Thermal injury and sepsis modulates beta-adrenergic receptors and cAMP responses in monocyte-committed bone marrow cells

Exendin-4 Exacerbates Burn-Induced Morbidity in Mice by Activation of the Sympathetic Nervous System

Background

Although glucagon-like peptide 1- (GLP-1-) based therapy of hyperglycemia in burn injury has shown great potential in clinical trials, its safety is seldom evaluated. We hypothesize that exendin-4, a GLP-1 analogue, might affect the immune response via the activation of the sympathetic nervous system in burn injury.

Methods

Male Balb/c mice were subjected to sham or thermal injury of 15% total body surface area. Exendin-4 on T cell function in vitro was examined in cultured splenocytes in the presence of β-adrenoceptor antagonist propranolol (1 nmol/L) or GLP-1R antagonist exendin (9-39) (1 μmol/L), whereas its in vivo effect was determined by i.p. injection of exendin-4 (2.4 nmol/kg) in mice. To further elucidate the sympathetic mechanism, propranolol (30 mg/kg) or vehicle was applied 30 min prior to injury.

Results

Although the exacerbated burn-induced mortality by exendin-4 was worsened by propranolol pretreatment, the inhibition of T cell proliferation by exendin-4 in vitro could be restored by propranolol instead of exendin (9-39). However, a Th2 switch by exendin-4 in vitro could only be reversed by exendin (9-39). Likewise, the inhibition of splenic T cell function and NFAT activity by exendin-4 in vivo was restored by propranolol. By contrast, the increased splenic NF-κB translocation by exendin-4 in vivo was potentiated by propranolol in sham mice but suppressed in burn mice. Accordingly, propranolol abrogated the heightened inflammatory response in the lung and the accelerated organ injuries by exendin-4 in burn mice. On the contrary, a Th2 switch and higher serum levels of inflammatory mediators by exendin-4 were potentiated by propranolol in burn mice. Lastly, exendin-4 raised serum stress hormones which could be remarkably augmented by propranolol.

Conclusions

Exendin-4 suppresses T cell function and promotes organ inflammation through the activation of the sympathetic nervous system, while elicits Th2 switch via GLP-1R in burn injury.

β-Blockade use for Traumatic Injuries and Immunomodulation: A Review of Proposed Mechanisms and Clinical Evidence

Sympathetic nervous system activation and catecholamine release are important events following injury and infection. The nature and timing of different pathophysiologic insults have significant effects on adrenergic pathways, inflammatory mediators, and the host response. Beta adrenergic receptor blockers (β-blockers) are commonly used for treatment of cardiovascular disease, and recent data suggests that the metabolic and immunomodulatory effects of β-blockers can expand their use. β-blocker therapy can reduce sympathetic activation and hypermetabolism as well as modify glucose homeostasis and cytokine expression. It is the purpose of this review to examine either the biologic basis for proposed mechanisms or to describe current available clinical evidence for the use of β-blockers in traumatic brain injury, spinal cord injury, hemorrhagic shock, acute traumatic coagulopathy, erythropoietic dysfunction, metabolic dysfunction, pulmonary dysfunction, burns, immunomodulation, and sepsis.

Pathophysiologic Mechanisms and Current Treatments for Cutaneous Sequelae of Burn Wounds

