Melatonin attenuates acute pancreatitis-associated lung injury in rats by modulating interleukin 22

Abstract

Aim: To investigate whether therapeutic treatment with melatonin could protect rats against acute pancreatitis and its associated lung injury.

Methods: Seventy-two male Sprague-Dawley rats were randomly divided into three groups: the sham operation (SO), severe acute pancreatitis (SAP), and melatonin treatment (MT) groups. Acute pancreatitis was induced by infusion of 1 mL/kg of sodium taurocholate (4% solution) into the biliopancreatic duct. Melatonin (50 mg/kg) was administered 30 min before pancreatitis was induced, and the severity of pancreatic and pulmonary injuries was evaluated 1, 4 and 8 h after induction. Serum samples were collected to measure amylase activities, and lung tissues were removed to measure levels of mRNAs encoding interleukin 22 (IL-22) and T helper cell 22 (Th22), as well as levels of IL-22.

Results: At each time point, levels of mRNAs encoding IL-22 and Th22 were significantly higher (P < 0.001) in the MT group than in the SAP group (0.526 ± 0.143 vs 0.156 ± 0.027, respectively, here and throughout, after 1 h; 0.489 ± 0.150 vs 0.113 ± 0.014 after 4 h; 0.524 ± 0.168 vs 0.069 ± 0.013 after 8 h, 0.378 ± 0.134 vs 0.122 ± 0.015 after 1 h; 0.205 ± 0.041 vs 0.076 ± 0.019 after 4 h; 0.302 ± 0.108 vs 0.045 ± 0.013 after 8 h, respectively) and significantly lower (P < 0.001) in the SAP group than in the SO group (0.156 ± 0.027 vs 1.000 ± 0.010 after 1 h; 0.113 ± 0.014 vs 1.041 ± 0.235 after 4 h; 0.069 ± 0.013 vs 1.110 ± 0.213 after 8 h, 0.122 ± 0.015 vs 1.000 ± 0.188 after 1 h; 0.076 ± 0.019 vs 0.899 ± 0.125 after 4 h; 0.045 ± 0.013 vs 0.991 ± 0.222 after 8 h, respectively). The mean pathological scores for pancreatic tissues in the MT group were significantly higher (P < 0.01) than those for samples in the SO group (1.088 ± 0.187 vs 0.488 ± 0.183 after 1 h; 2.450 ± 0.212 vs 0.469 ± 0.242 after 4 h; 4.994 ± 0.184 vs 0.513 ± 0.210 after 8 h), but were significantly lower (P < 0.01) than those for samples in the SAP group at each time point (1.088 ± 0.187 vs 1.969 ± 0.290 after 1 h; 2.450 ± 0.212 vs 3.344 ± 0.386 after 4 h; 4.994 ± 0.184 vs 6.981 ± 0.301 after 8 h). The severity of SAP increased significantly (P < 0.01) over time in the SAP group (1.088 ± 0.187 vs 2.450 ± 0.212 between 1 h and 4 h after inducing pancreatitis; and 2.450 ± 0.212 vs 4.994 ± 0.184 between 4 and 8 h after inducing pancreatitis).

Conclusion: Melatonin protects rats against acute pancreatitis-associated lung injury, probably through the upregulation of IL-22 and Th22, which increases the innate immunity of tissue cells and enhances their regeneration.

Keywords: Interleukin 22; Melatonin; Pancreatitis-associated lung injury; Severe acute pancreatitis; T helper 22 cell.

Figure 1

Histology of pulmonary tissues and pathological scores of pancreatic tissues from rats in the sham operation, severe acute pancreatitis, and melatonin treatment groups. A-C: Histological changes of pulmonary tissues in the SAP group (A) 1 h, (B) 4 h, and (C) 8 h after experimental induction of SAP; D: Histological changes of pulmonary tissues in the SO group 8 h after mock induction of SAP; E-G: Histological changes of pulmonary tissues in the MT group (E) 1 h, (F) 4 h, and (G) 8 h after experimental induction of SAP (hematoxylin and eosin stain; ×200). H: Pathological scores of pancreatic tissues (n = 8). ^bP < 0.01 vs the MT group; ^dP < 0.01 vs the SO and MT groups. SO: Sham operation; SAP: Severe acute pancreatitis; MT: Melatonin treatment.

Figure 2

Changes in serum amylase levels from rats in the sham operation, severe acute pancreatitis, and melatonin treatment groups over time. Serum amylase levels differed significantly (P < 0.01) between each pair of time points in the SAP group, but not at different levels in the SO group (n = 8 rats per group). ^bP < 0.01 vs the SO group; ^dP < 0.05 vs the SO and SAP groups. SO: Sham operation; SAP: Severe acute pancreatitis; MT: Melatonin treatment.

Figure 3

Levels of mRNAs encoding interleukin 22 and T helper cell 22 in lung tissue samples from rats in the sham operation, severe acute pancreatitis, and melatonin treatment groups. A: Expression of IL-22 mRNA 1, 4 and 8 h after induction of SAP; B: Expression of Th22 mRNA 1, 4 and 8 h after induction of SAP. Levels of mRNAs encoding IL-22 and Th22 decreased with continued progression of SAP (P < 0.01). ^bP < 0.01 vs the SO group; ^dP < 0.01 vs the SO and SAP groups (n = 8 rats per group). SO: Sham operation; SAP: Severe acute pancreatitis; IL: Interleukin; Th: T helper cell; MT: Melatonin treatment.

Figure 4

Levels of interleukin 22 in lung tissue samples from rats in the sham operation, severe acute pancreatitis, and melatonin treatment groups. Levels of IL-22 at 1, 4 and 8 h after induction of SAP. Levels of IL-22 decreased with continued progression of SAP (P < 0.01). ^bP < 0.01 vs the SO group; ^dP < 0.01 vs the SO and SAP groups (n = 8 rats per group). SO: Sham operation; SAP: Severe acute pancreatitis; IL: Interleukin; Th: T helper cell; MT: Melatonin treatment.