Lysosomes, membranes and aging

The lysosomal membrane protein SCAV-3 maintains lysosome integrity and adult longevity

Lysosomes degrade macromolecules and recycle metabolites as well as being involved in diverse processes that regulate cellular homeostasis. The lysosome is limited by a single phospholipid bilayer that forms a barrier to separate the potent luminal hydrolases from other cellular constituents, thus protecting the latter from unwanted degradation. The mechanisms that maintain lysosomal membrane integrity remain unknown. Here, we identified SCAV-3, the Caenorhabditis elegans homologue of human LIMP-2, as a key regulator of lysosome integrity, motility, and dynamics. Loss of scav-3 caused rupture of lysosome membranes and significantly shortened lifespan. Both of these phenotypes were suppressed by reinforced expression of LMP-1 or LMP-2, the C. elegans LAMPs, indicating that longevity requires maintenance of lysosome integrity. Remarkably, reduction in insulin/insulin-like growth factor 1 (IGF-1) signaling suppressed lysosomal damage and extended the lifespan in scav-3(lf) animals in a DAF-16-dependent manner. Our data reveal that SCAV-3 is essential for preserving lysosomal membrane stability and that modulation of lysosome integrity by the insulin/IGF-1 signaling pathway affects longevity.

Organization of polygenic systems: Cell death modifiers from natural populations ofDrosophila melanogaster

Expression of three wing-cell death mutants inDrosophilamelanogaster was used to survey cryptic polygenic modifiers of cell death in wild type strains. Females carrying the X-linked mutants Beadex-3, notchoid and scalloped were crossed to males from each of 20 isofemale strains. Phenotypic variation in the amount of cell death was measured in F1mutant males that were heterozygous for polygenic loci segregating in the wild strains. As expected, each mutant uncovered a broad range of polygenic variation among strains. Yet, when cluster analyses were used to evaluate the degree of correlation among the expressions ofBx3,sdandnd, the isofemale strains could be partitioned into a small number of groups that were similar in the effects they had upon the severity of cell death. Chromosome mapping of one cell death suppressor strain demonstrated that different polygenic loci could produce the same phenotype in different mutant backgrounds.

Mapping mechanisms and charting the time course of premature cell senescence and apoptosis: lysosomal dysfunction and ganglioside accumulation in endothelial cells

Endothelial cells subjected to glycated collagen I develop premature senescence within 3-5 days, as revealed by increased senescence-associated beta-galactosidase activity, decreased proliferation, and an increase in cell size. Here, we analyzed the time course and possible mechanisms of this process. Lysosomal integrity studies revealed a rapid collapse of pH gradient and lysosomal permeabilization, detectable after 30 min, and preceded by the increased production of reactive oxygen species. Measurement of mitochondrial membrane potential after application of glycated collagen demonstrated that depolarization was delayed by 4 h compared with changes in lysosomal pH and permeability. Based on the above findings of lysosomal permeabilization, we hypothesized that the reduced activity of senescence-associated beta-galactosidase could be responsible for the cellular accumulation of gangliosides, previously shown to induce cell senescence. After 5 days of exposure to glycated collagen, there was an increase in the levels of gangliosides GM3, GD1b, and GT1b, coincident with development of cell senescence. Treatment of endothelial cells with d-threo-EtDOP4, an inhibitor of glucosylceramide synthase, inhibited apoptosis, but not the development of senescence. In conclusion, collagen I modified by advanced glycation initially induces apoptosis of human umbilical vein endothelial cells. This process is initiated by the collapse of lysosomal pH and an increase in lysosomal permeability, with the subsequent mitochondrial depolarization and accumulation of gangliosides. Blockade of ganglioside synthesis suppresses apoptosis, but not senescence, which develops after 3 days of exposure to glycated collagen. These data imply a critical role for lysosomal permeabilization in triggering apoptosis of endothelial cells exposed to the diabetic milieu.

