Colon cancer and solar ultraviolet B radiation and prevention and treatment of colon cancer in mice with vitamin D and its Gemini analogs

It has been recognized that people who live at higher latitudes and who are vitamin D deficient are at higher risk of dying from many common cancers including colon cancer. To evaluate the role of vitamin D deficiency on colon tumor growth, Balb/c adult male mice were fed either a vitamin D sufficient or vitamin D deficient diet for 10 weeks. Mice were arranged into groups of six and each animal received subcutaneously 10(4) MC-26 cells in the posterior trunk. The tumor size was recorded daily. By day 9 there was a significant difference in tumor volume between the vitamin D sufficient and vitamin D deficient mice. By day 18 the vitamin D deficient animals had a tumor size that was 56% larger compared to the animals that were vitamin D sufficient. To determine whether treatment with active vitamin D analogs could further decrease colon tumor growth in a vitamin D sufficient state, groups of mice were treated with the novel 19-nor-Gemini compounds. The mice were fed a low calcium diet. Twenty-four hours after tumor implantation, the mice received, three times weekly, one of the vitamin D analogs or the vehicle. The group that received Gemini 1,25-dihydroxy-21(3-hydroxy-3-trifluoromethyl-4-trifluoro-butynyl)-19-nor-20S-cholecalciferol (3) showed a dose-dependent decrease in tumor volume. On day 19, at the dose level of 0.02microg molar equivalents (E), the tumor volume was reduced by 41% when compared to the control group. At the same time point, the hexadeuterated analog 1,25-dihydroxy-21(3-hydroxy-3-trifluoromethyl-4-trifluoro-butynyl)-26,27-hexadeutero-19-nor-20S-cholecalciferol (4), administered at the 10-fold lower dose of 0.002microgE, showed a 52% reduction in tumor volume (p<0.05), compared to the control group. Animals that received 1,25(OH)(2)D(3) at 0.002 and 0.02microg showed a trend in tumor volume reduction at the highest dose but the changes were not statistically significant. An evaluation of serum calcium concentrations revealed that the calcium levels were normal in all groups, except the group receiving 0.02microgE of 4. The results from these studies demonstrate that vitamin D deficiency may accelerate colon cancer growth and that novel Gemini analogs of 1,25(OH)(2)D(3) may be an effective new approach for colon cancer treatment.

Ultraviolet Exposure and Vitamin D Synthesis in a Sun‐Dwelling and a Shade‐Dwelling Species of Anolis: Are There Adaptations for Lower Ultraviolet B and Dietary Vitamin D3 Availability in the Shade?

We compared the natural ultraviolet B (UV-B) exposure, dietary vitamin D, and skin-generated vitamin D synthesis for adult males of two species of Jamaican anoles. The more shade-tolerant and thermal-conforming Anolis lineotopus merope, rarely exposed to full sun, experienced less UV-B irradiation in its shady environment than the more heliophilic and thermophilic Anolis sagrei, which frequently basked in full sun during the morning hours (0800-1100 hours). Both species obtained detectable levels of vitamin D(3) in their diet, but the heliophilic A. sagrei obtained more. To compensate for less availability of UV-B and dietary vitamin D, the skin of A. lineotopus merope seems to have acquired a greater sensitivity than that of A. sagrei regarding UV-B-induced vitamin D(3) photobiosynthesis. We assessed this by observing a greater conversion of provitamin D to photoproducts in skin exposed to UV-B from a sunlamp. The reduced skin sensitivity of A. sagrei regarding vitamin D photobiosynthesis may reflect a correlated response associated with less need for vitamin D photobiosynthesis and greater need for UV-B screening capacity as an adaptation to a more damaging UV-B environment. However, the possibility that adaptations for photobiosynthesis of vitamin D and for protection from skin damage could involve independent mechanisms needs investigation. Also, the ability to behaviorally regulate UV-B exposure, as shown for the panther chameleon, would benefit both species of Anolis and should be investigated.

