Multimodal preclinical assessment of glucocorticoid-induced disruption of bone remodeling in Sprague-Dawley rats

Skeletal toxicity is a critical consideration during drug development arising from on-target mechanisms and off-target effects. Standard histopathology used in preclinical toxicity studies lacks sensitivity to detect subtle skeletal alterations. Early detection of bone changes is essential especially for compounds that may interfere with skeletal remodeling, growth, or maintenance. We characterized serum markers of bone formation and turnover (procollagen type I N-terminal propeptide and osteocalcin) and resorption (C-terminal telopeptide of type I collagen) across developmental age group (1 to 8 mo) in naïve Sprague-Dawley rats and evaluated marker responsiveness in a positive-control prednisolone model (2-mo-old rats dosed 14 or 28 d). Biomarkers were interpreted alongside histology, imaging by micro-computed tomography and dual-energy X-ray absorptiometry. Serum biomarkers of bone formation and resorption decreased with age, along with physiological growth plate thinning in naive rats. In prednisolone-treated rats, biomarkers decreased at 14 and 28 d of daily dosing; histology demonstrated reduced growth plate thickness, increased marrow adiposity, and imaging revealed alteration of trabecular microarchitecture and bone mineral density relative to controls. These data indicate that serum bone biomarkers are sensitive to both normal maturational change and pharmacologic suppression of remodeling, and these biomarker shifts correspond with skeletal toxicity, reflecting early structural deterioration induced by glucocorticoid exposure. We show that integrating serum biomarkers with histology and high-resolution imaging enhances early detection of skeletal toxicity in preclinical studies with compounds having known or expected bone effects based on their pharmacology and informs selection of serum sampling time frame and translational monitoring strategies using imaging.