Rat Model Of Diabetic Peripheral Neuropathy Research Articles

Protective effect of alirocumab, a PCSK9 inhibitor, on the sciatic nerve of rats with diabetic peripheral neuropathy.

Dyslipidemia has been considered a risk factor for diabetic peripheral neuropathy. Proprotein convertase subtilisin-like/Kexin 9 inhibitor (PCSK9) inhibitors are a new type of lipid-lowering drug currently in clinical use. The role of PCSK9 in diabetic peripheral neuropathy is still unclear. In this study, the effect of alirocumab, a PCSK9 inhibitor, on the sciatic nerve in rats with diabetic peripheral neuropathy and its underlying mechanisms were investigated. The diabetic peripheral neuropathy rat model was established by using a high-fat diet combined with streptozotocin injection, and experimental subjects were divided into normal, diabetic peripheral neuropathy, and alirocumab groups. The results showed that Alirocumab improved nerve conduction, morphological changes, and small fiber deficits in rats with DPN, possibly related to its amelioration of oxidative stress and the inflammatory response.

Artesunate Inhibits Apoptosis and Promotes Survival in Schwann Cells via the PI3K/AKT/mTOR Axis in Diabetic Peripheral Neuropathy.

Diabetic peripheral neuropathy (DPN) is an early developing complication of diabetes mellitus associated with nerve dysfunction. Artesunate (ART), a natural compound extracted from the herb Artemisia annua L., was reported to benefit neural injury. However, whether ART has a role in preventing DPN is still unknown. In this study, a rat model of DPN with a high fat diet feeding and streptozotocin (STZ) injection was established. The findings indicated that ART treatment significantly ameliorated hyperglycemia-induced hot plate reaction latency (HPRL) decline, cold sensitivity and mechanical allodynia, and nerve injury by inhibiting sciatic nerve apoptosis. Further, ART restored high glucose (HG)-induced elevated apoptosis and deficient survival in rat neuronal Schwann cells, RSC96 cells. We demonstrated that ART promoted protein kinase B (AKT) phosphorylation as well as its downstream factor mammalian target of rapamycin (mTOR) in vivo and in vitro. Of note, the protective effects of ART in RSC96 cells under HG condition could be counteracted by LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor. Taken together, ART mitigated hyperglycemia-induced nerve injury by suppressing apoptosis and promoting the viability of Schwann cells via the PI3K/AKT/mTOR signaling pathway.

Blocking CXC Motif Chemokine Ligand 2 Ameliorates Diabetic Peripheral Neuropathy via Inhibiting Apoptosis and NLRP3 Inflammasome Activation.

Evidence suggests that CXC motif chemokines are involved in neuronal injury and inflammatory processes. Bioinformatics analysis by using data from the Gene Expression Omnibus (GEO) database was performed and identified CXC motif chemokine ligands (CXCLs) as associated with diabetic peripheral neuropathy (DPN). The present study focused on CXC motif chemokine ligand 2 (CXCL2), and the role and potential mechanisms of CXCL2 in DPN were investigated. The DPN rat model was generated by streptozotocin (STZ) injection in vivo, and high-glucose (HG)-stimulated Schwann cell RSC96 was considered a cell model of DPN in vitro. Neuropathic symptoms of DPN were explored by neurological tests and histological examinations. DPN rats showed a decreased level of motor nerve conduction velocity (MNCV) along with typical histological changes. CXCL2 expression was significantly increased in STZ-induced DPN rat sciatic nerve and HG-induced RSC96 cells. Functionally, CXCL2 knockdown inhibited cell apoptosis and inflammation activation under diabetic conditions in vitro and in vivo. CXCL2 knockdown increased cell viability in HG-treated RSC96 cells and reduced apoptosis concerning the decreased expression of cleaved Caspase 3/9. In addition, CXCL2 knockdown protected against NOD-like receptor protein 3 (NLRP3) inflammasome activation and reduced levels of pro-inflammatory cytokines, interleukin (IL)-1β and IL-18. The repressive effects of CXCL2 knockdown on inflammasome activation under HG conditions were significantly abolished by treatment of the NLRP3 activator nigericin. In conclusion, these results indicated that CXCL2 knockdown exhibited amelioration of hyperglycemia-induced DPN by inhibiting cell apoptosis and NLRP3 inflammasome activation, suggesting that targeting CXCL2 might be a potential strategy for DPN treatment.

