The modulation of astrocytic differentiation in cells derived from a medulloblastoma surgical specimen

Medulloblastomas are cerebellar tumors which are primarily composed of sheets of uniform, small malignant cells and may have astrocytic, neuronal or no features typical of these cell types. The assessment of astrocytic differentiation in medulloblastoma rests largely on the detection in malignant cells of glial fibrillary acidic protein (GFAP), a marker present in the later stages of normal astrocyte differentiation. It is still not known whether cells that do not contain GFAP in medulloblastomas with astrocytic differentiation correspond to highly proliferative astrocyte progenitors in maturation arrest at earlier stages of differentiation. The purpose of the current study was to examine whether cells in short term culture derived from a medulloblastoma tumor specimen with astrocytic differentiation were of the astrocytic lineage and if so, whether they represented proliferative astrocyte progenitors which would morphologically and antigenically mature in response to differentiating agents. A portion of tumor specimen from a 10-month-old child with recurrent posterior fossa medulloblastoma (RB2) that contained GFAP focally in tumor cells was grown in monolayer culture. We examined cellular structure and appearance of western immunoblotting and immunohistochemical studies for GFAP and neuron-specific enolase (NSE) in RB2 cells before and after treatment with retinoic acid (RA) and dibutyryl cyclic AMP (dBcAMP). RB2 in culture consisted of small polygonal cells (93%), large flat cells (3%), and polygonal cells with cytoplasmic processes (4%). In untreated RB2, 30% of cells expressed GFAP and staining for NSE was negative. RA treatment produced flattened cells and decreased GFAP. DBcAMP reversibly induced fine cytoplasmic processes containing GFAP in 85% of cells within 96 h. Neither agent induced NSE. The results suggest that cultured cells which are derived from a medulloblastoma with astrocytic differentiation do not spontaneously differentiate but that treatment with dBcAMP suppresses proliferation, enhances cytoplasmic process formation and increases cytoplasmic GFAP. Cells in culture and in medulloblastoma tumor specimens which do not contain GFAP may represent astrocyte progenitors in maturation arrest.

[The removability of pesticides during the production of dialysis water (2)]

In many cases it can be demonstrated that the amount of plant protectives and plant treatments (pesticides) in drinking-water exceeds the permitted levels of the drinking-water decree which will be effective on October 1st, 1989. These components are in parts toxicologically important. Therefore, an examination was made on how far pesticides are removed during the conventional purification of dialysis water, but especially during the reverse osmosis. Retention rates of a reverse osmosis plant for 14 different pesticides were discovered which were used in different concentrations and compositions. In part 2 of this contribution the results of the investigation are presented. The figures demonstrate that almost all of the examined components were retained with an effectiveness of 92-98%. The elimination efficiency did not depend on the basic concentration of the pesticides. After an initial phase of 50 h duration, the permeat concentration reached a constant value which did not alter even after more than 700 h.

In vitro DNA cytosine methylation of cis-regulatory elements modulates c-Ha-ras promoter activity in vivo

The effect of DNA cytosine methylation on promoter activity was assessed using a transient expression system employing pHrasCAT. This 551 bp Ha-ras-1 gene promoter region is enriched with 84 CpG dinucleotides, six functional GC boxes, and is prototypic of many genes possessing CpG islands in their promoter regions. Bacterial modification enzymes HhaI methyl transferase (MTase) and HpaII MTase, alone or in combination with a human placental DNA methyltransferase (HP MTase) that methylates CpG sites in a generalized manner, including asymmetric elements such as GC box CpG's, were used to methylate at different types of sites in the promoter. Methylation of HhaI and HpaII sites reduced CAT expression by approximately 70%-80%, whereas methylation at generalized CpG sites with HP MTase inactivated the promoter by greater than 95%. The inhibition of H-ras promoter activity was not attributable to methylation-induced differences in DNA uptake or stability in the cell, topological form of the plasmid, or methylation effects in non-promoter regions.

[Ability to remove pesticides in the production of dialysis water (1)]

In many cases it can be demonstrated that the amount of plant protective and plant treatment substances (pesticides) in drinking water exceeds the permitted levels of the drinking water ordinance which will come into effect on October 1st, 1989. Since some of these components are of toxicological relevance, an investigation was done on how far pesticides are removed during conventional purification of dialysis water, and especially during reverse osmosis. The retention rates of a reverse osmosis plant for 14 different pesticides applied in different concentrations and compositions were determined. Almost all of the substances examined were retained with an effectiveness of 92-98%. The elimination efficiency did not depend on the initial concentration of the pesticides. After an initial phase of 50 h duration, the concentration in the treated water reached a constant value which no longer changed even after more than 700 h. In part 1 of this contribution at first the fundamentals of dyalisis water purification are reviewed and a selection of the pesticides to be investigated is carried out. In addition experimental set up and procedure are described.

Altered expression of acute-phase reactants in mouse liver tumors

We studied the expression of eight liver acute-phase genes in spontaneous and diethylnitrosamine-induced mouse liver tumors (MLTs) under basal and induced conditions. Primary spontaneous and chemically induced MLTs were used for RNA isolation and histopathologic analysis. In the noninduced state, all MLTs showed similar levels of mRNA for albumin, serum amyloid A, alpha 1-acid glycoprotein, haptoglobin, and alpha-, beta-, and gamma-fibrinogens compared with control or background livers. The mRNA for the alpha 1-major acute-phase protein, however, was consistently elevated in both spontaneous and diethylnitrosamine-induced MLTs. The expression of these acute-phase reactants in 11 MLTs was examined following exposure of the mice to turpentine. The relative expression of these mRNAs in these MLTs varied widely compared with mRNA expression in controls. Though all MLTs expressed the same three species of fibrinogen mRNAs as did the controls, no MLT demonstrated downregulation of albumin mRNA levels, and only 1 of 11 MLTs showed a marginal increase in serum amyloid A mRNA levels. Synthesis of mRNA for alpha 1-acid glycoprotein and haptoglobin was intermediate. The study of the response of MLTs to specific acute-phase stimuli may make possible a better understanding of the basis for coordinated expression of acute-phase reactants and of the variable phenotypes associated with cancers.

