Hydrogel for body weight management

Abstract

A hydrogel comprising sodium carboxymethylcellulose cross-linked with a mixture of citric acid and a second cross-linker, selected from a standard amino acid, L-carnitine, N,N,N-trimethylglycine and choline and a pharmaceutically acceptable choline salt, a process for the production of the hydrogel, and its use in the body weight management.

Description

[0001] HYDROGEL FOR BODY WEIGHT MANAGEMENT

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of water-absorbent polymeric networks and more specifically, to hydrogels which can be used in weight management.

[0004] BACKGROUND OF THE INVENTION

[0005] Obesity is a chronic health condition characterized by excessive body fat accumulation, often leading to serious health risks such as heart disease, diabetes, and joint problems. Therapeutic approaches for obesity involve a combination of lifestyle modifications and medical treatments, such as diet and nutrition, physical activity, medications and bariatric surgery, tailored to individual needs and health conditions.

[0006] Weight management plays a vital role in pursuing a healthier lifestyle and improved well-being. Although surgical interventions and medications are available, non-invasive options like over-the-counter supplements and prescription medications are limited, encompassing effectiveness variability, potential side effects, limited long-term sustainability, and the potential for interactions with other medications or health conditions.

[0007] Hydrogels are three-dimensional, water-absorbent polymeric networks with a soft and flexible structure, capable of retaining a large amount of water or biological fluids. They find wide applications in biomedical engineering, drug delivery systems, wound dressings, and tissue engineering due to their biocompatibility and tunable properties.

[0008] In the market, there are hydrogel capsules designed to assist with weight management. These hydrogel capsules do not have a pharmacological effect but instead function mechanically within the gastrointestinal tract. When swallowed, these capsules are dissolved in the stomach and release hydrogel particles that can absorb water, for example, up to 100 times their original weight. Once fully hydrated, these individual particles aggregate, taking up approximately one-quarter of the average stomach volume. As they mix with food, they increase volume and enhance elasticity and viscosity in both the stomach and small intestine. This, in turn, promotes a feeling of satiety and fullness. These satiety inducing particles pass through the digestive system while maintaining their three-dimensional structure in the stomach and small intestine, eventually breaking down in the colon. Subsequently, water is released and reabsorbed by the body, and the hydrogel particles are excreted through normal bowel movements.

[0009] W02009021701 discloses a method for the production of a polymer hydrogel. This method involves cross-linking a hydrophilic polymer precursor, optionally combined with another hydrophilic polymer, using a polycarboxylic acid as the cross-linking agent. The document emphasizes the cross-linking of soluble cellulose derivatives with citric acid.

[0010] WO2012170682 discloses a method for producing a polymer hydrogel. The method involves several steps, including preparing an aqueous solution of a hydrophilic polymer and a polycarboxylic acid, optionally agitating the solution, isolating a hydrophilic polymer / polycarboxylic acid composite from the solution, and heating the composite at a temperature of at least about 80°C to cross-link the polymer with the polycarboxylic acid.

[0011] SUMMARY OF THE INVENTION

[0012] The present invention provides a hydrogel product with swelling capacity, which is significantly improved, compared to the swelling capacity of the hydrogels of the prior art.

[0013] The hydrogel of the present invention comprises sodium carboxymethylcellulose, which is cross-linked with a mixture of citric acid and a second cross-linker, wherein the second cross-linker is selected from the group consisting of a standard amino acid, L-carnitine, N,N,N-trimethylglycine and choline and a pharmaceutically acceptable choline salt.

[0014] The hydrogel of the present invention provides enhanced effectiveness in obesity treatment, upgraded patient compliance, and user-friendly application.

[0015] The present invention provides also a process for the preparation of a hydrogel as defined above.

[0016] Furthermore, the present invention provides a hydrogel as defined above for use in the treatment of obesity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 shows an FTIR spectrum of sodium CMC, citric acid, L-carnitine, and a hydrogel according to the present invention.

[0018] DETAILED DESCRIPTION OF THE INVENTION

[0019] The present inventors have found that a mixture of citric acid (CA), with another crosslinker can be used for the preparation of carboxymethylcellulose superabsorbent hydrogels (SAH) with excellent swelling properties.

