Evans Blue Reduces Neuropathic Pain Behavior by Inhibiting Spinal ATP Release

Abstract

Upon peripheral nerve injury, vesicular ATP is released from damaged primary afferent neurons. This extracellular ATP subsequently activates purinergic receptors of the spinal cord, which play a critical role in neuropathic pain. As an inhibitor of the vesicular nucleotide transporter (VNUT), Evans blue (EB) inhibits the vesicular storage and release of ATP in neurons. Thus, we tested whether EB could attenuate neuropathic pain behavior induced by spinal nerve ligation (SNL) in rats by targeting VNUT. An intrathecal injection of EB efficiently attenuated mechanical allodynia for five days in a dose-dependent manner and enhanced locomotive activity in an SNL rat model. Immunohistochemical analysis showed that EB was found in VNUT immunoreactivity on neurons in the dorsal root ganglion and the spinal dorsal horn. The level of ATP in cerebrospinal fluid in rats with SNL-induced neuropathic pain decreased upon administration of EB. Interestingly, EB blocked ATP release from neurons, but not glial cells in vitro. Eventually, the loss of ATP decreased microglial activity in the ipsilateral dorsal horn of the spinal cord, followed by a reduction in reactive oxygen species and proinflammatory mediators, such as interleukin (IL)-1β and IL-6. Finally, a similar analgesic effect of EB was demonstrated in rats with monoiodoacetate-induced osteoarthritis (OA) pain. Taken together, these data demonstrate that EB prevents ATP release in the spinal dorsal horn and reduces the ATP/purinergic receptor-induced activation of spinal microglia followed by a decline in algogenic substances, thereby relieving neuropathic pain in rats with SNL.

p66shc siRNA-Encapsulated PLGA Nanoparticles Ameliorate Neuropathic Pain Following Spinal Nerve Ligation

“…In the present study, intrathecal administration of p66shc siRNA-PLGA NPs decreased microglial activation in the ipsilateral spinal cord following SNL. Our and others' previous studies showed that microglia are activated distinctly, and that activated microglia lead to excessive neuroinflammation following peripheral nerve injury, which contributes to neuropathic pain and tissue damage [5,27,28,32,33,44]. In addition, in the present study, we showed that p66shc siRNA treatment decreased H 2 O 2 -induced elevation of the mRNA levels of proinflammatory mediators, including TNF-α, IL-1β, IL-6, COX2, and iNOS, in cultured HT22 cells.…”

“…Although many underlying mechanisms, related to the onset and development of neuropathic pain, have been suggested, mitochondrial dysfunction may be one of the most important pathophysiological mechanisms of neuropathic pain [3,4]. Our and other previous studies reported that mitochondrial reactive oxygen species (ROS) levels are increased in the neuropathic spinal cord, and that removal of ROS in neuropathic pain can lead to recovery of central sensitization and hyperalgesia to normal levels [5][6][7][8]. In addition to mitochondrial functions and ROS, autophagy has been regarded as one of the most important mechanisms for understanding neuropathic pain.…”

“…According to the method of our previous studies [5,28], L5 spinal cord was obtained and immunohistochemical staining was performed. At 7 days after SNL, the rats (n = 6 in each group) were anesthetized by intraperitoneal administration with sodium pentobarbital (100 mg/kg) and perfused transcardially with 5% heparin diluted in 0.05 M PBS, followed by 4% paraformaldehyde (PFA, Millipore, 104005, Burlington, MA, USA) dissolved in 0.05 M PBS.…”

Electroacupuncture may alleviate neuropathic pain via suppressing P2X7R expression

“…The damaged tissue cells and sensory nerve endings can release a large amount of ATP after peripheral nerve injury. 41 , 42 Studies have shown that ATP activates microglial cells, induces microglial cell aggregation and proliferation, and promotes the release of a variety of proinflammatory factors and neuroactive substances. 43 – 45 The release of proinflammatory factors and neuroactive substances can lead to the enhancement of excitatory synaptic transmission and hyperactivity of dorsal horn neurons (central sensitization).…”

Reduction of prefrontal purinergic signaling is necessary for the analgesic effect of morphine

“…In recent years, extensive studies have confirmed the pivotal role of ATP in pain. Many chemicals have been used to reduce the neuroinflammatory response and subsequently alleviate neuropathic pain by decreasing ATP release, for example, the inhibitor of vesicular nucleotide transporter ( Kato et al., 2017 ; Yin et al., 2019 ) and the inhibitor of mammalian target of rapamycin ( Cui et al., 2014 ). The decrease of ATP level in the mPFC may counter nociceptive input and transmission in the CNS.…”