Diabetes-induced endothelial dysfunction is prevented by long-term treatment with the modified iron chelator, hydroxyethyl starch conjugated-deferoxamine

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Role of Iron in the Molecular Pathogenesis of Diseases and Therapeutic Opportunities

Iron is an essential mineral that serves as a prosthetic group for a variety of proteins involved in vital cellular processes. The iron economy within humans is highly conserved in that there is no proper iron excretion pathway. Therefore, iron homeostasis is highly evolved to coordinate iron acquisition, storage, transport, and recycling efficiently. A disturbance in this state can result in excess iron burden in which an ensuing iron-mediated generation of reactive oxygen species imparts widespread oxidative damage to proteins, lipids, and DNA. On the contrary, problems in iron deficiency either due to genetic or nutritional causes can lead to a number of iron deficiency disorders. Iron chelation strategies have been in the works since the early 1900s, and they still remain the most viable therapeutic approach to mitigate the toxic side effects of excess iron. Intense investigations on improving the efficacy of chelation strategies while being well tolerated and accepted by patients have been a particular focus for many researchers over the past 30 years. Moreover, recent advances in our understanding on the role of iron in the pathogenesis of different diseases (both in iron overload and iron deficiency conditions) motivate the need to develop new therapeutics. We summarized recent investigations into the role of iron in health and disease conditions, iron chelation, and iron delivery strategies. Information regarding small molecule as well as macromolecular approaches and how they are employed within different disease pathogenesis such as primary and secondary iron overload diseases, cancer, diabetes, neurodegenerative diseases, infections, and in iron deficiency is provided.

Renal clearable nanochelators for iron overload therapy

Iron chelators have been widely used to remove excess toxic iron from patients with secondary iron overload. However, small molecule-based iron chelators can cause adverse side effects such as infection, gastrointestinal bleeding, kidney failure, and liver fibrosis. Here we report renal clearable nanochelators for iron overload disorders. First, after a singledose intravenous injection, the nanochelator shows favorable pharmacokinetic properties, such as kidney-specific biodistribution and rapid renal excretion (>80% injected dose in 4 h), compared to native deferoxamine (DFO). Second, subcutaneous (SC) administration of nanochelators improves pharmacodynamics, as evidenced by a 7-fold increase in efficiency of urinary iron excretion compared to intravenous injection. Third, daily SC injections of the nanochelator for 5 days to iron overload mice and rats decrease iron levels in serum and liver. Furthermore, the nanochelator significantly reduces kidney damage caused by iron overload without demonstrating DFO's own nephrotoxicity. This renal clearable nanochelator provides enhanced efficacy and safety.

Potential Role of Metal Chelation to Prevent the Cardiovascular Complications of Diabetes

CONTEXT

For decades, there has been epidemiologic evidence linking chronic toxic metal exposure with cardiovascular disease, suggesting a therapeutic role for metal chelation. Given the lack of compelling scientific evidence, however, the indications for metal chelation were never clearly defined. To determine the safety and efficacy of chelation therapy, the National Institutes of Health funded the Trial to Assess Chelation Therapy (TACT). TACT was the first double-blind, randomized, controlled trial to demonstrate an improvement in cardiovascular outcomes with edetate disodium therapy in patients with prior myocardial infarction. The therapeutic benefit was striking among the prespecified subgroup of patients with diabetes.

DESIGN

We review the published literature focusing on the atherogenic nature of diabetes, as well as available evidence from clinical trials, complete and in progress, of metal chelation with edetate disodium therapy in patients with diabetes.

RESULTS

The TACT results support the concept that ubiquitous toxic metals such as lead and cadmium may be modifiable risk factors for cardiovascular disease, particularly in patients with diabetes.

CONCLUSIONS

The purpose of this review is to discuss the potential mechanisms unifying the pathogenesis of atherogenic factors in diabetes with toxic metal exposure, and the potential role of metal chelation.

Diabetic neuropathy and the sensory neuron: New aspects of pathogenesis and their treatment implications

Diabetic polyneuropathy (DPN) continues to be generally considered as a "microvascular" complication of diabetes mellitus alongside nephropathy and retinopathy. The microvascular hypothesis, however, might be tempered by the concept that diabetes directly targets dorsal root ganglion sensory neurons. This neuron-specific concept, supported by accumulating evidence, might account for important features of DPN, such as its early sensory neuron degeneration. Diabetic sensory neurons develop neuronal atrophy alongside a series of messenger ribonucleic acid (RNA) changes related to declines in structural proteins, increases in heat shock protein, increases in the receptor for advanced glycation end-products, declines in growth factor signaling and other changes. Insulin is recognized as a potent neurotrophic factor, and insulin ligation enhances neurite outgrowth through activation of the phosphoinositide 3-kinase-protein kinase B pathway within sensory neurons and attenuates phenotypic features of experimental DPN. Several interventions, including glucagon-like peptide-1 agonism, and phosphatase and tensin homolog inhibition to activate growth signals in sensory neurons, or heat shock protein overexpression, prevent or reverse neuropathic abnormalities in experimental DPN. Diabetic sensory neurons show a unique pattern of microRNA alterations, a key element of messenger RNA silencing. For example, let-7i is widely expressed in sensory neurons, supports their growth and is depleted in experimental DPN; its replenishment improves features of DPN models. Finally, impairment of pre-messenger RNA splicing in diabetic sensory neurons including abnormal nuclear RNA metabolism and structure with loss of survival motor neuron protein, a neuron survival molecule, and overexpression of CWC22, a splicing factor, offer further novel insights. The present review addresses these new aspects of DPN sensory neurodegeneration.

Comparison of the Hydroxylase Inhibitor Dimethyloxalylglycine and the Iron Chelator Deferoxamine in Diabetic and Aged Wound Healing

BACKGROUND

A hallmark of diabetes mellitus is the breakdown of almost every reparative process in the human body, leading to critical impairments of wound healing. Stabilization and activity of the transcription factor hypoxia-inducible factor (HIF)-1α is impaired in diabetes, leading to deficits in new blood vessel formation in response to injury. In this article, the authors compare the effectiveness of two promising small-molecule therapeutics, the hydroxylase inhibitor dimethyloxalylglycine and the iron chelator deferoxamine, for attenuating diabetes-associated deficits in cutaneous wound healing by enhancing HIF-1α activation.

METHODS

HIF-1α stabilization, phosphorylation, and transactivation were measured in murine fibroblasts cultured under normoxic or hypoxic and low-glucose or high-glucose conditions following treatment with deferoxamine or dimethyloxalylglycine. In addition, diabetic wound healing and neovascularization were evaluated in db/db mice treated with topical solutions of either deferoxamine or dimethyloxalylglycine, and the efficacy of these molecules was also compared in aged mice.

RESULTS

The authors show that deferoxamine stabilizes HIF-1α expression and improves HIF-1α transactivity in hypoxic and hyperglycemic states in vitro, whereas the effects of dimethyloxalylglycine are significantly blunted under hyperglycemic hypoxic conditions. In vivo, both dimethyloxalylglycine and deferoxamine enhance wound healing and vascularity in aged mice, but only deferoxamine universally augmented wound healing and neovascularization in the setting of both advanced age and diabetes.

CONCLUSION

This first direct comparison of deferoxamine and dimethyloxalylglycine in the treatment of impaired wound healing suggests significant therapeutic potential for topical deferoxamine treatment in ischemic and diabetic disease.