Autophagy as a cell-repair mechanism: activation of chaperone-mediated autophagy during oxidative stress

Proper removal of oxidized proteins is an important determinant of success when evaluating the ability of cells to handle oxidative stress. The ubiquitin/proteasome system has been considered the main responsible mechanism for the removal of oxidized proteins, as it can discriminate between normal and altered proteins, and selectively target the latter ones for degradation. A possible role for lysosomes, the other major intracellular proteolytic system, in the removal of oxidized proteins has been often refused, mostly on the basis of the lack of selectivity of this system. Although most of the degradation of intracellular components in lysosomes (autophagy) takes place through "in bulk" sequestration of complete cytosolic regions, selective targeting of proteins to lysosomes for their degradation is also possible via what is known as chaperone-mediated autophagy (CMA). In this work, we review recent evidence supporting the participation of CMA in the clearance of oxidized proteins in the forefront of the cellular response to oxidative stress. The consequences of an impairment in CMA activity, observed during aging and in some age-related disorders, are also discussed.

Pharmacological interventions against aging through the cell plasma membrane: a review of the experimental results obtained in animals and humans

As was shown in a recent review by this author (Ann. N.Y. Acad. Sci., 928: 187-199, 2001), oxyradicals cannot be considered only as harmful by-products of the oxidative metabolism, but living cells and organisms implicitly require their production. This idea is supported by numerous facts and arguments, the most important of which is that the complete inhibition of the oxyradical production by KCN (or by any block of respiration) kills the living organisms long before the energy reserves would be exhausted. This new theoretical approach not only helps our understanding of the normal functions of the living organisms, such as the basic memory mechanisms in the brain cells, but also helps in identifying the site-specific, radical-induced damaging mechanisms that represent the undesirable side effects of oxygen free radicals. First of all, these effects make the cell plasma membrane vulnerable and cause a series of intracellular functional disorders, as described by the membrane hypothesis of aging (MHA). The logical way for any antiaging intervention therefore should be to increase the available number of loosely bound electrons inside the plasma membrane that are easily accessible for OH(*) free radical scavenging. The present review summarizes the available knowledge regarding the theory of the use of membrane-related antiaging pharmaca, like centrophenoxine (CPH), tested in both animal experiments and human clinical trials. A modified, developed version of CPH coded as BCE-001 is also reported.

When lysosomes get old

Changes in the lysosomes of senescent tissues and organisms are common and have been used as biomarkers of aging. Lysosomes are responsible for the degradation of many macromolecules, including proteins. At least five different pathways for the delivery of substrate proteins to lysosomes are known. Three of these pathways decline with age, and the molecular explanations for these deficiencies are currently being studied. Other aspects of lysosomal proteolysis increase or do not change with age in spite of marked changes in lysosomal morphology and biochemistry. Age-related changes in certain lysosomal pathways of proteolysis remain to be studied. This area of research is important because abnormalities in lysosomal protein degradation pathways may contribute to several characteristics and pathologies associated with aging.

Age-dependent sensitization to oxidative stress by dietary fatty acids

Experiments were designed to test the hypothesis that short-term feeding of a high polyunsaturated fatty acid (PUFA) diet would increase susceptibility to lipid peroxidation in an age-dependent manner. Young (6 month) and old (24 month) male B6C3F1 mice were fed modified AIN-76 diets containing either 5% corn oil (CO, N = 5 per age group) or 19% fish oil plus 1% corn oil (FO, N = 20 per age group) for two weeks. Five CO and five FO diet mice per age received an intraperitoneal injection of normal saline and were sacrificed one hour later; the remaining FO diet mice (N = 15 per age) were challenged with an acute systemic oxidative stress by intraperitoneal injection of 125 mg iron/kg body weight as iron dextran, and were sacrificed 1, 5, and 24 hours post-injection. Microsomal membrane fatty acid analysis revealed that increased age and a FO diet significantly increased membrane PUFA content. Serum iron levels increased significantly following iron treatment, peaking at 5 hours in both age groups. Formation of microsomal malondialdehyde (MDA), a product of lipid peroxidation, was significantly greater in the livers of the young mice. The temporal patterns of serum iron and microsomal MDA concentrations were significantly correlated in young mice, but not in old mice. Histochemical examination showed that liver iron accumulation following iron injection was similar in both age groups, but was associated with a significant temporal increase in liver apoptotic cells in young mice, but not in old mice. Thus, both age groups had similar iron exposure and iron accumulation, and the liver microsomal membranes of old mice were more unsaturated, yet there was significantly greater peroxidative damage (MDA formation) and cell death (apoptosis) in the young mouse livers. These findings suggest that the older animals have upregulated antioxidant defenses.