Defective DNA ligase I in Bloom's syndrome cells. Simultaneous analysis using immunoblotting and the ligase-[32P]AMP adduct assay

Cells from patients with Bloom's syndrome (BS), an autosomal recessive disorder associated with an increased risk of cancer, exhibit genomic instability. Increased numbers of sister-chromatid exchanges (SCE) and delayed DNA chain maturation are typically observed in BS cells. To elucidate the basis for the previously reported decreased DNA ligase I activity in BS cells, simultaneous immunoblot and activity assays for ligase-[32P]AMP adduct formation were performed on extracts from BS and normal lymphoblastoid cell lines. Immunoblot analysis using antibody to DNA ligase I indicate that the amount of the major reactive protein (98 kDa) in normal and BS cells is similar. However, a 50-90% decrease was observed in the ligase activity of the 98-kDa polypeptide in high-SCE BS cells (HG1514 and GM3403c). In contrast, the activity in low-SCE BS cells (HG1554) did not differ significantly from that in normal cells. The data, together with mixing experiments, indicate that the defect in BS ligase I is due at least in part to the loss of ATP binding and/or hydrolytic activity and not to differences in numbers of protein molecules or inhibitory substances. These results suggest that mutation of the DNA ligase I gene may account for the primary metabolic defect in BS.

Analysis of DNA adducts in putative premalignant hepatic nodules and nontarget tissues of rats during 2-acetylaminofluorene carcinogenesis

Exposure of rats to a standard four-cycle feeding regimen of 0.06% 2-acetylaminofluorene (AAF) results in the formation of putatively premalignant hepatic nodules, but the types and magnitude of DNA adducts formed in these nodules has not been previously examined. By using a sensitive 32P-adduct assay (R. C. Gupta, Cancer Res., 45: 5656-5662, 1985), we analyzed the DNA adduct lesions in individual hepatic nodules at various times during and after exposure to AAF. Kidney, spleen, and testis were included as nontarget tissues. No qualitative difference was observed in the DNA adducts found in hepatic nodules and nontarget tissues; however, quantitative differences occurred. At least one unknown and two known (dG-C8-AF and dG-N2-AAF) DNA adducts were detected, with dG-C8-AF being predominantly (96-98%) formed, in all tissues examined. At the end of the first three weeks of AAF feeding, the concentration of the deacetylated adduct dG-C8-AF in liver (223 fmol/micrograms DNA) was found to be about 2, 6, and 5 times higher than in kidney, spleen, and testis, respectively. The concentration of the N2-acetylated adduct in liver (4.5 fmol/micrograms DNA) was 4-fold higher than in kidney and strikingly higher (51- and 42-fold, respectively) than in spleen and testis. At the end of the fourth feeding cycle, total DNA adducts measured in the hepatic nodules ranged from 30-100 fmol/micrograms DNA, while the "surrounding liver," kidney, spleen, and testis showed 235, 218, 62, and 28 fmol adducts/micrograms DNA, respectively. Sixty days following the cessation of AAF, the binding in both the persistent nodules and liver had decreased to 7% of their respective levels measured at the end of the fourth cycle, while adducts in kidney, spleen, and testis were 32%, 18% and 19%. After 88 days, the binding levels in the nontarget tissues declined further, but no additional adduct removal occurred in the nodules. Our data indicate that (a) although the metabolic apparatus for activation of AAF is diminished in the hepatic nodules, a significant level of adduct formation occurs in the cells of this putative, premalignant lesion, and (b) unlike in the nontarget tissues, repair processes in the premalignant nodules may not be operative several weeks after the cessation of AAF exposure.

Failure of the viable yellow (Avy) and lethal yellow (Ay) genes to enhance chemical induction of thymic lymphomas

Two dominant mutations in the agouti locus of the mouse, viable yellow, Avy, and lethal yellow, Ay, are associated with increased susceptibility to spontaneous as well as virally or chemically induced tumors. Regardless of the mechanism of initiation, this effect is dependent upon the presence of initiated cells. Although complex, the numerous physiologic alterations associated with these mutations offer an interesting model for the study of endogenous promotion. To date, it has been reported that these genes enhance the growth and early appearance of tumors in all organ sites wherein initiated cells exist, suggesting that the system was pan-promoting. In our current study, however, neither Avy nor Ay enhanced the appearance of chemically induced thymic lymphomas in two mouse strains of differing susceptibility. Thus, the concept of a pan-promoting effect is not valid. However, the presence of Ay did enhance the appearance of chemically induced hepatocellular tumors as has been reported previously for Avy. This striking difference of thymomas from other carcinogenic sequences may make possible a better understanding of the nature of susceptibility to endogenous promoting factors.

UV-induced photoproducts of 5-methylcytosine in a DNA sequence context

In order to detect possible m5C photoproducts, highly purified rat liver DNA-cytosine methyltransferase was used to specifically generate m5C with a radioactive methyl group. When these DNAs were subjected to a large dose (10 kJ/m2) of 254 nm or 302 nm ultraviolet light (UVB) to enhance the yield, two labeled photoproducts were detected and isolated by reverse phase HPLC after formic acid hydrolysis. Further studies using acetone as a triplet state sensitizer and UVB irradiation suggested that photoproduct II was activated via a triplet state while the more polar photoproduct I was not. Photoreversion of the purified photoproducts with 10 kJ/m2 254 nm light demonstrated the following reactions: Photoproduct I regenerated m5C, while photoproduct II is split and regenerated m5C and photoproduct I. These results suggest that photoproduct I is monomeric while photoproduct II dimeric, and from the latter's elution position possibly a cyclobutyl type dimer arising from a reaction with an adjacent cytosine. Using d[TTG] and d[Cm5CG] as models of typical sequences, irradiation with 10 kJ/m2 254 nm or 302 nm, respectively, gave rise to a small component having altered mobility in sequencing gels. The altered mobility trinucleotides were resistant to degradation by PI and micrococcal nucleases as expected from photodimerization of the pyrimidine bases. Furthermore, oligonucleotide substrates containing m5C were synthesized and shown to be susceptible to T4 endonuclease v action at locations consistent with d[Cm5C] photodimer formation when irradiated in the UVB range.

Potassium inhibition of transforming protein P85gag-mos and reversal of the transformed phenotype in 6m2 cells

K+ at high concentrations (52-72 mM hypertonic KCl) has been reported to induce reverse transformation in the 6m2 cell, which is a clone of normal rat kidney cells (NRK) infected with a temperature-sensitive transformation virus. When exposed to high K+, 6m2 cells grown at the permissive temperature (33 degrees C) exhibit normal morphology and reduced soft agar growth, characteristics of cells grown at nonpermissive temperature (39 degrees C). In the current study, flattening of cells and rearrangement of surface microvilli were demonstrated by scanning electron microscopy to occur within 6 hr of exposure to high K+, similar to the effect of temperature shift to 39 degrees C. Exposure to K+ resulted in a 90% inhibition of P85gag-mos-associated serine kinase activity within 5 min, with a subsequent reduction of up to 75% of the synthesis of this protein. These alterations in the putative transforming protein were similar to those induced by temperature shift and were considered to be the basis for retrotransformation. The cell microtubular system and F-actin cables were affected more slowly by K+ than by a temperature shift to 39 degrees C. The former did not achieve the fine reticulum network seen in NRK cells until 72 hr later, but the latter remained aberrant. The effect on the enzyme might be mediated by alteration in phosphorylation, but the mechanism by which kinase inactivation induces retrotransformation is not yet known.

