Wnt signaling is involved in crotalphine-induced analgesia in a rat model of neuropathic pain

The aberrant activation of Wnt/β-catenin and atypical Wnt/Ryk signaling pathways in the spinal cord is critical for the development and maintenance of neuropathic pain. Crotalphine is a structural analog to a peptide first identified in Crotalus durissus terrificus snake venom, which induces antinociception by activating kappa-opioid and CB2 cannabinoid receptors. Consistent with previous data, we showed that the protein levels of the canonical Wnt/β-catenin and the atypical Wnt/Ryk signaling pathways are increased in neuropathic rats. Importantly, the administration of crotalphine downregulates these protein levels, including its downstream cascades, such as TCF4 from the canonical pathway and NR2B glutamatergic receptor and Ca2+-dependent signals, via the Ryk receptor. The CB2 receptor antagonist, AM630, abolished the crotalphine-induced atypical Wnt/Ryk signaling pathway activation. However, the selective CB2 agonist affects both canonical and non-canonical Wnt signaling in the spinal cord. Next, we showed that crotalphine blocked hypersensitivity and significantly decreased the concentration of IL-1ɑ, IL-1β, IL-6, IL-10, IL-18, TNF-ɑ, MIP-1ɑ and MIP-2 induced by intrathecal injection of exogenous Wnt-3a agonist. Taken together, our findings show that crotalphine induces analgesia in a neuropathic pain model by down-regulating the canonical Wnt/β-catenin and the atypical Wnt/Ryk signaling pathways and, consequently controlling neuroinflammation. This effect is, at least in part, mediated by CB2 receptor activation. These results open a perspective for new approaches that can be used to target Wnt signaling in the context of chronic pain.

The inhibitory effect of Phα1β toxin on diabetic neuropathic pain involves the CXCR4 chemokine receptor

Background Diabetic neuropathy is a common cause of painful diabetic neuropathy (PDN). C-X-C chemokine receptor type 4 (CXCR4) expression is increased in peripheral nerve samples from diabetes patients, suggesting a role for CXCR4 in PDN. Therefore, we evaluated the effects of Pha1ß, Ômega-conotoxin MVIIA, and AMD3100 in a model of streptozotocin (STZ)-induced PDN in rodents and naïve model of rats with the activation of the CXCR4/stromal cell-derived factor 1 (SDF-1) signal. Methods Diabetic neuropathy was induced by intraperitoneal (ip) injection of STZ in Wistar rats. Naïve rats were intrathecally injected with SDF-1 to test the CXCR4/SDF-1 signal. The effects of Pha1ß intrathecal (it), Ômega-conotoxin MVIIA intrathecal (it), and AMD3100 intraperitoneal (ip) on rat hypersensitivity, IL-6, and the intracellular calcium [Ca2+]i content of diabetic synaptosomes were studied. Results The drugs reduced the hypersensitivity in diabetic rats. SDF-1 (1.0 µg/it) administration in naïve rats induced hypersensitivity. Pha1ß (100 pmol/it) or AMD3100 (2.5 µg/ip) reduced this hypersensitivity after 2 h treatments, while Ômega-conotoxin MVIIA did not have an effect. IL-6 and [Ca2+]i content increased in the spinal cord synaptosomes in diabetic rats. The drug treatments reduced IL-6 and the calcium influx in diabetic synaptosomes. Conclusions Pha1ß, Ômega-conotoxin MVIIA, and AMD3100, after 2 h of treatment of STZ-induced PDN, reduced hypersensitivity in diabetic rats. In naïve rats with CXCR4/SDF-1 activation, the induced hypersensitivity decreased after 2 h treatments with Pha1ß or AMD-3100, while Ômega-conotoxin MVIIA did not affect. The inhibitory effects of Pha1ß on PDN may involve voltage-dependent calcium channels.

The inhibitory effect of Pha1ß toxin on diabetic neuropathic pain involves the CXCR4 chemokine receptor

