Methylsulfonylmethane (MSM) is naturally occurring organic sulfur that is known as a potent antioxidant/anti-inflammatory compound. The aim of this study was to investigate the effect of MSM on hemodynamics functions and oxidative stress in rats with monocrotaline- (MCT-) induced pulmonary arterial hypertension (PAH). Wistar rats were randomly assigned to 38-days treatment. MSM was administered to rats at 100, 200, and 400 mg/kg/day doses 10 days before a single dose of 60 mg/kg, IP, MCT. Hemodynamics of ventricles were determined by Powerlab AD instrument. Blood samples were obtained to evaluate changes in the antioxidative system including activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and the level of reduced glutathione (GSH) and malondialdehyde (MDA). Improvements in cardiopulmonary hemodynamics were observed in the MSM-treated pulmonary arterial hypertensive rats, with a significant reduction in right ventricular systolic pressure (RSVP) and an increase in the mean arterial pressure (MAP). The values of CAT, SOD, GSH-px activities, and GSH were significantly lower in MCT-induced PAH (
Pulmonary arterial hypertension (PAH) is a pathophysiological state characterized by a progressive increase in pulmonary vascular resistance. In addition to inducing myocardial hypertrophy, it also induces marked interstitial fibrosis to compensate for the increased ventricular workload. These adaptive changes often clinically lead to heart failure and sudden cardiac death [
Recent reports have implicated increased oxidative stress as a mediator in the pathogenesis and the development of PAH [
Methylsulfonylmethane (MSM) is naturally occurring organic sulfur that is known as a potent antioxidant/anti-inflammatory compound [
Monocrotaline (MCT) is a toxic pyrrolizidine alkaloid and has a selective toxic effect on pulmonary vessels without an effect on systemic vessels. Recently, we have observed that the expression of oxidative stress-related substances such as angiotensin II and endotheline 1 is increased in rats after exposure to MCT and that treatment with MSM suppresses these responses (unpublished findings). MSM was shown to act directly as free radical scavenger, which would further add to the efficiency of MSM as an antioxidant [
Two-month-old male Wistar rats (
PAH was induced by means of a single dose of MCT (Sigma-Aldrich; 60 mg/kg) [
All hemodynamic measurements were carried out in rats, as described previously [
Following the hemodynamic measurements, animals were sacrificed by an overdose of pentobarbital. The hearts and lungs were removed and weighed. Then, the tissues were cut into small pieces for drying at 55°C until a constant weight was reached. Wet-to-body weight ratios and wet-to-dry weight ratios of the tissues were calculated to assess the degree of the congestion [
The enzyme activities of CAT (Cayman, Chemical Company, MI), SOD, and GSH-Px (RANDOX Laboratories Ltd., UK) were determined by using spectrophotometric assay kits. Serum glutathione (GSH) and glutathione disulfide (GSSG) contents were measured using colorimetric enzymatic kits from Assay Designs/Stressgen Bioreagents. The MDA levels were measured spectrophotometrically based on the coupling of MDA with thiobarbituric acid [
Data were presented as mean ± SE. Comparisons between groups were made with Student's paired
Table
Morphometric parameters and hemodynamic data of control and monocrotaline-injected male rats.
