Peroxidative activation of o-phenylhydroquinone leads to the formation of DNA adducts in HL-60 cells.

Using 32P-postlabeling we studied DNA adduct formation in HL-60 cells treated with the o-phenylphenol metabolites o-phenylhydroquinone (o-PHQ) and o-phenylbenzoquinone (o-PBQ). Treatment with 25-500 microM o-PHQ for 8 h produced one principal and three minor adducts with a relative distribution of 80, 10, 6 and 4%. The relative adduct levels from these treatments were 0.26-2.31 adducts/10(7) nucleotides. Treatment with 25-250 microM o-PBQ for 2 h resulted in a similar level of DNA modification and adduct distribution. Reaction of purified calf thymus DNA with o-PBQ produced one DNA adduct, which did not correspond to the major adduct produced in HL-60 cells. These results show that o-PHQ and o-PBQ can form DNA adducts. Peroxidase activation of o-phenylphenol may therefore play a role in the carcinogenic effect of this compound.     

Venous "lakes" of the hands

Following pharmacologic vasodilatation, multiple vascular "lakes" were observed on angiograms of the hand in 55 patients. Most had no history of vascular anomalies or disease. The authors believe that these lakes are venous structures and that their filling is a physiologic phenomenon.     

The Jewish patient and terminal dehydration: a hospice ethical dilemma

Culturally competent nursing care regarding the ethical dilemma of terminal dehydration (withholding or withdrawing food and fluid) for the Jewish hospice patient involves applying the ethical principles of justice, autonomy, beneficence, and nonmaleficence to nursing interventions by identifying outcomes that focus on the high value Jews place on life; avoiding stereotyping as to what it means to be Jewish; knowledge of various Jewish traditions surrounding death and dying; and good communication with the patient and his or her family.     

N-Methyl-N-nitrosourea potentiation of cytogenetic damage induced by 1,3-bis(2-chloroethyl)-1-nitrosourea in normal human lymphocytes

DNA repair of O6-alkylguanine by O6-alkylguanine-DNA alkyltransferase (O6-AT) may be crucial in modulating the extent of cytogenetic damage induced by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an important anticancer chemotherapeutic agent. To test this idea we treated normal human lymphocytes for 1 h with methylnitrosourea (MNU), which inactivates O6-AT, and then treated them for 1 h with BCNU. The result was a synergistic increase in the number of sister chromatid exchanges (SCEs) and chromosomal aberrations induced. BCNU-induced SCEs were potentiated 1.4- to 2.5-fold in MNU-pretreated cultures. Pretreatment of lymphocytes with MNU resulted in a 4- to 28-fold increase in the number of BCNU-induced chromatid aberrations. The enhancement of both SCEs and aberrations induced was MNU-dose dependent. Treatment of lymphocytes with MNU alone did not affect cell cycle progression, suggesting that MNU does not influence the extent of BCNU-induced cytogenetic damage by selecting highly damaged cells through alterations in lymphocyte proliferation kinetics. The potentiation of SCE and aberration induction by pretreatment with MNU is postulated to be due to inhibition of O6-AT. This inhibition would permit the formation and persistence of BCNU-induced O6-(2-chloroethyl)guanine monoadducts, which can undergo subsequent reactions to form DNA cross-links. In humans variations in O6-AT resulting from acute alkylation exposure or genetic deficiency may be important in modulating the genotoxic effects of BCNU.     

Comprehensive EMX2 genotyping of a large schizencephaly case series

Schizencephaly is a brain malformation disorder characterized by one or more full-thickness clefts through the cerebral cortex. While initial reports suggested that EMX2 mutations are a common cause of schizencephaly, more recent evidence suggests that EMX2 mutations are not a common cause of this malformation. To determine the frequency of EMX2 mutations in patients with schizencephaly, we sequenced EMX2 in a cohort of 84 affected probands. No pathologic mutations were identified in this cohort, suggesting that EMX2 mutations are an uncommon cause of schizencephaly.     

Potentiation of DNA adduct formation in HL-60 cells by combinations of benzene metabolites.

Using P1 nuclease enhanced 32P postlabeling, we investigated DNA adduct formation in HL-60 promyelocytic leukemia cells treated with the benzene metabolites hydroquinone, catechol, and 1,2,4-benzenetriol. Comparison of the slopes of the dose-response curves showed that hydroquinone was 7-9 times more effective than 1,2,4,-benzenetriol and catechol at inducing DNA adducts. Comparison of hydroquinone with catechol showed a good correlation between adduct formation and cytotoxicity. Similar comparisons of hydroquinone and 1,2,4,-benzenetriol suggest that cellular processes in addition to DNA adduct formation contributed to cytotoxicity. In cells treated with the combination of hydroquinone and either catechol or 1,2,4,-benzenetriol, DNA adduct formation was 3-6 times greater than the sum of adduct formation produced by single-agent treatments. Treatment with hydroquinone and 1,2,4,-benzenetriol produced DNA adducts not detected after treatment with either metabolite alone. The synergistic interaction of benzene metabolites in the production of DNA adducts may play an important role in the genotoxic effects of benzene in vivo.     

