The effects of hypophysectomy and continuous food restriction, begun at ages 70 and 400 days, on collagen aging, proteinuria, incidence of pathology and longevity in the male rat

An integrated approach to investigate age-related modifications of morphological, mechanical and structural properties of type I collagen

The main propose of this study is to characterize the impact of chronological aging on mechanical, structural, biochemical, and morphological properties of type I collagen. We have developed an original approach combining a stress-strain measurement device with a portable Raman spectrometer to enable simultaneous measurement of Raman spectra during stress vs strain responses of young adult, adult and old rat tail tendon fascicles (RTTFs). Our data showed an increase in all mechanical properties such as Young's modulus, yield strength, and ultimate tensile strength with aging. At the molecular level, Raman data revealed that the most relevant frequency shift was observed at 938 cm^-1 in Old RTTFs, which is assigned to the C-C. This suggested a long axis deformation of the peptide chains in Old RTTFs during tensile stress. In addition, the intensity of the band at 872 cm^-1, corresponding to hydroxyproline decreased for young adult RTTFs and increased for the adult ones, while it remained unchanged for Old RTTFs during tensile stress. The amide III band (1242 and 1265 cm^-1) as well as the band ratios I₁₆₃₁/ I₁₆₆₃ and I₁₆₄₅ / I₁₆₆₃ responses to tensile stress were depending on mechanical phases (toe, elastic and plastic). The quantification of advanced glycation end-products by LC-MS/MS and spectrofluorometry showed an increase in their content with aging. This suggested that the accumulation of such products was correlated to the alterations observed in the mechanical and molecular properties of RTTFs. Analysis of the morphological properties of RTTFs by SHG combined with CT-FIRE software revealed an increase in length and straightness of collagen fibers, whereas their width and wavy fraction decreased. Our integrated study model could be useful to provide additional translational information to monitor progression of diseases related to collagen remodeling in musculoskeletal disorders. STATEMENT OF SIGNIFICANCE: Type I collagen is the major component of the extracellular matrix. Its architectural and structural organization plays an important role in the mechanical properties of many tissues at the physiological and pathological levels. The objective of this work is to develop an integrated approach to bring a new insight on the impact of chronological aging on the structural organization and mechanical properties of type I collagen. We combined a portable Raman spectrometer with a mechanical tensile testing device in order to monitor in real time the changes in the Raman fingerprint of type I collagen fibers during the mechanical stress. Raman spectroscopy allowed the identification of the type I collagen bonds that were affected by mechanical stress in a differential manner with aging.

Bring Back the Rat!

As 2020 is "The Year of the Rat" in the Chinese astrological calendar, it seems an appropriate time to consider whether we should bring back the laboratory rat to front-and-center in research on the basic biology of mammalian aging. Beginning in the 1970s, aging research with rats became common, peaking in 1992 but then declined dramatically by 2018 as the mouse became preeminent. The purpose of this review is to highlight some of the historical contributions as well as current advantages of the rat as a mammalian model of human aging, because we suspect at least a generation of researchers is no longer aware of this history or these advantages. Herein, we compare and contrast the mouse and rat in the context of several biological domains relevant to their use as appropriate models of aging: phylogeny/domestication, longevity interventions, pathology/physiology, and behavior/cognition. It is not the goal of this review to give a complete characterization of the differences between mice and rats, but to provide important examples of why using rats as well as mice is important to advance our understanding of the biology of aging.

Aging and aging-associated diseases: a microRNA-based endocrine regulation hypothesis

Although there are numerous hypotheses explaining the nature of aging and associated processes, two concepts are dominant: (i) aging is a result of cell-autonomous processes, such as the accumulation of DNA mutations, aberrant methylations, protein defects, and shortening of telomeres, leading to either inhibition of cellular proliferation and death of non-dividing terminally differentiated cells or tumor development; (ii) aging is a result of a central program that is switched on at a specific stage of organismic development. The microRNA-based endocrine regulation hypothesis combines the two above concepts by proposing central regulation of cell death occurrences via hypothalamus-pituitary gland (PG)-secreted miRNA hormones, the expression and/or secretion of which are regulated by sex hormones. This hypothesis explains such well-known phenomena as inverse comorbidity of either cancer or Alzheimer’s (AD) and other neurodegenerative diseases; higher AD morbidity and lower frequency of many common types of cancer in women vs. men; higher risk of early AD and lower risk of cancer in subjects with Down syndrome; longer life expectancy in women vs. men and much lower sex-dependent differences, if any, in other mammals; increased lifespans due to hypophysectomy or PG hypofunction; and parabiotic effects of blood or plasma transfusions between young and old animals.

