Impact of Tenofovir-Based Pre-exposure Prophylaxis on Biomarkers of Bone Formation, Bone Resorption, and Bone Mineral Metabolism in HIV-Negative Adults.

BACKGROUND: Pre-exposure prophylaxis (PrEP) with emtricitabine (FTC)/tenofovir disoproxil fumarate (TDF) reduces the risk of HIV seroconversion but may promote bone mineral density (BMD) decline. The mechanisms of BMD decline with FTC/TDF remain unclear, and studies in HIV-positive individuals have been confounded by the effects of HIV and concomitant antiretroviral medications. We evaluated the impact of FTC/TDF on biomarkers of bone remodeling and bone mineral metabolism in HIV-negative men and women enrolled in the Partners PrEP Study. METHODS: In a random sample of HIV-negative participants randomized to FTC/TDF PrEP (n = 50) or placebo (n = 50), serum parathyroid hormone (PTH), bone biomarkers (C-telopeptide, procollagen 1 intact N-terminal propeptide, and sclerostin), and plasma fibroblast growth factor 23 were measured at baseline and month 24, and the percentage change was compared between groups. In a complementary analysis, we compared the change in biomarkers between participants with and without a 25% decline in glomerular filtration rate (GFR) on FTC/TDF. RESULTS: Baseline characteristics were similar between the groups (median age, 38 years; 40% women). Vitamin D insufficiency was common, but baseline GFR and PTH were in the normal range. We observed a significantly greater percent increase in serum C-telopeptide in participants randomized to FTC/TDF vs placebo (P = .03), suggesting an increase in bone remodeling. We observed no differences in the other biomarkers, or in a separate analysis comparing participants with and without a decline in GFR. CONCLUSIONS: Increased bone remodeling may mediate the BMD decline observed with tenofovir-containing PrEP and antiretroviral therapy, independent of a TDF-mediated decrease in kidney function.

Therapy of Hypoparathyroidism With PTH(1-84): A Prospective Six Year Investigation of Efficacy and Safety.

CONTEXT: Human recombinant (rh)PTH(1-84) was recently approved for the treatment of refractory hypoparathyroidism, based upon a short-term phase 3 clinical trial. Long-term data are needed, because no time limit was placed on the treatment period. OBJECTIVE: We studied the effect of long-term rhPTH(1-84) treatment in hypoparathyroidism for up to 6 years. DESIGN: Prospective open-label study. SETTING: Referral center. PATIENTS: A total of 33 subjects with hypoparathyroidism. INTERVENTIONS: rhPTH(1-84) treatment was initiated at a starting dose of 100 µg every other day for 6 years. Due to the availability of new dosages during the 6-year time period of the study, the dose could be and was adjusted for most patients to a daily dosing regimen. MAIN OUTCOME MEASURES: Supplemental calcium and vitamin D requirements, serum and urinary calcium (monthly for 6 mo and then biannually), serum phosphorus, bone turnover markers, and bone mineral density (BMD) biannually. RESULTS: Treatment with rhPTH(1-84) progressively reduced supplemental calcium requirements over 6 years by 53% (P < .0001) and 1,25-dihydroxyvitamin D requirements by 67% (P < .0001). Sixteen subjects (48%) were able to eliminate 1,25-dihydroxyvitamin D supplementation completely. Serum calcium concentration remained stable, and urinary calcium excretion fell. Lumbar spine BMD increased (3.8 ± 1%, P = .004) as did total hip BMD (2.4 ± 1%, P = .02), whereas femoral neck BMD remained stable and the distal one third radius decreased (-4.4 ±1%, P < .0001). Bone turnover markers increased significantly, reaching a 3-fold peak above baseline values at 1 year and subsequently declining but remaining higher than pretreatment values. Hypercalcemia was uncommon (12 episodes over 6 y; 2.5% of all values). CONCLUSIONS: Long-term, continuous therapy of hypoparathyroidism for 6 years with rhPTH(1-84) is associated with reductions in supplemental calcium and calcitriol requirements, stable serum calcium concentration, and reduced urinary calcium excretion. The safety profile remains good. These data represent the longest experience with the therapeutic use of PTH for any condition and demonstrate its long-term efficacy and safety in hypoparathyroidism.

