(Hypertension. 2000;35:86.)
© 2000 American Heart Association, Inc.
Scientific Contributions |
From the Department of Cardiovascular Medicine, Cardiovascular Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Correspondence to Kensuke Egashira, MD, PhD, Department of Cardiovascular Medicine, Cardiovascular Science, Graduate School of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. E-mail egashira{at}cardiol.med.kyushu-u.ac.jp
| Abstract |
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-nitro-L-arginine methyl
ester (L-NAME) induces inflammatory changes (monocyte infiltration,
myofibroblast formation, and monocyte chemoattractant protein-1
[MCP-1] and transforming growth factor-ß1 [TGF-ß1] expression)
in the rat heart and vessel. There is debate regarding whether TGF-ß1
exhibits proinflammatory or anti-inflammatory activities. We used the
rat model to investigate the role of TGF-ß in the pathogenesis of
such inflammatory changes. We show here that infiltrating monocytes and
myofibroblasts in the inflammatory lesions produced TGF-ß1 on the
third day of L-NAME administration. Cotreatment with a monoclonal
antibody against TGF-ß1, but not with control IgG, prevented the
L-NAMEinduced cardiac inflammation. The antibody also significantly
inhibited the gene expression of MCP-1, P-selectin, and
intercellular adhesion molecule-1. In summary, the antibody
against TGF-ß1 prevented inflammatory changes in rat heart and vessel
induced by chronic inhibition of NO synthesis, suggesting that
increased production of TGF-ß1 is involved in the
inflammatory changes in this model.
Key Words: endothelium-derived factor growth substances inflammation adhesion molecule angiotensin II fibrosis
| Introduction |
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-nitro-L-arginine
methyl ester (L-NAME) induces marked monocyte infiltration into the
coronary vessels associated with induction of monocyte
chemoattractant protein-1 (MCP-1) during the first week of the
treatment and causes vascular remodeling (medial thickening and
fibrosis) and myocardial remodeling (fibrosis and
hypertrophy) after 4 to 8 weeks of the treatment in
animals. We have recently reported that early induction of transforming growth factor-ß1 (TGF-ß1) contributes to cardiac fibrosis in this model.10 However, the role of TGF-ß1 in the pathogenesis of early inflammatory changes in this model has not been examined. There is considerable debate regarding whether TGF-ß1 exhibits proinflammatory or anti-inflammatory activities (for review, see References 14 and 1514 15 ). For example, it has been demonstrated that in vivo gene transfer of TGF-ß1 causes tissue inflammatory changes and subsequent fibrosis in the lung16 and blood vessels,17 whereas the major phenotype of the TGF-ß1 knockout mice is an early-onset inflammation in most tissues of the body.18 19
TGF-ß1 is usually secreted from many cell types as a biologically inactive or latent form.20 The activation mechanisms of latent TGF-ß1 complex in vivo have not been fully elucidated. Thus, demonstration of mere expression of total TGF-ß1 may not provide sufficient evidence of its function. To address direct in vivo evidence for the functional importance of TGF-ß1, a neutralizing antibody targeted to block TGF-ß1 activity may be useful.
We tested the hypothesis that treatment with a neutralizing antibody against TGF-ß1 attenuates inflammatory and proliferative changes in the heart and vessel of an animal model of chronic inhibition of NO synthesis.
| Methods |
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An Animal Model of Chronic Inhibition of NO Synthesis
Twenty-week-old male Wistar-Kyoto rats were housed singly
in a pyrogen-free facility. Four groups of rats were studied. The first
(control) group received untreated chow and drinking water. The second
group (L-NAME) received L-NAME in its drinking water (1 mg/mL).
The third group (L-NAME+IgG) received L-NAME in its drinking water and
IgG (intraperitoneal injection at 1 mg/kg per day).
The fourth group (L-NAME+TGF-ßAb) received L-NAME in drinking water
and a monoclonal antibody neutralizing TGF-ß1
(intraperitoneal injection at 1 mg/kg per day). We
confirmed that drinking and eating patterns of the rats were unaffected
by any treatment protocol. Before and on the third day of treatment,
systolic blood pressure (the tail-cuff method), heart rate, and
body weight were measured.
