Hexafluoro-1,25-dihydroxyvitamin D3 has markedly increased potency in inhibiting proliferation of cultured human keratinocytes compared with 1,25-dihydroxyvitamin D3

BACKGROUND

Although topical 1,25-dihydroxyvitamin D3 (calcitriol, 1, 25(OH)2D3) and its analogues, calcipotriol and tacalcitol, are effective for patients with psoriasis, some patients show little or no response. There is a need to develop more potent analogues of 1, 25(OH)2D3. Hexafluoro-1,25(OH)2D3 (F6-1,25(OH)2D3) is at least 10 times more potent than 1,25(OH)2D3 on calcium metabolism.

OBJECTIVES

We were interested in whether F6-1,25(OH)2D3 was also more potent than 1,25(OH)2D3 in inhibiting normal human and psoriatic keratinocyte proliferation.

METHODS

The antiproliferative activity of F6-1,25(OH)2D3 and 1,25(OH)2D3 was determined by 3H-thymidine incorporation into keratinocyte DNA and by counting basal cells.

RESULTS

F6-1,25(OH)2D3 was approximately 10-fold more active and had a longer lasting antiproliferative effect than 1,25(OH)2D3 on normal human keratinocytes, and was about 100-fold more potent than 1, 25(OH)2D3 on human psoriatic keratinocytes as determined by 3H-thymidine incorporation. F6-1,25(OH)2D3 also caused a dose-dependent decrease in the number of basal cells and was 100-fold more active than 1,25(OH)2D3.

CONCLUSIONS

The increased potency and the long-lasting effects of F6-1,25(OH)2D3 suggest that F6-1,25(OH)2D3 may be a potent candidate agent for treating psoriasis.

Condition-dependent presence of beta-lipotropin-like peptide in human keratinocytes

This study aimed to characterize the beta-endorphin-immunoreactive material (betaE-IR) detectable in normal human keratinocytes (NHK). The effects of different culturing conditions and UV-irradiation on production of betaE-IR by NHK were assessed by radioimmunoassay and HPLC. All culture systems contained low levels of betaE-IR that was increased in conditioned media after UV-irradiation under certain conditions. NHK grown in nutrient-poor medium contained highest levels of betaE-IR that exhibited beta-lipotropin-like properties after HPLC analysis. The other culturing conditions displayed no authentic betaE-related peptides. Our results indicate that under certain culturing conditions NHK can produce POMC peptides like beta-lipotropin, which can be induced by UV-radiation.

An evaluation of the biologic activity and vitamin D receptor binding affinity of the photoisomers of vitamin D3 and previtamin D3

Skin is in the site of previtamin D3 and vitamin D3 synthesis and their isomerization in response to ultraviolet irradiation. At present, little is known about the function of the photoisomers of previtamin D3 and the vitamin D3 in skin cells. In this study we investigated the antiproliferative activity of the major photoisomers and their metabolites in the cultured human keratinocytes by determining their influence on 3H-thymidine incorporation into DNA. Our results demonstrated at both 10(-8) and 10(-6) M in a dose-dependent manner. Lumisterol, tachysterol3, 5,6-trans-vitamin D3, and 25-hydroxy-5,6-trans-vitamin D3 only induced significant inhibition at 10(-6) M. 25-Hydroxytachysterol3 was approximately 10- to 100-fold more active than tachysterol3. 7-Dehydrocholesterol was not active even at 10(-6) M. The dissociation constants of vitamin D receptor (VDR) for 25-hydroxytachysterol3, 25-hydroxy-5,6-trans-vitamin D3, and 5,6-trans-vitamin D3 were 22, 58, and 560 nM, respectively. The dissociation constants for 7-dehydrocholesterol, tachysterol, and lumisterol were greater than 20 microM. In conclusion, vitamin D3, its photoisomers and the photoisomers of previtamin D3 have antiproliferative activity in cultured human keratinocytes. However, the antiproliferative activity did not correlate with their binding affinity for VDR. The results suggest that some of the photoproducts may be metabolized to their 25-hydroxylated and 1 alpha,25-dihydroxylated counterparts before acting on VDR. Alternatively, a different receptor may recognize these photoproducts or another mechanism may be involved in modulating the antiproliferative activity of the photoisomers examined.

