Effect of cholesterol on the hydration properties of ester and ether lipid membrane interphases

Fluorescence spectroscopy and Molecular Dynamics results show that cholesterol reduces water along the chains in ether lipids by changing the water distribution pattern between tightly and loosely bound water molecules. Water distribution was followed by emission spectra and generalized polarization of 6-dodecanoyl-2-dimethyl aminonaphthalene (Laurdan) inserted in 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14: 0 Diether PC) membranes. Molecular Dynamics simulations indicate that the action of cholesterol could be different in ether PC in comparison to ester PC. In addition, Cholesterol seems to act "per se" as an additional hydration center in ether lipids. Regardless of the phase state, cholesterol both in DMPC and 14:0 Diether PC vesicles, changed the distribution of water molecules decreasing the dipole relaxation of the lipid interphase generating an increase in the non-relaxable population. Above 10% Cholesterol/14:0 Diether PC ratio vesicles' interphase present an environment around Laurdan molecules similar to that corresponding to ester PC.

Modulation of Interfacial Hydration by Carbonyl Groups in Lipid Membranes

The lack of carbonyl groups and the presence of ether bonds give the lipid interphase a different water organization around the phosphate groups that affects the compressibility and electrical properties of lipid membranes. Generalized polarization of 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14:0 diether PC) in correlation with Fourier transform infrared (FTIR) analysis indicates a higher level of polarizability of water molecules in the membrane phase around the phosphate groups both below and above T_m. This reorganization of water promotes a different response in compressibility and dipole moment of the interphase, which is related to different H bonding of water molecules with phosphates (PO) and carbonyl (CO) groups.

Prevalence and molecular characterization of G6PD deficiency in two Plasmodium vivax endemic areas in Venezuela: predominance of the African A-(202A/376G) variant

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency causes acute haemolytic anaemia triggered by oxidative drugs such as primaquine (PQ), used for Plasmodium vivax malaria radical cure. However, in many endemic areas of vivax malaria, patients are treated with PQ without any evaluation of their G6PD status.

METHODS

G6PD deficiency and its genetic heterogeneity were evaluated in northeastern and southeastern areas from Venezuela, Cajigal (Sucre state) and Sifontes (Bolívar state) municipalities, respectively. Blood samples from 664 randomly recruited unrelated individuals were screened for G6PD activity by a quantitative method. Mutation analysis for exons 4-8 of G6PD gen was performed on DNA isolated from G6PD-deficient (G6PDd) subjects through PCR-RFLP and direct DNA sequencing.

RESULTS

Quantitative biochemical characterization revealed that overall 24 (3.6%) subjects were G6PDd (average G6PD enzyme activity 4.5 ± 1.2 U/g Hb, moderately deficient, class III), while DNA analysis showed one or two mutated alleles in 19 of them (79.2%). The G6PD A-(202A/376G) variant was the only detected in 17 (70.8%) individuals, 13 of them hemizygous males and four heterozygous females. Two males carried only the 376A → G mutation. No other mutation was found in the analysed exons.

CONCLUSIONS

The G6PDd prevalence was as low as that one shown by nearby countries. This study contributes to the knowledge of the genetic background of Venezuelan population, especially of those living in malaria-endemic areas. Despite the high degree of genetic mixing described for Venezuelan population, a net predominance of the mild African G6PD A-(202A/376G) variant was observed among G6PDd subjects, suggesting a significant flow of G6PD genes from Africa to Americas, almost certainly introduced through African and/or Spanish immigrants during and after the colonization. The data suggest that 1:27 individuals of the studied population could be G6PDd and therefore at risk of haemolysis under precipitating factors. Information about PQ effect on G6PDd individuals carrying mild variant is limited, but since the regimen of 45 mg weekly dose for prevention of malaria relapse does not seem to be causing clinically significant haemolysis in people having the G6PD A-variant, a reasoned weighing of risk-benefit for its use in Venezuela should be done, when implementing public health strategies of control and elimination.

