Iron-induced oxidative DNA damage and its repair in primary rat hepatocyte culture

Iron-overload diseases frequently develop hepatocellular carcinoma. The genotoxic mechanism whereby iron is involved in hepatocarcinogenesis might involve an oxidative process via the intermediate production of reactive oxygen species. This was presently investigated by examining kinetics of formation and repair of DNA base lesions in primary rat hepatocyte cultures supplemented with the iron chelate, ferric nitrilotriacetate Fe-NTA (10 and 100 microM). Seven DNA base oxidation products have been identified in DNA extracts by gas chromatography- mass spectrometry, which showed a predominance of oxidized-purines (8- oxo-guanine, xanthine, fapy-adenine, 2-oxo-adenine) above oxidized pyrimidines (5-OHMe-uracil, 5-OH-uracil, 5-OH-cytosine) in control cultures. All these DNA oxidation products revealed a significant dose- dependent increase at 4 to 48 h after Fe-NTA supplementation, among which fapy-adenine showed the highest increase and 5-OH-cytosine was the least prominent. Involvement of iron in this oxidative process was established by a correlation between extent in DNA oxidation and intracellular level of toxic low molecular weight iron. DNA excision- repair activity was estimated by release of DNA oxidation products in culture medium. All the seven DNA oxidation products were detected in the medium of control cultures and showed basal repair activity. This DNA repair activity was increased in a time- and dose-dependent fashion with Fe-NTA. Oxidized-pyrimidines, among which was 5-OHMe-Uracil, were preferentially repaired, which explains the low levels detected in oxidized DNA. Since oxidized bases substantially differed from one another in terms of excision rates from cellular DNA, specific excision- repair enzymes might be involved. Our findings, however, demonstrate that even though DNA repair pathways were activated in iron-loaded hepatocyte cultures, these processes were not stimulated enough to prevent an accumulation of highly mutagenic DNA oxidative products in genomic DNA. The resulting genotoxic effect of Fe-NTA might be relevant in understanding the hepatocarcinogenic evolution of iron-overload diseases.      

Increased susceptibility to vancomycin-resistant Enterococcus intestinal colonization persists after completion of anti-anaerobic antibiotic treatment in mice.

BACKGROUND: Antibiotic-associated disruption of the indigenous intestinal microflora may persist beyond the treatment period. Although piperacillin/tazobactam inhibits the establishment of vancomycin-resistant Enterococcus (VRE) stool colonization in mice during treatment, we hypothesized that this agent and other anti-anaerobic antibiotics would increase susceptibility to colonization during the period of recovery of the intestinal microflora. DESIGN: Mice received 10(4) colony-forming units of vancomycin-resistant E. faecium by orogastric inoculation 2, 5, or 10 days after completing 5 days of subcutaneous antibiotic treatment, or both during and 2 days after the completion of treatment. Denaturing gradient gel electrophoresis (DGGE) was performed to assess changes in the intestinal microflora. RESULTS: Anti-anaerobic antibiotics (ie, piperacillin/ tazobactam, cefoxitin, and clindamycin) caused significant disruption of the indigenous microflora (mean DGGE similarity indices < or = 27% in comparison with saline controls) and promoted the establishment of high-density colonization when VRE was inoculated 2 or 5, but not 10, days following treatment (P < .001). Piperacillin/tazobactam exhibited a biphasic effect on the establishment of colonization (ie, inhibition when exposed to VRE during treatment and promotion when exposed to VRE after discontinuation of treatment), resulting in greater overall promotion of colonization than did agents with minimal anti-anaerobic activity (ie, levofloxacin, cefepime, and aztreonam) when VRE was inoculated both during and 2 days after treatment (P < .001). CONCLUSION: Patients receiving anti-anaerobic antibiotics, including piperacillin/tazobactam, may be susceptible to the establishment of high-density VRE colonization during the period of recovery of the anaerobic microflora.     

Mutations in the tyrosine kinase domain of the epidermal growth factor receptor in non-small cell lung cancer.

We evaluated somatic genetic alterations in the kinase domain of the EGFR gene in the tumors of 219 non-small cell lung cancer patients of primarily Caucasian and African American origins. We identified 26 patients (12%) whose tumors had a mutation in the EGFR gene, and 11 (5%) patients carried novel genomic variations consistent with germ-line polymorphisms. All but one mutation were identified in Caucasian patients affected with adenocarcinoma. EGFR mutations were more frequent in women and in nonsmokers, but a significant portion of the affected patients were men (12 of 26) and current or past smokers accounted for half of the patients affected (13 of 26). Screening subjects with EGFR mutations may identify patients whose tumors could respond to targeted therapy using tyrosine kinase inhibitors.     

Bromobenzene-induced hepatotoxicity at the transcriptome level.

Rats were exposed to three levels of bromobenzene, sampled at 6, 24, and 48 h, and liver gene expression profiles were determined to identify dose and time-related changes. Expression of many genes changed transiently, and dependent on the dose. Few changes were identified after 6 h, but many genes were differentially expressed after 24 h, while after 48 h, only the high dose elicited large effects. Differentially expressed genes were involved in drug metabolism (upregulated GSTs, mEH, NQO1, Mrps, downregulated CYPs, sulfotransferases), oxidative stress (induced HO-1, peroxiredoxin, ferritin), GSH depletion (induced GCS-l, GSTA, GSTM) the acute phase response, and in processes like cholesterol, fatty acid and protein metabolism, and intracellular signaling. Trancriptional regulation via the electrophile and sterol response elements seemed to mediate part of the response to bromobenzene. Recovery of the liver was suggested in response to BB by the altered expression of genes involved in protein synthesis and cytoskeleton rearrangement. Furthermore, after 48 h, rats in the mid dose group showed no toxicity, and gene expression patterns resembled the normal situation. For certain genes (e.g., CYP4A, metallothioneins), intraday variation in expression levels was found, regardless of the treatment. Selected cDNA microarray measurements were confirmed using the specific and sensitive branched DNA signal amplification assay.     

