Landscape of adenosine-to-inosine RNA recoding across human tissues

RNA editing by adenosine deaminases changes the information encoded in the mRNA from its genomic blueprint. Editing of protein-coding sequences can introduce novel, functionally distinct, protein isoforms and diversify the proteome. The functional importance of a few recoding sites has been appreciated for decades. However, systematic methods to uncover these sites perform poorly, and the full repertoire of recoding in human and other mammals is unknown. Here we present a new detection approach, and analyze 9125 GTEx RNA-seq samples, to produce a highly-accurate atlas of 1517 editing sites within the coding region and their editing levels across human tissues. Single-cell RNA-seq data shows protein recoding contributes to the variability across cell subpopulations. Most highly edited sites are evolutionary conserved in non-primate mammals, attesting for adaptation. This comprehensive set can facilitate understanding of the role of recoding in human physiology and diseases.

Gabay et al. provide a highly-accurate atlas of recoding by A-to-I RNA editing in human, profiled across tissues and cell subpopulations. Most highly edited sites are evolutionary conserved in non-primate mammals, attesting for adaptation.

Global quantification exposes abundant low-level off-target activity by base editors

Base editors are dedicated engineered deaminases that enable directed conversion of specific bases in the genome or transcriptome in a precise and efficient manner, and hold promise for correcting pathogenic mutations. A major concern limiting application of this powerful approach is the issue of off-target edits. Several recent studies have shown substantial off-target RNA activity induced by base editors and demonstrated that off-target mutations may be suppressed by improved deaminases versions or optimized guide RNAs. Here, we describe a new class of off-target events that are invisible to the established methods for detection of genomic variations and were thus far overlooked. We show that nonspecific, seemingly stochastic, off-target events affect a large number of sites throughout the genome or the transcriptome, and account for the majority of off-target activity. We develop and employ a different, complementary approach that is sensitive to the stochastic off-target activity and use it to quantify the abundant off-target RNA mutations due to current, optimized deaminase editors. We provide a computational tool to quantify global off-target activity, which can be used to optimize future base editors. Engineered base editors enable directed manipulation of the genome or transcriptome at single-base resolution. We believe that implementation of this computational approach would facilitate design of more specific base editors.

Quantifying RNA Editing in Deep Transcriptome Datasets

Massive transcriptome sequencing through the RNAseq technology has enabled quantitative transcriptome-wide investigation of co-/post-transcriptional mechanisms such as alternative splicing and RNA editing. The latter is abundant in human transcriptomes in which million adenosines are deaminated into inosines by the ADAR enzymes. RNA editing modulates the innate immune response and its deregulation has been associated with different human diseases including autoimmune and inflammatory pathologies, neurodegenerative and psychiatric disorders, and tumors. Accurate profiling of RNA editing using deep transcriptome data is still a challenge, and the results depend strongly on processing and alignment steps taken. Accurate calling of the inosinome repertoire, however, is required to reliably quantify RNA editing and, in turn, investigate its biological and functional role across multiple samples. Using real RNAseq data, we demonstrate the impact of different bioinformatics steps on RNA editing detection and describe the main metrics to quantify its level of activity.

Purifying selection of long dsRNA is the first line of defense against false activation of innate immunity

BACKGROUND

Mobile elements comprise a large fraction of metazoan genomes. Accumulation of mobile elements is bound to produce multiple putative double-stranded RNA (dsRNA) structures within the transcriptome. These endogenous dsRNA structures resemble viral RNA and may trigger false activation of the innate immune response, leading to severe damage to the host cell. Adenosine to inosine (A-to-I) RNA editing is a common post-transcriptional modification, abundant within repetitive elements of all metazoans. It was recently shown that a key function of A-to-I RNA editing by ADAR1 is to suppress the immunogenic response by endogenous dsRNAs.

RESULTS

Here, we analyze the transcriptomes of dozens of species across the Metazoa and identify a strong genomic selection against endogenous dsRNAs, resulting in their purification from the canonical transcriptome. This purifying selection is especially strong for long and nearly perfect dsRNAs. These are almost absent from mRNAs, but not pre-mRNAs, supporting the notion of selection due to cytoplasmic processes. The few long and nearly perfect structures found in human transcripts are weakly expressed and often heavily edited.

CONCLUSION

Purifying selection of long dsRNA is an important defense mechanism against false activation of innate immunity. This newly identified principle governs the integration of mobile elements into the genome, a major driving force of genome evolution. Furthermore, we find that most ADAR1 activity is not required to prevent an immune response to endogenous dsRNAs. The critical targets of ADAR1 editing are, likely, to be found mostly in non-canonical transcripts.

Genome-wide quantification of ADAR adenosine-to-inosine RNA editing activity

Adenosine-to-inosine (A-to-I) RNA editing by the adenosine deaminase that acts on RNA (ADAR) enzymes is a common RNA modification, preventing false activation of the innate immune system by endogenous double-stranded RNAs. Methods for quantification of ADAR activity are sought after, due to an increasing interest in the role of ADARs in cancer and autoimmune disorders, as well as attempts to harness the ADAR enzymes for RNA engineering. Here, we present the Alu editing index (AEI), a robust and simple-to-use computational tool devised for this purpose. We describe its properties and demonstrate its superiority to current quantification methods of ADAR activity. The AEI is used to map global editing across a large dataset of healthy human samples and identify putative regulators of ADAR, as well as previously unknown factors affecting the observed Alu editing levels. These should be taken into account in future comparative studies of ADAR activity. The AEI tool is available at https://github.com/a2iEditing/RNAEditingIndexer.

Increased RNA Editing May Provide a Source for Autoantigens in Systemic Lupus Erythematosus

RNA-editing mechanisms, which induce nucleotide substitution in the RNA, increase transcript and protein diversities. Editing dysregulation has been shown to lead to grave outcomes, and transcriptome-wide aberrant RNA editing has been found in tumors. However, little is known about the involvement of editing in other diseases. Systemic lupus erythematosus (SLE) is a multisystemic autoimmune disease characterized by a loss of tolerance for autoantigens from various tissues and the production of multiple autoantibodies. Here, we show that blood samples from individuals with SLE have abnormally high levels of RNA editing, some of which affect proteins and potentially generate novel autoantigens. We suggest that elevated RNA editing, either by ADARs or APOBECs, may be involved in the pathophysiology of SLE, as well as in other autoimmune diseases, by generating or increasing the autoantigen load, a key requisite for the progression of autoimmunity.

Anoxic depolarization of rat hippocampal slices is prevented by thiopental but not by propofol or isoflurane

BACKGROUND

There is strong evidence to suggest that anoxic depolarization (AD) is an important factor in hypoxia/ischaemia-induced neural damage. Treatments that prevent the occurrence of AD may be useful in providing neuronal protection against hypoxia. The current study was designed to determine whether general anaesthetics which have been suggested to 'induce prophylaxis' against hypoxia can attenuate the incidence of AD.

METHODS

The effects of anoxia (3 min) on evoked extracellularly recorded field potentials of CA1 neurons in rat hippocampal slices were assessed in the absence and presence of the i.v. general anaesthetics thiopental and propofol and the volatile anaesthetic isoflurane.

