DNA damage: air-breaks?

Cells deficient in repairing DNA double-strand breaks have an increased level of spontaneous chromosomal aberrations. Modulating the level of molecular oxygen and its reactive metabolites demonstrates that oxygen metabolism is a major source of genomic instability.     

Does hypothyroidism augment sun-induced skin damage?

Objectives: We investigated the mutual effects of overt hypothyroidism and prolonged sunlight exposure on free radical accumulation and oxidative skin damage.

Methods: Free radical accumulation was evaluated by monitoring the transformation of 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) into MTT-formazan. The pro-oxidant enzymes xanthine oxidase (XO) and NADPH-diaphorase were measured in the skin. XO activity was estimated based on the yield of uric acid, while NADPH-diaphorase reactivity was monitored histochemically as an indirect marker of nitric oxide synthase and nitric oxide activity. Cellular damage was determined by malondialdehyde formation, a marker for lipid peroxidation.

Results: In the skin of both euthyroid and hypothyroid animals, solar simulated ultraviolet irradiance increased the activity of XO and the NADPHdiaphorase reactivity as a protective response to formation of free radicals, such as reactive oxygen or nitrogen species. These pro-oxidant enzymes diminished in hypothyroid rats. Accumulation of the same amount of free radicals led to similar peroxidation in both hypothyroid and irradiated euthyroid rats. Hypothyroid skin after UV-exposure showed even greater lipid peroxidation.

Discussion: The hypothyroid state could be a risk factor for enhanced oxidative skin damage in chronic photo-exposed skin due to oxidative stress. The lipid peroxidation is one of the major pathways by which photo-oxidative stress promotes photocarcinogenesis and photo-aging.     

Does terbutaline damage the developing heart?

BACKGROUND: β₂‐Adrenoceptor (βAR) agonists, such as terbutaline, are widely used to arrest preterm labor. They also cross the placenta where they stimulate receptors in fetal tissues, which in turn use βAR input for trophic control of cell replication and differentiation. METHODS: As rats are altricial, we administered terbutaline in two different postnatal exposure periods (10 mg/kg given daily on Days 2–5 or 11–14). RESULTS: Hearts were examined twenty‐four hours after the last dose and on postnatal day 30 for cardiac damage. Neither treatment paradigm caused an increase in cardiac abnormalities compared to controls but quantitative analysis of the number of nuclei indicated reductions in females. CONCLUSIONS: These findings do not support earlier case reports of outright myocardial necrosis after terbutaline tocolysis in human infants. Nevertheless, the significant statistical association between terbutaline and cardiac anomalies in epidemiological studies suggest that terbutaline may sensitize the developing heart to other insults that affect development. Birth Defects Res B 68:449–455, 2003. © 2003 Wiley‐Liss, Inc.     

Can nucleotides prevent Cu-induced oxidative damage?

Cu-induced oxidative damage is associated with cancer, diabetes, neurodegenerative and age related diseases. The quest for Cu-chelators as potential antioxidants spans the past decades. Yet, biocompatible Cu-chelators that do not alter the normal metal-ion homeostasis are still lacking. Here, we explored the potential of natural and synthetic nucleotides and inorganic phosphates as inhibitors of the Cu(I)/(II)-induced ()OH formation via either the Fenton or Haber-Weiss mechanisms. For this purpose, we studied by ESR the modulation of Cu-induced ()OH production, from the decomposition of H(2)O(2), by nucleotides and phosphates. ATP inhibited both Cu(I) and Cu(II) catalyzed reactions (IC(50) 0.11 and 0.04mM, respectively). Likewise, adenosine 5'-beta,gamma-methylene triphosphate (AMP-PCP), adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S), ADP and tripolyphosphate were identified as good inhibitors. However, AMP and adenosine were poor inhibitors in the Cu(I)-H(2)O(2) system, IC(50) ca. 1.2mM, and radical enhancers in the Cu(II)-H(2)O(2) system. The best antioxidant was adenosine 5'-[beta,gamma-imino] triphosphate (AMP-PNP) (IC(50) 0.05mM at Cu(I)-H(2)O(2) system) which was 15 times more active than the known antioxidant Trolox. ATP and analogues inhibit Cu-induced ()OH formation through an ion chelation rather than a scavenging mechanism. Two phosphate groups are required for making active Fenton-reaction inhibitors. Nucleotides and phosphates triggered a biphasic modulation of the Haber-Weiss reaction, but a monophasic inhibition of the Fenton reaction. We conclude that nucleotides at sub mM concentrations can prevent Cu-induced OH radical formation from H(2)O(2), and hence may possibly prevent oxidative damage.     

