Identification of 1,3,8-Triazaspiro[4.5]Decane-2,4-Dione Derivatives as a Novel δ Opioid Receptor-Selective Agonist Chemotype

δ opioid receptors (DORs) hold potential as a target for neurologic and psychiatric disorders, yet no DOR agonist has proven efficacious in critical phase II clinical trials. The exact reasons for the failure to produce quality drug candidates for the DOR are unclear. However, it is known that certain DOR agonists can induce seizures and exhibit tachyphylaxis. Several studies have suggested that those adverse effects are more prevalent in delta agonists that share the (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80)/4-[(αR*)-α-((2S*,5R*)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-hydroxybenzyl]-N,N-diethylbenzamide chemotype. There is a need to find novel lead candidates for drug development that have improved pharmacological properties to differentiate them from the current failed delta agonists. Our objective in this study was to identify novel DOR agonists. We used a β-arrestin assay to screen a small G-protein coupled receptors (GPCR)-focused chemical library. We identified a novel chemotype of DOR agonists that appears to bind to the orthosteric site based of docking and molecular dynamic simulation. The most potent agonist hit compound is selective for the DOR over a panel of 167 other GPCRs, is slightly biased toward G-protein signaling and has anti-allodynic efficacy in a complete Freund's adjuvant model of inflammatory pain in C57BL/6 male and female mice. The newly discovered chemotype contrasts with molecules like SNC80 that are highly efficacious β-arrestin recruiters and may suggest this novel class of DOR agonists could be expanded on to develop a clinical candidate drug. SIGNIFICANCE STATEMENT: δ opioid receptors are a clinical target for various neurological disorders, including migraine and chronic pain. Many of the clinically tested delta opioid agonists share a single chemotype, which carries risks during drug development. Through a small-scale high-throughput screening assay, this study identified a novel δ opioid receptor agonist chemotype, which may serve as alternative for the current analgesic clinical candidates.

Histone deacetylase inhibitor decreases hyperalgesia in a mouse model of alcohol withdrawal-induced hyperalgesia

BACKGROUND

Alcohol withdrawal-induced hyperalgesia (AWH) is characterized as an increased pain sensitivity observed after cessation of chronic alcohol use. Alcohol withdrawal-induced hyperalgesia can contribute to the negative affective state associated with abstinence and can increase susceptibility to relapse. We aimed to characterize pain sensitivity in mice during withdrawal from two different models of alcohol exposure: chronic drinking in the dark (DID) and the Lieber-DeCarli liquid diet. We also investigated whether treatment with a histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), could ameliorate AWH in mice treated with the Lieber-DeCarli diet.

METHODS

Male and female C57BL/6J mice were used for these studies. In the DID model, mice received bottles of 20% ethanol or water during the dark cycle for 4 h per day on four consecutive days per week for 6 weeks. Peripheral mechanical sensitivity was measured weekly the morning of Day 5 using von Frey filaments. In the Lieber-DeCarli model, mice received ethanol (5% v/v) or control liquid diet for 10 days, along with a single binge ethanol gavage (5 g/kg) or control gavage, respectively, on Day 10. Peripheral mechanical sensitivity was measured during the liquid diet administration and at 24 and 72 h into ethanol withdrawal. An independent group of mice that received the Lieber-DeCarli diet were administered SAHA (50 mg/kg, i.p.) during withdrawal.

RESULTS

Male mice exhibited mechanical hypersensitivity after consuming ethanol for 5 weeks in the DID procedure. In the Lieber-DeCarli model, ethanol withdrawal led to hyperalgesia in both sexes. Suberoylanilide hydroxamic acid treatment during withdrawal from the ethanol liquid diet alleviated AWH.

CONCLUSIONS

These results demonstrate AWH in mice after chronic binge drinking in males and after Lieber-DeCarli liquid diet administration in both sexes. Like previous findings in rats, HDAC inhibition reduced AWH in mice, suggesting that epigenetic mechanisms are involved in AWH.

Regulation of headache response and transcriptomic network by the trigeminal ganglion clock

OBJECTIVE

To characterize the circadian features of the trigeminal ganglion in a mouse model of headache.

BACKGROUND

Several headache disorders, such as migraine and cluster headache, are known to exhibit distinct circadian rhythms of attacks. The circadian basis for these rhythmic pain responses, however, remains poorly understood.

METHODS

We examined trigeminal ganglion ex vivo and single-cell cultures from Per2::LucSV reporter mice and performed immunohistochemistry. Circadian behavior and transcriptomics were investigated using a novel combination of trigeminovascular and circadian models: a nitroglycerin mouse headache model with mechanical thresholds measured every 6 h, and trigeminal ganglion RNA sequencing measured every 4 h for 24 h. Finally, we performed pharmacogenomic analysis of gene targets for migraine, cluster headache, and trigeminal neuralgia treatments as well as trigeminal ganglion neuropeptides; this information was cross-referenced with our cycling genes from RNA sequencing data to identify potential targets for chronotherapy.

RESULTS

The trigeminal ganglion demonstrates strong circadian rhythms in both ex vivo and single-cell cultures, with core circadian proteins found in both neuronal and non-neuronal cells. Using our novel behavioral model, we showed that nitroglycerin-treated mice display circadian rhythms of pain sensitivity which were abolished in arrhythmic Per1/2 double knockout mice. Furthermore, RNA-sequencing analysis of the trigeminal ganglion revealed 466 genes that displayed circadian oscillations in the control group, including core clock genes and clock-regulated pain neurotransmitters. In the nitroglycerin group, we observed a profound circadian reprogramming of gene expression, as 331 of circadian genes in the control group lost rhythm and another 584 genes gained rhythm. Finally, pharmacogenetics analysis identified 10 genes in our trigeminal ganglion circadian transcriptome that encode target proteins of current medications used to treat migraine, cluster headache, or trigeminal neuralgia.

CONCLUSION

Our study unveiled robust circadian rhythms in the trigeminal ganglion at the behavioral, transcriptomic, and pharmacogenetic levels. These results support a fundamental role of the clock in pain pathophysiology.

PLAIN LANGUAGE SUMMARY

Several headache diseases, such as migraine and cluster headache, have headaches that occur at the same time each day. We learned that the trigeminal ganglion, an important pain structure in several headache diseases, has a 24-hour cycle that might be related to this daily cycle of headaches. Our genetic analysis suggests that some medications may be more effective in treating migraine and cluster headache when taken at specific times of the day.

PACAP-PAC1 receptor inhibition is effective in opioid induced hyperalgesia and medication overuse headache models

Opioids prescribed for pain and migraine can produce opioid-induced hyperalgesia (OIH) or medication overuse headache (MOH). We previously demonstrated that pituitary adenylate cyclase activating polypeptide (PACAP) is upregulated in OIH and chronic migraine models. Here we determined if PACAP acts as a bridge between opioids and pain chronification. We tested PACAP-PAC1 receptor inhibition in novel models of opioid-exacerbated trigeminovascular pain. The PAC1 antagonist, M65, reversed chronic allodynia in a model which combines morphine with the migraine trigger, nitroglycerin. Chronic opioids also exacerbated cortical spreading depression, a correlate of migraine aura; and M65 inhibited this augmentation. In situ hybridization showed MOR and PACAP co-expression in trigeminal ganglia, and near complete overlap between MOR and PAC1 in the trigeminal nucleus caudalis and periaqueductal gray. PACAPergic mechanisms appear to facilitate the transition to chronic headache following opioid use, and strategies targeting this system may be particularly beneficial for OIH and MOH.

