Calorie restriction and skeletal mass in rhesus monkeys (Macaca mulatta): evidence for an effect mediated through changes in body size

Quality of hematology and clinical chemistry results in laboratory and zoo nonhuman primates: Effects of the preanalytical phase. A review

Most errors in clinical pathology originate in the preanalytical phase, which includes all steps from the preparation of animals and equipment to the collection of the specimen and its management until analyzed. Blood is the most common specimen collected in nonhuman primates. Other specimens collected include urine, saliva, feces, and hair. The primary concern is the variability of blood hematology and biochemistry results due to sampling conditions with the effects of capture, restraint, and/or anesthesia. Housing and diet have fewer effects, with the exception of food restriction to reduce obesity. There has been less investigation regarding the impact of sampling conditions of nonblood specimens.

Cortical Thinning and Structural Bone Changes in Non-Human Primates after Single-Fraction Whole-Chest Irradiation

Stereotactic body radiation therapy (SBRT) is associated with an increased risk of vertebral compression fracture. While bone is typically considered radiation resistant, fractures frequently occur within the first year of SBRT. The goal of this work was to determine if rapid deterioration of bone occurs in vertebrae after irradiation. Sixteen male rhesus macaque non-human primates (NHPs) were analyzed after whole-chest irradiation to a midplane dose of 10 Gy. Ages at the time of exposure varied from 45-134 months. Computed tomography (CT) scans were taken 2 months prior to irradiation and 2, 4, 6 and 8 months postirradiation for all animals. Bone mineral density (BMD) and cortical thickness were calculated longitudinally for thoracic (T) 9, lumbar (L) 2 and L4 vertebral bodies; gross morphology and histopathology were assessed per vertebra. Greater mortality (related to pulmonary toxicity) was noted in NHPs <50 months at time of exposure versus NHPs >50 months ( P = 0.03). Animals older than 50 months at time of exposure lost cortical thickness in T9 by 2 months postirradiation ( P = 0.0009), which persisted to 8 months. In contrast, no loss of cortical thickness was observed in vertebrae out-of-field (L2 and L4). Loss of BMD was observed by 4 months postirradiation for T9, and 6 months postirradiation for L2 and L4 ( P < 0.01). For NHPs younger than 50 months at time of exposure, both cortical thickness and BMD decreased in T9, L2 and L4 by 2 months postirradiation ( P < 0.05). Regions that exhibited the greatest degree of cortical thinning as determined from CT scans also exhibited increased porosity histologically. Rapid loss of cortical thickness was observed after high-dose chest irradiation in NHPs. Younger age at time of exposure was associated with increased pneumonitis-related mortality, as well as greater loss of both BMD and cortical thickness at both in- and out-of-field vertebrae. Older NHPs exhibited rapid loss of BMD and cortical thickness from in-field vertebrae, but only loss of BMD in out-of-field vertebrae. Bone is sensitive to high-dose radiation, and rapid loss of bone structure and density increases the risk of fractures.

Does eating less make you live longer and better? An update on calorie restriction

The complexity of aging is hard to be captured. However, apart from its tissue-specific features, a structural and functional progressive decline of the whole organism that leads to death, often preceded by a phase of chronic morbidity, characterizes the common process of aging. Therefore, the research goal of scientists in the field moved from the search for strategies able to extend longevity to those ensuring healthy aging associated with a longer lifespan referred to as “healthspan”. The aging process is plastic and can be tuned by multiple mechanisms including dietary and genetic interventions. To date, the most robust approach, efficient in warding off the cellular markers of aging, is calorie restriction (CR). Here, after a preliminary presentation of the major debate originated by CR, we concisely overviewed the recent results of CR treatment on humans. We also provided an update on the molecular mechanisms involved by CR and the effects on some of the age-associated cellular markers. We finally reviewed a number of tested CR mimetics and concluded with an evaluation of future applications of such dietary approach.

