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PubMed2005

Tissue engineering for periodontal regeneration.

As a result of periodontal regeneration research, a series of clinical techniques have emerged that permit tissue engineering to be performed for more efficient regeneration and repair of periodontal defects and improved implant site development. Historically, periodontal regeneration research has focused on a quest for "magic filler" material. This search has led to the development of techniques utilizing autologous bone and bone marrow, allografts, xenografts, and various man-made bone substitutes. Though these techniques have had limited success, the desire for a more effective regenerative approach has resulted in the development of tissue engineering techniques. Tissue engineering is a relatively new field of reconstructive biology which utilizes mechanical, cellular, or biologic mediators to facilitate reconstruction/regeneration of a particular tissue. In periodontology, the concept of tissue engineering had its beginnings with guided tissue regeneration, a mechanical approach utilizing nonresorbable membranes to obtain regeneration in defects. In dental implantology, guided bone regeneration membranes +/- mechanical support are used for bone augmentation of proposed implant placement sites. With the availability of partially purified protein mixture from developing teeth and growth factors from recombinant technology, a new era of tissue engineering whereby biologic mediators can be used for periodontal regeneration. The advantage of recombinant growth factors is this tissue engineering device is consistent in its regenerative capacity, and variations in regenerative response are due to individual healing response and/or poor surgical techniques. In this article, the authors review how tissue engineering has advanced and discuss its impact on the clinical management of both periodontal and osseous defects in preparation for implant placement. An understanding of these new tissue engineering techniques is essential for comprehending today's ever-expanding oral plastic surgery procedures.

Algorithms↗
PubMed1983

The regeneration of skeletal muscle fibers following injury: a review.

Regeneration is a unique adaptation of skeletal muscle that occurs in response to injury. Following direct trauma or disease, regeneration results in restoration, to some degree, of the original structure and function of the muscle. Our purpose is to summarize the main features of the regeneration of skeletal muscle fibers and entire muscles with an emphasis on aspects of regeneration that may be important to the understanding and treatment of sports injuries. The regeneration of skeletal muscle is compared structurally and functionally with its embryonic development. The free muscle graft is used as a model to illustrate the integration of regenerating muscle with the rest of the body. Finally, the breakdown and regeneration of skeletal muscle fibers are discussed in relation to local anesthetics, sports injuries, and disease.

Anesthetics, Local↗
PubMed1984

Effects of radius--ulna removal on forelimb regeneration in Xenopus laevis froglets.

Regeneration of boneless amputated forearms of adult newts was found to progress at a rate and to a degree comparable to amputated control limbs in which stump bones were not removed. In contrast, regeneration of boneless amputated Xenopus froglet forearms was significantly delayed and did not occur until two to three weeks following amputation. This is in comparison with the initiation of distal cartilage formation observed one week postamputation in control forelimbs of Xenopus froglets. The regeneration of cartilage in boneless forearms of adult newts was found to occur distal to the amputation level. In contrast, distal as well as proximal (centripetal) regeneration of cartilage was observed in the amputated boneless forearms of Xenopus. In froglets and newts, unamputated forelimbs in which forearm bones were extirpated did not initiate cartilage regeneration. Our findings support the hypothesis that forelimb regeneration in Xenopus froglets is primarily a tissue response. In comparison, limb regeneration in the adult newt is predominantly an epimorphic response.

Animals↗
PubMedDate not supplied

Treatment of peri-implantitis using guided bone regeneration and bone grafts, alone or in combination, in beagle dogs. Part 1: Clinical findings and histologic observations.

