Efferent activity in the vagus nerve can prevent endotoxin-induced shock by attenuating tumor necrosis factor (TNF) synthesis. Termed the “cholinergic antiinflammatory pathway,” inhibition of TNF synthesis is dependent on nicotinic α-bungarotoxin-sensitive acetylcholine receptors on macrophages. Vagus nerve firing is also stimulated by CNI-1493, a tetravalent guanylhydrazone molecule that inhibits systemic inflammation. Here, we studied the effects of pharmacological and electrical stimulation of the intact vagus nerve in adult male Lewis rats subjected to endotoxin-induced shock to determine whether intact vagus nerve signaling is required for the antiinflammatory action of CNI-1493. CNI-1493 administered via the intracerebroventricular route was 100,000-fold more effective in suppressing endotoxin-induced TNF release and shock as compared with intravenous dosing. Surgical or chemical vagotomy rendered animals sensitive to TNF release and shock, despite treatment with CNI-1493, indicating that an intact cholinergic antiinflammatory pathway is required for antiinflammatory efficacy in vivo. Electrical stimulation of either the right or left intact vagus nerve conferred significant protection against endotoxin-induced shock, and specifically attenuated serum and myocardial TNF, but not pulmonary TNF synthesis, as compared with sham-operated animals. Together, these results indicate that stimulation of the cholinergic antiinflammatory pathway by either pharmacological or electrical methods can attenuate the systemic inflammatory response to endotoxin-induced shock.
Abstract HMGB1 is a cytokine mediator in the pathogenesis of inflammatory diseases including sepsis (Yang et al, BBA, 2009). Recently we demonstrated that haptoglobin (Hp), a naturally occurring serum protein, binds to HMGB1 and suppresses HMGB1-stimulated TNF and IL-8 release in cultured macrophages. Hp knockout mice subjected to cecal ligation and puncture (CLP)-induced sepsis had significantly higher serum HMGB1 levels and higher mortality rates compared to wild type animals (75% survival in wild type vs. 34% in Hp knockout mice; P<0.05). Wild type mice subjected to CLP and received injections of Hp were twice as likely to survive (63% survival in Hp-treated vs. 33% in vehicle control; P<0.05), suggesting the therapeutic potential of exogenous Hp in sepsis. Hp is composed of alpha and beta subunits in a polymeric form (Yueh, J. Chromat B Life Sci. 2007). Structure-functional analysis revealed that Hp beta subunit alone is sufficient to recapitulate effects of Hp to neutralize HMGB1 in vitro in macrophages. The survival advantage of Hp in CLP-induced sepsis was also fully reproduced by Hp beta. Surface plasmon resonance analysis showed that Hp beta binds HMGB1 with high affinity (Kd = 29 nM). Thus, our data reveal unexpected roles of Hp as an endogenous antagonist of HMGB1, preventing the harmful HMGB1-induced inflammation in sepsis. The essential domain of Hp maps to the beta subunit, making it a target in the design of therapeutics.
Abstract Obesity is a major risk factor for insulin resistance, type 2 diabetes mellitus, and atherosclerosis. A chronic inflammatory state plays a pathogenic role in the development and progression of obesity-related disorders. Adipose tissue is infiltrated with macrophages; however the factors mediating the inflammatory response are not yet clear. Here we have identified and characterized a mediator of inflammation that is secreted by adipocytes. Pigment epithelium-derived factor (PEDF), a non-inhibitory serine protease inhibitor, is expressed by differentiated adipocytes. PEDF induces dose dependent increase in expression of proinflammatory cytokines (TNF, IL1 and IL6) in macrophages. The PEDF receptor, adipose triglyceride lipase (ATGL), is expressed in macrophages, and inhibitors of ATGL attenuated PEDF mediated responses indicating importance of PEDF-ATGL interaction in PEDF mediated inflammatory responses. Analysis of downstream effects demonstrated that p38 and ERK1/2 kinases are phosphorylated following PEDF treatment and consistently, inhibitors of p38 and ERK1/2 kinases attenuate PEDF induced cytokine production. PEDF administration induced increased serum levels of TNF and IL6 in mice, while neutralizing PEDF attenuated inflammatory responses. These studies suggest that PEDF secreted by adipocytes contributes to onset and maintenance of chronic inflammation observed in obesity and may serve as a therapeutic target for treatment of obesity related disorders.
