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Research Article

CB2 Cannabinoid Receptors Contribute to Bacterial Invasion and Mortality in Polymicrobial Sepsis

  • Balázs Csóka,

    Affiliation: Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey, United States of America

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  • Zoltán H. Németh,

    Affiliations: Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey, United States of America, Department of Surgery, Morristown Memorial Hospital, Morristown, New Jersey, United States of America

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  • Partha Mukhopadhyay,

    Affiliation: National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland, United States of America

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  • Zoltán Spolarics,

    Affiliation: Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey, United States of America

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  • Mohanraj Rajesh,

    Affiliation: National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland, United States of America

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  • Stephanie Federici,

    Affiliation: Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey, United States of America

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  • Edwin A. Deitch,

    Affiliation: Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey, United States of America

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  • Sándor Bátkai,

    Affiliation: National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland, United States of America

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  • Pál Pacher mail,

    pacher@mail.nih.gov (PP); haskoge@umdnj.edu (GH)

    Affiliation: National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland, United States of America

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  • György Haskó mail

    pacher@mail.nih.gov (PP); haskoge@umdnj.edu (GH)

    Affiliation: Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey, United States of America

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  • Published: July 29, 2009
  • DOI: 10.1371/journal.pone.0006409

Abstract

Background

Sepsis is a major healthcare problem and current estimates suggest that the incidence of sepsis is approximately 750,000 annually. Sepsis is caused by an inability of the immune system to eliminate invading pathogens. It was recently proposed that endogenous mediators produced during sepsis can contribute to the immune dysfunction that is observed in sepsis. Endocannabinoids that are produced excessively in sepsis are potential factors leading to immune dysfunction, because they suppress immune cell function by binding to G-protein-coupled CB2 receptors on immune cells. Here we examined the role of CB2 receptors in regulating the host's response to sepsis.

Methods and Findings

The role of CB2 receptors was studied by subjecting CB2 receptor wild-type and knockout mice to bacterial sepsis induced by cecal ligation and puncture. We report that CB2 receptor inactivation by knockout decreases sepsis-induced mortality, and bacterial translocation into the bloodstream of septic animals. Furthermore, CB2 receptor inactivation decreases kidney and muscle injury, suppresses splenic nuclear factor (NF)-κB activation, and diminishes the production of IL-10, IL-6 and MIP-2. Finally, CB2 receptor deficiency prevents apoptosis in lymphoid organs and augments the number of CD11b+ and CD19+ cells during CLP.

Conclusions

Taken together, our results establish for the first time that CB2 receptors are important contributors to septic immune dysfunction and mortality, indicating that CB2 receptors may be therapeutically targeted for the benefit of patients suffering from sepsis.

Introduction

Sepsis is defined as systemic illness caused by microbial invasion of normally sterile parts of the body. Sepsis is a major healthcare problem because its incidence is in the order of sepsis is in the order of 750,000 annually, and sepsis causes more than 200,000 deaths each year in the United States alone [1], [2]. Currently, therapeutic management of sepsis is limited mostly to supportive measures, in a large part due to a failure to fully establish the pathophysiology of this complex and heterogeneous syndrome. Multiple organ dysfunction syndrome and death in sepsis are consequences of an inability to kill invading pathogens effectively due to immunosuppression [3], [4]. Potentially contributing to immune suppression after a septic insult are immune cell apoptosis, inefficient phagocytosis of microbial pathogens by neutrophils and macrophages, decreased ability of antigen-presenting cells to present antigens, as well as decreased responsiveness of macrophages and T cells to release proinflammatory cytokines in conjunction with overzealous production of the anti-inflammatory cytokine IL-10 [5][7].

One view holds that immune dysfunction during sepsis is a result of autocrine/paracrine immunoregulatory mediators that are produced primarily at the site of infection/injury (including the bloodstream) and suppress immune cell function via acting on G-protein-coupled receptors. One group of these mediators are endocannabinoids, which elicit their cellular effects by binding to two subtypes of G-protein-coupled cannabinoid receptor proteins on the cell surface, termed CB1 and CB2 receptors [8][10]. Endocannabinoids are released from macrophages, dendritic cells, platelets, and parenchimal cells in response to inflammatory stimuli and oxidative stress [11][15] and are present at elevated concentrations in the sera of patients and animals suffering from septic, hemorrhagic or cardiogenic shock [16][20]. CB2 receptors are the dominant cannabinoid receptors on macrophages, neutrophils, and lymphocytes, and triggering CB2 receptors has an overall anti-inflammatory and immunosuppressive effect [21]. CB2 receptor activation augments the production of the anti-inflammatory cytokine, IL-10, by murine macrophages [22], and disrupts antigen processing by these cells, which leads to incomplete antigen-presentation to T cells [23], [24].