The in vitro evaluation of 25-hydroxyvitamin D3 and 19-nor-1alpha,25-dihydroxyvitamin D2 as therapeutic agents for prostate cancer

Prostate cancer cells contain specific receptors [vitamin D receptors (VDRs)] for 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3), which is known to inhibit the proliferation and invasiveness of these cells. These findings support the use of 1alpha,25(OH)2D3 for prostate cancer therapy. However, because 1alpha,25(OH)2D3 can cause hypercalcemia, analogues of 1alpha,25(OH)2D3 that are less calcemic but that exhibit potent antiproliferative activity would be attractive as therapeutic agents. We investigated the effects of two different types of less calcemic vitamin D compounds, 25-hydroxyvitamin D3 [25(OH)D3] and 19-nor-1alpha,25-dihydroxyvitamin D2 [19-nor-1,25(OH)2D2], and compared their activity to 1alpha,25(OH)2D3 on (a) the proliferation of primary cultures and cell lines of human prostate cancer cells; and (b) the transactivation of the VDRs in the androgen-insensitive PC-3 cancer cell line stably transfected with VDR (PC-3/ VDR). 19-nor-1alpha,25(OH)2D2, an analogue of 1alpha,25(OH)2D3 that was originally developed for the treatment of parathyroid disease, has been shown to be less calcemic than 1alpha,25(OH)2D3 in clinical trials. Additionally, we recently showed that human prostate cells in primary culture possess 25(OH)D3-1alpha-hydroxylase, an enzyme that hydroxylates the inactive prohormone, 25(OH)D3, to the active hormone, 1alpha,25(OH)2D3, intracellularly. We reasoned that the hormone that is formed intracellularly would inhibit prostate cell proliferation in an autocrine fashion. We found that 1alpha,25(OH)2D3 and 19-nor-1alpha,25(OH)2D2 caused similar dose-dependent inhibition in the cell lines and primary cultures in the [3H]thymidine incorporation assay and that both compounds were significantly more active in the primary cultures than in LNCaP cells. Likewise, 25(OH)D3 had inhibitory effects comparable to those of 1alpha,25(OH)2D3 in the primary cultures. In the chloramphenicol acetyltransferase (CAT) reporter gene transactivation assay in PC-3/ VDR cells, 1alpha,25(OH)2D3 and 19-nor-1alpha,25(OH)2D2 caused similar increases in CAT activity between 10(-11)and 10(-9) M. Incubation of PC-3/VDR cells with 5 x 10(-8) M 25(OH)D3 induced a 29-fold increase in CAT activity, similar to that induced by 10(-8) M 1alpha,25(OH)2D3. In conclusion, our data indicate that 25(OH)D3 and 19-nor-1alpha,25(OH)2D2 represent two different solutions to the problem of hypercalcemia associated with vitamin D-based therapies: 25(OH)D3 requires the presence of 1alpha-hydroxylase, whereas 19-nor-1alpha,25(OH)2D2 does not. Both drugs are approved for human use and may be good candidates for human clinical trials in prostate cancer.

A human skin equivalent model that mimics the photoproduction of vitamin D3 in human skin

A human skin equivalent was prepared by culturing human keratinocytes on the surface of nylon filtration meshes containing human skin fibroblasts and by growing the epidermal cells at the air-liquid interface. This human skin equivalent model was used to mimic the photoproduction of vitamin D3 in human skin. It was found that the concentration of 7-dehydrocholesterol and its photoconversion to previtamin D3 and its subsequent thermal isomerization to vitamin D3 in the human skin equivalent was essentially identical to that of human skin. The 7-dehydrocholesterol content in the skin equivalent and human skin was 2187 +/- 296 and 2352 +/- 320 ng/cm2, respectively. The percentage of the major photoproducts of 7-dehydrocholesterol in the skin equivalent following ultraviolet B radiation (0.5 J/cm2) was 35% pre-vitamin D3, 29% lumisterol, and 6% tachysterol; 30% remained as 7-dehydrocholesterol. Similarly, in human skin they were 36%, 29%, 7%, and 28%, respectively. After incubation at 37 degrees C for 30 min, 11% and 12% of the previtamin D3 had thermally isomerized to vitamin D3 in the skin equivalent and human skin. In conclusion, compared with cultured keratinocytes or fibroblasts, the human skin equivalent model provides a superior in vitro system that better mimics the physiology and biochemistry of the photosynthesis of vitamin D3 in human skin.

