Variación diurna de la composición bacterioplanctónica y daño en el ADN de la comunidad microbiana de una laguna oligotrófica de los Andes / Diurnal variation in bacterioplankton composition and DNA damage in the microbial community from an Andean

La Laguna Azul es un ambiente oligotrófi co localizado a 4560 m de altura y sometido a elevados niveles de radiación solar. La composición de su comunidad bacterioplanctónica fue analizada empleando la técnica de electroforesis en gradiente desnaturalizante y se investigó el impacto de la radiación ultravioleta cuantifi cando los dímeros de pirimidina (CPD). Además, se expusieron simultáneamente cultivos puros de Acinetobacter johnsonii A2 y Rhodococcus sp. A5 para estudiar la acumulación de CPD. El análisis de los geles mostró siete secuencias pertenecientes a Alpha-proteobacteria (1 banda), Beta-proteobacteria (1 banda), Bacteroidetes (2 bandas), Actinobacteria (1 banda) y Firmicutes (1 banda). A lo largo del día se observaron cambios mínimos en la composición de la comunidad y no se detectaron CPD. A. johnsonii A2 presentó un daño bajo mientras que Rhodococcus sp. A5 no presentó daño en su ADN, sugiriendo que la comunidad bacteriana está muy bien adaptada a este ambiente altamente irradiado

Laguna Azul is an oligotrophic lake situated at 4,560 m above sea level and subject to a high level of solar radiation. Bacterioplankton community composition (BCC) was analysed by denaturing gradient gel electrophoresis and the impact of solar ultraviolet radiation was assessed by measuring cyclobutane pyrimidine dimers (CPD). Furthermore, pure cultures of Acinetobacter johnsonii A2 and Rhodococcus sp. A5 were exposed simultaneously and CPD accumulation was studied. Gel analyses generated a total of 7 sequences belonging to Alpha-proteobacteria (1 band), Beta-proteobacteria (1 band), Bacteroidetes (2 bands), Actinobacteria (1 band), and Firmicutes (1 band). DGGE profi les showed minimal changes in BCC and no CPD was detected even though a high level of damage was found in biodosimeters. A. johnsonii A2 showed low level of DNA damage while Rhodococcus sp. A5 exhibited high resistance since no CPD were detected under natural UV-B exposure, suggesting that the bacterial community is well adapted to this highly solar irradiated environment

Variación diurna en la composición del bacterioplancton y daño del ADN en la comunidad microbiana de un lago oligotrófico andino / Diurnal variation in bacterioplankton composition and DNA damage in the microbial community from an Andean oligotrophic lake

Laguna Azul is an oligotrophic lake situated at 4,560 m above sea level and subject to a high level of solar radiation. Bacterioplankton community composition (BCC) was analysed by denaturing gradient gel electrophoresis and the impact of solar ultraviolet radiation was assessed by measuring cyclobutane pyrimidine dimers (CPD). Furthermore, pure cultures of Acinetobacter johnsonii A2 and Rhodococcus sp. A5 were exposed simultaneously and CPD accumulation was studied. Gel analyses generated a total of 7 sequences belonging to Alpha-proteobacteria (1 band), Beta-proteobacteria (1 band), Bacteroidetes (2 bands), Actinobacteria (1 band), and Firmicutes (1 band). DGGE profiles showed minimal changes in BCC and no CPD was detected even though a high level of damage was found in biodosimeters. A. johnsonii A2 showed low level of DNA damage while Rhodococcus sp. A5 exhibited high resistance since no CPD were detected under natural UV-B exposure, suggesting that the bacterial community is well adapted to this highly solar irradiated environment.

