Mushrooms are fleshy, spore-bearing fruiting body of fungi belonging to the. subdivision of Basidiomycotina of the class Hymenomycetes.

Transcription

1 Chapter 1: Introduction

2 Mushrooms are fleshy, spore-bearing fruiting body of fungi belonging to the subdivision of Basidiomycotina of the class Hymenomycetes. Basidiomycetes include many of the familiar fleshly mushrooms. Most are saprophytes causing decay of litter, wood or dung, some are plant pathogens, while the fleshy mushrooms have a reputation for being poisonous, the majorities are harmless and several species are edible. They are unique components of biosphere and they have been one of the significant groups of plants in human affairs throughout the development of civilization. They are delicious, edible, hallucinogenic to poisonous and potentially medicinal. Mushrooms are basically consumed for their texture and flavor. However, they are rich source of high quality proteins (10-40% on dry weight basis) and low in fat content (2-8%) (Subramanian, 1995). The practice of using fungi as medicines are found in the traditions of many cultures, past and present. The first Chinese book on medicinal substance, The Shen Nung s Herbal, 2000 years ago, recorded the beneficial effect of various fungi. It was not until this century, when antibiotic was obtained from Pencillium, that the medicinal value of fungi gained worldwide attention. It is now well documented that many fungi produce antibiotic substances and a number of them have been shown to possess antitumor activities and other pharmaco dynamic properties (Jong and Birmingham, 1992). Extract and powders of mushroom (mycelia and sporocarps) in the form of sugar coated tablets are being marketed on commercial scale. Volvariella is a genus of basidiomycete with pink gills and spore prints. They lack a ring and have an Amanita like volva at the stem base, since the gills of young Volvariella are white at first. Some species of Volvariella are edible, accounting for 16% of total production of cultivated mushrooms in the world. Volvariella volvacea (Bull) Singer is well known as Paddy Straw mushroom 1

3 and cultivated in rich straw in the Philippines and Southeast Asia. V. volvacea is thought of as a rare relish for banquet with its tasty and refreshing flavor in fresh and strong fragrance when dried. It contains higher protein and vitamin C than that in vegetables and fruits. The eight types of essential amino acids favorable to human body can also be found, so it has been called the healthy food. In traditional Chinese medicine, V. volvacea has been used to relieve summer heat, bring down fever, enrich milk of women in childbirth, promote baby s health and make healthy liver and stomach. Unfortunately it is easy to mistake the death cap mushroom as well as some other Amanita species for this edible species, due to similarities in the appearance. This mistake is the leading cause of lethal mushroom poisoning in the United States. There is a tremendous increase in the possible role of nutrition in prevention of disease. In these context antioxidants, especially derived from natural sources, require special attention. Since mushrooms are a rich source of these beneficial compounds, they require a thorough investigation, especially in terms of their antioxidant activities. Antioxidants neutralize the toxic and volatile free radicals, which are defined as atoms or groups of atoms having an unpaired electron. They are inherently unstable since they contain extra energy. To reduce their energy load, free radicals reacts with certain chemicals in the body, and in that process, interfere with the normal functions of the cell. Once formed these highly reactive radicals can start a chain reaction. Their chief danger comes from the damage they cause when they react with important cellular components such as DNA, or the cell membrane and the cells may function poorly or die, if this occurs (Ames, 1989; Goetz et al., 1994). In biological systems most of the free radicals are derived from oxygen. It gives rise to a large number of free radicals and other reactive species 2

4 collectively known as 'reactive oxygen species' (ROS). Oxygen, because of its paramagnetic nature, has spin restriction that forbids it from reacting freely with other molecules. During cellular respiration oxygen undergoes incomplete reduction producing superoxide (O2 - ), hydrogen peroxide (H2O2), hydroxyl radical ( OH), and finally water. ROS can cause extensive DNA modification including modified bases; they can trigger oxidative damage to proteins and membrane lipids. Another group of reactive species termed as reactive nitrogen species (RNS), have both nitrogen and oxygen and include physiologically important nitric oxide (NO ) and toxic peroxynitrite (ONOO ). Apart from ROS/RNS, there are also other biologically relevant reactive species derived from sulphur (for instance thiyl radical, RS ), carbon etc., that are being formed in tissues (Von Sonntag, 1987; Abedinzadeh, 2001). All these reactive species have several biological implications. The major antioxidant defence systems include the intracellular superoxide dismutase, catalase, glutathione peroxidase and glutathione besides the dietary or oral supplements in the form of vitamin C, vitamin E, -carotene, zinc and selenium (Knight, 1999). Catalase inactivates H2O2 formed by SOD by converting it to water and oxygen. Glutathione peroxidase in the presence of glutathione, converts H2O2 to water. Zinc is an essential trace element, being a co-factor for about 200 human enzymes, including the cytoplasmic antioxidant Cu-Zn SOD. Selenium is also an essential trace element and a cofactor for glutathione peroxidase. Vitamins especially, Vitamin E and Vitamin C (ascorbic acid) are effective free radical scavengers (Meydani and Haytek, 1992; Frei, 1994). Beta-carotene, lycopene, lutein and other carotenoids function as important antioxidants: they quench singlet oxygen as well as peroxyl radicals and protect against DNA damage (Palozza and Krinsky, 1992; Devasagayam et al., 1992; Di Mascio et al., 1990). These compounds 3

