Modulation of age-related alterations in membrane composition and receptor-associated immune functions by food restriction in Fischer 344 rats

Calorie restriction modulates neuro-immune system differently in young and aged rats

Aging weakens and deregulates the immune system and plays an impact on the central nervous system (CNS). A crosstalk in between the CNS-mediated immune system and the body's overall innate immunity is often found to increase and subsequently accelerate neurodegeneration and behavioural impairment during aging. Dietary calorie restriction (CR) is found to be a beneficial non-invasive anti-aging therapy as it shows rejuvenation of stress response, brain functions and behaviour during aging. The present investigation deals with the consequence of CR diet supplementation for two different duration (one and two consecutive months) on aging-related alteration of the immune response in male albino Wistar rats at the level of (a) lymphocyte viability, proliferation, cytotoxicity, and DNA fragmentation in blood, spleen, and thymus and (b) cytokines (IL-6, IL-10, and TNF-α) in blood, spleen, thymus and different brain-regions to understand the effect of CR diet on neuroimmune system. The results depict that CR diet consumption for consecutive one and two months by the aged (18 and 24 months) rats significantly attenuated the aging-related (a) decrease of blood, splenic and thymic lymphocyte viability, proliferative activity, cytotoxicity, and IL-10 level and (b) increase of (i) blood, splenic and thymic DNA fragmentation and (ii) IL-6 and TNF-α level in those tissues and also in different brain regions. Unlike older rats, in young (4 months) rats, the consumption of CR diet under similar conditions affected those above-mentioned immune parameters reversibly and adversely. This study concludes that (a) aging significantly (p < 0.01) deregulates the above-mentioned immune parameters, (b) consecutive consumption of CR diet for one and two months is (i) beneficial (p < 0.05) to the aging-related immune system [lymphocyte viability, lymphocyte proliferation, cytotoxicity, pro (IL-6 and TNF-α)- and anti (IL-10)-inflammatory cytokines], but (ii) adverse (p < 0.05) to the immune parameters of the young rats, and (c) consumption of CR diet for consecutive two months is more potent (p < 0.05) than that due to one month.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following eight months of calorie restriction

Calorie restriction (CR) has been shown to decrease reactive oxygen species (ROS) production and retard aging in a variety of species. It has been proposed that alterations in membrane saturation are central to these actions of CR. As a step towards testing this theory, mice were assigned to 4 dietary groups (control and 3 CR groups) and fed AIN-93G diets at 95 % (control) or 60 % (CR) of ad libitum for 8 months. To manipulate membrane composition, the primary dietary fats for the CR groups were soybean oil (also used in the control diet), fish oil or lard. Skeletal muscle mitochondrial lipid composition, proton leak, and H(2)O(2) production were measured. Phospholipid fatty acid composition in CR mice was altered in a manner that reflected the n-3 and n-6 fatty acid profiles of their respective dietary lipid sources. Dietary lipid composition did not alter proton leak kinetics between the CR groups. However, the capacity of mitochondrial complex III to produce ROS was decreased in the CR lard compared to the other CR groups. The results of this study indicate that dietary lipid composition can influence ROS production in muscle mitochondria of CR mice. It remains to be determined if lard or other dietary oils can maximize the CR-induced decreases in ROS production.

Mitochondrial membrane lipid remodeling in pathophysiology: a new target for diet and therapeutic interventions

Mitochondria are arbiters in the fragile balance between cell life and death. These organelles present an intricate membrane system, with a peculiar lipid composition and displaying transverse as well as lateral asymmetry. Some lipids are synthesized inside mitochondria, while others have to be imported or acquired in the form of precursors. Here, we review different processes, including external interventions (e.g., diet) and a range of biological events (apoptosis, disease and aging), which may result in alterations of mitochondrial membrane lipid content. Cardiolipin, the mitochondria lipid trademark, whose biosynthetic pathway is highly regulated, will deserve special attention in this review. The modulation of mitochondrial membrane lipid composition, especially by diet, as a therapeutic strategy for the treatment of some pathologies will be also addressed.

