Effects of calorie restriction on polymicrobial peritonitis induced by cecum ligation and puncture in young C57BL/6 mice

Energy intake and response to infection with influenza

Influenza is a worldwide public health concern, particularly with emerging new strains of influenza to which vaccines are ineffective, limited, or unavailable. In addition, the relationship between adequate nutrition and immune function has been repeatedly demonstrated. Mouse models provide strong evidence that energy extremes, including energy restriction (ER) and diet-induced obesity (DIO), have deleterious effects on the immune response to influenza infection. Both ER and DIO mice demonstrate increased susceptibility and mortality to influenza infection. The effects of ER are more pronounced during innate responses to influenza infection, whereas the effects of DIO are evidenced during innate and adaptive responses to both primary and secondary infection. There are striking similarities between ER and DIO during influenza infection, including impaired natural killer cell function and altered inflammation. Future studies must develop effective nutritional paradigms to offset the effects of these energy extremes on the immune response to an acute infection.

Caloric restriction increases free radicals and inducible nitric oxide synthase expression in mice infected with Salmonella Typhimurium

It is well known that CR (caloric restriction) reduces oxidative damage to proteins, lipids and DNA, although the underlying mechanism is unclear. However, information concerning the effect of CR on the host response to infection is sparse. In this study, 6-month-old mice that were fed AL (ad libitum) or with a CR diet were infected with Salmonella serovar Typhimurium. EPR (electron paramagnetic resonance; also known as ESR (electron spin resonance)) was used to identify FRs (free radicals). These results were subsequently correlated with SOD (superoxide dismutase) catalytic activity, iNOS [inducible NOS (nitric oxide synthase) or NOSII] expression and NO (nitric oxide) content. EPR analysis of liver samples demonstrated that there was a higher quantity of FRs and iron-nitrosyl complex in infected mice provided with a CR diet as compared with those on an AL diet, indicating that CR was beneficial by increasing the host response to Salmonella Typhimurium. Furthermore, in infected mice on the CR diet, NOSII expression was higher, NO content was greater and spleen colonization was lower, compared with mice on the AL diet. No changes in SOD activity were detected, indicating that the NO produced participated more in the formation of iron-nitrosyl complexes than peroxynitrite. These results suggest that CR exerts a protective effect against Salmonella Typhimurium infection by increasing NO production.

Acute stress response modified by modest inhibition of growth hormone axis: a potential machinery of the anti-aging effect of calorie restriction

Calorie restriction (CR) may exert antiaging effects by inhibiting the growth hormone (GH)/IGF-1 axis. The present study investigated the effect of modest inhibition of GH signaling on stress response and compared it with the effect of CR. Heterozygous (tg/-) rats of a transgenic strain of male rats, whose GH signaling was inhibited by overexpression of the anti-sense GH gene, and wild-type (WT) rats were used. Rats were fed ad libitum (AL) or 30% CR diets from 6 weeks of age. At 6 months of age, rats were killed between 0 and 8h after lipopolysaccharide (LPS) injection to evaluate the acute phase stress response. tg/- rats had less tissue injury, indicated by blood aspartate aminotransferase (AST) concentrations, than WT rats. Successive waves of incremental plasma TNF-α, IL-6, and interferon (IFN)-γ levels were also attenuated in tg/- rats. Activation of NF-κB, a redox-sensitive transcription factor, was slightly diminished in tg/- rats, whereas the AP-1 activity was increased. Similar trends were also observed in the CR groups as compared to the AL groups. The present results suggest an involvement of the GH/IGF-1 axis in the effect of CR for stress response, even if CR does not act solely through the GH axis.

The fat-1 transgene in mice increases antioxidant potential, reduces pro-inflammatory cytokine levels, and enhances PPAR-gamma and SIRT-1 expression on a calorie restricted diet

