Reduced myocardial ischemia-reperfusion injury in toll-like receptor 4-deficient mice

Toll-like receptor 4 modulates myocardial ischaemia-reperfusion injury: Role of matrix metalloproteinases

Toll-like receptor 4 (TLR4) mediates innate immune responses following endotoxemia and myocardial ischaemia-reperfusion (I/R) injury. Pre-treatment with the major TLR4 ligand lipopolysaccharide (LPS) reduces infarct size. Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) play a crucial role in endotoxemia possibly also determining I/R injury.

AIMS

We investigated the influence of TLR4 on infarct size and assessed the influence of MMP and TIMP regulation on I/R injury.

METHODS

Left anterior descending artery (LAD) occlusion was performed on wild-type (C3H/HeN) and TLR4-deficient (C3H/HeJ) mice. Animals were stimulated with LPS (1 mg/kg) or PBS 16 h ahead of 60 min LAD ligation. After 24 h of reperfusion, triphenyltetrazolium chloride staining was performed and infarct size was measured by planimetry. MMP- and TIMP-mRNA expression were determined by RPA after 3 h of reperfusion. MMP zymographic activity was monitored 6 h after occlusion.

RESULTS

TLR4-deficient mice and LPS-treated wild-type mice showed significantly reduced infarct areas. LPS-stimulation significantly increased the overall MMP/TIMP mRNA expression ratio due to elevated MMP-3, -8, -9, and TIMP-1 in wild-type mice. I/R overall reduced the MMP/TIMP ratio due to increased MMP-1, TIMP-1, and -3 mRNA expression.

CONCLUSIONS

LPS pre-treatment and TLR4-deficiency led to a decreased infarct size. However, infarct area and MMP/TIMP ratio were not correlated. This means that in TLR4-deficient mice MMP/TIMP ratios are not determining the infarct size.

Elevated circulating levels of heat shock protein 70 are related to systemic inflammatory reaction through monocyte Toll signal in patients with heart failure after acute myocardial infarction

BACKGROUND

Recent studies have shown that heat shock protein (HSP) 70 may serve as a "damage signal" to the immune system and could be the endogenous ligand for Toll-like receptor (TLR) 4 mediating synthesis of inflammatory cytokines.

AIMS

To explore the relationship between circulating HSP70 levels and activation of monocyte TLR4 and myocardial damage after AMI.

METHODS AND RESULTS

This study examined circulating HSP70 and monocyte TLR4 levels in 52 patients with AMI and 20 controls, and analyzed ex vivo inflammatory cytokine productions using HSP70-stimulated monocytes. Circulating HSP70 levels were higher in AMI patients on day 1 after onset than in controls and remained elevated in AMI patients 14 days after onset. HSP70 levels were positively correlated with monocyte TLR4, plasma interleukin-6 and tumor necrosis factor-alpha levels in AMI patients. HSP70 levels 14 days after onset were higher in AMI patients with heart failure (n=15) than in those without heart failure. In our in vitro study, HSP70-stimulated monocytes resulted in dose-dependent TLR4 expression and release of inflammatory cytokines. TLR4 antibody inhibited inflammatory cytokines release.

CONCLUSIONS

Elevated circulating levels of HSP70 may be involved in TLR4 signal-mediated immune response and the progression of heart failure after AMI.

MyD88 and NOS2 are essential for toll-like receptor 4-mediated survival effect in cardiomyocytes