The influence of dietary lipid composition on liver mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of CR (calorie restriction), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and the CR groups were fed diets containing soya bean oil (also in the control diet), fish oil or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak and H₂O₂ production were measured in liver mitochondria following 1 month of CR. The results indicate that mitochondrial phospholipid fatty acids reflect the PUFA (polyunsaturated fatty acid) profile of the dietary lipid sources. CR significantly decreased the capacity of ROS (reactive oxygen species) production by Complex III but did not markedly alter proton leak and ETC (electron transport chain) enzyme activities. Within the CR regimens, the CR-fish group had decreased ROS production by both Complexes I and III, and increased proton leak when compared with the other CR groups. The CR-lard group showed the lowest proton leak compared with the other CR groups. The ETC enzyme activity measurements in the CR regimens showed that Complex I activity was decreased in both the CR-fish and CR-lard groups. Moreover, the CR-fish group also had lower Complex II activity compared with the other CR groups. These results indicate that dietary lipid composition does influence liver mitochondrial phospholipid composition, ROS production, proton leak and ETC enzyme activities in CR animals.

The influence of dietary lipid composition on skeletal muscle mitochondria from mice following 1 month of calorie restriction

To investigate the role mitochondrial membrane lipids play in the actions of calorie restriction (CR), C57BL/6 mice were assigned to four groups (control and three 40% CR groups) and fed diets containing soybean oil (also in the control diet), fish oil, or lard. The fatty acid composition of the major mitochondrial phospholipid classes, proton leak, and H(2)O(2) production were measured in muscle mitochondria following 1 month of CR. The results indicate that phospholipid fatty acids reflected the polyunsaturated fatty acid profile of the dietary lipid sources. Capacity for Complex I- and III-linked H(2)O(2) production was decreased with CR, although there was no difference between CR groups. The CR lard group had lower proton leak than all other groups. The results indicate that a decreased degree of unsaturation in muscle mitochondrial membranes is not required for reduced H(2)O(2) production with CR. However, dietary lipids do have some influence on proton leak with CR.

Calorie restriction attenuates LPS-induced sickness behavior and shifts hypothalamic signaling pathways to an anti-inflammatory bias

Calorie restriction (CR) has been demonstrated to alter cytokine levels; however, its potential to modify sickness behavior (fever, anorexia, cachexia) has not. The effect of CR on sickness behavior was examined in male C57BL/6J mice fed ad libitum or restricted 25% (CR25%) or restricted 50% (CR50%) in food intake for 28 days and injected with 50 μg/kg of LPS on day 29. Changes in body temperature, locomotor activity, body weight, and food intake were determined. A separate cohort of mice were fed ad libitum or CR50% for 28 days, and hypothalamic mRNA expression of inhibitory factor κB-α (IκB-α), cyclooxygenase-2 (COX-2), prostaglandin E(2) (PGE(2)), suppressor of cytokine signaling 3 (SOCS3), IL-10, neuropeptide Y (NPY), leptin, proopiomelanocortin (POMC), and corticotrophin-releasing hormone (CRH) were determined at 0, 2, and 4 h post-LPS. CR50% mice did not develop fevers, whereas the CR25% mice displayed a fever shorter in duration but with the same peak as the controls. Both CR25% and CR50% mice showed no sign of anorexia and reduced cachexia after LPS administration. Hypothalamic mRNA expression of NPY and CRH were both increased by severalfold in CR50% animals preinjection compared with controls. The CR50% mice did not demonstrate the expected rise in hypothalamic mRNA expression of COX-2, microsomal prostaglandin E synthase-1, POMC, or CRH 2 h post-LPS, and leptin expression was decreased at this time point. Increases in SOCS3, IL-10, and IκB-α expression in CR50% animals were enhanced compared with ad libitum-fed controls at 4 h post-LPS. CR results in a suppression of sickness behavior in a dose-dependent manner, which may be due to CR attenuating proinflammatory pathways and enhancing anti-inflammatory pathways.

Gross energy metabolism in mice under late onset, short term caloric restriction

Late onset, short-term moderate caloric restriction (CR) may have beneficial health effects. A 26% CR regime induced at 14 months of age for 70 days in male C57Bl/6 (ICRFa) mice resulted in a reduction in body mass of 17%. A decrease in daily energy expenditure was associated with decreased body mass in CR mice. There was no difference in total levels of physical activity between the CR and ad libitum (AL) groups; however, activity patterns were different. We developed a Bayesian model to dissect the impact of food anticipation activity (FAA) and feeding on physical activity. FAA was stronger in CR mice and remaining basal activity was higher in AL mice, but CR mice displayed larger diurnal variations as well as a phase shift in their diurnal activity. CR mice displayed lower body temperature, especially late during the dark phase. This was due to lower basal (activity-independent) temperature at all times of the day, coupled to a phase shift in the diurnal rhythm. The correlation between body temperature and physical activity was independent of feeding regimen and light/dark cycles. Reduction of body mass and basal temperature were major compensatory mechanisms to reduced food availability during late-onset, short-term CR.

