TRPA1 and issues relating to animal model selection for extrapolating toxicity data to humans

The transient receptor potential ankyrin 1 (TRPA1) ion channel is a sensor for irritant chemicals, has ancient lineage, and is distributed across animal species including humans, where it features in many organs. Its activation by a diverse panel of electrophilic molecules (TRPA1 agonists) through electrostatic binding and/or covalent attachment to the protein causes the sensation of pain. This article reviews the species differences between TRPA1 channels and their responses, to assess the suitability of different animals to model the effects of TRPA1-activating electrophiles in humans, referring to common TRPA1 activators (exogenous and endogenous) and possible mechanisms of action relating to their toxicology. It concludes that close matching of in vitro and in vivo models will help optimise the identification of relevant biochemical and physiological responses to benchmark the efficacy of potential therapeutic drugs, including TRPA1 antagonists, to counter the toxic effects of those electrophiles capable of harming humans. The analysis of the species issue provided should aid the development of medical treatments to counter poisoning by such chemicals.

Addressing bioterrorism concerns: options for investigating the mechanism of action of Staphylococcus aureus enterotoxin B

Staphylococcal enterotoxin B (SEB) is of concern to military and civilian populations as a bioterrorism threat agent. It is a highly potent toxin produced by Staphylococcus aureus and is stable in storage and under aerosolisation; it is able to produce prolonged highly incapacitating illness at very low-inhaled doses and death at elevated doses. Concerns regarding SEB are compounded by the lack of effective medical countermeasures for mass treatment of affected populations. This article considers the mechanism of action of SEB, the availability of appropriate experimental models for evaluating the efficacy of candidate medical countermeasures with particular reference to the need to realistically model SEB responses in man and the availability of candidate countermeasures (with an emphasis on commercial off-the-shelf options). The proposed in vitro approaches would be in keeping with Dstl’s commitment to reduction, refinement and replacement of animal models in biomedical research, particularly in relation to identifying valid alternatives to the use of nonhuman primates in experimental studies.

Examination of toxicity of Clostridium perfringens -toxin in the MDCK cell line

The epithelial Madin Darby canine kidney (MDCK) cell line was examined as a model to study the toxicity of Clostridium perfringens -toxin. The MDCK cell line was used because it is a monolayer cell line sensitive to -toxin. Using the neutral red (NR) retention assay (an indicator of lysosomal integrity), the concentration of toxin causing death in 50% of the cell population (LC(50)) was 900 pM, although this was found to vary between production batches. -Toxin was found to act rapidly but with a lag phase of 1 hr (NR assay). Pulsing the cultures with toxin (up to 4800 pM) indicated that the duration of exposure required to exert an effect was potentially very short (2.5 min). Increasing the duration of exposure beyond 3 hr did not decrease cell viability any further. Experiments with protease inhibitors failed to inactivate the toxin. Ethylenediaminetetraacetic acid (EDTA) was found to potentiate the lethality of the toxin by 90% This may be due to non-specific chaotropic effects such as membrane destabilization. By exposing cultures of MDCK cells to -toxin for a second time, resistance to the effects of the toxin was increased by 43%. The factor(s) controlling resistance to the toxin may have a heritable component.

Searches for Lepton flavor violation in the decays tau{+/-}-->e{+/-}gamma and tau{+/-}-->mu{+/-}gamma

Searches for lepton-flavor-violating decays of a tau lepton to a lighter mass lepton and a photon have been performed with the entire data set of (963+/-7)x10{6} tau decays collected by the BABAR detector near the Upsilon(4S), Upsilon(3S) and Upsilon(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of B(tau{+/-}-->e{+/-}gamma)<3.3x10{-8} and B(tau{+/-}-->mu{+/-}gamma)<4.4x10{-8} at 90% confidence level.