Both n-3 fatty acids (FA) and calorie-restriction (CR) are known to exert anti-inflammatory and anti-oxidative effects in animals and humans. In this study, we investigated the synergistic anti-inflammatory and anti-oxidative capacity of n-3 FA and CR using Fat-1 transgenic mice (Fat-1) that are capable of converting n-6 FA to n-3 FA endogenously. Wild type (WT) and Fat-1 mice were maintained on ad libitum (AL) or CR (40% less than AL) AIN-93 diet supplemented with 10% corn oil (rich in n-6 FA) for 5 months. Significantly lower levels of n-6/n-3 FA ratio were observed in serum, muscle and liver of Fat-1 mice fed AL or CR as compared to that of WT mice fed AL or CR. Muscle catalase (CAT), super oxide dismutase (SOD), glutathione peroxidase (GPX) activities, and liver CAT and SOD activities were found higher in Fat-1 mice as compared to that of WT mice. These activities were more pronounced in Fat-1/CR group as compared to other groups. Serum pro-inflammatory markers, such as tumor necrosis factor (TNF)α, interleukin (IL)-1β and IL-6 were found lower in Fat-1 mice, as compared to that of WT mice. This anti-inflammatory effect was also more pronounced in Fat-1/CR group as compared to that of other groups. Furthermore, significantly higher levels of peroxisome proliferator-activated receptor (PPA R)gamma and life prolonging gene, sirtuin (SIRT)-1 expression were found in liver of Fat-1/CR mice, as compared to that of WT/CR mice. These data suggest that n-3 FA along with moderate CR may prolong lifespan by attenuating inflammation and oxidative stress.

Caloric restriction reduces IgA levels and modifies cytokine mRNA expression in mouse small intestine

The aim of this study was to determine the effect of caloric restriction (CR) in mouse small intestine on the production and secretion of immunoglobulin (Ig) A, the population of lymphocytes in the lamina propria, and the expression of cytokines that mediate and regulate innate and adaptive immunity. One group of young Balb/c mice was fed ad libitum, while the CR group was fed ad libitum and fasted on alternate days. When mice were six months old, IgA levels in the proximal small intestine were quantified by enzyme-linked immunosorbent assay, while the number of IgA containing cells, CD4(+) T cells and CD8(+) T cells in the duodenal mucosa was determined by immunohistochemistry. Furthermore, the expression of several intestinal cytokines, the genes for α-chain IgA, and the polymeric Ig receptor (pIgR) were analyzed by real-time polymerase chain reaction. CR decreased the levels of IgA in the intestine, apparently a consequence of a reduced number of IgA(+) cells in the lamina propria that decrease the production and secretion of this Ig, and a reduced secretion of S-IgA into the bile, which in turn discharges into the proximal intestine. Contrarily, CR increased the expression of genes for α-chain IgA, and the pIgR, indicating that transport of IgA was not a key factor in the decrease of this Ig. Additionally, CR modified the expression of genes for tumor necrosis factor-α, interferon-γ, tumor growth factor-β, interleukin (IL)-2 and IL-10, all of which regulate the synthesis of IgA and pIgR, the inflammatory response, and the immune response in the intestine.

Starvation alters the liver transcriptome of the innate immune response in Atlantic salmon (Salmo salar)

BACKGROUND

The immune response is an energy demanding process, which has effects in many physiological pathways in the body including protein and lipid metabolism. During an inflammatory response the liver is required to produce high levels of acute phase response proteins that attempt to neutralise an invading pathogen. Although this has been extensively studied in both mammals and fish, little is known about how high and low energy reserves modulate the response to an infection in fish which are ectothermic vertebrates. Food withdrawal in fish causes a decrease in metabolic rate so as to preserve protein and lipid energy reserves, which occurs naturally during the life cycle of many salmonids. Here we investigated how the feeding or fasting of Atlantic salmon affected the transcriptional response in the liver to an acute bacterial infection.

RESULTS

Total liver RNA was extracted from four different groups of salmon. Two groups were fed or starved for 28 days. One of each of the fed or starved groups was then exposed to an acute bacterial infection. Twenty four hours later (day 29) the livers were isolated from all fish for RNA extraction. The transcriptional changes were examined by micro array analysis using a 17 K Atlantic salmon cDNA microarray. The expression profiling results showed major changes in gene transcription in each of the groups. Enrichment for particular biological pathways was examined by analysis of gene ontology. Those fish that were starved decreased immune gene transcription and reduced production of plasma protein genes, and upon infection there was a further decrease in genes encoding plasma proteins but a large increase in acute phase response proteins. The latter was greater in magnitude than in the fish that had been fed prior to infection. The expression of several genes that were found altered during microarray analysis was confirmed by real time PCR.

CONCLUSIONS

We demonstrate that both starvation and infection have profound effects on transcription in the liver of salmon. There was a significant effect on the transcriptional response to infection depending on the prior feeding regime of the fish. It is likely that the energy demands on protein synthesis for acute phase response proteins are relatively high in the starved fish which have reduced energy reserves. This has implications for dietary control of fish if an immune response is anticipated.

Update on the oxidative stress theory of aging: does oxidative stress play a role in aging or healthy aging?

