Diabetic neuropathy and oxidative stress

A study of the use of carbamazepine, pregabalin and alpha lipoic acid in patients of diabetic neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a common, symptomatic, long-term complication of diabetes mellitus. Many of the agents used to treat DN have not been compared with each other. This study was, therefore, undertaken to compare the efficacy and safety of carbamazepine, pregabalin and alpha-lipoic acid in diabetic neuropathy patients.

METHODS

This was a prospective, observational study. The patients were categorized into three groups, Group I included those patients who were prescribed carbamazepine while group II included those on pregabalin and group III patients received alpha-lipoic acid. Each patient was followed up at every month for total duration of 6 months. Demographic details, presenting symptoms, history of diabetes, laboratory values pertaining to diabetes (Fasting blood sugar, Post prandial blood sugar and HbA1c) were recorded. Intensity of pain, using a visual analogue scale (VAS), diabetic neuropathy symptom (DNS) score and diabetic neuropathy examination (DNE) score were assessed at baseline and then at each monthly follow-up. Nerve conduction velocity (NCV) was also measured at baseline and then at the end of 3 and 6 months.

RESULTS

A total of 101 patients were enrolled out of them 96 completed the study. Regarding VAS, the number of patients having pain was reduced substantially however, the speed and the quantum of this reduction were best in group II (pregabalin). Regarding DNS, also group II showed the best response in terms of number of patients as well as the speed of improvement. The results also imply that the relief from diabetic neuropathy (as per DNE score) is superior with pregabalin administration. However, no improvement in NCV was evident in any group.

CONCLUSION

Results of this study suggest that treatment with pregabalin gives faster and better improvement in diabetic neuropathy.

Pharmacological characterization of different fractions of Calotropis procera (Asclepiadaceae) in streptozotocin induced experimental model of diabetic neuropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Calotropis procera (Ait.) R.Br. is one of an ancient traditional shrub, which has been used for the treatment of diabetes, pain and inflammation for thousands of years in India. The root extract of Calotropis procera has been widely used by the tribal׳s of district Udaipur, Rajasthan (India) for treatment of diabetes mellitus and its associated complications like diabetic neuropathy. The present study was performed to explore the protective effect of root, stem and leaf extracts of Calotropis procera in diabetes and diabetic neuropathy against tactile allodynia, mechanical hyperalgesia and thermal hyperalgesia in streptozotocin induced diabetic rats.

MATERIALS AND METHODS

Diabetes and peripheral neuropathy were induced in Wistar rats by injection of streptozotocin (45 mg/kg/intraperitoneally). The roots, stem and leaves of Calotropis procera were sequentially extracted with petroleum ether, chloroform, ethyl acetate and methanol. All the extracts were assessed by oral administration at 100 and 250 mg/kg in streptozotocin diabetic rats. The following compounds were used as positive controls: insulin NPH (1 IU/kg/day), metformin (500 mg/kg/day), glibenclamide (2.5 mg/kg/day) and a combination of acarbose (20 mg/kg/day) with methylcobalamine (500 µg/kg/day). In contrast, the streptozotocin induced untreated diabetic rats termed as negative control. Thermal hyperalgesia, mechanical hyperalgesia and tactile allodynia were evaluated in all groups of streptozotocin diabetic rats to assess the extent of neuropathy by Eddy׳s hot plate, tail immersion, Randall-Selitto and Von Frey hair tests. The basal nociceptive thresholds were assessed in week 4 of post streptozotocin injection. All groups received their treatment on a regular basis from 28 to 42 days following a confirmation of diabetic neuropathy. The nociceptive thresholds were assessed in all groups in week 5 and 6. The histopathology of pancreas and biochemical estimations of plasma insulin and glycosylated haemoglobin (HbA1C%) levels were also performed in week 6 of post streptozotocin injection.

RESULTS

The negative control rats developed diabetes and diabetic neuropathy after 6 week of streptozotocin administration distinguished by significant (p<0.01) hyperalgesia and tactile allodynia with enhanced HbA1C% level compared to normoglycemic rats. Chronic administration of root methanol, stem methanol and leaf ethyl-acetate extracts of Calotropis procera for 2 weeks at 100 and 250 mg/kg doses significantly (p<0.01) attenuated the diabetes induced mechanical hyperalgesia, thermal hyperalgesia, tactile allodynia and HbA1C% level in streptozotocin diabetic rats as compared to negative control rats. Further, the root methanol extract of Calotropis procera in 100mg/kg dose showed the regeneration capability of β cells in the histology of pancreas with significant (p<0.01) improvement in plasma insulin level in streptozotocin diabetic rats compared to negative control rats.

CONCLUSION

Root methanol extract of Calotropis procera (100mg/kg) has shown ameliorative effect in diabetic neuropathy which may be attributed by its multiple actions including potent hypoglycemic and antioxidant.

Current status of diabetic peripheral neuropathy in Korea: report of a hospital-based study of type 2 diabetic patients in Korea by the diabetic neuropathy study group of the korean diabetes association

Diabetic peripheral neuropathy (DPN) is the most common complication associated with diabetes. DPN can present as a loss of sensation, may lead to neuropathic ulcers, and is a leading cause of amputation. Reported estimates of the prevalence of DPN vary due to differences in study populations and diagnostic criteria. Furthermore, the epidemiology and clinical characteristics of DPN in Korean patients with type 2 diabetes mellitus (T2DM) are not as well understood as those of other complications of diabetes such as retinal and renal disease. Recently, the Diabetic Neuropathy Study Group of the Korean Diabetes Association (KDA) conducted a study investigating the impact of DPN on disease burden and quality of life in patients with T2DM and has published some data that are representative of the nation. This review investigated the prevalence and associated clinical implications of DPN in Korean patients with diabetes based on the KDA study.

Physiological serum bilirubin concentrations are inversely associated with the prevalence of cardiovascular autonomic neuropathy in patients with Type 2 diabetes

AIMS

Although severe hyperbilirubinaemia causes kernicterus in neonates, normal to modestly elevated bilirubin concentrations have been reported to be neuroprotective. However, the relationship between serum bilirubin concentrations and cardiovascular autonomic neuropathy in patients with Type 2 diabetes is currently unknown. This study assessed the relationships between physiological serum total bilirubin concentrations and cardiovascular autonomic neuropathy in patients with Type 2 diabetes.

METHODS

A total of 2991 patients with Type 2 diabetes were investigated in this cross-sectional study. Cardiovascular autonomic neuropathy was diagnosed by a cardiovascular reflex test. According to the American Diabetes Association criteria, the degree of cardiovascular autonomic dysfunction was graded into normal, early, definite and severe. Cardiovascular autonomic neuropathy was either definite or severe in the present study. An analysis of covariance after adjustment for other covariates was performed. A logistic regression model was used to assess an association of cardiovascular autonomic neuropathy with serum total bilirubin tertiles.

RESULTS

Serum total bilirubin concentrations were significantly lower in subjects with cardiovascular autonomic neuropathy. The mean total bilirubin values differed significantly according to the severity of cardiovascular autonomic dysfunction (normal 13.0 μmol/l; early 12.3 μmol/l; definite 11.8 μmol/l; severe 10.1 μmol/l; P for trend < 0.001) after adjustment for other covariates. In multivariate analysis, serum total bilirubin levels were significantly associated with cardiovascular autonomic neuropathy (odds ratio 0.36; 95% CI 0.21-0.63 for the highest vs. the lowest bilirubin tertile, P < 0.001).

CONCLUSIONS

Serum total bilirubin concentrations within the physiologic range are inversely associated with the prevalence of cardiovascular autonomic neuropathy in patients with Type 2 diabetes.

The role of oxidative stress and inflammatory response in high-fat diet induced peripheral neuropathy

OBJECTIVE

Earlier studies suggest that high-calorie diet is an important risk factor for neuronal damage resulting from oxidative stress of lipid metabolism. In our experimental study of rats under high-fat diet, oxidative stress markers and axonal degeneration parameters were used to observe the sciatic nerve neuropathy. The aim of this study is to evaluate the pathophysiology of neuropathy induced by high-fat diet.

