Phytochemicals and their role in curing fatal diseases : A Review

Plants are serving mankind from the first day of his creation and have been a chief source of medicines from thousands of years. According to the latest report of the World Health Organization (WHO), more than eighty percent people are completely relying on the herbal medicines comprised of phytochemicals. These are biologically active, naturally occurring and non-essential nutrients. They are found in fruits (apples, grapes, berries, cherries, citrus fruits peel, apricots, oranges), vegetables (kale, cabbage, cauliflower, carrot, cooked tomato, sweet potato, soybean, bean) green tea, cereals, nuts, whole grains and seeds in a considerable quantity protecting human health from hazards. These compounds are major sources of a large number of medicines consisting of various groups like emetics, antispasmodics, antimicrobials, anti-cancerous etc. In traditional system of medications, large number of plants are considered to have therapeutic characteristics such as anti-pyretic, antioxidant, antibacterial, antidiarrheal, antifungal, anti-inflammatory and antidiabetic. They are extensively used worldwide for the treatment of various kinds of fatal diseases like cancer, neurodegenerative, cardio vascular diseases, type 2 diabetes etc. Various phytochemicals develop the immune system and protect the body from dangerous pathogens. It is believed that there is proper treatment mechanism for each and every disease by the nature in one or another way. Due to this reason, the researchers of the day are stressing to identify the role of these secondary metabolites against various diseases based on phytotherapeutical methods. In this paper, an attempt has been made to highlight the role of several phytochemicals in curing of various fatal diseases.


Introduction
Plants are serving the human beings in number of ways, therefore they are considered as gift from the nature for them.Their effective use as medicine have been reported since written human history.From immemorial times, these are known as constituents of phytomedicine.Wonderful collection of industrial chemicals have also been obtained from plants.These plant based natural chemicals can be extracted from different parts of the plant such as leaves, fruits, flowers, seeds, roots, stems, barks, rhizomes etc. which reveal that each and every part of the plant contain these biologically active components [1].In recent years, treatments through medicinal plants got tremendous attention worldwide [2].Several studies of traditional herbal therapies for different diseases have been carried out which led to the development of alternative drugs and therapeutic strategies.Since the intake of medicinal plants is increasing day by day, it is interesting to use these plants as supplement in diet.Moreover, these plants may arrange important nutrients and essential elements for living organisms [3-6].It was a primitive idea to find out the therapeutic power of plants therefore, various plants and herbs were used as drugs on large scale in the pre-historic human civilization [7].It has been proved that some 60,000 years back Neanderthals, in today's Iraq, used plants like hollyhock for the cure of different ailments.Even today, these herbs are extensively used in ethnomedicine throughout the world.Earlier Indian, Chinese and North African civilizations established the medicinal importance of a number of plants while curing various fatal diseases [8].
In late 19 th century, an invention was made when therapeutics float a plan to segregate bioactive compounds from analeptic plants.With the help of this idea, the most famous anti-malarial drug, quinine was prepared from the barks of cinchona tree by two French scientists, Caventou and Pelletier, which showed to be innovative in the field of phyto-remediation [9].In the year 2002, World Health Organization (WHO) reported that nearly eighty percent people all over the world in developing and nondeveloping nations depend on these herbal prescriptions to cater the need of their primary health care [10].Due to lack of health experts, deficient health facilities and shortage of medicines, herbal drugs obtained from medicinal plants got considerable importance nowadays due to their antibacterial, antimalarial, antipyretic, pain-relieving, anti-inflammatory, antiviral, anticancer, cytotoxic effects and antifungal activities [11,12].These therapeutic properties of medicinal plants are due to the presence of phytochemicals [13].The biologically active chemical compounds which occur naturally in medicinal plants are referred as phytochemicals."Phyto or phyton" is a Greek word, means "plant", hence the chemicals obtained from plants are called phytochemicals.These herbal chemicals are non-nutritive so they are regarded as non-essential for the proper life of human beings.Earlier, it was thought they only prevent plants from herbivorous mammals, predators, fungi and harmful insects but later on, it was revealed that they are equally beneficial for the safety of human beings from fatal disorders [14].Till now, more than twelve thousand phytochemicals have been isolated from various plants.Some very common phytochemicals like flavonoids from fruits, isoflavones from soy and lycopene from tomatoes have been extracted [15].These bioactive compounds are more effective with no or less side effects [16].Phytochemicals consist of medicaments which are responsible for plant pigments, aroma, appearance and flavor.Almost fifty percent communities of the world trust on herbal medicines as these are safe and beneficial.During the period of 1984-1995, out of 522 advanced medicines, approximately 39.5% were synthesized from medicinal plants.In the very beginning of 21 st century, a study was conducted revealing that round about 61% of all drugs were derived from plant sources.Besides this, 08 out of 30 highly marketed medicines were obtained from natural sources [17].These biologically active compounds act as synergistic agents which allow nutrients to be utilized by living organisms more efficiently.

History of phytochemicals
Since the existence of plants, bioactive compounds occur in them.However, they have been recognised for hundred years regarding their reality.Being the main source of phytochemicals, herbal plants are conventionally used throughout the world.It has been believed that the awareness about old-fashioned medicines established through trial and error concept over centuries.As per available record, Chinese own the oldest medicine and treatment system in the world.Over and above five thousand years ago, the Chinese utilized their drugs due to the effects of "yang" and "yin", and on the 05 constituents.Previously, herbal medicines date back to some 2800 BC when the Chinese emperor "Shen Nong" wrote the book "The Great Native Herbal".Likewise, the great scientists Aristotle (384-322 BC) and Hippocrates (460-377 BC) introduced herbal medicines for curing of fatal diseases for the first time.During 1800-1900, the fundamental goal of the investigators was to unearth the active compounds that had pesticidal or medicinal properties for instance, morphine, salicylic acid and pyrethroids (pesticides).During 1980s, many laboratories were established to find out phytochemicals in plants which will be used as medicines.Many of these discovered phytochemicals used to treat illnesses and other infections such as cancer, heart attack and stroke.Meanwhile, other scientists conducted epidemiological study to find out the relationship between the usage of special phytoconstituents and man life.Recent studies revealed that daily diet, rich in dietary plants, can minimize the danger of chronic diseases like cardio vascular illnesses, type 2 diabetes, neurodegeneration, tumour growth and cancer of different types to a greater extent.

