Introduction to Pharmacognosy PDF

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Pharmacognosy Lecture One....

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GENERAL PHARMACOGNOSY LESSON ONE

Definitions of Pharmacognosy1. From Greek words ‘pharmakon’ meaning ‘drug’ and ‘gignosco’ meaning ‘to acquire knowledge’. 2. Oldest modern science that is concerned with the use of plants and other natural products as medicines. 3. It is also the systematic study of natural medicines in terms of purity, potency, consistency and safety. 4. A science that aims at complete knowledge of crude drugs. 5. In the last 200 years, there has been a substantial metamorphosis in the principles and practices of Pharmacognosy. It has become an essential domain of modern pharmaceutical science as a multidisciplinary high-tech science of natural medicines. Clinical Pharmacognosy, Analytical Pharmacognosy and Industrial Pharmacognosy, Molecular

Pharmacognosy,

Genomic

Pharmacognosy

and

Metabolomic

Pharmacognosy have been established as the specialized and professional offshoots of Pharmacognosy to meet the contemporary advancements in the field of Pharmacognosy

Historical review on the use of plant medicines Previously, traditional medicinal knowledge was found in holy books, incantations, folklores. Some examples throughout history; 1. Evidence of use of medicinal plants has been found from Sumerian clay slabs from Nagpur dated approximately 5000 years old. 2. Emperor Shen Nung wrote a Chinese book on roots and grasses approximately 2500 BC e.g. cinnamon bark, ephedra, ginseng, etc. 3. The Vedas (Indian Holy books) talk of many plant medicines used to date e.g. Nutmeg, cloves, etc. This is known as Ayurvedic medicine. Ayuveda is a Sanskrit word meaning knowledge of life (‘ayur’ means ‘life’, ‘veda’ means ‘science/ knowledge’). This knowledge has been transmitted orally for thousands of years. 4. The Ebers Papyrus dated approximately 1550 BC gives a collection of Egyptian herbal medicine and refers to 700 plants species used as drugs e.g. castor oil, aloe, senna, garlic etc. 1

GENERAL PHARMACOGNOSY LESSON ONE

5. Homer’s epics (The IIiad and the Odysseys) dated approximately 8 BC lists 63 plant species from Minoan, Mycenaean and Egyptian Assyrians. The Greek word ‘artemis’ meaning ‘healthy’ is the basis for the plants of the genus Artemisia. 6. Theophrast (371-287 BC) authored two books; “De Causis Plantarium”( Plant Etiology) and “De Historia Plantarium” ( Plant History). He classified 500 medicinal plants including cinnamon, mint, cardamom, etc. He is considered the father of botany and was student of Plato and Aristotle. 7. An early Greek philosopher – Celsus (25 BC-50 AD) wrote of about 250 medicinal plants. 8. Dioscorides - the most prominent writer on plant drugs, is refer to as the father of Pharmacognosy. He was a military physician and a pharmacognosist in Nero’s army. He authored the book “De Materia Medica” which was the basic materia medica up to the late middle ages and it described 657 drugs of plant origin. 9. In the middle ages, the use of plants as medicines moved to monasteries were the monk used 16 medicinal plants which they grew themselves. They included sage, anise, mint, etc. 10. Charles the Great (742- 814 AD) who founded a medical school in Salerno (Italy) had medicinal plants grown on state lands. Plants grown included; sage (Salvia officinalis L.), mint, etc. 11. Arabs introduce many plant medicines still used today e.g. Coffee, saffron, curcuma, etc. found in Kitab- Al-Shifa or The Book of Healing. The combination of Greek, Persian and Arabic indigenous treatments is known as Unani. 12. Many plants used as medicines were brought into Europe from tropical countries, China and Persia a result of Marco Polo’s journeys (1254-1324). This resulted in botanical gardens emerging. 13. The discovery of America resulted in new plants such as cinchona, ipecacuanha, cacao, tobacco , senega, etc. 14. Paracelsus (1493-1541) prepared drugs chemically from plants and minerals. Using the ‘signature doctrine’, he proposed that God indicated healing plants based on how they looked. For example, the haselwort resembled the liver and hence could be used to treat liver ailments. 15. Between the 16th and 18th century, compounding of medicines took root. Previously people had used infusions, and decoctions.

