Mechanism of food restriction: protection of cellular homeostasis

Role of glucose and ketone bodies in the metabolic control of experimental brain cancer

Brain tumours lack metabolic versatility and are dependent largely on glucose for energy. This contrasts with normal brain tissue that can derive energy from both glucose and ketone bodies. We examined for the first time the potential efficacy of dietary therapies that reduce plasma glucose and elevate ketone bodies in the CT-2A syngeneic malignant mouse astrocytoma. C57BL/6J mice were fed either a standard diet unrestricted (SD-UR), a ketogenic diet unrestricted (KD-UR), the SD restricted to 40% (SD-R), or the KD restricted to 40% of the control standard diet (KD-R). Body weights, tumour weights, plasma glucose, beta-hydroxybutyrate (beta-OHB), and insulin-like growth factor 1 (IGF-1) were measured 13 days after tumour implantation. CT-2A growth was rapid in both the SD-UR and KD-UR groups, but was significantly reduced in both the SD-R and KD-R groups by about 80%. The results indicate that plasma glucose predicts CT-2A growth and that growth is dependent more on the amount than on the origin of dietary calories. Also, restriction of either diet significantly reduced the plasma levels of IGF-1, a biomarker for angiogenesis and tumour progression. Owing to a dependence on plasma glucose, IGF-1 was also predictive of CT-2A growth. Ketone bodies are proposed to reduce stromal inflammatory activities, while providing normal brain cells with a nonglycolytic high-energy substrate. Our results in a mouse astrocytoma suggest that malignant brain tumours are potentially manageable with dietary therapies that reduce glucose and elevate ketone bodies.

Protein oxidation and enzyme activity decline in old brown Norway rats are reduced by dietary restriction

The effect of aging and diet restriction (DR) on the activity of creatine kinase (CK), glutamine synthetase (GS) and protein carbonyl formation in the cerebellum, hippocampus and cortex of male and female brown Norway (BN) rats has been investigated. It was demonstrated that CK activity in three different regions of the rat brain declines with age by 30%. Age-related decrease of GS activity was only 10-13% and did not reach statistical significance. Consistent with previously published studies, age-related increase of protein carbonyl content in each brain area studied has been observed. Preventive effects of a caloric restricted diet on the age-associated protein oxidation and changes of the activity of CK and GS in the brain was observed for both aging male and female BN rats. DR delayed the accumulation of protein carbonyls. Age-related changes of CK activity in rat brain were abrogated by DR. The activity of GS in the brain of old rats subjected to the caloric restricted diet was higher than that in the brain of young animals fed ad libitum. The results are consistent with the notion that DR may relieve age-associated level of oxidative stress and lessen protein damage.

When will the biology of aging become useful? Future landmarks in biomedical gerontology

Where should we look to find the causes of and cure for aging? This essay considers a number of scientific discoveries, not yet made, that might dramatically increase the proportion of biogerontologists doing useful work. I will consider, in turn, problems and prospects in the areas of comparative biology, mammalian and invertebrate genetics, biomarker research, caloric restriction, and clonal senescence and then conclude with a discussion of potential links between aging and late life disease.

Effect of subchronic administration of antioxidants against cigarette smoke exposure in rats

