Neoplastic pathology in male Sprague-Dawley rats fed AIN-93M diet ad libitum or at restricted intakes

The primary purpose of this study was to evaluate the effects of age and long-term dietary reduction on neoplastic diseases in rats fed the AIN-93M purified diet. Second, pathologic profiles are critical to comprehensive dietary evaluation. Male Sprague-Dawley rats assigned to 2 groups, ad libitum (AL) and dietary restricted (DR), were fed the AIN-93M (casein protein) diet free choice and reduced in amount by 31%, respectively. At 58 weeks of age, the predominant types of lesions in AL and DR rats were pituitary and skin tumors. At 114 weeks of age, the most common lesions were pituitary, adrenal gland, skin, mammary, brain, and pancreatic tumors and mononuclear cell leukemia. However, DR had no significant effect on these lesions. Primary findings demonstrate that DR significantly reduced the total number of tumors per rat and incidence of benign and primary tumors (all organs) but did not reduce the incidence of malignant tumors (all organs). Dietary restriction increased the percentage of unknown deaths. These results may explain why survival rates for AL and DR rats were not significantly different at 114 weeks (43.3 vs 57.5%, respectively). These findings differ from previous studies using NIH-31 cereal diet (Aging Clin Exp Res 2001;13:263; J Nutr 2002;132:101; Aging Clin Exp Res 2003;16(6):68; Aging Clin Exp Res 2004;16:448) where neoplastic lesions rather than nonneoplastic lesions were linked to a significant increase in survival rate among cohorts of DR-fed rats (J Nutr 2002;132:101). Factors such as diet composition and digestibility, although not independent of body weight, may have contributed to differences in rat mortality and may affect humans in a similar manner.

Surgical caloric restriction ameliorates mitochondrial electron transport dysfunction in obese females

BACKGROUND

The authors examine the mitochondrial electron transport system (ETS) with regard to caloric restriction and body size in humans.

METHODS

The study population included 59 morbidly obese (MO) female subjects with mean body mass index (BMI) 49.6 +/- 1.7 and 40 age-matched previously morbidly obese patients with surgically-induced caloric restriction (SCR) and mean BMI 28.9 +/- 1.1. ETS function in the 2 study groups were made by measuring their lymphocyte mitochondrial ETS complexes I-IV activities and complex III binding kinetics. Linear regression analyses were used to analyze the interactions between ETS function and BMI, energy intake, and metabolic status.

RESULTS

The MO, as compared to SCR, subjects had significantly (P < 0.01) higher ETS complexes II-IV activities (complex II = 20.4 +/- 1.9 vs 15.3 +/- 1.1, complex III = 129.4 +/- 10.1 vs 72.3 +/- 4.9, complex IV = 3.1 +/- 0.3 vs 1.4 +/- 0.1 nmol/mg/min for the MO vs SCR, respectively). ETS complexes activities were positively and significantly correlated with subjects' BMI, carbohydrate caloric intake, and fasting plasma insulin levels. Michaelis-Menten kinetic analysis showed that the Km for ubiquinol-2 in complex III of MO patients was 2-fold greater than SCR values, reflecting an apparent reduction in substrate binding capacities producing a resistance to electron flow in the MO population. Caloric consumption, carbohydrate calories, insulin levels, and BMI were also each significantly (P < 0.05) and positively correlated with the Km of Complex III.

CONCLUSIONS

ETS function and efficiency are compromised by increasing BMI and caloric consumption in morbidly obese women, and caloric restriction may reduce the potential for excessive oxidative free radical generation via the ETS.

The effects of different levels of dietary restriction on neoplastic pathology in the male Sprague-Dawley rat

BACKGROUND AND AIMS

The primary purpose of this study was to evaluate the effects of varied levels of dietary restriction (DR) on neoplastic pathologies in rodents at 58 and 110 weeks of age.

METHODS

Male Sprague-Dawley (SD) rats were divided into four nutritional groups; an ad libitum (AL) control group, and three dietary restricted (DR) groups that were fed the NIH-31 diet reduced in amount by 10, 25, and 40%.

RESULTS

At 110 weeks of age, compared to AL rats, the incidence of benign tumors was significantly lower in all DR groups while primary tumors were significantly lower in the 10 and 40% DR groups; no malignant tumors were detected in the 10% DR group. Most defined mortalities were caused by neoplastic lesions. All levels of DR reduced the percentage of tumor-bearing animals, the incidence of skin tumors (combined), and the total number of tumors. Pituitary, skin, and pancreatic tumors were the most prolific lesions; pituitary and skin tumors were the most fatal. Compared to AL rats, the time to onset of skin and pancreatic tumors was longer in all of the DR groups.

CONCLUSION

In many cases, the incidences of neoplastic lesions were similar among the DR groups, clearly indicating that the DR effect is not linear and that even a very low level of DR (10%) can have a significant effect on many important neoplastic lesions and tumor burden. The main effect of DR was to decrease the incidence of some neoplastic lesions and to increase the time to onset and/or decrease the progression of tumors, thereby increasing the 110-week survival rate of DR rats.

Changes in expression level of genes as a function of time of day in the liver of rats

Daily, rhythmic variation in various biochemical, physiological, and behavioral events is a fundamental property of biological organization. Here, we report analysis of relative levels of gene expression in the liver of 16 Fischer 344 rats as a function of time of day. Expression levels were determined for 3906 genes using high-density oligonucleotide microarrays. Of the 3906 genes, 1171 (30%) were clearly expressed while 2735 (70%) were not expressed or the expression was too low to distinguish from background levels. The maximum estimated changes observed for most genes (1029, 88%) were less than 1.5-fold. Analysis of variance and the Kruskal-Wallis tests were used to identify 67 genes whose expression was significantly altered as a function of time of day. These significantly altered genes were classified according to their functions and fall into key cellular pathways including drug metabolism, ion transport, signal transduction, DNA binding and regulation of transcription, and immune response.