Does vitamin D protect against DNA damage?

Vitamin D is a secosteroid best known for its role in maintaining bone and muscle health. Adequate levels of vitamin D may also be beneficial in maintaining DNA integrity. This role of vitamin D can be divided into a primary function that prevents damage from DNA and a secondary function that regulates the growth rate of cells. The potential for vitamin D to reduce oxidative damage to DNA in a human has been suggested by clinical trial where vitamin D supplementation reduced 8-hydroxy-2'-deoxyguanosine, a marker of oxidative damage, in colorectal epithelial crypt cells. Studies in animal models and in different cell types have also shown marked reduction in oxidative stress damage and chromosomal aberrations, prevention of telomere shortening and inhibition of telomerase activity following treatment with vitamin D. The secondary function of vitamin D in preventing DNA damage includes regulation of the poly-ADP-ribose polymerase activity in the DNA damage response pathway involved in the detection of DNA lesions. It is also able to regulate the cell cycle to prevent the propagation of damaged DNA, and to regulate apoptosis to promote cell death. Vitamin D may contribute to prevention of human colorectal cancer, though there is little evidence to suggest that prevention of DNA damage mediates this effect, if real. Very limited human data mean that the intake of vitamin D required to minimise DNA damage remains uncertain.     

Aging by epigenetics--a consequence of chromatin damage?

Chromatin structure is not fixed. Instead, chromatin is dynamic and is subject to extensive developmental and age-associated remodeling. In some cases, this remodeling appears to counter the aging and age-associated diseases, such as cancer, and extend organismal lifespan. However, stochastic non-deterministic changes in chromatin structure might, over time, also contribute to the break down of nuclear, cell and tissue function, and consequently aging and age-associated diseases.     

Cytokine-mediated β-cell damage in PARP-1-deficient islets

Poly(ADP)-ribose polymerase (PARP) is an abundant nuclear protein that is activated by DNA damage; once active, it modifies nuclear proteins through attachment of poly(ADP)-ribose units derived from β-nicotinamide adenine dinucleotide (NAD(+)). In mice, the deletion of PARP-1 attenuates tissue injury in a number of animal models of human disease, including streptozotocin-induced diabetes. Also, inflammatory cell signaling and inflammatory gene expression are attenuated in macrophages isolated from endotoxin-treated PARP-1-deficient mice. In this study, the effects of PARP-1 deletion on cytokine-mediated β-cell damage and macrophage activation were evaluated. There are no defects in inflammatory mediator signaling or inflammatory gene expression in macrophages and islets isolated from PARP-1-deficient mice. While PARP-1 deficiency protects islets against cytokine-induced islet cell death as measured by biochemical assays of membrane polarization, the genetic absence of PARP-1 does not effect cytokine-induced inhibition of insulin secretion or cytokine-induced DNA damage in islets. While PARP-1 deficiency appears to provide protection from cell death, it fails to provide protection against the inhibitory actions of cytokines on insulin secretion or the damaging actions on islet DNA integrity.     

