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Biomedical subjects

R J Calvert

Publications and source records attributed to R J Calvert.

At least 37 records · Page 2Linked to original sources
PubMed1995

Lack of p53 point mutations in chemically induced mouse hepatoblastomas: an end-stage, highly malignant hepatocellular tumor.

Inactivation of the p53 tumor suppressor gene appears to be an important event in the progression of many types of human neoplasms; however its role in rodent experimental tumorigenesis is controversial. Previous studies have shown that a wide array of chemically induced and spontaneous mouse liver tumors lack p53 mutations within the evolutionarily conserved regions of exons 5-8. However, since p53 inactivation in human neoplasms occurs relatively late in tumor progression, it is possible that the mouse liver tumors evaluated previously were not suitably advanced to incur p53 aberrations. In the present study, we examined an end-stage, highly malignant embryonal mouse liver tumor known as the hepatoblastoma (HB) for p53 mutations utilizing the highly sensitive 'cold' single-strand conformation polymorphism (SSCP) technique. In addition, several of the HBs were examined by direct nucleotide sequencing. No aberrations of the p53 gene were detected within exons 5-8 of any of the 16 HBs examined. These results confirm that the p53 gene plays a minimal role in the development or malignant progression of hepatocellular tumors in mice.

Animals↗
PubMed1994

Squamous cell carcinoma of the maxillary antrum metastatic to the heart and skin.

A case of squamous cell carcinoma of the maxillary antrum is presented in which autopsy examination revealed wide-spread disseminated disease including metastatic deposits in the unusual sites of the myocardium and skin. Apart from the skin deposit the metastases were clinically unsuspected. This case demonstrates the role of the autopsy in the study of malignancy and the possible effects of local disease control on the natural history of the disease process.

Autopsy↗
PubMed1993

'Cold SSCP': a simple, rapid and non-radioactive method for optimized single-strand conformation polymorphism analyses.

A rapid (< 2.5 hrs) method for single-strand conformation polymorphism (SSCP) analysis of PCR products that allows the use of ethidium bromide staining is described. PCR products ranging in size from 117 to 256 bp were evaluated for point mutations and polymorphisms by 'cold SSCP' in commercially available pre-cast polyacrylamide mini-gels. Several electrophoretic parameters (running temperature, buffers, denaturants, DNA concentration, and gel polyacrylamide concentration) were found to influence the degree of strand separation and appeared to be PCR fragment specific. Use of the 'cold' SSCP technique and the mini-gel format allowed us to readily optimize the electrophoretic conditions for each PCR fragment. This greatly increased our ability to detect polymorphisms compared to conventional, radioisotope-labeled 'hot' SSCP, typically run under two standard temperature conditions. Excellent results have been obtained in resolving mutant PCR fragments from human p53 exons 5 through 8, human HLA-DQA, human K-ras exons 1 and 2, and rat K-ras exon 3. Polymorphisms could be detected when mutant DNA comprised as little as 3% of the total gene copies in a PCR mixture. Compared to standard 'hot' SSCP, this novel non-isotopic method has additional advantages of dramatically increased speed, precise temperature control, reproducibility, and easily and inexpensively obtainable reagents and equipment. This new method also lacks the safety and hazardous waste management concerns associated with radioactive methods.

Animals↗
PubMed1993

Coconut oil and sesame oil affect lymphatic absorption of cholesterol and fatty acids in rats.

Five groups of male Wistar rats weighing approximately 200 g consumed 12 or 24% sesame oil or coconut oil diets or a control diet (14% corn oil) ad libitum for 4 wk. The thoracic ducts of these rats were cannulated, and a lipid emulsion containing [3H]cholesterol and [14C]oleic acid was given through a duodenal catheter. Lymph was collected for 24 h and the isotopic tracers for cholesterol and fatty acid were measured. Rats fed the 24% sesame oil diet had significantly lower lymphatic cholesterol and fatty acid compared with the control group. Absorption of oleic acid in rats fed 24% coconut oil was significantly greater than in controls during 0-8 h but was not significantly different during 0-24 h. There were no differences among groups in the distribution of cholesterol and oleic acid either in the lymph lipoproteins or in the lipid classes. The significant reduction in lymph cholesterol and fatty acids due to sesame oil feeding may be an important factor in reducing hypercholesterolemia.

Absorption↗
PubMed1993

Starches of varied digestibilities differentially modify intestinal function in rats.

