Ultrastructural preservation of rat embryonic dental tissues after rapid fixation and dehydration under microwave irradiation

Poly(Aspartic Acid) Promotes Odontoblast-like Cell Differentiation in Rat Molars with Exposed Pulp

In recent years, alternative pulpal therapies targeting dentinogenesis signaling pathways using different peptides have been investigated. The aim of this study was to verify the effectiveness of poly(aspartic acid), pAsp, in dentin regeneration using an animal model.

METHODS

Mechanical pulp exposure was performed in the upper molars of 56 Wistar rats, randomly divided as follows (n = 14): control (no treatment); MTA group-pulp capping with mineral trioxide aggregate (MTA Angelus); pAsp group-application of 20 μL of pAsp solution (25 mg·mL-1); MTA+pAsp group-application of MTA mixed with pAsp (5:1 by mass). Animals were euthanized after 7 or 21 days. Histological sections were submitted to hematoxylin-eosin and Brown and Brenn staining and immunohistochemical analysis for osteopontin (OPN) and dentin matrix protein 1 (DMP 1).

RESULTS

At 7 days, an acute inflammatory infiltrate and the presence of disorganized mineralized tissue were observed in all groups. At 21 days, the quality and thickness of the reparative dentin in treated groups were superior to the control, and bacterial contamination was observed in two MTA-pAsp specimens. While all treated groups showed intense immunostaining for OPN at 21 days, only the pAsp group expressed DMP 1, indicating the presence of fully differentiated odontoblast-like cells.

CONCLUSION

Poly(aspartic) acid promoted dentin regeneration in rat molars in the absence of an additional calcium source and may be an alternative to MTA as a pulp-capping agent.

Effect of human dental pulp stem cell conditioned medium in the dentin-pulp complex regeneration: A pilot in vivo study

BACKGROUND

Dental trauma, restorative operative procedures and/or caries lesions can expose the dental pulp. Facing this clinical condition, where the maintenance of the dentin-pulp complex vitality is imperative, is challenging in Dentistry. Dental pulp stem cells conditioned medium contains trophic factors that could help in this task. This in vivo pilot study aimed to evaluate the effects of the human dental pulp stem cells conditioned medium on the dental pulp tissue response to vital pulp therapy.

MATERIAL AND METHODS

Concentrated conditioned medium was obtained by incubating characterized human dental pulp stem cells with fresh culture medium. Pulp exposures performed at the first upper molars (n = 20) of Wistar rats were directly capped with: MTA or MTA + Conditioned Medium. Four and 8 weeks later, the samples were qualitatively analyzed in histological sections (H&E).

RESULTS

When the conditioned medium was associated with MTA, there were a high percentage of samples presenting formation of dentin bridges and small percentage of pulp tissue with inflammatory signs in both experimental times. The conditioned medium improved the organization of the newly formed hard tissue.

CONCLUSIONS

The association of dental pulp stem cell conditioned medium with MTA showed beneficial effects on dentin-pulp complex regeneration and has promising potential for studies in regenerative dentistry.

Immunohistological study of the effect of vascular Endothelial Growth Factor on the angiogenesis of mature root canals in rat molars

Tissue bioengineering has been applied to Endodontics to seek a more biological treatment. The presence of blood vessels is crucial for cell nutrition during tissue formation.

Microwave Irradiation of Ethanol-fixed Bone Improves Preservation, Reduces Processing Time, and Allows Both Light and Electron Microscopy on the Same Sample

Methylmethacrylate (MMA) embedding is routinely used for histomorphometry of undecalcified bone preserved by prolonged immersion in ethanol, a procedure that yields poor ultrastructural detail. Because microwave irradiation (MWI) facilitates penetration of fixatives, we have investigated whether it can improve preservation by ethanol. Rat tibiae, some labeled with tetracycline, and a human iliac crest biopsy were immersed in 70% ethanol and dehydrated, both under MWI, for a total processing time of ~7 hr. Controls were not irradiated, and all specimens were embedded in MMA at 4C. They were then processed for histomorphometry, histochemistry, structural analysis, and immunolabeling. The results showed that histological preservation was improved with MWI. Static bone formation and resorption parameters and rate of mineral apposition were similar to those of conventionally processed specimens. Mineral distribution, as visualized by von Kossa staining and backscattered electron imaging, was not affected. Alkaline phosphatase and tartrate-resistant acid phosphatase activity, as well as immunolocalization of bone sialoprotein and osteopontin, were readily visualized. Ultrastructurally, osteopontin exhibited a typical distribution in mineralization foci, between calcified collagen fibrils, and at cement lines. These data show that MWI improves preservation and permits application of a broad spectrum of analytical methodologies on the same bone sample while considerably reducing processing time.