The mechanical and biochemical properties of tail tendon in a rat model of obesity: Effect of moderate exercise and prebiotic fibre supplementation

The worldwide trajectory of increasing obesity rates is a major health problem precipitating a rise in the prevalence of a variety of co-morbidities and chronic diseases. Tendinopathy, in weight and non-weight bearing tendons, in individuals with overweight or obesity has been linked to metabolic dysfunction resulting from obesity. Exercise and dietary fibre supplementation (DFS) are common countermeasures to combat obesity and therefore it seems reasonable to assume that they might protect tendons from structural and mechanical damage in a diet-induced obesity (DIO) model. The purpose of this study was to determine the effects of a DIO, DIO combined with moderate exercise, DIO combined with DFS (prebiotic oligofructose), and DIO combined with moderate exercise and DFS on the mechanical and biochemical properties of the rat tail tendon. Twenty-four male Sprague-Dawley rats, fed a high-fat/high-sucrose diet were randomized into a sedentary, a moderate exercise, a DFS, or a moderate exercise combined with DFS group for 12 weeks. Additionally, six lean age-matched animals were included as a sedentary control group. DIO in combination with exercise alone and with exercise and DFS reduced the Young's Modulus but not the collagen content of the rat tail tendons compared to lean control animals. However, no differences in the mechanical and biochemical properties of the rat tail tendon were detected between the DIO and the lean control group, suggesting that DIO by itself did not impact the tail tendon. It seems that longer DIO exposure periods may be needed to develop overt differences in our DIO model.

Animal models of aging research: implications for human aging and age-related diseases

Aging is characterized by an increasing morbidity and functional decline that eventually results in the death of an organism. Aging is the largest risk factor for numerous human diseases, and understanding the aging process may thereby facilitate the development of new treatments for age-associated diseases. The use of humans in aging research is complicated by many factors, including ethical issues; environmental and social factors; and perhaps most importantly, their long natural life span. Although cellular models of human disease provide valuable mechanistic information, they are limited in that they may not replicate the in vivo biology. Almost all organisms age, and thus animal models can be useful for studying aging. Herein, we review some of the major models currently used in aging research and discuss their benefits and pitfalls, including interventions known to extend life span and health span. Finally, we conclude by discussing the future of animal models in aging research.

The somatotropic axis and longevity in mice

The somatotropic signaling pathway has been implicated in aging and longevity studies in mice and other species. The physiology and lifespans of a variety of mutant mice, both spontaneous and genetically engineered, have contributed to our current understanding of the role of growth hormone and insulin-like growth factor I on aging-related processes. Several other mice discovered to live longer than their wild-type control counterparts also exhibit differences in growth factor levels; however, the complex nature of the phenotypic changes in these animals may also impact lifespan. The somatotropic axis impacts several pathways that dictate insulin sensitivity, nutrient sensing, mitochondrial function, and stress resistance as well as others that are thought to be involved in lifespan regulation.

Growth hormone action predicts age-related white adipose tissue dysfunction and senescent cell burden in mice

The aging process is associated with the development of several chronic diseases. White adipose tissue (WAT) may play a central role in age-related disease onset and progression due to declines in adipogenesis with advancing age. Recent reports indicate that the accumulation of senescent progenitor cells may be involved in age-related WAT dysfunction. Growth hormone (GH) action has profound effects on adiposity and metabolism and is known to influence lifespan. In the present study we tested the hypothesis that GH activity would predict age-related WAT dysfunction and accumulation of senescent cells. We found that long-lived GH-deficient and -resistant mice have reduced age-related lipid redistribution. Primary preadipocytes from GH-resistant mice also were found to have greater differentiation capacity at 20 months of age when compared to controls. GH activity was also found to be positively associated with senescent cell accumulation in WAT. Our results demonstrate an association between GH activity, age-related WAT dysfunction, and WAT senescent cell accumulation in mice. Further studies are needed to determine if GH is directly inducing cellular senescence in WAT or if GH actions on other target organs or alternative downstream alterations in insulin-like growth factor-1, insulin or glucose levels are responsible.

Somatotropic signaling: trade-offs between growth, reproductive development, and longevity

Growth hormone (GH) is a key determinant of postnatal growth and plays an important role in the control of metabolism and body composition. Surprisingly, deficiency in GH signaling delays aging and remarkably extends longevity in laboratory mice. In GH-deficient and GH-resistant animals, the "healthspan" is also extended with delays in cognitive decline and in the onset of age-related disease. The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast. The combination of reduced GH, IGF-I, and insulin signaling likely contributes to extended longevity in GH or GH receptor-deficient organisms. Diminutive body size and reduced fecundity of GH-deficient and GH-resistant mice can be viewed as trade-offs for extended longevity. Mechanisms responsible for delayed aging of GH-related mutants include enhanced stress resistance and xenobiotic metabolism, reduced inflammation, improved insulin signaling, and various metabolic adjustments. Pathological excess of GH reduces life expectancy in men as well as in mice, and GH resistance or deficiency provides protection from major age-related diseases, including diabetes and cancer, in both species. However, there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. Results obtained in GH-related mutant mice provide striking examples of mutations of a single gene delaying aging, reducing age-related disease, and extending lifespan in a mammal and providing novel experimental systems for the study of mechanisms of aging.

