Modulations by dietary restriction on antioxidant enzymes and lipid peroxidation in developing mice

Effects of dietary restriction on hepatic sulfur-containing amino acid metabolism and its significance in acetaminophen-induced liver injury

Dietary restriction (DR) has been revealed to have health benefits as it induces reduction in oxidative stress. Glutathione (GSH), an important cellular antioxidant, is increased in rodent livers owing to DR; however, the exact mechanism and clinical relevance of DR are yet to be fully understood. In this study, male C57BL/6 mice were administered a 50% restricted diet for 7 d, and the hepatic sulfur-containing amino acid (SAA) metabolism was determined to assess the biosynthesis of GSH. The hepatic methionine level was found to decrease, while the homocysteine, cysteine, and GSH levels were increased owing to decreased betaine-homocysteine methyltransferase (BHMT) and increased CβS, CγL, and glutamate cysteine ligase catalytic subunit (GCLC) proteins in the livers of mice subjected to DR. To determine the effects of DR on drug-induced oxidative liver injury, mice subjected to DR were injected with a toxic dose (300 mg/kg) of acetaminophen (APAP). DR significantly alleviated APAP-induced liver damage and oxidative stress, which might be attributed to the higher levels of GSH and related antioxidant enzyme (GPx, GSTα, and GSTµ) in the livers. The decrease in the levels of hepatic CYP1A, 2E1, and 3A, which imply the inhibition of APAP metabolic activation, could contribute to the lower hepatotoxicity in mice subjected to DR. Overall, our findings revealed that DR stimulated the hepatic transsulfuration pathway and GSH synthesis. The consequent elevation of GSH could thus serve as an important mechanism of DR-mediated liver protection against APAP intoxication.

Healthful aging mediated by inhibition of oxidative stress

The progressive increase in lifespan over the past century carries with it some adversity related to the accompanying burden of debilitating diseases prevalent in the older population. This review focuses on oxidative stress as a major mechanism limiting longevity in general, and healthful aging, in particular. Accordingly, the first goal of this review is to discuss the role of oxidative stress in limiting longevity, and compare healthful aging and its mechanisms in different longevity models. Secondly, we discuss common signaling pathways involved in protection against oxidative stress in aging and in the associated diseases of aging, e.g., neurological, cardiovascular and metabolic diseases, and cancer. Much of the literature has focused on murine models of longevity, which will be discussed first, followed by a comparison with human models of longevity and their relationship to oxidative stress protection. Finally, we discuss the extent to which the different longevity models exhibit the healthful aging features through physiological protective mechanisms related to exercise tolerance and increased β-adrenergic signaling and also protection against diabetes and other metabolic diseases, obesity, cancer, neurological diseases, aging-induced cardiomyopathy, cardiac stress and osteoporosis.

The effects of dietary restriction on oxidative stress in rodents

Oxidative stress is observed during aging and in numerous age-related diseases. Dietary restriction (DR) is a regimen that protects against disease and extends life span in multiple species. However, it is unknown how DR mediates its protective effects. One prominent and consistent effect of DR in a number of systems is the ability to reduce oxidative stress and damage. The purpose of this review is to comprehensively examine the hypothesis that dietary restriction reduces oxidative stress in rodents by decreasing reactive oxygen species (ROS) production and increasing antioxidant enzyme activity, leading to an overall reduction of oxidative damage to macromolecules. The literature reveals that the effects of DR on oxidative stress are complex and likely influenced by a variety of factors, including sex, species, tissue examined, types of ROS and antioxidant enzymes examined, and duration of DR. Here we present a comprehensive review of the existing literature on the effect of DR on mitochondrial ROS generation, antioxidant enzymes, and oxidative damage. In a majority of studies, dietary restriction had little effect on mitochondrial ROS production or antioxidant activity. On the other hand, DR decreased oxidative damage in the majority of cases. Although the effects of DR on endogenous antioxidants are mixed, we find that glutathione levels are the most likely antioxidant to be increased by dietary restriction, which supports the emerging redox-stress hypothesis of aging.

