Thymoquinone Alleviates the Experimental Diabetic Peripheral Neuropathy by Modulation of Inflammation

Pyroptosis in Diabetic Peripheral Neuropathy and its Therapeutic Regulation

Pyroptosis is a pro-inflammatory form of cell death resulting from the activation of gasdermins (GSDMs) pore-forming proteins and the release of several pro-inflammatory factors. However, inflammasomes are the intracellular protein complexes that cleave gasdermin D (GSDMD), leading to the formation of robust cell membrane pores and the initiation of pyroptosis. Inflammasome activation and gasdermin-mediated membrane pore formation are the important intrinsic processes in the classical pyroptotic signaling pathway. Overactivation of the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome triggers pyroptosis and amplifies inflammation. Current evidence suggests that the overactivation of inflammasomes and pyroptosis may further induce the progression of cancers, nerve injury, inflammatory disorders and metabolic dysfunctions. Current evidence also indicates that pyroptosis-dependent cell death accelerates the progression of diabetes and its frequent consequences including diabetic peripheral neuropathy (DPN). Pyroptosis-mediated inflammatory reaction further exacerbates DPN-mediated CNS injury. Accumulating evidence shows that several molecular signaling mechanisms trigger pyroptosis in insulin-producing cells, further leading to the development of DPN. Numerous studies have suggested that certain natural compounds or drugs may possess promising pharmacological properties by modulating inflammasomes and pyroptosis, thereby offering potential preventive and practical therapeutic approaches for the treatment and management of DPN. This review elaborates on the underlying molecular mechanisms of pyroptosis and explores possible therapeutic strategies for regulating pyroptosis-regulated cell death in the pharmacological treatment of DPN.

Thymoquinone attenuates diabetes-induced hepatic damage in rat via regulation of oxidative/nitrosative stress, apoptosis, and inflammatory cascade with molecular docking approach

Diabetes mellitus (DM) is a complex metabolic condition that causes organ dysfunction. The current experiment sought to determine the effect of thymoquinone (TQ) on hyperglycemia, hyperlipidemia, oxidative/nitrosative stress, inflammation, and apoptosis in diabetic rats prompted by streptozotocin (STZ) (55 mg/kg body weight i/p). The animals were allocated into control, TQ (50 mg/kg B.W. orally administered for 4 succeeding weeks), Diabetic, and Diabetic + TQ groups. This study confirmed that TQ preserves the levels of insulin, fasting blood glucose, HOMA β-cell indices, HbA1c %, body weight, and lipid profile substantially relative to the DC group. Furthermore, hepatic antioxidant (CAT, GSH, and T-SOD) values were reduced. Conversely, the enzymatic activity of liver functions (AST, ALT, ALP, cytochrome P450, and hepatic glucose-6-phosphatase), lipid peroxidation (MDA), pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6), nitric oxide (NO) and inflammatory marker (CRP) enhanced with STZ administration, which is substantially restored after TQ treatment. Relative to the diabetic rats, TQ reestablished the hepatic architectural changes and collagen fibers. Additionally, TQ downregulated the intensity of the immunohistochemical staining of pro-apoptotic marker (caspase-3), p53, and tumor necrosis factor-alpha (TNF-α) proteins in hepatic tissues. Furthermore, TQ displayed abilities to interact and inhibit the binding site of caspase-3, interleukin-6 receptor, interleukin-1 receptor type 1, TNF receptor superfamily member 1A, and TNF receptor superfamily member 1B in rats following the molecular docking modeling. All these data re-establish the liver functions, antioxidant enzymes, anti-inflammatory markers, and anti-apoptotic proteins impacts of TQ in STZ-induced DM rats. Founded on these outcomes, the experiment proposes that TQ is a novel natural supplement with various clinical applications, including managing DM, which in turn is recommended to play a pivotal role in preventing the progression of diabetes mellitus.

The Relationship Between UA/HDL and Diabetic Peripheral Neuropathy: A Cross-Sectional Analysis

Purpose

This study was designed to analyze correlations between the uric acid to high-density lipoprotein cholesterol ratio (UHR) and peripheral nerve conduction velocity (NCV) among type 2 diabetes mellitus (T2DM) patients.

Patients and Methods

This was a single-center cross-sectional analysis of 324 T2DM patients. All patients were separated into a group with normal NCV (NCVN) and a group with abnormal NCV (NCVA). Patients were also classified into groups with low and high UHR values based on the median UHR in this study cohort. Neurophysiological data including motor and sensory conduction velocity (MCV and SCV, respectively) were measured for all patients.

Results

Relative to patients with low UHR values, those in the high UHR group presented with greater NCVA prevalence (P = 0.002). UHR remained negatively correlated with bilateral superficial peroneal nerve SCV, bilateral common peroneal nerve MCV, bilateral ulnar nerve SCV, and bilateral right median nerve MCV even after adjustment for confounding factors. UHR was identified as an NCVA-related risk factor, with a 1.370-fold increase in NCVA prevalence for every unit rise in UHR (P < 0.001).

Conclusion

These results identify UHR as a risk factor associated with NCVA that was independently negatively associated with NCV among T2DM patients.