The oxidative stress theory of aging predicts that manipulations that alter oxidative stress/damage will alter aging. The gold standard for determining whether aging is altered is life span, i.e., does altering oxidative stress/damage change life span? Mice with genetic manipulations in their antioxidant defense system designed to directly address this prediction have, with few exceptions, shown no change in life span. However, when these transgenic/knockout mice are tested using models that develop various types of age-related pathology, they show alterations in progression and/or severity of pathology as predicted by the oxidative stress theory: increased oxidative stress accelerates pathology and reduced oxidative stress retards pathology. These contradictory observations might mean that (a) oxidative stress plays a very limited, if any, role in aging but a major role in health span and/or (b) the role that oxidative stress plays in aging depends on environment. In environments with minimal stress, as expected under optimal husbandry, oxidative damage plays little role in aging. However, under chronic stress, including pathological phenotypes that diminish optimal health, oxidative stress/damage plays a major role in aging. Under these conditions, enhanced antioxidant defenses exert an "antiaging" action, leading to changes in life span, age-related pathology, and physiological function as predicted by the oxidative stress theory of aging.

Short-term dietary restriction and fasting precondition against ischemia reperfusion injury in mice

Dietary restriction (DR) extends lifespan and increases resistance to multiple forms of stress, including ischemia reperfusion injury to the brain and heart in rodents. While maximal effects on lifespan require long-term restriction, the kinetics of onset of benefits against acute stress is not known. Here, we show that 2-4 weeks of 30% DR improved survival and kidney function following renal ischemia reperfusion injury in mice. Brief periods of water-only fasting were similarly effective at protecting against ischemic damage. Significant protection occurred within 1 day, persisted for several days beyond the fasting period and extended to another organ, the liver. Protection by both short-term DR and fasting correlated with improved insulin sensitivity, increased expression of markers of antioxidant defense and reduced expression of markers of inflammation and insulin/insulin-like growth factor-1 signaling. Unbiased transcriptional profiling of kidneys from mice subject to short-term DR or fasting revealed a significant enrichment of signature genes of long-term DR. These data demonstrate that brief periods of reduced food intake, including short-term daily restriction and fasting, can increase resistance to ischemia reperfusion injury in rodents and suggest a rapid onset of benefits of DR in mammals.

SIRT1 suppresses activator protein-1 transcriptional activity and cyclooxygenase-2 expression in macrophages

SIRT1 (Sirtuin type 1), a mammalian orthologue of yeast SIR2 (silent information regulator 2), has been shown to mediate a variety of calorie restriction (CR)-induced physiological events, such as cell fate regulation via deacetylation of the substrate proteins. However, whether SIRT1 deacetylates activator protein-1 (AP-1) to influence its transcriptional activity and target gene expression is still unknown. Here we demonstrate that SIRT1 directly interacts with the basic leucine zipper domains of c-Fos and c-Jun, the major components of AP-1, by which SIRT1 suppressed the transcriptional activity of AP-1. This process requires the deacetylase activity of SIRT1. Notably, SIRT1 reduced the expression of COX-2, a typical AP-1 target gene, and decreased prostaglandin E(2) (PGE(2)) production of peritoneal macrophages (pMPhis). pMPhis with SIRT1 overexpression displayed improved phagocytosis and tumoricidal functions, which are associated with depressed PGE(2). Furthermore, SIRT1 protein level was up-regulated in CR mouse pMPhis, whereas elevated SIRT1 decreased COX-2 expression and improved PGE(2)-related macrophage functions that were reversed following inhibition of SIRT1 deacetylase activity. Thus, our results indicate that SIRT1 may be a mediator of CR-induced macrophage regulation, and its deacetylase activity contributes to the inhibition of AP-1 transcriptional activity and COX-2 expression leading to amelioration of macrophage function.

Immune deviation and alleviation of allergic reactions in mice subjected to dietary restriction

We examined cytokine production and allergic reactions in mice fed ad libitum (AL) and subjected to dietary restriction (DR). DR retarded the increase in body weight, and peripheral blood T cells in the DR mice produced less IFN-gamma and more IL-4 in response to immobilized anti-CD3 mAb. Systemic immunization and intranasal challenge with ovalbumin (OVA) induced accumulation of leukocytes into the lung, increase in IL-4 level in bronchoalveolar lavage fluid (BALF), and rise in serum IgE in the AL mice. In contrast, these allergic symptoms were alleviated in the DR mice. Furthermore, the relative proportion of IL-4-producing T cells responsive to OVA was less in the DR mice than the AL mice. DR tended to decrease the proportion and cytolytic activity of NK cells in the spleen, especially in younger mice. These results indicate that DR can prevent the expansion of allergen-specific IL-4-producing T cells followed by suppression of the allergic reaction, but might dampen NK cell activity.

