TLR4 inactivation and rBPI(21) block burn-induced myocardial contractile dysfunction

Modulation of TLR4/NFκB Pathways in Autoimmune Myocarditis

Myocarditis is an inflammatory and oxidative disorder characterized by immune cell recruitment in the damaged tissue and organ dysfunction. In this paper, we evaluated the molecular pathways involved in myocarditis using a natural compound, Coriolus versicolor, in an experimental model of autoimmune myocarditis (EAM). Animals were immunized with an emulsion of pig cardiac myosin and complete Freund's adjuvant supplemented with mycobacterium tuberculosis; thereafter, Coriolus versicolor (200 mg/Kg) was orally administered for 21 days. At the end of the experiment, blood pressure and heart rate measurements were recorded and the body and heart weights as well. From the molecular point of view, the Coriolus versicolor administration reduced the activation of the TLR4/NF-κB pathway and the levels of pro-inflammatory cytokines (INF-γ, TNF-α, IL-6, IL-17, and IL-2) and restored the levels of anti-inflammatory cytokines (IL-10). These anti-inflammatory effects were accompanied with a reduced lipid peroxidation and nitrite levels and restored the antioxidant enzyme activities (SOD and CAT) and GSH levels. Additionally, it reduced the histological injury and the immune cell recruitment (CD4+ and CD68+ cells). Moreover, we observed an antiapoptotic activity in both intrinsic (Fas/FasL/caspase-3) and extrinsic (Bax/Bcl-2) pathways. Overall, our data showed that Coriolus versicolor administration modulates the TLR4/NF-κB signaling in EAM.

Damage-Associated Molecular Patterns and the Systemic Immune Consequences of Severe Thermal Injury

Thermal injury is often associated with a proinflammatory state resulting in serious complications. After a burn, the innate immune system is activated with subsequent immune cell infiltration and cytokine production. Although the innate immune response is typically beneficial, an excessive activation leads to cytokine storms, multiple organ failure, and even death. This overwhelming immune response is regulated by damage-associated molecular patterns (DAMPs). DAMPs are endogenous molecules that are actively secreted by immune cells or passively released by dead or dying cells that can bind to pathogen recognition receptors in immune and nonimmune cells. Recent studies involving animal models along with human studies have drawn great attention to the possible pathological role of DAMPs as an immune consequence of thermal injury. In this review, we outline DAMPs and their function in thermal injury, shedding light on the mechanism of sterile inflammation during tissue injury and identifying new immune targets for treating thermal injury.

Protective effects of triptolide on TLR4 mediated autoimmune and inflammatory response induced myocardial fibrosis in diabetic cardiomyopathy

ETHNOPHARMACOLOGICAL RELEVANCE

Triptolide is a most important active ingredient extracted from traditional Chinese medicine Tripterygium, which has been widely used to treat glomerulonephritis as well as immune-mediated disorders, likely for its immunosuppressive, anti-proliferative and anti-inflammatory effects.

AIM OF THE STUDY

In this study, we have investigated the potential protective effects of triptolide against diabetic cardiomyopathy (DCM) by regulating immune system, attenuating inflammatory response, thus resulting in decreased cardiac fibrosis and improved left ventricle function.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into 5 groups: normal group, diabetic group and diabetic rats treated with triptolide (50, 100, or 200μg/kg/day resp) for 8 weeks. Cardiac function was performed by echocardiography and histopathology of the hearts was examined with HE, Masson staining and scanning electron microscopy. Immune regulation mediator, macrophage infiltration, inflammatory response and cardiac fibrosis related cytokines were measured by RT-PCR, Western blot and Immunohistochemistry staining.

RESULTS

In the diabetic group, the expressions of TLR4 and NF-κB p65 were both up-regulated, which was associated with increased pro-inflammatory cytokines, coupled with cardiac fibrosis and impaired left ventricular function. Interestingly, pathological structure and function of left ventricle were both significantly improved in the triptolide treated groups. Furthermore, the immune mediator TLR4, downstream activator NF-κB p65, macrophage infiltration (CD68+), pro-inflammatory cytokines (TNF-α, IL-1β), cell adhesion molecule (VCAM-1) and chemokine (MCP-1) were significantly suppressed when treated with medium and high dosage triptolide compared with the diabetic group. Moreover, cardiac fibrosis pathway including α-SMA, TGF-β1, vimentin and collagen accumulations were observed significantly decreased in the triptolide treated groups.