Topical paricalcitol (19-nor-1 alpha,25-dihydroxyvitamin D2) is a novel, safe and effective treatment for plaque psoriasis: a pilot study

BACKGROUND

There continues to be a need to develop new pharmacological approaches for treating psoriasis. Topical active vitamin D compounds have proven to be both safe and effective for treating psoriasis. Paricalcitol (19-nor-1 alpha,25-dihydroxyvitamin D(2)) is a novel vitamin D analogue which has been developed for the prevention of secondary hyperparathyroidism in patients with chronic renal failure.

OBJECTIVES

To investigate the efficacy and safety of 12 weeks' therapy with a once-daily application of paricalcitol ointment (15 microg g(-1)) in comparison with placebo ointment.

METHODS

This pilot double-blinded self-controlled study was initiated in 11 patients with moderate plaque psoriasis. To characterize the biological effects further and to evaluate the efficacy of topical paricalcitol treatment in psoriasis, we have analysed immunohistochemically the expression of one of the markers for epidermal differentiation (transglutaminase K) in paricalcitol-treated skin as compared with placebo treatment.

RESULTS

Treatment with paricalcitol was superior to placebo treatment beginning at week 1. The global severity score for erythema, plaque elevation and scaling was improved significantly more by paricalcitol ointment than by placebo (P < 0.001). Similar results were obtained for assessments of scaling, erythema and plaque elevation. No symptoms of local skin irritation were noted. Laboratory parameters including serum calcium, phosphorus, parathyroid hormone and urinary calcium/creatinine ratio did not reveal any changes of clinical relevance during treatment. The immunoreactivity of transglutaminase K changed after 12 weeks of paricalcitol treatment almost completely to the pattern characteristic for nonlesional psoriatic skin.

CONCLUSIONS

Once-daily application of paricalcitol ointment was safe and effective for the treatment of plaque psoriasis.

Topical PTH (1-34) is a novel, safe and effective treatment for psoriasis: a randomized self-controlled trial and an open trial

BACKGROUND

There continues to be a need to develop new pharmacological approaches for treating the common skin disease psoriasis. Human skin produces parathyroid hormone related peptide. This peptide is a potent inhibitor of epidermal cell growth.

OBJECTIVES

A programme was initiated to determine whether an agonist of this peptide's receptor, PTH (1-34), could be developed as a drug to treat psoriasis.

METHODS

PTH (1-34) was formulated in Novasome A cream. Fifteen adult patients with chronic plaque psoriasis who had failed to respond to at least one standard treatment were enrolled in a randomized double-blinded placebo self-controlled trial. The patients topically applied to a 25-cm2 psoriatic lesion 0.1 g of either Novasome A cream or Novasome A cream that contained 20 microg of PTH (1-34) twice a day for 2 months. At the end of the double-blind study, patients were enrolled in an open large area study. Ten patients applied PTH (1-34) (50 microg per 0.1 g) once daily to their psoriatic lesions. The patients were evaluated for their global improvement and calcium metabolism.

RESULTS

Novasome A cream enhanced the percutaneous absorption of PTH (1-34) in human skin in comparison with formulations in propylene glycol or normal saline. Psoriatic lesions treated with PTH (1-34) showed marked improvement in scaling, erythema and induration. There was a 67.3% improvement in the global severity score for the lesion treated with PTH (1-34) compared with the placebo-treated lesion, which only showed a 17.8% improvement. Ten patients topically applied PTH (1-34) on all of their lesions in a stepwise manner. A Psoriasis Area and Severity Index score analysis of all the patients revealed improvement of 42.6% (P < 0.02). None of the patients experienced hypercalcaemia or hypercalciuria or developed any side-effect to the medication.

CONCLUSIONS

Patients who were resistant to at least one standard therapy for psoriasis had a remarkable improvement in their psoriasis when they applied PTH (1-34) to their lesion(s). No untoward toxicity was observed in any of the subjects. This pilot study suggests that topical PTH (1-34) is a safe and effective novel therapy for psoriasis.

