Characterization of Mechanical Allodynia and Skin Innervation in a Mouse Model of Type-2 Diabetes Induced by Cafeteria-Style Diet and Low-Doses of Streptozotocin

Upregulation of Acid-Sensing Ion Channel 1a in the Anterior Cingulate Cortex by TNF-α/NF-κB Pathway Contributes to Diabetes-Related Pain

Effective treatment strategies for diabetes-related pain are limited because of its complex pathogenesis, particularly brain mechanisms underlying this disease. The acid-sensing ion channel 1a (ASIC1a) has emerged as a key player in the development and treatment of various types of pain. We investigated the role of ASIC1a in diabetes-related pain and its molecular mechanisms in the anterior cingulate cortex (ACC). Our findings demonstrate that the upregulation of ASIC1a expression drives enhanced activity of excitatory glutamatergic neurons in the ACC (ACCGlu), promoting the development of pain hypersensitivity in streptozotocin (STZ)-induced diabetic male mice. Pharmacologic inhibition and genetic knockout of ASIC1a in ACCGlu neurons significantly reduced neuronal activity and alleviated mechanical and thermal pain sensitizations in STZ-induced diabetes. Furthermore, increased levels of tumor necrosis factor-α (TNF-α) in the ACC upregulated ASIC1a by triggering nuclear factor-κB (NF-κB) pathways, which led to the development of diabetes-related pain. Notably, the clinically used medication, infliximab, exhibited therapeutic effects on diabetes-related pain via its influence on TNF-α/NF-κB/ASIC1a pathway in STZ-treated mice. Collectively, this study identifies ASIC1a as a potential therapeutic target for diabetes-related pain and shows the neutralization of TNF-α leads to pain relief through the TNF-α/NF-κB/ASIC1a pathway in the ACC. These findings hold promise for the development of new clinical therapeutic strategies for diabetes-related pain.

ARTICLE HIGHLIGHTS

Upregulation of acid-sensing ion channel 1a (ASIC1a) expression in anterior cingulate cortex (ACC) glutamatergic (ACCGlu) neurons drives diabetes-related pain hypersensitivity in mice, and pharmacologic inhibition and genetic knockout of ASIC1a in ACCGlu neurons significantly reduce neuronal hyperactivity and alleviate pain. Tumor necrosis factor-α/nuclear factor-κB signaling in the ACC elevates ASIC1a expression, mechanistically linking neuroinflammation to pain development in diabetic mice. ASIC1a is a potential therapeutic target for diabetes-related pain, offering a pathway-specific strategy for treatment development.

Neuro-Nutritional Approach to Neuropathic Pain Management: A Critical Review

Pain is a significant global public health issue that can interfere with daily activities, sleep, and interpersonal relationships when it becomes chronic or worsens, ultimately impairing quality of life. Despite ongoing efforts, the efficacy of pain treatments in improving outcomes for patients remains limited. At present, the challenge lies in developing a personalized care and management plan that helps to maintain patient activity levels and effectively manages pain. Neuropathic pain is a chronic condition resulting from damage to the somatosensory nervous system, significantly impacting quality of life. It is partly thought to be caused by inflammation and oxidative stress, and clinical research has suggested a link between this condition and diet. However, these links are not yet well understood and require further investigation to evaluate the pathways involved in neuropathic pain. Specifically, the question remains whether supplementation with dietary antioxidants, such as melatonin, could serve as a potential adjunctive treatment for neuropathic pain modulation. Melatonin, primarily secreted by the pineal gland but also produced by other systems such as the digestive system, is known for its anti-inflammatory, antioxidant, and anti-aging properties. It is found in various fruits and vegetables, and its presence alongside other polyphenols in these foods may enhance melatonin intake and contribute to improved health. The aim of this review is to provide an overview of neuropathic pain and examine the potential role of melatonin as an adjunctive treatment in a neuro-nutritional approach to pain management.