The purpose of this study was to evaluate and compare the treatment of ligature-induced peri-implantitis using guided bone regeneration and two bone grafts alone and in combination. Mandibular premolars and first molars were extracted from four beagle dogs and after 3 months of healing, three Brånemark implants were placed on each side of the mandibles. Following abutment connection 3 months later, experimental peri-implantitis was induced by tying plaque-retentive ligatures around all abutments. Ligatures and abutments were removed after 3 months, and bony defects measured and treated with either: (1) debridement only; (2) debridement plus resorbable hydroxyapatite; (3) debridement plus canine freeze-dried demineralized bone; (4) debridement plus guided bone regeneration; (5) debridement plus resorbable hydroxyapatite and guided bone regeneration; or (6) debridement plus canine freeze-dried demineralized bone and guided bone regeneration. Pretreatment and 4-month-posttreatment comparison revealed a significant but variable degree of clinically appreciable hard tissue fill with all treatment procedures. Guided bone regeneration procedures resulted in the greatest fill, followed by bone grafts alone and flap debridement. There was no significant difference between guided bone regeneration and both guided bone regeneration/graft combinations; therefore, guided bone regeneration procedures appear to be a predictable treatment for plaque-induced peri-implant defects.

Alveolar Bone Loss↗
PubMed2004

Artificial liver support: potential to retard regeneration?

HYPOTHESIS: The concept of an "artificial liver" has been in development for over 40 years. Such devices aim to temporarily assume metabolic and excretory functions of the liver, with removal of potentially hepatotoxic substances, thereby clinically stabilizing patients and preventing deterioration while awaiting transplantation. If sufficient numbers of viable hepatocytes remain, regeneration and subsequent recovery of innate liver function may occur. However, these devices have not yet become part of routine clinical use. Much less is known regarding the effect such devices have, if any, on circulating cytokines and growth factors and the subsequent effects on the regenerating liver. If these devices remove or reduce factors known to promote regeneration, is the rate of regeneration retarded? Conversely, does the incorporation of hepatocytes into bioartificial support systems confer an advantage through the production of growth-promoting factors from these cultured hepatocytes?Data Sources, Extraction, and STUDY SELECTION: Data were obtained using PubMed search for reports involving liver support, extracorporeal circuits, dialysis, growth factors, and cytokines. Those reports specifically looking at the effect of artificial liver support on cytokines and growth factors are discussed. CONCLUSIONS: There is a paucity of information on the key events and substances involved in hepatic regeneration. In addition, there is a potential impact of liver support devices on the regeneration of substances associated with hepatic regeneration. Further study is needed.

Growth Substances↗
PubMed1996

Tuberous electroreceptor organs form in denervated regenerating skin of a weakly electric fish.

Weakly electric fish use tuberous electroreceptor organs to detect their own electric fields. We investigated the role of innervation upon regeneration and differentiation of tuberous electroreceptor organs. The left, infraorbital, anterior lateral line nerve of brown ghosts (Apteronotus leptorhynchus) was sectioned, and the proximal stump was dipped in ricin to prevent regrowth. Immediately after denervation, a piece of cheek skin (approximately 0.5 cm2) was removed bilaterally to induce skin regeneration. After survival periods of 3, 4, or 5 weeks, regenerated skin from the left (denervated) and the right (reinnervated) sides was removed and processed for immunocytochemistry or electron microscopy. Tuberous electroreceptor organs were present in regenerated reinnervated, as well as regenerated denervated skin patches at all survival times. With increased time after skin removal, the number of fully differentiated organs increased in the reinnervated regenerated skin while the number of organs with degenerating receptor cells or entirely devoid of receptor cells increased in the denervated regenerated skin. These results suggest that innervation is not essential for tuberous electroreceptor organ development, but that it is necessary for complete sensory cell differentiation and long-term survival.

Animals↗
PubMed1997

Reactivation and graded axial expression pattern of Wnt-10a gene during early regeneration stages of adult tail in amphibian urodele Pleurodeles waltl.