Nutrition, metabolism, and targeting aging in nonhuman primates

This short review focuses on the importance of nonhuman primate nutrition and aging studies and makes the case that a targeted expansion of the use of this highly translatable model would be advantageous to the biology of aging field. First, we describe the high degree of similarity of the model in terms of aging phenotypes including incidence and prevalence of common human age-related diseases. Second, we discuss the importance of the nonhuman primate nutrition and aging studies and the extent to which the outcomes of two ongoing long-term studies of caloric restriction are congruent with short-term equivalent studies in humans. Third, we showcase a number of pharmacological agents previously employed in nonhuman primate studies that display some potential as caloric restriction mimetics. Finally, we present nonhuman primates as an important model for translation of mechanisms of delayed aging identified in studies of shorter-lived animals. Proof of efficacy and safety of candidate longevity agents in nonhuman primates would be a cost-effective means to bring these exciting new avenues a step closer to clinical application.

Impact of moderate calorie restriction on testicular morphology and endocrine function in adult rhesus macaques (Macaca mulatta)

We previously reported that moderate calorie restriction (CR) has minimal impact on testicular gene expression in young adult rhesus macaques, and no obvious negative impact on semen quality or plasma testosterone levels. We now extend these findings by examining the influence of CR on various aspects of the reproductive axis of older males, including 24-h circulating testosterone levels, testicular gene expression, and testicular morphology. Young adult and old adult male rhesus macaques were subjected to either 30 % CR for 5-7 years, or were fed a standard control diet. Analysis of the 24-h plasma testosterone profiles revealed a significant age-associated decline, but no evidence for CR-induced suppression in either the young or old males. Similarly, expression profiling of key genes associated with testosterone biosynthesis and Leydig cell maintenance showed no significant CR-induced changes in either the young or old animals. The only evidence for CR-associated negative effects on the testis was detected in the old animals at the histological level; when old CR animals were compared with their age-matched controls, there was a modest decrease in seminiferous tubule diameter and epithelium height, with a concomitant increase in the number of depleted germ cell lines. Reassuringly, data from this study and our previous study suggest that moderate CR does not negatively impact 24-h plasma testosterone profiles or testicular gene expression. Although there appear to be some minor CR-induced effects on testicular morphology in old animals, it is unclear if these would significantly compromise fertility.

Gut-derived serotonin is a multifunctional determinant to fasting adaptation

Energy release from cellular storage is mandatory for survival during fasting. This is achieved through lipolysis and liver gluconeogenesis. We show here that in the mouse, gut-derived serotonin (GDS) is upregulated during fasting and that it favors both mechanisms. In adipocytes, GDS signals through the Htr2b receptor to favor lipolysis by increasing phosphorylation and activity of hormone-sensitive lipase. In hepatocytes, GDS signaling through Htr2b promotes gluconeogenesis by enhancing activity of two rate-limiting gluconeogenic enzymes, FBPase and G6Pase. In addition, GDS signaling in hepatocytes prevents glucose uptake in a Glut2-dependent manner, thereby further favoring maintenance of blood glucose levels. As a result, inhibition of GDS synthesis can improve glucose intolerance caused by high-fat diet. Hence, GDS opposes deleterious consequences of food deprivation by favoring lipolysis and liver gluconeogenesis while preventing glucose uptake by hepatocytes. As a result, pharmacological inhibition of its synthesis may contribute to improve type 2 diabetes.

Skeletal effects of long-term caloric restriction in rhesus monkeys

Age-related bone loss is well established in humans and is known to occur in nonhuman primates. There is little information, however, on the effect of dietary interventions, such as caloric restriction (CR), on age-related bone loss. This study examined the effects of long-term, moderate CR on skeletal parameters in rhesus monkeys. Thirty adult male rhesus monkeys were subjected to either a restricted (R, n = 15) or control (C, n = 15) diet for 20 years and examined throughout for body composition and biochemical markers of bone turnover. Total body, spine, and radius bone mass and density were assessed by dual-energy X-ray absorptiometry. Assessment of biochemical markers of bone turnover included circulating serum levels of osteocalcin, carboxyterminal telopeptide of type I collagen, cross-linked aminoterminal telopeptide of type I collagen, parathyroid hormone, and 25(OH)vitamin D. Overall, we found that bone mass and density declined over time with generally higher levels in C compared to R animals. Circulating serum markers of bone turnover were not different between C and R with nonsignficant diet-by-time interactions. We believe the lower bone mass in R animals reflects the smaller body size and not pathological osteopenia.

