Effect of a novel multipurpose contact lens solution on human corneal epithelial barrier function.

PURPOSE: To explore the effect of a novel multipurpose contact lens solution (MPS) on the junction protein distribution and barrier function of cultured human corneal epithelial cell monolayers. METHODS: Cultured human corneal epithelial cells (HCEpiC) were exposed to a novel MPS (MPS A; Biotrue™ multi-purpose solution, Bausch & Lomb Incorporated) at 50%, 75% and 100% for 10 or 30 min. Four commercially available MPS products, MPS B (AQuify, Ciba Vision), MPS C (COMPLETE MPS Easy Rub, AMO), MPS D (OPTI-FREE Express, Alcon) and MPS E (OPTI-FREE RepleniSH, Alcon) were tested in parallel. Tight junction structure and integrity were evaluated by confocal microscopy using ZO-1 antibody and scanning microscopy (SEM). Quantitative evaluation of MPSs on epithelial barrier function was determined by measuring transepithelial electrical resistance (TEER) across HCEpiC grown on Transwell Clear permeable supports and on electric cell-substrate impedance sensing (ECIS) electrode arrays. RESULTS: Overall after exposure to the three concentrations (50%, 75%, and 100%) of MPS A, ZO-1 distribution and fluorescent intensity on the cell surface appeared similar to the media control with continuous tight junctions and clear intercellular junctions. At all measured time points after exposure to MPS A (50% or 75%) there was also no effect on the TEER using both resistance methodologies, and SEM showed that MPS A appeared similar to the Hank's balanced salt solution (HBSS) control. In cells exposed to MPS D there was a dose-dependent change in the distribution of ZO-1, some cell detachment, and a decrease in monolayer resistance at all time points measured. Ultrastructurally, MPS D caused gross changes, including damage to cell junctions and plasma membranes. To a lesser extent, the remaining three commercial MPS products demonstrated some effects on tight junction ZO-1 distribution and/or TEER. CONCLUSIONS: Based on the in vitro measurements of tight junction protein expression, monolayer integrity, and transepithelial electrical resistance, the novel multipurpose contact lens solution (MPS A) did not alter corneal barrier function as compared to media, PBS or HBSS control. Clinical significance of the observed differences in epithelial barrier function among the MPSs tested needs further investigation.

Effect of gender, dose, and time on 3-(3,5-dichlorophenyl)-2,4-thiazolidinedione (DCPT)-induced hepatotoxicity in Fischer 344 rats.

1. The thiazolidinedione ring present in drugs available for type II diabetes can contribute to hepatic injury. Another thiazolidinedione ring-containing compound, 3-(3,5-dichlorophenyl)-2,4-thiazoli-dinedione (DCPT), produces liver damage in rats. Accordingly, the effects of gender, dose, and time on DCPT hepatotoxicity were therefore evaluated. 2. Male rats were more sensitive to DCPT (0.4-1.0 mmol kg(-1) by intraperitoneal administration) as shown by increased serum alanine aminotransferase levels and altered hepatic morphology 24 h post-dosing. Effects in both genders were dose dependent. In males, DCPT (0.6 mmol kg(-1)) produced elevations in alanine aminotransferases and changes in liver sections 3 h after dosing that progressively worsened up to 12 h. DCPT-induced renal effects were mild. 3. It is concluded that male rats are more susceptible to DCPT hepatotoxicity and that damage occurs rapidly. DCPT primarily affects the liver and can be a useful compound to investigate the role of the thiazolidinedione ring in hepatic injury. However, the gender dependency and rapid onset of DCPT hepatotoxicity require further investigation.

Physical characterization of thin semi-porous poly(L-lactic acid)/poly(ethylene glycol) membranes for tissue engineering.

