Detachment of Hexokinase II From Mitochondria Promotes Collateral Sensitivity in Multidrug Resistant Chronic Myeloid Leukemia Cells.

Chronic Myeloid Leukemia is a neoplastic disease characterized by the abnormal expansion of hematopoietic cells with compromised functions. Leukemic cells often display a multidrug resistance phenotype, enabling them to evade a number of structurally unrelated cytotoxic compounds. One of those mechanisms relies on the high expression of efflux transporters, such as the ABC proteins, whose activity depends on the hydrolysis of ATP to reduce intracellular drug accumulation. In the present work, we employed a well-known erythroleukemia cell line, K562, and a multidrug resistant derivative cell, FEPS, to evaluate how hexokinase II, a key regulator for the rate-limiting step glycolysis, contributes to the establishment of the multidrug resistance phenotype. We found that multidrug resistant cells primarily resort to glycolysis to generate ATP. Clotrimazole reduced the expression of mitochondrial hexokinase II, which destabilized bioenergetic parameters such as reactive oxygen species production, ATP, and glutathione levels on multidrug resistant cells. This impaired the activity of ABCC1, leading to increased drug accumulation and cell death. In summary, we propose that decoupling of hexokinase II from the mitochondria emerges as a promising strategy to generate collateral sensitivity and aid in the management of chronic myeloid leukemia in chemotherapy-refractory patients.

Tumor-Released Products Promote Bone Marrow-Derived Macrophage Survival and Proliferation.

Macrophages play a central role within the tumor microenvironment, with relevant implications for tumor progression. The modulation of their phenotype is one of the mechanisms used by tumors to escape from effective immune responses. This study was designed to analyze the influence of soluble products released by tumors, here represented by the tumor-conditioned media of two tumor cell lines (3LL from Lewis lung carcinoma and MN/MCA from fibrosarcoma), on murine macrophage differentiation and polarization in vitro. Data revealed that tumor-conditioned media stimulated macrophage differentiation but influenced the expression levels of macrophage polarization markers, cytokine production, and microRNAs of relevance for macrophage biology. Interestingly, tumor-derived soluble products supported the survival and proliferation rate of bone marrow precursor cells, an effect observed even with mature macrophages in the presence of M2 but not M1 inducers. Despite presenting low concentrations of macrophage colony-stimulating factor (M-CSF), tumor-conditioned media alone also supported the proliferation of cells to a similar extent as exogenous M-CSF. This effect was only evident in cells positive for the expression of the M-CSF receptor (CD115) and occurred preferentially within the CD16+ subset. Blocking CD115 partially reversed the effect on proliferation. These results suggest that tumors release soluble products that not only promote macrophage development from bone marrow precursors but also stimulate the proliferation of cells with specific phenotypes that could support protumoral functions.

Relation between ABCB1 overexpression and COX2 and ALOX5 genes in human erythroleukemia cell lines.

This study aimed to characterize the relationship between the COX2 and ALOX5 genes, as well as their link with the multidrug resistance (MDR) phenotype in sensitive (K562) and MDR (K562-Lucena and FEPS) erythroleukemia cells. For this, the inhibitors of 5-LOX (zileuton) and COX-2 (acetylsalicylic acid-ASA) and cells with the silenced ABCB1 gene were used. The treatment with ASA caused an increase in the gene expression of COX2 and ABCB1 in both MDR cell lines, and a decrease in the expression of ALOX5 in the FEPS cells. Silencing the ABCB1 gene induced a decrease in COX2 expression and an increase in the ALOX5 gene. Treatment with zileuton did not alter the expression of COX2 and ABCB1. Cytometry data showed that there was an increase in ABCB1 protein expression after exposure to ASA. In addition, the increased activity of ABCB1 in the K562-Lucena cell line indicates that ASA may be a substrate for this efflux pump, corroborating the molecular docking that showed that ASA can bind to ABCB1. Regardless of the genetic alteration in COX2 and ABCB1, the direct relationship between these genes and the inverse relationship with ALOX5 remained in the MDR cell lines. We assume that ABCB1 can play a regulatory role in COX2 and ALOX5 during the transformation of the parental cell line K562, explaining the increased gene expression of COX2 and decreased ALOX5 in the MDR cell lines.

In vitro antitumoral effects of the steroid ouabain on human thyroid papillary carcinoma cell lines.

