1,25-Dihydroxyvitamin D3 binds specifically to rat vascular smooth muscle cells and stimulates their proliferation in vitro

Interplay of Vitamin D and SIRT1 in Tissue-Specific Metabolism-Potential Roles in Prevention and Treatment of Non-Communicable Diseases Including Cancer

The importance of the prevention and control of non-communicable diseases, including obesity, metabolic syndrome, type 2 diabetes, cardiovascular diseases, and cancer, is increasing as a requirement of the aging population in developed countries and the sustainability of healthcare. Similarly, the 2013-2030 action plan of the WHO for the prevention and control of non-communicable diseases seeks these achievements. Adequate lifestyle changes, alone or with the necessary treatments, could reduce the risk of mortality or the deterioration of quality of life. In our recent work, we summarized the role of two central factors, i.e., appropriate levels of vitamin D and SIRT1, which are connected to adequate lifestyles with beneficial effects on the prevention and control of non-communicable diseases. Both of these factors have received increased attention in relation to the COVID-19 pandemic as they both take part in regulation of the main metabolic processes, i.e., lipid/glucose/energy homeostasis, oxidative stress, redox balance, and cell fate, as well as in the healthy regulation of the immune system. Vitamin D and SIRT1 have direct and indirect influence of the regulation of transcription and epigenetic changes and are related to cytoplasmic signaling pathways such as PLC/DAG/IP3/PKC/MAPK, MEK/Erk, insulin/mTOR/cell growth, proliferation; leptin/PI3K-Akt-mTORC1, Akt/NFĸB/COX-2, NFĸB/TNFα, IL-6, IL-8, IL-1β, and AMPK/PGC-1α/GLUT4, among others. Through their proper regulation, they maintain normal body weight, lipid profile, insulin secretion and sensitivity, balance between the pro- and anti-inflammatory processes under normal conditions and infections, maintain endothelial health; balance cell differentiation, proliferation, and fate; and balance the circadian rhythm of the cellular metabolism. The role of these two molecules is interconnected in the molecular network, and they regulate each other in several layers of the homeostasis of energy and the cellular metabolism. Both have a central role in the maintenance of healthy and balanced immune regulation and redox reactions; therefore, they could constitute promising targets either for prevention or as complementary therapies to achieve a better quality of life, at any age, for healthy people and patients under chronic conditions.

Potential impact of the steroid hormone, vitamin D, on the vasculature

The role of vitamin D in the cardiovascular system is complex because it regulates expression of genes involved in diverse metabolic processes. Although referred to as a vitamin, it is more accurately considered a steroid hormone, because it is produced endogenously in the presence of ultraviolet light. It occurs as a series of sequentially activated forms, here referred to as vitamin D-hormones. A little-known phenomenon, based on pre-clinical data, is that its biodistribution and potential effects on vascular disease likely depend on whether it is derived from diet or sunlight. Diet-derived vitamin D-hormones are carried in the blood, at least in part, in chylomicrons and lipoprotein particles, including low-density lipoprotein. Since low-density lipoprotein is known to accumulate in the artery wall and atherosclerotic plaque, diet-derived vitamin D-hormones may also collect there, and possibly promote the osteochondrogenic mineralization associated with plaque. Also, little known is the fact that the body stores vitamin D-hormones in adipose tissue with a half-life on the order of months, raising doubts about whether the use of the term "daily requirement" is appropriate. Cardiovascular effects of vitamin D-hormones are controversial, and risk appears to increase with both low and high blood levels. Since low serum vitamin D-hormone concentration is reportedly associated with increased cardiovascular and orthopedic risk, oral supplementation is widely used, often together with calcium supplements. However, meta-analyses show that oral vitamin D-hormone supplementation does not protect against cardiovascular events, findings that are also supported by a randomized controlled trial. These considerations suggest that prevalent recommendations for vitamin D-hormone supplementation for the purpose of cardiovascular protection should be carefully reconsidered.

Medial artery calcification increases neointimal hyperplasia after balloon injury

Arterial calcification predicts accelerated restenosis after angioplasty and stenting. We studied the effects of calcification on neointimal hyperplasia after balloon injury in the rat carotid. Arterial calcification was induced by subcutaneous injection of vitamin D₃ or by adventitial application of calcium chloride. After balloon catheter injury, neointimal hyperplasia was significantly increased in rats with medial calcification compared with controls. Neointimal cell proliferation in calcified arteries as assessed by proliferating cell nuclear antigen (PCNA) staining was also higher. In calcified arteries, bone morphogenetic protein 2 (BMP-2)levels were increased at the time of injury suggesting a possible explanation for the altered responses. In vascular smooth muscle cells (SMCs) grown under calcifying conditions , stimulation with BMP-2 significantly increased cell proliferation, however, this did not occur in those grown under non-calcifying conditions. These data suggest that neointimal hyperplasia is accelerated in calcified arteries and that this may be due in part to increased BMP-2 expression in medial SMCs. Treatments aimed at inhibiting restenosis in calcified arteries may differ from those that work in uncalcified vessels.