Thymoquinone Alleviates Paclitaxel-Induced Peripheral Neuropathy through Regulation of the TLR4-MyD88 Inflammatory Pathway

Paclitaxel-induced peripheral neuropathy (PIPN) is one of the common adverse effects during the paclitaxel (PTX) treatment of cancer. In this study, we investigated the neuroprotective effects and mechanisms of thymoquinone (TQ) in the PIPN model. Through pain behavioral assays and histological assessment, we demonstrated that TQ significantly alleviated the nociceptive behavior, modulated the pathological changes in peripheral nerves, and decreased the expression of inflammatory factors TNF-α, IL-1β, and IL-6 induced by PIPN in mice. In addition, TQ significantly reversed the reduced viability and inflammatory response of primary DRG neurons caused by PTX. Moreover, the gene expression of related pathways was detected by Western blot, qPCR, and immunofluorescence, and the results showed that TQ exerts neuroprotective effects by regulating TLR4/MyD88 and its downstream NF-κB and MAPKs inflammatory pathways in vivo and in vitro. The treatment with TLR4 antagonist TAK-242 further indicated the important role of the TLR4/MyD88 signaling pathway in PIPN. Furthermore, molecular docking and a cellular thermal shift assay were used to confirm the interaction of TQ with TLR4. In summary, our study shows that TQ can inhibit inflammatory responses against PIPN by regulating TLR4 and MyD88 and its downstream inflammatory pathways.

Thymoquinone Attenuates Retinal Expression of Mediators and Markers of Neurodegeneration in a Diabetic Animal Model

BACKGROUND

Diabetic retinopathy (DR) is a slow eye disease that affects the retina due to a long-standing uncontrolled diabetes mellitus. Hyperglycemia-induced oxidative stress can lead to neuronal damage leading to DR.

OBJECTIVE

The aim of the current investigation is to assess the protective effects of thymoquinone (TQ) as a potential compound for the treatment and/or prevention of neurovascular complications of diabetes, including DR.

METHODS

Diabetes was induced in rats by the administration of streptozotocin (55 mg/kg intraperitoneally, i.p.). Subsequently, diabetic rats were treated with either TQ (2 mg/kg i.p.) or vehicle on alternate days for three weeks. A healthy control group was also run in parallel. At the end of the treatment period, animals were euthanized, and the retinas were collected and analyzed for the expression levels of brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase (TH), nerve growth factor receptor (NGFR), and caspase-3 using Western blotting techniques in the retina of diabetic rats and compared with the normal control rats. In addition, dichlorofluorescein (DCF) levels in the retina were assessed as a marker of reactive oxygen species (ROS), and blood-retinal barrier breakdown (BRB) was examined for vascular permeability. The systemic effects of TQ treatments on glycemic control, kidney and liver functions were also assessed in all groups.

RESULTS

Diabetic animals treated with TQ showed improvements in the liver and kidney functions compared with control diabetic rats. Normalization in the levels of neuroprotective factors, including BDNF, TH, and NGFR, was observed in the retina of diabetic rats treated with TQ. In addition, TQ ameliorated the levels of apoptosis regulatory protein caspase-3 in the retina of diabetic rats and reduced disruption of the blood-retinal barrier, possibly through a reduction in reactive oxygen species (ROS) generation.

CONCLUSION

These findings suggest that TQ harbors a significant potential to limit the neurodegeneration and retinal damage that can be provoked by hyperglycemia in vivo.

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.

Inflammation, oxidative stress and altered heat shock response in type 2 diabetes: the basis for new pharmacological and non-pharmacological interventions

Type 2 diabetes mellitus (DM2) is a chronic disease characterised by variable degrees of insulin resistance and impaired insulin secretion. Besides, several pieces of evidence have shown that chronic inflammation, oxidative stress, and 70 kDa heat shock proteins (HSP70) are strongly involved in DM2 and its complications, and various pharmacological and non-pharmacological treatment alternatives act in these processes/molecules to modulate them and ameliorate the disease. Besides, uncontrolled hyperglycaemia is related to several complications as diabetic retinopathy, neuropathy and hepatic, renal and cardiac complications. In this review, we address discuss the involvement of different inflammatory and pro-oxidant pathways related to DM2, and we described molecular targets modulated by therapeutics currently available to treat DM2.

Peripheral Neuropathy Phenotyping in Rat Models of Type 2 Diabetes Mellitus: Evaluating Uptake of the Neurodiab Guidelines and Identifying Future Directions

Diabetic peripheral neuropathy (DPN) affects over half of type 2 diabetes mellitus (T2DM) patients, with an urgent need for effective pharmacotherapies. While many rat and mouse models of T2DM exist, the phenotyping of DPN has been challenging with inconsistencies across laboratories. To better characterize DPN in rodents, a consensus guideline was published in 2014 to accelerate the translation of preclinical findings. Here we review DPN phenotyping in rat models of T2DM against the 'Neurodiab' criteria to identify uptake of the guidelines and discuss how DPN phenotypes differ between models and according to diabetes duration and sex. A search of PubMed, Scopus and Web of Science databases identified 125 studies, categorised as either diet and/or chemically induced models or transgenic/spontaneous models of T2DM. The use of diet and chemically induced T2DM models has exceeded that of transgenic models in recent years, and the introduction of the Neurodiab guidelines has not appreciably increased the number of studies assessing all key DPN endpoints. Combined high-fat diet and low dose streptozotocin rat models are the most frequently used and well characterised. Overall, we recommend adherence to Neurodiab guidelines for creating better animal models of DPN to accelerate translation and drug development.

