Molecular analysis of mutations induced by acrolein in human fibroblast cells using supF shuttle vector plasmids

Chemobrain in Breast Cancer: Mechanisms, Clinical Manifestations, and Potential Interventions

Among the potential adverse effects of breast cancer treatment, chemotherapy-related cognitive impairment (CRCI) has gained increased attention in the past years. In this review, we provide an overview of the literature regarding CRCI in breast cancer, focusing on three main aspects. The first aspect relates to the molecular mechanisms linking individual drugs commonly used to treat breast cancer and CRCI, which include oxidative stress and inflammation, reduced neurogenesis, reduced levels of specific neurotransmitters, alterations in neuronal dendrites and spines, and impairment in myelin production. The second aspect is related to the clinical characteristics of CRCI in patients with breast cancer treated with different drug combinations. Data suggest the incidence rates of CRCI in breast cancer vary considerably, and may affect more than 50% of treated patients. Both chemotherapy regimens with or without anthracyclines have been associated with CRCI manifestations. While cross-sectional studies suggest the presence of symptoms up to 20 years after treatment, longitudinal studies confirm cognitive impairments lasting for at most 4 years after the end of chemotherapy. The third and final aspect is related to possible therapeutic interventions. Although there is still no standard of care to treat CRCI, several pharmacological and non-pharmacological approaches have shown interesting results. In summary, even if cognitive impairments derived from chemotherapy resolve with time, awareness of CRCI is crucial to provide patients with a better understanding of the syndrome and to offer them the best care directed at improving quality of life.

Acrolein contributes to human colorectal tumorigenesis through the activation of RAS-MAPK pathway

Colorectal cancer (CRC) is one of the most well-known malignancies with high prevalence and poor 5-year survival. Previous studies have demonstrated that a high-fat diet (HFD) is capable of increasing the odds of developing CRC. Acrolein, an IARC group 2A carcinogen, can be formed from carbohydrates, vegetable oils, animal fats, and amino acids through the Maillard reaction during the preparation of foods. Consequently, humans are at risk of acrolein exposure through the consumption of foods rich in fat. However, whether acrolein contributes to HFD-induced CRC has not been determined. In this study, we found that acrolein induced oncogenic transformation, including faster cell cycling, proliferation, soft agar formation, sphere formation and cell migration, in NIH/3T3 cells. Using xenograft tumorigenicity assays, the acrolein-transformed NIH/3T3 clone formed tumors. In addition, cDNA microarray and bioinformatics studies by Ingenuity Pathway Analysis pointed to the fact that RAS/MAPK pathway was activated in acrolein-transformed clones that contributed to colon tumorigenesis. Furthermore, acrolein-induced DNA damages (Acr-dG adducts) were higher in CRC tumor tissues than in normal epithelial cells in CRC patients. Notably, CRC patients with higher levels of Acr-dG adducts appeared to have better prognosis. The results of this study demonstrate for the first time that acrolein is important in oncogenic transformation through activation of the RAS/MAPK signaling pathway, contributing to colon tumorigenesis.

Formation and repair of unavoidable, endogenous interstrand cross-links in cellular DNA

Genome integrity is essential for life and, as a result, DNA repair systems evolved to remove unavoidable DNA lesions from cellular DNA. Many forms of life possess the capacity to remove interstrand DNA cross-links (ICLs) from their genome but the identity of the naturally-occurring, endogenous substrates that drove the evolution and retention of these DNA repair systems across a wide range of life forms remains uncertain. In this review, we describe more than a dozen chemical processes by which endogenous ICLs plausibly can be introduced into cellular DNA. The majority involve DNA degradation processes that introduce aldehyde residues into the double helix or reactions of DNA with endogenous low molecular weight aldehyde metabolites. A smaller number of the cross-linking processes involve reactions of DNA radicals generated by oxidation.

Fanconi anemia-independent DNA inter-strand crosslink repair in eukaryotes

DNA inter-strand crosslinks (ICLs) are dangerous lesions that can be caused by a variety of endogenous and exogenous bifunctional compounds. Because covalently linking both strands of the double helix locally disrupts DNA replication and transcription, failure to remove even a single ICL can be fatal to the cell. Thus, multiple ICL repair pathways have evolved, with the best studied being the canonical Fanconi anemia (FA) pathway. However, recent research demonstrates that different types of ICLs (e.g., backbone distorting vs. non-distorting) can be discriminated by the cell, which then mounts a specific repair response using the FA pathway or one of a variety of FA-independent ICL repair pathways. This review focuses on the latter, covering current work on the transcription-coupled, base excision, acetaldehyde-induced, and SNM1A/RecQ4 ICL repair pathways and highlighting unanswered questions in the field. Answering these questions will provide mechanistic insight into the various pathways of ICL repair and enable ICL-inducing agents to be more effectively used as chemotherapeutics.

Interplay between Cellular Metabolism and the DNA Damage Response in Cancer

Metabolism is a fundamental cellular process that can become harmful for cells by leading to DNA damage, for instance by an increase in oxidative stress or through the generation of toxic byproducts. To deal with such insults, cells have evolved sophisticated DNA damage response (DDR) pathways that allow for the maintenance of genome integrity. Recent years have seen remarkable progress in our understanding of the diverse DDR mechanisms, and, through such work, it has emerged that cellular metabolic regulation not only generates DNA damage but also impacts on DNA repair. Cancer cells show an alteration of the DDR coupled with modifications in cellular metabolism, further emphasizing links between these two fundamental processes. Taken together, these compelling findings indicate that metabolic enzymes and metabolites represent a key group of factors within the DDR. Here, we will compile the current knowledge on the dynamic interplay between metabolic factors and the DDR, with a specific focus on cancer. We will also discuss how recently developed high-throughput technologies allow for the identification of novel crosstalk between the DDR and metabolism, which is of crucial importance to better design efficient cancer treatments.

Evaluation of mutagenic and anti-mutagenic potential of alpha-lipoic acid by chromosomal aberration assay in mice

This study investigated both the mutagenicity and anti-mutagenicity of alpha-lipoic acid (ALA) in the bone marrow cells of mice using a chromosomal aberration assay. Cyclophosphamide (CP) 40 mg/kg was used as a clastogen in the positive control, and a vehicle-treated negative control group was also included. Multiple dose levels (15, 30, and 100 mg/kg of ALA) were given by intraperitoneal injection (IP) alone and in combination with CP (CP was administered 1 h prior to ALA). Bone marrow samples were collected 12 and 24 h after drug administration. The results demonstrated a significant increase in the frequency of chromosomal aberrations (CA) in bone marrow cells with depressions in the mitotic index (MI) of the positive control group of mice. However, in the groups of mice treated with different doses of ALA in the presence of CP, the percentages of CA decreased significantly with increases in mitotic activity. The results also indicate that ALA given alone in different doses had no mutagenic effect on mouse bone marrow cells. ALA has a dose and time-dependent protective effect against the mutagenicity induced by CP.

Protective Effects of Selenium on Cyclophosphamide-Induced Oxidative Stress and Kidney Injury

Cyclophosphamide (CP) is a common anticancer drug, but its use in cancer treatment is limited due to its severe toxicities induced mainly by oxidative stress in normal cells. Reactive oxygen species (ROS) lead to multiple organ injuries, including the kidneys. Selenium (Se) is a nutritionally essential trace element with antioxidant properties. In the present study, the possible protective effect of Se on CP-induced acute nephrotoxicity was investigated. Forty-two Sprague-Dawley rats were equally divided into six groups of seven rats in each. The control group received saline, and other groups were injected with CP (150 mg/kg), Se (0.5 or 1 mg/kg), or CP + Se intraperitoneally. Total antioxidant capacity (TAC), total oxidant state (TOS), oxidative stress index (OSI), creatinine, and cystatin C (Cys C) levels were measured in the sera. In addition, kidney tissues were examined histologically. In the CP alone treated rats, creatinine, Cys C, TOS, and OSI levels increased, while TAC level decreased. CP-induced histological damages were decreased by co-treatment of Se and biochemical results supported the microscopic observations. In conclusion, our study points to the therapeutic potential of Se and indicates a significant role of ROS in CP-induced kidney toxicity.

