title: Docosahexaenoic acid and butyrate synergistically induce colonocyte apoptosis by enhancing mitochondrial Ca2+ accumulation.
abstract: We have previously shown that butyrate, a short-chain fatty acid fiber fermentation product, induces colonocyte apoptosis via a nonmitochondrial, Fas-mediated, extrinsic pathway. Interestingly, fermentable fiber when combined with fish oil containing docosahexaenoic acid (DHA, 22:6n-3) exhibits an enhanced ability to induce apoptosis and protect against colon tumorigenesis. To determine the molecular mechanism of action, the effect of DHA and butyrate cotreatment on intracellular Ca2+ homeostasis was examined. Mouse colonocytes were treated with 50 micromol/L DHA or linoleic acid (LA) for 72 h +/- butyrate (0-10 mmol/L) for the final 24 h. Cytosolic and mitochondrial Ca2+ levels were measured using Fluo-4 and Rhod-2. DHA did not alter basal Ca2+ or the intracellular inositol trisphosphate (IP3) pool after 6 h butyrate cotreatment. In contrast, at 12 and 24 h, DHA- and butyrate-treated cultures exhibited a 25% and 38% decrease in cytosolic Ca2+ compared with LA and butyrate. Chelation of extracellular Ca2+ abolished the effect of thapsigargin on the IP3-releasable Ca2+ pool. DHA and butyrate cotreatment compared with untreated cells increased the mitochondrial-to-cytosolic Ca2+ ratio at 6, 12, and 24 h by 73%, 18%, and 37%, respectively. The accumulation of mitochondrial Ca2+ preceded the onset of apoptosis. RU-360, a mitochondrial-uniporter inhibitor, abrogated mitochondrial Ca2+ accumulation and also partially blocked apoptosis in DHA and butyrate cotreated cells. Collectively, these data show that the combination of DHA and butyrate, compared with butyrate alone, further enhances apoptosis by additionally recruiting a Ca2+ -mediated intrinsic mitochondrial pathway.
authors.affiliation: Faculty of Nutrition, Texas A&M University, College Station, Texas 77843-2253, USA.
authors.forename: Satya Sree N
authors.initials: SS
authors.lastname: Kolar
authors.forename: Rola
authors.initials: R
authors.lastname: Barhoumi
authors.forename: Joanne R
authors.initials: JR
authors.lastname: Lupton
authors.forename: Robert S
authors.initials: RS
authors.lastname: Chapkin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002087:Butyrates / Q000493:pharmacokinetics / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D003106:Colon / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004281:Docosahexaenoic Acids / Q000493:pharmacokinetics / Q000494:pharmacology*; D004357:Drug Synergism; D006706:Homeostasis / Q000187:drug effects; D019787:Linoleic Acid / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D017975:Ruthenium Compounds / Q000494:pharmacology
chemical_list: D002087:Butyrates; D002121:Calcium Channel Blockers; D015220:Calcium Channels; C112020:Ru 360; D017975:Ruthenium Compounds; C034703:mitochondrial calcium uniporter; D004281:Docosahexaenoic Acids; D019787:Linoleic Acid; D002118:Calcium