Time and dose-related ultraviolet B damage in viable pig skin explants held in a newly developed organ culture system.

For facilitating photochemical and toxicological studies an ex vivo skin model was developed in our laboratory using skin from domestic pigs. The model comprised the use of a complete skin piece, including the dermis and stratum corneum, of bigger areas to make future topical applications easier. Fully differentiated skin explants (5 x 50 mm, thickness 5 mm) were irradiated with ultraviolet B (UVB; 1-10 kJ/m2; 6 W/m2). Directly thereafter they were brought in culture (Dulbeccos modified Eagles medium containing hydrocortisone; air/liquid interface) for a maximum of 144 h. In nonirradiated skin explants, signs of tissue degeneration were observed after 48 h in culture (hematoxylin and eosin, light microscope). However, keratinocytes, isolated enzymatically (thermolysin and trypsin) at different time intervals in culture from nonirradiated skin explants showed negligible loss in viability (trypan blue exclusion) and increased apoptosis (terminal deoxynucleotidyl transferase-mediated deoxy uridine triphosphatase nick end labeling assay) for up to 72 h. Explants irradiated with a single dose of UVB showed a clear and reproducible dose- and time-dependent tissue degeneration, loss in keratinocyte viability and increase in apoptosis compared with nonirradiated explants at the same time interval. In conclusion, the presently designed ex vivo pig skin model can be a useful and cheap tool for future investigations of short-term UV-induced effects in combination with phototoxic and photoprotective compounds.

Are dietary fiber-induced alterations in colonic epithelial cell proliferation predictive of fiber's effect on colon cancer?

Alterations in cell proliferation of the colon have been observed as a result of changes in amount and type of dietary fiber and in relation to risk of developing colon cancer. Although some human observational and intervention studies contribute to the database, most information results from experiments on rodents. Because of numerous contradictory reports linking dietary fiber, cell proliferation, and colon cancer, we undertook a critical review of existing methods in an attempt to explain the inconsistencies. Although there may be some individual types of dietary fiber that protect against chemically induced colon cancer, dietary fiber as a single entity does not appear to afford any consistent protection. Because of significant differences in experimental protocols among laboratories, it is not yet possible to state with certainty that increases in cell proliferation, induced by fiber consumption, are predictive of increased tumorigenesis. Much of what has been observed and interpreted as elevation of risk may simply be normal homeostatic changes in cell proliferation. Even though fermentation to short-chain fatty acids is a mechanistically attractive hypothesis to explain why fiber modulates cytokinetics, data do not consistently support short-chain fatty acids as biological intermediates in risk of colon cancer. The state of the art in this field has not yet progressed to the point where a clear effect of dietary fiber on cytokinetics and colon carcinogenesis can be assessed with any degree of certainty. Additional markers of apoptosis, differentiation, and cell-cell communication may be required for a more accurate analysis of the relation among fiber, cytokinetics, and colon cancer.

Construction of an isogenic leukotoxin deletion mutant of Pasteurella haemolytica serotype 1: characterization and virulence.

Allelic replacement was used to generate two isogenic lktA deletion mutants of Pasteurella haemolytica serotype 1 that were incapable of synthesizing leukotoxin (Lkt). Southern blot data confirmed that lktA sequences were absent in the two P. haemolytica deletion mutants. Culture supernatants and whole cell lysates from the wild type P. haemolytica, D153 parent strain, but not the lktA deletion mutants, contained immunoreactive and bioactive leukotoxic protein. In addition, only the parent strain was haemolytic when grown on bovine and sheep blood agar plates. Virulence of the lktA deletion mutant, lktA 77, was compared with the parent in an experimentally infected calf model of pneumonic pasteurellosis. Results revealed significant reduction in virulence in the lktA mutant as measured by clinical and lung lesion scores. Notable differences in histological changes such as markedly reduced necrosis and lack of leukocyte degeneration occurred in calves infected with the lktA mutant in comparison with those infected with the parent wild-type strain. Thus, it appears that leukotoxin plays a important role in the pathogenesis of lung injury in bovine pneumonic pasteurellosis.

Validation of the galactose oxidase-Schiff's reagent sequence for early detection and prognosis in human colorectal adenocarcinoma.

