Hemolysis of human erythrocytes induced by melamine-cyanurate complex

Microfluidic paper analytic device (μPAD) technology for food safety applications

Foodborne pathogens, food adulterants, allergens, and toxic chemicals in food can cause major health hazards to humans and animals. Stringent quality control measures at all stages of food processing are required to ensure food safety. There is, therefore, a global need for affordable, reliable, and rapid tests that can be conducted at different process steps and processing sites, spanning the range from the sourcing of food to the end-product acquired by the consumer. Current laboratory-based food quality control tests are well established, but many are not suitable for rapid on-site investigations and are costly. Microfluidic paper analytical devices (μPADs) are a fast-growing field in medical diagnostics that can fill these gaps. In this review, we describe the latest developments in the applications of microfluidic paper analytic device (μPAD) technology in the food safety sector. State-of-the-art μPAD designs and fabrication methods, microfluidic assay principles, and various types of μPAD devices with food-specific applications are discussed. We have identified the prominent research and development trends and future directions for maximizing the value of microfluidic technology in the food sector and have highlighted key areas for improvement. We conclude that the μPAD technology is promising in food safety applications by using novel materials and improved methods to enhance the sensitivity and specificity of the assays, with low cost.

Selective Bias Virtual Screening for Discovery of Promising Antimalarial Candidates targeting Plasmodium N-Myristoyltransferase

Malaria remains a significant public health challenge, with Plasmodium vivax being the species responsible for the most prevalent form of the disease. Given the limited therapeutic options available, the search for new antimalarials against P. vivax is urgent. This study aims to identify new inhibitors for P. vivax N-myristoyltransferase (PvNMT), an essential drug target against malaria. Through a validated virtual screening campaign, we prioritized 23 candidates for further testing. In the yeast NMT system, seven compounds exhibit a potential inhibitor phenotype. In vitro antimalarial phenotypic assays confirmed the activity of four candidates while demonstrating an absence of cytotoxicity. Enzymatic assays reveal LabMol-394 as the most promising inhibitor, displaying selectivity against the parasite and a strong correlation within the yeast system. Furthermore, molecular dynamics simulations shed some light into its binding mode. This study constitutes a substantial contribution to the exploration of a selective quinoline scaffold and provides valuable insights into the development of new antimalarial candidates.

Crotofolane Diterpenoids and Other Constituents Isolated from Croton kilwae

Six new crotofolane diterpenoids (1-6) and 13 known compounds (7-19) were isolated from the MeOH-CH2Cl2 (1:1, v/v) extracts of the leaves and stem bark of Croton kilwae. The structures of the new compounds were elucidated by extensive analysis of spectroscopic and mass spectrometric data. The structure of crotokilwaepoxide A (1) was confirmed by single-crystal X-ray diffraction, allowing for the determination of its absolute configuration. The crude extracts and the isolated compounds were investigated for antiviral activity against respiratory syncytial virus (RSV) and human rhinovirus type-2 (HRV-2) in HEp-2 and HeLa cells, respectively, for antibacterial activity against the Gram-positive Bacillus subtilis and the Gram-negative Escherichia coli, and for antimalarial activity against the Plasmodium falciparum Dd2 strain. ent-3β,19-Dihydroxykaur-16-ene (7) and ayanin (16) displayed anti-RSV activities with IC50 values of 10.2 and 6.1 μM, respectively, while exhibiting only modest cytotoxic effects on HEp-2 cells that resulted in selectivity indices of 4.9 and 16.4. Compounds 2 and 5 exhibited modest anti-HRV-2 activity (IC50 of 44.6 μM for both compounds), while compound 16 inhibited HRV-2 with an IC50 value of 1.8 μM. Compounds 1-3 showed promising antiplasmodial activities (80-100% inhibition) at a 50 μM concentration.

Prenatal cyanuric acid exposure induced spatial learning impairments associated with alteration of acetylcholine-mediated neural information flow at the hippocampal CA3-CA1 synapses of male rats

Cyanuric acid (CA) is reported to induce nephrotoxicity but its toxic effect is not fully known. Prenatal CA exposure causes neurodevelopmental deficits and abnormal behavior in spatial learning ability. Dysfunction of the acetyl-cholinergic system in neural information processing is correlated with spatial learning impairment and was found in the previous reports of CA structural analogue melamine. To further investigate the neurotoxic effects and the potential mechanism, the acetylcholine (ACh) level was detected in the rats which were exposed to CA during the whole of gestation. Local field potentials (LFPs) were recorded when rats infused with ACh or cholinergic receptor agonist into hippocampal CA3 or CA1 region were trained in the Y-maze task. We found the expression of ACh in the hippocampus was significantly reduced in dose-dependent manners. Intra-hippocampal infusion of ACh into the CA1 but not the CA3 region could effectively mitigate learning deficits induced by CA exposure. However, activation of cholinergic receptors did not rescue the learning impairments. In the LFP recording, we found that the hippocampal ACh infusions could enhance the values of phase synchronization between CA3 and CA1 regions in theta and alpha oscillations. Meanwhile, the reduction in the coupling directional index and the strength of CA3 driving CA1 in the CA-treated groups was also reversed by the ACh infusions. Our findings are consistent with the hypothesis and provide the first evidence that prenatal CA exposure induced spatial learning defect is attributed to the weakened ACh-mediated neuronal coupling and NIF in the CA3-CA1 pathway.