Innate immune system such as Toll-like receptor 4 (TLR4) represents the first line of defense against infection. In addition to its pivotal role in host immunity, recent studies have suggested that TLR4 may play a broader role in mediating tissue inflammation and cell survival in response to noninfectious injury. We and other investigators have reported that cardiac TLR4 signaling is dynamically modulated in ischemic myocardium and that activation of TLR4 confers a survival benefit in the heart and in isolated cardiomyocytes. However, the signaling pathways leading to these effects are not completely understood. Here, we investigate the role of MyD88, an adaptor protein of TLR4 signaling, and inducible nitric oxide synthase (NOS2) in mediating TLR4-induced cardiomyocyte survival in an in vitro model of apoptosis. Serum deprivation induced a significant increase in the number of apoptotic cardiomyocytes as demonstrated by transferase-mediated dUTP nick-end labeling (TUNEL) assay, nuclear morphology, DNA laddering, and DNA-histone ELISA. Lipopolysaccharide (LPS), a TLR4 agonist, activated TLR4 signaling and led to significant reduction in apoptotic cardiomyocytes and improved cellular function of surviving cardiomyocytes with enhanced Ca(2+) transients and cell shortening. We found that both TLR4 and MyD88 are required for the LPS-induced beneficial effects as demonstrated by improved survival and function in wild-type but not in TLR4(-/-) or MyD88(-/-) cardiomyocytes. Moreover, genetic deletion or pharmacological inhibition of NOS2 abolished survival and functional rescue of cardiomyocytes treated with LPS. Taken together, these data suggest that TLR4 protects cardiomyocytes from stress-induced injury through MyD88- and NOS2-dependent mechanisms.

The Role of Toll-like Receptors in Solid Organ Transplantation

Toll-like receptors (TLR) are critical sentinels of the host innate immune system. Prior evidence has clearly demonstrated that these receptors are essential to immune recognition of invading pathogens. However, there is emerging evidence that TLR signaling participates in inflammation that is not driven by microorganisms. In the setting of solid organ transplantation, there is accumulating evidence, both in experimental and clinical studies, that TLR signaling is involved in the immune recognition of allografts. Further investigation of how innate immunity impacts solid organ transplantation will likely lead to improved therapeutics for transplant recipients.

Toll-like receptor-4 signaling mediates hepatic injury and systemic inflammation in hemorrhagic shock

BACKGROUND

Hemorrhagic shock and resuscitation (HS/R) activates inflammatory pathways leading to organ injury after trauma. Toll-like receptors (TLRs), such as TLR4, are required for activation of proinflammatory cellular signaling pathways in response to microbial products, but can also recognize endogenous molecules released from damaged tissues. Using mouse strains deficient in TLR4 protein or signaling, we hypothesized that TLR4 would be important for development of systemic inflammation and hepatic injury after HS/R. We sought to determine the role of lipolysaccharide through use of CD14-/- mice.

STUDY DESIGN

TLR4-mutant (C[3H]/HeJ), TLR4-deficient (TLR4-/-), CD14-/-, TLR2-/- mice and wild-type (WT) controls were subjected to HS/R or sham procedure (Sham). At 6.5 hours, mice were euthanized for determination of serum interleukin (IL)-6, IL-10, and alanine aminotransferase concentrations. Hepatic nuclear factor-kappaB DNA-binding (electrophoretic mobility shift assay) and tumor necrosis factor, IL-10, and inducible nitric oxide synthase mRNA expression (semiquantitative reverse transcriptase-polymerase chain reaction) were determined.

RESULTS

Relative to sham, TLR4-competent (C[3H]/HeOuJ) mice exhibited a significant increase in serum alanine aminotransferase, IL-6, and IL-10 after HS/R (p < 0.05). TLR4-mutant (C[3H]/HeJ) mice were protected from HS/R-induced hepatocellular injury and had lower circulating IL-6 and IL-10 levels than WT (p < 0.05). Similarly, TLR4-/- mice had lower circulating IL-6 and IL-10 levels than WT after HS/R (p < 0.05). Hepatic nuclear factor-kappaB activation and tumor necrosis factor, IL-10, and inducible nitric oxide synthase mRNA expression were lower in TLR4-mutant compared with TLR4-competent mice after HS/R. In contrast, serum ALT concentrations were comparable between CD14-/- and TLR2-/- mice and their WT counterparts after HS/R.

CONCLUSIONS

These results suggest that TLR4, but not TLR2, signaling is required for initiation of the systemic inflammatory response and development of hepatocellular injury after HS/R. Lack of involvement of CD14 argues for a lipolysaccharide-independent role for TLR4 in this process.

