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PubMed1997

The pharmacology of the antioxidant lipoic acid.

1. Lipoic acid is an example of an existing drug whose therapeutic effect has been related to its antioxidant activity. 2. Antioxidant activity is a relative concept: it depends on the kind of oxidative stress and the kind of oxidizable substrate (e.g., DNA, lipid, protein). 3. In vitro, the final antioxidant activity of lipoic acid is determined by its concentration and by its antioxidant properties. Four antioxidant properties of lipoic acid have been studied: its metal chelating capacity, its ability to scavenge reactive oxygen species (ROS), its ability to regenerate endogenous antioxidants and its ability to repair oxidative damage. 4. Dihydrolipoic acid (DHLA), formed by reduction of lipoic acid, has more antioxidant properties than does lipoic acid. Both DHLA and lipoic acid have metal-chelating capacity and scavenge ROS, whereas only DHLA is able to regenerate endogenous antioxidants and to repair oxidative damage. 5. As a metal chelator, lipoic acid was shown to provide antioxidant activity by chelating Fe2+ and Cu2+; DHLA can do so by chelating Cd2+. 6. As scavengers of ROS, lipoic acid and DHLA display antioxidant activity in most experiments, whereas, in particular cases, pro-oxidant activity has been observed. However, lipoic acid can act as an antioxidant against the pro-oxidant activity produced by DHLA. 7. DHLA has the capacity to regenerate the endogenous antioxidants vitamin E, vitamin C and glutathione. 8. DHLA can provide peptide methionine sulfoxide reductase with reducing equivalents. This enhances the repair of oxidatively damaged proteins such as alpha-1 antiprotease. 9. Through the lipoamide dehydrogenase-dependent reduction of lipoic acid, the cell can draw on its NADH pool for antioxidant activity additionally to its NADPH pool, which is usually consumed during oxidative stress. 10. Within drug-related antioxidant pharmacology, lipoic acid is a model compound that enhances understanding of the mode of action of antioxidants in drug therapy.

Animals↗
PubMed2001

Do mammalian cells synthesize lipoic acid? Identification of a mouse cDNA encoding a lipoic acid synthase located in mitochondria.

Lipoic acid is a coenzyme essential to the activity of enzymes such as pyruvate dehydrogenase, which play important roles in central metabolism. However, neither the enzymes responsible for biosynthesis nor the biosynthetic event of lipoic acid has been reported in mammalian cells. In this study, a mouse mLIP1 cDNA for lipoic acid synthase has been identified. We have shown that the cDNA encodes a lipoic acid synthase by its ability to complement a mutant of Escherichia coli defective in lipoic acid synthase and that mLIP1 is targeted into the mitochondria. These findings suggest that mammalian cells are able to synthesize lipoic acid in mitochondria.

Amino Acid Sequence↗
PubMed1980

Influence of thioctic acid (alpha-lipoic acid) on N-nitroso-diethylamine-induced carcinogenesis in male sprague-dawley rats.

Male Sprague-Dawley rats received 10 mg/kg body weight of N-nitroso-diethylamine by gavage twice weekly for life (group 1). An additional daily application of thioctic acid (alpha-lipoic acid) in drinking water (45 mg/kg body weight/day) (group 2) and 180 mg/kg body weight/day (group 3) did not significantly influence tumor frequencies, induction times and histology of the induced liver and esophageal tumors. A postulated enhancing mechanism on tumor development due to thioctic acid treatment could not be demonstrated.

Animals↗
PubMed1999

Treatment of symptomatic diabetic polyneuropathy with the antioxidant alpha-lipoic acid: a 7-month multicenter randomized controlled trial (ALADIN III Study). ALADIN III Study Group. Alpha-Lipoic Acid in Diabetic Neuropathy.

OBJECTIVE: To evaluate the efficacy and safety of alpha-lipoic acid given intravenously, followed by oral treatment in type 2 diabetic patients with symptomatic polyneuropathy. RESEARCH DESIGN AND METHODS: In a multicenter randomized double-blind placebo-controlled trial (Alpha-Lipoic Acid in Diabetic Neuropathy [ALADIN] III Study), 509 outpatients were randomly assigned to sequential treatment with 600 mg alpha-lipoic acid once daily intravenously for 3 weeks, followed by 600 mg alpha-lipoic acid three times a day orally for 6 months (A-A; n = 167); 600 mg alpha-lipoic acid once daily intravenously for 3 weeks, followed by placebo three times a day orally for 6 months (A-P; n = 174); and placebo once daily intravenously for 3 weeks, followed by placebo three times a day orally for 6 months (P-P; n = 168). Outcome measures included the Total Symptom Score (TSS) for neuropathic symptoms (pain, burning, paresthesias, and numbness) in the feet, and the Neuropathy Impairment Score (NIS). Data analysis was based on the intention to treat. RESULTS: No significant differences between the groups were noted for the demographic variables and the nerve function parameters at baseline. The TSS in the feet decreased from baseline to day 19 (median [range]) by -3.7 (-12.6 to 5.0) points in the group given alpha-lipoic acid intravenously and by -3.0 (-12.3 to 8.0) points in the placebo group (P = 0.447), but the area under curve on a daily basis was significantly smaller in the active as compared with the placebo group (85.6 [0-219] vs. 95.9 [5.5-220]); P = 0.033). After 7 months, the changes in the TSS from baseline were not significantly different between the three groups studied, which could be due to increasing intercenter variability in the TSS during the trial. The NIS decreased after 19 days by -4.34+/-0.35 points (mean +/- SEM) in A-A and A-P and -3.49+/-0.58 points in P-P (P = 0.02 for alpha-lipoic acid versus placebo) and after 7 months by -5.82+/-0.73 points in A-A, -5.76+/-0.69 points in A-P, and -4.37+/-0.83 points in P-P (P = 0.09 for A-A vs. P-P). The rates of adverse events were not different between the groups throughout the study. CONCLUSIONS: These findings indicate that a 3-week intravenous treatment with alpha-lipoic acid, followed by a 6-month oral treatment, had no effect on neuropathic symptoms distinguishable from placebo to a clinically meaningful degree, possibly due to increasing intercenter variability in symptom scoring during the study. However, this treatment was associated with a favorable effect on neuropathic deficits without causing significant adverse reactions. Long-term trials that focus on neuropathic deficits rather than symptoms as the primary criterion of efficacy are needed to see whether oral treatment with alpha-lipoic acid over several years may slow or reverse the progression of diabetic neuropathy.

