Clinical pharmacokinetics of nonsteroidal anti-inflammatory drugs in the cerebrospinal fluid

Antiseizure properties of fenamate NSAIDs determined in mature human stem-cell derived neuroglial circuits

Repeated and uncontrolled seizures in epilepsy result in brain cell loss and neural inflammation. Current anticonvulsants primarily target ion channels and receptors implicated in seizure activity. Identification of neurotherapeutics that can inhibit epileptiform activity and reduce inflammation in the brain may offer significant benefits in the long-term management of epilepsy. Fenamates are unique because they are both non-steroidal anti-inflammatory drugs (NSAIDs) and highly subunit selective modulators of GABAA receptors. In the current study we have investigated the hypothesis that fenamates have antiseizure properties using mature human stem cell-derived neuro-glia cell cultures, maintained in long-term culture, and previously shown to be sensitive to first, second and third generation antiepileptics. Mefenamic acid, flufenamic acid, meclofenamic acid, niflumic acid, and tolfenamic acid (each tested at 10-100 μM) attenuated 4-aminopyridine (4-AP, 100 μM) evoked epileptiform activity in a dose-dependent fashion. These actions were as effective diazepam (3-30 μM) and up to 200 times more potent than phenobarbital (300-1,000 μM). The low (micromolar) concentrations of fenamates that inhibited 4-AP evoked epileptiform activity correspond to those reported to potentiate GABAA receptor function. In contrast, the fenamates had no effect on neural spike amplitudes, indicating that their antiseizure actions did not result from inhibition of sodium-channels. The antiseizure actions of fenamates were also not replicated by either of the two non-fenamate NSAIDs, ibuprofen (10-100 μM) or indomethacin (10-100 μM), indicating that inhibition of cyclooxygenases is not the mechanism through which fenamates have anticonvulsant properties. This study therefore shows for the first time, using functionally mature human stem cell-derived neuroglial circuits, that fenamate NSAIDs have powerful antiseizure actions independent of, and in addition to their well-established anti-inflammatory properties, suggesting these drugs may provide a novel insight and new approach to the treatment of epilepsy in the future.

Modeling adult COX-2 cerebrospinal fluid pharmacokinetics to inform pediatric investigation

AIM

Hysteresis is reported between plasma concentration and analgesic effect from nonsteroidal anti-inflammatory drugs. It is possible that the temporal delay between plasma and CSF nonsteroidal anti-inflammatory drugs mirrors this hysteresis. The temporal relationship between plasma and CSF concentrations of COX-inhibitors (celecoxib, rofecoxib, valdecoxib) has been described. The purpose of this secondary data analysis was to develop a compartmental model for plasma and CSF disposition of these COX-2 inhibitors.

METHODS

Plasma and CSF concentration-time profiles and protein binding data in 10 adult volunteers given oral celecoxib 200 mg, valdecoxib 40 mg and rofecoxib 50 mg were available for study. Nonlinear mixed effects models with a single plasma compartment were used to link a single CSF compartment with a transfer factor and an equilibration rate constant (Keq). To enable predictive modeling in pediatrics, celecoxib pharmacokinetics were standardized using allometry.

RESULTS

Movement of all three unbound plasma COX-2 drugs into CSF was characterized by a common equilibration half-time (T_1/2 keq) of 0.84 h. Influx was faster than efflux and a transfer scaling factor of 2.01 was required to describe conditions at steady-state. Estimated celecoxib clearance was 49 (95% CI 34-80) L/h/70 kg and the volume of distribution was 346 (95% CI 237-468) L/70 kg. The celecoxib absorption half-time was 0.35 h with a lag time of 0.62 h. Simulations predicted a 70-kg adult given oral celecoxib 200 mg with maintenance 100 mg twice daily would have a mean steady-state total (bound and unbound) plasma concentration of 174 μg L^-1 and CSF concentration of 1.1 μg L^-1 . A child (e.g., 25 kg, typically 7 years) given oral celecoxib 6 mg kg^-1 with maintenance of 3 mg kg^-1 twice daily would have 282 and 1.7 μg L^-1 mean plasma and CSF concentrations, respectively.

CONCLUSIONS

Transfer of unbound COX-2 inhibitors from plasma to CSF compartment can be described with a delayed effect model using an equilibration rate constant to collapse observed hysteresis. An additional transfer factor was required to account for passage across the blood-brain barrier. Use of a target concentration strategy for dose and consequent plasma (total and unbound) and CSF concentration prediction could be used to inform pediatric clinical studies.

Molecular Imaging of Neuroinflammation in Alzheimer's Disease and Mild Cognitive Impairment

Alzheimer's disease (AD) is the most prevalent neurocognitive disorder. Due to the ineffectiveness of treatments targeting the amyloid cascade, molecular biomarkers for neuroinflammation are attracting attention with increasing knowledge about the role of neuroinflammation in the pathogenesis of AD. This chapter will explore the results of studies using molecular imaging for diagnosing AD and mild cognitive impairment (MCI). Because it is critical to interpreting the data to understand which substances are targeted in molecular imaging, this chapter will discuss the two most significant targets, microglia and astrocytes, as well as the best-known radioligands for each. Then, neuroimaging results with PET neuroinflammation imaging will be reviewed for AD and MCI. Although a growing body of evidence has suggested that these molecular imaging biomarkers for neuroinflammation may have a role in the diagnosis of AD and MCI, the findings are inconsistent or cross-sectional, which indicates that it is difficult to apply the contents in practice due to the need for additional study. In particular, because the results of multiple interventions targeting neuroinflammation were inconclusive, molecular imaging markers for neuroinflammation can be used in combination with conventional markers to select appropriate patients for early intervention for neuroinflammation rather than as a single marker.

The general anesthetic etomidate and fenamate mefenamic acid oppositely affect GABAAR and GlyR: a structural explanation

GABA and glycine act as inhibitory neurotransmitters in the CNS. Inhibitory neurotransmission is mediated via activation of ionotropic GABA_A and glycine receptors. We used a modeling approach to explain the opposite effects of the general anesthetic etomidate (ETM) and fenamate mefenamic acid (MFA) on GABA- and glycine-activated currents recorded in isolated cerebellar Purkinje cells and hippocampal pyramidal neurons, respectively. These drugs potentiated GABA_ARs but blocked GlyRs. We built a homology model of α1β GlyR based on the cryo-EM structure of open α1 GlyR, used the α1β3γ2 GABA_AR structure from the PDB, and applied Monte-Carlo energy minimization to optimize models of receptors and ligand-receptor complexes. In silico docking suggests that ETM/MFA bind at the transmembrane β( +)/α( -) intersubunit interface in GABA_AR. Our models predict that the bulky side chain of the highly conserved Arg^19' residue at the plus interface side wedges the interface and maintains the conducting receptor state. We hypothesized that MFA/ETM binding at the β( +)/α( -) interface leads to prolongation of receptor life-time in the open state. Having analyzed different GABA_AR and GlyR structures available in the PDB, we found that mutual arrangement of the Arg^19' and Gln^-26' side chains at the plus and minus interface sides, respectively, plays an important role when the receptor switches from the open to closed state. We show that this process is accompanied by narrowing of the intersubunit interfaces, leading to extrusion of the Arg^19' side chain from the interface. Our models allow us to explain the lack of GlyR potentiation in our electrophysiological experiments.