The free radical theory of aging matures

The free radical theory of aging, conceived in 1956, has turned 40 and is rapidly attracting the interest of the mainstream of biological research. From its origins in radiation biology, through a decade or so of dormancy and two decades of steady phenomenological research, it has attracted an increasing number of scientists from an expanding circle of fields. During the past decade, several lines of evidence have convinced a number of scientists that oxidants play an important role in aging. (For the sake of simplicity, we use the term oxidant to refer to all "reactive oxygen species," including O2-., H2O2, and .OH, even though the former often acts as a reductant and produces oxidants indirectly.) The pace and scope of research in the last few years have been particularly impressive and diverse. The only disadvantage of the current intellectual ferment is the difficulty in digesting the literature. Therefore, we have systematically reviewed the status of the free radical theory, by categorizing the literature in terms of the various types of experiments that have been performed. These include phenomenological measurements of age-associated oxidative stress, interspecies comparisons, dietary restriction, the manipulation of metabolic activity and oxygen tension, treatment with dietary and pharmacological antioxidants, in vitro senescence, classical and population genetics, molecular genetics, transgenic organisms, the study of human diseases of aging, epidemiological studies, and the ongoing elucidation of the role of active oxygen in biology.

Lipid peroxidation, antioxidant protection and aging

The free radical hypothesis of aging proposes that deleterious actions of oxygen-derived radicals are responsible for the functional deterioration associated with aging. Because cellular membranes house the production apparatus of these radicals and because membranes suffer great damage from these radicals, modification of membrane lipids has been proposed to play a major role in the process of aging. Although the relationships between lipid peroxidation and aging have been investigated extensively, the studies have produced conflicting results. Increased lipid peroxidation and decreased antioxidant protection frequently occur, but they are not universal features of aging. Instead, age-dependent changes in these parameters appear to be species-, strain-, sex- and tissue specific. Potential correlations between lipid peroxidation and transition metal concentrations or between lipid peroxidation and declining antioxidant protection have been obscured by the contradictory nature of the findings. Future studies should focus on new approaches for the measurement in vivo lipid peroxidation and on identification of the critical targets of lipid peroxidation.

Effect of dietary restriction on lysosomal bodies and total protein synthesis in hepatocytes of aging rats

The accumulation of lysosomal bodies has long been considered to be an important correlate of aging. However it is not well established whether these age related changes interfere with cellular function. In this study, an evaluation of lysosomes by ultrastructural analysis was performed in livers of 4-6 and 20-24-month-old Sprague-Dawley female rats, fed ad libitum (A) or a restricted diet (R). An attempt was made to relate this parameter to hepatic protein synthesis, a liver function known to decrease with age and increase with dietary restriction. Aging was accompanied in both A and R animals with higher number and size of secondary lysosomes (lipofuscin) and by a decrease in total protein synthesis in hepatocytes. When compared to age matched ad libitum fed animals, livers of food restricted rats contained higher number of secondary lysosomes, yet exhibited higher protein synthetic capacity. Thus in hepatocytes, lipofuscin accumulation does not seem to interfere with cellular function.

Characterization of liver lysosomal enzyme activity in hepatocytes, Kupffer and endothelial cells during aging: effect of dietary restriction

The specific activity of 4 lysosomal enzymes was studied in homogenate, hepatocytes, Kupffer and endothelial cells isolated from the livers of female Sprague-Dawley rats aged 3.5, 12 and 24 months. Cells were obtained by enzymatic digestion and centrifugal elutriation. Cell viability was not affected by age or diet. In hepatocytes, the activities of all enzymes (acid phosphatase, beta-galactosidase, arylsulfatase B and cathepsin D) increased with age in rats fed ad libitum (A) but were not altered significantly by dietary restriction. The activities of all enzymes except acid phosphatase were systematically higher at 3.5 months of age in Kupffer and endothelial cells than in hepatocytes. Acid phosphatase, arylsulfatase B and cathepsin D activities increased with age in both Kupffer and endothelial cells. Beta galactosidase was decreased significantly with age in Kupffer cells but was elevated in endothelial cells. Rats exposed to dietary restriction (R) showed higher activities of beta-galactosidase, arylsulfatase B and cathepsin D when compared to corresponding A animals with the exception of the younger age group. No clear cut pattern was observed in acid phosphatase activity. Thus, the activities of liver lysosomal enzymes increase with age but the pattern of change differs with respect to enzyme and cell populations. The heightened enzyme activity in Kupffer and endothelial cells from R rats may reflect a more efficient phagocytic capacity in these animals.

