Extracellular collagenase, proteoglycanase and products of their activity, released in organ culture by intact dermal inflammatory lesions produced by sulfur mustard

Multiple Cell Cultures for MRI Analysis

Magnetic resonance imaging (MRI) is an imaging method that enables diagnostics. In recent years, this technique has been widely used for research using cell cultures used in pharmaceutical science to understand the distribution of various drugs in a variety of biological samples, from cellular models to tissues. MRI's dynamic development in recent years, in addition to diagnostics, has allowed the method to be implemented to assess response to applied therapies. Conventional MRI imaging provides anatomical and pathological information. Due to advanced technology, MRI provides physiological information. The use of cell cultures is very important in the process of testing new synthesized drugs, cancer research, and stem cell research, among others. Two-dimensional (2D) cell cultures conducted under laboratory conditions, although they provide a lot of information, do not reflect the basic characteristics of the tumor. To replicate the tumor microenvironment in science, a three-dimensional (3D) culture of tumor cells was developed. This makes it possible to reproduce in vivo conditions where, in addition, there is a complex and dynamic process of cell-to-cell communication and cell-matrix interaction. In this work, we reviewed current research in 2D and 3D cultures and their use in MRI studies. Articles for each section were collected from PubMed, ScienceDirect, Web of Science, and Google Scholar.

A type IV collagenase inhibitor, N-hydroxy-3-phenyl-2-(4-phenylbenzenesulfonamido) propanamide (BiPS), suppresses skin injury induced by sulfur mustard

Sulfur mustard (SM) is a highly toxic blistering agent thought to mediate its action, in part, by activating matrix metalloproteinases (MMPs) in the skin and disrupting components of the basement membrane zone (BMZ). Type IV collagenases (MMP-9) degrade type IV collagen in the skin, a major component of the BMZ at the dermal-epidermal junction. In the present studies, a type IV collagenase inhibitor, N-hydroxy-3-phenyl-2-(4-phenylbenzenesulfonamido) propanamide (BiPS), was tested for its ability to protect the skin against injury induced by SM in the mouse ear vesicant model. SM induced inflammation, epidermal hyperplasia and microblistering at the dermal/epidermal junction of mouse ears 24-168 h post-exposure. This was associated with upregulation of MMP-9 mRNA and protein in the skin. Dual immunofluorescence labeling showed increases in MMP-9 in the epidermis and in the adjacent dermal matrix of the SM injured skin, as well as breakdown of type IV collagen in the basement membrane. Pretreatment of the skin with BiPS reduced signs of SM-induced cutaneous toxicity; expression of MMP-9 mRNA and protein was also downregulated in the skin by BiPS. Following BiPS pretreatment, type IV collagen appeared intact and was similar to control skin. These results demonstrate that inhibiting type IV collagenases in the skin improves basement membrane integrity after exposure to SM. BiPS may hold promise as a potential protective agent to mitigate SM induced skin injury.

Early indicators of survival following exposure to mustard gas: Protective role of 25(OH)D

The use of sulfur mustard (SM) as a chemical weapon for warfare has once again assumed center stage, endangering civilian and the military safety. SM causes rapid local skin vesication and late-onset systemic toxicity. Most studies on SM rely on obtaining tissue and blood for characterizing burn pathogenesis and assessment of systemic pathology, respectively. However the present study focuses on developing a non-invasive method to predict mortality from high dose skin SM exposure. We demonstrate that exposure to SM leads to a dose dependent increase in wound area size on the dorsal surface of mice that is accompanied by a progressive loss in body weight loss, blood cytopenia, bone marrow destruction, and death. Thus our model utilizes local skin destruction and systemic outcome measures as variables to predict mortality in a novel skin-based model of tissue injury. Based on our recent work using vitamin D (25(OH)D) as an intervention to treat toxicity from SM-related compounds, we explored the use of 25 (OH)D in mitigating the toxic effects of SM. Here we show that 25(OH)D offers protection against SM and is the first known demonstration of an intervention that prevents SM-induced mortality. Furthermore, 25 (OH)D represents a safe, novel, and readily translatable potential countermeasure following mass toxic exposure.

