Biomedical subjects

Takashi Okamoto

Publications and source records attributed to Takashi Okamoto.

At least 19 recordsLinked to original sources

PubMed2026

Monitoring the fate of paternal mitochondria and their elimination in rice zygotes.

Mitochondria are preferentially transmitted from the maternal plant in most angiosperms, including rice, and paternal mitochondria are generally eliminated during microgametogenesis and/or in zygotes. The mechanism by which paternal mitochondria are eliminated progresses during plant reproductive processes. In the present study, we examined the distribution of paternal mitochondria in rice sperm cells and zygotes produced through the in vitro fertilization (IVF) of isolated rice gametes. Male gametes of rice possess mitochondria with nucleoids, suggesting the potential transfer of paternal mitochondria and their DNA into zygotes on fertilization and subsequent selective elimination of paternal mitochondria in the zygote. To intensively monitor the fate of rice paternal mitochondria in zygotes immediately after gamete fusion, time-lapse observations were conducted in paternal mitochondria labeled with GFP from rice zygotes produced using an IVF system. The results showed that the paternal mitochondria are progressively degraded during the early developmental stage at 1 to 3 h after fusion (HAF), leaving a small number of paternal mitochondria at 6 HAF. The remaining paternal mitochondria were considered to be degraded in later developmental-stage zygotes because paternal mitochondrial DNA-derived single-nucleotide polymorphisms were not detected in the sequencing reads of genomic DNA prepared from inter-subspecific hybrid rice. In addition, treatment with autophagy inhibitors stabilized the paternal mitochondria in zygotes. This suggests that the autophagy-dependent massive and selective elimination machinery for male mitochondria functions in rice zygotes immediately after gamete fusion and supports the strict maternal inheritance of mitochondria in rice.

Oryza↗

PubMed2006

Spontaneous regression of osteochondromas.

Spontaneous regression of an osteochondroma is an infrequent event. In this report, two cases with spontaneous regression of osteochondromas are presented. The first case was a solitary osteochondroma of the pedunculated type involving the right proximal humerus in a 7-year-old boy. This lesion resolved over 15 months of observation. The second case was a 3-year-old girl with multiple osteochondromatosis, in whom sessile osteochondromas of the right tibia and left fibula regressed over 33 months. The mechanism of this phenomenon is discussed with a review of previous reports. Regarding treatment, careful observation may be acceptable for typical osteochondromas, especially in young children.

Bone Neoplasms↗

PubMed2006

A single-nucleotide synonymous mutation in the gag gene controlling human immunodeficiency virus type 1 virion production.

Viral factors as well as host ones play major roles in the disease progression of human immunodeficiency virus type 1 (HIV-1) infection. We have examined cytotoxic T-lymphocyte activity and HIV-1 DNA PCR results of 312 high-risk seronegative drug users in northern Thailand and identified four seronegative cases positive for both assays. Furthermore, we have identified a synonymous mutation in nucleotide position 75 of the gag p17 gene (A426G) of HIV-1 that belongs to the CRF01_AE virus circulating in Thailand. The replication-competent HIV-1 clone containing the A426G mutation demonstrated a dramatic reduction of virion production and perturbation of viral morphogenesis without affecting viral protein synthesis in cells.

DNA, Viral↗

PubMed2006

Aberrant MHC class II expression in mouse joints leads to arthritis with extraarticular manifestations similar to rheumatoid arthritis.

Genetic susceptibility to rheumatoid arthritis (RA) is associated with certain MHC class II molecules. To clarify the role of these determinants in RA, we generated the D1CC transgenic mouse that expressed genes involved in antigen processing and presentation by the MHC class II pathway in joints. The class II transactivator, which was transcribed from the rat collagen type II promoter and enhancer, directed the expression of these genes. In D1CC mice congenic for the H-2(q) (DBA/1) background, small amounts of bovine collagen type II in adjuvant induced reproducibly an inflammatory arthritis resembling RA. Importantly, these stimuli had no effect in DBA/1 mice. Eighty-nine percent of D1CC mice developed chronic disease with joint swelling, redness, and heat in association with synovial proliferation as well as pannus formation and mononuclear infiltration of synovial membranes. Granulomatous lesions resembling rheumatoid nodules and interstitial pneumonitis also were observed. As in patients with RA, anticyclic citrullinated peptide antibodies were detected during the inflammatory stage. Finally, joints in D1CC mice displayed juxtaarticular demineralization, severe joint space narrowing, and erosions, which led to ankylosis, but without the appearance of osteophytes. Thus, aberrant expression of MHC class II in joints facilitates the development of severe erosive inflammatory polyarthritis, which is very similar to RA.

