Cardioprotective Activity of Hibiscus sabdariffa Flower Extract in Isoproterenol-Induced Myocardial Infarction in Rats

1.1Cardiovascular Diseases and Myocardial Infarction

Cardiovascular diseases (CVDs) represent one of the leading causes of morbidity and mortality worldwide and continue to pose a major public health challenge. These disorders include hypertension, coronary artery disease, heart failure, stroke, and myocardial infarction. Among them, myocardial infarction (MI), commonly referred to as a heart attack, is considered one of the most severe and life-threatening cardiovascular conditions. MI occurs due to the interruption or reduction of blood flow to the myocardium, usually caused by blockage of the coronary arteries. The deprivation of oxygen and nutrients results in ischemic injury and irreversible necrosis of cardiac muscle tissue.^[1]

The prevalence of myocardial infarction has increased significantly because of changing lifestyles, unhealthy dietary habits, stress, obesity, diabetes mellitus, smoking, and lack of physical activity. Although modern diagnostic and therapeutic approaches such as thrombolytic therapy, angioplasty, and coronary artery bypass surgery have improved patient survival, myocardial infarction remains associated with high mortality and long-term complications. Damage to cardiac tissue following MI often leads to impaired ventricular function, arrhythmias, cardiac remodeling, and eventually heart failure. Therefore, there is a continuous need to explore safer and more effective therapeutic approaches for the prevention and management of myocardial injury.

Fig :1 Cardiovascular Diseases and Myocardial Infarction

Experimental models are widely used to study the pathogenesis of myocardial infarction and evaluate cardioprotective agents. Among these, isoproterenol-induced myocardial infarction in rats is one of the most commonly employed models because it closely mimics several biochemical and pathological alterations observed in human MI. Isoproterenol, a synthetic β-adrenergic agonist, produces severe stress on the myocardium, leading to oxidative damage, necrosis, and inflammatory changes in cardiac tissue. ^[2]

1.2 Pathophysiology of MI: Role of Oxidative Stress, Lipid Peroxidation, and Inflammation

The pathophysiology of myocardial infarction involves a complex interplay of oxidative stress, inflammation, calcium overload, mitochondrial dysfunction, and apoptotic pathways. During myocardial ischemia and subsequent reperfusion, there is excessive generation of reactive oxygen species (ROS) such as superoxide radicals, hydroxyl radicals, and hydrogen peroxide. These highly reactive molecules damage cellular membranes, proteins, nucleic acids, and enzymes, thereby contributing to myocardial cell death.

One of the major consequences of oxidative stress is lipid peroxidation, which refers to the oxidative degradation of membrane lipids. Lipid peroxidation disrupts membrane integrity and increases cellular permeability, ultimately causing leakage of intracellular enzymes such as creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and cardiac troponins into the bloodstream. Increased levels of these biomarkers are indicative of myocardial injury. ^[3]

Fig:2 Pathophysiology of MI:

Inflammation also plays a critical role in the progression of myocardial infarction. Ischemic injury activates inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukins, and nuclear factor-kappa B (NF-κB), which further aggravate tissue damage and promote infiltration of inflammatory cells into the myocardium. Persistent inflammation contributes to fibrosis, ventricular remodeling, and deterioration of cardiac function.

In addition to oxidative stress and inflammation, mitochondrial dysfunction and apoptosis significantly contribute to myocardial injury. Excessive ROS production impairs mitochondrial respiration and triggers apoptotic signaling pathways, leading to programmed cell death of cardiomyocytes. Therefore, therapeutic agents possessing antioxidant and anti-inflammatory properties may help attenuate myocardial damage and improve cardiac function. ^[4]

1.3 Need for Natural Cardioprotective Agents

Conventional drugs used in the treatment of cardiovascular diseases, including β-blockers, calcium channel blockers, nitrates, and thrombolytic agents, are effective but often associated with adverse effects, high cost, and limited long-term protection against oxidative stress-mediated cardiac damage. Consequently, attention has shifted toward natural products and medicinal plants as potential sources of cardioprotective agents.