Sulfur mustard toxicity: history, chemistry, pharmacokinetics, and pharmacodynamics

Sulfur mustard (SM) and similar bifunctional agents have been used as chemical weapons for almost 100 years. Victims of high-dose exposure, both combatants and civilians, may die within hours or weeks, but low-dose exposure causes both acute injury to the eyes, skin, respiratory tract and other parts of the body, and chronic sequelae in these organs are often debilitating and have a serious impact on quality of life. Ever since they were first used in warfare in 1917, SM and other mustard agents have been the subjects of intensive research, and their chemistry, pharmacokinetics and mechanisms of toxic action are now fairly well understood. In the present article we review this knowledge and relate the molecular-biological basis of SM toxicity, as far as it has been elucidated, to the pathological effects on exposure victims.

Peaceful use of disastrous neurotoxicants

The increasing exposure to environmental neurotoxicants in the last decades caused serious health problems in the world population. Some of the neurotoxic agents are being used in agriculture and household such as insecticides and rodenticides and others are of natural origin like snake and scorpion venoms. Additional group of harmful substances is the chemical warfare agents including nerve and blistering agents that are known for their disastrous effects on neuronal tissues. The present paper presents a combination of epidemiological/clinical and molecular approaches for investigating the effect of certain groups of neurotoxicants on a variety of pathologies. The work of Finkelstein and coworkers describes epidemiological and clinical studies on acute and chronic organophosphate (OP)-induced neurotoxicity in certain populations in Israel. They mainly investigated the neurotoxic effects of low-level long-term exposure to OP in agricultural areas but also dealt with acute exposures as well. A molecular approach to OP mechanism of neuronal injury was described by Milatovic and coworkers. They demonstrated OP-induced oxidative injury in pyramidal neurons in the CA1 hippocampal area and its suppression by antioxidants. Lecht and coworkers described the novel snake venom angioneurins as important mediators of the physiological cross-talk between the cardiovascular and nervous systems. They also showed that under certain conditions these angioneurins may induce pathologies such as tumor development or disruption of the vascular barrier function during envenomation. Additional mechanistic/therapeutic approach was presented by Brodsky, Rosengarten, Proscura, Shapira and Wormser. They developed a novel anti-inflammatory peptide that reduced skin irritation induced by heat and sulfur mustard (SM) stimuli. Since SM causes neuropsychiatric symptoms and alterations in neurological functions this peptide may serve as a potential treatment of neuronal injuries caused by environmental neurotoxicants. These reviews highlight different aspects of neurotoxicity, addressing epidemiology and mechanisms of toxicity; and identifying novel potential therapies.

Mechanisms mediating the vesicant actions of sulfur mustard after cutaneous exposure

Sulfur mustard (SM), a chemical weapon first employed during World War I, targets the skin, eyes, and lung. It remains a significant military and civilian threat. The characteristic response of human skin to SM involves erythema of delayed onset, followed by edema with inflammatory cell infiltration, the appearance of large blisters in the affected area, and a prolonged healing period. Several in vivo and in vitro models have been established to understand the pathology and investigate the mechanism of action of this vesicating agent in the skin. SM is a bifunctional alkylating agent which reacts with many targets including lipids, proteins, and DNA, forming both intra- and intermolecular cross-links. Despite the relatively nonselective chemical reactivity of this agent, basal keratinocytes are more sensitive, and blistering involves detachment of these cells from their basement membrane adherence zones. The sequence and manner in which these cells die and detach is still unresolved. Much has been discovered over the past two decades with respect to the mechanisms of SM-induced cytotoxicity and the intracellular and extracellular targets of this vesicant. In this review, the effects of SM exposure on the skin are described, as well as potential mechanisms mediating its actions. Successful therapy for SM poisoning will depend on following new mechanistic leads to develop drugs that target one or more of its sites of action.