Animals↗

PubMed2006

Pancreatitis-associated protein-III is a novel macrophage chemoattractant implicated in nerve regeneration.

Circulating macrophages are recruited to degenerating nerves in response to nerve injury to remove myelin and axonal debris, a process that is crucial for successful nerve regeneration. In this study, we demonstrate that pancreatitis-associated protein (PAP)-III is a macrophage chemoattractant that is induced in and released from injured nerves. In vitro experiments revealed that PAP-III possessed a strong macrophage chemoattractant activity that was comparable with that of monocyte chemoattractant protein-1. In addition, gene knockdown via adenovirus-mediated small interference RNA expression in isolated sciatic nerves successfully suppressed PAP-III expression and its macrophage chemoattractant activity. Furthermore, overexpression or knockdown of the PAP-III gene in crushed sciatic nerves in rats resulted in acceleration or retardation of macrophage recruitment and subsequent nerve regeneration, respectively. Collectively, our results demonstrate that PAP-III is a novel macrophage chemoattractant that is involved in peripheral nerve regeneration and further provide new insights into Schwann cell-macrophage interactions and therapeutic interventions.

Adenoviridae↗

PubMed2006

Organization pattern of nacre in Pteriidae (Bivalvia: Mollusca) explained by crystal competition.

Bivalve nacre is a brick-wall-patterned biocomposite of aragonite platelets surrounded by organic matter. SEM-electron back scatter diffraction analysis of nacre of the bivalve family Pteriidae reveals that early aragonite crystals grow with their c-axes oriented perpendicular to the growth surface but have their a- and b-axes disoriented. With the accumulation of successive lamellae, crystals progressively orient themselves with their b-axes mutually parallel and towards the growth direction. We propose that progressive orientation is a result of competition between nacre crystals at the growth front of lamellae, which favours selection of crystals whose fastest growth axis (b-axis) is oriented parallel to the direction of propagation of the lamella. A theoretical model has been developed, which simulates competition of rhombic plates at the lamellar growth front as well as epitaxial growth of crystals onto those of the preceding lamella. The model predicts that disordered nacre progressively produces bivalve-like oriented nacre. As growth fronts become diffuse (as is the common case in bivalves) it takes longer for nacre to become organized. Formation of microdomains of nacre platelets with different orientations is also reproduced. In conclusion, not only the organic matrix component, but also the mineral phase plays an active role in organizing the final microstructure.

Animals↗

PubMed2006

The tramadol metabolite, O-desmethyl tramadol, inhibits 5-hydroxytryptamine type 2C receptors expressed in Xenopus Oocytes.

PURPOSE: Tramadol is widely used clinically as an analgesic, yet the mechanism by which it produces antinociception remains unclear. O-Desmethyl tramadol, the main metabolite of tramadol, is a more potent analgesic than tramadol. We reported previously that tramadol inhibits the 5-hydroxytryptamine (5-HT) type 2C receptor (5-HT(2C)R), a G-protein-coupled receptor that is expressed widely within brain and that mediates several effects of 5-HT, including nociception, feeding, and locomotion. The effects of O-desmethyl tramadol on 5-HT(2C)R have not been studied. In this study, we investigated the effect of O-desmethyl tramadol on 5-HT(2C)R expressed in Xenopus oocytes. METHODS: We examined the effect of O-desmethyl tramadol on 5-HT(2C)R using the Xenopus oocyte expression system. Furthermore, we investigated the effects of O-desmethyl tramadol on the binding of [(3)H]5-HT by 5-HT(2C)R. RESULTS: O-Desmethyl tramadol, at pharmacologically relevant concentrations, inhibited 5-HT-evoked Ca(2+)-activated Cl(-) currents in oocytes that expressed 5-HT(2C)R. The inhibitory effect of O-desmethyl tramadol on 5-HT(2C)R was overcome at higher concentrations of 5-HT. Bisindolylmaleimide I (GF109203X), a protein kinase C inhibitor, increased 5-HT-evoked currents but had little effect on the inhibition of 5-HT-evoked currents by O-desmethyl tramadol. O-Desmethyl tramadol inhibited the specific binding of [(3)H]5-HT by 5-HT(2C)R expressed in oocytes. O-Desmethyl tramadol altered the apparent dissociation constant for binding of [(3)H]5-HT by 5-HT(2C)R without changing maximum binding, which indicated competitive inhibition. CONCLUSION: These results suggest that O-desmethyl tramadol inhibits 5-HT(2C)R, which provides further insight into the pharmacological properties of tramadol and O-desmethyl tramadol.

