DNA brain damage after stress in rats

Exploring the interplay between stress mediators and skin microbiota in shaping age-related hallmarks: A review

Psychological stress is a major contributing factor to several health problems (e.g., depression, cardiovascular disease). Around 35 % of the world's population suffers from it, including younger generations. Physiologically, stress manifests through neuroendocrine pathways (Hypothalamic-Pituitary-Adrenal (HPA) axis and Sympathetic-Adrenal-Medullary (SAM) system) which culminate in the production of stress mediators like cortisol, epinephrine and norepinephrine. Stress and its mediators have been associated to body aging, through molecular mechanisms such as telomere attrition, mitochondrial dysfunction, cellular senescence, chronic inflammation, and dysbiosis, among others. Regarding its impact in the skin, stress impacts its structural integrity and physiological function. Despite this review focusing on several hallmarks of aging, emphasis was placed on skin microbiota dysbiosis. In this line, several studies, comprising different age groups, demographic contexts and body sites, have reported skin microbiota alterations associated with aging, and some effects of stress mediators on skin microbiota have also been reviewed in this paper. From a different perspective, since it is not a "traditional" stress mediator, oxytocin, a cortisol antagonist, has been related to glucorticoids inhibition and to display positive effects on cellular aging. This hormone dysregulation has been associated to psychological issues such as depression, whereas its upregulation has been linked to positive social interaction.

Urinary levels of cortisol but not catecholamines are associated with those of 8-hydroxy-2'-deoxyguanosine in uncomplicated primary hypertension

OBJECTIVES

The relationships between stress hormones and oxidative DNA damage have not yet been explored in human hypertension. We investigated the associations of urinary levels of cortisol or catecholamines with those of 8-hydroxy-2'-deoxyguanosine, a marker of oxidative DNA damage in primary hypertension.

METHODS

Untreated 156 primary hypertensives without apparent cardiovascular diseases were entered into the study. Following blood sampling after an overnight fast, 24-h blood pressure monitoring and 24-h urinary sampling were performed simultaneously to determine 24-h averaged values for blood pressure and urinary levels of cortisol, catecholamines and 8-hydroxy-2'-deoxyguanosine.

RESULTS

Urinary cortisol significantly correlated positively with urinary 8-hydroxy-2'-deoxyguanosine in all studied participants (r = 0.334, P < 0.001). Contrary, either urinary adrenaline or urinary noradrenaline did not significantly correlate with urinary 8-hydroxy-2'-deoxyguanosine (r = 0.050, P = 0.553 or r = 0.063, P = 0.435). Additionally, the positive association of urinary cortisol with urinary 8-hydroxy-2'-deoxyguanosine remained highly significant after the adjustments for multiple confounders of oxidative stress such as age, gender, body mass index, smoking status, 24-h blood pressure, C-reactive protein and estimated glomerular filtration rate (partial r = 0.323, P < 0.001), although only approximately 10% of the variance in urinary cortisol was attributable to differences in urinary 8-OHdG (partial r2 = 0.104). Thus, our data indicate that cortisol but not catecholamines could at least partially contribute to the occurrence of oxidative DNA damage in primary hypertensives.

CONCLUSION

The present study suggested the possibility that the overactivation of hypothalamic-pituitary-adrenal axis rather than sympathoadrenal system could enhance oxidative stress and attendant DNA oxidation in uncomplicated primary hypertension.

Stress-induced biological aging: A review and guide for research priorities

Exposure to chronic adverse conditions, and the resultant activation of the neurobiological response cascade, has been associated with an increased risk of early onset of age-related disease and, recently, with an older biological age. This body of research has led to the hypothesis that exposure to stressful life experiences, when occurring repeatedly or over a prolonged period, may accelerate the rate at which the body ages. The mechanisms through which chronic psychosocial stress influences distinct biological aging pathways to alter rates of aging likely involve multiple layers in the physiological-molecular network. In this review, we integrate research using animal, human, and in vitro models to begin to delineate the distinct pathways through which chronic psychosocial stress may impact biological aging, as well as the neuroendocrine mediators (i.e., norepinephrine, epinephrine, and glucocorticoids) that may drive these effects. Findings highlight key connections between stress and aging, namely cellular metabolic activity, DNA damage, telomere length, cellular senescence, and inflammatory response patterns. We conclude with a guiding framework and conceptual model that outlines the most promising biological pathways by which chronic adverse conditions could accelerate aging and point to key missing gaps in knowledge where future research could best answer these pressing questions.

