Microcapsules containing seminal material for artificial insemination in pigs

Abstract: With the aim of protecting pig seminal material which may be used for artificial insemination from degradation, herein described are microcapsules containing: a) a liquid nucleus containing a suspension of pig seminal material and a biodegradable and/or biocompatible polymer; b) a film consisting of an alginate of a bivalent or trivalent metal, possibly cross-linked. These microcapsules containing the spermatozoa make it possible to obtain a prolonged and controlled release of seminal material and in addition a protection of the material from degradation, thus enabling a simplification in the procedures of artificial insemination and an increase in pig fertility.

Description: Scope of invention The present invention regards microcapsules that may be used for artificial insemination in pigs, containing pig seminal material, and the corresponding process of preparation. These capsules make it possible to obtain a prolonged and controlled release of seminal material and in addition a protection of the material from degradation, thus enabling a simplification in the procedure of artificial insemination and an increase in pig fertility. State of the art In the last few decades, artificial insemination (A.I.) in cattle has witnessed a considerable diffusion among stock breeders, enabling insemination to be carried out on the basis of precise physiological data which make it possible to intervene with considerable precision and high probability of success. This technique involves almost exclusively the use of fresh and/or refrigerated semen, the preparation of which is carried out at farm A.I. centres, also with the use of seminal material coming from external supplies. For improving the likelihood of success of artificial insemination, numerous techniques have been developed, above all in the field of cattle for milk production. In some domestic species, the technique of freezing fresh seminal material has led to a standardization of the methods of preservation and good likelihood of success of artificial insemination (e.g., cattle). Among the methods used to improve the possibility of fertilization in cattle, it may be recalled that Nebel, as many as 15 years ago, attempted a series of modifications of artificial insemination in cattle using micro-encapsulated material instead of fresh seminal material (see R.L. Nebel, et al., J. Anim. Sci., 60, 1631 (1985); R.L. Nebel, et al ., Reprod. Fertil. Dev., 5, 701 (1993)) and adopting a technique that involved the use of alginates and polyamines (poly I-lysine, protamine sulphate, polyvinyl amine) to obtain microcapsules consisting of semipermeable membranes. This procedure comprised three steps: 1) formation of a matrix of calcium alginate containing the seminal material; 2) formation of the semipermeable membrane by means of surface reticulation of the matrix with polyamines; 3) dissolution of the matrix nucleus of calcium alginate by substitution of calcium with sodium. With this procedure, then, the seminal material was initially immobilized in the calcium alginate matrix, and subsequently suspended in sodium alginate. This technique of protection of bovine seminal material was quite successful in so far as this material is particularly stable and sustains micro-encapsulation treatments without excessive power loss. On the other hand, artificial insemination (A.I.) is particularly problematical in pigs in so far as the technique of freezing, which has led to a good standardization of the methods of preservation in other domestic species, is practically inapplicable for pig seminal material, in that there exist considerable differences of efficiency of preservation using the freezing process. The results acquired experimentally with frozen semen have made it possible to reveal excessive variability of parameters, such as fertility and prolificacy. In particular, the reduction of percentages of prolificacy and fertility has been identified in a slowing-down and/or failure of the embryo to grow during the first 4-5 days of life (see F. Cairoli et al., Selezion Veterinaria, 32 (1 bis), 297 (1991)). In addition, pigs present a duration of oestrus that ranges from 40 to 48 hours, with a follicular and ovulatory dynamics influenced by several factors, both of endogenous and exogenous type. For this reason, technicians tend to carry out a double A.I. intervention in order to guarantee the presence, at the tubal level, of a high concentration of spermatozoa with high fertilizing capacity. Obviously, the double-intervention technique represents a considerable inconvenience both on account of the need for resorting to specialized operators and on account of the high consumption of seminal material. The reduction in the fertilizing capacity of the spermatozoa is very probably one of the causes that limit prolificacy. A high incidence of the loss of fertilizing capacity is found also as a result of the problematical aspects of the processes of preservation of seminal material referred to above. In fact, whilst in other domestic species the freezing technique has led to a standardization of the preservation procedures, this technique has not yet yielded satisfactory results in pigs. In addition, in order to enhance breeding productivity in pigs there is an increasingly urgent demand on the part of operators for being able to carry out a single A.I. intervention so as to reduce operating costs. Summary of invention Now we have unexpectedly found that it is possible to produce microcapsules containing active seminal material. Consequently, the present invention relates to microcapsules comprising: a) a liquid nucleus containing a suspension of pig seminal material and a biodegradable and/or a biocompatible polymer, b) a film consisting