Advanced analysis of biotin metabolites in body fluids allows a more accurate measurement of biotin bioavailability and metabolism in humans.
In previous studies, the bioavailability of biotin in humans was estimated from the recovery of biotin in urine; urinary biotin was measured by microbial growth assays or assays of avidin-binding activity. These assays underestimate concentrations of biotin metabolites, which originate from beta-oxidation, sulfur oxidation or a combination. We have developed an HPLC/avidin-binding assay that is specific for biotin and its metabolites. With the use of the HPLC/avidin-binding assay, TLC and derivatization with p-dimethylaminocinnamaldehyde, we have identified and quantitated biotin and metabolites in urine from six healthy adults. Of that total, biotin accounted for 32+/-12%, bisnorbiotin for 52+/-15%, bisnorbiotin methyl ketone for 7.9+/-5.8%, biotin-d,l-sulfoxide for 4.0+/-3.2% and biotin sulfone for 3.6+/-1.9%. After intravenous administration of 18.4 micromol of biotin, the urinary excretion of biotin metabolites increased 21-130 times above baseline values. Because the biliary excretion of biotin is quantitatively minor (1.9+/-0.2% of an intravenous [14C]biotin dose in rats), intravenously administered biotin is not exposed to intestinal microorganisms. Thus we conclude that biotin metabolites in human urine originate from biotin catabolism in human tissues rather than biotin catabolism by intestinal microorganisms. With the use of the HPLC/avidin-binding assay, we estimated the bioavailability of biotin in adults from the urinary excretion of biotin and metabolites after ingestion of 2.1, 8.2 and 81.9 micromol of biotin. These data provide evidence that biotin is nearly completely absorbed. (+info
The importance of pyruvate availability to PDC activation and anaplerosis in human skeletal muscle.
No studies have singularly investigated the relationship between pyruvate availability, pyruvate dehydrogenase complex (PDC) activation, and anaplerosis in skeletal muscle. This is surprising given the functional importance attributed to these processes in normal and disease states. We investigated the effects of changing pyruvate availability with dichloroacetate (DCA), epinephrine, and pyruvate infusions on PDC activation and accumulation of acetyl groups and tricarboxylic acid (TCA) cycle intermediates (TCAI) in human muscle. DCA increased resting PDC activity sixfold (P < 0.05) but decreased the muscle TCAI pool (mmol/kg dry muscle) from 1.174 +/- 0.042 to 0.747 +/- 0.055 (P < 0.05). This was probably a result of pyruvate being diverted to acetyl-CoA and acetylcarnitine after near-maximal activation of PDC by DCA. Conversely, neither epinephrine nor pyruvate activated PDC. However, both increased the TCAI pool (1.128 +/- 0.076 to 1.614 +/- 0.188, P < 0.05 and 1.098 +/- 0.059 to 1.385 +/- 0.114, P < 0.05, respectively) by providing a readily available pool of pyruvate for anaplerosis. These data support the hypothesis that TCAI pool expansion is principally a reflection of increased muscle pyruvate availability and, together with our previous work (J. A. Timmons, S. M. Poucher, D. Constantin-Teodosiu, V. Worrall, I. A. Macdonald, and P. L. Greenhaff. J. Clin. Invest. 97: 879-883, 1996), indicate that TCA cycle expansion may be of little functional significance to TCA cycle flux. It would appear therefore that the primary effect of DCA on oxidative ATP provision is to provide a readily available pool of acetyl groups to the TCA cycle at the onset of exercise rather than increasing TCA cycle flux by expanding the TCAI pool. (+info
Busulphan is active against neuroblastoma and medulloblastoma xenografts in athymic mice at clinically achievable plasma drug concentrations.
