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

High incidence, early onset of histiocytic sarcomas in mice with Hertwig's anemia

OBJECTIVE

Histiocytic sarcoma (HS) is a rare, rapidly disseminated, usually lethal tumor in humans. Treatment specific for HS has not been developed primarily due to deficiencies of appropriate animal models with high incidence/early onset. Mice with Hertwig's anemia (an/an) provide a potential model.

METHODS

Here, we compare HS susceptibility in an/an and unaffected control mice maintained on three genetic backgrounds. As a potential therapeutic measure, genetically marked bone marrow is transplanted between high and low susceptibility animals.

RESULTS

HS is detected earlier and the overall incidence is 15-fold higher in WBB6F1(F1)-an/an than in F1-+/?, B6-an/an and -+/? mice. Neither WB-an/an nor their normal WB-+/? littermates present with HS. Liver myelopoiesis and aneuploidy coexist with HS but the former is also rampant (33.7% incidence) in HS-free +/? and an/an mice. Marrow transplantation experiments provide evidence that (1) myelopoiesis is associated with HS and (2) early-onset/high-incidence HS is blocked by using late-onset F1-+/+ mice, as either donor or recipient.

CONCLUSIONS

Homozygosity for an on an F1 genetic background is essential for high-incidence/early-onset HS; myelopoiesis and HS coexist; and therapeutic transplantation may be feasible.

Accelerated aging pathology in ad libitum fed Xpd(TTD) mice is accompanied by features suggestive of caloric restriction

Trichothiodystrophy (TTD) patients with a mutation in the XPD gene of nucleotide excision repair (NER) have a short life span and show various features of premature aging, thereby linking DNA damage to the aging process. Xpd(TTD) mutant mice share many features with TTD patients, including a shorter life span, accompanied by a segmental progeroid phenotype. Here we report new pathology features supportive to the premature aging phenotype of Xpd(TTD) mice. Strikingly, accelerated aging pathology is accompanied by signs suggestive of caloric restriction (CR), a condition usually linked to retardation of age-related pathology and life extension. Accelerated aging symptoms in Xpd(TTD) mice are most likely due to accumulation of endogenously generated DNA damage and compromised transcription leading to cell death, whereas CR symptoms may reflect the need of Xpd(TTD) mice to reduce metabolism (ROS production) in an attempt to extend their life span. Our current findings in Xpd(TTD) mice further strengthen the link between DNA damage, repair and aging.

Dietary restriction counteracts age-related changes in cholesterol metabolism in the rat

The effects of ageing on the metabolism of cholesterol were examined in three different organs (liver, aorta and brain) of 6-, 12- and 24-month-old male Sprague-Dawley rats. Ageing was associated with a significant increase in intracellular cholesterol esters in all three organs. Steady state mRNA levels of multidrug resistance protein (MDR) and acylCoA:cholesterol acyl transferase (ACAT), enzymes involved in cholesterol import and esterification, were also increased. By contrast, expression of mRNA for neutral cholesterol ester hydrolase (nCEH) and caveolin-1, proteins involved in cholesterol ester hydrolysis and export, were significantly reduced. Dietary restriction is the only intervention shown to extend lifespan and retard age-related declines in function in mammals. To further explore the possible correlation between changes in cholesterol esterification and ageing, we analysed cholesterol metabolism in liver, aorta, and brain of aged rats exposed to two dietary restriction regimens: intermittent (alternate-day) fasting (IF) and food intake restriction (60% of ad libitum feeding). Both dietary regimens attenuated the age-related changes in cholesterol esters and in the expression of genes involved in cholesterol metabolism. These results provide evidence that distinctive age-associated changes in intracellular cholesterol metabolism occur in rats. Furthermore, these modifications can be partially reversed by dietary restriction, a condition known to affect the ageing process. Age-related changes in cholesterol metabolism may play a role in triggering and/or aggravating senescence-related disorders characterized by altered cholesterol homeostasis.