Treatment for Diabetic Peripheral Neuropathy: What have we Learned from Animal Models?

INTRODUCTION

Animal models have been widely used to investigate the etiology and potential treatments for diabetic peripheral neuropathy. What we have learned from these studies and the extent to which this information has been adapted for the human condition will be the subject of this review article.

METHODS

A comprehensive search of the PubMed database was performed, and relevant articles on the topic were included in this review.

RESULTS

Extensive study of diabetic animal models has shown that the etiology of diabetic peripheral neuropathy is complex, with multiple mechanisms affecting neurons, Schwann cells, and the microvasculature, which contribute to the phenotypic nature of this most common complication of diabetes. Moreover, animal studies have demonstrated that the mechanisms related to peripheral neuropathy occurring in type 1 and type 2 diabetes are likely different, with hyperglycemia being the primary factor for neuropathology in type 1 diabetes, which contributes to a lesser extent in type 2 diabetes, whereas insulin resistance, hyperlipidemia, and other factors may have a greater role. Two of the earliest mechanisms described from animal studies as a cause for diabetic peripheral neuropathy were the activation of the aldose reductase pathway and increased non-enzymatic glycation. However, continuing research has identified numerous other potential factors that may contribute to diabetic peripheral neuropathy, including oxidative and inflammatory stress, dysregulation of protein kinase C and hexosamine pathways, and decreased neurotrophic support. In addition, recent studies have demonstrated that peripheral neuropathy-like symptoms are present in animal models, representing pre-diabetes in the absence of hyperglycemia.

CONCLUSION

This complexity complicates the successful treatment of diabetic peripheral neuropathy, and results in the poor outcome of translating successful treatments from animal studies to human clinical trials.

Aging and the immune response in diabetic peripheral neuropathy

A large proportion of older individuals with diabetes go on to develop diabetic peripheral neuropathy (DPN). DPN is associated with an increase in inflammatory cells within the peripheral nerve, activation of nuclear factor kappa-light-chain-enhancer of activated B cells and receptors for advanced glycation end products/advanced glycation end products pathways, aberrant cytokine expression, oxidative stress, ischemia, as well as pro-inflammatory changes in the bone marrow; all processes that may be exacerbated with age. We review the immunological features of DPN and discuss whether age-related changes in relevant immunological areas may contribute to age being a risk factor for DPN.

Thymoquinone, the Most Prominent Constituent of Nigella Sativa, Attenuates Liver Damage in Streptozotocin-Induced Diabetic Rats via Regulation of Oxidative Stress, Inflammation and Cyclooxygenase-2 Protein Expression

Diabetes mellitus (DM) is a multifaceted metabolic disorder that results in dysfunction and failure of various organs. The present study aimed to evaluate the role of Thymoquinone (TQ), on antidiabetic, oxidative stress, and anti-inflammatory activities in streptozotocin (STZ)-induced (55 mg/kg b.w) diabetic rats. TQ was orally given for 8 consecutive weeks at dose of 150 mg/kg b.w. The blood glucose, insulin, total cholesterol, triglycerides, liver function enzymes, high density lipoprotein (HDL)-cholesterol, and low-density lipoprotein (LDL)-cholesterol levels were measured accordingly in control, diabetes control (DC), and TQ-treatment groups. These experiments confirmed that TQ conserves the insulin level (0.4 ng/mL vs. 0.23 ng/mL), fasting blood glucose (146 ± 7 mg/dL vs. 225 ± 5 mg/dL), and HbA1c (7.5% vs. 10.6%) quite considerably as compared to DC animals. Our results also confirmed that TQ treatment conserves the body weight and lipid profile significantly in STZ-treated animals as compared to the DC group. Moreover, the antioxidant enzymes (GSH, SOD, GST, and CAT) levels decreased, liver function enzymes (ALT, AST, and ALP), lipid peroxidation and inflammatory markers (TNF-α, CRP, IL-1β, IL-6) increased by STZ treatment, that is significantly restored after TQ treatment. As compared to untreated animals, TQ restored the hepatocytes architectural changes and collagen fibers and cox-2 protein expression in liver tissues as evaluated by hematoxylin and eosin, Masson’s trichrome, and immunohistochemistry staining. Taken together, all these findings indicated that TQ ameliorates glucose level and lipid metabolism. It restores liver function, antioxidant enzymes, anti-inflammatory markers, and maintains hepatocytes architecture in STZ-induced diabetes mellitus rats. Here, in this study, we have demonstrated for the first time the role of TQ in the reduction of the expression of cyclooxygenase-2 and fibrosis formation in diabetic rats. Based on the findings, the study suggests that TQ is a novel natural drug with a wide range of clinical applications including the management of diabetes mellitus.