Cortisone extends life span in the rotifer Asplanchna brightwelli

Cortisone at 100 and 200 microM concentrations produced a significant increase in both life span and reproduction in the rotifer Asplanchna brightwelli. Two possible mechanisms are discussed to explain these results: (1) cortisone stabilization of lysosomal membranes, or (2) recognition of cortisone as a hormone capable of altering resource allocation by the rotifers.

Gerontopsychological studies using NAI ('Nürnberger Alters-Inventar') on patients with organic psychosyndrome (DSM III, Category 1) treated with centrophenoxine in a double blind, comparative, randomized clinical trial

A double blind clinical trial was performed on 50 persons (25 men, 25 women) over the age 60 (average age: 77 years). They suffered from dementias of medium level (DSM III, Category 1, ICD No. 299), and had been residents in an old age home longer than 3 months at the start of the trial. The patients were treated first for 2 weeks by placebo tablets and their initial performance was recorded during this period by using the Nuremberg Gerontopsychological Inventory (NAI). This was then followed by a treatment for 8 weeks with the nootropic drug, centrophenoxine (CPH), the dose of which was 2 g/day distributed in 2 x 2 tablets of Helfergin500 (Promonta, Hamburg, FRG), or with placebo tablets of identical size, then the NAI test was repeated again. Verum or placebo treatment was selected randomly and the code was revealed only after having elaborated all the results of the trial. During the treatment period four drop-outs occurred for intercurrent diseases. Evaluation was based on a semi-quantitative, intra-individual comparison of the performance before and after treatment. The results obtained suggest that CPH treatment may be useful in dementias of medium level in quite old groups of patients, since 48% of the verum group displayed improvements in the memory functions against 28% of the placebo group. CPH seems to be a useful and harmless drug in the treatment and most probably also in prevention of the dementias.

Potential and limitations of cultivated fibroblasts in the study of senescence in animals. A review on the murine skin fibroblasts system

Senescence is the last period of the life span, leading to death. It happens in all animals, with the exception of a few didermic species (Hydras) having a stock of embryonic cells and being immortal. The causes of animal senescence are badly known. They depend both on genetic characters (maximum life span of a species) and on medium factors (mean expectation of life of the animals of a species). Animal senescence could depend on cell aging: (1) by senescence and death of the differentiated cells, (2) by modified proliferation of the stem cells of differentiated tissues, (3) by alterations in the extracellular matrices, (4) by interactions between factors (1) (2) and (3) in each tissue, and (5) by interactions between the several tissues of an organism. This complexity badly impedes the experimental study of animal senescence. Normal mammal cells are aging when they are cultivated (in vitro aging). Present literature upon in vitro aging of cultivated human fibroblasts consists essentially of papers devoted to proliferation and differentiation characteristics and not to cell senescence. Murine skin fibroblasts have been studied in our laboratory, using different systems: (1) primary cultures isolated from peeled skins of mouse embryos, (2) mouse derms analysed in the animals, (3) cultivated explants of skins, (4) serial sub-cultures of fibroblasts isolated from these explants, (5) cells cultivated comparably on plane substrates (glass, plastic, collagen films) and on three-dimensional matrices (collagen fibres). In primary cultures (system 1) all the cell generations have been analysed, including the last one until death of the culture. We have shown that many characters are varying with cell generation. All the observed variations were: progressive, non-linear and correlated (intracellular feedbacks). We come to the conclusion that the main effects of cell mitotic age are (1) to depress the plasticity of the chromatin, (2) to change the organization of the cytoplasmic filaments, (3) to change the organization of the extracellular matrix. The collagen fibres are also acting upon nucleus and filaments either in the animals or in the cultures. The phenotype of a fibroblastic cell is thus both age- and environment-dependent. Overall data on in vitro cell aging point to the hypothesis that senescent cells are phenotypic variants and not mutant cells. Aging cell cultures are remarkably useful to the studies on cell proliferation decrease and cell cycle lengthening shown by the stem cells in animal tissues. We propose the hypothesis that the fibroblasts of the vertebrates would be homologous to the pluripotent mesenchyme cells of their embryos.

