Biomedical subjects

Peter G Kremsner

Publications and source records attributed to Peter G Kremsner.

At least 19 recordsLinked to original sources

PubMed2006

Molecular surveillance of mutations in the cytochrome b gene of Plasmodium falciparum in Gabon and Ethiopia.

BACKGROUND: Atovaquone is part of the antimalarial drug combination atovaquone-proguanil (Malarone) and inhibits the cytochrome bc1 complex of the electron transport chain in Plasmodium spp. Molecular modelling showed that amino acid mutations are clustered around a putative atovaquone-binding site resulting in a reduced binding affinity of atovaquone for plasmodial cytochrome b, thus resulting in drug resistance. METHODS: The prevalence of cytochrome b point mutations possibly conferring atovaquone resistance in Plasmodium falciparum isolates in atovaquone treatment-naïve patient cohorts from Lambaréné, Gabon and from South Western Ethiopia was assessed. RESULTS: Four/40 (10%) mutant types (four different single polymorphisms, one leading to an amino acid change from M to I in a single case) in Gabonese isolates, but all 141/141 isolates were wild type in Ethiopia were found. CONCLUSION: In the absence of drug pressure, spontaneous and possibly resistance-conferring mutations are rare.

Animals↗

PubMed2006

No variation in the prevalence of point mutations in the Pfcrt and Pfmdr1 genes in isolates from Gabonese patients with uncomplicated or severe Plasmodium falciparum malaria.

In Lambaréné (Gabon), where a high level of Plasmodium falciparum resistance to chloroquine has been reported, we assessed the relationship between polymorphisms in the P. falciparum chloroquine resistance transporter (Pfcrt) and multidrug resistance-1 (Pfmdr1) genes and the clinical severity of malaria. Ninety-one and 60 P. falciparum isolates from children with uncomplicated or severe malaria were collected in 1996 and 2002, respectively. Single nucleotide mutations at codon 76 in the Pfcrt gene and at codons 86, 184, 1034, 1042, and 1246 in the Pfmdr1 gene were assessed by PCR-RFLP. All P. falciparum isolates presented the Pfcrt K76T mutation, whatever the clinical status. A high prevalence (>80%) of the Pfmdr1 86Tyr and 184Phe mutations was detected at both time points and in both clinical groups. We did not identify any specific mutation in the Pfmdr1 gene associated with the severity of disease, and the multiplicity of P. falciparum infection was also similar in both groups. Our results showed no change in the polymorphism of Pfcrt and Pfmdr1 genes in P. falciparum isolates collected in 1996 and 2002, and the severity of the disease was not associated with specific mutations neither in the Pfcrt nor in the Pfmdr1 genes in the study site.

Animals↗

PubMed2006

Differing activation status and immune effector molecule expression profiles of neonatal and maternal lymphocytes in an African population.

Higher susceptibility of newborns to infections has been attributed to the hypo-responsiveness of their cellular immune system. Here we compared the activation status and expression of cytokines and cytotoxic molecules of cord versus maternal peripheral blood mononuclear cells in an African population. Human leucocyte antigen-DR was expressed on a lower percentage of cord compared to maternal gammadelta and CD3(+) T cells. Similarly, a lower proportion of cord versus maternal gammadelta and CD3(+) T cells displayed perforin, granzyme B and cytokine activity either ex vivo or following non-specific stimulation in vitro. In contrast, comparable proportions of cord and maternal CD94(+) CD3(-) natural killer (NK) cells showed perforin and granzyme B expression ex vivo. We conclude that cord blood gammadelta and CD3(+) T cells are functionally hypo-responsive as reflected by reduced numbers of such cells expressing either an activation marker, T helper 1 (Th1) and Th2 cytokines or cytotoxic effector molecules. The similarity in numbers of cord and maternal CD94(+) CD3(-) cells expressing cytotoxic effector molecules suggests that neonatal Africans' NK cells may be functionally mature.

CD3 Complex↗

PubMed2006

A promoter polymorphism in the interferon alpha-2 gene is associated with the clinical presentation of hepatitis B.

Cytokine gene polymorphisms influence the severity of infectious diseases of viral and parasitic origin. Interferon alpha (IFN-alpha) is known to be involved in the defence against hepatitis B. The promoter of the IFN-alpha-2 gene was investigated for mutations in 344 hepatitis B virus (HBV)-infected Vietnamese patients and 293 uninfected Vietnamese. We found a deletion in the promoter, which was present significantly more frequently in HBV-infected patients than in control individuals; 20% of the healthy, whereas 35% of the HBV-infected cohort carries this deletion (P<0.001). Reporter gene assays showed that a construct with the deletion had a lower level of transcription in comparison to the wild type (P=0.011). These findings indicate that the deletion in the promoter of the IFN-alpha-2 gene reduces the transcription of this gene in vitro. This reduction could explain the individually different interferon levels in humans and could also be one cause of susceptibility to hepatitis B.

