Ambaliou Sanni

Molecular characterisation of Plasmodium reichenowi apical membrane antigen-1 (AMA-1), comparison with P. falciparum AMA-1, and antibody-mediated inhibition of red cell invasion☆

Apical membrane antigen 1 is a candidate vaccine component for malaria. It is encoded by a single copy gene and has been characterised in a number of malaria species as either an 83-kDa de novo product (Plasmodium falciparum; Pf AMA-1) or a 66-kDa product (all other species). All members of the AMA-1 family are expressed during merozoite formation in maturing schizonts and are initially routed to the rhoptries. Processed forms may subsequently be associated with the merozoite surface. Because of the unique occurrence of the 83-kDa form in P. falciparum we were interested to determine whether the phylogenetically closely related chimpanzee malaria Plasmodium reichenowi shared characteristics with Pf AMA-1. Here we show that the molecular structure, the localisation and processing are similar to that of Pf AMA-1 and that in vitro growth inhibitory mAbs reactive with Pf AMA-1 also inhibit P. reichenowi growth in an in vitro assay. Polymorphism in the 83-kDa AMA-1 family was analysed through comparison of Pr ama-1 with Pf ama-1 alleles, which showed the most significant evidence for selection maintaining polymorphism in Domains I-III of AMA-1 in P. falciparum. The most substantial divergence between Pr AMA-1 and Pf AMA-1 sequences was in the N-terminal region unique to the 83-kDa form of AMA-1. It was confirmed that the specific Pr ama-1-type allele was not present among P. falciparum parasites in an African population, and an allele coding for lysine at amino acid 187 was uniquely associated with field isolates in this population.

Evidence for additive and interaction effects of host genotype and infection in malaria

The host mechanisms responsible for protection against malaria remain poorly understood, with only a few protective genetic effects mapped in humans. Here, we characterize a host-specific genome-wide signature in whole-blood transcriptomes of Plasmodium falciparum-infected West African children and report a demonstration of genotype-by-infection interactions in vivo. Several associations involve transcripts sensitive to infection and implicate complement system, antigen processing and presentation, and T-cell activation (i.e., SLC39A8, C3AR1, FCGR3B, RAD21, RETN, LRRC25, SLC3A2, and TAPBP), including one association that validated a genome-wide association candidate gene (SCO1), implicating binding variation within a noncoding regulatory element. Gene expression profiles in mice infected with Plasmodium chabaudi revealed and validated similar responses and highlighted specific pathways and genes that are likely important responders in both hosts. These results suggest that host variation and its interplay with infection affect children’s ability to cope with infection and suggest a polygenic model mounted at the transcriptional level for susceptibility.

An X-linked haplotype of Neandertal origin is present among all non-African populations

Recent work on the Neandertal genome has raised the possibility of admixture between Neandertals and the expanding population of Homo sapiens who left Africa between 80 and 50 Kya (thousand years ago) to colonize the rest of the world. Here, we provide evidence of a notable presence (9% overall) of a Neandertal-derived X chromosome segment among all contemporary human populations outside Africa. Our analysis of 6,092 X-chromosomes from all inhabited continents supports earlier contentions that a mosaic of lineages of different time depths and different geographic provenance could have contributed to the genetic constitution of modern humans. It indicates a very early admixture between expanding African migrants and Neandertals prior to or very early on the route of the out-of-Africa expansion that led to the successful colonization of the planet.