Medicinal plants contain a wide variety of bioactive phytoconstituents such as flavonoids, phenolic compounds, alkaloids, tannins, saponins, and anthocyanins that exhibit potent antioxidant, anti-inflammatory, antihyperlipidemic, and free radical scavenging activities. These phytochemicals help stabilize cellular membranes, reduce oxidative stress, inhibit lipid peroxidation, and protect cardiomyocytes from ischemic injury.

Among various medicinal plants, Hibiscus sabdariffa has gained considerable scientific attention because of its significant pharmacological properties. The plant is rich in anthocyanins, flavonoids, hibiscus acid, ascorbic acid, and polyphenolic compounds, which contribute to its antioxidant and cardioprotective activities. Several experimental studies have demonstrated that Hibiscus sabdariffa possesses antihypertensive, hypolipidemic, anti-inflammatory, and free radical scavenging effects. These properties may help in reducing myocardial damage caused by oxidative stress and inflammation. ^[5]

The growing interest in herbal medicine and natural antioxidants has encouraged researchers to investigate the cardioprotective potential of Hibiscus sabdariffa in experimental models of myocardial infarction. Therefore, the present study aims to evaluate the cardioprotective activity of Hibiscus sabdariffa flower extract against isoproterenol-induced myocardial infarction in rats through biochemical, antioxidant, and histopathological assessments.

2. HIBISCUS SABDARIFFA: BOTANICAL DESCRIPTION AND TRADITIONAL USES

2.1 Botanical Description

Hibiscus sabdariffa L., commonly known as roselle or “Gongura” in India, belongs to the family Malvaceae. It is an annual or perennial shrub that grows up to 2–2.5 meters in height, with deep green, lobed leaves and conspicuous red calyces surrounding small yellow flowers. The plant produces fleshy, red calyces that are rich in bioactive compounds and are commonly used for medicinal and culinary purposes. Native to tropical regions of Africa, HS is now widely cultivated across Asia, the Americas, and parts of the Middle East due to its adaptability and economic importance. ^[6]

The plant parts, including leaves, flowers, and calyces, have distinct morphological and phytochemical characteristics. The calyces are particularly valued for their deep red color, acidic taste, and high content of anthocyanins and organic acids. Seeds are small, brown, and often used for oil extraction, while the leaves are consumed as a vegetable in several regions.

Fig: 3 Hibiscus sabdariffa:

2.2 Traditional Uses

Hibiscus sabdariffa has been widely used in traditional systems of medicine for many centuries because of its diverse therapeutic properties. Different parts of the plant, especially the calyces, are commonly utilized for the preparation of herbal beverages, syrups, teas, jams, and medicinal formulations. In many tropical and subtropical countries, the plant is valued not only as a nutritional ingredient but also as a natural remedy for several health disorders. The traditional applications of Hibiscus sabdariffa indicate its importance in folk and herbal medicine.

Cardiovascular Health

Traditionally, Hibiscus sabdariffa is extensively used for maintaining cardiovascular health. Herbal teas prepared from its calyces are commonly consumed to reduce elevated blood pressure and improve circulation. The plant is believed to strengthen heart function and promote healthy blood vessels. In traditional medicine, it has also been used for controlling cholesterol levels and reducing the risk of cardiovascular complications. The presence of antioxidant-rich phytoconstituents in the plant may contribute to its protective effects on the heart. ^[7]

Hepatoprotective Activity

Hibiscus sabdariffa has also been traditionally employed as a natural remedy for liver disorders. Herbal preparations of the plant are believed to support liver function and assist in detoxification processes. In folk medicine, it is commonly used to protect the liver from harmful substances and improve overall hepatic health. The antioxidant properties of the plant are thought to help in reducing oxidative stress and preventing liver damage.

