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Notes: Abstract  The new bispyridinium oximes HI 6 and HLö 7 are promising antidotes against poisoning by highly toxic organophosphorus compounds, i.e. nerve agents. Until now, their ability to reactivate pesticide inhibited human acetylcholinesterase (AChE) has not been elucidated. For this purpose human erythrocyte AChE (EC 3.1.1.7) was inhibited (30 min) by chlorfenvinphos, dichlorvos, dicrotophos, heptenophos, mevinphos, monocrotophos, paraoxon, phosphamidon, trichlorfon, malaoxon, omethoate, oxydemeton-methyl or methamidophos by 85–98% of control. After removal of excess inhibitor, obidoxime, pralidoxime (2-PAM), HI 6 or HLö 7 (10, 30 or 100 μmol/l) were added and the AChE activity was measured spectrophotometrically at various times thereafter (5–60 min). The oximes significantly, but not completely, reactivated organophosphate inhibited AChE. The velocity and extent of reactivation were dependent on the oxime and its concentration. In all cases obidoxime was superior to the three other oximes, followed by HLö 7, 2-PAM and HI 6. In most cases obidoxime and HLö 7 were most effective at 10 or 30 μmol/l while 2-PAM and HI 6 needed 100 μmol/l. These data suggest that 2-PAM, HI 6 and HLö 7 are less patent than obidoxime in reactivating human AChE inhibited by organophosphate pesticides.

Notes: Abstract The direct reaction of seven pyridinium oximes with the nerve agents sarin, soman, and tabun was followed by a spectrophotometric method. The half-lives (t 1/2) of the oximes, the first- and second-order rate constants (k 1, k 2), and the maximal reaction velocity ( $\roundv $ max) were calculated according to changes in the absorbance of the zwitterion (betaine) peak. In all cases the reaction velocity of the nerve agents with any of the oximes was highest with tabun, followed by sarin and then soman. Comparing the reaction rates of three therapeutically used oximes with the same nerve agent, the highest rate was obtained for soman with obidoxime, for sarin with 2-PAM, and for tabun with HI 6. The maximal reaction velocities reveal that the detoxification of the nerve agents by direct reaction with oximes and the subsequent decomposition of the phosphonyl oxime in vivo do not substantially contribute to the therapeutic effect of these antidotes.

Notes: Abstract The reactivation of organophosphate-inhibited acetylcholinesterase (AChE) by oximes inevitably results in the formation of highly reactive phosphoryloximes (POX), which are able to re-inhibit the enzyme. In this study, the dependence of POX formation on AChE concentration was investigated with sarin-inhibited human erythrocyte AChE (EryAChE). A marked dependence was found with obidoxime but not with the experimental oxime HI 6, suggesting great differences in the decomposition rates of the respective POXs. At a physiological erythrocyte content the reactivation of EryAChE was markedly affected by POX with obidoxime and pralidoxime (2-PAM) but not with the newer oximes HI 6 and HLö 7. Addition of extensively dialysed, sarin-treated human plasma reduced the reactivation by obidoxime and 2-PAM even more. Obidoxime and 2-PAM were superior to HI 6 and HLö 7 in reactivating butyrylcholinesterase (BChE). This effect was pronounced in diluted plasma, but was obscured in concentrated plasma, probably because of re-inhibition by the generated POX. Addition of native erythrocytes to sarin-treated plasma resulted in marked inhibition of EryAChE in the presence of obidoxime, suggesting a higher affinity of the POX for EryAChE. The results indicate that obidoxime and 2-PAM may reactivate sarin-inhibited AChE insufficiently due to re-inhibition by the POX formed. In addition, the re-inhibition of EryAChE may be aggravated by the POX that is produced during BChE reactivation. These reactions must be regarded as therapeutically detrimental and disqualify those oximes which are capable of forming stable POX by reactivation of BChE.

Notes: Abstract The effects of intravenously injected 4-dimethylaminophenol and Co2EDTA on peripheral circulation, respiration, acid-base balance, and several other physiological and biochemical parameters were studied on dogs. DMAP increased the respiratory minute volume and mean arterial pressure, diminished the lactate-to-pyruvate ratio, and induced an increase in arterial oxygen pressure caused by liberation of oxygen from oxyhemoglobin during the formation of ferrihemoglobin. A study in vitro of the fate of the oxygen during the reaction between DMAP and oxyhemoglobin showed that only 30–40% of the oxygen released by the formation of ferrihemoglobin appeared in the gas phase. Co2EDTA caused circulatory depression, hyperventilation, and metabolic acidosis resulting in a decrease in base-excess and pH. The concentrations of lactate, pyruvate, potassium, and urea nitrogen and the hemoglobin content were increased by Co2EDTA. The side effects of Co2EDTA in therapeutic doses were more serious than those of DMAP. Thus the latter is superior in the therapy of cyanide poisoning, all the more since it detoxifies more cyanide.