Effect of the oral iron chelator deferiprone in diabetic nephropathy rats

BACKGROUND

The aim of the present study was to investigate the effects of the iron chelator deferiprone in diabetic nephropathy (DN) rats and the mechanisms involved.

METHODS

Thirty-two male Wistar rats (180-220 g, 6 weeks old) were randomly divided into a control group, a DN group and two DN groups treated with either 50 or 100 mg/kg per day deferiprone. The DN group was established by feeding of a high-carbohydrate-fat diet and injection of 35 mg/kg streptozotocin into the vena caudalis. The duration of deferiprone treatment was 20 weeks. Histopathological changes were detected by hematoxylin-eosin and Masson staining, as well as transmission electron microscopy. Levels of nuclear factor (NF)-κB, monocyte chemotactic protein (MCP)-1, matrix metalloproteinase (MMP)-9, tissue-specific inhibitor of metalloproteinase (TIMP)-1, cyclo-oxygenase (COX)-2, and nitrotyrosine were determined in kidney tissues using reverse transcription-polymerase chain reaction (RT-PCR), western blotting, and immunohistochemistry.

RESULTS

Histopathological observations showed that deferiprone treatment alleviated inflammation infiltrates and collagenous fibrosis in DN rats. Results from RT-PCR and western blotting indicated that deferiprone inhibited the expression of NF-κB, MCP-1, COX-2, and nitrotyrosine, which were overexpressed in DN rats. Immunohistochemistry showed that the mechanism of deferiprone action may involve regulation of MMP-9 and TIMP-1. Decreased MMP-9 expression and increased TIMP-1 expression in DN rats were significantly promoted and inhibited by deferiprone, respectively.

CONCLUSION

Iron chelation by oral deferiprone has a renoprotective effect in DN rats by relieving oxidative stress, inflammation, and fibrosis, which is related to the cytokines NF-κB, MCP-1, MMP-9, TIMP-1, COX-2, and nitrotyrosine.

Efficacy of nobiletin, a citrus flavonoid, in the treatment of the cardiovascular dysfunction of diabetes in rats

Nobiletin, due to its MMP-2 & MMP-9 inhibitory and antioxidant effects, may ameliorate the cardiovascular dysfunction of diabetes.

Sex-specific vascular responses of the rat aorta: effects of moderate term (intermediate stage) streptozotocin-induced diabetes

Hyperglycemia affects male and female vascular beds differently. We have previously shown that 1 week after the induction of diabetes with streptozotocin (STZ), male and female rats exhibit differences in aortic endothelial function. To examine this phenomenon further, aortic responses were studied in male and female rats 8 weeks after the induction of diabetes (intermediate stage). Endothelium-dependent vasodilation (EDV) to acetylcholine (ACh) was measured in phenylephrine (PE) pre-contracted rat aortic rings. Concentration response curves to PE were generated before and after L-NAME, a nitric oxide synthase (NOS) inhibitor. Furthermore, mRNA expression of endothelial nitric oxide synthase (eNOS) and NADPH oxidase subunit (Nox1) were determined. At 8 weeks, diabetes impaired EDV to a greater extent in female than male aortae. Furthermore, the responsiveness to PE was significantly enhanced only in female diabetic rats, and basal NO, as indicated by the potentiation of the response to PE after L-NAME, was reduced in female diabetic rat aortae to the same levels as in males. In addition, eNOS mRNA expression was decreased, while the Nox1 expression was significantly enhanced in diabetic female rats. These results suggest that aortic function in female diabetic rats after 8 weeks exhibits a more prominent impairment and that NO may be involved.

Vascular Impairment of Epineurial Arterioles of the Sciatic Nerve: Implications for Diabetic Peripheral Neuropathy

This article reviews the impact of diabetes and its treatment on vascular function with a focus on the reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve. Another focus is the relationship between the dysregulation of neurovascular function and diabetic peripheral neuropathy. Diabetic peripheral neuropathy is a debilitating disorder that occurs in more than 50 percent of patients with diabetes. The etiology involves metabolic, vascular, and immunologic pathways besides neurohormonal growth factor deficiency and extracellular matrix remodeling. In the light of this complex etiology, an effective treatment for diabetic peripheral neuropathy has not yet been identified. Current opinion postulates that any effective treatment for diabetic peripheral neuropathy will require a combination of life style and therapeutic interventions. However, a more comprehensive understanding of the factors contributing to neurovascular and neural dysfunction in diabetes is needed before such a treatment strategy can be developed. After reading this review, the reader should have gained insight into the complex regulation of vascular function and blood flow to the sciatic nerve, and the impact of diabetes on numerous elements of vascular reactivity of epineurial arterioles of the sciatic nerve.

Post-translational regulation of endothelial nitric oxide synthase in vascular endothelium

Nitric oxide (NO) is a short-lived gaseous signaling molecule. In blood vessels, it is synthesized in a dynamic fashion by endothelial nitric oxide synthase (eNOS) and influences vascular function via two distinct mechanisms, the activation of soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)-dependent signaling and the S-nitrosylation of proteins with reactive thiols (S-nitrosylation). The regulation of eNOS activity and NO bioavailability is critical to maintain blood vessel function. The activity of eNOS and ability to generate NO is regulated at the transcriptional, posttranscriptional, and posttranslational levels. Post-translational modifications acutely impact eNOS activity and dysregulation of these mechanisms compromise eNOS activity and foster the development of cardiovascular diseases (CVDs). This review will intergrate past and current literature on the post-translational modifications of eNOS in both health and disease.

COX-2-derived prostanoids and oxidative stress additionally reduce endothelium-mediated relaxation in old type 2 diabetic rats

Endothelial dysfunction in resistance arteries alters end organ perfusion in type 2 diabetes. Superoxides and cyclooxygenase-2 (COX-2) derivatives have been shown separately to alter endothelium-mediated relaxation in aging and diabetes but their role in the alteration of vascular tone in old diabetic subjects is not clear, especially in resistance arteries. Consequently, we investigated the role of superoxide and COX-2-derivatives on endothelium-dependent relaxation in 3 and 12 month-old Zucker diabetic fatty (ZDF) and lean (LZ) rats. Mesenteric resistance arteries were isolated and vascular tone was investigated using wire-myography. Endothelium (acetylcholine)-dependent relaxation was lower in ZDF than in LZ rats (60 versus 84% maximal relaxation in young rats and 41 versus 69% in old rats). Blocking NO production with L-NAME was less efficient in old than in young rats. L-NAME had no effect in old ZDF rats although eNOS expression level in old ZDF rats was similar to that in old LZ rats. Superoxide level and NADPH-oxidase subunits (p67phox and gp91phox) expression level were greater in ZDF than in LZ rats and were further increased by aging in ZDF rats. In young ZDF rats reducing superoxide level with tempol restored acetylcholine-dependent relaxation to the level of LZ rats. In old ZDF rats tempol improved acetylcholine-dependent relaxation without increasing it to the level of LZ rats. COX-2 (immunolabelling and Western-blot) was present in arteries of ZDF rats and absent in LZ rats. In old ZDF rats arterial COX-2 level was higher than in young ZDF rats. COX-2 blockade with NS398 restored in part acetylcholine-dependent relaxation in arteries of old ZDF rats and the combination of tempol and NS398 fully restored relaxation in control (LZ rats) level. Accordingly, superoxide production and COX-2 derivatives together reduced endothelium-dependent relaxation in old ZDF rats whereas superoxides alone attenuated relaxation in young ZDF or old LZ rats.

