A synthetic analogue of vitamin D3, 22-oxa-1,25-dihydroxy-vitamin D3, stimulates the production of prostacyclin by vascular tissues

A prospective randomized controlled trial of the effects of vitamin D supplementation on cardiovascular disease risk

Vitamin D (VitD) supplementation has been advocated for cardiovascular risk reduction; however, supporting data are sparse. The objective of this study was to determine whether VitD supplementation reduces cardiovascular risk. Subjects in this prospective, randomized, double-blind, placebo-controlled trial of post-menopausal women with serum 25-hydroxyvitamin D concentrations >10 and <60 ng/mL were randomized to Vitamin D3 2500 IU or placebo, daily for 4 months. Primary endpoints were changes in brachial artery flow-mediated vasodilation (FMD), carotid-femoral pulse wave velocity (PWV), and aortic augmentation index (AIx). The 114 subjects were mean (standard deviation) 63.9 (3.0) years old with a 25-hydroxyvitamin D level of 31.3 (10.6) ng/mL. Low VitD (<30 ng/mL) was present in 47% and was associated with higher body-mass index, systolic blood pressure, glucose, CRP, and lower FMD (all p<0.05). After 4 months, 25-hydroxyvitamin D levels increased by 15.7 (9.3) ng/mL on vitamin D3 vs. −0.2 (6.1) ng/mL on placebo (p<0.001). There were no significant differences between groups in changes in FMD (0.3 [3.4] vs. 0.3 [2.6] %, p = 0.77), PWV (0.00 [1.06] vs. 0.05 [0.92] m/s, p = 0.65), AIx (2.7 [6.3] vs. 0.9 [5.6] %, p = 0.10), or CRP (0.3 [1.9] vs. 0.3 [4.2] mg/L, p = 0.97). Multivariable models showed no significant interactions between treatment group and low VitD status (<30 ng/mL) for changes in FMD (p = 0.65), PWV (p = 0.93), AIx (p = 0.97), or CRP (p = 0.26).In conclusion, VitD supplementation did not improve endothelial function, arterial stiffness, or inflammation. These observations do not support use of VitD supplementation to reduce cardiovascular disease risk.

Peroxisome proliferator-activated receptor delta is up-regulated during vascular lesion formation and promotes post-confluent cell proliferation in vascular smooth muscle cells

Although peroxisome proliferator-activated receptor (PPAR) delta is widely expressed in many tissues, the role of PPARdelta is poorly understood. In this study, we report that PPARdelta was up-regulated in vascular smooth muscle cells (VSMC) during vascular lesion formation. By using Northern blot analysis, we demonstrated that PPARdelta was increased by 3-4-fold in VSMC treated with platelet-derived growth factor (PDGF) (20 ng/ml). In addition, PDGF-induced PPARdelta mRNA expression neither needs de novo protein synthesis nor affects the stability of PPARdelta mRNA in VSMC. Preincubation of VSMC with phosphatidylinositol 3-kinase inhibitor (LY294002, 50 micromol/liter) or infection of VSMC with an adenovirus carrying the gene for a dominant negative form of Akt abrogated PDGF-induced PPARdelta mRNA expression, suggesting that phosphatidylinositol 3-kinase/Akt signaling pathway is involved in the regulation of PDGF-induced PPARdelta mRNA expression in VSMC. To explore the role of PPARdelta in VSMC, we generated rat vascular smooth muscle cells (A7r5) stably overexpressing PPARdelta and the control green fluorescent protein. Overexpression of PPARdelta in VSMC increased post-confluent cell proliferation by increasing the cyclin A and CDK2 as well as decreasing p57(kip2). Taken together, the results suggest that PPARdelta plays an important role in the pathology of diseases associated with VSMC proliferation, such as primary atherosclerosis and restenosis.

Anticoagulant Effects of 1α,25-Dihydroxyvitamin D3 on Human Myelogenous Leukemia Cells and Monocytes

