determination of mRNA expression in adipose tissue showed that the expression level of TNF-α in the SPE group was significantly decreased compared to that on the control group. These results suggest that SPE potentially has the ability to attenuate body weight gain. J. Med. Invest. 64: 20-23, February, 2017.