Potential therapeutic use of deferoxamine and mesenchymal stem cells in type-1 diabetes: assembling another piece of the jigsaw, in what is a complex puzzle

Mesenchymal stem cells (MSCs) are recognized for their potential in regenerative medicine. Due to long-term negative effects associated with insulin administration and difficulty with pancreas transplantation, patients with type-1 diabetes could significantly benefit from organ-targeted cell-based therapy. Although several pharmacological agents increase the homing capacity of MSCs, the mechanisms regulating this process are still poorly understood. In this issue, Najafi et al. have demonstrated that pre-treatment of bone marrow-derived MSCs with the iron chelator and hypoxia mimetic, deferoxamine, can increase homing to the pancreas in a rat model of diabetes. This effect appears to be driven through specific chemokines in addition to hypoxia-inducing factor 1-alpha. Results from this study provide important clues in our endeavour to solve a complex process. Further studies will help determine whether these findings may offer potential therapeutic benefit to patients with diabetes.

The AGE-breaker ALT-711 restores high blood flow-dependent remodeling in mesenteric resistance arteries in a rat model of type 2 diabetes

Flow-mediated remodeling of resistance arteries is essential for revascularization in ischemic diseases, but this is impaired in diabetes. We hypothesized that breaking advanced glycation end product (AGE) cross-links could improve remodeling in mesenteric resistance arteries in Zucker diabetic fatty (ZDF) rats compared with lean Zucker (LZ) rats. Arteries, exposed to high (HF) or normal (NF) blood flow after alternate arterial ligation in vivo, were collected after 2 weeks. In LZ rats, HF artery diameter was larger than for NF vessels, but this was not the case in ZDF rats. Endothelium-mediated dilation in ZDF rats, which was lower than in LZ rats, was further decreased in HF arteries. Treatment of rats with the AGE-breaker 4,5-dimethyl-3-phenacylthiazolium chloride (ALT-711) (3 mg/kg/day; 3 weeks) reversed diabetes-induced impairment of HF-dependent remodeling. ALT-711 also improved endothelium nitric oxide-dependent relaxation in mesenteric resistance arteries. Reactive oxygen species reduction restored relaxation in ZDF rats but not in LZ or ALT-711-treated rats. AGEs were reduced in ALT-711-treated ZDF rats compared with ZDF rats. Metalloproteinase activity, necessary for HF-dependent remodeling, was reduced in ZDF rats compared with LZ rats and restored by ALT-711. Thus, targeting AGE cross-links may provide a therapeutic potential for overcoming microvascular complications in ischemic disorders occurring in diabetes.

Glucose-induced regulation of novel iron transporters in vascular endothelial cell dysfunction

Increased iron indices have been associated with the development of diabetes and its complications. In the present study, we have investigated the glucose-induced alteration of iron transporters, divalent metal transporter-1 (DMT-1), iron regulated transporter protein-1 (IREG-1), and transferrin receptor (TfR), in endothelial cell iron accumulation and oxidative stress. Cells were exposed to high glucose levels and subjected to gene expression, protein expression, iron measurement and assessment of oxidative stress. Our results show, for the first time, expression of DMT-1 and IREG-1 in vascular endothelial cells. Our data further indicates upregulation of DMT-1 and IREG-1 mRNA and protein in response to high levels of glucose. TfR, however, exhibited a modest decrease in response to high levels of glucose. Increased expression of DMT-1 and IREG-1 was associated with iron accumulation and oxidative stress. Furthermore, our results show differential expression of iron transporters with treatment of high glucose-exposed cells with two different iron chelators. In conclusion, our study suggests that glucose-induced alteration of iron transporters may arbitrate iron accumulation and oxidative stress in endothelial cells.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

The role of endothelial dysfunction in the pathogenesis of impaired diabetic wound healing: a novel therapeutic target?

The global burden of diabetes is attributed to its multiple associated complications including impaired wound healing which can ultimately result in amputation. Peripheral vascular disease, infection, neuropathy and abnormal local cellular and cytokine activity are some of the traditionally cited pathological instigators of defective diabetic wound repair. Despite intensive research and subsequent advances in diabetic wound care technology a single treatment with measurable clinical impact has yet to be determined. The phenomenon of endothelial dysfunction as seen in atherosclerosis and recently identified as a characteristic of diabetic vasculature may contribute to impaired cutaneous healing in this group. Indicators of endothelial dysfunction have been demonstrated in diabetic wounds by a number of investigators. Successful results are being obtained with modifiers of endothelial function in the management of cardiovascular disease. We hypothesise that endothelial dysfunction plays a substantial contributory role in the pathogenesis of wound healing impairment of diabetes and holds potential as a target for therapeutic intervention.

Preventive and curative effect of edaravone on nerve functions and oxidative stress in experimental diabetic neuropathy

Oxidative stress is implicated as a final common pathway in the development of diabetic neuropathy and pharmacological interventions targeted at inhibiting free radical production have shown beneficial effects. In the present study, we have investigated the effects of edaravone (3 mg/kg; 3-Methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger (relatively selective to hydroxyl radicals) in streptozotocin (50 mg/kg i.p.) induced diabetic neuropathy in male Sprague-Dawley rats. Significant reduction (18%) in motor nerve conduction velocity, nerve blood flow (55%) and tail flick latency in cold (53%) and hot (50%) immersion test was observed in diabetic rats compared to age matched non-diabetic rats. Preventive (8 week) and curative (2 week) treatment of edaravone significantly improved the nerve conduction velocity and nociception but not nerve blood flow in diabetic rats. The changes in lipid peroxidation status and anti-oxidant enzymes (Superoxide dismutase and Catalase) levels observed in diabetic rats were significantly restored by edaravone treatment. Increase in blood pressure and vascular resistance was also significantly attenuated by edaravone treatment. This study provides experimental evidence to preventive and curative effect of edaravone on nerve function and oxidative stress in animal model of diabetic neuropathy. Hence edaravone may be tried clinically for the treatment of diabetic neuropathy since it is clinically used in stroke patients.

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.

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.

Feasibility of in vivo identification of endogenous ferritin with positive contrast MRI in rabbit carotid crush injury using GRASP

In vivo markers that allow for detection of ferritin within atheromatous plaque may be useful for identifying iron-catalyzed hydroxyl-radical formation and subsequent lipid peroxidation. Recently, a positive contrast MR technique--GRadient echo Acquisition for Superparamagnetic particles/suscePtibility (GRASP)--was used to identify the presence of magnetic entities in phantom models. The aim of the current study was to determine the feasibility of using GRASP in conjunction with conventional T(2) (*)-weighted (T(2) (*)W) gradient-echo (GRE) sequences for identifying ferritin/hemosiderin deposition using in vitro and in vivo models of thrombus. In vitro thrombi were prepared by incubating blood with ferritin. MRI was performed using conventional GRE sequences and GRASP. The results indicate that GRASP was able to verify ferritin deposition in in vitro thrombi. In vivo thrombi were created using a crush injury model in rabbits. The signal enhancement obtained using conventional GRE sequences and GRASP was compared with the location of iron deposition by histology. In all of the animals the GRASP signal correlated with signal loss by conventional GRE, and ferritin/hemosiderin deposition by histology. GRASP sequences in combination with conventional GRE sequences may be used to detect the presence of ferritin deposition in in vitro thrombi and in vivo crush-injured rabbit carotid arteries.

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.

Iron Chelation Suppresses Ferritin Upregulation and Attenuates Vascular Dysfunction in the Aorta of Angiotensin II–Infused Rats

Objective— We have investigated whether long-term administration of angiotensin (Ang) II causes ferritin induction and iron accumulation in the rat aorta, and their possible relation to regulatory effects on gene expression and vascular function in Ang II-infused animals.

