Differential Correlates of Irrational Belief

One hundred and ten students completed a battery which included Jones' Irrational Belief Test (IBT), and measures of subjective well-being, affect, alienation, personality, goal characteristics, and goat attainment. Correlations and canonical composites showed a general relationship between irrational beliefs and emotional difficulty, but the specific pattern differed for subgroups of IBT scales. Correlations supported the construct validity of IBT scales, but suggested they also reflect motives, conflicts, affects and personality characteristics. Interdependence of these processes was hypothesized and use of subscore composites rather than total IBT scores was suggested.

Biodistribution of NX211, liposomal lurtotecan, in tumor-bearing mice

Prolonging tumor exposure to topoisomerase I inhibitors has been correlated to enhance the efficacy of those agents. Lurtotecan, a water-soluble camptothecin analog, was formulated as a liposomal drug, NX211, to enhance the delivery of drug to tumors. Tumor-bearing mice were treated with either [14C]NX211 containing [14C]lurtotecan, [3H]NX211 containing [3H]phosphatidylcholine or [14C]lurtotecan, euthanized at selected times post-injection, and tissues, plasma, urine and feces were collected. These studies demonstrated that KB tumors of [14C]NX211-treated mice had approximately 70-fold greater concentrations of [14C]lurtotecan at 24 h, respectively, compared to concentrations of [14C]lurtotecan of the KB tumors of [14C]lurtotecan-treated mice. The area under curve (AUC) from 0 to 48 h of [14C]lurtotecan for the KB tumors of [14C]NX211-treated animals was over 17-fold greater than the AUC of [14C]lurtotecan for the tumors of [14C]lurtotecan-treated animals. Treatment with [3H]NX211 demonstrated that the lipid component continually accumulated over 24 h in the tissues. HPLC analysis of extracted material from tumors of [14C]NX211-treated mice showed that more than 95% of the radioactive material was intact [14C]lurtotecan. These findings are one of the keys justifying the development of a liposomal formulation of lurtotecan, which has the intent to increase tumor exposure and increase antitumor efficacy.

Modification of delayed rectifier potassium currents by the Kv9.1 potassium channel subunit

Within auditory pathways, the intrinsic electrical properties of neurons, and in particular their complement of potassium channels, play a key role in shaping the timing and pattern of action potentials produced by sound stimuli. The Kv9.1 gene encodes a potassium channel alpha subunit that is expressed in a variety of neurons, including those of the inferior colliculus. When cRNA encoding this subunit is injected into Xenopus oocytes, no functional channels are expressed. When, however, Kv9.1 is co-expressed with certain other alpha potassium channel subunits, it changes the characteristics of the currents produced by these functional channel proteins. We have found that Kv9.1 isolated from a rat brain cDNA library alters the kinetics and the voltage-dependence of activation and inactivation of Kv2.1, a channel subunit that generates slowly inactivating delayed rectifier potassium currents. The rate of activation of Kv2.1 is slowed by co-expression with Kv9.1. With Kv2.1 alone, the amplitude of evoked currents increases monotonically with increasing command potentials. In contrast, when Kv2.1 is co-expressed with Kv9.1, the amplitude of currents increases with increasing depolarization up to potentials of only approximately +60 mV, after which increasing depolarization results in a decrease in current amplitude. Currents produced by Kv2. 1 alone and by Kv2.1/Kv9.1 are both sensitive to the potassium channel blocker tetraethyl ammonium ions (TEA), but higher concentrations of TEA (20 mM) eliminate the biphasic voltage-dependence of the Kv2.1/Kv9.1 currents. Co-expression with Kv9.1 also produces an apparent negative shift in the voltage-dependence of inactivation and activation. Computer simulations of model neurons suggest that co-expression of Kv9.1 with Kv2.1 may have different effects in neurons depending on whether their firing pattern is limited by the inactivation of inward currents. In excitable cells in which the inward currents do not inactivate, co-expression with Kv9.1 could produce an inhibition of firing during sustained depolarization. In contrast, in model neurons with rapidly inactivating inward current, the change in the voltage-dependence of activation produced by Kv9.1 may allow the cells to follow high frequency stimulation more effectively.

Antitumor efficacy, pharmacokinetics, and biodistribution of NX 211: a low-clearance liposomal formulation of lurtotecan

Lurtotecan is a clinically active water-soluble camptothecin analogue that has been formulated into a low-clearance unilamellar liposome, NX 211. Comparative studies between free drug and NX 211 have been performed assessing pharmacokinetics in nude mice, tissue distribution in tumor-bearing mice, and antitumor efficacy in xenografts. Compared with lurtotecan, NX 211 demonstrated a significant increase in plasma residence time and a subsequent 1500-fold increase in the plasma area under the drug concentration curve. The volume of distribution was also greatly restricted, suggesting altered tissue distribution. Evaluation of tissues 24 h after administration of either [14C]NX 211 or [14C]lurtotecan to ES-2 tumor-bearing mice demonstrated a 40-fold increase in radiolabeled compound in the tumors of NX 211-treated mice compared with mice treated with lurtotecan. In single-dose efficacy studies, NX 211 produced a consistent 3-fold or greater increase in therapeutic index compared with lurtotecan in both the KB and ES-2 xenograft models. When compared at equitoxic levels in repeat-dose efficacy studies, NX 211 generated durable cures lasting >60 days and a 2-8-fold increase in log10 cell kill, compared with lurtotecan and topotecan, respectively. Together, these data demonstrate that NX 211 has significant therapeutic advantage over lurtotecan and that the improved antitumor activity is consistent with increased exposure and enhanced drug delivery to tumor sites.

Polymerization of 2'-fluoro- and 2'-O-methyl-dNTPs by human DNA polymerase alpha, polymerase gamma, and primase

Studies were undertaken to assess the ability of human polymerase alpha (pol alpha) and polymerase gamma (pol gamma) to incorporate 2'-fluoro- and 2'-O-methyldeoxynucleotides into DNA. In vitro DNA synthesis systems were used to detect incorporation and determine K(m) and V(max) for 2'-FdATP, 2'-FdUTP, 2'-FdCTP, 2'-FdGTP, 2'-O-MedATP, 2'-O-MedCTP, 2'-O-MedGTP, 2'-O-MedUTP, dUTP, UTP, and FIAUTP, in addition to normal deoxynucleotides. Pol alpha incorporated all 2'-FdNTPs except 2'-FdATP, but not 2'-O-MedNTPs. Pol gamma incorporated all 2'-FdNTPs, but not 2'-O-MedNTPs. In general, 2'-fluorine substitution decreased V(max)/K(m) 2'-FdUTP. Because kinetics of insertion of pol alpha can be affected by the nature of the primer, we examined the ability of pol alpha to polymerize 2'-fluoro- and 2'-O-MedATP and dGTP when elongating a primer synthesized by DNA primase. Under these conditions, both 2'-FdATP and 2'-FdGTP were polymerized, but 2'-O-MedATP and 2'-O-MedGTP were not. Primase alone could not readily polymerize these analogs into RNA primers. Previous studies showed that 2'-deoxy-2'-fluorocytosine (2'-FdC) is incorporated by several non-human DNA polymerases. The current studies showed that human polymerases can polymerize numerous 2'-FdNTPs but cannot polymerize 2'-O-MedNTPs.

