Effects of alpha-lipoic acid on neurovascular function in diabetic rats: interaction with essential fatty acids

A Double-Blind, Randomized, Placebo-Controlled Study to Assess the Efficacy of a Nerve Support Formula on Neuropathic Pain in Individuals Suffering from Type II Diabetes Mellitus

Background

The primary objective of the present study was to evaluate the effects of a Nerve Support Formula NeuropAWAY^® on diabetic neuropathic pain.

Methods

This double-blind, placebo-controlled, randomized trial was conducted between August 2020 and February 2021. Patients aged ≥40 and ≤65 years with a history of type 2 diabetes (T2D) with a confirmed diagnosis of diabetic neuropathic pain were included in the study. The primary efficacy endpoint was to assess the effect of the 42 days administration of the Nerve Support Formula on the neuropathic pain as assessed by the 11 point Pain Intensity Numeric Rating Scale (PI-NRS). The secondary objectives were to assess the effect on plasma vitamin B12 levels, nerve conduction velocity, blood flow velocity, Brief Pain Inventory, Neuropathy Total Symptom Score, and Insomnia Severity Index.

Results

The enrolled study population (n=59) was randomized in two study groups; the Investigational Product (IP) group - Nerve Support Formula (n=27) and placebo group (n=32). The mean age of these participants was 52.63 and 53.72 for IP and placebo group, respectively. The mean (SD) HbA1c levels for IP and placebo group were 8.37 (0.85) and 8.16 (0.86), respectively. By the end of the study (Day 42) the decrease in PI-NRS scores for the IP group was maximal (↓61.32%) and highly significant (p<0.001) in comparison to the placebo group (↑2.47%). Significant improvements (p<0.05) were also noted in the secondary efficacy variables after 42 days of IP intake.

Conclusion

The formula was found to be significantly effective as compared to placebo in reducing pain and other sensory symptoms related to the diabetic peripheral neuropathy.

Effects of alpha lipoic acid treatment during in vitro maturation on the development of porcine somatic cell nuclear transfer embryos

Oxidative stress influences the embryo production efficiency in vitro. We investigated the effects of alpha lipoic acid (ALA) treatment during the in vitro maturation (IVM) period on the porcine somatic cell nuclear transfer (SCNT) embryo production. After IVM, maturation rates of the 12.5- and 25-μM ALA-treated groups were not significantly different from those of the 0-μM ALA-treated group. Compared to those in the 0-μM ALA-treated group, the reactive oxygen species and glutathione levels were significantly decreased and increased, respectively, in the cytoplasm of matured oocytes in the 12.5-50-μM ALA-treated groups. Apoptosis rate in cumulus cells after IVM was significantly lower in the 12.5-50-μM ALA-treated groups than in the 0-μM ALA-treated group. Blastocyst formation rate was significantly higher in parthenogenetic oocytes treated with 12.5-μM ALA than in the 0-, 25-, and 50-μM ALA-treated groups. Similarly, in SCNT embryos, the 12.5-μM ALA-treated group showed a significantly higher blastocyst formation rate than the 0-μM ALA-treated group. Apoptosis rate in SCNT blastocysts was significantly decreased by 12.5-μM ALA treatment. The results showed that treatment with 12.5-μM ALA during IVM improves porcine SCNT embryo development and partial quality.

Effects of Theranekron and alpha-lipoic acid combined treatment on GAP-43 and Krox-20 gene expressions and inflammation markers in peripheral nerve injury

Peripheral nerve injury (PNI) is a major health problem that results in loss of motor and sensory functions. In treatment of PNI, various methods such as anastomosis, nerve grafts, nonneural tissue grafts, and nerve conduits are applied. In the present study, it was aimed to investigate the effects of Theranekron and Alpha-lipoic acid (ALA) combined treatment on nerve healing in experimental PNI by using histomorphometric, electron microscopic, immunohistochemical and molecular biological methods. Sixty-two Wistar rats were divided into six groups; the normal control group, sham operation group, experimental control group having a crush type injury with no treatment, Theranekron treatment group, ALA treatment group and Theranekron+ALA combined treatment group. Sciatic nerve tissue samples were obtained on days 1, 7 and 14 following injury in all groups. GAP-43 expression was upregulated in all PNI received groups compared to the control group. Krox-20 expression was downregulated in all groups that received PNI compared to the control group. While intensely positive TNF-α and IL-6 expressions were observed up to the 1st to the 14th day for the experimental control group, these expressions were seen as "weakly positive" in the treatment groups from the 1st day to the 14th day. The number of myelinated fibers was higher in the control and sham operation groups. Additionally, the number of myelinated nerve fibers increased in the combined treatment group. In conclusion, these findings suggest that combined therapy of Theranekron and ALA promotes structural recovery and it should be considered as an effective treatment protocol following PNI.

The Potential Role of Fatty Acids in Treating Diabetic Neuropathy

PURPOSE OF REVIEW

This review will summarize recent findings of the effect of supplemental fatty acids, with an emphasis on omega-3 polyunsaturated fatty acids, as a treatment for diabetic peripheral neuropathy.

RECENT FINDINGS

Pre-clinical studies have provided evidence that treating diabetic rodents with δ linolenic acid (omega-6 18:3) and to a greater extent with eicosapentaenoic and docosahexaenoic acids (omega-3 20:5 and 22:6, respectively) improve and even reverse vascular and neural deficits. Additional studies have shown resolvins, metabolites of eicosapentaenoic and docosahexaenoic acids, can induce neurite outgrowth in neuron cultures and that treating type 1 or type 2 diabetic mice with resolvin D1 or E1 provides benefit for peripheral neuropathy similar to fish oil. Omega-3 polyunsaturated fatty acids derived from fish oil and their derivatives have anti-inflammatory properties and could provide benefit for diabetic peripheral neuropathy. However, clinical trials are needed to determine whether this statement is true.

Pathology of cigarettes on the reproductive system and ameliorative effects of alpha lipoic acid: A rat model study

Cigarette smoking (CS) has some detrimental effects that occur via oxidative stress (OS). The aim of this work was to demonstrate the pathological and immunohistochemical effects of CS and the protective effects of a strong antioxidant alpha lipoic acid (ALA) on CS-induced genital system changes in a rat model. Twenty-eight female rats were randomly allocated to three groups as control, CS-exposed, and CS-exposed and ALA-treated. Reproductive tract organs were collected for biochemical and pathological examinations. In the CS group, OS markers increased in the tissues of both the ovary and fallopian tubes. Decreased follicle numbers in the ovary, marked cilial loss in the fallopian tubes, and pathologic changes in the uterus were observed in the CS group. Positive calcitonin gene–related peptide (CGRP), caspase 3α, hypoxia-inducible factor 1α (HIF-1α), tumor necrosis factor-α (TNF-α) immunoreactions were observed in uterine tissues and HIF-1α immunoreactions in tubal and uterine epithelial cells of the CS group. ALA reversed all these findings effectively. CS has negative effects on the female reproductive system via HIF-1α in tuba uterina and HIF-1α, HIF-2α, TNF-α, caspase 3, and CGRP in the uterus, and ALA could protect against the negative effects of CS on the female reproductive system.

Protection from spinal cord ischemia-reperfusion damage with alpha-lipoic acid preconditioning in an animal model

Background

This study aims to investigate whether preconditioning with alpha-lipoic acid has any protective effect in neuronal damage in an experimental spinal cord ischemia-reperfusion injury model.

Methods

Eighteen adult male New Zealand rabbits (2.4-3.5 kg) were equally divided into sham, control and treatment groups. The abdominal aorta was occluded for 30 min proximally 1 cm below the renal artery and distally 1 cm above the bifurcation using aneurysm clips in control and treatment groups. Treatment group received intraperitoneal 100 mg/kg lipoic acid 20 min before aortic cross-clamping. The animals were sacrificed 48 hours after the operation and spinal cord segments between L2 and L5 were removed for biochemical and histopathological analysis. Levels of glutathione, malondialdehyde, total nitrate/nitrite, advanced oxidation protein products, catalase, superoxide dismutase, and glutathione peroxidase were examined in spinal cord.

