Deficiency of Multidrug and Toxin Extrusion 1 Enhances Renal Accumulation of Paraquat and Deteriorates Kidney Injury in Mice

Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland Baltimore, Baltimore, Maryland, United States.
Molecular Pharmaceutics (Impact Factor: 4.38). 12/2011; 8(6):2476-83. DOI: 10.1021/mp200395f
Source: PubMed
ABSTRACT
Multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1) mediates cellular transport of a variety of structurally diverse compounds. Paraquat (PQ), which has been characterized in vitro as a MATE1 substrate, is a widely used herbicide and can cause severe toxicity to humans after exposure. However, the contribution of MATE1 to PQ disposition in vivo has not been determined. In the present study, we generated Mate1-deficient (Mate1-/-) mice and performed toxicokinetic analyses of PQ in Mate1-/- and wild-type (Mate1+/+) mice. After a single intravenous administration of PQ (50 mg/kg), Mate1-/- mice exhibited significantly higher plasma PQ concentrations than Mate1+/+ mice. The renal PQ concentration was markedly increased in Mate1-/- mice compared with Mate1+/+ mice. The subsequent nephrotoxicity of PQ were examined in these mice. Three days after intraperitoneal administration of PQ (20 mg/kg), the transcript levels of N-acetyl-β-D-glucosaminidase (Lcn2) and kidney injury molecule-1 (Kim-1) in the kidney were remarkably enhanced in the Mate1-/- mice. This was accompanied by apparent difference in renal histology between Mate1-/- and Mate1+/+ mice. In conclusion, we demonstrated that Mate1 is responsible for renal elimination of PQ in vivo and the deficiency of Mate1 function confers deteriorated kidney injury caused by PQ in mice.

Full-text

Available from: Yan Shu
Published: September 29, 2011
r
2011 American Chemical Society
2476 dx.doi.org/10.1021/mp200395f
|
Mol. Pharmaceutics 2011, 8, 24762483
BRIEF ARTICLE
pubs.acs.org/molecularpharmaceutics
Deficiency of Multidrug and Toxin Extrusion 1 Enhances Renal
Accumulation of Paraquat and Deteriorates Kidney Injury in Mice
Qing Li,
,
Xiujuan Peng,
Hyekyung Yang,
Hongbing Wang,
and Yan Shu*
,
Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland Baltimore, Baltimore, Maryland, United States
Institute of Clinical Pharmacology, Central South University, Hunan 410078, China
INTRODUCTION
Paraquat (N,N-dimethyl-4,4
0
-bipyridinium dichloride; PQ)
is a widely used herbicide due to its rapid eect and quick
deactivation once in contact with soil. However, it is of great
toxicological importance and associated with a high mortality
rate during human exposure.
15
Epidemiological studies also
suggest that PQ exposure may increase the risk for Parkinsons
disease.
6,7
PQ accumulates with high concentrations in lung, liver
and kidney,
8,9
which causes the primary symptoms of PQ
toxicity, including respiration diculty, hepatitis, and acute renal
failure, respectively.
10
PQ toxicity results from the overproduc-
tion of reactive oxygen species.
11,12
In cells, PQ is rst reduced to
form free radial monocation (PQ
+
) by the reactions mediated
by a series of enzymes, including NADPH cytochrome P-450
reductase,
13
NADPH cytochrome C reductase,
14
the mitochon-
drial complex I (known as NADH), and ubiquinone oxido-
reductase.
15
Subsequently, the monocation is rapidly oxi dized
while generating abundant superoxide radical (O
2
).
16
The super-
oxide radical starts a cascade of downstream reactions leading to
the production of reactive oxygen species, mainly hydrogen
peroxide (H
2
O
2
) and hydroxyl radical (HO
), which cause
DNA damage or genotoxicity, destroy the lipids of cell mem-
branes, and nally induce cell death.
17
PQ is an organic cation with two positive charges and is not
metabolized in vivo.
18
PQ is predominantly eliminated by urine
and, partly, by feces.
19
The capability of organic cation transpor-
ters to transport PQ across the basolateral membrane from blood
into the cell and consequently through the apical membrane
from intracellular into tubule lumina or bile duct may deter-
mine the elimination rate and retention time of PQ in vivo.
The transporters responsible for transporting organic cations
across cellular membrane include organic cation transporters
13 (OCT13), encoded by solute carrier family 22A 13
(SLC22A13),
1,20
organic cation/carnitine transporters 13
(OCTN13), encoded by SLC22A4, -5, and -21,
21
and multi-
drug and toxin extrusion protein 12 (MATE12), encoded by
SLC47A1 and -2.
22,23
Human OCT1 is mainly expressed in the
liver, while OCT2 in the basolateral membrane of renal proximal
tubules.
24
In rodents, OCT1 is also abundantly expressed in the
kidney.
24
OCT3, also called extraneuronal monoamine trans-
porter for its role in the extraneuronal monoamine uptake system
(uptake 2), is expressed ubiquitously in most tissues, but with
relatively low levels.
25
OCTNs are sodium-dependent and high-
anity carnitine transporters. The OCTN1 and OCTN2 ex-
pressed in the apical membrane of renal proximal tubules
mediate the reabsorption of carnitine and other organic cations
to maintain their plasma levels.
26
The MATE protein family,
including MATE1 and MATE2 in mammalians, has been
recently suggested to be responsible for renal or hepatic organic
Received: August 10, 2011
Accepted: September 29, 2011
Revised: September 14, 2011
ABSTRACT: Multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1)
mediates cellular transport of a variety of structurally diverse compounds.
Paraquat (PQ), which has been characterized in vitro as a MATE1 substrate, is
a widely used herbicide and can cause severe toxicity to humans after exposure.
However, the contribution of MATE1 to PQ disposition in vivo has not been
determined. In the present study, we generated Mate1-decient (Mate1/)
mice and performed toxicokinetic analyses of PQ in Mate1/ and wild-type
(Mate1+/+) mice. After a single intravenous administration of PQ (50 mg/kg),
Mate1/ mice exhibited signicantly higher plasma PQ concentrat ions than
Mate1+/+ mice. The renal PQ concentration was markedly increased in Mate1/ mice compared with Mate1+/+ mice. The
subsequent nephrotoxicity of PQ were examined in these mice. Three days after intraperitoneal administration of PQ (20 mg/kg), the
transcript levels of N-acetyl-β-
D-glucosaminidase (Lcn2) and kidney injury molecule-1 (Kim-1) in the kidney were remarkably enhanced in
the Mate1/ mice. This was accompanied by apparent dierence in renal histology between Mate1/ and Mate1+/+ mice. In
conclusion, we demonstrated that Mate1 is responsible for renal elimination of PQ in vivo and the deciency of Mate1 function confers
deteriorated kidney injury caused by PQ in mice.
