Spatio-temporal characterization of drought variability in data-scarce regions using global precipitation data: a case study in Cauto river basin, Cuba.

Drought is considered the most severe water-related disaster in the Cauto river basin, which is the longest river and the main agricultural producer in Cuba. Better understanding of drought characteristics is crucial to drought management. Given the sparsity of ground-based precipitation observations in the Cauto, this study aims at using gridded global precipitation to analyze the spatio-temporal variations of drought in this river basin. Firstly, the monthly Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) was calibrated with the gauged precipitation using the Thiessen polygon-based method and linear least squares regression equations. Then, the gridded standardized precipitation index (SPI) with time scales of 3, 6, 9 months and drought characteristics, namely, drought frequency, duration and intensity were calculated using the calibrated CHIRPS. Finally, the spatio-temporal analysis was performed to investigate the variations of drought in the Cauto river basin in time and space. The obtained results show that the calibrated CHIRPS is highly consistent with the gauged observations and is capable of determining the magnitude, time, and spatial extent of drought events in the Cauto river basin. The trend analysis by the Mann-Kendall test reveals that although the trend is not statistically significant, the SPI tends to decrease with time in the dry season, which indicates the more severe drought. The spatial analysis indicates that the lower altitude area of the Cauto river basin is suffered from longer drought duration and higher drought intensity than the upper one. This study expresses the importance of open global precipitation data sources in monitoring and quantifying drought characteristics in data-scarce regions.

BM-BronchoLC - A rich bronchoscopy dataset for anatomical landmarks and lung cancer lesion recognition.

Flexible bronchoscopy has revolutionized respiratory disease diagnosis. It offers direct visualization and detection of airway abnormalities, including lung cancer lesions. Accurate identification of airway lesions during flexible bronchoscopy plays an important role in the lung cancer diagnosis. The application of artificial intelligence (AI) aims to support physicians in recognizing anatomical landmarks and lung cancer lesions within bronchoscopic imagery. This work described the development of BM-BronchoLC, a rich bronchoscopy dataset encompassing 106 lung cancer and 102 non-lung cancer patients. The dataset incorporates detailed localization and categorical annotations for both anatomical landmarks and lesions, meticulously conducted by senior doctors at Bach Mai Hospital, Vietnam. To assess the dataset's quality, we evaluate two prevalent AI backbone models, namely UNet++ and ESFPNet, on the image segmentation and classification tasks with single-task and multi-task learning paradigms. We present BM-BronchoLC as a reference dataset in developing AI models to assist diagnostic accuracy for anatomical landmarks and lung cancer lesions in bronchoscopy data.

Novel melanin-derived stationary phase for immobilized metal ion affinity chromatography in recombinant His-tagged protein purification.

The matrix of the stationary phase is a crucial element in affinity chromatography for protein purification. Various materials, including polymer or magnetic materials, have been employed as the matrix in the purification of His-tagged protein. Here, for the first time, we utilized a combination of melanin and alginate, both natural polymer materials, to synthesize Ni-melanin/alginate (Ni-M/A) beads for His-tagged protein purification. We investigated the binding of His-tagged Mpro on the Ni-M/A beads, referred to as Ni-M/A-Mpro, and assessed the elution efficiency of Mpro from the beads. Our examination involved FTIR, EDS, XRD, SDS-PAGE, and Western blotting methods. FTIR spectra revealed notable changes in the stretching patterns and intensities of hydroxyl, amine, carbonyl, imine and amide chemical groups, when Mpro protein was present in the Ni-M/A sample. XRD spectra demonstrated the occurrence of two Nickel peaks at 35-40 deg and 40-45 deg in Ni-M/A, but only one nickel peak at 35-40 deg in Ni-M/A-Mpro, indicating the binding of Mpro on the Nickel ions. EDS analysis reported a decrease in the concentration of Nickel on the surface of Ni-M/A from 16% to 7% when Mpro protein was loaded into the stationary phase. Importantly, our data indicated that the purity of the His-tagged protein Mpro after purification reached 97% after just one-step purification using the Ni-M/A stationary phase. Moreover, the binding capacity of Ni-M/A for Mpro was approximately 5.2 mg/g with recovery efficiency of 40%. Our results suggested Ni-M/A as a highly potential solid phase for affinity chromatography in the purification of His-tagged protein.