CONCLUSIONS

Our data demonstrated that the protective effects of triptolide against DCM might attribute to inhibition of TLR4-induced NF-κB/IL-1β immune pathway, suppression of NF-κB/TNF-α/VCAM-1 inflammatory pathway and down-regulation of TGF-β1/α-SMA/Vimentin fibrosis pathway.

Selenium attenuates high glucose-induced ROS/TLR-4 involved apoptosis of rat cardiomyocyte

The potential mechanism of high glucose-induced cardiomyocyte apoptosis and selenium's protective effects were investigated in this study. Myocytes isolated from neonate rats were cultured in high-glucose medium (25.5 mmol/L glucose) to mimic sustained hyperglycemia. Before high-glucose incubation, myocytes were pretreated by sodium selenite solution. Cell apoptosis was evaluated by annexin V/propidium iodide (PI) staining and caspase activation. Expression of Toll-like receptor 4 (TLR-4) and myeloid differentiation factor 88 (MyD-88) was examined at both mRNA and protein levels. The intracellular reactive oxygen species (ROS) production and glutathione peroxidase (GPx) activity in myocytes were also detected. We found high glucose-induced cell apoptosis and activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling, accompanied by increased production of ROS. Selenium pretreatment attenuated apoptosis in high glucose-incubated myocytes, and mechanically, this protective effect was found to be associated with attenuating oxidative status by increasing activity of GPx, decreasing the generation of ROS, as well as inhibition of the activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling in myocytes. These results suggest that activation of TLR-4/MyD-88 signaling pathway plays an important role in high glucose-induced cardiomyocyte apoptosis. Additionally, by modulating TLR-4/MyD-88 signaling pathway, which is linked to ROS formation, selenium exerts its antioxidative and antiapoptotic effects in high glucose-incubated myocytes.

Mouse models and techniques for the isolation of the diabetic endothelium

Understanding the molecular mechanisms underlying diabetic endothelial dysfunction is necessary in order to improve the cardiovascular health of diabetic patients. Previously, we described an in vivo, murine model of insulin resistance induced by feeding a high-fat diet (HFD) whereby the endothelium may be isolated by fluorescence-activated cell sorting (FACS) based on Tie2-GFP expression and cell-surface staining. Here, we apply this model to two new strains of mice, ScN/Tie2-GFP and ApoE(−/−)/Tie2-GFP, and describe their metabolic responses and endothelial isolation. ScN/Tie2-GFP mice, which lack a functional toll-like receptor 4 (TLR4), display lower fasting glucose and insulin levels and improved glucose tolerance compared to Tie2-GFP mice, suggesting that TLR4 deficiency decreases susceptibility to the development of insulin resistance. ApoE(−/−)/Tie2-GFP mice display elevated glucose and cholesterol levels versus Tie2-GFP mice. Endothelial isolation by FACS achieves a pure population of endothelial cells that retain GFP fluorescence and endothelial functions. Transcriptional analysis of the aortic and muscle endothelium isolated from ApoE(−/−)/Tie2-GFP mice reveals a reduced endothelial response to HFD compared to Tie2-GFP mice, perhaps resulting from preexisting endothelial dysfunction in the hypercholesterolemic state. These mouse models and endothelial isolation techniques are valuable for assessing diabetic endothelial dysfunction and vascular responses in vivo.

