Pharmacokinetics of oral vitamin D(3) and calcifediol.

AIM: Long-term pharmacokinetics after supplementation with vitamin D3 or calcifediol (the 25-hydroxyvitamin D3 metabolite) is not well studied. Additionally, it is unclear whether bolus doses of vitamin D3 or calcifediol lead to 25(OH)D3 plasma concentrations considered desirable for fracture prevention (30 ng/mL). We therefore investigated plasma pharmacokinetics of 25(OH)D3 during different vitamin D3 and calcifediol supplementation regimens. METHODS: In this seven-arm, randomized, double-blind, controlled parallel-group study, 35 healthy females aged 50­70 years (5 per group) received 20 µg calcifediol or vitamin D(3) daily, 140 µg calcifediol or vitamin D(3) weekly, for 15 weeks, or a single bolus of either 140 µg calcifediol, or vitamin D(3), or both. 25(OH)D3 plasma concentrations were quantified using LC­MS/MS in 14 clinical visits among all participants. RESULTS: For daily (weekly) dosing, the area under the concentration­time curve (AUC0­24h), which is the measure for exposure, was 28% (67%) higher after the first dose of calcifediol than after the first dose of vitamin D3. After 15 weeks, this difference was 123% (178%). All women in the daily and weekly calcifediol groups achieved 25(OH)D3 concentrations > 30 ng/mL (mean, 16.8 days), but only 70% in the vitamin D3 daily or weekly groups reached this concentration (mean, 68.4 days). A single dose of 140 µg calcifediol led to 117% higher 25(OH)D3 AUC0­96h values than 140 µg vitamin D3, while the simultaneous intake of both did not further increase exposure. CONCLUSIONS: Calcifediol given daily, weekly, or as a single bolus is about 2­3 times more potent in increasing plasma 25(OH)D3 concentrations than vitamin D3. Plasma 25(OH)D3 concentrations of 30 ng/mL were reached more rapidly and reliably with calcifediol.

The role of menaquinones (vitamin K2) in human health.

Recent reports have attributed the potential health benefits of vitamin K beyond its function to activate hepatic coagulation factors. Moreover, several studies have suggested that menaquinones, also known as vitamin K2, may be more effective in activating extra-hepatic vitamin K-dependent proteins than phylloquinone, also known as vitamin K1. Nevertheless, present dietary reference values (DRV) for vitamin K are exclusively based on phylloquinone, and its function in coagulation. The present review describes the current knowledge on menaquinones based on the following criteria for setting DRV: optimal dietary intake; nutrient amount required to prevent deficiency, maintain optimal body stores and/or prevent chronic disease; factors influencing requirements such as absorption, metabolism, age and sex. Dietary intake of menaquinones accounts for up to 25% of total vitamin K intake and contributes to the biological functions of vitamin K. However, menaquinones are different from phylloquinone with respect to their chemical structure and pharmacokinetics, which affects bioavailability, metabolism and perhaps impact on health outcomes. There are significant gaps in the current knowledge on menaquinones based on the criteria for setting DRV. Therefore, we conclude that further investigations are needed to establish how differences among the vitamin K forms may influence tissue specificities and their role in human health. However, there is merit for considering both menaquinones and phylloquinone when developing future recommendations for vitamin K intake.

A glimpse of vitamin D status in Mainland China.

As an essential dietary micronutrient, vitamin D plays a pivotal role in promoting calcium absorption in the intestine and maintaining a healthy skeletal system throughout life. Beyond bone health, an emerging volume of scientific studies shows that vitamin D also may provide cardiovascular, metabolic, and immunologic benefits and reduce mortality. To our knowledge, in mainland China no national surveys have been conducted to date to depict the overall vitamin D status in the population. Therefore, the purpose of this contribution was to provide the best possible evaluation of vitamin D deficiency/insufficiency in China by reviewing publications that measured plasma/serum 25-hydroxyvitamin-D (25[OH]D) levels in various age groups and in different areas of China from January 2000 to June 2012. From these investigations conducted throughout the country and from newborns to adults to the elderly, it has been found that vitamin D deficiency/insufficiency is prevalent in the Chinese population in almost all age groups and areas if individuals are not taking vitamin D-fortified products/supplements or are lacking sufficient sunshine exposure. Some studies showed severe deficiency (25[OH]D <25 nmol/L) in Nanjing (north latitude 31) during the winter months and in Beijing (north latitude 40) in the fall. This unoptimistic situation represents a significant but modifiable public health risk that deserves greater attention and more efficient and timely management.