Treatment of vitamin D deficiency due to Crohn's disease with tanning bed ultraviolet B radiation

In Crohn's disease, severe skeletal demineralization, secondary hyperparathyroidism, and muscle weakness can occur. This may be caused by impaired vitamin D absorption, resulting from extensive intestinal disease and resection of duodenum and jejunum, where vitamin D is absorbed. We report a 57-year-old woman with a long history of Crohn's disease and short-bowel syndrome who had only 2 feet of small intestine remaining after 3 bowel resections. She was taking a daily multivitamin containing 400 IU of vitamin D(3) and was dependent on total parenteral nutrition that contained 200 IU of vitamin D and calcium (18 mEq in a 1-L bag infused over 8 hours daily) for a period of 36 months. Despite the above replacement, she complained of bone pain and muscle weakness, and she continued to be vitamin D-deficient with a 25(OH)D level <20 ng/mL. She was then exposed to ultraviolet B (UVB) radiation in a tanning bed wearing a 1-piece bathing suit for 10 minutes, 3 times a week for 6 months at the General Clinical Research Center, Boston University Medical Center. She tolerated the irradiation well without evidence of erythema. After 4 weeks, her serum 25(OH)D level increased by 357% from 7 to 32 ng/mL, parathyroid hormone level decreased by 52% from 92 to 44 pg/mL, and the serum calcium level increased from 7.8 to 8.5 mg/dL. After 6 months of UVB treatment, her serum 25(OH)D level was maintained in the normal range and was free of muscle weakness, and bone and muscle pain.

Perspective on the consequences of short- and long-duration space flight on human physiology

During the past three decades, humans have made significant progress in accomplishing their aspirations for exploring the Moon and the planets. It is now appreciated that humans undergo a remarkable number of physiologic adaptations in microgravity that affect most physiologic systems. Space motion sickness was one of the first adaptations that humans experienced in microgravity. However, it is self-limiting and, most of the time, is effectively treated pharmacologically. Of particular concern is that, in microgravity, there is marked wasting of the skeletal musculature and skeleton that appears to be unrelenting and could impact on the health and welfare of space travelers during prolonged space flights and on return to earth. Microgravity also has a significant impact on the cardiovascular system that could have potentially serious consequences in terms of cardiovascular health during long-duration space flights. Other adaptations such as decreased T-cell responsiveness and changes in circadian rhythms is only now being explored. We need to understand the role that microgravity has on human physiologic systems in order to develop strategies for permitting humans to experience prolonged microgravity without having significant impact on their health and welfare. Engineering some gravitational force as a component of long-duration space vehicles should be given a high priority.

A new strategy for modulating chemotherapy-induced alopecia, using PTH/PTHrP receptor agonist and antagonist

Parathyroid hormone (PTH) related peptide (PTHrP) and the PTH/PTHrP receptor (PTH/PTHrP-R) show prominent cutaneous expression, where this signaling system may exert important paracrine and/or autocrine functions, such as in hair growth control. Chemotherapy-induced alopecia - one of the fundamental unsolved problems of clinical oncology - is driven in part by defined abnormalities in hair follicle cycling. We have therefore explored the therapeutic potential of a PTH/PTHrP-R agonist and two PTH/PTHrP-R antagonists in a mouse model of cyclophosphamide-induced alopecia. Intraperitoneal administration of the agonist PTH(1-34) or the antagonists PTH(7-34) and PTHrP(7-34) significantly altered the follicular response to cyclophosphamide in vivo. PTH(7-34) and PTHrP(7-34) shifted it towards a mild form of "dystrophic anagen", associated with a significant reduction in apoptotic (TUNEL+) hair bulb cells, thus mitigating the degree of follicle damage and retarding the onset of cyclophosphamide-induced alopecia. PTH(1-34), in contrast, forced hair follicles into "dystrophic catagen", associated with enhanced intrafollicular apoptosis. We had previously shown that an induced shift in the follicular damage-response towards "dystrophic catagen" mitigates cyclophosphamide-induced alopecia, whereas a shift towards "dystrophic catagen" initially enhanced the hair loss, yet subsequently promoted accelerated hair follicle recovery. Therefore, this study in an established animal model of chemotherapy-induced alopecia, which closely mimics human chemotherapy-induced alopecia, strongly encourages the exploration of PTH/PTHrP-R agonists and antagonists as novel therapeutic agents in chemotherapy-induced alopecia.

