Inhibition of tropoelastin expression by 1,25-dihydroxyvitamin D3

Effectiveness of 1α-25-dihydroxyvitamin D3 active substance on anastomosis safety in the rat femoral artery end-to-end anastomosis experimental model: Macroscopic and histological analyses

Under inflammatory conditions, macrophage dominance affects the degree of inflammation. We assessed the effects of the active vitamin D (calcitriol) administration on inflammatory processes and macrophage dominance and aimed to determine the potential positive macroscopic and histological effects in supermicrosurgical arterial anastomosis model of rats. Forty rats were divided into five groups: control surgery (Group 1), surgery with preoperative (Group 2), post-operative (Group 3), perioperative (Group 4) systemic calcitriol and surgery with local calcitriol (Group 5). Eighty femoral artery anastomoses were planned in both legs of rats. Systemic calcitriol was administered intraperitoneally daily to the animals in the relevant groups. Preoperative vessel diameter measurements were taken before anastomosis. Three weeks post-surgery, post-operative vessel diameter measurements were taken, anastomosis patency was assessed and vascular segments were collected for histological examination, which included assessment of M1 and M2 macrophage depolarisation, leucocyte infiltration, intima-media ratio and luminal gap scoring. Systemic calcitriol administration (pre-, post- or perioperative) significantly improved the vessel diameter (p < 0.001); there was no significant difference among Groups 2-4. Histological findings revealed that Groups 3 and 4 had lower intima-media ratios (p < 0.05 and p < 0.01), higher M2-M1 macrophage ratios (p < 0.01 and p < 0.001) and lower leucocyte infiltration (p < 0.05, p < 0.01 and p < 0.001). Local calcitriol administration had no vasodilatory effects or resulted in positive histological outcomes. Although the administration of calcitriol pre- and post-operatively increased the vessel diameter, the latter appeared to have a more favourable impact on the histological analyses.

Paricalcitol Has a Potent Anti-Inflammatory Effect in Rat Endothelial Denudation-Induced Intimal Hyperplasia

Neointimal hyperplasia is the main cause of vascular graft failure in the medium term. Vitamin D receptor activation modulates the biology of vascular smooth muscle cells and has been reported to protect from neointimal hyperplasia following endothelial injury. However, the molecular mechanisms are poorly understood. We have now explored the impact of the selective vitamin D receptor activator, paricalcitol, on neointimal hyperplasia, following guidewire-induced endothelial cell injury in rats, and we have assessed the impact of paricalcitol or vehicle on the expression of key cell stress factors. Guidewire-induced endothelial cell injury caused neointimal hyperplasia and luminal stenosis and upregulated the expression of the growth factor growth/differentiation factor-15 (GDF-15), the cytokine receptor CD74, NFκB-inducing kinase (NIK, an upstream regulator of the proinflammatory transcription factor NFκB) and the chemokine monocyte chemoattractant protein-1 (MCP-1/CCL2). Immunohistochemistry confirmed the increased expression of the cellular proteins CD74 and NIK. Paricalcitol (administered in doses of 750 ng/kg of body weight, every other day) had a non-significant impact on neointimal hyperplasia and luminal stenosis. However, it significantly decreased GDF-15, CD74, NIK and MCP-1/CCL2 mRNA expression, which in paricalcitol-injured arteries remained within the levels found in control vehicle sham arteries. In conclusion, paricalcitol had a dramatic effect, suppressing the stress response to guidewire-induced endothelial cell injury, despite a limited impact on neointimal hyperplasia and luminal stenosis. This observation identifies novel molecular targets of paricalcitol in the vascular system, whose differential expression cannot be justified as a consequence of improved tissue injury.

