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Animal Studies of PCBs and Lung Cancer
Studies 32- 62
This may not be a complete list of all studies on this
topic. For more studies, visit the TOXNET
database operated by the National Library of Medicine (the source of these
abstracts.) Keep in mind that these studies are not all equal in size or
quality. Some were published in peer-reviewed journals, while others were
simply presented at conferences. A few are duplicates by the same author
(one conference-based, another published) but we presented both because
the descriptions were slightly different.
Study #32
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2 PAH’s [air & water pollutants] caused increased mutations
and increased DNA adduct levels if the test included lung microsomes from
PCB-treated animals
The genotoxic effects of the environmental contaminants benz(l)aceanthrylene
(B(j)A), benz(l)aceanthrylene (B(l)A) and benzo(a)pyrene (B(a)P), and the
metabolism of radiolabelled B(j)A, were studied using rat lung microsomes
and various types of isolated rat lung cells from control and Aroclor
1254 (PCB) treated animals. All three compounds (10 or 20 mug/plate)
resulted in low, but detectable, levels of His+ revertants in the Salmonella
assay when plated with control lung microsomes. The two cyclopenta polycyclic
aromatic hydrocarbons (CP-PAH) B(j)A and B(l)A, gave increased levels
of revertants when plated with microsomes from PCB-treated animals.
Clara cells, type 2 cells and alveolar macrophages isolated from control
rats were exposed to B(j)A, B(l)A or B(a)P (30 mug/ml, 1 h), but neither
of the cell types showed any DNA damage when measured by alkaline filter
elution. However, both B(j)A and B(l)A (30 mug/ml, 2 h) caused DNA adducts
in all three cell types, measured by the 32P-post-labelling technique,
whereas no B[a]P adducts were detected (30 microg/ml, 2 h). The total DNA
adduct levels in Clara cells, type 2 cells and macrophages exposed to B[j]A
were 0.085 +/- 0.033, 0.053 +/- 0.001 and 0.170 +/- 0.030 fmol/microg DNA,
respectively, whereas the total levels in cells exposed to B[l]A were 0.140
+/- 0.070, 0.140 +/- 0.030 and 0.220 +/- 0.080 fmol/microg DNA, respectively.
Cells exposed to B[j]A revealed only one adduct which corresponds with
the B[j]A-1,2-oxide DNA adduct. Judged from high performance liquid chromatography
(HPLC) analysis using radiolabelled B[j]A (30 microg/ml, 30 min), the major
metabolite formed in control microsomes was B[j]A-1,2-diol. Thus, oxidation
at the cyclopenta ring appears to be the most important activation pathway
for B[j]A with control rat lung cells. Exposure of lung cells to CP-PAH
(30 microg/ml, 2 h) isolated from PCB pretreated rats resulted in slightly
increased DNA adduct levels in Clara cells and macrophages when compared
to cells isolated from control rats. Furthermore, the adduct pattern
had shifted, and no apparent B[j]A-1,2-oxide adduct could be detected on
the thin layer chromatography (TLC) plate. In contrast, the major metabolite
formed with microsomes from PCB-treated animals was still the B[j]A-1,2-diol.
(JOHNSEN et al, 1997)
Study #33
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PCB pretreatment inhibited (S)-nicotine oxidation
Rabbit lung microsomes metabolize (S)-nicotine primarily
to (S)-nicotine DELTA1',5'-iminium ion, which is the precursor of (S)-cotinine,
the major urinary metabolite of (S)-nicotine in mammals. (S)-Nicotine-N'-oxide
and nornicotine are also produced as minor metabolites. alpha-Methylbenzylaminobenzotriazole,
a mechanism-based suicide inhibitor of rabbit lung cytochromes P-450 2
and 6, inhibited (S)-nicotine oxidation in parallel with inhibition of
benzphetamine N-demethylation and ethoxyresorufin O-deethylation. Pretreatment
of rabbits with TCDD or Aroclor 1260 had no effect and markedly
inhibited (S)-nicotine oxidation, respectively, strongly suggesting
that alpha-methylbenzylaminobenzotriazole inhibition was due to inactivation
of rabbit lung P-450 2. Reconstitution with cytochromes P-450 2 and
5 demonstrated that only P-450 2 was active toward (S)-nicotine, yielding
predominantly the iminium ion, with smaller amounts of nornicotine, (S)-nicotine
N'-oxide, and an unkn (incomplete abstract) (Williams et al, 1990)
Study #34
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Clara cells of the bronchiolar epithelium and Type II cells
of the alveolar epithelium are possible target cells in lung cancer
Clara cells of the bronchiolar epithelium and Type II
cells of the alveolar epithelium are possible target cells in lung carcinogenesis.
The 2 cell types were isolated from rat and rabbit lung by a combination
of protease treatment and centrifugal elutriation. Macrophages were isolated
by lavage. The cells were characterized by immunocytochemical staining
for cytokeratins and PCB binding protein, and staining with tannic
acid. Cyclopentafused polyaromatic hydrocarbons such as benzaceanthrylene
(B(L)A) were metabolized to form DNA adducts in Clara and Type II cells
and macrophages as measured by 32P-Postlabeling technique. Clara cells
had higher levels of adducts than Type II cells and much higher levels
than macrophages. B(L)A did not induce any significant DNA damage in any
of the cell types, as measured by alkaline elution of DNR. A similar degree
of DNA damage was induced by NNK and other compounds in both freshly isolated
and growing Clara and Type II cells. Much less damage was observed in lung
macrophages. The P450 IIB1 gene, which is mainly associated with NNK metabolism,
is constitutively express in untreated lung. Expression was reduced after
treatment of rats with Chromium (VI) and other lung carcinogens. Clara
cells and Type II cells maintained IIB1 gene expression in culture, in
accordance with constitutive expression. Expression of the IIE1 gene was
low in untreated lung, but is increased in lungs of rats treated with acetone
or alcohol. The IIE1 gene was expressed in uninduced and induced isolated
Clara cells at approximately the same level, whereas there was no detectable
expression in Type II cells, but strong induction after acetone treatment.
(BECHER et al, 1992)
Study #35
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PCB feeding did not consistently change oxygen utilization,
phagocytic activity or microbicidal activity in phagocytic cells.
-
certain individual parameters were altered by PCBs, but not
in any temporal pattern.