Effect of 28 days treatment of baricitinib on mechanical allodynia, osteopenia, and loss of nerve fibers in an experimental model of type-1 diabetes mellitus

BACKGROUND

Type-1 diabetes mellitus (T1DM) is associated with numerous health problems, including peripheral neuropathy, osteoporosis, and bone denervation, all of which diminish quality of life. However, there are relatively few therapies to treat these T1DM-related complications. Recent studies have shown that Janus kinase (JAK) inhibitors reverse aging- and rheumatoid arthritis-induced bone loss and reduce pain associated with peripheral nerve injuries, and rheumatoid arthritis. Thus, we assessed whether a JAK1/JAK2 inhibitor, baricitinib, ameliorates mechanical pain sensitivity (a measure of peripheral neuropathy), osteoporosis, and bone denervation in the femur of mice with T1DM.

METHODS

Female ICR mice (13 weeks old) received five daily administrations of streptozotocin (ip, 50 mg/kg) to induce T1DM. At thirty-one weeks of age, mice were treated with baricitinib (po; 40 mg/kg/bid; for 28 days) or vehicle. Mechanical sensitivity was evaluated at 30, 33, and 35 weeks of age on the plantar surface of the right hind paw. At the end of the treatment, mice were sacrificed, and lower extremities were harvested for microcomputed tomography and immunohistochemistry analyses.

RESULTS

Mice with T1DM exhibited greater blood glucose levels, hind paw mechanical hypersensitivity, trabecular bone loss, and decreased density of calcitonin gene-related peptide-positive and tyrosine hydroxylase-positive axons within the marrow of the femoral neck compared to control mice. Baricitinib treatment significantly reduced mechanical hypersensitivity and ameliorated sensory and sympathetic denervation at the femoral neck, but it did not reverse trabecular bone loss.

CONCLUSIONS

Our findings suggest that baricitinib may represent a new therapeutic alternative to treat T1DM-induced peripheral neuropathy and bone denervation.

Sexual Dimorphism in the Mechanism of Pain Central Sensitization

It has long been recognized that men and women have different degrees of susceptibility to chronic pain. Greater recognition of the sexual dimorphism in chronic pain has resulted in increasing numbers of both clinical and preclinical studies that have identified factors and mechanisms underlying sex differences in pain sensitization. Here, we review sexually dimorphic pain phenotypes in various research animal models and factors involved in the sex difference in pain phenotypes. We further discuss putative mechanisms for the sexual dimorphism in pain sensitization, which involves sex hormones, spinal cord microglia, and peripheral immune cells. Elucidating the sexually dimorphic mechanism of pain sensitization may provide important clinical implications and aid the development of sex-specific therapeutic strategies to treat chronic pain.

Response profile in a rat model of exercise-induced hypoalgesia is associated with duloxetine, pregabalin and diclofenac effect on constriction-induced neuropathy

BACKGROUND

Exercise is a known trigger of the inhibitory pain modulation system and its analgesic effect is termed exercise-induced hypoalgesia (EIH). Previous studies have demonstrated that rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury compared to rats with substantial analgesic response following exercise.

OBJECTIVES

A rat model of EIH as an indicator of the pain inhibitory system's efficiency was used to explore the association between EIH profiles and the effect of pharmacotherapy on rat's neuropathic pain.

METHODS

EIH profiles were assessed by evaluating paw responses to mechanical stimuli before and after exercise on a rotating rod. Rats with a reduction of ≤33% in responses were classified as low EIH and those with ≥67% as high EIH. Low and high EIH rats underwent sciatic nerve chronic constriction injury (CCI). Paw responses to mechanical stimuli were measured at baseline, following CCI, and after treatment with diclofenac, duloxetine or pregabalin. In a different group of low and high EIH rats, EIH was measured before and following treatment with the same medications.

RESULTS

Low EIH rats developed more significant hypersensitivity following CCI. Duloxetine and pregabalin successfully reduced hypersensitivity, although significantly more so in low EIH rats. Diclofenac had limited effects, and only on low EIH rats. Four days of duloxetine administration transformed low EIH rats' profiles to high EIH.

CONCLUSIONS

The findings of this study suggest that EIH profiles in rats can not only predict the development of hypersensitivity following injury but may also support targeted pharmacological treatment.

SIGNIFICANCE

Exercise is a known trigger of the inhibitory pain modulation. Rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury. Pain modulation profiles in rats can also support targeted pharmacological treatment; rats with deficient analgesic response following exercise benefit more from treatment with duloxetine and gabapentin. Treatment with duloxetine can improve pain modulation profile.