The β1-Adrenergic Receptor Contributes to Sepsis-Induced Immunosuppression Through Modulation of Regulatory T-Cell Inhibitory Function

β3-Adrenergic receptor antagonism improves cardiac and vascular functions but did not modulate survival in a murine resuscitated septic shock model

BACKGROUND

Recent findings suggest that β3-adrenergic receptors (β3-AR) could play a role in the hemodynamic regulation, but their function in septic shock remains unclear. This study investigates the modulation of β3-AR in an experimental murine model of resuscitated septic shock on in vivo hemodynamic, ex vivo vasoreactivity, inflammation and survival.

METHOD

Wild-type mice were used, undergoing cecal ligation and puncture (CLP) to induce septic shock, with SHAM as controls. Mice were treated with β3-AR agonist or antagonist three hours post-CLP, followed by resuscitation with fluids and antibiotics. Hemodynamic parameters were measured at 18 h following the surgery, and the expression of β-ARs in heart and aorta was assessed via immunostaining and western blot. Vascular reactivity was studied using myography, and inflammatory markers were analyzed through PCR and western blots. A 5-day survival study was conducted, documenting clinical severity scores and survival rates.

RESULTS

β3-AR was expressed in both endothelial and myocardial cells in healthy and septic mice. During septic shock model, β3-AR density on endothelial cells increased post-CLP, while β1- and β2-AR decreased or remained constant. β3-AR antagonist treatment improved hemodynamic parameters, increasing mean arterial pressure and cardiac index, unlike the agonist. Vascular reactivity to phenylephrine was enhanced in aortic rings from both β3-AR agonist and antagonist-treated mice. However, no significant differences in inducible NO synthase expression were observed among treated groups. Despite improved hemodynamic parameters with β3-AR antagonist treatment, survival rates in treated groups remained similar to CLP group.

CONCLUSIONS

In an experimental murine model of resuscitated septic shock, β3-AR is resistant to desensitization and its inhibition improves cardiac and vascular function without affecting the short-term survival.

Lymphopenia in sepsis: a narrative review

This narrative review provides an overview of the evolving significance of lymphopenia in sepsis, emphasizing its critical function in this complex and heterogeneous disease. We describe the causal relationship of lymphopenia with clinical outcomes, sustained immunosuppression, and its correlation with sepsis prediction markers and therapeutic targets. The primary mechanisms of septic lymphopenia are highlighted. In addition, the paper summarizes various attempts to treat lymphopenia and highlights the practical significance of promoting lymphocyte proliferation as the next research direction.

The role of esmolol in sepsis: a meta-analysis based on randomized controlled trials

BACKGROUND

Sepsis is associated with a high incidence and mortality and poses a significant challenge to the treatment. Although esmolol has shown promise in sepsis treatment, its efficacy and safety remain contentious. This meta-analysis aims to clarify the role of esmolol in sepsis management.

METHODS

PubMed, Embase, Web of Science, Cochrane library, clinicaltrials.gov and the Chinese Clinical Trial Registry were searched and references of relevant reviews and meta-analysis were also screened for appropriate studies. Keywords and free words of 'sepsis', 'esmolol' and 'randomized controlled trials' were used for search. Meta-analysis was performed using RevMan 5.3 software.

RESULTS

Fifteen studies involving 1100 patients were included. Compared with the control group, patients receiving esmolol exhibited significantly decreased 28-day mortality (RR, 0.69; 95% CI, 0.60 to 0.81; P < 0.0001), heart rate (HR) (SMD, -1.15; 95% CI, -1.34 to -0.96; P < 0.0001), cardiac troponin I levels (cTnI) (SMD, -0.88; 95% CI, -1.13 to -0.64; P < 0.0001), length of intensive care unit (ICU) stay (SMD, -0.46; 95% CI, -0.62 to -0.3; P < 0.0001) and duration of mechanical ventilation (SMD, -0.28; 95% CI, -0.48 to -0.09; P = 0.004) and significantly increased central venous oxygen saturation (ScvO2) (SMD, 0.66; 95% CI, 0.44 to 0.88; P < 0.0001).While, esmolol had no significant influence on norepinephrine dosage (SMD, 0.08; 95% CI, -0.13 to 0.29; P = 0.46), mean arterial pressure (MAP) (SMD, 0.17; 95% CI, -0.07 to 0.4; P = 0.16), central venous pressure (CVP) (SMD, 0.16; 95% CI, -0.04 to 0.35; P = 0.11) and left ventricular ejection fraction (LVEF) (SMD, 0.21; 95% CI, -2.9 to 0.7; P = 0.41).

CONCLUSION

Esmolol reduces 28-day mortality, length of ICU stay and duration of mechanical ventilation in sepsis patients. Furthermore, esmolol improves oxygen metabolism, mitigates myocardial injury and decreases heart rate without significantly affecting hemodynamic parameters.

