G2 repair and aging: influence of donor age on chromosomal aberrations in human lymphocytes

Evaluation of the relationship of the molecular aggregation state of amphotericin B in medium to its genotoxic potential

This work analyzes the genotoxicity potential, in the G2 phase of the cellular cycle, of an amphotericin B (AmB) commercially available form (Fungizone), and correlates it with the physicochemical properties of this product in aqueous media. The genotoxic studies were performed using peripheral blood lymphocytes from human donors. The chromosome aberrations and mitotic index were determined. Absorption spectra of Fungizone were obtained by dispersion of the stock solution in water for injection at various AmB concentrations, and using different cuvette path lengths for spectrophotometric determination. The absorption spectra of Fungizone in water are concentration dependent. High concentrations of Fungizone present a spectrum with an intense band at 340 nm, characteristic of AmB self-association. Conversely, at low concentrations, the spectra are similar to those obtained with AmB in methanol, with a positive band at 409 nm, assigned to AmB monomeric form. Similarly, the cytogenetic analysis shows an important decrease on the mitotic index, which is also concentration dependent when compared with control. Furthermore, the chromosome aberrations present a small, not statistically significant, increase only at the highest concentration. The results suggest that the Fungizone presents a cytotoxicity similar to membrane pore formation in mammalian cells that depends on the existence of self-associated AmB. In the presence of only monomeric forms, this phenomenon disappears. However, no genotoxicity was observed in this study.

Biological age--what is it and can it be measured?

Biological age is a concept used loosely and with little objectivity to describe a shortfall between a population cohort average life expectancy and the perceived life expectancy of an individual of the same age. Many biomarkers decline roughly linearly with age with a slope of <1% per annum. The use of a battery of 16 biomarkers is described as a method of calculating an individual biological age. They include: the concentration of prostacyclin in fibroblasts, cell membrane viscosity, the electroretinogram, baroreflex regulation of the heart rate, the concentration of lymphocytes, leucocyte density and velocity, grip strength, cells of the corneal endothelium and the buccal epithelium, neck muscle mobility, and vital capacity. Although not subjected to a prospective validation, the method might provide an objective approach to this widely used concept.

Study of chromosome damage in patients with breast cancer treated by two antineoplastic treatments

The frequencies of chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) were determined in peripheral blood lymphocyte cultures from women with breast cancer treated by chemotherapy (CT) with FEC (5-fluorouracil, epirubicin, and cyclophosphamide) or CMF (cyclophosphamide, methotrexate, and 5-fluorouracil) cocktail in six CT cycles. The number of patients in each CT cycle were from 1 to 3 for SCE and 2 to 5 for CA. Samples were collected before and 48 h after CT. Although the size of the sample was limited and interindividual variability was wide, it appears that a 21-day interval between CT sessions is sufficient for cell recovery. This fact was demonstrated by the reduction in CA and SCE frequencies between cycles in parallel with the unchanged mitotic index and proliferative index values.

Genotoxic action of the sesquiterpene lactone centratherin on mammalian cells in vitro and in vivo

Centratherin is a sesquiterpene lactone known for its antimicrobial, anti-inflammatory, and trypanocidal activities. The aim of this study was to determine the clastogenic and cytotoxic potential of centratherin in human lymphocytes and in mice. Human lymphocytes in culture were submitted to either continuous treatment or treatment during G(2) phase of the cell cycle. After continuous treatment the 0.2 microg/ml concentration induced a significant increase in total of chromosomal aberrations (CA) and sister chromatid exchange compared to control, and it reduced the mitotic index (MI). In the treatment during G(2) phase, centratherin induced a significant increase in the frequency of CA for all concentrations tested (0.1, 0.3, and 0.5 microg/ml). In the in vivo test system all three concentrations tested in mice (3.3, 6.7, and 13.3 mg/kg b.w.) induced a significant increase in CA compared to the negative control. On the basis of these results, centratherin showed clastogenic and cytotoxic activity on in vitro and in vivo mammalian systems.