Methods and Results— Sprague-Dawley rats were given Ang II for 7 days via subcutaneously implanted osmotic minipumps. Ang II infusion caused a >20-fold increase in ferritin protein expression over control values. Immunohistochemistry showed that Ang II infusion markedly increased the ferritin expression in the aortic endothelial and adventitial cells, with some of the latter being identified as monocytes/macrophages. Prussian blue staining showed that stainable iron was observed in the adventitial layer of aorta from Ang II-infused animals, but not in the endothelial layer. Chelation of iron suppressed aortic induction of ferritin and also the oxidative stress markers, heme oxygenase-1 and 4-hydroxynonenal-modified protein adducts. In addition, iron chelation attenuated Ang II-induced impairment of aortic relaxations in response to acetylcholine and sodium nitroprusside and suppressed upregulation of mRNA levels of monocyte chemoattractant protein-1. Iron chelation also partially attenuated the medial thickening and perivascular fibrosis induced by Ang II infusion for 4 weeks.

Conclusion— Ang II infusion caused ferritin induction and iron deposition in the aortas. These phenomena might have a role in the regulation of gene expression, impairment of vascular function, and arterial remodeling induced by Ang II, which are presumably mediated in part by enhancement of oxidative stress.

Effect of pioglitazone on L-NAME induced hypertension in diabetic rats

The present study investigates the effect of pioglitazone treatment on blood pressure, vascular reactivity and antioxidant enzymes in L-NAME induced hypertension in normal and STZ-diabetic rats. Diabetes was induced in male Sprague Dawley rats (200+/-15 g) by single intravenous injection of 55 mg/kg of streptozotocin (STZ). Rats were randomized into diabetic and nondiabetic groups, Nomega-nitro-L-arginine-methyl ester (L-NAME, 50 mg/kg) was administered in drinking water for 4 weeks. They were treated with pioglitazone (10 mg/kg/day, p.o.) for 4 weeks and following protocol was carried out. Blood pressure, blood glucose levels and body weight were measured. Thoracic aorta was isolated and dose response curve of phenylephrine (PE) with intact and denuded endothelium was recorded. Dose response curve of acetylcholine (Ach) and sodium nitroprusside (SNP) was recorded in precontracted rings. Lipid peroxidation, superoxide dismutase, catalase, and reduced glutathione were estimated in liver, kidney, and aorta. Pioglitazone produced no significant effect on blood glucose levels, body weight and blood pressure of L-NAME administered nondiabetic and diabetic rats. Pioglitazone treatment had no significant effect on PE induced contraction and Ach induced relaxation in L-NAME diabetic and nondiabetic rats. SNP completely relaxed aortic rings of all the groups. Higher oxidative stress in case of diabetic rats was significantly (p<0.05) reduced by pioglitazone treatment. Although pioglitazone reduced oxidative stress in diabetic rats, there was no significant effect on blood pressure as there was complete absence of nitric oxide due to administration of L-NAME. Hence from the present study it can be concluded that reduction in blood pressure in case of STZ-diabetic rats is nitric oxide mediated.

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.

Increased renal hypertrophy in diabetic mice genetically modified at the haptoglobin locus

BACKGROUND

The human haptoglobin (Hp) gene is polymorphic with two functional classes of alleles, denoted 1 and 2. We have demonstrated in three longitudinal studies and several cross-sectional studies that the Hp genotype is an independent risk factor for diabetic vascular disease. These studies have presented a compelling argument that diabetic individuals homozygous for the Hp 1 allele are at decreased risk of vascular complications as compared to diabetic individuals with the Hp 2 allele.

METHODS

The naturally occurring (wild type) mouse Hp is a class 1 Hp allele. We examined renal hypertrophy in wild-type mice, Hp knockout mice (Hp 0), and in mice with the Hp 2 allele (Hp 2) with and without diabetes.

RESULTS

In the absence of diabetes, we found that renal hypertrophy was significantly increased in Hp 0 mice and that this could be prevented with vitamin E. There was no difference between wild type and Hp 2 mice with regard to renal hypertrophy in the absence of diabetes. However, in the presence of diabetes, Hp 2 mice demonstrated a significant increase in renal hypertrophy as compared to wild-type mice.

CONCLUSIONS

These results support a direct linkage between diabetic vascular disease and the Hp genotype. These Hp-modified mice may serve as a platform on which to test a variety of pharmacological agents in order to decrease diabetic vascular disease.

Effect of the NAD(P)H oxidase inhibitor, apocynin, on peripheral nerve perfusion and function in diabetic rats

Upregulation of vascular NAD(P)H oxidase has been considered an important source for elevated levels of reactive oxygen species that contribute to several cardiovascular disease states, including the vascular complications of diabetes mellitus. Previous studies have shown that treatment with antioxidants corrects impaired nerve function and blood flow in diabetic rats. The aim was to assess the degree of involvement of NAD(P)H oxidase in experimental diabetic neuropathy. To this end, after 6 weeks of untreated streptozotocin-diabetes, rats were treated for 2 weeks with the NAD(P)H oxidase, apocynin. Two high doses (15 and 100 mg/kg) were used to ensure that maximal effects were registered. Diabetes caused a 20% reduction in sciatic nerve motor conduction velocity, and a 14% deficit for sensory saphenous nerve. Apocynin treatment corrected these defects by 32% and 48%, respectively: there were no significant differences between the effects of the 2 doses. Sciatic nerve nutritive endoneurial perfusion was measured by hydrogen clearance microelectrode polarography. Blood flow and vascular conductance were 47% and 40% reduced by diabetes, respectively. Both doses of apocynin had similar effects, correcting the blood flow deficit by 31% and conductance by 47%. Thus, the data show that NAD(P)H oxidase contributes to the neurovascular deficits in diabetic rats. While only accounting for part of the elevated reactive oxygen species production in diabetes, this mechanism could provide a novel therapeutic candidate for further investigation in diabetic neuropathy and vasculopathy.

Chronic or delayed treatment with an oral dithiocarbamate analog decreases glycation and protects diabetic arteries

In the present study, we examined the efficacy of a dithiocarbamate-based compound, denoted as NOX-700, on diabetes-induced endothelial dysfunction and glycosylation of hemoglobin (Hb). Streptozotocin-induced diabetic rats received 3 mg/ml NOX-700 in drinking water beginning at 72 h or 4 weeks and continued to 8 weeks. Oxidative and glycooxidative stress were examined by electrophoretic mobility shift assay (EMSA) for nuclear factor-kappaB (NF-kappaB) in nuclear fractions of aortic homogenates and by glycosylated Hb, respectively. Vascular reactivity was examined in aortic ring segments ex vivo. Treatment with NOX-700 inhibited glycosylated Hb formation when given long-term or after delayed administration. NOX-700 improved endothelium-dependent relaxation to acetylcholine but did not alter reactivity to norepinephrine or nitroglycerin, suggesting selective protection of the endothelium. Nuclear factor-kappaB (NF-kappaB) nuclear binding activity was significantly increased in diabetic aortas and abrogated by NOX-700. Thus, vascular protection by NOX-700 is believed to be mediated, in part, by an antioxidant mechanism and decreased protein glycation.

Ascorbic acid supplementation restores defective leukocyte-endothelial interaction in alloxan-diabetic rats

BACKGROUND

Defective leukocyte-endothelial interactions are observed in experimental diabetes and may reduce the capacity to mount an adequate inflammatory response. The present study investigated the effect of ascorbic acid, an inhibitor of free radical and glycated protein formation as well as an aldose reductase inhibitor, on leukocyte-endothelial interaction in alloxan-diabetic rats.

