Translational control in the spinal cord regulates gene expression and pain hypersensitivity in the chronic phase of neuropathic pain.

Sensitization of spinal nociceptive circuits plays a crucial role in neuropathic pain. This sensitization depends on new gene expression that is primarily regulated via transcriptional and translational control mechanisms. The relative roles of these mechanisms in regulating gene expression in the clinically relevant chronic phase of neuropathic pain are not well understood. Here, we show that changes in gene expression in the spinal cord during the chronic phase of neuropathic pain are substantially regulated at the translational level. Downregulating spinal translation at the chronic phase alleviated pain hypersensitivity. Cell-type-specific profiling revealed that spinal inhibitory neurons exhibited greater changes in translation after peripheral nerve injury compared to excitatory neurons. Notably, increasing translation selectively in all inhibitory neurons or parvalbumin-positive (PV+) interneurons, but not excitatory neurons, promoted mechanical pain hypersensitivity. Furthermore, increasing translation in PV+ neurons decreased their intrinsic excitability and spiking activity, whereas reducing translation in spinal PV+ neurons prevented the nerve injury-induced decrease in excitability. Thus, translational control mechanisms in the spinal cord, particularly in inhibitory neurons, play a role in mediating neuropathic pain hypersensitivity.

Gys1 Antisense Therapy Prevents Disease-Driving Aggregates and Epileptiform Discharges in a Lafora Disease Mouse Model.

Patients with Lafora disease have a mutation in EPM2A or EPM2B, resulting in dysregulation of glycogen metabolism throughout the body and aberrant glycogen molecules that aggregate into Lafora bodies. Lafora bodies are particularly damaging in the brain, where the aggregation drives seizures with increasing severity and frequency, coupled with neurodegeneration. Previous work employed mouse genetic models to reduce glycogen synthesis by approximately 50%, and this strategy significantly reduced Lafora body formation and disease phenotypes. Therefore, an antisense oligonucleotide (ASO) was developed to reduce glycogen synthesis in the brain by targeting glycogen synthase 1 (Gys1). To test the distribution and efficacy of this drug, the Gys1-ASO was administered to Epm2b-/- mice via intracerebroventricular administration at 4, 7, and 10 months. The mice were then sacrificed at 13 months and their brains analyzed for Gys1 expression, glycogen aggregation, and neuronal excitability. The mice treated with Gys1-ASO exhibited decreased Gys1 protein levels, decreased glycogen aggregation, and reduced epileptiform discharges compared to untreated Epm2b-/- mice. This work provides proof of concept that a Gys1-ASO halts disease progression of EPM2B mutations of Lafora disease.

Tau-targeting antisense oligonucleotide MAPTRx in mild Alzheimer's disease: a phase 1b, randomized, placebo-controlled trial.

Tau plays a key role in Alzheimer's disease (AD) pathophysiology, and accumulating evidence suggests that lowering tau may reduce this pathology. We sought to inhibit MAPT expression with a tau-targeting antisense oligonucleotide (MAPTRx) and reduce tau levels in patients with mild AD. A randomized, double-blind, placebo-controlled, multiple-ascending dose phase 1b trial evaluated the safety, pharmacokinetics and target engagement of MAPTRx. Four ascending dose cohorts were enrolled sequentially and randomized 3:1 to intrathecal bolus administrations of MAPTRx or placebo every 4 or 12 weeks during the 13-week treatment period, followed by a 23 week post-treatment period. The primary endpoint was safety. The secondary endpoint was MAPTRx pharmacokinetics in cerebrospinal fluid (CSF). The prespecified key exploratory outcome was CSF total-tau protein concentration. Forty-six patients enrolled in the trial, of whom 34 were randomized to MAPTRx and 12 to placebo. Adverse events were reported in 94% of MAPTRx-treated patients and 75% of placebo-treated patients; all were mild or moderate. No serious adverse events were reported in MAPTRx-treated patients. Dose-dependent reduction in the CSF total-tau concentration was observed with greater than 50% mean reduction from baseline at 24 weeks post-last dose in the 60 mg (four doses) and 115 mg (two doses) MAPTRx groups. Clinicaltrials.gov registration number: NCT03186989 .

