Cerebrospinal Fluid Studies in Kenyan Children with Severe Falciparum Malaria.

The pathogenesis of the neurological complications of Plasmodium falciparum malaria is unclear. We measured proteins and amino acids in paired plasma and cerebrospinal fluid (CSF) samples in children with severe falciparum malaria, to assess the integrity of the blood brain barrier (BBB), and look for evidence of intrathecal synthesis of immunoglobulins, excitotoxins and brain damage. METHODS: Proteins of different molecular sizes and immunoglobulins were measured in paired CSF and plasma samples in children with falciparum malaria and either impaired consciousness, prostrate, or seizures. RESULTS: The ratio of CSF to plasma albumin (Q(alb)) exceeded the reference values in 42 (51%) children. The CSF concentrations of the excitotoxic amino acid aspartate and many non-polar amino acids, except alanine, were above the reference value, despite normal plasma concentrations. IgM concentrations were elevated in 21 (46%) and the IgM index was raised in 22 (52%). Identical IgG oligoclonal bands were found in 9 (35%), but only one patient had an increase in the CSF IgG without a concomitant increase in plasma indicating intrathecal synthesis of IgG. CONCLUSIONS: This study indicates that the BBB is mildly impaired in some children with severe falciparum malaria, and this impairment is not confined to cerebral malaria, but also occurs in children with prostrate malaria and to a lesser extent the children with malaria and seizures. There is evidence of intrathecal synthesis of immunoglobulins in children with malaria, but this requires further investigation. This finding, together with raised level of excitotoxic amino acid aspartate could contribute to the pathogenesis of neurological complications in malaria.

Diamidine compounds: selective uptake and targeting in Plasmodium falciparum.

Extensive drug resistance in Plasmodium falciparum emphasizes the urgent requirement for novel antimalarial agents. Here we report potent antimalarial activity of a number of diamidine compounds. The lead compound pentamidine is concentrated 500-fold by erythrocytes infected with P. falciparum. Pentamidine accumulation can be blocked by inhibitors of hemoglobin digestion, suggesting that the drug binds to ferriprotoporphyrin IX (FPIX). All of the compounds bound to FPIX in vitro and inhibited the formation of hemozoin. Furthermore, inhibitors of hemoglobin digestion markedly antagonized the antimalarial activity of the diamidines, indicating that binding to FPIX is crucial for the activity of diamidine drugs. Pentamidine was not accumulated into uninfected erythrocytes. Pentamidine transport into infected cells exhibits an initial rapid phase, nonsaturable in the micromolar range and sensitive to inhibition by furosemide and glibenclamide. Changing the counter-ion in the order Cl(-) < Br(-) < NO(2)(-) < I(-)

Effectiveness of the particle repositioning maneuver in subtypes of benign paroxysmal positional vertigo.

OBJECTIVES: To assess the efficacy of the particle repositioning maneuver (PRM) in patients presenting with idiopathic benign paroxysmal positional vertigo (BPPV) compared with those with evidence of additional peripheral vestibulopathies. METHODS: Retrospective administration of the Dizziness Handicap Inventory (DHI) to 41 patients with primary BPPV and 31 patients with secondary BPPV to subjectively evaluate their symptoms before and after the PRM. RESULTS: Both groups indicated a marked improvement in symptoms after the PRM. Only two patients reported an increase in their symptoms after the PRM and both had secondary BPPV. CONCLUSIONS: The PRM was found to be highly effective in all forms of BPPV, but careful history and judicious testing may identify patients requiring additional intervention to relieve their symptoms.

Potent antimalarial activity of clotrimazole in in vitro cultures of Plasmodium falciparum.

