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INFLAMMATION AND IMMUNOPHARMACOLOGY
Department of Clinical and Experimental Medicine and Pharmacology, School of Medicine, University of Messina, Messina, Italy (T.G., E.M., C.C., R.D.P., C.M., S.C.); and Centro per lo Studio ed il Trattamento dei Neurolesi Lungodegenti, School of Medicine, University of Messina, Messina, Italy (P.B.)
Received October 14, 2005; accepted November 21, 2005.
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Abstract |
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(TNF-) in experimental model of spinal cord trauma, which was induced by the application of vascular clips (force of 24 g) to the dura via a four-level T5–T8 laminectomy. Spinal cord injury in mice resulted in severe trauma characterized by edema, neutrophil infiltration, and cytokine production that it is followed by recruitment of other inflammatory cells, such as production of a range of inflammation mediators, tissue damage, apoptosis, and disease. Treatment of the mice with etanercept significantly reduced the degree of 1) spinal cord inflammation and tissue injury (histological score); 2) neutrophil infiltration (myeloperoxidase evaluation); 3) inducible nitric-oxide synthase, nitrotyrosine, cyclooxygenase-2, and cytokines expression (TNF- and interleukin-1
); and 4) apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and Bax and Bcl-2 expression). In a separate set of experiment, we have also clearly demonstrated that TNF- inhibitor significantly ameliorated the recovery of limb function (evaluated by motor recovery score). Taken together, our results clearly demonstrate that treatment with etanercept reduces the development of inflammation and tissue injury events associated with spinal cord trauma.
). In fact, the primary traumatic mechanical injury to the spinal cord causes the death of a number of neurons that cannot be recovered or regenerated to date. However, neurons continue to die for hours after SCI and this represents a potentially avoidable event. This secondary neuronal death is determined by a large number of cellular, molecular, and biochemical cascades. One such cascade that has been touted to contribute importantly to the evolution of this secondary damage is the local inflammatory response in the injured spinal cord. The inflammatory response in the CNS involves the participation of different cellular types of the immune system and resident cells of the CNS, adhesion molecules, cytokines, and chemokines among other proteic components. During neuroinflammation, chemotaxis is an important event in the recruitment of cells to the CNS. If this process is not controlled but is prolonged, inflammation loses its repairing function and can be the cause of damage.
Both necrotic and apoptotic mechanisms of cell death after SCI have been well and extensively characterized in animal SCI models. It is has been thought that microglial cells might be the source of cytotoxic cytokines, such as tumor necrosis factor- (TNF-), that kill oligodendrocytes. Within 1 h after spinal cord injury, increased synthesis and/or secretion of TNF- is detectable at the injury site. Harrington et al. (2005) demonstrated that 6 h postacute SCI, there were an increased neuronal expression of TNF- and its receptors. They also demonstrated that, at 1 h after acute SCI, TNF- levels in the cerebrospinal fluid were significantly higher than those found in the sham-injured animals, indicating the release of this cytokine into the interstitial fluid. Likewise, other authors have shown that, after experimental SCI, the levels of TNF- and interleukin 1 (IL-1) are significantly increased within the first few hours (Hayashi et al., 2000).
TNF- has an important role in several pathologies, such as rheumatoid arthritis (Bazzoni and Beutler, 1996). TNF- binds to two receptors, the type 1 TNF receptor (p55) and the type 2 TNF receptor (p75), that are expressed on many types of the cells. The biologic activity of TNF- can be attenuated by soluble TNF receptors. Studies in animals have provided key evidence that antagonizing TNF- is a viable therapeutic strategy (Kapadia et al., 1995). Subsequent studies in patients with rheumatoid arthritis indicated that blocking TNF improved symptoms. Biological agents that are currently available include three agents that decrease the activity of tumor necrosis factor- (infliximab, adalimumab, and etanercept). The major therapeutic goal when administering TNF antagonists is to eliminate the surplus of TNF from the circulation and from sites of inflammation.
Etanercept inhibits TNF activity by competitively binding to it and preventing interactions with its cell-surface receptors. Etanercept is a recombinant dimer of human TNF receptor proteins fused and bound to human IgG1. It binds TNF- and TNF-, the binding is reversible, and when it is dissociated, TNF remains bioactive. Etanercept, although originally developed for rheumatoid arthritis and Crohn disease, has also demonstrated beneficial activity in other inflammatory diseases. This article investigated the role of TNF in the pathogenesis of SCI and evaluates the therapeutic effects of etanercept.