An evaluation of the toxicities of 2'-fluorouridine and 2'-fluorocytidine-HCl in F344 rats and woodchucks (Marmota monax)

The toxicities of 2'-fluorouridine (2'-FU) and 2'-fluorocytidine-HCl (2'-FC) were separately evaluated in 2 species, male Fischer 344 (F334) rats and woodchucks. Particular attention was focused on the ability of these nucleosides to induce toxicities similar to those induced by the antiviral drug fialuridine (FIAU). 2'-FU or 2'-FC was administered to F344 male rats by intravenous injection at doses of 5, 50, and 500 mg/kg/day for 90 consecutive days and to male and female woodchucks at doses of 0.75 and 7.5 mg/kg/day for 90 consecutive days. Clinical chemistry, hematology, and urinalysis (woodchuck only) profiles were assessed during and at the termination of the study. At necropsy, organs were weighed and tissues collected for routine histologic analysis. Cytochrome c oxidase activity, citrate synthase activity, and mitochondrial DNA content were measured, and micronucleus formation in the bone marrow (rats only) was evaluated. No adverse clinical effects were observed in either species. Rats treated with high doses of either 2'-FU or 2'-FC had body weights that were 90% of those of controls. 2'-FU and 2'-FC both induced a moderate decrease in the median lymphocyte count, and 2'-FC and 2'-FU induced a mild increase in mean corpuscular hemoglobin and mean corpuscular volume. Both compounds caused slight to moderate, reversible, histologic changes in the spleen and thymus. In the woodchuck, 2'-FC caused a slight increase in mean absolute lymphocytes, and 2'-FC and 2'-FU slightly increased hepatic periportal vacuolation and/or mononuclear cell infiltration. In summary, neither compound showed evidence of the toxicity induced by fialuridine in either species. Although compound effects were observed, none of these effects were considered to be adverse, and the no-observed adverse effect level was determined to be 500 mg/kg/day for both compounds in the male F344 rat and 7.5 mg/kg/day in the woodchuck.

Antiviral activity and toxicity of fialuridine in the woodchuck model of hepatitis B virus infection

Woodchucks were used to study the antiviral activity and toxicity of fialuridine (FIAU; 1,-2'deoxy-2'fluoro-1-beta-D-arabinofuranosyl-5-iodo-uracil). In an initial experiment, groups of six chronic woodchuck hepatitis virus (WHV) carrier woodchucks received daily doses of FIAU by intraperitoneal injection for 4 weeks. At 0.3 mg/kg/d, the antiviral effect was equivocal, but at 1.5 mg/kg/d, FIAU had significant antiviral activity. No evidence of drug toxicity was observed during the 4-week period of treatment or during posttreatment follow-up. In a second experiment, groups of nine WHV carriers or uninfected woodchucks were given 1.5 mg/kg/d of FIAU orally for 12 weeks, and the results compared with placebo-treated controls. After 4 weeks, the serum WHV-DNA concentration in the FIAU-treated carrier group was two to three logs lower than that in the placebo-treated group. After 12 weeks of FIAU treatment, serum WHV DNA was not detectable by conventional dot-blot analysis, hepatic WHV-DNA replicative intermediates (RI) had decreased 100-fold, and hepatic expression of WHV core antigen was remarkably decreased. No evidence of toxicity was observed after 4 weeks, but, after 6 to 7 weeks, food intake decreased and, after 8 weeks, the mean body weights of woodchucks treated with FIAU were significantly lower than controls. Anorexia, weight loss, muscle wasting, and lethargy became progressively severe, and all FIAU-treated woodchucks died or were euthanized 78 to 111 days after treatment began. Hepatic insufficiency (hyperbilirubinemia, decreased serum fibrinogen, elevated prothrombin time), lactic acidosis, and hepatic steatosis were characteristic findings in the final stages of FIAU toxicity in woodchucks. The syndrome of delayed toxicity in woodchucks was similar to that observed previously in humans treated with FIAU, suggesting that the woodchuck should be valuable in future investigations of the molecular mechanisms of FIAU toxicity in vivo and for preclinical toxicological evaluation of other nucleoside analogs before use in patients.

Fialuridine is phosphorylated and inhibits DNA synthesis in isolated rat hepatic mitochondria

Fialuridine (FIAU) is a thymidine analog effective against hepatitis B virus. Toxicity associated with FIAU treatment included clinical signs consistent with mitochondrial dysfunction, including severe lactic acidosis. To understand further the mechanism of FIAU toxicity, we examined the effect of FIAU on DNA synthesis in mitochondria. Mitochondria isolated from livers of naive rats were treated in vitro with concentrations of FIAU or FIAU triphosphate (FIAU-TP) ranging from 0.1 to 200 microM. A 14 or 32% decrease in mitochondrial DNA synthesis compared to controls was observed when isolated mitochondria were treated with 25 microM FIAU or FIAU-TP, respectively. Since it is thought that nucleosides must be phosphorylated to inhibit DNA polymerase, studies were conducted to determine whether isolated rat mitochondria could phosphorylate FIAU. Results using lanthanum chloride precipitation and HPLC analysis showed that enzymes present in a mitochondrial lysate were capable of phosphorylating FIAU to form FIAU monophosphate.

Differential effects of the incorporation of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) on the binding of the transcription factors, AP-1 and TFIID, to their cognate target DNA sequences

The thymidine analog, 1-(2-deoxy-2-fluoro-beta-D-arabino-furanosyl)-5-iodouracil (FIAU), is incorporated into DNA in cell culture and in vivo. To investigate the effect of incorporation of FIAU into DNA on the binding of transcription factors, oligonucleotide duplexes which bind specifically to activator protein 1 (AP-1) or to TFIID were synthesized and binding of these oligonucleotides to their respective proteins was studied using gel-shift analysis. When thymidine at position -3, -1, 1 or 7 (relative to the first thymidine of the core binding sequence) was replaced with FIAU, binding to AP-1 was approximately 82, 28, 86 and 51%, respectively, of the binding to the non-substituted oligonucleotide to AP-1. When thymidine at position 3 or 5 (each adjacent to the center of dyad symmetry) was replaced with FIAU, binding to AP-1 was abrogated. Oligonucleotides containing FIAU at positions -1, 3 or 5, were much less able to compete with radiolabeled wild-type oligonucleotides for binding to AP-1. In contrast, the presence of FIAU, depending on its location, resulted in the increased binding of TFIID to its consensus target DNA sequence. These results indicate that incorporation of FIAU into DNA may induce local conformational changes resulting in the altered ability of transcriptional factors to bind to their cognate DNA sequences. Additional studies demonstrated that the presence of FIAU at a position 5' to the cleavage site in the consensus sequence T*TAA (where * is the cleavage site) inhibited restriction of the oligomeric duplex by MseI.