An evolutionary perspective on stress responses, damage and repair

Variation in stress responses has been investigated in relation to environmental factors, species ecology, life history and fitness. Moreover, mechanistic studies have unravelled molecular mechanisms of how acute and chronic stress responses cause physiological impacts ('damage'), and how this damage can be repaired. However, it is not yet understood how the fitness effects of damage and repair influence stress response evolution. Here we study the evolution of hormone levels as a function of stressor occurrence, damage and the efficiency of repair. We hypothesise that the evolution of stress responses depends on the fitness consequences of damage and the ability to repair that damage. To obtain some general insights, we model a simplified scenario in which an organism repeatedly encounters a stressor with a certain frequency and predictability (temporal autocorrelation). The organism can defend itself by mounting a stress response (elevated hormone level), but this causes damage that takes time to repair. We identify optimal strategies in this scenario and then investigate how those strategies respond to acute and chronic exposures to the stressor. We find that for higher repair rates, baseline and peak hormone levels are higher. This typically means that the organism experiences higher levels of damage, which it can afford because that damage is repaired more quickly, but for very high repair rates the damage does not build up. With increasing predictability of the stressor, stress responses are sustained for longer, because the animal expects the stressor to persist, and thus damage builds up. This can result in very high (and potentially fatal) levels of damage when organisms are exposed to chronic stressors to which they are not evolutionarily adapted. Overall, our results highlight that at least three factors need to be considered jointly to advance our understanding of how stress physiology has evolved: (i) temporal dynamics of stressor occurrence; (ii) relative mortality risk imposed by the stressor itself versus damage caused by the stress response; and (iii) the efficiency of repair mechanisms.

Chronic stress increases transcriptomic indicators of biological aging in mouse bone marrow leukocytes

Research with animals and humans has demonstrated that chronic stress exposure can impact key biological aging pathways such as inflammation and DNA damage, suggesting a mechanism through which stress may increase risk for age-related disease. However, it is less clear whether these effects extend to other hallmarks of the aging process, such as cellular senescence. Male SCID mice were exposed to 14 days of restraint stress, with (n ​= ​6) or without (n ​= ​10) propranolol administration, or a non-stress control condition (n ​= ​10). Normal femoral bone marrow leukocytes were isolated from engrafted leukemia cells that had been injected prior to the stressor, as the mice were also under a cancer challenge. We performed whole genome transcriptional profiling to assess indicators of biological aging: cell stress, DNA damage repair, cellular senescence markers p16^INK4a and p21, and the pro-inflammatory senescence-associated secretory phenotype (SASP). ANCOVAs that adjusted for tumor load and Fisher's pairwise comparisons revealed that stressed mice had enhanced p16^INK4a (p ​= ​.02) and p21 (p ​= ​.004), lower DNA damage repair (p ​< ​.001), and higher SASP (p ​= ​.03) gene expression than control mice. Stressed mice also showed up-regulated beta-adrenergic (CREB) and inflammatory (NF-кB, AP-1) and down-regulated cell stress (Nrf2) transcription factor activity relative to control mice (ps ​< ​.01). Propranolol reversed CREB and Nrf2 activity (ps ​< ​.03). Findings suggest that chronic stress exposure can impact several key biological aging pathways within bone marrow leukocytes and these effects may be partially mediated by sympathetic beta-adrenergic receptor activation.

DNA damage, salivary cortisol levels, and cognitive parameters in a nursing team

In a cross-sectional study of women in a nursing team at a university hospital in southern Brazil, we studied DNA damage, salivary cortisol levels, and cognition. DNA damage was measured in blood leukocytes with the comet assay and the micronucleus test. Salivary cortisol levels were determined upon waking, 30 min later, and at bedtime. Cognition was evaluated according to the Stroop, Digit span and Word span tests. Cortisol levels on waking up were associated negatively with the number of years the employee worked at the institution and positively with the DNA damage in comet assay. Cognitive scores were lower when the cortisol levels were low at awakening and high at bedtime; and were associated positively with educational level. Cortisol status may influence overall health as well as essential work skills, such as attention.

Neurobehavioral effects of vigabatrin and its ability to induce DNA damage in brain cells after acute treatment in rats

RATIONALE

Vigabatrin (VGB) is a drug indicated mostly for the treatment of spasms in childhood and West's syndrome patients. This drug inhibits irreversibly the enzyme GABA-transaminase (GABA-T), increasing GABA concentrations and enhancing GABAergic neurotransmission in the brain, which is known to induce behavioral changes.

