Stage-specific ultrastructural effects of desferrioxamine on Plasmodium falciparum in vitro

Desferrioxamine (DFO) is an iron chelator that inhibits the in vitro and in vivo growth of rodent and human malarial parasites. Previous studies with this chelator have suggested that it might interfere with the intraerythrocytic growth of Plasmodium sp. by withholding iron from any of several essential iron-dependent parasite enzymes, including those involved in CO2 fixation, mitochondrial electron transport, pyrimidine synthesis, and the reduction of ribonucleotides for DNA synthesis. We studied the ultrastructural effects of DFO on synchronized cultures of P. falciparum to identify the specific site of action of this compound. Synchronized cultures of early rings or schizonts were exposed to 100 microM DFO for up to 48 hr, and fixed and processed at regular intervals for electron microscopy. Untreated cultures and cultures exposed to DFO saturated with Fe3+ were processed at the same time. When DFO was added to synchronized cultures containing early rings, parasites developed normally until the late trophozoite stage, when all growth ceased. Ultrastructural lesions included the breakdown of the nuclear envelope into small membranous fragments and progressive vacuolization of the nucleoplasm. Other organelles, including food vacuoles and mitochondria, were not affected. The addition of DFO to synchronized cultures of schizonts had similar effects on nuclei of early schizonts, but little or no effect on mature schizonts and segmenters. Erythrocyte invasion by merozoites proceeded in the presence of the chelator. These findings support the hypothesis that DFO acts specifically during the late trophozoite/early schizont stage of parasite maturation by preventing nuclear division, an effect consistent with inhibition of the iron-dependent enzyme ribonucleotide reductase.     

Diagnosis and therapy of iron overload with desferrioxamine

In polytransfused patients the diagnostics of the iron overload belongs to the strategic programme of the treatment. It is particularly referred to the value of the desferal test. In the therapy of the transfusion haemosiderosis desferrioxamine is the remedy of choice. Its at present most favourable form of application is the subcutaneous infusion by means of the infusion group. A success of the treatment is only to be guaranteed, when the therapy is consequently performed over years under balancing the iron supply and excretion.     

Preliminary report on the use of desferrioxamine in the treatment of Plasmodium falciparum malaria

The administration of 0.5 g (IM) of desferrioxamine every 12 hr for 3 days with 25 mg/kg (total dose for three days) of chloroquine abated the parasitemia of Plasmodium falciparum infected individuals more rapidly than chloroquine alone. Two patients with in vitro evidence of total or partial resistance to chloroquine also were successfully treated with the combination of drugs, and were free of parasitized red cells by day 7. Further clinical trials and development of desferrioxamine in the treatment of P. falciparum are warranted.     

Synergistic effect of nitrilotriacetate on iron mobilization by desferrioxamine in vivo

Removal of iron from biologically important ligands by desferrioxamine (DF), in vitro, is exceedingly slow because of a kinetic barrier. This kinetic barrier can be overcome by a variety of a small molecular weight anions, of which nitrilotriacetate (NTA) is a prototype. We explored the effect of NTA on DF iron mobilization in vivo. Iron mobilization was increased and the effect was synergistic.     

Polyamine oxidase in human retroplacental serum inhibits the growth of Plasmodium falciparum

Human retroplacental serum (RPS) containing polyamine oxidase inhibited the growth of the Camp strain of Plasmodium falciparum in vitro as assayed by the parasite's decreased incorporation of 3H-hypoxanthine. Inhibition was dose-dependent on the concentrations of serum polyamine oxidase and added polyamines. Almost complete inhibition was seen in 96-hr asynchronous cultures containing 10% RPS and in those containing 1.2% RPS plus 50 microM polyamine. Subtle morphologic changes in mature stages and decreased numbers of new rings were associated with inhibition seen in 19-hr synchronous cultures initiated at the trophozoite stage. These incubation times were longer than in previous reports showing inhibition of malaria parasites by bovine polyamine oxidase but not by human polyamine oxidase. Macrophages contain polyamine oxidase, the reaction products of which are known to be similar to those of RPS polyamine oxidase but different from those of bovine polyamine oxidase. It remains to be determined whether human polyamine oxidase, acting upon ubiquitous polyamines, contributes to host defenses against malaria.     

