An ALPHA7 Nicotinic Acetylcholine Receptor Agonist (GTS-21) Promotes C2C12 Myonuclear Accretion in Association with Release of Interleukin-6 (IL-6) and Improves Survival in Burned Mice

CLASSIC IL-6 SIGNALING IS ASSOCIATED WITH POOR OUTCOMES IN BURN PATIENTS

ABSTRACT

Background: Interleukin (IL)-6 is a multifunctional cytokine with both a proinflammatory and anti-inflammatory role. In many studies, IL-6 increases rapidly after burn injury and is associated with poor outcomes. However, there are two aspects to IL-6; it can signal via its soluble IL-6 receptor (sIL-6R), which is referred to as trans-signaling and is regarded as the proinflammatory pathway. The role of sIL-6R postburn injury has yet to be explored in its entirety. We hypothesized that patients with a lower ratio of IL-6 to sIL-6R would have worse outcomes. Methods: Patients admitted to our burn center within 7 days of injury were included in this study. Patients were divided into two groups based on IL-6 and sIL-6R levels measured within the first 7 days postburn injury. Patients were in the high ratio group if their IL-6/sIL-6R ratio was ≥0.185. Clinical outcomes included organ biomarkers, morbidities, and hospital length of stay. Groups were compared using Student's t test, Mann-Whitney U , and Fisher's exact test as appropriate; a P value of <0.05 was considered statistically significant. Results: We studied 86 patients with a median age of 50 years (36-66 years) and a median total body surface area burn of 18% (10-31). There were 40 patients categorized with a low IL-6/sIL-6R ratio and 46 patients with a high IL-6/sIL-6R ratio. Patients in the high IL-6/sIL-6R ratio group had a significantly greater total body surface area burn ( P < 0.001) and a significantly greater proportion of patients with inhalation injury ( P = 0.001). Levels of IL-6 were significantly higher in patients with a high IL-6/sIL-6R ratio ( P < 0.0001). However, levels of sIL-6R were not significantly different among the low and high groups ( P = 0.965). Mortality was significantly greater in the high IL-6/sIL-6R ratio group (3% vs. 26%; P = 0.002). Conclusions: Interestingly, patients with a higher ratio of IL-6/sIL-6R had significantly greater mortality. Using sIL-6R as a marker for the proinflammatory immune response, we expected patients with a lower IL-6/sIL-6R ratio to have poor outcomes, typically associated with a hyperinflammatory or exaggerated immune response. However, the absolute value of sIL-6R did not differ. This suggests that classical signaling of IL-6 via its membrane-bound receptor, with an anti-inflammatory function, is important.

Molecular mechanisms of muscular and non-muscular actions of neuromuscular blocking agents in critical illness: a narrative review

Despite frequent use of neuromuscular blocking agents in critical illness, changes in neuromuscular transmission with critical illness are not well appreciated. Recent studies have provided greater insights into the molecular mechanisms for beneficial muscular effects and non-muscular anti-inflammatory properties of neuromuscular blocking agents. This narrative review summarises the normal structure and function of the neuromuscular junction and its transformation to a 'denervation-like' state in critical illness, the underlying cause of aberrant neuromuscular blocking agent pharmacology. We also address the important favourable and adverse consequences and molecular bases for these consequences during neuromuscular blocking agent use in critical illness. This review, therefore, provides an enhanced understanding of clinical therapeutic effects and novel pathways for the salutary and aberrant effects of neuromuscular blocking agents when used during acquired pathologic states of critical illness.

Marine Origin Ligands of Nicotinic Receptors: Low Molecular Compounds, Peptides and Proteins for Fundamental Research and Practical Applications

The purpose of our review is to briefly show what different compounds of marine origin, from low molecular weight ones to peptides and proteins, offer for understanding the structure and mechanism of action of nicotinic acetylcholine receptors (nAChRs) and for finding novel drugs to combat the diseases where nAChRs may be involved. The importance of the mentioned classes of ligands has changed with time; a protein from the marine snake venom was the first excellent tool to characterize the muscle-type nAChRs from the electric ray, while at present, muscle and α7 receptors are labeled with the radioactive or fluorescent derivatives prepared from α-bungarotoxin isolated from the many-banded krait. The most sophisticated instruments to distinguish muscle from neuronal nAChRs, and especially distinct subtypes within the latter, are α-conotoxins. Such information is crucial for fundamental studies on the nAChR revealing the properties of their orthosteric and allosteric binding sites and mechanisms of the channel opening and closure. Similar data are provided by low-molecular weight compounds of marine origin, but here the main purpose is drug design. In our review we tried to show what has been obtained in the last decade when the listed classes of compounds were used in the nAChR research, applying computer modeling, synthetic analogues and receptor mutants, X-ray and electron-microscopy analyses of complexes with the nAChRs, and their models which are acetylcholine-binding proteins and heterologously-expressed ligand-binding domains.

