Medically reviewed on March 19, 2018
Scientific Name(s): 1,2-dithiolane-3-pentanoic acid ; 1,2-dithiolane-3-valeric acid ; 6,8-thioctic acid ; alpha-lipoic acid ; 5-(1,2-dithiolan-3-yl) valeric acid
Common Name(s): Alpha-lipoic acid , lipoic acid , thioctic acid , acetate replacing factor , biletan , lipoicin , thioctacid , thioctan
Alpha-lipoic acid (ALA) has been used as an antioxidant for the treatment of diabetes and HIV. It also has been used for cancer, liver ailments, and various other conditions.
Oral dosage of alpha-lipoic acid given in numerous clinical studies ranges from 300 to 1,800 mg daily. It also is given intravenously at similar daily dosages.
Contraindications have not yet been determined.
Information regarding safety and efficacy in pregnancy and lactation is lacking.
None well documented.
No adverse reactions have been reported.
Lipoic acid (LA) is a fat-soluble, sulfur-containing, vitamin-like antioxidant. It is not a true vitamin because it can be synthesized in the body and is not necessary in the diet of animals. LA functions in the same manner as many B-complex vitamins. Good sources of LA are yeast and liver. 1 , 2 Other sources include spinach, broccoli, potatoes, kidney, heart, and skeletal muscle. 3
In the 1930s, it was found that a certain potato growth factor was necessary for growth of some bacteria. 3 In 1951, a fat-soluble coenzyme factor was discovered from lactic acid bacteria. Researchers isolated and identified alpha-lipoic acid (ALA) and found it to be an important growth factor for many bacteria and protozoa. 4 It is the most active form of lipoic acid.
LA is a naturally occurring dithiol compound that functions as a cofactor for many mitochondrial enzymes involved in energy metabolism. Endogenous LA is bound to proteins and is involved in acyl-group transfer reactions. Both in vivo and in vitro studies demonstrate that LA exhibits the ability to scavenge free radicals, chelate redox-active transition metals, regulate the detoxification of heavy metals, and modulate various signal transduction pathways in physiological and pathological conditions. 5
LA is an 8-carbon sulfur containing fatty acid that has the International Union of Pure and Applied Chemistry name of 5-([ 3 R]-dithiolan-3-yl) pentanoic acid, and is also known as thioctic acid, ALA, and lipoate. It is synthesized de novo from octanoic acid by lipoic acid synthase in most prokaryotic and eukaryotic microorganisms, plants, and animals. LA can also be absorbed from the diet, and natural food sources, as well as from nutritional supplements. 5
Two liopate enatiomers ( R and S ) exist as a consequence of a chiral center at the C6 location; however only R -LA is endogenously synthesized. 5
LA can be oxidized and reduced, whereby the disulfide-containing ring is opened to form dihydrolipoic acid (DHLA) by the mitochondrial enzyme lipoamide dehydrogenase. LA/DHLA is recognized as an essential cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and other mitochondrial enzymes, thus making LA a necessary cofactor in catabolic and metabolic processes. 1 , 5
Numerous studies have demonstrated the ability of LA to stimulate various signal transduction pathways and activate transcription factors including activation of G-protein coupled receptors and adenosine 3',5'-cyclic phosphate production, mitogen activated protein kinase signaling cascade, insulin signaling, and protein kinase B and nuclear factor kappa B. 5
LA interacts with and recycles endogenous glutathione (GSH).Pharmacokinetics
Pharmacokinetics and bioavailability of both enantiomers of ALA have been studied in 12 subjects. 6
ALA appears to be readily absorbed orally and converted to its reduced form, DHLA, in many tissues of the body. The effects of ALA and DHLA are present both intra- and extracellularly. R -ALA is bound to a protein where it functions as an essential cofactor for several mitochondrial enzyme complexes in energy production and the catabolism of alpha-keto acids and amino acids. 7 Nutritional supplements of ALA are generally made up of R -ALA alone or a racemic mixture of the 2 isomers. Human studies using the oral racemic mixture have demonstrated plasma concentration of R -ALA to be higher than that of S -ALA. 6 , 8 One study found that following oral administration, the maximum plasma concentrations of R -ALA were double that of S -ALA. 8
Uses and Pharmacology
The pharmacology of ALA has been studied in the chelation of transition and heavy metals, CNS conditions, oxidation, diabetes, AIDS, cancer, and liver ailments.CNS diseases