Identification and characterization of a Ca(2+)-sensitive nonspecific cation channel underlying prolonged repetitive firing in Aplysia neurons

The afterdischarge of Aplysia bag cell neurons has served as a model system for the study of phosphorylation-mediated changes in neuronal excitability. The nature of the depolarization generating the afterdischarge, however, has remained unclear. We now have found that venom from Conus textile triggers a similar prolonged discharge, and we have identified a slow inward current and corresponding channel, the activation of which seems to contribute to the onset of the discharge. The slow inward current is voltage-dependent and Ca(2+)-sensitive, reverses at potentials slightly positive to O mV, exhibits a selectivity of K approximately equal to Na >> Tris > N-methyl-D-glucamine (NMDG), and is blocked by high concentrations of tetrodotoxin. Comparison of these features with those observed in channel recordings provides evidence that a Ca(2+)-sensitive, nonspecific cation channel is responsible for a slow inward current that regulates spontaneous repetitive firing and suggests that modulation of the cation channel underlies prolonged changes in neuronal response properties.

Dose-dependent induction of GST-P+ staining foci by the rat hepatocarcinogen methapyrilene in the medium-term bioassay

Previous studies have demonstrated that methapyrilene hydrochloride (MP) is a rat-specific nongenotoxic carcinogen which induces liver tumors in a dose-dependent manner following chronic exposure in the diet. This study was conducted to determine the dose response of MP in the medium-term bioassay and to compare the response to tumor incidence. Two weeks following a single initiating dose of diethylnitrosamine (DEN), male F344 rats were administered MP at doses of 0, 62.5, 125, 250, or 1000 ppm in the diet for 6 weeks. A 2/3 partial hepatectomy was performed 3 weeks post-DEN. At termination, sections from the remaining three lobes were stained with GST-P antibody. Number and size of foci were measured using an image analysis system with a digitizing board. MP induced a dose-dependent increase in the number of GST-P+ foci/cm2 (0 ppm = 0.85 foci/cm2; 62.5 ppm = 1.29 foci/cm2; 125 ppm = 1.59 foci/cm2; 250 ppm = 6.55 foci/cm2; 1000 ppm = 28.23 foci/cm2). A significantly greater number of foci were observed in the caudate lobe than in the anterior and posterior lobes. The size of individual foci was largely unaffected. This study demonstrates a strong correlation between foci induction and tumor incidence and suggests that this assay may have utility in predicting dose responses for the chronic bioassay.

Fialuridine accumulates in DNA of dogs, monkeys, and rats following long-term oral administration

Accumulation of the antiviral nucleoside analogue fialuridine (FIAU; 1-(2'-deoxy-2'-fluoro-beta-D-arab-inofuranosyl-5-iodouracil) in genomic DNA was examined with a modified version of a recently developed RIA for FIAU. DNA was obtained from tissues of dogs administered FIAU at 0, 1, 2, or 3 mg/kg of body weight per day for 90 days, monkeys administered FIAU at 0 or 25 mg/kg per day for 30 days, and rats administered FIAU at 0, 255, or 510 mg/kg per day for 70 days. FIAU incorporation was observed in all species. In the rat, FIAU was incorporated into DNA of all tissues examined, with highest concentrations in the liver followed by jejunum, spleen, and heart. FIAU was also incorporated into sperm DNA. Incorporation rates were as high as 11,000 pmol of FIAU per mumol of thymidine or 1 FIAU molecule per 90 thymidine molecules. In dogs and rats, the extent of incorporation was dose-dependent. Across species, FIAU concentrations in DNA were not singly dependent on the total dose administered but also may have been dependent on the duration of exposure. These studies show that FIAU accumulates to high concentrations in genomic DNA of liver as well as other tissues during chronic oral administration and suggest that net accumulation of FIAU in DNA may be a critical step in FIAU-induced toxicity.

Dose-responses in rat hepatic protein modification and expression following exposure to the rat hepatocarcinogen methapyrilene

Dose-related effects of methapyrilene (MP) on protein modification and expression were examined using two-dimensional gel electrophoresis (2-D PAGE) coupled with computer analysis. Methapyrilene was administered ad libitum at doses of 0, 62.5, 125, 250 and 1000 p.p.m. to male F-344 rats for 12 weeks beginning at 8 weeks of age. Following treatment, livers were removed and frozen for 2-D PAGE analysis. Separation of hepatic proteins was conducted using ISO-DALT technology. Changes in abundance and modification of hepatic proteins were determined using the Kepler software package. Covalent modifications of three specific mitochondrial proteins were quantified using a charge modification index. Dose-response relationships were analyzed using Tukey's trend test. Results demonstrated that covalent modification of the three mitochondrial proteins was linearly related to dose and that a dose effect could be found at all dose levels in 2 out of 3 proteins. Two forms of change in protein expression were observed: (i) a dose-dependent change with effects at all doses and (ii) a change only at the toxic dose of 1000 p.p.m. MP. These results demonstrate a molecular effect of MP at doses that do not produce cellular responses including toxicity or increases in cell replication suggesting that these specific mitochondrial modifications are molecular dosimeters but are probably not direct factors and/or sufficient factors in carcinogenesis. This study also demonstrates the potential use of 2-D PAGE electrophoresis to delineate the effect of dose on expression of specific proteins.

H-ras 61st codon activation in archival proliferative hepatic lesions isolated from female B6C3F1 mice exposed to the leukotriene D4-antagonist, LY171883

LY171883, a peroxisome proliferator and leukotriene D4-antagonist, induced a statistically significant increase in the number of hepatic lesions in B6C3F1 female mice in a 2 year oncogenicity study at dietary doses of 0.0225% and 0.075%. The mutation frequency and spectrum of the 61st codon of H-ras was determined for 64 independent, archived lesions from the LY171883 2 year oncogenicity study using the polymerase chain reaction (PCR), allele specific oligo hybridization (ASO) and DNA sequencing. Results showed 41 (64%) of these lesions had mutations at the 61st codon (16/21 hepatocellular carcinomas, 4/10 hepatocellular adenomas, 19/26 focal hepatocellular hyperplasias and 2/7 focal hepatocellular atypia). These mutations consisted of 18 C-A transversions, 16 A-G transitions and seven A-T transversions. Compared to the mutation frequency for spontaneously occurring archival B6C3F1 hepatic lesions (41%), the frequency of LY171883 lesions (64%) was significantly higher (P < 0.01). The frequencies of H-ras 61st codon mutations among the LY171883 lesion types (hepatocellular carcinomas 76%, hepatocellular adenomas 40%, focal hepatocellular hyperplasias 73% and hepatocellular atypia 29%) were also significantly different (P = 0.035). In contrast, spontaneous lesions showed no statistical difference in the frequencies of mutation among lesion types (P > 0.5). The mutation spectrum of the LY171883 lesions was not significantly different from the spontaneous spectra. It may be concluded that based on the similarity in mutation spectrum and the increase in mutation frequency, LY171883 may selectively promote spontaneous hepatic lesions containing H-ras 61st codon mutations. In addition, the difference in mutation frequency among lesion types does not support a linear progression of all LY171883 lesions through focal atypia, focal hepatocellular hyperplasias, hepatocellular adenomas and hepatocellular carcinomas.