Ouabain is a steroid described as a compound extracted from plants that is capable of binding to Na+ , K+ -ATPase, inhibiting ion transport and triggering cell signaling pathways. Due to its positive ionotropic effect, ouabain was used for more than 200 years for the treatment of cardiac dysfunctions. Numerous antitumor effects of ouabain have been described so far; however, its role on thyroid cancer is still poorly understood. Therefore, the aim of the present work was to evaluate the effect of ouabain on the biology of human papillary thyroid cancer cells. For this, three human thyroid cell lines were used: NTHY-ori, a non-tumor lineage, BCPAP and TPC-1, both derived from papillary carcinomas. Cells were cultured in the presence or absence of ouabain. Subsequently, we evaluated its effects on the viability, cell death, cell cycle, and migratory ability of these cell lines. We also investigated the impact of ouabain in IL-6/IL-6R and epithelial to mesenchymal transition markers expression. Our results indicate that ouabain (10-7 M), decreased the number of NTHY-ori, TPC-1 and BCPAP viable cells and induced cell cycle arrest after in vitro culture, but did not appear to promote cell death. In TPC-1 cells ouabain also inhibited cell migration; increased IL-6/IL-6R expression and IL-6 secretion; and diminished vimentin and SNAIL-1 expression. Collectively, our results indicate that ouabain has an antitumoral role on human papillary thyroid carcinomas in vitro. Even though additional studies are necessary, our work contributes to the discussion of the possibility of new clinical trials of ouabain.

Synthesis of new α-Aryl-α-tetralones and α-Fluoro-α-aryl-α-tetralones, preliminary antiproliferative evaluation on drug resistant cell lines and in silico prediction of ADMETox properties.

α-aryl-α-tetralones and α-fluoro-α-aryl-α-tetralones derivatives were synthesized by palladium catalyzed α-arylation reaction of α-tetralones and α-fluoro-α-tetralones, with bromoarenes in moderate to good yields. These compounds were evaluated for their in vitro anti-proliferative effects against human breast cancer and leukemia cell lines with diverse profiles of drug resistance. The most promising compounds, 3b, 3c, 8a and 8c, were effective on both neoplastic models. 3b and 8a induced higher toxicity on multidrug resistant cells and were able to avoid efflux by ABCB1 and ABCC1 transporters. Theoretical calculations of the physicochemical descriptors to predict ADMETox properties were favorable concerning Lipinski's rule of five, results that reflected on the low effects on non-tumor cells. Therefore, these compounds showed great potential for development of pharmaceutical agents against therapy refractory cancers.

Selective Cytotoxicity of Piperine Over Multidrug Resistance Leukemic Cells.

Multidrug resistance (MDR) is the main challenge in the treatment of chronic myeloid leukemia (CML), and P-glycoprotein (P-gp) overexpression is an important mechanism involved in this resistance process. However, some compounds can selectively affect MDR cells, inducing collateral sensitivity (CS), which may be dependent on P-gp. The aim of this study was to investigate the effect of piperine, a phytochemical from black pepper, on CS induction in CML MDR cells, and the mechanisms involved. The results indicate that piperine induced CS, being more cytotoxic to K562-derived MDR cells (Lucena-1 and FEPS) than to K562, the parental CML cell. CS was confirmed by analysis of cell metabolic activity and viability, cell morphology and apoptosis. P-gp was partially required for CS induction. To investigate a P-gp independent mechanism, we analyzed the possibility that poly (ADP-ribose) polymerase-1 (PARP-1) could be involved in piperine cytotoxic effects. It was previously shown that only MDR FEPS cells present a high level of 24 kDa fragment of PARP-1, which could protect these cells against cell death. In the present study, piperine was able to decrease the 24 kDa fragment of PARP-1 in MDR FEPS cells. We conclude that piperine targets selectively MDR cells, inducing CS, through a mechanism that might be dependent or not on P-gp.

Modulation of cytokine production by monocytes and developing-dendritic cells under the influence of leukemia and lymphoma cell products.

