Title: Prophylaxis against soman inhalation toxicity in guinea pigs by pretreatment alone with human serum butyrylcholinesterase Allon N, Raveh L, Gilat E, Cohen E, Grunwald J, Ashani Y Ref: Toxicol Sci, 43:121, 1998 : PubMed
Human butyrylcholinesterase (HuBChE) has previously been shown to protect mice, rats, and monkeys against multiple lethal toxic doses of organophosphorus (OP) anticholinesterases that were challenged by i.v. bolus injections. This study examines the concept of using a cholinesterase scavenger as a prophylactic measure against inhalation toxicity, which is the more realistic simulation of exposure to volatile OPs. HuBChE-treated awake guinea pigs were exposed to controlled concentration of soman vapors ranging from 417 to 430 micrograms/liter, for 45 to 70 s. The correlation between the inhibition of circulating HuBChE and the dose of soman administered by sequential i.v. injections and by respiratory exposure indicated that the fraction of the inhaled dose of soman that reached the blood was 0.29. HuBChE to soman molar ratio of 0.11 was sufficient to prevent the manifestation of toxic signs in guinea pigs following exposure to 2.17x the inhaled LD50 dose of soman (ILD50, 101 micrograms/kg). A slight increase in HuBChE:soman ratio (0.15) produced sign-free animals after two sequential respiratory exposures with a cumulative dose of 4.5x ILD50. Protection was exceptionally high and far superior to the currently used traditional approach that consisted of pretreatment with pyridostigmine and postexposure combined administration of atropine, benactyzine, and an oxime reactivator. Quantitative analysis of the results suggests that in vivo sequestration of soman, and presumably other OPs, by exogenously administered HuBChE, is independent of the species used or the route of challenge entry. This assuring conclusion significantly expands the database of the bioscavenger strategy that now offers a dependable extrapolation from animals to human.
Title: Current Capabilities in Extrapolating from Animal to Human the Capacity of Human Butyrylcholinesterase to Detoxify Organophosphates Ashani Y, Grauer E, Grunwald J, Allon N, Raveh L Ref: In: Structure and Function of Cholinesterases and Related Proteins - Proceedings of Sixth International Meeting on Cholinesterases, (Doctor, B.P., Taylor, P., Quinn, D.M., Rotundo, R.L., Gentry, M.K. Eds) Plenum Publishing Corp.:255, 1998 : PubMed
Title: Large-scale purification and long-term stability of human butyrylcholinesterase: a potential bioscavenger drug Grunwald J, Marcus D, Papier Y, Raveh L, Pittel Z, Ashani Y Ref: Journal of Biochemical & Biophysical Methods, 34:123, 1997 : PubMed
Butyrylcholinesterase from human plasma (HuBChE) is a potential drug candidate for detoxification of certain harmful chemicals that contain carboxylic or phosphoric acid ester bonds. Large quantities of purified HuBChE, displaying a high stability upon long-term storage, are required for the evaluation of its therapeutic capacity and its pharmaceutical properties. Several modifications of a previously reported procedure enabled us to purify the enzyme > 15,000-fold from pools of up to 100 1 of human plasma. The three-step procedure is based on precipitation of plasma proteins by ammonium sulfate (step I) and batch adsorption of HuBChE on procainamide-Sepharose 4B gel (step II). Ammonium sulfate was also employed in the third stage to fractionate the final product from procainamide-containing HuBChE solution. The overall yield (63%) of electrophoretically pure enzyme was significantly higher than that previously reported (34%) for the purification of HuBChE from 12.5 1 of plasma or from 5 kg of Cohn fraction IV-4. Purified HuBChE was stored at 5 degrees C in 10 mM phosphate buffer (pH 7.4) containing 1 mM EDTA and 0.02% NaN3. The specific activity, protein migration on gel electrophoresis, thermostability at 54 degrees C and the mean residence time in the circulation of mice remained essentially constant for at least 46 months. The modifications introduced can provide large quantities of purified enzyme that maintains its activity and bioavailability properties for several years.