Hormonal control of aging in rodents: the somatotropic axis

There is a growing body of literature focusing on the somatotropic axis and regulation of aging and longevity. Many of these reports derive data from multiple endocrine mutants, those that exhibit both elevated growth hormone (GH) and insulin-like growth factor I (IGF-1) or deficiencies in one or both of these hormones. In general, both spontaneous and genetically engineered GH and IGF-1 deficiencies have lead to small body size, delayed development of sexual maturation and age-related pathology, and life span extension. In contrast, characteristics of high circulating GH included larger body sizes, early puberty and reproductive senescence, increased cancer incidence and reduced life span when compared to wild-type animals with normal plasma hormone concentrations. This information, along with that found in multiple other species, implicates this anabolic pathway as the major regulator of longevity in animals.

Endocrine alterations in response to calorie restriction in humans

This review focuses on research involving calorie restriction (CR) in humans and the resulting changes observed in endocrine and neuroendocrine systems. Special emphasis is given to the clinical science studies designed to investigate the effects of controlled, high-quality, energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases of human aging. Prolonged CR has been shown to extend both the median and maximal lifespan in a variety of lower species such as yeast, worms, fish, rats and mice. The biological mechanisms of this lifespan extension via CR are not fully elucidated, but possibly involve significant alterations in energy metabolism, oxidative damage, insulin sensitivity and functional changes in both neuroendocrine and autonomic nervous systems. Most of the difficulty in characterizing the systemic endocrine and neuroendocrine changes with aging and CR is due to the limited capability to collect large and multiple blood samples from small animals, which are usually shorter lived, and hence the most studied. Ongoing studies of prolonged CR in humans are now making it possible to analyze changes in the "biomarkers of aging" to unravel some of the mechanisms of its anti-aging phenomenon. With the incremental expansion of research endeavors in the area of energy restriction, data on the effects of CR in non-human primates and human subjects are becoming more accessible. Detailed analyses from controlled human trials involving long-term CR will allow investigators to link observed alterations from body composition and endocrine systems down to changes in molecular pathways and gene expression, with their possible effects on aging.

Hungry for life: How the arcuate nucleus and neuropeptide Y may play a critical role in mediating the benefits of calorie restriction

Laboratory studies consistently demonstrate extended lifespan in animals on calorie restriction (CR), where total caloric intake is reduced by 10-40% but adequate nutrition is otherwise maintained. CR has been further shown to delay the onset and severity of chronic diseases associated with aging such as cancer, and to extend the functional health span of important faculties like cognition. Less understood are the underlying mechanisms through which CR might act to induce such alterations. One theory postulates that CR's beneficial effects are intimately tied to the neuroendocrine response to low energy availability, of which the arcuate nucleus in the hypothalamus plays a pivotal role. Neuropeptide Y (NPY), a neurotransmitter in the front line of the arcuate response to low energy availability, is the primary hunger signal affected by CR and therefore may be a critical mechanism for lifespan extension.

Hormonal regulation of longevity in mammals

Multiple biological and environmental factors impact the life span of an organism. The endocrine system is a highly integrated physiological system in mammals that regulates metabolism, growth, reproduction, and response to stress, among other functions. As such, this pervasive entity has a major influence on aging and longevity. The growth hormone, insulin-like growth factor-1 and insulin pathways have been at the forefront of hormonal control of aging research in the last few years. Other hormones, including those from the thyroid and reproductive system have also been studied in terms of life span regulation. The relevance of these hormones to human longevity remains to be established, however the evidence from other species including yeast, nematodes, and flies suggest that evolutionarily well-conserved mechanisms are at play and the endocrine system is a key determinant.

Pituitary removal in adult mice increases life span

Dwarf mutations reduce levels of pituitary hormones and increase life span in mice. But because these dwarf mutations confer life-long hormone deficits that alter development and dramatically reduce fecundity, the relevance of these models to normal aging has been questioned. We examined effects of pituitary hormone withdrawal at different ages using hypophysectomy (surgical removal of the pituitary). Hypophysectomy at 1 month of age extended life span significantly (15%), but hypophysectomy at 9 months of age extended life span to the greatest magnitude (21%) of any age we tested. These results demonstrate pituitary hormone withdrawal can extend life span even if these hormones are removed relatively late in life.

Mid-life stress and cognitive deficits during early aging in rats: individual differences and hippocampal correlates

We explored here the possibility that mid-life stress in rats could have deleterious effects on cognitive abilities during early aging, as well as the potential role of inter-individual differences on the development of such effects. Male Wistar rats were classified according to their reactivity to novelty (4 months old) as highly (HR) or low (LR) reactive and, at mid-life (12 months old), either submitted to chronic stress (28 days) or left undisturbed. At early aging (18 months old), their learning abilities were tested in the water maze, and a number of neuroendocrine (plasma corticosterone; hippocampal corticosteroid receptors) and neurobiological (hippocampal expression of neuronal cell adhesion molecules) parameters were evaluated. Impaired performance was observed in stressed HR rats, as compared to unstressed HR and stressed LR rats. Increased hippocampal mineralocorticoid receptors were found in stressed LR rats when compared with stressed HR and control LR groups. In addition, mid-life stress-induced an increased corticosterone response and a reduction in NCAM-180 isoform and L1 regardless of the behavioral trait of novelty reactivity. These findings highlight a role of stress experienced throughout life on cognitive impairment occurring during the early aging period, as well as the importance of taking into account individual differences to understand variability in such cognitive decline.

