The carcinogenic risk of high dose total body irradiation in non-human primates.

PURPOSE: High dose total body irradiation (TBI) in combination with chemotherapy, followed by rescue with bone marrow transplantation (BMT), is increasingly used for the treatment of haematological malignancies. With the increasing success of this treatment and its current introduction for treating refractory autoimmune diseases the risk of radiation carcinogenesis is of growing concern. Studies on tumour induction in non-human primates are of relevance in this context since the response of this species to radiation does not differ much from that in man. MATERIALS AND METHODS: Since the early sixties, studies have been performed on acute effects in Rhesus monkeys and the protective action of bone marrow transplantation after irradiation with X-rays (average total body dose 6.8 Gy) and fission neutrons (average dose 3.4 Gy). Of those monkeys, which were irradiated and reconstituted with autologous bone marrow, 20 animals in the X-irradiated group and nine animals in the neutron group survived more than 3 years. A group of 21 non-irradiated Rhesus monkeys of a comparable age distribution served as controls. All animals were regularly screened for the occurrence of neoplasms. Complete necropsies were performed after natural death or euthanasia. RESULTS: At post-irradiation intervals of 4-21 years an appreciable number of tumours was observed. In the neutron irradiated group eight out of nine animals died with one or more malignant tumours. In the X-irradiated group this fraction was 10 out of 20. The tumours in the control group, in seven out of the 21 animals, appeared at much older age compared with those in the irradiated cohorts. The histogenesis of the tumours was diverse with a preponderance of renal carcinoma, sarcomas among which osteosarcomas, and malignant glomus tumours in the irradiated groups. CONCLUSIONS: When corrected for competing risks, the carcinogenic risk of TBI in the Rhesus monkeys is similar to that derived from the studies of the Japanese atomic bomb survivors. The increase of the risk by a factor of 8, observed in the monkeys, indicates that patients are likely to develop malignancies more frequently and much earlier in life after TBI than non-exposed individuals. This finding underlines the necessity of regular screening of long-term surviving patients subjected to TBI and BMT.

Drug-induced changes in dogs after long term application of a beta-blocker.

Ocular irritation studies are important in the safety evaluation of ocular formulations. There are many reports on acute ocular irritation studies, but almost nothing about prolonged ocular instillation of ophthalmic formulations. This report discusses the predominantly lymphocytic infiltrates seen in the limbus corneae and eyelids of dogs treated with 1 and 2% solutions of L-653,328, an ocular hypotensive beta-adrenoceptor antagonist, for up to 53 weeks. The number of animals affected and severity of the lesions increased with time and concentration. A minimal effect was seen microscopically with the 2% solution as early as 14 weeks. Rabbits treated similarly for 14 weeks had no such changes. The first and only clinical sign in dogs was diffuse pinkness of the bulbar conjunctiva seen from Drug Week 22 onwards. Although not seen with similar molecular structures, given the equivocal results in sensitization studies and the long time required for the development of change, delayed contact hypersensitivity was suspected as the cause of the ocular infiltrates. Simple chronic irritation was not ruled out, however. These findings suggest that delayed contact hypersensitivity in dogs may be a phenomenon not limited to skin, but may also involve the eye after repeated ocular instillation.

Planning for health services for the elderly.

In order to create health services that effectively respond to the changing picture of health, governments should try to anticipate the health needs for the future. The scenarios for the elderly that are briefly discussed in this paper are approximations of developments that are largely autonomous if considered from the position of the individuals and organizations responsible for policies on health and health services. The three contextual scenarios developed are based on the forecasts, explorations and speculations to be found in the literature and also on the outcome of discussions with groups of experts in the fields of medical, biological and technological research and practice. The following variables have been incorporated in the study preparing the scenarios: demographic developments, the health status of the elderly, health services for the elderly, developments in medical, biological and technological fields, and societal developments, both economic and social. These scenarios provide policy makers with a learning environment in which they can test the strategies that are considered to answer the questions that they face, and evaluate the particular circumstances in which these strategies might be feasible.

Endotoxin-induced liver injury in aged and subacutely hypervitaminotic A rats.

