Thomas Koval | Johns Hopkins University (original) (raw)

Papers by Thomas Koval

Journal of Oral Implantology, 2014

Abstract Regulations for protecting humans against stochastic biological effects from ionizing ra... more Abstract Regulations for protecting humans against stochastic biological effects from ionizing radiation are based on the Linear No-Threshold (LNT) risk assessment model that any amount of radiation exposure may lead to cancer in a population. Based on the LNT model, risk from low dose radiation increases linearly with increasing doses of radiation. Imaging procedures in medicine and dentistry are an important source of low dose ionizing radiation. The increased utilization of computed tomography (CT) and cone beam computed tomography(CBCT) has raised health concerns regarding exposure to low dose ionizing radiation. In oral and maxillofacial surgery and implant dentistry, CBCT is now at the forefront of this controversy. Although caution has been expressed, there have been no direct studies linking radiation exposure from CT and CBCT used in dental imaging with cancer induction. This manuscript describes the concerns about radiation exposure in dental imaging regarding the use of computed tomography.

Frontiers in Bioscience, 2003

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Page 1. RADIATION RESEARCH 67, 305-313 (1976) The Effect of X Irradiation on Amino Acid Utilizati... more Page 1. RADIATION RESEARCH 67, 305-313 (1976) The Effect of X Irradiation on Amino Acid Utilization in Cultured Insect Cells THOMAS M. KOVAL,* WC MYSER,* AND WF HINKt *Department of Zoology and tDepartment ...

Mutation Research-fundamental and Molecular Mechanisms of Mutagenesis, 1978

Abbreviation: UDS, unscheduled DNA synthesis.

International Journal of Radiation Biology, 1992

Exponentially growing TN-368 lepidopteran insect cells have a normal growth temperature of 28 deg... more Exponentially growing TN-368 lepidopteran insect cells have a normal growth temperature of 28 degrees C. These cells were heated in water baths at various temperatures between 33 and 44 degrees C under conditions of constant or fractionated heating. Determinations of cell survival using colony formation as well as measurements of DNA and protein synthesis were performed to assess relative heat resistance and development of thermotolerance. The results demonstrate a marked heat resistance over previously reported findings from the same laboratory for dipteran Drosophila cells in culture. The degree of heat resistance is remarkable, especially when compared to the heat resistance of mammalian cells, i.e. TN-368 cell survival at 41.5 and 44 degrees C was somewhat similar to mammalian cell survival, even though these temperatures are 13.5 and 16 degrees C above the normal growth temperature for TN-368 cells and 4.5 and 7 degrees C above the growth temperature of mammalian cells. Furthermore, the lepidopteran cells maintain the ability to develop a notable amount of thermotolerance in addition to this heat resistance. Thermotolerance development alone is capable of enhancing survival by an additional 10,000-fold. Thermotolerance could also be detected at the level of protein synthesis as a more rapid recovery following heat treatment. In contrast, DNA synthesis inhibition was prolonged even further in cells receiving a prior heat treatment to induce thermotolerance. In summary, it appears that, in addition to their pronounced radiation resistance, the TN-368 cells are also quite resistant to heat. It remains to be seen whether a single mechanism could be responsible for resistance to these agents which act very differently.

Experientia, 1987

Cell survival and photoreactivation of 254 nm ultraviolet (UV) light damage in a wild type Drosop... more Cell survival and photoreactivation of 254 nm ultraviolet (UV) light damage in a wild type Drosophila cell line was assayed by colony formation in liquid medium. Fo, Fq, and extrapolation number for the exponential portion of survival curves are 21 J/m2, 3.6 J/m2, and 1.5 for non-photoreactivated cells and 110 J/m2, 11.2 J/m2, and 1.3 for those exposed to photoreactivating light. Maximal photoreactivation occurs at the 100 J/m2 region of the curve. At 10 and 50% survival, 75-80% of the UV damage was photoreactivable.

Journal of Invertebrate Pathology, 1977

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Carcinogenesis, 1981

The effect of exposing mice to both a chemical carcinogen and leukemia virus with and without an ... more The effect of exposing mice to both a chemical carcinogen and leukemia virus with and without an inhibitor of DNA repair were compared. The data indicated that benzo[a]pyrene (BP) could exert a potentiating effect of Friend viral leukemogenesis in mice, which was dependent on the relative times of administration of the chemical and virus. The addition of caffeine as an inhibitor of DNA repair further enhanced the potentiating effect of BP on the leukemia, but in the absence of BP, caffeine showed no carcinogenic effect either when given alone or in conjunction with Friend leukemia virus.

Experientia, 1978

A technique has been developed for obtaining absolute plating efficiencies as high as 79% for cul... more A technique has been developed for obtaining absolute plating efficiencies as high as 79% for culturedTrichoplusia ni (TN-368) cells. The method involves the use of conditioned medium and MES, BES, or ACES buffers. Cell growth and morphology are not altered under these conditions.

