| Lead Exposure Inhibits Fracture Healing and Is Associated with Increased Chondrogenesis, Delay in Cartilage Mineralization, and a Decrease in Osteoprogenitor Frequency Jonathan J. Carmouche,1 J. Edward Puzas,1 Xinping Zhang,1 Prarop Tiyapatanaputi,1 Deborah A. Cory-Slechta,2 Robert Gelein,2 Michael Zuscik,1 Randy N. Rosier,1 Brendan F. Boyce,1 Regis J. O'Keefe,1 and Edward M. Schwarz1 1Center for Musculoskeletal Research, University of Rochester Medical Center and 2Department of Environmental Medicine, University of Rochester, School of Medicine and Dentistry, Rochester, New York, USA Abstract
Lead exposure continues to be a significant public health problem. In addition to acute toxicity, Pb has an extremely long half-life in bone. Individuals with past exposure develop increased blood Pb levels during periods of high bone turnover or resorption. Pb is known to affect osteoblasts, osteoclasts, and chondrocytes and has been associated with osteoporosis. However, its effects on skeletal repair have not been studied. We exposed C57/B6 mice to various concentrations of Pb acetate in their drinking water to achieve environmentally relevant blood Pb levels, measured by atomic absorption. After exposure for 6 weeks, each mouse underwent closed tibia fracture. Radiographs were followed and histologic analysis was performed at 7, 14, and 21 days. In mice exposed to low Pb concentrations, fracture healing was characterized by a delay in bridging cartilage formation, decreased collagen type II and type X expression at 7 days, a 5-fold increase in cartilage formation at day 14 associated with delayed maturation and calcification, and a persistence of cartilage at day 21. Fibrous nonunions at 21 days were prevalent in mice receiving very high Pb exposures. Pb significantly inhibited ex vivo bone nodule formation but had no effect on osteoclasts isolated from Pb-exposed animals. No significant effects on osteoclast number or activity were observed. We conclude that Pb delays fracture healing at environmentally relevant doses and induces fibrous nonunions at higher doses by inhibiting the progression of endochondral ossification. Key words: endochondral ossification, fracture healing, lead, osteoblast, osteoclast, Pb, Pb toxicity. Environ Health Perspect 113: 749-755 (2005) . doi:10.1289/ehp.7596 available via http://dx.doi.org/ [Online 14 March 2005]
Address correspondence to E.M. Schwarz, Center for Musculoskeletal Research, University of Rochester Medical Center, 601 Elmwood Ave., Box 665, Rochester, NY 14642 USA. Telephone: (585) 275-3063. Fax: (585) 756-4721. E-mail: Edward_Schwarz@URMC.Rochester.Edu We thank J. Harvey and B. Stroyer for assistance with histology. This work was supported by Public Health Service grants NIH PO1 ES011854 and NIH P30 ES01247. The authors declare they have no competing financial interests. Received 21 September 2004 ; accepted 14 March 2005.
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