Despite the recent enormous advances in our knowledge of how CB2 receptors regulate immune function, the role of CB2 receptors in regulating bacterial sepsis is unknown. In the present study, using a genetic approach we examined the role of CB2 receptors in regulating the host's response to polymicrobial sepsis.

Materials and Methods

Experimental animals

CB2 knockout (KO) mice and their wild-type (WT) littermates were developed as described previously and had been backcrossed to a C57Bl/6J background [14]. All mice were maintained in accordance with the recommendations of the “Guide for the Care and Use of Laboratory Animals”, and the experiments were approved by the New Jersey Medical School Animal Care Committee.

Cecal ligation and puncture (CLP)

Polymicrobial sepsis was induced by subjecting mice to CLP, as we have described previously [25], [26]. Eight- to twelve-week-old male CB2 KO or WT mice were anesthetized with Pentobarbital (50 mg/kg), given intraperitoneally (i.p.). Under aseptic conditions, a 2-cm midline laparotomy was performed to allow exposure of the cecum with adjoining intestine. Approximately two-thirds of the cecum was tightly ligated with a 3.0 silk suture, and the ligated part of the cecum was perforated twice (through and through) with a 20-gauge needle (BD Biosciences). The cecum was then gently squeezed to extrude a small amount of feces from the perforation sites. The cecum was then returned to the peritoneal cavity and the laparotomy was closed in two layers with 4.0 silk sutures. The mice were resuscitated with 1 ml of physiological saline injected subcutaneously (s.c.) and returned to their cages with free access to food and water. One group of mice was monitored daily and survival was recorded for 7 days. Another group of mice was reanesthetized with Pentobarbital (80 mg/kg i.p.) 16 hour after the operation, and blood, peritoneal lavage fluid, and various organs were harvested.

Collection of blood, peritoneal lavage fluid, and organs

Blood samples were obtained aseptically by cardiac puncture using heparinized syringes after opening the chest and placed on ice into heparinized Eppendorf tubes until further processing for bacteriological analysis. After serial dilutions for bacteriological analysis were made (see below), the blood was centrifuged at 2,000×g for 10 min and the recovered plasma was stored at −70°C until further use. For peritoneal lavage, the abdominal skin was cleansed with 70% ethanol and the abdominal wall was exposed by opening the skin. Two milliliters of sterile physiological saline were then installed into the peritoneal cavity via an 18-gauge needle. The abdomen was massaged gently for 1 min while keeping the tip of the needle in the peritoneum, after which peritoneal fluid was recovered through the needle. Recovered peritoneal lavage fluid was placed on ice until processed for bacteriological examination. After serially diluting the peritoneal lavage fluid to determine colony forming unit (CFU) numbers (see below), the peritoneal lavage fluid was centrifuged at 5,000×g for 10 min and the supernatant was stored at −70°C until further analysis. Samples from spleen and thymus, were excised and immediately frozen in liquid nitrogen.

Quantification of bacterial CFUs from peritoneal lavage fluid and blood

100 µl of blood or peritoneal lavage fluid was diluted serially in sterile physiological saline. 50 µl of each dilution was aseptically plated and cultured on trypticase blood agar plates (BD Biosciences) at 37°C. After 24 hours, the number of bacterial colonies was counted. Quantitative cultures are expressed as CFUs per milliliter of blood or peritoneal lavage fluid.

Flow cytometric analysis of leukocyte subsets

Flow cytometric detection of leukocyte subsets was performed as previously described [27]. In brief, the percent distribution of leukocyte subsets in blood was analyzed by specifically staining CD3+ T-cells, CD19+ B-cells and CD11b+ myeloid cells using antibodies against CD markers conjugated with FITC, PERCP or PE (BD Biosciences) in three-color incubations. Aliquots of 0.1 ml whole blood were incubated with the respective markers for 15 min followed by incubation with BD FACS lysing solution (BD Biosciences) for 7 min at 37°C. Cells were washed twice with BD FACS wash buffer and then fixed with 1% methanol free formaldehyde. FACS acquisitions were performed in a centralized flow cytometry facility. At least 30,000 events were collected for each analysis.