Comparative study of the toxic effects of fumonisin B1 in rat C6 glioma cells and p53-null mouse embryo fibroblasts

The present experiments have been carried out in order to study (comparatively) oxidative stress and its consequences (i.e. modifications of DNA bases and/or DNA fragmentation), cell cycle progression (through two generations) and apoptosis in C6 glioma cells (with normal p53 status) and p53-null mouse embryonic fibroblasts (MEF) after incubation with fumonisin B(1) (FB(1)). Further endpoints, including protein and DNA syntheses as well as cytotoxicity, have been also studied. The results show that FB(1) (incubation) produced a significant increase of malondialdehyde (MDA) production (suggestive of lipid peroxidation) which was prevented by antioxidant agents in both cell types. Moreover, FB(1) induced a significant and dose-related increase of 8-OH-dG and DNA fragmentation in both C6 glioma and MEF cells. Unlike MEF cells, apoptotic C6 glioma cells were observed after FB(1) incubation. Moreover, suppression of cell cycle progression was observed in C6 glioma but not in MEF cell incubated with FB(1). The results suggest a possible loss of protective mechanisms (such as p53-dependent apoptosis and cell cycle arrest) in FB(1)-damaged MEF cells and confirm that cells lacking of mechanisms governed by p53 gene would be more susceptible to neoplastic cascade or mutation following DNA lesions induced by this mycotoxin.

Prevention by vitamin E of DNA fragmentation and apoptosis induced by fumonisin B1 in C6 glioma cells

Abstract Fumonisin B1 (FB1), produced by the fungus Fusarium moniliforme, belongs to a class of sphingosine analogue mycotoxins that occur widely in the food chain. Epidemiological studies have associated consumption of Fusarium moniliforme-contaminated food with human oesophageal cancer in China and South Africa. FB1 also causes equine leucoencephalomalacia. Evidence for induction of apoptosis by FB1 was first obtained when C6 glioma cells were incubated with fumonisin B1 (3–27 μM) causing DNA fragmentation profiles showing DNA laddering in gel electrophoresis and apoptotic bodies revealed by chromatin staining with acridine orange and ethidium bromide. Further confirmation experiments and comet assays have been performed under similar conditions. The results of the comet test show that FB1 at 9 and 18 μM induces respectively 50 ± 2% and 40 ± 1% of cells with a comet with an increased tail length of 93 ± 9 μm and 102 ± 17 μm respectively. Under these concentrations, FB1 induced DNA fragmentation and laddering and many apoptotic bodies. Pre-incubation of the cells with vitamin E (25 μM) for 24 h before FB1 (18 μM) significantly reduced DNA fragmentation and apoptotic bodies induced by FB1.

Combined effects of okadaic acid and cadmium on lipid peroxidation and DNA bases modifications (m5dC and 8-(OH)-dG) in Caco-2 cells

Abstract Okadaic acid (OA) is a marine toxin, a tumour promoter and an inducer of apoptosis. It mainly inhibits protein-phosphatases, protein synthesis and enhances lipid peroxidation. Cadmium (Cd) is known to be carcinogenic in animals and humans (group 1 according to the International Agency for Research on Cancer (IARC) classification). Cd also induces oxidative stress in living organisms. Since they are sometimes found simultaneously in mussels, we have evaluated in the present investigation, the lipid peroxidation, as malondialdehyde (MDA) production, in the variation of the ratios of 8-(OH)-dG/105dG and m5dC/ (dC + m5dC) induced by OA and/or Cd in Caco-2 cells. When cells were treated exclusively by OA (15 ng/ml) or Cd (0.625 and 5μg/ml) for 24 h, protein synthesis was inhibited (by 42 ± 5%, 18 ± 13%, and 90 ± 4% respectively) while MDA production was 2235 ± 129, 1710 ± 20, and 11496 ± 1624 pmol/mg protein respectively. In addition, each toxicant induced modified bases in DNA; increases in oxidised bases and methylated dC. The combination of OA and cadmium was more cytotoxic and caused more DNA base modifications; the ratio m5dC/(m5dC+dC) was increased from 3 ± 0.15 to 9 ± 0.15 and the ratio 8-(OH)-dG/105 dG also (from 36 ± 2 to 76 ± 6). The combination of OA and Cd also increased the level of MDA (16874 ± 2189 pmole/mg protein). The present results strongly suggest that DNA damage resulting from the oxidative stress induced by these two toxicants may significantly contribute to increasing their carcinogenicity via epigenetic processes.