Are glutathione S transferases involved in DNA damage signalling? Interactions with DNA damage and repair revealed from molecular epidemiology studies

Glutathione S-transferases (GSTs) are members of a multigene family of isoenzymes that are important in the control of oxidative stress and in phase II metabolism. Acting non-enzymically, GSTs can modulate signalling pathways of cell proliferation, cell differentiation and apoptosis. Using a molecular epidemiology approach, we have investigated a potential involvement of GSTs in DNA damage processing, specifically the modulation of DNA repair in a group of 388 healthy adult volunteers; 239 with at least 5 years of occupational exposure to asbestos, stone wool or glass fibre, and 149 reference subjects. We measured DNA damage in lymphocytes using the comet assay (alkaline single cell gel electrophoresis): strand breaks (SBs) and alkali-labile sites, oxidised pyrimidines with endonuclease III, and oxidised purines with formamidopyrimidine DNA glycosylase. We also measured GST activity in erythrocytes, and the capacity for base excision repair (BER) in a lymphocyte extract. Polymorphisms in genes encoding three GST isoenzymes were determined, namely deletion of GSTM1 and GSTT1 and single nucleotide polymorphism Ile105Val in GSTP1. Consumption of vegetables and wine correlated negatively with DNA damage and modulated BER. GST activity correlated with oxidised bases and with BER capacity, and differed depending on polymorphisms in GSTP1, GSTT1 and GSTM1. A significantly lower BER rate was associated with the homozygous GSTT1 deletion in all asbestos site subjects and in the corresponding reference group. Multifactorial analysis revealed effects of sex and exposure in GSTP1 Ile/Val heterozygotes but not in Ile/Ile homozygotes. These variants affected also SBs levels, mainly by interactions of GSTP1 genotype with exposure, with sex, and with smoking habit; and by an interaction between sex and smoking. Our results show that GST polymorphisms and GST activity can apparently influence DNA stability and repair of oxidised bases, suggesting a potential new role for these proteins in DNA damage processing via DNA damage signalling.     

Mitochondria-targeted antioxidants prevent TNFα-induced endothelial cell damage

Increased serum level of tumor necrosis factor α (TNFα) causes endothelial dysfunction and leads to serious vascular pathologies. TNFα signaling is known to involve reactive oxygen species (ROS). Using mitochondria-targeted antioxidant SkQR1, we studied the role of mitochondrial ROS in TNFα-induced apoptosis of human endothelial cell line EAhy926. We found that 0.2 nM SkQR1 prevents TNFα-induced apoptosis. SkQR1 has no influence on TNFα-dependent proteolytic activation of caspase-8 and Bid, but it inhibits cytochrome c release from mitochondria and cleavage of caspase-3 and its substrate PARP. SkQ analogs lacking the antioxidant moieties do not prevent TNFα-induced apoptosis. The antiapoptotic action of SkQR1 may be related to other observations made in these experiments, namely SkQR1-induced increase in Bcl-2 and corresponding decrease in Bax as well as p53. These results indicate that mitochondrial ROS production is involved in TNFα-initiated endothelial cell death, and they suggest the potential of mitochondria-targeted antioxidants as vasoprotectors.     

Melanogenesis: a photoprotective response to DNA damage?

Exposure to ultra violet radiation (UVR) is associated with significant long-term deleterious effects such as skin cancer. A well-recognised short-term consequence of UVR is increased skin pigmentation. Pigmentation, whether constitutive or facultative, has widely been viewed as photoprotective, largely because darkly pigmented skin is at a lower risk of photocarcinogenesis than fair skin. Research is increasingly suggesting that the relationship between pigmentation and photoprotection may be far more complex than previously assumed. For example, photoprotection against erythema and DNA damage has been shown to be independent of level of induced pigmentation in human white skin types. Growing evidence now suggests that UVR induced DNA photodamage, and its repair is one of the signals that stimulates melanogenesis and studies suggest that repeated exposure in skin type IV results in faster DNA repair in comparison to skin type II. These findings suggest that tanning may be a measure of inducible DNA repair capacity, and it is this rather than pigment per se which results in the lower incidence skin cancer observed in darker skinned individuals. This evokes the notion that epidermal pigmentation may in fact be the mammalian equivalent of a bacterial SOS response. Skin colour is one of most conspicuous ways in which humans vary yet the function of melanin remains controversial. Greater understanding of the role of pigmentation in skin is vital if one is to be able to give accurate advice to the general public about both the population at risk of skin carcinogenesis and also public perceptions of a tan as being healthy.     