Increasing evidence shows that mitochondrial dysfunction due to the oxidation of lipids, proteins, and nucleic acids plays an important role in brain aging and neurodegenerative diseases such as Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and Huntington disease. Mitochondria provide energy for basic metabolic processes, produce oxidants as inevitable by-products, and decay with age, impairing cellular metabolism and leading to cellular decline. Various mechanisms of LA's positive effects on cognitive function have been suggested, including improvement of memory-related signaling pathways, reduction of oxidative stress, and improvement of mitochondrial function. ALA may also restore the activity of acetylcholinesterase and Na + , K + -ATPase. The activity of acetylcholinesterase was decreased in the cerebral corex, cerebellum, striatum, hippocampus, and hypothalamus in aged rats, while administration of LA reversed the decrease in the activity in the discrete brain regions. Treatment with LA also protected cortical neurons against cytotoxicity induced by beta-amyloid or hydrogen peroxide.
A combination of nonsteroidal anti-inflammatory drugs and appropriate levels and types of micronutrients may be more effective than the individual agents in the prevention and treatment of Alzheimer disease. Based on epidemiological, laboratory, and clinical studies, using the optimal combinations of LA and other mitochondrial nutrients to target mitochondrial dysfunction may provide an effective strategy in delaying aging, and preventing and treating cognitive dysfunction. 9Multiple sclerosis
LA has been studied as an effective therapy in a rat model of multiple sclerosis and experimental autoimmune encephalomyelitis. ALA dose dependently prevented the development of clinical signs in this model. LA has a protective effect on encephalomyelitis development not only by affecting the migratory capacity of monocytes, but also by stabilizing the blood-brain barrier. 10
Mouse studies have shown that LA suppresses the migration of T cells across the blood-brain barrier in the spinal cord. Additionally, LA inhibited expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by CNS endothelial cells in experimental autoimmune encephalomyelitis. LA was also effective in preventing experimental autoimmune encephalomyelitis development in a dose-dependent fashion. It was shown that reactive oxygen species are important mediators of injury in experimental autoimmune encephalomyelitis and that generation of reactive oxygen species can be decreased by LA. LA also decreased the migration of monocytes across the blood-brain barrier, which correlated with clinical improvement seen in experimental autoimmune encephalomyelitis. In other studies, LA decreased the phagocytosis of myelin by macrophages by inhibiting the generation of reactive oxygen species. 5Clinical data
A placebo-controlled phase 1 clinical trail of 37 subjects studied the effects of oral racemic LA in multiple sclerosis. Subjects were randomly assigned to 4 groups, including placebo. The other 3 groups received LA 600 mg twice a day, 1,200 mg once a day, or 1,200 mg twice a day, for 14 days. The study found LA to be generally well tolerated, but peak plasma levels of LA varied among subjects. As would be expected in a short duration study, there was no change in disability caused by multiple sclerosis as assessed by the Expanded Disability Status Score. The study found that stable blood levels of LA required a dose of 1,200 mg, and treatment was associated with changes in serum immunologic markers associated with T-cell migration into the CNS. Longer-duration trials with a larger number of multiple sclerosis subjects are needed to establish the ability of LA to decrease disease activity. 5Alzheimer disease
A number of animal studies have demonstrated that ALA improves age-associated cognitive dysfunction associated with neurodegenerative diseases. ALA improved cognitive function in healthy older mice, as well as longer-term memory of aged female nuclear magnetic resonance imaging mice. ALA also demonstrated improvement with cognitive function in senescence-accelerated mice and in chemically-induced, aging-accelerated mice. ALA improved hippocampal-dependent memory deficits of Tg2576 mice, a transgenic model of cerebral amyloidosis associated with Alzheimer disease. It also showed improvement of cognitive function in X-irradiation-induced memory impaired in mice. 9Clinical data
Small studies utilizing LA in Alzheimer disease have been reported. Nine patients with Alzheimer-related dementias were given LA 600 mg for an average of 337 days. The treatment led to stabilization of cognitive function as measured by the Mini-Mental State Examination and the Alzheimer Disease Assessment Scale, cognitive subscale (ADAS-cog). 11 Though the study was small and not randomized, it suggests that treatment with LA is a possible neuroprotective therapy option for Alzheimer disease and related dementias.
