Transport of glutathione and glutathione conjugates by MRP1

Metabolism, toxicity and anticancer activities of arsenic compounds

A variety of studies indicated that inorganic arsenic and its methylated metabolites have paradoxical effects, namely, carcinogenic and anticancer effects. Epidemiological studies have shown that long term exposure to arsenic can increase the risk of cancers of lung, skin or bladder in man, which is probably associated with the arsenic metabolism. In fact, the enzymatic conversion of inorganic arsenic by Arsenic (+3 oxidation state) methyltransferase (AS3MT) to mono- and dimethylated arsenic species has long been considered as a major route for detoxification. However, several studies have also indicated that biomethylation of inorganic arsenic, particularly the production of trivalent methylated metabolites, is a process that activates arsenic as a toxin and a carcinogen. On the other hand, arsenic trioxide (As2O3) has recently been recognized as one of the most effective drugs for the treatment of APL. However, elaboration of the cytotoxic mechanisms of arsenic and its methylated metabolites in eradicating cancer is sorely lacking. To provide a deeper understanding of the toxicity and carcinogenicity along with them use of arsenic in chemotherapy, caution is required considering the poor understanding of its various mechanisms of exerting toxicity. Thereby, in this review, we have focused on arsenic metabolic pathway, the roles of the methylated arsenic metabolites in toxicity and in the therapeutic efficacy for the treatments of solid tumors, APL and/or non-APL malignancies.

ATP-binding cassette (ABC) proteins in aquatic invertebrates: Evolutionary significance and application in marine ecotoxicology

The ATP-binding cassette (ABC) protein superfamily is known to play a fundamental role in biological processes and is highly conserved across animal taxa. The ABC proteins function as active transporters for multiple substrates across the cellular membrane by ATP hydrolysis. As this superfamily is derived from a common ancestor, ABC genes have evolved via lineage-specific duplications through the process of adaptation. In this review, we summarized information about the ABC gene families in aquatic invertebrates, considering their evolution and putative functions in defense mechanisms. Phylogenetic analysis was conducted to examine the evolutionary significance of ABC gene families in aquatic invertebrates. Particularly, a massive expansion of multixenobiotic resistance (MXR)-mediated efflux transporters was identified in the absence of the ABCG2 (BCRP) gene in Ecdysozoa and Platyzoa, suggesting that a loss of Abcg2 gene occurred sporadically in these species during divergence of Protostome to Lophotrochozoa. Furthermore, in aquatic invertebrates, the ecotoxicological significance of MXR is discussed while considering the role of MXR-mediated efflux transporters in response to various environmental pollutants.

Structural Basis of Substrate Recognition by the Multidrug Resistance Protein MRP1

The multidrug resistance protein MRP1 is an ATP-binding cassette (ABC) transporter that confers resistance to many anticancer drugs and plays a role in the disposition and efficacy of several opiates, antidepressants, statins, and antibiotics. In addition, MRP1 regulates redox homeostasis, inflammation, and hormone secretion. Using electron cryomicroscopy, we determined the molecular structures of bovine MRP1 in two conformations: an apo form at 3.5 Å without any added substrate and a complex form at 3.3 Å with one of its physiological substrates, leukotriene C₄. These structures show that by forming a single bipartite binding site, MRP1 can recognize a spectrum of substrates with different chemical structures. We also observed large conformational changes induced by leukotriene C₄, explaining how substrate binding primes the transporter for ATP hydrolysis. Structural comparison of MRP1 and P-glycoprotein advances our understanding of the common and unique properties of these two important molecules in multidrug resistance to chemotherapy.

Reversal of Multidrug Resistance in Mouse Lymphoma Cells by Extracts and Flavonoids from Pistacia integerrima

Phytochemical investigation of Pistacia integerrima has highlighted isolation of two known compounds naringenin (1) and dihydrokaempferol (2). A crude extract and these isolated compounds were here evaluated for their effects on reversion of multidrug resistance (MDR) mediated by P-glycoprotein (P-gp). The multidrug resistance P-glycoprotein is a target for chemotherapeutic drugs from cancer cells. In the present study rhodamine- 123 exclusion screening test on human mdr1 gene transfected mouse gene transfected L5178 and L5178Y mouse T-cell lymphoma cells showed excellent MDR reversing effects in a dose dependent manner. In-silico molecular docking investigations demonstrated a common binding site for Rhodamine123, and compounds naringenin and dihydrokaempferol. Our results showed that the relative docking energies estimated by docking softwares were in satisfactory correlation with the experimental activities. Preliminary interaction profile of P-gp docked complexes were also analysed in order to understand the nature of binding modes of these compounds. Our computational investigation suggested that the compounds interactions with the hydrophobic pocket of P-gp are mainly related to the inhibitory activity. Moreover this study s a platform for the discovery of novel natural compounds from herbal origin, as inhibitor molecules against the P-glycoprotein for the treatment of cancer.

A Nitric Oxide Storage and Transport System That Protects Activated Macrophages from Endogenous Nitric Oxide Cytotoxicity

Nitric oxide (NO) is integral to macrophage cytotoxicity against tumors due to its ability to induce iron release from cancer cells. However, the mechanism for how activated macrophages protect themselves from endogenous NO remains unknown. We previously demonstrated by using tumor cells that glutathione S-transferase P1 (GSTP1) sequesters NO as dinitrosyl-dithiol iron complexes (DNICs) and inhibits NO-mediated iron release from cells via the transporter multidrug resistance protein 1 (MRP1/ABCC1). These prior studies also showed that MRP1 and GSTP1 protect tumor cells against NO cytotoxicity, which parallels their roles in defending cancer cells from cytotoxic drugs. Considering this, and because GSTP1 and MRP1 are up-regulated during macrophage activation, this investigation examined whether this NO storage/transport system protects macrophages against endogenous NO cytotoxicity in two well characterized macrophage cell types (J774 and RAW 264.7). MRP1 expression markedly increased upon macrophage activation, and the role of MRP1 in NO-induced ⁵⁹Fe release was demonstrated by Mrp1 siRNA and the MRP1 inhibitor, MK571, which inhibited NO-mediated iron efflux. Furthermore, Mrp1 silencing increased DNIC accumulation in macrophages, indicating a role for MRP1 in transporting DNICs out of cells. In addition, macrophage ⁵⁹Fe release was enhanced by silencing Gstp1, suggesting GSTP1 was responsible for DNIC binding/storage. Viability studies demonstrated that GSTP1 and MRP1 protect activated macrophages from NO cytotoxicity. This was confirmed by silencing nuclear factor-erythroid 2-related factor 2 (Nrf2), which decreased MRP1 and GSTP1 expression, concomitant with reduced ⁵⁹Fe release and macrophage survival. Together, these results demonstrate a mechanism by which macrophages protect themselves against NO cytotoxicity.

