Biomedical subjects

Masao Akagi

Publications and source records attributed to Masao Akagi.

At least 19 recordsLinked to original sources

PubMed2006

Oxidized LDL binding to LOX-1 upregulates VEGF expression in cultured bovine chondrocytes through activation of PPAR-gamma.

It has been reported that vascular endothelial growth factor (VEGF) and its receptors play an important role in the destruction of articular cartilage in osteoarthritis through increased production of matrix metalloproteinases. We investigated whether the oxidized low-density lipoprotein (ox-LDL) binding to lectin-like ox-LDL receptor-1 (LOX-1) upregulates VEGF expression in cultured bovine articular chondrocytes (BACs). Ox-LDL markedly increased VEGF mRNA expression and protein release in time- and dose-dependent manners, which was significantly suppressed by anti-LOX-1 antibody pretreatment. Activation of peroxisome proliferator-activated receptor (PPAR)-gamma was evident in BACs with ox-LDL addition and was attenuated by anti-LOX-1 antibody. The specific PPAR-gamma inhibitor GW9662 suppressed ox-LDL-induced VEGF expression. These results suggest that the ox-LDL/LOX-1 system upregulates VEGF expression in articular cartilage, at least in part, through activation of PPAR-gamma and supports the hypothesis that ox-LDL is involved in cartilage degradation via LOX-1.

Animals↗

PubMed2006

Axial shortening during distraction osteogenesis leads to enhanced bone formation in a rabbit model through the HIF-1alpha/vascular endothelial growth factor system.

Axial micromotion of bone fragments enhances callus formation during fracture repair or limb lengthening. To examine this, we used an axial-shortening model of the tibial callus in rabbits and performed histological analyses. After 10-mm lengthening of the left tibia with an external fixator, we shortened the callus by 2 mm. Radiographs and quantitative evaluation of corrected bone mineral density showed a significant increase in mineralization in the shortened callus (57.3 vs. 36.2%, p = 0.001). Histologically, greater osteoblast proliferation and more vigorous trabecular bone formation were noted in the shortened calluses than in the controls. Around the front of membranous bone formation in the shortened callus, there was a significant decrease in mean percentage area of vascular lumens (1.8 vs. 4.5%, p = 0.009), which seemed attributable to compressive force, and a significantly increased production of vascular endothelial growth factor (VEGF; 422.5 vs. 142.7 pg/mg protein, p = 0.007) and its receptors. There were also increased numbers of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts and proliferating cell nuclear antigen (PCNA)-positive cells. A marked increase of hypoxia inducible factor-1alpha (HIF-1alpha) expression in osteoblasts was also observed in this area. Thus, enhancement of membranous bone formation by static compression or axial dynamization may be at least partly attributable to HIF-1alpha-mediated VEGF induction following the local hypoxia caused by collapse of vascular lumens.

Alkaline Phosphatase↗

PubMed2006

Cyclic tensile stretch load and oxidized low density lipoprotein synergistically induce lectin-like oxidized ldl receptor-1 in cultured bovine chondrocytes, resulting in decreased cell viability and proteoglycan synthesis.

Mechanical stimulation is known to be an essential factor in the regulation of cartilage metabolism. We tested the hypothesis that expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) can be modulated by cyclic tensile stretch load in chondrocytes. Cyclic loading of repeated stretch stress at 10 cycles per minute with 10 kPa of stress for 6 h induced expression of LOX-1 to 2.6 times control in cultured bovine articular chondrocytes, equivalent to the addition of 10 microg/mL oxidized low density lipoprotein (ox-LDL) (2.4 times control). Application of the cyclic load to the chondrocytes along with 10 microg/mL ox-LDL resulted in synergistically increased LOX-1 expression to 6.3 times control. Individual application of cyclic loading and 10 microg/mL ox-LDL significantly suppressed chondrocytes viability (84.6% +/- 3.4% and 80.9% +/- 3.2% of control at 24 h, respectively; n = 3; p < 0.05) and proteoglycan synthesis [81.0% +/- 7.1% and 85.7% +/- 5.2% of control at 24 h, respectively; p < 0.05 when compared with 94.6% +/- 4.6% for native-LDL (n = 3)]. Cyclic loading and 10 microg/mL ox-LDL synergistically affected cell viability and proteoglycan synthesis, which were significantly suppressed to 45.6% +/- 4.9% and 48.7% +/- 6.7% of control at 24 h, respectively (n = 3; p < 0.01 when compared with individual application of cyclic loading or 10 microg/mL ox-LDL). In this study, we demonstrated synergistic effects of cyclic tensile stretch load and ox-LDL on cell viability and proteoglycan synthesis in chondrocytes, which may be mediated through enhanced expression of LOX-1 and which has important implications in the progression of cartilage degeneration in osteoarthritis.

