Hepatoprotective effects of rice-derived peptides against acetaminophen-induced damage in mice

Abstract

Glutathione, the most abundant intracellular antioxidant, protects cells against reactive oxygen species induced oxidative stress and regulates intracellular redox status. We found that rice peptides increased intracellular glutathione levels in human hepatoblastoma HepG2 cells. Acetaminophen is a commonly used analgesic. However, an overdose of acetaminophen causes severe hepatotoxicity via depletion of hepatic glutathione. Here, we investigated the protective effects of rice peptides on acetaminophen-induced hepatotoxicity in mice. ICR mice were orally administered rice peptides (0, 100 or 500 mg/kg) for seven days, followed by the induction of hepatotoxicity via intraperitoneal injection of acetaminophen (700 mg/kg). Pretreatment with rice peptides significantly prevented increases in serum alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase levels and protected against hepatic glutathione depletion. The expression of γ-glutamylcysteine synthetase, a key regulatory enzyme in the synthesis of glutathione, was decreased by treatment with acetaminophen, albeit rice peptides treatment recovered its expression compared to that achieved treatment with acetaminophen. In addition, histopathological evaluation of the livers also revealed that rice peptides prevented acetaminophen-induced centrilobular necrosis. These results suggest that rice peptides increased intracellular glutathione levels and could protect against acetaminophen-induced hepatotoxicity in mice.

Keywords: acetaminophen; glutathione; liver injury; rice-derived peptide.

Fig. 1

The effect of RP on total glutathione levels and γ-GCS expression in HepG2. Cells were incubated with the indicated concentrations of RP for 24 h. (A) Total glutathione levels. The values given are the mean ± SEM (n = 6). **p<0.01 vs RP-untreated control. (B) Western blot analysis of γ-GCS protein levels. (C, D) Percentage of target protein/β-actin was calculated by comparing to RP untreated control. The values given are the mean ± SEM (n = 4). **p<0.01 and *p<0.05 vs RP-untreated control.

Fig. 2

The effect of RP on serum AST (A), ALT (B) and LDH (C) in mice with an acetaminophen-induced liver injury. The values given are the mean ± SEM (n = 5–6). *p<0.01 vs APAP treated group.

Fig. 3

The effect of RP on hepatic glutathione levels in mice with an acetaminophen-induced liver injury. The values given are the mean ± SEM (n = 5–6). ^#p<0.01 vs control group. **p<0.01 and *p<0.05 vs APAP treated group.

Fig. 4

H&E staining of the livers after acetaminophen treatment. Typical images were chosen from the different experimental groups (original magnification ×20). (A) Control group: normal lobular architecture and cell structure, (B) APAP group: multiple and extensive areas of portal inflammation and hepatocellular necrosis and a moderate increase in inflammatory cells’ infiltration, (C) RP (100 mg/kg)-treated acetaminophen group: minimal hepatocellular necrosis and inflammatory cells’ infiltration and mild portal inflammation.

Fig. 5

The expression level of γ-GCS and CYP2E1 in mice liver. Protein extracts from liver tissue were analyzed by SDS-PAGE and immunoblotting by using antibodies against γ-GCSh, γ-GCSl and CYP2E1, respectively. (A) Western blot analysis of γ-GCS protein levels at 6 h after APAP treatment. Lane 1, Control; lane 2, RP 500 mg/kg; lane 3, APAP; lane 4, APAP + RP 100 mg/kg; and lane 5, APAP + RP 500 mg/kg. (B, C) Percentage of target protein/β-actin was calculated by comparing to RP untreated control. The values given are the mean ± SEM (n = 5–6). ^##p<0.01 vs control group. **p<0.01 and *p<0.05 vs APAP treated group. (D) Western blot analysis of CYP2E1 protein levels at 6 h after APAP treatment.