Improved DNA-repair parameters in PHA-stimulated peripheral blood lymphocytes of human subjects with low body mass index

Cellular Senescence in Neurodegenerative Diseases

Cellular senescence is a homeostatic biological process characterized by a permanent state of cell cycle arrest that can contribute to the decline of the regenerative potential and function of tissues. The increased presence of senescent cells in different neurodegenerative diseases suggests the contribution of senescence in the pathophysiology of these disorders. Although several factors can induce senescence, DNA damage, oxidative stress, neuroinflammation, and altered proteostasis have been shown to play a role in its onset. Oxidative stress contributes to accelerated aging and cognitive dysfunction stages affecting neurogenesis, neuronal differentiation, connectivity, and survival. During later life stages, it is implicated in the progression of cognitive decline, synapse loss, and neuronal degeneration. Also, neuroinflammation exacerbates oxidative stress, synaptic dysfunction, and neuronal death through the harmful effects of pro-inflammatory cytokines on cell proliferation and maturation. Both oxidative stress and neuroinflammation can induce DNA damage and alterations in DNA repair that, in turn, can exacerbate them. Another important feature associated with senescence is altered proteostasis. Because of the disruption in the function and balance of the proteome, senescence can modify the proper synthesis, folding, quality control, and degradation rate of proteins producing, in some diseases, misfolded proteins or aggregation of abnormal proteins. There is an extensive body of literature that associates cellular senescence with several neurodegenerative disorders including Alzheimer’s disease (AD), Down syndrome (DS), and Parkinson’s disease (PD). This review summarizes the evidence of the shared neuropathological events in these neurodegenerative diseases and the implication of cellular senescence in their onset or aggravation. Understanding the role that cellular senescence plays in them could help to develop new therapeutic strategies.

Loss of DNA polymerase β induces cellular senescence

We aim to establish that accelerated aging and premature cellular senescence seen in individuals with Down syndrome is related to reduced DNA polymeraseβ. We report here that primary fibroblasts from Down syndrome individuals exhibit greater SA-β-gal staining (fourfold increase, P < 0.001), increased p16 transcript abundance (threefold increase, P < 0.01), and reduced HMGB1 nuclear localization (1.5-fold lower, P < 0.01). We also find that DNA polymerase β expression is significantly reduced in Down syndrome primary fibroblasts (53% decline, P < 0.01). To evaluate whether DNA polymerase β might be causative in senescence induction, we evaluated the impact of murine DNA polymerase β nullizygosity on senescence. We find that unexposed DNA polymerase β -null primary fibroblasts exhibit a robust increase in the number of senescent cells compared to wild-type (11-fold, P < 0.001), demonstrating that loss DNA polymerase β is sufficient to induce senescence. We also see an additional increase in response to hydroxyurea (threefold greater than WT-HU, P < 0.05). These data demonstrate that loss of DNA polymerase β is sufficient to induce senescence. Additionally, we report a significant induction in spontaneous DNA double strand breaks in DNA polymerase β null MEFs (fivefold increase from wild-type, P < 0.0001). Our findings strongly suggest that DNA polymerase β is causative in senescence induction, reasonably pointing to DNA polymerase β as a likely factor driving the premature senescence in Down syndrome. Environ. Mol. Mutagen. 59:603-612, 2018. © 2018 Wiley Periodicals, Inc.

Effect of Amalaki rasayana on DNA damage and repair in randomized aged human individuals

ETHNOPHARMACOLOGICAL RELEVANCE

Preparations from Phyllanthus emblica called Amalaki rasayana is used in the Indian traditional medicinal system of Ayurveda for healthy living in elderly. The biological effects and its mechanisms are not fully understood. Since the diminishing DNA repair is the hallmark of ageing, we tested the influence of Amalaki rasayana on recognized DNA repair activities in healthy aged individuals.

METHODS

Amalaki rasayana was prepared fresh and healthy aged randomized human volunteers were administrated with either rasayana or placebo for 45 days strictly as per the traditional text. The DNA repair was analyzed in peripheral blood mononuclear cells before and after rasayana administration and after 45 days post-rasayana treatment regimen. UVC-induced DNA strand break repair (DSBR) based on extent of DNA unwinding by fluorometric analysis, nucleotide excision repair (NER) by flow cytometry and constitutive base excision repair (BER) by gap filling method were analyzed.

RESULTS

Amalaki rasayana administration stably maintained/enhanced the DSBR in aged individuals. There were no adverse side effects. Further, subjects with different body mass index showed differential DNA strand break repair capacity. No change in unscheduled DNA synthesis during NER and BER was observed between the groups.

CONCLUSION

Intake of Amalaki rasayana by aged individuals showed stable maintenance of DNA strand break repair without toxic effects. However, there was no change in nucleotide and base excision repair activities. Results warrant further studies on the effects of Amalaki rasayana on DSBR activities.

