Compositions for increasing the image contrast in diagnostic investigations of the digestive tract

Abstract: Suspensions of echogenic particles in aqueous bioadhesive carriers effectively improve imaging by echography of the digestive tract. Affinity of the compositions for the gastric mucosa can be adapted to the needs by appropriately selecting the carrier in function to its inherent bioadhesive capacity.

Description: The present invention concerns innocuous ingestible or enterally administrable compositions which can be used as contrast enhancer media in ultrasonic echography imaging of the gastro-intestinal tract of animal and human patients. Background Art It is well known that echography belongs to investigative diagnosis techniques which enable the direct electronic visualization of internal organs in living beings and is therefore powerful help and guide in prognosis, medical treatment and surgery. These techniques can often advantageously supplement or replace X-ray tomography as well as the use of radio-active tracer compounds which may have obvious undesirable side-effects. It is also well known that contrast echography relies on the administration to patients of dispersions or suspensions of echogenically responsive particles, e.g. microbodies containig air or a gas in a medium, and thereafter, applying ultrasonic waves which become reflected by said microbodies to provide desired echographic signals. In this connection, it has been recognized that air or gas-filled microspheres, e.g. microbubbles or microballoons, suspended in a liquid are exceptionally efficient ultrasound reflectors for echography. In this disclosure the term "microbubble" specifically designates air or gas globules in suspension in a liquid which generally results from the introduction therein of air or a gas in divided form, the liquid preferably also containing surfactants or tensides to control the surface properties and the stability of the bubbles. The term of "microcapsule" or "microballoon" designates preferably air or gas bodies with a material boundary envelope, e.g. a polymer membrane wall. Both microbubbles and microballoons are useful as ultrasonic contrast agents. For instance injecting into the blood-stream of living bodies suspensions of gas microbubbles or microballoons (in the range of 0.5 to 10 µm) in a carrier liquid will strongly reinforce ultrasonic echography imaging, thus aiding in the visualization of internal organs. Imaging of vessels and internal organs can strongly help in medical diagnosis, for instance for the detection of cardiovascular and other diseases. For ultrasonic imaging of the digestive tract, the particulate contrast agents in the form of gas-filled microspheres or particles are usually administered orally or rectally, preferably with a carrier. In Biomaterials 11 (1990), 713-717, M.A. Wheatley et al. have reported the preparation of polymer-coated microspheres by ionotropic gelation of alginate. The reference mentions several techniques to generate the microcapsules; in one case an alginate solution was forced through a needle in an air jet which produced a spray of nascent air filled capsules which were hardened in a bath of 1.2% aqueous CaCl 2 . In a second case involving co-extrusion of gas and liquid, gas bubbles were introduced into nascent capsules by means of a triple-barelled head, i.e. air was injected into a central capillary tube while an alginate solution was forced through a larger tube arranged coaxially with the capillary tube, and sterile air was flown around it through a mantle surrounding the second tube. Also in a third case, gas was trapped in the alginate solution before spraying either by using a homogeneizer or by sonication. The microballoons thus obtained had diameters in the range 30-100 µm. In EP-A-458 745, there are disclosed microcapsules or microballoons of micronic or sub-micronic size, bounded by a polymer membrane, filled with air or a gas and suitable, when in the form of suspensions in a liquid carrier, to be administered to human or animal patients for diagnostic applications, e.g. for the purpose of ultrasonic echography imaging. In these microballoons, the polymer of the membrane is a deformable and resilient interfacially deposited polymer. This polymer is biodegradable and selected from polysaccharides, polyamino-acids, polylactides and polyglycolides and their copolymers, copolymers of lactides and lactones, polypeptides, poly(ortho)esters, polydioxanone, poly-β-aminoketones, polyphosphazenes, polyanhydrides and poly(alkyl-cyanoacrylates). Invention Disclosure The present inventors found that for efficient and selective imaging of portions of the digestive tract, it is advantageous to select carrier phases that have essential particular selective affinity for the gastric mucosa, e.g. carrier phases which can form intestinal linings or coatings on all or selected portions of the internal lumen surfaces. Hence when the carrier phase has special affinity for the gastric and intestinal mucosa, it will tend to stay in immobilized layer form thereon, thus reducing particle mobility and preventing coalescence. This particularly pertains to the incorporation into the carrier phase of echogenic particles, e.g. air or gas-filled microspheres which, upon application of ultrasonic waves, will generate a reflected signal which permits visualizing by echography selected portions of the digestive tract or bladder. The foregoing findings form the basis of the present invention as recited below and in the annexed