The first method for determination of lipoyllysine in human urine after oral lipoic acid supplementation.

Aim: The first method on urinary excreted amounts of lipoyllysine (LLys) after lipoic acid (LA) supplementation was developed and validated. The suggested procedure allowed simultaneous determination of LLys and LA. Methodology & results: After the conversion of analytes into their reduced forms with tris(2-carboxyethyl)phosphine and derivatization via thiol group with 1-benzyl-2-chloropyridinium bromide, separation of analytes derivatives was performed on C18 column using a gradient mobile phase consisting of acetic acid and acetonitrile. The calibration curves for LA and LLys were linear (R2 > 0.999) in the range of 0.4-12 µM concentration and all validation results were acceptable, according to the US FDA bioanalytical method guidelines. Conclusion: This method was effectively applied for LA and LLys quantification in human urine after oral LA supplementation.

Application of simultaneous separation and derivatization for the determination of α-lipoic acid in urine samples by high-performance liquid chromatography with spectrofluorimetric detection.

To help to clarify therapeutic functions of lipoic acid (LA) in biochemical and clinical practice we have elaborated a fast, simple and accurate HPLC method enabling determination of LA in human urine. The proposed analytical approach includes reduction of LA with tris(2-carboxyethyl)phosphine and simultaneous separation and derivatization of the analyte with butylamine and o-phthaldialdehyde followed by spectrofluorimetric detection at λex = 340 nm and λem = 440 nm. The assay was performed using gradient elution and the mobile phase containing 0.0025 mol L-1 o-phthaldialdehyde in 0.0025 mol L-1 NaOH and acetonitrile. Linearity of the detector response for LA was observed in the range of 0.3-8 µmol L-1 . Limits of detection and quantification for LA in urine samples were 0.02 and 0.03 µmol L-1 , respectively. The total analysis time, including sample work-up, was <20 min. The analytical procedure was successfully applied to analysis of real urine samples delivered from six healthy volunteers who received a single 100 mg dose of LA.

Enantiomeric determination of α-lipoic acid in urine by LC/MS/MS.

An analytical method for the enantiomeric determination of α-lipoic acid in human urine was developed to evaluate the pharmacokinetics of α-lipoic acid, an ingredient in health food. Urine samples were collected over time after administering α-lipoic acid dietary supplement to healthy subjects. The samples were cleaned up by solid-phase extraction using an Oasis® MAX cartridge. In the LC/MS/MS method, CHIRALPAK AD-3R was used as the chiral separation column and acetonitrile-methanol-formic acid (10 mM) (25:25:50, v/v/v) was used as the mobile phase. 13C4 1,2,5,6-d-l-α-Lipoic acid was used as the internal standard. MS/MS was performed by electrospray ionization (ESI) in the negative ion mode using two monitoring ion transitions (m/z 205.0 → 170.9 and m/z 209.0 → 174.9). A calibration curve was prepared in the concentration range of 0.5-100 ng/mL for each enantiomer (r > 0.9999). The limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N > 10) were 0.1 ng/mL and 0.5 ng/mL, respectively. The intra-day and inter-day accuracy of α-lipoic acid enantiomers at the LOQ level (0.5 ng/mL), the low concentration level (5 ng/mL), the middle concentration level (50 ng/mL), and the high concentration level (100 ng/mL) ranged from 93.7 to 103.1%. The intra-day and inter-day precision were ≦ 6.94% and ≦ 7.05%, respectively. Calculating the mean values of pharmacokinetic parameters revealed that the AUC and Cmax values of d-α-lipoic acid were statistically significantly higher than those of l-α-lipoic acid (p < 0.05). It was suggested that l-α-lipoic acid is more bioavailable than d-α-lipoic acid despite individual differences in excretion rate.

Determination of lipoic acid in human urine by capillary zone electrophoresis.

