Relationships between the changes of serum levels of OPG and RANKL with age, menopause, bone biochemical markers and bone mineral density in Chinese women aged 20-75

Circulating leptin and osteoprotegerin levels affect insulin resistance in healthy premenopausal obese women

We investigated the relationship between circulating leptin and osteoprotegerin (OPG) levels and insulin resistance assessed by HOMA-IR in premenopausal obese and normal weight women. Thirty four obese women (age 31 +/- 8 years) (BMI 35 +/- 4 kg/m(2)) with 19 healthy controls (age 31 +/- 7 years) (BMI <25 kg/m(2)) (BMI 21 +/- 2 kg/m(2)) were included in the study. Women were healthy and had no osteoporosis. Circulating leptin levels were significantly higher in obese women (17.11 +/- 2.05 ng/mL vs. 8.38 +/- 4.71 ng/mL, p <0.0001) and decreased OPG levels were found (14.7 +/- 7.15 pg/mL vs. 19.17 +/- 6.37 pg/mL, p = 0.03). Leptin showed a positive correlation with BMI (r = 0.851, p <0.0001), waist-to-hip ratio (r = 0.692, p <0.0001), fasting insulin (r = 0.441, p <0.001), HOMA-IR (r = 0.412, p = 0.002), fibrinogen (r = 0.387, p = 0.004), uric acid (r = 0.293, p = 0.033), hematocrit (r = 0.394, p = 0.003), systolic (r = 0.504, p <0.0001), and diastolic blood pressure (r = 0.363, p = 0.008). OPG showed a negative correlation with insulin (r = -0.341, p = 0.013) and HOMA-IR (r = -0.324, p = 0.018). In obese women group, the regression equation of HOMA-IR was (HOMA-IR = [0.095 x leptin]-[0.051 x OPG] + 1.71). However, there was no relation between leptin and OPG levels. In conclusion, circulating leptin and OPG levels were related to insulin resistance in premenopausal obese women. However, leptin had no interference in OPG in premenopausal women.

The circadian rhythm of osteoprotegerin and its association with parathyroid hormone secretion

BACKGROUND

Osteoclast resorptive activity, which is known to demonstrate circadian rhythmicity, is regulated by various endocrine hormones and cytokines. PTH suppresses osteoprotegerin (OPG), a regulator of osteoclast activity that has recently been shown to have a circadian rhythm in healthy controls. We studied the differences in the relationship between PTH, OPG, and type I collagen C-telopeptide (betaCTX) over a 24-h period in premenopausal women, elderly postmenopausal women, and elderly men.

METHODS

Hourly peripheral venous blood samples were obtained from 18 healthy non-osteoporotic volunteers: premenopausal women (n = 6; mean age, 30.2 +/- 2.2 yr), postmenopausal women (n = 6; mean age, 68.2 +/- 2.6 yr), and elderly men (n = 6; mean age, 68.2 +/- 2.3 yr). Plasma PTH (1-84), OPG, betaCTX, and calcium were measured on all samples. Cosinor analysis was performed to analyze the circadian rhythm parameters. Cross-correlation analysis was used to determine the relationship between the time series of the variables.

RESULTS

The 24-h mean PTH, OPG, and betaCTX concentrations were significantly higher in postmenopausal women as compared with premenopausal women and elderly men (P < 0.001). Significant circadian rhythms were observed for PTH (P < 0.05), OPG (P < 0.05), and betaCTX (P < 0.001) in all subjects. PTH secretion was characterized by two peaks in premenopausal women and elderly men and by a sustained increase in PTH concentration in postmenopausal women. OPG secretion was circadian with a daytime increase and nocturnal decrease, and a greater percent decrease in OPG secretion was observed in the postmenopausal women between 1600 and 2400 h. OPG secretion was inversely related to PTH (r = -0.4) and betaCTX (r = -0.6) secretion over a 24-h period.

CONCLUSION

This report confirms a circadian rhythm for circulating OPG. The nocturnal decline in circulating OPG is greater in postmenopausal women as compared with premenopausal women and elderly men. Altered PTH secretion may contribute to the OPG secretory pattern in postmenopausal women resulting in increased nocturnal bone resorption.

Effects of estrogen-progestin therapy on serum levels of RANKL, osteoprotegerin, osteocalcin, leptin, and ghrelin in postmenopausal women

OBJECTIVE

The aim of this study was to evaluate the effects of estrogen-progestin therapy on serum levels of receptor-activating nuclear factor kappabeta ligand (RANKL), osteoprotegerin, osteocalcin, leptin, and ghrelin in a cross-sectional study of 99 healthy postmenopausal women conducted at the Menopause Clinic of our department.

