Role of metabolism by intestinal microbiota in pharmacokinetics of oral baicalin

Baicalin (baicalein-7-glucuronide) is a flavonoid purified from Scutellaria baicalensis Georgi that has traditionally been used for treatment of hypertension, cardiovascular diseases, and viral hepatitis. In this study, the effects of intestinal microbiota on the pharmacokinetics of baicalin were investigated in normal and antibiotic-pretreated rats following p.o. administration of 100 mg/kg baicalin by using liquid chromatography/ion trap mass spectrometry. When rats were pretreated orally with cefadroxil, oxytetracycline and erythromycin for 3 days to control the number of intestinal bacteria, the pharmacokinetic parameters of oral baicalin were significantly affected by antibiotics: C_max, T_1/2(β), K_el and AUC values were significantly changed compared to those in normal rats. These results indicate that intestinal microbiota might play a key role in the oral pharmacokinetics of baicalin.     

Nephrotoxic Potential and Toxicokinetics of Melamine Combined with Cyanuric Acid in Rats

To investigate the nephrotoxic potential of melamine (MEL) and cyanuric acid (CA) in male Sprague-Dawley rats, 7-d repeated-dose studies were performed. The experimental groups of MEL100 and CA100 were orally administered with MEL and CA at 100 mg/kg/d for 7 d, respectively. In groups dosed with MEL–CA mixtures, melamine and cyanuric acid (1:1) were simultaneously administered at 4, 20, or 100 mg/kg/d for 7 d (i.e., MEL-CA4, MEL-CA20, or MEL-CA100, respectively). Body weights were not markedly affected in MEL100, CA100, and MEL-CA4 groups, but significantly reduced in MEL-CA 20 and 100 rats. Most parameters determined in sera and tissues were not markedly altered in MEL100, CA100, and MEL-CA4-treated rodents. However, BUN, creatinine, total protein, and kidney weights were significantly increased in MEL-CA20- and MEL-CA100-treated animals. Renal histopathologic findings also revealed signs of toxicity, including tubular dilatation, crystal deposition, granulomatous tubulo-interstitial inflammation, and tubular necrosis with regeneration. Data suggested that the combination of MEL and CA might be responsible for observed nephrotoxicity that was not seen following individual exposure to either MEL or CA alone. Subsequently, the concentrations of MEL and CA were determined in serum, urine, and kidney tissues by using liquid chromatography–mass spectrometry. Toxicokinetic studies indicated that MEL or CA alone might be eliminated almost completely within 24 h after dosing showing no accumulation in kidney. However, the combined MEL-CA dose produced marked accumulation of chemicals in blood and kidneys. These results suggested that combined MEL and CA might produce renal toxicity due to significant chemical accumulation in kidney accompanied by low excretion.     

Quantitative determination of daumone in rat plasma by liquid chromatography-mass spectrometry

Daumone, 6-(3,5-dihydroxy-6-methyl-tetrahydro-pyran-2-yloxy)-heptanoic acid is a pheromone secreted by Caenorhabditis elegans, and has been known as a pivotal regulator of chemosensory processes in development and ageing. A quantification method using mass spectrometry was developed for the determination of daumone in rat plasma. After simple protein precipitation with acetonitrile including an internal standard, the analytes were chromatographed on a reversed-phase column and detected by liquid chromatography/tandem mass spectrometry with electrospray ionization. The accuracy and precision of the assay were in accordance with FDA regulations for validation of bioanalytical methods. This method was applied to measure the plasma daumone concentrations after a single intravenous administration of daumone in rats.     

