Levels of 5-Bromo-2′-deoxyuridine and Its Metabolites During Continuous Infusion Paradigms in a Transplacental System

The levels of 5-bromo-2'-deoxyuridine (BrdUrd) (a teratogen and mutagen) and its metabolites were measured using the hplc in maternal and fetal blood at 20–21 days of gestation in Sprague-Dawley derived CD rats during continuous infusion paradigms which are used in visualization of sister chromatid exchanges. The time course of the maternal values following a dose of 1 g/kg body weight was determined by sampling with an aortic catheter. Fetal levels were taken after a 2-hour intraperitoneal infusion of BrdUrd into the mother. It was found that the maternal level of BrdUrd plateaued at 0.4 mg%, while the level of metabolites gradually increased with time for both techniques. Also, although the overall amount of radioactivity indicated that approximately 40% of the total maternal dose reached the fetus, the fetal concentration of BrdUrd was less than one-seventh the maternal one.

Reactive Blending of Polyamide 6 and Polycarbonate

In this work structure and mechanical properties of blends of bisphenol-A polycarbonate with polyamide 6 with different molecular weights and different terminal groups are presented. The results show the important role played in the change of the morphology and in the improvements of the mechanical properties by the increasing content of NH2 terminal groups. These results are attributed to the reactions during melt mixing of such groups with polycarbonate.

Self-organization of polystyrenes into ordered microstructured films and their replication by soft lithography

We report on the formation of ordered arrays of micrometric holes on the surface of polystyrene (PS) films cast from volatile solvents in the presence of humidity at different temperatures. The formation mechanism is investigated for PS having different molecular weights, polydispersities, and carboxylic terminations. Among the chosen materials, a highly regular honeycomb microstructured morphology is obtained on the surface of films prepared with dicarboxy-terminated PS with <molecular weight> = 100,000. Experiments and observations on film formation indicate that polar groups are playing a fundamental role in this process. Tuning the surface tension by means of polar terminations allows the film morphology to be modified and in particular the preparation of two- or three-dimensional microstructured films. Finally, we show how these structures can be replicated by soft lithography and then used in the fields of photonic crystals and organic electronics.

Assessment and significance of 24-h energy intake patterns among young and aged non-affluent southern US women

Energy intake patterns that may impact health status among non-affluent southern U.S. women from small urban communities have not been evaluated extensively. Usual intake estimates are confounded by factors such as validity of intake methods and socioeconomic status. Typical 24-h energy intakes were reported by Caucasian (CA, n=149) and African-American (AA, n=110) women; at 43% of this sub-population, AA women are appropriately and proportionately represented. Daily energy intake was examined for these non-pregnant females, 24 to 93 y of age, to define typical energy, carbohydrate, protein, and fat intake. Study groups were: 24-29 y, 30-39 y, 40-49 y, 50-59 y, 60-69 y, 70-79 y, and 80-93 y. Statistical comparisons of nutrient variables by age were made by least squares means between groups. Body mass index (BMI) calculations accounted for differences in height and relative body mass. Both races reported similar energy intakes and significant (P<0.05) decreases with age were noted. Energy intakes were 15-40% below recommended levels, similar to reported values; senior lunch programs ameliorated declines among some women >60 y. More daily calories (52-62%) were provided by carbohydrates, followed by fat (26-35%) and protein (14-17%) findings in close agreement with health recommendations. Time-of-day intake patterns suggest women >59 y consume larger noon meals. BMI for AA women was greater (P<0.05) than that of CA women between 30-59 y. At 24-29 y, AA women had lowest BMI values; BMI decreases occurred in CA women after 80 y. These factors may impact the health of non-affluent southern AA and CA women, particularly the elderly who may require guidance for diet planning and intake intervention programs.

A Morphometric Investigation by TEM/AIA on Elastomer-Based Compounds Filled with an Untreated Precipitated Silica

An accurate morphological investigation has been carried out on vulcanized compounds based on different matrices, butadiene rubber, natural rubber and styrene-butadiene rubber, filled with 35phr of a precipitated silica. The analysis has been performed by using transmission electron microscopy (TEM) and automated image analysis (AIA) to achieve quantitative information on the filler dispersion. Significant differences in the aggregate size and shape distribution of silica within the different matrices which, in principle, can be related to the polymer-filler interactions, have been found. The results are in a very satisfactory agreement with thermodynamic predictions obtained by inverse gas chromatography. The use of two complementary techniques, TEM/AIA, allows attainment, in a reasonably short time, quantitative information on the filler dispersion and, consequently, on the performances of these elastomers-based composite materials.

A mechanistic approach to modelling the risk of liver tumours in mice exposed to fumonisin B1 in the diet

Data from the National Toxicology Program's carcinogenesis study of fumonisin B1 in B6C3F1 mice, conducted at the National Center for Toxicological Research, were used to fit the Moolgavkar-Venzon-Knudson (MVK) two-stage, clonal-expansion model of carcinogenesis. In addition to tumour data from the conventional 2-year bioassay, the study included data on tissue weights, cell proliferation, cell death, and sphingolipid metabolism in primary target organs. The model was used to predict 2-year liver tumour rates in female and male mice based on differences among dose groups in the effect of fumonisin B1 on the growth of normal tissue and on the proliferation of preneoplastic cells as a compensatory response to sphinganine-induced cell death. Fumonisin B1 was assumed to be non-genotoxic, i.e. the model did not include any effect of fumonisin B1 on either of the two mutation rates of the MVK model. The model was able to reproduce reasonably well the observed tumour rates in both female and male mice, predicting substantially increased rates above background only at the highest doses of fumonisin B1 in females.