Phytofabrication and characterization of Alchornea cordifolia silver nanoparticles and evaluation of antiplasmodial, hemocompatibility and larvicidal potential

Purpose: The recent emergence of Plasmodium falciparum (Pf) parasites resistant to current artemisinin-based combination therapies in Africa justifies the need to develop new strategies for successful malaria control. We synthesized, characterized and evaluated medical applications of optimized silver nanoparticles using Alchornea cordifolia (AC-AgNPs), a plant largely used in African and Asian traditional medicine. Methods: Fresh leaves of A. cordifolia were used to prepare aqueous crude extract, which was mixed with silver nitrate for AC-AgNPs synthesis and optimization. The optimized AC-AgNPs were characterized using several techniques including ultraviolet-visible spectrophotometry (UV-Vis), scanning/transmission electron microscopy (SEM/TEM), powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), Fourier transformed infrared spectroscopy (FTIR), dynamic light scattering (DLS) and Zeta potential. Thereafter, AC-AgNPs were evaluated for their hemocompatibility and antiplasmodial activity against Pf malaria strains 3D7 and RKL9. Finally, lethal activity of AC-AgNPs was assessed against mosquito larvae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti which are vectors of neglected diseases such as dengue, filariasis and chikungunya. Results: The AC-AgNPs were mostly spheroidal, polycrystalline (84.13%), stable and polydispersed with size of 11.77 ± 5.57 nm. FTIR revealed the presence of several peaks corresponding to functional chemical groups characteristics of alkanoids, terpenoids, flavonoids, phenols, steroids, anthraquonones and saponins. The AC-AgNPs had a high antiplasmodial activity, with IC₅₀ of 8.05 μg/mL and 10.31 μg/mL against 3D7 and RKL9 Plasmodium falciparum strains. Likewise, high larvicidal activity of AC-AgNPs was found after 24 h- and 48 h-exposure: LC₅₀ = 18.41 μg/mL and 8.97 μg/mL (Culex quinquefasciatus), LC₅₀ = 16.71 μg/mL and 7.52 μg/mL (Aedes aegypti) and LC₅₀ = 10.67 μg/mL and 5.85 μg/mL (Anopheles stephensi). The AC-AgNPs were highly hemocompatible (HC₅₀ > 500 μg/mL). Conclusion: In worrying context of resistance of parasite and mosquitoes, green nanotechnologies using plants could be a cutting-edge alternative for drug/insecticide discovery and development.

Exposure to melamine and its derivatives in Chinese adults: The cumulative risk assessment and the effect on routine blood parameters

Melamine (MEL) and its derivatives, ammeline (AMN), ammelide (AMD), cyanuric acid (CYA) are widely existed in environmental media. Animal studies have reported the cumulative risk assessment (CRA) of simultaneous exposure to MEL and its derivatives and explored the associations between exposure and routine blood parameters. Such information is largely unknown in human studies. In this study, we detected the urinary concentrations of MEL and its derivatives in 239 Chinese adults to conduct the CRA by evaluating their hazard quotients (HQ) and hazard Index (HI), and also explored the possible associations between exposure and measured routine blood parameters in study population. The detectable frequencies of MEL, AMN, AMD and CYA were 96.65%, 41.00%, 97.91% and 97.07%, respectively. The median values of creatinine (Cr)-adjusted MEL, AMN, AMD, CYA and the total concentrations of MEL and its derivatives (∑MEL) were 11.41 μg/g Cr, not detected (ND), 2.64 μg/g Cr, 15.30 μg/g Cr, 35.02 μg/g Cr, respectively. There were 9 (3.77%) participants with estimated daily intakes (EDIs) of CYA exceeding the tolerable daily intake (TDI) of 2500 ng/kg bw/day, and 12 (5.02%) participants with HI of ∑MEL exposure exceeding 1 based on the strictest TDI value. Urinary concentrations of MEL and its derivatives were positively associated with specific routine blood parameters, including hematocrit, hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin concentration, mean corpuscular hemoglobin, white blood cell, neutrophil count (P < 0.05). Meanwhile, exposure to MEL and its derivatives increased the risk of red blood cell abnormality (P < 0.05). Our study is the first study to provide evidence-based data on the CRA of exposure to MEL and its derivatives in Chinese adults, and to propose a possible association between such exposure and routine blood parameters in human.

A novel polymeric fluorescence sensor based on acrylated citric acid for detection of melamine adulteration: Application in milk powder

Melamine selective acrylate citric acid (ACA) based polymeric membrane sensor was prepared by radical polymerization method and the sensor was characterized. The sensor showed a selective fluorescent response to melamine (λ_ex/λ_em = 388/425 nm). The sensor response is linear in the concentration range of 3.96 × 10^-9 to 7.93 × 10^-8 mol L^-1, the optimum pH value is 6.0 and response time is less than 1 min. Limit of detection (LOD) and limit of quantification (LOQ) were calculated as 2.32 × 10^-10 mol L^-1 and as 7.74 × 10^-10 mol L^-1, respectively. The sensor showed great selectivity towards melamine in the presence of a large number of molecules and ions. The performance of sensor was also confirmed by determining of melamine in milk powder sample and the results were compared with HPLC results and acceptable results were obtained. As a conclusion, the results revealed that the proposed sensor is an interesting alternative for melamine determination.

