Bone Loss in Diabetes: Use of Antidiabetic Thiazolidinediones and Secondary Osteoporosis

Clinical evidence indicates that bone status is affected in patients with type 2 diabetes mellitus (T2DM). Regardless of normal or even high bone mineral density, T2DM patients have increased risk of fractures. One class of antidiabetic drugs, thiazolidinediones (TZDs), causes bone loss and further increases facture risk, placing TZDs in the category of drugs causing secondary osteoporosis. Risk factors for development of TZD-induced secondary osteoporosis are gender (women), age (elderly), and duration of treatment. TZDs exert their antidiabetic effects by activating peroxisome proliferator-activated receptor-γ (PPAR-γ) nuclear receptor, which controls glucose and fatty acid metabolism. In bone, PPAR-γ controls differentiation of cells of mesenchymal and hematopoietic lineages. PPAR-γ activation with TZDs leads to unbalanced bone remodeling: bone resorption increases and bone formation decreases. Laboratory research evidence points toward a possible separation of unwanted effects of PPAR-γ on bone from its beneficial antidiabetic effects by using selective PPAR-γ modulators. This review also discusses potential pharmacologic means to protect bone from detrimental effects of clinically used TZDs (pioglitazone and rosiglitazone) by using combinational therapy with approved antiosteoporotic drugs, or by using lower doses of TZDs in combination with other antidiabetic therapy. We also suggest a possible orthopedic complication, not yet supported by clinical studies, of delayed fracture healing in T2DM patients on TZD therapy

Measurement of vitamin D levels in inflammatory bowel disease patients reveals a subset of Crohn’s disease patients with elevated 1,25-dihydroxyvitamin D and low bone mineral density

Objectives: Many patients with Crohn’s disease (CD) have low bone mineral density (BMD) that may not be solely attributable to glucocorticoid use. We hypothesised that low BMD in patients with CD is associated with elevated circulating levels of the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)(2)D). We further hypothesised that this was secondary to increased synthesis of 1,25(OH)(2)D by inflammatory cells in the intestine. The aim of this study was to examine the relationship between 1,25(OH)(2)D levels and BMD in patients with CD. Methods: An IRB approved retrospective review of medical records from patients with CD (n = 138) or ulcerative colitis (UC, n = 29). Measurements of vitamin D metabolites and immunoreactive parathyroid hormone (iPTH) were carried out. BMD results were available for 88 CD and 20 UC patients. Immunohistochemistry or real time reverse transcription-polymerase chain reaction (RT-PCR) for the enzyme 1α-hydroxylase was performed on colonic biopsies from patients with CD (14) or UC (12) and normal colons (4). Results: Inappropriately high levels of serum 1,25(OH)(2)D (>60 pg/ml) were observed in 42% of patients with CD compared with only 7% in UC, despite no differences in mean iPTH. Serum 1,25(OH)(2)D levels were higher in CD (57 pg/ml) versus UC (41 pg/ml) (p = 0.0001). In patients with CD, there was a negative correlation between 1,25(OH)(2)D levels and lumbar BMD (r = −0.301, p = 0.005) independent of therapeutic glucocorticoid use. 1,25(OH)(2)D levels also correlated with CD activity. Lastly, immunohistochemistry and RT-PCR demonstrated increased expression of intestinal 1α-hydroxylase in patients with CD. Conclusions: These data demonstrate that elevated 1,25(OH)(2)D is more common in CD than previously appreciated and is independently associated with low bone mineral density. The source of the active vitamin D may be the inflamed intestine. Treatment of the underlying inflammation may improve metabolic bone disease in this subgroup of patients