Tech.Sight. Modeling--a tool for experimentalists.
Explore the source record for details and available documents.
Chemical Phenomena↗
Biomedical subjects
R Kazlauskas
Publications and source records attributed to R Kazlauskas.
Detection of recombinant human erythropoietin abuse in athletes utilizing markers of altered erythropoiesis.
BACKGROUND AND OBJECTIVES: The detection of recombinant human erythropoietin (r-HuEPO) abuse by athletes remains problematic. The main aim of this study was to demonstrate that the five indirect markers of altered erythropoiesis identified in our earlier work were reliable evidence of current or recently discontinued r-HuEPO use. A subsidiary aim was to refine weightings of the five markers in the initial model using a much larger data set than in the pilot study. A final aim was to verify that the hematologic response to r-HuEPO did not differ between Caucasian and Asiatic subjects. DESIGN AND METHODS: Recreational athletes resident in Sydney, Australia (Sydney, n = 49; 16 women, 33 men) or Beijing, China (Beijing, n=24; 12 women, 12 men) were randomly assigned to r-HuEPO or placebo groups prior to a 25 day administration phase. Injections of r-HuEPO (or saline) were administered double-blind at a dose of 50 IU/kg three times per week, with oral iron (105 mg) or placebo supplements taken daily by all subjects. Blood profiles were monitored during and for 4 weeks after drug administration for hematocrit (Hct), reticulocyte hematocrit (RetHct), percent macrocytes (%Macro), serum erythropoietin (EPO) and soluble transferrin receptor (sTfr), since we had previously shown that these five variables were indicative of r-HuEPO use. RESULTS: The changes in Hct, RetHct, %Macro, EPO and sTfr in the Sydney trial were qualitatively very similar to the changes noted in our previous administration trial involving recreational athletes of similar genetic origin. Statistical models developed from Fisher's discriminant analysis were able to categorize the user and placebo groups correctly. The same hematologic response was demonstrated in Beijing athletes also administered r-HuEPO. INTERPRETATION AND CONCLUSIONS: This paper confirms that r-HuEPO administration causes a predictable and reproducible hematologic response. These markers are disturbed both during and for several weeks following r-HuEPO administration. This work establishes an indirect blood test which offers a useful means of detecting and deterring r-HuEPO abuse. Ethnicity did not influence the markers identified as being able to detect athletes who abuse r-HuEPO.
Adult↗
Drug testing at the Sydney Olympics.
With pre-Olympic and out-of-competition testing, as well as a new, validated test for erythropoietin, athletes will be exposed to more comprehensive drug testing at the Sydney Olympics.
Doping in Sports↗
Drugs in sports: analytical trends.
A minority of athletes continues to use prohibited drugs in sports to enhance performance. Athletes discovered using these drugs can be subject to severe penalties, often resulting in media and public scrutiny, especially at major events such as the Olympic Games. The International Olympic Committee (IOC) has set out the classes of the substances it bans in the IOC Medical Code. In many cases "old" drugs such as anabolic steroids are still used, and current testing regimes can test for these. Advances in the therapeutic treatment of illness have resulted in new drugs or practices, many of which are difficult to detect and which have been turned to the sinister role of performance enhancement. Detection of some newly developed drugs which have been placed on the banned list offers a major challenge to laboratories involved in sports dope testing. In some cases this requires research into new applications of research techniques. These techniques involve the novel use of gas chromatography/ mass spectrometry (GC/MS) techniques, high-resolution mass spectrometry (HRMS), carbon isotope ratio mass spectrometry, and immunoassay techniques.
Anabolic Agents↗
Gas chromatographic-mass spectrometric quantitation of urinary buprenorphine and norbuprenorphine after derivatization by direct extractive alkylation.
A gas chromatographic-mass spectrometric procedure for the quantitation of buprenorphine and norbuprenorphine has been developed in which the analytes were converted, after enzyme hydrolysis, to their methyl derivatives by direct extractive alkylation using tetrahexylammonium hydrogen sulphate phase transfer reagent and iodomethane dissolved in tert.-butylmethyl ether. The procedure utilised a sample volume of 2 ml and gave a detection limit of 0.2 ng ml(-1) for buprenorphine and norbuprenorphine. The buprenorphine and norbuprenorphine standard curves were linear in the concentration range of 1-100 ng ml(-1) with r=0.999. The coefficients of variation for the intra-run precision were 1.3% for buprenorphine and 8.8% for norbuprenorphine (n=10). The coefficients of variation for the inter-run precision were 7.7% for buprenorphine and 10.1% for norbuprenorphine (n=5). The method recovery was 92% (C.V.=3.3%) for buprenorphine and 104% (C.V.=2.9%) for norbuprenorphine (n=10).