Therapeutic role of toll-like receptor modification in cardiovascular dysfunction

Toll-like receptors (TLR) are key pattern recognition receptors in the innate immune system. The TLR-mediated immune response against pathogens is usually protective however inappropriate TLR activation may lead to excessive tissue damage. It is well recognised that TLRs respond to a variety of endogenous as well as exogenous ligands. By responding to endogenous ligands that are exposed during cellular damage, TLRs have been implicated in a range of pathological conditions associated with cardiovascular dysfunction. Increasing knowledge on the mechanisms involved in TLR signalling has encouraged the exploration of therapeutic pharmacological modulation of TLR activation in conditions such as atherosclerosis, ischaemic heart disease, heart failure and ischaemic reperfusion injury. The aim of this review is to explore the translational potentials of TLR modification in cardiovascular dysfunction, where these agents have been studied.

Enhancement of antibody-induced arthritis via Toll-like receptor 2 stimulation is regulated by granulocyte reactive oxygen species

The suppressive role of phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX2) complex-derived reactive oxygen species (ROS) in adaptive immunity-driven arthritis models is well established. In this study, we aimed to investigate the role of NOX2 complex-derived ROS in a model of innate immunity-driven arthritis and to identify the ROS-regulated innate receptors that control arthritis. We used collagen antibody-induced arthritis (CAIA), which is a T and B lymphocyte-independent model of the effector phase of arthritis and is induced by well-defined monoclonal arthritogenic antibodies and enhanced by injection of lipopolysaccharide (LPS). CAIA was induced in both wild-type and Ncf1 mutant mice that lack phagocyte oxidative burst, and stimulated with LPS and other agents to activate innate immune responses. We found that both LPS and lipomannan enhanced CAIA more potently in the presence of functional phagocyte ROS production than in its absence. The ROS-dependent enhancement of CAIA was regulated by TLR2, but not by TLR4 stimulation, and was driven by granulocytes, whereas macrophages did not contribute to the phenotype. In addition, we report that collagen-induced arthritis was not affected by the functionality of the TLR4. We report that TLR2 signaling as an important ROS-regulated proinflammatory pathway leads to severe neutrophil-dependent inflammation in murine CAIA and conclude that the TLR2 pathway is modulated by phagocyte ROS to stimulate the development of arthritis.

Early interleukin 6 production by leukocytes during ischemic acute kidney injury is regulated by TLR4

Although leukocytes infiltrate the kidney during ischemic acute kidney injury (AKI) and release interleukin 6 (IL6), their mechanism of activation is unknown. Here, we tested whether Toll-like receptor 4 (TLR4) on leukocytes mediated this activation by interacting with high-mobility group protein B1 (HMGB1) released by renal cells as a consequence of ischemic kidney injury. We constructed radiation-induced bone marrow chimeras using C3H/HeJ and C57BL/10ScNJ strains of TLR4 (-/-) mice and their respective TLR4 (+/+) wild-type counterparts and studied them at 4 h after an ischemic insult. Leukocytes adopted from TLR4 (+/+) mice infiltrated the kidneys of TLR4 (-/-) mice, and TLR4 (-/-) leukocytes infiltrated the kidneys of TLR4 (+/+) mice but caused little functional renal impairment in each case. Maximal ischemic AKI required both radiosensitive leukocytes and radioresistant renal parenchymal and endothelial cells from TLR4 (+/+) mice. Only TLR4 (+/+) leukocytes produced IL6 in vivo and in response to HMGB1 in vitro. Thus, following infiltration of the injured kidney, leukocytes produce IL6 when their TLR4 receptors interact with HMGB1 released by injured renal cells. This underscores the importance of TLR4 in the pathogenesis of ischemic AKI.

Toll-like receptor-4 mediates intestinal barrier breakdown after thermal injury

OBJECTIVE

Toll-like receptor 4 (TLR-4) activation after sterile injury leads to organ dysfunction at distant sites. We have shown previously that intestinal barrier breakdown and alteration of tight junction proteins follows thermal injury; however, the role of TLR-4 in this process remains unclear. We hypothesized that increased intestinal permeability and barrier breakdown after burns is a TLR-4 dependent process; hence, knocking down the TLR-4 gene would have a protective effect on burn-induced intestinal dysfunction.