The role of chitosan in enhancing the solubility and antibacterial activity of emodin against drug-resistant bacteria.

Similar to most anthraquinone compounds, the pharmacological properties of emodin are limited because of its low water solubility. In this study, the formulation of chitosan and emodin (EMD/CS) was prepared by a bottom-up method with precipitation and sonication steps in order to enhance the solubility of emodin. Thanks to the interactions of oxygen-and nitrogen-containing groups in chitosan with emodin molecules, the solubility of emodin in the formulation was remarkably increased to 0.5 mg/mL. The EMD/CS particles were well dispersed and distributed in a range of sub-micrometer with an average particle size of 342 nm. The EMD/CS formulation exhibited synergic antibacterial activity of emodin and chitosan, against drug-resistant bacterial strains, namely Methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli O157:H7 (E. coli O157:H7). When the compositions of emodin and chitosan increased, the antibacterial effectiveness of the EMD/CS formulation increased. The EMD/CS formulation with compositions of 0.5 mg/mL of emodin and 9.0 mg/mL of chitosan could significantly inhibit the proliferation of E. coli O157:H7. Meanwhile, the EMD/CS formulation with a lower concentration of emodin (0.4 mg/mL) and chitosan (7.2 mg/mL) could cause an extermination effect on MRSA. The enhanced solubility of EMD/CS formulation suggests that this formulation can be a potential candidate for the treatment of infectious diseases caused by drug-resistant bacterial pathogens.

Bayesian merging of numerical modeling and remote sensing for saltwater intrusion quantification in the Vietnamese Mekong Delta.

Saltwater intrusion has become one of the most concerning issues in the Vietnamese Mekong Delta (VMD) due to its increasing impacts on agriculture and food security of Vietnam. Reliable estimation of salinity plays a crucial role to mitigate the impacts of saltwater intrusion. This study developed a hybrid technique that merges satellite imagery with numerical simulations to improve the estimation of salinity in the VMD. The salinity derived from Landsat images and by numerical simulations was fused using the Bayesian inference technique. The results indicate that our technique significantly reduces the uncertainties and improves the accuracy of salinity estimates. The Nash-Sutcliffe coefficient is 0.74, which is much higher than that of numerical simulation (0.63) and Landsat estimation (0.6). The correlation coefficient between the ensemble and measured salinity is relatively high (0.88). The variance of the ensemble salinity errors (5.0 ppt2) is lower than that of Landsat estimation (10.4 ppt2) and numerical simulations (9.6 ppt2). The proposed approach shows a great potential to combine multiple data sources of a variable of interest to improve its accuracy and reliability wherever these data are available.

Biological properties and diverse cytokine profiles followed by in vitro and in vivo infections with LSDV strain isolated in first outbreaks in Vietnam.