In particular, we have determined the following endpoints of the inflammatory response: 1) histological damage; 2) motor recovery; 3) neutrophil infiltration; 4) cytokine expression (TNF- and IL-1); 5) nitrotyrosine, inducible nitric-oxide synthase (iNOS), and COX-2 expression; 6) apoptosis (TUNEL staining); and 7) Bax and Bcl-2 expression.
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Materials and Methods |
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Spinal Cord Injury
Mice were anesthetized using chloral hydrate (40 µg/kg body weight). A longitudinal incision was made on the midline of the back, exposing the paravertebral muscles. These muscles were dissected away, exposing T5–T8 vertebrae. The spinal cord was exposed via a four-level T6–T7 laminectomy, and SCI was produced by extradural compression of the spinal cord using an aneurysm clip with a closing force of 24 g. After surgery, 1.0 cc of saline was administered subcutaneously to replace the blood volume lost during the surgery. During recovery from anesthesia, the mice were placed on a warm heating pad and covered with a warm towel. The mice were singly housed in a temperature-controlled room at 27°C for a survival period of 10 days. Food and water were provided to the mice ad libitum. During this time period, the bladders of the animals were manually voided twice a day until the mice were able to regain normal bladder function. In all of the injured groups, the spinal cord was compressed for 1 min. Sham-injured animals were only subjected to laminectomy.
Experimental Groups
Mice were randomly allocated into the following groups.
1) SCI + Saline Group. Mice were subjected to SCI plus administration of saline (n = 30).
2) Etanercept Group. This group was the same as the SCI + saline group, with the exception that etanercept at the dose of 5 mg/kg was administered 1 h before and 6 h after SCI i.p. (n = 30).
3) Sham + Saline Group. Mice were subjected to the surgical procedures as the above groups, with the exception that the aneurysm clip was not applied (n = 30).
4) Sham + Etanercept Group. This group was identical to sham + saline group, with the exception that the administration of etanercept was administered i.p. 1 h before and 6 h after SCI (n = 30).
In the experiments regarding the motor score, the animals were treated with etanercept 1 h before and 6 h after SCI daily until day 9. At different time points (see Fig. 1), the animals (n = 10 mice from each group for each time point) were sacrificed in order to evaluate the various parameter as described below.
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) at 4 h after SCI. The time of 4 h after SCI was chosen in agreement with other studies (Hamada et al., 1996). MPO activity was defined as the quantity of enzyme degrading 1 µmol of peroxide min–1 at 37°C and was expressed in milliunits grams–1 of wet tissue.
Immunohistochemical Localization of TNF-, IL-1, Nitrotyrosine, iNOS, COX-2, Bax, and Bcl-2
At 24 h after SCI, the tissues were fixed in 10% (w/v) PBS-buffered formaldehyde and 8-mm sections were prepared from paraffin-embedded tissues. After deparaffinization, endogenous peroxidase was quenched with 0.3% (v/v) hydrogen peroxide in 60% (v/v) methanol for 30 min. The sections were permeabilized with 0.1% (w/v) Triton X-100 in PBS for 20 min. Nonspecific adsorption was minimized by incubating the section in 2% (v/v) normal goat serum in PBS for 20 min. Endogenous biotin or avidin binding sites were blocked by sequential incubation for 15 min with biotin and avidin (DBA srl, Milan, Italy), respectively. Sections were incubated overnight with anti-TNF- (1:500 in PBS, v/v), anti-IL-1 polyclonal antibody (1:500 in PBS, v/v), antinitrotyrosine rabbit polyclonal antibody (1:500 in PBS, v/v), anti-iNOS polyclonal antibody rat (1:500 in PBS, v/v), anti-COX-2 monoclonal antibody (1:500 in PBS, v/v), anti-Bax rabbit polyclonal antibody (1:500 in PBS, v/v), or anti-Bcl-2 polyclonal antibody rat. Sections were washed with PBS and incubated with secondary antibody. Specific labeling was detected with a biotin-conjugated goat anti-rabbit IgG and avidin-biotin peroxidase complex. To verify the binding specificity for nitrotyrosine, iNOS, TNF-, IL-1, COX-2, Bax, and Bcl-2, some sections were also incubated with only the primary antibody (no secondary) or with only the secondary antibody (no primary). In these situations, no positive staining was found in the sections, indicating that the immunoreactions were positive in all of the experiments carried out. Immunohistochemical photographs (n = 5 photos from each samples collected from all mice in each experimental group) were assessed by densitometry as described previously (Shea, 1994; Cuzzocrea et al., 2001) by using Optilab Graftek software on a Macintosh personal computer.