Control | MCT-induced pulmonary hypertension groups. MSM (mg/kg/day) | ||||||
---|---|---|---|---|---|---|---|
0 | 100 | 200 | 400 |
|
| ||
Morphometric parameters | |||||||
Body wt (g) | 265 ± 8 | 204 ± 12* | 230 ± 10 | 244 ± 21 | 262 ± 11 | 0.39 | <0.01 |
Heart (g) | 0.71 ± 0.13 | 0.81 ± 0.19 | 0.78 ± 0.18 | 0.75 ± 0.20 | 0.74 ± 0.17 | 0.09 | 0.21 |
Heart/body wt (mg/g) | 2.67 ± 0.11 | 3.4 ± 0.14** | 3.44 ± 0.27 | 3.23 ± 0.53 | 2.84 ± 0.054 | 0.36 | <0.01 |
RV wt (g) | 0.16 ± 0.01 | 0.31 ± 0.04** | 0.25 ± 0.02 | 0.22 ± 0.03 | 0.18 ± 0.01 | 0.38 | <0.01 |
RV/body wt (mg/g) | 0.59 ± 0.04 | 1.54 ± 0.15** | 1.09 ± 0.15* | 0.92 ± 0.27 | 0.70 ± 0.38 | 0.46 | <0.01 |
LV + S wt (g) | 0.55 ± 0.02 | 0.50 ± 0.01 | 0.53 ± 0.02 | 0.53 ± 0.01 | 0.56 ± 0.02 | 0.23 | 0.04 |
LV + S/body wt (mg/mg) | 2.08 ± 0.08 | 2.46 ± 0.08 | 2.33 ± 0.15 | 2.24 ± 0.26 | 2.15 ± 0.07 | 0.15 | 0.11 |
RV/LV + S | 0.28 ± 0.02 | 0.62 ± 0.07** | 0.47 ± 0.04* | 0.42 ± 0.06 | 0.33 ± 0.03 | 0.50 | <0.01 |
Lung wet (g) | 1.11 ± 0.06 | 3.09 ± 0.14** | 2.23 ± 0.36* | 1.99 ± 0.26 | 1.28 ± 0.09 | 0.60 | <0.01 |
Lung dry (g) | 0.25 ± 0.01 | 0.52 ± 0.02** | 0.46 ± 0.06* | 0.41 ± 0.06 | 0.27 ± 0.02 | 0.50 | <0.01 |
Lung dry/wet | 0.22 ± 0.03 | 0.17 ± 0.02** | 0.20 ± 0.09 | 0.21 ± 0.03 | 0.21 ± 0.03 | 0.36 | 0.01 |
Lung wet/body wt (mg/g) | 4.19 ± 0.18 | 15.17 ± 1.15** | 9.35 ± 2.06* | 8.17 ± 2.38 | 4.83 ± 0.20 | 0.60 | <0.01 |
Hemodynamic data | |||||||
HR (beats/min) | 397 ± 31 | 274 ± 19* | 312 ± 16 | 326 ± 24 | 406 ± 31 | 0.47 | <0.01 |
MAP (mmHg) | 83.28 ± 7.42 | 54.07 ± 7.13** | 53.100 ± 2.76** | 58.68 ± 3.149* | 77.83 ± 1.31 | 0.62 | <0.01 |
RVSP (mmHg) | 22.56 ± 1.65 | 35.87 ± 1.76** | 29.21 ± 2.79 | 27.65 ± 2.60 | 22.62 ± 2.11 | 0.53 | <0.01 |
RV |
1958 ± 40 | 2376 ± 116* | 2196 ± 25 | 2130 ± 50 | 2027 ± 39 | 0.39 | <0.01 |
|
14.43 ± 0.92 | 22.62 ± 0.83** | 19.05 ± 1.43* | 17.44 ± 0.91 | 15.65 ± 0.97 | 0.53 | <0.01 |
Data are mean ± SE. Significant Tukey's post hoc differences compared with controls are indicated by asterisks (**
Levels of right ventricular systolic pressure (RSVP), peak rate of right ventricular pressure (
Levels of CAT, SOD, and GSH-Px in the serum of hypertensive rats were significantly decreased at week 4 of MCT treatment (Table
Effects of different doses of methylsulfonylmethane (MSM) on the activities of antioxidant enzymes in rats with monocrotaline-(MCT-) induced pulmonary hypertension.
Control | MCT-induced pulmonary hypertension groups, MSM (mg/kg/day) | ||||||
---|---|---|---|---|---|---|---|
0 | 100 | 200 | 400 |
|
| ||
CAT (U/mL) | 6.10 ± 0.83 | 2.02 ± 0.33* | 4.16 ± 0.57 | 5.02 ± 0.75 | 7.98 ± 1.68 | 0.48 | <0.001 |
SOD (U/mL) | 203.33 ± 3.80 | 168.33 ± 6.67** | 206.67 ± 5.11 | 210.00 ± 7.30 | 220.83 ± 3.96 | 0.50 | <0.001 |
GSH-px (U/mL) | 10.01 ± 0.12 | 7.05 ± 0.62** | 8.14 ± 1.09 | 9.80 ± 0.25 | 10.20 ± 0.20 | 0.40 | 0.001 |
Significant Tukey's post hoc differences compared with controls are indicated by asterisks (**
The effect of MSM treatment on the serum content of GSH and GSSG is shown in Table
Effects of different doses of methylsulfonylmethane (MSM) on the levels of reduced glutathione (GSH) and disulfide-oxidized glutathione (GSSG) and MDA in rats with monocrotaline- (MCT-) induced pulmonary hypertension.
