Age dependency of base modification in rabbit liver DNA

Methods for the discovery of new anti-aging products--targeted approaches

INTRODUCTION

Aging is considered to be one of the most complicated and heterogeneous phenomena and is the main risk factor for most chronic diseases, disabilities and declining health. Aging cells cease to divide and drive the progression of illness through various pathways. Over the years, a number of anti-aging medicines of natural and synthetic origin have been introduced. Indeed, some studies have identified senescent cells as potential therapeutic targets in the treatment of aging and age-related diseases.

AREAS COVERED

In this review, the authors highlight and critically review the possible mechanisms of the aging process and related illnesses. The authors give particular attention to illnesses, including Alzheimer's disease, Parkinson's disease, skin aging and cardiovascular diseases.

EXPERT OPINION

Several reports have highlighted that mitochondria are a key factor in the progression of aging and neurodegenerative illnesses. This is due to their production of extra amounts of reactive oxygen species, which leads into progressive caspase-dependent apoptosis and cell death. Therefore, strategies to prevent/reduce oxidative stress-mediated aging, whether environmental, nutritional and pharmacological, need to be taken into account. Presently, Drosophila melanogaster and Caenorhabditis elegans, which focus on the evolutionary and genetic foundations of aging, have helped to establish the screening of several synthetic and natural compounds with large cohorts in a quick manner. However, there is yet to be any efficient experimental evidence to prove the exact role of senescent cells in age-related dysfunction and further studies are required to better understand these processes.

The role of DNA damage and repair in aging through the prism of Koch-like criteria

Since the first publication on Somatic Mutation Theory of Aging (Szilárd, 1959), a great volume of knowledge in the field has been accumulated. Here we attempted to organize the evidence "for" and "against" the hypothesized causal role of DNA damage and mutation accumulation in aging in light of four Koch-like criteria. They are based on the assumption that some quantitative relationship between the levels of DNA damage/mutations and aging rate should exist, so that (i) the longer-lived individuals or species would have a lower rate of damage than the shorter-lived, and (ii) the interventions that modulate the level of DNA damage and repair capacity should also modulate the rate of aging and longevity and vice versa. The analysis of how the existing data meets the proposed criteria showed that many gaps should still be filled in order to reach a clear-cut conclusion. As a perspective, it seems that the main emphasis in future studies should be put on the role of DNA damage in stem cell aging.

Age-dependent accumulation of advanced glycosylation end products in human neurons

Glucose can react nonenzymatically with free amino groups on proteins and form advanced glycosylation end-products (AGEPs), that have been previously isolated and characterised in aging human connective tissues. In this study, we used immunocytochemistry to examine the distribution of AGEPs in the aging human brain. Our findings show that the pyramidal neurons selectively accumulate AGEP-containing vesicles in an age-dependent manner. In addition, our results demonstrate that AGEPs accumulate in the same type of neuron that degenerates in Alzheimer's disease.

Chromatographic separation of glycated nucleotides

A high-performance liquid chromatographic method for the separation of nucleotide glycation reaction product(s) has been developed. The product(s) arising during in vitro glycation of a nucleotide (AMP, GMP or CMP) with a reducing sugar (ribose or glucose) were clearly resolved from the non-glycated constituents of the reaction mixture. The peak(s) of the glycated product(s) increased when an amino acid (lysine, arginine, beta-alanine or N epsilon-acetyllysine) was added to the reaction mixture. This increase probably corresponds to the formation of a new product with a different absorption maximum (250 versus 260 nm). Conversely, formation of this product(s) was inhibited by the presence of the metal-chelating agent diethylenetriamine pentaacetic acid and by aminoguanidine.

Oxidative and other DNA damages as the basis of aging: a review

DNA damages occur continuously in cells of living organisms. While most of these damages are repaired, some accumulate. In particular, there is evidence for DNA damage accumulation in non-dividing cells of mammals. These accumulated DNA damages probably interfere with RNA transcription. We consider that the decline in the ability of DNA to serve as a template for gene expression is the primary cause of aging. Oxidative DNA damages are among the best documented and prevalent DNA damages and are likely to be a prominent cause of aging.

DNA damage metabolism and aging

As a result of permanent exposure to low levels of various endogenous and exogenous genotoxic agents, large numbers of lesions are continuously induced in the DNA of cells of living organisms. Such lesions could lead to dysfunction of cells and tissues, and they might well be the underlying cause of the age-related reduction of homeostatic capacity and the increased incidence of cancer and other diseases of old age. The rate of damage induction as well as the persistence of the lesions depends on the activity, efficiency and reliability of a wide variety of molecular defense systems. However, a certain degree of imperfection seems to be a general characteristic of most of these defense systems and this could lead to a gradual accumulation of DNA alterations during aging. Even when the original lesions are quickly removed, they can still lead to secondary changes in the DNA, such as DNA-sequence changes and changes in gene expression. This process would be accelerated in case of the occurrence of an age-related decline in the efficiency of these molecular defense systems. This review deals with the present knowledge on the occurrence of 'spontaneous' DNA damage in aging organisms, its potential sources, the influence of preventive and processive cellular defense mechanisms and its consequences in terms of DNA-sequence changes, DNA conformational and configurational changes and changes in gene expression. In general, it can be concluded from the data discussed here that, in spite of a number of discrepancies and conflicting results, an age-related accumulation of DNA alterations occurs at all levels, e.g., chemical structure, DNA-sequence organization and gene expression.

Organization of DNA in cerebellar neurons of ageing unirradiated and irradiated rats

Male Fischer 344 rats were either unirradiated or whole-brain irradiated with single doses of 10.83 or 17.16 Gy of X-rays at 4 months of age, and the organization of the DNA in permanently non-dividing cerebellar neurons examined as a function of age, dose and time after irradiation. In unirradiated rats and rats receiving a whole-brain dose of 10.83 Gy, there were no statistically significant changes in the organization of the bulk DNA and its association with the nuclear matrix as determined by: (a) the sensitivity of the DNA to digestion by micrococcal nuclease, (b) the sensitivity of the nuclear matrix-associated DNA to digestion by DNase I, (c) the relative DNA and protein content of undigested neuronal nuclei, and (d) the relative amount of DNA and protein that is tightly associated with the nuclear matrix after digestion with DNase I. In rats that were irradiated with 17.16 Gy at 4 months of age, there was a gradual decrease in the amount of nuclear proteins as a function of age (P less than 0.003). The amount of protein associated with the nuclear matrix in these irradiated aging rats was also consistently lower than that of their unirradiated counterparts (P less than 0.03). This decrease in the nuclear protein content of the cerebellar neurons in aging rats irradiated with 17.16 Gy may have caused a change in the overall organization of their neuronal DNA. Such a change in the organization of their neuronal DNA was indicated by a higher stainability of their bulk DNA by propidium iodide (P less than 0.03) and a higher sensitivity of the bulk DNA to digestion by m. nuclease (P = 0.087). Although these organizational changes in the neuronal DNA of aging rats irradiated with 17.16 Gy at 4 months of age are subtle, they might alter DNA repair processes or other neuronal functions that may be associated with the "natural" process of aging.