Chronic alcohol consumption during male rat adolescence impairs skeletal development through effects on osteoblast gene expression, bone mineral density, and bone strength

Background: The effect of chronic alcohol ingestion on bone formation is me diated through its direct actions on osteoblasts. The affected population o f mature osteoblasts declines in both number and function resulting in decr eased cancellous bone volume and cortical bone strength. Although the mecha nism of action on osteoblasts is unknown, alcohol alters osteoblast gene ex pression and matrix synthesis. Methods: Male rats consuming alcohol (EtOH) daily for 60 days from 35 days of age until 95 days of age (unrecovered group) were compared to rats switc hed to a regular diet of rat chow without EtOH for an additional 90 days (r ecovered group). The effects of chronic dietary EtOH on skeletal developmen t during adolescence were examined in the unrecovered and recovered rats by hormonal analysis, bone mineral density determination, bone histomorphomet ry, metaphyseal gene expression for osteoblast-specific proteins, and biome chanical analysis. Results: The unrecovered EtOH imbibing rats weighed less than their paired isocaloric-fed and ad libitum mates. Statistically significant reductions o ccurred in femur lengths in the unrecovered EtOH-fed group compared to cont rols. Serum testosterone levels were significantly decreased by EtOH consum ption but returned to higher normal levels during the recovery period. Seru m insulin-like growth factor-1 (IGF-I) levels were unaffected by EtOH. Seru m osteocalcin levels in the unrecovered EtOH-fed group were higher than tho se in the recovered group but EtOH intake did not elevate the unrecovered l evels compared to isocaloric or ad libitum control rats. Quantitative compu ted tomography (QCT) determination of bone mineral density (BMD) revealed a statistically significant reduction only in the distal femur metaphysis in the unrecovered EtOH-fed rats. BMD increased during recovery in the distal femur metaphysis and femur mid-cortex. Image analysis of midsagittal secti ons of the proximal tibial metaphysis of unrecovered rats revealed reductio ns in cancellous area, trabecular cellularity and thickness, and increased trabecular separation. Cortical widths were significantly reduced by chroni c EtOH consumption. These changes remained statistically significant at the end of the recovery period. Four-point biomechanical testing of femurs fro m EIOH-fed and control unrecovered groups revealed significant reductions i n cortical strength, energy-to-failure, and stiffness. These cortical chara cteristics returned to normal values with abstinence. Tibial metaphyseal al pha-1 type I collagen and osteocalcin mRNA expression levels were significa ntly elevated above the paired isocaloric control levels after 60 days of E tOH consumption. Metaphyseal alkaline phosphatase mRNA levels remained unal tered by EtOH consumption in the unrecovered group. After 90 days of abstin ence alpha-1 type I collagen and alkaline phosphatase gene expression level s remained significantly elevated over the isocaloric and ad libitum contro l levels (collagen) and the isocaloric control value (alkaline phosphatase) . However, metaphyseal osteocalcin mRNA levels declined to normal levels du ring abstinence. Conclusions: Chronic consumption of EtOH during the peripubertal period of skeletal growth leads directly to decreased meraphyseal and cortical bone m ediated through effects on osteoblasts. Removal of EtOH from the diet is ac companied by incomplete restoration of normal bone metabolism during skelet al growth.