Transient osteoporosis of hip in pregnancy

Transient osteoporosis in pregnancy is a relatively rare disorder characterized by disabling pain in the hip without prior trauma and by striking radiographic evidence of osteopenia that is limited to the hip. Clinical and radiographic findings regress spontaneously within months after pregnancy and without late sequelae. In this study, we report on a case of a 28-yr-old Caucasian woman who suffered from transient osteoporosis during pregnancy. Nine months later, the patient was asymptomatic and there was resolution of the bone marrow edema pattern seen on the initial magnetic resonance imaging scan of her hip. Follow-up bone densitometry at 1 yr revealed a dramatic increase (12.3%) in bone mineral density of the symptomatic hip. We review the literature and discuss possible mechanisms involved in the pathogenesis of transient osteoporosis in pregnancy.

An immunocytochemical approach to the study of beta-endorphin production in human keratinocytes using confocal microscopy

Proopiomelanocortin (POMC) is a protein that is posttranslationally processed to yield POMC peptides. The main site of POMC expression is the anterior pituitary lobe but many other sources have been identified. There is evidence that the skin produces POMC peptides, although their roles have not yet been defined. In the skin, regulation of POMC gene expression is known to be hair-cycle dependent, and it is localized to the sebaceous gland. In particular, beta-endorphin, a POMC peptide, has been shown to be modulated by TPA, IL-1 alpha, and ultraviolet radiation in keratinocytes. These results were obtained by examination of POMC mRNA levels using the Northern blot method; beta-endorphin protein production by the Western blot method on cultured cells; and immunocytochemistry for tissue preparations. This report represents an approach to use immunocytochemistry to quantify beta-endorphin production in cultured human keratinocytes. Additionally, we examined whether exposure to 20 mJ ultraviolet B radiation (UVB) and/or UVA could influence beta-endorphin production in these cells. Keratinocytes were grown in monolayers, in serum-free medium, fixed, and incubated with antiserum to whole synthetic beta-endorphin. Fluorescence microscopy was performed with a confocal laser scanning microscope. The integrated level of fluorescence was evaluated in n = 18 +/- 8 individual cells, and this was assumed to be proportional to beta-endorphin content. High variability was observed in the fluorescence intensity among cells. No significant differences between control and UVB- or UVA + UVB-treated cells was found. Similar results were produced by using brefeldin A, a compound that disrupts the secretory pathway, eliminating the possibility that the absence of a difference between beta-endorphin content in the treated and control cells was due to secretion of the peptide into the medium. We conclude that: (1) beta-endorphin or beta-endorphin-like peptides are produced in human keratinocytes and are readily detected by immunocytochemistry; (2) under the conditions tested, UVA and/or UVB did not increase beta-endorphin-like immunoreactivity in these cells.

Mechanistic studies to evaluate the enhanced antiproliferation of human keratinocytes by 1alpha,25-dihydroxyvitamin D(3)-3-bromoacetate, a covalent modifier of vitamin D receptor, compared to 1alpha,25-dihydroxyvitamin D(3)