The effects of different levels of dietary restriction on non-neoplastic diseases in male Sprague-Dawley rats

BACKGROUND AND AIMS

The primary purpose of the present study was to investigate the effects of 10, 25, and 40% dietary restriction (DR) on non-neoplastic diseases in rodents at 58 and 110 weeks of age, and to determine whether low-level DR (10 and 25%) can increase the survival rate and decrease variability in chronic bioassay studies.

METHODS

Male Sprague-Dawley (SD) rats (NCTR colony) were divided into four nutritional groups, consisting of an ad libitum (AL) group with unlimited access to the NIH-31 diet, and three dietary restricted (DR) groups given the NIH-31 diet reduced in amount by 10, 25, and 40%.

RESULTS

At 110 weeks of age, the incidence of cardiomyopathy was 95, 75, 45, and 15% for AL and 10, 25, and 40% DR rats, respectively; the incidence of nephropathy was 55, 20, 15, and 0% for AL and 10, 25, and 40% DR rats, respectively. The severity of chronic heart and kidney diseases was significantly reduced in all DR rat groups, with significant DR-dependent linear trends for these diseases. Moreover, DR prevented the progression of skin irritation to foot ulcers, and reduced the age-related degeneration in the adrenal, lacrimal, and thymus glands, and the liver.

CONCLUSIONS

These results clearly indicate that even low DR levels were effective in preventing or slowing the progression of these non-neoplastic diseases.

Nutrient intake and growth characteristics of male Sprague-Dawley rats fed AIN-93M purified diet or NIH-31 natural-ingredient diet in a chronic two-year study

BACKGROUND AND AIMS

Daily nutrient intake and growth of male Sprague-Dawley (SD) rats fed compositionally different diets were monitored over 114 weeks to determine whether rats fed ad libitum (AL) or diet restricted (DR) followed normal growth parameters. A second objective was to evaluate the usefulness of the American Institutes of Nutrition's AIN-93M (maintenance formulation) diet for aging and DR studies.

METHODS

Rats were fed NIH-31 cereal-based diet AL, or a vitamin-fortified modification of the NIH-31 diet at 10, 25, or 40% DR. Other SD rats were fed AIN-93M diet AL or 31% DR; daily nutrient intake and growth response were reported.

RESULTS

At all intervals up to 36 weeks of age, rats fed AL the NIH-31 diet consumed significantly (p<0.001) more than rats fed AL the AIN-93M diet, and required more diet per unit of gain than AIN-93M AL rats. However, body weight (BW) gain in rats AL-fed the AIN-93M diet demonstrated that energy components were more efficiently metabolized than in those fed the NIH-31 diet. Whereas diet restriction decreased BW, the rate of maturation, i.e., the rate of reaching a mature BW, increased as intake level decreased. Growth response showed all growth curves were normal, but intake level effects on mature BW and maturation rate differed significantly (p<0.001). Curves for rats AL- and DR-fed the AIN-93M diets were similar to those of rats AL- and DR-fed NIH-31 diet formulations, suggesting that diets adequately met growth requirements and supported normal growth parameters of male SD rats when fed AL or DR.

CONCLUSIONS

A modification in the AIN-93M energy components to reduce total calories and an evaluation of other nutrient profiles could improve its usefulness as a maintenance and aging diet.

Effect of the AIN-93M purified diet and dietary restriction on survival in Sprague-Dawley rats: implications for chronic studies

Survival, growth and dietary intake (DI) variables were monitored in a chronic 114-wk study in which male Sprague-Dawley rats [n = 120; National Center for Toxicological Research (NCTR) colony] consumed the AIN-93M purified diet ad libitum (AL), or an amount reduced by 31% of total AL intake inclusive of all macro- and micronutrients. The main objectives were to ascertain the survival characteristics of rats fed the AIN-93M diet and to determine whether dietary restriction (DR) increases longevity of rats fed this casein-based diet compared with the use of mixed-protein sources of the NIH-31 cereal-based diet in an earlier study. Body, liver, brain, the brain/body ratio, spleen, thymus and kidney weights, body length and body density were decreased (P < 0.05) by DR, whereas testis weight and skull length were not altered by DR. Significant age effects at 58 and 114 wk were found for body, brain, the brain/body ratio, liver and testis weights, and body density. Survival rates for the AL and 31% DR groups were 43.3 and 57.5%, respectively. Survival curves were not significantly different. The survival rate for AL rats fed the AIN-93M diet was not different from that of AL rats fed the NIH-31 diet (43.3 and 51.7%, respectively). However, the survival rate for 31% DR rats fed the AIN-93M diet was significantly lower than 25% DR rats fed the NIH-31 diet (57.5 and 87.5%, respectively) although both groups had similar body weights and energy intake at various ages. Nutritional components in the NIH-31 diet that are missing and/or reduced in the AIN-93M diet may interact with DR to increase 114-wk survival. Although the survivability, growth and anatomical results of this study suggest that the AIN-93M diet is suitable for chronic rodent studies, additional studies such as comprehensive histopathologic and physiologic investigations must be undertaken to complete the evaluation process.

The effects of different levels of dietary restriction on aging and survival in the Sprague-Dawley rat: implications for chronic studies

A study was undertaken to determine the effects of incremental levels of dietary restriction (DR) in rats. Survival, growth, reproductive, and dietary intake (DI) variables were monitored in a chronic study in which male Sprague Dawley (SD) rats (NCTR colony) were fed their ration ad libitum (AL), or DR. The main objectives were to determine if low levels of DR could be used to increase the survival rate of SD rats in the chronic bioassay, and to identify the survival characteristics of a long-lived SD rat strain (NCTR colony). The average life span of AL rats was 115 months. At 104 weeks on study (110 weeks of age), the survival rate for the AL and 10%, 25%, and 40% DR groups was 63.4, 87.5, 87.5, and 97.5%, respectively. The largest increase in survival (24.1%) occurred between AL and 10% DR, indicating that very low levels of DR have a significant effect on survival. Whole-body, liver, prostate, and epididymis weights and body length were decreased by DR, whereas brain weight, testicular weight, and skull length were not altered by DR. Rats from the NCTR colony were found to be ideal for chronic studies because they are much longer-lived than other SD stocks. Although the 104-week survival rate for these SD, non-obese AL rats exceeds the FDA's "Redbook" survival guideline (> 50%) for chronic bioassays, the use of DR is advocated because it reduces individual variability in body weight.