METHODS

A total of 14 male rats (Wistar albino) were randomly divided into two experimental groups as follows; control group (n=7) and the model group (n=7); while control group was fed with standard diet; where the model group was fed with a high-fat diet for 12 weeks. At the end of 12 weeks, the lipid profile and blood glucose levels, interleukin-1β (IL-1), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and transforming growth factor-β (TGF-β) levels were studied. Tissue malondialdehyde (MDA), nitric oxide (NO) levels and super-oxide dismutase (SOD), paraoxonase-1 (PON-1) and glutathione peroxidase (GPx) activities were studied. The distal blocks of the left sciatic nerves were evaluated for histomorphological analysis (including mean axon area, axon numbers, nerve fiber diameters, axon diameters, and thickness of myelin sheets).

RESULTS

Body weights, serum glucose and high-density lipoprotein (HDL) levels of rats were found not statistically significantly different compared between the model and the control groups (p>0.05). Serum cholesterol, triglyceride, TGF-β and TNF-α levels were significantly higher in the model group when compared with the control group (p<0.05). IL-1 and IL-6 levels were not statistically significantly different compared between the model group and the control group (p>0.05). The MDA and NO levels and the SOD and GPx activities of the sciatic nerves in model group were statistically significantly higher than the control group (p<0.05). In addition, the activities of PON-1 were statistically significantly lower in the model group when compared with the control group (p<0.05). The difference in the total number of myelinated axons between the control group and the model group was not statistically significant (p>0.05). The nerve fiber diameter and the thickness of the myelin sheet were statistically significantly lower in the model group when compared with the control group (p<0.05). The axon diameter and area were significantly decreased in the model group when compared with the control group (p<0.05).

CONCLUSION

Our results support that dyslipidemia is an independent risk factor for the development of neuropathy. In addition, we postulated that oxidative stress and inflammatory response may play an important role in the pathogenesis of high-fat diet induced neuropathy.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Glucose-induced metabolic memory in Schwann cells: prevention by PPAR agonists

A major barrier in reversing diabetic complications is that molecular and pathologic effects of elevated glucose persist despite normalization of glucose, a phenomenon referred to as metabolic memory. In the present studies we have investigated the effects of elevated glucose on Schwann cells, which are implicated in diabetic neuropathy. Using quantitative PCR arrays for glucose and fatty acid metabolism, we have found that chronic (>8 wk) 25 mM high glucose induces a persistent increase in genes that promote glycolysis, while inhibiting those that oppose glycolysis and alternate metabolic pathways such as fatty acid metabolism, the pentose phosphate pathway, and trichloroacetic acid cycle. These sustained effects were associated with decreased peroxisome proliferator-activated receptor (PPAR)γ binding and persistently increased reactive oxygen species, cellular NADH, and altered DNA methylation. Agonists of PPARγ and PPARα prevented select effects of glucose-induced gene expression. These observations suggest that Schwann cells exhibit features of metabolic memory that may be regulated at the transcriptional level. Furthermore, targeting PPAR may prevent metabolic memory and the development of diabetic complications.

Pathogenesis of diabetic neuropathy: focus on neurovascular mechanisms

Neuropathies of the peripheral and autonomic nervous systems affect up to half of all people with diabetes, and are major risk factors for foot ulceration and amputation. The aetiology is multifactorial: metabolic changes in diabetes may directly affect neural tissue, but importantly, neurodegenerative changes are precipitated by compromised nerve vascular supply. Experiments in animal models of diabetic neuropathy suggest that similar metabolic sequelae affect neurons and vasa nervorum endothelium. These include elevated polyol pathway activity, oxidative stress, the formation of advanced glycation and lipoxidation end products, and various pro-inflammatory changes such as elevated protein kinase C, nuclear factor κB and p38 mitogen activated protein kinase signalling. These mechanisms do not work in isolation but strongly interact in a mutually facilitatory fashion. Nitrosative stress and the induction of the enzyme poly (ADP-ribose) polymerase form one important link between physiological stressors such as reactive oxygen species and the pro-inflammatory mechanisms. Recently, evidence points to endoplasmic stress and the unfolded protein response as forming another crucial link. This review focuses on the aetiopathogenesis of neurovascular changes in diabetic neuropathy, elucidated in animal studies, and on putative therapeutic targets the majority of which have yet to be tested for efficacy in clinical trials.

Coenzyme Q10 prevents peripheral neuropathy and attenuates neuron loss in the db-/db- mouse, a type 2 diabetes model

Diabetic peripheral neuropathy (DPN) is the most common complication in both type 1 and type 2 diabetes. Here we studied some phenotypic features of a well-established animal model of type 2 diabetes, the leptin receptor-deficient db(-)/db(-) mouse, and also the effect of long-term (6 mo) treatment with coenzyme Q10 (CoQ10), an endogenous antioxidant. Diabetic mice at 8 mo of age exhibited loss of sensation, hypoalgesia (an increase in mechanical threshold), and decreases in mechanical hyperalgesia, cold allodynia, and sciatic nerve conduction velocity. All these changes were virtually completely absent after the 6-mo, daily CoQ10 treatment in db(-)/db(-) mice when started at 7 wk of age. There was a 33% neuronal loss in the lumbar 5 dorsal root ganglia (DRGs) of the db(-)/db(-) mouse versus controls at 8 mo of age, which was significantly attenuated by CoQ10. There was no difference in neuron number in 5/6-wk-old mice between diabetic and control mice. We observed a strong down-regulation of phospholipase C (PLC) β3 in the DRGs of diabetic mice at 8 mo of age, a key molecule in pain signaling, and this effect was also blocked by the 6-mo CoQ10 treatment. Many of the phenotypic, neurochemical regulations encountered in lumbar DRGs in standard models of peripheral nerve injury were not observed in diabetic mice at 8 mo of age. These results suggest that reactive oxygen species and reduced PLCβ3 expression may contribute to the sensory deficits in the late-stage diabetic db(-)/db(-) mouse, and that early long-term administration of the antioxidant CoQ10 may represent a promising therapeutic strategy for type 2 diabetes neuropathy.

Mitochondrial loss indicates early axonal damage in small fiber neuropathies

Evaluation of nerve fibers in the skin provides a useful tool for the diagnosis of small fiber neuropathies (SFNs). Our aim was to determine whether mitochondria are involved in SFN, indicating early axonal damage. We quantified mitochondrial respiratory chain complex IV (OXPHOS) and axonal (PGP 9.5) fluorescence on skin sections from 32 SFN patients and 14 healthy controls. Also, a group of six patients were recruited before and after 30-day treatment with the mitotoxic antibiotic linezolid. We measured the co-localization of OXPHOS within the intraepidermal and subpapillary dermal axons (PGP-immunoreactive [PGP-ir]). SFN patients with relatively preserved intraepidermal nerve fibers (SFN borderline) showed statistically significant reduction of OXPHOS (50.5 ± 33.9 µm(2) vs. 107.6 ± 81 µm(2) in controls, p < 0.02). A positive correlation was found between both PGP-ir and OXPHOS in controls (Pearson's coefficient r = 0.59, p < 0.001), whereas such correlation was absent in SFN. With respect to baseline measurements, linezolid therapy increased both PGP-ir and OXPHOS, which could be considered an initial compensatory toxic-induced response. This study set out to identify a possible marker of axonal pre-degenerative state in SFN borderline patients.