This study examines physical properties of solvent-cast poly(L-lactic acid) (PLLA): poly(ethylene glycol) PEG membranes as a function of PEG molecular weight (MW) and incubation in vitro for 6 weeks. PEGs of MW 400, 1450 and 8000 were used. The morphological, thermal, mechanical and permeability properties of the membranes were studied prior to and after 3 and 6 weeks of incubation in phosphate-buffered saline (PBS) at 37 degrees C. The membranes showed a thickness of about 35+/-5 microm and were found to be semi-porous, with a non-porous surface as well as a porous surface with pore-diameters of 0.5-5 microm. The surface pore size was found to be a function of PEG MW used. All membranes were mechanically strong, with elastic moduli and tensile strength of 150-440 MPa and 7-36 MPa, respectively, all through the 6-week incubation period. The lower-MW PEGs plasticized PLLA based on high initial percent elongation; however, the effect was lost after 3 weeks of incubation in PBS. All membranes except those fabricated with PEG 8000 were impermeable for up to 6 weeks of incubation in PBS. Permeability studies showed that only PLLA:PEG 8000 membranes were permeable to methylene blue after 3 weeks of degradation.

Stressed polystyrene causes increased membrane sensitivity of adherent cells to fluid shear force: technical note.

Adherent cells transduce signals from the extracellular matrix, which result in changes to various cell functions, including cell spreading and morphology. However, changes to mechanical properties of cell membranes due to adherence to a substratum have not been studied. Adherent Nara Bladder Tumour (NBT) II cells on polystyrene (PS) discs made from pure, atactic polystyrene react differently between the peripheral 1mm zone and centre of the disc. After application of a fluid shear force, cells on the peripheral zone resulted in 91.1-/+0.8% cell death due to instantaneous rupture of apical cell membrane, as determined by the Live/Dead cell assay, whereas cells on the disc's centre and surrounding glass surface showed 7.1-/+5.7% and 4.3-/+1.7% cell death, respectively. Under cross-polarized light, the edge of the PS disc showed a low degree of birefringence whereas the centre of the disc did not. We also detached the PS disc and applied various weights (0.0 g to 40 g) to the disc at 100 degrees C for 2 hours and then cooled rapidly at 4 degrees C. We found that birefringence developed with stress to PS. NBT II cells grown on stressed PS showed an average of 55.8-/+14.1% cell death after a fluid shear force while cells on the glass surfaces resulted in only 5.0-/+2.7% cell death. Interestingly, increased birefringence is associated with increased lipophilicity on stressed PS, as determined by Nile Red staining. We propose that NBT II cell interaction with certain molecular characteristics of stressed PS results in altered cell membrane sensitivity to mechanical forces.

Effect of processing methods and heat treatment on the formation of wax matrix tablets for sustained drug release.

The objective of this study was to evaluate the effects of processing methods and heat treatment on matrix formation and subsequent drug release from wax matrix tablets for controlled release. Phenylpropanolamine hydrochloride (PPA) and Compritol were processed with appropriate diluent(s) using either dry blending (DB), wet granulation (WG), partial melt granulation (PMG), or melt granulation (MG). Then the tablets were heat-treated at 80 degrees C. Particle size distribution and compressibility, along with drug release, tablet micro-morphology, wettability, porosity, and tortuosity were investigated. The drug release was different for the four processing methods even though the tablet formulation was identical. Heat treatment further retarded drug release and its effect was related to the previous manufacturing processes. Scanning Electron Microscopy (SEM) showed that heat treatment redistributed the wax and formed a film-like structure covering drug and excipients. The contact angle of tablets made from DB, WG, and PMG methods increased after heat treatment, while that of tablets made from MG remained constant. Tablet tortuosity calculated from drug release rate constants increased dramatically after heat treatment. Drug release from the wax tablets with or without heat treatment was best described by the Higuchi equation. Different processing methods produced different matrix structures that resulted in different drug release rates. Heat treatment retarded drug release mainly by increasing tortuosity of the matrix. Contact angle measurement and SEM analysis indicated that heat treatment caused the wax to melt, redistribute, coat the drug and diluents, and form a network structure.

Maturational changes in CYP2D16 expression and xenobiotic metabolism in adrenal glands from male and female guinea pigs.

