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Biomedical subjects

K Dai

Publications and source records attributed to K Dai.

At least 37 records · Page 2Linked to original sources
PubMed1997

[Polyethylene wear in periprosthetic tissue of failed cemented total hip arthroplasties].

To elucidate the relationship between polyethylene wear and loosening of total hip arthroplasty, we observed grossly the periprosthetic tissues, polyethylene wear debris and polyethylene acetabular liners retrieved from 6 failed cemented total hip arthroplasties during revisions by means of polar light miscroscope and scanning electron microscope. The production mechanism of polyethylene wear debris from acetabular liner was analyzed together with its role in periprosthetic fibrosis and prosthetic loosening. Results showed the abrasion of two bearing surfaces interposed with third-body particles as called three-body abrasion was the main model of polyethylene wear. All inner surfaces of the liners appeared clear abrasive scratches and big flat debris were found in most of the retrieved tissues. Histologically, the wear debris of various sizes embraced by 1 or several polynuclear giant cells that were found not only great in number but also active in function. The implication is that three body abrasion is the key factor of high rate wear of the polyethylene liner and that polynuclear giant cell is acting as an important cellular component leading to the prosthetic loosening.

Arthroplasty, Replacement, Hip↗
PubMed1996

Physical interaction of mammalian CDC37 with CDK4.

CDC37 was originally identified as a Start gene in budding yeast and has been shown to be required for association of CDC28 with cyclins. The exact functional mechanism by which CDC37 promotes this association, however, remains unknown. CDK4 is a cyclin D-dependent kinase that controls progression through G1 of the mammalian cell cycle. We have detected a specific association of CDK4 with the molecular chaperon HSP90 and a 44-kDa protein that we identify as mammalian CDC37. A physical interaction between CDC37 and CDK4 suggests that CDC37 may regulate the mammalian cell cycle through a direct effect on CDK4. Association of CDK4 with both CDC37 and HSP90 may also imply a mechanistic link between the functions of CDC37 and HSP90.

Amino Acid Sequence↗
PubMed1996

Topological characterization of the essential Escherichia coli cell division protein FtsN.

Genetic and biochemical approaches were used to analyze a topological model for FtsN, a 36-kDa protein with a putative transmembrane segment near the N terminus, and to ascertain the requirements of the putative cytoplasmic and membrane-spanning domains for the function of this protein. Analysis of FtsN-PhoA fusions revealed that the putative transmembrane segment of FtsN could act as a translocation signal. Protease accessibility studies of FtsN in spheroblasts and inverted membrane vesicles confirmed that FtsN had a simple bitopic topology with a short cytoplasmic amino terminus, a single membrane-spanning domain, and a large periplasmic carboxy terminus. To ascertain the functional requirements of the N-terminal segments of FtsN, various constructs were made. Deletion of the N-terminal cytoplasmic and membrane-spanning domains led to intracellular localization of the carboxy domain, instability,and loss of function. Replacement of the N-terminal cytoplasmic and membrane-spanning domains with a membrane-spanning domain from MalG restored subcellular localization and function. These N-terminal domains of FtsN could also be replaced by the cleavable MalE signal sequence with restoration of subcellular localization and function. It is concluded that the N-terminal, cytoplasmic, and transmembrane domains of FtsN are not required for function of the carboxy domain other than to transport it to the periplasm. FtsQ and FtsI were also analyzed.

ATP-Binding Cassette Transporters↗
PubMed1996

A new member of the hsp90 family of molecular chaperones interacts with the retinoblastoma protein during mitosis and after heat shock.

A gene encoding a new heat shock protein that may function as a molecular chaperone for the retinoblastoma protein (Rb) was characterized. The cDNA fragment was isolated by using the yeast two-hybrid system and Rb as bait. The open reading frame of the longest cDNA codes for a protein with substantial sequence homology to members of the hsp90 family. Antibodies prepared against fusions between glutathione S-transferase and portions of this new heat shock protein specifically recognized a 75-kDa cellular protein, hereafter designated hsp75, which is expressed ubiquitously and located in the cytoplasm. A unique LxCxE motif in hsp75, but not in other hsp90 family members, appears to be important for binding to the simian virus 40 T-antigen-binding domain of hypophosphorylated Rb, since a single mutation changing the cysteine to methionine abolishes the binding. In mammalian cells, Rb formed complexes with hsp75 under two special physiological conditions: (i) during M phase, when the envelope that separates the nuclear and cytoplasmic compartments broke down, and (ii) after heat shock, when hsp75 moved from its normal cytoplasmic location into the nucleus. In vitro, hsp75 had a biochemical activity to refold denatured Rb into its native conformation. Taken together, these results suggest that Rb may be a physiological substrate for the hsp75 chaperone molecule. The discovery of a heat shock protein that chaperones Rb identifies a mechanism, in addition to phosphorylation, by which Rb is regulated in response to progression of the cell cycle and to external stimuli.

