A quantitative study of lamina densa alterations in hamster cheek pouch carcinogenesis

Preliminary assessment of the epithelial nuclear-cytoplasmic ratio and nuclear volume density in human palatal lesions

We have analysed both the nuclear-cytoplasmic (N/C) ratio and nuclear volume densities (VVN) in defined strata from human hard palate lesions with and without malignant potential to determine the prognostic reliability and/or validity of this parameter. Measurements of cellular and nuclear areas of basal and spinous cells from normal (N) and pathological palatal epithelium were made on histological sections using an image analyser. The lesions comprised fibrous hyperplasia (FH), traumatic inflammation (INF), benign hyperkeratosis (HK), squamous cell papilloma (PP), dysplastic epithelium adjacent to invasive carcinoma (CE) and islands of invasive squamous cell carcinoma (CI). In basal cells, no significant differences were detected in comparisons of N/C and VVN between all pathological groups and the N control group. The mean value for CE was lower than that obtained for N. In spinous cells, the only statistically significant comparison was between IF and FH for both N/C and VVN. Both parameters were lower in CE than in N. Of all groups analysed except CI, the CE group is the only one likely to possess an increased malignant potential. The N/C ratio therefore seems to be of no value as a predictor of malignancy in palatal epithelial lesions.

Basement membrane and tumor invasion: ultrastructural observations in the basement membrane of rat bladder with invasive transitional cell carcinoma induced by N-butyl-N-(4-hydroxybutyl)nitrosamine

This study describes ultrastructural alterations in the basement membrane (BM) of rat bladder with invasive transitional cell carcinoma (TCC) induced by N-butyl-N-(4-hydroxybutyl)nitrosamine. Various alterations including thickening, degradation and neosynthesis were found in the bladder BM of one rat with invasive TCC. Focal destruction of both the BM lamina zones was found in addition to partially degraded BMs showing focal degradation and loss of only the BM lamina rara. Neosynthesis of complete BM including the lamina rara and lamina densa was observed surrounding the nests of carcinoma cells deep in the stroma, while neosynthesis of incomplete BM including only a lamina densa-like structure was also found around carcinoma cells which had just crossed the BM into the adjacent stroma from the original tumor masses. There was an increased hemidesmosomal frequency in some areas of thickened BM, and focal loss of hemidesmosome in the areas of degraded BM. It is suggested that BM degradation may take place in two steps, and that BM neosynthesis may also be a two-step process in invasive TCC of rat bladder.

Basement membrane and carcinogenesis: ultrastructural observations in the basement membrane of the bladder epithelium in rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)

This study investigated the structural alterations in the basement membrane (BM) of the bladder epithelium in rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) using transmission electron microscopy. Following administration of BBN, thickening of the BM of the bladder epithelium was observed and remained almost constant from 4 to 20 weeks, although the pathological changes in the rat bladder epithelium induced by BBN altered over the same period of 20 weeks. The reason for this phenomenon can be explained by the increased interfacial area between the basal epithelial cells and the BM of the rat bladder epithelium due to an increase in the number and size of the microvilli on the basal cell surfaces adjacent to the BM. Our results also showed that the frequency of hemidesmosomes increased progressively during the period of carcinogenesis, especially in the lesions of noninvasive transitional cell carcinoma (TCC) in the rat bladder. It is suggested that the neosynthesis of BM components can be carried out both by benign hyperplastic cells and by noninvasive TCC cells of rat bladder. The alterations in the BM thickness may be affected by the changes in the number and size of the microvilli occurring on the basal cell surfaces adjacent to the BM. Both an increased frequency of hemidesmosomes and the neosynthesis of BM are closely related to cell proliferation during carcinogenesis.

Differentiation of cyclophosphamide-treated hamster secondary palate: ultrastructural and biochemical observations

A study was undertaken to analyze the ultrastructural aspects and the enzyme acid phosphatase cytochemistry and biochemistry of the pathogenesis of cyclophosphamide (CP)-induced cleft palate in hamster fetuses. The initial CP-induced alterations were the appearance of lysosomes in the mesenchymal cells of the vertically developing palatal primordia within 8 hr of drug administration. The mesenchymal lysosomal activity, which increased during the next 16 hr, was abnormal and interpreted as a sub-lethal response to CP treatment. Subsequently, the lysosomal activity in the mesenchyme diminished gradually and, 48 hr after CP treatment, was absent. At this time, lysosomes were seen in the epithelial cells of the vertical palate. Fifty-six hours after CP treatment, unlike controls where palatal shelves were already fused, lysosomal activity subsided in the epithelial cells. Changes, however, continued to be seen at the epithelial-mesenchymal interface. These changes were characterized by discontinuity in the basal lamina, and by epithelial-mesenchymal contacts. They persisted for 8 hr but were absent thereafter. Sixty-four hours after CP administration, the vertical shelves became horizontal and remained so until term. Following analysis of data, both from the literature and from the present study, it was suggested that CP first affected mesenchymal cell proliferation, and then its cytodifferentiation, during the critical phase of early vertical development; consequently the reorientation of the shelves to a horizontal plane was delayed, inducing cleft palate.

