Eckol inhibits ultraviolet B-induced cell damage in human keratinocytes via a decrease in oxidative stress

In previous reports, the antioxidant effects of eckol were shown to protect cells against hydrogen peroxide- and gamma ray-induced oxidative stress. In this study, the role of eckol in protecting human skin keratinocytes (HaCaT) against UVB-induced oxidative cell damage was investigated. Also, triphlorethol-A, one of the chemical components in Ecklonia cava, and quercetin a well known antioxidant, were compared with eckol in terms of antioxidant activity based on chemical structure. Eckol decreased UVB-induced intracellular reactive oxygen species (ROS), decreased injury to cellular components resulting from UVB-induced oxidative stress, and restored cell viability. In addition, eckol reduced UVB-induced apoptosis by inhibiting the disruption of mitochondrial membranes. These results suggest that eckol protects human keratinocytes against UVB-induced oxidative stress by scavenging ROS, thereby lessening injury to cellular components.     

Gender differences in UV-induced skin inflammation,skin carcinogenesis and systemic damage

Ultraviolet (UV) radiation-induced chronic inflammation contributes to all stages of skin tumor development. In addition, gender plays an important role in inflammatory diseases or cancer. In this study, histopathology changes, hematology, oxidative stress and inflammatory response were used to evaluate sex differences in UV-induced chronic inflammation-associated cancer development. The results showed that the male and female mice had photoaging damage at the 9th week. However, skin tumors only appeared in male mice at 31st week. Furthermore, UV increased ROS production, p65, p-p65, IL-6 and TNF-α protein expressions in skin, and these factors elevated more in male mouse model. Hematology results showed that the parameters of blood systemic inflammation were changed in different degrees in model groups, while the pathological results showed inflammatory cell infiltration in the internal organs of both model groups in varying degrees. These results indicate that there are gender differences in UV-induced skin inflammation, carcinogenesis and systemic damage. Moreover, male mice are more sensitive to UV irradiation, which may be responsible to greater oxidative stress and inflammatory damage.     

姜黄素对长波紫外线所致DNA损伤的拮抗作用

目的　观察长波紫外线引起人表皮样癌细胞 DNA链断裂损伤的情况 ,以及姜黄素对这种损伤的拮抗作用。方法　用长波紫外线照射细胞 ,用单细胞凝胶电泳法检测 DNA损伤。结果　长波紫外线剂量依赖性地诱发表皮细胞的 DNA链断裂损伤 ,损伤的高峰出现在照射后 1h。而姜黄素可以拮抗长波紫外线引起的DNA链断裂 ,表现为彗星细胞百分比的降低和彗星尾巴长度的缩短 ,并有量效关系。结论　姜黄素可以预防长波紫外线照射引起的皮肤细胞 DNA链断裂损伤。     

Solidagenone from Solidago chilensis Meyen inhibits skin inflammation in experimental models

Solidagenone (SOL) is a labdane‐type diterpenoid found in Solidago chilensis, a plant traditionally used to treat skin diseases, kidney pain and ovarian inflammation. In this study, the topical anti‐inflammatory activity of SOL was evaluated using in vivo and in silico assays. Croton oil‐, arachidonic acid (AA)‐ and phenol‐induced ear oedema mouse models were applied in the in vivo studies. Myeloperoxidase (MPO) and N‐acetyl‐β‐D‐glucosaminidase (NAG) activities and tumour necrosis factor alpha (TNF‐α), interleukin‐6 (IL‐6) and nitric oxide (NO) levels were determined, as well as histopathological analyses were conducted. Interaction profiles between SOL and cyclooxygenase‐1 (COX‐1), cyclooxygenase‐2 (COX‐2), glucocorticoid receptor, estradiol‐17‐β‐dehydrogenase and prostaglandin‐E(2)‐9‐reductase were established using molecular docking. SOL significantly inhibited croton oil‐, AA‐ and phenol‐induced ear oedema (P < .001) at doses of 0.1, 0.5 and 1.0 mg/ear. The MPO and NAG activities and TNF‐α, IL‐6 and NO levels were decreased (P < .001). The histopathological data revealed that inflammatory parameters (oedema thickness, leucocyte infiltration and vasodilatation) were reduced by treatment with SOL at doses of 0.1, 0.5 and 1.0 mg/ear. The docking study showed that SOL interacts with COX‐1 and prostaglandin‐E(2)‐9‐reductase through hydrogen bonding, inhibiting these enzymes. These results indicate that SOL may be a promising compound for the treatment of cutaneous inflammatory disorders and has potential as a topical anti‐inflammatory agent.     

