The effect of alpha-lipoic acid on the neurovascular reflex arc in patients with diabetic neuropathy assessed by capillary microscopy

Impaired dermal microvascular reactivity and implications for diabetic wound formation and healing: an evidence review

Diabetic foot ulcers (DFUs) are among the most consequential and costly complications faced by patients with diabetes and the global healthcare system. Acknowledged risk factors for DFUs include diabetic peripheral neuropathy (DPN), peripheral arterial disease (PAD), microtrauma and foot deformities. Research on additional risk factors for DFUs has recently focused on dysregulated, autonomic vasomotor control in the skin of patients with DPN. In particular, impaired dermal microvascular reactivity (IDMR) with its attendant reduction in nutritive capillary blood flow has been identified as an emerging risk factor. This especially relates to refractory wounds noted in patients without overt PAD signs. In this paper, evidence will be reviewed supporting the evolving understanding of IDMR and its impact on DFU formation and healing. Advances in diagnostic instrumentation driving this research along with the most promising potential therapies aimed at improving microvascular function in the diabetic foot will be discussed in brief.

Bioavailability of an R-α-Lipoic Acid/γ-Cyclodextrin Complex in Healthy Volunteers

R-α-lipoic acid (R-LA) is a cofactor of mitochondrial enzymes and a very strong antioxidant. R-LA is available as a functional food ingredient but is unstable against heat or acid. Stabilized R-LA was prepared through complexation with γ-cyclodextrin (CD), yielding R-LA/CD. R-LA/CD was orally administered to six healthy volunteers and showed higher plasma levels with an area under the plasma concentration-time curve that was 2.5 times higher than that after oral administration of non-complexed R-LA, although the time to reach the maximum plasma concentration and half-life did not differ. Furthermore, the plasma glucose level after a single oral administration of R-LA/CD or R-LA was not affected and no side effects were observed. These results indicate that R-LA/CD could be easily absorbed in the intestine. In conclusion, γ-CD complexation is a promising technology for delivering functional but unstable ingredients like R-LA.

Alpha-Lipoic Acid and Antioxidant Diet Help to Improve Endothelial Dysfunction in Adolescents with Type 1 Diabetes: A Pilot Trial

After evaluating the prevalence of early endothelial dysfunction, as measured by means of reactive hyperemia in adolescents with type 1 diabetes, we started a 6-month, double-blind, randomized trial to test the efficacy of an antioxidant diet (± alpha-lipoic acid supplementation) to improve endothelial dysfunction. Seventy-one children and adolescents, ages 17 ± 3.9 yrs, with type 1 diabetes since 9.5 ± 5.3 yrs, using intensified insulin therapy, were randomized into 3 arms: (a) antioxidant diet 10.000 ORAC + alpha-lipoic acid; (b) antioxidant diet 10.000 ORAC + placebo; (c) controls. BMI, blood pressure, fasting lipid profile, HbA1c, insulin requirement, dietary habits, and body composition were determined in each patient. An antioxidant diet significantly improved endothelial dysfunction when supplemented with alpha-lipoic acid, unlike diet with placebo or controls. A significant reduction in bolus insulin was also observed. We speculate that alpha-lipoic acid might have an antioxidant effect in pediatric diabetes patients by reducing insulin.

Efficacy of α-lipoic acid in diabetic neuropathy

INTRODUCTION

Neuropathy is a serious complication of diabetes. Its management focuses on glycaemic control, multifactorial cardiovascular risk intervention, pathogenesis-oriented therapy, and analgesics where needed.

AREAS COVERED

The objective of this review is assessment of efficacy and safety of α lipoic acid (ALA, also thioctic acid) in pathogenesis-oriented treatment of diabetic neuropathy. The mechanisms of action of ALA in experimental diabetic neuropathy include reduction of oxidative stress along with improvement in nerve blood flow, nerve conduction velocity, and several other measures of nerve function. There is ample evidence from randomised, double-blind, placebo-controlled clinical trials and meta-analyses, suggesting that ALA is efficacious and safe for the diabetic neuropathy, accomplishing clinically meaningful improvements.