The mechanisms of potentiation and inhibition of GABAA receptors by non-steroidal anti-inflammatory drugs, mefenamic and niflumic acids

Fenamates mefanamic and niflumic acids (MFA and NFA) induced dual potentiating and inhibitory effects on GABA currents recorded in isolated cerebellar Purkinje cells using the whole-cell patch-clamp and fast-application techniques. Regardless of the concentration, both drugs induced a pronounced prolongation of the current response. We demonstrated that the same concentration of drugs can produce both potentiating and inhibitory effects, depending on the GABA concentration, which indicates that both processes take place simultaneously and the net effect depends on the concentrations of both the agonist and fenamate. We found that the NFA-induced block is strongly voltage-dependent. The Woodhull analysis of the block suggests that NFA has two binding sites in the pore - shallow and deep. We built a homology model of the open GABA_AR based on the cryo-EM structure of the open α1 GlyR and applied Monte-Carlo energy minimization to optimize the ligand-receptor complexes. A systematic search for MFA/NFA binding sites in the GABA_AR pore revealed the existence of two sites, the location of which coincides well with predictions of the Woodhull model. In silico docking suggests that two fenamate molecules are necessary to occlude the pore. We showed that MFA, acting as a PAM, competes with an intravenous anesthetic etomidate for a common binding site. We built structural models of MFA and NFA binding at the transmembrane β(+)/α(-) intersubunit interface. We suggested a hypothesis on the molecular mechanism underlying the prolongation of the receptor lifetime in open state after MFA/NFA binding and β subunit specificity of the fenamate potentiation.

Towards an Effective and Safe Treatment of Inflammatory Pain: A Delphi-Guided Expert Consensus

OBJECTIVE

The clinical management of inflammatory pain requires an optimal balance between effective analgesia and associated safety risks. To date, mechanisms associated with inflammatory pain are not completely understood because of their complex nature and the involvement of both peripheral and central mechanisms. This Expert Consensus document is intended to update clinicians about evolving areas of clinical practice and/or available treatment options for the management of patients with inflammatory pain.

METHOD

An international group of experts in pain management covering the pharmacology, neurology and rheumatology fields carried out an independent qualitative systematic literature search using MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials.

RESULTS

Existing guidelines for pain management provide recommendations that do not satisfactorily address the complex nature of pain. To achieve optimal outcomes, drug choices should be individualized to guarantee the best match between the characteristics of the patient and the properties of the medication. NSAIDs represent an important prescribing choice in the management of inflammatory pain, and the recent results on paracetamol question its appropriate use in clinical practice, raising the need for re-evaluation of the recommendations in the clinical practice guidelines.

CONCLUSIONS

Increasing clinicians' knowledge of the available pharmacologic options to treat different pain mechanisms offers the potential for safe, individualized treatment decisions. We hope that it will help implement the needed changes in the management of inflammatory pain by providing the best strategies and new insights to achieve the ultimate goal of managing the disease and obtaining optimal benefits for patients.

FUNDING

Dompé Farmaceutici SPA and Paolo Procacci Foundation.

No apparent effect of naproxen on CSF markers of innate immune activation

We studied 78 participants having a parental or multiple‐sibling history of Alzheimer’s disease (AD) in a two‐year randomized placebo‐controlled trial of naproxen 220 mg b.i.d. for mitigation of early AD pathogenesis. Naproxen was detected in cerebrospinal fluid at concentrations ~100 times lower than in plasma, but produced negligible change in immune markers. The repeated lack of benefit in AD prevention trials using naproxen and related drugs may reflect limited CNS permeability, lack of expected drug effects, or both. These findings suggest reconsideration of implications from results of AD prevention trials using anti‐inflammatory drugs.

Population scale retrospective analysis reveals distinctive antidepressant and anxiolytic effects of diclofenac, ketoprofen and naproxen in patients with pain

Currently approved monoamine modulating antidepressant and anxiolytic pharmaceutics fail in over one third of patients due to delayed and variable therapeutic effect, adverse reactions preceding the therapeutic action, and adherence issues. Even with adequate adherence to the regimen and tolerability, one third of the patients do not respond to any class of antidepressants. There is a strong correlation between treatment resistant depression and increase in inflammatory cytokines in plasma and cerebrospinal fluid. Furthermore, epidemiological studies suggest that depression and anxiety are commonly comorbid with pain and inflammation. While a link between pain, inflammation and depression has been suggested it remains unclear which anti-inflammatory treatment may be beneficial to patients with depression and anxiety due to pain. Here, we analyzed 430,783 FDA adverse effect reports of patients treated for pain to identify potential antidepressant and anxiolytic effects of various anti-inflammatory medications. Patients treated for depression or patients taking any known antidepressants were excluded. The odds ratio analysis of 139,072 NSAID reports revealed that ketoprofen was associated with decreased reports of depression by a factor of 2.32 (OR 0.43 and 95% Confidence Interval [0.31, 0.59]) and decreased reports of anxiety by a factor of 2.86 (OR 0.35 [0.22, 0.56]), diclofenac with decreased depression reports by a factor of 2.22 (OR 0.45 [0.40, 0.49]) and anxiety by a factor of 2.13 (OR 0.47 [0.41, 0.54]), while naproxen decreased depression reports by a factor of 1.92 (OR 0.52 [0.49, 0.57]) and anxiety by a factor of 1.23 (OR 0.81 [0.75, 0.88]). Other NSAIDs did not exhibit any noticeable antidepressant and/or anxiolytic effect.

Meloxicam in the management of post-operative pain: Narrative review

Oral formulations of meloxicam, a preferential cyclooxygenase-2 (COX-2) inhibitor, have long been used to treat osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, as well as various pain syndromes of skeletomuscular origin (e.g., low back pain). However, these preparations are rarely indicated for the treatment of acute pain due to a poor dissolution rate and consequently a slow onset of action. The recent introduction of an intravenous (IV) NanoCrystal Colloidal Dispersion formulation opens up the possibility of using this drug during the perioperative period. The present review summarizes the pharmacologic properties of meloxicam, including its pharmacokinetics, adverse effects, and tolerability. In addition, we critically examined a number of recently completed clinical trials that evaluated the efficacy and safety of meloxicam IV in the treatment of post-operative pain. Literature retrieval was performed through PubMed and Medline (through March 2018) using combinations of the terms meloxicam, acute pain, and pharmacology. In addition, bibliographical information, including contributory unpublished data, was requested from the company developing the drug. Clinical trials suggest that single IV doses of 30 mg meloxicam significantly reduce post-operative pain as well as opioid requirements. We conclude that meloxicam IV is an effective and well-tolerated analgesic agent for the management of moderate to severe post-operative pain.

Pharmacological Evaluation of Naproxen Metal Complexes on Antinociceptive, Anxiolytic, CNS Depressant, and Hypoglycemic Properties

Purpose. The present study was designed to investigate the antinociceptive, anxiolytic, CNS depressant, and hypoglycemic effects of the naproxen metal complexes. Methods. The antinociceptive activity was evaluated by acetic acid-induced writhing method and radiant heat tail-flick method while anxiolytic activity was evaluated by elevated plus maze model. The CNS depressant activity of naproxen metal complexes was assessed using phenobarbitone-induced sleeping time test and the hypoglycemic test was performed using oral glucose tolerance test. Results. Metal complexes significantly (P < 0.001) reduced the number of abdominal muscle contractions induced by 0.7% acetic acid solution in a dose dependent manner. At the dose of 25 mg/kg body weight p.o. copper, cobalt, and zinc complexes exhibited higher antinociceptive activity having 59.15%, 60.56%, and 57.75% of writhing inhibition, respectively, than the parent ligand naproxen (54.93%). In tail-flick test, at both doses of 25 and 50 mg/kg, the copper, cobalt, silver, and zinc complexes showed higher antinociceptive activity after 90 minutes than the parent drug naproxen. In elevated plus maze (EPM) model the cobalt and zinc complexes of naproxen showed significant anxiolytic effects in dose dependent manner, while the copper, cobalt, and zinc complexes showed significant CNS depressant and hypoglycemic activity. Conclusion. The present study demonstrated that copper, cobalt, and zinc complexes possess higher antinociceptive, anxiolytic, CNS depressant, and hypoglycemic properties than the parent ligand.

