Mutagenesis by the autoxidation of iron with isolated DNA

Fe2+ protects postharvest pitaya (Hylocereus undulatus britt) from Aspergillus. flavus infection by directly binding its genomic DNA

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Light was shield on Fe²⁺ application as antifungal agent on pitaya postharvest.

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Fe²⁺ prevents A. flavus infection by directly binding to A. flavus DNA.

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This research will promote the research on the mechanism of fungal death.

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A new strategy was provided to combat fungal infection in fruit postharvest industry.

Aspergillus flavus (A. flavus) is a postharvest fungus, causing pitaya fruit decay and limiting pitaya value and shelf life. However, safer and more efficient methods for preventing A. flavus contamination for pitaya fruit remain to be investigated. In this study, we successfully proved exogenous Fe²⁺ could inhibit A. flavus colonization in pitaya fruit and extend pitaya’s shelf life after harvest. Moreover, gel electrophoresis, CD analysis and Raman spectrum tests revealed Fe²⁺ could more effectively and thoroughly promote conidial death by directly binding to A. flavus DNA. Increased expression of DNA damage repair-related genes after Fe²⁺ treatment was observed by transcription analysis, which might eventually lead to SOS response in A. flavus. These results indicated Fe²⁺ could prevent A. flavus infestation on pitaya in a novel, quickly responsive mechanism. Our results shed light on the potential application of Fe²⁺ in the food industry and provided a more universal antifungal agent against food pathogens.

Hepatocellular Carcinoma in β-Thalassemia Patients: Review of the Literature with Molecular Insight into Liver Carcinogenesis

With the continuing progress in managing patients with thalassemia, especially in the setting of iron overload and iron chelation, the life span of these patients is increasing, while concomitantly increasing incidences of many diseases that were less likely to show when survival was rather limited. Hepatocellular carcinoma (HCC) is a major life-threatening cancer that is becoming more frequently identified in this population of patients. The two established risk factors for the development of HCC in thalassemia include iron overload and viral hepatitis with or without cirrhosis. Increased iron burden is becoming a major HCC risk factor in this patient population, especially in those in the older age group. As such, screening thalassemia patients using liver iron concentration (LIC) measurement by means of magnetic resonance imaging (MRI) and liver ultrasound is strongly recommended for the early detection of iron overload and for implementation of early iron chelation in an attempt to prevent organ-damaging iron overload and possibly HCC. There remain lacking data on HCC treatment outcomes in patients who have thalassemia. However, a personalized approach tailored to each patient’s comorbidities is essential to treatment success. Multicenter studies investigating the long-term outcomes of currently available therapeutic options in the thalassemia realm, in addition to novel HCC therapeutic targets, are needed to further improve the prognosis of these patients.

Detection of Carcinogen–Macromolecular Adducts in Humans

A major concern of molecular epidemiology is the identification of individuals at increased risk of cancer by obtaining evidence of high exposure to carcinogens that may lead to pathobiological lesions in target cells. DNA is considered to be a target for modification by mutagens and carcinogens; therefore, damage to DNA can be used as an internal, molecular dosimeter of carcinogen exposure. The reactive species of these carcinogens may bind either directly to DNA to form adducts or indirectly to cause secondary DNA lesions through free radicals and aldehydes. Highly sensitive and specific methods have been developed to measure DNA lesions and DNA repair products that are found in biological specimens from humans exposed to carcinogens in the environment. For example, DNA adducts have been measured in cells and tissues from people exposed environmentally to carcinogenic polycyclic aromatic hydrocarbons or alkylating agents. Antibodies recognizing carcinogen-DNA adducts have also been detected in human sera. Carcinogen-protein adducts are also being used as molecular dosimeters of carcinogen exposure. The advantages and limitations of the various methods used to measure carcinogen-macromolecular adducts are discussed here. The use of two or more complementary assays to obtain confirmatory results is recommended.

The role of genetic factors in patients with hepatocellular carcinoma and iron overload - a prospective series of 234 patients

BACKGROUND & AIMS

Iron overload (IO) in HFE-related hereditary haemochromatosis is associated with increased risk of liver cancer. This study aimed to investigate the role of other genes involved in hereditary IO among patients with hepatocellular carcinoma (HCC).

METHODS

Patients with HCC diagnosed in our institution were included in this prospective study. Those with ferritin levels ≥300 μg/L (males) or ≥200 μg/L (females) and/or transferrin saturation ≥50% (males) or ≥45% (females) had liver iron concentration (LIC) evaluated by MRI. HFE C282Y and H63D mutations were screened. Genetic analyses of genes involved in hereditary IO (HFE, HJV/HFE2, HAMP, TFR2, SLC40A1, GNPAT) were performed in patients with increased LIC.

RESULTS

A total of 234 patients were included; 215 (92%) had common acquired risk factors of HCC (mainly alcoholism or chronic viral hepatitis). 119 patients had abnormal iron parameters. Twelve (5.1%) were C282Y homozygotes, three were compound C282Y/H63D heterozygotes. LIC was measured by MRI in 100 patients. Thirteen patients with a LIC>70 μmol/g were enrolled in further genetic analyses: two unrelated patients bore the HAMP:c.-153C>T mutation at the heterozygous state, which is associated with increased risk of IO and severe haemochromatosis. Specific haplotypes of SLC40A1 were also studied.

CONCLUSIONS

Additional genetic risk factors of IO were found in 18 patients (7.7%) among a large series of 234 HCC patients. Screening for IO and the associated at-risk genotypes in patients who have developed HCC, is useful for both determining etiologic diagnosis and enabling family screening and possibly primary prevention in relatives.

Morphological and chemical mechanisms of elongated mineral particle toxicities

Much of our understanding regarding the mechanisms for induction of disease following inhalation of respirable elongated mineral particles (REMP) is based on studies involving the biological effects of asbestos fibers. The factors governing the disease potential of an exposure include duration and frequency of exposures; tissue-specific dose over time; impacts on dose persistence from in vivo REMP dissolution, comminution, and clearance; individual susceptibility; and the mineral type and surface characteristics. The mechanisms associated with asbestos particle toxicity involve two facets for each particle's contribution: (1) the physical features of the inhaled REMP, which include width, length, aspect ratio, and effective surface area available for cell contact; and (2) the surface chemical composition and reactivity of the individual fiber/elongated particle. Studies in cell-free systems and with cultured cells suggest an important way in which REMP from asbestos damage cellular molecules or influence cellular processes. This may involve an unfortunate combination of the ability of REMP to chemically generate potentially damaging reactive oxygen species, through surface iron, and the interaction of the unique surfaces with cell membranes to trigger membrane receptor activation. Together these events appear to lead to a cascade of cellular events, including the production of damaging reactive nitrogen species, which may contribute to the disease process. Thus, there is a need to be more cognizant of the potential impact that the total surface area of REMP contributes to the generation of events resulting in pathological changes in biological systems. The information presented has applicability to inhaled dusts, in general, and specifically to respirable elongated mineral particles.