Histological and radiological analyses of a maxillary sinus lift with extensive drilling of the schneider membrane using xenogeneic bone

The objective of this study is to report a clinical case of maxillary sinus with lyophilized, xenogeneic graft, in which, despite a large perforation of the sinus membrane, the surgery was not aborted and the results of histological examinations indicate bone neoformation in the surgical area. Results. This case showed that the biomaterials evaluated in this study and the procedure used to place them proved to be biocompatible and presented high osteogenic potential, leading to a successful surgery and osseointegration implant. Conclusion. Positioning Schneider's membrane and filling it with the graft biomaterial helped to achieve the desired osteoconduction and proliferation of bone cells even though the patient had a large perforation of the sinus membrane.

Evaluation of bone repair of critical size defects treated with simvastatin-loaded poly(lactic-co-glycolic acid) microspheres in rat calvaria

PURPOSE

Statins are hypolipemiant drugs with osteoinductive effect. We evaluated the potential of simvastatin loaded into poly(lactic-co-glycolic acid) (PLGA) microspheres to heal critical size defects in rat calvaria.

METHODS

PLGA scaffolds (50:50 ratio) were synthesized as pure membranes or as microspheres loaded with 2.5% simvastatin. Critical size defects (5-mm diameter) were created in the parietal bone of 3-month-old male Wistar rats; they were either left filled with blood clot (C group), covered with a PLGA membrane (M group) or with PLGA microspheres loaded with simvastatin (MSI group) or not (MM group), and then covered with the PLGA membrane. The defects were evaluated after 30 or 60 days by light and electron microscopy, immunohistochemistry for osteopontin (OPN), bone sialoprotein (BSP) and osteoadherin (OSAD), and immunocytochemistry for OPN.

RESULTS

Scanning electron microscopy showed that the calvarial defects treated with MSI were almost completely healed after 60 days, while groups M and C presented less bone formation, whereas the bone matrix formed into the defects of MSI group was more organized and mature. The immunolabeling for OPN and BSP on the matrix in groups C and M showed typical areas of primary bone unlike the MSI that presented weak labeling at the formed area. In the MSI group, there was an intense immunostaining for OSAD in osteoid, as well as in osteocyte cytoplasm. The immunocytochemistry showed intense labeling for OPN with homogeneous distribution in the interfibrillar spaces in all groups after 30 days and after 60 days; however, while C and M groups exhibited similar aspect, the MSI specimens showed weak labeling. The ultrastructural evaluation showed the interaction between the biomaterial and the surrounding tissue where some cells established intimate contact with microspheres.

CONCLUSIONS

The repair of critical size bone defects was accelerated and enhanced by the implantation of simvastatin-loaded PLGA microspheres.

Effects of the bisphosphonate alendronate on molars of young rats after lateral luxation

BACKGROUND AND AIM

The bisphosphonate alendronate (ALN) was employed with the aim of investigating its effects on dental and periodontal tissues after lateral luxation of developing molars.

MATERIAL AND METHODS

Twenty-one-day-old Wistar rats had their second upper molars laterally luxated. Daily 2.5 mg kg(-1) ALN injections started at the day of the luxation; controls received sterile saline solution. The teeth were analyzed 7, 14, and 21 days after the procedure. On the days cited, the maxillae were fixed, decalcified, and embedded in paraffin or Spurr resin. The paraffin sections were stained with H&E, incubated for TRAP histochemistry or immunolabeled for osteopontin (OPN). Spurr ultrathin sections were examined in a transmission electron microscope.

RESULTS

After 21 days, the root apex of luxated molars without ALN was wide open and disorganized and also covered by an irregular layer of cellular cementum, which was not observed in ALN-treated animals. Ankylosis sites were observed in ALN rats in both luxated and non-luxated teeth. The TRAP-positive osteoclasts were more numerous in ALN group, despite their latent ultrastructural appearance without the presence of resorption apparatus compared to controls. OPN immunolabeling revealed a thick immunopositive line in the dentin that must be resultant from the moment of the luxation, while ALN-treated specimens did not present alterations in dentin.