Animals↗

PubMed2006

Wear and toughness of crosslinked polyethylene for total knee replacements: a study using a simulator and small-punch testing.

Severe loading and complex kinematics in total knee replacement make wear performance and toughness of the polyethylene in tibial inserts important. We investigated wear of crosslinked polyethylene using a knee simulator and measured toughness using small-punch testing. GUR1050 rods were gamma-irradiated in air at doses from 0 to 200 kGy, annealed in nitrogen, and machined into tibial inserts. The simulator was run to 4 million cycles, and wear rates determined from weight loss. Wear rate decreased by 54, 78, and 95% as radiation dose increased from 50 to 75 to 100 kGy, respectively. At every dose, toughness was significantly less after simulator testing, but the difference between control and wear-tested polyethylene, considered to be due to fatigue damage accumulation, was smallest at 50 kGy. The simulator-tested polyethylene that received 35 to 75 kGy had slightly higher toughness than equivalent material that received no irradiation. However, the toughness of simulator-tested polyethylene that received 150 and 200 kGy was lower than that of the simulator-tested polyethylene that received no irradiation. Our results suggest that an optimal irradiation dose may exist for crosslinked polyethylene for use in TKR and that the optimum dose would be less than the 100 kGy or more that are used in some current crosslinked polyethylene for hip replacement.

Biomechanical Phenomena↗

PubMed2006

Structural studies of heterochiral DNA/DNA, RNA/RNA, and DNA/RNA duplexes.

Using DNA and RNA heptanucleotides containing an unnatural L-nucleotides as well as the complementary strands, effects of the introduction of an L-nucleotide on the structure of DNA/DNA, RNA/RNA, and DNA/RNA duplexes were investigated by circular dichroism experiments and RNase H-mediated RNA strand cleavage reaction. The results suggested that the substitution of the central D-nucleotide with an L-nucleotide in the duplexes causes the significant structural alterations as the duplex structures change to conformations with more B-form similarities.

Circular Dichroism↗

PubMed2006

Synthesis and properties of G-quartet oligonucleotide-HIV-1 tat peptide conjugate.

Zintevir is a single strand DNA that forms an intramolecular quadruplex structure and shows potent anti-human immunodeficiency virus type 1 (HIV-1) activity. Zintevir was discovered as a potent inhibitor for HIV-1 integrase. Recently, the primary molecular target of Zintevir, however, was shown to be the HIV-1 gp120. In fact, in our previous study, Zintevir was shown to inhibit the only processes of the viral adsorption and the entry into the cell. This result suggests that Zintevir is not able to penetrate through the cell membranes. Therefore, we designed and synthesized the complex of D-17mer with HIV-1 tat peptide that has the cell membrane permeability.

Anti-HIV Agents↗

PubMed2005

Kinetic analysis of hydrolytic reaction of homo- and heterochiral adenylyl(3'-5')adenosine isomers: breaking homochirality reduces hydrolytic stability of RNA.

The hydrolytic stability of the diastereomeric isomers of ApA was compared and the results show that heterochiral ApAs are more rapidly hydrolyzed than homochiral ApAs at low temperatures, suggesting that hydrolytic selection in cold environments in conjunction with selective polymerization may have been effective in enriching the homochirality of RNA.

Dinucleoside Phosphates↗

PubMed2005

The functional flexion-extension axis of the knee corresponds to the surgical epicondylar axis: in vivo analysis using a biplanar image-matching technique.

We investigated the concept that the knee has a fixed flexion-extension axis in the posterior femoral condyles and that this functional axis corresponds to the surgical epicondylar axis in vivo. We used a biplanar image-matching technique to perform the in vivo analysis of 9 normal knees to determine the location of the functional flexion-extension axis of the knee using an optimization technique. The functional flexion-extension axis passed through the sulcus of the medial epicondyle and the prominence of the lateral epicondyle. Flexion and extension of the knee could be represented as a rotation around a fixed axis, and this functional axis corresponded to the surgical epicondylar axis during a 0 degrees to 90 degrees flexion. This study assists more understanding of knee kinematics and provides useful information for the design and positioning of the prostheses used in total knee arthroplasty.

