Local osteogenic expression of cyclooxygenase-2 and systemic response in porcine models of osteomyelitis

It is suggested that cyclooxygenase 2 (COX-2) derived prostaglandins contributes to the progressive bone loss seen in osteomyelitis lesions. In the present study we examined the expression of COX-2 in bones from 23 pigs with experimental osteomyelitis. Osteomyelitis was induced with Staphylococcus aureus and groups of animals were euthanized following 6 h, 12 h, 24 h, 2 days, 5 days, 11 days and 15 days, respectively. Expression of COX-2 was evaluated immunohistochemically and combined with characterization of morphological changes in bone tissue. Furthermore, the serum concentrations of alkaline phosphatase and haptoglobin were measured. Extensive COX-2 expression by osteoblasts was present 2 days after inoculation together with many activated osteoclasts. Simultaneously, the serum concentration of alkaline phosphatase decreased whereas the haptoglobin concentration increased. This is the first in vivo study showing an early wave of COX-2 mediated bone resorption during osteomyelitis. Therefore, treatment aiming to reduce the break down of bone tissue directed by the COX-2 pathway might be suggested early in the course of the disease.

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► We examined the expression of cyclooxygenase-2 (COX-2) in bones with osteomyelitis.
► Extensive COX-2 expression was seen in osteoblasts during the initial phase of inflammation.
► Increased bone resorption by osteoclasts was combined with the presence of COX-2 positive osteoblasts.
► Initially serum concentrations of alkaline phosphatase decreased and haptoglobin increased.
► COX-2 is involved in the bone loss seen in osteomyelitis.