What's new in the ultrastructure of tumor invasion in vivo?

An important point emerging from the literature on tumor invasion in vivo is the great variability of nearly all aspects studied. It seems that there is neither one particular morphologic change which renders a cell invasive, nor one particular mechanism by which a cell crosses the boundaries of its original tissue compartment to occupy another. Nevertheless, some general trends are demonstrable. The majority of invasive tumor cells appear to be characterized by prominent surface protrusions, decreased junctional contacts and, in the case of epithelium-derived tumor cells, an incomplete basement membrane. The fact that some tumors can invade foreign tissues without loosing their basement membrane is emphasized. Invasive cells frequently form organized associations with preexistent non-neoplastic cells without damaging them. Apparently, the eventual disappearance of the preexistent cells in most invaded tissues is not necessarily due to a direct action on the part of the tumor cells. It rather seems a secondary phenomenon caused by, e.g., the insertion of invasive tumor cells between the preexistent cells and their original stroma. Very often, this seems to be due to the affinity of malignant cells for basement membranes. In addition, the adhesion of tumor cells to basement membranes frequently seems to determine their pattern of spread through a tissue. A process which may turn out to be a key factor in tumor invasion is desmoplasia, the series of host reactions which creates a new environment for the tumor cells which may favor their survival, proliferation, and locomotion. With the rapid development of new techniques, electron microscopy will probably contribute to the elucidation of the exact nature, the degree of similarity to granulation tissue, and the influence on invasion of desmoplastic tumor stroma.

Gross and cellular analysis of 6-mercaptopurine-induced cleft palate in hamster

The present study analyzes the morphological, histochemical, and ultrastructural aspects of the pathogenesis of 6-mercaptopurine (6MP)-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that 6MP stunts the growth of vertical palatal shelves and thus induces cleft palate. Ultrastructural analysis showed that, in contrast to controls, 6MP-induced alterations were first seen in the mesenchymal cells 24 hr after drug administration. The initial alterations were characterized by swelling of the nuclear membrane. During the next 12 hr, lysosomes were seen first in the mesenchymal cells and then in the cells of the medial edge epithelium (MEE) of the developing palatal primordia. The appearance of lysosomes was temporally abnormal and was interpreted as a sublethal response to 6MP treatment. Subsequently, the nuclear alterations and the lysosomes diminished; and 48 hr after 6MP administration, they were absent from the palatal tissues. Ninety hours after 6MP administration, unlike the controls (in which the palatal shelves were already fused), changes were seen at the epithelial-mesenchymal interface in the developing cleft palatal shelves. These changes were characterized by breakdown of the basal lamina and epithelial-mesenchymal contacts. Eventually, at term, the MEE of the vertical shelf stratified. It was suggested that 6MP affected cytodifferentiation in the palatal tissues during the critical phase of early vertical shelf development and thereby induced cleft palate.

A quantitative ultrastructural study of alterations in the area of the basal cell-stromal interface during experimental oral carcinogenesis

Because of its topographical location, the basal cell in carcinomas must play a significant role in the invasion of adjacent tissues. We have analysed the proportion of the basal cell plasma membrane in direct contact with the adjacent lamina propria during in vivo oral carcinogenesis. Samples of hamster cheek-pouch mucosa treated with DMBA were assigned to hyperplasia, dysplasia and carcinoma groups using strictly defined histopathological criteria. Electron micrographs of basal cells were subjected to stereological intersection counting to provide estimates of the proportion of the total basal cell membrane in contact with the connective tissue (SSBM,PM). In untreated controls, a mean value of 9% was obtained, whereas, for DMBA-induced hyperplasias, dysplasias and carcinomas, values were 8%, 12% and 16% respectively. Statistically, SSBM,PM values were significantly elevated in dysplasias and carcinomas. The changes in this parameter may reflect an increased motility in the transforming basal cell prior to and concomitant with cellular invasion, and may prove to be of value as a structural indicator of malignant transformation.