AGT Activity Towards Intrastrand Crosslinked DNA is Modulated by the Alkylene Linker

DNA oligomers containing dimethylene and trimethylene intrastrand crosslinks (IaCLs) between the O4 and O6 atoms of neighboring thymidine (T) and 2'-deoxyguanosine (dG) residues were prepared by solid-phase synthesis. UV thermal denaturation (T_m ) experiments revealed that these IaCLs had a destabilizing effect on the DNA duplex relative to the control. Circular dichroism spectroscopy suggested these IaCLs induced minimal structural distortions. Susceptibility to dealkylation by reaction with various O⁶ -alkylguanine DNA alkyltransferases (AGTs) from human and Escherichia coli was evaluated. It was revealed that only human AGT displayed activity towards the IaCL DNA, with reduced efficiency as the IaCL shortened (from four to two methylene linkages). Changing the site of attachment of the ethylene linkage at the 5'-end of the IaCL to the N3 atom of T had minimal influence on duplex stability and structure, and was refractory to AGT activity.

Genotoxicity of lipid oxidation compounds

Lipid peroxidation, the oxidative degradation of membrane lipids by reactive oxygen species generates a large variety of breakdown products such as alkanes, aldehydes, ketones, alcohols, furans and others. Due to their reactivity aldehydes (alkanals, 2-alkenals, 2,4-alkadienals, 4-hydroxyalkenals) received a lot of attention, in particular because they can diffuse from the site of formation and interact with proteins and nucleic acids thus acting as second toxic messengers. The major aldehydic peroxidation product of membrane lipids is 4-hydroxynonenal (HNE). Since HNE and other 4-hydroxyalkenals are strong alkylating agents they have therefore been considered to be the biologically most important peroxidation products. Although initially research focused on the toxicological potential of these compounds it is now well known that they play also a crucial role in cell signaling under physiological and pathophysiological conditions. Thus, it is obvious that the biological effects will be determined by the intracellular concentrations which can trigger adaptation, DNA damage and cell death. This review will not cover all these aspects but will concentrate on the genotoxic properties of selected lipid oxidation products important in the context of pathophysiological developments together with a chapter on epigenetic modifications.

Mutation Spectrum Induced by 8-Bromoguanine, a Base Damaged by Reactive Brominating Species, in Human Cells

To date, the types of mutations caused by 8-bromoguanine (8BrG), a major base lesion induced by reactive brominating species during inflammation, in human cells and the 8BrG repair system remain largely unknown. In this study, we performed a supF forward mutation assay using a shuttle vector plasmid containing a single 8BrG in three kinds of human cell lines and revealed that 8BrG in DNA predominantly induces a G → T mutation but can also induce G → C, G → A, and delG mutations in human cells. Next, we tested whether eight kinds of DNA glycosylases (MUTYH, MPG, NEIL1, OGG1, SMUG1, TDG, UNG2, and NTHL1) are capable of repairing 8BrG mispairs with any of the four bases using a DNA cleavage activity assay. We found that both the SMUG1 protein and the TDG protein exhibit DNA glycosylase activity against thymine mispaired with 8BrG and that the MUTYH protein exhibits DNA glycosylase activity against adenine mispaired with 8BrG. These results suggest that 8BrG induces some types of mutations, chiefly a G → T mutation, in human cells, and some DNA glycosylases are involved in the repair of 8BrG.

1,N6-α-hydroxypropanoadenine, the acrolein adduct to adenine, is a substrate for AlkB dioxygenase

1,N⁶-α-hydroxypropanoadenine (HPA) is an exocyclic DNA adduct of acrolein - an environmental pollutant and endocellular oxidative stress product. Escherichia coli AlkB dioxygenase belongs to the superfamily of α-ketoglutarate (αKG)- and iron-dependent dioxygenases which remove alkyl lesions from bases via an oxidative mechanism, thereby restoring native DNA structure. Here, we provide in vivo and in vitro evidence that HPA is mutagenic and is effectively repaired by AlkB dioxygenase. HPA generated in plasmid DNA caused A → C and A → T transversions and, less frequently, A → G transitions. The lesion was efficiently repaired by purified AlkB protein; the optimal pH, Fe(II), and αKG concentrations for this reaction were determined. In vitro kinetic data show that the protonated form of HPA is preferentially repaired by AlkB, albeit the reaction is stereoselective. Moreover, the number of reaction cycles carried out by an AlkB molecule remains limited. Molecular modeling of the T(HPA)T/AlkB complex demonstrated that the R stereoisomer in the equatorial conformation of the HPA hydroxyl group is strongly preferred, while the S stereoisomer seems to be susceptible to AlkB-directed oxidative hydroxylation only when HPA adopts the syn conformation around the glycosidic bond. In addition to the biochemical activity assays, substrate binding to the protein was monitored by differential scanning fluorimetry allowing identification of the active protein form, with cofactor and cosubstrate bound, and monitoring of substrate binding. In contrast FTO, a human AlkB homolog, failed to bind an ssDNA trimer carrying HPA.

Attenuation of cyclophosphamide-induced pulmonary toxicity in Swiss albino mice by naphthalimide-based organoselenium compound 2-(5-selenocyanatopentyl)-benzo[de]isoquinoline 1,3-dione

CONTEXT

The widely used antineoplastic drug cyclophosphamide causes pulmonary toxicity by inducing oxidative stress. Selenium, a dietary micronutrient, has been found to protect various organs from oxidative injuries.

OBJECTIVE

This study was designed to investigate the protective efficacy of an organoselenium compound 2-(5-selenocyanato-pentyl)-benzo[de]isoquinoline 1,3-dione against cyclophosphamide-induced pulmonary toxicity in Swiss albino mice.

MATERIALS AND METHODS

Cyclophosphamide (25 mg/kg b.w.) was administered intraperitoneally for 10 d and the organoselenium compound (3 mg/kg b.w.) was given by oral gavage in concomitant and pretreatment schedules. Various biochemical parameters related to oxidative stress and antioxidant enzymes along with histology of lungs were evaluated to assess the effect of the test compound.

RESULTS

The oral LD50 of the test compound was more than 1000 mg/kg b.w. in Swiss albino mice. The test compound substantially ameliorated cyclophosphamide-induced pulmonary injury by reducing the levels of reactive oxygen species, reactive nitrogen species, and lipid peroxidation, respectively, by 14.88, 18.54, and 21.10% in concomitant treatment schedule and by 23.89, 35.73, and 30.76% in the pretreatment schedule as well as by restoring the level of reduced glutathione and activities of glutathione-S-transferase, superoxide dismutase, catalase, and glutathione peroxidase, respectively, by 36.88, 42.43, 38.0, 35.0, and 34.06% in the concomitant treatment schedule and by 66.02, 59.29, 57.23, 71.59, and 57.22% in the pretreatment schedule. The test compound also attenuated cyclophosphamide-induced histological alterations of lung tissue.

DISCUSSION AND CONCLUSION

The test compound emerged as an efficient antioxidant protecting lungs tissue from cyclophosphamide-induced injury.

Mechanism of repair of acrolein- and malondialdehyde-derived exocyclic guanine adducts by the α-ketoglutarate/Fe(II) dioxygenase AlkB

The structurally related exocyclic guanine adducts α-hydroxypropano-dG (α-OH-PdG), γ-hydroxypropano-dG (γ-OH-PdG), and M₁dG are formed when DNA is exposed to the reactive aldehydes acrolein and malondialdehyde (MDA). These lesions are believed to form the basis for the observed cytotoxicity and mutagenicity of acrolein and MDA. In an effort to understand the enzymatic pathways and chemical mechanisms that are involved in the repair of acrolein- and MDA-induced DNA damage, we investigated the ability of the DNA repair enzyme AlkB, an α-ketoglutarate/Fe(II) dependent dioxygenase, to process α-OH-PdG, γ-OH-PdG, and M₁dG in both single- and double-stranded DNA contexts. By monitoring the repair reactions using quadrupole time-of-flight (Q-TOF) mass spectrometry, it was established that AlkB can oxidatively dealkylate γ-OH-PdG most efficiently, followed by M₁dG and α-OH-PdG. The AlkB repair mechanism involved multiple intermediates and complex, overlapping repair pathways. For example, the three exocyclic guanine adducts were shown to be in equilibrium with open-ring aldehydic forms, which were trapped using (pentafluorobenzyl)hydroxylamine (PFBHA) or NaBH₄. AlkB repaired the trapped open-ring form of γ-OH-PdG but not the trapped open-ring of α-OH-PdG. Taken together, this study provides a detailed mechanism by which three-carbon bridge exocyclic guanine adducts can be processed by AlkB and suggests an important role for the AlkB family of dioxygenases in protecting against the deleterious biological consequences of acrolein and MDA.