Delta opioid receptors in Nav1.8 expressing peripheral neurons partially regulate the effect of delta agonist in models of migraine and opioid-induced hyperalgesia

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DOR in Nav1.8 cells do not regulate anti-migraine effects of DOR agonist.

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DOR in Nav1.8 cells is critical for effect of DOR agonist in peripheral OIH.

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DOR in Nav1.8 cells is not necessary for effect of DOR agonist in cephalic OIH.

Migraine is one of the most common pain disorders and causes disability in millions of people every year. Delta opioid receptors (DOR) have been identified as a novel therapeutic target for migraine and other headache disorders. DORs are present in both peripheral and central regions and it is unclear which receptor populations regulate migraine-associated effects. The aim of this study was to determine if DOR expressed in peripheral nociceptors regulates headache associated endpoints and the effect of delta agonists within these mouse models. We used a conditional knockout, in which DOR was selectively deleted from Nav1.8 expressing cells. Nav1.8-DOR mice and loxP control littermates were tested in models of chronic migraine-associated allodynia, opioid-induced hyperalgesia, migraine-associated negative affect, and aura. Nav1.8-DOR and loxP mice had comparable effect sizes in all of these models. The anti-allodynic effect of the DOR agonist, SNC80, was slightly diminished in the nitroglycerin model of migraine. Intriguingly, in the OIH model the peripheral effects of SNC80 were completely lost in Nav1.8-DOR mice while the cephalic effects remained intact. Regardless of genotype, SNC80 continued to inhibit conditioned place aversion associated with nitroglycerin and decreased cortical spreading depression events associated with migraine aura. These results suggest that DOR in Nav1.8-expressing nociceptors do not critically regulate the anti-migraine effects of delta agonist; and that brain-penetrant delta agonists would be a more effective drug development strategy.

Migraine and peripheral pain models show differential alterations in neuronal complexity

Objective

Our laboratory has recently shown that there is a decrease in neuronal complexity in head pain processing regions in mouse models of chronic migraine‐associated pain and aura. Importantly, restoration of this neuronal complexity corresponds with anti‐migraine effects of known and experimental pharmacotherapies. The objective of the current study was to expand this work and examine other brain regions involved with pain or emotional processing. We also investigated the generalizability of our findings by analyzing neuronal cytoarchitectural changes in a model of complex regional pain syndrome (CRPS), a peripheral pain disorder.

Methods

We used the nitroglycerin (NTG) model of chronic migraine‐associated pain in which mice receive 10 mg/kg NTG every other day for 9 days. Cortical spreading depression (CSD), a physiological corelate of migraine aura, was evoked in anesthetized mice using KCl. CRPS was induced by tibial fracture followed by casting. Neuronal cytoarchitecture was visualized with Golgi stain and analyzed with Simple Neurite Tracer.

Results

In the NTG model, we previously showed decreased neuronal complexity in the trigeminal nucleus caudalis (TNC) and periaqueductal gray (PAG). In contrast, we found increased neuronal complexity in the thalamus and no change in the amygdala or caudate putamen in this study. Following CSD, we observed decreased neuronal complexity in the PAG, in line with decreases in the somatosensory cortex and TNC reported with this model previously. In the CRPS model there was decreased neuronal complexity in the hippocampus, as reported by others; increased complexity in the PAG; and no change within the somatosensory cortex.

Conclusions

Collectively these results demonstrate that alterations in neuronal complexity are a feature of both chronic migraine and chronic CRPS. However, each type of pain presents a unique cytoarchitectural signature, which may provide insight on how these pain states differentially transition from acute to chronic conditions.

Seq-ing the mechanisms of migraine

The trigeminal ganglia (TG) play a crucial role in migraine pathophysiology. In this issue of Neuron, Yang et al. developed a single-cell atlas profiling the transcriptome and epigenome of mouse and human TG, thus providing a roadmap for therapeutic targeting.

Alternative Splicing Mechanisms Underlying Opioid-Induced Hyperalgesia

Prolonged use of opioids can cause opioid-induced hyperalgesia (OIH). The impact of alternative splicing on OIH remains partially characterized. A study of the absolute and relative modes of action of alternative splicing further the understanding of the molecular mechanisms underlying OIH. Differential absolute and relative isoform profiles were detected in the trigeminal ganglia and nucleus accumbens of mice presenting OIH behaviors elicited by chronic morphine administration relative to control mice. Genes that participate in glutamatergic synapse (e.g., Grip1, Grin1, Wnk3), myelin protein processes (e.g., Mbp, Mpz), and axon guidance presented absolute and relative splicing associated with OIH. Splicing of genes in the gonadotropin-releasing hormone receptor pathway was detected in the nucleus accumbens while splicing in the vascular endothelial growth factor, endogenous cannabinoid signaling, circadian clock system, and metabotropic glutamate receptor pathways was detected in the trigeminal ganglia. A notable finding was the prevalence of alternatively spliced transcription factors and regulators (e.g., Ciart, Ablim2, Pbx1, Arntl2) in the trigeminal ganglia. Insights into the nociceptive and antinociceptive modulatory action of Hnrnpk were gained. The results from our study highlight the impact of alternative splicing and transcriptional regulators on OIH and expose the need for isoform-level research to advance the understanding of morphine-associated hyperalgesia.

Delta opioid receptor regulation of calcitonin gene-related peptide dynamics in the trigeminal complex

ABSTRACT

Migraine is highly prevalent and is the sixth leading cause worldwide for years lost to disability. Therapeutic options specifically targeting migraine are limited, and delta opioid receptor (DOP) agonists were recently identified as a promising pharmacotherapy. The mechanisms by which DOPs regulate migraine are currently unclear. Calcitonin gene-related peptide (CGRP) has been identified as an endogenous migraine trigger and plays a critical role in migraine initiation and susceptibility. The aim of this study was to determine the behavioral effects of DOP agonists on the development of chronic migraine-associated pain and to investigate DOP coexpression with CGRP and CGRP receptor (CGRPR) in the trigeminal system. Chronic migraine-associated pain was induced in mice through repeated intermittent injection of the known human migraine trigger, nitroglycerin. Chronic nitroglycerin resulted in severe chronic cephalic allodynia which was prevented with cotreatment of the DOP-selective agonist, SNC80. In addition, a corresponding increase in CGRP expression in the trigeminal ganglia and trigeminal nucleus caudalis was observed after chronic nitroglycerin, an augmentation that was blocked by SNC80. Moreover, DOP was also upregulated in these head pain-processing regions following the chronic migraine model. Immunohistochemical analysis of the trigeminal ganglia revealed coexpression of DOP with CGRP as well as with a primary component of the CGRPR, RAMP1. In the trigeminal nucleus caudalis, DOP was not coexpressed with CGRP but was highly coexpressed with RAMP1 and calcitonin receptor-like receptor. These results suggest that DOP agonists inhibit migraine-associated pain by attenuating CGRP release and blocking pronociceptive signaling of the CGRPR.