Preliminary information about LSD virus isolated from the first outbreaks in Vietnam has been reported by our laboratory. In the current study, LSDV strain, LSDV/Vietnam/Langson/HL01(HL01) was further analyzed to provide a better understanding of this viral pathogen. HL01 LSDV strain was propagated at MOI 0.01 in MDBK cells and then given to cattle at dose of 106.5 TCID50/ml (2ml/animal). The production of proinflammatory (IFN-γ, IL-1α, and TNF-α) and anti-inflammatory (IL-6, IL-10, and TGF-ß1) cytokines were measured by real-time PCR, both In vitro and In vivo. The results demonstrated that HL01 strain caused the typical signs of LSD and LSDV In vitro and In vivo, respectively suggesting a virulent field LSDV strain. Additionally, different cytokine profiles were observed in these In vitro and In vivo studies. In MDBK cells, different cytokines profiles were observed in two phases: in the early phase, the expression levels of all examined cytokines were significantly increased at 6 h (p < 0.05). In the later phase, the peak levels of the cytokine secretion were recognized from 72 to 96 h, with the exception of IL-1α when compared to controls. In cattle, the expression levels of all six cytokines were significantly higher at day 7 following LSDV challenge (p < 0.05) when compared to controls, especially expression levels of TGF-ß1 and IL-10. These findings suggest the important roles of these cytokines in protection against LSDV infections. Additionally, the data from diverse cytokine profiles followed by this LSDV strain challenge provides key understanding of the underlying cellular immune mechanisms in the host against LSDV infection In vitro and In vivo.

Nano-Lipids Based on Ginger Oil and Lecithin as a Potential Drug Delivery System.

Lipid nanoparticles based on lecithin are an interesting part of drug delivery systems. However, the stability of lecithin nano-lipids is problematic due to the degradation of lecithin, causing a decrease in pH. In this study, the modification of the conventional nano-lipid-based soybean lecithin was demonstrated. Ginger-oil-derived Zingiber officinale was used along with lecithin, cholesterol and span 80 to fabricate nano-lipids (GL nano-lipids) using a thin-film method. TEM and a confocal microscope were used to elucidate GL nano-lipids' liposome-like morphology. The average size of the resultant nano-lipid was 249.1 nm with monodistribution (PDI = 0.021). The ζ potential of GL nano-lipids was negative, similarly to as-prepared nano-lipid-based lecithin. GL nano-lipid were highly stable over 60 days of storage at room temperature in terms of size and ζ potential. A shift in pH value from alkaline to acid was detected in lecithin nano-lipids, while with the incorporation of ginger oil, the pH value of nano-lipid dispersion was around 7.0. Furthermore, due to the richness of shogaol-6 and other active compounds in ginger oil, the GL nano-lipid was endowed with intrinsic antibacterial activity. In addition, the sulforhodamine B (SRB) assay and live/dead imaging revealed the excellent biocompatibility of GL nano-lipids. Notably, GL nano-lipids were capable of carrying hydrophobic compounds such as curcumin and performed a pH-dependent release profile. A subsequent characterization showed their suitable potential for drug delivery systems.

Green biorefinery: Microalgae-bacteria microbiome on tolerance investigations in plants.

Co-culture of microalgae and microorganisms, supported with the resulting synergistic effects, can be used for wastewater treatment, biomass production, agricultural applications and etc. Therefore, this study aimed to explore the role of Bacillus subtilis (B. subtilis) in tolerance against the harsh environment of seafood wastewater, at which these microalgal-bacterial flocs were formed by microalgae cultivation. In this present study, B. subtilis isolated from the cultivation medium of Chlorella vulgaris and exposed to different salinity (0.1-4% w/v sodium chloride) and various pH range to determine the tolerant ability and biofilm formation. Interestingly, this bacteria strain that isolated from microalgae cultivation medium showed the intense viability in the salt concentration exceeding up to 4% (w/v) NaCl but demonstrated the decrease in cell division as environmental culture undergoing over pH 10. Cell viability was recorded higher than 71% and 92% for B. subtilis inoculum in media with salt concentration greater than 20 gL-1 and external pH 6.5-9, respectively. This showed that B. subtilis isolated from microalgal-bacteria cocultivation exhibited its tolerant ability to survive in the extremely harsh conditions and thus, mitigating the stresses due to salinity and pH.

Characterization of a Novel Alphaherpesvirus Isolated from the Fruit Bat Pteropus lylei in Vietnam.

