Cell proliferation and ageing in mouse colon. II. Late effects of repeated x-irradiation in young and old mice

Radiation therapy in the elderly

The purpose of this review is to highlight aspects of radiation oncology specifically related to aging and caring for the older patient with cancer. Particular emphasis is placed on the preclinical and clinical studies focusing on the efficacy and toxicity of RT in this population. Special techniques are also reviewed that have particular relevance to the treatment of the elderly.

Oral candidiasis in hematopoietic cell transplantation patients: an outcome-based analysis

OBJECTIVES

Despite aggressive antifungal prophylaxis, the increased risk for systemic fungal infection in recipients of hematopoietic cell transplants (HCT) continues to be a significant concern because Candida infection can cause morbidity and mortality in these patients. The objectives of this study were to examine the relationship of oral colonization by Candida species to systemic infection, mortality, and the impact of antifungal treatment on a population of recipients of HCT.

STUDY DESIGN

One hundred and fifteen consecutive patients undergoing hematopoietic cell transplantation were evaluated. Oral examinations and cultures for Candida were completed before transplantation and on a weekly basis until discharge. The oral complications were assessed, and the level of mucositis was scored by using the National Cancer Institute grade. Systemic antifungal prophylaxis was provided to all patients. Chlorhexidine oral rinses were also routinely provided.

RESULTS

Colonization by Candida species was identified in 31% of patients. Fifty-six percent of patients with colonization had clinical evidence of oral candidiasis. Significantly decreased Candida colonization was seen in patients using chlorhexidine alone compared with those using chlorhexidine and nystatin together (P <.046). Twenty-five patients died in the immediate posttransplantation period, 17 of whom were Candida-positive. The length of hospital stay ranged from 15 to 153 days; increased stay was also associated with Candida colonization (P =.04). Seventy-four percent of all patients developed ulcerative mucositis. More severe mucositis was seen in patients undergoing chemotherapy and radiation therapy. There was no significant difference between Candida colonization and the presence or severity of mucositis.

CONCLUSIONS

Despite systemic and topical antifungal prophylaxis, oropharyngeal colonization by Candida species was common in patients who had received HCT. Candidiasis was commonly present in those who did not survive the early transplant period. Of the 25 patients who died early after the transplantation, 92% had ulcerative mucositis in comparison with 70% of those who survived, reflecting the association of oral mucositis with the toxicity of HCT. There was a significant relationship among allogeneic and autologous HCT, length of stay, and colonization of Candida. In patients undergoing systemic antifungal prophylaxis, chlorhexidine rinse was statistically more effective in reducing colonization by Candida than chlorhexidine and nystatin combined (P =.046).

An investigation of antioxidant status, DNA repair capacity and mutation as a function of age in humans

We are constantly exposed, throughout life, to a wide variety of extrinsic and intrinsic agents which have the potential to damage cellular biomolecules, including DNA. Imperfections in cellular defence systems which protect against the fixation of DNA damage can lead to an accumulation of mutations which on their own, or in combination with other age-related changes, may contribute to ageing and the development of age-related pathologies. We have previously reported an increase in frequency of mutation with age in human lymphocytes taken from healthy males in the age groups, 35-39, 50-54 and 65-69 years. In this article we report on the findings of a recent study which was designed to assess whether the age-related increase in frequency of mutation was due to a decreased efficacy of the defence systems against ROS-induced DNA damage, namely antioxidant status and DNA repair processes, in the same study subjects. In vivo antioxidant status was assessed in each of the study subjects by measuring blood levels of; superoxide dismutase (SOD; EC 1.15.1.1), glutathione peroxidase (GPx; EC 1.11.1.9), catalase (EC 1.11.1.6), caeruloplasmin (CPL), uric acid and bilirubin. We did not find any statistically significant differences in the mean levels of these antioxidants between the three different age groups. To investigate the efficacy of DNA repair processes against ROS-induced DNA damage, an ELISA was used to quantitate DNA damage (as % single-stranded DNA; %SS-DNA) at various times following treatment of peripheral blood lymphocytes with hydrogen peroxide (H2O2). The results of this part of the study showed that in untreated lymphocytes, basal levels of %SS-DNA were significantly higher in individuals from the 65-69 years age group compared to the 35-39 years age group (p = 0.039, 0.0013; at 5% level of significance). No significant differences were found in H2O2 susceptibility with age immediately following treatment (p = 0.71, 1.00; at 5% level of significance) but a consistent and significant increase was observed in %SS-DNA remaining 90 min post-treatment in lymphocytes from subjects in the 65-69 years age group, compared to %SS-DNA present in lymphocytes from the 35-39 years age group (p = 0.013, 0.024; at 5% level of significance). The results of this study suggest that the age-related increase in frequency of mutations is not contributed to by alterations of in vivo antioxidant status with age but is by a decreased efficacy of the repair of ROS-induced DNA damage with age. The biological implications of somatic mutations in the ageing process are discussed.

