Telomere Abstracts 1

© 2010

Down-regulation of telomerase activity in DLD-1 human colorectal adenocarcinoma cells by tocotrienol

            (Eitsuka, Nakagawa et al. 2006) Download

As high telomerase activity is detected in most cancer cells, inhibition of telomerase by drug or dietary food components is a new strategy for cancer prevention. Here, we investigated the inhibitory effect of vitamin E, with particular emphasis on tocotrienol (unsaturated vitamin E), on human telomerase in cell-culture study. As results, tocotrienol inhibited telomerase activity of DLD-1 human colorectal adenocarcinoma cells in time- and dose-dependent manner, interestingly, with delta-tocotrienol exhibiting the highest inhibitory activity. Tocotrienol inhibited protein kinase C activity, resulting in down-regulation of c-myc and human telomerase reverse transcriptase (hTERT) expression, thereby reducing telomerase activity. In contrast to tocotrienol, tocopherol showed very weak telomerase inhibition. These results provide novel evidence for the first time indicating that tocotrienol acts as a potent candidate regulator of telomerase and supporting the anti-proliferative function of tocotrienol.

Accelerated telomere shortening in response to life stress

            (Epel, Blackburn et al. 2004) Download

Numerous studies demonstrate links between chronic stress and indices of poor health, including risk factors for cardiovascular disease and poorer immune function. Nevertheless, the exact mechanisms of how stress gets "under the skin" remain elusive. We investigated the hypothesis that stress impacts health by modulating the rate of cellular aging. Here we provide evidence that psychological stress--both perceived stress and chronicity of stress--is significantly associated with higher oxidative stress, lower telomerase activity, and shorter telomere length, which are known determinants of cell senescence and longevity, in peripheral blood mononuclear cells from healthy premenopausal women. Women with the highest levels of perceived stress have telomeres shorter on average by the equivalent of at least one decade of additional aging compared to low stress women. These findings have implications for understanding how, at the cellular level, stress may promote earlier onset of age-related diseases.

Age-dependent telomere shortening is slowed down by enrichment of intracellular vitamin C via suppression of oxidative stress

         (Furumoto, Inoue et al. 1998) Download

Telomeres in eukaryotic somatic cells are destined to the age-dependent shortening, which has not been demonstrated to correlate to direct lesion of telomeric DNA by reactive oxygen intermediates (ROI); still less explicable is the inhibitory effect of ROI-scavenging on telomere shortening. Here, we succeeded in artificial slowdown of age-dependent telomere shortening to 52-62% of the untreated control, in human vascular endothelial cells, by addition of the oxidation-resistant type of ascorbic acid (Asc), Asc-2-O-phosphate (Asc2P), which concurrently achieved both extension of cellular life-span and prevention of cell size enlargement indicative of cellular senescence. The results are attributable to a 3.9-fold more marked enrichment of intracellular Asc (Asc(in)) by addition of Asc2P, subsequently dephosphorylated before or during transmembrane influx, than by addition of Asc itself, and also attributed to diminution of intracellular ROI to 53% of the control level by Asc2P; telomerase activity was at a trace level and underwent an age-dependent decline, which was significantly decelerated by Asc2P. Thus, age-dependent telomere-shortening can be decelerated by suppression of intracellular oxidative stress and/or by telomerase retention, both of which are achieved by enriched Asc(in) but not by extracellular Asc overwhelmingly more abundant than Asc(in).

Telomere length assessment: biomarker of chronic oxidative stress?

            (Houben, Moonen et al. 2008) Download

Telomeres are nucleoprotein structures, located at the ends of chromosomes and are subject to shortening at each cycle of cell division. They prevent chromosomal ends from being recognized as double strand breaks and protect them from end to end fusion and degradation. Telomeres consist of stretches of repetitive DNA with a high G-C content and are reported to be highly sensitive to damage induced by oxidative stress. The resulting DNA strand breaks can be formed either directly or as an intermediate step during the repair of oxidative bases. In contrast to the majority of genomic DNA, there is evidence that telomeric DNA is deficient in the repair of single strand breaks. Since chronic oxidative stress plays a major role in the pathophysiology of several chronic inflammatory diseases, it is hypothesized that telomere length is reducing at a faster rate during oxidative stress. Therefore, assessment of telomere length might be a useful biomarker of disease progression. In this review several features of telomere length regulation, their relation with oxidative stress, and the potential application of measurement of telomere length as biomarker of chronic oxidative stress, will be discussed.

