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Biomedical subjects

H W Jansen

Publications and source records attributed to H W Jansen.

At least 19 recordsLinked to original sources
PubMed1992

Meniscal repair by fibrocartilage? An experimental study in the dog.

Longitudinal lesions in the avascular part of the dog's meniscus were repaired by implantation of a porous polyurethane. Ingrowing repair tissue was characterized by biochemical and immunological analysis. Histologically, repair tissue initially was composed of fibrous tissue containing type I collagen. After 3 months, fibrocartilaginous tissue developed inside the implants, whereas control defects only showed fibrous repair tissue. Both type I and II collagen, the major collagen types of normal meniscal fibrocartilage, could be detected in this newly formed fibrocartilage. It is concluded that fibrocartilage resembling normal meniscal tissue is formed and that longitudinal lesions can be healed after meniscal repair by implantation of a porous polymer.

Animals↗
PubMed1992

Porous polymer implants for repair of full-thickness defects of articular cartilage: an experimental study in rabbit and dog.

Full-thickness defects of articular cartilage were repaired by implantation of porous polymer implants in rabbits and dogs. The quality of the repair tissue was determined by collagen typing with antibodies. Implants with varying pore sizes and chemical composition were used. The effect of loading and motion was determined by inserting implants higher than, level with and lower than the surrounding cartilage. It appeared that healing took place by formation of fibrocartilaginous repair tissue containing both type I and type II collagen. Hyaline cartilage was observed in a minority of the rabbits used but not in the dog. Fibrocartilage formation in the dog was simulated by implantation of a porous polymer. Chemical composition of the polymer did not alter the results, neither did loading of the implant. It is concluded that the formation of fibrocartilaginous repair cartilage is stimulated by implantation of a porous polymer. This tissue seemed to function adequately in the dog but did show signs of degeneration in the rabbit.

Animals↗
PubMed1992

Secondary retention of permanent molars: an assessment of ankylosis by scanning electron and light microscopy.

Secondary retention refers to the cessation of eruption of a tooth after emergence. This may be the result of pathological changes in the periodontal ligament. The aim of this study was to describe the morphological and histological aspects of the radicular surface of secondarily retained permanent molars. The roots of 12 secondarily retained molars and two control molars, were examined by means of scanning electron microscopy (SEM) and light microscopy (LM) in order to analyse the occurrence and localisation of ankylosis. With SEM it was observed that the root surface of retained molars showed local areas covered with bonelike tissue. LM of these areas showed that this tissue was bone in direct contact with the root surface (ankylosis). In 11 cases, the areas of ankylosis were observed in the bifurcation area and at the interradicular root surface. In the remaining case, ankylosis was located at the outer root surface. The results of this study endorse the assumption that focal ankylosis is an important factor in secondary retention. Treatment recommendations must be based on this fundamental principle, because orthodontic movement of ankylotic molars is not possible.

Adolescent↗
PubMed1991

Porous polymer implant for repair of meniscal lesions: a preliminary study in dogs.

Artificial meniscal lesions extending into the avascular part of the meniscus, which do not heal by any other means, were repaired by suturing either a porous polymer implant or a synovial flap into the defect. The implant guided the ingrowth of vascular repair tissue into the defect. This fibrous tissue later on transformed into fibrocartilage. Reconstruction with a synovial flap was not successful. It appeared that healing can be achieved by implantation of a porous polymer implant in a large number of cases. Future research will be aiming at improvement of the results of meniscal repair and application of this type of polymer for repair of cartilage defects.

Animals↗
PubMed1991

Degradation of and tissue reaction to biodegradable poly(L-lactide) for use as internal fixation of fractures: a study in rats.

