Vitamin D in adipose tissue and serum 25-hydroxyvitamin D after roux-en-Y gastric bypass

Vitamin D is stored in body fat. The purpose of this study was to determine vitamin D concentration in abdominal fat of obese patients who underwent roux‐en‐Y gastric bypass (RYGB), and to describe changes in serum 25‐hydroxyvitamin D (25(OH)D) levels in relation to loss of body fat. Subjects from a single clinic who were scheduled for RYGB were invited into the study. Abdominal subcutaneous, omental, and mesenteric fat were obtained at time of surgery. Adipose vitamin D₂ and vitamin D₃ concentrations were measured by high‐performance liquid chromatography (HPLC). Weight and serum 25(OH)D were assessed at baseline and every 3 months up to 1 year. Seventeen subjects were included, and fat samples were available from eleven. Total vitamin D content in subcutaneous abdominal fat was 297.2 ± 727.7 ng/g tissue, and a wide range was observed (4–2,470 ng/g). Both vitamin D₂ and vitamin D₃ were detected in some of the fat samples. At baseline, 25(OH)D was 23.1 ± 12.6 ng/ml. Average weight loss was 54.8 kg at 12 months, of which ～40 kg was fat mass. Despite daily vitamin D intake of ≥2,500 IU throughout the study, no significant increase in serum 25(OH)D was observed, with mean serum concentration of 25(OH)D at 1 year of 26.2 ± 5.36 ng/ml (P = 0.58). We conclude that vitamin D in adipose tissue does not significantly contribute to serum 25(OH)D despite dramatic loss of fat mass after RYGB.     

Treatment with 50000 IU Vitamin D2 Every Other Week and Effect on Serum 25-Hydroxyvitamin D2, 25-Hydroxyvitamin D3, and Total 25-Hydroxyvitamin D in Aclinical Setting

ObjectiveTo examine the effect of 50 000 IU-vitamin D₂ supplementation in a clinical setting on serum total 25-hydroxyvitamin D (25[OH]D), 25-hydroxyvitamin D₂ (25[OH]D₂), and 25-hydroxyvitamin D₃ (25[OH]D₃).MethodsThis retrospective cohort study was performed in an urban tertiary referral hospital in Boston, Massachusetts. Patients who had been prescribed 50 000 IU vitamin D₂ repletion and maintenance programs were identified through a search of our electronic medical record. Baseline and follow-up total serum 25(OH)D, 25(OH)D₂, and 25(OH)D₃ levels were compared.ResultsWe examined the medical records of 48 patients who had been prescribed 50 000 IU vitamin D₂ in our clinic. Mean ± standard deviation baseline total 25(OH) D was 31.0 ± 10.6 ng/mL and rose to 48.3 ± 13.4 ng/mL after treatment (P <.001). 25(OH)D₂ increased from 4.2 ± 4.3 ng/mL to 34.6 ± 12.3 ng/mL after treatment (P <.001), for an average of 158 days (range, 35-735 days). Serum 25(OH)D3 decreased from 26.8 ± 10.8 ng/mL to 13.7 ± 7.9 ng/mL (P <.001).ConclusionsFifty thousand IU vitamin D₂ repletion and maintenance therapy substantially increases total 25(OH)D and 25(OH)D2 despite a decrease in serum 25(OH)D3. This treatment program is an appropriate and effective strategy to treat and prevent vitamin D deficiency.(Endocr Pract. 2012;18:399-402)     

Manifestations of vitamin D deficiency in chicks reared under different artificial lighting regimes

A problem observed with zoo animals that normally do not consume vitamin D-containing foods and that are not exposed to natural sunlight is a deficiency of vitamin D. This study was conducted to determine whether the amount of ultraviolet light emitted by certain commercially available lights is sufficient to promote vitamin D₃ synthesis as indicated by weight gain and various measures of skeletal calcification. Seventy-four, day-old male leghorn chicks were randomly assigned to six treatment groups for a 6-week trial. All groups were exposed to a cool white fluorescent light. In addition, group 1 was supplemented with 400 IU of vitamin D₃/kg diet, group 2 was supplemented with 100 IU of vitamin D₃/kg diet, group 3 served as the negative control, group 4 was exposed to a Vita-Lite for 12 hr per day, group 5 was exposed to a Sylvania sun lamp for 15 min twice daily, and group 6 was exposed to a Sylvania black light for 15 min twice daily. Groups 3 through 6 were not provided with dietary supplements of vitamin D₃. At termination of the experiment, groups 1, 2, and 5 all showed healthy beaks and ribs, the highest weight gain, and greatest percentage of bone ash. Group 4, in contrast, had the poorest calcification and lowest bone ash. This finding indicates that supplemental artificial lighting does affect vitamin D₃synthesis in chicks and presumably in other species but that certain lights that were presumed to be appropriate for this purpose proved to be unsuitable under the conditions of this study.     