Results

Preconditioning with alpha-lipoic acid demonstrated significantly favorable effects in all measured parameters of oxidative stress. Histopathological evaluation of the tissues also demonstrated significantly decreased neuronal degeneration, axonal damage, and microglial and astrocytic infiltration in the treatment group compared to the control group.

Conclusion

The results of this study indicate that alpha-lipoic acid administration before aortic cross-clamping has significant neuroprotective effect on spinal cord injury in rabbits.

Vasoregression: A Shared Vascular Pathology Underlying Macrovascular And Microvascular Pathologies?

Vasoregression is a common phenomenon underlying physiological vessel development as well as pathological microvascular diseases leading to peripheral neuropathy, nephropathy, and vascular oculopathies. In this review, we describe the hallmarks and pathways of vasoregression. We argue here that there is a parallel between characteristic features of vasoregression in the ocular microvessels and atherosclerosis in the larger vessels. Shared molecular pathways and molecular effectors in the two conditions are outlined, thus highlighting the possible systemic causes of local vascular diseases. Our review gives us a system-wide insight into factors leading to multiple synchronous vascular diseases. Because shared molecular pathways might usefully address the diagnostic and therapeutic needs of multiple common complex diseases, the literature analysis presented here is of broad interest to readership in integrative biology, rational drug development and systems medicine.

Glucotoxic Mechanisms and Related Therapeutic Approaches

Neuropathy is the earliest and commonest complication of diabetes. With increasing duration of diabetes, frequency and severity of neuropathy are worsened. Long-term hyperglycemia is therefore implicated in the development of this disorder. Nerve tissues require glucose energy to function and survive. Upon excessive glucose entry into the peripheral nerve, the glycolytic pathway and collateral glucose-utilizing pathways are overactivated and initiate adverse effects on nerve tissues. During hyperglycemia, flux through the polyol pathway, formation of advanced glycation end-products, production of free radicals, flux into the glucosamine pathway, and protein kinase C activity are all enhanced to negatively influence nerve function and structure. Suppression of these aberrant metabolic pathways has succeeded in prevention and inhibition of the development of neuropathy in animal models with diabetes. Satisfactory results were not attained, however, in patients with diabetes and further clinical trials are required. In this review, the author summarizes the hitherto proposed theories on the pathogenesis of diabetic neuropathy related to glucose metabolism and future prospects for the effective treatment of neuropathy.

Pancreatic damage induced by cigarette smoke: the specific pathological effects of cigarette smoke in the rat model

In recent years, pancreatic pathologies have become common problems and their etiology and pathogenesis are generally unknown. Studies have shown that smoking may increase the risk of pancreatic disorders but very scant knowledge is available about the pathogenesis of cigarette induced pancreatic pathology. This study aimed to evaluate the oxidative stress status, biochemical, pathological and immunohistochemical findings of rats exposed to cigarette smoke, pathogenesis of smoking related pancreatic damage and usability of Alpha Lipoic Acid (ALA) for amelioration of cigarette smoking induced harmful effects on rat pancreas. Twenty eight female, Sprague Dawley rats were randomly distributed into three groups. The sham group (S) (n = 8), rats were given 0.1 ml of physiological serum by oral gavage for 8 weeks. The cigarette smoke exposed group (CSE) (n = 10), rats were exposed to successive periods of cigarette smoke for 2 hours per day per 8 weeks and given 0.1 ml of physiological serum orally during the study. The cigarette smoke exposed and ALA treated group (CSE + ALA) (n = 10), animals were exposed to cigarette smoke (2 hours per day per 8 weeks) and simultaneously treated with 100 mg per kg per day ALA orally during the study. At the end of the study, the serum samples were collected for insulin, glucagon, glucose and amylase analyses. Tissue samples were collected for biochemical, histopathological and immunohistochemical examinations. Total oxidant status (TOS), total antioxidant status (TAS) levels and oxidative stress index (OSI) were evaluated in the pancreas samples. Immunohistochemical analyses of insulin, glucagon, calcitonin gene related protein (CGRP), active caspase-3, hypoxia inducible factor-1 (Hif-1), Hif-2 and tumor necrosis factor (TNF-α) expressions of pancreas were examined. Cigarette smoke caused statistically significant increase in serum amylase and glucose but decreased insulin levels indicating both endocrine and exocrine cell damage. There were no statistically significant differences in serum glucagon levels between the groups. Histopathological examination of the pancreas exhibited generally normal tissue architecture but slightly degenerative and apoptotic cells were noticed both in the endocrine and exocrine part of the pancreas in the CSE group. Immunohistochemical analyses revealed marked increase in active caspase-3, Hif-1 and Hif-2, CGRP and TNF-α expressions with a slight increase in glucagon immunoreactivity in cells while a marked decrease was observed in insulin expression in some Langerhans islets in the CSE group. ALA ameliorated biochemical and pathological findings in the CSE + ALA group. These findings clearly demonstrated that cigarette smoke can cause damage in both endocrine and exocrine cells in rat pancreas and ALA has an ameliorative effect of cigarette induced lesions.

Protective effects of alpha-lipoic acid on experimental sciatic nerve crush injury in rats: assessed with functional, molecular and electromicroscopic analyses

AIM

The present study aimed to demonstrate protective effects of alpha lipoic acid on experimental sciatic nerve crush injury model assessed with functional and electronmicroscopy analyses.

METHODS

In this study, groups were; Group 1; sham operated, Group 2; applied only sciatic nerve crush (Control), Group 3; Sciatic nerve crush + treated ALA 25 mg/kg (received orally) and Group 4; Sciatic nerve crush + treated ALA 50 mg/kg. Subsequently, sciatic nerves crush injury induced by forceps. At the second and fourth week, all animals were evaluated for sciatic functional index (SFI) and histomorphometric analyses with electronmicroscopy.

RESULTS

The SFI was significantly increased for both ALA-treated groups 30 days post-injury compared with control groups. The elecronmicroscopy results demonstrated that the axon diameter, the myelin diameter, the area of regenerating axon and miyelin were better in the treatment group than in the control group. Also ALA decreased IL-1β and Caspase 3 levels that increased in SNC group.

CONCLUSIONS

These results suggest that ALA neuroprotective agent for peripheral nerve injury (PNI) and promoted peripheral nerve regeneration via its anti-inflammatory and antiapoptotic effects.

Mechanisms of diabetic neuropathy: Schwann cells

As ensheathing and secretory cells, Schwann cells are a ubiquitous and vital component of the endoneurial microenvironment of peripheral nerves. The interdependence of axons and their ensheathing Schwann cells predisposes each to the impact of injury in the other. Further, the dependence of the blood-nerve interface on trophic support from Schwann cells during development, adulthood, and after injury suggests these glial cells promote the structural and functional integrity of nerve trunks. Here, the developmental origin, injury-induced changes, and mature myelinating and nonmyelinating phenotypes of Schwann cells are reviewed prior to a description of nerve fiber pathology and consideration of pathogenic mechanisms in human and experimental diabetic neuropathy. A fundamental role for aldose-reductase-containing Schwann cells in the pathogenesis of diabetic neuropathy, as well as the interrelationship of pathogenic mechanisms, is indicated by the sensitivity of hyperglycemia-induced biochemical alterations, such as polyol pathway flux, formation of reactive oxygen species, generation of advanced glycosylation end products (AGEs) and deficient neurotrophic support, to blocking polyol pathway flux.