Effects of dietary restriction on insulin resistance in obese mice

In many cases, development of insulin resistance has been linked to obesity and may contribute to mechanism of aging. The role of diet, irrespective of degree of obesity, in modulating insulin resistance and development of age degeneration disease remains uncertain. Lowered blood glucose levels are commonly associated with diet restriction (DR), which is an intervention shown to successfully retard aging and age associated disease. The effects of DR on blood glucose and insulin resistance were measured in yellow obese (A(vy)/A), lean black (a/a) mice and in another common inbred strain (B6C3F1) (at three different ages). The yellow obese mice become diabetic as a result of an insulin receptor defect which is not clearly understood. Insulin responses and radioinsulin binding were assayed in yellow obese and lean black mice fed either ad libitum (AL) or DR diets (YAL, BAL, YDR and YAL, respectively) at four different circadian intervals. The B6C3F1 controls were fed either AL (CAL) or DR (CDR) and measures were made at six circadian stages and three different ages. Within 23 days, DR produced a significant loss in body weight and a time-dependent 22-55% reduction in basal blood glucose levels in the yellow obese mice. Additionally, exogenous insulin produced circadian stage dependent (at the time of food intake) reductions in blood glucose in the YDR animals that were not present in YAL animals. (125)I-Insulin binding in liver was increased nearly 2-fold in YDR and BDR mice during the time of day that animals were active and eating. (125)I-Insulin binding was two-fold-higher in CDR mice at 4, 12 and >24 months of age. Binding decreased as a function of age in both the CAL and CDR animals. However, even in the >24 month group the CDR animals were found to have levels of binding that were as high as those found in younger CAL liver. The mechanism of action appears to be through resolution of insulin resistance by modulating an insulin receptor defect.

Induction of stress proteins by electromagnetic fields in cultured HL-60 cells

HL-60 cells in culture were exposed for 2 h to a sinusoidal 0.1 or 1 mT (1 or 10 Gauss) magnetic field at 60 Hz and pulse labeled after exposure with radioactive isotopes by incubation by using either [(35)S]methionine, [(3)H]leucine, or [(33)P]phosphate. The radioactive labels were incorporated into cellular proteins through synthesis or phosphorylation. Proteins were extracted from electrostatically sorted nuclei, and the heat shock/stress proteins (sp) were analyzed for synthesis and phosphorylation by two-dimensional polyacrylamide gel electrophoresis. In the control cultures (no exposure to the magnetic field), sp 72c (cognate form) was faintly observed. A 0.1 mT exposure did not show sp metabolism to be different from that of the controls; however, after a 1 mT exposure of the HL-60 cells, sp 70i (inducible form) was synthesized ([(35)S]methionine incorporation). Sp 90 was not synthesized at either field level, but was phosphorylated ([(33)P]phosphate incorporation) in the 1 mT exposure. Sp 27 (isoforms a and b) was induced after a 1 mT exposure as reflected by labeling with [(3)H]leucine. These sps were not detected after a 0.1 mT exposure. After a 1 mT exposure and labeling with [(33)P], sp 27 isoforms b and c were phosphorylated whereas isoform 'a' was not observed. Sps 70i, 72c, and 90 were identified by commercial sp antibodies. Likewise, polypeptides a, b, and c were verified as sp 27 isoforms by Western blotting. Statistical evaluation of sp areas and densities, determined from fluorographs by Western-blot analysis, revealed a significant increase in sps 90 and 27a after a 1 mT magnetic field exposure. The 1 mT magnetic field interacts at the cellular level to induce a variety of sp species. Bioelectromagnetics 20:347-357, 1999. Published 1999 Wiley-Liss, Inc.

Increased effective activity of rat liver catalase by dietary restriction

While dietary restriction (DR) increases maximum life span in many animal species, the mechanisms by which this is achieved remain unclear. One possibility is that DR may act in part to reduce free radical levels by retarding age-related declines in rat liver catalase activity. We measured liver cytosolic catalase activity at various times of day in 9-12 month old male (BN X F344)F1 rats fed ad libitum (AL) or subjected to a 30% DR from 14 weeks of age. Catalase activity (expressed as μmol·min(-1)·g liver(-1)) in both diet groups reached minimums at 0600 h but activity was 26% higher in DR as compared to AL rats. This traditional expression of catalase activity did not significantly differ between diet groups at other times of day. One must be careful in the interpretation of such data, however, since catalase is rapidly inactivated by its substrate (H2O2), thus displaying abnormal enzyme kinetics. In order to avoid this difficulty we evaluated the time period during which the reaction remained linear and multiplied it by its activity to yield the effective catalase activity. Using this method we found a significant increase in catalase activity in DR animals at several H2O2 concentrations during the light span. At 1800 h (the beginning of the dark span when the controls initiated peak food intake), fewer and smaller dietary differences were observed and no dietary effects were observed at 2400 h. These data suggest that DR reduces the rate of accumulation of inactive catalase and may contribute to an increased capacity in DR animals to remove free radicals.