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Total Protein Extraction and Western Blot Analysis for Bax and Bcl-2
Tissue samples from SCI-injured animals were homogenized with a Ultra-turrax T8 homogenizer (UNILAB CELBIO, Catania, Italy) in a buffer containing 20 mM HEPES, pH 7.9, 1.5 mM MgCl2, 400 mM NaCl, 1 mM EDTA, 1 mM EGTA, 1 mM dithiothreitol, 0.5 mM phenylmethylsulfonyl fluoride, 1.5 µg/ml trypsin inhibitor, 3 µg/ml pepstatin, 2 µg/ml leupeptin, 40 µM benzidamine, 1% Nonidet P-40, and 20% glycerol. The homogenates were centrifuged at 13,000 rpm for 15 min and at 4°C, and the supernatant was collected to evaluate contents of Bax and Bcl-2. Protein concentration was determined with the Bio-Rad protein assay kit (Hercules, CA). Proteins were mixed with gel-loading buffer [50 mM Tris, 10% (w/v–1) SDS, 10% (w/v–1) glycerol, 10% (v/v–1) 2-mercaptoethanol, and 2 mg ml–1 bromphenol blue], boiled for 3 min, and centrifuged at 10,000 rpm for a few seconds. Protein concentration was determined in equivalent amounts (75 µg) of each sample electrophoreses in a 12% (w/v–1) discontinuous polyacrylamide Minigel (BIORAD Laboratories srl, Milan, Italy). Proteins were separated electrophoretically and transferred to nitrocellulose membranes. For immunoblotting, membranes were blocked with 10% nonfat dry milk in Tris-buffered saline for 1 h and then incubated with primary antibodies against Bax and Bcl-2 (1:1000) overnight at 4°C. The membranes were washed three times for 10 min in Tris-buffered saline with 0.1% Tween 20 and incubated with AffiniPure Goat Anti-Rabbit IgG coupled to peroxidase (1:2000; DBA srl). The immune complexes were visualized using the SuperSignal West Pico chemiluminescence substrate (Pierce, Milan, Italy).
Light Microscopy
Spinal cord biopsies were taken at 24 h after trauma. The biopsies were fixed for 24 h in paraformaldehyde solution (4% in 0.1 M PBS) at room temperature, dehydrated by graded ethanol, and embedded in Paraplast (Sherwood Medical, Mahwah, NJ). Tissue sections (thickness 5 µm) were deparaffinized with xylene, stained with H&E and Luxol Fast Blue staining (used to assess demyelination; DBA srl) and studied using light microscopy (Dialux 22 Leitz; DBA srl). All the histological studies were performed in a blinded fashion.
Grading of Motor Disturbance
The motor function of mice subjected to compression trauma was assessed once a day for 10 days after injury. Recovery from motor disturbance was graded using the modified murine Basso, Beattie, and Bresnahan (BBB) (Basso et al., 1995) hind limb locomotor rating scale (Joshi and Fehlings, 2002a,b).
Materials
The primary antibodies directed at Bax and Bcl-2 were obtained from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA). The secondary antibody was obtained from Jackson ImmunoResearch, Laboratories, Inc. (West Grove, PA). Unless otherwise stated, all compounds were obtained from Sigma-Aldrich (Milan, Italy). All other chemicals were of the highest commercial grade available. All stock solutions were prepared in nonpyogenic saline (0.9% NaCl; Baxter, McGaw Park, IL).