METHODS

Rats were rendered diabetic by alloxan injection (40 mg/kg; iv). After 30 days, diabetic and nondiabetic controls were supplemented for 12 days with ascorbic acid (50 or 200 mg/kg/day) or received saline by gavage. The number of rollers, stickers after zymosan-activated plasma (10%) or leukotriene B(4) (1 microM) applied topically, and migrated cells after local injection of carrageenan (100 microg) were determined in the venules of the internal spermatic fascia by intravital microscopy. Erythrocyte velocity and wall shear rate were determined as well. Reactive oxygen species formation by endothelial cells was measured in vivo by the same technique. Immunocytochemistry for ICAM-1 detection on the endothelium of the venules of the internal spermatic fascia was carried out in cross sections of the whole testis of the animals.

RESULTS

The reduced number of rollers, stickers and migrated cells, as well as the higher production of reactive oxygen species by endothelial cells in diabetic rats was corrected by ascorbic acid supplementation. The low immunoreactivity for ICAM-1 in the venules of diabetic rats was improved by ascorbic acid supplementation. Ascorbic acid supplementation did not interfere with erythrocyte velocity or wall shear stress. Ascorbic acid administered to control rats did not alter the parameters studied above.

CONCLUSION

We conclude that ascorbic acid improves leukocyte-endothelial interaction in diabetic rats at least in part by restoring the expression of ICAM-1 in the venules of diabetic rats.

Effect of sodium selenite treatment on platelet aggregation of streptozotocin-induced diabetic rats

INTRODUCTION

There is a well-known association between diabetes and atherosclerosis. Platelets are involved in the development of atherosclerotic vascular diseases and play a key role in atherosclerotic complications. Diabetes mellitus is related to alteration in the homeostasis of selenium and the protective role of selenium against lipid peroxidation in diabetes is reported. In the present study, thrombin-induced platelet aggregation and thromboxane A2 (TxA2) formation in diabetes and the effect of sodium selenite were evaluated.

MATERIALS AND METHODS

Diabetes was induced by intraperitoneal injection of streptozotocin (STZ) in Wistar rats (n = 21). Thirty of them were used as control rats. A week after streptozotocin injection, 11 of the control rats and 12 of the diabetics were injected with 5 micromol/kg/day of sodium selenite for 4 weeks. Thrombin-induced aggregation of the platelets was evaluated by optical technique. Thromboxane B2 (TxB2), TxA2 metabolite, was measured by enzyme-linked immunoassay (EIA) in thrombin-induced platelets.

RESULTS AND CONCLUSION

The platelet aggregation and TxB2 level increased in diabetic rats. Sodium selenite reversed the increase in platelet aggregation and TxB2 and caused a small but significant (p < 0.05) decrease in the glucose level. The hyperaggregability of platelets in STZ-induced diabetic rats was thought to be related to the enhanced TxA2 formation of platelets. Increase in TxA2 formation implies lipid peroxidation. Sodium selenite decreased the TxA2 formation. Besides its antioxidative effect, further studies are needed to establish the insulin-like effect of selenite because of a small decrease in blood glucose.

Blood letting in high-ferritin type 2 diabetes: effects on vascular reactivity

OBJECTIVE

In a recent study, iron chelation with deferoxamine led to improvement of endothelial dysfunction in patients with coronary artery disease. We tested the hypothesis that decreasing circulating iron stores might improve vascular dysfunction in patients with type 2 diabetes and increased serum ferritin concentration.

RESEARCH DESIGN AND METHODS

A total of 28 type 2 diabetic male patients with serum ferritin levels >200 ng/ml ( approximately 18% of consecutive type 2 diabetic men attending our outpatient clinic) were randomized to iron depletion (three extractions of 500 ml blood at 2-week intervals; group 1A) or to observation (group 1B). C282Y mutation was absent in all patients. Vascular reactivity (high-resolution external ultrasound) was evaluated at baseline and at 4 and 12 months thereafter. The two groups of patients were matched for age, BMI, pharmacological treatment, and chronic diabetic complications.

RESULTS

Endothelium-dependent vasodilation remained essentially unchanged in both groups of patients. In contrast, the vasodilation induced by glyceryl trinitrate (GTN) improved significantly after iron depletion (P = 0.006). These changes occurred in parallel to decreases in transferrin saturation index and HbA(1c) levels (-0.6%, P < 0.05) only in group 1A patients. The best predictor of the modifications in endothelium-independent vasodilation was the change in HbA(1c) levels. Changes in endothelium-independent vasodilation also correlated with the change in serum ferritin (r = -0.45, P = 0.04). At 12 months, transferrin saturation index and GTN-induced vasodilation returned to values similar to those at baseline in both groups of subjects.

CONCLUSIONS

Iron depletion improves vascular dysfunction in type 2 diabetic patients with high ferritin concentrations. The mechanisms by which these changes occur should be further investigated.

Transition metals and polyol pathway in the development of diabetic neuropathy in rats

BACKGROUND

The transition metal-catalyzed reaction is a major source of oxygen free radicals, which play an important role in vascular dysfunction leading to ischemia in diabetic tissues. The inhibition of polyol pathway hyperactivity has been reported to ameliorate neurovascular abnormalities in diabetic rats and has been proposed to improve the oxygen free radical scavenging capacity. The present study was conducted to compare the effect of a transition metal chelating agent, trientine (TRI), on diabetic neuropathy with that of an aldose reductase inhibitor, NZ-314 (NZ).

METHODS

Diabetic rats were divided into three groups: (1). untreated, (2). TRI-treated, and (3). NZ-treated. TRI (20 mg/kg) or NZ (100 mg/kg) was administered by gavage or chow containing NZ, respectively, for 8 weeks. Motor nerve conduction velocity (MNCV), coefficient of variation of the R - R interval on electrocardiogram (CVr-r), sciatic nerve blood flow (SNBF), platelet aggregation activities, and serum concentrations of malondialdehyde were measured.

RESULTS

Untreated diabetic rats showed delayed MNCV, decreased CV(R-R), and reduced SNBF compared to normal rats. TRI or NZ completely prevented these deficits. Platelet hyperaggregation activities in diabetic rats were prevented by NZ, but not by TRI. Increased concentrations of malondialdehyde in diabetic rats were partially but significantly ameliorated by either TRI or NZ.

CONCLUSIONS

These observations suggest that increased free radical formation through the transition metal-catalyzed reaction plays an important role in the development of diabetic neuropathy and that the preventive effect of an aldose reductase inhibitor on diabetic neuropathy may also be mediated by decreasing oxygen free radicals.

Cross-talk between iron metabolism and diabetes

Emerging scientific evidence has disclosed unsuspected influences between iron metabolism and type 2 diabetes. The relationship is bi-directional--iron affects glucose metabolism, and glucose metabolism impinges on several iron metabolic pathways. Oxidative stress and inflammatory cytokines influence these relationships, amplifying and potentiating the initiated events. The clinical impact of these interactions depends on both the genetic predisposition and the time frame in which this network of closely related signals acts. In recent years, increased iron stores have been found to predict the development of type 2 diabetes while iron depletion was protective. Iron-induced damage might also modulate the development of chronic diabetes complications. Iron depletion has been demonstrated to be beneficial in coronary artery responses, endothelial dysfunction, insulin secretion, insulin action, and metabolic control in type 2 diabetes. Here, we show that iron modulates insulin action in healthy individuals and in patients with type 2 diabetes. The extent of this influence should be tested in large-scale clinical trials, searching for the usefulness and cost-effectiveness of therapeutic measures that decrease iron toxicity. The study of individual susceptibility and of the mechanisms that influence tissue iron deposition and damage are proposed to be valuable in anticipating and treating diabetes complications.

