Toll-like receptors and opportunities for new sepsis therapeutics

Advances in the Study of Immunosuppressive Mechanisms in Sepsis

Sepsis is a life-threatening disease caused by a systemic infection that triggers a dysregulated immune response. Sepsis is an important cause of death in intensive care units (ICUs), poses a major threat to human health, and is a common cause of death in ICUs worldwide. The pathogenesis of sepsis is intricate and involves a complex interplay of pro- and anti-inflammatory mechanisms that can lead to excessive inflammation, immunosuppression, and potentially long-term immune disorders. Recent evidence highlights the importance of immunosuppression in sepsis. Immunosuppression is recognized as a predisposing factor for increased susceptibility to secondary infections and mortality in patients. Immunosuppression due to sepsis increases a patient's chance of re-infection and increases organ load. In addition, antibiotics, fluid resuscitation, and organ support therapy have limited impact on the prognosis of septic patients. Therapeutic approaches by suppressing excessive inflammation have not achieved the desired results in clinical trials. Research into immunosuppression has brought new hope for the treatment of sepsis, and a number of therapeutic approaches have demonstrated the potential of immunostimulatory therapies. In this article, we will focus on the mechanisms of immunosuppression and markers of immune monitoring in sepsis and describe various targets for immunostimulatory therapy in sepsis.

Mulberry leaf reduces inflammation and insulin resistance in type 2 diabetic mice by TLRs and insulin Signalling pathway

Background

It has been testified that Diabetes mellitus (DM) has a close association with chronic inflammation and Toll-like Receptors (TLRs), and DM could be prevented by mulberry leaf. Therefore, a hypothesis came into being that mulberry leaf could ameliorate proinflammation and insulin resistance (IR) through TLRs and insulin signalling pathways.

Methods

Water extracts of mulberry leaf (WEM) was given to diabetic mice by gavage for 10 weeks, and the diabetic mice was injected with low-dose streptozocin, fed with high-fat and high-sugar diet. Oral glucose tolerance tests (OGTTs) were conducted. At the same time, homeostasis model assessment of insulin (HOMA-IR) and the level of the inflammatory factor, tumour necrosis factor-α (TNF-α) was measured. The expressions of critical nodes of TLRs and insulin signalling pathway were also examined.

Results

WEM contributed to a significant decrease in fasting blood glucose, AUC from the investigation of OGTTs and HOMA-IR. The levels of the inflammatory factor, tumour necrosis factor-α (TNF-α) also declined. Moreover, WEM suppressed the expression of TLR2, myeloid differentiation primary-response protein 88 (MyD88), tumour-necrosis-factor receptor-associated factor 6 (TRAF6), nuclear factor kappa B (NF-κB) in the skeletal muscle. WEM could up-regulate the expression of insulin receptor (InsR) and insulin receptor substrate 1 (IRS1), and down-regulate the phosphorylation of IRS1 in adipose tissue.

Conclusion

Through this study, a conclusion could be made that WEM mitigates hyperglycemia, IR, and inflammation through the interactions among TLR2 signalling pathway, insulin signalling pathway and TNF-α.

The Specific Organism: Not Bacterial Gram Type: Drives the Inflammatory Response in Septic Shock

BACKGROUND AND HYPOTHESIS

The inflammatory response was targeted by unsuccessful therapies but ignored pathogen. We hypothesized that the inflammatory response differs according to organism in human septic shock.

MATERIALS AND METHODS

We measured 39 cytokines at baseline and 24 h in patients (n = 363) in the Vasopressin and Septic Shock Trial (VASST). We compared cytokine profiles (cytokine functional class) at baseline and at 24 h by organism and used hierarchical clustering to classify cytokines according to 28-day outcomes.