Calorie restriction enhances T-cell-mediated immune response in adult overweight men and women

Calorie restriction (CR) enhances immune response and prolongs life span in animals. However, information on the applicability of these results to humans is limited. T-cell function declines with age. We examined effects of CR on T-cell function in humans. Forty-six overweight, nonobese participants aged 20-42 years were randomly assigned to 30% or 10% CR group for 6 months. Delayed-type hypersensitivity (DTH), T-cell proliferation (TP), and prostaglandin E(2) (PGE(2)) productions were determined before and after CR. DTH and TP to T-cell mitogens were increased in both groups over baseline (p < or = .019). However, number of positive responses to DTH antigens (p = .016) and TP to anti-CD3 reached statistical significance only after 30% CR (p = .001). Lipopolysaccharide-stimulated PGE(2) was reduced in both groups but reached statistical significance after 30% CR (p < or = .029). These results, for the first time, show that 6-month CR in humans improves T-cell function.

Energy restriction impairs natural killer cell function and increases the severity of influenza infection in young adult male C57BL/6 mice

Energy restriction (ER) without malnutrition extends lifespan in mice and postpones age-related changes in immunity. However, we have previously shown that aged (22 mo old) ER mice exhibit increased mortality, impaired viral clearance, and reduced natural killer (NK) cell cytotoxicity following influenza infection compared with aged mice that consumed food ad libitum (AL). To determine whether the detrimental effects of ER in response to influenza infection occur independently of advanced age, young adult (6 mo) male C57BL/6 mice consuming an AL or ER diet were infected with influenza A virus (H1N1, PR8). Young adult ER mice exhibited increased mortality (P < 0.05) and weight loss (P < 0.01) in response to infection. ER mice exhibited decreased total (P < 0.001) and NK1.1+ lymphocytes (P < 0.05) in lung and reduced influenza-induced NK cell cytotoxicity in both lung (P < 0.01) and spleen (P < 0.05). Importantly, the mRNA expression of interferon (IFN)alpha/beta (P < 0.05) was also reduced in the lungs of ER mice in response to infection, and in vitro stimulation of NK cells from ER mice with type I IFN resulted in cytotoxicity comparable to that in NK cells from AL mice. In contrast, NK cell activation was enhanced in ER mice, determined as an increase in the percentage of NK cells expressing B220 (P < 0.001) and increased intracellular production of IFNgamma (P < 0.01). These data describe an age-independent and detrimental effect of ER on the innate immune response to influenza infection and suggest that a decrease in NK cell number and alterations in the NK cell-activating environment may contribute to decreased innate immunity in ER mice.

Health promotion by dietary restriction--a focus

Food restriction, although long popular among gerontologists, has emerged as a new challenge in public health in postindustrial societies because this is the only intervention that repeatedly and strikingly increases maximum life span. The practice of food restriction is widespread for cosmetic, health, and economic reasons. The beneficial effects and the molecular mechanism of food restriction have been well established. The present review summarizes the rapidly accumulating evidence on the involvement of food restriction in various diseases and focuses on good dietary practices for health promotion in modern life style.

Mitochondrial dysfunctions during aging: vitamin E deficiency or caloric restriction--two different ways of modulating stress

Caloric restriction (CR), which has been demonstrated to offset the age-associated accrual of oxidative injury, involves a reduction in calory intake while maintaining adequate nutrition, preserves the activities of antioxidant enzymes in postmitotic tissues, maintains organ function, opposes the development of spontaneous diseases, and prolongs maximum life span in laboratory rodents. It has been proposed that reductions in Reactive Oxygen Species (ROS) production and cellular oxidative injury are central to the positive effects of CR. In the present investigation we studied the effect of CR and of a vitamin E deprived diet on mitochondrial structure and features in the liver of rats during aging, in order to ascertain the extent of modifications induced by these experimental conditions. CR rats displayed structural and functional mitochondrial properties (fatty acid pattern, respiratory chain activities, antioxidant levels, and hydroperoxide contents) similar to those of younger rats whilst vitamin E deficient rats appeared older than their own age. The mitochondria of the former, together with those of young rats, possessed the lowest Coenzyme Q9, hydroperoxide, and cytochrome contents as well as a suitable fatty acid membrane composition. Our study confirms that CR is a valuable tool in limiting aging-related free-radical damage also at mitochondrial liver level.

