Search

Long-term ethanol consumption at low to moderate levels exerts cardioprotective effects in the setting of ischemia and reperfusion (I/R). The aims of this study were to determine whether 1) a single orally administered dose of ethanol [ethanol preconditioning (EtOH-PC)] would induce a biphasic temporal pattern of protection (early and late phases) against the inflammatory responses to I/R and 2) adenosine and nitric oxide (NO) act as initiators of the late phase of protection. Ethanol was administered as a bolus to C57BL/6 mice at a dose that achieved a peak plasma concentration of ∼45 mg/dl 30 min after gavage and returned to control levels within 60 min of alcohol ingestion. The superior mesenteric artery was occluded for 45 min followed by 60 min of reperfusion beginning 10 min or 1, 2, 3, 4, or 24 h after ethanol ingestion, and the numbers of fluorescently labeled rolling and firmly adherent (stationary) leukocytes in single postcapillary venules of the small intestine were quantified using intravital microscopic approaches. I/R induced marked increases in leukocyte rolling and adhesion, effects that were attenuated by EtOH-PC 2–3 h before I/R (early phase), absent when assessed after 10 min, 1 h, and 4 h of ethanol ingestion, with an even more powerful late phase of protection reemerging when I/R was induced 24 h later. The anti-inflammatory effects of late EtOH-PC were abolished by treatment with adenosine deaminase, an adenosine A2(but not A1) receptor antagonist, or a NO synthase (NOS) inhibitor during the period of EtOH-PC. Preconditioning with an adenosine A2(but not an A1) receptor agonist in lieu of ethanol 24 h before I/R mimicked the protective actions of late phase EtOH-PC. Like EtOH-PC, the effect of preconditioning with an adenosine A2receptor agonist was abrogated by coincident NOS inhibition. These findings suggest that EtOH-PC induces a biphasic temporal pattern of protection against the proinflammatory effects of I/R. In addition, our observations are consistent with the hypothesis that the late phase of EtOH-PC is triggered by NO formed secondary to adenosine A2receptor-dependent activation of NOS during the period of ethanol exposure.

Ingestion of low levels of ethanol 24 h before [ethanol preconditioning (EPC)] ischemia and reperfusion (I/R) prevents postischemic leukocyte rolling (LR) and adhesion (LA), effects that were abolished by adenosine A2receptor (ADO-A2R) antagonists or nitric oxide (NO) synthase (NOS) inhibitors. The aims of this study were to determine whether NO derived from endothelial NOS (eNOS) during the period of ethanol exposure triggered entrance into this preconditioned state and whether these events were initiated by an ADO-A2R-dependent mechanism. Ethanol or distilled water vehicle was administered to C57BL/6J [wild type (WT)] or eNOS-deficient (eNOS−/−) mice by gavage. Twenty-four hours later, the superior mesenteric artery was occluded for 45 min. LR and LA were quantified by intravital microscopy after 30 and 60 min of reperfusion. I/R increased LR and LA in WT mice, effects that were abolished by EPC or NO donor preconditioning (NO-PC). NO-PC was not attenuated by coincident administration of an ADO-A2R antagonist. I/R increased LR and LA in eNOS−/− mice to levels comparable with those noted in WT animals. However, EPC only slightly attenuated postischemic LR and LA, whereas NO-PC remained effective as a preconditioning stimulus in eNOS−/− mice. Preconditioning with an ADO-A2R agonist (which we previously demonstrated prevents I/R-induced LR and LA in WT animals) failed to attenuate these postischemic adhesive responses in eNOS−/− mice. Our results indicate that EPC is triggered by NO formed secondary to ADO-A2R-dependent eNOS activation during the period of ethanol exposure 24 h before I/R.

The aim of this study was to determine whether protein kinase C (PKC) contributed to the effects of ethanol ingestion to prevent P-selectin expression, leukocyte rolling (LR), and stationary leukocyte adhesion (LA) induced by subjecting the small bowel to ischemia and reperfusion (I/R) 24 hr later. I/R increased P-selectin expression, LR, and LA, effects that were largely abolished by antecedent ethanol consumption. Exposing the bowel to a specific but nonisoform-selective PKC inhibitor (chelerythrine or bisindolylmaleimide I) during the period of ethanol exposure did not alter the anti-inflammatory effects induced by ethanol ingestion 24 hr prior to I/R. Go-6976, a PKC inhibitor that exhibits a high degree of selectivity for the calcium-dependent PKC isoforms, markedly reduced the effectiveness of antecedent ethanol exposure to abrogate these postischemic inflammatory responses. Our data indicate that antecedent ethanol exposure prevents postischemic P-selectin expression, LR, and LA by a mechanism that involves activation of calcium-dependent PKC isotypes.

