Effect of iron chelation therapy on mortality in Zambian children with cerebral malaria.

To examine the effect of iron chelation on mortality in cerebral malaria, we enrolled 352 children in a trial of deferoxamine in addition to standard quinine therapy at 2 centres in Zambia, one rural and one urban. Entrance criteria included age < 6 years, Plasmodium falciparum parasitaemia, normal cerebral spinal fluid, and unrousable coma. Deferoxamine (100 mg/kg/d infused for a total of 72 h) or placebo was added to a 7 d regimen of quinine that included a loading dose. Mortality overall was 18.3% (32/175) in the deferoxamine group and 10.7% (19/177) in the placebo group (adjusted odds ratio 1.8; 95% confidence interval 0.9-3.6; P = 0.074). At the rural study site, mortality was 15.4% (18/117) with deferoxamine compared to 12.7% (15/118) with placebo (P = 0.78, adjusted for covariates). At the urban site, mortality was 24.1% (14/58) with deferoxamine and 6.8% (4/59) with placebo (P = 0.061, adjusted for covariates). Among survivors, there was a non-significant trend to faster recovery from coma in the deferoxamine group (adjusted odds ratio 1.2; 95% confidence interval 0.97-1.6; P = 0.089). Hepatomegaly was significantly associated with higher mortality, while splenomegaly was associated with lower mortality. This study did not provide evidence for a beneficial effect on mortality in children with cerebral malaria when deferoxamine was added to quinine, given in a regimen that included a loading dose.

Assessment of the effect of the oral iron chelator deferiprone on asymptomatic Plasmodium falciparum parasitemia in humans.

While the parenteral iron-chelating agent desferrioxamine B has anti-malarial activity in humans, the usefulness of an orally active chelator for this indication has not been investigated previously in vivo. We conducted a prospective, double-blind, placebo-controlled, cross-over trial of deferiprone (L1; CP20; 1,2-dimethyl-3-hydroxypyridin-4-one) in 25 adult Zambians with asymptomatic Plasmodium falciparum parasitemia. Deferiprone was administered daily for three or four days in divided doses of 75 or 100 mg/kg of body weight, dosages that are effective for treating iron overload. No reduction in asexual intra-erythrocytic parasites was observed during or after deferiprone treatment. The mean peak plasma concentration of deferiprone (108.9 +/- 24.9 micromol/L) achieved was within the range demonstrated to inhibit the growth of P. falciparum in vitro, but the systemic exposure as determined by the 24-hr plasma concentration-time curve would not be predicted inhibit growth in vivo. No evidence of deferiprone-associated hematological toxicity was noted in this short-term study of these subjects, all of whom had clinical evidence of normal body iron stores. Because of the risk of neutropenia and other adverse effects with higher doses or prolonged use of the chelator, additional trials of deferiprone as a sole anti-malarial agent would not seem to be justified. In contrast, further efforts are needed to develop other orally active iron-chelating agents specifically for their anti-malarial action.

Cerebrospinal fluid levels of biopterin, nitric oxide metabolites, and immune activation markers and the clinical course of human cerebral malaria.

Cerebrospinal fluid samples from 130 children who presented with cerebral malaria were investigated to elucidate the impact of biopterin production, NO formation, and local immune activation on the clinical course of this disease. Biopterin levels were significantly lower in patients who were in a deeper coma (P = .02). Cerebrospinal fluid concentrations of NO were significantly higher in children who died than in survivors (P = .037); however, this was not the case for macrophage activation markers, neopterin, and soluble tumor necrosis factor receptor p75 (sTNFR-75). Biopterin, neopterin, and sTNFR-75 but not NO concentrations were significantly related to each other. Low biopterin levels in deep coma are compatible with an impaired local Th1 response, but the low levels could also be due to the scavenging of radicals or to decreased neurotransmitter synthesis. Local production of NO, most likely by nonimmune mechanisms, may be detrimental in cerebral malaria; however, this appears not to be the case for local Th1-mediated immune pathways.

Prolonged macrophage activation and persistent anaemia in children with complicated malaria.

OBJECTIVE: To determine if prolonged immune activation may be associated with the persistence of anaemia after treatment for severe malaria, we measured serum concentrations of neopterin and interleukin-4 during one week of antimalarial therapy and determined haemoglobin levels one month later. Neopterin is a clinically valuable marker for monitoring activation of macrophages by gamma-interferon and thus reflects the TH-1 immune response. Interleukin-4 is a major cytokine that tends to be inhibited by TH-1 activity. METHOD: The study population consisted of 26 Zambian children < 6 years of age who presented with cerebral malaria to a rural hospital in 1994 and who were treated with quinine for seven days. Six children (23%) were anaemic (haemoglobin < 11 g/dl) one month after completing antimalarial therapy. RESULTS: On admission, concentrations of neopterin were markedly elevated in all patients. During the seven days of anti-malarial therapy, neopterin levels remained elevated in the 6 children who proved to have persistent anaemia one month after finishing treatment but declined significantly (P = 0.008) in the 20 children who corrected their haemoglobin levels by that time. Conversely, interleukin-4 levels declined in the children with persistent anaemia (P = 0.043) but not in the other children. CONCLUSION: Persistence of the TH-1 mediated immune response and associated activation of macrophages may be involved in the pathogenesis of lingering anaemia after treatment of malaria.

Modulatory potential of iron chelation therapy on nitric oxide formation in cerebral malaria.