Notes: Abstract HLö 7 dimethanesulfonate (1-[[[4-(aminocarbonyl)pyridinio] methoxy] methyl] -2,4-bis [(hydroxyimino) methyl]pyridinium dimethanesulfonate) is a broad-spectrum reactivator against highly toxic organophosphorus compounds. The compound was synthesized by a new route with the carcinogenic bis(chloromethyl)ether being substituted by the non-mutagenic bis(methylsulfonoxymethyl)ether. The very soluble dimethanesulfonate of obidoxime was also prepared by this way. HLö 7 dimethanesulfonate is the first water-soluble salt of HLö 7 that should be suitable for the wet/dry autoinjector technology, because aqueous solutions of HLö 7 are not very stable (calculated shelf-life 0.2 years when stored at 8°C, 1 M solution, pH 2.5). The crystalline preparation contains 96% of thesyn/syn-isomer, less than 2% of thesyn/anti-isomer and some minor identified by-products. HLö 7 was very efficient in reactivating acetylcholinesterase (AChE) blocked by organophosphates as long as ageing did not prevent dephosphylation. HLö 7 was superior to HI 6 (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2-[(hydroxyimino)methyl]pyridinium dichloride) in reactivating soman and sarin-inhibited AChE from erythrocytes, and literature data indicate that HLö 7 exceeds HI 6 by far in reactivating tabun-inhibited AChE. In atropine-protected, soman-poisoned mice HLö 7 was three times more potent than HI 6 (protective ratio 5 versus 2.5), and in sarin-poisoned mice HLö 7 was 10 times more potent than HI 6 (protective ratio 8 for both oximes). In atropine-protected guinea-pigs HLö 7 was less effective than HI 6 (protective ratio: 2.3 versus 5.2 for soman; 5.2 versus 6.8 for sarin; 4.3 versus 3.8 for tabun). The mean survival time of anaesthetized guinea-pigs exposed to 5 LD50 soman (6.3 min) was increased by atropine (27 min) and atropine + HLö 7 (57 min). HLö 7 alone did not prolong the survival. The most impressive effect of HLö 7 was on respiration: 3 min after i.v. injection of HLö 7 and atropine, the depressed respiration increased rapidly to 60% of control and remained at that level during the observation period (60 min). With atropine alone, respiration recovered only slowly. Behavioural and physiologic parameters were determined in atropine-protected mice exposed to a sublethal soman dose. The running performance was significantly improved by HLö 7. Even central symptoms, e.g. hypothermia and convulsions, were decreased markedly by HLö 7 (evaluation 60 min after poisoning). The pharmacokinetic data for HLö 7 in male beagle dogs are similar to those of HI 6. After i.v. injection: t1/2α = 5 min; t1/2ß = 46 min; VD = 0.24 1/kg; Clp1 = 3.7 ml x min−1 x kg−1; Clren= 3.2 ml x min−1 x kg−1; renal excretion of unchanged HLö 7 = 86%. After i. m. injection: t1/2abs = 14 min; t1/2ß = 48 min; Vd = 0.27 1/kg; Clp1= 3.9 ml x min−1 x kg−1; Clren= 2.7 ml x min−1 x kg−1; renal excretion of unchanged HLö 7 = 76%; bioavailability 〉95%. Plasma protein binding was 〈5%; HLö 7 did not permeate into red cells. A dose of 20 μmol/kg was well tolerated both after i.v. and i.m. administration. In anaesthetized dogs (chloralose) HLö 7 i.v. (20 (imol/kg) showed marginal hypotensive effects, whereas 50 μmol/kg resulted in decreased mean blood pressure (−15%) and blood flow (−30%) without reflex tachycardia. One out of four dogs developed a circulatory shock syndrome with anuria. Respiration varied only transiently. Blood gases and pH were not influenced. Similar cardiovascular effects were observed in anaesthetized (urethane) guinea-pigs. In isolated guinea-pig hearts (Langendorff) sinus and ventricular heart rate were not influenced by HLö 7 〈500 μM. HLö 7 antagonized both carbachol and nicotine effects. Red cell AChE was inhibited by HLö 7 by up to 50%; C50 about 100 μM. Previously, HLö 7 was shown to block ganglionic transmission (IC50= 500 μM), probably due to ion-channel blockade. These data indicate that HLö 7 combines ganglion blocking, anticholinergic and indirect cholinergic properties like other bispyridinium compounds. The results suggest that HLö 7 may be tolerated by man at a dose of 10 μmol/kg. Vital functions are not expected to be impaired. At such a dose (250–500 mg), which can be injected by an autoinjector, HLö 7 is expected to be superior to HI 6.