Spinal antinociceptive effect of epidural nonsteroidal antiinflammatory drugs on nitric oxide-induced hyperalgesia in rats

No preemptive analgesic effect of preoperative ketorolac administration following total abdominal hysterectomy: A randomized study

BACKGROUND

Experimental models using short-duration noxious stimuli have led to the concept of preemptive analgesia. Ketorolac, a nonsteroidal anti-inflammatory drug, has been shown to have a postoperative narcotic-sparing effect when given preoperatively and alternatively to not have this effect. This study was undertaken to determine whether a single intravenous (IV) dose of ketorolac would result in decreased postoperative pain and narcotic requirements.

METHODS

In a double-blind, randomized controlled trial, 48 women undergoing abdominal hysterectomy were studied. Patients in the ketorolac group received 30 mg of IV ketorolac 30 min before surgical incision, while the control group received normal saline. The postoperative analgesia was performed with a continuous infusion of tramadol at 12 mg/h with the possibility of a 10 mg bolus for every 10 min. Pain was assessed using the visual analog scale (VAS), tramadol consumption, and hemodynamic parameters at 0, 1, 2, 4, 8, 12, 16, and 24 h postoperatively. We quantified times to rescue analgesic (morphine), adverse effects, and patient satisfaction.

RESULTS

There were neither significant differences in VAS scores between groups (P > 0.05) nor in the cumulative or incremental consumption of tramadol at any time point (P > 0.05). The time to first requested rescue analgesia was 66.25 ± 38.61 min in the ketorolac group and 65 ± 28.86 min in the control group (P = 0.765). There were no significant differences in systolic blood pressure (BP) between both groups, except at 2 h (P = 0.02) and 4 h (P = 0.045). There were no significant differences in diastolic BP between both groups, except at 4 h (P = 0.013). The respiratory rate showed no differences between groups, except at 8 h (P = 0.017), 16 h (P = 0.011), and 24 h (P = 0.049). These differences were not clinically significant. There were no statistically significant differences between groups in heart rate (P > 0.05).

CONCLUSIONS

Preoperative ketorolac neither showed a preemptive analgesic effect nor was it effective as an adjuvant for decreasing opioid requirements or postoperative pain in patients receiving IV analgesia with tramadol after abdominal hysterectomy.

[Subarachnoid meloxicam does not inhibit the mechanical hypernociception on carrageenan test in rats]

BACKGROUND AND OBJECTIVE

Evaluate the antinociceptive effects of subarachnoid meloxicam on the mechanical hypernociception induced by carrageenan in rats.

METHODS

Randomized controlled trial. Eighteen adult male Wistar rats underwent a cannula implantation into the subarachnoid space and were randomly divided into two groups: Group I (GI) received saline solution 5μL, while Group II (GII) received meloxicam 30mg. The mechanical hypernociception was induced by intraplantar injection of carrageenan and evaluated using a digital analgesymeter every 30minutes during a 4 hour period. The results were recorded as the Δ withdrawal threshold (in g), calculated by subtracting the measurement value after

RESULTS

The Δ withdrawal threshold mean values were lower in the group of patients treated with meloxicam over all time points between 45 and 165minutes, however, there was no statistical significance, (p=0.835) for this difference.

CONCLUSION

Subarachnoid meloxicam at a dose of 30μg.animal(-1) did not suppress the mechanical hypernociception in a model of inflammatory pain induced by intraplantar administration of carrageenan in rats. The data suggest that other dosages should be investigated the drug effect is discarded.