Suppression of thymic lymphomas and increased nonthymic lymphomagenesis inTrp53-deficient mice lacking inducible nitric oxide synthase gene

Trp53-deficient mice spontaneously develop lymphomas, mainly of thymic origin, although the molecular mechanism remains largely unknown. As several interaction effects between p53 and iNOS have been reported, we hypothesized that iNOS activity in the thymus is causally linked to lymphomagenesis in Trp53-deficient mice. We therefore created mouse strains with different combinations of the Trp53 and iNOS genes. Western blot and histologic analyses showed that the iNOS protein was constitutively expressed in the thymus independently of Trp53 status and its expression was enhanced in Trp53+/- and Trp53-/- mice compared to Trp53+/+ mice. Homozygous disruption of iNOS decreased the incidence of thymic lymphomas by almost 40% (p=0.087) and 90% (p<0.05) in Trp53-/- and Trp53+/- mice, respectively, compared to the respective iNOS wild-type mice but significantly (p<0.05) increased the development of nonthymic lymphomas in Trp53-/- and Trp53+/- mice. Although iNOS gene disruption did not affect the phenotype of thymic lymphomas, absence of the iNOS gene shifted the spectrum of nonthymic lymphoma from the B-cell to the T-cell lineage. RT-PCR analysis revealed enhanced expression of IL-10, which could have a promoting effect on lymphomagenesis, even without any stimulation, in the spleen of aging mice with the gene combinations Trp53-/-iNOS-/- and Trp53+/-iNOS-/- but not Trp53-/-iNOS+/+ or Trp53+/-iNOS+/+. These results suggest that iNOS could increase the development of thymic lymphomas in Trp53-deficient mice. While iNOS may have protective effects against nonthymic lymphomagenesis, the regulation of cytokine production by iNOS may be involved in the underlying mechanism of antilymphomagenesis effects in the peripheral lymphoid organ.

Life-long reduction in MnSOD activity results in increased DNA damage and higher incidence of cancer but does not accelerate aging

Mice heterozygous for the Sod2 gene (Sod2+/- mice) have been used to study the phenotype of life-long reduced Mn-superoxide dismutase (MnSOD) activity. The Sod2+/- mice have reduced MnSOD activity (50%) in all tissues throughout life. The Sod2+/- mice have increased oxidative damage as demonstrated by significantly elevated levels of 8-oxo-2-deoxyguanosine (8oxodG) in nuclear DNA in all tissues of Sod2+/- mice studied. The levels of 8oxodG in nuclear DNA increased with age in all tissues of Sod2+/- and wild-type (WT) mice, and at 26 mo of age, the levels of 8oxodG in nuclear DNA were significantly higher (from 15% in heart to over 60% in liver) in the Sod2+/- mice compared with WT mice. The level of 8oxodG was also higher in mitochondrial DNA isolated from liver and brain in Sod2+/- mice compared with WT mice. The increased oxidative damage to DNA in the Sod2+/- mice is associated with a 100% increase in tumor incidence (the number of mice with tumors) in old Sod2+/- mice compared with the old WT mice. However, the life spans (mean and maximum survival) of the Sod2+/- and WT mice were identical. In addition, biomarkers of aging, such as cataract formation, immune response, and formation of glycoxidation products carboxymethyl lysine and pentosidine in skin collagen changed with age to the same extent in both WT and Sod2+/- mice. Thus life-long reduction of MnSOD activity leads to increased levels of oxidative damage to DNA and increased cancer incidence but does not appear to affect aging.

Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake

Dietary restriction has been shown to have several health benefits including increased insulin sensitivity, stress resistance, reduced morbidity, and increased life span. The mechanism remains unknown, but the need for a long-term reduction in caloric intake to achieve these benefits has been assumed. We report that when C57BL6 mice are maintained on an intermittent fasting (alternate-day fasting) dietary-restriction regimen their overall food intake is not decreased and their body weight is maintained. Nevertheless, intermittent fasting resulted in beneficial effects that met or exceeded those of caloric restriction including reduced serum glucose and insulin levels and increased resistance of neurons in the brain to excitotoxic stress. Intermittent fasting therefore has beneficial effects on glucose regulation and neuronal resistance to injury in these mice that are independent of caloric intake.

Histiocytic sarcoma in C57BL/6J female mice is associated with liver hematopoiesis: review of 41 cases

Forty-one cases of histiocytic sarcoma (HS) in C57BL/6J mice were histopathologically studied with special regard to unexpected associated hematopoietic disorders. These cases were retrieved among C57BL/6J female mice used as control mice in a chronic low-dose irradiation experiment. Hematopoietic characteristics were analysed by comparison to 41 disease-free mice from the same cohort. Tumoral involvement of the liver was observed in all 41 HS-bearing mice, followed by infiltration of the spleen (61.8%), lung (32.4%), bone marrow (14.3%), uterus (12.2%), lymph node (9.8%), and kidney (2.4%). By comparative analysis, we were able to demonstrate a significant association of HS with liver hematopoiesis (89.5% in HS group vs 15% in control mice, p < 0.00001), and with central hematopoietic disorders involving the myelocytic cells (decreased in HS, p = 0.003) and erythrocytic cells (increased in HS, p = 0.001). Microscopic characteristics of these 41 cases and physiopathology of the newly described hematopoietic features in HS are further discussed.

