Evidence for humoral effects on the radiation response of rat foot skin.

The influence of perturbation of the physiologic state of the whole body on the outcome of radiation exposure has been examined in a rat foot model. Irradiation was carried out using 60Co gamma-rays. Moist desquamation was used as an endpoint. Rats were given a priming dose of 2 Gy, 4 Gy or 7 Gy to their whole body except their hind feet (partial body priming dose). After a variable time period both hind feet of these animals were irradiated with graded doses of 60Co gamma-rays. The incidence of moist desquamation in the irradiated feet of these animals was compared with the incidence of moist desquamation in animals that had not received the initial partial body priming dose. It was noticed that the incidence of moist desquamation in the rat foot skin of animals that received 7 Gy partial body priming dose 4 h prior to irradiation of their hind feet was significantly less than moist desquamation in control animals. The ED(50) value of 22.53+/-0.16 Gy for moist desquamation of the foot skin of control animals was significantly lower (p<0.01) than the value of 25.25+/-0.29 Gy obtained for animals that received a partial body priming dose of 7 Gy 4 h prior to irradiation of their hind feet. It was concluded that the response of rat foot skin to radiation was not purely the result of epidermal stem cell kill and that it can be modified by alterations in the overall physiological state of the animal's body brought about by a priming dose to the whole of the animal's body except the hind feet.

Modification of radiation myelopathy by the transplantation of neural stem cells in the rat.

In a novel approach, neural stem cells were transplanted to ameliorate radiation-induced myelopathy in the spinal cords of rats. A 12-mm section of the cervical spinal cord (T2-C2) of 5-week-old female Sprague-Dawley rats was locally irradiated with a single dose of 22 Gy of (60)Co gamma rays. This dose is known to produce myelopathy in all animals within 6 months of irradiation. After irradiation, the animals were subdivided into three groups, and at 90 days after irradiation, neural stem cells or saline (for controls) were injected into the spinal cord, intramedullary, at two sites positioned 6 mm apart on either side of the center of the irradiated length of spinal cord. The injection volume was 2 microl. Group I received a suspension of MHP36 cells, Group II MHP15 cells, and Group III (controls) two injections of 2 microl saline. All rats received 10 mg/kg cyclosporin (10 mg/ml) daily i.p. to produce immunosuppression. All animals that received saline (Group III) developed paralysis within 167 days of irradiation. The paralysis-free survival rates of rats that received transplanted MHP36 and MHP15 cells (Groups I and II) were 36.4% and 32% at 183 days, respectively. It was concluded that transplantation of neural stem cells 90 days after irradiation significantly (P = 0.03) ameliorated the expression of radiation-induced myelopathy in the spinal cords of rats.

Effects of Lipochromin and Levosinum in the modulation of radiation-induced injury to pig skin.

Pig skin was used as a model to study the effectiveness of two topically applied creams, Lipochromin and Levosinum, in modifying the development of both early and late radiation damage to pig skin. Irradiated skin sites that received daily topical application of Levosinum or Lipochromin after exposure were compared with sites on the contralateral flank of the same animal that received irradiation only. Irradiation was with graded doses of 90Sr/90Y beta-rays. Incidence of moist desquamation (acute) and ischaemic dermal necrosis (late) were used as end-points. The latency period for the development of moist desquamation and its healing time was also assessed. The latency period for the development of moist desquamation in this model ranged from 4.00-6.75 weeks. There was no significant difference between the cream treatment and control sites. Application of Levosinum shortened the healing time of moist desquamation at each dose level by 5-10 days. In three out of four dose levels used, this shortening of the healing time was statistically significant (p < 0.03). Treatment with these topical applications also reduced the incidence of late dermal necrosis and increased the ED50 values for the incidence of dermal necrosis. This increase in ED50 values was equivalent to a dose modification factor of 1.11-1.13.

Time- and dose-related changes in the thickness of skin in the pig after irradiation with single doses of thulium-170 beta particles.

Time-related changes in skin thickness have been evaluated in the pig using a noninvasive ultrasound technique after exposure to a range of single doses of 0.97 MeV beta particles from (170)Tm plaques. The reduction in relative skin thickness developed in two phases; the separation into two phases was statistically justified only after 120 Gy (P = 0.04). The first phase was between 12 weeks and 24 weeks after irradiation. No further changes were seen until 48-60 weeks after irradiation, when a second phase of skin thinning was observed. No further changes in relative skin thickness were seen in the follow-up period of 104 weeks. The timing of these phases of relative skin thinning was totally independent of the radiation dose; however, the severity of each phase of radiation-induced skin thinning was related to the dose. The pattern of changes was similar to that reported previously after irradiation with 2.27 MeV beta particles from (90)Sr/(90)Y, but the degree of dermal thinning was less for a similar skin surface dose. From a comparison of the depth-dose distribution of the beta particles from the two radionuclides, it was concluded that the target cell population responsible for both the first and second phase of skin thinning in pig skin after irradiation may be located at approximately 800 microm depth. This corresponds to an area in the reticular dermis in pig skin and may be the appropriate site at which to measure the average dose to the dermal tissue.

