Melatonin reduces bacterial translocation by preventing damage to the intestinal mucosa in an experimental severe acute pancreatitis rat model

Abstract

Recent studies have demonstrated that melatonin significantly decreased all studied acute pancreatitis-associated inflammatory parameters, in addition to reducing apoptosis and necrosis associated with pancreatic injury. However, the effect of melatonin on gut barrier dysfunction and bacterial translocation has not been fully elucidated. This study aimed to investigate the protective effects of melatonin on intestinal integrity in a rat model of severe acute pancreatitis (SAP) to evaluate whether melatonin prevented intestine barrier dysfunction and reduced bacterial translocation. Forty male Sprague Dawley (SD) rats were randomly divided into three groups, with 8 rats in the sham operation (SO) group, 18 rats in the SAP group and 14 SAP rats in the melatonin treatment (MT) group. SAP was induced by retrograde injection of 4% taurocholate into the biliopancreatic duct. Melatonin was administered 30 min prior to taurocholate injection in the melatonin-treated rats. All rats were sacrificed 24 h subsequent to pancreatitis induction. Real-time fluorescence quantitative polymerase chain reaction was used to detect and quantify Escherichia coli (E. coli) O157 in postcava blood. The microvilli structure was also analyzed with transmission electron microscopy. The level of E. coli DNA in the MT group was significantly lower than in rats in the SAP group. No E. coli DNA was detected in the control group. Villus height and crypt depth in the ileum were significantly higher in the MT and control groups compared to the SAP group, and were significantly higher in the MT group than in the SAP group. These results suggested that melatonin prevented gut barrier dysfunction and reduced bacterial translocation, resulting in reduced pancreatic-associated infections and decreased early mortality rates.

Keywords: acute pancreatitis; bacterial translocation; intestine barrier dysfunction; melatonin; microvilli structure.

Figure 1

Images of the sham operation (SO) group obtained via transmission electron microscopy with uranyl acetate staining. (A) The intestinal villi and goblet epithelial cells from the SO group were intact (magnification, ×8,000). (B) The intestinal villi and goblet epithelial cells of the SO group were intact, and the mitochondria, endoplasmic reticulum, ribosomes and other cellular organelles were normal (magnification, ×20,000).

Figure 2

Images of the severe acute pancreatitis (SAP) group obtained via transmission electron microscopy with uranyl acetate staining. (A) The intestinal villi and goblet epithelial cells of the SAP group were diffuse and the intestinal villi were absent in various areas of the sample examined (magnification, ×8,000). (B) The intestinal villi and goblet epithelial cells of the SAP group were diffuse, and the intestinal villi were absent in various locations of the sample examined. Mitochondrial membranes and mitochondrial cristae were absent and had changed into vacuoles. The amount of rough endoplasmic reticulum was increased and enlarged and ribosome numbers were significantly increased (magnification, ×20,000).

Figure 3

Images of the melatonin treatment (MT) group obtained via transmission electron microscopy with uranyl acetate staining. (A) The integrity of the intestinal villi and goblet epithelial cells in the MT group animals was maintained (magnification, ×8,000). (B) The intestinal villi and goblet epithelial cells of the MT group were intact (magnification, ×20,000). (C) Microrganelles, endoplasmic reticulum, ribosomes and other organelles remained intact in samples examined from rats in the MT group (magnification, ×20,000).

Figure 4

Villus height of the ileum mucosa (μm). ^*P≤0.05 vs. SO group; ^#P≤0.05 vs. MT group. Data are expressed as the mean ± standard deviation. SAP, severe acute pancreatitis; MT, melatonin treatment; SO, sham operation.

Figure 5

Crypt depth of the ileum mucosa (μm). ^*P≤0.05 vs. SO group; ^#P≤0.05 vs. MT group. Data are expressed as the mean ± standard deviation. SAP, severe acute pancreatitis; MT, melatonin treatment; SO, sham operation.

Figure 6

E. coli O157 polymerase chain reaction (PCR) augmentation dynamics curve.

Figure 7

Serum diamine oxidase (DAO) concentrations (U/l). ^*P>0.05 vs. SO group; ^#P≤0.05 vs. MT group. Data are expressed as the mean ± standard deviation. SAP, severe acute pancreatitis; MT, melatonin treatment; SO, sham operation.

Figure 8

Mucosal diamine oxidase (DAO) concentrations (U/l). ^*P>0.05 vs. SO group; ^#P≤0.05 vs. MT group. Data are expressed as the mean ± standard deviation. SAP, severe acute pancreatitis; MT, melatonin treatment; SO, sham operation.