Paeoniflorin inhibits skin lesions in imiquimod-induced psoriasis-like mice by downregulating inflammation

Psoriasis is a common chronic immune-mediated inflammatory disease. It is well known that macrophages, neutrophils and T-helper 1 (Th1)/T-helper 17 (Th17) cells play important roles in skin lesions by provoking inflammation. Paeoniflorin (PF) is the major effective component extracted from the root of Paeonia lactiflora, which has been widely used in China to treat inflammatory and autoimmune diseases, including psoriasis. Although PF shows a clinical therapeutic effect on psoriasis patients, how PF affects infiltrated immune cells in psoriasis skin lesions is still unknown. In this study, using a generated imiquimod (IMQ)-induced psoriasis-like mouse model, we found that PF ameliorates inflammation and skin lesions. Subsequent analyses showed that PF decreases the number of F4/80⁺CD68⁺ macrophages and their related cytokine production (TNF-α, IL-1β, IL-6, IL-12 and inducible nitric oxide synthase (iNOS)) in the skin of IMQ-challenged mice. Moreover, PF suppresses the number of CD11b⁺Gr-1⁺ neutrophils and the expression of macrophage inflammatory protein-2 (MIP-2; a counterpart of human IL-8, which is responsible for the recruitment of neutrophils in mice). Finally, PF also down-regulates Th1- and Th17-related cytokine expression. Therefore, our new findings reveal that PF alleviates psoriatic skin lesions by inhibiting inflammation, which provides new insights into the immunomodulatory effect of PF in psoriasis treatment.     

Jatropha curcas leaf and bark fractions protect against ultraviolet radiation-B induced DNA damage in human peripheral blood lymphocytes

The present study is conducted to investigate the antioxidant potential of Jatropha curcas root bark extract (RB4 fraction) and leaf extract (L1 fraction), and to study their effects on UVB-radiation-induced DNA damage in cultured human blood lymphocytes. In this study, J. curcas showed strong antioxidant property in different free radical scavenging systems. Both the fractions effectively scavenged hydroxyl (OH), superoxide anion (O₂^–), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid radical cation (ABTS⁺) in a concentration-dependent manner. The IC₅₀ (Inhibitory Concentration 50) values of J. curcas fractions were compared to standard ascorbic acid used in this study. The antioxidant potential of a compound was directly proportional to the photoprotective effect. In this study, human peripheral blood lymphocytes (HPBL) were exposed to UVB-radiation and there was an increase in comet attributes (% tail DNA, tail length, tail movement and Olive tail moment). Jatropha curcas RB4 fraction and L1 fraction treatment before UVB-irradiation significantly decreased the % tail DNA, tail length, tail moment and Olive tail moment in irradiated HPBL. These results suggested that J. curcas exhibited strong antioxidant property and RB4 and L1 fractions protected UVB-radiation-induced DNA damage in HPBL.     

Artocarpin attenuates ultraviolet B-induced skin damage in hairless mice by antioxidant and anti-inflammatory effect

Artocarpin, a prenylated flavonoid isolated from an agricultural plant Artocarpus communis, has been documented to possess anti-inflammation and anticancer activities. As oxidative stress and inflammation promote the development of ultraviolet B (UVB) irradiation-induced photodamage, the aim of the present study was to evaluate the photoprotective effect of artocarpin on UVB-induced skin damage in hairless mice. Artocarpin at a topical dose of 0.05% and 0.1% showed a significant photoprotective effect by decreasing histopathological changes, such as desquamation, epidermal thicken and sunburn cell formation, but 0.1% of artocarpin administration did not show better effect. Regarding the antioxidant activities, artocarpin exhibited a significant effect (P < 0.05) by decreasing levels of reactive species oxygen and lipid peroxidation. In addition, artocarpin can significantdecrease the level of tumor necrosis factor-α and interleukin-1β for downregulating the inflammation protein, including the synthesis of cytosolic phospholipase A2 and cyclooxygenase-2 (P < 0.05). In conclusion, these data suggest that artocarpin can prevent skin damage from UVB irradiation-induced photodamage in hairless mice and this is likely mediated through its antioxidant and anti-inflammation mechanisms. Therefore, we suggested that artocarpin could be a useful photoprotective agent in medicine and/or cosmetics.     