Vascular protective actions of a nitric oxide aspirin analog in both in vitro and in vivo models of diabetes mellitus

BACKGROUND

Defective endothelium-dependent relaxation is observed in experimental and human diabetes mellitus. The nature of this defect is not fully understood but may involve decreased nitric oxide (NO) bioactivity due to enhanced production of reactive oxygen species (ROS). In this paper, we examine the benefits and actions of a novel NO-donating, antioxidant called 2-acetoxybenzoic acid 2-(2-nitrooxymethyl) phenyl ester, and denoted as NCX4016, on NO-mediated endothelium-dependent relaxation in normal arteries exposed to acute elevations in glucose or in arteries derived from chronic diabetic animals.

MATERIAL AND METHODS

Intrinsic free radical scavenging by NO-NSAIDs in solution were evaluated using electron paramagnetic resonance (EPR) spectroscopy and spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In acute studies, normal rat aortas were exposed in tissue culture for 18 h to 5.5 mM or 40 mM in the presence or absence of NCX4016, a NO-donating NSAID unrelated to aspirin (NCX2216) or aspirin. Vascular reactivity of thoracic aortic rings to endothelium-dependent relaxation to acetylcholine in vitro was determined. For chronic hyperglycemia, diabetes was induced in rats by intravenous injection with streptozotocin. Vascular reactivity of thoracic aortic rings to endothelium-dependent relaxation to acetylcholine in vitro was determined after 8 wks in untreated animals or animals chronically-treated with NCX4016. Antioxidant efficacy in vivo was determined by measurement of plasma isoprostanes and by nuclear binding activity of NF-kappaB in nuclear fractions of aortae.

RESULTS

Incubation with NCX4016 and NCX2216 produced a concentration-dependent inhibition of DMPO-OH formation indicating scavenging of hydroxyl radicals (HO(*)). In contrast, little efficacy to scavenge superoxide anion radicals was noted. Acute incubation of normal arteries with elevated glucose concentration caused inhibition of normal relaxation to acetylcholine. This impairment was prevented by co-incubation with NCX4106 but not by mannitol, the parent compound (aspirin) or by NCX2216. In addition, chronic treatment with NCX4016 prevented the development of defective endothelium-dependent relaxation to acetylcholine. This protection did not occur as a result to any changes in blood glucose concentration or hemoglobin glycation. Treatment with NCX4016 did decrease the elevation in plasma isoprostanes and normalized the diabetes-induced increase in NF-kappaB binding activity in nuclear fractions derived from aortic tissue.

CONCLUSIONS

Collectively, these studies suggest that antioxidant interventions using NO-donating NSAIDs may provide an important novel therapeutic strategy to protect the diabetic endothelium.

Blood letting in high-ferritin type 2 diabetes: effects on insulin sensitivity and beta-cell function

Iron-related insulin-resistance is improved by iron depletion or treatment with iron chelators. The aim of this study was to evaluate insulin sensitivity and insulin secretion after blood letting in patients who had high-ferritin type 2 diabetes and were randomized to blood letting (three phlebotomies [500 ml of blood] at 2-week intervals, group 1) or to observation (group 2). Insulin secretion and sensitivity were tested at baseline and 4 and 12 months thereafter. The two groups were matched for age, BMI, pharmacologic treatment, and chronic diabetic complications. All patients were negative for C282Y mutation of hereditary hemochromatosis. Baseline glycated hemoglobin (6.27 +/- 0.9% vs. 6.39 +/- 1.2%), insulin sensitivity (2.75 +/- 1.8 vs. 3.2 +/- 2.1 mg.dl(-1).min(-1)), and area under the curve for C-peptide (AUC(C-peptide); 38.7 +/- 11.6 vs. 37.6 +/- 14.1 ng.ml(-1).min(-1)) were not significantly different between the two groups of patients. Body weight, blood pressure, blood hematocrit levels, and drug treatment remained essentially unchanged during the study period. As expected, serum ferritin, transferrin saturation index, and blood hemoglobin decreased significantly at 4 months only in patients who received blood letting. In parallel to this changes, blood HbA(1c) decreased significantly only in group 1 subjects (mean differences, -0.61; 95% CI, -0.17 to -1.048; P = 0.01). AUC(C-peptide) decreased by -10.2 +/- 6.3% after blood letting. In contrast, a 10.4 +/- 6.4% increase in AUC(C-peptide) was noted in group 2 subjects at 4 months (P = 0.032). At 12 months, AUC(C-peptide) returned to values not significantly different from baseline in the two groups of subjects. At 4 months, the change in insulin sensitivity from baseline was significantly different between the two groups (80.6 +/- 43.2% vs. -8.6 +/- 9.9% in groups 1 and 2, respectively, P = 0.049). At 12 months, the differences between the two groups were even more marked (55.5 +/- 24.8% vs. -26.8 +/- 9.9%; P = 0.005). When the analysis was restricted to those subjects who completed the follow-up until 12 months, results did not show differences compared with the changes observed at 4 months, except for insulin sensitivity. A statistically significant increase in insulin sensitivity was observed in the blood-letting group (from 2.30 +/- 1.81 to 3.08 +/- 2.55 mg.dl(-1).min(-1) at 4 months, to 3.16 +/- 1.85 mg.dl(-1).min(-1) at 12 months; P = 0,045) in contrast with group 2 subjects (from 3.24 +/- 1.9 to 3.26 +/- 2.05 mg.dl(-1).min(-1) at 4 months, to 2.31 +/- 1.35 mg.dl(-1).min(-1) at 12 months). In summary, blood letting led simultaneously to decreased blood HbA(1c) levels and to changes in insulin secretion and insulin resistance that were significantly different from those observed in a matched observational group of subjects with high-ferritin type 2 diabetes. The mechanisms for improvement in peripheral insulin sensitivity after blood letting should be investigated further.

Elimination of *O(2)(-)/H(2)O(2) by alpha-lipoic acid mediates the recovery of basal EDRF/NO availability and the reversal of superoxide dismutase-induced relaxation in diabetic rat aorta

AIM

The aims of this study were to ascertain the mechanism(s) of relaxant action of exogenous superoxide dismutase (SOD) in aortic rings obtained from 12-week, streptozotocin(STZ)-diabetic and age-matched control rats, and to examine the effects of alpha-lipoic acid (ALA) treatment (for 6 weeks, after 6 weeks of untreated diabetes) on SOD-induced relaxations.

MATERIALS AND METHODS

Thoracic aorta rings were suspended to isolated tissue chamber, and the changes in isometric tension were recorded.

RESULTS

SOD produced a greater relaxation in untreated-diabetic rings compared with control rings. ALA treatment partially reversed SOD-induced relaxation in diabetic aorta. Pretreatment of rings with N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microm) inhibited SOD-induced relaxation. This effect of L-NAME was markedly observed in control and ALA-treated-diabetic rings compared with untreated-diabetic rings. SOD-induced relaxation was also inhibited by catalase (60 U/ml) in untreated-diabetic rings but not in ALA-treated-diabetic and control rings. Pretreatment with the cyclooxygenase inhibitor, indomethacin, or the catalase inhibitor, aminotriazole, had no effect on SOD-induced relaxation in any ring.