Title: The stoichiometry of protection against soman and VX toxicity in monkeys pretreated with human butyrylcholinesterase Raveh L, Grauer E, Grunwald J, Cohen E, Ashani Y Ref: Toxicol Appl Pharmacol, 145:43, 1997 : PubMed
Bioscavengers of organophophates (OP) have been examined as potential substitutes for the currently approved drug treatment against OP toxicity. The present work was designed to assess the ability of butyrylcholinesterase, purified from human serum (HuBChE), to prevent the toxicity induced by soman and VX in rhesus monkeys. The consistency of the data across species was then evaluated as the basis for the extrapolation of the data to humans. The average mean residence time of the enzyme in the circulation of monkeys following an intravenous loading was 34 hr. High bioavailability of HuBChE in blood (>80%) was demonstrated after intramuscular injection. A molar ratio of HuBChE:OP approximately 1.2 protected against an i.v. bolus injection of 2.1 x LD50 VX, while a ratio of 0.62 was sufficient to protect monkeys against an i.v. dose of 3.3 x LD50 of soman, with no additional postexposure therapy. A remarkable protection was also seen against soman-induced behavioral deficits detected in the performance of a spatial discrimination task. The consistency of the results across several species offers a reliable prediction of both the stoichiometry of the scavenging and the extent of prophylaxis with HuBChE against nerve agent toxicity in humans.
Title: Protection of Guinea Pigs against Soman Inhalation by Pretreatment Alone with Human Butyrylcholinesterase Allon N, Raveh L, Gilat E, Grunwald J, Manistersky E, Cohen E, Ashani Y Ref: In Enzyme of the Cholinesterase Family - Proceedings of Fifth International Meeting on Cholinesterases, (Quinn, D.M., Balasubramanian, A.S., Doctor, B.P., Taylor, P., Eds) Plenum Publishing Corp.:398, 1995 : PubMed
Title: Human Butyrylcholinesterase as Prophylaxis Treatment against Soman Grauer E, Raveh L, Kapon J, Grunwald J, Cohen E, Ashani Y Ref: In Enzyme of the Cholinesterase Family - Proceedings of Fifth International Meeting on Cholinesterases, (Quinn, D.M., Balasubramanian, A.S., Doctor, B.P., Taylor, P., Eds) Plenum Publishing Corp.:400, 1995 : PubMed
Title: Prevention of Brain Damage and Behavioral Performance Changes following an IV Injection of Soman and VX in Rats Pretreated with Human Butyrylcholinesterase Kadar T, Raveh L, Brandeis R, Grunwald J, Cohen E, Ashani Y Ref: In Enzyme of the Cholinesterase Family - Proceedings of Fifth International Meeting on Cholinesterases, (Quinn, D.M., Balasubramanian, A.S., Doctor, B.P., Taylor, P., Eds) Plenum Publishing Corp.:404, 1995 : PubMed
Title: Efficacy of Prophylaxis with Human Butyrylcholinesterase against Soman and VX Poisoning Raveh L, Grunwald J, Cohen E, Ashani Y Ref: In Enzyme of the Cholinesterase Family - Proceedings of Fifth International Meeting on Cholinesterases, (Quinn, D.M., Balasubramanian, A.S., Doctor, B.P., Taylor, P., Eds) Plenum Publishing Corp.:402, 1995 : PubMed
Title: Role of tyrosine 337 in the binding of huperzine A to the active site of human acetylcholinesterase Ashani Y, Grunwald J, Kronman C, Velan B, Shafferman A Ref: Molecular Pharmacology, 45:555, 1994 : PubMed
Huperzine A (HUP), a natural, potent, 'slow,' reversible inhibitor of antiacetylcholinesterase (AChE), has been suggested to be superior to antiacetylcholinesterase drugs now being used for management of Alzheimer's disease. To delineate the binding site of human AChE (HuAChE) for HUP, the biochemical constants kon, koff, and Ki were determined for complexes formed between HUP and single-site (Y337F, Y337A, F295A, W286A, and E202Q) or double-site (F295L/F297V) mutants of recombinant HuAChE (rHuAChE). The kinetic and dissociation constants were compared with those obtained for wild-type rHuAChE and AChE from Torpedo californica. Results demonstrate that the inhibition of AChE by HUP occurs through association with residues located inside the active site 'gorge,' rather than at the rim of the gorge. Tyrosine at position 337 (Y337) is essential for inhibition of rHuAChE by HUP (Ki = 26 nM). An aromatic array constituted from residues Y337, F295, and probably W86 is likely to offer a multicontact subsite that interacts with the ammonium group and with both the exo-and endocyclic double bond moieties of HUP. Lack of the aromatic side chain in the position homologous to Y337 explains the poor inhibitory potency of HUP toward human butyrylcholinesterase (Ki > 20,000 nM). Replacement of the carboxylate-containing E202 by glutamine had only marginal effect on the stability of the complex formed between HUP and rHuAChE. The pH-rate profiles suggest that destabilization of the complex after proton gain cannot be attributed solely to protonation of E202. These findings are expected to establish HUP as a lead compound for the design of new anti-AChE drugs.
