Potentiation of osteoclast bone-resorption activity by inhibition of nitric oxide synthase.

Abstract

We have examined the effects of modulating nitric oxide (NO) levels on osteoclast-mediated bone resorption in vitro and the effects of nitric oxide synthase (NOS) inhibitors on bone mineral density in vivo. Diaphorase-based histochemical staining for NOS activity of bone sections or highly enriched osteoclast cultures suggested that osteoclasts exhibit substantial NOS activity that may account for basal NO production. Chicken osteoclasts were cultured for 36 hr on bovine bone slices in the presence or absence of the NOgenerating agent sodium nitroprusside or the NOS inhibitors N-nitro-L-arginine methyl ester and aminoguanidine. Nitroprusside markedly decreased the number of bone pits and the average pit area in comparison with control cultures. On the other hand, NOS inhibition by N-nitro-L-arginine methyl ester or aminoguanidine dramatically increased the number of bone pits and the average resorption area per pit. In a model of osteoporosis, aminoguanidine potentiated the loss of bone mineral density in ovariectomized rats. Aminoguanidine also caused a loss of bone mineral density in the sham-operated rats. Inhibition of NOS activity in vitro and in vivo resulted in an apparent potentiation of osteoclast activity. These findings suggest that endogenous NO production in osteoclast cultures may regulate resorption activity. The modulation of NOS and NO levels by cells within the bone microenvironment may be a sensitive mechanism for local control of osteoclast bone resorption.Bone-remodeling disorders such as osteoporosis, osteoarthritis, and periodontal disease are frequently associated with perturbations in the interplay between local and systemic bone-remodeling regulatory pathways. Inflammatory cytokines and arachidonic acid derivatives have been implicated as intercellular messengers involved in humoral-mediated and local osteopenia (1, 2). Postmenopausal bone loss associated with diminished estrogen levels is correlated with increased levels of interleukin 1 and stromal cell-derived interleukin 6, cytokines known to stimulate osteoclast activity and development (3, 4). Estrogen also directly inhibits osteoclast-mediated resorption (5,6) Howard (13) reported that NO-generating compounds may increase cGMP levels in isolated chicken osteoclasts. Furthermore, sodium nitroprusside (SNP) has been shown to inhibit the parathyroid hormone or 1,25-(OH)2-vitamin D3 stimulation of resorption in the 19-day fetal rat limb resorption assay system, with concomitant increases in cGMP (14).The current study was designed to investigate the role of NO in both an isolated in vitro avian osteoclast system and an in vivo rat osteoporosis model system using a NOgenerating agent and selective NOS inhibitors. These findings demonstrate that NO regulates osteoclast bone-resorption activity in vitro and in vivo and that similar effects are seen in birds and mammals.MATERIALS AND METHODS Animals. Three-month-old female Sprague-Dawley rats (250-300 g) from Charles River Breeding Laboratories were used in all in vivo experim...

Endothelial Nitric Oxide Synthase Gene-Deficient Mice Demonstrate Marked Retardation in Postnatal Bone Formation, Reduced Bone Volume, and Defects in Osteoblast Maturation and Activity

“…Furthermore, chronic administration of certain NOS inhibitors in adult rats significantly diminishes bone formation, independent of any marked affect on blood pressure. 12,29 Although such studies have tended to suggest that this was attributable more to inhibition of iNOS 12,29 than eNOS the compounds used are not sufficiently selective in their action to be able to state unequivocally which isoform(s) are involved. 37 Previous studies on NOS gene knockout mice have indicated that in certain tissues other NOS isoforms can substitute for the function of the disrupted one.…”

“…[25][26][27] Numerous studies have also shown that administration of NOS inhibitors to rats in vivo leads to a reversible osteopenia. 12,28,29 Rat models of ovariectomyinduced osteopenia have also revealed that osteoporotic bone loss can be alleviated by administration of NO donors and conversely, inhibition of endogenous NO suppresses the bone-conserving action of estradiol. 18 These observations have demonstrated that the synthesis and activity of both eNOS and iNOS is significant in bone biology although there is consensus that under physiological conditions eNOS probably represents the major NOS activity regulating bone formation.…”

No evidence that the skeletal non-response to potassium alkali supplements in healthy postmenopausal women depends on blood pressure or sodium chloride intake

“…52 NO synthases have been demonstrated in both osteoclasts and osteoblasts. 53,54 NO may be the mediator by which oestrogen or androgen therapy improves BMD. Nitrate use is associated higher BMD 32 and prevents bone loss in postmenopausal women.…”

Macrophage Endothelial Nitric-oxide Synthase Autoregulates Cellular Activation and Pro-inflammatory Protein Expression

“…These observations are in accord with a previous study in transgenic mice overexpressing eNOS that exhibit altered hemodynamics and resistance to LPS when compared with WT animals (32) and suggest that eNOS-derived NO may be important in vivo in expediting host defense. In addition, enhancement of NF-B activity and pro-inflammatory protein expression by NO may underlie control of osteoclast function, which appears to be regulated by a combination of constitutive and inducible NOS activity in vitro and in vivo (33,34).…”