1
|
Sharma R, Strelevitz TJ, Gao H, Clark AJ, Schildknegt K, Obach RS, Ripp SL, Spracklin DK, Tremaine LM, Vaz ADN. Deuterium Isotope Effects on Drug Pharmacokinetics. I. System-Dependent Effects of Specific Deuteration with Aldehyde Oxidase Cleared Drugs. Drug Metab Dispos 2011; 40:625-34. [DOI: 10.1124/dmd.111.042770] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
|
2
|
Vanderheiden S, Bulat B, Zevaco T, Jung N, Bräse S. Solid phase synthesis of selectively deuterated arenes. Chem Commun (Camb) 2011; 47:9063-5. [PMID: 21755074 DOI: 10.1039/c1cc12950c] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A novel access to deuterated and D(3)CO-substituted arenes has been developed using immobilized triazenes as precursors. The linker system and the deuterating cleavage methodology could be shown to be compatible with various functional groups and are therefore suitable for the synthesis of derivatives only hardly available via comparable protocols.
Collapse
Affiliation(s)
- Sylvia Vanderheiden
- Institute of Organic Chemistry, KIT-Campus South, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
| | | | | | | | | |
Collapse
|
3
|
Hanzlik RP, Fang J, Koen YM. Filling and mining the reactive metabolite target protein database. Chem Biol Interact 2008; 179:38-44. [PMID: 18823962 DOI: 10.1016/j.cbi.2008.08.016] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2008] [Revised: 08/22/2008] [Accepted: 08/26/2008] [Indexed: 12/13/2022]
Abstract
The post-translational modification of proteins is a well-known endogenous mechanism for regulating protein function and activity. Cellular proteins are also susceptible to post-translational modification by xenobiotic agents that possess, or whose metabolites possess, significant electrophilic character. Such non-physiological modifications to endogenous proteins are sometimes benign, but in other cases they are strongly associated with, and are presumed to cause, lethal cytotoxic consequences via necrosis and/or apoptosis. The Reactive Metabolite Target Protein Database (TPDB) is a searchable, freely web-accessible (http://tpdb.medchem.ku.edu:8080/protein_database/) resource that attempts to provide a comprehensive, up-to-date listing of known reactive metabolite target proteins. In this report we characterize the TPDB by reviewing briefly how the information it contains came to be known. We also compare its information to that provided by other types of "-omics" studies relevant to toxicology, and we illustrate how bioinformatic analysis of target proteins may help to elucidate mechanisms of cytotoxic responses to reactive metabolites.
Collapse
Affiliation(s)
- Robert P Hanzlik
- Department of Medicinal Chemistry and Bioinformatics Core Facility, University of Kansas, Lawrence, 66045-7582, USA.
| | | | | |
Collapse
|
4
|
Mutlib AE. Application of stable isotope-labeled compounds in metabolism and in metabolism-mediated toxicity studies. Chem Res Toxicol 2008; 21:1672-89. [PMID: 18702535 DOI: 10.1021/tx800139z] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Stable isotope-labeled compounds have been synthesized and utilized by scientists from various areas of biomedical research during the last several decades. Compounds labeled with stable isotopes, such as deuterium and carbon-13, have been used effectively by drug metabolism scientists and toxicologists to gain better understanding of drugs' disposition and their potential role in target organ toxicities. The combination of stable isotope-labeling techniques with mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy, which allows rapid acquisition and interpretation of data, has promoted greater use of these stable isotope-labeled compounds in absorption, distribution, metabolism, and excretion (ADME) studies. Examples of the use of stable isotope-labeled compounds in elucidating structures of metabolites and delineating complex metabolic pathways are presented in this review. The application of labeled compounds in mechanistic toxicity studies will be discussed by providing an example of how strategic placement of a deuterium atom in a drug molecule mitigated specific-specific renal toxicity. Other examples from the literature demonstrating the application of stable isotope-labeled compounds in understanding metabolism-mediated toxicities are presented. Furthermore, an example of how a stable isotope-labeled compound was utilized to better understand some of the gene changes in toxicogenomic studies is discussed. The interpretation of large sets of data produced from toxicogenomics studies can be a challenge. One approach that could be used to simplify interpretation of the data, especially from studies designed to link gene changes with the formation of reactive metabolites thought to be responsible for toxicities, is through the use of stable isotope-labeled compounds. This is a relatively unexplored territory and needs to be further investigated. The employment of analytical techniques, especially mass spectrometry and NMR, used in conjunction with stable isotope-labeled compounds to establish and understand mechanistic link between reactive metabolite formation, genomic, and proteomic changes and onset of toxicity is proposed. The use of stable isotope-labeled compounds in early human ADME studies as a way of identifying and possibly quantifying all drug-related components present in systemic circulation is suggested.