Exposure to melamine cyanuric acid in adult mice induced thyroid dysfunction and circadian rhythm disorder

MCA is a halogen-free flame retardant. It can cause damage to other tissues such as the kidneys and liver. However, the effects on the circadian rhythm and thyroid in adult mice have not been studied. In this article, adult male mice received MCA at concentrations of 0, 10, 20, 30 mg/kg. The results showed that the time spending on wheel-running and rest bouts changed in different period after MCA exposure. MCA disrupted the T3 and T4 hormone homeostasis and decreased the expression of thyroid hormone synthesis genes. The histological morphology of the thyroid gland was damaged. It was suggested that MCA exposure caused circadian rhythm disorder and thyroid dysfunction.

Chronic Cyanuric Acid Exposure Depresses Hippocampal LTP but Does Not Disrupt Spatial Learning or Memory in the Morris Water Maze

Exposure to cyanuric acid (CA) causes multiple organ failure accompanied by the involvement in kinds of target proteins, which are detectable and play central roles in the CNS. The hippocampus has been identified as a brain area which was especially vulnerable in developmental condition associated with cognitive dysfunction. No studies have examined the effects of CA on hippocampal function after in vitro or in vivo treatment. Here, we aimed to examine hippocampal synaptic function and adverse behavioral effects using a rat model administered CA intraperitoneally or intrahippocampally. We found that infusion of CA induced a depression in the frequency but not the amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), miniature excitatory postsynaptic currents (mEPSCs), or N-methyl-D-aspartate (NMDA)-mediated excitatory postsynaptic currents (EPSCs) of the CA1 neurons in dose-dependent pattern. Both intraperitoneal and intrahippocampal injections of CA suppressed hippocampal LTP from Schaffer collaterals to CA1 regions. Paired-pulse facilitation (PPF), a presynaptic phenomenon, was enhanced while the total and phosphorylated expression of NMDA-GluN1, NMDA-GluN2A, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-GluA1 subunits were comparable between CA-treated and control groups. In Morris water maze test, both groups could effectively learn and retain spatial memory. Our studies provide the first evidence for the neurotoxic effect of CA and the insight into its potential mechanisms.

Antimalarial activity of basic phospholipases A2 isolated from Paraguayan Bothrops diporus venom against Plasmodium falciparum

Malaria is a parasitic infectious disease and was responsible for 400.000 deaths in 2018. Plasmodium falciparum represents the species that causes most human deaths due to severe malaria. In addition, studies prove the resistance of P. falciparum to drugs used to treat malaria, making the search for new drugs with antiplasmodial potential necessary. In this context, the literature describes snake venoms as a rich source of molecules with microbicidal potential, including phospholipases A2 (PLA2s). In this sense, the present study aimed to isolate basic PLA2s from Paraguayan Bothrops diporus venom and evaluate their antiplasmodial potential. Basic PLA2s were obtained using two chromatographic steps. Initially, B. diporus venom was subjected to ion exchange chromatography (IEC). The electrophoretic profile of the fractions from the IEC permitted the selection of 3 basic fractions, which were subjected to reverse phase chromatography, resulting in the isolation of the PLA2s. The toxins were tested for enzymatic activity using a chromogenic substrate and finally, the antiplasmodial, cytotoxic potential and hemolytic activity of the isolated toxins were evaluated. The electrophoretic profile of the fractions from the IEC permitted the selection of 3 basic fractions, which were subjected to reverse phase chromatography, resulting in the isolation of the two enzymatically active PLA2s, BdTX-I and BdTX-II and the PLA2 homologue BdTX-III. The antiplasmodial potential was evaluated and the toxins showed IC50 values of: 2.44, 0.0153 and 0.59 μg/mL respectively, presenting PLA2 selectivity according to the selectivity index results (SI) calculated against HepG2 cells. The results show that the 3 basic phospholipases isolated in this study have a potent antiparasitic effect against the W2 strain of P. falciparum. In view of the results obtained in this work, further research are necessary to determine the mechanism of action by which these toxins cause cell death in parasites.

Synthesis, crystal structure and leishmanicidal activity of new trimethoprim Ru(III), Cu(II) and Pt(II) metal complexes

