Amoebic gill disease increases energy requirements and decreases hypoxia tolerance in Atlantic salmon (Salmo salar) smolts.

Globally, Atlantic salmon (Salmo salar Linnaeus) aquaculture is now routinely affected by amoebic gill disease (AGD; Neoparamoeba perurans). The disease proliferates throughout the summer and is implicated in decreasing tolerance of salmon to environmental perturbations, yet little empirical evidence exists to support these observations. Using salmon acclimated to 15 or 19 °C, our aim was to determine the effects of clinically light-moderate (industry-relevant) AGD on metabolism (MO2rest and MO2max), aerobic scope (MO2max - MO2rest), excess post-exercise oxygen consumption (EPOC), and hypoxia tolerance. An increase in MO2rest (~8% and ~ 13% increase within the 15 and 19 °C acclimation groups, respectively) with increasing disease signs demonstrated an increase in baseline energy requirements as the disease progressed. Conversely, MO2max remained stable at both temperatures (~364 mg O2 kg-1 h-1), resulting in a decline in aerobic scope by 13 and 19% in the 15 and 19 °C groups, respectively. There was evidence of a decrease in hypoxia tolerance as the dissolved oxygen concentrations at loss of equilibrium increased by ~8% with more severe lesion coverage of the gills. These results suggest an increase in basal energy requirements and reduction in hypoxia tolerance as AGD proliferates, lending support to the idea that AGD reduces environmental tolerance. However, the lack of an effect of acclimation temperature indicates that the temperature-disease interaction may be more complicated than currently thought.

Potential Biomarkers in Diagnosis of Renal Acanthamoebiasis.

Recent studies indicate that Acanthamoeba spp. may play a significant role in kidney dysfunction. The aim of the study was to examine the levels of kidney injury molecule 1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and monocyte chemotactic protein 1 (MCP-1), as well as an activity of matrix metalloproteinases 2 and 9 (MMP-2 and MMP-9, respectively) in the kidneys of immunocompetent and immunosuppressed mice infected with Acanthamoeba spp. The levels of KIM-1, NGAL, and MCP-1 were analyzed by enzyme-linked immunosorbent assay (ELISA), and the activity of MMPs was determined by gelatin zymography. The elevated KIM-1 level was found in the kidneys of immunocompetent mice at the beginning of Acanthamoeba spp. infection. In the immunosuppressed mice, the KIM-1 level was statistically different. The statistically decreased NGAL level was found in the kidneys of immunocompetent mice compared to the uninfected mice. In the immunocompromised mice, we found statistically significant differences in MCP-1 levels between the uninfected and infected groups. There was an increase in the expression of both MMP-2 and MMP-9 in the kidneys of immunocompetent and immunosuppressed mice infected with Acanthamoeba spp. compared to the uninfected mice. The results indicate that KIM-1, NGAL, MCP-1, MMP-2, MMP-9, and MMP-9/NGAL might be promising biomarkers of renal acanthamoebiasis.

The modulatory effect of Artemisia annua L. on toll-like receptor expression in Acanthamoeba infected mouse lungs.

The genus Acanthamoeba, which may cause different infections in humans, occurs widely in the environment. Lung inflammation caused by these parasites induces pulmonary pathological changes such as pulmonary necrosis, peribronchial plasma cell infiltration, moderate desquamation of alveolar cells and partial destruction of bronchial epithelial cells, and presence of numerous trophozoites and cysts among inflammatory cells. The aim of this study was to assess the influence of plant extracts from Artemisia annua L. on expression of the toll-like receptors TLR2 and TLR4 in lungs of mice with acanthamoebiasis. A. annua, which belongs to the family Asteraceae, is an annual plant that grows wild in Asia. In this study, statistically significant changes of expression of TLR2 and TLR4 were demonstrated. In the lungs of infected mice after application of extract from A. annua the expression of TLRs was observed mainly in bronchial epithelial cells, pneumocytes (to a lesser extent during the outbreak of infection), and in the course of high general TLR expression. TLR4 in particular was also visible in stromal cells of lung parenchyma. In conclusion, we confirmed that a plant extract of A. annua has a modulatory effect on components of the immune system such as TLR2 and TLR4.

