A General Latent Class Model for Performance Evaluation of Diagnostic Tests in the Absence of a Gold Standard: An Application to Chagas Disease

We propose a new general Bayesian latent class model for evaluation of the performance of multiple diagnostic tests in situations in which no gold standard test exists based on a computationally intensive approach. The modeling represents an interesting and suitable alternative to models with complex structures that involve the general case of several conditionally independent diagnostic tests, covariates, and strata with different disease prevalences. The technique of stratifying the population according to different disease prevalence rates does not add further marked complexity to the modeling, but it makes the model more flexible and interpretable. To illustrate the general model proposed, we evaluate the performance of six diagnostic screening tests for Chagas disease considering some epidemiological variables. Serology at the time of donation (negative, positive, inconclusive) was considered as a factor of stratification in the model. The general model with stratification of the population performed better in comparison with its concurrents without stratification. The group formed by the testing laboratory Biomanguinhos FIOCRUZ-kit (c-ELISA and rec-ELISA) is the best option in the confirmation process by presenting false-negative rate of 0.0002% from the serial scheme. We are 100% sure that the donor is healthy when these two tests have negative results and he is chagasic when they have positive results.

Diethylpropion produces psychostimulant and reward effects

Diethylpropion (DEP) is a stimulant drug widely used for weight control in Brazil and other American countries. However, its effects on behavior and addiction potential are not yet well known. Data suggest that sensitization resulting from pre-exposure to psychostimulants could be a possible risk factor in subsequent drug addiction. The purpose of this investigation was to verify whether pre-exposure to DEP would sensitize rats to the motor activating effect and to the rewarding value of DEP. Two experiments were conducted. In both experiments rats were pre-exposed to DEP (20 mg/kg) or vehicle for 7 consecutive days. The acute effect of DEP (0.0, 1.0, 2.5 or 5.0 mg/kg) on motor activity (Experiment 1) and induction of Conditioned Place Preference-CPP (Experiment 2) were then measured. Results from Experiment 1 showed that 2.5 and 5.0 mg/kg DEP increased motor activity. Sensitization of this motor effect was observed. In Experiment 2, the doses of 2.5 and 5.0 mg/kg DEP induced CPP, indicating their rewarding value. However, no sensitization effect was observed. The results suggest that DEP at low doses has psychostimulant and rewarding properties. It is recommended that more effort should be dedicated to elucidating DEP abuse Potential. (c) 2008 Elsevier Inc. All rights reserved.

Performance of six diagnostic tests to screen for Chagas disease in blood banks and prevalence of Trypanosoma cruzi infection among donors with inconclusive serology screening based on the analysis of epidemiological variables

OBJECTIVE: The frequent occurrence of inconclusive serology in blood banks and the absence of a gold standard test for Chagas'disease led us to examine the efficacy of the blood culture test and five commercial tests (ELISA, IIF, HAI, c-ELISA, rec-ELISA) used in screening blood donors for Chagas disease, as well as to investigate the prevalence of Trypanosoma cruzi infection among donors with inconclusive serology screening in respect to some epidemiological variables. METHODS: To obtain estimates of interest we considered a Bayesian latent class model with inclusion of covariates from the logit link. RESULTS: A better performance was observed with some categories of epidemiological variables. In addition, all pairs of tests (excluding the blood culture test) presented as good alternatives for both screening (sensitivity > 99.96% in parallel testing) and for confirmation (specificity > 99.93% in serial testing) of Chagas disease. The prevalence of 13.30% observed in the stratum of donors with inconclusive serology, means that probably most of these are non-reactive serology. In addition, depending on the level of specific epidemiological variables, the absence of infection can be predicted with a probability of 100% in this group from the pairs of tests using parallel testing. CONCLUSION: The epidemiological variables can lead to improved test results and thus assist in the clarification of inconclusive serology screening results. Moreover, all combinations of pairs using the five commercial tests are good alternatives to confirm results.

The Poisson-exponential regression model under different latent activation schemes

In this paper, a new family of survival distributions is presented. It is derived by considering that the latent number of failure causes follows a Poisson distribution and the time for these causes to be activated follows an exponential distribution. Three different activation schemes are also considered. Moreover, we propose the inclusion of covariates in the model formulation in order to study their effect on the expected value of the number of causes and on the failure rate function. Inferential procedure based on the maximum likelihood method is discussed and evaluated via simulation. The developed methodology is illustrated on a real data set on ovarian cancer.

Lateral inhibition and odor discrimination in a model of the olfactory bulb

DA is supported by a CAPES PhD grant and ACR is the recipient of research grants by CNPq and FAPESP.

