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Biomedical subjects

Masao Akagi

Publications and source records attributed to Masao Akagi.

33 records · Page 2Linked to original sources
PubMed2003

Bridging a 30-mm nerve defect using collagen filaments.

This article describes a 30-mm regeneration of severed peripheral nerve axons along collagen filaments. Two thousand or 4000 31-mm-long collagen filaments were grafted to bridge a 30-mm defect of the rat sciatic nerve. A collagen tube was grafted as a control. The mean number and mean fiber diameter of regenerated myelinated axons were 330 +/- 227 and 2.7 +/- 0.9 microm in the distal end of the 2000 collagen-filaments nerve guide, and 564 +/- 275 and 2.5 +/- 1.1 microm in the distal end of the 4000 collagen-filaments nerve guide at 12 weeks postoperatively, whereas in the distal end of the collagen tube, no regenerated axon was found. These results suggest that the collagen filaments guide axons of the rat's sciatic nerve to regenerate for 30 mm and act as a scaffold for axonal regeneration. Thirty-millimeter nerve regeneration of a 1-mm-diameter rat sciatic nerve by an artificial nerve guarantees a clinical application of the implant which should be very important for patients and surgeons.

Animals↗
PubMed2003

Bridging a spinal cord defect using collagen filament.

STUDY DESIGN: A rat model of spinal cord defect was designed to evaluate the effect of collagen filament implant on nerve regeneration in the spinal cord defect. OBJECTIVES: To bridge a spinal cord defect and restore the function in adult mammals. SUMMARY OF BACKGROUND DATA: Resection of the spinal cord in mammals is always followed by motor paralysis and loss of voluntary function below the lesion. Partial success in bridging the ends of the spinal cord after complete resection was reported. However, restoration of function has not been reported in adult mammalian. MATERIALS AND METHODS: Four thousand collagen filaments 5-mm-long were grafted to bridge a 5-mm defect of rat spinal cord. Controls had their spinal cord defect left ungrafted after resection. At 1-week intervals, animals were evaluated functionally. After 4 and 12 weeks, animals were evaluated histologically. After 12 weeks, animals were evaluated electrophysiologically. RESULTS: The severed spinal cord axons regenerated along the collagen filament implant crossing the proximal and distal spinal cord implant interfaces at 4 weeks after surgery. The rats with collagen filament grafts could walk, run, and climb with hind forelimb coordination at 12 weeks after surgery. Sensory-evoked potential waveform was found in the rats with collagen filament at 12 weeks after surgery. CONCLUSIONS: The collagen filaments support the axonal regeneration of the transected spinal cord and the restoration of function.

Animals↗
PubMed2003

Thermodynamic study of hybridization properties of heterochiral nucleic acids.

Heterochiral DNA and RNA heptamers, which contained an unnatural L-nucleotide, were synthesized, and thermodynamic analyses of their hybridization properties with complementary DNA and RNA strands were systematically conducted by UV melting experiments. The results clearly demonstrated that the incorporation of an L-ribonucleotide into the RNA strand leads to more significant destabilization of the duplexes than that of an L-deoxyribonucleotide into the DNA strand, regardless of whether the complementary strand is DNA or RNA. The destabilization of the duplexes by the substitution of D-thymidine with L-thymidine in the DNA strand is entropically driven, whereas that by the substitution of D-uridine with L-uridine in the RNA strand is enthalpically driven. The thermodynamic characteristic that the stability of homochiral duplex is far superior to that of heterochiral duplex is much more remarkable in RNA than in DNA. Thus, RNA might have been a self-replicating system superior to DNA to exclude the chiral antipode.

DNA↗
PubMed2003

Validation of acetabular cup wear volume based on direct and two-dimensional measurements: hip simulator analysis.

The volumetric wear in retrieved cups can be assessed by mathematical conversion based on linear measurements and by a fluid-displacement method. We used a hip simulator model to produce wear in 22-, 28-, and 32-mm hip implants and then assessed the volumetric wear using a gravimetric wear method. We then compared the findings with those obtained with the linear and fluid-displacement methods. For the linear method, we translated the linear wear to the volumetric wear using the equations developed by Charnley et al., Kabo et al., and Hashimoto et al. The fluid-displacement method showed the strongest correlation with the gravimetric wear method, and it was found to overestimate the volume slightly (by 3%-9%). According to the linear wear conversion, however, the equation by Kabo widely underestimated the volume by 33%-40%. The equation used by Charnley tended to overestimate the volume (by 4%-17%), whereas Hashimoto's equation tended to slightly underestimate the volume (by 2%-12%). The fluid-displacement method demonstrated an average error of 0.34% +/- 13.40% when the wear exceeded 400 mm(3). The linear wear was thus converted to the volume wear most accurately using Hashimoto's equation, with the average error being -3.8% +/- 14.0%. Of the four measurement modalities, the fluid-displacement method showed the most accurate results. We therefore confirmed that the fluid-displacement method is the most accurate way to determine volumetric wear in retrieved cups.