Title: Huperzine A as a pretreatment candidate drug against nerve agent toxicity Grunwald J, Raveh L, Doctor BP, Ashani Y Ref: Life Sciences, 54:991, 1994 : PubMed
Huperzine A (HUP) is a naturally-occurring, potent, reversible inhibitor of acetylcholinesterase (AChE) that crosses the blood-brain barrier. To examine its ability to protect against nerve agent poisoning, HUP was administered i.p. to mice, and the s.c. LD50 of soman was determined at various time intervals after pretreatment. Results were compared to those obtained for animals treated with physostigmine. A protective ratio of approximately 2 was maintained for at least 6 hr after a single injection of HUP, without the need for any post-challenge drug therapy. By contrast, pretreatment with physostigmine increased the LD50 of soman by 1.4- to 1.5-fold for only up to 90 min. The long-lasting antidotal efficacy displayed by HUP correlated with the time course of the blood-AChE inhibition. The results suggest that the protection of animals by HUP from soman poisoning was achieved by temporarily sequestering the active site region of the physiologically important AChE.
Title: Prevention of soman-induced cognitive deficits by pretreatment with human butyrylcholinesterase in rats Brandeis R, Raveh L, Grunwald J, Cohen E, Ashani Y Ref: Pharmacol Biochem Behav, 46:889, 1993 : PubMed
This study examined the ability of pretreatment with human serum butyrylcholinesterase (HuBChE) to prevent soman-induced cognitive impairments. Behavioral testing was carried out using the Morris water maze task evaluating learning, memory, and reversal learning processes. Pretreatment with HuBChE significantly prevented the memory and reversal learning impairments induced by soman. A small deficiency in performance was observed only during part of the learning period in HuBChE-treated rats after administration of soman. Results support the contention that pretreatment alone with HuBChE is sufficient to increase survival and to prevent impairment in cognitive functioning following exposure to soman.
Title: Human butyrylcholinesterase as a general prophylactic antidote for nerve agent toxicity. In vitro and in vivo quantitative characterization Raveh L, Grunwald J, Marcus D, Papier Y, Cohen E, Ashani Y Ref: Biochemical Pharmacology, 45:2465, 1993 : PubMed
Butyrylcholinesterase purified from human plasma (HuBChE) was evaluated both in vitro and in vivo in mice and rats as a single prophylactic antidote against the lethal effects of highly toxic organophosphates (OP). The variation among the bimolecular rate constants for the inhibition of HuBChE by tabun, VX, sarin, and soman was 10-fold (0.47 to 5.12 x 10(7) M-1 min-1; pH 8.0, 26 degrees). The half-life of HuBChE in blood after its i.v. administration in mice and rats was 21 and 46 hr, respectively. The peak blood-enzyme level was obtained in both species approximately 9-13 hr following i.m. injection of HuBChE, and the fraction of the enzyme activity absorbed into the blood was 0.9 and 0.54 for rats and mice, respectively. The stoichiometry of the in vivo sequestration of the anti-cholinesterase toxicants was consistent with the HuBChE/OP ratio of the molar concentration required to inhibit 100% enzyme activity in vitro. Linear correlation was demonstrated between the blood level of HuBChE and the extent of protection conferred against the toxicity of nerve agents. Pretreatment with HuBChE alone was sufficient not only to increase survivability following exposure to multiple median lethal doses of a wide range of potent OPs, but also to alleviate manifestation of toxic symptoms in mice and rats without the need for additional post-exposure therapy. It appeared that in order to confer protection against lethality nerve agents had to be scavenged to a level below their median lethal dose LD50 within less than one blood circulation time. Since the high rate of sequestration of nerve agents by HuBChE is expected to underlie the activity of the scavenger in other species as well, a reliable extrapolation of its efficacy from experimental animals to humans can be made.