claims, i.e. the invention mainly concerns diagnostic compositions to be used as contrast enhancing agents in the ultrasound imaging of portions of the digestive tract of humans and animals, said compositions comprising ultrasonically responsive particles, in admixture with, or chemically bonded to, at least one physiologically acceptable carrier phase The said carrier phase is substantially water insoluble, although swellable by hydration and gel forming, and, when hydrated, has differential affinity for the gastrointestinal mucosa, i.e. it adheres preferably to some areas thereof, thus forming luminal linings or coatings having specific echogenic contrast response patterns which enable improved visualization of specific portions of the oeso-gastro-duodenal tract. Carrier phases having affinity for the membrane mucosa of the digestive tract (bioadhesive carriers) can include most luminal coating materials in use for treatment, protection of medication of gastro-intestinal regions including, for instance, adhesives containing bismuth oxide, aluminium oxide and various clays such as montmorillonite and attapulgite designed for luminal applications. These materials also include cross-linked polymers such as polysiloxanes (Dimethicone®), magnesium and other metals alginates, bioadhesive pectins and carbohydrates polysubstituted with groups such as sulfate, phosphate, sulfonate and phosphonate. One convenient polysulfated carbohydrate is sucrose octasulfate (also named sucralfate). These carriers have the general property to get hydrated with water and form therewith substantially insoluble gels which strongly adhere to the membrane mucosa. Depending on the selected carrier phase, the compositions of the invention can be made to have controllable transit time through the gastro-intestinal tract and particular adhesion to selected portions thereof, thus enabling efficient imaging selected organs. The carrier phase of the present composition can also contain water-soluble polymers which can form homogeneous solutions in aqueous media, in which case the proportion of signal generating particles therein preferably not exceeds 10% by weight of solution, more preferable 5%, for optimalized stability against coalescence. The polymers which are convenient are for instance dextran, polyvinyl-pyrrolidone (PVP), carboxymethyl-cellulose (CMC) and the like. Although the compositions with water-soluble polymers have no recognized specific affinity for the internal mucosa membrane of the digestive tract, they are useful for controlling the transit therethrough of the echogenic particles, either alone or when preferably used in association with bioadhesive carrier phases. Normally, the compositions using polymers carriers having no or little bioadhesion will permit faster transit than the compositions using carriers with strong bioadhesive character, hence controlled transit can be achieved with compositions in which non-bioadhesive and bioadhesive carriers are admixed in suitable proportions. It has also been surprisingly found that the particular selection of carriers used in the compositions of the invention, i.e. the carriers with enhanced affinity for mucosa membranes at low pH and/or soluble carriers with high dispersive capacity for echogenic particles provide excellent luminal imaging homogeneity. One preferred type of bioadhesive polymers to be used as the carrier phase in this invention is a polymer or copolymer of acrylic acid containing a proportion of other monomers (generally di- or polyfunctional allyl ethers or acrylates) to impart a degree of water-insolubility and swelling capacity to form gels. Suitable polymers of this type are available on the market under the names of Carbopol® or Polycarbophil®, for instance from the Goodrich Company. Other suitable polymers of comparable type are disclosed in EP-A-0 309 404 (included for reference) and comprise copolymers of acrylic acid with allyl ethers of glycols or sugars. Upon addition of water these polymers will form viscous dispersions of microgels which have strong affinity for internal mucous membranes. Furthermore, the gelling and swelling properties of such polymers are pH dependent; hence the volume, bulk and adhesive properties of the carrier can be controlled by adjusting the pH to a desired value. The present ingestible ultrasound contrast compositions are stable even at pH 1 and this is another advantage over similar products of the prior art. Bioadhesivity is particularly effective under acid or near neutral conditions; at high pH the bioadhesivity is decreased and may become negligible. Hence control of bioadhesivity by pH control is another asset of the present invention. For manufacturing the contrast compositions according to the invention one usually admixes the signal generating particles with the carrier phase. The echogenic particles in the compositions will preferably be in the form of air- or gas-filled microspheres bounded by a material envelope, e.g. a polymer membrane. The obtention of such echogenic particles is disclosed in many references including EP-A-0 458 745. The microballoons whose preparation is disclosed in this reference have a soft and resilient membrane envelope and are convenient as echogenic particles in the present invention as they resist pressure variations due to peristaltic movements in the bowels. Notwithstanding, other types of ultrasonic echogenerating particles can be used as well, e.g. those disclosed in the following documents: WO-A-91/12 823, EP-A-0 327 490, EP-A-0 324 938. In an