Effect of Aescin on Inflammatory Responses in a Diabetic Peripheral Neuropathy Rat Model by Modulating HMGB1 and RAGE Levels

Effect of Aescin on Inflammatory Responses in a Diabetic Peripheral Neuropathy Rat Model by Modulating HMGB1 and RAGE Levels

Quercetin reduces inflammation in a rat model of diabetic peripheral neuropathy by regulating the TLR4/MyD88/NF-κB signalling pathway

Neuroinflammation contributes significantly to the pathogenesis of diabetic peripheral neuropathy (DPN). Quercetin reportedly exerts neuroprotective effects in DPN. Here, we aimed to evaluate the potential anti-inflammatory effects of quercetin in a DPN rat model. Eight weeks after streptozotocin administration, diabetic rats were treated with quercetin (30 and 60 mg/kg/day orally) for 6 weeks. We assessed the mechanical withdrawal threshold (MWT), nerve conduction velocity (NCV) and morphological changes in sciatic nerves. Additionally, we measured the levels of tumour necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and IL-6 by ELISA and the expression of TLR4, MyD88, and NF-κB in sciatic nerves by western blotting and immunohistochemical assays. Our results revealed that blood glucose levels and body weight were unaltered following quercetin treatment. However, quercetin improved MWT (p < 0.05), NCV (p < 0.05), and pathological changes in the sciatic nerves of DPN rats. Quercetin significantly alleviated the increased expression of TNF-α (p < 0.05) and IL-1β (p < 0.001). Furthermore, high-dose quercetin administration significantly downregulated the expression of TLR4 (p < 0.001), MyD88 (p < 0.001), and NF-κB (p < 0.001) in sciatic nerves of DPN rats. Our findings revealed that quercetin could reduce the levels of inflammatory factors in DPN rats, possibly mediated via the downregulation of the TLR4/MyD88/NF-κB signalling pathway. Collectively, these results suggest that although quercetin did not decreased blood glucose levels or reversed the reduced body weight, it showed anti-inflammatory and neuroprotective effects, which was beneficial for the treatment of DPN.

Lipin1 Alleviates Autophagy Disorder in Sciatic Nerve and Improves Diabetic Peripheral Neuropathy.

Diabetic peripheral neuropathy (DPN) is a chronic complication of diabetes, and its neural mechanisms underlying the pathogenesis remain unclear. Autophagy plays an important role in neurodegenerative diseases and nerve tissue injury. Lipin1 is a phosphatidic acid phosphatase enzyme that converts phosphatidic acid (PA) into diacylglycerol (DAG), a precursor of triacylglycerol and phospholipids which plays an important role in maintaining normal peripheral nerve conduction function. However, whether Lipin1 involved in the pathogenesis of DPN via regulation of autophagy is not elucidated. Here, we show that the Lipin1 expression was downregulated in streptozotocin (STZ)-induced DPN rat model. Interestingly, STZ prevented DAG synthesis, and resulted in autophagic hyperactivity, effects which may increase the apoptosis of Schwann cells and lead to demyelination in sciatic nerve in DPN rats. More importantly, upregulation of lipin1 in the DPN rats ameliorated autophagy disorders and pathological changes of the sciatic nerve, which associated with the increase of the motor nerve conductive velocity (MNCV) in DPN rats. In contrast, knockdown of lipin1 exacerbates neuronal abnormalities and facilitates the genesis of DPN phenotypes in rats. In addition, overexpression of lipin1 in RSC96 cells also significantly decreased the autophagic hyperactivity and apoptosis induced by hyperglycemia. These results suggest that lipin1 may exert neuroprotection within the sciatic nerve anomalies and may serve as a potential therapeutic target for the treatment of DPN.

