Formononetin Ameliorates Diabetic Neuropathy by Increasing Expression of SIRT1 and NGF

Diabetic neuropathy is commonly observed complication in more than 50 % of type 2 diabetic patients. Histone deacetylases including SIRT1 have significant role to protect neuron from hyperglycemia induced damage. Formononetin (FMNT) is known for its effect to control hyperglycemia and also activate SIRT1. In present study, we evaluated effect of FMNT as SIRT1 activator in type 2 diabetic neuropathy. Type 2 diabetic neuropathy was induced in rats by modification of diet for 15 days using high fat diet and administration of streptozotocin (35 mg/kg/day, i. p.). FMNT treatment was initiated after confirmation of type 2 diabetes. Treatment was given for 16 weeks at 10, 20 and 40 mg/kg/day dose orally. FMNT treatment‐controlled hypoglycemia and reduced insulin resistance significantly in diabetic animals. FMNT treatment reduced oxidative stress in sciatic nerve tissue. FMNT treatment also reduced thermal hyperalgesia and mechanical allodynia significantly. It improved conduction velocity in nerve and unregulated SIRT1 and NGF expression in sciatic nerve tissue. Results of present study indicate that continuous administration of FMNT protected diabetic animals from hyperglycemia induced neuronal damage by controlling hyperglycemia and increasing SIRT1 and NGF expression in nerve tissue. Thus, FMNT can be an effective candidate for treatment of type 2 diabetic neuropathy.     

Blockade of early and late retinal biochemical alterations associated with diabetes development by the selective bradykinin B1 receptor antagonist R-954

The chronic hyperglycemia measured alongside diabetes development is associated with significant long-term damage and failure of various organs. In the present study it was shown that hyperglycemia induced early and long term increases in nitric oxide (NO) levels, kallikrein activity and vascular capillary permeability measured as plasma extravasation, and decreases of Na/K ATPase activity in diabetic rat retina 4 and 12 weeks after streptozotocin (STZ) injection. Treatment of the animals for 5 consecutive days with a novel selective bradykinin B(1) receptor (BKB(1)-R) antagonist R-954 (2mg/kg s.c) at the end of the 4 and 12 week periods highly reduced NO, kallikrein and capillary permeability and increased Na/K ATPase activity in the retina. These results suggest that the BKB(1)-R receptor subtype is over-expressed during the streptozotocin-induced development of diabetes in rat retina as evidenced by the inhibitory effects of the BKB(1)-R antagonist R-954 on NO, kallikrein and vascular permeability increases as well as Na/K ATPase decreases. The beneficial role of the BKB(1)-R antagonist R-954 for the treatment of the diabetic retinopathy is also suggested.     

Enhanced dermal and retinal vascular permeability in streptozotocin-induced type 1 diabetes in Wistar rats: blockade with a selective bradykinin B1 receptor antagonist

The vascular complications associated with type 1 diabetes are to some extent related to the dysfunction of the endothelium leading to an increased vascular permeability and plasma extravasation in the surrounding tissues. The various micro- and macro-vascular complications of diabetes develop over time, leading to nephropathy, retinopathy and neuropathy and cardiomyopathy. In the present study, the effect of a novel selective bradykinin B1 receptor (BKB1-R) antagonist, R-954, was investigated on the changes of vascular permeability in the skin and retina of streptozotocin (STZ)-induced type 1 diabetic rats. Plasma extravasation increased in the skin and retina of STZ-diabetic rats after 1 week and persisted over 4 weeks following STZ injection. Acute treatment with R-954 (2 mg/kg, bolus s.c.) highly reduced the elevated vascular permeability in both 1- and 4-week STZ-diabetic rats. These results showed that the inducible BKB1-R subtype modulates the vascular permeability of the skin and retina of type 1 diabetic rats and suggests that BKB1-R antagonists could have a beneficial role in diabetic neuropathy and retinopathy.     