[0020] Thus, the present Invention provides a hydrogel comprising sodium carboxymethylcellulose, which is cross-linked with a mixture of citric acid and a second cross-linker, wherein the second cross-linker is selected from the group consisting of a standard amino acid, L-carnitine, N,N,N-trimethylglycine, choline and a pharmaceutically acceptable choline salt.

[0021] The hydrogel of the present invention is a polymer hydrogel of sodium carboxymethylcellulose. Carboxymethyl cellulose (CMC) is a cellulose derivative with carboxymethyl groups (-CH2-COOH) bound to some of the hydroxyl groups of the glucopyranose monomers that make up the cellulose backbone. Sodium carboxymethyl cellulose is the sodium salt of carboxymethylcellulose.

[0022] Preferably, the hydrogel of the present invention comprises carboxymethylcellulose (CMC) sodium salt with an average molecular weight of 90 - 1300 kDa. More preferably, the average molecular weight of sodium CMC in the hydrogel of the present invention is 700 kDa. The degree of substitution (DS) preferably ranges from 0.7 to 1 .2 and more preferably is 0.9. The viscosity of 1% CMC solution at 25 °C preferably ranges from 400 to 6000 mPa.s and more preferably from 3500 to 4500 mPa.s.

[0023] The cross-linking mixture of the hydrogel of the present invention comprises citric acid and a second cross-linker, which is selected from the group consisting of a standard amino acid, L-carnitine, N,N,N-trimethylglycine, choline and a pharmaceutically acceptable salt of choline.

[0024] Citric acid is a tricarboxylic organic acid which occurs naturally in citrus fruits. The term “standard amino acid” refers to any one of twenty naturally occurring compounds that contain amino (-NH+3, or -NH+2- in the case of proline) and carboxylate functional groups, attached to the same C atom (they are thus a-amino acids) and they are incorporated into peptides and encoded by the universal genetic code. With the exception of achiral glycine, standard amino acids have the L configuration.

[0025] The standard amino acids can be classified according to the side chain that they contain, as follows:

[0026] Aliphatic side-chain amino acids include leucine, glycine, alanine, valine, isoleucine and proline.

[0027] Sulfur-containing side-chain amino acids include methionine and cysteine.

[0028] Cationic side-chain amino acids include histidine, arginine and lysine.

[0029] Aromatic side-chain amino acids include phenylalanine, tyrosine and tryptophan. Anionic side-chains amino acids include aspartate and glutamate.

[0030] Polar neutral side-chain amino acids include serine and threonine.

[0031] Amide side-chain amino acids include asparagine and glutamine.

[0032] Preferably, the amino acid in the cross-linking mixture is proline, phenylalanine, serine or alanine and even more preferably the amino acid is proline.

[0033] L-Carnitine is a quaternary ammonium compound and amino acid derivative which is involved in metabolism of most mammals, and other organisms.

[0034] N,N,N-trimethylglycine is a quaternary ammonium compound also known as glycine betaine, or betaine. It is an amino acid derivative that occurs in plants.

[0035] Choline is a quaternary ammonium compound, which can be found in various organisms and plays a role in various biological processes. Examples of pharmaceutically acceptable salts of choline include choline chloride and choline bitartrate.

[0036] Preferably, the second cross-linker is selected from proline, or L-carnitine. The weight of the cross-linking mixture relative to the weight of sodium CMC in the hydrogel of the present invention is, preferably, from 0.005% to 5%, more preferably, from 0.02% to 2% and even more preferably, from 0.1% to 1%.

[0037] The weight of citric acid relative to the weight of sodium CMC in the hydrogel of the present invention is, preferably, from 0.001% to 4%, more preferably, from 0.01 % to 1 % and even more preferably, from 0.05% to 0.4%.

[0038] As used herein, the percentage of the weight of a component (for example, citric acid, cross-linking mixture) relative to the weight of sodium CMC refers to the grams of the component per 100 grams of sodium CMC, unless specified otherwise. For example, a weight of 1 % means that for 100 grams of sodium CMC the weight of a component is 1 gram.

