title: Differential accumulation of lead and zinc in double-tidemarks of articular cartilage.
abstract: BACKGROUND
  Long-term exposure to increased lead (Pb) concentrations is associated with several chronic diseases. The divalent cation zinc (Zn) is essential for numerous enzymes. In a recent study we found remarkably elevated concentrations of Pb and Zn in the tidemark (TM), which is the mineralization front of human articular cartilage.
  
  
  OBJECTIVE
  Duplication or multiplication of TMs occurs with advancing age or degeneration. We hypothesized that trace elements accumulate in TMs as a function of time. Thus, in cases of double TMs, the deep (older) TM should contain higher Pb and Zn concentrations than the superficial (younger) TM.
  
  
  METHODS
  Undecalcified tissue from articular cartilage and subchondral bone of femoral heads and patellae was examined by synchrotron radiation induced confocal micro X-ray fluorescence analysis and by quantitative backscattered electron imaging to determine the local distribution of Ca, Zn, and Pb in this tissue.
  
  
  RESULTS
  The evaluation of X-ray fluorescence intensities in double TMs revealed in average a 2.6-fold higher Pb level in the deep TM compared to the superficial TM while Zn concentrations were similar. Pb and Zn contents were significantly enhanced in the deep TM (Pb: 35-fold, Zn: five-fold) and in the superficial TM (Pb: 12-fold, Zn: five-fold) compared to the bone level.
  
  
  CONCLUSIONS
  For the first time a differential accumulation of Pb and Zn is documented in regions with double TMs revealing various timescales for the accumulation of these elements. Increased amounts of Pb are present in the TMs (up to the 62-fold of the bone level) featuring a potential source of internal Pb release if the TM region is destroyed.
authors.affiliation: Ludwig Boltzmann Institute of Osteology at the Hanusch Hospital of WGKK and AUVA Trauma Centre Meidling, 1st Medical Department, Hanusch Hospital, Vienna, Austria; Atominstitut, Technische Universitaet Wien, Stationallee 2, 1020 Vienna, Austria. Electronic address: andreas.roschger@osteologie.at.
authors.forename: A
authors.initials: A
authors.lastname: Roschger
authors.forename: J G
authors.initials: JG
authors.lastname: Hofstaetter
authors.forename: B
authors.initials: B
authors.lastname: Pemmer
authors.forename: N
authors.initials: N
authors.lastname: Zoeger
authors.forename: P
authors.initials: P
authors.lastname: Wobrauschek
authors.forename: G
authors.initials: G
authors.lastname: Falkenberg
authors.forename: R
authors.initials: R
authors.lastname: Simon
authors.forename: A
authors.initials: A
authors.lastname: Berzlanovich
authors.forename: H W
authors.initials: HW
authors.lastname: Thaler
authors.forename: P
authors.initials: P
authors.lastname: Roschger
authors.forename: K
authors.initials: K
authors.lastname: Klaushofer
authors.forename: C
authors.initials: C
authors.lastname: Streli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002358:Cartilage, Articular / Q000378:metabolism*; D005260:Female; D005270:Femur Head / Q000378:metabolism; D006801:Humans; D007854:Lead / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000378:metabolism; D010329:Patella / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D015032:Zinc / Q000378:metabolism*
chemical_list: D007854:Lead; D015032:Zinc
keywords: Cartilage; Lead; Quantitative backscattered electron imaging; Synchrotron radiation induced confocal micro X-ray fluorescence analysis; Tidemark; Trace elements; Zinc