Herpesviruses exist in nature within each host animal. Ten herpesviruses have been isolated from bats and their biological properties reported. A novel bat alphaherpesvirus, which we propose to name "Pteropus lylei-associated alphaherpesvirus (PLAHV)," was isolated from urine of the fruit bat Pteropus lylei in Vietnam and characterized. The entire genome sequence was determined to be 144,008 bp in length and predicted to include 72 genes. PLAHV was assigned to genus Simplexvirus with other bat alphaherpesviruses isolated from pteropodid bats in Southeast Asia and Africa. The replication capacity of PLAHV in several cells was evaluated in comparison with that of herpes simplex virus 1 (HSV-1). PLAHV replicated better in the bat-originated cell line and less in human embryonic lung fibroblasts than HSV-1 did. PLAHV was serologically related to another bat alphaherpesvirus, Pteropodid alphaherpesvirus 1 (PtAHV1), isolated from a Pteropus hypomelanus-related bat captured in Indonesia, but not with HSV-1. PLAHV caused lethal infection in mice. PLAHV was as susceptible to acyclovir as HSV-1 was. Characterization of this new member of bat alphaherpesviruses, PLAHV, expands the knowledge on bat-associated alphaherpesvirology.IMPORTANCE A novel bat alphaherpesvirus, Pteropus lylei-associated alphaherpesvirus (PLAHV), was isolated from urine of the fruit bat Pteropus lylei in Vietnam. The whole-genome sequence was determined and was predicted to include 72 open reading frames in the 144,008-bp genome. PLAHV is circulating in a species of fruit bats, Pteropus lylei, in Asia. This study expands the knowledge on bat-associated alphaherpesvirology.

Missed detections of influenza A(H1)pdm09 by real-time RT-PCR assay due to haemagglutinin sequence mutation, December 2017 to March 2018, northern Viet Nam.

INTRODUCTION: There are two methods of reverse transcription polymerase chain reaction (RT-PCR) that have been the common methods to detect influenza infections: conventional and real-time RT-PCR. From December 2017 to March 2018, several missed diagnoses of influenza A(H1)pdm09 using real-time RT-PCR were reported in northern Viet Nam. This study investigated how these missed detections occurred to determine their effect on the surveillance of influenza. METHODS: The haemagglutinin (HA) segments of A(H1N1)pdm09 from both real-time RT-PCR positive and negative samples were isolated and sequenced. The primer and probe sets in the HA gene were checked for mismatches, and phylogenetic analyses were performed to determine the molecular epidemiology of these viruses. RESULTS: There were 86 positive influenza A samples; 32 were A(H1)pdm09 positive by conventional RT-PCR but were negative by real-time RT-PCR. Sequencing was conducted on 23 influenza (H1N1)pdm09 isolates that were recovered from positive samples. Eight of these were negative for A(H1)pdm09 by real-time RT-PCR. There were two different mismatches in the probe target sites of the HA gene sequences of all isolates (n = 23) with additional mismatches only at position 7 (template binding site) identified for all eight negative real-time RT-PCR isolates. The prime target sites had no mismatches. Phylogenetic analysis of the HA gene showed that both the positive and negative real-time RT-PCR isolates were grouped in clade 6B.1; however, the real-time RT-PCR negative viruses were located in a subgroup that referred to substitution I295V. CONCLUSION: Constant monitoring of genetic changes in the circulating influenza A(H1N1)pdm09 viruses is important for maintaining the sensitivity of molecular detection assays.

Bioflocculation formation of microalgae-bacteria in enhancing microalgae harvesting and nutrient removal from wastewater effluent.