Effect of a template-located 2',2'-difluorodeoxycytidine on the kinetics and fidelity of base insertion by Klenow (3'-->5'exonuclease-) fragment

Gemcitabine [2',2'-difluorodeoxycytidine (dFdCyd)], a potent antitumor agent, inhibits DNA synthesis and is incorporated internally into DNA. The effect of a template-incorporated dFdCyd molecule (dFdCyd-) on DNA polymerase function was examined. Two 25-base deoxyoligonucleotides were synthesized with either a single dFdCyd- or template-incorporated deoxycytidine molecule (dCyd-) at the same position. Each was annealed separately to an identical complementary 5'-32P-labeled primer and extended by the Klenow fragment (3'-->5' exo-) of DNA polymerase I. "Correct" insertion of dGMP was 80-fold less efficient opposite dFdCyd- than dCyd-. A comparison of misinsertion efficiencies opposite template dFdCyd gave values of 2.7 x 10(-2) for dAMP insertion, 1.1 x 10(-3) for dTMP insertion, and 5.9 x 10(-4) for dCMP insertion. A similar measurement opposite template dC gave values of 1.8 x 10(-4), 1.7 x 10(-4), and 2.9 x 10(-6) for dAMP, dTMP, and dCMP insertion, respectively. Thus, the presence of dFdCyd on the template strand inhibited "normal" DNA synthesis and increased deoxyribonucleotide misinsertion frequencies. Pausing during DNA synthesis occurred directly opposite template dFdCyd suggesting that dFdC.dG base pairs might be less stable than normal dC.dG pairs, resulting in a decreased rate of primer extension beyond this site. Consistent with kinetic data, thermal denaturation measurements using comparable surrounding sequences showed that dFdC.dG "correct" pairs were less stable than dC.dG base pairs. Measurements on base mispairs showed that dFdC.dC was more stable than dC.dC, while no measurable Tm differences were found between polymers containing dFdC.dA and dC.dA or dFdC.dT, and dC.dT.

Expression of TRPM-2 during involution and regeneration of the rat liver

Increased message levels of testosterone-repressed prostate message-2 (TRPM-2) have been associated with programmed cell death in many tissues. To study its involvement in the apoptotic elimination of hepatocytes during liver involution and regeneration, levels of TRPM-2 message were evaluated in situ and by the ribonuclease protection assay. Although significant increases in apoptotic bodies were observed in rats 96 h following treatment with lead nitrate and ethylene dibromide, an increase in TRPM-2 message was not detected. Therefore, the expression of TRPM-2 mRNA may be a poor indicator of the extent to which apoptosis occurs during liver involution.

The evaluation of methapyrilene for bacterial mutation with metabolic activation by Aroclor-induced, methapyrilene-induced and noninduced rat-liver S9

The antihistamine methapyrilene (MP) has been shown to be a potent hepatocarcinogen in rats. However, it has demonstrated little genotoxic activity in a wide variety of short-term tests. In this study, Fischer 344 rats were fed a carcinogenic dose of 0.1% methapyrilene in the diet for 10 weeks prior to sacrifice. S9 was prepared from the livers of the control, MP-treated and Aroclor-induced Fischer 344 rats. Each type of S9 was analyzed for mixed function oxidase activity, cytochrome P-450, and protein content. MP was then evaluated for mutagenicity in 6 strains of S. typhimurium (TA1535, TA1537, TA98, TA100, TA2638 and TA104) and one strain of E. coli (WP2uvrA-) using the standard plate-incorporation assay. MP was not mutagenic in any of the 7 bacterial strains when tested at concentrations < or = 10 mg/ml in the presence of each type of S9. However, in the absence of metabolic activation, an approximate 2-fold increase in revertants was noted with strain TA1535. The data from this study show that MP was not converted to a mutagenic metabolite by any of the three S9 types examined. However, the "weak" positive response with strain 1535 in the absence of metabolic activation indicates that further research is needed to elucidate the mechanism of action of this rat carcinogen.

Comparisons of protein changes in human and rodent hepatocytes induced by the rat-specific carcinogen, methapyrilene

There is a growing concern that the rodent bioassay may not always serve as an appropriate model to assess the carcinogenic risk for humans exposed to certain compounds. Mechanistic research that examines the effects of a compound in rodent and man could help in the interpretation of bioassay results. This paper reports a novel use of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) technology to assess similarities and differences in the response of rodents and humans to the rat-specific hepatocarcinogen, methapyrilene (MP). A sequential examination of rodent and human hepatic proteins was conducted following in vivo exposure of rats and mice and in vitro exposure of rat, mouse, and human hepatocytes to MP. Results showed that covalent modifications observed in rats and mice in vivo were duplicated both qualitatively and quantitatively in the corresponding in vitro systems and that these modifications correlated with carcinogenic susceptibility. Covalent modifications in human hepatocytes were minimal despite exposure to concentrations of MP that were 6-fold higher than those used in rodent hepatocytes. These studies suggest that in the case of MP the rat is not the most appropriate model for assessing the human situation. Furthermore, these data show that in vitro-in vivo comparisons based on 2-D PAGE may provide adjunctive information for extrapolating rodent toxicity/bioassay results to human risk assessment.

Effects of methapyrilene on DNA synthesis in mice and rats following continuous dietary exposure

The effects of the antihistamine methapyrilene (MP) on DNA synthesis in rats and mice were investigated. Previous studies have demonstrated a dose response for tumor induction in the rat but no carcinogenic effect in the mouse. To study the role of DNA synthesis in MP carcinogenesis, rats and mice were administered MP at doses of 0, 62.5, 125, 250 or 1000 p.p.m. in the diet for a period of 1-12 weeks. Bromodeoxyuridine was administered continuously using an osmotic minipump during the last week of treatment to provide an index of DNA synthesis. Results demonstrated that in the rat 250 and 1000 p.p.m. MP increased DNA synthesis in a dose-dependent manner that correlated with the tumor response in previous oncogenic studies. MP at 62.5 p.p.m. did not increase DNA synthesis, indicating a no effect level for cell proliferation and suggesting a no effect level for carcinogenicity by this compound in the rat. MP did not induce DNA synthesis in mice after exposure to 1000 p.p.m. for 12 weeks, nor did it induce changes in serum chemistries or liver histopathology suggestive of overt toxicity as was seen in the rat at 1000 p.p.m. The correlations between labeling index and tumorigenicity in the rat and mouse strongly support a role of cell proliferation in the carcinogenic mechanism of MP.

