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GASTROINTESTINAL, HEPATIC, PULMONARY, AND RENAL
Department of Immunology (R.Ah., B.K., H.D., G.L., R.Ar.), and Department of Veterinary Resources (O.B.), the Weizmann Institute of Science, Rehovot, Israel
Received February 20, 2006; accepted April 17, 2006.
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Abstract |
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, and interferon-
expression was modulated by GA, whereas the regulatory anti-inflammatory transforming growth factor-
and IL-10 cytokines response was elevated. This was demonstrated on the level of protein secretion in splenocytes and local mesenteric lymphocytes in response to syngeneic colon extract and in the overall response to anti-CD3, as well as on the level of mRNA expression in the colon.
). Thus, it has been established that inflammatory mediators, such as tumor necrosis factor- (TNF-), and interferon- (IFN-), produced by infiltrating CD4 T cells and macrophages, exacerbate the disease, whereas regulatory cytokines, such as transforming growth factor- (TGF-) and interleukin-10 (IL-10), provide a beneficial effect; their intestinal level may ultimately determine whether an immune response to a gut antigen is detrimental or innocuous (Strober et al., 1997; Rogler and Andus, 1998).
Current medical treatments for IBD rely on the use of nonspecific anti-inflammatory agents and immunosuppressive drugs that cause severe side effects, and in significant percentage of the patients, they do not induce long-term benefit (Sandborn and Targan, 2002; Baert et al., 2004). Based on the immunopathological nature of IBD, novel strategies have been proposed in an attempt to deviate the CD4 pathogenic T cells from Th1 to Th2 phenotype. However, the newly designed medical interventions employed hitherto exhibited limited effect (Sandborn et al., 2005) or considerable toxicity with narrow therapeutic window (Kwon and Farrell, 2005). Therefore, there is a need for new, well tolerated therapies that effectively induce remission and alter the natural course of the disease.
The synthetic copolymer glatiramer acetate (GA, Copaxone, copolymer 1), an approved drug for the treatment of multiple sclerosis, is very well tolerated with high safety profile (Arnon and Sela, 2003). GA has been shown to be effective in several animal models, including experimental autoimmune encephalomyelitis (EAE) and immune rejection (Aharoni et al., 2001). Studies on the mechanism of action of GA revealed that it exerts its therapeutic activity by immunomodulating the immune response at different levels of specificity. Thus, it was demonstrated that GA binds promiscuously and with high affinity to various class II major histocompatibility (MHC) molecules of murine and human origin and can even displace antigens from the MHC antigen-binding groove (Fridkis-Hareli, 1994). This competition for MHC binding can hinder presentation of other antigens and consequently lead to inhibition of various pathological effector functions. In addition, GA was shown to be a potent inducer of Th2/3 cells that secrete high amounts of regulatory substances, such as IL-10 and TGF- but not Th1 inflammatory cytokines (Aharoni et al., 1997). Moreover, GA treatment leads to deviation of the immune reactivity from Th1 to Th2-biased cytokine profile in both experimental animals and humans (Aharoni et al., 1998; Neuhaus et al., 2000). In view of these immunomodulating activities of GA and the Th1-related immunopathological nature of IBD, it was of interest to test whether GA can be effective in the suppression of IBD animal models. Indeed recently, it was demonstrated that GA treatment ameliorates the various pathological manifestations of one experimental IBD model—trinitrobenzene sulfonic acid (TNBS)-induced colitis, administered rectally, in various mice strains (Aharoni et al., 2005; Gur et al., 2005).
None of the current IBD models constitutes a faithful equivalent for the human diseases. Therefore, it is essential to evaluate the effect of any candidate drug in several IBD models. Widely used is the dextran sulfate sodium (DSS) colitis induced by DSS administration in the drinking water, which leads to many of the events presumed to initiate and sustain human IBD (Boismenu and Chen, 2000). This model allows the generation of variable disease forms of acute and chronic nature, depending on the mouse strain or on the dose and frequency of DSS administration. Spontaneous models offer further advantage, because both environmental factors and genetic susceptibility contribute to the pathological immunoreactivity causing IBD in humans (Shanahan, 2001). One such model was developed by transferring a genetically disturbed IL-10 allele into the IBD-susceptible C3H/HeJBir substrain. The resulting C3H.IL10-/- mice develop an early nonremitting severe inflammation of both the cecum and the colon (Mahler and Leiter, 2002). In the present study, we investigated the effect of GA in these two colitis models. We report that GA treatment significantly ameliorated the various pathological manifestations of acute as well as chronic DSS-induced colitis and that it also led to a beneficial effect on spontaneous colitis in the C3H/HeJBir IL-10-deficient mice. Moreover, GA modulated the detrimental pro-inflammatory immune response provoked by the pathological process while enhancing the secretion of beneficial regulatory anti-inflammatory cytokines.