-
fibronectin, a surface binding glycoprotein, was significantly
decreased
-
certain PCB types did not increase tumor susceptibility in
a certain mouse strain
Male Balb/c mice were fed diets containing polychlorinated
biphenyl (Aroclor 1242), hexachlorobenzene, or dieldrin, at 167 ppm
for 3, 6, or 18 wk. Findings indicated that these contaminants under these
conditions did not significantly change in any consistent manner the
oxygen utilization, phagocytic activity or microbicidal activity in phagocytic
cells. However, certain individual parameters were altered, but not in
any temporal pattern. The phagocytic activity, phagocytic capacity,
and microbicidal activity of alveolar, splenic, and peritoneal macrophages
and PMNs was not altered in any consistent manner. Fibronectin, a surface
binding glycoprotein, was significantly decreased, primarily at wk
18 of testing. Tumor susceptibility of PCB 1242, HCB, and dieldrin treated
syngeneic mice was assessed using an ascites form of tumor cell implant
from chemical- and/or virus-transformed cell lines bearing diverse H-2
and Mls antigens. This lack of susceptibility to tumor challenge was observed
with all 4 tumor models. (Loose et al, 1981)
Study #36
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a certain protein in lung fluids binds selectively to certain
PCB metabolites, causing PCB accumulation in the lung
-
the toxicological significance of this behavior is unknown
Studies of a polychlorinated biphenyl (PCB) binding protein
in human bronchoalveolar fluid were described. Fiberoptic bronchoscopy
with bronchoalveolar lavage was performed on 20 healthy volunteers, ten
smokers and ten nonsmokers. Cellular analysis found that the total number
of cells and alveolar macrophages was significantly elevated in the lavage
fluid from the smokers compared to the nonsmokers. The presence of a
binding protein for a metabolite of 2,2',5,5'-tetrachlorobiphenyl (35693993)
(22'55'TCBP), 4,4'-bis(methylsulfonyl)-2,2',5,5'-tetrachlorobiphenyl (MeSOTCB)
was demonstrated. Saturation and Wolf analysis of the binding of tritiated
MeSOTCB to the lavage fluid showed that the maximum number of binding
sites was higher in the smokers than nonsmokers, with 248 and 90 sites
respectively. The binding affinity, however, was the same for both
smokers and nonsmokers at 2x10(-7) molar. The nucleases RNAse and DNAse
did not affect specific binding, whereas pronase abolished all binding
sites. The binding protein was found to have a molecular weight of 17,700
daltons and an acidic isoelectric point of 4.9. Competitive binding studies
showed that 4-methylsulfonyl-2,2',4',5,5'-pentachlorobiphenyl (37680732)
(two fold excess), 4-methylsulfonyl-2,3',4',5'-tetrachlorobiphenyl (32598111)
(12 fold excess) and 4-methylsulfonyl-2,2',5,5'-tetrachlorobiphenyl (60640553)
(16 fold excess) competed for 50 percent of the the specific MeSOCTCB binding
sites. Progesterone (57830) and 2,2',4,4',5,5'-hexachlorobiphenyl (35065271)
did not compete for binding sites. The authors conclude that the MeSOTCB
binding protein in human bronchoalveolar lavage fluid may be responsible
for accumulating PCB metabolites in the lung, although the toxicological
significance of the binding protein is not known. (Andersson et al,
1987)
Study #37
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PCBs caused proliferation and dilation of agranular endoplasmic
reticulum throughout the apical cytoplasm of Clara cells in the lung
-
ciliated cells were unaffected
-
such PCB doses did not induce severe bronchiolar lesions
in mice
Ultrastructural changes of the bronchiolar epithelium following
administration of PCB (polychlorinated biphenyl) (Kanechlor 400) were examined
by transmission and scanning electron microscopy. Adult male mice were
given orally 0.4 ml olive oil containing 1% PCB (100 mg PCB/kg body wt)
once daily for 2 wk. Controls received the same amount of olive oil for
the same period. For scanning electron microscopy, male mice were administered
PCB in the same way for 10 days. Oral administration of PCB caused Clara
cells to produce a proliferation and dilation of agranular endoplasmic
reticulum throughout the apical cytoplasm but ciliated cells remained unaffected.
Even in Clara cells, other cell constituents than agranular endoplasmic
reticulum did not exhibit structural changes at the ultrastructural level.
Findings indicating necrosis of exfoliation of the epithelial cells were
not observed. Clara cells played an important role in drug metabolism
in the lung and PCB administration induced a proliferation of agranular
endoplasmic reticulum in the cytoplasm. Such doses of PCB did not induce
severe bronchiolar lesions at least in mice. Further study is required
to clarify the detailed relationship between dosages of PCB and bronchiolar
damages. (Yamamoto et al, 1981)
Study #38
-
a certain protein in lung fluids binds selectively to certain
PCB metabolites, causing PCB accumulation in the lung
-
the protein was localized in the secretory granules of the
apical Clara cell cytoplasm
-
the protein plays an important role in determining the in-vivo
disposition of PCBs.
Levels of a binding protein for polychlorinated biphenyls
(PCBs) were investigated in cytosolic preparations using an in-vitro
ligand binding assay and a Western immunoblot assay. Cytosolic fractions
were obtained from Sprague-Dawley-rat lung cells. Most of the PCB binding
protein was found in the in-vitro ligand binding assay. Levels of immunoreactive
material, as determined by Western immunoblot analysis of the enriched
preparations, were similar to those seen for the binding protein. Antibodies
to the protein stained the Clara cells in lung sections and, particularly,
the airway epithelium. Further antibody investigation revealed that the
protein was localized in the secretory granules of the apical Clara cell
cytoplasm. Previous studies indicated selective accumulation of methylsulfonyl-PCBs
in Clara cells and present findings revealed the presence of a secretory
Mr 13000 protein in the Clara cells that binds methylsulfonyl-PCBs; both
suggest that the protein plays an important role in determining the
in-vivo disposition of PCBs. (Lund et al, 1988)
Study #39
-
dioxin increases the induction of ezymes in the lung, which
alters the reactivity of certain air pollutants in the lung [PCBs are frequently
contaminated with dioxins, and certain PCBs are dioxin-like]
The cytochrome-P-450 monooxygenase systems of Clara cells,
type-II cells, and alveolar macrophages isolated from the lungs of rabbits
treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (1746016) (TCDD) were
examined. Male white New-Zealand-rabbits were administered 10mg/kg of TCDD
intraperitoneally 72 to 96 hours prior to killing. Lungs were excised and
macrophages were removed by lavage. Clara cell fractions and type-II cell
fractions were also obtained. Isozymes were separated by polyacrylamide
gel electrophoresis and Western blotting. Cytochrome-P-450 isozyme 2 was
more evident in samples from Clara cells than from type-II cells and alveolar
macrophages of control rabbits. Cytochrome-P-450 isozyme 5 was about the
same in Clara and type-II cells in treated and untreated rabbits. The
TCDD treatment resulted in marked increases in cytochrome-P-450 isozyme
6 content in intact lung and all cell samples. Macrophages contained
the highest concentration of isozyme 6. The rates of O-deethylation of
7-ethoxycoumarin were higher in Clara and type-II cells than in microsomes
from the whole lung. The O-deethylation of 7-ethoxyresorufin and hydroxylation
of benzo(a)pyrene (50328) (BP) were greater in microsomal preparations
from the TCDD treated animals. TCDD increased the percentage of BP
metabolites eluting with 7,8-diol and 9,10-diol, and 9-hydroxy standards.