High incidence of epithelial cancers in mice deficient for DNA polymerase delta proofreading

Mutations are a hallmark of cancer. Normal cells minimize spontaneous mutations through the combined actions of polymerase base selectivity, 3' --> 5' exonucleolytic proofreading, mismatch correction, and DNA damage repair. To determine the consequences of defective proofreading in mammals, we created mice with a point mutation (D400A) in the proofreading domain of DNA polymerase delta (poldelta, encoded by the Pold1 gene). We show that this mutation inactivates the 3' --> 5' exonuclease of poldelta and causes a mutator and cancer phenotype in a recessive manner. By 18 months of age, 94% of homozygous Pold1(D400A/D400A) mice developed cancer and died (median survival = 10 months). In contrast, only 3-4% of Pold1(+/D400A) and Pold1(+/+) mice developed cancer in this time frame. Of the 66 tumors arising in 49 Pold1(D400A/D400A) mice, 40 were epithelial in origin (carcinomas), 24 were mesenchymal (lymphomas and sarcomas), and two were composite (teratomas); one-third of these animals developed tumors in more than one tissue. Skin squamous cell carcinoma was the most common tumor type, occurring in 60% of all Pold1(D400A/D400A) mice and in 90% of those surviving beyond 8 months of age. These data show that poldelta proofreading suppresses spontaneous tumor development and strongly suggest that unrepaired DNA polymerase errors contribute to carcinogenesis. Mice deficient in poldelta proofreading provide a tractable model to study mechanisms of epithelial tumorigenesis initiated by a mutator phenotype.

Survival characteristics and age-adjusted disease incidences in C57BL/6 mice fed a commonly used cereal-based diet modulated by dietary restriction

Studies of C57BL/6 mice are often restricted to one sex, with limited characterization of pathology as a function of age. As part of the National Institute on Aging/National Center for Toxicological Research Collaboration on Biomarkers, over 3000 males and 1500 females of this strain were raised, maintained, and used to evaluate longevity under specific pathogen-free conditions. A diet commonly used in testing the impact of agents was fed ad libitum or was restricted to 60% of normal consumption, starting when the mice were 14-16 weeks of age. Cardiac, renal, and central nervous system pathologies were significantly inhibited by dietary restriction (DR), as were bone degeneration, inflammation, hyperplasia, amyloid induction, and atrophy of secretory organs. Hematological disorders and tumors were among the most common problem in this strain, and they were ameliorated by DR. In males, for other neoplasms, adrenal adenomas, liver tumors, and hemangiomas combined with hemangiosarcomas were decreased by DR, variably in onset and progression. In females, DR decreased pituitary tumors, mammary tumors, and alveolar carcinomas, again variably in onset and progression.

Maternal methyl supplements in mice affect epigenetic variation and DNA methylation of offspring

This study was designed to determine if maternal dietary methyl supplements increase DNA methylation and methylation-dependent epigenetic phenotypes in mammalian offspring. Female mice of two strains were fed two levels of dietary methyl supplement or control diet prior to and during pregnancy. Offspring of these mice vary in phenotype, which is epigenetically determined and affects health and 2-y survival. Phenotype and DNA methylation of a long terminal repeat (LTR) controlling expression of the agouti gene were assayed in the resulting offspring. Methyl supplements increase the level of DNA methylation in the agouti LTR and change the phenotype of offspring in the healthy, longer-lived direction. This shows that methyl supplements have strong effects on DNA methylation and phenotype and are likely to affect long-term health. Optimum dietary supplements for the health and longevity of offspring should be intensively investigated. This should lead to public policy guidance that teaches optimal, rather than minimal, dose levels of maternal supplements.