The Beneficial Regulation of Extracellular Matrix and Heat Shock Proteins, and the Inhibition of Cellular Oxidative Stress Effects and Inflammatory Cytokines by 1α, 25 dihydroxyvitaminD3 in Non-Irradiated and Ultraviolet Radiated Dermal Fibroblasts

Intrinsic skin aging and photoaging, from exposure to ultraviolet (UV) radiation, are associated with altered regulation of genes associated with the extracellular matrix (ECM) and inflammation, as well as cellular damage from oxidative stress. The regulatory properties of 1α, 25dihydroxyvitamin D3 (vitamin D) include endocrine, ECM regulation, cell differentiation, photoprotection, and anti-inflammation. The goal of this research was to identify the beneficial effects of vitamin D in preventing intrinsic skin aging and photoaging, through its direct effects as well as its effects on the ECM, associated heat shock proteins (HSP-47, and -70), cellular oxidative stress effects, and inflammatory cytokines [interleukin (IL)-1 and IL-8] in non-irradiated, UVA-radiated, UVB-radiated dermal fibroblasts. With regard to the ECM, vitamin D stimulated type I collagen and inhibited cellular elastase activity in non-irradiated fibroblasts; and stimulated type I collagen and HSP-47, and inhibited elastin expression and elastase activity in UVA-radiated dermal fibroblasts. With regard to cellular protection, vitamin D inhibited oxidative damage to DNA, RNA, and lipids in non-irradiated, UVA-radiated and UVB-radiated fibroblasts, and, in addition, increased cell viability of UVB-radiated cells. With regard to anti-inflammation, vitamin D inhibited expression of Il-1 and IL-8 in UVA-radiated fibroblasts, and stimulated HSP-70 in UVA-radiated and UVB-radiated fibroblasts. Overall, vitamin D is predominantly beneficial in preventing UVA-radiation induced photoaging through the differential regulation of the ECM, HSPs, and inflammatory cytokines, and protective effects on the cellular biomolecules. It is also beneficial in preventing UVB-radiation associated photoaging through the stimulation of cell viability and HSP-70, and the inhibition of cellular oxidative damage, and in preventing intrinsic aging through the stimulation of type I collagen and inhibition of cellular oxidative damage.

Lower-limb veins are thicker and vascular reactivity is decreased in a rat PCOS model: concomitant vitamin D3 treatment partially prevents these changes

Polycystic ovary syndrome (PCOS) causes vascular damage to arteries; however, there are no data for its effect on veins. Our aim was to clarify the effects of dihydrotestosterone (DHT)-induced PCOS both on venous biomechanics and on pharmacological reactivity in a rat model and to test the possible modulatory role of vitamin D3 (vitD). PCOS was induced in female Wistar rats by DHT treatment (83 μg/day, subcutaneous pellet). After 10 wk, the venous biomechanics, norepinephrine (NE)-induced contractility, and acetylcholine-induced relaxation were tested in saphenous veins from control animals and from animals treated with DHT or DHT with vitD using pressure angiography. Additionally, the expression levels of endothelial nitric oxide synthase (eNOS) and cyclooxygenase (COX-2) were measured using immunohistochemistry. Increased diameter, wall thickness, and distensibility as well as decreased vasoconstriction were detected after the DHT treatment. Concomitant vitD treatment lowered the mechanical load on the veins, reduced distensibility, and resulted in vessels that were more relaxed. Although there was no difference in the endothelial dilation tested using acetylcholine (ACh), the blocking effect of N(G)-nitro-l-arginine methyl ester (l-NAME) was lower and was accompanied by lower COX-2 expression in the endothelium after the DHT treatment. Supplementation with vitD prevented these alterations. eNOS expression did not differ among the three groups. We conclude that the hyperandrogenic state resulted in thicker vein walls. These veins showed early remodeling and altered vasorelaxant mechanisms similar to those of varicose veins. Alterations caused by the chronic DHT treatment were prevented partially by concomitant vitD administration.

Vitamin D induces increased systolic arterial pressure via vascular reactivity and mechanical properties

Background/Aims

The aim of this study was to evaluate whether supplementation of high doses of cholecalciferol for two months in normotensive rats results in increased systolic arterial pressure and which are the mechanisms involved. Specifically, this study assesses the potential effect on cardiac output as well as the changes in aortic structure and functional properties.