Caloric restriction mimetics: physical activity and body composition changes

As the only paradigm that has consistently increased life span and inhibited the onset and/or progression of disease, dietary restriction has multiple effects on a variety of organ systems. In this brief review, the goal of the panel was to attempt to understand the role of changes in physical activity and body composition as possible modulators of the life span in experimental animals and humans. We focus on whether changes in exercise behavior and body composition produce similar changes as those found in dietary restriction and whether these changes can be used to either replace or enhance the beneficial effects of dietary restriction. The complexity of the two stimuli is emphasized in our report, with suggestions offered on how to better interpret existing research. Our panel briefly examines evidence in experimental animals and humans about the specific contributions of each of these factors to altering life span and age-related pathologies. We also discuss additional animal studies and/or human intervention studies that could be performed to clarify these issues. Finally, we provide suggested avenues for future research in this area of changes in physical activity and body composition as dietary restriction mimetics.

Does caloric restriction induce hormesis?

The question of whether caloric restriction (CR) is hormetic is addressed in terms of two common definitions of the term. In terms of the older definition, i.e., a growth-stimulatory effect when lower doses of a compound which resulted in growth inhibition at higher doses, CR is better characterized as a co-hormetic (i.e., a paradigm which at relatively "low doses," in combination with some stimulus, will evince increased growth (proliferation) and at higher "doses" will inhibit this increased proliferation) rather than a hormetic agent. Mechanisms such as cellular selection of cellular subpopulations, increases in receptor efficiency, and preservation of cellular proliferative potential can interact with agents and produce increased growth as long as the CR is not too severe. In terms of a broader definition, i.e., nonmonotonic dose-response behavior of a compound for any adverse response, CR appears to be hormetic, both as a result of body weight (BW) loss and other potential mechanisms. The impact of changes in BW, or frank CR, can be considered a component of every test for hormesis, and is thus capable for interaction with any other agent. The changes that BW loss (or CR) induce are so profound that any aspect of an agent's action - metabolism, pharmacokinetics, pharmacodynamics - can modulate the response of an organism to an agent. Similarly, other effects of a chemical that induce BW loss, e.g., physical activity or temperature dysregulation, can also induce dose-response curves that appear hormetic. The interaction of the hormetic agents of BW loss and CR can influence agent tests. Controlling these factors may make it possible to dissect the key components of a hormetic response. In addition, the effects of CR or BW loss appear to extrapolate well across species [Colman R, Kemnitz JW. Aging experiments using nonhuman primates. In: Yu BP (Ed), Methods in Aging Research. CRC Press, Boca Raton, FL, 1999, pp. 249-267]. Thus there is some reason to believe that these hormetic factors may be important for humans, and may already be a factor for tests of potentially adverse agents already conducted in humans.

Normal mouse and rat strains as models for age-related cataract and the effect of caloric restriction on its development

The purpose of this study was to determine: (1) which of the commonly used strains of laboratory rats and mice provide good models for human age-related cataract, and (2) whether long term caloric restriction, a regimen that prolongs both median and maximum life span in rodents, would also delay the time of appearance of this age-related pathology. Three strains of mice and two rat strains commonly used in laboratory work and maintained on either ad libitum (AL) or calorically restricted (CR) diets in the National Institutes of Aging and Diet Restriction colony were examined by slit lamp for age-related cataracts at four or more time points during their life spans. These strains were Brown Norway and Fischer 344 rats, and C57BL/6, (C57BL6 x DBA/2)F1 and (C57BL/6 x C3H)F1 mice. None of these strains develop congenital cataracts. Various stages of cataract were found in the great majority of these animals in old age. In both rat strains and one mouse strain the cataracts occurred after mid-life, were most advanced late in life, and were similar in locations and appearance to those in humans. In the two mouse strains in which some cataracts appeared as early as 10-14 months of age, previously identified genetic defects affecting the eye were probably involved in the early appearances. CR extended life spain in all five rat and mouse strains and also delayed both the time of first appearances and the subsequent increase in cataract severity over time in the four dark-eyed strains. CR did not delay cataract formation in the single albino rat strain studied. In summation: (1) commonly used strains of laboratory rats and mice that are free of congenital or early appearing cataracts due to genetic defects would appear to serve as appropriate models for human age-related cataract, (2) caloric restriction (CR) provides a protective effect, delaying development of cataracts in the dark-eyed mouse and rat strains, while also extending their life spans, (3) CR did not delay the development of lens damage in the nonpigmented eye of the single albino strain studied, although it extended life span.

Adaptive role of caloric intake on the degenerative disease processes

Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular events. Many of these events can be modified by caloric intake. Since most of these processes determine an organism's ability to cope with various environmental stressors, it is not surprising that a relationship (in the presence of a constant nutrient density) exists between caloric intake and time-to-tumor and/or life span. Our studies have clearly shown that generally, the greater the caloric intake, the greater the body weight, the higher the incidence of spontaneous tumor occurrence, the greater the susceptibility to chemical carcinogens, and the shorter the life span. It is also recognized that variables other than body weight influence the life span and carcinogenesis. We have focused our attention on the questions of how and to what extent caloric intake modifies those homeostatic processes believed to be critical in determining the ability of an organism to cope with endogenous and exogenous stresses such as chemical, physical, and biological carcinogens. The response of an organism to its environment can be divided into four categories--physiological, metabolic, molecular, and cellular. We have found that, from a physiological perspective, decreasing caloric intake causes body temperature in rodents to be decreased by 0.5 to 1.8 degrees C and water consumption to be increased by 80%, as is running activity. However, metabolic output per gram of lean body mass is not altered. Reproductive capacity declines, whereas the ECG waveform is preserved as caloric intake decreases. Alterations in these and other physiological functions suggests that energy intake serves as a signal to up-regulate or down-regulate functions related to the flight-or-fight response observed in placental mammals. A number of key metabolic pathways are altered as a function of lowered caloric intake, even though the rate of food consumption per gram of lean body mass remains steady during body weight decreases caused by decreasing caloric intake. Pharmacological compartmentalization, however, is altered. As caloric intake declines, changes occur in the expression of a number of drug-metabolizing enzymes, with the most striking effect seen in sex-specific growth hormones and liver-dependent phase I and phase II enzymes. Additionally, oxidative stress (free-radical and mediated damage to macromolecules) appears to decrease as a function of reduced caloric intake. A number of molecular processes also change with changes in energy consumption. Our studies have shown that, regardless of the source and nature of DNA damage, DNA repair is better preserved and/or enhanced when caloric consumption decreases. In addition, the fidelity of DNA replication increases and oncogene expression is stabilized, P53 gene expression is increased, and apoptosis is elevated by up to 500% with decreased caloric intake. At the cellular level, cell proliferation is decreased in direct proportion to lower energy intake in some but not all tissues. Studies have also shown an enhancement in immune capacity, changes in IGF1, and accelerated rates of wound healing proportionate to declines in energy consumption. Our most recent findings, however, have shown that the benefits associated with decreases in caloric intake only occur in the presence of sufficient nutrient quality and density. In the absence of proper nutrition, however, sensitivity to carcinogens and toxic substances appears to be enhanced. These findings are supported by independent studies. These observations have led us to conclude that, in certain organisms, when caloric intake is decreased, there is an up-regulation of those processes that modulate the responses to a wide range of environmental stressors. This response allows for a better survival rate and a down-regulation of reproductive activity. It is our belief that, during periods of environmental stress, these systems may be essential to perpetu