High-dose busulphan-containing chemotherapy regimens have shown high response rates in children with relapsed or refractory neuroblastoma, Ewing's sarcoma and medulloblastoma. However, the anti-tumour activity of busulfan as a single agent remains to be defined, and this was evaluated in athymic mice bearing advanced stage subcutaneous paediatric solid tumour xenografts. Because busulphan is highly insoluble in water, the use of several vehicles for enteral and parenteral administration was first investigated in terms of pharmacokinetics and toxicity. The highest bioavailability was obtained with busulphan in DMSO administered i.p. When busulphan was suspended in carboxymethylcellulose and given orally or i.p., the bioavailability was poor. Then, in the therapeutic experiments, busulphan in DMSO was administered i.p. on days 0 and 4. At the maximum tolerated total dose (50 mg kg(-1)), busulphan induced a significant tumour growth delay, ranging from 12 to 34 days in the three neuroblastomas evaluated and in one out of three medulloblastomas. At a dose level above the maximum tolerated dose, busulphan induced complete and partial tumour regressions. Busulphan was inactive in a peripheral primitive neuroectodermal tumour (PNET) xenograft. When busulphan pharmacokinetics in mice and humans were considered, the estimated systemic exposure at the therapeutically active dose in mice (113 microg h ml(-1)) was close to the mean total systemic exposure in children receiving high-dose busulphan (102.4 microg h ml(-1)). In conclusion, busulphan displayed a significant anti-tumour activity in neuroblastoma and medulloblastoma xenografts at plasma drug concentrations which can be achieved clinically in children receiving high-dose busulphan-containing regimens. (+info
Bioavailability and toxicity after oral administration of m-iodobenzylguanidine (MIBG).
meta-iodobenzylguanidine (MIBG) radiolabelled with iodine-131 is used for diagnosis and treatment of neuroadrenergic neoplasms such as phaeochromocytoma and neuroblastoma. In addition, non-radiolabelled MIBG, administered i.v., is used in several clinical studies. These include palliation of the carcinoid syndrome, in which MIBG proved to be effective in 60% of the patients. Oral MIBG administration might be convenient to maintain palliation and possibly improve the percentage of responders. We have, therefore, investigated the feasibility of oral administration of MIBG in an animal model. Orally administered MIBG demonstrated a bioavailability of 59%, with a maximal tolerated dose of 60 mg kg(-1). The first and only toxicity encountered was a decrease in renal function, measured by a reduced clearance of [51Cr]EDTA and accompanied by histological tubular damage. Repeated MIBG administration of 40 mg kg(-1) for 5 sequential days or of 20 mg kg(-1) for two courses of 5 sequential days with a 2-day interval did not affect renal clearance and was not accompanied by histological abnormalities in kidney, stomach, intestines, liver, heart, lungs, thymus, salivary glands and testes. Because of a sufficient bioavailability in absence of gastrointestinal toxicity, MIBG is considered suitable for further clinical investigation of repeated oral administration in patients. (+info
A phase I study of the lipophilic thymidylate synthase inhibitor Thymitaq (nolatrexed dihydrochloride) given by 10-day oral administration.
2-Amino-3,4-dihydro-6-methyl-4-oxo-5-(4-pyridylthio)-quinazoline dihydrochloride (nolatrexed dihydrochloride, Thymitaq, AG337), a specific inhibitor of thymidylate synthase, was developed using protein structure-based drug design. Intravenously administered nolatrexed is active clinically. As oral bioavailability is high (70-100%), nolatrexed was administered orally, 6 hourly for 10 days, at 3-week intervals, and dose escalated from 80 to 572 mg m(-2) day(-1) in 23 patients. Common toxicity criteria (CTC) grade 3 toxicities included nausea, vomiting, stomatitis and liver function test (LFT) abnormalities. Thrombocytopenia (grade 1 or 2) occurred at doses > or = 318 mg m(-2) day(-1) and neutropenia (grade 2) at 429 and 572 mg m(-2) day(-1). An erythematous maculopapular rash occurred at dosages > or = 318 mg m(-2) day(-1) (7 out of 19 patients). LFT abnormalities occurred in two out of six patients (grade 3 or 4 bilirubin and grade 3 alanine transaminase) at 572 mg m(-2) day(-1). Nolatrexed plasma concentrations 1 h after dosing were 6-16 microg ml(-1), and trough 3-8 microg ml(-1), at 572 mg m(-2) day(-1). Inhibition of thymidylate synthase was demonstrated by elevation of plasma deoxyuridine. Six-hourly oral nolatrexed for 10 days was associated with antiproliferative effects, but nausea and vomiting was dose limiting at 572 mg m(-2) day(-1). Nine patients were treated at 429 mg m(-2) day(-1); three out of nine experienced grade 3 nausea, but 17 out of 22 treatment courses were completed (with the co-administration of prophylactic antiemetics) and this dose level could be considered for phase II testing. (+info
Pharmacokinetics of recombinant human granulocyte colony-stimulating factor in rabbits and mice.