Collapse
Affiliation(s)
- Abdul E Mutlib
- Biotransformation Department, Drug Safety and Metabolism, Wyeth Research, Collegeville, Pennsylvania 19426, USA.
| |
Collapse
|
5
|
Ikehata K, Duzhak TG, Galeva NA, Ji T, Koen YM, Hanzlik RP. Protein targets of reactive metabolites of thiobenzamide in rat liver in vivo. Chem Res Toxicol 2008; 21:1432-42. [PMID: 18547066 PMCID: PMC2493440 DOI: 10.1021/tx800093k] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Thiobenzamide (TB) is a potent hepatotoxin in rats, causing dose-dependent hyperbilirubinemia, steatosis, and centrolobular necrosis. These effects arise subsequent to and appear to result from the covalent binding of the iminosulfinic acid metabolite of TB to cellular proteins and phosphatidylethanolamine lipids [ Ji et al. ( 2007) Chem. Res. Toxicol. 20, 701- 708 ]. To better understand the relationship between the protein covalent binding and the toxicity of TB, we investigated the chemistry of the adduction process and the identity of the target proteins. Cytosolic and microsomal proteins isolated from the livers of rats treated with a hepatotoxic dose of [ carboxyl- (14)C]TB contained high levels of covalently bound radioactivity (25.6 and 36.8 nmol equiv/mg protein, respectively). These proteins were fractionated by two-dimensional gel electrophoresis, and radioactive spots (154 cytosolic and 118 microsomal) were located by phosphorimaging. Corresponding spots from animals treated with a 1:1 mixture of TB and TB- d 5 were similarly separated, the spots were excised, and the proteins were digested in gel with trypsin. Peptide mass mapping identified 42 cytosolic and 24 microsomal proteins, many of which appeared in more than one spot on the gel; however, only a few spots contained more than one identifiable protein. Eighty-six peptides carrying either a benzoyl or a benzimidoyl adduct on a lysine side chain were clearly recognized by their d 0/ d 5 isotopic signature (sometimes both in the same digest). Because model studies showed that benzoyl adducts do not arise by hydrolysis of benzimidoyl adducts, it was proposed that TB undergoes S-oxidation twice to form iminosulfinic acid 4 [PhC(NH)SO 2H], which either benzimidoylates a lysine side chain or undergoes hydrolysis to 9 [PhC(O)SO 2H] and then benzoylates a lysine side chain. The proteins modified by TB metabolites serve a range of biological functions and form a set that overlaps partly with the sets of proteins known to be modified by several other metabolically activated hepatotoxins. The relationship of the adduction of these target proteins to the cytotoxicity of reactive metabolites is discussed in terms of three currently popular mechanisms of toxicity: inhibition of enzymes important to the maintenance of cellular energy and homeostasis, the unfolded protein response, and interference with kinase-based signaling pathways that affect cell survival.
Collapse
Affiliation(s)
- Keisuke Ikehata
- Department of Medicinal Chemistry University of Kansas, Lawrence, KS 66045
| | - Tatyana G. Duzhak
- Department of Medicinal Chemistry University of Kansas, Lawrence, KS 66045
| | | | - Tao Ji
- Department of Medicinal Chemistry University of Kansas, Lawrence, KS 66045
| | - Yakov M. Koen
- Department of Medicinal Chemistry University of Kansas, Lawrence, KS 66045
| | - Robert P. Hanzlik
- Department of Medicinal Chemistry University of Kansas, Lawrence, KS 66045
| |
Collapse
|
6
|
Mutlib AE, Gerson RJ, Meunier PC, Haley PJ, Chen H, Gan LS, Davies MH, Gemzik B, Christ DD, Krahn DF, Markwalder JA, Seitz SP, Robertson RT, Miwa GT. The species-dependent metabolism of efavirenz produces a nephrotoxic glutathione conjugate in rats. Toxicol Appl Pharmacol 2000; 169:102-13. [PMID: 11076702 DOI: 10.1006/taap.2000.9055] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Efavirenz, a potent nonnucleoside reverse transcriptase inhibitor widely prescribed for the treatment of HIV infection, produces renal tubular epithelial cell necrosis in rats but not in cynomolgus monkeys or humans. This species selectivity in nephrotoxicity could result from differences in the production or processing of reactive metabolites, or both. A detailed comparison of the metabolites produced by rats, monkeys, and humans revealed that rats produce a unique glutathione adduct. The mechanism of formation and role of this glutathione adduct in the renal toxicity were investigated using both chemical and biochemical probes. Efavirenz was labeled at the methine position on the cyclopropyl ring with the stable isotope deuterium, effectively reducing the formation of the cyclopropanol metabolite, an obligate precursor to the glutathione adduct. This substitution markedly reduced both the incidence and severity of nephrotoxicity as measured histologically. Further processing of this glutathione adduct was also important in producing the lesion and was demonstrated by inhibiting gamma-glutamyltranspeptidase with acivicin pretreatment (10 mg/kg, IV) prior to dosing with efavirenz. Again, both the incidence and severity of the nephrotoxicity were reduced, such that four of nine rats given acivicin were without detectable lesions. These studies provide compelling evidence that a species-specific formation of glutathione conjugate(s) from efavirenz is involved in producing nephrotoxicity in rats. Mechanisms are proposed for the formation of reactive metabolites that could be responsible for the renal toxicity observed in rats.
