Biomedical subjects

C M Weghorst

Publications and source records attributed to C M Weghorst.

63 records · Page 4Linked to original sources

PubMed1989

Comparison of the effects of acute and subacute treatment of phenobarbital in different strains of mice.

A strain specificity has been demonstrated for the effect of subsequent administration of phenobarbital (PB), in which diethylnitrosamine (DENA)-initiated hepatocarcinogenesis was promoted in C3H mice, inhibited in B6C3F1 (C57BL x C3H) and not affected in C57BL mice. A correlation has been established between the ability of barbiturates and hydantoins to promote tumor formation and their ability to induce liver growth, hepatic DNA synthesis and mixed function oxidase activities. Therefore, we examined in these 3 strains of mice and in C3B6F1 (C3H x C57BL) mice the effect of PB administered in their drinking water for 4 days or 28 days. The liver weight to body weight ratio was increased by PB in all types of mice. Microsomal protein concentrations were increased in C57BL mice after 28 days of treatment, in C3H after both 4 days and 28 days and in B6C3F1 after 4 days of treatment. No effect upon microsomal protein content was observed in C3B6F1 mice. DNA content was increased in C3H mice, both in the 4-day and 28-day treatment groups, while the other strains showed either a decrease or no difference from control. DNA synthesis was elevated in all strains of mice after 4 days of treatment with PB, however, after 28 days of treatment there was either a much reduced increase (C57BL and C3B6F1) or no difference (C3H and B6C3F1) from controls. In all 4 types of mice after 4 and 28 days of treatment, PB increased the concentration of cytochrome P-450, the activity of aminopyrine-N-demethylase (AmDm) and 7-ethoxyresorufin-O-deethylase (ErDe) and the oxidation of testosterone (T). The oxidative metabolites of T were similar in the 4 types of mice.

Aminopyrine N-Demethylase↗

PubMed1989

Phenobarbital promotion in diethylnitrosamine-initiated infant B6C3F1 mice: influence of gender.

Phenobarbital (PB) promotes hepatic tumorigenesis when chronically administered to male B6C3F1 mice after initiation with diethylnitrosamine (DENA) at 30 days of age. In contrast, when male B6C3F1 mice were initiated with DENA at 15 days of age, an inhibition of hepatic tumorigenesis occurred. The present study was undertaken to evaluate the influence of gender on the inhibiting ability of PB in the 15 day old DENA-initiated B6C3F1 mouse. Mice were injected with either DENA (5 micrograms/g) or saline at 15 days of age. At weaning mice were given either PB (500 p.p.m.) containing drinking water or deionized drinking water for 24 weeks. Male mice treated with DENA and PB demonstrated a significant decrease in the number of hepatocellular adenomas compared to males receiving DENA only. In contrast, females exposed to DENA and PB exhibited an enhancement of hepatic adenoma number compared to those receiving only DENA. In an additional experiment, individual preneoplastic foci from male and female B6C3F1 mice initiated with DENA at 15 days of age were examined for their responsiveness to the mitogenic stimuli of PB. Mice were exposed to either PB-containing or PB-free drinking water for 7 days. In non-PB treated males and females, preneoplastic hepatocytes demonstrated higher rates of DNA synthetic labelling compared to normal hepatocytes with no gender difference noted. Males exposed to PB exhibited increased levels of DNA synthesis in normal cells but not in preneoplastic foci. Females treated with PB, however, demonstrated significant increases in DNA synthesis in both preneoplastic and normal hepatocytes compared to non-PB treated females and PB-treated males. These findings suggest that in male mice initiated with DENA at 15 days of age, the preneoplastic foci are refractory to the proliferative effects of PB which may account for the observed inhibition of hepatic tumorigenesis by PB in this mouse strain.

Animals↗

PubMed1989

Strain differences in hepatic tumor promotion by phenobarbital in diethylnitrosamine- and dimethylnitrosamine-initiated infant male mice.