METHODS

Male C57BL/6J (TLR-4 wild type [WT]) and C57BL/10ScN (TLR-4 knockout [KO]) mice were assigned randomly to either 30% total body surface area steam burn or sham injury. At 4 h, permeability to intraluminally administered fluorescein isothiocyanate (FITC)-dextran was assessed by measuring the fluorescence of the serum. Intestinal samples were analyzed for the presence of the tight junction protein occludin by immunoblotting and immunohistochemistry. Tumor necrosis factor (TNF)-alpha concentrations in the serum and intestines were measured by enzyme-linked immunosorbent assay at 2 h post-burn.

RESULTS

Serum concentrations of FITC-dextran were decreased in TLR-4 KO mice compared with TLR-4 WT mice after burn injury (92.0 micrograms/mL and 264.5 micrograms/mL, respectively; p < 0.05). After injury, no difference in intestinal permeability was observed between the TLR-4 KO mice and the TLR-4 WT sham-treated mice. The TLR-4 KO mice had preservation of occludin concentrations after thermal injury in both immunoblot and immunohistochemistry assays, but concentrations were decreased in TLR-4 WT animals. The serum concentrations of TNF-alpha serum were higher in TLR-4 WT burned animals than in the sham-treated mice. The TLR-4 KO animals had unmeasurable concentrations of TNF-alpha. No differences in TNF-alpha were observed in the intestinal tissue at 2 h.

CONCLUSIONS

Mice with TLR-4 KO have less intestinal permeability to FITC-dextran than do TLR-4 WT mice after burn injury as a result of alterations in the tight junction protein occludin. These findings suggest that the greater intestinal permeability and barrier breakdown after burn injury is a TLR-4-dependent process. Toll-like receptor 4 may provide a useful target for the prevention and treatment of systemic inflammatory response syndrome and multisystem organ failure after injury.

Alterations in the cardiac inflammatory response to burn trauma in mice lacking a functional Toll-like receptor 4 gene

Our group and others have previously shown that Toll-like receptor 4 (TLR-4) inactivation prevents burn-induced myocardial contractile dysfunction; however, the molecular mechanisms that are involved in this cardioprotection are not well defined. This present study examines the involvement of TLR-4 in the cardiac inflammatory response to thermal insult. C3H/HeJ (TLR-4 mutant mice) and C3H/HeN wild-type (WT) mice were subjected to either a sham burn or 40% full-thickness burn injury and were fluid resuscitated with lactated Ringer using the Parkland formula. Mice (n = 7-9 per group) were killed at 2, 4, or 24 h postsham or burn, and heart tissue was harvested. Immunoblotting was performed to evaluate phosphorylated p38 mitogen-activated protein kinase (MAPK), nuclear p50, and cytoplasmic p50. Nuclear factor-kappaB was also characterized via electrophoretic mobility shift assay. Systemic and cardiac myocyte secretion of TNF-alpha, IL-1 beta, IL-6, and IL-10 were measured by enzyme-linked immunosorbent assay. Burn injury in WT mice promoted myocardial inflammatory signaling that included increased expression of phosphorylated p38 MAPK, nuclear p50, and increased cardiac myocyte secretion of cytokines. Systemic cytokines were also increased in WT animals, although not to the extent of the myocardial cytokine expression. Toll-like receptor 4 inactivation resulted in an attenuation of several burn-induced responses, including phosphorylation of p38 MAPK, nuclear translocation of nuclear factor-kappaB, and cytokine secretion. These data suggest that burn injury initiates an inflammatory response via Toll/IL-1 signaling in the heart, which contributes to cardiac injury and contractile dysfunction.

Molecular or pharmacologic inhibition of the CD14 signaling pathway protects against burn-related myocardial inflammation and dysfunction