The diet restriction paradigm: a brief review of the effects of every-other-day feeding

It has been known since the early 1900s that restriction of dietary intake relative to the ad libitum (AL) level increases stress resistance, cancer resistance, and longevity in many species. Studies investigating these phenomena have used three paradigms for dietary restriction. In the first, the AL intake of a control group is measured, and an experimental group is fed less than that amount in a specified proportion, e.g., 40%. In the second, food is provided AL to both the control and experimental groups: however, the experimental group is subjected to periods of fasting. Recent studies using this paradigm provide food every other day (EOD). Both of these paradigms have been in use since the early 1900s. A third paradigm that combines them was developed in the early 1970s: one or more days of fasting separate the provision of a limited amount of food. It was assumed for many years that the physiological responses to these paradigms were due exclusively to a net decrease in energy intake. Recently, however, it was found that some species and strains of laboratory animals, when fed AL every other day, are capable of gorging so that their net weekly intake is not greatly decreased. Despite having only a small deficit in energy intake relative to control levels, however, these animals experience enhanced longevity and stress resistance is enhanced in comparison to AL controls as much in animals enduring daily restriction of diet. These observations warrant renewed interest in this paradigm and suggest that comparisons of the paradigms and their effects can be used to determine which factors are critical to the beneficial effects of caloric restriction.

Not wisely but too well: aging as a cost of neuroendocrine activity

Progressive decline of some neuroendocrine signaling systems has long been assumed to cause age-related physiological impairments and limit life span. However, hypophysectomy--removal of the pituitary gland--can delay many aspects of the aging process, and recent genetic studies have confirmed that reducing the secretion of pituitary hormones can increase the life span of laboratory organisms. Most strikingly, reducing activity of the insulin/insulin-like growth factor-1 signaling system substantially increases life span. Conversely, activity of the reproductive system or activation of stress responses can curtail life span. Because caloric restriction also reduces the activity of several neuroendocrine systems while increasing life span, it now appears that the aging process is driven, at least in part, by neuroendocrine activity rather than by its decline with age.

Long-term dietary restriction causes negative effects on cognitive functions in rats

Long-term dietary restriction is reported to increase life span and improve age-related cognitive deficits. The present study shows that the restriction increases the life span of rats but decreases their cognitive ability. Thirty-two rats were divided into restricted and ad lib feeding groups at 2.5 months of age. The restricted rats were kept at a weight of 280g. The restricted rats were poor in performing the Morris water maze task at 7-12 months. At 17-18 months, they were poor in performing the delayed matching-to-place task. At 24-27 months, the surviving 13 restricted and 5 ad lib rats performed the spatial discrimination task. The restricted rats were also poor in performing this task. Injection of glucose prior to the discrimination task improved their performance to the level of the ad lib rats. These results suggest that dietary restriction is beneficial for longevity but has negative effects on the performance of cognitive tasks, and that the cause of the negative effects may be a reduced availability of glucose in the food-restricted aged rats.

Life extension in the dwarf mouse

Ames dwarf mice and Snell dwarf mice lack growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH), live much longer than their normal siblings, and exhibit many symptoms of delayed aging. "Laron dwarf mice," produced by targeted disruption of the GH receptor/GH-binding protein gene (GHR-KO mice), are GH resistant and also live much longer than normal animals from the same line. Isolated GH deficiency in "little" mice is similarly associated with increased life span, provided that obesity is prevented by reducing fat content in the diet. Long-lived dwarf mice share many phenotypic characteristics with genetically normal (wild-type) animals subjected to prolonged caloric restriction (CR) but are not CR mimetics. We propose that mechanisms linking GH deficiency and GH resistance with delayed aging include reduced hepatic synthesis of insulin-like growth factor 1 (IGF-1), reduced secretion of insulin, increased hepatic sensitivity to insulin actions, reduced plasma glucose, reduced generation of reactive oxygen species, improved antioxidant defenses, increased resistance to oxidative stress, and reduced oxidative damage. The possible role of hypothyroidism, reduced body temperature, reduced adult body size, delayed puberty, and reduced fecundity in producing the long-lived phenotype of dwarf mice remains to be evaluated. An important role of IGF-1 and insulin in the control of mammalian longevity is consistent with the well-documented actions of homologous signaling pathways in invertebrates.

