Phenobarbital and 3-methylcholanthrene treatment alters phase I and II enzymes and the sensitivity of the rat colon to the carcinogenic activity of azoxymethane

Chemopreventive effect of sinapic acid on 1,2-dimethylhydrazine-induced experimental rat colon carcinogenesis

Sinapic acid (SA) is a naturally occurring phenolic acid found in various herbal plants which is attributed with numerous pharmacological properties. This study was aimed to investigate the chemopreventive effect of SA on 1,2-dimethylhydrazine (DMH)-induced rat colon carcinogenesis. Rats were treated with DMH injections (20 mg kg(-1) bodyweight (b.w.) subcutaneously once a week for the first 4 consecutive weeks and SA (20, 40 and 80 mg kg(-1) b.w.) post orally for 16 weeks. At the end of the 16-week experimental period, all the rats were killed, and the tissues were evaluated biochemically. Our results reveal that DMH alone treatment decreased the levels/activities of lipid peroxidation by-products such as thiobarbituric acid reactive substances, conjugated dienes and antioxidants such as superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase and reduced glutathione in the intestine and colonic tissues which were reversed on supplementation with SA. Moreover, the activities of drug-metabolizing enzymes of phase I (cytochrome P450 and P4502E1) were enhanced and those of phase II (glutathione-S-transferase, DT-diaphorase and uridine diphosphate glucuronosyl transferase) were diminished in the liver and colonic mucosa of DMH alone-treated rats and were reversed on supplementation with SA. All the above changes were supported by the histopathological observations of the rat liver and colon. These findings suggest that SA at the dose of 40 mg kg(-1) b.w. was the most effective dose against DMH-induced colon carcinogenesis, and thus, SA could be used as a potential chemopreventive agent.

Differentiating stem cells into liver

Research involving differentiated embryonic stem (ES) cells may revolutionize the study of liver disease, improve the drug discovery process, and assist in the development of stem-cell-based clinical therapies. Generation of ES cell-derived hepatic tissue has benefited from an understanding of the cytokines, growth factors and biochemical compounds that are essential in liver development, and this knowledge has been used to mimic some aspects of embryonic development in vitro. Although great progress has been made in differentiating human ES cells into liver cells, current protocols have not yet produced cells with the phenotype of a mature hepatocyte. There is a significant need to formally establish criteria that would define what constitutes a functional human stem cell-derived hepatocyte. Here, we explore current challenges and future opportunities in development and use of ES cell-derived liver cells. ES-derived hepatocytes could be used to better understand liver biology, begin the process of "personalizing" health care, and to treat some forms of liver disease.

Hepatic stem cells and liver development

The liver consists of many cell types with specialized functions. Hepatocytes are one of the main players in the organ and therefore are the most vulnerable cells to damage. Since they are not everlasting cells, they need to be replenished throughout life. Although the capacity of hepatocytes to contribute to their own maintenance has long been recognized, recent studies have indicated the presence of both intrahepatic and extrahepatic stem/progenitor cell populations that serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults.The intrahepatic compartment most likely derives primarily from the biliary tree, particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extrahepatic compartment is at least in part derived from diverse populations of cells from the bone marrow. Embryonic stem cells (ES's) are considered as a part of the extrahepatic compartment. Due to their pluripotent capabilities, ES cell-derived cells form a potential future source of hepatocytes, to replace or restore hepatic tissues that have been damaged by disease or injury. Progressing knowledge about stem cells in the liver would allow a better understanding of the mechanisms of hepatic homeostasis and regeneration. Although a human stem cell-derived cell type equivalent to primary hepatocytes does not yet exist, the promising results obtained with extrahepatic stem cells would open the way to cell-based therapy for liver diseases.