Adult urodele amphibians such as Pleurodeles waltl are able to regenerate their amputated limbs or tail. The mechanisms implicated in growth control and formation of the blastema are unknown but it has been proposed that regeneration in newts may proceed through reactivation of genes involved in embryonic development. Knowing the role of Wnt genes in the patterning of the primary and secondary axes of the vertebrate embryo, we suspected that some of these genes could be involved in axial pattern during newt tail regeneration. Pwnt-10a gene, cloned from a newt tail regenerate cDNA library, showed an expression pattern compatible with such a role in tail regenerates. Pwnt-10a, which is highly expressed during embryonic development (from gastrula to tailbud-stage) and weakly expressed in the adult tail, is strongly re-expressed during tail regeneration. In the blastemal mesenchyme Pwnt-10a transcripts exhibited a graded distribution along the antero-posterior axis, the mRNA accumulation being maximal in the caudal most part corresponding to the growing zone. These findings strongly support the view that Pwnt-10a may act in cooperation with other factors to control growth and patterning in newt tail regeneration. Until now Wnt-10a was only known to be involved in central nervous system development; our results suggest that this gene may also play a role in other developmental processes.

Aging↗
PubMed1997

Possible roles for Wnt genes in growth and axial patterning during regeneration of the tail in urodele amphibians.

Urodele amphibians are nearly the only adult vertebrates able to regenerate their missing or amputated tail. An interesting aspect of this biological model lies in the ability of regenerates to differentiate the spinal cord (SC), the vertebral cartilage, and muscles. The main questions addressed in this study concern the possible roles of Wnt genes in these regenerative processes. We have previously reported the expression pattern of a Pleurodeles Waltl wnt-10a gene (Pwnt-10a) in tail blastema (Caubit et al. [1997] Dev. Dyn. 208:139-148). We report here the cloning and tissue distribution of three additional Wnt genes (Pwnt-5a, Pwnt-5b, and Pwnt-7a) in adult and regenerating tail tissues and in the central nervous system (CNS) of adult newt. In adult and regenerating tails, Pwnt-5a and Pwnt-5b transcripts exhibit a graded distribution along the antero-posterior (A-P) axis, the maximal accumulation of these transcripts being detected in the mesenchyme within the subectodermal apical region of the normal tail and blastema. In contrast to Pwnt-5a and Pwnt-5b, Pwnt-7a is expressed in adult normal tail skin and in the epidermis of the regenerating tail. In the adult CNS, Pwnt-5a, Pwnt-5b, Pwnt-7a, and Pwnt-10a genes are expressed in sharp overlapping but not identical domains along the A-P axis. The sustained expression of Wnt genes in the adult newt and the spatial distribution of transcripts in adult and regenerating tail tissues suggest roles of these genes in continuous growth capacities in the urodeles and may explain the ability for CNS and tail regeneration.

Amino Acid Sequence↗
PubMed1998

Regulation of lens regeneration by fibroblast growth factor receptor 1.

Lens regeneration in vivo is restricted to some urodeles only. After removal of the lens, this remarkable event is initiated from the dorsal iris. The pigmented epithelial cells from the dorsal iris dedifferentiate and subsequently transdifferentiate to form the regenerating lens. This property of the dorsal iris implies specific regulation along the dorsal-ventral axis. To date, no known genes are known to be specifically expressed in the dedifferentiating cells and to be involved in lens regeneration. In this paper, we show that FGFR-1 expression and function is correlated with the process of lens regeneration from the dorsal iris. Following lentectomy, FGFR-1 protein is specifically present in the dedifferentiating pigment epithelial cells in the dorsal iris, but is absent from the ventral iris. Subsequently, FGFR-1 protein is present throughout the process of lens regeneration and fiber differentiation. Furthermore, we show that an FGFR-1-specific inhibitor is able to inhibit the process of transdifferentiation and lens regeneration. In this sense, FGFR-1 can be regarded as the first known lens regeneration-associated factor.

Animals↗
PubMed1996

Leukemia inhibitory factor and interleukin-6 are produced by diseased and regenerating skeletal muscle.