Statin treatment reduces oxidative stress-associated apoptosis of sciatic nerve in diabetes mellitus

Abstract

Statins are lipid-lowering drugs that are widely used for treating hyperlipidemia, especially in diabetic patients. The aim of our study was to explore the effects of atorvastatin on oxidative stress and apoptosis in the sciatic nerve due to hyperglycemia. Diabetes was induced by streptozotocin. Atorvastatin was given orally for two weeks beginning from the sixth week. Microscopic examination of sciatic nerve revealed that normal tissue organization was disrupted in streptozotocin induced diabetic rats. Treatment with Atorvastatin reduced the histological damage and protected the morphological integrity of the sciatic nerve in streptozotocin induced diabetes. Increased expressions of transforming growth factor beta-1, endothelial nitric oxide synthase and TUNEL in sciatic nerve from streptozotocin induced diabetes were reduced by Atorvastatin. Atorvastatin could improve the effects of oxidative stress and apoptosis on the sciatic nerve due to diabetes.     

Beneficial effect of chronic treatment with the selective bradykinin B1 receptor antagonists, R-715 and R-954, in attenuating streptozotocin-diabetic thermal hyperalgesia in mice

Kinins are important mediators of cardiovascular homeostasis, inflammation and nociception. Bradykinin (BK) B(1) receptors (BKB1-R) are over-expressed in pathological conditions including diabetes, and were reported to play a role in hyperglycemia, renal abnormalities, and altered vascular permeability associated with type 1 diabetes. Recent studies from our laboratory demonstrated that BKB1-R are implicated in streptozotocin (STZ)-diabetes-mediated hyperalgesia, since acute administration of the selective BKB1-R antagonists significantly and dose-dependently inhibited such hyperalgesic activity. In the present study, we examined the effect of chronic treatment of STZ-diabetic mice with the selective BKB1-R agonist desArg9bradykinin (DBK) and two specific antagonists R-715 and R-954, on diabetic hyperalgesia. Diabetes was induced in male CD-1 mice by injecting a single high dose of STZ (200mg/kg, i.p.) and nociception was assessed using the hot plate, plantar stimulation, tail immersion and tail flick tests. Drugs were injected i.p. twice daily for 7 days, starting 4 days after STZ. We showed that chronically administered R-715 (400 micrograms/kg) and R-954 (200 micrograms/kg), significantly attenuated the hyperalgesic effect developed in STZ-diabetic mice as measured by the four thermal nociceptive tests. Further, chronic treatment with DBK (400 micrograms/kg) produced a marked potentiation of the hyperalgesic activity, an effect that was reversed by both R-715 and R-954. The results from this chronic study confirm a pivotal role of the BKB1-R in the development of STZ-diabetic hyperalgesia and suggest a novel approach to the treatment of this short-term diabetic complication using BKB1-R antagonists.     

The kinin system mediates hyperalgesia through the inducible bradykinin B1 receptor subtype: evidence in various experimental animal models of type 1 and type 2 diabetic neuropathy

Both insulin-dependent (type 1) and insulin-independent (type 2) diabetes are complex disorders characterized by symptomatic glucose intolerance due to either defective insulin secretion, insulin action or both. Unchecked hyperglycemia leads to a series of complications among which is painful diabetic neuropathy, for which the kinin system has been implicated. Here, we review and compare the profile of several experimental models of type 1 and 2 diabetes (chemically induced versus gene-prone) and the incidence of diabetic neuropathy upon aging. We discuss the efficacy of selective antagonists of the inducible bradykinin B1 receptor (BKB1-R) subtype against hyperalgesia assessed by various nociceptive tests. In either gene-prone models of type 1 and 2 diabetes, the incidence of hyperalgesia mostly precedes the development of hyperglycemia. The administration of insulin, achieving euglycemia, does not reverse hyperalgesia. Treatment with a selective BKB1-R antagonist does not affect basal nociception in most normal control rats, whereas it induces a significant time- and dose-dependent attenuation of hyperalgesia, or even restores nociceptive responses, in experimental diabetic neuropathy models. Diabetic hyperalgesia is absent in streptozotocin-induced type 1 diabetic BKB1-R knockout mice. Thus, selective antagonism of the inducible BKB1-R subtype may constitute a novel and potential therapeutic approach for the treatment of painful diabetic neuropathy.     