Protein extraction and Western blot analysis

Frozen organs were homogenized in a Dounce homogenizer in modified radioimmunoprecipitation assay buffer (50 mM Tris HCl, 150 mM NaCl, 1 mM EDTA, 0.25% sodium deoxycholate, 1% Nonidet P-40, 1 µg/ml pepstatin, 1 µg/ml leupeptin, 1 mM PMSF, 1 mM Na3VO4). The lysates were centrifuged at 15,000×g for 15 min, and the supernatant was recovered. Protein concentrations were determined using the Bio-Rad protein assay kit. A total of 40 µg of sample was separated on 8–12% Tris-glycine gel (Invitrogen Life Technologies) and transferred to nitrocellulose membrane. The membranes were probed with polyclonal rabbit anti-cleaved caspase-3, polyclonal rabbit anti-cleaved poly(ADP-ribose) polymerase (PARP), and polyclonal rabbit anti- inhibitory subunit of nuclear factor (NF)-κB (IκBα), (all from Cell Signaling Technology). Thereafter, the membranes were incubated with a secondary HRP-conjugated anti-rabbit antibody (Santa Cruz Biotechnology). HRP-conjugated polyclonal goat anti-β actin antibody to assess equal loading was used from Santa Cruz Biotechnology. Bands were detected using ECL Western Blotting Detection Reagent (Amersham Biosciences).

Determination of lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), and creatine phosphokinase (CK) levels

Plasma concentrations of LDH, AST, ALT, BUN, and CK were analyzed using a clinical chemistry analyzer system (VetTest8008, IDEXX Laboratories).

Determination of cytokine and chemokine levels

Concentrations of IL-10, IL-6, and MIP-2, were determined using commercially available ELISA kits (R&D Systems) according to the manufacturer's instructions. The lower detection limit for all these cytokines was 10 pg/ml.

Statistical Analysis

Survival statistics were performed using Kaplan-Meier curve and log rank test. Two-tailed t testing was used to compare cytokine concentrations, CFUs, and other laboratory parameters. Statistical significance was assigned to p values smaller than 0.05.

Results

CB2 receptors contribute to sepsis-induced mortality and bacterial invasion

To begin to study the role of CB2 receptors, we first investigated the effect of CB2 deficiency in CLP-induced septic peritonitis by monitoring the survival of CB2 WT and KO mice. As demonstrated in Figure 1a, CB2 receptor KO mice had significantly lower mortality rates compared with WT mice, which became apparent on the 2nd day of observation. On the 7th day following CLP, the mortality rate of CB2 KO mice was markedly (by more than 40%) lower than that of CB2 WT mice. No additional changes in mortality were detected when the mice were monitored for up to 10 days (data not shown). Because persistence of local bacterial infection and bloodstream invasion play important roles in mortality in the CLP model, we next assessed the impact of CB2 receptor inactivation on bacterial levels at the primary peritoneal site of infection and in the blood stream. We found markedly decreased numbers of bacteria in the blood but not peritoneal lavage fluid of CB2 receptor KO mice when compared to WT animals at 16 hours after CLP (Figure 1b, c).

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Figure 1. CB2 deficiency decreases mortality and bacterial burden in polymicrobial sepsis elicited by CLP.

(a) Surviving CB2 KO and WT mice were counted every day for 7 days after inducing polymicrobial sepsis by way of cecal ligation and puncture (CLP). p<0.001 versus WT. (b) Blood and (c) peritoneal lavage fluid obtained from CB2 KO or WT mice 16 hour after CLP were cultured on soy-trypticase agar plates, and the number of bacterial colonies was counted. Data are the mean±SEM of n = 6–9 mice per group. *p<0.05.

doi:10.1371/journal.pone.0006409.g001

Taken together, these studies document that CB2 receptors contribute to bacterial translocation into the bloodstream and mortality in polymicrobial sepsis.

CB2 receptor inactivation diminishes the production of IL-10, IL-6 and MIP-2 in CLP-induced sepsis

Because IL-10 overproduction contributes to the impairment of host antibacterial defenses seen in mice undergoing CLP [28][31], we next compared IL-10 in the plasma and peritoneal lavage fluid of CB2 KO and WT mice subjected to CLP. CB2 KO mice exhibited markedly lower levels of IL-10 at 16 h after CLP (Figure 2a, b).

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Figure 2. CB2 receptor deficiency decreases IL-10, IL-6, and MIP-2 levels in the plasma and peritoneal lavage fluid of mice subjected to CLP.

IL-10 (a,b), IL-6 (c,d) and MIP-2 (e,f) concentrations were measured at 16 hours after surgery using ELISA. Data are the mean±SEM of n = 6–9 mice per group. ***p<0.001; **p<0.01.

doi:10.1371/journal.pone.0006409.g002

Because IL-6 blockade with neutralizing Abs has been shown to be protective in CLP-induced sepsis [32], we next assessed the role of CB2 receptors in regulating IL-6 production during sepsis. Plasma and peritoneal lavage fluid had lower levels of IL-6 in CLP-induced CB2 KO mice than their WT littermates (Figure 2c,d).

