Melatonin effect on bone metabolism in rats treated with methylprednisolone.

The present study was undertaken to examine the effect of melatonin (25 microg/mL of drinking water, about 500 microg/day) on a 10-wk long treatment of male rats with methylprednisolone (5 mg/kg s.c., 5 days/wk). Bone densitometry and mechanical properties, calcemia, phosphatemia and serum bone alkaline phosphatase activity and C-telopeptide fragments of collagen type I (CTX) were measured. Both melatonin and methylprednisolone decreased significantly body weight (BW) and the combination of both treatments resulted in the lowest BW values found. Consequently, all results were analyzed with BW as a covariate. Densitometrically, methylprednisolone augmented bone mineral content (BMC), bone area (BA) and bone mineral density (BMD) in the entire skeleton, BMC in cortical bone, and BMC and BMD in trabecular bone. Melatonin increased BMC and BA in whole skeleton and BMC and BMD in trabecular bone. For BMC and BA of whole skeleton, BMC of cortical bone, and BMC and BMD of trabecular bone, the combination of glucocorticoids and melatonin resulted in the highest values observed. Femoral weight of rats receiving methylprednisolone or melatonin increased significantly and both treatments summated to achieve the greatest effect. In femoral biomechanical testing, methylprednisolone augmented ultimate load and work to failure significantly. Rats receiving the combined treatment of methylprednisolone and melatonin showed the highest values of work to failure. The circulating levels of CTX, an index of bone resorption, decreased after methylprednisolone or melatonin, both treatments summating to achieve the lowest CTX values found. Serum calcium increased after methylprednisolone and serum phosphorus decreased after treatment with methylprednisolone or melatonin while serum bone alkaline phosphatase levels remained unchanged. The results are compatible with the view that low doses of methylprednisolone or melatonin decrease bone resorption and have a bone-protecting effect.

Autonomic neural signals in bone: physiological implications for mandible and dental growth.

Signals derived from the autonomic nervous system exert potent effects on osteoclast and osteoblast function. A ubiquitous sympathetic and sensory innervation of all periosteal surfaces exists and its disruption affects bone remodeling. Several neuropeptides, neurohormones and neurotransmitters and their receptors are detectable in bone. Bone mineral content decreased in sympathetically denervated mandibular bone. When a mechanical stress was superimposed on mandibular bone by cutting out the lower incisors, an increase in bone density ensued providing the sympathetic innervation was intact. A lower eruption rate of sympathetically denervated incisors at the impeded eruption side, and a higher eruption rate of denervated incisors at the unimpeded side were also observed. A normal sympathetic neural activity appears to be a pre-requisite for maintaining a minimal normal unimpeded incisor eruption and for keeping the unimpeded eruption to attain abnormally high velocities under conditions of stimulated incisor growth. These and other results suggest that the sympathetic nervous system plays an important role in mandibular bone metabolism.

Melatonin effects on bone: experimental facts and clinical perspectives.

Bone formation proceeds through a remodeling process that runs continuously, involving the resorption of old bone by osteoclasts, and the subsequent formation of new bone by osteoblasts. This is controlled by growth factors and cytokines produced in bone marrow microenvironment and by the action of systemic hormones, like parathyroid hormone, estradiol or growth hormone (GH). One candidate for hormonal modulation of osteoblast and osteoclast formation is melatonin. Because circulating melatonin declines with age, its possible involvement in post-menopausal and senescence osteoporosis is considered. This review article discusses early studies on melatonin-bone relationships and recent data that suggest a direct effect of melatonin on bone. Melatonin could act as an autacoid in bone cells as it is present in high quantities in bone marrow, where precursors of bone cells are located. Melatonin dose-dependently augmented proteins that are incorporated into the bone matrix, like procollagen type I c-peptide. Osteoprotegerin, an osteoblastic protein that inhibits the differentiation of osteoclasts is also augmented by melatonin in vitro. Another possible target cell for melatonin is the osteoclast, which degrades bone partly by generating free radicals. Melatonin through its free radical scavenger and antioxidant properties may impair osteoclast activity and bone resorption. At least in one study melatonin was both inhibitory to osteoclastic and osteoblastic cells. Therefore, the documented bone-protecting effect of melatonin in ovariectomized rats can depend in part on the free radical scavenging properties of melatonin. Additionally, melatonin may impair development of osteopenia associated with senescence by improving non-rapid eye movement sleep and restoring GH secretion. Whether melatonin can be used as a novel mode of therapy for augmenting bone mass in diseases deserves to be studied.

Melatonin increases oestradiol-induced bone formation in ovariectomized rats.