Dietary Calorie Restriction from Adulthood Through Old Age in Rats: Improved DNA Polymerase β and DNA Gap Repair Activity in Cortical Neurons

It is well established now that dietary calorie restriction (CR) leads to extension of life span in many species, although the exact mechanism of this effect is still eluding. In the present study, we examined the effect of 40 % CR imposed during a prolonged period of life span (from 6 to 30 months) of rats on the activity of DNA polymerase β (pol β) in view of its role in short gap base excision DNA repair and template driven primer extension. DNA pol β activity is very low at this late age. However, cortical neuronal extracts prepared from CR rats of 30 months age showed significantly higher pol β protein levels and activity when compared to control 30 month old rats. Yet, one-nucleotide gap repair in old control neurons and an improved efficiency in CR neurons could be visualized only after supplementation of the extracts with T4 DNA ligase indicating the lack of CR affect on ligase activity. No impressive primer extension activity is seen either in the CR or old control neurons. These results are taken to convey that extended CR through adult life leads to improved pol β activity and therefore, pol β dependent DNA gap repair activity.

Principles and practice of hormetic treatment of aging and age-related diseases

Aging is characterized by stochastic accumulation of molecular damage, progressive failure of maintenance and repair, and consequent onset of age-related diseases. Applying hormesis in aging research and therapy is based on the principle of stimulation of maintenance and repair pathways by repeated exposure to mild stress. Studies on the beneficial biological effects of repeated mild heat shock on human cells in culture, and other studies on the anti-aging and life-prolonging effects of proxidants, hypergravity, irradiation and ethanol on cells and organisms suggest that hormesis as an antiaging and gerontomodulatory approach has a promising future. Its clinical applications include prevention and treatment of diabetes, cataract, osteoporosis, dementia and some cancers.

Hormesis in aging

Hormesis in aging is represented by mild stress-induced stimulation of protective mechanisms in cells and organisms resulting in biologically beneficial effects. Single or multiple exposure to low doses of otherwise harmful agents, such as irradiation, food limitation, heat stress, hypergravity, reactive oxygen species and other free radicals have a variety of anti-aging and longevity-extending hormetic effects. Detailed molecular mechanisms that bring about the hormetic effects are being increasingly understood, and comprise a cascade of stress response and other pathways of maintenance and repair. Although the extent of immediate hormetic effects after exposure to a particular stress may only be moderate, the chain of events following initial hormesis leads to biologically amplified effects that are much larger, synergistic and pleiotropic. A consequence of hormetic amplification is an increase in the homeodynamic space of a living system in terms of increased defence capacity and reduced load of damaged macromolecules. Hormetic strengthening of the homeodynamic space provides wider margins for metabolic fluctuation, stress tolerance, adaptation and survival. Hormesis thus counter-balances the progressive shrinkage of the homeodynamic space, which is the ultimate cause of aging, diseases and death. Healthy aging may be achieved by hormesis through mild and periodic, but not severe or chronic, physical and mental challenges, and by the use of nutritional hormesis incorporating mild stress-inducing molecules called hormetins. The established scientific foundations of hormesis are ready to pave the way for new and effective approaches in aging research and intervention.

Nutritional hormesis

OBJECTIVE

Hormesis, the biological and toxicological concept that small quantities have opposite effects from large quantities, is reviewed with emphasis on its relevance to nutrition.

RESULTS

Hormetic and other dose-response relationships are categorized, depicted, and discussed. Evidence for nutritional hormesis is presented for essential vitamin and mineral nutrients, dietary restriction, alcohol (ethanol), natural dietary and some synthetic pesticides, some herbicides, and acrylamide. Some of the different hormetic mechanisms that have been proposed are reviewed.

CONCLUSIONS

The credence and relevance of hormesis to nutrition are considered to be established. The roles of hormesis in nutritional research and in formulating nutritional guidelines are discussed.

SPONSORSHIP

The New York City Department of Health and Mental Hygiene.

Hormetic modulation of aging and longevity by mild heat stress

Aging is characterized by a stochastic accumulation of molecular damage, progressive failure of maintenance and repair, and consequent onset of age-related diseases. Applying hormesis in aging research and therapy is based on the principle of stimulation of maintenance and repair pathways by repeated exposure to mild stress. In a series of experimental studies we have shown that repetitive mild heat stress has anti-aging hormetic effects on growth and various other cellular and biochemical characteristics of human skin fibroblasts undergoing aging in vitro. These effects include the maintenance of stress protein profiles, reduction in the accumulation of oxidatively and glycoxidatively damaged proteins, stimulation of the proteasomal activities for the degradation of abnormal proteins, improved cellular resistance to ethanol, hydrogen peroxide and ultraviolet-B rays, and enhanced levels of various antioxidant enzymes. Anti-aging hormetic effects of mild heat shock appear to be facilitated by reducing protein damage and protein aggregation by activating internal antioxidant, repair and degradation processes.

