Jaime Miquel

Mitochondrial role in cell aging

The experimental studies on the mitochondria of insect and mammalian cells are examined with a view to an analysis of intrinsic mitochondrial senescence, and its relation to the age-related changes in other cell organelles. The fine structural and biochemical data support the concept that the mitochondria of fixed postmitotic cells may be the site of intrinsic aging because of the attack by free radicals and lipid peroxides originating in the organelles as a by-product of oxygen reduction during respiration. Although the cells have numerous mechanisms for counteracting lipid peroxidation injury, there is a slippage in the antioxidant protection. Intrinsic mitochondrial aging could thus be considered as a specific manifestation of oxygen toxicity. It is proposed that free radical injury renders an increasing number of the mitochondria unable to divide, probably because of damage to the lipids of the inner membrane and to mitochondrial DNA.

Effects of temperature on the life span, vitality and fine structure of Drosophila melanogaster

The effects of temperature on the aging process have been investigated in approximately 3500 imagoes of male Drosophila melanogaster (Oregon R), with focus on the following parameters: mortality, O2 utilization, vitality (as expressed by negative geotaxis and mating) and fine structural alterations in the abdominal organs and brain. The data on mortality kinetics of flies maintained continuously at 18 degrees, 21 degrees, 27 degrees or 30 degrees C or exposed in succession to 21 degrees and 27 degrees C or vice versa support the concept that life span is temperature dependent. Moreover, these data, together with the increased O2 utilization and accelerated loss of vitality at 21 degrees C as compared with 18 degrees C, suggest that, in agreement with the rate-of-living theory proposed by Alpatov and Pearl in 1929, the flies are living faster at the higher temperature. Fine structural aging changes, like ribosomal loss in the Malpighian tubules and lipofuscin-ceroid accumulation in the midgut cells, seem to be more intense at 27 degrees and at 29 degrees C than at 21 degrees C. Also, the low vitality exhibited through their lives by flies kept at previous exposure through many generations) to 21 degrees C. Flies maintained at 29 degrees C showed a striking degeneration of the brain with an almost complete loss of the cytoplasmic organelles of the nerve cells. This electron microscopic finding lends support to the view that nervous tissue injury (perhaps induced by thermal denaturation of membrane lipoproteins) may play a crucial role in life shortening induced by relatively high temperatures.

The curcuma antioxidants: pharmacological effects and prospects for future clinical use. A review

In agreement with the predictions of the oxygen-stress theory of aging and age-related degenerative diseases, diet supplementation with a number of phenolic or thiolic antioxidants has been able to increase the life span of laboratory animals, protect against senescent immune decline and preserve the respiratory function of aged mitochondria. In addition to the above, more recent data reviewed here suggest that the polyphenolic compound curcumin and related non-toxic antioxidants from the rhizome of the spice plant Curcuma longa have a favorable effect on experimental mouse tumorigenesis as well as on inflammatory processes such as psoriasis and ethanol-caused hepatic injury. Our own research has focused on the effects of diet supplementation with an antioxidant-rich hydroalcoholic extract of the curcuma rhizome on key risk factors of atherogenesis and related cardiovascular disease. Our reviewed data show that, in human healthy subjects, the daily intake of 200 mg of the above extract results in a decrease in total blood lipid peroxides as well as in HDL and LDL-lipid peroxidation. This anti-atherogenic effect was accompanied by a curcuma antioxidant-induced normalization of the plasma levels of fibrinogen and of the apo B/apo A ratio, that may also decrease the cardiovascular risk. The reviewed literature indicates that curcumin and related plant co-antioxidants are powerful anti-inflammatory agents. Further, since they potentiate the anti-atherogenic effect of alpha-tocopherol, more extensive clinical testing of their probable usefulness in cardiovascular risk reduction seems justified.

Is Cell Aging Caused by Respiration-Dependent Injury to the Mitochondrial Genome?

