Cyperus articulatus L. (Cyperaceae) Rhizome Essential Oil Causes Cell Cycle Arrest in the G2/M Phase and Cell Death in HepG2 Cells and Inhibits the Development of Tumors in a Xenograft Model.

Cyperus articulatus L. (Cyperaceae), popularly known in Brazil as "priprioca" or "piriprioca", is a tropical and subtropical plant used in popular medical practices to treat many diseases, including cancer. In this study, C. articulatus rhizome essential oil (EO), collected from the Brazilian Amazon rainforest, was addressed in relation to its chemical composition, induction of cell death in vitro and inhibition of tumor development in vivo, using human hepatocellular carcinoma HepG2 cells as a cell model. EO was obtained by hydrodistillation using a Clevenger-type apparatus and characterized qualitatively and quantitatively by gas chromatography coupled to mass spectrometry (GC-MS) and gas chromatography with flame ionization detection (GC-FID), respectively. The cytotoxic activity of EO was examined against five cancer cell lines (HepG2, HCT116, MCF-7, HL-60 and B16-F10) and one non-cancerous one (MRC-5) using the Alamar blue assay. Cell cycle distribution and cell death were investigated using flow cytometry in HepG2 cells treated with EO after 24, 48 and 72 h of incubation. The cells were also stained with May-Grunwald-Giemsa to analyze the morphological changes. The anti-liver-cancer activity of EO in vivo was evaluated in C.B-17 severe combined immunodeficient (SCID) mice with HepG2 cell xenografts. The main representative substances of this EO sample were muskatone (11.6%), cyclocolorenone (10.3%), α-pinene (8.26%), pogostol (6.36%), α-copaene (4.83%) and caryophyllene oxide (4.82%). EO showed IC50 values for cancer cell lines ranging from 28.5 µg/mL for HepG2 to >50 µg/mL for HCT116, and an IC50 value for non-cancerous of 46.0 µg/mL (MRC-5), showing selectivity indices below 2-fold for all cancer cells tested. HepG2 cells treated with EO showed cell cycle arrest at G2/M along with internucleosomal DNA fragmentation. The morphological alterations included cell shrinkage and chromatin condensation. Treatment with EO also increased the percentage of apoptotic-like cells. The in vivo tumor mass inhibition rates of EO were 46.5-50.0%. The results obtained indicate the anti-liver-cancer potential of C. articulatus rhizome EO.

Combination Therapy of Curcumin and Disulfiram Synergistically Inhibits the Growth of B16-F10 Melanoma Cells by Inducing Oxidative Stress.

Oxidative stress plays a central role in the pathophysiology of melanoma. Curcumin (CUR) is a polyphenolic phytochemical that stimulates reactive oxygen species (ROS) production, while disulfiram (DSS) is a US FDA-approved drug for the treatment of alcoholism that can act by inhibiting the intracellular antioxidant system. Therefore, we hypothesized that they act synergistically against melanoma cells. Herein, we aimed to study the antitumor potential of the combination of CUR with DSS in B16-F10 melanoma cells using in vitro and in vivo models. The cytotoxic effects of different combination ratios of CUR and DSS were evaluated using the Alamar Blue method, allowing the production of isobolograms. Apoptosis detection, DNA fragmentation, cell cycle distribution, and mitochondrial superoxide levels were quantified by flow cytometry. Tumor development in vivo was evaluated using C57BL/6 mice bearing B16-F10 cells. The combinations ratios of 1:2, 1:3, and 2:3 showed synergic effects. B16-F10 cells treated with these combinations showed improved apoptotic cell death and DNA fragmentation. Enhanced mitochondrial superoxide levels were observed at combination ratios of 1:2 and 1:3, indicating increased oxidative stress. In vivo tumor growth inhibition for CUR (20 mg/kg), DSS (60 mg/kg), and their combination were 17.0%, 19.8%, and 28.8%, respectively. This study provided data on the potential cytotoxic activity of the combination of CUR with DSS and may provide a useful tool for the development of a therapeutic combination against melanoma.

Cytochrome c Oxidase at Full Thrust: Regulation and Biological Consequences to Flying Insects.

