Changes in the disposition of substance P in the rostral ventromedial medulla after inflammatory injury in the rat

Naringenin attenuated airway cilia structural and functional injury induced by cigarette smoke extract via IL-17 and cAMP pathways

BACKGROUND

Cigarette smoke impairs mucociliary clearance via mechanisms such as inflammatory response and oxidative injury, which in turn induces various respiratory diseases. Naringenin, a naturally occurring flavonoid in grapes and grapefruit, has exhibited pharmacological properties such as anti-inflammatory, expectorant, and antioxidant properties. However, it is still unclear whether naringenin protects airway cilia from injury caused by cigarette smoke.

PURPOSE

This study aimed to investigate the effect of naringenin on cigarette smoke extract (CSE)-induced structural and functional abnormalities in airway cilia and highlight the potential regulatory mechanism.

METHODS

Initially, network pharmacology was used to predict the mechanism of action of naringenin in ciliary disease. Next, HE staining, immunofluorescence, TEM, qRT-PCR, western blot, and ELISA were performed to assess the effects of naringenin on airway cilia in tracheal rings and air-liquid interface (ALI) cultures of Sprague Dawley rats after co-exposure to CSE (10% or 20%) and naringenin (0, 25, 50, 100 μM) for 24 h. Finally, transcriptomics and molecular biotechnology methods were conducted to elucidate the mechanism by which naringenin protected cilia from CSE-induced damage in ALI cultures.

RESULTS

The targets of ciliary diseases regulated by naringenin were significantly enriched in inflammation and oxidative stress pathways. Also, the CSE decreased the number of cilia in the tracheal rings and ALI cultures and reduced the ciliary beat frequency (CBF). However, naringenin prevented CSE-induced cilia damage via mechanisms such as the downregulation of cilia-related genes (e.g., RFX3, DNAI1, DNAH5, IFT88) and ciliary marker proteins such as DNAI2, FOXJ1, and β-tubulin IV, the upregulation of inflammatory factors (e.g., IL-6, IL-8, IL-13), ROS and MDA. IL-17 signaling pathway might be involved in the protective effect of naringenin on airway cilia. Additionally, the cAMP signaling pathway might also be related to the enhancement of CBF by naringenin.

CONCLUSION

In this study, we first found that naringenin reduces CSE-induced structural disruption of airway cilia in part via modulation of the IL-17 signaling pathway. Furthermore, we also found that naringenin enhances CBF by activating the cAMP signaling pathway. This is the first report to reveal the beneficial effects of naringenin on airway cilia and the potential underlying mechanisms.

Medullary kappa-opioid receptor neurons inhibit pain and itch through a descending circuit

In perilous and stressful situations, the ability to suppress pain can be critical for survival. The rostral ventromedial medulla contains neurons that robustly inhibit nocioception at the level of the spinal cord through a top-down modulatory pathway. Although much is known about the role of the rostral ventromedial medulla in the inhibition of pain, the precise ability to directly manipulate pain-inhibitory neurons in the rostral ventromedial medulla has never been achieved. We now expose a cellular circuit that inhibits nocioception and itch in mice. Through a combination of molecular, tracing and behavioural approaches, we found that rostral ventromedial medulla neurons containing the kappa-opioid receptor inhibit itch and nocioception. With chemogenetic inhibition, we uncovered that these neurons are required for stress-induced analgesia. Using intersectional chemogenetic and pharmacological approaches, we determined that rostral ventromedial medulla kappa-opioid receptor neurons inhibit nocioception and itch through a descending circuit. Lastly, we identified a dynorphinergic pathway arising from the periaqueductal grey that modulates nociception within the rostral ventromedial medulla. These discoveries highlight a distinct population of rostral ventromedial medulla neurons capable of broadly and robustly inhibiting itch and nocioception.

Role of peripheral and central sensitization in the anti-hyperalgesic effect of hecogenin acetate, an acetylated sapogenin, complexed with β-cyclodextrin: Involvement of NFκB and p38 MAPK pathways