TRIAL REGISTRATION

This study was registered on the PROSPERO website (registration number: CRD42023484884).

Adenosine 2A receptor antagonists promote lymphocyte proliferation in sepsis by inhibiting Treg expression of PD-L1 in spleen

The spleen is essential for lymphocyte proliferation, which is associated to sepsis prognosis. Adenosine 2A receptor (A2AR) blocking promotes lymphocyte proliferation in sepsis, however the mechanism is uncertain. Our sepsis cecum ligation perforation model showed that blocking A2AR increased survival and CD4+ cell numbers in a spleen-dependent mechanism. The sequencing of the transcriptome of the spleen indicated alterations in the expression of genes involved in the control of lymphocyte proliferation by inhibiting A2AR, including a reduction in the expression of PD-L1. Flow cytometry analysis of PD-L1 expression intensity in splenic cell subpopulations revealed that the Treg cell subpopulation was the strongest PD-L1-expressing cell population, and Treg PD-L1 expression decreased after blocking A2AR. In vitro activation of A2AR was able to upregulate PD-L1 expression of Treg and boost Treg capacity to limit lymphocyte proliferation, while blockage of PD-L1 partly reduced A2AR-activated Treg's ability to inhibit lymphocyte proliferation. In addition, blocking CREB phosphorylation significantly inhibited A2AR-induced PD-L1 expression. According to the findings of our research, inhibiting A2AR improves the prognosis of sepsis by lowering the level of PD-L1 expression by Treg in the spleen and reducing the inhibition of lymphocyte proliferation.

Circulating Dipeptidyl Peptidase 3 Modulates Systemic and Renal Hemodynamics Through Cleavage of Angiotensin Peptides

BACKGROUND

High circulating DPP3 (dipeptidyl peptidase 3) has been associated with poor prognosis in critically ill patients with circulatory failure. In such situation, DPP3 could play a pathological role, putatively via an excessive angiotensin peptides cleavage. Our objective was to investigate the hemodynamics changes induced by DPP3 in mice and the relation between the observed effects and renin-angiotensin system modulation.

METHODS

Ten-week-old male C57Bl/6J mice were subjected to intravenous injection of purified human DPP3 or an anti-DPP3 antibody (procizumab). Invasive blood pressure and renal blood flow were monitored throughout the experiments. Circulating angiotensin peptides and catecholamines were measured and receptor blocking experiment performed to investigate the underlying mechanisms.

RESULTS

DPP3 administration significantly increased renal blood flow, while blood pressure was minimally affected. Conversely, procizumab led to significantly decreased renal blood flow. Angiotensin peptides measurement and an AT1R (angiotensin II receptor type 1) blockade experiment using valsartan demonstrated that the renovascular effect induced by DPP3 is due to reduced AT1R activation via decreased concentrations of circulating angiotensin II, III, and IV. Measurements of circulating catecholamines and an adrenergic receptor blockade by labetalol demonstrated a concomitant catecholamines release that explains blood pressure maintenance upon DPP3 administration.

CONCLUSIONS

High circulating DPP3 increases renal blood flow due to reduced AT1R activation via decreased concentrations of circulating angiotensin peptides while blood pressure is maintained by concomitant endogenous catecholamines release.

LOW DOSE OF ESMOLOL ATTENUATES SEPSIS-INDUCED IMMUNOSUPPRESSION VIA MODULATING T-LYMPHOCYTE APOPTOSIS AND DIFFERENTIATION

ABSTRACT

Background: Immunosuppression caused by immune cell apoptosis and an imbalance of T helper 2 cells (T H 2) and T helper 1 cells (T H 1), is associated with poor outcomes in septic patients. Esmolol was reported to improve survival by modulating immune responses in septic shock. Whether esmolol could alleviate sepsis-induced immunosuppression and the optimal dose are unclear. Methods: Four hours after cecal ligation and puncture (CLP), Wistar rats were randomized into CLP, CLP + E-5 (esmolol: 5 mg·kg -1 ·h -1 ) and CLP + E-18 (esmolol: 18 mg·kg -1 ·h -1 ) groups. Eight rats were underwent sham operation. Eighteen hours after CLP, hemodynamics and organ histological injuries were evaluated, peripheral blood mononuclear cells apoptosis and T-lymphocyte subsets counts were determined by flow cytometry, and the expression of p-Akt, Bcl-2, cleaved Caspase-3, and p-Erk1/2 in splenic CD4 + T-lymphocytes was determined by western blot and immunohistochemistry. β 1 -Adrenoreceptor expressions were evaluated using real-time polymerase chain reaction and immunohistochemistry. Results: Cecal ligation and puncture induced tachycardia, hypotension, hyperlactatemia, and multiple organ injury. Heart rate was unchanged in the CLP + E-5 group but decreased in the CLP + E-18 group. Hypotension, lactatemia, and multiple organ injuries were improved only in the CLP + E-5 group. T-lymphocyte apoptosis and T H 2/T H 1 ratio was decreased in CLP + E-5 but not in CLP + E-18. p-Akt and Bcl-2 expressions were increased, while cleaved Caspase-3 and p-Erk1/2 expressions were decreased in CLP + E-5. β 1 -Adrenoreceptor expressions were unchanged in both CLP + E-5 and CLP + E-18 groups. Conclusions: Low dose of esmolol reduced T-lymphocyte apoptosis and restored T H 2/T H 1 ratio in septic shock. Esmolol might modulate Akt/Bcl-2/Caspase-3 pathway to relieve T-lymphocyte apoptosis and inhibit Erk1/2 activity to decrease T H 0 differentiation to T H 2. Esmolol may be a potential immunoregulator of septic shock.