We used a monoclonal antibody against TGF-ß1 (Biosource, AHG0051) to block TGF-ß1 activity in vivo. This antibody was directed against human TGF-ß1 and shown to neutralize rat TGF-ß1. Previously, we evaluated the ability of the antiTGF-ß1 antibody to neutralize TGF-ß1 activity in vitro. In brief, this antibody completely abolished the suppression of [3H]thymidine incorporation induced by recombinant rat TGF-ß1 in the Mink Lung epithelial (MV1Lu) cells.
Histopathology and Immunohistochemistry
Five rats in each group were killed on the third day of
treatment, as we described previously.11 In brief, each
animal was anesthetized with
intraperitoneal pentobarbital, its abdomen was
opened, and the abdominal aorta was cannulated. The chest was opened,
and an incision was made in the right atrium. The heart was perfused
via the aorta with oxygenated Krebs-Henseleit solution at a
pressure of 90 mm Hg, and the coronary vasculature was
fixed for 60 minutes with methacarn solution. The heart was cut into 5
pieces perpendicular to the long axis. All tissue samples were fixed in
methacarn solution for a few days, dehydrated, embedded in paraffin,
and cut into slices 5 µm thick. Sections were mounted on slides
and stained with hematoxylin-eosin solution for estimation of
inflammatory cell infiltration.
For immunohistochemistry, paraffin slices 5 µm thick were
preincubated with 3% skim milk to decrease nonspecific binding.
Sections were incubated overnight at 4°C with mouse anti-rat
macrophage/monocyte antibody (ED1, Serotec); mouse anti-human
proliferating cell nuclear antigen (PCNA) antibody (Dako); mouse
anti-human TGF-ß1 antibody (1 µg/mL, AHG0051, Biosource); goat
anti-human TGF-ß1 latency-associated peptide antibody (10 µg/mL,
AB-246NA, R&D); anti-human
-smooth muscle actin antibody (1 µg/mL,
Dako), or nonimmune mouse or goat IgG (Zymed Laboratory). The slides
were washed and incubated with biotinylated, affinity-purified rabbit
anti-mouse or goat IgG as secondary antibody. After avidin-biotin
amplification, the slides were incubated with 3',3'-diaminobenzidine
and counterstained with hematoxylin.
To determine the cell type of the TGF-ßexpressing cells,
immunohistochemical double staining was performed.12 The
tissue sections were stained with an antibody against TGF-ß and with
a monoclonal antibody against
-smooth muscle actin or monocyte.
Morphometry and cell enumeration were performed by a single observer who was blinded to all treatment protocols, as we described.11 To quantify the number of immunopositive cells in hearts, 5 heart sections per heart immunohistochemically stained by antibodies against ED1 or PCNA were scanned at x100 magnification. The number of cells positive for ED1 or PCNA was counted, and the sum of total cells per section was reported.
Northern Blot Analysis
Five rats in each group were killed on the third day of
treatment. After the animals were killed, rat hearts were removed, and
the hearts were snap-frozen in liquid nitrogen and stored at
-80°C.
Total RNA was extracted from each sample by the acid guanidinium thiocyanate-phenol-chloroform method, poly(A)+ RNA was purified on an oligo(dT)-cellulose column, and then Northern blot hybridization was performed as we described previously.11 The cDNA probes used were as follows: a 1.0-kb EcoRI-EcoRI fragment of rat MCP-1 cDNA, a 1.6-kb EcoRI-EcoRI fragment of rat P-selectin cDNA, a 2.6-kb EcoRI-EcoRI fragment of rat intercellular adhesion molecule-1 (ICAM-1) cDNA, and a 1.3-kb PstI-PstI fragment of mouse GAPDH (American Type Culture Collection). Relative amounts of MCP-1, P-selectin, or ICAM-1 mRNA were normalized against the amounts of GAPDH mRNA.