Hyperglycaemia exacerbates choroidal neovascularisation in mice via the oxidative stress-induced activation of STAT3 signalling in RPE cells

Choroidal neovascularisation (CNV) that occurs as a result of age-related macular degeneration (AMD) causes severe vision loss among elderly patients. The relationship between diabetes and CNV remains controversial. However, oxidative stress plays a critical role in the pathogenesis of both AMD and diabetes. In the present study, we investigated the influence of diabetes on experimentally induced CNV and on the underlying molecular mechanisms of CNV. CNV was induced via photocoagulation in the ocular fundi of mice with streptozotocin-induced diabetes. The effect of diabetes on the severity of CNV was measured. An immunofluorescence technique was used to determine the levels of oxidative DNA damage by anti-8-hydroxy-2-deoxyguanosine (8-OHdG) antibody, the protein expression of phosphorylated signal transducer and activator of transcription 3 (p-STAT3) and vascular endothelial growth factor (VEGF), in mice with CNV. The production of reactive oxygen species (ROS) in retinal pigment epithelial (RPE) cells that had been cultured under high glucose was quantitated using the 2′,7′-dichlorofluorescein diacetate (DCFH-DA) method. p-STAT3 expression was examined using Western blot analysis. RT-PCR and ELISA processes were used to detect VEGF expression. Hyperglycaemia exacerbated the development of CNV in mice. Oxidative stress levels and the expression of p-STAT3 and VEGF were highly elevated both in mice and in cultured RPE cells. Treatment with the antioxidant compound N-acetyl-cysteine (NAC) rescued the severity of CNV in diabetic mice. NAC also inhibited the overexpression of p-STAT3 and VEGF in CNV and in RPE cells. The JAK-2/STAT3 pathway inhibitor AG490 blocked VEGF expression but had no effect on the production of ROS in vitro. These results suggest that hyperglycaemia promotes the development of CNV by inducing oxidative stress, which in turn activates STAT3 signalling in RPE cells. Antioxidant supplementation helped attenuate the development of CNV. Thus, our results reveal a potential strategy for the treatment and prevention of diseases involving CNV.

Cutaneous structural and biochemical correlates of foot complications in high-risk diabetes

OBJECTIVE

Impairment of skin quality may contribute to diabetic foot ulceration (DFU). Our goal was to determine whether high-risk patients exhibited specific skin structural and metabolic deficits that could predispose to foot complications.

RESEARCH DESIGN AND METHODS

A total of 46 patients comprising 9 diabetic control subjects, 16 with diabetic peripheral neuropathy (DPN) alone, and 21 with recurrent DFUs (including 9 with Charcot neuroarthropathy [CNA]) were recruited and compared with 14 nondiabetic control (NDC) subjects. DPN was assessed using the Michigan Neuropathy Screening Instrument (MNSI). Skin punch biopsies (3 mm) were performed on upper and lower leg skin for measurements of intraepidermal nerve fiber density (IENFD), structural analysis, type 1 procollagen abundance, tissue degrading matrix metalloproteinases (MMPs), and poly(ADP-ribose) (PAR) immunoreactivity.

RESULTS

MNSI scores were comparable across DPN groups. IENFD was decreased by diabetes and DPN but did not differ between neuropathic groups. Skin structural deficit scores were elevated in all neuropathic subjects, particularly in the DFU group. Type 1 procollagen abundance was reduced in DFU subjects 387 ± 256 units (mean ± 1 SD) compared with NDC subjects (715 ± 100, P < 0.001). MMP-1 and MMP-2 were activated by diabetes. PAR immunoreactivity was increased in DFU (particularly in the CNA group; P < 0.01) compared with other DPN subjects.

CONCLUSIONS

Increased PAR, reduced type 1 procollagen abundance, and impaired skin structure are associated with foot complications in diabetes. The potential of therapies that improve skin quality to reduce DFU needs to be investigated.

Prevalence and clinical characteristics of diabetic peripheral neuropathy in hospital patients with Type 2 diabetes in Korea

AIMS

Diabetic peripheral neuropathy is a common complication of diabetes. This cross-sectional study investigated the prevalence and clinical characteristics of this neuropathy in patients with Type 2 diabetic mellitus treated at hospitals in Korea.

METHODS

Questionnaires and medical records were used to collect data on 4000 patients with Type 2 diabetes from the diabetes clinics of 40 hospitals throughout Korea. Diabetic peripheral neuropathy was diagnosed based on a review of medical records or using the Michigan Neuropathy Screening Instrument score and monofilament test.

RESULTS

The prevalence of neuropathy was 33.5% (n = 1338). Multivariate analysis revealed that age, female sex, diabetes duration, lower glycated haemoglobin, treatment with oral hypoglycaemic agents or insulin, presence of retinopathy, history of cerebrovascular or peripheral arterial disease, presence of hypertension or dyslipidaemia, and history of foot ulcer were independently associated with diabetic peripheral neuropathy. Of the patients with neuropathy, 69.8% were treated for the condition and only 12.6% were aware of their neuropathy.

CONCLUSION

There was a high prevalence of peripheral neuropathy in patients with Type 2 diabetes in Korea and those patients were far more likely to have complications or co-morbidities. The proper management of diabetic peripheral neuropathy deserves attention from clinicians to ensure better management of diabetes in Korea.

Diabetic peripheral neuropathy: should a chaperone accompany our therapeutic approach?

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes that is associated with axonal atrophy, demyelination, blunted regenerative potential, and loss of peripheral nerve fibers. The development and progression of DPN is due in large part to hyperglycemia but is also affected by insulin deficiency and dyslipidemia. Although numerous biochemical mechanisms contribute to DPN, increased oxidative/nitrosative stress and mitochondrial dysfunction seem intimately associated with nerve dysfunction and diminished regenerative capacity. Despite advances in understanding the etiology of DPN, few approved therapies exist for the pharmacological management of painful or insensate DPN. Therefore, identifying novel therapeutic strategies remains paramount. Because DPN does not develop with either temporal or biochemical uniformity, its therapeutic management may benefit from a multifaceted approach that inhibits pathogenic mechanisms, manages inflammation, and increases cytoprotective responses. Finally, exercise has long been recognized as a part of the therapeutic management of diabetes, and exercise can delay and/or prevent the development of painful DPN. This review presents an overview of existing therapies that target both causal and symptomatic features of DPN and discusses the role of up-regulating cytoprotective pathways via modulating molecular chaperones. Overall, it may be unrealistic to expect that a single pharmacologic entity will suffice to ameliorate the multiple symptoms of human DPN. Thus, combinatorial therapies that target causal mechanisms and enhance endogenous reparative capacity may enhance nerve function and improve regeneration in DPN if they converge to decrease oxidative stress, improve mitochondrial bioenergetics, and increase response to trophic factors.

Glutathione deficiency in type 2 diabetes impairs cytokine responses and control of intracellular bacteria

Individuals with type 2 diabetes are at increased risk of acquiring melioidosis, a disease caused by Burkholderia pseudomallei infection. Although up to half of melioidosis patients have underlying diabetes, the mechanisms involved in this increased susceptibility are unknown. We found that B. pseudomallei-infected PBMCs from diabetic patients were impaired in IL-12p70 production, which resulted in decreased IFN-γ induction and poor bacterial killing. The defect was specific to the IL-12-IFN-γ axis. Defective IL-12 production was also observed during Mycobacterium tuberculosis infection, in which diabetes is likewise known to be a strong risk factor. In contrast, IL-12 production in diabetic cells was not affected upon Salmonella enterica infection or in response to TLR2, -3, -4, and -5 ligands. Poor IL-12 production correlated with a deficiency in intracellular reduced glutathione (GSH) concentrations in diabetic patients. Addition of GSH or N-acetylcysteine to PBMCs selectively restored IL-12 and IFN-γ production and improved bacterial killing. Furthermore, the depletion of GSH in mice led to increased susceptibility to melioidosis, reduced production of IL-12p70, and poorer disease outcome. Our data thus establish a link between GSH deficiency in diabetes and increased susceptibility to melioidosis that may open up new therapeutic avenues to protect diabetic patients against some intracellular bacterial pathogens.

Chromium picolinate and chromium histidinate protects against renal dysfunction by modulation of NF-κB pathway in high-fat diet fed and Streptozotocin-induced diabetic rats

Background

Diabetic nephropathy is one of major complications of diabetes mellitus. Although chromium is an essential element for carbohydrate and lipid metabolism, its effects on diabetic nephropathy are not well understood. The present study was conducted to investigate the effects of chromium picolinate (CrPic) and chromium histidinate (CrHis) on nuclear factor-kappa B (NF-κB) and nuclear factor-E2-related factor-2 (Nrf2) pathway in the rat kidney.

Methods

Male Wistar rats were divided into six groups. Group I received a standard diet (8% fat) and served as a control; Group II was fed with a standard diet and received CrPic; Group III was fed with a standard diet and received CrHis; Group IV received a high fat diet (HFD, 40% fat) for 2 weeks and then were injected with streptozotocin (STZ) (HFD/STZ); Group V was treated as group IV (HFD/STZ) but supplemented with CrPic for 12 weeks. Group VI was treated as group IV (HFD/STZ) but supplemented with CrHis.

