Natural product case study - malaria

What is malaria caused by?

Caused by parasites of genus species plasmodium and transmitted through an infected mosquito

Whah plasmodium species infects humans the most

Plasmodium falciparum

What are the 5 species of plasmodium they can cause

Plasmodium : falciparum, vivax, ovale, knowlesi, malariae

Describe the malarial life cycle

Malaria begins when infected female mosquito bites in to human

Then injected sporozoites into human

Sporozoites travel to the liver

Sporozoites can become shizonts which are specialised cells that multiply

In the liver - the 5 plasmodium species can develop - vivax, ovale, malariae, falciparum

Vivax and ovale can product dormant species called hypnozoites

Can become activated - and form shizonts

Parasites can then enter red blood cells and multiply, some parasites can become gametocytes

Then when next mosquito bites a human - it injests the gametocytes which go through sexual reproduction forming Sporozoites so next time it bites human will insert this in to the next human

What complications can falciparum cause

F- fever

A- ARDS

L- low blood sugar

C- cerebral malaria

I- infections

P- pulmonary oedema

A- anemia

R- renal failure

U- urine output is reduced

M- metabolic acidosis

Describe the basic pathogenesis of cerebral falciparum malaria

Compromised blood brain barrier - due to accumulation of infected red blood cells - toxic substances can enter brain parenchyma

Sequesteration of parasitised or non parasitised erthyrocytes - infected rbc has surface proteins - can bind to endothelial cell lining of blood vessels (sequesteration) makes it harder to clear out and leads to accumulation of small blood vessels throughout body

Cytokines storm

Damage to endothelial wall - causes activation of pro inflammatory or anti inflammatory cytokines

Infected rbc accumulation - can cause localised hypoxia and impaired perfusion - causes microvascular obstruction

Metabolic dysfunction

Why did quinine and chloroquine not work best as malaria medicines in the end

Plasmodium formed resistance

Not finishing treatment regimen

What can be given with quinine or chloroquine

Can give folate inhibitors - folate allow malaria to survive

What did the ethnobotanical search strategy involve

Tried to collect traditional Chinese medicines known to reduce fever

What was later found

Found that neutral ethyl ether extract of sample no. 191 was effective in removing rodent malaria at dose 1,0 g/kg taken for three days

What was the neutral portion of ethyl ether at no. 191 position called

Artemisinin

Why was discovery of artemisinin hard to pass

China was blocked from the world

Required looking at stero structure, the synthesis, other indications, any derivatives like Artemether,optimising and manufacturing to synthesise it

What key structures does artemisinin contain

Contains an endoperoxide bridge - important for activity

And carbonyl function

How can derivatives be formed

Can maintain core endoperoxide bridge

Can reduce carbonyl into hydroxyl group - to get an acetate derivative

List some common artemisinin derivatives

Artesunate - improved water solubility

Artemether - improved lipid solubility take with lumefantrine which has a longer half life

Dihydroartemisinin

Artemisone

Artemiside - modified epoxide bridge potent activity against sensitive and resistant plasmodium falciparum

How does artemisinin work?

Malaria - the parasites feed on hb in red blood cells and release toxic heme as a byproduct of digestion

Artemisinin - contains an endoperoxide bridge it's sensitive to the presence of iron ions - which can be present in parasites vacuole where digestion of hb occurs

When endoperoxide bridge encounters iron ion causes bridge to decompose and release carbon centred radicals

Those carbon centred radicals can alkylate parasitic proteins causing damage

This is heme mediated

Describe the basic process design and unit operations for plant based substances (liquid liquid extraction)

Percolation - pass solvent into plant material to extract desired compound

Then clarify to remove bulk of contaminants through filtration

Then capture - mix with new solvent that's immiscible with original solvent - desired compounds go into second solvent and contaminants in original solvent

Can change solvents to aid purification

Them purfiy through chromatography

Polish through crystallisation

Allow extract to crystallise out of solution

Describe what commercial solid liquid extraction and purification methods to obtain artemisinin from artemisia annua involves

Get the raw material and clean it , crush and grind to increase surface area for extraction

Then mix with ethanol (green chemistry) for extracting artemisinin

Then filter to separate liquid extract from solid plant and evaporation - allows ethanol to be removed to leave concentration extract

Hexane - used as a solvent it's immiscible with ethanol - so causes the artemisinin to move to hexane layer whilst contaminants like chlorophyll move in to the original layer, chromatography, filter, condense and evaporate , crystallise filter and dry

Why not choose artemisinin based monotherapy

Due to chance of resistance

What happens if patient doesn't take full course

Merrozoites - form of malaria parasite that infects and replicates inside red blood cell

Sporozoites - in blood stream to liver

If patients don't take full course means shizonts may survive can continue rupture red blood cells

Merozoites can be released in to blood stream and invade more red blood cells

What does recrudescence of p falciparum mean

Reappearance of malaria after period of treatment

Give an example of artemisinin resistance

Resistance

Mutations in pfkelch 13 encoding for k13 parasites propeller domains

What is ACT therapy?

Artemisinin combination therapy

Can use long acting therapy with artemisinin which gets eliminated quickly

And long acting can last a while to kill parasite

What combinations can we use

Can use artimistin derivatives

Like Artemether (lipophilic), artesunate (hydrophilic) dihydroartemisinin (metabolite)

Can combine with lumefantrine , mefloquine, sulfadoxine

Can create co formulated drug - with both drugs in there

Why are ACTS used

Reduce emergence of resistance

Achieve complete parasite clearance

Combine artemisinin derivative with slower acting drug

Why are children most susceptible to malaria

Can't use prophylaxis effectively like nets at night

How was Coartem tailor made for children

First standard drug had to be crushed, didn't taste nice

Then made dispersible tablets, sweet taste, disperses in water

Both are good at clearing fever and parasite equally