Effect of fidarestat and alpha-lipoic acid on diabetes-induced epineurial arteriole vascular dysfunction

Combination therapy is it in the future for successfully treating peripheral diabetic neuropathy?

In 2022, the Center for Disease Control and Prevention reported that 11.3% of the United States population, 37.3 million people, had diabetes and 38% of the population had prediabetes. A large American study conducted in 2021 and supported by many other studies, concluded that about 47% of diabetes patients have peripheral neuropathy and that diabetic neuropathy was present in 7.5% of patients at the time of diabetes diagnosis. In subjects deemed to be pre-diabetes and impaired glucose tolerance there was a wide range of prevalence estimates (interquartile range (IQR): 6%-34%), but most studies (72%) reported a prevalence of peripheral neuropathy ≥10%. There is no recognized treatment for diabetic peripheral neuropathy (DPN) other than good blood glucose control. Good glycemic control slows progression of DPN in patients with type 1 diabetes but for patients with type 2 diabetes it is less effective. With obesity and type 2 diabetes at epidemic levels the need of a treatment for DPN could not be more important. In this article I will first present background information on the "primary" mechanisms shown from pre-clinical studies to contribute to DPN and then discuss mono- and combination therapies that have demonstrated efficacy in animal studies and may have success when translated to human subjects. I like to compare the challenge of finding an effective treatment for DPN to the ongoing work being done to treat hypertension. Combination therapy is the recognized approach used to normalize blood pressure often requiring two, three or more drugs in addition to lifestyle modification to achieve the desired outcome. Hypertension, like DPN, is a progressive disease caused by multiple mechanisms. Therefore, it seems likely as well as logical that combination therapy combined with lifestyle adjustments will be required to successfully treat DPN.

How inflammation dictates diabetic peripheral neuropathy: An enlightening review

BACKGROUND

Diabetic peripheral neuropathy (DPN) constitutes a debilitating complication associated with diabetes. Although, the past decade has seen rapid developments in understanding the complex etiology of DPN, there are no approved therapies that can halt the development of DPN, or target the damaged nerve. Therefore, clarifying the pathogenesis of DPN and finding effective treatment are the crucial issues for the clinical management of DPN.

AIMS

This review is aiming to summary the current knowledge on the pathogenesis of DPN, especially the mechanism and application of inflammatory response.

METHODS

We systematically summarized the latest studies on the pathogenesis and therapeutic strategies of diabetic neuropathy in PubMed.

RESULTS

In this seminal review, the underappreciated role of immune activation in the progression of DPN is scrutinized. Novel insights into the inflammatory regulatory mechanisms of DPN have been unearthed, illuminating potential therapeutic strategies of notable clinical significance. Additionally, a nuanced examination of DPN's complex etiology, including aberrations in glycemic control and insulin signaling pathways, is presented. Crucially, an emphasis has been placed on translating these novel understandings into tangible clinical interventions to ameliorate patient outcomes.

CONCLUSIONS

This review is distinguished by synthesizing cutting-edge mechanisms linking inflammation to DPN and identifying innovative, inflammation-targeted therapeutic approaches.

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.

Effect of mitoquinone (Mito-Q) on neuropathic endpoints in an obese and type 2 diabetic rat model