SMTP-44D improves diabetic neuropathy symptoms in mice through its antioxidant and anti-inflammatory activities

Diabetic neuropathy (DN) is one of the major complications of diabetes. However, there are few approved effective therapies for painful or insensate DN. Recent studies have implicated oxidative stress and inflammation in the pathogenesis of DN, and suppressing these could be an important therapeutic strategy. We previously reported that Stachybotrys microspora triprenyl phenol-44D (SMTP-44D) exhibits both antioxidant and anti-inflammatory activities. The aim of this study was to evaluate the effects of SMTP-44D in a mouse model of streptozotocin-induced DN. SMTP-44D was administered for 3 weeks after the disease induction, and its effects were evaluated on the basis of mechanical and thermal thresholds, blood flow in the bilateral hind paw, and blood flow and conduction velocity in the sciatic nerve. Furthermore, the levels of inflammatory factors, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and malondialdehyde (MDA), in the sciatic nerve were assessed. Neurological degeneration was assessed by measuring myelin thickness and g-ratio in the sciatic nerve. SMTP-44D treatment significantly improved allodynia, hyperalgesia, blood flow, and conduction velocity in DN model mice in a dose-dependent manner. Neurological degeneration was also significantly improved, accompanied by decreased levels of inflammatory factors (TNF-α, 57.8%; IL-1β, 51.4%; IL-6, 62.8%; and MDA, 40.7% reduction rate against the diabetes mellitus + normal saline group). Thus, SMTP-44D can improve allodynia and hyperalgesia in DN without affecting the body weight and blood glucose levels, which may be due to its antioxidant and anti-inflammatory properties. In conclusion, SMTP-44D could be a potential therapeutic agent for the treatment of DN.

Satellite glia as a critical component of diabetic neuropathy: Role of lipocalin-2 and pyruvate dehydrogenase kinase-2 axis in the dorsal root ganglion

Diabetic peripheral neuropathy (DPN) is a common complication of uncontrolled diabetes. The pathogenesis of DPN is associated with chronic inflammation in dorsal root ganglion (DRG), eventually causing structural and functional changes. Studies on DPN have primarily focused on neuronal component, and there is limited knowledge about the role of satellite glial cells (SGCs), although they completely enclose neuronal soma in DRG. Lipocalin-2 (LCN2) is a pro-inflammatory acute-phase protein found in high levels in diverse neuroinflammatory and metabolic disorders. In diabetic DRG, the expression of LCN2 was increased exclusively in the SGCs. This upregulation of LCN2 in SGCs correlated with increased inflammatory responses in DRG and sciatic nerve. Furthermore, diabetes-induced inflammation and morphological changes in DRG, as well as sciatic nerve, were attenuated in Lcn2 knockout (KO) mice. Lcn2 gene ablation also ameliorated neuropathy phenotype as determined by nerve conduction velocity and intraepidermal nerve fiber density. Mechanistically, studies using specific gene KO mice, adenovirus-mediated gene overexpression strategy, and primary cultures of DRG SGCs and neurons have demonstrated that LCN2 enhances the expression of mitochondrial gate-keeping regulator pyruvate dehydrogenase kinase-2 (PDK2) through PPARβ/δ, thereby inhibiting pyruvate dehydrogenase activity and increasing production of glycolytic end product lactic acid in DRG SGCs and neurons of diabetic mice. Collectively, our findings reveal a crucial role of glial LCN2-PPARβ/δ-PDK2-lactic acid axis in progression of DPN. Our results establish a link between pro-inflammatory LCN2 and glycolytic PDK2 in DRG SGCs and neurons and propose a novel glia-based mechanism and drug target for therapy of DPN. MAIN POINTS: Diabetes upregulates LCN2 in satellite glia, which in turn increases pyruvate dehydrogenase kinase-2 (PDK2) expression and lactic acid production in dorsal root ganglia (DRG). Glial LCN2-PDK2-lactic acid axis in DRG plays a crucial role in the pathogenesis of diabetic neuropathy.

Long non-coding RNA HCG18 promotes M1 macrophage polarization through regulating the miR-146a/TRAF6 axis, facilitating the progression of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most important complications in diabetes mellitus (DM), which has been reported to be modulated by long non-coding RNAs (lncRNAs). The purpose of the current study is to explore the regulatory mechanism of lncRNA HCG18 on DPN in vitro. The expression of lncRNA HCG18, miR-146a, TRAF6, CD11c, and iNOS was detected by qRT-PCR. Through Enzyme-linked immunosorbent assay, the levels of inflammatory factors (TNF-α, IL-1β, and IL-6) were determined. M1 macrophage polarization was measured by flow cytometry analysis. The interactions between miR-146a and HCG18/TRAF6 were predicted by Starbase/Targetscan software and verified by the dual luciferase reporter assay. Western blot assay was performed to determine the protein expression of TRAF6. LncRNA HCG18 was highly expressed in DPN model and HG-induced macrophages. The levels of inflammatory factors (TNF-α, IL-1β, and IL-6) were elevated in DPN model. The expression of M1 markers (CD11c and iNOS) was visibly up-regulated in DPN model and was positively correlated with HCG18 expression. LncRNA HCG18 facilitated M1 macrophage polarization. In addition, miR-146a was identified as a target of lncRNA HCG18. Overexpression of miR-146a reversed the promoting effect of HCG18 on M1 macrophage polarization. Simultaneously, TRAF6 was a target gene of miR-146a TRAF6 expression was positively modulated by HCG18 and was negatively modulated by miR-146a. Down-regulation of TRAF6 reversed the promoting effect of HCG18 on M1 macrophage polarization. LncRNA HCG18 promotes M1 macrophage polarization via regulating the miR-146a/TRAF6 axis, facilitating the progression of DPN. This study provides a possible therapeutic strategy for DPN.

