The γ-irradiation of aqueous solutions of urea. Implications for chemical evolution

0.05 mole dm^–3, O₂-free aqueous solutions of urea were studies after receiving various doses of⁶⁰Co gamma rays (0.14–600 kGy). Urea was found to be relatively stable under radiation; its radiation chemical yield of decomposition was 0.47. Hydrogen (G=0.50), carbon dioxide (G=0.44), ammonia (G=0.22), oxalic acid (G=0.0054), malonic acid (G=0.000064) and three unidentified oligomers were found to be the main radiolytic products. The origin of these products is explained by free radical reactions initiated by the transients from water radiolysis (H·,·OH,e_aq^–).     

The decomposition of soluble collagen by γ-irradiation

1. The effect of gamma-irradiation in the range 1 krad-10 Mrads on freeze-dried acid-soluble collagen was studied. 2. The specific-rotation and reduced-viscosity recoveries after heating and cooling of the irradiated collagen in solution showed a high degree of dependence on irradiation dose, with reduced viscosity showing significantly less recovery than specific rotation on increasing the irradiation dose. 3. The dependence of reduced viscosity on concentration was greatly decreased with increased doses of gamma-irradiation. 4. The melting temperature measured by optical rotation also decreased as the irradiation dose was increased, and at low doses was distinctly biphasic. 5. Physical properties showed that the action of gamma-irradiation up to 10 Mrads occurred in two distinct phases, with the early changes being extremely sensitive to irradiation dose. 6. The action of the gamma-irradiation is discussed in terms of the structure of tropocollagen.     

The effect of γ-irradiation on soluble collagen

1. A study was made of the effect of gamma-irradiation on the sub-unit composition, as well as the conformational changes taking place in cooled solutions of thermally denatured neutral-salt-soluble and acid-soluble collagen. 2. The increase in negative rotation and viscosity at 15 degrees for irradiated and thermally denatured collagen solutions becomes less as the irradiation dose is increased. 3. The initial effect of gamma-irradiation is the depolymerization of the dimers found in both neutral-salt-soluble and acid-soluble collagen. 4. The principal effect of gamma-irradiation up to 10 Mrads is the fission of peptide bonds, yielding crystalline irradiation-resistant portions of the molecule incapable of associating to the native structure. 5. The effects of gamma-irradiation on both neutral-salt-soluble and acid-soluble collagen are very similar and bear a close resemblance to the effects induced by ultraviolet irradiation.     

The dissociation of histone from deoxyribonucleohistone by γ-irradiation

1. Experiments were carried out to determine the extent of dissociation of histone from deoxyribonucleohistone as a result of irradiation with γ-rays from ⁶⁰Co. 2. The bulk of the nucleohistone was removed from the irradiated solutions either by sedimentation or by precipitation with dilute sodium chloride solution. The supernatants were then analysed for DNA and histone. 3. The ratios of histone to DNA in these supernatants were less than for the original nucleohistone. This indicated that histone was dissociated by the irradiation, and then aggregated either with itself or with other nucleohistone molecules, and so was removed with the bulk of the nucleohistone during sedimentation or precipitation.     

The effect of ribose pre-treatment of cortical bone on γ-irradiation sterilization effectiveness

Reconstruction of large skeletal defects is a significant and challenging issue. Tissue banks often use γ-irradiation (15–35 kGy) to sterilize bone allografts, which, however, drastically impairs the post-yield mechanical properties. In previous studies, we reported the development of a method that protects human bone collagen connectivity through ribose crosslinking while still undergoing γ-irradiation. Given these promising results, the next step was to determine if the presence of ribose within the bone tissue would interfere with the effectiveness of the γ-irradiation sterilization against bacteria. This study had two stages. The aim of the first stage was to assess the protective effect of ribose in solution using a Bacillus pumilus spore strip model. The aim of the second stage was to assess the protective effect of ribose (R) on spores within a human cortical bone model in comparison to conventionally irradiated bone (I). Treatment of B. pumilus spore strips with ribose in solution led to temperature-dependent effects on spore viability versus spore strips treated with PBS alone. Ribose solution at 60 °C led to a notable two logs decrease in spore count relative to PBS at 60 °C. In the human bone model, the number of spores in the I and R groups were greatly decreased in comparison to the non-irradiated N group. No spore colonies were detected in the R group (n = 4) whereas two of the four plates of group I formed colonies. This study provides evidence that the method of pre-treating bone with ribose crosslinking prior to irradiation sterilization, while improving irradiation sterilized bone allograft quality, also may improve the effectiveness of the sterilization process.     

The effect of in vitro γ-irradiation on mitogenic responsiveness of murine lymphocytes

The objective of this study was to analyze the proliferative response of BALB/c mice lymphocytes after in vitro irradiation (0.05 to 6 Gy). The capability of irradiated lymphocytes for proliferating without any stimulation and after activation with specific T and B cell mitogens has been evaluated. The results show that ionizing radiation significantly inhibits spontaneous cellular proliferation and that induced by mitogens and that variations in the degree of inhibition are found depending on the inducing proliferation mitogens and the dosage applied. The conclusion drawn is that different lymphocyte populations have different radiosensitivities, being B cells more sensitive to ionizing irradiation than T cells. Besides, the effects of gamma-irradiation vary according to the different subpopulations of T cells or, alternatively, to different T-dependent activation mechanisms.     

