Malaria

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Malaria

• Caused by Plasmodium species.
• Kills 700,0002.7 million people a year.
• Children in Africa are most of the victims.
• Pregnant women have increased susceptibility.
• Drugs are toxic.
• Problems of strains resistant to available drugs.
• Targeting host specific mechanism to avoid
  resistance to treatment.

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Malaria lifecycle
www.hpa.org.uk
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Entry into erythrocytes

• Extracellular merozoites invades erythrocytes and
  becomes enveloped.
• The parasites develop and form a parasitophorous
  vacuolar membrane (PVM).
• Erythrocyte proteins recruited to the PVM for the
  endocytic process.

Proposed model for parasite endocytosis
Murphy, S. C. et al (2006)
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G-protein signaling pathway

• Particular proteins recruited for endocytosis
• Gs signaling pathway proteins
• ß2-adrenergic receptor (ß2-AR)

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Studying endogenous intracellular signaling

• Peptides designed to specifically target
  inhibition of endogenous G protein signal
  transduction.
• Chang, M. S. S. et al (2000)

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Signaling for erythrocyte infection?

• The last 11 a.a. of C-terminus of Ga is important
  for receptor interaction. Gilchrist, A., et al
  (1998)

• Tested for inhibition of infection
• Gas (wt sequence) ? 87 inhibition
• Gascr (scrambled) ? 4 inhibition
• Treatment with agonists of ß2-AR increased cAMP
  production and stimulated malarial entry.

Harrison, T. et al (2003)
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Feature article

• Is signaling required for intracellular
  survival/proliferation?
• Can this be used as an approach for
  pharmaceutical intervention?

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Experimental approach

• RBC ghosts to study the molecular processes.
• Enables loading markers and specific peptides for
  assays.
• Smaller dialysis membrane, K-rich resealing
  buffer, supports GTP cycle.

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Ghosts function similar to intact RBC

• Ghosts retain biconcave morphology but less
  pigment.
• Ghosts can hold both high and low molecular
  weight cargo.
• Membrane is intact protecting proteinaceous cargo
  from exogenous protease.

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• ß-AR signaling pathway is active in Ghosts

• Isoproterenol is an agonist of ß-AR .
• Propranolol is an antagonist of ß-AR.

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Ghosts support parasite infection

• Parasites show comparable morphology in ghosts.
• Schizonts matured in ghosts are capable of
  rupturing and reinvading ghosts.
• Ghosts supported normal parasite maturation in
  high and low parasitemia.

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Testing erythrocyte G protein activity
Peptide blocks signaling
Peptide inhibits invasion
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ß-Blockers as inhibitors for maturation
Propranolol decreases schizont formation
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Propranolol affecting morphology of parasites

• Schizont retardation seen at 44hr.
• Propranolol doesnt effect sorbitol sensitivity
  or protein export.

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Combination with propranolol decrease effective
doses
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Conclusions

• New method for ghost preparation is more similar
  to normal RBC and can sustain malarial
  infections.
• G protein signaling is necessary for infection
  and maturation in erythrocytes.
• ß-blockers (propranolol) inhibits maturation and
  seems to retard schizont formation.
• Propranolol coupled with existing drugs decreases
  effective dose.
• Issues still remain for ß-blockers as treatment
  due to possibilities of hypotension.
• Targeting a host mechanism can have significant
  effect in decreasing possible resistant
  parasites.

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