We then determined the levels of macrophage-inflammatory protein-2 (MIP-2), a crucial chemokine that mediates inflammatory responses, in the plasma and peritoneal lavage fluid of CB2 KO and WT mice subjected to CLP, and we found that CLP-induced concentrations of MIP-2 were diminished in CB2 KO mice as compared with their WT counterparts when measured at 16 h after CLP (Figure 2e, f).

Mice deficient in CB2 receptor show decreased level of markers of tissue damage, and kidney and muscle injury

We next measured markers of disease severity and organ damage in an attempt to provide further explanation for the improved survival of CB2 receptor KO mice. Levels of LDH (Figure 3a), were lower in CB2 KO mice, indicating less tissue damage in general. Markers of liver (AST and ALT) function were not different between the WT and KO groups (Figure 3b, c). In addition, we could not detect any lung inflammation in CLP-challenged mice as assessed by histological analysis of lung sections, and detecting myeloperoxidase activity in lung tissue homogenates after 16 hour of CLP (data not shown). Finally, CK activity and BUN levels were lower in CB2 KO mice indicating preserved kidney function and lessened muscle (both heart and skeletal) damage, respectively (Figure 3d,e).

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Figure 3. CB2 KO mice have less tissue damage, kidney and muscle injury in sepsis than their WT counterparts.

LDH (a), AST (b), ALT (c), and CK (d) activity, and BUN (e) levels were measured in plasma samples 16 hour after CLP using a clinical chemistry analyzer system (VetTest8008, IDEXX Laboratories). Data are the mean±SEM of n = 6–9 mice per group. **p<0.01; * p<0.05.

doi:10.1371/journal.pone.0006409.g003

CB2 receptor deficiency decreases NF-κB activation in CLP-induced sepsis

Microbial components and endogenous danger signals trigger the activation of signaling cascades leading to induction of the NF-κB system during sepsis. Persistent activation of NF-κB may cause excessive inflammatory responses culminating in tissue injury, organ dysfunction, and death. We, therefore, studied the activation of NF-κB by measuring levels of the IκBα in spleen of septic animals. As Figure 4 shows, the levels of IκBα were increased in the spleen of CB2 KO as compared to WT mice, indicating decreased NF-κB activation in KO mice.

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Figure 4. CB2 receptor deficiency is associated with augmented IκBα levels in CLP-induced sepsis.

IκBα degradation was assessed using Western blotting of spleen protein extracts of CB2 WT and KO mice. Protein extracts were generated from spleen taken 16 hours after sepsis induction. Bands were detected by enchanced chemiluminescence (ECL). Results (mean±SEM) shown are representative of 3 experiments. **p<0.01 versus WT.

doi:10.1371/journal.pone.0006409.g004

Genetic deletion of the CB2 receptor diminishes apoptosis in lymphoid organs

Sepsis provokes extensive immune cell apoptosis that contributes to immune dysregulation and mortality. This was borne out by studies demonstrating that transfer of apoptotic splenocytes worsens survival in CLP-induced sepsis [33]. Because proteolytic cleavage of caspase-3 and PARP is a good indicator of apoptosis, we tested whether CB2 receptor deficiency would affect the cleavage of caspase-3 and PARP in the spleen and thymus of mice subjected to CLP. Figure 5 shows that 16 hours after the onset of sepsis, the cleavage of both caspase-3 and PARP was markedly decreased in thymus and spleen of CB2 receptor KO mice.

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Figure 5. CB2 receptor deficiency decreases apoptosis in septic thymus and spleen.

Proteolytic cleavage of caspase-3 and PARP in thymus and spleen protein extracts from CB2 WT and KO mice was examined using Western blotting. Bands were detected by enchanced chemiluminescence (ECL). Results shown are representative of 3 experiments.

doi:10.1371/journal.pone.0006409.g005

Lack of CB2 receptors augments the number of CD11b+ and CD19+ cells during CLP

CLP-challenged mice exhibit a decrease in white blood cell numbers, which includes CD11b+ cells (mostly neutrophils), CD3+ T lymphocytes, and CD19+ B lymphocytes [34], [35]. Unchallenged CB2 KO mice have cell counts comparable to their WT counterparts [36]. Flow-cytometric analysis of cell counts revealed that CLP-challenged CB2 KO mice have increased numbers of total white blood cells (Figure 6a), CD11b+ (Figure 6b) cells and CD19+ B lymphocytes (Figure 6c) in comparison with CB2 WT mice, whereas the number of CD3+ T cells (Figure 6d) was comparable between WT and KO mice undergoing CLP. We propose that preserved white blood cell numbers in KO animals contribute to the decreased bacterial growth and mortality of these mice.