The process of skeletal muscle regeneration following injury or disease involves locally produced growth factors which control cellular proliferation and differentiation. Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) have previously been shown to promote the proliferation of myoblasts in vitro, and thus may be involved in muscle regeneration. In the present investigation, the in vivo expression of these two myogenic growth factors was examined in regenerating muscle after a crush injury of wild type mice, and in diseased skeletal muscle and diaphragm of the mdxmouse. Using Reverse transcription polymerase chain reaction we have demonstrated that while normal muscle rarely expresses mRNA for these two molecules, there is significant up-regulation following injury, coinciding with the active period of muscle regeneration. This suggests these molecules act as locally produced trauma factors. This observation is reinforced in mdxmouse muscle, which is undergoing a cycle of degeneration and regeneration, and expresses both LIF and IL-6. Using in situ hybridization we have localized mRNA for LIF expression in the mdx diaphragm, suggesting that local production of these molecules by regenerating muscle itself, as well as by other cells in muscle, plays an important role in muscle regeneration.

Animals↗
PubMed1999

Role of thyroid hormones and their receptors in peripheral nerve regeneration.

After peripheral nerve injury in adult mammals, reestablishment of functional connections depends on several parameters including neurotrophic factors, the extracellular matrix, and hormones. However, little is known about the contribution of hormones to peripheral nerve regeneration. Thyroid hormones, which are required for the development and maturation of the central nervous system, are also important for the development of peripheral nerves. The action of triiodothyronine (T3) on responsive cells is mediated through nuclear thyroid hormone receptors (TRs) which modulate the expression of specific genes in target cells. Thus, to study the effect of T3, it is first necessary to know whether the target tissues possess TRs. The fact that sciatic nerve cells possess functional TRs suggests that these cells can respond to T3 and, as a consequence, that thyroid hormone may be involved in peripheral nerve regeneration. The silicone nerve guide model provides an excellent system to study the action of local administration of T3. Evidence from such studies demonstrate that animals treated locally with T3 at the level of transection have more complete regeneration of sciatic nerve and better functional recovery. Among the possible regulatory mechanisms by which T3 enhances peripheral nerve regeneration is rapid action on both axotomized neurons and Schwann cells which, in turn, produce a lasting and stimulatory effect on peripheral nerve regeneration. It is probable that T3 up- or down-regulates gene expression of one or more growth factors, extracellular matrix, or cell adhesion molecules, all of which stimulate peripheral nerve regeneration. This could explain the greater effect of T3 on nerve regeneration compared with the effect of any one growth factor or adhesion molecule.

Animals↗
PubMed2000

Tissue specificity in rat peripheral nerve regeneration through combined skeletal muscle and vein conduit grafts.

Diffusible factors from the distal stumps of transected peripheral nerves exert a neurotropic effect on regenerating nerves in vivo (specificity). This morphological study was designed to investigate the existence of tissue specificity in peripheral nerve fiber regeneration through a graft of vein filled with fresh skeletal muscle. This tubulization technique demonstrated experimental and clinical results similar to those obtained with traditional autologous nerve grafts. Specifically, we used Y-shaped grafts to assess the orientation pattern of regenerating axons in the distal stump tissue. Animal models were divided into four experimental groups. The proximal part of the Y-shaped conduit was sutured to a severed tibial nerve in all experiments. The two distal stumps were sutured to different targets: group A to two intact nerves (tibial and peroneal), group B to an intact nerve and an unvascularized tendon, group C to an intact nerve and a vascularized tendon, and group D to a nerve graft and an unvascularized tendon. Morphological evaluation by light and electron microscopy was conducted in the distal forks of the Y-shaped tube. Data showed that almost all regenerating nerve fibers spontaneously oriented towards the nerve tissue (attached or not to the peripheral innervation field), showing a good morphological pattern of regeneration in both the early and late phases of regeneration. When the distal choice was represented by a tendon (vascularized or not), very few nerve fibers were detected in the corresponding distal fork of the Y-shaped graft. These results show that, using the muscle-vein-combined grafting technique, regenerating axons are able to correctly grow and orientate within the basement membranes of the graft guided by the neurotropic lure of the distal nerve stump.

Animals↗
PubMed2000

Induction of lef1 during zebrafish fin regeneration.

