CA2082388A1

CA2082388A1 - Cholesterol removal

Info

Publication number: CA2082388A1
Application number: CA002082388A
Authority: CA
Inventors: David George Oakenfull; Gurcharn Singh Sidhu; Michael Laurence Rooney
Original assignee: Individual
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 1990-05-08
Filing date: 1990-10-12
Publication date: 1991-11-09
Also published as: EP0527735A1; JPH05505932A; EP0527735A4; WO1991016824A1

Abstract

Cholesterol is removed from organic or biological substances such as milk and dairy products. Removal is carried out by contacting the substance with cyclodextrin which has been bound to an inert support. In order to reduce risk of spoilage the temperature may be maintained below 18 ·C during cholesterol removal. The cyclodextrin is regenerated by elution of the adsorbed cholesterol using acetic acid or mixtures of butanol and acetic acid as the eluant.

Description

~ ~91/168~ 1 PCTtAUg0t~90 C~OLESTEROL REMOVAL

Technical Field This invention concerns a method for removing cholesterol from organic or biological materials, such as lipid containing foodstuffs of animal origin, and especially from milk and dairy products.

Backaround Art It is widely accepted that serious health ri ~k.s ~ttach to hiah plasma cholesterol levels. In Australia, coronary heart disease is responsible for more than 50,000 deaths every year, and death from coronary heart disease is twice as frequent as death from cancer. Dairy products, in particular, are perceived as contributing significantly to dietary cholesterol - butterfat, for example, contains approximately 3mg cholesterol per gram, and consequently there is considerable interest internationally in reducing the cholesterol level of dairy products.

Disclosure of Invention This invention is based on the fact that certain steroids or triterpenes and cyclodextrins, have an affinity for cholesterol and bile acids, and we have showll that sucll agents on binding to selected solid supports form very effective and convenient adsorbents for cholesterol.

Accordingly, this invention provides a method for removlng cholesterol from organic or biological substances of animal origin wherein such substances are contacted, in emulsion form, with a cholesterol, adsorbent comprising a steroid, a WO91/168~, 2 PCT/AU90/00490 8~3 8~ triterpene or a cyclodextrin and/or mixtures thereof chemically bonded to a support.

In instances where the biological material is not in emulsion form it should be dispersed in a suitable liquid to form an 05 emulsion prior to contacting with the adsorbent. However biological materials already in such form, such as milk or cream, may be contacted directly with the adsorbent without any pre-treatment.

The term "emulsion" as used herein is intended to include miscellar solutions or cholesterol-containing fat associated with protein zc in lipoproteins.

Typical steroids for use in the practise of this invention include diosgenin, digitonin and tomatidine, and a particularly preferred compound is diosgenin. Suitable triterpenes are medicagenic acid and hederagenin.
Cyclodextrins include ~, ~- and ~-cyclodextrin, or their modified forms.

Suitable support materials will:
, .
i) not significantly impair the cholesterol affinity of the aforesaid steroids etc;
25 ii) be essentially inert to cholesterol and other components of the material to be treated;
iii) bind to the steroid etc in such a way that the bond is, not readily disrupted by processes for separation of cholesterol from the adsorbent.

Silica has proved to be a suitable support material.
Examples of other materials include, polystyrene, polymethylmethacrylate and cellulose.

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WOgltl68~ ~3~ P ~ ~ ~ ~ 0 The adsorbent may itself be the support if it can be presented in the form of relatively insoluble particles. This may be achieved by bonding the adsorbent to itself in such a way as to have active groups on the surface of the particles. The adsorbent may be cross linked to promote insolubility.

A further advantageous feature of the aforementioned adsorbents is that they can readily and economically be regenerated for further use by washing with solvents, such as acetic acid, or mixtures of butanol and acetic acid, which remove the cholesterol.

