Drugs from Natural Sources - Essay Example

?PHAMACOLOGY By: Drugs from Natural Sources Use of natural products with therapeutic value is as old as human civilization. Harvey (2000, p. 295) explains that prior to industrial revolution; minerals, animal and plant products were the main source of drugs. Many communities in different parts of the world have historically relied on natural products as the source of products. Tulp and Bohlin (2004, p.450) asserts that natural products have recorded the highest efficacy as a source of drugs. They further observe that plants were historically the most important natural source of drugs. However, Jensen et al. (2003 p.18) observes that Industrial Revolution and subsequent development of organic chemistry lead to the liking of synthetic products for manufacture of drugs. Tulp and Bohlin (2004, p.450) note that given the importance of plants as a source of drug, there have been research on ethno-pharmacology and toxicology which has helped to produce drugs from plants. Reliance on natural products as a source of drugs was overtaken by synthetic products because pure products could be obtained from synthetic compounds as argued by Newman (2003, p.1026). Moreover, it is easier to do structural modification to synthetic compounds which leads to the production of potentially safer and more active drugs. Furthermore, throughout human culture development, use of natural products is associated with magical and religious attachment. This stereotype thinking has worked against continued use of natural products as drugs in western countries where use of drugs sourced from natural products was considered as an alternative for the people with low income or those who are poorly educated. In these countries, reliance of natural products for drugs was also seen as a religious superstition that had no pharmacological importance. Despite these arguments, it is critical to carry out thorough evaluation on the place of natural products as a source of drugs in the current society. Umezu, et al (2002, p. 93) notes that throughout ages, nature has been the major source of most human medicines. Newman (2003, p.1026) notes that plants were the most used source of drugs with the first documented records on their use being on clay cuneiform in Mesopotamia while the best documented Egyptian medicine is that of Ebers Papyrus which was used from as early as 1500 BCE. Newman (2003, p.1026) explains that natural products are still available and being used as a direct or indirect source of leads to drugs against all classes of diseases. According to Harvey (2000, p. 295), it is not right to despise drugs from natural sources given that they were used traditionally, since at that time there was no systematic research on drugs and everything was based on trial and error. However, this has changed with the Fleming’s discovery of penicillin leading the more acceptance of the importance of natural products as source of drugs. Fungi as explained by Proksch et al. (2002, p.129) have led in breakthrough on antibiotics, anticancer drugs and immunosuppressants. In addition, there has been research on marine environment and this has bore fruits with several drug products in the market and others undergoing clinical trials. Weldon (2000, p.12948) explains that micro-organisms are also a source of drugs and asserts that ethnopharmacological, marine sources and microbiological sources must not be considered as exhaustive natural product for the manufacture of drugs. Plants as a source of drugs Rates (2000, p. 603) reports that about a quarter of all drugs prescribed international are from plants, pointing that 121 such active compounds are in current use. He further points out that out of the 252 drugs considered to by the World Health organisation as basic, 11 percent comes exclusively from plants while although a considerable number are synthetic, they are obtained from natural precursors. Some of the drugs obtained from plants include quinine and quinidine from the Cinchona species, digonin from Digitalis species and atropine from Attropa belladonna. Other examples of herbs that are believed to have healing power include nutmeg, sandalwood, senna, rhubarb, myrrh, cinnamon and rosewater (Castleman, 2001, p. 15). In addition, there are diverse drugs currently in use that cannot be manufactured economically and are obtained from the wild or from cultivated plants. It is possible that natural products hold a great potential in addressing some of the diseases afflicting humans and what is required is more research to be carried out. Microorganism drug sources Rates (2000, p. 603) observes that about 60 percent of anti-tumour and anti-infections drugs in the market or those under clinical trial come from natural products. He explains that compounds derived from marine organisms such as coral, sponges and fish have chemicals with antiviral, anticancer and inflammatory effects. Curacin A is derived from cyanobacterium and is seen as a potential antitumor therapy. Other natural sources of drugs from microorganisms include discodermolide, eleutherobin