This study sought to determine whether the addition of mitoquinone (Mito-Q) in the diet is an effective treatment for peripheral neuropathy in animal models of diet-induced obesity (pre-diabetes) and type 2 diabetes. Unlike other anti-oxidative stress compounds investigated as a treatment for peripheral neuropathy, Mito-Q specifically targets mitochondria. Although mito-Q has been shown to reduce oxidative stress generated by mitochondria there have been no studies performed of the effect of Mito-Q on peripheral neuropathy induced by diet-induced obesity or type 2 diabetes. Diet-induced obese (12 weeks after high fat diet) or type 2 diabetic rats (12 weeks of high fat diet and 4 weeks after the onset of hyperglycemia) were treated via the diet with Mito-Q (0.93 g/kg diet) for 12 weeks. Afterwards, glucose utilization, vascular reactivity of epineurial arterioles to acetylcholine and peripheral neuropathy related endpoints were examined. The addition of Mito-Q to the diets of obese and diabetic rats improved motor and/or sensory nerve conduction velocity, cornea and intraepidermal nerve fibre density, cornea sensitivity and thermal nociception. Surprisingly, treating obese and diabetic rats with Mito-Q did not improve glucose utilization or vascular reactivity by epineurial arterioles to acetylcholine. These studies imply that mitochondrial dysfunction contributes to peripheral neuropathy in animal models of pre-diabetes and late-stage type 2 diabetes. However, improvement in peripheral neuropathy following treatment with Mito-Q was not associated with improvement in glucose utilization or vascular reactivity of epineurial arterioles to acetylcholine.

Early vs. late intervention of high fat/low dose streptozotocin treated C57Bl/6J mice with enalapril, α-lipoic acid, menhaden oil or their combination: Effect on diabetic neuropathy related endpoints

We have previously demonstrated that enalapril, α-lipoic acid and menhaden (fish) oil has potential as a treatment for diabetic peripheral neuropathy. In this study we sought to determine the efficacy of these treatments individually or in combination on multiple neuropathic endpoints in a high fat fed low dose streptozotocin treated mouse, a model of type 2 diabetes, following early or late intervention. Four or twelve weeks after the onset of hyperglycemia, diabetic mice were treated with enalapril, α-lipoic acid, menhaden oil or their combination for 12 weeks. Afterwards, endpoints including glucose tolerance, motor and sensory nerve conduction velocity, thermal nociception, and intraepidermal and cornea nerve fiber density was determined. Glucose clearance was impaired in diabetic mice and significantly improved only with combination treatment and early intervention. Diabetes caused steatosis, slowing of motor and sensory nerve conduction velocity, thermal hypoalgesia and reduction in intraepidermal and cornea nerve fiber density. Treating diabetic mice with enalapril, α-lipoic acid or menhaden oil partially protected diabetic mice from these deficits, whereas the combination of these three treatments was more efficacious following early or late intervention. These studies suggest that a combination therapy may be more effective for treating neural complications of type 2 diabetes.

Effect of combination therapy consisting of enalapril, α-lipoic acid, and menhaden oil on diabetic neuropathy in a high fat/low dose streptozotocin treated rat

We have previously demonstrated that treating diabetic rats with enalapril, an angiotensin converting enzyme (ACE) inhibitor, α-lipoic acid, an antioxidant, or menhaden oil, a natural source of omega-3 fatty acids can partially improve diabetic peripheral neuropathy. In this study we sought to determine the efficacy of combining these three treatments on vascular and neural complications in a high fat fed low dose streptozotocin treated rat, a model of type 2 diabetes. Rats were fed a high fat diet for 8 weeks followed by a 30 mg/kg dose of streptozotocin. Eight weeks after the onset of hyperglycemia diabetic rats were treated with a combination of enalapril, α-lipoic acid and menhaden oil. Diabetic rats not receiving treatment were continued on the high fat diet. Glucose clearance was impaired in diabetic rats and significantly improved with treatment. Diabetes caused steatosis, elevated serum lipid levels, slowing of motor and sensory nerve conduction, thermal hypoalgesia, reduction in intraepidermal nerve fiber profiles, decrease in cornea sub-basal nerve fiber length and corneal sensitivity and impairment in vascular relaxation to acetylcholine and calcitonin gene-related peptide in epineurial arterioles of the sciatic nerve. Treating diabetic rats with the combination of enalapril, α-lipoic acid and menhaden oil reversed all these deficits to near control levels except for motor nerve conduction velocity which was also significantly improved compared to diabetic rats but remained significantly decreased compared to control rats. These studies suggest that a combination therapeutic approach may be most effective for treating vascular and neural complications of type 2 diabetes.

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.

