Biomedical subjects

H P Hsu

Publications and source records attributed to H P Hsu.

At least 19 recordsLinked to original sources

PubMed2004

A case of Collet-Sicard syndrome associated with traumatic atlas fractures and congenital basilar invagination.

An 18 year old man with congenital basilar invagination developed multiple lower cranial nerve (CN) palsies including CN IX to XII after a traffic accident. Computed tomography of his skull base revealed a two part atlas Jefferson fracture. Normally, lower cranial nerves (CN IX-XII) pass through a space between the styloid process and the atlas transverse process. Atlas burst fractures rarely cause neurological deficits because of a greater transverse and sagittal diameter of the spinal canal at the atlas, and a tendency of the lateral masses to slide away from the cord after injury. However, when associated with a rare condition-congenital basilar invagination-atlas fractures can compromise the space and make CN IX-XII more vulnerable to compression injury. This report discusses the correlation between the anatomical lesions and clinical features of this patient.

Accidents, Traffic↗

PubMed2001

Structure determination of organic molecules from diffraction data by simulated annealing.

We study simulated annealing techniques for crystal structure determination from diffraction data. We demonstrate that for this problem the efficiency of simulated annealing can be systematically improved by an iterative simulation protocol. Our approach is tested for the example of 9-(methylamino)-1 H-phenalen-1-one-1, 4-dioxan-2-yl hydroperoxide solvate (C18H19NO5).

Journal Article↗

PubMed2001

Universal scaling functions for bond percolation on planar-random and square lattices with multiple percolating clusters.

Percolation models with multiple percolating clusters have attracted much attention in recent years. Here we use Monte Carlo simulations to study bond percolation on L1xL2 planar random lattices, duals of random lattices, and square lattices with free and periodic boundary conditions, in vertical and horizontal directions, respectively, and with various aspect ratios L(1)/L(2). We calculate the probability for the appearance of n percolating clusters, W(n); the percolating probabilities P; the average fraction of lattice bonds (sites) in the percolating clusters, (n) ( (n)), and the probability distribution function for the fraction c of lattice bonds (sites), in percolating clusters of subgraphs with n percolating clusters, f(n)(c(b)) [f(n)(c(s))]. Using a small number of nonuniversal metric factors, we find that W(n), P, (n) ( (n)), and f(n)(c(b)) [f(n)(c(s))] for random lattices, duals of random lattices, and square lattices have the same universal finite-size scaling functions. We also find that nonuniversal metric factors are independent of boundary conditions and aspect ratios.

Journal Article↗

PubMed2001

Compressive properties of cancellous bone defects in a rabbit model treated with particles of natural bone mineral and synthetic hydroxyapatite.

A rabbit model was developed to evaluate the compressive mechanical properties of cancellous bone defects treated with particles of selected bone graft substitute materials. A novel feature of the model was the precise retrieval of the site of implantation. A notable finding was a 9-fold increase in the modulus of elasticity of the defect implanted with a synthetic hydroxyapatite material after 26 weeks when compared to the modulus of the trabecular bone normally at the site. The compressive modulus of lesions treated with particles of a natural bovine bone mineral (anorganic bovine bone) was closer to the normal modulus of the cancellous bone at the site. While the compressive strength of the anorganic bone particles was less than that of normal bone, the site implanted with the bone mineral particles achieved compressive strength greater than normal after 6 weeks. Moreover, the anorganic bone particles accelerated the increase in strength of the lesion, at 6 weeks exceeding the strength achieved by the untreated defect after 26 weeks. The potential problem associated with the disparity in the compressive modulus between sites implanted with the synthetic HA particles and surrounding bone is discussed.

Animals↗

PubMed2001

Autologous chondrocyte implantation in a canine model: change in composition of reparative tissue with time.

The objective of the study was to evaluate the tissue types filling 4-mm diameter defects in the canine trochlear groove 1.5, 3, and 6 months after autologous chondrocyte implantation (ACI). Untreated defects served as controls. Periosteum alone controls were also included at the 1.5-month time period. The results were compared with previously published findings obtained 12 and 18 months postoperative. After 3 months the ACI-treated defects contained significantly more reparative tissue than found in the untreated control group, including twice the amount of hyaline cartilage (HC). These findings, however, were the only significant effects of the ACI treatment when compared to the periosteum alone or empty control groups. The benefits of ACI found at 3 months did not persist to longer time periods. An evaluation of the inter-observer error associated with the histomorphometric method indicated that it was generally less than the inter-animal variation in the results.