Effects of resveratrol on nerve functions, oxidative stress and DNA fragmentation in experimental diabetic neuropathy

Oxidative stress has been implicated in pathophysiology of diabetic neuropathy. All the pathways responsible for development of diabetic neuropathy are linked to oxidative stress in one way or the other. In the present study, we have targeted oxidative stress in diabetic neuropathy using resveratrol, a potent antioxidant. Eight weeks streptozotocin-diabetic rats developed neuropathy which was evident from significant reduction in motor nerve conduction velocity (MNCV), nerve blood flow (NBF) and increased thermal hyperalgesia. The 2-week treatment with resveratrol (10 and 20 mg/kg, i.p.) started 6 weeks after diabetes induction significantly ameliorated the alterations in MNCV, NBF, and hyperalgesia. Resveratrol also attenuated enhanced levels of malondialdehyde (MDA), peroxynitrite and produced increase in catalase levels in diabetic rats. There was marked reduction in DNA fragmentation observed after resveratrol treatment in diabetic rats as evident from decrease in Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells in sciatic nerve sections. Results of the present study suggest the potential of resveratrol in treatment of diabetic neuropathy and its protective effect may be mediated through reduction in oxidative stress and DNA fragmentation.     

The TRPV1 receptor is associated with preferential stress in large dorsal root ganglion neurons in early diabetic sensory neuropathy

Chronic diabetic neuropathy is associated with peripheral demyelination and degeneration of nerve fibers. The mechanism(s) underlying neuronal injury in diabetic sensory neuropathy remain poorly understood. Recently, we reported increased expression and function of transient receptor potential vanilloid 1 (TRPV1) in large dorsal root ganglion (DRG) neurons in diabetic sensory neuropathy. In this study, we examined the effects of TRPV1 activation on cell injury pathways in this subpopulation of neurons in the streptozotocin-induced diabetic rat model. Large DRG neurons from diabetic (6–8 weeks) rats displayed increased oxidative stress and activation of cell injury markers compared with healthy controls. Capsaicin (CAP) treatment induced decreased labeling of MitoTracker Red and increased cytosolic cytochrome c and activation of caspase 3 in large neurons isolated from diabetic rats. CAP treatment also induced oxidative stress in large diabetic DRG neurons, which was blocked by pre-treatment with caspase or calpain inhibitor. In addition, both μ-calpain expression and calpain activity were significantly increased in DRG neurons from diabetic rats after CAP treatment. Treatment with capsazepine, a competitive TRPV1 antagonist, markedly reduced these abnormalities in vitro and prevented activation of cell injury in large DRG neurons in diabetic rats in vivo . These results suggest that activation of the TRPV1 receptor activates pathways associated with caspase-dependent and calpain-dependent stress in large DRG neurons in STZ-diabetic rats. Activation of the TRPV1 receptor may contribute to preferential neuronal stress in large DRG neurons relatively early in diabetic sensory neuropathy.     