Middle-aged C57BL/6 mice have impaired responses to leptin that are not improved by calorie restriction

Midlife weight gain occurs in many species, suggesting that leptin signaling is impaired at middle age. To test this hypothesis, we measured changes in food intake and body composition in young (Y) and middle-aged (MA) C57BL/6 male mice infused subcutaneously with phosphate-buffered saline or leptin. Leptin-induced decreases in food intake and body fat were delayed in MA mice and associated with catabolism after longer treatment periods. Endogenous plasma leptin levels did not correlate with body fat in MA mice. Calorie restriction (CR) reduced body fat, plasma leptin, and insulin in MA mice to levels in Y mice but did not upregulate leptin sensitivity. CR mice did not respond to leptin doses that inhibited food intake in MA mice and reduced food intake and body fat in Y mice significantly below levels in CR mice. Plasma corticosterone was significantly higher in leptin-treated CR vs. MA mice. We conclude that MA C57BL/6 mice exhibit impaired leptin signaling and that CR, possibly by elevating glucocorticoids, impairs appetite control without improving the metabolic actions of leptin.

Pathology of aging B6;129 mice

Fifty male and 49 female B6;129 mice (wild-type, +/+) were maintained until 2 years of age to study their age-related pathology. By 104-105 weeks, 14/50 (28%) of the males and 30/49 (61%) of the females were still alive. The most common contributing cause of morbidity or mortality was lymphoma. Lymphoma was observed in 21/50 (42%) of the males and 33/49 (67%) of the females with the most common sites being mesenteric lymph nodes, gut associated lymphoid tissue (Peyer's patches), and spleen. The lymphoma most often appeared to arise in the mesenteric node. Immunohistochemistry revealed CD45R expression as well as infiltration by many CD3+ T cells. IgH gene rearrangements were found in typical mesenteric node lymphomas indicating B-cell origin. They bore similarities to the human T-cell rich, B-cell lymphomas. Other tumors included hepatocellular adenoma or carcinoma (male 12%, females 10%), lung alveolar Type II cell adenoma or carcinoma (male 32%, female 20%), thyroid follicular adenoma or carcinoma (male 2%, female 8%), ovarian tumors (17%), and endometrial tumors (6%). Nonneoplastic lesions included amyloid-like material in the nasal septum (male and female 100%), otitis media (male 84%, female 79%), epididymal epithelial karyomegaly (88%), melanosis (high incidences in various tissues including brain, parathyroid, and spleen), membranoproliferative glomerulonephritis (male 52%, female 71%), hyalinosis with extracellular crystals in several tissues (respiratory tract, gall bladder, stomach), islet cell hyperplasia (male 45%, female 29%) and esophageal dilation (male 10%, female 6%). The B6;129 mouse is a mouse with aging lesions similar to those in other mouse strains but with a characteristic common lymphoma.

Dietary restriction attenuates the neuronal loss, induction of heme oxygenase-1 and blood-brain barrier breakdown induced by impaired oxidative metabolism

Experimental thiamine deficiency (TD) is a model of impaired oxidative metabolism associated with region-selective neuronal loss in the brain. Oxidative stress is a prominent feature of TD neuropathology, as evidenced by the accumulation of heme oxygenase-1 (HO-1), ferritin, reactive iron and superoxide dismutase in microglia, nitrotyrosine and 4-hydroxynonenal in neurons, as well as induction of endothelial nitric oxide synthase within the vulnerable areas. Dietary restriction (DR) reduces oxidative stress in several organ systems including the brain. DR increases lifespan and reduces neurodegeneration in a variety of models of neuronal injury. The possibility that DR can protect vulnerable neurons against TD-induced oxidative insults has not been tested. The current studies tested whether approximately 3 months of DR (60% of ad libitum intake) altered the response to TD. Six month-old ad libitum-fed or dietary restricted C57BL/6 mice received a thiamine-deficient diet either ad libitum, or under a DR regimen respectively for eleven days. The TD mice also received daily injections of the thiamine antagonist pyrithiamine. Control ad libitum-fed or DR mice received an unlimited amount, or 60% of ad libitum intake, respectively, of thiamine-supplemented diet. As in past studies, TD produced region-selective neuronal loss (-60%), HO-1 induction, and IgG extravasation in the thalamus of ad libitum-fed mice. DR attenuated the TD-induced neuronal loss (-30%), HO-1 induction and IgG extravasation in the thalamus. These studies suggest that oxidative damage is critical to the pathogenesis of TD, and that DR modulates the extent of free radical damage in the brain. Thus, TD is an important model for studying the relationship between aging, oxidative stress and nutrition.