La Laguna Azul es un ambiente oligotrófico localizado a 4560m de altura y sometido a elevados niveles de radiación solar. La composición de su comunidad bacterioplanctónica fue analizada empleando la técnica de electroforesis en gradiente desnaturalizante y se investigó el impacto de la radiación ultravioleta cuantificando los dímeros de pirimidina (CPD). Además, se expusieron simultáneamente cultivos puros de Acinetobacter johnsonii A2 y Rhodococcus sp. A5 para estudiar la acumulación de CPD. El análisis de los geles mostró siete secuencias pertenecientes a Alpha-proteobacteria (1 banda), Beta-proteobacteria (1 banda), Bacteroidetes (2 bandas), Actinobacteria (1 banda) y Firmicutes (1 banda). A lo largo del día se observaron cambios mínimos en la composición de la comunidad y no se detectaron CPD. A. johnsonii A2 presentó un daño bajo mientras que Rhodococcus sp. A5 no presentó daño en su ADN, sugiriendo que la comunidad bacteriana está muy bien adaptada a este ambiente altamente irradiado

Estudo do reparo das lesões induzidas no DNA de Escherichia coli pela radiação ultravioleta C (UVC) / Study of repair of induced lesions in the DNA of Escherichia coli by ultraviolet C (UVC)

Didaticamente, podemos dividir o espectro da radiação ultravioleta (UV) em três faixas: UVA (400 a 320 nm), UVB (320 a 290 nm) e UVC (290 a 100 nm). Apesar do UVC ou UV-curto ser eficientemente filtrado pela camada de ozônio da Terra e sua atmosfera, este é uma das faixas do espectro de UV mais usadas para explorar as consequências de danos causados ao DNA, já que a letalidade induzida por este agente está relacionada aos danos diretos no genoma celular, como as lesões dímero de pirimidina, que são letais se não reparadas. Contudo, demonstrou-se que a radiação UVC pode gerar espécies reativas de oxigênio (ERO), como o oxigênio singleto (1O2). Embora, o radical hidroxil (•OH) cause modificações oxidativas nas bases de DNA, alguns trabalhos indicam que o 1O2 também está envolvido nos danos oxidativos no DNA. Esta ERO é produzida por vários sistemas biológicos e reações fotossensibilização, quando cromóforos são expostos à luz visível ou são excitados pela luz UV, permitindo que essa energia possa ser transferida para o oxigênio sendo convertido em 1O2, que é conhecido por modificar resíduos de guanina, gerando 8-oxoG, que caso não seja reparada pode gerar uma transversão GC-TA. O objetivo deste trabalho foi o de elucidar a participação de ERO nos efeitos genotóxicos e mutagênicos gerados pela radiação UVC, assim como as enzimas envolvidas no processo de reparação destas lesões em células de Escherichia coli. Nos ensaios as culturas foram irradiadas com o UVC (254 nm; 15W General Electric G15T8 germicidal lamp, USA). Nossos resultados mostram que o uso de quelantes de ferro não alterou a letalidade induzida pelo UVC. A azida sódica, um captador de 1O2, protegeu as cepas contra os danos genotóxicos gerados pelo UVC e também diminuiu a frequência de mutações induzidas no teste com rifampicina. A reversão específica GC-TA foi induzida mais de 2,5 vezes no ensaio de mutagênese. A cepa deficiente na proteína de reparo Fpg, enzima que corrige a lesão 8-oxoG...

