Pharmacognosy Notes

Pharmacognosy

Introduction

  • Pharmacognosy: The study of natural products used as medicines.

  • Origin of the word: φάρμακον γνῶσις (pharmakon gnosis), meaning "Remedy Knowledge".

Historical Context

  • The word "pharmacognosy" debuted in the early 19th century to designate the discipline related to medicinal plants (Johann Adam Schmidt).

  • Medicinal plants were used in all cultures, irrespective of the underlying philosophical premise.

  • Traditional knowledge was orally transmitted, followed by written texts such as Papyrus Ebers (1600 BC) and baked clay tablets (650 BC).

  • Printed herbals appeared after the invention of printing.

  • Pharmacopoeias, such as the London Pharmacopoeia (1618), were developed.

Disciplines Involved

  • Pharmacognosy encompasses many disciplines:

    • Botany

    • Plant collection

    • Commerce

    • Plant chemistry (phytochemistry)

    • Enzymology

    • Genetics

    • Quality control

    • Pharmacology

Scope

  • Pharmacognosy is mainly concerned with plant material.

  • Animal products are also traditionally encompassed within pharmacognosy.

  • Includes plants, minerals, animals, and fungi.

Examples of Natural Products

  • Taxus brevifolia (Yew)

    • Contains Taxol (paclitaxel), used in breast carcinoma treatment.

    • Highlights the risk of wild plant exhaustion due to medicinal use.

  • Catharanthus roseus (Madagascar periwinkle)

    • Source of vincristine sulfate, used in acute leukemia treatment.

    • Illustrates the difference between using a purified molecule versus the whole plant.

Natural vs. Synthetic

  • Natural products are often perceived as natural, wholesome, and healthy.

  • Examples include Morphine and Ascorbic acid (vitamin C).

  • Efficacy and toxicity are the same regardless of whether a compound is synthesized by a plant or an organic chemist.

  • Natural vanilla is a complex mixture of flavors extracted from Vanilla planifolia and Vanilla tahitensis.

    • Vanillin (4-hydroxy-3-methoxybenzaldehyde) is the key component, present at 1-2% w/w in cured vanilla pods.

    • Production of 1 kg of vanillin requires approximately 500 kg of vanilla pods, corresponding to the pollination of approximately 40,000 vanilla orchid flowers.

    • Microbial transformations of natural precursors to generate vanillin are accepted as “natural” according to European and US food legislation.

Toxicity of Natural Products

  • Not all plants are good for health; some are toxic.

  • Poison Hemlock (Conium maculatum L.)

    • Contains toxic alkaloids such as Coniine.

    • Socrates' death in 399 B.C. was likely caused by poison hemlock.

  • Toxins and LD50 Values

    • Clostridium botulinum neurotoxin: LD_{50} = 0.03 ng/kg (i.p. in mouse).

    • Illustrates that natural products can be very toxic.

  • Strychnos nux vomica

    • Contains strychnine; minimum lethal oral dose in adults is 30–120 mg (probable lethal oral dose is 1.5 to 2 mg/kg).

Natural vs. Synthetic (Revisited)

  • Both natural and synthetic compounds can be healthy or toxic.

  • We may have more information on some natural products because they have been around longer.

  • Efficacy and toxicity of each molecule must be assessed.

Crude Drugs

  • Definition:

    • In ordinary language: Drug

    • In pharmacognosy: plant or part of plant which contains molecules endowed with pharmacologic efficacy defined as active principles, plant or part of plant which is used as medicine or to extract active principles.

  • Part of plant having therapeutic value

  • Crude drug active principle ≠ medicine

  • Examples:

    • **Cephaelis ipecacuanha

    • Wild plants, Cultivated plants, Both

    • KHARROB, AMIVISNAGA

  • Cascara sagrada

    • Contains Chrysophanic acid

  • Digitalis purpurea

    • Contains digoxin, used to treat heart conditions.

  • Morphine

    • From (old) German or Dutch words (troken – droog - droge) meaning «dry»

    • Whole plant or part of plant Juice, latex, extract…

    • Foxglove, Opium.

Crude Drug Nomenclature

  • Crude drug name:

    • Example: foxglove leaf, coca leaf, plantago seed, marshmallow root.

  • Word order in European Pharmacopoeia:

    • First word: Plant (genus, species, or Latin genitive case).

    • Second word: Part of the plant.

Types of Crude Drugs

  • Organised Crude Drugs

    • Part of plants, Plant cells

    • Macroscopic and microscopic characteristics

      • Radici, Justi, Erbe e Sommità

  • Unorganised Crude Drugs

    • Gums (Aloe).

Relationships

  • Medicinal plant → Crude drug → Phytochemical components → Active principle → Medicine

  • Leaves, roots, fruits… → Many molecules → One molecule

Classification of Crude Drugs

  • Alphabetical

  • Taxonomic

  • Morphological

  • Pharmacological (therapeutic)

  • Phytochemical

  • Ideal classification does not exist!

Active Principles/Constituents

  • Efficacy of crude drugs linked to their active principles.

  • Hamamelis virginiana

    • Contains hamamelitannin
      HO. C{14}H{12}O_{9}

Metabolites

  • Primary metabolites

    • Carbohydrates

    • Lipids

    • Proteins

    • Nucleic acids

  • Secondary metabolites

    • Terpenes

    • Anthraquinones

    • Alkaloids

    • Wide array of structurally complex and diverse molecules.

Accumulation of Metabolites

  • Metabolites can accumulate in different organs. Example: Nicotine biosynthesis.

  • Metabolite synthesis occurs in specialized organs.

Importance of Secondary Metabolites

  • To influence insect behavior

  • To attract pollinators or increase seed dispersal

  • As defense compounds against herbivores

  • As defense compounds against other plants

  • As defense compounds against microorganisms (bacteria, fungi, viruses)

  • To modify plant-associated microorganisms

  • As defense to abiotic stress (e.g. UV radiation)

Secondary Metabolite Transport

  • Mechanisms for transport and storage, including MDR-type, PDR-type, and WBC-type transporters.

  • Accumulation mainly occurs in the vacuole.

European Pharmacopoeia

  • Standards for herbal drugs, including tests for species, foreign matter, loss on drying, ash content, and assays for essential oils.

  • Example: Opium dry extract, standardised.

Plant Taxonomy

  • Hierarchical classification: Kingdom, Phylum, Subphylum, Class, Order, Family, Genus, Species.

  • Example: Sunflower (Helianthus annuus).

Plant Parts Used as Crude Drugs

  • Leaf (Folium), Flower (Flos), Fruit (Fructus), Seed (Semen), Whole plant (Herba), Wood (Lignum), Bark (Cortex), Rhizome (Rhizoma), Root (Radix).

  • Extracts, Exudates, Latices, Gums, Resins, Essential oils, Fixed oils, Balsams, Bulb (Bulbus).

Examples of Herbal Medicine.

  • SENNAE

  • MANNA

Phytotherapeutics in cancer invasion and metastasis

Antidiabetic plants improving insulin sensitivity

Drugs acting on the nasal and respiratory systems

*Aromatic inhalations
*Bronchodilators and nasal decongestants
*Expectorants
*Antiexpectorants
*Cough depressants
*Demulcents

Classes of Compounds

  • Alkaloids

  • Tannins

  • Flavonoids

  • Essential oils

  • Glycosides

  • Examples:

    • Morphine, Aloin, Ellagic acid, Eugenol, Quercetin