EXPERT OPINION

ALA is a valuable therapeutic option for diabetic neuropathy. When compared with currently licensed analgesic drugs, it is better tolerated, has a more rapid onset of action, and improves paraesthesiae, numbness, sensory deficits, and muscle strength in addition to neuropathic pain. In clinical practice, ALA may be chosen in patients with early neuropathic deficits and symptoms, in whom clinical improvement is more likely. ALA should also be considered when comorbidities render other analgesics less appropriate or in the presence of cardiovascular autonomic neuropathy.

Age and gender dependent bioavailability of R- and R,S-α-lipoic acid: a pilot study

Lipoic acid (LA) shows promise as a beneficial micronutrient toward improving elder health. Studies using old rats show that (R)-α-LA (R-LA) significantly increases low molecular weight antioxidants that otherwise decline with age. Despite this rationale for benefiting human health, little is known about age-associated alterations in absorption characteristics of LA, or whether the commercially available racemic mixture of LA (R,S-LA) is equally as bioavailable as the naturally occurring R-enantiomer. To address these discrepancies, a pilot study was performed to establish which form of LA is most effectively absorbed in older subjects relative to young volunteers. Young adults (average age=32 years) and older adults (average age=79 years) each received 500 mg of either R- or R,S-LA. Blood samples were collected for 3h after supplementation. After a washout period they were given the other chiral form of LA not originally ingested. Results showed that 2 out of 6 elder males exhibited greater maximal plasma LA and area under the curve for the R-form of LA versus the racemic mixture. The elder subjects also demonstrated a reduced time to reach maximal plasma LA concentration following R-LA supplementation than for the racemic mixture. In contrast, young males had a tendency for increased bioavailability of R,S-LA. Overall, bioavailability for either LA isoform was much more variable between older subjects compared to young adults. Plasma glutathione levels were not altered during the sampling period. Thus subject age, and potential for varied response, should be considered when determining an LA supplementation regimen.

Effect of alpha lipoic acid on cardiac autonomic dysfunction and platelet reactivity in type 1 diabetes: rationale and design of the AUTOnomic function and platelet REACTivity trial (AUTO-REACT protocol)

BACKGROUND

The aim of this study is to assess the relationship between cardiac autonomic dysfunction and increased platelet reactivity in patients with type 1 diabetes and whether alpha lipoic acid therapy (ALA) might improve both abnormalities in these patients.

METHODS AND MATERIALS

Cardiac autonomic function will be assessed by heart rate variability (HRV) analysis. Platelet reactivity will be investigated by both measuring the aggregation time on the PFA-100 method and flow cytometry. HRV and platelet reactivity will be re-assessed in the patients with depressed HRV after 4 weeks from randomization to ALA or placebo.

DISCUSSION

The cardiovascular autonomic system might play a role in the modulation of platelet reactivity which is increased in diabetes. Within this framework, ALA might be found to exercise antithrombotic effects in addition to its known antioxidants properties.

TRIAL REGISTRATION

Australian Clinical Trials Registry ACTRN 12610000291088.

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.

R-Lipoic Acid Inhibits Mammalian Pyruvate Dehydrogenase Kinase

The four pyruvate dehydrogenase kinase (PDK) and two pyruvate dehydrogenase phosphatase (PDP) isoenzymes that are present in mammalian tissues regulate activity of the pyruvate dehydrogenase complex (PDC) by phosphorylation/dephosphorylation of its pyruvate dehydrogenase (E1) component. The effect of lipoic acids on the activity of PDKs and PDPs was investigated in purified proteins system. R-lipoic acid, S-lipoic acid and R-dihydrolipoic acid did not significantly affect activities of PDPs and at the same time inhibited PDKs to different extents (PDK1>PDK4 approximately PDK2>PDK3 for R-LA). Since lipoic acids inhibited PDKs activity both when reconstituted in PDC and in the presence of E1 alone, dissociation of PDK from the lipoyl domains of dihydrolipoamide acetyltransferase in the presence of lipoic acids is not a likely explanation for inhibition. The activity of PDK1 towards phosphorylation sites 1, 2 and 3 of E1 was decreased to the same extent in the presence of R-lipoic acid, thus excluding protection of the E1 active site by lipoic acid from phosphorylation. R-lipoic acid inhibited autophosphorylation of PDK2 indicating that it exerted its effect on PDKs directly. Inhibition of PDK1 by R-lipoic acid was not altered by ADP but was decreased in the presence of pyruvate which itself inhibits PDKs. An inhibitory effect of lipoic acid on PDKs would result in less phosphorylation of E1 and hence increased PDC activity. This finding provides a possible mechanism for a glucose (and lactate) lowering effect of R-lipoic acid in diabetic subjects.