Familial multiple myeloma. Two more families

The authors report on two multiple myeloma sibling pairs. In the absence of a known disease-specific marker one can only speculate on an explanation: is it because of inherited errors or is it related to the same environmental exposure, or both? In this study HLA typing and metabolizing enzyme polymorphism studies have been carried out with the aim of finding inherited similarities in the siblings or characteristics that might differ from the average population. Sibling pair 1 shared an HLA haplotype. Sibling pair 2 shared only HLA-B51, DR4, DRw53, DQ3. Sibling 1/1 was GSTT1 / GSTM1 null and GSTP1 Ile105Val; sibling 1/2 was a GSTT1 / GSTM1 heterozygote and GSTP1 Ile105Val; sibling 2/1 and 2/2 were GSTT1 heterozygotes and shared GSTM1 null / GSTP1 Ile105Ile. The siblings had identical light chain or heavy chain secretion, or both. The similarities found in the inherited factors together with the same environmental exposure in the siblings’ first 20 years of life imply that the development of the same disease cannot be a coincidence.

Cytological and biochemical effects of St. John's Wort supplement (a complex mixture of St. John's Wort, Rosemary and Spirulina) on somatic and germ cells of Swiss Albino mice

Commercially available St. John’s wort supplement (SJWS) composed of an herbal mixture of St. John’s Wort (SJW), Rosemary (RM) and Spirulina (SP) is used as a dietary supplement for the treatment of psychiatric disorders. Although the minor ingredients, (RM and SP) are proven antioxidants, their quantity is quite insignificant as compared to the SJW, which is the major ingredient. Most of the toxic effects of SJWS are attributed to the main constituents of SJW which differ due to the influence of light (hypericin) and variations in temperature above freezing point (hyperforin). However, there are no reports on toxicity of SJWS maintained at room temperature in pharmacies and supermarkets. In view of the folkloric importance, immense (prescribed or unprescribed) use and a paucity of literature on SJWS, it was found worthwhile to (1) determine the genotoxic effects of SJWS in somatic and germ cells of mice and (2) investigate the role of biochemical changes, as a possible mechanism. The protocol included the oral treatment of mice with different doses (380, 760 and 1520 mg/kg/day) of SJWS for 7 days. The following experiments were conducted: (i) cytological studies on micronucleus test, (ii) cytogenetic analysis for meiotic chromosomes, (iii) cytological analysis of spermatozoa abnormalities, (iv) quantification of proteins and nucleic acids in hepatic and testicular cells and (v) estimation of malondialdehyde (MDA) and nonprotein sulfhydryl (NP-SH) in hepatic and testicular cells. The treatment increased the frequency of micronuclei in polychromatic erythrocytes (PCE) in the femora. It caused aberrations in chromosomes of testes and induced spermatozoa abnormalities. These changes might be attributed to the epigenetic mechanisms as revealed by an increase in concentrations of MDA and depletion of nucleic acids and NP-SH levels in both hepatic and testicular cells observed in the present study. Since, the samples of SJWS used were not drawn from extremities of light and temperature; the observed effect might not be related to the main constituents of SJW. However, these changes might be ascribed to the combined effect of terpenes, tannins, quercetin and flavonoids present in SJW.

Hepatic iron overload and hepatocellular carcinoma

The liver is the main storage site for iron in the body. Excess accumulation of iron in the liver has been well-documented in two human diseases, hereditary hemochromatosis and dietary iron overload in the African. Hepatic iron overload in these conditions often results in fibrosis and cirrhosis and may be complicated by the development of hepatocellular carcinoma. Malignant transformation usually occurs in the presence of cirrhosis, suggesting that free iron-induced chronic necroinflammatory hepatic disease plays a role in the hepatocarcinogenesis. However, the supervention of hepatocellular carcinoma in the absence of cirrhosis raises the possibility that ionic iron may also be directly hepatocarcinogenic. Support for this possibility is provided by a recently described animal model of dietary iron overload in which iron-free preneoplastic nodules and hepatocellular carcinoma developed in the absence of fibrosis or cirrhosis. The mechanisms by which iron induces malignant transformation have yet to be fully characterized but the most important appears to be the generation of oxidative stress. Free iron generates reactive oxygen intermediates that disrupt the redox balance of the cells and cause chronic oxidative stress. Oxidative stress leads to lipid peroxidation of unsaturated fatty acids in membranes of cells and organelles. Cytotoxic by-products of lipid peroxidation, such as malondialdehyde and 4-hydroxy-2'-nonenal, are produced and these impair cellular function and protein synthesis and damage DNA. Deoxyguanosine residues in DNA are also hydroxylated by reactive oxygen intermediates to form 8-hydroxy-2'-deoxyguanosine, a major promutagenic adduct that causes G:C to T:A transversions and DNA unwinding and strand breaks. Free iron also induces immunologic abnormalities that may decrease immune surveillance for malignant transformation.

Prevalence of hepatic iron overload and association with hepatocellular cancer in end-stage liver disease: results from the National Hemochromatosis Transplant Registry

BACKGROUND

It is unclear whether mild to moderate iron overload in liver diseases other than hereditary haemochromatosis (HH) contributes to hepatocellular carcinoma. This study examined the association between hepatic iron grade and hepatocellular carcinoma in patients with end-stage liver disease of diverse aetiologies.

METHODS

The prevalence of hepatic iron overload and hepatocellular carcinoma was examined in 5224 patients undergoing liver transplantation. Explant pathology reports were reviewed for the underlying pathological diagnosis, presence of hepatocellular carcinoma and degree of iron staining. The distribution of categorical variables was studied using chi(2) tests.

RESULTS

Both iron overload and hepatocellular carcinoma were the least common with biliary cirrhosis (1.8 and 2.8% respectively). Hepatocellular carcinoma was the most common in patients with hepatitis B (16.7%), followed by those with hepatitis C (15.1%) and HH (14.9%). In the overall cohort, any iron overload was significantly associated with hepatocellular carcinoma (P=0.001), even after adjustment for the underlying aetiology of liver disease. The association between hepatic iron content and hepatocellular carcinoma was the strongest in patients with biliary cirrhosis (P<0.001) and hepatitis C (P<0.001).