Traditional chinese medicine tang-luo-ning ameliorates sciatic nerve injuries in streptozotocin-induced diabetic rats

Diabetic peripheral neuropathy (DPN) is a common microvascular complication of diabetes associated with high disability rate and low quality of life. Tang-Luo-Ning (TLN) is an effective traditional Chinese medicine for the treatment of DPN. To illustrate the underlying neural protection mechanisms of TLN, the effect of TLN on electrophysiology and sciatic nerve morphology was investigated in a model of streptozotocin-induced DPN, as well as the underlying mechanism. Sciatic motor nerve conduction velocity and digital sensory nerve conduction velocity were reduced in DPN and were significantly improved by TLN or α-lipoic acid at 10 and 20 weeks after streptozotocin injection. It was demonstrated that TLN intervention for 20 weeks significantly alleviated pathological injury as well as increased the phosphorylation of ErbB2, Erk, Bad (Ser112), and the mRNA expression of neuregulin 1 (Nrg1), GRB2-associated binding protein 1 (Gab1), and mammalian target of rapamycin (Mtor) in injured sciatic nerve. These novel therapeutic properties of TLN to promote Schwann cell survival may offer a promising alternative medicine for the patients to delay the progression of DPN. The underlying mechanism may be that TLN exerts neural protection effect after sciatic nerve injury through Nrg1/ErbB2→Erk/Bad Schwann cell survival signaling pathway.

Improving development of cloned goat embryos by supplementing α-lipoic acid to oocyte in vitro maturation medium

α-Lipoic acid (LA) is a powerful antioxidant for clinical therapy of some metabolic diseases, but there are few reports about the effect of LA on animal occyte in vitro maturation (IVM). The objective of this study is to investigate the effect of supplementing LA to IVM medium on subsequently developmental competence of goat cloning embryos after somatic cell nucleus transfer (SCNT). Twenty-five micromolars LA significantly increased 12% oocyte maturation rate from control 57.8% to treated group 69.8% (P < 0.05). The reconstructed rate of cloning embryos in LA supplement group (67.3%) was significantly higher than control (56.5%, P < 0.05). Although the SCNT embryo cleavage rates did not have significant difference between the two groups (42.0% vs. 47.9%, P > 0.05), LA supplement group had significantly higher blastocyst formation rate and hatched rate than control (24.0% vs. 18.4% and 37.0% vs. 30.9%, respectively, P < 0.05). In addition, supplementing LA significantly reduced the cellular apoptosis rate of nucleus transfer blastocysts by inhibiting the expression of apoptotic activators, such as Bax, Bad, Caspase-3, and CytC genes and promoting cumulus-oocyte complexes to synthesize glutathione (GSH) and express antioxidant enzymes such as GPX4 and SOD genes. In conclusion, supplement of LA to oocyte IVM medium could improve the maturation rate and antioxidant ability of oocytes and increase the developmental competence of oocytes after SCNT.

A systematic review and meta-analysis of α-lipoic acid in the treatment of diabetic peripheral neuropathy

OBJECTIVE

To evaluate the effects and safety of 300-600 mg α-lipoic acid (ALA) given i.v. for diabetic peripheral neuropathy (DPN).

METHODS

We searched the databases of Medline, Embase, and Cochrane central register of Controlled Trials and Chinese biological medicine for clinical trials of ALA in the treatment of DPN. Data were extracted to examine methodological quality and describe characteristics of studies. The primary outcomes were efficacy, median motor nerve conduction velocity (MNCV), median sensory nerve conduction velocity (SNCV), peroneal MNCV, and peroneal SNCV. Secondary outcomes were adverse events.

RESULTS

Fifteen randomized controlled trials met the inclusion criteria. The treatment group involved the administration of ALA 300-600 mg i.v. per day. And the control group used the same interventions except for ALA. Compared with the control group, nerve conduction velocities increased significantly in the treatment group. The weighted mean differences in nerve conduction velocities were 4.63 (95% confidence interval 3.58-5.67) for median MNCV, 3.17 (1.75-4.59) for median SNCV, 4.25 (2.78-5.72) for peroneal MNCV, and 3.65 (1.50-5.80) for peroneal SNCV in favor of the treatment group. The odds ratio in terms of efficacy was 4.03 (2.73-5.94) for ALA. Furthermore, no serious adverse events were observed during the treatment period.

CONCLUSIONS

The results of this meta-analysis provide evidence that treatment with ALA (300-600 mg/day i.v. for 2-4 weeks) is safe and that the treatment can significantly improve both nerve conduction velocity and positive neuropathic symptoms. However, the evidence may not be strong because most of the studies included in this meta-analysis have poor methodological quality.

Triglyceride, nonesterified fatty acids, and prediabetic neuropathy: role for oxidative-nitrosative stress

Peripheral neuropathy develops in human subjects with prediabetes and metabolic syndrome before overt hyperglycemia. The contributions of impaired glucose tolerance and insulin signaling, hypertriglyceridemia and/or increased nonesterified fatty acids (NEFA), and hypercholesterolemia to this condition remain unknown. Niacin and its derivatives alleviate dyslipidemia with a minor effect on glucose homeostasis. This study evaluated the roles of impaired glucose tolerance versus dyslipidemia in prediabetic neuropathy using Zucker fatty (fa/fa) rats and the niacin derivative acipimox, as well as the interplay of hypertriglyceridemia, increased NEFA, and oxidative-nitrosative stress. Sixteen-week-old Zucker fatty rats with impaired glucose tolerance, obesity, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia, and increased NEFA displayed sensory nerve conduction velocity deficit, thermal and mechanical hypoalgesia, and tactile allodynia. Acipimox (100 mg kg(-1) day(-1), 4 weeks) reduced serum insulin, NEFA, and triglyceride concentrations without affecting glucose tolerance and hypercholesterolemia. It alleviated sensory nerve conduction velocity deficit and changes in behavioral measures of sensory function and corrected oxidative-nitrosative stress, but not impaired insulin signaling, in peripheral nerve. Elevated NEFA increased total and mitochondrial superoxide production and NAD(P)H oxidase activity in cultured human Schwann cells. In conclusion, hypertriglyceridemia and/or increased NEFA concentrations cause prediabetic neuropathy through oxidative-nitrosative stress. Lipid-lowering agents and antioxidants may find a use in the management of this condition.

Evaluation of the antioxidative capability of commonly used antioxidants in dermocosmetics by in vivo detection of protein carbonylation in human stratum corneum

We present an in vivo test platform to evaluate the antioxidative capability of seven frequently used dermocosmetic antioxidants on the human stratum corneum (SC). It has been reported that the protein carbonylation could be used as a biomarker for oxidative stress. The current study detects the change of the level of exposed protein carbonyl group in the most outer layer of human SC. The concentration of the antioxidant in each subject emulsion formulation was 0.5% (w/w). The data indicated that alpha-tocopherol (α-Vit E) and ascorbic acid (Vit C) have excellent antioxidative capability and α-Vit E-acetate possesses better than the average antioxidative capability. The bioconversion of α-Vit E-acetate to α-Vit E may occur in the human SC during a less than 2 weeks time course test. Lipoic acid possessed moderate antioxidative capability. Ascorbyl 6-palmitate had a low antioxidative capability. Ascorbic acid 2-glucoside represented an insignificant antioxidative capability. Glutathion (GSH) had no effect on reducing oxidative damage to human SC proteins, implying that the GSH recycling system could be absent in human SC. This test platform is an useful tool to evaluate the antioxidative efficiency of antioxidants on human SC proteins.

