Tomomi Kouguchi

The Bioavailable Octapeptide Gly-Ala-Hyp-Gly-Leu-Hyp-Gly-Pro Stimulates Nitric Oxide Synthesis in Vascular Endothelial Cells

Gly-Ala-Hyp-Gly-Leu-Hyp-Gly-Pro (GAXGLXGP, X: Hyp), an octapeptide contained in chicken collagen hydrolysate, inhibits angiotensin I-converting enzyme activity in vitro. Intestinal Caco-2 and bovine aortic endothelial cells (BAECs) were used to investigate whether the transported GAXGLXGP improves vascular function. When GAXGLXGP was added to the apical side of Caco-2 monolayers, the intact form of GAXGLXGP was released to the basolateral side without incorporation into the cells. This transport was energy-independent but was associated with tight junction permeability. GAXGLXGP was then added to BAECs, and endothelial nitric oxide (NO) synthase (eNOS) activation was examined. GAXGLXGP at a concentration of 10 microM stimulated production of NO during a 1 h incubation. This event involved phosphorylation of eNOS at Ser(1179) without a change in the total eNOS protein level. These findings indicate that GAXGLXGP absorbed intact through the intestinal epithelium has direct effects on eNOS activity in vascular endothelial cells, leading to NO synthesis, thereby suggesting the potential for improvement in vascular function.

Chicken Collagen Hydrolysate Protects Rats from Hypertension and Cardiovascular Damage

We previously reported that chicken collagen hydrolysate (CCH) has strong angiotensin I converting enzyme (ACE) inhibitory activity and antihypertensive effects on spontaneously hypertensive rats. Here, we investigated the chronic therapy effects of CCH on blood pressure and vascular relaxation in a cardiovascular damage model of Wistar-Kyoto rats induced by N-nitro-l-arginine methyl ester (L-NAME). Following co-treatment with CCH for 4 weeks, the increment of systolic blood pressure was suppressed significantly. At 8 weeks, the vasorelaxation of thoracic aorta increased significantly, and cardiovascular damage was ameliorated. The concentration of soluble intercellular adhesion molecule-1 (ICAM-1) in blood was reduced significantly by long-term administration of CCH, whereas the nitric oxide concentration was increased significantly at 1 hour post-treatment. The results suggest that beneficial effects of CCH result from antihypertensive function, but also from inhibition of cardiovascular damage to the endothelial cells via its ACE inhibitory activity and regulation of nitric oxide and ICAM-1, which suggests that CCH may be useful as a medicinal food for patients with cardiovascular disease.

Molecular Size of Collagen Peptide Reverses the Permeability of Caco-2 Cells

Intestinal permeability to size-classified fish collagen peptides (FCPs) was examined using Caco-2 monolayers. Minimum-sized FCPs were most efficiently transported across the Caco-2 monolayers. Permeability depended on peptide size. It was independent of the H+-coupled peptide transport system but was associated with tight junction permeability, suggesting that the paracellular pathway is responsible for transepithelial transport of collagen peptides.

Effects of a Chicken Collagen Hydrolysate on the Circulation System in Subjects with Mild Hypertension or High-Normal Blood Pressure

We investigated the effects of a chicken collagen hydrolysate (CCH) on the circulation system in humans. A total of 58 subjects with either mild hypertension (systolic blood pressure (SBP) of 140-159 mmHg or diastolic blood pressure (DBP) 90-99 mmHg) or high-normal blood pressure (SBP 130-139 mmHg or DBP 85-89 mmHg) were assigned to two groups, one involving a placebo and the other, the test food (including CCH of 2.9 g/d). The parameters related to each subjects circulation system were monitored over the study period of 18 weeks. The Δbrachial-ankle pulse wave velocity (baPWV), an indicator of arterial stiffness and marker of vascular damage, was significantly lower in the test food group than in the placebo group during the treatment period. The blood pressure in the test food group was also significantly lower than that in the placebo group, while the serum nitrogen oxide was higher in the test food group after the treatment. These results suggest that CCH exerted modulatory effects on the human circulation system.

Vasoprotective Effect of Foods as Treatments: Chicken Collagen Hydrolysate

Collagen is a major protein in living organisms and accounts for about one-third of all protein in mammalian bodies, including the human body. Recently, collagen peptides have been used as foods that take advantage of their tertiary functions. We have been focusing on the vasoprotective effect of collagen peptides. Chicken collagen hydrolysate (CCH) is obtained by treating chicken feet with enzymes to produce an angiotensin-converting enzyme (ACE) inhibitory peptide. Administration of this CCH for 12 weeks reduces blood pressure in humans. We therefore investigated the mechanism of the vasoprotective effect of CCH. We tested whether prolonged CCH treatment of rats or mice would restore endothelial cell function and improve proinflammatory cytokine levels. We found that CCH treatment improved the vasorelaxation of rat aorta damaged with L-NG-nitroarginine methyl ester , an NO synthesis inhibitor. CCH treatment also reduced the serum levels of IL-6, sICAM-1, and TNF-α in an atherosclerotic mouse model, C57BL/6.KOR-ApoEsh1. These findings indicate the usefulness of collagen peptides as foods promoting antiatherogenesis via a vasoprotective effect. Years have passed since functional foods and their tertiary function first attracted attention. The primary function of foods is to supply the nutrients required to sustain life, and the secondary function is to satisfy taste preferences. The tertiary function of foods is to exert biological regulatory effects, such as biophylaxis, homeostatic maintenance, and disease prevention, which are activated upon food intake. Purified food ingredients that have tertiary functions are widely consumed as supplements. Multitudes of supplements are available on today’s market: besides common vitamins, minerals, and amino acids, there are catechins, which are antioxidant constituents of tea (Katiyar, 2003), soy isoflavones, which have female hormone–like actions (Weijer, 2002), and docosahexaenoic acids and eicosapentaenoic acids, which decrease triglyceride levels (Tamai, 2004). Collagen is being used widely, not only in supplements but also as an ingredient of common food products such as beverages, yogurts, and breads. Collagen is a major protein in living organisms and accounts for about one-third of all protein in mammalian bodies, including the human body. It forms an extracellular matrix that plays a role in the formation of connective tissues and acts as a scaffold for cells, but its accumulation declines with age. The majority of the collagen in the body exhibits a triple