CONCLUSIONS

Iron overload is associated with hepatocellular carcinoma in patients with end-stage liver disease, suggesting a possible carcinogenic or cocarcinogenic role for iron in chronic liver disease.

Hepatocellular carcinoma: epidemiology and clinical aspects

Liver cancer is one of the most frequent solid cancers that kills more than 650,000 people around the world each year. Though great improvements have been done in last 10 years on the understanding the molecular mechanisms involved in liver oncogenesis, the prognosis of patients affected by liver cancer is still poor for most of them. Even in those where a relatively early diagnosis is done, the course of the disease is often fatal due to the underlying liver cirrhosis. In this review authors report the most recent findings on the pathogenesis of liver cancer and on therapeutic approaches, included those emerging from the most recent literature.

Determination of copper(I) and copper(II) ions after complexation with bicinchoninic acid by CE

A facile, sensitive, and selective method was developed for the simultaneous separation and determination of copper(I) [Cu(+)] and copper(II) [Cu(2+)] ions using CE with direct UV detection. The copper ions were complexed with a 1.5 mM bicinchoninic acid disodium salt solution at pH 8.7 prior to analysis. Acetate buffer (2 mM) was used as the CE running buffer. Parameters affecting CE separation such as sample pH, applied voltage, concentration of complexing agent, nature of the buffer solution, and interferences by other metal ions, were evaluated. The LODs for Cu(+) and Cu(2+) were 3.0 and 2.5 microg/mL (S/N = 3), respectively. The developed method allows the simultaneous determination of Cu(+) and Cu(2+) in less than 5 min with RSDs of between 5.3 and 9.5% for migration time and between 3.4 and 9.7% for peak areas, respectively. At optimum conditions, the percentage recoveries of Cu(+) and Cu(2+) were found to be 99.4 and 99.5%.

Studies on the cytological and biochemical effects of valerian in somatic and germ cells of Swiss albino mice

Valerian is widely known for its use as a sedative and an anti-anxiety drug in the folk medicine. Literature reports suggested valerian to induce genotoxicity in vitro (ECV304 cells) by reactive oxygen species-mediated mechanism; however, there are no reports on its genotoxicity and/or the epigenetic mechanism in vivo. In view of the folkloric significance, it was found worthwhile to (1) determine the genotoxic effects of valerian in somatic and germ cells of mice and (2) investigate the role of epigenetic mechanisms. The protocol included the oral treatment of mice with different doses (500, 1000 and 2000 mg/kg/day) of valerian for 7 days. The following experiments were conducted: (i) cytological studies on micronucleus test, (ii) cytogenetic analysis for meiotic chromosomes, (iii) cytological analysis of spermatozoa abnormalities, (iv) quantification of proteins and nucleic acids in testicular cells and (v) estimation of malondialdehyde (MDA) and nonprotein sulfhydryl (NP-SH) in hepatic and testicular cells. The treatment increased the frequency of micronuclei in the polychromatic erythrocytes (PCE) and decrease the ratio of PCE to normochromatic erythrocytes (NCE) in the femur. It caused aberrations in chromosomes of the testis and induced spermatozoa abnormalities. The concentration of nucleic acids was depleted in the testicular cells. These changes might be attributed to the epigenetic mechanisms as revealed by an increase in the concentrations of MDA and a decrease of NP-SH levels in hepatic and testicular cells observed in the present study. The observed changes may be ascribed to terpenoids (valepotriates) and flavonoids (6-methylapigenin and 2S(-)-hesperidin) present in valerian.

Glyoxal formation by Fenton-induced degradation of carbohydrates and related compounds

In this paper, we provide a systematic analysis of glyoxal (1) formation from a range of monosaccharides and related compounds, to determine their potential role as sources of this alpha-oxoaldehyde in vivo. Substrates were reacted with the Fenton reagent (Fe(2+)/EDTA/H(2)O(2)) and the mixtures were analyzed by HPLC using the 6-hydroxy-2,4,5-triaminopyrimidine fluorimetric assay. The rank order of hexoses and their derivatives as glyoxal sources was found to be fructose > glucose = mannose = galactose > glucose-6-phosphate > mannitol. Within the pentose group, arabinose and ribose gave the higher yields of 1 followed by deoxyribose and its adenine N-glycosides and ribulose. Among the tested substrates, three-carbon compounds, that is, trioses and glycerol, but not glyceraldehyde-3-phosphate, were by far the most effective sources of 1. The effects of H(2)O(2) and Fe(2+)/EDTA concentrations as well as of other metal ions were also investigated.

New Aspects of Copper and Iron Metabolism in the Myelodysplastic Syndromes

BACKGROUND

Myelodysplastic syndrome (MDS) is an iron overload condition. Copper deficiency itself might induce dysplastic changes and iron overload. The relationship between the iron and copper metabolism is analyzed in MDS patients.

METHODS

Copper, iron and ceruloplasmin levels were established, and transferrin saturation determination and HFE mutation analysis were performed in 32 MDS patients.

RESULTS

Eleven of 32 MDS patients were copper deficient. A decreased copper level occurred together with a significantly elevated iron level and transferrin saturation and in 45% HFE gene mutation. In the normal copper group, twice as many patients had a decreased rather than an elevated iron content and carried the wild-type HFE gene rather than the mutant.

CONCLUSIONS

Copper deficiency is a frequent finding in MDS. It is desirable to include copper level determination in the initial workup of MDS.

A Comparative study of Fe(II) and Fe(III) interactions with DNA duplex: major and minor grooves bindings

The involvement of the Fe cations in autoxidation in cells and tissues is well documented. DNA is a major target in such reaction, and can chelate Fe cation in many ways. The present study was designed to examine the interaction of calf-thymus DNA with Fe(II) and Fe(III), in aqueous solution at pH 6.5 with cation/DNA (P) (P = phosphate) molar ratios (r) of 1:160 to 1:2. Capillary electrophoresis and Fourier transform infrared (FTIR) difference spectroscopic methods were used to determine the cation binding site, the binding constant, helix stability and DNA conformation in Fe-DNA complexes. Structural analysis showed that at low cation concentration (r = 1/80 and 1/40), Fe(II) binds DNA through guanine N-7 and the backbone PO(2) group with specific binding constants of K(G) = 5.40 x 10(4) M(1) and K(P) = 2.40 x 10(4) M(1). At higher cation content, Fe(II) bindings to adenine N-7 and thymine O-2 are included. The Fe(III) cation shows stronger interaction with DNA bases and the backbone phosphate group. At low cation concentration (r = 1:80), Fe(III) binds mainly to the backbone phosphate group, while at higher metal ion content, cation binding to both guanine N-7 atom and the backbone phosphate group is prevailing with specific binding constants of K(G) = 1.36 x 10(5) M(-1) and K(P) = 5.50 x 10(4) M(-1). At r = 1:10, Fe(II) binding causes a minor helix destabilization, whereas Fe(III) induces DNA condensation. No major DNA conformational changes occurred upon iron complexation and DNA remains in the B-family structure.