Central Nervous Activity upon Systemic Salicylate Application in Animals with Kanamycin-Induced Hearing Loss--A Manganese-Enhanced MRI (MEMRI) Study

This study investigated the effect of systemic salicylate on central auditory and non-auditory structures in mice. Since cochlear hair cells are known to be one major target of salicylate, cochlear effects were reduced by using kanamycin to remove or impair hair cells. Neuronal brain activity was measured using the non-invasive manganese-enhanced magnetic resonance imaging technique. For all brain structures investigated, calcium-related neuronal activity was increased following systemic application of a sodium salicylate solution: probably due to neuronal hyperactivity. In addition, it was shown that the central effect of salicylate was not limited to the auditory system. A general alteration of calcium-related activity was indicated by an increase in manganese accumulation in the preoptic area of the anterior hypothalamus, as well as in the amygdala. The present data suggest that salicylate-induced activity changes in the auditory system differ from those shown in studies of noise trauma. Since salicylate action is reversible, central pharmacological effects of salicylate compared to those of (permanent) noise-induced hearing impairment and tinnitus might induce different pathophysiologies. These should therefore, be treated as different causes with the same symptoms.

Nonsteroidal anti-inflammatory medications are cytostatic against human vestibular schwannomas

Vestibular schwannomas (VSs) are the most common tumors of the cerebellopontine angle. Significant clinical need exists for pharmacotherapies against VSs. Motivated by previous findings that immunohistochemical expression of cyclooxygenase 2 (COX-2) correlates with VS growth rate, we investigated the role of COX-2 in VSs and tested COX-2 inhibiting salicylates against VSs. COX-2 was found to be aberrantly expressed in human VS and primary human VS cells in comparison with control human nerve specimens and primary Schwann cells (SCs), respectively. Furthermore, levels of prostaglandin E2, the downstream enzymatic product of COX-2, were correlated with primary VS culture proliferation rate. Because COX-2 inhibiting salicylates such as aspirin are well tolerated and frequently clinically used, we assessed their repurposing for VS. Changes in proliferation, cell death, and cell viability were analyzed in primary VS cultures treated with aspirin, sodium salicylate, or 5-aminosalicylic acid. These drugs neither increased VS cell death nor affected healthy SCs. The cytostatic effect of aspirin in vitro was in concurrence with our previous clinical finding that patients with VS taking aspirin demonstrate reduced tumor growth. Overall, this work suggests that COX-2 is a key modulator in VS cell proliferation and survival and highlights salicylates as promising pharmacotherapies against VS.

Modifications of diflunisal and meclofenamate carboxyl groups affect their allosteric effects on GABAA receptor ligand binding

Gamma-aminobutyric acid type A receptors (GABAAR) are allosterically modulated by the nonsteroidal anti-inflammatory drugs diflunisal and fenamates. The carboxyl group of these compounds is charged at physiological pH and therefore penetration of the compounds into the brain is low. In the present study we have transformed the carboxyl group of diflunisal and meclofenamate into non-ionizable functional groups and analyzed the effects of the modifications on stimulation of [(3)H]muscimol binding and on potentiation of γ-aminobutyric acid-induced displacement of 4'-ethenyl-4-n-[2,3-(3)H]propylbicycloorthobenzoate. N-Butylamide derivative of diflunisal modulated radioligand binding with equal or higher potency than the parent compound, while diflunisalamide showed reduced allosteric effect as compared to diflunisal. Amide derivative of meclofenamate equally affected radioligand binding parameters, while both diflunisal and meclofenamate methyl esters were less active than the parent compounds. Our study clearly demonstrates that an intact carboxyl group in diflunisal and meclofenamate is not indispensable for their positive GABAAR modulation. Further derivatization of the compound might yield compounds with higher selectivity for GABAARs that could be utilized in drug development.

Meclofenamic acid blocks the gap junction communication between the retinal pigment epithelial cells

AIM

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used to manage the pain and inflammation. NSAIDs can cause serious side effects, including vision problems. However, the underlying mechanisms are still unclear. Therefore, we aimed to investigate the effect of meclofenamic acid (MFA) on retinal pigment epithelium (RPE).

MATERIALS AND METHODS

In our study, we applied image analysis and whole-cell patch clamp recording to directly measure the effect of MFA on the gap junctional coupling between RPE cells.

RESULTS

Analysis of Lucifer yellow (LY) transfer revealed that the gap junction communication existed between RPE cells. Functional experiments using the whole-cell configuration of the patch clamp technique showed that a gap junction conductance also existed between this kind of cells. Importantly, MFA largely inhibited the gap junction conductance and induced the uncoupling of RPE cells. Other NSAIDs, like aspirin and flufenamic acid (FFA), had the same effect.

CONCLUSION

The gap junction functionally existed in RPE cells, which can be blocked by MFA. These findings may explain, at least partially, the vision problems with certain clinically used NSAIDs.

Retinal toxicity associated with high dose of meclofenamic acid

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used medications because they provide effective relief of chronic pain and inflammation through inhibition of cyclooxygenase (COX). However, visual side effects also have been reported, such as temporary blindness, visual field defect, blurred vision, scotomata, and color vision changes subsequent to short- or long-term use. Our aim was to investigate the effect of a high dose of meclofenamic acid (MFA) on the retina. In our study, we applied electroretinography (ERG) and histologic examination to study functional and morphological damage of the retina in rabbits after MFA treatment. We reveal that MFA markedly decreased the amplitudes of b-wave of Rod-response and a- and b-wave of the scotopic standard combined ERG, respectively, and induced morphological destruction of the retina, especially photoreceptor cells. We conclude that a high dose of MFA causes retinal toxicity and impairs visual transduction. These findings may explain, at least partially, the vision problems of certain clinically used NSAIDs.

A randomized, controlled trial validates a peripheral supra-additive antihyperalgesic effect of a paracetamol-ketorolac combination

The combination of paracetamol with non-steroidal anti-inflammatory drugs (NSAIDs) is widely used; however, the nature and mechanism of their interaction are still debated. A double-blind, pharmacokinetic/pharmacodynamic, randomized, cross-over, placebo-controlled study was carried out in human healthy volunteers. The aim was to explore the existence of a positive interaction between paracetamol 1 g and ketorolac 20 mg administered intravenously on experimental pain models in human beings. The effects of the paracetamol-ketotolac combination were compared with similar doses of respective single analgesic and to placebo on the sunburn model (UVB-induced inflammation), cold pain tolerance and the nociceptive flexion reflex. The kinetics of the plasma concentrations of paracetamol and ketorolac were measured using 2D-liquid chromatography-mass spectrometry. Thirteen volunteers were screened, and 11 completed the study. Ketorolac significantly decreased primary hyperalgesia to heat stimuli compared with paracetamol (p < 0.014). The combination performed better than paracetamol (p < 0.001) and placebo (p < 0.042), increasing heat pain threshold by 1.5°C. The combination radically reduced primary hyperalgesia to mechanical stimulation (39%) compared with placebo (p < 0.002) and single agents (paracetamol p < 0.024 and ketorolac p < 0.032). The combination also reduced, slightly although significantly, the intensity of pain (10%) for the cold pressor test (versus placebo: p < 0.012, paracetamol: p < 0.019 and ketorolac p < 0.004). None of the treatments significantly affected the central models of pain at this dosage level. No pharmacokinetic interactions were observed. These results suggest a supra-additive pharmacodynamic interaction between paracetamol and ketorolac in an inflammatory pain model. The mechanism of this interaction could mainly rely on a peripheral contribution of paracetamol to the effect of NSAIDs.

