The Slug Mucosal Irritation (SMI) assay: a tool for the evaluation of nasal discomfort

In this research project, the Slug Mucosal Irritation (SMI) assay was applied to predict nasal discomfort, investigating the correlation between responses in slugs and humans. Several SMI experiments and a Human Nose Irritation Test (HNIT) were performed with five NaCl solutions (0.4%, 1.3%, 2.6%, 5.4% and 10.4%) and two benzalkonium chloride solutions (BAC 0.02% and BAC 0.05%). In the HNIT, subjective evaluation of clinical discomfort was performed by 24 participants at several time points. Analyzes reveal that (1) a significant positive association existed between immediate stinging reaction reported by the participants and the mean total mucus production of the slugs (Spearman's Rank correlation=0.963, p<0.001); (2) NaCl 0.4% was best tolerated in both tests; (3) a concentration-response effect was observed for NaCl and BAC solutions; (4) NaCl 10.4% induced the highest mucus production in the slugs and received higher sting scores for immediate discomfort in the HNIT; (5) stinging sensations decreased rapidly in time and (6) based on these results a new classification prediction model for nasal applications was established. In conclusion, the SMI assay is a promising evaluation method for clinical nasal discomfort. Screening (prototype) formulations with this assay allows formula optimization prior to a clinical trial.