and bryostains. Uses of natural products in drugs According to Rates (2000, p. 603) natural compounds can be used as lead compounds; thereby acting as a guide in the design and planning of new drugs and for biometric synthesis development and discovery of new medicinal properties that are currently not attributed to known compounds. Compounds acquired from plants such as muscarine, cannabinoids, forskolin and phorbol esters are used in the studies dealing with pharmacological, biochemical and physiological research. There is growing interest in use of drugs from natural sources and especially those that are derived from plants. This change towards inclination to natural products as drugs is as a result of various advantages observed in use of these products. Convectional medicines are at times ineffective resulting in side effects. When inappropriately administered, convectional medicine leads to side effects. On the contrary, the large number of world’s population that does not have access to convectional drugs and rely on natural products to deal with different ailments and do not report experiencing any side effects. As described by Rates (2000, p. 603), WHO recognises the importance of phytotherapy in the health programs in developing countries and proposes some basic measures that should be used for the validation of these drugs. Countries have realised the great potential in the use of natural products as drugs. Rollinger (2006, p. 491) describes that some Asian countries such as India and China support the herbal medicine and this industry is well developed. Moreover, Latin Americans have initiated research programs on medicinal plants and are also working on standardization and regulation of drugs from plant sources. Rates (2000, p. 603) explains that in France and Germany, there have been standardization and regulation of drugs from natural products. Over the last few decades there has been renewed awareness on the importance of natural products as drugs. This is evidenced by the increased reliance of natural products in drug development. There are several advantages that are attributable to use of natural products as drug. One of the main explanations on the advocacy of natural products as drugs is that natural products are available world over even in parts where convectional medicine cannot be accessed by the majority poor. Therefore with the adoption of natural products and their global acceptance of their use as drugs, the population that does not access convectional medicine will have an alternative. Natural products have also been recognized as a lead for the manufacture of convectional drugs in the market today. How did people start using some natural products as drugs? It still remains a puzzle how traditional societies were able to select the right medicine natural product despite limited knowledge on their composition. Kapadia (2000) however explains that biologists and chemists have come up with a compelling explanation on why many compounds in world have biological consequences on humans and other species. Heifer (2003, p. 536) argues that following the long term interaction of organisms in close proximity, they developed compounds that may influence the biological processes of the other organisms. These traits were retained through natural selection and are now valuable compounds in natural products in their use as drugs. For example a chemicals developed by plants to protect them against herbivores where if consumed by them, they would have diverse consequences such as diarrhoea. These products are now used as laxatives, cardiotonics and emetics in humans. In addition, natural compounds that have been discovered to suppress growth of bacteria are currently useful in developing antimicrobial drugs. Despite their great potential in treatment, natural products taken as drugs are mostly not authorised by laws and regulations dealing with safety and quality procedures as described by Dumbacher et al (2000, p. 12970). Furthermore, most researchers have found that there lacks quality in production, prescription and marketing of herbal medicines. Most herbal medicine is prepared by boiling product to extract their medicinal value. There are no well defined ways to determine the quantities that should be mixed during preparation thus posing great threat on the patient. Additionally, there remains a huge challenge on how to identify natural compounds that can be used to effectively deal with a certain disease. Most users of the natural products as drugs choose the source from trial and error or in other cases they do it from what other have experienced. In conclusion compounds derived from plants, micro-organisms and animals have been used as drugs as long as human history is documented. Plants however are the major natural source of drugs. Natural products have the advantage that they are found in different regions of the world and can thus be accessed by the large population that lacks access to conventional medicine and is cheap than convectional medicines. Natural products are also used as a lead