Topical triiodothyronine stimulates epidermal proliferation, dermal thickening, and hair growth in mice and rats

The skin is a classic target tissue for thyroid hormone action. Although the histology of skin in hypothyroid states is well documented, the literature contains little assessment of skin in thyrotoxic states. In light of the paucity of information on skin under the influence of excess thyroid hormone, we investigated the direct effect of thyroid hormone on skin. Triiodothyronine (T3) was applied topically daily in liposomes to SKH-1 hairless mice for 7 days and to CD rats for 2 weeks. There was a dose-dependent increase in epidermal proliferation, dermal thickening, and hair growth in T3-treated animals. Mice that received 3.8 microg of T3 had 42% more hairs per millimeter than controls (p < 0.01), hair length that was 1,180% longer (p < 0.001), 49% greater epidermal 3H-thymidine incorporation (p < 0.01), and 80% more 5-bromo-2'-deoxyuridine (BrdU) stained cells (p < 0.05). Rats receiving 12.8 microg T3 had 48% greater dermal thickness than controls (p < 0.001), 26% greater epidermal thickness (p < 0.001), 85% more hairs per millimeter (p < 0.005), and 130% greater 3H-thymidine incorporation into the epidermis (p < 0.01). Thus, topically applied thyroid hormone has dramatic effects on both skin and hair growth. These observations offer a new strategy for developing thyroid hormone and its analogues for treating disorders of skin and hair growth.

Enhancing 1 alpha-hydroxylase activity with the 25-hydroxyvitamin D-1 alpha-hydroxylase gene in cultured human keratinocytes and mouse skin

1 alpha,25-Dihydroxyvitamin D(3) (1 alpha,25(OH(2))D(3)) and its analogs are used to treat psoriasis because of their potent antiproliferative activity. They have the potential for causing hypercalcemia, however, and patients often become resistant to the drug. We examined the feasibility of enhancing the cutaneous production of 1 alpha,25(OH(2))D(3) using a human 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-OHase) plasmid. The 1 alpha-OHase gene was fused to the green fluorescent protein gene (1 alpha-OHase-GFP) driven by the cytomegalovirus promoter. Transfection of cultured normal human keratinocytes with the 1 alpha-OHase-GFP plasmid resulted in a marked increase in the expression of 1 alpha-OHase-GFP in the mitochondria. Transfection of keratinocytes with 1 alpha-OHase-GFP or 1 alpha-OHase plasmids in vitro enhanced the 1 alpha-OHase activity substantially and increased the sensitivity of the keratinocytes to the antiproliferative effect of 25(OH)D(3). The 1 alpha-OHase-GFP plasmid was topically applied to shaved C57/BL6 mice. Twenty-four hours after topical application, immunohistochemical analysis of the skin for 1 alpha-OHase-GFP revealed the presence of 1 alpha-OHase-GFP in the epidermis and epidermal appendages including the hair follicles. The results from this study offer a unique new approach for the topical treatment of hyperproliferative disorders such as psoriasis and skin cancer using the 1 alpha-OHase gene that could locally increase the production of 1 alpha,25(OH(2))D(3) without causing hypercalcemia or resistance.

25-hydroxyvitamin D-1alpha-hydroxylase in normal and malignant colon tissue

Vitamin D affects calcium metabolism and prevents proliferation of colon cells in vitro. In human beings the main circulating form of vitamin D is 25-hydroxyvitamin D; to regulate calcium homoeostasis, this form must be converted to 1alpha, 25-dihydroxyvitamin D by 1alpha-hydroxylation in the kidney with 25-hydroxyvitamin D-1alpha-hydroxylase. Cultured transformed colon cancer cells can convert 25-hydroxyvitamin D(3) to 1alpha,25-dihydroxyvitamin D(3). We identified messenger RNA (mRNA) for 25-hydroxyvitamin D-1alpha-hydroxylase in normal colon tissue and in malignant and adjacent normal colon tissue. These findings support the notion that vitamin D might have a role in cell growth regulation and cancer protection, and might be the explanation for why the risk of dying from colorectal cancer is highest in areas with the least amount of sunlight.