Leishmaniasis is a parasitic disease caused by protozoa of the genus Leishmania, which has very limited treatment options and affects poor and underdeveloped populations. The current treatment is plagued by many complications, such as high toxicity, high cost and resistance to parasites; therefore, novel therapeutic agents are urgently needed. Herein, the synthesis, characterization and in vitro leishmanicidal potential of new complexes with the general formula [RuCl₃(TMP)(dppb)] (1), [PtCl(TMP)(PPh₃)₂]PF₆ (2) and [Cu(CH₃COO)₂(TMP)₂]·DMF (3) (dppb = 1,4-bis(diphenylphosphino)butane, PPH₃ = triphenylphosphine and TMP = trimethoprim) were evaluated. The complexes were characterized by infrared, UV-vis, cyclic voltammetry, molar conductance measurements, elemental analysis and NMR experiments. Also, the geometry of (2) and (3) were determined by single crystal X-ray diffraction. Despite being less potent against promastigote L. amazonensis proliferation than amphotericin B reference drug (IC₅₀ = 0.09 ± 0.02 μM), complex (2) (IC₅₀ = 3.6 ± 1.5 μM) was several times less cytotoxic (CC₅₀ = 17.8 μM, SI = 4.9) in comparison with amphotericin B (CC₅₀ = 3.3 μM, SI = 36.6) and gentian violet control (CC₅₀ = 0.8 μM). Additionally, complex (2) inhibited J774 macrophage infection and amastigote number by macrophages (IC₅₀ = 6.6 and SI = 2.7). Outstandingly, complex (2) was shown to be a promising candidate for a new leishmanicidal therapeutic agent, considering its biological power combined with low toxicity.

Novel Quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione Derivatives Against Chloroquine-resistant Plasmodium falciparum

INTRODUCTION

In this work DHPMs were combined with the quinoline nucleus to obtain new quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione compounds with improved antiplasmodial activity as well as decreased cytotoxicity. Nineteen quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione derivatives connected by a linker group to quinolone ring moieties with different substituents were synthesized and assayed against P. falciparum.

MATERIALS AND METHODS

Nineteen quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione derivatives connected by a linker group to quinoline ring moieties with different substituents were synthesized and assayed against chloroquine-resistant Plasmodium falciparum, along with the reference drug chloroquine. Among these compounds, the derivatives with two methylene carbon spacers showed the best activity accompanied by low cytotoxicity.

RESULTS

The derivative without substituents on the aromatic ring (2a) and the derivative with a chlorine group at position 4 (2d) provided the best results, with IC50 = 1.15 µM and 1.5 µM, respectively.

CONCLUSION

Compared to the parent drugs, these compounds presented marked decreases in cytotoxicity, with MDL50 values over 1,000 µM and selectivity indexes of >869.5 and >666.6, respectively. The quinolinyl-pyrrolo[3,4-d]pyrimidine-2,5-dione framework appears to be promising for further studies as an antimalarial for overcoming the burden of resistance in P. falciparum.

Identification of a peptide derived from a Bothrops moojeni metalloprotease with in vitro inhibitory action on the Plasmodium falciparum purine nucleoside phosphorylase enzyme (PfPNP)

There is a growing need for research on new antimalarial agents against Plasmodium falciparum infection, especially in regards to planning molecular architecture for specific molecular targets of the parasite. Thus, a metalloprotease from Bothrops moojeni, known as BmooMPα-I, was explored in this study, through in silico assays, aiming at the development of a peptide generated from this molecule with potential inhibitory action on PfPNP, an enzyme necessary for the survival of the parasite. In order to isolate BmooMPα-I, cation exchange and reverse phase chromatographies were performed, followed by in vitro assays of antiparasitic activity against the W2 strain of P. falciparum. The interactions between BmooMPα-I and PfPNP were evaluated via docking, and the resulting peptide, described as Pep1 BM, was selected according to the BmooMPα-I region demonstrating the best interaction score with the target of interest. The values for the specific activities of the PfPNP reaction were measured using the inorganic phosphate substrate and MESG. The fraction corresponding to BmooMPα-I was identified as fraction 4 in the cation exchange chromatography step, due to proteolytic activity on casein and the presence of a major band at ≅ 23 kDa. BmooMPα-I was able to inhibit in vitro growth of W2 P. falciparum, with an IC₅₀ value of 16.14 μg/mL. Virtual screening with Pep1 BM demonstrated two PfPNP target binding regions, with ΔG values at the interaction interface of -10.75 kcal/mol and -11.74 kcal/mol. A significant reduction in the enzymatic activity of PfPNP was observed in the presence of Pep 1 BM when compared to the assay in the absence of this possible inhibitor. BmooMPα-I showed activity in vitro against W2 P. falciparum. By means of in silico techniques, the Pep 1 BM was identified as having potential binding affinity to the catalytic site of PfPNP and of inhibiting its catalytic activity in vitro.

Antiplasmodial and antileishmanial activities of compounds from Piper tuberculatum Jacq fruits

INTRODUCTION

This study assessed the activity of compounds from Piper tuberculatum against Plasmodium falciparum and Leishmania guyanensis.

METHODS

The effects of compounds from P. tuberculatum fruits on P. falciparum and L. guyanensis promastigote growth in vitro were determined. Hemolytic action and cytotoxicity in HepG2 and J774 cells were measured.

RESULTS

Three compounds showed strong antiplasmodial activity and one compound showed strong antileishmanial activity. Two compounds were non-toxic to HepG2 cells and all were toxic to J774 cells. The compounds showed no hemolytic activity.

CONCLUSIONS

The tested compounds from P. tuberculatum exhibited antiparasitic and cytotoxic effects.