Hepatic ischemia/reperfusion injury involves functional TLR4 signaling in nonparenchymal cells

Endogenous ligands from damaged cells, so-called damage-associated molecular pattern molecules, can activate innate immunity via TLR4 signaling. Hepatic warm ischemia and reperfusion (I/R) injury and inflammation is largely TLR4 dependent. We produced TLR4 chimeric mice to assess whether the TLR4-dependent injury required TLR4 expression on liver parenchymal or nonparenchymal cells. Chimeric mice were produced by adoptive transfer of donor bone marrow cells into irradiated recipient animals using reciprocal combinations of TLR4 wild-type (WT; C3H/HeOuj) and TLR4 mutant (C3H/HeJ) mouse bone marrow. Wild-type chimeric mice bearing TLR4 mutant hemopoietic cells and TLR4 mutant mice transplanted with their own bone marrow-derived cells were protected from hepatic I/R and exhibited decreased JNK and NF-kappaB activation compared with WT chimeric mice transplanted with their own bone marrow. In contrast, TLR4 mutant mice transplanted with TLR4 WT bone marrow were not protected from liver I/R and demonstrated pronounced increases in JNK and NF-kappaB activation when compared with autochthonous transplanted mutant mice. In addition, depletion of phagocytes taking up gadolinium chloride failed to provide any additional protection to TLR4 mutant mice, but substantially reduced damage in WT mice after hepatic I/R. Together, these results demonstrate that TLR4 engagement on actively phagocytic nonparenchymal cells such as Kupffer cells is required for warm I/R-induced injury and inflammation in the liver.

PROTECTING THE PUMP: Controlling Myocardial Inflammatory Responses

Because of the anatomy, function, and nonregenerative nature of the myocardium, inflammation in this tissue is not well tolerated. Nevertheless, various diseases of the heart are characterized by inflammatory responses involving the effector mechanisms of innate and adaptive (lymphocyte-dependent) immunity. The innate immune response to ischemia-reperfusion injury is, by far, the most common cause of myocardial inflammation. Innate responses may have beneficial influences that preserve myocardial function in the short term but may be maladaptive in chronic states. Adaptive responses in the myocardium occur with infection or loss of tolerance, and lead to myocarditis. Given the narrow margin for benefit of cardiac inflammation, special regulatory mechanisms likely raise the threshold, compared to other tissues, for the induction and persistence of adaptive immune responses. These mechanisms include strong central and peripheral T cell tolerance to heart antigens and induction of anti-inflammatory feedback mechanisms involving cytokines such as interferon-gamma.

Up-regulation of cell cycle regulatory genes after renal ischemia/reperfusion: differential expression of p16(INK4a), p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor genes depending on reperfusion time

The aim of this study was to evaluate the influence of renal ischemia, cold preservation and reperfusion on the degree of renal kidney senescence. An experimental model of ex vivo renal hemoperfusion was used. Expression of p16(INK4a), p21(WAF1/CIP1) and p27(Kip1) cyclin-dependent kinase inhibitor genes (CDKIGs) was studied immunohistochemically in kidney biopsy samples at baseline and different time points after reperfusion. All three markers were up-regulated in kidney tissue after the reperfusion; however, their activation in different renal cells varied according to the reperfusion time. Expression of p16 was significantly increased in tubular cells at 180 min of reperfusion when compared with the baseline. Activation of p27 was detected in glomerular cells at 15 min and was significantly higher at 60, 120 and 180 min of reperfusion. The marker started increasing in tubular cells at 15 min and was elevated at every time point afterwards. p21 was significantly over-expressed in all renal cells after the reperfusion. It has been shown by the results of the current study that renal ischemia/reperfusion is associated with over-expression of CDKIGs indicating on substantial DNA damage and/or accelerated tissue senescence. For the first time it has been shown that tissue expression of CDKIGs is positively related with the reperfusion time.