Observations on serum 25-hydroxyvitamin D and calcium concentrations from wild-caught and captive neotropical bats, Artibeus jamaicensis

Most bats of the suborder Microchiroptera are nocturnal, actively avoid sunlight, and eat mineral-poor diets. In those bats previously studied with respect to mineral metabolism, extensive bone remodeling occurs, and it has been suggested that calcium has been an important constraint on reproduction. There have been no previous studies of vitamin D or its metabolites in microchiropteran bats with respect to calcium metabolism. Reported is the utilization of current advances for the determination of serum levels of the vitamin D metabolite 25-hyroxyvitamin D (25-OH-D) in a neotropical bat, Artibeus jamaicensis. Serum from wild-caught animals contained low levels of 25-OH-D (5.6 +/- 3.0 ng/ml, n = 8). Bats maintained on a vitamin-D-supplemented diet had higher serum 25-OH-D levels and when the diet containing vitamin D was discontinued, mean serum 25-OH-D levels declined significantly after 6 months. Serum calcium concentrations in wild-caught bats (8.5 +/- 0.4 mg%) showed very little variation and were not significantly different in any of the vitamin-D-supplemented animals. A pairwise correlation analysis between 25-OH-D and serum calcium levels revealed no linear correlation. The results indicate either that 25-OH-D does not appear to play a key role or that low levels of 25-OH-D may be adequate in regulating serum calcium levels in this bat.

Rationale for use and clinical responsiveness of hexafluoro-1,25-dihydroxyvitamin D3 for the treatment of plaque psoriasis: a pilot study

BACKGROUND

Vitamin D analogues are useful in topical therapy of psoriasis.

OBJECTIVES

To evaluate the effect of hexafluoro-1,25-dihydroxyvitamin D3 (F6-1,25(OH)2D3) in treatment of psoriasis.

METHODS

Fifteen patients with plaque-type psoriasis were enrolled in a single centre double-blind, right/left comparison, placebo-controlled study, and received 0.1 g of petrolatum containing 5 microg of F6-1,25(OH)2D3 or 0.1 g of petrolatum (placebo) for 3 months. After completion of this double-blind study, a subset of these patients (n = 12) applied F6-1,25(OH)2D3 ointment (50 microg g-1 of petrolatum) to all their lesions (total area, 100-5000 cm2, mean area: 3300 m2) for 2 months as a single application at night.

RESULTS

The mean severity score in the right/left-sided controlled topical F6-1,25(OH)2D3 (50 microg g-1) therapy group showed a decrease of 85%. In contrast, the mean severity score for the placebo-treated areas showed a decrease of 45% (P < 0.001). In the 12 patients who subsequently applied F6-1,25(OH)2D3 (50 microg g-1) ointment to all of their lesions, 91.6% showed moderate to excellent improvement. The mean Psoriasis Area and Severity Index score decreased by 44.9% (from 33.6 +/- 15 to 18.5 +/- 13). No effect on calcium homeostasis was noted. Adverse events included mild irritation in two patients that resolved during therapy.

CONCLUSIONS

Topical F6-1,25(OH)2D3 is a safe and effective once a day treatment for psoriasis.

Immunoreactivity of six monoclonal antibodies directed against 1,25-dihydroxyvitamin-D3 receptors in human skin

Using confocal laser scanning microscopy, we tested the suitability of five monoclonal mouse antibodies (IVA7E7, IVB12G12, IVG9C11, VD2F12, and VIIID8C12) that had been raised against different domains of the porcine intestinal 1,25-dihydroxyvitamin-D3 receptor (VDR), for the immunohistological detection of VDR in human skin. The VDR immunoreactivity of these antibodies was compared with the well-characterized VDR-staining pattern of the mouse monoclonal antibody 9A7gamma raised against chick intestinal VDR. All six antibodies revealed strong nuclear and qualitatively similar immunoreactivity in all cell layers of the viable epidermis. Our data demonstrate that the five mouse monoclonal antibodies are suitable for immunohistochemical detection of VDR in frozen sections. These antibodies show comparable staining patterns in human skin even though they had been raised against different functional domains of the 1,25-dihydroxyvitamin-D3 receptor.