Relation of hemochromatosis with hepatocellular carcinoma: epidemiology, natural history, pathophysiology, screening, treatment, and prevention

HH is a common inherited disorder of iron metabolism affecting about 1 out of 250 individuals of Northern European decent. Many of these patients do not have evident phenotypic expression and do not develop significant iron loading. Some patients, however, develop progressive iron overload and cirrhosis. These individuals are at risk of developing HCC. Cirrhotics with hemochromatosis should undergo regular screening for HCC. If HCC is identified early, treatment with either resection or liver transplantation is optimal. Palliative measures, including ablative therapy and chemoembolization, can be used. With increasing clinical recognition,hemochromatosis should be diagnosed earlier and progression to cirrhosis and HCC should be minimized.

Iron, hemochromatosis, and hepatocellular carcinoma

Hereditary hemochromatosis (HH) is associated with an increased risk for hepatocellular carcinoma (HCC). The risk previously had been estimated to be as high as 200-fold increased. Recent studies suggest that the risk for HCC in HFE -associated HH may be much lower and occurs predominantly in patients with cirrhosis at the time of diagnosis. The risk for HCC also is increased among patients with African iron overload and possibly in other iron-loading disorders such as homozygous beta thalassemia. The greatly increased iron stores in the liver observed in these disorders can stimulate carcinogenesis via both direct and indirect pathways. The prevalence of HCC also appears to be higher among patients with end-stage liver disease undergoing liver transplantation. It is not clear whether mildly to moderately increased hepatic iron stores or HFE mutations are associated independently with an increased risk for HCC among patients with other types of liver disease. In this article, the incidence and prevalence of HCC in patients with HH and other liver diseases associated with iron overload are discussed as well as the possible mechanisms for the increased risk for hepatic carcinogenesis in these disorders.

Synthesis of dimeric acridine derived antivirals

A series of antiviral compounds consisting of an intercalating acridine derived part, a spacer region and a reactive EDTA derived conjugate was synthesized in an easy sequence starting from 1,omega-alkyldiamines. As shown in model screenings, in the presence of ascorbic acid the Fe-complexes of these compounds reduced the phage-titer of MS2-phages by >8 logarithmic decades.

Ascorbic acid reduces the frequency of iron induced micronuclei in bone marrow cells of mice

Iron is a potent oxidant that can lead to the formation of genotoxic lipid peroxides. Ascorbic acid, which enhances dietary iron absorption, has been suggested to enhance the oxidant effects of iron and to directly lead to the formation of lipid peroxides. The combined effects of dietary iron and ascorbic acid on genotoxicity were investigated by measuring the frequency of micronuclei in the bone marrow cells of C3H/He mice. In addition, liver iron concentration was measured in all treated groups. Three weeks old mice were fed diets for 3 weeks containing iron at 100 or 300 mg/kg diet in the form of FeSO(4) that were supplemented either with or without ascorbic acid (15 g/kg diet). The results of the bone marrow micronucleus test revealed that the high iron diet resulted in an increased frequency of micronucleated polychromatic erythrocytes (MnPCEs) as compared to low iron. Ascorbic acid supplementation in the low iron diet did not show any effect on incidence of MnPCEs and protected against the increased frequency of MnPCEs induced by the high iron diet. However, liver iron concentration was significantly increased only in the high iron treated and ascorbic acid supplemented group as compared to all other groups. These results demonstrate that ascorbic acid protects against the clastogenic effects of iron.

Differential role of hydrogen peroxide and organic hydroperoxides in augmenting ferric nitrilotriacetate (Fe-NTA)-mediated DNA damage: implications for carcinogenesis

An iron chelate, ferric nitrilotriacetate (Fe-NTA), is a potent nephrotoxic agent, and induces acute and subacute renal proximal tubular necrosis, a consequence of the Fenton-like reaction that eventually leads to a high incidence of renal adenocarcinoma in rodents. In order to examine the possible mechanism for carcinogenic activity, we investigated the DNA damage with Fe-NTA in the presence of various peroxides/organic hydroperoxides. S1 nuclease hydrolysis and deoxyribose degradation assays were performed. Incubation of calf thymus DNA with ferric nitrilotriacetate (0.1 mM) in the presence of peroxides/organic hydroperoxides at a final concentration of 40 mM of each in phosphate buffer (0.1 M, pH 7.4) augmented DNA damage severalfold as compared to the damage caused by individual treatments. Fe-NTA in the presence of hydrogen peroxide caused DNA single-strand breaks and damage to its deoxyribose sugar moiety as measured, respectively, by S1 nuclease hydrolysis and deoxyribose degradation using calf thymus DNA. However, only deoxyribose degradation could be recorded in the presence of other peroxide/organic hydroperoxides. No DNA single-strand break was observed by this treatment. The observed differences in DNA damage by hydrogen peroxide and organic hydroperoxides/peroxide have been ascribed to the differential reactivity of DNA with hydroxyl and alkoxy/aryloxy free radicals produced, respectively, from these inorganic and organic peroxides. These studies suggest that Fe-NTA not only mediated the production of reactive oxygen species, but also catalysed the decomposition of these peroxides and organic hydroperoxides, which may cause a clastogenic change in DNA. This reactivity enhances the clastogenic activity in DNA. These changes in the DNA structure may ultimately be responsible, at least in part, for the induction of carcinogenesis in Fe-NTA-exposed animals.

Iron and liver cancer

Mechanisms whereby iron may act in carcinogenesis are induction of oxidative stress, facilitation of tumor growth, and modification of the immune system. Results of clinical and epidemiologic studies demonstrate a strong association between iron excess (even at mild levels) and the development of cancer at any site, but they do not indicate whether this reflects a causal link or an indirect association through other factors (i.e., aging, alcohol consumption, and insulin resistance). Findings obtained from experimental work are not conclusive with respect to a direct carcinogenic role of iron, but they support a carcinogenic or co-carcinogenic role of iron in chemically induced carcinogenesis.