Microalgal bacterial flocs can be a promising approach for microalgae harvesting and wastewater treatment. The present study provides an insight on the bioflocs formation to enhance harvesting of Chlorella vulgaris and the removal of nutrients from seafood wastewater effluent. The results showed that the untreated seafood wastewater was the optimal culture medium for the cultivation and bioflocculation of C. vulgaris, with the flocculating activity of 92.0 ±â€¯6.0%, total suspended solids removal of 93.0 ±â€¯5.5%, and nutrient removal of 88.0 ±â€¯2.2%. The bioflocs collected under this optimal condition contained dry matter of 107.2 ±â€¯5.6 g·L-1 and chlorophyll content of 25.5 ±â€¯0.2 mg·L-1. The results were promising when compared to those obtained from the auto-flocculation process that induced by the addition of calcium chloride and pH adjustment. Additionally, bacteria present in the wastewater aided to promote the formation of bioflocculation process.

Genome sequence of Rhizomucor pusillus FCH 5.7, a thermophilic zygomycete involved in plant biomass degradation harbouring putative GH9 endoglucanases.

We report here the annotated draft genome sequence of the thermophilic zygomycete Rhizomucor pusillus strain FCH 5.7, isolated from compost soil in Vietnam. The genome assembly contains 25.59 Mb with an overall GC content of 44.95%, and comprises 10,898 protein coding genes. Genes encoding putative cellulose-, xylan- and chitin-degrading proteins were identified, including two putative endoglucanases (EC 3.2.1.4) from glycoside hydrolase family 9, which have so far been mostly assigned to bacteria and plants.

Combined genome and transcriptome sequencing to investigate the plant cell wall degrading enzyme system in the thermophilic fungus Malbranchea cinnamomea.

BACKGROUND: Genome and transcriptome sequencing has greatly facilitated the understanding of biomass-degrading mechanisms in a number of fungal species. The information obtained enables the investigation and discovery of genes encoding proteins involved in plant cell wall degradation, which are crucial for saccharification of lignocellulosic biomass in second-generation biorefinery applications. The thermophilic fungus Malbranchea cinnamomea is an efficient producer of many industrially relevant enzymes and a detailed analysis of its genomic content will considerably enhance our understanding of its lignocellulolytic system and promote the discovery of novel proteins. RESULTS: The 25-million-base-pair genome of M. cinnamomea FCH 10.5 was sequenced with 225× coverage. A total of 9437 protein-coding genes were predicted and annotated, among which 301 carbohydrate-active enzyme (CAZyme) domains were found. The putative CAZymes of M. cinnamomea cover cellulases, hemicellulases, chitinases and pectinases, equipping the fungus with the ability to grow on a wide variety of biomass types. Upregulation of 438 and 150 genes during growth on wheat bran and xylan, respectively, in comparison to growth on glucose was revealed. Among the most highly upregulated CAZymes on xylan were glycoside hydrolase family GH10 and GH11 xylanases, as well as a putative glucuronoyl esterase and a putative lytic polysaccharide monooxygenase (LPMO). AA9-domain-containing proteins were also found to be upregulated on wheat bran, as well as a putative cutinase and a protein harbouring a CBM9 domain. Several genes encoding secreted proteins of unknown function were also more abundant on wheat bran and xylan than on glucose. CONCLUSIONS: The comprehensive combined genome and transcriptome analysis of M. cinnamomea provides a detailed insight into its response to growth on different types of biomass. In addition, the study facilitates the further exploration and exploitation of the repertoire of industrially relevant lignocellulolytic enzymes of this fungus.

A Randomized Comparison of Chloroquine Versus Dihydroartemisinin-Piperaquine for the Treatment of Plasmodium vivax Infection in Vietnam.

A total of 128 Vietnamese patients with symptomatic Plasmodium vivax mono-infections were enrolled in a prospective, open-label, randomized trial to receive either chloroquine or dihydroartemisinin-piperaquine (DHA-PPQ). The proportions of patients with adequate clinical and parasitological responses were 47% in the chloroquine arm (31 of 65 patients) and 66% in the DHA-PPQ arm (42 of 63 patients) in the Kaplan-Meier intention-to-treat analysis (absolute difference 19%, 95% confidence interval = 0-37%), thus establishing non-inferiority of DHA-PPQ. Fever clearance time (median 24 versus 12 hours,P= 0.02), parasite clearance time (median 36 versus 18 hours,P< 0.001), and parasite clearance half-life (mean 3.98 versus 1.80 hours,P< 0.001) were all significantly shorter in the DHA-PPQ arm. All cases of recurrent parasitemia in the chloroquine arm occurred from day 33 onward, with corresponding whole blood chloroquine concentration lower than 100 ng/mL in all patients. Chloroquine thus remains efficacious for the treatment of P. vivax malaria in southern Vietnam, but DHA-PPQ provides more rapid symptomatic and parasitological recovery.