P53 synthesis and phosphorylation in the aging diet-restricted rat following retinoic acid administration

Multiple doses of retinoic acid (RA) were administered intraperitoneally to three groups of male Fischer 344 rats over a 36 h period. The p53 isoforms from bone marrow nuclei in these three groups of rats were analyzed over time by two-dimensional polyacrylamide gel electrophoresis (PAGE) and fluorography for the incorporation of [35S]methionine (p53-synthesis) and [32P]phosphate (p53-phosphorylation). Two groups of rats, young (3.5 months) ad libitum (Y/AL) and old (28 months) ad libitum (O/AL), had free access to Purina rat chow; a third group of old (28 months) diet-restricted rats (O/DR) were maintained on a restricted caloric intake (60% of the AL diet) from 3 months of age. After 36 h of RA dosing, the PAGE patterns of p53 synthesis and phosphorylation in Y/AL and O/DR rats were very similar. In both groups, an increase in complexity was observed with labeling of additional isotypes possessing more acidic isoelectric values. In contrast, the O/AL animals showed a pattern of p53 isoform synthesis and phosphorylation that was considerably less complex and lacked the pronounced shift to more acidic forms following RA dosing. The p53 isoforms of O/AL rats as recognized by wild type (wt) Pab 246 antibody, were also much less dramatic in their increase to more acidic forms. Two-dimensional phospho-tryptic maps of Y/AL and O/DR rats were also very similar, both exhibiting two additional minor 32P-labeled fragments after RA dosing. The maps of O/AL rats did not show the two additional fragments following RA administration. After RA dosing, cyclin protein inhibitors (p16, p21, p27) revealed robust labeling with their respective antibodies in Y/AL and O/DR rats as analyzed by Western blotting. The O/AL animals showed marginally detectable antibody recognition of the cyclin inhibitors after RA dosing. Taken together, these data suggest that the biosynthesis and phosphorylation of p53 isoforms and the expression of cyclin dependent kinase inhibitor proteins is not significantly different between Y/AL and O/DR rats. Further, these results confirm and extend our previous observations that chronic diet-restriction attenuates the age related decline in the metabolic activity of nuclear protein products.

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.

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.

P48: a novel nuclear protein possibly associated with aging and mortality

The synthesis ([35S]-incorporation) of stress proteins (sps, i.e., 24, 25, 70, 90 Mr) and of nuclear protein 48 (p48) was investigated in the heart and bone marrow cells of three groups of male Fischer 344 rats following administration of isoproterenol (IPR). Two groups of rats, young ad libitum (Y/AL-3 1/2 months) and old/AL (O/AL-28 months), had full access to rat chow; a third group of old diet restricted (O/DR-28 months) rats was maintained on a diet restricted intake of 40% of the Y/AL animals. Sp synthesis in the bone marrow (25, 70, 90 Mr) and heart (24, 70, 90 Mr) nuclei of O/AL was significantly reduced, as compared with Y/AL and O/DR rats, following their induction with IPR. A unique sp24 was expressed in heart following IPR dosing. A 1 mg/kg dose of IPR was lethal for O/AL, but not for Y/AL or O/DR animals. This lethal dose induced synthesis of p48 in heart and bone marrow nuclei of O/AL rats only. P48 existed in isoform states in bone marrow, and when a lethal dose of IPR was administered in this tissue, it was expressed in O/AL rats in a cell-cycle regulated pattern. Stress proteins and other non-sps were seen as cell cycle regulated following IPR administration. P48 in bone marrow and heart nuclei from O/AL rats showed an antigenic response identical to that of p48 in HL60 nuclei. The presence of p48 is correlated with mortality and with an ad libitum diet in old rats, since it is absent in old diet restricted animals; therefore, DR may impede the expression of p48 through a mechanism(s) that is undisclosed at this time.

The effect of aging and dietary restriction on the retinoylation of nuclear matrix proteins in rats

The labeling in vivo of young ad libitum (Y/AL) and old diet restricted (O/DR) rats with [3H]retinoic acid (RA) for 6 hours, and the exposure of electrophoretically separated nuclear matrix proteins from bone marrow tissue on film for 48 days revealed the presence of eleven retinoylated proteins. Dosing with RA (100 mg/kg body weight) for 96 hours and exposure to [3H]RA enhanced the levels of radioactive incorporation of several nuclear matrix proteins, including p51, and p55, similarly in Y/AL and O/DR rats. Dosing of old ad libitum (O/AL) rats with [3H]RA for 6 hours showed the incorporation of six proteins following 48 days of exposure on film. Long-term dosing of RA (96 hours) did not increase [3H]RA incorporation in these proteins, including p51 and p55, in O/AL rats. Increasing the level of RA by two-fold (200 mg/kg body weight) in Y/AL and O/DR rats elicited an increase in the incorporation levels of [3H]RA in five proteins. This dose response following increased levels of RA was not seen in the retinoylated proteins of O/AL animals. Analysis by the Western blotting technique showed p51 and p55 from rat bone marrow cells to have the same immunochemical determinates with proteins of identical molecular masses in HL60 cells. The levels of retinoylation of nuclear matrix proteins in O/DR animals, altered by age- and diet-dependent factors, suggests a condition that is more reminiscent of Y/AL than of O/AL animals.

Chronic caloric restriction induces stress proteins in the hypothalamus of rats

The induction of stress proteins (sps) in the hypothalamus of female Fischer 344 rats in response to caloric restriction (CR) and to heat stress was investigated. Caloric restriction was found to elicit sps 27, 34, 70, and 90 in the hypothalamus of both young and old rats while none was found in the hypothalamus of ad libitum (AL) fed controls. Heat stress initiated heat shock proteins (hsps/sps) 27, 70, and 90 in the hypothalamus of the young (AL) fed animals, the same proteins evoked by feeding stress. The same sps were induced in the old (AL) rats although the expression showed substantial decline with age. This reduction was less marked, however, with the old CR rats. Stress protein 34, an infrequently reported protein, was related to feeding and was not induced by heat shock. Recent reports point to the important role sps play in the cellular reaction to stress, as well as their involvement in the higher functions. The findings reported here suggest that sps are involved in the regulatory mechanisms allowing CR animals to tolerate stress related to metabolic substrate deprivation.

