Medicinal Plants & Natural Drug Molecules Notes

LIFS 2080: Medicinal Plants & Natural Drug Molecules

Toxin or Medicine?

• The same molecule can be a toxin or a medicine depending on the dosage.
• Digoxin (from foxglove leaves):
  • Cardiac glycoside (terpenoid).
  • High dose: vomiting, cardiac arrest, death.
  • Low dose: treats congestive heart failure (CHF) and related edema.
  • Plant source: Digitalis purpurea.
• Morphine (from opium poppy capsule latex):
  • Alkaloid (nitrogenous compound).
  • Highly addictive; caused the Opium Wars.
  • Overdose: respiratory failure, death.
  • Central nervous system depressant for severe pain relief.
  • Plant source: Papaver somniferum.

Historical Use of Herbal Medicine

• Fossil records:
  • Evidence of use by Neanderthals (50,000 years ago.)
  • Neanderthals used early versions of penicillin and aspirin.
  • Evidence found by examining plaque on Neanderthal teeth.
• Written documents:
  • Sumerian clay tablet (4,000 years old).
  • Papyrus Ebers (ancient Egyptian medicine).
  • 本草綱目 (Bencao Gangmu) - a comprehensive traditional Chinese medicine book.

Current Use of Herbal Medicine

• Still used by 60% of the world population.
• Examples of herbal medicine ingredients: 木이버섯, 모과, 살구씨, 팔각, 치자, 오가지, 오미자, 구기자, 산수유, 맥문동, 감국, 햇녹차, 녹차, 홍화이트, 홍화씨, 헛개열매, 헛개나무, 장미차, 잔대, 유근피, 치커리, 봉일, 익모초, 인진쑥, 둥

Traditional Chinese Medicine (TCM)

• Accounts for >40% of China's pharmaceutical market.
• Annual turnover is >190 billion yuan.
• Governmental funding aims to:
  • Facilitate TCM inheritance & innovation.
  • Promote TCM internationalization.
  • Modernize & standardize TCM by identifying bioactive compounds.

Bioactive Compounds

• Produce physiological effects in living cells & tissues.
• Many are secondary metabolites produced under stress, including:
  • Terpenoids.
  • Phenolics.
  • Nitrogenous compounds (alkaloids).

Stress and Bioactive Compound Production

• Types of Stress:
  • Chemical.
  • Physical.
  • Climatic (warming, UV radiation, drought).
• Effects of Stress
  • Photosynthetic tissues induce PSMS biosynthesis.
  • PSMS react with PSMS.
  • Increased PSMS, decreased VOCs, high C/N ratio.
• Volatile Terpenoids (Isoprene, MT, SQT):
  • Increase in production: Drought, UV, Warming
• Phenolics (Tannins, Phenolic acids, Flavonoids):
  • Increase in production: UV
• Resin Acids
  • Increase in production: Warming
• Salicylates
  • Increase in production: Warming

Case 1: Malaria

• Most widespread & dangerous protist disease.
• Caused by Plasmodium spp., transmitted by female Anopheles mosquito.

Malaria Life Cycle

1. Transmission to human (injects sporozoites).
2. Sporozoites enter liver and infect hepatocytes.
3. Liver cells rupture and merozoites released.
4. Intraerythrocytic cycle.
5. Sexual cycle.
6. Transmission to mosquito.

• Symptoms include:
  • Toxins
  • Fever
  • Nausea and vomiting
  • Sweats
  • Chills
  • Headache
  • Fatigue

Quinine

• An alkaloid isolated from bark of fever tree in 1820.
• Antimalarial effect of bark powder discovered by a Spanish Jesuit priest in Peru in the 17th century.
• Source: Cinchona sp.
• Mechanism: Kills Plasmodium in bloodstream & prevents infection of red blood cells.
• Tonic water:
  • Soda & sugar mask bitter taste of quinine.
  • Effective but with side effects (blurred vision, nausea).
  • Quinine level later reduced in soft drinks.
• Production:
  • Total synthesis is cost-ineffective.
  • Extraction from fever tree bark is primary source, but high demand causes deforestation.