The effects of tin-protoporphyrin administration on hepatic xenobiotic metabolizing enzymes in the juvenile rat

The heme analogue tin-protoporphyrin IX (SnP) is a potent inhibitor of microsomal heme oxygenase. Administration of SnP to neonatal rats can prevent hyperbilirubinemia by blocking the postnatal increase of heme oxygenase activity. Apparently innocuous at therapeutic doses, it is of potential clinical value for chemoprevention of neonatal jaundice. We found that when 50-g male Sprague-Dawley rats were treated daily with 50 mumol of SnP/kg sc for 6 days, hepatic microsomal cytochromes b5 and P-450 were significantly diminished. Cytochrome P-450 reductase, two P-450-dependent monooxygenases, aminopyrine demethylase and benzo(a)pyrene hydroxylase, and catalase, a peroxisomal hemoprotein, were also significantly diminished. These results suggested that SnP might significantly affect the metabolism of other xenobiotics. This possibility was confirmed by the finding that hexobarbital-induced sleep lasted 4 times longer in SnP-treated rats than in controls. Inhibition of protein synthesis by SnP was ruled out as the cause of hemoprotein loss when administration of [3H]leucine to SnP-treated and control rats demonstrated that proteins of the microsomal, cytosolic, and plasma membrane fractions of the livers from both groups incorporated similar levels of leucine. When 55FeCl3 and [2-14C]glycine were administered to measure heme synthesis, heme extract from the livers of SnP-treated rats contained 4 times more label from iron and glycine than did heme from control livers. Despite the apparent increased rate of heme synthesis in SnP-treated rats, each of the three cell fractions demonstrated a significant loss of heme but contained sizable amounts of SnP. These findings suggest that SnP causes a decrease of functional hemoprotein and partial loss of enzymic activity by displacing intracellular heme.

Changes in cell surface charge and transmembrane potential accompanying neoplastic transformation of rat kidney cells

Free flow electrophoresis measurements have been used to determine the surface charge density of normal rat kidney (NRK) cells and a clone of NRK, designated as 6m2, that exhibit a transformed phenotype at 33 degrees C and a non-transformed phenotype at 39 degrees C. A clone of 6m2, designated 54-5A4, which is transformed at both 33 degrees C and 39 degrees C was also studied. A surface charge density of -1.42 microC/cm2 was obtained for the NRK and non-transformed 6m2 cells at 39 degrees C, whereas at 33 degrees C values of -1.85 and -1.78 microC/cm2 were determined for the transformed 6m2 and 54-5A4 cells, respectively. It was found that 72% of the increased charge that appeared on the transformed 6m2 cells compared with the non-transformed 6m2 cells was RNAase sensitive. The time-dependent decrease in surface charge that accompanied the shift of the 6m2 cells from their transformed to non-transformed state was found to mirror the increase in transmembrane potential previously reported using a fluorescent dye technique, and was also comparable to the reported temporal changes in their morphology and virally-coded protein content.

Heme enzyme patterns in rat liver nodules and tumors

Chemically induced rat hepatocyte nodules and carcinomas have a reduced capacity to oxidize drugs. The reduction in monoxygenase activity results largely from the partial loss of cytochrome P-450, a heme-containing terminal electron acceptor. To determine whether the cytochrome P-450 deficit was indicative of an altered heme metabolism, we quantitated four heme-containing proteins in normal rat liver and in rat liver nodules and cancers induced by 2-acetylaminofluorene or diethyl-nitrosamine: cytochrome P-450; cytochrome bs; catalase (EC 1.11.1.6); and tryptophan 2,3-dioxygenase (EC 1.13.11.11). The amounts of these components in nodules were 45%, 88%, 50%, and 59% of normal liver, respectively; in 2-acetylaminofluorene-induced cancers, 65%, 74%, 64%, and 65%, respectively; and in diethylnitrosamine-induced cancers, 40%, 69%, 56%, and 52%. delta-Aminolevulinic acid synthase (EC 2.3.1.37), the rate-limiting enzyme in the heme synthetic pathway, and heme oxygenase (EC 1.14.99.3), a degradative enzyme, were also quantitated. The amounts of these enzymes in nodules were 95% and 138% of normal liver, respectively, whereas in 2-acetylaminofluorene-induced cancers, they were 47% and 233%, and in diethylnitrosamine-induced cancers, they were 50% and 175%. These data indicate that four nonmitochondrial liver hemoproteins were diminished to about the same extent in hepatic nodules and cancers. Nodules and cancers also demonstrated an increased capacity for heme degradation, while cancers also demonstrated a decreased capacity for heme synthesis. Thus, the resistance of nodules and tumors to P-450-activated cytotoxic agents may ultimately result from a disturbance in heme metabolism.

Altered DNA ligase I activity in Bloom's syndrome cells

Cells from patients with Bloom's syndrome, a rare disease associated with increased cancer frequency, exhibit cytological abnormalities. These include increased numbers of homologous chromatid interchange figures and sister-chromatid exchanges, together with abnormally slow replicon-fork progression and retarded rate of DNA-chain maturation, and suggest that the primary defect in this recessive disorder affects S-phase DNA replication. DNA ligases and DNA polymerases have long been prime candidates for abnormality in Bloom's syndrome, but various studies of DNA polymerases in Bloom's syndrome cells have disclosed no abnormalities. Evidence is presented here, as in the accompanying paper from a different laboratory, for the existence in Bloom's syndrome of an abnormality of the DNA ligase involved in semi-conservative DNA replication.

Protective role of thiols in carcinogen-induced DNA damage in rat liver

Biological thiols are known to play an important role in the detoxification of xenobiotics, including chemical carcinogens. To determine the influence of cellular thiols on carcinogen induction of hepatic DNA damage in the rat, diethylmaleate (DEM) administration was used to deplete intracellular glutathione (GSH). The effects of administration of the synthetic thiols, N-acetylcysteine (NAC) and alpha-mercaptopropionylglycine (alpha MPG), on the induction of DNA lesions were also examined. Pretreatment with DEM reduced liver GSH levels by greater than 70%. As assessed by the technique of alkaline elution, subsequent administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) resulted in DNA damage 4 h post MNNG treatment which was 4- to 8-fold greater than that induced in the livers of rats treated with MNNG alone. However, DEM pretreatment had little effect on the extent of DNA damage induced by methylnitrosourea (MNU). DEM alone did not cause any measurable DNA damage. Pretreatment with alpha MPG or NAC reduced MNNG-induced DNA damage by as much as 77%. In contrast, MNU-induced DNA damage was increased by alpha MPG treatment whereas NAC treatment was without effect. These results indicated that in the rat liver, the activity of some DNA alkylating agents may be modulated in varying degree by the concentration of intracellular thiols. These data support the notion that thiols play an important role in protection against carcinogen damage, and that synthetic thiols such as alpha MPG and NAC may be useful as anti-carcinogenic agents against certain carcinogens.