An HPLC method with diode array detector for the simultaneous quantification of chloroquine and desethylchloroquine in plasma and whole blood samples from Plasmodium vivax patients in Vietnam, using quinine as an internal standard.

A sensitive, simple method for quantification of chloroquine (CQ) and desethylchloroquine (MCQ) in whole blood and plasma from Plasmodium vivax patients has been developed using HPLC with diode array detection (DAD). Solid-phase extraction on Isolute-96-CBA was employed to process 100 µL of plasma/whole blood samples. CQ, MCQ and quinine were separated using a mobile phase of phosphate buffer 25 mm, pH 2.60-acetonitrile (88:12, v/v) with 2 mm sodium perchlorate on a Zorbax SB-CN 150 × 4.6 mm, 5 µm column at a flow rate of 1.2 mL/min, at ambient temperature in 10 min, with the DAD wavelength of 343 nm. The method was linear over the range of 10-5000 ng/mL for both CQ and MCQ in plasma and whole blood. The limit of detection was 4 ng/mL and limit of quantification was 10 ng/mL in both plasma and blood for CQ and MCQ. The intra-, inter- and total assay precision were <10% for CQ and MCQ in plasma and whole blood. In plasma, the accuracies varied between 101 and 103%, whereas in whole blood, the accuracies ranged from 97.0 to 102% for CQ and MCQ. The method is an ideal technique with simple facilities and instruments, bringing about good separation in comparison with previous methods. © 2016 The Authors Biomedical Chromatography Published by John Wiley & Sons Ltd.

Viruses Occur Incorporated in Biogenic High-Mg Calcite from Hypersaline Microbial Mats.

Using three different microscopy techniques (epifluorescence, electronic and atomic force microscopy), we showed that high-Mg calcite grains in calcifying microbial mats from the hypersaline lake "La Salada de Chiprana", Spain, contain viruses with a diameter of 50-80 nm. Energy-dispersive X-ray spectrometer analysis revealed that they contain nitrogen and phosphorus in a molar ratio of ~9, which is typical for viruses. Nucleic acid staining revealed that they contain DNA or RNA. As characteristic for hypersaline environments, the concentrations of free and attached viruses were high (>10(10) viruses per g of mat). In addition, we showed that acid treatment (dissolution of calcite) resulted in release of viruses into suspension and estimated that there were ~15 × 10(9) viruses per g of calcite. We suggest that virus-mineral interactions are one of the possible ways for the formation of nano-sized structures often described as "nanobacteria" and that viruses may play a role in initiating calcification.

Coral Mucus Is a Hot Spot for Viral Infections.

There is increasing suspicion that viral communities play a pivotal role in maintaining coral health, yet their main ecological traits still remain poorly characterized. In this study, we examined the seasonal distribution and reproduction pathways of viruses inhabiting the mucus of the scleractinians Fungia repanda and Acropora formosa collected in Nha Trang Bay (Vietnam) during an 11-month survey. The strong coupling between epibiotic viral and bacterial abundance suggested that phages are dominant among coral-associated viral communities. Mucosal viruses also exhibited significant differences in their main features between the two coral species and were also remarkably contrasted with their planktonic counterparts. For example, their abundance (inferred from epifluorescence counts), lytic production rates (KCN incubations), and the proportion of lysogenic cells (mitomycin C inductions) were, respectively, 2.6-, 9.5-, and 2.2-fold higher in mucus than in the surrounding water. Both lytic and lysogenic indicators were tightly coupled with temperature and salinity, suggesting that the life strategy of viral epibionts is strongly dependent upon environmental circumstances. Finally, our results suggest that coral mucus may represent a highly favorable habitat for viral proliferation, promoting the development of both temperate and virulent phages. Here, we discuss how such an optimized viral arsenal could be crucial for coral viability by presumably forging complex links with both symbiotic and adjacent nonsymbiotic microorganisms.