Amino Acid Sequence↗
PubMed1996

Studies and applications of NiTi shape memory alloys in the medical field in China.

The biomedical study of NiTi shape memory alloys has been undertaken in China since 1978. A series of stimulating corrosion tests, histological observations, toxicity tests, carcinogenicity tests, trace nickel elements analysis and a number of clinical trials have been conducted. The results showed that the NiTi shape memory alloy is a good biomaterial with good biocompatibility and no obvious local tissue reaction, carcinogenesis or erosion of implants were found experimentally or clinically. In 1981, on the basis of fundamental studies, a shape memory staple was used for the first time inside the human body. Subsequently, various shape memory devices were designed and applied clinically for internal fixation of fractures, spine surgery, endoprostheses, gynaecological and craniofacial surgery. Since 1990, a series of internal stents have been developed for the management of biliary, tracheal and esophageal strictures and urethrostenosis as well as vascular obturator for tumour management. Several thousand cases have been treated and had a 1-10 year follow-up and good clinical results with a rather low complication rate were obtained.

Adult↗
PubMed1995

[Changes of proteoglycans in lumbar intervertebral disc of bipedal rats with aging].

Using a computer based image analysis system and histological sections stained with Safranin O, we investigated systematically the variation of proteoglycans (PG) contents in the low lumbar discs of bipedal rats. Topographically, the PG concentration increased from the outer annulus to the inner nucleus pulposus region, which possesses the highest PG concentration. The PG content decreased with age, and a significant loss of PG was observed in the lumbar discs of bipedal rats as compared with controls, especially in the nucleus pulposus. These observations support the view that the higher abnormal mechanical stress accelerates disc degeneration.

Aging↗
PubMed1995

[Influence of stress-relaxation plate on bone geometrics and mechanical property: an experimental study].

In order to maintain the effective fixation effect of rigid bone plate in the early stage of fracture and to prevent osteoporosis induced by stress shielding effect of rigid plate in later stage of fixation, a washer made of viscoelastic material was placed between the screw and the screw hole of plate to form a stress-relaxation plate system. Both in vitro and in vivo experiments demonstrated that there was no statistical difference between the stress shielding effect of padded and unpadded plate groups. The washer showed significant deformation and damaged 8 weeks after implantation, and 10 weeks after implantation the stress shielding rate of the padded plate group was significantly lower than that of the unpadded group (P < 0.05). As a consequence, the degree of osteoporosis of the tibia in the padded group was significantly milder than the unpadded group, and 20 weeks after implantation, the diameter of the tibia medullary cavity of the padded group was significantly smaller than that of the unpadded group. The thickness of cortical bone and the bending strength of the tibia of padded group were significantly larger than those of the unpadded group (P < 0.05-0.01). These results showed that the stress-relaxation plate system can effectively maintain the stability of fracture fixation at the similar level of rigid plate during the early stage of fracture and can gradually lower down the stress shielding rate so as to prevent severe osteoporosis and reduction of bone mechanical property in the later stage of fixation.

Animals↗
PubMed1995

Modified distal osteotomy of shortening the first metatarsal and for treatment of hallux valgus.

We evaluated the results of distal osteotomy of shortening the first metatarsal head with internal fixation of shape memory metal compression staple for hallux valgus in 26 feet of 17 women with a mean age of 41.0 years (30-65 years). The time for return to light work averaged 18.2 days, and to full work and normal walking 40.3 days after the operation. 16 patients (25 feet) had complete pain relief. Only in one foot, the pain was transferred under the 2nd metatarsal head. The appearance of the feet was markedly improved and the width of the forefeet was decreased by a mean of 0.92 cm after the operation. All of the patients were satisfied with the appearance of their feet. Radiographic analysis of feet showed that all osteotomies united, and the average angle of hallux valgus was improved from 30.1 degrees to 16.0 degrees, with the mean intermetatarsal angle of 11.2 degrees-6.5 degrees. No external fixation of plaster splintage was used and the distal fragment during healing of the osteotomy was stable. The time of bone healing was shortened and patients were allowed to bear weight at early stage.

Adult↗
PubMed1995

[An experimental study on the relationship between disc nutrition and disc degeneration].

Micro-angiography, scanning electron microscopy and hydrogen washout technique were used to investigate the disc nutrition condition and the nutritional pathway of endplate in bipedal rats with agting. Compared with the controls, the nutrition condition of bipedal rats underwent deterioration and the number of vascular distribution under the endplate decreased significantly, but no increase in thickness of endplate caused by microfractures of subchondral bone and callus formed during the healing process was observed. The abnormal stress may bring about vertebral body intra-osseous circulation disorder and then consequent decrease of vascular channels which related to the disturbance of disc nutrition. This strongly suggested that nutrition conditions of nucleus pulposus were not deteriorated by impaired diffusion capacity, but by decrease of vasculature that contacts with endplate.