embodiment for preparing the compositions of the invention, the particles are chemically bonded to the carrier phase by the use of either reactive functions of the carrier itself or of a coupler grafted to the particles, said coupler possessing also functions which will bind to the carrier. For instance, the coupler can be a silane which will bind to the particles by silanation (see EP-A-0 125 995) and which bears a function which may subsequently react with the carrier phase. For example, a useful function of the silane coupler can be an amine group which can further react with negative groups on the carrier material, e.g. COOH or SOH, sulfate or sulfonate groups, to form ammonium salts. Preferably, if the carrier is an organic polymer obtained by polymerization of one or more monomers, the silane coupler can comprise functions that will copolymerize with said one or more monomers. Thus for instance, in the case the carrier phase comprises a polymer or copolymer of acrylic acid, this can be prepared by copolymerizing a mixture of acrylic acid (and optionally other olefinic monomers) and echogenic particles carrying grafted thereon silanes with substituents bearing functions copolymerizable with acrylic acid. An appropriate silane for achieving this is trimethoxy-hydroxypropyl acrylate or methacrylate which possesses a double bond copolymerizable with other acrylates. The grafting technique is disclosed for instance in EP-A-0 113 367 and EP-A-0 125 995. For using the present compositions as an echogenic contrast agent in the study of the digestive tract, the compositions (when stored dry) are admixed with an aqueous phase suitable for oral administration in order to provide a gel which will adhere to a predetermined extent to the mucous membrane of the digestive tract and therefore will carry the particles through said tract to the portion thereof to be visualized. The rate of transfer and the transit time can be adapted by properly selecting the nature and degree of bioadhesion of the carrier phase. For this, variable proportions of contrast compositions including water-soluble carrier polymer can be admixed with the bioadhesive carrier, these proportions being selected to reach up to 99% by weight or more in the case where little restricted transit, unrestricted transit or accelerated transit is desired. For instance, for investigations using mainly dextran as the carrier phase gave a transit rate in rats similar to that observed with no carrier, while using mainly CMC as carrier gave accelerated transit. Using Carbopol® as the carrier phase gave strongly retarded transit, particularly in the duodenum portion of the intestinal tract. The present contrast compositions may also advantageously comprise isoosmolarity agents which minimize loss or gain of water during intestinal transit, i.e. diffusion by osmosis; such agents may comprise carbohydrates such as sorbitol, mannitol, xylitol and the like. During transit time, the patient having received a dose of the present compositions as echogenic contrast agent is subjected to periodical or continuous investigations using conventional echography, whereby the obtained processed images can thereafter be used for diagnostic or other medical applications. The invention is now illustrated by the following practical example. Example A suspension of echogenic microballoons was prepared as described in Example 4 of reference EP-A-0 458 745 using poly-L-lactic acid (commercially available under the name of Resomer® R-207 from Boehringer Ingelheim, Germany). There was obtained a suspension microballoons in distilled water (concentration 10 9 /ml; average size 5.2 mm). On the other hand, an aqueous suspension of gelled bioadhesive polymer was prepared by dispersing 1% by weight of Carbopol® resin (Goodrich Company) in water. The pH of this suspension was brought to 13 with concentrated NaOH and to 100 ml of the alkalinized solution were added 10 ml of the aforementioned microballoon suspension. After homogenizing the mixture under agitation, a quantity of ethanol was added sufficient to precipitate the solids; the polymer was drained on a filter under suction, washed with alcohol and dried under vacuum. The dry powder was then resuspended in 100 ml of a 0.3 M mannitol aqueous solution and the pH adjusted to 3 - 4 with HCl. This suspension was used to carry out echographic imaging experiments in-vivo: Laboratory rats were starved for 24 hrs before administration, then they were anesthesized with "Urethane" (1.4 g/kg) and a sample of the contrast suspension was administerd intragastrally in 10 sec (6.5 ml/rat). The imaging measurments were effected using an Acuson 128-XP/5 apparatus (ACUSON Corp. USA). Immediately after administration, there was observed a dilatation of the stomach the image of which became entirely white in the two-dimensional imaging mode. In the color Doppler imaging mode, the stomach area showed multiple colors (iridescent yellow-red, blue-green) indicating that the scatterers were in motion. Ten minutes later, imaging of the upper part of the intestine (duodenum) showed a similar colored patterns which indicated that composition containing the reflector microballoons was moving down in the intestinal tract. Expanded bowel loops could be distinguished very clearly and the presence of possible abnomalities could be spotted easily. The spleen was also easily identified. If in the present example there is used a suspension of microbubbles, for instance that disclosed in WO-A-91/15244, comparable results were noted.

