X-ray features of vitamin D-deficiency and vitamin D-resistant rickets

To study the age-related features of growth areas and to detect the x-ray background of recurrent deformities in patients with rickets-like diseases, the investigators analyzed knee arthrograms in 74 patients aged 4 to 16 years (28 and 46 patients with vitamin D-deficiency or vitamin D-resistant rickets (phosphate diabetes), respectively) prior to treatment and in the late period.     

Apoptosis-inducing activity of vitamin C and vitamin K.

Apoptosis-inducing activity of vitamins C and K and of their analogs are reviewed. Vitamin C shows both reducing and oxidizing activities, depending on the environment in which this vitamin is present. Higher concentrations of vitamin C induce apoptotic cell death in various tumor cell lines including oral squamous cell carcinoma and salivary gland tumor cell lines, possibly via its prooxidant action. The apoptosis-inducing activity of ascorbate is stimulated by Cu2+, lignin and ion chelator, and inhibited by catalase, Fe3+, Co2+ and saliva. On the other hand, at lower concentrations, ascorbic acid displays an antioxidant property, preventing the spontaneous and stress or antitumor agent-induced apoptosis. Sodium 5,6-benzylidene-L-ascorbate, intravenous administration of which induces degeneration of human inoperable tumors and rat hepatocellular carcinoma in vivo, induces apoptotic or non-apoptotic cell death, depending on the types of target cells. On the other hand, elevation of intracellular concentration of ascorbic acid by treatment with ascorbate 2-phosphate or dehydroascorbic acid makes the cells resistant to the oxidative stress-induced apoptosis. Vitamin K2, which has a geranylgeranyl group as a side chain,and vitamin K3 induces apoptosis of various cultured cells including osteoclasts and osteoblasts, by elevating peroxide and superoxide radicals. Synergistic apoptosis-inducing actions have been found between vitamins C and K, and between these vitamins and antiproliferative agents. The possible therapeutic application of these vitamins is discussed.     

Serum vitamin A and vitamin E concentrations after parenteral vitamin A administration in sheep

Twenty primiparous dairy sheep of the Mytilene breed, which were fed with a ration deficient in vitamin A and carotenes, were divided into 2 groups of 10 animals each after a 2-month adaptation period. The animals of group A were administered vitamin A palmitate by intramuscular injection (3500 IU/kg bodyweight), while the animals of group B were used as controls and received only the vehicle of the preparation without vitamin A. Serum vitamin A concentrations increased significantly in the animals of group A compared to the animals of group B (P < 0.01) from the first 24 h post-injection and remained significantly high for 8 days, and at 10 days post-injection they reached the pre-injection levels. The serum vitamin E concentration declined significantly (P < 0.05) in the animals of group A compared to the animals of group B for 8 days, when they reached the pre-injection levels. No changes in serum vitamins A and E levels in the animals of the 2 groups were observed 20 days after the injection of vitamin A.     

Oxygen dependence of vitamin K-dependent carboxylase and vitamin K epoxidase

A study of the oxygen requirements of the rat liver microsomal vitamin K-dependent carboxylase and vitamin K 2,3-epoxidase indicated that both enzymes had a Km for O2 in the range 60-80 microM. This value was not influenced by vitamin concentration, alterations in carboxylase substrate, Mn2+, or dithiothreitol, and is consistent with the hypothesis that both activities are catalyzed by the same enzyme.     

The conversion of vitamin K epoxide to vitamin K quinone and vitamin K quinone to vitamin K hydroquinone uses the same active site cysteines

Vitamin K epoxide (or oxido) reductase (VKOR) is the target of warfarin and provides vitamin K hydroquinone for the carboxylation of select glutamic acid residues of the vitamin K-dependent proteins which are important for coagulation, signaling, and bone metabolism. It has been known for at least 20 years that cysteines are required for VKOR function. To investigate their importance, we mutated each of the seven cysteines in VKOR. In addition, we made VKOR with both C43 and C51 mutated to alanine (C43A/C51A), as well as a VKOR with residues C43-C51 deleted. Each mutated enzyme was purified and characterized. We report here that C132 and C135 of the CXXC motif are essential for both the conversion of vitamin K epoxide to vitamin K and the conversion of vitamin K to vitamin K hydroquinone. Surprisingly, conserved cysteines, 43 and 51, appear not to be important for either reaction. For the in vitro reaction driven by dithiothreitol, the 43-51 deletion mutation retained 85% and C43A/C51A 112% of the wild-type activity. The facile purification of the nine different mutations reported here illustrates the ease and reproducibility of VKOR purification by the method reported in our recent publication [Chu, P.-H., Huang, T.-Y., Williams, J., and Stafford, D. W. (2006) Proc. Natl. Acad. Sci. U S A. 103, 19308-19313].     

