Age-dependence of molecular and functional changes in biological membrane properties

The impact of aging on enzyme proteins of rat liver peroxisomes: quantitative analysis by immunoblotting and immunoelectron microscopy

The alterations of hepatic peroxisomes and their enzymes during aging were investigated in male rats. Peroxisomes in the livers of young (2 months) and old (39 months) male Wistar rats were analyzed by morphometry and quantitative immunocytochemistry, as well as by immunoblotting of highly purified peroxisomal fractions. Immunoblots showed that catalase and acyl-CoA oxidase were decreased in peroxisomes of old animals but the trifunctional enzyme, thiolase, and urate oxidase were increased. The morphometrical analysis revealed a heterogeneous distribution of peroxisomes in the liver lobule of the old animals, with a significant elevation of peroxisomal volume density in pericentral over periportal hepatocytes, in contrast to the uniform pattern in the young rats. Furthermore, age-related lobular gradients were also observed by quantitative immunocytochemistry in the peroxisomal concentrations of trifunctional enzyme (central > portal) and, inversely, for catalase (portal > central). Whereas acyl-CoA oxidase was diminished across the liver lobule, the enzyme 3-ketoacyl-CoA thiolase was elevated. These observations show that peroxisomes are significantly altered in aged animals and suggest that these alterations may contribute to the disturbance of lipid metabolism in aged animals. Moreover, the diminution in catalase and the elevation of urate oxidase could contribute to the oxidative stress which is considered to be of fundamental importance in the aging process.

Age-dependent accumulation of phosphatidylcholine hydroperoxide in the brain and liver of the rat

Age-related changes in phosphatidylcholine hydroperoxide (PCOOH) content as an index for oxidative membrane lipid damage were determined by high-performance liquid chromatography using chemiluminescence detection. Brain and liver PCOOH content increased significantly in male and female rats with age. The brain PCOOH content of male 18-month-old rats was 4.4 times that of 1-month-old rats, and that of female 18-month-old rats was 3.5 times that of 1-month-old females. The liver PCOOH content of the male 18-month-old rats was 9.3 times that of the 1-month-old; and of the female 18-month-old rats was 4.7 times that of the 1-month-old. PCOOH levels in heart and lung did not show age dependency. In both brain and liver (but not in heart and lung), the phosphatidylcholine content significantly decreased upon aging. The results indicate that oxidative deterioration, such as phospholipid hydroperoxidation, is prevalent in the membrane lipids of brain and liver of the rat due to aging.

Distribution of transitory corpus callosum axons projecting to developing cat visual cortex revealed by DiI

Functional studies of the development of the corpus callosum in the cat have shown that an intact callosum during postnatal month 1 is necessary for normal visual development. In vivo tracing techniques have not provided enough information on corpus callosum connectivity to fully evaluate the evidence for a morphological mechanism for the functional effects of neonatal callosum section. However, lipophilic in vitro membrane tracers permit a more detailed search for such evidence because the entire limit of many cells can be labeled simultaneously. To investigate the morphological basis for the observed functional results in cats, the corpus callosum was labeled in vitro with the carbocyanine dye, DiI. Crystals of DiI were placed in the midsagittal callosum in tissue from 2 to 277-day-old cats. Tissue was coronally sectioned 3-22 months later. Sections were photographed and reconstructed to show the overall distribution of corpus callosum projections, as well as the locations of individual corpus callosum axons and their presumed terminals. The distribution of corpus callosum projections, examined in cortical areas 17-19, 7, and posterior medial lateral suprasylvian cortex, changes significantly during development. During postnatal week 1, callosal axons extend throughout these cortical areas to layer I. Numerous varicosities on callosal axons are located en passant and at axon terminals in layer I. During postnatal week 2, the density of callosal projections is reduced in all cortical areas, although many axons still extend to layer I. By postnatal month 2, the callosal axons extending to layer I are predominantly near the border with adjacent cortical areas; in the nonborder regions of these areas, many axons extend to layer VI while a much smaller number of axons extend to layers II-V. By postnatal month 3, the callosal projections to supragranular layers are almost exclusively restricted to cytoarchitectonic border regions; in the remaining regions, including medial area 17, there are occasional axons extending to the supragranular layers and only a moderate number of axons extending to infragranular layers. Thus, a substantial number of elaborately formed transitory corpus callosum axons, distributed throughout visual cortex, exist for several weeks during postnatal development; in area 17, these axons are found in central through peripheral visual field representations. The transitory callosal axons appear to have axon terminals in layer I as well as en passant terminals while extending through layers II-VI. If some of these terminals were to form synapses, there would be extensive opportunities for the corpus callosum to provide input to layers I-VI throughout visual cortex during the period of development in which cortical microcircuitry is being established.

Aging, training and exercise. A review of effects on plasma glutathione and lipid peroxides

Changes in plasma glutathione (reduced form: GSH; oxidised form: GSSG) and lipid peroxides (LPO) levels occur with aging, training and acute physical exercise. Sources of plasma GSH, GSSG and LPO include the liver and skeletal muscle. Aging appears to be accelerated because of a decrease in the antioxidant capacity of tissues reflected in a decreased plasma GSH level. This age-dependent change could be partly compensated by physical training. Skeletal muscle appears to be able to deliver GSH into circulation with the adaptation of muscle to exercise training reflected in an increased plasma GSH level in the trained subject. Decreased plasma GSH concentration following physical exercise demonstrates increased GSH consumption in skeletal muscle resulting in a reduced export rate from muscle into plasma. The GSH system is able to effectively protect tissues against lipid peroxidation initiated by oxygen-derived free radicals produced in the intermediate metabolism during exercise. It can be assumed that the rate of this free radical production is a function of oxygen flow through organ and muscle tissue.

