PubMed Health⌕ Search

Biomedical subjects

George Dimopoulos

Publications and source records attributed to George Dimopoulos.

At least 19 recordsLinked to original sources

Anopheles gambiae immune responses to Sephadex beads: involvement of anti-Plasmodium factors in regulating melanization.

We have performed a global genome expression analysis of mosquito responses to CM-25 Sephadex beads and identified 27 regulated immune genes, including several anti-Plasmodium factors and other components with likely roles in melanization. Silencing of two bead injection responsive genes, TEP1 and LRIM1, which encode proteins known to mediate Plasmodium killing, significantly compromised the ability to melanize the beads. In contrast, silencing of two Plasmodium protective c-type lectins, CTL4 and CTLMA2, did not affect bead melanization. This data suggest that the anti-Plasmodium factors have dual functions, as determinants of both Plasmodium killing and melanization of the parasite and other foreign bodies, while the Plasmodium protective factors are specifically utilized by the parasite for evasion of mosquito defense mechanisms.

Animals↗

Regulation of sexual development of Plasmodium by translational repression.

Translational repression of messenger RNAs (mRNAs) plays an important role in sexual differentiation and gametogenesis in multicellular eukaryotes. Translational repression and mRNA turnover were shown to influence stage-specific gene expression in the protozoan Plasmodium. The DDX6-class RNA helicase, DOZI (development of zygote inhibited), is found in a complex with mRNA species in cytoplasmic bodies of female, blood-stage gametocytes. These translationally repressed complexes are normally stored for translation after fertilization. Genetic disruption of pbdozi inhibits the formation of the ribonucleoprotein complexes, and instead, at least 370 transcripts are diverted to a degradation pathway.

Animals↗

Anopheles gambiae immune responses to human and rodent Plasmodium parasite species.

Transmission of malaria is dependent on the successful completion of the Plasmodium lifecycle in the Anopheles vector. Major obstacles are encountered in the midgut tissue, where most parasites are killed by the mosquito's immune system. In the present study, DNA microarray analyses have been used to compare Anopheles gambiae responses to invasion of the midgut epithelium by the ookinete stage of the human pathogen Plasmodium falciparum and the rodent experimental model pathogen P. berghei. Invasion by P. berghei had a more profound impact on the mosquito transcriptome, including a variety of functional gene classes, while P. falciparum elicited a broader immune response at the gene transcript level. Ingestion of human malaria-infected blood lacking invasive ookinetes also induced a variety of immune genes, including several anti-Plasmodium factors. Twelve selected genes were assessed for effect on infection with both parasite species and bacteria using RNAi gene silencing assays, and seven of these genes were found to influence mosquito resistance to both parasite species. An MD2-like receptor, AgMDL1, and an immunolectin, FBN39, showed specificity in regulating only resistance to P. falciparum, while the antimicrobial peptide gambicin and a novel putative short secreted peptide, IRSP5, were more specific for defense against the rodent parasite P. berghei. While all the genes that affected Plasmodium development also influenced mosquito resistance to bacterial infection, four of the antimicrobial genes had no effect on Plasmodium development. Our study shows that the impact of P. falciparum and P. berghei infection on A. gambiae biology at the gene transcript level is quite diverse, and the defense against the two Plasmodium species is mediated by antimicrobial factors with both universal and Plasmodium-species specific activities. Furthermore, our data indicate that the mosquito is capable of sensing infected blood constituents in the absence of invading ookinetes, thereby inducing anti-Plasmodium immune responses.

Animals↗

Blood warming during hemofiltration can improve hemodynamics and outcome in ovine septic shock.

BACKGROUND: This study was designed to evaluate the effects of blood warming during hemofiltration on global and regional hemodynamics, plasma lactate, and 24-h survival during septic shock. METHODS: Twenty anesthetized and mechanically ventilated sheep underwent induction of peritonitis and, 4 h later, were treated by hemofiltration with (n = 10) or without (n = 10) blood warming. RESULTS: In the group without blood warming, body temperature decreased after starting hemofiltration and remained below baseline. In the other animals, body temperature stabilized at baseline level during hemofiltration and increased to a maximum of 40.8 degrees C thereafter. The group without warming experienced a decrease in blood pressure (from 90 mmHg to 38 mmHg) and cardiac output (from 4.0 l/min to 2.3 l/min). Metabolic acidosis and the increase in lactate were less marked when temperature was maintained. None of the animals without warming but all of the animals with warming survived to 16 h. CONCLUSIONS: Differences in temperature during hemofiltration resulted in striking differences in hemodynamics, metabolic acidosis, and survival rate in this clinically relevant experimental model of septic shock.