Adult↗

PubMed2005

Characterization of Na+-montmorillonite-catalyzed reaction of racemic ribonucleotides.

We have reported that the oligomerization of racemic mononucleotides catalyzed by montmorillonite clay proceeds efficiently and gives up to 8-mer. Here, we attempted to identify the dimer products to show the characteristics of the racemic reaction. The results suggested that homochiral pApAs are formed in somewhat higher yield than heterochiral pApAs. Therefore, the oligomerization of racemic mononucleotides catalyzed by montmorillonite shows the homochiral selectivity.

Adenosine Monophosphate↗

PubMed2005

Variability of extraarticular tibial rotation references for total knee arthroplasty.

Anatomic reference axes that determine rotational alignment of the tibial component have not been established. To assess variability of three anatomic reference axes (a new tibial anteroposterior axis that we proposed, the transmalleolar axis of the ankle, and the second metatarsus bone axis of the foot), we measured the angles between a defined anteroposterior axis of the tibia (a line perpendicular to the transepicondylar axis) and each of the three axes in 57 knees of healthy subjects using computed tomography scans. The angle between the defined anteroposterior axis and our proposed anteroposterior axis (a line connecting the middle of the posterior cruciate ligament and the medial edge of the patellar tendon attachment) averaged -0.2 degrees +/- 2.8 degrees (range, -5.5 degrees -6.3 degrees). The angle between the defined anteroposterior axis and the transmalleolar axis averaged 25.9 degrees +/- 9 degrees (range, 8 degrees -49.4 degrees), and the angle between the defined anteroposterior axis and the second metatarsus bone axis averaged 5.2 degrees +/- 10 degrees (range, -21.9 degrees -24 degrees). The variability of the anteroposterior axis was less than than the other reference axes. These data indicate that our proposed tibial anteroposterior axis is more reliable for determining rotational alignment of the tibial component in total knee arthroplasty.

Adult↗

PubMed2004

Restoration of function after spinal cord transection using a collagen bridge.

The restoration of function of transected adult mammalian spinal cord without living tissue has not been reported previously. We report the first success of functional restoration of transected spinal cord without living tissue. We grafted collagen filaments parallel or transverse to the axis of the spinal cord to bridge 5-mm defects of 47 adult rat spinal cords. Twenty-five rats were used as a control. Of the 72 rats, 42 rats survived the experimental period. At 4 weeks postoperatively, regenerated axons crossed the proximal and distal spinal cord-implant interfaces in all 5 rats of the parallel-grafted group. At 12 weeks postoperatively, the rats in the parallel-grafted group (8 rats) could walk, run, and climb with hind-forelimb coordination. The somatosensory-evoked potentials were seen. Results suggest that the collagen filaments support the axonal regeneration of the transected spinal cord and the restoration of function when grafted parallel to the axis of the spinal cord. The functional restoration appeared to be permanent, raising the possibility of therapeutic application in humans.

Absorbable Implants↗

PubMed2004

Anti-HIV-1 activity and mode of action of mirror image oligodeoxynucleotide analogue of Zintevir.

Zintevir is an oligonucleotide analogue, which has the phosphorothioate modification at both termini, that forms a K(+)-induced quadruplex structure and shows potent anti-human immunodeficiency virus (HIV)-1 activity. We synthesized the non-modified analogue (D-17mer) of Zintevir and its enantiomer (L-17mer), and compared their anti-HIV-1 activity and molecular mechanism of action. Although L-17mer forms the exact mirror image quadruplex structure of D-17mer, which has a very similar structure with Zintevir, L-17mer showed comparable anti-HIV-1 activity with Zintevir. The results obtained by the time-of-addition experiments and the immunofluorescence binding assay strongly suggest that the primary molecular target of L-17mer is the viral gp120 envelope protein as well as Zintevir, regardless of their reciprocal chirality.

Anti-HIV Agents↗

PubMed2004

Lectin-like oxidized low-density lipoprotein receptor 1 mediates matrix metalloproteinase 3 synthesis enhanced by oxidized low-density lipoprotein in rheumatoid arthritis cartilage.