Escherichia coli mediated resistance of Entamoeba histolytica to oxidative stress is triggered by oxaloacetate.

Amebiasis, a global intestinal parasitic disease, is due to Entamoeba histolytica. This parasite, which feeds on bacteria in the large intestine of its human host, can trigger a strong inflammatory response upon invasion of the colonic mucosa. Whereas information about the mechanisms which are used by the parasite to cope with oxidative and nitrosative stresses during infection is available, knowledge about the contribution of bacteria to these mechanisms is lacking. In a recent study, we demonstrated that enteropathogenic Escherichia coli O55 protects E. histolytica against oxidative stress. Resin-assisted capture (RAC) of oxidized (OX) proteins coupled to mass spectrometry (OX-RAC) was used to investigate the oxidation status of cysteine residues in proteins present in E. histolytica trophozoites incubated with live or heat-killed E. coli O55 and then exposed to H2O2-mediated oxidative stress. We found that the redox proteome of E. histolytica exposed to heat-killed E. coli O55 is enriched with proteins involved in redox homeostasis, lipid metabolism, small molecule metabolism, carbohydrate derivative metabolism, and organonitrogen compound biosynthesis. In contrast, we found that proteins associated with redox homeostasis were the only OX-proteins that were enriched in E. histolytica trophozoites which were incubated with live E. coli O55. These data indicate that E. coli has a profound impact on the redox proteome of E. histolytica. Unexpectedly, some E. coli proteins were also co-identified with E. histolytica proteins by OX-RAC. We demonstrated that one of these proteins, E. coli malate dehydrogenase (EcMDH) and its product, oxaloacetate, are key elements of E. coli-mediated resistance of E. histolytica to oxidative stress and that oxaloacetate helps the parasite survive in the large intestine. We also provide evidence that the protective effect of oxaloacetate against oxidative stress extends to Caenorhabditis elegans.

Relationship between antioxidant defense in Acanthamoeba spp. infected lungs and host immunological status.

The role of oxidative stress in the pathogenicity of acanthamoebiasis is an important aspect of the intricate and complex host-parasite relationship. The aim of this experimental study was to determine oxidative stress through the assessment of lipid peroxidation product (LPO) levels and antioxidant defense mechanism in Acanthamoeba spp. lung infections in immunocompetent and immunosuppressed hosts. In Acanthamoeba spp. infected immunocompetent mice we noted a significant increase in lung lipid peroxidation products (LPO) at 8 days and 16 days post infection (dpi). There was a significant upregulation in lung LPO in immunocompetent and immunosuppressed mice infected by Acanthamoeba spp. at 16 dpi. The superoxide dismutase activity decreased significantly in lungs in immunosuppressed mice at 8 dpi. The catalase activity was significantly upregulated in lungs in immunocompetent vs. immunosuppressed group and in immunocompetent vs. control mice at 16 dpi. The glutathione reductase activity was significantly lower in immunosuppressed group vs. immunosuppressed control at 24 dpi. We found significant glutathione peroxidase downregulation in immunocompetent and immunosuppressed groups vs. controls at 8 dpi, and in immunosuppressed vs. immunosuppressed control at 16 dpi. The consequence of the inflammatory response in immunocompetent and immunosuppressed hosts in the course of experimental Acanthamoeba spp. infection was the reduction of the antioxidant capacity of the lungs resulting from changes in the activity of antioxidant enzymes. Therefore, the imbalance between oxidant and antioxidant processes may play a major role in pathology associated with Acanthamoeba pneumonia.

Influence of Artemisia annua L. on toll-like receptor expression in brain of mice infected with Acanthamoeba sp.