Statistical Evaluation
All values in the figures and text are expressed as mean ± S.E.M. of n observations. For the in vivo studies, n represents the number of animals studied. In the experiments involving histology or immunohistochemistry, the figures shown are representative of at least three experiments performed on different experimental days. The results were analyzed by one-way ANOVA followed by a Bonferroni's post hoc test for multiple comparisons. A p value of less than 0.05 was considered significant. BBB scale data were analyzed by the Mann-Whitney test and considered significant when p value was <0.05.
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Results |
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Myelin structure was observed by Luxol Fast Blue staining. In sham animals (Fig. 2A1), myelin structure was clearly stained by Luxol Fast Blue in both lateral and dorsal funiculi of the spinal cord. At 24 h after the injury in SCI + saline-operated mice (Fig. 2B1), a significant loss of myelin in lateral and dorsal funiculi was observed. In contrast, in etanercept-treated mice, myelin degradation was attenuated in the central part of lateral (Fig. 2C1) and dorsal funiculi.
To evaluate whether histological damage to the spinal cord was associated with a loss of motor function, the modified BBB hind limb locomotor rating scale score was evaluated. Although motor function was only slightly impaired in sham mice groups (Fig. 3A), operated mice undergoing SCI had significant deficits in hind limb movement (Fig. 3B). In contrast, a significant amelioration of hind limb motor disturbances was observed in etanercept-treated mice (Fig. 3B).
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on the neutrophil infiltration by measurement of the activity of MPO. MPO activity was significantly elevated at 4 h after SCI in SCI + saline-operated mice compared with spinal cord tissue collected from sham-operated mice (Fig. 4). In etanercept-treated mice, spinal cord MPO activity, at 4 h, was significantly attenuated compared with those of SCI + saline-operated animals.
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Etanercept Modulates Expression of TNF- and IL-1 after SCI. Sections of the spinal cord were taken at 24 h after SCI to also determine the immunohistological staining for TNF- and IL-1 expression to test whether administration of etanercept may modulate the secondary inflammatory reaction also through the regulation of the secretion of cytokines. A substantial increase of IL-1 (Fig. 5B) and TNF- (Fig. 5B1) formation was found in various cells in the white and gray matter of the spinal cord tissues collected from SCI + saline-treated mice at the 24th hour after SCI (see densitometry analysis in Fig. 6). Spinal cord levels of IL-1 (Fig. 5C) and TNF- (Fig. 5C1) were significantly attenuated in etanercept SCI-treated mice compared with those of SCI + saline-treated animals (see densitometry analysis in Fig. 6). There was no staining for either IL-1 or TNF- in spinal cord obtained from the sham group of mice (Fig. 5, A and A1, respectively).
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Etanercept Modulates Expression of Nitrotyrosine, iNOS, and COX-2 after SCI. To determine the localization of "peroxynitrite formation" and/or other nitrogen derivatives produced during SCI, nitrotyrosine, a specific marker of nitrosative stress, was measured by immunohistochemical analysis in the spinal cord sections of 10 µm at 24 h after SCI. Sections of the spinal cord were taken at the same hour after SCI to also determine the immunohistological staining for iNOS and COX-2. Sections of spinal cord from sham-operated mice did not stain for nitrotyrosine (Fig. 7A) or iNOS (Fig. 8A) or COX-2 (Fig. 8A1). Spinal cord sections obtained from SCI + saline-operated mice exhibited positive staining for nitrotyrosine (Figs. 6 and 7B), iNOS (Figs. 6 and 8B), and COX-2 (Figs. 6 and 8B1) localized in various cells in the white and gray matter of the spinal cord tissues collected from SCI + saline-treated mice. Etanercept (1 h before and 6 h after SCI induction) reduced the degree of positive staining for nitrotyrosine (Figs. 6 and 7C), iNOS (Figs. 6 and 8C), and COX-2 (Figs. 6 and 8C1) in the spinal cord section of SCI-treated mice.
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Effects of Etanercept on Apoptosis in Spinal Cord Tissue after Injury. To test whether tissue damage was associated with cell death by apoptosis, we measured TUNEL-like staining in the perilesional spinal cord tissue. Almost no apoptotic cells were detectable in the spinal cord tissue of sham-operated mice (Fig. 9A). After 24 h, the tissues obtained from SCI + saline-operated mice demonstrated a marked appearance of dark brown apoptotic cells and intercellular apoptotic fragments (Fig. 9, B and B1) in the gray matter of the spinal cord tissues. In contrast, tissues obtained from etanercept-treated mice (Fig. 9C) demonstrated a small number of apoptotic cells or fragments.