Collapse
Affiliation(s)
- A E Mutlib
- Drug Metabolism and Pharmacokinetics Section, DuPont Pharmaceuticals Company, Stine-Haskell Research Center, Elkton Road, Newark, Delaware 19714, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Brennan RJ, Schiestl RH. Chloroform and carbon tetrachloride induce intrachromosomal recombination and oxidative free radicals in Saccharomyces cerevisiae. Mutat Res 1998; 397:271-8. [PMID: 9541652 DOI: 10.1016/s0027-5107(97)00225-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Chlorination of drinking water results in the generation of low levels of numerous chlorinated hydrocarbons due to the reaction of chlorine with naturally occurring organic compounds in the water. Concern has been raised about the safety of these chlorinated contaminants as several of them, most notably chloroform (trichloromethane), have been shown to be carcinogenic in long-term rodent bioassays and weak correlations between trihalomethane levels in drinking water and an increased risk of bladder and colorectal cancer in humans have been found. Chloroform and carbon tetrachloride induce liver cancer in rats and mice only at doses where significant hepatotoxicity is observed and have been classed as non-genotoxic carcinogens. We have investigated the ability of chloroform, carbon tetrachloride and 1,1,1-trichloroethane to induce deletions via intrachromosomal recombination in the yeast Saccharomyces cerevisiae. Chloroform and carbon tetrachloride induced this genotoxic recombination event at similar doses, 1,1,1-Trichloroethane gave only a weak response in the DEL recombination assay and only at the highest dose. We further show that chloroform and carbon tetrachloride, but not trichloroethane, induced oxidative free radical species in our yeast strain. The free radical scavenger N-acetylcysteine reduced chloroform-induced toxicity and recombination, and both chloroform and carbon tetrachloride were able to oxidize the free radical-sensitive reporter compound dichlorofluorescein diacetate in vivo. The implications of these findings to the carcinogenic activities of the three compounds are discussed.
Collapse
Affiliation(s)
- R J Brennan
- Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, MA 02115-6012, USA
| | | |
Collapse
|
8
|
Appendix B: Chlorinated alkanes. Regul Toxicol Pharmacol 1994. [DOI: 10.1016/s0273-2300(05)80027-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
9
|
Osawa Y, Highet RJ, Pohl LR. The use of stable isotopes to identify reactive metabolites and target macromolecules associated with toxicities of halogenated hydrocarbon compounds. Xenobiotica 1992; 22:1147-56. [PMID: 1441605 DOI: 10.3109/00498259209051868] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
1. Halogenated compounds, such as the inhalation anaesthetics, halothane and enflurane, and the chemicals chloroform, carbon tetrachloride, and bromotrichloromethane can cause hepatotoxicity, nephrotoxicity, and inactivation of cytochromes P-450. Each of these toxicities is mediated by reactive metabolites. 2. Stable isotopes of hydrogen, carbon, chlorine and oxygen have been used in conjunction with mass spectrometry and n.m.r. spectrometry to identify the structures of these metabolites, to elucidate the mechanisms of their formation, and to characterize the structures of their macromolecular adducts. 3. In a number of cases, oxidative pathways of metabolism to toxic metabolites have been defined by kinetic deuterium isotope effects. 4. Recently, we have found that the trichloromethyl radical metabolite of bromotrichloromethane can activate myoglobin by causing the covalent cross-linking of haem to protein. The structure of a haem-myoglobin adduct has been defined by the use of stable isotope studies.
