NOS II Inhibition Restores Attenuation of Endothelium-Dependent Hyperpolarization in Rat Mesenteric Artery Exposed to Lipopolysaccharide

Kinin B1 receptor and TLR4 interaction in inflammatory response

OBJECTIVE

We aimed to broaden our understanding of a potential interaction between B1R and TLR4, considering earlier studies suggesting that lipopolysaccharide (LPS) may trigger B1R stimulation.

METHODS

We assessed the impact of DBK and LPS on the membrane potential of thoracic aortas from C57BL/6, B1R, or TLR4 knockout mice. Additionally, we examined the staining patterns of these receptors in the thoracic aortas of C57BL/6 and in endothelial cells (HBMEC).

RESULTS

DBK does not affect the resting membrane potential of aortic rings in C57BL/6 mice, but it hyperpolarizes preparations in B1KO and TLR4KO mice. The hyperpolarization mechanism in B1KO mice involves B2R, and the TLR4KO response is independent of cytoplasmic calcium influx but relies on potassium channels. Conversely, LPS hyperpolarizes thoracic aorta rings in both C57BL/6 and B1KO mice, with the response unaffected by a B1R antagonist. Interestingly, the absence of B1R alters the LPS response to potassium channels. These activities are independent of nitric oxide synthase (NOS). While exposure to DBK and LPS does not alter B1R and TLR4 mRNA expression, treatment with these agonists increases B1R staining in endothelial cells of thoracic aortic rings and modifies the staining pattern of B1R and TLR4 in endothelial cells. Proximity ligation assay suggests a interaction between the receptors.

CONCLUSION

Our findings provide additional support for a putative connection between B1R and TLR4 signaling. Given the involvement of these receptors and their agonists in inflammation, it suggests that drugs and therapies targeting their effects could be promising therapeutic avenues worth exploring.

Human serum albumin improves endothelial dysfunction and survival during experimental endotoxemia: concentration-dependent properties

OBJECTIVES

The mechanisms by which human serum albumin might protect against sepsis-induced organ dysfunction and improve survival are not elucidated. The present study was designed to assess the effects of two concentrations of human serum albumin on endotoxin-induced mortality as well as on endothelial and organ dysfunctions in both mouse and cell models.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University research laboratories.

SUBJECTS

Swiss mice (n = 10-15/group) were injected with either lipopolysaccharide or vehicle. Four and 12 hrs later, mice were infused or not with human serum albumin HSA (4% or 20%, 10 mL/kg) or normal saline (0.9% NaCl, 30 mL/kg). Human uterine vein endothelial cells were exposed to both lipopolysaccharide and tumor necrosis factor-α during 8 hrs in the presence or absence of human serum albumin (4% or 20%).

MEASUREMENTS AND MAIN RESULTS

Mice survival, reactivity of mesenteric arteries, and Western blot protein analysis were assessed. Circulating endothelin-1, gluthatione, gluthatione disulfide, and creatinine plasma levels were measured. Nitric oxide production, oxidative, and nitrosative stresses were also measured in situ in endothelial cells. Human serum albumin 4%, but not human serum albumin 20% or normal saline solution, improved survival time of endotoxemic mice. Furthermore, human serum albumin 4% activated endothelial nitric oxide synthase and restored lipopolysaccharide-impaired flow-dependent endothelial dilation in mesenteric arteries. This was associated with a downregulation of nuclear factor κB and an upregulation of nuclear respiratory factor-2 and heme oxygenase-1. Human serum albumin 4% reduced lipopolysaccharide-induced renal dysfunction, enhanced endothelin-1 production and glutathione plasmatic levels, whereas human serum albumin 20% increased gluthatione disulfide. Furthermore, human serum albumin 4% but not 20% blunted lipopolysaccharide-tumor necrosis factor-α-induced oxidative and nitrosative stresses in endothelial cells and increased their gluthatione levels.

CONCLUSIONS

The present data confirm a protective effect of 4% human serum albumin treatment both on mice survival and endothelial dysfunction by inhibiting inflammatory and oxidative stress pathways induced by endotoxins. Conversely, higher concentrations of human serum albumin were detrimental suggesting a dose-dependent effect.

Sivelestat relaxes porcine coronary artery via inhibition of Ca2+ sensitization induced by a receptor agonist

Sivelestat sodium hydrate (sivelestat) is a novel synthetic drug and specific inhibitor of neutrophil elastase that has been approved in Japan as a treatment for acute lung injury associated with systemic inflammatory response syndrome. There are no reports on the effects of sivelestat on the contractile regulation of vascular smooth muscle. The purpose of the present study was to assess the effects of sivelestat on porcine coronary artery. Sivelestat induced concentration-dependent (3 x 10 to 3 x 10 M) vasorelaxation in U46619 (100 nM)-precontracted porcine coronary artery with or without endothelium. Simultaneous measurements of tension and the cytosolic Ca concentration ([Ca]i) revealed that sivelestat shifted the [Ca]i-tension curve to the right and downward during stimulation with 118 mM K and 100 nM U46619. In beta-escin-permeabilized arterial strips, sivelestat abolished GTP plus U46619-induced contractions at constant [Ca]i, whereas it had no effect on Ca-induced contractions. Thus, sivelestat relaxes porcine coronary artery smooth muscle via the selective inhibition of Ca sensitization induced by a receptor agonist, without affecting Ca-induced contraction.

Lysozyme, a mediator of sepsis that produces vasodilation by hydrogen peroxide signaling in an arterial preparation

In septic shock, systemic vasodilation and myocardial depression contribute to the systemic hypotension observed. Both components can be attributed to the effects of mediators that are released as part of the inflammatory response. We previously found that lysozyme (Lzm-S), released from leukocytes, contributed to the myocardial depression that develops in a canine model of septic shock. Lzm-S binds to the endocardial endothelium, resulting in the production of nitric oxide (NO), which, in turn, activates the myocardial soluble guanylate cyclase (sGC) pathway. In the present study, we determined whether Lzm-S might also play a role in the systemic vasodilation that occurs in septic shock. In a phenylephrine-contracted canine carotid artery ring preparation, we found that both canine and human Lzm-S, at concentrations similar to those found in sepsis, produced vasorelaxation. This decrease in force could not be prevented by inhibitors of NO synthase, prostaglandin synthesis, or potassium channel inhibitors and was not dependent on the presence of the vascular endothelium. However, inhibitors of the sGC pathway prevented the vasodilatory activity of Lzm-S. In addition, Aspergillus niger catalase, which breaks down H(2)O(2), as well as hydroxyl radical scavengers, which included hydroquinone and mannitol, prevented the effect of Lzm-S. Electrochemical sensors corroborated that Lzm-S caused H(2)O(2) release from the carotid artery preparation. In conclusion, these results support the notion that when Lzm-S interacts with the arterial vasculature, this interaction results in the formation of H(2)O(2), which, in turn, activates the sGC pathway to cause relaxation. Lzm-S may contribute to the vasodilation that occurs in septic shock.