Burn injuries are a pervasive clinical problem. Extensive thermal trauma can be life-threatening or result in long-lasting complications, generating a significant impact on quality of life for patients as well as a cost burden to the healthcare system. The importance of addressing global or systemic issues such as resuscitation and management of inhalation injuries is not disputed but is beyond the scope of this review, which focuses on cutaneous pathophysiologic mechanisms for current treatments, both in the acute and long-term settings. Pathophysiological mechanisms of burn progression and wound healing are mediated by highly complex cascades of cellular and biochemical events, which become dysregulated in slow-healing wounds such as burns. Burns can result in fibroproliferative scarring, skin contractures, or chronic wounds that take weeks or months to heal. Burn injuries are highly individualized owing to wound-specific differences such as burn depth and surface area, in addition to patient-specific factors including genetics, immune competency, and age. Other extrinsic complications such as microbial infection can complicate wound healing, resulting in prolonged inflammation and delayed re-epithelialization. Although mortality is decreasing with advancements in burn care, morbidity from postburn deformities continues to be a challenge. Optimizing specialized acute care and late burn outcome intervention on a patient-by-patient basis is critical for successful management of burn wounds and the associated pathological scar outcome. Understanding the fundamentals of integument physiology and the cellular processes involved in wound healing is essential for designing effective treatment strategies for burn wound care as well as development of future therapies. Published 2018. Compr Physiol 8:371-405, 2018.

The immune system's role in sepsis progression, resolution, and long-term outcome

Sepsis occurs when an infection exceeds local tissue containment and induces a series of dysregulated physiologic responses that result in organ dysfunction. A subset of patients with sepsis progress to septic shock, defined by profound circulatory, cellular, and metabolic abnormalities, and associated with a greater mortality. Historically, sepsis-induced organ dysfunction and lethality were attributed to the complex interplay between the initial inflammatory and later anti-inflammatory responses. With advances in intensive care medicine and goal-directed interventions, early 30-day sepsis mortality has diminished, only to steadily escalate long after "recovery" from acute events. As so many sepsis survivors succumb later to persistent, recurrent, nosocomial, and secondary infections, many investigators have turned their attention to the long-term sepsis-induced alterations in cellular immune function. Sepsis clearly alters the innate and adaptive immune responses for sustained periods of time after clinical recovery, with immune suppression, chronic inflammation, and persistence of bacterial representing such alterations. Understanding that sepsis-associated immune cell defects correlate with long-term mortality, more investigations have centered on the potential for immune modulatory therapy to improve long-term patient outcomes. These efforts are focused on more clearly defining and effectively reversing the persistent immune cell dysfunction associated with long-term sepsis mortality.

Systematic review of use of β-blockers in sepsis

Background and Aims:

We proposed a review of present literature and systematic analysis of present literature to summarize the evidence on the use of β-blockers on the outcome of a patient with severe sepsis and septic shock.

Material and Methods:

Medline, EMBASE, Cochrane Library were searched from 1946 to December 2013. The bibliography of all relevant articles was hand searched. Full-text search of the grey literature was done through the medical institution database. The database search identified a total of 1241 possible studies. The citation list was hand searched by both the authors. A total of 9 studies were identified.

Results:

Most studies found a benefit from β-blocker administration in sepsis. This included improved heart rate (HR) control, decreased mortality and improvement in acid-base parameters. Chronic β-blocker usage in sepsis was also associated with improved mortality. The administration of β-blockers during sepsis was associated with better control of HR. The methodological quality of all the included studies, however, was poor.

Conclusion:

There is insufficient evidence to justify the routine use of β-blockers in sepsis. A large adequately powered multi-centered randomized controlled clinical trial is required to address the question on the efficacy of β-blocker usage in sepsis. This trial should also consider a number of important questions including the choice of β-blocker used, optimal dosing, timing of intervention, duration of intervention and discontinuation of the drug. Until such time based on the available evidence, there is no place for the use of β-blockers in sepsis in current clinical practice.

Is It Time to Beta Block the Septic Patient?

Beta blockers are some of the most studied drugs in the pharmacopoeia. They are already widely used in medicine for treating hypertension, chronic heart failure, tachyarrhythmias, and tremor. Whilst their use in the immediate perioperative patient has been questioned, the use of esmolol in the patients with established septic shock has been recently reported to have favourable outcomes. In this paper, we review the role of the adrenergic system in sepsis and the evidence for the use of beta stimulation and beta blockers from animal models to critically ill patients.