Flight dispersal represents a key aspect of the evolutionary and ecological success of insects, allowing escape from predators, mating, and colonization of new niches. The huge energy demand posed by flight activity is essentially met by oxidative phosphorylation (OXPHOS) in flight muscle mitochondria. In insects, mitochondrial ATP supply and oxidant production are regulated by several factors, including the energy demand exerted by changes in adenylate balance. Indeed, adenylate directly regulates OXPHOS by targeting both chemiosmotic ATP production and the activities of specific mitochondrial enzymes. In several organisms, cytochrome c oxidase (COX) is regulated at transcriptional, post-translational, and allosteric levels, impacting mitochondrial energy metabolism, and redox balance. This review will present the concepts on how COX function contributes to flying insect biology, focusing on the existing examples in the literature where its structure and activity are regulated not only by physiological and environmental factors but also how changes in its activity impacts insect biology. We also performed in silico sequence analyses and determined the structure models of three COX subunits (IV, VIa, and VIc) from different insect species to compare with mammalian orthologs. We observed that the sequences and structure models of COXIV, COXVIa, and COXVIc were quite similar to their mammalian counterparts. Remarkably, specific substitutions to phosphomimetic amino acids at critical phosphorylation sites emerge as hallmarks on insect COX sequences, suggesting a new regulatory mechanism of COX activity. Therefore, by providing a physiological and bioenergetic framework of COX regulation in such metabolically extreme models, we hope to expand the knowledge of this critical enzyme complex and the potential consequences for insect dispersal.

Cardiac effect induced by Crotalus durissus cascavella venom: Morphofunctional evidence and mechanism of action.

Envenoming, resulting from snake bites, is a global public health problem. The present study was undertaken to investigate the influence of Crotalus durissus cascavella (Cdcas) venom on cardiac activity and the mechanisms of action underlying its effect. To investigate the inotropic and chronotropic effects induced by Cdcas, studies were performed on the left and right atria. A series of tests were conducted to investigate whether the negative inotropic effect, induced by Cdcas, was related to cardiac damage. Cdcas venom (0.1-30 µg/mL) elicited a significant negative inotropic effect. The addition of Cdcas crude venom (7.5, 15 and 30 µg/mL) did not induce significant alterations in cell proliferation, nor in the enzymatic activity of total-CK and CKMB. Ultrastructural evaluation demonstrated that cardiac cells from isoproterenol and Cdcas groups revealed discreet swelling and displaced intermyofibrillar mitochondria with disorganization of the cristae. No change was observed in cardiac electrical activity in perfused isolated rat hearts with Cdcas. In addition, Cdcas reduced contractility in isolated cardiomyocytes from the rat left ventricle. The negative inotropic effect of Cdcas was reduced by l-NAME (100 µM), PTIO (100 µM), ODQ (10 µM) and KT5823 (1 µM), suggesting the participation of NO/cGMP/PKG pathway due to Cdcas. In non-anesthetized rats, Cdcas induced hypotension followed by bradycardia, the latter was also observed by ECG (anesthetized animals). Our results suggest that the negative inotropic effect induced by Cdcas venom is unrelated to cardiac toxicity, at least, at the concentrations tested; and occurs through of NO/cGMP/PKG pathway, likely leading to hypotension and bradycardia when administered in vivo.

"Chagas Express XXI": A new ArtScience social technology for health and science education-A case study in Brazilian endemic areas of Chagas disease with an active search of chronic cases.

BACKGROUND: Chagas Disease (CD) affects 6-7 million people worldwide and is related to poverty-promoting conditions. Chronic asymptomatic cases are mostly invisible to health systems. Aiming (1) to translate CD discoveries into education/information practices to raise alertness and empowerment of affected people; and (2) to perform an active search of CD cases, articulating intersectoral actions to improve the access of infected people to the local health service for the treatment of CD; our research group developed and tested under field conditions as innovative social technology: an itinerant education interdisciplinary setting named "Chagas Express XXI" (CE21). METHODOLOGY: CE21 was created as an "imaginary train" with ~40 ArtScience workshops, games, laboratory activities and conversation circles. An entry/exit plus six activity modules combined associations of affected people, microscopic observations, One Health education, and wellness activities. CE21 was conceived as a social technology, since all the processes were co-created with CD patients and inter-sector local partners. Descriptive statistics showed quantitative data collected throughout the expeditions (CD knowledge, serological results). Qualitative data accessed the public perceptions about the education activities. PRINCIPAL FINDINGS: CE21 was exhibited in local educational institutions (schools, universities) in four cities, engaging 2,117 people that evaluated the 41 activities carried out. Citizens and health professionals enjoyed acquisition of information related to blood, parasites, vectors, reservoirs, environmental changes, and social determinants of CD. Further, local legacies of 600 participants volunteer for health promotion groups and CD associations, local empowerment groups to fight for better health conditions, and 05 mural paintings. We observed that 81% of the participants ignored the possibility of treating CD while 52% of the participants requested a blood test for CD showing seropositivity in 20% of them. CONCLUSIONS: CE21 is a social technology potentially useful for health and science education and active search of asymptomatic CD chronic cases. Moreover, this technology may be adapted to understand and to cooperate in other potentially epidemic situations, especially NTDs related.