The treatment of acanthamoebiasis is a still a problem. Our previous studies showed that the application of extracts from Artemisia annua L. significantly prolonged the survival of mice infected by Acanthamoeba. This plant has medicinal properties in the treatment of human parasitic diseases. The aim of this study was to evaluate the effects of A. annua on expression of Toll-like receptors (TLRs) 2 and 4 in brain of mice with Acanthamoeba infection. Mice were infected with Acanthamoeba sp. strain Ac309 (KY203908) by intranasal inoculation without and after application of A. annua extract. The administration of extract from A. annua significantly reduced the level of expression of TLR2 and modified the level of expression of TLR4. A. annua extract is a natural substance that is well tolerated in animals and may be considered as a combination therapy in treatment of acanthamoebiasis. Our study suggested that A. annua extract may be used as an alternative therapeutic tool.

Centrofacial Balamuthiasis: case report of a rare cutaneous amebic infection.

Free-living amebae are ubiquitous in our environment, but rarely cause cutaneous infection. Balamuthia mandrillaris has a predilection for infecting skin of the central face. Infection may be restricted to the skin or associated with life-threatening central nervous system (CNS) involvement. We report a case of a 91-year-old woman, who presented with a non-healing red plaque over her right cheek. Several punch biopsies exhibited non-specific granulomatous inflammation without demonstrable fungi or mycobacteria in histochemical stains. She was treated empirically for granulomatous rosacea, but the lesion continued to progress. A larger incisional biopsy was performed in which amebae were observed in hematoxylin-eosin stained sections. These were retrospectively apparent in the prior punch biopsy specimens. Immunohistochemistry and polymerase chain reaction studies identified the organisms as Balamuthia mandrillaris. Cutaneous infection by B. mandrillaris is a rare condition that is sometimes complicated by life-threatening CNS involvement and which often evades timely diagnosis due to its rarity and nonspecific clinical manifestations. Moreover, these amebae are easily overlooked in histopathologic sections because of their small number and their resemblance to histiocytes. Dermatopathologists should be familiar with the histopathologic appearance of these organisms and include balamuthiasis and other amebic infections in the differential diagnosis of granulomatous dermatitis.

Acanthamoeba infection in lungs of mice expressed by toll-like receptors (TLR2 and TLR4).

Toll-like receptors (TLRs) play a key role in the innate immune responses to a variety of pathogens including parasites. TLRs are among the most highly conserved in the evolution of the receptor family, localized mainly on cells of the immune system and on other cells such as lung cells. The aim of this study was to determine for the first time the expression of TLR2 and TLR4 in the lung of Acanthamoeba spp. infected mice using quantitative real-time polymerase chain reaction (Q-PCR) and immunohistochemical (IHC) staining. The Acanthamoeba spp. were isolated from a patient with Acanthamoeba keratitis (AK) (strain Ac 55) and from environmental samples of water from Malta Lake (Poznan, Poland - strain Ac 43). We observed a significantly increased level of expression of TLR2 as well as TLR4 mRNA from 2 to 30 days post Acanthamoeba infection (dpi) in the lungs of mice infected with Ac55 (KP120880) and Ac43 (KP120879) strains. According to our observations, increased TLR2 and TLR4 expression in the pneumocytes, interstitial cells and epithelial cells of the bronchial tree may suggest an important role of these receptors in protective immunity against Acanthamoeba infection in the lung. Moreover, increased levels of TLR2 and TLR4 mRNA expression in infected Acanthamoeba mice may suggest the involvement of these TLRs in the recognition of this amoeba pathogen-associated molecular pattern (PAMP).

Artemether Exhibits Amoebicidal Activity against Acanthamoeba castellanii through Inhibition of the Serine Biosynthesis Pathway.