Animals↗

PubMed2001

Lapine and canine bone marrow stromal cells contain smooth muscle actin and contract a collagen-glycosaminoglycan matrix.

Lapine and canine marrow stromal cells were found to contain a contractile actin isoform, alpha-smooth muscle actin (SMA), by immunohistochemistry and Western blot analysis. The SMA was found to be incorporated into stress fibers that were prominently displayed by the cells in monolayer culture. The cell content of this actin isoform increased with passage number. The contractility of SMA-expressing stromal cells was demonstrated by their contraction of collagen-glycosaminoglycan analogs of extracellular matrix into which they were seeded. The demonstration that marrow-derived stromal cells express the SMA gene may explain recent findings of this expression in musculoskeletal connective tissue cells including osteoblasts, chondrocytes, and fibrochondrocytes that may be derived from this mesenchymal stem cell. The implications of these findings for tissue engineering strategies employing marrow stromal cells are also discussed.

Actins↗

PubMed2001

Transcriptional regulation of the Bacillus subtilis bscR-CYP102A3 operon by the BscR repressor and differential induction of cytochrome CYP102A3 expression by oleic acid and palmitate.

The adjacent yrhI and yrhJ genes were identified by the Bacillus subtilis genome sequencing project. We now report that yrhJ (renamed CYP102A3) encodes a cytochrome P450 and that yrhI (renamed bscR) encodes a repressor that negatively regulates the transcription of the bscR-CYP102A3 operon. The transcriptional initiation site of bscR has been mapped by primer extension analysis. An 18-bp perfect palindromic sequence centered 65.5 bp downstream from the transcriptional initiation site of bscR has been identified as the binding site for BscR by gel mobility shift assays. Base substitutions in the 18-bp inverted repeat resulted in derepression of the bscR-xylE transcriptional fusion in vivo. bscR-xylE fusion studies and Northern blot analysis revealed that oleic acid and palmitate could induce the expression of the bscR-CYP102A3 operon to a considerable extent. However, only oleic acid was capable of preventing the binding of BscR to its operator DNA in vitro, suggesting that the induction of CYP102A3 expression by oleic acid and palmitate in B. subtilis might be mediated through different mechanisms.

Amino Acid Sequence↗

PubMed2001

Tumour necrosis factor-alpha causes an increase in blood-brain barrier permeability during sepsis.

Blood-brain barrier (BBB) permeability during sepsis with Escherichia coli or Streptococcus pneumoniae was examined in a mouse model and measured by a circulating beta-galactosidase tracer. The leakage of brain microvascular vessels during sepsis was confirmed by transmission electron microscopic examination of brain tissues stained with horseradish peroxidase. The increase of BBB permeability induced by E. coli and S. pneumoniae, which was maximal at 3 h and 12 h after injection, respectively, was transient because of rapid clearance of the bacteria from the blood. Tumour necrosis factor-alpha (TNF-alpha) was stained on microvascular vessels of the brain during sepsis and intravenous injection of recombinant TNF-alpha also increased the BBB permeability. The increase in BBB permeability induced by either E. coli or S. pneumoniae could be inhibited by anti-TNF-alpha antibody. It was concluded that circulating TNF-alpha generated during sepsis induced the increase in BBB permeability.

Animals↗

PubMed2001

Chondral defects in animal models: effects of selected repair procedures in canines.

The defect made to the level of the tidemark in a canine model has been used in several prior investigations of various articular cartilage repair procedures. Direct comparison of the repair method, 15 weeks postoperatively, showed a significant correlation between the degree to which the calcified cartilage layer and subchondral bone were disrupted and the amount of tissue filling. Moreover, when it forms, hyaline cartilage most frequently occurs superficial to intact calcified cartilage. Many of the chondrocytic cells and fibroblasts expressed the gene for a contractile muscle actin, alpha-smooth muscle actin. However, the role of this actin isoform is yet in question. These findings may inform future strategies for cartilage repair.

Animals↗

PubMed2001

The effects of tubulation on healing and scar formation after transection of the adult rat spinal cord.