1alpha,25-Dihydroxyvitamin D(3)-3-bromoacetate (1, 25(OH)(2)D(3)-3-BE), an affinity labeling analog of 1alpha, 25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), displayed stronger antiproliferative activities than 1,25(OH)(2)D(3) at 10(-10)-10(-6) M dose levels in cultured human keratinocytes (CHK). Additionally, preincubation of the cells with 10(-6) M 1,25(OH)(2)D(3), followed by treatment with various doses of 1,25(OH)(2)D(3)-3-BE, resulted in a significantly stronger antiproliferative activity by the mixture than individual reagents at every dose level. To search for a mechanism of this observation, we determined that [(14)C]1, 25(OH)(2)D(3)-3-BE covalently labeled human recombinant 1alpha, 25-dihydroxyvitamin D(3) receptor (reVDR) swiftly (<1 min) with a 1:1 stoichiometry and induced conformational changes (in VDR) that are different from 1,25(OH)(2)D(3), by limited tryptic digestion. Furthermore, a protein band, corresponding to reVDR, was specifically labeled by [(14)C]1,25(OH)(2)D(3)-3-BE in CHK extract, indicating that VDR is the main target of [(14)C]1, 25(OH)(2)D(3)-3-BE. The above-mentioned observations suggest that a rapid covalent labeling of VDR in CHK might alter the interaction between the holo-VDR and 1,25(OH)(2)D(3)-controlled genes. Furthermore, we observed that 1,25(OH)(2)D(3)-3-BE significantly decreased the binding of VDR to human osteocalcin vitamin D responsive element (hOCVDRE), as well as the dissociation rate of VDR from hOCVDRE, compared with 1,25(OH)(2)D(3) in COS-1 cells, transiently transfected with a VDR construct. Additionally, 1, 25(OH)(2)D(3)-3-BE was found to be more potent in inducing 1alpha, 25-dihydroxyvitamin D(3)-24-hydroxylase (24-OHase) promoter activity and mRNA expression in keratinocytes. The accumulation of 24-OHase message was also prolonged by the analog. Collectively these results indicated that rapid covalent labeling of VDR in keratinocytes (by 1, 25(OH)(2)D(3)-3-BE) might result in the conversion of apo-VDR to a holo-form, with a conformation that is different from that of the 1, 25(OH)(2)D(3)-VDR complex. This resulted in an enhanced stability of the 1,25(OH)(2)D(3)-3-BE/VDR-VDRE complex and contributed to the amplified antiproliferative effect of 1,25(OH)(2)D(3)-3-BE in keratinocytes.

Analysis of 1,25-dihydroxyvitamin D(3) receptors (VDR) in basal cell carcinomas

We have analyzed expression of 1,25-dihydroxyvitamin D(3) receptor (VDR) protein and mRNA in basal cell carcinomas (BCC) of human skin. VDR immunoreactivity in BCCs was compared with the staining pattern of the proliferation marker Ki-67 in the same tumors. Additionally, VDR staining was compared to staining pattern of apoptotic cells by terminal UTP nucleotide end labeling assay. Frozen sections of superficial type, nodular type, and fibrosing type BCCs were consistently immunoreactive for VDR (mAb 9A7gamma) with almost every tumor cell labeled (n = 15). In general, VDR staining was pronounced in peripheral tumor cells. VDR immunoreactivity was consistently stronger in tumor cells than in adjacent or unaffected epidermis. No visual correlation was found in BCCs comparing labeling patterns of Ki-67-positive or apoptotic cells and mAb 9A7gamma. VDR mRNA was increased in BCCs (n = 6) compared to normal human skin (n = 5), as revealed by reverse transcription-polymerase chain reaction analysis. Our findings indicate that VDR is strongly expressed in BCCs and may be involved in the growth regulation of this tumour, and VDR mRNA and protein are increased in BCCs as compared to normal human epidermis.

Molecular cloning, characterization, and promoter analysis of the human 25-hydroxyvitamin D3-1alpha-hydroxylase gene

The human 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-OHase) gene has been cloned. It contained nine exons and eight introns spanning approximately 6.5 kb and a 1.4-kb 5'-flanking region. The 5'-flanking region contains consensus or highly conserved sequences for TATA, Pu, and CCAAT boxes, four cAMP response elements, two activator protein-1 (AP-1) response elements, two AP-2 response elements, three specific protein-1 (Sp1) response elements, and four NF-kappaB binding sites, but no vitamin D response element. By using luciferase reporter gene constructs of truncated forms of the 1alpha-OHase promoter transfected into a modified pig kidney cell line, AOK-B50, we identified regulatory regions of the 1.4-kb 1alpha-OHase promoter for parathyroid hormone 1-34 [PTH(1-34)], forskolin, and 1,25-hydroxyvitamin D3 [1,25(OH)2D3]. The 1.4-kb 1alpha-OHase promoter (AN1) modestly (1.7-fold) induced luciferase activity, whereas 1,100- (AN2), 827- (AN3), 672- (AN4), 463-(AN5), and 363-bp (AN6)-truncated promoters greatly stimulated luciferase activity by 494-fold, 18.4-fold, 55.3-fold, 643-fold, and 56.4-fold, respectively. PTH(1-34) and forskolin stimulated the activity of all constructs to varying degrees with significantly greater responsiveness for both compounds on AN2 and AN5. 1,25(OH)2D3 suppressed PTH(1-34)-induced activity on AN2 and AN5 constructs by 58% and 52%, respectively, but had no effect on the other constructs. These studies characterize the regulatory regions of the human 1alpha-OHase gene and provide insight into the physiologic basis for regulation of the expression of this gene by PTH and 1,25(OH)2D3.

