Coronary and myocardial effects of acetaminophen: protection during ischemia-reperfusion

Role of PI3K/Akt axis in mitigating hippocampal ischemia-reperfusion injury via CB1 receptor stimulation by paracetamol and FAAH inhibitor in rat

AIMS

Acetaminophen or paracetamol (PAR), the recommended antipyretic in COVID-19 and clinically used to alleviate stroke-associated hyperthermia interestingly activates cannabinoid receptor (CB1) through its AM404 metabolite, however, to date, no study reports the in vivo activation of PAR/AM404/CB1 axis in stroke. The current study deciphers the neuroprotective effect of PAR in cerebral ischemia/reperfusion (IR) rat model and unmasks its link with AM404/CB1/PI3K/Akt axis.

MATERIALS AND METHODS

Animals were allocated into 5 groups: (I) sham-operated (SO), (II) IR, (III) IR + PAR (100 mg/kg), (IV) IR + PAR (100 mg/kg) + URB597; anandamide degradation inhibitor (0.3 mg/kg) and (V) IR + PAR (100 mg/kg) + AM4113; CB1 Blocker (5 mg/kg). All drugs were intraperitoneally administered at the inception of the reperfusion period.

KEY FINDINGS

PAR administration alleviated the cognitive impairment in the Morris Water Maze as well as hippocampal histopathological and immunohistochemical examination of GFAP. The PAR signaling was associated with elevation of anandamide level, CB1 receptor expression and survival proteins as p^S473-Akt. P^{(tyr202/thr204)}-ERK1/2 and p^S9-GSK3β. Simultaneously, PAR increased hippocampal BDNF and ß-arrestin1 levels and decreased glutamate level. PAR restores the deranged redox milieu induced by IR Injury, by reducing lipid peroxides, myeloperoxidase activity and NF-κB and increasing NPSH, total antioxidant capacity, nitric oxide and Nrf2 levels. The pre-administration of AM4113 reversed PAR effects, while URB597 potentiated them.

SIGNIFICANCE

PAR poses a significant neuroprotective effect which may be mediated, at least in part, via activation of anandamide/CB1/PI3K/Akt pathway in the IR rat model.

Protective effect of paracetamol in doxorubicin-induced cardiotoxicity in ischemia/reperfused isolated rat heart

OBJECTIVE

Doxorubicin (DOX) induces cardiac dysfunction. Paracetamol (APAP) has also been established as an effective cardioprotective agent during ischemia/reperfusion. Therefore, this study aims to evaluate the effect of APAP on DOX-induced cardiotoxicity in ischemia/reperfused isolated rat heart.

METHODS

A total of 36 rats were equally divided into four groups: control, DOX (30 min, 20 µM DOX perfusion), APAP (15 min before and after ischemia, 0.35 mM APAP perfusion), and DOX+APAP (perfused with the same protocol in DOX and APAP groups). The isolated hearts were perfused according to the Langendorff method. Cardiac parameters, including left ventricular developed pressure (LVDP), heart rate (HR), coronary flow (CF), and rate pressure product (RPP; LVDP×HR) were measured. Lactate dehydrogenase (LDH) concentration was also assessed.

RESULTS

At the end of the baseline period, the RPP, HR, and CF values were lower in the DOX group than in the control group (p<0.01). Meanwhile, there were no significant differences between the values of cardiac function parameters in the DOX+APAP and control groups. In the reperfusion period, the RPP and CF values were significantly increased in the DOX+APAP group compared with the DOX group (p<0.05). Furthermore, the LDH concentration was decreased in the DOX+APAP group compared with the DOX group.

CONCLUSION

APAP perfusion protected the hearts against DOX-induced cardiotoxicity in the baseline and ischemia/reperfusion conditions. These findings can be explained by the effect of APAP on antioxidant capacity and mitochondrial permeability transition pores.

