Acetaminophen distribution in the rat central nervous system

Elderly mice with history of acetaminophen intoxication display worsened cognitive impairment and persistent elevation of astrocyte and microglia burden

Acetaminophen (APAP) is a leading cause of acute liver failure. The effect of APAP metabolite's effects in the periphery are well characterized; however, associated consequences in the brain remain poorly understood. Animal studies on this subject are few and reveal that frequent APAP intake can trigger cerebral abnormalities that vary depending on the subject's age. Alarmingly, experimental efforts have yet to examine associated consequences in elderly hosts, who correspond to the highest risk of medication overload, impaired drug clearance, and cognitive deficits. Here, we interrogated the cerebral and peripheral pathology of elderly mice submitted to monthly episodes of APAP intoxication since a young adult age. We found that weeks after the final episode of recurrent APAP exposure, mice exhibited worsened non-spatial memory deficit whereas spatial memory performance was unaltered. Interestingly, one month after the period of APAP intoxication, these mice showed increased glial burden without associated drivers, namely, blood-brain barrier disruption, cholesterol accumulation, and elevation of inflammatory molecules in the brain and/or periphery. Our experimental study reveals how recurrent APAP exposure affects the cognitive performance and cellular events in elderly brains. These data suggest that APAP-containing pharmacological interventions may foreshadow the elevated risk of neuropsychiatric disorders that afflict elderly populations.

Inhibition of Adult Neurogenesis in Male Mice after Repeated Exposure to Paracetamol Overdose

Paracetamol, or acetaminophen (N-acetyl-para-aminophenol, APAP), is an analgesic and antipyretic drug that is commonly used worldwide, implicated in numerous intoxications due to overdose, and causes serious liver damage. APAP can cross the blood-brain barrier and affects brain function in numerous ways, including pain signals, temperature regulation, neuroimmune response, and emotional behavior; however, its effect on adult neurogenesis has not been thoroughly investigated. We analyze, in a mouse model of hepatotoxicity, the effect of APAP overdose (750 mg/kg/day) for 3 and 4 consecutive days and after the cessation of APAP administration for 6 and 15 days on cell proliferation and survival in two relevant neurogenic zones: the subgranular zone of the dentate gyrus and the hypothalamus. The involvement of liver damage (plasma transaminases), neuronal activity (c-Fos), and astroglia (glial fibrillar acidic protein, GFAP) were also evaluated. Our results indicated that repeated APAP overdoses are associated with the inhibition of adult neurogenesis in the context of elevated liver transaminase levels, neuronal hyperactivity, and astrogliosis. These effects were partially reversed after the cessation of APAP administration for 6 and 15 days. In conclusion, these results suggest that APAP overdose impairs adult neurogenesis in the hippocampus and hypothalamus, a fact that may contribute to the effects of APAP on brain function.

A memory-improving dipeptide, Tyr-Pro, can reach the mouse brain after oral administration

The transport and accumulation of orally administered functional food-derived peptides in the brain was not fully explored. Thus, in the present study, we aimed to provide critical evidence regarding brain accumulation of a memory-improving soy dipeptide, Tyr-Pro, following oral administration. Stable isotope-labeled Tyr-Pro (Tyr-[13C5,15N]Pro) was orally administered to male ICR mice at 10 or 100 mg/kg. Surprisingly, the intact labeled Tyr-Pro exhibited maximal plasma and brain levels 15 min after administration (plasma: area under the curve [AUC0-120 min], 1331 ± 267 pmol·min/mL-plasma; brain: AUC0-120 min of 0.34 ± 0.11 pmol·min/mg-dry brain, at 10 mg/kg). In addition, we detected labeled Tyr-Pro in the brain parenchyma, indicating a validated blood-brain-barrier (BBB) transportability. Moreover, we confirmed the preferable accumulation of Tyr-Pro in the hypothalamus, hippocampus, and cortex with > 0.02 pmol/mg-tissue. In conclusion, we provided the first evidence that orally administered Tyr-Pro at 10 mg/kg directly entered the blood circulation with an absorption ratio of 0.15%, of which 2.5% of Tyr-Pro was transported from the plasma to the mouse brain parenchyma.

Participation of the descending noradrenergic inhibitory system in the anti-hyperalgesic effect of acetaminophen in a rat model of inflammation

AIMS

This study investigated the relationship between the analgesic efficacy of acetaminophen and the descending noradrenergic systems using rodent models of inflammatory pain.

MAIN METHODS

Inflammatory pain models were established by carrageenan injection into rats' paws. The models were defined as acute (4 h after carrageenan injection), subacute (24 h after carrageenan injection), and late (1 week after carrageenan injection) phase. To evaluate intravenous acetaminophen treatment, the withdrawal threshold to mechanical stimuli was assessed simultaneously with in vivo microdialysis assay of noradrenaline levels in the locus coeruleus (LC). Further analyses were performed to observe the effect of yohimbine on the treatment and the impact of AM404 treatment, a metabolite of acetaminophen, on noradrenaline levels in the LC.

KEY FINDINGS

In all phases, intravenous acetaminophen had a significant anti-hyperalgesic effect (p < 0.05). There was a significant time-dependent increase in the noradrenaline concentration within the LC (acetaminophen versus saline treatment; at 30 min, p < 0.001; 60 min, p < 0.01) in the subacute pain model, but not in the acute and late phase pain models. Intrathecal pre-injection of yohimbine attenuated the anti-hyperalgesic effect after acetaminophen injection only in the subacute model (p < 0.05). In the subacute pain model, intracerebroventricular administration of AM404 showed the same trend in noradrenaline levels as acetaminophen administration (AM404 versus vehicle group at 30 min, p < 0.001).

SIGNIFICANCE

We found the descending noradrenergic inhibitory system is involved in the antinociceptive action of acetaminophen in the subacute phase of inflammatory pain.

Systematic Review of Systemic and Neuraxial Effects of Acetaminophen in Preclinical Models of Nociceptive Processing

Acetaminophen (APAP) in humans has robust effects with a high therapeutic index in altering postoperative and inflammatory pain states in clinical and experimental pain paradigms with no known abuse potential. This review considers the literature reflecting the preclinical actions of acetaminophen in a variety of pain models. Significant observations arising from this review are as follows: 1) acetaminophen has little effect upon acute nociceptive thresholds; 2) acetaminophen robustly reduces facilitated states as generated by mechanical and thermal hyperalgesic end points in mouse and rat models of carrageenan and complete Freund’s adjuvant evoked inflammation; 3) an antihyperalgesic effect is observed in models of facilitated processing with minimal inflammation (eg, phase II intraplantar formalin); and 4) potent anti-hyperpathic effects on the thermal hyperalgesia, mechanical and cold allodynia, allodynic thresholds in rat and mouse models of polyneuropathy and mononeuropathies and bone cancer pain. These results reflect a surprisingly robust drug effect upon a variety of facilitated states that clearly translate into a wide range of efficacy in preclinical models and to important end points in human therapy. The specific systems upon which acetaminophen may act based on targeted delivery suggest both a spinal and a supraspinal action. Review of current targets for this molecule excludes a role of cyclooxygenase inhibitor but includes effects that may be mediated through metabolites acting on the TRPV1 channel, or by effect upon cannabinoid and serotonin signaling. These findings suggest that the mode of action of acetaminophen, a drug with a long therapeutic history of utilization, has surprisingly robust effects on a variety of pain states in clinical patients and in preclinical models with a good therapeutic index, but in spite of its extensive use, its mechanisms of action are yet poorly understood.

