Faculty Bibliography

Certain oxygenated derivatives of cholesterol have dramatic effects on cholesterol synthesis. The present study compared the effects of cholesterol and an oxygenated metabolite, cholesterol-alpha-epoxide, on sterol metabolism in rats. Sterol balance measurements using isotopic and chromatographic techniques were carried out in rats fed liquid control diets, control diets + cholesterol (1 mg/ml), and control diets + cholesterol-alpha-epoxide (1 mg/ml). Sterol metabolism was affected by both cholesterol and cholesterol-alpha-epoxide. Cholesterol feeding decreased cholesterol synthesis (-9.57 +/- 7.23 mg/day), increased endogenous bile acid synthesis (7.71 +/- 1.18 mg/day), and increased cholesterol turnover (7.78 +/- 2.33 mg/day) compared to controls. Cholesterol-alpha-epoxide had no effect on cholesterol synthesis, endogenous bile acid synthesis and cholesterol turnover compared to controls. However, animals fed cholesterol-alpha-epoxide had large increases in total acidic steroid output (determined by chromatographic analysis, 12.33 +/- 4.05 mg/day). This finding suggests that cholesterol-alpha-epoxide is absorbed and converted to bile acids. Apparently, the epoxide enters the bile acid biosynthetic pathway distal to the rate-limiting step of 7 alpha-hydroxylation. As a result, large amounts of bile acids are formed from the epoxide without affecting endogenous cholesterol or bile acid synthesis. This was confirmed in a separate experiment by feeding [4-14C]cholesterol-alpha-epoxide and recovering labeled bile acids (hyodeoxycholic acid and lithyocholic acid) as well as the starting radioactively labeled epoxide in the feces

Primary bile acids were studied as possible colon tumor promoters or inhibitors in a rat model of chemically induced colon cancer. Cholic acid feeding increased the number of animals with tumors, the number of tumors per animal, and the number of tumors per tumor-bearing animal. Tumor enhancement was attributed to deoxycholic acid, the bacterial metabolite of cholic acid. When chenodeoxycholic acid was fed to the rats in our model, tumor incidence was increased, but the number of tumors per animal and the number of tumors per tumor-bearing animal were similar to controls. The different fecal bile acid pattern obtained with chenodeoxycholic acid may be responsible for the differences in tumor incidence. The methodology to characterize and identify all steroidal components of the feces requires extraction, thin-layer chromatography, gas-liquid chromatography, and gas-liquid chromatography-mass spectrometry. Newer techniques include LH-20 chromatography (for sulfated steroids) and high-pressure liquid chromatography

The histologic and proliferative characteristics of 16 colonic biopsies taken from an operative specimen of a 38-year-old female patient with multiple polyposis are presented. Kinetic measurements are based on 3HTdR incorporation accomplished in vitro, using both single and double labelling techniques. Epithelial cells in adenomatous tissue were more actively engaged in DNA synthesis than those normal-appearing mucosa (L.I.13.0 +/- 6.9 versus 9.3 +/- 1.6); however, because of extreme variability between biopsies, the difference was not significant. No difference in S phase duration was found, but a faster turnover time (Tg) than that in the normal appearing colonic mucosa was estimated (Tg 52.6 hours versus 74.2 hours). Only two of ten biopsies containing normal-appearing mucosa had a completely normal incorporation pattern with proliferative cells located only in the lower two thirds of crypts. Eight biopsies showed extension of the proliferative compartment to the luminal surface. One of these eight also expressed an additional proliferative defect, namely, a shift of the major zone of DNA synthesis to the middle and upper regions of the crypts. This specimen had been located adjacent to an area of microscopic adenoma. Subpopulations of labelled epithelial cells showing transition from normal to hyperplastic or to adenomatous appearance were in the otherwise normal-appearing crypts. The majority of labelled hyperplastic-appearing cells occupied the lower thirds of the crypts, whereas 68% of labelled adenomatous-appearing cells were located in the middle and upper zones of the glands. Based on these observations, the development of an adenoma is believed forecast by the redistribution of the proliferative compartment toward the surface. A further stage in tumorogenesis before the appearance of a focus of neoplasia is the emergence of actively proliferating cells transforming to a more adenomatous appearance primarily in that same location, that is, the middle and upper third of the colonic crypts

Administration of cholic acid (1.0% of the diet) to male Fisher rats for 3 days resulted in increased numbers of DNA synthesizing epithelial cells per colonic crypt column as compared to those found in either control or 0.2% cholic acid-fed rats. The middle third of the crypt was the area stimulated to contribute the additional proliferating cells. The maximum number of 3H-TdR-labeled cells was doubled by 24 h and migration had processed further up the colonic crypt of the 1% cholic acid-fed rats than the 0.2% cholic acid or control animals. Compared with cholic acid-deprived rats, long-term dietary intake of 0.2% cholic acid (26 weeks) was found to heighten the numbers of labeled cells per column and expand the proliferative compartment. The enhanced manifestation of colonic neoplasia in MNU-induced rats consuming cholic acid (previously reported by us) appears related to the elevated levels of cell proliferation brought about in response to the deleterious action of the bile acid on the mucosa. Increased numbers of epithelial cells undergoing DNA synthesis in cholic acid-treated animals would allow the earlier expression of malignant transformation in the large intestine

Sterol metabolism studies using a combination of isotopic and chromatographic procedures were carried out in two strains of rats fed 5% ethanol (36% of calories) in the diet. Feeding ethanol to the Fisher rat over 17 days produced no significant changes in body weight. Cholesterol levels in various tissues were elevated in the ethanol-fed group: plasma cholesterol, +61%; liver cholesterol, +47%; and bile cholesterol, +57%. The alcohol-fed Fisher rat showed several changes in sterol metabolism over controls: fecal acidic steroid output, +13%; fecal neutral sterol output, +51%; endogenous neutral sterol output, +107%; cholesterol turnover, +54%; and cholesterol balance, +18%. Ethanol feeding to the Sprague Dawley rat showed similar differences between ethanol-fed vs. control rats. Cholesterol levels were significantly elevated in plasma (+35%) and in the liver (+81%). Sterol metabolism data showed the following differences (alcohol vs. control): fecal acidic steroid output, +9%; fecal neutral sterol output, +17%; endogenous neutral sterol output, +72%; cholesterol turnover, +33%; and cholesterol balance +13%. The Fisher rat maintained almost constant weight throughout the experimental period and is a preferable strain for sterol balance studies using liquid diets. A major finding of these experiments was the increased concentration of cholesterol in liver, plasma, and bile in both strains of rats. The sterol balance measurements indicated that this tissue accumulation of cholesterol was due to enhanced cholesterol synthesis as well as inhibition of bile acid syntheses

Sterol metabolism studies using isotopic and chromatographic techniques were performed on rats fed diets supplemented with colestipol (Upjohn). Compared to controls, colestipol altered sterol metabolism dramatically. Bile acid output increased from 7.0 mg/day to 12.2 mg/day (0.42% colestipol) and 39.6 mg/day (1.67% colestipol). Daily fecal neutral sterol output and daily endogenous neutral sterol output increased 36% and 55%, respectively, on the 1.67% colestipol diet. Cholesterol absorption was reduced by colestipol feeding. Cholesterol balance increased dramatically with 1.67% colestipol administration (43.5 mg/day vs -1.0 mg/day in controls). Colestipol exerts its effect by binding bile acids and by bile acid depletion interfering with cholesterol absorption