In vitro Evaluation of the Anti-inflammatory Effects of Thymoquinone in Osteoarthritis and in silico Analysis of Inter-Related Pathways in Age-Related Degenerative Diseases

Chronic inflammation is a common underlying factor in osteoarthritis (OA) and most age-related degenerative diseases. As conventional therapies help only in partial alleviation of symptoms in OA, stem cell-based therapies and herbal supplements are being widely explored. Thymoquinone (TQ), an active ingredient of Nigella sativa is reported to have immunomodulatory, anti-inflammatory and antioxidant properties. We evaluated the effects of TQ on bone marrow MSCs (BM-MSCs) derived from OA patients and its interrelated pathways in inflammation and age-related degenerative diseases using Ingenuity Pathway Analysis (IPA) as well as possible molecular targets using SwissTargetPrediction. BM-MSCs were derived from OA patients and their stemness properties were characterized by studying the MSCs related CD surface marker expression and differentiation into adipocytes, osteoblasts, and chondrocytes. Treatment with TQ (100 nM-5 μM) demonstrated cell death, especially at higher concentrations. MTT assay demonstrated a significant concentration-dependent decrease in cell viability which ranged from 20.04% to 69.76% with higher doses (300 nM, 1 μM, and 5 μM), especially at 48h and 72h. Additional cell viability testing with CellTiter-Blue also demonstrated a significant concentration-dependent decrease in cell viability which ranged from 27.80 to 73.67% with higher doses (300 nM, 1 μM, 3 μM, and 5 μM). Gene expression analysis following treatment of BM-MSCs with TQ (1 and 3 μM) for 48h showed upregulation of the anti-inflammatory genes IL-4 and IL-10. In contrast, the pro-inflammatory genes namely IFN-γ, TNF-α, COX-2, IL-6, IL-8, IL-16, and IL-12A although were upregulated, compared to the lower concentration of TQ (1 μM) they were all decreased at 3 μM. The pro-apoptotic BAX gene was downregulated while the SURVIVIN gene was upregulated. IPA of the molecular interaction of TQ in inflammation and age-related degenerative diseases identified canonical pathways directly related to synaptogenesis, neuroinflammation, TGF-β, and interleukin signaling. Further screening led to the identification of 36 molecules that are involved in apoptosis, cell cycle regulation, cytokines, chemokines, and growth factors. SwissTargetPrediction of TQ identified potential molecular targets with high probability. TQ exerted anti-inflammatory effects and therefore can be a useful adjuvant along with conventional therapies against inflammation in OA and other age-related degenerative diseases.

Schwann cells apoptosis is induced by high glucose in diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus that affects approximately half of patients with diabetes. Current treatment regimens cannot treat DPN effectively. Schwann cells (SCs) are very sensitive to glucose concentration and insulin, and closely associated with the occurrence and development of type 1 diabetic mellitus (T1DM) and DPN. Apoptosis of SCs is induced by hyperglycemia and is involved in the pathogenesis of DPN. This review considers the pathological processes of SCs apoptosis under high glucose, which include the following: oxidative stress, inflammatory reactions, endoplasmic reticulum stress, autophagy, nitrification and signaling pathways (PI3K/AKT, ERK, PERK/Nrf2, and Wnt/β-catenin). The clarification of mechanisms underlying SCs apoptosis induced by high glucose will help us to understand and identify more effective strategies for the treatment of T1DM DPN.

Association between Circulating B-Type Natriuretic Peptide and Diabetic Peripheral Neuropathy: A Cross-Sectional Study of a Chinese Type 2 Diabetic Population

Cardiovascular disease which is associated with cardiac dysfunction, usually measured with circulating levels of B-type natriuretic peptide (BNP), has been associated with incidence and progression of diabetic peripheral neuropathy (DPN). The potential relationship of circulating physiological levels of BNP with DPN, however, has not been reported. Circulating levels of BNP were measured in 258 patients with type 2 diabetes mellitus (T2DM), and participants were divided into a DPN group (n = 61) and no DPN group (n = 197). The relationship between circulating physiological levels of BNP and DPN and other parameters was analyzed. Circulating levels of BNP were significantly elevated in T2DM patients with DPN compared to those without (P = 0.001). Circulating levels of BNP were significantly and positively associated with systolic blood pressure (P = 0.035), neutrophil-to-lymphocyte ratio (P = 0.007), creatinine (P = 0.030), vibration perception threshold values (P = 0.021), and the prevalence of diabetic foot ulceration (P = 0.039), peripheral arterial disease (P = 0.013), DPN (P = 0.032), and diabetic nephropathy (P = 0.020) and negatively with lymphocyte count (P = 0.003) and ankle-brachial index (P = 0.038), irrespective of age, sex, and body mass index. Moreover, circulating levels of BNP was an independent decisive factor for the presence of DPN after multivariate adjustment (odds ratio, 1.044; 95% confidence interval, 1.006-1.084; P = 0.024). Additionally, the higher quartiles of circulating BNP were related significantly to an increased risk of DPN compared to the lowest quartile (P = 0.003). Last but most importantly, the analysis of receiver operating characteristic curves revealed that the best cutoff value for circulating levels of BNP to predict DPN was 15.18 pg/mL (sensitivity 78.7% and specificity 48.2%). These findings suggest that high circulating physiological levels of BNP may be associated with the development of DPN and may be a potential biomarker for DPN in patients with T2DM.