Vitamin D and regulation of vascular cell function

Vitamin D deficiency is linked to pathogenesis of many diseases including cardiovascular, cancer, and various eye diseases. In recent years, important roles for vitamin D in regulation of immune function, inflammation, angiogenesis, and aging have been demonstrated. Thus, vitamin D and its analogs have been evaluated for the treatment of various types of cancer and chronic diseases. We have previously shown that the active form of vitamin D [1,25(OH)₂D₃] is a potent inhibitor of angiogenesis. This activity is consistent with the important role proposed for vitamin D and its analogs in the mitigation of tumor growth through inhibition of angiogenesis. Here, we review the important nutritional value of vitamin D and the abnormalities linked to its deficiency. We will explore its potential role as a regulator of angiogenesis and vascular cell function and the role vitamin D receptor (VDR) expression plays in these activities during vascular development and neovascularization. Our studies have established an important role for 1,25(OH)₂D₃ and VDR in the regulation of perivascular supporting cell function. In addition, the interaction of 1,25(OH)₂D₃ and VDR is essential for these activities and inhibition of neovascularization. Delineating the signaling pathways involved and identification of genes that are the target of 1,25(OH)₂D₃ regulation in vascular cells will allow us to identify novel pathways that are targets for regulation of vascular function and angiogenesis.

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.

TRPV6 determines the effect of vitamin D3 on prostate cancer cell growth

Despite remarkable advances in the therapy and prevention of prostate cancer it is still the second cause of death from cancer in industrialized countries. Many therapies initially shown to be beneficial for the patients were abandoned due to the high drug resistance and the evolution rate of the tumors. One of the prospective therapeutical agents even used in the first stage clinical trials, 1,25-dihydroxyvitamin D3, was shown to be either unpredictable or inefficient in many cases. We have already shown that TRPV6 calcium channel, which is the direct target of 1,25-dihydroxyvitamin D3 receptor, positively controls prostate cancer proliferation and apoptosis resistance (Lehen'kyi et al., Oncogene, 2007). However, how the known 1,25-dihydroxyvitamin D3 antiproliferative effects may be compatible with the upregulation of pro-oncogenic TRPV6 channel remains a mystery. Here we demonstrate that in low steroid conditions 1,25-dihydroxyvitamin D3 upregulates the expression of TRPV6, enchances the proliferation by increasing the number of cells entering into S-phase. We show that these pro-proliferative effects of 1,25-dihydroxyvitamin D3 are directly mediated via the overexpression of TRPV6 channel which increases calcium uptake into LNCaP cells. The apoptosis resistance of androgen-dependent LNCaP cells conferred by TRPV6 channel is drastically inversed when 1,25-dihydroxyvitamin D3 effects were combined with the successful TRPV6 knockdown. In addition, the use of androgen-deficient DU-145 and androgen-insensitive LNCaP C4-2 cell lines allowed to suggest that the ability of 1,25-dihydroxyvitamin D3 to induce the expression of TRPV6 channel is a crucial determinant of the success or failure of 1,25-dihydroxyvitamin D3-based therapies.

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.

Enhanced proliferation of aortal smooth muscle cells treated by 1,25(OH)2D3 in vitro coincides with impaired formation of elastic fibres

Elastin is the major extracellular matrix component synthesized, secreted and deposited by vascular smooth muscle cells (SMCs) in the arterial media and thus plays an important role in vascular homeostasis. Results of our previous studies showed that 1alpha,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)-calcitriol] accelerates proliferation of SMCs and modulates their growth in vitro. The aim of this study was to find ultrastructural support for the idea that 1,25(OH)(2)D(3)-calcitriol affects elastic fibre formation due to accelerated proliferation of aortal SMCs in vitro. SMCs exposed 10 days to supraphysiological concentration (10 nM) of calcitriol in primary culture were examined by fluorescence and transmission electron microscopy. Morphological studies revealed that calcitriol altered elastin maturation by favouring accumulation of immature rather than fully processed elastic fibres. A substantial decrease in the amorphous elastin deposition and abnormal accumulation of microfibrillar component, in thickened multilayer culture, were observed. These studies suggest that 1,25(OH)(2)D(3) affect formation of elastic fibres due to enhanced proliferation of SMCs in culture.