Calorie restriction and aging: review of the literature and implications for studies in humans

Calorie restriction (CR) extends life span and retards age-related chronic diseases in a variety of species, including rats, mice, fish, flies, worms, and yeast. The mechanism or mechanisms through which this occurs are unclear. CR reduces metabolic rate and oxidative stress, improves insulin sensitivity, and alters neuroendocrine and sympathetic nervous system function in animals. Whether prolonged CR increases life span (or improves biomarkers of aging) in humans is unknown. In experiments of nature, humans have been subjected to periods of nonvolitional partial starvation. However, the diets in almost all of these cases have been of poor quality. The absence of adequate information on the effects of good-quality, calorie-restricted diets in nonobese humans reflects the difficulties involved in conducting long-term studies in an environment so conducive to overfeeding. Such studies in free-living persons also raise ethical and methodologic issues. Future studies in nonobese humans should focus on the effects of prolonged CR on metabolic rate, on neuroendocrine adaptations, on diverse biomarkers of aging, and on predictors of chronic age-related diseases.

Age-related alterations in the protein expression profile of C57BL/6J mouse pituitaries

The aim of our study was to monitor the protein expression profile in pituitary glands of healthy C57BL/6J mice during aging. Pituitary glands of 4-week old (immature), 3-month old (mature), and >25-month old mice were analysed by proteomic tools such as two-dimensional electrophoresis and N-terminal micro-sequencing. A change was detected in the expression of growth hormone after sexual maturation. Our particular interest, however, was directed against up-regulated proteins in the old pituitary glands, which are proposed to be involved in the process of neuroendocrine aging. Among these proteins, the expression of glutathione-S-transferase (GST) and apolipoprotein A-1 were increased in old pituitaries. Furthermore, ubiquitin carboxyl-terminal hydrolase (UCH-L1) was significantly up-regulated in senescent C57BL/6J mouse pituitaries. Since only the rat homologue was known, we isolated and analysed the mouse UCH-L1 sequence. Since GST is involved in antioxidative defence and UCH-L1 is part of the ubiquitin/proteasome system, which is responsible for the removal of damaged proteins, these results suggest increased oxidative burden and an increased activity of the ubiquitin system.

The Snell dwarf mutation Pit1(dw) can increase life span in mice

Over the past 30 years, the Snell dwarf mutation (Pit1(dw)) has been reported to shorten, to have no effect on, or to increase life span in various colonies; however, few details of these disparate results have been published. We now report that mean, median, and maximum life spans are increased by 40-50% for Snell dwarf (Pit1(dw)/Pit1(dw)) DW/J females, and 25-50% for dwarf DWC3F1 males and females with the compound heterozygous Pit1(dw)/Pit1(dw-J) genotype. We previously observed aspects of delayed senescence in Snell dwarf (Pit1(dw)/Pit1(dw)) DW/J males; however, their median life span was shortened by about 25% (Genetic Effects on Aging II, 1990, The Telford Press, Caldwell, NJ, pp. 435-456). This short life span was not an intrinsic effect of the mutation, but a consequence of housing male dwarfs with normal-sized male littermates; our present results demonstrate that Snell dwarf males attain very long life spans when housed with normal-sized females. We conclude that the dwarf mutation interacts with environmental factors to alter life spans and, probably, rates of ageing, over an extremely broad range. We propose that this variation in the effect of the Snell dwarf mutation results from a tradeoff between physical vigor and life span that is mediated by pituitary hormones, and that growth hormone, thyroid hormone, and possibly prolactin regulate mechanisms that schedule mortality in mammals.

Life span extension and cancer risk: myths and reality

A significant increase in the number of old people in the populations of developed countries was followed by an increase in morbidity and mortality resulting from main age-related diseases -- cardiovascular, cancer, neurodegenerative, diabetes mellitus, decrease in resistance to infections. Obviously, the development of the means of prevention of the premature aging of humans is crucial for the realization of this program. However, data available on such kind of means are rather scarce, contradictory and are often not reliable from the points of view of the adequacy of the experiments to current scientific requirements as well as the interpretation of the results and safety. Data available on the increase in life span and the adverse effects of the following geroprotectors were critically analyzed: antioxidants, chelate agents and lathyrogens, succinate, adaptogens and herbs, neurotropic drugs, inhibitors of monoamine oxidase, glucocorticoids, dehydroepiandrosterone, sex and growth hormones, melatonin, pineal peptide preparations, protein inhibitors, antidiabetic biguanides, thymic hormones and peptides, immunomodulators, enteroadsorbents, lypofuscin inhibitors, as well as calorie intake restriction and special diets. Most of the available results were insufficient and could not provide convincing evidence for the life span extension and the safety of the suggested geroprotectors. Drugs and means prolonging the life span could be subdivided into three groups: (a) geroprotectors prolonging the life span equally in all the members of the population: these postponed the beginning of the population's aging; (b) geroprotectors decreasing the mortality rate in a long-lived subpopulation, which raised their maximal life span: these slowed down the population's aging rate; (c) geroprotectors increasing the survival rate in a short-lived subpopulation without changes in the maximal life span: in this case, the aging rate increased. There was a high positive correlation between the type of geroprotector-induced aging delay and the pattern of tumour development in the same population of animals. The first type of geroprotectors did not influence the incidence of tumour but increased tumour latency. The second type of geroprotectors was effective both in the inhibition of spontaneous carcinogenesis and the increase in tumour latency. Certain drugs of the third type raised tumour incidence in the exposed populations. According to the multistage model, geroprotectors either inhibit or accelerate the passage of carcinogen-exposed cells form one stage to another. Thus, the efficacy of geroprotectors as preventive means of cancer development will decrease with respect to the age of exposure onset. Recommendations of the available drugs and means of life span increase should be carefully reconsidered under the international scientific control.