Adult↗

PubMed2006

Co-infection of human parvovirus B19 in Vietnamese patients with hepatitis B virus infection.

BACKGROUND/AIMS: Human parvovirus B19 (B19) has been identified in the serum of hepatitis B virus (HBV) infected patients. However, the effect of B19-infection on the course of HBV-associated liver disease has not previously been investigated. We examined the prevalence of B19-DNA in HBV-infected Vietnamese patients and analysed the association between co-infection and the clinical outcome of HBV-infection. METHODS: Serum samples from 399 HBV-infected patients and 64 healthy individuals were analysed for the presence of B19-DNA by PCR and DNA-sequencing. RESULTS: B19-DNA was detected in 99/463 (21.4%) individuals. The proportion of HBV-infected patients who were also co-infected with B19 was higher than the healthy controls (P<0.001). B19-DNA was detected more frequently in patients with HBV-associated hepatocellular carcinoma compared to patients with acute and chronic HBV, HBV-associated liver cirrhosis and healthy subjects (P<0.006). A positive correlation was also found between B19-DNA loads and both serum HBV-DNA loads and alanine aminotransferase (rho>0.250 and P<0.05). CONCLUSIONS: Our findings demonstrate that B19-infection is frequent in HBV-infected Vietnamese patients. Also, a significant correlation exists between HBV/B19 co-infection and a greater likelihood of progression to more severe hepatitis B-associated liver disease. Further studies are required to determine the role of B19-infection on HBV-associated pathogenesis.

Adult↗

PubMed2006

Suppression of prostaglandin E2 by malaria parasite products and antipyretics promotes overproduction of tumor necrosis factor-alpha: association with the pathogenesis of childhood malarial anemia.

Cytokines and effector molecules are important immunoregulatory molecules in human malaria. Tumor necrosis factor (TNF)-alpha limits malaria parasitemia but also promotes pathogenesis at high concentrations, whereas prostaglandin E2 (PGE2) inhibits TNF-alpha production and is reduced in childhood malaria, at least in part, through suppression of cyclooxygenase (COX)-2 following the ingestion of Plasmodium falciparum hemozoin (pfHz; malarial pigment) by peripheral blood mononuclear cells (PBMCs). Although molecular interactions between TNF-alpha and PGE2 are largely unexplored in human malaria, results presented here show that pfHz-induced suppression of PBMC COX-2 gene products induces overproduction of TNF-alpha. Moreover, addition of exogenous PGE2 to pfHz-treated PBMCs dose-dependently decreased TNF-alpha production, whereas experimental COX inhibitors and antipyretics used during human malaria generated increased TNF-alpha production. Healthy, malaria-exposed children had elevated levels of circulating bicyclo-PGE2/TNF-alpha, compared with children with malarial anemia (P<.01), with systemic bicyclo-PGE2 and TNF-alpha significantly associated with hemoglobin concentrations (r=0.745; P<.01). The results of the present study illustrate that pfHz-induced suppression of PGE2 promotes overproduction of TNF-alpha, which is associated with enhanced malarial anemia.

Adult↗

PubMed2006

Plasmodia express two threonine-peptidase complexes during asexual development.

Threonine-peptidases of the T1-family are multi-subunit complexes with broad substrate specificity. In eukaryotes, at least 14 genes encode subunits of the prototypic T1 threonine-peptidase, the proteasome. The proteasome determines the turnover of most proteins and thereby plays a fundamental role in diverse processes such as protein quality control, signal transduction, and cell cycle regulation. While eukaryotes and archaea possess a proteasome, bacteria generally express a second member of the T1-family, the proteasomal predecessor ClpQ/hslV that has a similar structure but is encoded by only one gene. The plasmodial genome is an exception because it encodes proteasomal subunits as well as a ClpQ/hslV-orthologe (Plasmodium falciparum-hslV; PfhslV). Structure, expression, and function of both types of peptidase-complex in P. falciparum are presently unknown. Our aim was to analyze both the coding sequences and derived proteins of both peptidase-complexes because highly specific and potent inhibitors can be designed against this class of enzymes. The proteasome was found expressed throughout the cell cycle, whereas PfhslV was detectable in schizonts and merozoites only. Treatment of P. falciparum with the threonine-peptidase inhibitor epoxomicin blocked two of three catalytically active proteasome subunits. This led to the accumulation of ubiquitinated proteins and, finally, to parasite death. In conclusion, we provide the first functional analysis of plasmodial threonine-peptidase-complexes and identify a lead compound for the development of a novel class of antimalarial drugs.