The effects of human recombinant tumor necrosis factor on glioma-derived cell lines: cellular proliferation, cytotoxicity, morphological and radioreceptor studies

To determine whether tumor necrosis factor is of potential value for the treatment of human malignant gliomas, we studied the effects of human recombinant tumor necrosis factor (rTNF-alpha) on the morphology, incorporation of tritiated thymidine, and proliferation of 5 established cell lines derived from human malignant gliomas and 3 normal human brain cell cultures. A radioreceptor analysis for rTNF-alpha was performed on all cell lines and cultures. Two of the 5 human glioma cell lines (SF-188 and U 343 MG-A) demonstrated a marked decrease (60% or less of untreated controls) in the uptake of tritiated thymidine when treated with rTNF-alpha at a concentration of 40 U/ml; rTNF-alpha at 100 U/ml had antiproliferative and cytotoxic effects on both cell lines. The growth and proliferation of cell lines SF-126 and U 251 MG were not affected by rTNF-alpha even at high concentrations (5,000 U/ml). The growth and proliferation of SF-539 were affected to an intermediate degree. A colony-forming efficiency assay corroborated the results of the proliferation studies: SF-126 was relatively resistant (surviving fraction of 0.9 at 500 U/ml) and SF-188 was relatively sensitive (surviving fraction of 0.08 at 500 U/ml) to the cytotoxic effects of rTNF-alpha. Time-sequence electron microscopy showed that rTNF-alpha at a concentration of 500 U/ml caused ultrastructural changes in SF-188, including increased intracytoplasmic vesiculation, swelling and degeneration of mitochondria, loss of cell:cell junctional complexes, and fragmentation of the plasma membrane. Studies with 125I-rTNF-alpha showed a variable degree of binding in all cell lines and cultures. SF-188, a highly sensitive cell line, demonstrated the strongest binding of 125I-rTNF-alpha (3,400 receptors/cell with high affinity; kd = 0.27 nM), while SF-126, a highly resistant cell line, had the weakest binding (809 receptors/cell; kd = 0.25 nM). We conclude that there is a spectrum of antiproliferative and cytotoxic activity among glioma-derived tumor cell lines exposed to rTNF-alpha. An increased number of rTNF-alpha receptors appears to be a necessary but insufficient condition to explain the antiproliferative effects observed in some glioma-derived cell lines.     

Formation of DNA Adducts and Oxidative Base Damage by Copper Mediated Oxidation of Dopamine and 6-Hydroxydopamine

We have investigated the formation of DNA adducts and oxidative base damage produced by copper sulfate activation of dopamine and 6-hydroxydopamine. In the presence of 10 μMcopper sulfate both 100 μMdopamine and 100 μM6-hydroxydopamine formed three similar DNA adducts with relative adduct levels of 8.36 ± 2.23 × 10⁻⁸and 7.98 ± 2.53 × 10⁻⁸, respectively. The levels of 8-hydroxy-2′-deoxyguanosine produced by these incubations were 5.2 ± 0.03, 32.6 ± 2.4, and 0.01 pmol/μg DNA for dopamine, 6-hydroxydopamine, and control incubations, respectively, representing a 520- to 3260-fold increase in the level of this base oxidation product. The use of specific chelators and catalase demonstrated that the reduction of Cu²⁺to Cu¹⁺and the formation of a peroxide plays an important role in the activation of dopamine and 6-hydroxydopamine to form adducts and oxidative base damage. Our results suggest that the oxidation of dopamine by transition metals present in the brain may lead to the formation of both DNA adducts and oxidative base damage in dopaminergic cells. We propose that these processes may contribute to the observed loss of dopaminergic neurons in patients with Parkinson's disease.     

DNA adduct formation by tamoxifen with rat and human liver microsomal activation systems

Using microsomal preparations from rat and human liver, we investigatedthe activation of the anti-estrogen compound tamoxifen (TMX)to form DNA adducts. Pretreatment of rats with phenobarbitalincreased DNA adduct formation by microsomal activation of TMX3- to 6-fold, depending on the cofactors used. When reducednicotinamide-adenine dinucleotide phosphate (NADPH) was usedas a cofactor in human and rat microsomal activation systems,the relative DNA adduct levels were 2.9 and 5.2 x 10^–8respectively and 1-3 TMX-DNA adducts were detected by ²³P-postlabeling;DNA adduct 1 was the same in both microsomal systems. When cumenehydroperoxide (CuOOH) was used as a cofactor, activation ofTMX produced four major DNA adducts and several minor DNA adductsin both rat and human liver microsomes; the relative adductlevels were 11.1 and 23.1 xlO^–8 respectively. TMX-DNAadducts 1, 4, 5 and 6 were similar in both human and rat microsomalsystems with CuOOH as the cofactor. The TMX-DNA adducts formedwith NADPH as the cofactor were clearly different from thoseformed with CuOOH as the cofactor, which implies that the metabolitesleading to the individual DNA adducts were different. Additionof a P450 inhibitor, either n-octylamine or