Didactically, we can divide the ultraviolet radiation (UV) spectrum into three bands: UVA (400 to 320 nm), UVB (320-290 nm) and UVC (290-100 nm). Despite the UVC or far-UV be efficiently filtered by Earth´s ozone layer and its atmosphere, this is one of bands of UV spectrum used to explore the consequences of DNA damages, since the UVC-induced lethality is related to direct damage in genome cells, such as pyrimidine dimers, which are lethal if not repaired. However, it was shown that UVC radiation can generate reactive oxygen species (ROS) such as singlet oxygen (1O2). Although hydroxyl radical (•OH) cause oxidative modifications in DNA bases, some works suggests that 1O2 is also involved in oxidative DNA damage. This ROS is produced by several biological systems and photosensitivity reactions when chromophores are exposed to visible light or excited by UV light, allowing that energy can be transferred to the oxygen being converted to 1O2, which is known to modify guanine residues, generating 8-oxoG, if not repaired can lead to a GC-TA transversion. The objective of this work was to elucidate the ROS involvement in the genotoxic and mutagenic effects generated by UVC radiation, as well as the enzymes involved in the repair process of these lesions in Escherichia coli cells. In the assays, cultures were irradiated with UVC (254 nm, 15 W General Electric germicidal lamp G15T8, USA). Our results show that the use of iron chelators did not affect the UVC-induced lethality. The sodium azide, a 1O2 quencher, protected strains against the genotoxic damage produced by UVC and also decreased the frequency of mutations induced in rifampicin assay. Reversal specific GC-TA was induced more than 2.5 fold in the mutagenesis assay. The deficient strain in the repair protein Fpg, an enzyme that corrects 8-oxoG lesions, had less DNA breakage than the wild strain in electrophoresis alkaline assay. The UVC-induced lethality was increased in mutants transformed with the pFPG...

Tromboembolia pulmonar aguda / Acute pulmonary thromboembolism

A tromboembolia pulmonar (TEP) representa frequentemente um desafio diagnóstico para os médicos na sala de emergência, devido aos sinais e sintomas inespecíficos que são muito comuns. O subdiagnóstico e o superdiagnóstico de TEP são associados a taxa substancial de morbidade e mortalidade. Nenhum teste não invasivo realizado isladamente para diagnóstico de TEP é sensível e específico satisfatoriamente. No entanto, alguns testes são considerados bons para confirmação do diagnóstico (p. ex., TC helicoidal) e outros, razoáveis para exclusão (p. ex., dimero-D). A escolha inicial do teste de diagnóstico deveria ser guiada pela avaliação clínica de probabilidade de TEP e pela característica clínica do paciente, que podem influenciar na acuráncia do teste. A utilização combinada de biomarcadores e ecocardiografia pode ser útil na estratégia de estratificação de risco de pacientes com TEP aguda. O autor aborda diferentes aspectos do diagnóstico da TEP aguda.

Pulmonary thromboembolism (PTE) frequently represents a dianostic challenge to emergency room physicians because the signs and symptoms are not specific and are very common. Both under diagnosis and over diagnosis are associated with substantial morbidity and mortality rates. No single noninvasive test for PTE is both sensitive and specific satisfactorily. However, some tests are good for ruling in diagnosis (e.g., helical CT) and some tests are reasonable for ruling of diagnosis (e. g., D-dimer). For optimal efficiency, choice of initial diagnostic test should be guided by clinical assessmente of the probability of PTE and by clinic characteristics of patients that may influence test accuracy. Combined use of biomarkers and echocardiography may be useful in risc stratification strategy of patients with acute PTE. In this article the author approaches about different aspects of the diagnosis in acute PTE.

Impact of neutrophil apoptosis on haemostatic activation in chronic liver disease patients

Recent studies suggest the impact of apoptosis on the mechanisms leading to hypercoagulability. We aimed to clarify the potential role of neutrophil apoptosis in neutropenia and hypercoagulable state encountered in chronic liver disease patients. This study was conducted on fifteen normal controls and fourty five patients with chronic liver disease classified according to modified Child Pugh classification into, Child A, B and C groups [15 cases each]. Studied Haemostatic parameters include, prothrombin time, partial thromboplastin time, tissue factor, protein C antigen, protein S antigen, and markers of haemostatic activation [prothrombin fragment 1+2, thrombus precursor protein and D-dimer]. Flowcytometric study was done for quantitative assay of neutrophil apoptotic subpopulations to detect the percentage of early and late apoptotic, and necrotic neutrophils using AnnexinV-FITC/Propidium iodide dye. Semiquantitative assay of apoptotic neutrophils showing DNA fragmentation was performed on neutrophil culture using terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling [TUNEL] test. In addition to enzyme linked immunosorbent assay for soluble Fas [APO-1/CD95] in culture supernatant. The results revealed a rise in the neutrophil apoptotic and necrotic markers with progression of the disease, and they were inversely correlated with the absolute neutrophil count. The apoptotic neutrophil cells showed a significant positive correlation with several haemostatic parameters [tissue factor, prothrombin fragment 1+2, thrombus precursor protein and Ddimer], which further incriminate the apoptotic mechanisms in the hypercoagulable state encountered in this clinical setting. Enhanced neutrophil apoptosis and necrosis in patients with chronic liver disease may explain in part the mechanism of neutropenia in these patients and may be one of the important factors which drive the haemostatic balance towards the hypercoagulable state