Animals↗

PubMed2006

Transcriptional repression of human immunodeficiency virus type 1 by AP-4.

Elucidation of the mechanism of transcriptional silencing of human immunodeficiency virus type 1 (HIV-1) provirus in latently infected cells is crucial to understand the pathophysiology of HIV-1 infection and to develop novel therapies. Here we demonstrate that AP-4 is responsible for the transcriptional repression of HIV-1. We found that AP-4 site within the viral long terminal repeat (LTR) is well conserved in the majority of HIV-1 subtypes and that AP-4 represses HIV-1 gene expression by recruiting histone deacetylase (HDAC) 1 as well as by masking TATA-binding protein to TATA box. AP-4-mediated transcriptional repression was inhibited by an HDAC inhibitor, tricostatin A, and could be exerted even at distant locations from the TATA box. In addition, AP-4 interacted with HDAC1 both in vivo and in vitro. Moreover, chromatin immunoprecipitation assays have revealed that AP-4 and HDAC1 are present in the HIV-1 LTR promoter in latently infected ACH2 and U1 cells, and they are dissociated from the promoter concomitantly with the association of acetylated histone H3, TBP, and RNA polymerase II upon TNF-alpha stimulation of HIV-1 replication. Furthermore, when AP-4 is knocked down by siRNA, HIV-1 production was greatly augmented in cells transfected with a full-length HIV-1 clone. These results suggest that AP-4 may be responsible for transcriptional quiescence of latent HIV-1 provirus and give a molecular basis to the reported efficacy of combination therapy of conventional anti-HIV drugs with an HDAC inhibitor in accelerating the clearance of HIV-1 from individuals infected with the virus.

Antiviral Agents↗

PubMed2006

Metal ions dramatically enhance the enantioselectivity for lipase-catalysed reactions in organic solvents.

We propose a simple and a powerful method to enhance the enantioselectivity for lipase-catalysed transformations in organic solvents by an addition of metal ion-containing water to the reaction mixture. In this paper, various metal ions such as LiCl or MgCl2 are tested to improve the enantioselectivity for the model reactions. The enantioselectivities obtained are dramatically enhanced, the E values of which are about 100-fold as compared with the ordinary conditions without a metal ion, for example, E = 200 by addition of LiCl. Furthermore, lowering the reaction temperature led to an almost perfect enantioselectivity of lipase in the presence of a metal ion, for example, E = 1,300 by addition of LiCl. Also, a mechanism for the drastic enhancement by metal ions is discussed briefly on the basis of the EPR spectroscopic study and the initial rate for each enantiomer of the substrate.

Candida↗

PubMed2006

Aortic valve myxoma mimicking vegetation: report of a case.

We report a case of cardiac myxoma of the aortic valve. To our knowledge, this represents only the seventh such case ever documented. A 61-year-old woman underwent an echocardiography to screen for hypertensive-diabetic cardiac complications, which showed a mass on her aortic valve. Although she had not experienced a fever, the mass closely resembled a vegetation, resulting in an initial diagnosis of infective endocarditis. We extirpated the mass and repaired the aortic valve with the patient under cardiopulmonary bypass. The postoperative course was uneventful. Histological examination confirmed that the mass was a myxoma.

Aortic Valve↗

PubMed2006

Initial clinical experience with the Heartstring.

OBJECTIVE: The Heartstring is one of the devices that enable proximal anastomosis without clamping the aorta. We have applied the device not only to low-risk patients with normal aortas but also to high-risk patients with diseased aortas. The purpose of this study was to investigate the initial outcomes of using this device. METHODS: The Heartstring was used on 87 patients between January and December 2004. The patients comprised 62 men and 25 women 48-86 years old (mean 68.4 +/- 8.4 years). The ascending aorta was evaluated by computed tomography (CT) scanning before surgery. If a patient's aorta was severely calcified, epiaortic echocardiography was performed. The aortas were ranked into four grades, and the preoperative patient's status were evaluated by the EuroSCORE. Angiography was performed on the third postoperative day. RESULTS: CT scanning revealed that 74 patients had no calcification in the ascending aorta, 10 patients had scattered calcification, and 3 patients had plate-like calcification. The EuroSCORE was 6.86 +/- 1.03. We performed 93 proximal anastomoses and 149 distal anastomoses. The average distal anastomosis was 1.6 +/- 0.6 sites per graft. Of the distal anastomoses, 74.2% were to the circumflex artery territory. Postoperative coronary angiography revealed that all grafts were patent. CONCLUSION: The Heartstring facilitates safe proximal anastomosis, even in high-risk patients. Their short-term outcome was good. The device assists in bypassing circumflex artery territory. Long-term follow-up is necessary.