Synthesis and molecular modelling studies of pyrimidinones and pyrrolo[3,4-d]-pyrimidinodiones as new antiplasmodial compounds

BACKGROUND

Malaria is responsible for 429,000 deaths per year worldwide, and more than 200 million cases were reported in 2015. Increasing parasite resistance has imposed restrictions to the currently available antimalarial drugs. Thus, the search for new, effective and safe antimalarial drugs is crucial. Heterocyclic compounds, such as dihydropyrimidinones (DHPM), synthesised via the Biginelli multicomponent reaction, as well as bicyclic compounds synthesised from DHPMs, have emerged as potential antimalarial candidates in the last few years.

METHODS

Thirty compounds were synthesised employing the Biginelli multicomponent reaction and subsequent one-pot substitution/cyclisation protocol; the compounds were then evaluated in vitro against chloroquine-resistant Plasmodium falciparum parasites (W2 strain). Drug cytotoxicity in baseline kidney African Green Monkey cells (BGM) was also evaluated. The most active in vitro compounds were evaluated against P. berghei parasites in mice. Additionally, we performed an in silico target fishing approach with the most active compounds, aiming to shed some light into the mechanism at a molecular level.

RESULTS

The synthetic route chosen was effective, leading to products with high purity and yields ranging from 10-84%. Three out of the 30 compounds tested were identified as active against the parasite and presented low toxicity. The in silico study suggested that among all the molecular targets identified by our target fishing approach, Protein Kinase 3 (PK5) and Glycogen Synthase Kinase 3β (GSK-3β) are the most likely molecular targets for the synthesised compounds.

CONCLUSIONS

We were able to easily obtain a collection of heterocyclic compounds with in vitro anti-P. falciparum activity that can be used as scaffolds for the design and development of new antiplasmodial drugs.

Colorimetric detection of melamine in milk based on Triton X-100 modified gold nanoparticles and its paper-based application

In this study, we have developed a method for rapid, highly efficient and selective detection of melamine. The negatively charged citrate ions form an electrostatic layer on gold nanoparticles (AuNPs) and keep the NPs dispersed and stable. When citrate-capped AuNPs were further modified with Triton X-100, it stabilized the AuNPs against the conditions of high ionic strength and a broad pH range. However, the addition of melamine caused the destabilization and aggregation of NPs. This may be attributed to the interaction between melamine and the AuNPs through the ligand exchange with citrate ions on the surface of AuNPs leading Triton X-100 to be removed. As a result, the AuNPs were unstable, resulting in the aggregation. The aggregation induced a wine red-to-blue color change, and a new absorption peak around 630nm appeared. Triton X-100-AuNPs could selectively detect melamine at the concentration as low as 5.1nM. This probe was successfully applied to detect melamine in milk. Furthermore, paper-based quantitative detection system using this colorimetric probe was also demonstrated by integrating with a smartphone.

Palliative effects of Moringa olifera ethanolic extract on hemato-immunologic impacts of melamine in rats

Melamine (MEL) is a widespread food contaminant and adulterant. Moringa olifera is a widely known medicinal plant with various pharmacological properties. Herein, this study aimed to investigate, for the first time, the probable protective or therapeutic role of M. olifera ethanolic extract (MOE) against MEL induced hemato-immune toxic hazards. Fifty Sprague Dawely male rats were orally treated with distilled water, MOE (800 mg/kg bw), MEL (700 mg/kg bw), MOE/MEl or MOE + MEl. Erythrogram and leukogram profiling were evaluated to assess hematological status. Innate immune functions were evaluated via measuring lysozyme levels, nitric oxide concentration, and bactericidal activity of phagocytes. Serum immunoglobulin levels were estimated as indicators of humoral immunity. Histologic and immunohistochemical evaluations of splenic tissues were also performed. The results indicated that MEL caused a significant decline in RBC, Hb, PCV, total WBC, neutrophil, lymphocyte, phagocytes bactericidal activity, lysozyme activity, nitric oxide, total IgM and IgG levels. Also, MEL induced various pathologic lesions in the spleen with strong expression of CD4 and CD8 positive cells. MOE significantly counteracted the former anaemic, leucopenic, innate and humoral depressant effects of MEL particularly at co-exposure. In conclusion, these findings revealed that MOE could be candidate therapy against MEL hemato-immunotoxic impacts.

Primaquine-thiazolidinones block malaria transmission and development of the liver exoerythrocytic forms

Background

Primaquine is an anti-malarial used to prevent Plasmodium vivax relapses and malaria transmission. However, PQ metabolites cause haemolysis in patients deficient in the enzyme glucose-6-phosphate dehydrogenase (G6PD). Fifteen PQ-thiazolidinone derivatives, synthesized through one-post reactions from primaquine, arenealdehydes and mercaptoacetic acid, were evaluated in parallel in several biological assays, including ability to block malaria transmission to mosquitoes.

Results

All primaquine derivatives (PQ-TZs) exhibited lower cell toxicity than primaquine; none caused haemolysis to normal or G6PD-deficient human erythrocytes in vitro. Sera from mice pretreated with the test compounds thus assumed to have drug metabolites, caused no in vitro haemolysis of human erythrocytes, whereas sera from mice pretreated with primaquine did cause haemolysis. The ability of the PQ-TZs to block malaria transmission was evaluated based on the oocyst production and percentage of mosquitoes infected after a blood meal in drug pre-treated animals with experimental malaria caused by either Plasmodium gallinaceum or Plasmodium berghei; four and five PQ-TZs significantly inhibited sporogony in avian and in rodent malaria, respectively. Selected PQ-TZs were tested for their inhibitory activity on P. berghei liver stage development, in mice and in vitro, one compound (4m) caused a 3-day delay in the malaria pre-patent period.

