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Opah muscle is one of the abundant biological sources of balenine (Bal), which together with carnosine (Car) and anserine (Ans), is among the most widely studied of vertebrate imidazole dipeptides. The characteristics of imidazole dipeptides have been extensively investigated. We examined changes in the concentration of Bal and its constituent amino acids in human plasma following the ingestion of opah muscle extract and opah flesh. Bal plasma concentrations increased after ingestion, with maximum plasma concentrations (Cmax) of 89.87, 152.13, and 81.82 nmol/mL observed after ingestion of 5 and 10 g of opah muscle extract and 80 g of opah flesh, respectively. The constituent amino acids of Bal, 3-methyl-histidine (3-Me-His) and β-alanine (β-Ala), increased in plasma after ingestion. The Cmax of Bal was the highest of any food-derived peptide in human plasma reported to date. The findings showed that ingestion of opah muscle and muscle extract may be beneficial for human health.

Agaro-oligosaccharides (AOSs) are known to have biological activities, such as anti-inflammatory, anti-tumor, and anti-obesity effects. Although existing evidence suggests the presence of AOSs in peripheral tissues after oral administration, whether AOSs permeate into the blood circulation remains unknown. Thus, we hypothesized that AOSs with low-molecular weight can permeate the human gastrointestinal tract. To test this hypothesis, the time course of absorption was examined by analyzing plasma samples before and 1, 2, and 4 h after ingestion. Analysis was performed using liquid chromatography/mass spectrometry after labeling with p-aminobenzoic ethyl ester. Our results showed that the plasma concentration of agarobiose (Abi) was higher than that of agarotetraose (Ate); however, agarohexaose was not detected. Additionally, plasma levels of Abi and Ate were proportional to the dose. These results suggest that permeation efficiency is dependent on the molecular weight and that the systemic absorption of Abi via the gastrointestinal tract is better than that of Ate. These findings will contribute to a better understanding of the bioactivity of orally administered AOSs in peripheral tissues.

Abstract There are increasing reports demonstrating high bioavailability of 4-hydroxyproline (4Hyp)-containing oligopeptides after oral ingestion of collagen hydrolysate and their bioactivity. In contrast, no study investigates the fate of another collagen-specific but minor amino acid, 3Hyp. Here, we identified Gly-3Hyp-4Hyp tripeptide in human blood at high concentrations, comparable to other 4Hyp-containing oligopeptides, after ingesting porcine skin collagen hydrolysate. Additionally, Gly-3Hyp-4Hyp uniquely maintained the maximum concentration until 4 h after the ingestion due to its exceptionally high resistance to peptidase/protease demonstrated by incubation with mouse plasma. In mice, oral administration of collagen hydrolysate prepared from bovine tendon, which contains a higher amount of 3Hyp, further increased blood Gly-3Hyp-4Hyp levels compared to that from bovine skin. Furthermore, Gly-3Hyp-4Hyp showed chemotactic activity on skin fibroblasts and promoted osteoblast differentiation. These results highlight the specific nature of the Gly-3Hyp-4Hyp tripeptide and its potential for health promotion and disease treatment.

Agaro-oligosaccharides (AOSs), even-numbered oligosaccharides prepared from agar, are applied to various food, including supplements, drinks, and jellies because of their biological activities. This study aimed to evaluate the AOS permeation in the gastrointestinal tract in vivo and in vitro. Agarobiose (Abi), agarotetraose (Ate), and agarohexaose (Ahe) were detected in rat plasma after oral administration of AOSs. The detection level of agarobiose in the plasma was higher than that of agarohexaose, which was consistent with the permeation study using Caco-2 cell monolayers. Further, the adenosine triphosphate inhibitor (sodium azide) or endocytosis inhibitor (colchicine) did not inhibit AOS permeation through Caco-2 cell monolayers. Conversely, AOS permeation enhanced upon treatment with cytochalasin B, a tight junction disrupter, suggesting that AOSs might have passed mainly through the tight junctions between the intestinal epithelial cells. These results indicate that AOSs, especially agarobiose, can be absorbed as an intact form via the gastrointestinal tract across the intestinal epithelium through the paracellular pathway.

We examined the absorption of balenine (Bal) in mouse blood after the administration of a high-purity Bal prepared from opah muscle. Using HPLC with phenyl isothiocyanate pre-column derivatization, we successfully isolated imidazole peptides and their constituents. We detected Bal and 3-methylhistidine (3-Me-His) in mouse blood 1 h after the administration of opah-derived Bal. The concentrations of Bal and 3-Me-His significantly increased to 128.27 and 69.09 nmol/mL in plasma, respectively, but were undetectable in control and carnosine (Car)-administrated mice. In contrast, β-alanine and histidine did not increase in mouse plasma 1 h after the administration of Car and opah-derived Bal. The present study is the first report on the absorption of food-derived Bal in mouse blood and serves as a pilot study for future clinical trials.