Plants as sources of biomolecules for pharmaceutical drugs

Jiten Sharma
Human evolution, during the course of time, has been related to continuous increases in primitive as well as advanced technological gains. Humans became capable of living in different environments, getting food and nutrients, and establish living conditions allowing the successful survival of their progenies. The characteristic human ability to observe, compare, analyse, and after careful evaluation, utilize natural resources constitutes basic milestones in the progress of human society.
Presently, science and technology are playing fundamental roles in the development of human society pushing it to newer frontiers and carry out careful re-investigations and re-evaluations of past anthropogenic activities. Plants have played basic roles for the existence of mankind and have been the sources for survival in the environment and for improvement of quality of life. It was discovered over the centuries that plants had specific properties which could be applied for benefits to human health.
Large variability of plant species located in different regions of the planet allowed the development of distinct cultures, use plants initially as traditional medicines, and later, as pharmaceutical drugs. Recently, in developed countries, the use of plants as pharmaceutical drugs has moved from an empirical knowledge and application to more scientific uses. In many cases, it has been possible to isolate and characterize the active principles or bio-active molecules, evaluate the molecular mechanism(s) and synthesize the molecule(s) by chemical procedures in the laboratories. Such scientific approaches allow more precise investigations both at research and clinical levels, accurate dose of drug administration and use of the products.
At present, the world over, a large number of pharmaceutical drugs from plants are used, and recently, in view of growing human needs and as a consequence, wider marketing perspectives, extensive research activities have been started for discovering novel molecules useful for human health. Further, new perspectives have emerged from the use of plant molecules as anti-bacterials applied in agriculture thus opening possibilities for plant molecules as environmental pharmaceuticals.
Traditional medicine consists of different components such as botany, anthropology and religions, and had crucial roles in human history. Different cultures grew in different regions and gained knowledge of plants having unique pharmaceutical properties. The history of pharmacy was, for a long time, accomplished with the history of pharmacognosy which deals with drugs originating from plants or animals in all aspects, except under the physiological effect. Recent advances in biology, pharmacy, chemistry and medicine have resulted in the development of several pharmaceutical drugs directly from laboratories.
Discovery of novel molecules as pharmaceutical drugs relates to ethno-botany which studies interrelationships of primitive men and plants and ethno-pharmacognosy which provides the guide towards different sources and classes of compounds. The use of plants in traditional medicine systems of many cultures has been widely documented and these systems have given rise to important drugs still widely in use.
The complex process that leads from plants to pharmaceutical drug production can be observed in the development of aspirin. Development of pharmaceutical drug started when the Salix bark extract showed curative property for malarial fever. Such observations stimulated research activities, mainly of chemical nature and in several laboratories to identify the active principles and their possible production by chemical synthesis. Finally, acetylsalicylic pills went into industrial production and medicinal use. Since then, many acetylsalicylic derivatives have been made, tested and widely used around the world.  
Another example of active principle standardised as pharmaceutical drug is Cinchona plant used in Peru by natives against malarial fever induced by Plasmodium falciparum. In the beginning of 19th Century, an alkaloid named quinine was isolated and chemically characterized, thus opening possibilities for development of pharmaceutical drugs. Thus, for several plants bio-active molecules were identified, chemically synthesised and used as pharmaceutical drugs in tune with their traditional uses. Consequently, the drug artemisinin extracted from Artemisia annua used in malarial treatment due to Plasmodium falciparum was discovered by Youyou Tu who got Nobel Prize in Medicine in 2015.
It has been estimated that only about 6% of plants has been investigated from a biological viewpoint and 15% in terms of their chemical components despite plants playing key roles in the system and representing a basic component of the human and animal diet. In addition, plants have wide uses in clothing, building, furniture and paper industries. Recently, biotechnological interventions have been carried out for using plants as molecule producers of industrial interest, for producing biofuels and biodegradable plastic to reduce plastic pollution. Plant tissue culture techniques have greatly contributed in this respect.
Although plants cannot move and have no complex organs as animals, depending on their cell structure and various biochemical and physiological processes similar to animal cells, they are eukaryotic organisms. Plant cells also have peculiarities like the presence of cell wall, specialized organelles, such as plastids, large vacuoles in the cytoplasm and complex cellular metabolism producing, in addition to primary compounds like sugars, proteins, lipids and nucleic acids, a wide number of molecules termed as secondary metabolites. Sugar, protein, lipid and other molecules of plant origin have been the main components of human diet, and consequently, some species are specifically selected and widely cultured.
Among hundreds of thousands of plant species found in the planet, only a few have played direct fundamental roles in human progress. Recently, scientists have widened their interests to plants that in the past were of lower interest and their secondary metabolites seem to open new perspectives for human needs and requirements.
That secondary metabolites result as specific components of specialised plant structures and organs have been already established. (To be contd)