RESULTS

In 363 patients, 88 and 176 patients had at least 1 species isolated from blood and other sites, respectively. Cytokine levels differed significantly according to organism: Neisseria meningitidis and Streptococcus pneumoniae had the highest (baseline and at 24 h), while Enterococcus faecalis (blood) had the lowest mean cytokine levels. N. meningitidis and Klebsiella pneumoniae had significantly higher cytokine levels at baseline versus 24 h (p = 0.01 and 0.02, respectively); E. faecalis had significantly higher cytokine levels at 24 h versus baseline. Hierarchical clustering heat maps showed that pathogens elicited similar cytokine responses not related to the functional cytokine class.

CONCLUSION

The organism type induces different cytokine profiles in septic shock. Specific gram-positive and gram-negative pathogens stimulated similar plasma cytokine-level patterns.

A novel 1,2-benzenediamine derivative FC-99 suppresses TLR3 expression and ameliorates disease symptoms in a mouse model of sepsis

BACKGROUND AND PURPOSE

Sepsis is a clinical condition characterized by overwhelming systemic inflammation with high mortality rate and high prevalence, but effective treatment is still lacking. Toll-like receptor 3 (TLR3) is an endogenous sensor, thought to regulate the amplification of immune response during sepsis. Modulators of TLR3 have an advantage in the treatment of sepsis. Here, we aimed to explore the mechanism of a monosubstituted 1,2-benzenediamine derivative FC-99 {N(1) -[(4-methoxy)methyl]-4-methyl-1,2-benzenediamine}on modulating TLR3 expression and its therapeutic potential on mouse model of sepsis.

EXPERIMENTAL APPROACH

Cells were pretreated with FC-99 followed by poly(I:C) or IFN-α stimulation; TLR3 and other indicators were assayed. Female C57BL/6 mice were subjected to sham or caecal ligation puncture (CLP) surgery after i.p. injection of vehicle or FC-99; serum and tissues were collected for further experiments.

KEY RESULTS

FC-99 suppressed inflammatory response induced by poly(I:C) with no effect on cell viability or uptake of poly(I:C). FC-99 also inhibited TLR3 expression induced by not only poly(I:C) but also by exogenous IFN-α. This inhibition of FC-99 was related to the poly(I:C)-evoked IRF3/IFN-α/JAK/STAT1 signalling pathway. In CLP-induced model of sepsis, FC-99 administration decreased mice mortality and serum levels of inflammatory factors, attenuated multiple organ dysfunction and enhanced bacterial clearance. Accordingly, systemic and local expression of TLR3 was reduced by FC-99 in vivo.

CONCLUSION AND IMPLICATIONS

FC-99 reversed TLR3 expression and ameliorate CLP-induced sepsis in mice. Thus, FC-99 will be a potential therapeutic candidate for sepsis.

Toll-like receptors hit calcium

Mitochondrial Ca(2+) uptake is a multifarious signal that controls both the activity of matrix dehydrogenases and the sensitivity to apoptotic and necrotic challenges. Recent evidence indicates that mitochondria also play a role in triggering inflammation, as mitochondrial DNA, when released by the cell, is an important damage-associated molecular pattern (DAMP). Now, Toll-like receptors (TLRs) are shown to close the loop, by affecting in turn mitochondrial activity. Two studies by Shintani and colleagues, one in this issue of EMBO reports, identify a new TLR transduction mechanism that impinges directly on mitochondrial function. Upon binding of CpG oligodeoxynucleotides, TLR9--which in non-immune cells is retained in the ER--inhibits SERCA2, thus reducing Ca(2+) transfer to the mitochondria and aerobic metabolism.