Expression of the circadian clock genes clock and period1 in human skin

The circadian clock is a cellular machine composed of proteins with regulated expression that gives rise to circadian rhythms. Two main new concepts have arisen from recent research in the field in the last few years: (i) at least three to five key genes are involved in maintaining the basic circadian cellular rhythms, and (ii) their expression is fairly ubiquitous, extending beyond the traditionally considered pacemaker in mammals, the suprachiasmatic nucleus. We have demonstrated the expression of two circadian clock genes, clock and period1, in human skin cells. Reverse transcriptase polymerase chain reaction revealed the presence of clock and period1 mRNA in cultured human keratinocytes, melanocytes, and dermal fibroblasts, as well as in the human keratinocyte cell line HaCaT and the human melanoma line A375. In addition, antibodies to these two proteins produced immuno-positive staining in these cell types. Our investigations demonstrate for the first time that skin cells express circadian clock proteins constitutively although regulation of their expression and activity has not been elucidated. These proteins may have a role in cutaneous and/or systemic circadian biology and the skin and skin cells may provide an attractive model for the study of circadian rhythms.

Metabolism of [3alpha-3H] 25-hydroxyvitamin D2 in kidneys isolated from normal and vitamin D2-intoxicated rats

With the availability of A-ring labelled 25OHD2, [3alpha-3H] 25OHD2, we have performed the present study to examine the metabolism of 25OHD2 using physiological substrate concentrations in perfused kidneys isolated from both normal and vitamin D2-intoxicated rats. Our results indicate that [3alpha-3H] 25OHD2 is metabolized into both 24(S),25,28-trihydroxyvitamin D2 [24(S),25,28(OH)3D2] and 24(R),25,26-trihydroxyvitamin D2 [24(R), 25,26(OH)3D2], and the amounts of these two metabolites produced in the kidney of vitamin D2-intoxicated rat were about 3-5 times higher than those produced in the kidney of normal rat. Similar results were also obtained with rat kidney homogenates incubated with [3alpha-3H] 25OHD2. Furthermore, we noted that the production of both 24(S),25,28(OH)3D2 and 24(R),25,26(OH)3D2 in the kidney homogenates of vitamin D2-intoxicated rats increased with the time of incubation and then subsequently decreased. The decrease in both 24(S),25,28(OH)3D2 and 24(R),25,26(OH)3D2 coincided with an increase in the fraction of total radioactivity distributed in the aqueous phase of the kidney homogenates. This finding suggested the possibility of further metabolism of 24(S),25,28(OH)3D2 and 24(R), 25,26(OH)3D2 into polar water-soluble metabolite(s). We then measured the radioactivity in the aqueous phase of kidney homogenates of both normal and vitamin D2-intoxicated rats incubated with [3alpha-3H] 25OHD2. It was noted that the amount of radioactivity in the aqueous phase of kidney homogenates of vitamin D2-intoxicated rats is higher than that present in the aqueous phase of kidney homogenates of normal rats. Thus, our study provides evidence for the first time for the formation of both 24(S),25,28(OH)3D2 and 24(R),25, 26(OH)3D2 under physiological conditions, and the possibility of their further metabolism into as yet unidentified polar water-soluble metabolite(s). As the formation of all these metabolites is increased in the kidney of vitamin D2-intoxicated rats when compared to normal rats, it appears that the increased rate of metabolism of 25OHD2 during hypervitaminosis D2 plays a significant role in the deactivation of 25OHD2.

Is psoriasis a T-cell disease?