Modulatory efficacy of hesperetin (citrus flavanone) on xenobiotic-metabolizing enzymes during 1,2-dimethylhydrazine-induced colon carcinogenesis

Colorectal cancer is the second leading cause of cancer death worldwide with diet playing a prominent role in disease initiation and progression. Diet and nutrition play an important role during this multistep colon carcinogenic process. We have investigated the modulatory efficacy of hesperetin on aberrant crypt foci (ACF) and xenobiotic-metabolizing enzymes on 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis. Male albino Wistar rats were randomly divided into six groups. Group 1 served as control, received modified pellet diet and group 2 rats received 20mg/kg body weight of hesperetin p.o. every day. Groups 3-6 rats were given subcutaneous injections of 1,2-dimethylhydrazine (20mg/kg body weight) once a week for 15 weeks to induce ACF in the colon. In addition, rats in group 4 received hesperetin as in group 2 orally for the first 15 weeks (initiation), group 5 rats received hesperetin as in group 2 after the last injection of DMH and continued till the end of the experimental period (post-initiation). Group 6 received hesperetin as in group 2 throughout the entire period of 32 weeks. DMH exposure showed high incidence (90%) of ACF (280+/-24.5 aberrant crypt/colon) and dysplastic ACF, elevated activities of phase I enzymes and reduced the activities of phase II enzymes in the liver and colonic mucosa of colon cancer bearing rats. Hesperetin supplementation significantly reversed these effects, the effect being more pronounced in group 6 rats (hesperetin supplemented throughout the study period). These findings suggest that hesperetin can significantly reduce the formation of preneoplastic lesions and effectively modulate the xenobiotic-metabolizing enzymes in rats.

Generation of human hepatocytes by stem cell technology: definition of the hepatocyte

Since 1999, numerous articles have reported the generation of hepatocytes from different types of extrahepatic stem or precursor cells. This opens exciting new possibilities for pharmacology and toxicology, as well as for cell therapy. Hepatocyte marker expression, including albumin, cytokeratin 18, c-met, alpha-fetoprotein and cytochrome P450 3A4 and -2B6, has been observed after transplantation of different types of human stem cells into the liver of laboratory animals or in vitro after incubation with cytokines. These intriguing observations have prompted scientists to classify stem cell-derived cell populations as hepatocytes. However, this conclusion may be premature. It has been shown that factors of the liver microenvironment can induce expression of a limited number of hepatocyte marker genes in nonhepatic cell types. To conclude on the grounds of a limited number of markers that these cells are true hepatocytes is not indicated. In this case one should carefully evaluate crucial hepatocyte-defining enzymatic properties. The present article: i) reviews studies describing the fate of extrahepatic human stem and precursor cells in livers of laboratory animals, including the possibility of cell fusion; and ii) critically discusses the phenotype of stem cells after application of various differentiation protocols aimed at generating human hepatocytes. In addition, the necessary criteria needed for defining a true hepatocyte are suggested. Establishing the necessary properties for stem cell-derived hepatocytes is timely and reasonable, and thus avoids further misleading semantic confusion. Finally, it is essential to understand that the definition of a bona fide hepatocyte should not be limited to qualitative assays, such as reverse transcriptase polymerase chain reaction and immunohistochemistry, but has to include a quantitative analysis of enzymatic activities, which allows direct comparison with primary hepatocytes. Although the stem cell-derived-hepatocyte does not yet exist there is a good chance that this aim may be achieved in the future.

Most effective colon cancer chemopreventive agents in rats: a systematic review of aberrant crypt foci and tumor data, ranked by potency

Potential chemopreventive agents for colorectal cancer are assessed in rodents. We speculated that the magnitude of the effect is meaningful and ranked all published agents according to their potency. Data were gathered systematically from 137 articles with the aberrant crypt foci (ACF) end point and from 146 articles with the tumor end point. The potency of each agent to reduce the number of ACF is listed in one table and the potency of each agent to reduce the tumor incidence in another table. Both tables are shown in this review and on a website with sorting abilities (http://www.inra.fr/reseau-nacre/sci-memb/corpet/indexan.html). Potency was estimated as the ratio of the value in control rats to the value in treated rats. From each article, only the most potent agent was kept, except in articles reporting the effect of more than seven agents. Among the 186 agents in the ACF table, the median agent reduced the number of ACF by one-half. The most potent agents to reduce azoxymethane-induced ACF were Pluronic, polyethylene glycol, perilla oil with beta-carotene, and sulindac sulfide. Among the 160 agents in the tumor table, the median agent reduced the tumor incidence in rats by one-half. The most potent agents to reduce the incidence of azoxymethane-induced tumors were celecoxib, a protease inhibitor from soy, difluoromethylornithine with piroxicam, polyethylene glycol, and a thiosulfonate. For the 57 agents present in both tables, a significant correlation (r) was found between the potencies against ACF and tumors (r = 0.45, P < 0.001); without celecoxib, a major outlying point in the correlation, r = 0.68 (P < 0.001, n = 56). In conclusion, this review gathers most known chemopreventive agents, ranks the most promising agents against colon carcinogenesis in rats or mice, and further supports the use of ACF as a surrogate end point for tumors in rats.

