Enhancement of vitamin D metabolites in the eye following vitamin D3 supplementation and UV-B irradiation.

PURPOSE: This study was designed to measure vitamin D metabolites in the aqueous and vitreous humor and in tear fluid, and to determine if dietary vitamin D3 supplementation affects these levels. We also determined if the corneal epithelium can synthesize vitamin D following UV-B exposure. METHODS: Rabbits were fed a control or vitamin D3 supplemented diet. Pilocarpine-stimulated tear fluid was collected and aqueous and vitreous humor were drawn from enucleated eyes. Plasma vitamin D was also measured. To test for epithelial vitamin D synthesis, a human corneal limbal epithelial cell line was irradiated with two doses of UV-B (10 and 20 mJ/cm(2)/day for 3 days) and vitamin D was measured in control or 7-dehydrocholesterol treated culture medium. Measurements were made using mass spectroscopy. RESULTS: 25(OH)-vitamin D3 and 24,25(OH)(2)-vitamin D3 increased significantly following D3 supplementation in all samples except vitreous humor. Tear fluid and aqueous humor had small but detectable 1,25(OH)(2)-vitamin D3 levels. Vitamin D2 metabolites were observed in all samples. Vitamin D3 levels were below the detection limit for all samples. Minimal vitamin D3 metabolites were observed in control and UV-B-irradiated epithelial culture medium except following 7-dehydrocholesterol treatment, which resulted in a UV-B-dose dependent increase in vitamin D3, 25(OH)-vitamin D3 and 24,25(OH)(2)-vitamin D3. CONCLUSIONS: There are measurable concentrations of vitamin D metabolites in tear fluid and aqueous and vitreous humor, and oral vitamin D supplementation affects vitamin D metabolite concentrations in the anterior segment of the eye. In addition, the UV exposure results lead us to conclude that corneal epithelial cells are likely capable of synthesizing vitamin D3 metabolites in the presence of 7-dehydrocholesterol following UV-B exposure.

Vitamin D enhances corneal epithelial barrier function.

PURPOSE: The purpose of this study was to determine whether 25-hydroxyvitamin D(3) (25(OH)D(3)) and/or its active metabolite, 1α,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), can enhance corneal epithelial barrier function. The authors also determined if corneas contain mRNA for the vitamin D receptor (VDR) and 1α-hydroxylase, the enzyme required to convert 25(OH)D(3) to 1,25(OH)(2)D(3), and measured vitamin D metabolite concentrations in aqueous and vitreous humor. METHODS: RT-PCR was used to examine mouse, rabbit, and human corneal epithelial VDR and 1α-hydroxylase mRNA. Vitamin D metabolites were measured using a selective vitamin D derivatizing agent and mass spectroscopy. Barrier function experiments were performed by measuring inulin permeability (IP) and/or transepithelial resistance (TER) in control, 25(OH)D(3)-, and 1,25(OH)(2)D(3)-treated human and rabbit corneal epithelial monolayers cultured on permeable inserts. Ca(2+) was removed, then reintroduced to the culture medium while IP and TER readings were taken. Occludin levels were examined using Western blotting. RESULTS: All corneal samples were positive for both VDR and 1α-hydroxylase mRNA. All vitamin D metabolites except for unhydroxylated vitamin D(3) were detected in aqueous and vitreous humor. Epithelial cells showed increased TER, decreased IP, and increased occludin levels when cultured with 25(OH)D(3) and 1,25(OH)(2)D(3). CONCLUSIONS: We conclude that corneas contain mRNA for VDR and 1α-hydroxylase as well as significant vitamin D concentrations. 25(OH)D(3) and its active metabolite 1,25(OH)(2)D(3), both enhance corneal epithelial barrier function.

Teriparatide is safe and effectively increases bone biomarkers in institutionalized individuals with osteoporosis.

Institutionalized adults with severe developmental disabilities have a high rate of minimal trauma and appendicular fracture. There is little information about osteoporosis treatment in this population. In this efficacy and safety study, men and women with severe developmental disabilities and osteoporosis received 20 mcg teriparatide subcutaneously daily for 18-24 months. Markers of bone formation [procollagen type 1 intact N-terminal propeptide (P1NP)] and resorption [C-telopeptide (CTx)] were measured at three-month intervals. Serum calcium was measured at two-week intervals for 12 weeks and thereafter at three-month intervals. Twenty-seven individuals received at least one injection. The incidence of hypercalcemia was 11.1% but was persistent and led to medication discontinuation in only one participant. Biomarkers of bone formation increased rapidly, doubling by three months. At 12 months, P1NP and CTx remained elevated from baseline; P1NP had risen from 66.95 +/- 83.71 microg/l (mean +/- SD) to 142.42 +/- 113.85 microg/l (P = 0.05), and CTx had increased from 0.377 +/- 0.253 to 1.016 +/- 1.048 ng/ml (P = 0.01). The majority of participants had an increase in P1NP of over 10 microg/l. In conclusion, teriparatide is safe and effective in developmentally disabled institutionalized adults. Serial calcium measurements are warranted, particularly during the first three months of therapy.

Effects of a low sodium diet on bone metabolism.

Osteoporosis is a serious public health problem, and dietary interventions may potentially be helpful in preventing this disorder. The purpose of this study was to determine the effects of a low sodium diet on bone metabolism in postmenopausal women. This was a longitudinal study to determine the effects of a low sodium (2-g/day) diet on bone. Forty postmenopausal African-American and Caucasian women were enrolled in a 2-g/day sodium diet for 6 months. Sodium and calcium excretion, bone turnover, and calcitropic hormones (intact parathyroid hormone (PTH) and 1,25 dihydroxyvitamin D) were measured before and 6 months after the intervention. In women who had baseline sodium excretions equal to or greater than the average sodium intake in the United States (> or =3.4 g/day), the low sodium diet resulted in significant decreases in sodium excretion (P = 0.01), in calcium excretion (P = 0.01), and in a biomarker of bone turnover, aminoterminal propeptide of type I collagen (P = 0.04). However, there were no significant changes in calcitropic hormones, including intact PTH (P = 0.97) or 1,25 dihydroxyvitamin D (P = 0.49) with the low sodium diet. These findings suggest that in postmenopausal women with sodium intakes > or =3.4 g/day, a low sodium diet may have benefits for skeletal health.