Oxidative DNA damage induced by copper and hydrogen peroxide promotes CG-->TT tandem mutations at methylated CpG dinucleotides in nucleotide excision repair-deficient cells

Oxidative DNA damage may play an important role in human disease including cancer. Previously, mutational spectra have been determined using systems that include transition metal ions and hydrogen peroxide (H2O2). G-->T transversions and C-->T transitions were the most common mutations observed including some CC-->TT tandem mutations. C-->T transition mutations at methylated CpG dinucleotides are the most common mutations in human genetic diseases. It has been hypothesized that oxidative stress may increase the frequency of mutations at methylated CpG sequences. Here we have used a CpG-methylated shuttle vector to derive mutational spectra of copper/H2O2-induced DNA damage upon passage of the shuttle vector through human fibroblasts. We find that copper/H2O2 treatment produces higher numbers of CpG transition mutations when the CpGs are methylated but does not create clear C-->T hotspots at these sites. More strikingly, we observed that this treatment produces a substantial frequency of mutations that were mCG-->TT tandem mutations. Six of seven tandem mutations were of this type. mCG-->TT mutations (6/63 = 10% of all mutations) were observed only in nucleotide excision repair-deficient (XP-A) cells but were not found in repair-proficient cells. The data suggest that this novel type of mutation may be produced by vicinal or cross-linked base damage involving 5-methylcytosine and a neighboring guanine, which is repaired by nucleotide excision repair. We suggest that the underlying oxidative lesions could be responsible for the progressive neurodegeneration seen in XP-A individuals.

Human mitochondrial transcription factor A binds preferentially to oxidatively damaged DNA

Mitochondrial transcription factor A (mtTFA) is necessary for both transcription and maintenance of mtDNA, and is also one of the high mobility group (HMG) proteins that preferentially binds to cisplatin-damaged DNA. In this study we confirmed the preferential binding of mtTFA to cisplatin-damaged DNA, and also discovered that mtTFA binds to oxidatively damaged DNA. The affinity for oxidatively damaged DNA of mtTFA is higher for A/8-oxo-dG and C/8-oxo-dG than for G/8-oxo-dG and T/8-oxo-dG. Our findings suggest that mtTFA plays an important role in the recognition of oxidative DNA damage.

Regulation, mechanisms and proposed function of ferritin translocation to cell nuclei

Ferritin is traditionally considered a cytoplasmic iron-storage protein,but recent reports indicate that it is also found in cell nuclei. Nuclear ferritin has been proposed to be involved in both the protection of DNA and the exacerbation of iron-induced oxidative damage to DNA. We demonstrate that H-rich ferritin is present in the nucleus of human astrocytoma tumor cells. To study the mechanism and regulation of ferritin translocation to the nucleus,we developed a cell culture model using SW1088 human astrocytoma cells. Changes in cellular iron levels, cytokine treatments and hydrogen peroxide exposure affected the distribution of ferritin between the cytosol and the nucleus. Ferritin enters the nucleus via active transport through the nuclear pore and does not require NLS-bearing cytosolic factors for transport. Furthermore, H-rich ferritin is preferred over L-rich ferritin for uptake into the nucleus. Whole cell crosslinking studies revealed that ferritin is associated with DNA. Ferritin protected DNA from iron-induced oxidative damage in both in vitro and in cell culture models. These results strongly suggest a novel role for ferritin in nuclear protection. This work should lead to novel characterization of ferritin functions in the context of genomic stability and may have unparalleled biological significance in terms of the accessibility of metals to DNA. The knowledge generated as a result of these studies will also improve our understanding of iron-induced damage of nuclear constituents.

Relations between clusters of oxidatively damaged nucleotides and active or open nucleosomes in the rat Nth 1 gene

The distribution of oxidative damage to bases such as 8-hydroxyguanine (8-OH-Gua), was determined at the nucleotide level of resolution using the ligation-mediated PCR technique. Administration of a renal carcinogen, ferric nitrilotriacetate (Fe-NTA), is known to induce oxidative stress and subsequent formation of 8-OH-Gua in the kidney. Whole genomic DNA was isolated from the rat kidney with or without Fe-NTA treatment and then digested with formamidopyrimidine-DNA glycosylase (Fpg). As a target, we focused on the gene of a DNA repair enzyme for thymine glycol, Nth 1. Cleaved signals were found in exon 1 and exon 3, but not exon 5. Nucleosomes in these regions, enriched in damaged nucleotides, were highly accessible to micrococcal nuclease, especially in the kidney. Taking into account the function of the protein segment encoded by these regions, we discussed the molecular mechanism of the restricted formation of the damaged nucleotides.

Iron and hepatocellular carcinoma

The high prevalence of hepatocellular carcinoma (HCC) in genetic hemochromatosis (GH) and the association between increased body iron stores and occurrence of HCC in subjects with iron overload unrelated to GH, and the experimental evidence of a co-carcinogenic role of iron strongly support that iron is involved in the development of HCC.

Mapping oxidative DNA damage using ligation-mediated polymerase chain reaction technology

Reactive oxygen species induce a pharmacopoeia of oxidized bases in DNA. DNA can be cleaved at most of the sites of these modified bases by digestion with a combination of two base excision repair glycosylases from Escherichia coli, Fpg glycosylase, and endonuclease III. The frequency of the resulting glycosylase-dependent 5'-phosphoryl ends can be mapped at nucleotide resolution along a sequencing gel autoradiogram by a genomic sequencing technique, ligation-mediated polymerase chain reaction (LMPCR). In cultured rat cells, the frequency of endogenous oxidized bases in mitochondrial DNA is sufficiently high, about one oxidized base per 100 kb, to be directly mapped from 0.1 microg of total cellular DNA preparations by LMPCR. Nuclear DNA has a lower frequency of endogenous oxidative base damage which cannot be mapped from 1-microg preparations of total cellular DNA. Preparative gel electrophoresis of the PGK1 and p53 genes from 300 microg of restriction endonuclease-digested genomic DNA showed a 25-fold enrichment for the genes and, after endonuclease digestion followed by LMPCR, gave sufficient signal to map the frequency of oxidized bases from human cells treated with 50 microM H2O2.