The increasing resistance of the malaria parasite Plasmodium falciparum to currently available drugs demands a continuous effort to develop new antimalarial agents. In this quest, the identification of antimalarial effects of drugs already in use for other therapies represents an attractive approach with potentially rapid clinical application. We have found that the extensively used antimycotic drug clotrimazole (CLT) effectively and rapidly inhibited parasite growth in five different strains of P. falciparum, in vitro, irrespective of their chloroquine sensitivity. The concentrations for 50% inhibition (IC(50)), assessed by parasite incorporation of [(3)H]hypoxanthine, were between 0.2 and 1.1 microM. CLT concentrations of 2 microM and above caused a sharp decline in parasitemia, complete inhibition of parasite replication, and destruction of parasites and host cells within a single intraerythrocytic asexual cycle (approximately 48 hr). These concentrations are within the plasma levels known to be attained in humans after oral administration of the drug. The effects were associated with distinct morphological changes. Transient exposure of ring-stage parasites to 2.5 microM CLT for a period of 12 hr caused a delay in development in a fraction of parasites that reverted to normal after drug removal; 24-hr exposure to the same concentration caused total destruction of parasites and parasitized cells. Chloroquine antagonized the effects of CLT whereas mefloquine was synergistic. The present study suggests that CLT holds much promise as an antimalarial agent and that it is suitable for a clinical study in P. falciparum malaria.

Plasma glutamine levels and falciparum malaria.

Glutamine deficiency is associated with increased rates of sepsis and mortality, which can be prevented by glutamine supplementation. Changes in glutamine concentration were examined in Ghanaian children with acute falciparum malaria and control cases. The mean (SD) plasma glutamine concentration was lower in patients with acute malaria (401 (82) mumol/L, n = 50) than in control patients (623 (67) mumol/L, n = 7; P < 0.001). Plasma glutamine concentrations all rose in convalescence. The mean (SD) increase in plasma glutamine was 202 (123) mumol/L (n = 18; P < 0.001) compared with acute infection. We conclude that acute falciparum malaria is associated with large decreases in plasma glutamine and these falls may increase susceptibility to sepsis and dyserythropoeisis.

Transport of diverse substrates into malaria-infected erythrocytes via a pathway showing functional characteristics of a chloride channel.

Following infection by the malaria parasite, Plasmodium falciparum, human erythrocytes show increased permeability to a variety of low molecular weight solutes. In this study a number of anion transport blockers were identified as potent inhibitors of the transport of a wide range of solutes into human erythrocytes infected in vitro with P. falciparum. 5-Nitro-2-(3-phenyl-propylamino)benzoic acid (NPPB), furosemide, and niflumate blocked the malaria-induced transport of monovalent cations, neutral amino acids, sugars, nucleosides, and monovalent anions. For all of the substrates tested the order of potency of these three inhibitors was the same (NPPB > furosemide > niflumate) and dose-response curves for the effect of these inhibitors on malaria-induced choline transport were similar to those for malaria-induced thymidine transport. The data suggest that much, if not all, of the high capacity (non-saturable) transport of low molecular weight solutes into P. falciparum-infected erythrocytes is via a single type of pathway. The broad specificity of the pathway, its non-saturability in the physiological concentration range, and its failure to distinguish between stereoisomers (L- and D-alanine) are consistent with its being a type of pore or channel. For those substrates for which quantitative influx measurements were made the magnitude of the malaria-induced (inhibitor-sensitive) transport was in the order: Cl- > lactate > thymidine, adenosine > carnitine > choline > K+. The pathway is therefore anion-selective. The pharmacological and substrate-selectivity properties of the pathway show marked similarities to those of chloride channels in other cell types; this raises the possibility that the high capacity transport of small organic solutes may be an important and, as yet, largely unrecognized role for such channels in other tissues.

Glibenclamide and meglitinide block the transport of low molecular weight solutes into malaria-infected erythrocytes.