Xenobiotic metabolizing enzymes in genetically and chemically initiated mouse liver tumors

Chemically induced rat liver nodules and cancers characteristically demonstrate a limited capacity to activate xenobiotics to reactive species mainly because of decreased amounts of cytochrome P-450. These lesions also show enhancement of xenobiotic detoxication by such mechanisms as enzymic conjugation or reduction of cytotoxic species. We recently demonstrated a similar pattern of metabolic alteration in spontaneous mouse liver tumors. These findings suggested that certain phenotypic alterations attributed to chronic chemical exposure are inherent in the genetic program for carcinogenesis, and that they may arise independently of chronic exposure. To extend that study, we examined spontaneous and diethylnitrosamine-induced mouse liver tumors for nine enzyme activities commonly reported to be altered in chemically induced rat liver nodules and cancers. The activities of benzo(a)pyrene monooxygenase (EC 1.14.14.1), aminopyrene demethylase, cytochrome P-450 reductase, epoxide hydrolase (EC 3.3.2.3), and UDPglucuronosyl transferase (EC 2.4.1.17) in microsomes from spontaneous tumors relative to those from normal liver were 0.25, 0.43, 1.27, 0.90, and 0.51, respectively. Similar values were obtained with microsomes from chemically induced tumors. The activities of DT-diaphorase (EC 1.6.99.2), glutathione reductase (EC 1.6.4.2), glutathione S-transferase (EC 2.5.1.18), and glutathione peroxidase (EC 1.11.1.9) in cytosol from spontaneous tumors relative to cytosol from normal liver were 2.24, 2.0, 2.43, and 0.31, respectively. Similar values were obtained with cytosol from chemically induced tumors. These results demonstrated that a significant portion of the enzymic phenotype observed in chemically induced rat liver nodules and cancers, which may confer resistance to cytotoxic chemicals, is manifest in spontaneous and chemically induced mouse liver tumors. Further, initiated cells that exhibit this phenotype replicated and progressed in the absence of continued chemical selection.

Heme enzyme patterns in genetically and chemically induced mouse liver tumors

Chemically induced rat hepatocyte nodules and hepatomas have repeatedly been shown to be deficient in Phase I drug-metabolizing enzymes. Some of these reduced activities are attributable to a diminution of the heme-containing terminal electron acceptor, cytochrome P-450. We recently demonstrated that spontaneous mouse liver tumors exhibit the same deficiency. Therefore, chemically induced and spontaneous liver tumors share common metabolic alterations which are likely to represent intrinsic characteristics of the tumorigenic process and are independent of its etiology. To determine whether the cytochrome P-450 deficit was the result of an altered heme metabolism, we quantitated four heme-containing proteins in normal mouse liver, spontaneous mouse liver tumors, and those induced by a single injection of diethylnitrosamine: cytochrome P-450; cytochrome b5; tryptophan 2,3-dioxygenase (EC 1.13.11.11); and catalase (EC 1.11.1.6). The amounts of these components in spontaneous tumors relative to normal liver were 0.35, 0.68, 0.76, and 0.51, respectively. Similar values were obtained with chemically induced tumors. The enzymes delta-aminolevulinic acid synthase (EC 2.3.1.37), the rate-limiting enzyme in the heme synthetic pathway, and heme oxygenase (EC 1.14.99.3), a degradative enzyme, were also quantitated. The amounts of these enzymes in spontaneous tumor relative to liver were 0.49 and 1.51, respectively. Again, similar values were observed for the chemically induced tumors. Alteration of the latter two enzyme activities may be sufficient for the altered hemoprotein patterns seen in mouse liver tumors. Further, this pattern of metabolic alteration is common to both chemically induced and spontaneous tumors. Thus, tumor resistance to cytotoxic agents activated by the monooxygenase system is not necessarily induced by exposure to these agents, nor as a result of selection.

Progression of tumor histiotype during mouse hepatocarcinogenesis associated with the viable yellow (Avy) gene

Increasing attention has been focused recently upon those factors in carcinogenesis that are responsible for the proliferation of initiated cells and the increasingly aberrant phenotype that they progressively manifest. The agouti locus allele Avy (viable yellow) has been shown to be associated with conditions which favor promotion of cells that have been initiated by a wide variety of causes, in many organs, but has not been previously associated with tumor progression in those systems. In the current study, the presence of the Avy gene in a strain of mice not normally predisposed to hepatocarcinogenesis, C57BL/6N was, for the first time, associated not only with much earlier appearance, but with progression of the histiotype of hepatic tumors, following neonatal administration of diethylnitrosamine. At 52 weeks, 28 C57BL/6N mice demonstrated 7 mouse liver tumors 0.5 cm or greater in diameter, all of more benign histiotype, without associated metastasis. The 31 C57BL/6N-Avy demonstrated 194 mouse liver tumors at that time, 22% of which were of malignant histiotype, 19% of which were associated with metastasis. This system would appear to offer the possibility of identifying the underlying mechanisms for components of the carcinogenic process. In addition, the C57BL/6N-Avy mouse appears to offer advantages as a test animal in bioassay procedures that use the liver as a target organ. Thus, it represents a mouse with little or no spontaneous predisposition to hepatocarcinogenesis, with a predicted short lag period toward response to hepatocarcinogens.

Potassium-induced reverse transformation of cells infected with a temperature-sensitive transformation mutant virus

High potassium concentrations altered the morphology and the ability to grow in soft agar in 6m2 cells, a clone of rat kidney cells infected with a temperature-sensitive mutant of Moloney sarcoma virus. Approximately 60% of cells exhibited normal morphology in the presence of 94.8 mM potassium in isotonic medium at the temperature permissive for transformation, whereas 100% were normal at 72 mM potassium in hypertonic media. A significant reduction of growth in soft agar was also induced with these conditions. However, the synthesis ratio of virus-specified transforming protein to marker viral protein was not altered. Na+K+-ATPase might play a role in this reverse-transformation process.