Analgesics, Opioid↗
Structural analogues of ZAPA as GABAA agonists.
Structural analogues of ZAPA, Z-3-[(aminoiminomethyl)thio]prop-2-enoic acid, an isothiouronium analogue of GABA, are potent GABAA agonists as seen in the isolated guinea-pig ileum and in the facilitation of [3H]diazepam binding to rat brain membranes. Compounds with guanidino or amidine groups replacing the amino functionality of GABA were also found to be active. The highest activity was displayed by the isothiouronium salts in which the conformational flexibility of the molecule is restricted by a Z-substituted carbon-carbon double bond. A series of bis-isothiouronium compounds was prepared from aliphatic alpha, omega-bis-thioureas as mixtures of E and Z adducts. Maximum GABAA agonist activity for this series was found with a C6-C8 carbon chain, and the results were consistent with an interaction at the GABAA receptor with only one end of the molecule, rather than the more potent effect expected of a molecule bridging two active sites. GABAA antagonist/partial agonist activity was observed on the guinea pig isolated ileum for a number of different analogue types, with the most potent being bis-isothiouronium derivatives. None of the substituted derivatives of ZAPA was as active as ZAPA itself, and maximum GABAA activity was found in the n-pentyl and n-hexyl analogues.
Acrylates↗
Profiling of urinary testosterone and luteinizing hormone in exercise-stressed male athletes, using gas chromatography-mass spectrometry and enzyme immunoassay techniques.
Knowledge of the effects of episodic or short-term exercise-stress on endogenous testosterone and luteinizing hormone levels still remains fragmentary and inconclusive. In this study, an approach based on the absolute concentrations of urinary total testosterone (T), luteinizing hormone (LH) and the T/LH concentration ratios, was used to profile short-term exercise-stress responses in healthy drug-free male athletes. Testosterone and luteinizing hormone concentrations were measured using gas chromatography-mass spectrometry (GC-MS) and microparticle enzyme immunoassay (MEIA) techniques, respectively. Stress profiles derived from exercise-stress at VO2max, 68.1% VO2max and 51.6% VO2max were plotted using the concentrations of T, LH and the ratios of T/LH found under non-stressed and stressed conditions. Significant changes in LH concentrations (p < 0.005) and T/LH ratios (p < 0.005) levels were observed between the pre-stress and post-exercise conditions during acute exercise-stress at VO2max but the T concentration did not show any marked change relative to the non-stressed condition. Whilst exercise-stress appeared to reduce the change in T concentrations between the pre- and post-exercise states compared to that in the non-stressed control condition, the change in LH concentrations showed a moderate increase at submaximal oxygen uptake values. The stress profiles derived from this study facilitated an assessment of the relationship between the endogenous T, LH and T/LH ratio stress-responses over a short period of applied exercise-stress.
Gas Chromatography-Mass Spectrometry↗
Gas chromatographic-mass spectrometric quantitation of urinary 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid after derivatization by direct extractive alkylation.
A gas chromatographic-mass spectrometric procedure for the quantitation of urinary 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) has been developed in which the THC-COOH was derivatized to its corresponding methyl ester-methyl ether derivative by direct extractive alkylation using tetrahexylammonium (THA+) counter-ion and iodomethane dissolved in toluene. The procedure utilised a sample volume of 2 ml and gave a detection limit of 0.25 ng/ml. The inter-run and intra-run coefficients of variation were 7.0% and 4.8%, respectively. The inter-day standard curves were linear in the concentration range 0-300 ng/ml with a mean r = 0.9997 (n = 4).
Alkylation↗
Diuretic screening in human urine by gas chromatography-mass spectrometry: use of a macroreticular acrylic copolymer for the efficient removal of the coextracted phase-transfer reagent after derivatization by direct extractive alkylation.
A simple and efficient procedure has been developed for the derivatization of diuretic agents in human urine by direct extractive alkylation and their detection by gas chromatography-mass spectrometry. The procedure is an improvement over previous extractive alkylation methods because of the development of a simple clean-up step using a macroreticular acrylic copolymer (SM-7 resin) to remove the coextracted phase-transfer reagent from the organic phase after derivatization. With 1 ml of sample the method gives detection limits in the range 10-50 ng/ml for acetazolamide, probenecid, dichlorphenamide, hydroflumethiazide, furosemide, chlorthalidone, bumetanide, hydrochlorothiazide, quinethazone, bendroflumethiazide, metolazone and cyclopenthiazide.
Acrylic Resins↗
Routine screening and quantitation of urinary corticosteroids using bench-top gas chromatography-mass-selective detection.