Signaling through toll-like receptor 4 (TLR4) plays an obligate role in burn-related myocardial dysfunction. We hypothesized that signaling through CD14, a cellular receptor for endotoxin that lacks a transmembrane domain but is coupled to TLR4, also plays a role in postburn myocardial inflammation and dysfunction. Burn covering 40% total body surface area (or sham burn for controls) was produced in wild-type (WT) and CD14 knockout (KO) as well as vehicle-treated and geldanamycin-treated WT mice (1 microg/g body weight) to inhibit CD14 signaling. Groups included (1) WT shams, (2) CD14 KO sham, (3) WT burns, (4) CD14 KO burns, (5) vehicle-treated WT shams, (6) geldanamycin-treated WT shams, (7) vehicle-treated WT burns, and (8) geldanamycin-treated WT burns. Twenty-four hours after burn, cardiac function (Langendorff) and cardiomyocyte secretion of inflammatory cytokines TNF-alpha, IL-1 beta, and IL-6 (in pg/mL; 5 x 10(4) myocytes) were studied in all groups. Relative to sham WT controls, burn trauma in increased cardiac myocyte secretion of inflammatory cytokines (TNF-alpha, IL-1 beta, and IL-6 rose from 59 +/- 10 to 171 +/- 8; 6 +/- 0.2 to 78 +/- 1; and 88 +/- 3 to 170 +/- 12 pg/mL, respectively; P < 0.05) and produced robust cardiac contractile dysfunction (left ventricular pressure and +dP/dt fell from 105 +/- 4 to 73 +/- 5 mmHg and 2,400 +/- 73 to 1,803 +/- 90 mmHg/s; P < 0.05). Inability to signal through the CD14/TLR4 pathway (induced by CD14/KO or inhibition of CD14 expression by administration of geldanamycin) attenuated TNF-alpha, IL-1 beta, and IL-6 production in response to burn injury and improved postburn myocardial contractile function. Our data suggest that signaling through the CD14 pathway plays an obligate role in cardiac inflammation/dysfunction which occurs after major burn injury.

Evidence for the pivotal role of endogenous toll-like receptor 4 ligands in liver ischemia and reperfusion injury

BACKGROUND

Although toll-like receptor 4 (TLR4) activation has been demonstrated to play a key role in the induction of intrahepatic inflammation, leading to hepatocellular damage in liver ischemia/reperfusion injury (IRI), the nature of TLR4 ligands generated during tissue injury remains to be elucidated. We hypothesized that endogenous TLR4 ligands, rather than endotoxin (lipopolysaccharide [LPS]), are instrumental in the activation of liver TLR4 leading to local inflammation response that culminates in ultimate organ IRI.

METHODS AND RESULTS

By using the LPS-neutralizing agent, recombinant bactericidal/permeability-increasing protein, we showed that the endotoxin blockade failed to protect mouse livers from warm IRI, as assessed by serum alanine aminotransferase levels, intrahepatic inflammatory gene induction profile, and liver pathology. The recombinant bactericidal/permeability-increasing protein did not cause any hepatocytoxicity by itself if injected into normal naive mice. Furthermore, we demonstrated that liver perfusates, generated by isolated liver perfusion system, contained LPS-independent, heat-sensitive protein molecules that activated macrophages to produce tumor necrosis factor (TNF)-alpha through TLR4 but not TLR2 pathway.

CONCLUSION

This study provides a definitive evidence that endogenous TLR4 ligands are critical in the pathogenesis of liver IRI.

Toll-like receptor 4 contributes to microvascular inflammation and barrier dysfunction in thermal injury

Systemic and microvascular inflammation plays a key role in the development of multiple organ failure after infection, sepsis, and traumatic injury. Toll-like receptors (TLRs) regulate host responses to pathogens and sterile, injury-associated inflammatory responses. We investigated whether TLR-4 contributes to microvascular dysfunction during thermal injury in vivo in anesthetized wild-type or TLR-4 (-/-) mice receiving either a 25% total body surface area full-thickness scald burn or sham treatment on the dorsal skin. Using intravital microscopy, we assessed the hemodynamics and leukocyte dynamics in the mesenteric microvasculature as representative of the splanchnic microcirculation at a site remote from the burn wound. The transvascular flux of fluorescein isothiocyanate-albumin across mesenteric venules was measured as an indicator of microvascular permeability. Furthermore, cultured microvascular endothelial cell models were used to evaluate the endothelial-specific mechanisms involved in TLR-4-mediated barrier dysfunction. The results showed significantly elevated microvascular permeability in wild-type mice after burn, whereas this response was markedly attenuated in TLR-4 (-/-) mice. Burn injury also increased leukocyte adhesion in mesenteric venules of wild-type mice, and a blunted leukocyte response was seen in the TLR-4 mice. Treatment of endothelial cell monolayers with burn plasma induced a rapid reduction in the transendothelial electrical resistance measured by electric cell-substrate impedance sensing, indicative of endothelial cell-cell adhesive barrier dysfunction. Reducing expression of TLR-4 with siRNA treatment attenuated this response. Taken together, these data indicate that TLR-4 plays an important role in microvascular leakage and leukocyte adhesion under the inflammatory condition associated with nonseptic thermal injury.