CONCLUSION

The present findings indicate that alendronate inhibits some alterations in dentin and cementum formation induced by dental trauma.

Reduced RANKL expression impedes osteoclast activation and tooth eruption in alendronate-treated rats

The creation of the eruption pathway requires the resorption of the occlusal alveolar bone by osteoclasts and signaling events between bone and dental follicle are necessary. The aim of the present study has been to evaluate the effect of alendronate on osteoclastogenesis and the expression of the regulator proteins of osteoclast activation, namely RANK, RANKL and OPG, in the bone that covers the first molar germ. Newborn Wistar rats were treated daily with 2.5 mg/kg alendronate for 4, 8, 14, 21 and 28 days, whereas controls received sterile saline solution. At the time points cited, maxillae were fixed, decalcified and processed for light and electron microscopic analysis. TRAP histochemistry was performed on semi-serial sections and the osteoclasts in the occlusal half of the bony crypt surface were counted. TUNEL analysis was carried out on paraffin sections. The occlusal bone that covers the upper first molar was removed in additional 4- and 8-day-old alendronate-treated and control rats in which the expression of RANK, RANKL and OPG was analyzed by SDS-polyacrylamide gel electrophoresis and Western blotting. TRAP-positive osteoclasts were more numerous in the alendronate group at all time points, despite their unactivated phenotype and the presence of apoptotic cells. RANKL expression in the alendronate specimens was inhibited at all time points, unlike in controls. Our findings indicate that the expression of RANKL in the occlusal portion of the bony crypt is unrelated to osteoclast recruitment and differentiation but is crucial to their activation during the creation of the eruption pathway.

Effect of alendronate on endochondral ossification in mandibular condyles of growing rats

The replacement of the calcified cartilage by bone tissue during the endochondral ossification of the mandibular condyle is dependent of the resorbing activity of osteoclats. After partial resorption, calcified cartilage septa are covered by a primary bone matrix secreted by osteoblasts. Osteoadherin (OSAD) is a small proteoglycan present in bone matrix but absent in cartilage during the endochondral ossification. The aim of this study was to analyze the effect of alendronate, a drug known to inhibit bone resorption by osteoclasts, on the endochondral ossification of the mandibular condyle of young rats, by evaluating the distribution of osteoclasts and the presence of OSAD in the bone matrix deposited. Wistar newborn rats (n=45) received daily injections of alendronate (n=27) or sterile saline solution as control (n=18) from the day of birth until the ages of 4, 14 and 30 days. At the days mentioned, the mandibular condyles were collected and processed for transmission electron microscopy analysis. Specimens were also submitted to tartrate resistant acid phosphatase (TRAP) histochemistry and ultrastructural immunodetection of OSAD. Alendronate treatment did not impede the recruitment and fusion of osteoclasts at the ossification zone during condyle growth, but they presented inactivated phenotype. The trabeculae at the ossification area consisted of cartilage matrix covered by a layer of primary bone matrix that was immunopositive to OSAD at all time points studied. Apparently, alendronate impeded the removal of calcified cartilage and maturation of bone trabeculae in the mandibular ramus, while in controls they occurred normally. These findings highlight for giving attention to the potential side-effects of bisphosphonates administered to young patients once it may represent a risk of disturbing maxillofacial development.

Immunocytochemical detection of dentine matrix protein 1 in experimentally induced reactionary and reparative dentine in rat incisors

OBJECTIVE

Although the general mechanisms of dentinogenesis are understood, several aspects regarding tertiary dentine formation still deserve investigation, especially regarding the presence and distribution of some noncollagenous matrix proteins. As dentine matrix protein 1 (DMP 1) is present in primary dentine, it is possible that this protein may also be present in the dentine matrix secreted after injury, but there are no immunocytochemical studies attempting its detection in tertiary dentine. The aim of this study was to examine the ultrastructural immunolocalization of DMP 1 in the tertiary dentine after extrusion of the rat incisor.

STUDY DESIGN

Upper incisors were extruded 3mm and then repositioned into their sockets. After several periods, the incisors were fixed and processed for transmission electron microscopy and for immunocytochemistry for DMP 1.

RESULTS

Extrusion yielded both types of tertiary dentine, which varied in aspect and related cells. DMP 1 was found in the mineralized matrix of all types of dentine, presenting high affinity for collagen, but rare colloidal gold particles over predentine. DMP 1 was evident in the supranuclear region and inside the nucleus of some odontoblast-like cells.