Methods

Male Wistar rats were divided into three groups: 1) Control group (C, n = 20), with no supplementation of vitamin D, 2) VD3 (n = 19), supplemented with 3,000 IU vitamin D/kg of chow; 3) VD10 (n = 21), supplemented with 10,000 IU vitamin D/kg of chow. After two months, echocardiographic analyses, measurements of systolic arterial pressure (SAP), vascular reactivity, reactive oxygen species (ROS) generation, mechanical properties, histological analysis and metalloproteinase-2 and -9 activity were performed.

Results

SAP was higher in VD3 and VD10 than in C rats (p = 0.001). Echocardiographic variables were not different among groups. Responses to phenylephrine in endothelium-denuded aortas was higher in VD3 compared to the C group (p = 0.041). Vascular relaxation induced by acetylcholine (p = 0.023) and sodium nitroprusside (p = 0.005) was impaired in both supplemented groups compared to the C group and apocynin treatment reversed impaired vasodilation. Collagen volume fraction (<0.001) and MMP-2 activity (p = 0.025) was higher in VD10 group compared to the VD3 group. Elastin volume fraction was lower in VD10 than in C and yield point was lower in VD3 than in C.

Conclusion

Our findings support the view that vitamin D supplementation increases arterial pressure in normotensive rats and this is associated with structural and functional vascular changes, modulated by NADPH oxidase, nitric oxide, and extracellular matrix components.

Sodium L-ascorbate enhances elastic fibers deposition by fibroblasts from normal and pathologic human skin

BACKGROUND

Vitamin C (L-ascorbic acid), a known enhancer of collagen deposition, has also been identified as an inhibitor of elastogenesis.

OBJECTIVE

Present studies explored whether and how the L-ascorbic acid derivative (+) sodium L-ascorbate (SA) would affect production of collagen and elastic fibers in cultures of fibroblasts derived from normal human skin and dermal fat, as well as in explants of normal human skin, stretch-marked skin and keloids.

METHODS

Effects of SA on the extracellular matrix production were assessed quantitatively by PCR analyses, western blots, biochemical assay of insoluble elastin and by immuno-histochemistry. We also evaluated effects of SA on production of the reactive oxygen species (ROS) and phosphorylation of IGF-I and insulin receptors.

RESULTS

SA, applied in 50-200 μM concentrations, stimulates production of both collagen and elastic fibers in all tested cultures. Moreover, combination of SA with a proline hydroxylase inhibitor induces a beneficial remodelling in explants of dermal scars, resulting in the inhibition of collagen deposition and induction of new elastogenesis. Importantly, we revealed that SA stimulates elastogenesis only after intracellular influx of non-oxidized ascorbate anions (facilitated by the sodium-dependent ascorbate transporter), that causes reduction of intracellular ROS, activation of c-Src tyrosine kinase and the enhancement of IGF-1-induced phosphorylation of the IGF-1 receptor that ultimately triggers elastogenic signalling pathway.

CONCLUSION

Our results endorse the use of this potent stimulator of collagen and elastin production in the treatment of wrinkled and stretch-marked skin. They also encourage inclusion of SA into therapeutic combinations with collagenogenesis inhibitors to prevent formation of dermal scars and keloids.

Vitamin D and cardiovascular disease

Vitamin D plays a classical hormonal role in skeletal health by regulating calcium and phosphorus metabolism. Vitamin D metabolites also have physiological functions in nonskeletal tissues, where local synthesis influences regulatory pathways via paracrine and autocrine mechanisms. The active metabolite of vitamin D, 1α,25-dihydroxyvitamin D, binds to the vitamin D receptor that regulates numerous genes involved in fundamental processes of potential relevance to cardiovascular disease, including cell proliferation and differentiation, apoptosis, oxidative stress, membrane transport, matrix homeostasis, and cell adhesion. Vitamin D receptors have been found in all the major cardiovascular cell types including cardiomyocytes, arterial wall cells, and immune cells. Experimental studies have established a role for vitamin D metabolites in pathways that are integral to cardiovascular function and disease, including inflammation, thrombosis, and the renin-angiotensin system. Clinical studies have generally demonstrated an independent association between vitamin D deficiency and various manifestations of degenerative cardiovascular disease including vascular calcification. However, the role of vitamin D supplementation in the management of cardiovascular disease remains to be established. This review summarizes the clinical studies showing associations between vitamin D status and cardiovascular disease and the experimental studies that explore the mechanistic basis for these associations.