Quercetin inhibits hydrogen peroxide-induced DNA damage and enhances DNA repair in Caco-2 cells

Flavonoids are known to have antioxidant activity that may limit DNA damage and help prevent degenerative diseases, including cancer. However, our knowledge of flavonoids’ role in DNA protection/repair mechanism(s) is limited. This study investigated the effects of quercetin on DNA oxidation and DNA repair in Caco-2 cells with or without oxidant (H₂O₂) challenge. Quercetin (1, 100 μM) significantly reduced oxidative DNA damage, as measured by the number of single-strand breaks identified by single cell gel electrophoresis. Quercetin treatment also caused a measurable increase in the mRNA expression of human 8-oxoguanine DNA glycosylase (hOGG1) at 0 and 4 h after H₂O₂ treatment (measured using RT-PCR). In addition, the highest level of quercetin tested (100 μM) maintained hOGG1 expression at basal levels or higher for up to 12 h after H₂O₂ treatment, while oxidant treatment alone resulted in significant reduction of hOGG1 at 8 h. Our study indicates that quercetin could protect DNA both by reducing oxidative DNA damage and by enhancing DNA repair through modulation of DNA repair enzyme expression.     

Bisdemethoxycurcumin induces DNA damage and inhibits DNA repair associated protein expressions in NCI‐H460 human lung cancer cells

Nonsmall cell lung carcinoma (NSCLC) is a devastating primary lung tumor resistant to conventional therapies. Bisdemethoxycurcumin (BDMC) is one of curcumin derivate from Turmeric and has been shown to induce NSCLC cell death. Although there is one report to show BDMC induced DNA double strand breaks, however, no available information to show BDMC induced DNA damage action with inhibited DNA repair protein in lung cancer cells in detail. In this study, we tested BDMC‐induced DNA damage and condensation in NCI‐H460 cells by using Comet assay and DAPI staining examinations, respectively and we found BDMC induced DNA damage and condension. Western blotting was used to examine the effects of BDMC on protein expression associated with DNA damage and repair and results indicated that BDMC suppressed the protein levels associated with DNA damage and repair, such as 14‐3‐3σ (an important checkpoint keeper of DDR), O6‐methylguanine‐DNA methyltransferase, DNA repair proteins breast cancer 1, early onset, mediator of DNA damage checkpoint 1 but activate phosphorylated p53 and p‐H2A.X (phospho Ser140) in NCI‐H460 cells. Confocal laser systems microscopy was used for examining the protein translocation and results show that BDMC increased the translocation of p‐p53 and p‐H2A.X (phospho Ser140) from cytosol to nuclei in NCI‐H460 cells. In conclusion, BDMC induced DNA damage and condension and affect DNA repair proteins in NCI‐H460 cells in vitro. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1859–1868, 2016.     

Inhibitory effect of polypeptide from Chlamys farreri on ultraviolet A-induced oxidative damage on human skin fibroblasts in vitro.

We have previously reported that polypeptide from Chlamys farreri (PCF) inhibits the oxidative damage of ultraviolet A (UVA) on HeLa cells in vitro [Acta Pharm. Sin. 23 (2002) 961]. To further elucidate a possible role for PCF on UVA-damaged normal human cells, we established the oxidative damage models of normal human dermal fibroblasts (NHDF) exposed to UVA to study the protective effect of PCF on human dermal fibroblasts in vitro. In this study, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method was used to detect the cell viability. The intracellular superoxide dismutase (SOD), glutathione peroxidase (GSH-px), catalase (CAT), xanthine oxidase (XOD), malondialdehyde (MDA), reactive oxygen species (ROS), total antioxidative capacity (T-AOC), and anti-superoxide anion capacity (A-ASC) were measured. The effect of PCF on UVA-induced apoptosis were investigated by Annexin V-FITC assay. Intracellular calcium was determined with the calcium-sensitive fluorochrome Fluo-3, and mitochondrial transmembrane potential with rhodamine 123. Comet assay was employed to detect the UVA-induced DNA damage. The ultrastructure of cell was observed under transmission electron microscope. The results indicated that PCF could greatly enhance the viability of NHDF and markedly promote SOD, GSH-px, T-AOC, and A-ASC, while the amounts of MDA and ROS, the activity of XOD were decreased. PCF could inhibit UVA-induced apoptosis and DNA damage in NHDF. The concentration of cellular free calcium was decreased and the mitochondrial transmembrane potential was increased by PCF. In ultrastructure of NHDF, PCF could greatly decrease UVA-induced damage, especially membrane. Our results suggest that the supplementation of PCF appears to reduce the UVA-induced normal human dermal fibroblasts damage efficiently. It may be involved in the PCF's abilities of scavenging oxygen free radical, inhibiting lipid peroxidation, increasing antioxidative enzymes, decreasing intracellular calcium and protection of membrane structure in NHDF irradiated by UVA.     