CONCLUSION

The observed association between DMP 1 and collagen seem to be essential for reactionary and reparative dentine formation.

Effects of alendronate on tooth eruption and molar root formation in young growing rats

Tooth eruption consists of the movement of teeth from the bony crypt in which they initiate their development to the occlusal plane in the oral cavity. Interactions between the tooth germ and its surrounding alveolar bone occur in order to offer spatial conditions for its development and eruption. This involves bone remodeling during which resorption is a key event. Bisphosphonates are a group of drugs that interfere with the resorption of mineralized tissues. With the purpose of investigating the effects of sodium alendronate (a potent bisphosphonate inhibitor of osteoclast activity) on alveolar bone during tooth development and eruption, we gave newborn rats daily doses of this drug for 4, 14, and 30 days. Samples of the maxillary alveolar process containing the tooth germs were processed for light, transmission, and scanning electron microscopy and were also submitted to tartrate-resistant acid phosphatase histochemistry and high-resolution colloidal-gold immunolabeling for osteopontin. Inhibition of osteoclast activity by sodium alendronate caused the absence of tooth eruption. The lack of alveolar bone remodeling resulted in primary bone with the presence of latent osteoclasts and abundant osteopontin at the interfibrillar regions. The developing bone trabeculae invaded the dental follicle and reached the molar tooth germs, provoking deformities in enamel surfaces. No root formation was observed. These findings suggested that alendronate effectively inhibited tooth eruption by interfering with the activation of osteoclasts, which remained in a latent stage.

Ultrastructural and immunocytochemical analyses of osteopontin in reactionary and reparative dentine formed after extrusion of upper rat incisors

Reactionary dentine and reparative dentine are two strategies used by the dentine-pulp complex to respond to injury. The reactionary dentine is secreted by original odontoblasts, while the reparative dentine is formed by odontoblast-like cells. Osteopontin (OPN) is a non-collagenous protein usually present in the repair of mineralized tissues. It is likely to be present in newly formed dentine but there are no studies attempting to detect it in reactionary and reparative dentine. The aim of the present study was to examine the ultrastructural characteristics, as well as the presence and distribution of OPN in reactionary and reparative dentine by provoking extrusion of the rat incisor. The right upper incisors of 3-month-old male rats were extruded 3 mm and then repositioned into their original sockets. At 3, 7, 10, 15, 20, 30 and 60 days after surgery, the incisors were fixed in glutaraldehyde-formaldehyde and then processed for scanning and transmission electron microscopy and for immunocytochemistry for OPN. After extrusive trauma, the dentine-pulp interface showed the presence of reactionary and reparative dentine, which varied in aspect, thickness and related cells. OPN was not detected in the physiological and reactionary dentine, while it was strongly immunoreactive in the matrix that surrounded the entrapped cells of reparative dentine. In addition, original odontoblasts subjacent to the physiological dentine contained OPN in their Golgi region. The present findings showed that reparative dentine shares some structural characteristics with primary bone, especially in relation to its OPN content. The odontoblast-like cells resemble osteoblasts rather than odontoblasts.

Effects of low-power red laser on dentine–pulp interface after cavity preparation. An ultrastructural study

OBJECTIVE

Studies on the influence of low-power red laser on the repair of dental structures are very scarce. This study investigated the effects of the laser therapy on the ultrastructure of the dentine-pulp interface after conservative class I cavity preparation.

DESIGN

Two female volunteers with 8 premolars indicated for extraction for orthodontic reasons were recruited. Class I cavities were prepared and the teeth were randomly divided into two groups. The first group received treatment with a GaA1As laser, lambda=660nm, power of 30mW and energy dose of 2J/cm(2), directly and perpendicularly into the cavity in a single visit. After the irradiation, the cavities were filled with composite resin. The second group received the same treatment, except by the laser therapy.

RESULTS

Twenty-eight days post-preparation, the teeth were extracted and processed for transmission electron microscopy analysis. Two sound teeth, without cavity preparation, were also studied. The irradiated group presented odontoblast process in higher contact with the extracellular matrix and the collagen fibrils appeared more aggregated and organised than those of control group. These results were also observed in the healthy teeth.

CONCLUSION

These findings suggest that laser irradiation accelerates the recovery of the dental structures involved in the cavity preparation at the predentine region.

