Medicinal Plants As Source of Bioactive Compunds

   In recent years the use of herbs for medicinal purposes has increased dramatically. Most of the earliest drugs were plant materials. The knowledge about plants and their effects on human health and activities was known in most societies and consequently plants were employed for treating diseases or symptoms. The development of chemistry resulted in isolation of active constituents and in most instances,the activity of the crude  plant extract could be reproduced by an equivalent dose of the isolated active constituent. This active could be isolated from natural sources or synthesized or structurally modified into related biologically active molecules, and  incorporated into a dosage form.
However, with the advancement of synthetic chemistry the use of plant extracts and the potential of the natural world to provide new biologically active compounds has not been taken seriously by the research pharmacologist and pharmaceutical industry. The knowledge of receptor characteristics and combinatorial chemistry of the drugs has led to the development of many novel synthetic molecules. Recently Biotechnology has revolutionized the process by which drugs are discovered.Some examples are

1. Cloning of genes and their expression can provide a new way of preparing essentially old drugs. For example, instead of purifying a protein from a biological source, it is often possible to prepare the protein by using high yield cell culture. Some examples will illustrate this point.

Factor VIII,a clotting protein used for the treatment of genetically linked bleeding disorder hemophilia. Till recently only source of factor VIII was its purification from human blood but now recombinant factor VIII is available from cultured mammalian cells.Similarly recombinant human insulin has replaced the purified insulin obtained from bovine and porcine pancreas. Human growth hormone, which is used for the treatment of growth hormone deficiency in children(dwarfism) . Till recentely the only source of human growth hormone was from the pituitaries of dead people. Recombinant human growth factor can now be produced by expression in bacterial cells.
b)Gene cloning has not only provided possible replacements for the preparation of existing biological agents, it is now also providing totally new agents for therapeutic use. Erythropoietin , which stimulate red cell production now can be produced by using this technology and has been approved for the treatment of anaemia associated with chronic renal failure.
Just as it seemed that this high tech approach would result in the production of a single golden  molecular bollet to treat complex diseases, interest in herbal medicines and phyto-therapeutic agents boomed. The developments that led to the renewed interest in natural products are as discussed below:

1. Discovery of New Drugs-  The ethnobotanical approach to drug discovery has resulted in the discovery of new pharmaceuticals such as vincristine, taxol and etoposides for the treatment of cancer. Although. These molecules have been synthesized but it is economical to extract them from materials.
2. Ethnopharmacolgy-  The scientific study of  the use of plants by a cultural group is called ethnopharmacology. The ethnopharmacological observations in past has resulted in discovery of several important drugs such as atropine, digoxin, reserpine, and arrow poison derived muscle relaxants curare. New molecules such as prostratin, a drug candidate for human immunodeficiency virus,  and several novel anti-inflammatory drugs are being isolated from traditional herbal drugs.
3. Chemical Ecology- As the production of biologically active molecules is essential for survival of living organism in a competitive environment, knowledge about the functions of these molecules may lead to design of drugs;e.g.blood feeding insects and leeches have effective anticoagulants, exenatide isolated from the saliva of the Gila monster lizard is used in type 2 diabetes.
4. Green Movement- The green movement has resulted in change in attitudes of general public towards drugs, cosmetics,and pesticides. The general public has become suspicious of safety and desirability of synthetic chemicals and they consider herbal drugs as safe alternative.
5. Effect of other cultures- As all the ancient major cultures use plants as medicine, exposure to these cultures due to population migration, international travel and worldwide communication has generated interest in herbal drugs like ginseng, garlic, biloba,  kava, St.John′s  wort and many others