Cardioprotective Activity of Cassia fistula L. Bark Extract in Isoproterenol-Induced Myocardial Infarction Rat Model.

Cassia fistula Linn, generally recognized as Indian laburnum, is one of the ancient trees in the Indian subcontinent used for its ornamental and diverse medicinal properties. It is known for its ethnic medicinal uses in inflammatory and infectious pathologies such as antihelmintic, purgative, carminative, antipyretic, expectorant, analgesic, laxative, antiseptic, and antidote against snake poison. The Cassia bark is rich in anthraquinones, flavanols glycosides, and sitosterols, which renders it cardioprotective properties. The existing experiments were designed to assess the potential of Cassia fistula bark against isoproterenol (ISP)-induced cardiotoxicity in rats, which has not been validated yet. The bark was successively extracted with five different solvents, and each extract was subjected to in vitro antioxidant studies. Further acute oral toxicity assays were carried out preceding in vivo myocardial studies. Cardiotoxicity-inducing agent, ISP, was administrated to the rats for two consecutive days (8th and 9th). Based on in vitro studies, the Cassia fistula methanolic extract (CFME) was administered in two doses: CFME-LD (lower dose 250 mg/kg) and CFME-HD (high dose 500 mg/kg) separately. It was found that CFME produced a substantial decrease in lipid peroxidation and an increase in antioxidants in myocardial tissues. CFME abrogated the levels of triglyceride and total cholesterol with a decrease in alanine transaminase (ALT) and aspartate transaminase (AST) activity in serum at both doses. 2,3,5-Triphenyltetrazolium chloride (TTC) staining and histopathology also revealed the protective effects of CFME against ISP-induced myocardial infarction. The study showed the significant role of the CFME as a strong antioxidant and cardioprotective action in ISP-induced toxicity.

1. Introduction

Cardiovascular toxicity embraces damage to the heart by means of oxidative stress, inflammation, and toxin-induced functional abnormality in electrophysiology and muscle damage. Environmental factors and our lifestyle play a key role in determining our cardiovascular health. There is a close and well-established link between pulmonary disease and cardiotoxicity. Drug-induced cardiotoxicity is the single most frequent and major adverse effect aligned with most of the clinically used different classes of drugs like anticancer, antiretroviral, sympathomimetic, female hormones, and nonsteroidal anti-inflammatory drugs. Drug-induced cardiotoxicity initially causes cardiac muscle dysfunction that progressively leads to myocardial infarction and heart failure [1].

The mechanism of drug-induced cardiotoxicity is very complex and may vary among the drugs, but in the general ground with the generation of free radical oxygen species and oxidative stress through various phases of drug metabolism. Isoproterenol (ISP)-induced cardiotoxicity is pathologically similar to acute myocardial infarction, hence, commonly used in experimental settings for acute myocardial infarction. Among the different animal models of myocardial infarction, the ISP-induced myocardial necrosis model is considered the most authentic one [1-3]. The positive chronotropic and positive inotropic effect on the heart by ISP is mediated through the activation of β1 adrenergic receptors [4, 5]. The generation of highly cytotoxic reactive oxygen species (ROS), toxic and unstable metabolites, overstimulation of β-adrenoceptors (cardiac β1 and β2-adrenoceptors), accumulation of calcium in cardiac cells, and chronic discharges of pro-inflammatory cytokine storm (tumor necrosis factor-α, interleukin-6, and interleukin-1β) by ISP causes irreversible alternations in myocardial structure, function, and biochemical markers. It is very difficult to manage, suppress, and reverse ISP-induced cardiac toxicity.

Subcutaneous administration of ISP leads to myocardial necrosis in the endocardium of the left ventricles and interventricular septum. Multiple mechanisms for ISP-induced myocardial necrosis have been described. One of the acknowledged pathways amid these is an upsurge in oxidative strain as a result of ISP metabolic products and the generation of redundant free radicals [6].