A comparison of sciatic nerve neuropathy in diabetic and aged rats

We compared the development of sciatic nerve neuropathy in young diabetic rats with that in non-diabetic aged rats. Diabetes was induced in six-month old rats by injection with alloxan and was moderately controlled by single daily injections of insulin. Blood insulin levels in diabetic rats were significantly reduced compared to the aged animals, and glucose was significantly higher in diabetic rats. Sciatic nerve conduction velocities were measured monthly. Both motor and sensory conduction velocities decreased in the diabetic rats to a level that was similar to those in 36-month old rats. The decreases in conduction velocities in the diabetic rats were most dramatic during months 6 through 12 of diabetes. After 6 and 12 months of diabetes, sciatic nerves were examined by electron microscopy and compared to nerves from 24- and 36-month old rats respectively. Ultrastructural changes in the sciatic nerves of diabetic rats at 6 months included disruptions of myelin and dense axoplasm. In comparison, the 24-month old rats only had distorted contours of the nerve fibres. After 12 months of diabetes, the axoplasm had large spaces and the myelin was thickened and deformed. The axoplasm of 36-month old rats was normal in appearance; however the myelin sheath was thickened and split into layers. The Schwann cells were vacuolated and irregular in shape. These observations indicate that diabetes results in the early onset of age-like changes in the sciatic nerve. It suggests that the control of hyperglycemia in humans may preserve sciatic nerve structure and function.     

Inhibitory effect of a novel bradykinin B1 receptor antagonist,R-954, on enhanced vascular permeability in type 1 diabetic mice

The morbidity and mortality associated with type 1 diabetes are essentially related to the micro- and macrovascular complications that develop over time and lead to several diabetic complications, including hypertension, atherosclerosis, and retinopathy, as well as coronary and renal failure. Normally absent in physiological conditions, the bradykinin B1 receptor (BKB1-R) was recently found to be overexpressed in pathological conditions, including type 1 diabetes. In the present study, we evaluated the effect of the new BKB1-R antagonist, R-954 (Ac-Orn-[Oic2, alpha-MePhe5, D-betaNal7, Ile8]desArg9-bradykinin, on the increase in vascular permeability in streptozotocin (STZ)-diabetic mice. The capillary permeability to albumin was measured by quantifying the extravasation of albumin-bound Evans blue dye in selected target tissues (liver, pancreas, duodenum, ileum, spleen, heart, kidney, stomach, skin, muscle, and thyroid gland). Acute single administration of R-954 (300 microg/kg, i.v.) to type 1 diabetic mice 4 weeks after STZ significantly inhibited the enhanced vascular permeability in most tissues. These data provide further experimental evidence for the implication of BKB1-R in the enhanced vascular permeability associated with type 1 diabetes.     

Suppression of NF-κB and NF-κB regulated oxidative stress and neuroinflammation by BAY 11-7082 (IκB phosphorylation inhibitor) in experimental diabetic neuropathy

Inflammation is an emerging patho-mechanism of diabetes and its complications. NF-κB pathway is one of the central machinery initiating and propagating inflammatory responses. The present study envisaged the involvement of NF-κB inflammatory cascade in the pathophysiology of diabetic neuropathy using BAY 11-7082, an IκB phosphorylation inhibitor. Streptozotocin was used to induce diabetes in Sprauge Dawley rats. BAY 11-7082 (1 &; 3 mg/kg) was administered to diabetic rats for 14 days starting from the end of six weeks post diabetic induction. Diabetic rats developed deficits in nerve functions and altered nociceptive parameters and also showed elevated expression of NF-κB (p65), IκB and p-IκB along with increased levels of IL-6 &; TNF-α and inducible enzymes (COX-2 and iNOS). Furthermore, there was an increase in oxidative stress and decrease in Nrf2/HO-1 expression. We observed that BAY 11-7082 alleviated abnormal sensory responses and deficits in nerve functions. BAY 11-7082 also ameliorated the increase in expression of NF-κB, IκB and p-IκB. BAY 11-7082 curbed down the levels of IL-6, TNF-α, COX-2 and iNOS in the sciatic nerve. Lowering of lipid peroxidation and improvement in GSH levels was also seen along with increased expression of Nrf2/HO-1. Thus it can be concluded that NF-κB expression and downstream expression of proinflammatory mediators are prominent features of nerve damage leading to inflammation and oxidative stress and BAY 11-7082 was able to ameliorate experimental diabetic neuropathy by modulating neuroinflammation and improving antioxidant defence.     