Inhibition of H2O2-induced apoptosis of lymphocytes by calorie restriction during aging

Calorie restriction (CR) is known to delay the aging process in rodents and is postulated to act by decreasing free radical generation and increasing antioxidant enzyme activity. The present study was designed to investigate the effect of CR and age on oxidative stress-induced apoptosis and associated changes in the levels of TNF-alpha, and Bcl-2 in splenic T lymphocytes. Ad libitum (AL)- or CR-fed C57BL/6J mice were sacrificed either at 6 (young) or 18 (old) months and splenic lymphocytes were incubated with or without 25 micro M H2O2 to induce apoptosis. Apoptosis increased with age in cells of AL-fed mice incubated with H2O2. CR prevented this rise in apoptosis in total splenic lymphocytes and in CD4(+) and CD8(+) T lymphocyte subsets either with or without H2O2. Free radicals increased and mitochondrial membrane potential decreased in aged mice. CR prevented these changes and also prevented the age-associated increase in TNF-alpha and loss of Bcl-2 in total splenic lymphocytes and in CD4(+) and CD8(+) lymphocyte subsets. In summary, lymphocytes in aged AL-fed mice were much more susceptible to oxidative stress-induced apoptosis whereas CR normalized apoptosis by preventing the increase in TNF-alpha and the decrease in Bcl-2 associated with aging.

Molecular mechanisms linking calorie restriction and longevity

Calorie-restricted feeding retards the rate of ageing in mammalian and invertebrate species. The molecular mechanisms underlying this effect include a lower rate of accrual of tissue oxidative damage that is associated with a significantly lower rate of mitochondrial free radical generation in rodent species. To identify the important sites of control and regulation for mitochondrial free radical generation during ageing and calorie-restricted feeding, metabolic control analysis is being applied to the study of mitochondrial bioenergetics. With ageing an increase in the mitochondrial proton leak is observed in mouse hepatocytes and in rat skeletal muscle. Limited data suggest that calorie-restricted feeding lowers the inner mitochondrial membrane potential and this may explain the reduced rate of free radical generation. A lowered unsaturation/saturation index is observed for mitochondrial membrane lipids in calorie-restricted rodents resulting in an altered membrane structure and function. Plasma concentrations of insulin and triiodothyronine are significantly lower under calorie-restricted feeding conditions and these hormones exert transcriptional control over desaturase enzymes that are important in the control of membrane lipid unsaturation. A loss of double bonds should make the mitochondrial membranes more resistant to peroxidation damage and would also reduce the proton conductance of the membrane, raising the membrane potential at a given respiration rate. This effect however, appears to be offset by other membrane changes that may include increased activity of uncoupling proteins. These unidentified adaptations increase the proton leak in calorie-restricted animals resulting in a lowering of the membrane potential and ROS generation.

Retardation of cognitive aging by life-long diet restriction: implications for genetic variance

Long-term moderate dietary restriction (DR) has been reported to extend life spans, delay the onset and decrease the incidence of a broad spectrum of age-associated diseases; however, its effect on cognition is still unclear. Our previous results indicated that long-term DR failed to retard cognitive and psychomotor aging in the inbred strain, Fischer-344 rats. In the present experiment, an anti-aging effect of DR on various types of cognitive and sensorimotor behaviors was found in F1 hybrid Fischer-344 x Brown Norway (F-344xBN) rats, while no effect of DR was detected in the second parental inbred strain, Brown-Norway (BN) rats. These findings show that the lack of an effect of DR on cognitive aging, which was previously found in Fischer-344 rats, is not a universal phenomenon. Instead, the effect of DR may depend upon the genetic makeup of the animals. Thus, a more diverse genetic milieu, such as in hybrid rats, relative to inbred rats, may increase the susceptibility to an effect of DR on age-related cognitive decline.