Acidosis, Lactic↗

AgDscam, a hypervariable immunoglobulin domain-containing receptor of the Anopheles gambiae innate immune system.

Activation of the insect innate immune system is dependent on a limited number of pattern recognition receptors (PRRs) capable of interacting with pathogen-associated molecular pattern. Here we report a novel role of an alternatively spliced hypervariable immunoglobulin domain-encoding gene, Dscam, in generating a broad range of PRRs implicated in immune defense in the malaria vector Anopheles gambiae. The mosquito Down syndrome cell adhesion molecule gene, AgDscam, has a complex genome organization with 101 exons that can produce over 31,000 potential alternative splice forms with different combinations of adhesive domains and interaction specificities. AgDscam responds to infection by producing pathogen challenge-specific splice form repertoires. Transient silencing of AgDscam compromises the mosquito's resistance to infections with bacteria and the malaria parasite Plasmodium. AgDscam is mediating phagocytosis of bacteria with which it can associate and defend against in a splice form-specific manner. AgDscam is a hypervariable PRR of the A. gambiae innate immune system.

Alternative Splicing↗

Bayesian coclustering of Anopheles gene expression time series: study of immune defense response to multiple experimental challenges.

We present a method for Bayesian model-based hierarchical coclustering of gene expression data and use it to study the temporal transcription responses of an Anopheles gambiae cell line upon challenge with multiple microbial elicitors. The method fits statistical regression models to the gene expression time series for each experiment and performs coclustering on the genes by optimizing a joint probability model, characterizing gene coregulation between multiple experiments. We compute the model using a two-stage Expectation-Maximization-type algorithm, first fixing the cross-experiment covariance structure and using efficient Bayesian hierarchical clustering to obtain a locally optimal clustering of the gene expression profiles and then, conditional on that clustering, carrying out Bayesian inference on the cross-experiment covariance using Markov chain Monte Carlo simulation to obtain an expectation. For the problem of model choice, we use a cross-validatory approach to decide between individual experiment modeling and varying levels of coclustering. Our method successfully generates tightly coregulated clusters of genes that are implicated in related processes and therefore can be used for analysis of global transcript responses to various stimuli and prediction of gene functions.

Algorithms↗

Recombinant human erythropoietin therapy in critically ill patients: a dose-response study [ISRCTN48523317].

INTRODUCTION: The aim of this study was to assess the efficacy of two dosing schedules of recombinant human erythropoietin (rHuEPO) in increasing haematocrit (Hct) and haemoglobin (Hb) and reducing exposure to allogeneic red blood cell (RBC) transfusion in critically ill patients. METHOD: This was a prospective, randomized, multicentre trial. A total of 13 intensive care units participated, and a total of 148 patients who met eligibility criteria were enrolled. Patients were randomly assigned to receive intravenous iron saccharate alone (control group), intravenous iron saccharate and subcutaneous rHuEPO 40,000 units once per week (group A), or intravenous iron saccharate and subcutaneous rHuEPO 40,000 units three times per week (group B). rHuEPO was given for a minimum of 2 weeks or until discharge from the intensive care unit or death. The maximum duration of therapy was 3 weeks. RESULTS: The cumulative number of RBC units transfused, the average numbers of RBC units transfused per patient and per transfused patient, the average volume of RBCs transfused per day, and the percentage of transfused patients were significantly higher in the control group than in groups A and B. No significant difference was observed between group A and B. The mean increases in Hct and Hb from baseline to final measurement were significantly greater in group B than in the control group. The mean increase in Hct was significantly greater in group B than in group A. The mean increase in Hct in group A was significantly greater than that in control individuals, whereas the mean increase in Hb did not differ significantly between the control group and group A. CONCLUSION: Administration of rHuEPO to critically ill patients significantly reduced the need for RBC transfusion. The magnitude of the reduction did not differ between the two dosing schedules, although there was a dose response for Hct and Hb to rHuEPO in these patients.