Amino Acid Sequence↗

PubMed2006

Decreased circulating macrophage migration inhibitory factor (MIF) protein and blood mononuclear cell MIF transcripts in children with Plasmodium falciparum malaria.

Plasmodium falciparum malaria remains one of the most frequently lethal diseases affecting children in sub-Saharan Africa, yet the immune mediators that regulate pathogenesis are only partially defined. Since macrophage migration inhibitory factor (MIF) is important for regulating innate immunity in bacterial and parasitic infections, circulating MIF and peripheral blood mononuclear cell (PBMC) MIF transcripts were investigated in children with acute falciparum malaria. Peripheral blood levels of MIF-regulatory cytokines and effector molecules, including interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, interleukin (IL)-12, IL-10, transforming growth factor (TGF)-beta1, bicyclo-prostaglandin (PG) E2, and nitric oxide synthase activity were also determined. Circulating MIF and PBMC MIF mRNA were significantly lower in children with acute malaria relative to healthy, malaria-exposed children. Peripheral blood MIF levels showed no association with either parasitemia or hemoglobin concentrations. Circulating MIF was, however, significantly associated with IL-12 and TGF-beta1. Multiple regression analyses revealed that IFN-gamma was the most significant predictor of peripheral blood MIF concentrations. These findings suggest that reduced MIF production may promote enhanced disease severity in children with falciparum malaria.

Animals↗

PubMed2006

Impact of the hepatitis B virus genotype and genotype mixtures on the course of liver disease in Vietnam.

Eight genotypes (A-H) of hepatitis B virus (HBV) have been identified. However, the impact of different genotypes on the clinical course of hepatitis B infection remains controversial. We investigated the frequency and clinical outcome of HBV genotypes and genotype mixtures in HBV-infected patients from Vietnam, Europe, and Africa. In addition, we analyzed the effects of genotype mixtures on alterations in in vitro viral replication. In Asian patients, seven genotypes (A-G) were detected, with A, C, and D predominating. In European and African patients, only genotypes A, C, D, and G were identified. Genotype mixtures were more frequently encountered in African than in Asian (P = .01) and European patients (P = .06). In Asian patients, the predominant genotype mixtures included A/C and C/D, compared to C/D in European and A/D in African patients. Genotype A was more frequent in asymptomatic compared with symptomatic patients (P < .0001). Genotype C was more frequent in patients with hepatocellular carcinoma (HCC; P = .02). Genotype mixtures were more frequently encountered in patients with chronic hepatitis in comparison to patients with acute hepatitis B (P = .015), liver cirrhosis (P = .013), and HCC (P = .002). Viral loads in patients infected with genotype mixtures were significantly higher in comparison to patients with a single genotype (P = .019). Genotype mixtures were also associated with increased in vitro HBV replication. In conclusion, infection with mixtures of HBV genotypes is frequent in Asia, Africa, and Europe. Differences in the replication-phenotype of single genotypes compared to genotype-mixtures suggest that co-infection with different HBV-genotypes is associated with altered pathogenesis and clinical outcome.

Adult↗

PubMed2006

Short course of quinine plus a single dose of sulfadoxine/pyrimethamine for Plasmodium falciparum malaria.

BACKGROUND: Quinine remains the treatment of choice in hospitalized malaria cases; however, adverse reactions and the long treatment duration of 7 days often hamper its adequate use. Shortening the treatment by adding sulfadoxine/pyrimethamine may enhance compliance and reduce side effects. We aimed to assess the efficacy of a 3-day course of quinine plus a single dose of sulfadoxine/pyrimethamine for the treatment of non-severe hospitalized malaria cases in Lambaréné, Gabon. METHODS: Fifty children aged between 2 and 7 years received quinine dihydrochloride (12 mg/kg every 12 hours for 72 hours), and then a single dose of oral SP (500 mg/25 mg tablet) was given according to weight category. The children were hospitalized for the duration of the treatment and until two consecutive blood smears were negative for malaria parasites. The follow-up period lasted 28 days. RESULTS: Parasites were cleared after 66 hours (SD: 15 hours) and the fever after 46 hours (SD: 24 hours). All patients evaluable by day 28 were negative for malaria parasites (100% efficacy rate, 95% CI: 0.92-1). Only two patients out of 49 had gametocytemia on days 7 and 14. There was no adverse event probably or possibly attributable to the study drugs. CONCLUSIONS: A very high efficacy can be reached using a 3-day course of quinine plus a single dose of sulfadoxine/pyrimethamine for the treatment of non-severe hospitalized malaria cases in our study area.