RESULTS

In the absence of anaesthetics, AD occurred in 81% of the preparations tested. Thiopental (2 x 10(-4) M) significantly reduced the incidence of AD (16%, P=0.0006). In comparison, propofol (2 x 10(-4) M) and isoflurane (1.5 vol%) were ineffective (69% and 60%, respectively). Furthermore, in the presence of thiopental, the population spike amplitude recovered with and without AD (90% and 94% of pre-anoxic value, respectively) following 3 min anoxia.

CONCLUSION

The prophylactic effect of thiopental against hypoxia might be induced, in part, by preventing the generation of AD.

Small-dose pentobarbital enhances synaptic transmission in rat hippocampus

We investigated the contribution of bicarbonate ion, gamma-aminobutyric acid-A (GABA(A)) receptors, and N-methyl-D-aspartate (NMDA) receptors to pentobarbital-induced enhancement of excitatory synaptic transmission in the hippocampal slice. Transverse hippocampal slices (400 microm thick) were prepared from 20- to 30-day-old Sprague-Dawley rats and maintained in an interface chamber perfused with warmed (35 degrees C) oxygenated artificial cerebrospinal fluid. Extracellular field potentials, evoked by orthodromic paired-pulse stimulation of the Schaffer collateral CA1 pathway, were analyzed for the population spike (PS) amplitude. Pentobarbital had a concentration-dependent, biphasic effect on PS amplitudes, which were increased approximately twofold (P < 0.001) when the slice was exposed to pentobarbital concentrations of 1 and 5 microM and depressed at drug concentrations larger than 10 microM. Pentobarbital (5 microM) did not increase the PS amplitude when stimulation was stopped during exposure to the drug. The enhancement of PS amplitude was suppressed in the presence of 10 microM acetazolamide, a nonselective carbonic anhydrase inhibitor, and when the slice was bathed in CO(2)/HCO(3)(-)-free artificial cerebrospinal fluid. Pretreatment with 1 microM picrotoxin, a GABA(A) receptor antagonist, or 5 microM 2-amino-5-phosphopentanoic acid, a specific NMDA receptor antagonist, also suppressed enhancement of PS amplitude by 5 microM pentobarbital. The results suggest that small concentrations of pentobarbital (1 and 5 microM) enhance synaptic transmission through mechanisms involving GABA(A) and NMDA receptors and the HCO(3)(-) ion.

IMPLICATIONS

Enhanced hippocampal synaptic transmission after exposure to subanesthetic concentrations of pentobarbital persists during drug washout. This finding may help to explain why some patients experience excitation and enhanced pain during emergence from anesthesia.

Effects of repeated hydrogen sulphide (H2S) exposure on learning and memory in the adult rat

The effects of repeated exposure (125 ppm) of hydrogen sulphide (H2S) on learning and memory in the rat were investigated. A 16-arm radial arm maze (RAM) was used to examine neurobehavioural functioning in a series of three experiments. Experiment 1 involved training animals on a complex spatial maze task, prior to a 5-week period of exposure to H2S or a control gas mixture. Rats were tested for maze retention after each 5-day exposure period. It was determined that repeated H2S exposure had no effect on memory for a previously learned spatial task. Experiment 2 was conducted to determine whether H2S interferes with the acquisition of a novel spatial task. Naïve animals received daily maze training and exposure (H2S or control) sessions over an extended 11-week period (48 sessions). The results indicated that the groups were comparable on four of five measures of maze performance. H2S animals were impaired in their ability to find all of the reinforcers prior to the end of a trial, suggesting that H2S had an effect on performance rate, but not acquisition of the maze task. Finally, Experiment 3 was conducted to determine what role proactive interference might play in H2S-related brain impairment. Animals from the preceding experiment were trained on a new reversed contingency maze task. H2S animals made more overall arm entries than controls, suggesting that H2S may impair learning by increasing the animals' susceptibility to interference from irrelevant stimuli. The prefrontal cortex was discussed as a potential target site of H2S. The pathophysiological mechanisms underlying the effect of H2S on normal brain function have yet to be identified.

[Rationale for using nabumetone and clinical experience]

Nabumetone's position as one of the most commonly used nonsteroidal anti-inflammatory drugs (NSAIDs) in the world today is based upon over a decade of clinical experience. The popularity of this drug lies in both its unique pharmacokinetic profile and special safety features in pharmacodynamic terms. This nonacidic prodrug with an active 6-methoxy-2-naphthylacetic acid (6-MNA) metabolite has COX-2 preferential features and is also devoid of enterohepatic recirculation. It is felt that these characteristics have provided the basis for its unique long term tolerability, documented in various at-risk osteoarthritis and rheumatoid arthritis populations. The excellent tolerability of nabumetone and its 24-hour half-life, which provides the advantages of a once-daily dosage regimen, make it uniquely suitable for long term anti-inflammatory therapy in arthritis. The tolerability profile of nabumetone has also demonstrated clear cost-effectiveness advantages, as confirmed by comparative and epidemiological studies. Selective COX-2 NSAIDs are likely to prove more expensive because of the increasing costs and demands of clinical research prior to FDA approval. These higher costs may limit and influence patient access, depending on the healthcare delivery system, and many years of experience will be required to document the putative tolerability advantages of these newer COX-2 inhibitor agents. In the meantime, it is comforting that nabumetone has established such an advantageous tolerability profile together with acknowledged efficacy.

Pentobarbital induces nocifensive yhyperreflexia, not hyperalgesia in rats

PURPOSE

To seek behavioural, reflexive and histochemical evidence of long-lasting changes in nociceptive stimulus transmission induced by exposure to doses of pentobarbital that induce nocifensive hyperreflexia.

METHODS

Nocifensive hyperreflexia was induced in 12 rats with 30 mg x kg(-1) pentobarbital ip. Reflex latency times for withdrawal of the hind paw from noxious radiant heat were measured with an automated electronic timer. Subjective responses to noxious stimulation (licking or biting of the stimulated hindpaw) and the level of sedation were recorded. Histological sections of lumbar spinal cord were stained for immunoreactivity of the immediate-early-gene (IEG), c-fos, in three rats that received repeated threshold noxious radiant heat stimulation during the period of nocifensive hyperreflexia induced by 30 mg x kg(-1) pentobarbital ip.

RESULTS

Reflex withdrawal latency decreased by 32 +/- 8% of control values (P < 0.001 ) following pentobarbital injection and returned to control values 120 min after drug injection. Once fully alert, pentobarbital-treated animals did not show any increase in nociceptive behaviour relative to saline-injected controls (P = 0.41). Sustained noxious stimulation to the hindpaw in halothane-anesthetized animals was associated with an increase in c-fos immunoreactivity in the dorsal horn of the lumbar spinal cord ipsilateral to the stimulation (P < 0.001). Threshold stimulation in the pentobarbital-treated animals was not associated with any increase in c-fos expression.

CONCLUSIONS

During pentobarbital-induced hyperreflexia, rats did not show any reflexive, behavioural, or histochemical evidence of long-lasting enhancement of nocifensive signal transmission. The results are consistent with previous observations that, in the absence of tissue injury, nocifensive hyperreflexia induced by barbiturates is a short-lived pharmacological effect.