Standard sub-thermoneutral caging temperature influences radiosensitivity of hematopoietic stem and progenitor cells

The production of new blood cells relies on a hierarchical network of hematopoietic stem and progenitor cells (HSPCs). To maintain lifelong hematopoiesis, HSPCs must be protected from ionizing radiation or other cytotoxic agents. For many years, murine models have been a valuable source of information regarding factors that either enhance or reduce the survival of HSPCs after exposure of marrow to ionizing radiation. In a recent series of studies, however, it has become clear that housing-related factors such as the cool room temperature required for laboratory mice can exert a surprising influence on the outcome of experiments. Here we report that the mild, but chronic cold-stress endured by mice housed under these conditions exerts a protective effect on HSPCs after both non-lethal and lethal doses of total body irradiation (TBI). Alleviation of this cold-stress by housing mice at a thermoneutral temperature (30°C) resulted in significantly greater baseline radiosensitivity to a lethal dose of TBI with more HSPCs from mice housed at thermoneutral temperature undergoing apoptosis following non-lethal TBI. Cold-stressed mice have elevated levels of norepinephrine, a key molecule of the sympathetic nervous system that binds to β-adrenergic receptors. We show that blocking this signaling pathway in vivo through use of the β-blocker propanolol completely mitigates the protective effect of cold-stress on HSPC apoptosis. Collectively this study demonstrates that chronic stress endured by the standard housing conditions of laboratory mice increases the resistance of HSPCs to TBI-induced apoptosis through a mechanism that depends upon β-adrenergic signaling. Since β-blockers are commonly prescribed to a wide variety of patients, this information could be important when predicting the clinical impact of HSPC sensitivity to TBI.

ß-adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms

CD14 is a glycoprotein that binds bacterial LPS in MØ. It is an essential component of the phagocytic system and is increased in septic shock. Critical injury and sepsis result in elevated endogenous CA levels. CAs have a significant impact on MØ inflammatory functions. We tested the hypothesis that β-adrenergic stimulation regulates CD14 expression and bacterial phagocytosis in BMØ. Murine BMØ stimulated with isoproterenol (>8 h) induced a dose-dependent increase in cell surface CD14 expression. Specific PKA inhibitor (H-89) and gene-silencing (siRNA) studies demonstrated the role of cAMP-dependent PKA in mediating this response. In addition, we observed a correlation between an isoproterenol-mediated increase in CD14 expression and live Escherichia coli uptake in BMØ. Further, the essential role of CD14 in an isoproterenol-mediated increase in E. coli uptake was highlighted from experiments using CD14(-/-) mice. Moreover, the dose response of isoproterenol stimulation to CD14 expression and E. coli phagocytosis overlapped with similar EC50. Additionally, isoproterenol-mediated E. coli phagocytosis was prevented by H-89, suggesting that β-adrenergic stimulus in BMØ increases CD14 expression and live E. coli phagocytosis through a common signaling pathway. Our studies indicate the potential impact of β-adrenergic agents on important innate immune functions.

Bench-to-bedside review: Beta-adrenergic modulation in sepsis

Sepsis, despite recent therapeutic progress, still carries unacceptably high mortality rates. The adrenergic system, a key modulator of organ function and cardiovascular homeostasis, could be an interesting new therapeutic target for septic shock. β-Adrenergic regulation of the immune function in sepsis is complex and is time dependent. However, β₂ activation as well as β₁ blockade seems to downregulate proinflammatory response by modulating the cytokine production profile. β₁ blockade improves cardiovascular homeostasis in septic animals, by lowering myocardial oxygen consumption without altering organ perfusion, and perhaps by restoring normal cardiovascular variability. β-Blockers could also be of interest in the systemic catabolic response to sepsis, as they oppose epinephrine which is known to promote hyperglycemia, lipid and protein catabolism. The role of β-blockers in coagulation is less clear cut. They could have a favorable role in the septic pro-coagulant state, as β₁ blockade may reduce platelet aggregation and normalize the depressed fibrinolytic status induced by adre-nergic stimulation. Therefore, β₁ blockade as well as β₂ activation improves sepsis-induced immune, cardiovascular and coagulation dysfunctions. β₂ blocking, however, seems beneficial in the metabolic field. Enough evidence has been accumulated in the literature to propose β- adrenergic modulation, β₁ blockade and β₂ activation in particular, as new promising therapeutic targets for septic dyshomeostasis, modulating favorably immune, cardiovascular, metabolic and coagulation systems.