Background Diabetic neuropathy is a common cause of painful diabetic neuropathy (PDN). C-X-C chemokine receptor type 4 (CXCR4) expression is increased in peripheral nerve samples from diabetes patients, suggesting a role for CXCR4 in PDN. Therefore, we evaluated the effects of Pha1ß, Ômega-conotoxin MVIIA, and AMD3100 in a model of streptozotocin (STZ)-induced PDN in rodents and naïve model of rats with the activation of the CXCR4/stromal cell-derived factor 1 (SDF-1) signal. Methods Diabetic neuropathy was induced by intraperitoneal (ip) injection of STZ in Wistar rats. Naïve rats were intrathecally injected with SDF-1 to test the CXCR4/SDF-1 signal. The effects of Pha1ß intrathecal (it), Ômega-conotoxin MVIIA intrathecal (it), and AMD3100 intraperitoneal (ip) on rat hypersensitivity, IL-6, and the intracellular calcium [Ca2+]i content of diabetic synaptosomes were studied. Results The drugs reduced the hypersensitivity in diabetic rats. SDF-1 (1.0 µg/it) administration in naïve rats induced hypersensitivity. Pha1ß (100 pmol/it) or AMD3100 (2.5 µg/ip) reduced this hypersensitivity after 2 h treatments, while Ômega-conotoxin MVIIA did not have an effect. IL-6 and [Ca2+]i content increased in the spinal cord synaptosomes in diabetic rats. The drug treatments reduced IL-6 and the calcium influx in diabetic synaptosomes. Conclusions Pha1ß, Ômega-conotoxin MVIIA, and AMD3100, after 2 h of treatment of STZ-induced PDN, reduced hypersensitivity in diabetic rats. In naïve rats with CXCR4/SDF-1 activation, the induced hypersensitivity decreased after 2 h treatments with Pha1ß or AMD-3100, while Ômega-conotoxin MVIIA did not affect. The inhibitory effects of Pha1ß on PDN may involve voltage-dependent calcium channels.

The Neuroprotective Effect of Doxycycline on Neurodegenerative Diseases.

Neurodegenerative diseases (NDs) are a group of chronic, progressive disorders characterized by the gradual loss of neurons that affect specific regions of the brain, which leads to deficits in specific functions (e.g., memory, movement, cognition). The mechanism that drives chronic progression of NDs remains elusive. Among the proposed underlying pathophysiological mechanisms, aggregation and accumulation of misfolded proteins and neuroinflammation have been credited to contribute to extensive neural loss. Therapeutic agents that confer neuroprotection by downregulating these shared characteristics could therefore have beneficial effects on a wide range of NDs. In this regard, a commonly used antibiotic, doxycycline (Doxy), has been shown to reduce the progression and severity of disease in different experimental models of neurodegeneration by counteracting these common features. This review will focus on the effects reported for Doxy regarding its neuroprotective properties, the "off-target" effects, thereby supporting its evaluation as a new therapeutic approach for diseases associated with a neurodegeneration.

Mitogen-activated protein kinase signaling mediates morphine induced-delayed hyperalgesia

The use of morphine, the standard opioid drug, is limited by its undesirable effects, such as tolerance, physical dependence, and hyperalgesia (increased pain sensitivity). Clinical and preclinical studies have reported development of hyperalgesia after prolonged opioid administration or after a single dose of intrathecal (i.t.) morphine in uninjured rats. However, whether a single standard systemic morphine dose is sufficient to decrease the nociceptive threshold in rats is unknown. Here, we showed that a single morphine subcutaneous injection induces analgesia followed by a long-lasting delayed hyperalgesia in uninjured and PGE2 sensitized rats. The i.t injection of extracellular signal-regulated kinase (ERK) inhibitor blocked morphine-induced analgesia, without interfering with the morphine-induced hyperalgesia. However, i.t. injection of SB20358, a p38 inhibitor and SP660125, a JNK inhibitor, decreased the morphine-induced hyperalgesia. Consistently with the behavioral data, Western Blot analysis showed that ERK is more phosphorylated 1 h after morphine, i.e., when the analgesia is detected. Moreover, phospho-p38 and phospho-JNK levels are upregulated 96 h after morphine injection, time that coincides with the hyperalgesic effect. Intrathecal (i.t.) oligodeoxynucleotide (ODN) antisense to cAMP-responsive element binding protein (CREB) attenuated morphine-induced hyperalgesia. Real-time polymerase chain reaction (RT-PCR) analysis showed that CREB downstream genes expressions were significantly up-regulated 96 h after morphine injection in spinal cord. Together, our data suggest that central ERK is involved in the analgesic and hyperalgesic effects of morphine while JNK, p38, and CREB are involved in the morphine-induced delayed hyperalgesia.