Samples of high-molecular-weight poly(L-lactide) (PLLA) (Mv = 9.0 x 10(5), a biomaterial developed for plates and screws used in internal fixation of jaw fractures, were implanted subcutaneously in the backs of rats to study tissue reaction to PLLA and to follow the degradation process. The PLLA seemed to follow the degradation pattern typical of biodegradable polyesters. After pure hydrolysis up to about 104 wk, phagocytic activity of macrophages was found at about 143 wk. Full resorption of PLLA was not demonstrated in this study. Except for the early and final parts of the implant period, no acute or chronic inflammatory reaction was observed. No implant was rejected. It is estimated that more than 3 yr will be required for total resorption of PLLA. For bone-healing this long period is of no practical importance. There is no need for removal of PLLA after fracture healing as is the case with metal fixation devices. Thus, PLLA has potential application in internal fixation of fractures and osteotomies in the maxillofacial region and other fractures that are not too heavily loaded in the human body.

Animals↗
PubMed1990

Poly(L-lactide) implants in repair of defects of the orbital floor: an animal study.

Because of the life-long presence of alloplastic, nonresorbable orbital floor implants and the complications of their use mentioned in literature, the use of a resorbable material appears to be preferable in the repair of orbital floor defects. A high-molecular-weight, as-polymerized poly(L-lactide) (PLLA) was used for repair of orbital floor defects of the blowout type in goats. An artificial defect was created in the bony floor of both orbits. Reconstruction of the orbital floor was then carried out using a concave PLLA implant of 0.4-mm thickness. At 3, 6, 12, 19, 26, 52, and 78 weeks postoperatively, one goat was killed. Microscopic examination showed full encapsulation of the implant by connective tissue after 3 weeks. After 6 weeks, resorption and remodeling of the bone at the points of support of the implant could be detected. A differentiation between the sinus and orbital sides of the connective tissue capsule was observed. The orbital side showed a significantly more dense capsule than the antral side, which had a loose appearance. At 19 weeks, a bony plate was progressively being formed, and at 78 weeks, new bone had fully covered the plate on the antral and orbital side. No inflammation or rejection of the PLLA implant was seen.

Animals↗
PubMed1989

Bone-plates and screws of bioabsorbable poly (L-lactide)--an animal pilot study.

Poly (L-lactide), a polymer of lactic acid (PLLA), with an extremely high molecular weight (Mv up to 1 x 10(6] has been synthesised under strictly controlled conditions resulting in a new microporous material with excellent mechanical properties. Bone-plates and screws machined from PLLA were used for fixation of two artificial mandibular fractures in sheep effected by a specially designed bone clamp. Fracture healing was uneventful without visible callus formation. Plates and screws of PLLA gave good stability over a sufficiently long period to enable normal fracture healing. Application in humans seems to be justified.

Absorption↗
PubMed1989

Secondary retention of permanent molars: a histologic study.

The etiology of secondary retention is not well understood, but ankylosis is often considered to be an important factor in primary molars. Data concerning the mechanism of secondary retention in the permanent dentition are insufficient, although a possible role of ankylosis has been suggested. In order to analyze the frequency of occurrence and localization of ankylosis in secondarily retained permanent teeth, 26 secondarily retained molars and for comparison six normal molars were studied histologically. These data were compared with the clinical and radiographic findings. Areas of ankylosis were observed along the roots of all secondarily retained molars. In 81% of the cases these areas were located at the bifurcation and interradicular root surface. No signs of ankylosis were found in normal molars. When these results were compared with the clinical and radiographic data, it was obvious that the latter gave many false negative results, because the areas of ankylosis were often too small to be detected clinically or radiographically.

Adolescent↗
PubMed1988

Expression of Met-(-1) angiogenin in Escherichia coli: conversion to the authentic less than Glu-1 protein.

A method for obtaining authentic human angiogenin utilizing an Escherichia coli recombinant expression system is described. A synthetic gene encoding angiogenin was placed into a vector for direct expression under the control of a modified E. coli trp promoter. The protein was produced by the bacteria in an insoluble form and purified to homogeneity by cation-exchange and reversed-phase HPLC following reduction/solubilization and reoxidation. The protein isolated was identified as Met-(-1) angiogenin by amino acid analysis and tryptic peptide mapping; the latter demonstrated that all three disulfide bonds had formed correctly. Both the enzymatic and angiogenic activities of the Met-(-1) protein were equivalent to those of native angiogenin. A Met-(-1) Leu-30 derivative of angiogenin was also isolated and found to be fully active. Conversion of Met-(-1) angiogenin to the authentic less than Glu-1 protein was achieved by treatment with Aeromonas aminopeptidase under conditions in which the new N-terminal glutamine readily cyclizes nonenzymatically. This aminopeptidase treatment may have more general applicability for removal of undesirable N-terminal methionine residues from foreign proteins expressed in bacteria.