Angiography↗
PubMed1995

[Long-term results of total ankle replacement].

Since July 1980, 12 cases of total ankle replacement and 2 cases of total ankle and talus replacement have been performed with the self-designed prosthesis. The age of patients ranged from 23 to 62, average 35.6 years. 12 patients were subject to long-term followup, the average follow-up time was 8 years and 7 months. 8 out of them were followed up for more than 10 years. According to McGuire standard, the results of the 12 were excellent in 9, good in 2, unapplicable in 1 with adjacent joint restriction. All the 11 patients resumed their original occupation with relief of clinical symptoms and great improvement of joint motion. Hence, we conclude that whenever a patient shows an indication for ankle arthrodesis, total ankle replacement can be of our first trial in some of them after overall consideration of the operative indications.

Adult↗
PubMed1995

Degenerative mechanism of articular cartilage induced by low stress. A morphological study.

Immobilization leads not only to diminished joint movement but also low stress of articular cartilage. The present investigation was undertaken to observe the morphological changes which arose in articular cartilage with low stress. The joint motion remained intact. Articular cartilage from the left knees of 66 rats whose left calcaneal tendons had been transected was examined under transmission electron microscope and light microscope. The degenerative changes were observed: decreased functional activity of chondrocytes progressively degenerated cartilage and lack of compensatory proliferation of chondrocytes at the early stage. We propose that the degeneration of articular cartilage induced by immobilization is the result of combination of low stress and lack of joint motion. The following degenerative mechanism begins with chondrocytes. Chondrocyte and matrix influence each other in a vicious cycle. Low stress may restrain the repair activities.

Animals↗
PubMed1995

[A comparative study of effects on bone healing and remodelling between embracing fixator and bone].

The authors made their own design of sawteeth-arm embracing internal fixator (SEIF) with NiTi shape memory alloy and used for fractured femoral shaft of dogs in comparison with 316L stainless steel plate-screw system. A transverse osteotomy on both sides of femoral diaphyses was performed in 15 adult dogs. One side was plated with bone plate and the other with SEIF. Five animals in each group were killed at 4, 8, 12 weeks after operation and observed under roentgen rays examination, light microscopy and transmission electron microscopy. The results showed that the fracture healing and the course of callus remodelling were similar in these two groups, but the cortical bone remodelling underneath the fixater near osteotomized area was significantly different. Eight-week post-implantation, osteocytes entered into degenerative phase were observed in cortical bone underneath SEIF, and 12-week after operation, the numbers of degenerative osteocytes increased remarkably. While in the case of bone plate, 4-week post-implantation, osteocytes entered into degenerative phase, and 8-week afterwards autolysis occurred in most of the degenerative osteocyles. In other words, the changes of osteocytes phase in bone plate side appeared earlier and more vigorous than that in the SEIF side. The authors are of the opinion that the elastic modulus of NiTi shape memory alloy is lower, the stress-shielding effect in the bone underneath SEIF is less, the axial compression stress of fracture line is kept larger and the contact of SEIF with the bone is not so close that is beneficial to the recovery of blood supply and bone remodelling.

Alloys↗
PubMed1995

[Modified distal osteotomy of shortening the first metatarsal for treatment of hallux valgus].

The results of distal osteotomy of shortening the first metatarsal with internal fixation of shape, memory metal compression staple for hallux valgus were evaluated in 26 feet of 17 women with a mean age of 41.0 years (30-65 yrs). The average time for return to light work was 18.2 days, and to full work and normal walk 40.3 days after the operation. 16 patients (25 feet) had complete relief from pain. Only in one foot the pain was transferred under the 2nd metatarsal head. The appearance of the feet was apparently improved and the width of the forefeet was decreased in a mean 0.92cm after the operation. All of the patients were satisfied with the appearance of their feet. Radiographic analysis of feet showed that all the osteotomies united, the average angle of hallux valgus was improved from 30.1 degrees to 16.0 degrees and the mean intermetatarsal angle from 11.2 degrees to 6.5 degrees. This new technique allows no external fixation of plaster splintage and the distal fragment during healing of the osteotomy was stable. The time of bone healing was shortened and patients were allowed to bear weight at early time.

Adult↗
PubMed1995

[A morphological study of degenerative mechanism of articular cartilage by abnormal high stress].