The use of doxycycline as a protectant against sulphur mustard in HaCaT cells

As part of an ongoing programme on medical countermeasures against the chemical warfare agent sulphur mustard (HD) and set against the background of the involvement of matrix metalloproteinases (MMPs) in the pathology of HD-induced vesication processes, the potentially beneficial effects of doxycycline on cell attachment was determined in confluent HaCaT cell cultures exposed to HD. Doxycycline was found to inhibit to a significant extent the tendency of HD-exposed cells to detach from the growth substrate, however, analysis of the metabolic activity of the adherent cells indicated that doxycycline treatment did not maintain cell viability. It was confirmed that apoptosis was the predominant mode of HD-induced cell death. The results suggested that doxycycline and other MMP inhibitors may have a role to play in therapeutic intervention against HD exposure, but only as part of a combination therapy. The specific value of protease inhibitors in this capacity remains to be determined.

Matrix metalloproteinase-9 expression and release from skin fibroblasts interacting with keratinocytes: Upregulation in response to sulphur mustard

Matrix metalloproteinases (MMPs), especially MMP-9 and MMP-2, degrade various proteins of the extracellular matrix, including collagen type IV the major component of basement membranes which also separate the epidermis from the dermis. Although previous work indicates the contribution of MMPs and their inhibitors (TIMPs) to the pathophysiology of skin lesions induced by the toxic chemical warefare agent sulphur mustard (SM), little is known about the underlying molecular and cellular mechanisms. In this study we demonstrate in a 3D-skin model that topical application of SM significantly upregulated basal MMP-9 mRNA expression and release from the cells as shown by qRT-PCR and zymography, whereas that of MMP-2, membrane-type 1 (MT1)-MMP, TIMP-1 and TIMP-2 remained almost unaffected by SM. Further studies in neonatal human dermal fibroblasts (NHDF) and HaCaT keratinocytes revealed that MMP-9 was not secreted from these cells, neither with or without exposure to SM. However, when NHDF and HaCaT were cocultivated, MMP-9 was expressed and released from the cell mixture, suggesting that interaction between both cell types is essential for MMP-9 production. Moreover, SM-treatment of NHDF/HaCaT cocultures further upregulated MMP-9 biosynthesis and secretion, which was consistent with our findings obtained in the 3D-skin model. Addition of conditioned medium derived from SM-exposed HaCaT cells to NHDF was able to stimulate MMP-9 secretion and also increased the migratory potential of NHDF as shown in a scratch-wound healing assay and a fluorescent cell invasion assay. In contrast, culture supernatants of SM-treated NHDF had not such an effect on HaCaT cells. Taken together, our findings provide first evidence that SM exposure of skin stimulates keratinocytes to release soluble factors which in turn induce enhanced MMP-9 secretion and invasiveness of fibroblasts in vitro. This provides a potential mechanism probably contributing to SM-evoked tissue injury in vivo.

Preferential expression of matrix metalloproteinase-9 in mouse skin after sulfur mustard exposure

Matrix metalloproteinases (MMPs), a class of enzymes responsible for the degradation of extracellular matrix proteins, play important roles in inflammatory and immune responses. In skin, MMP-2 (gelatinase A) and MMP-9 (gelatinase B) are normally inactive but can be expressed during tissue injury. Both degrade collagen IV and other critical components of the basement membrane zone that separates the epidermis from the dermis. The expression of MMP-2 and -9 was studied in sulfur mustard (SM)-exposed ear skin from mice to determine their role in tissue vesicant injury. Punch biopsies of mouse ears were collected between 6 and 168 h after exposure to 97.5 mM (0.08 mg) SM diluted in CH(2)Cl(2). They were examined histologically and assayed for MMP-2 and -9 expression by gelatinase activity assays, real-time reverse transcriptase-polymerase chain reaction and Western blot analysis. A time-related increase in overall gelatinase activity was observed in SM-treated ears. At 168 h after SM exposure, the relative levels of MMP-9 mRNA were increased 27-fold and MMP-9 protein 9-fold when compared with the control (CH(2)Cl(2) treated) ears. In contrast, there were no observable increases in the MMP-2 mRNA or protein levels between treated and control ears. These observations suggest the differential expression of MMP-2 and -9 during the cutaneous response to SM injury and suggest a role for MMP-9 in SM-induced injury.