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Materials and Methods |
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), were kindly provided by E. H. Leiter (Jackson Laboratory, Bar Harbor, ME) and maintained under conventional (nonpathogen-free) conditions. C3H.IL10-/- male mice, 3- to 4-month old, were used. All experiments were approved by the Institutional Animal Care and Use Committee. Induction of DSS Colitis. Mice were randomized into treatment groups of 6 to 12 animals, with identical average body weight in each group. Acute colitis in C57BL/6 mice was induced by giving DSS [mol. wt. 36,000-50,000 (MP Biomedicals, LLC, Eschwege, Germany)] in acidified drinking water [2-2.5% (wt./v)] for 4 to 5 days. Chronic colitis was induced by applying three DSS cycles of 5 days with intervals of 5 to 7 days of plain drinking water. In C57BL/6 mice, 1.5% DSS with a 1-week interval after the first DSS exposure and 5-day intervals after the second exposure and, in BALB/c mice, 5% DSS for 5 days with 5-day intervals were given. We did not observe differences in the water consumption among the various experimental groups (7.0-7.5 ml per day per mouse), excluding the possibility of volume-associated deviation.
Assessment of DSS Colitis. In all animals, body weight, rectal bleeding, stool consistency, and survival were monitored daily. Intestinal bleeding was followed by using Hemoccult test (Beckman Coulter, Inc., Fullerton, CA) as well as by observation of bleeding signs on the anus or gross bleeding. The daily disease activity index (DAI) was calculated by grading on a scale of 0 to 4 the following parameters: change in weight (0, 
1%; 1, 1-5%; 2, 5-10%; 3, 10-15%; and 4, >15%), intestinal bleeding (0, negative; 4, positive), and stool consistency (0, normal; 2, loose stools; 4, diarrhea). The combined scores were then divided by 3 to obtain the final disease activity index. Ten to thirty days following disease induction, mice were sacrificed and the large intestine was collected and evaluated for colon length and microscopic colonic damage.
Microscopic Scoring. Proximal, medial, and distal portions of colon and cecum were fixed in 10% phosphate-buffered formalin. Paraffin-embedded sections were stained with hematoxylin and eosin. The evaluation was based in part on that used elsewhere (Dieleman et al., 1998) and adapted to the pathology manifested in our laboratory. The degree of histological damage and inflammation was graded in a blinded fashion by an expert pathologist (O. Brenner). The following manifestations were included in the evaluations: the amount of inflammation (0, none; 1, mild; 2, moderate; 3, severe; and 4, accumulation of inflammatory cells in the gut lumen), distribution of lesions (0, none; 1, focal; 2, multifocal; 3, nearly diffuse; and 4, diffuse), depth of inflammation and layers involved (0, none; 1, mucosa only; 2, mucosa and submucosa; 3, limited transmural involvement; and 4, transmural), and nature of mucosal changes (0, none; 2, more degeneration; and 3, more necrosis). The overall histological score was the sum of the four manifestations (maximal score of 15). In C3H.IL10-/- mice, degeneration and necrosis were not included (maximal score of 12).
Glatiramer Acetate. GA, (Copaxone, copolymer 1) consists of acetate salts of synthetic polypeptides containing four amino acids: L-alanine, l-glutamate, L-lysine, and l-tyrosine (Arnon and Sela 2003). GA from batch 242990599, with an average molecular weight of 7300 and obtained from Teva Pharmaceutical Industries (Petach Tikva, Israel) was used throughout the study.
GA Treatment. GA was administrated by one of the following procedures, oral or parenteral. Oral treatment consisted of 250 µg/day in PBS through gastric intubation, with an 18-gauge feeding needle. Feedings were performed on days -7, -5, -3, -1, 0, 2, 4, and 6 relative to the day of DSS induction. Parenteral treatment by daily injections (2 or 1 mg/day) was administered s.c. in PBS, starting at the indicated day.
Colon Extract. Colons of syngeneic normal mice were cut into small strips and homogenized. The homogenate was diluted in PBS, passed through glass wool, and filtered (0.2µ). Protein quantity was measured by using a protein assay kit (Bio-Rad, Hercules, CA).