The authors conclude that the concentrations of major components in the
rabbit pulmonary P-450 system are similar in microsomal preparations from
the Clara and type-II cell fractions and from whole lung. In the induced
state macrophages play a major role in the metabolism of some aromatic
hydrocarbons. (Domin et al, 1986)
Study #40
-
PCB binding protein is synthesized in or secreted from Clara
cells.
-
studies of PCBs and lung toxicity should take methylsulfonyl
PCBs into consideration.
Studies of possible mechanisms of the selective accumulation
of 4,4'-bis(methylsulfonyl)-2,2',5,5'-tetrachlorobiphenyl (MeSOTCB), a
polychlorinated biphenyl (PCB) metabolite, were summarized. When tritium
labeled MeSOTCB was administered to rats and autoradiography was performed,
in conjunction with light microscopy of lung tissue sections, radioactivity
was found to accumulate in bronchiolar lumen and epithelium. Distribution
of radiolabel in epithelium was not uniform, but was concentrated in
nonciliated Clara cells. Binding studies conducted on cytosolic preparations
from rat lung showed MeSOTCB was reversibly, noncovalently bound to cytosol.
Competition studies with other 4-methylsulfonyl PCBs showed similar binding;
however, only one PCB competed for MeSOTCB binding sites. Gel permeation
chromatography and density gradient centrifugation showed that MeSOTCB
was bound to a nearly globular, low molecular weight, acidic protein. Analysis
of bronchoalveolar (BAL) fluid from rats and mice injected with tritiated
MeSOTCB indicated that over 80 percent of radioactivity was bound to entities
with physicochemical properties similar to those of MeSOTCB binding proteins
in lung cytosol. When BAL fluid from untreated rats was labeled with tritiated
MeSOTCB in-vitro, binding proteins with identical physicochemical properties
were found. The authors conclude that the MeSOTCB binding protein is
synthesized in or secreted from Clara cells. Studies designed to
elucidate the roles of individual PCB isomers and metabolites in causing
lung toxicity should take methylsulfonyl PCBs into consideration. (Lund
et al, 1986)
Study #41
-
the PCB binding protein in the lung has been specifically
identified
A binding protein for 4,4-bis(methylsulfonyl)-2,2,5,5-tetrachlorobiphenyl
(MSTCB), a metabolite of polychlorinated biphenyls (PCB), was partially
purified from lung cytosol of female Sprague-Dawley-rats. This compound
has been shown to selectively accumulate in the apical cytoplasm of nonciliated
bronchial (Clara) cells of the rat and mouse lung. Dried crude lung extract,
labeled with tritiated MSTCB was subjected to a series of column chromatographic
procedures followed by preparative polyacrylamide gel electrophoresis.
The resultant partially purified proteins were used as antigens to produce
antibodies in female mixed breed rabbits. The antibody immunoglobulins
were subsequently purified by affinity chromatography. Although two proteins
were isolated (molecular weights 13,000 and 16,000), the 13 kiloDalton
(kD) protein was responsible for the binding of methylsulfonyl-PCBs.
This protein consisted of two subunits joined by disulfide bridges. Immunochemical
characterization supported the contention that the 13kD protein constitutes
the major PCB binding protein in lung cytosol. The physiological role of
the 13kD protein and the toxicological implications of its interaction
with MSTCB remain to be determined. The monospecific antibodies against
this protein could be used as probes to examine localization in the Clara
cells and any possible role in PCB induced respiratory toxicity. (Lund
et al, 1988b)
Study #42
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Clara cell secretory protein may mediate the biological accumulation
of potentially harmful PCB metabolites in the lung
Clara cell secretory protein (CCSP) is a product of nonciliated
cells of the conducting airway epithelium. The normal physiological function
of CCSP is unknown. However, the ability of CCSP to bind small lipophilic
molecules, such as steroid hormones and certain pollutants, has led to
speculation that this protein may mediate the biological accumulation
of potentially harmful polychlorinated biphenyl (PCB) metabolites within
the lung. To investigate the contribution of CCSP in the in vivo accumulation
of methylsulfonyl-PCB, a line of mice was established that were homozygous
for a null allele of the CCSP gene. CCSP-deficient mice were healthy and
fertile, with no gross physiological or pathological abnormalities. Parenteral
challenge with the PCB metabolite 4-methylsulfonyl-2,2',4',5,5'-pentachlorobiphenyl
(MeSO2-PCB) demonstrated that CCSP-deficient mice no longer accumulate
this class of pollutants within lung and kidney tissues. These data demonstrate
that CCSP is th (incomplete abstract) (Stripp et al, 1996)
Study #43
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Clara cells contain a secretory protein of molecular weight
12800d that specifically binds PCB methyl sulfones with high affinity
-
this protein plays an important role in the in-vivo disposition
of these compounds
Studies on the physicochemical and immunochemical properties
of a binding protein for methyl sulfone derivatives of polychlorinated
biphenyls (1336363) (PCB), isolated form rat lung cytosol, were presented.
The binding protein was purified by CM-Sepharose, Sephadex-G75 and DEAE-Sepharose
chromatography, yielding a product having a purity of 60 percent, with
an overall recovery of 15 percent. Sodium-dodecyl-sulfate polyacrylamide
gel electrophoresis revealed two protein bands having molecular weights
of 16400 and 12800 daltons (d). The 12800d protein constituted about 70
percent of the purified product. In the presence of reducing agents the
12800d protein decomposed into subunits having molecular weights of 7800d.