Down-regulation of gene transcripts associated with ricin tolerance in human RPMI 2650 cells

The present study sought to determine if novel therapeutic approaches against ricin intoxication could be identified from human respiratory tract cells selected for increased resistance to this toxin. Initial studies indicated that the RPMI 2650 line was an appropriate model, owing to its sensitivity to ricin. Tolerant cultures were developed by exposing cells to a graded series of ricin concentrations from 6 to 192 pM. This resulted in the generation of cultures whose LC(50) values were increased by up to 4-fold following exposure to up to 96 pM ricin and by up to 6-fold following exposure to up to 192 pM ricin, compared to control cultures. DNA microarrays were employed to determine the gene transcript expression profile of cultures with increased resistance to ricin to investigate which gene products mediate ricin resistance. Transcripts (10) were identified that were greater than 2-fold down-regulated in the cells tolerant to 96 pM ricin, whereas 48 transcripts were seen to be down-regulated in cultures tolerant to 192 pM ricin. Gene transcripts (5) were up-regulated 2-fold or more in the 192 pM tolerant cultures in comparison to unexposed cells. The results indicate that ricin tolerance is the product of complex changes in gene expression profiles, most of which were found to involve down-regulation of transcript expression. It may be possible to modulate the gene expression profiles associated with ricin tolerance for potential therapeutic purposes using drugs and antisense technologies.

Kojic acid reduces the cytotoxic effects of sulfur mustard on cultures containing human melanoma cells in vitro

In vivo experiments have shown that melanocytes are more sensitive than keratinocytes to the cytotoxic effects of sulfur mustard when it is applied topically to pig skin.1 It has been hypothesized that this is caused by the uncoupling of the melanogenic pathway by depletion of cellular glutathione, resulting in the uncontrolled production of cytotoxic quinone free-radical species by tyrosinase.2. In the present study, the feasibility of blocking the melanogenic pathway as a means of reducing the cytotoxicity of sulfur mustard was evaluated using kojic acid. Kojic acid is a topically applied depigmenting agent that exerts its effect by acting as a slow-binding, competitive inhibitor of tyrosinase.3 Preincubation of G361 pigmented melanoma cells and mixed cultures of G361 cells and SVK keratinocytes with 2.5 mM kojic acid resulted in significant increases in the viability of these cultures as determined by neutral red (NR) and gentian violet (GV) dye binding assays for up to 48 h following exposure to 50 microM sulfur mustard. The highest levels of protection were seen in the G361 cultures, with a 26.8% increase in culture viability (NR assay) compared with the sulfur-mustard-only controls at 24 h. Preincubation of SVK cells alone with kojic acid resulted in lower increases in viability (2.5% at 24 h by the NR assay). Inhibition of the melanogenic pathway reduces the sensitivity of cultures containing pigment cells to sulfur mustard.

An in vitro comparison of the cytotoxicity of sulphur mustard in melanoma and keratinocyte cell lines

In vivo, the pigment producing melanocytes are the most susceptible cell type to sulphur mustard (HD) in the epidermal region of pig skin. It has been postulated that this is due to the melanogenic pathway producing a cytotoxic, free radical cascade within the melanocyte following HD poisoning, leading to cellular necrosis and subsequent inflammation. To test this hypothesis, the cytotoxicity of HD was tested in three human melanoma cell lines and compared to SVK-14 human keratinocytes, a cell line in which the response to HD has already been characterised. The results of both neutral red (NR) and gentian violet (GV) assays showed that all three melanoma cell lines, particularly the G361 line, were less susceptible to the toxic effects of HD than the SVK-14 keratinocyte cell line. Preliminary data indicate that the expression level of the DNA repair cofactor, proliferating cell nuclear antigen (PCNA), is up to 13-fold greater in the HD-resistant cell line G361 compared to the HD-sensitive SVK-14 cell line. The data point to the importance of DNA lesions in HD-induced cell death and to potential mechanisms associated with increased resistance to HD. A dose-response study was carried out to confirm the differences between these two cell lines. It was found that the G361 line is 5-fold more resistant to HD and 5.5-fold more resistant to the cytotoxic effects of H2O2 than the SVK-14 line, as determined by the MTT assay. The results suggest that differences in the relative efficiency of DNA repair processes may underlie these responses. Whilst the study indicates the limitations of using melanoma cell lines (in vitro) to model melanocyte responses to HD, analysis of the biochemical basis of the observed differences in sensitivity to HD could assist in the identification of novel therapeutic strategies against HD.

