title: NaCl strongly modifies the physicochemical properties of aluminum hydroxide vaccine adjuvants.
abstract: The immunostimulation capacity of most vaccines is enhanced through antigen adsorption on aluminum hydroxide (AH) adjuvants. Varying the adsorption conditions, i.e. pH and ionic strength (I), changes the antigen adsorbed amount and therefore the ability of the vaccine to stimulate the immune system. Vaccine formulations are thus resulting from an empirical screening of the adsorption conditions. This work aims at studying the physicochemical effects of adjusting the ionic strength of commercial AH adjuvant particles suspensions with sodium chloride (NaCl). X-ray photoelectron spectroscopy data show that AH particles surface chemical composition is neither altered by I adjustment with NaCl nor by deposition on gold surfaces. The latter result provides the opportunity to use AH-coated gold surfaces as a platform for advanced surface analysis of adjuvant particles, e.g. by atomic force microscopy (AFM). The morphology of adjuvant particles recovered from native and NaCl-treated AH suspensions, as studied by scanning electron microscopy and AFM, reveals that AH particles aggregation state is significantly altered by NaCl addition. This is further confirmed by nitrogen adsorption experiments: I adjustment to 150mM with NaCl strongly promotes AH particles aggregation leading to a strong decrease of the developed specific surface area. This work thus evidences the effect of NaCl on AH adjuvant structure, which may lead to alteration of formulated vaccines and to misinterpretation of data related to antigen adsorption on adjuvant particles.
authors.affiliation: Université catholique de Louvain, Institute of Condensed Matter and Nanosciences, Bio- and Soft Matter Division, Place Louis Pasteur 1/L4.01.10, 1348 Louvain-la-Neuve, Belgium. Electronic address: jean-francois.art@uclouvain.be.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Art
authors.affiliation: Université catholique de Louvain, Institute of Condensed Matter and Nanosciences, Bio- and Soft Matter Division, Place Louis Pasteur 1/L4.01.10, 1348 Louvain-la-Neuve, Belgium. Electronic address: aurelien.vanderstraeten@uclouvain.be.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Vander Straeten
authors.affiliation: Université catholique de Louvain, Institute of Condensed Matter and Nanosciences, Bio- and Soft Matter Division, Place Louis Pasteur 1/L4.01.10, 1348 Louvain-la-Neuve, Belgium. Electronic address: christine.dupont@uclouvain.be.
authors.forename: Christine C
authors.initials: CC
authors.lastname: Dupont-Gillain
mesh_terms: D000276:Adjuvants, Immunologic / Q000737:chemistry*; D000327:Adsorption; D000536:Aluminum Hydroxide / Q000737:chemistry*; D005612:Freeze Drying; D006046:Gold / Q000737:chemistry; D018625:Microscopy, Atomic Force; D064347:Microscopy, Electrochemical, Scanning; D009584:Nitrogen / Q000737:chemistry; D009994:Osmolar Concentration; D056951:Photoelectron Spectroscopy; D011208:Powders / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry*; D013499:Surface Properties; D013535:Suspensions / Q000737:chemistry*
chemical_list: D000276:Adjuvants, Immunologic; D011208:Powders; D013535:Suspensions; D012965:Sodium Chloride; D000536:Aluminum Hydroxide; D006046:Gold; D009584:Nitrogen
keywords: AFM; Aluminum hydroxide adjuvant; Ionic strength; Sodium chloride; Specific surface area; Vaccine formulation; XPS