Pharmacokinetics of different formulations of tioctic (alpha-lipoic) acid in healthy volunteers

This study was designed to evaluate in healthy volunteers plasma and cellular (in erythrocytes) of three formulations of alpha-lipoic acid (ALA) available in Italy with different rates of absorption, two with a claimed high absorption rate (Byodinoral 600 QR, Tiocronal 600 HR) and one with a claimed prolonged absorption rate (Tiobec 600 retard). These formulations were compared with the registered ethic formulation of the compound (Thioctacid 600 mg HR), available in Germany. Area under the curve from time 0 to last measured time (AUC(t)), peak plasma concentration (C(max)) of ALA, and time (T(max) ) at which C(max) was observed were the plasma kinetic parameters measured. Concentration of ALA at different sampling times was the only parameter assessed for erythrocytes. The AUC(t) values were similar for the four formulations of ALA tested. C(max) was significantly higher for Byodinoral 600 QR, Tiocronal 600 HR compared to Thioctacid 600 mg HR or Tiobec 600 retard, whereas T(max) value was significantly shorter for Byodinoral 600 QR in the order by Tiocronal 600 HR, Thioctacid 600 mg HR, and Tiobec 600 retard. ALA concentrations that accumulated in erytrocytes after the administration of the different formulations of the antioxidant are directly proportional to the plasma levels of each formulation. Because antioxidant capabilities of ALA depend on the glutathione regeneration the compound induces in cells, the most rationale approach for eliciting antioxidant activity at the cellular level is probably in the use of a formulation allowing the compound to reach its target at highest concentrations and in the shortest time.

The role of alpha-lipoic acid in diabetic polyneuropathy treatment

Diabetic neuropathy represents late diabetes complications, and diabetes duration and long-term hyperglycemia are the main reasons for polyneuropathy. The goal was to estimate the effects of alpha-lipoic acid on symptoms of diabetic neuropathy after 600 mg i.v. for 3 weeks and 3 months of 300-600 mg of alpha-lipoic acid per os. This study has been designed as a multicentric, in 5-centers in B&H, carried out by 5 physicians with 20 diabetic patients each. Following parameters were monitored in 100 diabetics suffering from Type 1 and Type 2 diabetes, both men and women: diabetes duration, diabetes therapy, duration of polyneuropathy symptoms, height, weight, BMI (body mass index), subjective assessment of patients, objective examinations of physicians and subjective assessment of physicians. 100 diabetics, average age 61,36; oldest 79, youngest 40, suffered from diabetes in average 11,9 years. There were 35 men and 65 women, 16 with Type 1 and 80 with Type 2 diabetes, while 4 patients were not classified. 69 were having insulin therapy and 31 oral hypoglicemics. Shortest diabetic status was less than a year, and longest was 28 years. Average duration of polyneuropathic symptoms was 3,02 years, shortest was less than a year, and the longest was 15 years. Average height was 1,70 m, average weight 76,13 kg, and average BMI 26,51 kg/m2. Significant statistic differences in improvement were recorded (P>0,05) according to Fridman's test for repeated measurements compared to initial findings in assessments: sensory symptoms of polyneuropathy, pain sensations as polyneuropathy symptoms, total score of polyneuropathy symptoms, subjective assessment of patients, subjective findings of physicians, and significant differences were not find (P>0,05) in autonomous and motoric neuropathy. Based on the conducted study, we have concluded that the application of alpha-lipoic acid during 3 months has helped to decrease the symptoms of diabetic neuropathy and in only one case out of 100 included patients there was no subjective improvement after drug application.

