Introduction - Malaria is a major global health problem, with more than 500 million reported cases and at least 1 million deaths each year. The main problem with malaria control is the emerging drug resistance. Plasmodium falciparum (P. falciparum) developed widespread resistance to antimalarial drugs such as chloroquine (CQ) and mefloquine, but not to the artemisinins. The World Health Organization (WHO) recommended artemisinin combination therapy (ACT) for the treatment of uncomplicated malaria in all chloroquine resistance areas. However, P. falciparum has recently started to display resistance to these ACTs, highlighting the need for new chemotherapeutic approaches for the treatment of P. falciparum infections. Aims - The aims of this study were: (i) to design and synthesise a new series of antimalarial hybrid drugs, consisting of dihydroartemisinin (DHA) and aminoquinoline moieties bound covalently through different, very distinctive linkers; (ii) to determine the in vitro antiplasmodial activity and cytotoxicity of the synthesised series; (iii) to ascertain whether the in vitro antiplasmodial activity of the promising compounds would be carried over in vivo against Plasmodium vinckei (P. vinckei); and, (iv) to obtain an indication of the pharmacokinetic properties of this class of antimalarial drugs by performing snapshot pharmacokinetic analysis. Methods - DHA was coupled via an aminoethylether bond to various aminoquinolines to give hybrids and hybrid-dimers. CQ-susceptible (D10 and 3D7) and CQ-resistant (Dd2) strains of P. falciparum were used to determine the in vitro antiplasmodial activity. In vitro cytotoxicity was assessed using a mammalian cell-line (Chinese Hamster Ovarian, CHO). The antiproliferative activity of the hybrid-dimers was tested against three cell lines; renal adenocarcinoma (TK-10), breast adenocarcinoma (MCF-7) and melanoma (UACC-62). P. vinckei-infected mice were treated with the hybrid drugs for four days at a dosage of 0.8 mg/kg, 2.5 mg/kg, 7.5 mg/kg or 15 mg/kg intraperitoneally (ip) or orally (po), with 2.7 mg/kg, 8.3 mg/kg, 25 mg/kg or 50 mg/kg, in order to determine their antimalarial activity. A snapshot oral and intravenous (IV) pharmacokinetic study was performed. Results - All compounds were obtained as the 10-β-isomers and were isolated as the oxalate salts. Low nanomolar in vitro antiplasmodial activities were displayed by several compounds in this series, with IC50 values ranging from 5.15 to 29.5 nM, in comparison with the values of 2.09–5.11 nM and 21.54–157.90 nM for each of DHA and CQ respectively. All compounds displayed good selectivity towards P. falciparum in vitro (selectivity index (SI) ≥ 20). Two of the hybrids, featuring non-methylated and methylated two-carbon diaminoalkyl linkers, exerted potent in vivo antimalarial activities, with ED50 values of 1.1 and 1.4 mg/kg by ip route and 12 and 16 mg/kg po, respectively. Long-term monitoring of parasitaemia showed a complete cure of mice (without recrudescence) at 15 mg/kg ip and at 50 mg/kg po for these two hybrids, whereas artesunate was able to provide a complete cure only at 30 mg/kg ip and 80 mg/kg po. Conclusions - These compounds may provide a lead into a new class of antimalarial drugs so badly needed for treatment of resistant strains. Despite shorter half-lives and moderate oral bioavailability in comparison with DHA, two of the compounds of this series were able to cure malaria in mice at very low dosages, implicating extremely active metabolites. The optimum linker length for antimalarial activity was found to be a diaminoalkyl linker consisting of two carbon atoms, either unmethylated or bearing a single methyl group. / Thesis (PhD (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2013