Root resorption repair in mandibular first premolars after rotation. A transmission electron microscopy analysis combined with immunolabeling of osteopontin

INTRODUCTION

A previous study with scanning electron microscopy showed that orthodontic root resorption occurs at the lateral surfaces of premolar roots for 2 to 6 weeks after orthodontic rotation. The purpose of this investigation was to observe how resorbed cementum repairs during rotation movement.

METHODS

Twenty-one mandibular first premolars from 12 patients, orthodontically indicated for extraction, were used. They were intra-individually divided into 2 groups: 8 teeth were not moved (control group), and 13 were rotated (experimental group). In the experimental group, a rotational force (25 g both buccally and lingually) with a precise biomechanical model, individually calibrated, was applied for 2, 3, 4, or 6 weeks. After extraction, the teeth were fixed and decalcified, and 8 were conventionally processed for transmission electron microscopy, and 13 teeth were processed for high-resolution immunocytochemistry by using an antibody against osteopontin. The samples were analyzed in a transmission electron microscope.

RESULTS

This examination showed areas of repair in previously resorbed lacunae in the experimental group. Both the clastic cells and the root surface showed immunolabeling for osteopontin. In addition to areas of cementum resorption and various degrees of cell and extracellular matrix degeneration, active cementoblasts and fibroblasts in several stages of differentiation and activity appeared adjacent to newly synthesized collagen fibers, thus reestablishing the function of the periodontal ligament.

CONCLUSIONS

We concluded that cementum repair occurs after resorption during rotation movement and that noncollagenous matrix protein osteopontin plays a role in both resorbing and repairing.

Immunocytochemical Study of Amelogenin Deposition during the Early Odontogenesis of Molars in Alendronate-treated Newborn Rats

Newborn rats were treated with sodium alendronate to study how enamel is formed and the effect of alendronate during early odontogenesis. Ultrastructural analysis combined with high-resolution immunocytochemistry for amelogenin was carried out. Twelve rats were subjected to daily SC injections of sodium alendronate (2.5 mg/kg/day) for 3 days on their dorsal region, whereas three rats were daily injected with saline solution as a control. Molar tooth germs from 3-day-old rats were fixed under microwave irradiation in 0.1% glutaraldehyde + 4% formaldehyde buffered at pH 7.2 with 0.1 M sodium cacodylate. The specimens were left undecalcified, postfixed with osmium tetroxide, dehydrated, and embedded in LR White resin. Ultrathin sections were incubated with a chicken anti-24-kDa rat amelogenin antibody, a secondary antibody, and finally with a protein A-gold complex. Large patches of amelogenin were present over the unmineralized mantle dentin and at early secretory ameloblasts. At more advanced stages, they were also detected at the enamel matrix, as well as in the mineralized dentin, at the periodontoblastic space of the dentinal tubules, and at the predentin. It is likely that the main effect of alendronate at early stages of odontogenesis is the increase of synthesis/secretion of amelogenin, promoting its deposition within the forming dentin and enamel.

Developmental appearance of dentin matrix protein 1 during the early dentinogenesis in rat molars as identified by high-resolution immunocytochemistry

Dentin matrix protein 1 (DMP 1) is an acidic phosphoprotein that has been postulated to play an important role in mineralized tissue formation. We have examined rat molar tooth germs by applying a high-resolution immunocytochemical approach with the purpose to identify the temporal and spatial localization of DMP 1 at the onset of dentinogenesis. Upper molar tooth germs of 2- to 3-day-old Wistar rats were fixed in a cacodylate-buffered 0.1% glutaraldehyde + 4% formaldehyde fixative, left unosmicated and embedded in LR White resin. The sections were incubated with a polyclonal DMP 1 antibody for postembedding colloidal gold immunolabeling and examined in a Jeol 1010 transmission electron microscope. The earliest localization of DMP 1 was in the Golgi region as well as in the nucleus of differentiating odontoblasts. When mineralization spread from matrix vesicles to the surrounding matrix, DMP 1 was extracellularly detected around the mineralizing globules. In the regions of fully mineralized mantle dentin, it was present in the mineralized regions, mainly around the peritubular dentin. The appearance of DMP 1 during early dentinogenesis implies a direct role for this protein in both odontoblast differentiation and matrix mineralization.