Mankind always seeks nature to rescue themselves from diseases. The remedial use of medicinal plants is as antique as mankind itself. Cassia fistula Linn, also recognized as Bactyrilobium fistula Willd, commonly known as Indian Laburnum or Amaltas or Golden Shower Tree, is an evergreen, fast-growing medium-size tree belonging to the family, Caesalpinioideae. It is indigenous to India and South Asia. Its flowers appear in a pendulous fashion and look highly attractive and beautiful and, hence, are usually cultivated with the ornamental objective. Cassia fistula is ethnomedicinally used to treat anorexia, dermal contaminations, jaundice, ulcers, and inflammatory circumstances like rheumatism [7]. It is also used as anthelmintic, purgative, carminative, antipyretic, expectorant, analgesic, laxative, antiseptic, bronchitis, and antidote against snake poison [8-10].

In the Ayurvedic classification of treatment, it is known as Aragvadha meaning “disease killer” plant. In the Unani system of medicine, Cassia fistula bark decoction is employed in the treatment of chronic diseases, namely, leprosy, syphilis, amenorrhea, and heart diseases. This plant is also documented in British Pharmacopoeia [11] because of its profuse and attractive medicinal properties.

Various parts of Cassia fistula Linn. Tree, namely, bark, heartwood, flowers, leaves, and seed kernels are attributed with medicinal properties. The high medicinal prominence of Cassia fistula is due to the presence of many bioactive phytocomponents particularly anthraquinone glycosides, lignans, flavonoids, alkaloids, tannins, resins, sesquiterpenes, and fatty acids [9]. Stem bark of Cassia fistula contains β-sitosterol, fistucacidin (3, 4, 7, 8, 4′-pentahydroxyflavon), leucocyanidin, lupeol, oxyanthraquinone, dihydroxyanthraquinone, and flavonol glycosides (Figure 1), and hexacosanol [12-14]. In numerous in vitro and in vivo experiments, these phytocompounds have exhibited considerable pharmacological activities including antioxidant, anti-inflammatory [15], antimicrobial [16], antiviral, anticancer [17], hepatoprotective [18], antidiabetic [19], hypolipidemic, antileishmaniatic [20], antipyretic, purgative, and wound healing potential in preclinical studies [9].

Figure 1

Major active phytoconstituents present in the stem bark of Cassia fistula L.

The plant genus Cassia has been indexed as an important constituent of various traditional herbal medicines due to its strong cardioprotective and antioxidant potentials. Cardioprotective role of Cassia fistula stem bark, flowers, and Cassia siamea Lamk. leaves against doxorubicin-induced cardiotoxicity murine prototypical was considered and described by Manonmani et al. and Khatib et al., respectively [19, 21]. However, the role of the plant in context to modulation of ISP-induced cardiotoxicity has never been reconnoitered. In the current experiments, we inspected the cardioprotective potential of the Cassia fistula stem bark extract in ISP-induced cardiotoxicity in rats.

2. Materials and Methods

2.1. Chemicals and Reagents

Isoproterenol hydrochloride from Sigma-Aldrich Co. (St. Louis, MO, United States) and kits for the analysis of aspartate aminotransferase (AST), alanine aminotransferase (ALT), triglycerides (TG), and total cholesterol (TC) were acquired from Arkray Healthcare Pvt., Ltd., Mumbai, India (AutoSpan®) and Reckon Diagnostics P. Ltd., Vadodara, India. Colorimetric kits were used to estimate malondialdehyde (MDA) (Cell Biolabs Inc.), reduced glutathione (GSH) (G-Biosciences), and superoxide dismutase (SOD) (BioVision) activity.

2.2. Preparation of Extracts

The bark of the stem of Cassia fistula (CF) was air-dried in shade and coarsely ground. 300 g of the powdered drug was consecutively extracted in the Soxhlet apparatus using five different solvents successively, that is, petroleum ether (PE), chloroform (CE), ethyl acetate (EE), methanol (ME), and aqueous extracts (AE). All the obtained extracts were dried using a rotary evaporator at 45°C and stored in vacuum desiccators.

2.3. In Vitro Antioxidant Activity

2.3.1. 2,2-Diphenyl-1-Picrylhydrazyl (DPPH) Free Radical Scavenging Assay

The DPPH free radical scavenging activity of various extracts of C. fistula bark was carried out, and the results were expressed in IC50 (half-maximal inhibitory concentration in μg/ml) with respect to butylated hydroxy toluene (BHT) [22].

2.3.2. Ferric Reducing Ability Power Assay (FRAPS)

FRAPSs of all of the above extracts were tested at five diverse strengths (20, 40, 60, 80, and 100 μg/ml) with respect to ascorbic acid (AA) [23].