Effect of doxycycline on sulfur mustard-induced respiratory lesions in guinea pigs

Respiratory tract lesions induced by the chemical warfare agent sulfur mustard (SM) are characterized by epithelial damages associated with inflammatory cell infiltration. Here we evaluated the imbalance between gelatinase and tissue inhibitors of metalloproteinases (TIMPs), and we tested pretreatment with the protease inhibitor doxycycline. Guinea pigs were intoxicated intratracheally with SM and evaluated 24 h after exposure. Matrix metalloproteinase (MMP) gelatinase activity of bronchial lavage (BL) fluid from SM-exposed guinea pigs was high compared with controls, as shown by both zymography and biotinylated substrate degradation, whereas TIMP-1 and -2 levels by immunoblotting were similar. Extensive areas of lysis were evidenced by in situ zymography, indicating imbalance between gelatinases and inhibitors towards net proteolytic activity. Doxycycline pretreatment resulted in 1) decreased gelatinase activity (zymography, free gelatinase activity assay, and in situ zymography); 2) decreased inflammation (BL fluid cellularity and protein level); and 3) dramatic decrease in histological epithelial lesions. Our results suggest inadequate levels of TIMP to counteract increased gelatinase activity and further support a role for MMP gelatinases in SM-induced respiratory lesions. They also suggest that doxycycline may hold promise as a therapeutic tool.

The role of interleukin-6 (IL-6) in human sulfur mustard (HD) toxicology

The authors applied in vitro models of controlled damage to human epidermal keratinocytes (HEKs), human skin fibroblasts (HSFs), and human breast skin tissue (HBST) to examine the mechanism responsible for sulfur mustard (HD)-induced interleukin-6 (IL-6) alterations. Treatment with 100 microM HD for 24 hours resulted in a significant increased amount of IL-6 being secreted by HEKs (HD-exposed to control ratio [E/C] = 4.15 +/- 0.07) and by HSFs (E/C = 7.66 +/- 0.04). Furthermore, the HD-induced secretion of IL-6 in HEKs was neutralized with monoclonal human IL-6 antibodies. The secretion of IL-6 in HBST supernatant exposed to HD produced conflicting results. Although an increase of IL-6 was observed in control superfusion media from HBST, IL-6 levels were observed to decrease as the concentration of HD increased. Time course of IL-6 mRNA levels were performed using a competitive polymerase chain reaction (PCR) and human IL-6 mRNA assay detection kit in control and HD (100 microM)-treated HEKs cells. IL-6 mRNA transcripts in HD-exposed HEKs were first observed within 2 hours, dropped at 5 to 6 hours, and increased by approximately 2.2-fold and 8.5-fold at 24 to 48 hours after HD exposure, respectively, as detected by the Xplore mRNA Quantification System. Surface-enhanced laser desorption ionization (SELDI) mass spectrometry was also applied to study the secretion pattern of IL-6 on lysate preparations of HBST. A peak in the area of 23,194 to 23,226 Da was detected using antibody coupled to the chip. This peak was assigned to correspond to the mass of the IL-6 glycoprotein. Recombinant human IL-6 (rhIL-6) exposed to HD lacked the second disulfide bridge and was partially unfolded, as determined by nuclear magnetic resonance-nuclear Overhauser enhancement and exchange spectroscopy (NMR-NOESY). The disappearance of the resonance peak at 3.54 ppm and the appearance of a new chemical shift at 1.85 ppm suggested that a change in structure had occurred in the presence of HD. From the data, the possibility cannot be excluded that IL-6 might be involved in the early event of structural changes of the signal transducer glycoprotein that indirectly initiates the cascade of events such as skin irritation and blister formation observed in the pathophysiology of HD injury.

