Interactions of Cholesterol with Cyclodextrins in Aqueous Solution

Abstract

. 1,2) Cholesterol also exisits in a buried form in phospholipid bilayer in the biomembrane.1,2) It is suggested that the interactions of cholesterol with phospholipids are based on the hydrophobic interaction. Therefore, it is presumed that cyclodextrins (CDs), cyclic oligosaccharides that have a hydrophobic cavity, interact with cholesterol to form inclusion complexes in aqueous solution. Several studies on the interactions of CDs with cholesterol have been reported. For example, intravenous administration of 2-hydroxypropyl-b-CD (HP-b-CD) in rats leads to a trasient decrease in plasma cholesterol levels.3) This phenomenon is explained as follows: in blood, high cholesterol concentration is available due to the complex formation with HP-b-CD, and this complex can be transported rapidly from the intravascular to the extravascular compartment. In other studies, it has been reported that cholesterol can be extracted from both cell and monolayer membranes by CDs.2,4,5) However, all studies concerning these interactions are qualitative and, to the best of our knowledge, no studies on the thermodynamic parameters of interaction of cholesterol with CDs in aqueous solution have been reported.We therefore investigated the interactions of cholesterol with CDs in aqueous solution quantitatively using the solubility measurement now common in pharmaceutical field, measurement of proton nuclear magnetic resonance ( 1 H-NMR), and Corey-Pauling-Koltun (CPK) atomic models. As CDs, a-CD, b-CD, HP-b-CD, g-CD, and heptakis (2,6-di-Omethyl)-b-CD (DOM-b-CD) were used. a-CD, b-CD, and g-CD contain six, seven, and eight glucopyranose units, respectively. The structure of the CDs is that of a truncated cone with average cavity diameters of 0.57, 0.78 and 0.95 nm for a-CD, b-CD, and g-CD, respectively. These three CDs are less hydrophobic, and HP-b-CD with the same cavity diameter as b-CD is even less hydrophobic. On the other hand, DOM-b-CD has a deeper cavity and is more hydrophobic than b-CD. ExperimentalMaterials a-CD, b-CD, g-CD, and DOM-b-CD, purchased from Nacalai Tesque Co. (Kyoto, Japan) were used after recrystallization from water. HP-b-CD was purchased from Aldrich Chemical Company, Inc. The average degree of the 2-hydroxylpropyl group per b-CD was 5.6. The CDs were dried for 12 h at 110°C in a vacuum before use. Cholesterol purchased from Sigma (St. Louis, MO, U.S.A.) was used without further purification. The water purified with Milli-Q Labo (Ͼ18 MW · cm) was used throughout experiment.Solubility Method (1): Solubility of Cholesterol First, the solubility of cholesterol in water was determined at 10, 25, 37, and 45Ϯ0.05°C. Excess cholesterol was added in L-type test tubes containing water and the test tubes were stoppered. The solutions containing excess cholesterol were shaken 100 times/min for 8 d to achieve the solubilitiy equilibrium. The solution was then filtered through a membrane filter (0.22 mm, PVDF Membrane, IWAKI) (Tokyo, Japan) and the filtrate (100.0 ml) was concentrated completely in rotary evaporater at 40°...

Limited cholesterol depletion causes aggregation of plasma membrane lipid rafts inducing T cell activation

“…MBCD acutely depletes cells of cholesterol by binding cholesterol at a ratio of 2:1 in its hydrophobic cavity [7,8]. Acute cholesterol depletion has been reported to abolish as well as to promote T cell signalling [10,11,31].…”

“…Most frequently, this is achieved using methyl--beta--cyclodextrin (MBCD), which acutely extracts cholesterol from the exoplasmic leaflet of the plasma membrane by harbouring cholesterol in a hydrophobic cavity in a 2:1 ratio [7,8]. We have developed a protocol for progressive cholesterol depletion that does not affect cell viability and have recently demonstrated that MBCD is not, in contrast to the current dogma, specific for lipid raft cholesterol [9].…”

Cholesterol Depletion Using Methyl-β-cyclodextrin

“…The most commonly used method is acute cholesterol depletion using MBCD. Unlike the cholesterol binding agents mentioned above that incorporate into membranes, MBCD has a central cavity able to form a 2:1 complex with cholesterol [9,10]. Inhibition of de novo cholesterol synthesis or growing cells in lipoprotein deficient medium require treatment over days which is plenty of time to allow redistribution of the remaining cholesterol [3].…”

Ultrasonic Relaxation for Complexation Reaction Between β-Cyclodextrin and Butanoic Acid in Aqueous Solution

“…A lot of equilibrium studies have been carried out using UV, NMR, titration calorimetry, and so on in order to determine the stability of complexes formed by hosts and guests [2][3][4][5] .…”