2.4. Animal Experimental Studies

Both male and female albino Wistar rats, weighing 180 ± 20 g body weight (b.w.), were chosen at random for the animal activity and were quarantined for one week when first received in the institutional animal house facility, and health of animals was checked regularly. Animals were housed in standard-sized polypropylene cages fitted with a filter top using envelope bedding under controlled temperature conditions (23 ± 2°C), humidity (40 ± 10%), and 12-hour artificial dark and light cycles (7 : 00 AM to 7 : 00 PM). Animals were fed with a standard feed based on pellets, and purified water was given ad libitum throughout the experimental period as per Committee for the Purpose of Control And Supervision of Experiments on Animals (CPCSEA) guidelines. The research study was conducted postclearance from the Institutional Animal Ethics Committee (IAEC) of Amar Shaheed Baba Ajit Singh Jujhar Singh Memorial College of Pharmacy, BELA, Ropar vide approval no. ASCB/IAEC/03/11/053. Five rats per cage were allowed to acclimate for one week in advance of the experiments.

2.5. Acute Oral Toxicity Studies

Acute oral toxicity studies were conducted as per OECD (Organisation for Economic Co-operation and Development) guidelines 423.

2.6. Myocardial Infarction Model and Study Design

The myocardial infarction was triggered using isoproterenol hydrochloride (ISP) injection (dose 5.25 and 8.5 mg/kg b.w.). The albino rats were randomly assorted into six groups of seven animals each using single blind mode. Group I (control) rats received normal saline solution through intragastric intubation and served as a control. Group II (ISP) rats were administered ISP (5.25 and 8.5 mg/kg b.w. in normal saline) intraperitoneally (i.p.) twice at 24-hour intervals on days 8 and 9. The rats in Group III (CFME-LD per se) received the methanolic extract of Cassia fistula stem bark at lower dose, that is, 250 mg/kg post-oral (p.o.) daily for up to 9 days. Group IV (CFME-HD per se) rats received the methanolic extract of Cassia fistula stem bark at higher dose, that is, 500 mg/kg p.o. (per oral) for 9 days. Group V (CFME-LD + ISP) received the methanolic extract of Cassia fistula stem bark (250 mg/kg, p.o.) daily for 9 days and ISP on days 8 and 9. Group VI (CHME-HD + SP) rats received the methanolic extract of Cassia fistula stem bark (500 mg/kg, p.o.) for 9 days and ISP on days 8 and 9. The blood sampling was carried out on the last day for biochemical estimation, and hemodynamic parameters were evaluated. The experiment ended after 9 days, and all animals were killed with cervical decapitation after a one-night fast. Figure 2 illustrates the schematic representation of the experimental design and its treatment regime.

Figure 2

Schematic demonstration of the experimental design. CFME: Cassia fistula methanolic extract of stem bark; ISP: isoproterenol.

2.6.1. Biochemical Analysis

(1) Blood and Tissue Sampling. The rats were anesthetized using urethane injection (0.4 g/kg, i.p.). 2 ml of blood was collected in heparinized vials through retro-orbital plexus. The vials were held at room temperature for 15 minutes and then centrifuged at 3000 revolutions per minute for 10 minutes. The collected serum was stored at −80°C for future analysis.

(2) Assessment of Oxidative Stress Biomarkers in Myocardial Tissue. The whole heart was harvested, pulverized (1 cm3), homogenized (REMI homogenizer motors, Mumbai) in 0.05 M ice-cold phosphate-buffered saline (PBS), and centrifuged (3000 × g) for 10 minutes at 4°C. The accumulated supernatant was kept for the assessment of the antioxidant activities such as lipid peroxidation [24] and reduced glutathione (GSH) [25] by the standard methods.

(3) Assessment of Hemodynamic Parameters. Rats were anesthetized at 37°C with 25% urethane (1.5 g/kg, i.p.). To execute tracheotomy, a ventral midline incision was made in the neck. A polyethylene tube with an internal diameter of 0.30 mm and an outside diameter of 0.40 mm, coupled to a three-way cannula, was used to cannulate the left carotid artery. The cannula was heparinized (300 IU/ml) and linked to an AD Instruments POWER LAB 4/30 system (NSW, Australia) via a pressure transducer to monitor systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), and heart rate (HR).