KEYWORDS: Paraquat, multidrug and toxin extrusion 1 (MATE1/solute carrier 47A1), genetic deciency, pharmacokinetics,
nephrotoxicity
Page 1
2477 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
cation elimination or secretion using a H
+
-coupled antiport
mechanism.
27,28
Limited in vitro evidence has suggested that hOCT2, not
hOCT1 or hOCT3, hMATE1 and rMATE1 transport PQ in a
time- and dose-dependent manner in the overexpr ession models
of HEK-293 cells.
29
However, the involvement of these organic
cation transporters in the disposition and toxicity of PQ in vivo
remains undened. In this study, we generated the mouse model
of Mate1 deciency (Mate1/) by the gene trap technique.
The toxicokinetics and toxicity of PQ were examined in the
Mate1/ and the wild-type mice. Our data indicated that
Mate1 played a critical role in the renal elimination of PQ and
disruption of Mate1 function remarkably potentiated PQ ne-
phrotoxicity in mice.
EXPERIMENTAL SECTION
Materials. Paraquat hydrochloride was purchased from Sig-
ma-Aldrich Co (St. Louis, MO). Paraqua t [methyl-
14
C] dichlor-
ide hydrate (0.1 mCi/mmol) was purchased from American
Radiolabeled Chemicals Inc. (St. Louis, MO). [
14
C]-Metformin
(50 μCi, 1.85 MBq) was purchased from Moravek Biochemicals
and Radiochemicals Inc. (Brea, CA). All other reagents were
commercially available.
Generation of the Mouse Deficient of Mate1. The C57BL/
6 ES cells with the Mate1 gene trapped by a retroviral gene trap
vector at intron 10 were obtained from the Texas A&M Institute
for Genomic Medicine (TIGM, College Station, TX).
30
The ES
cells were injected into 8-cell embryos isolated from timed
pregnant C57BL/6 albino females. Injected 8-cell embr yos were
cultured to blastocysts and then transferred into the uterus of
pseudopregnant females for development into individual pups.
Positive chimeric mice were identified by spotted white hairs.
The chimeric males were mated with C57BL/6 females to
generate F1 offspring from which the germ line transmission of
the target allele was confirmed by PCR method. Although the
mutant mice were derived from general C57BL/6 background,
the mice used in the present study had been backcrossed to
C57BL/6J for at least 5 generations to exclude potential subtle
genetic background effects.
Animals. All procedures were carried out in accordance with
NIH guidelines for animal experimentation, and all experimental
protocols were approved by the Institutional Animal Care and
Use Committee (IACUC) of the School of Pharmacy, University
of Maryland Baltim ore. Animals were housed under controlled
conditions (21 ( 2 °C, humidity 60 ( 10% and 12 h/12 h dark/
light cycle) and had free access to food and water. All animals
used in the present study were male mice with the same genetic
background of C57BL/6J, between 12 and 18 weeks of age.
Genomic DNA Extraction and Genotyping. The tail was
cut from all offsprings and genomic DN A isolated by QIAamp
DNA extraction mini kit (QIAGEN Co., Valencia, CA). The
genomic DNA was amplified with two pairs of primers to
genotype the mice (one pair for the w ild-type allele and the
other for the mutant allele: wild-type/mutant forward primer, 5
0
-
GAATGGGTGGGCCAAGTATG-3
0
; wild-type reverse primer,
5
0
-CATTGACCTGTCGTGCTGGAT-3
0
; mutant reverse pri-
mer, 5
0
-CTTGCAAAATGGCGTTACTTAAGC-3
0
). The PCR
condition was as follows: an initial 3-min denaturation at 94 °C,
then 94 °C for 30 s, 54 °C for 30 s, 72 °C for 45 s for 35 cycles,
72 °C for 10 min for last extension. The amplified PCR products
were separated in a 2% agarose gel and stained with ethidium
bromide.
Reverse Transcription and Real-Time PCR. Total RNA was
isolated from the liver and kidney of mice using TRIzol and
phenolchloroform method. The total RNA (2 μg) was reverse
transcribed using a high capability reverse transcip t kit (Roche
Applied Science, Indianapolis, IN). The reaction mixtures were
diluted by 4 times, and 1 μL was then used as the template for
regular PCR or real-time PCR. The regular PCR condition was as
follows: an initial 3-min denaturation step at 94 °C, then 94 °C
for 30 s, 54 °C for 30 s, 72 °C for 10 s for 25 cycles for Mate1 and
glyceraldehyde-3-phosphate dehydrogenase (Gapdh) in the liver
and kidney. The real-time PCR condition was as follows: an
initial 2-min incubation step at 50 °C, then 3-min denaturation at
94 °C, followed by 40 cycles of 2 steps at 94 °C for 30 s and 60 °C
for 60 s. Real-time PCR was performed on ABI PRISM 7700
(Applied Biosystems, Foster City, CA). The expression of
biomarker genes for kidney injury, including Kim-1 and Lcn2,
and drug transporters located in the liver and kidney, including
Oct13, Octn1 3, Mrp14, Oatp1a1, Oatp1a4, Oatp1b2, Mdr1,
Bcrp, and Bsep, were determined by real-time PCR.
Function Deficiency of Mate1 in Mate1/ Mice. Metfor-
min has been well characterized as a substrate for Mate1 in vitro
and in vivo.
31
In the previous report, metformin pharmacoki-
netics was significantly altered in the Mate1 knockout mice
created by traditional recombination gene targeting.
32
To func-
tionally validate our Mate1/ mouse model, we determined
and compared metformin tissue distribution in these mice and
wild-type control mice. Five milligram s per kilogram metformin,
containing 0.2 μCi/mL [
14
C]-metformin, was injected via tail
vein into Mate+/+ and Mate1/ mice. At 60 min after
injection, different tissues including liver and kidney were
removed, weighed, homogenized, and centrifuged. 100 μLof
supernatant was added into scintillation buffer and counted in a
multipurpose scintillation counter (Beckman LS6500 Counter,
Brea, CA) to determine tissue accumulation of metformin.
PQ Toxicokinetics. In humans, moderate-to-severe poisoning
is usually secondary to ingestion of 2050 mg/kg PQ.
33
In this
study, Mate1+/+ and Mate1/ mice were injected by tail
vein with 50 mg/kg PQ as described elsewhere.