A study on paracetamol cardiotoxicity

Background

Sri Lanka has a high suicide rate, with more than 40 % of poisoning admissions due to overdose of drugs with Paracetamol being the commonest. Data regarding cardiotoxicity to paracetamol is very minimal though hepatotoxicity following poisoning is well studied. Paracetamol cardiotoxicity has rarely been clinically significant and may have well been overlooked. The possibility that paracetamol overdose might be directly cardiotoxic has been the subject of a few reports. Unexplained deaths and electrocardiographic changes associated with paracetamol poisoning have also been reported in which cardiac origin cannot be clearly ruled out. Although some studies state that paracetamol poisoning has no direct cardiotoxic effect, electrocardiographic changes due to metabolic derangement of hepatotoxicity have been shown in certain studies. Thus, we conducted this study to assess in detail the cardiotoxic effect of paracetamol poisoning.

Methods

This is a cross sectional descriptive study done on those with confirmed paracetamol poisoning. Serum paracetamol levels, Electrocardiogram, Echocardiogram, troponin I, and other basic investigations were done.

Results

Paracetamol ingestion is more common among teenagers and the young population in Sri Lanka. Although several cases of paracetamol poisoning induced cardiotoxicity has been described in the past, this study demonstrated no electrocardiographic, echocardiographic or cardiac biomarkers changes of myocardial toxicity.

Conclusion

Though literature review support cardiotoxicity following paracetamol poisoning, our study does not provide enough evidence for this. Continuous cardiac monitoring, serial troponin and echocaediogram assessment would be voluble adjunct in its management. Further experiments and research in this subject would be useful with a larger number of samples to further evaluate this important problem.

Cardiolipin fatty acid remodeling regulates mitochondrial function by modifying the electron entry point in the respiratory chain

Modifications of cardiolipin (CL) levels or compositions are associated with changes in mitochondrial function in a wide range of pathologies. We have made the discovery that acetaminophen remodels CL fatty acids composition from tetralinoleoyl to linoleoyltrioleoyl-CL, a remodeling that is associated with decreased mitochondrial respiration. Our data show that CL remodeling causes a shift in electron entry from complex II to the β-oxidation electron transfer flavoprotein quinone oxidoreductase (ETF/QOR) pathway. These data demonstrate that electron entry in the respiratory chain is regulated by CL fatty acid composition and provide proof-of-concept that pharmacological intervention can be used to modify CL composition.

Acetaminophen from liver to brain: New insights into drug pharmacological action and toxicity

Acetaminophen (APAP) is a well-known analgesic and antipyretic drug. It is considered to be safe when administered within its therapeutic range, but in cases of acute intoxication, hepatotoxicity can occur. APAP overdose is the leading cause of acute liver failure in the northern hemisphere. Historically, studies on APAP toxicity have been focused on liver, with alterations in brain function attributed to secondary effects of acute liver failure. However, in the last decade the pharmacological mechanism of APAP as a cannabinoid system modulator has been documented and some articles have reported "in situ" toxicity by APAP in brain tissue at high doses. Paradoxically, low doses of APAP have been reported to produce the opposite, neuroprotective effects. In this paper we present a comprehensive, up-to-date overview of hepatic toxicity as well as a thorough review of both toxic and beneficial effects of APAP in brain.

Acetaminophen attenuates doxorubicin-induced cardiac fibrosis via osteopontin and GATA4 regulation: reduction of oxidant levels

It is well documented in animal and human studies that therapy with the anti-cancer drug doxorubicin (DOX) induces fibrosis, cardiac dysfunction, and cell death. The most widely accepted mechanism of cardiac injury is through production of reactive oxygen species (ROS), which cause mitochondrial damage, sarcomere structural alterations, and altered gene expression in myocytes and fibroblasts. Here we investigated the effects of acetaminophen (APAP, N-acetyl-para-aminophenol) on DOX-induced cardiac injury and fibrosis in the presence or absence of osteopontin (OPN). H9c2 rat heart-derived embryonic myoblasts were exposed to increasing concentrations of DOX ± APAP; cell viability, oxidative stress, and OPN transcript levels were analyzed. We found a dose-dependent decrease in cell viability and a corresponding increase in intracellular oxidants at the tested concentrations of DOX. These effects were attenuated in the presence of APAP. RT-PCR analysis revealed a small increase in OPN transcript levels in response to DOX, which was suppressed by APAP. When male 10-12-week-old mice (OPN(+/+) or OPN(-/-)) were given weekly injections of DOX ± APAP for 4 weeks there was substantial cardiac fibrosis in OPN(+/+) and, to a lesser extent, in OPN(-/-) mice. In both groups, APAP decreased fibrosis to near baseline levels. Activity of the pro-survival GATA4 transcription factor was diminished by DOX in both mouse genotypes, but retained baseline activity in the presence of APAP. These effects were mediated, in part, by the ability of APAP, acting as an anti-inflammatory agent, to decrease intracellular ROS levels, consequently diminishing the injury-induced increase in OPN levels.