Blocking β-adrenergic signaling attenuates reductions in circulating leptin, cancellous bone mass, and marrow adiposity seen with dietary energy restriction

We tested whether β-adrenergic blockade attenuates bone loss and increased marrow adiposity during energy restriction (ER) and whether such an effect is associated with changes in serum leptin and leptin expression in bone and marrow tissues. Female 4-mo-old Sprague-Dawley rats were assigned into four groups (n = 10 each): two groups of 40% ER treated with vehicle (ERVEH; saline) or β-blocker (ERBB; DL-propranolol; 250 μg · kg(-1) · h(-1)) during 12 wk, and two groups of ad libitum-fed controls treated with the same two agents (CONVEH, CONBB, respectively). Over 84 days, CONVEH and CONBB rats gained but ERVEH and ERBB rats lost body fat mass; lean mass did not change in any group. Reduction in serum leptin in ERVEH rats was mitigated in ERBB rats (-5.32 vs. -1.15 ng/ml, respectively). The decline in proximal tibia cancellous vBMD observed in ERVEH rats was attenuated in ERBB rats (-85.24 vs. -53.94 mg/cm(3), respectively). Adipocyte number in ERVEH rats was dramatically higher vs. CON rats at week 12, but this increment was abolished by β-blockade in ERBB animals. The number of osteoblastic cells and marrow adipocytes staining positively for leptin in ERVEH rats tended to be lower vs. that of both CON groups, but β-blockade appears to reverse this effect in ERBB rats. In summary, β-adrenergic blockade mitigated metaphyseal bone loss and bone marrow adiposity during energy restriction and attenuated reductions in serum leptin. These data suggest an important role for β-adrenoreceptor signaling pathway in the cancellous bone and marrow fat response to energy restriction.

The caloric restriction paradigm: implications for healthy human aging

Underlying the importance of research on the biology of aging is the fact that many nations face the demographic reality of a rapidly aging populace and the looming healthcare challenges that it brings. This reality is a result of aging itself being the most significant risk factor for a range of the most prevalent diseases, including many cancers, cardiovascular disease, and diabetes. Accordingly, interventions are sorely needed that would be able to delay or prevent diseases and disorders associated with the aging process and thereby increase the period of time that aging individuals are in good health (the health-span). Caloric restriction (CR) has emerged as a model of major interest as it is widely agreed that CR is the most potent environmental intervention that delays the onset of aging and extends life span in diverse experimental organisms. A better understanding of the mechanisms by which CR delays aging will reveal new insights into the aging process and the underlying causes of disease vulnerability with age. These novel insights will allow the development of novel treatments and preventive measures for age-associated diseases and disorders.

Can we live longer by eating less? A review of caloric restriction and longevity

Caloric restriction, decreasing caloric intake by 20-30%, was first shown to extend life in rats nearly 80 years ago. Since that time, limiting food intake for longevity has been investigated in species from yeast to humans. In yeast and lower animals, caloric restriction has repeatedly been demonstrated to lengthen the life span. Studies of caloric restriction in non-human primates and in humans are ongoing and initial results suggest prolongation of life as well as prevention of age-related disease. There is also data in rodents suggesting that short term caloric restriction has beneficial effects on fertility. Although caloric restriction has many positive effects on health and longevity, quality of life on a restricted diet as well as the ability to maintain that diet long term are concerns that must be considered in humans.