Collapse
Affiliation(s)
- Y Osawa
- Laboratory of Chemical Pharmacology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892
| | | | | |
Collapse
|
10
|
|
11
|
Thompson DC, Trush MA. Enhancement of butylated hydroxytoluene-induced mouse lung damage by butylated hydroxyanisole. Toxicol Appl Pharmacol 1988; 96:115-21. [PMID: 3188016 DOI: 10.1016/0041-008x(88)90253-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The phenolic antioxidant butylated hydroxytoluene (BHT) is known to produce a dose-dependent increase in mouse lung weight which is characterized by the necrosis of pulmonary type I and endothelial cells. We studied the ability of butylated hydroxyanisole (BHA) to modify BHT-induced changes in lung weight in male CD-1 mice. BHA alone had no effect on lung weight up to a dose of 500 mg/kg (sc). However, when injected 30 minutes prior to sub-threshold doses of BHT (0-250 mg/kg, ip), BHA significantly enhanced lung weight in a dose-dependent manner. The ability of BHA to enhance BHT-induced changes in lung weight was dependent on both the time and the route of administration of BHA relative to BHT. Deuteration of BHT abolished the in vivo toxicity from the combination of BHA and BHT. These results suggest that the toxicity resulting from the combination of BHA and BHT is due to the formation of BHT-quinone methide and that the role of BHA might be either to deplete some protective mechanism in the target pulmonary cells or to enhance the biotransformation of BHT into BHT-quinone methide.
Collapse
Affiliation(s)
- D C Thompson
- Department of Environmental Health Sciences, Johns Hopkins University, Baltimore, Maryland 21205
| | | |
Collapse
|
12
|
Søderlund EJ, Brunborg G, Omichinski JG, Holme JA, Dahl JE, Nelson SD, Dybing E. Testicular necrosis and DNA damage caused by deuterated and methylated analogs of 1,2-dibromo-3-chloropropane in the rat. Toxicol Appl Pharmacol 1988; 94:437-47. [PMID: 3400095 DOI: 10.1016/0041-008x(88)90284-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To study the role of metabolism in 1,2-dibromo-3-chloropropane (DBCP)-induced testicular damage in rats, selectively deuterated and methylated analogs of DBCP were given as a single ip dose of 340 mumol/kg and testicular toxicity was determined 10 days after treatment. None of the four deuterated analogs C1-D2-, C2-D1-, C3-D2-, or C1-C2-C3-D5-DBCP reduced the degree of testicular damage compared to DBCP, indicating that metabolic cleavage of a C-H bond was not rate-limiting in DBCP-induced testicular toxicity. Of the five methylated analogs, C1-methyl-, C1-dimethyl-, C2-methyl-, and C3-methyl-DBCP and 1,2-dibromo-4-chlorobutane, only C3-methyl-DBCP caused testicular toxicity. DBCP treatment resulted in increased testicular DNA damage at doses of 85-170 mumol/kg as measured by alkaline elution of DNA from testicular cells isolated 3 hr after in vivo treatment. The perdeutero-DBCP analog induced testicular DNA damage that was at least as extensive as that induced by DBCP. Of the methylated analogs tested, only C3-methyl-DBCP gave a marked dose-dependent increase in testicular DNA damage between 170 and 540 mumol/kg. There were no significant differences in the testicular tissue distribution between DBCP, perdeutero-DBCP, and the methylated DBCP analogs. Furthermore, in distribution studies with DBCP, C1-methyl- and C3-methyl-DBCP, and 1,2-dibromo-4-chlorobutane, the highest tissue concentrations were found in the kidneys, followed by the liver and then the testes. The fact that testicular DNA damage of DBCP and its deuterated and methylated analogs paralleled their ability to cause testicular necrosis and atrophy makes measurement of DNA damage a very useful correlate in mechanistic studies of DBCP-induced testicular cell death.
Collapse
Affiliation(s)
- E J Søderlund
- Department of Toxicology, National Institute of Public Health, Oslo, Norway
| | | | | | | | | | | | | |
Collapse
|
13
|
Abstract
Recent studies of quantitative and qualitative aspects of nicotine metabolism, and the use of metabolic data for estimating nicotine intake in humans are discussed. Previously reported methodology for determining nicotine bioavailability has been improved by using stable isotope-labeled nicotine administered intravenously. Combined gas chromatography-mass spectrometry with selected ion monitoring has been used to simultaneously determine concentrations of isotopically-labeled nicotine and tobacco-derived nicotine in blood. Nicotine intake from cigarette smoking was estimated from clearance of labeled nicotine and blood concentrations of tobacco-derived nicotine. Progress in elucidating the metabolic profile of nicotine in humans, and the use of nicotine metabolites as markers of tobacco smoke consumption is summarized.