Immunological responses to ultraviolet light B radiation in Black individuals

Immunological factors are important participants in the pathogenesis of experimental skin tumors. We therefore studied cutaneous immune responses in subjects with either low natural incidence (Black individuals), or a high frequency rate (White individuals) of skin cancer. We performed whole body irradiation with a low dose of ultraviolet light B (UV-B) and evaluated peripheral lymphocytes. UV-B irradiation was associated with small but significant changes in lymphocyte phenotype frequency. In White subjects this consisted of an increased number of CD19 (B cells) and CD 4/29 (inducer of helper T cells); Black subjects had a slight decrease in CD3 (T cells). Natural killer activity, not affected by UV-B in White subjects, increased significantly in Black subjects. UV-B was devoid of immunological effects in vitro for any of the parameters tested. As expected, the low UV-B dose used in this study induced increases of serum vitamin D3 concentrations in White subjects, with lack of response in the Black subjects. We conclude that Black individuals selectively exhibit an increase in Natural Killer activity in response to irradiation with low dose UV-B. This race group-specific immune response to ultraviolet radiation appears to require mediation by the skin. Enhanced Natural Killer activity could underlie at least partly the resistance in Black individuals to the development of photodependent skin cancer.

A liposomal model that mimics the cutaneous production of vitamin D3. Studies of the mechanism of the membrane-enhanced thermal isomerization of previtamin D3 to vitamin D3

We reported previously that the rate of previtamin D3 (preD3) <==> vitamin D3 isomerization was enhanced by about 10 times in the skin compared with that in organic solvents. To elucidate the mechanism by which the rate of this reaction is enhanced in the skin, we developed a liposomal model that mimicked the enhanced isomerization of preD3 to vitamin D3 that was described in human skin. Using this model we studied the effect of changing the polarity of preD3 as well as changing the chain length and the degree of saturation of liposomal phospholipids on the kinetics of preD3 <==> vitamin D3 isomerization. We found that a decrease in the hydrophilic interaction of the preD3 with liposomal phospholipids by an esterification of the 3beta-hydroxy of preD3 (previtamin D3-3beta-acetate) reduced the rate of the isomerization by 67%. The addition of a hydroxyl on C-25 of the hydrophobic side chain (25-hydroxyprevitamin D3), which decreased the hydrophobic interaction of preD3 with the phospholipids, reduced the rate by 87%. In contrast, in an isotropic n-hexane solution, there was little difference among the rates of the conversion of preD3, its 3beta-acetate, and 25-hydroxy derivatives to their corresponding vitamin D3 compounds. We also determined rate constants (k) of preD3 <==> vitamin D3 isomerization in liposomes containing phosphatidylcholines with different carbon chain lengths. The rates of the reaction were found to be enhanced as the number of carbons (Cn) in the hydrocarbon chain of the phospholipids increased from 10 to 18. In conclusion, these results support our hypothesis that amphipathic interactions between preD3 and membrane phospholipids stabilize preD3 in its "cholesterol like" cZc-conformer, the only conformer of preD3 that can convert to vitamin D3. The stronger these interactions were, the more preD3 was likely in its cZc conformation at any moment and the faster was the rate of its conversion to vitamin D3.