Neuroprotective and anti-oxidative effects of the hemodialysate actovegin on primary rat neurons in vitro

The recently described therapeutic benefits of the hemodialysate actovegin on neuropathic symptoms in diabetic patients with symptomatic polyneuropathy suggest a neuroprotective activity of the drug. To elucidate the possible cellular mechanism of the pharmacological effects of actovegin, we investigated its effects on cultured primary rat neurons in vitro. Primary neurons were cultured for up to 10 days in the presence of increasing doses of actovegin (0.3–1,000 mg/l). Total cell number, dendrite length and the number of excitatory synapses, i.e., the amount of the synaptic V-Glut1 protein, were measured by immunocytochemistry followed by fluorescence microscopy. The apoptotic level in neurons after induction of apoptosis by amyloid peptide Aβ_25–35 was assessed by the level of activated caspase-3. In addition, the capability of the neurons to diminish oxidative stress was assessed by measuring the cellular level of reactive oxygen species ROS in the presence of actovegin. Actovegin treatment yielded an increased maintenance of neuronal cells and total number of synapses and could lower the level of activated caspase-3 in a dose-dependent manner. Dendrite lengths were not significantly affected. In addition, actovegin reduced the cellular level of ROS in cultured neurons. The cellular effects observed suggest neuroprotective and anti-oxidative effects of the drug Actovegin^®, which could at least partially explain its therapeutic benefits.

Chronic treatment of silymarin improves hyperalgesia and motor nerve conduction velocity in diabetic neuropathic rat

The effect of chronic silymarin (SM) treatment on hyperalgesia, sciatic motor nerve conduction velocity (MNCV) and oxidative stress in streptozotocin (STZ)-diabetic neuropathic rat was evaluated. Rats were divided into control, diabetic, SM-treated control and diabetic, and sodium salisylate (SS)-treated control and diabetic. SM was administered daily at a dose of 100 mg/kg for two months. Finally, hyperalgesia and sciatic MNCV and oxidative stress markers were assessed. Diabetic rats showed a significant deficit in MNCV and markedly exhibited chemical and thermal hyperalgesia, indicating development of diabetic neuropathy. Antioxidant enzyme superoxide dismutase (SOD) level significantly reduced and malondialdehyde (MDA) level significantly increased in diabetic rats compared to control rats; SM treatment significantly ameliorated the alteration in MNCV, hyperalgesia, MDA level and antioxidant enzyme SOD in diabetic rats. These results clearly suggest the potential effect of SM in prevention and treatment of diabetic neuropathy.

Anti-apoptotic and neuroprotective effects of α-lipoic acid on spinal cord ischemia-reperfusion injury in rabbits

PURPOSE

Radical oxygen species produced after injury counteracts antioxidant activity and frequently causes severe oxidative stress for the tissues. Alpha-lipoic acid is a powerful metabolic antioxidant with immunomodulatory effects which provides neuroprotection. The aim of this study is to investigate the neuroprotective and anti-apoptotic effects of alpha-lipoic acid on spinal cord ischemia-reperfusion.

METHODS

Twenty-four adult, male, New Zealand rabbits were divided into sham (n = 8), control (n = 8), and treatment groups (n = 8). The abdominal aorta was clamped for 30 min by an aneurysm clip, approximately 1 cm below the renal artery and 1 cm above the iliac bifurcation in control and treatment groups. Only laparotomy was performed in the sham group. Twenty-five cubic centimeters of saline in control group and 100 mg/kg lipoic acid were administered intraperitoneally in the treatment group after closure of the incision. The animals were killed 48 h later. Spinal cord segments between L2 and S1 were harvested for analysis. Levels of nitric oxide, glutathione, malondialdehyde, advanced oxidation protein products, and superoxide dismutase were analyzed as markers of oxidative stress and inflammation. Caspase-3 activity was analyzed to detect the effect of lipoic acid on apoptosis.

RESULTS

In all measured parameters of oxidative stress, administration of lipoic acid significantly demonstrated favorable effects. Both plasma and tissue levels of nitric oxide, glutathione, malondialdehyde, and advanced oxidation protein products significantly changed in favor of antioxidant activity. There was no significant difference between the plasma superoxide dismutase levels of the groups. Histopathological evaluation of the tissues also demonstrated significant decrease in cellular degeneration and infiltration parameters after lipoic acid administration. However, lipoic acid has no effect on caspase-3 activity.

CONCLUSIONS

Although further studies considering different dose regimens and time intervals are required, the results of the present study prove that alpha-lipoic acid has favorable effects on experimental spinal cord ischemia-reperfusion injury.

The Association between Serum GGT Concentration and Diabetic Peripheral Polyneuropathy in Type 2 Diabetic Patients

BACKGROUND

Diabetic peripheral polyneuropathy (DPP) is one of the common complications of diabetes mellitus (DM) and can lead to foot ulcers or amputation. The pathophysiology of DPP includes several factors such as metabolic, vascular, autoimmune, oxidative stress and neurohormonal growth-factor deficiency and recent studies have suggested the use of serum gamma-glutamyl transferase (GGT) as an early marker of oxidative stress. Therefore, we investigated whether serum GGT may be useful in predicting DPP.

METHODS

We assessed 90 patients with type 2 DM who were evaluated for the presence of DPP using clnical neurologic examinations including nerve conduction velocity studies. We evaluated the association between serum GGT and the presence of DPP.

RESULTS

The prevalence of DPP was 40% (36 cases) according to clinical neurological examinations. The serum GGT concentration was significantly elevated in type 2 diabetic patients with DPP compared to patients without DPP (P < 0.01). There were other factors significantly associated with DPP including smoking (P = 0.019), retinopathy (P = 0.014), blood pressure (P < 0.05), aspartate aminotransferase (P = 0.022), C-reactive protein (P = 0.036) and urine microalbumin/creatinine ratio (P = 0.004). Serum GGT was independently related with DPP according to multiple logistic analysis (P < 0.01).

CONCLUSION

This study shows that increased levels of serum GGT may have important clinical implications in the presence of DPP in patients with type 2 diabetes.

Fluvastatin attenuates diabetes-induced cardiac sympathetic neuropathy in association with a decrease in oxidative stress

BACKGROUND

Increased oxidative stress might contribute to diabetic (DM) neuropathy, so the effects of long-term treatment with fluvastatin (FL) on myocardial oxidative stress and cardiac sympathetic neural function were investigated in diabetic rats.

METHODS AND RESULTS

FL (10 mg . kg(-1) . day(-1), DM-FL) or vehicle (DM-VE) was orally administered for 2 weeks to streptozotocin-induced DM rats. Cardiac oxidative stress was determined by myocardial 8-iso-prostaglandin F(2alpha) (PGF(2alpha)) and NADPH oxidase subunit p22(phox) mRNA expression. Sympathetic neural function was quantified by autoradiography using (131)I- and (125)I-metaiodobenzylguanidine (MIBG). FL did not affect plasma glucose levels but remarkably decreased PGF(2alpha) levels compared with DM-VE rats (13.8+/-9.2 vs 175.0+/-93.9 ng/g tissue), although PGF(2alpha) levels were below the detection limit in non-DM rats. FL significantly reduced myocardial p22(phox) mRNA expression. Cardiac (131)I-MIBG uptake was lower in DM-VE rats than in non-DM rats, but the decrease was attenuated in DM-FL rats (1.31+/-0.08, 1.88+/-0.22, and 1.58+/-0.18 %kg dose/g, respectively, P<0.01). Cardiac MIBG clearance was not affected by the induction of DM or by FL, indicating that the reduced MIBG uptake in DM rats might result from impaired neural function.

CONCLUSIONS

FL ameliorates cardiac sympathetic neural dysfunction in DM rats in association with attenuation of increased myocardial oxidative stress.

