New trends in the use of Al(OH)3-conjugated endotoxins and their subunits from the S- and R-forms of Shigella dysenteriae serovar 1 for model vaccination purposes

Comparison of the rabbit pyrogen test and Limulus amoebocyte lysate (LAL) assay for endotoxin in hepatitis B vaccines and the effect of aluminum hydroxide

The rabbit pyrogen test and Limulus amoebocyte lysate (LAL) assay have been used to detect endotoxins in vaccines, but interactions between the endotoxins and proteins or aluminum hydroxide can interfere with the results. Currently, the rabbit pyrogen test is used to detect endotoxin in hepatitis B (HB) vaccines even though the HB surface protein, the active ingredient, is over-expressed in and purified from eukaryotic cells which lack endotoxin. Therefore, we examined the possibility of replacing the animal tests with the more efficient LAL test. To this end, we determined whether the aluminum hydroxide in the HB vaccines affects the rabbit pyrogen test and the LAL assay. HB vaccines and HB protein solutions spiked with lipopolysaccharide (LPS) produced almost the same dose-dependent temperature rise in rabbits, indicating that the aluminum hydroxide in the HB vaccine does not interfere with the pyrogenic response in rabbit. In contrast, a spike recovery study showed that aluminum hydroxide interfered with the LAL clot and kinetic assays; however, the LAL clot assay was effective at detecting endotoxin without loss of LAL activity after serial dilution of the samples. Furthermore, there was good correlation in the LAL clot assay between the amount of LPS added and the amount recovered. However, both turbidimetric and chromogenic kinetic assays displayed no correlation between the LPS amount added and recovered. Our results suggest that the LAL clot assay is sensitive and reliable when samples are properly prepared, and can be used to replace the rabbit pyrogen test for the detection of endotoxin in HB vaccines.

Detoxification of endotoxin by aluminum hydroxide adjuvant

Langmuir adsorption isotherms of endotoxin and aluminum-containing adjuvants at pH 7.4 and 25 degrees C revealed that aluminum hydroxide adjuvant has a greater adsorption capacity (283 microg/mg Al) and adsorption coefficient (1.3x10(4) ml/miccrog) than aluminum phosphate adjuvant (3.0 microg/mg Al, 0.20 ml/microg). 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 force will be present with aluminum hydroxide adjuvant (iep=11.4), and an electrostatic 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 adjuvant but is inhibited by surface phosphate in aluminum phosphate adjuvant. In-vitro desorption experiments using components of interstitial fluid showed that endotoxin adsorbed by aluminum hydroxide adjuvant was not desorbed by interstitial anions (5 mM phosphate or 2.7 mM citrate) or interstitial proteins (25 mg albumin/ml). The effect of aluminum-containing adjuvants on the systemic response of Sprague-Dawley rats to a 15 microg/kg subcutaneous dose 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 endotoxin and aluminum phosphate adjuvant. No TNF-alpha or IL-6 was detected in the group that received endotoxin and aluminum hydroxide adjuvant. Aluminum hydroxide adjuvant detoxifies endotoxin by adsorbing it in the vaccine and then not releasing it in interstitial fluid upon administration.

Composition of lipid A in the S and R forms of Shigella dysenteriae serovar 1

A chemical analysis was performed of lipid A, isolated by acid hydrolysis of the lipopolysaccharide from the S and R forms of Shigella dysenteriae serovar 1. Differences in the moiety of both lipids and sugars were compared. The lipid portion consisted of a homologous series of fatty acids ranging from C12:0 to C18:0 (predominant homologues, C12:0, C14:0 and C16:0) and the homologous series of 3-hydroxy acids ranging from C12:0 to C16:0 (predominant homologue, 3-OH-C14:0). The major sugar portion consisted of D-glucosamine. The toxicity of lipid A in mice (LD50) ranged between 300-400 micrograms/mouse, and values from the Limulus amebocyte lysate assay were recorded as titres of 10(-5) to 10(-6) mg/ml.