Based on the multistage and multifocal nature of colorectal carcinogenesis, it is likely that reduction of cancer mortality through early detection and identification of new prognostic markers is an attainable goal. Well-documented changes occur in mucin glycoconjugates during neoplastic progression in the colon, and the nonneoplastic colonic mucosa in colon cancer patients is morphologically and histochemically abnormal. In this retrospective study, 152 archival colorectal tissues from 49 patients were studied for changes in mucin secretions as detected by the galactose oxidase-Schiff's (GOS) sequence. Intensity of the stain was evaluated in histological sections by semiquantitative analysis, and the area percentage of epithelium stained was quantified by image cytometry. The correlation between gender or tumor size, location and reactivity with peanut agglutinin and quantitative expression of GOS-reactive mucins was determined as well as intratumor and inter individual variability. Reactivity with GOS: (a) decreased during neoplastic progression and malignant conversion in the neoplasm; (b) increased in the normal colonic mucosa of patients with progressively more advanced disease; and (c) was of prognostic significance for patient survival or recurrence both in the normal colon of cancer patients and in invasive neoplasms. These data are consistent with the conclusion that GOS reactivity in the normal colonic mucosa is a dosimeter of exposure to environmental/lifestyle colorectal carcinogens rather than a marker for an oncodevelopmental cancer-associated antigen.

Aberrant crypt foci in the colonic mucosa of rats treated with a genotoxic and nongenotoxic colon carcinogen.

Aberrant crypt foci (ACFs) are putative preneoplastic lesions in the colonic mucosa identified by examining methylene blue-stained whole mounts of colon. ACFs have been previously described in rats treated with genotoxic colon carcinogens. This study determined whether or not a nongenotoxic colon carcinogen could induce ACFs and compared the morphology of these ACFs with those induced by a genotoxic colon carcinogen. Six-wk-old Fischer-344 rats were administered dextran sulfate (DSS, nongenotoxin) in the drinking water or azoxymethane (AOM, genotoxin) by single subcutaneous injection. Rats were sacrificed at 9 and 14 wk after study initiation. Colons were fixed and stained with methylene blue, and the mucosal surface of transilluminated whole mounts was examined with a microscope. The number of ACFs and number of crypts per focus (multiplicity) were recorded. Representative ACFs were processed into glycol methacrylate for hexosaminidase enzyme histochemistry and sections of the remaining colon containing ACFs were embedded in paraffin for morphologic evaluation. In whole mounts, ACFs from AOM- and DSS-treated rats had elongated slit-to-oval-shaped lumens surrounded by a thickened and intensely stained epithelium. DSS-induced aberrant crypts differed from those induced by AOM in that they were frequently larger, tended not to form discrete foci circumscribed by normal crypts, and were located adjacent to ulcers. Total ACFs and large foci (4 or more crypts/focus) were significantly more numerous in AOM-treated rats at both time points. Histologically, DSS-induced ACFs had segmental to diffuse loss of hexosaminidase activity, mucin depletion to increased prominence of goblet cells, and marked distortion of crypt architecture. AOM-induced ACFs had diffuse loss of hexosaminidase activity, variable depletion of mucin, and less distortion of crypt architecture. Variable degrees of epithelial dysplasia were seen in ACFs with both carcinogens, but dysplasia was more severe in DSS-induced ACFs. Colonic mucosal neoplasms were induced by both carcinogens. In subchronic studies, the ACF assay may be a useful method to improve the identification and characterization of xenobiotic-induced changes in colonic mucosal crypts.

Evaluation in rats of the dose-response relationship among colonic mucosal growth, colonic fermentation, and dietary fiber.