18,3335
PQ
was dissolved in 0.9% saline (the ratio of total paraquat to
[
14
C]-PQ was 130:1). Blood samples were collected by tail bleedi ng
at 5, 10, 20, 30, 60, and 90 min after injection. The radioactivity in
20 μL of blood was counted in a multipurpose scintillation counter
(Beckman LS6500 counter, Brea, CA). The mice were sacrificed
at 90 min, and the tissues were isolated, gently washed, weighed,
submerged in phosphate buffered saline, pH 7.4, and further
homogenized completely . The homogenized tissues were centri-
fuged at 15000 rpm for 10 min and the radioactivity in the
supernatant was counted.
Determination of Toxicokinetic Parameters. WinNonlin
version 5.2.1 (Pharsight Corporation, Mountain View, CA) was
used to analyze the plasma concentrationtime profiles of PQ
after the intravenous administration in mice. Toxicokinetic
parameters and the area under the blood concentrationtime
curve from time 0 to infinity (AUC
) were calculated by the
nonlinear least-squares method. The AUC until 90 min (AUC
090
)
was determined by the trapezoidal rule.
PQ Tissue Toxicity. For tissue toxicity experiments, Mate1+/+
and Mate1/ mice were injected with 20 mg/kg PQ as
described elsewhere.
34,35
PQ was dissolved in 0.9% saline and
injected ip. The mice were sacrificed at 72 h after injection. Total
Page 2
2478 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
RNA was extracted from one kidney. The expression of Lcn2
and Kim-1 genes, as indicators of acute kidney injury,
36,37
were determined by real-time PCR as described above. For
histopathological analysis, the other kidney and the liver were
collected and submerged immediately into 10% formalin saline
buffer overnight, and further processed to paraffin embedding
and hematoxylin and eosin (H&E) staining.
Statistical Analysis. All data were expressed as the mean (
standard deviation (SD). Data from real-time PCR were analyzed
statistically with the one-way analysis of variance (ANOVA)
followed by Dunnetts test. Data from blood biochemical analysis
and toxicokinetic analysis were analyzed statistically using the
unpaired Students t test. A P value of <0.05 was considered
statistically significant.
RESULTS
Disruption of the Mate1 Gene by a Gene Trap Vector in
Mice.
In order to understand the physiology and pharmacology
significance of Mate1, we generated a Mate1 mutant mouse
strain. The mice were derived from an embryonic stem cell line of
mutated C57BL/6 ES cell library created by gene trapping in the
Texas A&M Institute for Genomic Medicine (TIGM, College
Station, TX).
30
The ES cell line was integrated with a retrovirus
vector containing the 5
0
selectable marker β-geo, a functional
fusion between the β-galactosidase and neomycin resistance
genes, in the intron 10 of Mate1 genomic locus (Figure 1A).
Chimeric mice were first generated from ES cells and then
matedwithwild-typeC57BL/6J mice, resulting in germ line
transmission. A PCR-based genotyping assay was established to
distinguish wild-type, heterozygous, and homozygous mice
(Figures 1A and 1B). Heterozygous mice were intercrossed to
generate enough wild-type mice and homozygous mutant mice
for the following experiments. The Mate1 transcript level was also
determined by real-time PCR in RNA samples from mouse kidney.
There was at least 90% reduction in Mate1 expression in the kidney
of mutant mice compared to the wild-type mice (Figure 1C).
Phenotypic Characterization. We monitored all the mice for
at least 3 mo nths. We found that there was modest but significant
difference in body weight between the wild-type and homozy-
gous mutant mice at 3 months of age (wild-type 25.9 ( 1.14 g vs
mutant 30.18 ( 1.57 g, P = 0.03, n = 5). We did not detect any
other overt phenotypes in the homozygous mutant animals.
Homozygous mutant mice were observed to be viable and fe rtile,
consistent with previous results of the Mate1 knockout mice
created by gene targeting using homologous recombination.
32
Metformin is a well characterized substrate for Mate1.
38
The
accumulation of metformin has been previously demonstra ted to
be significantly different between wild-type and Mate1 knockout
mice.
32
In the present study, the accumulation of metformin in
the liver and kidney was determined to functionally validate our
mouse model. At 60 min after an intravenous dose of 5 mg/kg
metformin, hepatic and renal accumulation was 6.9- and 3.4-fold
higher in the homozygous mutant mice than in the wild-type
control mice, respectively (P < 0.05, Figure 2). The results were
comparable to those obtained by others between Mate1 knockout
mice and wild-type mice.
32
Based on the results from genotyping,
transcript and function measurement, we concluded that the
Mate1 gene was effectively disrupted in our homozygous mutant
mice, which are therefore designated as Mate1/ mice.
Drug Transporter Gene Expression in Mate1/ and
Mate1+/+ Mice.
To clarify whether mRNA levels of other drug
transporter genes, in particular organic cation transporter genes,
are altered in Mate1/ mice, the mRNA expression of main
Figure 1. Generation of Mate1-decient mice via gene trapping. (A)
Schematic of gene trapping and genotyping strategy. Forward and reverse
primers are located in intron 10 of Mate1 genomic locus; V76 reverse
primer located in backbone of the trapping vector (Omnibank Gene Trap
Vector 76).
30
(B) PCR-based genotyping distinguishes wild-type, hetero-
zygous, and homozygous animals. Two polymerase chain reactions (PCR)
are needed for genotyping every mouse. The two PCR products were
mixed equally and separated at 2% gel with ethidium bromide staining.
(C) Transcript levels of Mate1 in Mate1+/+ and Mate1/ male mice.
The mRNA level shown is relative to that of Gapdh. ***P < 0.001
Figure 2. Metformin accumulation in the liver and the kidney of Mate1+/+
mice and Mate1/ mice. The Mate1+/+ (white bar) and Mate1/
(black bar) mice were sacriced at 60 min after the administration of
5 mg/kg metformin containing 0.2 μci/ml [
14
C]-metformin via tail vein
injection. Each bar represents the mean ( SD for 6 male mice. ***P <0.001
signicantly dierent from Mate1+/+ mice.
Page 3
2479 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
transporters in the kidney and liver was determined by real-time
PCR. Except that Abcb1a expression was elev ated by 150% in the
liver of Mate1/ mice (Figure 3), there was no difference in
the expression of other transporter genes between Mate1+/+ and
Mate1/ mice (data not shown).
Toxicokinetics of PQ in Mate1+/+ and Mate1/ Mice. We
compared the toxicokinetics of PQ (50 mg/kg), a substrate of
Mate1 identified in vitro,
29
in Mate1/ and Mate1+/+ mice. The
plasma concentrations of PQ were markedly elevated in Mate1/
mice compared with Mate1+/+ mice (Figure 4A). The
AUC
090min
for PQ in Mate1/ was significantly increased
64% when compared with that in Mate1+/+ mice (5530 ( 394 vs
3380 ( 216 μg
3
min/mL, P = 0.005). C
max
in Mate1/ and
Mate1 +/+ was 127 ( 13.4 and 80.5 ( 21.7 μg
3
mL/mg,
respectively, increasing 57% in the Mate1/ mice (P = 0.03).