The effects of phenobarbital (PB) on hepatocellular carcinogenesis in three strains of nitrosamine-initiated infant male mice were evaluated. Fifteen-day-old C57Bl/6NCrlBR (C57Bl), C3H/HeNCr1BR (C3H) and B6C3F1 mice were treated with a single i.p. injection of either diethylnitrosamine (DENA) (5 micrograms/body wt), dimethylnitrosamine (DMNA) (5 micrograms/body wt) or saline. One-half of the treated mice received PB via the drinking water (500 mg/l) for 24 weeks. The remaining treated mice were given deionized drinking water. Mice were killed at 28 weeks of age and hepatic lesions were evaluated. Only animals that received DENA or DMNA exhibited tumors. C3H mice treated with DENA + PB demonstrated a significant increase in hepatic adenoma number compared to C3H mice exposed to DENA only. Conversely, B6C3F1 males treated with DENA + PB exhibited a significant decrease in the number of hepatic adenomas compared to B6C3F1 males treated with DENA alone. No change was noted in adenoma size in B6C3F1 mice treated with DENA + PB from those receiving DENA only. Chronic PB exposure of C57Bl males previously treated with DENA had no effect on hepatic adenoma number or size. C3H mice treated with DMNA + PB displayed an increase in both adenoma size and adenoma number compared to C3H mice receiving DMNA only. Similarly, in B6C3F1 mice, PB treatment increased both the adenoma incidence and adenoma number in DMNA initiated mice. PB had no effect on hepatic adenoma incidence or number in DMNA-treated C57Bl mice. These data suggest that the ability of PB to promote hepatic tumorigenesis in the 15-day-old initiated mouse is dependent on both the strain of the mouse and the initiating chemical carcinogen.

Animals↗

PubMed1989

Lack of promoting effect of clonazepam on the development of N-nitrosodiethylamine-initiated hepatocellular tumors in mice is correlated with its inability to inhibit cell-to-cell communication in mouse hepatocytes.

The tumor-promoting ability of clonazepam (CZP), a widely used benzodiazepine anticonvulsant, was investigated in an in vivo mouse liver tumor promotion assay and an in vitro mouse hepatocyte intercellular communication assay. The development of preneoplastic hepatocellular foci of cellular alteration and hepatocellular neoplasms was studied in male B6C3F1 mice initiated, at 5 weeks of age, with a single i.p. injection of N-nitrosodiethylamine (NDEA; 90 mg/kg body weight) in tricaprylin, followed by administration of either phenobarbital (PB; 0.05%) or CZP (0.068% or 0.136%) in diet beginning 2 weeks after carcinogen injection and continuing to 60 weeks of age. Several mice from each group were killed after 9, 21, 33 or 53 weeks on test diet, and portions of liver and other organs were fixed in formalin and examined histologically. Unlike PB, CZP did not promote the development of preneoplastic hepatocellular foci or neoplasms (adenomas and carcinomas) in NDEA-initiated mice. Following limited (2 weeks) dietary exposure at 0.15%, CZP was a potent inducer of hepatic P450IIB1-mediated alkoxyresorufin O-dealkylase activities. In contrast, the degree of induction in hepatic tissue from mice fed 0.136% CZP for 53 weeks was markedly lower than that in mice fed 0.05% PB for 53 weeks. In the in vitro assay, diazepam, a strong tumor promoter in mouse liver, significantly inhibited mouse hepatocyte gap junctional intercellular communication, while CZP had no significant effect on this parameter. Thus, CZP, a drug structurally related to diazepam, is inactive as a liver tumor promoter in mice.

Adenoma↗

PubMed1988

Dose-response relationship of diethylnitrosamine-initiated tumors in neonatal balb/c mice: effect of phenobarbital promotion.