Cinnamaldehyde inhibits inflammation and brain damage in a mouse model of permanent cerebral ischaemia

Background and Purpose

Recent findings suggest the importance of inflammation in the pathogenesis of cerebral ischaemia and its potential as a therapeutic target. Cinnamaldehyde is a diterpene with a wide range of anti‐inflammatory effects thus may be advantageous in the treatment of cerebral ischaemia. The present study examined the potential therapeutic effects of cinnamaldehyde on cerebral ischaemia using a mouse model with permanent middle cerebral artery occlusion.

Experimental Approach

Male CD‐1 mice, which had the middle cerebral artery occluded, were treated (i.p.) with cinnamaldehyde. Neuroprotection by cinnamaldehyde was analysed by evaluating neurological deficit scores, brain oedema and infarct volume. Expressionsof signal transduction molecules and inflammatory mediators were measured by Western blotting, qRT‐PCR and immunohistochemical staining. Activation of NF‐κB was assessed by Western blotting, immunohistochemistry and immunofluorescence.

Key Results

Cinnamaldehyde reduced the neurological deficit scores, brain oedema and infarct volume. Cinnamaldehyde suppressed the activation of signal transduction molecules including toll‐like receptor 4, tumour necrosis receptor‐associated factor 6 and NF‐κB, attenuated the increased levels of TNF‐α, IL‐1β, CCL2 and endothelial‐leukocyte adhesion molecule‐1 and ultimately reduced leukocyte infiltration into the ischaemic brain areas after cerebral ischaemia.

Conclusions and Implications

Cinnamaldehyde protects against cerebral ischaemia injury by inhibiting inflammation, partly mediated by reducing the expression of toll‐like receptor 4, tumour necrosis receptor‐associated factor 6 and the nuclear translocation of NF‐κB. Our findings suggest that cinnamaldehyde may serve as a new candidate for further development as a treatment for stroke.

Abbreviations

BBB

blood brain barrier

ELAM‐1

endothelial leukocyte adhesion molecule‐1

IHC

immunohistochemical staining

IRAK

IL‐1 receptor‐associated kinase

MAPKs

mitogen‐activated protein kinases

MPO

myeloperoxidase

pMCAO

permanent middle cerebral artery occlusion

qRT‐PCR

quantitative real‐time polymerase chain reaction

rCBF

relative regional cerebral blood flow

TRAF6

tumour necrosis factor receptor‐associated factor 6

TTC

2,3,5‐triphenyltetrazolium chloride

     

Nedocromil sodium inhibits histamine-induced itch and flare in human skin

This study was designed to test the hypothesis that nedocromil sodium inhibits sensory nerve function to reduce flare and itch in human skin. Nedocromil sodium (2%) or water (control) was introduced into the volar forearm skin of eight non-atopic volunteers by iontophoresis (8 mC) and histamine (20 microl of 1 microM and 300 nM) injected intradermally 10 min later at the same site. Itch was assessed on a visual analogue scale every 20 s for 5 min. Weal and flare areas and mean blood flux within the flare were assessed by scanning laser Doppler imaging at 10 min. The results showed that nedocromil sodium reduced itch scores, totalled over 5 min, by approximately 74.0% (P<0.005) and flare areas by approximately 65% (P<0.03). Neither weal areas nor blood flux within were reduced. These data demonstrate that nedocromil sodium is effective in reducing neurogenic itch and flare in the skin. We suggest that its mechanism of action is modulation of sensory neurone activation or conduction in the skin.     

