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D Broekaert

Publications and source records attributed to D Broekaert.

At least 37 records · Page 2Linked to original sources
PubMed1991

The keratinizing tympanic epithelium: an enigma.

Both the centrifugal keratin dispersion on the pars tensa as well as the centripetal proliferative properties at the inferior annular tympanic region are discussed. There is evidence, histological and clinical, that these features are two distinct and different phenomena which both have clinical implications. While the centrifugal keratin dispersion is a physiological cleaning mechanism, the cytokeratin expression demonstrates the unusual but for years clinically noticed proliferative nature of the lower annular epithelium and provides biochemical evidence for a relationship between this epithelium and cholesteatoma formation.

Cell Movement↗
PubMed1991

The problem of middle ear cholesteatoma: etiology, genesis and pathobiology. A review.

This review provides an overview of the problem of middle ear cholesteatoma, and encompasses the following areas: the definition, the light and ultramicroscopic structure, the etiology, the pathogenesis (with special emphasis on the congenital or "embryonic rest" theory, immigration, invagination and papillary ingrowth, traumatic or iatrogenic implantation and metaplastic origin), and finally the pathology of cholesteatoma including bone erosion. An attempt is made to distill the actual and leading thoughts concerning this intriguing entity.

Cholesteatoma↗
PubMed1990

Keratinization of middle ear cholesteatomas. I. A histochemical study of epidermal transglutaminase.

A histochemical study was performed to determine the involvement of epidermal transglutaminase (ETgase) in the keratinization of middle ear cholesteatomatous lesions, and to compare it with its role in the middle ear mucosa and epidermis. In a first assay, we localized the (E)Tgase activity in situ. A second immunohistochemical assay revealed the distribution of the particulate form of ETgase, which is involved in cross-linked envelope formation. A remarkable difference between strongly keratinized epidermal tissues and the cholesteatoma matrix is the frequent observation in the latter of the remnants of (E)Tgase activity in cytosol, even in advanced stages of differentiation. As a consequence, the cell-membrane-associated ETgase activity, and thus the extent of cross-linking within the envelope, is at a lower level than expected. This aspect is reminiscent of the keratinization phenomenon manifested by thin epidermal tissues. In addition, our findings are the first to show that ETgase is a substantial marker of middle ear mucosa.

Cholesteatoma↗
PubMed1990

Keratinization of middle ear cholesteatomas. II. A histochemical study of epidermal transglutaminase substrates.

A histochemical study was performed to clarify further the role played by epidermal transglutaminase (ETgase) in the keratinization of aural cholesteatoma. Weakly and strongly keratinized epidermal tissues and healthy middle ear mucosa were included as references. A first assay revealed the distribution of non-specified acyl donor substrates. In a second assay, the topography of involucrin was assessed immunohistochemically. In both epidermal and cholesteatoma matrix tissues, the presence of acyl donors was not restricted to the sites of (E)Tgase activity, but was almost uniformly extended throughout living layers. In reference tissues, residual acyl donors were poorly detected in horny layers, while they were more abundant in the stratum corneum of the cholesteatomas studied. The presence of involucrin along the cell membrane was observed at varying distances throughout the spinous and granular layers, depending upon the epidermal and matrix configurations. In thick epithelia, involucrin rapidly became concentrated at the cell periphery (in spinous keratinocytes), while in thin epithelia it was usually associated with cell flattening. This latter staining profile was observed more frequently in cholesteatomatous tissues. In addition, we regularly noticed an immediately suprabasal accumulation of involucrin, suggesting a locally hyperproliferative state of the matrix. An insufficient availability of acyl donors, especially involucrin, could not be used to explain the defective ETgase-mediated cross-linking of cholesteatoma cell membranes during terminal stages of differentiation. The present investigation may be the first to demonstrate the presence of involucrin in middle ear mucosa.

Cholesteatoma↗
PubMed1990

An investigation of cytokeratin expression in skin epithelial cysts and some uncommon types of cystic tumours using chain-specific antibodies.

The differentiation state of skin epithelial cysts and some uncommon types of epithelial skin tumours was investigated by immunohistochemical staining, mainly using cytokeratin (CK) polypeptide-specific monoclonal antibodies. Samples of interfollicular epidermis, hair follicles and eccrine sweat glands were included as reference tissues. The CK reactivity in epidermoid cysts and milia is not restricted to CKs involved in epidermal-type differentiation, i.e. CK1, 5, 10 and 14, but in addition CK16, a hyperproliferative keratinocyte marker is suprabasally expressed. CK1 and 10 are other prominent suprabasal markers, while CK14 seems to be preferentially expressed in the basal cell layer. Of the non-epidermal CKs, only CK4 was focally or more extensively detected in about 50% of the cases. In terms of CK reactivity, keratinization of trichilemmal cysts corresponds to the keratinization of the anagen-phase hair follicle in the isthmus. The CK reactivity is again restricted to CK1, 5, 10, 14 and 16. However, the CK1 as well as CK10 reactivity is subject to serious limitations, since both CKs were only convincingly observed in foci of terminal differentiation. Eccrine hydrocystoma obligatorily expresses a complex CK set, including CK7, 8, 14, 18 and 19. This CK set perfectly corresponds to the CK composition observed in acini of eccrine sweat glands. In addition, a discontinuous CK4 and 16 reactivity was seen in about 50% of the sites, while CK1 and 10 displayed a strictly focal appearance. On the other hand, syringoma produces in its distinct structures, a CK pattern reminiscent of the one observed in eccrine sweat gland ducts and includes CK1, 5, 10, 14, 16 and 19.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed1990

The migratory capacity of the external auditory canal epithelium. A critical minireview.

