Saponins from Quillaja saponaria Molina: isolation, characterization and ability to form immuno stimulatory complexes (ISCOMs).

ISCOMs have received much attention as vaccine adjuvants due to their immunostimulatory effects. They are colloidal particles typically comprised of phospholipids, cholesterol and Quil A, a crude mixture of saponins extracted from the bark of Quillaja saponaria Molina. We have previously shown that ISCOMs can be prepared by ether injection wherein an ether solution of phospholipids and cholesterol in a mass ratio of 5:2 is injected into a solution of Quil A at a mass ratio of 7 lipids: 3 Quil A. The aim of this study was firstly to isolate and characterise discrete fractions of Quil A and secondly to investigate which of these fractions were able to form ISCOMs by the method of ether injection. Six fractions of Quil A were isolated by semi-preparative reverse phase high performance liquid chromatography (RP-HPLC) and characterised by analytical HPLC, liquid chromatography tandem mass spectrometry (LC-MS) and the qualitative Liebermann-Burchard and Molisch tests for triterpenoids and carbohydrates respectively. ISCOMs were subsequently prepared from the isolated fractions by the method of ether injection and the resulting preparations characterized by photon correlation spectroscopy (PCS) and negative stain transmission electron microscopy (TEM). The molecular weights of the major compounds in the fractions ranged from approximately 1200 to approximately 2300 Da; all fractions tested positive for triterpenoids and saccharides and four of the fractions were identified as QS-7, QS-17, QS-18 and QS-21 by analysis (LC-MS and analytical HPLC). Injection of ether solutions of lipids into aqueous solutions of QS-17, QS-18 or QS-21 all resulted in homogeneous ISCOM dispersions. The combination of lipids and QS-7 by ether injection produced lamellae and liposomes as the prominent structures and a minor amount of ISCOMs. The remaining two hydrophilic, low molecular weight fractions of Quil A did not produce ISCOMs, instead liposomes and helical structures predominated in the samples.

Metal chelation, radical scavenging and inhibition of Aß42 fibrillation by food constituents in relation to Alzheimer's disease.

Various food constituents have been proposed as disease-modifying agents for Alzheimer's disease (AD), due to epidemiological evidence of their beneficial effects, and for their ability to ameliorate factors linked to AD pathogenesis, namely by: chelating iron, copper and zinc; scavenging reactive oxygen species; and suppressing the fibrillation of amyloid-beta peptide (Aß). In this study, nine different food constituents (l-ascorbic acid, caffeic acid, caffeine, curcumin, (-)-epigallocatechin gallate (EGCG), gallic acid, propyl gallate, resveratrol, and α-tocopherol) were investigated for their effects on the above factors, using metal chelation assays, antioxidant assays, and assays of Aß42 fibrillation. An assay method was developed using 5-Br-PAPS to examine the complexation of Zn(II) and Cu(II). EGCG, gallic acid, and curcumin were identified as a multifunctional compounds, however their poor brain uptake might limit their therapeutic effects. The antioxidants l-ascorbic acid and α-tocopherol, with better brain uptake, deserve further investigation for specifically addressing oxidative stress within the AD brain.

Synthesis of cationic derivatives of Quil A and the preparation of cationic immune-stimulating complexes (ISCOMs).

The aim of the study was to prepare cationic ISCOMs using cationic derivatives of the saponin Quil A. The polyamines ethylenediamine, spermidine and spermine were conjugated with the glucuronic acid moiety of Quil A. The aqueous solubility of the derivatives increased with decreasing pH, and the pK(a) values were between 6 and 7. The CMCs of the ionised derivatives were around 0.5-1.0 mg/mL. Using the method of hydration of freeze-dried monophase systems, the interaction of each of the Quil A derivatives with phosphatidylcholine and cholesterol, at a mass ratio of 4:4:2 and a pH of 3 and 7.4, was investigated. A few ISCOM-like structures were present in the systems prepared at pH 7.4, hence the ternary system of Quil A spermine derivative, phosphatidylcholine and cholesterol was further investigated at pH 7.4 using a variety of mass ratios. A relatively high number of cationic ISCOM-like structures were observed at the mass ratio of 6:2:2. These ISCOM-like structures were less homogeneous and more irregular in shape than ISCOMs prepared from unmodified Quil A. Colloidal particles with positive zeta potential were produced and may find application in the delivery of nucleic acids or anionic proteins.