Acrolein- and 4-Aminobiphenyl-DNA adducts in human bladder mucosa and tumor tissue and their mutagenicity in human urothelial cells

Tobacco smoke (TS) is a major cause of human bladder cancer (BC). Two components in TS, 4-aminobiphenyl (4-ABP) and acrolein, which also are environmental contaminants, can cause bladder tumor in rat models. Their role in TS related BC has not been forthcoming. To establish the relationship between acrolein and 4-ABP exposure and BC, we analyzed acrolein-deoxyguanosine (dG) and 4-ABP-DNA adducts in normal human urothelial mucosa (NHUM) and bladder tumor tissues (BTT), and measured their mutagenicity in human urothelial cells. We found that the acrolein-dG levels in NHUM and BTT are 10-30 fold higher than 4-ABP-DNA adduct levels and that the acrolein-dG levels in BTT are 2 fold higher than in NHUM. Both acrolein-dG and 4-ABP-DNA adducts are mutagenic; however, the former are 5 fold more mutagenic than the latter. These two types of DNA adducts induce different mutational signatures and spectra. We found that acrolein inhibits nucleotide excision and base excision repair and induces repair protein degradation in urothelial cells. Since acrolein is abundant in TS, inhaled acrolein is excreted into urine and accumulates in the bladder and because acrolein inhibits DNA repair and acrolein-dG DNA adducts are mutagenic, we propose that acrolein is a major bladder carcinogen in TS.

Oxidative stress--implications, source and its prevention

Oxidative stress has been a major predicament of present day living. It has been the product of imbalance between the processes involved in free radical generation and their neutralization by enzymatic and non-enzymatic defence mechanisms. The oxidative stress has been contributed by numerous factors including heavy metals, organic compound-rich industrial effluents, air pollutants and changing lifestyle pattern focussing mainly on alcohol consumption, dietary habits, sun exposure, nuclear emissions, etc. The most common outcome of oxidative stress is the increased damage of lipid, DNA and proteins that resulted in the development of different pathologies. Among these pathologies, cancer is the most devastating and linked to multiple mutations arising due to oxidative DNA and protein damage that ultimately affect the integrity of the genome. The chemopreventive agents particularly nutraceuticals are found to be effective in reducing cancer incidences as these components have immense antioxidative, antimutagenic and antiproliferative potentials and are an important part of our dietary components. These secondary metabolites, due to their unique chemical structure, facilitate cell-to-cell communication, repair DNA damage by the downregulation of transcription factors and inhibit the activity of protein kinases and cytochrome P450-dependent mixed function oxidases. These phytochemicals, therefore, are most appropriate in combating oxidative stress-related disorders due to their tendency to exert better protective effect without having any distinct side effect.

Repair kinetics of acrolein- and (E)-4-hydroxy-2-nonenal-derived DNA adducts in human colon cell extracts

ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) play a role in the pathogenesis of colon cancer. Upon oxidation, PUFAs generate α,β-unsaturated aldehydes or enals, such as acrolein (Acr) and (E)-4-hydroxy-2-nonenal (HNE), which can form cyclic adducts of deoxyguanosine (Acr-dG and HNE-dG, respectively) in DNA. Both Acr-dG and HNE-dG adducts have been detected in human and animal tissues and are potentially mutagenic and carcinogenic. In vivo levels of Acr-dG in DNA are at least two orders of magnitude higher than those of HNE-dG. In addition to the facile reaction with Acr, the higher levels of Acr-dG than HNE-dG in vivo may be due to a lower rate of repair. Previous studies have shown that HNE-dG adducts are repaired by the NER pathway (Choudhury et al. [42]). We hypothesize that Acr-dG adducts are repaired at a slower rate than HNE-dG and that HNE-dG in DNA may influence the repair of Acr-dG. In this study, using a DNA repair synthesis assay and a LC-MS/MS method, we showed that Acr-dG in a plasmid DNA is repaired by NER proteins, but it is repaired at a much slower rate than HNE-dG in human colon cell extracts, and the slow repair of Acr-dG is likely due to poor recognition/excision of the lesions in DNA. Furthermore, using a plasmid DNA containing both adducts we found the repair of Acr-dG is significantly inhibited by HNE-dG, however, the repair of HNE-dG is not much affected by Acr-dG. This study demonstrates that the NER repair efficiencies of the two major structurally-related in vivo cyclic DNA adducts from lipid oxidation vary greatly. More importantly, the repair of Acr-dG can be significantly retarded by the presence of HNE-dG in DNA. Therefore, this study provides a mechanistic explanation for the higher levels of Acr-dG than HNE-dG observed in tissue DNA.

Ring-opening of the γ-OH-PdG adduct promotes error-free bypass by the Sulfolobus solfataricus DNA polymerase Dpo4

Acrolein, a mutagenic aldehyde, reacts with deoxyguanosine (dG) to form 3-(2'-deoxy-β-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a] purin-10(3H)-one (γ-OH-PdG). When placed opposite deoxycytosine (dC) in DNA, γ-OH-PdG undergoes ring-opening to the N(2)-(3-oxopropyl)-dG. Ring-opening of the adduct has been hypothesized to facilitate nonmutagenic bypass, particularly by DNA polymerases of the Y family. This study examined the bypass of γ-OH-PdG by Sulfolobus solfataricus Dpo4, the prototypic Y-family DNA polymerase, using templates that contained the adduct in either the 5'-CXG-3' or the 5'-TXG-3' sequence context. Although γ-OH-PdG partially blocked Dpo4-catalyzed DNA synthesis, full primer extension was observed, and the majority of bypass products were error-free. Conversion of the adduct into an irreversibly ring-opened derivative prior to reaction facilitated bypass and further improved the fidelity. Structures of ternary Dpo4·DNA·dNTP complexes were determined with primers that either were positioned immediately upstream of the lesion (preinsertion complexes) or had a 3'-terminal dC opposite the lesion (postinsertion complexes); the incoming nucleotides, either dGTP or dATP, were complementary to the template 5'-neighbor nucleotide. In both postinsertion complexes, the adduct existed as ring-opened species, and the resulting base-pair featured Watson-Crick hydrogen bonding. The incoming nucleotide paired with the 5'-neighbor template, while the primer 3'-hydroxyl was positioned to facilitate extension. In contrast, γ-OH-PdG was in the ring-closed form in both preinsertion complexes, and the overall structure did not favor catalysis. These data provide insights into γ-OH-PdG chemistry during replication bypass by the Dpo4 DNA polymerase and may explain why γ-OH-PdG-induced mutations due to primer-template misalignment are uncommon.

