WO1984004932A1

WO1984004932A1 - Biochemical detection and/or treatment process

Info

Publication number: WO1984004932A1
Application number: PCT/US1984/000893
Authority: WO
Inventors: Thomas A Horbett; Buddy D Ratner
Original assignee: Washington Res Found
Priority date: 1983-06-10
Filing date: 1984-06-07
Publication date: 1984-12-20
Also published as: AU3062184A; EP0144410A1

Abstract

A membrane carries an enzyme such as glucose oxidase (GLUOX) which promotes conversion of a specific biochemical such as glucose (G) into a nonneutral material such as gluconic acid (-COOH or -COO-) that interacts with another nonneutral material such as an amine (NR2 or HNR2) carried by the membrane to produce fixed charge sites (+) which effects a change in volume and permeability of the membrane. Such change in volume can be measured for indicating the desirability and amount of a therapeutic agent such as insulin (I) to be administered to the body for treating the condition resulting from the presence of the biochemical or an excess or deficiency of the biochemical. Increase in permeability of the membrane can release into the body a therapeutic agent for treating the condition of the body resulting from the presence or increase or decrease in concentration of the specific biochemical.

Description

Biochemical Detection and/or Treatment Process

Technical Field

This invention relates to a process for detecting a specific biochemical in a living body and/or automatically releasing into that body a therapeutic agent in response to presence of the biochemical. Biochemical is used to mean any chemical in the body.

Background Art Prior medical practice has customarily determined the presence of a particular biochemical in the body, such as glucose, by extracorporeal testing of a body liquid sample, such as a blood sample or a urine sample, or by inserting a skin-penetrating detection system, such as a solute-sensitive electrode, for intracorporeal testing. An appropriate therapeutic agent has then been administered to correct for deviations from the desired concentration of the biochemical. Thus, if the biochemical was glucose, insulin has been administered as the therapeutic agent when the concentration was excessive, or glucogon or glucose itself when the glucose concentration was insufficient.

An implant container for insulin and glucose oxidase made of a semipermeable membrane is disclosed in Lossef United States Patent No. 4,364,385, issued December 21, 1982, but the administration of insulin to the blood lags behind the increase in glucose in the blood so as not to be able to stabilize the glucose content of the blood effectively.

Disclosure of the Invention

In accordance with the present invention, a biochemical detection and/or treatment process or material is provided which includes a body implant incorporating a membrane whose permeability can change by swelling or contraction of the membrane. The permeability change could occur in response to a change in the concentration of a biochemical such as glucose. An increase in the concentration of the biochemical which increases the permeability of the membrane will release from a reservoir into the body a therapeutic agent of a character which would not pass through the membrane in contracted condition. When the concentration has been reduced, the membrane will contract promptly to reduce or terminate the supply of therapeutic agent to the body.

The membrane also may be used to detect the presence, or excess or deficiency, of a specific biochemical in the body without the necessity of performing extracorporeal tests on a body fluid or utilizing elaborate electromechanical devices.

Brief Description of the Drawings of the Preferred Embodiment

The invention will be described in connection with the accompanying drawings in which,

Figure 1 is a chart of symbols used in subsequent figures of the drawings, and Figures 2, 3, 4, 5, 6 and 7 are enlarged diagrams illustrating successive conditions of a semipermeable membrane and its environment with reference to successive phases that occur in connection with the present invention.

Best Mode for Carrying Out the Invention

While the present invention can be used in response to the presence or concentration of different specific biochemicals to release different types of therapeutic agents into the body, the following description will describe as a representative application of the invention the presence of an excessive amount of glucose as the specific biochemical in the body and the release into the body of insulin as the therapeutic agent appropriate for treating the condition of the body resulting from the presence of excessive glucose. The following description is of a system in which a semipermeable membrane insoluble in water and nonerodible is swollen by the action of acid on it, although systems might be used which are dependent on the action of a base for effecting a change in volume of the membrane. In either event, the change in volume of the membrane is related to a change in pH of the aqueous environment to which the internal membrane is exposed. In particular, the semipermeable polymer membrane functions as a carrier for a biochemical modifying enzyme and for an ionizable group Where the biochemical of interest is glucose, the biochemical modifying enzyme will be glucose oxidase. The ionizable group immobilized within the polymer membrane may be an amine.