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16. Africa has failed to properly standardise its traditional medicine compared to Ayuvedic and Unani medicine. However, herbal drugs have been used for many centuries in the African continent. 17. Today, we have pharmacopoeias describing many medicinal plants. Many more plants are used unofficially.

Nomenclature, Classification and Identification of Plants The nomenclature of plants range from monomial, binomial to polynomial for many centuries. The names were mostly descriptive. In the 18th century Linnaeus (1707-1788) briefly described and classified plant species in his book Species Plantarium (1753). A polynomial system was used with the first word indicating the genus while the rest denoted the plant’s features. He later alter the system into a binomial system. The system was latter refined to what is used today. The first name indicated the genus (written with a capital letter, a noun) while the second name indicated the species (written with a small initial letter, an adjective). Example: Coffea arabia Linn. Usually in Greek or Latin. The species name differentiates a plant from all allied plants and indicates a striking feature of the plant. The species name is the basic unit of classification. In 1813 Augustin de Candolle, a Swiss botanist published ‘Theorie Elementaire de la Botanique’. In this book he stated that plant anatomy must be the sole basis for classification. He then coined the term taxonomy. Taxonomy is also systemic botany. In 1821, Stendel published ‘Nomenclator botanicus’ where he gave Latin names for all flowering plants. In 1840, he published ‘Index kewensis’- a basis for recording all botanical names for plants. By then, the Universal code of binomial nomenclature had been accepted universally. The problem with common names compared with botanical names 1. Indefinite i.e. a plant can have many common names hence confusion. Binomials are definite. 2. Restricted to people of the area e.g. the language of a geographical zone. 3. Not regulated by an authority. The binomial system creates uniformity Rules of Binomial nomenclature -

Binomials should always be underlined and when they are printed they must be italicized. 3

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The name of the scientist who first described the plant or his/ hers abbreviation follows. Example: Aloe barbadensis Mill.

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Albizia lebbeck (Linn.) Benth- Linn. Linnaeus: first described the species. Bentham: the second name is that of the scientist who is responsible for the currently recognised binomial. This helps in finding the original and subsequent description of the plant when need. And avoids confusion when different scientists use the same names to name different species.

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The year in which the plant was described can be added after the author’s name.

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s.l. means ‘sensu latiore’- ‘in widest sense’ and refers to collective species and varieties….e.g. (Citrus sinensis, orange or sweet orange, C. aurantium, and mandarin orange, C. reticulata)

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In the naming of plants the specific name may indicate a gender (‘us’-male, ‘a ‘– feminine and ‘un’ is neutral) e.g. albus, alba, album.

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The names may be commemorative e.g. Turraea Kokwaroana or geographical e.g. Vitex keniensis or show a specific descriptive character e.g. Croton megalocarpus etc.

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‘Changes can be made by the International Botanical Congress.

Taxon or taxonomic classification was introduce in 1956. This allows for precise and ordered classification of a plant. i.e Species- Genus- Family- Order- Class- Division- Kingdom. This was based on Engler’s system of plant taxonomy. This and Eichler’s system used phylogenetic principles to classify plants – use of characters that are capable of showing relationships. They used taxa/ units e. g. orders, families, etc. to show possible relationships of one taxon to another. However, such relationships may not be correct. Related plants may diverge (divergence). This means that modern phenotypes may appear dissimilar. Under favourable conditions, unrelated plants may developed a particular character e.g. the development of fused corollas. This is referred to as convergence. Parallelism is the similar evolution of characters in related plants. During the 19th and 20th century, conventional medical practices have been adopted for identification and authentication of natural remedies. This has given rise to a botanicochemical approach to Pharmacognosy or chemical plant taxonomy. The characters should have intermediate distribution in the plant kingdom. Ubiquitous compounds such as common sugars are not useful. Secondary metabolites are considered useful e.g. alkaloids, glycosides

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and flavonoids. The use of genetic profiles (random amplified polymorphic DNA analysis) is also of value in differentiating species e.g. Panax ginseng and P. quinquefolium Cronquist (1981) used not only morphological data, but also micromorphological (embryology and pollen structure) and chemical data (secondary metabolites and serology) and fossil records to classify plants. In 1983, Dahlgren used cladistics as a taxonomical method. A clad is group of plants at any level that share a common ancestor. It is formed by splitting to give two new species. They may also later on split. Kubitzki has written a modern replacement of Engel’s classification. It is an ongoing survey of vascular plants. Reasons for Classification 1. To allow description of plants since they are very many in the world 2. Classification is the basis of botany 3. Identification 4. Ease load of processing large amounts of information about plants Problems Encountered in Classification 1. Data on plants may be incomplete 2. Variations in plants exist 3. Evolution is ongoing 4. Geographical barriers may lead to adaptations 5. Hybridization can occur as various species interbreed.