Paracetamol (acetaminophen) rescues cognitive decline, neuroinflammation and cytoskeletal alterations in a model of post-operative cognitive decline (POCD) in middle-aged rats

Post-operative cognitive dysfunction (POCD) is a debilitating clinical phenomenon in elderly patients. Management of pain in elderly is complicated because analgesic opiates elicit major side effects. In contrast, paracetamol (acetaminophen) has shown analgesic efficacy, no impact on cognition, and its side effects are well tolerated. We investigated the efficacy of paracetamol, compared to the opioid analgesic buprenorphine, in a model of POCD by investigating cognitive decline, allodynia, peripheral and hippocampal cytokines levels, and hippocampal microtubule dynamics as a key modulator of synaptic plasticity. A POCD model was developed in middle-aged (MA) rats by inducing a tibia fracture via orthopaedic surgery. Control MA rats did not undergo any surgery and only received isoflurane anaesthesia. We demonstrated that cognitive decline and increased allodynia following surgery was prevented in paracetamol-treated animals, but not in animals which were exposed to anesthesia alone or underwent the surgery and received buprenorphine. Behavioral alterations were associated with different peripheral cytokine changes between buprenorphine and paracetamol treated animals. Buprenorphine showed no central effects, while paracetamol showed modulatory effects on hippocampal cytokines and markers of microtubule dynamics which were suggestive of neuroprotection. Our data provide the first experimental evidence corroborating the use of paracetamol as first-choice analgesic in POCD.

Comparison of effects of high and low dose paracetamol treatment and toxicity on brain and liver in rats

OBJECTIVE

Paracetamol is thought that it acts by inhibiting the central cyclooxygenase (COX) enzyme; its mechanism of action is still not fully explained. Although its most important side effect is hepatoxicity, it is thought to cause toxicity on the brain in recent years. The present study aims to investigate the treatment and toxic effects of low and high doses of paracetamol on the liver and brain.

METHODS

Wistar-albino rats were used in this study. At doses of 20-500 mg/kg, paracetamol was administered intraperitoneally once a day for one and three days. The brain and liver were used for immunohistochemical evaluation using COX-3, prostaglandin E₂ (PGE₂) and caspase 3 antibodies and for total antioxidant (TAS), total oxidant (TOS) and oxidative stress index (OSI) measurements. Results were evaluated using the Kruskal Wallis test (SPSS ver.24).

RESULTS

The liver COX-3 levels were significantly lower in both groups with higher doses (p<0.05). In the brain, there was no statistically significant difference in COX-3 levels between the groups. There was no statistically significant difference in PGE₂ levels in the liver and brain between the groups (p>0.05). The caspase 3 level in the liver was statistically significantly higher in the low dose group compared to the other groups (p<0.05). In both liver and brain, OSI values were significantly higher in the 3-day high-dose group compared to others (p<0.05). There was no statistically significant difference between the groups in ALT and AST values (p>0.05).

CONCLUSION

The results of our study show that paracetamol inhibits the COX-3 enzyme in the liver but has no effect in the brain, and COX-3 does not have an effect on PGE₂. Paracetamol causes apoptosis in the liver only in low doses; higher doses may cause toxicity by increasing oxidative stress, especially in the brain.

Can maternal exposure to paracetamol impair reproductive parameters of male rat offspring?

Paracetamol is a widely used medication during gestation and lactation periods for the treatment of pain and fever. Several studies have shown that exposure to paracetamol can increase the incidence of cryptorchidism and decrease testosterone production. Therefore, the present study aimed to evaluate if maternal treatment with paracetamol during gestation and gestation/lactation periods can alter reproductive and behavioral parameters in male offspring. Female Wistar rats were treated daily by gavage with water or paracetamol (350 mg/kg/day) during gestation (CTRG and PARG) or gestation/lactation periods (CTRGL and PARGL). There were significant differences in histomorphometry (increased volume and total length of the seminiferous tubules) and weight of testes (PARG group) and copulatory behavior and testosterone levels (PARG and PARGL groups) at PND 120. Therefore, the present study showed that maternal exposure to paracetamol has an impact on the reproductive system and sexual behavior of male adult offspring suggesting an impaired in sexual hypothalamic differentiation at the beginning of the development of the brain.

Nonsteroidal anti-inflammatory drugs and acetaminophen ameliorate muscular mechanical hyperalgesia developed after lengthening contractions via cyclooxygenase-2 independent mechanisms in rats

Nonsteroidal anti-inflammatory drugs and acetaminophen are cyclooxygenase inhibitors commonly used as symptomatic medicines for myofascial pain syndrome. Using the selective inhibitors celecoxib and zaltoprofen, cyclooxygenase-2 has been shown to be involved in the initiation, but not the maintenance, of muscular mechanical hyperalgesia induced by lengthening contractions, which serves as a useful model for the study of myofascial pain syndrome. The effect of other cyclooxygenase-2 inhibitors, such as acetylsalicylic acid, ibuprofen, loxoprofen sodium, and acetaminophen, on muscular mechanical hyperalgesia during maintenance has not been studied. Here, we examined the analgesic effects of the nonsteroidal anti-inflammatory drugs and acetaminophen on the model. Consistent with previous studies, mechanical withdrawal threshold of the muscle was significantly decreased and reached its lowest level 24 h after lengthening contractions. Celecoxib had no effect on muscular mechanical hyperalgesia, when orally administered 24 h after lengthening contractions. In contrast, acetylsalicylic acid, ibuprofen, loxoprofen sodium, and acetaminophen increased the withdrawal threshold, which had decreased by lengthening contractions, in a dose-dependent manner. These results demonstrate the analgesic actions of nonsteroidal anti-inflammatory drugs and acetaminophen in the maintenance process of lengthening contraction-induced muscular mechanical hyperalgesia, which may occur through cyclooxygenase-2 independent mechanisms.