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

Gram-negative bacteria (GNB) and their endotoxin present a constant environmental challenge. Endotoxins can potently signal mobilization of host defenses against invading GNB but also potentially induce severe pathophysiology, necessitating controlled initiation and resolution of endotoxin-induced inflammation to maintain host integrity. The bactericidal/permeability-increasing protein (BPI) is a pluripotent protein expressed, in humans, mainly neutrophils. BPI exhibits strong antimicrobial activity against GNB and potent endotoxin-neutralizing activity. BPI mobilized with neutrophils in response to invading GNB can promote intracellular and extracellular bacterial killing, endotoxin neutralization and clearance, and delivery of GNB outer membrane antigens to dendritic cells. Tissue expression by dermal fibroblasts and epithelia could further amplify local levels of BPI and local interaction with GNB and endotoxin, helping to constrain local tissue infection and inflammation and prevent systemic infection and systemic inflammation. This review article focuses on the structural and functional properties of BPI with respect to its contribution to host defense during GNB infections and endotoxin-induced inflammation and the genesis of autoantibodies against BPI that can blunt BPI activity and potentially contribute to chronic inflammatory disease.

Bactericidal/permeability increasing protein attenuates the myocardial inflammation/dysfunction that occurs with burn complicated by subsequent infection

Intubation and mechanical ventilation after burn contribute to pneumonia-related infection. Although postburn presence or absence of endotoxin has been described, inactivation of Toll-like receptor 4 signaling has been shown to improve postburn organ function, suggesting that LPS participates in burn-related susceptibility to infection. We hypothesized that bactericidal/permeability-increasing protein (rBPI) given postburn would attenuate myocardial inflammation/dysfunction associated with postburn septic challenge given 7 days postburn. Rats were given burn over 40% total body surface area, lactated Ringer 4 ml.kg(-1).% burn(-1); burns received either vehicle or rBPI, 1 mg.kg(-1).h(-1) for 48 h postburn. Postburn day 7, subgroups of burns and shams were given intratracheal Klebsiella pneumoniae, 4 x 10(6) CFU to produce burn complicated by sepsis; additional sham and burn subgroups received intratracheal vehicle to produce sham sepsis. Vehicle-treated groups: 1) sham burn + sham sepsis 2) sham burn + sepsis, 3) burn + sham sepsis, 4) burn + sepsis. rBPI-treated groups: 5) sham burn + sham sepsis, 6) sham burn + sepsis, 7) burn + sham sepsis, 8) burn + sepsis. Cardiomyocyte cytokine secretion and myocardial function were studied 24 h after septic challenge, postburn day 8. Pneumonia-related infection 8 days after vehicle-treated burn produced myocyte cytokine secretion (pg/ml), indicated by increased myocyte TNF-alpha, 549 +/- 46; IL-1beta, 50 +/- 8; IL-6, 286 +/- 3 levels compared with levels in sham myocytes (TNF-alpha, 88 +/- 11; IL-1beta, 7 +/- 1; IL-6, 74 +/- 10; P < 0.05). Contractile dysfunction was evident from lower left ventricular pressure +/-dP/dt values in this group compared with sham. rBPI attenuated myocyte cytokine responses to septic challenge and improved contractile function, suggesting that burn-related mobilization of microbial-like products contribute to postburn susceptibility to infection.