Aged↗

PubMed2006

Inhibition of human immunodeficiency virus type 1 replication in latently infected cells by a novel IkappaB kinase inhibitor.

In human immunodeficiency virus type 1 (HIV-1) latently infected cells, NF-kappaB plays a major role in the transcriptional induction of HIV-1 replication. Hence, downregulation of NF-kappaB activation has long been sought for effective anti-HIV therapy. Tumor necrosis factor alpha (TNF-alpha) stimulates IkappaB kinase (IKK) complex, a critical regulator in the NF-kappaB signaling pathway. A novel IKK inhibitor, ACHP {2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-piperidin-4-yl-nicotinonitrile}, was developed and evaluated as a potent and specific inhibitor for IKK-alpha and IKK-beta. In this study, we examined the ability of this compound to inhibit HIV-1 replication in OM10.1 cells latently infected with HIV. When these cells were pretreated with ACHP, TNF-alpha-induced HIV-1 replication was dramatically inhibited, as measured by the HIV p24 antigen levels in the culture supernatants. Its 50% effective concentration was approximately 0.56 microM, whereas its 50% cytotoxic concentration was about 15 microM. Western blot analysis revealed inhibition of IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 nuclear translocation, and p65 phosphorylation. ACHP was also found to suppress HIV-1 long terminal repeat (LTR)-driven gene expression through the inhibition of NF-kappaB activation. Furthermore, ACHP inhibited TNF-alpha-induced NF-kappaB (p65) recruitment to the HIV-1 LTR, as assessed by chromatin immunoprecipitation assay. These findings suggest that ACHP acts as a potent suppressor of TNF-alpha-induced HIV replication in latently infected cells and that this inhibition is mediated through suppression of IKK activity.

Active Transport, Cell Nucleus↗

PubMed2006

NF-kappaB and rheumatic diseases.

NF-kappaB is an inducible transcription factor that is controlled by the signal activation cascades. NF-kappaB controls a number of genes involved in immuno-inflammatory responses, cell cycle progression, inhibition of apoptosis, and cell adhesion, thus promoting chronic inflammatory responses. In fact, NF-kappaB is constitutively activated in some rheumatic conditions such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Interestingly, a number of anti-RA compounds have been shown to exhibit anti-NF-kappaB activities. In addition, NF-kappaB activation has been linked to carcinogenesis and its constitutive activation has been demonstrated in some cancers and leukemias. These findings have substantiated the long-standing proposal of the link among chronic inflammation, autoimmunity, and carcinogenesis by molecular terms. In this review, I have attempted to overview the pathologic involvement of NF-kappaB in rheumatic diseases and discuss the feasibility of a therapeutic strategy with NF-kappaB and its signaling cascade as novel molecular targets.

Animals↗

PubMed2005

Hyperpolarization-activated cation current (Ih) is an ethanol target in midbrain dopamine neurons of mice.

Ethanol stimulates the firing activity of midbrain dopamine (DA) neurons, leading to enhanced dopaminergic transmission in the mesolimbic system. This effect is thought to underlie the behavioral reinforcement of alcohol intake. Ethanol has been shown to directly enhance the intrinsic pacemaker activity of DA neurons, yet the cellular mechanism mediating this excitation remains poorly understood. The hyperpolarization-activated cation current, Ih, is known to contribute to the pacemaker firing of DA neurons. To determine the role of Ih in ethanol excitation of DA neurons, we performed patch-clamp recordings in acutely prepared mouse midbrain slices. Superfusion of ethanol increased the spontaneous firing frequency of DA neurons in a reversible fashion. Treatment with ZD7288, a blocker of Ih, irreversibly depressed basal firing frequency and significantly attenuated the stimulatory effect of ethanol on firing. Furthermore, ethanol reversibly augmented Ih amplitude and accelerated its activation kinetics. This effect of ethanol was accompanied by a shift in the voltage dependence of Ih activation to more depolarized potentials and an increase in the maximum Ih conductance. Cyclic AMP mediated the depolarizing shift in Ih activation but not the increase in the maximum conductance. Finally, repeated ethanol treatment in vivo induced downregulation of Ih density in DA neurons and an accompanying reduction in the magnitude of ethanol stimulation of firing. These results suggest an important role of Ih in the reinforcing actions of ethanol and in the neuroadaptations underlying escalation of alcohol consumption associated with alcoholism.

Action Potentials↗

PubMed2005

Estrogen stimulates transcription of human immunodeficiency virus type 1 (HIV-1).