Growth curves and survival characteristics of the animals used in the Biomarkers of Aging Program

The collaborative Interagency Agreement between the National Center for Toxicological Research (NCTR) and the National Institute on Aging (NIA) was aimed at identifying and validating a panel of biomarkers of aging in rodents in order to rapidly test the efficacy and safety of interventions designed to slow aging. Another aim was to provide a basis for developing biomarkers of aging in humans, using the assumption that biomarkers that were useful across different genotypes and species were sensitive to fundamental processes that would extrapolate to humans. Caloric restriction (CR), the only intervention that consistently extends both mean and maximal life span in a variety of species, was used to provide a model with extended life span. C57BI/6NNia, DBA/2JNia, B6D2F1, and B6C3F1 mice and Brown Norway (BN/RijNia), Fischer (F344/NNia) and Fischer x Brown Norway hybrid (F344 x BN F1) rats were bred and maintained on study. NCTR generated data from over 60,000 individually housed animals of the seven different genotypes and both sexes, approximately half ad libitum (AL) fed, the remainder CR. Approximately half the animals were shipped to offsite NIA investigators internationally, with the majority of the remainder maintained at NCTR until they died. The collaboration supplied a choice of healthy, long-lived rodent models to investigators, while allowing for the development of some of the most definitive information on life span, food consumption, and growth characteristics in these genotypes under diverse feeding paradigms.

Hormesis--implications for risk assessment caloric intake (body weight) as an exemplar

Hormesis can be considered as a parameter which has a non-monotonic relationship with some endpoint. Since caloric intake is such a parameter, and the impact of this parameter on risk assessment has been fairly well characterized, it can provide clues as to how to integrate the information from a hormetic parameter into risk assessments for toxicants. Based on the work with caloric intake, one could: (a) define a biomarker for hormetic effect; (b) integrate specific information on when in the animals lifespan the parameter is active to influence parameters such as survival; (c) evaluate component effects of the overall hormetic response; and (d) address the consequences of a non-monotonic relationship between the hormetic parameter and endpoints critical for risk assessment. These impacts on risk assessments have been characterized for chronic tests, but are also true for short-term tests. A priority is the characterization of the dose-response curves for hormetic parameters. This quantification will be critical in utilizing them in risk assessment. With this information, one could better quantitatively address the changes one expects to result from the hormetic parameter, and limit the uncertainty and variability which occurs in toxicity testing.

Upregulation of apoptosis with dietary restriction: implications for carcinogenesis and aging

The maintenance of cell number homeostasis in normal tissues reflects a highly regulated balance between the rates of cell proliferation and cell death. Under pathologic conditions such as exposure to cytotoxic, genotoxic, or nongenotoxic agents, an imbalance in these rates may indicate subsequent risk of carcinogenesis. Apoptotic cell death, as opposed to necrotic cell death, provides a protective mechanism by selective elimination of senescent, preneoplastic, or superfluous cells that could negatively affect normal function and/or promote cell transformation. The relative efficiency or dysfunction of the cell death program could therefore have a direct impact on the risk of degenerative or neoplastic disease. Dietary restriction of rodents is a noninvasive intervention that has been reproducibly shown to retard tumor development and most physiologic indices of aging relative to ad libitum-fed animals. As such, it provides a powerful model in which to study common mechanistic processes associated with both aging and cancer. In a recent study we established that chronic dietary restriction (DR) induces an increase in spontaneous apoptotic rate and a decrease in cell proliferation rate in hepatocytes of 12-month-old B6C3F1 DR mice relative to ad libitum (AL)-fed mice. This diet-induced shift in cell death/proliferation rates was associated with a marked reduction in subsequent development of spontaneous hepatoma and a marked increase in disease-free life span in DR relative to AL-fed mice. These results suggest that total caloric intake may modulate the rates of cell death and proliferation in a direction consistent with a cancer-protective effect in DR mice and a cancer-promoting effect in AL mice. To determine whether the increase in spontaneous apoptotic rate was maintained over the life span of DR mice, apoptotic rates were quantified in 12-, 18-, 24- and 30-month-old DR and AL mice. The rate of apoptosis was elevated with age in both diet groups; however, the rate of apoptosis was significantly and consistently higher in DR mice regardless of age. In double-labeling experiments, an age-associated increase in the glutathione S-transferase-II expression in putative preneoplastic hepatocytes in AL mice was rapidly reduced by apoptosis upon initiation of DR. Thus, intervention that promote a low-level increase in apoptotic cell death may be expected to protect genotypic and phenotypic stability with age. If during tumor promotion an adaptive increase in apoptosis effectively balances the dysregulated increase proliferation, the risk of permanent genetic error and carcinogenesis would be minimized.