Stimulation of C32 and G361 melanoma cells using oleoyl acetyl glycerol and its effect on sulphur mustard cytotoxicity

Epidermal melanocytes have a higher sensitivity to sulphur mustard (HD) compared with other skin cell types. This may be due to the enzymatic production of melanin precursors exerting an additional cytotoxic effect following HD depletion of the cellular protectant, GSH. Stimulation of the protein kinase C pathway in melanocytes is known to increase melanin production in melanocytes and melanoma cell lines. In order to investigate the role of pigment synthesis in HD toxicology, cultures of an unpigmented melanoma cell line (C32) and of a pigmented melanoma line (G361) were treated with the potent diacyl glycerol analogue, oleoyl acetyl glycerol (OAG), in order to determine if protein kinase C-mediated increases in pigment production could increase sensitivity to subsequent HD exposure. Stimulation of C32 cells with OAG exerted a significant protective effect against the cytotoxic effects of HD. However, this was not due to increased melanin synthesis because this cell line cannot synthesize melanin pigments. The protective action observed is postulated to be due to modulation of protein kinase C activity. In contrast, stimulation of G361 melanoma cells with OAG resulted in an increased level of cytotoxicity upon subsequent exposure to HD. Protein kinase C controls several cellular pathways including checkpoints in the cell cycle, stalling the cell in G and promoting transition through the G2/M boundary. Given the genotoxic properties of HD, these two points in the cell cycle are important in determining the overall cytotoxic effect of HD. Control of the cell cycle by protein kinase C modulation and manipulation of melanin synthetic pathways may have therapeutic benefits.

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.

An assessment of the in vitro toxicology of Clostridium perfringens type D epsilon-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 epsilon-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 epsilon-toxin sensitive. Using the MTS/PMS assay system the concentration of toxin reducing cell culture viability by 50% (LC50) was found to be 2 microg/ml in MDCK cells. The LC50 for G-402 cells was 280 microg/ml. Epsilon-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 epsilon-toxin. Investigations using an antibody probe indicated that epsilon-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 epsilon-toxin in the presence of sialic acid and several different sugars did not reduce the lethal effects of the toxin.

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 microM 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.

Protection of human upper respiratory tract cell lines against sulphur mustard toxicity by hexamethylenetetramine (HMT)

1. Sulphur mustard ('mustard gas', HD) is a highly toxic chemical warfare agent which affects the skin and respiratory tract. The primary targets of inhaled HD are the epithelia of the upper respiratory tract. Hexamethylenetetramine (HMT) has been shown to protect human lung cells against HD toxicity and has also been shown to be effective in vivo against the chemical warfare agent phosgene. The ability of HMT to protect against the toxicity of HD was investigated in the human upper respiratory tract cell lines BEAS-2B and RPMI 2650. 2. HD was highly toxic to both cell lines, with LC50 values of 15-30 microM. HMT, at a concentration of 10 mM, was shown to protect the cell lines against the toxic effects of 20 microM and 40 microM HD. Results demonstrated that it was necessary for HMT to be in situ at the time of exposure to HD for effective cytoprotection. No protection was seen when cells were treated with HMT following exposure to HD, or where HMT was removed prior to HD exposure. 3. Results suggest that HMT may be effective prophylaxis for exposure to HD by inhalation.

Protection of human upper respiratory tract cell lines against sulphur mustard toxicity by glutathione esters

1. Human and animal lung cells have been used successfully to model the toxic effects of inhaled sulphur mustard (HD). The epithelia of the upper respiratory tract are, however, the primary targets of inhaled HD. The aim of this study was to assess the potential of the mono- and di-isopropyl esters of glutathione (MIPE and DIPE respectively) as cytoprotectants in the human upper respiratory tract cell lines BEAS-2B and RPMI 2650. 2. The optimal concentrations for cytoprotection were shown to be 1.0 mg/ml for both DIPE and MIPE. Both compounds were found to protect cells by pretreatment, slightly less protection was observed in cells simultaneously exposed to sulphur mustard. The greatest protection was shown where MIPE or DIPE were in in situ at the time of exposure to HD. The optimum pre-treatment times were found to be 1 h for MIPE and 2 h for DIPE. Limited protection of cells treated with MIPE or DIPE immediately following HD exposure was also demonstrated. No protection was observed if MIPE or DIPE were not administered immediately following HD exposure. 3. Results suggest that MIPE and DIPE may be effective treatments for exposure to HD by inhalation.

