Development of physiologically relevant test methods to analyse potential irritant effects to the respiratory tract caused by e-cigarette aerosols is required. This paper reports the method development and optimisation of an acute in vitro MTT cytotoxicity assay using human 3D reconstructed airway tissues and an aerosol exposure system. The EpiAirway™ tissue is a highly differentiated in vitro human airway culture derived from primary human tracheal/bronchial epithelial cells grown at the air-liquid interface, which can be exposed to aerosols generated by the VITROCELL® smoking robot. Method development was supported by understanding the compatibility of these tissues within the VITROCELL® system, in terms of airflow (L/min), vacuum rate (mL/min) and exposure time. Dosimetry tools (QCM) were used to measure deposited mass, to confirm the provision of e-cigarette aerosol to the tissues. EpiAirway™ tissues were exposed to cigarette smoke and aerosol generated from two commercial e-cigarettes for up to 6 h. Cigarette smoke reduced cell viability in a time dependent manner to 12% at 6 h. E-cigarette aerosol showed no such decrease in cell viability and displayed similar results to that of the untreated air controls. Applicability of the EpiAirway™ model and exposure system was demonstrated, showing little cytotoxicity from e-cigarette aerosol and different aerosol formulations when compared directly with reference cigarette smoke, over the same exposure time.

The present publication surveys several applications of in silico (i.e., computational) toxicology approaches across different industries and institutions. It highlights the need to develop standardized protocols when conducting toxicity-related predictions. This contribution articulates the information needed for protocols to support in silico predictions for major toxicological endpoints of concern (e.g., genetic toxicity, carcinogenicity, acute toxicity, reproductive toxicity, developmental toxicity) across several industries and regulatory bodies. Such novel in silico toxicology (IST) protocols, when fully developed and implemented, will ensure in silico toxicological assessments are performed and evaluated in a consistent, reproducible, and well-documented manner across industries and regulatory bodies to support wider uptake and acceptance of the approaches. The development of IST protocols is an initiative developed through a collaboration among an international consortium to reflect the state-of-the-art in in silico toxicology for hazard identification and characterization. A general outline for describing the development of such protocols is included and it is based on in silico predictions and/or available experimental data for a defined series of relevant toxicological effects or mechanisms. The publication presents a novel approach for determining the reliability of in silico predictions alongside experimental data. In addition, we discuss how to determine the level of confidence in the assessment based on the relevance and reliability of the information.

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1 The limitations of the Draize rabbit skin irritation test for hazard evaluation for man are widely documented. Nevertheless it remains the prescribed method for deter mining acute skin irritation hazard. 2 While the use of human testing for risk assessment of irritants is well established, the use of predictive testing in man for hazard identification has not been explored widely, and this is the object of the research programme. 3 The experiment described in this report evaluates the sensitivity of four patch testing systems (Finn chamber, Hill Top patch, Van der Bend chamber, and Webril patch) using a total of six irritant substances. 4 Following preliminary range-finding experiments, test materials were applied to the upper outer arm for up to 4 h. Assessments were performed immediately after patch removal and at 1, 24, 48 and 72 h. 5 Webril and Hill Top patches generated the greatest lev els of response, although responses with Finn and Van der Bend were observed. Hill Top patches are recom mended for future development work. 6 The use of very small preliminary panels to predict the effects in larger panels using different volunteers was only of limited value as each volunteer was found to have different irritant thresholds.