N-acetylcysteine (NAC) alleviates the peripheral neuropathy associated with liver cirrhosis via modulation of neural MEG3/PAR2/ NF-ҡB axis

BACKGROUND AND AIM

Oxidative stress (OS) is accused in pathogenesis of many diseases, including liver cirrhosis by many mechanisms. One of them is the disturbance of long non coding maternally expressed 3 (MEG3)/protease activated receptor 2 (PAR2) downstream pathway. We aimed to investigate the role of this axis in cirrhotic neuropathy and whether an antioxidant compound such as N-acetylcysteine (NAC) could improve the peripheral nerve function through repression of MEG3/PAR2.

METHODS

Thirty Wistar rats were used and divided into 5 groups; naive, thiacetamide (TAA) (200 mg/kg 3 times/week. i.p. for 8 weeks) and TAA+NAC (50 or 100 or 200 mg/kg/day) groups. Von Frey (VF) test for mechanical nociceptive responses, hepatic& neural MEG3, NF-ҡB and neural PAR2 expression by PCR, histological studies for liver and sciatic nerve together with the dorsopedal skin thickness were done.

RESULTS

TAA induced significant decrease in liver function, negative VF test, an increase in the expression of hepatic& neural MEG3, NF-ҡB and neural PAR2. The histological studies showed cirrhotic changes with atrophy of the sciatic nerve and the dorsal skin. NAC improved the liver function together with reversal of the neural: functional, biochemical and histological changes in a dose dependent manner.

CONCLUSIONS

NAC could improve the peripheral neuropathy in cirrhotic rat through suppression of MEG3/PAR2 expression.

Association between serum uric acid and large-nerve fiber dysfunction in type 2 diabetes: a cross-sectional study

Background

Large-nerve fiber dysfunction, as assessed by vibration perception threshold (VPT) predicts risks of ulceration, amputation, and mortality in diabetes. Serum uric acid (UA) is closely associated with various metabolic disorders, especially diabetes. Thus, we sought to investigate the clinical relevance of UA to large-nerve fiber dysfunction, among patients with type 2 diabetes (T2D).

Methods

Medical records of consecutive patients with T2D who were admitted to Beijing Friendship Hospital Pinggu Campus between May 2014 and December 2016 were collected. Data for the 824 eligible patients included in the final analysis were extracted using a structured form. A VPT value ≥15 in either foot was defined as abnormal. We compared the clinical characteristics between patients with abnormal VPT and those with normal VPT (VPT value <15 in both feet) in the overall population and in gender subgroups. Logistic regression analysis was performed to explore the association of abnormal VPT with UA level. One-way analysis of variance was used to compare VPT values across four UA quartiles.

Results

UA levels were significantly lower in T2D patients with abnormal VPT than in those with normal VPT (294.5 ± 84.0 vs. 314.9 ± 92.8 μmol/L, P < 0.01), especially among male patients (311.7 ± 85.2 vs. 336.9 ± 89.6 μmol/L, P < 0.01). From the logistic regression analysis, hyperuricemia (males >420 μmol/L; females >360 μmol/L) was associated with a reduced risk of abnormal VPT (odds ratio [OR], 0.60; 95% confidence interval [CI], 0.39–0.91; P < 0.05). This association was robust in male patients (OR, 0.43; 95% CI, 0.24–0.76; P < 0.01) but not in female patients (OR, 0.92; 95% CI, 0.47–1.82; P = 0.816), even after adjustment for confounding factors. For the younger male subgroup (age <65 years), VPT values decreased as the UA level increased (P for trend = 0.002), but this trend was not significant in older male subgroup (age ≥65 years; P for trend = 0.400).

Conclusions

Low serum UA levels showed a significant association with an increased risk of large-nerve fiber dysfunction in male patients with T2D, but not in female patients with T2D. In addition, in only the younger subgroup of male patients (<65 years), lower levels of UA also correlated with higher VPT values.

Thymoquinone ameliorates oxidative damage and histopathological changes of developing brain neurotoxicity

Lead (Pb) toxicity is known to be a chief environmental health issue, especially for pregnant women and young children. Today, the use of medicinal herbs in the treatment of many diseases and different toxic agents has become highly accepted due to their effectiveness and lower costs. Thymoquinone (TQ), which is extracted from Nigella sativa seeds, is a potent antioxidant and anti-inflammatory agent. This study was designed to explore the optional protectivity of TQ against maternal and fetal oxidative stress and brain damage induced by Pb administration. Pregnant rats were distributed into seven groups: control group, TQ group, DMSO group, two groups Pb-treated (160 and 320 ppm), and two groups Pb-treated (160 and 320 ppm) co-treated with TQ. Administration started from gestation day 1 (GD1) to day 20 (GD20) through oral gavage once daily. Lead administration caused a dose-dependent toxicity for both mothers and fetuses. Also, the histopathological assessment of the brains from Pb-treated groups showed marked alterations. Co-treatment of with TQ and Pb caused a significant decrease in Pb levels as compared with those treated with Pb alone and amelioration of histopathological changes in the brains. It was concluded that co-treatment of TQ along with gestational Pb exposure could mitigate the effects against Pb-induced maternal and fetal neurotoxicity.