DNA damage and repair with age in individual human lymphocytes

Previous biochemical studies on DNA repair competence and aging have been limited to techniques, such as alkaline elution or nucleoid sedimentation, involving mass cell populations. These techniques provide no information about the distribution of DNA damage and repair among individual cells and are unlikely to detect age-dependent changes affecting a minor fraction of the cell population. We have recently described a microgel electrophoretic assay (Singh et al., 1988) that measures, at the level of the individual cell, single-strand DNA breaks and alkali-sensitive sites. Here, we employ this method to analyze DNA damage and repair in lymphocytes isolated from the peripheral blood of 31 subjects (23 males and 8 females aged 25-91 years) and exposed in vitro to 200 rads of X-irradiation. While basal (pre-irradiation) levels of damage were independent of the age of the donor, an age-dependent increase in DNA damage was observed immediately following irradiation. For all subjects, the mean level of DNA damage was restored to pre-irradiation control levels within 2 h of incubation at 37 degrees C. However, a distribution analysis of DNA damage among cells within each sample indicated the presence of a few highly damaged cells (4-16%) in the 2-h sample, the occurrence of which was significantly more common among aged individuals. These data indicate an age-related decline in DNA repair competence among a small subpopulation of lymphocytes.

Colonic proliferation is increased in senescent rats

Our previous studies suggested that crypt size enlarged and that proliferation rate might be greater in the small intestine of rats during senescence. Crypt cell numbers and crypt cell proliferation rates, using the vincristine-induced metaphase arrest technique, now have been measured in the colon of aging and young Fischer 344 rats. The proximal colon of 26-28-mo-old unfasted rats had 10% more crypt cells and a higher proliferative rate than 3-4-mo-old young controls. In the distal colon, the crypt cell proliferation rate in aging rats was 56% greater than in the young. A 3-day fast reduced crypt cell proliferation about fourfold in young rats but only by 20% in aging rats. One-day refeeding abruptly increased the crypt cell population and proliferation rate in rats of both age groups. The crypt zone of proliferating cells from aging rats was broader than that seen in young rats. In addition, starvation lowered colonic crypt cell cycling rate much less in aging than in young animals. We conclude that the colons of aging rats demonstrate a hyperproliferative state and a failure to adapt appropriately to changes in food intake. These observations may be relevant to states of altered proliferation that occur in the premalignant colon.

Misonidazole-induced radio-resistance in normal and preirradiated jejunal mucosa

Pretreatment of mice with a single dose of whole-abdomen irradiation led to a relative decrease in radiosensitivity in jejunal crypts given a second single dose of irradiation 2 months later. Hyperbaric oxygen (3.5 bars) restored the survival level to initial values, suggesting that there was radiation-induced hypoxia in the primed jejunum. However, misonidazole did not sensitize primed jejunal crypts; it reduced the radiosensitivity of both normal and primed crypts. This 'paradoxical' effect of misonidazole could well be due to the acute toxic side-effects of 1 mg/g body weight misonidazole i.p., as there was a sharp drop in the core temperature of mice immediately after drug injection. Artificially maintaining the temperature of miso-treated animals at a normal level produced crypt survival levels similar to those of both normal controls and primed controls. Thus, although the primed gut is chronically hypoxic, as suggested by the effects of hyperbaric oxygen, misonidazole is not a reliable tool for the study of this tissue hypoxia. In all in vivo experiments with misonidazole, core temperature must be controlled in order to avoid misleading interpretations of experimental results.