From skeletal muscle damage and regeneration to the hypertrophy induced by exercise: What is the role of different macrophages subsets?

Macrophages are one of the top players when considering immune cells involved with tissue homeostasis. Recently, increasing evidence has demonstrated that these macrophages could also present two major subsets during tissue healing; proliferative macrophages (M1-like), which are responsible for increasing myogenic cell proliferation, and restorative macrophages (M2-like), which are accountable for the end of the mature muscle myogenesis. The participation and characterization of these macrophage subsets is critical during myogenesis, not only to understand the inflammatory role of macrophages during muscle recovery but also to create supportive strategies that can improve mass muscle maintenance. Indeed, most of our knowledge about macrophage subsets comes from skeletal muscle damage protocols, and we still do not know how these subsets can contribute to skeletal muscle adaptation. This narrative review aims to collect and discuss studies demonstrating the involvement of different macrophage subsets during the skeletal muscle damage/regeneration process, showcasing an essential role of these macrophage subsets during muscle adaptation induced by acute and chronic exercise programs.

Inflammatory response of the peripheral neuroendocrine system following downhill running

Exploring the relationship between exercise inflammation and the peripheral neuroendocrine system is essential for understanding how acute or repetitive bouts of exercise can contribute to skeletal muscle adaption. In severe damage, some evidence demonstrates that peripheral neuroendocrine receptors might contribute to inflammatory resolution, supporting the muscle healing process through myogenesis. In this sense, the current study aimed to evaluate two classic peripheral neuronal receptors along with skeletal muscle inflammation and adaptation parameters in triceps brachii after exercise. We euthanized C57BL (10 to 12 weeks old) male mice before, and one, two, and three days after a downhill running protocol. The positive Ly6C cells, along with interleukin-6 (IL-6), nuclear factor kappa B (NF-κB), glucocorticoid receptor (GR), α7 subunits of the nicotinic acetylcholine receptor (nAChRs), and myonuclei accretion were analyzed. Our main results demonstrated that nAChRs increased with the inflammatory and myonuclei accretion responses regardless of NF-κB and GR protein expression. These results indicate that increased nAChR may contribute to skeletal muscle adaption after downhill running in mice.

Application of marine natural products in drug research

New diseases are emerging as the environment changes, so drug manufacturers are always on the lookout for new resources to develop effective and safe drugs. In recent years, many bioactive substances have been produced in the marine environment, which represents an alternative resource for new drugs used to combat major diseases such as cancer or inflammation. Many marine-derived medicinal substances are in preclinical or early stage of clinical development, and some marine drugs have been put on the market, such as ET743 (Yondelis®). This review presents the sources, activities, mechanisms of action and syntheses of bioactive substances based on marine natural products in clinical trials and on the market, which is helpful to understand the progress of drug research by application of marine natural products.

Mechanism of pulmonary immunosuppression: extrapulmonary burn injury suppresses bacterial endotoxin-induced pulmonary neutrophil recruitment and neutrophil extracellular trap (NET) formation

Pulmonary immunosuppression often occurs after burn injury (BI). However, the reasons for BI-induced pulmonary immunosuppression are not clearly understood. Neutrophil recruitment and neutrophil extracellular trap (NET) formation (NETosis) are important components of a robust pulmonary immune response, and we hypothesized that pulmonary inflammation and NETosis are defective after BI. To test this hypothesis, we established a mouse model with intranasal LPS instillation in the presence or absence of BI (15% of body surface burn) and determined the degree of immune cell infiltration, NETosis, and the cytokine levels in the airways and blood on d 2. Presence of LPS recruited monocytes and large numbers of neutrophils to the airways and induced NETosis (citrullinated histone H3, DNA, myeloperoxidase). By contrast, BI significantly reduced LPS-mediated leukocyte recruitment and NETosis. This BI-induced immunosuppression is attributable to the reduction of chemokine (C-C motif) ligand (CCL) 2 (monocyte chemoattractant protein 1) and CCL3 (macrophage inflammatory protein 1α). BI also suppressed LPS-induced increase in IL-17A, IL-17C, and IL-17E/IL-25 levels in the airways. Therefore, BI-mediated reduction in leukocyte recruitment and NETosis in the lungs are attributable to these cytokines. Regulating the levels of some of these key cytokines represents a potential therapeutic option for mitigating BI-mediated pulmonary immunosuppression.-Sakuma, M., Khan, M. A. S., Yasuhara, S., Martyn, J. A., Palaniyar, N. Mechanism of pulmonary immunosuppression: extrapulmonary burn injury suppresses bacterial endotoxin-induced pulmonary neutrophil recruitment and neutrophil extracellular trap (NET) formation.