Transplantation of engineered exosomes derived from bone marrow mesenchymal stromal cells ameliorate diabetic peripheral neuropathy under electrical stimulation

Diabetic peripheral neuropathy (DPN) is a long-term complication associated with nerve dysfunction and uncontrolled hyperglycemia. In spite of new drug discoveries, development of effective therapy is much needed to cure DPN. Here, we have developed a combinatorial approach to provide biochemical and electrical cues, considered to be important for nerve regeneration. Exosomes derived from bone marrow mesenchymal stromal cells (BMSCs) were fused with polypyrrole nanoparticles (PpyNps) containing liposomes to deliver both the cues in a single delivery vehicle. We developed DPN rat model and injected intramuscularly the fused exosomal system to understand its long-term therapeutic effect. We found that the fused system along with electrical stimulation normalized the nerve conduction velocity (57.60 ± 0.45 m/s) and compound muscle action potential (16.96 ± 0.73 mV) similar to healthy control (58.53 ± 1.10 m/s; 18.19 ± 1.45 mV). Gastrocnemius muscle morphology, muscle mass, and integrity were recovered after treatment. Interestingly, we also observed paracrine effect of delivered exosomes in controlling hyperglycemia and loss in body weight and also showed attenuation of damage to the tissues such as the pancreas, kidney, and liver. This work provides a promising effective treatment and also contribute cutting edge therapeutic approach for the treatment of DPN.

Approach to creating early diabetic peripheral neuropathy rat model

To create the early diabetic peripheral neuropathy (DPN) rat model. After one-week adaption, 26 male Sprague-Dawley (SD) rats were divided into two groups, the control group (n=6) and the model group (n=20). High-sucrose/high-fat diet (D12451, 35% of energy from carbohydrate, 45% of energy from fat) was given to the model group for six weeks to induce insulin resistance, meanwhile normal diet was given to the control group. Afterwards, streptozocin (STZ) buffer solution (35 mg/kg bodyweight) was injected into abdomen of the model group to induce specific pancreatic injury, meanwhile an equal amount of buffer solution was given to the control group. Then 48 h later, type 2 diabetes mellitus (T2DM) was supposed to be successfully induced according to the random blood glucose more than 16.7 mmol/L in the model group. Then the basic features of the T2DM rats were evaluated, including body weight, fasting blood glucose (FBG), glucose tolerance (oral glucose tolerance test, OGTT), and insulin tolerance (intraperitoneal insulin tolerance test, IPITT). Subsequently, withdrawal thermal latency (WTL) was measured regularly to determine when the early DPN occurred. Once confirmed, sciatic nerve conduction velocity (NCV) of all the rats was conducted. The T2DM rats were successfully induced in the model group through high-sucrose/high-fat diet for six weeks along with STZ intraperitoneal injection (35 mg/kg bodyweight). When compared to the control group, the T2DM rats had higher FBG (P<0.001), and the glucose tolerance and insulin tolerance were both damaged (P<0.001 in OGTT, P=0.002 in IPITT). It was on the 17th day when the T2DM rats became much more sensitive to heat stimulus compared to the control group (P=0.004). Meanwhile, the sciatic NCV was conducted. There was no significant difference between the early DPN group and the control group (P=0.196). High-sucrose/high-fat diet for six weeks along with STZ intraperitoneal injection (35 mg/kg bodyweight) could successfully induce T2DM rat model, manifested by a certain extent of insulin resistance and deficiency of insulin secretion. It was about 17 days later when the early DPN emerged. In the early DPN, small fiber neuropathy came out earlier than large fiber neuropathy.

Nanoparticle–microRNA-146a-5p polyplexes ameliorate diabetic peripheral neuropathy by modulating inflammation and apoptosis

Nontoxic and nonimmunogenic nanoparticles play an increasingly important role in the application of pharmaceutical nanocarriers. The pathogenesis of diabetic peripheral neuropathy (DPN) has been extensively studied. However, the role of microRNAs in DPN remains to be clarified. We verified in vitro that miR-146a-5p mimics inhibited the expression of proinflammatory cytokines and apoptosis. Then, we explored the protective effect of nanoparticle–miRNA-146a-5p polyplexes (nano-miR-146a-5p) on DPN rats. We demonstrated that nano-miR-146a-5p improved nerve conduction velocity and alleviated the morphological damage and demyelination of the sciatic nerve of DPN rats. The expression of the inflammatory cytokines, caspase-3, and cleaved caspase-3 in the sciatic nerve was inhibited by nano-miR-146a-5p. Additionally, nano-miR-146a-5p increased the expression of myelin basic protein. These results all indicated that nano-miR-146a-5p had a protective effect on peripheral nerves in the DPN rat model, which may occur through the regulation of the inflammatory response and apoptosis.