(4) Assessment of Myocardial Infarction. The hearts of the experimental rats were removed after cervical dislocation using anaesthesia. On 10th day of the study, a 2,3,5-triphenyl tetrazolium chloride (TTC) test was carried out as per the procedure of Fishbein et al. [26]. Cold water was used to wash the cardiac samples, preventing the deterioration of the tissue. The left ventricle was separated and cut into 0.01-cm-thick slices transversely using a microtome cutter. The heart slices were equally immersed in prewarmed TTC solution (1 percent in phosphate buffer) in a covered, darkened glass plate and incubated at 37–40°C for 30–45 minutes. The heart slices were rolled over one or twice to ensure that they were completely immersed in 1 cm of TTC solution. After incubation, the heart slices were transferred to fixing solution [27].

2.6.2. Histopathological Studies

The cardiac tissue samples were washed in PBS solution and secured in 10% neutral buffered formalin for 24 hours at room temperature for histopathological investigation. The samples were then dehydrated using a gradient of ethanol concentrations (70–100%), cleaned in xylene, and entrenched in paraffin wax. Permanent slides were equipped with 5-μm segments (using a microtome cutter) and tainted with hematoxylin and eosin (H&E) stains, enclosed using transparent concealment slips and artificial resin DPX (a mixture of distyrene, a plasticizer, and xylene). Under a light microscope at 100 magnifications, the pathologic structural alterations were studied [28].

2.7. Statistical Analysis

The data were analyzed using a one-way analysis of variance (ANOVA) followed by Tukey's multiple comparison test, using GraphPad Prism 5.0 software package. A value of p < 0.05 was considered to be significant. The data were expressed as mean ± standard error of mean (S.E.M.), respectively.

3. Results

3.1. Percentage Yield

Percentage yield of 4.12%, 4.88%, 8.87%, 17.56%, and 9.45% (w/w) was obtained from various extracts of PE, CE, EE, ME, and AE, respectively.

3.2. In Vitro Antioxidant Activity of Various Extracts

The in vitro DPPH free radical scavenging activity of diverse extracts revealed that the reducing power of the methanolic extract of Cassia fistula (CFME) stem bark is the highest with an IC50 value of 3.07 μg/ml as compared to standard BHT (2.91 μg/ml). The radical scavenging activity in the various extracts decreased in the following order ME > EE > CE > AE > PE as shown in Figure 3(a). Furthermore, the reducing power assay of all the abovementioned extract was analyzed at the diverse strengths (20, 40, 60, 80, and 100 μg/ml). The methanolic extract of Cassia fistula (CFME) exhibited a good reducing power at 100 μg/ml concentrations as shown in Figure 3(b). As methanolic extract (CFME) exhibited the best antioxidative power, it was taken for further in vivo studies.

Figure 3

Antioxidant effect of different extracts of Cassia fistula bark against (a) DPPH free radical scavenging assay and (b) reducing power assay. Ascorbic acid (AA), butylated hydroxy toluene (BHT), petroleum ether (PE), chloroform (CE), ethyl acetate (EE), methanol (ME), and aqueous extracts (AE).

3.3. Acute Oral Toxicity Studies

On the basis of 14-day observations, the 2000 mg/kg of methanolic extract of the Cassia fistula stem bark was revealed to be safer where no animal mortality is seen; therefore, the one-fourth and one-eighth of the maximum tolerated dose was chosen for further study.

3.4. Per Se Effects of CFME

Due to the high polyphenolic content and strong antioxidant potential, CFME was explored for cardioprotective activity. CFME at 250 mg/kg and 500 mg/kg of b.w. administered in Groups III and IV for a duration of 9 days did not show considerable changes in biochemical (AST, ALT, TG, TC, GSH, SOD, and MDA), hemodynamic, assessment of myocardium, and histopathological markers as equated to the normal control collection.

3.5. CFME Prevents the ISP-Induced Derangement of Serum Biomarkers

The acquaintance of ISP significantly (p < 0.001) amplified the serum levels AST, ALT, TG, and TC in rats as compared to the administration of saline in control groups. However, Groups V and VI showed a significantly reduced AST (p < 0.05, 0 < 0.01) and ALT (p < 0.01, 0 < 0.01) activity, and TG (p < 0.05, 0 < 0.05) and TC (p < 0.01, 0 < 0.01) concentrations as compared to Group II (Table 1).

