Effect of VDR gene polymorphisms on osteocalcin secretion in calcitriol-stimulated human osteoblasts.

BACKGROUND: The impact of vitamin D receptor (VDR) gene polymorphisms in bone metabolism remains controversial. Some authors have found a beneficial effect of some VDR gene polymorphisms, while others found no differences, or even a lower bone mass in subjects with the same type of polymorphisms. The aim of this study was to assess if the VDR gene polymorphisms could have an effect on the calcitriol-stimulated osteocalcin in human osteoblasts. METHODS: Osteoblasts were obtained from human femoral necks replaced because of osteoarthritis. Bones were cut into pieces of 1 to 2 mm and placed in a nylon mesh. After the migration of osteoblasts, the pieces were collected and cultured with different concentrations of calcitriol (10(-8), 10(-9), and 10(-1)0 mol/L). After 48 hours of incubation with calcitriol, the osteocalcin secreted into the medium (corrected by either total proteins or total DNA content) was measured. The DNA was extracted from the osteoblasts, amplified by polymerase chain reaction (PCR), and analyzed for target sequences sites of the BsmI, ApaI, TaqI, and FokI restriction enzymes. RESULTS: The response observed in osteocalcin secretion in the bb or TT genotypes doubled the response observed in the BB or tt genotypes (calcitriol 10(-8) and 10(-9) mol/L). A slight trend was also observed with the aa genotype. Men showed higher levels of osteocalcin secretion than women. Age did not show any influence in osteocalcin secretion. CONCLUSION: VDR alleles and gender demonstrated an effect on the osteocalcin secretion. BB or tt genotypes, and also the "A" allele, showed the lowest calcitriol-stimulated osteocalcin secretion.

Differential effects of 17beta-estradiol and raloxifene on bone and lipid metabolism in rats with chronic kidney disease and estrogen insufficiency.

OBJECTIVE: The aim of this study was to evaluate the effect of 17beta-estradiol, raloxifene, and 1-alpha,25-dihydroxycholecalciferol or calcitriol on bone and lipid metabolism in chronic kidney disease and estrogen insufficiency. METHODS: Six-month-old female Sprague-Dawley rats (n = 48) were ovariectomized and nephrectomized (seven eighths). One week after surgery, the rats were divided into six groups and treated with (1) placebo, (2) 17beta-estradiol 10 microg kg day, (3) raloxifene 1 mg kg day, (4) calcitriol 10 ng kg day, (5) 17beta-estradiol + calcitriol, and (6) raloxifene + calcitriol. A group of untreated animals with chronic kidney disease and normal ovarian function was used as a control group (n = 5). The rats were killed after 8 weeks of treatment. Blood samples were drawn for serum analyses; the right tibia was removed to perform histomorphometric analyses, uteri were used as tissue markers of estrogen replacement, and paraffin-embedded sections of the uterus and the fourth breast were used for histopathologic evaluation. RESULTS: Raloxifene, alone or combined with calcitriol, and 17beta-estradiol combined with calcitriol significantly diminished total cholesterol level compared with placebo. Qualitative histological and histomorphometric analyses showed that both the single treatments and their combinations were able to increase the trabecular connectivity compared with placebo. The less beneficial results were obtained with 17beta-estradiol alone, whereas the more beneficial results were obtained with the combined treatments, particularly with raloxifene and calcitriol. CONCLUSIONS: In summary, this experimental study demonstrates the advantages of replacing both hormonal deficiencies together. The combination of calcitriol and raloxifene, a selective estrogen receptor modulator, showed a better lipid, uterus, and bone profile.