Effect of lifetime administration of dimethylaminoethanol on longevity, aging changes, and cryptogenic neoplasms in C3H mice

The effects of lifetime treatment with dimethylaminoethanol on longevity and cryptogenic neoplasm formation were studied in females of two mouse sub-lines, the C3H/HeN which carries a germinal mammary tumor provirus and the C3H/HeJ(+) which also carries the exogenous mammary tumor virus. Administration in the drinking water of 10 mM dimethylaminoethanol to the C3H/HeN mice or 15 mM to the C3H/HeJ(+) mice did not result in significant differences between treated and untreated groups in average survival. No changes in age-related organ structure or morphology were observed with dimethylaminoethanol treatment, except for an apparent decrease in the amount of lipofuscin in the liver judged in histological sections. Among untreated C3H/HeJ(+) females, 89% developed neoplasms of the mammary gland, ovary, liver, lung and reticuloendothelial system, while the incidence was 88% in the treated mice. In C3H/HeN females, neoplasms of the mammary gland, ovary, liver, lung and lymphatic system occurred in 57% and in 60% of treated mice. Also, there was no statistically significant difference between control and treated animals in the age of onset or the type of specific neoplasms. Dimethylaminoethanol did not induce any neoplasms.

Maturation and degeneration of the fat body in the Drosophila larva and pupa as revealed by morphometric analysis

Using morphometric and cytochemical techniques we have described changes taking place in the fat body cells during three different stages of development. The cell number remains constant at about 2200 cells during larval life and then decreases gradually and continuously throughout metamorphosis and the first 3 days of the adult stage until no more cells can be observed. Cell size increases rapidly during the larval period and decreases steadily during metamorphosis and adult stage. The size of the nuclei increases during the larval instars and decreases during the pupal interval. The change in nuclear size is correlated with the amount of DNA present throughout development implying the nuclear DNA is synthesized during the larval period and degraded gradually during metamorphosis. The cell size changes are due in large part to accumulation or loss of reserve substances: lipid droplets, glycogen deposits and protein granules. During metamorphosis the amount of lipid decreases slightly whereas glycogen experiences two loss cycles. The protein granules in the form of lysosomes continue to increase in amount during the first day of metamorphosis because of a short period of massive autophagy. Then the lysosomes decrease in amount throughout the remainder of metamorphosis. The lysosomes stain positively for lipofuscin.

The influence of aging on lysosomal acid DNase of the rat submandibular gland

Lysosomal and cytoplasmic fractions were prepared from rat submandibular glands for investigation of the release of lysosomal acid DNase in relation to aging. It was found that the acid DNase activity ratio for cytoplasmic/lysosomal fractions in rats aged 27 months was higher than that in three-month-old rats. The release of acid DNase from the lysosomal fraction by shaking was markedly increased in the fraction from the older animals.

Phagocytosis and lipofuscin accumulation in lymph node macrophages

Lipofuscin is considered to be undigestible material present in secondary lysosomes. During histological and electron microscopical studies lipofuscin was observed in macrophages in popliteal lymph nodes in 3-6 month-old-male Wistar rats after occlusion of the afferent lymph flow to the lymph node. No pathological alterations were found in the lymph node after the operation. However, the number of macrophages was severely reduced. Simultaneously the number of secondary lysosomes increased in the remaining macrophages reaching a plateau 4 weeks after operation. At this time three quarters of the residual bodies already contained lipofuscin granules. In the following weeks almost all macrophages showed lipofuscin in increasing amounts. Macrophages in normal contralateral lymph nodes of the same rats rarely contained lipofuscin. The increased phagocytosis of the remaining macrophages thus preceded the appearance of lipofuscin. We suggest that lipofuscin results from an inadequate intralysosomal digestion.