Administration, Oral↗
PubMed2005

Irbesartan and lipoic acid improve endothelial function and reduce markers of inflammation in the metabolic syndrome: results of the Irbesartan and Lipoic Acid in Endothelial Dysfunction (ISLAND) study.

BACKGROUND: The metabolic syndrome is associated with increased angiotensin II activity, induction of a proinflammatory and oxidative state, and endothelial dysfunction. We evaluated the ability of irbesartan, an angiotensin receptor blocker, and lipoic acid, an antioxidant, to affect endothelial function and inflammation in patients with the metabolic syndrome. METHODS AND RESULTS: We randomized 58 subjects with the metabolic syndrome in a double-blinded manner to irbesartan 150 mg/d (n=14), lipoic acid 300 mg/d (n=15), both irbesartan and lipoic acid (n=15), or matching placebo (n=14) for 4 weeks. Endothelium-dependent and -independent flow-mediated vasodilation was determined under standard conditions. Plasma levels of interleukin-6, plasminogen activator-1, and 8-isoprostane were measured. After 4 weeks of therapy, endothelium-dependent flow-mediated vasodilation of the brachial artery was increased by 67%, 44%, and 75% in the irbesartan, lipoic acid, and irbesartan plus lipoic acid groups, respectively, compared with the placebo group. Treatment with irbesartan and/or lipoic acid was associated with statistically significant reductions in plasma levels of interleukin-6 and plasminogen activator-1. In addition, treatment with irbesartan or irbesartan plus lipoic acid decreased 8-isoprostane levels. No significant changes in blood pressure were noted in any of the study groups. CONCLUSIONS: Administration of irbesartan and/or lipoic acid to patients with the metabolic syndrome improves endothelial function and reduces proinflammatory markers, factors that are implicated in the pathogenesis of atherosclerosis.

Adult↗
PubMed2003

Effect of iron-sulfur cluster assembly proteins on the expression of Escherichia coli lipoic acid synthase.

Lipoic Acid Synthase (LipA) can accommodate a [4Fe-4S] cluster that is thought to be essential for the insertion of sulfur into an octanoyl substrate during the biosynthesis of lipoic acid. With the objective of improving soluble holo-LipA expression, a series of multi-cistronic plasmids were constructed carrying lipA in combination with one of the three systems: groE/SL, trxA, or the isc operon. Co-expression of lipA with the isc operon approximately trebled the isolated yield of soluble LipA and resulted in efficient assembly of the Fe-S cluster. This strategy may be helpful in the soluble expression of a wide range of Fe-S cluster-dependent proteins.

Electrophoresis, Polyacrylamide Gel↗
PubMed2004

Unraveling the pathway of lipoic acid biosynthesis.

Lipoic acid is almost universally required for aerobic metabolism. However, the mechanism for its synthesis and incorporation into proteins has remained elusive. A groundbreaking study published in the December issue of Chemistry & Biology uncovers critical features of the lipoic acid biosynthetic pathway.

Catalysis↗
PubMed1991

Lipoic acid metabolism in Escherichia coli: isolation of null mutants defective in lipoic acid biosynthesis, molecular cloning and characterization of the E. coli lip locus, and identification of the lipoylated protein of the glycine cleavage system.

We report the isolation and genetic characterization of novel Tn10dTc and Tn1000dKn insertion mutations in and near the lip locus of the Escherichia coli chromosome. The Tn10dTc and Tn1000dKn mutations define two genes, lipA and lipB, involved in lipoic acid biosynthesis. Two representative alleles (lip-2 and lip-9) from the previously reported genetic class of lipoic acid auxotrophic mutants (A. A. Herbert and J. R. Guest, J. Gen. Microbiol. 53:363-381, 1968) were assigned to the lipA complementation group. We have cloned the E. coli lip locus and developed a recombinant plasmid-based genetic system for fine-structure physical-genetic mapping of mutations in this region of the E. coli chromosome. We also report that a recombinant plasmid containing a 5.2-kbp PvuII restriction fragment from the E. coli lip locus produced three proteins of approximately 8, 12, and 36 kDa by using either a maxicell or in vitro transcription translation expression system. The 36-kDa protein was identified as the gene product encoded by the lipA locus. Finally, we have identified a previously unreported lipoylated protein that functions in the glycine cleavage system of E. coli.

Alleles↗