Binding to PCB methyl sulfones was due to the 12800d protein as demonstrated
by a radioimmunoassay procedure. Monospecific antibodies to the 12800d
protein raised in rabbits were used to localize the binding protein in
the rat lung. The binding protein was located mostly in cytosol from nonciliated
bronchiolar (Clara) cells and in the material lining the airways. The authors
conclude that Clara cells in the rat lung contain a secretory protein
of molecular weight 12800d that specifically binds PCB methyl sulfones
with high affinity, and that this protein plays an important role
in the in-vivo disposition of these compounds. (Lund et al, 1987)
Study #44
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PCBs accumulate and are retained longterm in the lungs’ tracheobronchial
mucosa
-
the PCB-binding protein complex has been shown to be subsequently
secreted into the airway lumen and spread over the entire surface lining
Studies of the tissue distribution of polychlorinated biphenyls
(1336363) (PCBs) in laboratory animals were summarized. Twenty eight PCBs
and six chlorinated compounds which are not PCBs were investigated. Studies
of the distribution of carbon-14 labeled PCBs in mice were discussed. Dose
and structure dependent accumulation and long term retention of the compounds
in the tracheobronchial mucosa have been observed. The greatest accumulation
occurred in PCBs having chlorines in the 2,2',4,4',5,5' positions. Most
of the PCBs were present as 4-methylsulfonyl metabolites. Radiolabeling
studies have indicated that the 4-methylsulfonyl PCB (MeSOPCB) metabolites
are bound initially to a specific MeSOPCB binding protein in the Clara
and goblet cells. This protein-MeSOPCB complex has been shown to be
subsequently secreted into the airway lumen and spread over the entire
surface lining. Studies on the accumulation of MeSOPCBs in kidney proximal
tubular cells in mice were discussed. These have shown that the extent
of accumulation is different from that of the lung, and apparently depends
on the nature of the substituent in the para position. Accumulation of
PCB metabolites in sites outside the lung and kidney were discussed. MeSOPCBs
have been found in the uterine and fetal soft tissues of mice, the ventral
prostate and large intestinal epithelium of rats, and the cerebral gray
matter of quail. Tissue binding of sulfur containing PCBs which are not
xenobiotics was considered. Studies with dimethylsulphone (67710) and chlorinated
benzenes in mice have shown that sulfur containing metabolites accumulate
in the lung, kidney, liver and adrenal cortex. (Brandt et al, 1987)
Study #45
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a structural relationship exists between the rat lung PCB
binding protein and uteroglobin, a hormonally regulated steroid binding
protein in rabbit lung
The cloning and expression of a cDNA encoding the rat
lung polychlorinated-biphenyl (1336363) (PCB) binding protein was described.
The DNA sequence analysis revealed a structural relationship between
the PCB binding protein and uteroglobin, a hormonally regulated steroid
binding protein in rabbit. The kinship of these proteins suggested
novel approaches to the elucidation of the physiological role of the PCB
binding protein and of its role in PCB induced lung toxicity. The
identity of the PCB binding protein was supported by expression of the
cDNA in Cos-1 cells where the homogenates from transfected cells revealed
specific binding of 4,4'-bis((3H)methylsulfonyl)-2,2'5,5'-tetrachlorobiphenyl,
a high affinity ligand for the PCB binding protein. A monospecific antiserum
to the PCB binding protein recognized a 13 kilodalton protein in the homogenates
of transfected cells but not in the corresponding fraction of mock transfected
cells. The cDNA detected a specific base pair messenger RNA which appeared
to be solely expressed in the lung. The PCB binding protein shared
a 53% positional amino acid identity with uteroglobin, a progesterone blinding
protein observed in rabbit uterus and lung. Amino acids that were
observed by x-ray crystallography to delineate the central cavity of uteroglobin
were highly conserved in the two proteins. (Nordlund-Moeller et al, 1990)
Study #46
-
certain PCB metabolites accumulate strikingly in rat lung
tissue, due to a uteroglobin-like macromolecule in the lung
When a 3H-labeled metabolite of polychlorinated biphenyls
(PCB), 4,4'-bis(3H)methylsulfonyl)-2,2'-5,5'-tetrachlorobiphenyl ((3H-MeSO2)2TCB)
was administered i.p. to rats, a selective labeling was registered in the
apical cytoplasm of the nonciliated bronchiolar (Clara) cells of the lung
as determined by microautoradiography of sections of methacrylate-embedded
tissue. (Polychlorinated biphenyls are industrial chemicals which have
become widespread environmental pollutants). In vitro, (3H-MeSO2)2TCB
bound with high affinity (Kd = 2.5-15 nM) and high capacity (Bmax (maximum
number of binding sites) = 30-70 pmol/mg of protein) to rat lung cytosol.
Binding of (3H-MeSo2)2TCB to the high affinity sites was temperature dependent,
reversible and saturable. The sites seemed to reside within a protein-like
component, since proteolytic enzymes significantly reduced the binding.
Physicochemical characterization of the (3H-MeSO2)2TCB-binding protein
indicated a Stokes radius of 22 of these parameters, an apparent MW of
16,000 was calculated. The binding entity had an apparent pI (negative
log of ionization constant) of 5.3 and eluted as a single radioactive peak
from CM (carboxymethyl)-Sepharose at 75 mM acetate. Binding with similar
affinities (IC50 (concentration giving 50% inhibition) values, 4-65 nM)
was shown to occur also with other PCB methyl sulfones, whereas only
one PCB, 2,2',4,4',5,5'-hexachlorobiphenyl, competed for (3H-MeSO2)2TCB
binding, but with a lower affinity (IC50 = 3 muM). Among other compounds
tested, only progesterone and some derivatives thereof displayed
an affinity for the (3H-MeSO2)2TCB-binding protein (IC50 values ranging
from 1-10 muM). Lung cytosol showed by far the highest amount of specific
(3H-MeSO2)2TCB binding. Low but detectable amounts were also found
in cytosolic preparations from prostate, kidney and large intestine. (3H-MeSO2)2TCB
also bound to an entity in mouse lung cytosol with the same physicochemical
characteristics as that in rat lung cytosol and to a progesterone-binding
protein purified from rabbit uterus (uteroglobin). Rat lung contains
a uteroglobin-like macromolecule with a pronounced affinity for at least
certain PCB methyl sulfones. This binding entity apparently is responsible
for the striking accumulation of such metabolites in lung tissue following
administration of PCB to rats and mice. (Lund et al, 1995)
Study #47
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immunological alteration may be different between peripheral
blood and respiratory system as one of the target organs of PCBs and furans
In order to investigate immunological abnormalities induced
by polychlorinated biphenyls and polychlorinated dibenzofurans, we
have performed bronchoalveolar lavage in the rats given polychlorinated
biphenyls and polychlorinated dibenzofurans. We have administrated 5.0
mg of polychlorinated biphenyls or 0.5 mg of polychlorinated dibenzofurans
to Sprague-Dawley rats intraperitoneally. Four weeks after the administration,
mild necrosis of bronchiolar Clara cells and mild edema associated with
chronic inflammatory infiltration in the alveoli were seen in both
groups. In the peripheral blood, percentage of T-lymphocyte, helper T-cell
and suppressor T-cell decreased significantly both in polychlorinated biphenyls
