Oral sildenafil increases skin hyperaemia induced by iontophoresis of sodium nitroprusside in healthy volunteers

Evidence of premature vascular dysfunction in young adults who regularly use e-cigarettes and the impact of usage length

BACKGROUND

Electronic (e-) cigarettes are increasingly popular tobacco products on the US market. Traditional tobacco products are known to cause vascular dysfunction, one of the earliest indicators of cardiovascular disease (CVD) development. However, little is known about the effect of regular e-cigarette use on vascular function. The purpose of this study was to investigate the impact of regular e-cigarette use on vascular function and cardiovascular health in young, healthy adults.

METHODS

Twenty-one regular users of e-cigarettes (ECU) and twenty-one demographically matched non-users (NU) completed this study. Vascular health was assessed in the cutaneous microcirculation through different reactivity tests to evaluate overall functionality, endothelium-dependent vasodilation (EDD), and endothelium-independent vasodilation (EID). Macrovascular function was assessed using flow-mediated dilation (FMD).

RESULTS

Our results suggest that regular users of e-cigarettes present with premature microvascular impairment when compared to non-users. Specifically, they exhibit lower hyperemic (p = 0.003), thermal (p = 0.010), and EDD (p = 0.004) responses. No differences in EID between the groups were identified. We also identified that individuals who use e-cigarettes for longer than 3 years also present with systemic manifestations, as observed by significantly reduced macrovascular (p = 0.002) and microvascular (p ≤ 0.044) function.

CONCLUSIONS

Our novel data suggests that young, apparently healthy, regular users of e-cigarettes present with premature vascular dysfunction in the microcirculation when compared to non-users. We have also identified systemic vascular dysfunction affecting both the micro and macrovasculature in those young individuals who used e-cigarettes for longer than 3 years. Taken together, these findings associate regular e-cigarette use with premature vascular dysfunctions and adverse cardiovascular outcomes.

Skin Microhemodynamics and Mechanisms of Its Regulation in Type 2 Diabetes Mellitus

The review presents modern ideas about peripheral microhemodynamics, approaches to the ana-lysis of skin blood flow oscillations and their diagnostic significance. Disorders of skin microhemodynamics in type 2 diabetes mellitus (DM) and the possibility of their interpretation from the standpoint of external and internal interactions between systems of skin blood flow regulation, based on a comparison of couplings in normal and pathological conditions, including models of pathologies on animals, are considered. The factors and mechanisms of vasomotor regulation, among them receptors and signaling events in endothelial and smooth muscle cells considered as models of microvessels are discussed. Attention was drawn to the disturbance of Ca2+-dependent regulation of coupling between vascular cells and NO-dependent regulation of vasodilation in diabetes mellitus. The main mechanisms of insulin resistance in type 2 DM are considered to be a defect in the number of insulin receptors and impaired signal transduction from the receptor to phosphatidylinositol-3-kinase and downstream targets. Reactive oxygen species plays an important role in vascular dysfunction in hyperglycemia. It is assumed that the considered molecular and cellular mechanisms of microhemodynamics regulation are involved in the formation of skin blood flow oscillations. Parameters of skin blood microcirculation can be used as diagnostic and prognostic markers for assessing the state of the body.

Current methods for the assessment of skin microcirculation: Part 1

Microcirculation accounts for about 99% of blood vessels in adults and mediates between the arterial and venous parts of the cardiovascular system, both structurally and functionally. Skin microcirculation consists of two vascular plexuses: superficial and deep. Microcirculation includes vessels with a diameter of less than 150 μm, i.e. arteries, small veins, lymphatic vessels and arteriovenous anastomoses, which build the microcirculation unit. Skin microcirculation may be affected both in systemic pathologies and specific skin disorders. Several non-invasive techniques are available to assess the skin microcirculation. The clinical value is recognised for capillaroscopy and videocapillaroscopy, laser Doppler flowmetry thermography and transcutaneous oxygen measurement. The list of methods that may be used in clinical research also includes: photoplethysmography, orthogonal spectral polarization, near infrared spectroscopy and tissue reflectance spectrophotometry and optical coherence tomography.

