Reverse kinetics of angiopoietin-2 and endotoxins in acute pyelonephritis: Implications for anti-inflammatory treatment?

Role of Angiopoietin/Tie2 System in Sepsis: A Potential Therapeutic Target

Sepsis is a disorder of host response caused by severe infection that can lead to life-threatening organ dysfunction. There is no specific treatment for sepsis. Although there are many different pathogens that can cause sepsis, endothelial dysfunction is a frequent mechanism resulting in vascular leakage and coagulation problem. Recent studies on the regulatory pathways of vascular endothelium have shown that the disturbance of angiopoietin (Ang) /Tie2 axis can induce endothelial cell activation, which is the core pathogenesis of sepsis. In this review, we aim to discuss the regulation of Ang/Tie2 axis and the biomarkers involved in the context of sepsis. Also, we attempt to explore the prospective and feasibility of Ang/Tie2 axis as a potential target for sepsis intervention to improve clinical outcomes.

Adiponectin alleviated renal cell apoptosis and inflammation via inactivation of JAK2/STAT3 signal pathway in an acute pyelonephritis mouse model

Background

Acute pyelonephritis (APN), an acute and severe kidney infection, is usually treated with antibiotics. However, APN treatment has become increasingly challenging because of bacterial resistance. Adiponectin, an adipokine, has recently been reported to exhibit profound anti-inflammatory and anti-apoptotic effects. However, the effect of adiponectin on the outcomes of APN treatment remains unclear. In this study, we aimed to investigate the effects of adiponectin on APN and the mechanisms underlying these effects.

Methods

Wild-type C57 mice and adiponectin-knockout (KO) mice were divided into 6 groups: the wild-type control group, the wild-type model group, the wild-type adiponectin intervention group, the KO control group, the KO model group, and the adiponectin-KO intervention group. We measured white blood cell (WBC) and neutrophil counts (NC) using a multispecies hematology analyzer; tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) using enzyme-linked immunosorbent assay (ELISA); blood urea nitrogen (BUN) and serum creatinine (SCr) levels using colorimetry; and the protein levels of JAK2, STAT3, p-JAK2, p-STAT3, Bcl-2, and Bax in renal tissues using western blot analysis. Apoptotic cells were detected using the transferase-mediated dUTP nick end labelling (TUNEL) assay.

Results

Compared to the wild-type mice, the KO mice showed a more severe inflammatory response and kidney damage after Escherichia coli infection. After treatment with exogenous adiponectin injection, the inflammatory response, oxidative stress, and kidney damage were partly alleviated. Adiponectin KO led to JAK2/STAT3 signaling activation, and exogenous adiponectin administration inactivated JAK2/STAT3 signaling in the APN model. APN can lead to an increase in the level of the protein Bax and a decrease in the level of the bcl-2 protein, thereby increasing apoptosis; this effect was inhibited by adiponectin.

Conclusions

Through use of a pyelonephritis mouse model, we demonstrated that adiponectin might alleviate renal cell apoptosis and inflammatory response by inactivating the JAK2/STAT3 signaling pathway.

Angiopoietin 2 Levels in the Risk Stratification and Mortality Outcome Prediction of Sepsis-Associated Coagulopathy

It has been well established that angiopoietin 2 (Ang-2), a glycoprotein involved in activation of the endothelium, plays an integral role in the pathophysiology of sepsis and many other inflammatory conditions. However, the role of Ang-2 in sepsis-associated coagulopathy (SAC) specifically has not been defined. The aim of this study was to measure Ang-2 plasma levels in patients with sepsis and suspected disseminated intravascular coagulation (DIC) in order to demonstrate its predictive value in SAC severity determination and 28-day mortality outcome. Plasma samples were collected from 102 patients with sepsis and suspected DIC at intensive care unit (ICU) admission. The Ang-2 plasma levels were quantified using a sandwich enzyme-linked immunosorbent assay method. The International Society on Thrombosis and Haemostasis DIC scoring system was used to compare the accuracy of Ang-2 levels versus clinical illness severity scores in predicting SAC severity. Mean Ang-2 levels in patients with sepsis and DIC were significantly higher in comparison to healthy controls (P < 0.0001), and median Ang-2 levels showed a downward trend over time (P = 0.0008). Baseline Ang-2 levels and clinical illness severity scores were higher with increasing severity of disease, and Ang-2 was a better predictor of DIC severity than clinical illness scores. This study demonstrates that Ang-2 levels are significantly upregulated in SAC, and this biomarker can be used to risk stratify patients with sepsis into non-overt DIC and overt DIC. Furthermore, the Ang-2 level at ICU admission in a patient with sepsis and suspected DIC may provide a predictive biomarker for mortality outcome.

Endothelial Activation: The Ang/Tie Axis in Sepsis

Sepsis, a dysregulated host response to infection that causes life-threatening organ dysfunction, is a highly heterogeneous syndrome with no specific treatment. Although sepsis can be caused by a wide variety of pathogenic organisms, endothelial dysfunction leading to vascular leak is a common mechanism of injury that contributes to the morbidity and mortality associated with the syndrome. Perturbations to the angiopoietin (Ang)/Tie2 axis cause endothelial cell activation and contribute to the pathogenesis of sepsis. In this review, we summarize how the Ang/Tie2 pathway is implicated in sepsis and describe its prognostic as well as therapeutic utility in life-threatening infections.

Role of angiopoietin-2 in infection - A double-edged sword?

The endothelial angiopoietin (Angpt)/Tie2 ligand receptor system maintains vascular quiescence and modulates the response to injury. Angpt-1 is considered the natural Tie2 agonist and receptor ligation leads to its phosphorylation inducing various protective downstream pathways. The natural antagonist - Angpt-2 - appears to inhibit these protective effects. In sepsis, the balance between both ligands is shifted in favor for Angpt-2 and the vasculature is highly dysfunctional, activated and leaky. Circulating levels of Angpt-2 strongly predict mortality in septic patients. Consistently, experimental strategies that target Angpt-2 (e.g. antibody, RNAi, etc.) can protect the vascular barrier and improve survival. However, in vitro is has also been shown that Angpt-2 can act as a dose-dependent Tie2 agonist/antagonist. Based on this, people have wondered if Angpt-2 is per se injurious or if it might have protective effects dependent on the scenario. A recent paper by Safioleas and colleagues showed survival benefits after a therapeutic injection of recombinant Angpt-2 in experimental pyelonephritis. Here, we discuss their counter-intuitive but interesting findings and put them into a global context with respect to the existent literature in the angiopoietin/Tie2 sepsis field.