Comparative effects of secondary bile acids, deoxycholic and lithocholic acids, on aberrant crypt foci growth in the postinitiation phases of colon carcinogenesis

The objective of this study was to investigate the effect of deoxycholic (DCA) and lithocholic (LCA) acids on the postinitiation phases of colon cancer. Male Sprague-Dawley rats (n = 170) were injected with azoxymethane (2 injections at 15 mg/kg body wt sc given 1 wk apart) and fed a control (CON) AIN-93 diet. Two weeks after the second azoxymethane injection, 10 animals were killed and aberrant crypt foci (ACF) were enumerated. The remaining animals were randomly assigned to four diet groups: 1) CON, 2) DCA, 3) LCA, and 4) high fat (HF, a positive control group). Bile acid diets consisted of 0.2% by weight DCA or LCA; HF diets consisted of 20% fat (5% soybean oil + 15% beef tallow by weight). Animals were killed at Weeks 3, 12, and 20 (from 1st carcinogen injection), and number and growth features of ACF and adenomatous lesions were enumerated in the colon. At Week 12, ACF number and small, medium, and large (1-3, 4-6, and > or = 7 crypts/focus, respectively) ACF were higher in the HF group than in the DCA, LCA, and CON groups (p < or = 0.05). By Week 20, ACF number and small, medium, and large ACF were similar in the LCA and HF groups, whereas the response was similar in the DCA and CON groups. Average crypt multiplicity was higher in the HF and LCA groups than in the DCA and CON groups (p < or = 0.05). Microadenoma (MA) incidence was higher in the HF group than in the CON and LCA groups (p < or = 0.05). Regional distribution patterns for ACF number were similar to MA and tumor distribution patterns within the CON, DCA, and HF groups. In the LCA group, ACF number and MA showed a proximal predominance in regional distribution, whereas tumors showed a distal predominance. HF diets provided the most stimulatory environment, immediately enhancing the number and growth of ACF and MA incidence. In conclusion, HF and LCA diets exerted distinct effects on postinitiation phases of colon cancer, whereas the DCA diet did not.

Modulation of colonic xenobiotic metabolizing enzymes by feeding bile acids: comparative effects of cholic, deoxycholic, lithocholic and ursodeoxycholic acids

Primary and secondary bile acids such as cholic (CHA), deoxycholic (DCA) and lithocholic (LCA) acids have been shown to increase colon tumorigenesis. It has been suggested that inhibition of xenobiotic metabolizing enzymes such as glutathione S-transferase (GST) and UDP-glucuronyltransferase (UGT) by bile acids may be a factor in the development of colon cancer. While enzyme inhibition has been demonstrated in vitro, it is unclear whether feeding bile acids modulates colonic GST and UGT in vivo. To test this notion, male, Sprague-Dawley rats (n = 100) were assigned to a control (CON) or test diets containing 0.2% CHA, DCA, LCA or ursodeoxycholic acid (UDCA). After 5 weeks, colonic tissue was harvested and used for enzyme and cell proliferation measurements. The response to bile acids varied with the enzyme measured and appeared isoenzyme specific. GST-alpha activity was lower in the bile acid fed groups compared with CON. While GST-mu was lower in the LCA-fed group, GST-pi was lower in the DCA-, CHA- and UDCA-fed groups. Unlike GST, both UGT and NADPH-cytochrome P-450 reductase (CYC) activities were increased by bile acids. The proliferative response of the colonic epithelium varied with the bile acids and was regionally specific. These data demonstrate that feeding bile acids alters the activity of colonic phase I and II enzymes; however, the physiological effect of these enzymatic perturbations is yet to be determined.