Collapse
Affiliation(s)
- P Jacob
- Department of Medicine, University of California, San Francisco
| | | | | |
Collapse
|
14
|
Omichinski JG, Brunborg G, Søderlund EJ, Dahl JE, Bausano JA, Holme JA, Nelson SD, Dybing E. Renal necrosis and DNA damage caused by selectively deuterated and methylated analogs of 1,2-dibromo-3-chloropropane in the rat. Toxicol Appl Pharmacol 1987; 91:358-70. [PMID: 3424370 DOI: 10.1016/0041-008x(87)90058-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Selectively deuterated and methylated analogs of the nematocide 1,2-dibromo-3-chloropropane (DBCP) were compared to DBCP in causing acute renal damage in rats. All of the six deuterated analogs tested at 340 mumol/kg, including the perdeutero compound, failed to significantly alter the kidney necrosis observed at 48 hr compared to DBCP. Furthermore, when the perdeutero analog was administered at several doses (42.5, 85, 170, and 340 mumol/kg), it caused kidney damage that was not significantly different than that caused by an equivalent molar dose of nondeuterated DBCP. Of the five methylated analogs tested at 170 and 340 mumol/kg, only C3-methyl-DBCP and 1,2-dibromo-4-chlorobutane caused nephrotoxicity. The C2-methyl-, C1-dimethyl-, and C2-methyl-DBCP analogs failed to cause renal necrosis determined 48 hr after dosing. In distribution studies DBCP, perdeutero-DBCP, and all the methylated analogs were found to concentrate in the kidney approximately 25 times relative to plasma 1 hr after administration. DBCP at doses of 4.3 mumol/kg and higher caused DNA damage in the kidney as early as 10 min after administration, as measured by alkaline elution of DNA from isolated kidney nuclear preparations. Perdeuteration did not decrease the DNA damaging effect of DBCP. The ability of the methylated DBCP analogs to induce renal DNA damage correlated with their necrogenic potential. Experiments using pretreatments that are known to decrease the nephrotoxicity caused by glutathione and cysteine conjugates of several halogenated alkenes were conducted to examine the effect of these pretreatments on DBCP-induced nephrotoxicity. Probenecid, L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125) and aminooxyacetic acid did not significantly alter renal necrosis or DNA damage induced by DBCP. Based on the absence of any significant isotope effects with the predeutero-DBCP analog, it appears that breaking of a carbon-hydrogen bond is not the rate-limiting step in DBCP-induced nephrotoxicity. Studies with the methylated DBCP analogs indicate that a vicinal dibromo ethyl group must minimally be present for nephrotoxic potential. Furthermore, it seems unlikely that metabolism by renal cysteine conjugate beta-lyase is rate-limiting for DBCP nephrotoxicity.
Collapse
Affiliation(s)
- J G Omichinski
- Department of Toxicology, National Institute of Public Health, Oslo, Norway
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Cherrah Y, Falconnet JB, Desage M, Brazier JL, Zini R, Tillement JP. Study of deuterium isotope effects on protein binding by gas chromatography/mass spectrometry. Caffeine and deuterated isotopomers. BIOMEDICAL & ENVIRONMENTAL MASS SPECTROMETRY 1987; 14:653-7. [PMID: 2962673 DOI: 10.1002/bms.1200141115] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A study of the binding to human serum albumin (HSA) of caffeine and its deuterated isotopomers, 1-C2H3-,3-C2H3-, 1,7-(C2H3)2-, 3,7-(C2H3)2- and 1,3,7-(C2H3)3-caffeine, was performed by equilibrium dialysis. Free and bound fractions were measured by gas chromatography/mass spectrometry. Important and significant (Fischer and Student tests) isotope effects were observed on binding parameters: sites total concentration (N = 1732 microM for 1,3,7-(C2H3)3-caffeine versus 822 microM for caffeine; number of sites (n = 3 for 1,3,7-(C2H3)3-caffeine v. 1 for caffeine); and extent of binding (46% for 1,3,7-(C2H3)3-caffeine v. 27% for caffeine). A study of competition for HSA binding between caffeine and its 1,3,7-(C2H3)3- and 3,7-(C2H3)2-isotopomers confirmed the results obtained in direct binding studies. These isotope effects are discussed in terms of (a) tools for molecular pharmacology, (b) precautions to be taken when such labelled drugs are used in clinical pharmacology.
Collapse
Affiliation(s)
- Y Cherrah
- LEACM Faculty of Pharmacy, Lyon, France
| | | | | | | | | | | |
Collapse
|