Adult↗

Transcriptome analysis of Anopheles stephensi-Plasmodium berghei interactions.

Simultaneous microarray-based transcription analysis of 4987 Anopheles stephensi midgut and Plasmodium berghei infection stage specific cDNAs was done at seven successive time points: 6, 20 and 40h, and 4, 8, 14 and 20 days after ingestion of malaria infected blood. The study reveals the molecular components of several Anopheles processes relating to blood digestion, midgut expansion and response to Plasmodium-infected blood such as digestive enzymes, transporters, cytoskeletal and structural components and stress and immune responsive factors. In parallel, the analysis provide detailed expression patterns of Plasmodium genes encoding essential developmental and metabolic factors and proteins implicated in interaction with the mosquito vector and vertebrate host such as kinases, transcription and translational factors, cytoskeletal components and a variety of surface proteins, some of which are potent vaccine targets. Temporal correlation between transcription profiles of both organisms identifies putative gene clusters of interacting processes, such as Plasmodium invasion of the midgut epithelium, Anopheles immune responses to Plasmodium infection, and apoptosis and expulsion of invaded midgut cells from the epithelium. Intriguing transcription patterns for highly variable Plasmodium surface antigens may indicate parasite strategies to avoid recognition by the mosquito's immune surveillance system.

Animals↗

Global gene expression analysis of Anopheles gambiae responses to microbial challenge.

Anopheles gambiae transcript responses to experimental challenge with heat inactivated Salmonella typhimurium, Staphylococcus aureus and Beauveria bassiana have been analyzed with an Affymetrix GeneChip comprising the entire predicted mosquito transcriptome. Significant up- or down-regulation (greater than 2-fold) can be assayed for approximately 2% of the mosquito transcriptome and affected genes represent a variety of functional classes that include immunity, apoptosis, stress response, detoxification, metabolism, blood digestion, olfaction and others. Transcript responses to the 3 microbial elicitors exhibit an exceptionally high degree of specificity and only a few genes are significantly regulated by more than 1 of the tested elicitors. This study identifies several transcripts that have not been linked directly to immune response in A. gambiae previously; their infection responsiveness and sequence features do however suggest implication in defence reactions; examples are genes encoding leucine-rich repeat domain proteins, cuticle domain proteins and proteins containing immunoglobulin and fibronectin domains.

Animals↗

Anopheles infection responses; laboratory models versus field malaria transmission systems.

The molecular biology of disease vectors, particularly mosquitoes, has experienced a remarkable progress in the past two decades. This is mainly attributed to methodological advances and the emerging genome sequences of vector species, which have brought experimental biology to an unprecedented level. It is now possible to determine the entire transcriptome of Anopheles gambiae at a variety of conditions, with a low per-gene effort and cost. Proteomic profiles can be generated for as small samples as the hemolymph, and transient reverse genetic and stable germ line based transgenic analyses can be performed to analyze gene function. High throughput screening for receptors and ligands can be used to characterize interactions between vectors and pathogens. At the current breathtaking rates of data production it is essential to question and evaluate the relevance of laboratory infection models to the real disease transmission systems. The majority of scientific discoveries in mosquito molecular biology have been based on highly inbred laboratory strains and rodent malaria parasite infection models, which may differ substantially to their counterparts that transmit human malaria in the field. This review addresses the recent advances in high throughput transcription analyses of Anopheles responses to infection, and discusses considerations for the use of laboratory malaria infection models.

Animals↗

Transcript profiles of Blumeria graminis development during infection reveal a cluster of genes that are potential virulence determinants.

High-density cDNA microarrays (2,027 unigenes) were used to analyze transcript profiles of the plant-pathogenic fungus Blumeria graminis f. sp. hordei throughout its asexual life cycle and development of infection. RNA was obtained from four stages preceding penetration and four stages after penetration of the host cells. The microarray data was validated by comparing the expression of a plasma membrane H+-ATPase and fructose-1,6-bis phosphatase with the data obtained from a quantitative polymerase chain reaction (PCR) assay. The results showed that there was a global switch in expression between the pre- and postpenetrative stages. This was largely due to accumulation of RNA encoding protein biosynthesis genes in the late stages. Other functional clusters, such as virulence-related genes and sterol metabolism genes, are up-regulated in pre- and postpenetration stages, respectively. A group of RNAs whose abundance correlated with the expression of cap20, a gene known to be required for virulence in Colletotrichum gloeosporioides, identified genes that are strong candidates for pathogenicity factors in B. graminis.