Animals↗

PubMed2006

Phylogenetic analysis of human parvovirus B19, indicating two subgroups of genotype 1 in Vietnamese patients.

Recently, three distinct genotypes (1, 2 and 3) of human parvovirus B19 (B19) have been identified. However, the characteristics and distribution of B19 genotypes in Vietnam have not been investigated. Phylogenetic analysis using 49 subgenomic NS1/VP1u regions and two coding NS1-VP1/VP2 regions has been applied to investigate the prevalence of B19 genotypes in Vietnamese patients co-infected with Hepatitis B virus. Genetic analysis of the subgenomic NS1/VP1u region of B19 revealed that two genotypes of B19 were identified in these populations, with predominance of genotype 1 (47/49, 96 %) followed by genotype 2 (2/49, 4 %), but not genotype 3. Further, phylogenetic analysis of subgenomic B19 genomes revealed two major subgroups within genotype 1 (B19-1A and B19-1B) with an estimated nucleotide difference of >5 % between each subgroup, forming different branches. The mean percentage of amino acid variation between subgroup B19-1A and B19-1B was >2 % of the NS1, VP1 and VP2 proteins. Our results indicated that two of the three known genotypes of B19 were present in Vietnamese patients, with genotype 1 predominating, and that this genotype can be classified into at least two subgroups, B19-1A and B19-1B.

Amino Acid Sequence↗

PubMed2006

Fosmidomycin plus clindamycin for treatment of pediatric patients aged 1 to 14 years with Plasmodium falciparum malaria.

Fosmidomycin plus clindamycin was shown to be efficacious in the treatment of uncomplicated Plasmodium falciparum malaria in a small cohort of pediatric patients aged 7 to 14 years, but more data, including data on younger children with less antiparasitic immunity, are needed to determine the potential value of this new antimalarial combination. We conducted a single-arm study to improve the precision of efficacy estimates for an oral 3-day fixed-ratio combination of fosmidomycin and clindamycin at 30 and 10 mg/kg of body weight, respectively, every 12 hours for the treatment of uncomplicated P. falciparum malaria in 51 pediatric outpatients aged 1 to 14 years. Fosmidomycin plus clindamycin was generally well tolerated, but relatively high rates of treatment-associated neutropenia (8/51 [16%]) and falls of hemoglobin concentrations of > or =2 g/dl (7/51 [14%]) are of concern. Asexual parasites and fever were cleared within median periods of 42 h and 38 h, respectively. All patients who could be evaluated were parasitologically and clinically cured by day 14 (49/49; 95% confidence interval [CI], 93 to 100%). The per-protocol, PCR-adjusted day 28 cure rate was 89% (42/47; 95% CI, 77 to 96%). Efficacy appeared to be significantly reduced in children aged 1 to 2 years, with a day 28 cure rate of only 62% for this small subgroup (5/8). The inadequate efficacy in children of <3 years highlights the need for continued systematic studies of the current dosing regimen, which should include randomized trial designs.

Administration, Oral↗

PubMed2006

Antimalarial activity of a synthetic endoperoxide (RBx-11160/OZ277) against Plasmodium falciparum isolates from Gabon.

OZ277 is a newly developed, fully synthetic endoperoxide antimalarial that we tested against field isolates from Gabon. A comparison of activities of OZ277 with artesunate, mefloquine, and chloroquine showed OZ277 to be highly active against all parasite isolates. Artesunate and mefloquine also showed potent antiparasitic activity, but all isolates were chloroquine resistant.

Animals↗

PubMed2006

Cord blood dendritic cell subsets in African newborns exposed to Plasmodium falciparum in utero.

Placental Plasmodium falciparum infection affects birth outcomes and sensitizes fetal lymphocytes to parasite antigens. We assessed the influence of maternal P. falciparum infection on fetal myeloid dendritic cells (mDC) and plasmacytoid dendritic cells (pDC), analyzing the cord blood of offspring of Gabonese mothers with different infection histories. Cord blood from newborns of mothers with malarial infection at delivery had significantly more mDC than that from nonexposed newborns (P = 0.028) but mDC and pDC HLA-DR expression was unrelated to maternal infection history. Independently of these findings, cord blood mDC and pDC numbers declined significantly as a function of increasing maternal age (P = 0.029 and P = 0.033, respectively). The inducible antigen-specific interleukin-10-producing regulatory-type T-cell population that we have previously detected in cord blood of newborns with prolonged in utero exposure to P. falciparum may directly reflect the altered DC numbers in such neonates, while the maintenance of cord blood DC HLA-DR expression contrasts with that of DC from P. falciparum malaria patients.

