Characterization of rhodamine-123, calcein and 5(6)-carboxy-2',7'-dichlorofluorescein (CDCF) export via MRP2 (ABCC2) in MES-SA and A549 cells

Aloe-emodin induces hepatotoxicity by the inhibition of multidrug resistance protein 2

BACKGROUND

Aloe-emodin (AE) is among the primary bioactive anthraquinones present in traditional Chinese medicinal plants such as Rheum palmatum L. Multidrug resistance protein 2 (ABCC2/ MRP2) is an important efflux transporter of substances associated with cellular oxidative stress. However, the effects of traditional Chinese medicine on this protein remain unclear.

PURPOSE

The aim of this research is to study the role of ABCC2 in AE-induced hepatotoxicity.

METHODS

The expression of ABCC2 protein and mRNA levels were analyzed by Western-Blotting and qRT-PCR, respectively. The intracellular oxidative stress caused by AE was evaluated by quantifying the levels of intracellular reactive oxygen species, malondialdehyde, glutathione reduced and oxidized glutathione. The levels of adenosine triphosphate, mitochondrial membrane potential and mitochondrial DNA were explored to evaluate the effects of AE on mitochondrial function. The effects of AE on cell apoptosis and cell cycle were detected by flow cytometry. To further clarify the key role of ABCC2 in AE induced cytotoxicity, we used pCI-neo-ABCC2 plasmid to over express ABCC2 protein, and small interfering RNA was used to knockdown ABCC2 in HepG2 cells. Additionally, we investigated the impact of AE on ABCC2 degradation pathway and the hepatotoxic effects of AE in mice.

RESULTS

AE was found to inhibit ABCC2 transport activity, downregulate ABCC2 expression and altered intracellular redox balance. Induction of oxidative stress resulted in depletion of intracellular glutathione reduced, mitochondria dysfunction and activation of apoptosis. ABCC2 overexpression significantly reduced AE-induced intracellular oxidative stress and cell death, which was enhanced by ABCC2 knockdown. Furthermore, AE was observed to promote ABCC2 degradation through induction of autophagy and hepatotoxicity was induced in mice by promoting ABCC2 degradation.

CONCLUSIONS

The inhibition of ABCC2 is a novel effect of AE that triggers oxidative stress and apoptosis. These findings are helpful in understanding the toxicological effects of AE-containing medicinal plants.

Endogenous, cholesterol-activated ATP-dependent transport in membrane vesicles from Spodoptera frugiperda cells

Transport proteins of the ATP-binding cassette (ABC) family are found in all kingdoms of life. In humans, several ABC efflux transporters play a role in drug disposition and excretion. Therefore, in vitro methods have been developed to characterize the substrate and inhibitor properties of drugs with respect to these transporters. In the vesicular transport assay, transport is studied using inverted membrane vesicles produced from transporter overexpressing cell lines of both mammalian and insect origin. Insect cell expression systems benefit from a higher expression compared to background, but are not as well characterized as their mammalian counterparts regarding endogenous transport. Therefore, the contribution of this transport in the assay might be underappreciated. In this study, endogenous transport in membrane vesicles from Spodoptera frugiperda -derived Sf9 cells was characterized using four typical substrates of human ABC transporters: 5(6)-carboxy-2,'7'-dichlorofluorescein (CDCF), estradiol-17β-glucuronide, estrone sulfate and N-methyl-quinidine. Significant ATP-dependent transport was observed for three of the substrates with cholesterol-loading of the vesicles, which is sometimes used to improve the activity of human transporters expressed in Sf9 cells. The highest effect of cholesterol was on CDCF transport, and this transport in the cholesterol-loaded Sf9 vesicles was time and concentration dependent with a K_m of 8.06 ± 1.11 μM. The observed CDCF transport was inhibited by known inhibitors of human ABCC transporters, but not by ABCB1 and ABCG2 inhibitors verapamil and Ko143, respectively. Two candidate genes for ABCC-type transporters in the S. frugiperda genome (SfABCC2 and SfABCC3) were identified based on sequence analysis as a hypothesis to explain the observed endogenous ABCC-type transport in Sf9 vesicles. Although further studies are needed to verify the role of SfABCC2 and SfABCC3 in Sf9 vesicles, the findings of this study highlight the need to carefully characterize background transport in Sf9 derived membrane vesicles to avoid false positive substrate findings for human ABC transporters studied with this overexpression system.

