Dipeptidyl Peptidase-IV Inhibitory Activity of Katsuobushi-Derived Peptides in Caco-2 Cell Assay and Oral Glucose Tolerance Test in ICR Mice.

Proteolytic products of bonito stock residue inhibit dipeptidyl peptidase-IV (DPP-IV). Here, we isolated, purified, and identified the components of its N5 fraction obtained after using neutral protease from Aspergillus oryzae. A 10% ethanol eluent (N5-2 fraction) from column chromatography was sequenced, yielding 18 peptides. Of these, Glu-Val-Phe, Ala-Val-Phe, and Gly-Val-Phe were identified as novel (IC50 values for DPP-IV inhibition were 525.56, 5466.49, and 2870.87 µM, respectively), whereas Trp-Val is the primary peptide (IC50 value of 36.99 µM, 1359 unit (mL/100 g N5-2 fraction) = (yield (mg)/100 g N5-2 fraction)/IC50 (µg/mL). Furthermore, the N5-2 fraction significantly decreased DPP-IV activity in Caco-2 intestinal epithelial cells (p < 0.05). From the oral glucose tolerance test using ICR mice, the N5-2 fraction significantly attenuated the rise in serum glucose levels compared with the control (p < 0.05) through cell-surface DPP-IV inhibition. We discuss the novelty, significance, and relevance of the findings in this study, as well as its broad applications for prevention of diabetes.

[Antihypertensive effect and safety evaluation of vegetable drink with peptides derived from sardine protein hydrolysates on mild hypertensive, high-normal and normal blood pressure subjects].

A randomized double-blind placebo-controlled study was conducted on 63 subjects to determine the antihypertensive effect of a vegetable drink in which sardine protein hydrolysates containing a dipeptide, Valyl-Tyrosine (VY), were incorporated. The subjects, consisting of people with mild hypertension, high-normal blood pressure and normal blood pressure, were randomly divided into test (male/female = 25/6, average age 50.1 +/- 10.4 years old) and control groups (26/6, 49.0 +/- 5.0). Each subject in the test group was given 195 g of the vegetable drink containing 0.5 g of sardine peptides (sardine protein hydrolysates) with 0.4 mg of VY (test drink) once a day for 13 weeks in a row, and subjects in the control group were given the same amount of the vegetable drink without sardine peptides (control drink) in the same manner. In the test group, 40 subjects with mild hypertension or high-normal blood pressure (130 mmHg < or = systolic blood pressure (SBP) < 160 mmHg and/or 80 mmHg < or = diastolic blood pressure (DBP) < 100 mmHg) showed a significant decrease in SBP, from 142.0 +/- 10.3 mmHg at the start of the test to 134.4 +/- 11.1 mmHg during the first week of the test period, after which similar values were seen throughout the test period (13 weeks). Compared to the control group, the difference in SBP from baseline was statistically significant in the test group throughout the intake period. DBP also decreased significantly from 88.0 +/- 7.9 mmHg at baseline to 83.5 +/- 8.6 mmHg after 13 weeks. In the control group, SBP and DBP were 140.8 +/- 8.4 mmHg and 90.5 +/- 6.6 mmHg respectively at the start of the test, and neither decreased during the test period. In subjects with normal blood pressure, neither those in the test group nor those in the control group showed a significant change in SBP and DBP during the test period. An excessive ingestion test was performed on 25 subjects with hypertension, mild hypertension, high-normal blood pressure, and normal blood pressure by giving 585 g (3 times the recommended amount of intake) of the test drink for 14 days in a row. As a result, a significant decrease of blood pressure was observed in the hypertension, mild hypertension and high-normal blood pressure groups, but no excessive decline in blood pressure or any side-effects were associated with any subjects during the test period. In the groups with normal blood pressure, the excessive ingestion of the test drink did not affect blood pressure. In these two studies, physical check-ups and biochemical analyses of blood and urine were also conducted in all subjects, and no abnormalities were observed. These results suggest that the test drink containing sardine protein hydrolysates exhibited the antihypertensive effect in only the subjects with mild hypertension or high-normal blood pressure. No adverse effects were observed in either hypertensive or normotensive subjects.

Absorption of Val-Tyr with in vitro angiotensin I-converting enzyme inhibitory activity into the circulating blood system of mild hypertensive subjects.

The change in plasma level of dipeptide, Val-Tyr (VY), with in vitro angiotensin I-converting enzyme inhibitory activity was investigated after a single oral administration of a VY-drink at doses of 0, 6 or 12 mg given to mild hypertensive subjects. During this protocol for up to 24 h after the intake, patient/subject blood pressure (BP) was measured for a 15 min period at designated times (0, 1, 2, 4, 8, 24 h) with the individual supine. Based on the VY determination, the maximal increment of plasma VY level was observed over the second hour postprandially (12 mg-dose; 2041+/-148 fmol/ml-plasma). In addition, the plasma VY level increased with the VY dosage. However, no marked BP change was observed with the increase of plasma VY level, suggesting that VY did not exert an acute hypotensive effect. The area under the curve at 12 mg-dose was estimated to be 8644+/-420 fmol x h/ml-plasma, comparable to that in normotensive subjects. This finding suggests that absorption of VY would not be influenced by a complaint of hypertension.

Val-Tyr as a natural antihypertensive dipeptide can be absorbed into the human circulatory blood system.

1. Intact absorption of the bioactive dipeptide Val-Tyr (VY), with in vivo antihypertensive ability in normotensive human subjects, was investigated. 2. As a result of a single oral administration of VY, the VY absorption curve occurred maximally over the second hour postprandially; a greater than 10-fold higher increment of VY following a dose of 12 mg was observed in the plasma at 2 h compared with the baseline concentration of VY at 0 h (1934 +/- 145 vs 159 +/- 11 fmol/mL plasma, respectively). 3. Plasma VY levels increased with dose administered (3, 6 and 12 mg), suggesting that exogenous VY could be absorbed intact into the human blood depending on the dose. The elimination half time (t1/2) of VY was estimated to be 3.1 h. The area under the curve for the 12 mg VY dose was 9185 +/- 688 fmol small middle doth/mL plasma.