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Figure 6. Effect of CB2 receptor inactivation on the leukocyte cell subsets in the blood during CLP.

Numbers of total white cell (a), as well as CD11b+ (b), CD19+ (c), and CD3+ (d) cells were monitored in blood by flow cytometric analysis after 16 hours of sepsis induced by CLP. Data are the mean±SEM of n = 6–9 mice per group. *p<0.05; **p<0.01.

doi:10.1371/journal.pone.0006409.g006

Discussion

Current concepts suggest that sepsis is the consequence of the inability of the immune system to ward off infecting pathogens due to immune system dysfunction. The mechanisms underlying these immune functional abnormalities are largely unknown. Recent studies have expanded the list of potential mediators to molecules that are produced locally by infected and inflamed tissues and act on specific G protein-coupled receptors expressed on immune cells to inhibit their function. These molecules include adenosine [37], [38], which bind to and trigger their receptors on lymphocytes, macrophages, and neutrophils, thereby diminishing anti-bacterial defenses. In these studies we have focused on a new type of immunosuppressive G protein-coupled receptor, the CB2 cannabinoid receptor, which is expressed primarily by immune cells and is activated by locally released endocannabinoids. Using the CLP model of sepsis, we found that CB2 receptor activation by endogenously released cannabinoids contributes to mortality, bacterial invasion, IL-10 production, and immune cell death in sepsis.

Studies utilizing antibiotic therapy have shown that systemic bacterial dissemination is a major factor contributing to the mortality of both experimental animals and humans during sepsis [39][41]. Our studies showed that bacterial burden was decreased in CB2 receptor KO mice suggesting that CB2 receptor activation contributes mortality by increasing systemic bacterial burden during sepsis. One potential explanation for the decreased bacterial load in mice lacking CB2 receptors is a decrease in the levels of the immunosuppressive IL-10 leading to a better preserved phagocytic response. IL-10 is an immunoregulatory cytokine that is released primarily by macrophages during sepsis. IL-10 is an important contributor to the dysregulated immune system that is observed in sepsis [28][31], [42]. Recent studies have shown that CB2 receptor activation can upregulate IL-10 production across a number of experimental systems that utilize macrophages [22], [43]. Given the relevance of IL-10 in sepsis, the effect of CB2 receptor activation on IL-10 release is likely to be a major determinant of the immunomodulatory action of CB2 receptor activation in sepsis.

Sepsis instigates widespread immune cell apoptosis, and mortality in this illness is thought to be, at least in part, a consequence of dysregulated immune cell death [44][46]. CB2 receptor triggering induces both T and B lymphocyte apoptosis in vitro [47][52]. Our data showing decreased levels of caspase-3 cleavage as well as PARP cleavage in CB2 KO mice following sepsis indicate that CB2 receptors are essential contributors to apoptotic processes also in vivo. Moreover, we found increased numbers of CD11b+ and CD19+cells in blood of CB2 KO mice suggesting that CB2 receptors contribute to bacterial invasion by CD11b+ and B cell depletion in the bloodstream. The immunosuppressive role of CB2 receptors has been confirmed recently in vivo by inducing immune-mediated inflammatory disease in CB2 receptor KO and WT mice. CB2 receptor KO mice develop a more severe form of experimental allergic encephalomyelitis in comparison with WT mice, which is a consequence of increased T-cell activation and decreased T-cell apoptosis in KO vs. WT mice [53]. In another model, CB2 receptor KO mice displayed increased allergic responses in the skin, which was secondary to increased production of proinflammatory cytokines [54]. Moreover, we have recently demonstrated that CB2 receptor KO mice exhibit exacerbated liver injury following hepatic ischemia/reperfusion, which is associated with increased production of pro-inflammatory cytokines and neutrophil infiltration into the liver [14]. Our results that CB2 receptor inactivation decreases mortality during CLP-induced bacterial (non-sterile) sepsis might seem contradictory to the observations in experimental allergic encephalomyelitis, allergic skin inflammation, and ischemia/reperfusion-induced inflammation in that CB2 receptor inactivation is injurious in these sterile inflammation models. But we believe the data seen as a whole suggests that differences in outcome in the two types of model are due to immunosuppression being beneficial in sterile inflammation/ischemia but detrimental in clinically relevant models of infection-induced sepsis where mortality depends more upon the inability to mount an immune response leading to a loss of control of bacterial growth.

In summary, we found that CB2 receptor activation by endogenously released cannabinoids contributes to mortality, bacterial invasion, IL-10 production, and immune cell death in sepsis. Based on these observations, we suggest that CB2 receptor triggering contributes to the development of immune system dysfunction that leads to mortality in sepsis.