1,25-Dihydroxyvitamin D3 stimulates vascular smooth muscle cell proliferation through a VEGF-mediated pathway

Atherosclerosis is a complex process characterized by an increase in the wall thickness owing to the accumulation of cells and extracellular matrix between the endothelium and the smooth muscle cell wall. This process is associated with different pathologies and it is accelerated in patients with chronic renal failure. In these patients, decreased synthesis of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) leads to secondary complications, like hyperparathyroidism, and treatment with 1,25(OH)(2)D(3) is a common practice. The effect of 1,25(OH)(2)D(3) on vascular smooth muscle cells (VSMCs) calcification has been widely studied, but the role of 1,25(OH)(2)D(3) on VSMC proliferation remains obscure. We have analyzed the effects of 1,25(OH)(2)D(3) in the proliferation of VSMC. We found that 1,25(OH)(2)D(3) (5-100 nM) induces a dose-dependent increase in VSMC proliferation in quiescent cells and in cells stimulated to grow. This increase in proliferation is achieved by shortening the G1 phase. The effect of 1,25(OH)(2)D(3) on VSMC proliferation is mediated by an increase of the expression of vascular endothelial growth factor A (VEGF), as the inhibition of VEGF activity totally blunted the 1,25(OH)(2) D(3)-induced VSMC proliferation. We found this increase in proliferation in vitro, ex vivo in aortic rings incubated with 1,25(OH)(2)D(3), and in vivo in animals with a model of chronic renal failure (5/6 nephrectomy) treated with 1,25(OH)(2)D(3) (1 mug/kg three times a week for 8 weeks). Thus, we conclude that 1,25(OH)(2)D(3) induces increases in VSMC proliferation through an increase on VEGF expression.

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.

High Blood Pressure, Bone-Mineral Loss and Insulin Resistance in Women

Increasing evidence indicates that high blood pressure is associated with abnormalities in calcium metabolism. Sustained calcium loss may lead to increased bone-mineral loss in subjects with elevated blood pressure. Furthermore, recent findings indicate a possible linkage between abnormal calcium metabolism and insulin resistance. In the present study, we investigated the relationship(s) among bone-mineral density (BMD), blood pressure, calcium-related and bone metabolic parameters (plasma intact parathyroid hormone (I-PTH), 1,25-dihydroxyvitamin D [1,25(OH)2D], osteocalcin, and urinary deoxypyridinoline), and insulin resistance, as assessed by a conventional homeostasis model (HOMA-R). We compared non-diabetic women with essential hypertension (WHT, n=34) with age-, body mass index- and menopause (yes or no)-matched normotensive, non-diabetic women (WNT, n=34). The BMD for WHT was significantly lower than that for WNT (0.596+/-0.019 vs. 0.666+/-0.024 g/cm2, p<0.05). The BMD was correlated inversely with systolic blood pressure in all subjects examined (r=-0.385, p<0.05). The 24-h urinary calcium/sodium excretion ratio (Ux-Ca/Na) was significantly greater in WHT compared with WNT (p<0.01). In addition, a negative relationship was apparent between Ux-Ca/Na and BMD (r=-0.58, p<0.05). The plasma levels of PTH and 1,25(OH)2D, and HOMA-R were significantly higher in WHT compared with WNT (p<0.01, p<0.05, and p<0.05, respectively), whereas the serum ionized calcium was lower in WHT compared with WNT (p<0.05). There were no significant differences in serum total calcium, inorganic phosphorus, osteocalcin, or urinary deoxypyridinoline between the two groups. These results indicate that high blood pressure is associated with abnormalities in calcium metabolism and insulin resistance in WHT.

Serum 25-hydroxyvitamin D3 levels are elevated in South Indian patients with ischemic heart disease

Several lines of evidence point to a possible relationship between vitamin D and cardiovascular disease. Animal experiments and observational studies in humans suggest vitamin D to be arteriotoxic and an association of high intake of vitamin D with increased incidence of ischemic heart disease (IHD). The major source of vitamin D in adults is vitamin D synthesized in the skin through exposure to the sun. In tropical environment there is a possibility of high level of solar exposure and enhanced serum levels of vitamin D in the population. We explored the relation between serum level of 25-hydroxyvitamin D3 and IHD in a case-control study involving 143 patients with either angiographic evidence of coronary artery disease or patients with acute myocardial infarction and 70 controls, all men in the age group of 45-65 years. Fasting blood samples were collected, serum separated and serum levels of 25-hydroxyvitamin D3 was measured by protein binding radioligand assay. Serum levels of cholesterol, triglyceride, calcium, magnesium and inorganic phosphate were also determined. Prevalences of diabetes, hypertension and smoking history were noted. Statistical comparisons of variables between cases and controls were done using chi2-tests. Multivariate logistic regression analysis was done to examine the association of IHD with serum levels of 25-hydroxyvitamin D3 controlling for selected variables. Serum levels of 25-hydroxyvitamin D3, calcium, inorganic phosphate, total cholesterol, low density lipoprotein and triglycerides were elevated in a higher proportion of patients, compared to controls. Serum levels of 25-OH-D3 above 222.5 nmol/l (89 ng/ml) was observed in 59.4% of cases compared to 22.1% in controls (p < 0.001; unadjusted odds ratio (OR): 5.17; 95% confidence interval (CI): 2.62-10.21). When controlled for age and selected variables using the multivariate logistic regression, the adjusted OR relating elevated serum 25-hydroxyvitamin D3 levels (> or = 222.5 nmol/l, > or = 89 ng/ml) and IHD is 3.18 (95% CI: 1.31-7.73). Given the evidences for the arteriotoxicity of vitamin D, further investigations are warranted to probe whether the elevated serum levels of 25-hydroxyvitamin D3 observed in patients with IHD in a tropical environment has any pathogenic significance.

