Improved Detection of Di-peptides by Liquid Chromatography-Tandem Mass Spectrometry with 2,4,6-Trinitrobenzene Sulfonate Conversion

Characteristics of Electrospray-Ionization Detection of Synthetic Di- to Penta-Oligopeptides by Amine Derivatizations

Chemical derivatizations have been extensively developed for highly sensitive detection of bioactive small peptides; however, their advantages from the viewpoint of longer oligopeptides remain unverified. In this study, electrospray-ionization (ESI)-mass spectrometric (MS) detection of synthetic di- to pentapeptides consisting of glycine and sarcosine were characterized by four amine derivatization methods. It was concluded that the ESI-MS detection of di- to pentapeptides was characterized by the molecular surface area of derivatized peptide moieties with an optimal value of 250 - 300 Ų, regardless of hydrophobicity and derivatization methods.

Soybean-Derived Glycine-Arginine Dipeptide Administration Promotes Neurotrophic Factor Expression in the Mouse Brain

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays an important role in cognitive abilities, including memory and learning. We demonstrated that soybean protein hydrolysate (SPH) diet suppresses age-related cognitive decline via the upregulation of BDNF in a mouse model of senescence. Our purpose was to identify novel bioactive peptides in SPH, which enhance BDNF expression. We treated mouse primary astrocytes with SPH as well as with its positively charged chromatographic fraction. Significant increases in the expression of BDNF were observed in the treatment with positively charged fraction of SPH. Among the synthesized peptides, the dipeptide glycine-arginine (GR) increased BDNF expression in vitro, and LC-TOF-MS analysis showed the presence of GR in the SPH. Furthermore, its administration in vivo increased the expression of BDNF in the cerebral cortex and the number of neurons in hippocampus and cerebral cortex. These data indicate that GR might promote neurogenesis by upregulating BDNF levels.

Effect of Aging on the Absorption of Small Peptides in Spontaneously Hypertensive Rats

In the present study, we aimed to evaluate the effect of aging on the absorption of small peptides in spontaneously hypertensive rats (SHRs). Three kinds of dipeptides, glycyl-sarcosine (Gly-Sar), Trp-His, and captopril (a dipeptidomimetic drug), a Gly-Sar-Sar tripeptide, a Gly-Sar-Sar-Sar tetrapeptide, and a Gly-Sar-Sar-Sar-Sar pentapeptide were administered at doses of 10 mg/kg each to 8- and 40-week-old SHRs. The peptides were all detected in their intact forms in the blood. There was a significantly promoted absorption of di/tripeptides in aged SHRs compared with young SHRs. In contrast, the absorption of tetra/pentapeptides was not affected by aging. PepT1 expression in the mid-jejunum was significantly increased in 40-week-old SHRs compared with 8-week-old SHRs, whereas aging did not alter the expression of claudin-1, a tight junction related protein. Thus, the present results suggest that SHR aging may enhance the absorption of di/tripeptides through the enhanced PepT1 transport route, although oligopeptides may be absorbed in an age-independent manner.

Structural Design of Oligopeptides for Intestinal Transport Model

Glycyl-sarcosine (Gly-Sar) is a well-known model substrate for the intestinal uptake of dipeptides through peptide transporter 1 (PepT1). However, there are no other model peptides larger than tripeptides to evaluate their intestinal transport ability. In this study, we designed new oligopeptides based on the Gly-Sar structure in terms of protease resistance. Gly-Sar-Sar was found to be an appropriate transport model for tripeptides because it does not degrade during the transport across the rat intestinal membrane, while Gly-Gly-Sar was degraded to Gly-Sar during the 60 min transport. Caco-2 cell transport experiments revealed that the designed oligopeptides based on Gly-Sar-Sar showed a significantly (p < 0.05) lower transport ability by factors of 1/10-, 1/25-, and 1/40-fold for Gly-Sar-Sar, Gly-Sar-Sar-Sar, and Gly-Sar-Sar-Sar-Sar, respectively, compared to Gly-Sar (apparent permeability coefficient: 38.6 ± 11.4 cm/s). Cell experiments also showed that the designed tripeptide and Gly-Sar were transported across Caco-2 cell via PepT1, whereas the tetra- and pentapeptides were transported through the paracellular tight-junction pathway.

Quantitative mass spectrometric analysis of dipeptides in protein hydrolysate by a TNBS derivatization-aided standard addition method

The aim of this study was to establish, through a standard addition method, a convenient quantification assay for dipeptides (GY, YG, SY, YS, and IY) in soybean hydrolysate using 2,4,6-trinitrobenzene sulfonate (TNBS) derivatization-aided LC-TOF-MS. Soybean hydrolysate samples (25.0 mg mL(-1)) spiked with target standards were subjected to TNBS derivatization. Under the optimal LC-MS conditions, five target dipeptides derivatized with TNBS were successfully detected. Examination of the standard addition curves, with a correlation coefficient of r(2) > 0.979, provided a reliable quantification of the target dipeptides, GY, YG, SY, YS, and IY, in soybean hydrolysate to be 424 ± 20, 184 ± 9, 2188 ± 199, 327 ± 16, and 2211 ± 133 μg g(-1) of hydrolysate, respectively. The proposed LC-MS assay is a reliable and convenient assay method, with no interference from matrix effects in hydrolysate, and with no requirement for the use of an isotope labeled internal standard.