Systemic administration of the antioxidant/iron chelator α-lipoic acid protects against light-induced photoreceptor degeneration in the mouse retina

PURPOSE

Oxidative stress and inflammation have key roles in the light damage (LD) model of retinal degeneration as well as in age-related macular degeneration (AMD). We sought to determine if lipoic acid (LA), an antioxidant and iron chelator, protects the retina against LD.

METHODS

Balb/c mice were treated with LA or control saline via intraperitoneal injection, and then were placed in constant cool white light-emitting diode (LED) light (10,000 lux) for 4 hours. Retinas were evaluated at several time points after LD. Photoreceptor apoptosis was assessed using the TUNEL assay. Retinal function was analyzed via electroretinography (ERG). Retinal degeneration was assessed after LD by optical coherence tomography (OCT), TUNEL analysis, and histology. The mRNAs of several oxidative stress, inflammation, and iron-related genes were quantified by quantitative PCR (qPCR).

RESULTS

The LD resulted in substantial photoreceptor-specific cell death. Dosing with LA protected photoreceptors, decreasing the numbers of TUNEL-positive photoreceptors and increasing the number of surviving photoreceptors. The retinal mRNA levels of genes indicating oxidative stress, inflammation, and iron accumulation were lower following LD in mice treated with LA than in control mice. The ERG analysis demonstrated functional protection by LA.

CONCLUSIONS

Systemic LA is protective against light-induced retinal degeneration. Since this agent already has proven protective in other retinal degeneration models, and is safe and protective against diabetic neuropathy in patients, it is worthy of consideration for a human clinical trial against retinal degeneration or AMD.

Nutrient excess and altered mitochondrial proteome and function contribute to neurodegeneration in diabetes

Diabetic neuropathy is a major complication of diabetes that results in the progressive deterioration of the sensory nervous system. Mitochondrial dysfunction has been proposed to play an important role in the pathogenesis of the neurodegeneration observed in diabetic neuropathy. Our recent work has shown that mitochondrial dysfunction occurs in dorsal root ganglia (DRG) sensory neurons in streptozotocin (STZ) induced diabetic rodents. In neurons, the nutrient excess associated with prolonged diabetes may trigger a switching off of AMP kinase (AMPK) and/or silent information regulator T1 (SIRT1) signaling leading to impaired peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1α) expression/activity and diminished mitochondrial activity. This review briefly summarizes the alterations of mitochondrial function and proteome in sensory neurons of STZ-diabetic rodents. We also discuss the possible involvement of AMPK/SIRT/PGC-1α pathway in other diabetic models and different tissues affected by diabetes.

Mitochondrial dysfunction in diabetes: from molecular mechanisms to functional significance and therapeutic opportunities

Given their essential function in aerobic metabolism, mitochondria are intuitively of interest in regard to the pathophysiology of diabetes. Qualitative, quantitative, and functional perturbations in mitochondria have been identified and affect the cause and complications of diabetes. Moreover, as a consequence of fuel oxidation, mitochondria generate considerable reactive oxygen species (ROS). Evidence is accumulating that these radicals per se are important in the pathophysiology of diabetes and its complications. In this review, we first present basic concepts underlying mitochondrial physiology. We then address mitochondrial function and ROS as related to diabetes. We consider different forms of diabetes and address both insulin secretion and insulin sensitivity. We also address the role of mitochondrial uncoupling and coenzyme Q. Finally, we address the potential for targeting mitochondria in the therapy of diabetes.

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.

Treatment of streptozotocin-induced diabetic rats with AVE7688, a vasopeptidase inhibitor: effect on vascular and neural disease