1,25-dihydroxyvitamin D3 receptor is upregulated in aortic smooth muscle cells during hypervitaminosis D

Several studies have demonstrated that excess of vitamin D3 is toxic particularly to vascular tissues. A notable pathological feature is arterial calcification. The nature of the toxic metabolite in hypervitaminosis D and the pathogenesis of arterial calcification are not clearly understood. The present study was undertaken to explore whether arterial calcification is a sequel of increased calcium uptake by arterial smooth muscle mediated by up regulation of vitamin D receptor in the cells in response to elevated circulating levels of vitamin D3 in serum. The experimental study was performed in 20 New Zealand white female rabbits aged 6 months. Animals in the test group were injected 10,000 IU of cholecalciferol intramuscularly twice a week for one month. Six control animals were given intra-muscular injections of plain cottonseed oil. Animals were sacrificed and aortas were examined for pathological lesions, 1,25-dihyroxyvitamin D3 (1,25(OH)2 D3) receptor levels and 45Ca uptake in smooth muscle cells. Serum samples collected at intervals were assayed for levels of 25-OH-D3 and calcium. The results showed that in animals given injections of cholecalciferol, serum levels of 25-OH-D3 were elevated. In four of these animals calcification and aneurysmal changes were seen in the aorta. Histological lesions comprised of fragmentation of elastic fibers as well as extensive loss of elastic layers. 1,25(OH)2 D3 receptor levels were up regulated and 45Ca uptake enhanced in aortas of animals which were given excessive vitamin D3. The evidences gathered suggest that excess vitamin D is arteriotoxic and that the vitamin induces arterial calcification through up regulation of 1,25(OH)2D3 receptor and increased calcium uptake in smooth muscle cells of the arteries.

Regulation of sodium, calcium and vitamin D metabolism in Dahl rats on a high-salt/low-potassium diet: genetic and neural influences

1. A dietary combination of high salt and low potassium (HSLK) exacerbates hypertension in Dahl salt-sensitive (DS) rats and renders previously normotensive Dahl salt-resistant (DR) rats hypertensive. In both strains, the severity of hypertension correlates with urinary calcium loss. However, the magnitude of excretory calcium losses is significantly greater in DS rats and is potentiated by chemical sympathectomy in both strains. 2. We hypothesized that a defect in vitamin D metabolism may underlie the observed strain-dependent differences in calcium balance. 3. Arterial blood pressure (ABP), water and mineral balance and serum concentrations of 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3) and 25-hydroxyvitamin D3 (25(OH)D3) were measured in intact and chemically sympathectomized (6-hydroxydopamine; 6-OHDA) DS and DR rats after 8 weeks on a HSLK diet. 4. Chronic ingestion of this diet resulted in marked and moderate levels of hypertension in DS and DR rats, respectively. The hypertension was abated and eliminated by 6-OHDA in the DS and DR strains, respectively. Independent of treatment, DS rats had significantly higher urinary excretion of calcium and reduced intestinal absorption of the ion compared with DR rats. The DS rats had significantly higher serum levels of 1,25(OH)2 D3 and markedly lower serum levels of 25(OH)D3 than DR rats. Chemical sympathectomy tended to increase 1,25(OH)2 D3 and to decrease 25(OH)D3 levels in both strains. 5. These data indicate a genetic difference in vitamin D metabolism between DS and DR rats. The abnormally elevated levels of 1,25(OH)2 D3 in DS rats may be an appropriate compensatory response to excessive excretory calcium loss and reduced target organ sensitivity to the hormone and may, maladaptively, directly contribute to hypertension, by stimulating vascular smooth muscle contractility.