[0039] In the cross-linking mixture, the molar ratio of citric acid to the second cross-linker is, preferably, from 1 :10 to 10:1 , more preferably, from 1 :1 to 1 :5 and even more preferably, 1 :1.

[0040] In the hydrogel of the present invention citric acid acts as a chemical cross-linker and the second cross-linker acts as a physical cross-linker.

[0041] The present invention provides also a process for the preparation of a hydrogel, wherein the process comprises a) providing an aqueous solution of a cross-linking mixture comprising citric acid and a second cross-linker, wherein the second cross-linker is selected from the group consisting of a standard amino acid, L-carnitine, N,N,N-trimethylglycine, choline, and a pharmaceutically acceptable choline salt, b) providing an aqueous solution of sodium CMC and the cross-linking mixture, c) cross-linking sodium CMC with the cross-linking mixture.

[0042] In the method of the present invention, the weight of the cross-linking mixture is preferably from 0.005% to 5% relative to the weight of sodium CMC, more preferably from 0.02% to 2% relative to the weight of sodium CMC and even more preferably from 0.1 % to 1 % relative to the weight of sodium CMC. According to a preferred embodiment of the method of the invention, the weight of citric acid (CA) contained in the mixture is from 0.001 % to 4% relative to the weight of sodium CMC, more preferably, from 0.01 % to 1 % relative to the weight of sodium CMC and even more preferably, from 0.05% to 0.4% relative to the weight of sodium CMC.

[0043] Preferably, citric acid and the physical cross-linker are mixed in a molar ratio from 1 :10 to 10:1. More preferably, the molar ratio ranges from 1 :1 to 1 :5. Most preferably the molar ratio is 1 :1.

[0044] Cross-linking is preferably carried out at a temperature which is higher than the room temperature. For example, cross-linking can be carried out at a temperature from 30°C to 150°C.

[0045] According to a preferred embodiment, the hydrogel preparation involves initially heating the aqueous solution of sodium CMC and the cross-linking mixture, for example at a temperature from 40°C to 60°C, in order to remove water and obtain the dried hydrogel. Then the dried hydrogel is heated at a temperature from 110°C to 130°C (preferably, at 120°C) for typically 4 hours to achieve the chemical cross-linking. Preferably, before the dried hydrogel is heated, it is cut into small pieces.

[0046] After cross-linking, the hydrogel may be purified. An example of a purification method includes keeping the hydrogel in water for 24 h. Then acetone is added and the hydrogel is obtained as a glassy precipitate (phase inversion method). The precipitate is dried in an oven at 50 °C for 24 h.

[0047] The hydrogel of the present invention exhibits excellent swelling properties.

[0048] Preferably, the swelling ratio of the hydrogel of the present invention in simulated gastric fluid / water weight ratio 1 :8 at 37° C is at least 50. More preferably, the swelling ratio in simulated gastric fluid / water weight ratio 1 :8 at 37° C is at least 70.

[0049] The hydrogel of the present invention can be used in a method for treating obesity, or reducing food intake in a subject. The subject is preferably a human. The method comprises administering the hydrogel of the invention, preferably orally, to the subject. The hydrogel can be administered without food, or in combination with food. As the hydrogel reaches the stomach of the subject, it absorbs water and its volume increases. This increases the volume and enhances elasticity and viscosity in both the stomach and small intestine. This, in turn, promotes a feeling of satiety and fullness. The hydrogel eventually breaks down in the colon. Subsequently, water is released from the hydrogel and the hydrogel particles are excreted from the body.

[0050] EXAMPLES

[0051] Example 1. Preparation of the CA-mixture

[0052] The CA-mixture is prepared by mixing citric acid, the physical cross-linker and water in appropriate molar ratios, as described below. The mixture is stirred at 60 °C for 3h until a viscous and transparent solution is obtained.