Determinants of drug entry into the developing brain

Background: A major concern for clinicians in prescribing medications to pregnant women and neonates is the possibility that drugs might have damaging effects, particularly on long-term brain development. Current understanding of drug permeability at placental and blood-brain barriers during development is poor. In adults, ABC transporters limit many drugs from entering the brain; however, little is known about their function during development. Methods: The transfer of clinically relevant doses of paracetamol (acetaminophen), digoxin and cimetidine into the brain and cerebrospinal fluid (CSF) was estimated using radiolabelled drugs in Sprague Dawley rats at three developmental stages: E19, P4 and adult. Drugs were applied intraperitoneally either acutely or following chronic exposure (for five days). Entry into brain, CSF and transfer across the placenta was measured and compared to three markers (L-glucose, sucrose, glycerol) that cross barriers by "passive diffusion". The expression of ABC transporters in the brain, choroid plexus and placenta was estimated using RT-qPCR. Results: All three drugs entered the developing brain and CSF in higher amounts than the adult brain and CSF. Comparisons with "passive" permeability markers suggested that this might be due to age-related differences in the functional capacity of ABC-efflux mechanisms. In adult animals, chronic treatment reduced digoxin (12% to 5%, p<0.01) and paracetamol (30% to 21%, p<0.05) entry compared to acute treatment, with the decrease in digoxin entry correlating with up-regulation of efflux transporter abcb1a (PGP). In fetal and newborn animals, no gene up-regulation or transfer decreases were observed. Instead, chronic paracetamol treatment resulted in increased transfer into the fetal brain (66% to 104%, p<0.001). Conclusions: These results suggest that the developing brain may be more at risk from acute drug exposure than the adult brain due to reduced efflux capacity and at greater risk from chronic treatment due to a lack of efflux mechanism regulatory capacity.

In vitro models and systems for evaluating the dynamics of drug delivery to the healthy and diseased brain

The blood-brain barrier (BBB) plays a crucial role in maintaining brain homeostasis and transport of drugs to the brain. The conventional animal and Transwell BBB models along with emerging microfluidic-based BBB-on-chip systems have provided fundamental functionalities of the BBB and facilitated the testing of drug delivery to the brain tissue. However, developing biomimetic and predictive BBB models capable of reasonably mimicking essential characteristics of the BBB functions is still a challenge. In addition, detailed analysis of the dynamics of drug delivery to the healthy or diseased brain requires not only biomimetic BBB tissue models but also new systems capable of monitoring the BBB microenvironment and dynamics of barrier function and delivery mechanisms. This review provides a comprehensive overview of recent advances in microengineering of BBB models with different functional complexity and mimicking capability of healthy and diseased states. It also discusses new technologies that can make the next generation of biomimetic human BBBs containing integrated biosensors for real-time monitoring the tissue microenvironment and barrier function and correlating it with the dynamics of drug delivery. Such integrated system addresses important brain drug delivery questions related to the treatment of brain diseases. We further discuss how the combination of in vitro BBB systems, computational models and nanotechnology supports for characterization of the dynamics of drug delivery to the brain.

Involvement of 5-HT1A/1B receptors in the antinociceptive effect of paracetamol in the rat formalin test

The mechanism of analgesic action of paracetamol (acetominophen) remains still unknown. However, a relationship between serotonergic system and the effect of paracetamol has been previously demonstrated. The serotonin activity in the brainstem is primarily under the control of 5-HT_1A somatodendritic receptors, although some data also suggest the involvement of 5-HT_1B receptors. To determine whether the 5-HT_1A and 5-HT_1B receptors are involved in the antinociceptive effect of paracetamol, we evaluated the effect of paracetamol (0.125-1 g/kg i.p.) followed by different antagonists [WAY 100,635 (0.8 mg/kg s.c.) and SB 216,641 (0.8 mg/kg s.c.)] or agonists [8-OH-DPAT (0.125 mg/kg s.c.) and CP 93,129 (0.125 mg/kg s.c.)] of 5-HT_1A and 5-HT_1B receptors, respectively, in the rat model of formalin-induced pain. We demonstrated that paracetamol administration showed a dose-dependent antinociceptive effect in the formalin test. WAY 100,635 (5-HT_1A antagonist) induced an increase in the antinociceptive effect of paracetamol at 250 mg/kg doses. Conversely, 8-OH-DPAT (5-HT_1A agonist) decreased the antinociceptive effect of paracetamol at 500-1000 mg/kg doses. However, SB216641 (5-HT_1B antagonist) modified weakly the antinociceptive effect of paracetamol at 250 mg/kg doses and CP 93,129 (5-HT_1B agonist) not produce a clear effect in the antinociceptive effect of paracetamol. These results suggest that the antinociceptive effect of paracetamol can be enhanced mainly by compounds having 5-HT_1A antagonist properties in the formalin test and maybe by 5-HT_1B receptors antagonists.

Paracetamol sharpens reflection and spatial memory: a double-blind randomized controlled study in healthy volunteers

Background

Acetaminophen (APAP, paracetamol) mechanism for analgesic and antipyretic outcomes has been largely addressed, but APAP action on cognitive function has not been studied in humans. Animal studies have suggested an improved cognitive performance but the link with analgesic and antipyretic modes of action is incomplete. This study aims at exploring cognitive tests in healthy volunteers in the context of antinociception and temperature regulation. A double-blind randomized controlled study (NCT01390467) was carried out from May 30, 2011 to July 12, 2011.

Methods

Forty healthy volunteers were included and analyzed. Nociceptive thresholds, core temperature (body temperature), and a battery of cognitive tests were recorded before and after oral APAP (2 g) or placebo: Information sampling task for predecisional processing, Stockings of Cambridge for spatial memory, reaction time, delayed matching of sample, and pattern recognition memory tests. Analysis of variance for repeated measures adapted to crossover design was performed and a two-tailed type I error was fixed at 5%.

Results

APAP improved information sampling task (diminution of the number of errors, latency to open boxes, and increased number of opened boxes; all P<0.05). Spatial planning and working memory initial thinking time were decreased (P=0.04). All other tests were not modified by APAP. APAP had an antinociceptive effect (P<0.01) and body temperature did not change.

Conclusion

This study shows for the first time that APAP sharpens decision making and planning strategy in healthy volunteers and that cognitive performance and antinociception are independent of APAP effect on thermogenesis. We suggest that cognitive performance mirrors the analgesic rather than thermic cascade of events, with possibly a central role for serotonergic and cannabinoid systems that need to be explored further in the context of pain and cognition.

Serotonergic System Does Not Contribute to the Hypothermic Action of Acetaminophen

Acetaminophen (AcAP), a widely-used antipyretic and analgesic drug, has been considered to exert its effects via central mechanisms, and many studies have demonstrated that the analgesic action of AcAP involves activation of the serotonergic system. Although the serotonergic system also plays an important role in thermoregulation, the contribution of serotonergic activity to the hypothermic effect of AcAP has remained unclear. In the present study, we examined whether the serotonergic system is involved in AcAP-induced hypothermia. In normal mice, AcAP (300 mg/kg, intraperitoneally (i.p.)) induced marked hypothermia (ca. -4°C). The same dose of AcAP reduced pain response behavior in the formalin test. Pretreatment with the serotonin synthesis inhibitor DL-p-chlorophenylalanine (PCPA, 300 mg/kg/d, i.p., 5 consecutive days) substantially decreased serotonin in the brain by 70% and significantly inhibited the analgesic, but not the hypothermic action of AcAP. The same PCPA treatment significantly inhibited the hypothermia induced by the selective serotonin reuptake inhibitor fluoxetine hydrochloride (20 mg/kg, i.p.) and the serotonin 5-HT₂ receptor antagonist cyproheptadine hydrochloride (3 mg/kg, i.p.). The lower doses of fluoxetine hydrochloride (3 mg/kg, i.p.) and cyproheptadine hydrochloride (0.3 mg/kg, i.p.) did not affect the AcAP-induced hypothermia. These results suggest that, in comparison with its analgesic effect, the hypothermic effect of AcAP is not mediated by the serotonergic system.