Slowing of Motor Nerve Conduction Velocity in Streptozotocin-induced Diabetic Rats is Preceded by Impaired Vasodilation in Arterioles that Overlie the Sciatic Nerve

Diabetes mellitus produces marked abnormalities in motor nerve conduction, but the mechanism is not clear. In the present study we hypothesized that in the streptozotocin (STZ)-induced diabetic rat impaired vasodilator function in arterioles that provide circulation to the region of the sciatic nerve is associated with reduced endoneural blood flow (EBF) and that these defects precede slowing of motor nerve conduction velocity, and thereby may contribute to nerve dysfunction. As early as three days after the induction of diabetes endoneural blood flow was reduced in the STZ-induced diabetic rat. Furthermore, after 1 week of diabetes acetylcholine- induced vasodilation was found to be impaired. This was accompanied by an increase in the superoxide level in arterioles that provide circulation to the region of the sciatic nerve as well as changes in the level of other markers of oxidative stress including an increase in serum levels of thiobarbituric acid reactive substances and a decrease in lens glutathione level. In contrast to the vascular related changes that occur within 1 week of diabetes, motor nerve conduction velocity and sciatic nerve Na⁺/k⁺ ATPase activity were significantly reduced following 2 and 4 weeks of diabetes, respectively. These studies demonstrate that changes in vascular function in the STZ-induced diabetic rat precede the slowing of motor nerve conduction velocity (MNCV) and are accompanied by an increase in superoxide levels in arterioles that provide circulation to the region of the sciatic nerve.     

Beneficial effects of n-hexane bark extract of Onosma echioides L. on diabetic peripheral neuropathy

Onosma echioides Linn (Boraginaceae) is the most frequently used curative herb widely used for kidney obstruction, sciatic pain, and gout. The present study was designed to investigate the therapeutic effects of n-hexane bark extract of O. echioides (OE) L. root in vivo against Streptozotocin-induced diabetic neuropathy in SD rats. For in vivo activity, the experiment was categorized into five different groups (n = 5). Group-I was considered as nondiabetic/normal control (NC) treated with 0.5% carboxymethyl cellulose (CMC), Group II as diabetic control, Group-III, IV, and V served as diabetic treated with OE 50, OE 100, and pregabalin at a dose of 50, 100, and 10 mg/kg body weight, orally, respectively. Body weight, blood glucose, oral glucose tolerance test, behavioral studies (motor coordination test, thermal hyperalgesia, cold allodynia, locomotor activity, oxidative biomarkers (thio barbituric acid reactive substances [TBARS], superoxide dismutase [SOD], glutathione [GSH], and catalase), and histopathology of the sciatic nerve were performed. Treatment with OE showed a dose-dependent increase in neuroprotective activity by improving the myelination and decreasing the axonal swelling of nerve fibers. The verdicts of behavioral activities showed a remarkable effect on animals after the treatment of extract and standard drug pregabalin. In conclusion, our findings supported the traditional application of OE and explored its importance in the management of diabetic neuropathy. Additional clinical experiments may provide novel therapeutic drugs for diabetes and its complications.     

Involvement of P2Y<Subscript>12</Subscript> receptor of stellate ganglion in diabetic cardiovascular autonomic neuropathy

Diabetes as a chronic epidemic disease with obvious symptom of hyperglycemia is seriously affecting human health globally due to the diverse diabetic complications. Diabetic cardiovascular autonomic neuropathy (DCAN) is a common complication of both type 1 and type 2 diabetes and incurs high morbidity and mortality. However, the underlying mechanism for DCAN is unclear. It is well known that purinergic signaling is involved in the regulation of cardiovascular function. In this study, we examined whether the P2Y₁₂ receptor could mediate DCAN-induced sympathetic reflexes. Our results revealed that the abnormal changes of blood pressure, heart rate, heart rate variability, and sympathetic nerve discharge were improved in diabetic rats treated with P2Y₁₂ short hairpin RNA (shRNA). Meanwhile, the expression of P2Y₁₂ receptor, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and connexin 43 (Cx43) in stellate ganglia (SG) was decreased in P2Y₁₂ shRNA-treated diabetic rats. In addition, knocking down the P2Y₁₂ receptor also inhibited the activation of p38 MARK in the SG of diabetic rats. Taken together, these findings demonstrated that P2Y₁₂ receptor in the SG may participate in developing diabetic autonomic neuropathy, suggesting that the P2Y₁₂ receptor could be a potential therapeutic target for the treatment of DCAN.     