Independent emergence of artemisinin resistance mutations among Plasmodium falciparum in Southeast Asia.

BACKGROUND: The emergence of artemisinin-resistant Plasmodium falciparum in Southeast Asia threatens malaria treatment efficacy. Mutations in a kelch protein encoded on P. falciparum chromosome 13 (K13) have been associated with resistance in vitro and in field samples from Cambodia. METHODS: P. falciparum infections from artesunate efficacy trials in Bangladesh, Cambodia, Laos, Myanmar, and Vietnam were genotyped at 33 716 genome-wide single-nucleotide polymorphisms (SNPs). Linear mixed models were used to test associations between parasite genotypes and parasite clearance half-lives following artesunate treatment. K13 mutations were tested for association with artemisinin resistance, and extended haplotypes on chromosome 13 were examined to determine whether mutations arose focally and spread or whether they emerged independently. RESULTS: The presence of nonreference K13 alleles was associated with prolonged parasite clearance half-life (P = 1.97 × 10(-12)). Parasites with a mutation in any of the K13 kelch domains displayed longer parasite clearance half-lives than parasites with wild-type alleles. Haplotype analysis revealed both population-specific emergence of mutations and independent emergence of the same mutation in different geographic areas. CONCLUSIONS: K13 appears to be a major determinant of artemisinin resistance throughout Southeast Asia. While we found some evidence of spreading resistance, there was no evidence of resistance moving westward from Cambodia into Myanmar.

Effect of Inducers, Incubation Time and Heme Concentration on IC(50) Value Variation in Anti-heme Crystallization Assay.

Heme detoxification through crystallization into hemozoin has been suggested as a good target for the development of screening assays for new antimalarials. However, comparisons among the data obtained from different experiments are difficult, and the IC(50) values (the concentrations of drug that are required to inhibit 50% of hemozoin formation) for the same drug vary widely. We studied the effects of changes in heme concentration (precursor of ß-hematin), incubation time and three inducers (SDS, Tween 20 and linoleic acid) on the IC(50) of some antimalarials (chloroquine, quinine, amodiaquine, and clotrimazole). The results showed that increasing both inducer concentration and incubation time raised the IC(50) of selected antimalarials. Any change in those factors caused the IC(50) value to vary. Standardization of assay conditions is, therefore, necessary to increase reproducibility and reduce discrepancies in assay performance. Considering all of the variables, the best choice of inducers is in the order of SDS > Tween 20 > linoleic acid.

Neutralization of toxic haem by Porphyromonas gingivalis haemoglobin receptor.

Free haem is known to be toxic to organs, tissues and cells. It enhances permeability by binding to a cell membrane, which leads to cell death, and damages lipids, proteins and DNA through the generation of reactive oxygen species. Lysine- and arginine-specific gingipains (Kgp and RgpA/B) are major proteinases that play an important role in the pathogenicity of a black-pigmented periodontopathogen named Porphyromonas gingivalis. One of the adhesin domains of gingipain, HbR could bind haem as an iron nutrient source for P. gingivalis. Using erythrocyte and its membrane as a model, results from the present study demonstrate that recombinant HbR expressed in Escherichia coli could inhibit haem-induced haemolysis, probably through removing haem from the haem-membrane complex and lowering free haem toxicity by mediating dimerization of haem molecules. The ability to protect a cell membrane from haem toxicity is a new function for HbR.