Reactivity Assays. Spleens and mesenteric lymph nodes (MLN) cells (0.5 x 106 /well) were cultured with GA (50 µg/ml), colon extract (200 µg/ml), immobilized anti-CD3 (5 µg/ml), or PBS control in a final volume of 250 µl/well (six wells for each antigen). For proliferation assay, cells were cultured in RPMI 1640 medium with 10% fetal calf serum, pulsed with 1 µCi of [3H]thymidine after a 48-h incubation, and harvested 12 h later. For cytokine assay, cells were cultured in serum-free medium (DCCM-1; Biological Industries, Beit Haemek, Israel), supernatants were collected after 24 h for TNF- and IFN-, 48 h for IL-10, and 72 h for TGF- and tested by ELISA (R&D Systems, Minneapolis, MN). The presence of nitric oxide (NO) was determined by measuring the amount of nitrite in culture supernatants using a colorimetric assay as described previously (Kayhan et al., 2003).
Reverse Transcription-Polymerase Chain Reaction. Samples for mRNA isolation were removed from the colons of three individual C57BL/6 mice in each of the following groups: naïve mice, DSS colitis-untreated mice, and DSS colitis mice treated with GA. Total RNA was isolated and processed according to Edelheit and Meiri (2004). The following sets of oligonucleotides and amplification conditions were used: TNF-, (sense) 5'-AGTCCGGGCAGGTCTACTTT-3' and (antisense) 5'-GAGGCAACCTGACCACTCTC-3' (60°/30 cycles); IFN-, (sense) 5'-ATCTGGAGGAACTGGCAAAA-3' and (antisense) 5'-TGAGCTCATTGAATGCTTGG-3' (63°/35 cycles); TGF-, (sense) 5'-TACAGGGCTTTCGATTCAGC-3' and (antisense) 5'-CGCACACAGCAGTTCTTCTC-3' (63°/35 cycles); IL-10, (sense) 5'-TCCTTGGGAAGCAATTGAAG-3' and (antisense) 5'-AACTGGCCACAGTTTTCAGG-3' (63°/35 cycles); T-bet, (sense) 5'-CTAAGCAAGGACGGCGAATGT-3' and (antisense) 5'-GGCTGGGAACAGGATACTGG-3' (60°/35 cycles); GATA-3, (sense) 5'-GCCTGCGGACTCTACCATAA-3' and (antisense) 5'-CAGGGATGACATGTGTCTGG-3' (54.8°/30 cycles); and GAPDH, (sense) 5'-GTGTTCCTACCCCCAATGTG-3' and (antisense) 5'-CTTGCTCAGTGTCCTTGCTG-3' (60°/25 cycles). The relative mRNA expression to the housekeeping GAPDH was performed using NIH image software and averaged from the three mice in each group.
Statistical Analysis. Weight and disease activity differences between GA-treated and untreated groups were analyzed using two-tailed Mann-Whitney U test. Statistics of survival curves were performed by Kaplan-Meier test. Differences in colon length, histological score, proliferation, Hemoccult assay, and cytokine responses were compared using the two-tailed independent t test. All of the tests were performed by the SPSS 10.0 program (SPSS Inc., Chicago, IL). The level of significance for all of the tests was set at <0.05.
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Results |
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), did not induce significant effect in this model (significance analyzed for the differences on day 7).
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The beneficial effect of the optimal GA treatment, daily injections of 2 mg/mouse from the day of induction, was further corroborated in DSS colitis of different severity levels, i.e., induced by 2% DSS for 5 days or by 2.5% DSS for 5 and 7 days (Fig. 1B). In all three systems, the GA-treated mice exhibited significantly higher body weights than those of the equivalent untreated mice as analyzed by day 10. The milder regimen (2% DSS, 5 days) led to 27% weight loss and 75% mortality in untreated animals; in contrast, all of the GA-treated mice subjected to this regimen survived, exhibiting only moderate weight loss (maximum of 9%) and subsequent weight regain up to complete restoration of their original weight. Moreover, when colitis was induced by 2.5% DSS for 5 or 7 days, all of the untreated mice succumbed to the disease by day 11, but GA treatment resulted in the survival of 6/8 and 3/8 mice, respectively.