CYP2D16 is expressed at high levels in the zona reticularis (ZR) of guinea pig adrenal glands and contributes to adrenal metabolism of xenobiotics. Studies were done to evaluate the effects of age and gender on adrenal CYP2D16 expression and xenobiotic metabolism. In both male and female guinea pigs at 1, 7, 14, or 30 weeks of age, in situ hybridization and immunohistochemistry confirmed that CYP2D16 was highly localized to the ZR of the adrenal gland. The steroidogenic P450 isozyme, CYP17, by contrast, was expressed in both the zona fasciculata and ZR. The intensity of CYP2D16 staining was not age- or gender-dependent. However, the proportion of each adrenal gland comprised by ZR and thus expressing CYP2D16 increased with aging in both sexes and was greater in males than in females. The rates of metabolism of bufuralol, a CYP2D-selective substrate, by adrenal microsomal preparations generally correlated with the amount of ZR (and CYP2D16) in the gland. Thus, adrenal xenobiotic-metabolizing activities were greater in males than in females at all ages and increased with aging in males. However, the rates of bufuralol metabolism declined in sexually mature females (14 weeks) from the levels found in prepubertal females (7 weeks) and then increased markedly in retired breeders (30 weeks), suggesting an inhibitory effect of estrogens on enzyme activity. The results indicate that the age and gender differences in adrenal CYP2D16 content are largely determined by differences in the size of the ZR rather than the concentrations of CYP2D16 within cells of the ZR. However, adrenal xenobiotic-metabolizing activities in females seem to be further modulated by an inhibitory effect of estrogens.

Effect of antioxidants on para-aminophenol-induced toxicity in LLC-PK1 cells.

The present studies were designed to investigate the susceptibility of LLC-PK1 cells to cytotoxicity induced by para-aminophenol (PAP) and the ability of antioxidants to prevent PAP-induced cytotoxicity. LLC-PK1 cells were incubated for 4 h with varying concentrations of PAP (0-0.2 mM). Incubation was continued for 20 h and viability was monitored at 24 h after initial exposure to PAP. For coincubation experiments, cells were incubated for 4 h with various antioxidants [including ascorbate, glutathione (GSH), butylated hydroxytoluene (BHT), beta-nicotinamide adenine dinucleotide (NADH), or beta-nicotinamide adenine dinucleotide phosphate (NADPH)] in the absence or presence of 0.1 mM PAP. For preincubation experiments, cells were incubated for 1 h with ascorbate, GSH or NADPH. Antioxidants were removed and cells were exposed to 0 or 0.1 mM PAP for 4 h. Viability was determined 24 h following PAP exposure. LLC-PK1 cells displayed a steep concentration-response relationship for PAP; 0.1 mM PAP caused approximately 50% loss of viability. Coincubation with ascorbate, GSH and NADPH was without effect on cell viability in the absence of PAP and attenuated PAP-induced losses in viability. In contrast, NADH was ineffective in preventing PAP-induced cytotoxicity. BHT alone produced a significant loss of cell viability and was ineffective in preventing PAP cytotoxicity. Inability of NADH to prevent PAP-induced cytotoxicity was related to rapid degradation of NADH in aqueous solution. Preincubation of cells with ascorbate or GSH but not NADPH was associated with attenuation of PAP-induced cytotoxicity. These data suggest that (1) PAP is cytotoxic to LLC-PK1 cells, (2) a portion of PAP cytotoxicity is due to nonenzymatic oxidation that occurs in the incubation medium, and (3) a portion of PAP cytotoxicity is due to enzymatic or nonenzymatic oxidation that occurs within cells.

Effects of ACTH administration on zonation of the guinea pig adrenal cortex.

