Smooth muscle cell proliferation in the rat coronary artery induced by vitamin D

Lack of vitamin D receptor causes stress-induced premature senescence in vascular smooth muscle cells through enhanced local angiotensin-II signals

OBJECTIVES

The inhibition of the renal renin-angiotensin system by the active form of vitamin D contributes to the cardiovascular health benefits of a normal vitamin D status. Local production of angiotensin-II in the vascular wall is a potent mediator of oxidative stress, prompting premature senescence. Herein, our objective was to examine the impact of defective vitamin D signalling on local angiotensin-II levels and arterial health.

METHODS

Primary cultures of aortic vascular smooth muscle cells (VSMC) from wild-type and vitamin D receptor-knockout (VDRKO) mice were used for the assessment of cell growth, angiotensin-II and superoxide anion production and expression levels of cathepsin D, angiotensin-II type 1 receptor and p57(Kip2). The in vitro findings were confirmed histologically in aortas from wild-type and VDRKO mice.

RESULTS

VSMC from VDRKO mice produced more angiotensin-II in culture, and elicited higher levels of cathepsin D, an enzyme with renin-like activity, and angiotensin-II type 1 receptor, than wild-type mice. Accordingly, VDRKO VSMC showed higher intracellular superoxide anion production, which could be suppressed by cathepsin D, angiotensin-II type 1 receptor or NADPH oxidase antagonists. VDRKO cells presented higher levels of p57(Kip2), impaired proliferation and premature senescence, all of them blunted upon inhibition of angiotensin-II signalling. In vivo studies confirmed higher levels of cathepsin D, angiotensin-II type 1 receptor and p57(Kip2) in aortas from VDRKO mice.

CONCLUSION

The beneficial effects of active vitamin D in vascular health could be a result of the attenuation of local production of angiotensin-II and downstream free radicals, thus preventing the premature senescence of VSMC.

Scanning electron microscopy evaluation of endothelialized tissue-engineered constructs

Scanning electron microscopy (SEM) is an important technique for evaluation of the efficiency of endothelialization of tissue-engineered constructs incorporating a surface endothelial cell layer. Here, we describe methodologies for the preparation of such constructs for SEM analysis that are applicable to a broad range of tissue-engineered constructs.

Effect of vitamin D deficiency and replacement on endothelial function in asymptomatic subjects

CONTEXT

Vitamin D receptors are present in many tissues. Hypovitaminosis D is considered to be a risk factor for atherosclerosis.

OBJECTIVE

This study explores the effects of vitamin D replacement on insulin sensitivity, endothelial function, inflammation, oxidative stress, and leptin in vitamin D-deficient subjects.

DESIGN, SETTING, AND PATIENTS

Twenty-three asymptomatic vitamin D-deficient subjects with 25-hydroxyvitamin D [25(OH)D] levels below 25 nmol/liter were compared with a control group that had a mean 25(OH)D level of 75 nmol/liter. The vitamin D-deficient group received 300,000 IU im monthly for 3 months. The following parameters were evaluated before and after treatment: vitamin D metabolites, leptin, endothelial function by brachial artery flow mediated dilatation (FMD), insulin sensitivity index based on oral glucose tolerance test, and lipid peroxidation as measures of thiobarbituric acid reactive substances (TBARS).

RESULTS

FMD measurements were significantly lower in 25(OH)D-deficient subjects than controls (P = 0.001) and improved after replacement therapy (P = 0.002). Posttreatment values of TBARS were significantly lower than pretreatment levels (P < 0.001). A positive correlation between FMD and 25(OH)D (r = 0.45; P = 0.001) and a negative correlation between FMD and TBARS (r = -0.28; P < 0.05) were observed. There was a significant increase in leptin levels after therapy, and the leptin levels were positively correlated with 25(OH)D levels (r = 0.45; P < 0.05).

CONCLUSIONS

This study shows that 25(OH)D deficiency is associated with endothelial dysfunction and increased lipid peroxidation. Replacement of vitamin D has favorable effects on endothelial function. Vitamin D deficiency can be seen as an independent risk factor of atherosclerosis. Hypovitaminosis D-associated endothelial dysfunction may predispose to higher rates of cardiovascular disease in the winter.

Vitamin D and the vasculature: can we teach an old drug new tricks?

BACKGROUND

Vitamin D is a steroid hormone known for its role in regulating levels of calcium and phosphorus. Vitamin D has important autocrine/paracrine roles and it is involved in vascular biology. Clinical studies have shown a relationship between vitamin D levels and cardiovascular health, and low levels of vitamin D metabolites have been associated with higher incidence of congestive heart failure and increases in mortality.

