Investigating the structural influence of surface mutations on acetylcholinesterase inhibition by organophosphorus compounds and oxime reactivation.

Organophosphates (OPs) exert their toxicity by inhibiting primarily acetylcholinesterase (AChE) and to a lesser extent butyrylcholinesterase (BChE). Binary mixtures of mammalian AChE and oximes of varying structure have been recently considered for treatment of OP poisoning as catalytic bioscavengers. In this study wild type human AChE and human AChE with residue mutations D134H, D134H_E202Q and D134H_F338A were characterized and investigated for inhibition by OPs and consequent oxime reactivation of phosphylated enzymes. The rationale for selecting these substitution positions was based on D134H being a naturally occurring single nucleotide polymorphism (SNP) in humans and that E202Q and F338A mutations slow aging of OP inhibited AChEs. Inhibition of D134H by paraoxon and analogues of cyclosarin was 2-8 times slower than inhibition of wild type (wt), while reactivation of the paraoxon inhibited enzyme by 2PAM was 6 times faster. Both inhibition and reactivation of D134H_E202Q and D134H_F338A double mutants were up to two orders of magnitude slower than the wt indicating that introduction of the active center substitutions abolished fully the effect of the peripherally located D134H. These results indicate that selected residues outside the active center influence inhibition, reactivation and catalysis rates through longer range interactions.

Decontamination of chemical and biological warfare agents with a single multi-functional material.

We report the synthesis of new polymers based on a dimethylacrylamide-methacrylate (DMAA-MA) co-polymer backbone that support both chemical and biological agent decontamination. Polyurethanes containing the redox enzymes glucose oxidase and horseradish peroxidase can convert halide ions into active halogens and exert striking bactericidal activity against gram positive and gram negative bacteria. New materials combining those biopolymers with a family of N-alkyl 4-pyridinium aldoxime (4-PAM) halide-acrylate co-polymers offer both nucleophilic activity for the detoxification of organophosphorus nerve agents and internal sources of halide ions for generation of biocidal activity. Generation of free bromine and iodine was observed in the combined material resulting in bactericidal activity of the enzymatically formed free halogens that caused complete kill of E. coli (>6 log units reduction) within 1 h at 37 degrees C. Detoxification of diisopropylfluorophosphate (DFP) by the polyDMAA MA-4-PAM iodide component was dose-dependent reaching 85% within 30 min. A subset of 4-PAM-halide co-polymers was designed to serve as a controlled release reservoir for N-hydroxyethyl 4-PAM (HE 4-PAM) molecules that reactivate nerve agent-inhibited acetylcholinesterase (AChE). Release rates for HE 4-PAM were consistent with hydrolysis of the HE 4-PAM from the polymer backbone. The HE 4-PAM that was released from the polymer reactivated DFP-inhibited AChE at a similar rate to the oxime antidote 4-PAM.

IBU-octyl-cytisine, a novel bifunctional compound eliciting anti-inflammatory and cholinergic activity, ameliorates CNS inflammation by inhibition of T-cell activity.

Experimental autoimmune encephalomyelitis (EAE) is a central nervous system (CNS) inflammatory model in which MOG-specific T-cells initiate an autoimmune attack leading to demyelinization and consequently, neurological damage and morbidity. As EAE pathogenesis results from the involvement of immune cells, CNS resident-cells and inflammatory mediators, our treatment strategy was to use a bifunctional compound with dual anti-inflammatory properties: a non-steroidal anti-inflammatory moiety and a nicotinic agonist moiety, intended to interact with the alpha7 nicotinic receptor present on immune cells. We used IBU-Octyl-Cytisine, with an ibuprofen (IBU) moiety and Cytisine, as the nicotinic agonist. The two moieties are attached by an eight carbon (octyl) spacer. Treatment of EAE with IBU-Octyl-Cytisine (2.5 mg/kg/day, i.p.) reduced significantly (by 70%) disease severity and inflammatory infiltrates in the spinal cord. An equivalent dose of IBU was ineffective, whereas Cytisine was significantly toxic. Treatment with IBU-Octyl-Cytisine inhibited the T-cell response toward the encephalitogenic epitope of myelin oligodendrocyte glycoprotein (MOG). In addition, expression of CCR5 by CD4(+)T-cells was lower, indicating a reduced migratory capacity following treatment. IBU-Octyl-Cytisine reduced Th(1) but not Th(2) cytokine production. This reduction was accompanied by a drop in the level of T-bet mRNA, a transcription factor pivotal to Th(1) lineage differentiation. Thus, IBU-Octyl-Cytisine is an effective treatment for EAE, influencing T-cell responses in several stages of disease pathogenesis. This bifunctional compound was more efficient than IBU or Cytisine separately, as well as than both moieties unconjugated. Thus, it seems that this strategy may be applicable in wider context.

Asymmetric fluorogenic organophosphates for the development of active organophosphate hydrolases with reversed stereoselectivity.