How valid is the assumption of equal effect per fraction?

BACKGROUND AND PURPOSE: The validity of the assumption of equal biological effect with dose per fraction in fractionated radiotherapy has been examined for the acute skin reaction in a rat foot model using a variable number of 2-Gy daily fractions followed by graded top-up doses. MATERIAL AND METHODS: Mature female rats were used. Both hind feet of each rat were irradiated with a range of fractionated and top-up doses of 60Co gamma-rays. The dose-related incidence of moist desquamation was used as an end-point. Quantal data for the incidence of moist desquamation were analysed using probit analysis and ED50 (+/-SE) values were obtained. The results were also compared with predicted values obtained from the application LQ-model. RESULTS: After a single 2-Gy fraction followed by top-up doses 24 h later, the dose effect curve for the top-up doses used was shifted to lower doses as expected and the ED50 for moist desquamation of 19.78 +/- 0.13 Gy was 1.16 Gy less than the ED50 of 20.94 +/- 0.15 Gy for large single dose exposure alone. This implied that only approximately 58% of the initial 2-Gy fraction was effective, and the rest was repaired within a 24-h interval between the 2 Gy and top-up doses. However, after two or three 2-Gy daily fractions the dose effect curves for the subsequent top-up doses moved to the higher doses again and the ED50 for top-up dose increased to 20.33 +/- 0.21 and 20.75 +/- 0.11 Gy, respectively. A further increase in the number of 2-Gy daily fractions shifted the dose effect curves for the top-up doses to lower doses and ED50 values for the top-up doses decreased progressively. CONCLUSIONS: The findings were not in keeping with values predicted based on the assumption of equal effect per fraction and could not be explained by the use of a single alpha/beta ratio in the LQ-model.

Late behavioural and neuropathological effects of local brain irradiation in the rat.

The delayed consequences of radiation damage on learning and memory in rats were assessed over a period of 44 weeks, commencing 26 weeks after local irradiation of the brain with single doses of X-rays. Doses were set at levels known to produce vascular changes alone (20 Gy) or vascular changes followed by necrosis (25 Gy). Following T-maze training, 29 weeks after irradiation, irradiated and sham control groups performed equally well on the forced choice alternation task. When tested 35 weeks after irradiation, treated rats achieved a much lower percentage of correct choices than controls in T-maze alternation, with no difference between the two irradiated groups. At 38-40 weeks after irradiation, rats receiving both doses showed marked deficits in water maze place learning compared with age-matched controls; performance was more adversely affected by the higher dose. The extent of impairment was equivalent in the two groups of rats irradiated with 25 Gy, those trained or not previously trained in the T-maze, suggesting that water maze acquisition deficits were not influenced by prior experience in a different spatial task. In contrast to water maze acquisition, rats irradiated with 20 Gy showed no deficits in working memory assessed in the water maze 44 weeks after irradiation, whereas rats receiving 25 Gy showed substantial impairment. Rats receiving 25 Gy irradiation showed marked necrosis of the fimbria and degeneration of the corpus callosum, damage to the callosum occurring in animals examined histologically 46 weeks after irradiation, but in only a third of the animals examined at 41 weeks. However, there was no evidence of white matter necrosis in rats irradiated with 20 Gy, examined 46 weeks after irradiation. These findings demonstrated that local cranial irradiation with single doses of 20 and 25 Gy of X-rays produced delayed impairment of spatial learning and working memory in the rat. The extent of these deficits appears to be task- and dose-related, since rats treated with 25 Gy showed marked impairments in all measures, whereas rats treated with the lower dose showed less impairment in water maze learning and no deficits water maze working memory, despite significant disruption of working memory in the T-maze. The findings further suggest that although high dose irradiation-induced white matter necrosis is associated with substantial impairment, cognitive deficits may also be detected after a lower dose, not associated with the development of necrosis.

Regional biological dosimetry: radiation induced changes of elemental concentrations in hair.

Irradiation of skin by ionizing radiation is reflected by changes in hair growth. Changes in hair diameter, which follows irradiation, are the basis of a biological dosimetry technique. Nuclear microscopy has also been used to measure changes in concentrations of trace and minor elements in hair of radiation treated test animals. Some of the elements show change in both their longitudinal and transversal distribution. These changes are related to the skin dose received.

Exploring sensory integrative dysfunction in process schizophrenia.