Conclusions

The compound 4m was the most promising, blocking malaria transmissions and reducing the number of exoerythrocytic forms of P. berghei (EEFs) in hepatoma cells in vitro and in mice in vivo. The same compound also caused a 3-day delay in the malaria pre-patent period.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1755-6) contains supplementary material, which is available to authorized users.

Influence of non-steroidal anti-inflammatory drugs on Drosophila melanogaster longevity

Most age-related diseases and aging itself are associated with chronic inflammation. Thus pharmacological inhibition of inflammatory processes may be effective antiaging strategy. In this study we demonstrated that treatment of Drosophila melanogaster with 10 non-steroidal anti-inflammatory drugs (NSAIDs: CAY10404, aspirin, APHS, SC-560, NS-398, SC-58125, valeroyl salicylate, trans-resveratrol, valdecoxib, licofelone) leads to extension of lifespan, delays age-dependent decline of locomotor activity and increases stress resistance. The effect of the lifespan increase was associated with decrease of fecundity. Depending on the concentration, NSAIDs demonstrated both anti- and pro-oxidant properties in Drosophila tissues. However, we failed to identify clear correlation between antioxidant properties of NSAIDs and their pro-longevity effects. The lifespan extending effects of APHS, SC-58125, valeroyl salicylate, trans-resveratrol, valdecoxib, and licofelone were more pronounced in males, valdecoxib and aspirin - in females. We demonstrated that lifespan extension effect of NSAIDs was abolished in flies with defective genes involved in Pkh2-ypk1-lem3-tat2 pathway.

High selective antileishmanial activity of vanadium complex with stilbene derivative

Leishmaniasis is a group of disease caused by different species of the parasite Leishmania affecting millions of people worldwide. Conventional therapy relies on multiple parenteral injections with pentavalent antimonials which exhibit high toxicity and various side effects have been reported. Hence, the research for an effective and low toxic effect drug is necessary. In the present work, the synthesis, spectroscopic and analytical characterizations of stilbene derivative (H2Salophen) and its vanadium complex (VOSalophen) are reported. Besides the chemical ancillary information, investigation of the leishmanicidal effects of these compounds were provided. The biological assays against promastigote and amastigote forms of L. amazonensis have been shown that VOSalophen exhibited a strong antiparasitic activity (IC50 of 6.65 and 3.51 μM, respectively). Furthermore, the leishmanicidal activity was concentration and time-dependent. Regarding toxicity and selectivity on mammalian cells, VOSalophen have not caused significant damage to human erythrocytes in all concentrations tested and VOSalophen was almost seven times more destructive for the intracellular parasite than for macrophages. Furthermore, the leishmanicidal activity of VOSalophen in promastigote forms of L. amazonensis could be associated to mitochondrial dysfunction and increase of the reactive oxygen species (ROS) production. In L. amazonensis-infected macrophages, VOSalophen induces ROS production and a microbicidal action NO-dependent. Our biological results indicate the effective and selective action of VOSalophen against L. amazonensis and the leishmanicidal effect can be associated to parasite disorders and immumodulatory effects.

Visual-test and Sorption-spectrophotometric Determination of Melamine in Biological Objects

Melamine may have toxic effects on humans and animals. It is well known that melamine accumulates in the body and causes reproductive damages, forms bladder or kidney stones, which can lead to bladder cancer. Trace amounts of melamine at ppm levels may occur in certain food commodities due to its migration from melamine-containing disposable tableware plastics. It was intentionally adulterated to milk products to show a false increase in protein concentration. Considering these facts there is a need for establishing sensitive and reliable methods of melamine determination. As uncostly, rapid and selective melamine detection methods are highly required, the hyphenated sorption-spectrophotometric and visual test methods seem to be perspective candidates. In the present work the optimal conditions of sorption concentration of melamine from aqueous solutions ontо the silica gel surface were studied. The calibration graph for the sorption-spectrophotometric method is linear in 0.02 – 9.8 μmol.L-1 mg L-1 melamine concentration range. Proposed method allows naked-eye monitoring of biological samples.

Melamine-cyanurate complexes and oxidative stress markers in trout kidney following melamine and cyanuric acid long-term co-exposure and withdrawal

In 2007, renal failure and death in pets were linked to pet food containing both melamine (MEL) and cyanuric acid (CYA). In mammals and fish, the co-administration of MEL and CYA causes renal crystal formation. Moreover, little is known about the process of crystal removal in fish. The aim of this study was to evaluate the formation of MEL-cyanurate crystals in kidney of rainbow trout (Oncorhynchus mykiss) fed combined MEL and CYA diets for 10 weeks at 250, 500 and 1,000 mg/kg in feed (equivalent to 2.5, 5, 10 mg/kg body weight of trout fed 1 % body weight per day). During the exposure trial and throughout a withdrawal period, prooxidant effects of MEL and CYA were evaluated on oxidative stress markers such as catalase, glutathione S-transferase and malondialdehyde. Crystal formation was dose and time dependent, and after six withdrawal weeks, crystals persisted in kidney of trout treated the highest triazine dose. Catalase and glutathione S-transferase activity in kidney of trout exposed to both triazines for 10 weeks indicated that MEL (with or without CYA) can exert a higher prooxidant effect than CYA dispensed singly. Although the enzymes activity increase appears to be reverted after two MEL withdrawal weeks, persistence of crystals may lead to severe damage in renal cells of fish.