Mutation Research Letters, 1986

Inducible repair of ionizing radiation damage in higher eukaryotic cells. TM Koval Mutation Resea... more Inducible repair of ionizing radiation damage in higher eukaryotic cells. TM Koval Mutation Research 173:44, 291-293, 1986. Although there is widespread acceptance of inducible repair pathways in prokaryotes and lower eukaryotes ...

In Vitro Cellular & …, Jan 1, 1987

Radiation research, Jan 1, 1984

TN-368 lepidopteran insect cells display a multiphasic survival response in both air and nitrogen... more TN-368 lepidopteran insect cells display a multiphasic survival response in both air and nitrogen. In each case the survival curve is characterized by an initial small- shouldered component having a steep slope, a plateau or broad- shouldered region near the 0.1 survival level, and finally a shallow slope component. The D0, Dq, and n values for the initial steep slope component in air and nitrogen are, respectively, 65.7 Gy, 9.0 Gy, and 1.2, and 104.4 Gy, 28.8 Gy, and 1.3. The oxygen enhancement ratio (OER) for this portion of the curve is 1.6. The D0, Dq, and n values for the shallow slope component in air and nitrogen are, respectively, 130.2 Gy,--36.1 Gy, and 0.8, and 226.8 Gy, 121.0 Gy, and 1.7. The OER for this portion of the curve is 1.7. The D0 values for each slope and the width of the plateau region all increase proportionally for the nitrogen curve over that of air, the OER being approximately the same for both curve components. A similar multiphasic response was observed at dose rates of 202, 49.6, and 9.1 Gy/min. In addition, the survival of cells which had previously been irradiated with a dose well into the logarithmic region of the more resistant shallow slope portion of the curve retained a multiphasic response. Although cell cycle variations in radiosensitivity may contribute slightly to the response, an inducible or activated repair process would be consistent with the results.

Radiation Research, Jan 1, 1976

Radiation Research, Jan 1, 1998

Page 1. Stress-Inducible Processes in Higher Eukaryotic Cells Edited by Thomas M. Koval Page 2. P... more Page 1. Stress-Inducible Processes in Higher Eukaryotic Cells Edited by Thomas M. Koval Page 2. Page 3. Page 4. Page 5. Stress-Inducible Processes in Higher Eukaryotic Cells This One A2A4-2N7-991W Page 6. Page 7. Stress ...

Proceedings of the National Academy of …, Jan 1, 1983

Plenum Press

Radiation research, Jan 1, 1988

TN-368 lepidopteran insect cells are on the order of 100 times more resistant to the lethal effec... more TN-368 lepidopteran insect cells are on the order of 100 times more resistant to the lethal effects of ionizing radiation than cultured mammalian cells. DNA double-strand breaks (DSB) are believed by many to be the critical molecular lesion leading to cell death. We have therefore compared the rejoining of DSB in TN-368 and V79 Chinese hamster cells. Cells were irradiated on ice with 137Cs gamma rays at a dose rate of 2.5 Gy/min, incubated for various periods of time, and assayed for DNA DSB using the method of neutral elution. The kinetics of DSB rejoining following a dose of 90.2 Gy is similar for both cell lines with 50% of the rejoining completed in about 12 min. Approximately 83 and 87% of the DSB are rejoined in the TN-368 and V79 cells, respectively, by 1 h postirradiation. However, no further rejoining occurs in the TN-368 cells through at least 6 h postirradiation, whereas approximately 92% of the DSB are rejoined in the V79 cells by 2 h postirradiation. Other studies (from 22.6 to 226 Gy) demonstrate that the amount of rejoining of DSB varies inversely with dose for both cell lines, but this relationship is not as pronounced for the TN-368 cells. In general, these findings do not support the hypothesis that unrejoined DNA DSB represent the critical molecular lesion responsible for cell death.

Experimental Cell Research, Jan 1, 1980

In Vitro Cellular & Developmental Biology-Plant, Jan 1, 1987

Insect cell lines are not well-suited to colony formation in liquid medium following low-density ... more Insect cell lines are not well-suited to colony formation in liquid medium following low-density cell plating. The present studies demonstrate that the time of addition of fetal bovine serum to the culture medium and the number of gamma-irradiated feeder cells added to each plate are important factors in developing a useful colony formation assay. TN-368 lepidopteran and WR69-DM-1 dipteran cell lines were used for these experiments. Both cell types display increased plating efficiencies if serum is added to the medium one or more days prior to plating as compared to adding serum immediately before plating. Growth curves obtained by seeding cells at higher densities also indicate that cell growth is slightly better if serum is added one or more days before seeding. These findings are especially important for survival and toxicity studies because the results demonstrate that even seemingly minor factors involved in cell survival assays may benefit treated cells to a greater degree than untreated control cells, thus providing an erroneous assessment of cell survival.