The role of anorexia in resistance and tolerance to infections in Drosophila

Most infections induce anorexia but its function, if any, remains unclear. Because this response is common among animals, we hypothesized that infection-induced diet restriction might be an adaptive trait that modulates the host's ability to fight infection. Two defense strategies protect hosts against infections: resistance, which is the ability to control pathogen levels, and tolerance, which helps the host endure infection-induced pathology. Here we show that infected fruit flies become anorexic and that diet restriction alters defenses, increasing the fly's tolerance to Salmonella typhimurium infections while decreasing resistance to Listeria monocytogenes. This suggests that attempts to extend lifespan through diet restriction or the manipulation of pathways mimicking this process will have complicated effects on a host's ability to fight infections.

Long-lived ames dwarf mice are resistant to chemical stressors

To probe the connection between longevity and stress resistance, we compared the sensitivity of Ames long-lived dwarf mice and control littermates with paraquat, diquat, and dobutamine. In young adult animals, 95% of male and 39% of female controls died after paraquat administration, but no dwarf animals died. When the experiment was repeated at an older age or a higher dosage of paraquat, dwarf mice still showed greater resistance. Dwarf mice also were more resistant to diquat; 80% of male and 60% of female controls died compared with 40% and 20% of dwarf mice, despite greater sensitivity of dwarf liver to diquat. Dwarf mice were also less sensitive to dobutamine-induced cardiac stress and had lower levels of liver and lung F(2)-isoprostanes. This is the first direct in vivo evidence that long-lived Ames dwarf mice have enhanced resistance to chemical insult, particularly oxidative stressors.

Optimal window of caloric restriction onset limits its beneficial impact on T-cell senescence in primates

We have recently shown in non-human primates that caloric restriction (CR) initiated during adulthood can delay T-cell aging and preserve naïve CD8 and CD4 T cells into advanced age. An important question is whether CR can be initiated at any time in life, and whether age at the time of onset would modulate the beneficial effects of CR. In the current study, we evaluated the impact of CR started before puberty or during advanced age on T-cell senescence and compared it to the effects of CR started in early adulthood. Our data demonstrate that the beneficial effects of adult-onset CR on T-cell aging were lost by both early and late CR onset. In fact, some of our results suggest that inappropriate initiation of CR may be harmful to the maintenance of T-cell function. This suggests that there may be an optimal window during adulthood where CR can delay immune senescence and improve correlates of immunity in primates.

Calorie restriction and susceptibility to intact pathogens

Long-term calorie restriction (CR) causes numerous physiological changes that ultimately increase mean and maximum lifespan of most species examined to date. One physiological change that occurs with CR is enhanced immune function, as tested using antigens and mitogens to stimulate an immune response. Fewer studies have used intact pathogen exposure to test whether the enhanced capacity of the immune response during CR actually decreases susceptibility of hosts to their pathogens. So far, studies using intact bacteria, virus, and helminth worm exposure indicate that, despite similar or enhanced immune system function, CR hosts are more susceptible to infection by intact pathogens than their fully fed counterparts. Long-term CR studies that examine susceptibility to a variety of parasite taxa will help determine if direct CR or CR mimetics will be beneficial to people living in pathogen-rich environments.

Chronic calorie restriction increases susceptibility of laboratory mice (Mus musculus) to a primary intestinal parasite infection

Long-term calorie restriction (CR) has numerous benefits; however, effects of CR on susceptibility to intact pathogens are not well understood. Because CR enhances immune function of laboratory mice (Mus musculus), it was hypothesized that mice subjected to CR would be less susceptible to experimental infections of the intestinal parasite Heligmosomoides bakeri. Furthermore, because H. bakeri must combat a greater host immune response by CR mice compared to fully fed mice, it also was also hypothesized that (i) worms living in CR hosts would have lower reproduction than worms from ad libitum-fed mice, and (ii) CR mice would have a more female-biased sex ratio as male worms may be more vulnerable to host immune response than female worms. Mice were subjected to CR for 6.7 months and were then infected with H. bakeri for one additional month. As expected, CR mice had equal or enhanced immune response (eosinophils and immunoglobin G1 production) to H. bakeri infection compared to ad libitum-fed mice, and CR mice harbored a more female-biased sex ratio than ad libitum-fed mice. Contrary to predictions, CR mice had more worms than ad libitum-fed mice and the worms from CR mice produced more eggs than worms from ad libitum-fed mice. These data indicate that, despite the evidence that long-term CR enhances traditional measures of immune function, CR may actually increase susceptibility to intact parasite infection. Furthermore, changes in worm reproduction and differential survival of male vs. female worms may influence host-parasite transmission dynamics during long-term host CR.

