Melatonin ameliorates ANIT‑induced cholestasis by activating Nrf2 through a PI3K/Akt‑dependent pathway in rats

Abstract

Cholestasis is a devastating liver condition which is increasing in prevalence worldwide; however, its underlying pathogenic mechanisms remain to be fully elucidated. It was hypothesised that melatonin may alleviate the hepatic injury associated with cholestasis due to its established antioxidant effects. Therefore, the effect and potential anticholestatic properties of melatonin were investigated in rats with α‑naphthylisothiocyanate (ANIT)‑induced liver injury, a common animal model that mimics the cholestasis‑associated liver injury in humans. The rats received intraperitoneal injection of ANIT with or without subsequent treatment with melatonin, and were sacrificed 24 h later. The serum biochemistry parameters of the liver were measured using conventional laboratory assays, and the liver tissue was subjected to conventional histological examination, reverse transcription‑quantitative polymerase chain reaction analysis and western blotting. The levels of alanine transaminase, aspartate transaminase, total bilirubin, direct bilirubin, total bile acids, alkaline phosphatase, γ‑glutamyl transferase and glutathione were restored in rats treated with melatonin. Histological examination provided further evidence supporting the protective effect of melatonin against ANIT‑induced cholestasis. In addition, the mRNA and protein expression levels of glutamate cysteine ligase, phosphorylated Akt and nuclear factor‑erythroid 2‑related factor‑2 were restored in rats treated with melatonin. These findings indicate that melatonin is a natural agent that appears to be promising for the treatment of cholestasis, and that the anticholestatic effects of melatonin involve the alleviation of oxidative stress.

Keywords: melatonin; cholestasis; nuclear factor-erythroid 2-related factor-2; phosphoinositide-3 kinase/Akt-dependent pathway.

Figure 1.

Melatonin reverses histological damage in the liver tissues of rats with α-naphthyl isothiocyanate-induced cholestasis. Control group images at magnifications of (A) ×50, (B) ×100 and (C) ×200; cholestasis model group images at magnifications of (D) ×50, (E) ×100 and (F) ×200; and melatonin treatment group images at magnifications of (G) ×50, (H) ×100 and (I) ×200. Liver tissue histological damage is indicated by black arrows.

Figure 2.

Effects of melatonin on serum biochemistry. The rats were treated with ANIT (75 mg/kg) with and without melatonin. The following liver function markers in the serum were assayed: (A) ALT, (B) AST, (C) TBIL, (D) DBIL, (E) ALP, (F) TBA, and (G) GGT. (H) Levels of GSH in liver tissues. Data are expressed as the mean ± standard error of the mean (n=6 per group). ^###P<0.001 and ^#P<0.05 compared with the control group; ***P<0.001 and *P<0.05 compared with the ANIT group. ANIT, α-naphthyl isothiocyanate; ALT, alanine transaminase; AST, aspartate transaminase; TBIL, total bilirubin; DBIL, direct bilirubin; ALP, alkaline phosphatase; TBA, total bile acids; GGT, γ-glutamyl transferase; GSH, glutathione.

Figure 3.

Effects of melatonin on hepatic protein and mRNA expression. (A) Effect of melatonin on hepatic protein expression. Effect of melatonin on hepatic protein expression of (B) GCLC, (C) GCLM, (D) pAkt and (E) Nrf2. Effect of melatonin on hepatic mRNA expression of (F) GCLC, (G) GCLM, (H) pAkt and (I) Nrf2. **P<0.01 and *P<0.05. CON, control; MOD, model; MT, melatonin; GCLC, glutamate cysteine ligase catalytic subunit; GCLM, glutamate cysteine ligase modifier subunit; Nrf2, nuclear factor-erythroid 2-related factor-2; ns, not significant.

Figure 4.

Schematic presentation of the proposed effects of melatonin against ANIT-induced intrahepatic cholestasis. ANIT, α-naphthyl isothiocyanate; GCLC, glutamate cysteine ligase catalytic subunit; GCLM, glutamate cysteine ligase modifier subunit; Nrf2, nuclear factor-erythroid 2-related factor-2; ARE, antioxidant response element; GSH, glutathione; GGT, γ-glutamyl transferase; PI3K, phosphoinositide-3 kinase; KEAP1, Kelch-like ECH-associated protein 1.