Urinary bladder sigma-1 receptors: A new target for cystitis treatment.

No adequate treatment is available for painful urinary bladder disorders such as interstitial cystitis/bladder pain syndrome, and the identification of new urological therapeutic targets is an unmet need. The sigma-1 receptor (σ1-R) modulates somatic pain, but its role in painful urological disorders is unexplored. The urothelium expresses many receptors typical of primary sensory neurons (e.g. TRPV1, TRPA1 and P2X3) and high levels of σ1-R have been found in these neurons; we therefore hypothesized that σ1-R may also be expressed in the urothelium and may have functional relevance in this tissue. With western blotting and immunohistochemical methods, we detected σ1-R in the urinary bladder in wild-type (WT) but not in σ1-R-knockout (σ1-KO) mice. Interestingly, σ1-R was located in the bladder urothelium not only in mouse, but also in human bladder sections. The severity of histopathological (edema, hemorrhage and urothelial desquamation) and biochemical alterations (enhanced myeloperoxidase activity and phosphorylation of extracellular regulated kinases 1/2 [pERK1/2]) that characterize cyclophosphamide-induced cystitis was lower in σ1-KO than in WT mice. Moreover, cyclophosphamide-induced pain behaviors and referred mechanical hyperalgesia were dose-dependently reduced by σ1-R antagonists (BD-1063, NE-100 and S1RA) in WT but not in σ1-KO mice. In contrast, the analgesic effect of morphine was greater in σ1-KO than in WT mice. Together these findings suggest that σ1-R plays a functional role in the mechanisms underlying cyclophosphamide-induced cystitis, and modulates morphine analgesia against urological pain. Therefore, σ1-R may represent a new drug target for urinary bladder disorders.

Genetic inactivation and pharmacological blockade of sigma-1 receptors prevent paclitaxel-induced sensory-nerve mitochondrial abnormalities and neuropathic pain in mice.

BACKGROUND: Paclitaxel, a widely-used antineoplastic drug, produces a painful peripheral neuropathy that in rodents is associated with peripheral-nerve mitochondrial alterations. The sigma-1 receptor (σ1R) is a ligand-regulated molecular chaperone involved in mitochondrial calcium homeostasis and pain hypersensitivity. This receptor plays a key role in paclitaxel-induced neuropathic pain, but it is not known whether it also modulates mitochondrial abnormalities.In this study, we used a mouse model of paclitaxel-induced neuropathic pain to test the involvement of the σ1R in the mitochondrial abnormalities associated with paclitaxel, by using genetic (σ1R knockout mice) and pharmacological (σ1R antagonist) approaches. RESULTS: Paclitaxel administration to wild-type (WT) mice produced cold- and mechanical-allodynia, and an increase in the frequency of swollen and vacuolated mitochondria in myelinated A-fibers, but not in C-fibers, of the saphenous nerve. Behavioral and mitochondrial alterations were marked at 10 days after paclitaxel-administration and had resolved at day 28. In contrast, paclitaxel treatment did not induce allodynia or mitochondrial abnormalities in σ1R knockout mice. Moreover, the prophylactic treatment of WT mice with BD-1063 also prevented the neuropathic pain and mitochondrial abnormalities induced by paclitaxel. CONCLUSIONS: These results suggest that activation of the σ1R is necessary for development of the sensory nerve mitochondrial damage and neuropathic pain produced by paclitaxel. Therefore, σ1R antagonists might have therapeutic value for the prevention of paclitaxel-induced neuropathy.

σ1 receptors are involved in the visceral pain induced by intracolonic administration of capsaicin in mice.