An ammonium bicarbonate-enhanced stable isotope dilution UHPLC-MS/MS method for sensitive and accurate quantification of acrolein-DNA adducts in human leukocytes

Acrolein (Acr), a ubiquitous environmental pollutant, can react directly with genomic DNA to form mutagenic adducts without undergoing metabolic activation. To sensitively and accurately quantify Acr-DNA adducts (including structural isomers and stereoisomers) in human leukocytes, we developed an enhanced stable isotope dilution ultrahigh performance liquid chromatography (UHPLC)-tandem mass spectrometry (MS/MS) method using ammonium bicarbonate (NH4HCO3), which is thermally unstable and degrades readily to carbon dioxide and ammonia in heated gas phase. Interestingly, ammonium bicarbonate (as an additive to the mobile phase) not only improves the protonation of AcrdG adducts but also suppresses the formation of MS signal-deteriorating metal-AcrdG complexes during electrospray ionization, leading to the enhancement of their MS detection by 2.3-8.7 times. In contrast, routinely used ammonium salts (ammonium acetate and ammonium formate) and formic acid do not show similar enhancement. The developed method is potentially useful for enhancing ESI-MS detection of other modified 2'-deoxyribonucleosides that have difficulty in protonation and may form excess metal complexes during electrospray ionization. The limits of detection (LODs, S/N = 3) are estimated to be about 40-80 amol. By the use of the developed method, we found that the Acr adducts of three nucleotides (dG, dA, and dC) can be detected in human leukocytes. In addition to the known γ-AcrdG, α-AcrdA is also identified as an Acr-adduct of high abundance (2.5-20 adducts per10(8) nts).

Investigation of antigenotoxic potential of Syzygium cumini extract (SCE) on cyclophosphamide-induced genotoxicity and oxidative stress in mice

The present study investigated the protective effects of Syzygium cumini extract (SCE; 100 and 200 mg/kg) against genotoxicity and oxidative stress (OS) induced by cyclophosphamide (CP) in mice. Animals were received 14 days pretreatment (oral) of SCE, followed by induction of genotoxicity by CP (40 mg/kg), 24 hours before sacrifice. Mice bone marrow chromosomal aberration assay, micronucleus assay, and sperm abnormality assay were employed for the study. Activities of hepatic antioxidant enzymes were also investigated. Phytochemical investigation was done to determine total phenolic and flavonoid content in SCE. Results showed that CP produced a significant increase in average percentage of aberrant metaphases and chromosomal aberrations (CAs) excluding gap, and micronuclei (MN) formation in polychromatic erythrocytes produced cytotoxicity in mouse bone marrow cells and induced abnormal sperms in a male germ line. CP also markedly inhibited the activities of superoxide dismutase (SOD), catalase (CAT), and reduced glutahione (GSH) and increased malondialdehyde (MDA) content. Pretreatments with SCE significantly inhibited the frequencies of aberrant metaphases, CAs, MN formation, and cytotoxicity in mouse bone marrow cells induced by CP. SCE also produced a significant reduction of abnormal sperm and antagonized the reduction of CP-induced SOD, CAT, and GSH activities and inhibited increased MDA content in the liver. Total phenolic content present in SCE was 24.68%, whereas total flavonoids were calculated as 3.80%. SCE has a protective effect against genotoxicity and OS induced by CP.

Effect of CpG methylation at different sequence context on acrolein- and BPDE-DNA binding and mutagenesis

Acrolein (Acr), an α,β-unsaturated aldehyde, is abundant in tobacco smoke and cooking and exhaust fumes. Acr induces mutagenic α- and γ- hydroxy-1,N(2)-cyclic propano-deoxyguanosine adducts in normal human bronchial epithelial cells. Our earlier work has found that Acr-induced DNA damage preferentially occurs at lung cancer p53 mutational hotspots that contain CpG sites and that methylation at CpG sites enhances Acr-DNA binding at these sites. Based on these results, we hypothesized that this enhancement of Acr-DNA binding leads to p53 mutational hotspots in lung cancer. In this study, using a shuttle vector supF system, we tested this hypothesis by determining the effect of CpG methylation on Acr-DNA binding and the mutations in human lung fibroblasts. We found that CpG methylation enhances Acr-induced mutations significantly. Although CpG methylation enhances Acr-DNA binging at all CpG sites, it enhances mutations at selective--TCGA--sites. Similarly, we found that CpG methylation enhances benzo(a)pyrene diol epoxide binding at all -CpG- sites. However, the methylated CpG sequences in which benzo(a)pyrene diol epoxide-induced mutations are enhanced are different from the CpG sequences in which Acr-induced mutations are enhanced. CpG methylation greatly increases Acr-induced G to T and G to A mutation frequency to levels similar to these types of mutations found in the CpG sites in the p53 gene in tobacco smoke-related lung cancer. These results indicate that both CpG sequence context and the chemical nature of the carcinogens are crucial factors for determining the effect of CpG methylation on mutagenesis.

Effect of carcinogenic acrolein on DNA repair and mutagenic susceptibility

Acrolein (Acr), a ubiquitous environmental contaminant, is a human carcinogen. Acr can react with DNA to form mutagenic α- and γ-hydroxy-1, N(2)-cyclic propano-2'-deoxyguanosine adducts (α-OH-Acr-dG and γ-OH-Acr-dG). We demonstrate here that Acr-dG adducts can be efficiently repaired by the nucleotide excision repair (NER) pathway in normal human bronchial epithelia (NHBE) and lung fibroblasts (NHLF). However, the same adducts were poorly processed in cell lysates isolated from Acr-treated NHBE and NHLF, suggesting that Acr inhibits NER. In addition, we show that Acr treatment also inhibits base excision repair and mismatch repair. Although Acr does not change the expression of XPA, XPC, hOGG1, PMS2 or MLH1 genes, it causes a reduction of XPA, XPC, hOGG1, PMS2, and MLH1 proteins; this effect, however, can be neutralized by the proteasome inhibitor MG132. Acr treatment further enhances both bulky and oxidative DNA damage-induced mutagenesis. These results indicate that Acr not only damages DNA but can also modify DNA repair proteins and further causes degradation of these modified repair proteins. We propose that these two detrimental effects contribute to Acr mutagenicity and carcinogenicity.

Investigation of antimutagenic potential of Foeniculum vulgare essential oil on cyclophosphamide induced genotoxicity and oxidative stress in mice

The present study investigated the protective effects of Foeniculum vulgare (fennel) essential oil (FEO) against genotoxicity induced by cyclophosphamide (CP). Mice bone marrow chromosomal aberration (CA), micronucleus, and sperm abnormality assays were employed to measure genotoxicity and cytotoxicity, respectively. The activities of superoxide dismutase (SOD), glutathione (GSH), catalase (CAT), and malondialdehyde (MDA) content in the liver were also investigated spectrophotometrically. Animals were administered two different doses of FEO (1 and 2 mL/kg) continuously for 3 days at intervals of 24 hours by the oral route before tissue sampling. The results showed that CP produced a significant increase in the average percentage of aberrant metaphases and CAs, excluding gap and micronuclei formation in polychromatic erythrocytes (PCEs), produced cytotoxicity in mouse bone marrow cells, and induced abnormal sperms in the male germ line. CP also markedly inhibited the activities of SOD, CAT, and GSH and increased MDA content. Pretreatments with FEO significantly inhibited the frequencies of aberrant metaphases, CAs, micronuclei formation, and cytotoxicity in mouse bone marrow cells induced by CP and also produced a significant reduction of abnormal sperm and antagonized the reduction of CP-induced SOD, CAT, and GSH activities and inhibited increased MDA content in the liver. FEO inhibits genotoxicity and oxidative stress induced by CP.

Chemistry and structural biology of DNA damage and biological consequences

The formation of adducts by the reaction of chemicals with DNA is a critical step for the initiation of carcinogenesis. The structural analysis of various DNA adducts reveals that conformational and chemical rearrangements and interconversions are a common theme. Conformational changes are modulated both by the nature of adduct and the base sequences neighboring the lesion sites. Equilibria between conformational states may modulate both DNA repair and error-prone replication past these adducts. Likewise, chemical rearrangements of initially formed DNA adducts are also modulated both by the nature of adducts and the base sequences neighboring the lesion sites. In this review, we focus on DNA damage caused by a number of environmental and endogenous agents, and biological consequences.

