[The influence of hormonal replacement therapy on bone density in postmenopausal women depending on polymorphism of vitamin D receptor (VDR) and estrogen receptor (ER) genes]

Abstract

Osteoporosis is still an important health problem in modern societies. The densitometric criterion for the diagnosis of this condition established by WHO in 1994 is bone mass density (BMD) lower than 2.5 standard deviation (SD) from the mean value for young healthy individuals of the same sex. Between 60 and 90% of bone density (quantity of bone tissue in the human skeleton) at the time when growth is terminated is genetically determined. For this reason, genes predisposing to osteoporosis and mechanisms of their activity remain the object of investigations. Among them are genes coding for vitamin D receptor (VDR), estrogen receptor (ER), type I collagen, TGF-beta and IL-6. Diminishing bone density past the age of thirty is a physiologic process. Bone loss averages 0.3-0.6% per year. Acceleration of this process to 1.2-6% per year in postmenopausal women has been attributed to constantly decreasing estrogen concentration. Hence, the gold standard in osteoporosis prevention and treatment includes estrogen-progestagen therapy enriched with vitamin D analogues, calcium-rich diet and regular physical exercises. Treatment of osteoporosis can be long and expensive. The condition may lead to disability. Osteoporotic fractures and their complications may be fatal. For these reasons, the chief priority in osteoporosis is prevention. Unfortunately, current diagnostic methods (for detection of osteoporosis and monitoring of treatment) remain unsatisfactory. Molecular techniques offer a promising approach to diagnosis and monitoring of therapy. Additionally, the risk of osteoporosis in 1st degree relatives can be assessed and early prevention can be started. The present study addressed the following questions: 1. Are there differences in spine BMD in untreated women with postmenopausal osteoporosis depending on polymorphism of VDR and ER genes? 2. Does efficacy of treatment (increase in spine BMD) in women with postmenopausal osteoporosis depend on polymorphism of VDR and ER genes? 3. What estrogen concentration is necessary to protect bone tissue depending on the polymorphism of VDR and ER genes? The study group included 44 postmenopausal women aged 44-75 years with primary osteoporosis on cyclic HRT (hormonal replacement therapy). Two hormonal preparations were administered: Systen 50 (Jansen Cilag) transdermal system twice per week between day 1 and 21 of the cycle; Provera (Upjohn) 5 mg tablets daily between day 16 and 27 of the cycle. This therapy was supplemented with vitamin D analogue (Alphacalcidolum, Glaxo-Poznan) orally at 0.25 microg per day, calcium-enriched (1200 mg daily) diet and regular physical exercise. Patients were qualified to the study on the basis of a questionnaire. Women with secondary osteoporosis were excluded. TSH, FT3, and FT4 concentrations, as well as fasting glucose were measured. 24 h glycemia was established in women with elevated glucose levels. Polymorphism of the ER gene was studied with Xba I and Pvu II restrictases. Polymorphism of the VDR gene was studied with Bsm I restrictase. Age and BMI were recorded. Spine BMD was determined with DEXA (Dual Energy X-ray Absorptiometry (Lunar instrument) before treatment and after 12 months of HRT. Serum estradiol concentrations were measured before treatment and after 2 months of HTR. The following conclusions were drawn: 1. There is no connection between VDR and ER gene polymorphism and degree of osteoporosis before treatment. 2. XX, PP and Bb markers or X, P, B alleles are associated with a significant decrease in therapeutic efficacy. Nevertheless, satisfactory results were achieved in each woman with primary osteoporosis. 3. Estradiol concentration in serum before and during HRT does not depend on the polymorphism of VDR and ER genes.