Calorie restriction and aging in nonhuman primates

In the 75 years since the seminal observation of Clive McCay that restriction of calorie intake extends the lifespan of rats, a great deal has been learned about the effects of calorie restriction (CR; reduced intake of a nutritious diet) on aging in various short-lived animal models. Studies have demonstrated many beneficial effects of CR on health, the rate of aging, and longevity. Two prospective investigations of the effects of CR on long-lived nonhuman primate (NHP) species began nearly 25 years ago and are still under way. This review presents the design, methods, and main findings of these and other important contributing studies, which have generally revealed beneficial effects of CR on physiological function and the retardation of disease consistent with studies in other species. Specifically, prolonged CR appears to extend the lifespan of rhesus monkeys, which exhibited lower body fat; slower rate of muscle loss with age; lower incidence of neoplasia, cardiovascular disease, type 2 diabetes mellitus, and endometriosis; improved insulin sensitivity and glucose tolerance; and no apparent adverse effect on bone health, as well as a reduction in total energy expenditure. In addition, there are no reports of deleterious effects of CR on reproductive endpoints, and brain morphology is preserved by CR. Adrenal and thyroid hormone profiles are inconsistently affected. More research is needed to delineate the mechanisms of the desirable outcomes of CR and to develop interventions that can produce similar beneficial outcomes for humans. This research offers tremendous potential for producing novel insights into aging and risk of disease.

Effects of moderate calorie restriction on testosterone production and semen characteristics in young rhesus macaques (Macaca mulatta)

We have previously reported a modest influence of moderate calorie restriction (CR) on testicular gene expression in young adult rhesus macaques (Macaca mulatta); however, it is unclear if these modifications correspond to subsequent changes in testicular function or sperm physiology. This study extends our earlier findings to examine potential physiological differences due to this differential gene expression. Animals were subjected to 30% CR (CR, n = 5) or were fed a standard control diet (CON, n = 5) starting during their peripubertal period. Circulating testosterone (T) levels were measured across a 24-h period after 7 yr of dietary treatment and were found to be similar in CR and CON males; however, maintenance of daily minimum T levels was significantly higher in the CR animals. Semen collection was performed on the same cohort of animals three times per male (CR, n = 4; CON, n = 4) after 8 yr of treatment, and samples were assessed by a variety of measures. Parameters, including semen quality and sperm cell viability and function, showed less variability in semen samples taken from CR males, but overall testicular function and sperm quality were comparable regardless of diet. There is mounting evidence that CR may promote health and longevity in a wide range of organisms, including nonhuman primates. Importantly, our data suggest that moderate CR has no obvious lasting detrimental effect on testicular function and sperm parameters in young adult primates and may in fact help maintain higher levels of circulating T.

Impact of Moderate Calorie Restriction on the Reproductive Neuroendocrine Axis of Male Rhesus Macaques

The impact of moderate calorie restriction on reproductive neuroendocrine function was investigated in young adult male rhesus macaques (Macaca mulatta). The animals were subjected to either 30% calorie restriction (CR; n=5), or were fed a standard control diet (CON; n=5), starting during their peripubertal period. Plasma LH and testosterone concentrations were examined after 7 years of differential dietary treatment, and were found to be similar in both groups, both during the day and during the night. Microarray profiling of pituitary gland and testicular gene expression was performed after 8 years of treatment, using GeneChip® Rhesus Macaque Genome Arrays (Affymetrix), and showed very little effect of caloric restriction. Using a 1.5-fold difference threshold, our microarray analysis revealed differential expression of only 145 probesets in the pituitary gland and 260 in the testes, out of a total of >54,000. Semi-quantitative RT-PCR performed on pituitary gland mRNA corroborated the microarray findings for selected modulated genes, including TSH receptor (TSHR) and sperm-specific antigen 2 (SSFA2). Most notably, significantly lower expression of TSH receptor mRNA was observed in the pituitary of CR compared to CON animals. Also, significantly lower expression of the glycoprotein hormone alpha subunit (CGA) was observed in CR animals, and this finding was further corroborated using quantitative real-time RT-PCR. No significant diet-induced changes were detected in the testis for genes associated with reproduction, circadian clocks, or oxidative stress. There is mounting evidence that CR may promote health and longevity in a wide range of organisms, including nonhuman primates. Importantly, our data suggest that moderate CR has no obvious lasting detrimental effect on the reproductive neuroendocrine axis of long-lived primates, and has only a modest influence on pituitary and testicular gene expression.

