NADPH Oxidases in Pain Processing

Vitamin D3 Attenuates Neuropathic Pain via Suppression of Mitochondria-Associated Ferroptosis by Inhibiting PKCα/NOX4 Signaling Pathway

AIMS

Neuropathic pain remains a significant unmet medical challenge due to its elusive mechanisms. Recent clinical observations suggest that vitamin D (VitD) holds promise in pain relief, yet its precise mechanism of action is still unclear. This study explores the therapeutical role and potential mechanism of VitD3 in spared nerve injury (SNI)-induced neuropathic pain rat model.

METHODS

The analgesic effects and underlying mechanisms of VitD3 were evaluated in SNI and naïve rat models. Mechanical allodynia was assessed using the Von Frey test. Western blotting, immunofluorescence, biochemical assay, and transmission electron microscope (TEM) were employed to investigate the molecular and cellular effects of VitD3.

RESULTS

Ferroptosis was observed in the spinal cord following SNI. Intrathecal administration of VitD3, the active form of VitD, activated the vitamin D receptor (VDR), suppressed ferroptosis, and alleviated mechanical nociceptive behaviors. VitD3 treatment preserved spinal GABAergic interneurons, and its neuroprotective effects were eliminated by the ferroptosis inducer RSL3. Additionally, VitD3 mitigated aberrant mitochondrial morphology and oxidative metabolism in the spinal cord. Mechanistically, VitD3 inhibited SNI-induced activation of spinal PKCα/NOX4 signaling. Inhibition of PKCα/NOX4 signaling alleviated mechanical pain hypersensitivity, accompanied by reduced ferroptosis and mitochondrial dysfunction in SNI rats. Conversely, activation of PKCα/NOX4 signaling in naïve rats induced hyperalgesia, ferroptosis, loss of GABAergic interneurons, and mitochondrial dysfunction in the spinal cord, all of which were reversed by VitD3 treatment.

CONCLUSIONS

Our findings provide evidence that VitD3 attenuates neuropathic pain by preserving spinal GABAergic interneurons through the suppression of mitochondria-associated ferroptosis mediated by PKCα/NOX4 signaling, probably via VDR activation. VitD, alone or in combination with existing analgesics, presents an innovative therapeutic avenue for neuropathic pain.

Tear Proteins Altered in Patients with Persistent Eye Pain after Refractive Surgery: Biomarker Candidate Discovery

Some patients develop persistent eye pain after refractive surgery, but factors that cause or sustain pain are unknown. We tested whether tear proteins of patients with pain 3 months after surgery differ from those of patients without pain. Patients undergoing refractive surgery (laser in situ keratomileusis or photorefractive keratectomy ) were recruited from 2 clinics, and tears were collected 3 months after surgery. Participants rated their eye pain using a numerical rating scale (NRS, 0-10; no pain-worst pain) at baseline, 1 day, and 3 months after surgery. Using tandem mass tag proteomic analysis, we examined tears from patients with pain [NRS ≥ 3 at 3 months (n = 16)] and patients with no pain [NRS ≤ 1 at 3 months (n = 32)] after surgery. A subset of proteins (83 of 2748 detected, 3.0%) were associated with pain 3 months after surgery. High-dimensional statistical models showed that the magnitude of differential expression was not the only important factor in classifying tear samples from pain patients. Models utilizing 3 or 4 proteins had better classification performance than single proteins and represented differences in both directions (higher or lower in pain). Thus, patterns of protein differences may serve as biomarkers of postsurgical eye pain as well as potential therapeutic targets.

Forced swim stress exacerbates inflammation-induced hyperalgesia and oxidative stress in the rat trigeminal ganglia

This study investigates the impact of combining psychophysical stress, induced by forced swim (FSS), with masseter inflammation on reactive oxygen species (ROS) production in trigeminal ganglia (TG), TRPA1 upregulation in TG, and mechanical hyperalgesia. In a rat model, we demonstrate that FSS potentiates and prolongs CFA-induced ROS upregulation within TG. The ROS levels in CFA combined with FSS group surpass those in the CFA-only group on days 4 and 28 post-treatment. FSS also enhances TRPA1 upregulation in TG, with prolonged expression compared to CFA alone. Furthermore, CFA-induced mechanical hyperalgesia is significantly prolonged by FSS, persisting up to day 28. PCR array analyses reveal distinct alterations in oxidative stress genes under CFA and CFA combined with FSS conditions, suggesting an intricate regulation of ROS within TG. Notably, genes like Nox4, Hba1, Gpx3, and Duox1 exhibit significant changes, providing potential targets for managing oxidative stress and inflammatory pain. Western blot and immunohistochemistry confirm DUOX1 protein upregulation and localization in TG neurons, indicating a role in ROS generation under inflammatory and stress conditions. This study underscores the complex interplay between psychophysical stress, inflammation, and oxidative stress in the trigeminal system, offering insights into novel therapeutic targets for pain management.