PURPOSE: The purpose of this study was to characterize the effects of implantation of a collagen tube on healing and scar formation following transection of tbc adult rat spinal cord. METHODS: The spinal cords of adult rats were completely transected at the mid-thoracic level. At 30 days after injury, the cellular and extra-cellular components of repair tissue present within tubulated and non-tubulated (control) wounds were compared using qualitative and quantitative histological techniques. RESULTS: The presence of the tube reduced fibrocollagenous scar invasion into the gap, promoted astrocyte migration, and oriented axonal and connective tissue components of the repair tissue. Tube implants supported the regeneration of a substantial number of myelinated axons. A notable finding was the identification of cells containing a contractile actin isoform in the healing spinal cord. CONCLUSIONS: The tubulation model allows for the study of spinal cord wound healing and axon elongation in a controlled experimental environment within the tube lumen. Using this model, it will be possible to study manipulation of the healing response by the introduction of exogenous agents within the tube.

Actins↗

PubMed2000

Near-terminus axonal structure and function following rat sciatic nerve regeneration through a collagen-GAG matrix in a ten-millimeter gap.

The objectives of this study were to evaluate the regenerated axon structure at near-terminal locations in the peroneal and tibial branches 1 year following implantation of several tubular devices in a 10-mm gap in the adult rat sciatic nerve and to determine the extent of recovery of selected sensory and motor functions. The devices were collagen and silicone tubes implanted alone or filled with a porous collagen-glycosaminoglycan matrix. Intact contralateral nerves and autografts were used as controls. Nerves were retrieved at 30 and 60 weeks postoperatively for histological evaluation of the number and diameter of regenerated axons proximal and distal to the gap and in the tibial and peroneal nerve branches, near the termination point. Several functional evaluation methods were employed: gait analysis, pinch test, muscle circumference, and response to electrical stimulation. A notable finding was that the matrix-filled collagen tube group had a significantly greater number of large-diameter myelinated axons (> or =6 microm in diameter) in the distal nerve branches than any other group, including the autograft group. These results were consistent with previously reported electrophysiological measurements that showed that the action potential amplitude for the A fibers in the matrix-filled collagen tube group was greater than for the autograft control group. Functional testing revealed the existence of both sensory and motor recovery following peripheral nerve regeneration through all devices; however, the tests employed in this study did not show differences among the groups with regeneration. Electrical stimulation in vivo showed that threshold parameters to elicit muscle twitch were the same for reinnervating and control nerves. The investigation is of importance in showing for the first time the superiority of a specific fully resorbable off-the-shelf device over an autograft for bridging gaps in peripheral nerve, with respect to the near-terminus axonal structure.

Animals↗

PubMed2000

Connective tissue response to tubular implants for peripheral nerve regeneration: the role of myofibroblasts.

The presence of contractile cells, their organization around regenerating nerve trunks, and the hypothetical effect of these organized structures on the extent of regeneration across a tubulated 10-mm gap in the rat sciatic nerve were investigated. Collagen and silicone tubes were implanted both empty and filled with a collagen-glycosaminoglycan (GAG) matrix. Nerves were retrieved at 6, 30, and 60 weeks postoperatively and time-dependent values of the nerve trunk diameter along the tubulated length were recorded. The presence of myofibroblasts was identified immunohistochemically using a monoclonal antibody to alpha-smooth muscle actin. Myofibroblasts were circumferentially arranged around the perimeter of regenerated nerve trunks, forming a capsule which was about 10 times thicker in silicone tubes than in collagen tubes. The nerve trunk diameter that formed inside collagen tubes was twice as large as that inside silicone tubes. In contrast, the collagen-GAG matrix had a relatively small effect on capsule thickness or diameter of regenerate. It was hypothesized that the frequency of successful bridging by axons depends on the balance between two competitive forces: the axial forces generated by the outgrowth of axons and nonneuronal cells from the proximal stump and the constrictive, circumferential forces imposed by the contractile tissue capsule that promote closure of the wounded stumps and prevent axon elongation. Because the presence of the collagen-GAG matrix has enhanced greatly the recovery of normal function of regenerates in silicone tubes, it was hypothesized that it accelerated axonal elongation sufficiently before the hypothetical forces constricting the nerve trunk in silicone tubes became sufficiently large. The combined data suggest a new mechanism for peripheral nerve regeneration along a tubulated gap.

Actins↗

PubMed2000

Healing of canine articular cartilage defects treated with microfracture, a type-II collagen matrix, or cultured autologous chondrocytes.