The difference of T
max
between Mate1/ (84.2 ( 11.4 min)
and Mate1+/+ (61.8 ( 15.2 min) did not reach a statistical
significance (P = 0.06). The toxicokinetic parameters were sum-
marized in Table 1. The accumulation of PQ in the major tissues
including lung, liver and kidney were also measured after the
single dose. The renal accumulation of PQ in Mate1/ mice
was increased by 147% as compared to the Mate1+/+ mice (P =
0.014). In the lung, PQ accumulation was elevated by 59.5% in
Mate1/ mice (P = 0.03). However, there was a reversed trend
regarding PQ accumulation in the liver. The hepatic accumula-
tion of PQ tended to be lower in Mate1/ mice than in Mate1
+/+ mice (P = 0.16) (Figure 4B). Although PQ accumulation
tended to be higher in other tissues such as brain, the differences
did not reach statistical significance (data not shown).
PQ Toxicity in Mate1+/+ and Mate1/ Mice. Themiceof
different Mate1 genotypes (Mate1+/+ and Mate1 /)werein-
jected ip with 20 mg/kg PQ. The respiration and behavior activities
were observed for 72 h after PQ administration. Mate1/ mice
exhibited more difficult respiration, less movement, and decreased
body weight in comparison to Mate1+/+ mice (data not shown). All
mice were sacrificed at 72 h. The total RNA was extracted from the
kidney and liver. The transcript levels of the Kim-1 and Lcn2 genes, as
indicators of acute kidney injury,
36,37
were determined. Lcn2 expres-
sionwasapparentlyelevatedbyPQtreatment,withmuchmore
dramatic increase in the Mate1/ mice when compared with
Mate1+/+ by over 40-fold (P < 0.001). Similarly, Kim-1 expression
was 27-fold higher in the Mate1/ mice than that in the Mate1+/+
mice after PQ treatment (P < 0.001) (Figures 5A and 5B). The data
indicated that PQ caused more severe acute kidney injury in
Mate1/ mice than in Mate1+/+ mice.
Histopathologic evaluation of kidneys from PQ-treated mice
demonstrated much more severe necrosis containing eosinophilic
amorphous material and pyknotic debris (depicted by arrows
in Figure 6B) in Mate1/ mice than in Mate1+/+ mice. In
addition, Mate1/ kidney showed degeneration including tub-
ular dilatation, tubular cell vacuolation, and tubular cell detach-
ment from basement membrane after the PQ treatment. In the
liver, the damage by PQ also showed the same trend as that in the
kidney between the two genotypes (Figures 7A and 7B). There
was no obvious damage in the liver of Mate1+/+ mice, while in
Mate1/ mice, balloon hepatocytes and apoptotic necrotic cells
adjacent to the central vein existed and the basal membrane
adjacent to the central vein was inconsecutive and broken.
Figure 3. Hepatic Abcb1a transcript levels in Mate1+/+ and Mate1/
mice. The mRNA level shown is relative to the transcript level of Gapdh.
*P < 0.05, signicantly dierent from Mate1+/+ mice.
Figure 4. PQ toxicokinetics in the mice of dierent Mate1 genotypes.
(A) The plasma concentration prole of PQ in Mate1/ (2) and
Mate1+/+ (9) mice. 50 mg/kg PQ in saline was administered via tail
vein injection. Blood samples were collected at the time points indicated.
PQ levels in the blood samples were determined by counting
14
C-PQ
(the ratio of labeled to total PQ is 1:130). Each point represents the
mean ( SD for 6 male mice. *P < 0.05; **P < 0.01; ***P < 0.001,
signicantly dierent from Mate1+/+ mice. (B) PQ accumulation in
dierent tissues from Mate1+/+ mice (white bar) and Mate1/ mice
(black bar) at 90 min after 50 mg/kg PQ administration via tail vein
injection. Each bar represents the mean ( SD for 6 male mice. *P < 0.05;
**P < 0.01, signicantly dierent from Mate1+/+ mice.
Table 1. Toxicokinetic Parameters of PQ in Mate1+/+ and
Mate1/ Mice after 50 mg/kg PQ Injection via Tail Vein
parameters Mate1+/+ Mate1/ P value
AUC
090
(μg
3
min/mL) 3380 ( 216 5530 ( 394 0.005
AUC
0
(μg
3
min/mL) 7000 ( 2200 9530 ( 2230 0.16
C
max
(min) 80.5 ( 21.7 127 ( 13.4 0.03
T
max
(μg/m) 61.8 ( 15.2 84.2 ( 11.4 0.06
T
1/2
(min) 64.5 ( 9.3 55.2 ( 14.4 0.67
Page 4
2480 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
DISCUSSION
In the present study, the mouse model of Mate1 deciency was
successfully established via the gene trap technology. Successful
gene trapping was conrmed by using the primers specictothe
trap vector and to the Mate1 genomic locus. Mate1 transcripts
were rarely detected in the kidney and liver of Mate1/ mice,
two tissues with high Mate1 expression in wild-type mice.
37
Using
metformin as a probe substrate, our Mate1/ mice exhibited
loss of Mate1 transporter function that was comparable to a
previous Mate1 knockout mouse model created by conventional
targeting recombination.
32
We did not detect any alteration in the
expression of other transporters, including those transporting
organic cations, except Abcb1a encoding P-glycoprotein (P-gp)
in the liver. The mouse model of Mate1 deciency should be an
appropriate tool to characterize the disposition of the xenobiotics
interacting with MATE1 in vivo.
PQ, a widely used herbicide, is rapidly distributed into tissues
and accumulated in the lung, liver and kidney with high con-
centrations, resulting in serious toxicity in these organs. The
kidney is mainly responsible for the elimination of most systemic
PQ with minor contribution from the liver.
18,39
In order to treat
patients with PQ poisoning, it is critical to understand the
mechanism of PQ elimination in the kidney and preserve renal
function. In the in vitro overexpression system of HEK-293 cells,
PQ has been characterized as a substrate toward OCT2 and
MATE1.
29
Human OCT2 is primarily expressed at the basolat-
eral membrane and is responsible for the entry of organic cations
into the renal proximal tubular cells.