Cholesterol is required for the fusion of single unilamellar vesicles with Mycoplasma capricolum

Small unilamellar vesicles (SUV) were prepared from the total lipid extract of Mycoplasma capricolum. The SUV were labeled with the fluorescent probe octadecylrhodamine B chloride (R18) to a level at which the R18 fluorescence was self-quenched. At pH 7.4 and 37 degrees C, and in the presence of 5% polyethylene glycol, an increase in the R18 fluorescence with time was observed when the R18-labeled SUV were introduced to a native M. capricolum cell suspension. The fluorescence dequenching resulting from dilution of the R18 into the unlabeled membranes of M. capricolum, was interpreted as a result of lipid mixing during fusion between the SUV and the mycoplasma cells. The presence of cholesterol in the SUV was found to be obligatory to allow SUV-mycoplasma fusion to occur. Adaptation of M. capricolum cells to grow in a medium containing low cholesterol concentration provided cells in which the unesterified cholesterol content was as low as 17 micrograms/mg cell protein. The fusion activity of the adapted cells was very low or nonexistent. Nonetheless, when an early exponential phase culture of the adapted cells was transferred to a cholesterol-rich medium, the cells accumulated cholesterol and regained their fusogenic activity. The cholesterol requirement for fusion in the target mycoplasma membrane was met by a variety of planar sterols having a free beta-hydroxyl group, but differing in the aliphatic side chain, e.g., beta-sitosterol or ergosterol, even though these sterols, having a bulky side chain, are preferentially localized in the outer leaflet of the lipid bilayer. It is suggested that the role of cholesterol in mycoplasma-SUV fusion is not at the level of bulk bilayer viscosity but rather, affecting local lipid-lipid or lipid-protein interactions that are relevant to the fusion event.

Protein oxidation associated with aging is reduced by dietary restriction of protein or calories

The accumulation of unrepaired oxidative damage products may be a major factor in cellular aging. Both oxidative lesions in DNA and oxidatively damaged proteins have been shown to accumulate during aging. The accumulation of oxidized proteins in Fischer 344 rats was compared for animals consuming protein-restricted and calorically restricted diets--both of which have been shown to extend lifespan. Rats were fed diets restricted in either protein (5% or 10% of the diet as compared with the normal 20% casein), or calories (25% or 40% less than normal), or total diet (40% less than normal). In addition, some of the rats fed a diet providing 5% or 20% protein were irradiated twice weekly (125 rads per exposure; 1 rad = 0.01 Gy). The level of oxidative damage to proteins (protein carbonyls) was determined in rats sacrificed at various times. The oxidative damage to proteins increased with aging and with radiation. Either protein or calorie restriction markedly inhibited the accumulation of oxidatively damaged proteins. Protein restriction reduced the accumulation of oxidatively damaged proteins during the oxidative stress of chronic irradiation.

Progressive loss of cytochrome c oxidase in the human extraocular muscles in ageing--a cytochemical-immunohistochemical study

Cytochrome c oxidase (complex IV of the respiratory chain) was studied histochemically in autoptic human extraocular muscles (n = 135), revealing randomly distributed single fibers without enzyme activity. The enzyme defect was expressed in all the mitochondria of an involved fiber as evidenced by ultracytochemistry. Succinate dehydrogenase showed normal histochemical reactivity. The defects occurred already in the second decade and were regularly seen from the third decade on. The defect density (defects/mm2) increased from approx. 1/mm2 below the fifth decade to about 4/mm2 in advanced age (P = 0.000). The highest defect density was observed in the levator palpebrae muscle. On the whole, the defect density was about 5-6 times higher in the extraocular muscles than in the limb muscle, diaphragm and heart (Müller-Höcker, 1989, 1990). Immunocytochemical detection of cytochrome c oxidase showed that loss of cytochrome c oxidase activity was due to an almost complete absence of both nuclear and mitochondria subunits of the enzyme. The results document different organ and heterogenic cellular sensitivity to the age-related loss of cytochrome c oxidase. The loss of both mitochondrial and nuclear subunits indicates that nuclear factors are most probably involved in the decline of the respiratory chain function in senescence.

Effect of age-related lipid peroxidation on membrane fluidity and phospholipase A2: modulation by dietary restriction

Age-related changes in membrane property are generally accepted phenomena. In this report, using the anti-lipoperoxidative measure of dietary restriction on membranes, the age-related effects of lipid peroxidation on membrane fluidity are explored in conjunction with the membrane-associated phospholipase A2. The fluidity of mitochondrial and microsomal membranes from ad libitum fed rats shows a progressive decline with age as indicated by a substantial decrease in two parameters, l/polarization and l/anisotropy. In contrast, the membrane fluidity of dietary restricted rats shows slight changes between 6 and 24 months of age. Evidence is presented to support the possibility that age-related peroxidation of membrane lipids may play a significant role in bringing about fluidity changes in aged membranes. The findings on the increased phospholipase A2 with age is also consistent with this conclusion.

Mitochondria and ageing

This work reviews the role of mitochondria in the ageing process and summarizes pathomorphological biochemical and molecular genetic data. The pathophysiological mechanisms underlying the phenomenon of ageing are only partly understood. There is, however, increasing evidence that mitochondria are essentially involved. In various tissues of various species a decline in the respiratory chain capacity is seen with ageing. Enzyme histochemistry of cytochrome c oxidase (complex IV of the respiratory chain) has revealed an age-related increase of randomly distributed defective fibres/cells in the skeletal and heart muscle the random pattern probably indicating cellular heterogeneity of the ageing process. Observed deletions of mitochondrial DNA during ageing may represent one causative factor. Similar to primary mitochondrial myopathies point mutations and depletion of the mtDNA are probably also involved. There is some evidence that damage of the mitochondrial genome and of other mitochondrial structures might be due to increased oxygen radical production during ageing. The role of nuclear influences on the degeneration of mitochondrial function remains, however, also to be determined. Nevertheless, the decline of respiratory chain function with ageing represents an important factor for the decline of functional organ reserve capacity in senescence.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of age on rat glutathione metabolism

The authors hypothesized that rat plasma or tissue glutathione metabolism could change with age due to possible decreases in glutathione-related enzyme activities. To test this hypothesis, the authors measured plasma and tissue concentrations of glutathione and glutathione-related enzymes. Animals were 3 months, 12 months, or 24 months old at the time of experiments. Plasma glutathione was found to be significantly increased in both the 12-month-old and 24-month-old groups compared to the 3-month-old rats. Tissue enzyme measurements showed no significant differences between the groups in lung or liver glutathione peroxidase or glutathione S-transferase. gamma-Glutamyl transpeptidase activity was significantly decreased in kidney and lung with aging. Decreases in tissue gamma-glutamyl transpeptidase activity occur with age; this may contribute to increases in plasma glutathione concentrations.