Unrestricted growth of Plasmodium falciparum in microcytic erythrocytes in iron deficiency and thalassaemia

The mechanism(s) underlying the apparent resistance to malaria in certain inherited red cell disorders and iron deficiency anaemia remain poorly understood. The possibility that microcytic erythrocytes might inhibit parasite development, by physical restriction or reduced supply of nutrients, has been considered for many years, and never formally investigated. We sought to determine whether in vitro growth studies of P. falciparum could provide evidence to suggest that small red cell size contributes to malaria resistance in those red cell disorders in which microcytosis is a characteristic feature.
Invasion and development of P. falciparum in iron deficient red cells (mean values for mean cell volume [MCV] 66 fl, mean cell haemoglobin [MCH] 19 pg) and in the red cells of two gene deletion forms of α-thalassaemia (mean MCV 71 fl, MCH 22 pg) were normal, assessed both morphologically, and by ³H-hypoxanthine incorporation. Although parasite appearances were normal in all cell types, morphological abnormalities were noted in iron deficient and thalassaemic cells parasitized by mature stages of P. falciparum , notably cellular ballooning and extreme hypochromia of the red cell cytoplasm. Using electron microscopy, the red cell cytoplasm in parasitized thalassaemic cells showed reduced electron density and abnormal reticulation. Normal invasion rates were observed following schizogony in microcytic cells of both types.
Our findings indicate that whilst minor morphological abnormalities may be detected in parasitized iron deficiency and thalassaemic erythrocytes, development of P. falciparum in these conditions is not limited by small erythrocyte size.     

Development of thalassaemic iron overload cardiomyopathy despite low liver iron levels and meticulous compliance to desferrioxamine

It is believed that myocardial iron deposition and the resultant cardiomyopathy only occur in the presence of severe liver iron overload. Using cardiovascular magnetic resonance, it is now possible to assess myocardial and liver iron levels as well as cardiac function in the same scan, allowing this supposition to be examined. We describe a patient with progressive myocardial iron deposition and the development of early iron overload cardiomyopathy despite excellent compliance to standard subcutaneous desferrioxamine, minimal liver iron and well-controlled serum ferritin levels. These indirect markers remained far below the thresholds conventionally believed to be associated with increased cardiac risk.     

Differential effects of iron on the growth of Listeria monocytogenes: minimum requirements and mechanism of acquisition

The differential effects of iron on the growth of virulent and avirulent Listeria monocytogenes were examined. We found that virulent strains exhibited faster rates of growth as a function of iron than did the avirulent strains. We also noted that serum was microbiostatic, but this microbiostasis was overcome either by saturating the serum transferrin with iron or by increasing the number of organisms initially inoculated into the serum. We were unable to identify any component of a high-affinity iron transport system. We did find, however, that this microorganism removes iron from Fe -transferrin-CO3-- by a reductive pathway, and we propose that this pathway is a nonspecific mechanism of iron acquisition.     

In vitro activity of chloroquine and quinine in combination with desferrioxamine against Plasmodium falciparum

The activity of chloroquine and quinine, alone and in combination with desferrioxamine (7 μmol/liter), was evaluated in vitro against susceptible and resistant clones of Plasmodium falciparum by a semimicroassay system. The addition of desferrioxamine had no effect on the activity of chloroquine against both clones. Desferrioxamine had no effect on the activity of quinine against the susceptible clone but had slightly enhanced quinine action against the resistant clone. Further development of desferrioxamine as an antimalarial drug may be of limited interest. © 1993 Wiley-Liss, Inc.     

Liver iron concentration and fibrosis in a cohort of transfusion-dependent patients on long-term desferrioxamine therapy

Secondary iron overload is associated with significant mortality and morbidity. Although new, less invasive techniques are becoming available, the most acceptable and readily accessible way to assess iron overload is to measure hepatic iron by liver biopsy. In this study, we report on serial liver biopsies (at least 2) in a cohort of transfusion-dependent patients (49) on long-term desferrioxamine treatment. There was no significant change in liver iron concentrations (LIC) even in the medication-compliant patients, although there was an upward trend (not statistically significant) in the poorly compliant patients. Fibrosis was present in both HCV RNA-positive and -negative patients, but was more common in positive patients and there was also a significant relationship between fibrosis and hepatic iron concentration. Liver iron levels appear to be maintained in patients who are compliant to desferrioxamine treatment, but overall there is little evidence of significant improvement in liver iron in these patients and in the group as a whole.     

Glucagon and diabetes: A reappraisal

Conclusions The metabolic properties of glucagon, demonstrated bothin vitro andin vivo, qualify it as a potential diabetogenic hormone. Plasma glucagon levels are usually elevated in diabetes, the highest levels being found in the absence of insulin. Numerous lines of evidence indicate that excess glucagon levels contribute to the metabolic abnormalities of diabetes. Nevertheless, diabetes can occur in the absence of glucagon (pancreatectomy in man). The absence of high intra-islet levels of insulin may explain the persistence of abnormally high plasma concentrations of glucagon in the diabetic receiving conventional insulin therapy. In maturity-onset type diabetes, the intimate mechanisms leading to abnormal circulating glucagon levels are completely unknown. A search for selective glucagon inhibitors represents an attractive new way in diabetes management.Maître de Recherches of the F.N.R.S. of Belgium