Effects of methapyrilene measured in mitochondria isolated from naive and methapyrilene-treated rat and mouse hepatocytes

Methapyrilene (MP) is a rat-specific liver carcinogen that alters mitochondrial number and morphology both in vivo and in vitro. This biological phenomenon may be due to the effects of MP on mitochondrial function. To test this hypothesis, studies were conducted to examine the effects of MP on DNA and protein synthesis and respiration in isolated mitochondria. DNA and protein synthesis activities were measured using [3H]thymidine and [3H]leucine incorporation. Mouse liver mitochondria were also examined for comparison since no tumor formation or alterations in mitochondrial morphology have been associated with MP treatment in mice. A significant decrease in basal DNA and protein synthesis levels was observed in mitochondria isolated from rats and mice following in vivo MP treatment. This effect could not be reproduced when mitochondria were exposed to 0 or 100 microM MP following isolation, despite the presence of an S9 activation system. Electron microscopic examinations were performed on isolated rat mitochondria and revealed morphologic differences between mitochondria from naive and MP-treated rats. Although significant differences in State 3 and State 4 respiratory rates were noted, the respiratory control ratio, ADP/O ratio, and uncoupler-stimulated respiratory rates were unaffected. Results demonstrate that: (1) MP irreversibly depresses DNA and protein synthesis in a majority of mitochondria, despite only localized morphologic changes; (2) these changes are not reflected by a decrease in respiratory function; and (3) depression of DNA and protein synthesis does not correlate with carcinogenic susceptibility.

Temporal changes in the mutant frequency and mutation spectra of the 61st codon of the H-ras oncogene following exposure of B6C3F1 mice to N-nitrosodiethylamine (DEN)

Hepatocellular tumors were induced in 15 day old male B6C3F1 mice following a single exposure to N-nitrosodiethylamine (DEN; 5 mg/kg, i.p.). Tumors were collected at 38 and 65 weeks to compare the frequencies and types of mutations in the 61st codon of the H-ras oncogene. The 61st codon was amplified using the polymerase chain reaction (PCR). Allele-specific oligonucleotide (ASO) probes were used to determine the frequency and types of mutations present in these tumors. Forty-nine nodular hepatic lesions were obtained from seven animals at the 38 week timepoint. Five of these samples (10%) had mutations at the 61st codon with one CAA-AAA, one CAA-CGA and three CAA-CTA. Thirty-six nodular hepatic lesions were obtained from six animals at the 65 week timepoint. Ten of these samples (28%) had mutations at the 61st codon with one CAA-AAA, five CAA-CGA and four CAA-CTA. These data indicate that DEN-induced mutations at the 61st codon of the mouse H-ras oncogene (i) are an infrequent event, (ii) have different frequencies at the 38 and 65 week timepoints and (iii) are different from the types of mutations seen in spontaneous lesions.

Covalent protein modifications and gene expression changes in rodent liver following administration of methapyrilene: a study using two-dimensional electrophoresis

The effect of methapyrilene (MP), a mitochondrial proliferator and presumed nongenotoxic carcinogen, has been examined in rodent liver by means of high-resolution two-dimensional electrophoretic analysis of total proteins. Using this approach, we have discovered protein modifications in rat liver resulting from 1 week MP treatment that suggest the involvement of a reactive drug metabolite. The restriction of these molecular charge modifications to mitochondrial proteins indicates that such a reactive metabolite must be generated and confined within the mitochondrion. Quantitative changes in numerous nonmitochondrial proteins are also observed. Following a 4-week recovery period, almost all the 1-week treatment changes are reversed, reestablishing a protein pattern close to that of the controls. At the end of a 10-week exposure, the mitochondrial protein modifications are increased and are accompanied by a variety of quantitative protein changes indicative of a large shift in gene expression and/or cell type composition. When a 4-week untreated recovery period follows the 10-week treatment, small quantitative changes persist. In the mouse, where MP appears not to induce mitochondrial proliferation or tumorigenesis, 1 week treatment nevertheless produces mitochondrial protein changes in vivo consistent with attack by a reactive metabolite, but at a level substantially lower than that seen in the rat. Features of the mitochondrial protein modification indicate that it is covalent, does not involve cysteine or tryptophan, and results from binding of a negatively charged adduct. The possibility that the putative reactive metabolite could also attack mitochondrial (but not nuclear) DNA suggests that MP could be genotoxic in an unconventional way. Detection of protein modification by two-dimensional gel analysis appears to offer a general method for the detection and characterization of processes generating reactive metabolites.

Synthesis and restriction enzyme analysis of oligodeoxyribonucleotides containing the anti-cancer drug 2',2'-difluoro-2'-deoxycytidine

The anti-cancer drug 2',2'-difluoro-2'-deoxycytidine (dFdC) is internally incorporated into DNA in vitro. To determine the effects of this incorporation on DNA structure and function, the beta-cyanoethyl phosphoramidite of dFdC was synthesized and oligodeoxyribonucleotides containing dFdC were made using automated solid phase DNA synthesis techniques. Extension of the coupling time was required to achieve high coupling efficiency, suggesting a significant reduction in the rate of phosphotriester formation. Insertion of dFdC 5' into the recognition sequence of restriction enzymes HpaII and KpnI reduced the rate of cutting by 4% and 14% over 60 minutes. This reduction is similar to the effects seen with arabinofuranosylcytidine (ara-C) but small compared to the reductions caused by base analogues and phosphothioates. Insertion of dFdC into the BamHI recognition sequence, but not 5' to the cut site, did not alter the rate of cutting/recognition. The presence of a single dFdC reduced the Tm's of oligomers by 2-4 degrees C, depending on sequence and location. These results demonstrate that, once incorporated into DNA, dFdC does not greatly alter recognition between DNA and restriction enzymes; however, it does significantly alter duplex stability.

Genetic alterations in the 61st codon of the H-ras oncogene isolated from archival sections of hepatic hyperplasias, adenomas and carcinomas in control groups of B6C3F1 mouse bioassay studies conducted from 1979 to 1986

In order to better understand the molecular events in murine hepatocarcinogenesis, the frequency and types of mutations in the murine H-ras proto-oncogene isolated from 184 independent, spontaneously occurring hepatic lesions were determined. Hepatocellular foci, hyperplasias, adenomas and carcinomas were obtained from archival samples of control male (134 samples) and female (50 samples) B6C3F1 mice used in oncogenicity studies that were conducted at Lilly Research Laboratories from 1979 to 1986. The 61st codon region of the H-ras oncogene from these sections was amplified using the polymerase chain reaction. Mutation frequencies were determined by restriction fragment length polymorphism analysis. The types of mutations were characterized by allele-specific oligonucleotide hybridization and confirmed by DNA sequencing. Forty-two per cent of the carcinomas, 44% of the adenomas, 42% of the hyperplasias and 29% of the foci contained mutations at the 61 codon. The mutation spectra for the carcinomas, adenomas and hyperplasias consisted of mostly CAA-AAA transversions, followed by CAA-CGA transitions, followed by CAA-CTA transversions. These results demonstrate that: (i) the frequency of spontaneous mutations in the H-ras 61st codon is equivalent in murine hyperplasias, adenomas and carcinomas, and (ii) sex was not a determining factor in either the mutation frequency or mutation spectrum for the spontaneous lesions. If these lesions represent successive stages in the carcinogenic process, then these results suggest that mutations in the 61st codon of H-ras are early events in spontaneous murine hepatocarcinogenesis.