TLR2 and TLR4 mediate the TNFα response to Vibrio vulnificus biotype 1

Vibrio vulnificus (Vv) is a pathogenic bacterium that can cause life-threatening infections in humans. Most fatal cases are due to septic shock that results from dysregulation of cytokines, particularly TNFα, which plays a critical role in the outcome of Vv infection. The goal of this study was to investigate the Toll-like receptor (TLR)-mediated TNFα response to four Vv biotype 1 strains using mice deficient for TLR2, TLR4, and TLR2/TLR4. Ex vivo assays were performed with blood, splenocytes, and Kupffer cells (KC) from wild-type (WT) and TLR-knockout (KO) mice using formalin-inactivated Vv (f-Vv) as stimulant. All f-Vv biotype 1 strains elicited strong TNFα production by WT mouse blood and cells, which was TLR2 and TLR4 dependent. OxPAPC, an inhibitor of TLR2 and TLR4 signaling, effectively blunted the TLR-mediated TNFα response to f-Vv. Furthermore, TLR2 KO and TLR2/TLR4 KO mice were more resistant to lethal infection with Vv ATCC 27562 than WT mice, perhaps due to attenuation of the TNFα response. These data suggest that it may be possible to devise strategies to specifically target the harmful TLR-mediated TNFα response as an adjunct to antibiotic treatment of severe Vv infection.

Expression of toll-like receptors in chronic otitis media and cholesteatoma

OBJECTIVE

Otitis media is one of the most common infectious diseases, especially in young children. Multiple factors affect the onset or development of otitis media. Human toll-like receptors recognize associated patterns and play a critical role in innate immune mechanisms. Toll-like receptors are considered to be important factors for clearance of infection and resolution of inflammation in otitis media. The purpose of this study was to evaluate the histological expression of toll-like receptor 2, which recognizes many kinds of pathogen-associated molecular patterns, and toll-like receptor 4, which recognizes lipopolysaccharide on Gram-negative bacteria, in tissue samples from patients with chronic otitis media and middle ear cholesteatoma.

METHODS

Human middle ear tissue samples from 12 patients with chronic otitis media (n=7) and acquired middle ear cholesteatoma (n=5) were examined. Normal control middle ear samples without any inflammation were also included (n=7). The expressions of toll-like receptors 2 and 4 in middle ear tissues were examined immunohistochemically.

RESULTS

Only one normal control middle ear sample showed weak expression of toll-like receptor 2, and toll-like receptor 4 was not observed in all control samples. On the other hand, both toll-like receptors 2 and 4 were markedly expressed in chronic otitis media and cholesteatoma. There was a significant difference between chronic otitis media and normal controls in the expressions of both toll-like receptors. Significant up-regulation of toll-like receptors 2 and 4 was observed in cholesteatoma as compared with control samples.

CONCLUSIONS

Toll-like receptors 2 and 4 were strongly expressed in chronic otitis media and middle ear cholesteatoma. These findings suggest that toll-like receptors may play a principal role in human chronic otitis media and cholesteatoma.

In vivo TLR9 inhibition attenuates CpG-induced myocardial dysfunction

The involvement of toll-like receptor 9 (TLR9), a receptor for bacterial DNA, in septic cardiac depression has not been clarified in vivo. Thus, the aim of the study was to test possible TLR9 inhibitors (H154-thioate, IRS954-thioate, and chloroquine) for their ability to protect the cardiovascular system in a murine model of CpG oligodeoxynucleotide- (ODN-) dependent systemic inflammation. Sepsis was induced by i.p. application of the TLR9 agonist 1668-thioate in C57BL/6 wild type (WT) and TLR9-deficient (TLR9-D) mice. Thirty minutes after stimulation TLR9 antagonists were applied i.v. Survival was monitored up to 18 h after stimulation. Cardiac mRNA expression of inflammatory mediators was analyzed 2 h and 6 h after stimulation with 1668-thioate and hemodynamic parameters were monitored at the later time point. Stimulation with 1668-thioate induced a severe sepsis-like state with significant drop of body temperature and significantly increased mortality in WT animals. Additionally, there was a time-dependent increase of inflammatory mediators in the heart accompanied by development of septic heart failure. These effects were not observed in TLR9-D mice. Inhibition of TLR9 by the suppressive ODN H154-thioate significantly ameliorated cardiac inflammation, preserved cardiac function, and improved survival. This suppressive ODN was the most efficient inhibitor of the tested substances.