Parathyroid hormone and calcitriol in hypertension caused by dietary calcium deficiency in rats

Hypertension caused by calcium deficiency in the diet has been linked with an increase in parathyroid hormone (PTH) and calcitriol levels. We evaluated arterial blood pressure (ABP), PTH, and calcitriol in normotensive Sprague-Dawley rats (SDR) and in spontaneously hypertensive rats (SHR) fed from weaning on a control diet with a normal calcium content (1%) or a low-calcium diet (0.1%). The calcemia was also measured in the rats by colorimetric methods. The low-calcium diet decreased the calcemia in both strains and brought about an increase in the ABP which was significant in adult SDR and particularly noticeable during the early hypertensive phase in SHR. The rats fed on this diet had higher hormonal plasma levels when compared with the corresponding values in rats fed on the control diet. In particular, the SDR fed on the low-calcium diet showed much higher PTH (122.6 +/- 31.0 pg/ml, p </= 0.05) and calcitriol (458.0 +/- 13.1 pg/ml, p </= 0.01) values than the SDR fed on the control diet (PTH 31.7 +/- 2.80 pg/ml; calcitriol 292.1 +/- 17.5 pg/ml). These endocrine alterations could justify the increase in ABP caused by dietary calcium deficiency in normotensive rats. Nevertheless, the results of this study indicate that the modifications of the ABP caused by the low-calcium diet in SHR could not be correlated with significant increases in these hormones.

1,25(OH)2-vitamin D3 affects the subcellular distribution of protein kinase C isoenzymes in muscle cells

Previous studies have shown the involvement of protein kinase C (PKC) in 1,25-dihydroxy-vitamin D3 [1,25(OH)2D3] regulation of DNA synthesis (long-term effect) and Ca2+ channel activity (short-term effect) in cultured myoblasts. Both events mediate stimulation of myoblast cell proliferation and growth by 1,25(OH)2D3. To characterise further the role of PKC in the hormone mode of action in muscle cells, the presence of PKC isoenzymes in chicken embryo myoblasts and changes in their total cell and subcellular levels after treatment (72 h and 5 min) with 1,25(OH)2D3 (1 nM), 12-O-tetradecanoyl phorbol 13-acetate (TPA; 100 nM) and 1,2-dioctanoyl-rac-glycerol (DOG; 50 microM) were investigated. Western blot analysis provided evidence on the expression of PKC alpha, beta and delta isoforms in avian myoblasts. Two immunoreactive bands of 80 kDa (intact molecule) and 50 kDa (catalytic fragment) were detected for each isoenzyme. 1,25(OH)2D3 and DOG, which increased myoblast PKC activity parallel with the stimulation of DNA synthesis and culture growth and the phorbol ester TPA which induced the opposite changes, exerted differential effects on PKC isoenzymes. Long-term (72 h) treatment with 1,25(OH)2D3 and DOG did not change total PKC isoform levels but decreased the 80 kDa species and increased the release of the catalytic fragment of PKC delta and beta, whereas TPA augmented the total amounts of the three PKC isoforms, increasing the band of 80 kDa of PKC beta and delta and the 50 kDa species for PKC alpha. Subcellular distribution studies showed that the 80 kDa molecule is only present in the cytosolic fraction whereas in the particulate fractions the 50 kDa fragments are detected. Increased amounts of the catalytic fragments of PKC beta and delta both in the nucleus and membranes were observed after 72 h treatment with DOG while 1,25(OH)2D3 increases PKC beta in the nucleus and PKC delta in membranes. TPA induced the appearance of the 50 kDa species of PKC alpha in the nuclear and membrane fractions. The phorbol ester also decreased the catalytic fragments of PKC beta and delta in membranes. Increased levels of PKC beta, and to a lesser extent of PKC delta, in membranes and cytosol could be detected after short exposure (5 min) of myoblasts to 1,25(OH)2D3, DOG and TPA. In conclusion, the data indicate the operation in myoblasts of PKC signal transduction pathways mediated by the Ca(2+)-dependent PKCs alpha and beta and the Ca(2+)-independent PKC delta. Moreover, the results suggest that the beta and delta isoforms of PKC could play a role in the regulation of muscle cell metabolism by 1,25(OH)2D3.

Vitamin D3 exacerbates intimal hyperplasia in balloon-injured arteries

Although a high dose of vitamin D3 is known to cause arterial calcification and degeneration, its effect on intimal hyperplasia has never been studied. The aim of this study was to examine the influence of a moderate supplement of vitamin D3 on intimal hyperplasia in the balloon-injured rat carotid artery. Forty-four rats had balloon injury to the carotid artery; 22 were given oral vitamin D3 supplementation (0.25 microgram kg-1 day-1). Animals were killed at 4 weeks and the carotid arteries were perfusion fixed and assessed morphometrically by means of computerized image analysis of transverse sections. Mean (s.e.m.) intimal area was significantly greater in the vitamin D3-treated animals than in controls: 0.92(0.05) versus 0.71(0.07) mm2 (P = 0.02). The area of the media of both injured and uninjured arteries was not influenced by vitamin D3 administration. A small dose of vitamin D3 resulted in significant exacerbation of intimal hyperplasia in this rat carotid artery model and raises the question of the role of dietary vitamin D3 in restenosis following vascular intervention.