A hetero-dimer model for concerted action of vitamin K carboxylase and vitamin K reductase in vitamin K cycle

Vitamin K carboxylase (VKC) is believed to convert vitamin K, in the vitamin K cycle, to an alkoxide-epoxide form which then reacts with CO₂ and glutamate to generate γ-carboxyglutamic acid (Gla). Subsequently, vitamin K epoxide reductase (VKOR) is thought to convert the alkoxide-epoxide to a hydroquinone form. By recycling vitamin K, the two integral-membrane proteins, VKC and VKOR, maintain vitamin K levels and sustain the blood coagulation cascade. Unfortunately, NMR or X-ray crystal structures of the two proteins have not been characterized. Thus, our understanding of the vitamin K cycle is only partial at the molecular level. In this study, based on prior biochemical experiments on VKC and VKOR, we propose a hetero-dimeric form of VKC and VKOR that may explain the efficient oxidation and reduction of vitamin K during the vitamin K cycle.     

Reactivity of vitamin A derivatives and analogues with vitamin A antibodies

Vitamin A antibodies were obtained using retinoic acid conjugated to human serum albumin as an immunogen. The following constraints governed the reactivity of vitamin A analogues with such an anti-serum. The stereochemistry of the side chain is relatively unimportant, and 9- and 13-cis retinal react almost as well as all-trans retinal. The nature of the ring is important; all of the compounds that react readily carry a beta-ionic ring; all of the compounds bearing an aromatic ring react poorly; the two compounds that display intermediate reactivity have non-aromatic 6- and 5-membered rings, respectively.     

Three-dimensional structure-function relationship of vitamin D and vitamin D receptor model

On the basis of conformational analysis of the vitamin D side chain and studies using conformationally restricted synthetic vitamin D analogs, we have suggested the active space region concept of vitamin D: The vitamin D side-chain region was grouped into four regions (A, G, EA and EG) and the A and EA regions were suggested to be important for vitamin D actions. We extended our theory to known highly potent vitamin D analogs and found a new region F. The analogs which occupy the F region have such modifications as 22-oxa, 22-ene, 16-ene and 18-nor. Altogether, the following relationship between the space region and activity was found: Affinity for vitamin D receptor (VDR), EA > A> F > G > EG; Affinity for vitamin D binding protein (DBP), A > G,EA,EG; Target gene transactivation, EA > F > A > EG > or = G; Cell differentiation, EA > F > A > EG > or = G; Bone calcium mobilization, EA > GA > F > or = EG; Intestinal calcium absorption, EA = A > or = G > EG. We modeled the 3D structure of VDR-LBD (ligand binding domain) using hRARgamma as a template, to develop our structure-function theory into a theory involving VDR. 1alpha,25(OH)(2)D(3) was docked into the ligand binding pocket of the VDR with the side chain heading the wide cavity at the H-11 site, the A-ring toward the narrow beta-turn site, and the beta-face of the CD ring facing H3. Amino acid residues forming hydrogen bonds with the 1alpha- and 25-OH groups were specified: S237 and R274 forming a pincer type hydrogen-bond for the 1alpha-OH and H397 for the 25-OH. Mutants of several amino acid residues that are hydrogen-bond candidates were prepared and their biologic properties were evaluated. All of our mutation results together with known mutation data support our VDR model docked with the natural ligand.     

SVCT与维生素C内稳态的保持

维生素C(又名抗坏血酸)是一种基本的微量营养素,作为辅助因子参与多个酶促反应,同时还是一种自由基清除剂。维生素C内稳态主要由两种钠离子依赖的维生素C转运蛋白(sodium-dependent vitamin C transporter,SVCT)——SVCT1和SVCT2来保持。SVCT1在内皮系统表达,介导了维生素C的肠吸收和肾脏重吸收;而SVCT2表达广泛,表达于脑、骨骼和其他组织,保护这些组织免遭氧化损伤。SVCT的遗传多态性与癌症的发生密切相关。对SVCT介导的维生素C内稳态的保持机制的研究,可使维生素C更好地应用于临床。     

The role of vitamin E in metabolism and reception of vitamin D

It was found that calcium exchange disturbances under vitamin E deficiency is due to changes in the metabolism of vitamin D. In vitamin E-deficient rats the serum blood levels of hydroxyvitamin D (25-OHD) showed no significant changes, whereas the concentration of the hormonal form of 1.25-hydroxyvitamin D [1.25(OH)2D], decreased by 40%. In vitro studies showed that the 25-hydroxylase D3 activity in the livers of rats with E-avitaminosis had a tendency to decrease (by 22%), whereas that of 24-hydroxylase dropped drastically (by 52%). The serum blood levels of the parathyroid hormone (PTH) and kidney levels of cAMP under E-avitaminosis were significantly lowered. Preincubation of kidney slices with the adenylate cyclase activator, forskolin, increased the activity of 1-OHase in about the same degree as that in vitamin E-rich rats. The free radical scavenger, BHT, added to kidney slices suppressed the activity of the both enzymes; this finding testifies to the low O2-binding affinity of these monooxygenases. The content of 1.25(OH)2D3 receptors occupied in vivo in the kidneys of vitamin E-deficient rats decreased 2.5-fold; however, the binding of 1.25(OH)2D3-receptor complexes to heterologous DNA was unaffected thereby. The vitamin deficiency in vivo results in the inhibition of vitamin D metabolism in the liver and kidney concomitant with the formation of active metabolites and decreases the concentration of hormone-receptor complexes in target tissues.