An international comparison of serum 25-hydroxyvitamin D measurements

Vitamin D status is usually assessed by measuring the serum 25-hydroxyvitamin D (25(OH)D) concentration. This mainly depends on sunshine exposure, nutrition and age. Interlaboratory variation may hamper comparison between results from different populations. This study reports cross-calibration of the 25(OH)D assays of five laboratories. In study 1, serum 25(OH)D was measured with three different assays in 104 serum samples from a large vitamin D supplementation study. The mean serum 25(OH)D level was 80% higher when measured by competitive protein binding (CPB) assay than by high-performance liquid chromatography (HPLC), while radioimmunoassay (RIA) gave intermediate values. The highest correlation was observed between RIA and HPLC (r = 0.84, p <0.01). Of the serum 25(OH)D values in the lowest quartile by HPLC, 25% were not recognized by CPB and 21% were not recognized by RIA as belonging to the lowest quartile. In study 2, the five laboratories analyzed serum 25(OH)D in eight serum samples covering the concentration range very low to high, with five different assays. The differences between the mean values for serum 25(OH)D between the laboratories with the highest and lowest values was 38%. The ranking order of individual samples according to the serum 25(OH)D value was very similar in all laboratories. The results show that 25(OH)D values from different laboratories can not be assumed to be comparable unless a careful cross-calibration has been performed.

Calcium supplementation prevents seasonal bone loss and changes in biochemical markers of bone turnover in elderly New England women: a randomized placebo-controlled trial

Elderly women are at increased risk for bone loss and fractures. In previous cross-sectional and longitudinal studies of women residing in northern latitudes, bone loss was most pronounced during winter months and in those consuming less than 1 g calcium per day. In this study we sought to test the hypothesis that calcium supplementation by either calcium carbonate or dietary means would prevent seasonal bone loss and preserve bone mass. Sixty older postmenopausal women without osteoporosis were randomized to one of three treatment arms: Dietary milk supplementation (D-4 glasses of milk/day), Calcium carbonate (CaCO3-1000 mg/day in two divided doses), or placebo (P). After 2 yr, placebo-treated women consumed a mean of 683 mg/day of calcium and lost 3.0% of their greater trochanteric (GT) bone mineral density (BMD) (P < 0.03 vs. baseline); Dietary supplemented women averaged a calcium intake of 1028 mg/day and sustained minimal loss from the GT (-1.5%; P = 0.30), whereas CaCO3-treated women (total Ca intake, 1633 mg/day) suffered no bone loss from the GT and showed a significant increase in spinal and femoral neck BMD (P < 0.05). Femoral bone loss occurred exclusively during the two winters of the study (i.e. total loss, -3.2%; P < 0.02 in placebo-treated women) with virtually no change in GT BMD during summer. Serum 25-OH vitamin D declined by more than 20% (P < 0.001) in all groups during the winter months but returned to baseline in summer; PTH levels rose approximately 20% (P < 0.001) during winter but did not return to baseline during the summers. Urine N-telopeptide and osteocalcin levels increased significantly but only in the P-treated women and only during winter. Serum insulin growth factor binding protein 4, an inhibitory insulin growth factor binding protein, rose 15% (P < 0.03) from summer to winter, but this increase was significant only in those women consuming <1000 mg/day of calcium. By multivariate analysis, total calcium intake was the strongest predictor of bone loss from the hip. Urinary N-telopeptide also closely correlated with GT BMD but only during winter (P = 0.003). We conclude that calcium supplementation prevents bone loss in elderly women by suppressing bone turnover during the winter when serum 25-OH vitamin D declines and serum PTH increases. The precise amount of calcium necessary to preserve BMD in elderly women requires further studies, although in this study, at least 1000 mg/day of supplemental calcium was adequate prophylaxis against femoral bone loss.

Serum vitamin D metabolite levels and the subsequent development of prostate cancer (Hawaii, United States)

OBJECTIVES

Because several serum studies of vitamin D metabolites have produced equivocal results on their relation to prostate cancer risk, the purpose of this study is to evaluate this association further.

METHODS

A nested case-control study in a cohort of 3,737 Japanese-American men examined from 1967 to 1970 was conducted in Hawaii (United States). At the time of examination, a single blood specimen was obtained, and the serum was frozen. After a surveillance period of over 23 years, 136 tissue-confirmed incident cases of prostate cancer were identified. Their stored sera and those of 136 matched controls were measured for the following: 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, calcium, phosphorus, and parathyroid hormone.