Acanthamoeba sp. parasites are the causative agents of Acanthamoeba keratitis, fatal granulomatous amoebic encephalitis, and cutaneous infections. However, there are currently no effective drugs for these organisms. Here, we evaluated the activity of the antimalarial agent artemether against Acanthamoeba castellanii trophozoites and identified potential targets of this agent through a proteomic approach. Artemether exhibited in vitro amoebicidal activity in a time- and dose-dependent manner and induced ultrastructural modification and cell apoptosis. The iTRAQ quantitative proteomic analysis identified 707 proteins that were differentially expressed after artemether treatment. We focused on phosphoglycerate dehydrogenase and phosphoserine aminotransferase in the serine biosynthesis pathway because of their importance to the growth and proliferation of protozoan and cancer cells. The expression of these proteins in Acanthamoeba was validated using quantitative real-time PCR and Western blotting after artemether treatment. The changes in the expression levels of phosphoserine aminotransferase were consistent with those of phosphoglycerate dehydrogenase. Therefore, the downregulation of phosphoserine aminotransferase may be due to the downregulation of phosphoglycerate dehydrogenase. Furthermore, exogenous serine might antagonize the activity of artemether against Acanthamoeba trophozoites. These results indicate that the serine biosynthesis pathway is important to amoeba survival and that targeting these enzymes would improve the treatment of Acanthamoeba infections. Artemether may be used as a phosphoglycerate dehydrogenase inhibitor to control or block Acanthamoeba infections.

Acanthamoeba protease activity promotes allergic airway inflammation via protease-activated receptor 2.

Acanthamoeba is a free-living amoeba commonly present in the environment and often found in human airway cavities. Acanthamoeba possesses strong proteases that can elicit allergic airway inflammation. To our knowledge, the aeroallergenicity of Acanthamoeba has not been reported. We repeatedly inoculated mice with Acanthamoeba trophozoites or excretory-secretory (ES) proteins intra-nasally and evaluated symptoms and airway immune responses. Acanthamoeba trophozoites or ES proteins elicited immune responses in mice that resembled allergic airway inflammation. ES proteins had strong protease activity and activated the expression of several chemokine genes (CCL11, CCL17, CCL22, TSLP, and IL-25) in mouse lung epithelial cells. The serine protease inhibitor phenyl-methane-sulfonyl fluoride (PMSF) inhibited ES protein activity. ES proteins also stimulated dendritic cells and enhanced the differentiation of naive T cells into IL-4-secreting T cells. After repeated inoculation of the protease-activated receptor 2 knockout mouse with ES proteins, airway inflammation and Th2 immune responses were markedly reduced, but not to basal levels. Furthermore, asthma patients had higher Acanthamoeba-specific IgE titers than healthy controls and we found Acanthamoeba specific antigen from house dust in typical living room. Our findings suggest that Acanthamoeba elicits allergic airway symptoms in mice via a protease allergen. In addition, it is possible that Acanthamoeba may be one of the triggers human airway allergic disease.

Metabolic effects of amoebic gill disease (AGD) and chloramine-T exposure in seawater-acclimated Atlantic salmon Salmo salar.

Our aim was to determine possible metabolic effects amoebic gill disease (AGD) on Atlantic salmon Salmo salar. Standard (R(S)) and routine (R(ROU)) metabolic rates were evaluated by continually measuring oxygen consumption in 2 independent tanks of fish (18.69 +/- 1.01 kg m(-3), mean +/- SE). Active metabolic rate (R(ACT)) and metabolic scope (R(ACT) - R(S)) were assessed using a chasing protocol and determined at 3 time periods: (1) pre-infection, (2) 3 d post-infection, and (3) 2 d post-treatment. On Day 3 of the study, the fish were infected with amoebae isolated from the gills of AGD-affected salmon (2300 cells l(-1)). No significant elevations in R(ACT) or metabolic scope were detected 3 d post-infection and 2 d post-treatment; however, significant elevations in R(S) and R(ROU) were detected 3 d post-infection and 2 d post-treatment. Assessment of R(ROU) data, especially for the light period, also indicated a rise in oxygen consumption rate over the course of the experiment. Treatment of AGD-affected Atlantic salmon with chloramine-T (CL-T) appeared to briefly mitigate the rise in R(S), as there was a 30% drop (though non-significant) in R(S) following treatment. Despite this, R(S) continued the upward trend 1 d following treatment. These results suggest that over the course of AGD development, R(S) in Atlantic salmon increases. Therefore, considering the physical conditions which constrain R(ACT), we expect that metabolic scope would become compromised in fish more heavily affected with AGD. Treatment with CL-T shows promise for mitigating the respiratory effects of AGD and potentially minimising the loss of metabolic scope.