Blocking the MyD88-dependent pathway protects the myocardium from ischemia/reperfusion injury in rat hearts

We examined whether blocking the MyD88 mediated pathway could protect myocardium from ischemia/reperfusion (I/R) injury by transfecting Ad5-dnMyD88 into the myocardium of rats (n=8) 3 days before the hearts were subjected to ischemia (45min) and reperfusion (4h). Ad5-GFP served as control (n=8). One group of rats was (n=8) subjected to I/R without transfection. Transfection of Ad5-dnMyD88 significantly reduced infarct size by 53.6% compared with the I/R group (15.1+/-3.02 vs 32.5+/-2.59) while transfection of Ad5-GFP did not affect I/R induced myocardial injury (35.4+/-2.59 vs 32.5+/-2.59). Transfection of Ad5-dnMyD88 significantly inhibited I/R-enhanced NFkappaB activity by 50% and increased the levels of phospho-Akt by 35.6% and BCL-2 by 81%, respectively. Cardiac myocyte apoptosis after I/R was significantly reduced by 59% in the Ad5-dnMyD88 group. The results demonstrate that both inhibition of the NFkappaB activation pathway and activation of the Akt signaling pathway may be responsible for the protective effect of transfection of dominant negative MyD88.

Role of Toll-Like Receptor–Driven Innate Immunity in Thoracic Organ Transplantation

Innate immunity represents the first line of defense against microbial invasion. Recent studies have determined that a group of germline-encoded receptors, termed Toll-like receptors (TLRs), are critical for recognizing foreign motifs on microbial organisms and initiating innate responses. An exciting area of research has recently linked activation of TLRs on antigen-presenting cells (APCs) to effective antigen presentation and activation of naive T cells. Most studies have shown that TLR-dependent immune function leads to T-helper 1 (TH1) immunity, although evidence also supports that TH2 immune responses may be initiated by TLR signaling in certain contexts. In either case, innate immune signaling via TLRs leads to a productive adaptive immune response. In contrast to studies in purely infectious models, emerging data from experimental and clinical studies have provided evidence that TLR immune function is important in acute allograft rejection. Specifically, MyD88, an important TLR signal adaptor, was found to be critical for the rejection of minor-mismatched skin allografts, and important for alloimmune priming and TH1 immunity against fully allogeneic skin grafts. Furthermore, a clinical study has shown that recipients with TLR 4 polymorphisms associated with endotoxin hyporesponsiveness manifest reduce acute lung allograft rejection. Collectively, these studies demonstrate that innate immunity is important for alloimmunity. Future therapeutic modalities that target innate rather than adaptive immune mechanisms represent a promising avenue for future studies in thoracic organ transplantation.

Toll-like receptors, endogenous ligands, and systemic autoimmune disease

The critical role of Toll-like receptors (TLRs) as mediators of pathogen recognition by the innate immune system is now firmly established. Such recognition results in the initiation of an inflammatory immune response and subsequent instruction of the adaptive immune system, both of which are designed to rid the host of the invading pathogen. More controversial is the potential role of TLRs in the recognition of endogenous ligands and what effect this might have on the consequent development of autoimmune or other chronic sterile inflammatory disorders. An increasing number of studies implicate TLRs as being involved in the immune response to self-molecules that have in some way been altered from their native state or accumulate in non-physiologic sites or amounts, although questions have been raised about possible contaminants in certain of these studies. In this review, we discuss the evidence for endogenous ligand-TLR interactions with particular emphasis on mammalian chromatin, systemic lupus erythematosus, and atherosclerosis. Overall, the data support the general concept of a role for TLRs in the recognition of endogenous ligands. However, the precise details of the interactions and the extent to which they may contribute to the pathogenesis of human disease remain to be clarified.

Toll-like receptor and heme oxygenase-1 signaling in hepatic ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) represents the major problem in clinical liver transplantation. We have shown that toll-like receptor 4 (TLR4) signaling is specifically required in initiating antigen-independent IRI leading to liver inflammation, whereas local induction of anti-oxidant heme oxygenase-1 (HO-1) is cytoprotective. This study analyzes in vivo interactions between HO-1 and sentinel TLR system in the pathophysiology of liver IRI. Using a 90-min lobar warm ischemia model, wild type (WT), TLR4 KO/mutant and TLR2 KO mice were first assessed for the severity of hepatocellular damage at 6 h postreperfusion. Unlike in WT or TLR2-deficient mice, disruption/absence of TLR4 pathway reduced IRI, as manifested by liver function (serum alanine aminotransferase levels), histology (Suzuki's scores), neutrophil infiltration (myeloperoxidase activity) and local/systemic TNF-alpha production (mRNA/protein levels). Moreover, defective TLR4 but not TLR2 signaling increased mRNA/protein HO-1 expression. In contrast, tin protoporphyrin-mediated HO-1 inhibition restored hepatic damage in otherwise IRI-resistant TLR4 mutant/KO mice. CoPP-induced HO-1 overexpression ameliorated hepatic damage in IRI-susceptible TLR2 KO mice, comparable with WT controls, and concomitantly diminished TLR4 levels. In conclusion, this study highlights the importance of cross talk between HO-1 and TLR system in the mechanism of hepatic IRI. Hepatic IRI represents a case for innate immunity in which HO-1 modulates proinflammatory responses that are triggered via TLR4 signaling, a putative HO-1 repressor.