Cytokines and other soluble factors released by tumor cells play an important role in modulating immune cells to favor tumor development. Monocyte differentiation into macrophages or dendritic cells (DCs) with specific phenotypes is deeply affected by tumor signals and understanding this context is paramount to prevent and propose new therapeutic possibilities. Hence, we developed a study to better describe the modulatory effects of leukemia and lymphoma cell products on human monocytes and monocyte-derived DCs secretion of cytokines such as interleukin (IL)-1ß, tumor necrosis factor-α (TNF-α), IL-6, and IL-12. Except with the promyelocytic leukemia cell supernatants (HL-60), the other two tumor supernatants (chronic myeloid leukemia, K562 and Burkitt lymphoma, DAUDI) increased both TNF-α and IL-1ß production by monocytes and monocytes undergoing differentiation. This effect was neither explained by alterations of cell number in culture nor by the high amount of vascular endothelial growth factor (VEGF) present in the tumor supernatants. Moreover, all supernatants used were able to induce drastic reduction of IL-12 secretion by cells induced to activation, suggesting a negative interference with Th1 antitumoral responses that should be a huge advantage for tumor progression.

Multidrug resistance phenotype: Relation between phenotype induction and its characteristics in erythroleukemia cells.

Chemotherapy may be followed by multiple drug resistance (MDR). This is an obstacle in the treatment of cancer. It is therefore essential to understand the mechanisms underlying tumor resistance, especially those involved in the cell target/MDR relationship. To investigate this, the effects of exposing cells to UVB (to target DNA), UVA, and H2 O2 (to target the cell membrane) were observed in K562 (non MDR) and FEPS (MDR) cell lines. The K562 cells were more sensitive to UVA than the FEPS cells. The FEPS cell line was more resistant to H2 O2 than K562, only presenting cytotoxicity 72 h after being exposed to 40 mM, with no ROS increase until 48 h. Both cell lines were sensitive to UVB, presenting cytotoxicity after 24 h, mainly by apoptosis, and showed an increase in ROS levels. Our results indicate that agents acting on DNA may be able to overcome the MDR phenotype.

Insights into the Biological Evaluation of Pterocarpanquinones and Carbapterocarpans with Anti-tumor Activity against MDR Leukemias.

In an attempt to find anticancer agents that could overcome multidrug resistance (MDR), two new classes of modified isoflavonoids were designed and synthesized, and their effectiveness evaluated against a vast array of tumor cell lines. Pterocarpanquinone (LQB-118) and 11a-aza-5-carbapterocarpan (LQB-223) were the most promising. LQB-118 induced cell death, in vitro, in the µM range, to a number of human cancer cell lines as well as to fresh tumor cells obtained from patients with acute or chronic myeloid leukemia, independent on whether they exhibit the MDR phenotype or not. Furthermore, leukemic cells were more sensitive to LQB- 118 compared to cells from solid tumors. Given to mice, in vivo, LQB-118 affected the growth of melanoma, Ehrlich carcinoma and prostate cancer cells. Conversely, no general toxicity was observed in vivo, by biochemical, hematological, anatomical or histological parameters and toxicity in vitro against normal cells was low. The process involved in tumor cell death seemed to vary according to cell type. Apoptosis was studied by externalization of phosphatidylserine, DNA fragmentation, caspase-3 activation, reduced expression of XIAP and survivin, ER stress, cytosolic calcium increase and mitochondrial membrane depolarization. Autophagy was also evaluated inhibiting caspase-9, with no effect observed in beclin 1, whereas pre-treatment with rapamycin increased cytotoxicity induced by LQB-118. In addition, LQB-118 increased ROS, inhibited NFκB nuclear translocation and secretion of TNF-α, modulated microRNAs miR-9 and miR-21 and modified the cell cycle. Despite being less studied, the cytotoxic effect of the 11a-aza-5-carbapterocarpan LQB-223 was present against several tumor cell lines, including those with the MDR phenotype.

Corrigendum: Metabolic Reprogramming During Multidrug Resistance in Leukemias.

[This corrects the article DOI: 10.3389/fonc.2018.00090.].

Glucocorticoid susceptibility and in vivo ABCB1 activity differ in murine B cell subsets.