Neuronal complexity is attenuated in preclinical models of migraine and restored by HDAC6 inhibition

Migraine is the sixth most prevalent disease worldwide but the mechanisms that underlie migraine chronicity are poorly understood. Cytoskeletal flexibility is fundamental to neuronal-plasticity and is dependent on dynamic microtubules. Histone-deacetylase-6 (HDAC6) decreases microtubule dynamics by deacetylating its primary substrate, α-tubulin. We use validated mouse models of migraine to show that HDAC6-inhibition is a promising migraine treatment and reveal an undiscovered cytoarchitectural basis for migraine chronicity. The human migraine trigger, nitroglycerin, produced chronic migraine-associated pain and decreased neurite growth in headache-processing regions, which were reversed by HDAC6 inhibition. Cortical spreading depression (CSD), a physiological correlate of migraine aura, also decreased cortical neurite growth, while HDAC6-inhibitor restored neuronal complexity and decreased CSD. Importantly, a calcitonin gene-related peptide receptor antagonist also restored blunted neuronal complexity induced by nitroglycerin. Our results demonstrate that disruptions in neuronal cytoarchitecture are a feature of chronic migraine, and effective migraine therapies might include agents that restore microtubule/neuronal plasticity.

A non-convulsant delta-opioid receptor agonist, KNT-127, reduces cortical spreading depression and nitroglycerin-induced allodynia

OBJECTIVE

The aim of this study was to determine if the non-convulsant delta-opioid receptor (DOR) agonist, KNT-127, could inhibit migraine-associated endpoints.

BACKGROUND

The DOR has been identified as a therapeutic target for migraine. However, the development of delta agonists is limited as some ligands have seizurogenic properties, which may be related to their ability to induce receptor internalization. While both pro- and non-convulsant delta agonists can reduce migraine-associated allodynia, only the proconvulsant agonist, SNC80, has been shown to decrease cortical spreading depression (CSD). It is unclear if the ability of delta agonists to modulate cortical activity is related to the same signaling mechanisms that produce proconvulsant effects.

METHODS

The effects of the non-convulsant delta agonist, KNT-127, were examined. Repetitive CSD was induced in female C57BL6/J (n = 6/group) mice by continuous application of KCl and the effect of KNT-127/vehicle (Veh) on both local field potentials and optical intrinsic signals was determined. To assess the effect of KNT-127 on established chronic migraine-associated pain, male and female C57BL6/J mice were treated with nitroglycerin (NTG; 10 mg/kg, ip) every other day for 9 days and tested with KNT-127 (5 mg/kg, sc) or Veh on day 10 (n = 6/group). DOR-enhanced green fluorescent protein mice (n = 4/group) were used to confirm the internalization properties of KNT-127 in the trigeminal ganglia, trigeminal nucleus caudalis, and somatosensory cortex.

RESULTS

KNT-127 inhibited CSD events (t(10)  = 3.570, p = 0.0051). In addition, this delta agonist also reversed established cephalic allodynia in the NTG model of chronic migraine (F(1, 20)  = 12.80, p < 0.01). Furthermore, KNT-127 caused limited internalization of DOR in key migraine processing regions.

CONCLUSIONS

This study shows that the antimigraine effects of DOR agonists can be separated from their proconvulsant effects. This data provides valuable information for the continued development of delta agonists for the treatment of migraine.

Forebrain delta opioid receptors regulate the response of delta agonist in models of migraine and opioid-induced hyperalgesia

Delta opioid receptor (DOR) agonists have been identified as a promising novel therapy for headache disorders. DORs are broadly expressed in several peripheral and central regions important for pain processing and mood regulation; and it is unclear which receptors regulate headache associated symptoms. In a model of chronic migraine-associated pain using the human migraine trigger, nitroglycerin, we observed increased expression of DOR in cortex, hippocampus, and striatum; suggesting a role for these forebrain regions in the regulation of migraine. To test this hypothesis, we used conditional knockout mice with DORs deleted from forebrain GABAergic neurons (Dlx-DOR), and investigated the outcome of this knockout on the effectiveness of the DOR agonist SNC80 in multiple headache models. In DOR loxP controls SNC80 blocked the development of acute and chronic cephalic allodynia in the chronic nitroglycerin model, an effect that was lost in Dlx-DOR mice. In addition, the anti-allodynic effects of SNC80 were lost in a model of opioid induced hyperalgesia/medication overuse headache in Dlx-DOR conditional knockouts. In a model reflecting negative affect associated with migraine, SNC80 was only effective in loxP controls and not Dlx-DOR mice. Similarly, SNC80 was ineffective in the cortical spreading depression model of migraine aura in conditional knockout mice. Taken together, these data indicate that forebrain DORs are necessary for the action of DOR agonists in relieving headache-related symptoms and suggest that forebrain regions may play an important role in migraine modulation.

Pain, Motivation, Migraine, and the Microbiome: New Frontiers for Opioid Systems and Disease

For decades the broad role of opioids in addiction, neuropsychiatric disorders, and pain states has been somewhat well established. However, in recent years, with the rise of technological advances, not only is the existing dogma being challenged, but we are identifying new disease areas in which opioids play a critical role. This review highlights four new areas of exploration in the opioid field. The most recent addition to the opioid family, the nociceptin receptor system, shows promise as the missing link in understanding the neurocircuitry of motivation. It is well known that activation of the kappa opioid receptor system modulates negative affect and dysphoria, but recent studies now implicate the kappa opioid system in the modulation of negative affect associated with pain. Opioids are critical in pain management; however, the often-forgotten delta opioid receptor system has been identified as a novel therapeutic target for headache disorders and migraine. Lastly, changes to the gut microbiome have been shown to directly contribute to many of the symptoms of chronic opioid use and opioid related behaviors. This review summarizes the findings from each of these areas with an emphasis on identifying new therapeutic targets. SIGNIFICANCE STATEMENT: The focus of this minireview is to highlight new disease areas or new aspects of disease in which opioids have been implicated; this includes pain, motivation, migraine, and the microbiome. In some cases, this has resulted in the pursuit of a novel therapeutic target and resultant clinical trial. We believe this is very timely and will be a refreshing take on reading about opioids and disease.

NOP receptor agonist attenuates nitroglycerin-induced migraine-like symptoms in mice

Migraine is an extraordinarily prevalent and disabling headache disorder that affects one billion people worldwide. Throbbing pain is one of several migraine symptoms including sensitivity to light (photophobia), sometimes to sounds, smell and touch. The basic mechanisms underlying migraine remain inadequately understood, and current treatments (with triptans being the primary standard of care) are not well tolerated by some patients. NOP (Nociceptin OPioid) receptors, the fourth member of the opioid receptor family, are expressed in the brain and periphery with particularly high expression known to be in trigeminal ganglia (TG). The aim of our study was to further explore the involvement of the NOP receptor system in migraine. To this end, we used immunohistochemistry to examine NOP receptor distribution in TG and trigeminal nucleus caudalus (TNC) in mice, including colocalization with specific cellular markers, and used nitroglycerin (NTG) models of migraine to assess the influence of the selective NOP receptor agonist, Ro 64-6198, on NTG-induced pain (sensitivity of paw and head using von Frey filaments) and photophobia in mice. Our immunohistochemical studies with NOP-eGFP knock-in mice indicate that NOP receptors are on the majority of neurons in the TG and are also very highly expressed in the TNC. In addition, Ro 64-6198 can dose dependently block NTG-induced paw and head allodynia, an effect that is blocked by the NOP antagonist, SB-612111. Moreover, Ro 64-6198, can decrease NTG-induced light sensitivity in mice. These results suggest that NOP receptor agonists should be futher explored as treatment for migraine symptoms. This article is part of the special issue on Neuropeptides.