To determine whether iron chelation modulates nitric oxide (NO) formation and cell-mediated immune effector function in children with cerebral malaria, serum concentrations were measured of the stable end products of NO, nitrite and nitrate (NO2-/NO3-), interleukin (IL)-4, -6, and -10, and neopterin in 39 Zambian children enrolled in a placebo-controlled trial of desferrioxamine B and quinine therapy. Mean concentrations of NO2-/NO3- increased significantly over 3 days in children receiving desferrioxamine plus quinine but not in those given placebo and quinine. Neopterin levels declined significantly with placebo but not with desferrioxamine. IL-4 levels increased progressively in the placebo group and ultimately decreased in the desferrioxamine group, but the trends were not statistically significant. IL-6 and IL-10 levels were elevated initially and decreased significantly in both groups over 3 days. These data are consistent with the hypothesis that iron chelation therapy in children with cerebral malaria strengthens Th1-mediated immune effector function involving increased production of NO.

Serum neopterin, interleukin-4, and interleukin-6 concentrations in cerebral malaria patients and the effect of iron chelation therapy.

To determine if iron chelation therapy alters immune responses in children with cerebral malaria, we retrospectively measured mean serum levels of neopterin, interleukin-4 (IL-4), and IL-6 in children who received desferrioxamine B or placebo for three days in addition to quinine-based therapy. Mean levels of neopterin, IL-4, and IL-6 were elevated above the expected normal range on admission. Neopterin correlated significantly with the degree of anemia, IL-4 with the duration of fever prior to admission, and IL-6 with parasite density. Serial measurements of cytokines and neopterin were performed over four days in 39 children, 21 randomized to receive desferrioxamine B and 18 to receive placebo. Mean concentrations of neopterin did not change significantly in either group while levels of IL-4 increased significantly in the placebo group (P = 0.04) but remained unchanged in the desferrioxamine B group. Interleukin-6 concentrations decreased markedly in both groups (P < 0.025). Stable IL-4 levels in children given desferrioxamine B may represent an inhibition of the T helper lymphocyte-2 (TH-2) response resulting from a strengthened TH-1 response associated with iron chelation therapy. Any effect of iron chelation on immunity in the setting of severe malaria will have to be confirmed in future prospective investigations.

Iron chelation as a chemotherapeutic strategy for falciparum malaria.

To examine the effect of iron chelation against human malaria, 37 Zambians with asymptomatic Plasmodium falciparum infections were randomly assigned to 72-hr infusions of desferrioxamine B or placebo. Mean concentrations of ring forms decreased significantly with desferrioxamine B (P < 0.001) but not with a placebo. Over seven days of observation, mean parasite concentrations remained at the initial levels in six individuals originally given placebo, but decreased promptly with administration of desferrioxamine B (P = 0.001). Mean parasitemia was significantly lower for up to four weeks in 16 subjects treated with desferrioxamine B when compared with the eight who had received placebo only (P = 0.027). We conclude that iron chelation has antiplasmodial activity and may offer a new therapeutic strategy for falciparum malaria.

The antimalarial effect of iron chelators: studies in animal models and in humans with mild falciparum malaria.

In this study we explore the antimalarial effects of 3-hydroxypyridin-4-ones (CP compounds), a family of bidentate orally effective iron chelators in experimental animal systems in vivo and in vitro, and examine whether the iron chelator deferoxamine (DF) is active against human infection with P. falciparum. There was direct relation between lipid solubility of the CP compounds, which would facilitate membrane transit, and their in vivo antimalarial action, suggesting direct intracellular iron chelation as the most likely explantation for the antimalarial effect of iron chelators. Results of the double-blind, placebo controlled trial of DF in humans with asymptomatic parasitemia provided unequivocal evidence that this iron-chelating agent has antimalarial activity. Depriving the parasite of a metabolically important source of iron may represent a novel approach to antimalarial drug development. DF is a relatively ineffective intraerythrocytic chelator, and our data indicate that other orally effective iron chelators may have superior antimalarial activity in vivo. A systematic screening of available iron chelating drugs may result in the identification of potentially useful antimalarial compounds.

Iron chelation with desferrioxamine B in adults with asymptomatic Plasmodium falciparum parasitemia.

To determine if iron chelation therapy has activity against human malaria, we administered desferrioxamine B in amounts of 100 mg/kg per day by continuous 72-hour subcutaneous infusions to 28 volunteers with asymptomatic Plasmodium falciparum infection in a randomized, double-blind, placebo-controlled crossover trial. Peripheral blood concentrations of P falciparum ring forms were determined at 12-hour intervals in all subjects and serum concentrations of desferrioxamine B + ferrioxamine (the iron complex of desferrioxamine B) were measured in 26 subjects. Geometric mean concentrations of asexual intraerythrocytic parasites decreased with both chelator and placebo treatment, but the decrement with desferrioxamine B was significantly greater than that with placebo (P less than .006) during both the initial and crossover periods. Compared with placebo, desferrioxamine B treatment was associated with an almost 10-fold enhancement of the rate of parasite clearance during both phases of the trial (P less than .007). Mean +/- SEM steady state concentrations of desferrioxamine B + ferrioxamine were 6.90 +/- 0.60 mumol/L at 36 hours and 7.72 +/- 0.68 mumol/L at 72 hours; in vitro, the ID50 has been reported to be approximately 4 to 20 mumol/L. No drug toxicity was detected. Parasitemia recurred in 19 of 24 participants followed-up over 1 to 6 months. We conclude that desferrioxamine B enhances the clearance of P falciparum parasitemia and that iron chelation may provide a new strategy to be developed for the treatment of malaria.