Modulation of the oscillatory mechanics of lung tissue and the oxidative stress response induced by arginase inhibition in a chronic allergic inflammation model

Abstract Background The importance of the lung parenchyma in the pathophysiology of asthma has previously been demonstrated. Considering that nitric oxide synthases (NOS) and arginases compete for the same substrate, it is worthwhile to elucidate the effects of complex NOS-arginase dysfunction in the pathophysiology of asthma, particularly, related to distal lung tissue. We evaluated the effects of arginase and iNOS inhibition on distal lung mechanics and oxidative stress pathway activation in a model of chronic pulmonary allergic inflammation in guinea pigs. Methods Guinea pigs were exposed to repeated ovalbumin inhalations (twice a week for 4 weeks). The animals received 1400 W (an iNOS-specific inhibitor) for 4 days beginning at the last inhalation. Afterwards, the animals were anesthetized and exsanguinated; then, a slice of the distal lung was evaluated by oscillatory mechanics, and an arginase inhibitor (nor-NOHA) or vehicle was infused in a Krebs solution bath. Tissue resistance (Rt) and elastance (Et) were assessed before and after ovalbumin challenge (0.1%), and lung strips were submitted to histopathological studies. Results Ovalbumin-exposed animals presented an increase in the maximal Rt and Et responses after antigen challenge (p<0.001), in the number of iNOS positive cells (p<0.001) and in the expression of arginase 2, 8-isoprostane and NF-kB (p<0.001) in distal lung tissue. The 1400 W administration reduced all these responses (p<0.001) in alveolar septa. Ovalbumin-exposed animals that received nor-NOHA had a reduction of Rt, Et after antigen challenge, iNOS positive cells and 8-isoprostane and NF-kB (p<0.001) in lung tissue. The activity of arginase 2 was reduced only in the groups treated with nor-NOHA (p <0.05). There was a reduction of 8-isoprostane expression in OVA-NOR-W compared to OVA-NOR (p<0.001). Conclusions In this experimental model, increased arginase content and iNOS-positive cells were associated with the constriction of distal lung parenchyma. This functional alteration may be due to a high expression of 8-isoprostane, which had a procontractile effect. The mechanism involved in this response is likely related to the modulation of NF-kB expression, which contributed to the activation of the arginase and iNOS pathways. The association of both inhibitors potentiated the reduction of 8-isoprostane expression in this animal model.

Inhibition of iNOS induces antidepressant-like effects in mice: Pharmacological and genetic evidence

Recent evidence has suggested that systemic administration of non-selective NOS inhibitors induces antidepressant-like effects in animal models. However, the precise involvement of the different NOS isoforms (neuronal-nNOS and inducible-iNOS) in these effects has not been clearly defined yet. Considering that mediators of the inflammatory response, that are able to induce iNOS expression, can be increased by exposure to stress, the aim of the present study was to investigate iNOS involvement in stress-induced behavioral consequences in the forced swimming test (FST), an animal model sensitive to antidepressant drugs. Therefore, we investigated the effects induced by systemic injection of aminoguanidine (preferential iNOS inhibitor), 1400W (selective iNOS inhibitor) or n-propyl-L-arginine (NPA, selective nNOS inhibitor) in mice submitted to the FST. We also investigated the behavior of mice with genetic deletion of iNOS (knockout) submitted to the FST. Aminoguanidine significantly decreased the immobility time (IT) in the FST. 1400W but not NPA, when administered at equivalent doses considering the magnitude of their Ki values for iNOS and nNOS, respectively, reduced the IT, thus suggesting that aminoguanidine-induced effects would be due to selective iNOS inhibition. Similarly, iNOS KO presented decreased IT in the FST when compared to wild-type mice. These results are the first to show that selective inhibition of iNOS or its knockdown induces antidepressant-like effects, therefore suggesting that iNOS-mediated NO synthesis is involved in the modulation of stress-induced behavioral consequences. Moreover, they further support NO involvement in the neurobiology of depression. This article is part of a Special Issue entitled 'Anxiety and Depression'. (C) 2011 Elsevier Ltd. All rights reserved.

Chronic VEGF Blockade Worsens Glomerular Injury in the Remnant Kidney Model

VEGF inhibition can promote renal vascular and parenchymal injury, causing proteinuria, hypertension and thrombotic microangiopathy. The mechanisms underlying these side effects are unclear. We investigated the renal effects of the administration, during 45 days, of sunitinib (Su), a VEGF receptor inhibitor, to rats with 5/6 renal ablation (Nx). Adult male Munich-Wistar rats were distributed among groups S+V, sham-operated rats receiving vehicle only; S+Su, S rats given Su, 4 mg/kg/day; Nx+V, Nx rats receiving V; and Nx+Su, Nx rats receiving Su. Su caused no change in Group S. Seven and 45 days after renal ablation, renal cortical interstitium was expanded, in association with rarefaction of peritubular capillaries. Su did not worsen hypertension, proteinuria or interstitial expansion, nor did it affect capillary rarefaction, suggesting little angiogenic activity in this model. Nx animals exhibited glomerulosclerosis (GS), which was aggravated by Su. This effect could not be explained by podocyte damage, nor could it be ascribed to tuft hypertrophy or hyperplasia. GS may have derived from organization of capillary microthrombi, frequently observed in Group Nx+Su. Treatment with Su did not reduce the fractional glomerular endothelial area, suggesting functional rather than structural cell injury. Chronic VEGF inhibition has little effect on normal rats, but can affect glomerular endothelium when renal damage is already present.