Food restriction slows down age-related changes in cell membrane parameters

The effect of undernutrition on some plasma membrane parameters has been analyzed. Diet restriction was applied to female Wistar rats on every-other-day schedule (EOD), starting from the age of 3.5 months. Membrane microviscosity of splenic lymphocytes was lower in EOD rats than in the ad libitum (AL) fed ones even if one assumes a decrease of body temperature of 2 degrees C. The decrease of membrane microviscosity due to diet restriction ran parallel with the improvement of proliferative response of lymphocytes. The analysis of Arrhenius plots of 1,6-diphenyl-1,3,5-hexatriene as well as of 5'-nucleotidase activity showed a diet-dependent improvement of membrane properties also of liver plasma membranes. Diet restriction was able to partially recover the age-dependent decrease of beta-adrenoceptor density of cerebellar membranes. On the contrary, beta-adrenoceptor density of lymphocytes, which did not show any age-dependent alteration, was not influenced by diet restriction. Present results support that undernutrition exerted a protective effect on cell membranes of old animals and it was able to improve those alterations which are related to aging.

Evaluation of age-related changes of physicochemical properties and functional activity of rat adipose plasma membranes and their possible relationship

Studies were carried out to evaluate structural state of adipose plasma membranes (PM) from mature adult and aged Wistar rats and its possible relation to functional changes in aging. PM lipids were probed by fluorescence of 1,6-diphenyl-1,3,5-hexatriene (DPH) and pyrene. The data on DPH anisotropy, pyrene excimerization and induction resonance energy transfer (IRET) from PM proteins to pyrene provided the evidence for age-dependent decrease in PM lipid phase fluidity inclusive of that of annular lipid. Interaction between PM lipids and integral proteins also changed in aging. The observed structural changes were due to age-related lipid compositional modification. Evidence for this conclusion was provided by the following data: (i) DPH anisotropy was increased in aging both in PM and liposomes from the same PM lipids; (ii) both saturation/unsaturation fatty acid ratio and relative content of phosphatidylethanolamine (PE) increased in aged PM, whereas cholesterol/phospholipid and lipid/protein ratios were age-independent; (iii) PM polypeptide composition remained practically unchanged during aging. Age-related changes of the PM structure were accompanied by a twofold decrease of high affinity insulin binding sites and elevation of their affinity to insulin. It was suggested that age-related changes of physicochemical properties of PM lipid phase might affect protein molecular conformation and function through either changes in bulk lipid fluidity or through specific lipid-protein interactions.

Myocardial magnesium: relation to laboratory and clinical variables in patients undergoing cardiac surgery

Magnesium concentration was measured in the right atrial appendage of 100 patients undergoing cardiac surgery and associations with serum and mononuclear blood cell magnesium, other laboratory values and patient clinical variables were studied. In addition, magnesium was measured in the right atrial appendage and left ventricular free wall in 23 autopsy subjects to determine whether there was a proportional relation between right atrial appendage and left ventricular free wall magnesium. The mean left ventricular free wall/right atrial appendage magnesium ratio was 2.13 +/- 0.39 (r = 0.67, p = 0.0009). In the group with cardiac surgery, the right atrial appendage magnesium concentration correlated inversely with age (r = -0.54, p = 0.001). The mean right atrial appendage magnesium concentration (micrograms/g wet weight tissue) was lower in patients with postoperative cardiac arrhythmia than in those without arrhythmia (103 +/- 13 versus 111 +/- 10, p = 0.009) and in diabetic than in nondiabetic patients (103 +/- 13 versus 109 +/- 12, p = 0.02). The right atrial appendage magnesium concentration also tended to be lower in patients receiving potassium/magnesium-losing diuretics, although this difference did not achieve statistical significance (105 +/- 14 versus 109 +/- 11, p = 0.16). Right atrial appendage magnesium concentration correlated positively with serum creatinine concentration (r = 0.31, p = 0.002) and negatively with serum calcium concentration (r = -0.29, p = 0.013). Serum magnesium did not correlate with right atrial appendage or mononuclear blood cell magnesium concentration or clinical variables. There was a statistically significant correlation between mononuclear blood cell and right atrial appendage magnesium concentrations in some subgroups of patients.

Diet restriction, body temperature and physicochemical properties of cell membranes

This paper summarizes some recent results of the effect of diet restriction upon body temperature and membrane microviscosity of lymphocytes, hepatocytes and cerebellar cells of diet-restricted female Wistar rats. The treated animals were fed on an every-other-day schedule starting from the age of 3.5 months. It is suggested that a decrease in average body temperature (-1 degree C) of diet-restricted animals as compared to the ad libitum fed ones may stimulate the cells to synthesize more fluid membranes. Together with these the maintenance of the activity of protective enzymes is another key event which helps to prevent the age-dependent deterioration of cell membrane functions.

Effect of aging on the activity of the phosphate carrier and on the lipid composition in rat liver mitochondria

The effect of aging on the activity of the phosphate carrier and on the lipid composition in rat liver mitochondria has been investigated. It was found that the rate of phosphate transport in mitochondria from aged rats (28 months old) is significantly reduced (around 40%) compared to that obtained in mitochondria from young control rats (5 months old). Kinetic analysis of the phosphate transport indicates that only the Vmax of this process is affected, while there is no change in the Km values. The lower activity of the phosphate carrier in mitochondria from aged rats is also documented by swelling experiments. The age-related decrement in the activity of the phosphate carrier was found not to be due neither to a change in the endogenous content of phosphate nor to a change in the transmembrane delta pH value. Inhibitor titrations with mersalyl provide no evidence for a lower content of functional phosphate translocase in mitochondria from aged rats. There is no difference either in the respiratory control ratios or in the ADP/O ratios between mitochondria from young and aged animals. The hepatic mitochondrial lipid composition is altered significantly in aged rats: the total cholesterol increases (31%), the phospholipids decrease (12%), and the cholesterol/phospholipid molar ratio increases (44%). Among the phospholipids cardiolipin shows the greatest alteration (30% decrease with age). Alterations were also found in the pattern of fatty acids. The age-related decrement in the activity of the phosphate carrier appears to be dependent on changes in the lipid domain surrounding the carrier protein molecule in the mitochondrial membrane.