Matrix metalloproteinase gelatinases in sulfur mustard-induced acute airway injury in guinea pigs

Respiratory tract lesions induced by sulfur mustard (SM), a chemical warfare agent, are characterized by epithelial damage associated with inflammatory cell infiltration. To test the potential role of matrix metalloproteinase gelatinases in these lesions, we evaluated gelatinase activity, albumin content, and total cell count in bronchoalveolar lavage fluid of guinea pigs 24 h after an intratracheal injection of 0.2 mg/kg of SM. The bronchial lavage and alveolar lavage fluids were analyzed separately. The increase in inflammatory cell content of the bronchial lavage fluid, mainly macrophages, observed in SM-intoxicated guinea pigs was accompanied by an increase in albumin and in 92-kDa gelatinase activity. There was a significant correlation between albumin content and 92-kDa gelatinase activity (r = 0.67) and between 92-kDa gelatinase and the number of macrophages. Immunohistochemistry performed on tracheal sections showed the presence of 92-kDa gelatinase at the site of intraepithelial cleavages. Zymography analysis of culture medium conditioned by guinea pig tracheal epithelial cells demonstrated that these cells produced in vitro 92-kDa gelatinase on stimulation. Culture of human bronchial epithelial cells obtained by the explant technique showed a marked increase in 92-kDa gelatinase after exposure to 5 x 10(-5) M SM that reinforced the relevance of our animal results to human exposure to SM. These results suggest that in SM respiratory intoxication, 92-kDa gelatinase of both inflammatory and epithelial cell origins could be involved in epithelial cell detachment.

Activation of poly [ADP-Ribose] polymerase in endothelial cells and keratinocytes: role in an in vitro model of sulfur mustard-mediated vesication

Although endothelial cells and keratinocytes appear to be the primary cellular targets of sulfur mustard (SM), the role of the nuclear enzyme poly (ADP-ribose) polymerase (PARP) in SM-induced vesication has not been clearly defined. PARP is thought to play a crucial role in DNA repair mechanisms following exposure to alkylating agents like SM. Using a combination of fluorescence microscopy and biochemical assays, we tested the hypothesis that SM causes activation of PARP in endothelial cells and keratinocytes with subsequent loss of nicotinamide adenine dinucleotide (NAD) and depletion of adenosine triphosphate (ATP) levels. To determine if PARP activation accounts for SM-induced vesication, keratinocyte adherence and permeability of endothelial monolayers were measured as in vitro correlates of vesication. As early as 2 to 3 h after exposure to SM concentrations as low as 250 microM, dramatic changes were induced in keratinocyte morphology and microfilament architecture. Exposure to 500 microM SM induced a fourfold increase in PARP activity in endothelial cells, and a two- to threefold increase in keratinocytes. SM induced a dose-related loss of NAD+ in both endothelial cells and keratinocytes. ATP levels fell to approximately 50% of control levels in response to SM concentrations >/=500 microM. SM concentrations >/=250 microM significantly reduced keratinocyte adherence as early as 3 h after exposure. Endothelial monolayer permeability increased substantially with concentrations of SM >250 microM. These observations support the hypothesis that the pathogenic events necessary for SM-induced vesication (i.e., capillary leak and loss of keratinocyte adherence) at higher vesicating doses of SM (>/=500 microM) may depend on NAD loss with PARP activation and subsequent ATP-dependent effects on microfilament architecture. Vesication developing as a result of exposure to lower concentrations of SM presumably occurs by mechanisms that do not depend on loss of cellular ATP (e.g., apoptosis and direct SM-mediated damage to integrins and the basement membrane).