Chronic toxicological effects of β-diketone antibiotics on Zebrafish (Danio rerio) using transcriptome profiling of deep sequencing

Transcriptome analysis is important for interpreting the functional elements of the genome and revealing the molecular constituents of cells and tissues. Herein, differentially transcribed genes were identified by deep sequencing after zebrafish (Danio rerio) were exposed to β-diketone antibiotics (DKAs); 23,129 and 23,550 mapped genes were detected in control and treatment groups, a total of 3238 genes were differentially expressed between control and treatment groups. Of these genes, 328 genes (213 up- and 115 down-regulation) had significant differential expression (p < 0.05) and an expression ratio (control/treatment) of >2 or <0.5. Additionally, we performed Gene Ontology (GO) category and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses, and found 266 genes in the treatment group with annotation terms linked to the GO category. A total of 77 differentially expressed transcriptional genes were associated with 132 predicted KEGG metabolic pathways. Serious liver tissue damage was reflected and consistent with the differences in genetic classification and function from the transcriptome analysis. These results enhance our understanding of zebrafish developmental processes under exposure to DKA stress. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1357-1371, 2016.

Detoxification and sensing mechanisms are of similar importance for Cd resistance in Caenorhabditis elegans

The present study employed mass spectrometry (ICP-MS) to measure the internal cadmium concentrations (Cd_int) in Caenorhabditis elegans to determine Cd uptake from a Cd-containing environment as well as Cd release under Cd-free conditions. To analyze the functional role of several ATP binding cassette (ABC) transporters (e.g., HMT-1 and MRP-1) and phytochelatin synthase (PCS), we compared wild-type (WT) and different mutant strains of C. elegans. As a pre-test on selected mutant strains, several time-resolved experiments were performed to determine the survival rate and avoidance behavior of C. elegans under Cd stress, which confirmed the already known Cd sensitivity of the deletion mutants mrp-1Δ, pcs-1Δ, and hmt-1Δ. In addition, these experiments revealed flight reactions under Cd stress to be almost completely absent in mrp-1Δ mutants. The ICP-MS studies showed Cd uptake to be significantly higher in mrp-1Δ and WT than in hmt-1Δ. As Cd is ingested with food, food refusal due to very early Cd stress and its perception was likely the reason for the reduced Cd uptake of hmt-1Δ. Cd release (detoxification) was found to be maximal in mrp-1Δ, minimal in hmt-1Δ, and intermediate in WT. High mortality under Cd stress, food refusal, and minimal Cd release in the case of hmt-1Δ suggest a vital importance of the HMT-1/PCS-1 detoxification system for the survival of C. elegans under Cd stress. High mortality under Cd stress, absence of an avoidance behavior, missing food refusal, and maximal Cd release in the case of mrp-1Δ indicate that MRP-1 is less important for Cd detoxification under severe stress, but is probably important for Cd perception. Accordingly, our results suggest that the survival of WT under Cd stress (or possibly other forms of metal stress) primarily depends on the function of the HMT-1/PCS-1 detoxification system and the presence of a sensing mechanism to control the uptake of Cd (or other metals), which keeps internal Cd (or metal) concentrations under control, to some extent, for the timely mobilization of protection and repair systems.

Genome-wide identification of ATP-binding cassette (ABC) transporters and conservation of their xenobiotic transporter function in the monogonont rotifer (Brachionus koreanus)

The ATP-binding cassette (ABC) transporter family is one of the largest gene family in animals, and members of this family are known to be involved in various biological processes due to their ability to transport a wide range of substrates across membranes using ATP cleavage-derived energy. We identified 61 ABC transporters in the genome of the monogonont rotifer Brachionus koreanus, and classified these into eight distinct subfamilies (A-H) by phylogenetic analysis. ABC transporters in the rotifer B. koreanus are comprised of 11 ABCA genes, 19 ABCB genes, 14 ABCC genes, 3 ABCD genes, 1 ABCE gene, 3 ABCF genes, 8 ABCG genes, and 2 ABCH genes. Extensive gene duplication and loss events in synteny were observed in several subfamilies. In particular, massive gene duplications of P-glycoproteins (P-gps), multidrug resistance proteins (MRPs), and Bk-Abcg-like proteins were observed. The ability of these B. koreanus proteins to function as multixenobiotic resistance (MXR) ABC transporters was validated using specific fluorescence substrates/inhibitors. The ABC transporter superfamily members identified in this study will be useful in future toxicological studies, and will facilitate comparative studies of the evolution of the ABC transporter superfamily in invertebrates.

Diverse relations between ABC transporters and lipids: An overview

It was first discovered in 1992 that P-glycoprotein (Pgp, ABCB1), an ATP binding cassette (ABC) transporter, can transport phospholipids such as phosphatidylcholine, -ethanolamine and -serine as well as glucosylceramide and glycosphingolipids. Subsequently, many other ABC transporters were identified to act as lipid transporters. For substrate transport by ABC transporters, typically a classic, alternating access model with an ATP-dependent conformational switch between a high and a low affinity substrate binding site is evoked. Transport of small hydrophilic substrates can easily be imagined this way, as the molecule can in principle enter and exit the transporter in the same orientation. Lipids on the other hand need to undergo a 180° degree turn as they translocate from one membrane leaflet to the other. Lipids and lipidated molecules are highly diverse, so there may be various ways how to achieve their flipping and flopping. Nonetheless, an increase in biophysical, biochemical and structural data is beginning to shed some light on specific aspects of lipid transport by ABC transporters. In addition, there is now abundant evidence that lipids affect ABC transporter conformation, dynamics as well as transport and ATPase activity in general. In this review, we will discuss different ways in which lipids and ABC transporters interact and how lipid translocation may be achieved with a focus on the techniques used to investigate these processes. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.

Substrate specificity and mapping of residues critical for transport in the high-affinity glutathione transporter Hgt1p

This study compares the substrate specificity of the yeast glutathione transporter Hgt1p towards reduced glutathione and glutathione conjugates. Mutational analysis of all 13 predicted TMDs identified residues critical for substrate transport and was placed in an ab initio model.

Arsenic Triglutathione [As(GS)3] Transport by Multidrug Resistance Protein 1 (MRP1/ABCC1) Is Selectively Modified by Phosphorylation of Tyr920/Ser921 and Glycosylation of Asn19/Asn23

The ATP-binding cassette (ABC) transporter multidrug resistance protein 1 (MRP1/ABCC1) is responsible for the cellular export of a chemically diverse array of xenobiotics and endogenous compounds. Arsenic, a human carcinogen, is a high-affinity MRP1 substrate as arsenic triglutathione [As(GS)3]. In this study, marked differences in As(GS)3 transport kinetics were observed between MRP1-enriched membrane vesicles prepared from human embryonic kidney 293 (HEK) (Km 3.8 µM and Vmax 307 pmol/mg per minute) and HeLa (Km 0.32 µM and Vmax 42 pmol/mg per minute) cells. Mutant MRP1 lacking N-linked glycosylation [Asn19/23/1006Gln; sugar-free (SF)-MRP1] expressed in either HEK293 or HeLa cells had low Km and Vmax values for As(GS)3, similar to HeLa wild-type (WT) MRP1. When prepared in the presence of phosphatase inhibitors, both WT- and SF-MRP1-enriched membrane vesicles had a high Km value for As(GS)3 (3-6 µM), regardless of the cell line. Kinetic parameters of As(GS)3 for HEK-Asn19/23Gln-MRP1 were similar to those of HeLa/HEK-SF-MRP1 and HeLa-WT-MRP1, whereas those of single glycosylation mutants were like those of HEK-WT-MRP1. Mutation of 19 potential MRP1 phosphorylation sites revealed that HEK-Tyr920Phe/Ser921Ala-MRP1 transported As(GS)3 like HeLa-WT-MRP1, whereas individual HEK-Tyr920Phe- and -Ser921Ala-MRP1 mutants were similar to HEK-WT-MRP1. Together, these results suggest that Asn19/Asn23 glycosylation and Tyr920/Ser921 phosphorylation are responsible for altering the kinetics of MRP1-mediated As(GS)3 transport. The kinetics of As(GS)3 transport by HEK-Asn19/23Gln/Tyr920Glu/Ser921Glu were similar to HEK-WT-MRP1, indicating that the phosphorylation-mimicking substitutions abrogated the influence of Asn19/23Gln glycosylation. Overall, these data suggest that cross-talk between MRP1 glycosylation and phosphorylation occurs and that phosphorylation of Tyr920 and Ser921 can switch MRP1 to a lower-affinity, higher-capacity As(GS)3 transporter, allowing arsenic detoxification over a broad concentration range.