The effects of n-alcohols on evoked synaptic potentials in rat hippocampal slices: Hill coefficients account for the cut-off phenomenon

The anesthetic potencies of n-alcohols increase progressively with lengthening of the carbon chain and then disappear at a cut-off point of a longer-chain n-alcohol. In order to assess the mechanisms for cut-off in mammalian central nervous system, the effects of a series of n-alcohols (C(2)-C(11)) were examined on the evoked synaptic potentials of the rat hippocampal preparation in vitro. The n-alcohols (C(2)-C(10)) reduced the slope of the excitatory post-synaptic potential in a concentration-dependent manner, and the inhibitory potencies enhanced as a function of carbon chain length. The effect disappeared at n-undecanol (C(11)). The Hill coefficients of the concentration-response curves of the n-alcohols negatively correlated with the number of carbon atoms. The decrease in the Hill coefficient could account for the cut-off phenomenon, indicating that the results can support the anesthetic pocket hypothesis.

Around-the-clock, controlled-release oxycodone therapy for osteoarthritis-related pain: placebo-controlled trial and long-term evaluation

BACKGROUND

Although opioid analgesics have well-defined efficacy and safety in treatment of chronic cancer pain, further research is needed to define their role in treatment of chronic noncancer pain.

OBJECTIVE

To evaluate the effects of controlled-release oxycodone (OxyContin tablets) treatment on pain and function and its safety vs placebo and in long-term use in patients with moderate to severe osteoarthritis pain.

METHODS

One hundred thirty-three patients experiencing persistent osteoarthritis-related pain for at least 1 month were randomized to double-blind treatment with placebo (n = 45) or 10 mg (n = 44) or 20 mg (n = 44) of controlled-release oxycodone every 12 hours for 14 days. One hundred six patients enrolled in an open-label, 6-month extension trial; treatment for an additional 12 months was optional.

RESULTS

Use of controlled-release oxycodone, 20 mg, was superior (P<.05) to placebo in reducing pain intensity and the interference of pain with mood, sleep, and enjoyment of life. During long-term treatment, the mean dose remained stable at approximately 40 mg/d after titration, and pain intensity was stable. Fifty-eight patients completed 6 months of treatment, 41 completed 12 months, and 15 completed 18 months. Common opioid side effects were reported, several of which decreased in duration as therapy continued.

CONCLUSIONS

Around-the-clock controlled-release oxycodone therapy seemed to be effective and safe for patients with chronic, moderate to severe, osteo-arthritis-related pain. Effective analgesia was accompanied by a reduction in the interference of pain with mood, sleep, and enjoyment of life. Analgesia was maintained during long-term treatment, and the daily dose remained stable after titration. Typical opioid side effects were reported during short- and long-term therapy.

The Prosorba column for treatment of refractory rheumatoid arthritis: a randomized, double-blind, sham-controlled trial

OBJECTIVE

To evaluate the efficacy and safety of the Prosorba column as a treatment for rheumatoid arthritis (RA) in patients with active and treatment-resistant (refractory) disease.

METHODS

A sham-controlled, randomized, double-blind, multicenter trial of Prosorba versus sham apheresis was performed in patients with RA who had failed to respond to treatment with methotrexate or at least 2 other second-line drugs. Patients received 12 weekly treatments with Prosorba or sham apheresis, with efficacy evaluated 7-8 weeks after treatment ended. Patients were characterized as responders if they experienced improvement according to the American College of Rheumatology (ACR) response criteria at the efficacy time point. A data safety monitoring board (DSMB) evaluated interim analyses for the possibility of early completion of the trial.

RESULTS

Patients in the trial had RA for an average of 15.5 years (range 1.7-50.6) and had failed an average of 4.2 second-line drug treatments prior to entry. After the completion of treatment of 91 randomized patients, the DSMB stopped the trial early due to successful outcomes. Of the 47 patients in the Prosorba arm, 31.9% experienced ACR-defined improvement versus 11.4% of the 44 patients in the sham-treated arm (P = 0.019 after adjustment for interim analysis). When results from 8 additional patients, who had completed blinded treatments at the time of DSMB action, were added to the analysis (n = 99), results were unchanged. The most common adverse events were a short-term flare in joint pain and swelling following treatment, a side effect that occurred in most subjects at least once in both treatment arms. Other side effects, although common, occurred equally as frequently in both treatment groups.

CONCLUSION

Apheresis with the Prosorba column is an efficacious treatment for RA in patients with active disease who have failed other treatments.

Sulfuric acid aerosol induces changes in alveolar surface tension in the guinea pig but not in the rat

The purpose of this study was to investigate the effects of an acid aerosol, at high concentration, on the surface properties of the extracellular fluid lining the airways and alveolae. Guinea pigs and rats were exposed to 43 mg/m3 and 94 mg/m3 of sulfuric acid aerosol mass median aerodynamic diameter (MMAD) 0.9 micron or water aerosol (control), respectively, for 4 hours in an exposure chamber. Surfactant material was extracted from bronchoalveolar lavage fluid (BAL) by centrifugation, and phospholipid, protein, and cell concentrations measured. The extract was reconstituted to 300 micrograms/mL of phospholipid, and its surface properties assessed with a captive bubble surfactometer. The minimum surface tension for the acid-exposed guinea pig BAL was 12.1 +/- 8.48 (mean +/- SD) mN/m, which was significantly higher than the control group, 2.0 +/- 0.43 (mean +/- SD) or the acid-exposed rats, 1.29 +/- 0.11 (mean +/- SD). The change in film area obtained by compressing the film from equilibrium surface tension (25 mN/m) to its minimum value (gamma min) was 62.9 +/- 13.83 (mean +/- SD)% for acid-exposed guinea pigs, compared to 16.3 +/- 5.77 (mean +/- SD)% for the control guinea pigs. The most sensitive index of surfactant inhibition was found to be the maximum film compressibility (Cmax) of the compression isotherm. This index was 119 times greater for the acid-exposed guinea pigs compared to control animals. These abnormalities were associated with an elevation of total protein (0.95 +/- 0.33 [mean +/- SD] mg/mL compared to 0.13 +/- 0.03 [mean +/- SD] mg/mL in controls) and polymorphonuclear leucocytes in the BAL. There was no change in total phospholipids. By contrast BAL retrieved from rats exposed to approximately twice the concentration of acid aerosol showed no cellular nor biochemical abnormalities and its surface tension properties were normal. We conclude that the abnormalities of surfactant activity in the acid-exposed guinea pigs result from the cellular and humoral responses of acute lung injury rather than a direct effect of acid.

Acetazolamide and amiloride inhibit pentobarbital-induced facilitation of nocifensive reflexes

BACKGROUND

Neuronal excitation may result from stimulation of gamma-aminobutyric acid A (GABA(A)) receptors that prolong the channel opening, depolarizing the postsynaptic membrane. Drugs such as acetazolamide or amiloride can block GABA depolarization. Barbiturates facilitate nociceptive reflexes and also prolong the GABA(A) channel open-time. To evaluate the possible mechanism, the authors studied the impact of acetazolamide and amiloride on pentobarbital-induced nocifensive reflex facilitation. Because nitric oxide (NO) is a mediator of reflex facilitation, the authors evaluated the effects of NO synthase inhibition.