Application of an active attachment model as a high-throughput demineralization biofilm model

Objectives: To investigate the potential of an active attachment biofilm model as a highthroughput demineralization biofilm model for the evaluation of caries-preventive agents. Methods: Streptococcus mutans UA159 biofilms were grown on bovine dentine discs in a highthroughput active attachment model. Biofilms were first formed in a medium with high buffer capacity for 24 h and then subjected to various photodynamic therapies (PACT) using the combination of Light Emitting Diodes (LEDs, Biotable (R)) and Photogem (R). Viability of the biofilms was evaluated by plate counts. To investigate treatment effects on dentine lesion formation, the treated biofilms were grown in a medium with low buffer capacity for an additional 24 h. Integrated mineral loss (IML) and lesion depth (LD) were assessed by transversal microradiography. Calcium release in the biofilm medium was measured by atomic absorption spectroscopy. Results: Compared to the water treated control group, significant reduction in viability of S. mutans biofilms was observed when the combination of LEDs and Photogem (R) was applied. LEDs or Photogem (R) only did not result in biofilm viability changes. Similar outcomes were also found for dentine lesion formation. Significant lower IML and LD values were only found in the group subjected to the combined treatment of LEDs and Photogem (R). There was a good correlation between the calcium release data and the IML or LD values. Conclusions: The high-throughput active attachment biofilm model is applicable for evaluating novel caries-preventive agents on both biofilm and demineralization inhibition. PACT had a killing effect on 24 h S. mutans biofilms and could inhibit the demineralization process. (C) 2011 Elsevier Ltd. All rights reserved.

Antifibrotic Effect of Tamoxifen in a Model of Progressive Renal Disease

Tamoxifen, a selective estrogen receptor modulator, has antifibrotic properties; however, whether it can attenuate renal fibrosis is unknown. In this study, we tested the effects of tamoxifen in a model of hypertensive nephrosclerosis (chronic inhibition of nitric oxide synthesis with L-NAME). After 30 days, treated rats had significantly lower levels of albuminuria as well as lower histologic scores for glomerulosclerosis and interstitial fibrosis than untreated controls. Tamoxifen was renoprotective despite having no effect on the sustained, severe hypertension induced by L-NAME. Tamoxifen prevented the accumulation of extracellular matrix by decreasing the expression of collagen I, collagen III, and fibronectin mRNA and protein. These renoprotective effects associated with inhibition of TGF-beta 1 and plasminogen activator inhibitor-1, and with a significant reduction in a-smooth muscle actin-positive cells in the renal interstitium. Furthermore, tamoxifen abrogated IL-1 beta- and angiotensin-II-induced proliferation of fibroblasts from both kidney explants and from the NRK-49F cell line. Tamoxifen also inhibited the expression of extracellular matrix components and the production and release of TGF-beta 1 into the supernatant of these cells. In summary, tamoxifen exhibits antifibrotic effects in the L-NAME model of hypertensive nephrosclerosis, likely through the inhibition of TGF-beta 1, suggesting that it may have therapeutic use in CKD treatment.

Proteasome inhibition and ROS generation by 4-nerolidylcatechol induces melanoma cell death

Induction of apoptotic cell death in response to chemotherapy and other external stimuli has proved extremely difficult in melanoma, leading to tumor progression, metastasis formation and resistance to therapy. A promising approach for cancer chemotherapy is the inhibition of proteasomal activity, as the half-life of the majority of cellular proteins is under proteasomal control and inhibitors have been shown to induce cell death programs in a wide variety of tumor cell types. 4-Nerolidylcatechol (4-NC) is a potent antioxidant whose cytotoxic potential has already been demonstrated in melanoma tumor cell lines. Furthermore, 4-NC was able to induce the accumulation of ubiquitinated proteins, including classic targets of this process such as Mcl-1. As shown for other proteasomal inhibitors in melanoma, the cytotoxic action of 4-NC is time-dependent upon the pro-apoptotic protein Noxa, which is able to bind and neutralize Mcl-1. We demonstrate the role of 4-NC as a potent inducer of ROS and p53. The use of an artificial skin model containing melanoma also provided evidence that 4-NC prevented melanoma proliferation in a 3D model that more closely resembles normal human skin.