Blood parameters as potential non invasive methods to diagnose deep venous thrombosis in T.H.R.

DVT is considered to be one of the major complications seen mainly after total joint replacement. The diagnosis of deep venous thrombosis [DVT] is carried out by clinical examination and objective investigations which confirm the clinical signs. Blood parameters as potential non-invasive methods are used to diagnose deep venous thrombosis in total hip replacement. The primary aim was to assess the accuracy of the blood tests, D-dimer, thrombin-antithrombin III complex and prothrombin fragments in diagnosing DVT in high risk patients using venography as a control. The second aim was to determine which of these blood markers is more accurate in diagnosing thrombosis. Blood samples were taken from 16 patients, 4 males and 12 females, aged from 55-86 years, all of them were admitted for hip replacement. In 5 out of 16 patients venography showed a positive DVT. Out of 16 patients only one had a clinically suspected DVT which was confirmed by venogram. The results showed significant differences for D-dimer when comparing pre-operative with post-operative levels in patients with proven DVT by venography. TAT results showed significant differences between pre-operative and post-operative results both in DVT positive and negative patients, and F 1 + 2 results were not significantly different between DVT positive and DVT negative patients. D-Dimer might be considered to be the most significant parameter among the three tests investigated which be might used as a screening test for DVT

Protective effect of the isoflavone equol against DNA damage induced by ultraviolet radiation to hairless mouse skin

Equol, an isoflavonoid metabolite produced from the dietary isoflavone daidzein by the gut microflora in mammals, has been found to protect not only against ultraviolet (UV) radiation-induced cutaneous inflammation and photoimmune suppression, but also have antiphotocarcinogenic properties in mice. Because the state of DNA damage has been correlated with suppression of the immune system and photocarcinogenesis, we have therefore examined the potential of equol to offer protection from solar-simulated UV (SSUV) radiation-induced DNA damage in hairless mice by the immunohistochemical approach using monoclonal antibody specific for cyclobutane pyrimidine dimers (CPDs; H3 antibody). Topical application of 20 micrometer equol lotion, which was applied both before and after SSUV significantly reduced the number of CPDs. This reduction was evident immediately after SSUV exposure, at 1 h after exposure, and at 24 h after exposure, revealing 54%, 50%, and 26% reduction in CPDs, respectively. When the same concentration was applied for 5 consecutive days after SSUV exposure, there was no significant difference in the reduction of CPDs immediately after SSUV irradiation or at 1 hour afterwards, but there were significant reductions of 23% and 42% at 24 and 48 h after SSUV exposure, respectively. Despite apparently reducing the number of CPDs post-SSUV, topically applied equol did not appear to increase the rate of dimer removal. To conclude, equol applied topically prior to SSUV irradiation offers protection against CPD formation in hairless mice, possibly by acting as a suncreen and thus inhibiting DNA photodamage.