Identification of MRP2 as a targetable factor limiting oxaliplatin accumulation and response in gastrointestinal cancer

Oxaliplatin is important for the clinical treatment of colorectal cancer and other gastrointestinal malignancies, but tumour resistance is limiting. Several oxaliplatin transporters were previously identified but their relative contributions to determining oxaliplatin tumour responses and gastrointestinal tumour cell sensitivity to oxaliplatin remains unclear. We studied clinical associations between tumour expression of oxaliplatin transporter candidate genes and patient response to oxaliplatin, then experimentally verified associations found with MRP2 in models of human gastrointestinal cancer. Among 18 oxaliplatin transporter candidate genes, MRP2 was the only one to be differentially expressed in the tumours of colorectal cancer patients who did or did not respond to FOLFOX chemotherapy. Over-expression of MRP2 (endogenously in HepG2 and PANC-1 cells, or induced by stable transfection of HEK293 cells) decreased oxaliplatin accumulation and cytotoxicity but those deficits were reversed by inhibition of MRP2 with myricetin or siRNA knockdown. Mice bearing subcutaneous HepG2 tumour xenografts were sensitised to oxaliplatin antitumour activity by concurrent myricetin treatment with little or no increase in toxicity. In conclusion, MRP2 limits oxaliplatin accumulation and response in human gastrointestinal cancer. Screening tumour MRP2 expression levels, to select patients for treatment with oxaliplatin-based chemotherapy alone or in combination with a MRP2 inhibitor, could improve treatment outcomes.

Cellular Pharmacokinetic Model-Based Analysis of Genistein, Glyceollin, and MK-571 Effects on 5 (and 6)-Carboxy-2',7'-Dichloroflourescein Disposition in Caco-2 Cells

Pharmacokinetic modeling was used to describe 5 (and 6)-carboxy-2',7'-dichloroflourescein (CDF) disposition in Caco-2 cells following CDF or CDFDA (CDF diacetate) dosing. CDF transcellular flux was modeled by simple passive diffusion. CDFDA dosing models were based on simultaneous fitting of CDF levels in apical, basolateral, and intracellular compartments. Predicted CDF efflux was 50% higher across the apical versus the basolateral membrane. This difference was similar following apical and basolateral CDFDA dosing, despite intracellular levels being 3-fold higher following basolateral dosing, thus supporting nonsaturable CDF efflux kinetics. A 3-compartment catenary model with intracellular CDFDA hydrolysis described CDF disposition. This model predicted that apical CDF efflux was not altered in the presence of MK-571, and that basolateral membrane clearance was enhanced to account for reduced intracellular CDF in the presence of this multidrug resistance-associated protein (MRP) inhibitor. Similar effects were predicted for glyceollin, while genistein exposure had no predicted effects on CDF efflux. These modulator effects are discussed in the context of model predicted intracellular CDF concentrations relative to reports of CDF affinity (measured by Km) for MRP2 and MRP3. This model-based analysis confirms the complexity of efflux kinetics and suggests that other transporters may have contributed to CDF efflux.