Cortical gene expression in the vitamin E-deficient rat: possible mechanisms for the electrophysiological abnormalities of visual and neural function.

In mammals, severe and chronic deficiency of vitamin E (alpha-tocopherol) is associated with a characteristic neurological syndrome. Previously, we have shown that this syndrome is accompanied by electrophysiological abnormalities of neural and visual function. To investigate the molecular basis of the observed abnormalities, we used microarrays to monitor the expression of approximately 14,000 genes in the cerebral cortex from rats which had received diets containing 0, 1.25 and 5.0 mg/kg diet of all-rac-alpha-tocopheryl acetate for 14 months. Compared to the groups receiving 1.25 and 5.0 mg/kg alpha-tocopheryl acetate, a total of 11 genes were statistically significantly upregulated (> or =1.3-fold) and 34 downregulated (< or =1.3-fold) in the vitamin E-deficient group. Increased expression was observed for the genes encoding the antioxidant enzyme catalase and the axon guidance molecule tenascin-R, while decreased expression was detected for genes encoding protein components of myelin and determinants of neuronal signal propagation. Thus our observations suggest that vitamin E deficiency results in transcriptional alterations in the cerebral cortex of the rat which are consistent with the observed neurological and electrophysiological alterations.

Effect of Vitamin E on Cytochrome P450 mRNA Levels in Cultured Hepatocytes (HepG2) and in Rat Liver.

Vitamin E has been described in the literature as a regulator of gene expression. The gene-regulatory activity of vitamin E with regard to genes encoding cytochrome P450 (CYP) enzymes, which play a pivotal role both in the metabolism of xenobiotics and vitamin E, has not been conclusively characterised. The objective of the current study was, therefore, to elucidate the short- and long-term effects of natural and synthetic vitamin E on CYP gene expression using Affymetrix GeneChip® technology. To this end, HepG2 cells were incubated with 0, 10, 30, 80 and 300 µM RRR-α-tocopheryl acetate (natural vitamin E) or all rac-α-tocopheryl acetate (synthetic vitamin E) for 7 days and the mRNA of CYP genes was quantified. The expression of only one (CYP20A1) of 14 CYP genes with detectable mRNA levels was dose-dependently up-regulated. No differences in gene-regulatory activity were observed between RRR- and all rac-α-tocopheryl acetate. To study the role of vitamin E in CYP gene expression in vivo, Fisher 344 rats were randomly assigned to either a vitamin E-enriched (60 mg/kg RRR-α-tocopheryl acetate) or - deficient (1.7 mg/kg RRR-α-tocopheryl acetate) diet for 290 days. Neither in the vitamin E-enriched, nor in the vitamin E-deficient rats, were significant changes in the liver CYP, mRNA levels observed. In conclusion, our data indicated that vitamin E does not appear to modulate cytochrome P450 mRNA expression in HepG2 cells or in rats.

Comparative quantification of pharmacodynamic parameters of chiral compounds (RRR- vs. all-rac-alpha tocopherol) by global gene expression profiling.