Damage induced by stannous chloride in plasmid DNA

Stannous chloride (SnCl(2)) is widely used in daily human life, for example, to conserve soft drinks, in food manufacturing and biocidal preparations. In nuclear medicine, stannous chloride is used as a reducing agent of Technetium-99m, a radionuclide used to label different cells and molecules. In spite of this, stannous chloride is able to generate reactive oxygen species (ROS) which can damage DNA. In this work, plasmid DNA (pUC 9.1) was incubated with SnCl(2) under different conditions and the results analyzed through DNA migration in agarose gel electrophoresis. Our data reinforce the powerful damaging effect induced by stannous ion and suggest that this salt can play a direct role in inducing DNA lesions.

Mapping oxidative DNA damage and mechanisms of repair

We developed a method to map oxidative-induced DNA damage at the nucleotide level using ligation-mediated polymerase chain reaction (LMPCR) technology. In vivo and in vitro DNA base modification patterns inflicted by reactive oxygen species (ROS) in the human P53 and PGK1 gene were nearly identical in vitro and in vivo. In human male fibroblasts, these patterns are independent of the transition metal used (Cu (II), Fe(II), or Cr(VI). Therefore, local probability of H2O2-mediated DNA base damage is determined primarily by DNA sequence. Moreover, in cells undergoing severe oxidative stress, extranuclear sites contribute metals that enhance nuclear DNA damage. The role of the base excision repair pathway in human cells responsible for the repair of the majority of ROS base damage is also discussed.

Hydroperoxide-induced DNA damage and mutations

Hydroperoxides (ROOH) are believed to play an important role in the generation of free radical damage in biology. Hydrogen peroxide (R=H) is produced by endogenous metabolic and catabolic processes in cells, while alkyl hydroperoxides (R=lipid, protein, DNA) are produced by free radical chain reactions involving molecular oxygen (autooxidation). The role of metal ions in generating DNA damage from hydroperoxides has long been recognized, and several distinct, biologically relevant mechanisms have been identified. Identification of the mechanistic pathways is important since it will largely determine the types of free radicals generated, which will largely determine the spectrum of DNA damage produced. Some mechanistic aspects of the reactions of low valent transition metal ions with ROOH and their role in mutagenesis are reviewed with a perspective on their possible role in the biological generation of DNA damage. A survey of hydroperoxide-induced mutagenesis studies is also presented. In vitro footprinting of DNA damage induced by hydroperoxides provides relevant information on sequence context dependent reactivity, and is valuable for the interpretation of mutation spectra since it represents the damage pattern prior to cellular repair. Efforts in this area are also reviewed.

Hepatocellular carcinoma in a patient with hereditary hemochromatosis and noncirrhotic liver. A case report

A case of a 62-year-old patient with hereditary hemochromatosis is reported, who developed hepatocellular carcinoma (HCC) in the absence of cirrhosis and other potential risk factors for HCC. Occurrence of HCC in patients with genetic hemochromatosis and noncirrhotic liver is a rare event which has previously been described only six times and appears to be limited to male patients.

The presence of traces of iron and copper ions during gamma-irradiation does not result in clear mutational hot spots in the lacI gene

Oxidative radicals, which are produced during ionizing irradiation of DNA in water, damage the DNA and may result in mutations, which are in general randomly distributed. Alternatively, the addition of transition metal ions, like iron or copper, to DNA in combination with H(2)O(2) and a reducing agent also results in the production of oxidative radicals. Due to binding of the transition metal ions to DNA, the production of these radicals is very local, and results in a mutational spectrum in which the mutations are not randomly distributed. If transition metal ions are complexed to the DNA during irradiation, and react with radiation-induced species such as hydrogen peroxide, site-specific formation of.OH radicals on these sites may occur, leading to the formation of mutational hot spots. This study examines the influence of the presence of traces of iron or copper ions during gamma-irradiation of plasmid DNA in water, on the possible formation of mutational hot spots in the lacI gene. Comparison of the mutational spectra, after irradiation in the presence or in the absence of transition metal ions, shows that there are indeed relatively more positions in the lacI gene where more than one mutation occurs, suggesting formation of mutational hot spots in the presence of transition metal ions. However, the appearance of these hot spots is rather weak. Although in all three mutational spectra G:C to A:T mutations are predominant, there are also some differences between the types of mutations in these spectra. These differences in mutational spectra might reflect the different preferences of iron and copper ions to bind specific sites in the DNA. Indeed, there appears to be a high association of mutations at CC or GG sites in the mutational spectrum in the presence of copper ions, confirming the observation that copper binds preferably at two adjacent guanines in the DNA. It can be concluded from this study that the presence of small amounts of transition metal ions during gamma-irradiation influences the types and distribution of gamma-radiation-induced mutations, although no major mutational hot spots can be observed.

Effects of dietary iron overload on progression in chemical hepatocarcinogenesis

AIM

The present study was undertaken to investigate possible effects of dietary iron during the progression step in hepatocarcinogenesis.

METHODS

Two experiments were performed, in which preneoplastic foci were produced in rat liver using the Solt & Farber protocol, with diethylnitrosamine as initiator and partial hepatectomy + 2-acetylaminofluorene as promoter. Two weeks after promotion, animals were fed 1.25-2.5% dietary carbonyl iron or a control diet until sacrifice. In the first experiment, animals were killed at different time points when they developed an abdominal mass in combination with weight loss. In the second experiment, animals were sacrificed 45 weeks post-promotion. Liver tumours were counted and histologically graded. Tumour levels of ubiquinone-9 and alpha-tocopherol were determined with HPLC, and labelling and apoptotic indices calculated using immunohistochemistry. The number and area of glutathione S-transferase 7,7 (GST-7,7)-positive foci were determined.

RESULTS

In experiment number 1, survival and tumour differentiation were similar in iron-treated animals and controls. In the second experiment, iron-treated rats had an increased number of GST-7,7-positive foci compared to controls. Number and size of carcinomas were similar between the groups, whereas tumour differentiation was higher in rats exposed to iron. Cell proliferation, apoptosis and concentrations of alpha-tocopherol in tumours were not altered by iron. The ratio of reduced/oxidized ubiquinone-9 was decreased in tumours from iron-treated animals.