The plasma disappearance of endotoxin and endotoxin-induced hepatic injury were studied in two rat models: the aging rat and the subacutely hypervitaminotic A rat. The choice of these models was based on their respective association with a decreased or increased Kupffer cell endocytic activity. The half-life of endotoxin (E. coli O26: B6, phenol extracted) in plasma was significantly prolonged in aged rats as measured by both the Limulus assay (t1/2 = 2.1 +/- 0.1 h in 3-6-month-old, and 3.3 +/- 0.3 h in 24-36-month-old rats) and 51Cr-labeled endotoxin radioactivity assay (t1/2 = 5.3 +/- 0.3 h in 3-6-month old and 7.7 +/- 0.6 h in 24 36-month-old rats). In subacute hypervitaminosis A, the half-life of endotoxin was significantly decreased in the Limulus assay (t1/2 = 2.1 +/- 0.1 h in 3-6-month old and 1.4 +/- 0.2 h in subacutely hypervitaminotic A rats), but not in the radioactivity assay (t1/2 = 5.3 +/- 0.3 h in 3-6-month-old and 5.0 +/- 0.4 h in subacutely hypervitaminotic A rats). Hundred percent mortality was observed at a dose of 2 mg endotoxin/100 g body wt. in old rats, but not in young rats. Only 1 of 7 young subacutely hypervitaminotic A rats died following injection of this dose of endotoxin. The dose of endotoxin which caused only minimal parenchymal liver cell injury in young rats induced substantial parenchymal cell injury in old rats and subacutely hypervitaminotic A rats as determined by both histological and biochemical parameters. It is concluded that some basic characteristics of experimental animals, such as age and nutritional status, can dramatically influence the sensitivity to endotoxin and this is not necessarily correlated with the rate of endotoxin clearance.

Analysis of survival data on aging rat cohorts: pitfalls and some practical considerations.

Experimental aging research is very dependent on the determination of the survival characteristics of the animal species or strain under study. Such data are generally inferred from mortality curves of cohorts of animals that are set aside at an early age for aging studies. Rectangular survival curves and the presence of multiple pathological lesions are a prerequisite for aging studies so as to resemble the situation in man. From 1977 onwards, many rat cohorts have been formed in the Institute for Experimental Gerontology (IVEG) for the study of aging processes. Data from these have been analysed for a period of 5 years up to and including 1982. (Males and females of the WAG/Rij and BN/BiRij strains were used.) The 50% survival and the maximum survival of cohorts varied considerably, but showed no consistent trend over the years. The median (50%) survival between the cohorts differed by as much as 7.9-10.7 months for the strains and sexes studied. Maximum survival between the cohorts varied from 3.7 to 9.9 months. Median and maximal survival were greater for the females. Maximum survival and 50% survival correlated significantly, the relation between the two being approximately linear. The effect of removing animals from cohorts on the estimation of 50% survival was only minor, whereas maximum survival was clearly diminished by this procedure. The wide variation in survival characteristics, even between successive cohorts, cautions against too simple a measure of the animals survival in only one number for median or maximal survival in months. An indication of the variance of 50% survival and of maximum survival should therefore be included in scientific publications. Moreover, the 50% survival is the parameter of choice to define cohorts, not only because this can be most reliably estimated with good confidence limits, but also because this measure is the least sensitive to removing animals from the cohorts. As this will often be the case in many research institutions, it might be of practical importance to order old animals from different cohorts since this diminishes the chance of using an extremely short or long lived cohort. Finally, the analysis revealed that combining intact or incomplete cohorts into larger survival curves resulted in nearly identical graphs. An attempt was made to calculate the minimum cohort size which yields survival curves with constant 95% confidence limits.

Anatomy, function and aging in the mouse liver.

A brief overview is given of the embryology, gross and microscopic anatomy and sinusoidal lining cells of the mouse liver. The handling of xenobiotics is also considered. So called phase I and II reactions are of major importance. Furthermore, heterogeneity of metabolism occurs in the different zones of the hepatic acinus. Finally, some of the manifest pathological changes are discussed. Despite the occurrence of these changes there is still no clearcut evidence that liver function declines with age.

Effects of X-irradiation, ovariohysterectomy and estradiol-17 beta on incidence, benign/malignant ratio and multiplicity of rat mammary neoplasms--a preliminary report.

An overview is given of the effects of X-irradiation, ovariohysterectomy and estradiol-17 beta administration on mammary tumorigenesis in females of 3 rat strains, viz. the WAG/Rij, BN/BiRij and SD. The 3 rat strains differed significantly in their spontaneous mammary tumor incidence. Female SD rats had the highest incidence (47%) and female BN/BiRij rats the lowest (17%). Female WAG/Rij rats had an intermediate incidence of 29%. The benign/malignant ratio in female WAG/Rij, BN/BiRij and SD rats was 1.0, 2.0 and 7.3, respectively. The average number of mammary gland neoplasms per untreated tumor-bearing female was 1.2 in the WAG/Rij, 1.0 in the BN/BiRij and 1.6 in the SD, whereas the respective maximum numbers were 2, 1 and 5. Ovariohysterectomy almost entirely prevented mammary tumor formation in all 3 rat strains, whereas estrogen treatment enhanced it. In addition, estrogen treatment resulted in an increased number of mammary tumors per tumor-bearing female and changed the benign/malignant ratio into the direction of malignant. X-irradiation increased the mammary tumor incidence in all 3 rat strains, especially of the benign tumors. Estrogen potentiated the effect of irradiation. An effect of irradiation on mammary tumorigenesis was not observed in ovariohysterectomized females of all 3 rat strains.