Amino Acid Sequence↗
PubMed1988

Morphological aspects of the gingiva in children with Down's syndrome during experimental gingivitis.

In a previous investigation, children with Down's syndrome (DS) showed an earlier, more rapid and more extensive gingival inflammation than normal healthy control children. These differences in gingival inflammation may be the result of aberrant morphology of the gingiva related to the genetic disorder in DS children. The aims of the present study were (i) to describe the structural composition of "normal" gingiva in DS compared to control children, (ii) to analyse the histological changes in the gingiva during plaque development and (iii) to investigate whether the clinical findings could be supported by morphological observations. The study was carried out in 8 DS and 8 matched control children. Their ages ranged from 5-10 years. Gingival normality was guaranteed by strict oral hygiene procedures. During a period of 21 days in which oral hygiene was abolished, gingival biopsies were taken from buccal sites of deciduous teeth following a predetermined schedule on days 0, 7, 14 and 21. Results on day 0 showed no morphological differences between the DS and control children regarding oral epithelium, junctional epithelium or connective tissue. During the experimental phase of the study, the amount of plaque accumulation in the DS children gave rise to a more extensive gingival inflammation than in the control children. The gingival inflammation in the DS group started earlier and included: (1) an acute inflammatory response, (2) an increase of the junctional epithelium area, (3) an increase of the infiltrated connective tissue area (ICT) and (4) a decrease in collagen fibre density of about 35-40% compared to day 0. The same phenomena were not seen until 7 days later in the control group. Conversely, the development of a perivascular lymphocyte infiltrate (LI) in the DS children was delayed compared to the control group. This may be caused by the impaired delayed-type hypersensitivity response in DS children. The development of 2 separate infiltrates (ICT and LI) in this age group and the different temporal development of ICT (day 7 for the DS and day 14 for the control group) and LI (day 14 for the DS and day 7 for the control group) does suggest different immunological mechanisms for both areas and both groups.

Basement Membrane↗
PubMed1988

Cellular aspects of and effects on the gingiva in children with Down's syndrome during experimental gingivitis.

In a previous experimental gingivitis study, it was shown that in children with Down's syndrome (DS), gingival inflammation started earlier, was more extensive and developed faster, than in normal healthy control children. In both groups, the start of the process was accompanied by an acute inflammatory response and an increase of the infiltrated connective tissue area (ICT). The purpose of the present study was to investigate how these facts were reflected at a cytological level. The study was carried out in 8 DS and 8 matched control children. Their ages ranged from 5-10 years. A "normal" healthy gingiva was attained after strict oral hygiene procedures. During a period of 21 days in which oral hygiene was abolished, gingival biopsies were taken on days 0, 7, 14, and 21. In both groups, junctional epithelium (JE) and ICT contained low numbers of polymorphonuclear leucocytes (PMNs). The start of the inflammation (day 7 for the DS and day 14 for the control children) was marked by a significant positive correlation between the numbers of PMNs in the JE and the ICT, and a significant increase of the numbers of PMNs in ICT. In ICT, a concomitant decrease in collagen fibre density was observed. In the control group, the decrease correlated with the numbers of PMNs in ICT, which suggests that this collagen breakdown is caused by PMN products. After the initial decrease, the collagen fibre density remained fairly constant in this group throughout the study. In the DS group, there was a tendency to a further decrease in the ICT3 area, correlated with the numbers of PMNs in ICT.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗
PubMed1988

Effects of polypeptide growth factors on mandibular condylar cartilage of the rat in vitro.