Acetaminophen: beyond pain and Fever-relieving

Acetaminophen, also known as APAP or paracetamol, is one of the most widely used analgesics (pain reliever) and antipyretics (fever reducer). According to the U.S. Food and Drug Administration, currently there are 235 approved prescription and over-the-counter drug products containing acetaminophen as an active ingredient. When used as directed, acetaminophen is very safe and effective; however when taken in excess or ingested with alcohol hepatotoxicity and irreversible liver damage can arise. In addition to well known use pain relief and fever reduction, recent laboratory and pre-clinical studies have demonstrated that acetaminophen may also have beneficial effects on blood glucose levels, skeletal muscle function, and potential use as cardioprotective and neuroprotective agents. Extensive laboratory and pre-clinical studies have revealed that these off-label applications may be derived from the ability of acetaminophen to function as an antioxidant. Herein, we will highlight these novel applications of acetaminophen, and attempt, where possible, to highlight how these findings may lead to new directions of inquiry and clinical relevance of other disorders.

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.

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.

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.

The effect of acetaminophen on oxidative modification of low-density lipoproteins in hypercholesterolemic rabbits

Oxidative modification of low-density lipoproteins (LDL) contributes to the pathology of atherosclerosis. Antioxidants may protect LDL against oxidative modification. Acetaminophen, a widely used analgesic and antipyretic agent, has significant antioxidant properties. However, there is little evidence to suggest that acetaminophen acts as an antioxidant for LDL oxidation in vivo. In this study, we investigated the in vivo effect of acetaminophen on LDL oxidation in hypercholesterolemic rabbits. The oxidative modification of LDL was identified by conjugated dienes and thiobarbituric acid-reactive substances (TBARS). In the cholesterol group which rabbits were fed a diet contained 1% g cholesterol for 8 weeks, TBARS contents and conjugated diene levels in the plasma and isolated LDL samples significantly increased compared with the control rabbits (p<0.05). However, in the cholesterol + acetaminophen group, the TBARS contents and conjugated diene levels were significantly lower than that of the cholesterol group (p<0.05). The results from in vitro studies also demonstrated that the LDL isolated from serum was oxidized by Cu(++) ions and this oxidation reduced in the presence of acetaminophen. The reduced oxidative modification of LDL by acetaminophen may be of therapeutic value in preventing the development and progression of atherosclerosis.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Role of acetaminophen in acute myocardial infarction

Acetaminophen, the active ingredient in Tylenol, is a widely used drug that is well known for its analgesic and antipyretic properties. Acetaminophen is a commonly used alternative to nonsteroidal anti-inflammatory drugs, which have recently been demonstrated to increase mortality after acute myocardial infarction (AMI). The safety and potential cardioprotective properties of acetaminophen in the setting of AMI have recently been investigated; however, the results from these studies have been inconclusive. Using both large (ovine) and small (rabbit) collateral-deficient animal models, we studied the effects of acetaminophen in the setting of reperfused AMI. In both species we studied the effects of acetaminophen on myocardial salvage and ventricular function. Additionally, we studied the effects of acetaminophen on myocardial perfusion in sheep and on myocyte apoptosis in rabbits. Sixteen sheep and twenty-two rabbits were divided into two groups and administered acetaminophen or a vehicle before undergoing ischemia and reperfusion. The ischemic period was 60 min in sheep and 30 min in rabbits. All animals were reperfused for 3 h. There were no significant differences observed in myocardial perfusion, myocyte apoptosis, or infarct size in acetaminophen-treated animals. Acetaminophen increased cardiac output and mean arterial pressure before ischemia in sheep but had no effect on any other hemodynamic parameter. In rabbits, no effect on cardiac output or blood pressure was detected. These results support the role of acetaminophen as a safe drug in the postmyocardial infarction setting; however, no significant cardioprotective effect of the drug could be demonstrated.