Evaluation of vitamin D3 metabolites in Callithrix jacchus (common marmoset)

Vitamin D₃ (cholecalciferol) is endogenously produced in the skin of primates when exposed to the appropriate wavelengths of ultraviolet light (UV-B). Common marmosets (Callithrix jacchus) maintained indoors require dietary provision of vitamin D₃ due to lack of sunlight exposure. The minimum dietary vitamin D₃ requirement and the maximum amount of vitamin D₃ that can be metabolized by marmosets is unknown. Observations of metabolic bone disease and gastrointestinal malabsorption have led to wide variation in dietary vitamin D₃ provision amongst research institutions, with resulting variation in circulating 25-hydroxyvitamin D₃ (25(OH)D₃), the accepted marker for vitamin D sufficiency/deficiency. Multiple studies have reported serum 25(OH)D₃ in captive marmosets, but 25(OH)D₃ is not the final product of vitamin D₃ metabolism. In addition to serum 25(OH)D_3, we measured the most physiologically active metabolite, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and the less well understood metabolite, 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃) to characterize the marmoset's ability to metabolize dietary vitamin D₃. We present vitamin D₃ metabolite and related serum chemistry value colony reference ranges in marmosets provided diets with 26,367 (Colony A, N = 113) or 8,888 (Colony B, N = 52) international units (IU) of dietary vitamin D₃ per kilogram of dry matter. Colony A marmosets had higher serum 25(OH)D₃ (426 ng/ml [SD 200] vs. 215 ng/ml [SD 113]) and 24,25(OH)₂D₃ (53 ng/ml [SD 35] vs. 7 ng/ml [SD 5]). There was no difference in serum 1,25(OH)₂D₃ between the colonies. Serum 1,25(OH)₂D₃ increased and 25(OH)D₃ decreased with age, but the effect was weak. Marmosets tightly regulate metabolism of dietary vitamin D₃ into the active metabolite 1,25(OH)₂D₃; excess 25(OH)D₃ is metabolized into 24,25(OH)₂D₃. This ability explains the tolerance of high levels of dietary vitamin D₃ by marmosets, however, our data suggest that these high dietary levels are not required.     

UVB Exposure of Farm Animals: Study on a Food-Based Strategy to Bridge the Gap between Current Vitamin D Intakes and Dietary Targets

Vitamin D deficiency is a global health problem. This study aimed to investigate the efficacy of ultraviolet (UV) B radiation for improving vitamin D₃ content of eggs and meat. In a two-factorial design hens that received diets with 0 (-D₃) or 3,000 IU (+D₃) vitamin D₃/kg were non-exposed (-UVB) or exposed to UVB radiation (+UVB) for 3 h daily over 4 weeks. Data show that UVB radiation was very effective in raising the vitamin D₃ content of egg yolk and meat. Egg yolk from +UVB/−D₃ hens had a higher vitamin D₃ content (17.5±7.2 µg/100 g dry matter (DM)) than those from the –UVB/+D₃ group (5.2±2.4 µg/100 g DM, p<0.01). Vitamin D₃ content in egg yolk of vitamin D₃-supplemented hens could be further increased by UVB radiation (32.4±10.9 µg/100 g DM). The content of 25-hydroxyvitamin D₃ (25(OH)D₃) in the egg yolk also increased in response to UVB, although less pronounced than vitamin D₃. Meat revealed about 4-fold higher vitamin D₃ contents in response to UVB than to dietary vitamin D₃ (p<0.001). In conclusion, exposure of hens to UVB is an efficient approach to provide consumers with vitamin D₃-enriched foods from animal sources.     