Aging in male primates: reproductive decline, effects of calorie restriction and future research potential

Although less dramatic than in females, male mammals experience decreasing reproductive function during aging. In primates, multiple facets of the hypothalamic-pituitary-gonadal axis show evidence of gradual age-related decline, including behavioral, neuroendocrine and endocrine alterations such as decreased testosterone levels, reduced circulating dehydroepiandrosterone sulfate (DHEAS) levels, increased numbers of sperm abnormalities, and a general decline in physiological responses. In this review we consider a range of age-related changes in males. These measures, including more subtle aging characteristics, are interesting additional indices for detecting the timing of age-related changes in behavioral, neuroendocrine, and endocrine responses. Evidence of potential effects of calorie restriction as an intervention in reproductive aging is also discussed. A discernable decline occurs in both metabolic and reproductive endocrine processes during male aging. This cascade of events includes neuroendocrine and behavioral changes; biomarkers such as circulating DHEAS also show clear age-related decline. The varied changes that occur during male aging are considered in the context of primate aging in general.

Influence of high and low protein intakes on age-related bone loss in rats submitted to adequate or restricted energy conditions

Low energy and protein intake has been suggested to contribute to the increased incidence of osteoporosis in the elderly. The impact of dietary protein on bone health is still a matter of debate. Therefore, we examined the effect of the modulation of protein intake under adequate or deficient energy conditions on bone status in 16-month-old male rats. The animals were randomly allocated to six groups (n = 10/group). Control animals were fed a diet providing either a normal-protein content (13%, C-NP) or a high-protein content (26%) (C-HP). The other groups received a 40% protein/energy-restricted diet (PER-NP and PER-HP) or a normal protein/energy-restricted diet (ER-NP and ER-HP). After 5 months of the experiment, protein intake (13% or 26%) did not modulate calcium retention or bone status in those rats, although a low-grade metabolic acidosis was induced with the HP diet. Both restrictions (PER and ER) decreased femoral bone mineral density and fracture load. Plasma osteocalcin and urinary deoxypyridinoline levels were lowered, suggesting a decrease in bone turnover in the PER and ER groups. Circulating insulin-like growth factor-I levels were also lowered by dietary restrictions, together with calcium retention. Adequate protein intake in the ER condition did not elicit any bone-sparing effect compared to PER rats. In conclusion, both energy and protein deficiencies may contribute to age-related bone loss. This study highlights the importance of sustaining adequate energy and protein provision to preserve skeletal integrity in the elderly.

Diet restriction and ageing in the dog: major observations over two decades

This report reviews decade two of the lifetime diet restriction study of the dog. Labrador retrievers (n 48) were paired at age 6 weeks by sex and weight within each of seven litters, and assigned randomly within the pair to control-feeding (CF) or 25 % diet restriction (DR). Feeding began at age 8 weeks. The same diet was fed to all dogs; only the quantity differed. Major lifetime observations included 1.8 years longer median lifespan among diet-restricted dogs, with delayed onset of late life diseases, especially osteoarthritis. Long-term DR did not negatively affect skeletal maturation, structure or metabolism. Among all dogs, high static fat mass and declining lean body mass predicted death, most strongly at 1 year prior. Fat mass above 25 % was associated with increasing insulin resistance, which independently predicted lifespan and chronic diseases. Metabolizable energy requirement/lean body mass most accurately explained energy metabolism due to diet restriction; diet-restricted dogs required 17 % less energy to maintain each lean kilogram. Metabonomics-based urine metabolite trajectories reflected DR-related differences, suggesting that signals from gut microbiota may be involved in the DR longevity and health responses. Independent of feeding group, increased hazard of earlier death was associated with lower lymphoproliferative responses to phytohaemagglutinin, concanavalin A, and pokeweed mitogen; lower total lymphocytes, T-cells, CD4 and CD8 cells; lower CD8 percentages and higher B-cell percentages. When diet group was taken into account, PWM responses and cell counts and percentages remained predictive of earlier death.

