Epithelial Cell Rests Research Articles

Proliferating Oral Epithelial Cells in Culture are Capable of Both Extracellular and Intracellular Degradation of Interstitial Collagen

The potential of epithelial cells to degrade interstitial collagen was studied by culturing human masticatory mucosa on decalcified dentin matrix. Morphological changes were observed in the underlying collagen substratum and in the connective tissue of the explant. Degradation of the substratum was initiated two days after the first contact with epithelial cells exhibiting basal cell markers. Electron microscopic studies confirmed extensive collagen degradation in the vicinity of these cells. No collagen degradation was observed underneath the connective tissue portion of the explant. Experiments in which the explant was partially separated from the underlying substratum by a filter further showed that connective tissue was apparently not involved in the collagen degradation by the epithelial cells. Lysis of connective tissue of the explant was observed in association with epithelial cells that showed a disrupted basal lamina and release of vesicular material from the exposed cell membrane. Collagen fibers were visible inside some epithelial cells suggesting intracellular collagenolysis. Primary cultures of human gingival epithelial cells and porcine periodontal ligament epithelial cells (epithelial cell rests of Malassez) that expressed similar basal cell cytokeratins as the active cells of the mucosal explants secreted collagenase, gelatinase and TIMP to the culture medium. They also contained acid collagenolytic proteinases. When cultured on a porous polycarbonate membrane the epithelial cells secreted collagenolytic enzymes from the pores at cell membrane sites lacking basal lamina. These results provide evidence that proliferating basal epithelial cells have a strong capacity for collagen degradation. It seems that the absence of basement membrane is the signal for these cells to secrete matrix degrading enzymes.

Epithelial cell rests of Malassez bind epidermal growth factor intensely.

The binding of 125I‐labelled epidermal growth factor (EGF) in the dental follicle was studied by autoradiography. The follicle of a surgically removed impacted premolar was cut into small pieces which were incubated in the presence of 125I‐EGF. Very intense binding was localized in the epithelial cell rests of Malassez, whereas only background labelling was seen in fibroblastic cells. EGF is a hormone‐like molecule which is believed to exert its effects locally and through binding to a specific cell surface receptor. The number of EGF receptors in many cells – e.g., basal epidermal cells ‐ is related to cell proliferation. The present observations indicate that EGF receptors are expressed in high amounts by the cells of the epithelial rests, and that these cells are thus potentially responsive to the actions of EGF. It can be speculated that activation of the epithelial rest cells in various pathologic conditions is associated with a local rise in the tissue level of EGF.

The effects of preventing movement of the rat incisor on the structure of its periodontal ligament

A quantitative, ultrastructural study was made on the periodontal ligaments of rat mandibular incisors immobilized for 18 days. Fibroblasts and their organelles (i.e. endoplasmic reticulum, mitochondria, microtubules, microfilament bundles, lysosomes, intracellular collagen profiles and intercellular contacts), oxytalan fibres, collagen fibrils and ground substance were quantified. There was re-orientation of tissue at the lateral borders of the ligament and an apparent increase in size of epithelial cell rests. Within the matrix, the mean collagen-fibril diameter decreased and the amount of ground substance increased. No change occurred in oxytalan fibres. Within the cells, effects were seen only in cell contacts and in the relative volume of intracellular collagen, lending no support to the view that fibroblast activity generates the force responsible for tooth eruption.

Mechanical stretching increases the number of epithelial cells synthesizing DNA in culture.

The influence of mechanical stretching on epithelial (E) cells was examined by culturing E cells derived from the epithelial cell rests of Malassez on a flexible plastic substrate and stretching the substrate by means of an orthodontic screw. A significant increase in the number of E cells synthesizing DNA was observed after just 30 min of stretching. In 17 experiments the ratio of cells labelled with tritiated thymidine in cultures stretched for 2 h to the number of labelled cells in unstretched controls was 1.92 +/- 0.34. An increase in labelling as a result of stretching was found for E cells cultured at either high or low cell-population densities but the effect was most pronounced for E cells cultured at higher concentrations of foetal bovine serum. Morphometric analysis of electron micrographs of stretched and unstretched cultures indicated that the stretched cultures had a higher volume fraction of filamentous structures and more desmosomes per unit length of cell membrane than unstretched cultures. The behaviour of E cells in response to stretching in vitro appears to be similar to the response of the epithelial rests in vivo when the latter are exposed to tension as a result of forces produced by orthodontic techniques.