Flexibilide obtained from cultured soft coral has anti-neuroinflammatory and analgesic effects through the upregulation of spinal transforming growth factor-β1 in neuropathic rats

Chronic neuroinflammation plays an important role in the development and maintenance of neuropathic pain. The compound flexibilide, which can be obtained from cultured soft coral, possesses anti-inflammatory and analgesic effects in the rat carrageenan peripheral inflammation model. In the present study, we investigated the antinociceptive properties of flexibilide in the rat chronic constriction injury (CCI) model of neuropathic pain. First, we found that a single intrathecal (i.t.) administration of flexibilide significantly attenuated CCI-induced thermal hyperalgesia at 14 days after surgery. Second, i.t. administration of 10-μg flexibilide twice daily was able to prevent the development of thermal hyperalgesia and weight-bearing deficits in CCI rats. Third, i.t. flexibilide significantly inhibited CCI-induced activation of microglia and astrocytes, as well as the upregulated proinflammatory enzyme, inducible nitric oxide synthase, in the ipsilateral spinal dorsal horn. Furthermore, flexibilide attenuated the CCI-induced downregulation of spinal transforming growth factor-β1 (TGF-β1) at 14 days after surgery. Finally, i.t. SB431542, a selective inhibitor of TGF-β type I receptor, blocked the analgesic effects of flexibilide in CCI rats. Our results suggest that flexibilide may serve as a therapeutic agent for neuropathic pain. In addition, spinal TGF-β1 may be involved in the anti-neuroinflammatory and analgesic effects of flexibilide.

Variants of neural nitric oxide synthase in the spinal cord of neuropathic rats and their effects on nuclear factor-kappaB (NF-kappaB) activity in PC12 cells

Neuropathic pain due to nerve injury is associated with overactivity of spinal N-methyl-D-aspartate (NMDA) receptors and nitric oxide synthases (NOS). Spinal NOS and NMDA receptors could act in a concerted manner to excite each other in nociceptive signaling. Among the 3 major NOS isoforms, neuronal NOS (nNOS) has the most functional relationship with NMDA receptors through a PDZ-PDZ (PSD-95, Dlg, ZO-1 homology) postsynapse interaction. However, some nNOS variants lack the PDZ domain, which may result in the changes in the interaction with the NMDA receptor and subsequent localization and enzymatic activity. The aim of this study was to determine which nNOS variants are expressed in the spinal cord in neuropathic rats and deduce their role in neuropathic pain by testing the effects of these kinds of nNOS on nuclear factor-kappaB (NF-kappaB) activity in PC12 cells. Western blot analysis revealed that there were at least 3 bands of nNOS (155, 135, and 125 kDa) in the spinal cord and, moreover, that nNOS at 135 kDa decreased significantly after development of neuropathic pain. 5'-RACE-PCR and Southern blots determined that the nNOS at 155 and 135 kDa corresponded to nNOSalpha and nNOSbeta, respectively, which was confirmed by RT-PCR. PC12 cells transfected with the nNOSalpha gene had no effect on NF-kappaB activity, but nNOSbeta without the PDZ domain significantly decreased that in PC12 cells. Considering the importance of spinal NF-kappaB signaling in neuropathic rat, it could be concluded that changes in spinal nNOS variants and quantity after peripheral nerve injury implicate nNOS in the generation of neuropathic pain.

PERSPECTIVE

This article presents data demonstrating that nNOS variants change in the spinal cord of the rats after neuropathic pain and result in differential effects on NF-kappaB activity in PC12 cells. These changes in nNOS variants and their different characteristics may account for the spinal NO paradox role in neuropathic pain. Furthermore, these data suggest that nNOSbeta may represent a new therapeutic target for the treatment of chronic neuropathic pain.

Epidural lornoxicam administration -- innocent

We aimed to determine the analgesic efficacy and clinical or histopathological neurotoxicity of epidural single-dose lornoxicam. Caudal epidural catheters were inserted into 28 rabbits, divided into four groups, on day 1. Pain latency and degree of motor and sensory loss for each animal for different concentrations of lornoxicam were determined on day 2. All animals were sacrificed on day 3 and laminectomy was performed. Five-mum thick sections of spinal cord, obtained from two segments caudal and two segments rostral from tip of the catheter, were fixed and were stained and evaluated by light microscopy. Lornoxicam produced dose-dependent analgesia (increase in pain latency), brief, mild and reversible motor and sensory block, and histopathological signs of neurotoxicity. Clinical application of epidural lornoxicam should proceed with caution.