Reactive oxygen species as mediators of cardiac injury and protection: the relevance to anesthesia practice

Reactive oxygen species (ROS) are central to cardiac ischemic and reperfusion injury. They contribute to myocardial stunning, infarction and apoptosis, and possibly to the genesis of arrhythmias. Multiple laboratory studies and clinical trials have evaluated the use of scavengers of ROS to protect the heart from the effects of ischemia and reperfusion. Generally, studies in animal models have shown such effects. Clinical trials have also shown protective effects of scavengers, but whether this protection confers meaningful clinical benefits is uncertain. Several IV anesthetic drugs act as ROS scavengers. In contrast, volatile anesthetics have recently been demonstrated to generate ROS in the heart, most likely because of inhibitory effects on cardiac mitochondria. ROS are involved in the signaling cascade for cardioprotection induced by brief exposure to a volatile anesthetic (termed "anesthetic preconditioning"). ROS, therefore, although injurious in large quantities, can have a paradoxical protective effect within the heart. In this review we provide background information on ROS formation and elimination relevant to anesthetic and adjuvant drugs with particular reference to the heart. The sources of ROS, the means by which they induce cardiac injury or activate protective signaling pathways, the results of clinical studies evaluating ROS scavengers, and the effects of anesthetic drugs on ROS are each discussed.

Acetaminophen in the hypoxic and reoxygenated guinea pig myocardium

We investigated the effects of 0.35-mM acetaminophen and its vehicle on isolated, perfused guinea pig hearts made hypoxic and subsequently reoxygenated. Hearts were allowed 30 min postinstrumentation to reach baseline, steady-state values, and then were exposed to 6 min of hypoxia (5% O(2), 5% CO(2), balance N(2)) followed by 36 min of reoxygenation (95% O(2), 5% CO(2)). We recorded hemodynamic, metabolic, and mechanical data in addition to assessing ultrastructure and the capacity of coronary venous effluent to reduce reactive oxygen species. We found that acetaminophen-treated hearts retained a greater fraction of mechanical function during hypoxia and reoxygenation. For example, the average percentage change from baseline of left ventricular developed pressure in acetaminophen- and vehicle-treated hearts at 6 min reoxygenation was 9 +/- 2% and -8 +/- 5% (P < 0.05), respectively. In addition, electron micrographs revealed greater preservation of myofibrillar ultrastructure in acetaminophen-treated hearts. Biochemical analyses revealed the potential of coronary effluent from acetaminophen-treated hearts to significantly neutralize peroxynitrite-dependent chemiluminescence in all recorded time periods. During early reoxygenation, the percentage inhibition of peroxynitrite-mediated chemiluminescence was 56 +/- 10% in vehicle-treated hearts and 99 +/- 1% in acetaminophen-treated hearts (P < 0.05). We conclude that acetaminophen has previously unreported cardioprotective properties in the nonischemic, hypoxic, and reoxygenated myocardium mediated through the reduction of reactive oxygen species.