Convective forces increase rostral delivery of intrathecal radiotracers and antisense oligonucleotides in the cynomolgus monkey nervous system.

BACKGROUND: The intrathecal (IT) dosing route introduces drugs directly into the CSF to bypass the blood-brain barrier and gain direct access to the CNS. We evaluated the use of convective forces acting on the cerebrospinal fluid as a means for increasing rostral delivery of IT dosed radioactive tracer molecules and antisense oligonucleotides (ASO) in the monkey CNS. We also measured the cerebral spinal fluid (CSF) volume in a group of cynomolgus monkeys. METHODS: There are three studies presented, in each of which cynomolgus monkeys were injected into the IT space with radioactive tracer molecules and/or ASO by lumbar puncture in either a low or high volume. The first study used the radioactive tracer 64Cu-DOTA and PET imaging to evaluate the effect of the convective forces. The second study combined the injection of the radioactive tracer 99mTc-DTPA and ASO, then used SPECT imaging and ex vivo tissue analysis of the effects of convective forces to bridge between the tracer and the ASO distributions. The third experiment evaluated the effects of different injection volumes on the distribution of an ASO. In the course of performing these studies we also measured the CSF volume in the subject monkeys by Magnetic Resonance Imaging. RESULTS: It was consistently found that larger bolus dose volumes produced greater rostral distribution along the neuraxis. Thoracic percussive treatment also increased rostral distribution of low volume injections. There was little added benefit on distribution by combining the thoracic percussive treatment with the high-volume injection. The CSF volume of the monkeys was found to be 11.9 ± 1.6 cm3. CONCLUSIONS: These results indicate that increasing convective forces after IT injection increases distribution of molecules up the neuraxis. In particular, the use of high IT injection volumes will be useful to increase rostral CNS distribution of therapeutic ASOs for CNS diseases in the clinic.

Inhibition of spinal 15-LOX-1 attenuates TLR4-dependent, nonsteroidal anti-inflammatory drug-unresponsive hyperalgesia in male rats.

Although nonsteroidal anti-inflammatory drugs are the first line of therapeutics for the treatment of mild to moderate somatic pain, they are not generally considered to be effective for neuropathic pain. In the current study, direct activation of spinal Toll-like 4 receptors (TLR4) by the intrathecal (IT) administration of KDO2 lipid A (KLA), the active component of lipopolysaccharide, elicits a robust tactile allodynia that is unresponsive to cyclooxygenase inhibition, despite elevated expression of cyclooxygenase metabolites in the spinal cord. Intrathecal KLA increases 12-lipoxygenase-mediated hepoxilin production in the lumbar spinal cord, concurrent with expression of the tactile allodynia. The TLR4-induced hepoxilin production was also observed in primary spinal microglia, but not in astrocytes, and was accompanied by increased microglial expression of the 12/15-lipoxygenase enzyme 15-LOX-1. Intrathecal KLA-induced tactile allodynia was completely prevented by spinal pretreatment with the 12/15-lipoxygenase inhibitor CDC or a selective antibody targeting rat 15-LOX-1. Similarly, pretreatment with the selective inhibitors ML127 or ML351 both reduced activity of the rat homolog of 15-LOX-1 heterologously expressed in HEK-293T cells and completely abrogated nonsteroidal anti-inflammatory drug-unresponsive allodynia in vivo after IT KLA. Finally, spinal 12/15-lipoxygenase inhibition by nordihydroguaiaretic acid (NDGA) both prevents phase II formalin flinching and reverses formalin-induced persistent tactile allodynia. Taken together, these findings suggest that spinal TLR4-mediated hyperpathic states are mediated at least in part through activation of microglial 15-LOX-1.