Modulation of prostaglandin activity, part 1: prostaglandin inhibition in the management of nonrheumatologic diseases: immunologic and hematologic aspects

Prostaglandins (PGs) are active biologic substances that are involved in a wide range of physiologic processes; when their production is out of balance, they are factors in the pathogenesis of illness. Modulation of PGs by inhibition or stimulation is promising for the management of various conditions. PG inhibitors are widely used to relieve pain and inflammation in patients with rheumatologic disease. Interest in the use of PG inhibitors to prevent cancer and cardiovascular events is growing. More than 27 y ago, investigators found that PG depresses antibody production in vivo; reduces serum iron, hemoglobin, and leukoid series in bone marrow during acute and chronic blood loss; reduces albumin during antigenic stimulation; suppresses hypercalcemia after bleeding; and reduces fasting blood sugar and hyperglycemia after ether anesthesia and bleeding. Chronic conditions that produce large quantities of PGs are associated with immunosuppression and secondary anemia. Investigators in the present study hypothesized (1) that the overproduction of PGs is responsible for immunosuppression and secondary anemia in conditions associated with increased PG synthesis, such as pathologic inflammation, malignancy, trauma, and injury, and (2) that PG inhibitors reverse immunosuppression and secondary anemia, thereby enhancing the immune response. This is supported by many reports that show the immunosuppressive effects of PGs and their role in the immunosuppression associated with pathologic inflammation, burns, trauma, and tumors. Inhibition of PGs can be achieved through the use of synthetic medicines and natural products. This article reviews the effects of PGs and inhibition of increased synthesis of PGs on the lymphoid system, hematologic indices, and bone marrow elements in trauma, injury, burns, and tumors. The Medline database (1966-2006) was used in this study. Investigators in the present study and others have provided evidence that shows the involvement of PGs in immunosuppression and secondary anemia, as well as the efficacy of inhibited overproduction of PGs in many pathologic conditions other than rheumatologic disease.

Dynorphin-mediated antinociceptive effects of l-arginine and SIN-1 (an NO donor) in mice

The antinociceptive response of mice to the amino acid L-arginine (L-ARG) has been attributed to either an opioid mechanism or a non-opioid but nitric oxide (NO)-dependent mechanism. Earlier it was reported that the mechanism of nitrous oxide-induced antinociception involved opioid components and was also dependent on brain NO. This study was designed to determine whether the antinociceptive effects of L-ARG and the NO donor 3-morpholinosydnoimine (SIN-1) might be mediated by brain mechanisms similar to those that are responsible for nitrous oxide (N(2)O) antinociception. L-ARG and SIN-1 were administered to mice intracerebroventricularly (i.c.v.), and antinociception was assessed using the acetic acid abdominal constriction test. Both L-ARG and SIN-1 caused dose-related antinociceptive effects that were blocked by naloxone and norbinaltorphimine. The antinociceptive effects of both SIN-1 and L-ARG were also blocked to a greater extent by i.c.v. administration of a rabbit antiserum against rat dynorphin 1-13 than an antiserum against methionine-enkephalin, suggesting that the SIN-1 and L-ARG effects may be related to stimulated release of dynorphin. The antinociceptive effect of L-ARG was antagonized by an inhibitor of neuoronal NO synthase enzyme, indicating that L-ARG had to be converted to NO for its antinociceptive action. These findings indicate that the mechanisms of antinociceptive action of L-ARG and SIN-1 are both mediated by dynorphin and dependent on NO.