The dose-response relationship among dietary fiber, colonic fermentation, fecal weight, and mucosal growth were evaluated in this study. The morphometric parameter of total mucosal volume was used to assess diet-induced differences in colonic mucosal growth. Dietary fibers with a wide range of fermentability and that have previously been shown to inhibit the development of colonic neoplasia in rats were used. Sprague-Dawley rats were fed Purina Rodent Chow, AIN-76a fiber-free diet, or an AIN-76a diet supplemented with three different dietary fibers, (cellulose, guar gum, or wheat bran) at 2, 5, 10, or 15% of the diet. Diets were fed for 28 days. Total colonic mucosal volume was determined using stereologic principles and computerized image analysis; 48-hr fecal weight was measured; and the concentration of short-chain fatty acids (SCFA) in colonic contents was determined at study termination. Each type of fiber induced a dose-dependent increase in total mucosal volume of the colon and fecal weight. Mucosal volume and fecal weight were closely correlated (R2 > 0.95). Total mucosal volume was not correlated with the concentration of total SCFA or butyrate in the colon. These results indicate that diet-induced change in colonic mucosal growth, as measured by total mucosal volume, is positively correlated with fecal weight and not related to alterations in colonic fermentation. Enhanced colonic mucosal growth occurs in rats fed dietary fibers that have previously been shown to inhibit the development of genotoxin-induced colonic neoplasia in rats.

The interactions of diet and colonic microflora in regulating colonic mucosal growth.

The colonic mucosa can adapt its growth to alterations in diet. Metabolites from colonic microflora are frequently implicated as the primary factor in mediating the colonic mucosal response to diet; however, there is also evidence indicating that diet may have a direct effect in mediating this response. The aim of this study was to determine the role of diet, microflora, and microflora metabolites in altering the growth of the colonic mucosa. Two 28-day feeding studies were conducted using Sprague-Dawley rats. The first study compared the growth of the colonic mucosa in germ-free and conventional rats fed 6 different diets. The second study compared the growth of the colonic mucosa to the concentration of bacterial-derived short-chain fatty acids (SCFs), bile acids, and ammonia. The diets that were fed consisted of (1) AIN-76a diet without dietary fiber; (2) standard AIN-76a diet, which contained 5% cellulose; (3) AIN-76a diet with 5% guar gum; (4) a "Western" human diet with 20% fat and 10% cellulose; (5) AIN-76a diet formulated to mimic Diet 4 in fat content but with 2.5% cellulose; and (6) Purina Rodent Chow. Quantitative volumetric and stereologic analysis was used to assess changes in total colonic mucosal volume as a measure of mucosal growth. In germ-free rats, Diets 2-4 and 6 induced a significant increase (18-38%) in mucosal volume compared to Diet 1. In conventional animals, only Diets 4 and 6 induced a significant increase (up to 63%) in mucosal volume compared to Diet 1. Relative to the germ-free animals, only conventional animals on Diets 4 and 6 had an increase in mucosal volume. The increases in mucosal volume in Diets 4 and 6 were not consistently associated with increased SCFAs, ammonia, or bile acids. There was a wide range in the colonic concentrations of SCFAs (2-fold), ammonia (6-fold), and bile acids (10-fold). The presence of colonic microflora in and of itself does not lead to enhanced colonic mucosal growth. Rather, there are unique interactions between specific types of diet and microflora that lead to a growth-promoting effect. This effect could not be explained by alterations in the concentration of SCFAs, ammonia, or bile acids in colonic contents.

Enhancement of neutrophil-mediated injury to bovine pulmonary endothelial cells by Pasteurella haemolytica leukotoxin.

In this study, we used an in vitro coculture system to determine which virulence factor from Pasteurella haemolytica A1 was responsible for augmenting bovine polymorphonuclear neutrophil (PMN)-mediated killing of bovine pulmonary artery endothelial cells (BPAEC). A 51Cr release cytotoxicity assay was used as a measure of BPAEC killing. The mechanisms associated with this BPAEC killing were also studied. Our results demonstrated that the leukotoxin and not the lipopolysaccharide from P. haemolytica was responsible for augmenting the PMN-mediated killing of BPAEC. Furthermore, this augmented killing was related to the stimulation of PMNs by the leukotoxin. Killing of BPAEC by leukotoxin-stimulated PMNs was diminished in the presence of the H2O2 inactivator, catalase. The membrane-permeant H2O2, hydroxyl radical (HO.) scavenger 1,3-dimethyl-2 thiourea, and the HO. scavenger dimethyl sulfoxide but not the myeloperoxidase inhibitor sodium azide attenuated this BPAEC killing. Pretreatment of BPAEC with a 21-aminosteroid (U74500A), a potent iron chelator-antioxidant, provided the most effective protection against BPAEC killing induced by leukotoxin-stimulated PMNs. These data were compatible with the concept that the H2O2 generated by leukotoxin-stimulated PMNs interacts with intracellular iron in the endothelial cell to form highly reactive HO.. We suggest that HO. may be a key factor in BPAEC killing. Furthermore, since the elastase-specific inhibitor N-methoxy-succinyl-Ala-Ala-Pro-Val-chloromethyl ketone (CMK) also attenuated BPAEC killing and both CMK and 1,3-dimethyl-2 thiourea functioned additively in protecting against BPAEC killing, we conclude that both HO. and elastase may jointly contribute to BPAEC killing induced by leukotoxin-stimulated PMNs. This study broadens our understanding of how leukotoxin-stimulated PMNs injure lung endothelial cells and provides new insight into the pathogenesis of bovine pneumonic pasteurellosis.