During a 6-week period, the effects of sensory integrative activities on a group of seven chronic nonparanoid schizophrenic adults were compared to the effects of sedentary activities in a control group of seven similar subjects. The effects of each therapeutic approach were evaluated by measuring the patients' performance in several areas using the Nurses Observation Scale of Inpatient Evaluation-30 (NOSIE-30), The Object Manipulation Speed Test, a gait analysis, and grip strength. The results indicated general improvement in the experimental group. Behaviors measured by the NOSIE-30 showed the most significant improvements. The control group showed isolated improvements in grooming (measured by the NOSIE-30) and in right-hand use (measured by The Object Manipulation Speed Test). These findings suggest that 6 weeks of sensory integrative activities can improve the overall functioning of chronic nonparanoid schizophrenic patients, facilitate their adaptive responses, and enable them to participate more fully in other areas of therapeutic intervention.

A quantitative study of age-related changes in the vascular architecture of the rat cerebral cortex.

A quantitative study of age related changes in the vascular architecture of the rat cerebral cortex is described. A special vessel-filling technique, which allowed the simultaneous fixation of the vasculature, aided the identification of the vessels in histological sections. Vascular parameters, which included the total number of vessel fragments, a blood volume and a vessel wall-surface area index were obtained using a Quantimet 720 shape-analysing computer. In animals aged 13-83 weeks, there was an increase in the above vascular parameters which could mainly be attributed to an increase in the number of vessels with a diameter greater than 8 micrometers. In very old rats, aged 124 weeks, the vascularity of the cerebral cortex was severely reduced. These changes, which are very similar to those reported in the ageing human cerebral cortex, may be explained by either direct or indirect effects on the cerebral vasculature. Possible mechanisms are discussed in relation to similar changes observed in the cerebral vasculature after several different insults.

Action of adenosine hosphates on the release of intracellular lactate dehydrogenase from human and rat lymphocytes.

Differences in the action of adenosine phosphates on the release of intracellular enzymes from human and rat lymphocytes have been studied. The protective effect of ATP on the human cells was found to be less than on the rat cells. The greatest discrepancy was exhibited by AMP which exerted a protective effect on human lymphocytes, but increased enzyme efflux from rat lymphocytes. The activities of adenosine kinase, adenylate kinase, phosphoribosyl-pyrophosphate synthetase, pyruvate kinase, phosphoglycerate kinase and creatine kinase were compared in the cells of both species. Although significant differences were observed, they were too small to suggest the presence of a mechanism for the conversion of AMP into ATP in human lymphocytes not found in the rat cells. It seems therefore that the protective effect exerted by AMP on the human cells is not mediated by its conversion into ATP, and hence that some factor other than the intracellular energy content is concerned in controlling the release of intracellular enzymes from human cells.

Inactivation in vitro of lactate dehydrogenase-5 in blood.

During incubation with rabbit blood in vitro rabbit-muscle lactate dehydrogenase-5 was inactivated at a rate similar to that observed in vivo. By contrast plasma and plasma containing erythrocytes had no effect on the enzyme activity, but plasma containing leucocytes inactivated the enzyme at the same rate as whole blood. The results obtained support the concept that intravascular inactivation accounts for the diappearance of enzymes from the circulation.

Catabolism of plasma enzymes, as studied with 125I-labeled lactate dehydrogenase-1 in the rabbit.

Circulating enzymes may be inactivated in the plasma and the inactive breakdown products may be hydrolyzed in the lumen of the small intestine. Evidence for this mechanism was based upon previous studies with 125I-labeled lactate dehydrogenase-5, and here similar studies with radioiodinated lactate dehydrogenase-1 are reported, to determine whether this isoenzyme is similarly catabolized. The pure rabbit enzyme was labeled with 125I by use of lactoperoxidase and hydrogen peroxide (the labeled enzyme had 80-85% of the original catalytic activity). After its intravenous injection into rabbits, plasma enzyme activity and radioactivity disappeared during the first 4 h at similar fast rates, apparently because of distribution of the injected enzyme throughout the extracellular fluid. During a second phase (30-h), catalytic activity disappeared significantly faster than radioactivity, suggesting inactivation of the enzyme in either the plasma or a compartment in close proximity to it, or both. Enzyme activity then remained constant while plasma radioactivity continued to decrease at a slower, exponential rate, apparently owing to removal of breakdown products. In no case did tissue radioactivity, studied 6 h after injection, approach that of plasma. We therefore conclude that removal of the enzyme protein or its breakdown products is a passive process. Appreciable radioactivity was detected in the intestinal contents, a finding which suggests that removal via the small intestine is an important route for the removal of inactivated enzyme products from the circulation. Less than 3% of the injected radioactivity appeared in the feces during the first three days; urinary excretion accounted for about 67% during the same period, about 60% of which consisted of radio-iodinated amino-acids, the remainder of iodide. Free mono- and di-iodotyrosines were among the products excreted. These appear to originate from absorption of the products of further breakdown of the enzyme molecule in the intestine.