Antimicrobial Effects

The plant has long been used in traditional medicine for the treatment of microbial infections and wounds. Extracts and decoctions of Hibiscus sabdariffa are believed to possess antibacterial and antifungal activities. In several cultures, the plant is applied externally on wounds and skin infections to promote healing and prevent microbial growth. These traditional claims have encouraged scientific studies investigating its antimicrobial potential. ^[8]

Digestive Health

Traditionally, Hibiscus sabdariffa is used to improve digestive function and maintain gastrointestinal health. It is commonly employed as a mild laxative to relieve constipation and promote bowel movement. Herbal drinks prepared from the calyces are also used to stimulate appetite and aid digestion. In traditional practices, the plant is considered beneficial for maintaining stomach health and reducing digestive discomfort.

Antipyretic and Anti-Inflammatory Uses

In many traditional systems of medicine, Hibiscus sabdariffa is used for reducing fever and inflammation. The plant is often administered in the form of herbal teas or decoctions to provide a cooling effect to the body during febrile conditions. It is also traditionally used to relieve inflammatory conditions and associated pain. The anti-inflammatory and antioxidant properties of the plant may be responsible for these therapeutic effects. ^[9]

Ethnomedicinal Importance

The wide range of traditional uses of Hibiscus sabdariffa demonstrates its significant ethnopharmacological value. The extensive use of this plant in folk medicine has provided a scientific basis for modern pharmacological investigations. Recent research studies have focused on evaluating its antioxidant, anti-inflammatory, antihyperlipidemic, hepatoprotective, and cardioprotective activities. These findings support the traditional claims and suggest that Hibiscus sabdariffa may serve as a promising natural therapeutic agent for the management of cardiovascular and other chronic diseases. ^[10]

3. PHYTOCHEMISTRY AND PHYTOPHARMACOLOGY OF HIBISCUS SABDARIFFA

3.1 Phytochemistry

Hibiscus sabdariffa is a medicinal plant well known for its rich phytochemical composition and wide range of therapeutic properties. Different parts of the plant such as calyces, flowers, leaves, and seeds contain numerous biologically active constituents that contribute to its pharmacological activities. Among these plant parts, the calyces are considered the most important due to their high concentration of polyphenolic compounds and natural antioxidants. The presence of these phytochemicals is mainly responsible for the antioxidant, anti-inflammatory, antihyperlipidemic, hepatoprotective, and cardioprotective effects of the plant. ^[11]

Anthocyanins

Anthocyanins are the major pigment compounds present in Hibiscus sabdariffa and are responsible for the characteristic deep red coloration of the calyces. The principal anthocyanins identified in the plant include delphinidin-3-sambubioside and cyanidin-3-sambubioside. These compounds possess strong antioxidant activity and help in neutralizing reactive oxygen species generated during oxidative stress. Anthocyanins also protect cellular membranes from lipid peroxidation and reduce oxidative damage in tissues, including the myocardium. Due to these properties, they are considered important contributors to the cardioprotective activity of Hibiscus sabdariffa. ^[12]

Flavonoids

Hibiscus sabdariffa contains several flavonoids such as quercetin, gossypetin, and hibiscetin. Flavonoids are well known for their antioxidant and anti-inflammatory activities. These compounds help inhibit inflammatory mediators, reduce oxidative stress, and stabilize cellular membranes. In addition, flavonoids exhibit anti-apoptotic effects by protecting cells from programmed cell death induced by free radicals and inflammatory cytokines. Their ability to improve vascular function and reduce tissue injury makes them beneficial in cardiovascular disorders.

Phenolic Acids

The plant also contains significant amounts of phenolic acids including gallic acid and chlorogenic acid. These phenolic compounds act as potent free radical scavengers and play an essential role in preventing oxidative damage. They protect lipids, proteins, and nucleic acids from oxidation and help reduce lipid peroxidation in biological membranes. Phenolic acids are also associated with anti-inflammatory and antihyperlipidemic activities, which further support the therapeutic potential of Hibiscus sabdariffa in cardiovascular diseases. ^[13]

Organic Acids

Organic acids such as hibiscus acid, citric acid, and tartaric acid are important constituents of Hibiscus sabdariffa. These compounds contribute to the sour taste of the calyces and possess antioxidant and metabolic regulatory properties. Hibiscus acid has been reported to exhibit protective effects against oxidative stress and may help regulate lipid metabolism and glucose homeostasis. Citric acid and tartaric acid also contribute to the plant’s antioxidant potential and improve overall metabolic function.

