Christopher D Lindsay

Morphology of ricin and abrin exposed endothelial cells is consistent with apoptotic cell death

Cultures of bovine pulmonary endothelial (BPE) cells were exposed to LC70 doses of ricin or abrin (15.5 and 4.5 pM respectively) over a period of up to 40 h. The viability of the cultures (as determined by the neutral red (NR) dye retention assay) declined after 6 h exposure to the toxins. From 15 h onwards, cellular material in toxin exposed cultures became detached from the substra tum of the culture vessels. Hoffman modulation contrast photomicrography showed that this process was due to ricin and abrin exposed cells collapsing into membrane bound vesicles which retained the NR dye, became detached and floated into the medium. These apoptotic-like structural changes were further investi gated by transmission electron microscopy (TEM) and by agarose gel electrophoresis of DNA from control and exposed cultures. Many of the characteristic changes associated with apoptotic cell death were seen using TEM, including heterochromatin condensation at the nuclear periphery, crenulation of the nuclear mem brane and progressive degeneration of residual nuclear and cytoplasmic structures. The plasma membrane of many cells remained intact, and contained nuclear and cytoplasmic debris. Agarose gel electrophoresis of DNA extracted from toxin-treated cells revealed oligonucleosome sized DNA fragments, characteristic of apoptosis, from adherent cells at 7 h and both adherent and floating populations when harvested from 15 h; DNA from unexposed control cells did not show this fragmentation. The identification of apopto sis as being a significant additional mechanism of toxicity following exposure to ricin and abrin holotox ins raises the possibility of developing new therapeutic strategies against poisoning by these phytotoxins.

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.

An assessment of the in vitro toxicology of Clostri di urn perfringens type D ε-toxin in human and animal cells

The epithelial Madin Darby canine kidney (MDCK) cell line and 17 human cell lines were examined for sensitivity to Clostridium perfringens type D a-toxin. MDCK cells were confirmed as being sensitive to the toxin. In addition, the Caucasian renal leiomyoblastoma (G-402) human cell line was identified as being ε-toxin sensitive. Using the MTS/PMS assay system the concentration of toxin reducing cell culture viability by 50% (LC50) was found to be 2 ug/ml in MDCK cells. The LC50 for G-402 cells was 280,ug/ml. a-Toxin was found to be rapid acting in MDCK cells exposed to a maximum lethal dose of the toxin (40% loss of viability after a 0.5 h exposure), but slower acting in G-402 cells (40% loss of viability after 1.7 h exposure). Photomicrography of toxin exposed cultures indicated necrotic cell death on exposure to a-toxin. Investigations using an antibody probe indicated that ε-toxin could bind to many cell surface proteins in both MDCK, G-402 and a toxin insensitive human cell line (CAKI-2). It has previously been found that the toxin may bind to the cell surface via glycosylated moieties. However, exposing MDCK and G-402 cells to a-toxin in the presence of sialic acid and several different sugars did not reduce the lethal effects of the toxin.

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.

Diisopropylglutathione ester protects A549 cells from the cytotoxic effects of sulphur mustard

The A549 cell line was used to assess the ability of diisopropylglutathione (DIPE) to protect against a 100 mM challenge dose of sulphur mustard (HD) using gentian violet (GV), thiazolyl blue (MTT) and neutral red (NR) assays as indicators of cell culture viability. As part of a continuing study of the efficacy of protective nucleophiles as candidate treatments for HD poisoning, several different combinations of protectant and HD were used to determine the optimal means of protecting A549 cells from the effects of HD. It was found that DIPE (4 mM) could protect cells against the effects of HD though for optimal effect, DIPE had to be present at the time of HD challenge. Cultures protected with DIPE were up to 2.9- fold more viable than HD exposed cells 48 h after HD challenge when using the GV, MTT and NR assays to assess viability. Observations by phase contrast microscopy of GV stained cultures confirmed these findings. Pretreating A549 cultures with DIPE for 1 h followed by its removal prior to HD challenge did maintain cell viability, though at a relatively low level (only up to 1.4- fold more viable than HD only exposed cells). DIPE was also able to protect HD exposed A549 cultures when added to cell cultures at intervals of up to 12 to 15 min after the initial HD exposure, though viability tended to decrease over this period, so that at 1 h, addition of DIPE did not maintain the viability of the cultures. This is the first such report of the anti-HD protectant properties of DIPE in A549 cells. It is concluded that the protection observed against HD is probably largely due to extracellular inactivation of HD by DIPE.

