Study of Vascular Function Before vs After Smoking an E-cigarette as Compared to a Normal Cigarette

The overall aim of this study is to compare the short-term vascular effects of smoking an e-cigarette versus smoking a conventional tobacco cigarette in vivo and in vitro.

The specific objectives are as follows:

i. To evaluate the effects of e-cigarette and conventional combustible cigarette (CCC) use on microvascular and macrovascular endothelial function and stiffness in healthy smokers.

ii. To assess circulating markers of endothelial function in response to e-cigarette and CCC smoking.

iii. To investigate the vascular effects of e-cigarette and CCC use on a molecular level by exposing endothelial cells with stimulated serum from the intervention study.

Primary Objective and Outcome Parameter:

The primary objective of this investigator initiated trial (IIT) is to evaluate the short-term effect of e-cigarette puffing on conduit artery function in comparison to smoking a CCC in healthy male long-term smokers.

The relative change in brachial artery diameter in response to reactive hyperemia (flow-mediated vasodilation), a validated surrogate marker of conduit endothelial function, will be used as primary endpoint. FMD [%] is defined as (brachial diameter 60 s after cuff deflation [mm] - baseline brachial diameter [mm]) x 100 / baseline brachial diameter [mm].

The primary outcome measure is the absolute difference of FMD after e-cigarette and CCC.

Secondary Objective and Outcome Parameter:

The secondary objectives are to evaluate in vivo endothelial function in other vascular beds, especially in the microcirculation and the systemic circulation, as well as other aspects of vascular function like stiffness of the arterial tree. Endothelial dysfunction, a key event of atherosclerosis development, is characterized by a respective increase or decrease of endothelium-derived molecules and changes in upstream signaling pathways that control the synthesis and bioavailability of these endothelium-derived molecules. Analysis of circulating biomarkers of endothelial function and expression studies of enzymes involved in endothelial activation will help to closely characterize possible effects of e-cigarette exposure on in vivo endothelial function.

Secondary endpoints are:

• Augmentation index in response to salbutamol (%) as surrogate of global endothelial function in relation to its response to glyceryl trinitrate (%)
• Augmentation index (%) as marker of pulse wave reflection and stiffness
• Retinal arterial and venous diameter in response to flicker-light stimulation (%) as surrogate of microvascular endothelial function
• Central retinal arterial and venous equivalent and arteriolar-to-venular ratio as indicators of generalized arterial narrowing
• Circulating biomarkers of endothelial function and activation (Endothelin-1; BH4/BH2) Secondary outcome measures are the absolute differences of secondary endpoints between e-cigarette and CCC (refer to section 13.4.2).

Functional in vitro assays and molecular analyses:

• mRNA and protein expression of endothelial nitric oxide synthase (eNOS), NRF2 target genes HMOX1, NQO1 and adhesion molecules (ICAM1, VCAM1, SELE, CCL2).
• Primary cultures of human umbilical vein endothelial cells will be stimulated with serum of human subjects (sampled before or after smoking of one cigarette or e-cigarette) and potential of wound healing will be determined.

Tertiary Objective and Outcome Parameter:

The tertiary objective is to assess differences in vascular function between smokers and never smokers. Tertiary endpoints are baseline values of primary and secondary endpoints.