Vertebrate aging research 2006

This Hot Topics review, the first in a projected annual series, discusses those articles, published in the last year, which seem likely to have a major impact on our understanding of the aging process in mammals and the links between aging and late-life illnesses. The year's highlights include studies of oxidation damage in the very-long-lived naked mole-rat, and of caloric restriction in monkeys, humans, and growth hormone-unresponsive mice. Two studies of resveratrol, one showing its ability to extend lifespan in a short-lived fish, the other demonstrating beneficial effects in mice subjected to a diet high in fat, may well be harbingers of a parade of intervention studies in the coming decade.

Effect of fish oil on bone mineral density in aging C57BL/6 female mice

Life expectancy has increased considerably over the last century in the United States. It is expected that this longevity will be accompanied by an increase in the prevalence of osteoporosis and accompanying complications in the elderly population. Age-related loss of bone mass and bone fragility are major risk factors for osteoporosis, leading to an increased risk of fractures. Therefore, nutritional strategies and lifestyle changes that prevent age-related osteoporosis and improve the quality of life for the elderly population are urgently needed. Hence, the present study compared the effects of corn oil (CO; n-6 fatty acids; commonly present in Western diets) and fish oil (FO; n-3 fatty acids) on bone mineral density (BMD) in aging C57BL/6 female mice. After 6 months of dietary treatment, we found that 18-month-old FO-fed mice maintained higher BMD in different bone regions compared to CO-fed mice. These findings were accompanied by a decreased activity of pro-inflammatory cytokines, tumor necrosis factor-alpha and interleukin-6 in stimulated splenocytes; a nonsignificant but greater increase in bone formation markers alkaline phosphatase and osteocalcin in the serum; and lower osteoclast generation in bone marrow cell cultures in FO-fed mice. In conclusion, these findings suggest that providing n-3 fatty acids may have a beneficial effect on bone mass during aging by modulating bone formation and bone resorption factors.

Different ratios of eicosapentaenoic and docosahexaenoic omega-3 fatty acids in commercial fish oils differentially alter pro-inflammatory cytokines in peritoneal macrophages from C57BL/6 female mice

The use of fish oil (FO) as a dietary supplement to prevent or reduce the severity of cardiovascular diseases and autoimmune disorders such as rheumatoid arthritis is receiving much attention. Several recent reports indicate that eating fish often or the use of small doses of FO capsules appears to have benefits against cardiovascular diseases. We have reported in the past that diets enriched with FO protect against renal diseases and prolong the life span of autoimmune-prone mice compared to corn oil (CO) diets. However, the optimum ratio of eicosapentaenoic acid (EPA) to docosahexaenoic acid (DHA) in commercially available FOs to reduce the production of various pro-inflammatory cytokines has not been well established. We, therefore, obtained deodorized FO from three sources containing different EPA/DHA contents, fed them to C57BL/6 mice for 8 weeks in a 10% (vol/wt) diet (oil A, 11/10; oil B, 14/9; oil C, 23/14) and compared them with (10%) CO-fed mice as control. TNF-alpha, IL-6 and IL-1beta were measured by enzyme-linked immunosorbent assay in thioglycollate-induced macrophages, 8 and 24 h after lipopolysaccharide treatment. The results showed a significant decrease in TNF-alpha after only 8 h in oil C. After 24 h, TNF-alpha, IL-6 and IL-1beta levels decreased only in mice fed oil C, although nonsignificant decreases were seen in mice fed oil A compared to mice fed CO. The antioxidant enzymes, catalase and glutathione transferase, were higher in kidneys of mice fed oil C compared to mice fed CO. The study suggests that anti-inflammatory activity may vary among different sources of FO due to variations in EPA/DHA content.