Table 1

Effect of Cassia fistula methanolic extract (CFME) on serum biomarkers after ISP-induced myocardial necrosis.

Groups	Triglycerides (TG) (mg/dl)		Total cholesterol (TC) (mg/dl)		AST (IU/L)		ALT (IU/L)
	0 day	10th day	0 day	10th day	0 day	10th day	0 day	10th day
Control	38.001 ± 1.447	39.142 ± 1.335	37.002 ± 1.690	42.141 ± 1.565	89.142 ± 2.781	83.431 ± 1.951	40.431 ± 0.812	39.141 ± 0.671
ISP	39.141 ± 2.473	54.712 ± 1.409∗	36.291 ± 2.008	56.431 ± 1.478∗	91.862 ± 1.317	116.122 ± 1.336∗	39.711 ± 0.968	55.862 ± 1.438∗
CFME-LD per se	34.862 ± 1.056	38.001 ± 1.363	37.712 ± 1.426	40.711 ± 0.808	89.291 ± 1.229	83.433 ± 2.487	39.863 ± 0.911	37.143 ± 1.262
CFME-HD per se	38.002 ± 1.345	38.862 ± 1.654	35.292 ± 1.796	41.432 ± 1.798	86.713 ± 1.304	80.863 ± 2.176	40.002 ± 1.113	39.572 ± 1.131
CFME-LD + ISP	37.291 ± 1.835	47.431 ± 2.192	37.001 ± 1.746	49.003 ± 0.6901∗∗	88.433 ± 2.171	107.421 ± 0.948∗∗∗	39.293 ± 1.409	50.143 ± 1.353∗∗∗
CFME-HD + ISP	37.002 ± 1.732	46.431 ± 0.896	36.862 ± 2.334	48.433 ± 1.131∗∗	86.711 ± 1.128	105.325 ± 1.874∗∗	38.715 ± 0.892	48.294 ± 0.993∗∗

ISP: Isoproterenol; CFME-LD: CFME at lower dose (250 mg/kg); CFME-HD: CFME at higher dose (500 mg/kg). Data are expressed as mean value ± S.E.M (n = 7) analyzed using one-way ANOVA followed by Tukey's multiple comparison test. p < 0.001 when compared to the control group, p < 0.05, p < 0.01 when compared to the ISP control group.

3.6. CFME Averts the ISP-Induced Oxidative Stress

Group II showed a significantly (p < 0.001) decreased GSH and SOD activity, whereas MDA levels were significantly (p < 0.001) increased as associated with saline control Group I. However, in this study, Groups V and VI displayed a substantial intensification in the GSH (p < 0.05, p < 0.01) and SOD (p < 0.05, p < 0.01) activity, whereas MDA levels were significantly (p < 0.05, p < 0.05) declined when juxtaposed with Group II (Table 2).

Table 2

Effect of Cassia fistula methanolic extract (CFME) on antioxidant parameters after ISP-induced myocardial necrosis.

Groups	GSH (μmol/g)	MDA (mmol/ml)	SOD (U/mg)
Control	7.733 ± 0.777	4.473 ± 0.302	14.621 ± 0.494
ISP	1.600 ± 0.267∗	10.131 ± 0.468∗	7.887 ± 0.599∗
CFME-LD per se	6.933 ± 0.499	3.940 ± 0.179	14.321 ± 0.315
CFME-HD per se	6.933 ± 0.499	3.740 ± 0.549	15.431 ± 0.249
CFME-LD + ISP	4.267 ± 0.499∗∗∗	7.460 ± 0.411∗∗∗	10.431 ± 0.631∗∗∗
CFME-HD + ISP	4.533 ± 0.533∗∗	7.753 ± 0.684∗∗	11.021 ± 0.464∗∗

ISP: Isoproterenol; CFME-LD: CFME at lower dose (250 mg/kg); CFME-HD: CFME at higher dose (500 mg/kg). Data are expressed as mean value ± S.E.M (n = 7) analyzed using one-way ANOVA followed by Tukey's multiple comparison test. p < 0.001 when compared to the control group, p < 0.05, p < 0.01 when compared to the ISP control group.