Combination treatment with 1alpha,25-dihydroxyvitamin D3 and 9-cis-retinoic acid directly inhibits human telomerase reverse transcriptase transcription in prostate cancer cells

            (Ikeda, Uemura et al. 2003) Download

The vitamin D(3) receptor, which is the nuclear receptor for 1alpha,25-dihydroxyvitamin D(3) (VD(3)), forms a heterodimer with the retinoid X receptor (RXR), which is the nuclear receptor for 9-cis-retinoic acid (9-cis-RA). The heterodimer binds to a specific response element consisting of two directly repeated pairs of motifs, AGGTGA, spaced by three nucleotides [direct repeat (DR) 3] and modulates the expression of VD(3)-responsive genes. Telomerase activity, which is seen in most immortal cells and germ cells, is a complex of enzymes that maintain the length of telomeres. One of the major components of human telomerase, human telomerase reverse transcriptase (hTERT), is the catalytic subunit, and the expression of hTERT might correlate most strongly with telomerase activity. We found that the sequence of 5'-AGTTCATGGAGTTCA-3' (DR3') is similar to that of DR3 in the promoter region of hTERT. Our results showed that the combination of VD(3) and 9-cis-RA inhibited telomerase activity through direct interaction of the heterodimer of vitamin D(3) receptor and RXR with the DR3' sequence in the hTERT promoter as well as the combination of VD(3) and selective RXR ligand did. Also, in vivo data showed that the growth of xenografts in nude mice was inhibited by VD(3) and 9-cis-RA. The results of the present study provide evidence on the molecular mechanism of the inhibition of cell growth by these agents, and they could be novel therapeutic agents for prostate cancer.

Induction of ovarian cancer cell apoptosis by 1,25-dihydroxyvitamin D3 through the down-regulation of telomerase

            (Jiang, Bao et al. 2004) Download

The maintenance of telomere length is required for continued cell proliferation, and approximately 85-90% of human cancers, including ovarian epithelial cancers (OCa), show high activity of telomerase. In the present study we report that 1,25-dihydroxyvitamin D(3) (1,25(OH)(2) VD)(3)induces OCa cell apoptosis by down-regulating telomerase. Quantitative reverse transcription-PCR analysis shows that 1,25(OH)(2)VD(3) decreases the level of human telomerase reverse transcriptase (hTERT) mRNA, the catalytic subunit of telomerase. The decrease is not due to transcriptional repression through the putative vitamin D response element present in the 5' regulatory region of hTERT gene. Instead, 1,25(OH)(2) VD(3) decreases the stability of the hTERT mRNA. Stable expression of hTERT in OCa cells decreases their response to 1,25(OH)(2)VD(3)-induced growth suppression. Although the cell cycle progression of these clones stably expressing hTERT is inhibited by 1,25(OH)(2)VD(3) to a similar degree as that of the parental cells, these clones are more resistant to apoptosis induced by 1,25(OH)(2)VD(3) .In contrast to parental cells, which lose proliferation potential after the 1,25(OH)(2)VD(3) treatment, hTERT-expressing clones resume rapid growth after withdrawal of 1,25(OH)(2)VD(3). Overall, the study suggests that the down-regulation of telomerase activity by 1,25(OH)(2)VD(3) and the resulting cell death are important components of the response of OCa cells to 1,25(OH)(2)VD(3)-induced growth suppression.

