A study of the mechanism of small-molecule soybean-protein-derived peptide supplement to promote sleep in a mouse model

Abstract

Here, the effects of dietary supplementation with small-molecule soybean-protein-derived peptide (SBP) on sleep duration in mice are described. The amounts of the neurotransmitters tryptophan (Trp, W), 5-hydroxytryptamine (5-HTP), serotonin (5-HT) and melatonin (MT) were determined by using an ELISA kit. Compared with the control group, the group of mice given 0.65 g kg^-1 SBP showed 59.21% prolonged sleep at the third day of administration and significantly increased MT levels, by 95.31%. Western blotting analysis of 0.65 g kg^-1 SBP revealed the presence of tryptophan hydroxylase (THP) and serotonin-N-acetyltransferase (AANAT) proteins, which increased the release of MT and upregulated the MT1 and MT2 receptor activities to alleviate sleep deprivation. Interestingly, the introduction of 2.60 g kg^-1 SBP doubled the 5-HT content in the brain and promoted an awake state. As a result, the produced 5-HT could not be converted into MT in large amounts, so the sleep duration was shorter than that of the control group. These findings suggested the potential of using SBP in appropriate amounts as functional ingredients in various food products to improve sleep in elderly people afflicted with sleep disorders.

Fig. 1. The synthetic route to MT.

Fig. 2. The preparation of peptides from SPI.

Fig. 3. Molecular weight distribution of SBP.

Fig. 4. Sleep latency in mice with different SPI/SBP administration patterns. Data are presented as the mean ± SD. P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***” vs. control group, n = 3 data points.

Fig. 5. Sleep duration in mice with different SPI/SBP administration patterns. Data are presented as the mean ± SD. P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***” vs. control group, n = 3 data points.

Fig. 6. Concentrations of Trp (A), 5-HTP (B), 5-HT (C), and MT (D) in the brains of tested mice. Data are presented as the mean ± SD. P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***” vs. control group, n = 3 data points.

Fig. 7. The effects of SBP on the expression of TPH. Data on the right are expressed as mean ± SD (n = 3). Data are presented as the mean ± SD. P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***” vs. control group, n = 3 data points.

Fig. 8. The effects of SBP on the expression of AANAT. Data on the left are expressed as mean ± SD (n = 3). Data are presented as the mean ± SD. P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***” vs. control group, n = 3 data points.

Fig. 9. The effects of SBP on the expression of MT1 and MT2. Data are expressed as mean ± SD (n = 3). Data are presented as the mean ± SD. P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***” vs. control group, n = 3 data points.