Acetaminophen and myocardial infarction in dogs

The hypothesis that acetaminophen can reduce necrosis during myocardial infarction was tested in male dogs. Two groups were studied: vehicle- ( n = 10) and acetaminophen-treated ( n = 10) dogs. All dogs were obtained from the same vendor, and there were no significant differences in their ages (18 ± 2 mo), weights (24 ± 1 kg), or housing conditions. Selected physiological data, e.g., coronary blood flow, nonspecific collateral flow, epicardial temperature, heart rate, systemic mean arterial pressure, left ventricular developed pressure, the maximal first derivative of left ventricular developed pressure, blood gases, and pH, were collected at baseline and during regional myocardial ischemia and reperfusion. There were no significant differences in coronary blood flow, nonspecific collateral flow, epicardial temperature, heart rate, systemic mean arterial pressure, or blood gases and pH between the two groups at any of the three time intervals, even though there was a trend toward improved function in the presence of acetaminophen. Infarct size, the main objective of the investigation, was markedly and significantly reduced by acetaminophen. For example, when expressed as a percentage of ventricular wet weight, infarct size was 8 ± 1 versus 3 ± 1%( P < 0.05) in vehicle- and acetaminophen-treated hearts, respectively. When infarct size was expressed as percentage of the area at risk, it was 35 ± 3 versus 13 ± 2% ( P < 0.05) in vehicle- and acetaminophen-treated groups, respectively. When area at risk was expressed as percentage of total ventricular mass, there were no differences in the two groups. Results reveal that the recently reported cardioprotective properties of acetaminophen in vitro can now be extended to the in vivo arena. They suggest that it is necessary to add acetaminophen to the growing list of pharmaceuticals that possess cardioprotective efficacy in mammals.

Effects of acetaminophen on myocardial infarct size in rats

OBJECTIVE

Acetaminophen is widely prescribed as an analgesic agent in hospitals and clinics. However, acetaminophen theoretically could influence myocardial infarct size by reducing prostaglandin synthesis in vivo. To date, the effect of acetaminophen on myocardial infarct size is unknown. The present study investigated (1) whether acetaminophen has any effect on myocardial infarct size when given in an analgesic dose and (2) whether acetaminophen can affect the cardioprotective effect of the early phase of ischemic preconditioning in rats.

METHODS

Female Sprague-Dawley rats were randomly assigned to four groups (n=12 each). Group 1 (no preconditioning): Vehicle (intravenous ethanol, 0.9 mL/kg) was given 39 minutes prior to ischemia. Group 2 (acetaminophen plus no preconditioning): intravenous acetaminophen (125 mg/kg) was given 39 minutes prior to ischemia. Group 3 (preconditioning): The heart was preconditioned before ischemia, and the vehicle (intravenous ethanol, 0.9 mL/kg) was given 39 minutes prior to the ischemia. Group 4 (acetaminophen plus preconditioning): The heart was preconditioned before ischemia, and intravenous acetaminophen (125 mg/kg) was given 39 minutes prior to the ischemia. The preconditioning protocol consisted of three cycles of 3 minutes of coronary occlusion and 5 minutes of reperfusion. The left coronary artery was then occluded for 60 minutes, followed by 3 hours of reperfusion. The end points were hemodynamics, body temperature, and risk area and area of necrosis of the left ventricle.

RESULTS

The area of risk was similar among the four groups. The area of necrosis, expressed as a percentage of the area at risk, was 55.7% +/- 6.1% in the no-preconditioning group, 62.8% +/- 2.4% in the acetaminophen plus no-preconditioning group, 24.7% +/- 7.3% in the preconditioning group, and 17.2% +/- 6.4% in the acetaminophen plus preconditioning group. The area of necrosis/area at risk was decreased significantly in the preconditioning group and in the acetaminophen plus preconditioning group compared with the no-preconditioning group (P<.05); but there were no significant differences between the no-preconditioning group and the acetaminophen plus no-preconditioning group (P=.29), or between the preconditioning group and acetaminophen plus preconditioning group (P=.45). Among the four groups, heart rate and body temperature were similar. The infusion of the vehicle or acetaminophen increased blood pressure in the four groups, but to a lesser extent in the acetaminophen group. However, during coronary artery occlusion and reperfusion, the four groups had comparable blood pressures.

CONCLUSION

Acetaminophen had no beneficial or adverse effects on infarct size in nonpreconditioned rats, and the beneficial effects of preconditioning were not blocked or prevented by acetaminophen at this analgesic dose.