Starches of different digestibilities may enter the colon to different extents and alter colonic function. Male Fischer 344 rats were fed diets containing 25% cooked potato starch, arrowroot starch, high amylose cornstarch or raw potato starch for 6 wk. Fecal weight, transit time, colonic thymidine kinase activity (a marker for cell proliferation), and weight, starch content and pH of the cecum and proximal and distal colon were measured. Raw potato starch was much less completely digested than high amylose cornstarch, resulting in a 32-fold greater amount of undigested starch entering the cecum in the raw potato starch group. Both the high amylose cornstarch and raw potato starch diets significantly enhanced fecal weight and produced large intestinal hypertrophy, effects that were greatest in the raw potato starch group. Raw potato starch feeding was associated with the highest level of thymidine kinase activity, although the differences in thymidine kinase activity among the four groups were not significant. This diet also produced a 50% longer transit time. Entry of a large amount of raw potato starch into the colon resulted in greater luminal acidity, greater luminal bulk and slower transit. A much smaller amount of starch entered the colon in the high amylose cornstarch group and resulted in fecal bulking but no alteration in transit.

Animals↗
PubMed1992

Hepatic toxicity of unmodified and time-release preparations of niacin.

Niacin (nicotinic acid) is used frequently in the treatment of hypercholesteremia. It is available in both unmodified and time-release preparations. The latter were developed in attempts to minimize the skin-flushing reaction that affects virtually all users and may limit acceptance. Adverse effects on the liver from both unmodified and time-release preparations have been recognized for many years. We reviewed the literature on the hepatic toxicity of both types of niacin preparations. Adverse reactions in six patients resulted from the exclusive use of unmodified niacin and in two patients from the exclusive use of time-release preparations. In 10 additional patients, adverse reactions developed after an abrupt change from unmodified to time-release preparations. Many of these patients were ingesting time-release niacin at doses well above the usual therapeutic doses currently recommended. Signs of liver toxicity developed in less than 7 days in four of these 10 patients. In doses that achieve equivalent reductions in serum lipids, hepatic toxicity occurred more frequently with time-release preparations than with unmodified preparations. An awareness of toxicity associated with ingestion of high doses of time-release niacin preparations is important because of their widespread availability and the potential for self-prescribed, unmonitored use.

Chemical and Drug Induced Liver Injury↗
PubMed1991

Alteration in levels of immunoreactive epidermal growth factor in the gastrointestinal mucosa of Fischer rats fed a diet containing 10% wheat bran.

This study evaluates the effect of dietary wheat bran on the levels of immunoreactive epidermal growth factor (EGF) in the gastrointestinal mucosa of Fischer 344 rats. Male rats were fed either a fiber-free diet or a diet containing 10% wheat bran (nine animals per group) for a period of 5 wk. The gastrointestinal tract of each animal was divided into four segments: proximal, middle and distal small intestine, and colon. Mucosa was removed by scraping, EGF was extracted by homogenization and the extracts were analyzed for immunoreactive rat EGF using a homologous RIA. Levels of immunoreactive EGF in all regions of the small intestine of Fischer rats were comparable to our previous measurements in Sprague-Dawley rats, and these levels were unaffected by diet. In contrast, the EGF levels in the colon of the Fischer rats were approximately fivefold greater than those of the Sprague-Dawley rats. These higher levels of immunoreactive EGF in the colon decreased 63% with the addition of 10% wheat bran to the diet (P less than 0.02). These results represent the first demonstration of dietary fiber modulating the content of EGF in the gastrointestinal tract.

Animals↗
PubMed1990

Alterations in rat intestinal mucin patterns following luminal infusion of acetylsalicylic acid and prostaglandin derivatives.

The secretion of gastrointestinal mucin and/or the formation of mucoid caps have been implicated in cytoprotective or repair mechanisms related to mucosal injury models. In this study, rats were treated with acetylsalicylic acid (ASA) or prostaglandins (PG), and their effects on the synthesis and secretion of small intestinal mucin were examined. A newly developed polyclonal antibody to rat intestinal mucin was used for immunoassay of rat intestinal luminal and tissue mucin. The mucin antigen source was obtained by vacuum aspiration of luminal mucus. A high-molecular-weight glycoprotein (2 x 10(6) Da) fraction injected into rabbits produced a primary mucin antibody. A sensitive and quantitative enzyme-linked immunosorbent assay (ELISA) was developed that yielded a highly reproducible and linear response with mucin aliquots containing 0-20 ng of protein/ml. Incorporation of the plasma tracers ([3H]glucose and [35S]sodium sulfate) into mucin derived from hexadecyltrimethylammonium bromide precipitation after treatment with ASA (100 mg/kg body wt) decreased, although administration of dimethylprostaglandin E2 (100 micrograms/kg body wt) significantly increased the specific tracer incorporation values for the sialomucin and sulfomucin indices in luminal mucin fractions. The immunoassay data pattern for the ELISA technique was virtually identical to the results of the radiolabeled tracer method obtained for the same pharmacologic treatments. These experiments demonstrate that the estimation of synthesized mucin (tissue source) or secreted mucin (luminal source) as determined by the ELISA technique is similar to that obtained by the time-consuming and labor-intensive tracer incorporation methodology.