Acrolein induced DNA damage, mutagenicity and effect on DNA repair

Acrolein (Acr) is a ubiquitous environmental contaminant; it also can be generated endogenously by lipid peroxidation. Acr contains a carbonyl group and an olefinic double bond; it can react with many cellular molecules including amino acids, proteins and nucleic acids. In this review article we focus on updating information regarding: (i) Acr-induced DNA damage and methods of detection, (ii) repair of Acr-DNA damage, (iii) mutagenicity of Acr-DNA adducts, (iv) sequence specificity and methylation effect on Acr-DNA adduct formation and (v) the role of Acr in human cancer. We have found that Acr can inhibit DNA repair and induces mutagenic Acr-dG adducts and that the binding spectrum of Acr in the p53 gene in normal human bronchial epithelial cells is similar to the p53 mutational spectrum in lung cancer. Since Acr-DNA adduct has been identified in human lung tissue and Acr causes bladder cancer in human and rat models, we conclude that Acr is a major lung and bladder carcinogen, and its carcinogenicity arises via induction of DNA damage and inhibition of DNA repair.

Mutagenicity and sequence specificity of acrolein-DNA adducts

Acrolein (Acr) is a major toxicant in cigarette smoke (CS); it can interact with DNA forming two major adduct isomers: alpha-OH-Acr-dG and gamma-OH-Acr-dG. Previously, we found that the Acr-DNA binding pattern in the human p53 gene coincides with the p53 mutational pattern in CS-related lung cancer; hence, we proposed that Acr is a major lung cancer etiological agent [ Feng , Z. , Hu , W. , Hu , Y. , and Tang , M.-s. ( 2006 ) Acrolein is a major cigarette-related lung cancer agent: Preferential binding at p53 mutational hotspots and inhibition of DNA repair . Proc. Natl. Acad. Sci. U.S.A. 103 , 15404 - 15409 ]. This hypothesis has been brought into question with recent work that failed to detect Acr-induced mutations in the pSP189 system [ Kim , S. I. , Pfeifer , G. P. , and Besaratinia , A. ( 2007 ) Lack of mutagenicity of acrolein-induced DNA adducts in mouse and human cells . Cancer Res. 67 , 11640 - 116472 ]. To resolve this controversy, we determined the level and the type of Acr-dG formation, and the mutagenicity of Acr-dG adducts in the same pSP189 system. We also mapped the Acr-dG adduct distribution at the nucleotide level and the Acr-dG-induced mutational spectrum in this system. We found that (1) gamma-OH-Acr-dG is the major adduct formed in Acr-modified DNA based on the LC-ESI-MS/MS analysis; (2) the mutation frequency is proportional to the extent of Acr modifications, the majority of which are G:C to T:A and G:C to A:T mutations; and (3) sequences with a run of Gs are the mutational hotspots. Using the UvrABC nuclease incision method to map the Acr-dG distribution in the supF gene sequence, we confirmed that Acr-DNA adducts preferentially form in guanine-rich sequences that are also mutational hotspots. These results reaffirm that Acr-dG adducts are mutagenic and support our hypothesis that Acr is a major etiological agent for CS and cooking fume-related lung cancer.

Formation of deoxyguanosine cross-links from calf thymus DNA treated with acrolein and 4-hydroxy-2-nonenal

Acrolein (AC) and 4-hydroxy-2-nonenal (HNE) are endogenous bis-electrophiles that arise from the oxidation of polyunsaturated fatty acids. AC is also found in high concentrations in cigarette smoke and automobile exhaust. These reactive α,β-unsaturated aldehyde (enal) covalently modify nucleic acids, to form exocyclic adducts, where the three-carbon hydroxypropano unit bridges the N1 and N(2) positions of deoxyguanosine (dG). The bifunctional nature of these enals allows them to undergo reaction with a second nucleophilic group and form DNA cross-links. These cross-linked enal adducts are likely to contribute to the genotoxic effects of both AC and HNE. We have developed a sensitive mass spectrometric method to detect cross-linked adducts of these enals in calf thymus DNA (CT DNA) treated with AC or HNE. The AC and HNE cross-linked adducts were measured by the stable isotope dilution method, employing a linear quadrupole ion trap mass spectrometer and consecutive reaction monitoring at the MS(3) or MS(4) scan stage. The lower limit of quantification of the cross-linked adducts is ∼1 adduct per 10(8) DNA bases, when 50 μg of DNA is assayed. The cross-linked adducts occur at levels that are ∼1-2% of the levels of the monomeric 1,N(2)-dG adducts in CT DNA treated with either enal.

Seleno L-methionine acts on cyclophosphamide-induced kidney toxicity

The anticancer drug cyclophosphamide (CP) has nephrotoxic effects besides its urotoxicity, which both in turn limit its clinical utility. The nephrotoxicity of CP is less common compared to its urotoxicity, and not much importance has been given for the study of mechanism of CP-induced nephrotoxicity so far. Overproduction of reactive oxygen species (ROS) during inflammation is one of the reasons of the kidney injury. Selenoproteins play crucial roles in regulating ROS and redox status in nearly all tissues; therefore, in this study, the nephrotoxicity of CP and the possible protective effects of seleno L-methionine (SLM) on rat kidneys were investigated. Forty-two Sprague-Dawley rats were equally divided into six groups of seven rats each. The control group received saline, and other rats were injected with CP (100 mg/kg), SLM (0.5 or 1 mg/kg), or CP + SLM intraperitoneally. Malondialdehyde (MDA) and glutathione (GSH) levels in kidney homogenates of rats were measured, and kidney tissues were examined under the microscope. CP-treated rats showed a depletion of renal GSH levels (28% of control), while CP + SLM-injected rats had GSH values close to the control group. MDA levels increased 36% of control following CP administration, which were significantly decreased after SLM treatment. Furthermore, these biochemical results were supported by microscopical observations. In conclusion, the present study not only points to the therapeutic potential of SLM in CP-induced kidney toxicity but also indicates a significant role for ROS and their relation to kidney dysfunction.

Mutagenicity of acrolein and acrolein-induced DNA adducts

Acrolein mutagenicity relies on DNA adduct formation. Reaction of acrolein with deoxyguanosine generates alpha-hydroxy-1, N(2)-propano-2'-deoxyguanosine (alpha-HOPdG) and gamma-hydroxy-1, N(2)-propano-2'-deoxyguanosine (gamma-HOPdG) adducts. These two DNA adducts behave differently in mutagenicity. gamma-HOPdG is the major DNA adduct and it can lead to interstrand DNA-DNA and DNA-peptide/protein cross-links, which may induce strong mutagenicity; however, gamma-HOPdG can be repaired by some DNA polymerases complex and lessen its mutagenic effects. alpha-HOPdG is formed much less than gamma-HOPdG, but difficult to be repaired, which contributes to accumulation in vivo. Results of acrolein mutagenicity studies haven't been confirmed, which is mainly due to the conflicting mutagenicity data of the major acrolein adduct (gamma-HOPdG). The minor alpha-HOPdG is mutagenic in both in vitro and in vivo test systems. The role of alpha-HOPdG in acrolein mutagenicity needs further investigation. The inconsistent result of acrolein mutagenicity can be attributed, at least partially, to a variety of acrolein-DNA adducts formation and their repair in diverse detection systems. Recent results of detection of acrolein-DNA adduct in human lung tissues and analysis of P53 mutation spectra in acrolein-treated cells may shed some light on mechanisms of acrolein mutagenicity. These aspects are covered in this mini review.

