Biomedical subjects

Linda Otis

Publications and source records attributed to Linda Otis.

5 recordsLinked to original sources

PubMed2006

Chondrocytes utilize a cholesterol-dependent lipid translocator to externalize phosphatidylserine.

During endochondral ossification, growth plate chondrocytes release plasma membrane (PM) derived matrix vesicles (MV), which are the site of initial hydroxyapatite crystal formation. MV constituents which facilitate the mineralization process include the integral membrane ectoenzymes alkaline phosphatase (ALPase) and nucleotide pyrophosphatase phosphodiesterase (NPP1/PC-1), along with a phosphatidylserine- (PS-) rich membrane surface that binds annexins and calcium, resulting in enhanced calcium entry into MV. In this study, we determined that chick growth plate MV were highly enriched in membrane raft microdomains containing high levels of cholesterol, glycophosphatidylinositol- (GPI-) anchored ALPase, and phosphatidylserine (PS) localized to the external leaflet of the bilayer. To determine how such membrane microdomains arise during chondrocyte maturation, we explored the role of PM cholesterol-dependent lipid assemblies in regulating the activities of lipid translocators involved in the externalization of PS. We first isolated and determined the composition of detergent-resistant membranes (DRMs) from chondrocyte PM. DRMs isolated from chondrocyte PM were enhanced in ganglioside 1 (GM1) and cholesterol as well as GPI-anchored ALPase. Furthermore, these membrane domains were enriched in PS (localized to the external leaflet of the bilayer) and had significantly higher ALPase activity than non-cholesterol-enriched domains. To understand the role of cholesterol-dependent lipid assemblies in the externalization of PS, we measured the activities of two lipid transporters involved in PS externalization, aminophospholipid translocase (APLT) and phospholipid scramblase (PLSCR1), during maturation of a murine chondrocytic cell line, N1511. In this report, we provide the first evidence that maturing chondrocytes express PLSCR1 and have scramblase activity. We propose that redistribution of PS is dependent on an increase in phospholipid scramblase activity and a decrease in APLT activity. Lastly, we show that translocator activity is most likely to be modulated by membrane cholesterol levels through a membrane raft microdomain.

Animals↗

PubMed2006

Cholesterol-rich membrane microdomains mediate cell cycle arrest induced by Actinobacillus actinomycetemcomitans cytolethal-distending toxin.

We have previously shown that Actinobacillus actinomycetemcomitans cytolethal-distending toxin (Cdt) is a potent immunosuppressive agent that induces G2/M arrest in human lymphocytes. In this study, we explored the possibility that Cdt-mediated immunotoxicity involves lipid membrane microdomains. We first determined that following treatment of Jurkat cells with Cdt holotoxin all three Cdt subunits localize to these microdomains. Laser confocal microscopy was employed to colocalize the subunits with GM1-enriched membrane regions which are characteristic of membrane rafts. Western blot analysis of isolated lipid rafts also demonstrated the presence of Cdt peptides. Cholesterol depletion, using methyl beta-cyclodextrin, protected cells from the ability of the Cdt holotoxin to induce G2 arrest. Moreover, cholesterol depletion reduced the ability of the toxin to associate with Jurkat cells. Thus, lipid raft integrity is vital to the action of Cdt on host cells. The implications of our observations with respect to Cdt mode of action are discussed.

Aggregatibacter actinomycetemcomitans↗

PubMed2005

Characterization of dentin, enamel, and carious lesions by a polarization-sensitive optical coherence tomography system.

Enamel and dentin are the primary components of human teeth. Both of them have a strong polarization effect. We designed a polarization-sensitive optical coherence tomography (PSOCT) system to study the spatially resolved scattering and polarization phenomena of teeth. The system is constructed in free space to avoid the complexity of polarization control in fiber-based PSOCT. The structural features of enamel were evaluated in five human teeth that had no visible evidence of caries. The teeth were subsequently sectioned in mesial distal orientation and coronal orientation. Then the structural aspects of dentin were evaluated. OCT images were made of the mantel dentin near the dentin-enamel junction. Five teeth with interproximal and occlusal caries were also studied. With two channel and phase-retardation images, PSOCT provided better functional contrast and more detailed structural information than conventional OCT. For a better description of the measured PSOCT data, we classify these features by two types, i.e., the local textural features and the global structural features. This study indicates that PSOCT has the potential to be a powerful tool for research of dental formation and caries diagnosis.

Algorithms↗

PubMed2004

Quantifying enamel luster.

OBJECTIVE: When the pH of the oral cavity drops below 5.5, the hydroxyapatite crystalline lattice is damaged and the tooth surface becomes rough. Consequently, specular reflection is decreased and results, clinically, in a loss of tooth luster. The aim of this study was to develop a digital image capture and processing algorithm to quantify enamel luster. METHODOLOGY: Extracted human teeth (n = 25) containing no restorations and with no clinical evidence of caries were used in this study. The teeth were sectioned longitudinally in a mesial-to-distal orientation to provide experimental and control groups. The experimental group was treated with six consecutive 60-minute exposures to an acidic soft drink, separated by tap water rinses; the control group was similarly treated with just the tap water. Standardized photographs were made before and after application of the treatment or control conditions. Images were converted to eight-bit monochrome digital format. The clinical crown was identified using a standard digital masking technique. Luster in the crown was quantified by determining pixels with luminescence values that were 65% above background. RESULTS: Overall, there was an average 53.6% change in luster in the experimental group, and a nominal 2.10% change in luster in the control group. Analysis of variance revealed a significant loss in luster as measured by this algorithm in the experimental group (p < 0.001), while no significant change in luster was found in the control group. The method reliably identified luster with a repeatability coefficient of 0.992. CONCLUSION: Our digital processing algorithm consistently quantified loss of enamel luster associated with exposure to an acidic beverage. This digit photographic technique may be valuable for evaluating changes in the esthetic chacteristics of teeth when they are exposed to a variety of adverse environments.

Algorithms↗

PubMed2002

Undiagnosed multiple myeloma causing extensive dental bleeding: report of a case and review.

A case of multiple myeloma causing profuse bleeding during a minor dental surgical procedure is presented. The value of dental radiography in detection of bone changes associated with an undiagnosed case of multiple myeloma is highlighted. We show that the extensive bleeding during the dental procedure could have been prevented if the panoramic radiograph had been evaluated carefully before initiation of the treatment. In addition, we briefly discuss the etiologic factors responsible for the formation of hemostatic abnormalities in multiple myeloma and the value of imaging methods used in diagnostic assessment of the disease.

Abscess↗