and polychlorinated dibenzofurans given rats. On the other hand, in the
bronchoalveolar lavage fluid, percentage of T-cell increased only in polychlorinated
dibenzofurans given rats and percentage of suppressor T-cell increased
in both groups. O2- release by alveolar macrophage increased significantly
both when stimulated with wheat germ lectin and with phorbol myristate
acetate. These results indicate that immunological alteration may be
different between peripheral blood and respiratory system as one of the
target organs of these chemicals. Further examination is needed for
the analysis of immunological abnormalities in the target organs of polychlorinated
biphenyls and polychlorinated dibenzofurans poisoning. (NAKANISHI et al,
1995)
Study #48
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PCB pretreatment did not alter the 50% lethal dose of 1-nitronaphthalene
-
PCB did prevent morphological signs of lung injury and any
increase in either lung weight or enzyme activity in bronchoalveolar lavage
fluid
-
PCBs made liver injury worse
In rats, 1-nitronaphthalene (1-NN) causes both pulmonary
and hepatic toxicity. Pulmonary toxicity is evident as bronchiolar damage,
with necrosis of Clara cells and ciliated cells, whereas hepatic injury
involves vacuolation of centrilobular hepatocytes. Pretreatment with O,O,S-trimethylphosphorodithioate
(OOS-MeP(S)) or p-xylene gave three- to fourfold protection against 1-NN
toxicity. These pretreatments also prevented both the increase in lung
weight and the rise in gamma-glutamyltranspeptidase and alkaline phosphatase
activity in bronchoalveolar lavage fluid normally associated with 1-NN
toxicity. Pretreatment with Aroclor 1254 or beta-naphthoflavone
(betaNF) did not alter the LD50 of 1-NN. Aroclor or beta-NF
pretreatment did, however, prevent morphological signs of lung
injury and any increase in either lung weight or enzyme activity in bronchoalveolar
lavage fluid. Liver damage was not prevented by these treatments; indeed,
injury was exacerbated and was transferr (incomplete abstract) (VERSCHOYLE
et al, 1993)
Study #49
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both lung tumor incidence and multiplicity were significantly
increased when mice exposed to environmental cigarette smoke were pretreated
with PCBs, as compared to exposure only to environmental cigarette smoke
In spite of the major role played by cigarette smoking in
the epidemiology of lung cancer, it is very difficult to reproduce the
carcinogenicity of this complex mixture in animal models. We implemented
a series of pilot experiments in three mouse strains, exposed either to
environmental cigarette smoke (ECS) or mainstream cigarette smoke (MCS)
or its condensate (MCSC). The whole-body exposure of Aroclor-treated
A/J mice to ECS resulted in a rapid and potent induction of micronuclei
in peripheral blood erythrocytes. After 6 months of exposure, 6 h a
day, followed by 4 months of recovery in filtered air, both lung tumor
incidence and multiplicity were significantly increased as compared
to sham-exposed mice (77.8% vs. 22.2%, and 1.11+/-0.26 vs. 0.22+/-0.15,
means +/- SE). Multiple i.p. injections of butylated hydroxytoluene did
not significantly enhance the tumor yield. Another experiment confirmed
the responsiveness of A/J mice exposed to ECS for 5 months, followed by
4 months of recovery in air (75.0% vs. 25.0%, and 1.05+/-0.17 vs. 0.25+/-0.10).
In contrast, the increase in lung tumor yield after exposure to ECS for
2 months, followed by recovery in air for 7 months, was not significant,
and the continuous exposure to ECS for 9 months was totally ineffective.
These data, in agreement with previous results of others, show that exposure
of A/J mice to ECS for 5-6 months, followed by recovery in air for 4 months,
is successful in inducing a weak but significant and reproducible increase
in lung tumor yield. Furthermore, the simultaneous exposure to the light
emitted by halogen quartz bulbs for 9 months and to ECS for 5 months, followed
by 4 months in air, was again weakly tumorigenic (incidence of 55.0% and
multiplicity of 0.75+/-0.19), whereas exposure to both ECS and light for
9 months was devoid of effect. The whole-body exposure of A/J mice to MCS,
1 h a day for 5 months, or weekly i.p. injections of MCSC for 5 months,
followed in both cases by 4 months of recovery in air, failed to enhance
the lung tumor yield. The whole-body exposure of SKH-1 hairless mice to
ECS for 6 months, followed by exposure to halogen light for 8 months, resulted
in the formation of multiple skin tumors but failed to produce lung tumors.
The whole-body exposure of C57BL/6 mice to ECS for 6 months failed to induce
any lung tumor but caused alopecia, gray hair, and hair bulb cell apoptosis,
which were prevented by the oral administration of N-acetylcysteine. (D'Agostini
et al, 2001)
Study #50
-
PCB 52 and its oxide failed to induce lung cancer
Sensitive assays for the induction of lung adenomas
in A/J mice or skin papillomas in SENCAR mice failed to show activity
for either 2,2',5,5'-tetrachlorobiphenyl or 2,2',5,5'-tetrachlorobiphenyl
3,4-oxide. Injections of the 3,4-oxide into preweanling A/J mice caused
considerable mortality, whereas the parent hydrocarbon did not. Both 2,2',5,5'-
and 2,2',4,4'-tetrachlorobiphenyl showed promoting activity for hepatic
gamma-glutamyl transpeptidase-positive foci initiated in rat liver by treatment
with diethylnitrosamine. The promoting activity of 2,2',4,4'-tetrachlorobiphenyl
was approximately 10-fold greater than that of the 2,2',5,5'-isomer. (Preston
et al, 1985)
Study #51
-
three P-450 enzymes induced by PCBs in rat lungs are involved
in the activation of several procarcinogens such as polycyclic aromatic
hydrocarbons [combustion byproducts]
Rat lung microsomal cytochrome P-450 (P-450) enzymes have
been characterized with regard to their catalytic specificities towards
activation of several procarcinogens to genotoxic metabolites in Salmonella
typhimurium TA1535/pSK1002. We first examined the roles of rat liver microsomal
P-450 enzymes in the activation of benzo[a]pyrene and its 7,8-diol enantiomers
to genotoxic products, and found that P-450 1A1 is a major catalyst for
the activation of these potential procarcinogens in rat livers. Using
lung microsomes isolated from rats treated with various P-450 inducers
we obtained evidence that at least three P-450 enzymes are involved in
the activation of several procarcinogens. Immunoinhibition studies
support the view that benzo[a]pyrene and its 7,8-diol derivatives, other
dihydrodiol derivatives of polycyclic aromatic hydrocarbons, and 3-amino-1-methyl-5H-pyrido[4,3-b]indole
are activated to genotoxins mainly by rat P-450 1A1, which is inducible
in rat lungs by 5,6-benzoflavone and the polychlorinated
biphenyl mixture Aroclor 1254. Activation of 2-amino-3,5-dimethylimidazo[4,5-f]quinoline
and 2-amino-3-methylimidazo[4,5-f]quinoline may be catalyzed by another
P-450 enzyme because the activities were not induced by treatment with
5,6-benzoflavone or Aroclor 1254. The observation that both activities
were inhibited by antibodies raised against P-450 1A2 and by 7,8-benzoflavone
suggests a role for an enzyme of P-450 1A family, probably P-450 1A2, in
rat lung microsomes. The activation of aflatoxin B1 and sterigmatocystin
appears to be catalyzed by other P-450 enzyme(s) rather than the P-450
1A family as judged by the different responses of activities to the P-450
inducers and the specific antibodies in rat lung microsomes. Interestingly,
lung microsomal activation of several procarcinogens was found to be suppressed
in rats treated with isosafrole and pregnenolone 16 alpha-carbonitrile.