The effects of pre-weaning undernutrition on the expression levels of free radical deactivating enzymes in the mouse brain

A mild degree of undernutrition brought about by restricting the amount of food in the diet is known to alter the life span of an animal. It has been hypothesised that this may be related to the effects of undernutrition on an animals anti-oxidant defense system. We have therefore, used real-time PCR (rt-PCR) techniques to determine the levels of mRNA expression for manganese superoxide dismutase (MnSOD), copper/zinc superoxide dismutase (Cu/ZnSOD), glutathione peroxidase 1 (GPx 1) and catalase in the brains of Quackenbush mice undernourished from conception until 21-post-natal days of age. It was found that 21- and 61-day-old undernourished mice had a deficit in the expression of Cu/ZnSOD in both the cerebellum and forebrain regions compared to age-matched controls. The expression of MnSOD was found to be greater in the cerebellum, but not the forebrain region, of 21-day-old undernourished mice. There were no significant differences in the expression of GPx 1 and catalase between control and undernourished or previously undernourished mice. Our results confirm that undernutrition during the early life of a mouse may disrupt some of the enzymes involved in the anti-oxidant defense systems.

Beneficial effects of a 6-month dietary restriction are time-dependently abolished within 2 weeks or 6 months of refeeding-genome-wide transcriptome analysis in mouse liver

Dietary restriction (DR) has been shown to exert a number of beneficial effects including the prolongation of life span. One of the mechanisms by which DR leads to these advantages seems to be the induction of endogenous antioxidant defense and stress response mechanisms. However, little is known about the persistence of DR benefits after return to an ad libitum diet. In this study, male C57BL/6 mice were fed 75% of a normal diet for 6 months (DR) followed by 6 months of ad libitum refeeding (RF) and compared to a continuously ad libitum fed control group. To study the impact of DR and RF on the liver transcriptome, a global gene expression profile was generated using microarray technology. In comparison, the DR group showed lower body weight, lower triglyceride and cholesterol levels, reduced lipid peroxidation, and a changed hepatic fatty acid pattern. mRNA transcription and activity of antioxidant and phase II enzymes, as well as metallothionein 1 gene expression, were increased and autophagy was induced. Shifting from long-term DR to RF abolished 96% of the DR-mediated changes in differential gene expression within 2 weeks, and after 6 months of refeeding all of the previously differentially expressed genes were similar in both groups. These results indicate that DR has to be maintained continuously to keep its beneficial effects.

Effect of early feed restriction on hepatic lipid metabolism and expression of lipogenic genes in broiler chickens

The study was conducted to investigate the effect of early feed restriction (ER) on lipid metabolism and mitochondrial function in the liver of broiler chickens. Newly hatched broiler chickens were randomly allocated into control and ER group which was subjected to feed restriction with feed provided on alternate days from hatch to 14 days of age (14 d), followed by ad libitum feeding until the end of the experiment on 63 d. ER group exhibited significantly lower body weight throughout the experiment. Serum concentrations of total cholesterol (TC) and high density lipoprotein cholesterol (HDLC) were significantly higher in ER group at 14 d (P<0.05), and the higher serum TC level in ER group was also observed at 63 d. In contrast, the contents of triglyceride (TG), TC and lipoprotein lipase (LPL) activity in liver were significantly lower in ER group at 14 d (P<0.05). At 14 d no significant difference was detected for the mRNA expression of the acetyl-CoA carboxylase-α (ACC-α), carnitine palmitoyltransferase I (CPT-I), sterol regulatory element binding protein-1c (SREBP-1c) or peroxisome proliferator-activated receptors α (PPAR-α) between control and ER group. At 63 d ACC-α mRNA expression was significantly down-regulated accompanied with a significantly up-regulated CPT-ImRNA and a decreased tendency of SREBP-1c mRNA expression in ER group (P=0.09). Swollen mitochondria with fragmented and reduced cristae were observed in liver of ER group at 14 d. Meanwhile the inner mitochondria membrane viscidity increased and hepatic mitochondrial superoxide dismutase (SOD) activity decreased at 14 d. The results suggest that feed restriction at early postnatal stage may produce long-term effect on lipid metabolism of broiler chicken, probably through, at least in part, alterations in mitochondria morphology and function.