Effect of folic acid and vitamin B[12] supplementation on isoprenaline induced myocardial infarction, endothelial dysfunction and atherothrombosis in experimental hyperhomocysteinemic rats

Elevated total plasma homocysteine [tHcy] concentration is an independent risk factor for ischemic heart disease and other vascular disorders. Treatment with vitamins [folic acid and B12] has shown to reduce plasma homocysteine level but it is not clear to what extent such treatment may reduce clinical vascular events or mortality. The aim of the present study was to evaluate hyperhomocysteinemia as a risk factor of isoprenaline induced myocardial infarction [MI], endothelial dysfunction and hypercoagulable state and to examine the effect of folic acid either alone or in combination with vitamin B[12] on the experimentally induced myocardial infarction and to evaluate the effect of such vitamin treatment on the biomarkers of endothelial dysfunction and hypercoagulable state in post-methionine load hyperhomocysteinemic rats. Hyperhomocysteinemia [Hhcy] was induced in rats by daily intake of methionine [1g/kg b.wt.] in the drinking water for 4 weeks. MI was then induced by subcutaneous injection of isoprenaline in a dose of 85mg/kg b.wt/day for two days. Serum marker enzymes, creatine kinase [CK] and lactate dehydrogenase [LDH] were measured. Lipid peroxidation was measured as malondialdehyde [MDA] and reduced glutathione [GSH] concentrations in heart tissue. Plasma concentrations of von Willebrand factor [vWF] and D-dimer as markers of endothelial dysfunction and prothrombotic state were measured either in the experimental untreated hyperhomocysteinemic rats or in the treated ones. Hhcy resulted in a significant increase in serum CK and LDH levels. Cardiac MDA was significantly increased while GSH was significantly decreased in Hhcy group compared to the normal control group, plasma concentrations of vWF and D-dimer were also significantly increased. Serum marker enzymes and markers of cardiac oxidative stress were greatly exaggerated in Hhcy rats treated with isoprenaline in comparison with isoprenaline group. Administration of folic acid [10mg/kg, b.wt orally via gavage] alone and in combination with vitamin B[12] [500 ug/kg b.wt. i.m], concurrently for 4 weeks during the induction of Hhcy markedly reduced the increase in serum CK and LDH as well as the plasma concentration of vWF and D-dimer. Cardiac MDA content was decreased while cardiac GSH was elevated in the treated group compared to untreated Hhcy rats. These results suggest that Hhcy aggravates MI via oxidative stress mechanisms and that Hhcy may impair endothelial function and increases the biomarkers of prothrombotic state Treatment with either folic acid alone or in combination with vitamin B[12] can ameliorate the detrimental effects of Hhcy, reduce the risk of MI, appears to improve endothelial dysfunction and decrease plasma concentration of biomarkers of hypercoagulability. This provides preliminary evidence that such vitamin supplementation may have beneficial cardiovascular effects. However clinical benefit of vitamin supplementation has not yet been demonstrated and clinical trials are urgently required

D-dimer, thrombin-antithrombin complexes and compression ultrasound in diagnosis of DVT during pregnancy

The objective of this study was to determine whether the fibrinolysis marker [D-dimer] as well as the coagulation activation maker [thrombin-antithrombin [TAT] complexes] would be of an additional help in the diagnosis of deep vein thrombosis [DVT] in pregnant women. Eighty pregnant women were chosen and divided into two groups: First, study group which comprises 40 pregnant women with DVT in the current pregnancy and second, control group which included 40 healthy pregnant women. The mean values of D-dimer and TAT were significantly higher in the study group compared to the control group. At a cutoff line 500 ng/ml, D-dimer sensitivity and specificity were 87.5% and 90.0%, respectively. At a cutoff line 2.2 ug/l, TAT sensitivity and specificity were 87.5% and 82.8%, respectively. Neither gestational age or parity nor type of DVT showed an effect on mean results of these markers. In conclusion, D-dimer and TAT have reasonable sensitivity and specificity in the diagnosis of DVT among pregnant women. These sensitivity and specificity are not affected by type of DVT, gestational age or parity

Predicción de la trombosis venosa profunda por el dímero-D / Prediction of deep venous thrombosis from D dimer

Las determinaciones del dímero-D se utilizarán cada vez con mayor frecuencia para descartar las trombosis venosas y la innecesaria utilización de la angiografía pulmonar. La generación de pruebas para la determinación de los niveles de dímero-D debería aportar ensayos confiables y reproducibles en la práctica clínica, ya que los ensayos cualitativos disponibles hasta el momento, basados en el método de aglutinación con látex, son poco confiables para su uso clínico