DESIGN

In this cross-sectional, observational study, 99 participants were divided into two groups. Group A was composed of 77 postmenopausal women who had never received estrogen-progestin therapy, and group B was composed of 22 postmenopausal women who had received transdermal 17beta-estradiol at a dose of 50 microg/day in a continuous regimen for at least 24 months and nomegestrol at a dose of 5 mg/day for 12 days/month in a sequential regimen. All participants underwent blood sampling in the morning and quantitative ultrasound bone-densitometry measurement of the proximal phalanges of the dominant hand.

RESULTS

T score and amplitude-dependent speed of sound were significantly higher in group B than in group A. No significant differences in RANKL, osteoprotegerin, and osteocalcin were observed between the two groups. Serum leptin levels were significantly lower in group B than in group A, whereas ghrelin was significantly higher in group B than in group A.

CONCLUSIONS

The data gathered in this preliminary study indicate that estrogen-progestin therapy may protect against postmenopausal bone loss, but this protective effect does not seem to be exerted through action on the RANK-RANKL-osteoprotegerin system. Similarly, although several reports suggest that leptin and ghrelin are involved in bone metabolism, we could not detect any important correlation of these two hormones with bone metabolism or bone status in treated and untreated postmenopausal women. Because of the limited number of treated participants and the study design, the results of this preliminary study must be confirmed in larger, prospective, longitudinal studies.

Circulating osteoprotegerin and receptor activator of NF-kappaB ligand system in patients with beta-thalassemia major

Osteoporosis represents an important cause of morbidity in patients with beta-thalassemia major, and its etiology is multifactorial. Thus, the aim of this study was to characterize the possible role of the osteoprotegerin (OPG) and receptor activator of the NF-kappaB ligand (RANKL) system in thalassemia-related bone loss. Serum concentrations of OPG, soluble RANKL (s-RANKL), markers of bone turnover, and lumbar spine bone mineral density (BMD) were measured in random samples of males (n = 29; mean age +/- SEM, 24.26 +/- 1.29 years; range, 13-41 years) and females (n = 31; age, 24.59 +/- 0.95 years; range, 12-34 years) with beta-thalassemia major and in 30 healthy age-, height-, and weight-matched subjects. Thalassemic patients had significantly lower levels of OPG compared with controls (2.54 +/- 0.12 vs. 3.25 +/- 0.122, respectively; P < 0.05) and higher, albeit not statistically significantly, serum levels of s-RANKL (0.350 +/- 0.03 vs. 0.295 +/- 0.046, respectively; P < 0.05). s-RANKL correlated negatively with age (r = -0.3, P < 0.05), and OPG correlated positively with the duration of the interval between the onset of transfusions and chelation therapy (r = 0.52, P < 0.001). Regarding markers of bone metabolism, plasma values of osteocalcin correlated positively with s-RANKL (r = 0.40, P < 0.05) and negatively with OPG/s-RANKL ratio (r = -0.55, P < 0.01). In multiple regression analysis only cross-linked N-teleopeptide of type I collagen (NTX) significantly accounted for BMD. Although the OPG/RANKL system may have some clinical usefulness as a marker of bone turnover in beta-thalassemia, conventional markers of bone turnover more accurately represent changes in the BMD of these patients.

Osteoimmunology

Osteoimmunology is an interdisciplinary research field combining the exciting fields of osteology and immunology. An observation that contributed enormously to the emergence of osteoimmunology was the accelerated bone loss caused by inflammatory diseases such as rheumatoid arthritis. Receptor activator of nuclear factor kappaB ligand (RANKL), which is the main regulator of osteoclastogenesis, was found to be the primary culprit responsible for the enhanced activation of osteoclasts: activated T cells directly and indirectly increased the expression of RANKL, and thereby promoted osteoclastic activity. Excessive bone loss is not only present in inflammatory diseases but also in autoimmune diseases and cancer. Furthermore, there is accumulating evidence that the very prevalent skeletal disorder osteoporosis is associated with alterations in the immune system. Meanwhile, numerous connections have been discovered in osteoimmunology beyond merely the actions of RANKL. These include the importance of osteoblasts in the maintenance of the hematopoietic stem cell niche and in lymphocyte development as well as the functions of immune cells participating in osteoblast and osteoclast development. Furthermore, research is being done investigating cytokines, chemokines, transcription factors and co-stimulatory molecules which are shared by both systems. Research in osteoimmunology promises the discovery of new strategies and the development of innovative therapeutics to cure or alleviate bone loss in inflammatory and autoimmune diseases as well as in osteoporosis. This review gives an introduction to bone remodeling and the cells governing that process and summarizes the most recent discoveries in the interdisciplinary field of osteoimmunology. Furthermore, an alternative large animal model will be discussed and the pathophysiological alterations of the immune system in osteoporosis will be highlighted.