Surprisingly it has been found that adsorbents usod in the method of the invention can work quite effectively at lower temperatures even though the conventional method would suggest that higher temperatures should be re~uired to obtain a satisfactory degree and ratio of adsorption. The cholesterol containing fats in many biological materials are solid at low temperature. It is therefore to be expected that the solid fats will reduce the rate of adsorption of cholesterol by the adsorbent in comparison with the liquid form of the fats at higher temperatures. It is believed that the size of cholesterol containing globules of fats in the emulsions is a factor in ensuring that a satisfactory adsorption rate is realised. ~len the fat globules are very small, as in the case of milk, the cholesterol tends to accumulate at the surface of the globules with the result that it can readily ..
transfer to the adsorbent even though the fat globules are solid. ' The low temperature capability of a preferred method of the invention is particularly useful in relation to biological materials, such as with milk or cream, which spoil if they are not chilled.

208~3~8 P~/~U90/~490 ~

Thus in a preferred aspect of the invention the temperature at which the absorption is carried out is below 18C. More preferably a temperature range of 0 to 8C is appropriate.
Where such low adsorption temperatures are used it i5 preferred that the fats in the emulsior. be of sufficiently 05 small size to ensure that at least 30% of the cholesterol is adsorbed within 20 minutes of being contacted with the adsorbent.

The average time the biological material will need to be in contact with the adsorbent to achieve an effective degree of adsorption will vary, depending~ on a number of factors, such as, ~uantity of adsGrbent ma,erial- and nature of tlle biological material being treated. However, generally speaking an average contact period of from 1/2 to 20 minutes more preferably 2 to 20 minutes will give satisfactory results.

In order to ensure a high level of adsorption, the molar ratio of adsorbent to cholesterol in the biological material should not be lower than 0.5, more preferably it should exceed 50.
The ratio may be such as to ensure removal of at least 35% of the cholesterol in the biological material, more preferably 60%.

In one fcrm, a process according to this invention will involve the following steps:-i) where necessary, rendering the material to be treated to liquid form, eg by dispersion in a solvent or emulsion, 30 ii) bringing the liquid material into intimate contact with the adsorbent, eg by flow through a column packed with the adsorbent, or by agitation with the adsorbent, iii) separating the cholesterol-reduced material from the adsorbent, .

: . . . , . .

~091/168~ ~5~ PCT/AU90/00490 2Q82~
iv) regenerating the ads~rbent by elution of the adsorbed cholesterol.

The invention also covers biological materials which have been reduced in cholesterol in accordance witll the method of the 05 invention, Best Modes for CarrVina Out the Invention The invention will now be described with reference to the following examples:

E~ample 1 Butterfat containing cholesterol isotopically labelled with 14C was dissolved in hexane and passed through a column packed with a steroid, (25R)-spirost-5en-38-ol (C27H423)' covalently linked to silica. The radioactivity from the labelled cholesterol was reduced by 42.6% as shown in Table 1.

TABLE 1 - Removal of cholesterol from butterfat by (25R)-spirost-Sen-38-ol ( 27H423) covalently linked to silica.

Activity of ,labelled cholesterol (DPM) . . .
Untreated butterfat 4440 Butterfat after passage through column 2550 Material recovered from column by extraction with acetic acid 1884 Chemical estimation of cholesterol in these samples further confirmed that cholesterol had been removed from the Butter,fat.

.,~ . ~ , . , -.. :, . . . .

WO91/168~ 6 PCT~AU90/0~90 2o82388 EXAMPLE 2 , Cholesterol labelled with 14C was emulsified by using a sonicator with oleic acid, nomo-olein and ta~lrocholic acid in phosphate buffer (pH7.0). This emulsioll was shaken with 05 (25R)-spirost-5en-38-ol ( 27H423) bollded to silica gel. The adsorbent removed 82% of the cl-olesterol from the emulsion. (As shown in Table 2.) Ordinary, untreated silica had no significant effect on the cholesterol content of the emulsion.

TABLE 2. Removal of cholesterol from an emulsion by the (25R)-spirost-5en-38-ol ( 27H42-3) ccvalQntly linked to silica.
., Activity of labelled cholesterol (DPM) , . . .
Untreated emulsion 455 After exposure to untreated silica 449 20 After exposure to the steroid linked to silica 80 Measurement of Cholesterol Adsorption In examples 3 to 6 standard emulsions containing 3H-labelled cholesterol were used for routine screenill~ of adsorbents.
The emulsions were prepared in isotonic phosphate buffer and contained 14C-labelled Cr-EDTA added to provide a means of monitoring any uptake of water by the adsorbent. Two emulsions were used:

"Weak emulsion" ~WE) containing cholesterol (O.l mM), oleic acid (1.2 mM), monolein (6.0 mM) and sodium taurocholare (10.0 mM).