Evaluation of antimalarial activity and toxicity of a new primaquine prodrug

Plasmodium vivax is the most prevalent of the five species causing malaria in humans. The current available treatment for P. vivax malaria is limited and unsatisfactory due to at least two drawbacks: the undesirable side effects of primaquine (PQ) and drug resistance to chloroquine. Phenylalanine-alanine-PQ (Phe-Ala-PQ) is a PQ prodrug with a more favorable pharmacokinetic profile compared to PQ. The toxicity of this prodrug was evaluated in in vitro assays using a human hepatoma cell line (HepG2), a monkey kidney cell line (BGM), and human red blood cells deficient in the enzyme glucose-6-phosphate-dehydrogenase (G6PD). In addition, in vivo toxicity assays were performed with rats that received multiple doses of Phe-Ala-PQ to evaluate biochemical, hematological, and histopathological parameters. The activity was assessed by the inhibition of the sporogonic cycle using a chicken malaria parasite. Phe-Ala-PQ blocked malaria transmission in Aedes mosquitoes. When compared with PQ, it was less cytotoxic to BGM and HepG2 cells and caused less hemolysis of G6PD-deficient red blood cells at similar concentrations. The prodrug caused less alteration in the biochemical parameters than did PQ. Histopathological analysis of the liver and kidney did show differences between the control and Phe-Ala-PQ-treated groups, but they were not statistically significant. Taken together, the results highlight the prodrug as a novel lead compound candidate for the treatment of P. vivax malaria and as a blocker of malaria transmission.

[Membrane protective properties of diastereomers of methylpheophorbide a 13(2)-n-n-octyl-N-(2-hydroxy-3-isobornyl-5-methylbenzyl)amide]

Two diastereomers of methylpheophorbide a 13(2)-N-n-octyl-N-(2-hydroxy-3-isobornyl-5-methylbenzyl)amide were obtained from (+)- and (-)-enantiomers of 2-isobornyl-4-methylphenol. Evaluation of membrane protective and antioxidant activity of individual diastereomers on the model of H2O2-induced hemolysis of blood erythrocytes showed that the stereochemistry of isobornyl substituent in the synthesized conjugates has no effect on their biological activity.

Urinary melamine: proposed parameter of melamine adulteration of food

Melamine is widely being reported as a food adulterant. Although its toxicity is currently recognized, melamine adulterations of food items are ongoing for falsely inflating the protein content of the food. Melamine alone or in combination with cyanuric acid or uric acid causes nephrotoxicity, and melamine-induced nephrotoxicity is now a global concern. It has been proven that when consumed, melamine is metabolized at a slower rate and excreted unchanged in urine. There is every possibility that when individuals consume melamine-adulterated food items, the melamine may be excreted unchanged in the urine. Therefore, melamine estimation in urine may be a yardstick to check for melamine adulteration of food items. In the present review, recent literature on this subject is analyzed justifying.

Antioxidant responses and renal crystal formation in rainbow trout treated with melamine administered individually or in combination with cyanuric acid

In 2007 and 2008, renal stone formation and kidney damage in human infants were linked to consumption of melamine (MEL)-contaminated infant formula, as well as renal failure and death in pets due to pet food containing both MEL and cyanuric acid (CYA). The aim of this study was to examine the effects of MEL and CYA administered individually or in combination on concentrations of certain metabolites and enzyme activities that serve as markers for oxidative stress in kidney and liver of rainbow trout. In addition, the levels of muscle MEL and renal crystal formation were determined. Trout were fed MEL and/or CYA for 8 wk at 250, 500, or 1000 mg of each compound/kg in feed. Fish muscle residues of MEL exhibited a dose-response relationship. Coexposure of trout to MEL and CYA at the highest dose led to lower MEL residue concentrations in muscle compared to exposure to MEL alone. Renal MEL-CYA complexes were found in kidneys of fish treated with combined MEL and CYA. A dose response was evident with respect to both (1) number of trout displaying renal crystals and (2) number of crystals per fish. Changes in concentration of antioxidant parameters, such as glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase, were recorded in both tissues of MEL- and CYA-dosed trout. Lipid peroxidation was more pronounced in kidney than liver. Therefore, feed contaminated with both MEL and CYA could be problematic for fish, as MEL administered to trout, individually or in combination with CYA, may facilitate the onset of oxidative damage in trout.

Toxicity of melamine: the public health concern

Melamine contamination in food has resulted in sickness and deaths of human infants, pets, and farm animals in the past decade. The majority of the victims suffered from acute kidney injury, nephrolithiasis, and urolithiasis. Since then, animal studies have revealed the possible target organs of the melamine toxicity and the extent of the adverse effects of the contaminant. State-of-the-art analytical methods have been developed to achieve the "zero tolerance" aim for such economically motivated adulteration. These studies provide in-depth understanding of the melamine toxicity and promising analytical methods, which can help us safeguard our dairy food source.

