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Anwar Gamal Mohamed Louisville

 

 

Abstract: Anwar Gamal Mohamed Louisville

 

1.                     Introduction


Anwar Gamal Mohamed realized that The aryl hydrocarbon receptor (AhR) is a ligand-activated helix–
loop–helix protein that exists as cytoplasmic aggregates bound to
two 90-kDa heat-shock proteins (HSP90), the co-chaperone p23
and the 43-kDa protein termed hepatitis B virus X-associated pro
tein. Upon ligand binding, the ligand-receptor complex dissociates
from HSP90 and translocates to the nucleus where it dimerizes
with the aryl hydrocarbon receptor nuclear translocator (ARNT).
After that, the whole cytoplasmic complex acts as a transcription
factor that binds to DNA promoter sequences termed xenobiotic
responsive elements (XREs), thereby enhancing the transcription
of the responsive genes. Among these genes are those encoding a
number of AhR-regulated genes, including three phase I enzymes:
cytochrome P4501A1 (Cyp1a1), Cyp1a2, and Cyp1b1; and four
phase II enzymes: NAD(P)H: quinone oxidoreductase-1 (Nqo1),
glutathione
S-transferase a1 subunit (Gsta1), cytosolic aldehyde
dehydrogenase and UDP-glucuronosyltransferase 1A6 (
Nebert
and Duffy, 1997
).

    


According to Anwar Gamal Mohamed It is well known that, the induction of phase II enzymes serves as
a detoxification mechanism for many mutagens, carcinogens and
other toxic compounds. However, the induction of Cyp1a1, Cyp1a2,and Cyp1b1 is counterproductive to this process. Several AhR ligands are environmental contaminants that not only serve as agonists of the AhR, but, with the exception of 2,3,7,8-tetrachlo
rodibenzo-
p-dioxin (TCDD), which is poorly metabolized, are also
substrates for the AhR-regulated phase I enzymes. The conversion
of AhR ligands into diol epoxide compounds by Cyp1a1, Cyp1a2,
or Cyp1b1 results in the formation of covalent adducts when these
genotoxic metabolites react with guanines in critical genes, poten
tially initiating tumorigenesis and other toxic responses. Such
responses include birth defects, immune suppression, and endo
crine disruption (
Spink et al., 2002).


Although, the majority of published studies intensely focused
on the toxic effects of individual AhR ligands forms, there are rel
atively few reports on the combined toxic effects of AhR ligands
and other environmental co-contaminants of concern such as hea
vy metals typified by Hg2+. Hg2+ is unique because it can exist in
several physical and chemical forms, for example elemental mer
cury is liquid at room temperature (
Fitzgerald and Clarkson,
1991
). All forms of mercury have toxic effects in a number of or
gans especially in the kidneys. In addition, Hg2+ is widely used in
the foundry, mining, and manufacturing industries and is a compo
nent in a number of electrical instruments and medical products
such as thermometers, thermostats, dental amalgams, switches,
and batteries (
Gochfeld, 2003). Importantly, both AhR ligands,
Corresponding author. Address: Faculty of Pharmacy and Pharmaceutical
Sciences, 2142 J Katz Group-Rexall Centre for Pharmacy and Health Research,


 

typified by TCDD, and heavy metals, typified by Hg2+, are ranked
high on the list of the most hazardous xenobiotics in the environment, as reported by the Agency for Toxic Substances and Diseases
Registry and the Canadian Environmental Protection Act (
ATSDR,
2011; CEPA, 2006
).

 


We have previously shown that, Hg
2+ differentially alters the
expression of several AhR-regulated genes in murine hepatoma
Hepa 1c1c7 and human hepatoma HepG2 cells. For example,
Hg
2+ inhibits the TCDD-mediated induction of CYP1A1 in HepG2
cells, while it potentiates it in murine hepatoma Hepa 1c1c7 cells
(
Amara et al., 2010; Korashy and El-Kadi, 2004, 2005). Moreover,
Hg
2+ increases the basal and inducible expression of NQO1 in
HepG2 cells through a transcriptional mechanism. Similarly Hg
2+
induces Nqo1 and Gsta1 in Hepa 1c1c7 cells (Amara and El-Kadi,
2011; Korashy and El-Kadi, 2006
).
Emerging evidence suggests that AhR ligands and metals coexposure generates different biological responses than what is expected based on the toxicological mechanisms of each class evaluated separately. However, to the best of our knowledge, there has
been no previous attempt to examine the effect of Hg
2+ on the regulation of AhR-regulated genes in the presence and absence of
TCDD in extrahepatic tissues. Therefore, we hypothesize that
Hg
2+ differentially alters the expression of AhR-regulated enzymes
in a time-, tissue-, and AhR-regulated enzyme genes manner. Thus,
the objective of the current study was to investigate the time-, tissue-, and AhR-regulated enzyme genes effects upon exposure to a
single dose of Hg
2+ in the absence and presence of TCDD in extrahepatic tissues, namely, kidney, lung, and heart.