Antipyretic effect of acetaminophen by inhibition of glutamate release after staphylococcal enterotoxin A fever in rabbits

The present study was designed to determine whether the inhibition of glutamate release in organum vasculosum laminae terminalis (OVLT) of rabbit brain by acetaminophen might be protective in a whole-animal model of staphylococcal enterotoxin A (SEA) fever. Unanesthetized rabbits were administered intravenously with SEA, and both colonic temperature (Tco) and glutamate release in OVLT were measured simultaneously. The glutamate release in OVLT was measured with a microdialysis probe previously implanted. Both the Tco and glutamate release in OVLT were simultaneously increased following intravenous administration of SEA. The SEA-induced rise in both the Tco and the levels of glutamate release in OVLT were suppressed by pretreatment with intravenous injection of acetaminophen (1, 5 or 10 mg/kg). Furthermore, treatment of OVLT with acetaminophen (50-150 microg) attenuated the fever-like hyperthermia induced by intra-OVLT injection of glutamate. Our results show acetaminophen may reduce glutamate release in OVLT and result in antipyresis.

Chronically administered acetaminophen and the ischemia/reperfused myocardium

Male and female Hartley strain guinea pigs weighing 280 +/- 10 g were given acetaminophen-treated water ad libitum for 10 days. Sham-treated control animals were given similar quantities of untreated tap water (vehicle-treated control group). On Day 10, hearts were extracted, instrumented, and exposed to an ischemia (low-flow, 20 min)/reperfusion protocol. Our objective was to compare and contrast ventricular function, coronary circulation, and selected biochemical and histological indices in the two treatment groups. Left ventricular developed pressure in the early minutes of reperfusion was significantly greater in the presence of acetaminophen, e.g., at 1 min, 40 +/- 4 vs 21 +/- 3 mmHg (P < 0.05). Coronary perfusion pressure was significantly less from 3 to 40 min of reperfusion in the presence of acetaminophen. Creatine kinase release in vehicle-treated hearts rose from 42 +/- 14 (baseline) to 78 +/- 25 units/liter by the end of ischemia. Corresponding values in acetaminophen-treated hearts were 36 +/- 8 and 44 +/- 14 units/liter. Acetaminophen significantly (P < 0.05) attenuated release of creatine kinase. Chemiluminescence, an indicator of the in vitro production of peroxynitrite via the in vivo release of superoxide and nitric oxide, was also significantly attenuated by acetaminophen. Electron microscopy indicated a well-preserved myofibrillar ultrastructure in the postischemic myocardium of acetaminophen-treated hearts relative to vehicle-treated hearts (e.g., few signs of contraction bands, little or no evidence of swollen mitochondria, and well-defined light and dark bands in sarcomeres with acetaminophen; opposite with vehicle). We conclude that chronic administration of acetaminophen provides cardioprotection to the postischemic, reperfused rodent myocardium.

Comparison of cardioprotective efficacy of two thromboxane A2 receptor antagonists

The purpose of the current study was to compare the efficacy of two structurally unrelated thromboxane A (TXA ) receptor antagonists, KT2-962 and daltroban (BM 13.505), in a dog model of myocardial ischemia/reperfusion injury. Pentobarbital-anesthetized dogs were subjected to left circumflex coronary artery occlusion for 90 minutes followed by 5 hours of reperfusion. Vehicle, KT2-962 (10 mg/kg), or daltroban (10 mg/kg) were administered as intravenous boluses 10 minutes before coronary occlusion. Systemic hemodynamics were measured throughout the experiments and regional myocardial blood flow was measured by the radioactive microsphere technique. At the end of the reperfusion period, myocardial infarct size was quantified by staining with triphenyltetrazolium chloride. Neither KT2-962 nor daltroban significantly altered heart rate, mean arterial blood pressure, or regional myocardial blood flow. The content of myeloperoxidase activity in the ischemic/reperfused tissue, an index of neutrophil infiltration, was not significantly different among the three treatment groups. However, administration of KT2-962, but not daltroban, significantly reduced the incidence of ventricular fibrillation during the ischemic period and significantly reduced myocardial infarct size expressed as a percentage of the risk region (approximately 40%). Subsequent in-vitro assays using electron spin resonance spectroscopy demonstrated that KT2-962 inhibited the formation of hydroxyl radicals, whereas daltroban had no effect. These results suggest that the beneficial effects of KT2-962 may be due to its direct free radical scavenging properties rather than its ability to block TXA receptors.(2) (2) (2)