Ascomycota↗

[Hospital-acquired pneumonia caused by methicillin-resistant Staphylococcus aureus].

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly common cause of hospital acquired pneumonia (HAP) and the second most frequently isolated pathogen from patients who die from HAP. High-risk units for MRSA colonization such as intensive care (ICU's) are the most affected. Multiple risk factors for transmission of MRSA have been identified, including colonization pressure and severity of illness at ICU admission. On the other hand, the most important predisposing factor for MRSA infection is prolonged mechanical ventilation and/or previous antibiotic therapy. Controlling the spread of MRSA remains a major challenge for hospitals. Screening programs, together with contact precautions for cases with MRSA and judicious antimicrobial use are major factors for a successful control. Early appropriate initial therapy is of crucial importance and improves outcome. The standard therapy has been glycopeptides but, in spite of its in vitro activity, mortality in critically ill patients treated with glycopeptides has consistently been reported high, mainly due to their poor lung penetration. Linezolid shows better clinical cure and survival rates, but further studies are needed. As the treatment options for MRSA pneumonia are limited and inadequate, development of more effective drugs is mandatory.

Anti-Bacterial Agents↗

[Comparison of dobutamine under different fluids resuscitation for shock induced by ischemia/reperfusion].

OBJECTIVE: To compare the effects of dobutamine under different fluids resuscitation for shock induced by intestinal ischemia/reperfusion (I/R) injury in rabbits. METHODS: Thirty-two anesthetized rabbits were randomized into four groups of eight animals each. The groups were followed as: (1) lactated Ringer's solution (LRS) resuscitation; (2) LRS+hydroxyethyl starch solution (HES) resuscitation; (3) LRS resuscitation+dobutamine treatment; (4) LRS+HES resuscitation+dobutamine treatment. All these rabbits underwent the intestinal I/R injury developed by occluding superior mesenteric artery (SMA) with a non-crushing vascular clamp for 60 minutes and then loosing the clamp for 300 minutes. The fluid resuscitation and drug treatment began at the same time of reperfusion. Hemodynamic parameters including mean artery pressure (MAP), heart rate (HR), aortic velocity (AoV, as cardiac output) and SMA blood flow (Qsma) were measured. Tissue oxygenation was assessed indirectly by measuring the tonometric parameters of the gut, including difference between partial pressure of carbon dioxide in intestinal intramucosal and partial pressure of carbon dioxide in arterial blood (Pt-a CO2 gap), intestinal intramucosal pH (pHi), arterial blood lactate acid concentration and oxygen delivery (DO2). RESULTS: HR, AoV and Qsma as measured in two dobutamine groups were significantly higher in values than LRS and LRS+HES groups (all P<0.05). But MAP as measured in two dobutamine groups were significantly higher in values than only LRS (P<0.05), and in LRS+HES resuscitation+dobutamine treatment group was also significantly higher in values than LRS resuscitation+dobutamine treatment group (P<0.05). Dobutamine in LRS resuscitation+dobutamine treatment and LRS+HES resuscitation+dobutamine treatment group could greatly decrease lactate and Pt-aCO2 gap, significantly improve pHi and DO2 compared with other two resuscitation groups (all P<0.05). Dobutamine in LRS+HES resuscitation+dobutamine treatment group could also greatly decrease lactate and Pt-aCO2 gap, significantly improve pHi compared with LRS resuscitation+dobutamine treatment group (all P<0.05). CONCLUSION: Dobutamine could improve hemodynamic parameters and tissue oxygenation in shock induced by intestinal I/R injury in rabbits, being better used under the LRS+HES resuscitation.

Animals↗

Post mortem examination in the intensive care unit: still useful?