Polysaccharides

Hibiscus sabdariffa contains water-soluble polysaccharides and dietary fibers that may provide various health benefits. These compounds are known to possess immunomodulatory and antihypertensive activities. Polysaccharides may help improve gastrointestinal health, enhance immune response, and regulate blood pressure. Their presence also contributes to the nutritional and medicinal value of the plant. ^[14]

Other Phytoconstituents

In addition to the major phytochemicals, Hibiscus sabdariffa also contains sterols, saponins, tannins, and essential oils. Sterols are known for their cholesterol-lowering properties, while saponins exhibit antioxidant and anti-inflammatory activities. Tannins contribute to antimicrobial and astringent effects, whereas essential oils may provide additional therapeutic benefits. These compounds collectively enhance the pharmacological profile of the plant and support its traditional medicinal uses.

The diverse phytochemical composition of Hibiscus sabdariffa provides a strong scientific basis for its pharmacological activities, especially its antioxidant and cardioprotective potential. The synergistic action of these bioactive constituents may help protect against myocardial injury and other oxidative stress-related disorders. ^[15]

Table 1: Major Phytoconstituents of Hibiscus sabdariffa and Their Biological Activities

3.2 Phytopharmacology

Hibiscus sabdariffa has been extensively investigated for its diverse pharmacological activities. Several in vitro and preclinical studies have demonstrated that the plant possesses antioxidant, anti-inflammatory, cardioprotective, antihypertensive, antihyperlipidemic, hepatoprotective, and nephroprotective properties. These pharmacological effects are mainly attributed to the presence of anthocyanins, flavonoids, phenolic acids, and other polyphenolic compounds. The combined action of these phytoconstituents plays an important role in protecting tissues against oxidative stress and inflammatory damage, especially in cardiovascular disorders. ^[16]

1. Antioxidant Activity

One of the most significant pharmacological properties of Hibiscus sabdariffa is its potent antioxidant activity. The plant contains high levels of anthocyanins, flavonoids, and phenolic acids that effectively neutralize reactive oxygen species (ROS) and free radicals generated during oxidative stress. Excessive ROS production is one of the major causes of myocardial injury and cellular damage in cardiovascular diseases.

The antioxidant constituents of Hibiscus sabdariffa help prevent lipid peroxidation of cellular membranes and protect cardiomyocytes from oxidative injury. These compounds also stabilize cell membranes and preserve the structural integrity of myocardial tissue. By reducing oxidative stress, the plant may help improve cardiac function and minimize tissue damage during myocardial infarction. ^[17]

2. Anti-inflammatory Activity

Hibiscus sabdariffa also exhibits remarkable anti-inflammatory activity due to the presence of flavonoids and polyphenolic compounds. These phytoconstituents inhibit the production of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), which are involved in the progression of myocardial inflammation and tissue injury.

The plant has also been reported to modulate nuclear factor-kappa B (NF-κB) signaling pathways, thereby reducing inflammatory responses associated with oxidative stress and myocardial damage. Suppression of inflammatory mediators helps protect cardiac tissue from further injury and contributes to improved myocardial recovery.

3. Cardioprotective Effects

Several experimental studies have demonstrated the cardioprotective effects of Hibiscus sabdariffa in isoproterenol-induced myocardial infarction models. Administration of the plant extract has been shown to significantly reduce elevated cardiac biomarkers such as creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST), which are indicators of myocardial damage.

