Relative Biological Efficiency Values Research Articles

Evaluation of relative biological efficiency of additives in sugarcane ensiling

The objective of this study was to evaluate the effects of adding alkalis on the fermentative pattern, aerobic stability and nutritive value of the sugarcane silage. A completely randomized design with 6 additives in two concentrations (1 or 2%), plus a control group, totalizing 13 treatments [(6×2)+1] with four replications, was used. The additives were sodium hydroxide (NaOH), limestone (CaCO3), urea (CO(NH2)2), sodium bicarbonate (NaHCO3), quicklime (CaO) and hydrated lime (Ca(OH)2). The material was ensiled in 52 laboratory silos using plastic buckets with 12 L of capacity. Silos were opened 60 days after ensiling, when organic acids concentration, aerobic stability and chemical composition were determined. The Relative Biological Efficiency (RBE) was calculated by the slope ratio method, using the data obtained from ratio between desirable and undesirable silage products, according to the equation: D/U ratio = [lactic/(ethanol + acetic + butyric)]. All additives affected dry matter, crude protein, acid detergent fiber, neutral detergent fiber contents and buffering capacity. Except for urea and quicklime, all additives increased the in vitro dry matter digestibility. In general, these additives altered the fermentative pattern of sugarcane silage, inhibiting alcoholic fermentation and improving lactic acid production. The additive that showed the best RBE in relation to sodium hydroxide (100%) was limestone (89.4%). The RBE values of urea, sodium bicarbonate and hydrated lime were 49.2%, 47.7% and 34.3%, respectively.

Induction and rejoining of DNA double-strand breaks in cho cells after heavy ion irradiation

DNA double-strand breaks (DSBs) are the crucial events ultimately leading to cell inactivation. Aimed at understanding the biological action of the charged particle component of cosmic radiation, the induction of DSBs and their repairability was evaluated in Chinese hamster ovary (CHO-KI) cells after exposure to accelerated particles. Irradiations were performed with various ion species including O, Ni and Ca, covering a LET range from 20 to 2000 keV/μm. DSBs were determined for plateau-phase cells using the electrophoretic elution of radiation-induced DNA fragments in a static electric field combined with fluorescence scanning of ethidium bromide stained gels. Assuming a DSB yield of 22 DSB per Gy per cell, as derived from X-irradiation, cross-sections for DSB production were calculated from the corresponding fluence-effect curves at a fraction of 0.7 of DNA retained. The same ordinate was used as a reference for the calculation of relative biological efficiency (RBE) for DSB induction. At low LETs (≤ 20 keV/μm) RBE values slightly above unity were obtained, but a decrease of RBE was observed with increasing LET. In the region of 100–200 keV/μm the RBE for initial DSB induction was clearly below unity. Rejoining of DSBs was assessed by measuring the fraction of DNA retained following post-irradiation incubation of cells under culture conditions. After exposure to Ca ions, DSB rejoining was considerably impaired compared to X-rays.

Heavy ion induced membrane damage: hemolysis of erythrocytes and changes in erythrocyte membrane fluidity.

Human erythrocytes were irradiated with heavy ions of energies between 4 and 18 MeV/u having linear energy transfer (LET) values between 92 and 14,000 keV/microns. Hemolysis has been studied as a macroscopic parameter for membrane damage and changes of the fluidity as a more microscopic parameter. The membrane fluidity changed in a characteristic dose-dependent manner as detected by electron spin resonance employing 12-doxylstearic acid methyl ester spin label (SL 12). Lysis cross sections and RBE values were determined from dose effect curves. The results demonstrate a high hemolytic efficiency of heavy ions compared to X rays. With increasing LET values the measured relative biological efficiency (RBE) values increase continuously. In the complete LET range the cross sections formed one common curve as function of LET and no saturation effects are observed. This is in direct contrast to other biological endpoints such as cell inactivation or DNA damage.

Prenatal death and malformations after irradiation of mouse zygotes with neutrons or X-rays.

Female mice (strain: "Heiligenberger Stamm") were irradiated with neutrons (7 MeV) or X-rays when embryos were at the early zygote stage; uterine contents were examined on gestation day 19 for prenatal mortality and malformed fetuses. For both radiation qualities, the dose-dependent survival curve fitted well to a simple exponential equation; the neutron relative biological efficiency (RBE) value was 2.3. The major fraction of deaths induced by exposure to neutrons or X-rays occurred before implantation. Aside from dead embryos, malformed fetuses were observed 19 days p.c. (postconception). The number of malformed fetuses increased with a linear-quadratic function of neutron or X-ray dose. Malformations were mainly gastroschisis, although omphaloceles and anencephalies were also observed. The neutron RBE value for the induction of malformations varied from 2.0 to 2.8 in the dose range tested. Except after 75-cGy neutrons, no significant increase in the proportion of stunted or skeletally malformed fetuses was noted. Our results indicated that the reaction of preimplantation embryos to irradiation could be more complex than the simple "all-or-none" response considered so far.