OBJECTIVE: Post mortem examination rates have decreased worldwide and their usefulness has been challenged. The aim of this study was to compare ante- versus post mortem findings in a multidisciplinary ICU. DESIGN: Retrospective study. SETTING: Thirty-one-bed, medico-surgical ICU. PATIENTS: All patients who died on the ICU and underwent an autopsy examination in 1999. MEASUREMENTS: Records from autopsies were compared with clinical records. A modified Goldman's criteria was used to categorize the post mortem diagnoses. Unexpected findings were evaluated according to the duration of hospitalization prior to death (fewer than or more than 10 days). RESULTS: Among 2,984 ICU admissions, there were 489 deaths; 222 autopsies were conducted (45.4% autopsy rate). Post mortem examination revealed unexpected findings in 50 patients (22.5%), including malignancy (22 [9.9%]), fungal infections (9 [4%]), pulmonary embolism (7 [3.2%]), nosocomial infections (3 [1.3%]), Hashimoto's disease (3 [1.3%]), mesenteric infarction (2 [0.9%]), Barrett's esophagus (2 [0.9%]), endocarditis (1 [0.5%]) and myocardial infarction (1 [0.5%]). These unexpected findings were considered as major (Class I/II) in 19 (8.5%), and minor (Class III) in 31 (14%) patients. In patients with a short ICU length of stay (<10 days), there were more major unexpected findings than minor, while after a prolonged stay (>10 days), minor unexpected findings were more common. CONCLUSIONS: After a short ICU stay (<10 days), autopsy revealed discrepancies primarily related to the cause of death associated with diseases whose diagnosis can be difficult. Following more prolonged ICU stays (>10 days), autopsy was more likely to reveal coexisting diseases unrelated to death.

Aged↗

Immediate post-operative effects of tracheotomy on respiratory function during mechanical ventilation.

INTRODUCTION: Tracheotomy is widely performed in the intensive care unit after long-term oral intubation. The present study investigates the immediate influence of tracheotomy on respiratory mechanics and blood gases during mechanical ventilation. METHODS: Tracheotomy was performed in 32 orally intubated patients for 10.5 +/- 4.66 days (all results are means +/- standard deviations). Airway pressure, flow and arterial blood gases were recorded immediately before tracheotomy and half an hour afterwards. Respiratory system elastance (Ers), resistance (Rrs) and end-expiratory pressure (EEP) were evaluated by multiple linear regression. Respiratory system reactance (Xrs), impedance (Zrs) and phase angle (phirs) were calculated from Ers and Rrs. Comparisons of the mechanical parameters, blood gases and pH were performed with the aid of the Wilcoxon signed-rank test (P = 0.05). RESULTS: Ers increased (7 +/- 11.3%, P = 0.001), whereas Rrs (-16 +/- 18.4%, P = 0.0003), Xrs (-6 +/- 11.6%, P = 0.006) and phi rs (-14.3 +/- 16.8%, P = <0.001) decreased immediately after tracheotomy. EEP, Zrs, blood gases and pH did not change significantly. CONCLUSION: Lower Rrs but also higher Ers were noted immediately after tracheotomy. The net effect is a non-significant change in the overall Rrs (impedance) and the effectiveness of respiratory function. The extra dose of anaesthetics (beyond that used for sedation at the beginning of the procedure) or a higher FiO2 (fraction of inspired oxygen) during tracheotomy or aspiration could be related to the immediate elastance increase.

Adult↗

The effect of hyperosmotic pressure on antibody production and gene expression in the GS-NS0 cell line.

It has been widely reported that metabolism, cell growth, cell density, product secretion and specific antibody productivity in mammalian cells are strongly affected by osmotic conditions. Previous studies have shown that hyperosmotic pressure suppresses cell growth while enhancing the productivity of individual cells, but the effect of these two changes does not result in an increase in final product concentration in the culture. An improved understanding of the basic cellular processes of a GS-NS0 mammalian cell culture system would assist in the design of a more efficient mammalian cell culture system and in further optimization of production processes. In this study, various properties of mammalian culture systems, such as productivity, cell viability, metabolism, ion balance and the genes regulated during the culture of the GS-NS0 system under osmotic pressure of iso- (290 mOsm/kg) and hyper- (450 mOsm/kg) osmolarity have been investigated, and we demonstrate that there is a decrease in the growth rate and an increase in specific production rate of hyperosmotic cultures as compared with iso-osmotic cultures. Furthermore, differences between iso- and hyper-osmotic cultures have been identified in calcium accumulation and metabolism of NH4+, glucose and lactate. Analysis of gene expression reveals regulation of over 600 genes that are implicated in processes known to be affected by changes in osmotic pressure, such as ion transport, accumulation of osmolytes, cell cycle distribution, proliferation, cytoskeletal organization and cell metabolism.