The neuroprotective effect of doxycycline on neurodegenerative diseases

Neurodegenerative diseases (NDs) are a group of chronic, progressive disorders characterized by the gradual loss of neurons that affect specific regions of the brain, which leads to deficits in specific functions (e.g., memory, movement, cognition). The mechanism that drives chronic progression of NDs remains elusive. Among the proposed underlying pathophysiological mechanisms, aggregation and accumulation of misfolded proteins and neuroinflammation have been credited to contribute to extensive neural loss. Therapeutic agents that confer neuroprotection by downregulating these shared characteristics could therefore have beneficial effects on a wide range of NDs. In this regard, a commonly used antibiotic, doxycycline (Doxy), has been shown to reduce the progression and severity of disease in different experimental models of neurodegeneration by counteracting these common features. This review will focus on the effects reported for Doxy regarding its neuroprotective properties, the "off-target" effects, thereby supporting its evaluation as a new therapeutic approach for diseases associated with a neurodegeneration.

Mitogen-activated protein kinase signaling mediates morphine induced-delayed hyperalgesia

The use of morphine, the standard opioid drug, is limited by its undesirable effects, such as tolerance, physical dependence, and hyperalgesia (increased pain sensitivity). Clinical and preclinical studies have reported development of hyperalgesia after prolonged opioid administration or after a single dose of intrathecal (i.t.) morphine in uninjured rats. However, whether a single standard systemic morphine dose is sufficient to decrease the nociceptive threshold in rats is unknown. Here, we showed that a single morphine subcutaneous injection induces analgesia followed by a long-lasting delayed hyperalgesia in uninjured and PGE2 sensitized rats. The i.t injection of extracellular signal-regulated kinase (ERK) inhibitor blocked morphine-induced analgesia, without interfering with the morphine-induced hyperalgesia. However, i.t. injection of SB20358, a p38 inhibitor and SP660125, a JNK inhibitor, decreased the morphine-induced hyperalgesia. Consistently with the behavioral data, Western Blot analysis showed that ERK is more phosphorylated 1 h after morphine, i.e., when the analgesia is detected. Moreover, phospho-p38 and phospho-JNK levels are upregulated 96 h after morphine injection, time that coincides with the hyperalgesic effect. Intrathecal (i.t.) oligodeoxynucleotide (ODN) antisense to cAMP-responsive element binding protein (CREB) attenuated morphine-induced hyperalgesia. Real-time polymerase chain reaction (RT-PCR) analysis showed that CREB downstream genes expressions were significantly up-regulated 96 h after morphine injection in spinal cord. Together, our data suggest that central ERK is involved in the analgesic and hyperalgesic effects of morphine while JNK, p38, and CREB are involved in the morphine-induced delayed hyperalgesia.

The neuroprotective effect of doxycycline on neurodegenerative diseases

Neurodegenerative diseases (NDs) are a group of chronic, progressive disorders characterized by the gradual loss of neurons that affect specific regions of the brain, which leads to deficits in specific functions (e.g., memory, movement, cognition). The mechanism that drives chronic progression of NDs remains elusive. Among the proposed underlying pathophysiological mechanisms, aggregation and accumulation of misfolded proteins and neuroinflammation have been credited to contribute to extensive neural loss. Therapeutic agents that confer neuroprotection by downregulating these shared characteristics could therefore have beneficial effects on a wide range of NDs. In this regard, a commonly used antibiotic, doxycycline (Doxy), has been shown to reduce the progression and severity of disease in different experimental models of neurodegeneration by counteracting these common features. This review will focus on the effects reported for Doxy regarding its neuroprotective properties, the "off-target" effects, thereby supporting its evaluation as a new therapeutic approach for diseases associated with a neurodegeneration.

The spider toxin Phα1ß recombinant possesses strong analgesic activity.

The native Phα1ß - a Voltage-Gated Calcium Channel (VGCC) blocker - and its Recombinant Version - were both tested in rodent pain models with an intraplantar injections of capsaicin or formalin, a chronic constriction injury, and melanoma cancer related pain. The formalin nociceptive behaviour in the neurogenic phase was not affected by the toxin pre-treatments, while in the inflammatory phase, Phα1ß and the Recombinant form caused a significant reduction. The nociception that was triggered by capsaicin, an agonist of the TRPV1 vanilloid receptor, was totally blocked by 100 pmol/site, i.t. of Phα1ß or the recombinant version. For the neuropathic pain that was induced by a chronic constriction injury of the sciatic nerve, Phα1ß and its Recombinant reduced the allodynia that was induced by the CCI procedure in the rats and the hypersensitivity lasted for 4 h. Fourteen days after the inoculation of the B16-F10 melanoma cells in the mice, a marked hyperalgesia was induced in the melanoma cancer pain model. Phα1ß and the Recombinant form reduced the hyperalgesia with a full reversion at 100 pmol/site i.t. The inhibitory effects of the nociception that was induced by native Phα1ß and the Recombinant in the studied pain models were not statistically different and they developed with no side effects.