Following infection by the malaria parasite, human erythrocytes show increased uptake of a wide variety of low molecular weight solutes via pathways with functional characteristics different from those of the transporters of normal erythrocytes. In this study glibenclamide and meglitinide were shown to inhibit the induced transport of a sugar alcohol (sorbitol), an amino acid (threonine), an inorganic anion (Cl-) and an organic cation (choline) into human erythrocytes infected in vitro with Plasmodium falciparum. The results are consistent with the hypothesis that a diverse range of substrates enter malaria-infected cells via common pathways which have features in common with Cl- channels in other cell types. glibenclamide and meglitinide were also shown to inhibit the in vitro growth of the intracellular parasite which would suggest that these pathways may be a viable chemotherapeutic target.

The increased K+ leak of malaria-infected erythrocytes is not via a Ca(2+)-activated K+ channel.

Charybdotoxin and nitrendipine both inhibited K+(86Rb+) influx via the Ca(2+)-activated channel of uninfected erythrocytes but had no effect on K+(86Rb+) transport in malaria-infected cells. Activation of the channel in uninfected cells in which the cytoplasmic [Na+]/[K+] ratio was adjusted to be comparable with that of late-stage malaria-infected erythrocytes resulted in a large (nitrendipine-sensitive) increase in K+(86Rb+) influx. These results suggest that the endogenous Ca(2+)-activated K+ channel remains inactive in human red cells infected with late-stage parasites. The identity of the pathway which mediates the increased K(+)-leak in infected erythrocytes remains to be established.

Antimalarial activity of Artemisia annua flavonoids from whole plants and cell cultures.

Cell suspension cultures developed from Artemisia annua exhibited antimalarial activity against Plasmodium faldparum in vitro both in the n-hexane extract of the plant cell culture medium and in the chloroform extract of the cells. Trace amounts of the antimalarial sesquiterpene lactone artemisinin may account for the activity of the n-hexane fraction but only the methoxylated flavonoids artemetin, chrysoplenetin, chrysosplenol-D and cirsilineol can account for the activity of the chloroform extract. These purified flavonoids were found to have IC50 values at 2.4 - 6.5 × 10(-5)M against P. falciparum in vitro compared with an IC50 value of about 3 × 10(-8)M for purified artimisinin. At concentrations of 5 × 10(-6)M these flavonoids were not active against P. falciparum but did have a marked and selective potentiating effect on the antiplasmodial activity of artemisinin.

Enhanced choline and Rb+ transport in human erythrocytes infected with the malaria parasite Plasmodium falciparum.

Human erythrocytes infected in vitro with the malaria parasite Plasmodium falciparum showed a markedly increased rate of choline influx compared with normal cells. Choline transport into uninfected cells (cultured in parallel with infected cells) obeyed Michaelis-Menten kinetics (Km approximately 11 microM). In malaria-parasite-infected cells there was an additional choline-transport component which failed to saturate at extracellular concentrations of up to 500 microM. This component was less sensitive than the endogenous transporter to inhibition by the Cinchona bark alkaloids quinine, quinidine, cinchonine and cinchonidine, but showed a much greater sensitivity than the native system to inhibition by piperine. The sensitivity of the induced choline transport to these reagents was similar to that of the malaria-induced (ouabain- and bumetanide-resistant) Rb(+)-transport pathway; however, the relative magnitudes of the piperine-sensitive choline and Rb+ fluxes in malaria-parasite-infected cells varied between cultures. This suggests either that the enhanced transport of the two cations was via functionally distinct (albeit pharmacologically similar) pathways, or that the transport was mediated by a pathway with variable substrate selectivity.

Characteristics of 86Rb+ transport in human erythrocytes infected with Plasmodium falciparum.

Human red cells infected in vitro with Plasmodium falciparum showed a significant increase in the rate of both ouabain-sensitive and ouabain-insensitive 86Rb+ influx. The increase in ouabain-insensitive 86Rb+ influx was due, in part, to increased transport via a bumetanide-sensitive system and, in part to transport via a pathway that was absent (or at least inactive) in uninfected cells. The parasite-induced pathway was inhibited by piperine and had a dose response very similar to that of the Gardos channel of uninfected cells but was less sensitive than the Gardos channel to inhibition by quinine.