OBJECTIVE: To investigate for the presence of oxidized low-density lipoprotein (ox-LDL) and lectin-like oxidized LDL receptor 1 (LOX-1) in cartilage specimens from rheumatoid arthritis (RA) joints and to determine whether the interaction of ox-LDL with LOX-1 can induce matrix metalloproteinase 3 (MMP-3) in articular cartilage explant culture. METHODS: Human articular cartilage specimens obtained from patients with RA, osteoarthritis (OA), and femoral neck fractures were examined for LOX-1 and ox-LDL by confocal fluorescence microscopy. The association between ox-LDL and LOX-1 was evaluated by immunofluorescence analysis. Articular cartilage specimens from patients with femoral neck fractures were incubated with ox-LDL, with or without preincubation with neutralizing anti-LOX-1 antibody. MMP-3 synthesis by chondrocytes in explant cartilage was evaluated by immunofluorescence, and protein secretion into conditioned medium was monitored by immunoblotting and enzyme-linked immunosorbent assay. RESULTS: The majority of the RA chondrocytes stained positively with both anti-LOX-1 and anti-ox-LDL antibodies; however, no positive cells were found in OA and normal cartilage specimens. Anti-LOX-1 antibody suppressed the binding of DiI-labeled ox-LDL to chondrocytes in explant culture, suggesting that the interaction was mediated by LOX-1. In contrast to native LDL, ox-LDL induced MMP-3 synthesis by articular chondrocytes in association with the induction of LOX-1, which resulted in enhanced secretion of MMP-3 into the culture medium. Anti-LOX-1 antibody reversed ox-LDL-stimulated MMP-3 synthesis to control levels. CONCLUSION: Ox-LDL, principally mediated by LOX-1, enhanced MMP-3 production in articular chondrocytes. Increased accumulation of ox-LDL with elevated expression of LOX-1 in RA cartilage indicates a specific role of the receptor-ligand interaction in cartilage pathology in RA.

Antibodies↗

PubMed2004

Late dissociation of an alumina-on-alumina bearing modular acetabular component.

Alumina-on-alumina bearings for total hip arthroplasty have been introduced as a promising alternative to reduce wear debris and to increase the life expectancy of the prosthesis. We report a case of a late dissociation of an alumina-on-alumina bearing modular acetabular component, which occurred 2 years, 8 months after surgery. Detailed analysis of the retrieved prosthesis suggested that the cause of the failure may be strong rotational torque developed by a roughening of the bearing's alumina surface caused by edge loading (microseparation). The strong friction torque in articulation may explain the higher reported rate of mechanical loosening of the acetabular component in alumina-on-alumina bearing total hip prostheses.

Acetabulum↗

PubMed2004

Oxidized low-density lipoprotein (ox-LDL) binding to lectin-like ox-LDL receptor-1 (LOX-1) in cultured bovine articular chondrocytes increases production of intracellular reactive oxygen species (ROS) resulting in the activation of NF-kappaB.

OBJECTIVE: To examine the effect of oxidized low-density lipoprotein (ox-LDL) on the intracellular production of reactive oxygen species (ROS) in bovine articular chondrocytes (BACs) and to investigate whether this increase occurs through binding to the receptor lectin-like ox-LDL receptor-1 (LOX-1). Furthermore, to ascertain whether the binding of ox-LDL to LOX-1 results in NF-kappaB activation. DESIGN: BACs were preincubated with 2',7'-dichlorofluorescin diacetate (DCFH-DA), a dye that allows the monitoring of intracellular ROS production for DCF by spectrofluorometry. BACs were incubated with native LDL and ox-LDL (10, 50, and 100 microg/ml) for 5 min at 37 degrees C and DCF formation was observed. BACs were also preincubated with anti-LOX-1 mAb (40 microg/ml) or ascorbic acid (10 microM). Nuclear extracts from BACs treated for the indicated periods with 50 microg/ml ox-LDL, and preincubated with anti-LOX-1 mAb or ascorbic acid, were prepared and analyzed by electrophoretic mobility shift assay (EMSA). RESULTS: ox-LDL induced a significant dose-dependent increase in ROS production after 5-min incubation with BACs (P < 0.001). ROS formation was markedly reduced in BACs preincubated with anti-LOX-1 mAb and ascorbic acid (P < 0.001). Activation in BACs of the transcription factor NF-kappaB was evident after 5-min incubation with ox-LDL and was attenuated by anti-LOX-1 mAb and ascorbic acid. CONCLUSION: ox-LDL binding to LOX-1 in BACs increased the production of intracellular ROS and activated NF-kappaB. Reduction of NF-kappaB activation by ascorbic acid indicates that the activation, at least in part, is ROS-dependent. These observations support the hypothesis that hypercholesterolemia is one of several risk factors for arthritis, and that lipid peroxidation products such as ox-LDL are involved in cartilage matrix degradation.