[An endogenous dithiol with antioxidant properties: alpha-lipoic acid, potential uses in cardiovascular diseases]

Alpha-Lipoic acid (ALA) is a natural compound, chemically named 1,2-dithiolane-3-pentanoic acid, also referred to as thioctic acid. In humans, ALA is synthetized by the liver and other tissues with high metabolic activity: heart, kidney. ALA is both water and fat soluble and therefore, is widely distributed in both cellular membranes and cytosol. Recently, a greater deal of attention has been given to antioxidant function for ALA and its reduced formed: dihydrolipoic acid (DHLA). ALA scavenges hydroxyl radicals, hypochlorous acid and singlet oxygen. It may also exert antioxidant effects in biological systems through transitional metal chelation. Dihydrolipoic acid has been shown to have antioxidant but also pro-oxidant properties in systems in which hydroxyl radical was generated. ALA/DHLA ratio has the capacity to recycle endogenous antioxidants such as vitamin E. A number of experimental as well as clinical studies point to the usefulness of ALA as a therapeutic agent for such diverse conditions as diabetes, atherosclerosis, insulin resistance, neuropathy, neurodegenerative diseases and ischemia-reperfusion injury. ALA represents a potential agent on the vascular endothelium, recording to ALA/DHLA redox couple is one of the most powerful biological antioxidant systems.

Comparative crossover, randomized, open-label bioequivalence study on the bioequivalence of two formulations of thioctic acid in healthy volunteers

An open-label, randomized, crossover single-dose study, using two periods and two sequences with a washout period of seven days was conducted to assess the comparative bioavailability of thioctic (alpha-lipoic) acid (ALA) 600 mg formulation and that of a reference formulation. Blood samples were collected up to +6 h post dosing, the plasma was separated, and thioctic acid concentrations were determined by high-performance liquid chromatographic method with single mass spectrometry detection (HPLC-MS) and a lower limit of quantification of 190.1 ng/ml. Mean values of the individual C(max) were 1338.6 +/- 751.8 ng/ml and 1215.8 +/- 560.5 ng/ml for the test and reference preparations, respectively. Mean +/- standard deviation (SD) total area under the curve up to the last measurable concentration (AUC(t)) was 3510.9 +/- 1088.6 ng x h/ml for the test formulation and 3563.5 +/- 1374.1 ng x h/ml for the reference formulation. Mean +/- SD total area under the curve (AUC(inf)) was 6925.6 +/- 4045.8 ng x h/ml for the test formulation and 7797.1 +/- 5963.1 ng x h/ml for the reference preparation. Terminal elimination half-life was 5.68 +/- 5.05 h for the test and 6.11 +/- 6.15 h for the reference formulations. Time of maximum concentration (t(max)) was 1.24 +/- 1.23 h for the test and 2.05 +/- 1.21 h for the reference formulations. Ninety percent confidence intervals were comprised within the bioequivalence acceptance criteria (80-125%) for all of the parameters analyzed except t(max). The comparison between males and females showed no significant difference for the two drug treatment.

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.

Thioctic acid for patients with symptomatic diabetic polyneuropathy: a critical review