1,25-Dihydroxyvitamin D(3) receptors in developing dorsal root ganglia of fetal rats

We observed immunostaining for the 1,25-dihydroxyvitamin D(3) receptor (VDR) and calbindin-D(28k) in neurons, but not glial cells, of fetal rat dorsal root ganglia (DRG) from days 13 through 21 of gestation. Dispersed cultures of DRG collected from rat fetuses at gestational day 15 also contained epitopes for VDR and calbindin-D(28k) in neurons, but not in glial cells. 1,25-Dihydroxyvitamin D(3), through VDR, may perform significant functions in the development of neuronal cells.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

The role of vitamin D3 in the aetiology of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) have traditionally been attributed to atherosclerosis, although there is increasing epidemiological, biochemical and genetic evidence that aneurysmal arterial disease is different from occlusive atherosclerosis. One of the most consistent biochemical findings in the aneurysmal aorta is a significant reduction in elastin protein; the cause, for this remains unclear. There is in vitro evidence that vitamin D3 (1,25 dihydrocholecalciferol) inhibits the production of elastin by smooth muscle cells. On the basis of this observation and the possibility that some subjects may be exposed to excess vitamin D3, the hypothesis that vitamin D3 may be a previously unrecognized aetiological factor in the pathogenesis of AAA is developed.

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.

Evidence for the participation of protein kinase C and 3',5'-cyclic AMP-dependent protein kinase in the stimulation of muscle cell proliferation by 1,25-dihydroxy-vitamin D3

Treatment with 1,25-dihydroxy-vitamin D3 (1,25(OH)2D3) (1-12 h, 10(-10) M) stimulates DNA synthesis in proliferating myoblasts, with an early response at 2-4 h of treatment followed by a maximal effect at 10 h. To investigate the mechanism involved in the mitogenic action of the hormone we studied the possible activation of intracellular messengers by 1,25(OH)2D3. The initial phase of stimulation of [3H]thymidine incorporation into DNA by the sterol was mimicked by the protein kinase C activator tetradecanoylphorbol acetate (TPA) in a manner which was dose dependent and specific as the inactive analog 4 alpha-phorbol was without effect. Maximal responses to TPA (100 nM) were obtained at 4 h. Staurosporine, a protein kinase C inhibitor, blocked the effect of 1,25(OH)2D3 on myoblast proliferation at 4 h. In addition, a fast (1-5 min) elevation of diacylglycerol levels and membrane-associated protein kinase C activity was observed in response to 1,25(OH)2D3. The adenylate cyclase activator forskolin (20 microM) and dibutyryl-cAMP (50 microM) increased DNA synthesis reproducing the second 1,25(OH)2D3-dependent stimulatory phase at 10 h. Inhibitors of protein kinase A blocked the increase in muscle cell DNA synthesis induced by 1,25(OH)2D3 at 10 h. Significant increases in cyclic AMP levels were detected in myoblasts treated with the sterol for 1-10 h. The calcium channel antagonist nifedipine (5-10 microM) abolished both the effects of 4-h treatment with 1,25(OH)2D3 or TPA and 10-h treatment with 1,25(OH)2D3 or dibutyryl-cAMP. Similar to the calcium channel agonist Bay K8644, 1,25(OH)2D3 stimulated myoblast 45Ca uptake and its effects were blocked by nifedipine.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial protection from salt-induced stroke and mortality by high oral calcium in hypertensive rats

BACKGROUND AND PURPOSE

Repeated demonstration of an antihypertensive effect of high oral calcium in stroke-prone spontaneously hypertensive rats led us to determine whether it also protects such rats from premature mortality and stroke-related lesions.

METHODS

Female stroke-prone rats (11-13 per diet) were fed high- and low-calcium (2.0% and 0.4%, respectively) diets with both high and low salt (7.0% and 0.3%, respectively) content from age 4 weeks until spontaneous death. In addition to life span, other variables measured included blood pressures, plasma chemistries, and histological characterization of stroke-related lesions.

RESULTS

Life span was increased from 51 +/- 4 to 68 +/- 1 weeks (p less than 0.05) by high versus low oral calcium in rats fed high-salt diets; it was further increased to greater than or equal to 82 weeks (p less than 0.05) in rats fed low-salt (+/- added calcium) diets. As seen previously, high oral calcium attenuated salt-induced hypertension but did not affect blood pressure in rats fed low-salt diets. High versus low oral calcium exerted contrasting effects (p less than 0.05) on brain lesions (hemorrhages and infarctions) in rats fed high-salt diets, decreasing lesion size (242 +/- 21 versus 712 +/- 276 microns per rat [diameters seen in histological sections]) but increasing lesion number (8.9 +/- 2.4 versus 3.4 +/- 2.2 per rat); it exerted little influence on the few brain lesions that appeared in rats fed low-salt diets.