Evolution and dietary restriction

Placing lifespan in the context of the life history of an organism, Alex Comfort's work has stimulated the analysis of dietary restriction (DR) and its effects on lifespan in an evolutionary context. DR results in the curtailment of energy-intensive nonfood-gathering activities, increased efficiency of food utilization, an increase in food acquisition activity, an increase in the reproductive lifespan, and an increase in the protection of genomic integrity. These result in further refinement of the Adaptive-Longevity Related Process Theory of the effects of dietary modulation to include increased protection of the genomic integrity of cells that result from delayed reproduction, and increased ability to compete for available food. These effects are discussed in the context of the "spacecraft" metaphor for the evolution of senescence. Also, the apparent paradox that increased body weight seems to be directly correlated to survival across species and inversely correlated to survival within a species is discussed in light of the importance of the cephalization index (a modified ratio of brain weight to body weight) for longevity.

Dietary restrictions and cancer

Dietary restriction (DR) alters a significant environmental factor in carcinogenesis, dietary intake, thus inhibiting both spontaneous and induced tumorigenesis. Potential mechanisms for the inhibition of spontaneous cancer may include the effects of DR to do the following: decrease body weight, which decreases cellular proliferation and increases apoptosis in a number of organs that increase and decrease with body size; decrease body temperature, thereby lowering the amount of endogenous DNA damage temperature generates; decrease oxidative damage, by increasing antioxidant damage defense systems; decrease, generally, cellular proliferation; and protect the fidelity of the genome by decreasing DNA damage, increasing DNA repair, and preventing aberrant gene expression. Potential mechanisms for reducing induced tumor incidence include lowering agent activation, changing agent disposition, decreasing the adducts most associated with agent toxicity, and inhibiting tumor progression through mechanisms similar to those that can effect spontaneous tumorigenesis. As a method to control a major source of environmental cancer, and as the major modulator of the agent induction of this disease, understanding how DR works may significantly contribute to the efforts to explain how diet impacts on development of cancer in the United States, and may suggest methods to reduce the adverse impacts of other environmental agents on the disease.

Age and temperature related changes in behavioral and physiological performance in the Peromyscus leucopus mouse

Age-related and ambient temperature-related changes in motor activity, body temperature, body weight (b.w.), and food consumption were studied in the long-lived Peromyscus leucopus mouse at environmental temperatures of 29 and 21 degrees C. Major changes in physiological performance were observed between the young (6 months) and old (60-72 month) age groups. The number of daily activity episodes, and total activity output was significantly lower in old mice. Maximum, average and minimum daily body temperature was lower in the old mice and a significant ambient temperature-by-age interaction was found. Maximum, minimum, and average daily b.w. was higher in old mice. Motor activity was evenly distributed over the active (night) phase in young mice but in old mice activity was significantly greater in the late night partition of the active cycle than in the early night partition. Both groups were significantly more active at night than during the day. Most of the food consumption in both groups occurred at night, but young mice consumed significantly more during the late night partition than the early night partition, and the consumption rates for old mice were not significantly different between early and late night partitions. The percentage of activity episodes involved with food consumption in both groups was significantly higher during the night partition, but the percentage during the early night partition was significantly higher in old mice than in young mice. Significant episodes of circadian torpor occurred in a high percentage of old mice at 06:00, on consecutive days, at both environmental temperatures, but young mice expressed no evidence of torpor.

Oral squamous cell carcinoma in ad libitum-fed and food-restricted Brown-Norway rats

A high incidence of oral squamous cell carcinoma was present in male and female Brown-Norway rats fed ad libitum or food-restricted dietary formulations. One hundred eight-nine rats were examined from 4 dietary treatment groups: male ad libitum, male food-restricted, female ad libitum, and female food-restricted. The ad libitum treatment groups for both males and females had significantly more cases of oral squamous cell carcinoma than cohort food-restricted groups. In ad libitum rats, 10 of 47 (21%) males and 15 of 47 (32%) females had oral squamous cell carcinoma, whereas only 4 of 47 (9%) males and 5 of 48 (10%) females in the food-restricted groups were similarly affected. The food-restricted rats lived significantly longer than ad libitum cohorts, so the higher incidence of squamous cell carcinoma was not dependent on extended lifespans. In addition to the dietary influence, a significant difference in oral squamous cell carcinoma incidence occurred between various familial lines. Family lines having representatives in both ad libitum and food-restricted groups had lower oral squamous cell carcinoma incidences in the food-restricted group whether comparing affected litters or individuals. Results suggest that the incidence of oral squamous cell carcinoma in our colony of Brown-Norway rats can be influenced by both the dietary treatment group and genetic predilection within certain pedigrees.

The physiologic, neurologic, and behavioral effects of caloric restriction related to aging, disease, and environmental factors

Little is known about the mechanisms by which acute and chronic caloric restriction (CR) modulate disease, longevity, and toxicity. To study these endpoints, behavioral parameters such as food and water consumption and physiologic parameters such as motor activity, body temperature, metabolic output (oxygen use), and respiratory quotient (RQ) were continuously monitored in 26-month-old male B6C3F1 mice and Fischer 344 rats fed either ad libitum (AL) or a CR diet (60% of AL). Different dietary regimens were used: rodents were (1) chronically food-restricted using daily feeding starting at 14 months of age, (2) chronically food-restricted using alternate day feeding, or (3) abruptly switched from CR to AL (acute CR). The physiologic and behavioral changes seen with chronic and acute CR were consistent across strains and species. Average body temperature, the number of meals, and the ratio of food/water consumption were significantly lower in CR rodents than in AL rodents. Also, the daily range of body temperature, oxygen metabolism, RQ, average water consumption, and motor activity was significantly higher in CR rodents. CR caused the onset of altered neurobehavioral functions such as abnormal water consumption; increases in motor activity, serum corticosterone, and stress proteins (HSP); and decreases in the basal setpoint for body temperature and brain metabolism. These changes strongly suggest that many beneficial effects of CR are controlled by the hypothalamic-pituitary-adrenal axis via hormonal regulation. This study supports the assertion that nutritional status may be a primary factor of consideration in development of safety standards and assessment of risk.