Thus, the results support the roles of different P-450 enzymes in the
activation of procarcinogens in rat lung microsomes. (Shimada et al,
1992)
Study #52
-
two PCBs produced greater lung enzyme activity than they
did liver enzyme activity
-
PCBs produced increases of two to five times control levels
-
relative induction potency of PCBs appears to be tissue specific
and EROD activity may not accurately reflect potency in non-liver tissues.
-
Dioxin Toxic Equivalency Factors (TEFs) proposed for PCBs
may overestimate potencies by factors of ten to 1000.
The induction of cytochrome-P450 (P450), cytochrome-P4501A1
(P4501A1), and cytochrome-P4501A2 (P4501A2) by various polychlorinated
biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and 2,3,7,8-tetrachlorodibenzo-p-dioxin
(1746016) (TCDD) after 4 weeks (wk) of treatment was compared in mice.
The relative potencies of these chemicals were evaluated using toxic equivalency
factors (TEFs). Female B6C3F1-mice were administered the test chemicals
by gavage at a dose volume of 10 milliliters/kilogram, 5 days/week for
4 weeks. Microsomal enzyme activities were determined using the ethoxyresorufin-O-deethylase
(EROD) assay for hepatic, skin, and lung P4501A1, and the acetanilide-4-hydroxylase
(ANH) assay for hepatic P4501A2. Results showed that using TEFs to derive
equipotent doses of PCBs, PCDFs, and TCDD did not result in an equal induction
of hepatic EROD activity. Of ten compounds tested only five showed significant
induction of EROD activity relative to controls. Hepatic ANH increased
significantly in treated animals compared to controls, with TCDD causing
the highest increase. Lung EROD was about 15 times lower than hepatic EROD
activity. Two PCBs produced greater lung EROD activity than they did
hepatic EROD activity. TCDD produced a skin EROD activity about 12
times higher than in controls, while the PCBs produced increases of
two to five times control levels. The authors conclude that following
low dose exposure, many TEFs do not adequately predict the ability of polyhalogenated
aromatic hydrocarbons to induce P4501A1 and P4501A2. The relative induction
potency of the chemicals appears to be tissue specific and EROD activity
may not accurately reflect potency in nonhepatic tissues. TEFs proposed
for PCBs may overestimate potencies of these compounds by factors of ten
to 1000. (De Vito et al, 1993)
Study #53
-
rates of individual BaP metabolite production are increased
in lungs from mice pretreated with PCBs
-
the existence of significant cytochrome P-450-dependent and
conjugative BaP metabolism in the intact mouse lung is supported, similar
to that examined in other species, and capable of contributing to the systemic
metabolism of this carcinogen.
A method is described for preparing and maintaining an isolated
perfused and ventilated mouse lung. The preparation is especially suited
for studying xenobiotic metabolism or toxicological interactions, in a
species with a broad spectrum of studies in pulmonary toxicology. The preparation
is viable with respect to drug metabolism for up to 2 h, as judged from
studies of aniline oxidation to p-aminophenol. With (14C)-benzo(a)pyrene
as substrate for the lungs of male ICR Swiss mice, the major ethyl acetate-extractable
metabolites are the 3-hydroxy, 9,10-dihydrodiol, 7,8-dihydrodiol and 4,5-dihydrodiol
derivatives. The rates of individual BaP metabolite production are increased
in lungs from mice pretreated with Aroclor 1254 or beta-naphthoflavone,
substances known to induce increased synthesis of cytochrome P-450. Small
amounts of water-soluble BaP metabolites were hydrolyzed by beta-glucuronidase
and aryl sulfatase, suggesting the presence of enzymes required for these
conjugations. The existence of significant cytochrome P-450-dependent
and conjugative BaP metabolism in the intact mouse lung is supported, similar
to that examined in other species, and capable of contributing to the systemic
metabolism of this carcinogen. (Skelly et al, 1983)
Study #54
-
PCBs are used to induce drug-metabolizing enzymes
-
PCBs are very good inducers of AHH enzyme activity in certain
mouse strains
-
strain of mouse and type of tissue are important variables
in assessing the potential effect of microsomal enzyme-inducing PCBs on
the metabolism of mutagenic substances.
Homogenates of liver, lung, kidney, stomach, small
intestine and colon from 8 strains of mice were compared for their ability
to metabolize benzo(a)pyrene (BP) and dimethylnitrosamine (DMN), known
carcinogens, to mutagens. Females of strains CF1, AKR, AU/SsJ, DBA/2J,
SWR/J, A/J, C3H/HeJ and C57BL/6J were either untreated or received phenobarbital
(BP), 3-methylcholanthrene (MC) or polychlorinated biphenyls (AR) to
induce drug-metabolizing enzymes. The effects of these drugs on organ
weight and on the amounts of DNA, S-10 protein and microsomal protein per
unit wt of tissue are reported. Salmonella typhimurium TA92 and TA98 were
used as indicators of the formation of mutagens. For each organ there was
an optimal balance between amount of tissue homogenate and concentration
of test compound for maximal yield of revertants. A sensitive radiometric
assay of DMN demethylase (DMND) is described which permits measurement
of the enzyme in liver, lung and kidney. DMN at 1 mM is used as
substrate. Aryl hydrocarbon hydroxylase (AHH) was measured in all tissue
using BP as substrate. AR and MC are very good inducers of AHH activity
in livers of mice classified as aromatic hydrocarbon responsive, but not
in those classified as hydrocarbon nonresponsive. Responsiveness is
strain-specific and genetically regulated. Metabolism of BP to mutagens
by liver homogenates was correlated with extent of AHH induction. This
dimorphism of response of AHH to inducers was present, but less pronounced,
in non-hepatic tissues. Basal activities of AHH and DMND were correlated
in livers and lungs from untreated mice. DMND activities were
increased less than 2-fold by PB, MC or AR treatments. Metabolism of
DMN to mutagens was not closely correlated with DMND activities. Strain
of mouse, type of tissue and test substance are important variables in
assessing the potential effect of microsomal enzyme-inducing agents on
the metabolism of mutagenic substances. (HUTTON et al, 1979)
Study #55
-
PCB induced enzymes enhanced the mutagenicity of 3 metabolites, but
decreased mutagenicity of other metabolites
The mutagenicity of 1-nitropyrene metabolites from rabbit lung S9 incubates
was evaluated using the Salmonella typhimurium plate incorporation assay
with strain TA98, with and without Aroclor-induced rat liver S9. The following
metabolites were isolated, identified and quantitated by HPLC(high performance
liquid chromatography): 1-nitropyrene -4,5- or -9,10-dihydrodiol (K-DHD),
N-acetyl-1-aminopyrene (NAAP), 1-aminopyrene (1-AMP), 10-hydroxyl-1-nitropyrene,
4-, 5-, 6-, 8- or 9-monohydroxy-1-nitropyrene (phenols) and 3-hydroxy-1-nitropyrene.