AIM: To study the pharmacokinetics of recombinant human granulocyte colony-stimulating factor (rhGCSF) in rabbits and mice. METHODS: 125I-rhGCSF was prepared by iodogen method and determined by size exclusive HPLC (SEHPLC). RESULTS: Concentration-time curves after i.v. 125I-rhGCSF in rabbits were best fitted with 2-compartment open model. The alpha and terminal elimination T1/2 were 0.25-0.33 and 3.2-4.6 h, respectively. AUC increased with doses, and Cls and K10 were similar. Tpeak was 0.59 +/- 0.25 h after s.c., and elimination T1/2 was similar to that after i.v. The bioavailability after sc was 1.0. In mice the highest level was found in renal system, the next was bile-enteric system. Levels in lymph nodes, bone marrow, and spleen were approximately equal to or slightly lower than that in plasma, while the levels in brain, fat, and muscles were the lowest. About 68%-86% were recovered in urine and feces. CONCLUSION: Pharamcokinetics of 125I-rhGCSF in rabbits and mice provided a useful index for clinical trial. (+info
Pharmacokinetics of bendazac lysine in 10 Chinese young men.
AIM: To compare the pharmacokinetics of domestic and imported tablets of bendazao lysine (BL). METHODS: A single oral dose of 500 mg BL of this 2 kinds of tablets was given to 10 Chinese volunteers of Han nationality in a randomized crossover study. Plasma levels were determined with HPLC-UV method. Data were analyzed automatically by using a CAPP program on microcomputer. RESULTS: The plasma concentration-time curve was fitted to 2-compartment open model, and the major pharmacokinetic parameters of domestic and imported BL tablets were shown respectively as following: Cmax 66 +/- 16 and 65 +/- 8 mg.L-1; Tmax 0.98 +/- 0.22 and 0.98 +/- 0.21 h; T1/2 beta 6.2 +/- 1.8 and 6.2 +/- 1.7 h; AUC 335 +/- 47 and 337 +/- 58 mg.h.L-1. There was no significant difference between domestic and imported tablets. The bioavailability of the domestic vs that of the imported tablet was 99 +/- 12%. The unchanged BL in urine were about 5.4% and 5.6% respectively of the dosage in 24 h after a single oral dose. CONCLUSION: The two kinds of tablets had the same biological effects. (+info
A study of the relative bioavailability of cysteamine hydrochloride, cysteamine bitartrate and phosphocysteamine in healthy adult male volunteers.
AIMS: Cysteamine, the only drug available for the treatment of cystinosis in paediatric patients, is available as the hydrochloride, the bitartrate and as sodium phosphocysteamine salts. It has been suggested that cysteamine bitartrate and phosphocysteamine are better tolerated and may have a better bioavailability than cysteamine hydrochloride. This has, however, never been demonstrated. METHODS: We compared the pharmacokinetics and tolerance of these three formulations of cysteamine in 18 healthy adult male volunteers in a double-blind, latin-square, three-period, single oral dose cross-over relative bioavailability study. RESULTS: No statistical difference was found between relative bioavailabilities, AUC (0, infinity) (geometric mean and s.d. in micromol l(-1) h: 169+/-51, 158+/-46, 173+/-49 with cysteamine hydrochloride, phosphocysteamine and cysteamine bitartrate respectively), Cmax (geometric mean and s.d. in micromol l(-1); 66+/-25.5, 59+/-12, 63+/-20) and tmax (median and range in h: 0.88 (0.25-2), 1.25 (0.25-2), 0.88 (0.25-2)) with each of the three forms of cysteamine tested. Bioequivalence statistics (90% confidence intervals) showed non equivalence of Cmax of cysteamine base as the only non equivalence of pharmacokinetics between the three formulations: 90% CI for Cmax relative ratios to cysteamine hydrochloride were [75.6-105.81 for phosphocysteamine and [74.2-124.2] for cysteamine bitartrate. The only significant adverse event was vomiting whose frequency was inversely correlated with body weight (Spearman's r=-0.76, P<0.001). The nature of the salt tested did not influence vomiting. CONCLUSIONS: While none of the three forms of cysteamine tested has a clear advantage over the others in terms of pharmacokinetics and tolerance profile, this should now however be addressed in patients treated for cystinosis during repeat administrations. (+info