DNA ligase activities during hepatocarcinogenesis induced by N-2-acetylaminofluorene

A progressive accumulation of DNA breaks has been reported to occur in nuclear DNA obtained from putative premalignant hepatic lesions induced by carcinogens. To determine if this alteration resulted from a defect in the level of, or functional activity of DNA ligases, we compared these enzymes in normal rat liver, 24-h regenerating liver, and hepatic nodules at intervals after cessation of N-2-acetylaminofluorene (AAF) treatment. Nuclear extracts of hepatocytes were separated into soluble and chromatin fractions, and multiple forms of DNA ligase activity were obtained by AcA34 gel filtration chromatography. In activities of the two largest species, DNA ligase Ia (480 kd) and DNA ligase Ib (240 kd), were present exclusively in soluble, nuclear fractions and were increased 4-fold and 2-fold, respectively, in 24-h regenerating livers. In AAF-induced nodules, these species were increased 3-fold and 1.5-fold, respectively, above those of normal rat liver, somewhat higher than predicted from the rate of cell division. In all of the test tissues, these ligase species demonstrated identical sensitivity to inhibition with 0.1 M NaCl or heating at 50 degrees C. DNA ligase II (80 kd) was found in both soluble nuclear fractions and chromatin at approximately identical levels in all tissues tested. Ligase II from all tissues also demonstrated identical responses to salt and heat. These data support the concept that DNA ligases Ia and Ib are related to DNA replication and suggest that ligase II may be a repair enzyme. The failure to detect significant alterations from expected values in the hepatic nodules and the lack of alteration in sensitivity to salt and heat indicate that the accumulation of DNA damage (presumably breaks) previously observed in carcinogen-induced altered hepatocytes is not due to an alteration in the level or the biochemical properties of DNA ligase.

Perturbation of maintenance and de novo DNA methylation in vitro by UVB (280-340 nm)-induced pyrimidine photodimers

The effect of pyrimidine photodimers on transmethylation reactions catalyzed by a highly purified rat liver DNA (cytosine-5-)-methyltransferase (EC 2.1.1.37) that exhibits maintenance and de novo methylation activities was studied in vitro, using the viral substrates M13 mp9 replicative form (RF) DNA and the hemimethylated analog formed from primed synthesis of phage DNA in the presence of 2'-deoxy-5-methylcytidine 5'-triphosphate. These DNAs were irradiated with UVB (280-340 nm) at 900-3600 J/m2 in the presence of the triplet-state sensitizers acetone or 3-dimethylaminopropiophenone. Under these conditions of irradiation, which approximate solar UV, pyrimidine cyclobutane photodimers were introduced without producing any evidence of single-strand breaks or alkali-sensitive sites [i.e., no (6-4)pyrimidine-pyrimidone photoproducts]. This was confirmed by gel analysis, a T4 UV endonuclease nicking assay specific for cyclobutane-type dimers, and HPLC analysis of the photoproducts. The methylation of irradiated templates by DNA methyltransferase was inhibited in an approximately linear fashion as a function of increasing UVB dose. This inhibition was correlated with the number of lethal photoproducts detected by the simultaneous measurement of the surviving fraction of infectious phage DNA. For approximately the same number of pyrimidine cyclobutane photoproducts introduced, de novo methylation activity was approximately 2-fold more sensitive than the maintenance mode of methylation. The ability of these putatively carcinogenic, pyrimidine photoproducts to inhibit DNA methylation suggests a common mechanism of action with several chemical carcinogens that are known to modify bases.

Proviral structure and differentiation antigen phenotype of spontaneous and chemically induced AKR lymphomas

AKR mice develop spontaneous thymomas after 6 months of age due to a novel class of murine leukemia viruses that are generated by a series of genetic recombinations between endogenous proviral loci. AKR mice also are more susceptible to N-methyl-N-nitrosourea (MNU)-induced thymomas than are low-leukemia-incidence mouse strains. To determine whether virally and chemically induced lymphomagenesis proceeds by similar pathways in AKR mice, spontaneous and MNU-induced thymic lymphomas were analyzed for a DNA restriction linkage generated during spontaneous tumor development by recombination between envelope genes of endogenous murine leukemia proviral loci. DNA from spontaneous thymic lymphomas invariably contained a restriction fragment characteristic of recombinant murine leukemia virus etiology, while four of five MNU-induced thymic lymphomas did not show this restriction linkage. In addition, analysis of lymphocyte differentiation antigen profiles indicated that MNU-induced lymphomas represent a more immature stage of T-cell differentiation than the majority of spontaneous lymphomas. These data suggest that there are fundamental differences in the mechanisms of induction of virally and chemically induced thymic lymphomas in AKR mice.

Indistinguishable physical and catalytic properties of DNA methyltransferase from normal rat liver and a transplantable rat hepatocellular carcinoma

DNA methyltransferase (DMase) was purified 700- and 1002-fold from normal rat liver and transplantable hepatocellular carcinoma 252 (THC 252) nuclei, respectively, using a four-step procedure that included chromatography on phosphocellulose, hydroxylapatite, DEAE-Sephacel and gel filtration on AcA 34. The enzymes had identical characteristics: pI = 7.4-7.6; Mr = 280 000 by gel filtration; preference for methylating double-stranded over single-stranded DNA and hemimethylated over unmethylated DNA templates; and apparent km of 10 microM for dinucleotide units in poly(dC-dG) and 0.5 microM for S-adenosylmethionine (SAM). Thermal inactivation profiles and sulfhydryl group alkylation inhibition curves for fraction III produced very similar single-transition curves, suggesting the presence of a single-functional enzyme species that is indistinguishable between normal and tumor tissue. Single-value Michaelis-Menten kinetics were obtained for fraction IV enzymes with respect to the concentration of SAM and dinucleotide units in poly(dC-dG), suggesting the absence of isozymic or multiple forms of DMase in normal and malignant liver tissues.

Alterations in nonhistone chromatin proteins during hepatocarcinogenesis induced by diverse acting carcinogens

Nonhistone chromosomal proteins (NHCP) from normal, regenerating rat liver, fetal liver, stages during acetylaminofluorene (AAF) and diethylnitrosamine (DEN) induced carcinogenesis, and resultant primary hepatocellular carcinomas (PHC) were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). These studies sought to determine if changes in proteins putatively involved in catalyzing specific gene expression (NHCP) occur during liver cancer development that might be related to the malignant phenotype. NHCP extracted in high salt-urea buffers, analyzed by 2D-PAGE and silver staining were resolved into some 530-560 polypeptides. Increases in number of NHCP amounting to 8.4, 8.6 and 8.8%, respectively, were detected in AAF induced nodules (AAF-NOD), AAF-PHCs and DEN-PHCs when compared to normal chromatins. The majority of the 51 qualitative changes detected reflected cell cycling and/or reexpression of fetal-NHCP. Within the total changes, seven new NHCP were found only in AAF- and DEN-induced PHCs. Further, four NHCP with isoelectric points and relative molecular weights (pI/MW) of 5.62/19.3, 5.96/30.7, 6.25/46.6 and 8.16/53.5 occurring in both AAF- and DEN-PHC also were found in AAF-NOD, a carcinogenesis stage considered to represent premalignant nodules. Reciprocally, three NHCP of pI/mol.wt.: 6.81/34.0, 5.82/43.7 and 8.18/67.0 present in normal liver, disappeared in all carcinogen involved tissues analyzed. These findings indicate that while AAF and DEN exposure results in a number of qualitative NHCP changes specific for the particular carcinogen, a total of only ten changes, seven inductions and three losses, occurred in common during hepatocarcinogenesis induced by these diverse agents. At least four of these NHCP may prove critical inductions during malignant conversion or alternatively might serve as tumor markers since they appear first in a well characterized premalignant stage and persist in resultant tumors.