In a follow-up study, analysis was extended to 37 patients over an observation period of 49 months. The study confirmed that LA treatment slowed the progression rate of dementia dramatically, compared with the rate in untreated patients or patients receiving cholinesterase inhibitors. 12Hearing loss
Age-related hearing loss is the most common form of hearing impairment in adults. As levels of ALA have been found to decrease with age, dietary supplementation with this compound may moderate age-related alterations in mitochondria.Animal data
A study in DBA mice found that those fed ALA exhibited preserved hearing during early-onset, age-related hearing loss, possibly caused by decreased reactive oxygen species production and enhanced antioxidant status in aged mice. Although hearing preservation was time dependent in that mice fed ALA sooner after birth had superior hearing than those fed ALA later in life, the latter mice had less hearing loss than control mice, perhaps indicating that feeding less ALA relatively late in life still has beneficial effects. 13Clinical data
Research reveals no clinical data for the use of ALA for hearing loss.Wound management
Research reveals no animal data for the use of ALA for wound management.Clinical data
A study in 20 patients investigated the use of ALA supplementation with hyperbaric oxygen therapy for the management of chronic wounds. Down regulation of inflammatory cytokines and growth factors affecting matrix metalloproteinase expression was observed. Disruption of the positive autocrine feedback loop that maintains the chronic wound state promotes progression of the healing process. 14Burning mouth syndrome
Burning mouth syndrome (BMS) refers to chronic oral pain diagnosed in the absence of any visible mucosal abnormality and where psychogenic factors are a possible cause.Animal data
Research reveals no animal data for the use of ALA for BMS.Clinical data
Sixty patients with BMS were randomized to receive either ALA 200 mg 3 times daily or placebo for 2 months. Statistically significant improvement was seen with ALA (97%) compared with placebo (40%) over 2 months without any notable adverse reactions. Follow-up after 12 months showed that improvement achieved with ALA was maintained completely in 73% of patients, whereas all patients receiving placebo who had improved during the course of the study had deteriorated to some extent. 15Oxidation
Mechanism of action
ALA's antioxidant properties have been demonstrated. It has the ability to chelate metals and to scavenge free radicals. 16
ALA is easily absorbed and transported across cell membranes; thus, free radical protection occurs both inside and outside of cells. It is water- and fat-soluble, which makes it more effective against a broader range of free radicals than vitamin C (water-soluble) and vitamin E (fat-soluble) alone. 2 ALA administration also increases intracellular levels of glutathione, an important antioxidant. 17Animal data
ALA regenerates or recycles antioxidant vitamins C and E 3 . However, in one report it had no affect on vitamin E tissue concentration in animals, contradicting this effect. 18
The body routinely converts ALA to DHLA, a more effective antioxidant. Both forms can quench peroxynitrite radicals, which are responsible in part for heart, lung, and neurological disease, as well as for inflammation. 19 In oxidative stress models, such as ischemia, reperfusion injury, and radiation injury, ALA was beneficial. 20 , 21Clinical data
Research reveals no clinical data regarding the use of ALA as an antioxidant.Diabetes
ALA has been shown to be beneficial in types 1 and 2 diabetes, preventing various pathologies associated with the disease, such as reperfusion injury, macular degeneration, cataracts, and neuropathy. 2 , 3 , 20 , 22