Neuropathic pain develops due to injury to the somatosensory system, affecting the patient's quality of life. In view of the ineffectiveness of the current pharmacotherapy, substances obtained from natural products (NPs) are a promising alternative. One NP that has been discussed in the literature is hecogenin acetate (HA), a steroidal sapogenin with anti-inflammatory and antinociceptive activity. However, HA has low water solubility, which affects its bioavailability. Thus, the objective of this study was to evaluate the anti-hyperalgesic activity of pure and complexed hecogenin acetate (HA/βCD) in an animal model of chronic neuropathic and inflammatory pain. The inclusion complex was prepared at a molar ratio of 1:2 (HA:βCD) by the lyophilization method. For the induction of chronic inflammatory pain, the mice received an intraplantar injection of CFA (complete Freund's adjuvant), and were evaluated for mechanical hyperalgesia and for the levels of myeloperoxidase (MPO) in the skin of the paw after eight days of treatment. HA and HA/βCD reduced mechanical hyperalgesia in relation to the vehicle group until the fourth and fifth hours, respectively, in the acute evaluation, with a superior effect of the complexed form over the pure form in the second and third hour after treatment (p < 0.001). In the chronic evaluation, HA and HA/βCD reduced hyperalgesia in relation to the vehicle in the eight days of treatment (p < 0.001). Both pure (p < 0.01) and complexed (p < 0.001) forms reduced myeloperoxidase activity in the skin of the animals' paw. Groups of animals subjected to the same pharmacological protocol were submitted to the partial sciatic nerve ligation (PSNL) model and evaluated for mechanical and thermal hyperalgesia, and cold allodynia. HA and HA/βCD reduced mechanical hyperalgesia until the fourth and sixth hours, respectively, and both reduced hyperalgesia in relation to the vehicle in the chronic evaluation (p < 0.001). HA and HA/βCD also reduced thermal hyperalgesia and cold allodynia (p < 0.05 and p < 0.001, respectively). The analysis of the spinal cord of these animals showed a decrease in the levels of the pro-inflammatory cytokines TNF-α, IL-1β and IL-6 and a reduction in the phosphorylation of NFκB and p38MAPK, as well as a decrease in microglioses compared to the vehicle group. In addition, HA/βCD reduced the nociception induced by intraplantar injection of agonist TRPA1 (p < 0.01) and TRPM8 (p < 0.05). Treatment for eight days with HA and HA/βCD showed no signs of gastric or liver damage. HA and HA/βCD were, therefore, shown to have antinociceptive effects in chronic pain models. Based on our exploration of the mechanisms of the action of HA, these effects are likely to be related to inhibited leukocyte migration, interaction with the TRPA1 and TRPM8 receptors, reduced pro-inflammatory cytokines levels, microglial expression and suppression of NF-κB p65 and p38 MAPK pathway signaling. Therefore, HA/βCD has great potential for use in the treatment of chronic pain.

Probucol Ameliorates Complete Freund's Adjuvant-Induced Hyperalgesia by Targeting Peripheral and Spinal Cord Inflammation

The effect of the lipid-lowering agent probucol in inflammatory hyperalgesia and leukocyte recruitment was evaluated in a model of subacute inflammation by Complete Freund's adjuvant (CFA). As CFA induces long-lasting nociception characterized by peripheral and spinal cord inflammation, the anti-inflammatory activity of probucol was assessed at both foci. Probucol at 0.3-3 mg/kg was administrated per oral daily starting 24 h after CFA intraplantar injection. Mechanical and thermal hyperalgesia induced by CFA were determined using an electronic anesthesiometer and hot plate apparatus, respectively. Post-treatment with probucol at 3 mg/kg inhibited CFA-induced hyperalgesia over the course of 7 days as well as paw edema. Overt pain-like behaviors, which were determined by the number of flinches and time spent licking paw immediately following CFA injection, were also reduced by probucol at 3 mg/kg administered as a pre-treatment. To investigate the mechanisms underlying the analgesic effect of probucol, neutrophil recruitment to paw was assessed by myeloperoxidase activity, cytokine production, Cox-2 expression, and NF-κB activation in both paw and spinal cord by ELISA. Iba-1, GFAP, and substance P protein expression and nuclear localization of phosphorylated NF-κB were evaluated in the spinal cord by immunofluorescence. Probucol at 3 mg/kg attenuated neutrophil recruitment, cytokine levels, and NF-κB activation as well microglia and astrocyte activation, and substance P staining in the spinal cord. Taken together, the results suggest that probucol exerts its analgesic and anti-inflammatory activity in an experimental model of persistent inflammation by targeting the NF-κB pathway in peripheral and spinal cord foci.

Plasticity in the Link between Pain-Transmitting and Pain-Modulating Systems in Acute and Persistent Inflammation