RESULTS

There were no notable differences between cases and controls in their median serum levels of the five laboratory measurements. Odds ratios (OR) for prostate cancer, based on the quartiles of serum levels in controls, were also determined. The ORs for the highest quartiles relative to the lowest were 0.8 (95 percent confidence interval [CI] = 0.4-1.8) for 25-hydroxyvitamin D and 1.0 (CI = 0.5-2.1) for 1,25-dihydroxyvitamin D.

CONCLUSION

It is possible that the lack of sufficient numbers of study subjects with low vitamin D levels affected the results. Nonetheless, the findings suggest that there is a lack of a strong association between vitamin D and prostate cancer.

Human prostate cells synthesize 1,25-dihydroxyvitamin D3 from 25-hydroxyvitamin D3

Epidemiological and laboratory data support a role for vitamin D in the growth and differentiation of human prostatic cells. These findings prompted us to ask whether prostatic cells could convert 25-hydroxyvitamin D3 (25-OH-D3), the major circulating metabolite of vitamin D3, to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the hormonally active metabolite, in a manner similar to cultured human keratinocytes. Therefore, we investigated three well-characterized human prostate cancer cell lines, LNCaP, DU 145, and PC-3; two primary cultures of cells derived from noncancerous human prostates (one normal and one benign prostatic hyperplasia); and primary cultures of normal human keratinocytes for their ability to synthesize 1,25(OH)2D3. Assays were performed in the presence of 25-OH-D3 as the enzyme substrate and 1,2-dianilinoethane, an antioxidant and free radical scavenger, and in the presence and absence of clotrimazole, a cytochrome P450 inhibitor. DU 145 and PC-3 cells produced 0.31 +/- 0.06 and 0.07 +/- 0.01 pmol of 1,25(OH)2D3/mg protein/h, respectively. No measurable 1,25(OH)2D3 was detected in LNCaP cells. The normal and benign prostatic hyperplasia primary cultures and keratinocyte cultures produced 3.08 +/- 1.56, 1.05 +/- 0.31, and 2.1 +/- 0.1 pmol of 1,25(OH)2D3/mg protein/h, respectively, using a calf thymus receptor binding assay to measure 1,25(OH)2D3 in the presence of 1,2-dianilinoethane. The identity of the analyte as 1,25(OH)2D3 was supported by high performance liquid chromatography using [3H]25-OH-D3 as the enzyme substrate and a solvent system that is specific for 1,25(OH)2D3. The production of 1,25(OH)2D3 in the prostate cancer cell lines and in the primary cultures was completely inhibited in the presence of clotrimazole. This report demonstrates that two of three human prostate cancer cell lines, as well as primary cultures of noncancerous prostatic cells, possess 1alpha-hydroxylase activity and can synthesize 1,25(OH)2D3 from 25-OH-D3. Together with recent data indicating that 1,25(OH)2D3 inhibits the invasiveness of human prostate cancer cells (G. G. Schwartz et al., Cancer Epidemiol. Biomark. Prev., 6: 727-732, 1997), these data suggest a potential role for 25-OH-D3 in the chemoprevention of invasive prostate cancer.

Perspective on the impact of weightlessness on calcium and bone metabolism

As humans venture into space to colonize the moon and travel to distant planets in the 21st century, they will be confronted with a bone disease that could potentially limit their space exploration activities or put them at risk for fracture when they return to earth. It is now recognized that an unloading of the skeleton, either due to strict bed rest or in zero gravity, leads on average to a 1%-2% reduction in bone mineral density at selected skeletal sites each month. The mechanism by which unloading of the skeleton results in rapid mobilization of calcium stores from the skeleton is not fully understood, but it is thought to be related to down regulation in PTH and 1,25-dihydroxyvitamin D3 production. Bone modeling and mineralization in chick embryos is not affected by microgravity, suggesting that bone cells adapt and ultimately become addicted to gravity in order to maintain a structurally sound skeleton. Strategies need to be developed to decrease microgravity-induced bone resorption by either mimicking gravity's effect on bone metabolism, or enhancing physically or pharmacologically bone formation in order to preserve astronauts' bone health.

