Sunil J. Wimalawansa

Nitric oxide and bone.

Age‐associated decrease in nitric oxide (NO) production may be related to an increase in cardiovascular events, sexual dysfunction, and osteoporosis. Relative NO deficiency is a plausible biological basis for NO replacement therapy. Hormone replacement therapy (HRT) enhances local NO production and rectifies NO deficiency in postmenopausal women. However, excess local production of NO aggravates bone destruction in inflammatory arthropathies. In addition to its use in alleviating angina and erectile dysfunction, NO compounds could be a valuable supplemental therapy for chronic conditions including osteoporosis. Estrogen mediates its beneficial effects in bone, in part via the NO/cGMP pathway; hence NO donor therapy is an alternative to estrogen, estrogen agonists‐antagonists, and androgen receptor modulator therapy in the prevention and treatment of osteoporosis. Large numbers of animal studies and human pilot studies support the concept of using NO donors for preventing bone loss. Administration of exogenous NO or prolonging endogenous NO activity are practical ways to supplement NO.

Involvement of calcitonin gene–related peptide in the modulation of human myometrial contractility during pregnancy

Calcitonin gene-related peptide (CGRP) is a potent vasodilator and relaxes smooth muscle of a variety of tissues, but the effects of CGRP on human myometrial contractions and the changes in CGRP receptors (CGRP-Rs) in human myometrium have not been described. We report that CGRP induced dose-dependent relaxation in spontaneously contracting myometrium from pregnant women. This relaxation effect is diminished in myometrium obtained from patients during labor and in the nonpregnant state. CGRP-induced relaxations are inhibited by a CGRP-R antagonist (CGRP(8-37)), a soluble guanylate cyclase inhibitor (LY(83583)), and a nitric oxide synthase inhibitor (L-NAME). Both Western blotting and mRNA analysis showed that CGRP-Rs are present in human myometrium, and that the expression of these receptors is increased during pregnancy and decreased during term labor. Immunofluorescent staining revealed that CGRP-Rs are abundant in the myometrial cells of pregnant women who are not in labor, and are minimal in uterine specimens from women in labor and in the nonpregnant state. We conclude that increased CGRP-Rs in myometrium, and resulting enhanced myometrial sensitivity to CGRP, may play a role in maintaining human myometrium in a quiescent state during pregnancy, and that a decline in the CGRP-Rs at term could contribute to the initiation of labor.

The efficacy of acute administration of pamidronate on the conservation of bone mass following severe burn injury in children: a double-blind, randomized, controlled study

Bone loss is a known complication of severe burn injury. It is, in part, due to increased endogenous glucocorticoids that contribute to the reduction in bone formation and osteoblast differentiation, hypercalciuria secondary to hypoparathyroidism, and vitaminxa0D deficiency. In this study we attempted to prevent post-burn bone loss by acute intravenous administration of the bisphosphonate pamidronate. We enrolled 43 children, with burns of >40% total body surface area, in a randomized, double-blind, placebo-controlled study, administering the study drug within 10 days of burn injury and again 1 week later. Dual energy X-ray absorptiometry was performed prior to drug therapy, at hospital discharge and at 6 months post-burn. Urine specimens were obtained at baseline and discharge for determination of calcium and free deoxypyridinoline. Blood was obtained along with the urine specimens for measurement of intact parathyroid hormone (iPTH) and ionized calcium (Ca) levels. Following doxycycline labeling, intra-operative iliac crest bone biopsies were obtained, and bone histomorphometry was determined. At time of discharge there were no differences in total body bone mineral content (BMC), but lumbar spine BMC was significantly higher in the pamidronate group (P<0.005). By 6 months post-burn the differences in lumbar spine BMC persisted, but, now, total body BMC was significantly higher in the pamidronate group (P<0.05). Bone histomorphometry and levels of urine Ca and free deoxypyridinoline failed to show significant increases in bone formation or decreases in bone resorption. Pamidronate did not exacerbate the hypocalcemia in burn patients. In summary, acute intravenous pamidronate administration following burns may help to preserve bone mass, perhaps by inhibiting the glucocorticoid-induced apoptosis of osteoblasts and osteocytes.

Nitric oxide: new evidence for novel therapeutic indications.