Arthropathy-related pain in a patient with congenital impairment of pain sensation due to hereditary sensory and autonomic neuropathy type II with a rare mutation in the WNK1/HSN2 gene: a case report

Background

Hereditary sensory and autonomic neuropathy (HSAN) type II with WNK1/HSN2 gene mutation is a rare disease characterized by early-onset demyelination sensory loss and skin ulceration. To the best of our knowledge, no cases of an autonomic disorder have been reported clearly in a patient with WNK/HSN2 gene mutation and only one case of a Japanese patient with the WNK/HSN2 gene mutation of HSAN type II was previously reported.

Case presentation

Here we describe a 54-year-old woman who had an early childhood onset of insensitivity to pain; superficial, vibration, and proprioception sensation disturbances; and several symptoms of autonomic failure (e.g., orthostatic hypotension, fluctuation in body temperature, and lack of urge to defecate). Genetic analyses revealed compound homozygous mutations in the WNK1/HSN2 gene (c.3237_3238insT; p.Asp1080fsX1). The patient demonstrated sensory loss in the “stocking and glove distribution” but could perceive visceral pain, such as menstrual or gastroenteritis pain. She experienced frequent fainting episodes. She had undergone exenteration of the left metatarsal because of metatarsal osteomyelitis at 18 years. Sural nerve biopsy revealed a severe loss of myelinated and unmyelinated nerves. She complained of severe pain in multiple joints, even on having pain impairment. Although non-steroidal anti-inflammatory drugs are generally more effective than acetaminophen for arthritis, in our case, they were ineffective and acetaminophen (2400 mg/day) adequately controlled her pain and improved quality of life. Over 3 months, the numerical rating scale, pain interference scale of the Brief Pain Inventory, and the Pain Catastrophizing Scale decreased from 6/10 to 3/10, from 52/70 to 20/70, and from 22/52 to 3/52 points, respectively.

Conclusions

This is the second reported case of a Japanese patient with WNK/HSN2 gene mutation of HSAN type II and the first reported case of an autonomic disorder in a patient with the WNK/HSN2 gene mutation. Acetaminophen adequately controlled arthropathy related pain in a patient with congenital impairment of pain sensation.

Cerebral analgesic response to nonsteroidal anti-inflammatory drug ibuprofen

Nonopioid agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs), are the most commonly used class of analgesics. Increasing evidence suggests that cyclooxygenase (COX) inhibition at both peripheral and central sites can contribute to the antihyperalgesic effects of NSAIDs, with the predominant clinical effect being mediated centrally. In this study, we examined the cerebral response to ibuprofen in presurgical and postsurgical states and looked at the analgesic interaction between surgical state and treatment. We used an established clinical pain model involving third molar extraction, and quantitative arterial spin labelling (ASL) imaging to measure changes in tonic/ongoing neural activity. Concurrent to the ASL scans, we presented visual analogue scales inside the scanner to evaluate the subjective experience of pain. This novel methodology was incorporated into a randomized double-blind placebo-controlled design, with an open method of drug administration. We found that independent of its antinociceptive action, ibuprofen has no effect on regional cerebral blood flow under pain-free conditions (presurgery). However, in the postsurgical state, we observed increased activation of top-down modulatory circuits, which was accompanied by decreases in the areas engaged because of ongoing pain. Our findings demonstrate that ibuprofen has a measurable analgesic response in the human brain, with the subjective effects of pain relief reflected in two distinct brain networks. The observed activation of descending modulatory circuits warrants further investigation, as this may provide new insights into the inhibitory mechanisms of analgesia that might be exploited to improve safety and efficacy in pain management.

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.

WNT signaling in glioblastoma and therapeutic opportunities

WNTs and their downstream effectors regulate proliferation, death, and migration and cell fate decision. Deregulation of WNT signaling is associated with various cancers including GBM, which is the most malignant primary brain cancer. In this review, we will summarize the experimental evidence supporting oncogenic roles of WNT signaling in GBM and discuss current progress in the targeting of WNT signaling as an anti-cancer approach. In particular, we will focus on (1) genetic and epigenetic alterations that lead to aberrant WNT pathway activation in GBM, (2) WNT-mediated control of GBM stem cell maintenance and invasion, and (3) cross-talk between WNT and other signaling pathways in GBM. We will then review the discovery of agents that can inhibit WNT signaling in preclinical models and the current status of human clinical trials.

New formulation of old aspirin for better delivery

For better use of cyclooxygenase dependent anti-inflammatory properties and mitochondrial activities of aspirin, new hydrophobic analogues of aspirin were developed and successfully encapsulated in polymeric nanoparticles (NPs). In vivo anti-inflammatory effects of these NPs using a mouse model demonstrated unique properties of an optimized aspirin analogue to inhibit production of pro-inflammatory and enrichment of anti-inflammatory cytokines.

Anti-arthritic agents: progress and potential

Osteoarthritis and rheumatoid arthritis are the two most common types of arthritis. Cartilage breakdown is a key feature of both diseases which contributes to the pain and joint deformity experienced by patients. Therefore, anti-arthritis drugs are of great importance. The aim of this review is to present recent progress in studies of various agents against osteoarthritis and rheumatoid arthritis. The structures and activities of anti-arthritic agents, which used in medical practice or are in development, are presented and discussed. The effects and mechanisms of action of opioids, glucocorticoids, non-steroidal anti-inflammatory drugs, disease-modifying anti-rheumatic drugs, natural products derived from plants, nutraceuticals, and a number of new and perspective agents are considered. Various perspective targets for the treatment of osteoarthritis and rheumatoid arthritis are also discussed. Trials of good quality are needed to draw solid conclusions regarding efficacy of many of the studied agents. Unfortunately, to date, there is no pharmacologic agent proven to prevent the progression of both diseases, and there is an urgent need for further development of better anti-arthritic agents.