Temporal and substrate-dependent patterns of stress protein expression in the hypothalamus of caloric restricted rats

Stress proteins (sps) 27, 34, 70 and 90 (Mr x 10(3)) were induced in the hypothalamus of caloric restricted (CR) rats by feeding stress. A definite time pattern for sps synthesis was observed when their induction was examined at several time points after the rats were fed, and the level of sps expression was found to vary significantly at different times of the day. The same group of proteins was induced in ad libitum fed rats when they were subjected to food deprivation for 48 h. Stress protein 34 expression in the hypothalamus of old caloric restricted rats was found to be dependent on blood glucose levels, and was substantially reduced when insulin was added to the glucose infusion. The expression of sps 27, 70 and 90, however, was little changed with glucose and/or insulin infusion.

The homology of a novel polypeptide with stress protein characteristics in embryonic mice brain and in the hypothalamus of caloric restricted rats as determined by ultramicro western blotting

A novel protein (p34) was observed in polyacrylamide gel fluorographs of gestation day 13 embryonic mouse brain following retinoic acid dosing of dams. Another p34 polypeptide with identical gel migratory characteristics was seen in the hypothalamus of old caloric restricted rats after "food deprivation stress". Western blotting, employing an ultramicro trans-blot cell developed in our laboratory, detected identical immunochemical determinants between these proteins, verifying their homology. Peptide mapping and Western blotting further validated the uniqueness of p34 compared with other stress proteins including heme oxygenase.

The temporal relationships of synthesis and phosphorylation in stress proteins 70 and 90 in aged caloric restricted rats exposed to bleomycin

A single intraperitoneal injection of the human therapeutic drug bleomycin (BL) was administered to three groups of male Fischer 344 rats at time 0, and the incorporation of [35S]methionine ("synthesis") and phosphorylation patterns of stress proteins (sps/hsps) from bone marrow cells were analyzed over time by two-dimensional electrophoresis and fluorography. Two groups of rats, young ad libitum (Y/AL--3 months) and old ad libitum (O/AL--28 months), had free access to rat chow, and a third group of old rats (O/CR--28 months) were maintained on a caloric restricted intake (60% of the AL diet). The administration of BL in Y/AL, O/AL and O/CR animals activated the 35S-labeling of sp 90 which reached a peak at 4 hours. Labeling of sp 90 was significantly greater in Y/AL compared to O/AL, and the incorporation pattern of O/CR was intermediate to Y/AL and O/AL animals. All labeling of sp 90 in each group had disappeared by 10 hours after BL administration. Stress protein 70x (inducible form) in these three animal groups displayed a similar pattern of 35S-incorporation, but the amount of labeling was less than that of sp 90. No labeling of sp 70x remained by 13 hours after BL administration. Phosphorylation ([32P] phosphate incorporation) of sp 90 reached a maximum level at 2 hours in all animals, and 32P-labeling in Y/AL was significantly increased over O/AL and O/CR with an intermediate level found in O/CR animals. The turnover rate (phosphorylation/dephosphorylation) of sp 90 induced by BL was significantly suppressed and temporarily extended in O/AL as compared with O/CR, which implied that CR not only increased incorporation of sp 90, but also enhanced a utilization of the phosphate pool very similar to that seen in Y/AL animals.

Modulation of toxicity by diet and dietary macronutrient restriction

Restriction of diet and macronutrients has been reported to modulate the toxicity of numerous chemical agents. Of the various forms of restriction studied, using nutritionally adequate diets, food restriction (FR) appears to be most effective, but protein restriction (PR), fat restriction (FtR), carbohydrate restriction (CbR), and excess of dietary fiber (FE) also affect toxicity and the spontaneous diseases that define the background incidence in toxicity tests. The heterogeneity of the dietary macronutrients complicates simple analysis of their effects. Additionally, the interrelationships between these various components in the complex dietary mixture often make experiments difficult to interpret. Despite these complexities, a simple model is presented, which considers the effects of dietary manipulations on the individual steps in the interaction of organism and agent, and puts the varied effects that can occur within an organism into context. Ultimately, many of the effects of dietary modulation on these steps in toxicogenesis can be considered as changing agent exposure and the biologically available dose. The effects of macronutrient restriction are discussed in terms of effects on agent at the interface of organism and toxicant, agent disposition, agent metabolism, and repair of toxicant-induced damage at the level of the genome. After illustrating the influence of these nutritional effects on the chronic bioassay, using mouse liver tumors as an example, the significance of these effects for chronic and short-term testing is discussed. Additionally, methods to address the impact of nutritional factors on toxicity testing are suggested.

Effects of caloric restriction on rodent drug and carcinogen metabolizing enzymes: implications for mutagenesis and cancer

Caloric restriction in rodents results in increased longevity and a decreased rate of spontaneous and chemically induced neoplasia. The low rates of spontaneous neoplasia and other pathologies have made calorically restricted rodents attractive for use in chronic bioassays. However, caloric restriction also alters hepatic drug metabolizing enzyme (DME) expression and so may also alter the biotransformation rates of test chemicals. These alterations in DME expression may be divided into two types: (1) those that are the direct result of caloric restriction itself and are detectable from shortly after the restriction is initiated; (2) those which are the result of pathological conditions that are delayed by caloric restriction. These latter alterations do not usually become apparent until late in the life of the organism. In rats, the largest direct effect of caloric restriction on liver DMEs is an apparent de-differentiation of sex-specific enzyme expression. This includes a 40-70% decrease in cytochrome P450 2C11 (CYP2C11) expression in males and a 20-30% reduction of corticosterone sulfotransferase activity in females. Changes in DME activities that occur late in life in calorically restricted rats include a stimulation of CYP2E1-dependent 4-nitrophenol hydroxylase activity and a delay in the disappearance of male-specific enzyme activities in senescent males. It is probable that altered DME expression is associated with altered metabolic activation of chemical carcinogens. For example the relative expression of hepatic CYP2C11 in ad libitum-fed or calorically restricted rats of different ages is closely correlated with the amount of genetic damage in 2-acetylaminofluorene- or aflatoxin B1-pretreated hepatocytes isolated from rats of the same age and caloric intake. This suggests that altered hepatic drug and carcinogen metabolism in calorically restricted rats can influence the carcinogenicity of test chemicals.

