Critical micelle concentration and particle size determine adjuvanticity of cyclic lipopeptides

Abstract

Cyclic lipopeptides such as surfactin and polymyxin have potent mucosal adjuvant properties. Cyclic lipopeptides are tensioactive compounds but the relationship between adjuvanticity and surface activity is unknown. Here, we show that the critical micelle concentration (cmc) of surfactant and particle size of the surfactant-protein complex are important determinants of cyclic lipopeptide adjuvanticity. We found that the diameter of cyclic lipopeptide-ovalbumin (OVA) complex particles was significantly larger than that in the solutions of OVA alone at cyclic lipopeptide concentrations above the cmc. OVA-specific antibody titers in mice immunized intranasally with OVA and a cyclic lipopeptide at concentrations above its cmc were significantly higher than those in mice immunized with OVA plus the same dose of the cyclic lipopeptide but administered with formulations in which cyclic lipopeptide concentration was below the cmc. Thus, the concentration of the cyclic lipopeptide in the formulation at immunization, but not its overall dose, was critical for its adjuvanticity. Furthermore, two types of aggregates, the cyclic lipopeptide simplex micelles and the cyclic lipopeptide-OVA complex micelles, were found in formulations with SF concentrations above its cmc. Degranulation of mast cells exposed to SF simplex micelles was more pronounced when SF concentration was above the cmc. In conclusion, our study showed that surface activity properties, such as the cmc and the size of surfactant-protein complex contribute to the adjuvanticity of cyclic lipopeptides. Our study proposes a novel idea that cmc is a key parameter for tensioactive adjuvants. This article is protected by copyright. All rights reserved.

Suitability of Polymyxin B as a Mucosal Adjuvant for Intranasal Influenza and COVID-19 Vaccines

“…For IN immunization, mice were administered a 10 µL aliquot (5 µL/nostril) of the immunization solution, whereas SC immunization was performed by injecting a 50 µL aliquot of the immunization solution into the interscapular region of the mice. Each mouse was immunized thrice at 0, 7, and 14 days, as previously described [2,21,24].…”

“…The particle diameters of the virus antigen and PMB-virus antigen complex were measured using a Zetasizer Nano ZS system (Malvern Instruments Ltd., Worcestershire, UK), as described previously [21,24].…”

“…We previously reported that the particle diameter of the OVA-PMB complex is related to the induction level of mucosal immunity [21]. Therefore, we measured the particle diameters of HA split with or without PMB in the immunization solutions (Figure 2, Table 1).…”

“…We used BALB/c mice to determine the suitability of PMB as a mucosal adjuvant for the following virus proteins: influenza A virus hemagglutinin (HA) and the S1 subunit and S protein of SARS-CoV-2. Furthermore, we analyzed the diameter of the PMB-virus antigen complex, which is a representative physicochemical property for efficient mucosal adjuvanticity [21]. Additionally, we assessed the histology of the nasal cavity, including that of the olfactory bulb, in intranasally immunized mice.…”

Synergistic Antimicrobial Activity by Light or Thermal Treatment and Lauric Arginate: Membrane Damage and Oxidative Stress

“…This evidence suggests that polymyxin B caused lysis of the liposomes based on its surfactant properties and potentially promoted the formation of mixed micelles, whereas LAE did not lyse the liposomes. It is important to note that the concentration of both LAE and polymyxin B is greater than the critical micelle concentrations (21,22). This suggests that LAE binds and potentially inserts itself in a phospholipid membrane, whereas polymyxin B disrupts the bilayer membrane and promotes the formation of mixed micelles.…”