A new study from the REPLICA project at CoEHAR (University of Catania) calls into question previous claims about the vascular toxicity of vanillin in e-cigarette aerosols, highlighting the critical role of methodology and reproducibility in toxicological research.
Published in Cardiovascular Toxicology, the study conceptually replicated key experiments from a widely cited 2018 paper by Fetterman et al., which had suggested that vanillin could impair endothelial function. However, under more realistic and standardized vaping conditions, the CoEHAR-led team found no meaningful evidence of vanillin-specific endothelial toxicity.
Instead, the apparent harmful effects reported in the original study were largely attributable to the ethanol-based trapping vehicle used in the experimental setup.
A matter of methodology, not molecule
By applying standardized aerosol generation and appropriate control conditions, the researchers were able to disentangle the effects of vanillin from those of the solvent system. The findings showed no significant vanillin-specific impact on key biological endpoints, including cytotoxicity, oxidative stress, nitric oxide production, or inflammatory markers such as IL-6 and ICAM-1, once proper controls were applied.
Crucially, the study also revealed that only cytotoxicity results were consistently reproducible across laboratories, while other endpoints — including oxidative stress and gene expression — showed substantial variability.
As explained by Prof. Giovanni Li Volti, Principal Investigator of the REPLICA project:
“This study highlights how sensitive in vitro toxicology results are to experimental design. Without standardized methods and appropriate controls, there is a real risk of attributing biological effects to the wrong compounds.”
The REPLICA Project: raising the bar for reproducibility
The REPLICA project was specifically designed to address one of the most pressing challenges in biomedical research: the reproducibility of experimental findings.
By coordinating multi-center conceptual replications of influential studies, REPLICA aims to verify whether previously reported results can be confirmed under standardized and transparent experimental conditions. This approach is particularly relevant in the field of e-cigarette research, where differences in exposure systems, laboratory protocols, and analytical methods can significantly affect outcomes.
The vanillin study represents a clear example of this approach: by replicating a high-impact experiment while controlling for key methodological variables, the REPLICA team was able to identify the source of the observed effect and clarify its interpretation.
As noted by Prof. Massimo Caruso, co-Principal Investigator of the REPLICA project:
“Replication is not a formality — it is essential to validate findings and ensure that conclusions are robust. Our results show that methodological differences can fundamentally change the interpretation of toxicological data.”
Implications for research and regulation
The study carries important implications for both researchers and regulators. From a scientific perspective, it underscores the need for standardized aerosol generation protocols, careful control of solvents and exposure systems and multi-laboratory validation of key findings. From a regulatory standpoint, it suggests that flavor-related risk assessments should be approached with caution, avoiding reliance on isolated in vitro results that may be influenced by experimental artifacts.
While the authors stress that “generally recognized as safe” (GRAS) for ingestion does not automatically translate to safety for inhalation, they also emphasize that not all reported toxic effects are necessarily intrinsic to the flavoring compound itself.
A more nuanced understanding
For consumers, the findings offer a more nuanced perspective. The study does not claim that vanillin-containing e-liquids are harmless, but it does suggest that vanillin alone may be less concerning for endothelial toxicity than previously reported.
As highlighted by Prof. Riccardo Polosa, co-author of the study and CoEHAR Founder:
“Blaming vanilla for damage actually caused by ethanol is scientifically indefensible. Because ethanol emerges as the key problem for vascular health, we should ban alcoholic beverages and not flavored vapes!”
Overall, the study reinforces a broader message: in complex areas such as e-cigarette toxicology, robust methodology and reproducibility are essential to distinguish real biological effects from experimental artifacts.
Reference
Emma R, Sun A, Partsinevelos K, Rust S, Volarevic V, Lesmana R, Giordano A, Goenawan H, Barliana MI, Arsenijevic A, Kastratovic N, Markovic V, Spasic B, Distefano A, Orlando L, Carota G, Polosa R, Caruso M, Li Volti G.
Toxicological Evaluation of Vanillin Flavor in E-Liquid Aerosols on Endothelial Cell Function: Findings from the Replica Project.
Cardiovascular Toxicology. 2026;26(4):42.
DOI: 10.1007/s12012-026-10111-0
