Frequency-Dependent Effect of Nitric Oxide Donor Nitroglycerin on Bone

Abstract

Recently, we showed that supplementation with nitric oxide (NO) via donor nitroglycerin (NG) alleviated the ovariectomy and corticosteroid-induced bone loss in rats. In humans, high doses or frequent applications of NG (i.e., for angina) lead to rapid loss of its efficacy in relieving angina. To examine whether there is a similar effect on the loss of efficacy of NG on bone, we examined the frequency-dependent effects of NG on bone mineral density (BMD), bone mass, trabecular bone volumes (BV/TV), and blood pressure in rats. Thirty 7-month-old female Brown Norway rats underwent ovariectomy, and an additional six rats were shamoperated. The ovariectomized rats were treated either with vehicle (ovariectomized control), 17␤-estradiol (E 2 ; positive control), or 0.2 mg NG (via dermal application) once, twice, or three times a day. Before and at the end of the 10-week treatment period, BMD of the lumbar spine was measured by dual-energy X-ray absorptiometric (DXA) scanning and expressed as a percentage change. BMD in ovariectomized rats was significantly lower (؊2.5 ؎ 2.0%) compared with the sham-operated rats (؉6.3 ؎ 5.3%; p < 0.01). Estrogen therapy completely abolished the ovariectomy-induced potential bone loss (؉5.9 ؎ 3.4%). Application of NG once daily also completely prevented (؉6.2 ؎ 2.8%; p < 0.01) the ovariectomy-induced bone loss (i.e., it was as effective as estrogen). However, the beneficial effects of NG on BMD were significantly reduced with increased frequency of application of NG (؉1.9 ؎ 2.1%, twice a day and ؊0.2 ؎ 3.3% three times a day). Estrogen or once daily administration of NG preserved femur weights, BV/TV, and decreased urinary deoxypyridinoline levels as expected. However, a higher level of serum osteocalcin and bone-specific alkaline phosphatase levels were maintained only with once daily administration of NG. There were no adverse effects of these doses of NG on blood pressure, but a tendency to lower blood pressure was noticed with increased frequency of NG. These results confirmed our previous findings that NO donors counteract the bone loss associated with estrogen deficiency. However, these beneficial effects of maintaining BMD are lost with increased frequency of NG application. (J Bone Miner Res 2000;15:1119 -1125) Key words: bone mineral density, osteoporosis, postmenopausal bone loss, osteocalcin, estrogen, nitric oxide synthase.

RETRACTED ARTICLE: Nitrate use and changes in bone mineral density: the Canadian Multicentre Osteoporosis Study

“…At the time, we hypothesised that the greater effects among intermittent compared to daily users may be due to tachyphylaxis associated with daily nitrate use. Tachyphylaxis is commonly observed when treating patients with coronary heart disease with nitrates [20] and similar effects have been observed in ovariectomised rats in which the beneficial effects of nitrates on bone mass decrease with increasing frequency of application [21].…”

Signaling by mechanical strain involves transcriptional regulation of proinflammatory genes in human periodontal ligament cells in vitro

“…This is not surprising as a number of reports have recently shown that inhibitors of PGE 2 synthesis inhibit bone synthesis, implicating the requirement of PGE 2 in the initiation of bone repair. 5,8,11,27 For example, Chambers et al 5,8 showed that, during the initial transduction of mechanical signals, the presence of PGE 2 is essential to induce an osteogenic response during bone formation in vivo. Similarly, a transient increase in COX-2 expression at the initial stages of bone adaptation has been observed by Chow et al 8 and Turner et al 26 The present findings also suggest that the signals generated by physiologic or low levels of TENS may require activation of the proinflammatory signal transduction cascade to initiate osteoinduction.…”

“…5,8,11,27 This has been attributed mainly to the production of endothelial NOS (eNOS) in response to mechanical strain. 30 We observed that neither iNOS mRNA nor high levels of NO are induced by IL-1β in PDL cells.…”

Organic nitrates for osteoporosis: an update

“…Data from the cardiovascular literature report tachyphylaxis to nitrates with increasing frequency of dose 30 Tachyphylaxis to nitrates may develop in bone: rats given NTG ointment daily for 12 weeks had increases in BMD similar to those with estrogen, yet more frequent administration abolished any beneficial effects. 31 We compared hip and heel BMD among nitrate users (391 women) and nonusers (5827 women) identified by self-report. Women who reported using ISMO, isosorbide dinitrate, or NTG more than once a day, every day, were classified as continuous users (n ¼ 317), and all other women were classified as intermittent users (n ¼ 74).…”