: ~, . - . :
:: . . . . . ~

~.WO91/1~8~ PCT/AU90/00490 * "Strong emulsion" (SE) containing cholesterol (0.25 mM), oleic acid (1.2 mM~, monolein (6.0 mM) and sodium taurocholate (lO.O mM). (The same cholesterol concentration as milk) Cvclodextrins and Sa~oqenins Attached to Solid Supports . .
A variety of solid adsorbents can be prepared. The choice of chemistry for the attachment procedure will depend on the nature of the solid support.
.
It is obviously essential not to destroy in the attachment process the ability of the cyclodextrin or saponin to form a stable complex with cholesterol. (e.g. the cyclodextrin cavity can easily be closed and rendered inaccessible to cholesterol.) Adsorption of cholesterol was determined by shaking 4 ml of milk or emulsion with (typically) O.1 g of the solid adsorbent.
(1) Silica ~
~' ~-cyclodextrin: Silicic acid (lO g) and glycido~.ypropyltrimethoxysilane (30 g) were made into a slurry with dry dimethyl formamide (600 ml). Dry ~-cyclodextrin (30 g) was dissolved in dry dimethyl formamide (375 ml) and sodium hydride (9 g) added with stirring, allowed to react for 15 min. and the solution filtered, taking precautions to exclude water. The slurry and the solution were mixed and then refluxed under dry conditions for 4 hours. The solid product ~ ~
was collected by filtration and washed with dimethyl :
formamide, methanol and water. The product was finally -~
`

W091/168~ -8- PCT/AU~/OW90 ~ ' 2 ~ 8 dried with gentle heat under vacuum. The effectiveness of the product is shown in Table 3.

TABLE 3. Adsorption of cholesterol from emulsion or milk by ~-cyclodextrin attached to silica.
Adsorbent Emulsion % Cholesterol Support Removed __ Coarse silicaaa WE 82 Fine Silica b WE 80 Coarse silica M 85 a 0.1 g adsorbent with 4 ml emulsion - coars silica particle size 70-230~ diameter - fine silica has a surface area of 200+ 3om2 per gram.
b lg adsorbent wites lOml milk.

Diosqenin: the procedure for attachment was the same as that described for cyclodextrin. Butterfat containing 14C-labelled cholesterol was passed through a column packed with the adsorbent. The results are shown in Table 4.

TABLE 4 Adsorption of cholesterol from butterfat by diosgenin attached to silica.

Adsorbent Emulsion % Cholesterol Support Removed Coarse silica Butterfat 42.6 . . . _ Polymethylmethacrylate B-cyclodextrin: Polymethylmethacrylate (4.1 g) was dissolved in pyridine (100 ml) and .~.,.~ . . . . . . . . . .

;, ' ': , ~-; - ,; . ~ . ~ .

~ 091/l68~ _9_ PCT/AU90/0~90 ~'` 2~823~8 .i ~-cyclodextrin (3.25 g) was added and dissolved. To this was added 1 ml of a methanolic solution of sodium methoxide (200 g/l) and the mixture refluxed for 30 min. The solid product that formed was filtered, washed with water and dried under vacuum.

TABLE 5 Adsorption of cholesterol from emulsion or milk by ~-cyclodextrin attached to polymethylmethacrylate.

10 Adsorbent Emulsion/Milk% Cholesterol Support (SE or WE~ (M)Removed Polymethyl WEa 91 methylacrylate SEb 97 aO.l of adsorbent added to 4.0 ml emulsion and held at 20 for 15 min. b0.1 g adsorbent added to 3.0 ml.
milk.

EXAM~LE 6 CROSS-LINKED ADSORBENTS
Tomatine: Tomatine (1 g) was dissolved in dry dimethyl formamide (5 ml) and sodium hydride (0.5 g) added. The reaction was allowed to proceed for 10 min.
Epichlorohydrin (20 ml) was then added and the solution heated at 120 for 4 hour. The excess epichlorohydrin was removed by distillation. The solid precipitate thus obtained was washed with dimethyl formamide and ethanol and dried under vacuum.