OBJECTIVE

To summarise the effect of vitamin D on cardiovascular pathology, the leading cause of death in chronic kidney disease patients.

CONCLUSIONS

All results indicate a potential effect of vitamin D on cardiovascular health. Therefore, maintaining optimum levels of circulating vitamin D is critical for a healthy cardiovascular system. In patients with low vitamin D status, like renal patients, supplementation with vitamin D metabolites has shown beneficial cardiovascular effects.

Pharmacological control of secondary hyperparathyroidism in chronic hemodialysis patients: cinacalcet is coming to Japan

Secondary hyperparathyroidism has a significant impact on morbidity and mortality due to skeletal and extraskeletal manifestations. Cinacalcet, a newly developed calcimimetic, is reported to decrease parathyroidism, as well as serum levels of phosphorus (P) and calcium (Ca) and therefore Ca x P product. Available evidence has shown that cinacalcet decreases the rate of parathyroidectomy and bone fracture in hemodialysis patients, but the death rate remains the same. Although, it is not yet available in Japan, cinacalcet is expected to be available as a possible drug for patients undergoing hemodialysis due to secondary hyperparathyroidism associated with refractory hyperphosphatemia and hypercalcemia. Except for the high cost, cinacalcet will be a welcome therapeutic option for end-stage renal disease and probably also for pre-end-stage renal disease patients. Dietary phosphate restriction and adequate hemodialysis, however, are still the main strategy for the control of hyperphosphatemia and secondary hyperparathyroidism.

Vitamin D, Shedding Light on the Development of Disease in Peripheral Arteries

Vitamin D is generally associated with calcium metabolism, especially in the context of uptake in the intestine and the formation and maintenance of bone. However, vitamin D influences a wide range of metabolic systems through both genomic and nongenomic pathways that have an impact on the properties of peripheral arteries. The genomic effects have wide importance for angiogenesis, elastogenesis, and immunomodulation; the nongenomic effects have mainly been observed in the presence of hypertension. Although some vitamin D is essential for cardiovascular health, excess may have detrimental effects, particularly on elastogenesis and inflammation of the arterial wall. Vitamin D is likely to have a role in the paradoxical association between arterial calcification and osteoporosis. This review explores the relationship between vitamin D and a range of physiological and pathological processes relevant to peripheral arteries.

Lower risk for cardiovascular mortality in oral 1alpha-hydroxy vitamin D3 users in a haemodialysis population

BACKGROUND

Renal failure results in deficiency of active vitamin D3 that has diverse effects on metabolism and organ functions. Treatment with active forms of vitamin D(3) ameliorates abnormalities in bone and mineral metabolism, cardiac function, immune response and others. We hypothesized that treatment with vitamin D(3) may be beneficial for survival in patients with end-stage renal disease (ESRD).

METHODS

We compared the risk of death between regular users (n = 162) and non-users (n = 80) of oral 1alpha-hydroxyvitamin D3 (alfacalcidol) in a cohort of ESRD patients undergoing haemodialysis for a follow-up of 61 +/- 23 months. The daily dose of alfacalcidol ranged from 0.25 to 1.5 microg, with a median of 0.5 microg.

RESULTS

The alfacalcidol users showed a lower risk of death from cardiovascular disease than the non-users in a univariate Cox model [hazards ratio (HR) 0.287, 95% confidence interval (CI) 0.127-0.649, P = 0.003], whereas the risk for death from non-cardiovascular disease was not different between the two groups. Stepwise multivariate Cox analysis showed that cardiovascular mortality was significantly associated with age, presence of diabetes mellitus and treatment with alfacalcidol (HR 0.377, 95% CI 0.246-0.578, P = 0.022).

CONCLUSIONS

These results indicate that use of oral alfacalcidol was associated with reduced risk for cardiovascular death in this cohort of ESRD patients. The result of this observational study warrants further randomized controlled trials with 1alpha-hydroxy vitamin D3 to confirm the possibility that such medication improves survival of ESRD patients.

Parathyroid hormone, vitamin D, and cardiovascular disease in chronic renal failure

BACKGROUND

Parathyroid hormone and vitamin D have been shown to influence cardiac and vascular growth and function experimentally in human subjects with normal renal function. Because of the increased prevalence of hyperparathyroidism and altered vitamin D status in chronic renal failure, these alterations have been considered to contribute to the increased prevalence of cardiovascular disease and hypertension seen in this patient population. Methods and Results. In this article, we review experimental and clinical literature on the cardiovascular effects of parathyroid hormone and vitamin D and relate them to the development of cardiac and vascular dysfunction in uremia, such as: cardiomyopathy, myocardial hypertrophy, and fibrosis, as well as to myocardial ischemia; uremic glucose intolerance, dyslipidemia, and atherosclerosis; hypertension; and vascular and cardiac calcifications.

