Studies on the fate of aldolase molecules in the aging rat lens.

It was found that aldolase activity declined considerably in the lens of adult animals with increasing age. Immunoassay showed that defective aldolase C molecules were accumulated. In addition, antibody prepared against denatured enzyme preferentially removes inactive molecules from lens homogenates without affecting active molecules. It is concluded that defective aldolase molecules encountered in aging lenses are at least partially denatured and are inactive.

The effect of donor and cell age on several characteristics of rat erythrocytes.

Erythrocytes from young and old WF rats were separated by discontinuous density gradient centrifugation. The density and mean life span of the erythrocytes were correlated with cell age by 59Fe pulse labeling. A mean half-life of 40 and 25 days was measured for erythrocytes in young and old animals, respectively, with a corresponding 4-fold increase of young cells and a 2.3-fold increase in circulating reticulocytes in old animals. Thus, the old rat has a chronologically younger population of circulating erythrocytes than the young animal. The mean hemoglobin concentration of red cells from old, but not young animals, was found to decrease from 18.5 +/- 2.1 pg to 11.8 +/- 1.8 pg per cell with increasing cell age. Premature exposure of a surface antigen, which is recognized by antibodies present in the serum, was observed in cells of old animals. This antigen-antibody complex is presumed to trigger sequestration by phagocytosis of senescent erythrocytes. The contribution of the observed age-related changes to early erythrocyte sequestration in old animals is discussed.

Some characteristics of the human erythrocyte as a function of donor and cell age.

Erythrocytes from healthy human donors of various ages (18-93 years) were separated on Percoll into four density fractions. Increased cell density has been reported to correlate with the age of the erythrocyte. Aged individuals, while having normal hematocrits, show an increased percentage of low-density young erythrocytes and almost twice as many reticulocytes in their circulation as do young adults. This evidence for increased, well-compensated, red cell turnover in elderly humans is supported by the finding in older individuals of increased levels of erythrocytes bearing autologous IgG on their membranes. Using fluorescent anti-IgG, erythrocytes with bound autologous IgG could be found in all density fractions from donors of all age groups. The old donors had an increased number of fluorescent cells that appeared in all density fractions albeit with a definite skewing toward the more dense cell fractions. Erythrocytes from young donors had higher levels of intact hemoglobin per cell than those from old donors. The relevance of these results to the aging process and the ability of senescing individuals to withstand hematologic stress are discussed.

The presence of NADPH-glyceraldehyde 3-phosphate oxidoreductase in macrophages.

The existence of an NADPH-oxidoreductase which utilizes D-glyceraldehyde 3-phosphate as substrate has been demonstrated in mouse peritoneal macrophages. D-Glyceraldehyde could also serve as substrate, albeit with a 10-fold lower efficiency. No NADH oxidation could be demonstrated with either substrate. Addition of D-glyceraldehyde to cultured macrophages increased the rate of activity of the hexose monophosphate shunt to about 65% of the level observed in zymosan A-stimulated macrophages. The possible involvement of the oxidoreductase in this phenomenon and in the inhibitory effect of D-glyceraldehyde on the production of oxygen free radicals by zymosan-stimulated cells is discussed.

The function of hypoxia-inducible factor 1 (HIF-1) is impaired in senescent mice.

Senescent organisms respond poorly to hypoxic stress. The transcription factor hypoxia-inducible factor 1 (HIF-1) plays a critical role in the coordinated genetic program that is induced in all tissues to adapt to hypoxic stress by binding to a specific DNA hypoxia-responsive recognition element (HRE). This study was designed to address whether aging is associated with an alteration in HIF-1 production and function. Young and old mice were exposed to hypoxia for various lengths of time. We found a severe impairment in the capacity of the old animals to form a HIF-1-HRE complex. This attenuation in the capacity to form HIF-1-HRE complexes in senescent tissues may explain the decreased ability of such tissues to respond to hypoxic stress.

Current status of age altered enzymes: alternative mechanisms.

