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Biomedical subjects

Peter G Kremsner

Publications and source records attributed to Peter G Kremsner.

At least 73 records · Page 4Linked to original sources

Fosmidomycin-clindamycin for Plasmodium falciparum Infections in African children.

BACKGROUND: Fosmidomycin is a new antimalarial drug with a novel mechanism of action. Studies in Africa that have evaluated fosmidomycin as monotherapeutic agent demonstrated its excellent tolerance, but 3-times-daily treatment regimens of >or=4 days were required to achieve radical cure, prompting further research to identify and validate a suitable combination partner to enhance its efficacy. METHODS: We conducted a randomized, controlled, open-label study to evaluate the efficacy and safety of fosmidomycin combined with clindamycin (n=12; 30 and 5 mg/kg body weight every 12 h for 5 days, respectively), compared with fosmidomycin alone (n=12; 30 mg/kg body weight every 12 h for 5 days) and clindamycin alone (n=12; 5 mg/kg body weight every 12 h for 5 days) for the clearance of asymptomatic Plasmodium falciparum infections in schoolchildren in Gabon aged 7-14 years. RESULTS: Asexual parasites were rapidly cleared in children treated with fosmidomycin-clindamycin (median time, 18 h) and fosmidomycin alone (25 h) but slowly in children treated with clindamycin alone (71 h; P=.004). However, only treatment with fosmidomycin-clindamycin or clindamycin alone led to the radical elimination of asexual parasites as measured by day 14 and 28 cure rates of 100%. Asexual parasites reappeared by day 28 in 7 children who received fosmidomycin (day 14 cure rate, 92% [11/12; day 28 cure rate, 42% [5/12]). All regimens were well tolerated, and no serious adverse events occurred. CONCLUSION: The combination of fosmidomycin and clindamycin is well tolerated and superior to either agent on its own with respect to the rapid and radical clearance of P. falciparum infections in African children.

Antimalarials↗

Depressed natural killer cell cytotoxicity against Plasmodium falciparum-infected erythrocytes during first pregnancies.

We measured natural killer (NK) cell cytotoxicity and cortisol and prolactin concentrations in peripheral venous blood samples obtained from pregnant Gabonese women at the time of delivery. The NK cell-mediated cytotoxicity against Plasmodium falciparum-infected erythrocytes in vitro was lower in samples obtained from primiparous women than in samples obtained from multiparous women; cortisol concentrations were significantly higher in primiparous women than in multiparous women, and prolactin concentrations were significantly lower. The highest cortisol concentrations were found in the plasma of P. falciparum-infected primiparous women. A positive correlation was found between cortisol concentration and parasite load; an inverse correlation was found between the magnitude of the NK cell cytolytic effect and cortisol production. A positive correlation was found between this effect and prolactin production. Thus, depressed NK cell cytotoxicity against P. falciparum-infected erythrocytes is correlated with high cortisol concentrations and may contribute to increased susceptibility to malaria during pregnancy.

Adult↗

Variations in the serum concentrations of soluble Fas and soluble Fas ligand in Vietnamese patients infected with hepatitis B virus.

Earlier studies of both chronic hepatitis B and C virus (HBV and HCV) patients have shown a strong correlation between the soluble membrane Fas (sFas) and Fas protein expression on hepatocytes. The serum concentrations of sFas and soluble Fas ligand (sFasL) was examined in both healthy and HBV-infected Vietnamese patients to determine their relationship with the outcome of HBV infection. Patients with chronic rather than acute HBV had significantly higher amounts of sFas and sFasL, whilst the highest concentrations of both molecules were detected in those with malignant forms of HBV infection. sFas and sFasL concentrations tended to increase with a profile that paralleled the progression from asymptomatic to acute through chronic to malignant states, most markedly in the case of sFas. The sFas:sFasL ratio highlighted the relative predominance of sFas in those with acute and chronic HBV compared with asymptomatic or severe forms. In patients with hepatocellular carcinoma (HCC) a significant correlation was also observed between sFasL and alpha-feto protein (AFP) levels. The results indicate that sFas and to a lesser extent sFasL levels are to some degree associated with clinical progression in HBV infection.

Adult↗

Submicroscopic Plasmodium falciparum infections and multiplicity of infection in matched peripheral, placental and umbilical cord blood samples from Gabonese women.