Reversible effects of long-term caloric restriction on protein oxidative damage

The age-associated increase in oxidative damage in ad libitum-fed mice is attenuated in mice fed calorically restricted (CR) diets. The objective of this study was to determine if this effect results from a slowing of age-related accumulation of oxidative damage, or from a reversible decrease of oxidative damage by caloric restriction. To address these possibilities, crossover studies were conducted in C57BL/6 mice aged 15 to 22 months that had been maintained, after 4 months of age, on ad libitum (AL) or a 60% of AL caloric regimen. One half of the mice in these groups were switched to the opposite regimen of caloric intake for periods up to 6 weeks, and protein oxidative damage (measured as carbonyl concentration and loss of sulfhydryl content) was measured in homogenates of brain and heart. In AL-fed mice, the protein carbonyl content increased with age, whereas the sulfhydryl content decreased. Old mice maintained continuously under CR had reduced levels of protein oxidative damage when compared with the old mice fed AL. The effects of chronic CR on the carbonyl content of the whole brain and the sulfhydryl content of the heart were fully reversible within 3-6 weeks following reinstatement of AL feeding. The effect of chronic CR on the sulfhydryl content of the brain cortex was only partially reversible. The introduction of CR for 6 weeks in the old mice resulted in a reduction of protein oxidative damage (as indicated by whole brain carbonyl content and cortex sulfhydryl), although this effect was not equivalent to that of CR from 4 months of age. The introduction of CR did not affect the sulfhydryl content of the heart. Overall, the current findings indicate that changes in the level of caloric intake may reversibly affect the concentration of oxidized proteins and sufhydryl content. In addition, chronic restriction of caloric intake also retards the age-associated accumulation of oxidative damage. The magnitude of the reversible and chronic effects appears to be dependent upon the tissue examined and the nature of the oxidative alteration.

Age- and disease-related decline in immune function: an opportunity for "thymus-boosting" therapies

The thymus is the site of production of mature T lymphocytes and thus is indispensable for the development and maintenance of the T cell-mediated arm of the immune system. Thymic production of mature T cells is critically dependent on an influx of bone marrow-derived progenitor T cells that undergo replication and selection within the thymus. Thymus cellularity and thymic hormone secretion reach a peak during the first year of life and then decline gradually until the age of 50-60 years, a process known as "thymic involution." A rapid reduction of thymus cellularity occurs in young patients following injuries, chemotherapy, and other forms of stress. The mechanisms underlying the involution process appear to be dependent on factors intrinsic to the thymic tissue, such as the local production of cytokines and chemoattractants, promoting the recruitment, growth, and differentiation of bone marrow-derived T cell progenitors in the thymus, as well as extrinsic factors, such as systemic levels of endocrine hormones and mediators released by intrathymic nerves of the autonomic nervous system. Knowledge of these factors provides a rational basis for the development of an approach based on tissue engineering that could be used to provide either temporary or permanent reconstitution of thymic function.

Effect of age and caloric restriction on bleomycin-chelatable and nonheme iron in different tissues of C57BL/6 mice

The objective of this study was to test the hypothesis that the widely observed age-associated increase in the amounts of macromolecular oxidative damage is due to an elevation in the availability of redox-active iron, that is believed to catalyze the scission of H2O2 to generate the highly reactive hydroxyl radical. Concentrations of bleomycin-chelatable iron and nonheme iron were measured in various tissues and different regions of the brain of mice fed on ad libitum (AL) or a calorically restricted (to 60% of AL) diet at different ages. The concentrations of these two pools of iron varied markedly as a function of tissue, age, and caloric intake. There was no consistent ratio between the amounts of nonheme and the bleomycin-chelatable iron pools across these conditions. Nonheme iron concentration increased with age in the liver, kidney, heart, striatum, hippocampus, midbrain and cerebellum of AL animals, whereas bleomycin-chelatable iron increased significantly with age only in the liver. Amounts of both nonheme and bleomycin-chelatable iron remained unaltered during aging in the cerebral cortex and hindbrain of AL mice. Caloric restriction had no effect on iron concentration in the brain or heart, but caused a marked increase in the concentration of both bleomycin-chelatable and nonheme iron in the liver and the kidney. The results do not support the hypothesis that accumulation of oxidative damage with age, or its attenuation by CR, are associated with corresponding variations in redox-active iron.