Histopathological studies have also revealed that treatment with Hibiscus sabdariffa preserves normal myocardial architecture, reduces edema and inflammatory infiltration, and prevents necrosis of cardiac tissue. The cardioprotective activity of the plant is mainly associated with its antioxidant, anti-inflammatory, and membrane-stabilizing properties. ^[18]

4. Anti-apoptotic and Anti-fibrotic Effects

The flavonoids and polyphenols present in Hibiscus sabdariffa possess anti-apoptotic effects that help protect cardiomyocytes from programmed cell death. These compounds regulate apoptosis-related proteins such as Bcl-2 and Bax and inhibit the activation of caspase enzymes responsible for cellular apoptosis.

In addition, Hibiscus sabdariffa has shown anti-fibrotic effects by reducing collagen deposition and minimizing fibrosis in damaged myocardial tissue. Reduction in fibrosis improves myocardial remodeling and helps maintain proper cardiac function following injury. These effects are important in preventing the progression of heart failure after myocardial infarction. ^[19]

5. Other Pharmacological Activities

Apart from cardioprotective activity, Hibiscus sabdariffa exhibits several other beneficial pharmacological properties that indirectly support cardiovascular health.

Antihypertensive Activity

The plant is traditionally used for the management of hypertension. Studies suggest that Hibiscus sabdariffa produces antihypertensive effects through vasodilation, antioxidant action, and inhibition of angiotensin-converting enzyme (ACE). These mechanisms help reduce blood pressure and improve vascular function.

Lipid-Lowering Activity

Hibiscus sabdariffa has also demonstrated antihyperlipidemic activity by improving serum lipid profiles. The plant helps reduce total cholesterol, triglycerides, and low-density lipoprotein (LDL) levels while increasing high-density lipoprotein (HDL) levels. This lipid-lowering effect reduces atherogenic risk and protects against cardiovascular complications.

Hepatoprotective and Nephroprotective Activity

The antioxidant and anti-inflammatory properties of Hibiscus sabdariffa also contribute to hepatoprotective and nephroprotective activities. The plant protects liver and kidney tissues from oxidative damage and improves their physiological function. Since hepatic and renal health are closely associated with cardiovascular function, these protective effects indirectly support overall cardiovascular health.

Overall, the broad spectrum of pharmacological activities exhibited by Hibiscus sabdariffa supports its potential as a natural therapeutic agent for the prevention and management of myocardial infarction and other cardiovascular disorders. ^[20]

4. PRECLINICAL MODELS OF MYOCARDIAL INFARCTION

4.1 Experimental MI Models

Experimental animal models play an important role in understanding the pathophysiology of myocardial infarction (MI) and in the evaluation of potential cardioprotective agents. These models help researchers investigate biochemical, histopathological, and molecular alterations associated with myocardial injury under controlled laboratory conditions. Various experimental approaches are used to induce myocardial infarction in animals, including surgical, chemical, and genetic methods.

Surgical models generally involve ligation of the coronary artery to produce ischemia and myocardial necrosis, closely resembling human myocardial infarction. Although these models are highly reliable, they require advanced surgical expertise and are associated with higher mortality rates in experimental animals. Genetic models are also employed to study specific molecular pathways involved in cardiovascular diseases; however, they are complex and expensive. ^[21]

Among all experimental methods, chemical induction of myocardial infarction using isoproterenol has gained wide acceptance because of its simplicity, reproducibility, and cost-effectiveness. Isoproterenol-induced myocardial infarction in rats closely resembles several pathological and biochemical changes observed in human myocardial injury. Therefore, this model is extensively used for screening cardioprotective agents, especially medicinal plant extracts and natural antioxidants. ^[22]

Isoproterenol-Induced Myocardial Infarction in Rats: Mechanism and Relevance

Isoproterenol is a synthetic β-adrenergic agonist that, when administered in high doses, produces severe stress on the myocardium and induces myocardial infarction in experimental animals. Excessive β-adrenergic stimulation caused by isoproterenol leads to increased heart rate, elevated myocardial contractility, and enhanced oxygen demand of cardiac tissue. The imbalance between oxygen supply and demand results in myocardial ischemia and necrosis.