Environmental influence on the worldwide prevalence of a 776C→G variant in the transcobalamin gene (TCN2)

Background: A 776C→G variant (dbSNP ID: rs1801198) in the transcobalamin gene (TCN2; MIM# 275350) decreases the cellular and plasma concentration of transcobalamin and thereby influences the cellular availability of vitamin B12. Objective: To evaluate the worldwide prevalence of this variant and its association with homocysteine plasma level. Methods: The study was performed in 1433 apparently healthy subjects, including Afro-Americans and Afro-Africans and in 251 Afro-Africans participants with severe malaria. Results: The frequencies of the 776G allele were the highest in China (0.607; 95% CI 0.554 to 0.659), low in West Africa (Bénin and Togo, 0.178; 0.154 to 0.206), and intermediate in France (0.445; 0.408 to 0.481), Italy (0.352; 0.299 to 0.409), Morocco (0.370; 0.300 to 0.447) and Mexico (0.374; 0.392 to 0.419). The 776G genotype was more frequent in Afro-Americans from New York (16.7; 8.4 to 30.7) and in Afro-African patients with severe malaria (6.0%; 95% CI 3.7 to 9.6) than in healthy Afro-African volunteers (p = 0.0004 and p = 0.033, respectively), while no difference was observed for MTHFR 677TT and 677T alleles. A disequilibrium of TCN2 genotype distribution was recorded in patients with severe malaria, with a twofold higher GG genotype than expected (p = 0.010). An association between the TCN2 polymorphism and homocysteine was observed only in Mexico and France, the two countries with the highest rate of low plasma concentration of vitamin B12 (<100 pmol/l). Conclusion: Given the dramatic heterogeneity of the 776G allele frequency worldwide, this polymorphism may be prone to a selective pressure or confers an evolutionary advantage in confronting environmental factors, one of which is malaria.

γδ T cells in the peripheral blood of individuals from an area of holoendemic Plasmodium falciparum transmission

gamma delta T cells bearing V gamma 9 T cell receptors from unexposed Caucasian donors make large responses to Plasmodium falciparum in vitro. This finding, together with observations of others showing high levels of V gamma 9+ T cells in the blood of infected non-immune individuals, led us to hypothesize that the response of these cells might contribute to the pathology of P. falciparum malaria. Acquisition of immunity to disease in people naturally exposed to infection may therefore be due in part to down-regulation or alteration of the function of gamma delta T cells. Supporting this view, and in contrast to infection in non-immune individuals, V gamma 9+ T cells are not elevated in peripheral blood of children or adults living in an endemic area despite constant exposure to P. falciparum. After in vitro stimulation with P. falciparum, however, the expansion of V gamma 9+ cells from the African donors is of similar magnitude to that observed for non-exposed Europeans. Thus, although these cells are not elevated in peripheral blood, they are still able to respond to P. falciparum antigens. In adult European donors the major gamma delta T cell population in peripheral blood is V gamma 9+ (approximately 70% of all gamma delta cells), whereas in the majority of adult Africans V delta 1+ V gamma 9- T cells predominated (approximately 70% of total gamma delta cells).

Is a Plasmodium lactate dehydrogenase (pLDH) enzyme-linked immunosorbent (ELISA)-based assay a valid tool for detecting risky malaria blood donations in Africa?