Balamuthia mandrillaris interactions with human brain microvascular endothelial cells in vitro.

Balamuthia amoebic encephalitis (BAE) is a serious human disease almost always leading to death. An important step in BAE is amoebae invasion of the bloodstream, followed by their haematogenous spread. Balamuthia mandrillaris entry into the central nervous system most likely occurs at the blood-brain barrier sites. Using human brain microvascular endothelial cells (HBMECs), which constitute the blood-brain barrier, this study determined (i) the ability of B. mandrillaris to bind to HBMECs and (ii) the associated molecular mechanisms. Adhesion assays revealed that B. mandrillaris exhibited greater than 90 % binding to HBMECs in vitro. To determine whether recognition of carbohydrate moieties on the surface of the HBMECs plays a role in B. mandrillaris adherence to the target cells, adhesion assays were performed in the presence of the saccharides mannose, galactose, xylose, glucose and fucose. It was observed that adherence of B. mandrillaris was significantly reduced by galactose, whilst the other saccharides had no effect. Acetone fixation of amoebae, but not of HBMECs, abolished adhesion, suggesting that B. mandrillaris adhesin(s) bind to galactose-containing glycoproteins of HBMECs. B. mandrillaris also bound to microtitre wells coated with galactose-BSA. By affinity chromatography using a galactose-Sepharose column, a galactose-binding protein (GBP) was isolated from detergent extracts of unlabelled amoebae. The isolation of a GBP from cell-surface-biotin-labelled amoebae suggested its membrane association. One-dimensional SDS-PAGE confirmed the proteinaceous nature of the GBP and determined its molecular mass as approximately 100 kDa. This is the first report suggesting the role of a GBP in B. mandrillaris interactions with HBMECs.

Molecular cloning and expression analysis of tumour necrosis factor-alpha in amoebic gill disease (AGD)-affected Atlantic salmon (Salmo salar L.).

Tumour necrosis factor-alpha (TNF-alpha) is a key mediator of inflammation during amoebiasis of humans and mice. Atlantic salmon (Salmo salar L.) are also susceptible to infection by amoebae (Neoparamoeba spp.), inflicting a condition known as amoebic gill disease (AGD). Here, the role of TNF-alpha in AGD-pathogenesis was examined. Two Atlantic salmon TNF-alpha transcripts designated TNF-alpha1 and TNF-alpha2 together with their respective genes were cloned and sequenced. TNF-alpha1 is 1379 bp and consists of a 738 bp open reading frame (ORF) translating into a predicted protein of 246 amino acids. TNF-alpha2 is 1412 bp containing an ORF and translated protein the same lengths as TNF-alpha1. An anti-rainbow trout TNF-alpha polyclonal antibody that bound recombinant Atlantic salmon TNF-alpha1 and TNF-alpha2 was used to detect constitutive and inducible expression of TNF-alpha in various tissues. The anti-TNF-alpha antibody bound to a TNF-like protein approximately 60 kDa that was constitutively expressed in a number of tissues in healthy Atlantic salmon. However, this protein was not detected in lysates from mitogen-stimulated head kidney leucocytes, despite up-regulation of TNF-alpha mRNAs under the same conditions. During the early onset of AGD in Atlantic salmon, there were no demonstrable differences in the gill tissue expression of TNF-alpha1, TNF-alpha2 nor the interleukin-1 beta (IL-1beta), inducible nitric oxide synthase (iNOS) and interferon gamma (IFN-gamma) mRNAs compared to tissue from healthy fish. In Atlantic salmon with advanced AGD, IL-1beta but not TNF-alpha1 or TNF-alpha2 mRNAs was up-regulated and was lesion-restricted. Given that Neoparamoeba spp. modulated both TNF-alpha2 and IL-1beta in head kidney leucocytes in vitro, it appears that rather than being recalcitrant to Neoparamoeba spp.-mediated TNF-alpha expression, either the parasite can influence the cytokine response during infection, there is ineffective signalling for TNF-alpha expression, or there are too few cells at the site of infection with the capacity to produce TNF-alpha. These data support our previous observation that IL-1beta mRNA expression is up-regulated in AGD-affected tissue and that TNF-alpha is not intrinsic in AGD-pathogenesis.