To assess the effect of melatonin on bone metabolism in ovariectomized rats, receiving oestradiol therapy or not, melatonin was administered in the drinking water (25 microg/mL water) and oestradiol (10 microg/kg body weight) or vehicle was given subcutaneously 5 days/week for up to 60 days after surgery. Urinary deoxypyridinoline (a marker of bone resorption) and circulating levels of bone alkaline phosphatase activity (a marker of bone formation), as well as serum calcium and phosphorus levels, were measured every 15 days. Bone area (BA), bone mineral content (BMC), bone mineral density (BMD) and total body fat (expressed as 100 g body weight) were measured by dual-energy X-ray absorptiometry at the end of the experiment. Body weight and total body fat were augmented after ovariectomy, and decreased after melatonin or oestradiol treatment. The effect of melatonin on body weight was seen in sham-operated rats only. Ovariectomy augmented, and melatonin or oestradiol lowered, urinary deoxypyridinoline excretion. This effect of melatonin and oestradiol was seen mainly in ovariectomized rats. The efficacy of oestradiol to counteract ovariectomy-induced bone resorption was increased by melatonin. Melatonin or oestradiol lowered serum bone alkaline phosphatase activity. Melatonin inhibition was seen mainly on the increase of bone alkaline phosphatase activity that followed ovariectomy. Serum phosphorus levels decreased after melatonin administration and were augmented after oestradiol injection; overall, melatonin impaired the increase of serum phosphorus caused by oestradiol. Ovariectomy decreased, and oestradiol increased, serum calcium levels while melatonin augmented serum calcium in sham-operated rats only. On day 60 after surgery, BMD and content decreased after ovariectomy and were increased after oestradiol injection. Melatonin augmented BA of spine and BMC of whole of the skeleton and tibia. The highest values observed were those of rats treated concurrently with oestradiol and melatonin. The present results indicate that: (i) melatonin treatment restrained bone remodelling after ovariectomy; (ii) the effect of melatonin required adequate concentrations of oestradiol; (iii) melatonin augmented oestradiol effects on bone in ovariectomized rats; (iv) a counter-regulation by melatonin of the increase in body fat caused by ovariectomy was uncovered. The melatonin doses employed were pharmacological in terms of circulating melatonin levels but not necessarily for some other fluids or tissues.

Precise measurement of bone mineral density in rats using dual-energy x-ray absorptiometry

El desarrollo de técnicas rápidas y sensibles para evaluar masa ósea en animales de experimentación resulta de gran utilidad para reemplazar y/o completar métodos más complejos como la histomorfometría y la cuantificación de cenizas del hueso. En este estudio hemos utilizado un densitómetro Hologic QDR-1000 con un programa de alta resolución para cuantificar el contenido mineral óseo (CMO), el área (A) y la densidad mineral ósea (FMO) en la rata, analizando la sensibilidad del método, su reproducibilidad y capacidad para detectar difernecias en distintas situaciones metabólicas. Las determinaciones se efectuaron en los sectores proximal (L1), diafisiario (L2 y L3) y distal (L4) del femur y tibia. La reproducibilidad se evaluó a través del coeficiente de variación de la DMO del fémur después de 10 mediciones sin y con reposición de baño de agua. Los valores fueron 0.47por ceiento y 0.52 por ciento respectivamente. La sensibilidad se determinó en fémur correlacionando del CMO con el contenido en cenizas (r=0.98, p<0.001). No se encontraron diferencias significativas entre huesos contralaterales. En ratas ovariectomizadas la DMO (gr/cm2) en fémur disminuyó comparada con grupo control, en los sectores L2(0.202 ñ 0.005 vs. 0.270 ñ 0.016p<0.005 vs 0.263ñ0.021, p<0.05). Asimismo, la DMO fue menor en hembras que en machos: en fémur para L4(0.263 ñ 0.021 vs. 0.315 ñ 0.009, p<0.05) y en tibia para L1 (0.259 ñ 0.016 vs. 0.315 ñ 0.013), p<0.02). Conclusiones: 1) La técnica desarrollada presenta alta reproducibilidad y sensibilidad permitiendo establecer diferencia estadísticas en variaciones pequeñas del CMO, A y DMO. 2) Evidencia un alto grado de correlación con otras metodologías que cuantifican la DMO. 3) En diferentes situaciones metabólicas permite localizar diferencias en distintos sectores del hueso. La DEXA resulta entonces de gran utilidad para efectuar estudios metabólicos y/o farmacológicos que involucren la masa ósea en ratas (AU)

Precise measurement of bone mineral density in rats using dual-energy x-ray absorptiometry

El desarrollo de técnicas rápidas y sensibles para evaluar masa ósea en animales de experimentación resulta de gran utilidad para reemplazar y/o completar métodos más complejos como la histomorfometría y la cuantificación de cenizas del hueso. En este estudio hemos utilizado un densitómetro Hologic QDR-1000 con un programa de alta resolución para cuantificar el contenido mineral óseo (CMO), el área (A) y la densidad mineral ósea (FMO) en la rata, analizando la sensibilidad del método, su reproducibilidad y capacidad para detectar difernecias en distintas situaciones metabólicas. Las determinaciones se efectuaron en los sectores proximal (L1), diafisiario (L2 y L3) y distal (L4) del femur y tibia. La reproducibilidad se evaluó a través del coeficiente de variación de la DMO del fémur después de 10 mediciones sin y con reposición de baño de agua. Los valores fueron 0.47por ceiento y 0.52 por ciento respectivamente. La sensibilidad se determinó en fémur correlacionando del CMO con el contenido en cenizas (r=0.98, p<0.001). No se encontraron diferencias significativas entre huesos contralaterales. En ratas ovariectomizadas la DMO (gr/cm2) en fémur disminuyó comparada con grupo control, en los sectores L2(0.202 ñ 0.005 vs. 0.270 ñ 0.016p<0.005 vs 0.263ñ0.021, p<0.05). Asimismo, la DMO fue menor en hembras que en machos: en fémur para L4(0.263 ñ 0.021 vs. 0.315 ñ 0.009, p<0.05) y en tibia para L1 (0.259 ñ 0.016 vs. 0.315 ñ 0.013), p<0.02). Conclusiones: 1) La técnica desarrollada presenta alta reproducibilidad y sensibilidad permitiendo establecer diferencia estadísticas en variaciones pequeñas del CMO, A y DMO. 2) Evidencia un alto grado de correlación con otras metodologías que cuantifican la DMO. 3) En diferentes situaciones metabólicas permite localizar diferencias en distintos sectores del hueso. La DEXA resulta entonces de gran utilidad para efectuar estudios metabólicos y/o farmacológicos que involucren la masa ósea en ratas