Diabetic neuropathy represents a major health problem, as it is responsible for substantial morbidity, increased mortality, and impaired quality of life. Near-normoglycemia is now generally accepted as the primary approach to prevention of diabetic neuropathy, but is not achievable in a considerable number of patients. A growing body of evidence suggests that oxidative stress resulting from enhanced free-radical formation and/or defects in antioxidant defense is implicated in the pathogenesis of diabetic neuropathy. Markers of oxidative stress such as superoxide anion and peroxynitrite production are increased in diabetic patients in relation to the severity of polyneuropathy. In experimental diabetic neuropathy, oxygen free-radical activity in the sciatic nerve is increased, and treatment with thioctic acid, a potent lipophilic antioxidant, results in prevention or improvement of the diabetes-induced neurovascular and metabolic abnormalities in various organ systems. Pharmacodynamic studies have shown that thioctic acid favorably influences the vascular abnormalities of diabetic polyneuropathy such as impaired microcirculation, increased indices of oxidative stress, and increased levels of markers for vascular dysfunction, such as thrombomodulin, albuminuria, and nuclear factor-kappaB. Thus far, seven controlled randomized clinical trials of thioctic acid in patients with diabetic neuropathy have been completed (Alpha-Lipoic Acid in Diabetic Neuropathy [ALADIN I-III], Deutsche Kardiale Autonome Neuropathie [DEKAN], Oral Pilot [ORPIL], Symptomatic Diabetic Neuropathy [SYDNEY], Neurological Assessment of Thioctic Acid in Neuropathy [NATHAN] II) using different study designs, durations of treatment, doses, sample sizes, and patient populations. Recently, a comprehensive analysis was undertaken of trials with comparable designs that met specific eligibility criteria for a meta-analysis to obtain a more precise estimate of the efficacy and safety of thioctic acid (600mg intravenously for 3 weeks) in diabetic patients with symptomatic polyneuropathy. This meta-analysis included the largest sample of diabetic patients (n = 1258) ever to have been treated with a single drug or class of drugs to reduce neuropathic symptoms, and confirmed the favorable effects of thioctic acid based on the highest level of evidence (Class Ia: evidence from meta-analyses of randomized, controlled trials). The following conclusions can be drawn from these trials: (i) short-term treatment for 3 weeks using intravenous thioctic acid 600 mg/day reduces the chief symptoms of diabetic polyneuropathy to a clinically meaningful degree; (ii) this effect on neuropathic symptoms is accompanied by an improvement of neuropathic deficits, suggesting potential for the drug to favorably influence underlying neuropathy; (iii) oral treatment for 4-7 months tends to reduce neuropathic deficits and improve cardiac autonomic neuropathy; and (iv) clinical and postmarketing surveillance studies have revealed a highly favorable safety profile of the drug. Based on these findings, a pivotal long-term multicenter trial of oral treatment with thioctic acid (NATHAN I) is being conducted in North America and Europe to investigate effects on progression of diabetic polyneuropathy, using a clinically meaningful and reliable primary outcome measure that combines clinical and neurophysiological assessment.

Loss of pain perception in diabetes is dependent on a receptor of the immunoglobulin superfamily

Molecular events that result in loss of pain perception are poorly understood in diabetic neuropathy. Our results show that the receptor for advanced glycation end products (RAGE), a receptor associated with sustained NF-kappaB activation in the diabetic microenvironment, has a central role in sensory neuronal dysfunction. In sural nerve biopsies, ligands of RAGE, the receptor itself, activated NF-kappaBp65, and IL-6 colocalized in the microvasculature of patients with diabetic neuropathy. Activation of NF-kappaB and NF-kappaB-dependent gene expression was upregulated in peripheral nerves of diabetic mice, induced by advanced glycation end products, and prevented by RAGE blockade. NF-kappaB activation was blunted in RAGE-null (RAGE(-/-)) mice compared with robust enhancement in strain-matched controls, even 6 months after diabetes induction. Loss of pain perception, indicative of long-standing diabetic neuropathy, was reversed in WT mice treated with soluble RAGE. Most importantly, loss of pain perception was largely prevented in RAGE(-/-) mice, although they were not protected from diabetes-induced loss of PGP9.5-positive plantar nerve fibers. These data demonstrate, for the first time to our knowledge, that the RAGE-NF-kappaB axis operates in diabetic neuropathy, by mediating functional sensory deficits, and that its inhibition may provide new therapeutic approaches.