Propranolol restores the tumor necrosis factor-alpha response of circulating inflammatory monocytes and granulocytes after burn injury and sepsis

Beta-adrenergic blockade ameliorates the hypermetabolism and catabolism in severe burn injury. Despite the salutary effects of beta-adrenergic blockade, the immunologic responses that accompany beta-blockade are not known. We have shown that burn sepsis is associated with increased sympathetic activation leading to altered monocytopoiesis and cytokine release in macrophages (MØ). Recent evidence suggests that murine MØ expressing F4/80+Gr1+ are the inflammatory phenotype. Here, we report that propranolol given after burn sepsis modulates the number and function of myeloid cells in circulation. B6D2F1 male mice were divided into sham (S), burn (B), and burn sepsis (BS) groups. Dorsal hair was shaved from S, B, and BS; B and BS received 15% scald burn; BS was inoculated with Pseudomonas Aeruginosa (PA 14, 4000-5000 colony-forming units) at the burn site. Mice from each group were then subjected to two different treatment regimens. One set received subcutaneous injections of propranolol (5 mg/kg body weight) at 24 and 48 hours after the injury while the control groups received saline. Blood was collected by cardiac puncture at 72 hours. The distribution of total F4/80+ monocyte population was determined by flow cytometry. Inflammatory monocyte subset was gated on Gr1+ expression in the F4/80+ fraction. Lipopolysaccharide-stimulated intracellular tumor necrosis factor (TNF)-alpha (ic-TNF) was also measured as an indicator of inflammatory response. The total F4/80+ monocyte fraction was significantly increased in BS (45 +/- 0.8%) vs S and B (10 +/- 0.8%; 9.5 +/- 0.6%). Propranolol treatment for 2 days reduced the number of circulating monocytes by 60% in BS. The mean fluorescent intensity (MFI) of ic-TNF produced per cell (F4/80+Gr1+ MØ) was significantly decreased in B and BS (S: 3043 +/- 213, B: 1638 +/- 343, BS: 1463 +/- 67). Of importance, propranolol treatment partially restored the MFI of ic-TNF (2177 +/- 114) and increased the percentage of inflammatory monocyte subset (F4/80+Gr1+) in BS by 70% compared with saline treatment. In contrast, beta-blockade after BS increased the percentage of granulocytes in circulation (28.4 +/- 3.6% in BS propranolol vs 15.4 +/- 0.3% in BS saline; P < .05) and augmented their TNF production (MFI = 903 +/- 102 in BS propranolol vs 644 +/- 5 in BS saline; P < .05). Propranolol reverses burn sepsis-induced monocytosis and simultaneously increases the number of granulocytes and enhances the inflammatory potential of the granulocytes and inflammatory monocyte subsets in circulation suggesting that monitoring MØ subsets and granulocytes in blood is a reliable biomarker to predict the efficacy of beta-blockade.