OBJECTIVES

The aims of this study were to evaluate the effects of VGB in the short-term memory (STM), long-term memory (LTM), motivation, locomotion, and exploratory behavior tests and to detect deleterious or protective effects on DNA in target tissues of the drug.

METHODS

Male Wistar rats were treated with a single dose of VGB (100, 250, or 500 mg/kg) or saline solution before the inhibitory avoidance and open-field tasks. DNA damage was evaluated using the alkaline comet assay in peripheral blood, cerebral cortex, and hippocampus after behavioral testing.

RESULTS

There was no significant difference in the inhibitory avoidance task between the treated groups and the saline group. In all tested doses, VGB reduced the number of rearings in the open-field task. Besides, VGB 500 mg/kg affected locomotion, though it was not able to induce any DNA damage.

CONCLUSIONS

VGB did not affect STM and LTM, but the drug impaired the exploration and locomotion likely associated with its sedative effect. In addition, no DNA damage in cortex and hippocampus was detected after behavioral testing, when brain GABA levels are already increased.

Hydrogen peroxide-induced oxidative damage in peripheral blood lymphocytes from rats chronically treated with corticosterone: The protective effect of oxytocin treatment

Contemporary lifestyle is commonly associated with chronic stress, an environmental factor contributing to development of various psychological and somatic disorders. Increased levels of glucocorticoids, observed in the chronic stress, induce the production of reactive oxygen species leading to genotoxicity. The aim of this study was to investigate whether chronic administration of oxytocin (OXY) 10 IU/400 μL/day, s.c., for 14 days, a hormone presumed to exert antioxidant effect, may prevent DNA damage in the comet assay of peripheral blood lymphocytes of Wistar rats treated chronically with corticosterone (CORT) 100 mg/L ad libitum, per os, for 21 days, as well as, to influence some plasma oxidative stress parameters, i.e. levels of total lipid hydroperoxide (LOOH), and malondialdehyde (MDA), and the activity of antioxidative enzyme superoxide dismutase (SOD). Even though there was no reduction in overall number of damaged cells after oxytocin treatment only, the marked increase in total comet score (TCS) after incubation with H2O2 in CORT group compared to controls, was absent in the CORT + OXY experimental group. Furthermore, significant decrease of highly damaged cells compared to corticosterone group was noted. Chronic oxytocin administration thus protected lymphocytes from high intensity damage that leads to cellular death. In addition, treatment with OXY along with CORT, significantly decreased concentration of LOOH in plasma, and increased SOD compared to CORT treatment only. This finding corresponds well with current reports on beneficial effects of OXY in conditions of HPA axis hyperactivity, and supports the hypothesis of OXY-mediated antioxidant action.

DNA Damage in Major Psychiatric Diseases

Human cells are exposed to exogenous insults and continuous production of different metabolites. These insults and unwanted metabolic products might interfere with the stability of genomic DNA. Recently, many studies have demonstrated that different psychiatric disorders show substantially high levels of oxidative DNA damage in the brain accompanied with morphological and functional alterations. It reveals that damaged genomic DNA may contribute to the pathophysiology of these mental illnesses. In this article, we review the roles of oxidative damage and reduced antioxidant ability in some vastly studied psychiatric disorders and emphasize the inclusion of treatment options involving DNA repair. In addition, while most currently used antidepressants are based on the manipulation of the neurotransmitter regulation in managing different mental abnormalities, they are able to prevent or reverse neurotoxin-induced DNA damage. Therefore, it may be plausible to target on genomic DNA alterations for psychiatric therapies, which is of pivotal importance for future antipsychiatric drug development.

Brain DNA damage and behavioral changes after repeated intermittent acute ethanol withdrawal by young rats

RATIONALE

Alcohol addiction causes severe problems, and its deprivation may potentiate symptoms such as anxiety. Furthermore, ethanol is a neurotoxic agent that induces degeneration and the consequences underlying alcohol-mediated brain damage remain unclear.

OBJECTIVES

This study assessed the behavioral changes during acute ethanol withdrawal periods and determined the levels of DNA damage and reactive oxygen species (ROS) in multiple brain areas.