The aim of the present paper was to review in detail and in an objective way, the most prominent data concerning the phenomenon of migration on the eardrum and deep on the bony part of the meatus. I present and discuss data obtained along different lines, in different species: e.g. ink dot migration, autoradiographic tracing, perforation studies, morphological and histological observations, tissue culture experiments, theoretical model studies, fetal and postnatal growth, immunohistochemical studies, probing molecular markers. Although the topic remains controversial, more and more it becomes clear that an active migration may occur deep in the stratified epithelia, and that a passive migration or keratin dispersion occurs additionally on the surface. The precise pattern along which the deep migration occurs, may differ in different species. In humans, the pars tensa more readily displays migration than the pars flaccida and the central area of the drum. Especially the inferior region of the annulus fulfils the criteria of a proliferation center stimulating active migration. The umbo region may represent the center of superficially radial dispersion.

Adult↗
PubMed1988

A comparative immunohistochemical study of cytokeratin and vimentin expression in middle ear mucosa and cholesteatoma, and in epidermis.

Cytokeratin expression was studied in human middle ear cholesteatoma lesions, using a variety of immunohistological techniques and a wide range of polyclonal antisera and monoclonal antibodies against cytokeratin (CK) subgroups or individual CK polypeptides. The expression of the other cytoskeletal proteins, vimentin and desmin, was also investigated. Middle ear mucosa and epidermal tissues were used as reference tissues. Our investigations also included epithelial structures present in the cholesteatoma perimatrix and in dermal tissues. The results indicate that, compared with epidermal tissues, the expression profile of CKs in cholesteatoma matrix is representative of a hyperproliferative disease. Evaluating the presence of a marker of terminal keratinization - the 56.5 kD acidic CK n degrees 10 - we found supportive evidence of a pronounced retardation of its expression, which did not parallel histological differentiation. In epidermal tissues, the first prickle cell layers are CK10 positive whereas in many cholesteatomas this finding was observed near the stratum granulosum only. Probing the early stages of keratinization - the 58 kD basic CK n degrees 5 and the 50 kD acidic CK n degrees 14 - we regularly observed an extended staining area in the cholesteatoma matrix. In epidermal reference tissues, only the basal and nearest suprabasal layers were convincingly labeled. As a rule, non-epidermal CKs did not belong to the cholesteatoma CK set. However, exceptions to that rule were noticed as a focal or more extended expression of one or more non-epidermal CKs in about half of the cases. Together with the extended CK5 topography, this is further evidence that CK expression is seriously affected by the diseased state. CK expression in the perimatrix is limited to mucous glands, either normal, atrophic or hyperplastic. CKs n degrees 4, 5, 7, 14, 18 and 19, also displayed by middle ear mucosa, were consistently observed. Where ductal arrangements were present, CK10 was also detected, in analogy with the CK10 registration in ductal portions of mucous glands in the external ear canal skin. The absence of CK8 in mucous glands of the perimatrix, however, strongly differentiates these structures from the mucous gland acini and ducti in the external ear canal, where CK8 is systematically expressed. Vimentin staining was restricted to dendritic cells of the matrix (Langerhans cells) and to perimatrix fibroblasts, blood cells and vascular endothelium. Coexpression of CK and vimentin was not observed.

Animals↗
PubMed1986

Nuclear differentiation and ultimate fate during epidermal keratinization. Two-wavelength and cytofluorometric DNA investigations completed by computerized scanning image analysis.

Quantitative DNA cytophotometric investigations were performed to clarify some aspects of the differentiation and fate of nuclei in bovine snout and human epidermis representing various sites and different degrees of keratinization. We elaborated optimal conditions for hydrolysis and Feulgen staining. Diverse cytophotometric techniques, including computerized scanning cytophotometry and image analysis were applied. This approach provided the first quantitative data concerning changes of nucleotype during soft keratinization. Cytophotometric DNA measurements provide evidence for a continuous decline of nuclear DNA content from immediately beyond the basal layer to the transition zone. The overall loss of DNA is an orderly process that intensifies gradually and culminates in the stratum granulosum. Gradual nuclear degeneration, however, is not a general phenomenon, and a significant number of nuclei retains a DNA content within the diploid limits throughout the entire stratum spinosum and part of the stratum granulosum. At any level of differentiation or decay, residual nucleoprotein complexes remain intact, as judged from their resistance to acid hydrolysis. Karyological features change completely during keratinization. Basal cell nuclei are rather compact, ellipsoid and heterochromatic. Beyond the basal layer, nuclei enlarge, round up and obviously evolve to an extremely euchromatic state, with preferential localization of the dispersed heterochromatic clumps at the more peripheral sites. In the upper stratum spinosum, nuclei undergo even more drastic changes: nuclear area and volume shrink, nuclei partially regain the ellipsoid shape and revert to heterochromasia. Nevertheless, euchromatin remains the major constituent of decaying nuclei. Terminal differentiation stages, except in human sole, are marked by heterochromatin clumping. In human sole, persistence or even progression of heterochromatin dispersion is observed. Heterochromatic dots are situated along the nuclear membrane in human terminal keratinocytes, but are almost randomly distributed in bovine stratum granulosum nuclei. Finally, nuclear contrast analysis partially reveals statistically significant changes throughout keratinization.