Acetabulum↗
PubMed2003

Reactive oxygen species depolymerize hyaluronan: involvement of the hydroxyl radical.

We have previously demonstrated that reactive oxygen species (ROS) are involved in cartilage degradation. A decrease in the size of hyaluronan (HA), which is the major macromolecule in synovial fluid and is responsible for imparting viscosity to it, is reported in arthritis patients. The purpose of this study is to determine the ROS that depolymerize HA. The luminol derivative, L-012, was used to determine the generation of ROS. To generate hydroxyl radicals, a mixture of hydrogen peroxide (H(2)O(2)) and ferrous ions (Fe(2+)) was added to HA. The antioxidants and the depolymerization of HA were studied in this system. The hydroxyl radical is one of the ROS, causing the depolymerization of HA, which reacts with L-01. These data suggest that hydroxyl radicals play an important role at the site of inflammation.

Journal Article↗
PubMed2003

Structure and physicochemical properties of diastereomeric isomers of ApA.

Heterochiral ApAs (ALpAD and ADpAL) together with homochiral D-(ApA) and L-(ApA) were synthesized and their helical structures were investigated by using spectroscopic techniques. The results indicate that the chirality of the 3'-end residue is the primary determinant for the helical sense of adenylyl-(3'-5')-adenosine (ApA).

Circular Dichroism↗
PubMed2003

In vivo three-dimensional patellar tracking on the femur.

In vivo three-dimensional patellar tracking under weightbearing conditions was investigated with the principal reference axes of the femur in the coronal and axial planes, using a biplanar image-matching technique. Three-dimensional knee models of eight healthy volunteers were constructed using computed tomography scanning. Projection images of the models were fitted onto anteroposterior and lateral radiographs of the knees at hyperextension and at every 15 degrees from 0 degrees to 120 degrees flexion. Knee motion then was reconstructed on a computer. Patellar tracking during knee flexion was described simply with a medial jerk shift of 8 mm in early flexion until 30 degrees and a linear tracking with minimal mediolateral translation. The linear tracking portion was located laterally 5 mm from the mediolateral center of the femoral condyles. On average, the direction of this linear tracking was almost perpendicular to the distal condylar line in the coronal plane and perpendicular to the posterior condylar axis in the axial plane. These results help improve the understanding of patellofemoral kinematics and provide useful information for the design and positioning of the prostheses used in total knee arthroplasty.

Adult↗
PubMed2002

30 mm regeneration of rat sciatic nerve along collagen filaments.

This paper describes 30 mm regeneration of peripheral nerve axons along collagen filaments; 31-mm-long collagen filaments or collagen tube were grafted to bridge a 30-mm defect of rat sciatic nerve. The mean number and the diameter of regenerated myelinated axons were 330+/-227 and 2.7+/-0.9 microm at the distal end of the collagen-filaments 12 weeks postoperatively; while at the distal end of the tube no axon was found.

Animals↗
PubMed2002

Lectin-like oxidized low-density lipoprotein receptor 1 mediates leukocyte infiltration and articular cartilage destruction in rat zymosan-induced arthritis.