16,16-Dimethylprostaglandin E2↗
PubMed1990

Alteration of gastrointestinal mucin by fiber feeding in rats.

Alterations in gastrointestinal mucin induced by dietary fiber may affect nutrient bioavailability, cytoprotection of the mucosa or other aspects of gastrointestinal function. To allow quantitative study of gastrointestinal mucin, a polyclonal antibody to the mucin of the rat small intestine was produced by injecting rabbits with a high-molecular-weight subfraction (MW 2 x 10(6)) of purified mucin glycoprotein derived from rat intestinal mucin. An enzyme-linked immunosorbent assay was developed and used for the mucin assay. Three groups of male Wistar rats consumed 5% guar gum, 5% citrus fiber or a fiber-free control diet ad libitum for 4 wk. After an overnight fast, luminal and tissue mucin antibody reactivities were determined in the rat stomach, colon and small intestine. In all groups, total (luminal and tissue) mucin reactivity was greater in the small intestine than in the colon or stomach. The group fed 5% citrus fiber had significantly greater mucin reactivity in luminal samples from stomach and intestine than did the fiber-free control group. Fiber-induced increments in gastrointestinal mucin production or availability may be responsible for several reported consequences of fiber feeding, such as more rapid transit times and delayed or impaired nutrient absorption.

Animals↗
PubMed1989

An improved method for oxidation of chromium(III) oxide-containing fecal samples by using sodium peroxide fusion.

A safer method of oxidation of Cr2O3-containing fecal samples from transit-time studies was developed using sodium peroxide to replace perchloric acid as the oxidizing agent. The percentage recovery of Cr2O3 with this method was compared with that of perchloric acid method for samples containing quantities of fecal ash and Cr2O3 typical of those from rodent transit-time studies. Both methods gave relatively constant percentage recoveries for Cr2O3 contents from 0.4 to 10 mg. Over this range, mean (+/- SD) percentage recoveries of Cr2O3 for sodium peroxide fusion and the perchloric acid method were 75.5 +/- 4.3 and 89.9 +/- 2.5, respectively. As long as percentage recovery is constant, the transit time as determined by calculation of the time of 80% excretion of the total recovered Cr2O3 is not affected. Sodium peroxide fusion provides a useful and safer alternative to perchloric acid oxidation in transit-time studies using Cr2O3 as a nonabsorbable marker.

Animals↗
PubMed1989

Consumption of raw potato starch alters intestinal function and colonic cell proliferation in the rat.

Raw potato starch (RPS) may escape complete digestion to enter the colon and produce alterations in colonic function, while cooked potato starch (CPS) is nearly completely digested in the rat small intestine. Effects of RPS and CPS on colonic function [fecal weight, transmit time and thymidine kinase (TK) activity (a marker for cell proliferation)] were contrasted in a 6-wk feeding study. Male F344 rats consumed either dextrose/sucrose (DS; control), 30% CPS or 30% RPS diet. RPS feeding resulted in a 3-fold increase in fecal weight and a 30% prolongation in transit time, as well as elevated levels of colonic mucosal total protein (50%) and TK activity (4- to 7-fold) compared to DS-fed rats. A second study revealed normal large intestinal histology in rats fed CPS or RPS, with elongated colonic crypts (33% increased over CPS) in group RPS. Large intestinal contents were heavier in group RPS than in group CPS. These studies demonstrate that RPS feeding significantly enhances fecal weight yet prolongs total gastrointestinal transit time. Enhanced colonic TK and elongated colonic crypts suggest that RPS stimulates colonic mucosal growth.

Analysis of Variance↗
PubMed1989

Influence of meal distribution of wheat bran on fecal bulk, gastrointestinal transit time and colonic thymidine kinase activity in the rat.

Male Fischer 344 rats were fed either fiber-free (FF), continuous 10% wheat bran (CWB) or intermittent 50% wheat bran (IWB) diets for 6 wk to investigate possible alterations in physiological effects associated with colon cancer (fecal bulk, transit time, colonic cell proliferation) induced by meal distribution of the bran. The FF and CWB groups consumed unvaried diets throughout the day. The IWB group consumed two consecutive meals of a 50% bran diet for a total of 4 hr each day followed by a fiber-free diet for the remaining hours of the day. Similar daily quantities of bran were consumed in the CWB and IWB groups. Dry fecal weights rose significantly and transit times declined in both bran-fed groups independent of the meal distribution of bran. Colonic cell proliferation (estimated by thymidine kinase activity) was similar in all groups. The results suggest that these physiological effects of wheat bran are independent of the meal distribution of the bran.