Chemotactic factors released in culture by intact developing and healing skin lesions produced in rabbits by the irritant sulfur mustard

Development, peak and healing lesions were induced in the skin of rabbits by topical applications (on different days) of the chemical irritant sulfur mustard (SM). Immediately after the rabbits were euthanized, the intact lesions were excised and organ-cultured for 17 to 20 hours. The culture fluids from early, peak and healing SM lesions all showed high chemotactic activity for both PMN and MN. This finding suggests that the PMN and MN, seen microscopically in tissue sections of the lesions, were entering continuously, even during the healing process. The chemotaxins identified were the eicosanoid LTB4, the chemokine IL-8, and proteases producing the complement fragment C5a. Other studies from our laboratory showed that the number of cells containing IL-1, IL-8, MCP-1, and GRO mRNAs was increased in SM lesions. Chemotactic activity was released by both live and dead (frozen and thawed) cell suspensions of PMN, MN, and fibroblasts, suggesting that these cells were major sources of the chemotaxins produced by the SM lesion explants. Explants of normal skin produced considerable chemotactic activity for MN, but not for PMN. Chemotactic activity for PMN, and the release of LTB4, IL-8 and proteases cleaving C5 to C5a, occurred only in explants infiltrated by leukocytes.

The cytokines NAP-1 (IL-8), MCP-1, IL-1 beta, and GRO in rabbit inflammatory skin lesions produced by the chemical irritant sulfur mustard

Developing and healing dermal inflammatory lesions were produced in rabbits by the topical application of dilute sulfur mustard (SM), the military vesicant. In tissue sections of such lesions, cells containing the mRNA of important cytokines were identified with in situ hybridization techniques. These cytokines were neutrophil attractant/activation protein-1 (NAP-1 (also called IL-8), monocyte chemoattractant (activating) protein 1 (MCP-1), interleukin 1 (beta) (IL-1 (beta)), and GRO (a growth factor and chemokine). Mononuclear cells (mainly macrophages and activated fibroblasts) contained the mRNA of all four of these cytokines. A higher percentage of cytokine-producing mononuclear cells (macrophages and activated fibroblasts) was present in lesions at 2 days (their peak size) than at 6 days, when they were almost healed. Granulocytes emigrated from the bloodstream, passed through the lesions, and were the major constituent of the protective crust. This sequence correlated with the distribution of cells able to produce NAP-1: At 2 days and 6 days, the mononuclears that contained messenger RNA for this granulocyte chemoattractant were found mainly in the upper part of the dermis. At 2 days and 6 days, cells containing the mRNA of IL-1, a primary cytokine, were also found predominantly in the upper dermis, i.e., nearest the site of injury. In contrast, mononuclears containing the mRNA of MCP-1 (a monocyte chemoattractant), and the mRNA of GRO (a granulocyte chemoattractant) were more equally distributed throughout the dermis. SM stimulated hair follicle epithelial cells to up-regulate GRO mRNA and, to a lesser degree, NAP-1 mRNA. Apparently, the irritation produced by SM directly or indirectly induces such epithelial cells to manufacture these growth factors. In the rabbit, hair follicles are known to be the main source of new epithelial cells after the covering epithelium has been destroyed. Therefore, GRO is probably a major autocrine-paracrine stimulus for such repair. A brief review of the role of cytokines in dermal inflammation is presented.

Production of type IV collagen and 72-kDa gelatinase by human endothelial cells cultured in high glucose. Effects of a protein kinase C inhibitor, GF 109203X