Neuroendocrine and pharmacological manipulations to assess how caloric restriction increases life span

As part of an effort to review current understanding of the mechanisms by which caloric restriction (CR) extends maximum life span, the authors of the present review were requested to develop a list of key issues concerning the potential role of neuroendocrine systems in mediating these effects. It has long been hypothesized that failure of specific neuroendocrine functions during aging leads to key age-related systemic and physiological failures, and more recently it has been postulated that physiological neuroendocrine responses to CR may increase life span. However, although the acute neuroendocrine responses to fasting have been well studied, it is not clear that these responses are necessarily identical to those observed in response to the chronic moderate (30% to 50% reduction) CR that increases maximum life span. Therefore the recommendations of this panel fall into two categories. First, further characterization of neuroendocrine responses to CR over the entire life span is needed. Second, rigorous interventional studies are needed to test the extent to which neuroendocrine responses to CR mediate the effects of CR on life span, or alternatively if CR protects the function of essential neuroendocrine cells whose impairment reduces life span. Complementary studies using rodent models, nonhuman primates, and humans will be essential to assess the generality of elucidated mechanisms, and to determine if such mechanisms might apply to humans.

An age-related decline in melatonin secretion is not altered by food restriction

Melatonin has been found to exhibit youth-maintaining and disease-preventing properties. The current study examined whether the age-retarding regimen of chronic food restriction (FR) slowed the decline in melatonin secretion reported to occur with age. Total nocturnal melatonin secretion was assessed by radioimmunoassay of the primary metabolite, 6-sulphatoxymelatonin (6-S-OH-MLT), in urine. Measurements were made through adulthood (70 to 765 days) on male Wistar rats maintained on the FR regimen (60% of the normal intake) with the control animals fed ad libitum (AL). The data of animals exhibiting gross pathology were excluded. Analyses of covariance found the FR regimen had no effect on either the levels or pattern of decline observed in 6-S-OH-MLT excretion through adulthood. However, the FR body-weight-indexed metabolite measures were approximately double those of the AL (p = .06). The possibility that this result may reflect unusually high melatonin peaks in the FR tissues is discussed.

Low body temperature in long-lived Ames dwarf mice at rest and during stress

Among homeothermic animals, larger species generally have lower metabolic rates and live longer than do smaller species. Because Ames dwarf mice (dwarfs) live approximately 1 year longer than their larger normal sex- and age-matched siblings (normals), we hypothesized that they would have lower body core temperature (Tco). We, therefore, measured Tco of six dwarfs and six normals during 24-h periods of ad lib feeding, 24-h food deprivation, and emotional stress induced by cage switching. With ad lib feeding, Tco of dwarfs averaged 1.6 degrees C lower than normals; during food deprivation, Tco of both dwarfs and controls was significantly lower than when food was available ad lib; and following cage switch, Tco was elevated in both groups. However, during all three experiments, Tco was significantly lower in dwarfs than in normals. These data support the hypothesis that Ames dwarf mice, which live longer than normal size controls, maintain lower Tco than normals. Because dwarfs are deficient in thyroid stimulating hormone (TSH) and growth hormone (GH), their low Tco may be a result of reduced thermogenesis due to lack of those hormones. However, whether low Tco per se is related to the increased longevity of the dwarf mice remains an interesting possibility to be investigated.

Does growth hormone prevent or accelerate aging?

It is very well documented that plasma growth hormone (GH) levels decline with age in the human and in experimental animals, and there is considerable evidence that age-related changes in body composition may be caused by reduced function of the GH-IGF-I system. However, excessive GH levels are associated with reduced life expectancy in acromegalic patients and with symptoms of accelerated aging in GH transgenic mice. Hereditary dwarf mice deficient in GH, prolactin, and TSH live much longer than their normal siblings. Possible mechanisms of delayed aging in dwarf mice include lower core body temperature and reduced oxidative processes. It is suggested that the controversies concerning the apparent potential of GH to both prevent and accelerate aging may be reconciled by interpreting the results in light of the negative relationship between body size and life span within a species.