Assessment of aspects of the toxicity of Clostridium perfringens E-toxin using the MDCK cell line

1 The epithelial Madin Darby Canine Kidney (MDCK) cell line was used to study the toxicity of ∈-toxin from Clostridium perfringens. The epithelial MDCK cell line is known to be sensitive to ∈-toxin of Clostridium perfringens and to investigate its mechanism of action, the neutral red assay has been used to determine the viability of cultures of this cell line. 2 Comparison of the LC 50s obtained at 34°C and 0°C showed that the lethality of ∈-toxin was reduced by 18- fold at the lower temperature. The effect of tempera ture on ∈-toxin lethality is unlikely to be due to reductions in membrane fluidity for the addition of Ca2+ or Mg2+ (2 mM) to buffer containing toxin was without effect. Varying the pH of the toxin-containing buffer from 6.9 to 8.7 did not increase the lethality of the toxin, though the most acidic pH used (5.8) was found to potentiate its action on MDCK cells. 3 The effect of inhibiting endocytosis on the lethality ofe toxin was also investigated by incubating cultures of MDCK cells with and without sodium azide over a range of concentrations of toxin. The co-administra tion of sodium azide did not reduce the toxicity of ∈ toxin, suggesting that energy-dependent uptake pro cesses such as endocytosis were unlikely to be involved in its mechanism of action. The results are, however, consistent with known receptor-based me chanisms of uptake and with other mechanisms of internalisation across the plasma membrane. ∈-toxin thus interacts with cell surfaces by a temperature sensitive mechanism potentiated by low pH.

Presence of methenamine/glutathione mixtures reduces the cytotoxic effect of sulphur mustard on cultured SVK-14 human keratinocytes in vitro:

1 The basal epidermal keratinocytes of the skin are a main target for the vesicating agent, sulphur mustard (SM). A human keratinocyte cell line (SVK-14) has been used to model the effects of SM on the basal epidermal keratinocytes and subsequently to test the efficacy of potential prophylactic compounds in reducing the SM-induced cytotoxicity. 2 The cultures were pretreated with mixtures of methe namine (HMT) and glutathione (GSH) for 1 h prior to exposure to 10 μM SM. The viability of the cultures was then assessed using neutral red (NR) dye uptake and crystal violet DNA staining assays at 24 h intervals post exposure. 3 Pretreatment led to a 1.9 fold increase in culture viability (NR assay) compared to those exposed to SM only, and a 2.3 fold increase in cell number (crystal violet assay). Photomicrography showed that pre treatment preserved the morphology of the cultured cells and maintained their mitotic activity whereas those exposed to SM only show non-proliterative cultures with extensive cellular damage. 4 The results of this study show that it is possible to protect mitotically active cultures from the effects of SM, however the measures must be in place prior to SM exposure.

Protection of A549 cells against the toxic effects of sulphur mustard by hexamethylenetetramine

The A549 cell line was used as a model of the deep lung to study the toxicity and mechanism of action of sulphur mustard (HD), using the neutral red (NR) dye retention and gentian violet (GV) assays as indices of cell viability. It was found that exposure to concentrations in excess of 40 μM HD resulted in a rapid onset of toxicity. Exposure to 1000 μM HD reduced viability in A549 cell cultures to 61% after 2 h (control cultures=100%), whereas exposure to 40 μM HD did not result in deleterious effects until 26 h at which point viability fell to only 84% (NR assay). Agarose gel electrophoresis of cell cultures exposed to 40 and 1000 μM HD and harvested at 4.5, 19 and 43 h after exposure to HD, indicated that cell death was due to necrosis, despite the observation that at the higher concentration of HD cells displayed many of the features common to cells undergoing apoptotic death. The ability of hexamethylenetetramine (HMT) to protect A549 cells against the effects of an LC50 challenge dose of HD was assessed using the GV and NR assays. It was found that HMT (15 mM) could protect cells against the effects of HD though HMT had to be present at the time of HD challenge. Cultures treated with HD only were 49% viable at 48 h after HD challenge, compared to 101% for protected cultures (NR assay) and 58% and 91% for unprotected and protected cultures respectively using the GV assay. Morphological observations of GV and NR stained cultures confirmed these findings. HMT concen trations of 2.5 to 25 mM were used. Maximal protection against the toxic effects of HD (LC50) was found at 10 to 25 mM HMT. Over this concentration range, HMT did not exert any toxic effects on A549 cells. Pretreatment of A549 cultures with HMT followed by its removal prior to HD challenge had no protective effect. Similarly, treating cultures with HD followed by addition of HMT did not increase the viability of the cultures, even if the HMT was added immediately after HD exposure. HMT was found to protect against the toxic effects ofHD, though it must be present at the time ofHD challenge. A549 cells were found to be a valuable experimental model for studying the toxicology of HD and other lung damaging agents, and for screening other compounds for potential therapeutic efficacy as a prelude to studies with non- transformed cell culture systems and in vivo models.

Stabilisation of Salmonella vaccine vectors by the induction of trehalose biosynthesis.

The growth of an aroA mutant of Salmonella typhimurium (SL3261) in minimal medium containing 0.5 M NaCl resulted in the intracellular accumulation of 2.2 micromol trehalose/mg total protein. The vacuum drying of these bacteria in the presence of trehalose allowed the recovery of 35% of the viable cells that were present before drying. In contrast, bacteria cultured in control medium accumulated 0.4 micromol trehalose/mg total protein and only 5% of the viable cells were recovered after vacuum drying with trehalose. Similar results were obtained when S. typhimurium SL3261, expressing the vaccine antigen (F1-antigen) of Yersinia pestis, was cultured in minimal medium with or without 0.5 M NaCl and dried in the presence of trehalose. Although these results indicate the potential for trehalose stabilisation of vaccine strains of S. typhimiurium, growth in minimal medium containing 0.5 M NaCl resulted in the loss of invasion competence of the bacteria.