Effect of food restriction on life span and immune functions in long-lived Fischer-344 x Brown Norway F1 rats

Life-long food restriction is known to slow aging and reduce the rate of occurrence of age-associated disease processes, but the mechanism by which this is accomplished is unknown. In this study we have examined the effect of food restriction on the proliferative response of spleen cells to mitogens and lymphokine production in 6-, 18-, and 30-month-old AL and FR Fischer-344 x Brown Norway (F-344 x BNF1) female rats whose average life span is 137 weeks on an ad libitum (AL) diet and 177 weeks on a food-restricted (FR) diet. In addition, the ability of food restriction to recall antigens was tested in 10-month-old rats by immunizing them with keyhole limpet and hen's egg albumin and measuring proliferative response of draining lymph node cells to these antigens. Our results indicated that the spleen-cell proliferative response to phytohemagglutinin and concanavalin A (Con A) was equal in 6- and 18-month-old rats but declined significantly in 30-month-old AL rats compared to FR rats. Although flow cytometric analyses did not reveal differences for CD4, CD8, and Ig+ cells with age, a significant rise in memory T cells (Ox-22low) in both CD4+ and CD8+ T-cell subset lineage was noted in AL-fed rats at 30 months of age. In FR rats, however, only a minimal shift of naive T cells (Ox-22high) to memory cells was observed. In FR rats, the observed changes in the naive and memory T-cell subsets correlate well with the observed higher levels of the antiinflammatory interleukin-2 (IL-2) and lower levels of the proinflammatory cytokines such as IL-6 and tumor necrosis factor-alpha. The ability of food-restricted animals to recall antigens was lower compared to their age-matched controls, though the proliferative response to T-cell mitogen Con A and superantigen staphylococcal enterotoxin B was higher. These findings indicate that food restriction may selectively act to maintain a lower number of antigen-induced memory T cells with age, thereby maintaining the organism's ability to produce higher levels of IL-2 with age. In summary, the increased cell-mediated immune function noted in aged FR rats appears to be due to the presence of a higher number of naive T cells, which are known to produce elevated levels of the antiinflammatory cytokines, which may in part be responsible for reducing the observed age-related rise in disease.

Rationale for the use of dietary control in toxicity studies--B6C3F1 mouse

Significant variability in critical study parameters such as tumor incidences and survival, increasing tumor incidence and decreasing survival in common toxicity test models, and agent-induced changes in body weight (BW) and BW distribution all generate concern about the reproducibility, consistency, and equity of chronic toxicity tests used in regulation. These concerns have led to suggestions to control BW in chronic tests by the modulation of dietary intake without inducing malnutrition [dietary control (DC)] thereby minimizing tumor and survival variability both between and within studies. Evaluating the reports of the best controlled set of chronic experiments, the National Toxicology Program bioassay series, from studies initiated from 1981 to 1990, there is an increase in tumor incidence, especially liver tumors, with a consistent increase in BW. The studies are classified as to whether normal or aberrant BW growth curves occur. When the studies with normal growth curves are considered, the variance in the BW at 12 mo on test (BW12) can account for over 50% of the variance in liver tumor incidence. Additional stratification by study type, which alter tumor prevalences, as well as appreciation of housing effects [group housing decreases survival (in male mice) and induces tumors in males and females when compared to individual housing], further increase the strength of the correlations, accounting for up to 90% of the variance seen in tumor incidences. These updated analyses further support the hypothesis that it is the BW variation that is resulting in much of the variability seen in tumor incidences and refine the suggestions for the BW curves used as the desired targets for DC.

Effects of caloric restriction on expression of testicular cytochrome P450 enzymes associated with the metabolic activation of carcinogens

Previous work demonstrated that microsomal cytochrome P4502A1 (CYP2A1) is expressed in rat testicular Leydig cells. The present study investigates the effects of diet, age, and strain on rat testicular CYP2A1 expression and assesses the potential role of testicular CYP2A1 in the metabolic activation of carcinogens. In ad libitum-fed 18-week-old Fischer 344 rats, testicular CYP2A1 immunoreactive protein and testosterone 7alpha-hydroxylase activity (7alpha-TOHase) exhibited a circadian variation with a daytime maximum and a night-time minimum (82.2 +/- 42.0 and 21.9 +/- 4.5 pmol 7alpha-hydroxytestosterone/min/mg protein, respectively). Caloric restriction (to 60% of ad libitum consumption), which reduces the severity of Leydig cell tumors in rats, decreased expression of both CYP2A1 and testicular 7alpha-TOHase >80% and eliminated their circadian variation. Conversely, caloric restriction induced a circadian rhythm in testicular 7-benzyloxyresorufin-O-dealkylase activity. Testicular microsomes from ad libitum-fed rats having peak diurnal 7alpha-TOHase activity had significantly greater (30%) microsome-mediated aflatoxin B1-DNA binding activity compared to microsomes prepared from nocturnal phase ad libitum-fed or calorically restricted rats which expressed low 7alpha-TOHase activity. In 12-month-old Fischer 344 rats, high CYP2A1 expression was correlated with severe Leydig cell hyperplasia (r = 0.80), whereas CYP2A immunoreactive protein and 7alpha-TOHase were expressed at lower levels in Sprague-Dawley than in Fischer 344 rats and were undetectable in pig, monkey, and human testes. These are strains/species that do not exhibit significant Leydig cell hyperplasia. This suggests that caloric intake, strain, and circadian factors may all mediate testicular CYP2A1 expression in the rat and that CYP2A1 may in turn influence carcinogen activation and pathological status in the testis.