Life span is prolonged in food-restricted autoimmune-prone (NZB x NZW)F(1) mice fed a diet enriched with (n-3) fatty acids

Moderate food and/or energy (calorie) restriction delays age-related immune dysfunction and prolongs life span in multiple animal models. The amount and type of dietary fatty acids can also profoundly affect life span. Marine-derived fish oils contain (n-3) fatty acids, which have potent anti-inflammatory properties. We therefore examined the influence of food restriction (40% overall reduction in intake of all dietary components) combined with substitution of fish oil for corn oil in a factorial design. Autoimmune-prone (NZB x NZW)F(1) (B/W) mice, which develop fatal autoimmune renal disease, were used. The food-restricted/fish oil diet maximally extended median life span to 645 d (vs. 494 d for the food-restricted corn oil diet). Similarly, fish oil prolonged life span in the ad libitum-fed mice to 345 d (vs. 242 for the ad libitum/corn oil diet). Increased life span was partially associated with decreased body weight, blunting renal proinflammatory cytokine (interferon-gamma, interleukins-10 and -12 and tumor necrosis factor-alpha) levels and lower nuclear factor-kappaB (NF-kappaB). Reductions in NF-kappaB were preceded by enhanced superoxide dismutase, catalase and glutathione peroxidase activities. These findings demonstrate the profound additive effects of food restriction and (n-3) fatty acids in prolonging life span in B/W mice. These observations may have additional implications in the management of obesity, diabetes, cancer and/or the aging process.

Caloric restriction mimetics: metabolic interventions

Caloric restriction (CR) retards diseases and aging in laboratory rodents and is now being tested in nonhuman primates. One way to apply these findings to human health is to identify and test agents that may mimic critical actions of CR. Panel 2 focused on two outcomes of CR, reduction of oxidative stress and improved glucoregulation, for which candidate metabolic mimics exist. It was recommended that studies on oxidative stress should emphasize mitochondrial function and to test the efficacy of nitrone and other antioxidants in mimicking CR's effects. Studies should also focus on the long-term effects of compounds known to lower circulating glucose and insulin concentrations or to increase insulin sensitivity. Also, four other developing areas were identified: intermediary metabolism, response to infection, stress responses, and source of dietary fat. These areas are important because either they hold promise for the discovery of new mimetics or they need to be explored prior to initiation of CR trials in humans. Other recommendations were that transgenic approaches and adult-onset CR should be emphasized in future studies.

Chronic caloric restriction alters muscle membrane fatty acid content

Chronic caloric restriction (CR) has been demonstrated to increase longevity in lower species and studies are ongoing to evaluate its effect in higher species. A consistent metabolic feature of CR is improved insulin sensitivity and lowered lifetime glycemia, yet the mechanism responsible is currently unknown. However, the membrane's physiochemical properties, as determined by phospholipid composition, have been related to insulin action in animal and human studies and CR has been reported to alter membrane lipid content. We evaluated muscle membrane fatty acid content in rodents randomized to CR versus control diets for up to 29 months. CR was observed to increase the membrane content of C22:6 (docosahexaenoate) and to decrease C18:2 content. The membrane lipid content was related to insulin levels but not to parameters assessing glycemic control. This study suggests that membrane lipids, in particular 22:6, may contribute to the variation in insulin sensitivity seen with age.

Food restriction beneficially affects renal transport and cortical membrane lipid content in rats

Food restriction (FR) exerts a variety of beneficial effects and may prolong life in both humans and animals. However, studies of its effects on the cortical brush border membrane (BBM) and basolateral membrane (BLM) lipid concentration, which may be pertinent to renal function, have not been reported in detail. We hypothesized that FR would decrease renal work and lower renal membrane lipid concentration. The changes in lipid concentration would be most dramatic in BBM because this membrane is the entry site for the recovery of filtered ions and nutrients. Young male Fischer 344 x Brown-Norway F1 rats consumed food ad libitum (AL) or were food-restricted (FR, 60% of AL consumption) for 6 wk. AL rats had higher fractional excretions of Na(+), K(+), and Cl(-) than did the FR group (P < 0.001). Renal Na,K-ATPase activity in AL rats was 100% higher than in FR rats (P < 0.001), reflecting greater renal work. The work required for renal proton secretion was lower in FR than in the AL rats. In FR rats, all BBM phospholipid concentrations (phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin) were approximately 50% lower than in the AL rats (P < 0.001). In the BLM, food restriction resulted only in lower phosphatidylcholine concentration, while the other phospholipids were unaffected. Plasma and renal membrane (BBM and BLM) cholesterol concentrations were significantly lower in FR than in AL rats. These results show that a nutritionally complete, but energy restricted, diet improves renal function. It also prevents renal membrane lipid deposition and decreases plasma cholesterol. Prolonged food restriction might attenuate the renal injury that occurs in obese humans as a consequence of insulin resistance and atherosclerosis.