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Western Blot Analysis and Immunohistochemistry for Bax and Bcl-2. The appearance of Bax in homogenates of spinal cord tissues was investigated by Western blot at 24 h after SCI. A basal level of Bax was detectable in the homogenized spinal cord tissues from sham-operated animals (Fig. 10, A and A1). Bax levels were substantially increased in the spinal cord tissues of saline-treated mice (Fig. 10, A and A1). On the contrary, etanercept treatment (1 h before and 6 h after SCI induction) prevented the SCI-mediated Bax expression (Fig. 10, A and A1).
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Moreover, spinal cord tissues were taken at 24 h after SCI to determine the immunohistological staining for Bax and Bcl-2. Sections of spinal cord from sham-operated mice did not stain for Bax (Fig. 11A). Spinal cord sections obtained from SCI + saline-operated mice exhibited positive staining for Bax (Fig. 11B). Etanercept treatment (1 h before and 6 h after SCI induction) reduced the degree of positive staining for Bax in the spinal cord section of SCI-treated mice (Fig. 11C).
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Discussion |
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and IL-1 in the injured spinal cord, 2) the infiltration of the injured spinal cord with neutrophils, 3) cell apoptosis, 4) the iNOS and COX-2 expression, 5) the nitrotyrosine formation, and 6) spinal cord damage. All of these findings support the view that TNF- plays a detrimental role in the development and persistence of post-traumatic injury associated with SCI in the mouse.
Spinal cord trauma initiates a sequence of events that lead to secondary neuronal cell damage. While the precise mechanisms responsible to damage in SCI remain under studying, there is evidence that early inflammatory events promote tissue damage in the acutely injured spinal cord (Popovich and Jones, 2003). An inflammatory response develops within hours after injury and is characterized by the infiltration of neutrophils and the activation of microglia (McTigue et al., 2000). This is followed by a second wave of response to localize the inflammatory response within the spinal cord tissue and to down-modulate this response. Moreover, it has been well demonstrated that, in SCI, the expression of proinflammatory cytokines, including TNF- and IL-1, at the site of injury regulates the precise cellular events after spinal cord injury (Streit et al., 1998). In the present study, we have clearly demonstrated, by immunohistochemistry, a significant increase of positive staining for TNF- and IL-1 in SCI compared with sham-control animals. On the contrary, no significant expression of TNF- and IL-1 was observed in the spinal cord sections obtained from etanercept-treated mice. There is a large amount of evidence that TNF and IL-1 also play an important role in the induction of iNOS, which is known to play an important role in the development of SCI (Matsuyama et al., 1998). In this study, we observe that etanercept treatment reduces the expression of iNOS in SCI-operated mice and we propose that the attenuation of the induction of iNOS expression observed in SCI-operated mice, which are treated with etanercept, is secondary to a reduced formation of endogenous TNF and IL-1. This observation is in agreement with other studies that have clearly demonstrated that iNOS expression is reduced by TNF- antagonists (Perkins et al., 1998). Similar to iNOS, the expression of COX-2 is also mediated by TNF and IL-1 (Tonai et al., 1999). Recently, Adachi et al. (2005) have point out COX-2 gene induction after traumatic SCI seems not to require any new protein synthesis and that COX-2 protein accumulated in endothelial cells may be a component of the successive inflammatory processes in the damaged area. In this study, we demonstrated that, in sections of spinal cord of etanercept-treated mice, there is a much less positive staining for COX-2 compared with that of SCI + saline-operated mice. Our results, in agreement with other observation (Sairanen et al., 1998), demonstrated a relationship between TNF- production and the COX-2 expression. In addition to prostaglandins and nitric oxide, several studies have implicated the formation of reactive species of oxygen and reactive species of nitrogen in the secondary neuronal damage of SCI (Xu et al., 2001). In particular, it has been demonstrated that peroxynitrite probably contributes to secondary neuronal damage through pathways resulting from the chemical modification of cellular proteins and lipids (Xu et al., 2001). To confirm the pathological