Plants used to treat infectious disease - II Antimalarials

Malaria History Statistics Caused by unicellular parasites in genus Plasmodium  Plasmodium vivax,  Plasmodium ovale,  Plasmodium malariae  P. falciparum cause of most fatalities Spread by bite of female Anopheles mosquito

Fever bark tree Genus Cinchona native to the slopes of the Andes Mountains in South America Member of the Rubiaceae, the coffee family Called quina-quina by Incas 38 species Cinchona - several used to treat malaria

Small specimen of Cinchona pubescens in the Rubiaceae

Cinchona sp.

Historical use of quina-quina Well known to Incas Shared with Jesuits Bark of tree used for many medicinal purposes  analgesic, anaesthetic, antibacterial, anti- malarial, anti-microbial, anti-parasitic, antiseptic, astringent, febrifuge, muscle- relaxant

Jesuit’s bark Countess of Cinchon, wife of the Viceroy of Peru Linnaeus named the genus Cinchona Late 17th century - standard treatment for malaria

Quinine alkaloid quinine isolated Purified quinine soon available Demand for the bark increased 36 alkaloids in Cinchona bark - 4 have anti- malarial properties  Quinine is the most effective Quinine yields Plantations

Quinine

Physiological action Quinine kills parasite in blood stream Also effective as a prophylactic to prevent initial infection of red blood cells in travelers  "gin and tonic” one of the earliest prophylactics  Not 100% effective

Quinine mode of action Parasite feeds on hemoglobin - Breaks down globin proteins into a.a. in lysosomes - heme converted to a non-toxic product by parasite Quinine accumulates in lysosome of parasite in RBC Quinine binds to heme and inhibits conversion of heme to non- toxic product Heme-quinine complex highly toxic to parasite May function by disrupting lysosome membrane

Side effects Ringing in the ears, possible hearing loss Dizziness Gastrointestinal upset: nausea, vomiting, diarrhea, abdominal pain Rashes Visual disturbances - blurred vision More serious side effects in rare cases

Synthetics During World War II synthetics were developed  In 1944 Robert Woodward and William Doering synthesized quinine from coal tar Several synthetics have similar mode of action to quinine  Chloroquine  Mefloquine  Piperaquine

Chloroquine

Chloroquinine Chloroquine is less toxic and more effective than quinine Most widely used drug for malaria Widespread use of chloroquine has resulted in chloroquine-resistance Parasites becoming resistant to other drugs as well

Piperaquine – seeing increased use in chloroquine resistant areas

Artemisinin Artemesia annua

Artemesia annua, wormwood, annual wormwood, sweet wormwood, sweet Annie, qinghaosu Member of the Asteraceae (sunflower family) Herbaceous annual native to Asia Plant became naturalized in many countries and now almost a worldwide distribution Often considered a weed

Artemesia annua Sweet Annie Sweet wormwood Annual wormwood Qinghaosu

Traditional uses of qinghaosu Used for treating malaria for over 2,000 yrs Mentioned in an early medical treatise that has been dated at 168 BC Mentioned in Chinese Handbook of Prescriptions for Emergency Treatments from 340 AD for the treatment of fevers Modern scientific studies on this plant began in the late 1960s and artemisinin isolated in 1972

Artemesinin Sesquiterpene lactone with an endoperoxide bridge Artemisinin and derivatives are being called endoperoxides

Distribution of artemisinin Essential oils of Artemisia annua contain at least 40 volatile oils and several nonvolatile sesquiterpenes components - artemisinin is one of these The essential oils are found in glandular trichomes on the leaves, stems, and flowers Artemisinin content appears to be highest in the trichomes of the flowers

Artemesinin derivatives and semi- synthetics Dihydroartemesinin (DHA) – reduced lactol derivative Artemether – semi-synthetic derivative Arteether – semi-synthetic derivative Artesunate – semi-synthetic derivative Artelinate – semi-synthetic derivative

Current uses Artemisinin and derivatives are effective in treating chloroquinine resistant strains of Plasmodium Artemisinin and/or derivatives used in China, Vietnam, Thailand, Myanmar (Burma) where multi-drug resistance has occurred Clinical trials on-going in many areas Combined therapy with piperaquine being used in many areas

Artemisinin Advantages - clear parasites from blood faster than other drugs Disadvantages  short half life so high rates of reinfection  poor oral bioavailability  liver stages are not affected so not good as a prophylactic or for radical cures (eradicating the dormant liver stage for P. vivax and ovale Derivatives should help overcome these