Oxidative DNA damage levels in rats fed low-fat, high-fat, or calorie-restricted diets

Increased fat and caloric content of the diet has been associated with increased mammary tumor incidence. The dietary modulation of cellular redox state may be one mechanism behind this association. We have examined the effects of changes in dietary fat and caloric intake on the levels of 5-hydroxymethyluracil in DNA from rat liver and mammary gland. Female Fischer 344 rats, 40 days old, were maintained on 3% (low-fat), 5% (control), or 20% (high-fat) corn oil diets for 2 weeks. A fourth group of rats had the same daily fat intake as the control group, but total caloric intake was restricted by 40%. As a measure of oxidative DNA damage, 5-hydroxymethyluracil levels were measured in the DNA extracted from liver and mammary gland by gas chromatography-mass spectrometry. 5-Hydroxymethyluracil levels in the liver DNA of the low-fat, high-fat, and calorie-restricted groups were decreased relative to that of control, but the only significant decrease was in the calorie-restricted group (p less than 0.01). In the mammary gland DNA, statistically significant decreases in damage were found in each group relative to control (p less than 0.05). The relationship between fat in the diet and oxidative stress is thus complex. These results show that changes in dietary intake of both fat and calories can modulate oxidative DNA damage levels, and the effect of diet was more clearly evident in the DNA from mammary gland than in DNA from liver.

Modulation of chemical toxicity by modification of caloric intake

Caloric restriction increases maximum achievable lifespan and offsets the time to development of degenerative disease. Part of these desirable effects may result from positive modulation of toxic events. We have shown that when rodents are placed on a diet that is reduced in total calories by 40%, several beneficial changes on biochemical systems which impact on toxicologic processes are positively enhanced. Lipid metabolism is reduced and, therefore, the potential for lipoperoxidation is reduced. Additionally, activity of enzymes that produce free radicals as byproducts (cytochrome P4502C11) are also reduced. Concurrently, we have shown that the "effective" activity of catalase and the activity of superoxide dismutase (which are required for the detoxification of toxic oxygen radicals) are significantly increased by caloric restriction. The activities of enzymes of drug and xenobiotic metabolism are also altered by caloric restriction. The effect upon activity may be to either decrease or increase activity, dependent upon whether the enzyme activates compounds to intermediates which may be more toxic or whether the enzyme acts to reduce toxicity. We have also shown that caloric restriction may affect the initiation stage of carcinogenesis. Aflatoxin B1 binding to hepatic nuclear DNA was reduced by caloric restriction (caloric restriction reduced both major adducts that are formed upon exposure to aflatoxin B1). caloric restriction also reduced cytochrome P4502C11 which converts aflatoxin B1 to its toxic epoxide, and may partly explain the reduction in binding. These results suggest that caloric restriction may, in part, extend the time to development of degenerative disease by altering basic biochemical mechanisms of toxicity.

Effect of chronic caloric restriction on the circadian regulation of physiological and behavioral variables in old male B6C3F1 mice

The circadian rhythms of food and water consumption, the number of feeding and drinking episodes, oxygen consumption, carbon dioxide production, respiratory quotient, gross motor activity, and body temperature were measured in male B6C3F1 mice that were fed ad libitum (AL) or fed a caloric-restricted diet (CR). The CR regimen (60% of the normal AL consumption) was fed to mice during the daytime (5 hr after lights on). CR animals exhibited fewer feeding episodes but consumed more food per feeding bout and spent more total time feeding than AL mice. It appears that CR caused mice to change from their normal "nibbling behavior" to meal feeding. Compared to AL animals, the mean body temperature was reduced in CR animals, while the amplitude of the body temperature rhythm was increased. Spans of reduced activity, metabolism, and body temperature (torpor) occurred in CR mice for several hours immediately before feeding, during times of high fatty acid metabolism (low RQ). The acute availability of exogenous substrates (energy supplies) seemed to modulate metabolism shifting metabolic pathways to promote energy efficiency. CR was also associated with lower DNA damage, higher DNA repair, and decreased proto-oncogene expression. Most of the circadian rhythms studied seemed to be synchronized primarily to the feeding rather than the photoperiod cycle. Night-time CR feeding was found to be better than daytime feeding because the circadian rhythms for AL and AR animals were highly synchronized when this regimen was used.

Effect of chronic caloric restriction on the synchronization of various physiological measures in old female Fischer 344 rats

A variety of physiological and behavioral parameters which relate to metabolism were continuously monitored in 18 month old female Fischer 344 rats which were maintained on either ad libitum or reduced calorie diets. Caloric restriction (CR) stimulated average motor activity per day, the duration of each feeding episode, food consumed per episode, and water consumed per gram lean body mass (LBM). However, CR limited total food consumption, feeding time, number of feeding episodes per day, total eating and drinking time, and the daily ratio of food consumed to water consumed, CR also decreased average body temperature per day, O2 consumption, CO2 production, and respiratory quotient. A variety of parameters concerning water consumption were not affected. CR rats ate their food immediately when food was presented during the light span, while ad libitum fed animals ate numerous small meals throughout the entire dark span. An anticipatory response to restricted feeding was also noted. Total motor activity, metabolism, and body temperature increased just prior to scheduled feeding and reached maximum values shortly after feeding, suggesting that these parameters were highly synchronized to feeding. Females and males were found to respond to caloric restriction in a similar fashion. Dramatic changes in respiratory quotient and body temperature suggest rapid shifts between metabolic pathways (glycolysis to gluconeogenesis) to obtain optimal efficiency. Lower body temperature and metabolism may provide protection against DNA damage, thereby increasing the survival potential of restricted rats. These responses may provide insight into the mechanisms by which caloric restriction acts to extend life span.