Effects of alpha-lipoic acid on cell proliferation and apoptosis in MDA-MB-231 human breast cells

The role that antioxidants play in the process of carcinogenesis has recently gained considerable attention. α-Lipoic acid, a naturally occurring disulfide molecule, is a powerful antioxidant that reportedly exerts beneficial effects in patients with advanced cancer by reducing the level of reactive oxygen species and increasing glutathione peroxidase activity. In this study, we examined changes in the protein and mRNA expression associated with cell proliferation and apoptosis in MDA-MB-231 breast cancer cultured in the presence of various concentrations (0, 250, 500, and 1000 µmol/L) of α-lipoic acid. The results revealed that α-lipoic acid inhibited the growth of breast cancer cells in a dose-independent manner (P < 0.05). Additionally, ErbB₂ and ErbB₃ protein and mRNA expressions were significantly decreased in a dose-dependent manner in response to α-lipoic acid (P < 0.05). Furthermore, the protein expression of phosphorylated Akt (p-Akt) levels and total Akt, and the mRNA expression of Akt were decreased dose-dependently in cells that were treated with α-lipoic acid (P < 0.05). Bcl-2 protein and mRNA expressions were also decreased in cells that were treated with α-lipoic acid (P < 0.05). However, Bax protein and mRNA expressions were increased in cells treated with α-lipoic acid (P < 0.05). Finally, caspase-3 activity was significantly increased in a dose-dependent manner in cells treated with α-lipoic acid (P < 0.05). In conclusion, we demonstrated that α-lipoic acid inhibits cell proliferation and induces apoptosis in MDA-MB-231 breast cancer cell lines.

Alpha-lipoic Acid and diabetic neuropathy

Diabetic neuropathy presents a major public health problem. It is defined by the symptoms and signs of peripheral nerve dysfunction in diabetic patients, in whom other causes of neuropathy have been excluded. Pathogenetic mechanisms that have been implicated in diabetic neuropathy are: a) increased flux through the polyol pathway, leading to accumulation of sorbitol, a reduction in myo-inositol, and an associated reduced Na+-K+-ATPase activity, and b) endoneurial microvascular damage and hypoxia due to nitric oxide inactivation by increased oxygen free radical activity. Alpha-lipoic acid seems to delay or reverse peripheral diabetic neuropathy through its multiple antioxidant properties. Treatment with alpha-lipoic acid increases reduced glutathione, an important endogenous antioxidant. In clinical trials, 600 mg alpha-lipoic acid has been shown to improve neuropathic deficits. This review focuses on the relationship of alpha-lipoic acid and auto-oxidative glycosylation. It discusses the impact of alpha-lipoic acid on hyperglycemia-induced oxidative stress, and examines the role of alpha-lipoic acid in preventing glycation process and nerve hypoxia.

The use of alpha-lipoic acid (ALA), gamma linolenic acid (GLA) and rehabilitation in the treatment of back pain: effect on health-related quality of life

The aim of this trial was to evaluate the effects of alpha-lipoic acid (ALA) and gamma-linolenic acid (GLA) and the beneficial effect of physical exercise on positive sensory symptoms and neuropathic pain in patients with compressive radiculopathy syndrome from disc-nerve root conflict. Often these painful syndromes after the acute event, tend to recurr becoming subacute or chronic syndromes that become for the period of interest disabiling is an event very important in these cases proper prevention, based on a maintenance drug therapy and the strengthening exercises of paravertebral muscles, flexibility exercises on the spine and when needed on the reduction of body weight. In this Observational Cohort, two-arm trial, 203 patients were enrolled and divided into two groups, the first, ALA and GLA group, (n = 101) received oral dose of 600 mg of alpha-lipoic acid (ALA) and 360 mg of gamma-linolenic acid (GLA) and a rehabilitation program for six weeks, the second (n = 102) treated with only rehabilitation program. Patients were recruited at the centre of Physical Medicine and Rehabilitation, they underwent a physiatric examination at the primary outcome (t0) and secondary outcomes were recorded at monitoring visits scheduled at two weeks = t1, four weeks = t2, six weeks = t3, and at the same has been administered the following scale: VAS scale, SF-36, Oswestry Low Back Pain Disability Questionnaire, Aberdeen Back Pain Scale (ABPS), Revised Leeds Disability Questionnaire (LDQ), Roland and Morris Disability Questionnaire. Significant improvements was noted in the ALA and GLA group for paresthesia, stabbing and burning pain, as showed by VAS (Visual Analogue Scale), Oswestry Low Back Pain Disability Questionnaire, Aberdeen Low Back Pain Scale; also, improvements of quality of life has been noted, in the same group, as showed by SF-36, LDQ (Revised Leeds Disability Questionnaire), Roland and Morris disability questionnaire. All these outcome measure showed statistically significant decreases. Oral treatment with alpha-lipoic acid (ALA) and gamma-linolenic acid (GLA) for six weeks in synergy with rehabilitation therapy improved neuropathic symptoms and deficits in patients with radicular neuropathy.

Elevated lipid peroxidation and DNA oxidation in nerve from diabetic rats: effects of aldose reductase inhibition, insulin, and neurotrophic factors

We investigated the effect of treatment with an aldose reductase inhibitor, insulin, or select neurotrophic factors on the generation of oxidative damage in peripheral nerve. Rats were either treated with streptozotocin to induce insulin-deficient diabetes or fed with a diet containing 40% d-galactose to promote hexose metabolism by aldose reductase. Initial time course studies showed that lipid peroxidation and DNA oxidation were significantly elevated in sciatic nerve after 1 week or 2 weeks of streptozotocin-induced diabetes, respectively, and that both remained elevated after 12 weeks of diabetes. The increase in nerve lipid peroxidation was completely prevented or reversed by treatment with the aldose reductase inhibitor, ICI 222155, or by insulin, but not by the neurotrophic factors, prosaptide TX14(A) or neurotrophin-3. The increase in nerve DNA oxidation was significantly prevented by insulin treatment. In contrast, up to 16 weeks of galactose feeding did not alter nerve lipid peroxidation or protein oxidation, despite evidence of ongoing nerve conduction deficits. These observations demonstrate that nerve oxidative damage develops early after the onset of insulin-deficient diabetes and that it is not induced by increased hexose metabolism by aldose reductase per se, but rather is a downstream consequence of flux through this enzyme. Furthermore, the beneficial effect of prosaptide TX14(A) and neurotrophin-3 on nerve function and structure in diabetic rats is not due to amelioration of increased lipid peroxidation.

Protective effects of 4-amino1,8-napthalimide, a poly (ADP-ribose) polymerase inhibitor in experimental diabetic neuropathy

Peripheral diabetic neuropathy is a heterogeneous group of disorders, and is known to affect 50-60% of diabetic patients. Poly (ADP-ribose) polymerase (PARP) activation has been identified as one of the key components in the pathogenesis of diabetic neuropathy. In the present study we have targeted PARP overactivation in diabetic neuropathy using a known PARP inhibitor, 4 amino 1, 8-napthalimide (4-ANI). Streptozotocin induced diabetic rats developed neuropathy within 6 weeks, which was evident from significant reduction in motor nerve conduction velocity (MNCV), nerve blood flow (NBF) along with neuropathic pain and abnormal sensory perception. Six weeks after diabetes induction Sprague Dawley rats were treated with 4-ANI (3 and 10 mg/kg, p.o.) for a period of two weeks (seventh and eighth weeks). Two week treatment with 4-ANI showed improvement in nerve conduction, nerve blood flow and reduction in tail flick responses and mechanical allodynia in diabetic animals. 4-ANI also attenuated PAR immunoreactivity and NAD depletion in nerves of diabetic animals. Results of present study suggest the potential of PARP inhibitors like 4-ANI in the treatment of diabetic neuropathy.