Health span and life span in transgenic mice with modulated DNA repair

One way to better understand the contribution of DNA repair, DNA damage, and mutagenesis in aging would be to enhance DNA repair activity, lower DNA damage, and lower mutagenesis. Because the repair protein O6-methylguanine-DNA methyltransferase (MGMT) acts alone and stoichiometrically, the human MGMT (hMGMT) cDNA was selected to test the feasibility of enhancing DNA repair activity in transgenic mice. MGMT activity is largely responsible for ameliorating the deleterious effects of O6-methylguanine (O6mG) lesions in DNA in a direct reversal mechanism. A transgene was constructed consisting of a portion of the human transferrin (TF) promoter and hMGMT cDNA such that hMGMT is expressed in transgenic mouse brain and liver. Expression of hMGMT was associated with a significant reduction in the occurrence of an age-related hepatocellular carcinoma in male mice at 15 months of age. Longitudinal and cross-sectional studies were initiated to determine whether the reduced incidence of hepatocellular carcinoma would impact median or maximum life span. The cross-sectional study performed on 15-month-old male animals confirmed the reduced occurrence of spontaneous hepatocellular carcinoma. At 30 months of age, however, the occurrence of hepatocellular carcinoma in at least one transgenic line was similar to that for nontransgenic animals. The longitudinal study is ongoing; however, at present no significant differences in life span have been detected. Tissues expressing the MGMT transgene also displayed greater resistance to alkylation-induced tumor formation. These results suggest that transgenes can be used to direct enhanced DNA repair gene expression and that enhanced expression can protect animals from certain spontaneous and induced tumors.

Fanconi anemia lymphocytes: effect of DL-alpha-tocopherol (Vitamin E) on chromatid breaks and on G2 repair efficiency

The high frequency of chromosomal breaks in Fanconi anemia (FA) lymphocytes has been related to the increased oxidative damage shown by these cells. The effect of 100 microM DL-alpha-tocopherol (Vitamin E) on the level of chromosomal damage in mitosis was studied in lymphocytes from five FA patients and from age matched controls, both under basal conditions and when G2 repair was prevented by 2.5 mM caffeine (G2 unrepaired damage). In addition, the effect of this antioxidant on G2 duration and the efficiency of G2 repair was also evaluated in the sample. alpha-Tocopherol (AT) decreased the frequency of chromosomal damage (under basal and inhibited G2 repair conditions) and the duration of G2 in FA cells. This antioxidant protective effect, expressed as the decrease in chromatid breaks, was greater in FA cells (50.8%) than in controls (25%). The efficiency of the G2 repair process (G2 R rate) defined as the ratio between the percentage of chromatid breaks repaired in G2 and the duration of this cell cycle phase was lesser in FA cells (10.6) than in controls (22.6). AT treatment slightly increased this G2 R rate, both in FA cells and controls. These results suggest that an increased oxidative damage and a lower G2 repair rate may be simultaneously involved in the high frequency of chromatid damage detected in FA cells.

Lifetime persistence and clonality of chromosome aberrations in the peripheral blood of mice acutely exposed to ionizing radiation

As the measurement of chromosomal translocations increases in popularity for quantifying prior radiation exposure, information on the possible decline of these "stable" aberrations over time is urgently needed. We report here information about the persistence of radiation-induced chromosome aberrations in vivo over the life span of a rodent. Female C57BL/6 mice were given a single whole-body acute exposure of 0, 1, 2, 3 or 4 Gy (137)Cs gamma rays at 8 weeks of age. Chromosome aberrations were analyzed from peripheral blood samples at various intervals between 1 day and 21 months after exposure. Aberrations were detected by painting chromosomes 2 and 8. Translocations decreased dramatically during the first 3 months after irradiation, beyond which time the frequencies remained relatively constant out to 1 year, when the effects of aging and clonal expansion became significant. Both reciprocal and nonreciprocal translocations increased with age in the unexposed control animals and were involved in clones. As expected of unstable aberrations, dicentrics decreased rapidly after exposure and reached baseline levels within 3 months. These results indicate that the persistence of translocations induced by ionizing radiation is complicated by aging and clonal expansion and that these factors must be considered when quantifying translocations at long times after exposure. These results have implications for biological dosimetry in human populations.