The hormonally active form of vitamin D is 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], which is a principal regulator of calcium homeostasis. It also affects hormone secretion, cell differentiation, and proliferation by a mode of action that involves stereospecific interaction with an intracellular vitamin D receptor (VDR). We recently found that retinoids, which are vitamin A derivatives, exert anticoagulant effects by upregulating thrombomodulin (TM) and downregulating tissue factor (TF) expression in acute promyelocytic leukemia cells and monoblastic leukemia cells. Both the VDR and retinoid receptors belong to the same family of receptors. A heterodimer consisting of the retinoid X receptor and the VDR binds to vitamin D responsive elements on genes regulated by vitamin D. To determine whether 1,25(OH)2D3 would exhibit anticoagulant effects similar to retinoids, we measured the antigen level, activity, and mRNA level of TM and TF in human leukemic cells, vascular endothelial cells, and monocytes treated with 1,25(OH)2D3. We found that 1,25(OH)2D3 upregulates antigen expression, activity, and mRNA levels of TM and downregulates antigen expression, activity, and mRNA levels of TF in human monocytic leukemia cells, some acute myelogenous leukemia cells, and monocytes, but not in umbilical vein endothelial cells. Transient transfection studies with reporter plasmids in monocytic leukemia cells and mobility gel-shift assay showed interaction with 1,25(OH)2D3 and functional retinoic acid responsive elements present in the 5′-flanking region of the TM gene. However, auxiliary factors or other elements in the TM gene may contribute to VDR specificity and transactivation of the gene in specific target cells. These findings indicate that 1,25(OH)2D3 resembles the retinoids in its control of the transcription of the TM and TF genes in human monocytic cells. Analogs of 1,25(OH)2D3with anticoagulant activity may serve as adjunctive antithrombotic agents in monocytic leukemia and atherosclerotic disease.

1alpha,25-dehydroxyvitamin D3 synergism toward transforming growth factor-beta1-induced AP-1 transcriptional activity in mouse osteoblastic cells via its nuclear receptor

The present study demonstrates 1alpha,25-dehydroxyvitamin D3 (1alpha-25-(OH)2D3) synergism toward transforming growth factor (TGF)-beta1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1alpha-25-(OH)2D3 synergistically stimulated TGF-beta1-induced expression of the c-jun gene in the cells but not that of the c-fos gene. We actually showed by a gel mobility shift assay 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced AP-1 binding to the 12-(O-tetradecanoylphorbol-13-acetate response element (TRE). 1alpha-25-(OH)2D3 markedly stimulated the transient activity of TGF-beta1-induced AP-1 in the cells transfected with a TRE-chloramphenicol acetyltransferase (CAT) reporter gene. Also, a synergistic increase in TGF-beta1-induced CAT activity was observed in the cells cotransfected with an expression vector encoding vitamin D3 receptor (VDR) and the reporter gene. However, the synergistic CAT activity was inhibited by pretreatment with VDR antisense oligonucleotides. In addition, in a Northern blot assay, we observed 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced expression of the c-jun gene in the cells transfected with the VDR expression vector and also found that the synergistic action was clearly blocked by VDR antisense oligonucleotide pretreatment. The present study strongly suggests a novel positive regulation by 1alpha-25-(OH)2D3 of TGF-beta1-induced AP-1 activity in osteoblasts via "genomic action."

High-resolution B-mode ultrasonography in evaluation of atherosclerosis in uremia

We sought to determine whether artherosclerosis may be accelerated in uremic patients on maintenance hemodialysis and investigated the risk factors for carotid and femoral atherosclerosis in such patients. High-resolution B-mode ultrasonography was used to determine the intima-media thickness (IMT) of the carotid and femoral arteries in 199 hemodialysis patients and 81 age-matched healthy controls subjects. The IMT values of the carotid and femoral arteries in the hemodialysis patients were significantly higher than in age-matched control subjects in most age groups. The IMT values of the carotid or femoral artery were significantly correlated with age in both the hemodialysis patients and the control subjects. There was a significant relationship between the IMT values of the two arteries in the hemodialysis patients (r = 0.418, P = 0.0001) and in the control subjects (r = 0.321, P = 0.0037). Multiple regression analysis showed that age, cigarette smoking, and uremic state were independent risk factors for atherosclerosis of both arteries in the patients and the control subjects (R2 = 0.174, P < 0.0001; R2 = 0.205, P < 0.0001, respectively). In the hemodialysis patients, the independent risk factors associated with the extent of the IMT of the carotid artery were age, cigarette smoking, and serum phosphorus level (R2 = 0.230, P < 0.0001), while those associated with the extent of the IMT of the femoral artery were age, cigarette-smoking, and serum m-PTH level (R2 = 0.230, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Prostacyclin, nitric oxide, and atherosclerosis

Disorders in arterial production of PGI2 and NO occur in atherosclerosis. Exogenous PGI2 and NO are capable of interacting pharmacologically. We claim that no such direct interactions occur between endogenous endothelial PGI2 and NO. Studying mechanisms of cardiac reactive hyperemia in guinea pigs and of thrombolysis in cats, we surmise that in vivo vascular intima releases PGI2 intraluminally while NO is secreted abluminally and thus these two ephemeral mediators do not see each other. Hence, in any disease, the disturbances in endothelial generation of PGI2 or NO have to be scrutinized separately. It may well be that endogenous PGI2 maintains endothelial thromboresistance while NO controls arterial myocytes and tissues in which microcirculation is embedded. These responsibilities remain unshared. Interactions between PGI2 and NO are confined to pharmacological domains.