Antimalarial activity and mechanisms of action of two novel 4-aminoquinolines against chloroquine-resistant parasites

Chloroquine (CQ) is a cost effective antimalarial drug with a relatively good safety profile (or therapeutic index). However, CQ is no longer used alone to treat patients with Plasmodium falciparum due to the emergence and spread of CQ-resistant strains, also reported for P. vivax. Despite CQ resistance, novel drug candidates based on the structure of CQ continue to be considered, as in the present work. One CQ analog was synthesized as monoquinoline (MAQ) and compared with a previously synthesized bisquinoline (BAQ), both tested against P. falciparum in vitro and against P. berghei in mice, then evaluated in vitro for their cytotoxicity and ability to inhibit hemozoin formation. Their interactions with residues present in the NADH binding site of P falciparum lactate dehydrogenase were evaluated using docking analysis software. Both compounds were active in the nanomolar range evaluated through the HRPII and hypoxanthine tests. MAQ and BAQ derivatives were not toxic, and both compounds significantly inhibited hemozoin formation, in a dose-dependent manner. MAQ had a higher selectivity index than BAQ and both compounds were weak PfLDH inhibitors, a result previously reported also for CQ. Taken together, the two CQ analogues represent promising molecules which seem to act in a crucial point for the parasite, inhibiting hemozoin formation.

Cytoprotective effect of trolox against oxidative damage and apoptosis in the NRK-52e cells induced by melamine

An outbreak of urinary stones associated with consumption of melamine-tainted milk products occurred in 2008 in China, leading to serious illness of many infants and even death. However, the toxicity of melamine in kidney epithelial cells remains unclear. We have explored the effects of melamine and trolox on renal NRK-52e (normal rat kidney 52e) cells. The IC(50) of melamine was measured by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. Total SOD (superoxide dismutase) was determined by NBT (Nitro Blue Tetrazolium) staining method. GSH-Px (glutathione peroxidase) activity was detected by UV colorimetric assay, and MDA (malondialdehyde) content was determined by thiobarbituric acid assay. Apoptosis induced by melamine was determined by flow cytometry. The IC(50) increased when NRK-52e cells were treated with both melamine and trolox compared with melamine only. SOD and GSH-Px activities were decreased, but MDA content was increased by melamine in a dose-dependent manner. Trolox significantly enhanced SOD and GSH-Px activity in melamine-treated NRK-52e cells, but it decreased their MDA content. LDH (lactate dehydrogenase) activity and the level of ROS (reactive oxygen species) of the NRK-52e cells were enhanced by melamine compared with the control. Furthermore, the apoptosis rate increased in NRK-52e cells treated with melamine, whereas trolox was protective. These results show that melamine has an obvious adverse effect on proliferation of NRK-52e cells, causing oxidative damage and apoptosis, thus providing a novel insight into renal cytotoxicology of melamine. Trolox ameliorates the effect on melamine toxicity.

Review of melamine scandal: still a long way ahead

In September 2008, in China, tens of thousands of children were hospitalized, several even died, as a result of infant-formula milk adulterated with a synthetic chemical compound, melamine, and in the next few months, this crisis became the focus of attention worldwide. Although there are a number of articles about melamine toxicity on different species of animals, the long-term effect of melamine on humans is still unknown. Besides, several recent in vitro studies indicated that melamine can damage cells of other parts of the body, including the central nervous system, breaking the previous view that melamine toxicity is limited to the urinary system. Hence, we strongly recommend a long-term follow-up for the overall health status of the victims, not confined to kidneys, to minimize the potential toxic effects in their later life; and research to study the specific mechanism of melamine should be encouraged.

Melamine impairs spatial cognition and hippocampal synaptic plasticity by presynaptic inhibition of glutamatergic transmission in infant rats

The scandal of melamine-contamination has not been quite blown out, since the toxicity of melamine continues to raise concerns for public health. It has been well known that fetus and infant periods play the most important roles in brain development, whereas little has been done on the harmful effects of melamine on the center nervous system (CNS) of children. In the present study, we investigated the effects of melamine on behavioral and electrophysiology alternations in rats, and the effects of melamine on synaptic transmission were examined using whole-cell patch-clamp technique in the hippocampal CA1 neurons of infant rats. Morris water maze (MWM) test showed that learning and memory abilities were impaired significantly by melamine. The long-time potentiation (LTP) test exhibited that the field excitatory postsynaptic potential (fEPSP) slopes were significantly lower in melamine group compared to that in control group. Furthermore, the data of whole-cell patch-clamp experiments showed that melamine decreased the frequencies of both spontaneous EPSCs (sEPSCs) and minitura EPSCs (mEPSCs) to the same extent (about 76% and 78% respectively). However, there were no significant changes in sEPSC or mEPSC amplitude or kinetics after melamine addition, indicating that the effect of melamine on glutamatergic transmission was probably presynaptic. In conclusion, melamine reduced the release of glutamate in presynaptic transmission of hippocampus, which partly resulted in diminished LTP and further damaged the function of learning and memory.