Nicotinamide extends replicative lifespan of human cells

            (Kang, Lee et al. 2006) Download

We found that an ongoing application of nicotinamide to normal human fibroblasts not only attenuated expression of the aging phenotype but also increased their replicative lifespan, causing a greater than 1.6-fold increase in the number of population doublings. Although nicotinamide by itself does not act as an antioxidant, the cells cultured in the presence of nicotinamide exhibited reduced levels of reactive oxygen species (ROS) and oxidative damage products associated with cellular senescence, and a decelerated telomere shortening rate without a detectable increase in telomerase activity. Furthermore, in the treated cells growing beyond the original Hayflick limit, the levels of p53, p21WAF1, and phospho-Rb proteins were similar to those in actively proliferating cells. The nicotinamide treatment caused a decrease in ATP levels, which was stably maintained until the delayed senescence point. Nicotinamide-treated cells also maintained high mitochondrial membrane potential but a lower respiration rate and superoxide anion level. Taken together, in contrast to its demonstrated pro-aging effect in yeast, nicotinamide extends the lifespan of human fibroblasts, possibly through reduction in mitochondrial activity and ROS production.

Mechanism of telomere shortening by oxidative stress

            (Kawanishi and Oikawa 2004) Download

We investigated whether oxidative stress, which contributes to aging, accelerates the telomere shortening in human cultured cells. The terminal restriction fragment (TRF) from WI-38 fibroblasts irradiated with UVA (365-nm light) decreased with increasing of the irradiation dose. Furthermore, UVA irradiation dose-dependently increased the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in both WI-38 fibroblasts and HL-60 cells. In order to clarify the mechanism of the acceleration of telomere shortening, we investigated site-specific DNA damage induced by UVA irradiation in the presence of endogenous photosensitizers using (32)P 5' end-labeled DNA fragments containing telomeric oligonucleotide (TTAGGG)(4). UVA irradiation with riboflavin induced 8-oxodG formation in the DNA fragments containing telomeric sequence, and Fpg protein treatment led to chain cleavages at the central guanine of 5'-GGG-3' in telomere sequence. Human 8-oxodG-DNA glycosylase introduces a chain break in a double-stranded oligonucleotide specifically at an 8-oxodG residue. The amount of 8-oxodG formation in DNA fragment containing telomere sequence [5'-CGC(TTAGGG)(7)CGC-3'] was approximately five times more than that in the DNA fragment containing nontelomere sequence [5'-CGC(TGTGAG)(7)CGC-3']. Furthermore, H(2)O(2) plus Cu(II) caused DNA damage, including 8-oxodG formation, specifically at the GGG sequence in the telomere sequence (5'-TTAGGG-3'). It is concluded that the formation of 8-oxodG at the GGG triplet in telomere sequence induced by oxidative stress could participate in acceleration of telomere shortening.

Alpha-tocopherol modulates hydrogen peroxide-induced DNA damage and telomere shortening of human skin fibroblasts derived from differently aged individuals

            (Makpol, Zainuddin et al. 2010) Download

Antioxidants such as vitamin E may act differently on skin cells depending on the age of the skin and the level of oxidative damage induced. The effects of alpha-tocopherol (ATF) on H(2)O(2)-induced DNA damage and telomere shortening of normal human skin fibroblast cells derived from young and old individual donors were determined. Fibroblasts were divided into five groups; untreated control, H(2)O(2)-induced oxidative stress, alpha-tocopherol treatment, and pre- and post-treatment with alpha-tocopherol for H(2)O(2)-induced oxidative stress. Our results showed that H(2)O(2)-induced oxidative stress increased DNA damage, shortened the telomere length and reduced the telomerase activity (p < 0.05) in fibroblasts obtained from young and old donors. Pre- and post-treatment with alpha-tocopherol protected against H(2)O(2)-induced DNA damage in fibroblasts obtained from young individuals (p = 0.005; p = 0.01, respectively). However, in fibroblasts obtained from old individuals, similar protective effects were only seen in cells pretreated with alpha-tocopherol (p = 0.05) but not in the post-treated cells. Protection against H(2)O(2)-induced telomere shortening was observed in fibroblasts obtained from both young and old donors which were pre-treated with alpha-tocopherol (p = 0.009; p = 0.008, respectively). However, similar protective effects against telomere shortening in fibroblasts obtained from both young and old donors were not observed in the post-treated fibroblasts. Protection against H(2)O(2)-induced telomerase activity loss was observed only in fibroblasts obtained from old donors which were pretreated with alpha-tocopherol (p = 0.04) but not in fibroblasts obtained from young donors. Similar protective effects against telomerase activity loss in fibroblasts obtained from both young and old donors were not observed in the post-treated fibroblasts. In conclusion, alpha-tocopherol protected against H(2)O(2)-induced telomere shortening by restoring the telomerase activity. It also modulated H(2)O(2)-induced DNA damage and this modulation was affected by donor age.