Structure of C-terminal fragment of merozoite surface protein-1 from Plasmodium vivax determined by homology modeling and molecular dynamics refinement

One current vaccine candidate against Plasmodium vivax targeting asexual blood stage is the major merozoite surface protein-1 of P. vivax (PvMSP-1). Vaccine trials with PvMSP-1(19) and PvMSP-1(33) have succeeded in protecting monkeys and a large proportion of individuals, naturally exposed to P. vivax transmission, develop specific antibodies to PvMSP-1(19). This study presents a model for the three-dimensional structure of the C-terminal 19kDa fragment of P. vivax MSP-1 determined by means of homology modeling and molecular dynamics refinement. The structure proved to be consistent with MSP-1(19) of known crystal or solution structures. The presence of a main binding pocket, well suited for protein-protein interactions, was determined by CASTp. Corrections reported to the sequence of PvMSP-1(19) Belem strain were also inspected. Our model is currently used as a basis to understand antibody interactions with PvMSP-1(19).

Caveolins and flotillin-2 are present in the blood stages of Plasmodium vivax

Blood stages of Plasmodium vivax induce the development of caveolae and caveola-vesicle complexes (CVC) in the membrane of their host erythrocyte. Caveolae are found in almost all types of cells and are involved in endogenous processes as calcium and cholesterol homeostasis, cell signalling, transporting, ligand internalization and transcytosis of serum components. Major structural components of caveolae are the proteins caveolins and flotillins. The functional role of caveolae in the P. vivax-infected erythrocyte is not properly understood. As these organelles have been shown to contain malaria antigens, it has been suggested that they are involved in the transport and release of specific parasite antigens from the infected erythrocyte and in the uptake of plasma proteins. Using specific antibodies to classical caveolae proteins and an immunolocalization approach, we found caveolin-2, caveolin-3, and flotillin-2 in the vesicle profiles and some CVC of P. vivax-infected erythrocytes. Caveolin-1-3 were not found in uninfected erythrocytes. This is the first report of identification and localization of caveolins in the CVC present in erythrocytes infected with P. vivax, thereby providing evidence of the role of this particular organelle in the protein-trafficking pathway that connect parasite-encoded proteins with the erythrocyte cytoplasm and the cell surface throughout the asexual blood cycle of vivax malaria parasite.

Oncospheral peptide-based ELISAs as potential seroepidemiological tools for Taenia solium cysticercosis/neurocysticercosis in Venezuela

This study evaluates five synthetic peptides derived from four, potentially protective, Taenia saginata oncosphere molecules for the serodiagnosis of T. solium cysticercosis/neurocysticercosis in three distinct Venezuelan endemic regions. The peptides, all of which have been described previously, are designated HP6-3, Ts45W-1, Ts45W-5, Ts45S-10 and TEG-1. In clinically verified and seropositive hospital cases, combining the results of three of the individual peptide-based ELISAs (HP6-3, Ts45W-1 and Ts45W-5) afforded the best balance between sensitivity (85%) and specificity (83.5%), a significant improvement on the 63.6% specificity obtained with the routinely employed T. solium cyst-fluid-based ELISA. Similarly, in the seropositive Venezuelan endemic zone samples, 89.09% of Amerindians, 77.27% of symptomatic rural subjects and 67.83% of non-symptomatic rural subjects were also classed as seropositive by the combined peptide-based ELISAs. The profile of antibody recognition to individual peptides varied between the different groups of samples examined. The relevance of the above findings for the serology and prognosis of T. solium cysticercosis/neurocysticercosis in hospital- and field-based situations is discussed.

[Toxoplasma gondii infection in Amerindians of Venezuelan Amazon]

We conducted a serological survey for Toxoplasma gondii in 121 Amerindians of the Guajibo ethnic group, 4 to 45 years of age, inhabiting Amazonas State, in the Venezuelan rain forest. The overall prevalence was 88%. Pattern of prevalence and antibody titres were compatible with constant transmission. Sex differences in antibody prevalence were not detected but antibody titres were significantly higher in females. The study is consistent with the presence of risk factors, which favour a frequent exposure of these Amerindians to T. gondii since childhood.

Malaria diagnosis by the polymerase chain reaction: a field study in south-eastern Venezuela

A polymerase chain reaction (PCR) method that amplifies genus- and species-specific sequences present within the small subunit of ribosomal ribonucleic acid (ssRNA) genes of the human malaria parasites was used for the diagnosis of malaria in south-eastern Venezuela. One hundred blood samples were submitted to deoxyribonucleic acid extraction, PCR amplification and electrophoretic analysis of the PCR products, and the results were compared to those of routine microscopical diagnosis. The sensitivity of PCR for detection of Plasmodium vivax and P. falciparum malaria was 99% and 100%, respectively. However, 6 patients (6%) harboured parasites undetected by microscopy. The PCR assay detected a high proportion of mixed infections: 29% (17/59) of the infections microscopically diagnosed as P. vivax were shown to be mixed infections of P. vivax and P. falciparum. Forty per cent (7/17) of the individuals with a missed P. falciparum infection had received chloroquine in the previous 30 d. These results suggest that, in places where transmission of both P. vivax and P. falciparum occurs, PCR detection of malaria parasites can be a very useful complement to microscopical diagnosis in order to ascertain the true incidence of each species and for the follow-up of patients after specific treatment.