Impact of energy and casein or whey protein intake on bone status in a rat model of age-related bone loss

In the elderly, nutritional deficiencies, such as low energy and protein intake, are suggested to increase the risk of osteoporotic fractures. Modulation of the amount and quality of protein intake under energy deficient conditions represents an interesting strategy to prevent aged-related bone loss. We investigated the effect of a 5-month dietary restriction on bone status in 16-month-old male rats. Rats were randomised into six groups (n 10 per group). Control animals were fed a normal diet containing either casein (N-C) or whey protein (N-WP). The other groups received a 40 % protein and energy-restricted diet with casein or whey protein (PER-C and PER-WP) or a normal protein and energy-restricted diet (ER-C and ER-WP). Both restrictions (PER and ER) induced a decrease in femoral bone mineral density (BMD), consistent with impaired biomechanical properties and a reduced cortical area at the diaphysis. Plasma osteocalcin and urinary deoxypyridinoline levels suggested a decrease in bone turnover in the PER and ER groups. Interestingly, circulating insulin-like growth factor 1 (IGF-1) levels were also lowered. Overall, normal protein intake did not elicit any bone sparing effect in energy-deficient rats. Regarding protein quality, neither casein nor WP appeared to significantly prevent the BMD decrease. This study confirms that nutritional deficiencies may contribute to osteopenia through decreased IGF-1 levels. Moreover, it seems that impaired bone status could not be significantly prevented by modulating the amount and quality of dietary proteins.

Dietary Supplements in Weight Reduction

We summarize evidence on the role of dietary supplements in weight reduction, with particular attention to their safety and benefits. Dietary supplements are used for two purposes in weight reduction: (a) providing nutrients that may be inadequate in calorie-restricted diets and (b) for their potential benefits in stimulating weight loss. The goal in planning weight-reduction diets is that total intake from food and supplements should meet recommended dietary allowance/adequate intake levels without greatly exceeding them for all nutrients, except energy. If nutrient amounts from food sources in the reducing diet fall short, dietary supplements containing a single nutrient/element or a multivitamin-mineral combination may be helpful. On hypocaloric diets, the addition of dietary supplements providing nutrients at a level equal to or below recommended dietary allowance/adequate intake levels or 100% daily value, as stated in a supplement's facts box on the label, may help dieters to achieve nutrient adequacy and maintain electrolyte balance while avoiding the risk of excessive nutrient intakes. Many botanical and other types of dietary supplements are purported to be useful for stimulating or enhancing weight loss. Evidence of their efficacy in stimulating weight loss is inconclusive at present. Although there are few examples of safety concerns related to products that are legal and on the market for this purpose, there is also a paucity of evidence on safety for this intended use. Ephedra and ephedrine-containing supplements, with or without caffeine, have been singled out in recent alerts from the Food and Drug Administration because of safety concerns, and use of products containing these substances cannot be recommended. Dietitians should periodically check the Food and Drug Administration Web site ( www.cfsan.fda.gov ) for updates and warnings and alert patients/clients to safety concerns. Dietetics professionals should also consult authoritative sources for new data on efficacy as it becomes available ( ods.od.nih.gov ).

Life extension versus improving quality of life

There are two principal directions in ageing research: (i) the quest for understanding the mechanisms that determine the length of life and the use of such knowledge in order to find a potentially life extending treatment and (ii) the attempt to improve the quality of life in the elderly by reversing or preventing functional decline of different tissues without primarily extending life span. This chapter addresses the importance of assessing the potential impact of interventions on quality of life rather than extending life.

Effects of parametric feeding manipulations on behavioral performance in macaques

Early experimental psychologists made broad use of knowledge that is undoubtedly as old as animal domestication, i.e., that the power of appetitive reinforcement is enhanced by restricting the subjects' access to food. This has led to the nearly universal practice of restricting common laboratory rodent and avian subjects to 85% of free-feeding weight for operant experiments. Appetitive operant procedures in nonhuman primates (NHPs) vary more widely, in part because of the time required for such animals to reach mature weight and greater individual variability in body size compared with inbred laboratory species. In addition, many NHPs will grow obese under true ad-libitum feeding. Therefore, food restriction protocols for monkeys tend to be highly individualized and conducted on the basis of laboratory experience within a given model. The present study was undertaken to determine to what extent short-term, ad-libitum food consumption in rhesus macaques would impair performance on an established neuropsychological testing battery. A second part of the study was to formalize food-restriction parameters to determine what degree of restriction was required to produce consistent behavioral performance. Results show clearly that behavioral performance on a range of tasks is detrimentally affected by short-term, ad-libitum chow feeding, even when the reinforcer is highly preferred or the tasks are well trained. Furthermore, it is shown that maintenance of weekly chow intake in the range of 70-85% of National Research Council recommendations for metabolizable energy is necessary for consistent behavioral responding.