Acid-sensing ion channel 3 blockade inhibits durovascular and nitric oxide-mediated trigeminal pain

Background and Purpose

There is a major unmet need to develop new therapies for migraine. We have previously demonstrated the therapeutic potential of the acid‐sensing ion channel (ASIC) blockade in migraine, via an ASIC1 mechanism. ASIC3 is expressed in the trigeminal ganglion and its response is potentiated by NO that can trigger migraine attacks in patients. Thus we sought to explore the potential therapeutic effect of ASIC3 blockade in migraine.

Experimental Approach

To investigate this, we utilised validated electrophysiological and behavioural rodent preclinical models. In rats, ASIC3 blockade using APETx2 (50 or 100 μg·kg⁻¹, i.v.) was measured by using durovascular and NO‐evoked trigeminal nociceptive responses along with cortical spreading depression models. In mice, we sought to determine if periorbital mechanical sensitivity, induced by acute nitroglycerin (10 mg·kg⁻¹, i.p.), was attenuated by APETx2 (230 μg·kg⁻¹, i.p.), as well as latent sensitisation induced by bright light stress in a chronic nitroglycerin model.

Key Results

Here, we show that the ASIC3 blocker APETx2 inhibits durovascular‐evoked and NO‐induced sensitisation of trigeminal nociceptive responses in rats. In agreement, acute and chronic periorbital mechanosensitivity induced in mice by nitroglycerin and subsequent bright light stress‐evoked latent sensitivity as a model of chronic migraine are all reversed by APETx2.

Conclusion and Implications

These results support the development of specific ASIC3 or combined ASIC1/3 blockers for migraine‐related pain and point to a potential role for ASIC‐dependent NO‐mediated attack triggering. This has key implications for migraine, given the major unmet need for novel therapeutic targets.

PACAP and Other Neuropeptide Targets Link Chronic Migraine and Opioid-induced Hyperalgesia in Mouse Models

Chronic use of opioids can produce opioid-induced hyperalgesia (OIH), and when used to treat migraine, these drugs can result in increased pain and headache chronicity. We hypothesized that overlapping mechanisms between OIH and chronic migraine occur through neuropeptide dysregulation. Using label-free, non-biased liquid chromatography-mass spectrometry to identify and measure changes in more than 1500 neuropeptides under these two conditions, we observed only 16 neuropeptides that were altered between the two conditions. The known pro-migraine molecule, calcitonin-gene related peptide, was among seven peptides associated with chronic migraine, with several pain-processing neuropeptides among the nine other peptides affected in OIH. Further, composite peptide complements Pituitary adenylate cyclase-activating polypeptide (PACAP), Vasoactive intestinal peptide (VIP) and Secretogranin (SCG) showed significant changes in both chronic migraine and OIH. In a follow-up pharmacological study, we confirmed the role of PACAP in models of these two disorders, validating the effectiveness of our peptidomic approach, and identifying PACAP as a mechanistic link between chronic migraine and OIH. Data are available via ProteomeXchange with identifier PXD013362.

Effect of Histone Deacetylase Inhibitor on Ethanol Withdrawal-Induced Hyperalgesia in Rats

BACKGROUND

Increased pain sensitivity is observed following alcohol withdrawal, and attempts to alleviate this hyperalgesia can contribute to the cycle of addiction. The aim of this study was to determine if alcohol withdrawal-induced hyperalgesia was observed in a chronic ethanol exposure model and if this pain was affected by histone deacetylase inhibitors, thus revealing an epigenetic mechanism.

METHODS

Adult male Sprague Dawley rats received Lieber-DeCarli liquid control or ethanol (9% v/v) diet for 15 days. Mechanical sensitivity was measured with von Frey hair stimulation of the hindpaw during ethanol administration and 24- and 72-hour withdrawal.

RESULTS

Ethanol withdrawal produced severe and sustained mechanical hyperalgesia, an effect not observed in the control or ethanol-maintained groups. Furthermore, this hyperalgesia was attenuated by the histone deacetylase inhibitor, suberoylanilide hydroxamic acid treatment.

CONCLUSIONS

Heightened pain sensitivity was observed following withdrawal from chronic ethanol exposure, and histone deacetylase inhibitors could be novel treatments for this alcohol withdrawal-induced hyperalgesia.

Delta opioid receptor agonists are effective for multiple types of headache disorders

Headaches are highly disabling and are among the most common neurological disorders worldwide. Despite the high prevalence of headache, therapeutic options are limited. We recently identified the delta opioid receptor (DOR) as an emerging therapeutic target for migraine. In this study, we examined the effectiveness of a hallmark DOR agonist, SNC80, in disease models reflecting diverse headache disorders including: chronic migraine, post-traumatic headache (PTH), medication overuse headache by triptans (MOH), and opioid-induced hyperalgesia (OIH). To model chronic migraine C57BL/6J mice received chronic intermittent treatment with the known human migraine trigger, nitroglycerin. PTH was modeled by combining the closed head weight drop model with the nitroglycerin model of chronic migraine. For MOH and OIH, mice were chronically treated with sumatriptan or morphine, respectively. The development of periorbital and peripheral allodynia was observed in all four models; and SNC80 significantly inhibited allodynia in all cases. In addition, we also determined if chronic daily treatment with SNC80 would induce MOH/OIH, and we observed limited hyperalgesia relative to sumatriptan or morphine. Together, our results indicate that DOR agonists could be effective in multiple headache disorders, despite their distinct etiology, thus presenting a novel therapeutic target for headache.

Gene Network Dysregulation in the Trigeminal Ganglia and Nucleus Accumbens of a Model of Chronic Migraine-Associated Hyperalgesia

The pharmacological agent nitroglycerin (NTG) elicits hyperalgesia and allodynia in mice. This model has been used to study the neurological disorder of trigeminovascular pain or migraine, a debilitating form of hyperalgesia. The present study validates hyperalgesia in an established mouse model of chronic migraine triggered by NTG and advances the understanding of the associated molecular mechanisms. The RNA-seq profiles of two nervous system regions associated with pain, the trigeminal ganglia (TG) and the nucleus accumbens (NAc), were compared in mice receiving chronic NTG treatment relative to control (CON) mice. Among the 109 genes that exhibited an NTG treatment-by-region interaction, solute carrier family 32 (GABA vesicular transporter) member 1 (Slc32a1) and preproenkephalin (Penk) exhibited reversal of expression patterns between the NTG and CON groups. Erb-b2 receptor tyrosine kinase 4 (Erbb4) and solute carrier family 1 (glial high affinity glutamate transporter) member 2 (Slc1a2) exhibited consistent differential expression between treatments across regions albeit at different magnitude. Period circadian clock 1 (Per1) was among the 165 genes that exhibited significant NTG treatment effect. Biological processes disrupted by NTG in a region-specific manner included adaptive and innate immune responses; whereas glutamatergic and dopaminergic synapses and rhythmic process were disrupted in both regions. Regulatory network reconstruction highlighted the widespread role of several transcription factors (including Snrnp70, Smad1, Pax6, Cebpa, and Smpx) among the NTG-disrupted target genes. These results advance the understanding of the molecular mechanisms of hyperalgesia that can be applied to therapies to ameliorate chronic pain and migraine.