Controlling caloric consumption: protocols for rodents and rhesus monkeys

One approach for investigating biological aging is to compare control-fed animals with others restricted in calorie intake by 20% or more. Caloric restriction (CR) is the only intervention shown to extend the maximum lifespan of several invertebrates and vertebrates including spiders, fish, rats and mice. The capacity of CR to retard aging in nonhuman primates is now being explored. The rodent studies show that CR opposes the development of many age-associated pathophysiological changes, including changes to the brain and changes in learning and behavior. One goal of studying CR in rodent is to determine the mechanisms by which it retards aging to design interventions that duplicate those effects. The methods that we use for conducting CR studies on mice and rhesus monkeys are described. We employ procedures designed to achieve a high degree of caloric control for all animals in the study. As used in our studies, this control includes the following features: 1) animals are individually housed, and 2) all individuals in the control group eat the same number of calories (i.e., they are not fed ad lib). Although this method results in strict caloric control for all animals, there seems to be considerable procedural flexibility for the successful conduct of CR studies.

Estimating age-related changes in psychomotor function: influence of practice and of level of caloric intake in different genotypes

This article presents a discussion of some key considerations in the measurement of age-related changes in psychomotor function of mice. We illustrate that "standard" measures of psychomotor performance, such as running speed on a rotorod task, are highly sensitive to practice effects. Examples are cited in which failure to assess practice effects can influence conclusions regarding the magnitude and rate of change in psychomotor capacity as a function of age. A second set of examples is focused on estimating the effect of an experimental intervention, caloric restriction, on age-related changes in psychomotor performance. These examples show that psychomotor performance at a given age may vary directly, and reversibly, with the level of caloric intake. Independent of such reversible effects, the level of caloric intake can also modulate the rate of change in capacity as a function of age. It is concluded that reversible, short-term effects must be considered in estimating the effect of an experimental intervention on the rate of age-associated change in psychomotor function.

Caloric restriction prevents age-associated accrual of oxidative damage to mouse skeletal muscle mitochondria

The purpose of this study was to understand the nature of the causes underlying the senescence-related decline in skeletal muscle mass and performance. Protein and lipid oxidative damage to upper hindlimb skeletal muscle mitochondria was compared between mice fed ad libitum and those restricted to 40% fewer calories--a regimen that increases life span by approximately 30-40% and attenuates the senescence-associated decrement in skeletal muscle mass and function. Oxidative damage to mitochondrial proteins, measured as amounts of protein carbonyls and loss of protein sulfhydryl content, and to mitochondrial lipids, determined as concentration of thiobarbituric acid reactive substances, significantly increased with age in the ad libitum-fed (AL) C57BL/6 mice. The rate of superoxide anion radical generation by submitochondrial particles increased whereas the activities of antioxidative enzymes superoxide dismutase, catalase, and glutathione peroxidase in muscle homogenates remained unaltered with age in the AL group. In calorically-restricted (CR) mice there was no age-associated increase in mitochondrial protein or lipid oxidative damage, or in superoxide anion radical generation. Crossover studies, involving the transfer of 18- to 22-month-old mice fed on the AL regimen to the CR regimen, and vice versa, indicated that the mitochondrial oxidative damage could not be reversed by CR or induced by AL feeding within a time frame of 6 weeks. Results of this study indicate that mitochondria in skeletal muscles accumulate significant amounts of oxidative damage during aging. Although such damage is largely irreversible, it can be prevented by restriction of caloric intake.

Influences of caloric restriction on age-associated skeletal muscle fiber characteristics and mitochondrial changes in rats and mice

The effect of caloric restriction (CR) initiated in adult rats (17 months of age) on the abundance of deleted mitochondrial genomes, mitochondrial enzymatic abnormalities, and fiber number was examined in rat skeletal muscle. Vastus lateralis muscle from young (3-4 months) ad libitum-fed, old (30-32 months) restricted (35% and 50% CR, designated CR35 and CR50, respectively), and old ad libitum-fed rats (29 months) was studied. CR preserved fiber number and fiber-type composition in the CR50 rats. In the old rats from all groups, individual fibers were found with either no detectable cytochrome-c oxidase activity (COX-), hyperactive for succinate dehydrogenase activity (SDH++), or both COX- and SDH++. Muscle from the CR50 rats contained significantly fewer COX- and SDH++ fibers than did the muscle from the CR35 rats. CR50 rats also had significantly lower numbers of mtDNA deletion products in two (adductor longus and soleus) of the four muscles examined compared to CR35 rats. These data indicate that CR begun in late middle age can retard age-associated fiber loss and fiber-type changes as well as lower the number of skeletal muscle fibers exhibiting mitochondrial enzyme abnormalities. CR can also decrease the accumulation of deleted mitochondrial genomes.