Cytochrome c oxidase deficient fibres in the limb muscle and diaphragm of man without muscular disease: an age-related alteration

Cytochrome c oxidase (complex IV of the respiratory chain) was studied histochemically in human limb muscle (n = 109) and diaphragm (n = 115) obtained at autopsy revealing randomly distributed muscle fibres without enzyme activity. The defects were present both in normal type I and type II fibres and in ragged red like fibres with increased content of mitochondria. In both organs an age associated manifestation of the defect was observed. First defects occurred sporadically in the 3rd and 4th decade, but were present from the 6th to 9th decade in 66-83% of the limb muscles and 75-100% of the diaphragms. Also the number of defects/cm2 (defect density) increased with age from approx. 5, and 7 in limb muscle and diaphragm below the 6th decade to 54 and 60 defects in the 8th-9th decade (P = 0.000). Between both muscles no statistically significant difference in defect density (P greater than 0.15) existed. Irrespective of the defect density the defect typically affected isolated fibres showing normal histochemical reactivity for succinate dehydrogenase (complex II). The results indicate that cytochrome c oxidase deficient muscle fibres in normal skeletal muscle represent an age related phenomenon which probably results from cellular ageing and might be involved in the reduction of muscle mass and strength during senescence.

Food restriction in female Wistar rats. III. Thermotropic transition of membrane lipid and 5'-nucleotidase activity in hepatocytes

The effect of diet restriction was measured on the anisotropy parameter of 1,6-diphenyl-1,3,5-hexatriene (DPH) and 5'-nucleotidase enzyme activity in liver plasma membrane preparates. Diet restriction was applied to rats 3.5 months old on an every-other-day schedule (EOD) and the rats were killed at the age of 28-29 months. Six months and 24 months rats, fed ad libitum (AL), were used as controls. The Arrhenius plots of anisotropy parameter of liver membranes from young, old AL and old EOD animals exhibited well defined breakpoints at 16.3 degrees C, 19.5 degrees C and 16.7 degrees C, respectively. The breakpoint temperature of 5'-nucleotidase activity was lower in samples from young rats as compared to those from old AL rats, whereas no difference was observed comparing young and EOD fed rats. Present results support the hypothesis that diet restriction modifies lipid composition of liver plasma membranes in such a way that the appearance of age-dependent alterations is delayed.

Cholesterol accumulation in plasma membrane and changes of membrane enzyme activity of Acholeplasma laidlawii cells during culture ageing

The data presented in this report show that the microviscosity of the plasma membrane and the cholesterol/phospholipid molar ratio of its lipid bilayer increases during ageing of Acholeplasma laidawii cultures. At the same time the age changes of other lipid components content do not correlate with the change of membrane viscosity. It is also shown that membrane enzyme activities of mycoplasma cell decrease with age. These results confirm the membrane hypothesis of ageing according to which increased microviscosity is the essential factor of cell ageing.

Lymphocyte Na,K-ATPase is reduced in aged people

Na,K-ATPase-dependent 86Rb uptake, maximum velocity (Vmax), Michaelis constant (Km) of the uptake, and [3H]-ouabain binding were investigated in the lymphocytes of 10 elderly subjects (age greater than 60 years), and in 10 middle-aged (41 to 60 years) and 10 young controls (age less than or equal to 40 years). 86Rb uptake was reduced in elderly versus both middle-aged and young subjects (20.14 +/- 3.30 v 35.60 +/- 2.67, P = .002, and v 36.53 +/- 4.49 nmol, P = .012), as was the number of [3H]-ouabain binding sites per cell (32,662 +/- 2,215 v 40,420 +/- 1,184, P = .011, and v 40,596 +/- 1,349, P = .014). Vmax was reduced in elderly v young subjects (1.20 +/- 0.10 v 1.64 +/- 0.13, P = .034), but not versus the middle-age group (1.20 +/- 0.10 v 1.54 +/- 0.12 nmol.min-1, NS). Km was no different among the three groups. No differences were found between middle-aged and young subjects. Significant correlations were observed between age and Na,K-ATPase-dependent 86Rb uptake (r = -.620, P = .00009), Vmax (r = -.439, P = .024), and [3H]-ouabain binding sites (r = -.648, P = .002). Moreover, the site number was positively correlated with both uptake (r = .635, P = .002) and Vmax (r = .554, P = .011). These differences were observed both in women and men. We conclude that there is an age-dependent reduction in lymphocyte Na,K-ATPase activity, which is fully manifested over 60 years, and that this alteration is probably due to the reduced number of functional units of Na,K-ATPase in advancing age.

A new method for testing cell ageing using two mitochondria specific fluorescent probes

Cell culture techniques have considerably improved our understanding of the numerous changes related to aging. For instance, murine lymphocytes obtained from animals older than 6 months progressively lose their, in vitro, proliferative capacity. Numerous studies have shown that this loss is due to changes in the mitochondrial compartment such as reduction in the transmembrane potential and/or membrane mass. Using two mitochondria specific probes with a potential-dependent (Rhodamine 123) or independent (Nonyl Acridine Orange) uptake, we found that the decline in the respiratory activity in the mouse occurred approximately 6 months prior to the decrease in mitochondrial membrane mass. The analysis of the Rh 123/NAO fluorescence ratio measured in splenocytes obtained from mice aged more than 6 months, showed that there was a linear loss of respiratory efficiency per unit of mitochondrial membrane mass. Moreover, cells with a ratio of less than 0.85 were incapable of proliferating and remained quiescent. The time separating the infection points of the two dye uptake curves might provide informations about the regulation and coordination of nuclear and/or mitochondrial genomes. Moreover, the ratio between the two fluorescent probes, in particular during the linear phase, may also have a predictive value.