Effect of 1α-25-dihydroxyvitamin D3 on intimal hyperplasia developing in vascular anastomoses: a rabbit model

INTRODUCTION

A common problem encountered in routine daily practice of cardiovascular surgery is migration of smooth muscle cells leading to intimal hyperplasia developing at vascular anastomosis sites which then causes luminal narrowing. The aim of this study was to investigate the antiproliferative effect of 1,25 (OH)2D3 on intimal hyperplasia.

MATERIAL AND METHODS

Twenty-one male white New Zealand rabbits weighing 2-3 kg were selected. There were 3 groups of animals each consisting of 7 rabbits. Group 1 was the control group. Group 2 was the sham group and group 3 consisted of rabbits receiving 1,25 (OH)2D3. The right carotid arteries of the subjects in groups 2 and 3 were transected and re-anastomosed. A daily dose of 25 ng 1,25 (OH)2D3 per 100 g body weight was administered for 14 days to rabbits in group 3. Rabbits in group 2 were not subject to any pharmaceutical agent. All the subjects were sacrificed at the end of the 28(th) postoperative day. Their right carotid arteries were resected and then investigated histopathologically.

RESULTS

Intimal thickness and intimal area were measured as significantly lower in group 1 when compared with the other groups (p = 0.004). In group 3, the ratios of thickness of tunica intima/thickness of tunica media and area of tunica intima/area of tunica media were significantly lower than those of group 2 (p = 0.015, p = 0.003).

CONCLUSIONS

1,25 (OH)2D3, the active metabolite of vitamin D, reduces the intimal hyperplasia developing after vascular anastomoses.

Vitamin D deficiency and toxicity in chronic kidney disease: in search of the therapeutic window

Both vitamin D deficiency and vitamin D toxicity are associated with cardiovascular complications in chronic kidney disease (CKD). Clinical and experiment data indicate that the association of vitamin D levels with cardiovascular disease is best illustrated as a biphasic, or U-shaped, curve. Children and adolescents with CKD need vitamin D due to the demands of a growing skeleton, to prevent renal rickets. However, this therapy carries the risk of severe side effects and chronic toxicity. Observational studies show that vitamin D deficiency and toxicity are frequently present in patients with CKD. In view of the importance of cardiovascular complications for the long-term survival of young patients, these findings demand a judicious use of vitamin D preparations. In clinical practice, the therapeutic window is rather small, presenting a therapeutic challenge to avoid both vitamin D deficiency and toxicity.

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.

Elastic fibres and vascular structure in hypertension

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

Systemic cardiovascular disease in uremic rats induced by 1,25(OH)2D3

OBJECTIVE

Vitamin D may contribute to cardiovascular disease in the absence of hypercalcemia in patients with chronic kidney disease.

METHODS

We investigated the effects of long-term (6-week) treatment with 1,25(OH)2D3, at a non-hypercalcemic dosage (0.25 microg/kg per day per orally) in 5/6 nephrectomized rats: (i) vehicle-treated, sham-operated rats; (ii) 1,25(OH)2D3-treated, sham-operated rats; (iii) vehicle-treated, 5/6 nephrectomized rats; and (iv) 1,25(OH)2D3-treated, 5/6 nephrectomized rats.

RESULTS

Creatinine clearance after 6 weeks was significantly lower and parathyroid hormone levels were significantly higher in 1,25(OH)2D3-treated uremic rats, compared with uremic controls (P < 0.01). Serum calcium levels, as well as the calcium-phosphorus product, did not differ between both groups. Mean systolic blood pressure in 1,25(OH)2D3-treated animals was significantly increased, compared with vehicle (each P < 0.01). In addition, 1,25(OH)2D3-treated uremic animals showed left ventricular hypertrophy. Diffuse aortic calcification involving the intima and media layer occurred in 1,25(OH)2D3-treated uremic animals, but not in other groups. The mean aortic wall area and lumen area were increased two-fold in 1,25(OH)2D3-treated uremic animals compared with vehicle (P < 0.01), whereas the wall/lumen ratio remained unchanged, indicating fusiform aneurysm formation.