Evaluation of the genotoxic potential of the isocoumarin paepalantine in in vivo and in vitro mammalian systems

Paepalantine is an isocoumarin isolated from Paepalanthus vellozioides which showed antimicrobial activity in in vitro experiments. In the present study, paepalantine was tested for possible clastogenic and cytotoxic action. Cultures from different individuals were treated with paepalantine at concentrations of 20, 40 and 80 microg/ml. The effect of isocoumarin was also tested in an in vivo assay using Wistar rat bone marrow cells. Paepalantine was administered intraperitoneally at concentrations of 6.25, 12.5 and 25 mg/kg body weight. Under these conditions paepalantine did not have a clastogenic effect, but was significantly cytotoxic in the in vitro and in vivo mammalian cell systems tested in the present work.

The influence of smoking on the risk of Alzheimer's disease

OBJECTIVE

To investigate the relationship between cigarette smoking and Alzheimer's disease (AD) in a prospective community-based study in northern Manhattan.

BACKGROUND

Results from previous case-control studies suggest that there is a protective effect of smoking on AD. However, the recent prospective Rotterdam Study found that there was an increased risk of AD for smokers, particularly those without an apolipoprotein E (APOE)-epsilon4 allele.

METHODS

The authors examined data from a community-based longitudinal study of local elders residing in northern Manhattan to determine whether tobacco use increases or decreases the risk of AD. Information regarding the frequency of tobacco use was obtained in structured interviews at the baseline assessment. Standardized clinical assessments were subsequently completed on each subject at annual visits during which incident cases of AD were identified.

RESULTS

The relative risk (RR) of AD among former smokers was 0.7 (95% CI, 0.5 to 1.1). The RR among current smokers was 1.9 (95% CI, 1.2 to 3.0). Smokers without an APOE-epsilon 4 allele had the highest risk of AD (RR = 2.1; 95% CI, 2.1 to 3.7) compared with those with an APOE-epsilon 4 allele (RR = 1.4; 95% CI, 0.6 to 3.3).

CONCLUSIONS

Our results are consistent with the observation that smoking increases the risk of AD. However, we found that among previous smokers who quit smoking, there may be a slight reduction in the risk of AD.

Age-associated decreases in human DNA repair capacity: Implications for the skin

Multiple pathways are involved in accurate synthesis and distribution of DNA during replication, repair and maintenance of genomic integrity. An increased error rate, abovethe spontaneous mutation baseline, has been implicated in carcinogenesis and aging. Moreover, cytogenetic abnormalities are increased in Down's, Edwards', Patau's, and Klinefelter's syndromes with increasing maternal age, and in Marfan's and Apert's syndromes with paternal age. In response to DNA damage, multiple overlapping systems of DNA repair have evolved, preferentially repairing the transcribed strand within transcriptionally-active regions of the genome. These include direct reversal of dimers and specific adducts and pathways for base excision, nucleotide excision, and mismatch repair. A consensus has emerged that some DNA repair capacities decline with organism age, contradictory reports notwithstanding. As is the case for inborn defects in humans, knockout mice lacking components of nucleotide excision repair or DNA-damage checkpoint arrest have increased frequencies of skin and internal cancers, whereas mice overexpressing DNA repair genes have fewer spontaneous cancers. Oxidative stress and resultant free radicals can damage genomic and mitochondrial DNA; damage increases with age but decreases with caloric restriction. We review recent studies of long-lived C. elegans mutants which appear to involve metabolic attenuation, the role of telomere shortening and telomerase in cellular senescence, and the genetic bases of progeroid syndromes in humans. Finally, we discuss roles of extrinsic and intrinsic factors in skin aging, and their association with DNA damage, emphasizing preventive and protective measures and prospects for intervention by modulating DNA repair pathways in the skin.