GA Activity on the Various Manifestations of DSS Colitis. A summary of three additional experiments (total of 25-26 mice per group) in DSS colitis mice induced by 2.5% DSS for 5 days, with 30 days follow-up, is demonstrated in Fig. 2. In these experiments, untreated mice lost 33% of their original body weight (A), and all of them died by day 12 (C). In contrast, GA-treated mice (2 mg/mouse daily starting from day 0) suffered only 10% weight loss (p = 0.005 for GA treatment in comparison to no treatment 10 days from induction) and, by day 14, regained their original weight, and all of them survived until the end of the experiments (1 month after disease induction). Intestinal bleeding, a pathological manifestation of DSS colitis, was followed by using Hemoccult test, as well as by observation of rectal bleeding signs (Fig. 2B). By both methods, GA treatment reduced intestinal bleeding. Hence, on day 10, when all of the untreated mice suffered from intestinal bleeding, only 43% and 14% GA-treated mice demonstrated positive Hemoccult test and bleeding signs, respectively. One month after DSS induction, intestinal bleeding was rarely observed in the GA0-treated animals using both methods when none of the untreated mice survived (Fig. 2C).
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An additional macroscopic manifestation of DSS-induced colitis is the reduction in colon length (Fig. 2D). Thus, 30% decrease in colonic length was found in untreated mice in comparison with naive mice, 5 and 10 days after DSS induction. In contrast, only 20% and 15% reduction, respectively, was obtained in the GA-treated mice. Furthermore, 1 month after disease induction, when none of the untreated mice survived, colon length of the GA-treated mice was similar to that of normal mice, manifesting only a minor insignificant decrease of 7% (p = 0.16). Histological assessment of colonic damage in untreated mice, 10 days after DSS induction, revealed extensive injury, i.e., severe inflammation, with nearly diffused distribution involving mucosa and submucosa and, in some cases, extending through all intestinal layers (transmural penetration). This was associated with severe disruption of the normal architecture, necrosis, and crypt loss, average histological score of 13.4 on a scale of 0 to 15 (Fig. 2, E and F). In colons of DSS-induced mice treated with GA and tested on the same day, a small but statistically significant reduction in the histological damage was observed, average score of 11.8. However, by day 30, when none of the untreated mice survived, the colonic damage in the GA-treated mice was lower (grade 7), and more conserved glandular structures were revealed, although widespread leukocyte infiltrations were still present (Fig. 2, E and F). Thus, GA treatment (daily injections of 2 mg/mouse) in an acute colitis model induced by one DSS cycle resulted in substantial beneficial effect on all pathological manifestations, weight loss, intestinal bleeding, colonic length, and histological damage, resulting in improved long-term survival.
The Effect of GA Treatment on Chronic Colitis Induced by Three DSS Cycles in Different Mouse Strains. Because IBD is characterized by multiple exacerbations, an additional model was used, in which three DSS cycles were applied in both the highly susceptible strain C57BL/6 and the less sensitive strain BALB/c. Indeed, three 5-day cycles of 1.5% DSS with 1 week interval after the first DSS exposure and 5-day intervals after the second exposure resulted in 20% body weight loss in C57BL/6, whereas a more vigorous regime, 5% DSS (for 5 days with 5-day intervals), were needed to obtain 15% weight loss in BALB/c mice.
The effect of GA treatment in these three DSS cycle models on the daily monitored DAI, combined score of body weight, bleeding, and stool consistency) and on survival is shown in Fig. 3. In both mouse strains, a daily dose of 2 mg/mouse GA drastically decreased disease activity and completely prevented mortality in comparison with 33% and 40% mortality in the untreated C57BL/6 and BALB/c mice, respectively. In BALB/c mice, 1 mg/day GA was sufficient, resulting in a suppressive effect similar to that of 2 mg/day, whereas in C57BL/6, 1 mg/day was less effective than 2 mg/day (similar to the results obtained for this strain in the acute one DSS cycle system Fig. 1). Using three DSS cycles in C57BL/6 mice, the ability of the optimal GA dose (2 mg/day) to ameliorate an established disease was tested. The results indicated that even when treatment was started 10 days following DSS induction, after the mice reached maximal weight lost (30% of their initial body weight), GA treatment still induced beneficial effect manifested in 15% higher body weight and 20% less mortality than the untreated mice (data not shown).