Role of nuclear factor-erythroid 2-related factor 2 (Nrf2) in the transcriptional regulation of brain ABC transporters during acute acetaminophen (APAP) intoxication in mice

Changes in expression of liver ABC transporters have been described during acute APAP intoxication. However, the effect of APAP on brain ABC transporters is poorly understood. The aim of this study was to evaluate the effect of APAP on brain ABC transporters expression and the role of the oxidative stress sensor Nrf2. Male C57BL/6J mice were administered APAP (400mg/kg) for analysis of brain mRNA and protein expression of Mrp1-6, Bcrp and P-gp. The results show induction of P-gp, Mrp2 and Mrp4 proteins, with no changes in Bcrp, Mrp1 or Mrp5-6. The protein values were accompanied by corresponding changes in mRNA levels. Additionally, brain Nrf2 nuclear translocation and expression of two Nrf2 target genes,

NAD(P)H

quinone oxidoreductase 1 (Nqo1) and Hemoxygenase 1 (Ho-1), was evaluated at 6, 12 and 24h after APAP treatment. Nrf2 nuclear content increased by 58% at 12h after APAP along with significant increments in mRNA and protein expression of Nqo1 and Ho-1. Furthermore, APAP treated Nrf2 knockout mice did not increase mRNA or protein expression of Mrp2 and Mrp4 as observed in wildtypes. In contrast, P-gp induction by APAP was observed in both genotypes. In conclusion, acute APAP intoxication induces protein expression of brain P-gp, Mrp2 and Mrp4. This study also suggests that brain changes in Mrp2 and Mrp4 expression may be due to in situ Nrf2 activation by APAP, while P-gp induction is independent of Nrf2 function. The functional consequences of these changes in brain ABC transporters by APAP deserve further attention.

Effect of α-tocopheryl succinate on the molecular damage induced by indomethacin in C6 glioma cells

Indomethacin is a member of the non-steroidal anti-inflammatory drug (NSAID) class, which has great potential for use in the treatment of glioma. However, it induces the generation of reactive oxygen species (ROS) and causes molecular damage while inducing its effects. Vitamin E is widely used in the complementary therapy of cancers. The main goal of the present study was to investigate the effects of α-tocopheryl succinate (α-TOS) against the oxidative damage induced by indomethacin in C6 glioma cells. Cells were treated with 10 μM α-TOS alone or in combination with 200 μM indomethacin for two days. The intracellular ROS level, molecular damage as revealed by lipid peroxidation and protein carbonyl formation, and the COX activity in C6 glioma cells were measured. Treatment of the cells with α-TOS and indomethacin, alone or in combination, caused the levels of ROS generation and protein damage to increase, but protected against lipid peroxidation and reduced COX activity.

Liquid microjunction surface sampling of acetaminophen, terfenadine and their metabolites in thin tissue sections

Background: The aim of this work was to evaluate the analytical performance of a fully automated droplet-based surface-sampling system for determining the distribution of the drugs acetaminophen and terfenadine, and their metabolites, in rat thin tissue sections. Results: The rank order of acetaminophen concentration observed in tissues was stomach > small intestine > liver, while the concentrations of its glucuronide and sulfate metabolites were greatest in the liver and small intestine. Terfenadine was most concentrated in the liver and kidney, while its major metabolite, fexofenadine, was found in the liver and small intestine. Conclusion: The spatial distributions of both drugs and their respective metabolites observed in this work were consistent with previous studies using radiolabeled drugs.

Paracetamol: a focus for the general pediatrician

Paracetamol (acetaminophen) is one of the most popular and widely used drugs for the treatment of pain and fever in children. This drug has multiple mechanisms of action, but its pharmacodynamic is still not well known. The central nervous system is the main site of action and it mirrors the paracetamol effect compartment. The recommended dosages and routes of administration should be different whether paracetamol is used for the treatment of pain or fever. For example, the rectal route, while being efficacious for the treatment of fever, should be avoided in pain management. Paracetamol is a safe drug, but some clinical conditions and concomitant drugs, which are frequent in clinical practice, may increase the risk of paracetamol toxicity. Therefore, it is important to optimize its administration to avoid overdoses and maximize its effect. The principal mediator of the paracetamol toxicity is the N-acetyl-p-benzo-quinone imine (NAPQI), a toxic product of the paracetamol metabolism, which could bind cysteine groups on proteins forming paracetamol-protein adduct in the liver.

CONCLUSION

Although frequently prescribed, the concept of "effect compartment concentration" and the possible co-factors that could cause toxicity at recommended doses are not familiar to all pediatricians and general practitioners. We reviewed the literature concerning paracetamol mechanisms of action, we highlighted some relevant pharmacodynamic concepts for clinical practice, and we summarized the possible risk factors for toxicity at therapeutic dosages.

Evaluation of paracetamol distribution and stability in case of acute intoxication in rats

Effects of different storing conditions on paracetamol concentration in biological samples of acute intoxicated rats were investigated. The stability and distribution of paracetamol was observed in postmortem serum, liver, kidney and brain tissues. The serum samples were stored for 30 days and daily changes were evaluated for paracetamol. A significant difference ( p = 0.05) was noticed on the 30th experimental day. Paracetamol serum levels changed as much as 66.30% and 33.78% for 4°C and −20°C, respectively. The stability of paracetamol in liver stored at −20°C was also evaluated for 30 days. The paracetamol concentration levels taken from liver samples dramatically decreased from 30.36% on the 1st day to 94.97% on the 30th day. The paracetamol distribution in organs was as 2.68 , 1.11 and 0.68 mg/g in liver, kidney and brain samples, respectively. Meaningful difference in paracetamol in serum and liver samples was in observed in 30th day values ( p = 0.05).

Systemic paracetamol-induced analgesic and antihyperalgesic effects through activation of descending serotonergic pathways involving spinal 5-HT₇ receptors

Although some studies have shown the essential role of descending serotonergic pathways and spinal 5-HT(1A), 5-HT(2A), or 5-HT(3) receptors in the antinociceptive effects of paracetamol, other studies have presented conflicting results, and the particular subtype of spinal 5-HT receptors involved in paracetamol-induced analgesia remains to be clarified. Recent studies have demonstrated the importance of spinal 5-HT(7) receptors in descending serotonergic pain inhibitory pathways. In this study, we investigated the role of descending serotonergic pathways and spinal 5-HT(7) receptors compared with 5-HT(3) and 5-HT(2A) receptors in the antinociceptive and antihyperalgesic effects of paracetamol. Tail-flick, hot plate and plantar incision tests were used to determine nociception in male BALB/c mice. Lesion of serotonergic bulbospinal pathways was performed by intrathecal (i.th.) injection of 5,7-dihydroxytryptamine (5,7-DHT), and spinal 5-HT levels were measured by HPLC. To evaluate the particular subtypes of the spinal 5-HT receptors, the selective 5-HT(7), 5-HT(3) and 5-HT(2A) receptor antagonists SB 269970, ondansetron and ketanserin, respectively, were given i.th. after oral administration of paracetamol. Oral paracetamol (200, 400 and 600 mg/kg) elicits dose-dependent antinociceptive and antihyperalgesic effects. I.th. pretreatment with 5,7-DHT (50 μg) sharply reduced 5-HT levels in the spinal cord. Depletion of spinal 5-HT totally abolished the antinociceptive and antihyperalgesic effects of paracetamol. I.th. injection of SB 2669970 (10 μg) blocked the antinociceptive and antihyperalgesic effects of paracetamol, but ondansetron and ketanserin (10 μg) did not. Our findings suggest that systemic administration of paracetamol may activate descending serotonergic pathways and spinal 5-HT(7) receptors to produce a central antinociceptive and antihyperalgesic effects.