Introduction - Malaria is a major global health problem, with more than 500 million reported cases and at least 1 million deaths each year. The main problem with malaria control is the emerging drug resistance. Plasmodium falciparum (P. falciparum) developed widespread resistance to antimalarial drugs such as chloroquine (CQ) and mefloquine, but not to the artemisinins. The World Health Organization (WHO) recommended artemisinin combination therapy (ACT) for the treatment of uncomplicated malaria in all chloroquine resistance areas. However, P. falciparum has recently started to display resistance to these ACTs, highlighting the need for new chemotherapeutic approaches for the treatment of P. falciparum infections. Aims - The aims of this study were: (i) to design and synthesise a new series of antimalarial hybrid drugs, consisting of dihydroartemisinin (DHA) and aminoquinoline moieties bound covalently through different, very distinctive linkers; (ii) to determine the in vitro antiplasmodial activity and cytotoxicity of the synthesised series; (iii) to ascertain whether the in vitro antiplasmodial activity of the promising compounds would be carried over in vivo against Plasmodium vinckei (P. vinckei); and, (iv) to obtain an indication of the pharmacokinetic properties of this class of antimalarial drugs by performing snapshot pharmacokinetic analysis. Methods - DHA was coupled via an aminoethylether bond to various aminoquinolines to give hybrids and hybrid-dimers. CQ-susceptible (D10 and 3D7) and CQ-resistant (Dd2) strains of P. falciparum were used to determine the in vitro antiplasmodial activity. In vitro cytotoxicity was assessed using a mammalian cell-line (Chinese Hamster Ovarian, CHO). The antiproliferative activity of the hybrid-dimers was tested against three cell lines; renal adenocarcinoma (TK-10), breast adenocarcinoma (MCF-7) and melanoma (UACC-62). P. vinckei-infected mice were treated with the hybrid drugs for four days at a dosage of 0.8 mg/kg, 2.5 mg/kg, 7.5 mg/kg or 15 mg/kg intraperitoneally (ip) or orally (po), with 2.7 mg/kg, 8.3 mg/kg, 25 mg/kg or 50 mg/kg, in order to determine their antimalarial activity. A snapshot oral and intravenous (IV) pharmacokinetic study was performed. Results - All compounds were obtained as the 10-β-isomers and were isolated as the oxalate salts. Low nanomolar in vitro antiplasmodial activities were displayed by several compounds in this series, with IC50 values ranging from 5.15 to 29.5 nM, in comparison with the values of 2.09–5.11 nM and 21.54–157.90 nM for each of DHA and CQ respectively. All compounds displayed good selectivity towards P. falciparum in vitro (selectivity index (SI) ≥ 20). Two of the hybrids, featuring non-methylated and methylated two-carbon diaminoalkyl linkers, exerted potent in vivo antimalarial activities, with ED50 values of 1.1 and 1.4 mg/kg by ip route and 12 and 16 mg/kg po, respectively. Long-term monitoring of parasitaemia showed a complete cure of mice (without recrudescence) at 15 mg/kg ip and at 50 mg/kg po for these two hybrids, whereas artesunate was able to provide a complete cure only at 30 mg/kg ip and 80 mg/kg po. Conclusions - These compounds may provide a lead into a new class of antimalarial drugs so badly needed for treatment of resistant strains. Despite shorter half-lives and moderate oral bioavailability in comparison with DHA, two of the compounds of this series were able to cure malaria in mice at very low dosages, implicating extremely active metabolites. The optimum linker length for antimalarial activity was found to be a diaminoalkyl linker consisting of two carbon atoms, either unmethylated or bearing a single methyl group. / Thesis (PhD (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2013

The debate regarding the advantages and disadvantages of using DDT for IRS has divided the scientific community. The health benefits of reducing malaria spreading are weighed against the potential health and environmental consequences of the chemical, and opinions also differ regarding the cost-effectiveness of the use of DDT. Global recommendations regarding use of DDT for IRS have been issued by the WHO, and the receipt of these on the local level is determined by the intended beneficiaries’ perception of legitimacy of the organisation. The WHO recommendations on DDT as well as interviews conducted with residents of a South African village and representatives for two South African NGOs have been reviewed using qualitative content analysis. This method was used to highlight different perceptions of and views on DDT use, as well as for examining the potential effect that the interviewees’ perception of international institutions’ legitimacy has on their views on DDT. This study shows that the controversy regarding DDT is not as prominent on the local level as on the global level, and that the perceptions of IRS with DDT differ between the WHO, the NGOs and the residents of the village. Further, this study shows that assessing legitimacy is dependent on a definition of “the people” in question, and that the accountability of authoritative actors on different levels needs to be evaluated further.

A significant challenge of the 21st century is the growing health threat stemming from drug-resistant infectious diseases. There is an undeniable need to discover new, safe and effective drugs with novel mechanisms of action to combat this threat. A study of drugs currently on the market showed that natural products account for approximately 75% of new anti-infective drugs, either as new agents or analogs based upon their structure. Unfortunately, major pharmaceutical companies have cut back tremendously in natural products research in part due to the frustrating obstacle of frequent rediscovery of compounds. Fungi in particular are difficult to work with in that they do not always produce the same variety and quantities of secondary metabolites under laboratory conditions. One of the groundbreaking discoveries evolving from genomics research is the observation that many fungi possess more gene clusters encoding for the production of secondary metabolites than the reported number of natural products isolated from those organisms. Simple epigenetic modifications such as DNA methlytransferase or histone deacetylase inhibition can activate silenced genes leading to the genesis of novel chemistry from the fungus. The work presented herein is a study of the isolation and characterization of anti-infective compounds from Floridian mangrove endophytes. In addition, epigenetic modifications were explored in order to increase the production of secondary metabolites as well as for the purpose of generating new analogs not found in the controls. Finally, structure activity relationship studies were performed in order to maximize the anti-malarial and antibiotic activity of cytosporone E.

