RESUMEN
Evidence is accumulating that a number of previously unexplained human diseases amy arise from a deficiency of DNA repair enzymes. Studies on the motoneurons of patients with amyotrophic lateral sclerosis (ALS), and those of an animal model of motoneuronal degeneration, the wobbler mouse, indicate the presence of major abnormalities of RNA metabolism. We advance the hypothesis that the primary abnormality in ALS is the accumulation of abnormal DNA, which is unable to undertake normal transcription, in motoneurons. This abnormal DNA may arise from a deficiency of an isozyme of one of the DNA repair enzymes.
Asunto(s)
Esclerosis Amiotrófica Lateral/etiología , ADN Ligasas/deficiencia , ADN/biosíntesis , Polinucleótido Ligasas/deficiencia , Esclerosis Amiotrófica Lateral/metabolismo , Animales , Reparación del ADN/efectos de la radiación , Replicación del ADN , Humanos , Ratones , Ratones Endogámicos , Neuronas Motoras/metabolismo , ARN/biosíntesisRESUMEN
The risk of carcinogenesis in breast tissue subject to low to moderate radiation doses may be of concern to the clinical radiotherapist. With earlier diagnosis, more women, and especially younger women, are electing breast preservation radiation therapy. During therapy, tissue outside the treatment field is exposed to leakage and scattered radiation. Such exposure could lead to significant doses of radiation resulting in carcinogenesis. Therefore, reduction of contralateral breast dose may be an important factor to consider when selecting a treatment technique. This study measured dose in the contralateral breast on 15 patients treated with 60Co gamma rays with the source to skin distance (SSD), 1/2 beam block, and the source to axis distance (SAD), no 1/2 beam block, techniques. Thermoluminescent dosimeters (TLD), with 0.5 cm of superflab used as build-up material, were placed on the contralateral breast to measure dose from the medial tangential beam and from the lateral tangential beam. Dose measurements were done on patients in the treatment position and do not represent phantom or formula calculation of dose to the opposite breast. Our results indicated that total opposite breast dose ranged from 325-650 cGy for SSD treatments as opposed to 200-450 cGy for SAD treatments, in patients receiving a total prescribed dose of 5,040 cGy in 28 fractions to the involved breast. This paper points out that a simple solution for reduction of opposite breast dose for patients treated with 60Co may be utilization of the modified SAD treatment technique.
Asunto(s)
Neoplasias de la Mama/radioterapia , Radioisótopos de Cobalto/uso terapéutico , Mama/efectos de la radiación , Femenino , Humanos , Métodos , Dosificación RadioterapéuticaRESUMEN
Previous studies from our institution have shown that 10(-4) M DDC enhances the effects of radiation and of hyperthermia treatment at 43 degrees C on the killing of Chinese hamster (DON) cells. We herein report studies on the combined effect seen at more modest temperatures (41 degrees C) which can be achieved in humans by whole body heating without the need for general anesthesia. Treatment of V79 cells with DDC for 60 minutes at 37 degrees C or 41 degrees C had minimal toxicity at concentrations up to 5 X 10(-5) M. When cells were irradiated with single doses up to 1000 rad (137Cs, 350 rad/min), pre-incubation with 10(-4) M DDC had no effect on cell survival at 37 degrees C, but markedly decreased survival at 41 degrees C (D37 = 475 rad without DDC, 270 rad with DDC). The mechanism of this increased cell killing is not known. We observed, however, that there is no repair of DNA single strand breaks in DNA from irradiated V79 cells previously held at 41 degrees C in the presence of 10(-4) M DDC. Without DDC, repair of SSB was similar at 37 degrees C and 41 degrees C.
Asunto(s)
Supervivencia Celular/efectos de la radiación , Reparación del ADN , Ditiocarba/farmacología , Hipertermia Inducida , Tiocarbamatos/farmacología , Animales , Línea Celular , Supervivencia Celular/efectos de los fármacos , Cricetinae , Cricetulus , Reparación del ADN/efectos de los fármacos , Relación Dosis-Respuesta en la Radiación , Protectores contra Radiación/farmacología , Factores de TiempoRESUMEN
One of the methods currently being used to treat choroidal melanoma employs an episcleral plaque containing I-125 radioactive seeds. However, comprehensive dosimetry studies on the plaque are scarce and controversial. For this work, we use film to study the dosimetry outside the lip of the gold shield of the eye plaque. This lip around the gold shield was made to protect the critical structures behind and adjacent to the lesion. Since the changes of energy spectrum of I-125 in tissue are negligible, film dosimetry seems to be a logical choice because of high spatial resolution required around the lip of the gold plaque. For this study, we first established an H and D curve with dose expressed in a unit of specific dose rate constant. This avoids absolute dose measurements. All film density measurements are made with a 1-mm aperture scan, normalized to the density at the prescription point for tumor of 3-5-mm apical height, i.e., 5 mm from the interior surface of sclera, and converted to percentage isodose curves. With a gold shield, it is found that when the plaque is placed against the optical nerve, the optical disk and macula, located at 2 mm outside the lip, on the exterior surface of sclera, may receive 85% of the prescription dose for a 12-mm plaque and 58% for a 16-mm plaque. For tumors of 8-mm apical height, the optical nerve would receive more than the prescription dose.