Effects of Nigella sativa and its major constituent, thymoquinone on sciatic nerves in experimental diabetic neuropathy

The aim of this study was designed to investigate the possible beneficial effects of Nigella sativa (NS) and thymoquinone (TQ) on histopathological changes of sciatic nerves in streptozotocin-induced diabetic rats. The rats were randomly allotted into one of four experimental groups: A (control), B (diabetic untreated), C (diabetic treated with NS) and D (diabetic treated with TQ); each group contain ten animals. B, C and D groups received streptozotocin (STZ) to induce diabetes. The rats in NS and TQ treated groups were given NS (in a dose of 400 mg/kg body weight) and TQ (50 mg/kg body weight) once a day orally by using intra-gastric intubation for 12 weeks starting 2 days after STZ injection, respectively. Blood and tissue samples were obtained for biochemical and histopathological investigation. The treatment of both NS and TQ caused a sharp decrease in the elevated serum glucose (P < 0.01, 0.05, respectively), and an increase in the lowered serum insulin concentrations (P < 0.01, 0.05, respectively), in STZ-induced diabetic rats. STZ induced a significant decrease in the area of insulin immunoreactive beta-cells (P < 0.0001). NS (P < 0.001) and TQ (P < 0.01) treatment resulted in increased area of insulin immunoreactive beta-cells significantly. To date, no histopathological changes of sciatic nerves in STZ induced diabetic rats by NS and TQ treatment have been reported. In this study, histologic evaluation of the tissues in diabetic animals treated with TQ and especially NS showed fewer morphologic alterations. Myelin breakdown decreased significantly after treatment with NS and TQ. The ultrastructural features of axons also showed remarkable improvement. We believe that further preclinical research into the utility of NS and TQ may indicate its usefulness as a potential treatment on peripheral neuropathy (PN) in STZ induced diabetic rats.

SOD2 protects neurons from injury in cell culture and animal models of diabetic neuropathy

Hyperglycemia-induced oxidative stress is an inciting event in the development of diabetic complications including diabetic neuropathy. Our observations of significant oxidative stress and morphological abnormalities in mitochondria led us to examine manganese superoxide dismutase (SOD2), the enzyme responsible for mitochondrial detoxification of oxygen radicals. We demonstrate that overexpression of SOD2 decreases superoxide (O(2)(-)) in cultured primary dorsal root ganglion (DRG) neurons and subsequently blocks caspase-3 activation and cellular injury. Underexpression of SOD2 in dissociated DRG cultures from adult SOD2(+/-) mice results in increased levels of O2-, activation of caspase-3 cleavage and decreased neurite outgrowth under basal conditions that are exacerbated by hyperglycemia. These profound changes in sensory neurons led us to explore the effects of decreased SOD2 on the development of diabetic neuropathy (DN) in mice. DN was assessed in SOD2(+/-) C57BL/6J mice and their SOD2(+/+) littermates following streptozotocin (STZ) treatment. These animals, while hyperglycemic, do not display any signs of DN. DN was observed in the C57BL/6Jdb/db mouse, and decreased expression of SOD2 in these animals increased DN. Our data suggest that SOD2 activity is an important cellular modifier of neuronal oxidative defense against hyperglycemic injury.

Inhibition of PKC β by Ruboxistaurin Does Not Enhance the Acute Blood Pressure Response to Nitroglycerin

Ruboxistaurin is a selective protein kinase C beta inhibitor undergoing clinical investigation for treatment of diabetic microvascular complications. This study assessed a possible blood pressure (BP) interaction between ruboxistaurin and the exogenous nitric oxide donor, glyceryl trinitrate (GTN). Subjects (N=22) with chronic stable angina received placebo or ruboxistaurin 96 mg/day orally to steady state in a crossover design. Graded GTN (0, 5, 10, 20, 40, 80, and 120 microg/min) or 5% dextrose solution was then infused intravenously and BP was measured following each dose. Ruboxistaurin did not alter the slope of change in standing systolic BP (DeltasSBP/1n[GTN dose]) curve (P=0.272 analysis of covariance) or affect the DeltasSBP at the estimated GTN dose producing a 10-mm Hg reduction in sSBP from baseline on placebo (mean difference -0.9 mm Hg; 95% confidence of interval, -3.3-1.5). In conclusion, ruboxistaurin does not potentiate the acute BP-lowering effects of GTN.

Efficacy of alpha-lipoic acid against diabetic cataract in rat

PURPOSE

alpha-Lipoic acid (LA) is well known as a powerful antioxidant. The efficacy of dihydrolipoate-LA for oral administration against streptozotocin (STZ)-induced diabetic cataract in rat was investigated.

METHODS

Rats were divided into three groups, control, diabetes mellitus (DM), and DM treated with LA (DM+LA). Diabetes was induced by intravenous injection of 50 mg/kg STZ. DM+LA rats were fed 30 mg/rat per day LA in their diet. Lens changes were assessed using Scheimpflug images (EAS-1000) and by measuring light-scattering intensity.

RESULTS

Increase in lens light scattering was less (P < 0.05) in DM+LA rats than in DM rats 5 weeks after induction of diabetes. DM rats had the highest and control rats the lowest blood glucose levels at every measurement point up to 111 days (P < 0.05).

CONCLUSION

LA treatment delayed development and progression of cataract in rats with streptozotocin-induced diabetes.

Effects of trolox on nerve dysfunction, thermal hyperalgesia and oxidative stress in experimental diabetic neuropathy

1. Diabetic neuropathy is one of the most common complications of diabetes and oxidative stress has been implicated to play a major role in its pathophysiology. 2. In the present study, we targeted oxidative stress using trolox, an anti-oxidant, in streptozotocin-induced diabetic neuropathy in rats. 3. Compared with control rats, diabetic rats showed significant deficits in motor nerve conduction velocity (MNCV; 49.91 +/- 1.94 vs 42.77 +/- 1.39 m/s, respectively) and nerve blood flow (NBF; 107.98 +/- 8.22 vs 38.9 +/- 2.7 arbitarary perfusion units, respectively) after 8 weeks of diabetes. Tail flick latencies for cold and hot immersion tests were also significantly reduced in diabetic rats, indicating thermal hyperalgesia. These observations indicate development of diabetic neuropathy. 4. A significant decrease in the activity of anti-oxidant enzymes (superoxide dismutase and catalase) and an increase in lipid peroxidation were observed in sciatic nerves from diabetic rats compared with age-matched control rats. Alterations in the activity of anti-oxidant enzymes and lipid peroxidation in diabetic rats indicate oxidative stress in diabetic neuropathy. 5. Two weeks treatment with trolox (10 and 30 mg/kg, i.p.) started on completion of the 6th week of diabetes significantly improved MNCV, NBF and inhibited thermal hyperalgesia. Trolox treatment also improved the activity of anti-oxidant enzymes and inhibited lipid peroxidation in sciatic nerves of diabetic rats. 6. The results of the present study suggest the beneficial effects of trolox in experimental diabetic neuropathy.

At low doses, a gamma-linolenic acid-lipoic acid conjugate is more effective than docosahexaenoic acid-enriched phospholipids in preventing neuropathy in diabetic rats

A deficiency in essential fatty acid metabolism has been reported in diabetes. Nutritional supplementations with (n-6) or (n-3) PUFA have differential efficiency on parameters of diabetic neuropathy, including nerve conduction velocity (NCV) and nerve blood flow (NBF). The aim of this study was to compare the neuroprotective effects of gamma-linolenic acid (GLA)-lipoic acid (LA) conjugate (GLA-LA) and docosahexaenoic acid (DHA)-enriched phospholipids (PL) supplementations on NCV and NBF. Streptozotocin-induced diabetic (D) and control (C) rats were supplemented for 8 wk with either DHA-enriched PL at a dose of 30 mg.kg-1.d-1 (DDHA and CDHA) or with corn oil enriched with GLA-LA at a dose of 30 mg.kg-1.d-1 (DGLA and CGLA). Moreover, a C and D group received no supplementation. After 8 wk, NCV (-30%) and NBF (-50%) were lower in the D group than in the C group. Supplementation with GLA-LA totally prevented the decrease in NCV and NBF in the DGLA group, in which values did not differ from group C. Supplementation with DHA only partially prevented the decrease in NCV in the DDHA group, in which value was different from groups C and D and did not affect NBF. We conclude that at the low doses used, supplementation with GLA-LA is more effective than supplementation with DHA in preventing experimental diabetic neuropathy. The difference could be due in part to an antioxidant protective effect of LA on GLA.

