The impact of serotonergic system dysfunction on the regulation of P4501A isoforms during liver insufficiency and consequences for thyroid hormone homeostasis

Tryptophan in the mouse diet is essential for embryo implantation and decidualization

Introduction

Nutritional deficiency occurs frequently during pregnancy and breastfeeding. Tryptophan (Trp), an essential amino acid which is critical for protein synthesis, serves as the precursor for serotonin, melatonin, and kynurenine (Kyn). The imbalance between serotonin and kynurenine pathways in Trp metabolism is closely related to inflammation and depression. This study assessed the effects of Trp deficiency on mouse early pregnancy.

Methods

Embryo implantation and decidualization were analyzed after female mice had been fed diets containing 0.2% Trp (for the control group), 0.062% Trp (for the low Trp group) and 0% Trp (for the Trp-free group) for two months. The uteri of the mice were collected on days 4, 5, and 8 of pregnancy for further analysis.

Results

On day 8 of pregnancy, the number of implantation sites were found to be similar between the control and the low Trp groups. However, no implantation sites were detected in the Trp-free group. On day 5 of pregnancy, plane polarity- and decidualization-related molecules showed abnormal expression pattern in the Trp-free group. On day 4 of pregnancy, there was no significant difference in uterine receptivity molecules between the low-Trp group and the control group, but uterine receptivity was abnormal in the Trp-free group. At implantation sites of the Trp-free group, IDO and AHR levels were markedly elevated. This potentially increased levels of Kyn, 2-hydroxy estradiol, and 4-hydroxy estradiol to affect decidualization.

Conclusions

Trp-free diet may impair decidualization via the IDO-KYN-AHR pathway.

Boosting Neurogenesis in the Adult Hippocampus Using Antidepressants and Mesenchymal Stem Cells

The hippocampus is one of the few privileged regions (neural stem cell niche) of the brain, where neural stem cells differentiate into new neurons throughout adulthood. However, dysregulation of hippocampal neurogenesis with aging, injury, depression and neurodegenerative disease leads to debilitating cognitive impacts. These debilitating symptoms deteriorate the quality of life in the afflicted individuals. Impaired hippocampal neurogenesis is especially difficult to rescue with increasing age and neurodegeneration. However, the potential to boost endogenous Wnt signaling by influencing pathway modulators such as receptors, agonists, and antagonists through drug and cell therapy-based interventions offers hope. Restoration and augmentation of hampered Wnt signaling to facilitate increased hippocampal neurogenesis would serve as an endogenous repair mechanism and contribute to hippocampal structural and functional plasticity. This review focuses on the possible interaction between neurogenesis and Wnt signaling under the control of antidepressants and mesenchymal stem cells (MSCs) to overcome debilitating symptoms caused by age, diseases, or environmental factors such as stress. It will also address some current limitations hindering the direct extrapolation of research from animal models to human application, and the technical challenges associated with the MSCs and their cellular products as potential therapeutic solutions.

Albumin is a secret factor involved in multidirectional interactions among the serotoninergic, immune and endocrine systems that supervises the mechanism of CYP1A and CYP3A regulation in the liver

This review focuses on albumin, which is involved in multidirectional interactions among the immune, endocrine and serotoninergic systems and supervises the regulation of cytochrome P450 (CYP) isoforms under conditions of both normal liver function and liver insufficiency. Special attention is paid to albumin, thyroid hormones, testosterone and tryptophan hydroxylase in these interactions as well as their potential roles in liver regeneration. The association of these factors with inflammation and the modification of the mechanism of hepatic drug-metabolizing CYP isoform regulation are also presented because changes in the expression of CYP isoforms in the liver may result in subsequent changes to a marker substance used for testing CYP activity, thus providing a simple way to control the liver regeneration process or the dangerous stimulation of hepatocarcinogenesis.

