title: Indoxyl sulfate promotes apoptosis in cultured osteoblast cells.
abstract: BACKGROUND
  Indoxyl sulfate (IS), an organic anion uremic toxin, promotes the progression of renal dysfunction. Some studies have suggested that IS inhibits osteoclast differentiation and suppresses parathyroid hormone (PTH)-stimulated intracellular cAMP production, decreases PTH receptor expression, and induces oxidative stress in primary mouse calvaria osteoblast cell culture. However, the direct effects of IS on osteoblast apoptosis have not been fully evaluated. Hence, we investigated whether IS acts as a bone toxin by studying whether IS induces apoptosis and inhibits differentiation in the cultured osteoblast cell line MC3T3-E1.
  
  
  METHODS
  We assessed the direct effect of IS on osteoblast differentiation and apoptosis in the MC3T3-E1 cell line. We examined caspase-3/7 activity, apoptosis-related proteins, free radical production, alkaline phosphatase activity, and mRNA expression of type 1 collagen and osteonectin. Furthermore, we investigated the uptake of IS via organic anion transport (OAT).
  
  
  RESULTS
  We found that IS increased caspase activity and induced apoptosis. Production of free radicals increased depending on the concentration of IS. Furthermore, IS inhibited the expression of mRNA type 1 collagen and osteonectin and alkaline phosphatase activity. The expression of OAT, which is known to mediate the cellular uptake of IS, was detected in in the MC3T3-E1 cell line. The inhibition of OAT improved cell viability and suppressed the production of reactive oxygen species. These results suggest that IS is transported in MC3T3-E1 cells via OAT, which causes oxidative stress to inhibit osteoblast differentiation.
  
  
  CONCLUSIONS
  IS acts as a bone toxin by inhibiting osteoblast differentiation and inducing apoptosis.
authors.forename: Young-Hee
authors.initials: YH
authors.lastname: Kim
authors.forename: Kyung-Ah
authors.initials: KA
authors.lastname: Kwak
authors.affiliation: Department of Internal Medicine, Soonchunhyang University Cheonan Hospital, 31 Soonchunhyang 6gil, Dongnam-gu, Cheonan, Chungnam 330-721, Korea. hwgil@schmc.ac.kr.
authors.forename: Hyo-Wook
authors.initials: HW
authors.lastname: Gil
authors.forename: Ho-Yeon
authors.initials: HY
authors.lastname: Song
authors.forename: Sae-Yong
authors.initials: SY
authors.lastname: Hong
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D024042:Collagen Type I / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005609:Free Radicals / Q000378:metabolism; D007200:Indican / Q000633:toxicity*; D051379:Mice; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D010012:Osteogenesis / Q000187:drug effects*; D015676:Osteonectin / Q000235:genetics; D018384:Oxidative Stress / Q000187:drug effects; D014511:Uremia / Q000378:metabolism
chemical_list: D024042:Collagen Type I; D005609:Free Radicals; D027361:Organic Anion Transporters; D015676:Osteonectin; D007200:Indican