METHODS

Nocifensive reflex thresholds were quantified with the hind paw withdrawal latency from radiant heat (HPW latency) in the rat. Nocifensive reflexes were facilitated with intraperitoneal injection of pentobarbital (30 mg/kg). The authors tested the roles of GABA-mediated depolarization and NO in reflex facilitation by pretreatment with acetazolamide and amiloride and inhibition of NO synthase with L-NAME and 7-NI, respectively. Sedative effects of pentobarbital were evaluated with the righting reflex, the response to vibrissal stimulation, and plasma drug concentrations.

RESULTS

Pentobarbital decreased the hind paw withdrawal latency from 11.2+/-1 to 8.3+/-1 s (P < 0.001). Pretreatment with each of the four test drugs limited the reduction in reflex facilitation after pentobarbital to 1.3 s or less, similar to the reduction seen after saline injection, without altering sedation. L-NAME increased plasma pentobarbital concentrations by 10% without changing the concentration associated with return of responsiveness.

CONCLUSIONS

Pentobarbital-induced nocifensive reflex facilitation was inhibited by all four tested drugs without evidence of increased sedation. The results are consistent with a role for GABA(A) receptor-mediated depolarization in barbiturate-induced hyper-reflexia.

The effects of general anesthetics on excitatory and inhibitory synaptic transmission in area CA1 of the rat hippocampus in vitro

It is unclear whether general anesthetics induce enhancement of neural inhibition and/or attenuation of neural excitation. We studied the effects of pentobarbital (5 x 10(-4) mol/L), propofol (5 x 10(-4) mol/L), ketamine (10(-3) mol/L), halothane (1.5 vol%), and isoflurane (2.0 vol%) on both excitatory and inhibitory synaptic transmission in rat hippocampal slices. Excitatory or inhibitory synaptic pathways were isolated using pharmacological antagonists. Extracellular microelectrodes were used to record electrically evoked CA1 neural population spikes (PSs). In the presence of the gamma-aminobutyric acid type A (GABA(A)) receptor antagonist (bicuculline), the inhibitory actions of pentobarbital and propofol were completely antagonized, whereas those of ketamine, halothane, and isoflurane were only partially blocked. To induce the N-methyl-D-aspartate (NMDA) receptor-mediated PS (NMDA PS), the non-NMDA and GABA(A) receptors were blocked in the absence of Mg2+. Ketamine, halothane, and isoflurane decreased the NMDA PS, and pentobarbital and propofol had no effect on the NMDA PS. The non-NMDA receptor-mediated PS (non-NMDA PS) was examined using the antagonists for the NMDA and GABA(A) receptors. Volatile, but not i.v., anesthetics reduced the non-NMDA PS. These findings indicate that pentobarbital and propofol produce inhibitory actions due to enhancement in the GABA(A) receptor; that ketamine reduces NMDA receptor-mediated responses and enhances GABA(A) receptor-mediated responses; and that halothane and isoflurane modulate GABA(A), NMDA, and non-NMDA receptor-mediated synaptic transmission.

IMPLICATIONS

Volatile anesthetics modulate both excitatory and inhibitory synaptic transmission of in vitro rat hippocampal pathways, whereas i.v. anesthetics produce more specific actions on inhibitory synaptic events. These results provide further support the idea that general anesthetics produce drug-specific and distinctive effects on different pathways in the central nervous system.

GABAergic mechanisms in the action of general anesthetics

1. The effects of volatile and intravenous anesthetics were studied on evoked field potentials in rat hippocampal CA1 neurons in vitro to determine the role of GABAergic mechanisms in the action of general anesthetics. 2. It was observed that both volatile (halothane, isoflurane, sevoflurane) and intravenous (thiopental, pentobarbital, propofol) anesthetics decreased population spike (PS) amplitudes. 3. Using paired-pulse paradigms, it was revealed that volatile agents enhance paired-pulse facilitation (PPF), and intravenous agents reduce PPF. Use-dependent effects on PS amplitudes were observed following application of the intravenous anesthetics, whereas volatile agents did not show use-dependency. The effects of the intravenous anesthetics were blocked by the GABA(A) receptor antagonist, bicuculline. 4. It is suggested that agent specific actions of general anesthetics are a result of differential effects on GABAergic mechanisms that modulate synaptic transmission.

Enhancement of CNS activity by thiopentone: comparison of nocifensive reflexes with hippocampal EEG

1. This study tested the hypothesis that the nociceptive effects of thiopentone, are pharmacodynamically distinct from EEG effects. 2. We concurrently examined the effects of thiopentone on nocifensive reflex thresholds and on the power spectrum of the hippocampal electroencephalogram (hEEG) in chronically instrumented rats. 3. Pharmacodynamic descriptors were derived to characterize the biphasic (enhancement followed by depression) relationship between plasma thiopentone concentrations and the CNS effects. 4. Peak facilitation of nocifensive reflexes occurred at 13 (10-16) microg/ml whereas maximal enhancement of hEEG was observed at 16 (12-20) microg/ml. 5. The enhancement produced by low concentrations of thiopentone on nocifensive reflexes appear to pharmacodynamically distinct from the hEEG excitation produced within a similar range of thiopentone concentrations.

Inhibition of respiratory and bioenergetic mechanisms by hydrogen sulfide in mammalian brain

The biochemical effects of hydrogen sulfide were investigated by treating enzyme homogenates and synaptosomes prepared from mammalian brain with sodium sulfide. Brain cytochrome c oxidase activity was highly sensitive to inhibition by sodium sulfide, as demonstrated by an IC50 of 0.13 microM. Sodium sulfide was also found to inhibit carbonic anhydrase activity in cerebellum, frontal cortex, and hippocampus. Synaptosomal oxygen consumption was significantly reduced as the concentration of sodium sulfide was increased from 20 to 100 microM; this was accompanied by a concentration-dependent depolarization of the synaptosomal mitochondrial membrane in situ and a reduction in synaptosomal ATP concentration. In other experiments using synaptosomes, sodium sulfide caused a significant calcium-independent increase in the extracellular accumulation of L-glutamate, inhibited Na+-dependent uptake of [3H]glutamate, but was unable to influence intrasynaptosomal free ionic Ca2+. Parallel studies conducted in vivo showed that rats exposed over a 5-d period to hydrogen sulfide (100 ppm for 3 h/d) had significantly higher concentrations of L-glutamate in the hippocampus compared to control animals. In summary, our results indicate that sulfide causes extensive disruption to respiratory and related mitochondrial functions in mammalian brain in vitro. The reduced capacity of nerve endings to take up L-glutamate may contribute to the raised L-glutamate levels observed in vivo.

Efficacy and safety of tramadol HCl in breakthrough musculoskeletal pain attributed to osteoarthritis

OBJECTIVE

To evaluate the efficacy of tramadol as adjunctive therapy in patients with musculoskeletal pain attributed to osteoarthritis (OA) who experienced breakthrough pain while taking a nonsteroidal antiinflammatory drug (NSAID).

METHODS

This single center, parallel, placebo controlled, 2 phase study was conducted in adults who experienced breakthrough OA pain while undergoing stable NSAID therapy. In a 24 h open label phase, patients took 100 mg of tramadol followed by 50 mg every 6 h (total 250 mg) in addition to their daily NSAID regimen. Supplemental analgesics were prohibited. Patients who met entry criteria and were willing to continue therapy were randomized to a 13 day double blind phase of adjunctive therapy with tramadol (50-100 mg every 4-6 h as needed for pain) or placebo; NSAID therapy was continued. The primary efficacy endpoint was the time to exit from the study because of therapeutic failure (i.e., insufficient pain relief or an inability to perform activities of daily living).