The occurrence of inactive enzyme molecules in a variety of tissues and animal species has been shown to be of a general nature. The levels of inactive enzyme molecules found in old animals were produced by amino acid analogs in young animals. These levels have been shown to be initially detrimental but subsequently the young system shows recovery by efficiently disposing of the analog-modified proteins. In old animals this disposal is considerably less efficient. Evidence is presented which suggests that post-translational modifications of proteins are the main cause of enzyme inactivation in old animals. Amino acid substitutions and modifications involving charge differences apparently do not contribute significantly to this phenomenon.

Age-related changes in inducible mouse liver enzymes: ornithine decarboxylase and tyrosine aminotransferase.

The time required to induce two inducible hepatic enzymes, ornithine decarboxylase (ODC) and tyrosine aminotransferase (TAT), by growth hormone and dexamethasone, respectively, increases with age. Specific activity at the peak of induction is the same for all ages. On the other hand, for basal TAT the specific activity per unit of TAT antigen was found to decrease considerably with age. The half-life of ODC was determined after cycloheximide administration. The apparent half-life at the peak of ODC induction increases from 15 minutes in 3-4-month-old mice to 30 minutes in 24-month-old animals. Loss of efficiency in the protein degradation system is implicated in this phenomenon as no apparent differences could be observed in the susceptibility of ODC and TAT from young or old mice to chymotrypsin. ODC and TAT are activated by temperatures of up to 37 degrees C and 50 degrees C, respectively. ODC is inactivated at 50 degrees C while TAT is inactivated at 76 degrees C. "Young" ODC and TAT are more readily activated or inactivated by heating than the "old" enzymes.

Oxygen free radical production by mouse peritoneal macrophages as a function of age.

The ability of thioglycollate-elicited peritoneal macrophages (PM) from young and senescent C57BL/6J mice to produce oxygen free radicals was assessed by luminol-dependent chemiluminescence (CL) after introduction of phagocytic stimuli. A significant age-dependent variation in the CL response was detected. A 2-fold increase in the oxygen reactive species was produced by senescent PM in response to latex and zymosan stimulation; but, the capacity to ingest latex and zymosan A particles did not vary significantly between PM from young and senescent mice. Peritoneal macrophages from both age groups responded much more vigorously to opsonized zymosan. The response of the PM from young mice was, however, 2.8-fold higher than that of old ones. There was no age-related difference in oxygen free radical production after stimulation with phorbol myristate acetate (PMA). Also, no age-dependent differences were found in the relative contribution of the various oxygen reactive species O2.-, OH., 1O2 and H2O2) to the overall oxidative burst, with latex zymosan A or PMA.

Paradigms in aging research: a critical review and assessment.

This is the first in a series of articles in which we intend to critically review some of the currently used models in gerontology research and evaluate their contribution to advancing our understanding of the phenomenon of senescence. The major theories of aging are considered. We discuss what makes a model useful in general and for aging research in particular. We suggest criteria for the selection of paradigms for the study of aging. The criteria we suggest for identifying underlying mechanisms that lead to age related changes are: intraspecies universality, intrinsicality, progressiveness, and interspecies universality. The subsequent articles of this series shall consider the merits and possible drawbacks of some of the most commonly used models of the biology of aging: (a) the yeast Saccharomyces cerevisiae; (b) the nematode, Caenorhabditis elegans and the fruitfly, Drosophila melanogaster; (c) mammalian cells in culture and telomerase model; (d) mitochondria and aging; (e) progeroid syndromes; (f) in vivo studies with laboratory rodent strains; and (g) plant senescence.

The budding yeast, Saccharomyces cerevisiae, as a model for aging research: a critical review.

