Activation of TRPV1 by capsaicin induces functional Kinin B1 receptor in rat spinal cord microglia

Abstract

BackgroundThe kinin B1 receptor (B1R) is upregulated by pro-inflammatory cytokines and oxydative stress, which are enhanced by transient receptor potential vanilloid subtype 1 (TRPV1) activation. To examine the link between TRPV1 and B1R in inflammatory pain, this study aimed to determine the ability of TRPV1 to regulate microglial B1R expression in the spinal cord dorsal horn, and the underlying mechanism.MethodsB1R expression (mRNA, protein and binding sites) was measured in cervical, thoracic and lumbar spinal cord in response to TRPV1 activation by systemic capsaicin (1-50 mg/kg, s.c) in rats pre-treated with TRPV1 antagonists (capsazepine or SB-366791), the antioxidant N-acetyl-L-cysteine (NAC), or vehicle. B1R function was assessed using a tail-flick test after intrathecal (i.t.) injection of a selective B1R agonist (des-Arg9-BK), and its microglial localization was investigated by confocal microscopy with the selective fluorescent B1R agonist, [Nα-bodipy]-des-Arg9-BK. The effect of i.t. capsaicin (1 μg/site) was also investigated.ResultsCapsaicin (10 to 50 mg/kg, s.c.) enhanced time-dependently (0-24h) B1R mRNA levels in the lumbar spinal cord; this effect was prevented by capsazepine (10 mg/kg, i.p.; 10 μg/site, i.t.) and SB-366791 (1 mg/kg, i.p.; 30 μg/site, i.t.). Increases of B1R mRNA were correlated with IL-1β mRNA levels, and they were significantly less in cervical and thoracic spinal cord. Intrathecal capsaicin (1 μg/site) also enhanced B1R mRNA in lumbar spinal cord. NAC (1 g/kg/d × 7 days) prevented B1R up-regulation, superoxide anion production and NF-kB activation induced by capsaicin (15 mg/kg). Des-Arg9-BK (9.6 nmol/site, i.t.) decreased by 25-30% the nociceptive threshold at 1 min post-injection in capsaicin-treated rats (10-50 mg/kg) while it was without effect in control rats. Des-Arg9-BK-induced thermal hyperalgesia was blocked by capsazepine, SB-366791 and by antagonists/inhibitors of B1R (SSR240612, 10 mg/kg, p.o.), glutamate NMDA receptor (DL-AP5, 10 μg/site, i.t.), substance P NK-1 receptor (RP-67580, 10 μg/site, i.t.) and nitric oxide synthase (L-NNA, 10 μg/site, i.t.). The B1R fluorescent agonist was co-localized with an immunomarker of microglia (Iba-1) in spinal cord dorsal horn of capsaicin-treated rats.ConclusionThis study highlights a new mechanism for B1R induction via TRPV1 activation and establishes a link between these two pro-nociceptive receptors in inflammatory pain.

Brain kinin B1 receptor is upregulated by the oxidative stress and its activation leads to stereotypic nociceptive behavior in insulin-resistant rats

“…This may be explained by its presence on microglia and reactive astrocytes rather than on neuronal elements [33,46,47].…”

“…administration of the kinin B1R agonist Sar-[D-Phe 8 ]-des-Arg 9 -BK in glucose-fed rats. The widespread distribution of B1R in the brain may suggest its presence on microglia and/or astrocytes as evidenced in models of pain and Alzheimer's disease [33,46,47]. Nitric oxide (NO) could also derive from iNOS based on findings showing an upregulation of iNOS by B1R in this model [16,18] and the ability of B1R to activate iNOS through G␣i and the Src-dependent activation of the ERK/MAP kinase pathway [5].…”

“…Collectively, these findings suggest that the stimulation of kinin B1R in the brain mimics behavioral activity induced by pain stimuli and therefore is associated with nocifensive behavior. Worth of noting, tachykinin NK1R, glutamate NMDA receptor and NO were proposed as downstream pathways in thermal hyperalgesia in response to the spinal activation of kinin B1R in pain models of diabetes and inflammation [6,47]. Thus, brain kinin B1R may exert a central regulatory function in the coordination of nocifensive behavior in response to stress and pain stimuli.…”

“…Hence, the pathologic role for the inducible B1R in diabetes appears linked to the oxidative stress. Interestingly, B1R is involved in thermal hyperalgesia through a spinal cord mechanism involving the release of substance P (SP), glutamate and nitric oxide (NO) in diabetic and inflammatory pain models [6,47]. The role of B1R in affective behavior remains, however, unknown in diabetes mellitus.…”

TRPs and Pain

“…It is not clear which if any of these factors subserve nociceptive functions by acting on TRP channels or in which direction the effect occurs. TRPV1 may stand upstream of some inflammatory responses, as suggested by the finding that systemic capsaicin upregulated B1R expression on spinal cord microglia (Talbot et al 2012). The secondary injury to the blood capillaries that follows spinal cord trauma is preceded by upregulation of the TRPM4 channel on the vessels (Gerzanich et al 2009).…”