Experiments were done to determine the actions of ACTH on the morphologic and functional characteristics of the zona fasciculata (ZF) and zona reticularis (ZR) in the guinea pig adrenal cortex. In control guinea pigs, a number of morphologic differences distinguished the ZF from the ZR, including the presence of far more lipid in the ZF than in the ZR. Treatment with ACTH decreased the lipid droplet content of the ZF cells, equalizing the amount of lipid in the two zones. Other morphologic differences between the ZF and ZR were also diminished by ACTH treatment. Immunohistochemical analyses indicated that CYP17 protein was found in both the ZF and ZR in control animals, but with greater immunostaining intensity in the ZF. The enzyme protein distribution corresponded with higher 17alpha-hydroxylase activity in the ZF than in the ZR. After ACTH treatment, the intensity of staining and enzyme activities in the two zones were similar, attributable largely to increases in the ZR. In situ hybridization-and immunohistochemistry showed that in control animals CYPD216 was highly expressed in the ZR but not in the ZF. ACTH treatment dramatically reduced the intensity of CYP2D16 mRNA and protein staining in the ZR. Bufuralol 1'-hydroxylase activity, a marker for CYP2D subfamily members, was also decreased significantly in the ZR by ACTH treatment. The data indicate that administration of ACTH to guinea pigs has opposite effects on the expression of CYP17 and CYP2D16 in the ZR, and diminishes or eliminates some of the structural and functional differences between the ZF and ZR. The results suggest a role for ACTH in establishing and maintaining adrenocortical zonation.

The effect of aromatic fluorine substitution on the nephrotoxicity and metabolism of N-(3,5-dichlorophenyl)succinimide in Fischer 344 rats.

N-(3,5-Difluorophenyl)succinimide (DFPS) is a non-toxic analogue of the nephrotoxic fungicide N-(3,5-dichlorophenyl)succinimide (NDPS). Although NDPS must be metabolized to produce renal damage, the metabolic fate of DFPS is unknown. These studies were therefore designed to examine the nephrotoxic potential of putative DFPS metabolites and to determine if DFPS is metabolized differently from NDPS. Male Fischer-344 rats were administered (1.0 mmol/kg. i.p. in corn oil) DFPS, N-(3,5-difluorophenyl)succinamic acid (DFPSA), N-(3,5-difluorophenyl)-2-hydroxysuccinimide (DFHS), N-(3,5-difluorophenyl)-2- or -3-hydroxysuccinamic acids (2- and 3-DFHSA, respectively), N-(3,5-difluoro-4-hydroxyphenyl)succinimide (DFHPS). N-(3,5-difluoro-4-hydroxyphenyl) succinamic acid (DFHPSA) or corn oil only (1.2 ml/kg). Although some of the compounds produced changes in renal function and histology, these alterations were not indicative of irreversible kidney damage. DFPSA, 2-DFHSA, 3-DFHSA and DFHPSA were detected in the urine of rats 3 h after administration of 0.2 mmol/kg [14C]DFPS. The same metabolites were produced by isolated rat hepatocytes, but not by renal proximal tubule cells. Formation of the oxidative metabolites in vitro was prevented by the cytochrome P450 inhibitor 1-aminobenzotriazole. It appears that DFPS undergoes hepatic biotransformation similar to NDPS and that some of its metabolites have reversible effects on renal proximal tubules.

Localization of CYP2D16 in the guinea pig adrenal cortex by immunohistochemistry and in situ hybridization.

Recent reports indicate that the cytochrome P450 isozyme, CYP2D16, is expressed at high levels in the inner regions of the guinea pig adrenal cortex and may contribute to xenobiotic and/or steroid metabolism in the gland. In the present studies, immunohistochemical and in situ hybridization techniques were employed to definitively establish the localization of CYP2D16 within the adrenal cortex. In male guinea pigs of various ages, CYP2D16 protein and mRNA were highly localized to the zona reticularis (ZR); none was detectable in the zona fasciculata (ZF), zona glomerulosa (ZG) or the medulla. In contrast, the steroidogenic P450 isozyme, CYP17, was distributed throughout the ZF and ZR. From the earliest stages of development of the ZR, CYP2D16 staining was intense. As guinea pigs aged, the ZR progressively enlarged and comprised a proportionately greater amount of the cortex. At all ages, CYP2D16 was uniformly distributed throughout only the ZR. Coinciding with the age-related growth of the ZR and increase in adrenal CYP2D16 content was an increase in adrenal xenobiotic-metabolizing activity. The results establish that CYP2D16 has an intraadrenal localization that is unique among P450 isozymes, suggesting novel regulatory mechanisms and indicating that CYP2D16 may serve as a specific marker for ZR cells. The increase in CYP2D16 expression with age probably accounts for increasing levels of xenobiotic metabolism and may also contribute to an increase in intraadrenal cortisol degradation in older animals.

