The role of alpha-lipoic acid in diabetic polyneuropathy treatment

The Role of Alpha-lipoic Acid Supplementation in the Prevention of Diabetes Complications: A Comprehensive Review of Clinical Trials

Alpha-lipoic acid (ALA) is a substantial antioxidant in the prevention of diabetes and diabetes complications. It can regenerate other antioxidants like vitamin E, vitamin C, Coenzyme Q10 and glutathione and is often known as a universal antioxidant. Antioxidants play a role in diabetes treatment due to hyperglycemia-induced stimulation of the polyol pathway and formation of advanced glycation end products (AGE) and reactive oxygen species (ROS). Clinical trials examining alpha-lipoic acid supplementation on diabetic neuropathy, nephropathy, cardiomyopathy and erectile dysfunction display positive results, particularly in pain amelioration in neuropathy, asymmetric dimethylarginine reductions in nephropathy and improved oscillatory potential and contrast sensitivity in retinopathy. In diabetic cardiomyopathy (DCM), ALA offers protection through inhibition of NF-kB activation, reduction of fas-ligand and decrease in matrix metalloproteinase-2. This comprehensive review summarises and provides an understanding of the importance of alpha- lipoic acid supplementation to prevent diabetes complications.

Effects of alpha-lipoic acid on expression of iron transport and storage proteins in BV-2 microglia cells

BACKGROUND

The antioxidant properties of alpha-lipoic acid (ALA) are associated with its ability to reduce iron in cells and tissues, which is partly due to its inhibiting effect on iron uptake from transferrin and its promoting effect on iron deposition into ferritin. However, the relevant mechanisms are unknown.

METHODS

We therefore investigated the effects of ALA on the expression of transferrin receptor 1 (TfR1), divalent metal transporter 1 (DMT1), ferroportin 1 (Fpn1) and ferritin in BV-2 microglia cells.

RESULTS

We demonstrated that ALA significantly inhibited DMT1 expression, lowered ferritin-light-chain (Ft-L) and ferritin-heavy-chain (Ft-H) content, and had no effect on TfR1 and Fpn1 in BV-2 microglia cells. This indicated that the inhibiting effect of ALA on DMT1 might be one of the causes of the ALA-induced reduction in cellular transferrin-bound-iron uptake. We also demonstrated that ALA enhanced DMT1 and TfR1 expression in ferric ammonium citrate (FAC)-treated cells. FAC treatment led to a significant increase in Ft-L, Ft-H and Fpn1, and pre-treatment with ALA resulted in a further increase in the contents of Ft-L and Ft-H but not Fpn1 in cells.

CONCLUSIONS

ALA could up-regulate TfR1, DMT1 and ferritin expression when iron is increased outside of the cell, promoting iron deposition into ferritin by increasing cell iron uptake, and then reducing free iron both inside and outside of the cell.

Current experience in testing mitochondrial nutrients in disorders featuring oxidative stress and mitochondrial dysfunction: rational design of chemoprevention trials

An extensive number of pathologies are associated with mitochondrial dysfunction (MDF) and oxidative stress (OS). Thus, mitochondrial cofactors termed "mitochondrial nutrients" (MN), such as α-lipoic acid (ALA), Coenzyme Q10 (CoQ10), and l-carnitine (CARN) (or its derivatives) have been tested in a number of clinical trials, and this review is focused on the use of MN-based clinical trials. The papers reporting on MN-based clinical trials were retrieved in MedLine up to July 2014, and evaluated for the following endpoints: (a) treated diseases; (b) dosages, number of enrolled patients and duration of treatment; (c) trial success for each MN or MN combinations as reported by authors. The reports satisfying the above endpoints included total numbers of trials and frequencies of randomized, controlled studies, i.e., 81 trials testing ALA, 107 reports testing CoQ10, and 74 reports testing CARN, while only 7 reports were retrieved testing double MN associations, while no report was found testing a triple MN combination. A total of 28 reports tested MN associations with "classical" antioxidants, such as antioxidant nutrients or drugs. Combinations of MN showed better outcomes than individual MN, suggesting forthcoming clinical studies. The criteria in study design and monitoring MN-based clinical trials are discussed.