Prostaglandins, glutamate and nitric oxide synthase mediate nitroglycerin-induced hyperalgesia in the formalin test

Increasing evidence supports a possible role for nitric oxide (NO) in the transmission of pain signals and in the development of central mechanisms of hyperalgesia. Previously, we have shown that nitroglycerin, an NO donor, is able to induce a long-lasting hyperalgesic state in rats. Nitroglycerin-induced hyperalgesia can be detected as an increase in the nociceptive behavior evoked by the formalin test. In the present study we investigated the possible mediators in the nitroglycerin-induced hyperalgesic state. Male Sprague-Dawley rats were injected with nitroglycerin and pretreated with indomethacin, 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate (MK-801) or N(omega)-nitro-L-arginine methyl ester (L-NAME). The results obtained showed that inhibition of prostaglandins or NO synthesis prevents nitroglycerin-induced hyperalgesia in Phase II of the formalin test. A similar inhibitory effect was also observed following pretreatment with the glutamate antagonist MK801. The present findings point to the role of prostaglandins, NO synthesis and glutamate activity in the induction of nitroglycerin-induced hyperalgesia.

The Effects of Epidural Deracoxib on the Ground Reaction Forces in an Acute Stifle Synovitis Model

OBJECTIVE

To evaluate the efficacy of epidurally administered deracoxib to mediate the signs of a sodium urate crystal-induced stifle synovitis in dogs, and to compare the efficacy of epidural versus subcutaneously administered deracoxib.

STUDY DESIGN

Experimental, randomized, blinded, placebo-controlled modified cross-over design.

ANIMALS

Random source, adult, mixed breed dogs (n = 24; 14 males, 10 females).

METHODS

Sodium urate crystals were used to create a stifle synovitis model to evaluate the efficacy of deracoxib. Dogs were divided into 4 groups: 3 mg/kg epidural deracoxib, 1.5 mg/kg epidural deracoxib, 3 mg/kg subcutaneous deracoxib, and a placebo (vehicle for deracoxib). Force plate and subjective evaluations were made at time 0, 2, 4, 8, 12, and 24 hours post-treatment. Repeated measures ANOVA with Bonferroni-corrected post hoc comparisons was used to determine significant treatment effects.

RESULTS

Peak vertical force (PVF) and vertical impulse (VI) were both significantly higher in deracoxib treated dogs compared with placebo. For 3 mg/kg epidural and subcutaneous deracoxib, PVF and VI were significantly greater than for 1.5 mg/kg epidural deracoxib. Overall pain score for all deracoxib-treated dogs was significantly lower than for placebo dogs.

CONCLUSIONS

Epidural administration of deracoxib is effective at providing analgesia in an acute joint pain model; however, it does not appear to be more effective than systemic administration.

CLINICAL RELEVANCE

Injectable deracoxib is effective in providing analgesia in acute inflammatory conditions of synovial joints.

Pharmacokinetic-pharmacodynamic correlations and biomarkers in the development of COX-2 inhibitors

The mechanism by which COX inhibitors exert their analgesic effect is well established. However, data show no direct correlation between drug concentrations in plasma and the analgesic or adverse effects in chronic inflammatory conditions. This represents a major problem in the development of COX inhibitors, since it is difficult to predict the appropriate dosing regimen for the treatment of chronic inflammatory pain, based upon information from pre-clinical studies and eventually early clinical studies. The factors that determine response in inflammatory pain must be understood in order to make predictions about the time course of the analgesic effect. In this review the determinants of drug response and their variability will be discussed: physicochemical properties, pharmacokinetics (PK), pathophysiology and disease progression. From a mechanistic point of view, endogenous mediators of inflammation might be used as a biomarker for the analgesic effect and safety assessment. Such a biomarker can be an intermediate step between drug exposure and response. In addition, its concentration-effect relationship could be characterized by pharmacokinetic-pharmacodynamic (PK/PD) modelling. Indeed, recent investigations have shown that COX-2 inhibition, as determined by modelling of prostaglandin E2 (PGE2) levels in the whole blood assay in vitro can be used as a marker to predict drug effects (analgesia) in humans. A model-derived parameter, IC80, (total and unbound) was found to correlate directly with the analgesic plasma concentration of different COX inhibitors varying in enzyme selectivity. These findings indicate that PGE2 and thromboxane B2 inhibition can be used to predict and select efficacious doses in humans.

