ABSTRACT
This study investigated the effect of cocoa polyphenol on isoproterenol-induced myocardial infarction in Wistar rats. Polyphenol was extracted from cocoa using a hydroalcohol solvent. Forty albino rats divided into six groups of four rats each were used for the study. Groups 3, 4, 5 and 6 were pretreated with the extract (300, 500 and 700 mg/kg) and 100 mg/kg of atenolol (standard drug) respectively before administration with isoproterenol. Group 1 served as normal control while group 2 was administered with isoproterenol without any treatment. The activities of marker enzymes such as aspartate amino transferase (AST), alanine amino transferase (ALT) and lactate dehydrogenase (LDH) in both serum and heart tissue homogenate were assayed and serum concentrations of total cholesterol, LDL-cholesterol, HDL- cholesterol, triglycerides and malondialdehyde (MDA) were used to determine success of isoproterenol induction and response to treatment. Enzyme assays carried out on the serum and heart tissue homogenates showed increased activities in the serum and low activities in the heart homogenate in the untreated group when compared to the normal control. Histological studies carried out on the heart tissues revealed marked degeneration of the myocardium in the untreated group and in groups that received lower concentrations (300 and 500 mg/kg) of the cocoa extract. This corresponded with increased activities of the marker enzymes in the serum and low activities in the heart homogenate in these same groups. However, almost a total cardioprotection was observed in the group that received 700 mg/kg extract as revealed by the activities of marker enzymes in serum and heart tissue homogenate, concentrations of lipid profile parameters, level of lipid peroxide product and histological observations that showed heart tissue morphology very similar to that of the normal group. The results showed that consumption of cocoa as a functional food could reduce the risk of cardiovascular diseases and improve treatment outcomes.
CHAPTER ONE
1.1 Theobroma cacao
INTRODUCTION
Cocoa (Theobroma cacao) is a major economic tree crop in Nigeria (Alamu, 2013). T. cacao grows in the subtropical areas of the world. Although it grows widely from the southeastern Mexico to the Amazon basin, two thirds of the world’s production comes from four West African countries, the Ivory Coast, Ghana, Nigeria and Cameroon. Ivory Coast is the world’s largest exporter of cocoa (Agarwal, 2013). The cocoa tree produces ‘cauliflory’ flowers in clusters directly on the trunk and older branches. After pollination, ‘cacao pod’ fruits are produced. Each pod contains about 20 to 60 seeds, called “cocoa beans”, embedded in a white pulp. These cocoa beans were considered divine by the Mayans, as they were presumably discovered by the god Quetzalcoatl. They believed that cocoa beans make one strong and invincible. Spaniards noted that cocoa consumption allowed the Aztecs greater stamina and they could walk long distances without fatigue. The Olmec, Mayan and some Mexican tribes also recognized the medicinal value of these beans (Agarwal, 2013). Cocoa products have been enjoyed by humans for centuries. Chocolate is made from cocoa (Theobroma cacao). Consumed world over for its pleasant taste and its pleasurable and stimulating effects, epidemiological and scientific studies have repeatedly demonstrated significant health benefits with its intake. Kuna Indians living on Panama’s San Blas Islands drink more than four cups of cocoa per week and rarely develop age related high blood pressure or heart disease. Bioactive compounds from plant sources such as phenolics have gained substantial interest in recent years owing to their unique functions and nutritional values including antioxidant, antimicrobial, antimutagenic and antitumor activities (Nsor-Atindana et al., 2012). Cocoa is rich in flavonoids which protect against cardiovascular diseases through their antioxidant, antiplatelet, and anti-inflammatory effects. Flavonoids may also lower blood pressure, increase high density lipoprotein cholesterol, positively modify insulin sensitivity and improve endothelial function (Agarwal, 2013). Cocoa and cocoa derivatives are recognized as major dietary source of antioxidants because of their high phenolic (procyanidins and flavanols mainly) content (Tomas-Barberan et al., 2007). Several groups of polyphenols are found in fruits, whereas the most important are the flavanols which can be further subdivided into the monomers epicatechin and
catechin (Arts et al., 2000) and their dimers, oligomers and polymers, the so-called procyanidins (Lazarus et al., 1999; Adamson et al., 1999) responsible for the bitterness of cacao, through the formation of the complexes with salivary proteins (Manach et al., 2004). Numerous dietary intervention studies in humans and animals indicate that flavanol-rich foods and beverages exert cardioprotective effects with respect to vascular function and platelet reactivity (Carl et al., 2005). The consumption of flavanol-rich cocoa has been reported to improve endothelial function (Wang-Polagruto et al., 2006) and reduce the incidence of atherosclerotic diseases (McCullough et al., 2006).
Cardiovascular disease (CVD) is one of the main causes of death worldwide and most common in industrial societies (Chiva-Blanch et al., 2013). It is developed by a multifactorial process. Most CVDs are due to atherosclerosis, a degenerative process of the arteries that is induced by oxidative stress and chronic inflammatory status. The risk factors of this disease are smoking, diabetes mellitus, arterial hypertension, abnormalities in serum levels of total cholesterol and its fractions, overweight/obesity, family history of early CVD and physical inactivity, amongst others (Chiva-Blanch et al., 2013). Myocardial infarction is the acute condition of necrosis of the myocardium that occurs as a result of imbalance between coronary blood supply and myocardial demand (Boudina et al., 2002). Ischemic tissues generate oxygen derived free radicals which have been implicated in cardiac diseases and metabolic disorder (Prabhu et al.,
2006). The model of isoproterenol-induced myocardial ischemia is considered as one of the most widely used experimental model to study the beneficial effects of many drugs on cardiac function (Grimm et al., 1998). The pathophysiological changes following isoproterenol administration are comparable to those taking place in human myocardial ischemia/infarction (Wexler, 1978). Increases in the formation of reactive oxygen species during ischemia/reperfusion and the adverse effects of oxyradicals on myocardium have been well established by both direct and indirect measurements (Wexler, 1978). Many epidemiological studies associate an increased consumption of foods and beverages rich in flavonoids, with a reduced risk of cardiovascular death (Kris-Etherton and Keen, 2002).
1.1.1 Scientific classification of Theobroma cacao
Theobroma cacao belongs to the family of Malvaceae (alternatively Sterculiaceae), and is characterized by three main cultivar groups: Criollo, Forastero and Trinitario, which are widespread in the (sub)humid tropics. All cultivated species originated
from America. Cocoa is one the world’s most valuable crops, cultivated worldwide on
8.2 million hectares, playing an important role in the social and economic life of more than 5 million households, and affecting 25 million people in poor rural areas. Ivory Coast, Ghana, Nigeria, Indonesia and Brazil are the most important cocoa producers (Pohlan and Perez, 2011). The cocoa plant is classified thus;
Kingdom Plantae
Viridaeplantae Infrakingdom Streptophyta Division Tracheophyta Subdivision Spermatophytina Infradivision Angiospermae Class Magnoliopsida Superorder Rosanae
Order Malvales Family Malvaceae Genus Theobroma L. Species cacao
Integrated Taxonomic Information System (ITIS) (version 2011)
This material content is developed to serve as a GUIDE for students to conduct academic research
THE EFFECT OF ETHANOL EXTRACT OF THEOBROMA CACAO POLYPHENOL ON ISOPROTERENOL-INDUCED MYOCARDIAL INFARCTION IN WISTAR RATS
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