Tumor phenotype and susceptibility to progression as an expression of subpopulations of initiated murine cells

Currently, it is conceived that a number of events, or hits, are required for the induction of tumors by chemical agents. The first phase of this sequence, initiation, is considered to result from at least one event in the genetic apparatus. Analyses of this sequence, however, usually give little consideration to the nature of the target cell or to the characteristics of the resultant tumors. Vesselinovitch et al. (Cancer Res., 38: 2003-2010, 1978) have reported that a single, small pulse of carcinogen can induce early and numerous liver tumors when administered neonatally to mice with a genetic predisposition to hepatotumorigenesis. In the current study, the nonpredisposed strain C57BL/6N was also shown to be highly susceptible to diethylnitrosamine during the neonatal period. C57BL/6N demonstrated large numbers of two of the three types of liver tumors seen in livers of genetically predisposed mice, one of which required the additional stimulus of dietary phenobarbital for growth. Tumors of more malignant phenotype were demonstrated only in genetically predisposed mice (C57BL/6N X C3H/HeN F1) that received one dose of carcinogen. These findings suggest that the phenotype of a tumor that results from a pulse of a chemical carcinogen may depend upon the target cell. The initiated cells that result from this hit may vary from those that demonstrate very little progression in cell type and may or may not require exogenous enhancement of growth to those that can progress very rapidly to fully malignant behavior. The latter might arise from a hit in a genetically initiated cell, the result of which is a more rapid progression in tumor type.

Mechanism of rat liver DNA methyltransferase interaction with anti-benzo[a]pyrenediol epoxide modified DNA templates

We investigated the methylation reaction catalyzed by 1500-fold purified rat liver DNA methyltransferase (DMase) on native Micrococcal luteus DNA (ML-DNA) and poly(dC-dG) templates containing covalently bound (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), the strongly carcinogenic, principal metabolite of benzo[a]pyrene. Since eukaryotic DNA methyltransferases recognize the dinucleotide 5'd[CG] in DNA as a substrate for methylation, the model polynucleotide poly(dC-dG) was used to study in more detail the mode of interaction and effect on incorporation. With either of these BPDE-modified templates, a progressive inhibition of methylation was correlated with increasing amount of BPDE substitution. The effect of BPDE-dG adducts did not alter the apparent km with respect to the concentration of d[CG] in either unmodified or BPDE-modified poly(dC-dG) (km = 10 microM) but lowered the relative apparent Vmax. In assays in which perturbation by salt of preformed enzyme-DNA complex is measured, no change in the relative stability to either unsubstituted or the carcinogen-modified template was noted, thus, excluding any change in the ionic component of this interaction. However, in competition-type experiments, BPDE-DNA is an inhibitor of the methylation reaction on native DNA. When BPDE-DNA is allowed to interact with the enzyme before the addition of native competitor DNA, the methylation rate is not stimulated, suggesting very tight hydrophobic binding of the enzyme to BPDE-DNA and an inhibition in the dissociation of DMase from the template following a methylation event.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature-dependent transmembrane potential changes in cells infected with a temperature-sensitive Moloney sarcoma virus

Normal rat kidney cells (NRK) infected with the temperature-sensitive (ts) transformation mutant of Moloney murine sarcoma virus yielded a clone of cells, 6m2, that exhibited a transformed morphology at 33 degrees C and a normal morphology at 39 degrees C. Transmembrane potential (Em) was measured fluorometrically using a cyanine dye diS-C3-(5). Fluorescence was inversely correlated with Em. Cells at 33 degrees C had lower Em. Em changes were recorded within 15 minutes of temperature shift from 33 degrees C to 39 degrees C in both directions, increasing in the 33 degrees C to 39 degrees C direction and decreasing in the 39 degrees C to 33 degrees C direction. Uninfected NRK cells when shifted under the same condition exhibited small fluorescence changes in the 33 degrees C to 39 degrees C direction. Shifting from 39 degrees C to 33 degrees C resulted in Em changes similar to those in 6m2 cells. Also studied was a cell line infected with a spontaneous revertant of the ts mutant, designated 54-5A4; it was transformed at both temperatures. Shifting from 33 degrees C to 39 degrees C in both directions yielded small changes. Transmembrane potential changes in 6m2 cells precede other transformation-specific changes that occur after a temperature shift.

A constitutive deficiency in the monooxygenase system of spontaneous mouse liver tumors

Exposure to chemical carcinogens evokes a population of altered hepatocytes that demonstrates significantly diminished monooxygenase activity. It has been suggested that this alteration permits the target cell to escape the toxic effects of the carcinogen and proliferate. In an attempt to determine whether this enzyme defect has broader implications for the carcinogenic process, we examined the monooxygenase system and additional components of spontaneous hepatocellular tumors in mice with a genetic predisposition to tumorigenesis. These tumors uniformly demonstrated a significant deficit in cytochrome P-450 and aminopyrine N-demethylase, despite the absence of known carcinogens, toxins, or promoting agents in their environment. Tumors of similar histiotype induced by a small, single neonatal administration of diethylnitrosamine demonstrated identical alterations. This report, therefore, suggests a strong link between a genetic program for tumorigenesis and a deficit in the monooxygenase system in spontaneous tumors. Further, it reveals that a toxic-selective environment is not required for the expansion of the cell population that possesses this phenotype.

DNA-ligase activities appear normal in the CHO mutant EM9

The Chinese hamster ovary (CHO) mutant strain EM9 was previously shown to be hypersensitive to killing by ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS), to have a 12-fold increased baseline incidence of sister-chromatid exchanges (SCE), and to be defective in rejoining DNA strand breaks after treatment with EMS, MMS, or X-rays. A study was performed to determine if the primary biochemical defect might be a DNA ligase. DNA-ligase activities were assayed and compared after separation of the multiple forms of ligase by AcA 34 gel-filtration chromatography of total cellular extracts. In EM9 cells the levels of the presumptive replicative forms, DNA ligase Ia (480 kd) and ligase Ib (240 kd) were about 50% and 60%, respectively, of those in the parental AA8 cells, whereas DNA ligase II (80 kd) was unaltered in EM9 . In a phenotypic revertant line ( 9R1 ) ligases Ia, Ib and II levels were 35%, 37% and 100%, respectively, of those in AA8 . The reduced levels of ligases Ia and Ib in EM9 and 9R1 cells are apparently not related directly to the mutant phenotype and may be attributable to the somewhat slower growth rates of these strains compared with those of AA8 . To determine if the repair defect in EM9 might reside in the ability to induce DNA-ligase activity after treatment with a DNA-damaging agent, AA8 and EM9 cells were treated with MMS at 30 micrograms/ml for 60 min before preparing fractions for ligase assays. Under these conditions the activities of ligases Ia and Ib decreases 70-80% in both cell lines, but ligase II increased 2.0- and 2.6-fold, respectively, in AA8 and EM9 . As a further test of defective ligase activities in EM9 , assays were performed in the presence of 0.1 M NaCl or after heating the fractions for 10 min at 50 degrees C. Although all 3 forms of ligase showed altered activity under both of these conditions, there were no significant differences between EM9 and AA8 cells. These data combined with the above results provide strong evidence that the site of the primary defect in EM9 is not in either of the DNA ligases .