Intrathecal administration of antisense oligonucleotide against p38α but not p38ß MAP kinase isoform reduces neuropathic and postoperative pain and TLR4-induced pain in male mice.

p38 mitogen-activated protein kinase (MAPK) consists of two major isoforms: p38α and p38ß; however, it remains unclear which isoform is more important for chronic pain development. Recently, we developed potent, long-lasting, and p38 MAPK subtype-specific antisense oligonucleotides (ASOs). We examined the therapeutic effects of isoform-specific ASOs in several chronic pain models following single intrathecal injection (300 µg/10 µl) in CD1 mice. In the chronic constriction injury (CCI) model, p38α MAPK ASO, given on post-operative day 5, reduced CCI-induced mechanical allodynia in male but not female mice. In contrast, mechanical allodynia after CCI in both sexes was not affected by p38ß MAPK ASO. Intrathecal injection of p38α or p38ß ASO resulted in a partial reduction (≈ 50%) of spinal p38α or p38ß mRNA level, respectively, in both sexes at two weeks. In contrast, intrathecal injection of the ASOs did not affect p38α and p38ß MAPK mRNA levels in dorsal root ganglia. Intrathecal p38α ASO also reduced postoperative pain (mechanical and cold allodynia) in male mice after tibia fracture. However, intrathecal p38α ASO had no effect on mechanical allodynia in male mice after paclitaxel treatment. Intrathecal p38α MAPK ASO pre-treatment also prevented TLR4-mediated mechanical allodynia and downregulated levels of p38α MAPK and phosphorylated p38 MAPK following intrathecal treatment of lipopolysaccharide. In summary, our findings suggest that p38α MAPK is the major p38 MAPK isoform in the spinal cord and regulates chronic pain in a sex and model-dependent manner. Intrathecal p38α MAPK ASO may offer a new treatment for some chronic pain conditions.

Antisense oligonucleotides selectively suppress target RNA in nociceptive neurons of the pain system and can ameliorate mechanical pain.

There is an urgent need for better treatments for chronic pain, which affects more than 1 billion people worldwide. Antisense oligonucleotides (ASOs) have proven successful in treating children with spinal muscular atrophy, a severe infantile neurological disorder, and several ASOs are currently being tested in clinical trials for various neurological disorders. Here, we characterize the pharmacodynamic activity of ASOs in spinal cord and dorsal root ganglia (DRG), key tissues for pain signaling. We demonstrate that activity of ASOs lasts up to 2 months after a single intrathecal bolus dose. Interestingly, comparison of subcutaneous, intracerebroventricular, and intrathecal administration shows that DRGs are targetable by systemic and central delivery of ASOs, while target reduction in the spinal cord is achieved only after direct central delivery. Upon detailed characterization of ASO activity in individual cell populations in DRG, we observe robust target suppression in all neuronal populations, thereby establishing that ASOs are effective in the cell populations involved in pain propagation. Furthermore, we confirm that ASOs are selective and do not modulate basal pain sensation. We also demonstrate that ASOs targeting the sodium channel Nav1.7 induce sustained analgesia up to 4 weeks. Taken together, our findings support the idea that ASOs possess the required pharmacodynamic properties, along with a long duration of action beneficial for treating pain.

Development of a simple, rapid, and robust intrathecal catheterization method in the rat.

BACKGROUND: The blood brain barrier (BBB) is an impediment to the development of large and highly charged molecules as therapeutics for diseases and injuries of the central nervous system (CNS). Antisense oligonucleotides (ASOs) are large (6000-8000MW) and highly charged and therefore do not cross the BBB. A method of circumventing the blood brain barrier to test ASOs, and other non-BBB penetrant molecules, as CNS therapeutics is the direct administration of these molecules to the CNS tissue or cerebral spinal fluid. NEW METHOD: We developed a rapid, simple and robust method for the intrathecal catheterization of rats to test putatively therapeutic antisense oligonucleotides. This method utilizes 23-gauge needles, simply constructed ½in. long 19-gauge guide cannulas and 8cm long plastic PE-10 sized catheters. COMPARISON WITH EXISTING METHODS: Unlike the cisterna magna approach, this method uses a lumbar approach for intrathecal catheterization with the catheter residing entirely in the cauda equina space minimizing spinal cord compression. Readily available materials and only a few specialized pieces of equipment, which are easily manufactured, are used for this intrathecal catheterization method. CONCLUSIONS: This method is easy to learn and has been taught to multiple in house surgeons, collaborators and contract laboratories. Greater than 90% catheterization success is routinely achieved with this method and as many as 100 catheters can be placed and test substance administered in one 6-h period. This method has allowed the pre-clinical testing of hundreds of ASOs as therapeutics for CNS indications.