Claims: Administrable composition for enhancing contrast in the ultrasound imaging of the digestive tract of patients, comprising a physiologically acceptable carrier phase in admixture with or chemically bonded to contrast enhancing ultrasonically responsive particles, characterized in that said carrier phase comprises water-insoluble, water-swellable, gel-forming bioadhesive luminal coating materials, and optionally water-soluble non-bioadhesive polymers, said composition having controllable transit time through the GI-tract and adhesion to selected portions thereof, thus forming luminal linings or coatings having specific imaging contrast response enabling improved visualization of the oeso-gastro-duodenal tract. The composition of claim 1, in which the carrier phase comprises bioadhesive pectins or carbohydrates substituted with groups selected from one or more of carboxy, sulfate, sulfonate, phosphate and phosphonate, these groups being either free or in the form of salts with alkali or alkaline-earth metals. The composition of claim 1, wherein the carrier phase comprises polymers and copolymers of acrylic acid cross-linked with polyfunctional allyl acrylates or polyfunctional allyl ethers of glycols and sugars The composition of claim 1, in which the carrier phase comprises luminal coating compounds selected from magnesium alginate, pectin, hydroxylated polysaccharides, attapulgite and montmorillonite clays. The composition of claim 1, in which the contrast enhancing particles are dispersed in an aqueous solution of one or more of said water-soluble non-bioadhesive polymers, the amount of said particles relative to said water-soluble polymer, measured dry, not exceeding 5%. The composition of claim 5, in which the water-soluble polymer is selected from dextran, polyvinyl-pyrrolidone (PVP), carboxymethyl-cellulose (CMC), hydroxypropyl-cellulose and other water-soluble non-metabolizable polymers. The composition of claim 1, in which the ultrasound responsive particles are air- or gas-filled microspheres bounded by a polymer envelope. The composition of claim 7, in which the microsphere envelope is of poly-L-lactic acid. The composition of claim 1, in which the particles are chemically bonded to the bioadhesive carrier material by means of reactive functions of the carrier and of the particles. The composition of claim 1, in which the particles are chemically bonded to the bioadhesive carrier material by means of a chemical coupler having at least two reactive functions, one of which binds to the particles and another binds to the carrier The composition of claim 10, in which the particles are magnetic and one reactive function of the coupler is a trialkoxysilane function which binds to the particles with formation of a silicon-containing bond. The composition of claim 10, in which the carrier is a polymer or copolymer of acrylic acid and, optionally other olefinic monomers, and in which said another function of the coupler comprises an ethylenically unsaturated double bond copolymerized with said polymer or copolymer of acrylic acid. A method for manufacturing ingestible compositions to be used as contrast enhancing agents in the ultrasonic imaging of the digestive tract of humans and animals, said compositions comprising echogenically responsive particles bound to a carrier phase consisting of a water-insoluble mineral or organic substrate, characterized in selecting a coupler with at least two reactive functions, grafting the coupler to the particles through one of said reactive functions and binding said grafted particles to said carrier phase through another of said reactive functions. The method of claim 13, in which the organic substrate is a polymer or copolymer of acrylic acid and, optionally, other copolymerizable monomers, characterized in copolymerizing said acrylic acid with said grafted particles, said other reactive function of the coupler having a double bond becoming then copolymerized with the acrylic acid. The use of bioadhesive copolymers of acrylic acid and polyfunctional allyl ethers as a carrier phase of echogenically responsive particles in the ultrasound imaging of the GI-tract. The use of bioadhesive copolymers of acrylic acid and polyfunctional allyl ethers in the manufacture of echogenic contrast agents for imaging the GI-tract.

Inventors: CAVAGNA FRIEDRICH, HYACINTHE ROLAND, TOURNIER HERVE, CAVAGNA, FRIEDRICH, HYACINTHE, ROLAND, TOURNIER, HERVE, Tournier, Hervé 
Applicants: BRACCO INT BV, BRACCO INTERNATIONAL B.V.
Application year: 1992
Main classification: A61K49
IPC codes: A61K49, G01R33, A61K47