BACKGROUND: Visceral pain is an important and prevalent clinical condition whose treatment is challenging. Sigma-1 (σ1) receptors modulate somatic pain, but their involvement in pure visceral pain is unexplored. METHODS: The authors evaluated the role of σ1 receptors in intracolonic capsaicin-induced visceral pain (pain-related behaviors and referred mechanical hyperalgesia to the abdominal wall) using wild-type (WT) (n = 12 per group) and σ1 receptor knockout (σ1-KO) (n = 10 per group) mice, selective σ1 receptor antagonists (BD-1063, S1RA, and NE-100), and control drugs (morphine and ketoprofen). RESULTS: The intracolonic administration of capsaicin (0.01-1%) induced concentration-dependent visceral pain-related behaviors and referred hyperalgesia in both WT and σ1-KO mice. However, the maximum number of pain-related behaviors induced by 1% capsaicin in σ1-KO mice (mean ± SEM, 22 ± 2.9) was 48% of that observed in WT animals (46 ± 4.2). Subcutaneous administration of the σ1 receptor antagonists BD-1063 (16-64 mg/kg), S1RA (32-128 mg/kg), and NE-100 (8-64 mg/kg) dose-dependently reduced the number of behavioral responses (by 53, 62, and 58%, respectively) and reversed the referred hyperalgesia to mechanical control threshold (0.53 ± 0.05 g) in WT mice. In contrast, these drugs produced no change in σ1-KO mice. Thus, the effects of these drugs are specifically mediated by σ1 receptors. Morphine produced an inhibition of capsaicin-induced visceral pain in WT and σ1-KO mice, whereas ketoprofen had no effect in either mouse type. CONCLUSION: These results suggest that σ1 receptors play a role in the mechanisms underlying capsaicin-induced visceral pain and raise novel perspectives for their potential therapeutic value.

Nociceptor-expressed ephrin-B2 regulates inflammatory and neuropathic pain.

BACKGROUND: EphB receptors and their ephrin-B ligands play an important role in nervous system development, as well as synapse formation and plasticity in the adult brain. Recent studies show that intrathecal treatment with EphB-receptor activator ephrinB2-Fc induced thermal hyperalgesia and mechanical allodynia in rat, indicating that ephrin-B2 in small dorsal root ganglia (DRG) neurons and EphB receptors in the spinal cord modulate pain processing. To examine the role of ephrin-B2 in peripheral pain pathways, we deleted ephrin-B2 in Nav1.8+ nociceptive sensory neurons with the Cre-loxP system. Sensory neuron numbers and terminals were examined using neuronal makers. Pain behavior in acute, inflammatory and neuropathic pain models was assessed in the ephrin-B2 conditional knockout (CKO) mice. We also investigated the c-Fos expression and NMDA receptor NR2B phosphorylation in ephrin-B2 CKO mice and littermate controls. RESULTS: The ephrin-B2 CKO mice were healthy with no sensory neuron loss. However, pain-related behavior was substantially altered. Although acute pain behavior and motor co-ordination were normal, inflammatory pain was attenuated in ephrin-B2 mutant mice. Complete Freund's adjuvant (CFA)-induced mechanical hyperalgesia was halved. Formalin-induced pain behavior was attenuated in the second phase, and this correlated with diminished tyrosine phosphorylation of N-methyl-D-aspartic acid (NMDA) receptor subunit NR2B in the dorsal horn. Thermal hyperalgesia and mechanical allodynia were significantly reduced in the Seltzer model of neuropathic pain. CONCLUSIONS: Presynaptic ephrin-B2 expression thus plays an important role in regulating inflammatory pain through the regulation of synaptic plasticity in the dorsal horn and is also involved in the pathogenesis of some types of neuropathic pain.

Antinociceptive effects of haloperidol and its metabolites in the formalin test in mice.

RATIONALE: Formalin-induced pain is reduced in sigma-1 (sigma1) receptor knockout mice; therefore, we hypothesized that haloperidol and its metabolites I and II, which have affinity for sigma1 receptors, may modulate formalin-induced pain. RESULTS: Intraplantar administration of formalin (2.5%) to CD-1 mice produced a biphasic period of pain. Haloperidol (0.03-1 mg/kg, s.c.) and reduced haloperidol (metabolite II, 0.25-8 mg/kg, s.c.) dose-dependently inhibited both phases of formalin-induced pain. Haloperidol metabolite I (4-128 mg/kg, s.c.) also produced dose-dependent antinociception in the second phase of the formalin test, but was less potent and effective against first-phase pain. Haloperidol metabolite III (16 and 128 mg/kg) and (-)sulpiride (200 mg/kg), which have no affinity for sigma1 receptors, did not produce significant antinociception in either phase of the formalin test. The order of potency of the drugs to produce their antinociceptive effect [haloperidol>metabolite II>metabolite I>>metabolite III= (-)sulpiride=inactive] correlated with their affinity for sigma1 receptors, but not with their affinity for sigma2 or dopamine D2 receptors. Naloxone (1 mg/kg, s.c.) did not antagonize the antinociception induced by haloperidol and its metabolites. None of the antinociceptive drugs in the formalin test produced any antinociception in the tail flick test. CONCLUSION: These results suggest that the antinociceptive effect of haloperidol and its metabolites in the formalin test is not due to unspecific/generalised inhibition of nociception or modulation of opioid receptors, and that it may be related, at least partially, to the ability of these drugs to interact with sigma1 receptors.

