Malaria is one the world’s most devastating diseases. Several classes of drugs are used to
treat malaria. Artemisinin combination therapy is the first line treatment of uncomplicated
malaria. The artemisinin derivative, artemisone in conjunction with the Pheroid® drug
delivery system, is the focus of this thesis.
The impact of the Pheroid® on the bioavailability of artemisone was evaluated in vervet
monkeys. The resulting artemisone plasma levels were much lower (Cmax of 47 and 114
ng/mL for reference and Pheroid® test formulations respectively) than expected for the
dosages administered (60 mg/kg). The Pheroid® improved the pharmacokinetic profile of
artemisone in a clinically significant manner. The metabolism of artemisone was assessed
in vitro by using human and monkey liver and intestinal microsomes, and recombinant
CYP3A4 enzymes. The Pheroid® inhibits the microsomal metabolism of artemisone. In
addition, there is a species difference in artemisone metabolism between man and monkey
since the in vitro intrinsic clearance of the reference formulation with monkey liver
microsomes is ~8 fold higher in the monkey liver microsomes compared to the human liver
microsomes and the estimated in vivo hepatic clearance for the monkey is almost twofold
higher than in humans.
Artemisone has potent antimalarial activity. Its in vitro efficacy was approximately twofold
higher than that of either artesunate or dihydroartemisinin when evaluated against P.
falciparum W2, D6, 7G8, TM90-C2B, TM91-C235 and TM93-C1088 parasite strains. The
Pheroid® drug delivery system did not improve or inhibit the in vitro efficacy of artemisone or
DHA. Artemisone (reference and Pheroid® test formulations) and metabolite M1 abruptly
arrested the growth of P. falciparum W2 parasites and induced the formation of dormant ring
stages in a manner similar to that of DHA.
Interaction of artemisone with the p-glycoprotein (p-gp) efflux transporter was investigated.
Artemisone stimulates ATPase activity in a concentration-dependent manner, whereas the
Pheroid® inhibited this p-gp ATPase activity. P-gp ATPase activity stimulation was fourfold
greater in human than cynomolgus monkey MDR1 expressed insect cell membranes.
Artemisone alone and artemisone entrapped in Pheroid® vesicles showed moderate apical
to basolateral and high basolateral to apical permeability (Papp) across Caco-2 cells. The
Papp efflux ratio of artemisone and artemisone entrapped in Pheroid® vesicles were both >5,
and decreased to ~1 when the p-gp inhibitor, verapamil, was added. Therefore, artemisone
is a substrate for mammalian p-gp. The cytotoxic properties of Pheroid® on Caco-2 cells
were assessed and the pro-Pheroid® seems to be non-toxic at concentrations of 1.25%. Vervet monkey plasma caused antibody-mediated growth inhibition of P. falciparum. Heat
inactivated or protein A treatment proved useful in the elimination of the growth-inhibitory
activity of the drug-free plasma. Plasma samples containing artemisone could not be
analysed by the ex-vivo bioassay method. The dual labelling ROS assay did not prove to be
useful in the evaluation of ROS production by artemisone and the Pheroid® delivery system.
In conclusion, entrapment of artemisone in the Pheroid® delivery system improves the
pharmacokinetic properties of artemisone, but does not improve or inhibit its antimalarial
efficacy in vitro. The Pheroid® inhibited both the microsomal metabolism of artemisone and
P-gp ATPase activity and was shown to be non-toxic at clinically usable concentrations. / PhD (Pharmaceutics), North-West University, Potchefstroom Campus, 2014
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/12241 |
| Date | January 2014 |
| Creators | Grobler, Lizette |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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