(Circulation. 2000;102:1420.)
© 2000 American Heart Association, Inc.
Basic Science Reports |
1-Acid Glycoprotein and
1-Antitrypsin Against Ischemia/Reperfusion Injury by Preventing Apoptosis and Inflammation
From the Department of General Surgery (M.A.R.C.D., V.H.H., C.v.V., T.G.A.M.W., W.A.B.), University of Maastricht, Maastricht, the Netherlands, and the Department of Molecular Biology (G.D., P.V.), Flanders Interuniversity Institute for Biotechnology and University of Ghent, Ghent, Belgium.
| Abstract |
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1-acid glycoprotein (AGP) and
1-antitrypsin (AAT) to the protective effect of
ischemic preconditioning in the kidney.
Methods and ResultsExogenous AGP and AAT inhibited
apoptosis and inflammation after 45 minutes of renal I/R in a
murine model. AGP and AAT administered at reperfusion prevented
apoptosis at 2 hours and 24 hours, as evaluated by the presence
of internucleosomal DNA cleavage, terminal
deoxynucleotidyl transferasemediated dUTP nick
end-labeling, and the determination of renal caspase-1 and
caspase-3like activity. AGP and AAT exerted anti-inflammatory
effects, as reflected by reduced renal tumor necrosis factor-
expression and neutrophil influx after 24 hours. In general, these
agents improved renal function. Similar effects were observed when AGP
and AAT were administered 2 hours after reperfusion but to a lesser
extent and without functional improvement. Moreover, I/R elicited an
acute phase response, as reflected by elevated serum AGP and serum
amyloid P (SAP) levels after 24 hours, and increased hepatic acute
phase protein mRNA levels after 18 hours of renal reperfusion.
ConclusionsWe propose that the antiapoptotic and anti-inflammatory effects of AGP and AAT contribute to the delayed type of protection associated with ischemic preconditioning and other insults. This mechanism is potentially involved in the course of many clinical conditions associated with I/R injury. Moreover, exogenous administration of these proteins may provide new therapeutic means of treatment.
Key Words: ischemia reperfusion kidney immune system apoptosis
| Introduction |
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(TNF-
), was shown to contribute to late apoptosis
in the course of renal I/R.2
TNF-
is also an inducer of the acute phase response (APR), a
complex series of reactions executed by the host in the immediate
aftermath of injury, trauma, or infection.3 Protection
against reperfusion injury can be induced by various means, including
antecedent administration of endotoxin,4 5 6 heat
shock,7 and single or multiple periods of brief antecedent
ischemia.8 Besides such protection, the latter
treatments are all expected to induce an APR.3 9 During
the APR, liver cells and various epithelial cells respond to increasing
levels of, among others, TNF-
by producing acute phase proteins,
including
1-acid glycoprotein
(AGP) and
1-antitrypsin (AAT).10
These 2 major acute phase proteins exhibit various anti-inflammatory
effects11 12 13 and have been shown to prevent
hepatocyte apoptosis in a model of
TNF-
/galactosamine toxicity.14
The present study investigates whether AGP and AAT can reduce I/R-induced apoptosis and inflammation and whether renal I/R induces an APR. The results show that physiological serum levels of exogenous AGP and AAT strongly reduce apoptosis and inflammation after I/R and that renal I/R induces an APR.
| Methods |
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Experimental Protocol
Male Swiss mice weighing 20 to 25 g from Charles River
Breeding Laboratories (Heidelberg, Germany) were housed individually in
standard cages with access to food and water ad libitum. The studies
were approved by the Institutional Animal Care Committee of the
University of Maastricht. Forty-five minutes of unilateral
ischemia of the left kidney was followed by contralateral
nephrectomy, as described in detail previously.2 The
animals were euthanized at indicated time points. At the time of
euthanization, blood was collected by orbital puncture, and the left
kidney was harvested.
At reperfusion, mice were administered intraperitoneally (IP) 5 mg bovine AGP (n=12) or 0.5 mg human AAT (n=12) in 0.5 mL sterile PBS, resulting in serum levels identical to those observed during the APR.10 In separate groups, mice received AGP (n=8) or AAT (n=8) after 2 hours of reperfusion. To further delineate the therapeutic efficacy of AGP treatment, mice received 1.7 mg AGP (n=3), 0.5 mg AGP (n=3), and 0.17 mg AGP (n=3) in 0.5 mL PBS at reperfusion and were euthanized after 2 hours. A control group received vehicle consisting of 0.5 mL PBS IP (n=10). A sham-operated group (n=12) was subjected to the same surgical procedure without clamping of the renal pedicle, treated with PBS, and euthanized at corresponding time points.