Effects of preliminary culture on the membrane microviscosity of lymphocytes from young and old donors. Microviscosity correlates with mitogenic response

Membrane microviscosity was assessed by a fluorescence polarization technique in fresh and precultured human peripheral blood lymphocytes of young and old subjects. Membrane microviscosity was significantly higher in fresh, non-treated cells of old donors as compared to young adults. Preincubation of cells in culture medium supplemented with pooled human serum diminishes the original microviscosity difference between the age groups. The observed increase in membrane fluidity correlates with the improvement of the mitogen-induced proliferative response due to preculturing cells from aged subjects. The results support the suggestion that membrane microviscosity can affect the proliferative response of lymphocytes, and it may play a role in the decline of the immune responsiveness in the elderly.

Effect of gemfibrozil on erythrocyte membrane lipids in geriatric patients

Twenty geriatric patients with primary or secondary hyperlipidemia and suffering from various other diseases received for three weeks once daily 900 mg gemfibrozil. The hyperlipidemia had not been treated before, and a cholesterol-reduced diet did not succeed in lowering total cholesterol below 6.75 mmol/l (260 mg/100 ml) and serum triglycerides below 1.97 mmol/l (175 mg/100 ml). The purpose of this study was to analyze the lipid composition of the erythrocyte membrane, serum lipids and rheological parameters before and after the therapy. Mean serum total cholesterol and triglyceride content decreased significantly by 16.3% (p less than 0.05) and 35.2% (p less than 0.01) on average, respectively. Aggregation of thrombocytes and of erythrocytes, thrombin time and partial thromboplastin time slightly varied during the three weeks' treatment, but without statistical significance. The content of total long-chain saturated fatty acids in the phospholipid fraction of the erythrocyte membrane decreased slightly from 41.3% to 40.9% (p less than 0.05), whereas the total w6-unsaturated fatty acids without the precursor linoleic acid increased by about the same extent from 15.66% to 16.0% (p less than 0.05). The molar ratio of phospholipid to cholesterol content decreased significantly (p less than 0.01) due to a reduced phospholipid content at the end of the therapy. In conclusion, in addition to reducing the serum lipids, gemfibrozil slightly effects the lipid composition of erythrocytes, but the effects of the varied concentrations of long-chain saturated and long-chain w6-unsaturated fatty acids in the phospholipid fraction on membrane fluidity might be compensated, at least partly, by the decrease of the ratio of membrane phospholipid to cholesterol.

Decrease of cholesterol concentration in human erythrocyte ghosts in old age

The lipid composition of the erythrocyte membrane ghosts of 95 relatively healthy elderly subjects was compared between four age groups: 70 to below 75 years (I), 75 to below 80 (II), 80 to below 85 (III) and 85 to below 90 years of age (IV). The molar ratio of phospholipid to cholesterol (PL/CH) in the erythrocyte ghosts increased with advancing age. Whilst PL levels did not change significantly, a decrease of membrane cholesterol was found. Therefore, the red cell membrane cholesterol seems to parallel the well-known pattern of variation of mean plasma total cholesterol and LDL cholesterol concentrations with age: an increase to a maximum in the sixth decade of life, and a decline thereafter. The processes which are responsible for these changes in cholesterol level with age have not been delineated. However, the findings suggest that one might get different results in studies of age-dependent membrane lipid alterations if rough age group divisions are made (below 30 years of age vs. over 70 years) or to subdivide the group of the elderly.

Age and membrane fluidity

Male rats aged 1, 9 and 19 months were used to study changes in membrane fluidity with age, employing the fluorescence polarization technique with 1,6-diphenyl-1,3,5-hexatriene (DPH) as the fluorescent probe. The intestinal microvillus membranes derived from the 19-month-old rats were found to possess lower fluidity than that observed with the membranes derived from the younger animals. The decrease in fluidity with age was also reflected in a corresponding increase in the gel-to-liquid crystalline transition temperature. Only small insignificant changes with age, were observed in the fluidity of the red blood cell membrane.

An in vitro analogue of immune dysfunction with altered immunoglobulin production in the aged

The consequences of aging of the immune system include impaired T-lymphocyte responsiveness and aberrant immunoglobulin production. Although T cells from elderly individuals have a well-described defect in lymphoblastic transformation in response to some polyclonal mitogens, immunoglobulin abnormalities have lacked a clear in vitro model. Peripheral blood mononuclear cells from 13 young and 13 old healthy donors were cultured with phytohemagglutinin (PHA) or pokeweed mitogen (PWM). Old-donor-cell phytohemagglutinin (PHA), but not PWM, cultures had significantly lower lymphoblastic transformation compared with young donor cultures. IgG, IgA, and IgM production tended to be lower in old- versus young-donor PWM cell cultures. By contrast, despite lower lymphoblastic transformation in old-donor PHA cell cultures, immunoglobulin production was higher for old- versus young-donor cell cultures. No significant age differences were present in initial lymphocyte counts, percent B cells, T cells or monocytes, or helper/suppressor ratios to explain this enhancement in immunoglobulin production. PHA-stimulated mononuclear cell cultures in the aged demonstrate not only a defect in proliferation but also increased immunoglobulin production. This in vitro system may be useful to characterize further the pathogenesis of altered immunoglobulin production in the elderly.

Effect of chronic food restriction in aging rats. I. Liver subcellular membranes

To assess which membrane properties are modulated by the action of food restriction, characteristics of liver membrane structures of ad libitum-fed and food restricted Fischer 344 rats were analyzed over a wide age range. The results show that the yields of mitochondrial and microsomal membranes decreased in ad libitum-fed rats, but this age-related loss did not occur in food restricted rats until 30 months. Changes in membrane fatty acid composition which occurred with age were substantially modified by food restriction. Linoleic acid content progressively decreased in the membranes of ad libitum-fed rats with a concomitant increase of docosapentaenoic acid while an opposite pattern of change occurred in food restricted rats. Furthermore, food restriction maintained a low docosahexaenoic acid level in microsomes at all ages studied. While serum tocopherol increased markedly with age, there was little change in membrane tocopherol content in ad libitum-fed rats.