Acrolein-derived DNA adduct formation in human colon cancer cells: its role in apoptosis induction by docosahexaenoic acid

The apoptotic effects of docosahexaenoic acid (DHA) and other omega-3 polyunsaturated fatty acids (PUFAs) have been documented in cell and animal studies. The molecular mechanism by which DHA induces apoptosis is unclear. Although there is no direct evidence, some studies have suggested that DNA damage generated through lipid peroxidation may be involved. Our previous studies showed that DHA, because it has a high degree of unsaturation, can give rise to the acrolein-derived 1,N(2)-propanodeoxyguanosine (Acr-dG) as a major class of DNA adducts via lipid oxidation. As a first step to investigate the possible role of oxidative DNA damage in apoptosis induced by DHA, we examined the relationships between oxidative DNA damage and apoptosis caused by DHA in human colon cancer HT-29 cells. Apoptosis and oxidative DNA damage, including Acr-dG and 8-oxo-deoxyguanosine (8-oxo-dG) formation, in cells treated with DHA and omega-6 PUFAs, including arachidonic acid (AA) and linoleic acid (LA), were measured. DHA induced apoptosis in a dose- and time-dependent manner with a concentration range from 0 to 300 microM as indicated by increased caspase-3 activity and PARP cleavage. In contrast, AA and LA had little or no effect at these concentrations. The Acr-dG levels were increased in HT-29 cells treated with DHA at 240 and 300 microM, and the increases were correlated with the induction of apoptosis at these concentrations, while no significant changes were observed for 8-oxo-dG. Because proteins may compete with DNA to react with acrolein, we then examined the effects of BSA on DHA-induced apoptosis and oxidative DNA damage. The addition of BSA to HT-29 cell culture media significantly decreases Acr-dG levels with a concomitant decrease in the apoptosis induced by DHA. The reduced Acr-dG formation is attributed to the reaction of BSA with acrolein as indicated by increased levels of total protein carbonyls. Similar correlations between Acr-dG formation and apoptosis were observed in HT-29 cells directly incubated with 0-200 microM acrolein. Additionally, DHA treatment increased the level of DNA strand breaks and caused cell cycle arrested at G1 phase. Taken together, these results demonstrate the parallel relationships between Acr-dG level and apoptosis in HT-29 cells, suggesting that the formation of Acr-dG in cellular DNA may contribute to apoptosis induced by DHA.

Chemistry and biology of DNA containing 1,N(2)-deoxyguanosine adducts of the alpha,beta-unsaturated aldehydes acrolein, crotonaldehyde, and 4-hydroxynonenal

The α,β-unsaturated aldehydes (enals) acrolein, crotonaldehyde, and trans-4-hydroxynonenal (4-HNE) are products of endogenous lipid peroxidation, arising as a consequence of oxidative stress. The addition of enals to dG involves Michael addition of the N²-amine to give N²-(3-oxopropyl)-dG adducts, followed by reversible cyclization of N1 with the aldehyde, yielding 1,N²-dG exocyclic products. The 1,N²-dG exocyclic adducts from acrolein, crotonaldehyde, and 4-HNE exist in human and rodent DNA. The enal-induced 1,N²-dG lesions are repaired by the nucleotide excision repair pathway in both Escherichia coli and mammalian cells. Oligodeoxynucleotides containing structurally defined 1,N²-dG adducts of acrolein, crotonaldehyde, and 4-HNE were synthesized via a postsynthetic modification strategy. Site-specific mutagenesis of enal adducts has been carried out in E. coli and various mammalian cells. In all cases, the predominant mutations observed are G→T transversions, but these adducts are not strongly miscoding. When placed into duplex DNA opposite dC, the 1,N²-dG exocyclic lesions undergo ring opening to the corresponding N²-(3-oxopropyl)-dG derivatives. Significantly, this places a reactive aldehyde in the minor groove of DNA, and the adducted base possesses a modestly perturbed Watson−Crick face. Replication bypass studies in vitro indicate that DNA synthesis past the ring-opened lesions can be catalyzed by pol η, pol ι, and pol κ. It also can be accomplished by a combination of Rev1 and pol ζ acting sequentially. However, efficient nucleotide insertion opposite the 1,N²-dG ring-closed adducts can be carried out only by pol ι and Rev1, two DNA polymerases that do not rely on the Watson−Crick pairing to recognize the template base. The N²-(3-oxopropyl)-dG adducts can undergo further chemistry, forming interstrand DNA cross-links in the 5′-CpG-3′ sequence, intrastrand DNA cross-links, or DNA−protein conjugates. NMR and mass spectrometric analyses indicate that the DNA interstand cross-links contain a mixture of carbinolamine and Schiff base, with the carbinolamine forms of the linkages predominating in duplex DNA. The reduced derivatives of the enal-mediated N²-dG:N²-dG interstrand cross-links can be processed in mammalian cells by a mechanism not requiring homologous recombination. Mutations are rarely generated during processing of these cross-links. In contrast, the reduced acrolein-mediated N²-dG peptide conjugates can be more mutagenic than the corresponding monoadduct. DNA polymerases of the DinB family, pol IV in E. coli and pol κ in human, are implicated in error-free bypass of model acrolein-mediated N²-dG secondary adducts, the interstrand cross-links, and the peptide conjugates.

Benefit of Satureja khuzestanica in subchronically rat model of cyclophosphamide-induced hemorrhagic cystitis

Cyclophosphamide (CP) as a widely used antineoplastic drug causes hemorrhagic cystitis (HC) mainly via induction of oxidative stress. Regarding established antioxidant potential of Satureja khuzestanica (Lamiaceae) essential oil (SKEO), we aimed to investigate its protective effects in a subchronic rat model of CP-induced HC. CP (6mg/kg/day) and SKEO (225mg/kg/day) were administered alone or in combination by gavage for 28 days. Histopathological changes were investigated by light microscopy. Plasma samples were assayed for lipid peroxidation and total antioxidant power as biomarkers of toxic stress. In the CP-treated animals, irregular mucus layer, severe hemorrhage and edema, infiltration of inflammatory cells, and accumulation of mast cells were observed. In the CP+SKEO group, a relatively normal urothelial topography with decreased number of mucosal mast cells and inflammatory cells were observed. Increased lipid peroxidation along with decreased total antioxidant capacity resulting from CP treatment was significantly recovered by SKEO co-treatment. It is concluded that SKEO protects rats from CP-induced HC by reduction of free radical-induced toxic stress. It is strongly recommended to examine SKEO in the clinic to approve its benefit in patients undertaking CP.

Acrolein health effects

Acrolein is a chemical used as an intermediate reactive aldehyde in chemical industry. It is used for synthesis of many organic substances, methionine production, and methyl chloride refrigerant. The general population is exposed to acrolein via smoking, second-hand smoke, exposure to wood and plastic smoke. Firefighters and population living or working in areas with heavy automotive traffic may expose to higher level of acrolein via inhalation of smoke or automotive exhaust. Degradation of acrolein in all environmental media occurs rapidly, therefore, environmental accumulation is not expected. Acrolein degrade in 6A days when applied to surface water, and it has not been found as a contaminant in municipal drinking water. Acrolein vapor may cause eye, nasal and respiratory tract irritations in low level exposure. A decrease in breathing rate was reported by volunteers acutely exposed to 0.3A ppm of acrolein. At similar level, mild nasal epithelial dysplasia, necrosis, and focal basal cell metaplasia have been observed in rats. The acrolein effects on gastrointestinal mucosa in the animals include epithelial hyperplasia, ulceration, and hemorrhage. The severity of the effects is dose dependent. Acrolein induces the respiratory, ocular, and gastrointestinal irritations by inducing the release of peptides in nerve terminals innervating these systems. Levels of acrolein between 22 and 249 ppm for 10 min induced a dose-related decrease in substance P (a short-chain polypeptide that functions as a neurotransmitter or neuromodulator).

Solution structure of DNA containing alpha-OH-PdG: the mutagenic adduct produced by acrolein

Acrolein is a cell metabolic product and a main component of cigarette smoke. Its reaction with DNA produces two guanine lesions γ-OH-PdG, a major adduct that is nonmutagenic in mammalian cells, and the positional isomer α-OH-PdG. We describe here the solution structure of a short DNA duplex containing a single α-OH-PdG lesion, as determined by solution NMR spectroscopy and restrained molecular dynamics simulations. The spectroscopic data show a mostly regular right-handed helix, locally perturbed at its center by the presence of the lesion. All undamaged residues of the duplex are in anti orientation, forming standard Watson–Crick base-pair alignments. Duplication of proton signals near the damaged site differentiates two enantiomeric duplexes, thus establishing the exocyclic nature of the lesion. At the lesion site, α-OH-PdG rotates to a syn conformation, pairing to its counter cytosine residue that is protonated at pH 5.9. Three-dimensional models produced by restrained molecular dynamics simulations show different hydrogen-bonding patterns between the lesion and its cytosine partner and identify further stabilization of α-OH-PdG in a syn conformation by intra-residue hydrogen bonds. We compare the α-OH-PdG•dC duplex structure with that of duplexes containing the analogous lesion propano-dG and discuss the implications of our findings for the mutagenic bypass of acrolein lesions.