Isolation of a new metabolite of vitamin D produced in vivo, 1 alpha,25-dihydroxyvitamin D3-26,23-lactone

A new vitamin D metabolite was isolated in pure form from the blood of rats given oral doses of 50 μg/kg of 1α-hydroxyvitamin D₃. The isolation involved methanol-chloroform extraction and four successive column chromatographic procedures. A tentative structure of the metabolite is proposed on the basis of its column chromatographic behavior via mass spectrometry, ultraviolet absorption spectrophotometry, and as 1α,3β,25-trihydroxy-9,10 (19)-cholestatrieno-26,23-lactone. The trivial name 1α,25-dihydroxyvitamin D₃-26,23-lactone is suggested for this compound.     

Vitamin D content in Alaskan Arctic zooplankton,fishes, and marine mammals

We postulated that dietary ingestion of vitamin D may be used by some Alaskan Arctic marine mammal species in addition to, or instead of, cutaneous production to meet nutritional requirements. Zooplankton (n=5) sampled near Kaktovik, Alaska, contained no measurable vitamin D₂ or D₃, but did contain provitamin D (7‐dehydrocholesterol), the cutaneous precursor for previtamin D₃ in mammals. Fillets and livers from five fish species were sampled near Barrow, Alaska, and evaluated for vitamin D₃ content (no vitamin D₂ was detected). Differences in vitamin D₃ content appeared significant (P≤0.10) among fish livers (Kruskal‐Wallis [H test]=8.25, df=4, P=0.08) and among fish fillets (H=7.80, df=4, P=0.01). We also found significant differences in several pairwise comparisons (Mann‐Whitney U‐test) of vitamin D₃ levels in fillets and livers. Blubber from six species of marine mammals had no detectable vitamin D₂. The H test results for blubber vitamin D₃ concentration were highly significant: 28.12, df=5, P<0.001. There were also significant differences in vitamin D₃ content from blubber in pairwise comparisons of primarily invertebrate feeders (bowhead whale (Balaena mysticetus) [mean=4.20 SD±1.10 ng/g], and Pacific walrus (Odobenus rosmarus divergens) [5.43±2.82 ng/g]) vs. primarily piscivorous feeders (ringed seal (Phoca hispida) [746.57±493.00 ng/g] and beluga whale (Delphinapterus leucas) [426.00±174.92 ng/g]) and a semiaquatic terrestrial carnivore (polar bear (Ursus maritimus) [406.17±311.70 ng/g]). The bearded seal (Erignathus barbatus) had intermediate blubber vitamin D₃ concentration (156.83±139.25 ng/g), which may reflect an intermediate‐type feeding strategy or an artifact of the small sample size. Zoo Biol 23:33–43, 2004. © 2004 Wiley‐Liss, Inc.     

Influence of ultraviolet B radiation on vitamin D3 metabolism in vitamin D3-resistant New World primates

We investigated the occurrence of rickets in adolescent tamarins (Saguinus imperator) residing at the Los Angeles Zoo. Compared to tamarins in the same colony without clinical evidence of bone disease (N = 6), rachitic platyrrhines (N = 3) had a decrease in their serum calcium concentration (P < .05). The affected tamarins also had lower serum 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) levels than did nonaffected colony mates, but 2–10-fold higher concentrations than in Old World primates of a comparable developmental stage. New World primates in many different genera are known to exhibit target organ resistance to the active vitamin D₃ metabolite, 1,25-(OH)₂D₃, compensated by maintenance of high circulating concentrations of 1,25-(OH)₂D₃. The relatively low serum 1,25-(OH)₂D₃ concentration in rachitic tamarins and ultraviolet B radiation deficient environment of these primates suggested that bone disease may be linked to a deficiency in substrate for 1,25-(OH)₂D₃, 25 hydroxyvtamin D₃ (25-OHD₃). Chronic exposure of platyrrhines in three different vitamin D resistant genera to an artificial UVB source resulted in 1) a significant increase in the mean serum 25-OHD₃ (P < .001) and 1,25-(OH)₂D₃ (P < .02) level over that encountered in platyrrhines not exposed to UVB; and 2) prevention of rachitic bone disease in irradiated individuals. These data further show that the serum 25-OHD₃ and 1,25-OH₂D₃ levels are positively correlated in vitamin D-resistant platyrrhines (r = 0.64; P= .0014) and suggest that a compromise in cutaneous vitamin D₃ production by means of UVB deprivation may limit necessary 1,25-(OH)₂D₃ production. © 1992 Wiley-Liss, Inc.     