Effect of cigarette smoke extract on P-glycoprotein function in primary cultured and newly developed alveolar epithelial cells

The effect of cigarette smoke extract (CSE) on P-glycoprotein (P-gp) function in the distal lung is unclear. In this study, we first examined the expression and function of P-gp and the effect of CSE in rat primary cultured alveolar epithelial cells. The expression of P-gp protein was observed in type I-like cells, but not in type II cells. In type I-like cells, rhodamine 123 (Rho123) accumulation was enhanced by various P-gp inhibitors such as verapamil and cyclosporine A. In addition, the expression of P-gp mRNAs, mdr1a and mdr1b, as well as P-gp activity increased along with the transdifferentiation. When type I-like cells were co-incubated with CSE, P-gp activity was suppressed. Next, we attempted to clarify the effect of CSE on P-gp function in human-derived cultured alveolar epithelial cells. For this purpose, we isolated an A549 clone (A549/P-gp) expressing P-gp, because P-gp expression in native A549 cells was negligible. In A549/P-gp cells, P-gp was functionally expressed, and the inhibitory effect of CSE on P-gp was observed. These results suggested that smoking would directly suppress P-gp activity, and that A549/P-gp cell line should be a useful model to further study the effect of xenobiotics on P-gp function in the alveolar epithelial cells.

Data showing the circumvention of oxaliplatin resistance by vatalanib in colon cancer

We have recently reported that vatalanib, an orally active small molecule multi-tyrosine kinase inhibitor (Hess-Stumpp et al., 2005 [1]), can sensitize multidrug resistant (MDR) colon cancer cells to chemotherapy under hypoxia by inhibiting two MDR transporters ABCB1 and ABCG2 (To et al., 2015 [2]). This data article describes the possible circumvention of resistance to specifically platinum (Pt)-based anticancer drugs by vatalanib via inhibition of two other efflux transporters ABCC2 and ATP7A. Data from the flow cytometric transporter efflux assay showed specific inhibition of ABCC2 activity by vatalanib in stable transfected cells and ABCC2-overexpressing oxaliplatin-resistant colon cancer cells HCT116/Oxa. We also performed the transporter ABCC2 ATPase assay and showed an increase in ATP hydrolysis by ABCC2 in the presence of vatalanib. ATP7A mRNA expression was also shown to be upregulated in HCT116/Oxa cells. Vatalanib was shown to suppress this upregulated ATP7A expression. Data from the cellular Pt accumulation assay showed a lower Pt accumulation in HCT116/Oxa cells than the parental sensitive HCT116 cells. Vatalanib was shown to increase cellular Pt accumulation in a concentration-dependent manner. Combination of oxaliplatin and vatalanib was shown to restore the suppressed apoptosis in HCT116/Oxa cells.

ATP Binding Cassette Transporter Mediates Both Heme and Pesticide Detoxification in Tick Midgut Cells

In ticks, the digestion of blood occurs intracellularly and proteolytic digestion of hemoglobin takes place in a dedicated type of lysosome, the digest vesicle, followed by transfer of the heme moiety of hemoglobin to a specialized organelle that accumulates large heme aggregates, called hemosomes. In the present work, we studied the uptake of fluorescent metalloporphyrins, used as heme analogs, and amitraz, one of the most regularly used acaricides to control cattle tick infestations, by Rhipicephalus (Boophilus) microplus midgut cells. Both compounds were taken up by midgut cells in vitro and accumulated inside the hemosomes. Transport of both molecules was sensitive to cyclosporine A (CsA), a well-known inhibitor of ATP binding cassette (ABC) transporters. Rhodamine 123, a fluorescent probe that is also a recognized ABC substrate, was similarly directed to the hemosome in a CsA-sensitive manner. Using an antibody against conserved domain of PgP-1-type ABC transporter, we were able to immunolocalize PgP-1 in the digest vesicle membranes. Comparison between two R. microplus strains that were resistant and susceptible to amitraz revealed that the resistant strain detoxified both amitraz and Sn-Pp IX more efficiently than the susceptible strain, a process that was also sensitive to CsA. A transcript containing an ABC transporter signature exhibited 2.5-fold increased expression in the amitraz-resistant strain when compared with the susceptible strain. RNAi-induced down-regulation of this ABC transporter led to the accumulation of metalloporphyrin in the digestive vacuole, interrupting heme traffic to the hemosome. This evidence further confirms that this transcript codes for a heme transporter. This is the first report of heme transport in a blood-feeding organism. While the primary physiological function of the hemosome is to detoxify heme and attenuate its toxicity, we suggest that the use of this acaricide detoxification pathway by ticks may represent a new molecular mechanism of resistance to pesticides.