Fast, simple, and accurate CE method enabling determination of lipoic acid (LA) in human urine has been developed and validated. LA is a disulfide-containing natural compound absorbed from the organism's diet. Due to powerful antioxidant activity, LA has been used for prevention and treatment of various diseases and disorders, e.g. cardiovascular diseases, neurodegenerative disorders, and cancer. The proposed analytical procedure consists of liquid-liquid sample extraction, reduction of LA with tris(2-carboxyethyl)phosphine, derivatization with 1-benzyl-2-chloropyridinium bromide (BCPB) followed by field amplified sample injection stacking, capillary zone electrophoresis separation, and ultraviolet-absorbance detection of LA-BCPB derivative at 322 nm. Effective baseline electrophoretic separation was achieved within 6 min under the separation voltage of 20 kV (∼80 µA) using a standard fused-silica capillary (effective length 51.5 cm, 75 µm id) and BGE consisted of 0.05 mol/L borate buffer adjusted to pH 9. The experimentally determined limit of detection for LA in urine was 1.2 µmol/L. The calibration curve obtained for LA in urine showed linearity in the range 2.5-80 µmol/L, with R2 0.9998. The relative standard deviation of the points of the calibration curve was lower than 10%. The analytical procedure was successfully applied to analysis of real urine samples from seven healthy volunteers who received single 100 mg dose of LA.

Mutations in human lipoyltransferase gene LIPT1 cause a Leigh disease with secondary deficiency for pyruvate and alpha-ketoglutarate dehydrogenase.

BACKGROUND: Synthesis and apoenzyme attachment of lipoic acid have emerged as a new complex metabolic pathway. Mutations in several genes involved in the lipoic acid de novo pathway have recently been described (i.e., LIAS, NFU1, BOLA3, IBA57), but no mutation was found so far in genes involved in the specific process of attachment of lipoic acid to apoenzymes pyruvate dehydrogenase (PDHc), α-ketoglutarate dehydrogenase (α-KGDHc) and branched chain α-keto acid dehydrogenase (BCKDHc) complexes. METHODS: Exome capture was performed in a boy who developed Leigh disease following a gastroenteritis and had combined PDH and α-KGDH deficiency with a unique amino acid profile that partly ressembled E3 subunit (dihydrolipoamide dehydrogenase / DLD) deficiency. Functional studies on patient fibroblasts were performed. Lipoic acid administration was tested on the LIPT1 ortholog lip3 deletion strain yeast and on patient fibroblasts. RESULTS: Exome sequencing identified two heterozygous mutations (c.875C > G and c.535A > G) in the LIPT1 gene that encodes a mitochondrial lipoyltransferase which is thought to catalyze the attachment of lipoic acid on PDHc, α-KGDHc, and BCKDHc. Anti-lipoic acid antibodies revealed absent expression of PDH E2, BCKDH E2 and α-KGDH E2 subunits. Accordingly, the production of 14CO2 by patient fibroblasts after incubation with 14Cglucose, 14Cbutyrate or 14C3OHbutyrate was very low compared to controls. cDNA transfection experiments on patient fibroblasts rescued PDH and α-KGDH activities and normalized the levels of pyruvate and 3OHbutyrate in cell supernatants. The yeast lip3 deletion strain showed improved growth on ethanol medium after lipoic acid supplementation and incubation of the patient fibroblasts with lipoic acid decreased lactate level in cell supernatants. CONCLUSION: We report here a putative case of impaired free or H protein-derived lipoic acid attachment due to LIPT1 mutations as a cause of PDH and α-KGDH deficiencies. Our study calls for renewed efforts to understand the mechanisms of pathology of lipoic acid-related defects and their heterogeneous biochemical expression, in order to devise efficient diagnostic procedures and possible therapies.

Dispersive liquid-liquid microextraction combined with microwave-assisted derivatization for determining lipoic acid and its metabolites in human urine.