Thymoquinone protects DRG neurons from axotomy-induced cell death

OBJECTIVE

Peripheral nerve injury (PNI) is a significant health problem that is linked to sensory, motor, and autonomic deficits. This pathological condition leads to a reduced quality of life in most affected individuals. Schwann cells (SCs) play a crucial role in the repair of PNI. Effective agents that promote SC activation may facilitate and accelerate peripheral nerve repair. Thymoquinone (TQ), a bioactive component of Nigella sativa seeds, has an antioxidant, anti-inflammatory, immunomodulatory, and neuroprotective properties. In the present study, the neuroprotective efficacy of TQ was investigated by using a laser microdissection technique in a mouse PNI model.

METHODS

Single cells were isolated from dorsal root ganglions (DRGs) of 6-8-week-old mice, maintained in defined culture conditions and treated with or without TQ at different concentrations. Axons were cut (axotomy) using a controllable laser microbeam to model axonal injury in vitro. Under fluorescence microscopy, cell viability was evaluated using the fluorescent dyes. The behavior of the cells was continuously monitored with time-lapse video microscopy.

RESULTS

TQ significantly increased neuronal survival by promoting the survival and proliferation of SCs and fibroblasts, as well as the migration of SCs. Furthermore, TQ improved the ability to extend neurites of axotomized neurons. The regenerative effect of TQ was dose-dependent suggesting a target specificity. Our studies warrant further preclinical and clinical investigations of TQ as a potential regenerative agent to treat peripheral nerve injuries.

CONCLUSION

TQ exhibits a regenerative potential for the treatment of damaged peripheral nerves.

Peripheral Glial Cells in the Development of Diabetic Neuropathy

The global prevalence of diabetes is rapidly increasing, affecting more than half a billion individuals within the next few years. As diabetes negatively affects several physiological systems, this dramatic increase represents not only impaired quality of life on the individual level but also a huge socioeconomic challenge. One of the physiological consequences affecting up to half of diabetic patients is the progressive deterioration of the peripheral nervous system, resulting in spontaneous pain and eventually loss of sensory function, motor weakness, and organ dysfunctions. Despite intense research on the consequences of hyperglycemia on nerve functions, the biological mechanisms underlying diabetic neuropathy are still largely unknown, and treatment options lacking. Research has mainly focused directly on the neuronal component, presumably from the perspective that this is the functional signal-transmitting unit of the nerve. However, it is noteworthy that each single peripheral sensory neuron is intimately associated with numerous glial cells; the neuronal soma is completely enclosed by satellite glial cells and the length of the longest axons covered by at least 1,000 Schwann cells. The glial cells are vital for the neuron, but very little is still known about these cells in general and especially how they respond to diabetes in terms of altered neuronal support. We will discuss current knowledge of peripheral glial cells and argue that increased research in these cells is imperative for a better understanding of the mechanisms underlying diabetic neuropathy.

Neuropharmacological Potential and Delivery Prospects of Thymoquinone for Neurological Disorders

Thymoquinone (TQ) is an active ingredient isolated from Nigella sativa and has various pharmacological activities, such as protection against oxidative stress, inflammation, and infections. In addition, it might be a potential neuropharmacological agent because it exhibits versatile potential for attenuating neurological impairments. It features greater beneficial effects in toxin-induced neuroinflammation and neurotoxicity. In various models of neurological disorders, it demonstrates emergent functions, including safeguarding various neurodegenerative diseases and other neurological diseases, such as stroke, schizophrenia, and epilepsy. TQ also has potential effects in trauma mediating and chemical-, radiation-, and drug-induced central nervous system injuries. Considering the pharmacokinetic limitations, research has concentrated on different TQ novel formulations and delivery systems. Here, we visualize the neuropharmacological potential, challenges, and delivery prospects of TQ, specifically focusing on neurological disorders along with its chemistry, pharmacokinetics, and toxicity.

Involvement of microRNA-146a in diabetic peripheral neuropathy through the regulation of inflammation

Purpose

Recent evidence has shown the involvement of inflammation in the development of diabetic peripheral neuropathy (DPN). MicroRNA-146a (miR-146a) is closely involved in the inflammatory response. However, the role of miR-146a in the inflammatory reaction in DPN has not been clarified. This study was designed to explore the role of miR-146a in the regulation of inflammatory responses in DPN.

Methods

Rats were randomly divided into three groups (n=6 per group): control group, type 2 diabetes mellitus (T2DM) group and DPN group. T2DM and DPN rats were intraperitoneally injected with streptozotocin. Sciatic nerve conduction velocity (NCV) was determined at the 6th week and the 12th week in each group. The expression of microRNAs was detected by quantitative real-time polymerase chain reaction in three sciatic nerves for each group of rats. Expression of inflammatory cytokines in nerve tissues and plasma was measured by Western blot and Bio-Plex Pro™ assays.