A method was developed for the routine screening, confirmation and quantitation of corticosteroids in human urine using bench top capillary gas chromatography (GC)-mass-selective detection. The free and conjugated corticosteroid fractions were isolated by liquid-liquid partition. After evaporation to dryness under vacuum the corticosteroid residues were derivatized to form the methyloxime trimethylsilyl ether derivatives. Both GC retention data and characteristic spectral data based on authentic reference standards were used for the identification and quantitation of cortisol, cortisone, tetrahydrocortisol and tetrahydrocortisone in the ppb (ng/ml) concentration range. The method is simpler and more efficient than the other GC-mass spectrometric (MS) techniques. It is also more sensitive than the liquid chromatographic-MS method.
Adrenal Cortex Hormones↗
Screening for diuretics in human urine by gas chromatography-mass spectrometry with derivatisation by direct extractive alkylation.
A rapid, sensitive and reliable gas chromatographic-mass spectrometric (GC-MS) screening procedure for diuretics in human urine has been developed. The procedure uses derivatisation by extractive methylation directly from the urine. The suitability of a number of phase transfer reagents and solvents were studied for the detection of sixteen diuretics. The results obtained indicate that the screening procedure employing tetrahexylammonium hydrogensulphate at pH 12 with methyl iodide in toluene at room temperature was the most effective. This method gives selectivity and sensitivities down to 0.03-0.1 microgram/ml and provides a substrate suitable for GC-MS confirmation without further manipulation. The application of the method is demonstrated by the screening of urine for bumetanide, ethacrynic acid, acetazolamide, chlorothiazide and hydrochlorothiazide.
Acetazolamide↗
Isothiouronium compounds as gamma-aminobutyric acid agonists.
Analogues of gamma-aminobutyric acid (GABA) incorporating an isothiouronium salt as a replacement for a protonated amino functional group have been investigated for activity on: GABA receptors in the guinea-pig ileum; [3H]-GABA and [3H]-diazepam binding to rat brain membranes; and GABA uptake and transamination. For the homologous series of omega-isothiouronium alkanoic acids, maximum GABA-mimetic activity was found at 3-[(aminoiminomethyl)thio]propanoic acid. Introduction of unsaturation into this compound gave two isomeric conformationally restricted analogues. The trans isomer was inactive at GABA receptors while the cis compound ((Z)-3-[(aminoiminomethyl)thio]prop-2-enoic acid (ZAPA)) was more potent than muscimol and GABA as a GABA agonist with respect to low affinity GABA receptor sites. Both isomers were moderately potent at inhibiting the uptake of [3H]-GABA into rat brain slices. Comparison of possible conformations of the two unsaturated isomers by interactive computer graphics modelling and comparison with muscimol has led to a plausible active conformation of ZAPA, which may be a selective and potent agonist for low affinity GABA binding sites.
4-Aminobutyrate Transaminase↗
Halogenated pyrrolopyrimidine analogues of adenosine from marine organisms: pharmacological activities and potent inhibition of adenosine kinase.
Two novel halogenated pyrrolopyrimidine analogues of adenosine, isolated from marine sources, have been examined for pharmacological and biochemical activities. 4-Amino-5-bromo-pyrrolo[2,3-d]pyrimidine, from a sponge of the genus Echinodictyum, had bronchodilator activity at least as potent as theophylline but with a different biochemical profile; unlike theophylline it had no antagonist activity at CNS adenosine receptors and it was quite a potent inhibitor of adenosine uptake and adenosine kinase in brain tissue. 5'-Deoxy-5-iodotubercidin, isolated from the red alga Hypnea valentiae, caused potent muscle relaxation and hypothermia when injected into mice. This compound was a very potent inhibitor of adenosine uptake into rat and guinea-pig brain slices and an extremely potent inhibitor of adenosine kinase from guinea-pig brain and rat brain and liver. Neither of these two pyrrolopyrimidine analogues was a substrate for, or an inhibitor of, adenosine deaminase. Neither compound appeared to have any direct agonist activity on guinea-pig brain adenosine-stimulated adenylate cyclase (A2 adenosine receptors). 5'-Deoxy-5-iodotubercidin is unique in two respects: it appears to be the first naturally-occurring example of a 5'-deoxyribosyl nucleoside and is the first example of a specifically iodinated nucleoside from natural sources. It may be the most potent adenosine kinase inhibitor yet described and, by virtue of its structure, may prove to be the most specific.
3',5'-Cyclic-AMP Phosphodiesterases↗
Conversion of lanosterol into a compound with the carbon skeleton of fusidic acid.
Explore the source record for details and available documents.
Chemical Phenomena↗