Chronic Nerve Compression Accelerates the Progression of Diabetic Peripheral Neuropathy in a Rat Model: A Study of Gene Expression Profiling.

This article investigates the role of chronic nerve compression in the progression of diabetic peripheral neuropathy (DPN) by gene expression profiling. Chronic nerve compression was created in streptozotocin (STZ)-induced diabetic rats by wrapping a silicone tube around the sciatic nerve (SCN). Neurological deficits were evaluated using pain threshold test, motor nerve conduction velocity (MNCV), and histopathologic examination. Differentially expressed genes (DGEs) and metabolic processes associated with chronic nerve compression were analyzed. Significant changes in withdrawal threshold and MNCV were observed in diabetic rats 6 weeks after diabetes induction, and in DPN rats 4 weeks after diabetes induction. Histopathologic examination of the SCN in DPN rats presented typical changes of myelin degeneration in DPN. Function analyses of DEGs demonstrated that biological processes related to inflammatory response, extracellular matrix component, and synaptic transmission were upregulated after diabetes induction, and chronic nerve compression further enhanced those changes. While processes related to lipid and glucose metabolism, response to insulin, and apoptosis regulation were inhibited after diabetes induction, chronic nerve compression further enhanced these inhibitions. Our study suggests that additional silicone tube wrapping on the SCN of rat with diabetes closely mimics the course and pathologic findings of human DPN. Further studies are needed to verify the effectiveness of this rat model of DPN and elucidate the roles of the individual genes in the progression of DPN.

GLP‑1R agonists ameliorate peripheral nerve dysfunction and inflammation via p38 MAPK/NF‑κB signaling pathways in streptozotocin‑induced diabetic rats.

The present study aimed to investigate the mechanism of glucagon‑like peptide‑1 receptor (GLP‑1R) agonists in the progression of diabetic peripheral neuropathy (DPN) in streptozotocin (STZ)‑induced diabetic rats, through inflammatory signaling pathways. The DPN rat model was generated by intraperitoneal injection of STZ and then treated with the GLP‑1R agonist liraglutide or saline for 8 weeks. These animals were randomly divided into 4groups (10rats in each): The normal control+saline group, the normal control+liraglutide group, the diabetic+saline (DM) group and the diabetic+liraglutide (DML) group. The nerve conduction velocity (NCV) in the sciatic nerves of the rats was monitored over a period of 8weeks. Peripheral serum was obtained for the measurement of blood glucose, tumor necrosis factor‑α (TNF‑α), interleukin‑6 (IL‑6) and IL‑1β level. The protein levels of phosphorylated (p‑) and total extracellular signal‑regulated kinase, c‑Jun NH2‑terminal kinases, p38mitogen‑activated protein kinases (MAPK), and nuclear and cytoplasmic nuclear factor‑κB (NF‑κB) were measured through western blot analysis. Sciatic nerve mRNA expression levels of proinflammatory chemokines (TNF‑α, IL‑6 and IL‑1β), chemokines [monocyte chemoattractant protein‑1 (MCP‑1)], adhesion molecules [intercellular adhesion molecule1 (ICAM‑1)], neurotrophic factors [neuritin, nerve growth factor (NGF) and neuron‑specific enolase(NSE)] and NADPH oxidase4 (NOX4) were evaluated by reverse transcription-quantitative polymerase chain reaction. Subsequent to 8weeks of treatment with liraglutide, the density of myelin nerve fibers was partially restored in the DML group. The delayed motor NCV and sensory NCV in the DML group were improved. The IOD value of NOX4 staining in the DML group (24.43±9.01) was reduced compared with that in the DM group (56.60±6.91). The levels of TNF‑α, IL‑1β and IL‑6 in the peripheral serum of the DML group were significantly suppressed compared with those of the DM group. It was also observed that the mRNA expression levels of TNF‑α, IL‑6, IL‑1β, MCP‑1, ICAM‑1 and NOX4 in the sciatic nerve were attenuated in the DML group. The mRNA expression of neuritin and NGF was significantly increased in the DML group compared with that of the DM group; NSE was reduced in the sciatic nerves of the DML group compared with that of the DM group. Additionally, the protein expression of p‑p38MAPK and NF‑κB in the DML group was significantly suppressed. These data demonstrated that GLP‑1R agonists may prevent nerve dysfunction in the sciatic nerves of diabetic rats via p38MAPK/NF‑κB signaling pathways independent of glycemic control. GLP‑1R agonists may be a useful therapeutic strategy for slowing the progression of DPN.