Protection of cyclophosphamide-induced toxicity in reproductive tract histology, sperm characteristics, and DNA damage by an herbal source; evidence for role of free-radical toxic stress

Cyclophosphamide (CP) as an anticancer alkylating agent has been known as a male reproductive tract toxicant. The aim of this study was to examine whether Satureja khuzestanica essential oil (SKEO) as an established herbal antioxidant, might protect tract rat reproductive system from toxicity of CP. To reach this aim, total antioxidant power (TAP) and lipid peroxidation (LPO) in testis and plasma, blood levels of sex hormones, sperm characteristics, DNA integrity and chromatin quality, and fertility in male rats were tested. Histopathological analysis of testes and epididymides and staining of mast cells were performed for assessment of spermatogenic disorders. CP (6 mg/kg/day) and SKEO (225 mg/kg/day) were administered alone or in combination by gavage for 28 days. In the CP-exposed rats, testicular and plasma LPO increased, TAP decreased, plasma testosterone diminished, and both spermatogenesis and fertility were impaired. In CP-treated rats, a decrease in sperm quality was associated with increased DNA damage and decreased chromatin quality. Coadministration of SKEO significantly improved CP-induced changes in plasma testosterone, sperm quality, spermatogenesis and fertility, toxic stress, and DNA damage. It is concluded that CP-induced toxic effects on androgenesis and spermatogenesis is mediated by free radicals. SKEO protects reproductive system from toxicity of CP through its antioxidant potential and androgenic activity.

Interstrand DNA cross-links induced by alpha,beta-unsaturated aldehydes derived from lipid peroxidation and environmental sources

Significant levels of the 1, N(2)-gamma-hydroxypropano-dG adducts of the alpha,beta-unsaturated aldehydes acrolein, crotonaldehyde, and 4-hydroxy-2E-nonenal (HNE) have been identified in human DNA, arising from both exogenous and endogenous exposures. They yield interstrand DNA cross-links between guanines in the neighboring C.G and G.C base pairs located in 5'-CpG-3' sequences, as a result of opening of the 1,N(2)-gamma-hydroxypropano-dG adducts to form reactive aldehydes that are positioned within the minor groove of duplex DNA. Using a combination of chemical, spectroscopic, and computational methods, we have elucidated the chemistry of cross-link formation in duplex DNA. NMR spectroscopy revealed that, at equilibrium, the acrolein and crotonaldehyde cross-links consist primarily of interstrand carbinolamine linkages between the exocyclic amines of the two guanines located in the neighboring C.G and G.C base pairs located in 5'-CpG-3' sequences, that maintain the Watson-Crick hydrogen bonding of the cross-linked base pairs. The ability of crotonaldehyde and HNE to form interstrand cross-links depends upon their common relative stereochemistry at the C6 position of the 1,N(2)-gamma-hydroxypropano-dG adduct. The stereochemistry at this center modulates the orientation of the reactive aldehyde within the minor groove of the double-stranded DNA, either facilitating or hindering the cross-linking reactions; it also affects the stabilities of the resulting diastereoisomeric cross-links. The presence of these cross-links in vivo is anticipated to interfere with DNA replication and transcription, thereby contributing to the etiology of human disease. Reduced derivatives of these cross-links are useful tools for studying their biological processing.

Modifications of nucleosides by endogenous mutagens-DNA adducts arising from cellular processes

DNA damage plays a significant role in mutagenesis, carcinogenesis and ageing. Chemical transformations leading to DNA damage include reactions of the base units with agents of endogenous and exogenous origin. The vast majority of damage arising from cellular processes such as metabolism and lipid peroxidation are identical or very similar to those induced by exposure to environmental agents. A detailed knowledge of the types and prevalence of endogenous DNA damage provides insight into the chemical nature of species involved in these modifications and may be of help in understanding their influence on the induction of cancer or other diseases. This knowledge may also be essential to the development of rational chemopreventive strategies directed against the initiation of oxidative stress- and lipid peroxidation-associated pathology. The present work reviews findings regarding the interaction between DNA bases and various reactive species arising from lipid peroxidation and other cellular processes, drawing attention to the mechanism responsible for the formation of the resulted modifications. The biological consequences of these interactions are also briefly discussed.

Acrolein is a major cigarette-related lung cancer agent: Preferential binding at p53 mutational hotspots and inhibition of DNA repair

The tumor suppressor gene p53 is frequently mutated in cigarette smoke (CS)-related lung cancer. The p53 binding pattern of carcinogenic polycyclic aromatic hydrocarbons (PAHs) found in CS coincides with the p53 mutational pattern found in lung cancer, and PAHs have thus been considered to be major culprits for lung cancer. However, compared with other carcinogenic compounds, such as aldehydes, the amount of PAHs in CS is minute. Acrolein (Acr) is abundant in CS, and it can directly adduct DNA. Acr-DNA adducts, similar to PAH-DNA adducts, induce predominantly G-to-T transversions in human cells. These findings raise the question of whether Acr-DNA adducts are responsible for p53 mutations in CS-related lung cancer. To determine the role of Acr-DNA adducts in p53 mutagenesis in CS-related lung cancer we mapped the distribution of Acr-DNA adducts at the sequence level in the p53 gene of lung cells using the UvrABC incision method in combination with ligation-mediated PCR. We found that the Acr-DNA binding pattern is similar to the p53 mutational pattern in human lung cancer. Acr preferentially binds at CpG sites, and this enhancement of binding is due to cytosine methylation at these sequences. Furthermore, we found that Acr can greatly reduce the DNA repair capacity for damage induced by benzo[a]pyrene diol epoxide. Together these results suggest that Acr is a major etiological agent for CS-related lung cancer and that it contributes to lung carcinogenesis through two detrimental effects: DNA damage and inhibition of DNA repair.

Attenuation of cyclophosphamide induced toxicity by squalene in experimental rats

Cyclophosphamide (CP) is a widely used antineoplastic drug, which could cause toxicity of the normal cells due to its toxic metabolites. In this study, the protective role of squalene (SQ) towards the tissue defense system in the toxicity induced by CP (150 mg/kg b.w., twice, in 2 consecutive days) was studied in the experimental rats. The significant (P<0.05) alterations in the levels of enzymic [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR)] and non-enzymic antioxidants [total reduced glutathione (GSH), Vitamin E (Vit.E), Vitamin C (Vit.C) and ceruloplasmin] of the heart, red blood cell (RBC) hemolysate and plasma were investigated in the CP toxicity. Alterations in the levels of thiobarbutric acid reactive substance (TBARS) in heart, RBC hemolysate and plasma were also observed as a measure of lipid peroxidation (LPO). These pathological alterations due to CP administration were attenuated by the oral treatment of SQ at a dose of 0.4 ml/day/rat. These observations demonstrate the protective role of SQ towards the tissue defense system of the rats in the CP induced toxicity.

Spectroscopic characterization of interstrand carbinolamine cross-links formed in the 5'-CpG-3' sequence by the acrolein-derived gamma-OH-1,N2-propano-2'-deoxyguanosine DNA adduct

The interstrand N2,N2-dG DNA cross-linking chemistry of the acrolein-derived gamma-OH-1,N2-propanodeoxyguanosine (gamma-OH-PdG) adduct in the 5'-CpG-3' sequence was monitored within a dodecamer duplex by NMR spectroscopy, in situ, using a series of site-specific 13C- and 15N-edited experiments. At equilibrium 40% of the DNA was cross-linked, with the carbinolamine form of the cross-link predominating. The cross-link existed in equilibrium with the non-crosslinked N2-(3-oxo-propyl)-dG aldehyde and its geminal diol hydrate. The ratio of aldehyde/diol increased at higher temperatures. The 1,N2-dG cyclic adduct was not detected. Molecular modeling suggested that the carbinolamine linkage should be capable of maintaining Watson-Crick hydrogen bonding at both of the tandem C x G base pairs. In contrast, dehydration of the carbinolamine cross-link to an imine (Schiff base) cross-link, or cyclization of the latter to form a pyrimidopurinone cross-link, was predicted to require disruption of Watson-Crick hydrogen bonding at one or both of the tandem cross-linked C x G base pairs. When the gamma-OH-PdG adduct contained within the 5'-CpG-3' sequence was instead annealed into duplex DNA opposite T, a mixture of the 1,N2-dG cyclic adduct, the aldehyde, and the diol, but no cross-link, was observed. With this mismatched duplex, reaction with the tetrapeptide KWKK formed DNA-peptide cross-links efficiently. When annealed opposite dA, gamma-OH-PdG remained as the 1,N2-dG cyclic adduct although transient epimerization was detected by trapping with the peptide KWKK. The results provide a rationale for the stability of interstrand cross-links formed by acrolein and perhaps other alpha,beta-unsaturated aldehydes. These sequence-specific carbinolamine cross-links are anticipated to interfere with DNA replication and contribute to acrolein-mediated genotoxicity.