Choline levels are increased in cerebrospinal fluid of Alzheimer patients

We measured choline (Ch), acetylcholinesterase activity (AChE) and total protein in the cerebrospinal fluid (CSF) of 66 Alzheimer patients (ages 54-89 years) and 22 age-matched controls (ages 52-80 years), looking for markers of the well-established cholinergic deficit and neuronal degeneration in Alzheimer disease (AD). Three or more lumbar punctures were performed in 21 patients over a span of 24 months in order to study the changes in these CSF components with disease progression. We found a statistically significant reduction in AChE and an increase in Ch with advancing dementia. These changes were not related to patient age. We suggest that the rise in CSF choline is related to neuronal membrane breakdown and reduced Ch uptake by cholinergic neurons. The reduction in CSF AChE is consistent with the depletion of cholinergic neurons in AD.

Changes in some hepatic enzyme activities related to phase II drug metabolism in male and female rats as a function of age

Changes in activity of some hepatic enzymes related to UDP-glucuronic acid conjugation (UDP-glucose dehydrogenase and UDP-glucuronyl transferase) and glutathione-related enzymes (glutathione reductase and glutathione peroxidase) were investigated in male and female Wistar rats as a function of age. UDP-glucose dehydrogenase activity showed a decrease in the ageing period in both sexes (26.4% and 37.7% in males and females respectively), and no sex differences were found in all the ages studied. The UDP-glucuronyl transferase (using p-nitrophenol as substrate) showed an age-dependent decrease in its activity for males, but an increase for female rats. A sex difference (male values were higher than female values) was observed only in young rats (1 and 3 months old). Glutathione peroxidase activity increased with age in both sexes (the activity found in male and female old rats was about 162% and 149% respectively to those found in adulthood), and a marked difference was observed between sexes in young and old rats (57.8% and 45.4% higher in females in young and old rats respectively). In contrast, the glutathione reductase activity showed a decrease in the ageing (39% in male and 35.5% in female) and the highest levels during lifetime was found in males.

Influence of aging and drug treatment on the cerebral glutathione system

Age-related changes of the components of the glutathione system (reduced and oxidized glutathione) were evaluated in forebrains from male Wistar rats aged 5, 10, 15, 20, 25, 30 and 35 months. The trend of both forms of glutathione and the glutathione redox index markedly differs with age. Reduced glutathione increases during the first third of a rat's life and decreases thereafter. In contrast, oxidized glutathione remains relatively constant during the first half of the life-span and increases thereafter. Thus, the glutathione redox index steadily declines with age after an increase during the first third of the rat's life-span. In rats aged 10, 20 or 30 months, chronic IP treatment for two months with drugs known to modify cerebral circulation (papaverine) or the cerebral metabolism (ergot alkaloids dihydroergocristine, dihydroergocriptine) indicates that, according to the age, the cerebral glutathione system may be modified by metabolic changes rather than by circulatory events.

Decreased proliferation, interleukin 2 synthesis, and interleukin 2 receptor expression are accompanied by decreased mRNA expression in phytohemagglutinin-stimulated cells from elderly donors

Using cDNA probes to human interleukin 2 (IL2) and interleukin 2 receptor (IL2R), the amount of IL2 and IL2R mRNA produced by PHA stimulated peripheral blood mononuclear cells from young (less than 40 yr) and old (greater than 60 yr) donors was quantitated. Stimulated cell cultures from each individual were also examined for proliferative ability, expression of membrane IL2R, membrane IL2R density, and for the amount of IL2R shed into the culture supernatant. Induction of IL2 and IL2R mRNAs were decreased in cells from elderly individuals, as were the levels of IL2 secretion, the percentage of IL2R+ T cells and the density of membrane IL2R per cell. The results suggest that decreased expression of both IL2 and IL2R mRNA contributes to the low synthesis of IL2 and membrane IL2R, respectively, and is partially responsible for the diminished proliferative activity observed in lymphocytes from the elderly.

Modification of ATP-dependent Ca2+ transport in rat parotid basolateral membranes during aging

Previous experiments have shown that senescent rat parotid acinar cells display marked reductions in Ca2+ release following alpha 1-adrenoreceptor stimulation. We report here, that in this naturally occurring perturbation of exocrine secretion, ATP-dependent Ca2+ transport in the parotid basolateral plasma membrane, the principal Ca2+ extrusion pathway in the parotid, is also modified. ATP-dependent Ca2+ transport in membrane vesicles isolated from senescent rats (approx. 24 months) is decreased approximately 30-50% as compared to that in vesicles isolated from younger rats (approx. 4 months). This alteration in Ca2+ pump activity is not due to (i) non-specific effects of vesicle preparation in the two animal groups, (ii) increased leakiness to Ca2+, or (iii) any apparent alteration in permeability of the membrane to K+ and Cl-. Kinetic studies demonstrate that the ATP-dependent Ca2+ transport activity in vesicles from senescent rats has similar maximal velocity to that of vesicles from young adult rats (27 vs. 31 nmol Ca2+/mg protein per min), however, it exhibits an approximately 50% increase in Km for Ca2+ (91 nM vs. 60 nM). Cytosolic free Ca2+, measured by Quin 2 fluorescence, in parotid acini following alpha 1-adrenoreceptor stimulation was much less elevated in preparations from senescent rats. These results may account, at least in part, for the previously reported physiological alteration in Ca2+ efflux seen in senescent rat parotid cells.

Changes in superoxide radical and lipid peroxide formation in the brain, heart and liver during the lifetime of the rat

The free radical theory of aging was examined by measuring the formation of superoxide radical (SOR) and the level of lipid peroxides in various tissues of the aging rat. A significant increase in SOR production was seen in mitochondria prepared from the brain and the heart as rats aged. An elevation in the level of lipid peroxidation was also found in whole tissue homogenates of the brain and the liver. Vitamin E concentrations in the blood rose rapidly in young rats and remained steady except for a non significant drop in old animals. These results suggest that age-related degeneration of various tissues in the rat may be due to a rise in free radical production in the mitochondria.