Caspase inhibition reduces cardiac myocyte dyshomeostasis and improves cardiac contractile function after major burn injury

In the heart, thermal injury activates a group of intracellular cysteine proteases known as caspases, which have been suggested to contribute to myocyte inflammation and dyshomeostasis. In this study, Sprague-Dawley rats were given either a third-degree burn over 40% total body surface area plus conventional fluid resuscitation or sham burn injury. Experimental groups included 1) sham burn given vehicle, 400 microl DMSO; 2) sham burn given Q-VD-OPh (6 mg/kg), a highly specific and stable caspase inhibitor, 24 and 1 h prior to sham burn; 3) burn given vehicle, DMSO as above; 4) burn given Q-VD-OPh (6 mg/kg) 24 and 1 h prior to burn. Twenty-four hours postburn, hearts were harvested and studied with regard to myocardial intracellular sodium concentration, intracellular pH, ATP, and phosphocreatine (23Na/31P nuclear magnetic resonance); myocardial caspase-1, -3,and -8 expression; myocyte Na+ (fluorescent indicator, sodium-binding benzofurzan isophthalate); myocyte secretion of TNF-alpha, IL-1beta, IL-6, and IL-10; and myocardial performance (Langendorff). Burn injury treated with vehicle alone produced increased myocardial expression of caspase-1, -3, and -8, myocyte Na+ loading, cytokine secretion, and myocardial contractile depression; cellular pH, ATP, and phosphocreatine were stable. Q-VD-OPh treatment in burned rats attenuated myocardial caspase expression, prevented burn-related myocardial Na+ loading, attenuated myocyte cytokine responses, and improved myocardial contraction and relaxation. The present data suggest that signaling through myocardial caspases plays a pivotal role in burn-related myocyte sodium dyshomeostasis and myocyte inflammation, perhaps contributing to burn-related contractile dysfunction.

The Impact on Coronary Artery Disease of Common Polymorphisms Known to Modulate Responses to Pathogens

There are two distinct models to explain how genetic variants contributing to cardiovascular disease may have arisen. Firstly, variants may result from random, initially neutral, mutations whose effects are largely revealed in post-reproductive individuals in industrialized societies. Alternatively, the introduced variants may confer an adaptive advantage in certain circumstances. Resistance to pathogens is one of the strongest selection pressures on human proteins. To determine whether this evolutionary pressure has made a large contribution to heart disease we tested whether seventeen polymorphisms in fourteen innate-immunity genes, with documented evidence of modulating response to pathogens, had an impact on heart disease. Genotyping was performed in 1,598 CAD subjects (ACS or stable angina) and 332 controls. The TLR4 399Ile allele had the greatest impact on ACS risk (uncorrected p = 0.006); however there was no evidence overall that the resistance alleles cumulatively influenced the risk of ACS compared to controls or stable angina patients (p = 0.12, and p = 0.40, respectively). We did note a significant interaction between age at onset of disease and combined resistance allele carriership when the ACS and non-thrombotic, stable angina groups were compared (p = 0.04, 16 d.f.). This suggests that innate immunity factors could have a greater impact on thrombus formation among younger CAD patients.

EMERGING PARADIGM

The systemic inflammatory response syndrome initiated by infection shares many features in common with the trauma-induced systemic response. The toll-like receptors (TLRs) stand at the interface of innate immune activation in the settings of both infection and sterile injury by responding to a variety of microbial and endogenous ligands alike. Recently, a body of literature has evolved describing a key role for TLRs in acute injury using rodent models of hemorrhagic shock, ischemia and reperfusion, tissue trauma and wound repair, and various toxic exposures. This review will detail the observations implicating a TLR family member, TLR4, as a key component of the initial injury response.

