The role of vitamin D in the development and progression of experimental abdominal aortic aneurysm

Vianne Nsengiyumva conducted experimental investigations into the role of vitamin D on abdominal aortic aneurysms (AAA). Vitamin D supplementation to achieve optimal circulating levels slowed the growth of AAA. Findings from this thesis are supportive of clinical trials to examine regulating vitamin D levels in AAA patients

Vitamin D deficiency promotes large rupture-prone abdominal aortic aneurysms and cholecalciferol supplementation limits progression of aneurysms in a mouse model

Vitamin D deficiency has been associated with human abdominal aortic aneurysm (AAA); however, its role in AAA pathogenesis is unclear. The aim of the present study was to inves-tigate the effect of vitamin D deficiency on AAA development and examine if administering cholecalciferol (CCF) could limit growth of established AAA within the angiotensin-II (AngII) infused apolipoprotein E-deficient mouse model. Mice were rendered vitamin D deficiency through dietary restriction and during AngII infusion developed larger AAAs as assessed by ultrasound and ex vivo morphometry that ruptured more commonly (48% vs. 19%; P=0.028) than controls. Vitamin D deficiency was associated with increased aortic expression of osteopontin and matrix metalloproteinase-2 and -9 than controls. CCF administration to mice with established aortic aneurysms limited AAA growth as assessed by ultrasound (P<0.001) and ex vivo morphometry (P=0.036) and reduced rupture rate (8% vs. 46%; P=0.031). This effect was associated with up-regulation of circulating and aortic sclerostin. Incubation of human aortic smooth muscle cells with 1,25-dihyroxyvitamin D3 (the active metabolite of vitamin D) for 48 h induced up-regulation of sclerostin (P<0.001) and changed the expression of a range of other genes important in extracellular matrix remodeling. The present study suggests that vitamin D deficiency promotes development of large rupture-prone aortic aneurysms in an experimental model. CCF administration limited both growth and rupture of established aneurysms. These effects of vitamin D appeared to be mediated via changes in genes involved in extracellular matrix remodeling, particularly sclerostin

The efficacy of extraembryonic stem cells in improving blood flow within animal models of lower limb ischaemia

Background: Stem cell (SC) administration is a potential therapeutic strategy to improve blood supply in patients with peripheral artery disease (PAD). The aim of this systematic review and meta-analysis was to investigate the efficacy of extraembryonic tissue-derived SC (ETSC) in improving blood flow within animal models of hindlimb ischaemia (HLI).\ud \ud Methods: PubMed, ScienceDirect and Web of Science were searched to identify studies which investigated ETSCs within animal HLI models. A meta-analysis was performed focusing on the effect of ETSCs on limb blood flow assessed by laser Doppler imaging using a random effects model. Methodological quality was assessed using a newly devised quality assessment tool.\ud \ud Results: Five studies investigating umbilical cord-derived SCs (three studies), placental SCs (one study), amnion and chorionic SCs (one study) were included. A meta-analysis suggested that administration of ETSCs improved the restoration of blood flow within the HLI models used. The methodological quality of the included studies was assessed as poor. Problems identified included lack of randomised design and blinding of outcome assessors; that the animal models did not incorporate recognised risk factors for human PAD or atherosclerosis; the models used did not have established chronic ischaemia as is the cases in most patients presenting with PAD; and the studies lacked a clear rationale for the dosage and frequency of SCs administered.\ud \ud Conclusions: The identified studies suggest that ETSCs improve recovery of limb blood supply within current animal HLI models. Improved study quality is, however, needed to provide support for the likelihood of translating these findings to patients with PAD

Effect of Australian propolis from stingless bees (Tetragonula carbonaria) on pre-contracted human and porcine isolated arteries.

Bee propolis is a mixture of plant resins and bee secretions. While bioactivity of honeybee propolis has been reported previously, information is limited on propolis from Australian stingless bees (Tetragonula carbonaria). The aim of this study was to investigate possible vasomodulatory effects of propolis in KCl-precontracted porcine coronary arteries using an ex vivo tissue bath assay. Polar extracts of propolis produced a dose-dependent relaxant response (EC50=44.7±7.0 μg/ml), which was unaffected by endothelial denudation, suggesting a direct effect on smooth muscle. Propolis markedly attenuated a contractile response to Ca(2+) in vessels that were depolarised with 60 mM KCl, in Ca(2+)-free Krebs solution. Propolis (160 µg/ml) reduced vascular tone in KCl pre-contracted vessels to near-baseline levels over 90 min, and this effect was partially reversible with 6 h washout. Some loss in membrane integrity, but no loss in mitochondrial function was detected after 90 min exposure of human cultured umbilical vein endothelial cells to 160 µg/ml propolis. We conclude that Australian stingless bee (T. carbonaria) propolis relaxes porcine coronary artery in an endothelial-independent manner that involves inhibition of voltage-gated Ca(2+) channels. This effect is partially and slowly reversible upon washout. Further studies are required to determine the therapeutic potential of Australian stingless bee propolis for conditions in which vascular supply is compromised

Effect of propolis on voltage-gated calcium channels in endothelial-intact porcine coronary arteries.