Chen, G.; Li, J.; Ochani, M.; Rendon-Mitchell, B.; Ulloa, L.; Yang, H.; Wang, P.; Sama, A. E.; Govert, S. M.; Tracev, K. J.; Wang, H. Author Information
Patients surviving a septic episode exhibit persistent immune impairment and increased mortality due to enhanced vulnerability to infections. In the present study, using the cecal ligation and puncture (CLP) model of polymicrobial sepsis, we addressed the hypothesis that altered vagus nerve activity contributes to immune impairment in sepsis survivors. CLP-surviving mice exhibited less TNFα in serum following administration of LPS, a surrogate for an infectious challenge, than control-operated (control) mice. To evaluate the role of the vagus nerve in the diminished response to LPS, mice were subjected to bilateral subdiaphragmatic vagotomy at 2 weeks post-CLP. CLP-surviving vagotomized mice exhibited increased serum and tissue TNFα levels in response to LPS-challenge compared to CLP-surviving, non-vagotomized mice. Moreover, vagus nerve stimulation in control mice diminished the LPS-induced TNFα responses while having no effect in CLP mice, suggesting constitutive activation of vagus nerve signaling in CLP-survivors. The percentage of splenic CD4+ ChAT-EGFP+ T cells that relay vagus signals to macrophages was increased in CLP-survivors compared to control mice, and vagotomy in CLP-survivors resulted in a reduced percentage of ChAT-EGFP+ cells. Moreover, CD4 knockout CLP-surviving mice exhibited an enhanced LPS-induced TNFα response compared to wild-type mice, supporting a functional role for CD4+ ChAT+ T cells in mediating inhibition of LPS-induced TNFα responses in CLP-survivors. Blockade of the cholinergic anti-inflammatory pathway with methyllcaconitine, an α7 nicotinic acetylcholine receptor antagonist, restored LPS-induced TNFα responses in CLP-survivors. Our study demonstrates that the vagus nerve is constitutively active in CLP-survivors and contributes to the immune impairment.
The cholinergic anti-inflammatory pathway is a physiological mechanism that inhibits cytokine production and diminishes tissue injury during inflammation. Recent studies demonstrate that cholinergic signaling reduces adhesion molecule expression and chemokine production by endothelial cells and suppresses leukocyte migration during inflammation. It is unclear how vagus nerve stimulation regulates leukocyte trafficking because the vagus nerve does not innervate endothelial cells. Using mouse models of leukocyte trafficking, we show that the spleen, which is a major point of control for cholinergic modulation of cytokine production, is essential for vagus nerve-mediated regulation of neutrophil activation and migration. Administration of nicotine, a pharmacologic agonist of the cholinergic anti-inflammatory pathway, significantly reduces levels of CD11b, a beta(2)-integrin involved in cell adhesion and leukocyte chemotaxis, on the surface of neutrophils in a dose-dependent manner and this function requires the spleen. Similarly, vagus nerve stimulation significantly attenuates neutrophil surface CD11b levels only in the presence of an intact and innervated spleen. Further mechanistic studies reveal that nicotine suppresses F-actin polymerization, the rate-limiting step for CD11b surface expression. These studies demonstrate that modulation of leukocyte trafficking via cholinergic signaling to the spleen is a specific, centralized neural pathway positioned to suppress the excessive accumulation of neutrophils at inflammatory sites. Activating this mechanism may have important therapeutic potential for preventing tissue injury during inflammation.