METHODS

Male Wistar rats were subjected to an oral ethanol self-administration procedure with a forced diet where they were offered 8% (v/v) ethanol solution for 21 days followed by five repeated 24-h cycles alternating between ethanol withdrawal and re-exposure. Control animals received an isocaloric control diet without ethanol. Behavioral changes were analyzed on ethanol withdrawal days in the open-field (OF) and elevated plus-maze (EPM) tests within the first 6 h of ethanol deprivation. The pre-frontal cortex, hypothalamus, striatum, hippocampus, and cerebellum were dissected for alkaline and neutral comet assays and for dichlorofluorescein ROS testing.

RESULTS

The repeated intermittent ethanol access enhanced solution intake and alcohol-seeking behavior. Decreased exploratory activity was observed in the OF test, and the animals stretched less in the EPM test. DNA single-strand breaks and ROS production were significantly higher in all structures evaluated in the ethanol-treated rats compared with controls.

CONCLUSIONS

The animal model of repeated intermittent ethanol access induced behavioral changes in rats, and this ethanol exposure model induced an increase in DNA single-strand breaks and ROS production in all brain areas. Our results suggest that these brain damages may influence future behaviors.

Anxious phenotypes plus environmental stressors are related to brain DNA damage and changes in NMDA receptor subunits and glutamate uptake

This study aimed at investigating the effects of chronic mild stress on DNA damage, NMDA receptor subunits and glutamate transport levels in the brains of rats with an anxious phenotype, which were selected to represent both the high-freezing (CHF) and low-freezing (CLF) lines. The anxious phenotype induced DNA damage in the hippocampus, amygdala and nucleus accumbens (NAc). CHF rats subjected to chronic stress presented a more pronounced DNA damage in the hippocampus and NAc. NMDAR1 were increased in the prefrontal cortex (PC), hippocampus and amygdala of CHF, and decreased in the hippocampus, amygdala and NAc of CHF stressed. NMDAR2A were decreased in the amygdala of the CHF and stressed; and increased in CHF stressed. NMDRA2A in the NAc was increased after stress, and decreased in the CLF. NMDAR2B were increased in the hippocampus of CLF and CHF. In the amygdala, there was a decrease in the NMDAR2B for stress in the CLF and CHF. NMDAR2B in the NAc were decreased for stress and increased in the CHF; in the PC NMDAR2B increased in the CHF. EAAT1 increased in the PC of CLF+stress. In the hippocampus, EAAT1 decreased in all groups. In the amygdala, EAAT1 decreased in the CLF+stress and CHF. EAAT2 were decreased in the PC for stress, and increased in CHF+control. In the hippocampus, the EAAT2 were increased for the CLF and decreased in the CLF+stress. In the amygdala, there was a decrease in the EATT2 in the CLF+stress and CHF. These findings suggest that an anxious phenotype plus stress may induce a more pronounced DNA damage, and promote more alterations in the glutamatergic system. These findings may help to explain, at least in part, the common point of the mechanisms involved with the pathophysiology of depression and anxiety.

Spousal loss and cognitive function in later life: a 25-year follow-up in the AGES-Reykjavik study

The aim of this study was to investigate the associations between loss of a life partner and the development of dementia and decline in cognitive function in later life. We used an Icelandic cohort of 4,370 participants in the Age, Gene/Environment Susceptibility-Reykjavik Study who were living as married in 1978 (born in 1907-1935) and were either still married (unexposed cohort) or widowed (exposed cohort) at follow-up (in 2002-2006). We ascertained history of marital status and spouse's death by record linkage to the Registry of the Total Population, Statistics Iceland. The outcome measures were as follows: 1) dementia and mild cognitive impairment; and 2) memory, speed of processing, and executive function. During the observation period, 3,007 individuals remained married and 1,363 lost a spouse through death. We did not find any significant associations between loss of a spouse and our outcome variables, except that widowed women had poorer executive function (mean = -0.08) during the first 2 years after their husbands' deaths compared with still-married women (mean = 0.09). Our findings do not support the notion that the risk of dementia is increased following the loss of a spouse, yet women demonstrate a seemingly temporary decline in executive function following the death of a partner.