DNA damage in telomeres and mitochondria during cellular senescence: is there a connection?

            (Passos, Saretzki et al. 2007) Download

Cellular senescence is the ultimate and irreversible loss of replicative capacity occurring in primary somatic cell culture. It is triggered as a stereotypic response to unrepaired nuclear DNA damage or to uncapped telomeres. In addition to a direct role of nuclear DNA double-strand breaks as inducer of a DNA damage response, two more subtle types of DNA damage induced by physiological levels of reactive oxygen species (ROS) can have a significant impact on cellular senescence: Firstly, it has been established that telomere shortening, which is the major contributor to telomere uncapping, is stress dependent and largely caused by a telomere-specific DNA single-strand break repair inefficiency. Secondly, mitochondrial DNA (mtDNA) damage is closely interrelated with mitochondrial ROS production, and this might also play a causal role for cellular senescence. Improvement of mitochondrial function results in less telomeric damage and slower telomere shortening, while telomere-dependent growth arrest is associated with increased mitochondrial dysfunction. Moreover, telomerase, the enzyme complex that is known to re-elongate shortened telomeres, also appears to have functions independent of telomeres that protect against oxidative stress. Together, these data suggest a self-amplifying cycle between mitochondrial and telomeric DNA damage during cellular senescence.

Telomere length in peripheral blood mononuclear cells is associated with folate status in men

            (Paul, Cattaneo et al. 2009) Download

Human chromosomes are capped by telomeres, which consist of tandem repeats of DNA and associated proteins. The length of the telomeres is reduced with increasing cell divisions except when the enzyme telomerase is active, as in stem cells and germ cells. Telomere dysfunction has been associated with development of age-related pathologies, including cancer, cardiovascular disease, Alzheimer's disease, and Parkinson's disease. DNA damage in the telomeric region causes attrition of telomeres. Because folate provides precursors for nucleotide synthesis and thus affects the integrity of DNA, including that of the telomeric region, folate status has the potential to influence telomere length. Telomere length is epigenetically regulated by DNA methylation, which in turn could be modulated by folate status. In this study, we determined whether folate status and the 677C > T polymorphism of the methylene tetrahydrofolate reductase (MTHFR) gene are associated with the telomere length of peripheral blood mononuclear cells in healthy men. The results of our study showed that plasma concentration of folate was associated with telomere length of peripheral blood mononuclear cells in a nonlinear manner. When plasma folate concentration was above the median, there was a positive relationship between folate and telomere length. In contrast, there was an inverse relationship between folate and telomere length when plasma folate concentration was below the median. The MTHFR 677C > T polymorphism was weakly associated (P = 0.065) with increased telomere length at below-median folate status. We propose that folate status influences telomere length by affecting DNA integrity and the epigenetic regulation of telomere length through DNA methylation.

Modelling telomere shortening and the role of oxidative stress

            (Proctor and Kirkwood 2002) Download

Extensive evidence supports the idea that progressive telomere loss contributes to the phenomenon of cell replicative senescence, but the mechanisms responsible for telomere loss are still unclear. In addition to the widely recognized end-replication problem, there is evidence that oxidative stress plays a major role in determining the rate of loss of telomeric DNA, and the action of a C-strand-specific exonuclease is also suggested to be important. We describe a mathematical model which examines the different contributions of these mechanisms to telomere loss and its role in triggering cell senescence. The model allows us to make quantitative predictions about the rates of telomere loss resulting from these alternative mechanisms, and their interactions. By varying the key parameters of the model, it is possible to examine the extent to which the different hypotheses are compatible with quantitative and qualitative features of the experimental data. For example, the model predicts that under low levels of oxidative stress, the main mechanisms of telomere shortening are the end-replication problem plus C-strand processing. However, when levels of oxidative stress are higher, as in cell cultures grown under normoxic or hyperoxic conditions, the model predicts that single strand breaks make an important contribution to telomere loss and their inclusion within the model is necessary to explain the data. We suggest that theoretical models of this kind are valuable tools to bridge the gap between the verbal statements of hypotheses and their rigorous experimental test.