Immunoglobulin-like domains on bacteriophage: weapons of modest damage?

Recent work has shown that Immunoglobulin-like (Ig-like) domains occur frequently on the surface of tailed dsDNA bacteriophages. Several of these Ig-like domains are added to bacteriophage structural proteins via programmed ribosomal frameshifts, and their evolutionary patterns suggest that they can be exchanged by horizontal transfer, independently of the protein to which they are attached. We propose that Ig-like domains on phages interact with carbohydrates on the cell surface and facilitate phage adsorption. Furthermore, Ig-like domains appear to be one of a number of conserved domains displayed on phage surfaces that serve to increase infectivity by binding to or degrading polysaccharides.     

Do quiescent human peripheral lymphocytes repair radiation-induced chromosome damage?

Peripheral blood samples from seven healthy donors were exposed to 2 Gy of (60)Co gamma rays. Lymphocyte cultures were prepared from the samples and stimulated to proliferate either immediately after the exposure or after 1, 2 or 4 h. No significant differences were found between the frequencies of chromosome aberrations (breaks or exchange) observed in lymphocytes stimulated after different postirradiation periods. We conclude that unstimulated lymphocytes do not undergo significant levels of recovery from potentially lethal damage at the chromosomal level.     

A special issue on DNA damage responses and genome maintenance

There is nothing more fundamental than the genome for the existence and maintenance of all living beings. The importance of the genome is increasingly appreciated as recent discoveries have revealed that changes in the human genome, regardless of being inherited or induced, can result in diseases that either significantly shorten lives （as seen in cancer） or dramatically affect the quality of lives （often seen in neurodegenerative diseases）. Therefore, maintaining genome integrity is critical for not only the continuation of a species in evolution （although mutations may be occasionally beneficial during evolution） but also for longevity and general health.     

α-Methylspermidine protects against carbon tetrachloride-induced hepatic and pancreatic damage

The role of polyamines in carbon tetrachloride (CCl₄)-induced organ injury was studied in syngenic rats and transgenic rats with activated polyamine catabolism. In syngenic rats, administration of CCl₄ resulted in the induction of hepatic spermidine/spermine N ¹-acetyltransferase (SSAT), accumulation of putrescine, reduction in spermine level and appearance of moderate hepatic injury within 24 h. Upon treatment with CCl₄, transgenic rats overexpressing SSAT displayed induction of both hepatic and pancreatic SSAT, with subsequent accumulation of putrescine and decrease of both spermidine and spermine pools. Administration of CCl₄ in SSAT transgenic rats induced not only massive hepatic injury, but also severe acute necrotizing pancreatitis. Pretreatment of the animals with catabolically stable functional polyamine mimetic, α-methylspermidine (MeSpd) prevented pancreatic and hepatic injury in SSAT rats and markedly reduced liver damage in syngenic animals. As assessed by immunostaining of proliferating cell nuclear antigen, MeSpd increased the amount of regenerating hepatocytes in both genotypes. These results show that CCl₄ induces hepatic and pancreatic polyamine catabolism, and the extent of organ damage correlates with the degree of polyamine depletion. Furthermore, MeSpd protects against CCl₄-induced hepatic and pancreatic damage and promotes tissue regeneration.     

Can antioxidant vitamins materially reduce oxidative damage in humans?

