Stability of trimedoxime in concentrated acidic injectable solutions.

The degradation of trimedoxime in concentrated (114 mg/ml) acidic solutions was studied at several temperatures in the pH range 3.0 to 4.3. The degradation profile showed a relationship indicative of first-order kinetics. Trimedoxime was found to be stable in the pH range 3.0 to 3.8, with maximum stability at pH 3.0. The activation energy of the hydrolysis reaction at pH 3.0 was found to be 19.4 kcal/mol, and the half-life was 124 years. General equations were derived relating the half-life of trimedoxime solution to pH and temperature. The t90 value at 25 degrees C was calculated for each pH value studied and was found to be 11 to 18 years within the pH range 3.0 to 3.8.

Interactions of oxime reactivators with diethylphosphoryl adducts of human acetylcholinesterase and its mutant derivatives.

Diethylphosphoryl conjugates of human acetylcholinesterase (AChE) and selected mutants, carrying amino acid replacements at the active center and at the peripheral anionic site, were subjected to reactivation with the monopyridinium oxime 2-hydroxy-iminomethyl-1-methylpyridinium chloride and the bispyridinium oximes 1,3-bis(4'-hydroxyiminomethyl-1'-pyridinium),propane dibromide (TMB-4) and 1-(2'-hydroxyiminomethyl-1'-pyridinium)-3-(4"-carbamoyl-1"-pyridinium)-2 - oxapropane dichloride (HI-6). The kinetic profiles for all of the reactivation reactions indicate single populations of reactivatable species. Replacement of Trp86, the anionic subsite in the active center, lowered the affinity of the free enzyme toward all three reactivators, but in the corresponding diethylphosphoryl conjugate, only affinity toward TMB-4 was affected. Replacement of other constituents of the hydrophobic subsite (Tyr337, Phe338) had no major effect on either affinity to the free enzymes or rates of reactivation. Substitution of residues of the acyl pocket (Phe295, Phe297) lowered the affinities toward reactivators except for the 20-fold increase in affinity of F295A toward HI-6. Replacement of the acidic residues in the active center (Glu202, Glu450) affected mainly the rates of nucleophilic displacement of the phosphoryl moiety. The effect of substituting residues constituting the peripheral anionic site at the rim of the active site gorge (Tyr72, Asp74, Trp286) was particularly puzzling because for 2-hydroxy-iminomethyl-1-methylpyridinium chloride and HI-6, mainly the nucleophilic reaction rate constants were affected, whereas for TMB-4, the affinities of the phosphorylated enzymes were significantly reduced. The fact that perturbations of the functional architecture of HuAChE active center can account for only some of the observed effects on the reactivation rates suggests that the binding modes of oxime to the phosphorylated and nonphosphorylated enzymes are considerably different and/or that interactions of the reactivators with the phosphoryl moieties play a dominant role in the reactivation process.

In vitro binding of oxime acetylcholinesterase reactivators to proteoglycans synthesized by cultured chondrocytes and fibroblasts.

The incorporation of the 14C-labelled acetylcholinesterase reactivators 1-(methyl-imidazolium)-3 (4-carbaldoxime-pyridinium) propane dibromide (pyrimidoxime) and N,N'-trimethylene bis(pyridinium-4-aldoxime) dibromide (TMB4) into cultured chondrocytes and fibroblasts was measured and their binding to macromolecules synthesized by these cells studied. The results showed that these drugs concentrated slowly and poorly into these cells, but bound firmly to high molecular mass materials in the culture supernatants. The chromatographic properties of these macromolecules on Sepharose CL-2B in non-dissociative or dissociative conditions were similar to those of the proteoglycans synthesized by these cells. Dialysis of the macromolecule-bound drugs against increasing pH buffers showed half-dissociation pH > 8, identical to those for chondroitin sulphate. These results suggest strongly that pyrimidoxime and TMB4 are bound to proteoglycans by ionic interactions, and this together with their poor lipophilicity can explain their high selectivity for the cartilaginous tissues as opposed to other proteoglycan-containing structures such as skin.

[Pharmacokinetics of dipyroxime in the body of rats and dogs]. / Farmakokinetika dipiroksima v organizme krys i sobak.

Pharmacokinetics of dipyroxime was studied following intravenous injection to noninbred albino male rats. Dipyroxime is a cholinesterase reactivating drug now widely used as an antidote in poisonings caused by organophosphorus pesticides. Dipyroxime pharmacokinetics analysis made it possible to propose a formula for approximation of the data on another animal species (dogs). The drug concentration in the dog blood plasma is in a good correlation with the predicted level.

Reversible and irreversible inhibition of rat brain muscarinic receptors is related to different substitutions on bisquaternary pyridinium oximes.

The role of the functional substituents on the pyridinium ring of bisquaternary pyridinium compounds, mostly oximes, in exerting reversible and irreversible inhibition of binding of [3H]-N-methyl-4-piperidyl benzilate [( 3H]-4NMPB) to rat brain stem muscarinic receptors was studied. The drugs tested, i.e. HGG-42, HGG-12, HGG-52, HI-6, obidoxim, SAD-128 and TMB-4, could reversibly inhibit binding of [3H]-4NMPB, with the highest potency (KI = 1.7 - 6 microM) exhibited by analogs possessing hydrophobic substituents at position 3 or 4 of the pyridinium ring. Bisquaternary drugs possessing an oxime moiety at position 2, but not at position 4 of the pyridinium ring, could also induce about 30% reduction of maximal binding capacity (Bmax) (loss of muscarinic receptors) in addition to their reversible effect. Thus the structural correlates of the reversible and the irreversible effects of these drugs are different.

Metabolic disposition of the alkylphosphate antagonist, 1,1'-trimethylenebis(4-aldoximinopyridinium) ion (TMB-4), in the rat. III. Trimethylene-1-(4-aldoximinopyridinium)-1'-(4-carboxamidopyridinium) ion.

1,1'-Trimethylene [1,1'-14C]bis(4-aldoximinopyridinium) ion (TMB-4) was synthesized and its metabolic disposition was investigated in vivo. Rats were administered multiple doses of TMB-4 (25 mg/kg) by the intraperitoneal route and urine was collected over a 48-hr period. Approximately 98% of the administered radioactive dose could be accounted for in the urine during that time. A urinary metabolite, trimethylene-1-(4-aldoximinopyridinium)-1'-(4-carboxamidopyridinium) ion (TACARB), was isolated by ethanol extraction, charcoal adsorption chromatography, and ion-exchange chromatography. The metabolite was then characterized by comparing its spectral, chromatographic, and electrophoretic properties with those of authentic TACARB ion. Possible reaction mechanisms involved in the biochemical pathways for the formation of this metabolite from TMB-4 are discussed.