Multidrug Resistance-Associated Protein 2 (MRP2) Mediated Transport of Oxaliplatin-Derived Platinum in Membrane Vesicles

The platinum-based anticancer drug oxaliplatin is important clinically in cancer treatment. However, the role of multidrug resistance-associated protein 2 (MRP2) in controlling oxaliplatin membrane transport, in vivo handling, toxicity and therapeutic responses is unclear. In the current study, preparations of MRP2-expressing and control membrane vesicles, containing inside-out orientated vesicles, were used to directly characterise the membrane transport of oxaliplatin-derived platinum measured by inductively coupled plasma mass spectrometry. Oxaliplatin inhibited the ATP-dependent accumulation of the model MRP2 fluorescent probe, 5(6)-carboxy-2,'7'-dichlorofluorescein, in MRP2-expressing membrane vesicles. MRP2-expressing membrane vesicles accumulated up to 19-fold more platinum during their incubation with oxaliplatin and ATP as compared to control membrane vesicles and in the absence of ATP. The rate of ATP-dependent MRP2-mediated active transport of oxaliplatin-derived platinum increased non-linearly with increasing oxaliplatin exposure concentration, approaching a plateau value (Vmax) of 2680 pmol Pt/mg protein/10 minutes (95%CI, 2010 to 3360 pmol Pt/mg protein/10 minutes), with the half-maximal platinum accumulation rate (Km) at an oxaliplatin exposure concentration of 301 μM (95% CI, 163 to 438 μM), in accordance with Michaelis-Menten kinetics (r² = 0.954). MRP2 inhibitors (myricetin and MK571) reduced the ATP-dependent accumulation of oxaliplatin-derived platinum in MRP2-expressing membrane vesicles in a concentration-dependent manner. To identify whether oxaliplatin, or perhaps a degradation product, was the likely substrate for this active transport, HPLC studies were undertaken showing that oxaliplatin degraded slowly in membrane vesicle incubation buffer containing chloride ions and glutathione, with approximately 95% remaining intact after a 10 minute incubation time and a degradation half-life of 2.24 hours (95%CI, 2.08 to 2.43 hours). In conclusion, MRP2 mediates the ATP-dependent active membrane transport of oxaliplatin-derived platinum. Intact oxaliplatin and its anionic monochloro oxalate ring-opened intermediate appear likely candidates as substrates for MRP2-mediated transport.

Distinct alterations in ATP-binding cassette transporter expression in liver, kidney, small intestine, and brain in adjuvant-induced arthritic rats

Pathophysiological changes of infection or inflammation are associated with alterations in the production of numerous absorption, distribution, metabolism and excretion-related proteins. However, little information is available on the effects of inflammation on the expression levels and activities of ATP-binding cassette (ABC) transporters. We examined the effect of acute (on day 7) and chronic (on day 21) inflammation on the expression of ABC transporters in some major tissues in rat. Adjuvant-induced arthritis (AA) in rats was used as an animal model for inflammation. The mRNA levels of mdr1a and mdr1b encoding P-glycoprotein (P-gp) decreased significantly in livers of AA rats on day 21. Hepatic protein levels of P-gp, Mrp2, and Bcrp decreased significantly in membranes but not homogenates of AA rats after 7 days and after 21 days of treatment with adjuvant. Contrary to liver, protein levels of P-gp and Mrp2, but not Bcrp in kidney, increased significantly in membranes. The biliary excretion of rhodamine 123 was decreased in rats with chronic inflammation owing to decreases in efflux activities of P-gp. Our results showed that the expression of transporters in response to inflammation was organ dependent. In particular, hepatic and renal P-gp and Mrp2 exhibited opposite changes in membrane protein levels.