Interaction of DNA methyltransferase with aminofluorene and N-acetylaminofluorene modified poly(dC-dG)

Poly(dC-dG) was reacted in vitro to yield templates containing similar amounts of aminofluorene (AF) or acetylaminofluorene (AAF) adducts. These modified poly(dC-dG) templates were tested in an in vitro DNA methylation system utilizing 1500-fold purified rat liver methyltransferase (DMase) to compare and quantitate the effects of these adducts on the kinetics of methylation and the interaction of DMase with such templates. Enzymatic methylation is severely impaired by arylamine adducts, with bound AF inhibiting more than AAF (relative Vmax 0.24 for AAF-poly(dC-dG) and 0.066 for AF-poly(dC-dG). The apparent km for the reaction is not appreciably altered by AAF modification: 10 microM for dCdG dinucleotide units, but it is threefold lower (3 microM) for AF-poly(dC-dG). In competition experiments it was demonstrated that a translocational block is imposed by the adducts. From differential salt inhibition assays and preincubation assays, no change in the ionic binding to the altered templates could be detected, which suggests that the enzyme interacts very strongly through hydrophobic interactions with the fluorene ring. Evidence that the fluorene ring is exposed is supported by circular dichroism spectra of the templates under the conditions of the assay, which indicated that the AF adducts do not appreciably change the normal B conformation of the template, while the template with 9.5% modification by AAF adducts adopted a Z form. These results suggest that the inhibitory effects of AAF and, in particular, AF upon DMase-catalyzed methylation reactions are not dependent upon helix conformation. Instead, they appear to depend upon DMase recognition of an altered dG base configuration, which is responsible for altered binding and methylation kinetics.

Methylation of the alpha-fetoprotein gene in productive and nonproductive rat hepatocellular carcinomas

The extent of methylation of Hpall-Mspl and Hhal sites in DNAs isolated from normal rat livers and from the transplantable hepatocellular carcinomas (THC) THC 7777 and THC 252 was compared. It was found that the overall level of methylation of the internal cytosine in CCGG sequences was lower in the THC DNAs than in the normal liver DNAs. This difference could also be detected in the extent of methylation of CCGG sites flanking a 400-base pair repetitive sequence. Examination of methylation of specific sites within the alpha-fetoprotein gene revealed differences between the DNAs that appear to reflect both the level of activity of the gene and the overall level of methylation of cellular DNA. This gene, which is repressed in normal adult liver and the nonproductive THC 252 and highly active in the productive THC 7777 (S. Sell et al., Cell Biol. Int. Rep., 4: 235-254, 1980), contains several CCGG sites that are methylated in both normal liver and THC 252 DNA but not in THC 7777 DNA. However, Hhal (GCGC) sites in the alpha-fetoprotein gene were less methylated in both hepatoma DNAs than in liver DNA, which the exception of one site in the productive tumor found to be no longer methylated.

The protective role of thiol reducing agents in the in vitro inhibition of rat liver DNA methylase by direct acting carcinogens

The direct-acting carcinogens N-acetoxy-N-acetyl-2-aminofluorene (AcAAF), methyl nitrosourea (MNU), and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were tested for their ability to inhibit highly purified, rat liver DNA methylase in vitro. Fifty percent inhibition of DNA methylase activity was achieved with 4.3 mM AcAAF, 47 mM MNU and 2.8 mM MNNG. When the enzyme was reassayed in the presence and absence of dithiothreitol, it was shown that DNA methylase was protected by increasing amounts of the thiol reducing agent. When other thiol reducing agents were tested for their ability to protect DNA methylase from carcinogen damage, a differential protective ability was observed. Dithiothreitol, beta-mercaptoethanol, and reduced glutathione were effective in protecting DNA methylase from carcinogen inhibition, while the effect of cysteine was intermediary and the effect of ergothioneine was minimal. These results may be related to the hypomethylation of DNA observed in several cancers, suggesting that the carcinogens achieve this effect at least in part by inhibiting crucial sulfhydryl group(s) in the methylase molecule. These data also suggest that various intracellular thiols may play an important role in protecting DNA-modifying enzymes from carcinogen damage.

Thioacetamide hepatocarcinogenesis

Thioacetamide (TAA) was administered to inbred male ACI rats for 1 year to determine its hepatocarcinogenicity. The carcinogen was fed at a level of 0.035% in a semipurified diet so that other components could be manipulated. The following groups were used: group I, TAA alone; group II, TAA with riboflavin content at 0.002% (one-third of the daily requirement); group III, TAA plus a supplement of 0.05% crude bovine thyroid; and group IV, TAA, 0.002% riboflavin, and thyroid supplement. All groups demonstrated cirrhosis, neoplastic nodules, and cholangiofibromas to varying degrees. Group IV was invariably the most advanced in all lesions, while group II demonstrated the next most advanced picture of cholangiofibromas. These lesions persisted for 1 year after cessation of the diet. Primary hepatocarcinomas (PHC) were produced by groups I, III, and IV, with the highest number being in group IV. Group II evoked only primary cholangiocarcinomas (PCC). A number of both types of carcinomas transplanted successfully. Thus TAA appears to be a hepatocarcinogen capable of inducing either PHC or PCC, with the tumor type evoked somewhat dependent on the associated diet.

Immunocytochemical localization of gamma-glutamyltransferase in induced hyperplastic nodules of rat liver

The immunocytochemical localization of gamma-glutamyltransferase [(5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC 2.3.2.2; gamma-GluTase] was demonstrated in hyperplastic liver induced by the carcinogen 2-acetylaminofluorene (2-AAF). The method used a specific antiserum and protein A-horseradish peroxidase and permitted visualization of antigenic sites at both the light and electron microscopic levels. Electron microscopy revealed deposits of 3,3'-diaminobenzidine (DAB) reaction product in the plasma membranes of (i) hyperplastic cells, (ii) bile canaliculi, (iii) endothelial cell membranes, and (iv) lymphocytes. The so-called ATPase activity was localized in the plasma membrane in bile canaliculi and in endothelial cells; the hyperplastic cells show marked variability in the levels of this activity.