Effects of calorie restriction and ω-3 dietary fat on aging in short-and long-lived rodents

Aging is accompanied by a steady increase in the incidence of spontaneous tumors and a decline in immune function. Calorie restriction (CR) or supplementation with ω-3 fats prolongs life span, suppresses tumorigenesis, and ameliorates immune function in a variety of experimental models. We suggest that decreased oxidant stress and upregulation of apoptosis mediate the effects of calorie restriction on immunity and longevity. CR prolongs life span in several animal models and our studies have examined the effects of CR on the immune system and on tumorigenesis. CR maintains naive T cells, prevents the rise in "double-negative" T cells, maintains lymphocyte responsiveness to mitogens, and preserves Dexamethasone induced apoptosis in spleen cells of MRL/Ipr mice. CR also modulates the expression of inflammatory mediators and cytokines. CR decreases the Sjögren's syndrome-like chronic inflammation of salivary glands of B/W animals while increasing expression of the immunosuppressive cytokine TGFβ1 and decreasing expression of the pro-inflammatory cytokines IL-6 and TNFα. The autoimmune disease in the B/W mouse also affects the kidneys, and we find that renal expression of platelet derived growth factor-A, (PDGF-A) and thrombin receptor are decreased in CR animals. Similarly, CR decreases the expression and localization of plasminogen activator inhibitor type 1 in glomeruli of B/W animals. CR also modulates expression and function of androgen receptors and the binding of insulin to liver nuclei. Finally, CR suppresses the development of breast tumors in the Ras oncomouse. These effects of calorie restriction are paralleled in short-lived B/W animals fed diets supplemented with ω-3 fatty acids. Omega-3 fatty acids induce the expression of hepatic antioxidant enzymes, and enhance apoptosis in lymphocytes of B/W animals.

Intervention in the aging immune system: Influence of dietary restriction, dehydroepiandrosterone, melatonin, and exercise

The decline in immunologic function with age is associated with an increase in susceptibility to infections and the occurrence of autoimmune diseases and cancers. Hence, the restoration of immunologic function is expected to have a beneficial effect in reducing pathology and maintaining a healthy condition in advanced age. A number of therapeutic strategies have been employed to intervene in the aging immune system. This article reviews the effect of dietary restriction (DR), dehydroepiandrosterone (DHEA) treatment, melatonin (MLT) therapy, and exercise on modulating the immune responses and retarding/reducing immunosenescence. DR has been subject to intensive research and is known to be the most efficacious means of increasing longevity, reducing pathology and enhancing immune function. The circulatory levels of the androgenic hormone DHEA and the pineal hormone MLT decrease with increasing age, and this decrease has been correlated with the age-related decline in the immune system. Therefore, the observation that immunosenescence is associated with low levels of DHEA and MLT has provided a rationale for therapeutic intervention. DHEA treatment and MLT therapy both exhibit immunostimulatory actions and preliminary reports indicate that hormonal (DHEA or MLT) substitution therapy reverses immunosenescence in mice. Similarly, exercise in some studies has been shown to enhance the immune response. However, these findings have not been confirmed by other laboratories. Thus, at the present time, it is difficult to draw any definitive conclusions on the efficacy of DHEA, MLT, and exercise on reversing or restoring the aging immune system.

Caloric restriction and experimental mammary carcinogenesis

It has been demonstrated repeatedly that caloric restriction, or underfeeding, will inhibit the growth of spontaneous, transplanted, or induced tumors in mice and rats. Caloric restriction will inhibit tumorigenesis even in the face of a high fat diet. The mechanism of action is moot but caloric restriction reduces plasma insulin levels, increases activities of antioxidant enzymes, and enhances DNA repair. It also reduces oncogene expression. The cancer growth-inhibiting action of caloric restriction may be reversed by adrenalectomy.