The utility of portable dual-energy X-ray absorptiometry of the wrist in patients referred to a bone health clinic: a pilot study

Fifty white female patients referred to a bone health care clinic were studied. Patients with a history of fracture were excluded. At the time of hip and spine dual-energy X-ray absorptiometry (DXA), those willing underwent portable dual-energy X-ray absorptiometry (pDXA) of the wrist. The mean age of the patients was 57 yr. Bone mineral density (BMD) assessment was performed on each patient at four different sites: posterior-anterior lumbar spine, nondominant hip, the distal radius and ulna, and the proximal radius and ulna of the nondominant arm. Comparison of the pDXA results with that of the conventional DXA results showed the highest correlation between pDXA of the distal radius and ulna (DR + U) and the DXA of the femoral neck and lumbar spine. By defining a pDXA (DR + U) T-score </= -1 as a positive test and DXA T-score </=-1 as the presence of disease, we obtained a specificity of 93% and a sensitivity of 82% for decreased lumbar spine bone density (positive predictive value 97% and the negative predictive value 70%) and a specificity of 100% and a sensitivity of 83% (positive predictive value is 100% and the negative predictive value is 70%) for decreased femoral neck bone density.

Oncogenic osteomalacia: clinical presentation, densitometric findings, and response to therapy

A 72-yr-old white female who had previously enjoyed excellent health presented with global bone and muscle pain, and chronic fatigue. Her evaluation revealed an increased sedimentation rate and mild anemia, and a diagnosis of polymyalgia rheumatica was made. Prednisone therapy was of little benefit. A laboratory evaluation revealed mild hypocalcemia, marked hypophosphatemia, elevated alkaline phosphatase, normal 25- hydroxyvitamin D, and undectable 1,25-dihydroxyvitamin D. A diagnosis of oncogenic osteomalacia was made and the patient received calcitriol and neutraphos therapy. The patient's initial bone density by dual energy X-ray absorptiometry of the lumbar spine was 0.847 g/cm2 (T score -1.96) and of the femoral neck was 0.669 gm/cm2 (T score -2.89). After 40 mo of treatment with calcitriol and neutraphos, the bone mineral density of the lumbar spine and hip rose dramatically by 47.8 and 59.1%, respectively. Although oncogenic osteomalacia is a very rare metabolic bone disease, its recognition and appropriate treatment can have a dramatic effect not only on the bone mineral density of the patient, but also on the patient's general health and feeling of well-being.

Vitamin D and its major metabolites: serum levels after graded oral dosing in healthy men

We determined the quantitative relationships between graded oral dosing with vitamin D3, 25(OH)D3, and 1,25(OH)2D3 for short treatment periods and changes in circulating levels of these substances. The subjects were 116 healthy men (mean age, 28 +/- 4 years, with usual milk consumption of < or = 0.47 l/day and mean serum 25(OH)D of 67 +/- 25 nmol/l). They were distributed among nine open-label treatment groups: vitamin D3 (25, 250 or 1250 micrograms/day for 8 weeks), 25(OH)D3 (10, 20 or 50 micrograms/day for 4 weeks) and 1,25(OH)2D3 (0.5, 1.0 or 1.0 microgram/day for 2 weeks). All treatment occurred between January 3 and April 3. We measured fasting serum, calcium, parathyroid hormone, vitamin D3, 25(OH)D and 1,25(OH)2D immediately before and after treatment. In the three groups treated with vitamin D3, mean values for circulating vitamin D3 increased by 13, 137 and 883 nmol/l and serum 25(OH)D increased by 29, 146 and 643 nmol/l for the three dosage groups, respectively. Treatment with 25(OH)D3 increased circulating 25(OH)D by 40, 76 and 206 nmol/l, respectively. Neither compound changed serum 1,25(OH)2D levels. However, treatment with 1,25(OH)2D3 increased circulating 1,25(OH)2D by 10, 46 and 60 pmol/l, respectively. Slopes calculated from these data allow the following estimates of mean treatment effects for typical dosage units in healthy 70-kg adults: an 8-week course of vitamin D3 at 10 micrograms/day (400 IU/day) would raise serum vitamin D by 9 nmol/l and serum 25(OH)D by 11 nmol/l; a 4-week course of 25(OH)D3 at 20 micrograms/day would raise serum 25(OH)D by 94 nmol/l; and a 2-week course of 1,25(OH)2D3 at 0.5 microgram/day would raise serum 1,25(OH)2D by 17 pmol/l.