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- Author or Editor: Wan-chun Sun x
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Objective—To assess the anti-inflammatory effects of an adenosine analogue on lipopolysaccharide (LPS)-stimulated equine neutrophils.
Sample Population—Neutrophils obtained from 10 healthy horses.
Procedures—An adenosine analogue (5′-N-ethylcarboxamidoadenosine [NECA]) was tested for its ability to inhibit production of reactive oxygen species (ROS) in LPS-stimulated equine neutrophils. Selective adenosine receptor antagonists were used to identify the receptor subtype responsible for effects. To assess the mechanism of action of NECA, cAMP concentrations were measured, and effects of dibutyryl cAMP (a stable analogue of cAMP) and rolipram (a type 4 phosphodiesterase inhibitor) were investigated.
Results—NECA elicited concentration-dependent inhibition of ROS production that was inhibited by ZM241385, a selective adenosine A2A receptor antagonist; this effect of NECA was not affected by the adenosine A2B receptor antagonist MRS1706. Also, ZM241385 blocked NECA-induced increases in cAMP concentrations, whereas MRS1706 did not alter this effect of NECA. Rolipram potentiated NECA-induced inhibition of ROS production, and dibutyryl cAMP also inhibited ROS production.
Conclusions and Clinical Relevance—Activation of adenosine A2A receptors inhibited ROS production by LPS-stimulated equine neutrophils in a cAMP-dependent manner. These results suggest that stable adenosine A2A receptor agonists may be developed as suitable anti-inflammatory drugs in horses.
Objective—To evaluate anti-inflammatory effects of several novel adenosine receptor agonists and to determine their specificity for various adenosine receptor subtypes on neutrophils, cells heterologously expressing equine adenosine receptors, or equine brain membranes.
Sample Population—Neutrophils isolated from 8 healthy horses.
Procedures—Radioligand binding experiments were performed to compare binding affinities of adenosine receptor agonists to equine adenosine A1, A2A, and A3 receptor subtypes. Effects of these agonists on endotoxin-induced production of reactive oxygen species (ROS) by equine neutrophils and roles of specific adenosine receptor subtypes and cAMP production in mediating these effects were determined.
Results—Radioligand binding experiments yielded a ranked order of affinity for the brain equine A2A receptor on the basis of 50% inhibitory concentrations (IC50) of the agonists as follows: ATL307 (IC50 = 1.9nM) and ATL313 > ATL309 and ATL310 > ATL202 > 2-([p-2- carboxyethyl] phenylethylamino)-5′-N-ethylcarboxyamidoadenosine > 5′-N-ethylcarboxamidoadenosine. Furthermore, ATL313 had approximately 100-fold greater selectivity for A2A over A1 and A3 receptors. In functional assays with equine neutrophils, the compounds inhibited endotoxin-induced ROS production and stimulated production of cAMP with the same ranked order of potency. Results of experiments performed with selective adenosine receptor antagonists indicated that functional effects of ATL313 were via stimulation of A2A receptors.
Conclusions and Clinical Relevance—Results indicated that activation of A2A receptors exerted anti-inflammatory effects on equine neutrophils and that stable, highly selective adenosine A2A receptor agonists may be developed for use in management of horses and other domestic animals with septic and nonseptic inflammatory diseases.
Objective—To evaluate proinflammatory effects of the second-generation synthetic lipid A analogue E5564 on equine whole blood and isolated monocytes and to determine the ability of E5564 to prevent LPS (lipopolysaccharide)-induced procoagulant activity (PCA); tumor necrosis factor (TNF)-α production; and mRNA expression of TNF-α, interleukin (IL)-1β, IL-6, and IL-10 by equine monocytes.
Sample Population—Venous blood samples obtained from 19 healthy horses.
Procedures—Whole blood and monocytes were incubated with Escherichia coli O111:B4 LPS, E5564, or E5564 plus E coli O111:B4 LPS. Whole blood and cell supernatants were assayed for TNF-α, and cell lysates were assayed to determine PCA. Expression of mRNA for TNF-α, IL-1β, IL-6, and IL-10 by monocytes was determined by use of real-time quantitative PCR assay.
Results—Minimal proinflammatory effects were detected in whole blood and monocytes. In addition, E5564 inhibited LPS-induced PCA and TNF-α production in a concentration-dependent manner. Furthermore, E5564 significantly inhibited LPS-induced mRNA expression of TNF-α, IL-1β, and IL-10 and decreased LPS-induced expression of IL-6.
Conclusions and Clinical Relevance—The second-generation synthetic lipid A analogue E5564 lacked agonist activity in equine whole blood and monocytes and was a potent antagonist of enteric LPS. Therefore, E5564 appeared to be the first lipid A analogue that has potential as an effective therapeutic agent in horses with endotoxemia.