Activated toll-like receptor 4 in monocytes is associated with heart failure after acute myocardial infarction

Peripheral monocytosis may affect the development of heart failure (HF) after acute myocardial infarction (AMI). Activated toll-like receptor (TLR) 4 in monocytes plays an important role in the synthesis of proinflammatory cytokines. We examined TLR4 expression in monocytes, which may be a possible source of proinflammatory cytokines in AMI. Sixty-five patients with AMI and 20 healthy subjects (HS) were studied. Monocytes were isolated from peripheral blood on days 1 and 14 after the onset of AMI. TLR4 levels in monocytes were measured using real-time RT-PCR and flow cytometry. Generation capacity was evaluated by TLR4 levels and cytokine concentrations in the culture medium with lipopolysaccharide (LPS) stimulation. On day 1 after onset, baseline levels of TLR4 and plasma proinflammatory cytokines, notably IL-6 and TNF-alpha, were higher in AMI patients than in HS. These levels remained elevated in AMI patients 14 days after onset. Generation capacities of TLR4 and proinflammatory cytokines (IL-2, IL-6, IL-8, IL-10, GM-CSF and TNF-alpha) were increased in AMI patients compared to HS. LPS-stimulated TLR4 levels were positively correlated with IL-6 and TNF-alpha levels in AMI patients. Baseline TLR4 levels and plasma proinflammatory cytokine (IL-6, GM-CSF and TNF-alpha) levels were higher in AMI patients with HF (n = 22) than in those without HF. Generation capacities of TLR4 and proinflammatory cytokines (IL-6, GM-CSF and TNF-alpha) were greater in AMI patients with HF than in those without HF. Activation of TLR4 through a myocytic inflammatory reaction is associated with HF after AMI. These observations suggest that TLR4 signaling in monocytes may play a role in the development of HF after AMI.

Dissection of Systems, Cell Populations and Molecules

This paper summarizes studies on antibody formation in the bone marrow and the suppressive effects of intravenous immunization with allogeneic blood cells on T-cell function in mice. The latter studies were extended by employing the limiting dilution culture system developed in Ivan Lefkovits' laboratory and implemented in collaboration with Lucien Aarden. Thereby, the functional data were complemented with frequencies of alloantigen-activated helper (Th) and suppressor T cells after intravenous alloimmunization. These results led the Rotterdam group to studies on the prevention of rejection of the foetal 'allograft'. Th cells are central in foetal allograft rejection and pregnancy success. Characteristic for human pregnancy is the production of the glycoprotein chorionic gonadotropin (hCG) hormone. The in vivo liberated peptide fragments originating from nicking of the sequence MTRVLQGVLPALPQ in the beta-chain of hCG were considered for their immunoregulating capacity related to pregnancy success. These peptides - prepared synthetically - (MTR, MTRV, LQG, LQGV, VLPALP and others) indeed showed a remarkable spectrum of biological effects (e.g. modulation of angiogenesis, inhibition of septic shock syndrome, prevention of diabetes and reduction of ischaemia-reperfusion damage). The paper interprets and generalizes these findings and projects them into various research directions, especially towards the proteomics framework studies built up in Ivan Lefkovits' laboratory in the nineties. During the time period, when Ivan spent a mini-sabbatical in Rotterdam (months after closing down the BII) more detailed discussions were intiated. This paper is meant to keep the discussions between the involved research groups going on.

