Jens Teichert

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 β‐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 β‐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.

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 alphalipoic 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.

Pharmacokinetics and pharmacodynamics of GH: dependence on route and dosage of administration

OBJECTIVE Pharmacokinetic and pharmacodynamic data after recombinant human GH (rhGH) administration in adults are scarce, but necessary to optimize replacement therapy and to detect doping. We examined pharmacokinetics, pharmacodynamics, and 20 kDa GH after injection of rhGH at different doses and routes of administration. DESIGN Open-label crossover study with single boluses of rhGH. METHODS Healthy trained subjects (10 males, 10 females) received bolus injections of rhGH on three occasions: 0.033 mg/kg s.c., 0.083 mg/kg s.c., and 0.033 mg/kg i.m. Concentrations of 22 and 20 kDa GH, IGF-I, and IGF-binding proteins (IGFBP)-3 were measured repeatedly before and up to 36 h after injection. RESULTS Serum GH maximal concentration (Cmax) and area under the time-concentration curve (AUC) were higher after i.m. than s.c. administration of 0.033 mg/kg (Cmax 35.5 and 12.0 microg/l; AUC 196.2 and 123.8). Cmax and AUC were higher in males than in females (P < 0.01) and pharmacodynamic changes were more pronounced. IGFBP-3 concentrations showed no dose dependency. In response to rhGH administration, 20 kDa GH decreased in females and remained suppressed for 14-18 h (low dose) and 30 h (high dose). In males, 20 kDa GH was undetectable at baseline and throughout the study. CONCLUSIONS After rhGH administration, pharmacokinetic parameters are mainly influenced by route of administration, whereas pharmacodynamic variables and 20 kDa GH concentrations are determined mainly by gender. These differences need to be considered for therapeutic use and for detection of rhGH doping.

Determination of voriconazole in human plasma and saliva using high-performance liquid chromatography with fluorescence detection.

Voriconazole is a widely used triazole antifungal agent with a broad spectrum including Aspergillus species. A simple, sensitive and selective high-performance liquid chromatography method for the determination of voriconazole in human plasma and saliva was developed. Drug and internal standard (UK-115 794) were extracted from alkaline plasma and saliva with n-hexane-ethyl acetate (3:1, v/v) and analyzed on a Luna C 18 column with fluorimetric detection set at excitation and emission wavelengths of 254 and 372 nm, respectively. The calibration curve was linear through the range of 0.1-10 microg/ml using a 0.3 ml sample volume. The intra- and inter-day precisions were all below 6.1% for plasma and below 9.1% for saliva. Accuracies ranged from 94 to 109% for both matrices. Mean recovery was 86+/-4% for voriconazole. The method showed acceptable values for precision, recovery and sensitivity and is well suited for routine analysis work and for pharmacokinetic studies.

Gastric Bypass Surgery Recruits a Gut PPAR-α-Striatal D1R Pathway to Reduce Fat Appetite in Obese Rats

Bariatric surgery remains the single most effective long-term treatment modality for morbid obesity, achieved mainly by lowering caloric intake through as yet ill-defined mechanisms. Here we show in rats that Roux-en-Y gastric bypass (RYGB)-like rerouting of ingested fat mobilizes lower small intestine production of the fat-satiety molecule oleoylethanolamide (OEA). This was associated with vagus nerve-driven increases in dorsal striatal dopamine release. We also demonstrate that RYGB upregulates striatal dopamine 1 receptor (D1R) expression specifically under high-fat diet feeding conditions. Mechanistically, interfering with local OEA, vagal, and dorsal striatal D1R signaling negated the beneficial effects of RYGB on fat intake and preferences. These findings delineate a molecular/systems pathway through which bariatric surgery improves feeding behavior and may aid in the development of novel weight loss strategies that similarly modify brain reward circuits compromised in obesity.

Identification and Quantitation of the N-Acetyl-L-cysteine S-Conjugates of Bendamustine and Its Sulfoxides in Human Bile after Administration of Bendamustine Hydrochloride

We recently reported the detection of mercapturic acid pathway metabolites of bendamustine, namely, cysteine S-conjugates in human bile, which are supposed to subsequently undergo further metabolism. In this study, we describe the identification and quantitation of consecutive bendamustine metabolites occurring in human bile using authentic reference standards and the synthesis and structural confirmation of these compounds. Mass spectrometry data along with high-performance liquid chromatography retention data (fluorescence detection) of the synthetic reference standards were consistent with those of the metabolites found in human bile after administration of bendamustine hydrochloride to cancer patients. Analysis of the purified synthetic reference compounds showed a purity of at least 95%. Structural confirmation was achieved by one- and two-dimensional proton as well as carbon-13 NMR spectroscopy and mass spectrometry. A total of 16 bendamustine-related compounds were detected in the bile of patients, 11 of them were recovered as conjugates. Eight conjugates have been structurally confirmed as novel mercapturic acids and sulfoxides. Biliary excretion of the sulfoxides was twice that of the mercapturate precursors. Glutathione S-conjugates of bendamustine have not been detected in bile samples, indicating rapid enzymatic cleavage in humans. Both the lack of glutathione (GSH) conjugates and occurrence of diastereomeric sulfoxides emphasize species-related differences in the GSH conjugation of bendamustine between humans and rats. The total amount recovered in the bile as the sum of all conjugates over the period of 24 h after dosing averaged 5.2% of the administered dose. The question of whether the novel metabolites contribute to urinary excretion should be a target of future investigations.

[17] High-performance liquid chromatography methods for determination of lipoic and dihydrolipoic acid in human plasma

This assay method was applied to determine plasma levels of lipoic acid in humans. The method consists of enzymatic hydrolysis to release the protein-bound lipoic acid, solid-phase extraction, and electrochemical detection at a potential of +1.1 V. Previous methods did not provide adequate sensitivity for these studies or required procedural modifications for detection of low levels of plasma lipoic acid. The chromatographic system is capable of separating lipoic acid from dihydrolipoic acid. Both reduced and oxidized lipoic acid can be detected. Therefore, oxidation of dihydrolipoic acid must be prevented. In the described procedure, we do not prevent oxidation and the whole content is measured as lipoic acid. The method does not detect lipoic acid covalently bound to lysine. The detection limit for this method is 1 ng of lipoic acid per milliliter of plasma.