Osteopontin expression during early cerebral ischemia-reperfusion in rats: enhanced expression in the right cortex is suppressed by acetaminophen.

Osteopontin (OPN) is a pleiotropic protein implicated in various inflammatory responses including ischemia-reperfusion (I-R) injury. Two distinct forms of the protein have been identified: an extensively studied secreted form (sOPN) and a less-well-known intracellular form (iOPN). Studies have shown that increased OPN expression parallels the time course of macrophage infiltration into injured tissue, a late event in the development of cerebral infarcts. sOPN has been suggested to promote remodeling of the extracellular matrix in the brain; the function of iOPN may be to facilitate certain signal transduction processes. Here, we studied OPN expression in adult male Sprague-Dawley rats subjected to global forebrain I-R injury. We found iOPN in the cytoplasm of both cortices and the hippocampus, but unexpectedly only the right cortex exhibited a marked increase in the iOPN level after 45 min of reperfusion. Acetaminophen, a drug recently shown to decrease apoptotic incidence, caspase-9 activation, and mitochondrial dysfunction during global I-R, significantly inhibited the increase in iOPN protein in the right cortex, suggesting a role for iOPN in the response to I-R injury in the right cortex.

Acetaminophen reduces mitochondrial dysfunction during early cerebral postischemic reperfusion in rats.

Acetaminophen, a popular analgesic and antipyretic, has been found to be effective against neuronal cell death in in vivo and in vitro models of neurological disorders. Acute neuronal death has been attributed to loss of mitochondrial permeability transition coupled with mitochondrial dysfunction. The potential impact of acetaminophen on acute injury from cerebral ischemia-reperfusion has not been studied. We investigated the effects of acetaminophen on cerebral ischemia-reperfusion-induced injury using a transient global forebrain ischemia model. Male Sprague-Dawley rats received 15mg/kg of acetaminophen intravenously during ischemia induced by hypovolemic hypotension and bilateral common carotid arterial occlusion, which was followed by reperfusion. Acetaminophen reduced tissue damage, degree of mitochondrial swelling, and loss of mitochondrial membrane potential. Acetaminophen maintained mitochondrial cytochrome c content and reduced activation of caspase-9 and incidence of apoptosis. Our data show that acetaminophen reduces apoptosis via a mitochondrial-mediated mechanism in an in vivo model of cerebral ischemia-reperfusion. These findings suggest a novel role for acetaminophen as a potential stroke therapeutic.

Acetaminophen is cardioprotective against H2O2-induced injury in vivo.

Here we report our ongoing investigation of the cardiovascular effects of acetaminophen, with emphasis on oxidation-induced canine myocardial dysfunction. The objective of the current study was to investigate whether acetaminophen could attenuate exogenous H(2)O(2)-mediated myocardial dysfunction in vivo. Respiratory, metabolic, and hemodynamic indices such as left ventricular function (LVDP and +/-dP/dt(max)), and percent ectopy were measured in anesthetized, open-chest dogs during intravenous administration of 0.88 mM, 2.2 mM, 6.6 mM H(2)O(2). Following 6.6 mM H(2)O(2), tissue from the left ventricle was harvested for electron microscopy. Left ventricular function did not vary significantly between vehicle and acetaminophen groups under baseline conditions. Acetaminophen-treated dogs regained a significantly greater fraction of baseline function after high concentrations of H(2)O(2) than vehicle-treated dogs. Moreover, the incidence of H(2)O(2)-induced ventricular arrhythmias was significantly reduced in the acetaminophen-treated group. Percent ectopy following 6.6 mM concentrations of H(2)O(2) was 1 +/- 0.3 vs. 0.3 +/- 0.1 (P < 0.05) for vehicle- and acetaminophen-treated dogs, respectively. Additionally, electron micrograph images of left ventricular tissue confirmed preservation of tissue ultrastructure in acetaminophen-treated hearts when compared to vehicle. We conclude that, in the canine myocardium, acetaminophen is both functionally cardioprotective and antiarrhythmic against H(2)O(2)-induced oxidative injury.

Acetaminophen-mediated cardioprotection via inhibition of the mitochondrial permeability transition pore-induced apoptotic pathway.

Our laboratory has previously reported that acetaminophen confers functional cardioprotection following cardiac insult, including ischemia/reperfusion, hypoxia/reoxygenation, and exogenous peroxynitrite administration. In the present study, we further examined the mechanism of acetaminophen-mediated cardioprotection following ischemia/reperfusion injury. Langendorff-perfused guinea pig hearts were exposed to acute treatment with acetaminophen (0.35 mM) or vehicle beginning at 15 min of a 30-min baseline stabilization period. Low-flow global myocardial ischemia was subsequently induced for 30 min followed by 60 min of reperfusion. At the completion of reperfusion, hearts were homogenized and separated into cytosolic and mitochondrial fractions. Mitochondrial swelling and mitochondrial cytochromec release were assessed and found to be significantly and completely reduced in acetaminophen- vs. vehicle-treated hearts following reperfusion. In a separate group of hearts, ventricular myocytes were isolated and subjected to fluorescence-activated cell sorting. Acetaminophen-treated hearts showed a significant decrease in late stage apoptotic myocytes compared with vehicle-treated hearts following injury (58 +/- 1 vs. 81 +/- 5%, respectively). These data, together with electron micrograph analysis, suggest that acetaminophen mediates cardioprotection, in part, via inhibition of the mitochondrial permeability transition pore and subsequent apoptotic pathway.

Antiarrhythmic properties of acetaminophen in the dog.

Mongrel dogs bred for research and weighing 25 +/- 3 kg were used to test the hypothesis that acetaminophen has antiar-rhythmic properties. Only ventricular arrhythmias defined by the Lambeth Conventions were investigated. Dogs were exposed either to 60 mins of regional myocardial ischemia followed by 180 mins of reperfusion (n = 14) or were administered a high dose of ouabain (n = 14). Both groups of 14 dogs were further divided into vehicle and acetaminophen treatment groups (n = 7 in each). During selected 10-min intervals, we recorded the numbers of ventricular premature beats, ventricular salvos, ventricular bigeminy, ventricular tachycardia (nonsustained and sustained), and we recorded the heart rate, systemic arterial blood pressure, and left ventricular function. Neither heart rate nor the number of ventricular arrhythmias differed significantly under baseline conditions. Conversely, the combined average number of ventricular ectopic beats during ischemia and reperfusion was significantly less in the presence of acetaminophen (28 +/- 4 vs. 6 +/- 1; P < 0.05). Similarly, percent ectopy during reperfusion in vehicle- and acetaminophen-treated dogs was 1.4 +/- 0.4 and 0.4 +/- 0.2, respectively (P < 0.05). The number of all ventricular ectopic beats except ventricular salvos was also significantly reduced in the presence of acetaminophen. Similar results were obtained with ouabain. Our results reveal that systemic administration of a therapeutic dose of acetaminophen has previously unreported antiarrhythmic effects in the dog.