Zinc chloride rapidly stimulates efflux transporters in renal proximal tubules of killifish ( Fundulus heteroclitus )

Aluminum and ABC transporter activity

Aluminum is the third most common element on Earth´s crust and despite its wide use in our workaday life it has been associated with several health risks after overexposure. In the present study the impact of aluminum salts upon ABC transporter activity was studied in the P-GP-expressing human blood-brain barrier cell line hCMEC/D3, in MDCKII cells overexpressing BCRP and MRP2, respectively, and in freshly isolated, functionally intact kidney tubules from Atlantic killifish (Fundulus heteroclitus), which express the analog ABC transporters, P-gp, Bcrp and Mrp2. In contrast to previous findings with heavy metals salts (cadmium(II) chloride or mercury(II) chloride), which have a strong inhibitory effect on ABC transporter activity, or zinc(II) chloride and sodium arsenite, which have a stimulatory effect upon ABC transport function, the results indicate no modulatory effect of aluminum salts on the efflux activity of the human ABC transporters P-GP, BCRP and MRP2 nor on the analog transporters P-gp, Bcrp and Mrp2.

Nephrotoxicity of iopamidol is associated with mitochondrial impairment in human cell and teleost models

Iopamidol is a nonionic, low-osmolar iodinated contrast agent used for angiography. Its clinical use is associated with renal dysfunction. Patients suffering from preexisting kidney disease have an increased risk of renal failure upon iopamidol administration. Studies in animals confirmed renal toxicity, but the involved mechanisms remain unclear. Therefore, the aim of the present study was to use human embryonic kidney cells (HEK293T) as a general cell model of mitochondrial damage, as well as, zebrafish larvae, and isolated proximal tubules of killifish to investigate factors promoting renal tubular toxicity of iopamidol with a focus on mitochondrial damage. Results from in vitro HEK293T cell-based assays indicate that iopamidol affects mitochondrial function Treatment with iopamidol induces ATP depletion, reduces the mitochondrial membrane potential, and elevates mitochondrial superoxide and reactive oxygen species accumulation. Similar results were obtained with gentamicin sulfate and cadmium chloride, two well-known model compounds associated with renal tubular toxicity. Confocal microscopy confirms changes in mitochondrial morphology, such as mitochondrial fission. Importantly, these results were confirmed in proximal renal tubular epithelial cells using ex vivo and in vivo teleost models. In conclusion, this study provides evidence for iopamidol-induced mitochondrial damage in proximal renal epithelial cells. Teleost models allow studying proximal tubular toxicity with translational relevance for humans.

Sodium arsenite but not aluminum chloride stimulates ABC transporter activity in renal proximal tubules of killifish (Fundulus heteroclitus)

ABC export proteins including Multidrug resistance-related protein 2 (Mrp2) serve as detoxification mechanism in renal proximal tubules due to active transport of xenobiotics and metabolic waste products into primary urine. The environmental pollutants aluminum and arsenic interfere with a multitude of regulatory mechanisms in the body and here their impact on ABC transporter function was studied. NaAsO₂ but not AlCl₃ rapidly stimulated Mrp2-mediated Texas Red (TR) transport in isolated renal proximal tubules from killifish, a well-established laboratory model for the determination of efflux transporter activity by utilizing fluorescent substrates for the ABC transporters of interest and confocal microscopy followed by image analysis. This observed stimulation remained unaffected by the translation inhibitor cycloheximide (CHX), but it was abrogated by antagonists and inhibitors of the endothelin receptor type B (ET_B)/nitric oxide synthase (NOS)/protein kinase C (PKC) signaling pathway. NaAsO₂-triggered effects were abolished as a consequence of PKCα inhibition through Gö6976 and PKCα inhibitor peptide C2-4. Phosphatidylinositol 3-kinase (PI3K) inhibitor LY 294,002 as well as the mammalian target of rapamycin (mTOR) inhibitor rapamycin suppressed NaAsO₂-triggered stimulation of luminal TR transport. In addition, the stimulatory effect of NaAsO₂ was abolished by GSK650394, an inhibitor of serum- and glucocorticoid-inducible kinase 1 (SGK1), which is an important downstream target. Environmentally relevant concentrations of NaAsO₂ further stimulated transport function of P-glycoprotein (P-gp), Multidrug resistance-related protein 4 (Mrp4) and Breast cancer resistance protein (Bcrp) while AlCl₃ was ineffective. To our knowledge, this is the first report engaging in the impact of NaAsO₂ on efflux transporter signaling and it may contribute to the understanding of defense mechanisms versus this worrying pollutant.