Altered alveolar macrophage function in calorie-restricted rats

Alveolar macrophage functions associated with clearance of bacteria from the lung were assessed in male Fischer 344 rats maintained on a 25% calorie-restricted diet. Calorie-restricted and ad libitum-fed (control) rats were exposed to concentrations of ozone known to compromise phagocytic function of alveolar macrophages. Ozone suppressed alveolar macrophage phagocytosis of latex beads in vitro in ad libitum-fed rats, but not in calorie-restricted rats. In fact, caloric restriction enhanced phagocytic function in both control and ozone-exposed animals. Ad libitum-fed rats exposed to ozone and challenged with Streptococcus zooepidemicus experienced a prolonged infection and influx of polymorphonuclear leukocytes (PMN), whereas calorie-restricted rats exposed to ozone cleared the bacteria in 24 h without an inflammatory response. Bacterial endotoxin-stimulated in vitro production of nitric oxide and tumor necrosis factor (TNF)-alpha as well as expression of TNF-alpha and interleukin-6 messenger RNAs were all lower in alveolar macrophages isolated from calorie-restricted rats. Together, the data suggest that caloric restriction enhances resistance to gram-positive bacteria, while lowering the production of proinflammatory mediators elicited by endotoxin, a component of gram-negative bacteria. Although increased bacterial resistance is considered beneficial, reduction in the lung's ability to induce inflammatory mediators can have both positive and pathophysiologic consequences.

D-glucose combined chronic toxicity and carcinogenicity studies in Sprague-Dawley rats and Syrian golden hamsters

After an initial period of 16 weeks with increasing concentrations, D-glucose was administered at 30% in the diet to 50 male and 50 female Sprague-Dawley rats from the 17th to the 112th study week. Additional 10 male and 10 female animals were treated for 14 months and then sacrificed for interim examination. Groups of 60 male and 60 female Syrian golden hamsters received D-glucose in the form of 20% solution in tap water for a period of 80 weeks. In each case, groups consisting of an equal number of untreated animals served as controls. General behavior and mortality were not affected by the treatment. The rats and hamsters treated with glucose showed significantly higher body weights of up to a maximum of 16% in male and 26% in female rats, or 15% in male and female hamsters. In rats, the increase was evident by week 14, and in the hamsters by week 10. Glucose-dosed rats displayed a slightly increased feed intake and a reduced water intake. Both parameters, however, were not influenced in hamsters. Hematological and histopathological examination showed no pertinent changes in hematopoetic tissue. Sharply increased blood glucose and renal glucose excretion values were present in rats beginning with 18 months and were indicative of the development of non-insulin-dependent diabetes mellitus (NIDDM). The insulin concentrations in peripheral blood were not appreciably affected, although there was a trend to higher values in males at all evaluation times and in females only at 3 months. Pathological evaluation did not show any compound related non-neoplastic lesions. The incidences of islet cell adenomas in the pancreas of male rats were significantly increased and the cortical adenomas in the adrenals of females were decreased. In addition, the mammary gland adenomas (in females) and the Leydig cell tumors of the testes were decreased. In hamsters, the incidence of adrenocortical adenomas were increased in the females. No other pertinent neoplastic changes were observed. In conclusion, the increases and decreases in benign neoplasms of hormone-sensitive tissues, appear to be the result of nutritionally/metabolism-induced modulation of the homeostasis in these 4 tissues in both species, and not the result of chronic glucose administration.

Effect of dietary optimization on growth, survival, tumor incidences and clinical pathology parameters in CD Sprague-Dawley and Fischer-344 rats: a 104-week study

