Medicinal Plants

History of Medicinal plants • Use of plants for medicines traces way to back to ancient 6mes • Western medicine traces back to Greek physician Hippocrates (Father of medicine), who used herbal remedies • Dioscorides, Roman physician wrote account of over 600 species of plants with medicinal value • Many of these plants incorporated into western medicine History of Medicinal plants One important plant that is not s/ll used… • Silphium (Ferula sp.; Apiaceae) • Seeds used as contracep6ve by Greek and Roman women for >1,000 years—ex6nct by 3rd or 4th century. • Grown mainly in Cyrene (currently Libya, N. Africa); main component of economy, illustrated on Cyrenian coins Giant fennel History of Medicinal plants Doctrine of Signatures defined in 16th century in west; same idea used by various cultures. Idea that the outer morphology of the plant or plant part corresponds to part of human body for which plant is effec6ve. • Lobed leaves of liverwort (Hepa/ca) to be used for liver problems • Bloodroot (Sanguinaria), with its red sap, used for blood ailments • Dutchman’s breeches (Dicentra) used for syphilis History of Medicinal plants 19th century—purifica6on of extracts from plants; led to formula6on of synthe6c drugs based on natural plant products •1806: Morphine extracted from opium poppy •1839: Salicylic acid iden6fied as ac6ve ingredient in various plants that reduced pain •1853: Salicylic acid first synthesized •1898: Chemist at Bayer Company synthesized acetylsalicylic acid, more palatable, named Aspirin Aspirin •Salicylic acid, a common hormone in many plants, s6mulates immune response, causing produc6on/release of defense compounds •Some converted to methyl salicylate (vola6le compound—wintergreen) that allows for plant communica6on •Aspirin (acetylsalicylic acid) inhibits enzyme cyclooxygenase (COX) •Suppresses prostaglandins, hormones that mediate various physiological responses; overproduc6on can lead to headaches, cramps, inflamma6on Salix sp. (Willow; Salicaceae) Filipendula (Spirea) ulmaria (Meadowsweet; Rosaceae) Currently 25‐50% of prescrip6on drugs in US include a plant product or contain a compound synthesized using a plant product as a model 75‐90% of rural popula6on in other parts of the world use herbal medicine as only health care. •China: Major user of herbal medicine, strong history of ancient Chinese medicine •India: Ayurvedic medicine •Unani: Islamic herbal tradi6on . . Two major categories of secondary compounds used as medicines Alkaloids: Contain nitrogen; examples include caffeine, nico6ne, quinine, atropine, morphine, ephedrine •Found in 15% plants •Some plant families especially alkaloid‐rich including Rubiaceae, Solanaceae, and Apocynaceae •Alkaloids stored in 6ssues that are important for survival and reproduc6on of plant •Oken in epidermal 6ssues as primary defense, also in latex •Alkaloids may affect neurotransmilers or structures (especially microtubules) necessary for cell division (mitosis) Quinine Ephedrine Alkaloids: Quinine Cinchona pubescens (Fever bark tree; Rubiaceae) • Quinine from bark; well known to Incas • Historically important an6malarial drug • Acts on Plasmodium parasite by inhibi6ng its metabolism • Also works as prophylac6c • Gin and tonic to make quinine palatable • Recent development of artemisinin, terpenoid compound (as opposed to an alkaloid) to combat malaria--less side effects, effective against resistant strains, works very fast (24 hrs) • From Chinese wormwood (Artemisia annua; Asteraceae); long used in China to reduce fevers Artemisinin Alkaloids: Ephedrine Ephedra sp. (Mormon Tea; Ephedraceae) • Dried stems as source of ephedrine, pseudoephedrine • Stimulatory effects similar to adrenaline, also relieves nasal congestion by relaxing bronchial muscles Alkaloids: Taxol Taxus brevifolia (Pacific yew, Taxaceae) •Bark and leaves contain drug •Other Taxus species used too •Inhibits cell division, important an6‐cancer drug Alkaloids: Vinblas6ne Catharanthus roseus (rosy periwinkle; Apocynaceae) •Alkaloids in roots and leaves; leaves generally used today •Tradi6onally used for diabetes (no evidence for this effect) •Two alkaloids; vincris6ne and vinblas6ne block cell division, important an6‐cancer drugs Alkaloids: Camptothecin Camptotheca acuminata (Cornaceae) •Chinese happy tree •Bark and wood, now use young leaves •Used for centuries in China to treat cancer •Inhibits DNA replica6on, cell division; •Deriva6ves used in chemotherapy; some of most promising new an6cancer drugs Local plant used as an:‐cancer drug (phenypropanoid class of compounds): Podophyllotoxin Podophyllum peltatum (May apple; Berberidaceae) • Use dried rhizome • Root extracts used by Native Americans as purgative, for skin disorders and growths • Podophyllotoxin and peltatins • Highly toxic, inhibit cell division Two major categories of secondary compounds used as medicines Glycosides: Sugar molecule (glyco‐) alached to ac6ve molecule, usually glucose Most common are cyanogenic glycosides, cardiac glycosides, and saponins H Cyanogenic glycosides: Cyanogenic glycosides: • Release cyanide (carbon atom triple‐bonded to nitrogen) upon breakdown; occur in >2600 species, especially families Rosaceae, Fabaceae, Poaceae, Araceae • Inhibits enzymes required for respira6on (blocks produc6on of ATP) • Foods with cyanogens include cassava (Manihot esculenta) and sorghum (Sorghum bicolor); food processing important, plant breeding for lower levels of compounds • Seeds of various Rosaceae also contain cyanogens, including almonds, apples, and cherries H Dhurrin: Sorghum Prunasin: Rosaceae Glycosides Cardiac glycosides and saponins: steroid molecule is ac6ve molecule •Cardiac glycosides affect contrac6on of heart muscle Digitoxin Digitalis purpurea and D. lanata (Foxglove; Scrophulariaceae) •Digitoxin (and other cardiac glycosides) from leaves •Slows heart rate while increasing the strength of each heartbeat Glycosides Saponins oken affect membranes Diosgenin in tubers of yams (Dioscorea sp.; Dioscoreaceae) Diosgenin •Compound converted to progesterone for first birth control pills •Precursor for cor6sone synthesis (an6‐ inflammatory) Why don’t we use more plant compounds in western medicine? How do we identify useful new plants? • Survey plants in the field--preferentially sample those without insect or pathogen damage, suggesting they are well defended • Work with local healers to identify plants; importance of conserving indigenous knowledge, which may be disappearing even faster than tropical forests • Ecological correlates: young/old leaves; shade/sun; phylogenetic relationships Why would Coley et al. predict that young leaves would contain more bioactive compounds? Why would Coley et al. predict that mature leaves of shade tolerant species would be more biologically active than leaves in high light (gap) areas? Phylogeny does inform utility; some clades more bioactive than others