In a comparative study, the influence of several polypeptide growth factors on proliferation and matrix synthesis in secondary mandibular condylar and primary costal cartilage of the rat were determined using a serum-free culture system. Somatomedin-C, multiplication-stimulating activity (MSA), epidermal growth factor (EGF) and insulin had a significant dose-dependent stimulating effect on proliferation in mandibular condylar cartilage. In costal cartilage, the same factors as well as parathyroid hormone (fragment 1-34), platelet-derived growth factor (PDGF) and high doses of human growth hormone (1 microgram/ml) significantly stimulated proliferation. Matrix synthesis in both cartilages could only be stimulated by high doses of insulin (100 micrograms/ml) and in costal cartilage also by parathyroid hormone. In this culture system fibroblast growth factor reduced proliferation and matrix production, while cartilage-derived factor had no marked effect on the growth processes in both cartilage types. Prominent differences between condylar and costal cartilage were demonstrated by the effects of parathyroid hormone and fetal calf serum. Although the effects on matrix synthesis were very moderate in the tissue culture system used, this study demonstrates that most factors conducive to growth in primary cartilage also stimulate growth in condylar cartilage only exposure to growth substances that interfere with the differentiation of prechondroblasts into chondroblasts, a process that is specific for appositionally growing secondary cartilage, may result in different responses between primary and secondary cartilage.

Animals↗
PubMed1987

Visualization of vascular channels in the mandibular cortex.

Several methods to visualize the vascular pattern of the mandibular cortex were tested. The most suitable method for young jaws proved to be one in which the organic material was partially removed to increase access to the vascular channels. The vessels were vacuum infiltrated with an India ink solution, and the jaws were then decalcified and cleared in glycerin. This resulted in completely transparent flexible cortical plates showing a sharp outline of the vascular pattern. The flexibility of the plates also improved the morphological study of the emergence of blood capillaries at the cortical surface in relation to bone remodeling.

Capillaries↗
PubMed1987

Structure of mutant and wild-type MC29 v-myc alleles and biochemical properties of their protein products.

Proviral DNAs of three fibroblast-transforming MC29 deletion mutants (MC29-10A, MC29-10C, MC29-10H) with defects in hemopoietic cell transformation and tumor induction were molecularly cloned and their deletions were defined by nucleotide sequence analysis. The MC29-10C and MC29-10H v-myc alleles have identical internal deletions overlapping with a smaller one in the MC29-10A v-myc allele, and MC29-10H has an additional internal deletion in the partial gag complement. All deletions are in frame, and the deduced sequences of the mutant gag-myc hybrid proteins lack 56 (MC29-10A) or 120 (MC29-10C, MC29-10H) myc-specific and 44 gag-specific (MC29-10H) amino acid residues. The deleted v-myc nucleotide sequences correspond to the 3' end of exon 2 and the 5' end of exon 3 of the cellular c-myc gene including a region that encodes a high number of acidic amino acid residues. Based on these structural analyses, biochemical properties of mutant and wild-type gag-myc hybrid proteins were compared. Tryptic digests of all three mutant proteins lack a large myc-specific peptide that is present in digests of the wild-type protein and is extensively phosphorylated at serine and threonine residues. Concordantly, the sequence analyses predict that such a large tryptic peptide with putative phosphorylation sites at serine and threonine residues is present in the wild-type gag-myc protein but absent in all three mutant proteins due to the v-myc deletions. Chromatography of wild-type and mutant gag-myc proteins on DNA-cellulose revealed that their in vitro DNA affinities are indistinguishable from each other. Correspondingly, the sequence analyses predict that the carboxyl-terminal region rich in basic amino acid residues and with putative DNA affinity is conserved in wild-type and mutant gag-myc proteins. We conclude that the internal v-myc protein sequences defined by the deletions are necessary for hemopoietic cell transformation and complete phosphorylation, but dispensable for fibroblast transformation and in vitro DNA binding.

Amino Acid Sequence↗
PubMed1986

Nucleotide sequence of the CMII v-myc allele.