Background: Nitric oxide (NO) deficiency is implicated in many pathophysiological processes in mammals. NO is a ubiquitous molecule involved in multiple cellular functions. Uncontrolled or inappropriate production of NO may lead to several disease states including septic shock, rheumatoid and inflammatory arthropathies, and expansion of cerebral damage after stroke. However, to date, there are no therapeutic agents available that can overcome these conditions. Similarly, underproduction of NO by NO synthase or enhanced breakdown of NO also leads to diseases such as hypertension, ischemic conditions, pre-eclampsia, premature delivery, among others. NO donor therapies are indicated in these conditions. Results: Nitroglycerin and nitrates (NO donors) have been used as therapeutic agents for the past century, particularly to treat vascular disease, and the only significant adverse effects are headaches. NO donors are highly cost-effective and have beneficial effects in multiple body systems. When the body cannot generate NO via NO synthase or due to rapid turnover leading to inadequate amounts of NO available for biological homeostasis, administration of exogenous NO, or prolongation of the actions of endogenous NO, are practical ways to supplement NO. Conclusion: Recipients of such therapy include patients with angina pectoris, coronary artery disease, hypertension, osteoporosis, gastrointestinal motility disorders, pregnancy-related disorders including premature delivery, pre-eclampsia, vulvodynia, and erectile dysfunction in men. Postmenopausal NO deficiency is rectified with hormone replacement therapy, which enhances local production of NO. Declining local NO production secondary to estrogen deficiency in postmenopausal women and perhaps in older men could be one of the reasons for age-related increased incidences of cardiovascular events and sexual dysfunction. Thus, in addition to supplementation of NO compounds in acute situations like alleviating angina and erectile dysfunction, chronic NO therapy is cost-effective in decreasing cardiovascular events, and improving the urogenital system and skeletal health.

Vitamin D in the New Millennium

The incidence of vitamin D deficiency is rising worldwide, yet in the vast majority of patients, the condition remains undiagnosed and untreated. Current evidence overwhelmingly indicates that supplemental doses greater than 800xa0IU/day have beneficial effects on the musculoskeletal system, improving skeletal homeostasis, thus leading to fewer falls and fractures. Evidence is also accumulating on the beneficial effects of vitamin D on extraskeletal systems, such as improving immune health, autoimmune disorders, cancer, neuromodulation, diabetes, and metabolic syndrome. The cause-effect relationship of vitamin D deficiency with increasing incidences of nonskeletal disorders is being investigated. Published reports support the definition of sufficiency, serum levels of 25-hydroxyvitamin D [25(OH)D] greater than 30xa0ng/mL (75xa0nmol/L). To achieve this, most people need vitamin D supplementation ranging from 600 to 2000xa0IU/day; consumption up to of 5000 international units (IU) per day of vitamin D is reported as safe. Although light-skinned individuals need 1000xa0IU/day of vitamin D, elderly and dark-skinned individuals are likely to need approximately 2000xa0IU/day to maintain serum 25(OH)D levels greater than 30xa0ng/mL. Other vulnerable patients, such as the obese, those who have undergone bariatric surgery, and those with gastrointestinal malabsorption syndromes, may require higher doses of vitamin D to maintain normal serum levels and be healthy.

Amylin‐amide: a new bone‐conserving peptide from the pancreas

Amylin‐amide is a new member of the family of peptides encoded by the calcitonin multigene complex. In the present study, we have compared directly, the hypocalcaemic potency and duration of action of human amylin‐amide and human calcitonin in an in vivo rat bioassay and an in vitro osteoclast bone resorption assay. Amylin‐amide was found to have a potency approximately 40‐fold lower than human calcitonin, whilst both peptides followed the same time course. This suggests that amylin‐amide is the most potent non‐calcitonin hypocalcaemic peptide so far reported. An important physiological implication follows. It would seem that amylin‐amide can play a central role in the maintenance of the skeleton by virtue of its inhibitory influence on osteoclastic function.

Rationale for Using Nitric Oxide Donor Therapy for Prevention of Bone Loss and Treatment of Osteoporosis in Humans

Abstract:u2002 Nitric oxide (NO) is a ubiquitous molecule involved in most cellular functions. While osteocytes communicate between bone cells, diffusible small molecules—H+ and NO—are involved in short‐term regulation of bone metabolism. Studies conducted over the past two decades have demonstrated the regulatory role of NO in bone metabolism. Circulating NO products are significantly lower in postmenopausal women, and estrogen supplementation restores this. Skeletal beneficial effects of estrogen are abolished with NO‐synthase enzyme inhibitors, suggesting some estrogenic skeletal effects are mediated through NO/cGMP pathway. Since estrogen/hormone replacement therapy (HRT) has potential adverse effects, supplementing NO directly is sensible. NO is also involved with other cellular functions, such as isoprenylation of the Rho GTPase that stimulates Rho‐PK (the functioning Rho‐PK in turn inactivates something that would otherwise turn on the BMP‐2/Cbfa1‐Runx‐2 cycle), and likely to be the final common pathway of other agents including statins. The first human study using nitroglycerine in the prevention of oophorectomy‐induced bone loss demonstrated an equivalent efficacy to estrogen in the prevention of bone loss. A randomized NIH‐funded NOVEL clinical study is currently assessing the effectiveness of topically administered nitroglycerine in the prevention of postmenopausal bone loss. If efficacy of nitroglycerine is confirmed, it may become a highly cost‐effective and safe alternative therapy to treat osteoporosis. Nitroglycerine has beneficial effects in multiple systems, especially the cardiovascular system. If results of this study confirm our hypothesis, it is plausible that nitroglycerine therapy may supplant estrogen replacement and SERMs in preventing and treating postmenopausal osteoporosis.