In addition, isoproterenol administration generates excessive reactive oxygen species (ROS), causing oxidative stress and lipid peroxidation in cardiac tissue. The oxidative damage disrupts cellular membranes, alters calcium homeostasis, and leads to calcium overload in cardiomyocytes. These pathological changes ultimately result in degeneration and necrosis of myocardial cells. ^[23]

The isoproterenol-induced myocardial infarction model exhibits several characteristic features similar to human MI, including elevated cardiac biomarkers, inflammatory cell infiltration, myocardial edema, necrosis, and oxidative stress. Histopathological alterations such as myocardial fiber disruption and inflammatory changes are also observed in this model. Due to its reproducibility, simplicity, and ability to mimic human cardiac injury, the isoproterenol-induced model is widely preferred for evaluating the cardioprotective activity of medicinal plants such as Hibiscus sabdariffa.

4.2 Biomarkers of MI in Preclinical Studies

Biomarkers are important indicators used to assess the extent of myocardial injury and oxidative stress in experimental myocardial infarction studies. Measurement of biochemical markers helps evaluate the severity of cardiac damage and the protective effects of therapeutic agents.

Cardiac Enzymes

Creatine Kinase-MB (CK-MB)

Creatine kinase-MB is one of the most important biomarkers of myocardial injury. It is predominantly present in cardiac muscle tissue and is released into the bloodstream following damage to cardiomyocytes. Elevated serum CK-MB levels indicate myocardial cell membrane disruption and cardiac tissue injury. Therefore, CK-MB is widely used as a reliable marker for assessing myocardial infarction in experimental studies. ^[24]

Lactate Dehydrogenase (LDH)

Lactate dehydrogenase is an intracellular enzyme involved in carbohydrate metabolism. During myocardial necrosis, damage to cardiac cell membranes causes leakage of LDH into the circulation. Increased serum LDH levels reflect the extent of cardiomyocyte damage and necrosis. Measurement of LDH is commonly used to evaluate myocardial injury in isoproterenol-induced MI models.

Aspartate Aminotransferase (AST)

Aspartate aminotransferase is another important enzyme released during myocardial injury. Elevated serum AST levels indicate damage to cardiac tissue and cellular membrane permeability alterations. Although AST is also present in other tissues such as the liver, significant elevation in myocardial infarction models is considered an indicator of cardiac damage.

Oxidative Stress Markers

Malondialdehyde (MDA)

Malondialdehyde is a major end product of lipid peroxidation and serves as an important marker of oxidative stress. Increased MDA levels indicate enhanced free radical generation and oxidative damage to cellular membranes. Elevated MDA concentration in cardiac tissue is commonly observed in isoproterenol-induced myocardial infarction.

Superoxide Dismutase (SOD) and Catalase (CAT)

Superoxide dismutase and catalase are important endogenous antioxidant enzymes that protect cells against oxidative stress. SOD converts superoxide radicals into hydrogen peroxide, while catalase further converts hydrogen peroxide into water and oxygen. Reduction in the activity of these antioxidant enzymes indicates impaired antioxidant defense mechanisms during myocardial injury.

Reduced Glutathione (GSH)

Reduced glutathione is a major non-enzymatic antioxidant present in cells and plays a critical role in maintaining cellular redox balance. GSH protects cardiomyocytes from oxidative stress by scavenging free radicals and detoxifying harmful oxidants. Depletion of GSH levels during myocardial infarction reflects increased oxidative stress and reduced antioxidant capacity.