In epineurial arterioles, acetylcholine-mediated vascular relaxation is mediated by nitric oxide and endothelium-derived hyperpolarizing factor (EDHF), and both mechanisms are impaired by diabetes. The mediator responsible for the effect of EDHF is unknown. In epineurial arterioles, C-type natriuretic peptide (CNP) has properties consistent with EDHF-like activity. Epineurial arterioles express CNP, and exogenous CNP causes a concentration-dependent vascular relaxation. In streptozotocin-induced diabetic rats, CNP-mediated vascular relaxation in epineurial arterioles is decreased. Since CNP may be a regulator of vascular function, a vasopeptidase inhibitor may be an effective treatment for diabetes-induced vascular and neural disease. Vasopeptidase inhibitors inhibit ACE activity and neutral endopeptidase, which degrades natriuretic peptides. Streptozotocin-induced diabetic rats were treated with AVE7688 (450 mg/kg in the diet), a vasopeptidase inhibitor, for 8-10 weeks after 4 weeks of untreated diabetes. Treatment of diabetic rats corrected the diabetes-induced decrease in endoneurial blood flow, significantly improved motor and sensory nerve conduction velocity, prevented the development of hypoalgesia in the hind paw, and reduced superoxide and nitrotyrosine levels in epineurial arterioles. The diabetes-induced decrease in acetylcholine-mediated vascular relaxation by epineurial arterioles was significantly improved with treatment. These studies suggest that vasopeptidase inhibitors may be an effective approach for the treatment of diabetic vascular and neural dysfunction.

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.

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.

alpha-Lipoic acid prevents the increase in atherosclerosis induced by diabetes in apolipoprotein E-deficient mice fed high-fat/low-cholesterol diet

Considerable evidence indicates that hyperglycemia increases oxidative stress and contributes to the increased incidence of atherosclerosis and cardiovascular complications in diabetic patients. To examine the effect of alpha-lipoic acid, a potent natural antioxidant, on atherosclerosis in diabetic mice, 3-month-old apolipoprotein (apo) E-deficient (apoE(-/-)) mice were made diabetic by administering streptozotocin (STZ). At 4 weeks after starting the STZ administration, a high-fat diet with or without alpha-lipoic acid (1.65 g/kg) was given to the mice and to nondiabetic apoE(-/-) controls. At 20 weeks, markers of oxidative stress were significantly lower in both the diabetic apoE(-/-) mice and their nondiabetic apoE(-/-) controls with alpha-lipoic acid supplement than in those without it. Remarkably, alpha-lipoic acid completely prevented the increase in plasma total cholesterol, atherosclerotic lesions, and the general deterioration of health caused by diabetes. These protective effects of alpha-lipoic acid were accompanied by a reduction of plasma glucose and an accelerated recovery of insulin-producing cells in the pancreas, suggesting that part of its effects are attributable to protecting pancreatic beta-cells from damage. Our results suggest that dietary alpha-lipoic acid is a promising protective agent for reducing cardiovascular complications of diabetes.

Aldose reductase pathway inhibition improved vascular and C-fiber functions, allowing for pressure-induced vasodilation restoration during severe diabetic neuropathy

Pressure-induced vasodilation, a neurovascular mechanism relying on the interaction between mechanosensitive C-fibers and vessels, allows skin blood flow to increase in response to locally nonnociceptive applied pressure that in turn may protect against pressure ulcers. We expected that severe neuropathy would dramatically affect pressure-induced vasodilation in diabetic mice, and we aimed to determine whether pressure-induced vasodilation alteration could be reversed in 8-week diabetic mice. Control and diabetic mice received no treatment or sorbinil, an aldose reductase inhibitor, or alagebrium, an advanced glycation end product breaker, the last 2 weeks of diabetes. Laser Doppler flowmetry was used to evaluate pressure-induced vasodilation and endothelium-dependent vasodilation after iontophoretic delivery of acetylcholine (ACh). We assessed the nervous function with measurements of motor nerve conduction velocity (MNCV) as well as the C-fiber-mediated nociception threshold. Pressure-induced vasodilation, endothelial response, C-fiber threshold, and MNCV were all altered in 8-week diabetic mice. None of the treatments had a significant effect on MNCV. Although sorbinil and alagebrium both restored ACh-dependent vasodilation, sorbinil was the sole treatment to restore the C-fiber threshold as well as pressure-induced vasodilation development. Therefore, the inhibition of aldose reductase pathway by sorbinil improved vascular and C-fiber functions that allow pressure-induced vasodilation restoration that could limit neuropathic diabetic cutaneous pressure ulcers.