Glucocorticoids are produced and released by the adrenal gland and become elevated in response to stress. Although glucocorticoids are well known for their immunosuppressive effects, less is known about their effects on B cells. ABCB1 is an efflux pump expressed in both cancer and normal cells, modulating the gradient of various metabolites, including hydrocortisone. Our goal was to evaluate the effect of this glucocorticoid on murine B cell differentiation and whether sensitivity to hydrocortisone could be related to ABCB1 activity in vivo. C57BL/6 mice received one or three consecutive i.p. injections of hydrocortisone (70, 140 and 200 mg/kg/day). ABCB1 activity was evaluated via the rhodamine-123 transport and inhibited by cyclosporin A in hydrocortisone-treated and control mice. Cells from bone marrow, spleen and blood were counted, incubated with antibodies and analyzed by flow cytometry. A single hydrocortisone injection did not alter the number of bone marrow subsets. Conversely, three daily injections were able to reduce the cell number of most bone marrow subsets, excepting c-kit-sca-1+ and mature B cells. This treatment reduced marginal zone, follicular and transitional B cells, though splenic subsets were more resistant than bone marrow B cells. Recirculating follicular B cells in the blood were resistant to hydrocortisone. With the exception of follicular B cells, all subpopulations exhibited ABCB1 activity. However, hydrocortisone treatment did not affect ABCB1 activity in most subsets analyzed. Results suggest that hydrocortisone is able to regulate B cell lymphopoiesis although ABCB1 activity is not related to the susceptibility to that glucocorticoid in B cell subsets.

Metabolic Reprogramming During Multidrug Resistance in Leukemias.

Cancer outcome has improved since introduction of target therapy. However, treatment success is still impaired by the same drug resistance mechanism of classical chemotherapy, known as multidrug resistance (MDR) phenotype. This phenotype promotes resistance to drugs with different structures and mechanism of action. Recent reports have shown that resistance acquisition is coupled to metabolic reprogramming. High-gene expression, increase of active transport, and conservation of redox status are one of the few examples that increase energy and substrate demands. It is not clear if the role of this metabolic shift in the MDR phenotype is related to its maintenance or to its induction. Apart from the nature of this relation, the metabolism may represent a new target to avoid or to block the mechanism that has been impairing treatment success. In this mini-review, we discuss the relation between metabolism and MDR resistance focusing on the multiple non-metabolic functions that enzymes of the glycolytic pathway are known to display, with emphasis with the diverse activities of glyceraldehyde-3-phosphate dehydrogenase.

Towards Comprehension of the ABCB1/P-Glycoprotein Role in Chronic Myeloid Leukemia.

Abstract: The introduction of imatinib (IM), a BCR-ABL1 tyrosine kinase inhibitor (TKI), has represented a significant advance in the first-line treatment of chronic myeloid leukemia (CML). However, approximately 30% of patients need to discontinue IM due to resistance or intolerance to this drug. Both resistance and intolerance have also been observed in treatment with the second-generation TKIs-dasatinib, nilotinib, and bosutinib-and the third-generation TKI-ponatinib. The mechanisms of resistance to TKIs may be BCR-ABL1-dependent and/or BCR-ABL1-independent. Although the role of efflux pump P-glycoprotein (Pgp), codified by the ABCB1 gene, is unquestionable in drug resistance of many neoplasms, a longstanding question exists about whether Pgp has a firm implication in TKI resistance in the clinical scenario. The goal of this review is to offer an overview of ABCB1/Pgp expression/activity/polymorphisms in CML. Understanding how interactions, associations, or cooperation between Pgp and other molecules-such as inhibitor apoptosis proteins, microRNAs, or microvesicles-impact IM resistance risk may be critical in evaluating the response to TKIs in CML patients. In addition, new non-TKI compounds may be necessary in order to overcome the resistance mediated by Pgp in CML.

Mechanism Underlying the Reversal of Drug Resistance in P-Glycoprotein-Expressing Leukemia Cells by Pinoresinol and the Study of a Derivative.