CONCLUSIONS

High oral calcium may protect stroke-prone hypertensive rats from early salt-induced mortality at least partially by decreasing severity (size) of stroke-related lesions, an effect which may relate to decreased blood pressure. However, this protection may be limited by increased number (incidence) of such lesions, an effect which suggests that high oral calcium may increase the number of brain vessels susceptible to stroke-related injury independent of change in blood pressure.

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.

Calcium metabolism in elderly hypertensive patients: possible participation of exaggerated sodium, calcium and phosphate excretion

1. Renal handling of electrolytes, including calcium (Ca), in response to physiological saline infusion (20 mL/kg, i.v., for 2 h) as well as basal circulating levels of Ca-regulating hormones were compared in 27 hypertensive elderly females (mean age 80 +/- 9 years), in 44 normotensive elderly females (79 +/- 9 years) and in 19 young normotensive females (23 +/- 4 years). 2. The hypertensive elderly females showed excessive increase in urine volume and urinary excretions of sodium (Na), Ca and inorganic phosphate (P) in response to saline infusion, associated with slight but significant decrease in circulating levels of Na and ionized Ca compared with those in the other groups. These hypertensive elderly patients also showed characteristic features both in circulating blood pressure and Ca regulating factors; they showed significantly low levels of plasma renin activity and aldosterone concentration, significantly high plasma levels of atrial natriuretic peptide and noradrenalin, compared with those in young controls and normotensive elderly females. 3. Moreover they showed significant increase in basal serum levels of parathyroid hormone and 1,25-dihydroxyvitamin D, and significant decrease in basal serum levels of calcitonin, 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D, compared with those in the other groups. 4. These results suggest that the exaggerated natriuresis associated with excessive loss of Ca and P in urine may participate in the abnormality of Ca metabolism in low-renin hypertensive elderly patients.

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.

1,25-dihydroxyvitamin D3 modulates growth of vascular smooth muscle cells

We examined the effects of 1,25-dihydroxyvitamin D3(1,25-(OH)2D3) on the proliferation of vascular smooth muscle (VSM) cells. Receptors for 1,25-(OH)2D3 were demonstrated in fresh rabbit aortic tissue and in cultured rat VSM using binding of [3H]-1,25-(OH)2D3 in sucrose density gradients of the tissue or cell homogenates. The receptor sedimented at 3.6 S, the sedimentation velocity of 1,25-(OH)2D3 receptors from other sources. 1,25-(OH)2D3 dramatically altered the growth of VSM, but this effect depended importantly on the basal conditions in which the cells were grown. In quiescent VSM deprived of serum for 72 h, 1,25-(OH)2D3 (0.1-10 nM), but not 25-(OH)D3 (up to 100 nM) increased thymidine incorporation up to 12-fold and cell number up to 2.6-fold compared with controls. The maximal effect of 1,25-(OH)2D3 on thymidine incorporation was similar to the maximal effect of the growth factors alpha-thrombin or PDGF. Furthermore, the effects of 1,25-(OH)2D3 and thrombin on thymidine incorporation in quiescent cells were markedly synergistic, yielding a 78-fold increase in thymidine incorporation when both agents were added simultaneously. In "nonquiescent cells" which were exposed to serum-free medium for only 24 h, 1,25-(OH)2D3 (10 nM) also increased DNA synthesis 10-fold compared with controls. However, in striking contrast to what was observed in quiescent cells, 1,25-(OH)2D3 diminished the mitogenic response to thrombin by as much as 50% in nonquiescent cells. 1,25-(OH)2D3 also modulated the transcription of c-myc in response to thrombin. In quiescent cells, transcription was enhanced by 1,25-(OH)2D3, whereas in nonquiescent cells, thrombin-induced c-myc transcription was blunted. Thus, 1,25-(OH)2D3 is a potent modulator of the growth of cultured VSM. The direction of this modulation depends strongly on the conditions under which the cells are cultured.