Aldose reductase inhibition counteracts nitrosative stress and poly(ADP-ribose) polymerase activation in diabetic rat kidney and high-glucose-exposed human mesangial cells

Both increased aldose reductase (AR) activity and oxidative/nitrosative stress have been implicated in the pathogenesis of diabetic nephropathy, but the relation between the two factors remains a subject of debate. This study evaluated the effects of AR inhibition on nitrosative stress and poly(ADP-ribose) polymerase (PARP) activation in diabetic rat kidney and high-glucose-exposed human mesangial cells. In animal experiments, control (C) and streptozotocin-diabetic (D) rats were treated with/without the AR inhibitor fidarestat (F, 16 mg kg(-1) day(-1)) for 6 weeks starting from induction of diabetes. Glucose, sorbitol, and fructose concentrations were significantly increased in the renal cortex of D vs C (p < 0.01 for all three comparisons), and sorbitol pathway intermediate, but not glucose, accumulation, was completely prevented in D + F. F at least partially prevented diabetes-induced increase in kidney weight as well as nitrotyrosine (NT, a marker of peroxynitrite-induced injury and nitrosative stress), and poly(ADP-ribose) (a marker of PARP activation) accumulation, assessed by both immunohistochemistry and Western blot analysis, in glomerular and tubular compartments of the renal cortex. In vitro studies revealed the presence of both AR and PARP-1 in human mesangial cells, and none of these two variables were affected by high glucose or F treatment. Nitrosylated and poly(ADP-ribosyl)ated proteins (Western blot analysis) accumulated in cells cultured in 30 mM D-glucose (vs 5.55 mM glucose, p < 0.01), but not in cells cultured in 30 mM L-glucose or 30 mM D-glucose plus 10 microM F. AR inhibition counteracts nitrosative stress and PARP activation in the diabetic renal cortex and high-glucose-exposed human mesangial cells. These findings reveal new beneficial properties of the AR inhibitor F and provide the rationale for detailed studies of F on diabetic nephropathy.

Low-dose poly(ADP-ribose) polymerase inhibitor-containing combination therapies reverse early peripheral diabetic neuropathy

Poly(ADP-ribose) polymerase (PARP) inhibition has recently been identified as a novel approach to treatment of experimental peripheral diabetic neuropathy (PDN). However, long-term inhibition of PARP, an enzyme involved in DNA repair, can potentially result in premature aging, loss of genome stability, and other side effects. This study evaluated potential synergistic interactions between low doses of the potent and specific PARP inhibitor 1,5-isoquinolinediol (ISO) and one of two vasodilators, the ACE inhibitor lisinopril (LIS) and the beta2-adrenoceptor agonist salbutamol (SAL) in the model of early PDN. Control and streptozotocin (STZ)-induced diabetic rats were treated with either ISO plus LIS or ISO plus SAL for 2 weeks after an initial 2 weeks without treatment. ISO (intraperitoneally) and LIS and SAL (both in the drinking water) were used in subtherapeutic doses, resulting in a minor correction of diabetes-associated sciatic motor and hind-limb digital sensory nerve conduction deficits when administered as monotherapies. Both combination treatments corrected endoneurial blood flow and vascular conductance deficits in STZ-induced diabetic rats. ISO plus SAL corrected all other changes of PDN, i.e., motor nerve conduction velocity (MNCV) and sensory nerve conduction velocity (SNCV) deficits as well as thermal and mechanical hyperalgesia. With ISO plus LIS, no significant correction of MNCV was observed, and the effect on thermal hyperalgesia was quite modest. SNCV and mechanical hyperalgesia were corrected. In vitro studies in human endothelial and Schwann cells showed early accumulation of poly(ADP-ribosyl)ated proteins (Western blot analysis) in response to high glucose, thus suggesting the importance of PARP activation in human PDN. In conclusion, low-dose PARP inhibitor-containing combination therapies may constitute a new approach for treatment of PDN.