3.7. CFME Prevented ISP-Induced Hemodynamic Derangements

Group II rats showed a significant (p < 0.001) decrease in systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP) as compared to Group I. Despite the fact that the Group II rats had a higher heart rate (HR), the difference was not statistically significant. In comparison with Group II rats, there was no substantial variance in AP, SAP, MAP, and DAP levels in Group V rats. Group VI showed that the levels of AP (p < 0.01), SAP (p < 0.05), MAP (p < 0.05), and DAP (p < 0.05) were significantly increased as compared to Group II rats, whereas there was no significant alteration in HR between both Groups V and VI (Table 3).

Table 3

Effects of Cassia fistula methanolic extract (CFME) on hemodynamic parameters after ISP-induced myocardial necrosis.

Group	AP (mmHg)	SAP (mmHg)	DAP (mmHg)	MAP (mmHg)	HR (per min)
Control	112.502 ± 0.772	126.903 ± 1.321	99.241 ± 0.971	110.722 ± 0.691	399.723 ± 1.732
ISP	95.152 ± 1.911∗	94.543 ± 0.953∗	79.512 ± 0.602∗	90.181 ± 1.413∗	408.112 ± 1.443
CFME-LD per se	110.521 ± 1.382	126.822 ± 1.433	100.723 ± 2.333	111.012 ± 0.981	388.522 ± 2.250
CFME-HD per se	110.721 ± 1.523	129.844 ± 0.803	103.933 ± 1.714	114.521 ± 1.149	392.122 ± 3.851
CFME-LD + ISP	100.722 ± 1.413	94.082 ± 1.772	83.801 ± 0.562	95.101 ± 1.172	405.221 ± 1.773
CFME-HD + ISP	102.443 ± 1.154∗∗	101.021 ± 1.432∗∗∗	86.372 ± 1.322∗∗∗	96.391 ± 2.063∗∗∗	397.344 ± 1.134

ISP: Isoproterenol; CFME-LD: CFME at lower dose (250 mg/kg); CFME-HD: CFME at higher dose (500 mg/kg); AP: arterial pressure; SAP: systolic arterial pressure, DAP: diastolic arterial pressure; MAP: mean arterial pressure; HR: heart rate. Data are expressed as mean value ± S.E.M (n = 7) analyzed using one-way ANOVA followed by Tukey's multiple comparison test. p < 0.001 when compared to the control group, p < 0.05, p < 0.01 when compared to the ISP control group.

3.8. Assessment of Myocardial Infarction

When compared to the control group, ISP-treated rats had a higher percentage of mean infarct size (Table 4). When compared to ISP-treated rats (Group II), Groups V and VI (CFME-pretreated animals) had a somewhat small infarct size and less staining. When compared to the control group (Group I), the study Groups III and IV had no significant effect on heart tissue. The TTC test was supposed to provide the following results: normal myocardium and/or normal myocardium colored bright red. As illustrated in Figure 4, the ischemic myocardium became pale grey, greyish yellow, or uncolored, and fibrous scars became white.

Table 4

Assessment of percent (%) myocardial infarction using TTC staining.

Group	Mean weight of tissue slice (mg)	Mean weight of stained portion (mg)	Mean weight of unstained portion (mg)	% Infarction
Control	63.721 ± 1.223	63.722 ± 1.353	0.00	0.00
ISP	60.523 ± 2.113	24.433 ± 1.926	36.532 ± 0.822	60.32
CFME-LD per se	54.312 ± 1.522	54.322 ± 0.063	0.00	0.00
CFME-HD per se	66.223 ± 1.355	66.224 ± 0.263	0.00	0.00
CFME-LD + ISP	61.334 ± 1.934	31.343 ± 1.036	28.632 ± 0.922	46.64
CFME-HD + ISP	66.622 ± 1.633	42.324 ± 1.073	24.333 ± 1.002	36.42

Figure 4

Assessment of myocardial infarction using TTC staining technique in different groups of animals. ISP: Isoproterenol; CFME-LD: CFME at lower dose (250 mg/kg); CFME-HD: CFME at higher dose (500 mg/kg).