The dose-response of diethylnitrosamine (DENA) initiation of hepatocarcinogenesis was determined in infant Balb/c male mice with and without subsequent phenobarbital treatment. Male Balb/c mice received a single intraperitoneal injection of DENA (0, 2.5, 10.0, 25.0 or 50.0 micrograms/gbw) in saline on day 15 of age. Ninety mice were treated at each dose level. At weaning, mice received either deionized drinking water (45 mice per group) or deionized drinking water containing 500 mg/L sodium phenobarbital (PB) (45 mice per group). Mice from each group were sacrificed 12, 24, and 40 weeks post-weaning. Liver and lung tumors were found in DENA-only-treated and DENA + PB-treated mice. In DENA-only-treated mice, the incidence and number of hepatic adenomas were similar (not dose-dependent) at DENA doses of 10, 25, and 50 micrograms/gbw at each of the 3 sampling times. DENA-only-treated mice did display a time-related increase in hepatic adenoma incidence and number at each dose. In PB-treated mice, the hepatic adenoma number was dependent upon the dose of DENA between 2.5 and 50 micrograms/gbw. PB treatment following DENA administration resulted in a decrease in the time required for the detection of hepatic adenomas and increased the number of hepatic adenomas at most sampling times compared to the mice that received DENA only. Hepatocellular carcinomas (HPC) were detected in mice receiving the highest DENA doses (25 and 50 micrograms/gbw). PB treatment increased the number and incidence of HPC and decreased the time of first detection of HPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗

PubMed1987

Effect of the age of B6C3F1 mice on phenobarbital promotion of diethylnitrosamine-initiated liver tumors.

Chronic exposure to phenobarbital (PB) in the drinking water of male B6C3F1 mice starting at 4 weeks of age and subsequent to a single (ip) injection of diethylnitrosamine (DENA) administered on Day 15 of age has been shown to result in the inhibition of hepatic tumor formation. In this study, we varied the time of onset of PB administration to determine if sexual maturity would affect liver tumor formation and progression. Male B6C3F1 mice were divided into eight groups. Groups 1-4 received a single (ip) dose of 5 mg/kg DENA at 15 days of age while mice in groups 5-8 received saline. At weaning (4 weeks of age), groups 1 and 5 received deionized drinking water (DDW) for 24 weeks; groups 2 and 6 received PB (500 ppm) in the drinking water (PB DW) for 16 weeks followed by DDW for 8 weeks; groups 3 and 7 received DDW for 4 weeks, PB DW for 16 weeks, and then DDW for 4 weeks; and groups 4 and 8 received DDW for 8 weeks and PB DW for 16 weeks. Mice were killed at 28 weeks of age and hepatic lesions were evaluated. Mice which did not receive DENA (groups 5-8) exhibited no liver tumors. Animals in groups 1-4 exhibited hepatocellular foci and adenomas. PB treatment in groups 2, 3, or 4 resulted in a significant decrease in the incidence of DENA-initiated hepatocellular foci and adenomas when compared to those observed in group 1. The number of foci in group 4 was significantly decreased compared to those in groups 2 and 3. There was no significant difference in the adenoma incidence among groups 2, 3, and 4. No significant differences were observed in the sizes of foci or adenomas among groups 1-4. Data from this study suggest that the inhibition of hepatocellular tumorigenesis by PB remains intact even when the start of the administration of PB is withheld up to 12 weeks of age.

Adenoma↗

PubMedDate not supplied

Effect of phenobarbital on diethylnitrosamine and dimethylnitrosamine induced hepatocellular tumors in male B6C3F1 mice.