Pi-class glutathione-S-transferase-positive hepatocytes in aging B6C3F1 mice undergo apoptosis induced by dietary restriction

Liver sections from aging ad libitum-fed and diet-restricted B6C3F1 male mice were evaluated immunohistochemically for pi-class glutathione S-transferase (GST-II). GST-II immunostaining of hepatocytes was diffuse and occurred in periportal regions of hepatic acinus, whereas perivenous areas were weakly stained or were stain-free. Expression of GST-II was significantly diminished in diet-restricted mice in all age groups and was associated with a marked decrease in liver tumor development. As most spontaneous liver tumors were GST-II positive, it can be speculated that they developed from GST-II positive initiated hepatocytes. To determine whether dietary restriction induces apoptosis in GST-II-positive hepatocytes, 24-month-old ad libitum-fed mice were introduced to 40% diet restriction. After 1 week of diet restriction, a decrease in GST-II expression was associated with a threefold increase in the frequency of apoptotic bodies as detected by terminal deoxynucleotidyl transferase-mediated d-UTP nick end labeling of DNA fragments. A two-step immunohistochemical procedure revealed that approximately 70% of apoptotic bodies were GST-II positive. These results suggest that spontaneous, potentially preneoplastic hepatocytes in tumor-prone B6C3F1 mice are eliminated by apoptosis with dietary restriction.

FDA points-to-consider documents: the need for dietary control for the reduction of experimental variability within animal assays and the use of dietary restriction to achieve dietary control

Standard protocols for conducting chronic toxicity and carcinogenicity studies have been refined over the years to carefully control for many variables. Nevertheless, over the last 2 decades, there has been a steady increase in variability, a decrease in survival, an increase in tumor incidence rates, and an increase in the average body weight of control animals among the various rodent species and strains used for toxicity testing. These observations have prompted an evaluation of chronic study designs to determine what factor(s) may be responsible for such confounding changes. Ad libitum feeding and the selection of successful breeders with rapid offspring growth is believed to be at least partially responsible for the heavier, obese rodents with which many laboratories are coping today. As a result of these changes, some studies used for the evaluation of safety have been deemed inconclusive or inadequate for regulatory purposes and either additional supportive studies have been requested and/or studies per se have been repeated. Research on the molecular mechanisms of caloric restriction and agent-induced toxicity at the Food and Drug Administration (FDA) National Center for Toxicological Research stimulated the first international conference on the biological effects of dietary restriction in 1989; this was followed in 1993 by an FDA workshop exploring the utility of dietary restriction in controlling reduced survival in chronic tests and an international conference in 1994 exploring the implications for the regulatory community of using dietary restriction in toxicity and carcinogenicity studies used in support of a sponsor's submission or in risk assessments. The outcome of that conference was the FDA's commitment to develop Points-to-Consider documents that address the issue of dietary control in chronic toxicity and carcinogenicity studies.

Anthropometric measures and metabolic rate in association with risk of breast cancer (United States)

To investigate whether cancer risk-reduction seen in calorie-restricted animals also applies to breast cancer in women, we have analyzed data from the first National Health and Nutrition Examination Survey in the United States and subsequent follow-up surveys. During the follow-up of one to 155 months, 182 out of 7,622 women developed breast cancer. Due to biased under-reporting of dietary intake, the analysis did not examine calorie intake as an exposure variable, but rather focused on anthropometric measures and metabolic rate as biomarkers of nutritional balance. Multiple Cox regression analysis showed elevated odds ratios (OR) for height, elbow width, and skinfolds among postmenopausal women. ORs for the fifth quintile were 2.0 (95 percent confidence interval [CI] = 1.0-3.8), 2.3 (CI = 1.2-4.7), and 2.0 (CI = 1.0-4.0), respectively. Weight (OR = 2.5, CI = 1.2-5.1) and resting metabolic rate (OR = 2.0, CI = 1.0-4.0) were significant relative to the second quintile. Bitrochanteric breadth, sitting height, body fat, body mass index, or combination variables were not associated with cancer risk. It was concluded that in the analysis of breast cancer data, skeletal measures ought to be considered as routine potential confounders, and that using measured rather than estimated metabolic rates may improve risk prediction.

Proliferative lesions of the testis in ad libitum-fed and food-restricted Fischer-344 and FBNF1 rats

The effect of 40% food restriction on spontaneous proliferative lesions of the testis was evaluated in lifetime and cross-sectional (serial sacrifice) studies of 419 Fischer (F-344) and 304 Fischer x Brown Norway (FBNF1) male rats. Interstitial cell hyperplasia and interstitial cell adenoma (ICA) were the most common proliferative lesions in each genotype; incidence of each was less in the FBNF1. In each genotype, food restriction delayed the onset of both lesions and reduced the incidence of ICA. At 12 months interstitial cell hyperplasia was present in 11 of 12 ad libitum (AL)-fed and 0 of 12 food-restricted (FR) F-344 rats. In FBNF1 rats interstitial cell hyperplasia was observed first at 18 months in AL-fed and at 36 months in FR groups. Interstitial cell adenoma developed in 5 of 12 AL-fed F-344 rats by 18 months and in 2 of 12 FR rats by 24 months; 2 of 12 AL-fed FBNF1 rats had ICA at 30 months, and 1 of 12 FR rats had ICA at 42 months. In these cross-sectional studies approximately half the ICA cases in F-344 rats were bilateral; no FBNF1 rats had bilateral ICA. In lifetime studies the incidence of ICA was reduced from 49% in AL-fed rats to 19% in FR F-344 rats and from 9% in AL to 4% in FR FBNF1 rats. The incidence of mesothelioma was low in both genotypes and was not obviously altered by food restriction. A malignant embryonal neoplasm, an unclassified benign neoplasm, and three seminomas were present in the testes of FBNF1 rats.