Diabetic cardiomyopathy: evidence, mechanisms, and therapeutic implications

The presence of a diabetic cardiomyopathy, independent of hypertension and coronary artery disease, is still controversial. This systematic review seeks to evaluate the evidence for the existence of this condition, to clarify the possible mechanisms responsible, and to consider possible therapeutic implications. The existence of a diabetic cardiomyopathy is supported by epidemiological findings showing the association of diabetes with heart failure; clinical studies confirming the association of diabetes with left ventricular dysfunction independent of hypertension, coronary artery disease, and other heart disease; and experimental evidence of myocardial structural and functional changes. The most important mechanisms of diabetic cardiomyopathy are metabolic disturbances (depletion of glucose transporter 4, increased free fatty acids, carnitine deficiency, changes in calcium homeostasis), myocardial fibrosis (association with increases in angiotensin II, IGF-I, and inflammatory cytokines), small vessel disease (microangiopathy, impaired coronary flow reserve, and endothelial dysfunction), cardiac autonomic neuropathy (denervation and alterations in myocardial catecholamine levels), and insulin resistance (hyperinsulinemia and reduced insulin sensitivity). This review presents evidence that diabetes is associated with a cardiomyopathy, independent of comorbid conditions, and that metabolic disturbances, myocardial fibrosis, small vessel disease, cardiac autonomic neuropathy, and insulin resistance may all contribute to the development of diabetic heart disease.

Diabetic neuropathies

Diabetic neuropathy (DN) is a common complication of diabetes that often is associated with considerable morbidity and mortality. The epidemiology and natural history of DN is clouded with uncertainty because of confusion regarding the definition and measurement of this disorder. The recent resurgence of interest in the vascular hypothesis, oxidative stress, the neurotrophic hypothesis,and the possibility of the role of autoimmunity has opened up new avenues of investigation for therapeutic intervention. The ability to manage successfully the many different manifestations of diabetic neuropathy depends ultimately on success in uncovering the pathogenic processes underlying this disorder.

Treatment of symptomatic diabetic polyneuropathy with the antioxidant alpha-lipoic acid: a meta-analysis

AIMS

To determine the efficacy and safety of 600 mg of alpha-lipoic acid given intravenously over 3 weeks in diabetic patients with symptomatic polyneuropathy.

METHODS

We searched the database of VIATRIS GmbH, Frankfurt, Germany, for clinical trials of alpha-lipoic acid according to the following prerequisites: randomized, double-masked, placebo-controlled, parallel-group trial using alpha-lipoic acid infusions of 600 mg i.v. per day for 3 weeks, except for weekends, in diabetic patients with positive sensory symptoms of polyneuropathy which were scored by the Total Symptom Score (TSS) in the feet on a daily basis. Four trials (ALADIN I, ALADIN III, SYDNEY, NATHAN II) comprised n=1258 patients (alpha-lipoic acid n=716; placebo n=542) met these eligibility criteria and were included in a meta-analysis based on the intention-to-treat principle. Primary analysis involved a comparison of the differences in TSS from baseline to the end of i.v. Treatment between the groups treated with alpha-lipoic acid or placebo. Secondary analyses included daily changes in TSS, responder rates (> or =50% improvement in TSS), individual TSS components, Neuropathy Impairment Score (NIS), NIS of the lower limbs (NIS-LL), individual NIS-LL components, and the rates of adverse events.

RESULTS

After 3 weeks the relative difference in favour of alpha-lipoic acid vs. placebo was 24.1% (13.5, 33.4) (geometric mean with 95% confidence interval) for TSS and 16.0% (5.7, 25.2) for NIS-LL. The responder rates were 52.7% in patients treated with alpha-lipoic acid and 36.9% in those on placebo (P<0.05). On a daily basis there was a continuous increase in the magnitude of TSS improvement in favour of alpha-lipoic acid vs. placebo which was noted first after 8 days of treatment. Among the individual components of the TSS, pain, burning, and numbness decreased in favour of alpha-lipoic acid compared with placebo, while among the NIS-LL components pin-prick and touch-pressure sensation as well as ankle reflexes were improved in favour of alpha-lipoic acid after 3 weeks. The rates of adverse events did not differ between the groups.

CONCLUSIONS

The results of this meta-analysis provide evidence that treatment with alpha-lipoic acid (600 mg/day i.v.) over 3 weeks is safe and significantly improves both positive neuropathic symptoms and neuropathic deficits to a clinically meaningful degree in diabetic patients with symptomatic polyneuropathy.