31P NMR spectroscopy of butyrylcholinesterase (BChE), acetylcholinesterase (AChE), and chymotrypsin (Cht) inhibited by pinacolyl methylphosphonofluoridate (soman), methylphosphonodifluoridate (MPDF), and diisopropyl phosphorofluoridate (DFP) allowed direct observation of the OP-linked moiety of aged (nonreactivatable) and nonaged organophosphorus (OP)-ChE conjugates. The 31P NMR chemical shifts of OP-ChE conjugates clearly demonstrated insertion of a P-O- bond into the active site of aged OP-ChE adducts. The OP moiety of nonaged OP-ChEs was shown to be uncharged. The OP-bound pinacolyl moiety of soman-inhibited and aged AChE was detached completely, whereas only partial dealkylation of the pinacolyl group was observed for soman-inhibited BChEs. This suggests that the latter enzyme reacted with the less active stereoisomer(s) of soman. In the case of soman-inhibited Cht, no dealkylation could be experimentally detected for any of the four stereoisomers of OP-Cht adducts. Results are consistent with the contention that the phenomenon of enzyme-catalyzed dealkylation of OP adducts of serine hydrolases strongly depends on the orientation of both the catalytic His and the carboxyl side chain of either Glu or Asp positioned next to the catalytic Ser. The denatured protein of aged OP-ChE or OP-Cht is a convenient leaving group in nucleophilic displacements of tetrahedral OP compounds despite the presence of a P-O- bond. This indicates that the unusual resistance to reactivation of the aged enzyme cannot be ascribed to simple electrostatic repulsion of an approaching nucleophile. The broadening of the 31P NMR signal of native OP-ChEs relative to that of OP-Cht is in agreement with the crystal structure of AChE, showing that the active site region of ChEs in solution resides in a deep, narrow gorge.
Title: Poster: Physicochemical and crystallographic studies on the stability and structure of aged and nonaged organophosphoryl conjugates of chymotrypsin Su CT, Steinberg N, Silman I, Harel M, Sussman JL, Grunwald J, Ashani Y Ref: In: Cholinesterases: Structure, Function, Mechanism, Genetics, and Cell Biology, (Massoulie J, Barnard EA, Chatonnet A, Bacou F, Doctor BP, Quinn DM) American Chemical Society, Washington, DC:274, 1991 : PubMed
Homologous aged and nonaged fluorescent organophosphorus conjugates of alpha-chymotrypsin (Cht) were used in a comparative spectroscopic study of the conformation of their active sites, employing the pyrene group as the fluorescent probe. Steady-state fluorescence measurements showed that the quantum yield of the pyrene probe which is stoichiometrically attached to the active site is ca. 20% lower in the aged conjugate, pyrenebutyl-O-P(O)(O-)-Cht (PBP-Cht), than in the nonaged conjugate, pyrenebutyl-O-P-(O)(OC2H5)-Cht (PBEP-Cht). Furthermore, fluorescence decay data indicate that quenching is dynamic and is not caused by oxygen. These data, together with collisional quenching data, imply that quenching originates in an internal interaction of the fluorophore with a group within the protein. Thus, interaction of the pyrene moiety with the polypeptide chain is significantly stronger in the aged than in the nonaged conjugate, implying a different orientation of the fluorophore with respect to the protein. Circular dichroism measurements, which reflect the asymmetry of the bound pyrene in the ground state, as well as circularly polarized luminescence studies, which reflect its asymmetry in the excited state, also show that the relative configuration of the pyrene moiety and the polypeptide chain is significantly altered upon aging. Aged conjugates obtained by use of various fluorescenct organophosphates [pyrenebutyl-O-P(O)Cl2, pyrenebutyl-O-P(O)(p-nitrophenoxy)Cl, pyrenebutyl-O-P(O)(p-nitrophenoxy)2] exhibit similar spectroscopic features, thus substantiating the hypothesis that instantaneous aging, by use of pyrenebutyl-O-P(O)Cl2, and dynamic aging, by gradual removal of an aryloxy group, yield a similar product. This finding provides strong support for the formation of a P-O- moiety in the aged conjugates, since the only expected common product of the two processes is PB-O-P(O)(O-)-Cht. Formation of excimers of the pyrene-containing organophosphorylchymotrypsin conjugates at concentrations above 3 X 10(-6) M is also reported.