Animals↗
PubMed1986

Polyploidization and localisation of poly(A)+ RNA in the different cell types of the vitellogenic meroistic ovary of the fleshfly, Sarcophaga bullata.

The degree of polyploidization, the level of transcriptional activity and the volume of the different cell types present in the meroistic ovary of Sarcophaga bullata were measured during different vitellogenic stages. The nurse cells and the germinal vesicle exhibited very pronounced differences with regard to DNA content and mRNA synthesis, even though they are genetically identical. During the 4C stage (late vitellogenesis), we observed different degrees of polyploidy in follicle cells adjacent to the oocyte and those surrounding the nurse cells. Although the chromatin of the germinal vesicle is condensed into a karyosome, in situ hybridisation revealed the presence of transcriptional activity. The volume of the germinal vesicle, which contains only 4C DNA, is big enough to contain 2048C DNA. The meroistic ovary is a highly polarized differentiating system. Our results are discussed in the light of the fact that the polytrophic ovary is a miniature electrophoresis chamber.

Animals↗
PubMed1984

Histochemical changes in protein disulphide bonds in rat liver and kidney after chronic cadmium administration, and the possible relation to metallothionein.

After chronic exposure to low doses of CdCl2 an increase in disulphide bonds has been established in rat liver using a specific staining method for disulphide bonds and cytophotometric quantitation. This increase is dependent on doses and length of exposure time. Evidence is presented that this increase might be related to the accumulation of metallothionein or some other cadmium binding protein. Using the same staining method after long exposure to low doses of CdCl2 a large number of large dark blue stained granules were observed in the proximal tubule cells, with blue stained deposits in the lumen of the proximal and some renal medulla tubules of the kidney. Evidence is presented that this staining pattern corresponds to the destruction of the proximal tubule cell by the cadmium thionein complex.

Animals↗
PubMed1982

A quantitative histochemical study of sulphydryl and disulphide content during normal epidermal keratinization.

A quantitative histochemical study was carried out on the distribution of protein thiol and disulphide groups in normal human plantar epidermal tissue. Histochemical demonstration of reactive groups was achieved by addition of N-(4-aminophenyl) maleimide, subsequent diazotization and final coupling with a Nitro Red or chromotropic acid label as first described by Sippel. The quantitative reliability of the method was tested by absorption cytophotometry, and evaluated on the basis of the internal consistency of the results reported. Our histological observations and histophotometric data support accepted views on epidermal keratinization. A limited, though reproducible, amount of disulphide bonds was observed near the basement membrane. The free thiol concentration in basal and prickle cells was low and almost constant, but was higher in the granular cells, where deposition of sulphur-containing proteins on cell membranes is initiated. In Malpighian layers, disulphide cross-links only occurred just beneath the transition zone in thickened cell membranes. The staining pattern of the inner stratum corneum resembled a mosaic and was characterized by a Sharp rise of the disulphide content, which exceeded the decrease in free thiol groups. The free thiol concentration decreased further throughout the cornified layers whilst the disulphide content remained fairly constant. Staining of thiol and disulphide groups together corresponded, within the limits of the standard error, to the sum of the thiol and disulphide concentrations when they were assayed separately in living ahd horny cells. These results confirm that living cells are the main site of free thiol groups, while horny cells are the most prominent of site of disulphide cross-links.

Disulfides↗
PubMed1982

Quantitative determination of free thiol and disulphide groups by a fluorescent maleimide procedure.

To determine the quantitative reliability of thiol histofluorometry, the distribution of protein thiol and disulphide groups was reinvestigated in normal human epidermis, labelled with DACM-3 after cryocutting. Microscopical observations roughly confirmed, that living keratinocytes and inner stratum corneum are the main sites of free thiol groups, while disulphide crosslinks are almost exclusively found in cornified cells. Histofluorometric quantitation led to free--SH, --S--S-- or combined --SH and --S--S-profiles through the different strata, that were not compatible with previous absorption-histophotometric studies and lacked internal consistency. The difficulties reside mainly at the methodological level and may partially be resolved--at least in keratinocytes--by extraction of nonstructural SH-groups in a prerinsing step. Permanent mounting further contribute to the realization of normal fluorescence behaviour, as visualized by the decay curves. DACM-saturation of structural protein reactive groups was only reached after prolonged staining.

Disulfides↗