The effects of three different treatments on the healing of articular cartilage defects were compared with use of a previously developed canine model. In the articular surface of the trochlear grooves of 12 adult mongrel dogs, two 4-mm-diameter defects were made to the depth of the tidemark. Four dogs were assigned to each treatment group: (a) microfracture treatment, (b) microfracture with a type-II collagen matrix placed in the defect, and (c) type-II matrix seeded with cultured autologous chondrocytes. After 15 weeks, the defects were studied histologically. Data quantified on histological cross sections included areal or linear percentages of specific tissue types filling the defect, integration of reparative tissue with the calcified and the adjacent cartilage, and integrity of the subchondral plate. Total defect filling (i.e., the percentage of the cross-sectional area of the original defect filled with any type of reparative tissue) averaged 56-86%, with the greatest amount found in the dogs in the microfracture group implanted with a type-II collagen matrix. The profiles of tissue types for the dogs in each treatment group were similar: the tissue filling the defect was predominantly fibrocartilage, with the balance being fibrous tissue. There were no significant differences in the percentages of the various tissue types among dogs in the three groups.

Animals↗

PubMed2000

Effects of harvest and selected cartilage repair procedures on the physical and biochemical properties of articular cartilage in the canine knee.

This study utilizes a canine model to quantify changes in articular cartilage 15-18 weeks after a knee joint is subjected to surgical treatment of isolated chondral defects. Clinical and experimental treatment of articular cartilage defects may include implantation of matrix materials or cells, or both. Three cartilage repair methods were evaluated: microfracture, microfracture and implantation of a type-II collagen matrix, and implantation of an autologous chondrocyte-seeded collagen matrix. The properties of articular cartilage in other knee joints subjected to harvest of articular cartilage from the trochlear ridge (to obtain cells for the cell-seeded procedure) were also evaluated. Physical properties (thickness, equilibrium compressive modulus, dynamic compressive stiffness, and streaming potential) and biochemical composition (hydration, glycosaminoglycan content, and DNA content) of the cartilage from sites distant to the surgical treatment were compared with values measured for site-matched controls in untreated knee joints. No significant differences were seen in joints subjected to any of the three cartilage repair procedures. However, a number of changes were induced by the harvest operation. The largest changes (displaying up to 3-fold increases) were seen in dynamic stiffness and streaming potential of patellar groove cartilage from joints subjected to the harvest procedure. Whether the changes reported will lead to osteoarthritic degeneration is unknown, but this study provides evidence that the harvest procedure associated with autologous cell transplantation for treatment of chondral defects may result in changes in the articular cartilage in the joint.

Animals↗

PubMed1999

TNFalpha-induced cyclooxygenase 2 not only increases the vasopermeability of blood-brain barrier but also enhances the neutrophil survival in Escherichia coli-induced brain inflammation.

In Escherichia coli-induced brain inflammation, cyclooxygenase-2 was induced not only on brain arterioles at 3 h, but also on infiltrating neutrophils at 9 h post-intracerebral injection. Intravenous injection of E. coli or recombinant TNFalpha also induced cyclooxygenase-2 expression on arterioles. Cyclooxygenase-2 and TNFalpha were co-localized on the arterioles as well as the infiltrating neutrophils by serial-section staining, indicating that cyclooxygenase-2 was induced by TNFalpha. NS398 (a cyclooxygenase-2 selective inhibitor) not only inhibited the increase of blood-brain barrier permeability, but also enhanced the apoptosis of the infiltrating neutrophils after E. coli stimulation. This suggests that TNFalpha-stimulated cyclooxygenase-2 induction play an important role on E. coli-induced brain inflammation. Its inhibition would help the resolution of neutrophil-mediated brain inflammation.

Animals↗

PubMed1999

Percolation thresholds, critical exponents, and scaling functions on planar random lattices and their duals.

The bond-percolation process is studied on periodic planar random lattices and their duals. The thresholds and critical exponents of the percolation transition are determined. The scaling functions of the percolating probability, the existence probability of the appearance of percolating clusters, and the mean cluster size are also calculated. The simulation result of the percolation threshold is p(c)=0.3333+/-0.0001 for planar random lattices, and 0.6670+/-0.0001 for the duals of planar random lattices. We conjecture that the exact value of p(c) is 1/3 for a planar random lattice and 2/3 for the dual of a planar random lattice. By taking possible errors into account, the results of our critical exponents agree with the values given by the universality hypothesis. By properly adjusting the metric factors on random lattices and their duals, we demonstrate explicitly that the idea of a universal scaling function with nonuniversal metric factors in the finite-size scaling theory can be extended to random lattices and their duals for the existence probability, the percolating probability, and the mean cluster size.