Tolerance to high-internalizing δ opioid receptor agonist is critically mediated by arrestin 2

BACKGROUND AND PURPOSE

Opioid δ receptor agonists are potent antihyperalgesics in chronic pain models, but tolerance develops after prolonged use. Previous evidence indicates that distinct forms of tolerance occur depending on the internalization properties of δ receptor agonists. As arrestins are important in receptor internalization, we investigated the role of arrestin 2 (β-arrestin 1) in mediating the development of tolerance induced by high- and low-internalizing δ receptor agonists.

EXPERIMENTAL APPROACH

We evaluated the effect of two δ receptor agonists with similar analgesic potencies, but either high-(SNC80) or low-(ARM390) internalization properties in wild-type (WT) and arrestin 2 knockout (KO) mice. We compared tolerance to the antihyperalgesic effects of these compounds in a model of inflammatory pain. We also examined tolerance to the convulsant effect of SNC80. Furthermore, effect of chronic treatment with SNC80 on δ agonist-stimulated [³⁵ S]-GTPγS binding was determined in WT and KO mice.

KEY RESULTS

Arrestin 2 KO resulted in increased drug potency, duration of action and decreased acute tolerance to the antihyperalgesic effects of SNC80. In contrast, ARM390 produced similar effects in both WT and KO animals. Following chronic treatment, we found a marked decrease in the extent of tolerance to SNC80-induced antihyperalgesia and convulsions in arrestin 2 KO mice. Accordingly, δ receptors remained functionally coupled to G proteins in arrestin 2 KO mice chronically treated with SNC80.

CONCLUSIONS AND IMPLICATIONS

Overall, these results suggest that δ receptor agonists interact with arrestins in a ligand-specific manner, and tolerance to high- but not low-internalizing agonists are preferentially regulated by arrestin 2.

Targeted Nitric Oxide Synthase Inhibitors for Migraine

Nitric oxide (NO) is a small gaseous signaling molecule that has important biological effects. It has been heavily implicated in migraine; and the NO donor, nitroglycerin, has been used extensively as a human migraine trigger. Correspondingly, a number of components of the NO signaling cascade have been shown to be upregulated in migraine patients. NO is endogenously produced in the body by NO synthase (NOS), of which there are three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Based on the accumulating evidence that endogenous NO regulation is altered in migraine pathogenesis, global and isoform-selective inhibitors of NOS have been targeted for migraine drug development. This review highlights the evidence for the role of NO in migraine and focuses on the use of NOS inhibitors for the treatment of this disorder. In addition, we discuss other molecules within the NO signaling pathway that may be promising therapeutic targets for migraine.

Ligand-Directed Signaling at the Delta Opioid Receptor

Delta opioid receptors (δORs) regulate a number of physiological functions, and agonists for this receptor are being pursued for the treatment of mood disorders, chronic pain, and migraine. A major challenge to the development of these compounds is that, like many G-protein coupled receptors (GPCRs), agonists at the δOR can induce very different signaling and receptor trafficking events. This concept, known as ligand-directed signaling, functional selectivity, or biased agonism, can result in different agonists producing highly distinct behavioral consequences. In this chapter, we highlight the in vitro and in vivo evidence for ligand-directed signaling and trafficking at the δOR. A number of biological implications of agonist-directed signaling at the δOR have been demonstrated. Importantly, ligand-specific effects can impact both acute behavioral effects of delta agonists, as well as the long-term adaptations induced by chronic drug treatment. A better understanding of the specific signaling cascades that regulate these differential behavioral effects would help to guide rational drug design, ultimately resulting in δOR agonists with fewer adverse effects.

Soluble guanylyl cyclase is a critical regulator of migraine-associated pain

Background Nitric oxide (NO) has been heavily implicated in migraine. Nitroglycerin is a prototypic NO-donor, and triggers migraine in humans. However, nitroglycerin also induces oxidative/nitrosative stress and is a source of peroxynitrite - factors previously linked with migraine etiology. Soluble guanylyl cyclase (sGC) is the high affinity NO receptor in the body, and the aim of this study was to identify the precise role of sGC in acute and chronic migraine. Methods We developed a novel brain-bioavailable sGC stimulator (VL-102), and tested its hyperalgesic properties in mice. We also determined the effect of VL-102 on c-fos and calcitonin gene related peptide (CGRP) immunoreactivity within the trigeminovascular complex. In addition, we also tested the known sGC inhibitor, ODQ, within the chronic nitroglycerin migraine model. Results VL-102-evoked acute and chronic mechanical cephalic and hind-paw allodynia in a dose-dependent manner, which was blocked by the migraine medications sumatriptan, propranolol, and topiramate. In addition, VL-102 also increased c-fos and CGRP expressing cells within the trigeminovascular complex. Importantly, ODQ completely inhibited acute and chronic hyperalgesia induced by nitroglycerin. ODQ also blocked hyperalgesia already established by chronic nitroglycerin, implicating this pathway in migraine chronicity. Conclusions These results indicate that nitroglycerin causes migraine-related pain through stimulation of the sGC pathway, and that super-activation of this receptor may be an important component for the maintenance of chronic migraine. This work opens the possibility for negative sGC modulators as novel migraine therapies.

From blast to bench: A translational mini-review of posttraumatic headache

Current events within the military and professional sports have resulted in an increased recognition of the long-term and debilitating consequences of traumatic brain injury. Mild traumatic brain injury accounts for the majority of head injuries, and posttraumatic headache is the most common adverse effect. It is estimated that between 30% to 90% of traumatic brain injuries result in posttraumatic headache, and for a significant number of people this headache disorder can continue for up to and over a year post injury. Often, the most severe and chronic posttraumatic headache has a migraine-like phenotype and is difficult to resolve. In this review we discuss the preclinical findings from animal models of posttraumatic headache. We also describe potential mechanisms by which traumatic brain injury leads to chronic posttraumatic headache, including neuroinflammatory mediators and migraine-associated neuropeptides. There are surprisingly few preclinical studies that have investigated overlapping mechanisms between posttraumatic headache and migraine, especially considering the prevalence and debilitating nature of posttraumatic headache. Given this context, posttraumatic headache is a field with many emerging opportunities for growth. The frequency of posttraumatic headache in the general and military population is rising, and further preclinical research is required to understand, ameliorate, and treat this disabling disorder. © 2017 Wiley Periodicals, Inc.