Comparative studies on the contents of vitamin D3, 25-hydroxy vitamin D3 and 7-dehydrocholesterol in fish liver

• 1.1. The contents of vitamin D₃, 25-hydroxyvitamin D₃ (25-OH-D₃) and 7-dehydrocholesterol (7-DHC) in 22 kinds of fish liver samples were determined by a high-performance liquid chromatographic (HPLC) method.
• 2.2. Vitamin D₃ was detected in all fish liver samples, but its contents varied from 84 to 264,000 ng/g wet tissue. The liver of fish belonging to Carangidae and Scombridae contained large amounts of the vitamin and therefore we deduced that vitamin D₃ levels in liver might have some relations with taxonomical positions of fishes.
• 3.3. 25-OH-D₃ was detected in 7 out of 22 kinds of fish liver samples, while 7-DHC was in 14 out of 22. The contents of the two sterols were generally much lower than those of vitamin D₃ and there was no special relationship between the contents of the sterols and the vitamin.

     

Inhibition of vitamin D metabolism by ethane-1-hydroxyl-1, 1-diphosphonate

The administration of disodium-ethane-1-hydroxy-1,1-diphosphonate (20 mg/kg body weight subcutaneously) to chicks given adequate amounts of vitamin D₃ causes a hypercalcemia, inhibits bone mineralization, and inhibits intestinal calcium transport. The administration of 1,25-dihydroxyvitamin D₃, a metabolically active form of vitamin D₃, restores intestinal calcium absorption to normal but does not restore bone mineralization in disodium-ethane-1-hydroxy-1,1-diphosphonate-treated chicks. In rachitic chicks, the disodium-ethane-1-hydroxy-1,1-diphosphonate treatment does not further reduce the low intestinal calcium transport values while it nevertheless further reduces bone ash levels and increases serum calcium concentration.These observations prompted a more detailed study of the relationship between disodium-ethane-1-hydroxy-1,1-diphosphonate treatment and vitamin D metabolism. A study of the hydroxylation of 25-hydroxyvitamin D₃ in an in vitro system employing kidney mitochondria from chicks receiving disodium-ethane-1-hydroxy-1,1-diphosphonate treatment demonstrates a marked decrease in 1,25-dihydroxyvitamin D₃ production and a marked increase in the 24,25-dihydroxyvitamin D₃ production. In addition, the in vivo metabolism of 25-hydroxy-[26,27-³H]vitamin D₃ in disodium-ethane-1-hydroxy-1,1-diphosphonate treated chicks supports the in vitro observations. In rachitic chicks the disodium-ethane-1-hydroxy-1,1-diphosphonate treatment markedly reduces the 25-hydroxyvitamin D₃-1-hydroxylase activity of kidney, but does not increase the 25-hydroxyvitamin D₃-24-hydroxylase.These results provide strong evidence that large doses of disodium-ethane-1-hydroxy-1,1-diphosphonate produce a marked effect on calcium metabolism via alterations in the metabolism of vitamin D as well as the expected direct effect on the bone.     

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

Summary 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% previtamin 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°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.     

The determination of the vitamin D metabolites on a single plasma sample: changes during parturition in dairy cows.

Methods have been developed for the precise measurement of the major known vitamin D metabolites in a single sample of cow plasma (~5 ml). The procedure involves initial extraction with methylene chloride-methanol followed by chromatography on Sephadex LH-20. 25-Hydroxyvitamin D₂ and 25-hydroxyvitamin D₃ were determined using high-pressure liquid chromatography and comparing ultraviolet absorption peak height with absorption peak heights of standards. The dihydroxylated metabolites were further purified and resolved by high-pressure liquid chromatography and determined by radioligand binding assays. The assays were employed to measure the total vitamin D metabolite levels in the plasma of paretic and normal dairy cows at parturition. Parturition had no effect on 25-hydroxyvitamin D levels in either group of cows (paretic, 37–44 ng/ml; normal, 35–38 ng/ml). However, normal cows did show lower mean 25-hydroxyvitamin D levels at every sampling period with the lowest levels in both groups occurring at 7 days postpartum. Plasma 25, 26-dihydroxyvitamin D was higher in paretic animals prepartum and at parturition (0.7–1.0 ng/ml) when compared to nonparetic animals (0.4–0.45 ng/ml). Similar levels (0.6 ng/ml) were observed in both groups postpartum. Cows developing parturient paresis showed a significant (P < 0.05) elevation of 1,25-dihydroxyvitamin D at parturition with a maximum level of 350 pg/ml attained at 1 day postpartum compared to prepartum levels of 60 pg/ml. Normal animals also showed a rise in plasma levels of 1,25-dihydroxyvitamin D with a maximum level of 185 pg/ml observed at 1 day postpartum. Plasma 24,25-dihydroxyvitamin D was initially higher in paretic cows (1.9 ng/ml) with a significant (P < 0.05) drop to 1.05 ng/ml occurring at parturition. This level was maintained for 7 days postpartum. The levels of this steroid were maintained at 1.3–1.4 ng/ml in the normal cows throughout the entire sampling period.     