Journal Article↗

PubMed1998

Collagen-GAG substrate enhances the quality of nerve regeneration through collagen tubes up to level of autograft.

Peripheral nerve regeneration was studied across a tubulated 10-mm gap in the rat sciatic nerve using histomorphometry and electrophysiological measurements of A-fiber, B-fiber, and C-fiber peaks of the evoked action potentials. Tubes fabricated from large-pore collagen (max. pore diameter, 22 nm), small-pore collagen (max. pore diameter, 4 nm), and silicone were implanted either saline-filled or filled with a highly porous, collagen-glycosaminoglycan (CG) matrix. The CG matrix was deliberately synthesized, based on a previous optimization study, to degrade with a half-life of about 6 weeks and to have a very high specific surface through a combination of high pore volume fraction (0.95) and relatively small average pore diameter (35 microm). Nerves regenerated through tubes fabricated from large-pore collagen and filled with the CG matrix had significantly more large-diameter axons, more total axons, and significantly higher A-fiber conduction velocities than any other tubulated group; and, although lower than normal, their histomorphometric and electrophysiological properties were statistically indistinguishable from those of the autograft control. Although the total number of myelinated axons in nerves regenerated by tubulation had reached a plateau by 30 weeks, the number of axons with diameter larger than 6 microm, which have been uniquely associated with the A-fiber peak of the action potential, continued to increase at substantial rates through the completion of the study (60 weeks). The kinetic data strongly suggest that a nerve trunk maturation process, not previously reported in studies of the tubulated 10-mm gap in the rat sciatic nerve, and consisting in increase of axonal tissue area with decrease in total tissue area, continues beyond 60 weeks after injury, resulting in a nerve trunk which increasingly approaches the structure of the normal control.

Animals↗

PubMed1998

Early peripheral nerve healing in collagen and silicone tube implants: myofibroblasts and the cellular response.

Injuries to peripheral nerves innervating a limb cause paralysis, and can necessitate amputation. The inability of the nerves to regenerate spontaneously and the limitations of autograft procedures led to the development of treatments involving insertion of the nerve ends into prosthetic tubular devices. Previous work showed that 'entubulation' of the nerve ends in a silicone tube containing a specific porous, resorbable collagen-GAG (CG) copolymer, serving as an analog of extracellular matrix, improved regeneration compared to an empty silicone tube. However, long-term treatment with silicone tubes produced constriction that caused partial degradation of the regenerated axons; for this and other reasons, implementation of a nondegradable tube may require a second surgical procedure for removal. In this study the silicone tube was replaced with porous and non-porous collagen tubes in order to produce fully degradable devices. CG-filled collagen tubes and controls (CG-filled silicone tubes and empty collagen and silicone tubes) were implanted in a 10-mm gap in the rat sciatic nerve, with three rats in each group. The regeneration was evaluated after six weeks using light microscope images of cross sections of the nerve that were digitized and analyzed. Histograms of the diameters of the axons were generated and compared. The cellular response to the implanted biomaterials was assessed histologically, and immunohistochemistry was performed using an antibody to alpha-smooth muscle actin in order to determine the presence of myofibroblasts (contractile cells). Axonal regrowth was comparable in porous collagen, non-porous collagen, and silicone tubes filled with a CG matrix. These results support the implementation of a degradable collagen tube in place of a silicone device. Confirming earlier work, regeneration through the silicone and collagen tubes was enhanced by the CG copolymer, compared to empty tubes. A notable finding was a continuous layer of myofibroblasts on the surfaces of all of the six silicone tube prostheses, but on the inner surface of only one of six collagen tubes (Fisher's exact tests; P < 0.01). This is the first report of contractile capsules around silicone tubes, and supports the use of degradable collagen tubes in peripheral nerve regeneration. Macrophages were found bordering both the silicone and collagen tubes, and in the case of the collagen tubes, appeared to be participating in the regulation of the tubes.

Absorbable Implants↗