Antinociceptive effects of NCX-701 (nitro-paracetamol) in neuropathic rats: enhancement of antinociception by co-administration with gabapentin

BACKGROUND AND PURPOSE

Neuropathic pain is characterized by a poor response to classic analgesics. In the present study, we have assessed the antinociceptive activity of NCX-701 (nitro-paracetamol) in neuropathic rats, after systemic and intrathecal (i.t.) administration. In addition, we analysed the possible benefit of the combination of NCX-701 and gabapentin, a well-known potent analgesic, in the treatment of neuropathic pain.

EXPERIMENTAL APPROACH

The antinociceptive effects of i.v. and i.t. NCX-701 and paracetamol were studied in spinal cord neuronal responses from neuropathic adult male Wistar rats, using the recording of single motor units technique. The effect of i.v. and i.t. NCX-701 in combination with i.v. gabapentin was studied by isobolographic analysis.

KEY RESULTS

The experiments showed that NCX-701, but not paracetamol, dose-dependently reduced the nociceptive responses evoked by noxious mechanical and electrical stimulation, after i.v. (ID(50) 542 +/- 5 micromol kg(-1) for noxious mechanical stimulation) or i.t. (ID(50) 932 +/- 16 nmol kg(-1)) administration. The combined administration of i.v. or i.t. NCX-701 and i.v. gabapentin induced a more intense antinociceptive effect than any of the two drugs given alone. The isobolographic analysis showed a synergistic effect.

CONCLUSIONS AND IMPLICATIONS

NCX-701 is an effective antinociceptive compound in situations of neuropathy-induced sensitization, with an action mainly located in the spinal cord. The combination of NCX-701 and gabapentin induces a synergistic enhancement of the depression of nociceptive responses evoked by natural noxious stimulation. The use of NCX-701 alone or in combination with gabapentin might open up new and promising perspectives in the treatment of neuropathic pain.

Evidence for neuroprotection by the fenamate NSAID, mefenamic acid

Fenamate NSAIDs are inhibitors of cyclooxygenases, antagonists of non-selective cation channels, subtype-selective modulators of GABA(A) receptors, weak inhibitors of glutamate receptors and activators of some potassium channels. These pharmacological actions are all implicated in the pathogenesis of ischemic stroke. The aim of this study was to investigate the hypothesis that the fenamate, mefenamic acid, is neuroprotective in an in vitro and in vivo model of stroke. Embryonic rat hippocampal neurons were cultured and maintained for up to 14 days in vitro. At 9 or 14 days, cells were exposed to glutamate (5microM) or glutamate (5microM) plus mefenamic acid (10-100microM) or the control agent, MK-801 (10microM) for 10min. 24h later, cell death was determined by measuring lactate dehydrogenase (LDH) levels in the culture media. In vivo, male Wistar rats (300-350g) were subjected to 2h middle cerebral artery occlusion (MCAO) followed by 24h reperfusion. Animals received either a single i.v. dose of MFA (10mg/kg or 30mg/kg), or MK-801 (2mg/kg) or saline prior to MCAO or, four equal doses of MFA (20mg/kg) at 1h intervals beginning 1h prior to MCAO. Ischemic damage was then assessed 24h after MCAO. In vitro, mefenamic acid (10-100microM) and MK-801 (10microM) significantly reduced glutamate-evoked cell death compared with control cultures. In vivo, MFA (20mg/kgx4) significantly reduced infarct volume, total ischemic brain damage and edema by 53% (p< or =0.02), 41% (p< or =0.002) and 45% (p< or =0.002) respectively. Furthermore, mefenamic acid reduced cerebral edema when measured as a function of brain water content. MK-801 was also neuroprotective against MCAO brain injury. This study demonstrates a significant neuroprotective effect by a fenamate NSAID against glutamate-induced cell toxicity, in vitro and against ischemic stroke in vivo. Further experiments are currently addressing the mechanism(s) of this neuroprotection.

Challenges for blood-brain barrier (BBB) screening

Whilst blood-brain barrier permeability is an important determinant in achieving efficacious central nervous system drug concentrations, it should not be viewed or measured in isolation. Recent studies have highlighted the need for an integrated approach where optimal central nervous system penetration is achieved through the correct balance of permeability, a low potential for active efflux, and the appropriate physicochemical properties that allow for drug partitioning and distribution into brain tissue. Integrating data from permeability studies performed incorporating an assessment of active efflux by P-glycoprotein in combination with drug-free fraction measurements in blood and brain has furthered the understanding of the impact of the blood-brain barrier on central nervous system uptake and the underlying physicochemical properties that contribute to central nervous system drug disposition. This approach moves away from screening and ranking compounds in assays designed to measure or predict central nervous system penetration in the somewhat arbitrary units of brain-blood (or plasma) ratios.

Characterization of the interaction between fenamates and hippocampal neuron GABA(A) receptors

Fenamate NSAIDs have several central effects, including anti-epileptic and neuroprotective actions. The underlying mechanism(s) of these actions are not presently understood. In this study, the effects of five members of the fenamate NSAID group were investigated on native ligand-gated ion channels expressed in cultured rat hippocampal neurons. All fenamates tested (1-100 microM) dose-dependently potentiated GABA-evoked currents; mefenamic acid (MFA) was the most potent and efficacious and was found to shift the GABA dose-response curve to the left without effect on the maximum amplitude or the GABA Hill Slope. The modulation of GABA receptors by MFA was not reduced in the presence of the benzodiazepine antagonist, flumazenil (10 microM) and was moderately voltage-dependent. MFA at concentrations >or=10 microM evoked dose-dependent currents in the absence of GABA. These currents were potentiated by diazepam (1 microM) and blocked by bicuculline (10 microM). The MFA (50 microM) current-voltage relationship and reversal potential were similar to that evoked by GABA. MFA (1-100 microM) had no effects on sub-maximal glycine, glutamate or NMDA evoked currents. These data show that fenamate NSAIDs are a highly effective class of GABA(A) receptor modulator and activators.

Preoperative administration of intravenous flurbiprofen axetil reduces postoperative pain for spinal fusion surgery

PURPOSE

The aim of the study was to investigate postoperative analgesia and the opioid-sparing effect of the preoperative administration of intravenous flurbiprofen axetil in patients undergoing spinal fusion surgery.

METHODS

Thirty-six patients were randomly allocated into one of three groups. Group A received preoperative flurbiprofen axetil, 1 mg x kg(-1). Group B received postoperative flurbiprofen axetil, 1 mg x kg(-1). Group C received a placebo. All groups were given a standardized anesthesia and intravenous morphine via a patient-controlled analgesia device for postoperative analgesia. The pain score was evaluated by a visual analog scale (VAS) at 0 (T(0)), 1 (T(1)), 2 (T(2)), 6 (T(3)), 12 (T(4)), and 24 (T(5)) h after surgery, and the morphine requirement was recorded during the study period.

RESULTS

VAS in group A was significantly lower than that in group B at T(0) and T(1). VAS in group A was significantly lower than that in group C throughout the time course after surgery. Postoperative morphine consumption in group A was significantly lower than that in groups B and C at T(0) to T(3).

CONCLUSION

As compared with postoperative administration, preoperative administration of intravenous flurbiprofen axetil provides better postoperative analgesia and an opioid-sparing effect in patients undergoing spinal fusion surgery under general anesthesia.

Brain uptake of nonsteroidal anti-inflammatory drugs: ibuprofen, flurbiprofen, and indomethacin

PURPOSE

To determine the roles of blood-brain barrier (BBB) transport and plasma protein binding in brain uptake of nonsteroidal anti-inflammatory drugs (NSAIDs)-ibuprofen, flurbiprofen, and indomethacin.