The bradykinin B1 receptor antagonist R-954 inhibits Ehrlich tumor growth in rodents

The present study investigated the effects of a new bradykinin B₁ receptor antagonist, R-954, on the development of Ehrlich ascitic tumor (EAT) induced by the intraperitoneal inoculation of EAT cells in mice and the formation of a solid tumor by the subcutaneous injection of the cells in rat paw. The development of the tumor was associated with an increase in mouse total cell counts in bone marrow (10.8-fold), ascitic fluid (14.6-fold), and blood (12.6-fold). R-954 (2 mg/kg, s.c.) significantly reduced the ascitic fluid volume (63.7%) and the mouse weight gain (30.5%) after 10 consecutive days of treatment. The B₁ antagonist as well as the anti-neoplasic drug vincristine also significantly inhibited the increase in total cell count in bone marrow, ascitic fluid, and blood. R-954 reduced significantly the total protein extravasation (57.3%), the production of nitric oxide (56%), PGE₂ production (82%), and TNFα release (85.7%) in mice peritoneal cavity whereas vincristine reduced the release of these inflammatory mediators by 84-94%. The increase in paw edema after intraplantar injection of EAT cells was reduced by approximately 52% by either R-954 or vincristine treatment. In conclusion, this study presents for the first time the antitumoral activity of a new bradykinin B₁ receptor antagonist on ascitic and solid tumors induced by Ehrlich cell inoculation in mice and rats.     

Effects of U83836E on nerve functions, hyperalgesia and oxidative stress in experimental diabetic neuropathy

Oxidative stress has been implicated to play an important role in the pathogenesis of diabetic neuropathy, which is the most common complication of diabetes mellitus affecting more than 50% of diabetic patients. In the present study, we have investigated the effect of U83836E [(-)-2-((4-(2,6-Di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl)methyl)-3,4-dihydro-2,3,7,8-tetramethyl-2H-1-benzopyran-6-ol, 2HCl], a potent free radical scavenger in streptozotocin (STZ)-induced diabetic neuropathy in rats. STZ-induced diabetic rats showed significant deficit in motor nerve conduction velocity (MNCV), nerve blood flow (NBF) and thermal hyperalgesia after 8 weeks of diabetes induction, indicating development of diabetic neuropathy. Antioxidant enzyme (superoxide dismutase and catalase) levels were reduced and malondialdehyde (MDA) levels were significantly increased in diabetic rats as compared to the age-matched control rats, this indicates the involvement of oxidative stress in diabetic neuropathy. The 2-week treatment with U83836E (3 and 9 mg/kg, i.p.) started 6 weeks after diabetes induction significantly ameliorated the alterations in MNCV, NBF, hyperalgesia, MDA levels and antioxidant enzymes in diabetic rats. Results of the present study suggest the potential of U83836E in treatment of diabetic neuropathy.     

Evaluation of alpha(1)-adrenoceptor antagonist on diabetes-induced changes in peripheral nerve function, metabolism, and antioxidative defense.