Impact of vitamin D3 on cardiovascular responses to glucocorticoid excess

Although the cardiovascular system is not a classical target for 1,25-dihydroxyvitamin D₃, both cardiac myocytes and vascular smooth muscle cells respond to this hormone. The present study aimed to elucidate the effect of active vitamin D₃ on cardiovascular functions in rats exposed to glucocorticoid excess. Adult male Wistar rats were allocated into three groups: control group, dexamethasone (Dex)-treated group receiving Dex (200 μg/kg) subcutaneously for 12 days, and vitamin D₃-Dex-treated group receiving 1,25-(OH)₂D₃ (100 ng/kg) and Dex (200 μg/kg) subcutaneously for 12 days. Rats were subjected to measurement of systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressures and heart rate. Rate pressure product (RPP) was calculated. Rats’ isolated hearts were perfused in Langendorff preparation and studied for basal activities (heart rate, peaked developed tension, time to peak tension, half relaxation time, and myocardial flow rate) and their responses to isoproterenol infusion. Blood samples were collected for determination of plasma level of nitrite, nitric oxide surrogate. Dex-treated group showed significant increase in SBP, DBP, MAP, and RPP, as well as cardiac hypertrophy and enhancement of basal cardiac performance evidenced by increased heart rate, rapid and increased contractility, and accelerated lusitropy, together with impaired contractile and myocardial flow rate responsiveness to beta-adrenergic activation and depressed inotropic and coronary vascular reserves. Such alterations were accompanied by low plasma nitrite. These changes were markedly improved by vitamin D₃ treatment. In conclusion, vitamin D₃ is an efficacious modulator of the deleterious cardiovascular responses induced by glucocorticoid excess, probably via accentuation of nitric oxide.     

Circulating vitamin D3 and 25-hydroxyvitamin D in humans: An important tool to define adequate nutritional vitamin D status

Circulating 25-hydroxyvitamin D [25(OH)D] is generally considered the means by which we define nutritional vitamin D status. There is much debate, however, with respect to what a healthy minimum level of circulation 25(OH)D should be. Recent data using various biomarkers such as intact parathyroid hormone (PTH), intestinal calcium absorption, and skeletal density measurements suggest this minimum level to be 80 nmol (32 ng/mL). Surprisingly, the relationship between circulating vitamin D₃ and its metabolic product—25(OH)D₃ has not been studied. We investigated this relationship in two separate populations: the first, individuals from Hawaii who received significant sun exposure; the second, subjects from a lactation study who received up to 6400 IU vitamin D₃/day for 6 months.Results (1) the relationship between circulating vitamin D₃ and 25(OH)D in both groups was not linear, but appeared saturable and controlled; (2) optimal nutritional vitamin D status appeared to occur when molar ratios of circulating vitamin D₃ and 25(OH)D exceeded 0.3; at this point, the V_max of the 25-hydroxylase appeared to be achieved. This was achieved when circulating 25(OH)D exceeded 100 nmol.We hypothesize that as humans live today, the 25-hydroxylase operates well below its V_max because of chronic substrate deficiency, namely vitamin D₃. When humans are sun (or dietary) replete, the vitamin D endocrine system will function in a fashion as do these other steroid synthetic pathways, not limited by substrate. Thus, the relationship between circulating vitamin D and 25(OH)D may represent what “normal” vitamin D status should be.     