Adaptation, Physiological↗

[Roles of hydroxyethyl starch solution in resuscitation for shock induced by ischemia/reperfusion injury of the intestine].

OBJECTIVE: To compare the effects of high and low doses of 6% hydroxyethyl starch solution (HES) on resuscitation for shock induced by ischemia/reperfusion injury of the intestine in rabbits. METHODS: Thirty-two anesthetized rabbits were randomized into four groups of eight animals each. The animals in the control group received no fluid resuscitation, animals in group 2 received lactated Ringer's solution (LRS, 20 ml x kg(-1) x h(-1)), those in group 3 received LRS+HES (LRS 18 ml x kg(-1) x h(1)+HES 2 ml x kg(-1) x h(-1), low dosage of HES), and those in group 4 received HES only in high dosage of HES (20 ml x kg(-1) x h(-1)). All these rabbits underwent intestinal ischemia/reperfusion injury developed by occluding superior mesenteric artery (SMA) with a non-crushing vascular clamp for 60 minutes and then the clamp was loosened for 240 minutes. The fluid resuscitation began at the same time of reperfusion. Hemodynamic parameters including mean artery pressure, heart rate, aortic velocity (as cardiac output), and SMA blood flow were measured. Tissue oxygenation was assessed indirectly by measuring the tonometric parameters of the gut, including difference between partial pressure of carbon dioxide in intestinal intramucosal and partial pressure of carbon dioxide in arterial blood (Pt-aCO(2) gap), intestinal intramucosal pH (pHi), arterial blood lactate acid concentration and oxygen delivery. Mortality of the rabbits was counted at the end of the experiment. RESULTS: Hemodynamic parameters as measured in low and high doses of HES groups were significantly higher in values than LRS group (LRS) and control (all P<0.05). Low dose of HES was better in restoring hemodynamic parameters than high dose of HES (all P<0.05). Low dose of HES could greatly decrease lactate and Pt-aCO(2) gap, significantly improve pHi compared with other three groups (all P<0.05), but high dose of HES did not do so, and oral and nasal bleeding even death of some animals were seen. Low dose and high dose of HES significantly improved oxygen delivery while LRS did not (all P<0.05). CONCLUSION: Low dose of HES together with LRS is more effective than only high dose of HES or LRS in the resuscitation for shock induced by ischemia/reperfusion injury of the intestine in rabbits, resulting in better hemodynamic parameters and tissue oxygenation.

Animals↗

Analysis of the Plasmodium and Anopheles transcriptional repertoire during ookinete development and midgut invasion.

Plasmodium, the causative agent of malaria, has to undergo sexual differentiation and development in anopheline mosquitoes for transmission to occur. To isolate genes specifically induced in both organisms during the early stages of Plasmodium differentiation in the mosquito, two cDNA libraries were constructed, one enriched for sequences expressed in differentiating Plasmodium berghei ookinetes and another enriched for sequences expressed in Anopheles stephensi guts containing invading ookinetes and early oocysts. Sequencing of 457 ookinete library clones and 652 early oocyst clones represented 175 and 346 unique expressed sequence tags, respectively. Nine of 13 Plasmodium and four of the five Anopheles novel expressed sequence tags analyzed on Northern blots were induced during ookinete differentiation and mosquito gut invasion. Ancaspase-7, an Anopheles effector caspase, is proteolytically activated during Plasmodium invasion of the midgut. WARP, a gene encoding a Plasmodium surface protein with a von Willebrand factor A-like adhesive domain, is expressed only in ookinetes and early oocysts. An anti-WARP polyclonal antibody strongly inhibits (70-92%) Plasmodium development in the mosquito, making it a candidate antigen for transmission blocking vaccines. The present results and those of an accompanying report (Srinivasan, P., Abraham, E. G., Ghosh, A. K., Valenzuela, J., Ribeiro, J. M. C., Dimopoulos G., Kafatos, F. C., Adams, J. H., and Jacobs-Lorena, M. (2004) J. Biol. Chem. 279, 5581-5587) provide the foundation for further analysis of Plasmodium differentiation in the mosquito and of mosquito responses to the parasite.

Amino Acid Sequence↗