Innate immunity and organ transplantation: the potential role of toll-like receptors

Traditionally, the recognition and tolerance of transplanted grafts has been considered to be within the realm of the adaptive immune system. Innate immunity, on the other hand, as the first line of host defense, plays a role in fighting against invading microorganisms. Recently, with the discovery of the Toll-like receptors (TLRs), the role of innate immune responses in the control of adaptive immunity has become a new area of interest. Emerging evidence suggests that in addition to responding to pathogen-associated molecular patterns of microorganisms, TLRs can be activated by endogenous ligands, expressed by mammalian cells. These 'danger signals' may participate in ischemia-reperfusion related organ damage and subsequently influence function and survival of transplanted grafts. Furthermore, it has been suggested that adaptive immune responses can enhance the acute inflammatory responses controlled by innate immunity in organ transplantation. This review addresses the potential involvement of TLRs in different stages of organ transplantation. Intriguing and controversial findings are presented and discussed in order to stimulate more attention to this emerging and potentially important area of research in organ transplantation.

The role of postischemic reperfusion injury and other nonantigen-dependent inflammatory pathways in transplantation

The Injury Hypothesis, first published in 1994 and modified several times between 1996 and 2002, holds that the reactive oxygen species-mediated reperfusion injury to allografts initiates and induces the alloimmune response and contributes to alloatherogenesis. Recent experimental and clinical evidence in support of the concept is presented suggesting that (1) reactive oxygen species-mediated allograft injury activates the innate immune system of the donor and recipient; (2) injury-induced putative endogenous ligands of Toll-like receptors (TLRs) of host origin such as heat shock proteins interact with and activate TLR4-bearing dendritic cells that mature and induce the adaptive alloimmune response (acute rejection), and interact with and activate TLR4-bearing vascular cells contributing to the development of alloatherosclerosis (chronic rejection); and (3) TLR4-triggered signaling, involved in the establishment of a reperfusion injury, seems to use myeloid differentiation marker 88-independent, Toll/interleukin-1 receptor domain containing adaptor inducing interferon-beta-dependent pathways that are associated with the maturation of dendritic cells and induction of interferon-inducible genes.

Lipopolysaccharide improves cardiomyocyte survival and function after serum deprivation

Toll-like receptor-4 (TLR4) and its signaling molecule interleukin-1 receptor-associated kinase (IRAK-1) play an important role in host defense and tissue inflammation. Intriguingly, systemic administration of lipopolysaccharide (LPS), the agonist for TLR4, confers a cardio-protective effect against ischemic injury. However, the mechanisms leading to the cardiac protection remain largely unknown. The present study was designed to investigate the role of TLR4 activation by LPS in protecting cardiomyocytes (CM) against apoptosis in an in vitro model of ischemia and to explore the downstream mechanisms leading to the protective effect. Incubation with LPS led to activation of IRAK-1 and protected CMs against serum deprivation (SD)-induced apoptosis as demonstrated by DNA laddering, histone-DNA fragment enzyme-linked immunosorbent assay, and activation of caspase-3. Phosphatidylinositol 3-kinase/Akt, extracellular signal-regulated kinase 1/2, and IkappaB kinase beta appear to contribute to the anti-apoptotic effect of LPS since the specific inhibitors, wortmannin, PD98059, and dominant negative IKKbeta transgene expression reversed the LPS effect. To assess whether LPS improves CM function, we examined intracellular Ca(2+) transients and cell shortening in single adult rat CMs. SD for 6 h dramatically inhibited Ca(2+) transients and CM contractility. LPS at 500 ng/ml significantly improved the [Ca(2+)](i) transients and enhanced contractility in control CMs as well as in CMs subjected to SD. Importantly, transient ischemia led to rapid activation of IRAK-1 in cultured CMs and in adult rat myocardium. Adenovirus-mediated transgene expression of IRAK-1 but not its kinase-deficient mutant IRAK-1(K239S) protected CMs against SD-induced apoptosis. Taken together, these data suggest an important role of TLR4 signaling via IRAK-1 in protecting against SD-induced apoptosis.