Biological and clinical consequences of longitudinal studies in rodents: their possibilities and limitations. An overview.

Rats and mice are used in gerontological research primarily because of their relatively short life spans, ease of handling, and the relatively low costs of production and maintenance under controlled environmental conditions of large number of rodents as compared to larger laboratory animal species. They are being used as models for studying intrinsic aging processes, processes that give rise to diseases associated with aging, and the influence of environmental factors on these processes. Contrary to the situation in man, longitudinal studies in rodents can be conducted under well controlled environmental conditions. It has been shown that multiple pathology, the hallmark of aging in man, also occurs in inbred strains of rodents. Some of these lesions are genetically determined and some of them are randomly distributed amongst members of the same inbred strain. Serial killing experiments are necessary to obtain information on the time of development of these lesions in order to interpret properly the outcome of investigations. Furthermore, it has been shown that a considerable variation can exist in the observed maximum ages of the longest-lived animals in cohorts of rats kept under well controlled conditions. For this reason, caution should be exercised in interpreting data from studies which claim maximum lifespan prolongation.

Differences in DMBA-induced mammary neoplastic responses in two lines of Sprague-Dawley rats.

It has been reported that female Sprague-Dawley rats obtained from a U.S. source and studied in the U.S. gave a larger and more rapid mammary neoplastic response to radiation than did female Sprague-Dawley rats obtained from a Dutch source and studied in The Netherlands. To learn if the different mammary neoplastic responses of the two 'lines' of Sprague-Dawley rats are due to inherent differences between the lines of rats or due to differences in experimental conditions, two groups of rats from the American source and one group from the Dutch source were studied for their response to a chemical carcinogen, dimethylbenzanthracene (DMBA), at the same laboratory. When 10 mg of DMBA per 100 g body wt was given by stomach tube to 28 rats from the Dutch source, 367 days later approximately 25% of these rats had developed mammary carcinomas and approximately 18% had developed mammary fibroadenomas. When the same dose of DMBA was given to rats from the U.S. source, 300 days later 90 and 100% had developed mammary carcinomas and 83 and 95% had developed mammary fibroadenomas. Similar trends were found for the number of neoplasms per rat and the mean time of appearance of the neoplasms. It was concluded that there are inherent differences between Sprague-Dawley rats obtained in the U.S. and Sprague-Dawley rats obtained in The Netherlands in regard to their mammary neoplastic responses to DMBA, as well as in their responses to radiation. Genetic differences between the two lines were confirmed by establishing dissimilarities in the expression of erythrocyte antigens coded for by RT1 (major histocompatibility complex).

Animals in aging research: requirements, pitfalls and a challenge for the laboratory animal specialist.

The prime goal of aging research is to gain some insight into the basic mechanisms underlying the aging process. The long lifespan and frequent mobility of humans as well as the legal and ethical constraints on human experimentation make man unsuitable for studying the aging process. Therefore animals, particularly rodents, are used in aging research. In studying the aging process in animals, one hopes to find means for the prevention or amelioration of at least some of the disabilities of old age in man. Many intrinsic and extrinsic factors can influence the outcome of animal experiments; hence an extensive monitoring program is a prerequisite in aging research. An important role in controlling the quality of the animals is reserved for the laboratory animal specialist. Since he is faced with all aspects of laboratory animal science, aging research is a challenging area for such a specialist.

A histopathological survey of aged Praomys (mastomys) natalensis.

This histopathological study shows that Mastomys develops a wide variety of neoplastic and nonneoplastic lesions with age. In comparing neoplastic lesions of Mastomys with those generally found in mice and rats, Mastomys is more or less unique with respect to the development of lymphoepithelial thymomas (40%), parathyroid adenomas (11%), prostatic adenocarcinomas (5%), and gastric carcinoids (4%) and the absence of brain, lung, and mammary tumors. Of the nonneoplastic lesions, prostatic (38%), thymic (12%) and parathyroid (11%) hyperplasia, and moderate to severe generalized degenerative joint disease (96%) occur rarely in mice and rats. Within the limits of this study, in which the age of the animals ranged from 18 to 39 months, a clear-cut age-related pattern was seldom found for most of the lesions occurring in Mastomys.