A continuous correlation between oxidative stress and telomere shortening in fibroblasts

         (Richter and von Zglinicki 2007) Download

Telomere shortening in cells with low intrinsic telomerase activity like fibroblasts is governed by various mechanisms including the so-called end-replication problem, end processing and oxidative DNA damage. To assess the impact of oxidative stress on telomere shortening rates, we compared telomere shortening rates measured in fibroblasts from two different donor species (human and sheep) under both pro- and antioxidative culture regimes. Over an almost 50-fold change in peroxide indicator dye fluorescence intensity, we found a continuous, exponential correlation between cellular oxidative stress levels and telomere shortening rates, which was independent of donor species and cell strain. This correlation suggests stress-mediated telomere DNA damage as an important determinant of telomere shortening.        

Telomere shortening and oxidative stress in aged macrophages results in impaired STAT5a phosphorylation

            (Sebastian, Herrero et al. 2009) Download

Macrophages are an essential component of both innate and adaptive immunity, and altered function of these cells with aging may play a key role in immunosenescence. To determine the effect of aging on macrophages, we produced bone marrow-derived macrophages in vitro. In these conditions, we analyzed the effect of aging on macrophages without the influence of other cell types that may be affected by aging. We showed that telomeres shorten with age in macrophages leading to a decreased GM-CSF but not M-CSF-dependent proliferation of these cells as a result of decreased phosphorylation of STAT5a. Macrophages from aged mice showed increased susceptibility to oxidants and an accumulation of intracellular reactive oxygen species. In these macrophages STAT5a oxidation was reduced, which led to the decreased phosphorylation observed. Interestingly, the same cellular defects were found in macrophages from telomerase knockout (Terc(-/-)) mice suggesting that telomere loss is the cause for the enhanced oxidative stress, the reduced Stat5a oxidation and phosphorylation and, ultimately, for the impaired GM-CSF-dependent macrophage proliferation.

Telomere length, oxidative damage, antioxidants and breast cancer risk

            (Shen, Gammon et al. 2009) Download

Telomeres play a critical role in maintaining the integrity and stability of the genome, and are susceptible to oxidative damage after telomere shortening to a critical length. In the present study, we explored the role of white blood cell DNA telomere length on breast cancer risk, and examined whether urinary 15-F(2)-isoprostanes (15-F(2t)-IsoP) and 8-oxo-7,8-dihydrodeoxyguanosine (8-oxodG) or dietary antioxidant intake modified the relationship between telomere length and breast cancer risk. A population-based case-control study-the Long Island Breast Cancer Study Project-was conducted among 1,067 cases and 1,110 controls. Telomere length was assessed by quantitative PCR. Overall, the mean levels of telomere length (T/S ratio), 15-F(2t)-IsoP and 8-oxodG were not significantly different between cases and controls. Among premenopausal women only, carrying shorter telomeres (Q3 and Q4), as compared with the longest (Q1), was associated with significantly increased breast cancer risk. Age-adjusted OR and 95% CI were 1.71 (1.10-2.67) and 1.61 (1.05-2.45). The 5-F(2t)-IsoP and 8-oxodG biomarkers did not modify the telomere-breast cancer association. A moderate increase in breast cancer risk was observed among women with the shortest telomeres (Q4) and lower dietary and supplemental intake of beta-carotene, vitamin C or E intake [OR (95% CI) = 1.48 (1.08-2.03), 1.39 (1.01-1.92) and 1.57 (1.14-2.18), respectively], although the trend test exhibited statistical significance only within the lower vitamin E intake subgroup (p(trend) = 0.01). These results provided the strongest evidence to date that breast cancer risk may be affected by telomere length among premenopausal women or women with low dietary intake of antioxidants or antioxidant supplements.