1
In contrast , MATE1 is
located in the brush-border mem brane and responsible for the
second step of renal secretion of organic cations. In the present
study, we sought to determine the role of Mate1 in determining
PQ disposition and toxicity in vivo by using our established
Mate1/ mouse model. We performed the toxicokinetics of
PQ in Mate1/ mice and Mate1+/+ mice. The concentrations
of PQ in the blood were markedly higher in Mate1/ mice
compared with Mate1+/+ mice, along with signicant dierences
in multiple toxicokinetic parameters. The data indicate that
Mate1 plays a critical role in PQ disposition. It should be noted
that the Mate1/ mice gained more body weight at 3 months
Figure 6. Histopathologic changes in the kidney from the mice received
PQ treatment. The Mate1+/+ (A) and Mate1/ (B) mice were
treated with a 20 mg/kg single ip dose for 72 h. Mate1/ kidney shows
sever necrosis containing eosinophilic amorphous material and pyknotic
debris (white arrows). The black scale bar represents 10 μm.
Figure 5. Renal transcript levels of the biomarker genes for acute kidney
injury in the mice received PQ treatment. (A) Lcn2 transcript levels. (B)
Kim-1 transcript levels, in the kidney of Mate1+/+ (white bar) and
Mate1/ (black bar) genotypes, respectively. The mRNA level shown
is relative to Gapdh transcript level. ***P < 0.001, signicantly dierent
from Mate1+/+ mice.
Page 5
2481 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
of age than wild-type mice. The reason remains to be determined.
Currently, there were no reports on eect of body weight on PQ
disposition. In this study, PQ was dosed based on the body
weight and the reported dierences between Mate1/ mice
and wild-type mice had been normalized with body weight,
suggesting that the toxicokinetic dierences between the two
genotypes are not secondary to the body weight dierence.
PQ accumulation in the kidney and lung, two of the major
organs responsible for PQ acute toxicity, was signicantly higher
for the Mate1/ mice than for the Mate1+/+ mice after an
acute single dose of 50 mg/kg. However, unexpectedly, PQ
accumulation in the liver, another major organ responsible for
PQ toxicity, tended to, while not signicantly, be lower for the
former after the acute dose. Since the hepatic accumulation of
metformin, a probe substrate of Mate1,
38
is signicantly higher in
the mice decient of Mate1 function,
32
we speculate that the
dierence in hepatic PQ accumulation between Mate1/ and
Mate1+/+ mice was secondary to Mate1 deciency. One possi-
bility is that Mate1 deciency caused functional changes for other
PQ transporters in the liver. We detected the transcript levels of
multiple drug transporter genes in the livers and kidneys from
Mate1/ and Mate1+/+ mice with and without PQ treatment.
While PQ treatment seemed to downregulate several transporter
genes in the kidney and liver of both Mate1+/+ and Mate/
mice, only hepatic Abcb1a was found to be dierently expressed
between these two mice, with Mate1/ mice showing 150%
higher expression . P-gp, encoded by Abcb1a in mice, is an ATP-
driven transmembrane transporter capable of transporting a wide
variety of structurally diverse and functionally unrelated com-
pounds out of the cell.
40
Dinis-Oliveira et al. have reported that
the induction of de novo synthe sis of P-gp by dexamethasone
decreases PQ lung accumulation and consequently its toxicity.
41
On the other hand, verapamil, a competitive inhibitor of this
transporter, when given one hour before dexamethasone,
blocked these protective eects and caused an increase of PQ
lung concentration and an aggravation in toxicity.
42
It is thus
likely that the increased Abcb1a expression was able to overcome
Mate1 deciency and responsible for the less or unaltered PQ
accumulation in the Mate1/ mice during the studied time.
However, this hypothesis needs to be further tested. In particular,
it is necessary to directly conrm PQ as a P-gp substrate and
determine the mechanism of hepatic Abcb1a upregulation sec-
ondary to Mate1 deciency. It should be noted that Mate1/
mice still exhibited more severe hepatoxicity than Mate1+/+
mice after three days of PQ exposure, which may be explained by
a much higher systemic PQ exposure over time and/or severe
toxicity in other critical organs including kidney and lung.
PQ poisoning can cause acute kidney injury (AKI).
3
Kid-
ney injury molecular-1 protein (Kim-1),
36,43
and lipocalin 2 gene
(Lcn2), encoding neutrophil gelatinase-associated lipocalin
(NGAL),
37,44
have been demonstrated to be highly upregulated
during AKI. They are both primarily potential biomarkers of the
early stage of AKI in rodents and humans.
36,37
We found that the
mRNA expression of Kim-1 and Lcn2 genes were elevated
dramatically in the Mate1/ mice treated by 20 mg/kg PQ
for three days, with only marginal increase detected in the Mate1+/+
mice. Moreover, the histology of kidney and liver showed
more severe damage in Mate1/ mice when compared to
Mate1+/+ mice. We also observed apparent toxic symptoms such
as respiration diculty and body weight loss in Mate1/ mice
but not in Mate1+/+ mice. These results, coupled with the
toxicokinetic ones, indicated that Mate1 played a critical role in
PQ-induced acute toxicity including AKI by modulation of PQ
elimination in the kidney. In humans, MATE1 is highly expressed
in the kidney and the liver. MATE2 (MATE2-K) exhibits a
kidney-specic expression. MATE1 and MATE2 are detected
at similar mRNA levels in human kidney. In mice, Mate1 is
highly expressed in both the kidney and the liver. The
tissue distribution of Mate1 in mice is generally consistent with
Figure 7. Histopathologic changes in the liver from the mice received
PQ treatment. The Mate1+/+ (A) and Mate1/ (B) mice were
treated with a 20 mg/kg single ip dose for 72 h. Mate1/ liver shows
balloon hepatocytes and apoptotic necrotic cells adjacent to the central
vein and the basal membrane adjacent to the central v ein was in-
consecutiveandbroken(whitearrows).Theblackscalebarrepre-
sents 10 μm.
Page 6
2482 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
that in humans. However, MATE2 is not expressed in mice.
Therefore, in the case of MATE, Mate1/ mice may represent
a model of decien cy in both MATE1 and MATE2 in human
kidney.
32
Previous dat a suggest a positive doseresponse relationship
between lifetime cumulative exposure to PQ and risk of PD.
4547
Future studies are warranted to use the Mate1/ mice to
determine the role of Mate1 in PQ-induced chronic toxicity such
as PD risk. Our data suggest that the toxic response to PQ in
patients may vary because of dierent activity of MATE and that
we should avoid the drugs and factors inhibiting MATE function
when treating these patients. For example, patients with certain
genetic variants of MATE including MATE1 and MATE2 may
have dierent susceptibility to PQ toxicity. Two variants of
human MATE1 with no function and four with altered function
have been reported.