Sensitive detection of Plasmodium vivax in blood by a cell-ELISA using a monoclonal antibody

An IgM monoclonal antibody (7C5B71) which reacted with the blood stages of Plasmodium vivax, but not with those of Plasmodium falciparum was used in a cell-ELISA to detect parasites in samples of peripheral blood. Blood thin smears were probed with monoclonal antibody 7C5B71 and then reacted with a peroxidase conjugate of the appropriate specificity and the insoluble chromogen amino-ethyl-carbazole. Infected cells which appeared dark red coloured were rapidly identified under a light microscope using a low magnification. The conventional microscopic examination of thin films coloured with Giemsa was used as reference test. Under laboratory conditions the test showed a positive result in samples with a level of parasitaemia of < or = 500 parasites/microliter of blood. In a preliminary field trial the test showed 100 % specificity for the diagnosis of P. vivax malaria.

Diagnosis of malaria by acridine orange fluorescent microscopy in an endemic area of venezuela

Fluorescent (acridine orange) microscopical examination of capillary centrifuged blood (quantitative buffy coat [QBC] analysis) and Giemsa stained thick blood smears (GTS) were compared for diagnosis of malaria in blood specimens from adults living in malaria transmission areas of the States of Bolivar and Amazonas in southeastern and south Venezuela, respectively. Of a total of 198 GTS examined, 95 subjects (48%) showed parasitaemia. Among the 95 blood films with a positive GTS, 94 were judged positive by the QBC. However, positive QBC tubes were found in 29 out of 103 blood specimens with a negative GTS. Thus, relative to a GTS standard, the sensitivity and specificity of the QBC-test was 99.2% and 72%, respectively. Young trophozoites of Plasmodium vivax and P. falciparum could not be distinguished with certainty. It is confirmed that the QBC offers many advantages compared with the standard diagnosis of malaria parasites, specifically in the speed of staining and ease of interpretation. However, in places where P. falciparum and P. vivax occur, species and stage differentiation should be confirmed with the GTS.

[Activation of suppressor cells of the delayed hypersensitivity response in BALB/c mice infected or immunized with Leishmania mexicana pifanoi]

A T suppressor cell population that specifically shut down delayed hypersensitivity responses (DHR) to the parasite was found in both BALB/c mice chronically infected with Leishmania mexicana pifanoi and in naive mice which had received a single IV supraoptimal dose of killed parasites. At the early phase of infection mice exhibited a transitory state of cell-mediated immunity against the parasite that was abrogated when lesions reached their accelerated phase of growth. Results suggest that in both infected and high-dose immunized mice, the activation of T suppressor cells of DHR is related to antigen overload.

Lymph node cell responsiveness in BALB/c mice infected with Leishmania mexicana

In the present study we measured the blastogenic response of lymph node cells from BALB/c mice infected with Leishmania mexicana throughout the course of infection. Results showed that infected mice displayed normal blastogenic responses in the lymph nodes until twenty weeks of infection. Thereafter, there was a gradual suppression. Comparison of the immunoresponsiveness in the spleen and lymph nodes, revealed normal responses in the lymph nodes several weeks after suppression in the spleen had occurred. Suppression of blastogenic responses in the lymph nodes was related to an adherent macrophage-like cell which actively suppressed normal proliferative responses to mitogens.

The immunomodulatory effect of yeast glucan on delayed hypersensitivity

The effect of yeast beta-1, 3-glucan as an immunopotentiator of delayed type-hypersensitivity reactions (DHR) was studied. Delayed-type-hypersensitivity reactions in mice sensitized intraperitoneally (IP) with sheep red blood cells (SRBC) and pretreated three days previously with glucan given IP were significantly increased. However, mice sensitized IP with SRBC three days after the subcutaneous (SC) administration of glucan showed depressed DHR. Glucan given at the same site but not at distance strongly potentiated the DHR induced by SC sensitization with SRBC. Subcutaneous injection of glucan and SRBC given together also resulted in a sustained DHR which persisted twelve days after sensitization when DHR of control mice had waned.