Regional myocardial function abnormalities are associated with macro- and microcirculation dysfunction in the metabolic syndrome: the RESOLVE study

Abnormalities in myocardial and vascular function have been reported in the metabolic syndrome (MetS), but whether these alterations are related remains poorly documented. Our aim was accordingly to investigate interrelationships between macro- and microcirculatory vasoreactivity and left ventricular (LV) myocardial function in MetS patients. Eighty-eight MetS individuals and 44 age- and gender-matched healthy controls were enrolled. LV global longitudinal strain (GLS) was measured using Vector Velocity Imaging. Endothelial-dependent and independent reactivity in macro- and microcirculatory territories was established using flow-mediated dilation and nitrate-mediated dilation of the brachial artery and cutaneous blood flow measured with laser Doppler flowmetry in response to iontophoresis of acetylcholine and sodium nitroprusside, respectively. Carotid intima-media thickness (cIMT) was measured according to the Mannheim consensus. Compared to controls, MetS patients presented with reduced GLS (p < 0.001) increased cIMT and impaired (p < 0.001) endothelial and smooth muscle function of the brachial artery and the forearm skin microcirculation. Highly significant relationships (p < 0.01) were noticed between GLS and vascular outcomes. In addition, cIMT (β = 0.21, p = 0.024) and microcirculatory endothelium-dependent reactivity (β = - 0.20, p = 0.035) were identified as independent predictors of GLS. In MetS, abnormalities in myocardial function and endothelial as well as smooth muscle function of small and large arteries co-exist and are closely associated. This study supports a role for microvascular dysfunction in the pathogenesis of LV myocardial dysfunction.

Potentiation of the NO-cGMP pathway and blood flow responses during dynamic exercise in healthy humans

PURPOSE

Previous work has shown nitric oxide (NO) contributes to ~15% of the hyperemic response to dynamic exercise in healthy humans. This NO-mediated vasodilation occurs, in part, via increases in intracellular cyclic guanosine monophosphate (cGMP), which is catabolized by phosphodiesterase. We sought to examine the effect of phosphodiesterase-5 (PDE-5) inhibition on forearm blood flow (FBF) responses to dynamic handgrip exercise in healthy humans and the role of NO. We hypothesized exercise hyperemia would be augmented by sildenafil citrate (SDF, PDE-5 inhibitor). We further hypothesized any effect of SDF on exercise hyperemia would be abolished with intra-arterial infusion of the NO synthase (NOS) inhibitor L-N^G-monomethyl arginine (L-NMMA).

METHODS

FBF (Doppler ultrasound) was assessed at rest and during 5 min of dynamic forearm handgrip exercise at 15% of maximal voluntary contraction under control (saline) conditions and during 3 experimental protocols: (1) oral SDF (n = 10), (2) intra-arterial L-NMMA (n = 20), (3) SDF and L-NMMA (n = 10). FBF responses to intra-arterial sodium nitroprusside (NTP, NO donor) were also assessed.

RESULTS

FBF increased with exercise (p < 0.01). Intra-arterial infusion of L-NMMA resulted in a reduction in exercise hyperemia (17 ± 1 to 15 ± 1 mL/dL/min, p < 0.01). Although the hyperemic response to NTP was augmented by SDF (area under the curve: 41 ± 7 vs 61 ± 11 AU, p < 0.01), there was no effect of SDF on exercise hyperemia (p = 0.33).

CONCLUSIONS

Despite improving NTP-mediated vasodilation, oral SDF failed to augment exercise hyperemia in young, healthy adults. These observations reflect a minor contribution of NO and the cGMP pathway during exercise hyperemia in healthy young humans.

Evaluation of test characteristics for outcome measures used in Raynaud's phenomenon clinical trials

OBJECTIVE

Randomized controlled trials (RCTs) in Raynaud's phenomenon (RP) have shown conflicting efficacy data. Also, there is no consensus on the outcome measures that should be used. Our objectives were to assess the reliability of individual core set measures used in 3 RCTs, evaluate the placebo response for individual core set measures, and determine if a composite of individual core set measures will decrease the placebo response, which may improve our ability to see treatment effects in future trials.

METHODS

We analyzed core set measures from 249 patients in the placebo-treated groups from 3 RCTs. Core set measures analyzed included the Raynaud's Condition Score (RCS); patient and physician assessment of RP; pain, numbness, and tingling during an RP attack; average number of attacks/day; and duration of attacks. Intraclass correlation coefficients (ICCs) were calculated during the run-in period to the RCTs.

RESULTS

ICCs of ≥0.70 were observed for the RCS, attack symptoms, and average attacks/day. A high placebo response rate was observed for all individual core measures except the duration of attacks. For the RCS, the placebo response ranged from 56% with ≥10% improvement to 19.5% with ≥60% improvement. In contrast, placebo response rates of 10-20% were observed when several core set measures were combined to develop a composite score.