The effects of acute and preventive migraine therapies in a mouse model of chronic migraine

Background The development of novel migraine therapies has been slow, in part because of the small number of clinically relevant animal models. We have recently developed a new mouse model of chronic migraine using chronic intermittent nitroglycerin, a known human migraine trigger. The objective of this study was to validate this model by testing known and potential migraine-preventive treatments. Methods Migraine therapies were administered to male and female mice for 11 days. On day 3, mice were tested with nitroglycerin every second day for nine days. Basal and nitroglycerin-evoked mechanical hypersensitivity was evaluated using von Frey filaments. Results Chronic intermittent nitroglycerin produced acute hyperalgesia with each administration, and progressive and sustained basal hypersensitivity. The established preventive migraine therapy propranolol effectively blocked the development of acute and chronic nitroglycerin-induced hyperalgesia, while valproate had no effect. Potential migraine-preventive therapies were also tested: Amiloride inhibited nitroglycerin-induced acute and chronic hyperalgesia; while memantine was ineffective. We also tested the acute migraine therapy sumatriptan, which did not alter nitroglycerin-induced hyperalgesia, but instead resulted in acute and chronic hyperalgesia similar to that observed following nitroglycerin administration. Conclusions This study establishes the chronic nitroglycerin model as an additional screening tool to test novel migraine-preventive therapies.

The delta opioid receptor tool box

In recent years, the delta opioid receptor has attracted increasing interest as a target for the treatment of chronic pain and emotional disorders. Due to their therapeutic potential, numerous tools have been developed to study the delta opioid receptor from both a molecular and a functional perspective. This review summarizes the most commonly available tools, with an emphasis on their use and limitations. Here, we describe (1) the cell-based assays used to study the delta opioid receptor. (2) The features of several delta opioid receptor ligands, including peptide and non-peptide drugs. (3) The existing approaches to detect delta opioid receptors in fixed tissue, and debates that surround these techniques. (4) Behavioral assays used to study the in vivo effects of delta opioid receptor agonists; including locomotor stimulation and convulsions that are induced by some ligands, but not others. (5) The characterization of genetically modified mice used specifically to study the delta opioid receptor. Overall, this review aims to provide a guideline for the use of these tools with the final goal of increasing our understanding of delta opioid receptor physiology.

Cell-autonomous regulation of Mu-opioid receptor recycling by substance P

How neurons coordinate and reprogram multiple neurotransmitter signals is an area of broad interest. Here, we show that substance P (SP), a neuropeptide associated with inflammatory pain, reprograms opioid receptor recycling and signaling. SP, through activation of the neurokinin 1 (NK1R) receptor, increases the post-endocytic recycling of the mu-opioid receptor (MOR) in trigeminal ganglion (TG) neurons in an agonist-selective manner. SP-mediated protein kinase C (PKC) activation is both required and sufficient for increasing recycling of exogenous and endogenous MOR in TG neurons. The target of this cross-regulation is MOR itself, given that mutation of either of two PKC phosphorylation sites on MOR abolishes the SP-induced increase in recycling and resensitization. Furthermore, SP enhances the resensitization of fentanyl-induced, but not morphine-induced, antinociception in mice. Our results define a physiological pathway that cross-regulates opioid receptor recycling via direct modification of MOR and suggest a mode of homeostatic interaction between the pain and analgesic systems.

In vivo techniques to investigate the internalization profile of opioid receptors

G-protein-coupled receptors (GPCRs) regulate a remarkable diversity of biological functions, and are thus often targeted for drug therapies. Receptor internalization is commonly observed following agonist binding and activation. Receptor trafficking events have been well characterized in cell systems, but the in vivo significance of GPCR internalization is still poorly understood. To address this issue, we have developed an innovative knock-in mouse model, where an opioid receptor is directly visible in vivo. These knockin mice express functional fluorescent delta opioid receptors (DOR-eGFP) in place of the endogenous receptor, and these receptors are expressed at physiological levels within their native environment. DOR-eGFP mice have proven to be an extraordinary tool in studying receptor neuroanatomy, real-time receptor trafficking in live neurons, and in vivo receptor internalization. We have used this animal model to determine the relationship between receptor trafficking in neurons and receptor function at a behavioral level. Here, we describe in detail the construction and characterization of this knockin mouse. We also outline how to use these mice to examine the behavioral consequences of agonist-specific trafficking at the delta opioid receptor. These techniques are potentially applicable to any GPCR, and highlight the powerful nature of this imaging tool.

δ-Opioid receptor agonists inhibit migraine-related hyperalgesia, aversive state and cortical spreading depression in mice

BACKGROUND AND PURPOSE

Migraine is an extraordinarily common brain disorder for which treatment options continue to be limited. Agonists that activate the δ-opioid receptor may be promising for the treatment of migraine as they are highly effective for the treatment of chronic rather than acute pain, do not induce hyperalgesia, have low abuse potential and have anxiolytic and antidepressant properties. The aim of this study was to investigate the therapeutic potential of δ-opioid receptor agonists for migraine by characterizing their effects in mouse migraine models.

EXPERIMENTAL APPROACH

Mechanical hypersensitivity was assessed in mice treated with acute and chronic doses of nitroglycerin (NTG), a known human migraine trigger. Conditioned place aversion to NTG was also measured as a model of migraine-associated negative affect. In addition, we assessed evoked cortical spreading depression (CSD), an established model of migraine aura, in a thinned skull preparation.

KEY RESULTS

NTG evoked acute and chronic mechanical and thermal hyperalgesia in mice, as well as conditioned place aversion. Three different δ-opioid receptor agonists, SNC80, ARM390 and JNJ20788560, significantly reduced NTG-evoked hyperalgesia. SNC80 also abolished NTG-induced conditioned place aversion, suggesting that δ-opioid receptor activation may also alleviate the negative emotional state associated with migraine. We also found that SNC80 significantly attenuated CSD, a model that is considered predictive of migraine preventive therapies.

CONCLUSIONS AND IMPLICATIONS

These data show that δ-opioid receptor agonists modulate multiple basic mechanisms associated with migraine, indicating that δ-opioid receptors are a promising therapeutic target for this disorder.

Anti-nociception mediated by a κ opioid receptor agonist is blocked by a δ receptor agonist

BACKGROUND AND PURPOSE

The opioid receptor family comprises four structurally homologous but functionally distinct sub-groups, the μ (MOP), δ (DOP), κ (KOP) and nociceptin (NOP) receptors. As most opioid agonists are selective but not specific, a broad spectrum of behaviours due to activation of different opioid receptors is expected. In this study, we examine whether other opioid receptor systems influenced KOP-mediated antinociception.

EXPERIMENTAL APPROACH

We used a tail withdrawal assay in C57Bl/6 mice to assay the antinociceptive effect of systemically administered opioid agonists with varying selectivity at KOP receptors. Pharmacological and genetic approaches were used to analyse the interactions of the other opioid receptors in modulating KOP-mediated antinociception.

KEY RESULTS

Etorphine, a potent agonist at all four opioid receptors, was not anti-nociceptive in MOP knockout (KO) mice, although etorphine is an efficacious KOP receptor agonist and specific KOP receptor agonists remain analgesic in MOP KO mice. As KOP receptor agonists are aversive, we considered KOP-mediated antinociception might be a form of stress-induced analgesia that is blocked by the anxiolytic effects of DOP receptor agonists. In support of this hypothesis, pretreatment with the DOP antagonist, naltrindole (10 mg·kg(-1) ), unmasked etorphine (3 mg·kg(-1) ) antinociception in MOP KO mice. Further, in wild-type mice, KOP-mediated antinociception by systemic U50,488H (10 mg·kg(-1) ) was blocked by pretreatment with the DOP agonist SNC80 (5 mg·kg(-1) ) and diazepam (1 mg·kg(-1) ).