Insulin in aging and cancer: antidiabetic drug Diabenol as geroprotector and anticarcinogen

The effects of new antidiabetic drug Diabenol (9-beta-diethylaminoethyl-2,3-dihydroimidazo-(1,2-alpha)benzimidazol dihydrochloride) on life span and spontaneous tumor incidence in NMRI and transgenic HER-2/neu mice as well as on colon carcinogenesis induced by 1,2-dimethylhydrazine in rats are studied. It is shown that treatment with the drug failed influence body weight gain dynamics, food and water consumption and the body temperature, slowed down age-related disturbances in estrous function and increased life span of all and 10% most long-living NMRI mice. The treatment with Diabenol inhibited spontaneous tumor incidence and increased the mammary tumor latency in these mice. Diabenol treatment slowed down age-related changes in estrous function in HER-2/neu mice, failed influence survival of these mice and slightly inhibited the incidence and decreased the size of mammary adenocarcinoma metastases into the lung. In rats exposed to 1,2-dimethylhydrazine, treatment with Diabenol significantly inhibited multiplicity of all colon tumors, decreased by 2.2 times the incidence of carcinomas in ascending colon and by 3.1 times their multiplicity. Treatment with Diabenol was followed by higher incidence of exophytic and well-differentiated colon tumors as compared with the control rats exposed to the carcinogen alone (76.3% and 50%, and 47.4% and 14.7%, respectively). Thus, the drug increases survival and inhibits spontaneous carcinogenesis in mice and inhibits colon carcinogenesis in rats.

The Combination of Dietary Conjugated Linoleic Acid and Treadmill Exercise Lowers Gain in Body Fat Mass and Enhances Lean Body Mass in High Fat–Fed Male Balb/C Mice

Nearly half of the U.S. adult population is overweight or obese, which may be related to increased energy intake combined with lack of physical activity. Obesity increases the risk of several chronic diseases including diabetes, coronary heart disease, hypertension, and stroke. Conjugated linoleic acids (CLA) were shown to decrease fat and increase lean mass in several animal studies. However, the effects of CLA in combination with exercise (Ex) on body composition have not been studied in an animal model. We examined the effect of a low concentration of either safflower oil as control (0.5%) or mixed isomers of CLA (0.4%) along with treadmill exercise on body composition in male Balb/C mice fed a high-fat diet (20% corn oil) in a 2 x 2 factorial design. CLA consumption lowered change in fat mass (P < 0.001) confirming the results of other studies, and change in fat mass decreased further (P < 0.001) with CLA and exercise. Change in lean mass did not increase with exercise alone; it increased, although not significantly, with CLA alone and increased significantly (P < 0.05) due to the combination of CLA and exercise. This effect was accompanied by decreased serum leptin levels and lower leptin mRNA expression in peritoneal fat (P < 0.001). Serum insulin, glucose, tumor necrosis factor (TNF)-alpha, and interleukin-6 were lower in CLA-fed mice than in controls (P < 0.05), whereas serum TNF-alpha was increased by exercise (P < 0.05). Exercise increased oxygen consumption and energy expenditure when measured under resting conditions (P < 0.05). In summary, the combination of dietary CLA and exercise decreased fat mass and increased lean mass in mice fed a high-fat diet, and these effects may be related in part to decreased serum leptin and exercise-induced increases in oxygen consumption and energy expenditure.

Mild energy restriction alters mouse–nematode transmission dynamics in free-running indoor arenas

Energy restriction reduces Heligmosomoides polygyrus (Dujardin, 1845) (Nematoda) infection by reducing transmission-related behaviours but prolongs parasite survival by suppressing immune responses in individually housed mice. To determine the relative importance of these two processes in accumulation of worms in mouse populations, 10 female CD1 mice were housed in each of eight indoor arenas with ad libitum access to either an energy-sufficient (ES) diet or an energy-restricted (ER) diet with 20% less metabolizable energy (four arenas per diet). After 3 weeks, H. polygyrus transmission was initiated by introducing larvae onto damp peat trays. Mice adapted to the ER diet through increased food intake and nesting and reduced overall activity; after 6 weeks, nutritional and immunological measures were comparable between diet groups. With continuing exposure to parasite larvae, mice in both ER and ES arenas developed resistance to the incoming larvae; however, mice in the ER arenas accumulated lower worm burdens than mice in the ES arenas despite their increased contact with peat. We suggest that the comparable immunocompetence of mice in the ER and ES arenas enabled the ER mice exposed to higher transmission rates to more rapidly reject the parasites, leading to lower final worm numbers, a pattern frequently observed in other helminth infections.