Summary In malaria-endemic regions, pregnant women are more susceptible to malarial infections than non-pregnant women. The main objective of this study, which was conducted in the malaria hyperendemic town of Lambaréné (Gabon, Central Africa), was to characterize Plasmodium falciparum infections in peripheral, placental and cord blood from women of different gravidities with submicroscopic infections. Using the P. falciparum merozoite surface protein 2 (MSP 2)* gene as a polymorphic marker in polymerase chain reactions, we analysed genetic diversity and multiplicity of infection in isolates from all three kinds of samples of 184 pregnant women at delivery. We detected infection in 44% of the women who were originally negative by microscopy. Equally important was the finding that the placenta had the highest prevalence of infection (P < 0.001). There was no correlation with gravidity status or age of the patients. The multiplicities of infection in the peripheral and placental blood samples did not differ and single infection was observed in cord blood, independently of the gravidity. The FC27/MSP 2 was the predominant allelic family. The major FC27 alleles detected in the peripheral, placental and cord blood were sequenced and found to be closely related to the published K1 form sequence. Below microscopy level, the placenta remains the most infected organ and this submicroscopic carriage of parasites may contribute to the development and maintenance of immunity to malaria during pregnancy.

Adolescent↗

Immunoglobulin G isotype responses to variant surface antigens of Plasmodium falciparum in healthy Gabonese adults and children during and after successive malaria attacks.

We assessed immunoglobulin G (IgG) isotype responses with specificity for the variant surface antigens (VSA) of heterologous Plasmodium falciparum isolates by using flow cytometry and plasma from healthy Gabonese adults and from children during and after two consecutive malaria episodes. The individual isolate-specific antibody profiles differed markedly in terms of their isotype content but were similar for healthy adults and healthy uninfected children. In healthy adults, IgG3 and IgG2 responses were the highest, while in healthy children, IgG3 and IgG4 predominated. A transiently elevated IgG1 response was observed during the second of two successive malaria episodes in children, signaling P. falciparum infection-induced cross-reactive anti-VSA responses. Our findings highlight the prominence of IgG3 in the overall profile of these responses but also indicate a marked age-related increase in the prevalence of anti-VSA antibodies of the classically noncytophilic IgG2 isotype, possibly reflecting the high frequency of the histidine-131 variant of FcgammaRIIA in the Gabonese population.

Adolescent↗

Elevated nitric oxide production in children with malarial anemia: hemozoin-induced nitric oxide synthase type 2 transcripts and nitric oxide in blood mononuclear cells.

Experiments outlined here investigate the role of nitric oxide (NO) in the pathogenesis of Plasmodium falciparum-induced malarial anemia (MA). The results show that ex vivo and in vitro NO synthase (NOS) activity in peripheral blood mononuclear cells (PBMCs) is significantly elevated in children with MA and inversely associated with hemoglobin levels. Additional experiments using PBMCs from non-malaria-exposed donors demonstrate that physiologic amounts of P. falciparum-derived hemozoin augment NOS type 2 (NOS2) transcripts and NO production. Results of these experiments illustrate that elevated NO production in children with MA is associated with decreased hemoglobin concentrations and that hemozoin can induce NOS2-derived NO formation in cultured blood mononuclear cells.

Anemia↗

Antibodies to rifin: a component of naturally acquired responses to Plasmodium falciparum variant surface antigens on infected erythrocytes.

We used a pool of recombinant rifin proteins to pre-adsorb antibodies to rifin in the plasma of semi-immune African (Gabonese) adults and showed that this results in a reduction in the level of IgG antibody reactivity to variant surface antigens (VSA) measured in a standardized flow cytometric assay with a panel of heterologous parasite isolates. The same methods demonstrated a similar but less-marked contribution of antibodies to the duffy binding-like 1alpha (DBL-1alpha ) domain to the overall anti-VSA response. Thus, we conclude that both antibodies to rifin and, to a lesser extent, antibodies directed to conserved regions of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) DBL-1alpha domain contribute to the overall antibody response to VSA. We also assessed the associations between these different antibody responses in a cohort of Gabonese children. We found marked differences related to the childrens' history of presentation with either mild or severe malaria, but no consistent pattern that would indicate a specific role or influence of antibody responses to rifin.

Adult↗

Short report: evaluation of a simple and inexpensive photometric device for the measurement of hemoglobin.

We have evaluated the accuracy of a simple and inexpensive photometric device (DHT) for the estimation of the blood concentration of hemoglobin by comparison with an automated, high-resolution, flow cytometry-based hematology analyzer (CellDyn 3000) and a centrifugal quantitative buffy coat hematology system (QBC I). We have analyzed the hemoglobin values of 163 individual blood samples. Bland-Altman analysis showed that the methods agreed only poorly: mean differences were 1.0 g/dL with limits of agreement (LOA) of -1.2 g/dL to 3.2 g/dL for the comparison of DHT and CellDyn measurements, 0.5 g/dL with LOA of -2.0 g/dL to 3.0 g/dL for the comparison of DHT with QBC measurements, and 0.5 g/dL with LOA of -1.1 g/dL to 2.1 g/dL for the comparison of QBC with CellDyn measurements. We conclude that the poor agreement of the DHT with the CellDyn does not permit the use of the DHT for critical hemoglobin measurements, particularly in transfusion services.

