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Biomedical subjects

A Thakur

Publications and source records attributed to A Thakur.

82 records · Page 5Linked to original sources
PubMedDate not supplied

Effect of lysozyme on adhesion and toxin release by Staphylococcus aureus.

PURPOSE: Staphylococcus aureus is a common cause of ocular infection and inflammation. We hypothesized that potential for S. aureus to cause an ocular infection would be enhanced if these bacteria are able to adhere to the biomaterials used in contact lenses. In turn, bacterial adhesion could also be influenced by other factors, such as properties of contact lenses and the absorbance of some tear components. We investigated the effect of the tear protein lysozyme on S. aureus adhesion to contact lenses and its effect on production of toxins or enzymes. METHODS: Bacterial adhesion on contact lenses was determined by counting the total number of bacteria as well as viable bacteria on lysozyme-coated or non-coated lenses, and by counting bacteria grown in the presence or absence of lysozyme in the medium. Toxin and enzyme production was assessed by haemolysis and proteolysis assays. RESULTS: Our results indicate that adhesion was significantly increased in the presence of lysozyme, both in the medium and coated onto contact lenses (P=0.04). The presence of lysozyme did not alter the production of alpha- or beta- toxins. However, the presence of lysozyme inhibited elastase activity. CONCLUSION: These results indicate that lysozyme deposition on contact lenses promoted S. aureus adhesion. The tear protein lysozyme might modify elastase activity and thus modulate the production of corneal degradation resulting from the action of this enzyme.

Bacterial Adhesion↗
PubMedDate not supplied

A novel apoptotic interaction between HSV-1 and human corneal epithelial cells.

PURPOSE: Herpes simplex virus type 1 (HSV-1) infects the cornea possibly causing blindness. The specific mechanisms of herpetic keratitis are unclear. We aimed to investigate whether HSV-1 would up- or down-regulate the apoptotic pathway of human corneal epithelial (HCE) cells. METHODS: HSV-1 infection of HCE and Vero cells was demonstrated (immunofluorescence) and apoptotic gene expression was quantified (ribonuclease protection assay). Caspase 8 protein activity (colorimetric assay) was quantified and compared to caspase 8 mRNA amounts from RPA experiments. The apoptotic index of HSV-1 infected HCE and Vero cells (apoptotic index = % of apoptotic cells in infected samples/mock treated samples) was obtained and compared to gene expression. RESULTS: A down-regulation in apoptotic gene expression was observed in HSV-1 infected HCE cells in contrast to Vero cells (infected and mock treated). Caspase 8 protein levels mirrored caspase 8 mRNA levels in HSV-1 infected HCE cells. The apoptotic index also supports this down-regulation. HSV-1 infected human corneal epithelial cells and Vero cells at similar rates. CONCLUSION: HSV-1 down-regulates the apoptotic pathway of human corneal epithelial cells. This down-regulation of apoptotic gene expression seems to be cell specific. Also infectivity is excluded in playing a role in regulation of the apoptotic pathway because HSV-1 replicated at similar rates in HCE and Vero cells.

Animals↗
PubMedDate not supplied

Transfection of major histocompatibility complex class I and class II genes causes tumour rejection.

Many human and mouse tumours do not express MHC class II antigens and have reduced levels of class I antigens. Because of the requirement for class I and/or class II antigen for antigen presentation to Th and Tc cells, these phenotypes may enable tumour cells to 'escape' the host's immune response. Experiments presented here are designed to assess the role of MHC class I and class II antigens in tumour immunity, and to overcome the MHC class I- or class II-negative phenotype. When transfected with the syngeneic H-2Db gene, the MHC antigen-negative 402AX teratocarcinoma expresses high levels of H-2Db antigen. 402AX/Db cells are rejected by MHC allogeneic and some MHC syngeneic 402AX-susceptible mice, however the fully syngeneic strain of origin (129) remains tumour-susceptible. Induction of MHC class I gene products on class I antigen-negative embryonal carcinoma cells therefore increases tumour immunogenicity in some hosts, but not in the fully syngeneic mouse. In an attempt to enhance antigen presentation of tumour-associated antigens to Th cells, MHC class I antigen-positive SaI (KkDd) sarcoma cells were transfected with syngeneic A alpha k and A beta k genes to generate Iak-expressing tumour cells. SaI/Ak cells are efficiently rejected by syngeneic A/J (KkDd) mice, while untransfected SaI cells are lethal. Induction of MHC class II antigen expression on the class I antigen-positive SaI sarcoma therefore completely abrogates malignancy.

Animals↗
PubMedDate not supplied

Development of a stable single-vial formulation for a new technetium complex using bilayer lyophilization.

The interaction between different components used in the preparation of a new radiodiagnostic agent, BMS-181321, was overcome by its lyophilization as a bilayered product. BMS-181321 is composed of a nitroimidazole ligand BMS-181032, that is complexed with technetium-99m just before it is used in radionuclide imaging studies. Stannous chloride is required to reduce technetium from the +7 to the +5 oxidation state before it can be complexed by the ligand. Because BMS-181032 is unstable in the presence of stannous chloride (when mixed in the liquid or solid state), the two components must be contained in separate vials. A bilayered lyophile was manufactured, containing the ligand and stannous chloride in separate layers in a single vial. The bilayered product was manufactured by first filling a solution of the ligand into a vial and freezing the solution. A solution containing stannous chloride was then filled into the same vial on top of the frozen layer of ligand, and this second layer was also frozen. The two frozen layers were then lyophilized to a dry solid cake. The resulting bilayered product showed stability comparable to that seen when the ligand and the reducing agent were contained in separate vials. The separation provided by the layering was sufficient to prevent any significant interaction between the reducing agent and the ligand.

Chemistry, Pharmaceutical↗
PubMedDate not supplied

Strength properties of visible-light-cured resin-modified glass-ionomer cements.

A new generation of glass ionomers containing polymerizable methacrylate monomers and/or prepolymers are now available for use as direct esthetic restorative materials. Proper clinical application of these new resin-modified glass ionomers requires an understanding of their benefits and limitations. The purpose of this investigation was to compare the compressive and diametral tensile strength at 1 hour, 24 hours, and 7 days of three visible-light-cured glass-ionomer cements, a polyacid-modified composite resin, and a composite resin core build-up material under both light-cure and dark-cure conditions. Statistical analysis indicated significant differences between several of the cements tested for both compressive and diametral tensile strengths at all three testing times (P > 0.05). Prosthodent composite resin and Vitremer tricure visible-light-cured glass-ionomer cement are significantly greater in both compressive and diametral tensile strength than any of the other materials tested after 7 days.

Acrylic Resins↗