Effects of Pasteurella haemolytica A1 leukotoxin on bovine neutrophils: degranulation and generation of oxygen-derived free radicals.

To further define the role of Pasteurella haemolytica A1 leukotoxin in the pathogenesis of bovine pneumonic pasteurellosis, its in vitro effects on bovine neutrophils were investigated. Leukotoxin-containing culture supernatant, from P. haemolytica, stimulated a neutrophil respiratory burst as measured by the generation of oxygen-derived free radicals O2- and H2O2. This effect was immediate because preincubation of neutrophils with the culture supernatant for 5 min or longer substantially suppressed this respiratory burst. This suppression was due to cytolysis of the neutrophils. Prolonged incubation of neutrophils with the same culture supernatant caused further cytolysis and degranulation. Heat-inactivated P. haemolytica culture supernatant that had lost its cytotoxic properties failed to stimulate respiratory burst by neutrophils. Furthermore, the respiratory burst, cytolysis and degranulation were abrogated only by leukotoxin-neutralizing monoclonal and polyclonal antibodies, but not by antibodies against the lipopolysaccharide. These studies show that the leukotoxin component in the culture supernatant was responsible for the generation of oxygen-derived free radicals and proteolytic enzymes from neutrophils which may participate in direct lung injury.

Pasteurella haemolytica A1 and bovine respiratory disease: pathogenesis.

The severe fibrinonecrotic pneumonia associated with pneumonic pasteurellosis usually results from colonization of the lower respiratory tract by Pasteurella haemolytica biotype A, serotype 1(A1). Despite recent research efforts, the authors lack a detailed understanding of the interactions and host response to P. haemolytica in the respiratory tract. The authors hypothesize that management and environmental stress factors or viral infection alters the upper respiratory tract (URT) epithelium allowing P. haemolytica to colonize the epithelium. Once the URT is colonized, large numbers of organisms enter the lung where they interact with alveolar macrophages. Endotoxin, released from the bacteria, crosses the alveolar wall where it activates pulmonary intravascular macrophages, endothelium, neutrophils, lymphocytes, platelets, complement, and Hageman factor leading to complex interactions of cells and mediators. It is the progression of this inflammatory response with neutrophil influx that is ultimately responsible for the pulmonary injury. Leukotoxin is a major virulence factor of P. haemolytica that allows it to survive by destroying phagocytic cells. At subcytolytic concentrations it may also enhance the inflammatory response by activating cells to produce mediators and release reactive oxygen metabolites and proteases.

Alterations in pulmonary morphology and peripheral coagulation profiles caused by intratracheal inoculation of live and ultraviolet light-killed Pasteurella haemolytica A1 in calves.

Eighteen male Holstein calves were divided into groups of three and inoculated intratracheally with 5 x 10(9) logarithmic phase or ultraviolet light-killed Pasteurella haemolytica biotype A serotype 1. Serial coagulation profiles were done on one calf from each group during the first 24 hours after inoculation. One calf from each group was necropsied at 4, 12, and 24 hours after inoculation and lesions were characterized with light and transmission electron microscopy. We found that 1) the pulmonary intravascular macrophage may have an important role in the early intravascular inflammatory events; 2) there was morphologic evidence for local initiation of the coagulation cascade in the lung early in the disease process but it was not a consumptive process; and 3) killed-bacteria were capable of causing fibrin exudation, platelet aggregation and alveolar epithelial damage similar to live bacteria, but the degenerative changes in neutrophils, endothelial cells and intravascular fibrin formation that occur with live bacteria were not seen.