Sources of Drugs Geographical and Biological Sources In many parts of the world, folk medicine has led to the knowledge of plants that can be used as medicines. The plant medicines found in western pharmacopoeias are from the Greek and Roman eras e.g. spices. Others were discovered during travel and colonial expansion from areas where they were used by resident populations e.g. cinchona.

Others are recent

discoveries from screening of local drugs e.g. vinblastine. Plants can also be cultivated to

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provide drugs. For example, cinnamon was traditionally from Sri Lanka. Now it is grown commercially in Seychelles. However, constituents produced by the same plant in different locations may differ. Most drugs derived from natural source are Spermatophyta (dominant seedbearing plants). Phyla Gymnospermae yields oils, resins and alkaloid ephedrine. Angiospermae, especially the dicotyledons provide many useful drugs. Fungi provide antibiotics. Algae provide alginic acid and agar. Land animal provide wool fat, beeswax, gelatin, cochineal, etc. Microbes have been genetically engineered to produce precursors of artemisinin.

Herbarium It is a repository/ library for plants. A collection of dried plants that have been catalogued and arrange systematically. It serves to permanently fix the identity of plants for future reference. The person employed to care for the herbarium is referred to as a curator. There are about 2639 herbaria worldwide Examples of herbaria are The Museum of Kenya, Oxford University Herbarium, Smithsonian Museum of Natural history and Kew in London (with about 7 million specimen). How to collect a Herbarium Specimen The plant of interest is selected. Collection of as wholesome a sample as possible is advised. If a small plant, collect entire sample. If large, collect a sample of all parts to allow for accurate identification. Plants are pressed between sheets of newspaper (to absorb the moisture). A plant press is used. The specimen can be dried under a low heat, in purpose-built stoves or by leaving the press in the sun (possible in hot, dry climates). Quick drying and drying ‘on- site’ conserves as much of the plants original colour and features as possible.

Frequent changes of

newspapers in the press hastens drying. These days, large sheets of blotting paper, cardboard and corrugated sheets of aluminium in between the specimens are used to ensure quick drying. The plants are then quarantined and then identified into families by a botanist. Mounting on hard paper or herbarium sheets (42 cm by 27-30 cm) is then done. Mounting is done using wood glue (Museum of Kenya). Care is taken to show all possible aspects of the plant i.e. 6

GENERAL PHARMACOGNOSY LESSON ONE

flowers - with all their petals; fruit; seeds; the hairs on both upper and lower surfaces of the leaf, etc. Mounted, identified specimens are stored in cupboards. Classification of plant species into genera and the grouping of these genera into families facilitates organisation of the collection. Delicate plant parts such as flowers can be preserved in spirit, bulky parts of a plant such as large fruits, very large fronds (as in some palms) or other vegetative parts (as for some cacti) will simply be dried and placed in large boxes. Kew has a separate collection of fruits dried in this way — it's called the carpological collection. Kew's Jodrell Laboratory has a DNA Bank. Kew's Economic Botany collection includes a large selection of wood samples. Such collections are normally cross-referenced to herbarium dried-pressed specimens. Labelling of Plant Specimen The specimens are labelled individually. Reasons for having a label on each and every specimen in the collection are: 

To distinguish between one collection and another

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To record additional important information about the plant as it was when collected. This is especially important for large specimen such as trees where the herbarium specimen is small.