Though intrinsic mitochondrial aging has been considered before as a possible cause of cellular senescence, the mechanisms of such mitochondrial aging have remained obscure. In this article we expand on our hypothesis of free-radical-induced inhibition of mitochondrial replenishment in fixed postmitotic cells. We maintain that the respiration-dependent production of superoxide and hydroxyl radicals may not be fully counteracted, leading to a continuous production of lipoperoxides and malonaldehyde in actively respiring mitochondria. These compounds, in turn, can easily react with the mitochondrial DNA which is in close spatial relationship with the inner mitochondrial membrane, producing an injury that the mitochondria may be unable to counteract because of their apparent lack of adequate repair mechanisms. Mitochondrial division may thus be inhibited leading to age-related reduction of mitochondrial numbers, a deficit in energy production with a concomitant decrease in protein synthesis, deterioration of physiological performance, and therefore, of organismic performance.

An integrated theory of aging as the result of mitochondrial-DNA mutation in differentiated cells☆

We maintain that aging of humans and animals derives from a mutation or inactivation (probably followed by endonuclease digestion) of the mitochondrial genome of differentiated cells. This extranuclear somatic mutation hypothesis of aging is based on the finding that mitochondrial DNA (mtDNA) synthesis takes place at the inner mitochondrial membrane near the sites of formation of highly reactive oxygen species and their products, such as lipoperoxides and malonaldehyde. The mtDNA may be unable to counteract the damage inflicted by those by-products of respiration because, in contrast to the nuclear genome, it lacks histone protection and scission repair. Since the mitochondrial genome controls the synthesis of several hydrophobic proteins of the inner mitochondrial membrane, the postulated mutation, inactivation or loss of mtDNA will prevent the replication of the organelles. Thus deprived of the ability to regenerate their mitochondrial populations, the cells will sustain an irreversible decline in their bioenergetic ability, with concomitant senescent loss of physiological performance and eventual death. The above hypothesis is integrated with the concepts of Minot, Pearl and others in order to offer a more comprehensive view of aging.

An update of the oxidation-inflammation theory of aging: the involvement of the immune system in oxi-inflamm-aging.

The aging process is one of the best examples of the effects of a deterioration of homeostasis, since aging is accompanied by an impairment of the physiological systems including the homeostatic systems such as the immune system. We propose an integrative theory of aging providing answers to the how (oxidation), where first (mitochondria of differentiated cells) and why (pleiotropic genes) this process occurs. In agreement with this oxidation-mitochondrial theory of aging, we have observed that the age-related changes of immune functions have as their basis an oxidative and inflammatory stress situation, which has among its intracellular mechanisms the activation of NFkappaB in immune cells. Moreover, we have also observed that several functions of immune cells are good markers of biological age and predictors of longevity. Based on the above we have proposed the theory of oxidation-inflammation as the main cause of aging. Accordingly, the chronic oxidative stress that appears with age affects all cells and especially those of the regulatory systems, such as the nervous, endocrine and immune systems and the communication between them. This fact prevents an adequate homeostasis and, therefore, the preservation of health. We have also proposed a key involvement of the immune system in the aging process of the organism, concretely in the rate of aging, since there is a relation between the redox state and functional capacity of the immune cells and the longevity of individuals. Moreover, the role of the immune system in senescence could be of universal application. A confirmation of the central role of the immune system in oxi-inflamm-aging is that the administration of adequate amounts of antioxidants in the diet, improves the immune functions, decreasing their oxidative stress, and consequently increases the longevity of the subjects.

Effects of Alpha Particle Radiation on the Rat Brain, Including Vascular Permeability and Glycogen Studies

Dorsal pants of rat cerebrum and cerebellum were exposed to alpha radiation (12 Mev per nucleon) from a 60-in. cyclotron at a brain surface dose of 6000 rad (a Bragg-peak dose of 30000 rad). The animals were sacrificed at time intervals from 5 min to 5 months and the brains were subjected to various techniques, including fluorescein-labeled serum protein (FLSP), sodium fluorescein (NaFl), and other procedures for assessment of vascuiar permeability. Histochemical methods were employed for evaluation of changes in brain tissue components, especially for demonstration of glycogen. The results suggest that alphaparticle energy exerts an injurious effect on cellular elements primarily according to its physical properties and distribution in the tissue and that the vascular permeability disturbances play a secondary role. Also from the appearance of glycogen in glial cells, the possibility is suggested that disruption of protein-bound tissue glycogen due to radiation injury may lead to its liberation and subsequent uptake by the glial cells, presumably by pinocytosis. (P.C.H.)