Altered expression of transforming growth factor-alpha in hereditary rat renal cell carcinoma.

A hereditary form of renal cell carcinoma exists in rats that results from a single gene mutation and is histologically similar to that described in humans. Cell lines derived from these rat tumors were shown to express abundant transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF)-receptor RNA transcripts, but no EGF mRNA. In contrast, normal kidney expressed EGF and EGF-receptor transcripts, but TGF-alpha transcripts were barely detectable. Other kidney epithelial cell lines examined (NRK 52E, MDCK, and LLCPK) were negative for expression of both TGF-alpha and EGF transcripts, but expressed EGF receptors. In addition, the renal cell carcinoma-derived lines secreted TGF-alpha into the media. Immunohistochemistry of normal kidney with a TGF-alpha specific antibody revealed a characteristic pattern of staining of collecting ducts and, to a lesser degree, proximal tubules. In the neoplastic kidney tissue, both the cystic and solid portions of the tumors displayed intense immunoreactivity, indicating that altered expression of this growth factor by the transformed cells occurred in situ. These results suggest that altered TGF-alpha expression is an important aspect of the neoplastic phenotype in rodent as well as human renal cell carcinoma, and support the use of this hereditary rodent tumor model for studying the pathogenesis of this disease.

Changes in blood and bronchoalveolar lavage fluid components in calves with experimentally induced pneumonic pasteurellosis.

Pneumonic pasteurellosis was experimentally induced in calves by inoculation of 5 x 10(8) Pasteurella haemolytica organisms into the right diaphragmatic lung lobe. Blood and bronchoalveolar lavage fluid samples were obtained prior to inoculation and at postinoculation hour (PIH) 2, 4, and 6. Calves developed acute lung injury, characteristic of pneumonic pasteurellosis. Lesions were found only in the right diaphragmatic lobe. By PIH 4, significant (P less than 0.01) increases were detected in lavage fluid total cell count, neutrophil count, total protein and albumin concentrations, and alkaline phosphatase (ALP) and lactic dehydrogenase (LD) activities. Myeloperoxidase and elastase activities did not increase. Neutrophil depletion ameliorated the lung lesions and prevented the increase in lavage fluid cell count, total protein, and albumin concentrations and ALP and LD activities. Treatment with the iron chelator, deferoxamine mesylatehydroxyethyl starch, attenuated the increase in total protein and albumin concentrations and ALP and LD activities at PID 4, but not PIH 6. Treatment with a neutrophil function inhibitor, pentoxifylline, prevented the increase in lavage fluid neutrophil numbers, but accentuated the increase in total protein and albumin concentrations, and ALP, LD, myeloperoxidase, and elastase activities.

Morphological and morphometrical analysis of the acute response of the bovine alveolar wall to Pasteurella haemolytica A1-derived endotoxin and leucotoxin.

Endotoxin or leucotoxin derived from Pasteurella haemolytica biotype A serotype 1 or saline was deposited by fibreoptic bronchoscopy into the caudal segment of the right anterior lung lobe of calves, and the lesions were characterized by light and transmission electron microscopy. Morphometric techniques were used to determine if changes in the arithmetic mean thickness of the alveolar wall occurred. Group 1 calves (n = 2) were inoculated with 6 ml saline, groups 2 calves (n = 3) received 6 ml of a partially purified leucotoxin preparation, group 3 calves (n = 3) received 96 micrograms of endotoxin in 6 ml of saline and group 4 calves (n = 3) received 2.5 mg of endotoxin in 6 ml of saline. Calves were killed 4 h after inoculation. Lesions in groups 2, 3 and 4 were similar and we found that (a) endotoxin alone is capable of initiating an inflammatory response in the bovine lung, (b) leucotoxin causes cytotoxic changes in alveolar macrophages but not in parenchymal cells of the lung, (c) neutrophil sequestration and platelet aggregation occur in alveolar capillaries in association with pulmonary intravascular macrophages, (d) neutrophils and fibrin were found in the alveolus in close association with alveolar macrophages, (e) disruption of the alveolar epithelial layer occurred in association with neutrophils and (f) there were no significant increases in the arithmetic mean thickness of the alveolar wall.