METHODS

Brain uptake was measured using in situ rat brain perfusion technique.

RESULTS

[14C]Ibuprofen, [3H]flurbiprofen, and [14C]indomethacin were rapidly taken up into the brain in the absence of plasma protein with BBB permeability-surface area products (PS(u)) to free drug of (2.63 +/- 0.11) x 10(-2), (1.60 +/- 0.08) x 10(-2), and (0.64 +/- 0.05) x 10(-2) mL s(-1) g(-1) (n = 9-11), respectively. BBB [14C]ibuprofen uptake was inhibited by unlabeled ibuprofen (Km = 0.85 +/- 0.02 mM, Vmax = 13.5 +/- 0.4 nmol s(-1) g(-1)) and indomethacin, but not by pyruvate, probenecid, digoxin, or valproate. No evidence was found for saturable BBB uptake of [3H]flurbiprofen or [14C]indomethacin. Initial brain uptake for all three NSAIDs was reduced by the addition of albumin to the perfusion buffer. The magnitude of the brain uptake reduction correlated with the NSAID free fraction in the perfusate.

CONCLUSIONS

Free ibuprofen, flurbiprofen, and indomethacin rapidly cross the BBB, with ibuprofen exhibiting a saturable component of transport. Plasma protein binding limits brain NSAID uptake by reducing the free fraction of NSAID in the circulation.

Synergism between paracetamol and nonsteroidal anti-inflammatory drugs in experimental acute pain

The antinociception induced by the intraperitoneal coadministration of combinations of paracetamol with the nonsteroidal anti-inflammatory drugs (NSAIDs) diclofenac, ibuprofen, ketoprofen, meloxicam, metamizol, naproxen, nimesulide, parecoxib and piroxicam was studied by isobolographic analysis in the acetic acid abdominal constriction test of mice (writhing test). The effective dose that produced 50% antinociception (ED50) was calculated from the log dose-response curves of fixed ratio combinations of paracetamol with each NSAID. By isobolographic analysis, this ED50 was compared to the theoretical additive ED50 calculated from the ED(50) of paracetamol and of each NSAID alone obtained from ED50 dose-response curves. As shown by isobolographic analysis, all the combinations were synergistic, the experimental ED50s being significantly smaller than the theoretically calculated ED50s. The results of this study demonstrate potent interactions between paracetamol and NSAIDs and validate the clinical use of combinations of these drugs in the treatment of pain conditions.

COX-dependent mechanisms involved in the antinociceptive action of NSAIDs at central and peripheral sites

Despite the diverse chemical structure of aspirin-like drugs, the antinociceptive effect of NSAIDs is mainly due to their common property of inhibiting cyclooxygenases involved in the formation of prostaglandins. Prostaglandins are potent hyperalgesic mediators which modulate multiple sites along the nociceptive pathway and enhance both transduction (peripheral sensitizing effect) and transmission (central sensitizing effect) of nociceptive information. Inhibition of the formation of prostaglandins at peripheral and central sites by NSAIDs thus leads to the normalisation of the increased pain threshold associated with inflammation. The contribution of peripheral and central mechanisms to the overall antinociceptive action of NSAIDs depends on several factors including the location of the targets of drug action, the site of drug delivery and the uptake and distribution to the site of action. The present work reviews the data on the regulation and location of cyclooxygenases at central and peripheral sites of the nociceptive pathway and focuses on the role of COX in the generation and maintenance of pain hypersensitivity. Experimental and clinical evidences are used to evaluate the significance of the peripheral and central antihyperalgesic effects of NSAIDs.

Sodium salicylate reduces gamma aminobutyric acid-induced current in rat spinal dorsal horn neurons

Sodium salicylate is one of the nonsteroidal antiinflammatory drugs and is clinically used for antiinflammation and chronic pain relief. In the present study, we investigated the actions of sodium salicylate on gamma-aminobutyric acid type A receptor (GABA(A)) current in cultured rat spinal dorsal horn neurons. Sodium salicylate was found to reduce GABA(A) current in a reversible and concentration-dependent manner, but did not change its ion selectivity. Sodium salicylate was effective only when GABA and sodium salicylate were applied together. Application of sodium salicylate immediately before, but not during, the application of GABA did not result in a significant reduction of GABA(A) current. Our results demonstrate that sodium salicylate reversibly attenuates the GABA(A) response of dorsal horn neurons, suggesting that GABA(A) receptors in the region are pharmacological targets of sodium salicylate.

Acute treatment with the PPARγ agonist pioglitazone and ibuprofen reduces glial inflammation and Aβ1–42 levels in APPV717I transgenic mice

Neuritic plaques in the brain of Alzheimer's disease patients are characterized by beta-amyloid deposits associated with a glia-mediated inflammatory response. Non-steroidal anti-inflammatory drug (NSAID) therapy reduces Alzheimer's disease risk and ameliorates microglial reactivity in Alzheimer's disease brains; however, the molecular mechanisms subserving this effect are not yet clear. Since several NSAIDs bind to and activate the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) which acts to inhibit the expression of proinflammatory genes, this receptor appears a good candidate to mediate the observed anti-inflammatory effects. Recent data in vitro suggested that NSAIDs negatively regulate microglial activation and immunostimulated amyloid precursor protein processing via PPARgamma activation. We report that an acute 7 day oral treatment of 10-month-old APPV717I mice with the PPARgamma agonist pioglitazone or the NSAID ibuprofen resulted in a reduction in the number of activated microglia and reactive astrocytes in the hippocampus and cortex. Drug treatment reduced the expression of the proinflammatory enzymes cyclooxygenase 2 (COX2) and inducible nitric oxide synthase (iNOS). In parallel to the suppression of inflammatory markers, pioglitazone and ibuprofen treatment decreased beta-secretase-1 (BACE1) mRNA and protein levels. Importantly, we observed a significant reduction of the total area and staining intensity of Abeta1-42-positive amyloid deposits in the hippocampus and cortex. Additionally, animals treated with pioglitazone revealed a 27% reduction in the levels of soluble Abeta1-42 peptide. These findings demonstrate that anti-inflammatory drugs can act rapidly to inhibit inflammatory responses in the brain and negatively modulate amyloidogenesis.

Compounds exhibiting selective efficacy for different beta subunits of human recombinant gamma-aminobutyric acid A receptors

