Interferon-α, unlike interferon-γ, does not cause bone loss in the rat

Interferons (IFN) are a group of related glycoproteins. IFN-γ, in vitro, has been shown to inhibit resorption; however, an in vivo experiment showed that it had the opposite effect, resulting in bone loss that was comparable to that caused by cyclosporine A. IFN-α has numerous clinical applications but is used most extensively in the treatment of chronic hepatitis B and chronic hepatitis C. Research into the effects of IFN-α on bone mineral metabolism has been very sparse, and the majority of studies reflect in vitro models. Like IFN-γ, there exists discordance between in vitro and in vivo studies on IFN-α. Both in vivo and in vitro studies demonstrate that IFN-α decreases bone resorption, whereas osteoblasts may or may not be affected in vivo. This study was designed to provide information on the in vivo effects of IFN-α in the rat model, because we feel that, given its widespread clinical use, this is an extremely important issue. Rats were given low dose IFN-α (1.6 × 106 IU/m2), intermediate dose IFN-α (5.35 × 106 IU/m2), and high dose IFN-α (30 × 106 IU/m2) three times per week for 28 days. Serum osteocalcin (bone gla protein, or BGP) and parathyroid hormone (PTH) were measured serially and, after double labeling, the bones were examined histomorphometrically. IFN-α did not alter any of the histomorphometric parameters measured and did not affect PTH. However, it produced a disparate BGP response. Low dose IFN-α resulted in a statistically significant increase in serum BGP on days 14 and 28, whereas intermediate and high doses of IFN-α did not. Overall, these results provide no evidence of a deleterious effect of IFN-α on bone metabolism and confirm the limited clinical study.