Endoplasmic reticular stress as an emerging therapeutic target for chronic pain: a narrative review

Chronic pain is a severely debilitating condition with enormous socioeconomic costs. Current treatment regimens with nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, or opioids have been largely unsatisfactory with uncertain benefits or severe long-term side effects. This is mainly because chronic pain has a multifactorial aetiology. Although conventional pain medications can alleviate pain by keeping several dysfunctional pathways under control, they can mask other underlying pathological causes, ultimately worsening nerve pathologies and pain outcome. Recent preclinical studies have shown that endoplasmic reticulum (ER) stress could be a central hub for triggering multiple molecular cascades involved in the development of chronic pain. Several ER stress inhibitors and unfolded protein response modulators, which have been tested in randomised clinical trials or apprpoved by the US Food and Drug Administration for other chronic diseases, significantly alleviated hyperalgesia in multiple preclinical pain models. Although the role of ER stress in neurodegenerative disorders, metabolic disorders, and cancer has been well established, research on ER stress and chronic pain is still in its infancy. Here, we critically analyse preclinical studies and explore how ER stress can mechanistically act as a central node to drive development and progression of chronic pain. We also discuss therapeutic prospects, benefits, and pitfalls of using ER stress inhibitors and unfolded protein response modulators for managing intractable chronic pain. In the future, targeting ER stress to impact multiple molecular networks might be an attractive therapeutic strategy against chronic pain refractory to steroids, NSAIDs, or opioids. This novel therapeutic strategy could provide solutions for the opioid crisis and public health challenge.

Role and anti-inflammatory mechanisms of acupuncture and moxibustion therapy on pain relief through NOX-ROS-NLRP3 pathway in CCI rats models

OBJECTIVE

To observe the effects of acupuncture and moxibustion therapy on pain relief in sciatica rats and to explore the mechanism of its anti-inflammatory effect.

METHODS

SPF grade 4-6-week-old Kunming rats were randomly divided into 5 groups including a blank group, sham-operated group, model group, acupuncture, and moxibustion (AnM) group, and positive group. A total of 10 rats were included in each group. The model group, the AnM group, and the positive group were prepared by ligating the left sciatic nerve. AnM group was used for acupuncture and moxibustion therapy intervention, and the positive group was rendered to quick-acting sciatica pills once a day for 7 days (3 courses of treatment). The blank group, sham-operated group, and model group were not treated. The changes in thermal and mechanical pain thresholds were observed before and after the operation, and the morphological changes of the dorsal horn of the spinal cord in the lumbosacral region of the rats in each group were observed by HE staining after the courses of treatment finished. The contents of IL-1β, IL-6, IL-18, and TNF-α were measured by ELISA and the expressions of NOX1, NOX2, NOX4, and NLRP3 genes were detected by RT-qPCR while the protein expressions of NOX1, NOX2, NOX4 and NLRP3 were analyzed by Western blotting.

RESULTS

The AnM and positive group showed a significant increase in thermal and mechanical pain thresholds after treatment, while there was no significant change in the model group. As compared to the control group, the contents of IL- 1β, IL-6, IL-18, and TNF-α, as well as the relative expressions of NOX1, NOX2, NOX4, and NLRP3 genes were significantly increased in the model group (P < 0.05 or P < 0.01). As compared to the model group, the contents of IL-1β, IL-6, IL-18, and TNF-α, as well as the relative expressions of NOX1, NOX2, NOX4, and NLRP3 genes significantly decreased in the AnM and positive groups (P < 0.05 or P < 0.01). The pathological changes of inflammatory infiltration of tissue cells in the dorsal horn of the lumbosacral spinal cord were slowed in the AnM group.

CONCLUSION

Acupuncture and moxibustion therapy have a positive effect on pain relief and anti-inflammatory effects in CCI sciatica rats, which may point to the regulation of NOX1, NOX2, NOX4, and NLRP3 expressions, and inhibition of ROS.

Alpha-Lipoic Acid as an Antioxidant Strategy for Managing Neuropathic Pain

Neuropathic pain (NP) is the most prevalent and debilitating form of chronic pain, caused by injuries or diseases of the somatosensory system. Since current first-line treatments only provide poor symptomatic relief, the search for new therapeutic strategies for managing NP is an active field of investigation. Multiple mechanisms contribute to the genesis and maintenance of NP, including damage caused by oxidative stress. The naturally occurring antioxidant alpha-lipoic acid (ALA) is a promising therapeutic agent for the management of NP. Several pre-clinical in vitro and in vivo studies as well as clinical trials demonstrate the analgesic potential of ALA in the management of NP. The beneficial biological activities of ALA are reflected in the various patents for the development of ALA-based innovative products. This review demonstrates the therapeutic potential of ALA in the management of NP by discussing its analgesic effects by multiple antioxidant mechanisms as well as the use of patented ALA-based products and how technological approaches have been applied to enhance ALA's pharmacological properties.