3.9. Histopathological Analysis

When compared to the ISP-induced Group II animal's heart, the histopathological findings of the myocardial-infracted heart pretreated with CFME-LD (250 mg/kg) and CFME-HD (500 mg/kg) demonstrated a well-preserved normal morphology of cardiac muscle with little necrosis. The histo-architecture of the ISP-treated group clearly showed signs of cell infiltration, myocardial phagocytosis, and extravasations of RBCs (red blood cells) followed by characterized by inflammation, oedema, and necrosis (Figure 5), whereas the rats treated with methanolic 250 and 500 mg/kg dose followed by ISP administration indicated the protection from myocardial injury evidenced by abated oedema, inflammation, and cellular necrosis. When compared to the normal group animals, Groups III and IV getting a low and a high dose of Cassia fistula stem bark extract had a similar histo-architecture (Figure 5).

Figure 5

Histopathological observation (magnification at ×100) of ISP-induced myocardial infarction in different groups of the animal model. ISP: Isoproterenol; CFME-LD: CFME at lower dose (250 mg/kg); CFME-HD: CFME at higher dose (500 mg/kg). The arrow mark represents inflammatory accumulation.

4. Discussion

Heart is one of the most imperative organs of the human organ system pumping blood throughout the body. Even minor imbalances in heart functioning leads to the arousal of acute and chronic complications. As per one of the WHO (World Health Organisation) reports, heart-related diseases including inflammations and strokes will become the prime cause of mortality and disability globally by 2020 [29]. Myocardial infarction is one of the leading cardiovascular diseases (CVD) nowadays, which needs urgent concern over its treatment. An irreversible damage to myocardial occurs during infarction due to the starvation of myocardial cells for oxygen, which further leads to myocardial necrosis. Various allopathic drugs such as Corlanor, Entresto, pyrvinium pamoate, conivaptan, and tolvaptan used for heart failure approved by U.S. FDA (Food and Drug Administration) have shown severe side effects including bradycardia, hypertension, atrial fibrillation, and renal impairment. [30-36]. It was researched that most of the allopathic medicines for myocardial infarction themselves lead to cardiotoxicity instead of treatment due to their free radical generating ability. Therefore, safe and efficient herbal drugs and formulations are the need of the present era. In this context, plant-based medicine may prove to be better intervention for investigating the cardioprotective potential of various phytoconstituents and plant extracts through different pharmacological models.

This study investigated stem bark extracts of Cassia fistula for cardioprotective effect using the chemical-based ISP-induced myocardial necrosis model in rats. Cassia species are known for their antioxidative and cardioprotective potential enlisted in various treaties, traditional medicine books, and pharmacopoeias [11]. Cassia siamea Lamk. (leaves) and Cassia fistula (stem bark, flowers) has been already reported for cardiac potential via doxorubicin-induced cardiotoxicity model [19, 21]. However, doxorubicin induced in hearts leads to oxidative stress, forming toxic adducts causing acute cardiotoxicity and final death; we inspected cardiotoxic effects in the ISP-based induction model as ISP shows progressive damage in both fractionated and larger doses for acute damage to the heart in contrast to doxorubicin. Also, the morphological and physiological changes brought by ISP were found relatively similar to human myocardial infarction. That is why ISP-based cardiac injury model is better and nowadays used widely for both acute and chronic cardiotoxicity and basically for the intervention of various phytoconstituents, herbal products, and novel biocomponents [37-39].

In the present research, polarity-based successive extractions were carried out, of which the highest yield was found in the methanol extract (ME) followed by AE > EE > CE > PE. Further in vitro antioxidant assays were carried out for all the five extracts using the DPPH free radical scavenging method and reducing power assay. In both the assays, the methanol extract showed a significant antioxidant activity as compared to EE > CE > AE > PE, respectively. Based on the in vitro results and documented literature of Cassia fistula bark, the methanol extract (CFME) was further accounted for in vivo studies.

It was found that on the induction of myocardial infarction by ISP in rats given on the 8th and 9th days, the level of all serum biomarkers was significantly increased (p < 0.001) as compared to saline-treated control groups (Group I) as well as Groups III and IV (CFME per se groups). The changes brought in serum biomarker concentrations were due to ISP-induced myocardial injury, which alters cardiac cells' membrane permeability, thus releasing marker enzymes in the blood stream [40-43]. The levels of AST and ALT reported an abnormal increase in concentration, that is, 39.15% and 42.71%, respectively. However, in case of Groups V and VI, a significant decrease in AST, ALT, TG, and TC concentration was observed with respect to Group II due to CFME low and high doses, respectively. Also, a significant decrease in the levels of AST (7.49% at LD; 9.3% at HD) and ALT (10.23% at LD; 13.55% at HD) was reported, respectively, in CFME-pretreated rats that signifies that the membrane leakage-based cardiotoxicity can be minimized through CFME pretreatments.