Animals↗
PubMed1988

Alterations in colonic thymidine kinase enzyme activity induced by consumption of various dietary fibers.

Dietary fibers may tend to enhance or inhibit chemically induced experimental colon cancer, depending on the particular fiber consumed. This study examined the relationship between colonic thymidine kinase enzyme activity and mucin histochemistry and the reported effects of various dietary fibers on chemically induced colon carcinogenesis. Fiber-supplemented diets containing fibers reported to inhibit (wheat bran) or enhance (guar gum, carrageenan) chemically induced colon carcinogenesis in the rat were selected. Four groups of male Fischer 344 rats consumed 10% wheat bran, 5% guar gum, 5% carrageenan, or fiber-free diets ad libitum for 4 weeks. At the completion of the treatment period, the distal 12 cm of colonic mucosa was scraped off and homogenized for determination of thymidine kinase activity, and a 0.5-cm section of midcolon was processed by the high-iron diamine/Alcian blue method for mucin histochemistry. Final animal weights did not differ significantly among groups. Thymidine kinase enzyme specific activity (mumole thymidine phosphate formed x 10(6)/min/mg protein, means +/- SEMs) was not significantly different in the fiber-free, wheat bran, and guar gum groups (10.98 +/- 1.50, 7.41 +/- 1.09, and 9.11 +/- 2.04, respectively) but was markedly elevated at 41.84 +/- 4.65 in the carrageenan group (alpha less than 0.001). Mucin histochemistry failed to reveal any significant differences among dietary groups.

Animals↗
PubMed1988

Effects of prolonged acetaminophen ingestion and dietary methionine on mouse liver glutathione.

Acetaminophen (ACAP) was fed to adult Swiss-Webster mice for 4 weeks to examine the effect of prolonged ACAP ingestion on hepatic reduced glutathione (GSH) concentrations. In the first experiment, male and female mice were pair-fed diets containing ACAP at levels of 0.0 (control), 0.3, 0.6, and 1.0% of diet on a dry weight basis with the total sulfur-amino acids provided at 0.5% of the diet. Hepatic GSH was depleted, and the percentage of dose excreted as the urinary ACAP-GSH-derived conjugate increased in a dose-dependent manner with increasing ACAP. Serum glutamic-pyruvic transaminase activity, relative liver weight, and hepatic microsomal protein content increased in the group given 1.0% ACAP, but microsomal aniline hydroxylation decreased. In the second experiment, adult male mice were fed ad libitum diets containing 0.0 or 0.6% ACAP with total L-methionine provided at 0.25, 0.5 (requirement level), or 1.0%. Hepatic GSH was markedly depleted 1 week after initiation of ACAP treatment in all groups except those receiving 1.0% methionine. This reduction persisted throughout the 4-week treatment period. After 4 weeks, liver cysteine was also reduced as a result of ACAP ingestion and methionine deficiency, whereas serum inorganic sulfate concentration was not changed. Reduction in hepatic cysteine levels was also prevented by 1.0% dietary methionine. The dose-dependent depletion of GSH, the trend toward an increase in ACAP-GSH-derived conjugate excretion, and the prevention of GSH depletion by providing dietary methionine in excess of requirement indicate that prolonged ingestion of ACAP may increase the requirement for sulfur-containing amino acids and limit the availability of methionine and cysteine for protein synthesis, methylation reactions, and drug detoxification.

Acetaminophen↗
PubMed1987

Reduction of colonic carcinogenesis by wheat bran independent of fecal bile acid concentration.

It has been reported previously that populations with a decreased concentration of fecal bile acids have a lower incidence of colon cancer. We examined the importance of fecal bile acid dilution by wheat bran (WB) in inhibiting colonic tumorigenesis in an experimental animal model. Male F344 rats received oral doses of the colon carcinogen 1,2-dimethylhydrazine [CAS: 540-73-8] and were assigned randomly to groups fed one of four semipurified diets for 26 weeks. The diets were fiber-free (FF), 10% WB, FF + bile salts, or WB + bile salts. The amount of bile salts added was adjusted to produce a fecal bile acid concentration in the group fed WB + bile salts equal to that found in the FF groups. Fecal bile acid concentrations at 12 and 24 weeks in the WB + bile salts group were similar to those in the FF group. Gross and microscopic findings at necropsy revealed a reduced total number and multiplicity of colon tumors in both bran-fed groups. Although the fecal bile acid concentrations of the FF and WB + bile salts groups were equal, the latter showed a significant reduction in tumor yield.

1,2-Dimethylhydrazine↗