Increased bone resorption and impaired bone microarchitecture in short-term and extended high-fat diet-induced obesity

Abstract

Although obesity traditionally has been considered a condition of low risk for osteoporosis, this classic view has recently been questioned. The aim of this study was to assess bone microarchitecture and turnover in a mouse model of high-fat diet-induced obesity. Seven-week-old male C57BL/6J mice (n = 18) were randomized into 3 diet groups. One third (n = 6) received a low-fat diet for 24 weeks, one third was kept on an extended high-fat diet (eHF), and the remaining was switched from low-fat to high-fat chow 3 weeks before sacrifice (sHF). Serum levels of insulin, leptin, adiponectin, osteocalcin, and cross-linked telopeptides of type I collagen (CTX) were measured. In addition, bone microarchitecture was analyzed by micro-computed tomography; and lumbar spine bone density was assessed by dual-energy x-ray absorptiometry. The CTX, body weight, insulin, and leptin were significantly elevated in obese animals (sHF: +48%, +24%, +265%, and +102%; eHF: +43%, +52%, +761%, and +292%). The CTX, body weight, insulin, and leptin showed a negative correlation with bone density and bone volume. Interestingly, short-term high-fat chow caused similar bone loss as extended high-fat feeding. Bone volume was decreased by 12% in sHF and 19% in eHF. Bone mineral density was 25% (sHF) and 27% (eHF) lower when compared with control mice on low-fat diet. As assessed by the structure model index, bone microarchitecture changed from plate- to rod-like appearance upon high-fat challenge. Trabecular and cortical thickness remained unaffected. Short-term and extended high-fat diet-induced obesity caused significant bone loss in male C57BL/6J mice mainly because of resorptive changes in trabecular architecture.

Fig. 1

Micro–computed tomography and DXA. The μCT-based cross section of fourth lumbar vertebral body representative per group (A-C), bone density as assessed by DXA (D), and bone volume as assessed by μCT (E). The asterisk (*) indicates a P value < .05.

Fig. 2

Bone microarchitecture. All parameters are μCT derived. The asterisk (*) indicates a P value < .05.

Fig. 3

Explanatory scheme for plate-to-rod transformation without decrease in trabecular thickness. Measurement of trabecular thickness is based on the most frequent diameter of a virtual ball fitting into trabecular structures. Plate-to-rod changes are captured by increases in the SMI. In our animal model, trabecular thickness still remained unchanged.