There is strong evidence that spinoparabrachial neurons in the superficial dorsal horn contribute to persistent pain states, and that the lateral parabrachial complex (PB) conveys relevant nociceptive information to higher structures. The role of PB itself in hyperalgesia and how it recruits descending facilitation has nevertheless received significantly less attention. The current study is a first step toward delineating the functional dynamics of PB and its link to descending control in acute and persistent inflammatory pain. In lightly anesthetized rats, we recorded behavioral withdrawal evoked by mechanical stimulation of the hindpaw and, simultaneously, the activity of identified pain-modulating neurons, "ON-cells" and "OFF-cells," in the rostral ventromedial medulla (RVM). This was done before and after the inactivation of PB, contralateral or ipsilateral to an inflamed paw [1 h, 1 d, or 5-6 d after intraplantar injection of Complete Freund's Adjuvant (CFA)]. The inactivation of contralateral, but not ipsilateral, PB interfered with nociceptive input to RVM under basal conditions, as well as in acute inflammation. By contrast, blocking ipsilateral, but not contralateral, PB in established inflammation interfered with behavioral hyperalgesia and ON-cell and OFF-cell responses. The lesioning of contralateral PB before CFA injection prevented this recruitment of ipsilateral PB in persistent inflammation. These experiments show that contralateral PB is required to initiate hyperalgesia, which is then maintained by ipsilateral PB, most likely in both cases via the engagement of pain-modulating neurons of the RVM.SIGNIFICANCE STATEMENT The lateral parabrachial complex (PB) relays nociceptive information to brain circuits that are important for the transmission and modulation of pain, but its specific role in persistent pain and engagement of descending control mechanisms has received relatively little attention. We show here that PB contralateral and ipsilateral to an inflammatory insult demonstrate different functions as inflammation persists, likely by engaging pain-facilitating neurons of the rostral ventromedial medulla. While the contralateral PB, the target of the major spinoparabrachial pathway, relays acute nociceptive information, the ipsilateral PB is recruited or unmasked in persistent inflammation to maintain hyperalgesia. These data point to plasticity in the PB itself or its direct and indirect connections with pain-modulating systems as central to the development and maintenance of persistent pain.

Hyperalgesia and sensitization of dorsal horn neurons following activation of NK-1 receptors in the rostral ventromedial medulla

Neurons in the rostral ventromedial medulla (RVM) project to the spinal cord and are involved in descending modulation of pain. Several studies have shown that activation of neurokinin-1 (NK-1) receptors in the RVM produces hyperalgesia, although the underlying mechanisms are not clear. In parallel studies, we compared behavioral measures of hyperalgesia to electrophysiological responses of nociceptive dorsal horn neurons produced by activation of NK-1 receptors in the RVM. Injection of the selective NK-1 receptor agonist Sar9,Met(O2)11-substance P (SSP) into the RVM produced dose-dependent mechanical and heat hyperalgesia that was blocked by coadministration of the selective NK-1 receptor antagonist L-733,060. In electrophysiological studies, responses evoked by mechanical and heat stimuli were obtained from identified high-threshold (HT) and wide dynamic range (WDR) neurons. Injection of SSP into the RVM enhanced responses of WDR neurons, including identified neurons that project to the parabrachial area, to mechanical and heat stimuli. Since intraplantar injection of capsaicin produces robust hyperalgesia and sensitization of nociceptive spinal neurons, we examined whether this sensitization was dependent on NK-1 receptors in the RVM. Pretreatment with L-733,060 into the RVM blocked the sensitization of dorsal horn neurons produced by capsaicin. c-Fos labeling was used to determine the spatial distribution of dorsal horn neurons that were sensitized by NK-1 receptor activation in the RVM. Consistent with our electrophysiological results, administration of SSP into the RVM increased pinch-evoked c-Fos expression in the dorsal horn. It is suggested that targeting this descending pathway may be effective in reducing persistent pain.NEW & NOTEWORTHY It is known that activation of neurokinin-1 (NK-1) receptors in the rostral ventromedial medulla (RVM), a main output area for descending modulation of pain, produces hyperalgesia. Here we show that activation of NK-1 receptors produces hyperalgesia by sensitizing nociceptive dorsal horn neurons. Targeting this pathway at its origin or in the spinal cord may be an effective approach for pain management.

Analgesic Effects of Transcutaneous Ultrasound Nerve Stimulation in a Rat Model of Oxaliplatin-Induced Mechanical Hyperalgesia and Cold Allodynia

This study investigated the effects and underlying mechanisms of therapeutic ultrasound (TUS) in a rat model of oxaliplatin-induced peripheral neuropathy. Animals received a total of eight injections with oxaliplatin (4 mg/kg), administered at 3-d intervals. TUS intervention (1 MHz, 0.5 W/cm²) started on the fifth oxaliplatin administration and continued for 10 consecutive d. Sensory behavioral examinations, protein levels of transient receptor potential channels (TRPM8 and TRPV1) in dorsal root ganglia (DRG) and substance P (SP) in spinal dorsal horn were examined. Results indicated that TUS can reduce mechanical and cold hyper-responsive behaviors caused by repeated administration of oxaliplatin. Oxaliplatin-related increases in protein levels of TRPM8 in DRG and SP in the dorsal horn were also reduced after TUS. Taken together, the results revealed beneficial effects of TUS on oxaliplatin-induced mechanical hyperalgesia and cold allodynia and suggested involvement of TUS biochemicals in suppressing TRPM8 in DRG and SP in spinal cords.