Downregulation of selected cytokines in amebiasis.

A 220-kDa E. histolytica lectin is capable of downregulating some inflammatory cytokines (IL-5, IL-6, INF-gamma and TNF-alpha) and thus of inducing an overall anti-inflammatory Th-phenotype in leucocytes of selected, perhaps constitutionally predisposed, individuals irrespective of their HLA-DR3 profile (i.e., in this study patients long recovered from amebic abscess of the liver). This probably inhibited cytokine response pattern could increase the risk for developing amebic abscess of the liver in the course of invasive intestinal amebiasis.

Transcriptome profiling the gills of amoebic gill disease (AGD)-affected Atlantic salmon (Salmo salar L.): a role for tumor suppressor p53 in AGD pathogenesis?

Neoparamoeba spp. are amphizoic amoebae with the capacity to colonize the gills of some marine fish, causing AGD. Here, the gill tissue transcriptome response of Atlantic salmon (Salmo salar L.) to AGD is described. Tanks housing Atlantic salmon were inoculated with Neoparamoeba spp. and fish sampled at time points up to 8 days postinoculation (pi.). Gill tissues were taken from AGD-affected fish, and a DNA microarray was used to compare global gene expression against tissues from AGD-unaffected fish. A total of 206 genes, representing 190 unique transcripts, were reproducibly identified as up- or downregulated in response to Neoparamoeba spp. infection. Informative transcripts having GO biological process identifiers were grouped according to function. Although a number of genes were placed into each category, no distinct patterns were observed. One Atlantic salmon cDNA that was upregulated in infected gill relative to noninfected gill at 114 and 189 h pi. showed significant identity with the Xenopus, mouse, and human anterior gradient-2 (AG-2) homologs. Two Atlantic salmon AG-2 mRNA transcripts, designated asAG-2/1 and asAG-2/2, were cloned, sequenced, and shown to be predominantly expressed in the gill, intestine, and brain of a healthy fish. In AGD-affected fish, differential asAG-2 expression was confirmed in samples used for microarray analyses as well as in AGD-affected gill tissue taken from fish in an independent experiment. The asAG-2 upregulation was restricted to AGD lesions relative to unaffected tissue from the same gill arch, while p53 tumor suppressor protein mRNA was concurrently downregulated in AGD lesions. Differential expression of p53-regulated transcripts, proliferating cell nuclear antigen and growth arrest and DNA damage-inducible gene-45beta (GADD45beta) in AGD lesions, suggests a role for p53 in AGD pathogenesis. Thus AGD may represent a novel model for comparative analysis of p53 and p53-regulated pathways.

Comparative ionic flux and gill mucous cell histochemistry: effects of salinity and disease status in Atlantic salmon (Salmo salar L.).

Two experiments were conducted to assess the physiological effects of freshwater exposure and amoebic gill disease (AGD) in marine Atlantic salmon (Salmo salar L.). The first experiment monitored marine salmon during a 3 h freshwater exposure, the standard treatment for AGD in Tasmania. The second experiment described the gill mucous cell histochemistry for freshwater adapted and seawater acclimated fish (AGD affected and unaffected) for possible correlations to ionoregulation. When exposed to freshwater, marine Atlantic salmon experienced a minor ionoregulatory dysfunction represented by a net efflux of Cl(-) ions at 3 h. AGD affected fish experienced the net efflux of Cl(-) ions 1 h sooner, and had a significantly greater net efflux of total ammonia. Changes to gill mucous cell populations corresponded to differing salinity and the presence of AGD. In AGD affected fish, these populations significantly differed between lesion and non-lesion associated areas of the gill filament. Our results have shown changes in the ionoregulatory capacity of Atlantic salmon due to freshwater exposure and AGD. Gill mucous cell histochemistry indicates the potential importance of the mucous layer in ionoregulation and disease. In comparison to previous studies on rainbow trout, these results suggest that Atlantic salmon have a greater short-term ionoregulatory capacity.