Role of membrane lipid asymmetry in aging

Recent advances in our understanding of the asymmetric distribution of lipids across nervous system membranes coupled with the application of biophysical techniques to examine transbilayer structure and function have led to the formulation of a new hypothesis. The author hopes that the insights presented herein will stimulate investigation into this developing new field. The theory provides an approach to correlation the accumulation of nervous tissue membrane peroxidative and cross-linking damage, the loss of transbilayer lipid asymmetry, and loss of transbilayer neuroendocrine, transport, secretory and immunoregulatory functions. Central to this scheme is the role of membrane lipid asymmetry in regulation to and/or coupling of transbilayer functions.

Inhibitors of lysosomal enzymes: accumulation of lipofuscin-like dense bodies in the brain

Injections of leupeptin (a thiol proteinase inhibitor) or chloroquine (a general lysosomal enzyme inhibitor) into the brains of young rats induced the formation of lysosome-associated granular aggregates (dense bodies) which closely resembled the ceroid-lipofuscin that accumulates in certain disease states and during aging. The dense material increased in a dose- and time-dependent fashion and was differentially distributed across brain regions and cell types. These observations provide clues to the origins of ceroid-lipofuscin and suggest means for studying the consequences of its accumulation.

Centrophenoxine increases the rates of total and mRNA synthesis in the brain cortex of old rats: an explanation of its action in terms of the membrane hypothesis of aging

The rates of total and polyA+ RNA (mRNA) synthesis were measured by radioisotope technique in the brain cortex of female CFY rats. There was practically no significant difference between the young (1.5 months) and adult (13 months) rats; however, the old group (26 months) displayed a considerable decrease of the rates of synthesis of both classes of RNA studied. Centrophenoxine treatment (100 mg per kg body weight per day, for 2 months) reversed this tendency, and increased significantly the synthesis rates of old rats almost to the adult level. The results are interpreted in terms of the membrane hypothesis of aging, attributing a free-radical scavenger function of the dimethylamino-ethanol incorporated into the nerve cell membrane from the centrophenoxine.

Changes in the serine-specific transfer ribonucleic acid pattern of guinea pig epidermis after corticosteroid treatment

The pattern of serine-specific tRNAs from guinea pig epidermis was determined and compared to that from liver by employing reversed phase chromatography on total tRNA preparations aminoacylated with 3H- or 14C-serine. Five tRNAserS (I-V) were found, two of which, tRNAserI and tRNAserV, appear to be "typical" for epidermis and in so far probably reflect in some way metabolic peculiarities of epidermal cell differentiation. This hypothesis was further corroborated by showing that the locally applied corticosteroid triamcinolon selectively increases tRNAserI and tRNAserV 2-3-fold. The implications of these findings were discussed in detail.

Morphometric studies on synapses of the cerebellar glomerulus: the effect of centrophenoxine treatment in old rats

Young, adult and old female Wistar rats (3, 18 and 28 months of age, respectively), were studied using electron-microscopic stereology. Synaptic parameters of the cerebellar glomerulus were calculated and compared with similar data obtained from old Wistar rats of the same breed treated with centrophenoxine (CPH; HelferginR, Promonta, Hamburg) in the form of intraperitoneal injections (100 mg/kg body weight) for 40 days. This treatment resulted in a sort of "rejuvenation" of synaptic structures. Namely, the surface density and the total length of synaptic contact zones were markedly reduced in the untreated old group, but in the treated animals these parameters returned to the values found in the young and adult animals. At the same time the numerical density of synapses remained unaltered in the treated group, while the average synaptic length displayed some further increase. The results are interpreted in terms of the age-dependent decrease in reactive synaptogenesis, suggesting that CPH stimulates the metabolism of the nervous elements persisting in old brain. The possible mechanism of CPH effect is also discussed.