RESULTS

The time to exit from the study because of insufficient pain relief tended to be longer in the tramadol group (250 mg/day) compared with the placebo group (p = 0.066). At the end of the double blind phase, pain at rest was significantly less severe in tramadol treated patients (p = 0.046). In addition, severity of pain on motion tended to be less severe in tramadol treated patients (p = 0.059). General severity of current pain and ability to perform activities of daily living were not significantly different with tramadol or placebo. Patients' overall assessment of therapy (p = 0.022) and investigator's rating of global improvement (p = 0.004) were significantly better with tramadol than with placebo.

CONCLUSION

Tramadol may have a role as adjunctive treatment for breakthrough pain in patients receiving NSAID therapy for musculoskeletal pain attributed to OA.

Ventilatory responses in awake guinea pigs exposed to acid aerosols

This study reports experiments designed to evaluate the dose and temporal effects of an atmospheric pollutant, sulfuric acid (H2SO4) aerosol, on the dynamic components of the respiratory cycle. Ventilation was measured in a whole-body barometric plethysmograph in unanesthetized, unrestrained animals following a 4-h exposure to H2SO4 aerosol at 14.1, 20.1, or 43.3 mg/m3. Lung injury was assessed by histopathology and bronchoalveolar lavage (BAL). Aerosol exposure with H2SO4 caused marked alterations in both the magnitude and composition of the ventilatory response, which were both dose and time dependent. At the highest concentration tested, there was a significant increase in tidal volume (deltaVt) and a decrease in breathing frequency (f) immediately after exposure. Analysis of BAL fluid at this time showed increased inflammatory cells and protein in the acid exposed animals, and histology showed hyaline membranes and acute inflammatory cells in the proximal acinar region. By 24 h postexposure, f significantly increased whereas deltaVt decreased. This pattern of breathing was interspersed with short periods of apnea. The onset of rapid, shallow breathing was associated with histological evidence of diffuse pulmonary edema. By contrast, the immediate postexposure period at the lowest concentration of H2SO4 aerosol was characterized by a significant increase in f and little or no effect on deltaVt. These effects diminished with time, and at 24 h postexposure ventilatory parameters were indistinguishable from baseline values. An apparent crossover between the effects associated with the high and low exposure concentrations was seen at the intermediate exposure concentration; however, closer inspection of these findings on an animal-by-animal basis revealed two populations of animals with respiratory characteristics of either the high-exposure or low-exposure groups. The data suggest that the guinea pig exhibits complex interactions between dose and time to response that are consistent with the activation of neural reflexes. The indirect plethysmographic method provides a simple means to assess these responses in a model system that avoids the use of anesthetics, surgery, and restraint.

Pharmacodynamics of thiopentone: nocifensive reflex threshold changes correlate with hippocampal electroencephalography

The electroencephalographic (EEG) effects of thiopentone have been used extensively in the pharmacodynamic and pharmacokinetic modelling of drug effects in the central nervous system (CNS). Thiopentone has a biphasic (enhancement followed by inhibition) effect on nocifensive reflexes that occurs in a dose range similar to that which activates the EEG. In this study we have used rats chronically instrumented with hippocampal EEG (hEEG) electrodes to simultaneously characterize the effects of thiopentone on the hEEG and nocifensive reflex thresholds. Enhancement of these two measures of CNS effect correlated well with plasma thiopentone concentrations of 10-30 micrograms ml-1 (35-75 mumol litre-1) but maximal reflex enhancement occurred at concentrations of 3 micrograms ml-1 (11 mumol litre-1) less than the peak hEEG effect. The results validate the usefulness of nocifensive reflex thresholds for measurement of the CNS effects of thiopentone at subanaesthetic concentrations.

The effects of sevoflurane on population spikes in CA1 and dentate gyrus of the rat hippocampus in vitro

We studied the effects of sevoflurane on population spikes (PSs) in two synaptic pathways in rat hippocampal slices. Stimulating electrodes were placed on Schaffer collateral fibers or perforant path to activate inputs to CA1 pyramidal neurons or dentate gyrus (DG) neurons, respectively. Extracellular glass microelectrodes were used to record PSs. The paired-pulse stimulus was used to induce the paired-pulse facilitation (PPF). Sevoflurane (0.4-5.0 vol%) significantly decreased the amplitudes of PSs of CA1 and DG in a dose-dependent and reversible manner (25% effective dose values were 4.1 and 0.9 vol%, respectively). The stimulus-response relationships for PS amplitudes revealed that sevoflurane increased the threshold for PS generation in CA1 and DG. Sevoflurane (2.0 vol%) significantly enhanced PPF from 127% and 263% to 153% and 494% in CA1 and DG, respectively. The results imply that the effects of sevoflurane on PSs are greater in DG than in CA1 neurons, that sevoflurane enhances the PPF in both CA1 and DG, and that the actions of sevoflurane are not similar to those of other volatile or intravenous anesthetics previously reported in hippocampal preparations.

IMPLICATIONS

The volatile anesthetic sevoflurane alters neural excitability of individual pathways in the hippocampus in a manner different from other general anesthetics. The results are consistent with a site-specific mechanism of action for general anesthesia.

Nocifensive reflex thresholds in rats: measures of central nervous system effects of barbiturates

PURPOSE

To characterize the pharmacodynamic relationships between plasma pentobarbitone and thiopentone concentrations and nocifensive reflexes during emergence from anaesthesia.

METHODS

Forty-nine rats were studied. Plasma barbiturate concentrations were measured with high performance liquid chromatography. Nocifensive reflexes were assessed with the hindlimb withdrawal latency (WL) to heat and the somatic motor response threshold (SMRT) to tail pressure. In Protocol I, SMRT, WL, sedation, and the presence of paw-licking and the righting reflex were assessed in unrestrained rats before and every 10 min for two hours after an intraperitoneal injection of pentobarbitone (30 mg.kg-1). Plasma pentobarbitone kinetics were determined in a separate group of rats. In Protocol II, SMRT and drug concentrations were measured concurrently in partially restrained animals before and for 35 min after a computer-controlled i.v. bolus of thiopentone. In Protocol III the SMRT-plasma thiopentone relationship was determined during increasing and decreasing plasma thiopentone concentrations.

RESULTS

Enhancement of both nocifensive reflexes was observed in the unrestrained animals. Enhancement of SMRT was maximal [175% (153-197) of control values] at a mean plasma thiopentone concentration of 11 (9-13) micrograms.ml-1. The SMRT-plasma thiopentone curve showed a mean efflux-influx difference in plasma thiopentone concentration of 4(2.3-5.7) micrograms.ml-1.

CONCLUSIONS

Barbiturate-associated nocifensive reflex enhancement occurs in unrestrained animals with both thermal and pressure stimuli. The SMRT-plasma thiopentone concentration relationship during emergence from anaesthesia was similar to that observed previously during induction. The thiopentone plasma concentration-SMRT plot showed an equilibrium delay similar to that previously described by others for thiopentone at an electroencephalographic effect site.