The articular cartilage from the right knee of 87 rats whose left calcaneal tendons had been transected was examined under transmission and scanning electron microscopes, and light microscope. Morphological observation showed a few small focal areas of cartilage surface disruption, pit and collagen fibrillation at 2 weeks after operation. After 1 month, many clusters of chondrocytes could be found, showing hyperactive synthetic and secretary activity. The cartilage degenerated progressively. The initial lesion in high stress side was at the matrix of cartilage, the collagen network was disrupted, then proteoglycan become degraded. The microenvironment of chondrocytes was changed with degradation of matrix. The chondrocytes became degenerative. The degeneration of chondrocytes influence the matrix again. A vicious cycle was thus formed. At the early stage of the degeneration of the cartilage induced by high-stress, som chondrocytes proliferate and have hyperactive synthetic and secretive functional activity. But soon, most of the chondrocytes degenerate. That is because of the chondrocytes have got repaired in response to initial matrix lesion and the normal microenvironment had degraded with aggravation of matrix lesion. These chondrocytes again became degenerative quickly.

Animals↗
PubMed1995

[An experimental study of the effects of stress-relaxation plate on bone remodeling].

An ideal bone plate would provide rigid fixation to ensure stabilization of bone fragments at the early stage after fracture, while at the late stage osteoporosis induced by stress shielding effect of the plate should be prevented. However, there is no report of such a plate that could meet with all these requirements. Twenty-eight adult New Zealand rabbits were used in this experiment. Ordinary stainless-steel plate (no washer plate) and similar plate padded with ultrahigh molecular polyethylene washers in its screw holes (washer plate) were fixed respectively on mid-shelf of each side of tibiae. The animals were killed at 2, 4, 8, 12, 16, 20 and 24 weeks after operation, and the fixed bone segments of both tibiae were removed for light microscopy, polarized light microscopy and fluoroscopy. The results showed that the tibiae fixed with plate fixation both appeared bone resorption, but there was more severe resorption in bone with no washer plate fixation than that with washer plate fixation. Cancelization of cortical bone was seen in the former but not in the latter at 12 weeks postopertively. This demonstrated that the washer might creep and damage with fixation time, resulting in gradual decrease in the rigidity of the plate-screw system and thus reducing bone resorption as caused by stress shielding.

Animals↗
PubMed1994

Amylin/islet amyloid polypeptide expression in medullary carcinoma of the thyroid: correlation with the expression of the related calcitonin/CGRP genes.

OBJECTIVE: The amylin/islet amyloid polypeptide (IAPP) gene is the third member of the calcitonin (CT)/calcitonin gene related peptide (CGRP) gene family, which includes the alpha CT/CGRP (CALC-I) and beta CGRP (CALC-II) genes. CT is predominantly expressed in thyroid C cells, alpha and beta CGRP (CGRP-I and II) in neural tissue and amylin/IAPP in pancreatic beta cells. Both the detailed tissue distribution and the physiological role of amylin are subjects of current research. We sought to characterize the RNAs transcribed from the IAPP gene in normal human pancreas and to investigate possible ectopic expression of this gene in neuroendocrine tumours. DESIGN AND TISSUES: RNA was extracted from normal human pancreas, five phaeochromocytomas and 12 medullary thyroid carcinomas (MTCs) and studied by Northern blotting. RESULTS: We found that in normal human pancreas the IAPP gene transcripts differ in size from those reported for human insulinoma. Expression of the amylin/IAPP gene was detected in seven of the MTCs, while it was not detected in phaeochromocytomas. There were no apparent clinical or histological differences between IAPP positive and IAPP negative MTCs. The relative expression levels of the four mRNAs of the CT/CGRP gene family varied between the different tumours. CONCLUSIONS: Our findings are consistent with the view that ectopic hormone production may occasionally be causally related to the common origin of related genes. The possibility that IAPP may constitute a minor component of MTC amyloid should be considered.

Amyloid↗
PubMed1994

Synaptonemal complex analysis of hybrid and purebred water buffaloes (Bubalus bubalis).

The morphology of the synaptonemal complex (SC) in river (2n = 50) and swamp (2n = 48) water buffaloes and their hybrids, was studied by electron microscopic analysis. In 2n = 49 hybrids, F2 and backcrosses the formation and pairing behaviour of a trivalent at zygotene-pachytene confirmed that river and swamp buffaloes differ by a centromere-to-telomere (C-T) tandem fusion. While 29% of spermatocytes from a purebred river buffalo and 16% from a purebred swamp buffalo had pairing abnormalities, a significantly higher frequency of abnormalities (48-72%) was recorded in F1, F2, and backcrosses with 2n = 48, 49 or 50. Highest abnormality frequencies occurred in 2n = 49 bulls. Abnormal pairing configurations often resulted from interactions between unpaired chromosome axes or segments. Zygotene-pachytene meiotic progress appeared delayed in hybrid bulls, and the frequency of SC abnormalities decreased from XY type I substage to type V substage. The variation in SC abnormality data from hybrids was consistent with the levels of sperm abnormality previously reported.

Animals↗