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

1. The A549 cell line was used to assess the toxicity of sulphur mustard (HD), using gentian violet (GV) and neutral red (NR) dyes as indicators of cell viability. It was found that exposure to concentrations in excess of 40 microM HD resulted in a rapid onset of toxicity. 2. The ability of monoisopropylglutathione ester (MIPE) to protect A549 cells against the effects of a 100 microM challenge dose of HD was determined using the NR and GV assays. It was found that MIPE (8 mM) could protect cells against the effects of HD though MIPE had to be present at the time of HD challenge. Cultures protected with MIPE were two times more viable than HD exposed cells 48 h after HD challenge when using the GV and NR assays to assess viability. Observations by phase contrast microscopy of NR and GV stained cultures confirmed these findings. Addition of MIPE after previously exposing the A549 cultures to HD (for up to 5 min) maintained cell viability at 72% compared to 37% for unprotected cultures, after which time viability fell significantly so that at 10 min there was no difference in viability between the MIPE treated and untreated cultures. 3. Pretreating A549 cultures with MIPE for 1 h followed by its removal prior to HD challenge did not maintain cell viability. Treatment of cultures with HD for 1 h followed by addition of MIPE did not maintain the viability of the cultures, thus the window within which it was possible for MIPE to rescue cell cultures from the effects of HD was of short duration. 4. High performance liquid chromatography was used to determine the biochemical basis of the actions of MIPE. It was found that whilst intracellular levels of cysteine were increased up to 40-fold following treatment of A549 cell cultures with MIPE, levels of reduced glutathione did not rise. The lack of protection seen in cultures pretreated with MIPE for 1 h prior to HD exposure suggests that raising intracellular cysteine levels was not an effective strategy for protecting cells from the effects of HD. The protection observed is probably due to extracellular inactivation of HD by MIPE.

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

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. The cultures were pretreated with mixtures of methenamine (HMT) and glutathione (GSH) for 1 h prior to exposure to 10 microM 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. 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 pretreatment 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. 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 microM HD resulted in a rapid onset of toxicity. Exposure to 1000 microM HD reduced viability in A549 cell cultures to 61% after 2 h (control cultures = 100%), whereas exposure to 40 microM 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 microM 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 concentrations 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 of HD, though it must be present at the time of HD 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.

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

1. The epithelial Madin Darby Canine Kidney (MDCK) cell line was used to study the toxicity of epsilon-toxin from Clostridium perfringens. The epithelial MDCK cell line is known to be sensitive to epsilon-toxin of Clostridium perfrigens and to investigate its mechanism of action, the neutral red assay has been used to dermine the viability of cultures of this cell line. 2. Comparison of the LC50s obtained at 34 degrees C and 0 degree C showed that the lethality of epsilon-toxin was reduced by 18-fold at the lower temperature. The effect of temperature on epsilon-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 of epsilon-toxin was also investigated by incubating cultures of MDCK cells with and without sodium azide over a range of concentrations of toxin. The co-administration of sodium azide did not reduce the toxicity of epsilon-toxin, suggesting that energy-dependent uptake processes such as endocytosis were unlikely to be involved in its mechanism of action. The results are, however, consistent with known receptor-based mechanisms of uptake and with other mechanisms of internalisation across the plasma membrane. epsilon-toxin thus interacts with cell surfaces by a temperature sensitive mechanism potentiated by low pH.

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 substratum 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 investigated 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 membrane 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 apoptosis as being a significant additional mechanism of toxicity following exposure to ricin and abrin holotoxins raises the possibility of developing new therapeutic strategies against poisoning by these phytotoxins.

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 percutaneous 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 concentrations 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, including the associated inflammatory response.