CONCLUSION

In this model, dietary iron overload resulted in an increased number of preneoplastic foci but did not enhance the progression of these into hepatocellular carcinomas. Iron decreased the ratio of reduced/oxidized ubiquinone-9 in tumours, indicating that neoplastic liver cells utilize intracellular ubiquinones as a defense mechanism against iron-induced oxidative stress.

p53 mutations in british patients with hepatocellular carcinoma: clustering in genetic hemochromatosis

BACKGROUND & AIMS

Environmental factors are important in the etiology of hepatocellular carcinoma (HCC). Aflatoxin B1 causes a specific point mutation in the p53 tumor-suppressor gene in exposed individuals. In Western populations, mutations of this gene seem to be less frequent. We have investigated the role of p53 mutations in tumorigenesis in British patients with HCC. The aim of this study was to determine the frequency and mutational spectrum of the p53 gene in HCCs from British patients.

METHODS

DNA from 170 HCCs, of well-defined etiology, in British patients was analyzed by single-stranded conformational polymorphism using the polymerase chain reaction technique. Mutations were then characterized by direct sequencing.

RESULTS

Twenty-nine percent of tumors had p53 mutations. Ten of 14 (71%) hemochromatotic cancers had mutations within the p53 gene, and clustering of these mutations at codon 220 (A-G) was found in 5 cases; 3 others had T-A mutations. No clustering was found in HCCs with other etiologies.

CONCLUSIONS

p53 mutations are more common than was thought in Northern European HCCs. This is the first demonstration of p53 mutational clustering in HCCs from hemochromatotic subjects.

Analysis of 8-hydroxyguanine in rat kidney genomic DNA after administration of a renal carcinogen, ferric nitrilotriacetate

The frequency of oxidative base damage, such as 8-hydroxyguanine (8-OH-Gua), was determined at the nucleotide level of resolution using the ligation-mediated PCR technique. Administration of a renal carcinogen, ferric nitrilotriacetate (Fe-NTA), is known to induce oxidative stress and subsequent formation of 8-OH-Gua in the rat kidney. Whole genomic DNA was isolated from the rat kidney after or without Fe-NTA treatment and then cleaved with hot piperidine. In order to assess the frequency of 8-OH-Gua formation, we chose three genes, the tumor suppressor gene p53, the heat shock protein 70 (HSP70-1) gene and the Na,K-ATPase alpha1 subunit gene. No alteration in the cleavage profile was observed in the p53 and HSP70 genes after Fe-NTA treatment. In the case of the p53 gene, a low incidence of point mutations has been observed in this carcinogenesis system. On the other hand, time-dependent alterations, corresponding to the time course of overall 8-OH-Gua formation and repair, were detected in the promoter region of the Na,K-ATPase alpha1 subunit gene. GpG and GpGpG in specific regions seem to be hotspots for the formation of 8-OH-Gua. These results were confirmed by formamidopyrimidine-DNA glycosylase-dependent DNA cleavage patterns. Thus, oxidative base damage, such as 8-OH-Gua, was not distributed uniformly along the whole genome, but seemed to be restricted to particular genes and regions.

Dietary iron overload inhibits carbon tetrachloride-induced promotion in chemical hepatocarcinogenesis: effects on cell proliferation, apoptosis, and antioxidation

BACKGROUND/AIMS

The aim of this study was to investigate if feeding with carbonyl iron would facilitate the development of preneoplastic lesions initiated by diethylnitrosamine (DEN) and promoted by CCl4-induced liver cirrhosis.

METHODS

Male Wistar rats were fed a diet with 1.25%-2.5% carbonyl iron for 23 weeks and received intragastric injections of CCl4 (1.0 or 2.0 ml/kg per week) for 13 weeks, followed by one i.p. injection of DEN (200 mg/kg), after which CCl4 was administered for 8 additional weeks. Animals were killed 48 h after the first CCl4 injection to evaluate liver necrosis, 8 weeks later to evaluate fibrosis, and 9 weeks after DEN to determine formation of glutathione S-transferase 7,7 (GST-7,7) positive foci.

RESULTS

Treatment with iron counteracted the increased serum alanine aminotransferase levels and liver necrosis following CCl4 administration. Hepatic levels of reduced Q9 and alpha-tocopherol were elevated in rats treated with CCl4 and decreased in rats treated with iron compared to the controls. Fibrogenesis was not altered by iron treatment. Nine weeks after DEN initiation, the number and volume density of GST-7,7-positive foci in rats treated with CCl4 were significantly increased as compared with controls, but co-treatment with iron inhibited this increase. Apoptotic index was increased in iron-loaded livers, and labelling index (the fraction of S-phase hepatocytes) was decreased by co-treatment with iron in livers exposed to CCl4.

CONCLUSION

Carbonyl iron depleted hepatic levels of antioxidants, it decreased CCl4-induced necrosis and cell proliferation, it enhanced apoptosis and did not facilitate fibrogenesis. These effects together may explain the suppression of CCl4-induced promotion after DEN initiation exerted by carbonyl iron in the present study.

Mapping oxidative DNA damage at nucleotide level

DNA damage induced by reactive oxygen species (ROS) is considered an important intermediate in the pathogenesis of human conditions such as cancer and aging. By developing an oxidative-induced DNA damage mapping version of the Ligation-mediated polymerase chain reaction (LMPCR) technique, we investigated the il vivo and in vitro frequencies of DNA base modifications caused by ROS in the human p53 and PGK1 gene. Intact human male fibroblasts were exposed to 50mM H2O2, or purified genomic DNA was treated with 5 mM H2O2, 100 microM Ascorbate, and 50 microM, 100 microM, or 100 microM of Cu(II), Fe(II), or Cr(VI) respectively. The damage pattern generated in vivo was nearly identical to the in vitro Cu(II) or Fe(III) damage patterns; damage was non-random with guanine bases heavily damaged. Cr(VI) generated an in vitro damage pattern similar to the other metal ions, although several unique thymine positions were damaged. Also, extra nuclear sites are a major contributor of metal ions (or metal-like ligands). These data show that the local probability of H2O2-mediated DNA damage is determined by the primary DNA sequence, with chromatin structure having a limited effect. The data suggest a model in which DNA-metal ion binding domains can accommodate different metalions. LMPCR's unique aspect is a blunt-end ligation of an asymmetric double-stranded linker, permitting exponential PCR amplification. An important factor limiting the sensitivity of LMPCR is the representation of target gene DNA relative to non-targeted genes; therefore, we recently developed a method to eliminate excess non-targeted genomic DNA. Restriction enzyme-digested genomic DNA is size fractionated by Continuous Elution Electrophoresis (CEE), capturing the target sequence of interest. The amount of target DNA in the starting material for LMPCR is enriched, resulting in a stronger amplification signal. CEE provided a 24-fold increase in the signal strength attributable to strand breaks plus modified bases created by ROS in the human p53 and PGK1 genes, detected by LMPCR. We are currently taking advantage of the enhanced sensitivity of target gene-enriched LMPCR to map DNA damage induced in human breast epithelial cells exposed to non-cytotoxic concentrations of H2O2.

