title: In vitro toxicokinetic studies of cyclosarin: molecular mechanisms of elimination.
abstract: The toxicokinetics of in vitro elimination of highly toxic cyclosarin (GF) in biological systems revealed striking stereoselective differences in the range of 0.01μM to 1mM GF. While weak concentration dependency was detected for elimination of the toxic (-)-enantiomer indicating catalytic processes, elimination of less toxic (+)-GF followed unusual kinetics with relatively high concentration dependency. Fast initial GF binding in human heparinised plasma increased only at lower initial GF concentrations while (+)-GF binding strongly increased with decreasing GF concentration. In displacement experiments it was shown for the first time that GF binding on plasma components in rats and mice plasma was reversible. Investigations with human plasma require further methodical improvement. GF elimination by diisopropylfluorophosphatase (DFPase) wildtype as phosphotriesterase (PTE) model showed some similarities compared to human heparinised plasma. Impact of human serum albumin is negligible. When comparing kinetics of GF elimination with metabolite formation (fluoride and cyclohexyl methyl phosphonic acid, CHMPA), marked differences were detected. From the results a model was postulated illustrating possible steps of molecular mechanisms of GF interaction with plasma proteins including high affine fast initial binding followed by formation of metastable phosphonylated plasma proteins with subsequent hydrolysis and release of metabolites.
authors.affiliation: Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, 80937 Munich, Germany. Electronic address: georgreiter@bundeswehr.org.
authors.forename: Georg
authors.initials: G
authors.lastname: Reiter
authors.affiliation: Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, 80937 Munich, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Müller
authors.affiliation: Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, 80937 Munich, Germany.
authors.forename: Marianne
authors.initials: M
authors.lastname: Koller
authors.affiliation: Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, 80937 Munich, Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Thiermann
authors.affiliation: Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, 80937 Munich, Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Worek
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D043303:Aryldialkylphosphatase / Q000378:metabolism; D001711:Biotransformation; D001798:Blood Proteins / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D005459:Fluorides / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D051379:Mice; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D009994:Osmolar Concentration; D044345:Phosphoric Triester Hydrolases / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012709:Serum Albumin / Q000378:metabolism; D000075462:Serum Albumin, Human; D012995:Solubility; D013237:Stereoisomerism
chemical_list: C422455:ALB protein, human; D001798:Blood Proteins; D002800:Cholinesterase Inhibitors; D050505:Mutant Proteins; D009943:Organophosphorus Compounds; D011994:Recombinant Proteins; D012709:Serum Albumin; C073636:cyclohexyl methylphosphonic acid; D044345:Phosphoric Triester Hydrolases; D043303:Aryldialkylphosphatase; C468406:PON1 protein, human; C020061:diisopropyl-fluorophosphatase; D005459:Fluorides; C053914:cyclohexyl methylphosphonofluoridate; D000075462:Serum Albumin, Human
keywords: Cyclosarin; Enantiomers; Organophosphate; Paraoxonase; Plasma; Toxicokinetics