Protective role of metabolism by intestinal microflora in butyl paraben-induced toxicity in HepG2 cell cultures

Parabens are alkyl esters of p-hydroxybenzoic acid (BA), including methyl paraben (MP), ethyl paraben, propyl paraben (PP), and butyl paraben (BP). In the present study, possible role of metabolism by fecalase in BP-induced cytotoxicity was investigated in HepG2 cell cultures. As an intestinal bacterial metabolic system, a human fecalase prepared from human fecal specimen was employed. Among the parabens tested, cytotoxicity of BP was most severe. BA, the de-esterified metabolite, did not induce cytotoxicity when compared to other parabens. When BP was incubated with fecalase, it rapidly disappeared, in association with reduced cytotoxicity in HepG2 cells. In addition, BP incubated with fecalase significantly caused an increase in Bcl-2 expression together with a decrease in Bax expression and cleaved caspase-3. Moreover, anti-apoptotic effect by the incubation of BP with fecalase was also confirmed by the TUNEL assay. Furthermore, BP induced a sustained activation of the phosphorylation of JNK only when it was treated alone. Meanwhile, BP-induced cell death was reversed by the pre-incubation of BP with either fecalase or SP600125. Taken together, the findings suggested that metabolism of BP by human fecalase might have protective effects against BP-induced toxicity in HepG2 cells.     

The effects of food on the bioavailability of fenofibrate administered orally in healthy volunteers via sustained-release capsule

OBJECTIVE: To examine the effects of food on plasma concentration and bioavailability of fenofibrate administered as a sustained-release capsule. METHODS: Twenty-four healthy Korean volunteers were enrolled in a randomised, open-label, balanced, three-treatment, three-period, three-sequence, single oral dose, crossover pharmacokinetic study. A single dose of fenofibrate (250 mg sustained-release capsule) was administered on three occasions -- after overnight fasting, after consumption of a standard breakfast and after a high-fat breakfast. Serial blood samples were collected for the next 72 hours. Plasma fenofibric acid concentrations were measured by high-performance liquid chromatography, and pharmacokinetic parameters were calculated. RESULTS: The pharmacokinetic parameters were significantly affected by food intake. The high-fat breakfast affected the rate of absorption of fenofibrate more than the standard breakfast and fasted conditions. Specifically, the area under the plasma concentration-time curve from time zero to infinity (AUC(infinity)) and peak plasma concentration (C(max)) increased 2.45-fold and 2.89-fold, respectively, between the fasted and standard-fed conditions (p < 0.01). In addition, the high-fat meal caused 3.34-fold and 3.82-fold increases compared with the fasted condition in AUC(infinity) and C(max), respectively. A one-compartment open model with lag time successfully described the plasma concentrations of fenofibric acid. CONCLUSION: In healthy volunteers, AUC(infinity) and C(max) of fenofibrate, when administered via sustained-release capsules immediately after the consumption of food, was increased significantly from the fasting conditions (p < 0.01). The greatest AUC(infinity) and C(max) occurred when the capsules were taken after a high-fat breakfast.     

Simple and sensitive determination of menatetrenone and its epoxide metabolite in human plasma

A simple and rapid quantification method was developed for determining menatetrenone and its epoxide metabolite in human plasma. After a simple protein precipitation with methanol, the analytes were chromatographed on a reversed-phase C₁₈ column and detected by LC/MS/MS with atmospheric pressure chemical ionization. The coefficient of variation of the assay precision was less than 10.1%, and the accuracy ranged from 98.0 to 106.5%. The limit of detection of menatetrenone and its epoxide was 0.5 and 0.2 ng/ml, respectively. This method was used to simultaneously measure the plasma concentration of menatetrenone and its epoxide metabolite from healthy subjects after a single 30 mg oral dose of menatetrenone.     

Enantioselective determination of sibutramine and its active metabolites in human plasma

Although racemic sibutramine has been widely used for the treatment of obesity, its enantioselective detection method has not been elucidated in human plasma. In this report we introduce a validated analytical method for the determination of sibutramine and its two active metabolites, desmethylsibutramines using LC–MS/MS. R- and S-isomers of those compounds in human plasma were extracted using diethyl ether–hexane (4:1, v/v) followed by an addition of NaOH solution. After removing the organic layer, the residue was reconstituted in the mobile phase 10 mM ammonium acetate solution adjusted to pH 4.0 with acetic acid–acetonitrile (94:6, v/v). Both isomers in the extract were separated on a Chiralcel AGP chiral stationary-phase column and were quantified in a tandem mass spectrometry. The assay method was in accordance with FDA regulations for the validation of bioanalytical methods. This method was successfully used to profile the plasma concentrations of the stereoisomers of sibutramine and its two active metabolites with time in healthy volunteers.     