Circumoral chemical peel combined with cervicofacial rhytidectomy

Forty consecutive cervicofacial rhytidectomies were performed; 36 were carried out in women and four in men, giving a rate of 10% for male rhytidectomies. Thirty-one of the female patients and one male patient had a circumoral chemical peel performed the day of surgery or the following day for a rate of 80% circumoral peel combined with rhytidectomy. The cases were carefully reviewed for results, and it was believed that circumoral chemical peeling combined with rhytidectomy greatly enhanced the overall result in the majority of cases in which it was performed. The only complication noted was slight hypopigmentation of the peeled skin compared with the surrounding cheek skin in some cases, which is easily covered with cosmetics and did not present a problem in any of the cases.

The direct and indirect effects of promoters may depend upon the nature of the initiated cell

The sequence of events in carcinogenesis may be more complex than previously proposed. We cannot as yet define the nature of initiation, nor in fact the obligate aspects of promotion. Administering small doses of diethylnitrosamine (DEN) to neonatal mice genetically predisposed to hepatocarcinogenesis, or to lines that are not (with and without subsequent phenobarbital (PB) administration), gave evidence that different types of initiated cells might exist. The majority of tumors that resulted were identical in morphology and biology to those that arise spontaneously from basophilic, diploid cells. However, a second tumor type was seen only in DEN-PB treated mice. This was composed of huge eosinophilic, polyploid cells. A third tumor type, rapidly progressing to a fully malignant form, was seen only in predisposed mice that received DEN, suggesting a genetic "hit" in a genetically predisposed cell. In addition to demonstrating the spectrum of initiated cells available for the action of promoters, evidence was obtained that indicated that one major action of PB was to stimulate growth of these altered cell populations rather than to induce new phenotypic alterations commensurate with progression. Thus, characteristics of PB-expanded, altered hepatocyte populations could be identified in very early cell foci.

Morphological classification of mouse liver tumors based on biological characteristics

Examination of three strains of inbred mice suggested that specific morphological types of hepatic tumors are the result of genetic predisposition while other types of tumors are associated with exposure to chemical carcinogens. A simple classification system is proposed. Additional studies indicated that a putative promoting agent, such as phenobarbital, increased the incidence of those tumor types usually associated with spontaneous appearance and only in strains with a genetic predisposition to spontaneous tumorigenesis. Carcinogens induce an increase in all types of tumors.

Presentation of the rous-whipple award to emmanuel farber: 1982

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Lateral tarsal strip procedure for the correction of paralytic ectropion

Otolaryngologists are frequently confronted with patients suffering from permanent facial paralysis. This condition often results in a severe cosmetic and functional deformity of the lower eyelid called paralytic ectropion. Conservative measures are often unsatisfactory and surgical correction is needed. Tarsorrhaphy and cautery have been advocated in the past, but are usually unsatisfactory. The most standard surgical procedure in use at the present time is a modification of the Kuhnt-Szymanowski procedure which is useful in repositioning the lax eyelid and allowing for lid shortening. This procedure involves removal of a portion of the midtarsal plate, but does not correct the lax lateral canthal tendon which is the cause of the pathology in paralytic ectropion. In 1979, in the ophthalmologic literature, Anderson and Gordy reported the tarsal strip procedure for the correction of paralytic and senile ectropion. This paper describes the lateral tarsal strip procedure which involves a lateral canthotomy, division of the lateral portion of the lower eyelid into musculocutaneous and tarsoconjunctival layers, removal of a portion of the conjunctiva and suturing the resulting tarsal strip to the periosteum of the inner aspect of the orbital rim laterally to shorten and elevate the lower eyelid. The procedure is presented in diagrams and close-up operative photographs. Before and after photographic documentations of two clinical cases are also presented. Since this procedure has been employed for only about two years, long-term results are not yet available; however, the author feels that this procedure will offer a significant improvement in the surgical treatment of paralytic ectropion.

The characterization of trypan blue-induced tumors in Wistar rats

Trypan blue is an azo dye widely used for testing cell viability. The dye has been identified as a mutagen and a carcinogen. In some strains of rats, particular Wistar rats, chronic exposure induces a reticuloendothelial neoplasm, predominantly in the liver. These tumors were studied with the use of immunologic cell membrane markers, electron microscopy, and histochemistry to characterize tumor cell type. The authors have studied this tumor in two inbred lines of Wistar rats to compare the efficacy of two previously described dye regimens on tumor incidence and to ascertain whether a short, intense exposure was as effective as chronic protracted exposure. No significant difference in tumor incidence was observed between the two regimens. These studies suggest that the tumor is composed of a macrophage-like cell that retains some characteristics of normal macrophages and that is a reproducible model for carcinogen-induced lymphoreticular human lymphomas.

Occurrence of progressive DNA damage coincident with the appearance of foci of altered hepatocytes

The technique of alkaline elution was used to evaluate alterations in nuclear DNA obtained from livers of rats that had received a single 6.6 mg/kg dose of diethylnitrosamine (DEN) during liver regeneration and subsequent exposure (7 days after partial hepatectomy) to phenobarbital (BP). DNA from normal and regenerating liver demonstrated a significant increase in the rate of elution following DEN administration. In those DEN-treated groups that did not receive PB, the rate of DNA elution decreased slowly but failed to return to normal by 44 weeks. Exposure to PB hastened recovery of a normal DNA elution profile in normal liver following DEN treatment, by 44 weeks, DNA from these rats eluted at a normal rate. However, in rats treated with DEN during liver regeneration, the rate of DNA elution began to increase at 28 weeks of PB exposure and became progressively more rapid through the 36th and 44th weeks. This latter group also demonstrated foci of gamma-glutamyl-transferase (GGT)-positive hepatocytes at 28 weeks of PB exposure that increased in number and size concomitantly with the increasing rate of DNA elution. AT 44 weeks, one or more primary hepatocellular carcinomas were present in 73% of the rats in this group; none was seen in any other group. Foci of GGT positive hepatocytes, an increasing rate of DNA elution and eventual primary hepatocellular carcinoma were seen in a group of rats that was begun on PB as late as 85 days after partial hepatectomy and DEN treatment.

Hepatocellular ligandin during N-2-fluorenylacetamide carcinogenesis

Ligandin was decreased by 75% as determined immunologically and by glutathione-S-transferase or steroid isomerase activities in rat hepatocellular carcinomas induced by exposure to N-2-fluorenylacetamide. Minor variable differences in ligandin levels were noted between the putative, premalignant nodules induced by this regimen and normal liver.