Because the transcription factor Lef1 is important for development of several vertebrate organs but has not been investigated for involvement in epimorphic regeneration, we examined its expression during regeneration of amputated adult zebrafish caudal fins. We found that lef1 is markedly up-regulated in the newly formed wound epidermis of the fin regenerate and is maintained in the basal epidermal layer during formation of the regeneration blastema. During regenerative outgrowth, lef1 expression is strongest in epidermal cells adjacent to newly aligned scleroblasts that secrete bone matrix, while it is low or undetectable in epidermis adjacent to mesenchymal areas with either mature bone or proliferative distal blastema cells. This localization is similar to that of the putative fin ray patterning signal Shh. In addition, brief treatments of fin regenerates with retinoic acid or the synthetic Fgfr1 inhibitor SU5402 down-regulate epidermal lef1, similar to their effects on shh. These results suggest a role for Lef1 in scleroblast alignment analogous to that proposed for Shh. Other Wnt signaling pathway members wnt3a, wnt5, and beta-catenin are also expressed in the fin regenerate. Our data suggest that Lef1 has specific roles in inducing and patterning vertebrate regenerating tissue.

Animals↗
PubMed2000

Reciprocal interactions between perisynaptic Schwann cells and regenerating nerve terminals at the frog neuromuscular junction.

The perisynaptic Schwann cell (PSC) has gained recent attention with respect to its roles in synaptic function, remodeling, and regeneration at the vertebrate neuromuscular junction (NMJ). Here we test the hypothesis that, following nerve injury, processes extended by PSCs guide regenerating nerve terminals (NTs) in vivo, and that the extension of sprouts by PSCs is triggered by the arrival of regenerating NTs. Frog NMJs were double-stained with a fluorescent dye, FM4-64, for NTs, and fluorescein isothiocyanate (FITC)-tagged peanut agglutinin (PNA) for PSCs. Identified NMJs were imaged in vivo repeatedly for several months after nerve injury. PSCs sprouted profusely beginning 3-4 weeks after nerve transection and, as reinnervation progressed, regenerating NTs closely followed the preceding PSC sprouts, which could extend tens to hundreds of microns beyond the original synaptic site. The pattern of reinnervation was dictated by PSC sprouts, which could form novel routes joining neighboring junctions or develop into new myelinated axonal pathways. In contrast to mammals, profuse PSC sprouting in frog muscles was not seen in response to axotomy alone, and did not occur at chronically denervated NMJs. Instead, sprouting coincided with the arrival of regenerating NTs. Immunofluorescent staining revealed that in muscle undergoing reinnervation 4 weeks after axotomy, 91% of NMJs bore PSC sprouts, compared to only 6% of NMJs in muscle that was chronically denervated for 4 weeks. These results suggest that reciprocal interactions between regenerating NTs and PSCs govern the process of reinnervation at frog NMJs: regenerating NTs induce PSCs to sprout, and PSC sprouts, in turn, lead and guide the elaboration of NTs.

Animals↗
PubMed1980

Fine structure of the surfaces of the epithelium and mesenchyme of the newt limb regenerate, separated in salt solution: 14 to 25 days.

Forelimbs of the newt Notophthalmus (Triturus) viridescens were amputated at the wrist, and at 14 to 25 days, the new limb regenerates were removed by a razor-blade cut. After incubation of the isolated regenerates in a medium containing only inorganic salts, the epithelium was removed easily from the underlying mesenchyme. The surfaces separated in the salt solution were examined using scanning and transmission electron microscopy to evaluate the completeness of the separation and the extent of tissue damage near the plane of separation. Rarely was an epithelial cell found clinging to the mesenchymal surface, supporting previous light microscopic observations. The most apparent morphological damage was sustained by the basal epithelial cell surfaces, which exhibited blebbing; the formation of vacant vesicles within the cytoplasm near the newly exposed plasma membranes; the structural disruption of some organelles; and the tearing away of fragments of the basal epithelial cell plasma membranes, which remained adherent to the mesenchymal surface during separation procedure. Examination of the structure of the epithelial-mesenchymal interface of intact regenerates showed that the plane of epithelial-mesenchymal separation was, for the most part, between the basal epithelial cell membrane and its substrate, an extracellular material which remained at the mesenchymal surface after separation. This substrate was in the form of an extracellular material closely adherent to the basal epithelial cell membrane at the distal tips of the regenerates; a developing basal lamina at the periphery of regenerates undergoing blastema accumulation; or a mature basal lamina at the base of digit stage regenerates. The usefulness of these separated tissues for future experimentation and the evaluation of the nature of the epithelial substratum throughout the course of limb regeneration are discussed.