[0053] Example 2. Polymer Hydrogel Synthesis

[0054] Polymer hydrogel samples were obtained by reacting CMC sodium salt (MW 700 kDa, degree of substitution 0.9) with a mixture of citric acid, water and the physical crosslinker according to the following procedure. First, the CA-mixture was added in 25 mL of distilled water at different amounts (0.01 - 5% w / w relative to the amount of the polymer) in order to obtain samples with various degrees of cross-linking. Then, sodium CMC was added in order to obtain a total concentration of 2% w / v (i.e. , 2 grams of sodium CMC per 100 ml of the solution) and the mixture was stirred gently at room temperature until a clear solution was obtained. All samples were dried at 50 °C for 48 h to remove absorbed water and then cut into pieces of 0.1 - 0.5 cm and kept at 120°C for 4 h for the cross-linking reaction to be completed.

[0055] Preparation of Polymer Hydrogel A:

[0056] 1.88 mg of the CA-mixture citric acid / L-proline / H2O (molar ratio 1 :1 :3) and 500 mg of CMC sodium salt are added in 25 mL H2O (final amount of citric acid in relation to CMC sodium salt 0.2% w / w) and the final mixture is magnetically stirred for 24 h to completely dissolve CMC. The resulting viscous solution is then placed in an oven at 50 °C for 48 h until completely dry. The dried hydrogel is cut into pieces of approximately 0.1 - 0.5 cm and it is placed in an oven at 120 °C for 4 h to achieve the cross-linking. The hydrogel is then purified by adding 30mL water in two portions and left in water for 24 h. 50mL of acetone is then added and the hydrogel is obtained as a glassy precipitate (phase inversion method). The precipitate is dried in an oven at 50 °C for 24 h. Preparation of Polymer Hydrogel B:

[0057] Hydrogel B was prepared following the general procedure described above, using a citric acid / L-carnitine / H2O mixture in a molar ratio of 1 :1 :5 as a cross-linker (final amount of citric acid in relation to CMC sodium salt 0.2% w / w).

[0058] Preparation of Polymer Hydrogel C:

[0059] Hydrogel C was prepared following the general procedure described above, using a citric acid / L-carnitine / H2O mixture in a molar ratio of 1 :1 :5 as a cross-linker (final amount of citric acid in relation to CMC sodium salt 0.4% w / w).

[0060] Preparation of Polymer Hydrogel D:

[0061] Hydrogel D was prepared following the general procedure described above, using a citric acid / L-carnitine / H2O mixture in a molar ratio of 1 :1 :5 as a cross-linker (final amount of citric acid in relation to CMC sodium salt 0.05% w / w).

[0062] Preparation of Polymer Hydrogel E:

[0063] Hydrogel E was prepared following the general procedure described above, using citric acid as a cross-linker (final amount of citric acid in relation to CMC sodium salt 0.4% w / w).

[0064] The final amount of citric acid in the prepared hydrogels is summarized in Table 1.

[0065] TABLE 1

[0066] Example 3. Characterization of the SAHs using FTIR spectroscopy

[0067] FTIR spectra of sodium CMC, citric acid, L-carnitine and a hydrogel prepared using the citric acid / L-carnitine / H2O 1 :1 :5 mixture were recorded (Figure 1). In order to amplify the FTIR signals, the hydrogel was prepared using a higher amount of the citric acid / L- carnitine / H2O 1 :1 :5 mixture (10% w / w CA to sodium CMC) and the FTIR spectrum was obtained at 1 h of cross-linking so as to observe the anhydride formation which is indicative of the successful chemical cross-linking between CA and sodium CMC. In the FTIR spectrum of the prepared hydrogel, the characteristic bands of C=O stretching vibration of sodium CMC and L-carnitine at 1588 cm-1and C-N stretching vibration of L-carnitine at 1264 cm-1are observed. Moreover, a new peak at 1731 cm-1appears which can be attributed to the formation of the anhydride, which indicates the chemical cross-linking of citric acid and sodium CMC.

[0068] Example 4. Swelling ratio

[0069] Swelling studies for all the samples were carried out in buffer solutions that simulated bodily fluids of the gastrointestinal tract: SGF (Simulated Gastric Fluid), SIF (Simulated Intestinal Fluid) and SCF (Simulated Colon Fluid). The buffer solutions were prepared according to USP Test Solutions procedures [USP29-NF24, 4535: Reagents (Test Solutions (TS))], which are known in the art.

