Remote postconditioning. Brief renal ischemia and reperfusion applied before coronary artery reperfusion reduces myocardial infarct size via endogenous activation of adenosine receptors.

OBJECTIVES: A series of brief coronary artery reperfusions and reocclusions applied during the early minutes of coronary artery reflow ("postconditioning") attenuates reperfusion injury. However, it is not known whether brief ischemia-reperfusion applied to a distant organ at the onset of myocardial reperfusion (i.e. "remote postconditioning", remote PostC) reduces infarct size in the reperfused myocardium. In an in vivo anesthetized rat model of myocardial infarction induced by coronary artery occlusion and reperfusion, this study tested the hypothesis that remote postC induced by a single 5 minute episode of renal artery (RA) occlusion and reperfusion applied immediately before the onset of coronary artery reperfusion protects the myocardium from reperfusion injury by mechanisms involving endogenous adenosine receptor activation. METHODS: All rats were subjected to a total of 30 minutes of left coronary artery occlusion (LCAO) and 3 hours of reperfusion. The rats were randomized to one of six groups: 1) CONTROL: LCAO and reperfusion only with no other intervention; 2) Remote PostC: after 24 minutes of LCAO the RA was occluded for 5 minutes and released 1 min before coronary artery reperfusion; 3) Permanent RA occlusion: the RA was permanently occluded after 24 minutes LCAO continuing to the end of reperfusion; 4) Delayed Remote PostC: after 26 minutes LCAO the RA was occluded for 5 minutes, and its release was delayed until 1 min after coronary artery reperfusion; 5) CON + SPT: rats with LCAO and reperfusion received 10 mg/kg IV of the non-selective adenosine receptor antagonist 8-sulfophenyl theophylline [SPT] administered 5 minutes before coronary artery reperfusion; and 6) Remote PostC + SPT: after 24 minutes of LCAO the RA was occluded for 5 minutes and released 1 minute before coronary artery reperfusion in the presence of 10 mg/kg SPT given 5 min before coronary artery reperfusion. RESULTS: Myocardial infarct size (percentage necrosis/area at risk, mean +/- SEM) was reduced by 50% in Remote PostC (25 +/- 4%) compared to CONTROL (49 +/- 4%, p = 0.003), consistent with a reduction in plasma CK activity (44 +/- 5 vs. 67 +/- 6 U/ml, p = 0.023). In contrast, permanent RA occlusion before LCAO and reperfusion failed to reduce myocardial infarct size (47 +/- 5%) vs CONTROL. Delaying the release of the RA occlusion (delayed Remote PostC) abrogated the myocardial infarct reduction observed with Remote PostC (48 +/- 6%). SPT alone had no effect on infarct size (47 +/- 4% in CON + SPT vs. 49 +/- 4% in CON); however, Remote PostC+SPT abrogated the myocardial infarct size reduction in Remote PostC (50 +/- 3% in Remote PostC + SPT vs. 25 +/- 4% in Remote PostC). CONCLUSIONS: Remote renal postconditioning applied immediately before the onset of coronary artery reperfusion provides potent myocardial infarct size reduction likely exerted during the first minutes of coronary artery reperfusion. This inter-organ remote postconditioning phenomenon is likely mediated in part by release of adenosine by the ischemic-reperfused kidney and subsequent activation of adenosine receptors.

Postconditioning--A new link in nature's armor against myocardial ischemia-reperfusion injury.

Reperfusion injury is a complex process involving several cell types (endothelial cells, neutrophils, and cardiomyocytes), soluble proinflammatory mediators, oxidants, ionic and metabolic dyshomeostasis, and cellular and molecular signals. These participants in the pathobiology of reperfusion injury are not mutually exclusive. Some of these events take place during the very early moments of reperfusion, while others, seemingly triggered in part by the early events, are activated within a later timeframe. Postconditioning is a series of brief mechanical interruptions of reperfusion following a specific prescribed algorithm applied at the very onset of reperfusion. This algorithm lasts only from 1 to 3 minutes depending on species. Although associated with re-occlusion of the coronary artery or re-imposition of hypoxia in cell culture, the reference to ischemia has been dropped. Postconditioning has been observed to reduce infarct size and apoptosis as the "end games" in myocardial therapeutics; salvage of infarct size was similar to that achieved by the gold standard of protection, ischemic preconditioning. The cardioprotection was also associated with a reduction in: endothelial cell activation and dysfunction, tissue superoxide anion generation, neutrophil activation and accumulation in reperfused myocardium, microvascular injury, tissue edema, intracellular and mitochondrial calcium accumulation. Postconditioning sets in motion triggers and signals that are functionally related to reduced cell death. Adenosine has been implicated in the cardioprotection of postconditioning, as has e-NOS, nitric oxide and guanylyl cyclase, opening of K(ATP) channels and closing of the mitochondrial permeability transition pore. Cardioprotection by postconditioning has also been associated with the activation of intracellular survival pathways such as ERK1/2 and PI3 kinase - Akt pathways. Other pathways have yet to be identified. Although many of the pathways involved in postconditioning have also been identified in ischemic preconditioning, some may not be involved in preconditioning (ERK1/2). The timing of action of these pathways and other mediators of protection in postconditioning differs from that of preconditioning. In contrast to preconditioning, which requires a foreknowledge of the ischemic event, postconditioning can be applied at the onset of reperfusion at the point of clinical service, i.e. angioplasty, cardiac surgery, transplantation.

Effects of homocysteine on smooth muscle cell proliferation in both cell culture and artery perfusion culture models.

BACKGROUND: Hyperhomocysteinemia is associated with increased risk for vascular disease. However, the pathogenic mechanisms of homocysteine are largely unknown. We evaluated the effects of homocysteine on smooth muscle cell (SMC) and endothelial cell proliferation in cell culture and on SMC proliferation of balloon angioplasty-injured arteries in a perfusion culture model. METHODS: Human and pig SMCs and endothelial cells were cultured with variable amounts of homocysteine for 72 h and the total cells were counted using a hemocytometer. Fresh pig carotid arteries were harvested from a local slaughterhouse and cultured in a newly designed artery perfusion culture system. Five groups of arteries (six per group) were cultured for 48 h under different conditions: normal control, balloon angioplasty injury alone, and injury with three different doses of homocysteine. Vessel viability was evaluated. SMC proliferation was assayed by bromodeoxyuridine (BrdU) DNA labeling. RESULTS: At concentrations equivalent to those in human hyperhomocysteinemia, homocysteine significantly stimulated both cultured human and pig SMC proliferation with a dose-dependent effect, while it inhibited cultured endothelial cell growth. Perfusion-cultured pig carotid arteries remained contractile in response to norepinephrine and relaxant to nitroglycerine, and viable cells were also isolated from the cultured arteries. SMC proliferation (BrdU index) showed significant differences among the groups. SMC proliferation was stimulated by vascular injury and further enhanced by homocysteine in a dose-dependent manner. The proliferative response occurred strongly on the luminal side of the vessel wall, with the effects tapering toward the adventitia. CONCLUSIONS: Homocysteine had a mitogenic effect on vascular SMCs and a cytotoxic effect on endothelial cells. This differential effect of homocysteine on vascular cells may represent a pathogenic mechanism of vascular lesion formation in patients with hyperhomocysteinemia.