Effect of secondary radiation produced by 70 GeV protons on DNA of mammalian cells

It is shown that the RBE of the 70 GeV proton secondary radiation for the induction of single-strand break is 1.6–7.6 in Chinese hamster fibroblasts and 1.04–3.8 in limphoid cells and for the lethality of Chinese hamster cells 1.14–1.7. The RBE value increases with decreasing dose of the secondary radiation. On post-irradiation incubation of mammalian cells at 37°C, single-strand breaks induced by the secondary radiation are repaired with the same time course as those induced by ▪-rays. In our earlier works we have made an attempt to estimate the biological efficiency of radiation generated by the 70 GeV protons on bacteria, phage T4 and Vicia faba beans /1,2,3/. The obtained values of the relative biological efficiency (RBE) of this radiation varied between 1.4 and 5.5, depending on the object, criterion of estimation, times of registration and other experimental conditions. The aim of the present work is to estimate the biological efficiency of synchrotron radiation by its effect on mammalian cells.

Induction of micronuclei in bean roots by 250 GeV hadrons.

Vicia Faba bean roots were irradiated with 250 GeV hadrons and the induction of micronuclei was evaluated. A Relative Biological Efficiency (RBE) of about 1.8 was found using60Coγ-rays as reference radiation. For the production of multiple micronuclei the RBE value was determined to be 2.1. Cytological anomalies were detected after the hadron irradiation.

Biological Responses to Various Neutron Energies from 1 to 600 MeV: I. Testes Weight Loss in Mice

Testes weight loss in mice has been used as a test system to determine the relative biological efficiency (RBE) of neutrons ranging in energy from fission to a beam of 600 MeV nominal energy. The RBE values, calculated as equal effect dose ratios show a maximum at the neutron energy of 1 MeV. No significant dependence was found on the level of absorbed dose. Analyses of the dose-effect relations obtained suggest the existence of a radiation-insensitive component of the testes that accounts for 32.5% of the total weight. By considering only the radiosensitive component, the X-ray data show an exponential dose-effect relation. When the same correction is applied to the neutron data, dose-effect curves with an extrapolation number less than one are obtained for some neutron energies.

Dose-response relationship for chromosome aberrations induced by X-rays or 50 MeV protons in human peripheral lymphocytes

The dose-response relationship has been investigated for chromosome aberration yields produced in human peripheral lymphocytes by exposure to X rays or 50 MeV protons in vitro. Both sets of data on dicentric aberrations were fitted to the power law expression Y = bD n, with dose exponents of 1.47 ± 0.012 and 1.36 ± 0.027 for X-rays and protons, respectively. The proton RBE (relative biological efficiency) value obtained was 0.88 ± 0.01.

Response of Mouse Jejunal Crypt Cells to Low Dose Rate Irradiation with Californium Neutrons or Radium Gamma-Rays

Californium-252 emits neutrons and gamma-rays and has a potential use in radiotherapy as a replacement for radium. There is no single value for the relative biological efficiency (RBE) of radiations from californium and radium. At high dose rates, the RBE for killing of mammalian cells usually varies with the degree of injury, being highest at low doses. At low dose rates, the RBE is more likely to be constant at all levels of injury but will vary with dose rate and distance from the californium. The RBE (Cf neutrons/Ra gamma rays) is ∼5 for killing of intestinal crypt cells when the dose rate from radium is 160 rads/hour. At the lower dose rates used in radium therapy (30-70 rads/hour), the RBE (for Cf neutrons only) may be greater than 5. If the total dose (neutrons + gamma rays) from californium had been used in calculating the RBE at a source distance of 2 cm, the value would have been about 3.2. However, the better way of determining radium-equivalent doses is to apply RBE values separately to the ne...

The relative biological efficiency (RBE) of 30-MeV electrons on haploid yeast.

The biological efficiency of 30-MeV electrons on a haploid strain ofSaccharomyces cerevisiae was studied. The ability of a yeast cell to form a macrocolony defined survival. Cell suspensions were irradiated homogeneously by test and reference radiation simultaneously in different phantoms. The dose measurements were based on Fricke dosimeters. The RBE values obtained for 30-MeV electrons were: 1.04±0.03 with Cobalt-60 gamma rays as reference and 0.88 ± 0.03 with 200-kVcp X-rays as reference. The values agree closely with those recently reported for highly energetic photons from a betatron.

A HIGH RELATIVE BIOLOGICAL EFFICIENCY OF 650-KEV NEUTRONS AND 250-KVP X-RAYS IN SOMATIC MUTATION INDUCTION.

THE mean linear energy transfers of 650-keV neutrons and of 250-kVp X-rays are so markedly different that it is not usually possible to establish a unique value for their relative biological efficiency. For example, it is well known that the densely ionizing neutrons induce linear dose-response relationships for chromosome aberrations, whereas the dose-response curves for X-rays are often non-linear. Moreover, the former radiation but not the latter is almost independent of environmental factors such as oxygen tension during irradiation. Under certain conditions, and with certain biological test systems, however, some of these difficulties are minimized. For example, Neary et al.1 compared the relative biological efficiency, in terms of chromosome aberration induction, of 0.7- and 3.0-MeV neutrons with cobalt-60 γ-rays administered at low dose rates. There the dose-response relationships were almost linear, and relative biological efficiency values of 35 were obtained; they also derived ultimate maximum relative biological efficiency values from a comparison of the one-hit components of the neutron and γ-dose-response curves and found that these could be as high as 100. Similarly, Smith et al.2, using a test system (somatic mutation induction in dry seed) in which the dose-response relationship for X-rays was linear, obtained an average relative biological efficiency value of about 75 for mono-energetic neutrons of 0.43–1.80 MeV.