Formulation and evaluation of an effective pH balanced topical antimicrobial product containing tea tree oil

The effect of pH on the antimicrobial activity of Melaleuca alternifolia essential oil formulations was studied. Microemulsions, liposomal dispersions, multiple emulsions and a colloidal bed of sterile clay were formulated using 5% w/w of tea tree oil. A number of formulations were prepared at various pH values (5.0, 5.5, 6.0, 6.5, and 7.0). Thermal stability studies showed that the formulations were stable for more than eight months. Agar dilution tests showed MICs of 1.0% v/v S. aureus and S. epidermidis. In the broth dilution test, MBC of the oil for P. acnes was 0.5% v/v. MIC and MBC values were comparable to those of non-formulated tea tree oil, indicating that tea tree oil retained its activity in the above-mentioned formulations. The microbiological evaluation showed that the formulations containing 5% w/w tea tree oil had a maximum effect at pH 5.5.     

Effects of nitrite and nitrate on DNA damage induced by ultraviolet light

UV light is a major cause of human skin cancers. Nitrite and nitrate are well-known potential risk factors for gastric cancer. Little attention has been paid to the relationship between UV light and nitrite or nitrate on cancer. We examined the effects of nitrite and nitrate on the damage to nucleosides and DNA induced by UV light from a mercury lamp and by sunlight at neutral pH. A biologically relevant dose of nitrite and nitrate increased the generation of nucleobases and malondialdehyde on the reaction of nucleosides and DNA with UV light. The efficiency of nitrite enhancing the reaction was higher than that of nitrate at low doses. The contribution of the hydroxyl radical as the reactive species was suggested from the results of the inhibitory effects of hydroxyl radical scavengers. Nitrite and nitrate also enhanced the formation of nucleobases and malondialdehyde from DNA induced by sunlight. In the presence of 5 muM nitrite, the concentration in human skin cells, the product yields by sunlight were 5-10-fold greater than those in the absence of nitrite. The addition of 80 muM NO(3)(-), a concentration in human skin cells, also increased the yields significantly. Nitrite and nitrate may play a role in enhancing the genotoxic effects of UV light in humans.     

Pimecrolimus: skin disposition after topical administration in minipigs in vivo and in human skin in vitro.

The dermal disposition of pimecrolimus, a non-steroid, anti-inflammatory calcineurin inhibitor used for the treatment of atopic dermatitis, was evaluated in minipigs in vivo and in human skin in vitro using tritium-radiolabeled compound, and in dermal toxicokinetic investigations in minipigs using unlabeled compound. Following topical application of pimecrolimus 1% market form (MF) cream to minipig skin, approximately 2% of the dose penetrated into the stratum corneum and part of it into deeper skin layers. The remainder of the dose was recovered non-absorbed on the skin surface. The total systemic absorption was or=94% of dose remained non-absorbed, 3.1% was found in the epidermis (including stratum corneum) and 2.9% in the dermis. There was no indication of metabolism of pimecrolimus in human skin in vitro or minipig skin in vivo. No drug accumulation was observed in minipig skin after up to 13 weeks of once daily topical application of 0.1% or 0.3% pimecrolimus cream.     

Lecithin microemulsions for the topical administration of ketoprofen: percutaneous adsorption through human skin and in vivo human skin tolerability

The potential application of highly biocompatible o/w microemulsions as topical drug carrier systems for the percutaneous delivery of anti-inflammatory drugs, i.e. ketoprofen, was investigated. Microemulsions were made up of triglycerides as oil phase, a mixture of lecithin and n-butanol as a surfactant/co-surfactant system and an aqueous solution as the external phase. To evaluate the percutaneous enhancing effect of oleic acid, this compound was used as a component of some o/w microemulsions. The topical carrier potentialities of lecithin-based o/w microemulsions were compared with respect to conventional formulations, i.e. a w/o emulsion, a o/w emulsion and a gel. Physicochemical characterisation of microemulsions was carried out by light scattering and zeta potential analyses. Microemulsions showed mean droplet size < 35 nm and a negative zeta potential, that is -39.5 mV for the oleic acid-lecithin microemulsion and -19.7 mV for the lecithin-based microemulsion. The percutaneous adsorption of the various topical formulations was evaluated through healthy adult human skin, which was obtained from abdominal reduction surgery. Ketoprofen-loaded microemulsions showed an enhanced permeation through human skin with respect to conventional formulations. No significant percutaneous enhancer effect was observed for ketoprofen-loaded oleic acid-lecithin microemulsions. The human skin tolerability of various microemulsion formulations was evaluated on human volunteers. Microemulsions showed a good human skin tolerability.     