5 modulate host defense systems. Similar protection was also observed with flavonoids and polyphenols (Tiwari, 2001). In a normal healthy organism or human body, the generation of pro-oxidants in the form of ROS and RNS are effectively kept in check by the various levels of antioxidant defense. However, when the humans get exposed to adverse physiochemical, environmental or pathological agents this delicately maintained balance is shifted in favor of pro-oxidants resulting in oxidative stress (Sies, 1996). Certain environmental agents can deplete cellular antioxidants thereby reducing the antioxidant defense that normally counteracts the pro-oxidants, also leading to oxidative stress. Cellular damage induced by oxidative stress has been implicated in the etiology of a large number of human diseases as well as the process of ageing. The degenerative diseases associated with oxidative stress include (i) cardiovascular ailments like coronary heart disease, cardiomyopathy etc., (ii) neurodegenerative diseases like Parkinson's disease, Alzheimer's disease, brain dysfunction, lateral sclerosis, (iii) multistage process of carcinogenesis, (iv) immune system decline during ageing, (v) cataract formation and so on. Other pathological conditions implicating ROS/RNS are diabetes, rheumatoid arthritis, cystic fibrosis, hemorrhagic shock, gastrointestinal ulcerogenesis, AIDS, metabolic disorders like erythropoietic porphyria, lung diseases like adult respiratory distress syndrome, chronic obstructive pulmonary diseases, asthma, emphysema, drug induced lung lesions etc., hepatotoxicities induced by chemicals, radiation injury, toxicities due to physicochemical agents/pollutants/toxicants, inflammation resulting from infection, Down's syndrome, ischaemia-reperfusion type injuries associated with heart, brain, kidney, liver and gastrointestinal tract. Various antioxidants may prevent and/or improve diseased states. 4

6 Conventional cancer chemotherapy aims to kill or disable tumour cells while preserving the normal cells in the body by the application of synthetic compounds (Ratain, 1997). Over 500 compounds have been identified with potential chemoprevention properties as a result of their ability to inhibit tumor formation or cell transformation (Smith and Gupta, 1996). Many agents have been shown to be effective for certain cancer chemoprevention, while other compounds are undergoing clinical trials. These agents have a narrow margin of safety, and the therapy may fail because of drug resistance and dose limiting toxicities. Nephro toxicity, cardio toxicity and hepatotoxicity are the major side effect and the limiting factor that occur either acutely or after repeated treatments with many chemo therapeutic agents. Despite of the great advantages of radiotherapy, its deleterious effects on normal cells limit the total dose that can be given and may cause lasting discomfort and disability for the patient. The interaction of ionising radiations with biological systems results in generation of free radicals. Since the ionising radiations and free radicals can destroy both cancer cells and normal cells alike, an agent producing differential response in the malignant and normal cells would be of great interest in effective radio and chemotherapy for cancer. The invention of a chemo and radioprotectors, especially from natural origin that exhibit no side effects, is of great importance for the sake of improvement in chemo and radiotherapies. Natural products have been of exceptional values in drug discovery programs and also mechanistic studies involving biological components of relevance in health management. Crude drugs or natural diets that possess antioxidant or free radical scavenging activity are of significant importance to prevent or ameliorate tissue injury caused by the free radicals and subsequent disease management. Among the microbial source, fungi are currently of major interest. A large number of medicinal mushrooms have recently been 5

7 reported to possess significant antioxidant activity (Nitha et al., 2010; Mathew et al., 2008; Jose et al., 2002; Ajith and Janardhanan, 2001; Lakshmi et al., 2004). Many of these mushrooms are known to be non toxic; they may be more easily and safely implemented for human use than other synthetic antioxidant chemicals. The major objective of the current investigations is to evaluate the various therapeutic potential of V. volvacea mycelium. It is the most favorite mycelium in South Asian countries because of its excellent delicacy, high protein, amino acid, vitamin and minerals contents (Thakur and Yadav, 2006). Recent investigations reveal that V. volvacea contains isomerization protein that could improve the function of immunity, reduce cholesterol and prevent atherosclerosis. However not much information is available on its antioxidant activity and its capability to ameliorate oxidative stress and genotoxicity. Since the available information on the medicinal properties and uses of V. volvacea is inadequate, studies on the therapeutic potential of this mushroom was considered important. Production of mushroom mycelium by submerged culture technique is now considered to be the most suitable method for the production of mushroom biomass on a large scale. Hence, cultured mycelium of V. volvacea was selected for the investigation. The current investigations were undertaken to evaluate the medicinal properties of V. volvacea mycelium and to demonstrate its therapeutic potentials as antioxidant, antiulcer, antiarthritis, hepatoprotective, nephroprotective and cardio protective agents. The findings are presented in this dissertation. 6