Acute stress response in calorie-restricted rats to lipopolysaccharide-induced inflammation

Calorie restriction (CR) reduces morbidity and mortality in a wide range of organisms, possibly through the stress response machinery. We analyzed the acute phase response of CR rats to lipopolysaccharide (LPS)-induced inflammatory challenge. Six-month-old male F344 rats, fed ad libitum (AL) or a 30% calorie-restricted diet from 6 weeks of age, received an intravenous LPS injection and were then sacrificed between 0 and 8 h. CR attenuated liver injury without reduction in the plasma concentrations of proinflammatory cytokines or nitric oxide (NO). Western blotting analysis of liver tissue demonstrated that CR did not affect the degradation of cytoplasmic I-kappaB and subsequent nuclear translocation of NF-kappaB, a key transcription factor after inflammatory challenge. We also analyzed the liver gene expression profiles at 0, 1 and 4 h with DNA arrays and cluster analysis. Compared with the AL group, CR upregulated the expression of several genes for inflammatory mediators or their related molecules at 0 h, but not at 1 or 4 h. CR downregulated genes for energy or xenobiotic metabolism and stress response proteins at 0 h. At 1 h, the relatively downregulated genes by CR were those for proteases and the ubiquitin-proteasome pathway. The present results suggest that CR attenuates liver injury without suppression of the proinflammatory response, and that the protective effect emerges from constitutively, rather than inductively, expressed gene products.

Dietary restriction and immune function

Dietary restriction is beneficial in preventing a multitude of diseases, many of which may involve the immune system in their etiology. Recent reports examining dietary restriction focused on T lymphocytes and macrophages. Dietary restriction delays the onset of T-lymphocyte-dependent autoimmune disease; this may be attributed to improved antioxidant defense mechanisms, blunting shifts in T-lymphocyte subset proportions and preventing DNA mutation frequencies. The beneficial effects of dietary restriction were shown in both the CD4 and CD8 T-lymphocyte subsets as well as in various immune compartments such as the spleen, mesenteric lymph nodes, peripheral blood, thymus, and salivary glands. In contrast, dietary restriction may have negative effects on macrophage function because recent evidence showed that dietary restriction rendered mice more susceptible to peritonitis and stimulated macrophages produced lower amounts of cytokines. The application of dietary restriction regimens to humans would be difficult; however, understanding the biochemical and molecular targets of dietary restriction in the immune system may lead to the development of new dietary strategies to delay or prevent the onset of aging, cancer, and autoimmune disease.

Dietary n-3 fatty acids decrease osteoclastogenesis and loss of bone mass in ovariectomized mice

The mechanisms of action of dietary fish oil (FO) on osteoporosis are not fully understood. This study showed FO decreased bone loss in ovariectomized mice because of inhibition of osteoclastogenesis. This finding supports a beneficial effect of FO on the attenuation of osteoporosis.

INTRODUCTION

Consumption of fish or n-3 fatty acids protects against cardiovascular and autoimmune disorders. Beneficial effects on bone mineral density have also been reported in rats and humans, but the precise mechanisms involved have not been described.

METHODS

Sham and ovariectomized (OVX) mice were fed diets containing either 5% corn oil (CO) or 5% fish oil (FO). Bone mineral density was analyzed by DXA. The serum lipid profile was analyzed by gas chromatography. Receptor activator of NF-kappaB ligand (RANKL) expression and cytokine production in activated T-cells were analyzed by flow cytometry and ELISA, respectively. Osteoclasts were generated by culturing bone marrow (BM) cells with 1,25(OH)2D3. NF-kappaB activation in BM macrophages was measured by an electrophoretic mobility shift assay.

RESULTS AND CONCLUSION

Plasma lipid C16:1n6, C20:5n3, and C22:6n3 were significantly increased and C20:4n6 and C18:2n6 decreased in FO-fed mice. Significantly increased bone mineral density loss (20% in distal left femur and 22.6% in lumbar vertebrae) was observed in OVX mice fed CO, whereas FO-fed mice showed only 10% and no change, respectively. Bone mineral density loss was correlated with increased RANKL expression in activated CD4+ T-cells from CO-fed OVX mice, but there was no change in FO-fed mice. Selected n-3 fatty acids (docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]) added in vitro caused a significant decrease in TRACP activity and TRACP+ multinuclear cell formation from BM cells compared with selected n-6 fatty acids (linoleic acid [LA] and arachidonic acid [AA]). DHA and EPA also inhibited BM macrophage NF-kappaB activation induced by RANKL in vitro. TNF-alpha, interleukin (IL)-2, and interferon (IFN)-gamma concentrations from both sham and OVX FO-fed mice were decreased in the culture medium of splenocytes, and interleukin-6 was decreased in sham-operated FO-fed mice. In conclusion, inhibition of osteoclast generation and activation may be one of the mechanisms by which dietary n-3 fatty acids reduce bone loss in OVX mice.