Effect of splenectomy on attenuation of LPS-induced AKI through GTS-21-induced cholinergic anti-inflammatory pathway

This work was undertaken to explore the role of splenectomy on attenuation of lipopolysaccharide (LPS)-induced acute kidney injury (AKI) through GTS-21-induced cholinergic anti-inflammatory pathway. C57BL/6 mice were used to construct models of sepsis-induced renal injury. HE, Tunel and blood assays were used to determine the success of the model. The animals were examined after splenectomy with or without LPS and GTS-21+LPS treatments. The pathological changes and apoptosis in the renal tissue were detected using HE and Tunel assays. The contents of creatinine (Cr) and cystatin-C (Cys-C) were measured using ELISA. The expression of IL-6, NF-kB p65, Caspase-3, anti-apoptotic protein Bcl-2, apoptotic protein Bax and α7nAChR was quantified using qRT-PCR. The expression of Bcl-2, Bax, Caspase-3, IL-6, NF-kB p65, α7nAChR and p-STAT3 was using assessed using Western blot analysis. HE, Tunel, BUN and serum creatinine (SC) assay showed that renal injury models were successfully established. Compared with the control, the apoptosis in the LPS group was significantly increased and decreased after GTS-21 treatment. However, splenectomy combined with GTS-21 increased the apoptosis, indicating that splenectomy could partially offset the anti-apoptosis effect of GTS-21. In animals treated with LPS, the contents of Cr and Cys-C increased significantly. These contents reduced following GTS-21 treatment, but increased after splenectomy. After LPS treatment, the expression of IL-6, NF-kB p65, p-STAT3, Caspase-3 and Bax was significantly up-regulated, while the expression of α7nAChR and Bcl-2 significantly down-regulated. Compared with LPS treated mice, splenectomy reduced the expression of IL-6, NF-kB p65 and p-STAT3, suggesting that splenectomy inhibits the activation of α7nAChR pathway by the GTS-21. It is clear that GTS-21 effectively attenuates LPS-induced renal injury; splenectomy suppresses the anti-inflammatory and anti-apoptosis activity and renal protective effect of GTS-21. On other hand, splenectomy reduces the production of inflammatory cytokines in the circulation, and has certain protective effect on the kidney. Therefore, the impact of splenectomy on LPS-induced AKI depends on the strength of the two aspects.

The effect of the cholinergic anti-inflammatory pathway on collagen-induced arthritis involves the modulation of dendritic cell differentiation

BACKGROUND

The cholinergic anti-inflammatory pathway (CAP) has a strong anti-inflammatory effect on collagen-induced arthritis (CIA), a classic animal model of rheumatoid arthritis (RA). However, the underlying immune regulatory mechanism remains unclear. Here, we investigated the effect of the CAP on arthritis development and the involvement of dendritic cells (DCs).

METHODS

Forty DBA/1 mice were randomly divided into five groups: a control group (sham vagotomy+ phosphate-buffered saline; shamVGX+PBS), a CIA group (shamVGX+CIA + PBS), a vagotomy group (VGX + CIA + PBS), a GTS-21 (4 mg/kg) group (shamVGX+CIA + GTS-4), and a GTS-21 (8 mg/kg) group (shamVGX+CIA + GTS-8). The vagotomy group underwent left cervical vagotomy 4 days before arthritis induction, whereas the sham-vagotomy group underwent vagus nerve exposure. Mice were pretreated with GTS-21 by intraperitoneal injection on the day of surgery. The degree of arthritis was measured by using the arthritis score, hematoxylin and eosin staining, and TRAP (tartrate-resistant acid phosphatase) staining. Flow cytometry was used to detect the expression of CD80 and major histocompatibility complex II (MHC II) on CD11c⁺ DCs in the spleen. Luminex was used to detect the serum concentration of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNFα), and IL-10. Immunohistochemistry was used to detect CD11c expression in the synovium. The effects of GTS-21 on DC differentiation and maturation were examined in vitro by treating bone marrow-derived DCs with GTS-21 and assessing differentiation and maturation. Flow cytometry was used to analyze CD80 and MHC II expression on the surface of DCs.