Porcine skin as a model system for studies of ultraviolet a effects in human skin

The range of diagnostic and therapeutic applications of ultraviolet A (UVA) radiation has been continuously expanding. UVA radiation is a well-known mutagenic factor capable of damaging both cells and tissues. At the same time there is a very limited information on long-term consequences of irradiating the skin with different doses of UVA and long-wavelength ultraviolet B (UVB) radiation used in therapies of skin disorders. It was demonstrated that for UVA doses of 0.1 to 1000 mJ/cm2 the sensitivity of the porcine skin to the UVA-induced breaking of nuclear DNA is similar to that of the human skin. Results indicate that porcine skin may serve as a model system for population studies of the deleterious effects of UVA irradiation of the skin cells.     

Surface modification of quartz inhibits toxicity,particle uptake,and oxidative DNA damage in human lung epithelial cells

Quartz (crystalline silica) is not consistently carcinogenic across different industries where similar quartz exposure occurs. In addition, there are reports that surface modification of quartz affects its cytotoxicity, inflammogenicity, and fibrogenicity. Taken together, these data suggest that the carcinogenicity of quartz is also related to particle surface characteristics, and so we determined the genotoxic effects of DQ12 quartz particles versus DQ12 whose surface was modified by treating with either aluminum lactate or polyvinylpyridine-N-oxide (PVNO). The different particle preparations were characterized for hydroxyl-radical generation using electron spin resonance (ESR). DNA damage was determined by immunocytochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG) and the alkaline comet-assay using A549 human lung epithelial cells. Cytotoxicity was measured using the LDH- and MTT-assays, and particle uptake by the A549 cells was quantified by light microscopy, using digital light imaging evaluation of 800 nm sections. The ability of quartz to generate hydroxyl-radicals in the presence of hydrogen peroxide was markedly reduced upon surface modification with aluminum lactate or PVNO. DNA strand breakage and 8-OHdG formation, as produced by quartz at nontoxic concentrations, could be completely prevented by both coating materials. Particle uptake into A549 cells appeared to be significantly inhibited by the PVNO-coating, and to a lesser extent by the aluminum-lactate coating. Our data demonstrate that respirable quartz particles induce oxidative DNA damage in human lung epithelial cells and indicates that surface properties of the quartz as well as particle uptake by these target cells are important in the cytotoxic and the genotoxic effects of quartz in vitro.     

5‐Fluorouracil and its active metabolite FdUMP cause DNA damage in human SW620 colon adenocarcinoma cell line

5‐Fluorouracil (5‐FU) is an antineoplasic drug widely used to treat cancer. Its cytotoxic effect has been principally ascribed to the misincorporation of fluoronucleotides into DNA and RNA during their synthesis, and the inhibition of thymidylate synthase (TS) by FdUMP (one of the 5‐FU active metabolites), which leads to nucleotide pool imbalance. In the present study, we compared the ability of 5‐FU and FdUMP to induce apoptosis and to influence the cell cycle progression in human colon SW620 adenocarcinoma cells in regards to their genotoxic and clastogenic activities. Our study demonstrates that 5‐FU induces SSB, DSB and apoptosis earlier than FdUMP. Interestingly, while both drugs are able to induce apoptosis, their effect on the cell cycle progression differed. Indeed, 5‐FU induces an arrest in G1/S while FdUMP causes an arrest in G2/M. Independently of the temporal difference in strand breaks and apoptosis induction, as well as the differential cell cycle modulation, both drugs presented similar clastogenic effects. The different pattern of cell cycle arrest suggests that the two drugs induce different types of primary DNA lesions that could lead to the activation of different checkpoints and recruit different DNA repair pathways. Copyright © 2008 John Wiley & Sons, Ltd.