The role of the endothelial cell in secreting the important local regulatory substances that control the vascular system has been established for many years [1, 2]. The cells produce several smooth muscle relaxing factors such as nitric oxide (NO), which is derived from the transformation of the amino acid L-arginine by the activity of NO synthase (NOS). As well as the beneficial effects for the vascular system, [i]in vitro[/i] and [i]in vivo[/i] data have revealed the efficacy of nitroglycerine and nitrates on bone cells . NO has a stimulatory effect on osteoblasts and bone formation with concomitant inhibition of osteoclastic bone resorption [1, 2]. It also has been proven that some of the effects of estrogen in bone are mediated via the NO pathway. Several animal studies consistently support this theory. Indeed, a body of evidence taken from a variety of animal studies has shown that NO donor therapy could prevent ovariectomy-induced as well as corticosteroid-induced bone loss [2–4]. If this is the case, it seems that NO/nitroglycerine therapy may become an affordable and cost-effective option for preventing and treating osteoporosis. Unfortunately, not all human studies have shown the same positive result [2–6].
One of the recent papers published by Wimalawansa and colleagues has reported on the use of transdermal nitroglycerine in postmenopausal women . This single-center, randomized, double-blind, placebo-controlled clinical trial was intended to compare the effect of a NO donor compound, 2% nitroglycerine ointment, with placebo. The primary endpoint was the percentage change in lumbar vertebrae bone mineral density (BMD) from baseline to 36 months. The secondary endpoints were the changes in hip BMD, total body bone mineral content and height.
Inclusion criteria were: lumbar spine [i]T[/i] score of 0 to -2.5 (0 to -2.0 for women aged 61–65 years); level of 25-hydroxyvitamin D > 15 ng/ml; body mass index of 18–32 kg/m[+]2[/+]; and achieving the prerequisite compliance with calcium and vitamin D therapy during the run-in period. Exclusion criteria were: prior spine or hip fracture; cardiac or coronary artery disease requiring medication; abnormal hepatic or renal function; metabolic bone diseases other than postmenopausal osteopenia; insulin-dependent diabetes mellitus; severe hypertension; significant migraine headaches; history of renal calculi or cancer. Participants taking the following medications were also excluded or required to undergo a wash-out period: bisphosphonates, hormone therapy, raloxifene, calcitonin, routine use of nitrates, corticosteroids and estrogen.
A total of 186 women were randomized to the study. At the end of the study, 88 participants remained in the active arm and 83 remained in the placebo arm. Participants were randomly assigned to receive either active 22.5 mg/day nitroglycerine 2% or placebo ointment and were studied for 36 months.
The result showed no significant difference for primary efficacy outcomes: at the end of study, a -2.1% (95% confidence interval (CI) -3.1 to -1.0%) change in lumbar spine BMD in the active group and a -2.5% (95% CI -3.6 to -1.4%) change in the placebo group from baseline were seen ([i]p[/i] = 0.59). It should be noted that there were no significant treatment arm differences for any absolute BMD measurements at 36 months as well as percentage change from baseline measurements at 36 months. The active group reported more headaches compared to the placebo group ([i]p[/i] = 0.001). Other serious adverse effects were not different between the two groups.
The authors conclude that a 3-year evaluation using randomized, controlled trial methodology did not support the effectiveness of the NO donor nitroglycerine in preventing postmenopausal decreases in BMD. Nevertheless, based on the data collected from three previous clinical studies using the nitrate product, which demonstrated a positive effect on BMD as well as bone turnover, the authors still believe that further research using higher doses of NO donor is warranted before discarding this as a novel therapy for osteoporosis.
M. Sjarief Darmasetiawan
Senior Lecturer, Division of Reproductive Endocrinology & Fertility, Department of Obstetrics & Gynecology, Gatot Soebroto Central Army Hospital, Pembangunan National University, Indonesia
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Wimalawansa SJ, Grimes SJ, Grimes JP, Wilson AC, Hoover DR. Transdermal nitroglycerin therapy may not prevent early postmenopausal bone loss. J Clin Endocrinol Metab 2009,94:3356-64. Published September 2009.
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