In an experiment to investigate whether renal I/R induced an APR, mice were subjected to renal I/R, and blood was collected by orbital puncture at 8, 16, and 24 hours after ischemia (n=12). Additional animals received 30 µg IP lipopolysaccharide (LPS, Escherichia coli serotype O55:B5) (n=3) or 0.5 mL of PBS IP (n=3) and served, respectively, as positive and negative controls for the development of an APR.
Apoptosis Assays
Presence of internucleosomal DNA cleavage in kidneys was
investigated with a commercial ligase-mediated polymerase chain
reaction assay kit (Apoalert, Clontech) according to the
manufacturers instructions. Renal caspase-1 and caspase-3like
activities were assessed as described15 by measuring the
release of fluorescent 7-amino-4-methylcoumarin
for 1 hour after incubating renal lysates with the fluorogenic
substrate Ac-YVAD-amc (caspase-1like) or Ac-DEVD-amc
(caspase-3like).
MPO, BUN, and Serum Creatinine
Renal neutrophil accumulation was quantified by measuring renal
myeloperoxidase (MPO) content as described.2 MPO activity
is expressed per milligram tissue by comparing the optical
density of samples with a horseradish peroxidase titration curve and
standardized with respect to wet/dry ratios. Blood urea nitrogen (BUN)
content and serum creatinine levels were measured in serum
by using a BUN Unimate 5 kit and a CREA MPR3 kit
(Boehringer-Mannheim) in a Cobas Fara autoanalyzer
(Roche).
Histology
Kidney specimens were immediately frozen and stored at -70°C
or fixed in buffered formalin and embedded in paraffin. Frozen sections
(5 µm) were stained for neutrophils with mAb Gr-1 as
described.1 Immunostaining for TNF-
with digoxigenin-labeled mAb 52B83 was performed on paraffin sections
as described.2 Histological aspects of
apoptosis were studied by standard terminal
deoxynucleotidyl transferasemediated dUTP nick
end-labeling (TUNEL) as described.16
SAP ELISA and Single Radial Immunodiffusion for Serum AGP
Serum SAP was measured by use of a sandwich ELISA. A 96-well
Immunomaxisorp plate (Nunc) was coated with a rabbit anti-mouse SAP
IgG. Aspecific binding was blocked with BSA; after washing procedures,
samples were diluted, and a standard titration curve of a known
quantity of murine SAP was obtained. Detection was performed by use of
a biotinylated rabbit anti-mouse SAP IgG, followed by incubation with
substrate. Serum AGP levels were determined by single radial
immunodiffusion17 with use of agar gels containing 5%
anti-AGP serum. Because purified murine AGP was not readily available,
the obtained results were calibrated against a dilution of murine
plasma obtained 36 hours after pretreatment with 30 µg LPS, which
also served as a positive control.
Measurement of Hepatic Acute Phase Protein mRNA Content
Total RNA was extracted from livers and transcribed into cDNA,
of which the concentration was subsequently standardized on the basis
of the ß-actin cDNA fraction. To determine hepatic AGP, AAT, and SAP
mRNA content, three 2-fold serial dilutions of cDNA were amplified with
specific primers. Murine AGP mRNAspecific primers, designed on the
basis of sequence homology with an acute phaseinducible gene in
Mus caroli,18 were sense primer
5'-GCGGCTGTCCTAAACCCT-3' and antisense primer
5'-CAAGTCAAAGGCAAGCATG-3'; murine AAT mRNAspecific primers were sense
primer 5'-TCCCATGAGATCGCTACAAAC-3' and antisense primer
5'-TGATAATGGTTCTTGGCCTCT-3'; murine SAP mRNAspecific primers were
sense primer 5'-CTTCACCAGCCTTCTTTCAGA-3' and antisense primer
5'-ACGGACTGTGACTTTTGATTGT-3'; and ß-actinspecific primers were
sense primer 5'-TAAAACGCAGCTCAGTAACA-GTCCG-3' and antisense primer
5'-TGCAATCCTGTGGCAT-CCATGAAAC-3'. After separation on a 1.5%
agarose gel, band proportions were estimated by measuring the intensity
of ethidium bromide fluorescence with a digital camera
(Imagemaster VDS, Pharmacia) by using commercial gel analysis
software (Sigma Gel, SPSS).