Expression of Nrf2 Promotes Schwann Cell-Mediated Sciatic Nerve Recovery in Diabetic Peripheral Neuropathy

Background/Aims: High glucose-induced oxidative stress and inflammatory responses play an important role in painful diabetic neuropathy by activating the TLR4/NFκB signal pathway. Schwann cells (SCs) are integral to peripheral nerve biology, contributing to saltatory conduction along axons, nerve and axon development, and axonal regeneration. SCs provide a microenvironment favoring vascular regeneration but their low survival ratio in hyperglycemic conditions suppress the function to promote nerve growth. Nuclear factor erythroid 2-related factor 2 (Nrf2) promotes remyelination after peripheral nerve injury. The aim of this study was to identify the role of Nrf2 in SC-mediated functional recovery after sciatic nerve injury. Methods: We compared plasma inflammatory factors in diabetic patients (DN) with/without diabetic peripheral neuropathy (DPN) and assessed whether Nrf2 expression in SCs could repair peripheral nerve injury in a rat model. Nrf2, TLR4/NFκB signal pathway and apoptosis relative protein expression were detected by western blot. Apoptosis and angiogenesis were determined by immunofluorescence and tubule formation assay, respectively. Regenerated nerves were determined by transmission electron microscope. Results: Higher levels of inflammatory factors and VEGF expression were found in DPN patients. Cellular experiments indicate that Nrf2 expression inhibits hyperglycemia-induced apoptosis and promotes angiogenesis by regulating the TLR4/NFκB signal pathway. Animal experiments show that nerve conduction velocity, myelin sheath thickness, and sciatic vasa nervorum are restored with transplantation of SCs overexpressing Nrf2. Conclusions: Taken together, the high survival ratio of SCs in a DPN rat model indicates that overexpression of Nrf2 restores nerve injury.

Effects of moderate exercise training and detraining on diabetic peripheral neuropathy in streptozotocin-induced diabetic rats

Context Exercise training programs have been shown to have prophylactic effects on diabetes-associated complications in murine models. Objective The present study aimed to elucidate the effect of moderate exercise training for 4 weeks and detraining for 2 weeks on diabetic peripheral neuropathy in type 1 diabetic rat model. Materials and methods Type 1 diabetes was induced by a single intraperitoneal injection of streptzotocin (45 mg/kg). Exercise training lasted for 4 weeks in trained group, whereas the detrained group stopped training for 2 weeks after training for 4 weeks. After 4 weeks, tail flick test latency, body weight, serum glucose, inflammatory markers, and nerve growth factor levels were measured, and the same was done in detrained diabetic rats after 2 weeks of detraining. Results Moderate exercise training for 4 weeks increased significantly tail flick latency and nerve growth factor levels, whereas the inflammatory markers were significantly improved compared with diabetic sedentary rats. Interestingly, the prophylactic effects of exercise training were maintained in the detrained rats after 2 weeks of detraining. Conclusion Our results explore the prophylactic mechanisms underlying the exercise training in diabetic peripheral neuropathy rat model and give further insights into the maintained prophylactic effects that lasted after 2 weeks of detraining.