BackgroundMalaria is a leading cause of mortality in southern Benin. The main causative agent, Plasmodium falciparum, poses a threat on critical transfusions in pregnant women and children. This study’s objective was to compare the performance of different malaria screening methods in blood donors in southern Benin, a malaria-endemic country.MethodsBlood from 2,515 voluntary blood donors in Benin was collected over a period of 10 months in ethylenediaminetetraacetic acid (EDTA) tubes, which were then classified according to extraction time: long rainy season, short dry season, short rainy season, and long dry season. Microscopic examination was used to count parasites. Parasite density (PD) was expressed as the number of parasites per μL of blood. Pan Plasmodium pLDH detection was assessed by an ELISA-malaria antigen test. Using crude soluble P. falciparum antigens, an ELISA-malaria antibody test detected anti-Plasmodium antibodies.ResultsAmong the 2,515 blood donors (2,025 males and 488 females) screened, the rate of asymptomatic Plasmodium carriage was 295/2,515 (11.72%, 95% CI: 10.5-13.1%). Males had a higher infection rate (12.4%) than did females (8.8%). Parasite density was very low: between seven and100 parasites per μL of blood was reported in 80% of donors with parasitaemia. Three Plasmodium species were diagnosed: P. falciparum in 280/295 patients (95.0%), Plasmodium malariae in 14/295 (5.0%), and Plasmodium ovale in 1/295 (0.34%). Malaria prevalence in donors was higher during the rainy seasons (13.7%) compared with the dry seasons (9.9%). The use of a highly sensitive assay enabled pan Plasmodium pLDH detection in 966/2,515 (38.4%, 95% CI: 36.5%-40.3%). Malaria antibody prevalence was 1,859/2,515 (73.9%, 95% CI: 72.16-75.6%). Donors’ antigenaemia and antibody levels varied significantly (P <0.05) over the course of the four seasons. The highest antigenaemia rate 323/630 (51.3%), was observed during the short rainy season, while the highest antibody prevalence, 751/886 (84.7%), was recorded during the long dry season.ConclusionBlood donations infected with Plasmodium can transmit malaria to donation recipients. Malaria diagnostic methods are currently available, but the feasibility criteria for mass screening in endemic areas become preponderant. Detection of the pLDH antigen seems to be an adequate screening tool in endemic areas, for this antigen indicates parasite presence. Routine screening of all donated blood would prevent infected blood donations and reduce P. falciparum transmission in critical patients, such as children and pregnant women. This tool would also decrease medical prophylaxis in donation recipients and contribute to lower Plasmodium resistance.

DNA-adducts in subjects exposed to urban air pollution by benzene and polycyclic aromatic hydrocarbons (PAHs) in Cotonou, Benin

Air pollution effect on humans represents a major public health problem. Exposure to genotoxic compounds in the ambient air is evaluated using different biomarkers. In the present study we assessed DNA‐adducts levels in apparently healthy people living and working in the city of Cotonou (Benin) in which exposure to air pollutants such as benzene and polycyclic aromatic hydrocarbons (PAHs) mainly benzo(a)pyrene has been evidenced. Rural inhabitants were enrolled as control group. Taxi‐motorbike drivers, street food vendors, and gasoline salesmen were recruited in Cotonou whereas suburban residents were recruited in Godomey, 12 km from Cotonou. We found that taxi‐motorbike drivers, roadside residents, street vendors, taxi‐motor‐bike drivers and gasoline sellers had significantly higher levels of DNA‐adducts than suburban and village inhabitants (P < 0.001; post hoc, LSD). Means values were 24.6 ± 6.4, 23.78 ± 6.9, 34.7 ± 9.8, and 37.2 ± 8.1 in the exposed groups versus 2.1 ± 0.6 and 3.1 ± 0.8 adducts/108 nucleotides, in the two control groups, respectively. We did not find any significant difference within the high exposuregroups and inside low exposure subgroups (namely suburban residents and villagers) because the mean individual exposure values to both PAHs and benzene were similar among subjects exposed in the city of Cotonou and those in suburban and village areas. However, there is significant interindividual variations in adducts levels that may reflect variation of genetic susceptibility factors. Ranges of adduct level/108 nucleotides were: 1–69, 1–76, 3–169, 4–124, 0–9, 0–8 adducts/108 for taxi‐motorbike drivers, roadside residents, street vendors, gasoline sellers, suburban and village inhabitants, respectively. Our study demonstrated a clear‐cut elevated level of DNA adducts in city residents than in none exposed people (or very low exposure levels people) and designate these city residents groups as people at risks for the chronic diseases possibly caused by benzene and PAHs.