Essential oil from leaves of Conobea scoparioides (Cham. & Schltdl.) Benth. (Plantaginaceae) causes cell death in HepG2 cells and inhibits tumor development in a xenograft model.

Conobea scoparioides (Cham. & Schltdl.) Benth. (syn. Sphaerotheca scoparioides Cham. & Schldtl.) (Plantaginaceae), popularly known as "pataqueira", "vassourinha-do-brejo" and/or "hierba-de-sapo", is a popular medicinal plant used to treat leishmaniasis, pain and beriberi. In addition, inhibition of cell adhesion, antioxidant, cytotoxic and leishmanicidal activities of compounds or fractions of C. scoparioides have been reported. In the present work, chemical constituents and in vitro and in vivo anti-liver cancer potential of essential oil (EO) from leaves of C. scoparioides were investigated using human hepatocellular carcinoma HepG2 cells as a cell model. EO was obtained by hydrodistillation using a Clevenger-type apparatus and characterized by GC-MS and GC-FID. The in vitro cytotoxic effect was evaluated on three human cancer cell lines (MCF-7, HepG2 and HCT116) and one human non-cancerous cell line (MRC-5) using the Alamar blue assay. Phosphatidylserine externalization and cell cycle distribution were quantified in HepG2 cells by flow cytometry after 48 h incubation. The effectiveness of EO in anti-liver cancer model was studied with HepG2 cells grafted on C.B. 17 SCID mice. The main constituents of EO were thymol methyl ether (62 %), thymol (16 %) and α-phellandrene (14 %). EO displayed an in vitro cytotoxic effect against all human cancer cell lines and caused externalization of phosphatidylserine and DNA fragmentation in HepG2 cells, suggesting induction of apoptotic-like cell death. In vivo tumor mass inhibition of 36.7 and 55.8 % was observed for treatment with EO at doses of 40 and 80 mg/kg, respectively. These results indicate in vitro and in vivo anti-liver cancer potential of EO from leaves of C. scoparioides.

Transmission electron microscopy revealing the mechanism of action of photodynamic therapy on Trichomonas vaginalis.

Trichomonas vaginalis is an amitochondrial parasite that causes human trichomoniasis. Despite metronidazole effectiveness, resistant cases are becoming more frequent. This scenario reveals the need to develop new therapeutic options. Photodynamic Therapy (PDT) is an experimental treatment that involves the activation of photosensitive substances and the generation of cytotoxic oxygen species and free radicals to promote the selective destruction of target tissues. In previous work, we identified an excellent in vitro PDT activity using methylene blue and light emitting diode against metronidazole sensitive and resistant strains of T. vaginalis. Here, we evaluated the efficacy of PDT in vivo and its high trichomonicidal activity was assessed through transmission electron microscopy. Female Balb/c mice were infected intravaginally with T. vaginalis trophozoites. On the third day of infection, methylene blue was introduced into the vaginal canal, which then received 68.1 J/cm2 of radiation for 35.6 s. Twenty-four hours after treatment the vaginal canal of the animals was scraped and the samples processed by the immunocytochemistry technique. Besides that, in vitro photodynamic treatment was performed and T. vaginalis trophozoites were processed by transmission electron microscopy. PDT significantly reduced infection in animals treated, compared to control groups, being as efficient as metronidazole. Morphological changes observed have suggested that PDT activity on T. vaginalis was due to necrosis. These results, added to the high trichomonicidal activity of PDT confirm its feasibility for trichomoniasis treatment.

Rattus norvegicus as a model for persistent renal colonization by pathogenic Leptospira interrogans.