Dietary iron overload as a risk factor for hepatocellular carcinoma in Black Africans

Although the iron-loading disease, hereditary hemochromatosis, has a strong causal association with hepatocellular carcinoma (HCC), the carcinogenic potential of dietary iron overload in Black Africans is not known. We investigated this potential by evaluating iron status, alcohol consumption, markers for hepatitis B (HBV) and C virus (HCV) infections, and exposure to dietary aflatoxin B1 in 24 rural patients with this tumor, 48 race-, sex-, and age-matched hospital-based controls, and 75 related or unrelated close family members of the cancer patients. Iron overload was defined as a raised serum ferritin concentration in combination with a transferrin saturation > or = 60%, and was confirmed histologically when possible. Among 24 patients and 48 hospital controls, the risk of developing HCC in the iron-loaded subjects was 10.6 (95% confidence limits of 1.5 and 76.8) relative to individuals with normal iron status, after adjusting for alcohol consumption, chronic HBV and HBC infections, and exposure to aflatoxin B1. The risk of HCC in subjects with HBV infection was 33.2 (7.2, 153.4) (odds ratio [95% confidence limits]), HCV infection 6.4 (0.3, 133.5), and alcohol consumption 2.0 (0.5, 8.2). Aflatoxin B1 exposure did not appear to increase the risk of HCC. The population attributable risk of iron overload in the development of HCC was estimated to be 29%. Among 20 cancer patients and 75 family members, the risk of developing HCC with iron overload was 4.1 (0.5, 32.2). We conclude that dietary iron overload may contribute to the development of HCC in Black Africans.

African iron overload and hepatocellular carcinoma (HA-7-0-080)

Although HLA-linked hemochromatosis greatly increases the risk for hepatocellular carcinoma in people of European ancestry, iron overload in Africa is not thought to be etiologically related to this malignancy. To determine if African iron overload may be associated with hepatocellular carcinoma, we reviewed 320 consecutive diagnostic liver biopsies processed at the University of Zimbabwe from 1992 to 1994 and we selected for analysis 215 biopsies from adults that were suitable for the histological assessment of hepatocellular iron. Subjects were stratified according to hepatocellular iron grades of 0-2+ (normal levels to mild siderosis; n = 183) and grades of 3+ and 4+ (distinctly elevated levels consistent with iron overload; n = 32). Thirty-six subjects had hepatocellular carcinoma. Logistic regression modeling revealed a significant association between iron overload and hepatocellular carcinoma after adjustment for age, sex and and the presence of portal fibrosis or cirrhosis (p = 0.041). The odds of hepatocellular carcinoma in subjects with iron overload was 3.1 (95% confidence interval of 1.05-9.4) times that of subjects without iron overload. While we could not test for exposure to viral hepatitis or to aflatoxins in this study, our findings suggest that iron overload may be a risk factor for hepatocellular carcinoma in Africa.

Studies on genotoxic effects of iron overload and alcohol in an animal model of hepatocarcinogenesis

BACKGROUND/AIMS

In order to examine whether iron and alcohol act synergistically during tumor initiation in vivo, we investigated the effects of dietary iron overload and a liquid ethanol-containing diet on the initiation phase of the Solt & Farber model of chemical hepatocarcinogenesis.

METHODS

Following dietary supplementation with carbonyl iron for 8 weeks and ethanol pair-feeding according to Lieber deCarli for 5 weeks, animals were subjected to partial hepatectomy in order to induce regenerative cell proliferation and thereby "fix" putative DNA lesions. Levels of malondialdehyde, reduced and oxidized ubiquinone-9, alpha-tocopherol and 8-oxo-2'-deoxyguanosine were analyzed in liver tissue removed at the time of partial hepatectomy, and blood was collected for determination of alanine amino-transferase activities. Following a 2-week recovery period, promotion was achieved with 0.02% dietary 2-acetylaminofluorene and carbon tetrachloride. Two weeks after the completion of promotion, animals were sacrificed and the number of preneoplastic, glutathione S-transferase 7,7-positive lesions counted. Animals initiated with diethylnitrosamine served as a positive control group.

RESULTS

Serum aminotransferase activities were significantly increased, and hepatic contents of ubiquinol-9 (reduced ubiquinone-9) were significantly decreased in animals exposed to the combination of iron and ethanol in comparison to the other groups. Livers from iron-treated animals had decreased levels of alpha-tocopherol and increased contents of malondialdehyde, whereas treatment with ethanol did not further enhance these alterations. Levels of 8-oxo-2'-deoxyguanosine were not significantly different in animals treated with iron, ethanol or iron + ethanol as compared with controls. The number of preneoplastic foci at the time of sacrifice was not increased in livers exposed to iron and/or ethanol as compared with those from control animals. As expected, the number of foci was significantly increased in positive controls which were initiated with diethylnitrosamine.

CONCLUSIONS

Iron potentiated the cytotoxic effects of ethanol, resulting in increased serum aminotransferase activities and decreased hepatic contents of ubiquinol. However, the combination of iron and ethanol did not exert genotoxic effects detectable as enhanced hepatic levels of 8-oxo-2'-deoxyguanosine, or increased formation of preneoplastic, glutathione S-transferase 7,7-positive lesions in the Solt & Farber model of chemical hepatocarcinogenesis.

Glyoxal, a major product of DNA oxidation, induces mutations at G:C sites on a shuttle vector plasmid replicated in mammalian cells

Glyoxal is a major product of DNA oxidation in which Fenton-type oxygen free radical-forming systems are involved. To determine the mutation spectrum of glyoxal in mammalian cells and to compare the spectrum with those observed in other experimental systems, we analyzed mutations in a bacterial suppressor tRNA gene (supF) in the shuttle vector plasmid pMY189. We treated pMY189 with glyoxal and immediately transfected it into simian COS-7 cells. The cytotoxicity and mutation frequency increased according to the dose of glyoxal. The majority of glyoxal-induced mutations (48%) were single-base substitutions. Eighty three percent of the single-base substitutions occurred at G:C base pairs. Among them, G:C-->T:A transversions were predominant, followed by G:C-->C:G transversions and G:C-->A:T transitions. A:T-->T:A transversions were also observed. Mutational hotspots within the supF gene were detected. These results suggest that glyoxal may play an important role in mutagenesis induced by oxygen free radicals.