48,49
Three of them w ere polymorphic in
a particular ethnic population with allele frequencies g reater
than 2%. Clinical signicance of human MATE polymor-
phisms in PQ-associated symptoms and diseases merits further
investigation.
In summary, we generated a mouse model of Mate1 functional
deciency by gene trapping. The mouse model can be used to
characterize in vivo xenobiotic disposition and explore Mate1
physiology. By using this model, we have demonstrated for the
rst time that the Mate1 transporter plays a critical role in the
renal elimination of PQ in mice and in conferring PQ toxicity.
Future studies are require d to dene the eect of MATE
transporter function on PQ toxicity in humans.
AUTHOR INFORMATION
Corresponding Author
*Department of Pharmaceutical Sciences, School of Pharmacy,
University of Maryland at Baltimore, 20 Penn Street, HSF II
Room 555, Baltimore, MD 21201, USA. Phone: + 01 410-706-
7358. Fax: +01 410-706-7015. E-mail: yshu@r x.umaryland.edu.
ACKNOWLEDGMENT
Dr. Yan Shu receives intramural start-u p funds from the
School of Pha rmacy, University of Maryland Baltimore. Dr.
Hongbing Wang receives a research grant from the National
Institutes of Health, National Institute of Diabetes and Digestive
and Kidney Diseases (Grant No. DK061652) .
REFERENCES
(1) Wright, S. H. Role of organic cation transporters in the renal
handling of therapeutic agents and xenobiotics. Toxicol. Appl. Pharmacol.
2005, 204 (3), 309319.
(2) Aleksunes, L. M.; Augustine, L. M.; Scheer, G. L.; Cherrington,
N. J.; Manautou, J. E. Renal xenobiotic transporters are dierentially
expressed in mice following cisplatin treatment. Toxicology 2008, 250
(23), 8288.
(3) Kimbrough, R. D. Toxic eects of the herbicide paraquat. Chest
1974, 65 (Suppl.), 65S67S.
(4) Rogers, P. A.; Spillane, T. A.; Fenlon, M.; Henaghan, T. Suspected
paraquat poisoning in pigs and dogs. Vet. Rec. 1973, 93 (2), 4445.
(5) Vale, J. A.; Meredith, T. J.; Buckley, B. M. Paraquat poisoning:
clinical features and immediate general management. Hum. Toxicol.
1987, 6 (1), 4147.
(6) Ascherio, A.; Chen, H.; Weisskopf, M. G.; OReilly, E.; McCullough,
M. L.; Calle, E. E.; et al. Pesticide exposure and risk for Parkinsonsdisease.
Ann. Neurol. 2006, 60 (2), 197203.
(7) Kamel, F.; Engel, L. S.; Gladen, B. C.; Hoppin, J. A.; Alavanja,
M. C.; Sandler, D. P. Neurologic symptoms in licensed pesticide
applicators in the Agricultural Health Study. Hum. Exp. Toxicol. 2007,
26 (3), 243250.
(8) Samai, M.; Sharpe, M. A.; Gard, P. R.; Chatterjee, P. K. Compar-
ison of the eects of the superoxide dismutase mimetics EUK-134 and
tempol on paraquat-induced nephrotoxicity. Free Radical Biol. Med.
2007, 43 (4), 528534.
(9) Molck, A. M.; Friis, C. Transport of paraquat by isolated renal
proximal tubular segments from rabbits. Pharmacol. Toxicol. 1998, 83
(5), 208213.
(10) Cristovao, A. C.; Choi, D. H.; Baltazar, G.; Beal, M. F.; Kim,
Y. S. The role of NADPH oxidase 1-derived reactive oxygen species in
paraquat-mediated dopaminergic cell death. Antioxid. Redox Signaling
2009,
11 (9), 21052118.
(11) Liochev, S. I.; Fridovich, I. The role of O2.- in the production of
HO.: in vitro and in vivo. Free Radical Biol. Med. 1994, 16 (1), 2933.
(12) Winterbourn, C. C.; Sutton, H. C. Hydroxyl radical production
from hydrogen peroxide and enzymatically generated paraquat radicals:
catalytic requirements and oxygen dependence. Arch. Biochem. Biophys.
1984, 235 (1), 116126.
(13) Clejan, L.; Cederbaum, A. I. Synergistic interactions between
NADPH-cytochrome P-450 reductase, paraquat, and iron in the gen-
eration of active oxygen radicals. Biochem. Pharmacol. 1989, 38 (11),
17791786.
(14) Fernandez, A.; Kiefer, J.; Fosdick, L.; McConkey, D. J. Oxygen
radical production and thiol depletion are required for Ca(2+)-mediated
endogenous endonuclease activation in apoptotic thymocytes. J. Im-
munol. 1995, 155 (11), 51335139.
(15) Fukushima, T.; Yamada, K.; Isobe, A.; Shiwaku, K.; Yamane, Y.
Mechanism of cytotoxicity of paraquat. I. NADH oxidation and paraquat
radical formation via complex I. Exp. Toxicol. Pathol. 1993, 45 (56),
345349.
(16) Ge, W.; Zhang, Y.; Han, X.; Ren, J. Cardiac-specic over-
expression of catalase attenuates paraquat-induced myocardial geo-
metric and contractile alteration: role of ER stress. Free Radical Biol.
Med. 2010, 49 (12), 20682077.
(17) Niso-Santano, M.; Bravo-San Pedro, J. M.; Gomez-Sanchez, R.;
Climent, V.; Soler, G.; Fuentes, J. M.; et al. ASK1 overexpression
accelerates paraquat-induced autophagy via endoplasmic reticulum
stress. Toxicol. Sci. 2011, 119 (1), 156168.
(18) Chan, B. S.; Lazzaro, V. A.; Seale, J. P.; Duggin, G. G. The renal
excretory mechanisms and the role of organic cations in modulating the
renal handling of paraquat. Pharmacol. Ther. 1998, 79 (3), 193203.
(19) Chui, Y. C.; Poon, G.; Law, F. Toxicokinetics and bioavailability
of paraquat in rats following dierent routes of administration. Toxicol.
Ind. Health 1988, 4 (2), 203219.
(20) Jonker, J. W.; Schinkel, A. H. Pharmacological and physiological
functions of the polyspeci
c organic cation transporters: OCT1, 2, and 3
(SLC22A13). J. Pharmacol. Exp. Ther. 2004, 308 (1), 29.
(21) Lash, L. H.; Putt, D. A.; Cai, H. Membrane transport function in
primary cultures of human proximal tubular cells. Toxicology 2006, 228
(23), 200218.