Results

The increased NF-κβ p65 in the HFD/STZ group was inhibited by CrPic and CrHis supplementation (P < 0.05). In STZ-treated rats, a significant decrease in levels of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) was found in kidney tissues when compared to control rats (P < 0.05). A significant increase in the levels of IκBα was observed in CrPic- and CrHis-treated rats when compared with STZ-treated rats. Renal Nrf2 levels were significantly decreased in diabetic rats compared with the control rats. There was a higher tendency for increase of kidney Nrf2 level and decrease in kidney NFκBp65 levels and 4- hydroxyl nonenal (4-HNE) protein adducts (P < 0.05) in diabetic rats.

Conclusion

Our result show that in kidney tissue CrHis/CrPic increases Nrf2 level, parallelly decreases NF-κB and partially restores IκBα levels in HFD/STZ group, suggesting that CrPic and CrHis may play a role in antioxidant defense system via the Nrf2 pathway by reducing inflammation through NF-κβ p65 inhibition. Moreover, a greater reduction in NF-κB expression and greater increases in expressions of IκBα and Nrf2 in diabetic rats supplemented with CrHis than rats supplemented with CrPic suggest that CrHis has more favorable effects than CrPic.

C-terminal heat shock protein 90 inhibitor decreases hyperglycemia-induced oxidative stress and improves mitochondrial bioenergetics in sensory neurons

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes in which hyperglycemia-induced mitochondrial dysfunction and enhanced oxidative stress contribute to sensory neuron pathology. KU-32 is a novobiocin-based, C-terminal inhibitor of the molecular chaperone, heat shock protein 90 (Hsp90). KU-32 ameliorates multiple sensory deficits associated with the progression of DPN and protects unmyelinated sensory neurons from glucose-induced toxicity. Mechanistically, KU-32 increased the expression of Hsp70, and this protein was critical for drug efficacy in reversing DPN. However, it remained unclear if KU-32 had a broader effect on chaperone induction and if its efficacy was linked to improving mitochondrial dysfunction. Using cultures of hyperglycemically stressed primary sensory neurons, the present study investigated whether KU-32 had an effect on the translational induction of other chaperones and improved mitochondrial oxidative stress and bioenergetics. A variation of stable isotope labeling with amino acids in cell culture called pulse SILAC (pSILAC) was used to unbiasedly assess changes in protein translation. Hyperglycemia decreased the translation of numerous mitochondrial proteins that affect superoxide levels and respiratory activity. Importantly, this correlated with a decrease in mitochondrial oxygen consumption and an increase in superoxide levels. KU-32 increased the translation of Mn superoxide dismutase and several cytosolic and mitochondrial chaperones. Consistent with these changes, KU-32 decreased mitochondrial superoxide levels and significantly enhanced respiratory activity. These data indicate that efficacy of modulating molecular chaperones in DPN may be due in part to improved neuronal mitochondrial bioenergetics and decreased oxidative stress.

Protective effects of mineralocorticoid receptor blockade against neuropathy in experimental diabetic rats

AIMS

Mineralocorticoid receptor (MR) blockade is an effective treatment for hypertension and diabetic nephropathy. There are no data on the effects of MR blockade on diabetic peripheral neuropathy (DPN). The aim of this study was to determine whether MRs are present in the peripheral nerves and to investigate the effectiveness of MR blockade on DPN in streptozotocin (STZ)-induced diabetic rats.

METHODS

Expression of MR protein and messenger RNA (mRNA) was examined in the peripheral nerves using Western blot analysis and RT-PCR. We next studied the effects of the selective MR antagonist eplerenone and the angiotensin II receptor blocker candesartan on motor and sensory nerve conduction velocity (NCV), morphometric changes and cyclooxygenase-2 (COX-2) gene and NF-κB protein expression in the peripheral nerves of STZ-induced diabetic rats.

RESULTS

Expression of MR protein and mRNA in peripheral nerves was equal to that in the kidney. Motor NCV was significantly improved by 8 weeks of treatment with either eplerenone (39.1 ± 1.2 m/s) or candesartan (46.4 ± 6.8 m/s) compared with control diabetic rats (33.7 ± 2.0 m/s) (p < 0.05). Sensory NCV was also improved by treatment with candesartan or eplerenone in diabetic rats. Eplerenone and candesartan caused significant improvement in mean myelin fibre area and mean myelin area compared with control diabetic rats (p < 0.05). COX-2 mRNA and NF-κB protein were significantly elevated in the peripheral nerves of diabetic rats compared with control rats, and treatment with eplerenone or candesartan reduced these changes in gene expression (p < 0.05).

CONCLUSION

MR blockade may have neuroprotective effects on DPN.

Effect of dipyrone and thalidomide alone and in combination on STZ-induced diabetic neuropathic pain

Diabetic neuropathy is recognized as one of the most common complications of chronic diabetes, but its pathophysiological mechanism is complex and yet to be completely explored. Monotherapy with conventional analgesics fails to provide adequate pain relief in peripheral diabetic neuropathy. There are a number of evidence suggesting that tumor necrosis factor (TNF-α) plays an important role in the pathogenesis of peripheral diabetic neuropathy. TNF-α up-regulation activates nuclear factor κB, which further up-regulates cyclooxygenase (COX)-2 leading to altered prostaglandin profile. Inhibition of TNF-α and COX-2 provides beneficial effect on diabetic neuropathy by decreasing the oxidative stress level and by preventing neuronal hypersensitivity due to an increased prostaglandin level. The present study was designed to assess the effect of dipyrone and thalidomide on streptozotocin (STZ)-induced neuropathic pain behavior in rats. STZ 50 mg/kg, i.p. was administered to induce experimental diabetes in the rats. Three weeks following STZ, dipyrone (300 and 600 mg/kg, i.p.) and thalidomide (25 and 50 mg/kg, i.p.) alone and subeffective dose combination of dipyrone and thalidomide (300 and 25 mg/kg(-1), i.p.) administered daily for 2 weeks significantly attenuated thermal hyperalgesia, mechanical allodynia, and formalin-induced phase-2 flinching response. Moreover, the subeffective dose combination of dipyrone and thalidomide and preemptive treatment with thalidomide (50 mg/kg) reduces oxidative stress in diabetic rats. In conclusion, the combination of subeffective dose of dipyrone and thalidomide prevented the development and maintenance of experimental diabetic neuropathy. The combination of thalidomide (TNF-α inhibitor) and dipyrone (COX inhibitor) may be used as a potential therapeutic agent for the treatment of diabetic neuropathy.

Date fruit extract is a neuroprotective agent in diabetic peripheral neuropathy in streptozotocin-induced diabetic rats: a multimodal analysis

Background. To study the effects of an aqueous extract of date fruit (Phoenix dactylifera L. Arecaceae) diet on diabetic polyneuropathy (DPN) in streptozotocin- (STZ-) induced diabetic rats. Methods. The effects of a date fruit extract (DFE) diet on diabetic neuropathy in STZ-induced diabetic rats were evaluated and compared with a nondiabetic control group, diabetic control group (sham), and vehicle group with respect to the following parameters: open field behavioral test, motor nerve conduction velocity (MNCV), and morphological observations. Results. In the model of STZ-induced of diabetic neuropathy, chronic treatment for 6 weeks with DFE counteracted the impairment of the explorative activity of the rats in an open field behavioral test and of the conduction velocity of the sciatic nerve (MNCV). In addition, pretreatment with DFE significantly reversed each nerve diameter reduction in diabetic rats. Conclusion. DFE treatment shows efficacy for preventing diabetic deterioration and for improving pathological parameters of diabetic neuropathy in rats, as compared with control groups.