1,25 (OH)2 vitamin D3 attenuates the loss of resistance artery contractile function associated with incubation in culture media

Contractile properties of rat mesenteric resistance arteries were studied immediately after isolation or after 48-hr incubation in culture medium [Dulbecco's modified Eagle's/Ham's F-12 (1:1) with insulin, transferrin and antibiotics]. Incubation in culture medium depressed active stress generating capacity, increased sensitivity to norepinephrine and ablated endothelium-dependent relaxation. The decrease in stress generation results from the loss of a releasable pool of intracellular Ca2+; the enhanced sensitivity is associated with decreased neuronal amine pump function. Addition of 300 pg/ml 1,25 (OH)2 vitamin D3 to the culture medium afforded nearly complete protection against the loss of stress generating capacity and partially preserved endothelial function. It is concluded that 1,25 (OH)2 vitamin D3 partially prevents phenotypic modulation of the vascular myocyte induced by culture conditions.

Contrasting hemodynamic effects of high oral calcium in genetic models of salt-sensitive hypertension

Interest in effects of oral calcium (Ca) on blood pressure is now generally focused on salt-induced hypertension. In this study hemodynamic effects of long-term high oral Ca were examined in two different genetic models of salt-sensitive hypertension, stroke-prone spontaneously hypertensive rats (spSHR) and Dahl salt-sensitive (DS) hypertensive rats. High vs low oral Ca (2.0 vs 0.4% Ca, 8-13 rats/diet) significantly (p less than 0.05) attenuated salt-induced hypertension (7% NaCl intake) in female spSHR (mean arterial pressure = 137 vs 175 mmHg) but aggravated such hypertension in female DS rats (141 vs 124 mmHg). Pressor responsiveness to norepinephrine (NE) and angiotensin (A) II were examined in the same rats. High oral Ca decreased pressor responses to graded intravenous injections of NE and AII in spSHR and increased such responses in DS rats. In spSHR, the decreased pressor responsiveness preceded the antihypertensive effect of high oral Ca. In summary, 2.0 vs 0.4% oral Ca produces contrasting effects on blood pressure in two genetic models of salt-sensitive hypertension (stroke-prone SHR and Dahl salt-sensitive rats). These contrasting effects on blood pressure may be related to differential effects of oral Ca on vascular responsiveness to endogenous vasoconstrictors in these two genetic models of salt-sensitive hypertension.

Injection of 1,25-(OH)2 vitamin D3 enhances resistance artery contractile properties

The hypothesis that 1,25-dihydroxyvitamin D3 [1,25-(OH)2 vitamin D3] modulates vascular smooth muscle contractile function was tested. 1,25-(OH)2 vitamin D3 (50 ng/day) was administered by intraperitoneal injection over a 3-day period to 13-15-week-old male spontaneously hypertensive and Wistar-Kyoto normotensive rats. On the fourth day, serum was prepared and contractile force generation of isolated mesenteric resistance arteries was examined. Treatment with 1,25-(OH)2 vitamin D3 approximately doubled serum levels of the hormone and increased ionized and total serum Ca2+ and phosphate by 5-10%. No effect on blood pressure was detected. 1,25-(OH)2 vitamin D3 injection in both strains enhanced maximal stress generation to norepinephrine and serotonin by 30-40%, with no effect on apparent sensitivity of the vessels to the agonists. To assess the effect of a maneuver that elevates serum ionized Ca2+ without the addition of exogenous hormone, maximal stress generation was examined in resistance arteries isolated from rats fed diets containing 0.5% or 2% calcium over a 6-7-week period. Maximal stress generation in response to norepinephrine was greater in vessels from rats of both strains maintained on 0.5% calcium. It is concluded that 72-hour in vivo treatment with 1,25-(OH)2 vitamin D3 increases contractile force-generating capacity of resistance arteries without affecting blood pressure. It is proposed that this action of 1,25-(OH)2 vitamin D3 is the result of a direct action of the hormone on the vascular wall.

Effects of 1,25-dihydroxyvitamin D3 on the syntheses of DNA and glycosaminoglycans by rat aortic smooth muscle cells in vitro

Studies were made on the effects of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] on the syntheses of DNA and glycosaminoglycans (GAG) by rat aortic smooth muscle cells (SMC) in vitro. DNA synthesis in cell cultures without fetal calf serum (FCS) was stimulated by incubation for 24 hr with 1,25-(OH)2D3 at concentrations of more than 10(-12) M, stimulation being maximal at a concentration of 10(-8) M. On the other hand, GAG synthesis was inhibited dose-dependently by 1,25-(OH)2D3 at concentrations of more than 10(-11) M. Other vitamin D3 metabolites had similar, but weaker effects on the syntheses of DNA and GAG by SMC, which were proportional to their affinities for the 1,25-(OH)2D3 receptor. These effects of 1,25-(OH)2D3 were not seen after short-term incubation (1 hr). These findings suggested that 1,25-(OH)2D3 stimulated the proliferation of SMC independent of growth factors in FCS, and that its effects were dependent on its specific receptor. Excess 1,25-(OH)2D3 might cause arteriosclerosis not only by stimulating proliferation but also by suppressing GAG synthesis.

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.