Characterization of Enantiomeric Bile Acid-induced Apoptosis in Colon Cancer Cell Lines

Abstract

Bile acids are steroid detergents that are toxic to mammalian cells at high concentrations; increased exposure to these steroids is pertinent in the pathogenesis of cholestatic disease and colon cancer. Understanding the mechanisms of bile acid toxicity and apoptosis, which could include nonspecific detergent effects and/or specific receptor activation, has potential therapeutic significance. In this report we investigate the ability of synthetic enantiomers of lithocholic acid (ent-LCA), chenodeoxycholic acid (ent-CDCA), and deoxycholic acid (ent-DCA) to induce toxicity and apoptosis in HT-29 and HCT-116 cells. Natural bile acids were found to induce more apoptotic nuclear morphology, cause increased cellular detachment, and lead to greater capase-3 and -9 cleavage compared with enantiomeric bile acids in both cell lines. In contrast, natural and enantiomeric bile acids showed similar effects on cellular proliferation. These data show that bile acid-induced apoptosis in HT-29 and HCT-116 cells is enantiospecific, hence correlated with the absolute configuration of the bile steroid rather than its detergent properties. The mechanism of LCA-and ent-LCA-induced apoptosis was also investigated in HT-29 and HCT-116 cells. These bile acids differentially activate initiator caspases-2 and -8 and induce cleavage of full-length Bid. LCA and ent-LCA mediated apoptosis was inhibited by both pan-caspase and selective caspase-8 inhibitors, whereas a selective caspase-2 inhibitor provided no protection. LCA also induced increased CD95 localization to the plasma membrane and generated increased reactive oxygen species compared with ent-LCA. This suggests that LCA/ ent-LCA induce apoptosis enantioselectively through CD95 activation, likely because of increased reactive oxygen species generation, with resulting procaspase-8 cleavage.Bile acids are physiologic steroids that are necessary for the proper absorption of fats and fat-soluble vitamins. Their ability to aid in these processes is largely due to their amphipathic nature and thus their ability to act as detergents. Despite the beneficial effects, high concentrations of bile acids are toxic to cells (1-11).High fat western diets induce extensive recirculation of the bile acid pool, resulting in increased exposure of the colonic epithelial cells to these toxic steroids (12, 13). A high fat diet is also a risk factor for colon carcinogenesis; increased bile acid exposure is responsible for some of this risk. Bile acids can contribute to both colon cancer formation and progression, and their effects on colonic proliferation and apoptosis aid this process by disrupting the balance between cell growth and cell death, as well as helping to select for bile acid-resistant cells (14,15).In colonocyte-derived cell lines bile acid-induced apoptosis is thought to proceed through mitochondrial destabilization with resulting mitochondrial permeability transition formation and cytochrome c release as well as generation of oxidative stress (1, 9 -11). Bile acid-induced apoptosis has also ...

Deoxycholic and chenodeoxycholic bile acids induce apoptosis via oxidative stress in human colon adenocarcinoma cells

“…This behavior could be explained by the fact that, during the first hours of treatment, DCA and CDCA are able to trigger the apoptotic program, with the consequent cell detachment. The induction of cell detachment by bile acids in colon carcinoma cells has been previously reported for HCT-116 and HT-29 cells, and DAPI staining revealed apoptotic nuclear morphology in the detached cells [31]. The apparent decrease in the number of detached cells that we detect after 2 h is probably due to extensive cell damage or lysis, as we confirmed by the analysis of LDH activity into the culture medium.…”

“…Despite this beneficial property, their presence has been related with different cytotoxic effects [29,30], and these effects are highly stereospecific and enantiospecific [31]. Several studies are being carried out in vitro using cell cultures from colorectal carcinomas, mainly the tumorigenic HCT-116, HT-29 and Caco-2 cells.…”

“…In addition, it is generally assumed that their toxicity is strongly dependent on their hydrophobicity. It has been postulated that highly hydrophobic bile acids may diffuse through the plasma membrane and interact with DNA and/or intracellular molecules, causing DNA damage and triggering signaling cascades [31,32]. However, although bile acid uptake in hepatocytes is higher for hydrophobic bile acids, colon carcinoma cells behave differently.…”

Right Colon Carcinoma Infiltrating the Alimentary Limb in a Patient With Biliopancreatic Diversion

“…9 stimulation of mutation; induction of apoptosis in the short term [10][11][12] and selection for apoptosis resistance in the long term. 13 There is growing evidence that secondary bile acids, particularly deoxycholic and lithocholic acids, are potent colon-tumor promoters in humans.…”

Lithocholic acid is an endogenous inhibitor of MDM4 and MDM2

“…LCA is a secondary bile acid formed by bacteria in the gut from its precursor chenodeoxycholic acid (CDCA, Fig S1). It has been variously reported to show both carcinogenic and apoptotic activities (20,21). LCA is a rare example of a toxic endobiotic that is efficiently detoxicated by conjugation with taurine or glycine, sulfation at C-3 by the sulfotransferase SULT2A1, or metabolism through cytochrome P450 CYP3A enzymes (20).…”