Stereospecific formation of interstrand carbinolamine DNA cross-links by crotonaldehyde- and acetaldehyde-derived alpha-CH3-gamma-OH-1,N2-propano-2'-deoxyguanosine adducts in the 5'-CpG-3' sequence

The crotonaldehyde- and acetaldehyde-derived R- and S-alpha-CH3-gamma-OH-1,N2-propanodeoxyguanosine adducts were monitored in single-stranded and duplex oligodeoxynucleotides using NMR spectroscopy. In both instances, the cis and trans diastereomers of the alpha-CH3 and gamma-OH groups underwent slow exchange, with the trans diastereomers being favored. In single-stranded oligodeoxynucleotides, the aldehyde intermediates were not detected spectroscopically, but their presence was revealed through the formation of N-terminal conjugates with the tetrapeptide KWKK. When annealed into 5'-d(GCTAGCXAGTCC)-3'.5'-d(GGACTCYCTAGC)-3' containing the 5'-CpG-3' sequence context (X = R- or S-alpha-CH3-gamma-13C-OH-PdG; Y = 15N2-dG) at pH 7, partial opening of the R- or S-alpha-CH3-gamma-13C-OH-PdG adducts to the corresponding N2-(3-oxo-1-methyl-propyl)-dG aldehydes was observed at temperatures below the T(m) of the duplexes. These aldehydes equilibrated with their geminal diol hydrates; higher temperatures favored the aldehydes. When annealed opposite T, the S-alpha-CH3-gamma-13C-OH-PdG adduct was stable. At 37 degrees C, an interstrand DNA cross-link was observed spectroscopically only for the R-alpha-CH3-gamma-OH-PdG adduct. Molecular modeling predicted that the interstrand cross-link formed by the R-alpha-CH3-gamma-OH-PdG adduct introduced less disruption into the duplex structure than did the cross-link arising from the S-alpha-CH3-gamma-OH-PdG adduct, due to differing orientations of the R- and S-CH3 groups. Modeling also predicted that the alpha-methyl group of the aldehyde arising from the R-alpha-CH3-gamma-OH-PdG adduct is oriented in the 3'-direction in the minor groove, facilitating cross-linking. In contrast, the alpha-methyl group of the aldehyde arising from the S-alpha-CH3-gamma-OH-PdG adduct is oriented in the 5'-direction within the minor groove, potentially hindering cross-linking. NMR revealed that for the R-alpha-CH3-gamma-OH-PdG adduct, the carbinolamine form of the cross-link was favored in duplex DNA with the imine (Schiff base) form of the cross-link remaining below the level of spectroscopic detection. Molecular modeling predicted that the carbinolamine linkage maintained Watson-Crick hydrogen bonding at both of the tandem C.G base pairs. Dehydration of the carbinolamine cross-link to an imine, or cyclization of the latter to form a pyrimidopurinone cross-link, required disruption of Watson-Crick hydrogen bonding at one or both of the cross-linked base pairs.

Effect of gamma-hydroxypropano deoxyguanosine, the major acrolein-derived adduct, on monomolecular quadruplex structure of telomeric repeat d(TTAGGG)(4)

The three oligodeoxyribonucleotides (ODNs) a-c, having the telomeric repeat d(TTAGGG)(4) sequence and incorporating gamma-hydroxypropano deoxyguanosine at different positions, were synthesized. Gel electrophoresis and CD analyses indicated that the ODNs assume monomolecular quadruplex structures in Na+ and in K+ buffers. The T(m) values, obtained by CD melting experiments, showed that the presence of the acrolein-dG adduct into the ODN b decreases the thermal stability of the monomolecular quadruplex structure in Na+ solution, whereas for a and c no significant effect could be detected in the same experimental conditions. On the contrary, all ODNs a-d show the same behaviour in K+ buffer. These findings are briefly discussed.

Role of oxygen radicals in DNA damage and cancer incidence

The development of cancer in humans and animals is a multistep process. The complex series of cellular and molecular changes participating in cancer development are mediated by a diversity of endogenous and exogenous stimuli. One type of endogenous damage is that arising from intermediates of oxygen (dioxygen) reduction - oxygen-free radicals (OFR), which attacks not only the bases but also the deoxyribosyl backbone of DNA. Thanks to improvements in analytical techniques, a major achievement in the understanding of carcinogenesis in the past two decades has been the identification and quantification of various adducts of OFR with DNA. OFR are also known to attack other cellular components such as lipids, leaving behind reactive species that in turn can couple to DNA bases. Endogenous DNA lesions are genotoxic and induce mutations. The most extensively studied lesion is the formation of 8-OH-dG. This lesion is important because it is relatively easily formed and is mutagenic and therefore is a potential biomarker of carcinogenesis. Mutations that may arise from formation of 8-OH-dG involve GC --> TA transversions. In view of these findings, OFR are considered as an important class of carcinogens. The effect of OFR is balanced by the antioxidant action of non-enzymatic antioxidants as well as antioxidant enzymes. Non-enzymatic antioxidants involve vitamin C, vitamin E, carotenoids (CAR), selenium and others. However, under certain conditions, some antioxidants can also exhibit a pro-oxidant mechanism of action. For example, beta-carotene at high concentration and with increased partial pressure of dioxygen is known to behave as a pro-oxidant. Some concerns have also been raised over the potentially deleterious transition metal ion-mediated (iron, copper) pro-oxidant effect of vitamin C. Clinical studies mapping the effect of preventive antioxidants have shown surprisingly little or no effect on cancer incidence. The epidemiological trials together with in vitro experiments suggest that the optimal approach is to reduce endogenous and exogenous sources of oxidative stress, rather than increase intake of anti-oxidants. In this review, we highlight some major achievements in the study of DNA damage caused by OFR and the role in carcinogenesis played by oxidatively damaged DNA. The protective effect of antioxidants against free radicals is also discussed.

Detoxication of the environmental pollutant acrolein by a rat liver aldo-keto reductase

Acrolein is a highly reactive hazardous air pollutant of human health concern, particularly as it is a component of cigarette smoke. It can be metabolized by enzymes including the aldo-keto reductase (AKR) family of enzymes. AKR7A1 is a member of the AKR7 sub-family and can catalyse the reduction of toxic aldehydes, including alpha-unsaturated carbonyl compounds, to alcohols [Biochem. J. 312 (1995) 535]. In this study, the role of AKR7A1 in protecting against acrolein toxicity has been assessed by stably-expressing a cDNA encoding AKR7A1 in Chinese hamster V79 cells. Cells expressing AKR7A1 showed over 2-fold increased resistance to acrolein compared to V79 cells alone, as measured by 3-[4,4-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays. IC50 increased from 45 microM in control V79-pCI-neo cells to 125microM for V79-AKR7A1 cells. Cells expressing AKR7A1 were also found to be less susceptible to DNA damage, showing a decrease in mutation rate in the presence of acrolein as measured by hypoxanthine guanine phosphoribosyl transferase (HGPRT) mutagenicity assays. The mutation rate for acrolein-exposed control cells was 20-fold higher than for acrolein-exposed AKR7A1-expressing cells. These results indicate that AKR7A1 has the potential to protect against acrolein-induced damage in vivo.