CONCLUSIONS

Hypertension, left ventricular hypertrophy, aortic calcification, and aneurysm, without hypercalcemia, occurred in 1,25(OH)2D3-treated, 5/6 nephrectomized rats. These data indicate a permissive effect of uremia for cardiovascular damage induced by non-hypercalcemic doses of 1,25(OH)2D3.

Fluctuations of intracellular iron modulate elastin production

Production of insoluble elastin, the major component of elastic fibers, can be modulated by numerous intrinsic and exogenous factors. Because patients with hemolytic disorders characterized with fluctuations in iron concentration demonstrate defective elastic fibers, we speculated that iron might also modulate elastogenesis. In the present report we demonstrate that treatment of cultured human skin fibroblasts with low concentration of iron 2-20 microm (ferric ammonium citrate) induced a significant increase in the synthesis of tropoelastin and deposition of insoluble elastin. Northern blot and real-time reverse transcription-PCR analysis revealed that treatment with 20 microm iron led to an increase of approximately 3-fold in elastin mRNA levels. Because treatment with an intracellular iron chelator, desferrioxamine, caused a significant decrease in elastin mRNA level and consequent inhibition of elastin deposition, we conclude that iron facilitates elastin gene expression. Our experimental evidence also demonstrates the existence of an opposite effect, in which higher, but not cytotoxic concentrations of iron (100-400 microm) induced the production of intracellular reactive oxygen species that coincided with a significant decrease in elastin message stability and the disappearance of iron-dependent stimulatory effect on elastogenesis. This stimulatory elastogenic effect was reversed, however, in cultures simultaneously treated with high iron concentration (200 microm) and the intracellular hydroxyl radical scavenger, dimethylthiourea. Thus, presented data, for the first time, demonstrate the existence of two opposite iron-dependent mechanisms that may affect the steady state of elastin message. We speculate that extreme fluctuations in intracellular iron levels result in impaired elastic fiber production as observed in hemolytic diseases.

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.

Novel arterial pathology in mice and humans hemizygous for elastin

Obstructive vascular disease is an important health problem in the industrialized world. Through a series of molecular genetic studies, we demonstrated that loss-of-function mutations in one elastin allele cause an inherited obstructive arterial disease, supravalvular aortic stenosis (SVAS). To define the mechanism of elastin's effect, we generated mice hemizygous for the elastin gene (ELN +/-). Although ELN mRNA and protein were reduced by 50% in ELN +/- mice, arterial compliance at physiologic pressures was nearly normal. This discrepancy was explained by a paradoxical increase of 35% in the number of elastic lamellae and smooth muscle in ELN +/- arteries. Examination of humans with ELN hemizygosity revealed a 2. 5-fold increase in elastic lamellae and smooth muscle. Thus, ELN hemizygosity in mice and humans induces a compensatory increase in the number of rings of elastic lamellae and smooth muscle during arterial development. Humans are exquisitely sensitive to reduced ELN expression, developing profound arterial thickening and markedly increased risk of obstructive vascular disease.

Expression of integrin subunits and CD44 isoforms in psoriatic skin and effects of topical calcitriol application

Increasing evidence suggests involvement of integrins and CD44 isoforms in the pathogenesis of psoriasis, contributing to uncontrolled keratinocyte proliferation, neovascularization, and invasion of inflammatory cells. We have analyzed immunohistochemically in situ expression of integrins (CD29, CDw49b, CDw49c, CDw49e, CDw49f) and CD44 isoforms (CD44 standard, CD44 var/v6, CD44 v10) on frozen sections of normal and psoriatic skin (nonlesional skin, lesional skin before and along with topical calcitriol treatment). We did not observe visual changes of immunoreactivity in normal as compared to nonlesional psoriatic skin, while the staining pattern of CDw49c, CDw49f, and CD29 was severely altered in untreated lesional psoriatic skin. Most markedly, CDw49c, CDw49f, and CD29 were focally upregulated in suprapapillar epidermal compartments of lesional psoriatic skin, a staining pattern that is in accordance with the phenomenon that was described by Pinkus as "squirting papilla". Additionally, an increased proportion of inflammatory and endothelial cells revealed immunoreactivity for CD44(std.) in untreated lesional psoriatic as compared to nonlesional psoriatic or normal skin. After 8 weeks of topical calcitriol treatment (15 micrograms/g ointment), the staining pattern for CDw49c, CDw49f and CD29 was markedly changed in epidermis of lesional psoriatic skin, reverting to the staining pattern characteristic for the nonlesional psoriatic or normal human skin, although epidermal expression of CDw49f was still upregulated and CDw49e-, CDw49f-, CD29-, and CD44(std.)-immunoreactive inflammatory and endothelial cells were still to be found in the dermal compartment.