The effect of dietary n-3 long-chain polyunsaturated fatty acids on femur mineral density and biomarkers of bone metabolism in healthy, diabetic and dietary-restricted growing rats

INTRODUCTION

Dietary fish oil promotes bone formation in healthy states, but its effect during insulin deficiency or nutrient restriction is unclear.

METHODS

Eighty weanling male rats were randomized to receive an injection of streptozotocin to induce insulin deficiency (diabetes) or saline (control) and a diet containing soy oil or corn + fish oil for 35 days. Half of the saline-injected rats were randomized to 20% dietary restriction. Measurements were growth, biomarkers of bone metabolism and femur bone mass.

RESULTS

Density of femur was elevated in the corn + fish group and reduced in the diabetes group. Plasma osteocalcin and bone prostaglandin E2 (PGE2) were reduced by the corn + fish diet. N-telopeptide, IGF-1, bone PGE2 and urinary Ca were highest and calcitriol lowest in the diabetes group.

CONCLUSIONS

These data suggest that the benefit of a diet high in n-3 long-chain polyunsaturated fatty acid is most advantageous to long bone density in healthy states.

Effects of dietary restriction on total body, femoral, and vertebral bone in SENCAR, C57BL/6, and DBA/2 mice

Dietary restriction (DR) increases the life span and retards aging, in part, by limiting free radical generation and oxidative damage. DR also reduces body mass, a major determinant of bone mass across the life span. We tested the hypothesis that DR has its most beneficial effects on bone in mouse strains with high free radical generation (sensitive to carcinogenesis [SENCAR] > C57 > DBA) versus the hypothesis that bone mass at weight-bearing sites is determined by body mass in DR and ad libitum (AL)-fed mice. Male mice of each strain were killed at 10 weeks of age (t(0)) or randomized to an AL-fed or 30% DR feeding regimen for 6 months. Food consumption by AL-fed mice was measured daily, and DR mice received 70% of the amount of food consumed by their respective AL-fed mice the previous day. Body fat (%) and bone mineral density (BMD) and content (BMC) were determined by PIXImus densitometry. There were strain-dependent effects on body mass, crown-to-rump length, percent body fat, and total body, femoral, and vertebral BMD and BMC under all conditions. SENCAR mice were heavier, longer, had larger bones, and generally exhibited higher total body, femoral, and vertebral BMC and BMD than C57 and DBA mice. DR had beneficial effects on BMD and BMC in the vertebrae of the SENCAR mouse model of high free radical generation and in the obese, diabetes-prone C57 mouse model of high end-stage protein glycation. DR DBA and SENCAR mice had lower femoral BMDs and BMCs than their respective AL-fed controls. Regression analysis confirmed linear relationships between total and lean body mass and total body and femoral BMDs and BMCs, suggesting that physiologic adaptation to a lower body mass accounts for the lower femoral bone mineral values observed in DR versus AL-fed mice. Thus, both hypotheses are, at least, partially valid. DR is beneficial in the trabeculae-rich vertebrae of animal models of high oxidant stress, and total/lean body mass determines BMD and BMC in the weight-bearing femur in DR and AL-fed mice.

The effects of dietary restriction on humeral and mandibular bone in SENCAR, C57BL/6, and DBA/2 mice

