The Encapsulation of Squid Diisopropylphosphorofluoridate-Hydrolyzing Enzyme within Mouse Erythrocytes

This study describes the entrapment of squid-type diisopropylphosphorofluoridate-hydrolyzingenzyme (DFPase) within mouse red blood cells. These erythrocytesthereby gain the ability to rapidly hydrolyze alkylphosphatecholinesterase (ChE) inhibitors such as diisopropyl fluorophosphate(DFP). DFPase rapidly hydrolyzes DFP to diisopropyl phosphate.Resealed erythrocytes provide a stable carrier system that canpreserve the activity of encapsulated enzymes against otherwiserapid in vivo degradation; thus, ChE inhibitors can be degradedto relatively nontoxic metabolites by these erythrocyte carriers.Squid DFPase was purified from the hepatopancreas of Atlanticsquid and DFPase activity was determined by measuring changesin fluoride ion concentration using a fluoride ion selectiveelectrode. Mouse erythrocytes in suspension with excess squidDFPase were dialyzed against hypotonic buffer to allow the encapsulationof the enzyme to occur. Cells were then resealed by returningthe suspension to isosmotic with saline. Rate of DFP hydrolysisobserved with these cells was much greater than the rate ofnonenzymatic hydrolysis and was directly proportional to theamount of the erythrocyte suspension added to the assay solution.The rate of hydrolysis was first order in substrate. Erythrocytecontrols showed no endogenous DFPase activity. These resultssuggest that enzyme entrapment may be developed as a methodto prevent and antagonize organophosphate poisoning.     

Implantable Cardioverter Defibrillator Implanted by Nonthoracotomy Approach: Initial Clinical Experience with the Redesigned Transvenous Lead System

Standard implantation procedure for the implantable Cardioverter defibrillator (ICD) has traditionary required a thoracotomy approach. A newly revised nonthoracotomy defibrillator lead system that uses a single transvenous tripolar endocardial lead alone or in combination with a subcutaneous/submuscular patch lead was introduced into clinical trials in September, 1990. Fourteen patients requiring a Cardioverter defibrillafor for recurrent sustained ventricular tachycardia (eight patients) or aborted sudden cardiac death (six patients) were evaluated for implantation of this lead system. Primary successful lead system implantation was obtained in nine patients. The remaining five patients had unacceptably high defibrillation thresholds (DFTs) for implantation. One of the nine initially successful implants demonstrated unacceptable DFTs and cross-talk inhibition from a permanent pacemaker necessitating removal of the nonthoracotomy lead system and replacement with a conventional lead system via thoracotomy. All remaining primary implanted patients experienced successful conversion of induced ventricular fibrillation prior to hospital discharge. Continued follow-up and greater experience to confirm the durability and efficacy of the nonthoracotomy AICD lead system are needed.     

Cyanide Antagonism with Carrier Erythrocytes and Organic Thiosulfonates

Previous studies reported that resealed erythrocytes containingrhodanese (CRBC) and Na₂S₂O₃ rapidly metabolize cyanide to theless toxic thiocyanate both in vitro and in vivo. This provideda new conceptual approach to prevent and treat cyanide intoxication.Although the rhodanese-containing carrier cells with thiosulfateas the sulfur donor were efficacious, this approach has potentialdisadvantages, as thiosulfate has limited penetration of cellmembrane and product inhibition of rhodanese can occur due toinorganic sulfite accumulation. In order to circumvent substratelimitation and product inhibition by sodium thiosulfate, organicthiosulfonates were explored. These thiosulfonates have higherlipid solubility than thiosulfate and therefore can replenishthe depleted sulfur donor, as they can readily penetrate cellmembranes. Also, product inhibition of rhodanese is less aptto occur. This change in sulfur donors should greatly enhancecyanide detoxication, replenish the sulfur donor, and minimizeproduct inhibition of rhodanese. Present studies demonstratethe enhanced efficacy of exogenous organic thiosulfonates oversodium thiosulfate in the CRBC antidotal system to detoxifythe lethal effects of cyanide either alone or in combinationswith exogenously administered NaNO₂. Murine carrier erythrocytescontaining purified bovine liver rhodanese were administeredintravenously into male Balb/C mice. Subsequently, butanethiosulfonate(BTS) or Na₂S₂O₃ (ip), and NaNO₂ (sc) were co-administered priorto KCN (sc). Potency ratios, derived from the LD₅₀ values, werecompared in groups of mice treated with CRBC-Na₂S₂O₃ or CRBC-BTSeither alone or in combination with NaNO₂. The CRBC-BTS antidotalsystem shows strikingly enhanced protective effect over thatof the CRBC-thiosulfate system either alone or in combinationwith sodium nitrate.