This study explored dispersive liquid-liquid microextraction for extraction and concentration of lipoic acid in human urine. To improve the detection of lipoic acid by both capillary liquid chromatography (CapLC) with UV detection and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), microwave-assisted derivatization with 4-bromomethyl-6,7-dimethoxycoumarin was performed to render lipoic acid chromophores for UV detection and also high ionization efficiency in MALDI. All parameters that affected lipoic acid extraction and derivatization from urine were investigated and optimized. In the analyses of human urine samples, the two methods had a linear range of 0.1-20 µM with a correlation coefficient of 0.999. The detection limits of CapLC-UV and MALDI-TOF MS were 0.03 and 0.02 µM (S/N ≧ 3), respectively. The major metabolites of lipoic acid, including 6,8-bismethylthio-octanoic acid, 4,6-bismethylthio-hexanoic acid, and 2,4-bismethylthio-butanoic acid were also extracted by dispersive liquid-liquid microextraction and detected by MALDI-TOF MS. The minor metabolites (undetectable by MALDI-TOF MS), bisnorlipoic acid and tetranorlipoic acid were also extracted by dispersive liquid-liquid microextraction and identified with an LTQ Orbitrap mass spectrometer. After dispersive liquid-liquid microextraction and microwave-assisted derivatization, all lipoic acid derivatizations and metabolites were structurally confirmed by LTQ Orbitrap.

Novel lipoate-selective membrane sensor for the flow injection determination of alpha-lipoic acid in pharmaceutical preparations and urine.

A potentiometric lipoate-selective sensor based on mercuric lipoate ion-pair as a membrane carrier is reported. The electrode was prepared by coating the membrane solution containing PVC, plasticizer, and carrier on the surface of graphite electrode. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The sensor exhibits significantly enhanced response toward lipoate ions over the concentration range 1 x 10(-7) molL(-1) to 1 x 10(-2) molL(-1) with a lower detection limit of (LDL) of 9 x 10(-8) molL(-1) and a slope of -29.4 m V decade(-1), with S.D. of the slope is 0.214 mV. Fast and stable response, good reproducibility, long-term stability, applicability over a pH range of 8.0-9.5 is demonstrated. The sensor has a response time of

Pharmacokinetics of alpha-lipoic acid in subjects with severe kidney damage and end-stage renal disease.

In an open-label, parallel-group study involving 16 patients (8 with severely reduced renal function, 8 with end-stage renal disease needing hemodialysis), the effect of renal function on the pharmacokinetics, metabolism, and safety and of alpha-lipoic acid (thioctic acid) was evaluated by comparing the pharmacokinetic parameters with those of a reference group of 8 healthy subjects. Alpha-lipoic acid 600 mg was administered orally once daily for 4 days, and the pharmacokinetic parameters were measured on days 1 and 4. The mean percentage of the administered dose excreted in urine as parent compound was 0.2 and 0.05 in healthy subjects and subjects with severely reduced renal function, respectively. Assuming a bioavailability of 30%, this represents 0.67% and 0.17% of the bioavailable amount of alpha-lipoic acid, respectively. The percentage of total urinary recovered amounts of alpha-lipoic acid and 5 of its metabolites was 12.0 on both days. The respective values for patients with severe kidney damage were 5.2% (day 1) and 6.4% (day 4). The total percentage of the administered dose removed by hemodialysis was 4.0 in patients with end-stage renal disease. Renal clearance of alpha-lipoic acid and its major metabolites, 6,8-bismethylthio-octanoic acid, 4,6-bismethylthio-hexanoic acid and 2,4-bismethylthio-butanoic acid, were significantly decreased in subjects with kidney damage compared to the reference group. Apparent total clearance of alpha-lipoic acid was poorly correlated with creatinine clearance. There is strong evidence that alpha-lipoic acid is mainly excreted by nonrenal mechanism or further degraded to smaller units in the catabolic process. The significantly increased area under the curve values of 4,6-bismethylthio-hexanoic acid and half-lives of 2,4-bismethylthio-butanoic acid on both days in patients with severely reduced function and end-stage renal disease were not considered to be clinically relevant. Although trough levels of both metabolites tend to increase slightly in these subjects, no accumulation effects were detected. We conclude that the pharmacokinetics of alpha-lipoic acid are not influenced by creatinine clearance and are unaffected in subjects with severely reduced kidney function or end-stage renal disease. Hemodialysis did not significantly contribute to the clearance of alpha-lipoic acid. Hence, dose adjustment of alpha-lipoic acid is not necessary in patients with renal dysfunction.