A review of why and how we age: a defense of multifactorial aging

Part 1: Longevity is optimized such that reproduction is maximized. Williams (Evolution, 11 (1957) 398-411) proposed pleiotropic genes with beneficial effects during youth and harmful effects at older ages. Because of environmental death (e.g. predation, disease, accidents), even a small increase in younger reproduction could outweigh a large harmful effect at older ages. Guthrie (Perspect. Biol. Med., 12 (1969) 313-324) and Kirkwood (Nature, 270 (1977) 301-304; New Sci., 81 (1979) 1040-1042; Physiological Ecology: An Evolutionary Approach, Blackwell, Oxford, 1981, pp. 165-189; Hum. Genet., 60 (1982) 101-121; Proc. R. Soc. Lond., B205 (1979) 531-546; Handbook of the Biology of Aging, 2nd Edn., Von Nostrand Reinhold New York, 1985, pp. 27-44) proposed that additional longevity requires a further investment of resources when young, thereby reducing the resources available for reproduction when young. The gene(s) controlling this partitioning of resources between younger and older reproduction are a good example of Williams's pleiotropic genes. Population biology provides a great deal of evidence of a tradeoff between younger and older reproduction. A "marginal longevity theorem" is proposed which states that for a population in equilibrium with its environment a marginal change in any gene affecting longevity should cause equal and opposite marginal changes in younger and older expected reproduction. Senescence is not irrelevant in the wild; rather, the amount of senescence in the wild results from a balance between its marginal costs to older reproduction and its associated marginal benefits in younger reproduction. Part 2: The wide variety of damage prevention processes in the body are subject to the problem of diminishing returns. Consequently, a broad spectrum of damage occurs in the body, varying in frequency, harmfulness, and ease of repair. The types of damage which are prevented or repaired tend to be more frequent, harmful, and easily prevented or repaired. In contrast, aging damage (which accumulates) consists of a large number of different types of damage which (when considered separately) are relatively infrequent, less harmful, and/or more difficult to repair. Only when these types of damage accumulate to become very numerous do they (when considered collectively) become significant. Since the selective advantages associated with senescence apply to all parts of the body, primary aging damage occurs in all tissues, cells, and subcellular organelles. The distribution of metabolic resources among the various damage repair and prevention processes is optimized.(ABSTRACT TRUNCATED AT 400 WORDS)

Genotypic differences in central neurotransmitter responses to aging in mice

Dopamine, serotonin, cholinergic and somatostatin responses to aging have been followed in striatum and hippocampus of two inbred strains of mice (C57BL and BALB/c). A striking strain dependency is noted. Dopaminergic mechanisms in BALB/c mice become particularly defective in striatum where both dopamine release and dopamine turnover are affected. Also, striatal cholinergic activity and somatostatin levels are more disturbed in BALB/c than in C57BL mice. For cholinergic neurotransmission and somatostatin levels, similar results are noted in hippocampus. Conversely, C57BL mice react to aging by increased serotonin turnover in hippocampus and decreased 5HIAA levels in both structures studied, whereas the BALB/c strain remains unaffected. Also, structure dependency is observed: in C57BL mice serotonin turnover appears to be unchanged in striatum and increased in hippocampus; in the BALB/c the slowing down of dopamine activity in striatum is not observed in hippocampus. This unequal capacity of central neurotransmitters and neuromodulators to adapt to aging processes, depending upon the genotype, the nervous structure and the neurotransmitter considered may be involved in man in specific pathologies in aged individuals.

Glutathione and lipid peroxidation in the aging rat

1. Tissue extracts were prepared from liver, kidney, heart, brain, lung and spleen of male Sprague-Dawley rats of different ages (1-36 months); each of the extracts was analyzed for reduced glutathione (GSH) and lipid peroxides. 2. At all ages the GSH content in the liver was 3-10 times higher than that in other tissues. 3. In the old (36 months) rat the GSH content of all the tissues studied were lower (35-60%) than that in 2.5 month old rat. 4. The lipid peroxides levels increased by age in all tissues studied. 5. These findings indicate that general characteristics of aging tissue may include a decrease in GSH content and increase in lipid peroxides showing a decrease in reducing potential in senescence.

Effects of chronic administration of doxorubicin on myocardial beta-adrenergic receptors

The effects of multiple doses of doxorubicin (DXR) on myocardial beta-adrenergic receptor density and dissociation constant were investigated in male Sprague Dawley rats. The rats received DXR (2 mg/kg) or vehicle weekly by the SC route for 13 weeks. One group of DXR-treated rats plus corresponding controls were sacrificed at 14 weeks, one week after the last dose. Another group of DXR-treated rats plus corresponding controls were sacrificed at 19 weeks, six weeks after the last dose. The myocardial beta-adrenergic receptor was characterized by radio-ligand binding studies using [125I]iodocyanopindolol. Beta--receptor densities in DXR-treated rats of 7.0 and 7.4 fm/mg protein were unchanged from control levels of 7.2 fm/mg protein at both 14 and 19 weeks, respectively. Receptor dissociation constants in DXR-treated rats of 36.7 and 36.9 pM were increased over control levels of 24.6 and 30.0 pM at 14 and 19 weeks, respectively. However, the change in dissociation constant is only significant at 14 weeks. The increased dissociation constants suggest diminished agonist binding affinity of the myocardial beta-receptor. This impaired response of the receptor to catecholamines would tend to diminish the ability of myocardium to adequately respond to adrenergic stimuli.