The generation of a human dermal equivalent to assess the potential contribution of human dermal fibroblasts to the sulphur mustard-induced vesication response

1. A human dermal equivalent (HDE) gel was constructed from rat tail tendon collagen (type 1) and human dermal fibroblasts (HFs). Histological studies revealed that the HFs within the HDE gel matrix assumed the shape of differentiated dermal fibroblasts and were metabolically viable as determined by the MTT assay. 2. The HDE system was developed to determine if viable, differentiated HFs have the potential to contribute to tissue damage by releasing the proteolytic enzyme elastase following exposure to sulphur mustard (HD). Elastase was measured, using the substrate suc-ala-ala-val-p-nitroanilide (SAAVNA), because of its association with various human pathological bullous skin diseases. An additional elastase substrate (suc-ala-ala-ala-p-nitroanilide; SAAANA) was also used. A miniaturised assay was employed to measure lactate dehydrogenase (LDH), a cytosolic enzyme released following damage to the cell membrane. 3. Elastase levels (measured with SAAVNA) increased to over 740% of those in control culture medium at 24 h after exposure of the HDE to HD (2 mM) and may therefore be part of the mechanism associated with dermo-epidermal separation and blistering in humans following exposure of skin to HD. LDH was released from the HDE after exposure to HD in a time dependent fashion, suggesting a steady leakage of cytosolic constituents after the initial exposure. 4. The results suggest that differentiated human dermal fibroblasts have the potential to contribute to the development of the vesication response by releasing proteases such as elastase extracellularly after HD exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

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-linking of type IV collagen or laminin. Laminin was, however, found to be partially degraded as determined by the resolution of 132 and 143 kDa fragments, possibly by the activation 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 microblisters 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 contention 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 protease 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 efficacy of prophylactic and therapeutic regimes.

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 LCt50's 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 LCt50's 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.

Examination of the toxicity of several protein toxins of plant origin using bovine pulmonary endothelial cells

The bovine pulmonary endothelial (BPE) cell line was examined as a model to study the toxicity of ricin and abrin toxins currently under investigation. The BPE cell line was examined because ricin has been shown to bind to endothelial cells. Cell viability was assessed using several different biochemical parameters including growth (DNA by binding of gentian violet stain), mitochondrial function (succinate dehydrogenase activity) using MTT and lysosomal integrity (neutral red retention assay). In order to compare toxicities and investigate potential protective compounds, concentrations of toxins causing death of 50% and 70% of the (control) cell population (LC50 and LC70, respectively) were determined. It is concluded that while ricin and abrin share a common mechanism of action ricin is slightly less toxic than abrin. BPE cells are a good model for future mechanistic studies and particularly for initial phase screening of potentially therapeutic compounds. Carbohydrates were used in an attempt to examine which receptor types were involved in the binding and uptake of ricin and abrin by the cell line. It was found that only high concentrations of galactose prevented lethality while mannose apparently had no effect. Furthermore, the molar excess of carbohydrate to toxin required in order to achieve protection indicated that this would be an impractical approach to adopt in vivo.

Bovine aorta contains at least two related forms of heparan sulphate proteoglycan

1. The proteoglycan peak from anion exchange chromatography of an extract of bovine aorta was digested with chondroitinase ABC. The residual heparan sulphate proteoglycans were further purified by chromatography on Sepharose CL4B and DEAE-Sephacel to yield two species, of high and low charge density. 2. Higher molecular weight material had a higher proportion of high charge density proteoglycan, while the lower molecular weight species had a higher proportion of low charge density heparan sulphate proteoglycan. 3. The two species shared epitopes as they both reacted with an antibody to heparan sulphate proteoglycan from bovine glomerular basement membrane. 4. On electron microscopy, both high and low charge density proteoglycans were visualized as 'tadpole-like' molecules, which showed a tendency to aggregate via their globular heads. 5. Bovine aortic smooth muscle cells were cultured in the presence of [35S]sulphate and [3H]glucosamine. Proteoglycans were isolated from medium and cell layer extract by the methods outlined above. 6. The major HSPG species isolated from medium were significantly larger than those from cell layer and displayed substantial heterogeneity in both size of HS chain after papain digestion and size of protein core after heparitinase digestion. 7. The major cell layer species yielded two HS species of widely differing mol. wt after papain digestion, and a very small protein core after heparitinase digestion. Therefore cell layer-associated HSPGs show a good deal more homogeneity than those found in the medium. 8. Further ion-exchange chromatography after digestion with chondroitinase ABC revealed HSPG species of lower charge density, possibly derived from a hybrid chondroitin sulphate-dermatan sulphate proteoglycan (CS/DSPG) after removal of the CS/DS chains.