Plasma kinetics, metabolism, and urinary excretion of alpha-lipoic acid following oral administration in healthy volunteers.

R(+)-alpha-lipoic acid is a natural occurring compound that acts as an essential cofactor for certain dehydrogenase complexes. The redox couple alpha-lipoic acid/dihydrolipoic acid possesses potent antioxidant activity. Exogenous racemic alpha-lipoic acid orally administered for the symptomatic treatment of diabetic polyneuropathy is readily and nearly completely absorbed, with a limited absolute bioavailability of about 30% caused by high hepatic extraction. Although the pharmacokinetics of the parent drug have been well characterized in humans, relatively little is known regarding the excretion of alpha-lipoic acid and the pharmacokinetics of any metabolites in humans. In the present study, plasma concentration-time courses, urinary excreted amounts, and pharmacokinetic parameters of alpha-lipoic acid metabolites were evaluated in 9 healthy volunteers after multiple once-daily oral administration of 600 mg racemic alpha-lipoic acid. The primary metabolic pathways of alpha-lipoic acid in man, S-methylation and beta-oxidation, were quantitatively confirmed by an HPLC-electrochemical assay newly established prior to the beginning of this study. Major circulating metabolites were the S-methylated beta-oxidation products 4,6-bismethylthio-hexanoic acid and 2,4-bismethylthio-butanoic acid, whereas its conjugated forms accounted for the major portion excreted in urine. There was no statistically significant difference in the pharmacokinetic parameters Cmax, AUC, and tmax between day 1 and day 4. Despite the prolonged half-lives of the major metabolites compared to the parent drug, no evidence of accumulation was found. Mean values of 12.4% of the administered dose were recovered in the urine after 24 hours as the sum of alpha-lipoic acid and its metabolites. The results of the present study revealed that urinary excretion of alpha-lipoic acid and five of its main metabolites does not play a significant role in the elimination of alpha-lipoic acid. Therefore, biliary excretion, further electrochemically inactive degradation products, and complete utilization of alpha-lipoic acid as a primary substrate in the endogenous metabolism should be considered.

High-performance liquid chromatographic assay for alpha-lipoic acid and five of its metabolites in human plasma and urine.

An isocratic reversed-phase HPLC method for the simultaneous quantitation of alpha-lipoic acid and five of its metabolites in human plasma as well as in human urine employing solid-phase extraction and pulsed amperometric detection was developed and validated. The method was found to be sufficiently precise and accurate for the measurement of alpha-lipoic acid and its metabolites 6,8-bis(methylthio)octanoic acid, 4,6-bis(methylthio)hexanoic acid and 2,4-bis(methylthio)butanoic acid in plasma and urine samples, obtained from patients suffering from diabetic neuropathy as well as from healthy volunteers following daily oral administration of 600 mg alpha-lipoic acid. The quantitation of the metabolite bisnorlipoic acid was often impaired by interferences caused by an unidentified metabolite. However, bisnorlipoic acid was detected in few test samples and the concentrations were consistently low. Despite the poor recovery of the metabolite tetranorlipoic acid from plasma, reproducibility and accuracy were found to be from acceptable magnitude to assess concentration time courses. Thus, the obtained analytical results are considered as reliable and well suited for pharmacokinetic studies of alpha-lipoic acid and its metabolites.

New metabolic pathways of alpha-lipoic acid.