The predominant metabolites formed by using S9 incubates were K-DHD, 3-OH-1-nitropyrene
and phenols. All of the metabolites were mutagenic in the absence of the
exogenous rat liver S9 metabolic activation system, and several, including
2 unidentified metabolites were more potent than the parent 1-nitropyrene.
The mutagenicity of 3 of the metabolites (NAAP, 10-OH-1-nitropyrene and
phenols) were enhanced by S9 while most of the other metabolites
were less mutagenic in the presence of S9. Lung tissue is capable of
oxidative and reductive metabolism which produced mutagenic metabolites,
several of which were more potent than the parent compound, 1-NP. (1-NP
is a carcinogen.) (King et al, 1984)
Study #56
-
PCB induced enzymes increased the mutagenic response due
to several common air pollutants
Nitrated polycyclic aromatic hydrocarbons are wide-spread
environmental pollutants that have been detected in photocopier toners,
airborne particulates, coal fly ash, and diesel engine exhaust emissions.
1-Nitropyrene, a representative nitropolycyclic aromatic hydrocarbon present
in diesel particulates, is a mutagen in Salmonella typhimurium and a tumorigen
in laboratory animals. The activation of 1-nitropyrene to a bacterial mutagen
has been attributed to nitroreduction; however, the metabolic pathways
involved in its metabolism to a tumorigen are not known, but may involve
nitroreduction, ring oxidation, or a combination of the two. In these experiments,
we examined the importance of ring oxidation in the activation of 1-nitropyrene
(99.85 to 99.98 percent 1-nitropyrene, 0.15 to 0.02 percent 1,3-, 1,6-,
and 1,8-dinitropyrene by mass spectral analyses) to a mammalian-cell mutagen
and carcinogen. Chinese hamster ovary cells were used to assess the mutagenicity
of ring-oxidized 1-nitropyrene metabolites. In the absence of a rat
liver 9,000 x g supernatant, 6-hydroxy-1-nitropyrene, 1-nitropyrene-9,10-oxide,
and pyrene-4,5-oxide were the most mutagenic compounds tested. 3-Hydroxy-1-nitropyrene,
8-hydroxy-1-nitropyrene, and 1-nitropyrene-4,5-oxide were weaker mutagens,
whereas pyrene and 1-nitropyrene were essentially nonmutagenic. The order
of mutagenic potency with S9 was: 1-nitropyrene-4,5-oxide greater
than 6-hydroxy-1-nitropyrene approximately 1-nitropyrene-9,10-oxide greater
than 1-nitropyrene approximately 3-hydroxy-1-nitropyrene approximately
8-hydroxy-1-nitropyrene greater than pyrene approximately pyrene-4,5-oxide,
with the last two compounds being nearly nonmutagenic. The epoxide hydrase
inhibitor 1,2-epoxy-3,3,3-trichloropropane increased the mutation frequency
fivefold. In addition, guinea pig liver microsomes and Aroclor-induced
rat liver microsomes, which increased the formation of 1-nitropyrene-4,5-oxide
and 1-nitropyrene-9,10-oxide, increased the mutagenic response. Incubation
of 1-nitropyrene-4,5-oxide with calf thymus DNA resulted in the formation
of three DNA adducts. A similar adduct pattern was observed when Chinese
hamster ovary cells were incubated with the oxide. Inclusion of a nitroreductase,
xanthine oxidase, in the in vitro incubations resulted in the formation
of an additional adduct identified as N-(deoxyguanosin-8-yl)-1-aminopyrene.
This adduct was not observed in Chinese hamster ovary cells treated with
1-nitropyrene-4,5-oxide. 1-Nitropyrene-9,10-oxide reacted with calf thymus
DNA to give an adduct pattern similar to that observed with 1-nitropyrene-4,5-oxide.
The distribution of adducts was not affected by conducting the reactions
in the presence of xanthine oxidase. (Beland, 1991)
Study #57
-
conversion of certain procarcinogens to active mutagens occurred
only in the presence of enzymes
-
enzymes induced by dioxins and PCBs strongly increased mutagenic
activity of aromatic amines
-
dioxin induced activity was higher than that of PCBs
The in vitro mutagenic activation of several procarcinogens
by the 9000-g supernatant (S9) of tissue extracts was studied using the
Ames test with Salmonella strain TA98. Assays were performed with rat
lung, liver or mammary gland S9 or S9 from the human cell lines 734B,
SkBr3, MDA-MB-330 or the hamster lung line V79. Conversion of the procarcinogens
2-aminoanthracene (613138) (AA), 2,4-diaminoanisole (615054) (DAA), and
2,7-diaminofluorene (525644) (DAF) to active mutagens for TA98 occurred
only in the presence of S9. The presence of a nicotinamide-adenine-dinucleotide-phosphate
generating system was essential for mutagenic activity. S9 induced by
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Arochlor-1254 (AR) strongly
increased mutagenic activity of aromatic amines. TCDD induced activity
was higher than that of AR in the range from 20 to 200 micrograms S9 protein
per plate and increased continuously at the high dose level. The mutagenic
potencies of DAA and DAF were similar. AA was suggested for use as a standard
compound for distinguishing P-450 induction, while TCDD could be advantageous
in characterization of aromatic amine activities. The procarcinogens
2-aminofluorene (153786), benzo(a)pyrene (50328), and aflatoxin-Bl (1162658)
were not detectably activated by S9. Use of alpha-naphthoflavone decreased
the mutagenic affects of AA, DAA, and DAF, but metyrapone was ineffective.
The authors suggest that the Ames test is suitable for characterizing activation
of many potential mutagens and carcinogens for mammary glands. (Maack et
al, 1986)
Study #58
-
pretreatment of rats with PCBs markedly induced reductase
(enzyme) activity in livers
-
the effect in lungs was 6% of the effect in livers
The reduction of N-hydroxy-2-acetylaminofluorene(N-hydroxy-AAF)
(a carcinogen) to 2-acetylaminofluorene and 2-aminofluorene (metabolic
activation) by liver microsomes was studied. The reductase preferred NADPH
rather than NADH as a cofactor and was strongly inhibited by carbon monoxide
and oxygen. The inhibitors of hepatic mixed function oxidase effectively
inhibited the reductase activity. Pretreatments of rats with 3-methylcholanthrene
and PCB markedly induced the reductase activity. Evidently the reduction
of N-hydroxy-AAF was catalyzed by cytochrome P-450, especially by cytochrome
P-448. The reductase activity was also detected in microsomes from lung,
kidney and small intestinal mucosa, and the rates of the reduction were
about 6, 7 and 27%, respectively, of that in liver microsomes. Species
difference in the reductase activity of liver microsomes was also examined.