Treatment with the xanthine oxidase inhibitor, allopurinol, improves nerve and vascular function in diabetic rats

Several putative sources of reactive oxygen species could potentially contribute to diabetic neuropathy and vasculopathy. The aim was to assess the involvement of elevated xanthine oxidase activity. After 6 weeks of streptozotocin-diabetes, groups of rats were given 2 weeks of high-dose allopurinol treatment (50 and 250 mg/kg) to gauge the effect of maximal blockade of xanthine oxidase. In the final experiments, rats were subjected to sensory testing and, under butabarbital anaesthesia, measurements were made on nerve conduction velocities and neural tissue blood flow estimated by hydrogen clearance microelectrode polarography. Further groups were used to study detailed responses of the isolated mesenteric vascular bed after 4 weeks of diabetes and allopurinol (150 mg/kg) treatment. Diabetes caused 20% and 14% reduction in motor and sensory conduction velocity, which were 78% and 81% corrected by allopurinol treatment respectively, both doses giving similar results. Diabetic rats showed tactile allodynia and thermal hyperalgesia, which were completely corrected by allopurinol, whereas mechanical hyperalgesia was only 45% ameliorated. Sciatic nerve and superior cervical ganglion blood flow was halved by diabetes and allopurinol corrected this by approximately 63%. Mesenteric endothelium-dependent vascular responses to acetylcholine, which depend upon nitric oxide and endothelium derived hyperpolarizing factor, were attenuated by diabetes. Allopurinol treatment gave approximately 50% protection for both components. Thus, xanthine oxidase is an important source of reactive oxygen species that contributes to neurovascular dysfunction in experimental diabetes. Inhibition of xanthine oxidase could be a potential therapeutic approach to diabetic neuropathy and vasculopathy.

Oral treatment with alpha-lipoic acid improves symptomatic diabetic polyneuropathy: the SYDNEY 2 trial

OBJECTIVE

The aim of this trial was to evaluate the effects of alpha-lipoic acid (ALA) on positive sensory symptoms and neuropathic deficits in diabetic patients with distal symmetric polyneuropathy (DSP).

RESEARCH DESIGN AND METHODS

In this multicenter, randomized, double-blind, placebo-controlled trial, 181 diabetic patients in Russia and Israel received once-daily oral doses of 600 mg (n = 45) (ALA600), 1,200 mg (n = 47) (ALA1200), and 1,800 mg (ALA1800) of ALA (n = 46) or placebo (n = 43) for 5 weeks after a 1-week placebo run-in period. The primary outcome measure was the change from baseline of the Total Symptom Score (TSS), including stabbing pain, burning pain, paresthesia, and asleep numbness of the feet. Secondary end points included individual symptoms of TSS, Neuropathy Symptoms and Change (NSC) score, Neuropathy Impairment Score (NIS), and patients' global assessment of efficacy.

RESULTS

Mean TSS did not differ significantly at baseline among the treatment groups and on average decreased by 4.9 points (51%) in ALA600, 4.5 (48%) in ALA1200, and 4.7 (52%) in ALA1800 compared with 2.9 points (32%) in the placebo group (all P < 0.05 vs. placebo). The corresponding response rates (>/=50% reduction in TSS) were 62, 50, 56, and 26%, respectively. Significant improvements favoring all three ALA groups were also noted for stabbing and burning pain, the NSC score, and the patients' global assessment of efficacy. The NIS was numerically reduced. Safety analysis showed a dose-dependent increase in nausea, vomiting, and vertigo.

CONCLUSIONS

Oral treatment with ALA for 5 weeks improved neuropathic symptoms and deficits in patients with DSP. An oral dose of 600 mg once daily appears to provide the optimum risk-to-benefit ratio.

Diabetic neuropathy and oxidative stress

This review will focus on the impact of hyperglycemia-induced oxidative stress in the development of diabetes-related neural dysfunction. Oxidative stress occurs when the balance between the production of reactive oxygen species (ROS) and the ability of cells or tissues to detoxify the free radicals produced during metabolic activity is tilted in the favor of the former. Although hyperglycemia plays a key role in inducing oxidative stress in the diabetic nerve, the contribution of other factors, such as endoneurial hypoxia, transition metal imbalances, and hyperlipidemia have been also suggested. The possible sources for the overproduction of ROS in diabetes are widespread and include enzymatic pathways, auto-oxidation of glucose, and mitochondrial superoxide production. Increase in oxidative stress has clearly been shown to contribute to the pathology of neural and vascular dysfunction in diabetes. Potential therapies for preventing increased oxidative stress in diabetic nerve dysfunction will be discussed.

High glucose-induced activation of the polyol pathway and changes of gene expression profiles in immortalized adult mouse Schwann cells IMS32

We investigated the polyol pathway activity and the gene expression profiles in immortalized adult mouse Schwann cells (IMS32) under normal (5.6 mM) and high (30 and 56 mM) glucose conditions for 7-14 days in culture. Messenger RNA and the protein expression of aldose reductase (AR) and the intracellular sorbitol and fructose contents were up-regulated in IMS32 under high glucose conditions compared with normal glucose conditions. By employing DNA microarray and subsequent RT-PCR/northern blot analyses, we observed significant up-regulation of the mRNA expressions for serum amyloid A3 (SAA3), angiopoietin-like 4 (ANGPTL4) and ecotropic viral integration site 3 (Evi3), and the down-regulation of aldehyde reductase (AKR1A4) mRNA expression in the cells under high glucose (30 mM) conditions. The application of an AR inhibitor, SNK-860, to the high glucose medium ameliorated the increased sorbitol and fructose contents and the reduced AKR1A4 mRNA expression, while it had no effect on mRNA expressions for SAA3, ANGPTL4 or Evi3. Considering that the exposure to the high glucose (>or= 30 mM) conditions mimicking hyperglycaemia in vivo accelerated the polyol pathway in IMS32, but not in other previously reported Schwann cells, the culture system of IMS32 under those conditions may provide novel findings about the polyol pathway-related abnormalities in diabetic neuropathy.

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.

Potential risk factors for diabetic neuropathy: a case control study

Background

Diabetes mellitus type II afflicts at least 2 million people in Iran. Neuropathy is one of the most common complications of diabetes and lowers the patient's quality of life. Since neuropathy often leads to ulceration and amputation, we have tried to elucidate the factors that can affect its progression.

Methods

In this case-control study, 110 diabetic patients were selected from the Shariati Hospital diabetes clinic. Michigan Neuropathic Diabetic Scoring (MNDS) was used to differentiate cases from controls. The diagnosis of neuropathy was confirmed by nerve conduction studies (nerve conduction velocity and electromyography). The multiple factors compared between the two groups included consumption of angiotensin converting enzyme inhibitors (ACEI), blood pressure, serum lipid level, sex, smoking, method of diabetes control and its quality.

Results

Statistically significant relationships were found between neuropathy and age, gender, quality of diabetes control and duration of disease (P values in the order: 0.04, 0.04, < 0.001 and 0.005). No correlation was found with any atherosclerosis risk factor (high BP, hyperlipidemia, cigarette smoking).

Conclusion

In this study, hyperglycemia was the only modifiable risk factor for diabetic neuropathy. Glycemic control reduces the incidence of neuropathy, slows its progression and improves the diabetic patient's quality of life. More attention must be paid to elderly male diabetic patients with poor diabetes control with regard to regular foot examinations and more practical education.