Selective decontamination of the digestive tract attenuated the myocardial inflammation and dysfunction that occur with burn injury

This study examined the effects of oral antibiotics to selectively decontaminate the digestive tract (SDD) on postburn myocardial signaling, inflammation, and function. We hypothesized that antibiotic therapy to eliminate pathogens from the gastrointestinal (GI) tract would reduce myocardial inflammatory responses and improve postburn myocardial performance. Sprague-Dawley rats received polymyxin E (15 mg), tobramycin (6 mg), and 5-flucytosin (100 mg) by oral gavage twice daily for 3 days preburn and 24 h postburn. Experimental groups included 1) sham burn given vehicle (3 ml water), 2) sham plus SDD, 3) burn over 40% total body surface area (TBSA) plus SDD, and 4) burn over 40% TBSA given vehicle. All burns received lactated Ringer solution (4 mg·kg−1·%burn−1); myocardial signaling (PKCε/p38 MAPK/NF-κB) was studied 2, 4, and 24 h postburn; and cytokine secretion (systemic and myocyte secreted cytokines, ELISA) and cardiac function were examined 24 h postburn. Vehicle-treated burn injury increased myocardial PKCε/p38 MAPK expression, promoted NF-κB nuclear translocation, promoted TNF-α, IL-1β, IL-6, and IL-10 secretion, and impaired myocardial function. SDD attenuated burn-related proinflammatory myocardial signaling, cytokine secretion, and myocardial contractile defects. Our data suggest that burn-related loss of GI barrier function and translocation of microbial products serve as upstream mediators of postburn myocardial inflammatory signaling and dysfunction.

Macrophage migration inhibitory factor mediates late cardiac dysfunction after burn injury

We have recently demonstrated that macrophage migration inhibitory factor (MIF) is a myocardial depressant protein and that MIF mediates late, prolonged cardiac dysfunction after endotoxin challenge in mice. Because many factors, including endotoxin, have been implicated in the pathogenesis of cardiac dysfunction after burn injury, we tested the hypothesis that MIF might also be the mediator of prolonged cardiac dysfunction in this model. At 4 h after 40% total body surface area burn in anesthetized mice, serum MIF levels increased significantly compared with baseline (2.2-fold). This increase was accompanied by a significant decrease in cardiac tissue MIF levels (2.1-fold decrease compared with controls). This pattern was consistent with MIF release from preformed cytoplasmic stores in the heart and other organs. To determine whether MIF mediates cardiac dysfunction after burn injury, mice were pretreated with anti-MIF neutralizing monoclonal antibodies or isotype control antibodies. Beginning 4 h after burn injury (and continuing through 48 h), burned mice demonstrated a significantly depressed left ventricular shortening fraction of 38.6 +/- 1.8%, compared with the normal controls (56.0 +/- 2.6%). Mice treated with anti-MIF displayed an initial depression of cardiac function similar to nontreated animals but then showed rapid restoration of cardiac function with complete recovery by 24 h, which persisted for the duration of the protocol. This study is the first to demonstrate that MIF mediates late, prolonged cardiac dysfunction after burn injury and suggests that MIF blockade should be considered a therapeutic target for the treatment of burn injury.

IRAK1 deletion disrupts cardiac Toll/IL-1 signaling and protects against contractile dysfunction

Myocardial contractile dysfunction accompanies both systemic and cardiac insults. Septic shock and burn trauma can lead to reversible contractile deficits, whereas ischemia and direct inflammation of the heart can precipitate transient or permanent impairments in contractility. Many of the insults that trigger contractile dysfunction also activate the innate immune system. Activation of the innate immune response to infection is coordinated by the conserved Toll/interleukin-1 (IL-1) signal transduction pathway. Interestingly, components of this pathway are also expressed in normal and failing hearts, although their function is unknown. The hypotheses that Toll/IL-1 signaling occurs in the heart and that intact pathway function is required for contractile dysfunction after different insults were tested. Results from these experiments demonstrate that lipopolysaccharides (LPS) activate Toll/IL-1 signaling and IL-1 receptor-associated kinase-1 (IRAK1), a critical pathway intermediate in the heart, indicating that the function of this pathway is not limited to immune system tissues. Moreover, hearts lacking IRAK1 exhibit impaired LPS-triggered downstream signal transduction. Hearts from IRAK1-deficient mice also resist acute LPS-induced contractile dysfunction. Finally, IRAK1 inactivation enhances survival of transgenic mice that develop severe myocarditis and lethal heart failure. Thus the Toll/IL-1 pathway is active in myocardial tissue and interference with pathway function, through IRAK1 inactivation, may represent a novel strategy to protect against cardiac contractile dysfunction.