Effect of vitamin E on chromosomal aberrations in lymphocytes from patients with Down's syndrome

A possible protective effect of vitamin E (DL-alpha-tocopherol) on chromosomal damage was evaluated in lymphocytes from patients with Down's syndrome (DS) and from controls. This included the analysis of the basal and G2 chromosomal aberration frequencies in lymphocytes cultured with and without 100 microM vitamin E. The chromosomal damage in G2 was determined by scoring the number of chromosomal aberrations in lymphocyte cultures treated with 5 mM caffeine, 2 h before harvesting. Vitamin E treatment decreased the basal and G2 chromosomal aberrations both in control and DS lymphocytes. In DS cells, this protective effect, expressed as a decrease in the chromosomal damage, was greater (50%) than in controls (30%). These results suggest that the increment in basal and G2 aberrations yield in DS lymphocytes may be related to the increase in oxidative damage reported in these patients.

Aging, increasing genomic entropy, and neurodegenerative disease

The genome, as biologic information, can be conceptualized in terms of entropy. The second law of thermodynamics dictates that entropy must increase over time. Consequently, aging can be viewed as increasing genomic entropy. Genetic instability is the biophysical correlate of increasing genomic entropy. Rates of increasing genomic entropy can be determined from age-specific mortality rate dynamics (e.g., Parkinson's disease and amyotrophic lateral sclerosis). These observations are consistent with a model of neurodegenerative disease as a manifestation of increasing genomic entropy with aging.

G2 repair in Nijmegen breakage syndrome: G2 duration and effect of caffeine and cycloheximide in control and X-ray irradiated lymphocytes

Lymphocytes from a patient with the Nijmegen breakage syndrome (NBS/NBS) and his parents (NBS/+) have been analyzed to identify possible disturbances in chromosomal G2 repair. The study included the determination of G2 duration and the analysis of the chromosomal aberration frequencies in lymphocytes with/without caffeine and cyclohexemide (CHM) treatments during G2, under control and X-irradiated conditions. Under control conditions, NBS/NBS lymphocytes showed that the basal chromosomal damage as well as the damage detected in G2, with caffeine treatment, and the G2 duration were higher than cells from an age-matched control. In X-irradiated NBS/NBS lymphocytes, the basal and G2 chromosome aberration frequencies were higher than in the controls; however, no significant differences in G2 duration were detected between these two type of cells. Under X-irradiated conditions, NBS/+ lymphocytes showed that while the level of chromosomal damage in G2 and the duration of this cell cycle phase were similar to the control cells, the frequency of unrepaired chromosomal lesions was higher than in the control lymphocytes. No significant differences in chromosomal damage and G2 duration were detected in NBS/+ lymphocytes compared to the control cells, under control conditions. CHM treatment, which induces an increase in G2 duration, decreased the basal spontaneous and X-ray induced chromosome aberration frequency in NBS/NBS and NBS/+ lymphocytes. These results suggest that NBS lymphocytes might be affected by some disturbances in their ability to extend the G2 duration, which may be influencing their DNA repair efficiency in this phase of the cell cycle.

A fast comet assay variant for solid tissue cells. The assessment of DNA damage in higher plants

The single-cell gel electrophoresis or comet assay, under high alkaline conditions, detects low levels of DNA damage. In it, broken DNA migrates from the nucleus to the anode providing images similar to comets. To adapt this assay to solid tissue cells, nuclei were directly obtained from Allium cepa L. roots. The surface of each single fresh sharply cut meristem was exposed to a small drop of 50 mM Sörensen buffer at pH 6.8, placed on a regular agarose-coated slide. By immediately adding low melting point agarose at 30 degrees C, nuclei resulted embedded in agarose. A final layer of this agarose ended the preparative steps. Conventionaly prepared leukocytes were used as a control. The treatment with detergent (lysis step of the conventional assay) proved to be unnecessary for the nude nuclei. A 20 min-long electrophoresis (at 0.65 V. cm-1, 230 mA and 10 degrees C) was more sensitive than a 10 min-long one for detecting the differential response of plant nuclei to 2 and 4 Gy of gamma-irradiation. A short fixation in methanol transformed the preparations into semi-permanent ones, without altering their later DNA staining by ethidium bromide. The use of instantaneously isolated nuclei simplifies and expands the use of this technique to any eukaryotic cell from solid tissues.