Increased carotid intimal medial thickness in type 2 diabetes: relation to D-dimers

We investigated common carotid artery intimal - medial thickness [CCA-IMT] as an evidence of generalized atherosclerosis and D-dimers plasma concentrations as a measure of fibrinolytic activity, in 30 type 2 diabetic subjects [with no clinical coronary artery disease [CAD] cerebrovascular or peripheral vascular disease] and 15 healthy control subjects. Also the interrelation between CCA-IMT and D-dimers plasma concentrations and their relations with lipid status and blood sugar levels were evaluated. Diabetic subjects had significantly higher CCA-IMT and D-dimers plasma concentrations than control subjects. In diabetic subjects CCA-IMT and D-dimers plasma concentrations were significantly directly correlated with each other [P<0.01] and with FBS. 2 hPPBS, HbA[Ic], duration of diabetes, plasma fibrinogen, serum cholesterol, LDL-C and age of diabetic subjects. Diabetic subjects with better blood sugar control [FBS<140mg/dl] had significantly lower D-dimers plasma concentrations and non significantly less CCA-IMT than those with poor blood sugar control [FBS>140mg/dl]. suggesting that control of hyperglycaemia reduce haemostatic activation significantly. It is concluded that type 2 diabetic subjects without clinical CAD.cerebrovascular or peripheral vascular diseases, have a higher degree of atherosclerosis than normal control. Also this atherosclerosis is associated with enhanced Fibrin deposition and degradation as evidenced by increased D-dimers plasma concentrations. The control of hyperglycaemia and dyslipidemia that accompanies diabetes, possibly reduce or even prevent the progression of intimal medial thickening and will reduce significantly the activation of haemostasis leading to reduction of CAD and stroke risk

Dímero D, marcador plasmático precoz para trombosis venosa profunda en pacientes de riesgo / Dimer Test, precous plasmatic marker for profunded venous thrombosis in patients of risks

La trombosis ocurre por activación patológica de una mecanismo normal: el hemostático. Dentro de las pruebas de laboratorio para el diagnóstico de trombosis venosa profunda y embolia pulmonar se encuentra el DIMERO-D (Dimer test), que es un test in-vitro, cualitativo/semicuantitativo, que detecta enlaces cruzados de degradación de fibrina (XL-FDP). En el presente estudio se evaluaron a 120 pacientes, todos asintomáticos para trombosis venosa profunda y embolia pulmonar, que calificaron de riesgo alto para desarrollar ésta patología, todos internados en el Hospital Militar Central de Lima Perú; y, se les realizó el test de Dímero D (Dimer test), resultando 67 casos (55,8 por ciento) positivos y 53 casos (42.2 por ciento) negativos. En las áreas quirúrgicas se observó mas casos de positividad (61,8 por ciento), en las áreas médicas 36,3 por ciento. El test de Dímero D, se muestra en el presente trabajo como marcador precoz para trombosis venosa profunda en pacientes hospitalizados, lo cual obliga a tomar medidas de profilaxis en forma precoz.

Determinación del Dímero D en pacientes con anticoagulante lúpico / Determination of the Dimer D patients with lupic anticoagulats

La determinación del Dímero D es de gran utilidad para establecer el diagnóstico de trombosis venosa profunda; sin embargo, en los pacientes que presentan anticoagulante lúpico su hallazgo e importancia no ha sido claramente definidos. Se analizan 80 pacientes con cuadros sugetivos del síndrome antifosfolipídico. Todos los pacientes estuvieron comprendidos entre 0 y 40 años de edad, 13 (16 por ciento) casos mostraron alguna prueba positiva del citado síndrome, cinco de ellos, 4 mujeres y 2 varones evidenciaron anticuerpos anticardiolipina positivos. A los 13 pacientes se les realizó el Dímero D por dos métodos, así como, los niveles de fibrinógeno y la presencia de productos de degradación del fibrinógeno (PDF). Los métodos de Dímero D que se utilizaron fueron: la técnica de aglutinación indirecta con partículas de látex y la técnica de ELISA. Los resultados obtenidos muestran que los pacientes con antocoagulante lípico y/o anticuerpos anticardiolipina positivos y que presentan dimero D, muestran un cuadro de oclusión venosa que puede contribuir a la génesis de su problema trombótico.