Alterations in DNA-restriction enzyme interactions by O4-alkyldeoxythymidines

O4-Alkyldeoxythymidines have been extensively studied for their ability to cause mutations and to induce cancer. Since these adducts can change DNA conformation, they may also have a more immediate effect of altering DNA-protein interactions. To address this issue, the effects of these adducts on restriction enzyme activity were examined. Oligodeoxyribonucleosides containing O4-ethyldeoxythymidine (O4-EtdT) or O4-methyldeoxythymidine (O4-MedT) at a unique site within the sequence 5'-GAATGGATCCTAATGAGATC-3' were constructed by automated DNA synthesis. This sequence contains the recognition site for various restriction enzymes. These oligomers were annealed to various complementary strands and digested with restriction enzymes: BamHI or BstI (GGATCC); Sau3A, NdeII, or MboI (GATC); DpnI (GmATC); and BstYI, MflI, or XhoII (PuGATCPy). Analysis of the digests demonstrated that the presence of either O4-EtdT or O4-MedT abolished the ability of XhoII, MboI, MflI, or NdeII to cut at the restriction site. DpnI failed to cut any of the oligomers. BamHI, Sau3A, BstI, and BstYI exhibited alterations in cutting specificity depending upon the oligomers used. These results demonstrated that O4-alkyldeoxythymidine adducts alter DNA-restriction enzyme interactions in a protein- and sequence-dependent manner. Because of the importance of natural methylation in genetic regulation, it is possible that aberrant methylation in the form of DNA adducts could also alter protein-DNA interactions in cells exposed to DNA-modifying agents.

Sequence-dependent formation of alkyl DNA adducts: a review of methods, results, and biological correlates

Understanding the influence of the DNA sequence on chemical-DNA interactions may provide insight into the processes of chemical carcinogenesis and mutagenesis. This article provides a brief overview of studies and methods devoted to examining the distribution of DNA adducts produced by alkylating agents. Particular emphasis is placed on discussion of DNA adducts generated by simple alkylating agents and the role that their distribution may play in the generation of mutational hotspots.

Dose response of hepatocyte replication in rats following continuous exposure to diethylnitrosamine

Chronic exposure to the hepatocellular carcinogen diethylnitrosamine (DEN) causes a dose-dependent accumulation of the promutagenic DNA adduct O4-ethyldeoxythymidine in hepatocytes and increases in the number of initiated hepatocytes as indicated by gamma-glutamyl transpeptidase positive foci. Initiation is thought to be dependent on the quantity of promutagenic DNA adducts, their efficiency for causing base pair mismatch, and the extent of replication in the target tissue. If the extent of replication is also dose dependent, then this dependence could alter the number of promutagenic DNA adducts that mispair prior to repair and enhance the clonal expansion of initiated cells. We have examined the effect of DEN on hepatocellular proliferation over a wide range of doses. Six-week-old male F-344 rats were exposed to drinking water containing 0.4, 1, 4, 10, 40, or 100 ppm DEN for 1, 4, or 10 weeks. Following exposures to DEN, rats were injected i.p. with [3H]thymidine, sections from the left, right median and anterior right lobes of the liver were processed for autoradiography and the labeling index of hepatocytes determined. A progressive increase in hepatocyte replication was induced by exposure to 40 and 100 ppm DEN. This was especially marked in the left lobe where 40 and 100 ppm DEN induced increases of 800 and 1500%, respectively, over controls after 10 weeks of exposure. Exposure to 4 and 10 ppm DEN resulted in a 300 to 400% increase in hepatocyte replication in all lobes, whereas 1 and 0.4 ppm DEN did not significantly increase cell proliferation compared to unexposed controls.

Formation of O6-methyldeoxyguanosine at specific sites in a synthetic oligonucleotide designed to resemble a known mutagenic hotspot

Four synthetic oligodeoxyribonucleotides of the sequence 5'-CCG1TG2G3G4ATATGGGCTG-3' were constructed with a 1',2'-[3H]deoxyguanosine located at one of the four sites indicated (1, 2, 3, or 4). This sequence was derived from a region of the Escherichia coli xanthine-guanine phosphoribosyltransferase gene where position 4 is a site frequently mutated by N-methyl-N'-nitrosourea as compared to sites 1-3. These four oligomers were alkylated in both single- and double-stranded form with N-methyl-N'-nitrosourea, and the relative amount of O6-methyldeoxyguanosine (O6-MedGuo) formed at each position was quantitated. Up to a 5-6-fold greater formation of O6-MedGuo was observed at positions 3 and 4 as compared to positions 1 and 2. This uneven distribution was only observed in oligomers in the double-stranded form, suggesting that secondary structure was an important determinant in generating the uneven distribution of O6-MedGuo. Comparisons between the extent of O6-MedGuo formation and mutation frequency at the four positions suggest that a difference in the formation of promutagenic adducts at specific sites is just one of the factors involved in the generation of mutagenic "hotspots." The novel method developed was applied to the study of formation of O6-MedGuo at specific sites; however, it should be suitable for studying the formation and repair of DNA adducts generated by a variety of chemicals in a wide variety of DNA sequences.

Hepatocyte initiation during continuous administration of diethylnitrosamine and 1,2-sym-dimethylhydrazine

Hepatocyte initiation, as indexed by growth-selected gamma-glutamyl transferase-positive foci, was measured during continuous exposure to diethylnitrosamine (DEN) at concentrations used in previous DEN bioassay, DNA adduct, and cell replication studies. Hepatocyte initiation increased in a dose- and lobe-specific manner. The efficiency of DEN as an initiating agent was not affected by DEN dose rate over concentrations ranging from 4 to 40 ppm. In a similar experiment the initiating abilities of 1,2-sym-dimethylhydrazine and DEN were compared under continuous exposure regimens. Foci induction increased in a lobe- and time-dependent manner. When left and median lobes were compared, the initiating ability of the two compounds correlated with their carcinogenicity. However, when corresponding anterior lobes were compared, no such correlation was observed.

High- to low-dose extrapolation: critical determinants involved in the dose response of carcinogenic substances

Recent investigations on mechanism of carcinogenesis have demonstrated important quantitative relationships between the induction of neoplasia, the molecular dose of promutagenic DNA adducts and their efficiency for causing base-pair mismatch, and the extent of cell proliferation in target organ. These factors are involved in the multistage process of carcinogenesis, including initiation, promotion, and progression. The molecular dose of DNA adducts can exhibit supralinear, linear, or sublinear relationships to external dose due to differences in absorption, biotransformation, and DNA repair at high versus low doses. In contrast, increased cell proliferation is a common phenomena that is associated with exposures to relatively high doses of toxic chemicals. As such, it enhances the carcinogenic response at high doses, but has little effect at low doses. Since data on cell proliferation can be obtained for any exposure scenario and molecular dosimetry studies are beginning to emerge on selected chemical carcinogens, methods are needed so that these critical factors can be utilized in extrapolation from high to low doses and across species. The use of such information may provide a scientific basis for quantitative risk assessment.