Endogenous oxidative damage to proteins, lipids, and DNA is thought to be an important etiologic factor in aging and the development of chronic diseases such as cancer, atherosclerosis, and cataract formation. The pathology associated with these diseases is likely to occur only after the production of reactive oxygen species has exceeded the body's or cell's capacity to protect itself and effectively repair oxidative damage. Vitamin C, vitamin E, and beta-carotene, often referred to as "antioxidant vitamins," have been suggested to limit oxidative damage in humans, thereby lowering the risk of certain chronic diseases. However, epidemiological studies and clinical trials examining the efficacy of antioxidant vitamins, either individually or in combination, to affect disease outcome rarely address possible underlying mechanisms. Thus, in these studies it is often assumed that antioxidant vitamins act by lowering oxidative damage, but evidence in support of this contention is not provided. Therefore, in this review, we examine the scientific evidence that supplementation of humans with vitamin C, vitamin E, or beta-carotene lowers in vivo oxidative damage to lipids, proteins, or DNA based on the measurement of oxidative biomarkers, not disease outcome. With the only exception of supplemental vitamin E, and possibly vitamin C, being able to significantly lower lipid oxidative damage in both smokers and nonsmokers, the current evidence is insufficient to conclude that antioxidant vitamin supplementation materially reduces oxidative damage in humans.     

Amyloid β-induced erythrocytic damage and its attenuation by carotenoids

The presence of amyloid β-peptide (Aβ) in human blood has recently been established, and it has been hypothesized that Aβ readily contacts red blood cells (RBC) and oxidatively impairs RBC functions. In this study, we conducted in vitro and in vivo studies, which provide evidence that Aβ induces oxidative injury to RBC by binding to them, causing RBC phospholipid peroxidation and diminishing RBC endogenous carotenoids, especially xanthophylls. This type of damage is likely to injure the vasculature, potentially reducing oxygen delivery to the brain and facilitating Alzheimer's disease (AD). As a preventive strategy, because the Aβ-induced RBC damage could be attenuated by treatment of RBC with xanthophylls, we suggest that xanthophylls may contribute to the prevention of AD.     

N-acetyl-cysteine: protective agent or promoter of gastric damage?

N-acetyl-cysteine (NAC), when given orally, has been shown to prevent gastric damage induced by ethanol, but when administered intraperitoneally, it appears to potentiate such damage. In an effort to resolve these seemingly discordant findings, fasted rats (six per group) received 1 ml of saline or 20% NAC orally or intraperitoneally (ip). Two hours or 15 min later, they received 1 ml of 100% ethanol orally. At sacrifice 5 min later, rats receiving oral pretreatment with 20% NAC at both 15 and 120 min prior to ethanol exposure demonstrated a significant reduction in the magnitude of gastric injury when compared with saline controls. In contrast, actual promotion of ethanol damage was noted when NAC was given intraperitoneally, but was more pronounced when NAC was administered 15 min prior to exposing the mucosa to 100% ethanol. In all animals receiving intraperitoneal NAC, large amounts of peritoneal fluid (4-6 ml/rat) were recovered at the time of sacrifice, most of which occurred within 15 min of NAC administration; these more pronounced peritoneal effects at 15 min after NAC correlated with the more severe injury from ethanol at this time period compared to 120 min after intraperitoneal NAC. Saline controls had no peritoneal fluid. Mucosal glutathione (GSH) levels generally paralleled these results in that a significant decrease in tissue GSH occurred at 15 min following intraperitoneal NAC when compared with controls; at 120 min after intraperitoneal NAC, GSH levels were similar to control values. Additional experiments demonstrated that within 15 min following NAC administration, systemic blood pressure dropped by approximately 20% and basically remained unchanged over the next 2 hr; intraperitoneal saline had no sustained adverse effects on blood pressure. It was concluded that the inability of NAC to prevent ethanol injury when given intraperitoneally in contrast to orally is related to the drop in blood pressure secondary to NAC's peritoneal irritant effects, which presumably altered gastric mucosal blood flow, thus obivating its ability to prevent ethanol damage under these conditions. Furthermore, the decreased levels in mucosal GSH following the hypotension induced by intraperitoneal NAC suggest that perturbations in GSH metabolism may also have contributed to the decreased resistance to ethanol injury.