Aspirin: pharmacology and clinical applications

Antiplatelet therapy has been documented to reduce risks of cardiovascular disease after acute myocardial infarction, coronary artery bypass graft, and in chronic atrial fibrillation patients, amongst other risk factors. Conventional management of thrombosis-based disorders includes the use of heparin, oral anticoagulants, and the preferred antiplatelet agent aspirin. Interestingly, aspirin was not intended to be used as an antiplatelet agent; rather, after being repurposed, it has become one of the most widely prescribed antithrombotic drugs. To this end, there have been several milestones in the development of antiplatelet agents in the last few decades, such as adenosine diphosphate receptor inhibitors, phosphodiesterase inhibitors, and GPIIb/IIIa inhibitors. However, given some of the limitations of these therapies, aspirin continues to play a major role in the management of thrombotic and cardiovascular disorders and is expected to do so for years to come.

What do we (not) know about how paracetamol (acetaminophen) works?

WHAT IS KNOWN AND BACKGROUND

Although paracetamol (acetaminophen), N-(4-Hydroxyphenyl)acetamide, is one of the world's most widely used analgesics, the mechanism by which it produces its analgesic effect is largely unknown. This lack is relevant because: (i) optimal pain treatment matches the analgesic mechanism to the (patho)physiology of the pain and (ii) modern drug discovery relies on an appropriate screening assay.

OBJECTIVE

To review the clinical profile and preclinical studies of paracetamol as means of gaining insight into its mechanism of analgesic action.

METHODS

A literature search was conducted of clinical and preclinical literature and the information obtained was organized and reviewed from the perspective of its contribution to an understanding of the mechanism of analgesic action of paracetamol.

RESULTS

Paracetamol's broad spectrum of analgesic and other pharmacological actions is presented, along with its multiple postulated mechanism(s) of action. No one mechanism has been definitively shown to account for its analgesic activity.

WHAT IS NEW AND CONCLUSION

Further research is needed to uncover the mechanism of analgesic action of paracetamol. The lack of this knowledge affects optimal clinical use and impedes drug discovery efforts.

The effects of preoperative intravenous acetaminophen in patients undergoing abdominal hysterectomy

PURPOSE

Although intravenous acetaminophen is commonly used for the management of postoperative pain, very limited evidence supports the usefulness of preoperative administration. The aim of this study was to determine the analgesic effect of preoperative acetaminophen on opioid consumption, pain scores, and side effects in patients receiving an elective abdominal hysterectomy.

METHODS

A randomized, double-blinded, placebo-controlled clinical trial was performed in 76 women undergoing abdominal hysterectomy. Patients received either acetaminophen 2 g (group A) or placebo (group C) intravenously 30 min before surgery under general anesthesia. Postoperative pain was treated with patient-controlled intravenous hydromorphone 0.2 mg bolus. Hydromorphone consumption, pain scores during rest and movement, and any adverse effects were recorded at 1, 2, 6, 12, and 24 h after the operation.

RESULTS

Overall hydromorphone consumption was significantly lower in group A compared with group C at all the time points (P = 0.013). The total 24-h hydromorphone consumption was reduced by 30% in group A. There was no significant difference in pain scores. The incidence of postoperative nausea and vomiting after the operation were significantly lower in group A than in group C (P < 0.05).

CONCLUSIONS

Premedication with acetaminophen reduced hydromorphone consumption and opioid-related side effect in patients undergoing abdominal hysterectomy, but did not significantly reduce pain intensity.

Non-Steroidal Anti-Inflammatory Drugs and Brain Inflammation: Effects on Microglial Functions

The term NSAID refers to structurally diverse chemical compounds that share the ability to inhibit the activity of the prostaglandin (PG) biosynthetic enzymes, the cyclooxygenase (COX) isoforms 1 and 2. The suppression of PG synthesis at sites of inflammation has been regarded as primarily responsible for the beneficial properties of NSAIDs, but several COX-independent effects have been described in recent years. Epidemiological studies indicate that NSAIDs are neuroprotective, although the mechanisms underlying their beneficial effect remain largely unknown. Microglial cells play a major role in brain inflammation and are often viewed as major contributors to the neurodegeneration. Therefore, microglia represent a likely target for NSAIDs within the brain. In the present review, we focused on the direct effects of NSAIDs and selective COX-2 inhibitors on microglial functions and discuss the potential efficacy in controlling brain inflammation.

Transport across the blood-brain barrier of pluronic leptin

Leptin is a peptide hormone produced primarily by adipose tissue that acts as a major regulator of food intake and energy homeostasis. Impaired transport of leptin across the blood-brain barrier (BBB) contributes to leptin resistance, which is a cause of obesity. Leptin as a candidate for the treatment of this obesity is limited because of the short half-life in circulation and the decreased BBB transport that arises in obesity. Chemical modification of polypeptides with amphiphilic poly(ethylene oxide)-poly(propylene oxide) block copolymers (Pluronic) is a promising technology to improve efficiency of delivery of polypeptides to the brain. In the present study, we determined the effects of Pluronic P85 (P85) with intermediate hydrophilic-lipophilic balance conjugated with leptin via a degradable SS bond [leptin(ss)-P85] on food intake, clearance, stability, and BBB uptake. The leptin(ss)-P85 exhibited biological activity when injected intracerebroventricularly after overnight food deprivation and 125I-leptin(ss)-P85 was stable in blood, with a half-time clearance of 32.3 min (versus 5.46 min for leptin). 125I-Leptin(ss)-P85 crossed the BBB [blood-to-brain unidirectional influx rate (K(i)) = 0.272 +/- 0.037 microl/g x min] by a nonsaturable mechanism unrelated to the leptin transporter. Capillary depletion showed that most of the 125I-leptin(ss)-P85 taken up by the brain reached the brain parenchyma. Food intake was reduced when 3 mg of leptin(ss)-P85 was administered via tail vein in normal body weight mice [0-30 min, p < 0.0005; 0-2 h, p < 0.001]. These studies show that the structure based Pluronic modification of leptin increased metabolic stability, reduced food intake, and allowed BBB penetration by a mechanism-independent BBB leptin transporter.