Statistics
Data are expressed as mean±SEM, and statistical
analysis was performed by Student t test.
A value of P<0.05 was taken to denote statistical
significance.
| Results |
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We previously demonstrated that inhibition of early apoptosis
prevents the initiation of inflammation as well as secondary
apoptosis caused by inflammation in our model.1
The present study indicates that abrogation of inflammation does
not occur when apoptosis inhibitors are
administered after 2 hours of reperfusion. Hence, apoptosis
precedes the inflammatory response at 2 hours of reperfusion.
Therefore, administration of AGP or AAT at 2 hours of reperfusion
enabled us to differentiate primary apoptosis from secondary
apoptosis and to study the possible involvement of an
anti-inflammatory effect of these acute phase proteins. Compared with
PBS treatment, AAT administered at 2 hours of reperfusion decreased
caspase-1 and caspase-3like activities after 24 hours of
reperfusion (Figure 3
). However, AAT did not reduce
internucleosomal DNA cleavage (Figure 1
), whereas AGP reduced
caspase-1 and caspase-3like activities (Figure 3
) and
prevented internucleosomal DNA cleavage after 24 hours (Figure 1
). These data suggest that reduced secondary apoptosis
is a result of the anti-inflammatory effect of AGP and AAT, although we
cannot exclude a contribution via direct inhibition of secondary
apoptosis.
To investigate the therapeutic efficacy of AGP treatment, the effect of
a dose range of AGP on internucleosomal DNA cleavage after 2 hours of
reperfusion was studied. A single dose of 1.7 mg AGP at reperfusion
sufficed to reduce renal internucleosomal DNA cleavage (Figure 1
). This therapeutic effect gradually declined when dosages of
0.5 of 0.17 mg of AGP were used (Figure 1
). Rodent acute phase
plasma has been reported to contain up to 3.5 mg/mL AGP compared with
almost undetectable constitutive levels,10 indicating that
systemic rises in endogenous AGP during an APR are
potentially protective against I/R-induced apoptosis.
AGP and AAT Reduce Inflammation After I/R
We studied the effects of AGP and AAT on I/R-induced inflammation
by assessing renal TNF-
expression and neutrophil influx. At 24
hours after I/R, AGP and AAT administered at reperfusion limited
TNF-
expression (Figure 5D
and 5E
) and neutrophil influx
(Figure 4
). These effects are most
likely the result of direct inhibition of early primary
apoptosis, implicated in the subsequent induction of
inflammation.1 Alternatively, direct anti-inflammatory
effects may also be involved. Nevertheless, these findings explain the
observed inhibition of secondary apoptosis in mice treated at
reperfusion.
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AGP and AAT given after 2 hours of reperfusion attenuated the
inflammation at 24 hours to a lesser extent than did treatment given at
reperfusion (Figure 4
). However, treatments at both time points
decreased inflammation compared with PBS treatment at 24 hours of
reperfusion (Figure 4
). The PBS-treated control mice showed
significant renal inflammation as reflected by TNF-
expression in
the outer stripe of the outer medulla, along the damaged tubular
epithelium (Figure 5B
), and in
infiltrating leukocytes (Figure 5C
). Also, significant renal
neutrophil accumulation was reflected by an enhanced MPO content
(Figure 4
) and evident accumulation of Gr-1positive cells
(Figure 6
). AGP and AAT administered at 2
hours prevented inflammation as reflected by these
parameters, revealing a direct anti-inflammatory potential
of AGP and AAT.
|
AGP and AAT Prevent I/R-Induced Renal Dysfunction
Renal dysfunction was reflected by increased BUN content and serum
creatinine levels after 24 hours of reperfusion (Figure 7
). Compared with PBS, both AGP and AAT
administered at reperfusion lowered BUN content and serum
creatinine levels. However, compared with PBS, AGP and AAT
administered after 2 hours of reperfusion failed to significantly
decrease BUN or serum creatinine. These findings illustrate
the necessity for the prevention of primary apoptosis-induced
inflammation in addition to the direct prevention of inflammation after
I/R for optimal therapeutic effects.