Author Contributions

Conceived and designed the experiments: BC. Performed the experiments: BC ZHN PM MR SF. Analyzed the data: BC ZS PP GH. Contributed reagents/materials/analysis tools: ED SB PP. Wrote the paper: BC PP GH.

References

  1. 1. Angus DC, Linde-Zwirble WT, Lidicker J, Clermont G, Carcillo J, et al. (2001) Epidemiology of severe sepsis in the united states: Analysis of incidence, outcome, and associated costs of care. Crit Care Med 29(7): 1303–1310.
  2. 2. Martin GS, Mannino DM, Eaton S, Moss M (2003) The epidemiology of sepsis in the united states from 1979 through 2000. N Engl J Med 348(16): 1546–1554.
  3. 3. Benjamim CF, Hogaboam CM, Kunkel SL (2004) The chronic consequences of severe sepsis. J Leukoc Biol 75(3): 408–412.
  4. 4. Oberholzer A, Oberholzer C, Moldawer LL (2001) Sepsis syndromes: Understanding the role of innate and acquired immunity. Shock 16(2): 83–96.
  5. 5. Hotchkiss RS, Karl IE (2003) The pathophysiology and treatment of sepsis. N Engl J Med 348(2): 138–150.
  6. 6. Riedemann NC, Guo RF, Bernacki KD, Reuben JS, Laudes IJ, et al. (2003) Regulation by C5a of neutrophil activation during sepsis. Immunity 19(2): 193–202.
  7. 7. Ayala A, Chaudry IH (1996) Immune dysfunction in murine polymicrobial sepsis: Mediators, macrophages, lymphocytes and apoptosis. Shock 6: Suppl 1S27–38.
  8. 8. Pacher P, Batkai S, Kunos G (2006) The endocannabinoid system as an emerging target of pharmacotherapy. Pharmacol Rev 58(3): 389–462.
  9. 9. Di Marzo V (2008) Targeting the endocannabinoid system: To enhance or reduce? Nat Rev Drug Discov 7(5): 438–455.
  10. 10. Howlett AC, Barth F, Bonner TI, Cabral G, Casellas P, et al. (2002) International union of pharmacology. XXVII. classification of cannabinoid receptors. Pharmacol Rev 54(2): 161–202.
  11. 11. Di Marzo V, De Petrocellis L, Sepe N, Buono A (1996) Biosynthesis of anandamide and related acylethanolamides in mouse J774 macrophages and N18 neuroblastoma cells. Biochem J 316 ( Pt 3)(Pt 3): 977–984.
  12. 12. Pacher P, Hasko G (2008) Endocannabinoids and cannabinoid receptors in ischaemia-reperfusion injury and preconditioning. Br J Pharmacol 153(2): 252–262.
  13. 13. Matias I, Pochard P, Orlando P, Salzet M, Pestel J, et al. (2002) Presence and regulation of the endocannabinoid system in human dendritic cells. Eur J Biochem 269(15): 3771–3778.
  14. 14. Batkai S, Osei-Hyiaman D, Pan H, El-Assal O, Rajesh M, et al. (2007) Cannabinoid-2 receptor mediates protection against hepatic ischemia/reperfusion injury. FASEB J 21(8): 1788–1800.
  15. 15. Mukhopadhyay P, Batkai S, Rajesh M, Czifra N, Harvey-White J, et al. (2007) Pharmacological inhibition of CB1 cannabinoid receptor protects against doxorubicin-induced cardiotoxicity. J Am Coll Cardiol 50(6): 528–536.
  16. 16. Wang Y, Liu Y, Ito Y, Hashiguchi T, Kitajima I, et al. (2001) Simultaneous measurement of anandamide and 2-arachidonoylglycerol by polymyxin B-selective adsorption and subsequent high-performance liquid chromatography analysis: Increase in endogenous cannabinoids in the sera of patients with endotoxic shock. Anal Biochem 294(1): 73–82.
  17. 17. Varga K, Wagner JA, Bridgen DT, Kunos G (1998) Platelet- and macrophage-derived endogenous cannabinoids are involved in endotoxin-induced hypotension. FASEB J 12(11): 1035–1044.
  18. 18. Wagner JA, Varga K, Kunos G (1998) Cardiovascular actions of cannabinoids and their generation during shock. J Mol Med 76(12): 824–836.
  19. 19. Wagner JA, Varga K, Ellis EF, Rzigalinski BA, Martin BR, et al. (1997) Activation of peripheral CB1 cannabinoid receptors in haemorrhagic shock. Nature 390(6659): 518–521.