CONCLUSION

Findings suggested that: (i) in normal physiological conditions, the relaxant effect of SOD is related to the inhibition of superoxide anion radicals (*O(2)(-))-induced endothelium-derived relaxing factor/nitric oxide (EDRF/NO) destruction in the rat aorta; (ii) in diabetic state, excess *O(2)(-) increasingly inhibits basal EDRF/NO, and the dismutation of excess *O(2)(-) to H(2)O(2) is enhanced by exogenous SOD. H(2)O(2) a vasorelaxant molecule, which probably accounts for the increased responsiveness of diabetic rings to exogenous SOD; and (iii) the reversal effect of in vivo ALA treatment on SOD-induced relaxation in diabetic aorta is probably linked with the elimination of *O(2)(-)/H(2)O(2), which mediates the recovery of basal EDRF/NO availability.

Effect of M40403 treatment of diabetic rats on endoneurial blood flow, motor nerve conduction velocity and vascular function of epineurial arterioles of the sciatic nerve

1. To further explore the effect of antioxidants in preventing diabetes-induced vascular and neural dysfunction we treated streptozotocin-induced diabetic rats daily with subcutaneous injections of 10 mg kg(-1) of M40403 (n=11) and compared the results obtained from 17 control rats and 14 untreated diabetic rats. M40403 is a manganese(II) complex with a bis(cyclo-hexylpyridine)-substituted macrocyclic ligand that was designed to be a selective functional mimetic of superoxide dismutase. Thus, M40403 provides a useful tool to evaluate the roles of superoxide in disease states. 2. Treatment with M40403 significantly improved diabetes-induced decrease in endoneurial blood flow, acetylcholine-mediated vascular relaxation in arterioles that provide circulation to the region of the sciatic nerve, and motor nerve conduction velocity (P<0.05). M40403 treatment also reduced the appearance of superoxide in the aorta and epineurial vessels and peroxynitrite in epineurial vessels. Treating diabetic rats with M40403 reduced the diabetes-induced increase in thiobarbituric acid reactive substances in serum but did not prevent the decrease in lens glutathione level. Treating diabetic rats with M40403 did not improve sciatic nerve Na(+)/K(+) ATPase activity or the sorbitol, fructose or myo-inositol content of the sciatic nerve. 3. These studies provide additional evidence that diabetes-induced oxidative stress and the generation of superoxide and perhaps peroxynitrite may be partially responsible for the development of diabetic vascular and neural complications.

Effect of antioxidant treatment of streptozotocin-induced diabetic rats on endoneurial blood flow, motor nerve conduction velocity, and vascular reactivity of epineurial arterioles of the sciatic nerve

We have shown that diabetes-induced reduction in endoneurial blood flow (EBF) and impaired endothelium-dependent vascular relaxation precede slowing of motor nerve conduction velocity (MNCV) and decreased sciatic nerve Na(+)/K(+) ATPase activity. Furthermore, vascular dysfunction was accompanied by an accumulation of superoxide in arterioles that provide circulation to the sciatic nerve. In the present study, we examined the effect that treatment of streptozotocin-induced diabetic rats with antioxidants has on vascular and neural function. Diabetic rats were treated with 0.5% alpha-lipoic acid as a diet supplement or with hydroxyethyl starch deferoxamine (HES-DFO) by weekly intravenous injections at a dose of 75 mg/kg. The treatments significantly improved diabetes-induced decrease in EBF, acetylcholine-mediated vascular relaxation in arterioles that provide circulation to the region of the sciatic nerve, and MNCV. The treatments also reduced the production of superoxide by the aorta and superoxide and peroxynitrite by arterioles that provide circulation to the region of the sciatic nerve. Treating diabetic rats with alpha-lipoic acid prevented the diabetes-induced increase in thiobarbituric acid-reactive substances in serum and significantly improved lens glutathione levels. In contrast, treating diabetic rats with HES-DFO did not prevent diabetes-induced changes of either of these markers of oxidative stress. Diabetes-induced increase in sciatic nerve conjugated diene levels was not improved by treatment with either alpha-lipoic acid or HES-DFO. Treating diabetic rats with alpha-lipoic acid but not HES-DFO partially improved sciatic nerve Na(+)/K(+) ATPase activity and myo-inositol content. The increase in sciatic nerve sorbitol levels in diabetic rats was unchanged by either treatment. These studies suggest that diabetes-induced oxidative stress and the generation of superoxide may be partially responsible for the development of diabetic vascular and neural complications.

Effects of aminoguanidine and desferrioxamine on some vascular and biochemical changes associated with streptozotocin-induced hyperglycaemia in rats

The effects of aminoguanidine (AG; 100 mg x kg(-1)) and desferrioxamine (DFO; 50 mg x kg(-1)) on some vascular and biochemical changes associated with streptozotocin (STZ; 65 mg x kg(-1); i.p.)-induced hyperglycaemia were investigated in rats. Both AG and DFO were administered i.p., once daily, for 14 consecutive days to normal and hyperglycaemic animals. The responsiveness of the isolated aortic rings to phenylephrine (PE) was tested. In addition, biochemical markers for oxidative stress such as plasma levels of lipid peroxides and total thiols, as well as the activities of erythrocytic superoxide dismutase (SOD) and whole blood glutathione peroxidase (GSH-Px) were assessed. Results of the present study indicated that induction of hyperglycaemia was associated with increased aortic ring responsiveness to PE, loss in body weight, increase in urine volume, elevation of plasma total thiols and lipid peroxide levels and elevated SOD and GSH-Px enzymatic activities. Treatment of normal rats with AG reduced the response of their aortae to PE. Furthermore, a profound increase in body weight without any significant change in the measured biochemical parameters was observed. In hyperglycaemic animals, AG tended to normalize the enhanced aortic response to PE and modulated STZ-induced biochemical changes without affecting the elevated plasma glucose level. Treatment of normal rats with DFO reduced the response of their aortae to PE and decreased their body weight without altering any of the chosen biochemical parameters. In hyperglycaemic animals, DFO attenuated the responsiveness of their aortae to PE and at the same time, did not affect the loss in body weight and the elevation of plasma glucose level observed in the hyperglycaemic group. Additionally, DFO normalized the elevated plasma level of total thiols and exerted a modulatory influence on the enhanced activities of SOD and GSH-Px as well as on the increased levels of lipid peroxides. Our data lend further credence for the contribution of oxidative stress in the vascular and biochemical changes associated with STZ-induced hyperglycaemia. It is also apparent that advanced glycosylation end products and nitric oxide might be involved. Until clinical studies prove the efficacy and safety of these drugs, specific agents which could scavenge free radicals and block protein glycosylation seem beneficial as a helpful adjunct to the therapy of diabetes.