Increased apoptosis of CD45RO- T cells with aging

Increasing susceptibility to infectious and autoimmune phenomena have long been recognized to accompany advancing age in otherwise healthy individuals. Recently animal models of aging have suggested that age-associated immune dysfunction may correlate with defects in T cell apoptosis. We have examined activation-induced apoptosis defects in human peripheral T cells from young individuals (mean age = 31 +/- 3 years old) compared to aged individuals (mean age = 67 +/- 8 years old). Following in vitro activation of T cells with PHA and IL-2, apoptosis was measured in T cell subsets using 7-amino actinomycin D (7-AAD) staining and analysis via three colour flow cytometry. There was no significant difference in apoptosis of the total CD3+ T cell population at early and late time points. Interestingly, increased apoptosis in the CD3+ CD45RO- T cell population of older adults was observed by culture day 6. While the total number of CD3+ CD45RO- cells was not different between young (< 33 years) and old (> 65 years) individuals, 32% of these cells did not undergo apoptosis in younger individuals while only 10% of these cells avoided this fate in older individuals. These results suggest that accumulation of CD45RO+ T cells may occur in aged subjects due in part to preferential elimination of CD45RO- cells with activation. Furthermore, as new or continued immune response requires differentiation of CD45RO+ T cells to CD45RO+ T cells after activation, increased apoptosis instead of survival in aged individuals could lead to observed T cell immune deficiency.

Exercise, immunity and aging

In general population, many protective immune responses are impaired in old age, leading to an increased risk of infection. However, recent studies in SENIEUR subjects (healthy centenarians who are examples of successful aging) suggest that complex remodeling and reshaping of the immune system occurs with aging. An appropriate regular regimen of endurance exercise might help elderly to lead a quality of life by preserving immune function. However, very little is known regarding the interaction between exercise, aging and the immune system. Given that a number of age-related changes occur in many physiological systems which are known to alter the immune function both at rest and during exercise, it would be of value to learn the extent to which both acute and chronic exercise influence immune function in the elderly. The immune system response to exercise is multifaceted, depending on the nature of exercise. Significant interaction between the neuroendocrine and immune systems, and the role of lifestyle factors in immune function are known to occur. In theory, moderate exercise should help to reverse the adverse effects of aging upon the immune system by increasing the production of endocrine hormones which may contribute to less accumulation of autoreactive immune cells by enhancing the programmed cell death. Active elderly subjects demonstrated a significantly greater proliferative response to phytohemagglutinins (PHA) and to pokeweed mitogen (PWM), and higher rates of interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) production. A moderate training program can enhance the resting natural killer (NK) cell function of healthy elderly people, potentially increasing resistance to both viral infections and preventing the formation of malignant cells. Recent studies have suggested that endurance training in later life is associated with a lesser age-related decline in certain aspects of circulating T cell function and related cytokine production. It is important that the dose of physical activity needed to optimize immune function be defined more clearly at various points during the aging process both in females and males in order to optimize the immune function and to prevent any rise in adverse effects of exercise on the elderly population.

The effect of age on the expression of interleukin-2

Interleukin-2 (IL-2) is a growth promoting cytokine that has received a great deal of attention over the past decade with respect to aging and cancer. It is produced primarily by helper T cells and regulates the growth and function of various cells that are involved in cellular and humoral immunity. The expression of IL-2 has been found to decrease with age in humans and rodents. The decline in IL-2 production has been shown to parallel the age-related decrease in immunologic function. Several studies indicate that treatment of lymphocytes from old subjects with exogenous IL-2 or infusion of IL-2 into old animals partially or completely restores some of the immune functions that decline with age. The age-related decline in IL-2 production has been shown to arise from a decline in IL-2 transcription, and a recent study suggests that the transcription factor NFAT (nuclear factor of activated T cells) may play a role in the decline in IL-2 transcription.

Effects of caloric restriction on age-related oxidative modifications of macromolecules and lymphocyte proliferation in rats

Decreased immune function associated with aging has been demonstrated in both humans and animals. We hypothesize that reactive oxygen species (ROS)-mediated damage to biological macromolecules may contribute to compromised immune response during aging. In this study, we compared the levels of lipid peroxidation and oxidatively modified proteins in plasma and splenocytes, and the mitogen-induced T lymphocyte proliferation in ad lib-fed (AL) and caloric restricted (CR) Fischer 344 x BNF1 male rats at the ages of 5, 18, and 31 months. The results show that AL rats exhibit an age-related decrease in proliferative response of splenic lymphocytes to phytohemagglutinin (PHA) and concanavalin A (Con A). This functional decline in T-lymphocytes during aging is inversely correlated to the levels of both lipid peroxidation and protein carbonyl in the plasma and splenic lymphocytes. Caloric restriction, however, can partially reverse the age-dependent decrease in T lymphocyte proliferation and significantly reduce lipid peroxidation and protein carbonyl contents in plasma and splenocytes. The above observations support the hypothesis that the age-associated declines in immune function are related to the oxidative modification of biological macromolecules, which in turn may lead to enzyme inactivation, membrane disruption, and cell senescence. One of the mechanisms by which caloric restriction reverses declined immune function in aged rats is hypothesized to be through reduction in ROS production and thereby protection of cellular macromolecules against oxidative damage.