Diabetes and alpha lipoic Acid

Diabetes mellitus is a multi-faceted metabolic disorder where there is increased oxidative stress that contributes to the pathogenesis of this debilitating disease. This has prompted several investigations into the use of antioxidants as a complementary therapeutic approach. Alpha lipoic acid, a naturally occurring dithiol compound which plays an essential role in mitochondrial bioenergetic reactions, has gained considerable attention as an antioxidant for use in managing diabetic complications. Lipoic acid quenches reactive oxygen species, chelates metal ions, and reduces the oxidized forms of other antioxidants such as vitamin C, vitamin E, and glutathione. It also boosts antioxidant defense system through Nrf-2-mediated antioxidant gene expression and by modulation of peroxisome proliferator activated receptors-regulated genes. ALA inhibits nuclear factor kappa B and activates AMPK in skeletal muscles, which in turn have a plethora of metabolic consequences. These diverse actions suggest that lipoic acid acts by multiple mechanisms, many of which have only been uncovered recently. In this review we briefly summarize the known biochemical properties of lipoic acid and then discussed the oxidative mechanisms implicated in diabetic complications and the mechanisms by which lipoic acid may ameliorate these reactions. The findings of some of the clinical trials in which lipoic acid administration has been tested in diabetic patients during the last 10 years are summarized. It appears that the clearest benefit of lipoic acid supplementation is in patients with diabetic neuropathy.

Role of Drp1, a key mitochondrial fission protein, in neuropathic pain

While oxidative stress has been implicated in small-fiber painful peripheral neuropathies, antioxidants are only partially effective to treat patients. We have tested the hypothesis that Drp1 (dynamin-related protein 1), a GTPase that catalyzes the process of mitochondrial fission, which is a mechanism central for the effect and production of reactive oxygen species (ROS), plays a central role in these neuropathic pain syndromes. Intrathecal administration of oligodeoxynucleotide antisense against Drp1 produced a decrease in its expression in peripheral nerve and markedly attenuated neuropathic mechanical hyperalgesia caused by HIV/AIDS antiretroviral [ddC (2',3'-dideoxycytidine)] and anticancer (oxaliplatin) chemotherapy in male Sprague Dawley rats. To confirm the role of Drp1 in these models of neuropathic pain, as well as to demonstrate its contribution at the site of sensory transduction, we injected a highly selective Drp1 inhibitor, mdivi-1, at the site of nociceptive testing on the dorsum of the rat's hindpaw. mdivi-1 attenuated both forms of neuropathic pain. To evaluate the role of Drp1 in hyperalgesia induced by ROS, we demonstrated that intradermal hydrogen peroxide produced dose-dependent hyperalgesia that was inhibited by mdivi-1. Finally, mechanical hyperalgesia induced by diverse pronociceptive mediators involved in inflammatory and neuropathic pain-tumor necrosis factor α, glial-derived neurotrophic factor, and nitric oxide-was also inhibited by mdivi-1. These studies provide support for a substantial role of mitochondrial fission in preclinical models of inflammatory and neuropathic pain.

Clinical Approach to the Treatment of Painful Diabetic Neuropathy

Painful neuropathy is a common and often progressive complication of diabetes. Patients frequently report symptoms of tingling, burning, lancinating pain, hyperesthesia and allodynia. The natural history of the disease may vary from intermittent mild symptoms to severe chronic daily pain; the latter is often associated with diminished quality of life. There are a variety of pharmaceutical agents from different medicinal categories available for the symptomatic treatment of painful diabetic neuropathy, however selecting an agent is often challenging given the breadth of choices and lack of consistent guidelines. As a result, many patients remain untreated or undertreated.This article presents a practical clinical approach to the treatment of pain in diabetic neuropathy. Recommendations for first, second and third line medications are based on specific evidence for the treatment of painful diabetic neuropathy as well as safety, tolerability, drug interactions and cost. Additional topics of discussion include breakthrough pain, opioid use and topical therapies. This review does not comprehensively discuss all possible treatments for painful neuropathy, but provides a systematic approach designed to guide clinicians in tailoring therapies to the individual patient.