Boronate oxidation as a bioorthogonal reaction approach for studying the chemistry of hydrogen peroxide in living systems

Reactive oxygen species (ROS), such as hydrogen peroxide, are important products of oxygen metabolism that, when misregulated, can accumulate and cause oxidative stress inside cells. Accordingly, organisms have evolved molecular systems, including antioxidant metalloenzymes (such as superoxide dismutase and catalase) and an array of thiol-based redox couples, to neutralize this threat to the cell when it occurs. On the other hand, emerging evidence shows that the controlled generation of ROS, particularly H(2)O(2), is necessary to maintain cellular fitness. The identification of NADPH oxidase enzymes, which generate specific ROS and reside in virtually all cell types throughout the body, is a prime example. Indeed, a growing body of work shows that H(2)O(2) and other ROS have essential functions in healthy physiological signaling pathways. The signal-stress dichotomy of H(2)O(2) serves as a source of motivation for disentangling its beneficial from its detrimental effects on living systems. Molecular imaging of this oxygen metabolite with reaction-based probes is a powerful approach for real-time, noninvasive monitoring of H(2)O(2) chemistry in biological specimens, but two key challenges to studying H(2)O(2) in this way are chemoselectivity and bioorthogonality of probe molecules. Chemoselectivity is problematic because traditional methods for ROS detection suffer from nonspecific reactivity with other ROS. Moreover, some methods require enzymatic additives not compatible with live-cell or live-animal specimens. Additionally, bioorthogonality requires that the reactions must not compete with or disturb intrinsic cellular chemistry; this requirement is particularly critical with thiol- or metal-based couples mediating the major redox events within the cell. Chemoselective bioorthogonal reactions, such as alkyne-azide cycloadditions and related click reactions, the Staudinger-Bertozzi ligation, and the transformations used in various reaction-based molecular probes, have found widespread application in the modification, labeling, and detection of biological molecules and processes. In this Account, we summarize H(2)O(2) studies from our laboratory using the H(2)O(2)-mediated oxidation of aryl boronates to phenols as a bioorthogonal approach to detect fluxes of this important ROS in living systems. We have installed this versatile switch onto organic and inorganic scaffolds to serve as "turn-on" probes for visible and near-infrared (NIR) fluorescence, ratiometric fluorescence, time-gated lanthanide luminescence, and in vivo bioluminescence detection of H(2)O(2) in living cells and animals. Further chemical and genetic manipulations target these probes to specific organelles and other subcellular locales and can also allow them to be trapped intracellularly, enhancing their sensitivity. These novel chemical tools have revealed fundamental new biological insights into the production, localization, trafficking, and in vivo roles of H(2)O(2) in a wide variety of living systems, including immune, cancer, stem, and neural cell models.

α-Lipoic acid normalizes nociceptive neuronal activity at the spinal cord of diabetic rats

AIM

To evaluate the effects of antioxidant treatment of streptozotocin (STZ)-diabetic rats with α-lipoic acid (α-LA) in neuronal and microglial activation at the spinal cord, an important relay station of nociceptive transmission. Because of the role of the potassium chloride co-transporter 2 (KCC2) in neuronal activation at the spinal cord and the influence of microglia in KCC2 expression, we also evaluated the effects of α-LA in KCC2 expression at the spinal cord.

METHODS

Four weeks after STZ injection, the rats received daily intraperitoneal injections of α-LA (100 mg/kg), during 2 weeks. Mechanical nociception was evaluated before and after α-LA treatment. Spinal cords were immunoreacted against 8-OH-dG (marker of oxidative stress damage), Fos (marker of neuronal activation) and CD11b (marker of microglia). KCC2 expression was evaluated by immunohistochemistry and western blotting.

RESULTS

Treatment with α-LA decreased the 8-OH-dG and Fos expressions to controls' levels, but did not affect CD11b. Treatment with α-LA alleviated mechanical hyperalgesia and partially corrected KCC2 expression.

CONCLUSIONS

This study shows that neuronal hyperactivity at the spinal cord of STZ-diabetic rats can be corrected by α-LA, which may account for alleviation of mechanical hyperalgesia. These effects are probably partially mediated by KCC2, but are independent from microglia.

Vitamin C partially attenuates male reproductive deficits in hyperglycemic rats

BACKGROUND

Hyperglycemia can impair the male reproductive system in experimental animals and in men during reproductive age. Studies have shown that vitamin C has some good effects on male reproductive system, and therefore vitamin C treatment could attenuate the dysfunctions in this system caused by hyperglycemia. Thus, the objective of this work was to evaluate whether vitamin C treatment could attenuate reproductive dysfunctions in hyperglycemic male rats.

METHODS

Adult male rats were divided into 3 groups: a normoglycemic (n = 10) and two hyperglycemic (that received a single dose of streptozotocin - 40 mg/kg BW). The two last groups (n = 10 per group) were divided into: hyperglycemic control (Hy) and hyperglycemic + 150 mg of vitamin C (HyC), by gavage during 30 consecutive days. The normoglycemic and hyperglycemic control groups received the vehicle (water). The first day after the treatment, the rats were anesthetized and killed to evaluate oxidative stress biomarkers (TBARS, SOD, GSHt and GSH-Px) in the erythrocytes, body and reproductive organ weights, sperm parameters, plasma hormone levels (FSH, LH and testosterone), testicular and epididymal histo-morphometry and histopathology.

RESULTS

Compared with the normoglycemic animals, hyperglycemic control rats showed reduced weight of the body and reproductive organ but testis weight was maintained. It was also observed reduction of testosterone and LH levels, seminiferous tubular diameter, sperm motility and sperm counts in the epididymis. In addition, there was an increase in morphological abnormalities on spermatozoa as well as in oxidative stress level. Vitamin C reduced the oxidative stress level, diminished the number of abnormal sperm, and increased testosterone and LH levels and seminiferous tubular diameter but did not show improvement of sperm motility in relation to the hyperglycemic control group. Hyperglycemia caused a rearrangement in the epididymal tissue components (stroma, ephitelium and lumen) as demonstrated by the stereological analysis results. However, this alteration was partially prevented by vitamin C treatment.

CONCLUSIONS

We conclude that vitamin C partially attenuated some male reproductive system dysfunctions in hyperglycemic rats.

A brief review of in vitro models of diabetic neuropathy

The neuropathies of the peripheral, central and autonomic nervous systems are known to be caused by hyperglycemia, a consequence of the deregulation of glucose in diabetes. Several in vivo models such as streptozotocin-induced diabetic rats, mice and Chinese hamsters have been used to study the pathogenesis of diabetic neuropathy because of their resemblance to human pathology. However, these in vivo models have met with strong ethical oppositions. Further, the system complexity has inherent limitations of inconvenience of analyzing ephemeral molecular events and crosstalk of signal transduction pathways. Alternative in vitro models have been selected and put to effective use in diabetic studies. We critically review the use of these in vitro models such as primary cultures of dorsal root ganglia, Schwann cells and neural tissue as well as neural cell lines which have proved to be excellent systems for detailed study. We also assess the use of embryo cultures for the study of hyperglycemic effects on development, especially of the nervous system. These systems function as useful models to scrutinize the molecular events underlying hyperglycemia-induced stress in neuronal systems and have been very effectively used for the same. This comprehensive overview of advantages and disadvantages of in vitro systems that are currently in use will be of interest especially for comparative assessment of results and for appropriate choice of models for experiments in diabetic neuropathy.

Pharmacological treatment of diabetic neuropathic pain

Neuropathic pain continues to be a difficult and challenging clinical issue to deal with effectively. Painful diabetic polyneuropathy is a complex pain condition that occurs with reasonable frequency in the population and it may be extremely difficult for clinicians to provide patients with effective analgesia. Chronic neuropathic pain may occur in approximately one of every four diabetic patients. The pain may be described as burning or a deep-seated ache with sporadic paroxysms of lancinating painful exacerbations. The pain is often constant, moderate to severe in intensity, usually primarily involves the feet and generally tends to worsen at night. Treatment may be multimodal but largely involves pharmacological approaches. Pharmacological therapeutic options include antidepressants (tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors), α2δ ligands and topical (5%) lidocaine patch. Other agents may be different antiepileptic drugs (carbamazepine, lamotrigine, topiramate), topical capsaicin, tramadol and other opioids. Progress continues with respect to understanding various mechanisms that may contribute to painful diabetic neuropathy. Agents that may hold some promise include neurotrophic factors, growth factors, immunomodulators, gene therapy and poly (adenosine diphosphate-ribose) polymerase inhibitors. It is hoped that in the future clinicians will be able to assess patient pathophysiology, which may help them to match optimal therapeutic agents to target individual patient aberrant mechanisms.

