Paul Rice

The Role of Oximes in the Treatment of Nerve Agent Poisoning in Civilian Casualties

There are important differences between on-target military attacks against relatively well protected Armed Forces and nerve agent attacks initiated by terrorists against a civilian population. In contrast to military personnel, civilians are unlikely to be pre-treated with pyridostigmine and protected by personal protective equipment. Furthermore, the time after exposure when specific therapy can first be administered to civilians is likely to be delayed. Even conservative estimates suggest a delay between exposure and the first administration of atropine/oxime of at least 30 minutes.The organophosphorus nerve agents are related chemically to organophosphorus insecticides and have a similar mechanism of toxicity, but a much higher mammalian acute toxicity, particularly via the dermal route. Nerve agents phosphonylate a serine hydroxyl group in the active site of the enzyme, acetylcholinesterase (AChE), which results in accumulation of acetylcholine and, in turn, causes enhancement and prolongation of cholinergic effects and depolarisation blockade. The rate of spontaneous reactivation of AChE is variable, which partly accounts for differences in acute toxicity between the nerve agents. With soman in particular, an additional reaction occurs known as ‘aging’. This consists of monodealkylation of the dialkylphosphonyl enzyme, which is then resistant to spontaneous hydrolysis and reactivation by oximes. Monodealkylation occurs to some extent with all dialkylphosphonylated AChE complexes; however, in general, is only of clinical importance in relation to the treatment of soman poisoning, where it is a very serious problem. With soman, aging occurs so fast that no clinically relevant spontaneous reactivation of AChE occurs before aging has taken place. Hence, recovery of function depends on resynthesis of AChE. As a result, it is important that an oxime is administered as soon after soman exposure as possible so that some reactivation of AChE occurs before all the enzyme becomes aged. Even though aging occurs more slowly and reactivation occurs relatively rapidly in the case of nerve agents other than soman, early oxime administration is still clinically important in patients poisoned with these agents.Experimental studies on the treatment of nerve agent poisoning have to be interpreted with caution. Some studies have used prophylactic protocols, whereas the drugs concerned (atropine, oxime, diazepam) would only be given to a civilian population after exposure. The experimental use of pyridostigmine before nerve agent exposure, although rational, is not of relevance in the civilian context. With the possible exception of the treatment of cyclosarin (GF) and soman poisoning, when HI-6 might be preferred, a review of available experimental evidence suggests that there are no clinically important differences between pralidoxime, obidoxime and HI-6 in the treatment of nerve agent poisoning, if studies employing pre-treatment with pyridostigmine are excluded.

Human skin absorption of bis-2-(chloroethyl)sulphide (sulphur mustard) in vitro

The purpose of this study was to measure the absorption and intra‐epidermal fate of 35S‐radiolabelled sulphur mustard (35SM) in human breast skin in vitro. Skin (full‐thickness or heat‐separated epidermis) was placed into static diffusion cells and was exposed to droplets of liquid 35SM or saturated 35SM vapour. Amounts of 35SM penetrating the skin were measured from which skin absorption rates were calculated. Unbound radiolabel was washed from the surface, extracted from the skin and analysed to determine the identity of the radiolabelled species in order to measure the extent of hydrolysis of sulphur mustard.

Inhalation Toxicology and Histopathology of Ricin and Abrin Toxins

AbstractThe inhalation toxicology of ricin (supplied by Sigma) from the seed variety “Hale Queen” and abrin was examined following head-only exposure of rats to a range of concentrations of each toxin generated as an aerosol from solution using a constant-output nebulizer. The inhalation toxicity of an in-house preparation of ricin from a different seed type, Ricinus communis var. zanzibariensis (R. zanzibariensis), was also assessed for comparison. The approximate LCt50 values determined were very similar for the Sigma ricin and abrin (4.54–5.96 and 4.54 mg min m-3, respectively). However, the LCt50 of ricin toxin prepared in-house from seeds of the R. zanzibariensis variety was assessed to be 12.7 mg min m-3. Ricin prepared from this seed variety was therefore less toxic than Sigma ricin by a factor of almost threefold. Given that both ricin preparations were pure by silver-stained, sodium dodecyl sulfate polyacrylamide electrophoresis gels, the data must reflect differences in specific toxicity between...

Protection against inhalation toxicity of ricin and abrin by immunisation.