Forced swim test induces divergent global transcriptomic alterations in the hippocampus of high versus low novelty-seeker rats

BACKGROUND

Many neuropsychiatric disorders, including stress-related mood disorders, are complex multi-parametric syndromes. Susceptibility to stress and depression is individually different. The best animal model of individual differences that can be used to study the neurobiology of affect regards spontaneous reactions to novelty. Experimentally, when naive rats are exposed to the stress of a novel environment, they display a highly variable exploratory activity and are classified as high or low responders (HR or LR, respectively). Importantly, HR and LR rats do not seem to exhibit a substantial differentiation in relation to their 'depressive-like' status in the forced swim test (FST), a widely used animal model of 'behavioral despair'. In the present study, we investigated whether FST exposure would be accompanied by phenotype-dependent differences in hippocampal gene expression in HR and LR rats.

RESULTS

HR and LR rats present a distinct behavioral pattern in the pre-test session but develop comparable depressive-like status in the second FST session. At 24 h following the second FST session, HR and LR rats (stressed and unstressed controls) were sacrificed and hippocampal samples were independently analyzed on whole rat genome Illumina arrays. Functional analysis into pathways and networks was performed using Ingenuity Pathway Analysis (IPA) software. Notably, hippocampal gene expression signatures between HR and LR rats were markedly divergent, despite their comparable depressive-like status in the FST. These molecular differences are reflected in both the extent of transcriptional remodeling (number of significantly changed genes) and the types of molecular pathways affected following FST exposure. A markedly higher number of genes (i.e., 2.28-fold) were statistically significantly changed following FST in LR rats, as compared to their HR counterparts. Notably, genes associated with neurogenesis and synaptic plasticity were induced in the hippocampus of LR rats in response to FST, whereas in HR rats, FST induced pathways directly or indirectly associated with induction of apoptotic mechanisms.

CONCLUSIONS

The markedly divergent gene expression signatures exposed herein support the notion that the hippocampus of HR and LR rats undergoes distinct transcriptional remodeling in response to the same stress regimen, thus yielding a different FST-related 'endophenotype', despite the seemingly similar depressive-like phenotype.

Acute stress further decreases the effect of ovariectomy on immobility behavior and hippocampal cell survival in rats

Most studies relating experimental depression and neurogenesis use mainly male rodents subjected to models of chronic stress. The forced swimming test (FST) is a widely utilized model of acute stress, but its effects on the neurogenic process in the hippocampus using females in different endocrine conditions has not been explored. The aim of this study was to evaluate the cell proliferation and early-, short- and long-lasting effects of forced swimming (FS) on adult hippocampal neurogenesis in rats in two endocrine conditions: proestrous and ovariectomized. To determine cell proliferation we used the endogenous marker Ki67. Cell survival was established with the thymidine analog, BrdU (75mg/kg, 2/12, i.p.), which was administered before FS to proestrous and ovariectomized rats. FS increased immobility and corticosterone levels in OVX but not in rats in proestrus. In addition, FS did not affect cell proliferation but significantly decreased the number of BrdU-labeled cells at 2h only in OVX-rats, an effect that remained for 3 and 14 days after FS. Data are discussed taking into consideration the relationship between gonadal and adrenal hormones in adult hippocampal neurogenesis in adult females. Our data also support the use of FS as a model for studying neurogenesis.

Chronic restraint stress in rats causes sustained increase in urinary corticosterone excretion without affecting cerebral or systemic oxidatively generated DNA/RNA damage

Increased oxidatively generated damage to nucleic acids (DNA/RNA) may be a common mechanism underlying accelerated aging in psychological stress states and mental disorders. In the present study, we measured the urinary excretion of corticosterone and markers of systemic oxidative stress on nucleic acids, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanosine (8-oxoGuo), respectively, in rats subjected to chronic restraint stress. To reliably collect 24h urine samples, the full 3-week restraint stress paradigm was performed in metabolism cages. We further determined frontal cortex and hippocampal levels of oxidatively generated nuclear DNA damage, as measured by oxoguanine DNA glycosylase and formamidopyrimidine DNA glycosylase sensitive sites detected by the comet assay, as well as the expression of genes involved in DNA repair (Ogg1 and Nudt1) and inflammation (Ccl2 and Tnf). The metabolism cage housing in itself did not significantly influence a range of biological stress markers. In the restraint stress group, there was a sustained 2.5 fold increase in 24h corticosterone excretion from day 2 after stress initiation. However, neither whole-body nor cerebral measures of nucleic acid damage from oxidation were affected by stress. In contrast, cerebral DNA repair enzymes exhibited a general trend towards an induction, which was significant for hippocampal Nudt1. The results and their implications for stress sensitivity and resilience are discussed.