Age-dependent telomere-shortening is repressed by phosphorylated alpha-tocopherol together with cellular longevity and intracellular oxidative-stress reduction in human brain microvascular endotheliocytes

            (Tanaka, Moritoh et al. 2007) Download

Cellular life-span of neonatal human brain microvascular endotheliocytes (HBME) was estimated by population doubling levels (PDLs) for serial subcultivations until spontaneous proliferation stoppage, and was 2.4-fold longer for continuous administration with the 6-O-phosphorylated derivative (TocP) of alpha-tocopherol (Toc), being bio-available owing to its water-solubility, or TocP plus 2-O-phosphorylated ascorbate (Asc2P), and 1.3-fold longer with Asc2P, at a dose of 150 microM, than for the non-administered control. Enlarged cell diameters indicative of cellular aging were repressed for TocP-administered cells as analyzed with a channelizer. Age-dependent shortening of telomeric DNA length (291 bp/PDL) was slowed markedly for TocP (165 bp/PDL) or TocP plus Asc2P, but slightly for Asc2P. Telomerase activity as assessed by the PCR-based TRAP method was detectable slightly at younger ages but no longer at middle ages for the non-administered cells, but, for TocP-administered cells, was intensely detected at younger ages and appreciably until middle ages. Intracellular TocP amounts were not changed age-dependently in contrast to a marked decrease in Toc which accrued from TocP esterolysis. This may be partly attributed to age-dependent changes in the lipid peroxidation product acrolein (ACR), which was abundant at older ages in non-administered cells, but scarcely in TocP-administered cells. Furthermore, intracellular reactive oxygen species (ROS) such as H(2)O(2) and hydroperoxides as detected using the redox indicator CDCFH-DA was less abundant in TocP-administered cells than in non-administered cells. Thus the telomeric-DNA retention, concurrently with retained telomerase activity, was shown to be correlated with cellular longevity, and may be supported by diminished oxidative stress, in hydrophobic microenvironment, which can be achieved by TocP rather than AscP.


Role of oxidative stress in telomere shortening in cultured fibroblasts from normal individuals and patients with ataxia-telangiectasia

            (Tchirkov and Lansdorp 2003) Download

Cells from patients with the autosomal recessive disorder ataxia-telangiectasia (A-T) display accelerated telomere shortening upon culture in vitro. It has been suggested that A-T cells are in a chronic state of oxidative stress, which could contribute to their enhanced telomere shortening. In order to examine this hypothesis, we monitored the changes in telomere length in A-T homozygous, heterozygous and control fibroblasts cultured in vitro under various conditions of oxidative stress using quantitative fluorescent in situ hybridization. Compared with normal cells, the rate of telomere shortening was 1.5-fold increased under 'normal' levels of oxidative stress in A-T heterozygous cells and 2.4-3.2-fold in A-T homozygous cells. Mild chronic oxidative stress induced by hydrogen peroxide increased the rate of telomere shortening in A-T cells but not in normal fibroblasts and the telomere shortening rate decreased in both normal and A-T fibroblasts if cultures were supplemented with the anti-oxidant phenyl-butyl-nitrone. Increased telomere shortening upon oxidative stress in A-T cells was associated with a significant increase in the number of extra-chromosomal fragments of telomeric DNA and chromosome ends without detectable telomere repeats. We propose that the ATM (A-T mutated) protein has a role in the prevention or repair of oxidative damage to telomeric DNA and that enhanced sensitivity of telomeric DNA to oxidative damage in A-T cells results in accelerated telomere shortening and chromosomal instability.

Role of oxidative stress in telomere length regulation and replicative senescence

            (von Zglinicki 2000) Download

Replicative senescence is tied into organismal aging processes in more than one respect, and telomeres appear to be the major trigger of replicative senescence under many conditions in vitro and in vivo. However, the structure-function relationships in telomeres, the mechanisms of telomere shortening with advancing replicative age, and the regulation of senescence by telomeres are far from understood. Combining recent data on telomere structure, function of telomere-binding proteins, and sensitivity of telomeres to oxidative damage, an integrative model of telomere shortening and signaling is developed. The model suggests that t-loop formation hinders access of repair proteins to telomeres, leading to accumulation of a basic sites and single-strand breaks. These might contribute to accelerated telomere shortening by transient stalling of replication as well as, if present in high concentrations, to a relief of torsional tension which might destabilize the telomeric loop structure. As a result, the single-stranded G-rich overhang, which is present at the very ends of telomeres but is normally protected at the base of the telomeric loop, will be exposed to the nucleoplasm. Free G-rich telomeric single strands are a strong inductor of the p53 pathway, and exposure of the overhangs seems to be the first step in the signal transduction cascade to replicative senescence.