Sequential conditions believed to occur in the system are illustrated by Figures 2 to 7 that can be interpreted by the keys on the chart of Figure 1.

Under the conditions illustrated by Figure 2, the semipermeable membrane is in its contracted condition carrying the glucose oxidase and the amine. The glucose oxidase is entrapped by its covalent combination with the material of the membrane so that it cannot have a deleterious effect on the body or leach from the membrane.

Even in its shrunken condition of Figure 2, the membrane does not serve as a barrier to the diffusion into it of glucose molecules which, as illustrated in Figure 3, can come into contact with the glucose oxidase. Such contact results in the catalytic conversion of glucose to gluconic acid (Figure 4) which also is of a molecular size to permeate freely through the membrane. As indicated in Figure 5, the gluconic acid can donate a proton to the amine groups in the membrane, thereby creating positively-charged sites. It is believed that adjacent positively-charged sites produce electrostatic repulsion which distends the membrane from a condition such as shown in Figure 5 to a condition such as shown in Figure 6. This distension results in the overall swelling of the membrane and an increase in its permeability so that relatively large molecules such as those of insulin can penetrate into and through the membrane, as illustrated in Figure 7.

It will be evident that the higher the concentration of the biochemical glucose in the body, the more glucose will be converted to gluconic acid and the greater will be the number of positively-charged repulsion sites occurring in the membrane. Corresponding to the quantity of such postively charged sites, the internal distension and overall swelling of the membrane will be greater. The increase in volume of the membrane will be related to the increase in glucose concentration and the resultant increase in permeability of the membrane will enable dispensing of insulin through the membrane in response to the concentration of glucose in the body. A specific example of polymer system that can be used for the production of the semipermeable membrane includes amine or carboxylic acid-containing crosslinked copolymer materials based upon monomers from each of the following groups: (a) major membrane component

2-hydroxyethyl methacrylate or aerylate; 2-hydroxypropyl methacrylate or aerylate; N-vinyl pyrrolidone; acrylamide or methacrylamide; other hydrophilic monomers without ionizable groups; (b) crosslinking agent ethylene glycol dimethacrylate; tetramethylene glycol dimethacrylate; N,N methylenebisacrylamide; other difunctional vinyl, acrylic, methacrylic or diisocyanate crosslinkers, (c) amine-containing monomers or acid-containing monomers acrylic or methacrylic acid; N,N dimethylaminoethyl methacrylate; N,N dimethylaminopropyl methacrylate; p-aminostyrene.