The highest activity of the reductase was found in hamsters, followed by
guinea pigs and rabbits. (Yamazoe et al, 1980)
Study #59
-
PCBs traveled to the lungs and other organs after injection
intraperitoneally, though less than to the liver and kidneys
PCBs are complete rodent carcinogens and their potent tumor
promoting activity has been reported, but their tumor-initiating activity
remains controversial. Macromolecular binding of PCB metabolites has been
demonstrated in vitro, but this issue remains unclear in vivo. The purpose
of this study was to determine the binding affinity of 4-chlorobiphenyl
and 3,3',4,4'-tetrachlorobiphenyl to proteins and DNA in vivo. C57/BL6
female mice were treated intraperitoneally with hepatic enzyme inducers
(phenobarbital and beta-naphthoflavone) and then with 14C-labelled polychlorinated
biphenyls or benzo[a]pyrene. The short-term distribution of labeled compounds
into liver, lungs and kidneys and into different sub-cellular fractions
of these tissues was assessed and the DNA and proteins from the 700 x g
pellet were further purified to assess covalent binding. All compounds
were distributed in low amounts into the liver, kidneys and lungs,
with the greatest accumulation in the liver, and the lowest in lungs.
In all tissues, test compounds were mostly found in cytosols and organellar
pellets (10,000 x g), and lower amounts were present in nuclear pellets
(700 x g) and microsomes. In lungs and kidneys, only benzo[a]pyrene
showed significant covalent binding to proteins. In the liver, protein
binding indices were significant for all compounds (P<0.05), but no
significant binding of the test compounds to DNA could be demonstrated
with this approach. Our results suggest that at the 24 h time point, all
compounds were activated to electrophilic intermediates prone to macromolecular
binding. Hepatic proteins apparently act as a sink for PCB-derived electrophiles,
thus preventing detectable levels of covalent binding to hepatic DNA or
to proteins in less metabolically active tissues. (Pereg et al, 2001)
Study #60
-
PCB induced enzymes caused a noticeable accumulation of two
common carcinogens in the lungs’ alveolar region
-
irreversible binding in lung tissue was present in endothelial
cells of arteries and veins, in the alveolar septal walls, and in type
2 pneumocytes
Autoradiography was used to investigate the cellular sites
of irreversible binding of 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA)
and benzo[a]pyrene (B[a]P) in mice. Autoradiograms obtained from solvent-extracted
tape-sections revealed an even distribution of DMBA- and B[a]P-derived
radioactivity in control mice lacking sites of selective binding in the
tissues. In mice pretreated with a cytochrome P4501A (CYP1A) inducer,
beta-naphthoflavone (BNF) or 3,3',4,4', 5-pentachlorobiphenyl (PCB 126),
a noticeable accumulation of bound radioactivity was observed in the pulmonary
alveolar region. Increased labelling was also observed in heart tissue
of induced mice. As demonstrated by microautoradiography of tissues from
CYP1A-induced mice treated with 3H-DMBA or 3H-B[a]P in vivo, irreversible
binding in lung tissue was present in endothelial cells of arteries and
veins, in the alveolar septal walls, and in type 2 pneumocytes. In
heart tissue, binding was confined to endothelial cells of arteries, capillaries
and veins. In liver, binding was found in the hepatocytes as well as in
endothelial cells of the portal veins, whereas no binding was seen in endothelial
cells of the sinusoids, central veins, or arteries. These findings were
confirmed in vitro using 3H-DMBA-exposed precision-cut slices, indicating
that reactive intermediates of DMBA and B(a)P were formed in situ. The
addition of the CYP1A inhibitor ellipticine abolished binding in the target
endothelial cells. Increased endothelial binding in the lungs and
liver of CYP1A-induced mice was concomitant with increased 7-ethoxyresorufin
O-deethylase (EROD) and DMBA hydroxylase activity. In heart, endothelial
binding was positively correlated with EROD, but not with DMBA hydroxylase.
The
results suggest that endothelial cells may be targets for CYP-dependent
activation of such toxicants as polycyclic aromatic hydrocarbons. Consequently,
the possibility that chemically induced endothelial dysfunction is a risk
factor in the aetiology of cardiovascular disease demands consideration.
(Granberg et al, 2000)
Study #61
-
PCB pretreatment enhanced the metabolic activation of 4-nitroquinoline
diaphorase in the lung, leading to possible disorders in steroid homeostasis
and cancer
The present paper describes a marked induction of liver microsomal
cytochrome P-450 and cytosolic DT-diaphorase to cause possible disorder
of steroid homeostasis and promotion of carcinogenicity of 4-nitroquinoline
N-oxide (4-NQO) in rats by pretreatment with 3,4,5,3',4'-pentachlorobiphenyl
(PenCB) or 2,3,4,7,8-pentachlorodibenzofuran (PenCDF). The animals were
sacrificed 5 days after the pretreatment. These induction experiments showed
that 7 alpha-hydroxylation of both progesterone and testosterone in liver
microsomes was selectively increased to a great extent, but hydroxylations
at the 2 alpha-, 6 beta- and 16 alpha-positions were depressed, together
with 5 alpha-reduction. From the same microsomes, three of the strongly
induced P-450 isozymes, i.e., high- and low-spin P-448s and P-452, were
purified. The last isozyme was most responsible for 7 alpha-hydroxylation
of testosterone. The pretreatment, also increased activity of DT-diaphorase
and reduction of 4-NQO about 10-fold in liver 9000g supernatants. This
reduction of 4-NQO was solely catalyzed by DT-diaphorase and the only product
was 4-hydroxylaminoquinoline N-oxide, a proximate carcinogen, indicating
that the pretreatment strongly increased production of a proximate carcinogen
from 4-NQO. Such an enhancement of the metabolic activation of 4-NQO
by the pretreatment was also observed to some extent in the lung and
the skin. Persistency of PenCB and PenCDF in the liver of rats was also
discussed. (Yoshimura et al, 1985)
Study #62
-
PCB induced enzymes converted a non-mutagenic chemical (phenanthridine)
into a mutagenic one.
The comparative metabolism of phenanthridine (3,4-benzoquinoline) by rat
lung and liver microsomes has been investigated. The array of metabolites
produced by induced lung and liver are qualitatively similar. Phenanthridone
has been identified as a phenanthridine metabolite produced by induced
rat liver and lung. Phenanthridone is directly mutagenic
in Salmonella tester strain TA-98 while phenanthridine is not. Although
phenanthridone is more mutagenic than phenanthridine after incubation with
rat liver 9000g supernatant fraction, it is less cytotoxic to Chinese hamster
ovary cells in vitro. (Lung microsomes were induced by PCBs.) (Benson et
al, 1983)
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