Glaucoma in food-restricted and ad libitum-fed DBA/2NNia mice

We allocated 110 DBA/2NNia mice of either sex to one of two feeding regimens: ad libitum (AL) or food restriction (FR) to 60% of the amount consumed by the AL group. The mice were examined at 3, 6, 9, 12, 18, and 24 months (at 3 months, only AL mice were examined). During the remaining periods approximately equal numbers (n = 10) of mice of both sexes and diet groups were examined. Peripheral anterior synechia was the first glaucoma-associated lesion observed and was present in 8 of 10 AL female mice, 6 of 10 AL males, and 1 FR male at 6 months. At 9 months peripheral anterior synechia was present in all AL females and was accompanied by depletion of retinal ganglion cells and degeneration of the optic nerves and optic tracts. Ninety percent of the eyes in the AL males also had peripheral anterior synechia at 9 months, but ganglion cell depletion and optic nerve degeneration were not observed as frequently. Neovascular membranes in the iridocorneal angle, a component of peripheral anterior synechia, were first observed at 9 months in approximately 55% of the globes of the AL mice and 5% of the FR mice. This was a major difference in the microscopic features of synechia between the diet groups and resulted in increased severity of synechia in the AL mice compared with their FR cohorts. Degeneration of the optic nerves and tracts was characterized by atrophy, astrogliosis, increase in cellularity, fragmentation of axons, and loss of myelin. Glaucoma in the FR mice of both sexes was less severe than in their AL counterparts. The most severely affected were AL females, followed by FR females, AL males, and FR males. Food restriction reduced the incidence and severity of the ocular lesions in females at all periods. The primary benefit of FR in males occurred during the 6- and 9-month periods when the incidence and severity of the glaucoma-related lesions were reduced; in the succeeding months the major benefit was minimal reduction of the severity of the lesions.

Longevity, body weight, and neoplasia in ad libitum-fed and diet-restricted C57BL6 mice fed NIH-31 open formula diet

Groups of C57BL6 mice of each sex were assigned to one of 2 dietary regimens, ad libitum (AL) or dietary restriction (DR), to study effects of food restriction on body weight, survival, and neoplasia. The AL and DR groups were subdivided into a scheduled sacrifice group for examination at 6-mo intervals, and a lifetime group to provide longevity data. Necropsies and microscopic examinations were conducted on 911 animals. In the lifetime group food consumption averaged 33.6 and 34.4 g per week by AL males and AL females, respectively; the DR counterparts were given 40% less. The diet contained 4.35 kcal/g. The average lifetime body weights were 34.8, 26.8, 22.6, and 21.6 g for AL males, AL females, DR males, and DR females, respectively, and their age at 50% survival was 27.5, 26.9, 31.7, and 33.5 mo. Maximal lifespan was increased 18% in DR males and females. Lifetime incidence of tumor-bearing mice was 89% and 86% for AL males and females, versus 64% for each sex of DR mice. Dramatic reduction occurred in female DR mice in lymphoma (9% vs 29%), pituitary neoplasms (1% vs 37%), and thyroid neoplasms (0.4% vs 8%). In males, hepatocellular tumors were reduced to 1% from 10% by DR. In contrast, the incidence of histiocytic sarcoma was increased in DR females and unaffected in DR males. Tumor onset was delayed in DR animals; 87% of all neoplasms in males and 95% in females had occurred in the AL mice by 24 mo, whereas the DR animals had only 52% and 39% of their lifetime incidence, respectively, by that age. This study provided comparative AL and DR data from C57BL6 mice examined randomly at 6-mo intervals (cross-sectional group) in parallel with data from animals in similar cohort that was unsampled and allowed to succumb naturally (longevity group). Dietary restriction reduced the lifetime percentage of tumor-bearing animals and the number of tumors per animal, and delayed the age at onset of most neoplasms.

Spontaneous renal tubular carcinoma in Fischer-344 rat littermates

Two of 632 Fischer-344 rats in a food restriction study had spontaneous, bilateral, multicentric renal tubular cell carcinomas. Although there were 104 litters represented in this study, both rats that developed this rare neoplasm were from the same litter. The littermates, one male and one female, were in the food-restricted treatment groups (60% of ad libitum intake) and were 550 and 447 days old, respectively, at death. The probability that the two rare bilateral renal neoplasms occurred by a chance event in littermates is approximately 0.8%. The apparent familial predisposition for development of specific types of neoplasms emphasizes the importance of randomization of individuals into treatment groups and consideration of lineage for rare tumors.

Age-related changes in the intrinsic rate of apoptosis in livers of diet-restricted and ad libitum-fed B6C3F1 mice

Cancer incidence increases progressively with age. This observation suggests that a mechanistic relationship may exist at the cellular level between these two apparently diverse processes. Indirect evidence for this fundamental relationship is derived from the fact that interventions that retard the rate of aging simultaneously retard the incidence of many forms of cancer. Dietary restriction of rodents is a noninvasive manipulation that reproducibly retards most physiological indices of aging as well as the incidence of spontaneous and chemically induced tumors. As such, it provides a powerful model in which to study common mechanistic processes associated with both aging and cancer. In a recent study, we established that chronic dietary restriction induces an increase in the spontaneous rate of apoptotic cell death in hepatocytes of 12-month-old B6C3F1 mice and is associated with a significant reduction in the subsequent development of spontaneous hepatoma in this genetically susceptible strain. The purpose of the present investigation was to extend and confirm these original observations by determining whether the increased rate of spontaneous apoptosis with chronic dietary restriction is maintained throughout the life span in this strain. We quantified the spontaneous apoptotic rate by histological examination of liver sections from diet-restricted and ad libitum-fed B6C3F1 mice at age intervals of 12, 18, 24, and 30 months. The incidence of apoptotic bodies was enumerated in non-tumor-bearing mice by scoring 50,000 hepatocytes per liver by in situ end-labeling immunohistochemistry and was expressed as the mean incidence per 100 cells. The rate of apoptotic cell death was found to be elevated with age in both diet groups; however, the rate of apoptosis was significantly and consistently higher in the diet-restricted mice, relative to the ad libitum-fed mice, regardless of age. It has been proposed that apoptosis, or physiological cell death, provides a protective mechanism whereby DNA-damaged or potentially neoplastic cells are selectively eliminated. Thus, interventions that increase cellular sensitivity to apoptotic cell death would tend to protect genotypic and phenotypic stability with age; on the other hand, the failure to initiate or respond to appropriate signals for apoptosis would tend to accelerate the accumulation of age-associated genetic lesions and age-related neoplasia. An increase in the intrinsic rate of apoptotic cell death may contribute, in part, to decreased tumor incidence and increased life span potential with dietary restriction.

