In modern times, cardiac disease has become the main cause of death worldwide. The World Health Organization reported that 16.7 million deaths in 2003 were caused by some form of cardiovascular disease. Myocardial infarction or acute myocardial infarction, commonly known as heart attack is due to the interruption of blood supply to the heart, causing anoxia and death of heart cells.

Isoproterenol (ISO), a synthetic catecholamine and nonselective b-adrenoceptor agonist, at high doses, has been reported to produce weakening of endogenous antioxidant system, contractile dysfunction, cardiotoxicity, and cardiac damage due to positive chronotropic and inotropic effects.

Herbal treatment for heart disease has been used hundreds of years. Bombyx mori cocoon is one of the main drugs of this treatment. The cocoon shell of the silkworm Bombyx mori consists of silk fibroin fiber (70%) surrounded by a sericin layer made up of sericin (25 %) and non-sericin (5 %) components. The non-sericin component consists of carbohydrate, salt, wax, flavanoids and derivatives.

Bombyx mori. cocoon is very popular, which has been used for decades for cardiac problems. To investigate the potential activity of Bombyx mori and its formulations against ISO induced cardiotoxicity, Indian Scientists carried out a study as below:
Wistar rats were orally pretreated with of Bombyx mori cocoon extract in two doses (250 and 500 mg/kg) for 30 days; rats were similarly pretreated with standard drug metoprolol (10 mg/kg) and normal saline for 30 days. Cardiotoxicity was induced by administration of isoproterenol (85 mg/kg) given twice on days 29 and 30 in all six pre-treated groups except the normal control. Cardiotoxicity was assessed by morphological and biochemical evaluation and further confirmed by histopathological studies.

The study shows the cardio protective potential of Bombyx mori against isoproterenol induced necrosis, oxidative stress and cardiotoxicity. Cardiac damage was assessed by grading of hearts of rats of different groups. Hearts of control group were healthy, while ISO caused severe myocardial damage, Bombyx mori pre-treated groups shows slight recovery at low dose, but the recovery was high in the higher dose (500 mg/kg) which was similar to the effect of the standard drug, metoprolol (10 mg/kg) group.

The diagnostic marker enzymes of myocardial damage, asparate transaminase, alanine transaminase, lactate dehydrogenase and creatinine kinase serves as a sensitive index to assess the degree of myocardial necrosis. ISO treated rats exhibited marked increase of these marker enzymes in serum compared to sham.

Pretreatment with Bombyx mori (500 mg/kg) to rats challenged with ISO significantly attenuated the elevated activities of these cardiac marker enzymes. Apart from these traditional cardiac marker enzymes, one enzyme which is specific for myocardial damage is troponin T&I.

Presence of troponin in blood/serum is usually considered a gold marker for cardiac damage. Troponin appears in blood after 4 -5 hours and disappears after 8 -10 hours. ISO-treated rats exhibited positive test result showing the presence of troponin I. Pretreatment of Bombyx mori cocoon at doses 250 and 500 mg/kg to rats challenged with ISO showed negative test result, indicating the absence of troponin. It shows that ISO induced myocardial damage which was protected by Bombyx mori cocoon.

Heart weight: body weight ratio (HW: BW) is another important parameter to evaluate the cardiac hypertrophy. ISO causes significant increase in HW: BW ratio as compared to control. HW: BW ratio significantly decreased in pre-treatment groups, p < 0.01 in Bombyx mori 250 mg/kg and p < 0.01 in Bombyx mori 500 mg/kg group.

Isoprenaline is known to induce oxidative stress by generating free radical moieties via its quinine metabolites which react with oxygen to produce super-oxide anions and other reactive oxygen species in rat myocardium. Free radical scavenging antioxidants such as SOD, Catalase, and GSH are the first line of cellular defence against oxidative injury.

The role of ISO has been well documented in the reduction of myocardial SOD and catalase activities and GSH content, decreased SOD activity in isoprenaline control animals may be due to excessive formation of superoxide anions or the decreased removal of superoxide anions, which can be harmful to the myocardium.

In present study there was a significant decrease in these endogenous antioxidants SOD and catalase in ISO challenged group compared to sham control. Pretreatment with Bombyx mori 250 mg/kg increased and Bombyx mori 500 mg/kg very significantly increased the activities of SOD and catalase levels in ISO-injected rats by preventing the depletion of antioxidants which is similar to the increase with metoprolol.

Glutathione antioxidant system plays a fundamental role in cellular defence against reactive free radicals and other oxidant species. It protects the myocardial cellular membrane against oxidative damage by regulating the redox status of proteins in the cell-surface membrane.

In present study there is significant decrease in GSH level in ISO challenged group compared to sham control. Pretreatment with Bombyx mori 250 mg/kg increased and Bombyx mori 500 mg/kg, significantly increased GSH level in ISO-injected rats and preventing the depletion of antioxidant which is as same as the increase with metoprolol. Glutathione depletion further increases the susceptibility of myocardial membrane to reactive oxygen metabolites and lipoperoxidative necrotic damage.

Lipid peroxidation is an important pathogenic event in myocardial necrosis and the accumulation of lipid hydroperoxides reflects cardiac damage. The increased lipid peroxides in isoprenaline-induced myocardial necrosis might be due to free radical mediated membrane damage. Increased levels of lipid peroxidation products injured blood vessels, causing increased adherence and aggregation of platelets to the injured sites.

ISO treated rats showed significantly elevated levels of TBARS (p<0.01) as marker of lipid peroxidation in heart compared to normal control. Pretreatment with Bombyx mori cocoon 250 mg/kg increased (p<0.05) and Bombyx mori cocoon 500 mg/kg, significantly increased (p<0.01) TBARS level in ISO-injected rats which is similar to the increase produced by metoprolol. Cardioprotection of Bombyx mori cocoon, was also confirmed by histopathological studies. Isoprenaline induced rat heart showed the extensive myofibrillar degeneration, severe myocardial necrosis, oedema and separation of myofibrils compare to sham group which showed architecture of myocardium.

Pretreatment with Bombyx mori cocoon 250 mg/kg shows some degree of control on this cardiac damage and Bombyx mori cocoon 500 mg/kg showed highly significant protection showing very lesser degree of necrosis, edema and myofibrillar degeneration. The reference drug, metoprolol, showed normal myofibrils, in continuity with adjacent myofibrils.

Bombyx mori cocoon has potent cardioprotective effect, so also is its formulations. The cardioprotective effect of Bombyx mori is possibly due to its high protein content and very small quantities of non-sericin components of silk cocoons, especially the flavonoids, which have potential free radical scavenging and antioxidant activities.