Inhibitory GABA(A) receptor modulators are widely used therapeutic agents for a variety of central nervous system disorders. Ltk(-) cells stably expressing human recombinant GABA(A) subunits (alpha1beta1-3gamma2s) were seeded into 96-well plates, loaded with chlorocoumarin-2-dimyristoyl phosphatidylethanolamine and bis(1,3-diethyl-2-thiobarbiturate)trimethineoxonol, and rapid fluorescence resonance energy transfer technique (FRET) measurements were made of GABA-evoked depolarizations in low-Cl(-) buffer using a voltage/ion probe reader. The influence of different betasubunits on the ability of agents to modulate and directly activate the ion channel was examined. GABA evoked concentration-dependent decreases in FRET, increasing fluorescence emission ratio (460/580 nm) at alpha1beta1gamma2, alpha1beta2gamma2, and alpha1beta3gamma2 receptors with similar maximal amplitude (P > 0.05, n = 17) and EC(50) values of 2.4 +/- 0.2, 2.5 +/- 0.2, and 1.3 +/- 0.1 microM, respectively. Piperidine-4-sulfonic acid and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol were less potent, with EC(50) values of 8.7 +/- 0.9, 9.2 +/- 0.5, and 11.7 +/- 1.2, and 43.7 +/- 6.4, 24.8 +/- 1.6, and 26.1 +/- 2.4 microM, respectively. Potency and maximal efficacy of propofol, methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, pentobarbital, and steroids, 5alpha-pregnan-3alpha-ol-20-one and 5beta-pregnan-3alpha-ol-20-one, were unaffected by the beta isoform present in the receptor complex. However, several compounds displayed beta2/3 subunit selectivity, notably loreclezole, R(-)-etomidate, and a group of anti-inflammatory agents including mefenamic acid, flufenamic acid, meclofenamic acid, tolfenamic acid, niflumic acid, and diflunisal. The anti-inflammatories exhibited varying levels of efficacy at beta2/3 subunits, with micromolar potency, while having antagonist or weak inverse agonist profiles at alpha1beta1gamma2. Diflunisal was the most efficacious compound, eliciting greater potentiation than loreclezole (90 +/- 14% and 109 +/- 14% at beta3 and beta2, respectively, compared with 62 +/- 6% and 56 +/- 3%), whereas niflumic acid exhibited the lowest efficacy. An additional agent, olsalazine, weakly potentiated responses at all three receptors without any selectivity. This study identifies and characterizes a variety of allosteric modulators for which betasubunits are an important determinant of efficacy and potency.

The effects of sham and full spinalization on the antinociceptive effects of NCX-701 (nitroparacetamol) in monoarthritic rats

Nitric oxide (NO)-releasing NSAIDs have been shown to be safer and more potent as antinociceptive and anti-inflammatory agents than their parent compounds. NCX-701 (nitroparacetamol), in contrast to paracetamol, is an effective antinociceptive drug in normal animals but their effectiveness in monoarthritis has not been compared. We have now investigated this question by comparing the antinociceptive effects of i.v. NCX-701 and paracetamol in monoarthritic rats under alpha-chloralose anesthesia. The influence of spinalization on the effects of NCX-701 was also studied. NCX-701 and paracetamol were equipotent in reducing single motor unit responses to noxious mechanical stimulation, ID50s of 320+/-1.2 and 305+/-1.2 micromol/kg, respectively. The mechanism of action seems to be different since NCX-701, but not paracetamol, reduced wind-up. This effect suggests a central action, probably within the spinal cord. Sham spinalization reduced the effect of NCX-701 on nociceptive responses drastically. In spinalized animals, however, the effect was similar to that observed in intact animals, indicating a strong effect of NCX-701 at spinal sites, which counterbalances the decrease in the activity induced by the surgery. We conclude that NCX-701 is an effective antinociceptive drug in arthritic animals, with a mechanism of action located in the spinal cord, and different to that of paracetamol.

Receptor subtype-dependent positive and negative modulation of GABA(A) receptor function by niflumic acid, a nonsteroidal anti-inflammatory drug

In addition to blocking cyclooxygenases, members of the fenamate group of nonsteroidal anti-inflammatory drugs have been proposed to affect brain GABAA receptors. Using quantitative autoradiography with GABAA receptor-associated ionophore ligand [35S]t-butylbicyclophosphorothionate (TBPS) on rat brain sections, one of the fenamates, niflumate, at micromolar concentration was found to potentiate GABA actions in most brain areas, whereas being in the cerebellar granule cell layer an efficient antagonist similar to furosemide. With recombinant GABAA receptors expressed in Xenopus laevis oocytes, we found that niflumate potentiated 3 microM GABA responses up to 160% and shifted the GABA concentration-response curve to the left in alpha1beta2gamma2 receptors, the predominant GABAA receptor subtype in the brain. This effect needed the gamma2 subunit, because on alpha1beta2 receptors, niflumate exhibited solely an antagonistic effect at high concentrations. The potentiation was not abolished by the specific benzodiazepine site antagonist flumazenil. Niflumate acted as a potent antagonist of alpha6beta2 receptors (with or without gamma2 subunit) and of alphaXbeta2gamma2 receptors containing a chimeric alpha1 to alpha6 subunit, which suggests that niflumate antagonism is dependent on the same transmembrane domain 1- and 2-including fragment of the alpha6 subunit as furosemide antagonism. This antagonism was noncompetitive because the maximal GABA response, but not the potency, was reduced by niflumate. These data show receptor subtype-dependent positive and negative modulatory actions of niflumate on GABAA receptors at clinically relevant concentrations, and they suggest the existence of a novel positive modulatory site on alpha1beta2gamma2 receptors that is dependent on the gamma2 subunit but not associated with the benzodiazepine binding site.

Nitric oxide releasing acetaminophen (nitroacetaminophen)

The nitric oxide releasing derivative of acetaminophen (nitroacetaminophen) exhibits potent anti-inflammatory and anti-nociceptive activity in a variety of animal models. On a mol for mol basis nitroacetaminophen is some 3-20 times more potent than acetaminophen. Nitroacetaminophen exhibits little or no hepatotoxicity following administration in rat or mouse and indeed protects against the hepatotoxic activity of acetaminophen. Nitroacetaminophen does not affect blood pressure or heart rate of anaesthetised rats but has similar potency to acetaminophen as an anti-pyretic agent. The enhanced anti-inflammatory and anti-nociceptive activity of nitroacetaminophen and the reduced hepatotoxicity in these animal models is likely to be secondary to the slow release of nitric oxide from the molecule. As yet the precise molecular mechanism(s) underlying these actions of nitroacetaminophen are not clear. Evidence for inhibition of cytokine-directed formation of pro-inflammatory molecule production (e.g. COX-2, iNOS) by an effect on the NF-kappaB transduction system and/or nitrosylation (and thence inhibition) of caspase enzyme activity has been reported. Data described in this review indicate that the profile of pharmacological activity of nitroacetaminophen and acetaminophen are markedly different. The possibility that nitroacetaminophen could be an attractive alternative to acetaminophen in the clinic is discussed.

Epidural injections of indomethacin for postlaminectomy syndrome: a preliminary report

Since there have been side effects reported with the administration of corticosteroids epidurally, their application has been limited. Because some nonsteroidal antiinflammatory drugs have central and spinal antinociceptive actions, we have compared the effects of indomethacin (INM) given by the epidural route to methylprednisolone (MTP). This was a prospective, comparative study in an ambulatory pain care center. Two hundred six patients with recurrent low back pain (Visual Analog Scale >7) and radiculopathy after they had had 2 or more lumbar laminectomies with the diagnosis of "postlaminectomy syndrome" were randomly assigned to 1 of 3 groups. Group I (64 patients) was given 2 epidural injections of lyophilized INM 1 mg. Group II (60 patients) received 2 injections of 2 mg of INM at the same intervals. Group III (82 patients) was treated by 2 epidural injections of MTP 80 mg. In every case, the medication was diluted in 3 mL of 0.5% bupivacaine. Reductions of pain were assessed by changes in the Visual Analog Scale; physical activities, attitude, and medication intake were graded by the Pain Progress Score recorded before each treatment and 2 wk after the last. After each injection, all patients had pain relief to Visual Analog Scale <3. Increased analgesia (P < 0.05) was noted when a double dose of INM was used (Group II) or when 80 mg of MTP was given. The total average scores of the Pain Progress Score showed significant differences at the second injection in Groups II and III only. Physical activity, emotional attitudes, and medication intake were also improved but the changes were not statistically significant. In conclusion, in this group of patients, INM produced adequate analgesia in Groups I and II, with evidence suggesting that 2 mg of INM may produce a similar degree of pain relief as 80 mg of MTP after the second injection. Other nonsteroidal antiinflammatory drugs may be explored in the future for the same purpose.