One or more substances from groups (a), (b) and (c) are mixed in the presence of an enzyme and polymerized by any of a variety of possible methods to form the primary bioresponsive polymer. The semipermeable membrane suitable for determining the amount of excess glucose concentration in the body and for providing a separation between an insulin reservoir and the body can be made from the monomers 2-hydroxyethyl methacrylate (HEMA), N,N, -dimethylaminoethyl methacrylate (NNDMAEM), and tetraethylene glycol dimethacrylate (TEGDMA). Glucose oxidase (GO) type VII derived from Aspergillus niger (125,000 units per gram solid) can be obtained from Sigma Chemical Co., St. Louis, Missouri, U.S.A. The buffer can be 0.01M citrate, 0.01M phosphate, 0.125M NaCl, 0.02% sodium azide, pH 7.4 (CPBSz). From such monomers semipermeable membranes can be produced by low temperature radiation initiated polymerization. The HEMA, NNDMAEM, TEGDMA and ethylene glycol can be mixed and then added to water containing the enzyme glucose oxidase. The membrane can be formed by pouring such mixture between two glass plates separated by stainless steel shims and the assembly frozen., at -70° C. The frozen assembly can then be irradiated by exposure to 0.25M Rad in a ⁶⁰Co source. After such irradiation, the plates can be separated from the membrane by soaking the assembly in CPBSz in a refrigerator for several days. While the interior structure of the semipermeable membrane will be distended and its overall volume will be swelled by supplying an excess of glucose to it, the structure of the membrane is sufficiently elastic that its internal structure and total volume will contract when the glucose supplied to it is reduced. Correspondingly, while increased quantities of insulin can penetrate the membrane as it is distended by the action of increased amounts of glucose, the opposite result- will also occur, namely, the rate of insulin diffusion through the membrane will decrease because of the contraction of the internal structure of the membrane as the amount of glucose entering the membrane structure is reduced. Preferably, the membrane is of a type that will not dissolve or erode in the solution to which it is exposed so that it will continue to be responsive to the concentration of the biochemical over a long period.

If a supply of insulin is provided within an enclosure or enclosures of semipermeable membrane as a body implant, insulin could be supplied through the semipermeable membrane to the body automatically in response to distension of the membrane structure resulting from an increase in glucose concentration in the body which would provide therapeutic treatment for the body condition resulting from the higher glucose concentration. Alternatively, the overall swelling of the membrane resulting from an increase in glucose concentration in the body could be detected by measuring the amount of swelling, swelling pressure, linear displacement, ultrasonic scanning, changes in ultrasound reflectivity, or changes in light-scattering properties, and such measurements could be used as the basis for determining glucose concentration and for voluntary administration of insulin in appropriate quantity to the body. Such a distensible semipermeable membrane could also be used for automatically treating allergic reactions produced by bee venom in a body. In such case, the therapeutic agent could be an antihistamine bound via biodegradable covalent bonds to a soluble polymer or polymer bound epinephrine which would pass through the semipermeable membrane when its internal structure has been distended by the action of entrapped diamine oxidase or histamine. Ammonia generated from this reaction can cause ionization of membrane groups.

A further application for utilization of a swellable membrane for automatic therapeutic treatment would be to discourage addiction to drugs such as morphine, heroin, cocaine, marijuana and alcohol. For example, in a system to respond to alcohol, the semipermeable membrane used could be an amine-containing polymer which would carry the enzymes, alcohol dehydrogenase and aldehyde dehydrogenase to that the alcohol would be converted into acetic acid which, in the presence of amine groups carried by the membrane, would produce similarly electrostatically charged sites in the interior of the membrane to distend it and consequently increase its permeability. The therapeutic agents which would be released into the body through the distended membrane could be disulfiram which would produce nausea that would deter the desire to administer such drugs to the body in the future.

Another application would be for controlling cholesterol, triglyceride or very low density lipoprotein concentrations in blood. An enzyme from bovine corpus luteum which catalyzes the conversion of cholesterol to isocaproic acid and pregnenolone would be immobilized on the amine-containing polymer. When cholesterol levels were increased, the increased isocaproic acid generated in the membrane would cause it to swell and allow faster release of the therapeutic agent. The therapeutic agent released could be chlorophenoxyisobutyric acid bound to serum albumin which suppresses cholesterol synthesis. Alternatively, heparin would be the therapeutic agent to reduce triglyceride or very low density lipoproteins in the blood.

Claims

1. The process of changing the permeability of a semipermeable membrane in response to the presence of a predetermined biochemical in a solution which comprises forming a semipermeable membrane having immobilized on that membrane an enzyme for promoting conversion of the biochemical into a chemical solute which alters the pH of the solution and thereby effects a change in permeability of the semipermeable membrane when exposed to the biochemical.