CONCLUSIONS

The hyperparathyroid state and altered vitamin D status found in uremia contribute to the cardiovascular pathology seen clinically in uremia and also to the excess mortality from cardiovascular causes found in this patient group. The therapeutic implications of these observations are also discussed.

Development of an avian model for restenosis

Recurrence of atherosclerotic plaque growth after interventional therapy, restenosis, is a significant clinical problem occurring in 20%-50% of cases. We have developed a new avian model for the investigation of restenosis after arterial injury in cholesterol fed White Leghorn roosters. Atherosclerotic plaque growth 1-30 weeks after angioplasty balloon mediated endothelial injury in the abdominal aorta was studied in 37 roosters. Roosters were maintained on either normal poultry diet or high cholesterol diet. Twelve cholesterol fed roosters were also fed a hormone supplemented diet in order to modify plaque morphology. The procedural success rate was high. Angiographic stenoses (mean 36% with maximum of 74%) were detectable in cholesterol fed roosters after balloon angioplasty with associated histological evidence of plaque growth (P < 0.017). Cholesterol feeding enhanced fatty plaque growth; hormone manipulation increased calcific and ulcerated plaque but with high associated morbidity. Three interventional devices were subsequently examined in 32 roosters (16 laser angioplasty, 7 atherectomy, and 9 stent implant). Plaque development was again assessed by contrast angiography and histological analysis. We conclude that balloon mediated arterial injury in cholesterol fed roosters produces early proliferative and late, complex atherosclerotic lesions providing an inexpensive model for plaque development after intimal injury.

Comparable beneficial effects of defibrotide and nifedipine in calcium induced atherosclerosis

The present study demonstrates the antiatherosclerotic property of Defibrotide (DFT) in an experimental model in which the pathology is secondary to calcium deposition in the vessel wall and various organs. Rats were treated by gavage for 21 consecutive days with Vitamin D3 and/or, twice a day, with DFT or Nifedipine (N). The calcium contents of aorta, heart and kidney were determined by atomic absorption spectrometry. Specimens of these tissues were examined histologically. DFT or N administered alone did not modify the calcium contents of aorta, heart or kidney. On the contrary, Vitamin D3 caused a huge increase in the calcium concentration in the aorta and in the kidney, whereas the heart content was only double that of control animals. In rats treated with Vitamin D3, contemporaneous administration of DFT or N sharply and highly significantly reduced the aorta calcium concentration and there were less striking, although still significant, reductions in the other two tissues. Histological examination paralleled these data; the effect of DFT or N in reducing the mineralization of aorta and heart was very evident, and more pronounced for DFT. These results confirm that DFT, even though not belonging to the class of the calcium antagonists, has comparable antiatherosclerotic properties, possibly due to its endothelial protective efficacy, as evidenced by the lesser amount of calcium in the aortic tissue.

Enhancement of vasoconstrictor response by a noncalcemic analogue of vitamin D3

To clarify the effects of active vitamin D3 on pressor and vascular responses to vasoconstrictor substances, we studied pressor responses to the intravenous injection of norepinephrine or angiotensin II (Ang II) and vasoconstrictor responses to norepinephrine. Sprague-Dawley rats were given 1,25-dihydroxyvitamin D3 subcutaneously (200 ng/kg per day) for 14 days. The administration of 1,25-dihydroxyvitamin D3 augmented the pressor responses to norepinephrine and Ang II in conscious rats and was associated with a significant increase in serum calcium concentration (11.0 +/- 0.2 mg/dl). To further clarify whether the increased pressor response to vasoconstrictors may be due to the calcemic or direct action of active vitamin D3, we studied the effect of its noncalcemic analogue, 22-oxacalcitriol, and its inactive analogue, 24,25-dihydroxyvitamin D3, on the pressor response to vasoconstrictors in rats. The pressor responses to norepinephrine and Ang II were apparently augmented in 22-oxacalcitriol-treated rats similarly to 1,25-dihydroxyvitamin D3-treated rats. In contrast, the pressor responses were not affected by either 24,25-dihydroxyvitamin D3 or the intravenous infusion of calcium chloride. In an ex vivo experiment using a mesenteric preparation, the vascular sensitivity to norepinephrine was moderately augmented in rats treated with both 22-oxacalcitriol and 1,25-dihydroxyvitamin D3 but was not affected in rats treated with 24,25-dihydroxyvitamin D3. The results suggest that the enhanced pressor responses to norepinephrine and Ang II could be attributed to the direct effect of active vitamin D3 on vasculature rather than to hypercalcemia.