~-cyclodextrin: B-cyclodextrin (5 g) was wetted with water ( 2ml) and dissolved in 50% aqueous sodium hydroxide ~6ml). Epichlorohydrin (50ml) was added and allowed to react at room temperature (ca 20) for : ~ - . : - - . ., .............................. :
.. .... , . . .. . `
:,~ . . : . .: ~ . :: :
,:.. -:: .:: , . .... . . . . . . . .

WO91/168~ -10- PCT/AU90/00490 ~
2o823~8 12hr. The solid product was washed with methanol, hot water and cold water.

TABLE 6 Adsorption of cholesterol from emulsion or milk by cross-linked tomatine or B-cyclodextrin.

_ _ Adsorbant Emulsion/Milk % Cholesterol (SE) (M) Removed Tomatine SE' 30 10 B-cyclodextrin SE 75 B-Cyclodextrin Linked to Diosgenin Diosgenin (3g) was dissolved in pyridine (25ml) and acidified 15 with sulphuric acid to approximately pH=4. Cyclodextrin `~
(8.2g) in pyridine (75ml) was added at 85C with stirring over 15 minutes. After 45 minutes, the mixture was poured into water (600ml). The solid product was collected by filtration and washed with water, followed by acetone.

TABLE 7 Adsorption of cholesterol from emulsion by ~-cyclodextrin linked to diosgenin.

.
25 Adsorbent Emulsion % Cholesterol `
Removed B-cyclodextrin linked to WE 57 diosgenin i... .

~ .' . - :-: ~ ::' :. :::` :: :

WO9l/168~ -11- PCT/AU90/00490 2~8238~

In addition to their value in the treatment of cholesterol-containing foodstuffs, it is envisaged that adsorbents according to this invention might form the basis of 05 pharmaceutical products or dietary supplements for reducing intestinal absorption of cholesterol or bile acids.

Also, the adsorbents of this invention might be used to extract cholesterol and bile acids from source material, such as bile (an abattoir waste). The adsorbed cholesterol or bile acids could then be selectively released by washing with suitable so'vents, and used as precursors for the synthesis of steroid-based drugs.

Claims

C L A I M S

The claims defining the invention are as follows:

1. A method for removing cholesterol from organic or biological substances wherein such substances are contacted in emulsion form, with a cholesterol adsorbent comprising a steroid, a triterpene or a cyclodextrin, and/or mixtures thereof, chemically bonded to a support.

2. A method according to claim 1 wherein the organic or biological material is milk, or modified milk, or cream.

3. A method according to claim 1 or claim 2 wherein the molar ratio of the adsorbent to cholesterol in the emulsion is at least 0.5.

4. A method according to claim 3 wherein the molar ratio is at least 50

5. A method according to any one of the preceding claims wherein the emulsion is at a temperature below 18°C
when it is contacted with the adsorbent.

6. A method according to claim 5 wherein the temperature is within the range 0°C to 8°C.

7. A method according to claim 5 or claim 6 wherein the emulsion comprises fat globules containing cholesterol and the size of the fat globules is reduced where necessary to ensure that at least 30% of the cholesterol is adsorbed within 20 minutes of being contacted with the adsorbent.

8. A method according to any one of the preceding claims wherein the contact time lies within the range 0.5 to 20 minutes.

9. A method according to claim 8 wherein the contact time is 2 to 10 minutes.

10. A method according to any one of the preceding claims wherein the emulsion is contacted with the adsorbent by flowing the emulsion through a column packed with adsorbent, or by agitation with the adsorbent, the cholesterol reduced emulsion is separated from the adsorbent and the adsorbent is regenerated by elution of the adsorbed cholesterol.

11. A method according to claim 10 wherein the elution is carried out using acetic acid or mixtures of butanol and acetic acid as the eluant.

12. A method according to any one of the preceding claims wherein the support is silica, polystyrene, cellulose or mixtures thereof.

13. Organic or biological materials having reduced cholesterol levels as a result of being treated in accordance with the method of any one of claims 1 to 12.