Light-Responsive Biodegradable Nanomedicine Overcomes Multidrug Resistance via NO-Enhanced Chemosensitization

Multidrug resistance (MDR) is responsible for the relatively low effectiveness of chemotherapeutics. Herein, a nitric oxide (NO) gas-enhanced chemosensitization strategy is proposed to overcome MDR by construction of a biodegradable nanomedicine formula based on BNN6/DOX coloaded monomethoxy(polyethylene glycol)-poly(lactic-co-glycolic acid) (mPEG-PLGA). On one hand, the nanomedicine features high biocompatibility due to the high density of PEG and biodegradable PLGA. On the other hand, the nanoformula exhibits excellent stability under physiological conditions but exhibits stimuli-responsive decomposition of BNN6 for NO gas release upon ultraviolet-visible irradiation. More importantly, after NO release is triggered, gas molecules are generated that break the nanoparticle shell and lead to the release of doxorubicin. Furthermore, NO was demonstrated to reverse the MDR of tumor cells and enhance the chemosensitization for doxorubicin therapy.

Multiple myeloma and persistence of drug resistance in the age of novel drugs (Review)

Multiple myeloma (MM) is a mature B cell neoplasm that results in multi-organ failure. The median age of onset, diverse clinical manifestations, heterogeneous survival rate, clonal evolution, intrinsic and acquired drug resistance have impact on the therapeutic management of the disease. Specifically, the emergence of multidrug resistance (MDR) during the course of treatment contributes significantly to treatment failure. The introduction of the immunomodulatory agents and proteasome inhibitors has seen an increase in overall patient survival, however, for the majority of patients, relapse remains inevitable with evidence that these agents, like the conventional chemotherapeutics are also subject to the development of MDR. Clinical management of patients with MM is currently compromised by lack of a suitable procedure to monitor the development of clinical drug resistance in individual patients. The current MM prognostic measures fail to pick the clonotypic tumor cells overexpressing drug efflux pumps, and invasive biopsy is insufficient in detecting sporadic tumors in the skeletal system. This review summarizes the challenges associated with treating the complex disease spectrum of myeloma, with an emphasis on the role of deleterious multidrug resistant clones orchestrating relapse.

Influence of MRP1 G1666A and GSTP1 Ile105Val genetic variants on the urinary and blood arsenic levels of Turkish smelter workers

To understand the cellular mechanisms responsible for arsenic metabolism and transport pathways plays a fundamental role in order to prevent the arsenic-induced toxicity. The effect of MRP1 G1666A and GSTP1 Ile105Val polymorphisms on blood and urinary arsenic levels were determined in 95 Turkish smelter workers. Blood and urinary arsenic concentrations were measured by GF-AAS with Zeeman correction and gene polymorphisms were investigated by PCR-RFLP method. The mean blood and urinary arsenic levels were 21.60±12.28μg/L and 5.58±4.37μg/L, respectively. A significant association between MRP1 1666A allele and urinary arsenic levels was found (p=0.001). GSTP1 Ile105Val polymorphism was detected not to be associated with either blood or urinary arsenic levels (p=0.384, p=0.440, respectively). Significant association was also detected between MRP1A(-)/GSTP1Val(-) genotypes and urinary arsenic levels (p=0.001). This study suggested that MRP1 G1666A alone and, also, combined with GSTP1 Ile105Val were associated with inter-individual variations in urinary arsenic levels, but not with blood arsenic levels.

Thiol-Disulfide Exchange Reactions in the Mammalian Extracellular Environment

Disulfide bonds represent versatile posttranslational modifications whose roles encompass the structure, catalysis, and regulation of protein function. Due to the oxidizing nature of the extracellular environment, disulfide bonds found in secreted proteins were once believed to be inert. This notion has been challenged by the discovery of redox-sensitive disulfides that, once cleaved, can lead to changes in protein activity. These functional disulfides are twisted into unique configurations, leading to high strain and potential energy. In some cases, cleavage of these disulfides can lead to a gain of function in protein activity. Thus, these motifs can be referred to as switches. We describe the couples that control redox in the extracellular environment, examine several examples of proteins with switchable disulfides, and discuss the potential applications of disulfides in molecular biology.

Protective mechanisms of Cucumis sativus in diabetes-related modelsof oxidative stress and carbonyl stress

INTRODUCTION

Oxidative stress and carbonyl stress have essential mediatory roles in the development of diabetes and its related complications through increasing free radicals production and impairing antioxidant defense systems. Different chemical and natural compounds have been suggested for decreasing such disorders associated with diabetes. The objectives of the present study were to investigate the protective effects of Cucumis sativus (C. sativus) fruit (cucumber) in oxidative and carbonyl stress models. These diabetes-related models with overproduction of reactive oxygen species (ROS) and reactive carbonyl species (RCS) simulate conditions observed in chronic hyperglycemia.

METHODS

Cytotoxicity induced by cumene hydroperoxide (oxidative stress model) or glyoxal (carbonyl stress model) were measured and the protective effects of C. sativus were evaluated using freshly isolated rat hepatocytes.

RESULTS

Aqueous extract of C. sativus fruit (40 μg/mL) prevented all cytotoxicity markers in both the oxidative and carbonyl stress models including cell lysis, ROS formation, membrane lipid peroxidation, depletion of glutathione, mitochondrial membrane potential decline, lysosomal labialization, and proteolysis. The extract also protected hepatocytes from protein carbonylation induced by glyoxal. Our results indicated that C. sativus is able to prevent oxidative stress and carbonyl stress in the isolated hepatocytes.

CONCLUSION

It can be concluded that C. sativus has protective effects in diabetes complications and can be considered a safe and suitable candidate for decreasing the oxidative stress and carbonyl stress that is typically observed in diabetes mellitus.

A Rare Class of New Dimeric Naphthoquinones from Diospyros lotus have Multidrug Reversal and Antiproliferative Effects

Three new dimeric naphthoquinones, 5,4′-dihydroxy-1′-methoxy-6,6′-dimethyl-7,3′-binaphthyl-1,4,5′,8′-tetraone (1), 5′,8′-dihydroxy-5-methoxy-6,6′-dimethyl-7,3′-binaphthyl-1,4,1′,4′-tetraone (2) and 8,5′,8′-trihydroxy-6,6′-dimethyl-7,3′-binaphthyl-1,4,1′,4′-tetraone (3), were isolated from the roots of Diospyros lotus. Their structures were elucidated by spectroscopic techniques, including 1D and 2D NMR, such as HSQC, HMBS, NOESY, and J-resolved. Compounds 1–3 were evaluated for their effects on the reversion of multidrug resistance (MDR) mediated by P-glycoprotein through use of the rhodamine-123 exclusion screening test on human ABCB1 gene transfected L5178Y mouse T-cell lymphoma. Compounds 1–3 were also assessed for their antiproliferative and cytotoxic effects on L5178 and L5178Y mouse T-cell lymphoma lines. Both 1 and 2 exhibited promising antiproliferative and MDR-reversing effects in a dose-dependent manner. The effects of the tested compounds on the activity of doxorubicin were observed to vary from slight antagonism to antagonism.