Binding properties of 23S,25-dihydroxyvitamin D3: an in vivo metabolite of vitamin D3

23$\text{S}$,25-Dihydroxyvitamin D₃ was isolated from the plasma of vitamin D₃-toxic pigs. An ultraviolet absorbance spectrum confirmed its purity. The configuration of the 23-hydroxyl group was determined to be S by comparison of the natural product with synthetic 23$\text{R}$,25- and 23$\text{S}$,25-dihydroxyvitamin D₃ by high-pressure liquid chromatography. The affinity of both 23$\text{S}$,25- and 23$\text{R}$,25-dihydroxyvitamin D₃ for the plasma vitamin D binding protein was similar to vitamin D₃. Thus, with respect to the plasma vitamin D binding protein, 23$\text{S}$,25-dihydroxyvitamin D₃ is the least potent, naturally-occurring, dihydroxylated vitamin D₃ metabolite known.     

Effect of vitamin D3 supplementation on hepatic lipid dysregulation associated with autophagy regulatory AMPK/Akt-mTOR signaling in type 2 diabetic mice

Vitamin D₃ has been reported to protect liver against non-alcoholic fatty liver disease (NAFLD) by attenuating hepatic lipid dysregulation in type 2 diabetes mellitus (T2DM). However, the mechanism of vitamin D₃ on hepatic lipid metabolism-associated autophagy in hyperglycemia-induced NAFLD remains yet to be exactly elucidated. C57BL/6J mice were intraperitoneally injected with 30 mg/kg of streptozotocin and fed a high-fat diet for induction of diabetes. All mice were administered with vehicle or vitamin D₃ (300 ng/kg or 600 ng/kg) by oral gavage for 12 weeks. Histological demonstrations of the hepatic tissues were obtained by H&E staining and the protein levels related to lipid metabolism and autophagy signaling were analyzed by Western blot. Treatment with vitamin D₃ improved insulin resistance, liver damage, and plasma lipid profiles, and decreased hepatic lipid content in the diabetic mice. Moreover, vitamin D₃ administration ameliorated hepatic lipid dysregulation by downregulating lipogenesis and upregulating lipid oxidation under diabetic condition. Importantly, vitamin D₃ treatment induced autophagy by activating AMP-activated protein kinase (AMPK), inactivating Akt and ultimately blocking mammalian target of rapamycin (mTOR) activation in the T2DM mice. Additionally, vitamin D₃ was found to be effective in anti-apoptosis and anti-fibrosis in the liver of diabetic mice. The results suggested that vitamin D₃ may ameliorate hepatic lipid dysregulation by activating autophagy regulatory AMPK/Akt-mTOR signaling in T2DM, providing insights into its beneficial effects on NAFLD in type 2 diabetic patients.     

Long-Term Bioavailability of Single Doses of Intramuscular Vitamin D2

Objective: We sought to determine the long-term bioavailability of single doses of intramuscular (IM) vita-min D₂ (D₂) in healthy adults.Methods: Forty healthy volunteers with hypovitaminosis D received a single dose of 200,000, 400,000, or 600,000 IU intramuscular D₂ or no treatment. Levels of 25-hydroxyvitamin D₂ (25&lsqb;OH]D₂) and 25-hydroxyvitamin D₃ (25&lsqb;OH]D₃) in serum were measured by liquid chromatography-tandem mass spectrometry. Vitamin D binding protein (DBP) and intact parathyroid hormone (iPTH), bone turnover markers (BTMs), and serum and urinary calcium were also measured.Results: After a single dose of D₂ injection, the level of 25(OH)D₂ increased slowly and reached a plateau at 8 weeks. The plateau remained stable for 12 weeks. The mean increase in 25(OH)D₂ was 6.8, 9.6, or 15.6 ng/mL after injection of 200,000 IU, 400,000 IU, or 600,000 IU D₂. Although endogenous 25(OH)D₃ levels were reduced by IM D₂, the total 25(OH)D levels increased by 5.0, 7.0, or 10.3 ng/mL in average after injection of 200,000 IU, 400,000 IU, or 600,000 IU D₂. The iPTH levels were also decreased by IM D₂. However, levels of serum calcium, BTMs, and DBP and urinary calcium were not altered by IM D₂.Conclusion: A single dose of 200,000 IU, 400,000 IU, or 600,000 IU IM D₂ raises total 25-hydroxyvitamin D levels by 5.0, 7.0, or 10.3 ng/mL on average for at least 12 weeks and reduces iPTH and endogenous 25(OH)D₃ levels without affecting levels of serum calcium, BTMs, DBP, and urinary calcium.     