Nephrotoxic potential of N-(3,5-dichlorophenyl)glutarimide and N-(3,5-dichlorophenyl)glutaramic acid in Fischer 344 rats.

The agricultural fungicide N-(3,5-dichlorophenyl)succinimide (NDPS) produces kidney damage in rats. Although many NDPS analogues have been screened as possible nephrotoxicants, the one-carbon homologue, N-(3,5-dichlorophenyl)glutarimide (NDPG), has not been evaluated. This study examined the nephrotoxic potential of NDPG and a putative metabolite, N-(3,5-dichlorophenyl)glutaramic acid (NDPGA). Male Fischer 344 rats (N = 3-4 per group) were administered a single i.p. injection in corn oil of NDPG or NDPGA (0.4 or 1.0 mmol/kg), NDPS (0.4 mmol/kg), or corn oil alone. Renal function was monitored for 48 h. In contrast to NDPS, NDPG and NDPGA did not significantly alter renal function or kidney morphology when compared to corn oil-treated controls. These experiments show that replacement of the succinimide ring in NDPS with a glutarimide ring abolishes toxicity.

Regulation of motility and cytoskeletal organization of rat bladder carcinoma cells by cyclic AMP.

Cyclic AMP (cAMP) has been implicated in the regulation of movement of certain cultured cell types. We have studied the effects of cAMP on epithelial cell motility using serum-free NBT-II cells, derived from a rat bladder carcinoma. The random movement of these cells on type I collagen was reduced upon elevation of intracellular cAMP by several means and this effect was reversible. Alterations in the organization of the cytoskeletal proteins F-actin and alpha-actinin occurred concurrently with the reduction in motility, and the arrangement of these proteins resembled that seen in non-motile cells on glass. In addition, pretreatment of cells with KT5720, a cAMP-dependent protein kinase (PKA)-specific inhibitor, prevented the dibutyryl cAMP-induced reduction in cell movement as well as the associated cytoskeletal changes. These results suggest that elevation of PKA is responsible for the observed effects on cell motility and cytoskeletal reorganization and demonstrate a role for PKA in the regulation of cell motility in this system.

Epithelial cell interaction in air-liquid interface culture.

A novel culture method has been developed to study the interaction of epithelial cells in the absence of a solid substratum. Starting with either a single cell suspension or aggregates, cells were floated at the interface of air and liquid culture medium. Two epithelial cell lines have been studied in this system: Madin-Darby canine kidney cells (MDCK), and a rat bladder tumor cell line (NBT-II). Starting with a single cell suspension of MDCK, the floating cells coalesced in 24 h into sheets of cells. The cells were morphologically polarized with the apical surface facing the liquid medium. Domes were observed regularly in these sheets of cells. NBT-II cells migrated actively from aggregates at the air-liquid interface. In this floating culture, NBT-II cells produced extensive cell processes similar to those seen in cells grown on a solid surface. Because cells at the air-liquid interface lack a solid substratum for adhesion, cell membrane processes such as lamellapodia, retraction fibers, pseudopods, and long, intercellular connections can only exert a tension equal to or less than the surface tension of the liquid. Dimethyl sulfoxide 2% stimulated desmosome formation in floating NBT-II cells, resulting in a cribriform pattern in the sheet of cells. This method of interface can lead to new understanding of morphogenesis of epithelial cells, and the mechanism of cell motility and formation of cell processess.

Interactions between newly formed endothelial channels and carcinoma cells in plasma clot culture.