Morphology of peritumoral proteoglycan alterations in the rabbit mesentery invaded by V2 carcinoma cells

After intraperitoneal implantation into Swiss Silver rabbits, V2 rabbit carcinoma cells invade the mesentery where they form nodules of different size and texture: compact (less than 120 microns in diameter), loose (120-250 microns) and mixed (above 200 microns). Together with tumor development, certain changes take place in the loose connective tissue of the mesentery. Application of TEM, together with use of safranin O, has shown that, in areas free of tumor growth, collagen bundles become thick and heavy and proteoglycan density is increased. Concurrently, the number of fibrocytes, now transformed to fibroblasts, increases. Small, compact nodules are surrounded by a concentrically arranged extracellular matrix. Its overall density is similar to that of nodule-free areas. In the immediate vicinity of large, loose nodules, all constituents of the extracellular matrix disappear. Adjacent connective tissue is partly destroyed but still contains collagen fibers and proteoglycans. These findings suggest the following: The presence of V2 carcinoma cells induces marked alterations in the structured and non-structured components of the extracellular matrix. These changes are, at the same time, progressive and regressive and the occurrence of one or the other depends on local tumor progression. Progressive alterations may result from an increased activity of fibroblasts. Since degradative effects, on the other hand, are only seen in the immediate vicinity of larger tumor aggregates, it is assumed that a minimal number of tumor cells is essential for destruction of extracellular matrix.

Ultrastructural and cytochemical observations on 5-fluorouracil-induced cleft-palate development in hamster

Sequential alterations in 5-fluorouracil-treated hamster fetal palate were studied by light and electron microscopy and by acid phosphatase cytochemistry. At an early stage in 5-fluorouracil-treated fetuses, when the palatal shelves were vertical, lysosomes first appeared in cells of the prospective fusion epithelium and then in the cells of subjacent mesenchyme. In contrast to controls, increasing numbers of both the epithelial and mesenchymal cells of the vertical palate showed lysosomal injury in 5-fluorouracil-treated fetuses as development progressed. Subsequently, the basal lamina in the vertical palate showed alterations, characterized initially by disturbances in lamina lucida, by fingerlike extensions of lamina densa, and ultimately by its complete breakdown. At a later stage, when shelves became horizontal, the lysosomes were absent in both the epithelial and mesenchymal cells, and the basal lamina continuity was restored. Unlike controls, however, 5-fluorouracil-treated horizontal shelves never contacted one another. Instead, the epithelia of the horizontal shelves underwent stratification. It appears that premature formation of lysosomes in palatal epithelial and mesenchymal cells following 5-fluorouracil treatment disrupts normal cytodifferentiation and affects the integrity of the basal lamina; both effects are associated with cleft-palate development.

Alterations in the volume of the intercellular space between epithelial cells of the hamster cheek-pouch: quantitative studies of normal and carcinogen-treated tissues

The present report investigated the extent of the epithelial dysplastic feature known as "loss of cellular adherence" at the ultrastructural level by quantifying the volume of the intercellular space during hamster cheek-pouch carcinogenesis. Following topical application of DMBA to cheek-pouches, lesions were classified as hyperplasia, dysplasia and carcinoma, with untreated pouches serving as a control. Stereological point counting procedures were used to determine the volume density of intercellular space in defined basal, spinous and granular layers for each group. In general, progressive increases in volume density were detected within each stratum during carcinogenesis. These results indicate that increasing separation of epithelial cells occurs during carcinogenesis, although it is not yet known whether this results from loss of cohesion between specialised (i.e., desmosomal) or nonspecialised membrane areas. In addition, a simple indicator of pathological alteration, the Pathological Alteration Ratio (PAR), is described and was used to evaluate existing published data for intercellular spaces in various oral mucosal conditions. Values of the PAR were found to be substantially higher in carcinogen-treated epithelia than in reports describing changes in wound healing, lichen planus and leukoplakia simplex. These objective techniques are of value for investigating the pathogenesis of diseased epithelium and may find applications in the diagnosis of oral premalignant lesions.

Ultrastructural morphometry of collagen from lamina propria during experimental oral carcinogenesis and chronic inflammation

Stereological point-counting methods were used to determine the volumetric alterations in collagen from the lamina propria immediately beneath the epithelial-connective tissue junction in hamster check-pouch mucosa treated with the chemical carcinogen DMBA. In addition, a non-neoplastic inflammatory control was evaluated in which a delayed hypersensitivity reaction was induced by the contact-sensitising agent DNCB. DMBA-treated tissues were assigned to histopathologically defined hyperplasia, dysplasia and carcinoma stages. The volume densities of collagen present in unit volume of extracellular lamina propria were found to decrease progressively and significantly in DMBA-treated tissues when compared with values obtained from normal untreated mucosa. Values from the inflammatory control were comparable with those from the dysplasia stage of carcinogenesis. The mechanisms responsible for these decreases in collagen volume density are unknown, but contributory factors might include collagen destruction by enzymes originating in either the epithelium or the cells of the inflammatory infiltrate, dilution of collagen produced by inflammatory oedema or alterations in the synthetic capabilities of fibroblasts.