The effects of γ-irradiation on the priming by deoxyribonucleohistone of ribonucleic acid polymerase

1. The effect of gamma-irradiation of solutions of DNA and deoxyribonucleohistone (DNH) on their ability to prime the synthesis of RNA by DNA-dependent RNA polymerase has been studied. 2. The priming ability of both DNA and DNH decreased continuously with increasing radiation dose, but more rapidly with DNH. 3. These decreases have been compared with decreases in molecular weight and with the breakdown of the specific hydrogen-bonded structure of DNA. 4. It is concluded that a process was occurring during gamma-irradiation of DNH that, although involving a decrease in molecular weight, did not diminish and even enhanced its priming ability. This is consistent with previous physicochemical evidence that gamma-irradiation causes dissociation of histone from DNH.     

The effects of γ-rays on poly-L-glutamic acid in aqueous solution

Summary Salt-free and 0.2 M NaCl oxygenated aqueous solutions of poly-L-glutamic acid were irradiated with⁶⁰Co--radiation at variouspH's to examine whether or not the changes caused by the exposure to ionizing radiation depend onpH, that is, the conformations of polypeptide.TheG-values (the number of main-chain scissions per 100 eV of energy absorbed) in both salt-free and 0.2 M NaCl solutions of poly-L-glutamic acid were found to change sharply withpH. and to have a maximum value at thepH of a mid-point of helix-coil transition. The change ofG-values withpH was discussed in terms of the conformational change of poly-L-glutamic acid.     

Parthenocarpy of watermelon cultivars induced by γ-irradiation

We found that diploid seedless watermelon can be produced by pollination with partially functional pollen, which was irradiated with γ-rays at the doses of 600 and 800 Gy. The diploid seedless fruits were almost similar to normal fruits in development from pollination to maturity. The number of empty seeds in the diploid seedless fruits varied among the cultivars used. Seedless watermelon cultivars revealed a significant increase in total sugar and carotenoids (lycopene and gb-carotene) contents. The pollen tubes of the pollen subjected to γ-radiation penetrated normally into the synergid, and sperm cells were discharged. Subsequently, the egg nucleus and sperm nucleus became attached to each other in the egg cell and a globular embryo was formed. However, the embryo failed to differentiate the tissues and degenerated. It is suggested that seedless watermelon fruits induced by γ-rays are characterized by increasing yield and better quality due to higher carotenoid and total sugar contents and fruit weight. In some cultivars, there is a tendency in decreasing the thickness of rind.     

Influence of a single γ-irradiation on rat microflora

Changes in leukocyte counts and in the gut microflora of laboratory rats irradiated with a single whole-body dose of γ rays (5.0 Gy) were determined. The number of leukocytes was lower especially 1 and 2 weeks after irradiation. A significant decrease in lymphocytes was observed 1 week and in monocytes 1 and 2 weeks after irradiation. In parallel with these changes, an increase in common microflora was observed; some microorganisms, which normally are not present in duodenum, liver and mouth cavity, were detected in these organs.     

Localization of lipid peroxidation products in liposomes after γ-irradiation

The distribution of lipid peroxidation products in liposomes after γ-irradiation at various doses was studied. Increases in thiobarbituric-acid-reactive substances, in the absorbance at 232 nm and in hydroperoxides were observed mainly in liposomal membranes after relatively low doses of irradiation, while carbonyl compounds were distributed both inside and outside the membranes. After higher doses of irradiation, however, the absorbance at 232 nm and the amount of hydroperoxides reached a maximal level in the membrane portion and then decreased when the decomposition products were released from the membranes. Under this condition, malondialdehyde and other carbonyl compounds were increased mainly in the medium of liposomal suspension. These results are discussed with reference to the lipid peroxidation process which is induced quantitatively by ionizing radiation.     

Effects of γ-irradiation on antioxidant activity in soybean seeds

There are some reports that low doses of γ-irradiation could induce antioxidant activities in plant material, including soybean. Irradiation, required for the inactivation of some pathogens and induction of mutations, may have adverse effects on sensorial, nutritional and antioxidant qualities. The effects of different γ-irradiation doses (100–200 Gy) on antioxidant properties of soybean seeds was investigated. In this study, we report the results obtained by analysis of antioxidant enzyme activities, reduced glutathione, malonyldialdehyde (MDA) and hydroxyl (HO⁻) radical quantities, soluble protein content, and total antioxidant activity in irradiated soybean seeds. Antioxidant enzyme activities were affected due to high irradiation intensity. Significant changes of total antioxidant activity and MDA and HO.quantities were observed only under the highest irradiation dose, with a 15.7% reduction in total antioxidant activity, MDA quantity increase of 21.6%, and HO⁻ radical quantity increase of 79.3% compared to the non-irradiated control. The total soluble protein content increased slightly.     