2. The process defined in claim 1, in which the enzyme promotes conversion of the biochemical into an acid and the membrane has nonneutral material immobilized within it which interacts with the acid produced from the biochemical to change the permeability of the membrane.

3. The process defined in claim 1, in which the enzyme promotes conversion of the biochemical into nonneutral material and the membrane has nonneutral material which interacts with the material to which the biochemical is converted to distend the internal structure of the membrane.

4. The process defined in claim 1, in which the biochemical is glucose and the permeability of the semipermeable membrane changes in response to a change in concentration of the glucose.

5. The process defined in claim 1, in which the biochemical is glucose, alcchol or venom.

6. The process defined in claim 1, in which a change in pH in one sense effects an increase in permeability of the membrane and a change in pH in the opposite sense effects a reduction in permeability of the membrane.

7. A semipermeable membrane comprising a crosslinked polymer network compound having a major membrane component, a crosslinking agent, an amine- containing monomer or acid-containing monomer, and an enzyme immobilized in said network compound.

8. The semipermeable membrane defined in claim 7, in which the enzyme is glucose oxidase.

9. The semipermeable membrane defined in claim 7, in which the major membrane component is 2-hydroxyethyl methacrylate, 2-hydroxyethyl aerylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl aerylate, N-vinyl pyrrolidone, methacrylamide or acrylamide; the crosslinking agent is ethylene glycol dimethacrylate, tetramethylene glycol dimethacrylate or N,N methylenebisacrylamide; and. the amine-containing monomer or acid- containing monomer is acrylic acid, methacrylic acid, N,N dimethylaminoethyl methacrylate, N,N dimethylaminopropyl methacrylate or p-aminostyrene.

10. A semipermeable membrane comprising a crosslinked polymer network compound of 2-hydroxyethyl methacrylate, N,N dimethylaminoethyl methacrylate and an enzyme immobilized in said network compound.

11. The method of making a semipermeable membrane which comprises crosslinking a major membrane component, an amine-containing monomer or acid-containing monomer and an enzyme by mixing the enzyme, major membrane component and amine-containing monomer or acid-containing monomer in the presence of a crosslinking agent and subjecting the mixture to radiation.

12. The method defined in claim 11, in which the enzyme is glucose oxidase.

13. The method defined in claim 11, in which the major membrane component is 2-hydroxyethyl methacrylate, 2-hydroxyethyl aerylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl aerylate, N-vinyl pyrrolidone, methacrylamide or acrylamide, the amine-containing monomer or acid-containing monomer is acrylic acid, methacrylic acid, N,N dimethylaminoethyl methacrylate, N,N dimethylaminopropyl methacrylate or p-aminostyrene; and the crosslinking agent is ethylene glycol dimethacrylate, tetramethylene glycol dimethacrylate or N,N methylenebisacrylamide.

14. The method of making a semipermeable membrane which comprises crosslinking 2-hydroxyethyl methacrylate, N,N dimethylaminoethyl methacrylate and an enzyme by mixing the enzyme, 2-hydroxyethyl methacrylate and N,N dimethylaminoethyl methacrylate in the presence of tetramethylene glycol dimethacrylate and subjecting the mixture to radiation at a temperature no greater than -70° C.

15. In a body implant for administering a therapeutic agent for treating a body condition resulting from a biochemical in the body, such implant including a membrane reservoir normally confining the therapeutic agent, permeable by the biochemical and of a type the permeability of which changes in response to a change in pH of the solution, the improvement comprising an enzyme carried by the membrane and of a type that promotes conversion of the biochemical into a solute which alters the pH of the solution and nonneutral amine material interactable with the acid produced from the biochemical to change the permeability of the membrane.

16. A process of forming a chemical composition responsive to a predetermined biochemical in aqueous solution which comprises binding to a membrane of a type the permeability of which changes in response to a change in pH of the solution to which the membrane is exposed an enzyme of a type that promotes conversion of the biochemical into a solute which alters the pH of the solution.