Effects of subchronic administration of antioxidants against pulmonary damage mediated by cigarette smoke were investigated in rats. Rats were continuously received ascorbic acid, N-acetylcysteine and ginseng extract together drinking water from day 25 after birth. After 30 days of antioxidant supplementation, rats were exposed to cigarette smoke generated from six cigarettes (11 mg tar) for 20 min per day throughout 30 days, and then several biochemical markers related to the redox status in vivo were analyzed in the respiratory system. The cigarette smoke induced mild histological changes in trachea and lungs. The activity of superoxide dismutase (SOD) in the lung was significantly increased, and catalase and glutathione peroxidase activities were increased less than SOD, but total sulfhydryl compounds (Total-SH) content was decreased by cigarette smoking. In spite of the increase in activities of antioxidant enzymes, the inhibitory capacity of lung preparations on in vitro lipid peroxidation using ox brain homogenates was decreased and the change in the capacity was not related to the changes of these intracellular enzymes activities, but with the content of Total-SH. On the other hand, the content of thiobarbituric acid reactive substances and the ratio of elastase to anti-protease in the lung homogenates were significantly increased. Supplementation of antioxidants, however, effectively attenuated all of such alterations induced by cigarette smoke. These results indicate that although cigarette smoking induces antioxidant enzymes in the lung as a self defense mechanism, it seems to be not sufficient to protect the pulmonary system, and that chronic antioxidant feeding could be effective to reduce pulmonary damage induced by free radicals.

Human longevity and aging: possible role of reactive oxygen species

A brief overview has been given of the biological nature of human aging processes, where it has been emphasized that, in addition to the diseases of aging, there is also great economic loss as a result of human aging processes that began many years before medical costs related to aging begin to escalate. Because of the ubiquitous nature of aging, reducing the function of essentially all physiological processes, it appears that the only long-term solution to human aging problems is to decrease uniformly the aging rate of the entire body. Although the uniform decrease of aging rate has usually been considered impossible, where emphasis has consequently been placed on diseases of aging by the medically-orientated investigator, there is now at least one theoretical argument, accompanied by some experimental data, that suggests that progress can be made in achieving this goal. This progress has been based on the longevity determinant gene hypothesis predicting the existence of a relatively few key regulatory factors governing aging rate of the entire organism. If this hypothesis is not true, then indeed the prospect for significant intervention into human aging would appear impossible in the near future. Experiments have been briefly reviewed testing the longevity determinant gene hypothesis, the possibility that aging may be a result of dysdifferentiation and if aging rate is determined by mechanisms acting to stabilize the differentiated state of cells. In testing the dysdifferentiation hypothesis of aging, there is not yet much data one way or the other. It is evident, however, that changes in gene expression do occur with age, sometimes involving endogenous retroviruses or oncogenes. Other morphological evidence shows an increase with age in unusual cell type such as metaplasia cells. However, there is considerably more evidence indicating that aging may be a result of genetic instability (as it is in cancer) and that longer-lived species appear to have a more stable genetic apparatus and superior protective mechanisms against reactive oxygen species. There is a striking similarity in this model of aging and models of cancer, and much might be gained in bringing together these two fields of research. Taking all of these data together, as summarized in Table 14, it appears we may be on the right track and that mechanisms acting to protect DNA against oxidative damage may be one class of longevity determinant mechanisms. There is of course much work remaining to be done, some of which is listed in Table 15 in terms of our knowledge and our gaps of knowledge in this field.

Modulation of free radicals and superoxide dismutases by age and dietary restriction

Reducing dietary intake has been shown to be the most effective means for modulating aging processes in laboratory rodents. Dietary restriction has also been shown to be a modulator of membrane lipid peroxidation and cytosolic antioxidant status. In the present study, anti-radical action of dietary restriction was investigated further by quantitating the formation of the superoxide radical, hydroxyl radical and hydrogen peroxide by liver microsomes from rats of various ages. The results show that the ad libitum fed group maintained a higher production of superoxide and hydroxyl radicals when compared to the food restricted group of the same age. Hydrogen peroxide formation followed the same trend but was statistically greater only at 3 and 6 months of age. The food restricted group tended to show a higher superoxide dismutase (SOD) activity in both cytosolic and mitochondrial fractions than ad libitum fed controls. These data indicate that the free radical activity observed in the liver microsomes of ad libitum fed rats can be attenuated by dietary restriction, thereby providing a possible biochemical mechanism for its anti-lipoxidative action on membrane lipid peroxidation as reported in an earlier study. This action may in part underlie the life span-prolonging action of food restriction.