Hyperglycemia in streptozotocin-induced diabetic rat increases infarct size associated with low levels of myocardial HO-1 during ischemia/reperfusion

This study investigated the role of heme oxygenase (HO)-1 in the cardiac tissue injury of acute ischemia/reperfusion (I/R) in diabetic streptozotocin (STZ)-induced hyperglycemic rats. The effects of 1) hemin, an inducer of HO expression and activity, and 2) zinc protoporphyrin IX (ZnPP-IX), an inhibitor of HO activity, have also been investigated on the tissue injury by I/R and some mediators released in these circumstances. STZ hyperglycemic rats had impaired levels of HO-1 within the cardiac tissue and increased myocardial infarct size (IS) following I/R, as compared with the nondiabetic rats. In these rats, administration of hemin 4 mg/kg 18 h before I/R increases the levels of HO-1 within the tissue. However, the values of HO-1 assayed in these circumstances were significantly lower (P < 0.01) than those assayed in nondiabetic animals subjected to the same procedures; IS was much more extended (P < 0.01) than in the parent nondiabetic group. STZ hyperglycemic rats also predisposed the heart to produce high levels of the cytokines interleukin (IL)-1beta and CXCL8. Subsequent I/R further increased (P < 0.01) the cytokine production, an effect partly prevented by hemin treatment. This recovered the huge number of infiltrated polymorphonuclear (PMN) leukocytes within the cardiac tissue associated with the STZ hyperglycemic state and I/R damage.

Cutting edge: TLR4 activation mediates liver ischemia/reperfusion inflammatory response via IFN regulatory factor 3-dependent MyD88-independent pathway

The triggering molecular mechanism of ischemia-reperfusion injury (IRI), which in clinical settings results in excessive and detrimental inflammatory responses, remains unclear. This study analyzes the role of the TLR system in an established murine model of liver warm ischemia followed by reperfusion. By contrasting in parallel TLR knockout mice with their wild-type counterparts, we found that TLR4, but not TLR2, was specifically required in initiating the IRI cascade, as manifested by liver function (serum alanine aminotransferase levels), pathology, and local induction of proinflammatory cytokines/chemokines (TNF-alpha, IL-6, IFN-inducible protein 10). We then investigated the downstream signaling pathway of TLR4 activation. Our results show that IFN regulatory factor 3, but not MyD88, mediated IRI-induced TLR4 activation leading to liver inflammation and hepatocellular damage. This study documents the selective usage of TLR in a clinically relevant noninfectious disease model, and identifies a triggering molecular mechanism in the pathophysiology of liver IRI.

Bone marrow-derived cells contribute to contractile dysfunction in endotoxic shock

How infection precipitates depressed contractility is incompletely understood but may involve the immune, nervous, and endocrine systems as well as the heart itself. In this study, we examined the role of Toll-like receptor 4 (TLR4) in LPS-induced myocardial contractile depression. Eighteen hours following endotoxin challenge, we compared contractile responses in hearts from wild-type (WT) and TLR4-deficient mice using modified Langendorff preparations. Unlike hearts from WT mice, TLR4-deficient hearts did not reveal significant contractile dysfunction following LPS administration, as measured by decreased responses in maximal left ventricular pressure, +dP/d tmax, and −dP/d tmaxin ex vivo Langendorff preparations. These findings indicate a requirement for TLR4 in LPS-induced contractile depression. To determine the contribution of bone marrow-derived TLR4 function to LPS-induced myocardial dysfunction, we generated TLR4 chimeras using adoptive transfer between histocompatible mouse strains: either TLR4-deficient mice with TLR4+/+ bone marrow-derived cells or TLR4+/+ animals lacking TLR4 in their hematopoietic cells. We then compared the contractile responses of engrafted animals after LPS challenges. Engraftment of TLR4-deficient mice with WT marrow restored sensitivity to the myocardial depressant effects of LPS in TLR4-deficient hearts ( P < 0.05). Inactivation of bone marrow-derived TLR4 function, via transplantation of WT mice with TLR4−/− marrow, however, did not protect against the depressant effect of endotoxin. These findings indicate that bone marrow-derived TLR4 activity is sufficient to confer sensitivity to mice lacking TLR4 in all other tissues. However, because inactivation of marrow-derived TLR4 function alone does not protect against endotoxin-triggered contractile dysfunction, TLR4 function in other tissues may also contribute to this response.