CONCLUSION

Outcome measures used in RCTs of RP are associated with marked variability. A combination of outcome measures is associated with low placebo responses. Future studies are needed to assess if a composite score will be able to differentiate placebo from an effective agent.

Iontophoresis of endothelin receptor antagonists in rats and men

Introduction

The treatment of scleroderma-related digital ulcers is challenging. The oral endothelin receptor antagonist (ERA) bosentan has been approved but it may induce liver toxicity. The objective of this study was to test whether ERAs bosentan and sitaxentan could be locally delivered using iontophoresis.

Methods

Cathodal and anodal iontophoresis of bosentan and sitaxentan were performed on anaesthetized rat hindquarters without and during endothelin-1 infusion. Skin blood flow was quantified using laser-Doppler imaging and cutaneous tolerability was assessed. Iontophoresis of sitaxentan (20 min, 20 or 100 µA) was subsequently performed on the forearm skin of healthy men (n = 5).

Results

In rats neither bosentan nor sitaxentan increased skin blood flux compared to NaCl. When simultaneously infusing endothelin-1, cathodal iontophoresis of sitaxentan increased skin blood flux compared to NaCl (AUC_0–20 were 44032.2±12277 and 14957.5±23818.8 %BL.s, respectively; P = 0.01). In humans, sitaxentan did not significantly increase skin blood flux as compared to NaCl. Iontophoresis of ERAs was well tolerated both in animals and humans.

Conclusions

This study shows that cathodal iontophoresis of sitaxentan but not bosentan partially reverses endothelin-induced skin vasoconstriction in rats, suggesting that sitaxentan diffuses into the dermis. However, sitaxentan does not influence basal skin microvascular tone in rats or in humans.

Sildenafil increases digital skin blood flow during all phases of local cooling in primary Raynaud's phenomenon

Digital skin vasoconstriction on local cooling is exaggerated in primary Raynaud's phenomenon (RP) as compared with controls. A significant part of such vasoconstriction relies on the inhibition of the nitric oxide (NO) pathway. We tested the effect of the phosphodiesterase 5 (PDE5) inhibitor sildenafil, which potentiates the effect of NO, on skin blood flow. We recruited 15 patients with primary RP, performing local cooling without sildenafil (day 1), after a single oral dose of 50 mg (day 2), and after a dose of 100 mg (day 3). Skin blood flow, skin temperature, and arterial pressure were recorded, and data were expressed as cutaneous vascular conductance (CVC). Sildenafil at 100 mg, but not 50 mg, significantly lessened the cooling-induced decrease in CVC. It also increased resting CVC and skin temperature. These data suggest that 100 mg sildenafil improves digital skin perfusion during local cooling in primary RP. The benefit of sildenafil "as required" should be confirmed in a randomized, controlled trial.

Cathodal iontophoresis of treprostinil and iloprost induces a sustained increase in cutaneous flux in rats

BACKGROUND AND PURPOSE

The treatment of scleroderma-related digital ulcers is still a therapeutic challenge. The most effective drugs are prostacyclin analogues. However, their usage is limited to an intravenous route of administration and by their frequent side effects. The objective of this study was to test whether treprostinil, iloprost and epoprostenol can induce sustained vasodilatation in rats when delivered locally using cutaneous iontophoresis.

EXPERIMENTAL APPROACH

Treprostinil, iloprost and epoprostenol were delivered by cathodal and anodal iontophoresis onto the hindquarters of anaesthesized rats (n= 8 for each group). Skin blood flow was quantified using laser Doppler imaging and cutaneous tolerance was assessed from day 0 to day 3.

KEY RESULTS

Cathodal but not anodal iontophoresis of treprostinil (6.4 mM), iloprost (0.2 mM) and epoprostenol (1.4 mM) induced a significant and sustained increase in cutaneous blood flow. The effects of treprostinil and iloprost were significantly different from those of treprostinil vehicle. Only weak effects were observed when both drugs were applied locally without current. Skin resistance was unchanged in areas treated with prostacyclin analogues. Finally, skin tolerance was good, with no evidence of epidermal damage.

CONCLUSIONS AND IMPLICATIONS

Cathodal iontophoresis of treprostinil and iloprost increases cutaneous blood flow with a good local tolerance. The effects of cathodal iontophoresis of these drugs should be investigated in humans, as they could have potential as new local therapies for digital ulcers in patients with scleroderma.