In order to enhance the enzymatic detoxification rate of organophosphorus (OP) nerve agents we have searched for more active variants of recombinant mammalian paraoxonase (PON1). We have previously identified three key positions in PON1 that affect OP hydrolysis: Leu69, Val346 and His115, that significantly enhance the hydrolysis of cyclosarin (GF), soman, chlorpyrifos-oxon (ChPo), O-isopropyl-O-(p-nitrophenyl)methylphosphonate (IMP-pNP) and diisopropyl fluorophosphate (DFP). GC/FPD analysis compared to residual AChE inhibition assay displayed stereoselective hydrolysis of GF, soman and IMP-pNP, indicating that wild type PON1 and its variant V346A are more active toward the less toxic P(+) optical isomer. In order to obtain new PON1 variants with reversed stereoselectivity, displaying augmented activity toward the more toxic isomer P(-) of nerve agents, we synthesized new asymmetric fluorogenic OPs (Flu-OPs). Six Flu-OPs were prepared containing either ethyl (E), cyclohexyl (C) or pinacolyl (P) alkyl radicals attached to methyl-phosphonyl (MP) moiety analogous to the structure of VX, GF and soman, respectively. The fluorescent moieties are either 3-cyano-4-methyl-7-hydroxy coumarin (MeCyC) or 1,3-dichloro-7-hydroxy-9,9-dimethyl-9H-acridin-2-one (DDAO). The kinetics of AChE and BChE inhibition by these new Flu-OPs display k(i) values 8.5x10(4) to 8.5x10(7) and 5x10(4) to 2x10(6)M(-1)min(-1), respectively. EMP-MeCyC and EMP-DDAO are the most active inhibitors of AChE whereas CMP-MeCyC and CMP-DDAO are better inhibitors of BChE than AChE, indicating accommodation of bulky cyclohexyl group inside the active site of BChE. PMP-MeCyC and PMP-DDAO are the least active inhibitors of both AChE and BChE. CMP-MeCyC and CMP-DDAO were significantly detoxified only by the five-site mutations PON1 variant L69V/S138L/S193P/N287D/V346A. Degradation kinetics of Flu-OPs measured by increase in absorbance of the released fluorogenic group was fit by a two exponential function, indicating faster hydrolysis of the less toxic optical isomer. Interestingly, wt PON1 caused only 50% degradation of racemic EMP-MeCyC, CMP-MeCyC and CMP-DDAO indicating complete hydrolysis of P(+) isomer. This remarkable stereoselectivity was used for the enzymatic separation of the P(-) isomer of CMP-MeCyC. The bimolecular rate constant k(i) for human AChE inhibition by the isolated P(-) isomer of CMP-MeCyC is five-fold larger than that of its P(+) isomer. The marked preference of wt PON1 toward P(+) stereo-isomer of CMP-MeCyC and CMP-DDAO renders their P(-) stereo-isomers suitable for the selection of new OP hydrolase variants with reversed stereoselectivity.

Novel approaches to treatment of autoimmune neuroinflammation and lessons for drug development.

Drug development, and especially that intended for central nervous system (CNS) disorders, still poses a challenge. We investigated both the use of bifunctional compounds designed for multiple targeting and enhanced CNS permeability, and of recombinant alpha-fetoprotein (AFP), a natural pregnancy-associated immunomodulating protein for the treatment of CNS inflammation. Bifunctional compounds showed a novel pharmacokinetic profile due to the conjugation, yet retained, and even improved pharmacodynamics. AFP was well tolerated and decreased various aspects of neuroinflammation, including disease severity, axonal loss and damage, T-cell reactivity, and antigen presentation. Our results show that both strategies may serve as future drug modalities.

Bifunctional compounds eliciting anti-inflammatory and anti-cholinesterase activity as potential treatment of nerve and blister chemical agents poisoning.

Certain organophosphorus (OP) nerve agents (e.g. soman) induce neuroinflammatory processes during acute poisoning. An increased level of typical inflammation markers was also observed in poisoning by alkylating agents such as sulfur mustard (HD). The therapeutic potential of new bifunctional compounds was investigated, eliciting activity of non-steroidal anti-inflammatory drug (NSAID) and anti-cholinesterase (anti-ChE) activity, as an antidotal treatment for both soman and HD poisoning in mice. Three bifunctional compounds were used that include the ChE inhibitor pyridostigmine (PYR) coupled to either ibuprofen (IBU) or diclofenac (DICLO) through an eight (octyl) or ten (decyl) hydrocarbon chain spacer: IBU-PO, IBU-PD and DICLO-PD. These compounds are 15-25 fold less toxic than PYR in mice and exert peripheral and central anti-inflammatory and anti-ChE activity in vivo. IBU-PO (4 mg kg(-1), i.p.), IBU-PD (4 mg kg(-1), i.p.) and PYR (0.13 mg kg(-1), i.p.) reduced to control levels the brain edema in soman-poisoned mice (1.1 LD50, s.c.). Pre-treatment with IBU-PO, IBU-PD and DICLO-PD 4-5 h before soman challenge (2.2-2.3 LD50, s.c.) combined with antidotal treatment (atropine, 11 mg kg(-1), 2-PAM-Cl, 25 mg kg(-1), i.m.) afforded a longer 24 h survival rate (SR) than with PYR pre-treatment. DICLO-PD exhibited the largest protection efficacy (SR = 70% vs 17% with PYR). These results indicate a longer duration of action of bifunctional compounds compared with PYR. DICLO-PD (5% in propyleneglycol) reduced significantly the HD-induced edema in mouse ear-skin (51% increase in biopsy weight compared with 100% without treatment). Quantitative evaluation of ear-skin sections showed that only following DICLO-PD treatment was there a marked decrease in edema. DICLO-PD also elicited a significant decrease in HD-induced vesication as displayed by the reduced sub-epidermal blister level. The data indicate possible use of NSAID-ChEI bifunctional compounds for the medical treatment of both nerve and alkylating chemical agents.