Asunto(s)
Braquiterapia , Neoplasias de la Coroides/radioterapia , Oro , Radioisótopos de Yodo/uso terapéutico , Melanoma/radioterapia , Protección Radiológica , Dosimetría por Película , HumanosRESUMEN
Two sets of newly designed large wedge filters for field sizes up to 20 X 20 cm2 have become commercially available for use with 4- and 6-MV linear accelerators. Such field sizes are sometimes required to ensure adequate coverage in certain treatment techniques. This work reports base line data resulting from an investigation of the dosimetric properties of these wedges. Measurements of wedge angles, transmission factors, and beam hardening effects are described, and comparisons are made with the smaller standard wedges.
Asunto(s)
Neoplasias/radioterapia , Radioterapia de Alta Energía/instrumentación , Humanos , Aceleradores de Partículas , Fenómenos Físicos , Física , Radiometría , Dosificación RadioterapéuticaRESUMEN
A theory by Zimm [B.H.Zimm, Biophys. Chem. 1-(1974)279] predicts that for a given centrifuge speed, there is a broad maximum in a plot of the sedimentation coefficient of DNA against molecular wight. Experimental measurements of these maxima for various centrifuge speeds were made for double-helical DNA in neutral sucrose gradients and singlestrand DNA in alkaline gradients. The measurements are in quantitative agreement with the theory, providing good evidence for its validity. The existence of the maximum shows that there is a limit to the sedimentation rate under specified conditions for KNA in the linear form. By implication, DNA observed to sediment faster than this limit is not in the linear form to which most sedimentation theory is applicable.
Asunto(s)
ADN , Centrifugación por Gradiente de Densidad , Colifagos , ADN Bacteriano , ADN Viral , Escherichia coli , Peso Molecular , UltracentrifugaciónAsunto(s)
Adenina , Colifagos/metabolismo , ADN de Cadena Simple , ADN Viral , Escherichia coli/metabolismo , Guanina , Adenina/metabolismo , Sitios de Unión , ADN Bacteriano , ADN de Cadena Simple/metabolismo , ADN Viral/metabolismo , Congelación , Guanina/metabolismo , Marcaje Isotópico , Matemática , Peso Molecular , Conformación de Ácido Nucleico , Renaturación de Ácido Nucleico , TritioAsunto(s)
Esclerosis Amiotrófica Lateral/metabolismo , ADN/metabolismo , Adulto , Factores de Edad , Anciano , Esclerosis Amiotrófica Lateral/etiología , ADN Ligasas/metabolismo , Reparación del ADN , Replicación del ADN , Humanos , Persona de Mediana Edad , Neuronas Motoras/metabolismo , ARN/metabolismoRESUMEN
The repair of DNA double-strand breaks in Escherichia coli cells irradiated with gamma rays occurs only after new proteins are synthesized in response to damage introduced in the genome DNA. One protein whose synthesis is thus induced is the recA protein, and previous work has shown that recA- cells do not repair double-strand breaks. However, inducing recA protein by treating cells with nalidixic acid does not induce repair of double-strand breaks, so this repair requires more than the presence of the recA protein. When repair of double-strand breaks is blocked, the genome DNA is degraded by an endonuclease-like action. Evidence is presented to show that the inducible inhibition of DNA degradation after x-irradiation [Pollard, E. C. & Randall, E. P. (1973) Radiat. Res. 55, 265] is probably caused by the inducible repair of DNA double-strand breaks.
Asunto(s)
Proteínas Bacterianas/biosíntesis , Reparación del ADN , ADN Bacteriano/genética , Escherichia coli/genética , Rayos Ultravioleta , Proteínas Bacterianas/genética , Reparación del ADN/efectos de los fármacos , ADN Bacteriano/efectos de la radiación , Rayos gamma , Rec A Recombinasas , Recombinación Genética , Rifampin/farmacologíaRESUMEN
Ultraviolet irradiation of Escherichia coli cells with a low level of 5-bromouracil incorporated produces DNA double-strand breaks by single photochemical events, one such break per 100 single-strand breaks, the latter assayed in alkali-denatured DNA. About 2.5--4 double-strand breaks are produced per "lethal hit," compared with about 6 double-strand breaks per lethal hit induced by gamma rays. These results are consistent with the hypothesis that an unrepaired DNA double-strand break is a major lethal event in both cases. The increase in sensitivity to ultraviolet (measured by colony-forming ability) seems linear in the number of bromouracils incorporated (0--20% of the thymines), and the linear relationship is much the same for incorporation in one or in both strands of the DNA double helix.