Protective effects of methanolic extract of Juglans regia L. leaf on streptozotocin-induced diabetic peripheral neuropathy in rats

BackgroundOxidative stress has a pivotal role in the pathogenesis and development of diabetic peripheral neuropathy (DPN), the most common and debilitating complications of diabetes mellitus. There is accumulating evidence that Juglans regia L. (GRL) leaf extract, a rich source of phenolic components, has hypoglycemic and antioxidative properties. This study aimed to determine the protective effects of Juglans regia L. leaf extract against streptozotocin-induced diabetic neuropathy in rat.MethodsThe DPN rat model was generated by intraperitoneal injection of a single 55 mg/kg dose of streptozotocin (STZ). A subset of the STZ-induced diabetic rats intragastically administered with GRL leaf extract (200 mg/kg/day) before or after the onset of neuropathy, whereas other diabetic rats received only isotonic saline as the same volume of GRL leaf extract. To evaluate the effects of GRL leaf extract on the diabetic neuropathy various parameters, including histopathology and immunohistochemistry of apoptotic and inflammatory factors were assessed along with nociceptive and biochemical assessments.ResultsDegeneration of the sciatic nerves which was detected in the STZ-diabetic rats attenuated after GRL leaf extract administration. Greater caspase-3, COX-2, and iNOS expression could be detected in the STZ-diabetic rats, which were significantly attenuated after GRL leaf extract administration. Also, attenuation of lipid peroxidation and nociceptive response along with improved antioxidant status in the sciatic nerve of diabetic rats were detected after GRL leaf extract administration. In other word, GRL leaf extract ameliorated the behavioral and structural indices of diabetic neuropathy even after the onset of neuropathy, in addition to blood sugar reduction.ConclusionOur results suggest that GRL leaf extract exert preventive and curative effects against STZ-induced diabetic neuropathy in rats which might be due to its antioxidant, anti-inflammatory, and antiapoptotic properties.Graphical abstractProtection against neuropathy

Beneficial effect of TNF-α inhibition on diabetic peripheral neuropathy

BackgroundTumor necrosis factor-α (TNF-α) is an important inflammatory factor produced by activated macrophages and monocytes and plays an important role in the pathogenesis of diabetic peripheral neuropathy (DPN). To evaluate the effect of TNF-α signaling suppression and the potential of TNF-α in the treatment of DPN, a recombinant human TNF-α receptor-antibody fusion protein (rhTNFR:Fc) was used. We focused on the pathophysiology of the sciatic nerve and examined the expression of myelin basic protein (MBP) under DPN status with or without TNF-α inhibition.MethodsThe DPN rat model was generated by intraperitoneal injection of streptozotocin and by feeding with a high-fat, high-sugar diet. The nerve conduction velocity (NCV) in sciatic nerve of rat was monitored over a period of four weeks. The histopathological changes in nerve tissue were examined through traditional tissue histology and ultrastructure transmission electron microscopy (TEM). The expression of MBP was examined through western blot analysis.ResultsThe DPN induced rats showed significant signs of nerve damage including lower NCV, demyelination of nerve fibers, disorganization of lamellar and axonal structures, and decreased expression of MBP in the nerve tissue. The inhibition of TNF-α in the DPN rats resulted in a significant recovery from those symptoms compared to the DPN rats.ConclusionsOur study demonstrates that TNF-α plays a key role in the pathogenesis of DPN and its inhibition by rhTNFR:Fc can prove to be a useful therapeutic strategy for the treatment of and/or prevention from DPN symptoms.

Continuous Buprenorphine Delivery Effect in Streptozotocine-Induced Painful Diabetic Neuropathy in Rats

Diabetic peripheral neuropathy (DPN) can induce loss of nociception as well as mechanical hyperalgesia and tactile allodynia. Pharmacological and clinical studies have shown that buprenorphine, a low-molecular-weight, lipophilic, opioid analgesic available as a transdermal matrix patch formulation, acts on neuropathic pain. To assess the role of buprenorphine in the treatment of DPN-associated neuropathic pain, we used a well-established experimental rat model of DPN in which buprenorphine at doses of 1.2 and 2.4 microg/kg/h was administered by implantable Alzet osmotic pumps for 3 weeks. After 6 weeks of diabetes, nerve conduction velocity (NCV) and behavioural responses to noxious mechanical and thermal stimuli were assessed. Diabetic rats showed an impairment of NCV, mechanical allodynia, and thermal hypoalgesia. Both doses of buprenorphine significantly reversed the diabetes-induced allodynia up to day 7 of treatment. Buprenorphine did not alter either thermal perception or NCV. This study evaluated, through a multimodal approach, the analgesic effect of buprenorphine in an experimental rat model of painful DPN. Our results suggest a possible role for buprenorphine in the management of DPN-associated neuropathic pain.