Upregulation of cellular glutathione levels in human ABCB5- and murine Abcb5-transfected cells

Background

Previously, we have demonstrated that human ABCB5 is a full-sized ATP-binding cassette transporter that shares strong homology with ABCB1/P-glycoprotein. ABCB5-transfected cells showed resistance to taxanes and anthracyclines. Herein, we further screened ABCB5 substrates, and explored the mechanism of resistance.

Methods

Sensitivity of the cells to test compounds was evaluated using cell growth inhibition assay. Cellular levels of buthionine sulfoximine (BSO), glutathione and amino acids were measured using HPLC and an enzyme-based assay. Cellular and vesicular transport of glutathione was evaluated by a radiolabeled substrate. Expression levels of glutathione-metabolizing enzymes were assessed by RT-PCR.

Results

Human ABCB5-transfected 293/B5-11 cells and murine Abcb5-transfected 293/mb5-8 cells showed 6.5- and 14-fold higher resistance to BSO than the mock-transfected 293/mock cells, respectively. BSO is an inhibitor of gamma-glutamylcysteine ligase (GCL), which is a key enzyme of glutathione synthesis. 293/B5-11 and 293/mb5-8 cells also showed resistance to methionine sulfoximine, another GCL inhibitor. A cellular uptake experiment revealed that BSO accumulation in 293/B5-11 and 293/mb5-8 cells was similar to that in 293/mock cells, suggesting that BSO is not an ABCB5 substrate. The cellular glutathione content in 293/B5-11 and 293/mb5-8 cells was significantly higher than that in 293/mock cells. Evaluation of the BSO effect on the cellular glutathione content showed that compared with 293/mock cells the BSO concentration required for a 50 % reduction in glutathione content in 293/B5-11 and 293/mb5-8 cells was approximately 2- to 3-fold higher. This result suggests that the BSO resistance of the ABCB5- and Abcb5-transfected cells can be attributed to the reduced effect of BSO on the transfectants. Cellular and vesicular transport assays showed that the transport of radiolabeled glutathione in 293/B5-11 cells was similar to that in 293/mock cells. The mRNA expression of genes encoding glutathione-metabolizing enzymes in 293/B5-11 cells was similar to that in 293/mock cells. The cellular content of Glu, a precursor of glutathione, in 293/B5-11 and 293/mb5-8 cells was higher than that in 293/mock cells.

Conclusions

ABCB5/Abcb5-transfected cells showed resistance to BSO, which is not a substrate of ABCB5. Our results suggest that ABCB5/Abcb5 upregulates cellular glutathione levels to protect cells from various poisons.

Developmental effects of two different copper oxide nanomaterials in sea urchin (Lytechinus pictus) embryos

Copper oxide nanomaterials (nano-CuOs) are widely used and can be inadvertently introduced into estuarine and marine environments. We analyzed the effects of different nano-CuOs (a synthesized and a less-pure commercial form), as well as ionic copper (CuSO4) on embryo development in the white sea urchin, a well-known marine model. After 96 h of development with both nano-CuO exposures, we did not detect significant oxidative damage to proteins but did detect decreases in total antioxidant capacity. We show that the physicochemical characteristics of the two nano-CuOs play an essential role in their toxicities. Both nano-CuOs were internalized by embryos and their differential dissolution was the most important toxicological parameter. The synthesized nano-CuO showed greater toxicity (EC50 = 450 ppb of copper) and had increased dissolution (2.5% by weight over 96 h) as compared with the less-pure commercial nano-CuO (EC50 = 5395 ppb of copper, 0.73% dissolution by weight over 96 h). Copper caused specific developmental abnormalities in sea urchin embryos including disruption of the aboral-oral axis as a result in changes to the redox environment caused by dissolution of internalized nano-CuO. Abnormal skeleton formation also occurred.

MRP1 expression in bronchoalveolar lavage cells in subjects with lung cancer who were chronically exposed to arsenic

Alteration of multidrug resistance-associated protein-1 (MRP1) expression has been associated with certain lung diseases, and this protein may be pivotal in protecting the lungs against endogenous or exogenous toxic compounds. The aim of this study was to evaluate and compare the expression of MRP1 in bronchoalveolar cells from subjects with and without lung cancer who had been chronically exposed to arsenic through drinking water. MRP1 expression was assessed in bronchoalveolar cells in a total of 102 participants. MRP1 expression was significantly decreased in those with arsenic urinary levels >50 μg/L when compared with the controls. In conclusion, chronic arsenic exposure negatively correlates with the expression of MRP1 in BAL cells in patients with lung cancer.

Pseudoxanthoma elasticum and skin: Clinical manifestations, histopathology, pathomechanism, perspectives of treatment

Pseudoxantoma elasticum (PXE), also known as Groenblad-Strandberg syndrome, is a rare heritable disease with an estimated prevalence of 1:50,000 in the general population. PXE is considered a prototype of multisystem ectopic mineralization disorders and it is characterized by aberrant mineralization of soft connective tissue with degeneration of the elastic fibers, involving primarily the eyes, the cardiovascular system, and the skin. Cutaneous lesions consist of small, asymptomatic, yellowish papules or larger coalescent plaques, typically located on the neck and the flexural areas. PXE is caused by mutations in the ABCC6 (ATP-binding cassette subfamily C member 6) gene that encodes a transmembrane ATP binding efflux transporter, normally expressed in the liver and the kidney; however, the exact mechanism of ectopic mineralization remains largely unknown. The histological examination of cutaneous lesions, revealing accumulation of pleomorphic elastic structures in middermis, is essential for the definitive diagnosis of PXE, excluding PXE-like conditions. PXE is currently an intractable disease; although the cutaneous findings primarily present a cosmetic problem, they signify the risk for development of ocular and cardiovascular complications associated with considerable morbidity and mortality. The purpose of this review is to present a comprehensive overview of this rare form of hereditary connective tissue disorders, focus on the pathogenesis, the clinical manifestation, and the differential diagnosis of PXE. Emphasis is also placed on the management of cutaneous lesions and treatment perspectives of PXE.

Resistance to cancer chemotherapy: failure in drug response from ADME to P-gp

Cancer chemotherapy resistance (MDR) is the innate and/or acquired ability of cancer cells to evade the effects of chemotherapeutics and is one of the most pressing major dilemmas in cancer therapy. Chemotherapy resistance can arise due to several host or tumor-related factors. However, most current research is focused on tumor-specific factors and specifically genes that handle expression of pumps that efflux accumulated drugs inside malignantly transformed types of cells. In this work, we suggest a wider and alternative perspective that sets the stage for a future platform in modifying drug resistance with respect to the treatment of cancer.