The passive transfer of immunoglobulin G serum antibodies from patients with longstanding Complex Regional Pain Syndrome.

BACKGROUND: The aetiology of Complex Regional Pain Syndrome (CRPS) is unknown. Recent evidence suggests that there may be autoantibodies directed against peripheral nerves, but it is unclear whether such autoantibodies are merely biomarkers or whether they cause or contribute to the underlying pathology. The transfer of disease after injection of a patient's serum or IgG fraction into mice ('passive transfer') is the classic way to demonstrate a functional role of autoantibodies. AIMS: Based on previous preliminary results, we wished to investigate whether the transfer of IgG antibodies affected mouse behaviour or produced signs of CRPS. METHODS: We injected purified serum-IgG from 12 patients and 12 controls into groups of 6-10 mice (∼ 17 mg/mouse intraperitoneally) on 2 consecutive days and looked for any evidence for altered behaviour or signs of CRPS. The observer, blinded as to test or control group, measured behaviour in the open field, stimulus-evoked pain and motor coordination, and inspected limbs for autonomic CRPS signs. RESULTS: Stimulus-evoked pain and autonomic signs were not detected, but CRPS-IgG induced significant depression of rearing behaviour (17.9 rears/3 min (n = 84) vs. 22.1 rears/3 min (n = 83), p = 0.0004), confirming previous observations in a single case study. Moreover, motor impairment, one of the four cardinal signs of CRPS, was evident in the three CRPS-IgG injected groups tested with a sensitive rota-rod protocol (p < 0.0001 vs. control-IgG injected groups). CONCLUSIONS: These results lend support to a pathophysiological role for IgG autoantibodies in CRPS.

Antagonism by haloperidol and its metabolites of mechanical hypersensitivity induced by intraplantar capsaicin in mice: role of sigma-1 receptors.

RATIONALE: We evaluated the effects of haloperidol and its metabolites on capsaicin-induced mechanical hypersensitivity (allodynia) and on nociceptive pain induced by punctate mechanical stimuli in mice. RESULTS: Subcutaneous administration of haloperidol or its metabolites I or II (reduced haloperidol) dose-dependently reversed capsaicin-induced (1 microg, intraplantar) mechanical hypersensitivity of the hind paw (stimulated with a nonpainful, 0.5-g force, punctate stimulus). The order of potency of these drugs to induce antiallodynic effects was the order of their affinity for brain sigma-1 (sigma(1)) receptor ([(3)H](+)-pentazocine-labeled). Antiallodynic activity of haloperidol and its metabolites was dose-dependently prevented by the selective sigma(1) receptor agonist PRE-084, but not by naloxone. These results suggest the involvement of sigma(1) receptors, but discard any role of the endogenous opioid system, on the antiallodynic effects. Dopamine receptor antagonism also appears unlikely to be involved in these effects, since the D(2)/D(3) receptor antagonist (-)-sulpiride, which had no affinity for sigma(1) receptors, showed no antiallodynic effect. None of these drugs modified hind-paw withdrawal after a painful (4 g force) punctate mechanical stimulus in noncapsaicin-sensitized animals. As expected, the control drug gabapentin showed antiallodynic but not antinociceptive activity, whereas clonidine exhibited both activities and rofecoxib, used as negative control, showed neither. CONCLUSION: These results show that haloperidol and its metabolites I and II produce antiallodynic but not antinociceptive effects against punctate mechanical stimuli and suggest that their antiallodynic effect may be due to blockade of sigma(1) receptors but not to dopamine receptor antagonism.