Oxidative stress shortens telomeres

            (von Zglinicki 2002) Download

Telomeres in most human cells shorten with each round of DNA replication, because they lack the enzyme telomerase. This is not, however, the only determinant of the rate of loss of telomeric DNA. Oxidative damage is repaired less well in telomeric DNA than elsewhere in the chromosome, and oxidative stress accelerates telomere loss, whereas antioxidants decelerate it. I suggest here that oxidative stress is an important modulator of telomere loss and that telomere-driven replicative senescence is primarily a stress response. This might have evolved to block the growth of cells that have been exposed to a high risk of mutation.

The two isomers of HDTIC compounds from Astragali Radix slow down telomere shortening rate via attenuating oxidative stress and increasing DNA repair ability in human fetal lung diploid fibroblast cells

            (Wang, Zhang et al. 2010) Download

4-Hydroxy-5-hydroxymethyl-[1,3]dioxolan-2,6'-spirane-5',6',7',8'-tetrahydr o-indolizine-3'-carbaldehyde (HDTIC)-1 and HDTIC-2 are two isomers extracted from Astragalus membranaceus (Fisch) Bunge Var. mongholicus (Bge) Hsiao. Our previous study had demonstrated that they could extend the lifespan of human fetal lung diploid fibroblasts (2BS). To investigate the mechanisms of the HDTIC-induced delay of replicative senescence, in this study, we assessed the effects of these two compounds on telomere shortening rate and DNA repair ability in 2BS cells. The telomere shortening rates of the cells cultured with HDTIC-1 or HDTIC-2 were 31.5 and 41.1 bp with each division, respectively, which were much less than that of the control cells (71.1 bp/PD). We also found that 2BS cells pretreated with HDTIC-1 or HDTIC-2 had a significant reduction in DNA damage after exposure to 200 microM H(2)O(2) for 5 min. Moreover, the 100 microM H(2)O(2)-induced DNA damage was significantly repaired after the damaged cells were continually cultured with HDTIC for 1 h. These results suggest that HDTIC compounds slow down the telomere shortening rate of 2BS cells, which is mainly due to the biological properties of the compounds including the reduction of DNA damage and the improvement of DNA repair ability. In addition, the slow down of telomere shortening rate, the reduction of DNA damage, and the improvement of DNA repair ability induced by HDTIC may be responsible for their delay of replicative senescence.

Multivitamin use and telomere length in women

            (Xu, Parks et al. 2009) Download

BACKGROUND: Telomere length may be a marker of biological aging. Multivitamin supplements represent a major source of micronutrients, which may affect telomere length by modulating oxidative stress and chronic inflammation. OBJECTIVE: The objective was to examine whether multivitamin use is associated with longer telomeres in women. DESIGN: We performed a cross-sectional analysis of data from 586 early participants (age 35-74 y) in the Sister Study. Multivitamin use and nutrient intakes were assessed with a 146-item food-frequency questionnaire, and relative telomere length of leukocyte DNA was measured by quantitative polymerase chain reaction. RESULTS: After age and other potential confounders were adjusted for, multivitamin use was associated with longer telomeres. Compared with nonusers, the relative telomere length of leukocyte DNA was on average 5.1% longer among daily multivitamin users (P for trend = 0.002). In the analysis of micronutrients, higher intakes of vitamins C and E from foods were each associated with longer telomeres, even after adjustment for multivitamin use. Furthermore, intakes of both nutrients were associated with telomere length among women who did not take multivitamins. CONCLUSION: This study provides the first epidemiologic evidence that multivitamin use is associated with longer telomere length among women.