1 Abrin and ricin are highly toxic plant proteins which are very similar in structure and function and inhibit protein synthesis in eukaryotes. 2 Rats have been immunised against either toxin using formaldehyde-toxoids by three subcutaneous injections at intervals of 3 weeks. For abrin, serum titres in 14 out of 15 rats were raised to between 1 : 12800 and 1 : 51200 after two injections, 6 weeks from the start of the experiment. Titres of between 1 : 256 and 1 : 1024 were also measured in lung washes after challenge with active abrin toxin. 3 The three major antibody classes, IgG, IgM and IgA were present in the immune sera but IgG and IgA only were detected in lung washes. The proportion of IgA to IgG was higher in the lung fluid than in sera. Rats immunised by abrin toxoid were protected against 5 LCt50s of abrin by inhalation but others exposed to ricin were not. 4 For ricin, serum titres ranged from 1 : 800 to 1 : 25600 after two injections and after a third injection the titre range was the same but population samples were weighted towards the higher titres. All rats immunised with ricin toxoid survived the challenge of 5 LCt50s of ricin toxin by inhalation over the observation period of 28 days post-challenge. 5 Representative immunised rats (abrin toxoid) were taken at various times post-exposure, humanely killed and tissues were examined for pathological changes. It was concluded that an apparently severe lung lesion occurred at a later time than in non-immunised, toxin challenged rats. This damage was not lethal over the experimental observation periods. 6 Immunisation by the sub-cutaneous route therefore protects against lethality from challenge by inhalation of ricin or abrin toxins but does not prevent significant lung damage.

Dermabrasion--a novel concept in the surgical management of sulphur mustard injuries.

Since its first use on the battlefields of Northern France during the First World War (1914-1918), sulphur mustard has remained a significant chemical threat to military forces around the world. Progress towards an effective treatment for these injuries has been slow due to the lack of suitable animal models upon which to study the toxicology and pathology. However, porcine and human skin are similar in structure and exposures to sulphur mustard vapour have been performed on porcine models to define the development and subsequent resolution of mustard-induced skin injuries. Yucatan miniature (n = 12) and large white (n = 6) pig models were used to assess the usefulness of mechanical dermabrasion in accelerating the naturally slow rate of healing of sulphur mustard vapour-induced injuries to the skin. Burn injuries underwent debridement at 4 days post-exposure and the resulting lesions were assessed at various time points up to 8 weeks post-abrasion. Rates of re-epithelialisation were accelerated in the dermabrasion (treated) vs the control (untreated) group by up to a factor of three (ANOVA: p = .0196, Yucatan; p = 0.165, large white pig). It was concluded that dermabrasion of sulphur mustard burns is a valuable procedure in the surgical management of these injuries.

Evaluation of the Efficacy of Dimercapto Chelating Agents for the Treatment of Systemic Organic Arsenic Poisoning in Rabbits

1 The standard drug for the treatment of arsenic poisoning is BAL (dimercaprol). BAL possesses marked side-effects and a low safety ratio, drawbacks which new BAL analogues, DMPS and DMSA, do not possess. 2 The efficacy of three chelating agents, BAL, DMPS and DMSA, has been evaluated as a treatment for systemic organic arsenic poisoning, induced by intravenous dichloro(2-chlorovinyl)arsine (lewisite) administration to rabbits. Equimolar dosing schedules were used based upon realistic doses for the most toxic agent, BAL. 3 It was concluded that all three dimercapto chelating agents provided signficant protection against the lethal systemic effects of lewisite, and, under the test conditions reported here, there was no significant difference between them in therapeutic efficacy. 4 The cause of mortality following intravenous lewisite in treated and untreated rabbits was pulmonary damage. 5 It is considered that DMPS and DMSA are worthy of further study as replacements for BAL in the treatment of systemic poisoning by lewisite.