Perturbed bone marrow monocyte development following burn injury and sepsis promote hyporesponsive monocytes

The mechanism of monocyte deactivation in critically injured burn patients remains unresolved. Two functionally distinct F4/80+Gr-1+ and F4/80+Gr-1- monocyte subsets have been characterized based on their homing to inflammatory or noninflammatory tissues, respectively. We hypothesized that the posttraumatic milieu in the bone marrow (BM) blunts the production of "inflammatory" monocytes. C57Blk/J male mice were divided into sham (S), burn (B), and burn sepsis (BS) groups. B and BS received a 15% dorsal scald burn and BS was inoculated with 15K colony forming units Pseudomonas aeruginosa at the burn site. Animals were killed and blood and femoral BM were collected 48, 72, and 96 hours after injury. ER-MP20 monocyte progenitors were isolated from BM and differentiated into macrophage (MØ) or dendritic cells (DCs) and characterized by the cell surface expression of F4/80 and CD11c, respectively. In both cell types, TLR-4 agonist induced cytokine levels were determined. Results showed a 2-fold increase in the F4/80+Gr-1+ subset at 48 hours in BS that started to decline at 72 hours and remained low at 96 hours. ER-MP20 progenitors isolated at 48 hours exhibited robust MØ differentiation potential but a significant decline in the percentage of the F4/80+Gr-1+ subset (P < .05 vs S) with a concomitant decrease in tumor necrosis factor alpha production. DC development from ER-MP20 progenitors and LPS-stimulated tumor necrosis factor alpha production were impaired. Therefore, BM progenitor derived MØ will replace the transient hyper-responsive circulating monocytes later during the course of the septic insult. Hypo-reactivity of the developing monocytes and DC in the BM and their subsequent egress to the periphery provide a plausible explanation for the immunosuppression that ensues a critical burn injury and sepsis.

Cytotoxicity of Pseudomonas secreted exotoxins requires OxyR expression

BACKGROUND

Nosocomial infections often lead to sepsis and multisystem organ failure in critically injured patients, including burn and trauma patients. A better understanding of the bacterial response to the host immune system is essential to develop better antimicrobials against pathogens. Pseudomonas aeruginosa combats host-initiated oxidant stress through expression of the transactivating factor, OxyR. Here we have tested the premise that OxyR regulates Pseudomonal cytotoxicity through secreted exotoxin production.

MATERIALS AND METHODS

Wild-type P. aeruginosa (PAO1) and a deletion mutant lacking the oxyR gene (Delta oxyR) were grown for 18 h in Luria broth and the supernatant containing the secreted products was removed using centrifugation. Secreted proteins were isolated using ammonium sulfate precipitation. ER-MP20(+) myeloid progenitor cells were harvested from the bone marrow of C57Blk/6J mice. These cells were differentiated into dendritic cells and macrophages. Various concentrations (0-20 microg/100 microL) of the bacterial proteins were added to the medium and cells were allowed to differentiate for 7 days. Cellular viability was then assayed using a proliferation assay. These studies were repeated on two other macrophage cell lines, human U937 and murine P388D1.

RESULTS

At a protein concentration of 5 microg/100 microL PAO1 supernatant protein, cellular proliferation was significantly reduced to 4.2 +/- 2.8% compared to untreated controls, while the DeltaoxyR supernatant protein remained at 103.3 +/- 4.0% of untreated controls (P < 0.05). Similar significant results were seen in the U937-, P388D1-, and ER-MP20(+)-derived macrophage cells.

CONCLUSIONS

Taken together, our data indicate that OxyR regulates the secretion of potent cytotoxic factors by P. aeruginosa.

Murine hematopoietic stem cells and progenitors express adrenergic receptors

Association between the nervous and immune system is well documented. Immune cells originate within the bone marrow that is innervated. Thermal injury induces adrenergic stimulation, augments monocytopoiesis and alters the beta-adrenergic receptor (AR) profile of bone marrow monocyte committed progenitors. This provides an impetus to study AR expression in hematopoietic progenitors along myeloid lineage. Using FACS analysis and confocal microscopy, we report the expression of alpha1-, alpha2- and beta(2)-AR in enriched populations of ER-MP209(+) and ER-MP12(+) myeloid progenitors, CD117(+) and CD34(+) multi-potential progenitors and more importantly pluripotent stem cells suggesting a plausible role for catecholamine in hematopoietic development.