Oonagh Dowling

Cholinergic Neural Signals to the Spleen Down-Regulate Leukocyte Trafficking via CD11b

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 β2-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.

Magnesium sulfate suppresses inflammatory responses by human umbilical vein endothelial cells (HuVECs) through the NFκB pathway

Dysfunctional endothelial cell activation and cytokines are implicated in preterm labor, a condition commonly treated with the tocolytic agent, magnesium sulfate (MgSO(4)). Based on recent findings showing the inflammatory effects of magnesium deficiency, we examined the effect of MgSO(4) on human umbilical vein endothelial cell (HuVEC) inflammatory responses in vitro. HuVECs isolated from term umbilical cords were incubated with MgSO(4) prior to stimulation with lipopolysaccharide (LPS) and then assessed for endothelial cell activation. Endothelial cell supernatants were assayed for inflammatory mediator production (interleukin-8; IL-8), and endothelial cell-associated intercellular adhesion molecule (ICAM-1) expression was determined. In the absence of LPS stimulation, MgSO(4) had no effect on HuVEC responses. Treatment of HuVECs with MgSO(4) prior to LPS stimulation inhibited inflammatory mediator production (p<0.05) and cell adhesion molecule expression (p<0.05) in a dose-dependent manner. Mechanistic studies showed that MgSO(4) reduced NFkappaB nuclear translocation and protected cytoplasmic IkappaBalpha from degradation in LPS-treated HuVECs. In conclusion, MgSO(4) inhibits endothelial cell activation, as measured by levels of IL-8 and ICAM-1 expression, via NFkappaB. Our results support the hypothesis that MgSO(4) treatment may function as an anti-inflammatory agent during preterm labor.

Nicotinic Acetylcholine Receptor Agonists Attenuate Septic Acute Kidney Injury in Mice by Suppressing Inflammation and Proteasome Activity

Sepsis is one of the leading causes of acute kidney injury (AKI). Septic patients who develop acute kidney injury (AKI) are at increased risk of death. To date there is no effective treatment for AKI or septic AKI. Based on their anti-inflammatory properties, we examined the effects of nicotinic acetylcholine receptor agonists on renal damage using a mouse model of lipopolysaccharide (LPS)-induced AKI where localized LPS promotes inflammation-mediated kidney damage. Administration of nicotine (1 mg/kg) or GTS-21 (4 mg/kg) significantly abrogated renal leukocyte infiltration (by 40%) and attenuated kidney injury. These renoprotective effects were accompanied by reduced systemic and localized kidney inflammation during LPS-induced AKI. Consistent with these observations, nicotinic agonist treatment significantly decreased renal IκBα degradation and NFκB activation during LPS-induced AKI. Treatment of human kidney cells with nicotinic agonists, an NFκB inhibitor (Bay11), or a proteasome inhibitor (MG132) effectively inhibited their inflammatory responses following stimulation with LPS or TNFα. Renal proteasome activity, a major regulator of NFκB-mediated inflammation, was enhanced by approximately 50% during LPS-induced AKI and elevated proteasome activity was significantly blunted by nicotinic agonist administration in vivo. Taken together, our results identify enhanced renal proteasome activity during LPS-induced AKI and the suppression of both proteasome activity and inflammation by nicotinic agonists to attenuate LPS-induced kidney injury.

Magnesium sulfate ameliorates maternal and fetal inflammation in a rat model of maternal infection

OBJECTIVE Magnesium sulfate is proposed to have neuroprotective effects in the offspring. We examined the effects of maternal magnesium sulfate administration on maternal and fetal inflammatory responses in a rat model of maternal infection. STUDY DESIGN Pregnant rats were injected with saline, Gram-negative bacterial endotoxin lipopolysaccharide or lipopolysaccharide with magnesium sulfate (pre- and/or after lipopolysaccharide) to mimic infection. Maternal blood, amniotic fluid, fetal blood, and fetal brains were collected 4 hours after lipopolysaccharide and assayed for tumor necrosis factor, interleukin-6, monocyte chemoattractant protein-1, and growth-related oncogene-KC. In addition, the effect of magnesium sulfate on cytokine production by an astrocytoma cell line was assessed. RESULTS Lipopolysaccharide administration induced tumor necrosis factor, interleukin-6, monocyte chemoattractant protein-1, and growth-related oncogene-KC expression in maternal and fetal compartments. Maternal magnesium sulfate treatment significantly attenuated lipopolysaccharide-induced multiple proinflammatory mediator levels in maternal and fetal compartments. CONCLUSION Antenatal magnesium sulfate administration significantly ameliorated maternal, fetal, and gestational tissue-associated inflammatory responses in an experimental model of maternal infection.

Progesterone suppresses the fetal inflammatory response ex vivo.

OBJECTIVE Progesterone supplementation has been shown to be efficacious in preventing preterm birth. We sought to investigate the effects of progesterone on fetal inflammatory responses. STUDY DESIGN Fetal mononuclear cells were isolated from umbilical cord blood and exposed to vehicle or progesterone (P4) for 1 hour prior to lipopolysaccharide (LPS) stimulation. Supernatants were assayed for tumor necrosis factor-alpha. Similar experiments were performed using cyclic adenosine monophosphate (cAMP) and progesterone modulators. The effect of P4 treatment on intracellular cAMP levels was also determined. RESULTS LPS treatment led to a significant increase in cytokine production by fetal mononuclear cells. Despite the lack of detectable nuclear progesterone receptors, P4 suppressed this inflammatory response. R5020 (progesterone agonist), forskolin (cAMP inducer), and dibutyryl cAMP (cAMP agonist) all achieved immunosuppression. The cAMP antagonist, Rp-cAMP, blocked the inhibitory effect of progesterone. P4 significantly increased intracellular cAMP levels. CONCLUSION Progesterone rapidly suppresses the fetal inflammatory response, possibly via nongenomic activation of the cAMP cascade.