in the design and planning of the synthetic drugs. However, preparation and quality of natural products as drugs is in doubts since most researchers have found that they are not regulated in most countries. There is therefore need for the regulation given the great potential of these sources. Recommendations To unleash the full potential of natural products as drugs, countries must step up efforts towards coming up with regulations and standards to define the quality and efficacy of natural products as drugs. It is also critical to invest in research that will enhance the identification of the right combination of natural products to treat a particular ailment. Further research must be carried to understand interactions of these products and any possible antagonistic effects described. It is also important to step up efforts to conserve rare plant species since continued research may identify their medicinal value. Drug Design by Computer modelling As technology advances, computers are continuously being employed to aid in the design and planning processes. Pharmaceutical industry has not been left behind in harnessing this great potential of computers. Computers are being used to enhance development of drugs in a technique known as computer assisted drug design (CADD) otherwise referred to as computer assisted molecular design. CADD is described by Funk et al (2004, p. 2750) as the use of computers as a tool to enhance the process of drug design. The technique relies on the state of the art technology to enhance the speed of drug development. However, it is important to remember that computer cannot be used as a substitute to gaining understanding of the system but only acts as a tool for gaining better insights into the process. Kitchen et al (2004, p.935) describes that development in computer graphics technology has the ability to create vector models of chemical designs and to manipulate them in real-time. This ability has facilitated studying of ligand structures and to understand how they interact with receptors after binding. Klebe (2006, p. 580) explains that computational and experimental techniques are critical in the discovery and development of drugs; they are complementary in the process. Computer Assisted Drug design involves the application of the computing power to organize the drug discovery and development process. CADD is also used to leverage information of chemical and biological about ligands. Furthermore, CADD helps in the designing of in silico filters which help to eliminate compounds that have detrimental properties such as those poorly absorbed, distributed, metabolised, or are poorly excreted. The methods used in computer modelling include knowledge-accelerated drug development which is usually a step by step process which companies can adopt taking fully advantage of computer technology (Mamelok & Olson, 2000, p. 88). The methodologies used in computer modelling include computer-based trial management and computer-assisted trial design. Power analysis software is the main tool used by statisticians in computer based trials management. This examines the estimated magnitude of the drug on the disease, differences in effect in the treatment arms and the variation of the efficacy variable to estimate the number of samples to be included in the trial (Mamelok & Olson, 2000, p. 90). Computer-assisted trial design allows pharmaceutical companies to implore the effects of trial and design a trial which is more robust. The method is used to calculate the probability and in which frequency that a particular dose would be effective in treating a particular disease. Kubinyi (2006, p.377) notes that advancement in hardware and software, computational abilities, identification of molecular targets and more databases publicly available on protein structures have spurred growth in the use of CADD. Kubinyi (2006, p.377) gives examples of software that can be used in general molecular modelling. The list includes software that can be used in workstations, supercomputers and minicomputers and those that can run in personal computers. Software that can run in workstations includes Amber, Midas Plus, CHARMM, Insight and SYBYL though the list is not exhaustive. For personal computers, Alchemy III, Desktop Molecular Modeller and Chem3D Pro are among the software that may be used. Strengths of computer modelling in drug design Drug modelling by use of computer modelling has various advantages compared to the traditional drug screening as argued by Cobb (2007, p.20). In contrast to the traditional drug screening which is random and based on trial and error, CADD is specific to a particular target and is structure based. CADD is fast and automatic which has done away with the time consuming traditional method. Moreover, CADD is inexpensive and leads to high success rates of drugs as opposed to the traditional method. According to Perola (2006, p. 423), currently scientists are avoiding the trial and error method in drug design by relying on computers in design of drugs. He explains that computers in drug design are used