<p>Arteries were incubated with 60 mM KCl in calcium-free Krebs solution to depolarise the cells (A-C), or with 100 nM calyculin A in Krebs solution (D). In the presence of dimethyl sulfoxide (DMSO), arteries produced a concentration-dependent contractile response to Ca²⁺ (32 μM-10 mM; A, C). The relaxant response was markedly attenuated in the presence of 160 μg/ml propolis (B, C), and responses were blocked by the calcium channel inhibitor, nifedipine (Nif., 10 μM; A-C). Propolis was ineffective in relaxing endothelium-denuded coronary arteries that were pre-contracted with calyculin A (D).</p

Cell viability assays.

<p>MTT assay showing cell viability for human cultured umbilical vein endothelial cells (HUVECs) exposed to stingless bee <i>T. carbonaria</i> propolis or dimethyl sulfoxide (DMSO) for 90 min at 37°C (A). Propolis (20-160 µg/ml) and isovolumetric DMSO (0.26%) had no effect on cell viability. A punctuate pattern of formazan crystal staining was evident in the cytoplasm of HUVECs treated with 160 µg/ml propolis for 90 min at 37°C, confirming retention of mitochondrial enzyme activity (B). Propolis (80 and 160 µg/ml) caused some leakage of lactate dehydrogenase (LDH) into the culture medium (C). Water, DMSO (0.26%) and propolis (20 and 40 µg/ml) had no effect on LDH leakage.</p

Reversibility of the vasorelaxant response to stingless bee <i>T. carbonaria</i> propolis in 60 mM KCl-precontracted porcine coronary arteries.

<p>Propolis (160 µg/ml) caused a near-maximal reduction in coronary artery tone within 90 min of incubation. The contractile response to KCl immediately after washout was markedly lower than the KCl response obtained prior to addition of propolis (A). The KCl response was not blunted in dimethyl sulfoxide (DMSO)-treated tissues (B). The relaxant response to propolis was partially reversed during half-hourly wash-KCl cycles over a 6 hour period (open bars, DMSO-treated tissues; closed bars, propolis-treated tissues (C). W, washout.</p

Original traces showing the effect of Australian stingless bee <i>T. carbonaria</i> propolis on vascular tone in isolated blood vessel preparations.

<p>Propolis relaxed porcine coronary arteries that were pre-contracted with 60 mM KCl (A), or 2 mM histamine (B). Propolis relaxed human umbilical arteries that were pre-contracted with 60 mM KCl (C, E; open bar), while the solvent dimethyl sulfoxide (DMSO) was without effect (D, E; closed bar, n=3, * P<0.05).</p

Examination of the role of endothelial cells in the relaxant response to stingless bee <i>T. carbonaria</i> propolis in porcine coronary arteries.

<p>Propolis (40 and 160 μg/ml) relaxed endothelial-intact (A) and endothelial-denuded coronary arteries (B). No relaxation was observed in endothelial-intact, time-control tissues treated with DMSO (C). There was no difference in relaxant response to propolis in endothelial-intact and endothelial-denuded arteries (D), indicating an endothelial-independent mechanism.</p

The association of circulating 25-hydroxyvitamin D concentration with peripheral arterial disease: a meta-analysis of observational studies

Background and aims: The association of vitamin D deficiency with cardiovascular disease is controversial. The present meta-analysis was performed to examine if circulating levels of 25-hydroxyvitamin D [25(OH)D] were lower in patients with peripheral artery disease (PAD) when compared to non-PAD controls.\ud \ud Methods: A comprehensive database search was conducted in Web of science, Scopus, PubMed, EMBASE and The Cochrane Library to identify observational studies reporting 25(OH)D concentrations in PAD patients and non-PAD participants. Data extraction and study quality assessments were conducted independently. A random-effects model was used to meta-analyse extracted data and generate standardized mean differences (SMDs) in circulating 25(OH)D levels between PAD patients and non-PAD controls. Subgroup analyses were conducted focussing on patients presenting with intermittent claudication (IC) and critical limb ischaemia (CLI).\ud \ud Results: Six case-control studies assessing 6418 individuals fulfilled the inclusion criteria. Two studies were considered to be of moderate methodological quality and four were considered to be of high quality. A meta-analysis of data from 1217 PAD patients and 5201 non-PAD participants showed that circulating 25(OH)D concentrations were lower in PAD patients compared with non-PAD participants (SMD = −0.32, 95% CI: −0.58, −0.05; P = 0.02). Subgroup analyses showed that 25(OH)D levels were significantly lower among PAD patients with CLI, but not IC, when compared to non-PAD controls (SMD = −1.29, 95% CI: −1.66, −0.91; P < 0.001 and SMD = −0.01, 95% CI: −0.15, 0.13; P = 0.88, respectively).\ud \ud Conclusions: This meta-analysis suggests that low levels of circulating 25(OH)D are associated with PAD presence, particularly in patients presenting with CLI. These data suggest the possibility that vitamin D insufficiency may contribute to the development of more advanced PAD although this remains to be confirmed