Low serum osteoprotegerin levels in premenopausal infertile women with low bone density: an association of relevance?

MR. Are skeletally mature female rats a suitable model to study osteoporosis?

OBJECTIVE: To analyze if female Wistar rats at 56 weeks of age are a suitable model to study osteoporosis. MATERIALS AND METHODS: Female rats with 6 and 36 weeks of age (n = 8 per group) were kept over a 20-week period and fed a diet for mature rodents complete in terms of Ca, phosphorous, and vitamin D. Excised femurs were measured for bone mass using dual-energy x-ray absorptiometry, morphometry, and biomechanical properties. The following serum mar-kers of bone metabolism were analyzed: parathyroid hormone (PTH), osteocalcin (OC), osteoprotegerin (OPG), receptor activator of nuclear factor Κappa B ligand (RANKL), C-terminal peptides of type I collagen (CTX-I), total calcium, and alkaline phosphatase (ALP) activity. RESULTS: Rats at 56 weeks of age showed important bone metabolism differences when compared with the younger group, such as, highest diaphysis energy to failure, lowest levels of OC, CTX-I, and ALP, and elevated PTH, even with adequate dietary Ca. CONCLUSION: Rats at 26-week-old rats may be too young to study age-related bone loss, whereas the 56-week-old rats may be good models to represent the early stages of age-related changes in bone metabolism.

Skeletal status and body composition in young women with functional hypothalamic amenorrhea

CONTEXT

Functional hypothalamic amenorrhea (FHA) related to hypoestrogenism and hormonal status may influence skeletal homeostasis and body composition. The study aimed to evaluate hormones concentrations, body composition and bone strength in FHA cases.

PATIENTS AND METHODS

Total body scans using DXA method (DPX-L, GE Lunar) were performed in a group of 27 women aged 21.8 years ± 3.9 with FHA related to weight loss. References of healthy control subjects were used to calculate Z-scores (age and gender matched), SD-scores (height and gender matched), and SDs-scores (weight and gender matched). Whole skeleton bone mineral content (TBBMC, g) and density (TBBMD, g/cm(2)), lumbar spine (L2-L4) bone mineral density (SBMD; g/cm(2)), lean body mass (LBM, g) and fat mass (FM, g) were investigated. Relative bone strength index was calculated as the TBBMC/LBM ratio. Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, testosterone, and prolactin (PRL) concentrations were assayed to characterize hormonal profile of FHA cases.

RESULTS

Hormonal evaluation in patients with FHA revealed significantly decreased serum concentrations of gonadotropins and estradiol. Serum LH concentrations were 1.47 ± 0.89 mIU/ml, FSH 4.44 ± 1.94 mIU/ml. Estradiol concentrations in serum were 27.08 ± 13.10 pg/ml. As evidenced by Z-scores, FHA cases had decreased SBMD, TBBMD and TBBMC Z-scores of -1.23 ± 0.90 (p < 0.0001), -0.72 ± 0.86 (p < 0.001), and -0.90 ± 1.40 (p < 0.01), respectively. Reduced FM, LBM and FM/LBM ratio Z-scores of -1.80 ± 2.28 (p < 0.001), -0.59 ± 1.49 (p < 0.05) and -0.74 ± 1.55 (p < 0.05), but not TBBMC/LBM Z-score of -0.54 ± 2.14 (ns) were noted in FHA cases compared with healthy control cases. TBBMC, TBBMD, TBBMC/LBM when BH- or BW-matched were normal as evidenced by SD-scores and SDs-scores. SBMD remained reduced when BH-matched (SD-score = -0.40 ± 0.86; p < 0.05) whereas FM and FM/LBM were lower than expected in healthy, both compared to BH- and BW-dependent references. The length of amenorrhea in months negatively correlated with SBMD Z-score (R = -0.39, p < 0.05), and SD-scores for SBMD (R = -0.48), TBBMD (R = -0.43), TBBMC (R = -0.46) (all p < 0.05) and positively with SDs-scores for FM (R = 0.44, p < 0.05).

CONCLUSION

Patients with FHA were characterized by lower concentrations of serum FSH, LH and estradiol concentrations. Moreover, FHA cases had decreased FM and an imbalanced relationship between BW, FM, and LBM. Despite reduced BMD and BMC, bone strength was not significantly affected by FHA.

Hypoestrogenism in young women and its influence on bone mass density

One of the most important hormonal factors responsible for bone health is estradiol. Genetic factors, adequacy of hormonal functioning, nutrition and physical activity may be the markers of bone status and development in young women. During adolescence, women reach peak bone acquisition and develop a skeletal mass. This process is largely regulated by endocrine factors mainly such as adequate levels of gonadal, adrenal and pituitary hormones. The crucial role played by estradiol and its impact on bones are very multiple. Estradiol induces growth factors' activation, receptor activator of nuclear factor kappa B ligand (RANKL) production inhibition and is mainly referred to antiresorptive activity. Clinical situations leading to hypoestrogenism has been linked to decreased bone mineral density leading to osteopenia and osteoporosis. This status both in fertile and perimenopausal women can increase the risk of pathological fractures. Such conditions as hypothalamic-pituitary insufficiency (functional hypothalamic amenorrhea, anorexia nervosa, Kallmann syndrome, hyperprolactinemia), ovarian failure (gonadal dysgenesis, premature ovarian failure) and iatrogenic treatment (surgery, chemotherapy, radiotherapy) can cause hypoestrogenism. The treatment of osteopenia and osteoporosis caused by hypoestrogenism is very essential and multidirectional. The crucial role of the therapy is the achievement of proper serum estradiol concentration and eliminate the causes of hypoestrogenism.