Pharmacologically active compounds (e.g. from the groups of pharmaceutical drugs, cofactors or vitamins) often consist of two or more stereoisomers (enantiomers or diastereoisomers) which may differ in their pharmacodynamic/kinetic, toxicological and biological properties. A well-known example is vitamin E which is predominantly administered as two different forms, one derived from natural sources (mainly soybeans), and one from production by chemical total-synthesis. While vitamin E from natural sources occurs as a single stereoisomer (RRR-alpha-tocopherol), synthetic vitamin E (all-rac-alpha-tocopherol) is an equimolar mixture of eight stereoisomers. Based on a number of animal studies it has been suggested that the biological potency of natural-source vitamin E is 1.36 greater compared to its counterpart produced by chemical synthesis. In this study, we have used the Affymetrix GeneChip technology to evaluate the feasibility of a new bio-assay where the gene regulatory activities of RRR-alpha-tocopherol and all-rac-alpha-tocopherol were quantified and compared on the genome-wide level. For this purpose, HepG2 cells were supplemented with increasing amounts of RRR- or all-rac-alpha-tocopherol for 7 days. Genes showing a dose-related induction/repression were identified by global gene expression profiling. Our findings show that RRR- and all-rac-alpha-tocopherol share an identical transcriptional activity, i.e. induce/repress the expression of the same set of genes. Based on the transcriptional dose-response data, EC50 and IC50 values were determined for each of these genes. The feasibility of calculating a "transcriptional potency factor" of RRR- vs. all-rac-e-tocopherol was evaluated by dividing the EC50/IC50 of RRR-alpha-tocopherol by the corresponding EC50/IC50 of all-rac-alpha-tocopherol for every of the vitamin E responsive genes. Using this approach we have calculated 215 single biopotency ratios. Subsequently, the mean of all potency ratios was found to be 1.05. In the present work we propose a new assay for the analysis and comparison of the biological activity and potency of chiral compounds in vivo.

Dietary vitamin E modulates differential gene expression in the rat hippocampus: potential implications for its neuroprotective properties.

A wide range of cell culture, animal and human epidemiological studies are suggestive of a role of vitamin E (VE) in brain function and in the prevention of neurodegeneration. However, the underlying molecular mechanisms remain largely unknown. In the current investigation Affymetrix gene chip technology was utilised to establish the impact of chronic VE deficiency on hippocampal genes expression. Male albino rats were fed either a VE deficient or standard diet (60 mg/kg feed) for a period of 9 months. Rats were sacrificed, the hippocampus removed and genes expression established in individual animals. VE deficiency showed to have a strong impact on genes expression in the hippocampus. An important number of genes found to be regulated by VE was associated with hormones and hormone metabolism, nerve growth factor, apoptosis, dopaminergic neurotransmission, and clearance of amyloid-beta and advanced glycated endproducts. In particular, VE strongly affected the expression of an array of genes encoding for proteins directly or indirectly involved in the clearance of amyloid beta, changes which are consistent with a protective effect of VE on Alzheimer's disease progression.

Modulation of hepatic gene expression by alpha-tocopherol in cultured cells and in vivo.

To obtain a comprehensive understanding of the molecular mechanisms of action of vitamin E (VE), global gene expression profiles using DNA arrays in rat liver and hepatocellular liver carcinoma cells (HepG2) were obtained. For the analysis of short-term (49 days) and long-term (290 days) VE deficiency, rats were fed semisynthetic diets either supplemented with or deficient in VE. In addition, HepG2 cells were treated with VE concentrations comparable to those that were achieved in the in vivo experiment. Differential gene expression in rat liver and that in HepG2 cells were measured by DNA arrays comprising up to 7,000 genes. Dietary VE deficiency over a 7-week period did not induce any significant changes in the expression profile among the genes evaluated. However, long-term VE deficiency upregulated coagulation factor IX (FIX), 5-alpha-steroid reductase type 1, and CD36 mRNA levels. Furthermore, VE deficiency resulted in a significant downregulation of hepatic gamma-glutamyl-cysteinyl synthetase, the rate-limiting enzyme of glutathione synthesis. According to the rat experiment, VE supplementation changed coagulation factor IX and CD36 expression in HepG2 cells; thus, in vivo data could be partly confirmed with the in vitro model. Overall, the current studies reveal that dietary VE has important long-term effects on liver gene expression with potential downstream effects on extrahepatic tissues.