The excretion and biotransformation of rac-alpha-lipoic acid (LA), which is used for the symptomatic treatment of diabetic polyneuropathy, were investigated following single oral dosing of [(14)C]LA to mice (30 mg/kg), rats (30 mg/kg), dogs (10 mg/kg), and unlabeled LA to humans (600 mg). More than 80% of the radioactivity given was renally excreted. Metabolite profiles obtained by radiometric high-performance liquid chromatography revealed that LA was extensively metabolized irrespective of the species. Based on a new on-line liquid chromatography/tandem mass spectroscopy assay developed for negative ions, LA and a total of 12 metabolites were identified. Mitochondrial beta-oxidation played the paramount role in the metabolism of LA. Simultaneously, the circulating metabolites were subjected to reduction of the 1,2-dithiolane ring and subsequent S-methylation. In addition, evidence is given for the first time that the methyl sulfides formed were partly oxidized to give sulfoxides, predominantly in dogs. The disulfoxide of 2,4-bismethylmercapto-butanoic acid, the most polar metabolite identified, was the major metabolite in dogs. Furthermore, new data are presented that suggest conjugation with glycine occurred as a separate metabolic pathway in competition with beta-oxidation, predominantly in mice.

Determination of lipoic acid and dihydrolipoic acid in human plasma and urine by high-performance liquid chromatography with fluorimetric detection.

A highly sensitive method for the determination of alpha-lipoic acid (LA) and dihydrolipoic acid (DHLA) in human plasma and urine has been developed. Samples were acidified and extracted with organic solvent, and the free sulfhydryls of DHLA protected as the dicarboxyethylate by treatment with ethylchloroformate. The free carboxylic function of LA and the SH-protected DHLA were converted into their amide derivatives with the strong fluorophore 2-(4-aminophenyl)-6-methylbenzothiazole in the presence of a coupling agent and a base catalyst. The resulting fluorescent amides of both LA and DHLA were separated on a reversed-phase column (Ultrasphere C8) using simple isocratic elution with acetonitrile-water (80:20) and detected fluorimetrically (excitation 343, emission 423 nm). The method is highly sensitive, reproducible, and is easily applied for the simultaneous determination of LA and DHLA in biological samples.

Lipoic acid reduces the activities of biotin-dependent carboxylases in rat liver.

In the past, lipoic acid has been administered to patients and test animals as therapy for diabetic neuropathy and various intoxications. Lipoic acid and the vitamin biotin have structural similarities. We sought to determine whether the chronic administration of lipoic acid affects the activities of biotin-dependent carboxylases. For 28 d, rats received daily intraperitoneal injections of one of the following: 1) a small dose of lipoic acid [4.3 micromol/( kg.d)]; 2) a large dose of lipoic acid [15.6 micromol/(kg.d)]; or 3) a large dose of lipoic acid plus biotin [15.6 and 2.0 micromol/(kg.d), respectively]. Another group received n-hexanoic acid [14.5 micromol/(kg.d)], which has structural similarities to lipoic acid and biotin and thus served as a control for the specificity of lipoic acid. A fifth group received phosphatidylcholine in saline injections and served as the vehicle control. The rat livers were assayed for the activities of acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and beta-methylcrotonyl-CoA carboxylase. Urine was analyzed for lipoic acid; serum was analyzed for indicators of liver damage and metabolic aberrations. The mean activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase were 28-36% lower in the lipoic acid-treated rats compared with vehicle controls (P < 0.05). Rats treated with lipoic acid plus biotin had normal carboxylase activities. Carboxylase activities in livers of n-hexanoic acid-treated rats were normal despite some evidence of liver injury. Propionyl-CoA carboxylase and acetyl-CoA carboxylase were not significantly affected by administration of lipoic acid. This study provides evidence consistent with the hypothesis that chronic administration of lipoic acid lowers the activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase in vivo by competing with biotin.