Overproduction of reactive oxygen species in mitochondria induced by hyperglycemia is central to the pathogenesis of endothelial damage in diabetes. Several experimental and clinical trials have shown that antioxidants fail to protect against diabetic vascular damage. However, R -ALA is thought to be an exception. 23Animal data
ALA reduced diabetic neuropathy in a rat model in a dose-dependent manner. In part, the mechanism was suggested to be a reduction of the effects of oxidative stress. 22
The retina is markedly sensitive to oxygen free radical damage, due to its high levels of polyunsaturated lipids. A study in mice tested the effect of LA on the retina after a short diabetic insult. The results showed that after 3 weeks of diabetes, malondialdehyde (MDA) levels in the retina were increased when compared with controls and that LA was able to prevent this effect. MDA is a well-accepted oxidative stress marker for pathological processes. 24
Another study in rats has shown that treatment with R -ALA reduced oxidative stress, preventing microvascular damage through normalized pathways downstream of mitochondrial overproduction of reactive oxygen species and preserving pericyte coverage of retinal capillaries, which may provide additional endothelial protection. 23
LA may prevent formation of experimentally induced cataracts by increasing glutathione, ascorbate, and vitamin E levels. In turn, LA restores glutathione, peroxidase, catalase, and ascorbate free radical-reductase activity. The effect was seen in the lenses of 60% of rats treated with L-buthionnine sulfoximine, an inhibitor of glutathione synthesis. 25
The efficacy of ALA in delaying the development and progression of cataracts in rats with streptozotocin-induced diabetes has also been demonstrated. 26
ALA improves the diabetic condition by facilitating more efficient conversion of sugar into energy, therefore improving blood sugar metabolism. 2
A study investigated the efficacy of ALA in preventing diabetes mellitus in diabetes-prone obese rats. At 40 weeks, glycosuria occurred in 78% of untreated rats compared with none of the ALA treated animals. Compared with results in untreated rats, ALA reduced body weight and protected pancreatic beta-cells from destruction. ALA also reduced triglyceride accumulation in skeletal muscle and pancreatic islets. 27Clinical data
In 13 noninsulin-dependent diabetes mellitus patients, ALA increased insulin-stimulated glucose disposal. The metabolic clearance rate for glucose rose 50% in the treated group compared with the control group. 28 ALA improves blood flow to peripheral nerves and stimulates regeneration of nerve fibers. 2 In a German study evaluating patients with autonomic nervous system damage due to diabetes, treatment with ALA 800 mg/day was compared with placebo. After 4 months, sympathetic systems showed improvement and autonomic nerve disorders decreased in the ALA group. 29
In general, antioxidants may lead to regression of diabetic complications. When ALA was compared with the antioxidant vitamin E, results failed to justify the higher cost of ALA over less expensive and equally effective nutritional antioxidants. 2
In numerous studies, ALA has improved signs and symptoms of diabetic neuropathy. In a meta-analysis of 4 placebo-controlled studies that randomized more than 1,200 patients, ALA 600 mg/day improved the total symptom score in patients with diabetic neuropathy. 30 Both pain and burning were improved in the ALA group as compared with those receiving placebo. The disadvantage of ALA in this meta-analysis was that it had to be given intravenously (IV). In one study, there was no difference in symptoms between patients administered oral ALA or placebo, after both groups had received an initial 3 weeks of IV treatment. 31 A later study used oral doses of ALA 1.8 g/day or less. This study suggested that ALA may be effective for alleviating some neuropathic symptoms (stabbing and burning pain). 32HIV and AIDS