Metabolism of vitamin D3 in the chick embryo

In agreement with previous reports, chick intestinal calcium-binding protein does not appear in the chick embryo until 1 day after hatching while intestinal alkaline phosphatase begins to appear at 19–20 days of embryonic life. The ability of chick embryo to metabolize vitamin D₃ to 25-hydroxyvitamin D₃, 1,25-dihydroxyvitamin D₃, and 24,25-dihydroxyvitamin D₃ is present at least by day 18 of embryonic life as demonstrated by in vivo and in vitro techniques. It also illustrates that metabolism of vitamin D₃ was not the limiting factor in the appearance of calcium-binding protein and alkaline phosphatase in intestine. Instead, the uptake of 1,25-dihydroxyvitamin D₃ by the duodenum was very low prior to hatching, even though significant amounts were present in the yolk sac. Injection of a physiological dose of 1,25-dihydroxyvitamin D₃ to chick embryo at 9 days failed to stimulate appearance of calcium binding protein by 18 days of embryonic life. Thus, it appears that either the normal mechanism for transport of 1,25-dihydroxyvitamin D₃ to intestine or its receptors in intestine may not be present prior to day 18–19.A large fraction of radioactive vitamin D₃ injected into the yolk sac was found esterified especially in the embryonic liver. The significance of this is not yet understood.Injection of 1,25-dihydroxyvitamin D₃ at 325 pmoles/per egg at 9 days resulted in 70% mortality of embryos while a 32-pmole dose resulted in no significant increase in mortality. The basis for this toxicity is not yet understood.     

Evaluation of Vitamin D Repletion Regimens to Correct Vitamin D Status in Adults

ObjectiveTo determine the efficacy and safety of commonly prescribed regimens for the treatment of vitamin D insufficiency.MethodsWe performed a retrospective analysis of 306 consecutive patients who were prescribed ergocalciferol (vitamin D₂) for correction of vitamin D insufficiency at the Atlanta Veterans Affairs Medical Center between February 2003 and May 2006. Serum levels of parathyroid hormone, 25-hydroxyvitamin D (25-OHD), and calcium were compared before and after treatment with ergocalciferol. Patients who did not have a 25-OHD determination (n = 41) were excluded from analysis. Vitamin D deficiency, insufficiency, and sufficiency were defined as a serum 25-OHD level of < 20 ng/mL, 21 to 29 ng/mL, and > 30 ng/mL, respectively.ResultsWe identified 36 discrete prescribing regimens. The 3 most common regimens were ergocalciferol 50,000 IU once weekly for 4 weeks followed by 50,000 IU once monthly for 5 months (n = 48); ergocalciferol 50,000 IU once monthly for 6 months (n = 80); and ergocalciferol 50,000 IU 3 times weekly for 6 weeks (n = 27). Each of these 3 treatments significantly increased serum 25-OHD (P < .01), but vitamin D sufficiency was achieved in only 38%, 42%, and 82% of study subjects, respectively. Regimens with > 600,000 IU of ergocalciferol given for a mean of 60 ± 40 days achieved sufficiency in 64% of cases, without vitamin D toxicity.ConclusionIn this study, regimens that contained at least 600,000 IU of ergocalciferol appeared to be the most effective in achieving vitamin D sufficiency. Guidelines for the treatment of vitamin D insufficiency in healthy adults should be developed. (Endocr Pract. 2009;15:95-103)     

1,25-Dihydroxyvitamin D3 increases serum levels of the vitamin K-dependent bone protein

1,25-dihydroxyvitamin D₃ increases serum levels of bone Gla protein (BGP). The maximal increase occurs 12 h after injection and is given by 350 ng 1,25(OH)₂D₃ per 180 g body weight. In both 2 and 11 month-old male rats, the maximal increase is about 3 times the normal level, while in 2 month old female rats, the maximal increase is 2 times the normal level. These effects of 1,25(OH)₂D₃ in rats parallel the previously described effects of the vitamin on BGP secretion by rat osteosarcoma cells in culture.BGP is the first bone-specific protein whose synthesis in animals is dramatically increased by 1,25(OH)₂D₃. The possible functions of BGP in the biological actions of 1,25(OH)₂D₃ on bone are discussed.