Ethanol ingestion 24 h prior to ischemia and reperfusion (I/R) prevents postischemic leukocyte rolling and adhesion in postcapillary venules of the small bowel. Since I/R-induced leukocyte rolling is critically dependent on the expression of P-selectin by endothelial cells lining postcapillary venules, the authors hypothesized that antecedent ethanol consumption would attenuate postischemic expression of this adhesive ligand.To address this postulate, P-selectin expression was evaluated using a dual radiolabeled monoclonal antibody technique in the jejunum of mice that received either distilled water vehicle or ethanol by gavage (dose) on day 1 and then were subjected to sham I/R (nonischemic controls) or I/R (20 min ischemia/60 min reperfusion) 24 h later.I/R was associated with a 2-fold increase in P-selectin expression relative to nonischemic controls, an effect that was largely abolished by antecedent ethanol ingestion. Exposing the bowel to adenosine deaminase or adenosine A2 receptor antagonists (DMPX or ZM241385), an NO synthase inhibitor (L-NIO) or an NO scavenger (PTIO), or an antioxidant (mercaptoproprionyl glycine) during the period of ethanol exposure on day 1 prevented the beneficial effect of ethanol to limit I/R-induced P-selectin expression, on day 2.The data indicate that antecedent ethanol exposure prevents postischemic P-selectin expression on day 2 by a mechanism that is triggered by adenosine A2 receptor activation and the formation of nitric oxide (NO) and reactive oxygen species (ROS) during the period of ethanol exposure on day 1.

Prolonged ischemia followed by reperfusion (I/R) results in impaired endothelial cell function in all segments of the microvasculature. Moreover, microcirculatory dysfunction plays a major role in the genesis of the reperfusion component of total tissue injury in I/R. Thus, preservation of endothelial function is an important therapeutic goal for ameliorating injury in tissues subjected to I/R. An accumulating body of evidence indicates that low to moderate ethanol consumption produces an adaptive transformation to a protected phenotype in both microvascular endothelium and parenchymal cells such that they are rendered resistant to the pathologic effects of I/R. The purpose of this review is to summarize our current understanding of the signaling pathways underlying the development of the preconditioned state induced by antecedent ethanol in arteriolar, capillary, and venular endothelium. In addition, we will highlight understudied areas with regard to microvascular protection afforded by antecedent ethanol in the hopes that this will stimulate investigation of its underlying mechanisms. Understanding these signaling pathways may provide a mechanistic rationale for the development of novel treatment interventions that target both the microcirculatory and parenchymal sequelae to I/R, thereby maximizing the therapeutic potential of the protected phenotypes produced by pharmacologic preconditioning.

Preconditioning refers to a phenomenon whereby tissues are rendered resistant to the deleterious effects of prolonged ischemia and reperfusion (I/R) by prior exposure to oxidants, brief periods of vascular occlusion, endotoxin derivatives, heat shock, a variety of pharmacologic agents (chemical or pharmacologic preconditioning) or chronic ethanol consumption (6, 11, 16, 26, 29, 35, 40, 42, 48, 55, 71). Of these perturbations, our best understanding of the mechanisms involved in conferring protection is related to ischemic preconditioning (IPC). The beneficial effects of IPC are not related to improved collateral flow but instead represent an enhanced intrinsic ability of tissues to tolerate ischemia. However, recent work indicates that in addition to its anti-ischemic effects, IPC also completely prevents the reperfusion component of tissue injury by abrogating the inflammatory changes that are initiated in the microcirculation upon restitution of blood flow (1, 7, 14, 29, 36, 40, 41, 75). Additional support for this concept is provided by the demonstration that endothelium-dependent vasoregulatory mechanisms remain intact in preconditioned tissues (42, 71). Taken together, these observations indicate that adaptive changes in the microvasculature play a key role in the development of the preconditioned state. Thus, understanding the mechanisms whereby both arterial and venular endothelium enter a protective or defensive phenotype as a result of preconditioning may lead to the development of novel therapeutic strategies to manage I/R injury.