Patients with HIV have a compromised antioxidant defense system, which may benefit from ALA's antioxidant effect. 2Mechanism of action
Several reports have suggested that impaired antioxidant defenses, particularly glutathione deficiency, may play a role in the immunopathogenesis of HIV infection. Glutathione is the major redox buffering thiol within cells and a central molecule for lymphocytic function. It is necessary for T-cell activation, interleukin-2-dependent proliferation, and antibody/cell-mediated cytotoxicity. Both HIV-infected and AIDs patients manifest depressed systemic glutathione levels. Because several immunologic functions relevant to HIV infection are dependent on adequate intracellular total glutathione balance, glutathione-replenishing compounds have been suggested in the treatment of HIV infection. 33Animal data
ALA suppressed HIV replication in cultured cells and enhanced helper T cells in mice. ALA inhibits replication of HIV by reducing the activity of reverse transcriptase, the enzyme responsible for manufacturing the virus from the DNA of lymphocytes. 2 In another report, ALA inhibited activation of nuclear factor kappa-B, which is involved in AIDS progression. 34Clinical data
A small pilot study was conducted administering ALA 150 mg 3 times daily to 10 HIV-infected patients. ALA increased glutathione in all patients and vitamin C in most patients. In addition, it improved the T-helper lymphocyte to T-helper suppressor cell ratio in 6 patients. 2
Another study was carried out in 33 HIV-infected patients with a history of highly active antiretroviral treatment (HAART) unresponsiveness (ie, viral load greater than 10,000 copies per cm 3 despite HAART), to test the hypothesis of whether supplementation with ALA would increase blood total glutathione and improve immune T-cell function. After 6 months of treatment, the mean whole blood total glutathione level in the ALA-treated group increased significantly ( P = 0.03) compared with placebo. Lymphocyte proliferative response was either stabilized or enhanced in the ALA-treated group, depending on the mitogen used. In response to the CD3 monoclonal antibody, lymphocyte proliferation decreased approximately 66% in the placebo group over 6 months, compared with approximately a 3.7-fold enhancement in the anti-CD3 response in the ALA-treatment group. No difference was seen between the ALA-treatment group and the placebo group for viral load, CD4, or CD8 count. 33Cancer
There is limited information available concerning ALA's role in cancer. Its mechanism of action and anticarcinogenic and cytoprotective effects have been addressed. 35Animal data
ALA administration, in conjunction with cyclophosphamide, lowered the toxic effects of this anticancer drug when tested in animals. 36Clinical data
Research reveals no clinical data regarding the use of ALA in cancer treatment.Chelation of transition and heavy metals
Under physiological conditions, metal ions such as iron, copper, and zinc are important and necessary cofactors for normal function of many proteins. Transition metal deficiency or excess can lead to or affect the progression of diseases. Both ALA and DHLA have been shown to chelate metal ions by forming stable complexes with the ions. Consequently, ALA may have therapeutic potential in transition metal-mediated cellular toxicity in diseases. In addition, LA and DHLA contribute to heavy metal detoxification. More recently, it has been suggested that LA may be useful to protect against and reverse arsenic-induced cell toxicity. 5Reduction of drug toxicity
The effect of ALA on cyclophosphamide-induced testicular toxicity has been investigated in rats. Two groups of male rats were administered cyclophosphamide 15 mg/kg once a week for 10 weeks to induce testicular toxicity. One of these groups received LA treatment (35 mg/kg) 24 hours before cyclophosphamide administration once a week for 10 weeks.