Sevoflurane modulates both GABAA and GABAB receptors in area CA1 of rat hippocampus

It has been suggested that volatile anaesthetics enhance synaptic inhibition via gamma-aminobutyric acid (GABA) in the central nervous system. We have examined the effects of sevoflurane on GABAA and GABAB receptors in rat hippocampus in vitro. Extracellular recordings were used to record field potentials in rat CA1 pyramidal neurones of transverse hippocampal slices, stimulated electrically via stratum radiatum input. Sevoflurane 0.4-5.0 vol% decreased the amplitudes of population spikes (PS) of CA1 neurones in a concentration-dependent (calculated ED50 = 6.31 vol%) and reversible manner. The GABAA antagonist, bicuculline methiodide 5 x 10(-5) mol litre-1, induced oscillations (multiple spikes) and blocked the inhibitory actions of sevoflurane in the initial component (up to 24.8 ms) of the oscillation. The latter portion of the oscillation (greater than 24.8 ms) was depressed by sevoflurane. The GABAB antagonist, phaclofen 5 x 10(-4) mol litre-1 partially blocked the effects of sevoflurane on the latter portion of the bicuculline-induced oscillation. Sevoflurane 2.0 vol% significantly enhanced paired-pulse (PS2/PS1) facilitation (from 128.4% to 155.5% at an inter-stimulus interval of 37.9 ms); this enhancement was blocked by phaclofen. Stimulus-response relationships revealed that 2.0 vol% sevoflurane increased the intensity of threshold for PS generation to 109.8% of control. Both the GABAA agonist, muscimol 2 x 10(-5) mol litre-1 and the GABAB agonist, (+/-)-baclofen 10(-5) mol litre-1, potentiated the effects of sevoflurane. Sevoflurane enhanced thresholds by 137.1% and 138.5% of control in the presence of muscimol and (+/-)-baclofen, respectively. The results demonstrate that sevoflurane at clinical concentrations activated both GABAA- and GABAB-mediated inhibitions in area CA1 of the hippocampus, and that sevoflurane and GABA agonists (muscimol and baclofen) acted on different domains on the GABAA and GABAB receptors, respectively.

Evidence that GABA, serotonin, and norepinephrine are involved in the modulation of in vitro rhythmical activity in rat hippocampal slices

Cholinergic agonists induce a rhythmical slow activity (RSA) in the in vitro rat hippocampus. RSA consists of bursts of activity separated by quiescent periods (interburst intervals). The activity involves activation of muscarinic receptors; however, the role of other neurotransmitter substances is still controversial. The present study demonstrates that 500 microM GABA, 15 microM serotonin (5HT), or 20 microM norepinephrine (NE) can alter the pattern of carbachol-induced RSA. Application of GABA, 5HT, or NE increases interburst interval; 5HT and NE also increase burst length. Total power of RSA is decreased by GABA and 5HT but increased by NE. None of the three receptor agonists alters RSA frequency. The pattern of RSA is also dependent upon carbachol concentration: low concentrations (0.5 and 1 microM) produce only population spikes, whereas concentrations of 3 to 100 microM produce burst activity (50 microM is optimal for the generation of RSA). Burst length and peak frequency of RSA are enhanced with increasing concentrations of carbachol, whereas interburst interval is decreased. The results illustrate that the pattern of RSA is not only dependent upon carbachol concentration but can be modulated by GABA, 5HT, and NE. This suggests that more than one neurotransmitter system contributes to the production and modulation of RSA.

NSAID gastropathy. A new understanding

Nonsteroidal anti-inflammatory drug (NSAID) gastropathy is associated with substantial morbidity and mortality, which result in high costs to both the patient and society. The subset of patients who are at greatest risk for developing NSAID gastropathy continues to be better defined, but various risk factors, such as age and previous gastrointestinal tract disease, have been identified. In patients receiving older NSAIDs, the choice of NSAID should be based on differences in formulations at the lowest effective dose. Gastroprotective cotherapy should be instituted if treatment with older NSAIDs is continued in at-risk patients; misoprostol is currently the only agent approved for this indication. The impact of misoprostol on clinical gastrointestinal tract end points has recently been documented. Newer NSAIDs may have an improved safety profile over older NSAIDs; some have a clinically documented reduction in the incidence of adverse gastrointestinal tract effects. An understanding of these issues should enable the informed clinician to choose an NSAID on the basis of risk-benefit and cost-benefit considerations.

Thiopentone induced enhancement of somatic motor responses to noxious stimulation: influence of GABAA receptor modulation

PURPOSE

This study was conducted to determine whether hyperalgesic effects of subanaesthetic concentrations of thiopentone could be attributed to GABAA receptor effects.

METHODS

All studies were performed on 50 rats in a prospective, randomized, blinded fashion using saline-injected animals as controls. Using a modified Randall-Selitto technique, the motor behavior stimulated by noxious stimulation was quantified by determining the lowest tail pressure required to provoke a withdrawal response (somatic motor response threshold, SMRT). In the first protocol (21 rats), we studied the effects of 0.5, 1.5 and 5 mg.kg-1 i.v. of the GABAA agonist, muscimol, on SMRT. In the second protocol (20 rats), the effects of administration of saline, muscimol 0.5 mg.kg-1, or the competitive GABAA antagonist, bicuculline 0.25 mg.kg-1, upon the SMRT-reducing effects of a standardized thiopentone infusion were observed.

RESULTS

No dose of muscimol produced hyperalgesia. The highest dose of muscimol used (5 mg.kg-1) produced pronounced analgesic effects, raising the SMRT above 750 g. No change in SMRT was detected with the smaller doses of muscimol. Given in combination with muscimol (0.5 mg.kg-1), thiopentone produced analgesia, as shown by an increase in SMRT (P = 0.009). In the bicuculline treated animals, SMRT decreased linearly with increasing plasma thiopentone concentrations (P < 0.001). The slope of the relationship in the bicuculine group was not significantly different from that observed in the saline-treated group, indicating that bicuculline did not block the hyperalgesic effects of thiopentone.

CONCLUSION

The results of these studies suggest that hyperalgesia associated with thiopentone is not mediated primarily by GABAA receptors.

Effects of repeated exposures of hydrogen sulphide on rat hippocampal EEG

Exposure to high levels of hydrogen sulphide (H2S) in humans has been associated with a number of respiratory and neurological symptoms. Acute toxicity following exposure to high concentrations is well-documented, however, there is little scientific information concerning the effects of exposure to low concentrations. The effects of low levels of H2S on electroencephalographic (EEG) activity in the hippocampus and neocortex were investigated on the freely moving rat (Sprague-Dawley). Hippocampal electrodes were implanted in the dentate gyrus (DG) and CA1 region. Activity was recorded for 10 min just prior to H2S exposure in the presence of air (pre-exposure). Rats were exposed to H2S (25, 50, 75, or 100 ppm) for 3 h/day; data was collected during the final 10 min of each exposure. The total power of hippocampal theta activity increased in a concentration-dependent manner in both DG and CA1; repeated exposures for 5 consecutive days resulted in a cumulative effect that required 2 weeks for complete recovery. The effects were found to be highly significant at all concentrations within subjects. Neocortical EEG and LIA (Large Amplitude Irregular Activity) were unaffected. The results demonstrate that repeated exposure to low levels of H2S can produce cumulative changes in hippocampal function and suggest selectivity of action of this toxicant.