Malaria is currently one of the most imperative parasitic diseases of the developing world. Current effective treatment options are limited because of increasing drug resistance, treatment cost effectiveness and treatment availability. Novel drug delivery systems are a new approach for increased efficacy in the treatment of the disease. Pheroid™ technology, a proven drug delivery system, in combination with anti-malarial drugs was evaluated in this study. The aim of this study was to evaluate the possible enhancement of the efficacy of the existing anti-malarial drugs in combination with Pheroid™ technology. The efficacy of existing anti-malarial drugs in combination with Pheroids was investigated in vitro with a chloroquine RB-1-resistant strain of P. falciparum. Two different Pheroid formulations, vesicles and microsponges, were used and the control medium consisted of sterile water for injection. Parasitaemia levels were determined microscopically and expressed as a percentage. An in vivo pilot study was also conducted using the P. berghei mouse model. The mice were grouped into seven batches of three mice each. The control group was treated with a Pheroid vesicle formulation only. Three of the groups were treated with three different concentrations of chloroquine dissolved in water namely 2 mg/kg; 5 mg/kg and 10 mg/kg bodyweight (bw) respectively, while the other three groups received the same three concentrations of chloroquine entrapped in Pheroid vesicle formulations. The measure of parasite growth inhibition (percentage parasitaemia), the survival rates and the percentage chemosuppresion was determined. In the in vivo study, all concentrations of chloroquine entrapped in Pheroid vesicles showed suppressed parasitaemia levels up to 11 days post infection. From day 11, the parasitaemia increases rapidly and becomes higher than that in groups treated with chloroquine in water. Chloroquine entrapped in Pheroid vesicles showed improved activity against a chloroquine resistant strain (RB-1) in vitro. The efficacy was enhanced by 1544.62%. The efficacy of mefloquine, artemether and artesunate in Pheroid microsponges were enhanced by 314.32%, 254.86% and 238.78% respectively. It can be concluded that Pheroid™ technology has potential to enhance the efficacy of anti-malaria drugs. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2008.

This thesis reports the results of a large number of experiments which were designed to elucidate the mechanisms whereby Gambian children, suffering from acute Plasmodium falciparum malaria may eventually control their infections. These experiments were carried out in vitro and success or failure of the various test systems was judged by their effect on parasite multiplication. Early in the course of these investiqations it was demonstrated that mononuclear cells from these children could cooperate with antibodies present in their serum to bring about a marked reduction in parasite growth. The efficiency of this antibody-dependent cellular cytotoxicity (ADCC) mechanism was related to levels of parasitaemia in the children, being greater in convalescent children than in those with acute malaria. Attempts were now made to identify the effector cells in this ADCC. Purified T and B cells were ineffective and although purified adherent cells (A) had an effect, it was much less than that mediated by the undepleted mononuclear cell population. Adherent cells were, however, fully effective in ADCC if they were exposed to the supernatant from T cells non-specifically activated by PHA. Thus cell cooperation leading to activation appears to play an important role in this system. Finally, experiments were set up to determine whether activated mononuclear cells could exert an inhibitory effect on parasite multiplication which was independent of anti-malarial antibody. It was shown that depression of parasite growth could be achieved by mononuclear cells, either from the children or from Europeans, if these cells were exposed to supernatants of previously stimulated mononuclear cells. These findings can be assembled to provide a tentative model of the development of protective responses in vivo. Perhaps following phagocytosis of parasite antigens and their presentation on the cell surface, T cells become activated: they may cooperate with B cells to produce parasite specific antibodies; they may also activate other mononuclear cells (non T, non B) to become effector cells. These cells, either alone, or perhaps more efficiently in cooperation with antibody, are able to kill parasites by the release of toxic factors, and the infection is brought under control. Finally, large amounts of specific antibodies of appropriate isotypes are synthesized. Acting as opsonins or by activating complement, they may serve to destroy remaining parasites. Their continued presence, by preventing merozoite penetration, may provide at least a temporary defense against reinfection. It is assumed that Gambian adults who have suffered repeated malaria infections and are now immune are defended by their possession of circulating IgG antibodies and B memory cells of all appropriate specificities.