Investigations into the antinociceptive activity of Sapindus trifoliatus in various pain models

The effect of the aqueous extract of Sapindus trifoliatus (ST) on chemical, thermal-induced pain, nitroglycerin-induced hyperalgesia and pain on inflamed tissue was investigated. The extract (20 and 100 mg x kg(-1), i.p.) significantly inhibited acetic-acid-induced abdominal constrictions, formalin-induced pain licking and hotplate-induced pain in mice. Furthermore, the extract significantly increased the response latencies of nitroglycerin-induced hyperalgesia by the tail-flick method and mechanical pain on carrageenan-induced inflamed paw in rats. The data suggest that ST has an inhibitory activity on both peripheral and central pain mechanisms and has a modulatory role in NO-mediated nociceptive transmission.

The Effects of Remifentanil and Gabapentin on Hyperalgesia in a New Extended Inflammatory Skin Pain Model in Healthy Volunteers

We tested the responsiveness of measures of hyperalgesia in a model of UVB-induced inflammatory hyperalgesia with remifentanil, gabapentin, and the combination of both drugs in a double-blinded, active placebo-controlled, 4-way-crossover design in 16 volunteers. A circular skin area was irradiated with UVB-light 20 h before the application of gabapentin (600 mg) and 2 h later remifentanil (0.08 microg.kg(-1).min(-1), 40 min). In the sunburn spots we observed stable decreases of the heat pain perception thresholds (HPPT, mean difference, 4.45 degrees C; 95% confidence interval [CI], 3.32 degrees -5.59 degrees ) and heat pain tolerance thresholds (HPTT; mean difference, 5.43 degrees C; 95% CI, 4.50 degrees -6.35 degrees ) compared with normal skin. Further, large areas of mechanical hyperalgesia to pinprick adjacent to the erythema spots developed in all subjects. Overall remifentanil increased the HPPT (mean increase, 2.47 degrees C; 95% CI, 1.86 degrees -3.09 degrees, P < 0.001) and HPTT (mean increase, 3.18 degrees C; 95% CI, 2.65 degrees -3.71 degrees, P < 0.001) and reduced the area of secondary hyperalgesia by 59% (mean decrease, 5326 mm(2); 95% CI, 4233-6419 mm(2), P < 0.001) compared with placebo. In the sunburn remifentanil markedly increased the HPTT by 86% compared with normal skin (additional increase, 2.57 degrees C; 95% CI, 1.71 degrees -3.43 degrees). This different effect was not seen in the HPPT. With the exception of a small increase of HPTT in the sunburn (P = 0.02) gabapentin had no noticeable effect on either hyperalgesia. In conclusion, opioid analgesia was reliably demonstrated in this new extended pain model.

IMPLICATIONS

Opioid analgesia was reliably demonstrated in a new inflammatory model of primary and secondary hyperalgesia. Gabapentin showed no antihyperalgesic and no opioid-enhancing effect in this model.

Nitroglycerin induces hyperalgesia in rats--a time-course study

Nitroglycerin is a nitric oxide (NO) donor which activates nuclei involved in nociceptive transmission following systemic administration. The effect of nitroglycerin on the nociceptive threshold was studied in rats by means of two experimental tests that explore different modalities of pain: the tail-flick test and the formalin test. Nitroglycerin induced a significant reduction in the latency of the tail flick 2 and 4 h after its administration. Similarly, formalin-induced pain-related behaviour increased significantly 2 and 4 h after nitroglycerin administration.