Dietary restriction (DR) increases the life span and retards the development of age-related disorders. However, the low body mass that accompanies DR is associated with risk factors for fracture that may outweigh the beneficial effects of DR on cellular aging that are mediated, in part, by limiting free radical generation and oxidative damage. We tested the effects of DR in murine models that differ in free radical generation capacity (SENCAR > C57 > DBA). Male mice of each strain were killed at 10 weeks of age (t(0); time zero) or randomized to an ad libitum-fed (AL-fed) or 30% DR feeding regimen for 6 months. The food consumption of AL-fed mice was measured daily. DR mice received 70% of the amount of food consumed by their respective AL-fed mice the previous day. The DR diet was normalized with respect to calcium (Ca), phosphorus (P), and micronutrients. Lean body mass (LBM), bone mineral density (BMD), and bone mineral content (BMC) in the humerus and mandible were determined by PIXImus densitometry. The length and midshaft width of the humerus were determined by direct measurement. There were highly strain- and diet/time-dependent effects on LBM, humerus length, mandibular and humeral BMD, and humeral BMC. The interaction between diet/time and strain was more significant in the humerus than the mandible. All 30% DR mice had lower humeral BMDs and BMCs than their respective AL-fed controls. However, 30% DR C57 and DBA (but not SENCAR) mice had higher humeral BMD and BMC than their respective t(0) controls. There was a linear relationship between LBM and humeral BMD and BMC in both AL-fed and 30% DR mice, suggesting that the lower BMD and BMC in 30% DR mice, relative to AL-fed controls, reflects a physiologic adaptation to lower biomechanical loading. Mandibular BMC in 30% DR C57 (but not DBA or SENCAR) mice was lower than that observed in their AL-fed controls. Mandibular BMD and BMC increased versus t(0) values in 30% DR mice of all strains.

Nutrition and molecular markers of bone remodelling

PURPOSE OF REVIEW

Molecular markers of bone remodelling are noninvasive and comparatively inexpensive tools to evaluate the two major processes of bone renewal: bone formation and bone resorption. Over the past 10 years, research has generated a number of novel and specific bone markers that enable us to investigate those processes even more closely.

RECENT FINDINGS

It has been known for some time that nutritional and lifestyle factors are of great importance in the development and maintenance of normal bone mass and remodelling. Recent studies suggest that hypovitaminosis D is frequent in children and adolescent persons, and may affect their bone health. Clearly, chronic eating disorders such as anorexia nervosa are associated with high rates of bone resorption and bone loss, and increased fracture risk. In obese patients weight loss is associated with changes in both bone mineral density and bone remodelling, although the pathogenesis of these changes is ill defined.

SUMMARY

Nutritional and lifestyle factors influence bone mass and remodelling. Malnutrition, vitamin D deficiency, chronic and acute eating disorders, and diet-induced weight loss often induce high rates of bone resorption and bone loss.

Calorie restriction in biosphere 2: alterations in physiologic, hematologic, hormonal, and biochemical parameters in humans restricted for a 2-year period

Four female and four male crew members, including two of the present authors (R. Walford and T. MacCallum)--seven of the crew being ages 27 to 42 years, and one aged 67 years--were sealed inside Biosphere 2 for two years. During seven eighths of that period they consumed a low-calorie (1750-2100 kcal/d) nutrient-dense diet of vegetables, fruits, nuts, grains, and legumes, with small amounts of dairy, eggs, and meat (approximately 12% calories from protein, approximately 11% from fat, and approximately 77% from complex carbohydrates). They experienced a marked and sustained weight loss of 17 +/- 5%, mostly in the first 8 months. Blood was drawn before entry into Biosphere 2, at many time-points inside it, and four times during the 30 months following exit from it and return to an ad libitum diet. Longitudinal studies of 50 variables on each crew member compared outside and inside values by means of a Bayesian statistical analysis. The data show that physiologic (e.g., body mass index, with a decrease of 19% for men and 13% for women; blood pressure, with a systolic decrease of 25% and a diastolic decrease of 22%), hematologic (e.g., white blood cell count, decreased 31%), hormonal (e.g., insulin, decreased 42%; T3, decreased 19%), biochemical (e.g., blood sugar, decreased 21%; cholesterol, decreased 30%), and a number of additional changes, including values for rT3, cortisol, glycated hemoglobin, plus others, resembled those of rodents or monkeys maintained on a calorie-restricted regime. Significant variations in several substances not hitherto studied in calorie-restricted animals are also reported (e.g., androstenedione, thyroid binding globulin, renin, and transferrin). We conclude that healthy nonobese humans on a low-calorie, nutrient-dense diet show physiologic, hematologic, hormonal, and biochemical changes resembling those of rodents and monkeys on such diets. With regard to the health of humans on such a diet, we observed that despite the selective restriction in calories and marked weight loss, all crew members remained in excellent health and sustained a high level of physical and mental activity throughout the entire 2 years.