NCX-701 (nitroparacetamol) is an effective antinociceptive agent in rat withdrawal reflexes and wind-up

1. Non-steroidal anti-inflammatory drugs (NSAIDs) are effective anti-inflammatory and analgesic drugs although they also induce unwanted side effects due to the inhibition of the physiological effects regulated by prostaglandins. This has led to the search for new compounds with fewer side effects, such as the nitro-NSAIDs (NO-NSAIDs). Paracetamol is an analgesic drug devoid of some of the side effect of the NSAIDs but without anti-inflammatory activity. NCX-701 is a nitric oxide releasing version of paracetamol with anti-inflammatory and analgesic properties. 2. We have tested, in the single motor unit technique, the antinociceptive actions of intravenous cumulative doses of NCX-701 vs paracetamol, studying their antinociceptive effects in responses to noxious mechanical and electrical stimulation (wind-up). 3. Paracetamol did not induce any significant effect at the doses tested (maximum of 480 micromol kg(-1), 72.5 mg kg(-1)). NCX-701 however was very effective in reducing responses to noxious mechanical stimulation (32+/-10% of control response) and wind-up (ED(50) of 147+/-1 micromol kg(-1), 41.5+/-0.3 mg kg(-1)). The inhibition was not reversed by 1 mg kg(-1) of the opioid antagonist naloxone. In control experiments performed with either the vehicle or the NO donor NOC-18, no significant changes were observed in the nociceptive responses studied. 4. We conclude that NCX-701 is a very effective non-opioid antinociceptive agent in normal animals and its action is located mainly at central areas. The antinociceptive effect was not due solely to the release of NO.

Influence of a polymeric formulation of ketoprofen on its diffusion into cerebrospinal fluid in rats

Poly(D,L)lactide nanocapsules (NCs) have been proposed as an alternative carrier for many drugs. We investigated the influence of this formulation on the pharmacokinetics of ketoprofen in the plasma and cerebrospinal fluid (CSF). Male Wistar rats were given intraperitoneal dose of ketoprofen (5 mg/kg) in a suspension of NCs or in a carboxymethylcellulose (CMC) solution (reference preparation). Blood and CSF samples were collected at different times up to 24 h after dosing. The unbound fraction of ketoprofen in plasma (f(u)) was determined using ultrafiltration. The total (C(T)) and free (C(F)) concentrations of ketoprofen in plasma and the simultaneous CSF concentrations (C(CSF)) were measured by a HPLC method and the areas under the curve (AUC(T), AUC(F), AUC(CSF)) were calculated. AUC(T) of ketoprofen-loaded NCs in plasma was similar to that of the reference solution, while AUC(F) of the former (5.41 mg/l x h) was higher than that produced by the latter (4.03 mg/l x h). Accordingly, the unbound fraction (f(u)) was higher after administration of NCs than that of the solution (2.5 and 1.8%, respectively). Finally, AUC(CSF) were identical for both formulations. These findings suggest that the binding of ketoprofen to plasma proteins is not the major factor that governs its blood-to-CSF exchanges.

Prostaglandins and cyclooxygenases [correction of cycloxygenases] in the spinal cord

The spinal cord is one of the sites where non-steroidal anti-inflammatory drugs (NSAIDs) act to produce analgesia and antinociception. Expression of cyclooxygenase(COX)-1 and COX-2 in the spinal cord and primary afferents suggests that NSAIDs act here by inhibiting the synthesis of prostaglandins (PGs). Basal release of PGD(2), PGE(2), PGF(2alpha) and PGI(2) occurs in the spinal cord and dorsal root ganglia. Prostaglandins then bind to G-protein-coupled receptors located in intrinsic spinal neurons (receptor types DP and EP2) and primary afferent neurons (EP1, EP3, EP4 and IP). Acute and chronic peripheral inflammation, interleukins and spinal cord injury increase the expression of COX-2 and release of PGE(2) and PGI(2). By activating the cAMP and protein kinase A pathway, PGs enhance tetrodotoxin-resistant sodium currents, inhibit voltage-dependent potassium currents and increase voltage-dependent calcium inflow in nociceptive afferents. This decreases firing threshold, increases firing rate and induces release of excitatory amino acids, substance P, calcitonin gene-related peptide (CGRP) and nitric oxide. Conversely, glutamate, substance P and CGRP increase PG release. Prostaglandins also facilitate membrane currents and release of substance P and CGRP induced by low pH, bradykinin and capsaicin. All this should enhance elicitation and synaptic transfer of pain signals in the spinal cord. Direct administration of PGs to the spinal cord causes hyperalgesia and allodynia, and some studies have shown an association between induction of COX-2, increased PG release and enhanced nociception. NSAIDs diminish both basal and enhanced PG release in the spinal cord. Correspondingly, spinal application of NSAIDs generally diminishes neuronal and behavioral responses to acute nociceptive stimulation, and always attenuates behavioral responses to persistent nociception. Spinal application of specific COX-2 inhibitors sometimes diminishes behavioral responses to persistent nociception.

In vivo indomethacin treatment causes microglial activation in adult mice

The current study was undertaken to study the role of prostaglandins in regulating microglial activation. Mice were treated with indomethacin (2 microg/ml) in their drinking water to selectively inhibit cyclooxygenase activity. After 4-8 days, the effect of inhibiting prostaglandin synthesis on microglial activity was evaluated. This was accomplished by analyzing microglial expression of Mac-1 (C3 complement receptor) as an indicator of activation. Mac-1 expression was assessed by immunohistochemistry of fixed brain cryosections, and by flow cytometric analysis of immunostained single cell suspensions. Both methods demonstrated that compared to age-matched, untreated controls, brains of indomethacin-treated mice had increased levels of Mac-1 expression, suggesting an increase in the state of microglial activation. These results demonstrate the importance of prostaglandins in down regulating microglial activity, and that inhibition of prostaglandin synthesis with indomethacin may act to increase the reactivity of the brain's immune system.

Subunit-selective modulation of GABAA receptors by the non-steroidal anti-inflammatory agent, mefenamic acid

Mefenamic acid (MFA) has anti-convulsant and pro-convulsant effects in vivo, and has been shown to potentiate and inhibit GABAA (gamma-aminobutyric acid) receptors in vitro. In this study, whole-cell currents were recorded from Xenopus oocytes and human embryonic kidney (HEK) cells expressing human recombinant GABAA receptors to resolve the molecular mechanisms by which MFA modulates GABAA receptor function. We demonstrate that MFA potentiated GABA-activated currents for alpha1beta2 gamma2S (EC50 = 3.2 +/- 0.5 microM), but not for alpha1beta1 gamma2S receptors. MFA also enhanced GABA-activated responses and directly activated alpha1beta2/beta3 GABAA receptors, but inhibited responses to GABA on alpha1beta1 constructs (IC50 = 40 +/- 7.2 microM). A comparison of beta1, beta2 and beta3 subunits suggested that the positive modulatory action of MFA involved asparagine (N) 290 in the second transmembrane domain (TM2) of the beta2 and beta3 subunits. Mutation of N290 to serine (S) markedly reduced modulation by MFA in alpha1beta2(N290S)gamma2S receptors, whereas alpha1beta1(S290N)gamma2S constructs revealed potentiated responses to GABA (EC50 = 7.8 +/- 1.7 microM) and direct activation by MFA. The potentiation by MFA displayed voltage sensitivity. The direct activation, potentiation and inhibitory aspects of MFA action were predominantly conferred by the beta subunits as the spontaneously active homomeric beta1 and beta3 receptors were susceptible to modulation by MFA. Molecular comparisons of MFA, loreclezole and etomidate, agents which exhibit similar selectivity for GABAA receptors, revealed their ability to adopt similar structural conformations. This study indicates that N290 in TM2 of beta2 and beta3 subunits is important for the regulation of GABAA receptor function by MFA. Our data provide a potential molecular mechanism for the complex central effects of MFA in vivo.

