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Molecular Radiation Biology
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
Thymidine kinase and DNA polymerase are important enzymes for the synthesis of DNA. The radiation effects on these enzymes have been investigated in considerable detail. In the rat regenerating liver, the levels of both thymidine kinase and DNA polymerase appear to rise together. The increase in enzyme activity is most pronounced between 18 and 24 hr after hepatectomy, and then declines slowly. In rats receiving 1500 R whole-body exposure 6 hr after hepatectomy, the activities of thymidine kinase and DNA polymerase 24 hr later are reduced to 1 and 20% of controls, respectively. However, when the animals are irradiated 16 hr after hepatectomy, none of the enzyme activity shows any significant change when measured 24 hr after hepatectomy. This indicates that enzymes are more radiosensitive when they are being induced; however, after the completion of synthesis they become highly radioresistant. In contrast to rat regenerating liver, a dose of 2000 rads 1 hr after mitosis did not interfere with the synthesis of thymidine kinase in HeLa cells. The enzyme activity in this cell type rises to a maximum when the cells enter the S phase, but drops rapidly when they enter the G1 phase. Therefore, the prolonged elevation of the thymidine kinase activity in X-irradiated cells reflects interference with the progression of the cell population to a phase which reduces the enzyme level.13 The difference in radiation effect on thymidine kinase of regenerating liver and HeLa cell culture may reflect inherent differences in the control mechanism between the two systems.
Multiple Sclerosis
Published in Irun R. Cohen, Perspectives on Autoimmunity, 2020
Attempts to recognize specifically reactive populations among CSF T-cells have led to the conclusion that these cells are in fact poly- (or oligo-) clonal. Salmi and colleagues,210 for example, in a study of 20 patients over a 6- to 13-month period, found T-lymphocytes stimulated to incorporate thymidine by test viruses in CSF of 15 subjects at one time or another (only 4 viruses were used: measles, rubella, mumps, and herpes simplex). One half (7 of 15) of these patients’ cells reacted simultaneously to several viruses.
ExperimentaL Oral Medicine
Published in Samuel Dreizen, Barnet M. Levy, Handbook of Experimental Stomatology, 2020
Samuel Dreizen, Barnet M. Levy
The cell kinetics of the oral epithelium of adrenalectomized mice were elicited by Dickler et al.2 Twenty-five CD Number 1 white mice 45 to 50 days of age, with an average weight of 30 g were adrenalectomized. Three days later each was injected with 1 μCi of tritiated thymidine per gram of body weight. Single animals were sacrificed at intervals between 30 min and 5 days postinjection. Sample preparation for microscopic and radioautographic examinations was identical to that in previously described studies in hypophysectomized mice by the same investigators.2 The doubling time of the labeled oral epithelial cell population in the adrenalectomized mice was 14 hr compared to 10 hr in normal mice. As in the hypophysectomized mice, cell migration and exfoliation patterns in the adrenalectomized animals were slower than normal.
Engraftment and Proliferation of Thermoreversible-Gelation-Polymer-Encapsulated Human Corneal Limbal-Stem-Cells on Ocular Surface of a Cadaver Cornea
Published in Current Eye Research, 2023
Rajappa Senthilkumar, Hiroshi Yoshioka, Shojiro Katoh, Masaru Iwasaki, Vaddi Surya Prakash, Madasamy Balamurugan, Vidyasagar Devaprasad Dedeepiya, Senthilkumar Preethy, Samuel J. K. Abraham
3H thymidine incorporation assay was used to evaluate the proliferative capacity of the cells. In this assay, the cells are incubated with 3H-thymidine for a few hours to overnight. Only proliferating cells can integrate the radioactive labelled thymidine into their nascent DNA and after the incubation period a scintillation counter is used to measure the uptake. In the current study, one µCi of 3H thymidine (BRIT, Mumbai, India) was incorporated into some of the wells of TGP and hAM cultured tissues. Fifty µL of medium from each well was sampled every day and relative consumption over ten days was evaluated. Beckmann LS 6500 scintillation system (Beckmann Instruments Inc, USA) was used for the 3H thymidine incorporation assay following the manufacturer’s protocol and following Sudha et al.21
The discovery of novel antivirals for the treatment of mpox: is drug repurposing the answer?
Published in Expert Opinion on Drug Discovery, 2023
Ahmed A. Ezat, Jameel M. Abduljalil, Ahmed M. Elghareib, Ahmed Samir, Abdo A. Elfiky
Idoxuridine is the first antiviral drug to gain approval in June 1963 for human use. Indeed, it was originally described as an antitumor agent. Still, later studies found that it competes with thymidine for incorporation into the newly synthesized DNA and subsequently inhibits viral DNA polymerase [44]. Additionally, the 4´-thio derivative of idoxuridine was found to retain its antiviral activity against viral strains resistant to cidofovir or tecovirimat [45]. This compound is believed to require viral thymidine kinases for activation purposes. In mice models intranasally infected with the vaccinia virus or cowpox virus, the 4´-thio derivative of idoxuridine showed 87% survival for a dose of 1.5 mg/kg administered intraperitoneally twice a day beginning three days after infection [44].
The Postnatal Leptin Surge Supports Immune Cell Function in Rats
Published in Immunological Investigations, 2022
Caroline Hunsche, Oskarina Hernandez, Virginia Mela, M. Paz Viveros, Mónica De la Fuente
The proliferation of lymphocytes in response to the mitogens concanavalin A (ConA) and lipopolysaccharide (LPS) was measured following a method previously described (De la Fuente et al. 2004). Aliquots (200 µl) of spleen leukocytes (106 cells/ml complete medium) were seeded in 96 well flat-bottomed microtiter plates (Numc, Roskilde, Denmark), and 20 µl of ConA (1 μg/ml; Sigma-Aldrich), a T-cell mitogen (lectin) or 20 µl of lipopolysaccharide (Escherichia coli, 055:B5 1 µg/ml; Sigma-Aldrich), a B-cell mitogen, were added per well. After 48 h of incubation at 37°C in an atmosphere of 5% CO2, 0.5 µCi 3H-thymidine (Du Pont, Boston, MA, USA) were added to each well. The cells were harvested in a semiautomatic microharvester 24 h later. Thymidine uptake was measured using a beta counter (LKB, Uppsala, Sweden) and the results were expressed as 3H-thymidine uptake (cpm).