  20. 20. Wagner JA, Hu K, Bauersachs J, Karcher J, Wiesler M, et al. (2001) Endogenous cannabinoids mediate hypotension after experimental myocardial infarction. J Am Coll Cardiol 38(7): 2048–2054.
  21. 21. Klein TW (2005) Cannabinoid-based drugs as anti-inflammatory therapeutics. Nat Rev Immunol 5(5): 400–411.
  22. 22. Correa F, Mestre L, Docagne F, Guaza C (2005) Activation of cannabinoid CB2 receptor negatively regulates IL-12p40 production in murine macrophages: Role of IL-10 and ERK1/2 kinase signaling. Br J Pharmacol 145(4): 441–448.
  23. 23. McCoy KL, Matveyeva M, Carlisle SJ, Cabral GA (1999) Cannabinoid inhibition of the processing of intact lysozyme by macrophages: Evidence for CB2 receptor participation. J Pharmacol Exp Ther 289(3): 1620–1625.
  24. 24. Matveyeva M, Hartmann CB, Harrison MT, Cabral GA, McCoy KL (2000) Delta(9)-tetrahydrocannabinol selectively increases aspartyl cathepsin D proteolytic activity and impairs lysozyme processing by macrophages. Int J Immunopharmacol 22(5): 373–381.
  25. 25. Nemeth ZH, Csoka B, Wilmanski J, Xu D, Lu Q, et al. (2006) Adenosine A2A receptor inactivation increases survival in polymicrobial sepsis. J Immunol 176(9): 5616–5626.
  26. 26. Csoka B, Nemeth ZH, Selmeczy Z, Koscso B, Pacher P, et al. (2007) Role of A(2A) adenosine receptors in regulation of opsonized E. coli-induced macrophage function. Purinergic Signal 3(4): 447–452.
  27. 27. Chandra R, Villanueva E, Feketova E, Machiedo GW, Hasko G, et al. (2008) Endotoxemia down-regulates bone marrow lymphopoiesis but stimulates myelopoiesis: The effect of G6PD deficiency. J Leukoc Biol 83(6): 1541–1550.
  28. 28. Lyons A, Kelly JL, Rodrick ML, Mannick JA, Lederer JA (1997) Major injury induces increased production of interleukin-10 by cells of the immune system with a negative impact on resistance to infection. Ann Surg 226(4): 450–8; discussion 458–60.
  29. 29. Steinhauser ML, Hogaboam CM, Kunkel SL, Lukacs NW, Strieter RM, et al. (1999) IL-10 is a major mediator of sepsis-induced impairment in lung antibacterial host defense. J Immunol 162(1): 392–399.
  30. 30. Song GY, Chung CS, Chaudry IH, Ayala A (2000) Immune suppression in polymicrobial sepsis: Differential regulation of Th1 and Th2 responses by p38 MAPK. J Surg Res 91(2): 141–146.
  31. 31. Kalechman Y, Gafter U, Gal R, Rushkin G, Yan D, et al. (2002) Anti-IL-10 therapeutic strategy using the immunomodulator AS101 in protecting mice from sepsis-induced death: Dependence on timing of immunomodulating intervention. J Immunol 169(1): 384–392.
  32. 32. Riedemann NC, Neff TA, Guo RF, Bernacki KD, Laudes IJ, et al. (2003) Protective effects of IL-6 blockade in sepsis are linked to reduced C5a receptor expression. J Immunol 170(1): 503–507.
  33. 33. Hotchkiss RS, Chang KC, Grayson MH, Tinsley KW, Dunne BS, et al. (2003) Adoptive transfer of apoptotic splenocytes worsens survival, whereas adoptive transfer of necrotic splenocytes improves survival in sepsis. Proc Natl Acad Sci U S A 100(11): 6724–6729.
  34. 34. Hotchkiss RS, Swanson PE, Cobb JP, Jacobson A, Buchman TG, et al. (1997) Apoptosis in lymphoid and parenchymal cells during sepsis: Findings in normal and T- and B-cell-deficient mice. Crit Care Med 25(8): 1298–1307.
  35. 35. Shelley O, Murphy T, Paterson H, Mannick JA, Lederer JA (2003) Interaction between the innate and adaptive immune systems is required to survive sepsis and control inflammation after injury. Shock 20(2): 123–129.
  36. 36. Buckley NE, McCoy KL, Mezey E, Bonner T, Zimmer A, et al. (2000) Immunomodulation by cannabinoids is absent in mice deficient for the cannabinoid CB(2) receptor. Eur J Pharmacol 396(2–3): 141–149.
  37. 37. Hasko G, Cronstein BN (2004) Adenosine: An endogenous regulator of innate immunity. Trends Immunol 25(1): 33–39.
