Influence of dietary protein restriction on cell number, cell size and growth of mouse organs during the course of aging

Dietary Protein, Metabolism, and Aging

Dietary restriction (DR), a moderate reduction in food intake, improves health during aging and extends life span across multiple species. Specific nutrients, rather than overall calories, mediate the effects of DR, with protein and specific amino acids (AAs) playing a key role. Modulations of single dietary AAs affect traits including growth, reproduction, physiology, health, and longevity in animals. Epidemiological data in humans also link the quality and quantity of dietary proteins to long-term health. Intricate nutrient-sensing pathways fine tune the metabolic responses to dietary AAs in a highly conserved manner. In turn, these metabolic responses can affect the onset of insulin resistance, obesity, neurodegenerative disease, and other age-related diseases. In this review we discuss how AA requirements are shaped and how ingested AAs regulate a spectrum of homeostatic processes. Finally, we highlight the resulting opportunity to develop nutritional strategies to improve human health during aging.

Early growth determines longevity in male rats and may be related to telomere shortening in the kidney

Maternal protein undernutrition can influence the growth and longevity of male offspring in the rat. We tested the hypothesis that these differences in longevity were associated with changes in the rate of telomere shortening. We found age-related shortening of telomeres in the liver and kidney but not in the brain of male rats. Growth retardation in postnatal life was associated with significantly longer kidney telomeres and an increased longevity. Conversely, growth retardation during the foetal life followed by postnatal catch-up growth was associated with a shorter life span and shorter kidney telomeres. These findings may provide a mechanistic basis for epidemiological studies linking early growth retardation to adult degenerative diseases.

A model of whole-body protein turnover based on leucine kinetics in rodents

The measurement of fractional synthesis rate is based on the following assumptions: amino acids for protein synthesis are supplied by an intracellular pool; amino acids from protein degradation are not recycled preferentially to protein synthesis; and proteins turn over at a homogeneous rate. To test these assumptions, a mechanistic, theoretical model of protein turnover for a nongrowing 26-g mouse was developed on the basis of data from the literature. The model consisted of three protein pools turning over at fast (102 micromol Leu, t1/2= 11.5 h), medium (212 micromol Leu, t1/2 = 16.6 h) or slow (536 micromol Leu, t1/2 = 71.5 h) rates and extracellular (1.69 micromol Leu), leucyl-tRNA (0.0226 micromol Leu) and intracellular (5.72 micromol Leu) amino acid pools that exchanged amino acids. The flow of amino acids from the protein pools to the leucyl-tRNA pool determined the amount of recycling. The flow of amino acids from the extracellular pool to aminoacyl tRNA determined the amount of channeling. Two flooding dose data sets were used to evaluate specific radioactivity changes predicted by the model. Predictions of specific radioactivities using flooding dose, pulse dose or continuous infusion methods indicated that the model can be a useful tool in estimating the rates of channeling and recycling. However, it was found that use of data from flooding dose experiments might cause inaccurate predictions of certain fluxes.

Prevention of cancer: restriction of nutritional energy intake (joules)

1. The reduction of nutritional energy intake (joules) often reduces the incidence of both spontaneous and induced cancers in humans and experimental animals in an approximately dose-dependent manner. 2. To achieve the best preventive effect, the reduction of dietary intake should begin well before the carcinogen insult, should be intense enough (lowering the intake of joules by at least approx. 25-30%) and should last a long time, preferably even life-long. 3. This preventive effect depends upon the strain, sex and age of animals, the kind of carcinogenic insult and also the susceptibility of the target tissue. 4. The mechanism by which the dietary restriction may exert its protective action may involve changes in the hormonal equilibria, influences upon the immuno-surveillance, changes of activities of enzymes involved in carcinogen metabolism and other factors. 5. Since over-eating and the resulting obesity constitutes a pronounced risk factor for the incidence of cancer and other diseases, lowering the nutritional energy intake represents today the simplest, cheapest and most effective way to prevent cancer in the general population.