(22) Meyer zu Schwabedissen, H. E.; Verstuyft, C.; Kroemer, H. K.;
Becquemont, L.; Kim, R. B. Human multidrug and toxin extrusion 1
(MATE1/SLC47A1) transporter: functional characterization, interac-
tion with OCT2 (SLC22A2), and single nucleotide polymorphisms. Am.
J. Physiol. 2010, 298 (4), F997F1005.
(23) Ohta, K. Y.; Inoue, K.; Yasujima, T.; Ishimaru, M.; Yuasa, H.
Functional characteristics of two human MATE transporters: kinetics of
cimetidine transport and proles of inhibition by various compounds.
J. Pharm. Pharm. Sci. 2009, 12 (3), 388396.
(24) Alnouti, Y.; Petrick, J. S.; Klaassen, C. D. Tissue distribution and
ontogeny of organic cation transporters in mice. Drug Metab. Dispos.
2006, 34 (3), 477482.
(25) Duan, H.; Wang, J. Selective transport of monoamine neurotrans-
mitters by human plasma membrane monoamine transporter and organic
cation transporter 3. J. Pharmacol. Exp. Ther. 2010, 335 (3), 743753.
Page 7
2483 dx.doi.org/10.1021/mp200395f |Mol. Pharmaceutics 2011, 8, 2476–2483
Molecular Pharmaceutics
BRIEF ARTICLE
(26) Iwata, D.; Kato, Y.; Wakayama, T.; Sai, Y.; Kubo, Y.; Iseki, S.; et al.
Involvement of carnitine/organic cation transporter OCTN2 (SLC22A5)
in distribution of its substrate carnitine to the heart. Drug Metab. Pharma-
cokinet. 2008, 23 (3), 207215.
(27) Masuda, S.; Terada, T.; Yonezawa, A.; Tanihara, Y.; Kishimoto,
K.; Katsura, T.; et al. Identication and functional characterization of a
new human kidney-specic H+/organic cation antiporter, kidney-spe-
cic multidrug and toxin extrusion 2. J. Am. Soc. Nephrol. 2006, 17 (8),
21272135.
(28) Tsuda, M.; Terada, T.; Ueba, M.; Sato, T.; Masuda, S.; Katsura,
T.; et al. Involvement of human multidrug and toxin extrusion 1 in the
drug interaction between cimetidine and metformin in renal epithelial
cells. J. Pharmacol. Exp. Ther. 2009, 329 (1), 185191.
(29) Chen, Y.; Zhang, S.; Sorani, M.; Giacomini, K. M. Transport of
paraquat by human organic cation transporters and multidrug and toxic
compound extrusion family. J. Pharmacol. Exp. Ther. 2007, 322 (2),
695700.
(30) Zambrowicz, B. P.; Abuin, A.; Ramirez-Solis, R.; Richter, L. J.;
Piggott, J.; BeltrandelRio, H.; et al. Wnk1 kinase deciency lowers blood
pressure in mice: a gene-trap screen to identify potential targets for
therapeutic intervention. Proc. Natl. Acad. Sci. U.S.A. 2003, 100 (24),
1410914114.
(31) Konig, J.; Zolk, O.; Singer, K.; Homann, C.; Fromm, M.
Double-transfected MDCK cells expressing human OCT1/MATE1 or
OCT2/MATE1: determinants of uptake and transcellular translocation
of organic cations. Br. J. Pharmacol. 2011, 163 (3), 546555.
(32) Tsuda, M.; Terada, T.; Mizuno, T.; Katsura, T.; Shimakura, J.;
Inui, K. Targeted disruption of the multidrug and toxin extrusion 1
(mate1) gene in mice reduces renal secretion of metformin. Mol.
Pharmacol. 2009, 75 (6), 12801286.
(33) Neves, F. F.; Sousa, R. B.; Pazin-Filho, A.; Cupo, P.; Elias Junior,
J.; Nogueira-Barbosa, M. H. Severe paraquat poisoning: clinical and
radiological ndings in a survivor. J. B ra s. Pn eum ol. 2010, 36 (4 ),
5135 16.
(34) Ecker, J. L.; Hook, J. B.; Gibson, J. E. Nephrotoxicity of
paraquat in mice. Toxicol. Appl. Pharmacol. 1975
, 34 (1), 178186.
(35) Nakagawa, I.; Suzuki, M.; Imura, N.; Naganuma, A. Enhance-
ment of paraquat toxicity by glutathione depletion in mice in vivo and in
vitro. J. Toxicol. Sci. 1995 , 20 (5), 557564.
(36) Wang, E. J.; Snyder, R. D.; Fielden, M. R.; Smith, R. J.; Gu, Y. Z.
Validation of putative genomic biomarkers of nephrotoxicity in rats.
Toxicology 2008, 246 (23), 91100.
(37) Wasilewska, A.; Zoch-Zwierz, W.; Taranta-Janusz, K.; Michaluk-
Skutnik, J. Neutrophil gelatinase-associated lipocalin (NGAL): a new
marker of cyclosporine nephrotoxicity? Pediatr. Nephrol. 2010, 25 (5),
889897.
(38) Nies, A. T.; Koepsell, H.; Damme, K.; Schwab, M. Organic
cation transporters (OCTs, MATEs), in vitro and in vivo evidence for
the importance in drug therapy. Handb. Exp. Pharmacol. 2011,
201, 105167.
(39) Chan, B. S.; Lazzaro, V. A.; Seale, J. P.; Duggin, G. G. Transport
of paraquat by a renal epithelial cell line, MDCK. Renal Failure 1997, 19
(6), 745751.
(40) Li, Y.; Yuan, H.; Yang, K.; Xu, W.; Tang, W.; Li, X. The structure
and functions of P-glycoprotein. Curr. Med. Chem. 2010, 17 (8),
786800.
(41) Dinis-Oliveira, R. J.; Remiao, F.; Duarte, J. A.; Ferreira, R.;
Sanchez Navarro, A.; Bastos, M. L.; et al. P-glycoprotein induction: an
antidotal pathway for paraquat-induced lung toxicity. Free Radical Biol.
Med. 2006, 41 (8), 12131224.
(42) Stein, W. D. Kinetics of the multidrug transporter (P-
glycoprotein) and its reversal. Physiol. Rev. 199 7, 77 (2), 545590.
(43) Ko, G. J.; Grigoryev, D. N.; Linfert, D.; Jang, H. R.; Watkins, T.;
Cheadle, C.; et al. Transcriptional analysis of kidneys during repair
from AKI reveals possible roles for NGAL and KIM-1 as biomarkers
of AKI-to-CKD transition. Am.J.Physiol.2010, 298 (6), F1472F1483.
(44) Ferguson, M. A.; Vaidya, V. S.; Bonventre, J. V. Biomarkers of
nephrotoxic acute kidney injury. Toxicology 2008, 245
(3), 182193.