Sympathetic System in Wound Healing: Multistage Control in Normal and Diabetic Skin

In this review, we discuss sympathetic regulation in normal and diabetic wound healing. Experimental denervation studies have confirmed that sympathetic nerve endings in skin have an important and complex role in wound healing. Vasoconstrictor neurons secrete norepinephrine (NE) and neuropeptide Y (NPY). Both mediators decrease blood flow and interact with inflammatory cells and keratinocytes. NE acts in an ambiguous way depending on receptor type. Beta2-adrenoceptors could be activated near sympathetic endings; they suppress inflammation and re-epithelialization. Alpha1- and alpha2-adrenoceptors induce inflammation and activate keratinocytes. Sudomotor neurons secrete acetylcholine (ACh) and vasoactive intestinal peptide (VIP). Both induce vasodilatation, angiogenesis, inflammation, keratinocytes proliferation and migration. In healthy skin, all effects are important for successful healing. In treatment of diabetic ulcers, mediator balance could be shifted in different ways. Beta2-adrenoceptors blockade and nicotinic ACh receptors activation are the most promising directions in treatment of diabetic ulcers with neuropathy, but they require further research.

Of mice and men: Laboratory murine models for recapitulating the immunosuppression of human sepsis

Prolonged immunosuppression is increasingly recognized as the major cause of late phase and long-term mortality in sepsis. Numerous murine models with different paradigms, such as lipopolysaccharide injection, bacterial inoculation, and barrier disruption, have been used to explore the pathogenesis of immunosuppression in sepsis or to test the efficacy of potential therapeutic agents. Nonetheless, the reproducibility and translational value of such models are often questioned, owing to a highly heterogeneric, complex, and dynamic nature of immunopathology in human sepsis, which cannot be consistently and stably recapitulated in mice. Despite of the inherent discrepancies that exist between mice and humans, we can increase the feasibility of murine models by minimizing inconsistency and increasing their clinical relevance. In this mini review, we summarize the current knowledge of murine models that are most commonly used to investigate sepsis-induced immunopathology, highlighting their strengths and limitations in mimicking the dysregulated immune response encountered in human sepsis. We also propose potential directions for refining murine sepsis models, such as reducing experimental inconsistencies, increasing the clinical relevance, and enhancing immunological similarities between mice and humans; such modifications may optimize the value of murine models in meeting research and translational demands when applied in studies of sepsis-induced immunosuppression.

Alternatives to norepinephrine in septic shock: Which agents and when?

Vasopressors are the cornerstone of hemodynamic management in patients with septic shock. Norepinephrine is currently recommended as the first-line vasopressor in these patients. In addition to norepinephrine, there are many other potent vasopressors with specific properties and/or advantages that act on vessels through different pathways after activation of specific receptors; these could be of interest in patients with septic shock. Dopamine is no longer recommended in patients with septic shock because its use is associated with a higher rate of cardiac arrhythmias without any benefit in terms of mortality or organ dysfunction. Epinephrine is currently considered as a second-line vasopressor therapy, because of the higher rate of associated metabolic and cardiac adverse effects compared with norepinephrine; however, it may be considered in settings where norepinephrine is unavailable or in patients with refractory septic shock and myocardial dysfunction. Owing to its potential effects on mortality and renal function and its norepinephrine-sparing effect, vasopressin is recommended as second-line vasopressor therapy instead of norepinephrine dose escalation in patients with septic shock and persistent arterial hypotension. However, two synthetic analogs of vasopressin, namely, terlipressin and selepressin, have not yet been employed in the management of patients with septic shock, as their use is associated with a higher rate of digital ischemia. Finally, angiotensin Ⅱ also appears to be a promising vasopressor in patients with septic shock, especially in the most severe cases and/or in patients with acute kidney injury requiring renal replacement therapy. Nevertheless, due to limited evidence and concerns regarding safety (which remains unclear because of potential adverse effects related to its marked vasopressor activity), angiotensin Ⅱ is currently not recommended in patients with septic shock. Further studies are needed to better define the role of these vasopressors in the management of these patients.