Diabetic peripheral neuropathy (DPN) is caused by hyperglycemia, which induces oxidative stress and inflammatory responses that damage nerve tissue. Excessive generation of reactive oxygen species (ROS) and NOD-like receptor protein 3 (NLRP3) inflammasome activation trigger the inflammation and pyroptosis in diabetes. Schwann cell dysfunction further promotes DPN progression. Loganin has been shown to have antioxidant and anti-inflammatory neuroprotective activities. This study evaluated the neuroprotective effect of loganin on high-glucose (25 mM)-induced rat Schwann cell line RSC96 injury, a recognized in vitro cell model of DPN. RSC96 cells were pretreated with loganin (0.1, 1, 10, 25, 50 μM) before exposure to high glucose. Loganin’s effects were examined by CCK-8 assay, ROS assay, cell death assay, immunofluorescence staining, quantitative RT–PCR and western blot. High-glucose-treated RSC96 cells sustained cell viability loss, ROS generation, NF-κB nuclear translocation, P2 × 7 purinergic receptor and TXNIP (thioredoxin-interacting protein) expression, NLRP3 inflammasome (NLRP3, ASC, caspase-1) activation, IL-1β and IL-18 maturation and gasdermin D cleavage. Those effects were reduced by loganin pretreatment. In conclusion, we found that loganin’s antioxidant effects prevent RSC96 Schwann cell pyroptosis by inhibiting ROS generation and suppressing NLRP3 inflammasome activation.

Valproate (VPA) is a well-known drug for treating epilepsy and mania, but its action in neuropathic pain is unclear. We used a chronic constriction injury (CCI) model to explore whether VPA prevents neuropathic pain-mediated inflammation and neuronal death. Rats were treated with or without VPA. CCI + VPA rats were intraperitoneally injected with VPA (300 mg/kg/day) from postoperative day (POD) 1 to 14. We measured paw withdrawal latency (PWL) and paw withdrawal threshold (PWT) 1 day before surgery and 1, 3, 7, 14 days after CCI and harvested the sciatic nerves (SN), spinal cord (SC) and dorsal root ganglia (DRG) on POD 3, 7, and 14. PWL and PWT were reduced in CCI rats, but increased in CCI + VPA rats on POD 7 and POD 14. VPA lowered CCI-induced inflammatory proteins (pNFκB, iNOS and COX-2), pro-apoptotic proteins (pAKT/AKT and pGSK-3β/GSK-3β), proinflammatory cytokines (TNF-α and IL-1β) and nuclear pNFκB activation in the SN, DRG and SC in CCI rats. COX-2 and pGSK-3 proteins were decreased by VPA on immunofluorescence analysis. VPA attenuated CCI-induced thermal and mechanical pain behaviors in rats in correlation with anti-neuroinflammation action involving reduction of pNFκB/iNOS/COX-2 activation and inhibition of pAKT/pGSK-3β-mediated neuronal death from injury to peripheral nerves.

Loganin is an iridoid glycoside with antioxidant, anti-inflammatory, glucose-lowering activities which may address the pathological mechanisms of painful diabetic neuropathy (PDN) related to inflammation, oxidative stress, and hyperglycemia. This study investigated the underlying mechanisms of action of loganin on PDN. The in vivo model of PDN was established by streptozotocin-nicotinamide (STZ-NA) induction in Sprague Dawley (SD) rats. Subsequently, loganin (5 mg/kg) was administered by daily intraperitoneal injection. High-glucose stimulated human SH-SY5Y cells co-incubated with loganin were used to mimic the in vitro model of PDN. Loganin improved PDN rats’ associated pain behaviors (allodynia and hyperalgesia), insulin resistance index (HOMA-IR), and serum levels of superoxide dismutase (SOD), catalase and glutathione. Loganin also reduced pain-associated channel protein Ca_V3.2 and calcitonin gene-related peptide (CGRP) in the surficial spinal dorsal horn of PDN rats. Loganin inhibited oxidative stress and NF-κB activation and decreased the levels of mRNA and protein of proinflammatory factors IL-1β and TNF-α. Moreover, loganin attenuated insulin resistance by modulating the JNK-IRS-1 (insulin receptor substrate-1)-Akt-GSK3β signaling pathway in PDN rats. These results suggested that loganin improved PDN-mediated pain behaviors by inhibiting oxidative stress-provoked inflammation in the spinal cord, resulting in improved neuropathic pain.

Eugenosedin‐A has been demonstrated to possess α/β‐adrenoceptor and serotonergic receptor blocking activities. We have investigated by what mechanisms eugenosedin‐A prevents lipopolysaccharide (LPS)‐induced hypotension, vascular hyporeactivity, hyperglycaemia, oxidative injury or inflammatory cytokines formation in rats. Intravenous administration of eugenosedin‐A, trazodone, yohimbine (1 mg kg⁻¹), aminoguanidine or ascorbic acid (15 mg kg⁻¹) normalized LPS (10 mg kg⁻¹)‐induced hypotension. Pretreatment with eugenosedin‐A or the other agents 30 min before LPS injection reduced aortic hyporeactivity. LPS‐induced increases in plasma interleukin‐1β (IL‐β), IL‐6, interferon‐γ (IFN‐γ), tumour necrosis factor‐α (TNF‐α) and blood glucose levels were significantly inhibited by eugenosedin‐A (1 mg kg⁻¹, i.v.). The same dose of trazodone, a chloropiperazinylbenzene‐type antidepressant, and yohimbine, an α₂‐adrenoceptor antagonist, reduced IL‐1β and TNF‐α, but it could not inhibit hyperglycaemia. Aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, and ascorbic acid, an antioxidant, decreased IL‐1β, TNF‐α contents and hyperglycaemia. Eugenosedin‐A and the other agents inhibited Fe²⁺‐ascorbic acid‐induced peroxidation in rat cortex, indicating that those agents had antioxidant effects, with the exception of aminoguanidine. In free radical scavenged experiments, eugenosedin‐A and ascorbic acid eliminated peroxyl radicals. All test agents inhibited the LPS‐induced increase of malondialdehyde (MDA) content in rat brain homogenates. When mice were administered an intraperitoneal injection of LPS alone, mortality occurred from 4 to 16 h, after which time all were dead. However, eugenosedin‐A significantly prolonged the survival time after LPS injection, suggesting that eugenosedin‐A protected against LPS‐induced cardiovascular dysfunction, hyperglycaemia, tissue injury and inflammatory cytokine production. This was attributable mainly to the antioxidant and peroxyl radical scavenged effects of eugenosedin‐A, and which may be, at least in part, due to its blockade on α/β‐adrenergic and serotonergic receptors.