Intrathecal neurosteroids and a neurosteroid antagonist: effects on inflammation-evoked thermal hyperalgesia and tactile allodynia.

Neurosteroids regulate neuronal excitability though binding sites associated with the ionotropic γ-aminobutyric acid (GABAA) receptor. We sought to characterize the spinal analgesic actions in rats of two 5α-reduced neurosteroids, allopregnanolone and alphaxalone, on nociceptive processing and to determine whether a putative neurosteroid antagonist attenuates this effect: (3α,5α)-17-phenylandrost-16-en-3-ol (17PA). Intrathecal (IT) injection of allopregnanolone (1-30 µg/10 µL in 20% cyclodextrin) delivered through lumbar catheters produced a dose-dependent analgesia in rats as measured by thermal thresholds in the ipsilateral (inflamed by intraplantar carrageenan) and in the contralateral (un-inflamed paws). Similar observations were made with alphaxalone (30-60 µg in 20% cyclodextrin). Effective doses were not associated with suppressive effects on pinnae, blink or placing and stepping reflex. Effects of allopregnanolone (30 µg) on the normal and hyperalgesic paw were completely prevented by IT 17PA (30 µg). Reversal by IT 17PA of an equi-analgesic dose of alphaxalone occurred only at higher antagonist dosing. These results suggest that a spinal neurosteroid-binding site with which 17PA interacts may regulate spinal nociceptive processing in normal and inflamed tissue.

Evaluation of spinal toxicity and long-term spinal reflex function after intrathecal levobupivaciane in the neonatal rat.

BACKGROUND: Neuraxial anesthesia is utilized in children of all ages. Local anesthetics produce dose-dependent toxicity in certain adult models, but the developing spinal cord may also be susceptible to drug-induced apoptosis. In postnatal rodents, we examined the effects of intrathecal levobupivacaine on neuropathology and long-term sensorimotor outcomes. METHODS: Postnatal day 3 (P3) or P7 rat pups received intrathecal levobupivacaine 2.5 mg/kg (0.5%) or saline. Mechanical withdrawal thresholds and motor block were assessed. Spinal cord tissue analysis included apoptosis counts (activated caspase-3, Fluoro-Jade C) at 24 h, glial reactivity at 7 days, and histopathology in cord and cauda equina at 24 h and 7 days. Long-term spinal function in young adults (P35) was assessed by hind limb withdrawal thresholds, electromyography responses to suprathreshold stimuli, and gait analysis. RESULTS: Intrathecal levobupivacaine produced spinal anesthesia at P3 and P7. No increase in apoptosis or histopathological change was seen in the cord or cauda equina. In the P3 saline group, activated caspase-3 (mean±SEM per lumbar cord section 6.1±0.3) and Fluoro-Jade C (12.1±1.2) counts were higher than at P7, but were not altered by levobupivacaine (P=0.62 and P=0.11, two-tailed Mann-Whitney test). At P35, mechanical withdrawal thresholds, thermal withdrawal latency, and electromyographic reflex responses did not differ across P3 or P7 levobupivacaine or saline groups (one way ANOVA with Bonferroni comparisons). Intrathecal bupivacaine at P3 did not alter gait. CONCLUSION: Single dose intrathecal levobupivacaine 0.5% did not increase apoptosis or produce spinal toxicity in neonatal rat pups. This study provides preclinical safety data relevant to neonatal use of neuraxial local anesthesia.

Systematic analysis of rat 12/15-lipoxygenase enzymes reveals critical role for spinal eLOX3 hepoxilin synthase activity in inflammatory hyperalgesia.