Arrhenius plots of membrane-bound enzymes of mitochondria and microsomes in the brain cortex of developing and old rats

To study changes in lipid-protein-interaction and fluidity in mitochondrial and microsomal membranes of brain during development and aging, the Arrhenius plots of marker enzymes for mitochondrial inner and outer membranes as well as those of microsomal membranes were compared at different ages. The enzymes were, beta-hydroxybutyrate dehydrogenase (BDH) for the inner mitochondrial membrane and rotenone-insensitive-NADH-cytochrome c reductase (Mit-NADH-CytR) for the outer membrane; also antimycin-insensitive-NADH-cytochrome c reductase (Micr-NADH-CytR) and NADPH-cytochrome c reductase for the microsomal membranes. The ages studied were, 1, 5, 30, 60 days postnatal and 2 years. In the microsomes, the plots of NADH-cytochrome c reductase were found to be biphasic at all ages except in the newborn where no break temperature was observed. The activation energy of this enzyme in the physiological range of temperature was found to be high in the newborn, declining with brain maturation. The plot of this enzyme in the old rat showed no difference when compared with the mature. The specific activity of the enzyme, however, was markedly reduced in the old brain microsomal fraction. In contrast, comparison of the plots of microsomal NADPH-cytochrome c reductase at the various ages revealed no break temperature and very similar energies of activation. For the inner mitochondrial membrane beta-hydroxybutyrate dehydrogenase, the Arrhenius plots were generally biphasic at all ages studied with a break temperature of about 20 degrees C. However, the newborn plot was only barely biphasic showing a high energy of activation in the physiological range of temperature. In contrast, for the outer membrane NADH-cytochrome c reductase, the newborn plots were definitely biphasic, exhibiting low activation energy above the breaks. There was also a significant decline in the break temperature with brain development. No significant differences in the plots of this enzyme were found between the old and mature brain cortex. It is concluded that the enzymes of inner and outer mitochondrial membranes as well as the oxidative enzymes of microsomal membranes may show differential patterns of change in lipid-protein-interaction during development and aging, the changes being more marked in development than in aging.

NADPH-induced microsomal lipid peroxidation as measured by malondialdehyde production in rat liver. Inhibitory effect of naftidrofuryl

The effects of naftidrofuryl have been studied on NADPH-induced microsomal lipid peroxidation by measuring malondialdehyde (MDA) production. Conditions adequate to measure MDA production and effects of naftidrofuryl on MDA production have been tested. It has been shown that the addition of ferric ions is essential with Tris or Pipes buffers while it can be omitted with phosphate known to contain traces of ferric ions. However the initial rate of MDA production is much lower with phosphate in the absence of added ferric ions, showing that the initiation of lipid peroxidation is limited by ferric ions. The effects of naftidrofuryl have been studied on MDA production in phosphate buffer in the presence or absence of ferric ions. Naftidrofuryl inhibits lipid peroxidation in both conditions indicating that the inhibition is not related to an interaction with added ferric ions. Naftidrofuryl is efficient at concentrations slightly higher than butylhydroxytoluene but lower than aminopyrine.

Age-related changes in rat liver plasma membrane phospholipase A2 activity

The alterations of the lipid composition and fluidity of liver plasma membranes as well as the activity of membrane-bound phospholipase A2 (EC 3.1.1.4) in male and female rats of different ages are investigated. An age-induced increase of the protein/phospholipid and cholesterol/phospholipid ratios is observed, as well as a decrease in the unsaturation index of plasma membrane phosphatidylcholine. These changes induce an augmentation of the steady-state fluorescent anisotropy-rs and structural order parameter for 1,6-diphenyl-1,3,5-hexatriene-SDPH in plasma membranes. The membrane-bound phospholipase A2 activity is enhanced with aging, correlating well with the reduced membrane fluidity. The sex-determined alterations in all these parameters is also investigated.

Chronic ethanol consumption and aging: changes in lipid composition of liver microsomes

Both aging and chronic ethanol consumption have been found to produce changes in lipid composition. Severity of intoxication, withdrawal and release of gamma-aminobutyric acid following chronic ethanol consumption have been shown to be associated with age. It was predicted in this study that aged mice would differ in response to ethanol-induced changes in lipid composition of liver microsomes as compared to younger mice. Two different age groups of C57BL/6NNIA male mice (6 and 28 months) were administered an ethanol or control liquid diet for 24 days. Liver microsomes were prepared on Day 25. Age and ethanol consumption significantly affected liver weight and the ratio of liver weight to body weight. PC significantly decreased and PE significantly increased in both the young and old ethanol groups. Cholesterol and total phospholipid content were not affected by age or chronic ethanol consumption. Aged animals were able to adapt to the effects of chronic ethanol administration to the same extent as younger animals. These findings differ from studies that have examined effects of chronic ethanol consumption on behavior and neurotransmitter release among different age groups of mice. While the results are specific for liver microsomes, it appears that chronic ethanol consumption has less of an effect on liver function as compared to brain function in aged mice.

Macrophage phagocytosis and membrane fluidity in mice: the effect of age and dietary protein

Male C57BL/6NNia mice were used to investigate the effects of age and dietary protein intake on Fc and C3b receptor-mediated phagocytosis and on membrane fluidity. Six-month-old (adult) and 24-month-old (aged) mice were fed a 6% or 25% protein diet for 3, 5, or 6 weeks at which time thioglycollate elicited peritoneal macrophages were isolated. Both binding of IgG-coated sheep red blood cells to the macrophages and ingestion via the Fc-receptor were identical in all 4 groups after 3 and 6 weeks of feeding but were decreased at 5 weeks in the aged animals fed 6% protein. Phagocytosis via the C3b receptor was not depressed in either age group fed the low protein diet; it was, however, augmented significantly in the aged animals fed the 25% protein diet for 5 and 6 weeks. Membrane fluidity of the plasma membrane outer hemileaflet was monitored with an impermeant fluorescent probe. No changes were observed between adult and aged mice maintained up to 6 weeks on the diets.

Changes in oxygen-metabolizing enzymes and lipid peroxidation in human erythrocytes as a function of age of donor

We have studied the activities of enzymes, which afford protection against superoxide radical anion and hydrogen peroxide and estimated the content of malondialdehyde. Superoxide dismutase activity decreased slightly with advanced age of donors. The activities of catalase and peroxidases were higher in the erythrocytes of the middle age group and the old age group than in the young individuals. Thiobarbituric acid-reactive product was also significantly elevated in the aged donors. These results support the hypothesis that observed differences in the activities of enzymes and the level of malondialdehyde may contribute to the changes associated with aging, produced by the free radical reactions.