Cholera toxin and dibutyrl cyclic-AMP stimulate the growth of epithelial cells derived from epithelial rests from porcine periodontal ligament

The epithelial cells (E-cells) grew best at high (> 5 per cent) concentrations of fetal bovine serum (FBS). Growth could be obtained at low concentrations of dialysed FBS (DFBS) if the medium (α-MEM) was modified so that the levels of Ca 2+ and K + were reduced to 0.1 and 1.0 mM, respectively (β-MEM). The addition of 0.5 per cent DFBS to the β-MEM did not initiate good growth but was sufficiently supportive to enable the effects of various growth promoters to be tested. Cholera toxin and dibutyrl cyclic-3′5′-adenosine monophosphate (Bt 2cAMP), which are known to increase intracellular cAMP levels, at concentrations of 1 ng/ml and 0.5 mM, respectively increased cell number. Cholera toxin caused the E-cells to be more flattened when viewed by phase-contrast; this appeared to be due to spread of the cells. No difference in cell-size distributions obtained between the trypsinized E-cells grown in the presence or absence of cholera toxin was observed. Epithelial proliferation that occurs in dental cysts could result from a rise in intracellular cAMP levels in epithelial cell rests.

Effect of cells of epithelial rests of Malassez and endothelial cells on synthesis of glycosaminoglycans by periodontal ligament fibroblasts in vitro

Cultures of fibroblast-like cells (PLF) and epithelial rest cells (PLE) prepared from explants of porcine periodontal ligament synthesized and secreted four glycosaminoglycans (GAG) in differing proportions. The PLF produced predominantly chondroitin sulphate (>60%) with smaller amounts of hyaluronic acid (HA) (17%), dermatan sulfate (13%), and heparan sulfate (7%), whereas PLE produced predominantly HA (>80%). In coculture and under conditions of reciprocal transfer of conditioned media neither cell type affected the other's GAG synthesis. Endothelial cells (EC), however, or their conditioned growth media, were able to stimulate increased GAG synthesis, especially HA, in PLF. A similar result was obtained with smooth muscle cells (SMC) cultured in EC growth media but here again PLE were unable to stimulate GAG synthesis by SMC. These findings suggest that the spectrum of GAG found in whole ligament results both from independent production by, and from interaction between, the different cell types within the ligament. The results also provide support for a general hypothesis that loose connective tissues, which are rich in HA, are formed and maintained under the influence of epithelial, including endothelial, cells.

The rôle of immunological reactions in apical cyst formation and the fate of epithelial cells after root canal therapy: a theory

Activation of the epithelial cell rests of Malassez by various means, results in proliferation of these cells and formation of apical periodontal cysts. Several theories for the genesis of apical periodontal cysts have been suggested which are not satisfactory. Available evidence indicates that development and destruction of these lesions are mediated by immunological reactions.

An in vivo and in vitro study of dissociated tooth germs of rats

Single-cell suspensions of dissociated rat molar tooth germs were grown in vitro in modified Rose chambers and in vivo in diffusion chambers implanted subcutaneously in host rats. Using phase contrast microscopy and time lapse cinemicrophotography, the cells were observed in vitro to form aggregates consisting of groups of mesenchyme-like and epithelium-like cells. In material from the in vivo study, it was also observed that the dissociated cells re-aggregated to form sheets of epithelial and mesenchymal cells and sometimes to form more organized structures resembling epithelial cell rests of Malassez. Storage of the tooth germs at −196 °C for 3 weeks prior to trypsinization aided dissociation and appeared to have no deleterious effect on the subsequent viability and behaviour of the stored cells.

The epithelial cell rests of Malassez and the genesis of the dental cyst

Activation of the epithelial cell rests of Malassez, both in vivo and in vitro, involves a switch in their metabolism and the utilization of the hexose-monophosphate shunt. This response of the epithelial rests is common to other epithelia when their supporting connective tissue is altered. It is suggested that the potential that activated cell rests have for dental cyst formation, as distinct from other epithelia, is due to their anatomic location. It is further suggested that intraepithelial cavitation of trabeculae of activated cell rests is the mechanism for initial cyst formation.

Craniopharyngioma originating in the sphenoid bone. Case report.

✓ A case of craniopharyngioma originating in the sphenoid bone is presented. The tumor probably originated in the midline from epithelial cell rests along the path of the involuted craniopharyngeal duct. There was bone invasion and destruction of the floor of the middle fossa with intradural extension of tumor into the left temporal lobe. Survival from onset of symptoms was 37 years. Irradiation probably played a significant part in this patient's long survival. Modern techniques now in use might achieve cures with surgically unresectable intrasphenoidal craniopharyngiomas.