Previously, we observed significant increases in spinal 12-lipoxygenase (LOX) metabolites, in particular, hepoxilins, which contribute to peripheral inflammation-induced tactile allodynia. However, the enzymatic sources of hepoxilin synthase (HXS) activity in rats remain elusive. Therefore, we overexpressed each of the 6 rat 12/15-LOX enzymes in HEK-293T cells and measured by LC-MS/MS the formation of HXB3, 12-HETE, 8-HETE, and 15-HETE from arachidonic acid (AA) at baseline and in the presence of LOX inhibitors (NDGA, AA-861, CDC, baicalein, and PD146176) vs. vehicle-treated and mock-transfected controls. We detected the following primary intrinsic activities: 12-LOX (Alox12, Alox15), 15-LOX (Alox15b), and HXS (Alox12, Alox15). Similar to human and mouse orthologs, proteins encoded by rat Alox12b and Alox12e possessed minimal 12-LOX activity with AA as substrate, while eLOX3 (encoded by Aloxe3) exhibited HXS without 12-LOX activity when coexpressed with Alox12b or supplemented with 12-HpETE. CDC potently inhibited HXS and 12-LOX activity in vitro (relative IC50s: CDC, ~0.5 and 0.8 µM, respectively) and carrageenan-evoked tactile allodynia in vivo. Notably, peripheral inflammation significantly increased spinal eLOX3; intrathecal pretreatment with either siRNA targeting Aloxe3 or an eLOX3-selective antibody attenuated the associated allodynia. These findings implicate spinal eLOX3-mediated hepoxilin synthesis in inflammatory hyperesthesia and underscore the importance of developing more selective 12-LOX/HXS inhibitors.

Spinal astrocytes produce and secrete dynorphin neuropeptides.

Dynorphin peptide neurotransmitters (neuropeptides) have been implicated in spinal pain processing based on the observations that intrathecal delivery of dynorphin results in proalgesic effects and disruption of extracellular dynorphin activity (by antisera) prevents injury evoked hyperalgesia. However, the cellular source of secreted spinal dynorphin has been unknown. For this reason, this study investigated the expression and secretion of dynorphin-related neuropeptides from spinal astrocytes (rat) in primary culture. Dynorphin A (1-17), dynorphin B, and α-neoendorphin were found to be present in the astrocytes, illustrated by immunofluorescence confocal microscopy, in a discrete punctate pattern of cellular localization. Measurement of astrocyte cellular levels of these dynorphins by radioimmunoassays confirmed the expression of these three dynorphin-related neuropeptides. Notably, BzATP (3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate) and KLA (di[3-deoxy-D-manno-octulosonyl]-lipid A) activation of purinergic and toll-like receptors, respectively, resulted in stimulated secretion of dynorphins A and B. However, α-neoendorphin secretion was not affected by BzATP or KLA. These findings suggest that dynorphins A and B undergo regulated secretion from spinal astrocytes. These findings also suggest that spinal astrocytes may provide secreted dynorphins that participate in spinal pain processing.

Spinal 12-lipoxygenase-derived hepoxilin A3 contributes to inflammatory hyperalgesia via activation of TRPV1 and TRPA1 receptors.

Peripheral inflammation initiates changes in spinal nociceptive processing leading to hyperalgesia. Previously, we demonstrated that among 102 lipid species detected by LC-MS/MS analysis in rat spinal cord, the most notable increases that occur after intraplantar carrageenan are metabolites of 12-lipoxygenases (12-LOX), particularly hepoxilins (HXA(3) and HXB(3)). Thus, we examined involvement of spinal LOX enzymes in inflammatory hyperalgesia. In the current work, we found that intrathecal (IT) delivery of the LOX inhibitor nordihydroguaiaretic acid prevented the carrageenan-evoked increase in spinal HXB(3) at doses that attenuated the associated hyperalgesia. Furthermore, IT delivery of inhibitors targeting 12-LOX (CDC, Baicalein), but not 5-LOX (Zileuton) dose-dependently attenuated tactile allodynia. Similarly, IT delivery of 12-LOX metabolites of arachidonic acid 12(S)-HpETE, 12(S)-HETE, HXA(3), or HXB(3) evoked profound, persistent tactile allodynia, but 12(S)-HpETE and HXA(3) produced relatively modest, transient heat hyperalgesia. The pronociceptive effect of HXA(3) correlated with enhanced release of Substance P from primary sensory afferents. Importantly, HXA(3) triggered sustained mobilization of calcium in cells stably overexpressing TRPV1 or TRPA1 receptors and in acutely dissociated rodent sensory neurons. Constitutive deletion or antagonists of TRPV1 (AMG9810) or TRPA1 (HC030031) attenuated this action. Furthermore, pretreatment with antihyperalgesic doses of AMG9810 or HC030031 reduced spinal HXA(3)-evoked allodynia. These data indicate that spinal HXA(3) is increased by peripheral inflammation and promotes initiation of facilitated nociceptive processing through direct activation of TRPV1 and TRPA1 at central terminals.

