Glucagon-like peptide 1 (GLP-1) receptor agonists are frequently used to treat type 2 diabetes and obesity. Despite the development of several drugs for neuropathic pain management, their poor efficacy, tolerance, addiction potential, and side effects limit their usage. Teneligliptin, a DPP-4 inhibitor, has been shown to reduce spinal astrocyte activation and neuropathic pain caused by partial sciatic nerve transection. Additionally, we showed its capacity to improve the analgesic effects of morphine and reduce analgesic tolerance. Recent studies indicate that GLP-1 synthesized in the brain activates GLP-1 receptor signaling pathways, essential for neuroprotection and anti-inflammatory effects. Multiple in vitro and in vivo studies using preclinical models of neurodegenerative disorders have shown the anti-inflammatory properties associated with glucagon-like peptide-1 receptor (GLP-1R) activation. This study aimed to investigate the mechanism of antinociception and the effects of the GLP-1 agonist semaglutide (SEMA) on diabetic neuropathic pain in diabetic rats. Methods: Male Wistar rats, each weighing between 300 and 350 g, were categorized into four groups: one non-diabetic sham group and three diabetic groups. The diabetic group received a single intraperitoneal injection of streptozotocin (STZ) at a dosage of 60 mg/kg to induce diabetic neuropathy. After 4 weeks of STZ injection, one diabetic group was given saline (vehicle), and the other two were treated with either 1× SEMA (1.44 mg/kg, orally) or 2× SEMA (2.88 mg/kg, orally). Following a 4-week course of oral drug treatment, behavioral, biochemical, and immunohistochemical analyses were carried out. The mechanical allodynia, thermal hyperalgesia, blood glucose, advanced glycation end products (AGEs), plasma HbA1C, and spinal inflammatory markers were evaluated. Results: SEMA treatment significantly reduced both allodynia and hyperalgesia in the diabetic group. SEMA therapy had a limited impact on body weight restoration and blood glucose reduction. In diabetic rats, SEMA lowered the amounts of pro-inflammatory cytokines in the spinal cord and dorsal horn. It also lowered the activation of microglia and astrocytes in the dorsal horn. SEMA significantly reduced HbA1c and AGE levels in diabetic rats compared to the sham control group. Conclusions: These results indicate SEMA’s neuroprotective benefits against diabetic neuropathic pain, most likely by reducing inflammation and oxidative stress by inhibiting astrocyte and microglial activity. Our findings suggest that we can repurpose GLP-1 agonists as potent anti-hyperalgesic and anti-inflammatory drugs to treat neuropathic pain without serious side effects.

Morphine (MOR) is a commonly prescribed drug for the treatment of moderate to severe diabetic neuropathic pain (DNP). However, long-term MOR treatment is limited by morphine analgesic tolerance (MAT). The activation of microglial cells and the release of glia-derived proinflammatory cytokines are known to play an important role in the development of MAT. In this study, we aimed to investigate the effects of the dipeptidyl peptidase-4 inhibitor (DPP-4i) teneligliptin (TEN) on MOR-induced microglial cell activation and MAT in DNP rats. DNP was induced in four groups of male Wistar rats through a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg, freshly dissolved in 5 mmol/L citrate buffer, pH 4.5). Sham rats were administered with the vehicle. Seven days after STZ injection, all rats were implanted with an intrathecal (i.t) catheter connected to a mini-osmotic pump, divided into five groups, and infused with the following combinations: sham + saline (1 µL/h, i.t), DNP + saline (1 µL/h, i.t), DNP + MOR (15 µg/h, i.t), DNP + TEN (2 µg/h, i.t), and DNP + MOR (15 µg/h, i.t) + TEN (2 µg/h, i.t) for 7 days at a rate of 1 μL/h. The MAT was confirmed through the measurement of mechanical paw withdrawal threshold and tail-flick tests. The mRNA expression of neuroprotective proteins nuclear factor erythroid 2-related factor (Nrf2) and heme oxygenase-1 (HO-1) in the dorsal horn was evaluated by quantitative PCR (qPCR). Microglial cell activation and mononucleate cell infiltration in the spinal cord dorsal horn were assessed by immunofluorescence assay (IFA) and Western blotting (WB). The results showed that co-infusion of TEN with MOR significantly attenuated MAT in DNP rats through the restoration of neuroprotective proteins Nrf2 and HO-1 and suppression of microglial cell activation in the dorsal horn. Though TEN at a dose of 2 μg has mild antinociceptive effects, it is highly effective in limiting MAT.