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The Effect of GA Treatment on Spontaneous Colitis in C3H.IL10-/- Mice. The IL-10-deficient transgenic mice C3H/HeJBir IL-10-/- (Jackson ImmunoResearch Laboratories Inc. (Bar Harbor, ME) were shown to develop spontaneous colitis (Mahler and Leiter, 2002). In our laboratory, when these C3H.IL10-/- mice were maintained in SPF environment, clinical signs were not apparent and histological abnormalities in their intestines were minimal. When the mice were transferred and bred under conventional (nonpathogen-free) conditions, disease manifestations were gradually revealed, mainly histologically as inflammation of the cecum and the colon (in male mice more than in female mice). Disease was increasingly aggravated in direct relation to the time passed from their SPF departure (Fig. 4; Table 1). Hence, 5 months from transfer, most of the 3 to 4-month-old male mice manifested focal or multifocal mild inflammation in the mucosa, average histological score of 4 on a scale of 0 to 12 (Fig. 4A; Table 1, experiment 1). Five months later, multifocal lesions and moderate inflammation in the mucosa and submucosa, average score 6, were observed (experiment 2). One year after transfer of the colony, the entire male population at the age of 3 to 4 months had severe colitis often with transmural involvement, score of 7.6 (Fig. 4C; Table 1, experiment 3). Toward the fourth month of their life, the C3H.IL10-/- mice also suffered from intestinal bleeding, as revealed in Hemoccult test (average 1-1.3 from maximal grade of 2 in the different experiments). GA treatment, starting at the age of three months when disease was already established, daily injections of 2 mg/mouse for one month ameliorated the spontaneous colitis in C3H.IL10-/- mice at all of the levels of severity (Fig. 4, B and D; Table 1). This was manifested in the reduction of the histological score of 3 points in the mild disease (experiment 1) and in a smaller reduction of 1.7 and 1.4 in the more severe disease (experiments 2 and 3, respectively). However, in experiment 3, the differences in histological score did not reach statistical significance. GA treatment almost eliminated intestinal bleeding; only three of 17 mice were found positive in Hemoccult tests (average grade of 0.1) compared with nine from 10 of the control-untreated mice.
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Lymphocyte Reactivity in GA-Treated DSS-Induced Mice. To explore the consequence of GA treatment on lymphocyte activity in DSS-induced colitis mice, we studied cell proliferation and their cytokine profile in the DSS-administered C57BL/6 mice, treated with GA, compared with untreated mice and naive healthy controls. The reactivity of lymphocytes from local MLN that are adjacent to the diseased organ, as well as those from spleen cells, was analyzed.
The proliferation in response to colonic extract (CE), obtained from normal syngeneic mice, and to the treatment agent GA is depicted in Fig. 5. A prominent response to colonic extract was demonstrated by MLN cells of DSS-induced mice, i.e., 12-fold over that of naive controls. This augmented response to CE was restricted to the local MLN, because in spleens of colitis-induced mice, proliferation to CE was similar to that of naive mice. The local MLN response to CE was significantly suppressed by GA treatment, resulting in 32% inhibition. Lymphocytes from GA-treated mice from both spleens and MLN proliferated in response to GA, the systemic response being considerably higher than the response of the MLN cells.
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and IFN-—as well as of two regulatory anti-inflammatory cytokines—TGF- (Th3) and IL-10 (Th2)—was investigated by stimulating MLN and spleen lymphocytes with anti-CD3 (Fig. 6). Both MLN and spleen cells from mice with DSS colitis secreted elevated amounts of TNF- (A) and IFN- (B) but not TGF- (C) or IL-10 (D) in response to the broad stimulation by anti-CD3. The most prominent increase (7-fold from naive controls) was manifested for TNF- by MLN lymphocytes. GA treatment led to significant reduction of the overall TNF- and IFN- secretion by MLN (43% and 37% inhibition, respectively) and spleen lymphocytes (secretion similar to that of naive controls). In contrast to its inhibitory effect on the pro-inflammatory cytokines, GA treatment triggered the secretion of the anti-inflammatory cytokines TGF- and IL-10 (40-fold increase from untreated mice for TGF- in MLN as well as in the spleen and 10-fold for IL-10 in MLN). IL-10 secretion in spleens of DSS-untreated mice was reduced by half compared with healthy controls, and GA treatment restored it to the normal level.