Characterisation of Dermanyssus gallinae glutathione S-transferases and their potential as acaricide detoxification proteins

BACKGROUND

Glutathione S-transferases (GSTs) facilitate detoxification of drugs by catalysing the conjugation of the reduced glutathione (GSH) to electrophilic xenobiotic substrates and therefore have a function in multi-drug resistance. As a result, knowledge of GSTs can inform both drug resistance in, and novel interventions for, the control of endo- and ectoparasite species. Acaricide resistance and the need for novel control methods are both pressing needs for Dermanyssus gallinae, a highly economically important haematophagous ectoparasite of poultry.

METHODS

A transcriptomic database representing D. gallinae was examined and 11 contig sequences were identified with GST BlastX identities. The transcripts represented by 3 contigs, designated Deg-GST-1, -2 and -3, were fully sequenced and further characterized by phylogenetic analysis. Recombinant versions of Deg-GST-1, -2 and -3 (rDeg-GST) were enzymically active and acaricide-binding properties of the rDeg-GSTs were established by evaluating the ability of selected acaricides to inhibit the enzymatic activity of rDeg-GSTs.

RESULTS

6 of the identified GSTs belonged to the mu class, followed by 3 kappa, 1 omega and 1 delta class molecules. Deg-GST-1 and -3 clearly partitioned with orthologous mu class GSTs and Deg-GST-2 partitioned with delta class GSTs. Phoxim, permethrin and abamectin significantly inhibited rDeg-GST-1 activity by 56, 35 and 17% respectively. Phoxim also inhibited rDeg-2-GST (14.8%) and rDeg-GST-3 (20.6%) activities.

CONCLUSIONS

Deg-GSTs may have important roles in the detoxification of pesticides and, with the increased occurrence of acaricide resistance in this species worldwide, Deg-GSTs are attractive targets for novel interventions.

Multidrug resistance characterization in multicellular tumour spheroids from two human lung cancer cell lines

Background

Most of the knowledge about the mechanisms of multidrug resistance in lung cancer has been achieved through the use of cell lines isolated from tumours cultivated either in suspensions of isolated cells or in monolayers and following exposition to different cytostatic agents. However, tumour cell lines growing as multicellular tumour spheroids (MTS) frequently develop multicellular resistance in a drug-independent form. The aim of this study was to characterize the phenotypic and functional differences between two human NSCLC cell lines (INER-37 and INER-51) grown as traditional monolayer cultures versus as MTS.

Methods

After 72 hours treatment with anticancer drugs, chemosensitivity in monolayers and tumour spheroids cultures was assessed using MTT assay. Reverse transcription-polymerase chain reaction was employed to detect the mRNAs of multidrug resistance-related genes. The expression of P-gp was analyzed by immunohistochemical staining and cell cycle profiles were analyzed using FACS.

Results

The results indicate that when grown as MTS each lung cancer cell line had different morphologies as well as and abrogation of cell proliferation with decrease of the G₂/M phase. Also, MTS acquired multicellular resistance to several chemotherapeutic agents in only a few days of culture which were accomplished by significant changes in the expression of MDR-related genes.

Conclusion

Overall, the MTS culture changed the cellular response to drugs nevertheless each of the cell lines studied seems to implement different mechanisms to acquire multicellular resistance.

Influence of multidrug resistance and drug transport proteins on chemotherapy drug metabolism

INTRODUCTION

Chemotherapy involving the use of anticancer drugs remains an important strategy in the overall management of patients with metastatic cancer. Acquisition of multidrug resistance remains a major impediment to successful chemotherapy. Drug transporters in cell membranes and intracellular drug metabolizing enzymes contribute to the resistance phenotype and determine the pharmacokinetics of anticancer drugs in the body.

AREAS COVERED

ATP-binding cassette (ABC) transporters mediate the transport of endogenous metabolites and xenobiotics including cytotoxic drugs out of cells. Solute carrier (SLC) transporters mediate the influx of cytotoxic drugs into cells. This review focuses on the substrate interaction of these transporters, on their biology and what role they play together with drug metabolizing enzymes in eliminating therapeutic drugs from cells.

EXPERT OPINION

The majority of anticancer drugs are substrates for the ABC transporter and SLC transporter families. Together, these proteins have the ability to control the influx and the efflux of structurally unrelated chemotherapeutic drugs, thereby modulating the intracellular drug concentration. These interactions have important clinical implications for chemotherapy because ultimately they determine therapeutic efficacy, disease progression/relapse and the success or failure of patient treatment.

Glutathione and multidrug resistance protein transporter mediate a self-propelled disposal of bismuth in human cells

Glutathione and multidrug resistance protein (MRP) play an important role on the metabolism of a variety of drugs. Bismuth drugs have been used to treat gastrointestinal disorder and Helicobacter pylori infection for decades without exerting acute toxicity. They were found to interact with a wide variety of biomolecules, but the major metabolic pathway remains unknown. For the first time (to our knowledge), we systematically and quantitatively studied the metabolism of bismuth in human cells. Our data demonstrated that over 90% of bismuth was passively absorbed, conjugated to glutathione, and transported into vesicles by MRP transporter. Mathematical modeling of the system reveals an interesting phenomenon. Passively absorbed bismuth consumes intracellular glutathione, which therefore activates de novo biosynthesis of glutathione. Reciprocally, sequestration by glutathione facilitates the passive uptake of bismuth and thus completes a self-sustaining positive feedback circle. This mechanism robustly removes bismuth from both intra- and extracellular space, protecting critical systems of human body from acute toxicity. It elucidates the selectivity of bismuth drugs between human and pathogens that lack of glutathione, such as Helicobacter pylori, opening new horizons for further drug development.

Multi-Drug Resistance ABC Transporter Inhibition Enhances Murine Ventral Prostate Stem/Progenitor Cell Differentiation

Multi-drug resistance (MDR)-ATP binding cassette (ABC) transporters, ABCB1, ABCC1, and ABCG2 participate in the efflux of steroid hormones, estrogens, and androgens, which regulate prostate development and differentiation. The role of MDR-ABC efflux transporters in prostate epithelial proliferation and differentiation remains unclear. We hypothesized that MDR-ABC transporters regulate prostate differentiation and epithelium regeneration. Prostate epithelial differentiation was studied using histology, sphere formation assay, and prostate regeneration induced by cycles of repeated androgen withdrawal and replacement. Embryonic deletion of Abcg2 resulted in a decreased number of luminal cells in the prostate and increased sphere formation efficiency, indicating an imbalance in the prostate epithelial differentiation pattern. Decreased luminal cell number in the Abcg2 null prostate implies reduced differentiation. Enhanced sphere formation efficiency in Abcg2 null prostate cells implies activation of the stem/progenitor cells. Prostate regeneration was associated with profound activation of the stem/progenitor cells, indicating the role of Abcg2 in maintaining stem/progenitor cell pool. Since embryonic deletion of Abcg2 may result in compensation by other ABC transporters, pharmacological inhibition of MDR-ABC efflux was performed. Pharmacological inhibition of MDR-ABC efflux enhanced prostate epithelial differentiation in sphere culture and during prostate regeneration. In conclusion, Abcg2 deletion leads to activation of the stem/progenitor cells and enhances differentiating divisions; and pharmacological inhibition of MDR-ABC efflux leads to epithelial differentiation. Our study demonstrates for the first time that MDR-ABC efflux transporter inhibition results in enhanced prostate epithelial cell differentiation.