Since diabetic microangiopathy and macroangiopathy are characterized by type IV collagen accumulation in vascular basement membranes, it was of interest to study type IV collagen production and type IV collagenase secretion by endothelial cells (EC) cultured in high glucose and to evaluate the role of protein kinase C (PKC) activation in the alterations induced by high glucose. Primary cultures of human umbilical vein EC were exposed to high glucose concentration for 3 days at the beginning of confluence. The number of EC decreased with glucose concentration from 5 to 50 mM. At 16.7 mM glucose concentration, the amount of type IV collagen, determined by a two-step ELISA, increased in the culture supernatant and in the insoluble fraction associated with the extracellular matrix and cells; proline incorporation was more markedly elevated in the collagenous than in the total proteins of the culture supernatant and of the extracellular matrix and cell extracts. Gelatin zymography of the culture supernatant showed that EC mainly produce a 72-kDa gelatinase known to degrade type IV collagen. At 16.7 mM glucose concentration, total gelatinase activity per millilitre of culture supernatant was reduced and the 72-kDa gelatinase activity measured on the zymogram scan was lowered. When EC were exposed to 16.7 mM glucose, the specific PKC inhibitor GF 109203X corrected the increases in type IV collagen concentration and in proline incorporation into the collagenous or total proteins present in he culture supernatant or in the extract of the insoluble fraction, including the extracellular matrix and cells. Our results show that soluble and insoluble type IV collagen accumulation by EC cultured at high glucose concentration is not only associated with increased synthesis of the collagenous and total proteins but also with decreased total 72-kDa gelatinase activity in the extracellular fluid. The observed effects of GF 109203X are in favor of the involvement of PKC activation in the type IV collagen accumulation.

Role of monocyte/macrophage derived matrix-metalloproteinases (gelatinases) in prolonged skin inflammation

Neutral metalloproteinase activities in dermal extracellular space have been studied in several models of prolonged cutaneous inflammation in guinea pigs, by the following techniques: lysis of type I 14C-collagen fibrils, electrophoretic analysis of types I or IV collagen hydrolytic fragments and zymography. For 2-3 weeks, in parallel to mononuclear cell infiltration, collagenase activity was increased 3-4-fold. Constitutive gelatinases (67 and 72 kDa) augmented and larger molecular species emerged (92, 110 and 185 kDa), all of neutral metalloproteinase type. Guinea pig peritoneal monocytes/macrophages cultured with appropriate stimulation released large gelatinases in a similar set (92, 110, 210 kDa). These were purified from culture media by gelatin affinity and used in vivo as follows: (a) direct injection of monocyte/macrophage gelatinases; (b) injection of collagen I fragments (M(r) < 10,000) split off by gelatinases from preincubated (pH 5 and 38.5 degrees C) collagen I. In both instances, a mononuclear cell invasion of dermis occurred, indistinguishable from prolonged inflammation. These analogies suggest that monocyte/macrophage-derived metalloproteinases have an early and basic participation in the mechanism of prolonged inflammation.

Mediators, initiating the inflammatory response, released in organ culture by full-thickness human skin explants exposed to the irritant, sulfur mustard

Mediators released from injured human skin that initiate the inflammatory response have not been adequately identified. Organ culture of full-thickness skin explants enables us to do so, because injury to the skin can be made in vitro, eliminating the rapid leakage of serum and infiltration of leukocytes that occur in vivo. In our studies, the military vesicant sulfur mustard (SM) (10 microliters of a 0.01 to 1.0% dilution) was topically applied to injure the epidermis of the explant. Then, the explants were cultured in small Petri dishes, usually for 18 h at 36 degrees C, and the organ-culture fluids were assayed for various inflammatory mediators. We found that the culture fluids from SM-exposed and control explants contained similar amounts of angiotensin-converting enzyme, trypsin-like and chymotrypsin-like proteases, acid phosphatase, beta-glucuronidase, beta-galactosidase, lysozyme, deoxyribonuclease, ribonuclease, interleukin 1, and lactic dehydrogenase. However, the culture fluids from SM-exposed explants contained increased amounts of histamine and plasminogen-activating activity, and often prostaglandin E2, when compared to culture fluids from control explants. After 3 to 4 d in culture, full-thickness human skin explants, when exposed to 0.2% SM (but not when exposed to 1.0% SM), sometimes showed separation of the epidermis and increased collagenase activity (i.e., hydroxyproline release). Thus, histamine (from local mast cells), and prostaglandin E2 and plasminogen-activating activity (probably from both mast cells and epidermal cells) are apparently involved in early mediation of the inflammatory response.