Colorimetry↗

Atovaquone and proguanil versus amodiaquine for the treatment of Plasmodium falciparum malaria in African infants and young children.

Malaria-related morbidity and mortality are greatest among young children in areas with high malaria transmission intensity. An open-label, randomized study was done to evaluate the efficacy and safety of the combination of atovaquone and proguanil formulated as pediatric-strength tablets (20 and 8 mg/kg of body weight, respectively, administered once daily for 3 days), compared with amodiaquine (10 mg/kg of body weight, once daily for 3 days), among children weighing > or =5 and <11 kg in Gabon. Two hundred patients aged 3-43 months were recruited. Use of atovaquone/proguanil resulted in a cure rate on day 28 of 95% (87 of 92 children), compared with 53% (41 of 78 children) for amodiaquine (difference, 42%; 95% CI, 30%-54%; P<.001). The incidence of adverse events was similar in both groups, and no serious adverse events were attributed to the use of atovaquone/proguanil. Atovaquone/proguanil was found to be highly effective and safe for the treatment of Plasmodium falciparum malaria in infants and young children weighing 5-10 kg in Africa.

Amodiaquine↗

Commonly recognised Plasmodium falciparum parasites cause cerebral malaria.

Cerebral malaria (CM) is a devastating form of Plasmodium falciparum malaria, in which adherence and sequestration of infected red blood cells in cerebral blood vessels play a major role. In order to determine whether a distinct parasite phenotype favours the development of this severe complication, P. falciparum isolates from Gabonese children suffering from CM or uncomplicated malaria (UM) were analysed for their binding phenotypes and their recognition in flow cytometry. CM isolates exhibited the ability to form rosettes and to bind ICAM-1, in line with previous studies correlating these phenotypes with CM disease pathology. CM isolates were more reactive with plasma from our cohort than UM parasites. This observation, together with the finding that some CM isolates were highly correlated with each other in their immunoreactivities, confirms that common parasites bearing conserved epitopes, which are capable of inducing cross-reactive antibodies, can cause CM in children.

Animals↗

Recombinant Duffy binding-like-alpha domains of Plasmodium falciparum erythrocyte membrane protein 1 elicit antibodies in rats that recognise conserved epitopes.

Plasmodium falciparum parasites remodel the surface of human erythrocytes on invasion by the insertion of parasite-derived proteins in knob-like protrusions. P. falciparum erythrocyte membrane protein 1 (PfEMP-1), a variant surface antigen, has been shown to be anchored in these knobs and mediates adhesion to various host endothelial receptors. These proteins also undergo clonal antigenic variation as a means of immune evasion. Duffy binding-like-alpha(DBL-alpha) domain together with the cysteine-rich interdomain region form the head structure of the PfEMP1 molecule. In this report, we used ten different recombinant DBL-alpha fusion proteins expressed in Escherichia coli to generate antibodies in experimental animals. Five out of ten recombinant DBL-alpha fusion proteins were immunogenic and induced antibodies that reacted with conserved peptides derived from PfEMP1. Indirect immunofluorescence assay was used to localise PfEMP-1-DBL-alpha expressed in parasitised erythrocytes. Positive fluorescence reactivity was observed within the cytoplasm and with membrane structures but not on the surface of intact P. falciparum-infected erythrocytes.

Amino Acid Sequence↗

Uncommon asymptomatic Plasmodium falciparum infections in Gabonese children.

To assess the frequency of asymptomatic plasmodial infections in young children living in an area of hyperendemicity, a cohort of 200 children in Gabon was investigated longitudinally. Of 660 cases of Plasmodium falciparum infection, 77% were symptomatic at the time they were identified and only 7% were preceded by an asymptomatic phase of >4 days. Sickle cell trait, glucose-6-phosphate dehydrogenase deficiency, and mutation in the promoter region of tumor necrosis factor (TNF(-376A/-238A)) were significantly associated with asymptomatic P. falciparum infection (P=.03, P=.009, and P<.001, respectively). We conclude that true asymptomatic cases of P. falciparum infection are uncommon in young children and that single measurements or measurements made at long time intervals will lead to a strong underestimation of the incidence of malaria.

Animals↗

Antibody responses to Plasmodium falciparum merozoite surface protein-1 and efficacy of amodiaquine in Gabonese children with P. falciparum malaria.