The effects of age and lifestyle factors on the accumulation of cytogenetic damage as measured by chromosome painting

Individual responses to the aging process are variable and are affected by genetic as well as environmental factors. Fluorescent in situ hybridization with whole chromosome probes ('chromosome painting') provides an efficient approach for detecting structural chromosome aberrations in human lymphocytes. This rapid and sensitive technique is an effective tool for quantifying chronic exposure to environmental agents which may result in an accumulation of cytogenetic damage with age. We have applied this technology to a normal, putatively unexposed, population to document the relationship between age and the accumulation of cytogenetic damage, as well as to establish a baseline frequency of stable aberrations. Using probes for chromosomes 1, 2 and 4 simultaneously, the equivalent of 1000 metaphases was scored for stable and unstable aberrations from each of 91 subjects ranging in age from newborns (umbilical cord bloods; n = 14) to adults aged 19 to 79 years. Each subject (or one parent of each newborn) completed an extensive questionnaire to identify possible lifestyle factors that may influence the frequency of cytogenetic damage. Our findings show a significant increase in stable aberrations (translocations and insertions) with age (p < 0.0001). We also observed age-related increases with dicentrics (p < 0.0001) and acentric fragments (p < 0.0001). Relative to the frequencies observed in cord bloods, the frequencies of stable aberrations, dicentrics, and acentric fragments in adults aged 50 and over were elevated 10.6-fold, 3.3-fold, and 2.9-fold, respectively. Nine variables other than age are significantly associated with the frequency of stable aberrations; these are: smoking (two variables), consumption of diet drinks and/or diet sweeteners (4 variables), exposure to asbestos or coal products (1 variable each), and having a previous major illness (1 variable). Newborns whose mothers smoked during pregnancy had a 1.5-fold increase in stable aberrations (p = 0.029). Repeat samples from a subset of the adults indicate that for most subjects there is little change in individual translocation frequencies over a period of two to three years. These results support the hypothesis that stable chromosome aberrations show a greater accumulation with age than do unstable aberrations and suggest that lifestyle factors contribute to the accumulation of cytogenetic damage.

Osteoporosis, sedentary lifestyle, and increasing hip fractures: pathogenic relationship or differential survival bias

Osteoporosis, although a disorder of antiquity, has become more prevalent in developed countries and is a major risk factor for skeletal fracture. Accordingly, the increasing incidence of hip fracture among the elderly within developed nations has been attributed to an increased prevalence of osteoporosis. An increasingly sedentary lifestyle has been suggested as a significant contributing factor for the increased prevalence of osteoporosis. However, differential survival, reflecting changing competing mortality risks, will alter the gene pool of a surviving population cohort. Thus, the gene pool (and hence, disease susceptibilities) of 70-year-old individuals in 1990, for example, should not implicitly be assumed to be the same as 70-year-old individuals in 1950. Consequently, differences in the prevalence of osteoporosis or incidence of hip fracture between current and past elderly cohorts do not necessarily imply differences in environmental risk factors such as levels of physical activity. Instead, variation in competing mortality risks over time may produce differential survival with selection bias and "naturally" lead to increases in the incidence and prevalence of some aging-related disorders such as osteoporosis.

Aging, genomic entropy and carcinogenesis: implications derived from longitudinal age-specific colon cancer mortality rate dynamics

Many types of cancer are intrinsically linked to the process of aging. Aging, from the perspective of the second law of thermodynamics, can be viewed as associated with the inevitable and natural increase in informational entropy of the genome. The molecular biologic basis of increasing genetic informational entropy is the inherent and variable instability of different regions of genome. Colon cancer cells have been shown to have characteristic acquired genetic abnormalities, most commonly, deletions in presumed tumor suppressor genes. Age-specific colon cancer mortality rates in the US from 1958 to 1988 were subjected to longitudinal Gompertzian analysis, a method that may identify and distinguish among genetic, environmental and competitive influences upon mortality. The Strehler-Mildvan modification of the Gompertz relationship between aging and mortality can be used to determine a relative measure of the rate of increase in informational entropy (a reflection of genetic instability) for those genetic factors that are involved in the pathogenesis of colon cancer.