Immunocytochemical examination of the presence of amelogenin during the root development of rat molars

The presence of enamel proteins, especially amelogenins, during root development has been a subject of controversy for a long time. Whereas some studies have reported the presence of enamel proteins on the root surface, others were not able to detect them at these places. Since microwave (MW) processing has been shown to improve the antigen retention in mineralised tissues, we have applied MW techniques to ultrastructurally analyse the presence of amelogenin during root formation in rat molars. Upper molar tooth germs from 12 and 13-day-old Wistar rats were fixed in 0.1% glutaraldehyde + 4% formaldehyde under MW irradiation. They were then decalcified in 4.13% EDTA, dehydrated in graded concentrations of ethanol and embedded in LR White Resin. Ultrathin sections were processed for post-embedding colloidal gold immunolabelling using a chicken egg yolk antibody against a 24 kDa rat amelogenin. Then, the grids were incubated with a rabbit anti-chicken IgG secondary antibody and with a protein A-gold complex. The immunoreactivity for 24-kDa amelogenin was detected in the cytoplasm of the epithelial diaphragm cells--the most apical portion of the Hertwig's epithelial root sheath (HERS), and in less amounts on the adjacent dental papilla extracellular matrix. Amelogenin was no longer observed at advanced stages of root dentinogenesis or later, during cementogenesis. The restricted presence of amelogenin at the early stages of root formation suggests that this protein may play a role in the differentiation of ectomesenchymal cells into root odontoblasts.

Ultrastructure of bone healing in defects grafted with a copolymer of polylactic/polyglycolic acids

Bone substitutes have been used for the treatment of bone defects. The objective of this study was to ultrastructurally evaluate the healing pattern of bone defects filled with a copolymer of polylactic/polyglycolic acid (FisiograftR) at a time point in which it is expected to be only partially degraded, with the purpose to ultrastructurally analyze how the bone is forming around the grafting material. Three 5-mm-diameter bone defects were created in each tibia from 5 rabbits (average weight 2.5 kg) in which the material was randomly implanted. Animals were sacrificed 30 days after surgery and the 30 bone defects were fixed in 2% glutaraldehyde-2.5% formaldehyde, under microwave irradiation, decalcified in EDTA, embedded in Spurr resin, and examined in a Jeol 1010 TEM. All the bone defects were filled with connective tissue, interspersed with different amounts of the filling material and newly formed bone trabeculae. In areas where the degrading copolymer was present in small amounts, newly formed bone matrix was detected; it was deposited by osteoblast-like cells in close relation to the copolymer. In areas where the degrading copolymer formed accumulates, an amorphous multilayered material was identified between the connective tissue and the copolymer. In summary, the copolymer of PLA/PGA studied appears to be an osteoconductive material when it is used to fill bone defects.

Ultrastructural and histochemical examination of alveolar bone at the pressure areas of rat molars submitted to continuous orthodontic force

It is usually believed that repair in alveolar bone during orthodontic movement occurs after decreasing of force. However, we have recently observed signs of repair in previously resorbed cementum from human teeth exposed to continuous forces. In order to test the hypothesis that bone resorption and deposition occur concomitantly at the pressure areas, a continuous 15 cN force was applied in a buccal direction to upper first molars from eight 2.5-month-old male Wistar rats for 3 d (n = 4) and 7 d (n = 4). As a control, two additional rats did not have their molars moved. Maxillae were fixed in 2% glutaraldehyde + 2.5% formaldehyde, under microwave irradiation, decalcified in ethylenediaminetetraacetic acid, and processed for transmission electron microscopy. Specimens from one rat from each group were processed for tartrate-resistant acid phosphatase (TRAP) histochemistry. At both the times studied, the alveolar bone surface at the pressure areas showed numerous TRAP-positive osteoclasts, which were apposed to resorption lacunae. In addition, osteoblasts with numerous synthesis organelles were present in the neighboring areas overlying an organic matrix. Thus, this study provides evidence that the application of continuous forces produces concomitant bone resorption and formation at the pressure areas in rat molars.