P-glycoprotein (P-gp) is a membrane protein associated with multidrug resistance (MDR) due to its key role in mediating the traffic of chemotherapeutic drugs outside cancer cells, leading to a cellular response that hinders efforts toward successful therapy. With the aim of finding agents that circumvent the MDR phenotype mediated by P-gp, 15 compounds isolated from native and naturalized plants of Argentina were screened. Among these, the non-cytotoxic lignan (±) pinoresinol successfully restored sensitivity to doxorubicin from 7 µM in the P-gp overexpressed human myelogenous leukemia cells, Lucena 1. This resistance-reversing effect was confirmed by competitively increasing the intracellular doxorubicin accumulation and by significantly inhibiting the efflux of doxorubicin and, to a lesser extent, that of rhodamine 123. The activity obtained was similar to that observed with verapamil. No such results were observed in the sensitive parental K562 cell line. To gain deeper insight into the mode of action of pinoresinol, its effect on P-gp function and expression was examined. The docking simulations indicated that the lignan bound to P-gp at the apex of the V-shaped transmembrane cavity, involving transmembrane helices 4, 5, and 6, and partially overlapped the binding region of tariquidar, which was used as a positive control. These results would shed some light on the nature of its interaction with P-gp at molecular level and merit further mechanistic and kinetic studies. In addition, it showed a maximum 29% activation of ATP hydrolysis and antagonized verapamil-stimulated ATPase activity with an IC50 of 20.9 µM. On the other hand, pinoresinol decreased the presence of P-gp in the cell surface. Derivatives of pinoresinol with improved activity were identified by docking studies. The most promising one, the non-cytotoxic 1-acetoxypinoresinol, caused a reversion of doxorubicin resistance from 0.11 µM and thus higher activity than the lead compound. It also caused a significant increase in doxorubicin accumulation. Results were similar to those observed with verapamil. The results obtained positioned these compounds as potential candidates for effective agents to overcome P-gp-mediated MDR, leading to better outcomes for leukemia chemotherapy.

Chronic sleep restriction promotes brain inflammation and synapse loss, and potentiates memory impairment induced by amyloid-ß oligomers in mice.

It is increasingly recognized that sleep disturbances and Alzheimer's disease (AD) share a bidirectional relationship. AD patients exhibit sleep problems and alterations in the regulation of circadian rhythms; conversely, poor quality of sleep increases the risk of development of AD. The aim of the current study was to determine whether chronic sleep restriction potentiates the brain impact of amyloid-ß oligomers (AßOs), toxins that build up in AD brains and are thought to underlie synapse damage and memory impairment. We further investigated whether alterations in levels of pro-inflammatory mediators could play a role in memory impairment in sleep-restricted mice. We found that a single intracerebroventricular (i.c.v.) infusion of AßOs disturbed sleep pattern in mice. Conversely, chronically sleep-restricted mice exhibited higher brain expression of pro-inflammatory mediators, reductions in levels of pre- and post-synaptic marker proteins, and exhibited increased susceptibility to the impact of i.c.v. infusion of a sub-toxic dose of AßOs (1pmol) on performance in the novel object recognition memory task. Sleep-restricted mice further exhibited an increase in brain TNF-α levels in response to AßOs. Interestingly, memory impairment in sleep-restricted AßO-infused mice was prevented by treatment with the TNF-α neutralizing monoclonal antibody, infliximab. Results substantiate the notion of a dual relationship between sleep and AD, whereby AßOs disrupt sleep/wake patterns and chronic sleep restriction increases brain vulnerability to AßOs, and point to a key role of brain inflammation in increased susceptibility to AßOs in sleep-restricted mice.

Low ABCB1 and high OCT1 levels play a favorable role in the molecular response to imatinib in CML patients in the community clinical practice.

Despite the favorable clinical evolution of patients with chronic myeloid leukemia (CML), resistance or intolerance to imatinib is present in approximately 35% of patients. Sokal score is a widely used risk factor, however efflux and influx transporters are provisional risk factors implicated in imatinib resistance. This study analyzed Sokal score, ABCB1, ABCG2 and OCT1 mRNA transporter expression levels as well as P-glycoprotein expression and efflux transporters activity to seek a possible correlation between these factors and the molecular response at 12 months from imatinib start as well as 8-year overall survival (OS). Low plus intermediate Sokal score correlated to optimal imatinib responses, as well as OS at 8-years, thus confirming the established role of Sokal score as a prognostic factor in CML patients. Low ABCB1 and high OCT1 mRNA levels were associated with an optimal molecular response, while the inverse levels were associated with non-responders (warning and failure) patients. Our results suggest that ABCB1 and OCT1 mRNA expressions may present biological relevance to identify responder and non-responder patients to imatinib treatment.

In vitro and in vivo antineoplastic and immunological effects of pterocarpanquinone LQB-118.