Enhanced cell proliferation and biosynthesis mediate improved wound repair in refed, caloric-restricted mice

Aged mice that have undergone long-term caloric-restriction (CR) have improved health and enhanced longevity in comparison to aged mice that are ad libitum-fed (AL). However, caloric-restriction does not benefit the impaired wound healing of aged mice. To test the hypothesis that CR mice have the capacity for enhanced wound repair, but require a short-term period of additional nutrient intake to show this advantage, we assessed wound healing in CR mice that had been refed (RF) an ad libitum diet for 4 weeks prior to wounding. Two strains of AL young (Y AL) (4-6 months), AL middle-aged (M AL) (15-17 months), and three different, matched cohorts of old mice (O) (30-33 months): O AL, O CR, and O RF were studied. Two full-thickness 4 mm diameter punch biopsy skin wounds were created on the dorsum of each mouse. Animals were sacrificed and wounds were harvested at 1,2,3,5, and 7 days post-wounding. Repair of wounds was slower in O AL and O CR mice compared to Y AL and M AL animals. In contrast, the O RF mice healed similarly to that of the Y AL and M AL mice, as assessed by measures of wound area and histologic criteria. O RF mice demonstrated enhanced synthesis of type I collagen mRNA in comparison to O AL and O CR mice. A greater number of endothelial cells and fibroblasts at the wound edge of the O RF mice exhibited replication in vivo as measured by uptake of BrdU. O RF mice had higher levels of insulin-like binding protein 3 (IGFBP-3). Furthermore, fibroblasts derived from the explant of the punch biopsy of O CR mouse skin revealed enhanced proliferation and contraction in vitro, in comparison to fibroblasts from the O AL mice. In conclusion, O RF mice demonstrate an enhanced capacity to undergo wound repair in comparison to O AL mice. This effect appears to be mediated, in part, by enhanced cell proliferation, contraction, and collagen biosynthesis. In addition, short-term refeeding induced an increase in the serum level of IGFBP-3, the major binding protein for IGF-1. These data confirm that cells from O CR animals have a preserved proliferative, biosynthetic, and contractile capacity, but that an adequate source of nutrients is necessary to demonstrate this advantage in wound healing.

The effect of neonatal pinealectomy on the inhibitory actions of food restriction on vaginal opening and collagen aging in the rat

Long-term food restriction is known to inhibit development and aging in the rat. These actions may be mediated by the pineal hormone, melatonin, whose secretion is increased by food restriction. This mechanism was investigated by studying the effects of pinealectomy in ad libitum fed and food restricted rats of both sexes living under normal conditions of temperature (23 degrees C) and lighting 12 h light:12 h dark cycle) over a period of 400 days. Pinealectomies were performed at the age of 5 days. Pinealectomy did not affect the amount of food eaten per day. Vaginal opening occurred at age 35 days in ad libitum fed female rats and was delayed to 49 days (P < 0.001) in rats whose food intake was restricted by 35%, but only to 41 days (P < 0.001) if food restricted (FR) rats were pinealectomized (Px). The inhibitory effect of food restriction on body growth and tail tendon collagen fibre aging was the same in both intact and pinealectomized rats. At the conclusion of the study in middle age at 400 days, plasma melatonin levels 4 h into the dark cycle were higher in food restricted than in ad libitum fed rats (P = 0.015). This study provides evidence for a role of the pineal in mediating the inhibitory action of food restriction on vaginal opening, but not on body growth or collagen aging in tail tendon up to middle age.

Molecular hysteresis: residual effects of hormones and glucose on genes during aging

The basic concept of molecular hysteresis may be succintly summarized as follows in the following Limerick:. Hormones behave like Don Juan: They show up, do their thing, then they're gone. But when genes have been kissed Some effects may persist, And the melody still lingers on.

Effects of caloric restriction in animals on cellular function, oncogene expression, and DNA methylation in vitro

While the life-extending and disease-modulating effects of caloric restriction (CR) are well documented in whole animal studies and in correlative experiments using cells taken from CR animals, very few studies have used cells in culture after their removal from the CR-fed animal. In using this in vivo-->in vitro approach we have attempted to examine the proposition that the effects of CR can be transferred to individual cells by analyzing the cellular functions of proliferation and transformation, the activation of oncogenes, and the methylation of DNA as a function only of diet. Pancreatic acinar cells excised from CR-fed Brown-Norway rats and placed in rich medium showed different responses compared to cells from ad libitum (AL)-fed controls. CR had the effect of slowing growth rate and protecting against spontaneous and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced transformation over 14 passages of cells in culture. At the molecular level, cells from the CR animals showed reduced c-Ha-ras oncogene expression and mutation as well as reduced mutation of the p53 suppressor gene. CR also increased genomic methylation of ras DNA. We conclude that the effects of CR treatment of the animal are transferred to individual cells and note that these responses (decreased proliferation and transformation; depressed oncogene expression and mutation and decreased suppressor gene mutation; and increased oncogene methylation) are cellular and molecular analogs of in vivo weight loss, life extension, and carcinogenesis modulation, which are hallmarks of CR in the whole animal. The fact that these responses are seen generations after the cells are removed from the CR-treated animal indicates that CR causes a permanent predisposition of pancreatic acinar cells to these modulated responses and shows the value of the in vivo-->in vitro protocol in studies that relate diet to cellular and molecular function.

