Type 2 diabetes is associated with increased fracture risk and the mechanisms underlying the detrimental effects of diabetes on skeletal health are only partially understood.
Antidiabetic drugs are indispensable for
glycemic control in most type 2 diabetics, however, they may, at least in part, modulate fracture risk in exposed patients. Preclinical and clinical data clearly demonstrate an unfavorable effect of
thiazolidinediones on the skeleton with impaired osteoblast function and activated osteoclastogenesis. The negative effect of
thiazolidinediones on osteoblastogenesis includes decreased activity of osteoblast-specific
transcription factors (e.g. Runx2, Dlx5, osterix) and decreased activity of osteoblast-specific signaling pathways (e.g. Wnt, TGF-β/BMP, IGF-1). In contrast,
metformin has a positive effect on osteoblast differentiation due to increased activity of Runx2 via the AMPK/USF-1/SHP regulatory cascade resulting in a neutral or potentially protective effect on bone. Recently marketed
antidiabetic drugs include
incretin-based
therapies (
GLP-1 receptor agonists,
DPP-4 inhibitors) and
sodium-
glucose co-transporter 2 (SGLT2)-inhibitors. Preclinical studies indicate that
incretins (GIP,
GLP-1, and GLP-2) play an important role in the regulation of bone turnover. Clinical safety data are limited, however, meta-analyses of trials investigating the glycemic-lowering effect of both,
GLP-1 receptor agonists and DPP4-inhibitors, suggest a neutral effect of
incretin-based
therapies on fracture risk. For SGLT2-inhibitors recent data indicate that due to their mode of action they may alter
calcium and
phosphate homeostasis (
secondary hyperparathyroidism induced by increased
phosphate reabsorption) and thereby potentially affect bone mass and fracture risk. Clinical studies are needed to elucidate the effect of SGLT2-inhibitors on bone metabolism. Meanwhile SGLT2-inhibitors should be used with caution in patients with high fracture risk, which is specifically true for the use of
thiazolidinediones.