Slow-down of age-dependent telomere shortening is executed in human skin keratinocytes by hormesis-like-effects of trace hydrogen peroxide or by anti-oxidative effects of pro-vitamin C in common concurrently with reduction of intracellular oxidative stress

            (Yokoo, Furumoto et al. 2004) Download

The cellular life-span of cultivated human skin epidermis keratinocytes NHEK-F was shown to be extended up to 150% of population doubling levels (PDLs) by repetitive addition with two autooxidation-resistant derivatives of ascorbic acid (Asc), Asc-2-O-phosphate (Asc2P), and Asc-2-O-alpha-glucoside (Asc2G), respectively, but to be not extended with Asc itself. In contrast, hydrogen peroxide (H(2)O(2)) as dilute as 20 microM which was non-cytotoxic to the keratinocytes, or at 60 microM being marginally cytotoxic achieved the cellular longevity, unexpectedly, up to 160 and 120% of PDLs, respectively, being regarded as a hormesis-like stimulatory effect. The lifespan-extended cells that were administered with Asc2P, Asc2G, or 20 microM H(2)O(2) were prevented from senescence-induced symptoms such as PDL-dependent enlargement of a cell size of 14.7 microm finally up to 17.4 microm upon Hayflick's limit-called loss of proliferation ability as estimated with a channelizer, and retained young cell morphological aspects such as thick and compact shape and intense attachment to the culture substratum even upon advanced PDLs, whereas other non-extended cells looked like thin or fibrous shape and large size upon lower PDLs. The PDL-dependent shortening of telomeric DNA of 11.5 kb finally down to 9.12-8.10 kb upon Hayflick's limit was observed in common for each additive-given cells, but was decelerated in the following order: 20 microM H(2)O(2) > Asc2P = Asc2G > 60 microM H(2)O(2) > Asc = no additive, being in accord with the order of cell longevity. Intracellular reactive oxygen species (ROS) was diminished by Asc2P, Asc2G or 20 microM H(2)O(2), but not significantly by Asc or 60 microM H(2)O(2) as estimated by fluorometry using the redox indicator dye CDCFH. There was no appreciable difference among NHEK keratinocytes that were administered with or without diverse additives in terms of telomerase activity per cell, which was 1.40 x 10(4)-4.48 x 10(4) times lower for the keratinocytes than for HeLa cells which were examined as the typical tumor cells. Thus longevity of the keratinocytes was suggested to be achieved by slowdown of age-dependent shortening of telomeric DNA rather than by telomerase; telomeres may suffer from less DNA lesions due to the continuous and thorough repression of intracellular ROS, which was realized either by pro-vitamin C such as Asc2P or Asc2G that exerted an antioxidant ability more persistent than Asc itself or by 20 microM H(2)O(2) which diminished intracellular ROS assumedly through a hormesis-like effect.

Telomerase-associated apoptotic events by mushroom ganoderma lucidum on premalignant human urothelial cells

            (Yuen, Gohel et al. 2008) Download

The chemopreventive effects of Ganoderma lucidum was tested, using a tumorigenic transformable human urothelial cell (HUC-PC) model. These in vitro data show that G. lucidum can inhibit the viability and growth of HUC-PC. This could be explained by a concomitant induction of apoptosis and inhibition of telomerase activity. Significant exteriorization of phosphatidylserine was detected by Annexin-V on cell surface, and the cells subsequently lost membrane integrity for uptake of 7-amino-actinomycin D dye. Additionally, the levels of hydrogen peroxide and 8-hydroxy-2'-deoxyguanosine (8-OHdG) production of the apoptotic cells were significantly increased. The induction of apoptosis and suppression of telomerase activity help to explain the anti-HUC-PC growth properties; however, the induction of oxidative stress requires further study. This study strongly suggests that G. lucidum is a potential source of chemopreventive agents for bladder cancer based on its effectiveness in controlling the premalignant urothelial cell growth and carcinogen-induced transformation.


References

Eitsuka, T., K. Nakagawa, et al. (2006). "Down-regulation of telomerase activity in DLD-1 human colorectal adenocarcinoma cells by tocotrienol." Biochem Biophys Res Commun 348(1): 170-5.

Epel, E. S., E. H. Blackburn, et al. (2004). "Accelerated telomere shortening in response to life stress." Proc Natl Acad Sci U S A 101(49): 17312-5.

Furumoto, K., E. Inoue, et al. (1998). "Age-dependent telomere shortening is slowed down by enrichment of intracellular vitamin C via suppression of oxidative stress." Life Sci 63(11): 935-48.

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