Acetaminophen prevents hyperalgesia in central pain cascade

Acetaminophen is an analgesic and antipyretic drug believed to exert its effect through interruption of nociceptive processing. In order to determine whether this effect is due to peripheral or central activity, we studied the efficacy of systemic (oral) and intrathecal (IT) application of acetaminophen in preventing the development of hyperalgesia induced through the direct activation of pro-algogenic spinal receptors. Spinal administration of substance P (SP, 30 nmol, IT) in rats produced a decreased thermal threshold, indicating centrally mediated hyperalgesia. Pretreatment of rats with oral acetaminophen (300 mg/kg), but not vehicle, significantly attenuated IT SP-induced hyperalgesia. Acetaminophen given IT also produced a dose-dependent (10-200 microg) antinociceptive effect. In addition, oral acetaminophen suppressed spinal PGE(2) release evoked by IT SP in an in vivo IT dialysis model. The ability of IT as well as oral acetaminophen to reverse this spinally initiated hyperalgesia emphasizes the likely central action and bioavailability of the systemically delivered drug. Jointly, these data argue for an important central antihyperalgesic action of acetaminophen.

Acetaminophen: antipyretic or hypothermic in mice? In either case, PGHS-1b (COX-3) is irrelevant

Acetaminophen (AC) reduces the core temperatures (T(c)) of febrile and non-febrile mice alike. Evidence has been adduced that the selectively AC-sensitive PGHS isoform, PGHS-1b (COX-3), mediates these effects. PGHS-1b, however, has no catalytic potency in mice. To resolve this contradiction, AC was injected intravenously (i.v.) into conscious PGHS-1 gene-sufficient (wild-type (WT)) and -deficient (PGHS-1(-/-)) mice 60 min before or after pyrogen-free saline (PFS) or E. coli LPS (10 microg/kg) i.v. T(c) was monitored continuously; brain and plasma PGE(2) levels were determined hourly. AC at <160 mg/kg did not affect T(c) when given before PFS or LPS; at 160 mg/kg, it caused a approximately 2.5 degrees C T(c) fall in 60 min. LPS given after AC (all doses) induced a approximately 1 degrees C fever, not different from that in AC-untreated mice. But this rise was insufficient to overcome the hypothermia of the 160 mg/kg-treated mice; their T(c) culminated 1 degrees C below baseline. LPS given before AC similarly elevated T(c) approximately 1 degrees C. This rise was reduced to baseline in 30 min by 80 mg AC/kg; T(c) rebounded to its febrile level over the next 30 min. At 160 mg/kg, AC reduced T(c) to 4 degrees C below baseline in 60 min, where it remained until the end of the experiment. WT and PGHS-1(-/-) mice responded similarly to all the treatments. The basal brain and plasma PGE(2) levels of PFS mice and the elevated plasma levels of LPS mice were unchanged by AC at 160 mg/kg; but the latter's brain levels were reduced at 1h, then recovered. Thus, AC could exert an anti-PGHS-2 effect when this enzyme is upregulated in the brain of febrile mice. The hypothermia it induces in non-febrile mice, therefore, is due to another mechanism. PGHS-1b is not involved in either case.

Nitroparacetamol (NCX-701) and pain: first in a series of novel analgesics

The combination of numerous classic drugs with nitric oxide donors has led to the development of new compounds with promising therapeutic activities in a great variety of situations, including cardiovascular and respiratory systems, ocular pressure, inflammation, and pain. One of the first compounds developed was NCX-701 or nitroparacetamol, resulting from the combination of paracetamol, a classic and popular analgesic used in a great number of over-the-counter medications because of its antipyretic and analgesic properties, and a nitrooxybutyroyl moiety, which releases nitric oxide at a low but steady level. Although paracetamol is devoid of most of the gastrointestinal toxicity associated with aspirin-like drugs, this type of compounds was first designed to take advantage of the cytoprotective properties of nitric oxide when released at low concentrations. However, the combination of these molecules also resulted in an unexpected enhancement of the analgesic activity of paracetamol. In fact, NCX-701 has been shown to be effective in acute nociception as well as in neuropathic pain, situations in which paracetamol and other COX inhibitors are devoid of any effect. In addition, NCX-701 is more potent and, in some circumstances, more effective than its parent compound in different models of inflammatory pain. Furthermore, whereas paracetamol lacks any effective antiinflammatory action, NCX-701 might reduce inflammation. All these results taken together imply that the mechanism of action of NCX-701 is different from that of paracetamol, although it is not yet established for either molecule. NCX-701 appears to be a promising compound in the treatment of different types of pain, with a likely better profile of side effects than its parent molecule, paracetamol. Although recent clinical trials provided data consistent with the preclinical profile of NCX-701, further studies are needed to support its clinical use.

Effect of acetaminophen, a cyclooxygenase inhibitor, on Morris water maze task performance in mice

Although the mechanism of action of acetaminophen (AAP) is not fully understood, some studies suggest that AAP and phenacetin (PHE) are selective cyclooxygenase (COX)-3 inhibitors. To examine the participation of COX-3 in memory formation, water maze performance was studied in mice treated with AAP, PHE or other COX inhibitors. Mice received intraperitoneal injections of drugs immediately after each training session. Administration of high-dose AAP [302.3 mg/kg (IC50 for COX-2)] or PHE [179.2 mg/kg (IC50 for COX-2)] and of non-specific (indomethacin: 20 mg/kg) or specific COX-2 (NS-398: 10 mg/kg) inhibitor impaired the performance in hidden platform (HP) not visible platform (VP) tasks, whereas low-dose (15.1 mg/kg) AAP facilitated performance in HP and VP tasks. The facilitation of performance by low-dose AAP was reversed by co-administration with a 5-HT(1/2) receptor antagonist (methysergide: 0.47 mg/kg). The middle-dose [69.5 mg/kg (IC50 for COX-3)] of AAP, the PHE [17.9 mg/kg (IC50 for COX-3)] and a specific COX-1 inhibitor (piroxicam: 10-20 mg/kg) did not influence performance in either task. These results suggest that the memory impairment by high-dose AAP and PHE and facilitation of performance by low-dose AAP could involve endogenous COX-2 and serotonergic neuronal activity, but not COX-3, respectively.

Indomethacin stimulates activity and expression of ecto-5'-nucleotidase/CD73 in glioma cell lines

Gliomas are the most common and devastating primary tumors of the central nervous system. Ecto-NTPDases and ecto-5'-nucleotidase/CD73 can control extracellular ATP/adenosine levels, which have been described as proliferation factors. Here, we investigate the influence of indomethacin on the enzyme cascade that catalyses the interconversion of purine nucleotides in U138-MG and C6 glioma cell lines. Exposure of glioma cells to 100 microM indomethacin for 48 h caused increases of 52% (P < 0.05) and 62% (P < 0.05) in the AMP hydrolysis rate in C6 and U138-MG cell lines, respectively. Indomethacin treatments also increased ATP hydrolysis. Significant increase in ecto-5'-nucleotidase/CD73 mRNA and protein levels were observed after treatment with indomethacin. Pretreatment of glioma cells with a specific antagonist of the adenosine A(3) receptor, MRS1220 (1 microM; 9-Chloro-2-(2-furanyl)-5-((phenylacetyl)amino)-[1,2,4]triazolo[1,5-c]quinazoline), significantly reduced the inhibition of cell proliferation induced by indomethacin. In addition, a significant increase in mRNA levels of the adenosine A(3) receptor was observed after treatment with indomethacin. In conclusion, our data indicate that adenosine A(3) receptors and the enzyme, ecto-5'-nucleotidase/CD73, are involved in the anti-proliferative effect of indomethacin in glioma cells.