P-glycoprotein mediated efflux limits substrate and drug uptake in a preclinical brain metastases of breast cancer model

The blood–brain barrier (BBB) is a specialized vascular interface that restricts the entry of many compounds into brain. This is accomplished through the sealing of vascular endothelial cells together with tight junction proteins to prevent paracellular diffusion. In addition, the BBB has a high degree of expression of numerous efflux transporters which actively extrude compounds back into blood. However, when a metastatic lesion develops in brain the vasculature is typically compromised with increases in passive permeability (blood-tumor barrier; BTB). What is not well documented is to what degree active efflux retains function at the BTB despite the changes observed in passive permeability. In addition, there have been previous reports documenting both increased and decreased expression of P-glycoprotein (P-gp) in lesion vasculature. Herein, we simultaneously administer a passive diffusion marker (¹⁴C-AIB) and a tracer subject to P-gp efflux (rhodamine 123) into a murine preclinical model of brain metastases of breast cancer. We observed that the metastatic lesions had similar expression (p > 0.05; n = 756–1214 vessels evaluated) at the BBB and the BTB. Moreover, tissue distribution of R123 was not significantly (p > 0.05) different between normal brain and the metastatic lesion. It is possible that the similar expression of P-gp on the BBB and the BTB contribute to this phenomenon. Additionally we observed P-gp expression at the metastatic cancer cells adjacent to the vasculature which may also contribute to reduced R123 uptake into the lesion. The data suggest that despite the disrupted integrity of the BTB, efflux mechanisms appear to be intact, and may be functionally comparable to the normal BBB. The BTB is a significant hurdle to delivering drugs to brain metastasis.

Luteolin ameliorates cisplatin-induced nephrotoxicity in mice through inhibition of platinum accumulation, inflammation and apoptosis in the kidney

The aim of this study was to investigate the effects of flavone luteolin against cisplatin (CP)-induced kidney injury in mice. Luteolin at doses of 10mg/kg was administered intraperitoneally (ip) once daily for 3 days following single CP (10 or 20mg/kg) ip injection. Mice were sacrificed 24h after the last dose of luteolin. The CP treatment significantly increased serum creatinine and blood urea nitrogen and induced pathohistological changes in the kidneys. Renal oxidative/nitrosative stress was evidenced by decreased glutathione (GSH) levels and increased 3-nitrotyrosine (3-NT) and 4-hydroxynonenal (4-HNE) formation as well as cytochrome P450 2E1 (CYP2E1) expression. The CP administration triggered inflammatory response in mice kidneys through activation of nuclear factor-kappaB (NF-κB) and overexpression of tumor necrosis factor-alpha (TNF-α) and cyclooxygenase-2 (COX-2). Simultaneously, the increase in renal p53 and caspase-3 expression indicated apoptosis of tubular cells. The administration of luteolin significantly reduced histological and biochemical changes induced by CP, decreased platinum (Pt) levels and suppressed oxidative/nitrosative stress, inflammation and apoptosis in the kidneys. These results suggest that luteolin is an effective nephroprotective agent, with potential to reduce Pt accumulation in the kidneys and ameliorate CP-induced nephrotoxicity.

src family kinases regulate renal epithelial paracellular permeability barrier through an occludin-independent mechanism

Paracellular permeability is mediated by the epithelial cell tight junction. Studies in intestinal and other epithelia have suggested that the activity of src family kinases (SFKs) increases epithelial paracellular permeability through its action on the tight junction protein, occludin, but the involvement of SFKs and occludin in regulation of renal epithelial paracellular permeability is unclear. In this study, the role of SFKs in regulation of renal epithelial paracellular permeability and the involvement of occludin protein in this regulatory event was examined in two renal epithelial cell lines, LLC-PK(1) (proximal tubule-like) and MDCK (distal tubule-like). The effect of broad spectrum SFK inhibitors on paracellular permeability of calcein and fluorescein-dextran3000 were examined. SFK inhibitor treatment increased paracellular movement of both compounds in both renal epithelial cell lines. The SFK inhibitor effect was concentration-dependent and, at low concentrations, was not associated with cell damage/death. Response to SFK inhibitors was acquired progressively after cell populations attained confluence suggesting maturation of the regulatory mechanism. Increased paracellular permeability was not associated with dramatic changes in total cell content of occludin protein, its partitioning between detergent-soluble and -insoluble fractions, or its subcellular localization. Further, the SFK-induced increase in paracellular permeability was unaffected by either occludin protein overexpression or occludin protein knockdown. These results demonstrate that SFK activity decreases paracellular permeability of renal epithelial cells, as opposed to its effect in intestinal epithelial cells, and that this regulation is not mediated by occludin protein.