Asunto(s)
Bromouracilo/farmacología , ADN Bacteriano/efectos de la radiación , Bromouracilo/metabolismo , Centrifugación por Gradiente de Densidad , Ensayo de Unidades Formadoras de Colonias , ADN de Cadena Simple/efectos de la radiación , Escherichia coli/metabolismo , Escherichia coli/efectos de la radiación , Desnaturalización de Ácido Nucleico , Fotoquímica , Rayos UltravioletaRESUMEN
Supercircular gamma phage DNA with 10 bromouracils/100 thymine bases, irradiated with 313 nm light in Tris buffer and sedimented on alkaline and neutral gradients, showed 4.6 alkali-labile bonds per true single-strand break, in agreement with Hewitt and Marburger (1975 Photochem. Photobiol. 21:413). The same DNA irradiated in Escherichia coli host cells showed about the same number of breaks in alkaline gradients for equal fluence, but only 0.5 alkali-labile bond per true break. Similarly, E. coli DNA with bromouracil irradiated in the cells showed only 10--20% more breaks when denatured with 0.1 M NaOH than under neutral conditions with 9 M sodium perchlorate at 50 degrees C. These results show that true single-strand breaks occur more frequently than alkali-labile bonds after ultraviolet irradiation of DNA containing bromouracil in cells.
Asunto(s)
Bromouracilo/farmacología , ADN Viral/efectos de la radiación , Álcalis/farmacología , Bromouracilo/metabolismo , Centrifugación por Gradiente de Densidad , Colifagos/efectos de los fármacos , Colifagos/efectos de la radiación , ADN de Cadena Simple/efectos de la radiación , ADN Superhelicoidal/efectos de la radiación , Escherichia coli/metabolismo , Escherichia coli/efectos de la radiación , Desnaturalización de Ácido Nucleico , Rayos UltravioletaRESUMEN
Iodine-125 decays by electron capture and is known to cause extensive molecular fragmentation via the Augur effect. 125I was incorporated into the DNA of exponentially-growing E. coli K12 AB2487, a recA mutant, and E. coli K12 AB2497, the corresponding rec+ strain, as 5-iododeoxyuridine (IUdR), an analogue of thymidine. Radioactive bacteria were stored at - 196 degrees C, and samples were periodically assayed for loss of viability and for the induction of double-strand breaks (DSBs) in DNA. Each 125I decay in the DNA of either strain induces one DSB, i.e. alpha(DSB) = 1.0. For the recA strain, alpha(lethal) = 0.9 and for the rec+ strain, 0.4. Assays for biological repair of DSBs, involving incubation of thawed samples in growth-medium at 37 degrees C before the extraction of DNA, demonstrate significant repair of 125I-induced DSBs by rec+ cells but none by recA cells. For small numbers of decays, there is approximately a 1:1 correlation, for either strain, between lethal decays and post-incubation residual DSBs. Comparison with data for larger numbers of decays indicates that a typical rec+ cell can repair no more than three to four DSBs per completed genome (2.5 x 10(9) daltons).
Asunto(s)
Reparación del ADN , ADN Bacteriano/efectos de la radiación , Escherichia coli/efectos de la radiación , Radioisótopos de Yodo , Genética de Radiación , Supervivencia Celular/efectos de la radiaciónRESUMEN
Effects of 125I decay in DNA were investigated by measurements of strand breaks and lethal efficiencies of the decays. In bacteriophages T1 and T4, local decay effects were compared with effects of the emitted electrons by induction of both single (ssb) and double strand breaks (dsb) in the intact phage head and in extended free state DNA. Most dsbs were found to result from local decay effects whereas most real ssbs are caused by the electrons. A simple one-to-one relationship seems to exist in the phages between the decays of 125I, numbers of dsbs and lethal effects. In E. coli rec+ and recA repair of dsbs was studied in addition to lethal decay efficiencies. In rec+ more than 70% of the dsbs were repaired within 1 h at 37 degrees C. No repair was observed in recA. The probability of lethality per 125I decay per completed genome was found to be 0.37 for rec+ and 0.93 for recA cells. The number of lethal events per unrepaired dsb was found to be practically equal to unity. Unrepaired dsbs thus seem to be the primary mechanism of lethality caused by 125I decay, and all unrepaired dsbs seem to be lethal.