CONCLUSIONS AND IMPLICATIONS

Systemic DOP receptor agonists blocked systemic KOP antinociception, and these results identify DOP receptor agonists as potential agents for reversing stress-driven addictive and depressive behaviours mediated through KOP receptor activation.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Evaluation of cre recombinase delivery in mammalian cells using baculovirus infection

In vivo conditional knock-out of a protein is a method of choice to decipher its biological function. It can be achieved by encoding the cre-recombinase on a recombinant virus to exert spatio-temporal control of its expression and enzymatic activity and, subsequently, of the target gene deletion. Recombinant baculoviruses have been successfully used to express a wide range of proteins in insect cells. More recently, their potential to infect mammalian cells has been addressed but, so far, their ability to yield a conditional knock-out as a result of efficient in vivo cre-recombinase gene delivery has not been examined. Cre-recombinase fused to the green fluorescent protein was cloned under the control of the CAG promoter in a recombinant Autographa californica baculovirus expressing the vesicular stomatitis virus envelope G protein for increased mammalian cell infection. Gene delivery was evaluated in vitro in mammalian cells, neuroblastoma and mouse primary neuronal cultures as well as in vivo in the mouse brain. Infection with adeno-associated viruses encoding the cre-recombinase fused to the green fluorescent protein was performed as a positive control. Our results indicate that baculovirus infection leads to functional cre-recombinase expression in non-neuronal and neuroblastoma cell lines but not in mouse primary neuronal cultures or brain.

Ligand-directed signalling within the opioid receptor family

The classic model of GPCR activation proposed that all agonists induce the same active receptor conformation. However, research over the last decade has shown that GPCRs exist in multiple conformations, and that agonists can stabilize different active states. The distinct receptor conformations induced by ligands result in distinct receptor-effector complexes, which produce varying levels of activation or inhibition of subsequent signalling cascades. This concept, referred to as ligand-directed signalling or biased agonism has important biological and therapeutic implications. Opioid receptors are G(i/o) GPCRs and regulate a number of important physiological functions, including pain, reward, mood, stress, gastrointestinal transport and respiration. A number of in vitro studies have shown biased agonism at the three opioid receptors (µ, δ and κ); however, in vivo consequences of this phenomenon have only recently been demonstrated. For the µ and δ opioid receptors, the majority of reported ligand selective behavioural effects are observed as differential adaptations to repeated drug administration. In terms of the κ opioid receptor, clear links between ligand-selective signalling events and specific in vivo responses have been recently characterized. Drugs for all three receptors are either already used or are being developed for clinical applications. There is clearly a need to better characterize the specific events that occur following agonist stimulation and how these relate to in vivo responses. This understanding could eventually lead to the development of tailor-made pharmacotherapies where advantageous drug effects can be selectively targeted over adverse effects.

Renal autotransplantation as savior in hybrid surgery for aortic aneurysm repair

Renal autotransplantation is a safe and effective procedure to reconstruct the urinary tract. The current indications for autotransplantation include renal vascular disease, severe ureteral damage, tumours of the kidney and ureter, complex nephrolithiasis and retroperitoneal fibrosis. We report a rare case where we had to perform renal autotransplantation along with hybrid surgery for aortic aneurysm repair. To our knowledge, this is the first case report of its kind for this specific condition.

Sequential and opposing alterations of 5-HT(1A) receptor function during withdrawal from chronic morphine

Addiction is a brain chronic relapsing disorder associated with emotional distress. The serotonergic system and especially the 5-HT(1A) receptor crucially regulate emotional behaviors both in humans and rodents. Using [(35)S]GTPγS autoradiography in mice, we show that 5-HT(1A) receptor function is enhanced by chronic morphine treatment in the medial prefrontal cortex, and decreased in dorsal raphe nucleus one week later, two regions involved in emotional processing. These molecular adaptations could contribute to the development of emotional disorders experienced by former opiate addicts.

The delta opioid receptor: an evolving target for the treatment of brain disorders

Compared to the better-known mu opioid receptor, delta opioid receptors have been relatively understudied. However, the development of highly selective delta opioid agonists and the availability of genetic mouse models have extended our knowledge of delta opioid receptors in vivo. Here we review recent developments in the characterization of delta opioid receptor biology and aspects of delta opioid receptor function that have potential for therapeutic targeting. Preclinical data have confirmed that delta opioid receptor activation reduces persistent pain and improves negative emotional states; clinical trials have been initiated to assess the effectiveness of delta opioid agonists in chronic pain and depression. Furthermore, a possible role for these receptors in neuroprotection is being investigated. The usefulness of targeting delta opioid receptors in drug abuse remains open and a role for these receptors in impulse control disorders is emerging. Finally, the recent demonstration of biased agonism at the delta opioid receptor in vivo opens novel perspectives towards targeting specific therapeutic effects through drug design.

Endopyelotomy - a Minimally Invasive Surgical Option for Pelvi-ureteric Junction Obstruction: a Study Of 34 Cases

We performed antegrade endopyelotomy in 34 cases in the last 2½ years. In all cases standardized antegrade percutaneous method was used. A single guide wire and a cold knife were used to perform the endopyelotomy. Nephrostomy tube was retained for 48 hours and the repair stented for 6 weeks. Patients were followed up at 3 months, 6 months and 1 year post-operatively for subjective improvement and objectively by DTPA scans/IVU and ultrasound. The population included 2 bilateral cases, one horseshoe kidney and 3 children. The patient's age ranged from 9-59 years, average 32 years. There were 21 males and 13 females. 28 renal units were primary and 8 were secondary pelviureteric junction (PUJ) obstruction. Follow up period was 3-28 months. Most cases had significant symptomatic and functional recovery postoperatively. Five cases presented with urinary tract infection, which regressed after treatment. At 3(rd) month postoperatively the DTPA/IVU scan was equivocal in 7 cases. In these, a RGP was done which in every case showed a patent PUJ. In 5 cases that were still symptomatic, 6-8 weeks of further stenting produced symptom regression. Two cases failed and needed revision, one by open pyeloplasty and the other by endopyelotomy. Our success rate overall in these cases followed upto 1 year post operatively is 91.6%. We conclude that endopyelotomy is successful across a wide spectrum of cases.

Warfarin use in atrial fibrillation: A random sample survey of family physician beliefs and preferences

BACKGROUND

In clinical practice, warfarin is underused for the prevention of stroke in individuals with atrial fibrillation despite unequivocal evidence of benefit and acceptable safety.

OBJECTIVE

To ascertain, from primary care physicians, their beliefs and preferences regarding the use of warfarin in patients with atrial fibrillation.

MATERIALS AND METHODS

A questionnaire was mailed to a random sample of 1000 primary care physicians in Ontario. Physician prescribing preferences from among treatment options available (warfarin, acetylsalicylic acid, ticlopidine, no therapy and other) were recorded for four separate scenarios of atrial fibrillation with varying degrees of risk for stroke. Physician perception of the risks associated with warfarin use and their awareness of the evidence of benefit were assessed.

RESULTS

Three hundred twenty-four physicians returned completed questionnaires. Among the four scenarios, physicians choosing not to use warfarin were three to six times more likely than physicians choosing to use warfarin to believe that there was inadequate evidence of benefit of warfarin for stroke prophylaxis, and they were four to six times more likely to be concerned about the risks of hemorrhage. These beliefs did not change significantly with scenarios describing patients with a high risk of stroke.