Hemidesmosomal dimensions and frequency in experimental oral carcinogenesis: a stereological investigation

Connective tissue invasion by carcinomas results in a variety of morphological changes at the epithelial-connective tissue junction. In this report, hemidesmosomal size (-delta) and frequency (Ns) were quantified using established stereological methods. Following treatment of hamster cheek pouches with the chemical carcinogen DMBA, lesions defined as hyperplasias, dysplasias and carcinomas were evaluated using electron microscopical techniques. Untreated pouches served as controls. Stereological intersection counting procedures were used to quantify hemidesmosomes at the epithelial-connective tissue junction. During carcinogenesis, hemidesmosomal diameter decreased progressively, although the reductions were not statistically significant. Hemidesmosomal frequency also decreased progressively between control and carcinoma groups. Normal basal plasma membranes possessed approximately 8 hemidesmosomes/micron 2 whereas values were reduced to approximately 3/micron 2 in the carcinoma group. The reductions in hemidesmosomal frequency during carcinogenesis may reflect an increased motility of basal epithelial cells and a decreased adherence of basal cells to the adjacent lamina propria. The specificity of this alteration in the pathogenesis of malignancy can be readily determined by the application of stereological methods to various neoplastic and non-neoplastic lesions.

Inter-animal variation and its influence on the overall precision of morphometric estimates based on nested sampling designs

This paper provides additional experimental evidence that biological variation between individuals is likely to be the major factor influencing the overall precision and efficiency of nested sampling schemes for morphometric analysis of thin sections. Four distinct experimental systems (two based on nervous tissue and two on epithelia) have been investigated. Morphometric estimates were obtained from measurements made on micrographs generated by sampling tissues at several levels. Sources of sampling variation were isolated so that the contributions to overall variance made by inter-animal differences could be evaluated. In each case, biological variation was the cardinal component of total observed variance between animals. Relative contributions ranged from 53% to 78%. Examining more animals would be the most efficient way of reducing the variance of the group mean in these sampling designs.

Towards economy of effort in quantitative ultrastructural pathology: efficient sampling schemes for studying experimental carcinogenesis

Hamster cheek pouch mucosa was painted with DMBA in order to compare samples of epithelium at different pathological stages of carcinogenesis. Stereological methods were applied to ultrathin sections of tissue to estimate one ultrastructural index of change, the surface ratio of lamina densa compared with the overlying plasma membrane of cells in stratum basale. Analysis of variance techniques were then employed to isolate and quantify the contributions which different levels of sampling (animals, tissue blocks, microscopic fields) made to the total observed variation in this surface ratio. Economical sampling schemes for future use were calculated from the sampling variances by taking into account the relative costs at each sampling level. Though illustrated by means of the hamster cheek pouch-DMBA model, our results are pertinent to many other experimental models for quantitative histopathology.

Cellular and nuclear volumetric alterations during differentiation of normal hamster cheek pouch epithelium

The aim of this investigation was to determine whether volumetric changes occurred in differentiating layers of stratified squamous epithelium. Samples of cheek pouch mucosa from 5 hamsters were obtained, prepared for electron microscopy using carefully controlled methods, and electron micrographs obtained from defined basal, spinous and granular layers of the epithelium. Stereological point counting procedures were used to determine the ratio of nucleus to cytoplasm for each of the defined cell layers. From direct measurement of nuclear profiles, major and minor axes were transformed to diameters of circles of equivalent area and it was thus possible to obtain an estimate of nuclear volume. Using the previously determined nuclear-cytoplasmic ratio, the volume of cytoplasm and hence cell volume, could be estimated for the cell layers. Between basal and granular layers, nuclear-cytoplasmic ratios decreased from 0.42 to 0.08, whereas cytoplasmic and cellular volumes increased progressively from 248 to 1052 microns 3 and from 352 to 1144 microns 3, respectively. Nuclear axial ratios were highest in the granular layers. These methods can be used in a variety of comparative ultrastructural studies of epithelia, and will also prove valuable in generating additional biological information from more conventionally presented stereological data.