Enantioselective pharmacokinetics of sibutramine in rat

Racemic sibutramine is widely used to treat obesity owing to its inhibition of serotonin and noradrenaline reuptake in synapses. Although the enantioselective effects of sibutramine and its two active desmethyl-metabolites, monodesmethylsibutramine (MDS) and didesmethylsibutramine (DDS), on anorexia and energy expenditure have been elucidated, the enantioselective pharmacokinetics of sibutramine are still unclear. Therefore, we aimed to characterize the enantioselective pharmacokinetics of sibutramine and its metabolites in plasma and urine following an intravenous and a single oral administration of sibutramine in rats. The absolute bioavailability of sibutramine was only about 7%. The pharmacologically less effective S-isomer of DDS was predominant in the plasma: the C _max and the AUC _inf were 28 and 30 times higher than those of the R-isomer, respectively (p<0.001). In the urine, the concentrations of the R-isomers of hydroxylated DDS and hydroxylated and carbamoylglucuronized MDS and DDS appeared to be 11.3-, 5.1-, and 5.3-times the concentrations of the respective S-isomers. Thus, regardless of increased potency than the S-enantiomers, the R-enantiomers of the sibutramine metabolites MDS and DDS were present at lower concentrations, owing to their rapid biotransformation to hydroxylated and/or carbamoylglucuronized forms and their faster excretion in the urine. The present study is the first to elucidate the enantioselective pharmacokinetics of sibutramine in rats.     

A rapid method to determine tetrabromobisphenol a in rat serum and urine by liquid chromatography-tandem mass spectrometry

Tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardants in the world, is used to improve fire safety of laminates in electrical and electronic equipment. A liquid chromatography-tandem mass spectrometry was developed for the determination of TBBPA in rat serum and urine, and applied to the toxicokinetic study of TBBPA in rats. Acceptable linearity was observed over the concentration ranges of 0.25–50 and 0.01–5 μg/mL in serum and urine, respectively. The limits of detection of TBBPA were 0.04 μg/mL in serum, and 0.0025 μg/mL in urine. The precisions for the assay in serum and urine were below 13 and 14%, respectively, and the accuracies ranged 95–111% and 98–101% for intraday and 97–107% and 97–102% for inter-day, respectively. Serum and urine concentrations of TBBPA were successfully monitored following oral administrations at the dose of 200 mg/kg in male Sprague Dawley rats. Toxic signs were not observed at 200 mg/kg of TBBPA. The present results suggest that the rapid method developed in the present study affords sensitivity, accuracy and precision necessary for quantitative measurements in toxicokinetic studies of TBBPA in vivo.     

Pharmacokinetics of Uridine Following Ocular,Oral and Intravenous Administration in Rabbits

The pyrimidine nucleoside uridine has recently been reported to have a protective effect on cultured human corneal epithelial cells, in an animal model of dry eye and in patients. In this study, we investigate the pharmacokinetic profile of uridine in rabbits, following topical ocular (8 mg/eye), oral (450 mg/kg) and intravenous (100 mg/kg) administration. Blood and urine samples were serially taken, and uridine was measured by high-performance liquid chromatography-tandem mass spectrometry. No symptoms were noted in the animals after uridine treatment. Uridine was not detected in either plasma or urine after topical ocular administration, indicating no systemic exposure to uridine with this treatment route. Following a single intravenous dose, the plasma concentration of uridine showed a bi-exponential decay, with a rapid decline over 10 min, followed by a slow decay with a terminal half-life of 0.36 ± 0.05 h. Clearance and volume of distribution were 1.8 ± 0.6 L/h/kg and 0.58 ± 0.32 L/kg, respectively. The area under the plasma concentration-time curves (AUC) was 59.7 ± 18.2 μg·hr/ml, and urinary excretion up to 12 hr was ~7.7% of the dose. Plasma uridine reached a peak of 25.8 ± 4.1 μg/ml at 2.3 ± 0.8 hr after oral administration. The AUC was 79.0 ± 13.9 μg·hr/ml, representing ~29.4% of absolute bioavailability. About 1% of the oral dose was excreted in the urine. These results should prove useful in the design of future clinical and nonclinical studies conducted with uridine.