The entire nucleotide sequence of the transduced v-myc allele in the genome of avian oncogenic retrovirus CMII was determined. The CMII v-myc and the chicken c-myc alleles differ in their shared coding sequences by a single nucleotide substitution causing a glutamic acid/alanine exchange in the predicted sequences of the corresponding protein products. This mutation has not been found in the transduced v-myc alleles of avian oncogenic retroviruses MC29, MH2, and OK10. We conclude that no specific, if any, missense mutation of the c-myc coding sequence is necessary for oncogenic activation upon transduction of the cellular gene.

Alleles↗
PubMed1986

Interaction between Raf and Myc oncogenes in transformation in vivo and in vitro.

3611 MSV, a raf-oncogene-transducing murine retrovirus, induces fibrosarcomas and erythroid hyperplasia in newborn mice after a latency of 4-8 wk. In contrast, new recombinant murine retroviruses carrying the myc oncogene (J-3, J-5 construct viruses) do not induce tumors before greater than 9 wk. A combination of both oncogenes in an infectious murine retrovirus (J-2) induces hematopoietic neoplasms in addition to less prominent fibrosarcomas and pancreatic adenocarcinoma 1-3 wk after inoculation. The hematologic neoplasms consist of immunoblastic lymphomas of T and B cell lineage and erythroblastosis. If animals were inoculated with a variant of the J-3 virus, which induces altered foci in cultures of NIH 3T3 cells, carcinoma developed in the pancreas with a 2-6 mo latency. In parallel to the synergistic action of both oncogenes on hematopoietic cells in vivo, we find that raf-oncogene-induced transformation of bone marrow cells in culture is enhanced by the addition of myc, which by itself does not transform these cells when grown in standard media. We conclude that concomitant expression of raf and myc oncogenes in hematopoietic and epithelial cells alters their respective transforming activities. The contribution of v-myc in this synergism was examined by use of a series of recombinant murine retroviruses capable of expressing the avian v-myc to study the effect of altered myc expression on hematopoietic/lymphoid cells. With either interleukin 3- or interleukin 2-dependent cell lines, introduction of the recombinant viruses abrogated the requirement for IL 3 or IL 2 for growth, and associated with this was the suppression of c-myc expression. The findings suggest that myc is a component in the signal transduction pathway for IL 3 and IL 2 and support an autoregulatory mechanism of c-myc expression. In contrast to v-myc, expression of v-raf in primary lymphoid/hematopoietic cells has an immortalizing function without abrogating the requirement for IL 3 for growth. This suggests that v-raf and v-myc affect different components of growth regulation, as, for example, commitment (v-myc) and cell cycle progression (v-raf).

Animals↗
PubMed1986

Growth and growth pressure of mandibular condylar and some primary cartilages of the rat in vitro.

To compare the in vitro development of the secondary cartilage of the mandibular condyle with that of primary cartilages, several cartilaginous explants derived from 4-day-old rats were cultured in a serum-free culture system. The following cartilages were used: the mandibular condylar cartilage, the distal epiphyseal cartilage (including the growth plate) of the third metatarsal, a fragment of costal cartilage (including the osteochondral junction) of the fourth rib, the spheno-occipital synchondrosis and the chondroepiphysis of the femoral head. In addition, with a specially designed, in vitro pressure registration system, the maximal growth pressures for each of the explants, except the femoral head, were determined. The results show an independent growth potential for the primary cartilages of the epiphyseal and costal growth plates with a maximal growth pressure of 9.5 and 7.8 g/mm2, respectively. The primary cartilage of the spheno-occipital synchondrosis, on the other hand, although it possesses an independent growth potential, could exert a maximum growth pressure of only 1.5 g/mm2. The secondary cartilage of the mandibular condyle showed a limited intrinsic growth potential, as well as a low maximal growth pressure (2.6 g/mm2). If calculated per dividing and/or matrix synthesizing cell (cells mainly responsible for the cartilage growth), the cells of the condylar cartilage showed the least growth potency (0.08 mg/cell in comparison to 1.9, 1.5 and 0.3 for epiphyseal, costal, and synchondroseal cartilages, respectively.

Animals↗