Effect of chronic caloric restriction on physiological variables related to energy metabolism in the male Fischer 344 rat

In the present study, a number of physiological and behavioral measures that are related to metabolism were continuously monitored in 19-month-old male Fischer 344 rats that were fed ad libitum or fed a caloric restricted diet. Caloric restricted rats ate fewer meals but consumed more food during each meal and spent more time eating per meal than did rats fed ad libitum. Therefore, the timing and duration of meals as well as the total number of calories consumed may be associated with life extension. Average body temperature per day was significantly lower in restricted rats but body temperature range per day and motor activity were higher in restricted rats. Dramatic changes in respiratory quotient, indicating rapid changes in metabolic pathway and lower temperature, occurred in caloric restricted rats when carbohydrate reserves were depleted. Lower body temperature and metabolism during this time interval may result in less DNA damage, thereby increasing the survival potential of restricted rats. Nighttime feeding was found to synchronize physiological performance between ad libitum and caloric restricted rats better than daytime feeding, thereby allowing investigators to distinguish the effects of caloric restriction from those related solely to the time-of-day of feeding.

Effect of chronic caloric restriction on hepatic enzymes of intermediary metabolism in the male Fischer 344 rat

It is well established that caloric restriction extends life span and significantly retards the rate of occurrence of most age-associated degenerative disease processes. A paucity of data exists relative to the mechanisms by which caloric restriction accomplishes these events. We have examined the effect of caloric restriction in rats on several hepatic enzymes of intermediary metabolism. The activities of glycolytic and supporting enzymes including lactate dehydrogenase, pyruvate kinase, sorbitol dehydrogenase, and alcohol dehydrogenase were all decreased in response to caloric restriction. Fructose 1-phosphate aldolase and creatine phosphokinase were not altered. Likewise, enzymes associated with lipid metabolism (malic enzyme and glycerokinase) were reduced (fatty acid synthetase was reduced, but not to a statistically significant degree). Activities of enzymes supporting gluconeogenesis (glutamate oxaloacetate transaminase, tyrosine aminotransferase, glutamate pyruvate transaminase, glutamate dehydrogenase, amino acid oxidase, malate dehydrogenase, and glucose 6-phosphatase) were either unchanged or increased significantly by caloric restriction. Glucagon levels were decreased. Comparisons between young ad libitum fed and older calorically restricted rats revealed similar but not identical metabolic activity. These results suggest that caloric restriction produces an effect on intermediary metabolism, favoring the role of glucagon and glucose synthesis; but limiting the role of insulin and glucose catabolism in the liver. The former observation provides for the efficient support of peripheral tissues and the latter a level of energy production necessary only for self maintenance. Limited lipid metabolism suggests decreased potential for fatty acid epoxide formation and free radical damage to cellular macromolecules. Additionally, caloric restriction may delay the progressive age associated changes in the activities of some of the enzymes investigated.

The effect of dietary restriction on myc protooncogene expression in mice: a preliminary study

The effect of chronic dietary restriction on the expression of the c-myc protooncogene was determined in the livers of a hybrid mouse strain (C57Bl6 x C3H F1 hybrid) at three time points during a 24-h period: 1 h after lights on (1 HALO), 5 h prior to feeding (12 HALO), and 2 h after feeding (19 HALO). In addition, in whole animals studies, changes in core body temperature were monitored. In mice which had been subjected to a chronic diet restriction (60% of the intake of ad libitum controls), c-myc expression was significantly reduced at 1 HALO and 19 HALO compared to corresponding ad libitum animals. In addition, significant differences in c-myc expression were found between time points, in both the ad libitum and restricted groups, suggesting that myc protooncogene expression in the liver may be regulated in a circadian fashion. C-myc expression may correlate with body temperature, suggesting a possible association with metabolic output.

Effects of aging and caloric restriction on hepatic drug metabolizing enzymes in the Fischer 344 rat. II: Effects on conjugating enzymes

The effects of long-term caloric restriction on the hepatic phase II drug metabolizing enzymes were investigated in the male Fischer 344 rat. Rats that had been restricted to 60% of their pair-fed control consumption from 14 weeks post-partum exhibited altered conjugating enzyme activities at 22 months. Caloric restriction significantly reduced the age-related decrease in glutathione-S-transferase activity towards 1,2-dichloro-4-nitrobenzene, but did not significantly alter the age-related changes in UDP-glucuronyltransferase or sulfotransferase activities towards hydroxysteroids. Caloric restriction appeared to increase hepatic microsomal UDP-glucuronyltransferase activity toward bilirubin and gamma-glutamyltranspeptidase activities. These observations suggest that caloric restriction has multiple effects on the hepatic phase II drug metabolizing enzymes in the rat. Such effects may alter hepatic metabolism and activation or detoxification of drugs and carcinogens.

Effects of aging and caloric restriction on hepatic drug metabolizing enzymes in the Fischer 344 rat. I: The cytochrome P-450 dependent monooxygenase system

The effects of long-term caloric restriction on the hepatic cytochrome P-450 dependent monooxygenase system were investigated in the 22-month-old Fischer 344 rat. Caloric restriction decreased the age-related changes in hepatic testosterone metabolism, which are associated with demasculinization of the liver. Caloric restriction also increased hepatic microsomal testosterone 6 beta-hydroxylase, lauric acid 12-hydroxylase and 4-nitrophenol hydroxylase activities over corresponding values in both ad libitum fed 22-month and 60-day-old control male rats. This suggests that cytochrome P-450 isozymes, P-450 pcn1&2, P-452 and P450j may be induced by caloric restriction. Such changes in cytochrome P-450 isozyme profiles could result in altered carcinogen activation, radical formation or drug detoxication in the calorically restricted rat.