Stress-age syndrome

With aging a set of neurohormonal, tissue and cellular changes develop which can be defined as stress-age syndrome. They include irregular changes in the excitability of structures of the limbic system and hypothalamus, rise of the blood concentration of catecholamines, vasopressin, ACTH and cortisol, fall of the concentration of testosterone, thyroxin and other substances, change of the concentration of opioid peptides, immunodepression, dyslipoproteidemia hypercoagulation and free-radical damage of cells. One group of components of the above syndrome is of adaptive importance, while the other is damaging. Symptoms of stress-age syndrome have their individual peculiarities and cannot explain the whole complexity of symptoms of the organism's aging. Against the background of stress-age syndrome the course of developing stress reactions undergoes a change.

Skin fibroblasts from aged Fischer 344 rats undergo similar changes in replicative life span but not immortalization with caloric restriction of donors

We have compared the in vitro replicative life span and characteristics of immortalization of skin fibroblast cultures derived from ad libitum-fed and caloric-restricted Fischer 344 rats of 6, 24, and 29 months of age. Cells from all 6-, 24-, and 29-month-old animals showed a gradual decline in proliferative potential as evidenced by decreases in harvest density, in the fraction of cells initiating DNA synthesis, and in the number of population doublings per passage. These declines were accompanied by morphological changes including cell enlargement. The replicative life span prior to immortalization decreased significantly with donor age (P less than 0.0001), while caloric restriction had no effect on the cumulative population doubling level. Prior to immortalization mitotic cells from all cultures showed a normal rat karyotype. Postcrisis cultures tended to have more polyploid cells but there were no characteristic or specific chromosomal changes found in the cells with an immortalized phenotype. Interestingly, fibroblasts derived from caloric-restricted animals had a significantly slower growth rate through the tenth week after immortalization (P less than 0.005). When these cultures were seeded at one-quarter the normal seeding density, to favor the outgrowth of the fastest growing cells, a population with a more "transformed" phenotype emerged.

Effects of dietary restriction on radial-arm maze performance and flavor memory in aged rats

Two groups of aged rats, a dietary restricted group fed approximately 10 g per day from 6 weeks of age and a group fed ad lib throughout their life span, were compared with a young adult group on an 8-arm radial maze and a flavor memory task. The young adult displayed efficient performance on the radial-arm maze within the 15 day test period. In contrast, both aged groups exhibited significantly poorer performance in the maze in comparison with the young adult group neither aged group differed from chance at the end of the 15 days. The flavor memory task required the animals to consume a novel flavor. Their loss of neophobia, as indexed by their subsequent consumption, was then taken as an indication of the extent to which they remembered the novel flavor and its effects. The young adult group lost their neophobia more rapidly than either of the aged groups, which did not appear to differ from each other. Taken together, this pattern of results indicates that dietary restriction does not protect animals from the memory loss observed in aged animals.

The effect of low protein-high dextrin diet and subsequent food restriction upon life prolongation in Fischer 344 male rats

Fischer 344 rats fed low protein-high dextrin diet exhibit a higher median (but not 10th percentile) survival as compared to controls. The effect of this diet appears already if the diet is administered between 6 weeks and 6 months of age; after this treatment median survival of experimental animals is increased by 96 days while the 10th percentile is not different from standard diet-fed controls. Further treatment of animals with the same diet has minimum effect as animals that lived on this regimen throughout the whole life exhibited a median lifespan increase by 120 days and increase in the 10th percentile by 41 days. However, if such animals at the age of 6 months are transferred to a restricted (60%) food intake regimen (control diet, not carbohydrate enriched) a further increase in median and 10th percentile lifespan prolongation can be observed reaching +328 and +396 days respectively as compared to controls. The effects of this early feeding (6 weeks to 6 months) with a low protein-high carbohydrate diet available ad libitum and the food restricted regimen (standard diet 60% controls) fed from the age 6 months onwards are additive, the final results being identical to those obtained if the animals were kept on the 60% food restricted intake throughout the whole life. The fact that animals fed the low protein-high carbohydrate diet and those kept on 60% standard diet food restriction had different survival though they were equal in daily (identical) protein intake is emphasized.

Inhibitory effect of hypophysectomy and food restriction on glomerular basement membrane thickening, proteinuria and renal enlargement in aging male Wistar rats

Age-related thickening of the glomerular basement membrane (GBM) was studied in three groups of male Wistar rats: (a) ad libitum fed, (b) hypophysectomized and (c) food-restricted eating the same amount of food as hypophysectomized rats, but about 45% of the ad libitum fed group. Studies were begun at 50 days (2 months) and continued throughout life. Multiple regression was used to statistically assess the effects of age and treatments. In ad libitum fed male rats GBM thickness increased from 114 nm at 50 days (2 months) to 632 nm at 1,000 days (33 months). GBM thickness at 1,000 days was 296 nm in hypophysectomized rats and 392 nm in food restricted rats. Hypophysectomy had a significantly greater inhibitory action on GBM thickening than food restriction, in rats eating the same quantity of food per day. However, a major part of the effect of hypophysectomy may be due to the permanent fall in food intake (from 16.3 to 7.9 g/day) resulting from the operation. Accompanying the age-related thickening of the GBM in ad libitum fed rats were proteinuria and renal enlargement, both of which were inhibited by hypophysectomy and food restriction.