Understanding and modulating ageing

Ageing is characterized by a progressive accumulation of molecular damage in nucleic acids, proteins and lipids. The inefficiency and failure of maintenance, repair and turnover pathways is the main cause of age-related accumulation of damage. Research in molecular gerontology is aimed at understanding the genetic and epigenetic regulation of survival and maintenance mechanisms at the levels of transcription, post-transcriptional processing, post-translational modifications, and interactions among various gene products. Concurrently, several approaches are being tried and tested to modulate ageing in a wide variety of organisms. The ultimate aim of such studies is to improve the quality of human life in old age and prolong the health-span. Various gerontomodulatory approaches include gene therapy, hormonal supplementation, nutritional modulation and intervention by free radical scavengers and other molecules. A recent approach is that of applying hormesis in ageing research and therapy, which is based on the principle of stimulation of maintenance and repair pathways by repeated exposure to mild stress. A combination of molecular, physiological and psychological modulatory approaches can realize "healthy ageing" as an achievable goal in the not-so-distant future.

Dietary calorie restriction, DNA-repair and brain aging

It is now well established, in many species, that dietary calorie restriction confers beneficial effects like slowing down many age dependent processes and extending the lifespan. There are indications that this phenomenon may be applicable even in non-human primates and humans. However the precise mechanism through which these effects are achieved is not known. Since decreasing DNA repair has been correlated with increasing age, information available on the effect of dietary calorie restriction on DNA repair potential in different species, including humans, is reviewed with special emphasis on brain in view of its uniqueness and the age related appearance of several neurodegenerative disorders. There is considerable evidence to indicate that calorie restriction reduces the rate of, among other things, the age dependent decrease in DNA repair potential thus leading to a better maintenance of genomic integrity. In brain also dietary calorie restriction is found to improve the activities of some enzymes supposedly involved in DNA repair. It is suggested that one of the lifespan extending mechanisms of calorie restriction may be to channel the limited energy resource available to maintain a process like DNA repair rather than towards reproductive and anabolic activities.

Polymorphisms XRCC1-R399Q and XRCC3-T241M and the Risk of Breast Cancer at the Ontario Site of the Breast Cancer Family Registry

This study investigates the role of two nonsynonymous single nucleotide polymorphisms in DNA repair genes, X-ray repair cross-complementing group 1 (XRCC1)-R399Q and X-ray repair cross-complementing group 3 (XRCC3)-T241M, in breast cancer. Incident cases of invasive breast cancer in Caucasian women [n = 402, mean age = 45.7 (SD = 6.2) years] and female Caucasian controls [n = 402, mean age = 45.2 (6.5) years] frequency matched on 5-year age intervals were identified from the Ontario Familial Breast Cancer Registry. No evidence for a main effect of the XRCC1-R399Q genotype on breast cancer risk was observed. Estimates of risk for a family history (FH) of breast cancer compared with no FH differed by XRCC1-R399Q genotype (P value for interaction = 0.001). Homozygote XRCC1-399 R/R individuals and FH+ were at a 2.92-fold [95% confidence interval (95% CI) = 1.47–5.79] increased risk of disease compared with FH− individuals; the estimate of risk increased for R/Q heterozygotes with FH+ [odds ratio (OR) = 3.85, 95% CI = 1.94–7.65] but not for Q/Q homozygotes with FH+ (OR = 0.54, 95% CI = 0.20–1.47) compared with homozygous R/R and FH− individuals. A marginal positive association for XRCC3-241 M/M compared with T/T genotype was found (OR = 1.44, 95% CI = 0.94–2.19), but the heterozygous T/M was not associated with an increase in risk (OR = 0.96, 95% CI = 0.71–1.32). There was also some evidence for a combined effect of body mass index and XRCC3-T241M on estimates of risk. Our results suggest that these polymorphisms may influence breast cancer risk by modifying the effect of risk factors such as FH. There is a need for further study into the role of these polymorphisms as effect modifiers.

Loss of base excision repair in aging rat neurons and its restoration by DNA polymerase beta

Synthetic staggered oligodeoxynucleotide duplexes are formed by annealing a 5'-32P-labeled 14-mer with four different 21-mers. These duplexes have either a correct or mismatched base pair at 3'-end of the primer. With these model template primers the ability of neuronal extracts, obtained from rats of different ages, to extend the primer to the predicted length was tested. While the neuronal extracts of all ages were able to degrade the 14-mer to shorter lengths, extension of the primers in general and in particular, the mismatched, is achieved only feebly by the young and adult neuronal extracts and undetectable with old neuronal extracts. The possibility of restoring the lost activity by supplementing the neuronal extracts with pure DNA polymerases was examined. Of the three polymerases tested (calf thymus alpha polymerase, E. coli DNA polymerase I and rat liver DNA polymerase beta) only polymerase beta gave consistent and encouraging results although the extension was slow and distributive in nature and mismatched primers were extended much less efficiently than the correctly paired primer. However, significantly improved extension, including those of mismatched primers, was achieved by prior removal of mismatched bases in a preincubation with just the neuronal extracts (3'-5'exonuclease activity) followed by extension by the added polymerase beta and dNTPs in the presence of Mn(2+) instead of the usual Mg(2+). These results are taken to indicate that the activity of polymerase beta in brain cells is compromised with age and that this deficit can be corrected in vitro by the addition of pure recombinant rat liver polymerase beta under appropriate conditions.