Refolding and assembly of penicillin acylase, an enzyme composed of two polypeptide chains that result from proteolytic activation

The in vitro folding and assembly of penicillin acylase (EC 3.5.1.11) (PA) to active enzyme has been studied. PA is a large bacterial protein (Mr = 86,000) comprising two peptides, alpha and beta, produced by proteolytic processing and activation of a 92-kDa precursor. Proteins that result from proteolytic processing are characteristically difficult if not impossible to refold. Different factors that affect folding and assembly of PA, including pH, ionic strength, and temperature, have been studied. Yields of 60% can be obtained, based on recovery of enzyme activity, together with another 20% of folded and associated monomer with conformation closely similar to that of the active enzyme but with the active site not formed. Evidence is presented for in vitro assembly proceeding via initial folding of the N-terminal alpha-peptide with subsequent collapse of the transiently folded beta-chain on to the surface of the former. A slow process of rearrangement follows association in vitro. Competition experiments support the proposal that the linker endopeptide in the precursor serves to increase the probability of productive collision between folded alpha- and beta-peptides. The effect of raised temperature is to interfere with the folding of the alpha-peptide, thus preventing proper folding of the precursor. This finding accounts for the basis of the temperature regulation of PA production in vivo.

Site-directed chemical conversion of serine to cysteine in penicillin acylase from Escherichia coli ATCC 11105. Effect on conformation and catalytic activity

Penicillin acylase (EC 3.5.1.11) was completely inactivated with equimolar phenylmethane [35S]sulphonyl fluoride (PhMe35SO2F); the stability of the sulphonyl group in the modified protein was determined by measurement of the radioactivity in ultrafiltrates. In 8 M urea, the rate of loss of the sulphonyl group was similar to that observed in PhMeSO2F-inactivated chymotrypsin [Gold, A.M. & Fahrney, D. (1964) Biochemistry 3, 783-791]. Incubation of the PhMeSO2F-inactivated acylase with 0.7 M potassium thioacetate yielded an acetylthiol enzyme which was subsequently converted to a thiol-enzyme during incubation with 10 mM 6-aminopenicillanic acid. 4-Pyridyl-ethylcysteine was released by acid hydrolysis after reaction of the thiol-protein with 4-vinylpyridine. The rates of reaction of thiol-penicillin acylase with iodoacetic acid and 2,2'-dipyridyl disulphide were consistent with the presence of an incompletely accessible cysteinyl sidechain. After carboxymethylating the thiol-enzyme with iodo[2-3H]acetic acid, the label was shown by SDS/PAGE and sequencing analysis to be associated exclusively with the beta-chain NH2-terminal residue, indicating conversion of Ser290 to S-carboxymethyl-cysteine. Near-ultraviolet CD spectra showed the conformation of thiol-penicillin acylase to be indistinguishable from that of the native protein but the catalytic activity was less than 0.02% of that of the normal enzyme. The possibility that Ser290 acts as a nucleophile in catalysis is discussed.

The folding and solution conformation of penicillin G acylase

The solution conformation properties of penicillin G acylase (EC 3.5.1.11) have been characterised by near- and far-ultraviolet circular dichroism, steady-state and time-resolved fluorescence spectroscopy and differential sedimentation velocity. The enzyme (86 kDa) was found to be spherical and stable unfolding over a narrow range of urea concentrations in an apparently cooperative fashion with a mid-point of 4.5 M urea. Separation of its constituent alpha and beta peptides (23.8 kDa and 62.2 kDa, respectively) was accompanied by loss of enzyme activity and unfolding, the kinetics of unfolding being highly dependent upon urea concentration. Urea gradient gel electrophoresis showed that the separated beta peptide aggregates over a wide range of urea concentrations but that the alpha peptide refolds reversibly to a compact state. Physical studies showed that the refolded alpha peptide has a compact but asymmetric structure with more alpha helix than the native enzyme, but is more sensitive to denaturant. The latter is suggested to be due to a hydrophobic patch detected by 8-anilino-1-naphthalene sulfonic acid binding and which is normally covered by the beta peptide in the native enzyme. The results of these investigations indicate that the alpha peptide constitutes a folding domain and suggest that it plays a key role in folding of the precursor for penicillin acylase.