Abstract
Serotonin is involved in the pathological processes of several liver diseases via the regulation of inflammatory response and oxidative stress. We aimed to investigate the role of serotonin in Concanavalin A- (Con A-) induced acute liver injury (ALI). ALI was induced in C57B/6 wild-type (WT) mice and tryptophan hydroxylase 1 (TPH1) knockout mice through tail vein injection of Con A (15 mg/kg body weight). Another group of TPH1 knockout ALI mice was supplied with 5-hydroxytryptophan (5-HTP) in advance to recover serotonin. The blood and liver tissues of mice were collected in all groups. Markedly increased serum levels of serotonin were identified after the injection of Con A. Increased serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and stronger hepatic tissue pathology were detected, suggesting that serotonin could mediate Con A-induced liver damage. Serotonin significantly facilitated the release of serum and intrahepatic inflammatory cytokines, including interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-17A (IL-17A), interferon-gamma (IFN-γ), and tumor necrosis-alpha (TNF-α), after the administration of Con A. In addition, serotonin significantly increased the intrahepatic levels of oxidative stress markers malonaldehyde (MDA), myeloperoxidase (MPO), and nitric oxide (NO) and decreased antioxidant stress indicator glutathione (GSH) in Con A-treated mice. Additionally, serotonin promoted hepatocyte apoptosis and autophagy based on B-cell lymphoma-2 (Bcl-2), Bcl-2-asociated X protein (Bax), and Beclin-1 levels and TUNEL staining. More importantly, serotonin activated nuclear factor kappa B (NF-κB) and upregulated the hepatic expressions of high mobility group protein B1 (HMGB1), toll-like receptor-4 (TLR4), and downstream molecules in Con A-mediated liver injury. Serotonin 2A receptor was upregulated in liver tissue after Con A injection, and serotonin 2A receptor antagonist Ketanserin protected against Con A-induced hepatitis. These results indicated that serotonin has the potential to aggravate Con A-induced ALI via the promotion of inflammatory response, oxidative stress injury, and hepatocyte apoptosis and the activation of hepatic HMGB1-TLR signaling pathway and serotonin 2A receptor.
Highlights
Acute liver injury (ALI) refers to a destructive hepatic inflammatory disease, which can be caused by virus infection, hepatotoxic drugs, alcohol abuse, and so forth [1, 2]
We found that the mRNA expressions of proinflammatory IL-2 (P = 0:002), IL-6 (P = 0:002), IL-17A (P < 0:001), IFNγ (P < 0:001), and TNF- α (P = 0:003) in liver tissue were significantly lower in the tryptophan hydroxylase 1 (TPH1)-/- model group than those in the WT model group (Figure 3, P < 0 05)
The administration of 5-HTP significantly upregulated the expression of high mobility group protein B1 (HMGB1), TLR2, and toll-like receptor-4 (TLR4) and downstream molecules in Concanavalin A- (Con A-)treated TPH1-/- mice. These results suggested that serotonin may regulate NF-κB activation and inflammatory response by activating the HMGB-toll-like receptors (TLRs) signaling pathway in Concanavalin A (Con A)-induced hepatitis
Summary
Acute liver injury (ALI) refers to a destructive hepatic inflammatory disease, which can be caused by virus infection, hepatotoxic drugs, alcohol abuse, and so forth [1, 2]. Severe and persistent ALI can eventually lead to liver failure, liver cirrhosis, and tumorigenesis [3]. The pathological mechanism of ALI is not completely clear. Concanavalin A (Con A) is a lectin-like polysaccharide derived from plants. In 1992, Tiegs et al successfully established the mouse model of ALI by tail vein injection of Con A [4]. This model is accompanied by massive liver tissue
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