Statistical Analysis
Data are expressed as mean±SE. Differences in
parameters of a group were compared by Students
t test. Differences between groups were determined by 2-way
ANOVA and a Fishers multiple comparison test. A level of
P
0.05 was considered statistically significant.
| Results |
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Localization of TGF-ßProducing Cells
A marked infiltration of mononuclear leukocytes in the
perivascular areas immediately surrounding the coronary
arteries and veins and the myocardial interstitial spaces
was observed in the L-NAME and L-NAME+IgG groups (Figure 1). Attachment of mononuclear
leukocytes to the endothelium of coronary
vessels was also seen in those 2 groups. The majority of leukocytes
that had infiltrated into the lesions were found to be ED1-positive
monocytes (Figure 1). Spindle-shaped
-smooth muscle actinpositive
cell (myofibroblasts transformed usually from fibroblasts or pericytes)
is another major cell type (Figure 1) that had appeared in the
inflammatory lesions. Although
-smooth muscle actin is used as a
marker for myofibroblasts, the antibody against
-smooth muscle actin
also recognizes vascular smooth muscle cells. Therefore, it is possible
that these immunopositive cells might have derived from vascular smooth
muscle cells that migrated into the perivascular and
interstitial inflammatory lesions. Nuclear staining for
PCNA antibody was observed in some endothelial cells,
vascular smooth muscle cells in the media, monocytes, or
myofibroblast-like cells (data not shown). No such inflammatory and
proliferative changes were observed in the control group.
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Immunoreactivity for TGF-ß1 and TGF-ß1 latency-associated peptide
was weakly present in the areas that normally contain collagens,
such as the perivascular and myocardial interstitial spaces
in the control group (Figure 1). In the L-NAME and L-NAME+IgG
groups, both TGF-ß1 and TGF-ß1 latency-associated peptide
immunoreactivity were intensely present in monocytes and/or
spindle-shaped fibroblast-like cells (possibly myofibroblasts) (Figure 1). Immunological double staining showed that a considerable
proportion of TGF-ß1positive cells were positive for antibodies
against both monocytes and
-smooth muscle actin (data not
shown).
Effects of the AntiTGF-ß1 Antibody on Inflammatory and
Proliferative Changes
When ED1-positive monocytes or PCNA-positive cells were counted by
use of immunohistochemistry, the number of immunopositive cells per
section was significantly greater in the L-NAME and L-NAME+IgG groups
than in the control group (Figure 2). The increases in ED1-positive
cells and PCNA-positive cells were markedly reduced by treatment with
the antibody against TGF-ß1. Treatment with the antibody
significantly reduced the appearance of
-smooth muscle
actinpositive myofibroblasts (data not shown).
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Effects of a Neutralizing Antibody Against TGF-ß on mRNA Levels
for MCP-1, P-Selectin, and ICAM-1
The cardiac mRNA levels for MCP-1, P-selectin, and ICAM-1 were
significantly higher in the L-NAME and L-NAME+IgG groups than in
the control group (Figure 3). The
increases in gene expression of those molecules were significantly
reduced by treatment with the antiTGF-ß1 antibody (Figure 3).
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| Discussion |
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Immunoreactivity for TGF-ß1 and TGF-ß1 latency-associated peptide was found to be increased in the inflammatory lesions. The former antibody recognizes both extracellular and intracellular TGF-ß1, and the latter antibody recognizes intracellular TGF-ß1 precursor.20 Thus, the cells stained with the both antibodies are thought to produce TGF-ß1. Our immunohistochemical double staining revealed that infiltrating monocytes and myofibroblasts are the major source of increased production of TGF-ß1. Although the activation mechanisms of latent TGF-ß1 complex are unclear in the present study, the effect of the antibody suggests that the active form of TGF-ß1 was generated from the latent complex, which induced the inflammatory and proliferative changes.
The underlying mechanism of the increase in TGF-ß1 production
involves increased local activity of angiotensin II via
AT1 receptors in this model, because we
previously demonstrated that treatment with AT1
receptor antagonist prevented the increases in gene
expression of TGF-ß1 and extracellular matrix proteins such as type 1
collagen and fibronectin after L-NAME treatment.10 Others
have also shown that angiotensin II infusion induces
TGF-ß1 expression in hearts and vessels in vivo.21 22 We
previously demonstrated that cotreatment with a polyclonal antibody
against TGF-ß (different from that used in the present study)
blocked the increases in gene expression of extracellular matrix
proteins,10 suggesting that the increases in matrix
protein production and fibrosis are mediated by TGF-ß1.