Many specimens of the same plant species might have been collected in different places, at different times and by different people and so we need some other way of referring unambiguously to the individual specimen. Each specimen is labelled using two pieces of information: the name of the person(s) that collected the plant and that person's collection number. For example; specimen R.Harley 50594 is the 50594 th specimen collected by Ray Harley. This number is unique: Harley will have no other collection sharing this number. "R.Harley 50594" is a particular collection of Agrianthus guiliettiae which he made on the 31 December, 1991 in Bahia, Brazil. At the time Harley will have made duplicate collections and sent copies to various herbaria in Brazil and around the world. Every one of these duplicates, in whichever institution it is found, will be referred to, and recognised as, "R.Harley 50594". As electronic databases and management of large collections become more sophisticated, herbaria such as Kew, have started to bar-code their collections or provide some other unique electronic tag for each specimen. 7

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A plant in the reference collection is most useful when we know exactly where it was collected (in modern collections this is recorded using GPS equipment) and a description of its habitat (ecology), appearance when alive (especially important since flower colour for example will be lost when the plant is dried) and other information such as the uses to which it may be put locally or insects that were seen visiting the flowers. A label typically includes the plant family, a first attempt to identify it, any popular (common) names used locally, plus its position and locality and the date of collection. The latter gives biologists studying reproductive behaviour vital clues to the times of the year a plant can be expected to be in flower and fruit. Features of the plant that cannot be collected (the height of a tree, the presence of latex) or that get lost upon pressing (colours and odours) are also annotated, as they can help identify the specimen later on. Challenges in a Herbarium Setting 1. Insects- Some insects are feeding primarily on plant materials, for example the Anobiid biscuit beetle (Stegobium paniceum), cigarette beetle (Lasioderma serricorne), or spider beetles like the Australian spider beetle ( Ptinus tectus), the golden spider beetle (Niptus hololeucus), the white marked spider beetle (Ptinus fur) or the hump-back spider beetle (Gibbium psylloides). The two khapra/cabinet beetles (Trogoderma angustum and Trogoderma germarium) are also found inside buildings infesting herbaria. The Odd beetle (Thylodrias contractus) is also a pest in herbariums and other natural history collections . Treatment: Freezing the specimen in a clear polyester bag with excess air removed. Heat sealing is done and the bag is placed in a normal domestic freezer at temperature of – 18° C for at least 14 days or at -30°C for 72 hours . Anoxia to stave the insect of oxygen. This is done by using sealed barrier films such as aluminium laminate. Enclose oxygen scavengers and relative humidity buffers. Heating will kill insects much more rapidly than freezing but it is essential to ensure that elevated temperatures do not harm the objects involved. In the past a number of museums have used ovens to `disinfest' insect collections and this often resulted in brittle specimens.

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Nitrogen has proven to be very effective and safe for treatment of sensitive objects. The procedure relies on exclusion of oxygen which then kills insects by anoxia and is relatively simple to conduct. Oxygen levels must be very tow, less than 0.1% and this can only be achieved in a special chamber or in individual bags made of an oxygen barrier film. Gamma radiation will kill insects at high doses.

Fumigation involves the introduction of a toxic pesticidal gas into an enclosed space. Fumigant gases will penetrate materials and will kill all insects within the target objects but the treatment provides no residual protection.

2. Light: Avoid direct sunlight and limit other light sources. 3. Humidity: Relative humidity should be kept between 45-55%. 4. Temperature: Temperature should be maintained between 18-22° C. 5. Degraded DNA- Herbarium specimen are potential sources of DNA. However, the DNA is degraded such that it is difficult to get amplified DNA. Occurrence of apuric sites, deaminated cytosine residues, and oxidized guanine residues are the main types of damage known from studies in vivo and on ancient DNA.

References 1. Anna De Pasquale. Pharmacognosy: The Oldest Modern Science. Journal of Ethnopharmacology. 1983 Vo11, Issue 1, 1984:1-16 2. Namraj Dhami. Trends in Pharmacognosy: A modern science of natural medicines . Journal of Herbal Medicine. Volume 3, Issue 4, 2013, Pages 123-131 3. Biljana Bauer Petrovska. Historical review of medicinal plants’ usage. Pharmacogn Rev. 2012 Jan-Jun; 6(11): 1–5. 4. Trease and Evans. Pharmacognosy. Elsevier. 16th Edition; 2009.

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5. Arvind Chopra. Ayuvedic Medicine and Arthritis. Rheumatic Disease Clinics of North America. Volume 26, Issue 1, 1 February 2000, Pages 133-144. 6. Kapur Malavika. Gleanings from Unani Medicine. Springer Link, 2015.Psychological Perspectives on Childcare in Indian Indigenous Health Systems pp 209-214. 7. Girish Sharma. Systematics of Fruit Crops. New India Publishing. 8. Harika Gupta. Nomenclature Plants: History, Common names.. 9. The Herbarium Catalogue, Royal Botanic Gardens, Kew. Published on ...