Epidural injections of indomethacin for postlaminectomy syndrome: a preliminary report

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

Role of spinal nitric oxide in the inhibitory effect of [D-Pen2, D-Pen5]-enkephalin on ascending dorsal horn neurons in normal and diabetic rats

Intrathecal [D-Pen2,D-Pen5]-enkephalin (DPDPE; a delta-opioid agonist) has a profound antinociceptive effect in neuropathic pain. Spinal nitric oxide (NO) has been implicated in the analgesic effect of several G protein-coupled receptor agonists. Little, however, is known about the role of spinal NO in the inhibitory effect of DPDPE on spinal dorsal horn neurons. In the present study, we determined the role of NO in the inhibitory effect of DPDPE on ascending dorsal horn neurons in normal rats and in a rat model of diabetic neuropathic pain. Single-unit activity of ascending dorsal horn neurons was recorded in anesthetized rats. The responses of dorsal horn neurons to graded mechanical stimuli and von Frey filaments were determined before and after local spinal application of 0.1 to 5 microM DPDPE. The influence of an NO synthase inhibitor, 1-(2-trifluoromethylphenyl) imidazole (TRIM; 30 microM), on the effect of DPDPE was then studied in separate groups of dorsal horn neurons in normal and diabetic rats. DPDPE inhibited the response of dorsal horn neurons in both normal and diabetic rats in a concentration-dependent fashion. The inhibitory effect of 1 microM DPDPE was abolished by 1 microM naltrindole, a delta-opioid antagonist. Furthermore, the inhibitory effect of DPDPE on the evoked response of dorsal horn neurons was largely eliminated by TRIM in normal and diabetic rats. These data suggest that DPDPE has a profound inhibitory effect on dorsal horn neurons in normal and diabetic rats. Spinal endogenous NO is essential for the inhibitory effect of DPDPE on ascending dorsal horn neurons in both normal and diabetic rats.

Topical bicuculline to the rat spinal cord induces highly localized allodynia that is mediated by spinal prostaglandins

The purpose of this study was to investigate the allodynic effect of bicuculline (BIC) given topically to the dorsal surface of the rat spinal cord, and to determine if spinal prostaglandins (PGs) mediate the allodynic state arising from spinal GABA(A)-receptor blockade. Male Sprague-Dawley rats (325-400 g) were anaesthetized with halothane and maintained with urethane for the continuous monitoring of blood pressure (MAP), heart rate (HR) and cortical electroencephalogram (EEG). A laminectomy was performed to expose the dorsal surface of the spinal cord. Unilateral application of BIC (0.1 microg in 0.1 microl) to the L5 or L6 spinal segment induced a highly localized allodynia (e.g. one or two digits) on the ipsilateral hind paw. Thus, hair deflection (brushing the hair with a cotton-tipped applicator) in the presence, but not absence of BIC, evoked an increase in MAP and HR, abrupt motor responses (MR; e.g. withdrawal of the hind leg, kicking, and/or scratching) on the affected side, and desynchrony of the EEG. BIC-allodynia was dose-dependent, yielding ED(50)'s (95% CI's) of 45 ng (31-65) for MAP; 68 ng (46-101) for HR and 76 ng (60-97) for MR. Allodynia was sustained for up to 2 h with repeated BIC application without any detectable change in the location or area of peripheral sensitization. Pretreatment with either the EP(1)- receptor antagonist, SC-51322, the cyclooxygenase (COX)-2 selective inhibitor, NS-398, or the NMDA-receptor antagonist, AP-7, inhibited BIC-allodynia in a dose-dependent manner. The results demonstrate: (a) BIC, applied to the dorsal surface of the spinal cord, induces highly localized allodynia; (b) this effect can be sustained with repeated BIC application; (c) it is evoked by NMDA-dependent afferent input; (d) spinal PGs are synthesized by constitutive COX-2 during BIC-allodynia; and (e) spinal PGs contribute to the abnormal processing of tactile input via spinal EP1-receptors.