Importance of phytochemicals
Researchers have recognized more than twelve thousands of various phytochemicals present in nuts, fruits, whole grains, beans, seeds and vegetables in a reasonable quantity.It has been reported that eating fruits, rich in phytochemicals, in maximum quantity may help in preventing at least one in every five (20%) cases of cancer along with other serious illnesses like heart disease.Phytochemicals are supportive in the prevention and healing of following infections and illnesses.1. Phytochemicals stimulate the body's immune system against various diseases causing agents like bacteria, fungi, viruses, etc. 2. Inhibit the potential for cancer causing substances (carcinogens) which are formed in the body due to the substances we take from the environment in the form of food or beverages.3. Diminish oxidation, the damage of cells that arises with aging and exposure to pollution.Free radicals are accountable for oxidation which leads to the formation of irregularities in cell and resultantly may lead to cancer.4. Slow the growing rate of cells which can cause cancer.5. Reduce tenderness which causes cancer growth.
6. Activate death (apoptosis process) of injured cells that may be a forerunner to cancer.7.Not only stop the damage in DNA but also useful in its repair mechanism.8. Accommodating in the regulation of hormones like insulin and estrogen in the body.The excess level of these hormones will increase the danger of colon and breast cancer [23].Recently, the application and exploration for plants based dietary supplements and medicines are more accelerated than past.The biochemists, microbiologists, botanists and ethnopharmacologists are rigorously searching for phytochemicals and their development for the curing of chronic illnesses.Traditional naturopaths have long applied medicinal herbs for the prevention of infectious diseases.As mentioned earlier, phytochemicals are present in fruits, vegetables, various herbs and shrubs and are using from centuries for the treatment of various fatal diseases as shown in (Table 1).Phytochemicals extracted from various medicinal plants show one or more bioactivities against the competitors, predators, insects and herbivorous mammals.Prominent phytochemicals along with their structural features and important bioactivities are illustrated in (Table 2).Usually, catechin, polyphenols of tea, are solely credited for these effects.However, research studies have not established a clear and vibrant association in human beings.The dearth of a reliable effect in human beings could be due to the genetic diversity, inaccurate quantity of tea intake and the nonconsuming of comparatively larger dose used in animal studies [52].In laboratory research, the polyphenols present in cocoa have been originated to restrict the cancer cell's progression, initiation and promotion.As black chocolate is full of polyphenols which is ambiguous that their cancer prevention effects may or may not apply in the body.Secondly, the required dose for their effectiveness is also uncertain [53].Type 2 diabetes Research reveals that the risk of type 2 diabetes may be directly decreased by the intake of diet rich in phytochemicals.This is due to the improvement in the sensitivity of insulin and also reducing inflammation.It further helps in stopping obesity indirectly which is considered as the most important risk factor of this illness [54-56].Inspiring effects on blood glucose level during fasting and insulin sensitivity have been initiated specifically with the consumption of polyphenols revealed by animal studies and laboratory work.Those polyphenols which are part of our diet may constrain digestion of carbohydrate and absorption of glucose in small intestine.They also boost insulin secretion in pancreas, control the secretion of glucose from liver, activate insulin receptors and absorb glucose in insulin-sensitive tissues, their signalling pathways as well as gene expression [57].Certain research reports exposed that by the use of vegetables with green leaves, the reduction of risk is increased due to the presence of phytochemicals in the green leafy vegetables.In a study carried on the Nurses and Health Professionals, it was conveyed that development of type 2 diabetes was at lower risk due to the maximum intake of fruits rich in anthocyanin like onions, coffee, apples, soya beans, tea, citrus fruits and soy products [58].While in another study about women's health, the relationship between anthocyanin and type 2 diabetes did not link in spite the researchers proposed that the maximum intake of tea and apples have an uncertain risk decreasing effect [59].The polyphenols found in cocoa and tea may also help in reducing type 2 diabetes risk and improve the sensitivity of insulin.A study carried out in eight countries of continent of Europe about a large population revealed that maximum tea intake decreases considerably the danger of developing type 2 diabetes [60].It was also reported that those tea users who take more than four cups of tea daily, have 16% less risk of type 2 diabetes as compared to nontea users.Improved insulin sensitivity, decreased HDL ratio, total cholesterol, LDL cholesterol and reduced insulin level was reported in those diabetes patients who were given chocolate rich in flavonoid and isoflavones supplements in their diet for one year [61].During a systematic survey, it was conveyed that 26% low risk of type 2 diabetes was reported in those whose daily intake of whole grains is 48 to 80 grams compared to those who rarely or never take the whole grains in their diet.The same nature of another study conducted in which 161,737 US women having no history of diabetes were investigated.As per the findings of the study, 37% low risk of type 2 diabetes was reported of those whose daily intake was higher than those with low whole grains intake [62].The Dietary Guidelines Committee (DGC) (2010) concluded in his report that there is limited indication exists regarding the relationship between the low risk reduction of type 2 diabetes and whole grains intake [63].But on the other hand, the German Nutrition Society (GNS) determined that there are strong evidences revealing that there is inverse relationship between type 2 diabetes and intake of whole grains