Phyllanthin and hypophyllanthin inhibit function of P-gp but not MRP2 in Caco-2 cells

OBJECTIVES

The purposes of this study were to investigate the inhibitory effects of two lignans, phyllanthin and hypophyllanthin, on the function of P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2), using the in-vitro model of Caco-2 cells. In addition, the effect of prolonged exposure to these two compounds on the expression of active P-gp was also determined.

METHODS

The activity of P-gp and MRP2 was determined in the uptake assays by monitoring the intracellular accumulation of their specific substrates (calcein acetoxymethyl ester and 5(6)-carboxy-2',7'-dichlorofluorescein diacetate, respectively) with fluorescence spectroscopy.

KEY FINDINGS

Hypophyllanthin and phyllanthin inhibited P-gp function with comparable potencies, but neither compound affected MRP2 activity. When the lignans were washed out before addition of substrate, the inhibitory action of both compounds against P-gp function was lost. These results suggested the reversibility of the inhibition. Moreover, prolonged exposure of the Caco-2 cells to both lignans (up to 7 days) had no effect on P-gp function.

CONCLUSIONS

Phyllanthin and hypophyllanthin directly inhibited P-gp activity and did not interfere with MRP2 activity. It was likely that both phyllanthin and hypophyllanthin could reversibly inhibit P-gp function.

HIF-1 activation induces doxorubicin resistance in MCF7 3-D spheroids via P-glycoprotein expression: a potential model of the chemo-resistance of invasive micropapillary carcinoma of the breast

Background

Invasive micropapillary carcinoma (IMPC) of the breast is a distinct and aggressive variant of luminal type B breast cancer that does not respond to neoadjuvant chemotherapy. It is characterized by small pseudopapillary clusters of cancer cells with inverted cell polarity. To investigate whether hypoxia-inducible factor-1 (HIF-1) activation may be related to the drug resistance described in this tumor, we used MCF7 cancer cells cultured as 3-D spheroids, which morphologically simulate IMPC cell clusters.

Methods

HIF-1 activation was measured by EMSA and ELISA in MCF7 3-D spheroids and MCF7 monolayers. Binding of HIF-1α to MDR-1 gene promoter and modulation of P-glycoprotein (Pgp) expression was evaluated by ChIP assay and FACS analysis, respectively. Intracellular doxorubicin retention was measured by spectrofluorimetric assay and drug cytotoxicity by annexin V-FITC measurement and caspase activity assay.

Results

In MCF7 3-D spheroids HIF-1 was activated and recruited to participate to the transcriptional activity of MDR-1 gene, coding for Pgp. In addition, Pgp expression on the surface of cells obtained from 3-D spheroids was increased. MCF7 3-D spheroids accumulate less doxorubicin and are less sensitive to its cytotoxic effects than MCF7 cells cultured as monolayer. Finally, HIF-1α inhibition either by incubating cells with 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (a widely used HIF-1α inhibitor) or by transfecting cells with specific siRNA for HIF-1α significantly decreased the expression of Pgp on the surface of cells and increased the intracellular doxorubicin accumulation in MCF7 3-D spheroids.

Conclusions

MCF7 breast cancer cells cultured as 3-D spheroids are resistant to doxorubicin and this resistance is associated with an increased Pgp expression in the plasma membrane via activation of HIF-1. The same mechanism may be suggested for IMPC drug resistance.