In vivo gene knockdown in rat dorsal root ganglia mediated by self-complementary adeno-associated virus serotype 5 following intrathecal delivery.

We report here in adult rat viral vector mediate-gene knockdown in the primary sensory neurons and the associated cellular and behavior consequences. Self-complementary adeno-associated virus serotype 5 (AAV5) was constructed to express green fluorescent protein (GFP) and a small interfering RNA (siRNA) targeting mammalian target of rapamycin (mTOR). The AAV vectors were injected via an intrathecal catheter. We observed profound GFP expression in lumbar DRG neurons beginning at 2-week post-injection. Of those neurons, over 85% were large to medium-diameter and co-labeled with NF200, a marker for myelinated fibers. Western blotting of mTOR revealed an 80% reduction in the lumbar DRGs (L4-L6) of rats treated with the active siRNA vectors compared to the control siRNA vector. Gene knockdown became apparent as early as 7-day post-injection and lasted for at least 5 weeks. Importantly, mTOR knockdown occurred in large (NF200) and small-diameter neurons (nociceptors). The viral administration induced an increase of Iba1 immunoreactivity in the DRGs, which was likely attributed to the expression of GFP but not siRNA. Rats with mTOR knockdown in DRG neurons showed normal general behavior and unaltered responses to noxious stimuli. In conclusion, intrathecal AAV5 is a highly efficient vehicle to deliver siRNA and generate gene knockdown in DRG neurons. This will be valuable for both basic research and clinic intervention of diseases involving primary sensory neurons.

Spinal phosphinositide 3-kinase-Akt-mammalian target of rapamycin signaling cascades in inflammation-induced hyperalgesia.

Phosphinositide 3-kinase (PI3K), Akt, and their downstream kinase, mammalian target of rapamycin (mTOR), are implicated in neural plasticity. The functional linkages of this signaling cascade in spinal dorsal horn and their role in inflammatory hyperalgesia have not been elucidated. In the present work, we identified the following characteristics of this cascade. (1) Local inflammation led to increase in rat dorsal horn phosphorylation (activation) of Akt (pAkt) and mTOR (pmTOR), as assessed by Western blotting and immunocytochemistry. (2) Increased pAkt and pmTOR were prominent in neurons in laminae I, III, and IV, whereas pmTOR and its downstream targets (pS6, p4EBP) were also observed in glial cells. (3) Intrathecal treatment with inhibitors to PI3K or Akt attenuated Formalin-induced second-phase flinching behavior, as well as carrageenan-induced thermal hyperalgesia and tactile allodynia. (4) Intrathecal rapamycin (an mTORC1 inhibitor) displayed anti-hyperalgesic effect in both inflammatory pain models. Importantly, intrathecal wortmannin at anti-hyperalgesic doses reversed the evoked increase not only in Akt but also in mTORC1 signaling (pS6/p4EBP). (5) pAkt and pmTOR are expressed in neurokinin 1 receptor-positive neurons in laminae I-III after peripheral inflammation. Intrathecal injection of Substance P activated this cascade (increased phosphorylation) and resulted in hyperalgesia, both of which effects were blocked by intrathecal wortmannin and rapamycin. Together, these findings reveal that afferent inputs trigged by peripheral inflammation initiate spinal activation of PI3K-Akt-mTOR signaling pathway, a component of which participates in neuronal circuits of facilitated pain processing.

Inflammatory hyperalgesia induces essential bioactive lipid production in the spinal cord.