Gender-related difference in liver injury induced by Dioscorea bulbifera L. rhizome in mice

The present study was undertaken to investigate the gender-related liver injury induced by Dioscorea bulbifera L. (DB), a traditional medicinal plant, in mice, and further explored its hepatotoxic chemical compound. Serum and liver tissue samples were collected at 0, 4, 8, 12 h, after mice were administrated orally with 640 mg/kg ethyl acetate extracts (EF) isolated from DB. After treatments, serum alanine transaminase (ALT) and aspartate transaminase (AST) activities were both significantly elevated. Liver lipid peroxidation (LPO) level increased, while glutathione amounts, glutathione- S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activities all decreased in the time-dependent manner. Further analysis demonstrated that ALT and AST activities in female mice were significantly lower than those in male. Meanwhile, liver glutathione amounts and CAT activity in female mice after giving EF for 12 h were both higher than those in male. Further, comparing the liver injury induced by Diosbulbin B isolated from DB with that induced by EF on the basis of chemical analysis for the amounts of Diosbulbin B in EF of DB, we found that Diosbulbin B could be the main hepatotoxic chemical compound in DB. Taken together, our results show that DB can induce gender-related liver oxidative stress injury in mice, and its main hepatotoxic chemical compound is Diosbulbin B, for the first time.

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.

Review article: epidemiology, pathogenesis and potential treatments of paediatric non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of paediatric liver disease. Similar to NAFLD in adults, NAFLD in children is associated with obesity and insulin resistance and requires liver histology for diagnosis and staging. However, significant histological differences exist between adult and paediatric NAFLD to warrant caution in extrapolation of adult data.

AIM

To review the available data on the epidemiology, pathogenesis, diagnosis and treatment of paediatric NAFLD.

METHODS

Relevant articles were identified by Medline searches using the keywords: nonalcoholic fatty liver disease, steatohepatitis, obesity and children.

RESULTS

The rise in childhood obesity has been accompanied by an increase in paediatric NAFLD. Age, gender and race/ethnicity are significant determinants of risk, and sex hormones, insulin sensitivity and adipocytokines are implicated in the pathogenesis of paediatric NAFLD. There is no consensus for treatment of NAFLD; however, data suggest that diet, exercise and some pharmacological therapies may be of benefit.

CONCLUSIONS

To evaluate and effectively treat paediatric NAFLD, the pathophysiology and natural history of the disease should be clarified and non-invasive methods for screening, diagnosis, and longitudinal assessment developed. Randomized, controlled, double-blind trials of pharmacological therapies in children with biopsy-proven disease are necessary.

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.

The effect of dietary restriction on mitochondrial protein density and flight muscle mitochondrial morphology in Drosophila

Dietary restriction (DR) extends life span in diverse organisms and may do so by attenuating production of mitochondrial reactive oxygen species (ROS). However, measurements of ROS production from isolated mitochondria of organisms subjected to DR have produced inconsistent results. In the fruit fly Drosophila, DR does not reduce production of ROS from isolated mitochondria. In this study, we used Drosophila to test whether DR lowered mitochondrial density. We assessed mitochondrial densities of flies on DR and Control diets using (a) the activities of mitochondrial enzymes and (b) electron microscopy. Both methods showed no overall effect of DR on mitochondrial density; however, mitochondrial enzyme activities and morphology differed significantly between DR and Control flies. We concluded that life-span extension by DR in Drosophila is not mediated through a reduction in mitochondrial density. If DR in Drosophila extends life span by reducing ROS production, then it does so through mechanisms that operate only in vivo.

Proton leak and hydrogen peroxide production in liver mitochondria from energy-restricted rats

Energy restriction (ER), without malnutrition, is the only environmental intervention that consistently increases maximum life span in laboratory rodents. One theory proposes that a reduction in energy expenditure and reactive oxygen species production is the mechanism responsible for this action of ER. To further test this theory, proton leak, H2O2 production, lipid peroxidation, and protein carbonyls were measured in mitochondria from FBNF1 rats fed either a control or 40% ER diet (onset at 6 mo of age). Liver mitochondria were isolated at 7 and 12 mo of age. Liver weight decreased 25 and 36% at 1 and 6 mo of ER, respectively (P < 0.05). ER resulted in an increase (P < 0.05) in percent total polyunsaturates, n-6 polyunsaturates, and total unsaturates (6 mo only) in mitochondrial lipids. These changes, however, were not associated with significant alterations in mitochondrial function. State 4 respiration and membrane potential were not different (P > 0.05) between groups at either assessment period. Similarly, proton leak kinetics were not different between control and ER animals. Top-down metabolic control analysis and its extension, elasticity analysis, were used at the 6-mo assessment and revealed no difference in control of the oxidative phosphorylation system between control and ER rats. H2O2 production with either succinate or pyruvate/malate substrates was also not different (P > 0.05) between groups at either time point. In conclusion, ER did not alter proton leak or H2O2 production at this age or stage of restriction in liver.