The turnover of radiolabeled nuclear proteins in rats exposed to environmental and chemical stress

Exposure to a 12 h light/12 h dark (L/D) cycle for 1 month, followed by reversal to a 12 h D/12 h L (D/L) cycle stimulated within 18 h the incorporation of [3H]leucine and [32P]orthophosphoric acid into new proteins (130-25 kDa) in the G0 phase of the cell cycle of the non-regenerating and regenerating rat liver as observed in two-dimensional gel autoradiograms. Six additional proteins from the rat submaxillary gland (130-20 kDa) revealed labeling with 32P within 3 h following combined administration of isoproterenol and sodium arsenite. Labeling disappeared within 7 days for all stressed proteins.

Relationship between field strength and arousal response in mice exposed to 60-Hz electric fields

White-footed mice, Peromyscus leucopus, were exposed to 60-Hz electric fields to study the relationship between field strength and three measures of the transient arousal response previously reported to occur with exposures at 100 kV/m. Five groups of 12 mice each were given a series of four 1-h exposures, separated by an hour, with each group exposed at one of the following field strengths: 75, 50, 35, 25, and 10 kV/m; 8 additional mice were sham-exposed with no voltage applied to the field generator. All mice were experimentally naive before the start of the experiment, and all exposures occurred during the inactive (lights-on) phase of the circadian cycle. The first exposure produced immediate increases in arousal measures, but subsequent exposures had no significant effect on any measure. These arousal responses were defined by significant increases of gross motor activity, carbon dioxide production, and oxygen consumption, and were frequently recorded with field strengths of 50 kV/m or higher. Significant arousal responses rarely occurred with exposures at lower field strengths. Responses of mice exposed at 75 and 50 kV/m were similar to previously described transient arousal responses in mice exposed to 100-kV/m electric fields. Less than half of the mice in each of the field strength groups below 50 kV/m showed arousal responses based on Z (standard) scores, but the arousals of the mice that did respond were similar to those of mice exposed at higher field strengths. Polynomial regression was used to calculate the field strength producing the greatest increases for each of the arousal measures. The results show that the amplitude of the transient arousal response is related to the strength of the electric field, but different measures of arousal may have different relationships to field strength.

Effects of intermittent 60-Hz high voltage electric fields on metabolism, activity, and temperature in mice

Transient effects of 100-kV/m extremely low frequency electric fields were studied in the white footed deermouse, Peromyscus leucopus. Gross motor activity, carbon dioxide production, oxygen consumption, and core body temperature were monitored before, during, and after intermittent field exposures (four hour-long exposures, at one-hour intervals). Thirty-four mice were exposed in cages with plastic floors floating above ground potential, and 21 mice were exposed in cages with grounded metal floor plates. The first field exposure produced an immediate, transient increase of activity and gas measures during the inactive phase of the circadian cycle. All measures returned to baseline levels before the second exposure and were not significantly changed throughout the remainder of the exposures. The rapid habituation of field-induced arousal suggests that significant metabolic changes will not be measured in experiments in which the interval between exposure and measurement is greater than two hours.

Odontomas in Peromyscus leucopus

A colony of Peromyscus leucopus was established 15 years ago from animals trapped in the deciduous forest at Argonne National Laboratory, Argonne, Illinois. A roentgenographic survey of the skeletons of 189 of these untreated animals dying during a 13-month period disclosed 48 odontogenic growths in 21 of the mice. These growths were diagnosed on histopathologic examination as complex odontomas, the incidence of which was higher in males than in females. In this relatively small sample, these benign tumors appeared to be associated with youth rather than old age.

Genetic relation of life span to metabolic rate for inbred mouse strains and their hybrids

Average life spans were estimated for the male progeny from 21 of the 25 possible matings of 5 inbred mouse strains. Oxygen consumption was measured in an open system over a 48-hour interval. Resting metabolism, Mre, and average metabolism, Mav, were determined at 6-8 months of age, and at 24-34 months. Body weight, W, was determined at the time metabolism was measured. Life span, L, is negatively correlated with Mre and Mav, and positively correlated with W at both ages of measurement. This is in accord with the metabolic wear factor that had previously been established among 85 different species of mammals. A new metabolism variable, the energy partition coefficient, defined as the ratio of average to resting metabolic rate, Mav/Mre, has a parabolic relation to body weight, i.e., is maximal at an intermediate body size. The squared body weight deviation in turn has a negative correlation with life span. The correlation of L with Mav/Mre is positive, as expected, but not significant. These data suggest the existence of a longevity factor dependent on the partition of energy between the phasic metabolism of activity and the continuous maintenance metabolism.

Age-dependence of body weight and linear dimensions in adult Mus and Peromyscus

Head plus body length (HBL), tail length (TL) and body weight (BW) were measured on two species of small myomorph rodents, Mus musculus and Peromyscus leucopus, throughout adult life. Both sexes of Mus show about a 15 per cent increase of HBL and TL between 5 and 24 months of age, and a BW increase of about 47 per cent. There is no age-trend of HBL in either sex of Peromyscus between 5 and 67 months of age, while TL increases about 7 per cent. In both species, cessation of skeletal growth is followed by a steady decrement of body mass, which averages about 0.23 per cent per month throughout adult life for the two sexes of Peromyscus, and over two per cent per month after cessation of skeletal growth in Mus. The weight loss in Mus in the last half of the lifespan is shown to be associated with age, rather than with the duration of subsequent survival. This evidence against the hypothesis that the late weight loss in Mus is due to terminal disease.