2. Materials and methods


2.1. Materials
Dr. Anwar Gamal Mohamed Archives showed that TRIzol reagent was purchased from Invitrogen (Carlsbad, CA). High-Capacity cDNA
Reverse Transcription Kit, SYBR Green SuperMix, and 96-well optical reaction plates
with optical adhesive films were purchased from Applied Biosystems (Foster City,
CA). Real-time PCR primers were synthesized by Integrated DNA Technologies, Inc.
7-ethoxyresorufin, anti-goat IgG peroxidase secondary antibody, protease inhibitor
cocktail, and mercuric chloride (HgCl
2) were purchased from Sigma Chemical Co.
(St. Louis, MO). TCDD, >99% pure, was purchased from Cambridge Isotope Laboratories
(Woburn, MA). Chemiluminescence Western blotting detection reagents were from
GE Healthcare Life Sciences (Piscataway, NJ). Nitrocellulose membrane was purchased
from Bio-Rad Laboratories (Hercules, CA). Cyp1a1/1a2 mouse polyclonal primary antibody, glyceraldehyde-3-phosphate dehydrogenase (Gapdh) rabbit polyclonal antibody, heme oxygenase-1 (HO-1) goat polyclonal primary antibody, and anti-rabbit
IgG peroxidase secondary antibody were purchased from Santa Cruz Biotechnology,
Inc. (Santa Cruz, CA). Cyp1b1 polyclonal primary antibody was purchased from BD Biosciences (Mississauga, ON). Gsta1 primary polyclonal antibody was purchased from
Abcam (Cambridge, MA). Nqo1 polyclonal primary antibody and anti-mouse IgG peroxidase secondary antibody was purchased from R&D Systems, Inc. (Minneapolis,
MN). All other chemicals were purchased from Fisher Scientific (Toronto, ON).


2.2. Animal treatment
 
acording that Anwar Gamal Mohamed Frankfort Male C57Bl/6J (22–30 g) mice were obtained from Charles River, Canada
(Montreal, QC, Canada). Animals were injected intraperitoneally (i.p.) with Hg
2+
(dissolved in saline) at 2.5 mg/kg, with or without TCDD 15 lg/kg (dissolved in corn
oil). The mice were divided into four groups. The first group (
n = 12) was control
which was injected with saline (0.4 mL) and corn oil (0.4 mL). The second group
(
n = 12) was Hg2+ treated mice which received Hg2+ dissolved in saline (0.4 mL) plus
corn oil (0.4 mL) The third group (
n = 12) was TCDD treated mice which received
TCDD dissolved in corn oil (0.4 mL) plus saline (0.4 mL). The fourth group (
n = 12)
was Hg
2+ plus TCDD treated mice which received Hg2+ dissolved in saline
(0.4 mL) plus TCDD dissolved in corn oil (0.4 mL). Thereafter, the animals were
euthanized after a single injection at 6 h (
n = 6) and 24 h (n = 6) via cervical dislocation. Kidney, lung and heart, tissues were excised, immediately frozen in liquid nitrogen, and stored at 80 C until analysis. All experimental procedures involving
animals were approved by the University of Alberta Health Sciences Animal Policy
and Welfare Committee. All animals were allowed free access to food and water
throughout the treatment period. Furthermore, the concentrations of Hg
2+ and
TCDD utilized in the current study were selected based on previous
in vivo studies
that used the same and different mouse strains (
Hu et al., 1999; Mehra and Kanwar,
1980; Tanaka-Kagawa et al., 1998; Uno et al., 2008; Wong et al., 2010
).
2.3. RNA isolation and real-time polymerase chain reaction (real-time PCR)
Total RNA from the frozen tissues was isolated using TRIzol reagent, according to
the manufacturer’s instructions (Invitrogen). Real-time PCR reactions were performed on an ABI 7500 instrument, using SYBR
Green PCR Master Mix (Applied Biosystems). The amplification reactions were performed as follows: 10 min at 95 C,
and 40 cycles of 94 C for 15 s and 60 C for 1 min. The primers used in the current
study were chosen from previously published studies and are listed in
Table 1. The
real-time PCR data were analyzed using the relative gene expression (i.e.,
DDCt)
method, as described in Applied Biosystems User Bulletin No. 2 and explained further by
Livak and Schmittgen (2001).
2.4. Preparation of microsomal and cytosolic protein fractions