contributions of peroxynitrite to secondary damage after SCI, we have evaluated the nitrotyrosine formation in the injured tissue. We have observed in this study that the immunostaining for nitrotyrosine is reduced in SCI-operated mice treated with etanercept. Nitrotyrosine formation, along with its detection by immunostaining, was initially proposed as a relatively specific marker for the detection of the endogenous formation "footprint" of peroxynitrite (Beckman, 1996). However, there is recent evidence that certain other reactions can also induce tyrosine nitration; e.g., the reaction of nitrite with hypochlorous acid and the reaction of myeloperoxidase with hydrogen peroxide can lead to the formation of nitrotyrosine (Endoh et al., 1994). Therefore, increased nitrotyrosine staining is considered as an indication of "increased nitrosative stress" rather than a specific marker of the peroxynitrite generation. Recent studies have demonstrated the induction of apoptosis in a different cell line in response to reactive oxygen species, peroxynitrite, and nitric oxide (Merrill et al., 1993). One of the most important biological triggers of oligodendrocyte apoptosis in spinal cord injury is TNF-. In particular, it has been shown that TNF- induces apoptosis in oligodendrocytes both in vitro and in vivo (Muzio et al., 1997) by the activation of caspase-3 and caspase-8 (Hisahara et al., 1997). In the present study, using the tunnel coloration, we have clearly confirmed that TNF- plays an important role in the induction of apoptosis during SCI and that the treatment with etanercept attenuates the degree of apoptosis. Moreover, it is well known that Bax, a proapoptotic gene, plays an important role in developmental cell death (Chittenden et al., 1995) and in CNS injury (Bar-Peled et al., 1999). Likewise, it has been shown that the administration of Bcl-xL fusion protein (Bcl-2 is the most expressed antiapoptotic molecule in adult central nervous system) into injured spinal cords significantly increased neuronal survival, suggesting that SCI-induced changes in Bcl-xL contribute considerably to neuronal death (Nesic-Taylor et al., 2005). Based on these evidences, we have identified proapoptotic transcriptional changes, including up-regulation of proapoptotic Bax and down-regulation of antiapo-ptotic Bcl-2, using Western blot assay and by immunohistochemical staining. We report in the present study for the first time that the treatment with etanercept by inhibiting by TNF- in SCI prevents the loss of the antiapoptotic way and reduces the proapoptotic pathway activation with a mechanism still to discover. Finally, in this study, we demonstrate that etanercept treatment significantly reduced the SCI-induced spinal cord tissues alteration and improve the motor function. The purpose of this article was to highlight our current knowledge on the interaction of post-traumatic immune reactivity and the development of complications. A better understanding of these mechanisms might lead to the introduction of preventive and therapeutic strategies into clinical practice.
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Footnotes |
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ABBREVIATIONS: SCI, spinal cord injury; CNS, central nervous system; TNF, tumor necrosis factor-; iNOS, inducible nitric-oxide synthase; PBS, phosphate-buffered saline; COX-2, cyclooxygenase-2; TUNEL, terminal deoxynucleotidyl transferase dUTP nick-end labeling staining; IL-1, interleukin 1; BBB, Basso, Beattie, and Bresnahan (score); TdT, terminal deoxynucleotidyltransferase; MPO, myeloperoxidase.
Address correspondence to: Dr. Salvatore Cuzzocrea, Department of Clinical and Experimental Medicine and Pharmacology, School of Medicine, University of Messina, Torre Biologica, Policlinico Universitario Via C. Valeria, Gazzi, 98100 Messina Italy. E-mail: salvator{at}unime.it
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T. Genovese, E. Esposito, E. Mazzon, C. Muia, R. Di Paola, R. Meli, P. Bramanti, and S. Cuzzocrea Evidence for the Role of Mitogen-Activated Protein Kinase Signaling Pathways in the Development of Spinal Cord Injury J. Pharmacol. Exp. Ther., April 1, 2008; 325(1): 100 - 114. [Abstract] [Full Text] [PDF]
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 W. Fries, C. Muja, C. Crisafulli, S. Cuzzocrea, and E. Mazzon Dynamics of enterocyte tight junctions: effect of experimental colitis and two different anti-TNF strategies Am J Physiol Gastrointest Liver Physiol, April 1, 2008; 294(4): G938 - G947. [Abstract] [Full Text] [PDF]
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, p < 0.01 versus SCI.