Effects of acid aerosol exposure on the surface properties of airway mucus

It was hypothesized that the mucous layer lining the tracheas of rats and guinea pigs contains surfactant material capable of lowering the air/mucus surface tension, gamma, and that exposure to an irritant aerosol would raise the gamma. The gamma of the surface film was measured directly by a spreading droplet technique and indirectly by displacement of polymethyl methacrylate particles into the aqueous layer. The morphology of the mucous film was examined by electron microscopy after nonaqueous fixation. gamma was 33.3 +/- 0.70 (SE) mN/m and 32.3 +/- 0.68 (SE) mN/m for the normal rat and guinea pig trachea, respectively. Exposure for 4 h to aerosols of sulfuric acid (94.1 +/- 18.68 (SD) and 43.3 +/- 4.57 (SD) mg/m3) caused a several-fold increase in thickness of the mucous layer with exudation of protein-like material. The osmiophilic surfactant film at the air/mucus interface became irregularly thickened and multilayered. Despite these morphological changes gamma remained low, 33.2 +/- 0.43 (SE) mN/m and 32.6 +/- 0.60 (SE) mN/m for rats and guinea pigs, respectively, and displacement of particles into the subphase was not compromised. The results indicate that rodent tracheas are able to maintain a low surface tension in the presence of injury.

Hyperalgesia during sedation: effects of barbiturates and propofol in the rat

Subhypnotic doses of thiopentone are considered to possess antianalgesic or hyperalgesic properties. In this study, we have tested the hypothesis that the coincidence of sedation and hyperalgesia is a property of both barbiturate and non-barbiturate anaesthetic agents. In a randomized, prospective, blinded study, the effects of slow (20 min) iv infusions of thiopentone, pentobarbitone, methohexitone or propofol on nociceptive threshold were measured in rats by tail pressure analgesimetry and compared with saline-infused control animals. Nociceptive thresholds were correlated with measurements of plasma drug concentrations and behavioural assessments. Comparison of pre-infusion nociceptive threshold with the lowest threshold obtained during drug infusion revealed decreases in all four treatment groups. As a percentage of the pre-infusion values, the decreases were: thiopentone: 42.5% (P < 0.001), pentobarbitone: 27.8% (P = 0.014), methohexitone: 24.9% (P = 0.013), propofol: 21.6% (P = 0.006). There were no changes in nociceptive threshold in the control groups. The relationship between nociceptive threshold and plasma drug concentration was usually characterized by an initial decline followed by a rise in nociceptive threshold as the plasma concentration and degree of sedation increased. The results support the hypothesis that hyperalgesia is a property of different anaesthetic agents when administered at sub-hynotic concentrations.

From peptic ulcer disease to NSAID gastropathy. An evolving nosology

Nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathy is an important clinical entity, most commonly encountered in elderly female patients. The expanding use of NSAIDs in the elderly population has led to an increased incidence of NSAID-induced gastropathy. The risk of gastric bleeding in these patients is 7-fold higher than in the younger population. Long term NSAID therapy in the elderly is apparently associated with failure of normal gastric mucosal adaptation. Silent unidentified gastric lesions are likely to be common with long term NSAID therapy, as symptomatology does not parallel pathological progression. This gastropathy, in contrast to peptic ulcer disease, is responsive to prostaglandins and other cytoprotective agents. A new generation of prostaglandin-sparing NSAIDs (e.g. nabumetone), in addition to the older nonacetylated salicylates, may represent less gastrotoxic alternatives. Therefore, these agents may substantially reduce the risk of NSAID-induced gastropathy. The debate continues as to whether to use NSAIDs, and under which circumstances. More importantly, the cost-benefit implications and justification for concomitant therapy with gastroprotective agents cloud the picture. Currently, there is a definite consensus that NSAIDs should not be casually used on a chronic basis, especially in patients at risk for serious gastropathy complications. In all cases, where possible, gastric prostaglandin-sparing NSAIDs or nonacetylated salicylates should be used in lowest effective dosages. In special circumstances, gastroprotective co-therapy can be considered. NSAID therapy probably should not be used or continued in elderly patients with a history of bleeding ulcers or recent major gastric ulcer activity.

Alteration of the morphology and neurochemistry of the developing mammalian nervous system by hydrogen sulphide

1. Hydrogen sulphide (H2S) is a broad spectrum toxicant that occurs widely in nature and is also released by a variety of industrial activities and processes. 2. The central nervous system (CNS) appears to be the major target organ. 3. There is great potential for insult or injury to the developing or immature CNS. 4. The risk of chronic or repeated exposures to low concentrations have not been well defined. 5. Exposure to low concentrations of H2S to time-pregnant rats from day 5 postcoitus until day 21 postnatal results in architectural modification of cerebellar Purkinje cells, alteration of putative amino acid neurotransmitters and changes in monoamine levels in the developing rat brain up to day 21 postnatal. 6. H2S-induced alterations in monoamine tissue levels observed in the developing rat brain return to control values if exposure is discontinued during development, that is, at day 21 postnatal.

A controlled clinical investigation of 3% diclofenac/2.5% sodium hyaluronate topical gel in the treatment of uncontrolled pain in chronic oral NSAID users with osteoarthritis

Topical application, 4 times daily for 2 weeks, of the diclofenac-hyaluronan gel to 59 osteoarthritis patients induced a significantly greater (p = 0.057) analgesic effect than placebo gel lacking the active substance applied to 60 control patients.

Healing of NSAID-induced gastric ulcers with a synthetic prostaglandin analog (enprostil)

OBJECTIVE

Conventional ulcer therapy has not been proven effective in healing gastric ulcers caused by nonsteroidal anti-inflammatory drugs (NSAIDs) if the NSAIDs are continued. Our objective in this study was to determine whether a prostaglandin analog is an effective treatment for such NSAID-induced lesions.

METHODS

To make this determination, we conducted a 9-wk double-blind trial comparing placebo with enprostil 35 micrograms twice daily and three times daily. Use of antacids was not allowed. Three centers entered 145 patients with chronic inflammatory arthritis and osteoarthritis, mean age 63 yr, who required continuous fixed-dose NSAID therapy within the range of therapeutic dosage. The minimum entrance criterion was the presence of either four gastric erosions or one gastric ulcer. Two pretreatment endoscopies within a 2-wk interval were performed to establish the presence of stable baseline gastric lesions. Endoscopy was repeated at wk 6 and 9 during treatment. All groups were similar with regard to age distribution, sex, weight, height, smoking usage, and alcohol consumption.

RESULTS

The ulcer healing rates were 14%, 57%, and 68% at 6 wk and 19%, 68%, and 74% at 9 wk for the groups receiving placebo, enprostil twice daily, and enprostil three times daily, respectively (p < 0.01). Complete mucosal healing of all erosions and ulcers at 9 wk occurred in 59% of enprostil-treated patients and in 10% of placebo-treated patients. Additional gastric erosions and gastric ulcers developed in 16% of placebo patients and 4% of the enprostil patients. Eighteen percent of enprostil patients withdrew early from the study due to adverse experiences, such as diarrhea and abdominal pain.