[0070] Swelling measurements were carried out using a Kern balance (10-4sensitivity). The swelling ratio was measured by weighing samples before and after their immersion in the buffer solutions for about 7 h. The swelling ratio (SR) is defined as following:

[0071] Ws - Wd SR = — — - where l / l / sis the weight of the swollen polymer hydrogel and Wd is the weight of the dried sample.

[0072] Swelling Studies

[0073] The Swelling Ratio of the prepared hydrogels is determined according to the following protocol:

[0074] 1 . Place a dried glass funnel with a filter paper on a support and pour 20 mL±0.5 g of purified water into the funnel.

[0075] 2. After the funnel has been dried (no droplets are detected in its neck), dry the tip of the funnel with a filter paper.

[0076] Place the funnel with the filter paper into an empty and dry conical flask, place them on a tared scale and record the weight of the empty apparatus (Wtare).

[0077] 3. Weigh 125 mg of the hydrogel pieces using into a glass beaker. 4. Add 20.0±0.5 g of the appropriate buffer solution prepared according to USP Test Solutions procedures [USP29-NF24, 4535: Reagents (Test Solutions (TS))].

[0078] 5. Place the beaker in an incubator at 37°C and 90 rpm.

[0079] 6. Before each measurement, place the pre-weighted funnel on a support and pour the suspension into the funnel, collecting any remaining material with a spatula.

[0080] 7. Allow the material to drain for 10±1 min and dry the tip of the funnel with a filter paper.

[0081] 8. Place the funnel containing the drained material inside the conical flask and weight it (Wfjn)

[0082] 9. The swelling ratio (SR) is calculated according to: where H / „, is the weight of the dried sample.

[0083] Results

[0084] Kinetics of Swelling (in SGF / Water 1 / 8 weight ratio), Collapsing (in SGF) and ReSwelling (in SI F)

[0085] The determination of the swelling ability of the hydrogels is performed by immersing the hydrogel in appropriate buffer solutions which are prepared according to the USP specifications, simulating the gastrointestinal route: SGF (Simulated Gastric Fluid), which contains pepsin (pH 1.2) and simulates the stomach conditions, SIF (Simulated Intestinal Fluid), which contains pancreatin (pH 6.8) and simulates the small intestine conditions and SCF (Simulated Colon Fluid), which contains pectinase and simulates the colon conditions (pH 6.8). When immersed in the SGF / water 1 / 8 solution the hydrogel swells, presenting a maximum swelling at 60 min. In continuation, the hydrogel is immersed in SGF / water weight ratio 1 / 4 and SGF solutions and the medium uptake ratio of the hydrogel is decreased (collapsing), while in the SIF solution the hydrogel swells due to medium penetration into the void space between the polymeric chain network (re-swelling). Finally, the hydrogels are dissolved when immersed in the SCF solution containing pectinase.

[0086] Experiments were conducted by monitoring the Swelling ratio through a full cycle of swelling in 1 :8 weight ratio SGF / water, collapsing in SGF, and re-swelling in simulated intestinal fluid (SIF) (then degradation in SCF), all at 37°C.

[0087] Experiments performed and results for the hydrogels of Example 2 are provided in Table 2.

[0088] TABLE 2

[0089] Hydrogel A B C D E

[0090] Time Ratio (g / g)

[0091] 60 min (max 109.0 103.6 118.8 121.2 80.3 swelling) 180 min

[0092] 49.2 59.3 67.7 51.6 44.5 (collapsing) 270 min

[0093] 100.1 127.7 107.9 138.2 90.9 (re-swelling)

[0094] Hydrogel C (prepared with the CA / L-carnitine / H2O mixture) and hydrogel E (prepared using only citric acid) exhibit different swelling profiles, with hydrogel C achieving the best results. Additionally, hydrogel A (prepared with the CA / L-Proline / H2O mixture) and hydrogel B (prepared with the CA / L-carnitine / H2O mixture) exhibit good swelling properties. These differences indicate that the second component of the CA-mixture, affects the swelling profile of the hydrogel. More specifically, the swelling properties of the hydrogel are improved when citric acid is combined with a second component and the final CA-mixture is used as a cross-linking agent.