Profibrotic activity of TGF-ß1 has been shown to depend on
differentiation of interstitial fibroblast and/or pericyte
to myofibroblast with acquiring
-smooth muscle
actin.23 24 25 Myofibroblasts produce extracellular
matrix proteins via autocrine/paracrine action of TGF-ß1 and thus are
responsible for tissue fibrosis/remodeling. Myofibroblasts are
eliminated by apoptosis when the fibrotic process is
completed.25 Although additional studies that examine the
effect of long-term suppression of TGF-ß1 activity on fibrotic
changes would be more interesting, it is recognized that chronic
administration of an antibody for longer periods may not be possible.
Thus, further studies are needed to more accurately address the notion
that TGF-ß1 is involved in the development of
cardiovascular tissue fibrosis in this model.
Since inflammatory changes in coronary vessels have been reported in animal models with angiotensin IIinduced hypertension,22 genetic hypertension,26 and renovascular hypertension,27 inflammatory changes associated with increased production of TGF-ß1 seen in our experimental model might result, at least in part, from the rapid increase in systolic arterial pressure induced by L-NAME administration. However, we previously reported that the normalization of hypertension by treatment with hydralazine did not prevent inflammatory changes or upregulation of TGF-ß1.10 12 Furthermore, in the present study we have shown that treatment with TGF-ß1 antibody did not decrease L-NAMEinduced hypertension. Others have demonstrated that infusion of angiotensin II at a low dose, which did not produce hypertension, upregulates TGF-ß1 expression and induces subsequent fibroinflammatory changes in the rat heart.28 Thus, it is unlikely that the increase in systolic arterial pressure largely contributed to the induction of inflammatory changes and TGF-ß1 expression in our experimental model.
In the present study treatment with antiTGF-ß1 antibody prevented the increased expression of MCP-1, P-selectin, and ICAM-1, suggesting that those inflammation-promoting molecules contribute to inflammatory changes in this model. Under our experimental conditions, it was not possible to discriminate between the primary and secondary actions of TGF-ß1 because the antiTGF-ß1 antibody prevented both inflammatory changes and the gene expression of those inflammation-promoting molecules. The relationship among those molecules such as MCP-1, P-selectin, ICAM-1, and TGF-ß1 should be clarified in the future to determine the most important molecule and a therapeutic molecular target for fibroinflammatory disorders in this model.
There are discrepancies between the results presented here and the results of knockout mice for TGF-ß1. Mice lacking TGF-ß1 develop an early inflammation in multiple organs, including the heart, culminating in death at approximately 3 weeks of age.18 19 Diebold et al29 recently indicated that such tissue inflammation in the TGF-ß1 null mice was secondary to lymphocyte proliferation and activation but was not primarily due to the deficiency of TGF-ß1; immunosuppressive interventions blunted the tissue inflammation in the TGF-ß1 null mice. Therefore, it appears that such inflammation in TGF-ß1 null mice resulted, at least in part, from the production of inflammatory cytokines from TGF-ß1 null lymphocytes. The notion that TGF-ß1 is responsible for chronic fibroinflammatory disorders is supported by prior data that in vivo gene transfer of TGF-ß1 causes inflammatory tissue changes and subsequent fibrosis16 17 and that transgenic mice in which mature (biologically active) TGF-ß1 is locally expressed in the hepatocytes develop hepatic inflammation and fibrosis.29
In summary, we demonstrated that the increase in TGF-ß1 production is of functional importance in the pathogenesis of inflammatory and proliferative changes of hearts and vessels in a rat model of chronic inhibition of NO synthesis. It is suggested that TGF-ß1 may be one of the therapeutic molecular targets for fibroinflammatory disorders such as arteriosclerosis or restenotic lesions after angioplasty.
| Acknowledgments |
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Received May 20, 1999; first decision June 10, 1999; accepted September 2, 1999.
| References |
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