Leptospirosis continues to be a disease with a poorly understood pathogenesis. The experimental rat model is amenable for the investigation of leptospiral dissemination, tropism, persistence of renal colonization and factors related to disease resistance. In this study, Wistar rats were infected intraperitoneally with virulent Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130. The detection of leptospires in tissue samples was based on culture, silver staining and immunofluorescence techniques. An inoculum of 10,000 leptospires induced colonization in 50% of rats and colonization persisted for the 4-month period of the study. Dissemination kinetics revealed that renal colonization took place 7-9 days after infection, with no underlying histopathology. The peak leptospiral load occurred on day 5 post-infection, followed by rapid clearance in all tissues except the kidneys, where dense leptospiral aggregates persisted in the renal tubules. We conclude that the experimental rat model is suitable for studies contributing towards the understanding of the mechanisms of colonization and resistance to severe disease in leptospirosis.

High- and low-frequency transcutaneous electrical nerve stimulation delay sciatic nerve regeneration after crush lesion in the mouse.

The stimulation of peripheral nerve regeneration has been studied in different ways, including the use of electrical fields. The capacity of this modality to enhance nerve regeneration is influenced by the parameters used, including current type, frequency, intensity, and means of administration. Transcutaneous electrical nerve stimulation (TENS) is a frequently used form of administering electrical current to the body, but its effects on peripheral nerve regeneration are not known. This study assessed the influence of TENS on sciatic nerve regeneration, using a model of crush lesion in the mouse. Mice were stimulated 30 min a day, 5 days a week, for 5 weeks with both high- (100 Hz) and low- (4 Hz) frequency TENS. Control animals had the sciatic nerve crushed but were not stimulated. Assessment was performed weekly by functional analysis using the Static Sciatic Index for the mouse and at the end of the experiment by light and electron microscopy. The results showed that although there were no differences between the groups regarding the Static Sciatic Index values, TENS led to nerves with morphological signs of impaired regeneration. At light microscopy level, TENS nerves presented more axons with dark axoplasm, signs of edema, and a less organized cytoarchitecture. Electronmicrographs showed fewer and thinner thick myelinated fibers and increased number of Schwann cell nuclei. Myelinated axon diameters and density and diameter of nonmyelinated fibers were not affected by TENS, leading to the conclusion that this regimen of electrical stimulation leads to a delayed regeneration after a crush lesion of the sciatic nerve in the mouse. All these effects were more pronounced on high-frequency TENS nerves.

Extracellular lipid droplets promote hemozoin crystallization in the gut of the blood fluke Schistosoma mansoni.

Hemozoin (Hz) is a heme crystal produced upon hemoglobin digestion as the main mechanism of heme disposal in several hematophagous organisms. Here, we show that, in the helminth Schistosoma mansoni, Hz formation occurs in extracellular lipid droplets (LDs). Transmission electron microscopy of adult worms revealed the presence of numerous electron-lucent round structures similar to LDs in gut lumen, where multicrystalline Hz assemblies were found associated to their surfaces. Female regurgitates promoted Hz formation in vitro in reactions partially inhibited by boiling. Fractionation of regurgitates showed that Hz crystallization activity was essentially concentrated on lower density fractions, which have small amounts of pre-formed Hz crystals, suggesting that hydrophilic-hydrophobic interfaces, and not Hz itself, play a key catalytic role in Hz formation in S. mansoni. Thus, these data demonstrate that LDs present in the gut lumen of S. mansoni support Hz formation possibly by allowing association of heme to the lipid-water interface of these structures.

Role of Polyamines in Parasite Cell Architecture and Function.

In the absence of accessible, effective vaccines, the fight against parasitic disease relies mostly on chemotherapy. Nevertheless, the considerable side effects, high costs and growing number of refractory cases comprise substantial drawbacks. Thus, the search for new antiparasitic compounds remains a high priority. The polyamine biosynthesis, conversion and transport pathways offer different targets for selective chemotherapy. Polyamine analogues and other antagonists may provide tools in the search for new lead compounds. Light and electron microscopy techniques may encompass valuable approaches to elucidate the possible mechanisms of action of different antiparasitic compounds, allowing the identification of subcellular target compartments, presumably establishing the basis for a more rational drug design and/or planning of therapeutic strategies.

Modulation of Human Immune Response by Fungal Biocontrol Agents.

Although the vast majority of biological control agents is generally regarded as safe for humans and environment, the increased exposure of agriculture workers, and consumer population to fungal substances may affect the immune system. Those compounds may be associated with both intense stimulation, resulting in IgE-mediated allergy and immune downmodulation induced by molecules such as cyclosporin A and mycotoxins. This review discusses the potential effects of biocontrol fungal components on human immune responses, possibly associated to infectious, inflammatory diseases, and defective defenses.

