Detoxification of endotoxin by aluminum hydroxide adjuvant

Langmuir adsorption isotherms of endotoxin and aluminum-containing adjuvant s at pH 7.4 and 25 degreesC revealed that aluminum hydroxide adjuvant has a greater adsorption capacity (283 mug/mg Al) and adsorption coefficient (1. 3 x 10(4) ml/mug) than aluminum phosphate adjuvant (3.0 mug/mg Al, 0.20 ml/ mug). The difference in endotoxin adsorption was related to two adsorption mechanisms: electrostatic attraction and covalent bonding. The isoelectric point (iep) of endotoxin is approximately 2. An electrostatic attractive fo rce will be present with aluminum hydroxide adjuvant (iep = 11.4), and an e lectrostatic repulsive force will operate with aluminum phosphate adjuvant (iep = 4.6). Endotoxin contains two phosphate groups in the lipid A portion . Covalent bonding occurs with surface aluminum in aluminum hydroxide adjuv ant but is inhibited by surface phosphate in aluminum phosphate adjuvant. I n-vitro desorption experiments using components of interstitial fluid showe d that endotoxin adsorbed by aluminum hydroxide adjuvant was not desorbed b y interstitial anions (5 mM phosphate or 2.7 mM citrate) or interstitial pr oteins (25 mg albumin/ml). The effect of aluminum-containing adjuvants on t he systemic response of Sprague-Dawley rats to a 15 mug/kg subcutaneous dos e of endotoxin was determined by measuring the serum concentration of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). TNF-alpha and IL-6 were observed in the group which received an endotoxin solution or end otoxin and aluminum phosphate adjuvant. No TNF-alpha or IL-6 was detected i n the group that received endotoxin and aluminum hydroxide adjuvant. Alumin um hydroxide adjuvant detoxifies endotoxin by adsorbing it in the vaccine a nd then not releasing it in interstitial fluid upon administration. (C) 200 1 Elsevier Science Ltd. All rights reserved.