A two-step hypothesis on the mechanisms of in vitro cell aging: cell differentiation followed by intrinsic mitochondrial mutagenesis.

Despite vigorous research, there is yet no agreement on the biochemical mechanisms responsible for the loss of replicative potential of diploid cultured cells. In contrast to the program theories of in vitro cell aging, we propose that, as already suggested by Minot in 1907, senescence is the result of cell differentiation. We further maintain that the fundamental cause of cell aging is an instability of the mitochondrial genome because of a lack of balance between mitochondrial repair and the disorganizing effects of oxygen radicals which arise in the respiring mitochondria of terminally differentiated cells. This probably results in intrinsic mitochondrial mutagenesis which may be followed by endonuclease degradation of the altered mitochondrial DNA. Since the mitochondrial genome controls the synthesis of several hydrophobic proteins of the inner mitochondrial membrane, the postulated denaturation or loss of mtDNA will prevent the replication of the organelles. Thus, deprived of the ability to regenerate their mitochondrial populations, the cells will sustain an irreversible decline in their ability to synthesize ATP, with concomitant senescent degradation of physiological performance and eventual death.

Favorable effects of the antioxidants sodium and magnesium thiazolidine carboxylate on the vitality and life span of Drosophila and mice

Abstract We have investigated the effects of two antioxidants, sodium and magnesium L-thiazolidine-4-carboxylate (NaTC, MgTC), on vitality and life span of female mice and male Drosophila melanogaster (fruit flies). NaTC or MgTC was added to the food medium of populations of flies (about 170 flies each) at a 0·2% concentration from the 26th day of their adult life, whereas MgTC was given to 39 mice at the concentration of 0·07% in their standard chow, starting at the age of 23 months. The antioxidant treatment resulted in mean life span increases of 8 and 14% in flies treated with NaTC and MgTC, respectively. Apparently, the maximum life span was similarly increased as reflected in the ages of the longest lived individuals, although much larger populations should be studied for statistical evaluation. It seems that mouse aging was also influenced by antioxidant treatment, although to a lesser degree than Drosophila aging. This is suggested by our observation that mice given MgTC had a median life span about 7% longer than the control animals. Vitality of middle aged flies (assessed by measuring their mating capacity) receiving MgTC was increased considerably in comparison with the controls. The mean body weights of groups of treated flies and mice were not different from those of the controls and the food intake was about the same for control and treated mice. Therefore, the favorable effects of the antioxidants MgTC and NaTC on mortality kinetics of flies and mice and on the vitality of flies cannot be explained as the outcome of caloric restriction. In our opinion, the favorable results which are consistently associated with the use of NaTC, MgTC or other sulphur-containing substances are related to their free radical scavenger action. In accordance with this concept, the above substances may be effective in reducing the rate of the aging process.

Fine structural changes in the lateral vestibular nucleus of aging rats

Abstract The fine structure of the lateral vestibular nucleus was investigated in Sprague-Dawley rats, that were sacrificed at 4 weeks, 6–8 weeks, 6–8 months, and 18–20 months of age. In the neuronal perikaria, the following age-associated changes were seen with increasing frequency with advancing age: rodlike nuclear inclusions and nuclear membrane invaginations; cytoplasmic dense bodies with the characteristics of lipofuscin; and moderate disorganization of the granular endoplasmic reticulum. Dense bodies were also seen in glial cells. Rats 18 to 20 months old showed dendritic swellings, axonal degeneration, and an apparent increase in the number of axosomatic synaptic terminals containing flattened vesicles (presumed to be inhibitory in function). In our opinion, the lateral vestibular nucleus of the rat is an excellent model to define aging changes in the nerve cells, as opposed to changes linked to vascular degeneration, which is frequently seen in time-associated degeneration of the human brain.