(45) Liou, H. H.; Tsai, M. C.; Chen, C. J.; Jeng, J. S.; Chang, Y. C.;
Chen, S. Y.; et al. Environmental risk factors and Parkinsons disease: a
case-control study in Taiwan. Neurology 1997, 48 (6), 15831588.
(46) Nistico, R.; Mehdawy, B.; Piccirilli, S.; Mercuri, N. Paraquat-
and rotenone-induced models of Parkinsons disease. Int. J. Immuno-
pathol. Pharmacol. 2011, 24 (2), 313322.
(47) Wang, A.; Costello, S.; Cockburn, M.; Zhang, X.; Bronstein, J.;
Ritz, B. Parkinsons disease risk from ambient exposure to pesticides.
Eur. J. Epidemiol. 2011, 26 (7), 547555.
(48) Chen, Y.; Teranishi, K.; Li, S.; Yee, S. W.; Hesselson, S.; Stryke,
D.; et al. Genetic variants in multidrug and toxic compound extrusion-1,
hMATE1, alter transport function. Pharmacogenomics J. 2009, 9 (2),
127136.
(49) Becker, M. L.; Visser, L. E.; van Schaik, R. H.; Hofman, A.;
Uitterlinden, A. G.; Stricker, B. H. Genetic variation in the multidrug and
toxin extrusion 1 transporter protein inuences the glucose-lowering
eect of metformin in patients with diabetes: a preliminary study.
Diabetes 2009, 58 (3), 745749.
Page 8
  • Source
    • "Further, the levels of creatinine and BUN in the mice treated with cisplatin were significantly enhanced by pyrimethamine, a potent MATE in- hibitor [132]. Li et al. later reported that much severer nephrotoxicity of cisplatin was observed in Mate1-/-mice than in wild-type mice [133]. Thus, reduced function of MATEs, which serves as efflux transporters for cisplatin elimination in the kidney, may be responsible for cisplatin-induced nephrotoxicity. "
    [Show abstract] [Hide abstract] ABSTRACT: Membrane transporters play critical roles in moving a variety of anticancer drugs across cancer cell membrane, thereby determining chemotherapy efficacy and/or toxicity. The retention of anticancer drugs in cancer cells is the result of net function of efflux and influx transporters. The ATP-binding cassette (ABC) transporters are mainly the efflux transporters expressing at cancer cells, conferring the chemo-resistance in various malignant tumors, which has been well documented over the past decades. However, the function of influx transporters, in particular the solute carriers (SLC) in cancer cells, has only been recently well recognized to have significant impact on cancer therapy. The SLC transporters not only directly bring anticancer agents into cancer cells but also serve as the uptake mediators of essential nutrients for tumor growth and survival. In this review, we concentrate on the interaction of SLC transporters with anticancer drugs and nutrients, and their impact on chemo-sensitivity or -resistance of cancer cells. The differential expression patterns of SLC transporters between normal and tumor tissues may be well utilized to achieve specific delivery of chemotherapeutic agents.
    Full-text · Article · May 2014
  • Source
    • "The hypothesis that puts agrochemicals front and center is highly plausible, given the documented harmful effects of these prod- ucts.484950 Nevertheless, going forward, it would be imprudent for any research to pose the predominance of agrochemicals as CKDnc causal factors without a methodology designed to promote in-depth investigation into the quite possibly synergistic involvement of suspected co-factors. "
    [Show abstract] [Hide abstract] ABSTRACT: This paper contextualizes the chronic kidney disease epidemic and related burden of disease affecting Central American farming communities. It summarizes the two main causal hypotheses (heat stress and agrochemicals), draws attention to the consequences of dichotomous reasoning concerning causality, and warns of potential confl icts of interest and their role in “manufacturing doubt.” It describes some methodological errors that compromise past study fi ndings and cautions against delaying public health actions until a conclusive understanding is reached about the epidemic’s causes and underlying mechanisms. It makes the case for a comprehensive approach to the historical, social and epidemiological facts of the epidemic, for critically assessing existing studies and for enhanced rigor in new research.
    Full-text · Article · Apr 2014 · MEDICC review
    • "Bradykinin causes activation and association of PKCz, PKCD, and PKCe with OAT3 in COS-7 cells, thereby leading to an increase in OAT3 cell surface expression and transport activity via an increased maximal transport rate (Li, Duan, & You, 2010). Both insulin and epidermal growth factor increase surface expression and activity of OAT1 and OAT3 via a complex signaling cascade involving PKA activation (Pelis & Wright, 2011). Using renal cortical slices from mice, Barros et al. (2009) showed that PKCz activation is downstream of PKA and is likely the end mediator in the signaling cascade involved in insulin and epidermal growth factor stimulation of OAT activity. "
    [Show abstract] [Hide abstract] ABSTRACT: Transporters within the SLC22, SLC44, and SLC47 families of solute carriers mediate transport of a structurally diverse array of organic electrolytes, that is, molecules that are generally charged (cationic, anionic, or zwitterionic) at physiological pH. Transporters in the SLC22 family-all of which are members of the major facilitator superfamily (MFS) of transporters-represent a mechanistically diverse set of processes, including the organic anion transporters (OATs and URAT1) that physiologically operate as organic anion (OA) exchangers, the organic cation transporters (OCTs) that operate as electrogenic uniporters of organic cations (OCs), and the so-called "novel" organic cation transporters (OCTNs) that support Na-cotransport of selected zwitterions. Whereas the OCTNs display a high degree of substrate selectivity, the physiological hallmark of the OATs and OCTs is their multiselectivity-consistent with a principal role in renal and hepatic clearance of a wide array of both endogenous and xenobiotic compounds. SLC47 consists of members of the multidrug and toxin extruder (MATE) family, which are carriers that are obligatory exchangers and that physiologically support electroneutral H(+) exchange. The MATEs also display a characteristic multiselectivity and are frequently paired with OCTs to mediate transepithelial OC secretion, with the OCTs typically supporting basolateral OC entry and the MATEs supporting apical OC efflux. The SLC44 family contains the choline transporter-like (CTL) transporters. Largely restricted to choline and a limited set of structural congeners, the CTLs appear to support the Na-independent, electrogenic uniport of choline, thereby providing choline for membrane biogenesis. The solution of X-ray crystal structures of representative prokaryotic MFS and MATE transporters has led to the development of homology models of mammalian OAT, OCT, and MATE transporters that, in turn, have supplemented studies of the molecular basis of the complex interactions of ligands with these multiselective proteins.
    No preview · Article · Apr 2014 · Current Topics in Membranes
Show more