Repetitive postprandial hyperglycemia increases cardiac ischemia/reperfusion injury: prevention by the α‐glucosidase inhibitor acarbose

Protective effects of the alpha-glucosidase inhibitor acarbose have been reported for various diabetic complications. In the STOP-NIDDM study, even patients without overt diabetes, but with impaired glucose tolerance, had a reduction in cardiovascular events when treated with acarbose. Therefore, we investigated the effect of repetitive postprandial hyperglycemia on the cardiac ischemia/reperfusion injury in vivo. Mice were treated daily by single applications of placebo, sucrose (4 g/kg body weight), or sucrose + acarbose (10 mg/kg body weight) by gavage for 7 days. Acarbose treatment significantly reduced the sucrose-induced increase in plasma glucose concentration. Subsequently, animals underwent 30 min of ischemia by coronary artery ligation and 24 h of reperfusion in vivo. In the sucrose group, ischemia/reperfusion damage was significantly increased (infarct/area at risk, placebo vs. sucrose, 38.8+/-7.5% vs. 62.2+/-4.8%, P<0.05). This was prevented by acarbose treatment (infarct/area at risk 30.7+/-7.2%). While myocardial inflammation was similar in all groups, oxidative stress as indicated by a significant increase in lipid peroxides was enhanced in the sucrose, but not in the sucrose + acarbose group. In summary, repetitive postprandial hyperglycemia increases ischemia/reperfusion damage. This effect can be prevented by treatment with the alpha-glucosidase inhibitor acarbose.

Potential Role of Endotoxin as a Proinflammatory Mediator of Atherosclerosis

Atherosclerosis is increasingly recognized as a chronic inflammatory disease. Although a variety of inflammatory markers (ie, C-reactive protein) have been associated with atherosclerosis and its consequences, it is important to identify principal mediators of the inflammatory responses. One potentially important source of vascular inflammation in atherosclerosis is bacterial endotoxin. Mutations in Toll-like receptor 4 (TLR-4), an integral component of the endotoxin signaling complex, are fairly common in the Caucasian population and have recently been associated with reduced incidence of atherosclerosis and other cardiovascular diseases in some studies. Moreover, epidemiological studies suggest that endotoxemia at levels as low as 50 pg/mL constitutes a strong risk factor for the development of atherosclerosis. Endotoxin concentrations in this range may be produced by a variety of common subclinical Gram-negative infections. In this article, we outline the main elements of the endotoxin signaling receptor complex that initiates proinflammatory signaling (lipopolysaccharide binding protein [LBP], CD14, TLR-4, and MD-2) and discuss how changes in expression of these molecules may affect proatherogenic responses in the vessel wall. We also describe some of the proinflammatory effects of endotoxin that may be relevant to atherosclerosis, and discuss how serum lipoproteins, especially high-density lipoprotein, may modulate endotoxin-induced inflammatory responses. Further, we discuss recent findings suggesting that the lipid-lowering statins may have an additional protective role in blocking at least some of these proinflammatory signaling pathways. Finally, we discuss species diversity with regard to endotoxin signaling that should be considered when extrapolating experimental data from animal models to humans.

The remote ischemic preconditioning stimulus modifies inflammatory gene expression in humans

Remote ischemic preconditioning (IPC) reduces tissue injury caused by ischemia-reperfusion (IR) in distant organs. We tested the hypothesis that remote IPC (rIPC) modifies inflammatory gene transcription in humans. Using a microarray method, we demonstrated that a simple model of brief forearm ischemia suppresses proinflammatory gene expression in circulating leukocytes. Genes encoding key proteins involved in cytokine synthesis, leukocyte chemotaxis, adhesion and migration, exocytosis, innate immunity signaling pathways, and apoptosis were all suppressed within 15 min (early phase IPC) and more so after 24 h (second window IPC). Changes in leukocyte CD11b expression measured by flow cytometry mirrored this pattern, with there being a significant (P = 0.01) reduction at 24 h. The results of this study show that the rIPC stimulus modifies leukocyte inflammatory gene expression. This effect may contribute to the protective effect of IPC against IR injury and may have broader implications in other inflammatory processes. This is the first study of human gene expression following rIPC stimulus. rIPC stimulus suppressed proinflammatory gene transcription in human leukocytes.