Rates of disappearance from plasma of enzymes labeled by coupling with a radioactive lodo-ester.

Lactate dehydrogenase-5 and creatine kinase from rabbit muscle were labeled by coupling with N-hydroxysuccinimidyl 3-(4'-hydroxy-[3',5'-125I]diiodophenyl)propionate. After purification, the analytical recovery of catalytically-active labeled enzyme averaged 90% for lactate dehydrogenase, 81% for creatine kinase. The labeled enzymes were injected intravenously into rabbits and disappearance from plasma of catalytic activity and radioactivity was measured. The disappearance curves for lactate dehydrogenase-5 differed considerably from those observed with the enzyme labeled by direct iodination. The discrepancy was due to rapid hydrolysis in vivo of the labeled amide-enzyme linkage, because about 50% of the injected radioactivity appeared in the urine as 125I-labeled 3-(4'-hydroxy-3',5'-diiodophenyl)propionic acid within 4-8 h of injection. Similar outputs were observed after administration of this acid to rabbits. The free acid was also detected in the urines of rabbits within 4-8 h of the intravenous injection of creatine kinase labeled similarly. We conclude that this method of labeling is unsuitable for preparing radioactive enzymes for study of their catabolism.

Membrane permeability in normal human lymphocytes and lymphocytes from patients with chronic lymphatic leukaemia.

The rate of release of intracellular enzymes from the lymphocytes of patients with chronic lymphatic leukaemia has been shown to be slower than that from normal lymphocytes, despite their lower enzyme contents. Addition of ATP, ADP and AMP to the medium reduces enzyme efflux in a manner similar to that in normal lymphocytes. Iodoacetate, however, causes a marked increase in enzyme leakage from both normal and leukaemic cells. It appears therefore that the membrane permeability of leukaemic lymphocytes is at least partly dependent upon the intracellular energy content. Since the ATP contents of the leukaemic cells were lower than those of normal lymphocytes, however, it is concluded that some additional factor is concerned in reducing permeability to enzymes in chronic lymphatic leukaemia. The possibility that the immunoglobulin associated with the cell membrane of leukaemic cells may play a part in reducing its permeability has been explored, but washed and unwashed cells were found to lose enzymes at similar rates. The lower permeability of the membranes of such cells may partly explain their longer lifespan in chronic lymphatic leukaemia.

The fate of circulating lactate dehydrogenase-5 in the rabbit.

1. In an attempt to determine the mechanism whereby enzymes are removed from the circulating plasma, purified rabbit-muscle lactate dehydrogenase-5 was labelled with 125I and injected intravenously into rabbits. During the first hour after injection enzyme activity and radioactivity disappeared from the plasma at comparable fast rates, which are attributed mainly to distribution of the enzyme throughout the extracellular fluid. This was followed by a phase lasting about 7 h during which enzyme activity disappeared at a faster rate than the radioactivity, an observation indicating either intravascular breakdown of the enzyme protein or its degradation in the tissues, followed by release of labelled fragments into the circulation. Enzyme activity then reached a constant value and the plasma radioactivity continued to decrease at a slower exponential rate; it is suggested that this is due to removal of breakdown products. 2. The radioactivity of the tissues was measured at various time-intervals after injection. After 2 h and 8 h highest concentrations were found in the spleen, liver, jejunum and duodenum. Relatively high concentrations were also found in the intestinal juices throughout the period of study, an observation which suggests that discharge via the small intestine is a major route whereby inactivated enzyme fragments are removed from the circulation. 3. About 5% of the injected radioactivity was recovered in the faeces during the first 3 days, and the urine accounted for 73% during the same period. About 35% of the urinary radioactivity was shown by silver nitrate precipitation and by chromatography to consist of free iodide and the remainder appeared to consist of radio-iodinated amino acids or peptides. Free mono- and di-iodotyrosine were identified among the products. These results suggest that further breakdown in the intestine is followed by absorption of the products, which are excreted in the urine.

Action of metabolic inhibitors on the release of intracellular enzymes from human and rat lymphocytes and human erythrocytes.

A number of inhibitors of glycolysis and uncouplers of oxidative phosphorylation have been shown to increase the leakage of intracellular enzymes from preparations of rat lymphocytes and human lymphocytes and erythrocytes. The effect of each reagent on all three cell preparations is reversed in the presence of ATP in the medium. ADP is somewhat less effective. AMP exerts a slight protective effect on the human cells, but causes an increase in enzyme efflux from the rat cells. This species difference appears to be related to the concentration of adenylate kinase activity in the cells. The results are interpreted as supporting the theory that membrane permeability to enzymes and other intracellular proteins is dependent upon the energy content of the cell.