The etiology and pathogenesis of psoriasis--one of the most common chronic, inflammatory, hyperproliferative skin disorders of man--have long fascinated dermatologists, pathologists and biologists alike. Here, we have a model disease that offers to study neuroectodermal-mesenchymal interactions in the widest sense possible. Epithelial, endothelial, and hematopoietic cells as well as neurons projecting into the skin apparently all interact with each other to generate the characteristic psoriatic lesion. For decades, the ongoing controversy on the molecular nature, choreography and hierarchy of these complex interactions e.g. between epidermal keratinocytes, T cells, neurotrophils, endothelial cells and sensory nerves has served as a driving force propelling investigative dermatology to ever new horizons. This debate has not only been at the heart of our quest to develop more effective forms of therapy for this socially crippling disease, but it also has profoundly influenced how we view the skin as a whole: the numerous competing theories on the pathogenesis of psoriasis published so far also are reflections on the evolution of mainstream thought in skin biology over the last decades. These days, conventional wisdom infatuated with a T-cell-centered approach to inflammatory skin diseases-- portrays psoriasis as an autoimmune disease, where misguided T lymphocyte activities cause secondary epithelial abnormalities. And yet, as this CONTROVERSIES feature reminds us, some authoritative "pockets of academic resistance" are still quite alive, and interpret psoriasis e.g. as a genetically determined, abnormal epithelial response pattern to infectious and/or physicochemical skin insults. Weighing the corresponding lines of argumentation is not only an intriguing, clinically relevant intellectual exercise, but also serves as a wonderful instrument for questioning our own views of the skin universe and its patterns of deviation from a state of homeostasis.

Calcium and vitamin D. Diagnostics and therapeutics

Vitamin D is neither a vitamin nor a nutrient if adequate exposure to sunlight is available to produce adequate quantities of vitamin D3 in the skin. It is well known that an adequate supply of vitamin D, either from the diet or from the skin, is important for maximum bone health throughout life. The new revelation that 25(OH)D can be metabolized to 1,25(OH)2D in the colon, prostate, and skin opens a new chapter in the vitamin D story. It is quite possible that there are two levels of vitamin D sufficiency. One level requires that the serum 25(OH)D levels be at least 20 ng/mL to satisfy the body's requirement for the renal production of 1,25(OH)2D that regulates calcium absorption, and bone calcium mobilization and bone mineralization. The second level may need higher circulating levels of 25(OH)D for maximum cellular health because of the conversion of 25(OH)D to 1,25(OH)2D in extrarenal tissues, such as the prostate, colon, and skin.

Decreased bioavailability of vitamin D in obesity

BACKGROUND

Obesity is associated with vitamin D insufficiency and secondary hyperparathyroidism.

OBJECTIVE

This study assessed whether obesity alters the cutaneous production of vitamin D(3) (cholecalciferol) or the intestinal absorption of vitamin D(2) (ergocalciferol).

DESIGN

Healthy, white, obese [body mass index (BMI; in kg/m(2)) > or = 30] and matched lean control subjects (BMI </= 25) received either whole-body ultraviolet radiation or a pharmacologic dose of vitamin D(2) orally.

RESULTS

Obese subjects had significantly lower basal 25-hydroxyvitamin D concentrations and higher parathyroid hormone concentrations than did age-matched control subjects. Evaluation of blood vitamin D(3) concentrations 24 h after whole-body irradiation showed that the incremental increase in vitamin D(3) was 57% lower in obese than in nonobese subjects. The content of the vitamin D(3) precursor 7-dehydrocholesterol in the skin of obese and nonobese subjects did not differ significantly between groups nor did its conversion to previtamin D(3) after irradiation in vitro. The obese and nonobese subjects received an oral dose of 50000 IU (1.25 mg) vitamin D(2). BMI was inversely correlated with serum vitamin D(3) concentrations after irradiation (r = -0.55, P: = 0.003) and with peak serum vitamin D(2) concentrations after vitamin D(2) intake (r = -0.56, P: = 0.007).

CONCLUSIONS

Obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D(3) from cutaneous and dietary sources because of its deposition in body fat compartments.