Peripheral vascular disease and peripheral neuropathy in individuals with cardiometabolic clustering and obesity: National Health and Nutrition Examination Survey 2001-2004

OBJECTIVE

Two lower-extremity diseases (LEDs), including peripheral neuropathy and peripheral vascular disease (PVD), are leading causes of disability in the U.S. Although LEDs can be complications of diabetes, their prevelances and risk factors apart from diabetes are poorly described. This study describes the prevalence of LEDs and examines the association of obesity and cardiometabolic clustering in a population-based sample.

RESEARCH DESIGN AND METHODS

Adults aged≥40 years (n=2,514) were evaluated in the 2001-2004 National Health and Nutrition Examination Survey for clustering of two or more cardiometabolic characteristics, including elevated triglycerides or plasma glucose, low HDL cholesterol levels, increased waist circumference, or hypertension. Clustering was combined with BMI (dichotomized at ≥30 kg/m2) to generate three groups: obese (with or without clustering); nonobese with clustering; and nonobese without clustering. Multivariate logistic regression procedures incorporated the complex survey sampling design.

RESULTS

Overall, 9.0% of individuals had peripheral neuropathy alone, 8.5% had PVD alone, and 2.4% had both LEDs. The obese group was more likely to have peripheral neuropathy (odds ratio 2.20 [95% CI 1.43-3.39]), PVD (3.10 [1.84-5.22]), and both LEDs (6.91 [2.64-18.06]) compared with nonobese subjects without clustering. Within the nonobese group, clustering increased the odds of peripheral neuropathy (1.50 [1.00-2.25]) and PVD (2.48 [1.38-4.44]) compared with no clustering.

CONCLUSIONS

Obesity and clustering markedly increased the likelihood of LEDs in this sample and identified a group for whom preventive activities may reduce the risk of future disability.

Chondroprotective role of sesamol by inhibiting MMPs expression via retaining NF-κB signaling in activated SW1353 cells

Overexpression of matrix metalloproteinases (MMPs) is a major pathological factor causing cartilage destruction in osteoarthritis (OA). This study aimed to investigate the effects and mechanisms of sesamol on expression of MMPs in activated chondrosarcoma cells. Sesamol significantly attenuated TNF-α- and IL-1β-induced gelatinolysis and expression of MMP-9 in a concentration-dependent manner in SW1353 cells. Additionally, both MMP-1 and -13 stimulated by PMA were inhibited by sesamol. On the other hand, the NF-κB signaling activation through IκB-α degradation was restored by sesamol under TNF-α or PMA stimulation. Furthermore, this bioactive compound exerted the reduction on phosphorylation of ERK1/2 or p38 MAPKs after either PMA or IL-1β stimulation. This study also evaluated whether sesamol down-regulates MMP expression in the joint cartilage of monosodium iodoacetate (MIA)-induced OA in rats. Sesamol prevented the expression of MMP-1 and -9 in the cartilage of MIA-induced OA in rats. The results of this study demonstrate that sesamol inhibits cytokine- or PMA-induced MMPs expression through the signal pathways of either NF-κB or ERK/p38 MAPKs down-regulation. This study also showed that sesamol attenuates destructive factor expression in vivo, providing a potential strategy for the chondroprotective therapy in OA.

A hydrogen peroxide-responsive hyperpolarized 13C MRI contrast agent

We report a new reaction-based approach for the detection of hydrogen peroxide (H(2)O(2)) using hyperpolarized (13)C magnetic resonance imaging ((13)C MRI) and the H(2)O(2)-mediated oxidation of α-ketoacids to carboxylic acids. (13)C-Benzoylformic acid reacts selectively with H(2)O(2) over other reactive oxygen species to generate (13)C-benzoic acid and can be hyperpolarized using dynamic nuclear polarization, providing a method for dual-frequency detection of H(2)O(2). Phantom images collected using frequency-specific imaging sequences demonstrate the efficacy of this responsive contrast agent to monitor H(2)O(2) at pre-clinical field strengths. The combination of reaction-based detection chemistry and hyperpolarized (13)C MRI provides a potentially powerful new methodology for non-invasive multi-analyte imaging in living systems.

Mechanisms of vascular complications in prediabetes

Although the state of prediabetes is defined by its role as a diabetes risk factor, it also carries a significant risk of cardiovascular disease, independent of progression to diabetes. Typical diabetic microvascular complications also occur, albeit at low rates, in prediabetes. There is evidence that both glucose-related and glucose-independent mechanisms contribute to these vascular complications. Effective preventive strategies will likely require control of glycemia, as well as other metabolic risk factors. This article reviews some of the proposed mechanisms for the vascular complications of the prediabetic state.

Increased susceptibility to ischemia and macrophage activation in STZ-diabetic rat nerve

Ischemic vulnerability in diabetic nerve plays a paramount role in the development of diabetic neuropathy, yet little is known of the underlying mechanism. Diabetes enhances the inflammatory response to ischemia and reperfusion. We investigated pathological characteristics of nerve fibers and endoneurial macrophages along the length of sciatic-tibial nerves before and after ischemia (60 to 90 min) and reperfusion (6h to 7 days) in 8 weeks of STZ-induced diabetic rats. Without ischemia, diabetic nerves revealed significantly increased the density of Iba-1-positive endoneurial macrophages when compared with controls. Most of macrophages appeared slim and triangular in shape, but in diabetic nerves, some were rounded with bromodeoxyuridine (BrdU) incorporation, suggesting proliferating macrophages. Seventy-five minutes of ischemia is the minimal ischemic time to cause pathological changes in diabetic nerves. Following 90 min of ischemia and 6h of reperfusion in diabetic rats, the number of Iba-1-positive endoneurial macrophages was increased significantly at the thigh level of sciatic nerve when compared with those before ischemia. Endoneurial macrophages in diabetic nerves increased in number further significantly after 24 and 48 h of reperfusion and underwent morphological alterations; swollen and rounded including phagocytosis. After 90 min of ischemia and 7 days of reperfusion, severe pathological alterations, e.g., demyelination and endoneurial edema at proximal nerves and axonal degeneration distally, were observed in diabetic nerves, while control nerves showed normal morphology. We conclude that macrophage proliferation occurs in STZ-diabetic nerves. The acute inflammatory response after ischemia and reperfusion was intensified in diabetic nerves. Activation of resident macrophages and infiltration by recruited macrophages could be casually linked to ischemic susceptibility in diabetic nerve.

Changes of mitochondrial ultrastructures and function in central nervous tissue of hens treated with tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus ester, is capable of producing organophosphorus ester-induced delayed neurotoxicity (OPIDN) in humans and sensitive animals. The mechanism of OPIDN has not been fully understood. The present study has been designed to evaluate the role of mitochondrial dysfunctions in the development of OPIDN. Adult hens were treated with 750 mg/kg·bw TOCP by gavage and control hens were given an equivalent volume of corn oil. On day 1, 5, 15, 21 post-dosing, respectively, hens were anesthetized by intraperitoneal injection of sodium pentobarbital and perfused with 4% paraformaldehyde. The cerebral cortex cinerea and the ventral horn of lumbar spinal cord were dissected for electron microscopy. Another batch of hens were randomly divided into three experimental groups and control group. Hens in experimental groups were, respectively, given 185, 375, 750 mg/kg·bw TOCP orally and control group received solvent. After 1, 5, 15, 21 days of administration, they were sacrificed and the cerebrum and spinal cord dissected for the determination of the mitochondrial permeability transition (MPT), membrane potential (Δψ(m)) and the activity of succinate dehydrogenase. Structural changes of mitochondria were observed in hens' nervous tissues, including vacuolation and fission, which increased with time post-dosing. MPT was increased in both the cerebrum and spinal cord, with the most noticeable increase in the spinal cord. Δψ(m) was decreased in both the cerebrum and spinal cord, although there was no significant difference in the three treated groups and control group. The activity of mitochondrial succinate dehydrogenase assayed by methyl thiazolyl tetrazolium (MTT) reduction also confirmed mitochondrial dysfunctions following development of OPIDN. The results suggested mitochondrial dysfunction might partly account for the development of OPIDN induced by TOCP.