Heart, lung and kidney microsomes were prepared by differential centrifugation
of homogenized tissues as previously described (
Barakat et al., 2001). Briefly, individual heart, lung and kidney tissues were rapidly removed and washed in ice-cold
potassium chloride [1.15% (w/v)]. Consequently, they cut into pieces, and homogenized separately in cold sucrose solution (1 g of tissue in 5 mL of 0.25 M sucrose).
After homogenizing, the tissues were separated by different ultracentrifugation.
The final pellet was reconstituted in cold sucrose and supernatant, cytosol, were
stored at 80 C. Thereafter, microsomal and cytosolic protein concentrations were
determined by the Lowry method using bovine serum albumin as a standard (
Lowry

et al., 1951
).


2.5. Western blot analysis
Western blot analysis was performed using a previously described method (Zordoky et al., 2010). Briefly, 20 lg of kidney lung and microsomal or cytosolic proteins
was separated by 10% sodium dodecyl sulfate–polyacrylamide gel (SDS–PAGE), and
then electrophoretically transferred to nitrocellulose membrane. Protein blots were
then blocked overnight at 4 C in blocking solution containing 0.15 M sodium chloride, 3 mM potassium chloride, 25 mM Tris-base (TBS), 5% skim milk, 2% bovine serum albumin, and 0.5% Tween-20. After blocking, the blots were incubated with the
following antibodies: primary polyclonal mouse anti-rat Cyp1a1/1a2, primary polyclonal rabbit anti-rat Cyp1b1, primary polyclonal goat anti-mouse Nqo1, primary
polyclonal goat anti-rat Gsta1, primary polyclonal rabbit anti-mouse actin, or primary polyclonal goat anti-mouse Gapdh for 2 h at room temperature. Incubation
with a peroxidase-conjugated goat anti-rabbit IgG secondary antibody for Nqo1,
Cyp1b1, and actin or goat anti-mouse IgG secondary antibody for Cyp1a1/1a2, or
rabbit anti-goat IgG secondary antibody for Gsta1, HO-1 and Gapdh was carried
out for another 2 h at room temperature. The bands were visualized using the enhanced chemiluminescence method according to the manufacturer’s instructions
(GE Healthcare Life Sciences, Piscataway, NJ). The intensity of the protein bands were
quantified, relative to the signals obtained for actin, using ImageJ software [National
Institutes of Health, Bethesda, MD,
http://rsb.info.nih.gov/ij.].

 

2.7. Determination of Nqo1 enzymatic activity


Dr. Anwar Gamal Mohamed Archives The Nqo1 activity was determined by the continuous spectrophotometric assay
to quantitate the reduction of its substrate, 2,6-dichlorophenolindophenol (DCPIP)
as described previously (
Korashy and El-Kadi, 2006; Preusch et al., 1991). Briefly,
20
lg of cytosolic protein was incubated with 1 mL of the assay buffer [40 lM
DCPIP, 0.2 mM NADPH, 25 mM Tris–HCl, pH 7.8, 0.1% (v/v) Tween 20, and 0.7 mg/
mL bovine serum albumin, 0 or 30
lM dicoumarol]. The rate of DCPIP reduction
was monitored over 90 s at 600 nm with an extinction coefficient (
e) of
2.1 mM
1 cm1. The Nqo1 activity was calculated as the decrease in absorbance
per min per mg of total protein of the sample which quantitates the dicoumarolinhibitable reduction of DCPIP.


2.8. Determination of Gsta1 activity


Anwar Mohamed Louisville
Gsta1 activity was determined spectrophotometrically using 1-chloro-2,4-dinitrobenzene (CDNB) as a substrate according to the method of Habig (Habig et al.,
1974
). Briefly, 20 lg of cytosolic or microsomal proteins were incubated with
1 mM CDNB, 1 mM lower glutathione in 0.1 M potassium phosphate buffer, pH
6.5 at 25 C in a total volume of 1 mL. Gsta1 activity was measured as the amount
of CDNB conjugate formed by recording the absorbance at 340 nm for 1.5 min with
an extinction coefficient of 9600 M
1 cm1. The enzyme activity was expressed as
nmol/min/mg protein.

 

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