Flow heterogeneity following global no-flow ischemia in isolated rabbit heart

The purpose of this study was to evaluate flow heterogeneity and impaired reflow during reperfusion after 60-min global no-flow ischemia in the isolated rabbit heart. Radiolabeled microspheres were used to measure relative flow in small left ventricular (LV) segments in five ischemia + reperfused hearts and in five nonischemic controls. Relative flow heterogeneity was expressed as relative dispersion (RD) and computed as standard deviation/mean. In postischemic vs. preischemic hearts, RD was increased for the whole LV (0.92 +/- 0.41 vs. 0.37 +/- 0.07, P < 0.05) as well as the subendocardium (Endo) and subepicardium considered separately (1.28 +/- 0.74 vs. 0.30 +/- 0.09 and 0.69 +/- 0.22 vs. 0.38 +/- 0.08; P < 0.05 for both comparisons, respectively) during early reperfusion. During late reperfusion, the increased RD for the whole LV and Endo remained significant (0.70 +/- 0.22 vs. 0.37 +/- 0.07 and 1.06 +/- 0.55 vs. 0.30 +/- 0.09; P < 0.05 for both comparisons, respectively). In addition to the increase in postischemic flow heterogeneity, there were some regions demonstrating severely impaired reflow, indicating that regional ischemia can persist despite restoration of normal global flow. Also, the relationship between regional and global flow was altered by the increased postischemic flow heterogeneity, substantially reducing the significance of measured global LV reflow. These observations emphasize the need to quantify regional flow during reperfusion after sustained no-flow ischemia in the isolated rabbit heart.

A case-control study of acetaminophen use in relation to the risk of first myocardial infarction in men

PURPOSE

Experimental evidence raises the possibility that acetaminophen use could reduce the risk of myocardial infarction (MI). We assessed the relation of acetaminophen use, and also of aspirin use, to first MI in a case-control study.

METHODS

Data on analgesic use and other factors were collected in a hospital-based case-control study of first MI in men under 55 years of age conducted from 1980 to 1983. We compared 2035 men with first MIs to 2656 control men admitted for conditions unrelated to analgesic use. Odds ratios (ORs) for acetaminophen use relative to nonuse were estimated with logistic regression analysis, controlling for major MI risk factors.

RESULTS

The OR was 0.9 (95% confidence interval (CI): 0.6-1.3) for acetaminophen use at least once a week for at least 3 months, 0.7 (95% CI: 0.4-1.1) for daily use for at least 3 months, and 0.5 (95% CI: 0.2-1.6) for daily use for at least 5 years. In analyses of aspirin use, the OR was 0.9 (95% CI: 0.7-1.2) for use at least once a week for at least 3 moths, 0.9 (95% CI: 0.6-1.2) for daily use lasting at least 3 months, 0.6 (95% CI: 0.4-1.1) for daily use for at least 5 years, and 0.4 (95% CI: 0.2-1.0) for daily use for at least 10 years.

CONCLUSIONS

While our results raise the possibility of a protective effect of long-term regular acetaminophen use against first MI, they are compatible with no effect. The data suggest a potential protective effect of long-term regular aspirin use.

Acetaminophen in the post-ischemia reperfused myocardium

Acetaminophen was administered acutely at the onset of reperfusion after 20 min of low-flow, global myocardial ischemia in isolated, perfused guinea pig hearts (Langendorff) to evaluate its influence in the postischemia, reperfused myocardium. Similarly prepared hearts were treated with vehicle or with uric acid (another phenol for comparison). Functionally, acetaminophen-treated hearts (0.35 mM) achieved significantly greater recovery during reperfusion. For example, left ventricular developed pressures at 40 min reperfusion were 38 +/- 3, 27 +/- 3, and 20 +/- 2 in the presence of acetaminophen (P < 0.05, relative to the other two groups), vehicle, and uric acid, respectively. Coronary perfusion pressures and calculated coronary vascular resistances, in the acetaminophen-treated hearts, were significantly lower at the same time (e.g., coronary perfusion pressures in the three groups, respectively, were 40 +/- 2 [P < 0.05], 51 +/- 3, and 65 +/- 12 mm Hg). Under baseline, control conditions, creatine kinase ranged from 12-15 units/liter in the three groups. It increased to 35-40 units/liter (P < 0.05) during ischemia but was significantly reduced by acetaminophen during reperfusion (e.g., 5.3 +/- 0.8 units/liter at 40 min). Oxidant-mediated chemiluminescence in all three treatment groups during baseline conditions and ischemia was similar (i.e., approximately 1.5-2.0 min for peak luminescence to reach its half maximal value). It took significantly more time during reperfusion for the oxidation of luminol in the presence of acetaminophen (>20 min, P < 0.05) than in its absence (3-8 min in uric acid- and vehicle-treated hearts). These results suggest that administration of acetaminophen (0.35 mM), at the onset of reperfusion, provides anti-oxidant-mediated cardioprotection in the postischemia, reperfused myocardium.