Artemisinin

• A terpenoid from leaves of sweet wormwood.
• Kills Plasmodium effectively with fewer side effects.
• Also shows anti-inflammatory & anti-cancer effects.
• Source: Artemisia annua.
• Rapid response but short-acting.
• Needs prolonged therapy to reduce recurrence.
• Monotherapy may lead to drug resistance.
• Artemisinin-based Combination Therapy (ACT):
  • Completes clearance of Plasmodium.
  • Hinders development of resistance.
  • Artemisinin + a long-acting antimalarial drug.
• Production:
  • Extraction:
    • Inconsistent natural harvest.
    • Long lead time (~15 months) from cultivation.
    • Low yield (0.01 – 0.8%).
  • Total synthesis:
    • Short lead time, but low yield & high cost.
    • Scheme 1. First total synthesis of artemisinin by Schmid and Hofheinz.
  • Semi-synthesis:
    • Pathway is known.
    • Medium lead time.
    • High cost.
    • Uses Saccharomyces cerevisiae Fermentation + Photochemistry.
  • Biosynthesis:
    • Higher yield.
    • Under development.
    • Transgenic plant, Hairy roots, Transformed callus, Transgenic cell suspension culture.

Case 2: Cancer

• Malignant tumor with abnormal cell growth & potentials to spread to other parts.
• Process:
  • Normal skin cells transforming into a tumor.
  • Tumor growing and invading underlying tissues.
  • Cancer cells invading blood vessels.
  • Cancer cell traveling to other parts of the body.

Causes

• Caused by genetic mutation:
  • Hyperactive oncogenes.
  • Inactive tumor suppressor genes.
  • Inactive DNA repair genes.
• Effects of mutation:
  • Reprogram metabolism.
  • Secrete TGF-B.
  • Produce own growth factors (Bombesin-like peptides).
  • Sustained proliferation signalling.
  • Evade destruction by immune cells.
  • Uncontrolled replication.
  • Angiogenesis (↑ VEGFR-A): Endothelial cell migration & proliferation.
  • Resistance to cell death.
  • Metastasis & invasion: Alter cell morphology & adherence.

Vincristine

• One of the first plant-derived anticancer agents.
• An alkaloid from leaves of Madagascar periwinkle.
• Antimitosis by preventing microtubule formation.
• Source: Catharanthus roseus.
• Production:
  • Very low yield (<0.0003%) from extraction.
  • Possible total synthesis & biosynthesis to increase yield.
  • Mainly by semi-synthesis from 2 natural precursors with higher yield, using coupling and oxidation.

Paclitaxel

• A terpenoid from bark of Pacific yew.
• Antimitosis by preventing microtubule disassembly.
• Broader anticancer activity & less cytotoxic effect.
• Source: Taxus brevifolia.
• Mechanism: Prevents microtubule disassembly, leading to cell death.
• Production:
  • Extraction:
    • Low yield.
    • Slow growth.
    • Significant ecological impact.
  • Total synthesis:
    • Complicated steps.
    • Low yield.
    • High cost.
  • Semi-synthesis:
    • Abundant precursors in needles & twigs.
    • > 20 possible methods.
    • High yield.
  • Biosynthesis:
    • Entire pathway & enzymes involved are not fully understood.
    • Low & unstable yield from yew tissue culture or Taxol-producing endophytic fungi.

Omics

• Search for plant biosynthesis genes
  • Madagascar periwinkle (Catharanthus roseus), Happy tree (Camptotheca acuminata), Pacific yew (Taxus brevifolia), Mayapple (Podophyllum peltatum), Opium poppy (Papaver somniferum), Hemp (Cannabis sativa)
• Enzyme function validation
• Systems biology - Synthetic biology - Metabolic engineering
• Transfer in a microbial model
  • DNA assembly
  • Genetic transformation
• Improvement of the metabolic flux
  • Enzyme engineering
  • Balancing co-factors
• Optimization of the fermentation strategy
  • Media optimization
  • Co-culture
• Semisynthesis is an option if high enough precursors are available.

Considerations of Production Method

• Extraction:
  • Growth rate.
  • Bioactive compound concentration.
• Total synthesis:
  • Chirality (R vs S):
    • Chiral molecule with non-superposable mirror image.

Cytoprotective Effect of 20(S)-Rg3 on Benzo[a]pyrene-Induced DNA Damage

• 20(S)-ginsenoside Rg3 shows cytoprotective effect.
• 20(R)-ginsenoside Rg3 does not.

Production Method Considerations (Continued)

• Semi-synthesis:
  • Suitable precursor.
• Biosynthesis:
  • Optimal conditions.
  • Potential contamination.
• Other considerations:
  • Usage & demand.
  • Chemical complexity.
  • Cost effectiveness.