In Vitro PLK1 Inhibition by BI 2536 Decreases Proliferation and Induces Cell-Cycle Arrest in Melanoma Cells

Melanoma is one of the most treatment-resistant malignancies and regardless of new therapeutic tactics the outcome remains dismal. Polo-like kinase 1 (PLK1) has been shown to be over-expressed in a variety of tumors, becoming an attractive target for cancer management. In the present study we tested the in vitro antitumor activities of BI 2536, a selective inhibitor of PLK1, against two melanoma cell lines. Our results showed that nanomolar concentrations (10-150 nmol/L) of the drug significantly decreased cell proliferation and clonogenicity, promoting cell cycle arrest in G2/M. Targeting the cell cycle offers an attractive potential cancer-treatment option. Herein we show that PLK1 inhibition may be a feasible approach for the impairment of tumor progression and dissemination. This in vitro profile of melanoma cell growth inhibition by PLK1 modulation may be an interesting model to be tested in association with first-line antineoplasic agents in melanomas.

Latent residual analysis in binary regression with skewed link

Model diagnostics is an integral part of model determination and an important part of the model diagnostics is residual analysis. We adapt and implement residuals considered in the literature for the probit, logistic and skew-probit links under binary regression. New latent residuals for the skew-probit link are proposed here. We have detected the presence of outliers using the residuals proposed here for different models in a simulated dataset and a real medical dataset.

Rho-kinase inhibition attenuates airway responsiveness, inflammation, matrix remodeling, and oxidative stress activation induced by chronic inflammation

Possa SS, Charafeddine HT, Righetti RF, da Silva PA, Almeida-Reis R, Saraiva-Romanholo BM, Perini A, Prado CM, Leick-Maldonado EA, Martins MA, Tiberio ID. Rho-kinase inhibition attenuates airway responsiveness, inflammation, matrix remodeling, and oxidative stress activation induced by chronic inflammation. Am J Physiol Lung Cell Mol Physiol 303: L939-L952, 2012. First published September 21, 2012; doi:10.1152/ajplung.00034.2012.-Several studies have demonstrated the importance of Rho-kinase in the modulation of smooth muscle contraction, airway hyperresponsiveness, and inflammation. However, the effects of repeated treatment with a specific inhibitor of this pathway have not been previously investigated. We evaluated the effects of repeated treatment with Y-27632, a highly selective Rho-kinase inhibitor, on airway hyperresponsiveness, oxidative stress activation, extracellular matrix remodeling, eosinophilic inflammation, and cytokine expression in an animal model of chronic airway inflammation. Guinea pigs were subjected to seven ovalbumin or saline exposures. The treatment with Y-27632 (1 mM) started at the fifth inhalation. Seventy-two hours after the seventh inhalation, the animals' pulmonary mechanics were evaluated, and exhaled nitric oxide (E-NO) was collected. The lungs were removed, and histological analysis was performed using morphometry. Treatment with Y-27632 in sensitized animals reduced E-NO concentrations, maximal responses of resistance, elastance of the respiratory system, eosinophil counts, collagen and elastic fiber contents, the numbers of cells positive for IL-2, IL-4, IL-5, IL-13, inducible nitric oxide synthase, matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, transforming growth factor-beta, NF-kappa B, IFN-gamma, and 8-iso-prostaglandin F2 alpha contents compared with the untreated group (P < 0.05). We observed positive correlations among the functional responses and inflammation, remodeling, and oxidative stress pathway activation markers evaluated. In conclusion, Rho-kinase pathway activation contributes to the potentiation of the hyperresponsiveness, inflammation, the extracellular matrix remodeling process, and oxidative stress activation. These results suggest that Rho-kinase inhibitors represent potential pharmacological tools for the control of asthma.

A biophysical model of Sugarcane growth

Scientists predict that global agricultural lands will expand over the next few decades due to increasing demands for food production and an exponential increase in crop-based biofuel production. These changes in land use will greatly impact biogeochemical and biogeophysical cycles across the globe. It is therefore important to develop models that can accurately simulate the interactions between the atmosphere and important crops. In this study, we develop and validate a new process-based sugarcane model (included as a module within the Agro-IBIS dynamic agro-ecosystem model) which can be applied at multiple spatial scales. At site level, the model systematically under/overestimated the daily sensible/latent heat flux (by -10.5% and 14.8%, H and E, respectively) when compared against the micrometeorological observations from southeast Brazil. The model underestimated ET (relative bias between -10.1% and 12.5%) when compared against an agro-meteorological field experiment from northeast Australia. At the regional level, the model accurately simulated average yield for the four largest mesoregions (clusters of municipalities) in the state of Sao Paulo, Brazil, over a period of 16 years, with a yield relative bias of -0.68% to 1.08%. Finally, the simulated annual average sugarcane yield over 31 years for the state of Louisiana (US) had a low relative bias (-2.67%), but exhibited a lower interannual variability than the observed yields.