On the course of thermal denaturation of deoxyribonucleic acids after γ-irradiation

Summary The changes which are caused by action of-irradiation onDNAs of various origin were followed by spectrophotometric method at differing thermal denaturation curves. It was found that all measured bacterialDNAs as well asDNA isolated from calf thymus, irradiated by exposures higher that 5×10⁴ R, produced significantly decreasedT _m values with concomittantly decreased hyperchromic effect and changed transition intervals obtained in 10^–2 M sodium phosphate, 10^–3 M EDTA medium at pH 7. It was also observed that higher-irradiation exposures caused the loss of renaturation ability ofEscherichia coli DNA.Abbreviations used DNA deoxyribonucleic acid - G guanine - C cytosine - E ₂₆₀ extinction (absorbancy) measured at 260m - T _m the temperature corresponding to the midpoint of the absorbance rise - 2/3 the transition interval of the denaturation curve corresponding to the temperature interval between 17–83% of the total absorbancy increment of the denaturation curve - SSC standard saline citrate buffer (0.15 M NaCl, 0.015 M sodium citrate, pH 7) - PE 10^–2 M sodium phosphate buffer [molarity related to (PO₄)] - PE 10^–3 M EDTA, pH 7. 1.000 ml prepared as follows: 0.608 g NaH₂PO₄.2 H₂O, 0.218 g Na₂HPO₄.12 H₂O, 0.372 g disodium salt of EDTA, 1.0 ml 1 M NaOH. Concentration of Na ions — 0.02 M.     

The human lymphocyte micronucleus assay: Response of cord blood lymphocytes to γ-irradiation and bleomycin

The induction of micronuclei in human cord blood lymphocytes by treatment with γ-irradiation and bleomycin has been measured. Culture durations which gave peak MN frequencies were determined. The lowest tested doses, 0.1 Gy irradiation and 1.25 μg/ml bleomycin, produced significant increases in the frequency of micronuclei. The spontaneous frequency of micronucleated lymphocytes in 28 cord blood samples ranged between 0.5 and 9.5 per thousand lymphocytes, with a modal value of 2.5. The method is evaluated for its potential usefulness in monitoring populations for chromosome breakage.     

Alleviation of salt stress by low dose γ-irradiation in rice

The effects of salt stress on the growth, photosynthesis, and antioxidative ability of the rice (Oryza sativa L.) plants raising from -irradiated seeds were investigated using two cultivars, Ilpumbyeo and Sanghaehyanghyella. The 50 and 100 mM NaCl solutions caused a remarkable decrease of the early germination rate and seedling growth. However, the salt stress-induced inhibition of the growth was significantly alleviated in the -irradiated plants. The chlorophyll contents and the effective quantum yield of photosystem 2 ( _{PS 2}) were lower in the NaCl-treated plants than in the control ones, while the non-photochemical quenching was higher in the former ones. Activities of the antioxidant enzymes such as superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased with increasing NaCl concentrations, and the irradiated groups had even higher SOD and APX activities than the non-irradiated ones. These alleviation effects were observed similarly in both the cultivars tested.     

Effects of γ-irradiation on Na,K-ATPase in cardiac sarcolemma

Previous studies showed that adverse effect of ionizing radiation on the cardiovascular system is beside other factors mostly mediated by reactive oxygen and nitrogen species, which deplete antioxidant stores. One of the structures highly sensitive to radicals is the Na,K-ATPase the main system responsible for extrusion of superfluous Na⁺ out of the cell which utilizes the energy derived from ATP. The aim of present study was the investigation of functional properties of cardiac Na,K-ATPase in 20-week-old male rats 6 weeks after γ-irradiation by a dose 25 Gy (IR). Irradiation induced decrease of systolic blood pressure from 133 in controls to 85 mmHg in IR group together with hypertrophy of right ventricle (RV) and hypotrophy of left ventricle (LV). When activating the cardiac Na,K-ATPase with substrate, its activity was lower in IR in the whole concentration range of ATP. Evaluation of kinetic parameters revealed a decrease of the maximum velocity (V _max) by 40 % with no changes in the value of Michaelis–Menten constant (K _m). During activation with Na⁺, we observed a decrease of the enzyme activity in hearts from IR at all tested Na⁺ concentrations. The value of V _max decreased by 38 %, and the concentration of Na⁺ that gives half maximal reaction velocity (K _Na) increased by 62 %. This impairment in the affinity of the Na⁺-binding site together with decreased number of active Na,K-ATPase molecules, as indicated by lowered V _max values, are probably responsible for the deteriorated efflux of the excessive Na⁺ from the intracellular space in hearts of irradiated rats.     

Fluorinated piperidine acetic acids as γ-secretase modulators

We report herein a novel series of difluoropiperidine acetic acids as modulators of γ-secretase. Synthesis of 2-aryl-3,3-difluoropiperidine analogs was facilitated by a unique and selective β-difluorination with Selectfluor®. Compounds 1f and 2c were selected for in vivo assessment and demonstrated selective lowering of Aβ42 in a genetically engineered mouse model of APP processing. Moreover, in a 7-day safety study, rats treated orally with compound 1f (250 mg/kg per day, AUC_0–24 = 2100 μM h) did not exhibit Notch-related effects.