Controversy regarding the use of ad libitum feeding in chronic rodent toxicity studies will soon result in issue of a FDA Points to Consider document. Caloric intakes are now recognized to be important uncontrolled variables in bioassays because rodents chronically fed ad libitum become obese, reproductively senile and have increased incidences of age-related diseases, higher tumor burdens and decreased survival. The available literature suggests that ad libitum feeding neither optimizes the health and well-being of rodents nor provides the best model for use in evaluation of pharmacological and toxicological profiles. Use of an optimized diet, restricted in terms of caloric intakes, has been proposed for chronic toxicity and carcinogenicity studies in rodents. It is suggested that limiting caloric intakes to 50-80% of ad libitum consumption would result in lower body weights, decreased tumor incidences and prolonged survival in the controls. To evaluate the influence of diet on chronic toxicity and carcinogenicity studies in rats, two 104-week studies were conducted. These studies consisted of 280 CD Sprague-Dawley and 280 Fischer-344 rats fed ad libitum, and 140 CD Sprague-Dawley and 140 Fischer-344 rats fed a diet that was optimized by limiting caloric intakes by 15-35%. Both diets consisted of certified commercial diet in meal form. The optimized diet reduced weight gain approximately 50% after 100 weeks. Clinical chemistry and hematology parameters showed negligible effects of reduced diet, with the exception that serum triglycerides were lower in males and females in both strains at weeks 52 and 104. The ad libitum-fed animals had a higher incidence of pseudopregnancy, aggressiveness, foot sores and abscesses than the animals fed an optimized diet. These effects were more pronounced in the CD Sprague-Dawley rats than in the Fischer-344 rats. At the completion of the 104-week study, survival in the ad libitum fed CD Sprague-Dawley rats was approximately one-half that of the animals fed an optimized diet (39% versus 76%). The difference in survival between Fischer-344 rats fed ad libitum and those fed an optimized diet was less pronounced (78% versus 89%). A reduced incidence of palpable tissue masses in the ad libitum-fed CD Sprague-Dawley rats versus the animals fed an optimized diet reflected inability to detect small masses in the obese ad libitum-fed animals. In contrast, the leaner Fischer-344 ad libitum-fed animals had an increased incidence of palpable tissue masses. After 52 weeks, 40 animals from each strain and feeding regimen were killed and subjected to complete necropsy and histopathological examination; the remainder of the survivors was examined at the completion of the study (104 weeks). Use of an optimized diet substantially reduced the incidences of endocrine-mediated tumors in both rat strains and delayed the onset of leukemia in Fischer-344 rats. These results indicate the need to further investigate the relationship of increased caloric intakes and endocrine-mediated or strain specific tumors and support FDA's and others' positions that use of diet optimization in chronic toxicity and carcinogenicity rodent bioassays has the potential to remarkably improve the scientific quality and relevance of these studies. It also identified that the small increases in cost associated with diet optimization are far exceeded by the advantages of increased survival of animals, reduced intercurrent disease and rumor burdens, and increased ease of histopathological processing and evaluation.

Murine models of brain aging and age-related neurodegenerative diseases

In the past, structural changes in the brain with aging have been studied using a variety of animal models, with rats and nonhuman primates being the most popular. With the rapid evolution of mouse genetics, murine models have gained increased attention in the neurobiology of aging. The genetic contribution of age-related traits as well as specific mechanistic hypotheses underlying brain aging and age-related neurodegenerative diseases can now be assessed by using genetically-selected and genetically-manipulated mice. Against this background of increased demand for aging research in mouse models, relatively few studies have examined structural alterations with aging in the normal mouse brain, and the data available are almost exclusively restricted to the C57BL/6 strain. Moreover, many older studies have used quantitative techniques which today can be questioned regarding their accuracy. Here we review the state of knowledge about structural changes with aging in outbred, inbred, genetically-selected, and genetically-engineered murine models. Moreover, we suggest several new opportunities that are emerging to study brain aging and age-related neurodegenerative diseases using genetically-defined mouse models. By reviewing the literature, it has become clear to us that in light of the rapid progress in genetically-engineered and selected mouse models for brain aging and age-related neurodegenerative diseases, there is a great and urgent need to study and define morphological changes in the aging brain of normal inbred mice and to analyze the structural changes in genetically-engineered mice more carefully and completely than accomplished to date. Such investigations will broaden knowledge in the neurobiology of aging, particularly regarding the genetics of aging, and possibly identify the most useful murine models.

Anti-ageing effect of aged garlic extract in the inbred brain atrophy mouse model

1. The effects of chronically administered aged garlic extract (AGE) on the age-related changes in a novel strain of senescence accelerated mouse (SAM) characterized by age-related brain atrophy (SAMP10) were investigated. 2. A solid diet containing 2% (w/w) AGE was given to SAM from 2 months of age. 3. The grading score of senescence in SAMP10 at 10 months of age was significantly higher than that of SAMR1, a reference strain for SAMP10. 4. Administration of AGE prevented the increase in the grading score of SAMP10 and SAMR1. 5. In behavioural evaluation, AGE improved learning and memory deficits of SAMP10 in both the passive and conditioned avoidance tests as well as the spatial memory test. 6. Treatment with AGE in SAMP10 prevented the decrease in brain weight and the atrophic changes in frontal brain at 12 months of age. 7. These results raise the possibility that AGE prevents physiological ageing and may be beneficial for age-related cognitive disorders in humans.