Newer concepts of odontogenic cysts

There are two main classes of odontogenic cysts, and they originate in different types of epithelial cell rests. Those which are lined with non-keratinized epithelium may increase in size, primarily because of the degenerative characteristics of their linings, which result in increased osmolality of the cyst contents. The absence of lymphatic access to such a cyst cavity is thought to be fundamental to the cyst's sustained growth in the tissues. A less frequent class of cysts, the odontogenic keratocyst, is lined with a keratinizing epithelium which shows the characteristics of cell maturation rather than degeneration, and may increase in size predominantly by a process of epithelial cell multiplication. The rate of epithelial cell turnover in odontogenic keratocysts has been shown to be greater than in other cysts. Keratocysts tend to recur after conservative surgery. Planning the correct surgical procedure can be assisted by certain tests which help to establish the preoperative diagnosis. Many epithelial cysts have been shown to invoke a local immunologic reaction in the surrounding tissues. This reaction may be associated with the mechanism whereby some cystic lesions spontaneously regress.

Hertwigs sheath in the rat incisor. 2. Autoradiographic study.

The histodynamic nature of Hertwig's sheath of the mandibular rat incisor was studied utilizing tritiated thymidine. The epithelial sheath is composed of three distinct cell layers: (1) inner dental epithelium, (2) stellate reticulum, and (3) outer dental epithelium. Incisal to the basal loop area, the outer layers eventually diminish and disappear leaving only the inner dental epithelium. This layer ultimately becomes perforated and is replaced by connective tissue elements. Epithelial rest cells are not identifiable in the periodontal ligament. Autoradiographic study shows labeling to be more frequent in the inner dental epithelium than the other two epithelial layers. At the one hour period, 97 per cent of the labeled cells in the inner dental epithelium are located in the basal two‐thirds of the area between the basal loop and the site of predentin deposition. A study of cell kinetics indicates that the inner dental epithelium is made up of a renewing cell population. The cells have a total generation time of 25.3 hours; a synthesis period of nine hours; a G2 period of two to six hours; a mitotic period of approximately one‐half hour, and a G1 period ranging from 9.8 to 13.8 hours. The rate of cell migration is of the same order as the rate of tooth eruption (358 μ per day).

A histochemical and radiobiological study of in vitro and in vivo human epithelial cell rest proliferation

Epithelial cell rests from periodontal ligament in vitro and epithelial trabeculae in apical granulomata were studied. The epithelial lining of dental cysts was also examined because of its probable origin from proliferated cell rest epithelium. Proliferated cell rests were obtained by culturing periodontal ligament explants in a closed culture system with McCoy's medium. DNA synthesis in this epithelium was confirmed by labelling explants with tritiated thymidine. A characteristic feature of the proliferated cells was their greatly increased amount of cytoplasm. Proliferated cell rest epithelium in vitro and in vivo exhibited little succinic dehydrogenase activity and contained no glycogen. However, lactic dehydrogenase and glucose-6-phosphate dehydrogenase activity was readily demonstrable. Lipid accumulation was a characteristic feature of proliferated epithelium. These findings are interpreted to formulate the thesis that in response to local environmental change, probably to change in oxygen/carbon dioxide tension, epithelial cells proliferate and are able to do so by virtue of their ability to undertake anaerobic glycolysis. It is suggested that endogenous protein synthesis required for cell multiplication is brought about partly by pentose shunt activity which is, in turn, linked with lipid synthesis.

The histochemical demonstration of specific oxidative enzymes and glycogen in the epithelial cell rests of malassez

Transverse cold microtome sections through the apical region of young teeth and cold microtome sections of periodontal ligament scraped off the root surfaces of extracted teeth were used to obtain fresh frozen sections of the epithelial cell rests of Malassez. Using nitro blue tetrazolium (Nitro BT), histochemical evidence was obtained for the localization of lactic dehydrogenase, glucose-6-phosphate dehydrogenase, succinic dehydrogenase, DPND and TPND in epithelial rests. In addition the presence of glycogen in the epithelial rests was established. These results indicate that the metabolic pathways in epithelial rests involve aerobic/anaerobic glycolysis and that glycolysis is also mediated through a functional pentose shunt pathway.

Peripheral ameloblastoma: Report of a case

A peripheral ameloblastoma is described. The rarity of this lesion is discussed. The required histopathologic characteristics of such a lesion are fulfilled. The origin of the tumor was not proved, although it most probably arose from odontogenic epithelial cell rests outside the jawbone proper. The minute size of the neoplasm is also of particular interest.

The radiology of endocrine disorders; a symposium. I. The diagnostic value of radiology in endocrine disorders.