DNA base changes induced following in vivo exposure of unadapted, adapted or ada- Escherichia coli to N-methyl-N'-nitro-N-nitrosoguanidine

The adaptive response is one of the major repair pathways in Escherichia coli that removes DNA alkylation damage. To investigate the role of the adaptive response in mutagenesis, the E. coli gpt forward mutation assay system was used to determine the mutation spectrum of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in MNNG-adapted and unadapted GP120 (wild-type) and unadapted PJ5 (ada-5) cells. We observed that 34/37 mutations in the unadapted GP120 cells, 38/40 mutations in the adapted GP120 cells, and 10/10 mutations in the PJ5 cells were GC----AT transitions. The remaining 3/37 mutations in the unadapted GP120 cells were large insertions. The remaining 2/40 mutations in the adapted GP120 cells were transversions with one a GC----CG and the other an AT----CG. A surrounding sequence specificity of mutagenesis was observed for the GC----AT transitions in both the unadapted (GP120 and PJ5) and adapted (GP120) cells, with 70% of the unadapted PJ5, 68% of the unadapted GP120, and 61% of the adapted GP120 mutations occurring at the middle G of the sequence 5'--GG(A or T)--3'. Both strains also displayed a statistically significant preference for mutagenesis at guanine bases in the non-transcribed strand. The overall distribution of mutated sites in the gpt gene in adapted and unadapted cells was similar, although the rate of mutations at certain sites appeared different. These minor differences could result from either non-uniform repair of alkylation damage at different sites on the DNA, or altered processing of the alkylated bases to mutations in the adapted state.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular dosimetry of O4-ethyldeoxythymidine in rats continuously exposed to diethylnitrosamine

There is considerable interest in incorporating mechanistically based biological data into the process of quantitative risk assessment. Presently, no adequate data bases for internal dosimeters, such as DNA adducts, exist for humans or experimental animals. Therefore, the major promutagenic ethyl adduct, O4-ethyldeoxythymidine (O4-EtdT), has been quantitated in liver DNA after continuous exposure of rats to drinking water containing 0.4, 1, 4, 10, 40, or 100 ppm diethylnitrosamine (DEN) for 1, 4, 7, 14, 28, 49, or 70 days. The rate of O4-EtdT accumulation was modeled as the difference between a DEN-dependent rate of formation and an O4-EtdT concentration-dependent rate of loss. In general, O4-EtdT concentrations increased rapidly during the first 7 days of exposure and by 7-28 days O4-EtdT had accumulated to apparent steady-state concentrations that were DEN concentration-dependent over the entire dose range. The concentration of the adduct increased with DEN concentration over the entire dose range for exposures of 28 days or less and for doses of 0.4 to 40 ppm DEN the adduct level increased with DEN concentration for exposures of 70 days or less. Although the dose response of O4-EtdT was relatively linear, with increasing DEN concentration a trend toward a less than linear relationship was observed. This suggests that there was a lower efficiency of formation and/or greater loss of O4-EtdT during high-dose exposures. This study provides a data base that can be used to qualitatively and quantitatively examine the relationship between external dose and O4-EtdT over a DEN dose range covering several orders of magnitude.

DNA base changes and alkylation following in vivo exposure of Escherichia coli to N-methyl-N-nitrosourea or N-ethyl-N-nitrosourea

Dideoxy chain-termination DNA sequencing was used to determine the specific DNA base changes induced after in vivo exposure of Escherichia coli to N-methyl-N-nitrosourea (MNU) and N-ethyl-N-nitrosourea (ENU) using the xanthine guanine phosphoribosyltransferase (gpt) gene as the genetic target. The resultant mutation spectra were compared with the levels of O6-alkylguanine and O4-alkylthymidine in genomic DNA immediately after exposure. All (39/39) of the MNU-induced mutations were G X C----A X T transitions. In contrast, 24/33 point mutations isolated following ENU treatment were G X C----A X T transitions, 7/33 were A X T----G X C transitions, 1/33 was a G X C----C X G transversion, and 1/33 was an A X T----C X G transversion. Three large insertions, probably of spontaneous origin, were also isolated. O4-alkylthymidine/O6-alkylguanine ratios were 0.014 for MNU and 0.28 for ENU. These data suggest that the difference in the mutation spectrum of MNU versus ENU may be attributed, in part, to the different ratio of O6-alkylguanine versus O4-alkylthymidine produced in the DNA. Of the G X C----A X T transitions, 82% of the MNU- and 71% of the ENU-induced mutations occurred at the middle guanine of the sequence 5'-GG(A or T)-3'.

Accumulation and persistence of DNA adducts in respiratory tissue of rats following multiple administrations of the tobacco specific carcinogen 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone

4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major nitrosamine formed in tobacco smoke, induces a high incidence of lung, liver, and nasal cavity tumors in rats. Since alpha-hydroxylation of NNK by target tissues can lead to the generation of a methylating agent, the formation and removal of 7-methylguanine and the promutagenic lesions O6-methylguanine (O6mGua) and O4-methyldeoxythymidine were determined over 12 days of NNK administration to rats (100 mg/kg/day). DNA alkylation was greatest in the nasal mucosa, followed by liver and lung after 1 dose of NNK. No DNA adducts were detected in kidney and brain under these conditions. The concentration of O6mGua increased steadily in lung throughout the treatment regimen, while O6-methylguanine-DNA methyltransferase decreased to less than 5% of control. The concentration of O4-methyldeoxythymidine in lung DNA reached a steady state after 4 days of carcinogen treatment. After NNK treatment was discontinued, O6mGua persisted, while O4-methyldeoxythymidine was removed rapidly in the lung, suggesting that different repair pathways exist for the removal of these adducts in vivo. In hepatocytes, nonparenchymal cells, and nasal mucosa, O6mGua concentrations were maximal after 1-2 days and declined by 50-80% during the remaining 10 days of treatment. The decrease in O6mGua levels in nasal mucosa paralleled a decline in O6-methylguanine-DNA methyltransferase activity and was associated with marked cytotoxicity to Bowman's glands, portions of the lateral nasal gland, and the olfactory and respiratory mucosa during carcinogen treatment. In contrast, the decline in O6mGua in hepatocytes was attributed to the induction of O6-methylguanine-DNA methyltransferase activity, since an 18-fold reduction in the ratio of O6mGua:7-methylguanine was observed over the 12 days of treatment. These studies have demonstrated a marked accumulation of promutagenic DNA adducts in target tissues during repeated exposure to NNK.