Animals↗

PubMed2004

An anteroposterior axis of the tibia for total knee arthroplasty.

The objective of the current study was to identify a new extraarticular anatomic landmark indicating the anteroposterior orientation of the tibia using computed tomography. In 39 volunteers (20 males, 19 females), computed tomography scans for healthy right knees in extension were done perpendicular to the tibial shaft axis. The anteroposterior axis of the tibia was defined as a line perpendicular to the transepicondylar axis and passing through the middle of the posterior cruciate ligament. At the level of the tibial plateau and the patellar tendon attachment, the mean medial percentage width of intersecting point of the patellar tendon and the anteroposterior axis was 10.8% +/- 9.8% (range, -9.3% - +30.0%) and -0.2% +/- 10.4% (range, -23.6% -+23.0%), respectively. The mean angle between the anteroposterior axis and a line connecting the middle of the posterior cruciate ligament to the medial border of the patellar tendon attachment was 0.0 degrees +/- 2.8 degrees (range, -6.3 degrees -+5.2 degrees). The medial border of this attachment therefore can serve as a reliable anterior anatomic landmark to determine the anteroposterior axis of the tibia, and the line connecting the middle of the posterior cruciate ligament and the medial border of the attachment may be useful as a reference axis indicating the anteroposterior orientation of the tibia.

Adult↗

PubMed2004

Nerve regeneration along collagen filament and the presence of distal nerve stump.

This article describes the regeneration of severed peripheral nerve axons along collagen filaments in the absence of the distal nerve stump. 22-mm long nerve guides made of collagen filaments were sutured to the proximal ends of severed rat sciatic nerves. The distal ends of the guides were sutured to the distal stumps of the nerves in a group and not sutured in the other. Nerve autografts and collagen tubes were used as controls. At 8 weeks postoperatively, the mean number and the mean diameter of myelinated axons were 5491 +/- 617 (mean +/- SD) and 2.3 +/- 1.3 microns at the distal ends of the collagen filaments nerve guides those the distal ends were sutured to the distal stumps of the nerves, while in the nerve autografts these were 4837 +/- 604 and 3.3 +/- 1.4 microns. These were 1992 +/- 770 and 2.7 +/- 1.2 microns at the distal ends of the collagen-filaments guides those the distal ends were not sutured to the distal stumps of the nerves, while in the nerve autografts these were 3041 +/- 847 and 2.3 +/- 1.1 microns. No axon was found at the distal ends of the collagen tubes. The results suggested that the contact guidance and the chemotaxis guided regenerating axons along the collagen filaments.

Animals↗

PubMed2003

Synthesis and hybridization properties of l-oligodeoxynucleotide analogues fixed in a low anti glycosyl conformation.

We have synthesized l-type enantiomers (cU and cA) of nucleoside analogues, whose glycosyl bonds are fixed in a low anti conformation (ap glycosyl conformation, [small chi][approximate] 180[degree]), and incorporated them into oligonucleotides to evaluate the hybridization ability with natural DNA and RNA sequences. Although the incorporation of the modified nucleosides into oligonucleotides decreased the hybridization ability with unmodified complementary DNA sequences, the fully-substituted 12mers (cU(12) and cA(12)) still retained the hybridization ability with the complementary unmodified DNA 12mers, regardless of their unnatural l-chirality. In contrast, cU(12) and cA(12) showed different hybridization behavior with complementary unmodified RNA 12mers. cU(12) forms a more stable duplex with rA(12) than the corresponding natural 12mer (dT(12)), whereas cA(12) cannot hybridize with rU(12). Based on the model structure of cU(12)-rA(12), we discuss these experimental results.

Animals↗