Biochemistry and molecular regulation of matrix macromolecules in abdominal aortic aneurysms

Past concepts of aneurysmal dilatation as a passive process of attenuation are oversimplified and inaccurate. Aneurysm formation is a complex remodeling process that involves both synthesis and degradation of matrix proteins. Interstitial procollagen gene expression is increased in AAA compared to AOD or normal aorta, whereas tropoelastin gene expression is decreased in both AOD and AAA. The medial elastin network is disrupted and discontinuous in small AAA. Thus, the growth rate of an established AAA may well relate to the balance between collagen synthesis and degradation. Although the increased procollagen expression found in AAA may represent a compensatory response, understanding the factors that modulate matrix metabolism in AAA may allow for development of pharmacologic strategies which effectively inhibit the growth of small aneurysms.

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.

Decreased elastin synthesis in normal development and in long-term aortic organ and cell cultures is related to rapid and selective destabilization of mRNA for elastin

We have previously shown that aortic organ cultures from 1- to 3-day-old chickens initially mimic the high levels of elastin production seen in vivo. However, more prolonged incubation of these tissues results in decreased synthesis of elastin. In the present study, we demonstrate that decreased production of elastin in these aortic organ cultures is selective for elastin compared with collagen and is correlated with decreased steady state levels of mRNA for elastin. These decreases in steady state levels of elastin mRNA are due at least in part to a rapid and selective destabilization of mRNA for elastin, the half-life of which falls from approximately 25 hours in fresh aortic tissues to approximately 15 hours after incubation for only 8 hours. Destabilization of elastin mRNA can be prevented by incubation in the presence of blockers of DNA transcription (5,6-dichlorobenzimidazole riboside and actinomycin D) and mRNA translation (cycloheximide). Furthermore, the half-life of aortic elastin mRNA decreases from approximately 25 hours in the 1-day-old chicken to approximately 7 hours in the 8-week-old chicken, demonstrating that destabilization of mRNA is an important contributing factor in the decline in production of aortic elastin taking place during normal postnatal growth.

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.

Phorbol ester-mediated downregulation of tropoelastin expression is controlled by a posttranscriptional mechanism

Expression of tropoelastin, the principal precursor of elastic fibers, is tissue-specific and is limited to a brief developmental period. Little is known, however, about the mechanisms that regulate the tissue- and temporal-specific expression of elastogenesis. The tropoelastin promoter contains putative phorbol ester responsive elements, or AP-1 binding sites, but the functional significance of these sequences is unknown. To test if tropoelastin expression is influenced by phorbol esters, we exposed elastogenic fetal bovine chondrocytes to 10(-7) M 12-O-tetradecanoylphorbol 13-acetate (TPA). Tropoelastin mRNA levels decreased greater than 10-fold in response to TPA, and this downregulation was paralleled by a decline in the secretion of tropoelastin protein into the culture medium. As determined by nuclear-runoff assay and transient transfection with a human gene promoter-CAT construct, tropoelastin transcription was unaffected after exposure to TPA. As indicated by actinomycin D experiments, the half-life of tropoelastin mRNA in control cells was about 20 h, but exposure to TPA resulted in an accelerated decay of the tropoelastin transcript (t1/2 = 2.2 h). These data indicate that downregulation of tropoelastin expression was controlled by a posttranscriptional mechanism and that the AP-1 elements in the bovine tropoelastin promoter may not be involved in regulation of production.