Effect of dietary vitamin E supplementation on vascular reactivity of thoracic aorta in streptozotocin-diabetic rats

The present study evaluated the effect of dietary vitamin E supplementation (1,000 mg/kg chow) on the alterations in vascular reactivity of streptozotocin-diabetic aorta of Wistar rats. After 12 weeks of treatment, thoracic aortic rings of rats were mounted in organ baths and contractile responses to phenylephrine and 5-hydroxytryptamine and relaxant responses to acetylcholine, calcium ionophore and sodium nitroprusside were assessed. Plasma vitamin E concentration as measured by HPLC was markedly decreased in diabetic rats and increased with dietary vitamin E supplementation. Induction of diabetes significantly impaired endothelium-dependent relaxations to acetylcholine and calcium ionophore in aortic rings, but did not change endothelium-independent relaxation to sodium nitroprusside. Vitamin E significantly improved the impaired endothelium-dependent relaxations, further it decreased the enhanced contractile response to phenylephrine and 5-hydroxytryptamine in diabetic rings. The mechanical denudation of endothelium or the chemical inhibition of endothelium-dependent relaxation with N(omega)-nitro-L-arginine methyl ester (100 micromol/l) significantly increased phenylephrine contractility in control rings and the rings of diabetic rats treated with vitamin E; such a difference was not observed in diabetic rats fed with normal diet. Liver and lung malondialdehyde concentrations, as an index of lipid peroxidation, were increased in diabetic rats and significantly decreased with vitamin E supplementation. It is concluded that dietary supplementation of vitamin E improved endothelial dysfunction in insulin-dependent model of uncontrolled diabetes, probably decreasing membranal lipid peroxidation.

Temocapril, an angiotensin converting enzyme inhibitor, protects against diabetes-induced endothelial dysfunction

The effect of chronic treatment with the angiotensin converting enzyme inhibitor, temocapril, on prevention of endothelial dysfunction was evaluated in an experimental model of diabetes mellitus. Endothelium-dependent relaxation to acetylcholine was impaired while endothelium-independent relaxation to nitroglycerin was unaltered in diabetic aortic ring segments. Treatment of diabetic animals with temocapril prevented the impaired endothelium-dependent relaxation without altering responses to nitroglycerin. Acetylcholine-induced relaxation was largely due to nitric oxide (NO)-mediated relaxation; however, a small but significant portion of relaxation in aortic rings from temocapril-treated diabetic rats was resistant to inhibition by the nitric oxide synthase (NOS) inhibitor, L-nitroarginine.

Effects of aldose reductase inhibition on responses of the corpus cavernosum and mesenteric vascular bed of diabetic rats

We examined the effects of 2 months of streptozotocin-induced diabetes mellitus in rats on relaxation and contraction of corpus cavernosum and the mesenteric vascular bed in vitro. A further diabetic group was treated from diabetes induction with 10 mg/kg/day of the aldose reductase inhibitor, WAY121509. For corpus cavernosum, maximal acetylcholine-induced relaxation was 35.5% reduced (p < 0.001) by diabetes, and this deficit was completely prevented by WAY121509 treatment. Neither diabetes nor treatment affected contractile responses to field stimulation of noradrenergic nerves; however, nonadrenergic noncholinergic nerve relaxation responses were 32.9% decreased by diabetes and WAY 121509 attenuated this by 84% (p < 0.001). For the mesenteric vascular bed, diabetes depressed maximal endothelium-dependent vasodilation to acetylcholine by 25.2% (p < 0.001), and this was partially (50.6%; p < 0.01) prevented by WAY121509. Nitric oxide synthase blockade revealed endothelium-derived hyperpolarising factor-mediated vasodilation to acetylcholine that was 73.5% (p < 0.001) depressed by diabetes; WAY121509 provided partial (43.4%; p < 0.001) protection. Neither diabetes nor treatment affected endothelium-independent vasorelaxation to the nitric oxide donor, sodium nitroprusside, in corpus cavernosum or mesenteric vessels. Thus the data show protective effects of WAY121509 on nitric oxide-mediated cavernosal vasorelaxation responses and on mesenteric endothelium-derived hyperpolarising factor responses. Together these findings could account for the beneficial effects of aldose reductase inhibition on diabetic complications in experimental models.

Time course of changes in endothelium-dependent and -independent relaxation of chronically diabetic aorta: role of reactive oxygen species

In the present study, the role of reactive oxygen species and the contribution of antioxidant defence in the time course of changes in acetylcholine-stimulated endothelium-dependent and sodium nitroprusside-stimulated endothelium-independent relaxation were investigated in aortic rings isolated from 6-month streptozotocin-diabetic and age-matched control rats. Although there were no significant differences in the degree of the peak relaxations produced by a single administration of acetylcholine (1 microM) or sodium nitroprusside (0.01 microM) between control and diabetic rings, the endothelium-dependent and -independent relaxant responses were more transient and the time required to reach a peak relaxation after addition of acetylcholine was shorter in diabetic vessels. Pretreatment of diabetic vessels with superoxide dismutase (100 U/ml) normalized the recovery phases of endothelium-dependent and -independent relaxations, but had no effect on the peak responses to acetylcholine and sodium nitroprusside. In the presence of diethyldithiocarbamate (5 mM), an inhibitor of superoxide dismutase, the transient nature of the relaxant response to acetylcholine or sodium nitroprusside was more marked and the peak relaxations were inhibited; these effects of diethyldithiocarbamate were more pronounced in diabetic than in control rings. Catalase, 160 U/ml, decreased the peak relaxant response to acetylcholine and accelerated fading of the relaxation in diabetic aorta. Similar results were obtained for control aorta with a higher concentration of catalase (550 U/ml). Pretreatment with 3-amino-1,2,4 triazole (5 mM), a catalase inhibitor, inhibited the peak relaxant response to acetylcholine in diabetic rings. The combination of superoxide dismutase (100 U/ml) plus 3-amino-1,2,4 triazole (5 mM) produced an increase of the transient nature of endothelium-dependent relaxation of diabetic rings greater than that with 3-amino-1,2,4 triazole alone. Neither catalase nor 3-amino-1,2,4 triazole affected the characteristics of sodium nitroprusside-induced relaxation. Desferrioxamine, an inhibitor of hydroxyl radical (.OH) production, or mannitol, a.OH scavenger, had no effect on the characteristics of either acetylcholine- or sodium nitroprusside-induced relaxation in control and diabetic rings. Biochemical measurements revealed an inhibited superoxide dismutase activity in diabetic aorta together with activated catalase. Our findings suggest that, during the chronic phase of streptozotocin-diabetes, excess superoxide (O(2)(. -)) is responsible for the enhanced transient nature of endothelium-dependent and -independent relaxation of aorta via a reduction in bioavailable concentrations of nitric oxide (NO). However, the involvement of hydrogen peroxide (H(2)O(2)) in the establishment of acetylcholine-stimulated relaxation may be increased, which is likely to account for the maintenance of the relaxant effect of acetylcholine in chronically diabetic vessels.

Glycochelates and the etiology of diabetic peripheral neuropathy

People with diabetes are prone to develop peripheral vascular and nerve abnormalities which, in extreme cases, can lead to limb amputations. Although numerous theories have been advanced for these complications, no firm explanation is yet available. Recently, evidence has appeared suggesting that these vascular and nerve abnormalities may involve transition metals; administration of chelators such as desferrioxamine has been shown to prevent or actually reverse slowed peripheral nerve conduction and neuronal blood flow, as well as impaired endothelium-dependent arterial relaxation. Here, we argue that (i) the heavily glycated proteins known to accumulate in people with diabetes gain an increased affinity for transition metals such as iron and copper, (ii) as a result, proteins such as elastin and collagen within the arterial wall-which are known to be particularly heavily glycosylated in diabetes-may accumulate bound metal, especially copper, (iii) the bound metal causes the catalytic destruction of endothelium derived relaxing factor (nitric oxide or a derivative thereof), thereby engendering a state of chronic vasoconstriction. The resulting impairment of blood flow to peripheral nerves restricts the delivery of oxygen and nutrients and, in extremis, nerve death eventuates. If this hypothesis is proved correct, there are important implications for the development of novel pharmaceuticals for the treatment of diabetic peripheral neuropathy.