Protection of acute and late radiation damage of the gastrointestinal tract by WR-2721

WR-2721 was investigated for its protective effect against acute and late damage produced by irradiation of the esophagus, small intestine, and colon of mice. The microcolony assay was used to measure the acute response of the small intestine and the colon, and an LD50 assay (within the 28- to 42-day time range) was used to measure acute esophageal damage. A dose of WR-2721 at 400 mg/kg, injected 30 min prior to irradiation, resulted in a protection factor (PF) of 1.6 against radiation damage in these three regions of the gastrointestinal tract. Lethality and histology scores were applied to determine late radiation damage to the rectum, at times ranging from 3 to 15 months after irradiation. Deaths occurred after doses of 20 Gy and above throughout the postirradiation period. WR-2721 increased the survival of mice; the PF calculated from the LD50 values was 1.5. PFs of animal survival did not vary during the observation period. Histological studies showed evidence of ulceration, fibrosis, and vascular changes as late radiation damage. WR-2721 protected against radiation-induced histological damage with a PF of 1.3. There was no qualitative difference between the types of histological damage observed in the group undergoing only irradiation and the group treated with WR-2721. Biochemical measurements of fibrosis by hydroxyproline determination of collagen 16 months after irradiation showed an increase in collagen per milligram wet weight of rectal tissue in all irradiated groups, but no increase in the amount of collagen per 5 mm segment of the rectum. Thus it appears that the apparent fibrosis is a result of atrophy rather than collagen accumulation. We conclude that WR-2721 is indeed effective at protection against late damage from large single doses of radiation to the rectum as measured histologically and also improves the long-term survival of the mice, although the target cells for this damage are not known.

Late effects of irradiation in mouse jejunum

The response of mouse jejunum at intervals up to 1 year after single 'priming' doses of X-rays has been assessed by crypt survival after retreatment with single doses of X-rays and morphometric analysis of changes in the intestinal submucosa. The first 'priming' dose was given as a single dose to the whole abdomen. To assess crypt survival, groups of mice were retreated to the whole body with a range of test doses 2, 6 or 12 months later, while other groups of mice were given only the priming doses. These data were compared to crypt survival in mice not previously irradiated. The crypt dose-survival curves in mice re-irradiated at all three intervals after priming irradiation were displaced to higher doses in pre-treated than in non-pre-treated mice and were characterized by higher D0 values. Misonidazole given before the test exposure reversed this effect so that the dose survival curve for crypts in pre-treated mice were superimposed on that for mice not previously irradiated, suggesting that the increase in isoeffect dose and the change in the D0 in previously exposed mice was due to crypt hypoxia. Quantification of the area of the submucosa showed that its area was increased at all three times after the priming doses and was a result of collagen deposition and oedema. Thus, the hypoxia in the crypts was probably secondary to these changes. Deaths began at 6-7 months after priming irradiation and were due to intestinal obstruction and stenosis. Thus, as in other tissues, two phases of injury can be assayed in the intestine of experimental animals.

RBE values for colo-rectal injury after caesium 137 gamma-ray and neutron irradiation. I. Single doses

Colo-rectal damage in mice has been assessed after caesium gamma irradiation and 3 MeV neutrons given as single doses. Several assays were used, including body weight changes, faecal deformity and lethality. Dose response curves have been constructed for each assay at different times after irradiation, ranging from 10 days to 16 months. The data have been analysed in terms of the time course of expression of damage and the RBE for neutrons. An initial loss of weight at 10-20 days was presumably related to epithelial denudation, but a dose-dependent weight reduction (compared with controls) persisted over the animal's life span. Mice died progressively after localised pelvic gamma irradiation; there was no sharp demarcation between an early and late phase of lethal injury. Death resulted from intestinal stricture or stenosis. The time course for lethality was qualitatively different after neutrons, with little progression of damage between 5 and 11 months. Faecal deformity was detectable as a higher proportion of small pellets when the rectum became constricted by fibrosis. No significant faecal deformity was observed before 6 months after which time dose response curves could be obtained. The RBE for early damage (assessed at 1-3 months) was 2.2-2.7. This fell to 1.7-1.9 for late damage (determined at 10-15 months) over the range of neutron doses of 7.5-12 Gy. The need for sublethal assays allowing for sequential evaluation of radiation damage within the same animal is stressed, as is the need to compare RBE values from early and late endpoints at equivalent neutron doses.