Control | MCT-induced pulmonary hypertension groups, MSM (mg/kg/day) | ||||||
---|---|---|---|---|---|---|---|
0 | 100 | 200 | 400 |
|
| ||
GSH (nmol/mL) | 543.54 ± 16.22 | 347.33 ± 41.54* | 551.65 ± 93.28 | 695.95 ± 106.36 | 774.62 ± 45.62 | 0.41 | <0.01 |
GSSG (nmol/mL) | 50.71 ± 2.17 |
|
62.98 ± 9.36 | 59.05 ± 4.80 | 51.31 ± 2.41 | 0.26 | 0.01 |
Significant Tukey’s post hoc differences compared with controls are indicated by asterisks (**
Effects of different doses (0–400 mg/kg/day) of methylsulfonylmethane (MSM) on the reduced to oxidized glutathione (GSH/GSSG) in rats with monocrotaline- (MCT-) induced pulmonary hypertension (regression coefficient
The serum levels of MDA were assayed as index of lipid peroxidation. Levels of MDA in the serum of hypertensive rats were significantly increased versus control (Figure
Effects of different doses (0–400 mg/kg/day) of methylsulfonylmethane (MSM) on lipid peroxidation expressed as the contents of malondialdehyde (MDA) in rats with monocrotaline- (MCT-) induced pulmonary hypertension (regression coefficient
In this study, significant changes in the hemodynamics, serum antioxidative enzymes, glutathione, and MDA were observed in MCT-induced pulmonary hypertensive rats, and these changes were modulated with MSM in the experimental treatments.
Our findings are in agreement with previous reports showing adverse effects on the hemodynamics and lower final body weight gain in rats treated with MCT [
Consistent with the current study, several studies have reported that cardiovascular system of MCT-induced pulmonary hypertensive rats showed inflammatory alterations similar to those observed in human PAH [
Furthermore, the finding of increased RAAS and ET-1 in rats with MCT-induced pulmonary hypertension supports the presence of enhanced oxidative stress in the RV of PAH rats. The PAH-induced increase in RAAS and ET-1 was reverted by treatment of MSM, indicating an improvement in the oxidative status of the cells.
In this study, enzymatic activity assay showed reduced CAT, SOD, and GSH-Px in serum of PAH rats compared with control. Biphasic changes in antioxidant enzymes have been described in association with the time point of sampling during MCT-induced PAH. These changes include an increase in antioxidant enzymes during hypertrophy stage and a decrease during heart failure stage [
In this study, CAT and SOD activities were higher in 400 mg/kg/day MSM-treated pulmonary hypertensive rats than in either the normotensive controls or the MCT-induced pulmonary hypertensive rats. A similar observation was previously made by Jin et al. [
Recent reports have implicated increased lipid peroxidation as a mediator in the pathogenesis and the development of PAH [
In pretreatment assessments, a decrease in circulating elevation of oxidative markers and an improved overall antioxidant potential with MSM treatment were evident. To the authors' knowledge, there are no specific data regarding the effect of MSM on oxidative parameters in pulmonary hypertensive rats. Although no mechanistic interpretation can be made at this point, the results obtained in the present study provide evidence for the first time that the MSM could limit oxidative response following pulmonary hypertension. Future studies regarding the effects of MSM treatment on antioxidative defense function in PAH are clearly warranted.
MSM could exert protective antioxidative effects through the induction of CAT, SOD, and GSH-px activities along with associated reducing agents, such as GSH. In addition, these results suggest that MCT-induced PAH could induce harmful effects on the RV function, probably due to a decrease in antioxidant enzyme activity and subsequent oxidative damage.
This study was partially supported by a Grant from the Tabriz University of Medical Sciences (1388/4/20-5/4/3255).