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Similar cytokine patterns to those obtained for the broad stimulation to anti-CD3 were found for the restricted responses to colonic extract demonstrated for MLN lymphocytes, as shown in Fig. 7. Thus, cells from mice with DSS colitis secreted elevated amounts of TNF- (A) and IFN- (B) in response to CE (2-fold increase from naive control). This specific response was completely abrogated by GA treatment, and thus the level of the cytokines was similar to that of naive mice. The anti-inflammatory response to CE differed between the two tested cytokines, whereas secretion of TGF- (C) could not be detected in naive and colitis-induced mice, and considerable amounts of IL-10 (D) were secreted in response to the colon antigen by all experimental groups. These amounts were decreased in the colitis-untreated mice and increased by GA treatment to an even higher level than in naive controls. Interestingly, decreased IL-10 secretion in untreated mice and elevation by GA were also seen in the background response (with no antigenic stimulation). In vitro stimulation by GA did not result in secretion of either TNF- or IFN- in any of the treatment groups. However, cells from GA-treated mice responded to GA by extensive secretion of TGF- and IL-10. Similar secretion patterns, i.e., decrease in Th1 and increase in Th2 cytokines, were also found in cells originating from spleens (systemic response, data not shown). Thus, it can be concluded that, with regard to both the overall cytokine secretion and the restricted response to specific colonic antigens, GA treatment inhibited the augmented pro-inflammatory reactivity provoked by the pathological process while enhancing the secretion of regulatory anti-inflammatory cytokines.
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The Effect of GA on Cytokine mRNA Expression in the Colons of DSS-Induced Mice. Employing RT-PCR on colon mRNA, the levels of pro-inflammatory and anti-inflammatory cytokines in the DSS-induced mice treated by GA, were evaluated and compared with untreated colitic mice and with naive healthy controls. mRNA expression in colons of three representative mice from each group, as well as their relative levels to GAPDH, are demonstrated in Fig. 8. As shown, the expression of the two pro-inflammatory (Th1) cytokines, TNF- and IFN-, was markedly increased in the colons of DSS-induced untreated mice, 5.2- and 15-fold over the naive mice, respectively. GA treatment reduced the colonic expression of the Th1 cytokines. In particular, the augmentation in TNF- was completely abrogated, so that its expression was similar to that of naive mice. As for the anti-inflammatory cytokines, a marked increase in the colonic expression of TGF- was induced by GA treatment (5.8-fold from normal mice and 4.5-fold from untreated colitic mice). Unlike TGF-, the level of IL-10 expression was increased in colitis-untreated mice in comparison with naive control, but GA treatment led to a further 2-fold elevation in its expression.
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The most effective treatment regimen in the C57BL/6 strain was daily s.c. injections, a dose of 2 mg/mouse, starting at the day of DSS administration, but even when treatment started two days after induction, a significant beneficial effect was observed (Fig. 1A). Moreover, in a therapeutic setting of three DSS cycles when treatment was started after the mice reached maximal weight loss, GA treatment still induced a beneficial effect. A daily dose of 1 mg was less effective than 2 mg in the highly susceptible strain C57BL/6 when either one or three DSS cycles were applied (Figs. 1A and 3, A and B). Interestingly, in the chronic disease form in the less susceptible BALB/c mice, 1 mg/day GA was a sufficient dose resulting in a suppressive effect similar to that of 2 mg/day (Fig. 3, C and D). Oral administration of GA in a regimen, previously found effective in another experimental disease, EAE (250 µg/feeding) (Teitelbaum et al., 1999), did not induce significant effect in the DSS model in C57BL/6 mice (Fig. 1). The oral route for IBD, besides the practical advantage, has the benefit of specific administration into the diseased organ, so local modulatory mechanisms may be activated in addition to the systemic processes. Indeed, feeding with GA-ameliorated TNBS colitis in BALB/c mice but in highly susceptible strains in which TNBS induced more intensive disease, oral administration was less effective than the parenteral way (Aharoni et al., 2004).
The curative effects demonstrated by GA on acute and chronic DSS colitis, as well as on TNBS-induced colitis, are of therapeutic significance, because these widely used models recapitulates many of the events proposed to initiate and sustain human IBD (Boismenu and Yaping 2000). Yet, because IBD is believed to occur in genetically predisposed individuals, the spontaneous colitis model offers additional advantageous (Mahler and Leiter, 2002). In our hands, these mice did not exhibit disease manifestations under SPF environment but gradually developed inflammation of both the cecum (typhlitis) and the colon (colitis) upon transfer to conventional conditions, supporting the involvement of environmental factors as well as genetic susceptibility in the pathological immunoreactivity causing IBD. GA treatment, starting at the age of 3 months (when disease was already established), ameliorated spontaneous colitis in C3H.IL10-/- mice (Fig. 4, Table 1). It should be noted that the most prominent effect (reduction of 3 points in the histological index) was obtained in the mild disease, whereas, in the case of severe disease, the histological improvement was smaller. Thus, the demonstration of GA therapeutic activity in two chemically induced models, TNBS colitis (in three mouse strains) and DSS colitis (acute and chronic in two mouse strains), as well as in spontaneous colitis (in C3H.IL10-/- mice), indicate that this effect is not restricted to a single strain/model but represents a more general phenomenon.