The effect of the type of carcinogen initiator on the ability of phenobarbital (PB) to promote hepatic tumor formation in 15-day-old initiated male B6C3F1 mice was evaluated. Fifteen-day-old male B6C3F1 mice were divided into 6 groups of 10 mice each. Groups 1 and 2 received a single intraperitoneal (i.p.) injection of diethylnitrosamine (DENA) (5 micrograms/body wt). Groups 3 and 4 received a single i.p. injection of diethylnitrosamine (DENA) (5 micrograms/g body wt). Groups 3 and 4 received a single i.p. injection of dimethylnitrosamine (DMNA) (5 micrograms/g body wt). Groups 5 and 6 received a single i.p. injection of saline. At weaning (28 days of age), mice in groups 2, 4 and 6 received PB (500 mg/ml) in their drinking water. Mice in groups 1, 3 and 5 received deionized drinking water. Drinking water treatment continued for 24 weeks at which time mice were sampled. At sampling, mice were examined for hepatic tumors by histology. Mice in groups 5 (no treatment) and 6 (PB only) did not exhibit hepatic tumors. Groups 2 (DENA + PB) displayed a decrease in hepatic adenomas from that of group 1 (DENA only), confirming previous observations. Treatment with DMNA and PB (group 4), however, resulted in a significant increase in both hepatic adenoma incidence and number over that of DMNA only (group 3) treated mice. The promoted adenomas appeared to be predominantly eosinophilic in appearance. The type of initiator therefore appears important in determining if 15-day-old initiated male B6C3F1 mice respond to the promotion effects of PB.

Adenoma↗

PubMedDate not supplied

Expression of cell cycle proteins in 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced mouse lung tumors.

Cyclin D1 dysregulation and differential inactivation of p16INK4a and Rb have been observed in human lung cancer. In chemically induced mouse lung tumors, the p16INK4a gene is a target of inactivation, and Rb is reduced at the mRNA level (Northern blot) although similar at the protein level (Western blot) when compared to normal lung tissues. The expression of cyclin D1, cdk4, p16INK4a, and Rb protein was examined by immunohistochemistry in 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced mouse lung tumors. Immunohistochemical staining revealed exclusive nuclear staining of both cyclin D1 and cdk4 that was light to moderate in normal mouse lung tissues, but intense in lung adenomas and adenocarcinomas. Western blot analysis confirmed the increased expression of cyclin D1 and cdk4 in lung tumors compared to normal lung. Immunohistochemical analyses of lung tumors showed focal areas which lacked p16INK4a staining. Expression of p16INK4a, as determined by RT-PCR, was variable in lung tumors. Mutations in p16INK4a were not found by SSCP analysis. Immunohistochemical analyses of normal lung tissues showed intense staining for Rb protein in alveolar epithelial cells and in other lung cell types; however, in the lung tumors the staining intensity was reduced and the distribution was altered. Expression of Rb was detected in normal lung tissues but was barely detectable by Northern blot hybridization in lung tumors. Western blot analysis indicated the presence of both hypophosphorylated and hyperphosphorylated Rb protein in lung tumors and in normal lung tissues. These results suggest that alterations in the cell cycle proteins, cyclin D1, cdk4, p16INK4a, and Rb, may play a role in the acquisition of autonomous growth by adenomas. Furthermore, they demonstrate the importance of immunohistochemical studies to examine expression in tissues that contain multiple cell types, such as the lung, and in tumors that by nature are heterogeneous.

Adenocarcinoma↗

PubMedDate not supplied

Liver tumorigenesis by Helicobacter hepaticus: considerations of mechanism.

A new animal model for the causation of liver tumors via a bacterial infection presented itself fortuitously in the form of a new species, Helicobacter hepaticus. This species of Helicobacter colonizes the hepatic bile canaliculi in susceptible strains of mice, resulting in hepatitis and hepatocellular and hepatocholangiolar adenomas and carcinomas. The mechanism by which this infection leads to cancer is unknown. Tests with Helicobacter hepaticus have revealed thus far that the bacteria do not secrete a mutagen which is capable of detection by the Ames Assay. Measurement of oxidatively damaged bases in the liver DNA of hepaticus infected mice have shown accumulation of 8-oxodeoxyguanosine with disease progression. Other promutagenic DNA lesions, 7-methylguanine and O6-methylguanine, indicative of nitrosation of endogenous amines by nitric oxide, were not detected. Analysis of carcinomas and adenomas taken from H. hepaticus infected A/JCr mice revealed no mutations in ras oncogenes or in exons 5-8 of the p53 gene. These preliminary results indicate that a non-genotoxic tumor promotion mechanism, possibly implemented by reactive oxygen species from the immune response, is more likely than a genotoxic mechanism.

Alkylation↗