Gamma-glutamyl transpeptidase: redox regulation and drug resistance

The expression of gamma-glutamyl transpeptidase (GGT) is essential to maintaining cysteine levels in the body. GGT is a cell surface enzyme that hydrolyzes the gamma-glutamyl bond of extracellular reduced and oxidized glutathione, initiating their cleavage into glutamate, cysteine (cystine), and glycine. GGT is normally expressed on the apical surface of ducts and glands, salvaging the amino acids from glutathione in the ductal fluids. GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress. The induction of GGT is observed in tumors with elevated levels of intracellular glutathione. Studies in models of hepatocarcinogenesis show that GGT expression in foci of preneoplastic hepatocytes provides a selective advantage to the cells during tumor promotion with agents that deplete intracellular glutathione. Similarly, expression of GGT in tumors enables cells to maintain elevated levels of intracellular glutathione and to rapidly replenish glutathione during treatment with prooxidant anticancer therapy. In the clinic, the expression of GGT in tumors is correlated with drug resistance. The inhibitors of GGT block GGT-positive tumors from accessing the cysteine in extracellular glutathione. They also inhibit GGT activity in the kidney, which results in the excretion of GSH in the urine and a rapid decrease in blood cysteine levels, leading to depletion of intracellular GSH in both GGT-positive and GGT-negative tumors. GGT inhibitors are being developed for clinical use to sensitize tumors to chemotherapy.

A practical fluorogenic substrate for high-throughput screening of glutathione S-transferase inhibitors

We report herein 3,4-DNADCF, a pH less sensitive new fluorogenic substrate, for high-throughput screening of GST inhibitors.

The flavonoid quercetin: possible solution for anthracycline-induced cardiotoxicity and multidrug resistance

Anthracycline chemotherapy is often used in the treatment of various malignancies. Its application, however, encounters several limitations due to development of serious side effects, mainly cardiotoxicity and may be ineffective due to multidrug resistance (MDR). Many different compounds have been evaluated as poorly effective in the protection against anthracycline side effects and in the prevention from MDR. Thus, continuous investigational efforts are necessary to find valuable protectants and the flavonoid quercetin (Q) seems to be a promising candidate. It is present in relatively high amounts in a human diet and the lack of its toxicity, including genotoxicity has been confirmed. The structure of Q favours its high antioxidant activity, the potential to inhibit the activity of oxidative enzymes and to interact with membrane transporter proteins responsible for development of MDR, e.g. P-glycoprotein. Furthermore, Q can influence cellular signalling and gene expression, and thus, alter response to exogenous genotoxicants and oxidative stress in normal cells. It accounts for its chemopreventive and anticancer properties. Overall, these properties might indicate the possibility of application of Q as cardioprotectant during anthracycline chemotherapy. Moreover, numerous biological properties displayed by Q might possibly result in the reversal of MDR in tumour cells and improve the efficacy of chemotherapy. However, these beneficial effects towards anthracycline-induced complications of chemotherapy have to be further explored and confirmed both in animal and clinical studies. Concurrently, investigations aimed at improvement of the bioavailability of Q and further elucidation of its metabolism after application in combination with anthracyclines are needed.

Multidrug resistance protein 1 (MRP1, ABCC1), a "multitasking" ATP-binding cassette (ABC) transporter

The multidrug resistance protein 1 (MRP1) encoded by ABCC1 was originally discovered as a cause of multidrug resistance in tumor cells. However, it is now clear that MRP1 serves a broader role than simply mediating the ATP-dependent efflux of drugs from cells. The antioxidant GSH and the pro-inflammatory cysteinyl leukotriene C4 have been identified as key physiological organic anions effluxed by MRP1, and an ever growing body of evidence indicates that additional lipid-derived mediators are also substrates of this transporter. As such, MRP1 is a multitasking transporter that likely influences the etiology and progression of a host of human diseases.

YCF1-mediated cadmium resistance in yeast is dependent on copper metabolism and antioxidant enzymes

AIMS

Acquisition and detoxification of metal ions are vital biological processes. Given the requirement of metallochaperones in cellular copper distribution and metallation of cuproproteins, this study investigates whether the metallochaperones also deliver metal ions for transporters functioning in metal detoxification.

RESULTS

Resistance to excess cadmium and copper of the yeast Saccharomyces cerevisiae, which is conferred by PCA1 and CaCRP1 metal efflux P-type ATPases, respectively, does not rely on known metallochaperones, Atx1p, Ccs1p, and Cox17p. Copper deficiency induced by the expression of CaCRP1 encoding a copper exporter occurs in the absence of Atx1p. Intriguingly, CCS1 encoding the copper chaperone for superoxide dismutase 1 (Sod1p) is necessary for cadmium resistance that is mediated by Ycf1p, a vacuolar cadmium sequestration transporter. This is attributed to Ccs1p's role in the maturation of Sod1p rather than its direct interaction with Ycf1p for cadmium transfer. Functional defect in Ycf1p associated with the absence of Sod1p as well as another antioxidant enzyme Glr1p is rescued by anaerobic growth or substitutions of specific cysteine residues of Ycf1p to alanine or serine. This further supports oxidative inactivation of Ycf1p in the absence of Ccs1p, Sod1p, or Glr1p.

INNOVATION

These results provide new insights into the mechanisms of metal metabolism, interaction among metal ions, and the roles for antioxidant systems in metal detoxification.

CONCLUSION

Copper metabolism and antioxidant enzymes maintain the function of Ycf1p for cadmium defense.

Lapatinib antagonizes multidrug resistance-associated protein 1-mediated multidrug resistance by inhibiting its transport function

Lapatinib, a tyrosine kinase inhibitor, is used in the treatment of advanced or metastatic breast cancer overexpressing human epidermal receptor 2 (HER2). Lapatinib can modulate the function of ATP-binding cassette (ABC) transporters (ABCB1 and ABCG2), which are the major mechanism responsible for multidrug resistance (MDR) in cancer. In this study, we investigated the effect of lapatinib on multidrug resistance-associated protein 1 (MRP1 [ABCC1]), MRP2 (ABCC2), MRP4 (ABCC4) and lung relative resistance protein (LRP) drug efflux pumps. We demonstrated that lapatinib could enhance the efficacy of conventional chemotherapeutic agents in MRP1-overexpressing cells in vitro and in vivo, but no effect in MRP2-, MPR4- and LRP-overexpressing cells. Furthermore, lapatinib significantly increased the accumulation of rhodamine 123 (Rho123) and doxorubicin (DOX) in MRP1-overexpressing cells. However, lapatinib did not alter the protein or mRNA expression levels of MRP1. Further studies showed that the level of phosphorylation of AKT and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) were not altered at the indicated concentrations of lapatinib. In conclusion, lapatinib enhanced the efficacy of conventional chemotherapeutic agents in MRP1-overexpressing cells by inhibiting MRP1 transport function without altering the level of AKT or ERK1/2 phosphorylation. These findings will encourage the clinical research of lapatinib combined with conventional chemotherapeutic drugs in MRP1-overexpressing cancer patients.