Assessment of these cardiac and oxidative stress biomarkers is essential for evaluating the severity of myocardial damage and determining the cardioprotective potential of therapeutic agents in preclinical studies. ^[25]

5. CARDIOPROTECTIVE EFFECTS OF HIBISCUS SABDARIFFA IN ISO-INDUCED MI

5.1 Biochemical Evidence

Several preclinical studies have demonstrated that Hibiscus sabdariffa possesses significant cardioprotective activity against isoproterenol-induced myocardial infarction in experimental animals. Administration of Hibiscus sabdariffa flower extract has been shown to markedly reduce the elevated levels of serum cardiac biomarkers associated with myocardial injury. ^[26] During myocardial infarction, damage to cardiomyocytes leads to leakage of intracellular enzymes such as creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) into the bloodstream. Treatment with Hibiscus sabdariffa significantly lowers the serum concentration of these enzymes, indicating protection of myocardial cell membranes and reduction in cardiac tissue damage. ^[27]

In addition to reducing cardiac biomarkers, Hibiscus sabdariffa has also demonstrated beneficial effects on lipid metabolism. Experimental studies have reported that administration of the extract decreases serum total cholesterol, triglycerides, and low-density lipoprotein (LDL) levels while increasing high-density lipoprotein (HDL) levels. Improvement in lipid profile helps reduce atherogenic risk and provides additional cardiovascular protection. These biochemical findings support the role of Hibiscus sabdariffa as a potential natural cardioprotective agent. ^[28]

5.2 Antioxidant Effects

The cardioprotective activity of Hibiscus sabdariffa is strongly associated with its potent antioxidant properties. The plant contains anthocyanins, flavonoids, and phenolic compounds that effectively neutralize reactive oxygen species generated during isoproterenol-induced oxidative stress. Excessive oxidative stress causes lipid peroxidation, cellular membrane damage, and myocardial necrosis. ^[29]

Treatment with Hibiscus sabdariffa extract has been shown to significantly reduce malondialdehyde (MDA) levels, which is an important marker of lipid peroxidation and oxidative damage. Lower MDA levels indicate reduced membrane lipid degradation and improved protection against oxidative injury. ^[30]

Furthermore, Hibiscus sabdariffa restores the activity of endogenous antioxidant defense systems including superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH). Enhancement of these antioxidant enzymes improves the ability of cardiac tissue to neutralize free radicals and maintain cellular redox balance. By reducing oxidative stress and stabilizing myocardial cell membranes, Hibiscus sabdariffa helps preserve cardiac tissue integrity and function. ^[31]

5.3 Anti-inflammatory Effects

Inflammation plays a major role in the progression of myocardial injury following ischemic insult. Hibiscus sabdariffa exhibits significant anti-inflammatory activity due to the presence of bioactive flavonoids and polyphenolic compounds. Experimental studies have demonstrated that the extract suppresses the production of important pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), which are involved in myocardial inflammation and tissue damage. ^[32]

Reduction in inflammatory mediators decreases myocardial edema and limits infiltration of inflammatory cells into cardiac tissue. Suppression of inflammatory responses helps minimize secondary tissue injury and improves recovery of myocardial structure and function. The anti-inflammatory action of Hibiscus sabdariffa therefore contributes significantly to its overall cardioprotective potential. ^[33]

5.4 Histopathological Evidence

Histopathological evaluation provides important evidence regarding the structural protective effects of Hibiscus sabdariffa on cardiac tissue. In untreated isoproterenol-induced myocardial infarction models, cardiac sections typically show severe pathological alterations including myocardial necrosis, edema, inflammatory cell infiltration, and disruption of myocardial fibers. ^[34]

In contrast, treatment with Hibiscus sabdariffa extract demonstrates significant preservation of normal myocardial architecture. Histological studies reveal reduced necrosis, decreased edema, and minimal inflammatory infiltration in treated animals compared to untreated controls. Cardiac muscle fibers appear more organized and less damaged following administration of the extract. ^[35]

These histopathological findings confirm that Hibiscus sabdariffa not only improves biochemical and antioxidant parameters but also provides direct structural protection to myocardial tissue at the cellular level. The combined antioxidant, anti-inflammatory, and membrane-stabilizing properties of the plant contribute to its protective effects against isoproterenol-induced myocardial injury. ^[36]

Table 2: Preclinical Studies on HS Flower Extract in ISO-Induced MI