Evaluation of Barrier Creams against Sulphur Mustard

The purpose of this study was to assess the effectiveness of a range of passive and reactive barrier cream formulations against the chemical warfare agent sulphur mustard (SM) using an in vitro diffusion cell system containing human skin. In general, proprietary formulations were relatively effective under occluded conditions, but ineffective under unoccluded conditions. For example, SM skin absorption rates through occluded control and Stokoderm® pre-treated skin were 538 ± 193 and 200 ± 51 µg·cm–2·h–1, respectively (p < 0.05). Under unoccluded conditions, control and Stokoderm pre-treated skin absorption rates were 4.41 ± 1.90 and 36.84 ± 15.19 µg·cm–2·h–1 (p < 0.05). Novel (perfluorinated) barrier creams were generally more effective under unoccluded conditions; pre-treatment with one formulation led to an 18-fold reduction in skin absorption rate and reduced the total amount of SM penetrated by 95% of the applied dose. Several proprietary formulations also had adverse effects on the effectiveness of the skin decontaminant fuller’s earth. The rate (Jss) and total amount (percentage of dose) of SM absorbed through the skin were deemed to be independent parameters of barrier cream performance. These data indicate that (1) perceived conditions of use, (2) compatibility with existing protective equipment and (3) the rate and extent of SM skin absorption must all be taken into account when evaluating barrier creams in vitro.

Efficacy of Dimercapto Chelatin Agents for the Treatment of Poisoning by Percutaneously Applied Dichloro(2-chlorovinyl)arsine in Rabbits

The efficacy of three chelating agents, BAL, DMPS and DMSA has been evaluated in rabbits as treatments for systemic dichloro(2-chlorovinyl)arsine [lewisite] poisoning by the percutaneous route. Chelating agent treatment reduced the incidence and severity of pathological liver changes following lewisite poisoning. There was no marked difference between the three chelating agents for protection against lethality when screened at an equimolar dose of 40 μmol kg-1. The results indicated DMPS and DMSA may prolong survival time compared with BAL. The low toxicity of DMPS and DMSA compared to BAL enabled doses of 160 μmol kg-1 on a more prolonged dosing schedule to be used for DMPS and DMSA. This schedule showed DMPS and DMSA to give a significant improvement in protection against the lethal effects of percutaneous lewisite compared to that of BAL. It was concluded that DMPS and DMSA have significant advantages over BAL for use as treatment for systemic lewisite poisoning.

Changes in connective tissue macromolecular components of Yucatan mini-pig skin following application of sulphur mustard vapour

1 The aim of this study was to determine the nature of the macromolecular alterations in Yucatan mini-pig skin which occur following application of sulphur mustard vapour, with particular reference to laminin and type IV collagen. 2 The immunostaining of transfer blots from skin extracts run on SDS-PAGE gels revealed no evidence of cross-link ing of type IV collagen or laminin. Laminin was, however, found to be partially degraded as determined by the reso lution of 132 and 143 kDa fragments, possibly by the acti vation of proteases, following the application of sulphur mustard to pig skin. Type IV collagen was not subject to this form of degradation in the skin samples exposed to sulphur mustard. 3 Yucatan mini-pig skin was found to develop microblis ters after exposure to sulphur mustard vapour. The immunohistochemical studies of sulphur mustard exposed skin revealed that separation of the epidermis from the dermis was found to occur within the lamina lucida of the subepidermal basement membrane, supporting the con tention that cleavage of laminin networks occurs following mustard challenge. Immunohistochemical staining with anti-type IV collagen antibodies was restricted to the floor of the micro-blister lesions. 4 The results suggest that laminin may be a target for pro tease activation at the dermo-epidermal junction. This may account for the tendency of certain skin models to develop sulphur mustard-induced blistering. The Yucatan mini-pig may be valuable as a model to determine the effi cacy of prophylactic and therapeutic regimes.

Assessment of the biochemical effects of percutaneous exposure of sulphur mustard in an in vitro human skin system

1 Sulphur mustard (HD) is a potent chemical warfare agent which causes incapacitating blisters on human skin. There is no specific pretreatment nor therapy against this agent and the mechanism of dermo-epidermal cleavage is unclear. The aim of this study was to use a human skin explant system to determine the consequences of percuta neous exposure to HD. 2 Increased activities of serine proteases associated with blistering disorders in humans were detected from human skin explants after exposure to HD. The most consistent response and the highest protease activities measured were found for trypsin. This class of enzyme is therefore implicated in the dermo-epidermal separation which is associated with blistering in humans following exposure to HD. 3 An inflammatory response was observed in the skin explants exposed to HD. At low doses of HD it was characterised by the presence of neutrophils in the papillary dermis, culminating in the infiltration of the epidermis by these inflammatory cells at higher concen trations of HD. A variety of other histopathological changes in the explants was found such as focal dermo- epidermal separation, nuclear pyknosis and perinuclear vacuolation. 4 The study indicates that full thickness human skin explants can be used to investigate various aspects of the possible pathogenesis of HD-induced skin damage, in cluding the associated inflammatory response.