Bovine capillary endothelial cells (BCEC), cultured in suspension on a rotary shaker, formed aggregates ranging from 50 to 300 micron in diameter. In plasma clot these aggregates sprouted in multiple directions and gave rise to vascular channels. Aggregates of the squamous cell carcinoma line of rat bladder NBT-II-81, cultured in plasma clot, formed solid spheroids that grew slowly by expansion. When cultured together with BCEC, however, NBT-II-81 infiltrated the plasma clot extensively. The tumor cells, after establishing contacts with the vascular channels, spread into the fibrin meshwork using the subendothelial space as their path of propagation. Endothelial cells that were separated from the surrounding matrix by invading tumor cells degenerated, leaving behind channels lined only by neoplastic epithelium. The adhesive properties of the subendothelial matrix were studied by seeding NBT-II-81 cells on dishes coated with the extracellular matrix produced by BCEC. Tumor cells attached readily and in large numbers to dishes coated with the subendothelial matrix. In contrast they attached poorly to dishes coated with fibrin. We conclude that the spread of carcinoma cells into plasma clot is markedly enhanced by endothelial channels, developed in the absence of blood flow. The production of a highly adhesive extracellular matrix by the capillary endothelium during angiogenesis may represent an important element in the preferential growth of the tumor along the vascular route.

Radial gradient culture on the inner surface of collagen tubes: organoid growth of normal rat bladder and rat bladder cancer cell line NBT-II.

Radial histophysiologic gradient culture uses thin walled, permeable collagen tubes to house inocula in the form of either tissue explants, aggregates of cells, or dissociated cells. The outgrowth from these inocula spreads on the inner surface of the cylindrical tube, completely lining the lumen. Metabolites are exchanged through the wall of the collagen tube by diffusion from the pool of medium surrounding the cylinder. Urothelial cells form organoid stratified epithelium. A histophysiologic gradient occurs with the basal surface of the epithelium attached to the collagen wall. At this interface, for normal bladder, the initiation of epithelial renewal is seen in the basal zone, as shown by incorporation of tritiated thymidine. The simulation of conditions in nature is attained by the exchange of metabolites between the pool of medium and the basal zone of the epithelium. NBT-II appears as two concentric stratified epithelia. Isotopic labelling is seen throughout the epithelium attached to the collagen membrane. In the superficial stratified epithelium remnants of nuclei are seen without isotopic labelling. Preparation of living cultures and, after fixation, of histologic sections is technically easy.

The chick embryo in toxicology: an alternative to the rabbit eye.

The chorioallantoic membrane (CAM) of the chick embryo is readily accessible for experimentation. It is a complete tissue that responds to injury with classical inflammatory reactions. It is limited to the late phase of embryologic life, and is without the sense of pain. Focal topical application of various household products onto the CAM results in local injury and reactions that differ in severity from one product to another. For any single product, tested as a sequence of dilutions on a series of membranes, the CAM responds with decreasing intensity that parallels the decreasing dosage. The membrane is prepared for study according to the method of Zwilling (Transplantn Bull 1959, 6, 115). The test material is applied in a Teflon ring to the 14-day-old CAM, to localize the application site. The macroscopic response is scored on day 17 of incubation. The results of analysis of histological preparations are found to correlate with macroscopic appearance. When a series of preparations was ranked according to the severity of the response each induced on the CAM, there was a good correlation with the ranking of the same preparations in the Draize test.

Migration inhibition of an epithelial cell line by s-Con A and the effect on its invasiveness.