Nuclear receptor, pregname X receptor, is required for induction of UDP-glucuronosyltranferases in mouse liver by pregnenolone-16 alpha-carbonitrile.

The aim of this study was to determine the role of pregnane X receptor (PXR) in the induction of UDP-glucuronosyltransferases (UGTs) by pregnenolone-16 alpha-carbonitrile (PCN). Four- to six-month-old male wild-type and PXR-null mice received control or PCN-treated (1500 ppm) diet for 21 days. On day 22, livers were taken to prepare microsomes and total RNA to determine UGT activity and mRNA levels, respectively. In wild-type mice, PCN treatment significantly increased UGT activities toward bilirubin, 1-naphthol, chloramphenicol, thyroxine, and triiodothyronine. On control diet, the UGT activities toward the above substrates (except for 1-naphthol) in the PXR-null mice were significantly higher than those of wild-type mice. However, UGT activities in PXR-null mice were not increased by PCN. In agreement with the above findings, mRNA levels of mouse Ugt1a1 and Ugt1a9, which are involved in the glucuronidation of bilirubin and phenolic compounds, were increased about 100% in wild-type mice following PCN treatment, whereas the expression of Ugt1a2, 1a6, and 2b5 was not affected. In contrast, PCN treatment had no effect on the mRNA levels of these UGTs in PXR-null mice. Taken together, these results indicate that PCN treatment induces glucuronidation in mouse liver, and that PXR regulates constitutive and PCN-inducible expression of some UGTs.     

Circulating serum xenoestrogens and mammographic breast density

Introduction

Humans are widely exposed to estrogenically active phthalates, parabens, and phenols, raising concerns about potential effects on breast tissue and breast cancer risk. We sought to determine the association of circulating serum levels of these chemicals (reflecting recent exposure) with mammographic breast density (a marker of breast cancer risk).

Methods

We recruited postmenopausal women aged 55 to 70 years from mammography clinics in Madison, Wisconsin (N = 264). Subjects completed a questionnaire and provided a blood sample that was analyzed for mono-ethyl phthalate, mono-butyl phthalate, mono-benzyl phthalate, butyl paraben, propyl paraben, octylphenol, nonylphenol, and bisphenol A (BPA). Percentage breast density was measured from mammograms by using a computer-assisted thresholding method.

Results

Serum BPA was positively associated with mammographic breast density after adjusting for age, body mass index, and other potentially confounding factors. Mean percentage density was 12.6% (95% confidence interval (CI), 11.4 to 14.0) among the 193 women with nondetectable BPA levels, 13.7% (95% CI, 10.7 to 17.1) among the 35 women with detectable levels below the median (<0.55 ng/ml), and 17.6% (95% CI, 14.1 to 21.5) among the 34 women with detectable levels above the median (>0.55 ng/ml; P_trend = 0.01). Percentage breast density was also elevated (18.2%; 95% CI, 13.4 to 23.7) among the 18 women with serum mono-ethyl phthalate above the median detected level (>3.77 ng/ml) compared with women with nondetectable BPA levels (13.1%; 95% CI, 11.9 to 14.3; P_trend = 0.07). No other chemicals demonstrated associations with percentage breast density.

Conclusions

Postmenopausal women with high serum levels of BPA and mono-ethyl phthalate had elevated breast density. Further investigation of the impact of BPA and mono-ethyl phthalate on breast cancer risk by using repeated serum measurements or other markers of xenoestrogen exposure are needed.     

Neurodevelopmental changes of fetal pain

Pain in the developing fetus is controversial because of the difficulty in measuring and interpreting pain during gestation. It has received increased attention lately because of recently introduced legislation that would require consideration of fetal pain during intentional termination of pregnancy. During development, sensory fibers are abundant by 20 weeks; a functional spinal reflex is present by 19 weeks; connections to the thalamus are present by 20 weeks; and connections to subplate neurons are present by 17 weeks with intensive differentiation by 25 weeks. These cells are important developmentally, but decline as a result of natural apoptosis. Mature thalamocortical projections are not present until 29 to 30 weeks, which has led many to believe the fetus does not experience emotional "pain" until then. Pain requires both nociception and emotional reaction or interpretation. Nociception causes physiologic stress, which in turn causes increases in catecholamines, cortisol, and other stress hormones. Physiological stress is different from the emotional pain felt by the more mature fetus or infant, and this stress is mitigated by pain medication such as opiates. The plasticity of the developing brain makes it vulnerable to the stressors that cause long-term developmental changes, ultimately leading to adverse neurological outcomes. Whereas evidence for conscious pain perception is indirect, evidence for the subconscious incorporation of pain into neurological development and plasticity is incontrovertible. Scientific data, not religious or political conviction, should guide the desperately needed research in this field. In the meantime, it seems prudent to avoid pain during gestation.     

A simple model of the build-up of resistance to mixtures of anti-malarial drugs

In an organism with a life-cycle modelled on that of Plasmodium two separate resistance genes are assumed, each protecting against one of two unrelated drugs. The model was used to compare the rates of build-up of resistance in a population where the two drugs are used either as a mixture or in sequence. The model suggests that the use of a mixture would be advantageous if: both resistances are initially rare; there is recombination between the genes; a large proportion of the parasite population is unexposed to the drugs.