Calorie restriction modulates lymphocyte subset phenotype and increases apoptosis in MRL/lpr mice

Defective expression of the Fas apoptotic gene may account for overproduction of CD4- CD8- B220+ cells (double-negative) in MRL/MpJ-lpr/lpr (lpr) mice. Previous studies have shown that calorie restriction (CR) inhibits the development of autoimmune disease and extends life span in these animals. The present studies describe the effects of CR on the distribution of lymphocyte phenotypes, lymphocyte proliferative response, and cytokine release. The effects of CR on dexamethasone (DEX)-induced apoptosis were also studied using propidium iodide (PI) uptake and DNA fragmentation in splenocytes and lymph node (LN) cells. Weanling female mice were fed a nutritionally adequate semipurified diet either ad libitum (AL) or with 40% fewer calories than AL (CR), and killed at 5 months of age. CR mice had fewer palpable lymph nodes, and decreased serum anti-dsDNA antibodies. Mitogen (ConA, anti-CD3, and LPS) and superantigen (SEB)-induced proliferative response was significantly lower in lymphoid cells from AL fed animals. FACS analysis of cells from CR animals showed decreased CD4- CD8- cells in spleen (1.7-fold, P < 0.025) and LN (1.6-fold P < 0.01) and significantly higher CD4+ (spleen, 1.7-fold, P < 0.0001; LN, 2.6-fold, P < 0.025) and CD8+ (spleen, 1.6-fold, P < 0.001; LN, 5.2-fold, P < 0.005) cells. ConA-stimulated IL-2 release was increased in CR animals (splenocytes, 7.5-fold, P < 0.001; LN cells, 6.1-fold, P < 0.01). Finally, apoptosis in response to Dex was increased in CR animals as indicated by the presence of more PI-positive cells (spleen, 15.8%; LN, 10.7%; P < 0.01) and increased DNA fragmentation. In summary, the amelioration of autoimmune disease in MRL/lpr mice by CR is accompanied by prevention of the rise in 'double-negative' T cells and by maintenance of lymphocyte responsiveness to mitogens and DEX-induced apoptosis at higher levels.

Modulation of antioxidant activities and immune response by food restriction in aging Fisher-344 rats

Food restriction delays the loss of several cellular immune functions, retards the onset of many diseases during aging and, consequently, extends life span significantly in laboratory rodents. The present study was undertaken to determine whether the age-associated loss in immune function is linked to changes in microsomal and mitochondrial membranes of spleens in Fischer-344 (F-344) male rats. In this study, we determined cytosolic superoxide dismutase activity (SOD), fluidity and cholesterol content in the splenic microsomal and mitochondrial membranes, and DNA synthesis and IL-2 production in spleen cells from young and old ad libitum-fed (AL) and food restricted (FR) rats. The results show that proliferative response to phytohemagglutinin (PHA) and concanavalin A (Con-A) was significantly higher in the spleen cells of 18-month- and 24-month-old FR rats, as compared to their age-matched AL controls. Cytosolic SOD activity in the 24-month-old AL rats decreased by 28% as compared to 6-month-old AL rats, whereas in FR old rats, the loss was only 12%, suggesting that food restriction prevents loss in cytosolic SOD activity in spleens. Our data are consistent with the notion that food restriction modulates loss in immune response of splenocytes by maintaining both cytosolic SOD activity and membrane fluidity during aging.

Cell mediated immunity changes in ageing, relative importance of cell subpopulation switches and of nutritional factors

Decreased T-cell functions with ageing have been extensively described. This review focuses on recent data on changes in T-cell subpopulations related to ageing and their consequences on T-cell proliferation. Increase of immature T cells CD2+ CD3- is an ageing phenomenon related to T-cell declining proliferation. Recently it was shown that increase of immature T cells was due to an increase in different subtypes of the CD2+ CD3- population, double-negative CD2+ CD4- CD8- and double-positive CD2+ CD4+ CD8+ subpopulations, the former being associated with nutritional deficit, the latter with associated diseases. Other authors have focused on decreases of native T cells with parallel increase of memory T cells; such a switch is also relevant to declining T-cell proliferation. This review focuses on two major factors which influence immune ageing; nutritional parameters and antigen exposure.