No description available.

Biomarkers measured in the blood can provide information about disease pathophysiology, diagnosis and prognosis. Pronounced proinflammatory responses are characteristic of severe malaria, and excessive activation of the immune system is central to the pathophysiology of both cerebral malaria and placental malaria. Severe malaria is characterized by cytoadherence of parasitized erythrocytes to the microvasculature; impaired tissue perfusion; dysregulated inflammatory responses; and activation of the complement system, mononuclear cells, and endothelium. Despite the availability of effective antimalarial drugs, the mortality rate in severe malaria remains unacceptably high. To glean further insight into malaria pathophysiology, we investigated host biomarkers of immune activation in the blood of subjects with different manifestations of severe disease. C5 has been identified as being necessary and sufficient for the development of experimental cerebral malaria. We hypothesized that C5a (a terminal component of the complement cascade with potent inflammatory properties) may mediate its action by inducing and exacerbating inflammatory processes in severe malaria, leading to endothelial activation and dysregulated angiogenesis. I tested this hypothesis in vitro, and found that C5a interacted with malaria toxin PfGPI to drive deleterious inflammatory and anti-angiogenic responses. As C5a and anti-angiogenic factor sFlt-1 have been implicated in models of pathologic pregnancies, we asked whether increased levels of C5a in subjects with placental malaria were associated with altered angiogenesis and poor birth outcomes. Our results suggest that C5a impairs angiogenic remodelling in placental malaria leading to vascular insufficiency and fetal growth restriction. Further, altered profiles of inflammatory and angiogenic biomarkers in the periphery may identify occult placental malaria infections. We extended these observations to cerebral malaria where similar pathogenic pathways contribute to disease pathophysiology. In adults and children with cerebral malaria, altered profiles of angiogenic proteins were associated with disease severity and mortality and represent putative diagnostic and prognostic biomarkers in severe malaria.

Malaria has exerted a major selective pressure for red blood cell (RBC) polymorphisms that confer protection to severe disease. There is a predominance of blood type O in malaria endemic regions, and several lines of evidence suggest that the outcome of Plasmodium falciparum infection may be influenced by ABO blood type antigens. Based on observations that enhanced phagocytosis of infected polymorphic RBCs is associated with protection to malaria in other red cell disorders, we hypothesized that infected type O RBCs may be more efficiently cleared by the innate immune system than infected type A and B RBCs. The present work demonstrates human macrophages in vitro and murine monocytes in vivo phagocytosed P. falciparum infected O RBCs more avidly than infected A and B RBCs independent of macrophage donor blood type. This difference in clearance may confer relative resistance to severe malaria in individuals with blood type O.

Biomarkers measured in the blood can provide information about disease pathophysiology, diagnosis and prognosis. Pronounced proinflammatory responses are characteristic of severe malaria, and excessive activation of the immune system is central to the pathophysiology of both cerebral malaria and placental malaria. Severe malaria is characterized by cytoadherence of parasitized erythrocytes to the microvasculature; impaired tissue perfusion; dysregulated inflammatory responses; and activation of the complement system, mononuclear cells, and endothelium. Despite the availability of effective antimalarial drugs, the mortality rate in severe malaria remains unacceptably high. To glean further insight into malaria pathophysiology, we investigated host biomarkers of immune activation in the blood of subjects with different manifestations of severe disease. C5 has been identified as being necessary and sufficient for the development of experimental cerebral malaria. We hypothesized that C5a (a terminal component of the complement cascade with potent inflammatory properties) may mediate its action by inducing and exacerbating inflammatory processes in severe malaria, leading to endothelial activation and dysregulated angiogenesis. I tested this hypothesis in vitro, and found that C5a interacted with malaria toxin PfGPI to drive deleterious inflammatory and anti-angiogenic responses. As C5a and anti-angiogenic factor sFlt-1 have been implicated in models of pathologic pregnancies, we asked whether increased levels of C5a in subjects with placental malaria were associated with altered angiogenesis and poor birth outcomes. Our results suggest that C5a impairs angiogenic remodelling in placental malaria leading to vascular insufficiency and fetal growth restriction. Further, altered profiles of inflammatory and angiogenic biomarkers in the periphery may identify occult placental malaria infections. We extended these observations to cerebral malaria where similar pathogenic pathways contribute to disease pathophysiology. In adults and children with cerebral malaria, altered profiles of angiogenic proteins were associated with disease severity and mortality and represent putative diagnostic and prognostic biomarkers in severe malaria.