Passage of S-(+)- and R-(-)-ketoprofen across the human isolated perfused placenta

Ketoprofen is a chiral non-steroidal anti-inflammatory drug (NSAID) available as a racemic (rac) mixture of S-(+)- and R-(-)-isomers. Its inhibitory effect on prostaglandin biosynthesis resides virtually in the S-form. Interestingly, R-ketoprofen does not undergo substantial metabolic inversion in humans. Though contraindicated during the last trimester of pregnancy, NSAIDs, including ketoprofen, are used as tocolytic agents in some cases. The S/R plasma concentration ratio was reported to average 2.3 in premature neonates whose mothers were given rac-ketoprofen and to be close to 1 in the maternal plasma. Thus, we investigated the placental transfer of rac-ketoprofen in vitro using Schneider's perfused human cotyledon model. Glucosed Earle solutions with and without human serum albumin (HSA) were used. Several maternal perfusates were tested with different rac-ketoprofen concentrations together with 20 mg L-1 of antipyrine as a reference substance. Ketoprofen enantiomers were assayed by a specific HPLC method with derivatization procedure. HSA concentrations in maternal perfusate influenced the placental transfer of ketoprofen enantiomers. In the absence of HSA in the maternal perfusate, the S-(+)/R-(-) concentration ratio was close to 1 in the fetal perfusate. By contrast, this ratio averaged 1.44 after addition of HSA 10 g L-1 on the maternal side. Similar results were found for dialysis experiments using an inert Spectrapor 2 membrane suggesting that the S-(+)-free concentration is superior to the R-(-)-free concentration in the presence of HSA. Direct measurements of the free concentrations by centrifugal ultrafiltration confirmed this hypothesis. Accordingly, the data observed in vivo may result, at least in part, from the stereoselective protein binding of ketoprofen.

Influence of lipophilicity on the diffusion of cephalosporins into the cerebrospinal fluid

The aim of this quantitative structure-activity relationship (QSAR) study was to investigate the influence of lipophilicity on the diffusion of cephalosporins into the cerebrospinal fluid (CSF). The lipophilicity was expressed as the chromatographic capacity factor (log k'w) determined by high-performance liquid chromatography in a reversed-phase system. The penetration of eight cephalosporins into CSF was studied in male Wistar rats receiving the drugs intramuscularly (1.5 mg/kg). One hour after administration, CSF and blood samples were collected, and concentrations of free drug were measured in CSF (CCSF) and in plasma (CP). A significant parabolic relationship was sought between lipophilicity (log k'w) and the capacity of diffusion across the blood-brain barrier expressed as log (CCSF/CP). The cephalosporins exhibiting a moderate lipophilicity diffused well into CSF. A pharmacokinetic study was performed at 1, 2 and 4 h after administration of three cephalosporins: cefazolin, ceftriaxone and cefsulodin. These compounds were choosen according to their lipophilicities (low, moderate and high values, respectively). The AUC0-4h for both free plasma (AUCP) and cerebrospinal fluid (AUCCSF) concentrations were determined. The AUCCSF/AUCP ratio presented a maximum value for a strongly albumin bound cephalosporin, ceftriaxone. In our experimental conditions, the ideal lipophilicity (log k'w) range for diffusion of cephalosporins from plasma into CSF was between 1.6 and 1.8.

Central analgesic effects of aspirin-like drugs

Aspirin-like drugs mainly include paracetamol, salicylates and other non-steroidal anti-inflammatory drugs, and metamizole. Their analgesic effect is classically ascribed to a peripheral site of action, within the pain-processing site. There is, however, convincing evidence that a central component contributes to the overall analgesia provided by these agents. Experimental and clinical studies referring to this challenging proposal are reviewed here. The exact site and mode of action of aspirin-like drugs within the central nervous system remains controversial. It is likely that supraspinal mechanisms play an important role. Some experiments lend support to the involvement of monoaminergic control systems. Other data indicate that these drugs act centrally through the inhibition of cyclo-oxygenase activity. The interactions between prostaglandins and various neurotransmitters suggest that both mechanisms may be linked.

The spinal actions of nonsteroidal anti-inflammatory drugs and the dissociation between their anti-inflammatory and analgesic effects

The traditional classification of nonsteroidal anti-inflammatory drugs (NSAIDs) as exclusively 'peripherally acting' agents is no longer valid. For many of these agents there is a growing body of evidence in favour of an additional central mechanism for their anti-inflammatory and analgesic effects. This view is further supported by the recent discovery that a substantial component of the hyperalgesia and allodynia that characterise postinjury hypersensitivity occurs in the CNS, notably the spinal dorsal horn. An important corollary is that inhibition of central nociceptive processing may represent an important analgesic mode of action for those NSAIDs that are effective in the management of pain after tissue injury. Historically, attempts to group this heterogeneous class of compounds into a single entity are largely derived from the observation that the majority of clinically useful NSAIDs are weak organic acids (pKa 3 to 5), bind extensively to plasma albumin (= 99%), and inhibit (to varying degrees) prostaglandin synthesis. However, the significance of these various unifying features is becoming increasingly obscure. While inhibition of prostaglandin synthesis apparently remains an important analgesic mode of action for NSAIDs both in the periphery and the CNS, other mechanisms should be considered. Some NSAIDs, in addition to their effects on prostaglandin synthesis, also affect the synthesis and activity of other neuroactive substances believed to have key roles in processing nociceptive input within the dorsal horn. It has been argued that these other actions, in conjunction with inhibition of prostaglandin synthesis, may synergistically augment the effects of NSAIDs on spinal nociceptive processing. Despite much effort, it remains a formidable task to assess the significance of these differential mechanisms upon clinical pain states. In the meantime, however, it may be possible, on the basis of in vivo studies, to evaluate the impact of putative spinal analgesic mechanisms that are unrelated to inhibition of prostaglandin synthesis. This approach has recently been extended to include the identification of pharmacokinetic and clinical correlates of these derived in vivo parameters, and in this way attempt to demonstrate clinical relevance.

Ketorolac penetration into the cerebrospinal fluid of humans

STUDY OBJECTIVE

To determine the cerebrospinal fluid (CSF): total plasma concentration ratio of ketorolac tromethamine following a single intramuscular (IM) dose.

DESIGN

Open, single-dose, IM-administration study.

SETTING

General operating theaters of a medical school hospital.

PATIENTS

29 ASA physical status I and II patients scheduled to undergo elective surgery with spinal anesthesia.

INTERVENTIONS

Patients were premedicated with ketorolac 90 mg IM formulated as 3 ml of a 3% solution. Between 1 and 4 1/2 hours later, an intravenous infusion of 500 ml of compound sodium lactate was begun. Lumbar puncture was then performed, and 2 ml of CSF was collected prior to administration of the spinal anesthetic. In addition, a 5 ml sample of venous blood was taken within 5 minutes of the CSF sample.

MEASUREMENTS AND MAIN RESULTS

Simultaneous plasma and CSF concentrations of ketorolac were measured between 62 and 277 minutes following IM administration in 29 patients undergoing spinal anesthesia. The CSF concentrations were on the order of 1,000 times less than the total plasma concentrations; free concentrations of ketorolac in plasma were estimated to be about 10 times more than those in CSF. There appeared to be no constant time factor relating the appearance of ketorolac in the CSF to its plasma concentration following IM administration.

CONCLUSION

Although the sensitivity of central prostaglandin synthetase systems to inhibition is unknown, it is unlikely from this pharmacokinetic data that there is a major central mechanism of analgesia for ketorolac.