In this review we discuss the yeast as a paradigm for the study of aging. The budding yeast Saccharomyces cerevisiae, which can proliferate in both haploid and diploid states, has been used extensively in aging research. The budding yeast divides asymmetrically to form a 'mother' cell and a bud. Two major approaches, 'budding life span' and 'stationary phase' have been used to determine 'senescence' and 'life span' in yeast. Discrepancies observed in metabolic behavior and longevity between cells studied by these two systems raise questions of how 'life span' in yeast is defined and measured. Added to this variability in experimental approach and results is the variety of yeast strains with different genetic make up used as 'wild type' and experimental organisms. Another problematic genetic point in the published studies on yeast is the use of both diploid and haploid strains. We discuss the inherent, advantageous attributes that make the yeast an attractive choice for modern biological research as well as certain pitfalls in the choice of this model for the study of aging. The significance of the purported roles of the Sir2 gene, histone deacetylases, gene silencing, rDNA circles and stress genes in determination of yeast 'life span' and aging is evaluated. The relationship between cultivation conditions and longevity are assessed. Discrepancies between the yeast and mammalian systems with regard to aging are pointed out. We discuss unresolved problems concerning the suitability of the budding yeast for the study of basic aging phenomena.

The effect of age on the protein degradation system in the nematode Turbatrix aceti.

The administration of 0.2% of the amino acid analogues canavanine and 6-fluorotryptophan to young nematode cultures caused the appearance of inactive but antigenically reactive aldolase molecules at levels comparable to those found in old untreated cultures. Concomitant with the rapid appearance of inactive enzyme molecules a rapid rate of mortality could be detected. Mortality, however, ceased when a massive disappearance of inactive molecules could be observed. Subsequently, mortality resumed at a rate similar to that found in untreated cultures. The NaH14CO3 method of Swick and Ip (J. Biol. Chem., 249 (1974) 6836-6841) was used to estimate the half-life of proteins. The half-life of total soluble proteins in old and intermediate age animals was 4 times and 2.5 times longer, respectively, than that of young nematodes. No differences could be discerned in the half-lives of total proteins between analogue-treated and control animals of young and intermediate ages. However, the rate of disposal of inactive molecules was slower in intermediate age as compared to young animals as it was closely related to the general rate of protein degradation in the different age groups. The results suggest that (a) the proportion of inactive enzyme molecules encountered in old animals is potentially detrimental, (b) the decline in efficiency of the degradation system in older animals may account for the accumulation of altered protein molecules in aging organisms.

Age related alterations in purified fructose-1,6-diphosphate aldolase from the nematode Turbatrix aceti.

Fructose-1,6-diphosphate aldolase has been purified to homogeneity 62.0 and 58.3 fold from young and old nematodes respectively. The aldolase preparations from young (7 days) and old (35 days) animals are indistinguishable in their electrophoretic mobility, molecular weight of the tetramer (158,000) and monomer (40,000), and Km, although the "old" enzyme is more heat stable than the "young" enzyme. Enzyme from old animals has only about 55% specific activity per mg purified protein of the "young" enzyme and its catalytic activity per unit of enzyme antigen is about 50% of that of the enzyme from young animals. Immunological identity of purified enzyme from old and young animals was established by the Ouchterlony technique by antiserum produced against purified "young" enzyme and antiserum against purified "old" enzyme. Thus, this work shows for the first time that the altered form of an enzyme which appears in senescent animals apparently does not possess extra antigenic sites which are acquired as a function of age.

Glyceraldehyde 3-phosphate dehydrogenase activity in rat and human lenses and the fate of enzyme molecules in the aging lens.

The specific activity of the enzyme glyceraldehyde 3-phosphate dehydrogenase declines as a function of age. Immunotitration with monospecific antibodies demonstrated that with age there is an increase of catalytically defective, but antigenically reactive enzyme molecules in the lens. Antiserum, produced against denatured enzyme, removed the inactive molecules from lens homogenates, without effects on the levels of enzyme activity. These studies suggest that inactive enzyme molecules in aging lenses are totally devoid of catalytic activity, and are at least partially denatured.

The effect of short- and long-term exercise on aldolase activity in muscles of CW-1 and C57/BL mice of various ages.

The effect of wheel running on the levels of fructose 1,6-bisphosphate aldolase A (EC 4.1.2.13) in striated muscles of young and old mice was compared. Short-term (6-10 weeks) and long-term (over 12 months) regimens were included in the study. The studies were conducted on the CW-1 outbred strain and on the C57/BL inbred strain of mice. It was shown that, in the short-term regimens, old animals of both strains showed either no increase (C57/BL) or a reduction (CW-1) in aldolase activity in hind leg muscles. On the other hand, young animals of both strains showed increases in aldolase activity of 10-20%. In the long-term regimen young and intermediate age animals showed 30-100% increases in aldolase activity in hind leg muscles over control sedentary animals. This adaptive capacity to exercise was not observed in old animals. However, long-term exercise regimen prevented the age-associated decline in aldolase activity found in sedentary animals.