Calcitonin gene-related peptide in pregnancy and its emerging receptor heterogeneity

Calcitonin gene-related peptide (CGRP) is the most potent vasodilator, and there is a growing body of evidence that this peptide might have multiple other functions. During pregnancy, circulating CGRP levels in rats increase up to the time of delivery, followed by a sharp decline at term and postpartum. In addition, the sensitivity of various vascular beds to CGRP in rats appears to increase with advancing pregnancy. This increased sensitivity might be involved in regulating uteroplacental blood flow, in addition to other vascular adaptations that occur during normal pregnancy. Furthermore, the uterine relaxation response to CGRP is elevated during pregnancy and decreased at term. Sex steroid hormones, estrogens and progesterone, regulate CGRP synthesis and its effects on both myometrial and uterine vascular tissues. These changes in smooth muscle relaxation sensitivity to CGRP appear to be a consequence of changes in CGRP-receptor levels in these tissues. There appear to be two receptors for CGRP: the CGRP-A receptor, a well-characterized receptor consisting of calcitonin receptor-like receptor and receptor activity modifying protein 1, and the CGRP-B receptor. The CGRP system might play a role in the maintenance of normal pregnancy, and a defect in this system might lead to complications.

Placental and Fetal Growth and Development in Late Rat Gestation Is Dependent on Adrenomedullin

Abstract Adrenomedullin is a potent, endogenous vasodilator peptide synthesized and secreted by diverse locations such as adrenal glands, lungs, kidneys, vascular smooth muscle, and endothelium. Homozygous deletion of the adrenomedullin gene is embryonic lethal. We hypothesized that adrenomedullin has an important role in placental and fetal growth and development in rat pregnancy. The current study evaluated maternal systolic blood pressure, litter size, placental and pup weight, pup mortality, and placental pathology in pregnant rats following continuous in utero exposure to an adrenomedullin antagonist. Osmotic minipumps were inserted on Gestational Day 14 to continuously deliver either adrenomedullin, adrenomedullin antagonist, or vehicle control. Systolic blood pressure was recorded daily. Pregnant rats were killed on Gestational Day 15–18, 20, and/or 22 to evaluate placental development and fetal growth. The placentas were graded for the presence of necrosis in the decidua and fetal labyrinth as well as fetal vessel development in the labyrinth. A trend toward increased systolic blood pressure was noted between Gestational Days 17 and 20 in mothers treated with adrenomedullin antagonist, but the difference was not statistically significant. Antagonism of adrenomedullin function during rat pregnancy caused fetal growth restriction, decreased placental size, gross necrosis of placental margins and amniotic membranes, histologically deficient fetal vessel development in the labyrinth, and fetal edema. Adrenomedullin contributes to angiogenesis, functions as a growth factor, and helps regulate vascular tone during rat gestation.

Calcitonin gene-related peptide and its specific binding sites in the cardiovascular system of rat

The concentration of calcitonin gene-related peptide in rat cardiovascular tissues was determined by a specific and sensitive radioimmunoassay and the distribution of its specific binding sites was assessed by radioligand binding studies. The binding of [125I]calcitonin gene-related peptide to cardiovascular membranes was rapid, saturable, reversible and specific. In atrial membranes a single binding site with high affinity (Kd 1.5 nM) and low capacity (120 fmol/mg protein) was detected. The highest concentrations of both calcitonin gene-related peptide and its binding sites were found in the peripheral and mesenteric arteries. The immunoreactive calcitonin gene-related peptide levels were lower in major vessels and lowest in the heart. The number of calcitonin gene-related peptide specific binding sites also showed a similar pattern with the exception of a high concentration of binding sites present in the atria. These findings, together with the proven vasodilatory activity of calcitonin gene-related peptide, suggest that this peptide has an important role as a modulator of peripheral vascular tone and perhaps a direct action of the heart.