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

We investigated the effect of 22-oxa-1,25-dihydroxyvitamin D3, a synthetic analogue of vitamin D3, on the production of prostacyclin by vascular tissues using rat aortic rings and A7r5 cells derived from fetal rat aortic smooth muscle. Prostacyclin synthesis by aortic rings of rats treated with 22-oxa-1,25-dihydroxyvitamin D3 was much higher than that of non-treated controls, but did not cause any significant hypercalcemia. Treatment with 22-oxa-1,25-dihydroxyvitamin D3 significantly increased the production of prostacyclin by A7r5 cells for 48 hours in a dose-dependent manner. In time-course studies, cells incubated with 22-oxa-1,25-dihydroxyvitamin D3 or 1,25-dihydroxyvitamin D3 produced prostacyclin progressively over a period of 48 hours. The shortest period of incubation that produced a significant amount of prostacyclin compared with control cultures was 24 hours. We observed that treatment with 22-oxa-1,25-dihydroxyvitamin D3 induced cyclooxygenase mRNA in A7r5 cells. Our data suggest that 22-oxa-1,25-dihydroxyvitamin D3 may possibly be a protective substance against the development of atherosclerosis by modulating prostaglandin metabolism.

Vitamin D3 stimulates the production of prostacyclin by vascular smooth muscle cells

The effects of vitamin D3 on the production of prostacyclin (PGI2) by cultured rabbit vascular smooth muscle cells (VSMCs) were investigated. PGI2 synthesis by VSMCs was significantly increased in the presence of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 1 alpha hydroxyvitamin D3 (1 alpha(OH)D3) at 48 hours [1,25(OH)2D3 greater than 1 alpha(OH)D3]. Physiological concentration of 1,25(OH)2D3 (10(-10) M) significantly increased the synthesis of PGI2. Further, we observed that treatment with 1,25(OH)2D3 significantly induced the activity of cyclooxygenase without changing the activity of phospholipase A2. These findings suggest that the mechanism of action of 1,25(OH)2D3 on the synthesis of PGI2 is mediated by the cyclooxygenase pathway. It seems possible that vitamin D3 is a vasoactive agent and may play a protective role in the development of atherosclerosis.

Coronary heart disease: the significance of coronary pathology in infancy and the role of mitogens such as vitamin D

Intimal hyperplasia, damage to the internal elastic lamina, and proliferation of medial smooth muscle cells characterise the early response of an artery to damage. These changes are seen in the coronary arteries of the transplanted human heart, and are commonly seen in "normal" infants. Lipid incursion occurs only later, and the end-result is atheroma. These lesions of infancy are probably pathologic rather than physiologic, and are the precursors of later coronary heart disease. The early intimal and medial changes may be immune-engendered, encouraged by mitogens such as Vitamin D, and evolve in infancy as an aberration of the normal mechanisms controlling cellular proliferation.

Protective action of a calcium antagonist, nilvadipine, against aortic calcium deposition--a pathogenic factor in atherosclerosis

Nilvadipine and other calcium antagonists were studied for their effect on 1-alpha-hydroxyvitamin D3 (1 - alpha (OH)D3)-induced aortic calcium deposition in rats. The animals were treated orally with 1-alpha (OH)D3 (10 micrograms/kg) for 2 weeks. Calcium antagonists were given orally twice a day during the same period. The aortic calcium content in 1-alpha (OH)D3-treated rats increased to about 100 times that in the control. Nilvadipine reduced the aortic calcium deposition dose-dependently, with percent inhibition of 6, 43, 72 and 92%, at doses of 0.1, 1, 10 and 100 mg/kg, respectively. Similar activities were obtained for the other calcium antagonists except diltiazem which had no effect even at the largest dose of 100 mg/kg. According to the ED50 values, nilvadipine (2.2 mg/kg) was more potent than nifedipine (23.2 mg/kg), nicardipine (12.4 mg/kg) and verapamil (32.0 mg/kg). Scanning and transmission electron microscopy showed clear-cut degenerative changes in the endothelial cells after 1-alpha (OH)D3 treatment. Nilvadipine exerted a protective effect against these degenerative changes but not against 1-alpha (OH)D3-induced hypercalcemia. Furthermore, the drug had only minimal effect on in vitro calcification of the aorta. Our findings suggest that nilvadipine inhibits aortic calcification by protecting the aortic wall cells.