The role for nerve blood flow (NBF) vs. other factors in motor nerve conduction (MNC) slowing in short-term diabetes was assessed by evaluating alpha(1)-adrenoceptor antagonist prazosin on NBF, MNC, as well as metabolic imbalances and oxidative stress in the neural tissue. Control and diabetic rats were treated with or without prazosin (5 mg.kg(-1).d(-1) for 3 wk). NBF was measured by hydrogen clearance. Both endoneurial vascular conductance and MNC velocity were decreased in diabetic rats vs. controls, and this decrease was prevented by prazosin. Free NAD(+):NADH ratios in mitochondrial cristae, matrix, and cytosol assessed by metabolite indicator method, as well as phosphocreatine levels and phosphocreatine/creatine ratios, were decreased in diabetic rats, and this reduction was ameliorated by prazosin. Neither diabetes-induced accumulation of two major glycation agents, glucose and fructose, as well as sorbitol and total malondialdehyde plus 4-hydroxyalkenals nor depletion of myo-inositol, GSH, and taurine or decrease in (Na/K)-ATP-ase activity were affected by prazosin. In conclusion, decreased NBF, but not metabolic imbalances or oxidative stress in the neural tissue, is a key mechanism of MNC slowing in short-term diabetes. Further experiments are needed to estimate whether preservation of NBF is sufficient for prevention of nerve dysfunction and morphological abnormalities in long-standing diabetes or whether the aforementioned metabolic imbalances closely associated with impaired neurotropism are of greater importance in advanced than in early diabetic neuropathy.     

Proanthocyanidins protect against early diabetic peripheral neuropathy by modulating endoplasmic reticulum stress

Diabetic peripheral neuropathy (DPN) is the most common and troublesome complication of type 2 diabetes mellitus (T2DM). Recent findings reveal an important role of endoplasmic reticulum (ER) stress in the development of DPN and identify a potential new therapeutic target. Schwann cells (SC), the myelinating cells in peripheral nervous system, are highly susceptible to ER homeostasis. Grape seed proanthocyanidins (GSPs) have been reported to improve DPN of type 1 diabetic rats and relieve ER stress in skeletal muscles and pancreas of T2DM. We investigated the potential role of ER stress in SC in regulating DPN of T2DM and assessed whether early intervention of GSPs would prevent DPN by modulating ER stress. The present study was performed in Sprague–Dawley rats made T2DM with low-dose streptozotocin and a high-carbohydrate/high-fat diet and in rat SC cultured in serum from type 2 diabetic rats. Diabetic rats showed a typical characteristic of T2DM and slowing of nerve conduction velocity (NCV) in sciatic/tibial nerves. The lesions of SC, Ca²⁺ overload and ER stress were present in sciatic nerves of diabetic rats, as well as in cell culture models. GSPs administration significantly decreased the low-density lipoprotein level and increased NCV in diabetic rats. GSPs or their metabolites also partially prevented cell injury, Ca²⁺ overload and ER stress in animal and cell culture models. Therefore, ER stress is implicated in peripheral neuropathy in animal and cell culture models of T2DM. Prophylactic GSPs treatment might have auxiliary preventive potential for DPN partially by alleviating ER stress.     

Isoform Specific Reductions in Na+,K+-ATPase Catalytic (α) Subunits in the Nerve of Rats with Streptozotocin-Induced Diabetes

Abstract: Na⁺,K⁺-ATPase activity in nerve is reduced in rats with streptozotocin-induced diabetes; three different isoforms of the α (catalytic) subunit of the enzyme are present in nerve. Using western blot to determine subunit isoform polypeptide levels in sciatic nerve, we found a substantial reduction in α1-isoform polypeptide (88% at 3 weeks, 94% at 8 weeks) after induction of diabetes by streptozotocin. Reductions in α2 and α3 polypeptide were smaller and not statistically significant. The reduction in amount of all three isoform polypeptides in the nerve of 3-week diabetic animals was corrected by administration of insulin. Accumulation of α1 polypeptide at a nerve ligature indicated that rapid transport of that polypeptide in nerve occurs with normal kinetics. The results implicate a specific marked deficit in α1, much more than α2 or α3, catalytic subunit isoform of Na⁺,K⁺-ATPase in the pathogenesis of diabetic neuropathy.