Vitamin D-related gene polymorphisms, plasma 25-hydroxyvitamin D, and breast cancer risk.

PURPOSE: Studies of vitamin D-pathway genetic variants in relation to cancer risk have been inconsistent. We examined the associations between vitamin D-related genetic polymorphisms, plasma 25-hydroxyvitamin D [25(OH)D], and breast cancer risk. METHODS: In a population-based case-control study of 967 incident breast cancer cases and 993 controls, we genotyped 25 polymorphisms encoding the vitamin D receptor (VDR) gene, 1α-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1), and vitamin D-binding protein (GC) and measured plasma 25(OH)D. We used multivariable logistic regression to estimate adjusted odds ratios (ORs) and 95 % confidence intervals (CIs). RESULTS: Among CYP24A1 polymorphisms, rs6068816 was associated with a 72 % reduction in breast cancer risk (TT vs. CC, OR 0.28, 95 % CI 0.10-0.76; p trend = 0.01), but for rs13038432, the 46 % decrease included the null value (GG vs. AA, OR 0.54, 95 % CI 0.17-1.67; p trend = 0.03). Increased risk that included the null value was noted for CYP24A1 rs3787557 (CC vs. TT, OR 1.34, 95 % CI 0.92-1.89). The VDR polymorphism, TaqI (rs731236), was associated with a 26 % risk reduction (TT vs. CC, OR 0.74, 95 % CI 0.56-0.98; p trend = 0.01). For other polymorphisms, ORs were weak and included the null value. The inverse association for plasma 25(OH)D with breast cancer was more pronounced (OR 0.43, 95 % CI 0.27-0.68) among women with the common allele for CYP24A1, rs927650 (p for interaction on a multiplicative scale = 0.01). CONCLUSION: Breast cancer risk may be associated with specific vitamin D-related polymorphisms, particularly CYP24A1. Genetic variation in the vitamin D pathway should be considered when designing potential intervention strategies with vitamin D supplementation.

Association between plasma 25-hydroxyvitamin D and breast cancer risk.

Vitamin D has been associated with decreased risk of several cancers. In experimental studies, vitamin D has been shown to inhibit cell proliferation and induce differentiation and apoptosis in normal and malignant breast cells. Using a population-based case-control study on Long Island, New York, we examined the association of breast cancer with plasma 25-hydroxyvitamin D (25-OHD) levels, a measure of vitamin D body stores. In-person interviews and blood specimens were obtained from 1,026 incident breast cancer cases diagnosed in 1996 to 1997 and 1,075 population-based controls. Plasma 25-OHD was measured in batched, archived specimens by Diasorin RIA. The mean (SD) plasma 25-OHD concentration was 27.1 (13.0) and 29.7 (15.1) ng/mL in the cases and controls, respectively (P < 0.0001). Plasma 25-OHD was inversely associated with breast cancer risk in a concentration-dependent fashion (P(trend) = 0.002). Compared with women with vitamin D deficiency (25-OHD, <20 ng/mL), levels above 40 ng/mL were associated with decreased breast cancer risk (odds ratio, 0.56; 95% confidence interval, 0.41-0.78). The reduction in risk was greater among postmenopausal women (odds ratio, 0.46; 95% confidence interval, 0.09-0.83), and the effect did not vary according to tumor hormone receptor status. In summary, these results add to a growing body of evidence that adequate vitamin D stores may prevent breast cancer development. Whereas circulating 25-OHD levels of >32 ng/mL are associated with normal bone mineral metabolism, our data suggest that the optimal level for breast cancer prevention is >or=40 ng/mL. Well-designed clinical trials are urgently needed to determine whether vitamin D supplementation is effective for breast cancer chemoprevention.