Lovastatin inhibits bone marrow-derived dendritic cell maturation and upregulates proinflammatory cytokine production

Statins are a group of hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors which are most effective as lipid lowering agents, and are currently extensively used clinically. Recently, it was also shown that statins affect the immune response. We investigated the effects of lovastatin on the maturation and functional changes of bone marrow-derived dendritic cells (BM-DC). Lovastatin inhibited MHC class II and CD40 expression on DC in a dose-dependent manner, but had lesser effects on CD16, CD80, CD86, and CD11b expression. Nuclear extracts of lovastatin treated DC had decreased NF-kappaB DNA binding activity. Although antigen capture capacity of DC was not affected by lovastatin, the T-cell stimulatory activity of DC was inhibited. Lovastatin up-regulated DC pro-inflammatory cytokine production induced by LPS as measured by intracellular cytokine staining, ELISA and cDNA microarrays. Mevalonate, added in vitro, prevented these effects. These results indicate that lovastatin may inhibit BM-DC maturation and up-regulate cytokine production through a mevalonate dependent pathway, and may cause adverse effects on either innate or adaptive immunity.

Age-related impairment of the transcriptional responses to oxidative stress in the mouse heart

To investigate the transcriptional response to oxidative stress in the heart and how it changes with age, we examined the cardiac gene expression profiles of young (5-mo-old), middle-aged (15-mo-old), and old (25-mo-old) C57BL/6 mice treated with a single intraperitoneal injection of paraquat (50 mg/kg). Mice were killed at 0, 1, 3, 5, and 7 h after paraquat treatment, and the gene expression profile was obtained with high-density oligonucleotide microarrays. Of 9,977 genes represented on the microarray, 249 transcripts in the young mice, 298 transcripts in the middle-aged mice, and 256 transcripts in the old mice displayed a significant change in mRNA levels (ANOVA, P < 0.01). Among these, a total of 55 transcripts were determined to be paraquat responsive for all age groups. Genes commonly induced in all age groups include those associated with stress, inflammatory, immune, and growth factor responses. Interestingly, only young mice displayed a significant increase in expression of all three isoforms of GADD45, a DNA damage-responsive gene. Additionally, the number of immediate early response genes (IEGs) found to be induced by paraquat was considerably higher in the younger animals. These results demonstrate that, at the transcriptional level, there is an age-related impairment of specific inducible pathways in the response to oxidative stress in the mouse heart.

Analysis of tyrosine phosphorylation in resident peritoneal cells during diet restriction by laser scanning cytometry

Tyrosine phosphorylation plays a critical role in signal transduction pathways in immune cells. Laser scanning cytometer (LSC), a newly developed microscope-based cytofluorometer, may overcome shortcomings of Western blotting and flow cytometry in the detection of intracellular signaling transduction. The aims of this study were to visualize and quantitate intracellular phosphotyrosine in the peritoneal cells harvested from diet-restricted mice by LSC. In addition, using LSC, we identified the main cell type with activated tyrosine phosphorylation in response to an inflammatory stimulus and we investigated the intracellular distribution of tyrosine phosphorylation within the peritoneal macrophages. Mice were assigned to the ad libitum and diet-restricted, i.e., 75% restricted food intake, groups. After 7 days of pair feeding, the peritoneal cells were harvested. Tyrosine phosphorylation in the harvested cells with either N-formyl-methionyl-leucyle-phenylalanine (fMLP) or lipopolysaccharide (LPS) stimulation was examined using LSC. Tyrosine phosphorylation of peritoneal cells from the diet-restricted group was significantly higher than that from the ad libitum group, regardless of stimulation. Stimulation of peritoneal cells with either fMLP or LPS significantly increased tyrosine phosphorylation in the ad libitum group, but not in the diet-restricted group. The relocation feature of LSC revealed that the cells with distinct tyrosine phosphorylation were macrophages. Topographic analysis demonstrated that phosphotyrosine was localized mainly in the cytoplasm of these cells. In summary, LSC revealed that tyrosine phosphorylation is mainly in the cytoplasm of the peritoneal macrophages and is deranged by diet restriction. LSC is a powerful tool for the study of intracellular signaling transduction.

Dietary drawbacks

The benefits of dietary restriction are well documented: Creatures that consume one-third fewer calories are leaner, livelier, and longer lived than their fully fed kin. But such drastic dieting also has a dark side. Restricted animals get chilled and pick up infections unusually easily, and they're less fertile than their more portly compatriots are. Furthermore, cutting calories doesn't enhance longevity in all animals, according to several studies. These observations have many researchers wondering what dietary restriction--or a drug that mimics its effects--might do for people who are hoping to live longer and healthier lives.