Neurovascular disease, antioxidants and glycation in diabetes

People with diabetes are ten to fifteen times more likely to have a lower limb amputation (LLA) than non-diabetic individuals. Fifteen percent of people with diabetes will develop a foot ulcer during their lifetime, the rate of major amputation amongst diabetic individuals continues to rise, foot problems remain the commonest reason for diabetes-related hospitalisation and recurrence rates in patients with previous foot ulcers are 50% or more. Hyperglycaemia-induced oxidative stress has been shown to result in decreased nerve conduction velocity, and decreased endoneural blood flow-both precursors for neuropathy. Vitamin antioxidants have been shown to be effective therapy in experimental models in reducing free radical species and inhibiting the oxidative process in diabetes subjects. Little work has been published, however, regarding the dietary use of antioxidants from foods, and their specific effects on neurovascular disease and glycation within the diabetes population. Aetiological and prevention studies with dietary antioxidants from foods aimed at the complex nature of foot problems in diabetes are needed.

Molecular aspects of lipoic acid in the prevention of diabetes complications

Alpha-lipoic acid (LA) and its reduced form, dihydrolipoic acid, are powerful antioxidants. LA scavenges hydroxyl radicals, hypochlorous acid, peroxynitrite, and singlet oxygen. Dihydrolipoic acid also scavenges superoxide and peroxyl radicals and can regenerate thioredoxin, vitamin C, and glutathione, which in turn can recycle vitamin E. There are several possible sources of oxidative stress in diabetes including glycation reactions, decompartmentalization of transition metals, and a shift in the reduced-oxygen status of the diabetic cells. Diabetics have increased levels of lipid hydroperoxides, DNA adducts, and protein carbonyls. Available data strongly suggest that LA, because of its antioxidant properties, is particularly suited to the prevention and/or treatment of diabetic complications that arise from an overproduction of reactive oxygen and nitrogen species. In addition to its antioxidant properties, LA increases glucose uptake through recruitment of the glucose transporter-4 to plasma membranes, a mechanism that is shared with insulin-stimulated glucose uptake. Further, recent trials have demonstrated that LA improves glucose disposal in patients with type II diabetes. In experimental and clinical studies, LA markedly reduced the symptoms of diabetic pathologies, including cataract formation, vascular damage, and polyneuropathy. To develop a better understanding of the preventative and therapeutic potentials of LA, much of the current interest is focused on elucidating its molecular mechanisms in redox dependent gene expression.

Pathophysiology of oxidative stress in diabetes mellitus

Oxidative stress is believed to play an important role, albeit not fully recognized, in the development of vascular complications in diabetes mellitus (DM) particularly type 2. In the majority of studies, attention was focused on lipid oxidation, specifically on that of low-density lipoproteins (LDLs). More recent investigations have revealed that it is not only the lipid but also the apolipoprotein moiety of LDL that becomes oxidatively modified resulting in the formation of insoluble aggregates. Consequently, it has been documented that LDL aggregation was due to the hydroxyl radical-induced dityrosine crosslinking between apo B monomers. In DM patients with atherosclerotic complications, intravascular fibrous deposits were shown to contain, in addition to oxidized LDL, a fibrin-like material (FLM). This material is immunologically identical to fibrin that is normally formed as a result of intravascular activation of the blood coagulation cascade. Although DM patients with vascular disease display increased concentration of plasma fibrinogen (Fbg), the precursor of fibrin, no markers of full blown activation of blood coagulation could be found.

Diabetic neuropathy--a continuing enigma

In this article we will review the clinical signs and symptoms of diabetic somatic polyneuropathy (DPN), its prevalence and clinical management. Staging and classification of DPN will be exemplified by various staging paradigms of varied sophistication. The results of therapeutic clinical trials will be summarized. The pathogenesis of diabetic neuropathy reviews an extremely complex issue that is still not fully understood. Various recent advances in the understanding of the disease will be discussed, particularly with respect to the differences between neuropathy in the two major types of diabetes. The neuropathology and natural history of diabetic neuropathy will be discussed pointing out the heterogeneities of the disease. Finally, the various prospective therapeutic avenues will be dealt with and discussed.