Antifungal mechanism of [RuIII(NH3)4catechol]+ complex on fluconazole-resistant Candida tropicalis.

Candidiasis, a major opportunistic mycosis caused by Candida sp., may comprise life-threatening systemic infections. The incidence of non-albicans species is rising, particularly in South America and they are frequently drug resistant, causing unresponsive cases. Thus, novel antimycotic agents are required. Here we tested the antifungal activity of [RuIII(NH3)4catechol]+ complex (RuCat), approaching possible action mechanisms on fluconazole-resistant Candida tropicalis. RuCat significantly (P < 0.05) inhibited the growth and viability of C. tropicalis dose-dependently (IC50 20.3 µM). Cytotoxicity of RuCat upon murine splenocytes was lower (Selectivity Index = 16). Scanning electron microscopy analysis showed pseudohyphae formation, yeast aggregation and surface damage. RuCat-treated samples investigated by transmission electron microscopy showed melanin granule trafficking to cell surfaces and extracellular milieu. Surface-adherent membrane fragments and extracellular debris were also observed. RuCat treatment produced intense H2DCFDA labeling, indicating reactive oxygen species (ROS) production which caused increased lipoperoxidation. ROS are involved in the fungicidal effect as N-acetyl-L-cysteine completely restored cell viability. Calcofluor White chitin staining suggests that 70 or 140 µM RuCat treatment for 2 h affected cell-wall structure. PI labeling indicated necrotic cell death. The present data indicate that RuCat triggers ROS production, lipoperoxidation and cell surface damage, culminating in selective necrotic death of drug-resistant C. tropicalis.

Physalin F, a seco-steroid from Physalis angulata L., has immunosuppressive activity in peripheral blood mononuclear cells from patients with HTLV1-associated myelopathy.

Human T-lymphotropic virus type 1 (HTLV-1) induces a strong activation of the immune system, especially in individuals with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Physalin F is a secosteroid with potent anti-inflammatory and immunomodulatory activities. The present study aimed to investigate the effects of physalin F on peripheral blood mononuclear cells (PBMC) of HAM/TSP subjects. A concentration-dependent inhibition of spontaneous proliferation of PBMC from HAM/TSP subjects was observed in the presence of physalin F, as evaluated by (3)H-thymidine uptake. The IC50 for physalin F was 0.97 ± 0.11 µM. Flow cytometry analysis using Cytometric Bead Array (CBA) showed that physalin F (10 µM) significantly reduced the levels of IL-2, IL-6, IL-10, TNF-α and IFN-γ, but not IL-17A, in supernatants of PBMC cultures. Next, apoptosis induction was addressed by using flow cytometry to evaluate annexin V expression. Treatment with physalin F (10 µM) increased the apoptotic population of PBMC in HAM/TSP subjects. Transmission electron microscopy analysis of PBMC showed that physalin F induced ultrastructural changes, such as pyknotic nuclei, damaged mitochondria, enhanced autophagic vacuole formation, and the presence of myelin-like figures. In conclusion, physalin F induces apoptosis of PBMC, decreasing the spontaneous proliferation and cytokine production caused by HTLV-1 infection.

Cytochemical techniques and energy-filtering transmission electron microscopy applied to the study of parasitic protozoa.

The study of parasitic protozoa plays a major role in cell biology, biochemistry and molecular biology. Numerous cytochemical techniques have been developed in order to unequivocally identify the nature of subcellular compartments. Enzyme and immuno-cytochemistry allow the detection of, respectively, enzymatic activity products and antigens in particular sites within the cell. Energy-filtering transmission electron microscopy permits the detection of specific elements within such compartments. These approaches are particularly useful for studies employing antimicrobial agents where cellular compartments may be destroyed or remarkably altered and thus hardly identified by standard methods of observation. In this regard cytochemical and spectroscopic techniques provide valuable data allowing the determination of the mechanisms of action of such compounds.

Complete amino acid sequence and location of Omp-28, an important immunogenic protein from Salmonella enterica serovar typhi.