The protein kinase C-β inhibitor, ruboxistaurin, for the treatment of diabetic microvascular complications

The potential for addressing the underlying biological abnormalities in diabetes has eluded most investigators because of the complex mechanisms underlying the effects of diabetes on the pathogenesis of the complications. Although macrovascular complications, such as myocardial infarction, stroke and gangrene, are only partially attributable to hyperglycaemia and its attendant effects, the microvascular complications including retinopathy, nephropathy and neuropathy are directly related to the degree of hyperglycaemia. In controlled trials, a 22-34% reduction in one of these side effects was achieved for every 1% reduction in glycosylated haemoglobin. Theoretically, it should be feasible to eliminate these complications in a perfect world. However, achieving euglycaemia is nearly impossible and there is increasing data to suggest that it may be an elusive target with ever lower levels being implicated in the pathogenesis of microvascular disease and there is a price to be paid of hypoglycaemia if further intensification is pursued. A logical argument would be to block pathways that are activated by hyperglycaemia. A major pathway implicated is the activation of protein kinase C-beta in all of the targeted tissues, and there is animal data to support the notion that blocking this pathway can reverse or abrogate the untoward effects of diabetes. The possible role of the protein kinase C-beta inhibitor, ruboxistaurin, in animal studies and the recently reported clinical studies to place in perspective a possible addition to the therapeutic armamentarium of the imperfect world of diabetes control will be reviewed.

Peripheral nerve dysfunction in experimental diabetes is mediated by cyclooxygenase-2 and oxidative stress

Glucose-mediated oxidative stress and alterations in cyclooxygenase (COX) pathway activity with secondary deficits of endoneurial perfusion have been implicated in the pathogenesis of experimental diabetic neuropathy (EDN). We have previously reported that activation of the COX-2 pathway is an important mediator of neurochemical and neurovascular defects in EDN in a rat model. Considering that chemical COX inhibition may exert other pharmacological effects in addition to inhibition of COX activity, the aim of this study was to explore the role of COX-2 in experimental diabetic neuropathy, using a COX-2 knockout mouse model. Here we provide evidence that COX-2 inactivation had a protective effect against diabetes-induced motor and sensory nerve conduction slowing and impaired nerve antioxidative defense that were clearly manifest in the wild-type (COX-2(+/+)) diabetic mice. These preliminary data support the role of the activation of the COX-2 pathway in mediating sensory and motor nerve conduction velocity deficits in EDN. These findings also suggest that the COX-2 pathway seems to be an important modulator of oxidative stress in EDN.

Cell culture modeling to test therapies against hyperglycemia-mediated oxidative stress and injury

The concept that oxidative stress is a key mediator of nerve injury in diabetes has led us to design therapies that target oxidative stress mechanisms. Using an in vitro model of glucose-treated dorsal root ganglion (DRG) neurons in culture, we can examine both free radical generation, using fluorimetric probes for reactive oxygen species, and cell death via the TUNEL assay. The cell culture system is scaled down to a 96-well plate format, and so is well suited to high-throughput screening. In the present study, we test the ability of three drugs, nicotinamide, allopurinol, and alpha-lipoic acid, alone and in combination to prevent DRG neuron oxidative stress and cell death. This combination of drugs is currently in clinical trial in type 1 diabetic patients. We demonstrate independent effects on oxidative stress and neuronal survival for the three drugs, and neuronal protection using the three drugs in combination. The data strengthen the rationale for the current clinical trial. In addition, we describe an effective tool for rapid preclinical testing of novel therapies against diabetic neuropathy.

Endogenous production of lipoic acid is essential for mouse development

alpha-Lipoic acid (LA) is a cofactor for mitochondrial alpha-ketoacid dehydrogenase complexes and is one of the most potent, natural antioxidants. Reduction of oxidative stress by LA supplementation has been demonstrated in patients with diabetic neuropathy and in animal models. To determine how normal development or pathological conditions are affected by genetic alterations in the ability of mammalian cells to synthesize LA and whether dietary LA can circumvent its endogenous absence, we have generated mice deficient in lipoic acid synthase (Lias). Mice heterozygous for disruption of the Lias gene develop normally, and their plasma levels of thiobarbituric acid-reactive substances do not differ from those of wild-type mice. However, the heterozygotes have significantly reduced erythrocyte glutathione levels, indicating that their endogenous antioxidant capacity is lower than those of wild-type mice. Homozygous embryos lacking Lias appear healthy at the blastocyst stage, but their development is retarded globally by 7.5 days postcoitum (dpc), and all the null embryos die before 9.5 dpc. Supplementing the diet of heterozygous mothers with LA (1.65 g/kg of body weight) during pregnancy fails to prevent the prenatal deaths of homozygous embryos. Thus, endogenous LA synthesis is essential for developmental survival and cannot be replaced by LA in maternal tissues and blood.

The diabetic neuropathies

BACKGROUND

Diabetes remains the most common cause of neuropathy in the United States and is a significant source of morbidity and mortality, accounting for substantial suffering and billions of dollars in health care expenditures each year.

REVIEW SUMMARY

Our insight into the pathophysiology of the diabetic neuropathies has increased considerably over the last decade. aided by advances in the basic science of diabetes itself. A wide variety of potential mechanisms for nerve injury in diabetes has been identified, including the polyol pathway of glucose metabolism, oxidative nerve injury, the deposition of advanced glycosylation end products within the nerve and the effects of vascular insufficiency, among others. Diabetic neuropathy may take a variety of clinical forms beyond the well-known distal symmetric neuropathy, many of which are often misdiagnosed or overlooked entirely, sometimes with serious consequences for the patient. Proper therapy after diagnosis is also critical and may include not only primary management, but also treatment of painful diabetic neuropathy through an expanding repertoire of increasingly effective pharmacologic agents. Though primary treatment trials have not yet provided effective therapies, ongoing and future trials offer continuing promise.

CONCLUSIONS

The diabetic neuropathies are exceedingly common, but often improperly diagnosed and incompletely treated. A proper understanding of the mechanisms underlying these diseases and the clinical recognition of their various forms is highly important as appropriate primary and symptomatic management can substantially reduce the morbidity and mortality associated with these disorders.

M40403 prevents myocardial injury induced by acute hyperglycaemia in perfused rat heart

M40403 is a low-molecular-weight, synthetic manganese-containing biscyclohexylpyridine superoxide dismutase mimetic (SODm) that removes superoxide anions (O(2)(-)) without interfering with other reactive species known to be involved in cardiovascular alterations (e.g. nitric oxide [NO] and peroxynitrite [ONOO(-)]). As such, M40403 represents an important pharmacological tool to dissect the roles of O(2)(-) in functional and biochemical cardiovascular alterations induced by perfusion of high glucose concentrations into the heart. Perfusion of a high glucose concentration of glucose into the heart elicited important cardiovascular alterations characterized by QT interval prolongation, increase in coronary perfusion pressure (CPP), lipid peroxidation, decrease in MnSOD activity and DNA damage. All parameters of cardiovascular alteration were attenuated by M40403 (1-10 mg/l). Furthermore, perfusion of a high of glucose concentration induced a significant formation of nitrotyrosine as well as an activation of poly(adenosine diphosphate [ADP]-ribose) synthetase (PARS), as determined by immunohistochemical analysis of heart tissue. The extent of staining for nitrotyrosine and PARS was reduced by M40403. These results clearly indicate that O(2)(-) plays a critical role in the development of the functional and biochemical cardiovascular alterations induced by perfusion of a high concentration of glucose into the heart. Therefore, synthetic enzymes of SOD, such as M40403, offer a novel therapeutic approach for the management of various cardiovascular diseases where these radicals have been postulated to play a role.