919 Syrup Alleviates Postpartum Depression by Modulating the Structure and Metabolism of Gut Microbes and Affecting the Function of the Hippocampal GABA/Glutamate System

Abstract

Postpartum depression (PPD) is a mental disorder that affects pregnant women around the world, with serious consequences for mothers, families, and children. Its pathogenesis remains unclear, and medications for treating PPD that can be used during lactation remain to be identified. 919 syrup (919 TJ) is a Chinese herbal medicine that has been shown to be beneficial in the treatment of postpartum depression in both clinical and experimental studies. The mechanism of action of 919 TJ is unclear. 919 syrup is ingested orally, making the potential interaction between the drug and the gut microbiome impossible to ignore. We therefore hypothesized that 919 syrup could improve the symptoms of postpartum depression by affecting the structure and function of the intestinal flora, thereby altering hippocampal metabolism. We compared changes in hippocampal metabolism, fecal metabolism, and intestinal microflora of control BALB/c mice, mice with induced untreated PPD, and mice with induced PPD treated with 919 TJ, and found that 4-aminobutyric acid (GABA) in the hippocampus corresponded with PPD behaviors. Based on changes in GABA levels, multiple key gut bacterial species (Mucispirillum schaedleri, Bifidobacterium pseudolongum, Desulfovibrio piger, Alloprevotella tannerae, Bacteroides sp.2.1.33B and Prevotella sp. CAG:755) were associated with PPD. Metabolic markers that may represent the function of the intestinal microbiota in mice with PPD were identified (Met-Arg, urocanic acid, thioetheramide-PC, L-pipecolic acid, and linoleoyl ethanolamide). The relationship between these factors is not a simple one-to-one correspondence, but more likely a network of staggered functions. We therefore believe that the composition and function of the entire intestinal flora should be emphasized in research studying the gut and PPD, rather than changes in the abundance of individual bacterial species. The introduction of this concept of "GutBalance" may help clarify the relationship between gut bacteria and systemic disease.

Keywords: Chinese herbal medicine; GABA; gut microbiome; metabonomics; postpartum depression.

Figure 1

Effects of 919 TJ on the depression-related behaviors of PPD mice. The PPD model was successfully established after 3 weeks of 3-h maternal separation and restraint stress. A concurrent gavage of an equal volume of 919 TJ vs. saline was performed once a day. (A) The tail suspension test (TST) and (B) the forced swimming test (FST) were performed on the 23^rd postpartum day. Discovery set: CON, n = 9; PPD, n = 10; 919 TJ, n = 9.

Figure 2

Alteration of metabolites in the hippocampus and feces. Twelve altered metabolites were selected for their differences between both the PPD group vs. controls (A) and 919 TJ vs. PPD (B). Eight altered metabolites were selected for their variant expression in comparisons of the PPD group vs. controls (C) and 919 TJ vs. PPD (D). Five metabolites (Met-Arg, urocanic acid, thioetheramide-PC, L-pipecolic acid and linoleoyl ethanolamide) demonstrated opposite trends in the two comparisons. Discriminative variants were identified on the basis of a VIP value > 1 and p values < 0.1. (*P < 0.05; **P < 0.01; ***P < 0.001). Discovery set: CON, n = 9; PPD, n = 10; 919 TJ, n = 9.

Figure 3

Gut bacteria differences between groups at the species level. At the species level, PPD subjects (versus the control group) enriched 5 species and decreased 2 (A). At the species level, the 919 TJ group (versus the PPD group) decreased 3 bacterial species and enriched 11 (B). Relative abundances of 35 bacterial species responsible for discriminating between the control, PPD, and 919 TJ groups (C). Discovery set: CON, n = 9; PPD, n = 10; 919 TJ, n = 9.

Figure 4

Correlation analysis between fecal bacteria species and hippocampal GABA (A) or fecal metabolites (B, C). 4-aminobutyric acid (GABA), a key differential metabolite in the hippocampus, was anchored and a correlation analysis of the differential bacteria species was performed. The green dots represent significantly different bacterial species present in the control group vs. the PPD group. The blue dots represent significantly different bacterial species between the PPD group and the 919 TJ group. The magnitude of the correlation coefficient is shown by the thickness of the line. A positive correlation is in orange and a negative correlation is in blue. The heatmap reflects the degree of correlation between fecal differential metabolites (abscissa) and fecal differential bacterial species (ordinate) between CON versus PPD (B) and PPD vs. 919 TJ (C). Red is a positive correlation, blue is a negative correlation, and the depth of the color indicates the degree of relevance. Correlation coefficients (r values) are numerically indicated.

Figure 5

Correlation analysis between fecal metabolites and bacteria species based on GABA-associated bacteria species The heatmap reflects the degree of correlation between key bacterial species associated with GABA (abscissa) and fecal differential metabolites (ordinate) between CON versus PPD (A) and PPD vs. 919 TJ (B). Red is a positive correlation, blue is a negative correlation, and the depth of the color indicates the degree of relevance. Correlation coefficients (r-values) are numerically indicated.