The relationship between the efficacy of amodiaquine for the treatment of uncomplicated Plasmodium falciparum malaria and preexisting antibodies against merozoite surface protein (MSP)-1, a blood-stage P. falciparum antigen, was investigated. The immunoglobulin G antibody response to different MSP-1 recombinant proteins was evaluated in plasma samples from Gabonese children with uncomplicated malaria who were treated with amodiaquine. The prevalence of anti-MSP-1 antibodies was similar among patients with either parasitological and clinical cure after treatment (n=102) or treatment failure (n=51) by day 28 (83% in both groups). However, associations between antibody responses to K1 and MAD20 allelic families and therapeutic success were found (P< .001 and P= .034, respectively). A high proportion of plasma samples recognizing several antigens was found in the cured group. This association was significant even when data were stratified by age, particularly for the K1 family antigens (P= .029). These results suggest that humoral immune responses play a supportive role in the efficacy of amodiaquine treatment.

Amodiaquine↗

Severe malaria in a splenectomised Gabonese woman.

BACKGROUND: The intact splenic function is of utmost importance for the host's defence capacity against Plasmodium spp. not only by limiting the acute infection through the removal of parasites from the blood stream, but also by modulating parasite antigen expression on the surface of infected red blood cells as well as cellular and humoral immune response. Splenectomised individuals are at high risk to develop a more severe and prolonged disease, even if they had acquired semi-immunity prior to their loss of splenic tissue. CASE REPORT: We report on a 37 year old splenectomised Gabonese woman who developed severe falciparum malaria with hyperparasitaemia, profound anaemia, and an overwhelming gametocytaemia, recovering very slowly following quinine therapy. Whereas the clinical course is not at odds with previous descriptions, the massive occurrence of mature gametocytes as documented here has not been reported before. Whether the high gametocyte count observed in our patient was primarily due to the impaired clearance of asexual forms or to the induction of gametocytogenesis remains unclear. Regarding the optimal drug regimen for treating malaria in splenectomized patients, a combination of an aminoquinoline with an artemisinin derivative might be the optimal choice.

Adult↗

Mannose-binding lectin gene polymorphisms and hepatitis B virus infection in Vietnamese patients.

Mannose-binding lectin (MBL) is a constituent of the human innate immune system which may play an important role in combating a variety of infectious diseases. We investigated the distribution of MBL gene mutations in a Vietnamese population, using polymerase chain reaction and DNA sequence analysis, and sought associations with the outcome of hepatitis B virus (HBV) infection. For this purpose we used samples from a total of 123 patients with confirmed, well-defined HBV infections, representing a full spectrum of clinical presentation from acute to chronic to malignant states, as well as from 112 healthy controls. The only MBL gene mutation found in this population, that at codon 54 of exon 1, was present at an overall frequency of 0.12, with a trend towards a higher frequency in the HBV-infected group compared with controls (0.15 versus 0.08, P = 0.079). Within the HBV-infected group there was a non-significant trend towards higher viral loads in those with this mutation, accompanied by significantly higher serum transaminase levels in the same individuals. Segregation according to clinical presentation showed that the mutation was present at a significantly higher frequency in the group with acute hepatitis B (AHB) compared with the healthy control group (0.25 versus 0.08, P = 0.01), and was associated with higher serum transaminase levels. Our results indicate that a mutation of the MBL gene might influence the clinical outcome of HBV infection in Vietnamese patients.

Gene Frequency↗

Common surface-antigen var genes of limited diversity expressed by Plasmodium falciparum placental isolates separated by time and space.

Plasmodium falciparum placental parasites from Cameroon have been shown to express surface variant var genes encoding Duffy binding-like (DBL)-gamma domains that bind chondroitin sulfate A. All 5 domains exhibited sequences with 39%-55% amino acid (aa) identities and appear sufficiently conserved to function in receptor binding. Transcripts of 2 samples showed complete conservation over 4 kb, demonstrating for the first time distinct conserved placental var genes. Four placental isolates from Gabon collected 4 years later expressed DBL-gamma sequences with 85%-99% aa identities to those from Cameroon, confirming the conserved nature of placental variants separated by time and location. Five peripheral parasites from children also displayed DBL-gamma sequences with 75%-97% homologies. From this, it can be concluded that P. falciparum parasites expressing unique var DBL-gamma genes can cause placental malaria, referred to as varPAM genes. This demonstration of structurally/functionally constrained DBL-gamma chondroitin sulfate A-binding domains is relevant to understanding pregnancy-associated malaria pathogenesis and to vaccine development.

Animals↗