Effect of NC-1900, an active fragment analog of arginine vasopressin, and inhibitors of arachidonic acid metabolism on performance of a passive avoidance task in mice

In this study, we investigated the effect of administration of inhibitors of each of the arachidonic acid metabolism pathways and the effect of co-administration of these inhibitors with NC-1900, a fragment analog of arginine vasopressin, on step-through passive avoidance task performance. All drugs were administered just after the acquisition trial in the passive avoidance task. Intracerebroventricular (i.c.v.) administration of nordihydroguaiaretic acid (NDGA, 1 and 10 microg), a phospholipase A2 (PLA2) and lipoxygenase (LOX) inhibitor, and of arachidonyl trifluoromethyl ketone (ATK, 1 and 10 microg), a specific PLA2 inhibitor caused reductions in latency on the retention trial. The i.c.v. administration of either of baicalein (0.1-10 microg), a 12-LOX inhibitor, or AA-861 (0.1-10 microg), a 5-LOX inhibitor, did not influence the latency. Intraperitoneal administration of indomethacin (20 mg/kg), a non-specific COX inhibitor, or NS-398 (10 mg/kg), a specific COX-2 inhibitor, impaired performance on the retention trial in the task, while piroxicam (20 mg/kg), a specific COX-1 inhibitor, did not. Subcutaneous administration of NC-1900 (0.1 ng/kg) ameliorated the reduction of latency caused by NDGA, ATK, indomethacin, or NS-398. These results suggested that the COX-2 pathway of arachidonic acid metabolism may be important for learning and/or memory in the passive avoidance task in mice, and that the ameliorating effect of NC-1900, in part, is due to mimicking of the effects of metabolites of the COX-2 pathway.

The CNS as a target for peptides and peptide-based drugs

Peptides hold great potential as CNS drugs, but their delivery to the CNS is problematic. However, actual roadblocks to peptide delivery are different from those often perceived. Many peptides cross the blood-brain barrier by saturable and non-saturable mechanisms, and accumulate in brain in amounts sufficient to produce physiological effects. Peripheral factors (e.g., short half-life in blood) can be dominant factors limiting therapeutic use. Production of therapeutics that are enzymatically resistant and have long circulation times, even when the blood-brain barrier penetration is low, can result in substances with significant CNS accumulation. Surprisingly low amounts of peptide in brain can result in CNS effects, and so the dose needed for brain delivery is generally much smaller than for peripheral tissues. Brain-to-blood transporters can greatly limit CNS accumulation of a potential therapeutic. Finally, intranasal and intrathecal routes may be especially useful for substances that are rapidly degraded in blood or are large and hydrophobic, respectively.

Nonsteroidal anti-inflammatory drugs inhibit the growth of C6 and U138-MG glioma cell lines

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used drugs for the treatment of inflammatory disease and have a chemopreventive effect in a variety of tumors. Several studies have demonstrated unequivocally that certain NSAIDs cause antiproliferative effects independent of cyclooxygenase (COX) activity. In this study, we investigated the effect of chemically unrelated NSAIDs in the proliferation of glioma cell lines and the possible mechanisms involved in indomethacin-mediated inhibition of proliferation in glioma cells lines. The glioma cell lines were treated with NSAIDs and proliferation was measured by cell counting. Indomethacin, acetaminophen, sulindac sulfide and NS-398 (N-[2-cyclohexyloxy)-4-nitrophenyl]methane-sulfonamide) induced a time- and concentration-dependent inhibition of C6 rat glioma cell proliferation. The inhibition of COX by chemically unrelated NSAIDs leads to inhibition of rat and human glioma cell proliferation. The tetrazolium reduction assay (MTT) indicated a reduction in cell viability induced by indomethacin. None of the NSAIDs tested induced caspase-3/7 activation, assayed with a fluorigenic substrate. The indomethacin-induced inhibition of C6 cells proliferation was abrogated by the use of the c-Src inhibitor, PP2 and the MEK inhibitor, PD 098059, suggesting COX-independent mechanisms. Indomethacin decreased the percentage of cells in the S phase, with relative increases in the G0/G1 and/or the G2/M phase. NSAIDs may be clinically important for pharmacological intervention in gliomas.

Labeling of Acetaminophen with I-131 and Biodistribution in Rats

The aim of the present study was to label acetaminophen (APAP) with I-131 and to determine its radiopharmaceutical potential in rats. Acetaminophen was labeled with I-131 using the iodogen method. The radiochemical purity of (131)I-APAP was determined by RTLC and paper electrophoresis. The labeling yield was 94 +/- 4%. The biodistribution studies of the labeled compound (specific activity; 56.60 GBq/mmol) were performed in male Albino Wistar rats. The uptake of (131)I-APAP in some organs were determined at different time after injection to the rats. The radioactivity in each organ was counted and the percentage of injected activity per gram of tissue weight (%ID/g) for each organ and blood was calculated. (131)I-APAP uptake in the lung, liver, kidneys, pancreas, blood, stomach and some brain region, were observed. Thus, (131)I-APAP may be radiopharmaceutical for the imaging of the brain.

Opioid receptors and acetaminophen (paracetamol)

We report that the acetaminophen (paracetamol)-induced spinal (intrathecal, i.t.)/supraspinal (intracerebroventricular, i.c.v.) site/site antinociceptive 'self-synergy' in mice is attenuated by the opioid receptor subtype selective antagonists beta-funaltrexamine hydrochloride (beta-FNA; mu), naltrindole (delta), and nor-binaltorphine hydrochloride (nor-BNI; kappa). These findings further implicate endogenous opioids (viz., endorphins, enkephalins, and dynorphins) and their pathways as contributors to the central antinociceptive action of acetaminophen.

COX-3 and the mechanism of action of paracetamol/acetaminophen

Paracetamol produces analgesia in the mouse writhing test through a central action which is paralleled by a reduction in brain PGE(2) concentrations. In contrast, diclofenac has a peripheral analgesic action in this test. Paracetamol-induced hypothermia is also accompanied by a reduction in brain PGE(2) concentrations in C57/Bl6 mice. This hypothermic effect of paracetamol was reduced in COX-1 but not in COX-2 gene-deleted mice. These results support the view that analgesia and hypothermia due to paracetamol are mediated by inhibition of a third COX isoenzyme (designated COX-3). In cultured mouse macrophages, COX-2 is induced by treatment with LPS or with high concentrations of diclofenac. Diclofenac-induced COX-2 is inhibited with low concentrations of paracetamol, whereas LPS-induced COX-2 is insensitive to paracetamol inhibition. The mechanisms of induction and possibly the functions of these two COX-2 enzymes are also different.