I Feel honoured at having been invited to open this symposium on radiology in endocrine disorders. It is a particular pleasure to me to be able to acknowledge the ever-increasing debt which the physician owes to the radiologist, with his improved and improving techniques, for the greater accuracy he has acquired in the diagnosis of certain endocrine diseases. This greater accuracy in diagnosis, more especially in adrenocortical syndromes, has spared the patient unnecessary surgery, for instance laparotomy, and has guided the physician in his choice of treatment. As opening speaker I consider it to be my function to endeavour to cover the field as widely as possible and perhaps to deal with certain aspects somewhat superficially, leaving to subsequent speakers the task of discussing specific subjects in greater detail. Pituitary tumours. The main part played by radiology in the diagnosis of diseases of the pituitary gland is the determination of the presence or absence of a pituitary tumour. A tumour may be the cause of acromegaly, gigantism, Cushing's syndrome, hypopituitarism, infantilism, Fröhlich's syndrome, obesity and diabetes insipidus. The tumours of the pituitary gland may be divided into two main groups: (1) those derived from the cells of the anterior lobe—the chromophobe, the acidophil and the basophil adenomas—and (2) those derived from epithelial cell rests, which are the remains of Rathke's pouch from which the anterior lobe developed—the craniopharyngioma and the cysts of Rathke's pouch.

Epidermoids; clinical evaluation and surgical results.

T HE EPIDERMOIDS or eholesteatomas often present opportunities for complete removal and cure. This is due to their frequent epidural position, avascular character, and extremely slow development. Our paper deals with the surgical t rea tment and results of the group of ~r epidermoids verified on the Neurosurgical Service of the Hospital of the University of Pennsylvania and the Graduate Hospital of the University of Pennsylvania since 1930. I t is not intended at this time to go into the slightly controversial etiology of these tumors, as they are now generally accepted to be the product of epithelial cell rests. Discussion has arisen concerning the better name for these tumors. At present, the term choles teatoma is synonymous with pearly and epidermoid, the latter being the term of choice. 5'15'1s A difference of opiaion also arises as to whet [er the cholesterin-containing masses, arising in the petrous portion of the temporal bone, should be classified as true tumors of the cholesteatoma group. The majority of pathologists believe these cholesteatomatous masses, often associated with chronic otitis media, to be unrelated to true epidermoid tumors. They are merely the result of some chronic inflammatory desquamative process2 '18 These are best designated by the term cholesteatoses. ''2 The fact that both epidermoids and contain cholesterin often serves to confuse their differential diagnosis. The differential point is that the dermoids contain hair or other dermal elements due to their mode of origin. Critchley and Ferguson ~ pointed out that both occur as the result of a fetal inclusion of epidermal cells which, depending on the depth of the layer or according to their embryonic age, produce an epidermoid or dermoid type of tumor. A complete review of the literature is not intended at this time, and one is referred to the more exhaustive works of Mahoney, 12 King, 1~ and Rand and Reeves. 18 However, a brief historical outline is included to reveal the development of terminology and theory of origin of these tumors. 1807--Pinson, 17 an artist in the School of Medicine of Paris, first described an epidermoid tumor from Dupuytren ' s service at the HStel Dieu. 18~9--Cruveilhier, 6 in his Anatomie Pathologique, fully described the tumor of Pinson and also a parapitui tary tumor of the same type. Because of their highly refractile and nodular surface, he gave them the name, tumeur perlde.

Adamantinoma or Ameloblastoma of the Hypophyseal-Duct Region: With Report of a Case

In Duffy's (11) discussion of tumors of the hypophyseal duct (1920) is included an historical survey in which it appears that Rathke was the first to state, in 1838, that the hypophysis developed from a diverticulum of the pharynx. Zenker in 1857 demonstrated squamous-lined cysts in the anterior lobe of the hypophysis, and in 1860 Luschka first noted the presence of groups of squamous epithelial cells in the sections of some normal hypophyses. It was not until 1875, however, that the essential points in the formation and structure of the hypophysis were finally settled and clearly presented. This was done by Goette and von Mihalkovics, who independently demonstrated the ectodermal origin of the anterior lobe. In 1892 Onanoff drew attention to the similarity of certain tumors of the hypophyseal region to the adamantinomas of the jaw. In 1904 Erdheim, in making serial sections of thirteen normal adult hypophyses, found squamous epithelial cell rests in ten. These epithelial rests were usually located along the anterior surface of the infundibulum and beneath the capsule of the upper surface of the anterior lobe. Erdheim believed that these cell groups formed the point of origin for the adamantinomas. In 1926 Critchley and Ironside (12) defined this tumor of the hypophyseal-duct region as follows: “The pituitary adamantinoma may be defined as a variety of epithelial tumor growing in the neighborhood of the infundibulum, and originating in unobliterated portions of the fetal craniopharyngeal duct; its minute structure is a duplicate of the embryonic enamel organ, the general histological appearance resembles that of the adamantine tumors of the jaw.”