In an attempt to delineate the role of tumor-cell motility in the process of invasion, we compared the migration of NBT II in a two-dimensional migration assay with its migration in a three-dimensional invasion assay. Both systems were maintained with and without succinylated concanavalin A (s-Con A) dissolved in the culture medium. This lectin has a reversible inhibitory effect on the migration of cells in vitro. The migration of NBT-II aggregates, seeded in flasks containing 200 micrograms/ml s-Con A or without s-Con A, was studied by time-lapse photomicrography. In the presence of s-Con A, migration was immediately stopped. When the treated medium was replaced by culture medium to which 10 mM alpha-methyl-mannose was added, the inhibition of migration was abolished. The invasive capacity of NBT II in the presence or absence of s-Con A was studied by confronting precultured fragments of 9- to 11-day-old embryonic chick heart (0.4 mm in diameter) with NBT-II aggregates (0.2 mm) made in the presence or absence of s-Con A. Light microscopy showed no difference in the extent of invasion. To demonstrate the presence of s-Con A in the invading tumor cells, immunoperoxidase staining for Con A was done. The treated cultures stained positively while the controls were negative. The data presented here question the correlation between tumor-cell motility in two-dimensional system and the invasive behavior of these cells in three dimensions, and implies that the ability or inability of cells to migrate on plastic does not necessarily reflect their invasiveness in vitro.

Organoid structure of normal rat bladder in unilaminar and bilaminar histophysiologic gradient culture : methods and observations.

In lining epithelium of mammals certain recurrent architectural patterns are recognized that may be critical for epithelial organization in culture. Among these structural imperatives are three dimensional growth, restricted migration of cells, histophysiologic gradients, and continuity of epithelial membranes. Histophysiologic gradient culture procedures have been developed to comply with requirements suggested by normal tissue architecture. In a small chamber, 5 mm diam, epithelium grows attached to a thin permeable transparent collagen membrane or sandwiched between two apposed collagen membranes. The chamber is held in a plastic capsule so that metabolic exchange is limited to substances that diffuse across the collagen membranes to the adherent basal layer of epithelium. On a single membrane after 2 wk of growth, normal urothelium appears as a diffusely hypercellular urothelium, 6 to 10 cells thick. As the culture period is extended by 2 or more wk, multiple nodules of urothelium extend from the basal surface into the subepithelial space between the epithelium and the collagen membrane. Normal bladder, cultured between two apposed collagen membranes, gives rise in a few days to confluent epithelium that contains many extracellular cysts. Through an apparent merging of cysts, after 2 wk the urothelium appears as a highly organoid structure, a flattened cyst lined by completely stratified polarized urothelium. Such microbladders consist of a stratified epithelium without interruption of continuity. With histophysiologic gradient culture, processes in carcinoma and precursor lesions are accessible to study at the level of tissue organization.

Comparison of invasiveness and non-invasiveness of two epithelial cell lines in vitro.

Two epithelial cell lines of urological origin have been compared for their invasiveness in an in vitro three-dimensional culture system, using embryonic chick cardiac muscle as host tissue. Cells from the Nara bladder tumor line (NBT-II), an invasive tumor in the rat, invaded and progressively occupied the cardiac muscle which degenerated. Cells from a dog kidney line (MDCK), which are of low tumorigenicity in nude mice, failed to invade into the cardiac muscle in vitro. MDCK cells formed a structurally polarized epithelium around the heart tissue. MDCK is the first established epithelial cell line that has been found to grow in this invasion assay culture system and yet did not invade the heart fragment.

The propagation of cancer, a process of tissue remodeling. Studies in histophysiologic gradient culture.

Effective study of the malignant phenotype at the tissue level requires model systems that are intelligible both to cell biologists and to pathologists, and that also observe the spatial imperatives intrinsic to tissues in nature. Malignant cells commonly appear in multicellular units, and growth of tumor tissue is seen as an increase in the number of cells and multicellular units. The supporting stroma frequently has an abnormal appearance, and this component of the tissue also increases in mass as the tumor enlarges and spreads. The direction of invasion is influenced by the direction of available metabolites. Histophysiologic gradient culture complies with nature's spatial rationale, since at the substrate-parenchymal interface three functions coincide. These are anchorage, initiation of epithelial renewal, and complete exchange of metabolites. Our model system provides a setting for reconstructing and manipulating many features of the malignant phenotype seen in cancer tissues in nature, such as abnormalities in the sequence of maturation of stratified epithelium, hyperplasias, dysplasias, interaction between different types of epithelium, aggregate formation, tumor angiogenesis, and neoplastic blockade.