Bifunctional compounds eliciting both anti-inflammatory and cholinergic activity as potential drugs for neuroinflammatory impairments.

We tested two novel bifunctional compounds: ibuprofen-N-octyl-pyridostigmine bromide (IBU-PO) and ibuprofen-N-decyl-pyridostigmine bromide (IBU-PD). They both contain a non-steroidal anti-inflammatory drug (NSAID), ibuprofen (IBU) and pyridostigmine (PO), a cholinesterase inhibitor that acts as a cholinergic up-regulator (CURE). The two moieties are conjugated by a hydrocarbon spacer consisting of 8 (octyl) and 10 (decyl) carbons, respectively. The compounds were tested for their efficiency in reducing the neurological symptoms observed in experimental autoimmune encephalomyelitis induced in mice by myelin oligodendrocyte glycoprotein (MOG). IBU-PO and IBU-PD significantly ameliorated the clinical score (a 40-50% reduction in disease severity) over a period of 30 days, following daily administration of 1 and 0.1mg/kg, i.p., respectively. Clinical improvement was accompanied by reduced responsiveness of MOG-specific T-cells. In addition, IBU-PO and IBU-PD down-regulated the production of nitric oxide (NO) and prostaglandin E2 (PGE2) in cultured astrocytes. To determine which moiety was responsible for these effects, we tested each of the two components, IBU and PO. Our findings indicate that combining NSAID with cholinergic intervention contributes an added therapeutic value for each distinct entity and that these bifunctional compounds act both on the peripheral immunological system and on the central nervous system (CNS) inflammatory pathways.

The anti-inflammatory and cholinesterase inhibitor bifunctional compound IBU-PO protects from beta-amyloid neurotoxicity by acting on Wnt signaling components.

Changes in signal transduction are implicated in neuronal responses to the Alzheimer's amyloid-beta-peptide (Abeta), which include neurotransmitter systems and pathways involved in the maintenance of the nervous system. We report here that a new bifunctional compound IBU-PO, which combines a non-steroidal anti-inflammatory drug (NSAID) (Ibuprofen) and a cholinesterase (ChE) inhibitor (Octyl-Pyridostigmine), is neuroprotective against Abeta-neurotoxicity, and its activity is associated to Wnt signaling components in rat hippocampal and mouse cortical neurons. IBU-PO (0.01-1 microM) inhibits glycogen-synthase-kinase-3beta (GSK-3beta) and stabilizes cytoplasmic beta-catenin reverting the silencing of the Wnt pathway caused by Abeta-toxicity and GSK-3beta overexpression. In addition, IBU-PO enhances, dose-dependently, the non-amyloidogenic amyloid precursor protein (APP) cleavage by increasing secreted APP and decreasing endogenous Abeta1-40 in rat hippocampal neurons.

Bifunctional compounds eliciting anti-inflammatory and anti-cholinesterase activity as potential treatment of nerve and blister chemical agents poisoning.

Studies cited by Cowan et al. [J. Appl. Toxicol. 23, 177 (2003)] indicate existence of inflammatory and cholinergic pathways in both nerve agents and sulfur mustard (HD) injury. Increase in AChE synthesis and neurite extension was noted after exposure to HD [K.W. Lanks et al., Exp. Cell Res. 355 (1975)]. Moreover, anti-inflammatory drugs reduce the dermal, respiratory and ocular damage caused by exposure to HD. On the other hand, recent studies have noted the involvement of neuro-inflammatory processes during exposure to the nerve agents sarin or soman [Cowan et al., 2003]. The use of various anti-inflammatory drugs in addition to the classical antidotal drugs (e.g. atropine and oximes) caused decrease in certain toxic symptoms and inflammation-induced brain damage. Our new bifunctional drugs (Scheme 1) are based on CNS-permeable molecular combination of pseudo-reversible AChE inhibitor (pyridostigmine, PYR) coupled via a hydrophobic spacer (octyl or decyl hydrocarbon chain) to a non-steroidal anti-inflammatory drug (NSAID) such as Ibuprofen or Diclofenac (Scheme 1). This study evaluates the efficacy of certain bifunctional compounds against HD and soman poisoning in mice in vivo.