  38. 38. Hasko G, Linden J, Cronstein B, Pacher P (2008) Adenosine receptors: Therapeutic aspects for inflammatory and immune diseases. Nat Rev Drug Discov 7(9): 759–770.
  39. 39. Enoh VT, Fairchild CD, Lin CY, Varma TK, Sherwood ER (2006) Differential effect of imipenem treatment on wild-type and NK cell-deficient CD8 knockout mice during acute intra-abdominal injury. Am J Physiol Regul Integr Comp Physiol 290(3): R685–93.
  40. 40. Enoh VT, Lin CY, Varma TK, Sherwood ER (2006) Differential effect of imipenem treatment on injury caused by cecal ligation and puncture in wild-type and NK cell-deficient beta(2)-microgloblin knockout mice. Am J Physiol Gastrointest Liver Physiol 290(2): G277–84.
  41. 41. Leibovici L, Drucker M, Konigsberger H, Samra Z, Harrari S, et al. (1997) Septic shock in bacteremic patients: Risk factors, features and prognosis. Scand J Infect Dis 29(1): 71–75.
  42. 42. Oberholzer A, Oberholzer C, Moldawer LL (2002) Interleukin-10: A complex role in the pathogenesis of sepsis syndromes and its potential as an anti-inflammatory drug. Crit Care Med 30(1 Supp): S58–S63.
  43. 43. Zhu LX, Sharma S, Stolina M, Gardner B, Roth MD, et al. (2000) Delta-9-tetrahydrocannabinol inhibits antitumor immunity by a CB2 receptor-mediated, cytokine-dependent pathway. J Immunol 165(1): 373–380.
  44. 44. Chung CS, Xu YX, Wang W, Chaudry IH, Ayala A (1998) Is fas ligand or endotoxin responsible for mucosal lymphocyte apoptosis in sepsis? Arch Surg 133(11): 1213–1220.
  45. 45. Hotchkiss RS, Tinsley KW, Swanson PE, Chang KC, Cobb JP, et al. (1999) Prevention of lymphocyte cell death in sepsis improves survival in mice. Proc Natl Acad Sci U S A 96(25): 14541–14546.
  46. 46. Hotchkiss RS, Tinsley KW, Swanson PE, Schmieg RE Jr, Hui JJ, et al. (2001) Sepsis-induced apoptosis causes progressive profound depletion of B and CD4+ T lymphocytes in humans. J Immunol 166(11): 6952–6963.
  47. 47. Lombard C, Nagarkatti M, Nagarkatti P (2007) CB2 cannabinoid receptor agonist, JWH-015, triggers apoptosis in immune cells: Potential role for CB2-selective ligands as immunosuppressive agents. Clin Immunol 122(3): 259–270.
  48. 48. Rieder SA, Chauhan A, Singh U, Nagarkatti M, Nagarkatti P (2009) Cannabinoid-induced apoptosis in immune cells as a pathway to immunosuppression. Immunobiology.
  49. 49. Jia W, Hegde VL, Singh NP, Sisco D, Grant S, et al. (2006) Delta9-tetrahydrocannabinol-induced apoptosis in jurkat leukemia T cells is regulated by translocation of bad to mitochondria. Mol Cancer Res 4(8): 549–562.
  50. 50. McKallip RJ, Jia W, Schlomer J, Warren JW, Nagarkatti PS, et al. (2006) Cannabidiol-induced apoptosis in human leukemia cells: A novel role of cannabidiol in the regulation of p22phox and Nox4 expression. Mol Pharmacol 70(3): 897–908.
  51. 51. McKallip RJ, Lombard C, Martin BR, Nagarkatti M, Nagarkatti PS (2002) Delta(9)-tetrahydrocannabinol-induced apoptosis in the thymus and spleen as a mechanism of immunosuppression in vitro and in vivo. J Pharmacol Exp Ther 302(2): 451–465.
  52. 52. Do Y, McKallip RJ, Nagarkatti M, Nagarkatti PS (2004) Activation through cannabinoid receptors 1 and 2 on dendritic cells triggers NF-kappaB-dependent apoptosis: Novel role for endogenous and exogenous cannabinoids in immunoregulation. J Immunol 173(4): 2373–2382.
  53. 53. Maresz K, Pryce G, Ponomarev ED, Marsicano G, Croxford JL, et al. (2007) Direct suppression of CNS autoimmune inflammation via the cannabinoid receptor CB1 on neurons and CB2 on autoreactive T cells. Nat Med 13(4): 492–497.
  54. 54. Karsak M, Gaffal E, Date R, Wang-Eckhardt L, Rehnelt J, et al. (2007) Attenuation of allergic contact dermatitis through the endocannabinoid system. Science 316(5830): 1494–1497.