To further understand the protective activity of GA in DSS colitis, we investigated the effect of GA treatment on lymphocyte reactivity. We found that the prominent response to syngeneic colonic extract in C57BL/6 mice with acute DSS-induced colitis, manifested by local MLN cells adjacent to the diseased organ, was reduced by GA treatment (Fig. 5). This proliferation in response to CE was manifested only by MLN of colitis-induced mice and not by MLN of naive mice or systemically by spleen cells of colitis-induced mice. Moreover, the MLN cells were cultured in the presence of irradiated spleen cells from syngeneic naive mice (as antigen-presenting cells), and there was no background response to these cells, suggesting local reactivity toward this colonic extract. It was previously shown that GA binds promiscuously with high affinity to various MHC class II molecules from mouse and human and even displaces antigens from the MHC groove (Fridkis-Hareli et al., 1994). Such efficient binding to local antigen-presenting cells in the intestine may interfere with the presentation of floral/self-antigens and thus hinder pathological T-cell activation. Indeed, in TNBS colitis in which GA treatment blocked the MLN response to colonic extract (Aharoni et al., 2005), a role of class II molecules as a target site for GA competition with the antigens was demonstrated (Gur et al., 2005). MHC blocking by GA also proved to be effective in other pathological conditions, such as MS and EAE (Arnon and Sela, 2003), graft versus host disease, and graft rejection (Aharoni et al., 2001).
GA treatment resulted not only in inhibition of the proliferative response but also in significant reduction in the Th1 cytokines TNF- and IFN-. These prototype pro-inflammatory cytokines were significantly elevated systemically in splenocytes and locally in MLN in colitis-untreated mice. Both their overall secretion (in response to anti-CD3) as well as their secretion in response to colonic extract were decreased in the GA-treated mice (Figs. 6, A and B, and 7, A and B). Inflammatory cytokines play a central role in the pathology of the intestine, amplifying and prolonging inflammation (Rogler and Andus, 1998). Rapidly synthesized and secreted upon stimulation, they induced production of inflammatory mediators, such as nitric oxide. Indeed in this study, the changes in TNF- and IFN- secretion were associated with parallel variations in NO, i.e., elevation upon stimulation with colon extract in DSS colitis-untreated mice, and complete abrogation of this response by GA treatment (Fig. 7E).
An essential mechanism by which GA had been shown to induce therapeutic effect, in EAE/MS as well as in immune rejection, is the generation of regulatory T cells that secrete Th2/3 anti-inflammatory cytokines (Aharoni et al., 1997). In the present study, a systemic and, to a lesser extent, local proliferation in response to GA was evident (Fig. 5), suggesting the generation of GA specific T cells in the treated mice. Furthermore, elevation in the anti-inflammatory cytokines TGF- and IL-10 on the level of overall secretion (Fig. 6, C and D), as well as in response to the treatment antigen (Fig. 7, C and D), was found in the GA-treated mice systemically and locally, indicating that GA also promoted specific Th2/3 regulatory T cells in this model. It is noteworthy that a significant increase in IL-10 secretion was found not only after stimulation by GA but also by colonic extract in the MLN of treated mice (Fig. 7D), suggesting a bystander therapeutic effect similar to that demonstrated for GA in other systems (Aharoni et al., 1998). In the case of EAE, GA-specific cells were even shown to reach the diseased organ (the CNS) and secrete there anti-inflammatory cytokines (Aharoni et al., 2003).
Regulatory cytokines are the key factor in maintaining gut homeostasis. In particular, TGF- and IL-10 may ultimately determine whether an immune response to gut antigen is detrimental or innocuous (Strober et al., 1997). Hence, in two models of Th1-mediated murine colitis, alleviation of disease was shown to be strictly associated with increased numbers and up-regulation of TGF--producing cells (Neurath et al., 1996; Powrie et al., 1996). In humans as well, mucosal T-cell unresponsiveness to luminal antigens is mediated by TGF-, and its production in lamina propria mononuclear cells and in T cells isolated from Crohn's disease (CD) patients is significantly reduced (Del Zotto et al., 2003). Elevation in TGF- induced by GA treatment was found in an additional IBD model, TNBS-induced colitis mice (Aharoni et al., 2005). Therefore, it is likely that TGF- plays an important role in the inhibitory effect of GA in IBD. The role of IL-10 for gut homeostasis has been demonstrated by the development of colitis in IL-10-deficient mice (Rogler and Andus, 1998). The ability of GA to suppress colitis, even in the IL-10-deficient mice (Table 1), could be attributed to compensatory activity of other mechanisms activated by GA treatment, e.g., competition for MHC binding, inhibition of TNF- and IFN- secretion, and elevation in TGF-.