The rats exposed to cyclophosphamide showed an increase in testicular reactive oxygen species along with a decrease in cellular thiol levels. The activities of testicular marker enzymes such as gamma-glutamyl transferase, beta-glucuronidase, acid phosphatase, and alkaline phosphatase were increased, whereas the activities of sorbitol dehydrogenase and lactate dehydrogenase-X were decreased in animals treated with cyclophosphamide. However, those pretreated with LA showed normal marker enzyme patterns and normal levels of reactive oxygen species and thiols. Testicular protection with LA is further supported by normal histological findings, compared with those of cyclophosphamide-treated rats. 37Cyclosporine
Cyclosporine A is associated with a variety of adverse reactions, the most important being nephrotoxicity. It has been speculated that different mechanisms are responsible for cyclosporine-induced nephrotoxicity, with oxidant stress playing a central role as a pathogenetic factor. Cyclosporine A-induced nephrotoxicity was assessed in terms of increased serum marker enzyme, alkaline phosphatase, acid phosphatase, and lactate dehydrogenase activity. An apparent rise in the activities of N-acetyl-beta-D-glucosaminidase, beta-glucuronidase, and cathepsin D activity was seen in the renal tissue of rats given cyclosporine A, which was reversed upon treatment with LA. Cyclosporine A administration elevated lipid peroxidation along with abnormal levels of enzymic and nonenzymic antioxidants in the kidney. LA administration improved renal function by bringing about a decrease in peroxidative levels and an increase in antioxidant status. 38Acetaminophen
The potential protective effect of ALA against acetaminophen-induced hepatotoxicity and nephrotoxicity has been investigated. Pretreatment of rats with oral ALA 100 mg/kg protected against hepatotoxicity and nephrotoxicity induced by an acute oral toxic dose of acetaminophen 2.5g/kg, as assessed by biochemical measurements and histopathological examination. Similarly, daily treatment of rats with a smaller dose of ALA 25 mg/kg concurrently with a smaller toxic dose of acetaminophen 750 mg/kg for 1 week protected against acetaminophen-induced hepatotoxicity and nephrotoxicity. 39Clinical data
Research reveals no clinical data for ALA in reducing drug toxicity.Other drug effects
Cyclophosphamide is a potent alkylating agent used in cancer chemotherapy and immunosuppression. A study in adult male Wistar rats demonstrated that administration of cyclophosphamide resulted in abnormal elevation of serum lipids. In cardiac tissue, the levels of free cholesterol, esterified cholesterol, and triglycerides were increased, while the levels of phospholipids and free fatty acids were reduced. Serum low density lipoprotein and very low density lipoprotein cholesterol increased, while high density lipoprotein cholesterol decreased when compared with controls. LA supplementation reverted these abnormalities in the lipid levels and activities of lipid metabolizing enzymes to near healthy levels after cyclophosphamide administration. 40
Animal studies have also demonstrated that the combination of LA and glyceryl trinitrate can efficiently counteract glyceryl trinitrate tolerance. 41
ALA and vitamin E have shown synergistic effects against lipid peroxidation by oxidant radicals in several pathological conditions, such as thromboembolic stroke model in rats from neurological functions, glial reactivity, and neuronal remodeling. 9Other uses
Oral dosage of ALA given in clinical studies ranges from 300 to 1,800 mg daily. It is also given IV at similar daily dosages. 29 R -LA is more efficiently absorbed and utilized by the body than the racemate, and lower doses may be effective. 42
Information regarding safety and efficacy in pregnancy and lactation is lacking.
None well documented.
No adverse reactions from ALA supplementation have been reported in either animal or human studies, even with large doses or extended use. 2 Its use in diabetes may warrant a reduction in insulin or other oral diabetic medications. Close monitoring of blood sugar levels must be performed. In addition, ALA use may spare vitamins C and E, as well as other antioxidants. 2
Allergic skin conditions are among the few reported adverse reactions of LA administration in humans.
A case report of insulin autoimmune syndrome was reported in a woman who regularly took ALA 200 mg/day. After discontinuing ALA, hypoglycemia disappeared and the titer of anti-insulin antibodies was markedly decreased. 43
The LD 50 of ALA is 400 to 500 mg/kg after oral dosage in dogs 44 ; however, lower dosages (20 mg/kg) given intraperitoneally to severely thiamine-deficient rats proved fatal. The lethal effect was prevented when thiamine was administered with LA. 45 Anecdotal evidence suggests ALA may be hepatotoxic to cats at doses greater than 20 mg daily.
Long-term toxicity of ALA was tested in Sprague-Dawley rats. Rats were fed either 20, 60, or 180 mg/kg/day of ALA for 24 months. No difference was seen between the control animals and treated animals at 20 or 60 mg/kg/day. In treatment groups, mortality was slightly lower than in the control group. The only notable findings in rats of both sexes dosed at 180 mg/kg/day was a reduction in food intake relative to the controls and a concomitant decrease in body weight. The level at which no adverse reactions were observed is considered to be 60 mg/kg/day. In addition, the study demonstrated that ALA had no carcinogenic potential in rats at doses up to 180 mg/kg/day. 46
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