Cancer is a malignancy of worldwide prevalence, and although new therapeutic strategies are under investigation, patients still resort to reductive or palliative chemotherapy. Side effects are a great concern, since treatment can render patients susceptible to infections or secondary cancers. Thus, design of safer chemotherapeutic drugs must consider the risk of immunotoxicity. Pterocarpans are natural isoflavones that possess immunomodulatory and antineoplastic properties. Ubiquitous in nature, quinones are present in chemotherapeutic drugs such as doxorubicin and mitoxantrone. Our group has patented a hybrid molecule, the pterocarpanquinone LQB-118, and demonstrated its antineoplastic effect in vitro. In this report we describe its antineoplastic effect in vivo and assess its toxicity toward the immune system. Treated mice presented no changes in weight of primary and secondary organs of the immune system nor their cellular composition. Immunophenotyping showed that treatment increased CD4(+) thymocytes and proportionally reduced the CD4(+)CD8(+) subpopulation in the thymus. No significant changes were observed in T CD8(+) peripheral lymphocytes nor was the activation of fresh T cells affected after treatment. LQB-118 induced apoptosis in murine tumor cells in vitro, being synergistic with the autophagy promoter rapamycin. Furthermore, treatment significantly reduced ascites or solid Ehrlich and B16F10 melanoma growth in vivo, and ameliorated side effects such as cachexia. Based on its favorable preclinical profile and considering previous results obtained in vitro, this drug emerges as a promising candidate for further development.

Sensitivity of Dendritic Cells to Microenvironment Signals.

Dendritic cells are antigen-presenting cells capable of either activating the immune response or inducing and maintaining immune tolerance. They do this by integrating stimuli from the environment and changing their functional status as a result of plasticity. The modifications suffered by these cells have consequences in the way the organism may respond. In the present work two opposing situations known to affect dendritic cells are analyzed: tumor growth, leading to a microenvironment that favors the induction of a tolerogenic profile, and organ transplantation, which leads to a proinflammatory profile. Lessons learned from these situations may help to understand the mechanisms of modulation resulting not only from the above circumstances, but also from other pathologies.

Dynamics of murine B lymphocytes is modulated by in vivo treatment with steroid ouabain.

Ouabain (OUA) is a steroid hormone capable of inhibiting the protein Na+K+ATPase present in the plasma membrane of cells. Ouabain was initially extracted from the roots of African trees such as Acocanthera ouabaio and Strophantus gratus seeds and later described as an endogenous component found in higher mammals. The adrenal gland is the main site of synthesis of ouabain and it is released in stressful situations, conditions similar to those where there is secretion of corticosteroids. Immunological functions have been shown to be regulated by ouabain. In order to understand the effects of ouabain on B lymphocyte populations in different lymphoid organs, mice received intraperitoneal injections of ouabain for 3 consecutive days. Twenty-four hours after the last injection, cells were analyzed by flow cytometry. In the spleen, ouabain modulated especially follicular B cells, inducing a significant decrease in the percentage and absolute numbers of those cells. Ouabain also reduced the absolute number of marginal zone B lymphocytes. No difference in the percentage or absolute number of B lymphocytes in the spleen forty-eight hours after the last injection was observed. An increase in the number of B cells was seen in mesenteric lymph nodes and this retention appears to be directly related to increased expression of CXCR5 chemokine receptor and reduction of CD62L, which also explains the observed reduction of B cells in the spleen. Our results indicate that ouabain regulates the dynamics of B lymphocytes in peripheral organs but production of total IgM and IgG in the serum of animals treated in vivo with ouabain was not affected.

Ouabain Modulates Zymosan-Induced Peritonitis in Mice.

Ouabain, a potent inhibitor of the Na(+), K(+)-ATPase, was identified as an endogenous substance. Recently, ouabain was shown to affect various immunological processes. We have previously demonstrated the ability of ouabain to modulate inflammation, but little is known about the mechanisms involved. Thus, the aim of the present work is to evaluate the immune modulatory role of ouabain on zymosan-induced peritonitis in mice. Our results show that ouabain decreased plasma exudation (33%). After induction of inflammation, OUA treatment led to a 46% reduction in the total number of cells, as a reflex of a decrease of polymorphonuclear leukocytes, which does not appear to be due to cell death. Furthermore, OUA decreased TNF-α (57%) and IL-1ß (58%) levels, without interfering with IL-6 and IL-10. Also, in vitro experiments show that ouabain did not affect endocytic capacity. Moreover, electrophoretic mobility shift assay (EMSA) shows that zymosan treatment increased (85%) NF-κB binding activity and that ouabain reduced (30%) NF-κB binding activity induced by zymosan. Therefore, our data suggest that ouabain modulated acute inflammatory response, reducing the number of cells and cytokines levels in the peritoneal cavity, as well as NFκB activation, suggesting a new mode of action of this substance.