Also, an increase in the levels of total cholesterol (39.78%) and triglycerides was observed in ISP-treated rats. It may be due to cyclic AMP (adenosine monophosphate) alterations in cardiac cells, which further leads to myocardial infarction making it a vicious circle for other cardiovascular diseases [44, 45]. However, CFME-pretreated groups exhibited a significant reduction in both cholesterol (13.30% at LD; 15.13% for HD) and triglyceride (13.16% at LD; 14.17% for HD) levels, respectively. This lipid-reducing effect of Cassia fistula bark denotes its hypo-lipidemic property, which is a boon in cardiovascular diseases (CVDs).

As discussed above that ISP induces oxidative stress chemically in the heart that in turn leads to the decline of both SOD activity and GSH level, while plasma TBARS levels shoot up [46-48]. Also, from the literature it was found that both GSH and SOD are inter-related to lipid peroxidation, and thus, GSH or SOD depletion leads to a rise in lipid peroxidation and vice versa [46-48]. Our study reported that upon ISP induction, a considerable drop in the GSH level by 79.30% and 46.05% in the SOD activity was observable; however, CFME-pretreated rats showed a significant increase in both the GSH content (62% at LD; 64% at HD) and SOD activity (32% at LD; 39% at HD) with respect to the Group II. Further on performing the TBRAS assay, it was found that a significant rise in TBRAS levels (55.84%) in ISP-induced rats was abrogated in CFME-pretreated rats (TBRAS level decreased by 23.46% and 26.35% by lower and higher doses 250 and 500 mg/kg, respectively).

Previous literature research reported the effect of ISP-induced myocardial necrosis in rats by alterations in systolic and diastolic functions in the heart that were similar to the present study as a substantial decrease in their AP (15.4%), SAP (25.5%); DAP (19.8%), and MAP (18.5%) was observed in ISP-induced rats. CFME at higher dose demonstrated a significant improvement in AP, SAP, DAP, and MAP by 7.6%, 6.8%, 8.6%, and 6.8%, respectively, while no significant difference in heart pressure was found on the administration of CFME at lower dose. According to a report by Rona and Zhou, an increased heart rate give rise to more oxygen demand and consumption in the body, which further aggravates myocardial necrosis [3, 48]. However, present work reports no significant variation in the heart rate of the control group in comparison with experimental groups. In histopathological studies, it was found that pretreatment with CFME in ISP-induced rats exhibited moderate necrosis and kept normal morphology of cardiac muscles significantly by reducing infarct size as compared to the other groups.

The present research justifies the cardioprotective effect of Cassia fistula bark methanolic extract in ISP-induced chemical model of cardiotoxicity. CFME showed a significant reduction in myocardial infarction in rats without producing any serious side effects. The present ISP model was found better in comparison with the earlier used doxorubicin model in evaluating the cardioprotective properties of Cassia fistula methanolic stem bark extract. Hence, natural plant-based products containing secondary metabolites such as glycosides, flavonoids, and carotenoids [49] can play an important role in healthcare settings that has the potential to alleviate many of the adverse effects and drug-related complications in patients.

5. Conclusion

The Cassia fistula is a bioremedial plant known for the abolition of a number of diseases. The extract of its stem bark is reported to contain fistucacidin (3,4,7,8,4′-pentahydroxyflavon), β-sitosterol, lupeol leucocyanidin, hexacosanol oxyanthraquinone, dihydroxyanthraquinone, and flavonol glycosides. Numerous bioactive constituents present in the plant contributed to enhance its medicinal value. The methanolic extract of Cassia fistula in our study revealed that it possesses marked antioxidant and antihyperlipidemic activity. The extract had no significant effect on the hemodynamic parameters; that is, the heart rate remains stable. Altogether, it can be concluded that the methanolic extract of Cassia fistula has a potent cardioprotective effect via adrenergic inhibition. The phytoconstituents responsible for the cardioprotective effect might be the area of research in future.