Osteoporosis is characterized by loss of bone mass and strength, leading to fractures that cause pain, loss of independence, and increased mortality. Most FDA-approved drugs for osteoporosis have drawbacks, and only teriparatide (PTH) improves bone formation. We have shown that the nitric oxide (NO)/cGMP/protein kinase G (PKG) signaling pathway mediates anabolic effects of estrogens and mechanical stimulation in bone cells, through increased proliferation and survival of osteoblasts/osteocytes. Nitrates, which generate NO, prevent bone loss in estrogen-deficient rats and increase bone mineral density, cortical thickness, and bone formation markers in post-menopausal women-with changes superior to those reported for PTH. However, nitrates are limited by development of tolerance, induction of oxidative stress, and increased cardiovascular mortality after long-term use. We propose pre-clinical studies testing the effects of cGMP-elevating agents with different mechanisms of action in mouse models of osteoporosis: nitrosyl-cobinamide (NO-Cbi), a novel direct NO- releasing agent that, in contrast to nitrates, does not generate superoxide and may even lower oxidative stress, and two prototype guanylate cyclase (sGC) stimulators, BAY58-2667 and BAY41-8543, which target oxidized or reduced sGC, respectively, to generate cGMP NO-independently.
In Specific Aim I, we will test the hypothesis that NO-Cbi and BAY58/41 restore and/or prevent estrogen-deficiency-induced bone loss in mice. We will subject mice to ovariectomy or sham operation, and treat them for 8 weeks with NO-Cbi, BAY58, BAY41, 17-estradiol, or vehicle, starting week 1 or 8 post surgery. We will measure bone architecture and mineral content by micro-CT, bone strength by three-point bending, bone turnover by histomorphometry and serum markers, and osteoblast- and osteoclast-specific gene expression by quantitative RT-PCR. We will examine effects of all three drugs on osteoclast differentiation and function ex vivo.
In Specific Aim II, we will test the hypothesis that NO-Cbi and BAY58/41 improve bone quality and bone formation in senescence- accelerated SAMP6 mice, who develop osteoporosis at an early age. We will randomize SAMP6 mice and syngeneic SAMR1 control mice to receive NO-Cbi, BAY58, BAY41, vehicle, or PTH for 4 or 12 weeks, and measure skeletal parameters as in Aim I. Since SAMP6 mice have mesenchymal stem cell deficiencies similar to humans with senile osteoporosis, we will determine effects of NO-Cbi and BAY58/41 on osteogenic differentiation of mesenchymal stem cells ex vivo. By comparing effects of NO-Cbi, BAY58, and BAY41 at doses that increase serum cGMP concentrations to a similar degree, we will determine if NO exerts cGMP- independent effects in bone and assess whether estrogen deficiency and aging produce clinically-significant levels of oxidized sGC. While many pathways are implicated in skeletal maintenance and health, few are as suitable as the NO/cGMP pathway to prevent and treat osteoporosis, because cGMP-elevating agents have recently shown favorable toxicity profiles and beneficial effects in cardiovascular diseases and other disorders.
Osteoporosis is a major health problem affecting millions of Americans, with post- menopausal women being particularly vulnerable; among existing osteoporosis therapies, most inhibit bone resorption and have poor patient acceptance due to fear of potentially serious side effects such as osteonecrosis of the jaw. We recently found that the nitric oxide (NO)/cGMP/Protein Kinase G signaling cascade stimulates important growth and survival pathways in bone-forming cells and has potential anabolic effects in bone. We now propose to explore whether three novel NO/cGMP-generating agents can prevent bone loss in mouse models of osteoporosis caused by estrogen-deficiency or accelerated aging; these studies may allow us to develop a new treatment strategy for osteoporosis.
| Ramdani, Ghania; Schall, Nadine; Kalyanaraman, Hema et al. (2018) cGMP-dependent protein kinase-2 regulates bone mass and prevents diabetic bone loss. J Endocrinol 238:203-219 |
| Kalyanaraman, Hema; Schwaerzer, Gerburg; Ramdani, Ghania et al. (2018) Protein Kinase G Activation Reverses Oxidative Stress and Restores Osteoblast Function and Bone Formation in Male Mice With Type 1 Diabetes. Diabetes 67:607-623 |
| Kalyanaraman, Hema; Ramdani, Ghania; Joshua, Jisha et al. (2017) A Novel, Direct NO Donor Regulates Osteoblast and Osteoclast Functions and Increases Bone Mass in Ovariectomized Mice. J Bone Miner Res 32:46-59 |