Kinin B1 receptor enhances the oxidative stress in a rat model of insulin resistance: outcome in hypertension, allodynia and metabolic complications

Background

Kinin B₁ receptor (B₁R) is induced by the oxidative stress in models of diabetes mellitus. This study aims at determining whether B₁R activation could perpetuate the oxidative stress which leads to diabetic complications.

Methods and Findings

Young Sprague-Dawley rats were fed with 10% D-Glucose or tap water (controls) for 8–12 weeks. A selective B₁R antagonist (SSR240612) was administered acutely (3–30 mg/kg) or daily for a period of 7 days (10 mg/kg) and the impact was measured on systolic blood pressure, allodynia, protein and/or mRNA B₁R expression, aortic superoxide anion (O₂^•−) production and expression of superoxide dismutase (MnSOD) and catalase. SSR240612 reduced dose-dependently (3–30 mg/kg) high blood pressure in 12-week glucose-fed rats, but had no effect in controls. Eight-week glucose-fed rats exhibited insulin resistance (HOMA index), hypertension, tactile and cold allodynia and significant increases of plasma levels of glucose and insulin. This was associated with higher aortic levels of O₂^•−, NADPH oxidase activity, MnSOD and catalase expression. All these abnormalities including B₁R overexpression (spinal cord, aorta, liver and gastrocnemius muscle) were normalized by the prolonged treatment with SSR240612. The production of O₂^•− in the aorta of glucose-fed rats was also measured in the presence and absence of inhibitors (10–100 µM) of NADPH oxidase (apocynin), xanthine oxidase (allopurinol) or nitric oxide synthase (L-NAME) with and without Sar[D-Phe⁸]des-Arg⁹-BK (20 µM; B₁R agonist). Data show that the greater aortic O₂^•− production induced by the B₁R agonist was blocked only by apocynin.

Conclusions

Activation of kinin B₁R increased O₂^•− through the activation of NADPH oxidase in the vasculature. Prolonged blockade of B₁R restored cardiovascular, sensory and metabolic abnormalities by reducing oxidative stress and B₁R gene expression in this model.

Inhibiting heat-shock protein 90 reverses sensory hypoalgesia in diabetic mice

Increasing the expression of Hsp70 (heat-shock protein 70) can inhibit sensory neuron degeneration after axotomy. Since the onset of DPN (diabetic peripheral neuropathy) is associated with the gradual decline of sensory neuron function, we evaluated whether increasing Hsp70 was sufficient to improve several indices of neuronal function. Hsp90 is the master regulator of the heat-shock response and its inhibition can up-regulate Hsp70. KU-32 (N-{7-[(2R,3R,4S,5R)-3,4-dihydroxy-5-methoxy-6,6-dimethyl-tetrahydro-2H-pyran-2-yloxy]-8-methyl-2-oxo-2H-chromen-3-yl}acetamide) was developed as a novel, novobiocin-based, C-terminal inhibitor of Hsp90 whose ability to increase Hsp70 expression is linked to the presence of an acetamide substitution of the prenylated benzamide moiety of novobiocin. KU-32 protected against glucose-induced death of embryonic DRG (dorsal root ganglia) neurons cultured for 3 days in vitro. Similarly, KU-32 significantly decreased neuregulin 1-induced degeneration of myelinated Schwann cell DRG neuron co-cultures prepared from WT (wild-type) mice. This protection was lost if the co-cultures were prepared from Hsp70.1 and Hsp70.3 KO (knockout) mice. KU-32 is readily bioavailable and was administered once a week for 6 weeks at a dose of 20 mg/kg to WT and Hsp70 KO mice that had been rendered diabetic with streptozotocin for 12 weeks. After 12 weeks of diabetes, both WT and Hsp70 KO mice developed deficits in NCV (nerve conduction velocity) and a sensory hypoalgesia. Although KU-32 did not improve glucose levels, HbA1c (glycated haemoglobin) or insulin levels, it reversed the NCV and sensory deficits in WT but not Hsp70 KO mice. These studies provide the first evidence that targeting molecular chaperones reverses the sensory hypoalgesia associated with DPN.

The major green tea polyphenol, (-)-epigallocatechin-3-gallate, induces heme oxygenase in rat neurons and acts as an effective neuroprotective agent against oxidative stress

BACKGROUND

Oxidative stress induced by hyperglycemia is a key factor in the pathogenesis of diabetic complications, such as neuropathy. Recently, green tea catechins have received much attention, as they can facilitate a number of antioxidative mechanisms and improve glycemic control.

OBJECTIVE

The aim of this study was to investigate the cytoprotective effects of (-)-epigallocatechin-3-gallate (EGCG) against oxidative stress damage in a cell line of rat neurons. The role of heme oxygenase 1 (HO-1) induction by EGCG and the transcriptional mechanisms involved were also evaluated.

METHODS

Immortalized rat neurons (H 19-7) were exposed to various concentrations of EGCG (10-200 microM). After treatments (6 or 24 hours), cells were harvested for the determination of heme oxygenase activity, mRNA levels, and protein expression. Nuclear levels of Nrf2, a transcriptional factor involved in HO-1 activation, were also measured. Neurons were pretreated for 12 hours with EGCG 50 microM or EGCG 50 microM + zinc protoporphyrin IX 10 microM and then exposed for 2 hours to 50 mmicro/mL glucose-oxidase before cell viability was determined.

RESULTS

In cultured neurons, elevated expression of HO-1 mRNA and protein were detected after 6 hours of incubation with 25-100 microM EGCG, and its induction relates with the activation of Nrf2. Interestingly, pre-incubation (12 hours) with EGCG 50 microM resulted in an enhanced cellular resistance to glucose oxidase-mediated oxidative damage; this cytoprotective effect was considerably attenuated by zinc protoporphyrin IX, an inhibitor of heme oxygenase activity.

CONCLUSIONS

In this study, we demonstrated that EGCG, the major green tea catechin, induced HO-1 expression in cultured neurons, possibly by activation of the transcription factor Nrf2, and by this mechanism was able to protect against oxidative stress-induced cell death.

Global transcriptional programs in peripheral nerve endoneurium and DRG are resistant to the onset of type 1 diabetic neuropathy in Ins2 mice

While the morphological and electrophysiological changes underlying diabetic peripheral neuropathy (DPN) are relatively well described, the involved molecular mechanisms remain poorly understood. In this study, we investigated whether phenotypic changes associated with early DPN are correlated with transcriptional alterations in the neuronal (dorsal root ganglia [DRG]) or the glial (endoneurium) compartments of the peripheral nerve. We used Ins2(Akita/+) mice to study transcriptional changes underlying the onset of DPN in type 1 diabetes mellitus (DM). Weight, blood glucose and motor nerve conduction velocity (MNCV) were measured in Ins2(Akita/+) and control mice during the first three months of life in order to determine the onset of DPN. Based on this phenotypic characterization, we performed gene expression profiling using sciatic nerve endoneurium and DRG isolated from pre-symptomatic and early symptomatic Ins2(Akita/+) mice and sex-matched littermate controls. Our phenotypic analysis of Ins2(Akita/+) mice revealed that DPN, as measured by reduced MNCV, is detectable in affected animals already one week after the onset of hyperglycemia. Surprisingly, the onset of DPN was not associated with any major persistent changes in gene expression profiles in either sciatic nerve endoneurium or DRG. Our data thus demonstrated that the transcriptional programs in both endoneurial and neuronal compartments of the peripheral nerve are relatively resistant to the onset of hyperglycemia and hypoinsulinemia suggesting that either minor transcriptional alterations or changes on the proteomic level are responsible for the functional deficits associated with the onset of DPN in type 1 DM.