Gene expression from human immunodeficiency virus (HIV) provirus is a crucial step for the viral replication. Here we examined a potential role of 17beta-estradiol (E2) in HIV-1 transcription. Transient luciferase expression studies revealed that E2 activated HIV-LTR reporter gene in HEK293 cells when the cells were co-transfected with estrogen receptor alpha (ERalpha) but not ERbeta expression plasmid. This E2 effect was abrogated by a specific antagonist to ER, ICI 182,780, indicating that it was mediated by ERalpha. Mutation analysis revealed that Sp1 binding site but not nuclear factor-kappa B (NF-kappaB) binding site of HIV-1 LTR is critical to the E2 effect. In addition, whereas E2 could not induce DNA-binding activity of NF-kappaB, E2 could augment both Sp1 DNA-binding and transcriptional activity. These findings suggest a contribution of estrogen for HIV-1 replication through ERalpha by augmenting Sp1 DNA-binding and transcriptional activity.

Blotting, Western↗

PubMed2005

Prevention of the ultraviolet B-mediated skin photoaging by a nuclear factor kappaB inhibitor, parthenolide.

The skin photoaging is characterized by keratinocyte hyperproliferation and degradation of collagen fibers, causing skin wrinkling and laxity and melanocyte proliferation that leads to pigmentation. UV is considered to be a major cause of such skin changes. It is well established that nuclear factor kappaB (NF-kappaB) is activated upon UV irradiation and induces various genes including interleukin-1 (IL-1), tumor necrosis factor alpha (TNFalpha), and matrix metalloprotease-1 (MMP-1). It is also known that basic fibroblast growth factor (bFGF) production is induced by UV and promotes the proliferation of skin keratinocytes and melanocytes. We found that UVB, IL-1, and TNFalpha induced NF-kappaB activation and then produced MMP-1 and bFGF in HaCaT keratinocytes and skin fibroblasts. In this experiment, we examined if parthenolide, an NF-kappaB inhibitor, could block the UVB-mediated skin changes. We found that parthenolide could effectively inhibit the gene expression mediated by NF-kappaB and the production of bFGF and MMP-1 from cells overexpressing p65, a major subunit of NF-kappaB. We also found that parthenolide could inhibit the UVB-induced proliferation of keratinocytes and melanocytes in the mouse skin. These findings suggest that NF-kappaB inhibitors should be useful for the prevention of skin photoaging.

Animals↗

PubMed2005

Induction of OGG1 gene expression by HIV-1 Tat.

To identify the cellular gene target for Tat, we performed gene expression profile analysis and found that Tat up-regulates the expression of the OGG1 (8-oxoguanine-DNA glycosylase-1) gene, which encodes an enzyme responsible for repairing the oxidatively damaged guanosine, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG). We observed that Tat induced OGG1 gene expression by enhancing its promoter activity without changing its mRNA stability. We found that the upstream AP-4 site within the OGG1 promoter is responsible and that Tat interacted with AP-4 and removed AP-4 from the OGG1 promoter by in vivo chromatin immunoprecipitation assay. Thus, Tat appears to activate OGG1 expression by sequestrating AP-4. Interestingly, although Tat induces oxidative stress known to generate 8-oxo-dG, which causes the G:C to T:A transversion, we observed that the amount of 8-oxo-dG was reduced by Tat. When OGG1 was knocked down by small interfering RNA, Tat increased the amount of 8-oxo-dG, thus confirming the role of OGG1 in preventing the formation of 8-oxo-dG. These findings collectively indicate the possibility that Tat may play a role in maintenance of the genetic integrity of the proviral and host cellular genomes by up-regulating OGG1 as a feed-forward mechanism.

Binding Sites↗

PubMed2005

Establishment of a simple and quantitative immunospot assay for detecting anti-type II collagen antibody using an infrared fluorescence imaging system (IFIS).

Antibodies to type II collagen (col II) have been detected in patients with rheumatoid arthritis and in animal models of collagen induced arthritis. Here, we describe a novel method to detect anti-col II antibodies using an immunospot assay with an infrared fluorescence imaging system. This method showed very high sensitivity and specificity, and was simple, with low background levels. It also showed higher reproducibility and linearity, with a dynamic range of approximately 500-fold, than the conventional immunospot assay with enhanced chemiluminescence detection. Using this method we were able to demonstrate the antibody affinity maturation process in mice immunized with col II. In these immunized mice, although cross-reactive antibodies reacting with other collagen species were detected in earlier stages of immunization, the titers of cross-reactive antibodies rapidly diminished after the antigen boost, concomitantly with the elevation of the anti-col II antibody. The method and its possible applications are discussed.

Animals↗