[0095] The sodium CMC cross-linked hydrogels with different amounts of the citric acidmixture (hydrogels B, C, D), also exhibited a different swelling profile. The best results were achieved for hydrogel D, which was produced using the lowest amount of the CA / L-carnitine / H2O 1 :1 :5 mixture (0.0.5% w / w citric acid to CMC).

[0096] A comparison between polymer hydrogels A, B and the chemically cross-linked hydrogel with citric acid according to the work published by the team of Gelesis LLC (M. Madaghiele et al., Biomimetic cellulose-based superabsorbent hydrogels for treating obesity, Scientific Reports, 2021, 11:21394), which contain the same amount of citric acid (0.2% w / w to CMC) is presented in Table 3.

[0097] TABLE 3 *The values are estimated approximately by the data presented in Figure 4a of the publication

[0098] The sodium CMC cross-linked hydrogels with CA-mixtures exhibited a higher swelling capacity at 60 min (maximum swelling ratio) and re-swelling capacity after 180 min, compared to the cross-linked hydrogel with citric acid according to Gelesis LCC publication.

[0099] The swelling studies last a total of 7 hours. During the last hour in SCF solution, total dissolution of the hydrogels was observed, as desired.

Claims

CLAIMS1. A hydrogel comprising sodium carboxymethylcellulose cross-linked with a mixture of citric acid and a second cross-linker, wherein the second cross-linker is selected from the group consisting of a standard amino acid, L-carnitine, N,N,N-trimethylglycine, choline and a pharmaceutically acceptable choline salt.

2. The hydrogel according to claim 1 , wherein the second cross-linker is L-proline, or L-carnitine.

3. The hydrogel according to claim 1 or 2, wherein the weight of the cross-linking mixture relative to the weight of sodium carboxymethylcellulose in the hydrogel is from 0.005% to 5%.

4. The hydrogel according to any one of the preceding claims, wherein the weight of the cross-linking mixture relative to the weight of sodium carboxymethylcellulose in the hydrogel is from 0.02% to 2%.

5. The hydrogel according to any one of the preceding claims, wherein the weight of the cross-linking mixture relative to the weight of sodium carboxymethylcellulose in the hydrogel is from 0.1% to 1 %.

6. The hydrogel according to any one of the preceding claims, wherein the molar ratio of citric acid to the second cross-linker is from 1 :10 to 10:1.

7. The hydrogel according to any one of the preceding claims, wherein the molar ratio of citric acid to the second cross-linker is from 1 :1 to 1 :5.

8. The hydrogel according to any one of the preceding claims, wherein sodium carboxymethylcellulose has an average molecular weight from 90 kDa to 1300 kDa.

9. The hydrogel according to any one of claims 1 to 8 for use in the treatment of obesity.

10. A process for the preparation of a hydrogel as defined in any one of claims 1 to 8, wherein the process comprises a) providing an aqueous solution of a cross-linking mixture comprising citric acid and a second cross-linker, wherein the second cross-linker is selectedfrom the group consisting of a standard amino acid, L-carnitine, N,N,N- trimethylglycine choline and a pharmaceutically acceptable choline salt, b) providing an aqueous solution of sodium CMC and the cross-linking mixture, c) cross-linking sodium CMC with the cross-linking mixture.

11. The process according to claim 10, wherein the cross-linking of sodium CMC with the cross-linking mixture is carried out at a temperature from 30°C to 150°C.

12. The process according to claim 10, wherein step c) comprises i) heating the aqueous solution of sodium CMC and the cross-linking mixture to remove water and obtain the dried hydrogel, and ii) heating the dried hydrogel at a temperature which is higher than the temperature of step i).

13. The process according to claim 12, wherein the heating in step i) is carried out at a temperature from 40°C to 60°C.

14. The process according to claims 12 or 13, wherein the heating in step ii) is carried out at a temperature from 110°C to 130°C.

15. The process according to any one of claims 12 to 14, wherein the heating in step ii) is carried out at 120°C.

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