Glutathione depletion regulates both extrinsic and intrinsic apoptotic signaling cascades independent from multidrug resistance protein 1

Glutathione (GSH) depletion is an important hallmark of apoptosis. We previously demonstrated that GSH depletion, by its efflux, regulates apoptosis by modulation of executioner caspase activity. However, both the molecular identity of the GSH transporter(s) involved and the signaling cascades regulating GSH loss remain obscure. We sought to determine the role of multidrug resistance protein 1 (MRP1) in GSH depletion and its regulatory role on extrinsic and intrinsic pathways of apoptosis. In human lymphoma cells, GSH depletion was stimulated rather than inhibited by pharmacological blockage of MRP1 with MK571. GSH loss was dependent on initiator caspases 8 and 9 activity. Genetic knock-down (>60 %) of MRP1 by stable transfection with short hairpin small interfering RNA significantly reduced MRP1 protein levels, which correlated directly with the loss of MRP1-mediated anion transport. However, GSH depletion and apoptosis induced by both extrinsic and intrinsic pathways were not affected by MRP1 knock-down. Interestingly, stimulation of GSH loss by MK571 also enhanced the initiator phase of apoptosis by stimulating initiator caspase 8 and 9 activity and pro-apoptotic BCL-2 interacting domain cleavage. Our results clearly show that caspase-dependent GSH loss and apoptosis are not mediated by MRP1 proteins and that GSH depletion stimulates the initiation phase of apoptosis in lymphoid cells.

3β-Acetyl tormentic acid reverts MRP1/ABCC1 mediated cancer resistance through modulation of intracellular levels of GSH and inhibition of GST activity

ABC transporter overexpression is an important mechanism of multidrug resistance (MDR) and one of the main obstacles to successful cancer treatment. As these proteins actively remove chemotherapeutics from the tumor cells, the pharmacological inhibition of their activity is a possible strategy to revert drug resistance. Moreover, the ability of MDR inhibitors to sensitize resistant cells to conventional drugs is important for their clinical use. Evidence has shown that the multidrug resistance protein 1 (MRP1/ABCC1) is a negative prognostic marker in patients with lung, gastric, or breast cancers or neuroblastoma. Previous data have shown that 3β-acetyl tormentic acid (3ATA) inhibits the transport activity of the protein MRP1/ABCC1. In this study, we evaluated the ability of 3ATA to sensitize an MDR cell line (GLC4/ADR), which overexpresses MRP1, and investigated the anti-MRP1 mechanisms activated by 3ATA. The results showed that 3ATA is able to reverse the resistance of the MDR cell line to doxorubicin and vincristine, two drugs that are commonly used in cancer chemotherapy. Regarding the sensitizing mechanism induced by 3ATA, this work shows that the triterpene does not modulate the expression of MRP1/ABCC1 but is able to reduce total intracellular glutathione (GSH) levels and decrease the activity of glutathione-s-transferase (GST), the enzyme responsible for the glutathione conjugation of xenobiotics. Together, these results show that 3ATA sensitizes the MDR cell line overexpressing MRP1/ABCC1 to antineoplastic drugs and that this effect is mediated by the modulation of intracellular levels of GSH and GST activity.

A conserved mitochondrial ATP-binding cassette transporter exports glutathione polysulfide for cytosolic metal cofactor assembly

An ATP-binding cassette transporter located in the inner mitochondrial membrane is involved in iron-sulfur cluster and molybdenum cofactor assembly in the cytosol, but the transported substrate is unknown. ATM3 (ABCB25) from Arabidopsis thaliana and its functional orthologue Atm1 from Saccharomyces cerevisiae were expressed in Lactococcus lactis and studied in inside-out membrane vesicles and in purified form. Both proteins selectively transported glutathione disulfide (GSSG) but not reduced glutathione in agreement with a 3-fold stimulation of ATPase activity by GSSG. By contrast, Fe²⁺ alone or in combination with glutathione did not stimulate ATPase activity. Arabidopsis atm3 mutants were hypersensitive to an inhibitor of glutathione biosynthesis and accumulated GSSG in the mitochondria. The growth phenotype of atm3-1 was strongly enhanced by depletion of the mitochondrion-localized, GSH-dependent persulfide oxygenase ETHE1, suggesting that the physiological substrate of ATM3 contains persulfide in addition to glutathione. Consistent with this idea, a transportomics approach using mass spectrometry showed that glutathione trisulfide (GS-S-SG) was transported by Atm1. We propose that mitochondria export glutathione polysulfide, containing glutathione and persulfide, for iron-sulfur cluster assembly in the cytosol.

Structure and function of the bacterial heterodimeric ABC transporter CydDC: stimulation of ATPase activity by thiol and heme compounds

In Escherichia coli, the biogenesis of both cytochrome bd-type quinol oxidases and periplasmic cytochromes requires the ATP-binding cassette-type cysteine/GSH transporter, CydDC. Recombinant CydDC was purified as a heterodimer and found to be an active ATPase both in soluble form with detergent and when reconstituted into a lipid environment. Two-dimensional crystals of CydDC were analyzed by electron cryomicroscopy, and the protein was shown to be made up of two non-identical domains corresponding to the putative CydD and CydC subunits, with dimensions characteristic of other ATP-binding cassette transporters. CydDC binds heme b. Detergent-solubilized CydDC appears to adopt at least two structural states, each associated with a characteristic level of bound heme. The purified protein in detergent showed a weak basal ATPase activity (approximately 100 nmol P_i/min/mg) that was stimulated ∼3-fold by various thiol compounds, suggesting that CydDC could act as a thiol transporter. The presence of heme (either intrinsic or added in the form of hemin) led to a further enhancement of thiol-stimulated ATPase activity, although a large excess of heme inhibited activity. Similar responses of the ATPase activity were observed with CydDC reconstituted into E. coli lipids. These results suggest that heme may have a regulatory role in CydDC-mediated transmembrane thiol transport.

Transcriptomic evidence for a dramatic functional transition of the malpighian tubules after a blood meal in the Asian tiger mosquito Aedes albopictus

Background

The consumption of a vertebrate blood meal by adult female mosquitoes is necessary for their reproduction, but it also presents significant physiological challenges to mosquito osmoregulation and metabolism. The renal (Malpighian) tubules of mosquitoes play critical roles in the initial processing of the blood meal by excreting excess water and salts that are ingested. However, it is unclear how the tubules contribute to the metabolism and excretion of wastes (e.g., heme, ammonia) produced during the digestion of blood.

Methodology/Principal Findings

Here we used RNA-Seq to examine global changes in transcript expression in the Malpighian tubules of the highly-invasive Asian tiger mosquito Aedes albopictus during the first 24 h after consuming a blood meal. We found progressive, global changes in the transcriptome of the Malpighian tubules isolated from mosquitoes at 3 h, 12 h, and 24 h after a blood meal. Notably, a DAVID functional cluster analysis of the differentially-expressed transcripts revealed 1) a down-regulation of transcripts associated with oxidative metabolism, active transport, and mRNA translation, and 2) an up-regulation of transcripts associated with antioxidants and detoxification, proteolytic activity, amino-acid metabolism, and cytoskeletal dynamics.

Conclusions/Significance

The results suggest that blood feeding elicits a functional transition of the epithelium from one specializing in active transepithelial fluid secretion (e.g., diuresis) to one specializing in detoxification and metabolic waste excretion. Our findings provide the first insights into the putative roles of mosquito Malpighian tubules in the chronic processing of blood meals.