Diabetic peripheral neuropathy (DPN) remains a leading cause of disability in diabetes, yet current care is largely symptomatic and does not directly address early neurovascular-immune pathology. This narrative review synthesizes clinical, redox, vascular, and immunological evidence into a peripheral nerve neurovascular unit (PNVU)/blood–nerve barrier (BNB)-centered framework for DPN. First, the review outlines the diagnostic and translational endpoint landscape of DPN, emphasizing that commonly used clinical, neurophysiological, small-fiber, and imaging-based tools capture important disease domains but do not directly assess early BNB dysfunction. It then reviews the anatomical and functional basis of the PNVU and BNB, including endoneurial microvascular endothelial cells, pericytes, basement membrane components, immune cells, and tight-junction proteins. Next, it discusses how chronic hyperglycemia and dyslipidemia drive metabolic-to-vascular coupling, redox imbalance, antioxidant defense failure, advanced glycation end products (AGEs), receptor for AGEs (RAGE), and nuclear factor-κB (NF-κB) signaling, endothelial activation, leukocyte recruitment, macrophage polarization, and junctional disassembly, culminating in increased BNB permeability and exposure of peripheral nerves to pro-inflammatory and neurotoxic mediators. Finally, it evaluates incretin-based therapies—including glucagon-like peptide-1 receptor agonists (GLP-1RAs), dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors, DPP-4is), and emerging multi-agonists—as potential modulators of oxidative and inflammatory stress within this framework. Although semaglutide and related agents show mechanistic plausibility and preclinical promise, direct evidence for incretin-mediated BNB stabilization in human DPN remains limited. By reframing DPN as a redox-driven neurovascular-immune disorder, this review highlights barrier-focused biomarkers, translational endpoints, and hypothesis-generating therapeutic opportunities that require clinical validation.

Diabetic peripheral neuropathy (DPN) remains a leading cause of disability in diabetes, yet current care is largely symptomatic. Increasing evidence places early dysfunction of the blood-nerve barrier (BNB)—a core element of the peripheral nerve neurovascular unit (PNVU)—at the intersection of metabolic stress and neuroinflammation. This review synthesizes a redox-centered model of BNB failure in DPN: (i) chronic hyperglycemia and dyslipidemia overwhelm endogenous antioxidant defenses, driving reactive oxygen species (ROS) imbalance; (ii) ROS-associated endothelial activation promotes endothelial-immune crosstalk, leukocyte recruitment, and macrophage polarization; and (iii) progressive loss of tight-junction and barrier homeostasis increases paracellular permeability and exposure of nerves to pro-inflammatory and neurotoxic mediators. We then evaluate incretin-based therapies—GLP-1 receptor agonists, DPP-4 inhibitors, and emerging multi-agonists—as potential modulators of PNVU/BNB stress. Beyond glucose and weight effects, these agents may dampen oxidative and inflammatory signaling, engage antioxidant pathways (e.g., Nrf2), and potentially support molecular determinants of BNB integrity via indirect metabolic unloading and possible GLP-1R-dependent vascular-immune actions. By reframing DPN as a neurovascular-immune disorder driven by redox imbalance, we highlight barrier-focused biomarkers and hypothesis-generating therapeutic opportunities that require clinical validation.