Awareness of kidney disease in the US population: findings from the National Health and Nutrition Examination Survey (NHANES) 1999 to 2000.

BACKGROUND: The prevalence of end-stage renal disease (ESRD) in the US population has been predicted to increase by 48% during the next decade and will pose a significant health cost burden. Early identification and treatment of chronic kidney disease (CKD) is necessary to delay progression from CKD to ESRD. CKD awareness among patients is crucial to early intervention programs, but its prevalence and characteristics in the noninstitutionalized US population are unknown. METHODS: The National Health and Nutrition Examination Survey 1999 to 2000 was used to determine prevalence estimates of kidney disease awareness, as well as demographics, health care access, and comorbid characteristics, of participants with CKD. RESULTS: In participants with CKD, 40.5% of patients with stage 1, 29.3% of patients with stage 2, 22.0% of patients with stage 3, and 44.5% of patients with stage 4 CKD were aware of their kidney disease, respectively. The aware and unaware groups did not differ by health care access. In multivariate regression modeling, lack of awareness was significantly associated with sex, race-ethnicity distribution, and hypertension. CONCLUSION: Kidney disease awareness is low among a representative sample of the noninstitutionalized US population. Groups at greater risk for kidney disease, such as non-Hispanic blacks, patients with hypertension, and men, were more likely to be unaware of having kidney disease, even with health care access similar to that of the aware group. Increased efforts to promote kidney disease awareness are needed and probably should target primary care providers involved in the screening process.

The mitochondrial theory of aging: is the culprit a faulty disposal system rather than indigenous mitochondrial alterations?

Mitochondrial damage and the proportion of effete mitochondria in cells increase with age. According to the mitochondrial theory of aging, this phenomenon is mostly due to oxidative damage and is a major (and, some argue, the main) determinant of aging. It will be argued briefly that this phenomenon plays a role that is not exclusively crucial in aging. It will also be contended, essentially on theoretical grounds (for lack of sufficient current information), that there is low probability that the accumulation of reduced degradation of affected mitochondria is due to diminished production of hydroxyl radicals, as suggested by Aubrey and de Grey (1997) and expanded by Kowald (in this issue). What seems more likely is that the phagolysosomal disposal system of effete mitochondria is considerably altered in cells of aging organisms. Also, in view of the significant role of damaged mitochondria in the initial steps in apoptosis and the lack of evidence of massive apoptosis of cells in senescent individuals, the damage that exists may be milder than anticipated by the mitochondrial theory of aging. A brief fundamental summary on the biology of mitochondria is included for the sake of better understanding the arguments presented in this article. Also, suggestions are made for experimental testing of the hypotheses presented by Aubrey and de Grey (1997) and Kowald (1999).

The effects of enforced running on the gastrocnemius muscle in aging mice: an ultrastructural study.

C57BL/6J mice (6, 19 and 27 months old) were trained in an electrically driven treadmill for a total period of 10 weeks. The training program started with 5 min. run per day and reached a maximum of 30 min. per day. Light and electron microscopy examinations of the gastrocnemius muscle showed that in young animals endurance training did not evoke any appreciable changes. In contrast, both test animals and their controls in the old group revealed clear signs of muscle cell atrophy which for the most part was accompanied by focal loss of myofilaments, mitochondrial changes and an increase in the amount of endomyseal collagen fibrils. In the old-trained group, the most obvious abnormality comprised of multiplication of both the T-tubules and of the tubules of the sarcoplasmic reticulum. Consequently, most of these animals showed the formation of tubular aggregates in their gastrocnemius muscle. Hence, it appears that endurance training in old animals tends to enhance the regressive changes that accompany the aging process of mammalian skeletal muscle.