to identify the molecular structures with the greatest potential in medication. He further expounds that drugs are mostly designed to work on proteins that mostly function improperly thus leading to disease in the body. Perola (2006, p. 423) describes that the active ingredient of these drugs is usually one molecule that interact with protein in a similar way to the lock and key hypothesis. CADD is used to select the active sites for drug action, identify structures that require further evaluation and transform the biological active compounds to effective drugs through improving the pharmaceutical, physicochemical and ADMET/PK properties. Richards (2002, p. 551) describes that finding a molecule that can interact with protein is usually not an easy task. He further asserts that molecules of drugs are made up of fragments joined together by chemical bonds. The molecule needs to be shaped and built to allow fragments bind on the surface of protein with the effectiveness of the drug being determined by the number of hot spots on protein surface that they bind to. Previously, methods to come up with molecules dealt with finding fragments that can attach to a hot spot at a time. As such, the process of identifying structures that attach to all the hot spots was time intensive, tedious and prone to making errors. This has been substituted by use of computer simulations which assist in identifying molecular fragments that attach simultaneously to multiple hot spots on protein. According to Richards (2002, p. 551), drug design by use of computer modelling holds the potential of complementing and increasing the efficiency of traditional drug screening methods such as nuclear magnetic resonance and x-ray crystallography. He argues that with x-ray crystallography, it may be hard to interpret them because of noise that is created by fragments that fail to bind well with proteins. In a research carried out in Ohio University on the use of computer modelling in drug design, Klebe (2006, p. 580) explains that the researchers instructs the molecular fragments to interact by a technique known as ligand simultaneous docking before actual clinical trials are conducted. This helps to remain with only those fragments that can bind on the protein hot spots. The fragments feel each other’s through molecular attraction. To design the molecule, one must obtain information on a specific protein structure. This information comes from databases in cases where others have already established the protein structure and the hotspots when using computers in modelling of drugs. Richards (2002, p. 551) describes that in computer assisted drug design, databases are created and are important for the storage and retrieval of molecular structure data which helps for sharing of information and saves on time. Therefore these databases store so much information on drug design process that can be used by different stakeholders. In drug design, complex computations are required as observed by Simon-Hettich, Rothfuss and Steger-Hartmann (2006, p.156). They observe that there may be need to carry out quantum chemistry calculations which are complex. Consequently, computers come in handy since they help in doing these computations. Results from the computations can later be stored in computer databases which eliminate the need to carry to out more computational in subsequent drug design efforts. Kola and Landis (2004, p. 715) explain that the role of computational models used in CADD is to enhance prediction in the design method based on available knowledge. In the use of computers modelling in drug design, the graphic ability of computers is useful in coming up with molecular models by use of programs to visualize molecules. Molecular modelling involves data analysis and theory and prediction. Data that has to analyzed by use of computes includes structural data, biological data and chemical data. In theory and prediction, computers help in determination of molecular energy, allow for conformational changes to the molecular and help in molecular recognition. In drug modelling, De novo Ligand Design Methods are used. These methods include fragment location, fragment connection method, site point connection methods, sequential build up methods, whole molecule methods and random connection methods. These methods are use to inform the designing of drugs in computer modelling. In fragment location method, computers are used to determine the best location of fragments on the protein surface. Fragment connection method starts with previously positioned fragments and the computer is to come up with linkers that can be used to connect the fragments in the expected orientation. Computers may also be used in whole molecule method where known compounds are fitted into the active sites and computers software is used to manipulate it until the best orientation is achieved. Use of computer assisted drug design has been reported to result to better and more precise models. Virtual screening has proved to be more efficient than other methods used in screening of drugs. Alvarez and Shoichet (2005) reported that the number of compounds that bind to the target against the compounds tested proves high efficiency in drugs modelled by use of virtual screening. CADD has been used effectively in the discovery of some drugs. Alvarez and Shoichet (2005) explain that computer modelling was used in the discovery of the HIV/AIDS anti-viral drug. CADD was used in the development of molecules since they had information on the 3-D structure of HIV protease which is an important enzyme in the lifecycle of the virus. Using the capability of CADD, researchers can up with a molecule that fitted into the enzyme and locking the lifecycle of HIV. This was achieved in record time which helped to slow down the impacts of HIV. In conclusion, computer modelling in drug design holds a massive potential for the pharmaceutical industry. The technique leads to cost saving, saves time and increases the chances of success in the discovery process. CADD involves using the advancing power of computer hardware and software to streamline the drug discovery and development process. The technique also helps in ensuring that compounds that are not desirable such as those that are poorly excreted or absorbed do not find their way into the drug. CADD is also used to identify leads and transform those leads into effective drugs. CADD does away with trial and error method where the fragments are first tested to identify their ability to bind with the active sites before the drug is taken for clinical tests. In CADD, computers are used to carry out data analysis in drug modelling. In addition, computers are used to create databases where researchers can share information and access protein structures. CADD was critical in the discovery of Relenza; an anti-viral drug that helped to slow down the deaths of HIV victims. References Alvarez, J. and Shoichet, B 2005, ‘Virtual Screening in Drug Discovery’. CRC Press; Boca Raton, FL Cobb, K 2007, ‘Dock this: In Silicon Drug Design Feeds Drug Development’. Biomedical Computation Review pp. 20-31 Castleman, M. 2001, ‘‘The New Healing Herbs: The Classic Guide to Nature's Best Medicines Featuring the Top 100 Time-Tested Herbs’’. Rodale. p. 15. Dumbacher, J.et al 2000, ‘Batrachotoxin alkaloids from passerine birds: a second toxic bird genus (Ifrita kowaldi) from New Guinea’. Proc. Natl. Acad. Sci. U. S. A. 97: pp.12970–12975 Funk O., et al 2004, ‘Chemical function based pharmacophore generation of endothelin-A selective receptor antagonists’. J Med Chem 47(11):pp. 2750–2760. Haefner, B. 2003, ‘Drugs from the deep: marine natural products as drug candidates’. Drug Discov. Today 8: pp.536–544 Harvey, A 2000, ‘Strategies for discovering drugs from previously unexplored natural products’. Drug Discov. Today 5, pp.294–300 Hou, T. and Xu, X. 2004, ‘Recent development and application of virtual screening in drug discovery: an overview’. Curr Pharm Des. 10(9): pp. 1011–1033 Jensen, P. et al. 2003, ‘The true potential of the marine microorganism’. Curr. Drug Discov. January, 17–19 Kapadia, G 2000, ‘Inhibitory effect of synthetic and natural colorants on carcinogenesis III’. 6,080,411 Kitchen, D., et al 2004, ‘Docking and scoring in virtual screening for drug discovery: methods and applications’. Nat Rev Drug Discov 3(11):pp.935–949. Klebe, G 2006, ‘Virtual ligand screening: strategies, perspectives and limitations’. Drug Discovery Today. 11(13–14):pp. 580–594 Mamelok, R. D., & Olson, C. 2000, ‘’Knowledge-accelerated drug development’’. Pharmaceutical Executive, 18(4), 88-96 Kola, I. and Landis, J 2004, ‘Can the pharmaceutical industry reduce attrition rates’? Nat Rev Drug Discov. 3(8): pp. 711–715 Kubinyi, H 2006, ‘Success stories of computer-aided design. In: Ekins S, Wang B, editors. Computer Applications in Pharmaceutical Research and Development’. Wiley-Interscience. pp. 377–424. Newman, D. et al. 2003, ‘Natural products as sources of new drugs over the period 1981 – 2002’. J. Nat. Prod. 66, pp. 1022–1037 Perola, E 2006 ‘Minimizing false positives in kinase virtual screens’. Proteins 64(2): pp. 422–435. Proksch, P. et al. 2002, ‘Drugs from the sea – current status and microbiological implications’. Appl. Microbiol. Biotechnol. 59, pp. 125–134 Rollinger J. 2006, ‘Strategies for efficient lead structure discovery from natural products’. Current medicinal chemistry. 13(13):1 pp. 491–1507. Rates, S 2000, ‘Plants as source of drugs’. Toxicon 39: pp. 603-613 Richards, W 2002, ’Virtual screening using grid computing: the screensaver project’. Nat Rev Drug Discov.1 (7):pp. 551–555. Simon-Hettich, B., Rothfuss, A. and Steger-Hartmann T. 2006, ‘Use of computer-assisted prediction of toxic effects of chemical substances. Toxicology. 224(1–2): pp. 156–162. Tulp, M. and Bohlin, L 2004, ‘Unconventional natural sources for future drug discovery’. DDT vol. 9, No. 10: pp. 450-458 Umezu, T. et al. 2002, ‘Anticonflict effects of rose oil and identification of its active constituents’. Life Sci. 72, pp. 91–102 Weldon, P.2000, ‘Avian chemical defense: toxic birds not of a feather’. Proc. Natl. Acad. Sci. U. S. A. 97, pp.12948–12949. Read More