Cytochrome oxidase activity and confocal laser scanning microscopic analysis of the hamster submandibular gland using microwave irradiated fixation

Submandibular glands of the hamster were irradiated in 2% paraformaldehyde (pFA)-0.5% pure glutaraldehyde (PGA) with a microwave (MW) processor at temperatures of 10 degrees and 37 degrees C. Electron microscopy showed that cytochrome oxidase activity was taking place in the mitochondrial intermembrane-intracristal space of the granular duct cell when the temperature of the MW-irradiated fixatives was at 10 degrees C. However, a decrease of this activity was observed when we took care to keep the temperature of the MW-irradiated fixatives at 37 degrees C. The distinct reduction of cytochrome oxidase activity allowed by MW irradiation seems to be due the thermal affects of fixatives. Of course, the possibility cannot be excluded that MW irradiation caused other undetectable membrane damage. Then, we used confocal laser scanning microscopy for the preservation check of the mitochondrial membrane for cytochemistry with MW-irradiated fixation. The fluorescence of rhodamine 123 was observed in the inner spaces of the mitochondria at temperatures of 10 degrees and 37 degrees C. When the same tissues were fixed with 2% pFA using an MW processor as the sole fixative at 10 degrees C, no mitochondrial fluorescence was observed. Cytochrome oxidase activity, by contrast, could be seen in the mitochondrial intermembrane-intracristal spaces in the same condition. Formaldehyde is not the best aldehyde for the purpose of ultrastructural preservation. On the other hand, light and electron microscopy showed that the endogenous peroxidase activity was localized in the nuclear envelope, endoplasmic reticulum, secretory granules, and Golgi apparatus of the hamster submandibular gland using 2% pFA-0.5% PGA fixative with and without MW irradiations at temperatures of 10 degrees and 37 degrees C. Some of the same cells were fixed with only 2% pFA under MW irradiation at 10 degrees C; however, marked diffuseness of the peroxidase activity was observed. Therefore, these results indicated that cytochrome oxidase activity was sensitive to heat with MW-irradiated fixation. Peroxidase activity was very resistant to heat with MW-irradiated fixation but not with pFA solo fixation, therefore, PGA had to be used.

High-resolution immunocytochemistry of noncollagenous matrix proteins in rat mandibles processed with microwave irradiation

The mineral phase in calcified tissues represents an additional factor to be considered during their preservation for ultrastructural analyses. Microwave (MW) irradiation has been shown to facilitate fixative penetration and to improve structural preservation and immunolabeling in a variety of soft tissues. The aim of the present study was to determine whether MW processing could offer similar advantages for hard tissues. Rat hemimandibles were immersed in 4% formaldehyde + 0.1% glutaraldehyde buffered with 0.1 M sodium cacodylate, pH 7.2, and exposed to MWs for three periods of 5 min at temperatures not exceeding 37C. They were then decalcified in 4.13% EDTA, pH 7.2, for 15 hr, also under MW irradiation. Osmicated and non-osmicated samples were dehydrated in graded concentrations of ethanol and embedded in LR White resin. Sections of incisor, molars, and alveolar bone were processed for postembedding colloidal gold immunolabeling using antibodies against ameloblastin, amelogenin, bone sialoprotein, or osteopontin. Ultrastructural preservation of tissues was in most cases comparable to that obtained by perfusion-fixation, and there was no difference in distribution of labeling with those previously reported for the antibodies used. However, the immunoreactivities obtained were generally more intense, particularly at early stages of tooth formation. Amelogenin was abundant between differentiating ameloblasts and labeling for osteopontin appeared over the Golgi apparatus of odontoblasts after initiation of dentine mineralization. We conclude that MW irradiation represents a simple method that can accelerate the processing of calcified tissues while yielding good structural preservation and antigen retention. (J Histochem Cytochem 49:1099-1109, 2001)

Lysine: Is it worth more?

Lysine, an essential cationic amino acid, has a positively charged R group. The structure of lysine is given as (H(3)N(+)-)CH(-COO(-))-CH(2)-CH(2)-CH(2)-CH(2)-N(+)H(3).While the anabolic role(s) of the molecule has been in focus for quite a few decades now, its biological properties, e.g. role in cellular proliferation in vitro (both anchorage dependent and anchorage independent) and in vivo, its ability to induce strong inflammatory and immune responses - both humoral and cell mediated, its role in augmented healing of all types of wounds in animal models as well as in human subjects (both acute and chronic), as well as its role in inducing extensive angiogenic responses, have never received reasonable attention so far. In the current brief and indicative review (rather than exhaustive reviews of each area), we intend to bring these biological properties of the molecule to focus while discussing a few other interesting aspects - lysine as a food preservative as well as its possible role(s) in immune therapy. While the areas look extremely divergent, we propose a common denominator in the form of a possible molecular mechanism of action of the molecule in all these diverse situations.