Conservation of ribosomal fidelity during ageing

The function of ribosomes prepared from the liver of young (2--5 months old) and senescent (15--26 months old) mice were compared in vitro. The conclusions that can be drawn from the liver of senescent mice is 10 to 40% lower than that of young mice; (2) the fidelity of translation does not change grossly with age; (3) the thermosensitivity of translational activity of ribosomes and the activity of ribosome-associated ribonuclease do not change with age; (4) there is an age-dependent accumulation of free 40S ribosomal subunits in the cytoplasm of mouse liver. The relation of age-dependent changes in the structure and function of ribosomes is discussed.

Membrene turnover in imbibed and dormant embryos of the wild oat (Avena fatua L.) : I. Protein turnover and membrane replacement

A comparative study of protein synthesis has been carried out with embryos excised from dormant (D) and non-dormant (ND) caryopses of the wild oat. Although D embryos imbibed in water or ND embryos imbibed in abscisic acid do not germinate, they incorporate [(14)C]leucine into TCA-insoluble material for the first 48 h as readily as embryos that do germinate (ND embryos imbibed in water, or D embryos imbibed in gibberellic acid). Pulsechase experiments with [(14)]leucine show that in both D and ND embryos the proteins associated with the membranes undergo turnover. The rates of decay of incorporated radioactivity are similar in both dormant and germinating embryos up to 98 h following embryo excision. Fractionation of the membrane proteins in SDS-polyacrylamide gels indicates that the different polypeptides have different rates of turnover. It is concluded that membrane proteins in imbibed D embryos are in a state of constant turnover, and that this is a part of the replacement processes necessary to maintain the integrity of hydrated cells. The continuation of such synthetic events could account for long term survival of dormant Avena fatua in the imbibed state.

Stable lipid peroxidation products in human skin: detection, ultraviolet light-induced increase, pathogenic importance

Products of lipid peroxidation (malonaldehyde, Schiff-bases) were detected in human skin. These products were increased after UV-light exposition, on chronically sun-exposed areas as well as with advancing age. Malonaldehyde cross linked epidermal glucose-6-phosphate-dehydrogenase and diminished their activity.

Loss of endocytic capacity in aging Paramecium. The importance of cytoplasmic organelles

Aged cells have significantly fewer food vacuoles and ingest fewer bacteria than young cells. Loss of food vacuoles was explained by a decreasing difference in the food vacuole formation and excretion rates; the formation rate declined more rapidly than the excretion rate, approaching equivalence at 160 fissions, when the proportion of cells with no food vacuoles, in the presence of excess food, abruptly increased. A model for cellular aging is presented in which control of organelle numbers and cyclical interactions between the nucleus and cytoplasm may be of critical importance.

Ageing of Neurospora crassa. III. Induction of cellular death and clonal senescence of an inositol-less mutant by inositol starvation and the protective effect of dietary antioxidants

Clonal growth rate and cellular viability of an inositol-less mutant of Neurospora crassa decline rapidly during deprivation of dietary inositol. Dietary antioxidants, either nordihydroguaiaretic acid, vitamin E or 3,5-ditert.-butyl-4-hydroxybenzyl alcohol, protected cells and clones of the mutant from death and senescence. Membrane deterioration with associated lipid autoxidation and consequent deleterious free radical reactions appear to be, in part at least, the causes of the mutant's death and senescence.

Morphological changes in aging cell lines of Paramecium aurella. I. Alterations in the cytoplasm

Electron microscopical examination of aging P. aurelia revealed that definitive changes occur in the cytoplasm of old cells. There was an increase in the number of mitochondria and lysosomal bodies as well as the appearance of large dense bodies and autophagous vacuoles. The mitochondria were altered morphologically and many appeared to be coalesced with lysosome-like bodies and were also observed to be degenerating within autophagous vacuoles. The large dense bodies were considered to be similar to the lipofuscin or age pigments reported in other aging cells. The relationship of the large dense bodies to the lipofuscin pigments and their probable origin are discussed as is the involvement of the cytoplasm in the aging death process in P. aurelia.

Benign rheumatoid arthritis of the aged

A severe type of rheumatoid arthritis which is seen in 25% of cases that present with the disease after the age of 60 is a self-limiting illness. It can be well controlled during the acute severe phase and has a good prognosis. This paper describes 29 patients with this pattern of disease who were separated from a larger group of 110 elderly onset cases.