RESULTS

GTS-21 treatment ameliorated clinical arthritis in a mouse model of CIA in vivo, decreasing the secretion of pro-inflammatory cytokines in the serum and downregulating CD80 and MHC II expression on DCs in the spleen of CIA mice. GTS-21 treatment strongly suppressed the infiltration of DCs into the synovium. Vagotomy itself did not exacerbate the severity of arthritis in CIA mice. In vitro, GTS-21 (10 μmol/L) significantly downregulated CD80 and MHC II in bone marrow-derived immature DCs and this effect was blocked by the α7-nicotinic acetylcholine receptor antagonist methyllycaconitine (MLA). However, GTS-21 had no effects on mature DCs.

CONCLUSIONS

The present study provides new insight into the mechanism underlying the effects of the CAP on RA and indicates that the immunosuppressive effect of GTS-21 may be mediated by the inhibition of DC differentiation.

GTS-21 attenuates loss of body mass, muscle mass, and function in rats having systemic inflammation with and without disuse atrophy

Muscle changes of critical illness are attributed to systemic inflammatory responses and disuse atrophy. GTS-21 (3-(2,4-dimethoxy-benzylidene)anabaseine), also known as DMBX-A) is a synthetic derivative of the natural product anabaseine that acts as an agonist at α7-acetylcholine receptors (α7nAChRs). Hypothesis tested was that modulation of inflammation by agonist GTS-21 (10 mg/kg b.i.d. intraperitoneally) will attenuate body weight (BW) and muscle changes. Systemic sham inflammation was produced in 125 rats by Cornyebacterium parvum (C.p.) or saline injection on days 0/4/8. Seventy-four rats had one immobilized-limb producing disuse atrophy. GTS-21 effects on BW, tibialis muscle mass (TMM), and function were assessed on day 12. Systemically, methemoglobin levels increased 26-fold with C.p. (p < 0.001) and decreased significantly (p < 0.033) with GTS-21. Control BW increased (+ 30 ± 9 g, mean ± SD) at day 12, but decreased with C.p. and superimposed disuse (p = 0.005). GTS-21 attenuated BW loss in C.p. (p = 0.005). Compared to controls, TMM decreased with C.p. (0.43 ± 0.06 g to 0.26 ± 0.03 g) and with superimposed disuse (0.18 ± 0.04 g); GTS-21 ameliorated TMM loss to 0.32 ± 0.04 (no disuse, p = 0.028) and to 0.22 ± 0.03 (with disuse, p = 0.004). Tetanic tensions decreased with C.p. or disuse and GTS-21 attenuated tension decrease in animals with disuse (p = 0.006) and in animals with C.p. and disuse (p = 0.029). C.p.-induced 11-fold increased muscle α7nAChR expression was decreased by > 60% with GTS-21 treatment. In conclusion, GTS-21 modulates systemic inflammation, evidenced by both decreased methemoglobin levels and decrease of α7nAChR expression, and mitigates inflammation-mediated loss of BW, TMM, fiber size, and function.

GTS-21 attenuates LPS-induced renal injury via the cholinergic anti-inflammatory pathway in mice

This study aimed to investigate the role of GTS-21 in cholinergic anti-inflammatory pathway-mediated protection of LPS-induced septic renal injury in mice. C57BL/6 mice were used to construct septic injury models. The optimal duration of lipopolysaccharide (LPS) treatment was determined using HE staining and TUNEL assay. Mice injected with saline were used as blank control and with LPS (10 mg/kg) as model, which were further treated with α-bungarotoxin (BT-LPS), GTS-21 (GTS-21-LPS) and BT and GTS-21 (BT-GTS-21-LPS). The pathological examinations were performed on HE stained renal tissues, apoptosis was determined using TUNEL assay, mRNA expression of NF-kB p65, Caspase-3, Caspase-8, Bcl-2, Bax, p53 and a7nACh was quantified using qRT-PCR, protein levels of IL-6, IL-1β, TNF-α and phosphorylated STAT3 (p-STAT3) were analyzed using Western blots. HE staining and TUNEL assays showed that the optimal LPS treatment time for renal injury induction was 16 h. Compared with the blank control, mice in LPS group had significantly higher levels of NF-Kb p65, Caspase-3, Caspase-8, Bax, p53, IL-6, IL-1β, TNF-α and p-STAT3, while α7nAChR and Bcl-2 levels were decreased significantly (P < 0.01); GTS-21 and BT significantly increased the expression of NF-Kb p65, Caspase-3, Caspase-8, Bax, p53, IL-6, IL-1β, TNF-α and p-STAT3, while α7nAChR and Bcl-2 levels were decreased significantly (P < 0.01). It is concluded that GTS-21 can effective alleviate the renal injury, while α7nAChR-specific blocker BT is antagonistic against the anti-inflammatory effect of GTS-21 on sepsis in mice.