Animals↗
PubMed1986

Regeneration of growth plates in the long bones of the neonatal rat hindlimb.

Twenty-seven male albino rats underwent hindlimb amputations through the lower femur or the midshaft of the tibiofibula on the tenth to 12th day of life. Amputation stumps were examined grossly and histologically in order to assess the significance of level and angle of transaction as determinants of subsequent growth and regeneration and to ascertain whether growth plates can regenerate following their complete excision. Amputees survived for 17-73 days. In order to exclude limbs which had been severed at or distal to the level of the growth plate, amputated limb segments either were cleared to transparency and inspected under low magnification or were sectioned serially and examined by using a compound microscope. Following amputations through the femur, the predominant response involved repair of the skeletal defect and healing of adjacent soft tissues (ten of 17 rats). Among five other animals the skeletal terminus was covered with a plate of cartilage which, in three, included areas of growth-plate architecture. Two additional transfemoral amputees regenerated incomplete growth plates, each overlying a single epicondylar surface, and one provided with a regenerated hemiepiphysis. Five of ten transtibiofibular amputees formed cartilage plates which covered the skeletal terminus in whole or in part and one regenerated an entire growth plate restricted to the distal fibula. It is concluded that angle and level of transection are not pivotal modifiers of growth and regeneration processes, and that distal growth plates may regenerate entirely or in part following their complete removal from the hindlimb.

Amputation, Surgical↗
PubMed1992

Effects of tunicamycin on retinoic acid induced respecification of positional values in regenerating limbs of the larval axolotl, Ambystoma mexicanum.

Urodele amphibians possess a remarkable ability to regenerate limbs following experimental or accidental amputation. Since only those parts of the limb distal to the plane of amputation usually regenerate, this suggests the existence of level-specific positional values within the cells of the limb. Vitamin A and other retinoids respecify the positional values of regenerating limbs such that structures proximal to the actual plane of amputation are formed in the regenerating limb producing proximodistal duplications. Regenerating limbs of larval axolotls (Ambystoma mexicanum) treated with sufficient retinoic acid to induce proximodistal duplication were also treated via implantation with tunicamycin, a drug which blocks the synthesis of glycoproteins by blocking N-glycosylation of proteins. Tunicamycin was shown to inhibit the proximalizing effects of retinoic acid. This indicates that asparagine-linked glycoproteins may be essential to the process through which retinoic acid induces these effects in the regenerating limb and that glycoproteins may be responsible for specifying positional values in regeneration blastema cells.

Ambystoma↗
PubMed1982

Comparison of lens regeneration in adult newts, Triturus viridescens, between light and dark preadapted and non-preadapted animals.

It is well known that if the original lens is removed from the eyeball in certain Urodeles, a new lens will regenerate from the dorsal iris. Experiments were designed to study the different effects on lens regeneration in the newt, Triturus viridescens, between the light and dark preadapted animals and light and dark non-preadapted animals. The preadapted animals were preadapted to continuous light or dark for 90 days prior to lentectomy. The newts remained in the same controlled environments postlentectomy for 25 days to test the effect of light preadaptation on lens regeneration. The non-preadapted animals were placed in the light controlled environment immediately after lentectomy for a 25-day regeneration period. The results indicated that there was no difference in the rate of regeneration between continuous light preadapted and non preadapted animals. However, the dark non-preadapted animals regenerated new lenses at a much slower rate than the dark preadapted animals. The rate of lens regeneration was similar among the controls with 12 hours of light per 24-hour period, the dark preadapted, the continuous light preadapted, and continuous light non-preadapted groups.

Adaptation, Physiological↗