Comparative study between molecular hybridization and electron microscopy for the detection of hepatitis E virus.

The study describes a comparison between molecular hybridization using a non-radiolabeled, thymine-thymine (TT) dimerized synthetic oligonucleotide complementary DNA probe and electron microscopy for the detection of hepatitis E virus genome in bile. Spot hybridization with the TT dimerized probe was found to be more sensitive and specific compared to electron microscopy.

Coagulation status and fibrinolytic activity in normal and abnormal pregnancy: case control study

Haemostatic and fibrinolytic activity changes during normal pregnancy particularly at the time of the placental separation. This study was designed to detect the changes in fibrinogen, plasminogen and factor XIII; and fibrin degradation products [FOPs], antiplasminogen and for the first time the "D-dimer" in different types of pregnancy associated complications. Twenty seven patients with aberrations of the pregnancy during first and second trimester and 26 patients with hypertensive disorders of pregnancy were compared to the 36 normal pregnancies. Plasminogen, fibrinogen and factor XIII showed a significant reduction in both abnormal groups compared to the normal pregnancy. The FOPs, antiplasminogen and the D-dimer, on the other hand showed a significant increase. These findings suggest using some of these parameters in early diagnosis of placental-associated abnormalities of the pregnancy

Conformations of deoxydinucleoside phosphates containing pyrimidine-pyrimidine photodimers.

Conformational analysis of deoxydinucleoside monophosphates with the sequences TpT and CpC have been carried out with the incorporation of both cyclobutane type pyrimidine dimers and 6-4 photoadducts using the methods of molecular mechanics energy minimization. The effect of flexibility with respect to sugar geometries and glycosidic torsions have been studied and the relative energies of a large variety of structures have been compared. The salient features obtained from these calculations have been compared with the crystallographic and spectroscopic data on pyrimidine dimer incorporated deoxydinucleoside monophosphates. Effects of "inserting" the energetically favourable conformations of such structures into B-DNA helices have been discussed in terms of the distortions in helical structures.

A Study on UVI - induced DNA Synthesis in Mouse Skin in Vivo Studied by Autoradiography / 대한피부과학회지

The status of DNA synthesis and the effect of UV radiation on the DNA synthesis were studied in mouse skin by microautoradiography. Mice exposed to 100mJ/cm of UVB were injected intradermally with tritiated thymidine, 5 minutes, 2, 6 and 24 hours after irradiation and biopsies were processed for light microscopic autoradiography, A total of 25 ICR female albino haired mice were used as subjects. We compared heavily labeled cells(>10 grains/nucleus) and sparsely labeled cells (3-10 grains/nucleus) in UVL irradiated skin with nonirradiated control skin. 1. Within 5 minutes after UVL exposure an apparent depression in the number of heavily labeled cells occurred. This reduction was statistically significant and remained so for at least six hours post,irradiation. By 24 hours after UVL exposure, the reduction was recovered to nearly control level. 2. By five minutes after UVL exposure, sparsely labeled cells were observed in basal cell layer and differentiated cell layer. The nurriber of sparsely labeled cells appeared highest at five minutes after UVL exposure and then tended to fall to nearly control level at 24 hours. This aberrant type of TdR H incorporation is thought to represent unscheduled DNA synthesis to repair pyrimidine dimers formed in UVL injured DNA molecules,

DNA repair aystems.

Sistemas de reparo do DNA tem merecido atencao, principalmente devido ao papel que exercem em mutagenese e carcinogenese. Sao revistos fatos ja estabelecidos e avancos recentes, no assunto, com enfase nos eventos enzimaticos, envolvidos nas celulas bacterianas