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Renal I/R Induces an APR
To investigate whether renal I/R induces an APR, serum SAP
and AGP levels and hepatic acute phase protein mRNA content were
measured. SAP was used as a marker for the APR because it is coreleased
with AGP and AAT during the APR. Renal I/R induced an elevation in
plasma SAP levels at 16 and 24 hours after ischemia
(Table
). LPS administration served as a
positive control and increased SAP levels after 36 hours. Serum AGP
levels increased to a similar extent (an approximate factor 10 compared
with constitutive levels) after 24 hours of reperfusion and 36 hours
after LPS (data not shown). In contrast to previous
reports,9 10 our results show no apparent rise in hepatic
AAT mRNA levels after renal I/R or LPS administration (Figure 8
). Conversely, after 16 hours of
reperfusion, hepatic AGP and SAP mRNA levels increased compared with
levels in sham-operated control mice or mice that received only PBS
(Figure 8
). This rise in hepatic acute phase protein mRNA was
similar to that observed in mice 16 hours after 30 µg LPS (Figure 8
.). These data clearly demonstrate that renal I/R induces an
APR.
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| Discussion |
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Early primary19 20 as well as late
secondary2 21 apoptosis after I/R has been
reported to be caused by various means. The present results,
showing that AGP and (to a lesser extent) AAT protect against
TNF-
dependent late apoptosis,2 are in line
with data from Van Molle et al.14 They showed that AGP
protects against TNF-
induced liver apoptosis in both
galactosamine-pretreated and actinomycin Dpretreated mice, whereas
AAT conferred protection in only the galactosamine model. Because
inflammation is not involved in the process of primary
apoptosis after I/R, our results show that the
antiapoptotic potential of AGP and AAT is not limited to
TNF-
induced apoptosis.
AGP has been reported to exhibit anti-inflammatory properties,
such as inhibition of neutrophil activation and induction of
macrophage-derived interleukin-1 receptor
antagonist release.11 AGP also binds to
bacterial endotoxin and protects mice from endotoxin-induced septic and
hypovolemic shock.22 23 Currently, no clear
antiapoptotic property can be deduced from the AGP molecule.
AAT can inhibit neutrophil superoxide
production,24 induce
macrophage-derived interleukin-1 receptor
antagonist release,11 and reduce
TNF-
induced lethality.25 AAT additionally inhibits
elastase26 and, as a consequence,
elastase-dependent synthesis and release of platelet-activating
factor,26 a mediator of I/R-induced
inflammation.27 Elastase has been reported to cleave
tyrosyl-tRNA synthetase during apoptosis to fragments with
interleukin-8like chemotactic properties,28 a process
potentially involved in primary I/R-induced
apoptosis.1 AGP or AAT may interact with the
proteolytic cascade of enzymes involved in apoptosis. However,
both acute phase proteins lack inhibitory effects on
caspases in vitro (Dr C. Libert, personal communication, 1999).
Further studies are needed to establish the molecular mechanisms by
which AGP and AAT prevent I/R-induced apoptosis and
inflammation.
Antecedent ischemia can induce protection from I/R-induced injury in a biphasic pattern.8 Such protection lasts for 30 minutes to 2 hours and is followed by a second window of protection appearing 12 to 24 hours later. This so-called ischemic preconditioning has been attributed to local protective mechanisms, including induction of heat-shock proteins29 and adenosine formation.30 However, brief ischemia in remote organs31 32 or endotoxin pretreatment4 5 6 has been shown to confer similar protection, suggesting involvement of other than local mechanisms. Indeed, the observed I/R-induced SAP and AGP increase and elevated hepatic acute phase protein mRNA content show that renal I/R induces an APR. Our data also indicate that the serum AGP increase during the APR is of potentially sufficient extent to protect against I/R-induced apoptosis. Thus, an APR likely confers systemic protection against I/R injury, which could contribute to the second window of protection associated with ischemic preconditioning.
The physiological mode of protection outlined above may determine the natural history of clinical conditions associated with I/R as observed during severe trauma or septic shock. For instance, sepsis mortality is highest during the initial stages of the disease, and the chances of survival increase with disease duration.33 This increased survival may well be a consequence of protection against shocklike complications because systemic levels of acute phase proteins increase as the disease progresses.34 Moreover, protective acute phase proteins such as AGP and AAT may provide new means to treat clinical conditions associated with I/R injury.
We conclude that the APR may be part of a physiological protection mechanism against I/R injury and show that protection conferred by acute phase proteins such as AGP and AAT is mediated by distinct antiapoptotic as well as anti-inflammatory effects. We additionally demonstrate that I/R itself induces an APR, which may explain the second window of protection induced by ischemic preconditioning.
| Acknowledgments |
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| Footnotes |
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Received December 31, 1999; revision received April 25, 2000; accepted April 26, 2000.
| References |
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