Age-related neoplasia in a lifetime study of ad libitum-fed and food-restricted B6C3F1 mice

Longevity, body weight, and age-specific neoplasia were determined in 1,064 B6C3F1 mice as part of a coordinated study of food restriction (FR). Restricted animals were offered 60% of the diet consumed by the ad libitum (AL) group. Longevity data were derived from a set of 56 animals of each sex from each diet group, which were examined whenever dead or moribund. For cross-sectional data, a parallel set of 210 animals were sacrificed in groups of 12-15 at 6-mo intervals. Lifetime body weight was reduced in the FR mice approximately proportional to restriction (i.e., 40%). Food restriction increased the age at 50% survival (median) by 36% in both sexes and increased the maximal lifespan (mean age of oldest 10%) by 21.5% in males and by 32.5% in females. In 56 males of the longevity groups, there were 89 neoplasms in the AL subgroup versus 53 in FR; 56 AL females had 100, versus 58 in 55 FR females. Increase in lifespan of the restricted animals was achieved primarily by decrease in incidence and delay of onset of fatal tumors, of which lymphoma was the most prominent. This report catalogs all of the neoplasms (1,103) observed in longevity and cross-sectional groups, by diet, sex, and age. These data add to the existing knowledge base needed for future studies of dietary restriction and aging as well to evaluate nutrition of animals used in bioassays.

Caloric restriction and toxicity

The modulatory effects of caloric intake on the rate and extent of both spontaneous and induced disease incidence is well known, but the significance of these effects in the interpretation of testing data has only recently become appreciated. This is especially true relative to the impact of caloric intake on both survival and background incidence for common tumors. In order to enhance the health and survival of animals ongoing chronic toxicity testing it has been suggested that such tests should restrict food consumption. Although this restriction will result in increasing survival of the test animals, it may also effect the expression of toxicity by altering agent metabolism and disease progression. Focus in this symposium is on the necessity to control dietary consumption in toxicity tests (dietary control), and if such a need does exist to what level of consumption should be diet be focused (caloric restriction).

A murine leukemia virus expressed in aged DBA/2 mice is derived by recombination of the Emv-3 locus and another endogenous gag sequence

Although most inbred strains of mice contain endogenous retroviral sequences, these sequences are usually not capable of producing infectious retroviruses. In some cases, the retroviral sequences are small fragments of viral genomes. In a few cases the sequences for complete retroviruses exist, but contain small defects which prevent the production of infectious virus. While the ability of reversions of these defects to produce retroviruses has been studied by site-directed mutagenesis and chemical-mediated mutagenesis, the presence of spontaneously occurring reversions has not been completely evaluated. We characterized an infectious ecotropic retrovirus spontaneously expressed in aged DBA/2 mice, which carries the complete but defective Emv-3. Although this endogenously produced retrovirus was related to the endogenous Emv-3 sequence, it had undergone recombination with another retroviral sequence to correct the defect which resided in the gag of Emv-3. Thus, recombination of endogenous ecotropic retroviral sequences may be a mechanism to produce infectious retroviruses in adult animals that contributes to pathologic disease.

Mechanisms of caloric restriction affecting aging and disease

Caloric restriction (CR) appears to affect aging by the inhibition of the specific chronic diseases which occur at increasing frequency with age. A common disease in F-344 rats, granulocytic leukemia, appears to have a window where it is sensitive to the effects of CR. Other diseases, such as pituitary adenomas, appear to have a different relationship to growth in the animal. Additionally, a model for the major disease for a number of long-lived strains of mice, lymphoma, which CR effects by inhibiting the expression of the causative agent, is being developed. Evaluation of the effects of CR on neoplasia, degenerative disease and physiological parameters suggests that the major factors in expression of these diseases is the alteration of growth factors, hormonal status, etc., and that these alterations also affect strain-specific pathologies depending on when they are changed in the life span. Effecting different diseases at different times in the life span, long-term CR, by limiting exposure to endogenous growth factors, altering physiological characteristics, and limiting exposure to food toxicants, inhibits the onset of disease, and its sequela, aging.

Survival, body weight, and spontaneous neoplasms in ad Libitum-fed and food-restricted Fischer-344 rats

Ad libitum-fed (AL) and food-restricted (FR) Fischer-344 male and female rats were monitored for survival, body weight, and spontaneous neoplasms. Mean and maximal lifespans for each group were inversely related to mean body weights. AL males were the shortest lived (mean lifespan 101 wk) followed by AL females (118 wk), FR males (125 wk), and FR females (132 wk). Gross and microscopic examinations were performed on 851 rats from cross-sectional and longevity components of the study. In FR groups, the incidence of mammary gland fibroadenomas, testicular interstitial cell tumors, and pituitary neoplasms was decreased while the latency of these neoplasms was increased. In longevity components, most FR groups had a higher incidence of leukemia than AL cohorts, but all FR groups had a higher mean age at death for the rats with leukemia. Higher leukemia rate in the FR groups was thought to be a result of their extended mean lifespan.