Results

The NCV and expression levels of miR-146a in the DPN group were significantly decreased (P<0.01) compared to the other two groups. Expression of tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in the DPN group was significantly increased compared with the control and T2DM groups (P<0.01). Pearson’s correlation analysis showed that the expression level of miR-146a was negatively correlated with the levels of IL-1β, TNF-α and NF-κB.

Conclusion

miR-146a is involved in the pathogenesis of DPN, and its expression level is closely related to the inflammatory responses that aggravate sciatic nerve injuries.

Correlation between serum uric acid and diabetic peripheral neuropathy in T2DM patients

AIM

To investigate the correlation between serum uric acid (SUA) and diabetic peripheral neuropathy (DPN) in type 2 diabetes mellitus (T2DM) patients.

METHODS

Two hundred T2DM patients were divided into four groups at the cut-off points of 5, 7, and 9mg/dL of SUA levels. Nerve conduction studies (NCS), Semmes-Weinstein monofilament testing (SWMT), and vibration perception threshold (VPT) tests were performed on these patients.

RESULTS

Significant differences in motor/sensory nerve amplitude and conduction velocity (CV) parameters among different SUA level groups were observed (all P<0.05). SUA levels were negatively correlated with the means of motor/sensory nerve amplitude and CV (all P<0.05). Duration of T2DM >10years, SUA >9mg/dL and total cholesterol (TC) >5.2mmol/L were found to be significantly associated with DPN (all P<0.05). Receiver-operating characteristic (ROC) analysis revealed that the cut-off points of T2DM duration combined with SUA and TC were 9years, 7.8mg/dL, and 4.97mmol/L, respectively (AUC=0.65; 95% CI: 0.53-0.77; sensitivity, 70.6%; specificity, 65.2%, P=0.009).

CONCLUSION

There is a significant association between elevated SUA levels and DPN, and T2DM duration, SUA, and TC may be valuable indicators to predict the occurrence of DPN in T2DM patients.

Pharmacotherapy with Thymoquinone Improved Pancreatic β-Cell Integrity and Functional Activity, Enhanced Islets Revascularization, and Alleviated Metabolic and Hepato-Renal Disturbances in Streptozotocin-Induced Diabetes in Rats

Aims: This study is aimed at evaluating the antidiabetic effects of thymoquinone (TQ) on streptozotocin (STZ)-induced diabetes in rats, and exploring the possible underlying mechanisms. Methods: Diabetes was induced in adult male Wistar rats by intraperitoneal injection of freshly prepared STZ (65 mg/kg). After disease induction, 42 rats were equally assigned to: controls, STZ-diabetic group, and STZ-diabetic group treated with oral TQ (35 mg/kg/day) for 5 weeks. Fasting blood glucose levels were determined weekly, and the animals were euthanized at day 38 post-STZ injection. Blood samples were assessed for glucose-insulin homeostasis parameters (plasma glucose, glycated hemoglobin, serum insulin, homeostatic model assessment of insulin resistance, and insulin sensitivity index) and lipid profile. Resected pancreases were subjected to histological examination and immunohistochemical or enzyme-linked immunosorbent assay assessment to determine the pancreatic expression of insulin sensitizing β-cells, anti-apoptotic protein “survivin,” apoptosis-inducer “caspase-3,” prototypic angiogenic factors (vascular endothelial growth factor [VEGF] and endothelial cluster of differentiation 31 [CD31]), pro- and anti-inflammatory cytokines (interleukin-1beta [IL-1β] and interleukin-10 [IL-10], respectively), thiobarbituric acid reactive substances (TBARS), total glutathione (GSH), and superoxide dismutase (SOD). The hepato-renal statuses were assessed biochemically and histologically. Results: Therapy with TQ markedly improved the integrity of pancreatic islets, glucose-insulin homeostasis-related parameters, lipid profile parameters, and hepato-renal functional and histomorphological statuses that collectively were severely deteriorated in untreated diabetic group. Mechanistically, TQ therapy efficiently increased insulin producing β-cells, upregulated survivin, VEGF, CD31, IL-10, GSH and SOD, and downregulated caspase-3, IL-1β, and TBARSs in the pancreatic tissues of STZ-diabetic rats. Conclusions: These findings prove the anti-diabetic potential of TQ and its efficacy in regenerating pancreatic β-cells and ameliorating pancreatic inflammation and oxidative stress, and highlight its novelty in repressing apoptosis of β-cells and enhancing islet revascularization in STZ-diabetic rats. Further studies are required to support these findings and realize their possible clinical significance.

New Horizons in Diabetic Neuropathy: Mechanisms, Bioenergetics, and Pain

Pre-diabetes and diabetes are a global epidemic, and the associated neuropathic complications create a substantial burden on both the afflicted patients and society as a whole. Given the enormity of the problem and the lack of effective therapies, there is a pressing need to understand the mechanisms underlying diabetic neuropathy (DN). In this review, we present the structural components of the peripheral nervous system that underlie its susceptibility to metabolic insults and then discuss the pathways that contribute to peripheral nerve injury in DN. We also discuss systems biology insights gleaned from the recent advances in biotechnology and bioinformatics, emerging ideas centered on the axon-Schwann cell relationship and associated bioenergetic crosstalk, and the rapid expansion of our knowledge of the mechanisms contributing to neuropathic pain in diabetes. These recent advances in our understanding of DN pathogenesis are paving the way for critical mechanism-based therapy development.