Zebrafish (Danio rerio) larva as an in vivo vertebrate model to study renal function

There is an increasing interest in using zebrafish (Danio rerio) larva as a vertebrate screening model to study drug disposition. As the pronephric kidney of zebrafish larvae shares high similarity with the anatomy of nephrons in higher vertebrates including humans, we explored in this study whether 3- to 4-day-old zebrafish larvae have a fully functional pronephron. Intravenous injection of fluorescent polyethylene glycol and dextran derivatives of different molecular weight revealed a cutoff of 4.4-7.6 nm in hydrodynamic diameter for passive glomerular filtration, which is in agreement with corresponding values in rodents and humans. Distal tubular reabsorption of a FITC-folate conjugate, covalently modified with PEG2000, via folate receptor 1 was shown. Transport experiments of fluorescent substrates were assessed in the presence and absence of specific inhibitors in the blood systems. Thereby, functional expression in the proximal tubule of organic anion transporter oat (slc22) multidrug resistance-associated protein mrp1 (abcc1), mrp2 (abcc2), mrp4 (abcc4), and zebrafish larva p-glycoprotein analog abcb4 was shown. In addition, nonrenal clearance of fluorescent substrates and plasma protein binding characteristics were assessed in vivo. The results of transporter experiments were confirmed by extrapolation to ex vivo experiments in killifish (Fundulus heteroclitus) proximal kidney tubules. We conclude that the zebrafish larva has a fully functional pronephron at 96 h postfertilization and is therefore an attractive translational vertebrate screening model to bridge the gap between cell culture-based test systems and pharmacokinetic experiments in higher vertebrates.NEW & NOTEWORTHY The study of renal function remains a challenge. In vitro cell-based assays are approved to study, e.g., ABC/SLC-mediated drug transport but do not cover other renal functions such as glomerular filtration. Here, in vivo studies combined with in vitro assays are needed, which are time consuming and expensive. In view of these limitations, our proof-of-concept study demonstrates that the zebrafish larva is a translational in vivo test model that allows for mechanistic investigations to study renal function.

Calcineurin Immune Signaling in Response to Zinc Challenge in the Naked Carp Gymnocypris eckloni

Zinc pollution impairs neural processes and protein function and also effects calcium-related transcriptional regulation and enzyme activity. In this study, we investigated pathways that potentially respond to calcium signaling under Zn²⁺ stress. Specifically we measured relative expressions of GeCNAα, GeCNB, GeMT, GeTNF-α, GeIL-1β, and GeHsp90 in gills, livers, and kidneys of the indicator species Gymnocypris eckloni and found wide variation in their expression between tissues during the course of Zn²⁺ exposure. Notably, GeCNAα, GeCNB, GeTNF-α, GeIL-1β, and GeMT were rapidly and strongly up-regulated in gills; GeIL-1β and GeHsp90 transcription was quickly induced in kidneys; and GeCNB, GeTNF-α, GeIL-1β, and GeHsp90 were most rapidly up-regulated in livers. GeCNAα and GeMT showed a contrasting late transcriptional up-regulation. These results suggest independent branches for chelation and immune responses during self-protection against Zn²⁺ toxicity, and the immune response appears to be faster than metal chelation.

A Combination of Clioquinol, Zinc and Copper Increases the Abundance and Function of Breast Cancer Resistance Protein in Human Brain Microvascular Endothelial Cells

Modulating the abundance of the blood-brain barrier (BBB) efflux transporter breast cancer resistance protein (BCRP) has the potential to impact brain levels of drugs and endogenous substrates. Studies have demonstrated that the metal ionophore clioquinol (CQ) increases BBB abundance of P-glycoprotein (P-gp), an effect associated with increased endothelial cell levels of Cu²⁺. This study therefore assessed whether human brain endothelial (hCMEC/D3) cell abundance and function of BCRP is modulated by CQ. hCMEC/D3 cells were treated with CQ, Zn²⁺ and Cu²⁺ (CZC) (0.5 μM, 0.5 μM, 0.1 μM, respectively) for 24 h and BCRP mRNA and protein abundance was determined by Western blot and qPCR, respectively. After a series of optimisation studies assessing specificity of bodipy prazosin (BP) and Ko143 as a substrate and inhibitor of BCRP, respectively, the impact of CZC on BP uptake was assessed. While CZC did not increase mRNA expression of BCRP, BCRP abundance was increased 1.8 ± 0.1-fold; this was associated with a 68.1 ± 3.3% reduction in accumulation of BP in hCMEC/D3 cells. This is the first study to demonstrate that augmenting metal ion availability enhances protein abundance and function of BCRP at the BBB, which may be exploited to modulate CNS access of therapeutics and endogenous substrates.

Effects of sublethal and realistic concentrations of the commercial herbicide atrazine in Pacu (Piaractus mesopotamicus): Long-term exposure and recovery assays

Background and Aim:

The commercial formulations of the herbicide atrazine (cATZ) are widely employed in Brazilian agriculture, and, as a consequence, ATZ has been found at levels above that established by law in the river basins in Brazil. Although the toxicity of ATZ in fish is well documented, there are few studies on the recovery capacity after cATZ exposure. This work aimed to evaluate, using several biomarkers, the toxic effects of long-term exposure to the sublethal (3.57 mg/L) and nonlethal realistic (3.00 µg/L) cATZ concentrations followed by a recovery assay, in fingerlings of a Brazilian teleost, the Piaractus mesopotamicus (pacu).