CONCLUSION

We concluded that during continued NSAID therapy 1) enprostil 35 micrograms (taken either twice daily or three times daily) heals NSAID-induced gastric ulcers and erosions and protects the mucosa from further NSAID-induced gastric injury; 2) gastric ulcers and erosions rarely heal spontaneously, and 3) enprostil results in a high incidence of diarrhea.

A longterm endoscopic evaluation of patients with arthritis treated with nabumetone vs naproxen

OBJECTIVE

To compare the gastrointestinal safety, ulcerogenic potential, and clinical efficacy over 5 years of nabumetone and naproxen therapy, in patients with rheumatoid arthritis (RA) or osteoarthritis (OA).

METHODS

Fifty-two patients entered a randomized, double blind study. Patients were randomized to 3 months treatment with either nabumetone, 1000 mg nightly, or naproxen, 250 mg twice daily, followed by an endoscopist-blind 5-year followup study. After the double blind phase, 15 patients in the nabumetone group and 12 in the naproxen group continued in the longterm endoscopist-blind phase. Endoscopic evaluations for gastroduodenal damage and global assessments of arthritis activity and degree of pain for efficacy were measured.

RESULTS

Over the 5-year period, endoscopically visible gastroduodenal ulceration was found in 8 of the naproxen treated patients compared with one of the nabumetone treated patients (p = 0.02). There was a significant difference in the time to develop an ulcer, with a greater risk of developing an ulcer sooner while taking naproxen (p < 0.01). Patients in both groups reported significant improvements in arthritis symptoms (p < 0.01).

CONCLUSION

Nabumetone appears to have a significantly lower ulcerogenic potential than naproxen over a 5-year period, and there is a trend toward better tolerability as measured by withdrawals for adverse experiences.

A double blind study comparing the efficacy and safety of enteric coated naproxen to naproxen in the management of NSAID intolerant patients with rheumatoid arthritis and osteoarthritis. Naproxen EC Study Group

OBJECTIVE

To compare efficacy and gastrointestinal (GI) tolerability of a new enteric coated formulation of naproxen (NAP-EC) with standard immediate release naproxen (NAP-STD).

METHODS

One hundred seventy-nine patients with osteoarthritis (OA) and one hundred seventy-six patients with rheumatoid arthritis (RA) at high risk for developing GI side effects to nonsteroidal antiinflammatory drug (NSAID) therapy were enrolled in a double blind, parallel, multicenter study. All patients had either discontinued as NSAID during the previous one year or required cotreatment with antiulcer drugs for control of GI complaints related to NSAID use. The treatments were evenly divided in both diagnostic cohorts.

RESULTS

Except for minor differences in alcohol consumption, baseline characteristics of patients in both treatment groups were statistically similar. Both naproxen formulations were highly efficacious by all variables of disease activity when changes were measured from baseline. No statistically significant between formulation difference was found in the primary efficacy variable, overall disease activity. Overall, between formulation differences in efficacy measures were few, though most favored NAP-STD. GI complaints were reduced by 15% (51% NAP-EC vs 60% NAP-STD, p = 0.077) and GI complaints thought to be drug related were reduced by 36% (16% NAP-EC vs 25% NAP-STD, p = 0.024). Withdrawals due to GI complaints were reduced by 37% in the NAP-EC group (12% NAP-EC vs 19% NAP-STD, p = 0.054), and withdrawals due to GI complaints judged to be drug related were reduced by 55% in the NAP-EC group (6% NAP-EC vs 12% NAP-STD, p = 0.025).

CONCLUSION

Enteric coated naproxen is an effective treatment for OA and RA. All observed differences in GI tolerability favor NAP-EC over NAP-STD.

Plasma, brain, and spinal cord concentrations of thiopental associated with hyperalgesia in the rat

BACKGROUND

Although low doses of barbiturates are widely believed to increase sensitivity to pain, studies of the electrophysiologic effects of these drugs on the neurons involved in nociception in the spinal cord have detected only depressant effects. The goal of the studies reported here was to quantify the hyperalgesia resulting from low-dose thiopental infusions and to measure the associated concentrations of thiopental in the plasma, brain, and spinal cord.

METHODS

Nociception was measured using the threshold for motor response to pressure stimulation of the tail (nociceptive threshold) and tail flick latency in the rat. Thiopental was administered by intravenous infusions designed to produce plasma concentrations that either slowly increased or remained at a steady state. Plasma and tissue thiopental concentrations were measured by high-performance liquid chromatography.

RESULTS

We observed a reduction in nociceptive threshold that was correlated with the plasma thiopental concentration over the range 2-20 micrograms.ml-1 (7.6-76 microM). The relationship was nonlinear. Nociceptive threshold reached a nadir (36% less than control values) at a mean plasma thiopental concentration of 13.7 micrograms.ml-1 (51.9 microM). The steady-state study showed a similar reduction in nociceptive threshold, with an equilibrium plasma thiopental concentration of 7.6 +/- 1.3 micrograms.ml-1 (28.8 +/- 4.9 microM). Concentrations of thiopental in brain and spinal cord samples were 1.7 +/- 0.03 and 3.5 +/- 1.7 micrograms.g-1, respectively.

CONCLUSIONS

These studies confirm previous reports of hyperalgesia in association with small doses of thiopental. Reductions in nociceptive threshold and tail flick latency were observed in association with spinal cord concentrations of thiopental in a range reported by others to depress the electrophysiologic activity of neurons involved in nociception.

A controlled study comparing the effects of nabumetone, ibuprofen, and ibuprofen plus misoprostol on the upper gastrointestinal tract mucosa

BACKGROUND

This study was developed to compare the incidence of endoscopically diagnosed ulcers in elderly patients taking nabumetone, ibuprofen, or concomitant ibuprofen/misoprostol. Further research is indicated to better establish the clinical relevance of these endoscopy findings.

METHODS

We conducted a prospective, multicenter, randomized, endoscopist-blinded, 12-week study involving 171 patients with osteoarthritis aged 60 years and older. Patients were randomized to receive nabumetone, 1000 mg (n = 58); ibuprofen, 600 mg four times daily (n = 53); or ibuprofen, 600 mg four times daily, administered concomitantly with misoprostol, 200 micrograms four times daily (n = 60). Endoscopy was performed at baseline and at weeks 2, 6, and 12. Endoscopy results were scored on a scale of 1 to 9. Significant ulcers were defined as breaks in the mucosa greater than 5 mm with appreciable depth.

RESULTS

Of the 171 randomized patients, 148 completed the study. There was no significant difference in the incidence of significant ulcers between the nabumetone group and the ibuprofen/misoprostol group (one vs zero). There were significantly fewer significant ulcers in the nabumetone and ibuprofen/misoprostol groups than in the ibuprofen monotherapy group (one and zero vs eight; P < .01). There also was a significant difference in the time to ulcer development, with a greater risk of developing an ulcer sooner with ibuprofen treatment (P < .01) than either nabumetone or ibuprofen/misoprostol treatment. The severity of osteoarthritis, based on physicians' assessments, improved in 64% of patients in the nabumetone group, 55% of those in the ibuprofen group, and 63% of those in the ibuprofen/misoprostol group.

CONCLUSIONS

Nabumetone is equivalent in ulcerogenicity to concomitant ibuprofen/misoprostol and is significantly less ulcerogenic than ibuprofen alone.