Lipid molecules play an important role in regulating the sensitivity of sensory neurons and enhancing pain perception, and growing evidence indicates that the effect occurs both at the site of injury and in the spinal cord. Using high-throughput mass spectrometry methodology, we sought to determine the contribution of spinal bioactive lipid species to inflammation-induced hyperalgesia in rats. Quantitative analysis of CSF and spinal cord tissue for eicosanoids, ethanolamides and fatty acids revealed the presence of 102 distinct lipid species. After induction of peripheral inflammation by intra-plantar injection of carrageenan to the ipsilateral hind paw, lipid changes in cyclooxygenase (COX) and 12-lipoxygenase (12-LOX) signaling pathways peaked at 4 h in the CSF. In contrast, changes occurred in a temporally disparate manner in the spinal cord with LOX-derived hepoxilins followed by COX-derived prostaglandin E(2), and subsequently the ethanolamine anandamide. Systemic treatment with the mu opioid agonist morphine, the COX inhibitor ketorolac, or the LOX inhibitor nordihydroguaiaretic acid significantly reduced tactile allodynia, while their effects on the lipid metabolites were different. Morphine did not alter the lipid profile in the presence or absence of carrageenan inflammation. Ketorolac caused a global reduction in eicosanoid metabolism in naïve animals that remained suppressed following injection of carrageenan. Nordihydroguaiaretic acid-treated animals also displayed reduced basal levels of COX and 12-LOX metabolites, but only 12-LOX metabolites remained decreased after carrageenan treatment. These findings suggest that both COX and 12-LOX play an important role in the induction of carrageenan-mediated hyperalgesia through these pathways.

Role of spinal p38alpha and beta MAPK in inflammatory hyperalgesia and spinal COX-2 expression.

Pharmacological studies indicate that spinal p38 mitogen-activated protein kinase plays a role in the development of hyperalgesia. We investigated whether either the spinal isoform p38alpha or p38beta is involved in peripheral inflammation evoked pain state and increased expression of spinal COX-2. Using intrathecal antisense oligonucleotides, we show that hyperalgesia is prevented by downregulation of p38beta but not p38alpha, whereas increases in spinal COX-2 protein expression at 8 hours are mediated by both p38alpha and beta isoforms. These data suggest that early activation of spinal p38beta isoform may affect acute facilitatory processing, and both p38beta and alpha isoforms mediate temporally delayed upregulation of spinal COX-2.

Acetaminophen prevents hyperalgesia in central pain cascade.

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

Inhibition of spinal constitutive NOS-2 by 1400W attenuates tissue injury and inflammation-induced hyperalgesia and spinal p38 activation.

Nitric oxide (NO) and its synthesizing enzymes, including NO synthase-2 (NOS-2, also called inducible NOS, iNOS), have been implicated in spinal nociception. 1400W is a highly selective NOS-2 inhibitor, as compared with either NOS-1 (neuronal NOS, nNOS) or NOS-3 (endothelial NOS). Here we examined the anti-nociceptive effects of intrathecal (IT) administration of 1400W in two experimental models of hyperalgesia (formalin and carrageenan models), in addition to the effect of 1400W on stimulation-induced activation of spinal p38 mitogen-activated protein kinase (p38). IT treatment of rats with 1400W produced a dose-dependent inhibition of paw formalin-induced phase II flinches, and attenuated carrageenan-induced thermal hyperalgesia. In contrast, IT injection of a selective inhibitor of NOS-1, nNOS inhibitor-I, had no effect in either model. Furthermore, 1400W at a dose that suppressed formalin-induced flinching behavior also blocked formalin-evoked p38 phosphorylation (activation) in the spinal cord, while nNOS inhibitor-I displayed no activity. The prompt effects of IT 1400W suggest involvement of constitutively expressed NOS-2 in spinal nociception. The NOS-2 protein in rat spinal cords was undetectable by Western blotting. However, when the protein was immunoprecipitated prior to Western blotting, NOS-2-immunoreactive bands were detected in the tissues, including naïve spinal cords. The presence of constitutive spinal NOS-2 was further confirmed by reverse transcriptase-polymerase chain reaction. Taken together, the present studies suggest that constitutively expressed spinal NOS-2 mediates tissue injury and inflammation-induced hyperalgesia, and that activation of p38 is one of the downstream factors in NO-mediated signaling in the initial processing of spinal nociception.