In Vivo Toxicity of Solasonine and Its Effects on cyp450 Family Gene Expression in the Livers of Male Mice from Four Strains

Solasonine was reported to inhibit tumour cell growth in several different models. The in vivo toxicity of solasonine, the effects of genetic background on its toxicity, and its possible roles in regulating the expression of cyp450 family genes were still unclear and required characterisation. Here, Horn’s assays were performed on male mice from four different strains, and the expression of cyp450 family genes in their livers was examined by RT-PCR and ELISA. Mice treated by intraperitoneal injection with high levels of solasonine showed immediate post-excitatory depression, intraperitoneal tissue adhesion, and dissolving of cells in the liver. Furthermore, these four mouse strains showed different toxicological sensitivity to solasonine. The strains, in decreasing order of LD50 value, rescuing speed of body weight, and more severe pathological symptoms, were KM, ICR, C57BL/6, and BALB/c. Interestingly, more cyp450 genes were downregulated at the mRNA and/or protein level in the livers of male mice from C57BL/6 or BALB/c strains than those from KM or ICR strains. These results suggest that (1) Solasonine has hepatic toxicity and downregulates cyp450 genes expression at transcriptional and/or post-transcriptional levels; (2) Genetic background is an important factor which can affect the in vivo toxicity; (3) Downregulation of cyp450 gene expression in the liver may be a clue to help understand whether or not a given strain is sensitive to solasonine; (4) Influences on the expression of cyp450 genes should be considered when using solasonine alone, or in combination with other drugs.

Dose-response relationship of tryptophan with large neutral amino acids, and its impact on physiological responses in the chick model

Tryptophan (Trp) has been associated with the regulation of several behavioral and physiological processes, through stimulation of serotonergic activity. Tryptophan utilization at the metabolic level is influenced by the competitive carrier system it shares with large neutral amino acids (LNAA). This study was carried out using meat-type chicken as a model, to investigate the dose response effects of Trp/LNAA on fear response (tonic immobility; TI) and hormonal responses, including corticosterone (CORT), serotonin (5-HT), triiodothyronine (T₃) and thyroxine (T₄). A total of 12 cages (48 birds) were assigned to each of the six experimental groups at 29-42 days of age. Experimental diets were formulated to have incremental levels of Trp/LNAA (0.025, 0.030, 0.035, 0.040, 0.045, and 0.050). The results revealed that, Trp/NAA had no significant effect on growth performance and TI of the birds. However, elevation of Trp/LNAA was concurred with a linear reduction in CORT (P < .0001, r² = 0.819) and linear increases in 5-HT (P < .0001, r² = 0.945), T₃ (P = .0003, r² = 0.403) and T₄ (P < .0001, r² = 0.937) levels. In conclusion, the results from the current study demonstrated that, although incremental levels of Trp/LNAA did not affect bird growth performance or fearfulness, it increased 5-HT, T₃ and T_4, and decreased CORT levels in a linear dose-dependent manner. Manipulation of Trp feeding levels could be applied to manage stressful conditions in birds.

Altered cytokine profile under control of the serotonergic system determines the regulation of CYP2C11 and CYP3A isoforms

The aim of this study is to assess a potential mechanism by which the serotonergic system can control the expression and activity of cytochrome (CYP) 2C11 and CYP3A isoforms during liver insufficiency. A rat model of diethylnitrosamine (DEN)-induced liver insufficiency was developed by administering 50 mg/kg of DEN twice a week for 7 weeks. Dysfunction of the serotonergic system was evoked by feeding the rats with a tryptophan-free diet for three weeks. Dysfunction of the serotonergic system during liver insufficiency decreased the level of proinflammatory cytokines (TGF-β and IL-1β) and increased the level of an anti-inflammatory cytokine (IL-4). Simultaneously, activation of the repressive mechanism IL-4/JAK1/STAT6/SOCS1 of the JAK2/STAT5b-mediated signal transduction pathway and the pERK1/2/GR/STAT6 signal transduction pathway resulted in the suppression of the CYP2C11 and CYP3A isoforms. Moreover, dysfunction of the serotonergic system during liver insufficiency equalized the level of testosterone to the basal level, did not change the steady state of the corticosterone level and significantly enhanced the reduced level of growth hormone. An altered cytokine profile under control of the serotonergic system determines the regulation of CYP2C11 and CYP3A isoforms during liver insufficiency through mechanisms based on posttranscriptional and posttranslational processes.