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Poorly controlled type 2 or non-insulin dependent diabetes mellitus (NIDDM) patients exhibit high bone turnover, which decelerate with treatment according to the degree of improvement in glycemic control. In adults, higher bone turnover results in rapid bone loss. Therefore, deceleration of bone turnover is beneficial for bone. Troglitazone (Tro), a new anti-diabetic drug, is a thiazolidinedione (TZD) which promotes adipocyte differentiation by activating peroxisome proliferator activated receptor gamma (PPARgamma). Because, in the bone marrow, adipocytes and osteoblasts originate in common mesenchymal stem cells that are also essential for osteoclastogenesis, TZDs may directly affect bone metabolism. Thus, we examined the effects of Tro on metabolic bone markers in type 2 DM patients. Tro (400 mg/day) was administered to 33 type 2 DM patients for four weeks. The day before and four weeks after starting Tro, serum and urine samples were collected after overnight fasting. Metabolic bone markers and glycemic indices were assessed. As bone resorption markers, urinary free and total deoxypyridinoline as well as urinary collagen type I C-terminal telopeptide were measured; as bone formation markers, serum bone type and total alkaline phosphatase (BALP and ALP) levels along with osteocalcin (OC) were used. No significant changes in fasting plasma glucose or HbA1c levels were observed in our short-term treatment with Tro. All the bone resorption markers, BALP and ALP were significantly decreased. OC was not significantly changed. The discrepant changes of OC from all the other metabolic bone markers suggest limitation of the use of OC as a reliable bone formation marker in diabetics. Our results that Tro decreased metabolic bone markers before significantly improving glucose metabolism suggest that it has direct effects on bone and decreased bone turnover. TZDs may spare bone mass in NIDDM subjects through its dual effects on glucose and bone metabolism.
Okazaki et al. (Fri,) studied this question.