The augmented pro-inflammatory reactivity provoked by the pathological process and its modulation by GA treatment, as well as the ability of GA to increase the regulatory anti-inflammatory pathway, was demonstrated in DSS colitis mice on the level of protein secretion in response to broad and specific antigens for the periphery and for local lymph nodes. Similar secretion patterns were obtained after GA treatment in TNBS-induced colitis mice for TNF- and TGF- (Aharoni et al., 2005). In this study, these results were corroborated on the level of mRNA expression in the diseased organ, the colon (Fig. 8). Hence, mRNA expression of the two pro-inflammatory cytokines, TNF- and IFN-, were increased in colons of DSS-induced untreated mice, and GA treatment decreased their level while inducing a significant elevation in the colonic mRNA of the anti-inflammatory cytokines TGF- and IL-10. These conclusions are supported by the decrease found in the Th1 transcription factor T-bet and the increase in the Th2 transcription factors GATA-3 in the colons of the GA-treated mice. These factors have a critical role in the pathogenesis and the control of IBD by regulating the cytokine balance in mucosal T cells. Interestingly, TGF- was found to suppress T-bet expression; this is in accordance with the elevated TGF- and reduced T-bet levels observed after GA treatment (Neurath et al., 2002).
The role of lymphocyte reactivity in the pathogenic process of DSS-induced colitis is controversial, because DSS colitis could be induced in the absence of lymphocytes in severe combined immunodeficiency mice (Dieleman et al., 1998). Still, even in this model, large numbers of activated T cells are located near diseased segments (Boismenu and Chen 2000), and lymphocyte reactivity may be important in initiating gut inflammation (Pizarro et al., 2003). The modulatory effect of GA on inflammatory lymphocytes could thus contribute to the suppression of DSS colitis. In addition, GA can alleviate pathological processes by other mechanisms, such as its effect on components of the innate immune system, specifically on monocytes and dendritic cells, to stimulate Th2 response (Farina et al., 2005). GA has also been shown to inhibit nuclear factor-
B (NF-kB) activation system, resulting in reduced production of inflammatory mediators, such as chemokines, e.g., RANTES (Li et al., 2001), TNF-, and nitrite (Kayhan et al., 2003). These activities of GA may play a role in its beneficial effect on IBD.
It should be noted that the cumulative results on the mechanism of action of GA, on the one hand, and the nature of the T-cell response mediating IBD, on the other hand, support its application for the treatment of CD, which manifests pro-inflammatory immunopathological features, rather than for ulcerative colitis (UC), which presents a less clear immunological basis involving Th2 immunopathology (Gordon et al., 2005). In conclusion, GA is effective in ameliorating the pathological manifestations in several models of experimental colitis, possibly due to its immunomodulating properties. In view of its high safety profile, these results warrant further evaluation of GA treatment for human inflammatory bowel disease, in particular, for Crohn's disease.
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Footnotes |
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS: IBD, inflammatory bowel diseases; DSS, dextran sulfate sodium; GA, glatiramer acetate; Th, T-helper; TNF-, tumor necrosis factor-; IFN-, interferon-; TGF-, transforming growth factor ; IL-10, interlukin-10; CD, Crohn's disease; MHC, major histocompatibility; EAE, experimental autoimmune encephalomyelitis; CE, colon extract; TNBS, trinitrobenzene sulfonic acid; MLN, mesenteric lymph nodes; RANTES, regulated on activation normal T cell expressed and secreted; RT-PCR, reverse transcription-polymerase chain reaction; NO, nitric oxide; SPF, specific pathogen-free; PBS, phosphate-buffered saline; ELISA, enzyme-linked immunosorbent assay; DSS, dextran sulfate sodium; DAI, disease activity index.
Address correspondence to: Prof. Ruth Arnon, Department of Immunology, The Weizmann Institute of Science, Rehovot, Israel 76100. E-mail: ruth.arnon{at}weizmann.ac.il
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