Omp-28 isolated from Salmonella enterica serovar typhi presented a subunit molecular mass of 9,632 Da by MALDI-TOF MS. It was denatured, S-alkylated, and 1) directly submitted to Edman sequencing, 2) cleaved with CNBr, and 3) hydrolyzed either with endoproteinase Glu-C or Asp-N. The major CNBr peptide containing the C-terminal portion of Omp-28 was isolated by tricine-SDS-PAGE and electroblotted whereas Omp-28 enzymatic peptides were isolated by C18-RP-HPLC. All peptides were sequenced. This approach allowed the elucidation of the complete primary structure of Omp-28. Its amino acid sequence is identical to that deduced from part of the DNA of the "putative periplasmic transport protein" of either S. enterica serovar typhimurium and a multiple drug resistant S. enterica serovar typhi. Omp-28 homologous protein sequences were also deduced from Escherichia coli and Yersinia pestis genomic DNA. All proteins had their secondary structures predicted. Immunogold cytochemistry indicated that Omp-28 is found on the bacterium outer membrane.

Modes of action of arjunolic acid and derivatives on Trypanosoma cruzi cells.

Chagas disease causes considerable morbimortality in the Americas, with circa 7 to 8 million infected people, causing at least 12,000 annual deaths and 100 million people at risk. Its chemotherapy is poorly selective and effective, associated to severe side effects and unresponsive cases. Thus, R&D on therapeutic alternatives is undoubtedly required. The Brazilian poorly studied biodiversity offers uncountable bioagents, which may be exploited for chemotherapy. The triterpene arjunolic acid (AA), reduced the Trypanosoma cruzi epimastigote in vitro proliferation with an apparent IC50 of 171 µM. Electron microscopy analysis revealed remarkable effects on the parasite surface and architecture. AA-treated parasites displayed minutely corrugated plasma membranes devoid of subpellicular microtubules as well as biogenesis of multiple basal bodies. As the AA effects appeared mainly restricted or originated at the parasite peripheral cytoplasm, including the cytoskeleton membrane linkage, we inferred that the compound targeted primarily the lipid bilayer; therefore, we performed synthetic modification to increase the molecule lipophilicity and thus membrane permeability. The methyl ester (MeAA) and tri-acetylated derivatives (3AcAA) had potentiated trypanocidal activity, producing IC50 values of 21.9 and 15.8 µM, respectively. Both derivatives were able to produce remarkable ultrastructural alterations in the parasites, including inner compartments such as Golgi apparatus and the endocytic/autophagic pathway. Parasites cultured with both derivatives displayed numerous and large autophagic vacuoles, altered flagellar length and cell body connection. These data indicate that synthetically-modified natural products comprise valuable tools in antiparasitic chemotherapy and that electron microscopy may be useful not only in determining the mechanisms of action but also in directing such modifications for rational drug design.

Effects of metronidazole analogues on Giardia lamblia: experimental infection and cell organization.

The chemotherapeutic agents used for the treatment of giardiasis are often associated with adverse side effects and are refractory cases, due to the development of resistant parasites. Therefore the search for new drugs is required. We have previously reported the giardicidal effects of metronidazole (MTZ) and its analogues (MTZ-Ms, MTZ-Br, MTZ-N(3), and MTZ-I) on the trophozoites of Giardia lamblia. Now we evaluated the activity of some giardicidal MTZ analogues in experimental infections in gerbils and its effects on the morphology and ultrastructural organization of Giardia. The giardicidal activity in experimental infections showed ED(50) values significantly lower for MTZ-I and MTZ-Br when compared to MTZ. Transmission electron microscopy was employed to approach the mechanism(s) of action of MTZ analogues upon the protozoan. MTZ analogues were more active than MTZ in changing significantly the morphology and ultrastructure of the parasite. The analogues affected parasite cell vesicle trafficking, autophagy, and triggered differentiation into cysts. These results coupled with the excellent giardicidal activity and lower toxicity demonstrate that these nitroimidazole derivates may be important therapeutic alternatives for combating giardiasis. In addition, our results suggest a therapeutic advantage in obtaining synthetic metronidazole analogues for screening of activities against other infectious agents.

Parasites or cohabitants: cruel omnipresent usurpers or creative "éminences grises"?

This paper presents many types of interplays between parasites and the host, showing the history of parasites, the effects of parasites on the outcome of wars, invasions, migrations, and on the development of numerous regions of the globe, and the impact of parasitic diseases on the society and on the course of human evolution. It also emphasizes the pressing need to change the look at the parasitism phenomenon, proposing that the term "cohabitant" is more accurate than parasite, because every living being, from bacteria to mammals, is a consortium of living beings in the pangenome. Even the term parasitology should be replaced by cohabitology because there is no parasite alone and host alone: both together compose a new adaptive system: the parasitized-host or the cohabitant-cohabited being. It also suggests switching the old paradigm based on attrition and destruction, to a new one founded on adaptation and living together.