Correlation of O4-ethyldeoxythymidine accumulation, hepatic initiation and hepatocellular carcinoma induction in rats continuously administered diethylnitrosamine

Recent experiments have demonstrated that O6-ethyldeoxyguanosine (O6-EtdG) is efficiently repaired while O4-ethyldeoxythymidine (O4-EtdT) accumulates in hepatocyte DNA of 8-week-old F-344 rats during continuous diethylnitrosamine (DEN) administration. To determine if O4-EtdT accumulation correlates with hepatic initiation, we have quantitated O4-EtdT concentrations, and the incidence of gamma-glutamyl transferase positive (GGT+) foci and hepatocellular carcinoma induced by increasing duration of exposure to DEN in the drinking water (40 p.p.m.). In 8-week-old F-344 rats the number of GGT+ foci increased non-linearly with duration of exposure and reached a maximum of approximately 500 foci/cm3 after 10 weeks. Administration of DEN to 8-week-old F-344 rats for 6 weeks followed by a 15-week administration of 0.05% phenobarbital (PB) in the diet did not result in the induction of hepatocellular carcinoma. Exposure of 4-week-old F-344 rats to DEN for up to 10 weeks produced an O4-EtdT steady-state concentration (approximately 7-10 X 10(-6) mol O4-EtdT/mol dT) similar to that previously observed after administration of DEN to 8-week-old F-344 rats. However, the maximal concentration of O4-EtdT was detectable after a shorter period of DEN administration in the younger rats. The incidence of GGT+ foci also increased more rapidly in 4-week-old rats, but again plateaued at approximately 500 foci/cm3 after 4, 6 or 8 weeks of DEN administration. A 100% incidence of hepatocellular carcinoma occurred in 4-week-old rats administered DEN for 6, 8 or 10 weeks, followed by promotion with 0.05% PB in the diet until week 22 of the study. Lower incidences of hepato-cellular carcinoma (89 and 6%) were observed following PB-promotion of rats administered DEN for 4 and 2 weeks, respectively. The influence of age on DEN-induced hepatic initiation was examined further by quantitating GGT+ foci induced by 4 weeks of DEN administration in groups of rats which were 4-14 weeks old at the start of the carcinogen exposure. The results demonstrated that the younger rats were 15-fold more susceptible than the older rats to the initiating effects of DEN. This growth-dependent effect on hepatic initiation in the presence of nearly equivalent amounts of pro-mutagenic DNA damage further implicates the necessity of replication for hepatic initiation.

Biochemical and morphologic studies of heterogeneous lobe responses in hepatocarcinogenesis

Experiments have demonstrated interlobe differences in the incidence of diethylnitrosamine (DEN)-induced hepatocellular carcinoma (HCCA), with a 100% incidence in the left and right median lobes and a 30% incidence in the right anterior lobe 20 weeks after exposure began. These tumor data provide a model to test the hypothesis that chemically induced neoplasia can be qualitatively and quantitatively related to promutagenic DNA damage and concurrent cell replication. Experiments were performed to measure O4-ethyldeoxythymidine (O4-EtdT) (a major pro-mutagenic lesion in hepatic DNA of rats exposed to DEN), N7-ethylguanine, cell replication and hepatocyte initiation using the induction of growth-selected gamma-glutamyl transferase-positive (GGT+) foci in the left and right median and right anterior hepatic lobes following 0, 3, 7, 14 or 28 days of DEN administration. Results demonstrated that O4-EtdT concentrations were consistently higher in the left and right median versus the right anterior hepatic lobes, while cell replication was transiently higher in the right median and right anterior lobes. Likewise, high numbers of GGT+ foci were observed in the left and right median lobes in DEN-exposed rats subjected to a Cayama-Farber growth selection protocol. Following administration of [14C]DEN, the distribution of radioactivity showed a marked left lobe preference in 4-week-old rats that had no prior exposure to DEN and in 8-week-old rats exposed to DEN for 4 weeks. This study suggests that interlobe differences in hepatocyte initiation and the incidence of HCCA may be due in part to differences in cell replication and in DNA alkylation resulting from differential DEN distribution and/or metabolism.

Relationships between DNA adduct formation and carcinogenesis

An impressive array of evidence has been obtained during the past decade establishing correlations between specific DNA adducts and carcinogenesis. Many of the studies utilized organ specific differences in carcinogenesis to establish the correlations. More recently, we have investigated similar relationships between target and nontarget cell populations within the liver. Chronic exposure to methylating hepatocarcinogens predominantly induces hemangiosarcomas, whereas exposure to ethylating agents causes hepatocellular carcinomas. This cell specificity in carcinogenesis correlates well with the presence of promutagenic DNA adducts. In the case of methylating agents, the nonparenchymal cells accumulate O6-methylguanine whereas the hepatocytes do not. Exposure to ethylating agents leads to accumulation of O4-ethyldeoxythymidine, but not O6-ethyldeoxyguanosine in hepatocytes. These differences reflect the ability of the two cell populations to repair O6-alkylguanine and the extent of purine and pyrimidine alkylation with methylating and ethylating agents. Hepatocytes of rats exposed to diethylnitrosamine for 28 days have four to five times more promutagenic DNA adducts (O6-alkyldeoxyguanosine and O4-alkyldeoxythymidine) than hepatocytes of rats exposed to nearly equimolar doses of dimethylhydrazine. Both O6-methylguanine and O4-methyldeoxythymidine are rapidly repaired by rat hepatocytes, while only O6-ethyldeoxyguanosine is rapidly repaired. Studies comparing the relationship between the induction of gamma-glutamyl transpeptidase-positive foci, hepatocellular carcinoma and promutagenic lesions such as O4-ethyldeoxythymidine will be useful in understanding associations between the molecular dosimetry of DNA adducts, initiation, and progression of hepatocarcinogenesis.

Differential repair of O4-alkylthymidine following exposure to methylating and ethylating hepatocarcinogens

Recent experiments have demonstrated that O6-alkylguanine is rapidly removed from hepatocyte DNA following continuous exposure to 1,2-dimethylhydrazine or diethylnitrosamine. In contrast, O4-ethyldeoxythymidine accumulates to concentrations more than 50 times greater than O6-ethyldexyguanosine. Studies on the formation and persistence of O4-methyldeoxythymidine in vivo have not been reported. This study reports the development of sensitive radioimmune assays to O4-methyldeoxythymidine and O4-ethyldeoxythymidine. Utilizing this method, the accumulation and removal of O4-methyldeoxythymidine and O4-ethyldeoxythymidine in liver DNA from rats exposed to 1,2-dimethylhydrazine or diethylnitrosamine were measured. The results demonstrated that O4-methyldeoxythymidine was formed at an O6-methylguanine/O4-methyldeoxythymidine ratio of approximately 100/1 and was repaired with a half-time of approximately 20 h. In contrast, O4-ethyldeoxythymidine removal was 13 times slower with a t 1/2 of approximately 11 days after both pulse dose and cessation of continuous DEN administration. Combined with previously reported data, results presented here suggest that (i) despite a lower rate of formation, O4-methyldeoxythymidine becomes nearly equal in importance to O6-methylguanine as a promutagenic adduct in hepatocytes from continuously exposed rats and (ii) differential repair of O4-alkylthymidine adducts provides a mechanism that may explain in part the superior ability of ethylating versus methylating agents to induce hepatocellular carcinomas in the rat.

Congruence of spouses' personal constructs and reported marital success: pitfalls in instrumentation

24 married couples completed a marital adjustment test and a measure of shared Personal Constructs. The number of shared Personal Constructs and marital adjustment test scores were not significantly related; nor was a significant relationship found between spouse's responses on the marital adjustment test. In addition, no significant differences were found between the number of shared Personal Constructs for these couples and couples with members assigned at random. Difficulties in instrumentation are discussed.