Effect of emodin in suppressing acute rejection following liver allograft transplantation in rats

The effect of emodin on liver disease -- comprehensive advances in molecular mechanisms

Liver injury could be caused by a variety of causes, including alcohol, drug poisoning, autoimmune overreaction, etc. In the period of liver injury, hepatic stellate cells (HSCs) will be activated and produce excessive extracellular matrix (ECM). If injury cannot be suppressed, liver injury will develop into fibrosis, even cirrhosis and liver cancer. It is reported that some monomer components extracted from traditional Chinese medicine have better effects on protecting liver. Emodin, an anthraquinone compound extracted from the traditional Chinese medicine RHEI RADIX ET RHIZOMA, has anti-inflammatory, antioxidant, liver protection and anti-cancer effects, and can prevent liver injury induced by a variety of factors. By searching literatures related to the liver protection of emodin in PUBMED, SINOMED, EBM and CNKI databases, it was found that emodin could inhibit the production and promote the secretion of bile acids, and have a protective effect on intrahepatic cholestasis. Also, emodin reduce collagen synthesis and anti-hepatic fibrosis by inhibiting oxidative stress, TGF-β/Smad pathway and HSCs proliferation, and promoting apoptosis of HSCs. Emodin can also regulate lipid metabolism and regulate the synthesis and oxidation of lipids and cholesterol to protect the nonalcoholic fatty liver. Besides, emodin can induce the apoptosis of hepatocellular carcinoma cells by acting on the death receptor pathway and mitochondrial apoptosis pathway, thus inhibiting the development of hepatocellular carcinoma. Moreover, emodin can modulate immunity and improve immune rejection in liver transplantation animals. In conclusion, emodin has a good effect on liver protection, but further experimental data are needed to verify it.

A New Immunosuppressive Molecule Emodin Induces both CD4+FoxP3+ and CD8+CD122+ Regulatory T Cells and Suppresses Murine Allograft Rejection

Due to vigorous alloimmunity, an allograft is usually rejected without any conventional immunosuppressive treatment. However, continuous global immunosuppression may cause severe side effects, including tumors and infections. Mounting evidence has shown that cyclosporine (CsA), a common immunosuppressant used in clinic, impedes allograft tolerance by dampening regulatory T cells (Tregs), although it inhibits allograft rejection at the same time. Therefore, it is necessary to seek an alternative immunosuppressive drug that spares Tregs with high efficiency in suppression but low toxicity. In this study, we investigated the capacity of emodin, an anthraquinone molecule originally extracted from certain natural plants, to prolong transplant survival in a mouse model and explored the cellular and molecular mechanisms underlying its action. We found that emodin significantly extended skin allograft survival and hindered CD3⁺ T cell infiltration in the allograft, accompanied by an increase in CD4⁺Foxp3⁺ and CD8⁺CD122⁺ Treg frequencies and numbers but a reduction in effector CD8⁺CD44^highCD62L^low T cells in recipient mice. Emodin also inhibited effector CD8⁺ T cells proliferation in vivo. However, CD4⁺CD25⁺, but not CD8⁺CD122⁺, Tregs derived from emodin-treated recipients were more potent in suppression of allograft rejection than those isolated from control recipients, suggesting that emodin also enhances the suppressive function of CD4⁺CD25⁺ Tregs. Interestingly, depleting CD25⁺ Tregs largely reversed skin allograft survival prolonged by emodin while depleting CD122⁺ Tregs only partially abrogated the same allograft survival. Furthermore, we found that emodin hindered dendritic cell (DC) maturation and reduced alloantibody production posttransplantation. Finally, we demonstrated that emodin inhibited in vitro proliferation of T cells and blocked their mTOR signaling as well. Therefore, emodin may be a novel mTOR inhibitor that suppresses alloimmunity by inducing both CD4⁺FoxP3⁺ and CD8⁺CD122⁺ Tregs, suppressing alloantibody production, and hindering DC maturation. Thus, emodin is a newly emerging immunosuppressant and could be utilized in clinical transplantation in the future.