Animals↗

PubMed2006

Malarial parasites vs. antimalarials: never-ending rumble in the jungle.

Development of resistance is an increasing problem for antimalarial chemotherapy because resistance against most available drugs has developed in the majority of world-wide parasite populations. Therefore, several strategies to counteract resistance-development are in place. From the pharmaceutical side, identification of new targets and compounds, development of structural relatives of known antimalarials, and fixed combination therapy are pursued. On the other hand, clinical studies focus on novel regimens, distribution schemes and drug combinations. A third possibility to diminish progression of resistance is the application of evolutionary concepts to design new strategies for validation, monitoring and interference with the selection-process that leads to the spread of multidrug-resistance. Since the pharmacologic and clinical side of antimalarial chemotherapy is covered by recent reviews we refer to the newest developments only and lay our focus on determinants of selection for drug resistance in human malaria.

Animals↗

PubMed2006

Simplified multi-organ dysfunction score predicts disability in African children with Plasmodium falciparum malaria.

In this prospective study, we assessed the simplified multi-organ dysfunction score (sMODS) in 485 consecutive African children, hospitalized with Plasmodium falciparum malaria. Children were grouped according to their ability to walk unaided (Group 1, N = 414), sit unaided (Group 2, N = 63), or inability of both (Group 3, N = 8) before contracting malaria. The sMODS on admission to hospital was highly correlated with prolonged disease duration in Groups 1 and 2 (Spearman r = 0.79 and r = 0.78, respectively). A sMODS of > or = 16 was indicative for prolonged disease duration in Group 1 (> 48 hours of inability to walk, sensitivity of 87%, specificity of 82%) and Group 2 (> 24 hours of inability to sit, sensitivity of 100%, and specificity of 78%.). The simplified MODS is a simple and sensitive measure merit of severity of illness in children with P. falciparum malaria and allows early prognostic evaluation.

Child, Preschool↗

PubMed2006

In vitro activity of artemisone compared with artesunate against Plasmodium falciparum.

Artemisinins show the potential for neurotoxicity in preclinical studies. Artemisone is a leading candidate of second-generation semi-synthetic artemisinin derivatives for antimalarial therapy devoid of neurotoxicity. Artemisone showed 3-5-fold higher in vitro activity (50% effective concentration (EC50) = 0.14 nmol/L, EC90 = 2.55 nmol/L) than artesunate against fresh Plasmodium falciparum isolates from Gabon and a high-activity correlation indicates a shared drug target.

Animals↗

PubMed2006

Microscopic and sub-microscopic Plasmodium falciparum infection, but not inflammation caused by infection, is associated with low birth weight.

Pregnancy-associated malaria is one of the leading causes of low birth weight in malaria endemic areas. In this study, 145 parturient women residing in areas endemic for Plasmodium falciparum in Lambaréné, Gabon, were recruited into the study after delivery, and the association of maternal P. falciparum infection, inflammatory response, and birth weight was studied. At delivery, 10% (15) of the mothers (12 were positive in both peripheral and placental blood smears, 1 was positive in peripheral blood only, and 2 were positive in placenta blood only) were positive for P. falciparum by microscopy and 23% (30) by real-time polymerase chain reaction (PCR). The level of C-reactive protein (CRP) was significantly elevated in microscopically P. falciparum-positive pregnant women (34 mg/L; 95% CI: 3-458) but not in those with sub-microscopic infections (6 mg/L; 95% CI: 1-40) compared with those free of P. falciparum infection (7 mg/L; 95% CI: 1-43). In a multivariate analysis, the presence of microscopic (adjusted OR = 28.6, 95% CI = 4.8-169.0) or sub-microscopic (adjusted OR = 13.2, 95% CI = 2.4-73.0) P. falciparum infection in pregnant women and age of mothers < 21 years (adjusted OR = 9.7 CI = 1.0-89.7), but not CRP levels, were independent predictors for low birth weight. This finding may have important operational implications and emphasizes the need for appropriate diagnostic methods in studies evaluating the outcome of pregnancy-associated malaria.

Adolescent↗