Immunohistochemical localization of Pasteurella haemolytica A1-derived endotoxin, leukotoxin, and capsular polysaccharide in experimental bovine Pasteurella pneumonia.

Six, 5- to 10-week-old male Holstein calves were inoculated intratracheally with 5 x 10(9) logarithmic growth phase Pasteurella haemolytica biotype A serotype 1 (A1). Immunohistochemical techniques in conjunction with the use of monoclonal antibodies directed against P. haemolytica A1-derived lipopolysaccharide (LPS), capsular polysaccharide, and a polyclonal rabbit anti-leukotoxin antibody were used to localize their respective antigens in tissue sections of pneumonic lung at the light and electron microscopic levels. We found the following: 1) LPS, capsular polysaccharide, and leukotoxin were released into the inflammatory exudate; 2) LPS was found within the cytoplasm of neutrophils (located in the alveolus and alveolar wall), alveolar macrophages, endothelial cells, pulmonary intravascular macrophages, and on epithelial cell surfaces; 3) capsular polysaccharide was found in the alveolus and alveolar macrophages but not in cells of the alveolar wall; and 4) leukotoxin was associated with cell membranes of degenerating inflammatory cells located in the alveolus. This is the first study that demonstrates the presence of leukotoxin in the pulmonary inflammatory lesions caused by P. haemolytica A1 and implicates endotoxin as an important factor in the genesis of the pulmonary lesions.

Ultrasonographic appearance of primary and metastatic canine hepatic tumors. A review of 48 cases.

Forty-eight cases of dogs with primary and metastatic hepatic neoplasia were reviewed to determine if a predictable relationship between sonographic appearance and neoplastic cell type could be found. A focal mass was almost always a hepatocellular carcinoma (14 of 15) and 71% of these were hyperechoic. Focal or multifocal hyperechoic masses were most likely to be carcinomas (14 of 15). Focal or multifocal mixed neoplasms were most likely to be carcinomas (6 of 7). Two distinct patterns of lymphosarcoma were found: diffuse, mildly hyperechoic (6/11) and multifocal, hypoechoic (5/11). No neoplastic cell-type predictions could be made for focal or multifocal hypoechoic lesions. Diffuse fine or coarse patterns with minimal architectural distortions could be mistaken for normal or degenerative processes. However, in the presence of increased serum liver enzyme values, these subtle sonographic changes would warrant a liver biopsy to differentiate neoplastic infiltrate from non-neoplastic infiltrative and degenerative processes.

Production and partial characterization of monoclonal antibodies to Pasteurella haemolytica A1 capsular polysaccharide and lipopolysaccharide.

Hybridoma-derived monoclonal antibodies (MAB) against the cell surface antigens of Pasteurella haemolytica serotype 1 were obtained by the fusion of murine myeloma cells (P3 X 63 - Ag 8.653) with splenocytes of BALB/c mice immunized with crude logarithmic growth-phase culture supernatant. Initial screening was performed, using an ELISA, with the same bacterial growth culture supernatant as coating antigens. Further selection was done, using a panel of purified antigens--either capsular polysaccharide or lipopolysaccharide--as the coating antigen in an ELISA, and then performing a leukotoxin-neutralization assay. Two MAB, designated IIB-6 and H-2, reacted specifically with the capsular polysaccharide and the other 3, designated IVG-3, IH-3, and IIC-2, reacted with the lipopolysaccharide. One MAB, designated IH-6, did not react with leukotoxin, capsular polysaccharide, or lipopolysaccharide. The MAB to the capsular polysaccharide (IIB-6 and H-2) were characterized further; both antibodies belonged to the IgM class and were agglutinating. In addition, they promoted neutrophil-mediated opsonophagocytosis and complement-mediated immune bacteriolysis of P haemolytica serotype 1. Results from 3 studies indicated that the MAB IIB-6 and H-2 were specific only to the capsular polysaccharide of serotype 1 of P haemolytica. The MAB to the lipopolysaccharide (IVG-3, IH-3, and IIC-2) were of the IgG1, IgG3, and IgM classes, respectively and were not characterized further. The availability of a MAB identifying a serotype-specific, surface-exposed determinant on the capsule of P haemolytica serotype 1 should facilitate and expand studies concerning the role of the capsular material and lipopolysaccharide in the pathogenicity of P haemolytica infection in cattle.