OBJECTIVE: The relationship between rheumatoid arthritis and atherosclerosis has been recognized for >20 years. This study aimed to elucidate the roles of oxidized low-density lipoprotein (ox-LDL; one of the main pathogenic factors of atherosclerosis) and its endothelial receptor, lectin-like ox-LDL receptor 1 (LOX-1), in arthritic joints using a rat zymosan-induced arthritis (ZIA) model. METHODS: LOX-1 expression and ox-LDL accumulation in arthritic joints were detected by immunohistochemistry using specific mouse anti-LOX-1 and anti-ox-LDL monoclonal antibodies, respectively. To elucidate the effects of the expressed LOX-1 on arthritis, ZIA rats were treated with anti-LOX-1 antibody or normal mouse IgG. The severity of arthritis was analyzed by joint swelling. Cell infiltration, synovial hyperplasia, and proteoglycan losses were also determined by histologic scoring. Proinflammatory cytokine and nitrite levels in serum and joint fluid were also measured. RESULTS: Immunohistochemical study of ZIA demonstrated LOX-1 expression on synovial endothelium and postcapillary venules at 6 hours after the induction of inflammation, with maximum expression detected at 24 hours. LOX-1 was also expressed weakly on both joint cartilage and synovium. Ox-LDL, a ligand of LOX-1, was also detected in articular chondrocytes. Administration of anti-LOX-1 antibody, which blocks LOX-1 activity, suppressed joint swelling (by 33.5%), leukocyte infiltration, and joint nitrite accumulation at 24 hours, as well as cartilage destruction at 7 days, compared with control rats. CONCLUSION: LOX-1 induction in arthritic joints might play a role in promoting joint inflammation and cartilage destruction by mediating leukocyte infiltration into the arthritic joints of ZIA rats.

Animals↗
PubMed2002

Micro-wear patterns on UHMWPE tibial inserts in total knee joint simulation.

The objective of this study was to examine both simulator and retrieved total knee replacement polyethylene inserts to confirm, using scanning electron microscopy, whether similar micro-wear patterns to those seen on retrieved inserts were reproduced on simulator specimens. The simulator specimens consisted of samples subjected to sliding and rolling movement (Experiment 1) and to sliding movement only (Experiment 2). Samples from Experiment 1 demonstrated longitudinal patterns in the middle of the wear track and transverse patterns in the anterior and posterior ends, whereas in Experiment 2, only transverse patterns were observed. In the retrieved specimens, both longitudinal and transverse patterns were observed. The results showed that the simulator study reproduced similar patterns of micro-damage on polyethylene, and that the longitudinal micro-wear pattern was related to the rolling movement that is distinctive in knee kinematics.

Biomechanical Phenomena↗
PubMed2002

A mechanical comparison of 2 posterior-stabilizing designs: Insall/Burstein 2 knee and Bisurface knee.

A posterior-stabilizing knee prosthesis, called the Bisurface knee (Kyocera Corp, Kyoto, Japan), with a ball-and-socket joint installed in the midposterior portion of the tibiofemoral joint, has been developed to satisfy 2 conflicting demands in knee joint design: kinematics and wear resistance. To confirm if the prosthesis has achieved its design objectives, a contact area and stress study was done throughout the range of motion and compared with results obtained for the Insall-Burstein 2 knee. The posterior-stabilizing ability of the ball-and-socket joint also was assessed. This study showed that the ball-and-socket joint could provide sufficient posterior stability, earlier start of flexion, and lower contact stress in the tibial polyethylene insert in flexion. The design of the Bisurface knee could provide a good balance between kinematics, stability, and wear resistance.

Arthroplasty, Replacement, Knee↗
PubMed2002

Anti-HIV-1 activity of L-DNA quadruplex.

Zintevir is a DNA 17mer that forms a quadruplex and shows strong anti-human immunodeficiency virus (HIV)-1 activity. The quadruplex formation is thought to be essential for the anti-HIV-1 activity of Zintevir. We synthesized the enantiomer of Zintevir and evaluated its structure and anti-HIV-1 activity. The results showed that the enantiomer has anti-HIV-1 activity comparable to that of Zintevir although it forms the mirror image quadruplex structure of Zintevir.

Anti-HIV Agents↗
PubMed2002

A modification of the retrograde medullary screw for the treatment of bilateral pubic ramus nonunions: a case report.

We describe a patient with bilateral pubic ramus nonunions who was treated successfully with a modification of the retrograde medullary screw technique, in which the screw orientation was altered so that it engaged the cancellous bone in the inferior part of the anterior column and the anterior-inferior cortex of the fossa acetabuli. The modification should be one option when the original technique is judged to be difficult to perform.

Adult↗
PubMed2002

A practical synthesis of L-ribose.

L-Ribose was synthesized by a simple four-step method with overall yield of 76.3% from a protected L-arabinose derivative, which is a compatible intermediate for the synthesis of L-deoxyribose. The key step of this strategy is the Swern oxidation and subsequent stereoselective reduction accompanied by inversion of the 2-hydroxy group of protected L-arabinose.

Arabinose↗