Granulomatous amebic encephalitis: a review and report of a spontaneous case from Venezuela.

Granulomatous amebic encephalitis (GAE), or meningoencephalitis due to Acanthamoeba spp. and leptomyxid ameba are uncommon CNS infections that generally occur in immunocompromised hosts. We describe a case of GAE caused by Balamuthia mandrillaris previously designated as a leptomyxid ameba, in an apparently healthy 14-year-old Venezuelan boy. This case was characterized by sudden onset of seizures, focal neurologic signs and by a prolonged clinical course (from November 1992 to March 1993). Neuroimaging studies showed cerebral hypodense lesions in cerebral hemispheres, brain stem and cerebellum. Microscopically, we found a chronic granulomatous inflammatory reaction with necrotizing angiitis, large numbers of amebic trophozoites and few cysts in perivascular spaces and within necrotic CNS tissue. The amebas were identified as B. mandrillaris based on their immunofluorescence reactivity with the anti-B. mandrillaris serum. So far, 30 cases of GAE due to B. mandrillaris have been recognized in humans, two in AIDS patients. No visceral involvement by free-living amebas or any other significant abnormality was observed. This patient developed "spontaneous" GAE, but it remains possible that an undiagnosed abnormality in cell-mediated immunity or a deficient humoral immune response may explain the susceptibility of this patient to this opportunistic infection.

Role of prostaglandins and calcium in the effects of Entamoeba histolytica on colonic electrolyte transport.

We have previously shown that Entamoeba histolytica lysates contain the neurohormones serotonin, neurotensin, immunoreactive substance P, and probably acetylcholine, and that amebic lysates inhibit sodium and chloride absorption and stimulate chloride secretion in the rat descending colon as measured by the Ussing chamber-voltage clamp technique. We now demonstrate that these transport effects have both calcium-dependent and calcium-independent components. In addition, arachidonic acid metabolites of the cyclooxygenase pathway are probably involved in the Entamoeba histolytica-induced changes in colonic transport that are not dependent on Ca++ entry. Prostaglandin E2 (10(-5) M), indomethacin (10(-6) M), piroxicam (5 x 10(-5) M), and mepacrine (10(-4) M) partially inhibited the amebic lysate effect on active transport in the rat descending colon. In addition, verapamil (10(-4) M) partially inhibited the effect of amebic lysates. The effect of verapamil was additive with that of indomethacin, totally blocking the effect of amebic lysate on short-circuit current. However, amebic lysates do not contain prostaglandin E2 as measured by sensitive radioimmunoassay. Amebic lysates stimulated prostaglandin E2 release from rat colonic mucosal strips. Amebic lysate significantly increased colonic cyclic adenosine monophosphate content. Piroxicam inhibited the lysate-induced increase in colonic cyclic adenosine monophosphate content. These results indicate that although amebic lysate does not contain prostaglandin E2, it caused arachidonic acid metabolites to be produced by the cyclooxygenase pathway, and these are probably involved in the Entamoeba histolytica-induced changes in colonic transport. Neurohormones in Entamoeba histolytica may act directly on colonic tissue to stimulate intestinal secretion, probably via a Ca+(+)-dependent mechanism that is blockable by verapamil, or indirectly via stimulation of prostaglandin E2 generation and release from the rat colon via a cyclic adenosine monophosphate-dependent mechanism. These effects appear separate. The cyclic adenosine monophosphate-dependent secretion is the predominant mechanism in this model of colonic amebic diarrhea.