Areas of emerging interest in analgesia: cardiovascular complications

Many people obtain symptomatic relief from acute, chronic, or recurring pain conditions by using an over-the-counter analgesic. As with the use of any drug, this involves achieving the appropriate balance between potential benefit and risk of harm. The adverse effects of aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) in the gastrointestinal (GI) tract are widely appreciated. On the basis of their pharmacology, however, these drugs also have the potential for causing adverse effects in the cardiovascular system. This is particularly the case in certain overlapping populations (eg, the elderly or those with cardiac failure, hypertension, or renal impairment). And the size of the exposed populations and the fact they comprise people likely to require pain management because of concomitant illnesses make the cardiovascular implications of analgesic use potentially a more serious issue for public health than the more widely recognized GI complications of aspirin and NSAID use. This article discusses the impact on the cardiovascular system of different classes of analgesics (NSAIDs, the new cyclooxygenase-2-selective inhibitors [CSIs], and paracetamol) in terms of cardiac function, thrombotic and cardioprotective potential, and hypertension. It identifies patients at risk for analgesic-related cardiovascular adverse events, and considers their options for managing mild-to-moderate pain. Unlike that of the NSAIDs and CSIs, the pharmacology of paracetamol provides no signal for risk of cardiovascular adverse events, and paracetamol should, therefore, be considered as first-line therapy in patients with cardiovascular disease.

Acetaminophen and low-flow myocardial ischemia: efficacy and antioxidant mechanisms

In the current study, the cardioprotective efficacy of 0.35 mmol/l acetaminophen administered 10 min after the onset of a 20-min period of global, low-flow myocardial ischemia was investigated. Matched control hearts were administered an equal volume of Krebs-Henseleit physiological buffer solution (vehicle). In separate groups of hearts, the concentration-dependent, negative inotropic properties of hydrogen peroxide and the ability of acetaminophen to attenuate these actions, as well as the effects of acetaminophen on ischemia-reperfusion-mediated protein oxidation, were studied. Acetaminophen-treated hearts regained a significantly greater fraction of baseline, preischemia control function during reperfusion than vehicle-treated hearts. For example, contractility [rate of maximal developed pressure in the left ventricle (+/-dP/dt(max))] after 10 min of reperfusion was 109 +/- 24 and 42 +/- 9 mmHg/s (P < 0.05), respectively, in the two groups. The corresponding pressure-rate products were 1,840 +/- 434 vs. 588 +/- 169 mmHg*beats*min(-1) (P < 0.05). Acetaminophen attenuated peroxynitrite-mediated chemiluminescence in the early minutes of reperfusion (e.g., at 6 min, corresponding values for peak light production were approximately 8 x 10(6) counts/min for vehicle vs. <4 x 10(6) counts/min for acetaminophen, P < 0.05) and the negative inotropic effects of exogenously administered hydrogen peroxide (e.g., at 0.4 mmol/l hydrogen peroxide, pressure-rate products were approximately 1.0 x 10(4) and 3.8 x 10(3) mmHg*beats*min(-1) in acetaminophen- and vehicle-treated hearts, respectively, P < 0.05). Ischemia-mediated protein oxidation was reduced by acetaminophen. The ability of acetaminophen to attenuate the damaging effects of peroxynitrite and hydrogen peroxide and to limit protein oxidation suggest antioxidant mechanisms are responsible for its cardioprotective properties during postischemia-reperfusion.