CONCLUSIONS

Physician reluctance to use warfarin is associated with a false understanding of the benefit to risk ratio, which arises from a low appreciation of therapeutic benefits and a high concern regarding hemorrhage.

Enhanced calcium signaling to bradykinin in airway smooth muscle from hyperresponsive inbred rats

Inbred Fischer 344 rats display airway hyperresponsiveness (AHR) in vivo compared with the normoresponsive Lewis strain. Fischer AHR has been linked with increased airway smooth muscle (ASM) contraction ex vivo and enhanced ASM cell intracellular Ca(2+) mobilization in response to serotonin compared with Lewis. To determine the generality of this association, we tested whether bradykinin (BK) also stimulates greater contraction of Fischer airways and greater Ca(2+) mobilization in Fischer ASM cells. Explants of Fischer intraparenchymal airways constricted faster and to a greater degree in response to BK than Lewis airways. BK also evoked higher Ca(2+) transients in Fischer than in Lewis ASM cells. ASM cell B(2) receptor expression was similar between the two strains. BK activated both phosphatidylinositide-specific phospholipase C (PI-PLC) and phosphatidylcholine-specific PLC to mobilize Ca(2+) in Fischer and Lewis ASM cells. PI-PLC activity, as measured by inositol polyphosphate accumulation, was similar in the two strains. PKC inhibition with GF109203X, Go6973, or Go6983 attenuated BK-mediated Ca(2+) transients in Fischer cells, whereas GF109203X potentiated while Go6976 and Go6983 did not affect Ca(2+) transients in Lewis cells. Enhanced Ca(2+) mobilization in ASM cells can arise from variations in PKC and may be an important component of nonspecific, innate AHR.

Supraspinal antinociceptive response to [D-Pen(2,5)]-enkephalin (DPDPE) is pharmacologically distinct from that to other delta-agonists in the rat

The cloned delta-opioid receptor (DOR) is being investigated as a potential target for novel analgesics with an improved safety profile over mu-opioid receptor agonists such as morphine. The current study used antisense techniques to evaluate the role of DOR in mediating supraspinal antinociception in rats. All of the opioid agonists tested (delta-selective: deltorphin II, DPDPE, pCl-DPDPE, SNC80; mu-selective: DAMGO; i.c.v.) provided significant, dose-dependent antinociception in the paw pressure assay. Administration of a phosphodiester antisense oligonucleotide (i.c.v. ) targeted against DOR inhibited antinociception in response to SNC80, deltorphin II, and pCl-DPDPE compared with mismatch and saline-treated controls. However, antisense treatment did not inhibit the response to DPDPE or DAMGO. In contrast, the highly selective mu-antagonist CTOP blocked antinociception in response to ED(80) concentrations of DAMGO and DPDPE, reduced the response to pCl-DPDPE, and did not alter the response to deltorphin II or SNC80. In total, these data suggest that DOR mediates the antinociceptive response to deltorphin II, SNC80, and pCl-DPDPE at supraspinal sites and further demonstrates that the DOR-mediated response to deltorphin II and SNC80 is independent of mu-receptor activation. Conversely, supraspinal antinociception in response to DPDPE is mediated by a receptor distinct from DOR; this response is directly or indirectly sensitive to mu-receptor blockade. The distinct pharmacological profile of DPDPE suggests that either this prototypical delta-agonist mediates antinociception by a direct, nonselective interaction at mu-receptors or DPDPE interacts with a novel delta-subtype that, in turn, indirectly activates mu-receptors in the brain.

Mechanisms of the potentiation by adenosine of adenosine triphosphate-induced calcium release in tracheal smooth-muscle cells

The effects of concomitant P1-receptor stimulation on peak intracellular Ca2+ release by extracellular adenosine 5'-triphosphate (ATP) and 5-hydroxytryptamine (5-HT) were investigated in cultured airway smooth-muscle (ASM) cells. The results show that peak Ca2+ release to ATP is enhanced by preincubation with adenosine (ADO) and with the specific A3 receptor agonist 1-Deoxy-1-(6-([(3-iodophenyl)methyl] amino)-9H-purin-9-yl)-N-methyl-beta-D-ribofuranuronamide (1B-MECA). The response to 5-HT, a smooth-muscle contractile agonist, was also enhanced after preincubation with ADO. Further measurements showed that this enhancement of the response to ATP was dependent on extracellular calcium because it was abolished by the removal of Ca2+ from the extracellular fluid and by incubation with the calcium channel blocker nifedipine. In addition, there was no difference between the levels of total inositol phosphates measured in the presence of ATP alone or of ADO + ATP. AACOCF3, a specific blocker of phospholipase A2, decreased the peak Ca2+ response to ATP and abolished the enhanced response to ATP and 5-HT produced by ADO. We conclude that stimulation of P1 and P2 receptors in ASM cells activates not only phospholipase C but also phospholipase A2. The enhancement of ATP-induced and 5-HT-induced Ca2+ release is due to Ca2+ influx from the extracellular fluid through a Ca2+ channel presumably modulated by arachidonic acid. These data show that endogenous ADO may modulate airway hyperresponsiveness by enhancing the ASM response to contractile agonists.

Colorectal screening patterns and perceptions of risk among African-American users of a community health center

This study investigated risk perceptions and screening patterns for colorectal cancer among predominately low-income African-Americans age 50 and older who used a community health center. The majority of respondents either rated their risk as below average (36%) or did not know their risk (37%) for colorectal cancer. Individuals who provided a risk estimate versus those who did not know their risk were younger and held more accurate beliefs about colorectal cancer. Attributions of perceived risk best distinguished respondents who evaluated their risk to be below average versus average and above average. Compared to respondents who could not explain their risk, those who provided psychological, personal action, and heredity causes were more likely to view their risk as below average than average or above average. In comparison to national norms, these subjects reported higher frequencies of ever having had a digital rectal exam (DRE, 90%), fecal occult blood test (FOBT, 75%) and sigmoidoscopy (SIG, 33%). Moreover, 63%, 53%, and 81% reported their most recent screening for DRE, FOBT, and SIG, respectively, in accordance with ACS and NCI recommended guidelines. However, a subsequent medical audit failed to confirm these self-reports. These results suggest that: 1) educational efforts are needed to enhance knowledge and accuracy of risk perceptions for colorectal cancer; 2) further studies on attributions of risk are needed that may prove useful for developing intervention programs, and 3) studies need to interpret self-report data for colorectal cancer with caution.

Microbial biosorption of copper and lead from aqueous systems

Biosorption of metal ions from aqueous systems was evaluated using a culture of acidic soil isolates grown in a completely mixed, aerobic, semi-batch culture reactor. The laboratory scale system was used to test single and bimetallic solutions of copper and lead with sulfates, chlorides, or nitrates. To elucidate the key factors influencing biosorption and to characterize metal uptake by cellular and extra cellular components of the microbial system, a dialysis testing procedure was developed. A direct contact technique was used to determine the rate of metal sorption on cellular surfaces. The effectiveness of biosorption was influenced by pH, initial metal concentrations, and anionic composition. Respirometric tests were carried out to identify potential inhibitory effects of metal accumulation on microbial oxygen uptake rates.