Organelle-targetable fluorescent probes for imaging hydrogen peroxide in living cells via SNAP-Tag protein labeling

Hydrogen peroxide (H(2)O(2)) is a potent small-molecule oxidant that can exert a diverse array of physiological and/or pathological effects within living systems depending on the timing and location of its production, accumulation, trafficking, and consumption. To help study the chemistry and biology of this reactive oxygen species (ROS) in its native cellular context, we now present a new method for monitoring local, subcellular changes in H(2)O(2) levels by fluorescence imaging. Specifically, we have exploited the versatility of the SNAP-tag technology for site-specific protein labeling with small molecules on the surface or interior of living cells with the use of boronate-capped dyes to selectively visualize H(2)O(2). The resulting SNAP-Peroxy-Green (SNAP-PG) probes consist of appropriately derivatized boronates bioconjugated to SNAP-tag fusion proteins. Spectroscopic measurements of the SNAP-PG constructs confirm their ability to detect H(2)O(2) with specificity over other biologically relevant ROS. Moreover, these hybrid small-molecule/protein reporters can be used in live mammalian cells expressing SNAP-tag fusion proteins directed to the plasma membrane, nucleus, mitochondria, and endoplasmic reticulum. Imaging experiments using scanning confocal microscopy establish organelle-specific localization of the SNAP-tag probes and their fluorescence turn-on in response to changes in local H(2)O(2) levels. This work provides a general molecular imaging platform for assaying H(2)O(2) chemistry in living cells with subcellular resolution.

Hyperglycemia alters the schwann cell mitochondrial proteome and decreases coupled respiration in the absence of superoxide production

Hyperglycemia-induced mitochondrial dysfunction contributes to sensory neuron pathology in diabetic neuropathy. Although Schwann cells (SCs) also undergo substantial degeneration in diabetic neuropathy, the effect of hyperglycemia on the SC mitochondrial proteome and mitochondrial function has not been examined. Stable isotope labeling with amino acids in cell culture (SILAC) was used to quantify the temporal effect of hyperglycemia on the mitochondrial proteome of primary SCs isolated from neonatal rats. Of 317 mitochondrial proteins identified, about 78% were quantified and detected at multiple time points. Pathway analysis indicated that proteins associated with mitochondrial dysfunction, oxidative phosphorylation, the TCA cycle, and detoxification were significantly increased in expression and over-represented. Assessing mitochondrial respiration in intact SCs indicated that hyperglycemia increased the overall rate of oxygen consumption but decreased the efficiency of coupled respiration. Although a glucose-dependent increase in superoxide production occurs in embryonic sensory neurons, hyperglycemia did not induce a substantial change in superoxide levels in SCs. This correlated with a 1.9-fold increase in Mn superoxide dismutase expression, which was confirmed by immunoblot and enzymatic activity assays. These data support that hyperglycemia alters mitochondrial respiration and can cause remodeling of the SC mitochondrial proteome independent of significant contributions from glucose-induced superoxide production.

Diabetes induces changes in ILK, PINCH and components of related pathways in the spinal cord of rats

Recent work suggests that diabetes affects processing of peripheral, spinal and supraspinal signals in the spinal cord. However, there is little evidence for spinal cord lesions that would account for alterations in behavioral responses induced by experimental diabetes. Therefore, we assessed the expression of proteins that might affect neuronal cytoskeletal stability and thus promote dendritic and synaptic reorganization in diabetic rats. Expression of ILK, PINCH, PI3K, GSK-3beta, tau, MAP2, synaptophysin and drebrin in the lumbar spinal cord of non-diabetic and streptozotocin-diabetic rats was assessed by Western-blot analysis and immunocytochemistry after 8 and 20weeks of diabetes. The impact of diabetes on the proteins studied was duration-dependent with changes observed after 20 but not 8weeks of diabetes. ILK and PINCH proteins levels were significantly decreased and both colocalized to neurons and oligodendrocytes. PI3K protein levels were also significantly decreased, while GSK-3beta activity tended to be increased. Phosphorylation of tau and MAP2A/B protein expression were significantly increased, and expression of synaptophysin and drebrin were reduced in diabetic rats. Decreased ILK and PINCH as well as alterations of components of related signaling pathways are associated with tau hyperphosphorylation, MAP2 overexpression and reduction of synaptic proteins in the spinal cord of diabetic rats, suggesting that ILK and PINCH contribute to stabilization of axonal and dendritic structures. However, these changes are not likely the cause of altered behavioral responses in diabetic rats that occur after short-term diabetes, but may contribute to structural changes occurring in long-term diabetes.

Diabetic cataracts: mechanisms and management

Diabetes mellitus is associated with a 5-fold higher prevalence of cataracts, which remains a major cause of blindness in the world. Typical diabetic cataracts contain cortical and/or posterior subcapsular opacities. Adult onset diabetic cataracts also often contain nuclear opacities. Mechanisms of diabetic cataractogenesis have been studied in less detail than those of other diabetic complications. Both animal and human studies support important contribution of increased aldose reductase activity. Surgical extraction is the only cure of diabetic cataract today. An improved understanding of pathogenetic mechanisms, together with finding effective therapeutic agents, remain highest priority for diabetic cataract-related research and pharmaceutical development.

The management of diabetic neuropathy in CKD

A 64-year-old male with a 15-year history of poorly controlled type 2 diabetes and a 10-year history of hypertension and hyperlipidemia had developed multiple diabetes-related complications within the last 5 years. He first developed albuminuria 5 years ago, and over the next several years experienced fairly rapid decline in kidney function, with eGFR of 55 mL/min/1.73m2 noted 2 years ago. He was diagnosed with proliferative retinopathy 5 years ago and underwent laser photocoagulation. Four years ago, he noted symptoms of peripheral neuropathy manifested as shooting pain and numbness with loss of light touch, thermal and vibratory sensation in a stocking distribution. Last year he developed a non-healing ulcer on the plantar aspect of his left foot which was complicated with gangrene and resulted in a below-the-knee amputation of the left leg one year ago. He now reports a new onset of weakness, lightheadedness and dizziness on standing that affects his daily activities. He reports lancinating pain in his right lower extremity, worse in the evening. Medications include: neutral protamine Hagedorn insulin twice daily and regular insulin on a sliding scale, metoprolol 50 mg/d, lisinopril 40 mg/d, atorvastatin 80 mg/d, furosemide 40 mg/d and aspirin 81 mg/d. Blood pressure is 127/69 mm Hg with a pulse rate of 96 bpm while supine and 94/50 mmHg with a pulse rate of 102 bpm while standing. Strength is normal but with a complete loss of all sensory modalities to the knee in his remaining limb and up to the wrists in both upper extremities, and he is areflexic. Today's laboratory evaluations show a serum creatinine of 2.8 mg/dl, an estimated GFR (eGFR) of 24 ml/min/1.73m2, a hemoglobin A1c (HbA1c) of 7.9 % and 2.1 g of urine protein per gram of creatinine. What would be the most appropriate management for this patient?

NF-kappaB-induced oxidative stress contributes to mitochondrial and cardiac dysfunction in type II diabetes

AIMS

Inflammatory molecules and their transcription factor, nuclear factor kappa-B (NF-kappaB), are thought to play important roles in diabetes-induced cardiac dysfunction. Here, we investigated the effects of pyrrolidine dithiocarbamate (PDTC), a NF-kappaB inhibitor, in diabetic mice.

METHODS AND RESULTS

Obese db/db mice and heterozygous lean mice (n = 8) were allowed free access to drinking water (control) or water containing PDTC (100 mg/kg) for 20 weeks. Left ventricular (LV) function was measured using echocardiography at baseline and at study end. Mice were sacrificed and LV removed for gene expression, biochemical, immunofluorescence, and mitochondrial assays. LV and mitochondrial reactive oxygen species (ROS), superoxide and peroxynitrite were measured using electron spin resonance spectroscopy. Enhanced NF-kappaB activity in db/db mice was associated with increased oxidative stress as demonstrated by increased ROS, superoxide, and peroxynitrite production, and increased NF-kappaB, gp91phox, and Nox1 expression; PDTC ameliorated these effects. Mitochondrial free radical production and structural damage were higher in the db/db group than in the control, db/db PDTC, and PDTC-treated heterozygous animal groups.

CONCLUSION

This study demonstrates that NF-kappaB blockade with PDTC mitigates oxidative stress and improves mitochondrial structural integrity directly, through down-regulation of increased oxygen-free radicals, thereby increasing ATP synthesis and thus restoring cardiac function in type II diabetes.