The Asian tiger mosquito Aedes albopictus is a vector of several medically-important arboviruses and one of the most invasive mosquito species in the world. Existing control measures for mosquitoes are presently being challenged by the emergence of resistance to insecticides that target the nervous system. Thus, it is necessary to identify novel physiological targets to guide the development of new insecticides. We recently demonstrated that the ‘kidneys’ (Malpighian tubules) of mosquitoes offer a valuable, new physiological target for insecticides. However, our understanding of how this tissue contributes to the chronic metabolic processing of blood meals by mosquitoes is limited. Here we characterize the changes in transcript expression that occur in the Malpighian tubules of adult female A. albopictus with the goal of identifying key molecular pathways that may reveal valuable targets for insecticide development. We find dramatic changes in transcript accumulation in Malpighian tubules, which 1) provide new insights into the potential functional roles of Malpighian tubules after a blood meal, and 2) reveal new potential molecular pathways and targets to guide the development of new insecticides that would disrupt the renal functions of mosquitoes.

The accumulation and efflux of lead partly depend on ATP-dependent efflux pump-multidrug resistance protein 1 and glutathione in testis Sertoli cells

Since lead accumulation is toxic to cells, its excretion is crucial for organisms to survive the toxicity. In this study, mouse testis sertoli (TM4) and Mrp1 lower-expression TM4-sh cells were used to explore the lead accumulation characteristics, and the role of ATP-dependent efflux pump-multidrug resistance protein 1 (Mrp1) in lead excretion. TM4 cells possess Mrp-like transport activity. The expression levels of mrp1 mRNA and Mrp1 increased after lead treatments at first and then decreased. The maximum difference of relative mRNA expression reached 10 times. In the presence of lead acetate, the amount of cumulative lead in TM4-sh was much higher than that in TM4. After the treatment with lead acetate at 10-40 μM for 12h or 24h, the differences were about 2-8 times. After with the switch to lead-free medium, the cellular lead content in TM4-sh remains higher than that in TM4 cells at 1,3, 6, and 9h time points (P<0.01). Energy inhibitor sodium azide, Mrp inhibitors MK571 and glutathione (GSH) biosynthesis inhibitor BSO could block lead efflux from TM4 cells significantly. These results indicate that lead excretion may be mediated by Mrp1 and GSH in TM4 cells. Mrp1 could be one of the important intervention points for lead detoxification.

Inflammation, DAMPs, tumor development, and progression: a vicious circle orchestrated by redox signaling

SIGNIFICANCE

Increasing evidence indicates that cancer development and progression are promoted by the joint action of redox distress and inflammation, supporting the potential impact of therapies aimed at restoring the redox homeostasis and fighting inflammation.

RECENT ADVANCES

Most of the literature of the last 40 years converges to the view that continuous oxidative stress and chronic inflammation sustain each other, leads to transformation of a normal cell to a neoplastic cell, and promotes tumor progression. Some recent findings, however, support an alternative model whereby the increased production of reactive oxygen species (ROS) is an attempt to defend more than a pathogenetic factor in cancer. Rather, tumor development and progression may be promoted by an excess of antioxidants, induced in both transformed cells and recruited inflammatory cells as an adaptive response to ROS.

CRITICAL ISSUES

Although the link among redox stress, chronic inflammation, and cancer is widely recognized, the underlying mechanisms are far to be understood. The redox unbalance of the microenvironment is likely to modulate the bioactivity of damage-associated molecular pattern molecules such as HMGB1, which are released by stressed tissues and play pleiotropic functions on tumor and inflammatory cells, but how this occur, and the relevant consequences, are still unclear.

FUTURE DIRECTIONS

In vivo measurement of cell redox status is an important challenge for future investigations. The improvement of the methodologies for ROS and antioxidant detection will allow a better understanding of the redox-related events in the tumor microenvironment with tremendous application potential in the development of rational combination therapies for cancer treatment.

Mechanism of cellular accumulation of an iridium(III) pentamethylcyclopentadienyl anticancer complex containing a C,N-chelating ligand

The effect of replacement of the N,N-chelating ligand 1,10-phenanthroline (phen) in the Ir(III) pentamethylcyclopentadienyl (Cp*) complex [(η(5)-Cp*)(Ir)(phen)Cl](+) (2) with the C,N-chelating ligand 7,8-benzoquinoline (bq) to give [(η(5)-Cp*)(Ir)(bq)Cl] (1) on the cytotoxicity of these Cp*Ir(III) complexes toward cancer cell lines was investigated. Complex 2 is inactive, similar to other Cp*Ir(III) complexes containing the N,N-chelating ligands. In contrast, a single atom change (C(-) for N) in the chelating N,N ligand resulted in potency in human ovarian carcinoma cisplatin-sensitive A2780 cells, and, strikingly, 1 is active in the cisplatin-resistant human breast cancer MCF-7 and A2780/cisR cells. Replacement of the N,N-chelating ligand with the C,N-chelating ligand gives rise to increased hydrophobicity, leading to higher cellular accumulation, higher DNA-bound iridium in cells and higher cytotoxicity. The pathways involved in cellular accumulation of 1 have been further explored and compared with conventional cisplatin. The results show that both energy-independent passive diffusion and energy-dependent transport play a role in accumulation of 1. Further results were consistent with involvement of p-glycoprotein, multidrug resistance-associated protein 1 and glutathione metabolism in the efflux of 1. In contrast, the internalization of 1 mediated by the endocytotic uptake pathway(s) seems less likely. Understanding the factors which contribute to the mechanism of cellular accumulation of this Ir(III) complex can now lead to the design of structurally similar metal complexes for antitumor chemotherapy.

Reversal of ATP-binding cassette drug transporter activity to modulate chemoresistance: why has it failed to provide clinical benefit?

Enhanced drug extrusion from cells due to the overexpression of the ATP-binding cassette (ABC) drug transporters inhibits the cytotoxic effects of structurally diverse and mechanistically unrelated anticancer agents and is a major cause of multidrug resistance (MDR) of human malignancies. Multiple compounds can suppress the activity of these efflux transporters and sensitize resistant tumor cells, but despite promising preclinical and early clinical data, they have yet to find a role in oncologic practice. Based on the knowledge of the structure, function, and distribution of MDR-related ABC transporters and the results of their preclinical and clinical evaluation, we discuss probable reasons why these inhibitors have not improved the outcome of therapy for cancer patients. We also outline new MDR-reversing strategies that directly target ABC transporters or circumvent relevant signaling pathways.

Oxidative stress in sickle cell disease: an overview of erythrocyte redox metabolism and current antioxidant therapeutic strategies

Erythrocytes have an environment of continuous pro-oxidant generation due to the presence of hemoglobin (Hb), which represents an additional and quantitatively significant source of superoxide (O2(-)) generation in biological systems. To counteract oxidative stress, erythrocytes have a self-sustaining antioxidant defense system. Thus, red blood cells uniquely function to protect Hb via a selective barrier allowing gaseous and other ligand transport as well as providing antioxidant protection not only to themselves but also to other tissues and organs in the body. Sickle hemoglobin molecules suffer repeated polymerization/depolymerization generating greater amounts of reactive oxygen species, which can lead to a cyclic cascade characterized by blood cell adhesion, hemolysis, vaso-occlusion, and ischemia-reperfusion injury. In other words, sickle cell disease is intimately linked to a pathophysiologic condition of multiple sources of pro-oxidant processes with consequent chronic and systemic oxidative stress. For this reason, newer therapeutic agents that can target oxidative stress may constitute a valuable means for preventing or delaying the development of organ complications.