Materials and Methods:

Pacu fingerlings were housed in glass tanks and divided into the following experimental groups (two tanks/group): Exposure control = EC, recovery control = RC, the sublethal groups exposed to 3.57 mg/L of cATZ, (sublethal exposure group = SLE and sublethal recovery group = SLR) and the nonlethal groups treated with 3.00 µg/L of cATZ (nonlethal exposure group = NLE and nonlethal recovery group = NLR). The exposure assay was semi-static with a duration of 30 days and the recovery assay (after cATZ withdrawal) lasted 14 days. Several biomarkers were evaluated in fingerlings from all groups: The swimming behavior, the body weight gain, the micronucleus formation and nuclear alterations in erythrocytes, and the hepatic and renal histopathology analyzed by qualitative and semi-quantitative morphological methods (using light and electron microscopy).

Results:

No significant difference in weight gain was observed among the groups after the exposure and recovery assays. The sublethal exposure induced impaired swimming movements, significant histopathological alterations, including necrosis in the liver and kidney, and a significant increase in the frequency of micronuclei in erythrocytes. The nonlethal exposure induced only subtle histopathological changes in the liver and kidney. After recovery assay, no genotoxic alteration was noted in pacu exposed to sublethal concentration, while the cATZ-induced kidney damage was partially reversed but not the hepatic injury.

Conclusion:

cATZ exhibits long-term toxic effects on pacu, even at relatively low concentrations, affecting mainly the liver and the kidney, and the effects of sublethal concentration are only partially reversed after cATZ withdrawal.

2,4,6-Tribromophenol Exposure Decreases P-Glycoprotein Transport at the Blood-Brain Barrier

2,4,6-Tribromophenol (TBP, CAS No. 118-79-6) is a brominated chemical used in the production of flame-retardant epoxy resins and as a wood preservative. In marine environments, TBP is incorporated into shellfish and consumed by predatory fish. Food processing and water treatment facilities produce TBP as a byproduct. 2,4,6-Tribromophenol has been detected in human blood and breast milk. Biologically, TBP interferes with estrogen and thyroid hormone signaling, which regulate important transporters of the blood-brain barrier (BBB). The BBB is a selectively permeable barrier characterized by brain microvessels which are composed of endothelial cells mortared by tight-junction proteins. ATP-binding cassette (ABC) efflux transporters on the luminal membrane facilitate the removal of unwanted endobiotics and xenobiotics from the brain. In this study, we examined the in vivo and ex vivo effects of TBP on two important transporters of the BBB: P-glycoprotein (P-gp, ABCB1) and Multidrug Resistance-associated Protein 2 (MRP2, ABCC2), using male and female rats and mice. 2,4,6-Tribromophenol exposure ex vivo resulted in a time- (1-3 h) and dose- (1-100 nM) dependent decrease in P-gp transport activity. MRP2 transport activity was unchanged under identical conditions. Immunofluorescence and western blotting measured decreases in P-gp expression after TBP treatment. ATPase assays indicate that TBP is not a substrate and does not directly interact with P-gp. In vivo dosing with TBP (0.4 µmol/kg) produced decreases in P-gp transport. Co-treatment with selective protein kinase C (PKC) inhibitors prevented the TBP-mediated decreases in P-gp transport activity.

The lagged effects of environmentally relevant zinc on non-specific immunity in zebrafish

Responses to zinc (Zn) during exposure have well studied but the effects after the exposure are commonly neglected. In the study, non-specific immune response to zinc in blood and spleen of zebrafish was evaluated after exposure. At first, fish were subjected to 0 (control) and 200 μg/L zinc (Zn) for 6 weeks. Specific growth rate, survival rate, blood albumin level, and the activities of Cu/Zn-SOD and iNOS were not significantly changed by Zn exposure. Conversely, Zn increased the levels of globulin and hemoglobin, CAT activity, and mRNA levels of nrf2, sod1, cat, hsf1, hsp70, p65, il-6, il-1β, tnf-α and inos. In the second experiment, zebrafish were transferred to a recovery period for 4 and 8 days. The increased activities of Cu/Zn-SOD and CAT and the up-regulated mRNA levels of nrf2, cat, p65, tnf-α, and inos still were observed. In the third experiment, zebrafish from 4 d post-exposure were re-exposed to the high levels of Zn and cadmium (Cd) (600, 1200 μg/L Zn; 100, 200 μg/L Cd) for 4 days. 100 μg/L Cd caused a higher survival rate in the Zn-exposed fish than the control, suggesting Zn pre-exposure might develop the tolerance to Zn and Cd. Although transcriptional levels of sod1, hsf1, hsf2, hsp70, il-6 and il-1β and activity levels of iNOS recovered to the control levels at 4 and 8 d post-exposure, differences in magnitude of responsiveness were observed between normal fish and Zn-exposed fish. Overall, Zn acclimation persisted when fish recovered, which provides a new perspective about Zn toxicology.