of a possibly cross-linked alginate of a bivalent or trivalent metal, possibly reticulated. With this type of preparations it is possible both to overcome the drawbacks linked to the limited stability of the seminal material and to enable the use of a single operation of artificial insemination, with considerable economic advantages resulting from the drastic reduction in the intervention of the operator and from the use of a reduced amount of seminal material. Furthermore, the seminal material is appropriately protected and is released from the formulation that forms the subject of the present patent over a prolonged time range. It must moreover be emphasized that a further complication of fertilization in pigs is linked to the ovulation times and modalities that are typical of this species. In fact, the fertile period is very short and may vary according to the seasonal period, as was said previously. For this reason, at present a single intervention of fertilization with diluted and refrigerated seminal material does not provide sufficient guarantees of success for a complete fertilization of the egg cells. We have now found and experimentally proved that, with the micro-encapsulation of pig seminal material, in which no type of reaction within the nucleus containing the seminal material is expected, it is possible to protect pig semen, which is characterized by high instability. As a result, we obtain the encapsulation of pig semen in the above-mentioned biocompatible and biodegradable polymer, which enables prolonged and controlled release of the active seminal material. In this way, it is possible to maintain high concentrations of spermatozoa in the uterus for the entire duration of oestrus, and consequently bring about an increase in fertility and prolificacy. In addition, the use of micro-encapsulated pig seminal material enables a single operation of artificial insemination to be carried out, in so far as the active spermatozoa are released in a time range that covers the entire duration of oestrus of the sow. The present invention further relates to the new technique of preparation of the microcapsules according to the present invention, which in particular comprises the following steps: 1. Pig seminal material is suspended in a suitable amount of solution, normally indicated as diluter, generally consisting of an aqueous solution containing: glucose in a concentration of between 0.5 and 10%, sodium bicarbonate in a concentration of between 0.02 and 4.0 %, potassium chloride in a concentration of between 0.01 and 3.0 %, penicillin in a concentration of between 10 2 U.l/l and 10 10 U.l./l, streptomycin in concentration of between 0.01 and 2.0 %, or another antibiotic normally used for this purpose in suitable concentrations, so as to obtain a concentration of spermatozoa of from 1 x 10 4 up to a 5 x 10 10 cells/ml, 2. the biocompatible and/or biodegradable polymer and then an aqueous solution of halides of bivalent metals, such as salts of calcium, strontium, zinc, or halides of trivalent metals, such as aluminium, iron, chromium, etc., are added to the suspension obtained in step (1), 3. the suspension resulting from step (2) is added, drop by drop, to a solution of sodium alginate, keeping the temperature of the entire system within a range of between 5°C and 45°C, and microcapsules of a gelatinous type are obtained, which are subsequently dispersed in the diluter for pig semen described previously, 4. the microcapsules obtained in the previous step may possibly be reticulated by means of suspension in an aqueous solution of a cross-linked agent of a polyamine type, which is maintained under stirring, to bring rigid microcapsules. Detailed description of invention The microcapsules according to the present invention may therefore be of a gelatinous or of a rigid type, according to whether the outer film consisting of an alginate of a bivalent or trivalent metal has not undergone or has undergone cross-linking. The microcapsules of a gelatinous type consist of a liquid nucleus containing the suspension of seminal material and biodegradable polymer, and of a bio-erodible gelatinous film of non-crosslinked alginate. The biodegradable and/or biocompatible polymeric material according to the present invention contained in the liquid nucleus of the microcapsules that form the subject of the present invention is preferably chosen from among the group consisting of glucans, scleroglucans, mannans, galactomannans, gellans, carrageenans, chitosans, pectins, xanthanes, polyanhydrides, polyamino acids, poly-(methyl vinyl ethers / maleic anhydride), carboxymethyl cellulose and derivatives, sodium carboxymethyl cellulose, polyvinyl alcohols, hydroxypropyl cellulose having a mean molecular weight of from 2,000 to 4,000,000, but preferably of from 10,000 to 2,000,000, hydroxypropyl methylcellulose, carboxyvinyl polymers, alginic acid and derivatives thereof, polyvinyl alcohols, ethylcellulose, methylcellulose and cellulose derivatives in general, starches, starch derivatives, as well as alpha-, beta-, gamma-cyclodextrins and dextrin derivatives in general. For all the polymers referred to there exist different types available on the market characterized by different physical-chemical properties of solubility and gelation. These polymers are generally present in concentrations of between 1.0 and 90% of the total weight of the microcapsule, but preferably between 20 and 80%. Preferably, hydroxypropyl methylcellulose is used, having different molecular weights, in general of between 1000 and 4,000,000 Daltons, and preferably of between 10,000 and 1,500,000 and a different degree of methoxyl substitution, in general between 15 and 30%, and a degree of hydroxypropoxyl substitution of between 4 and 30%, as biodegradable and/or biocompatible polymer for the liquid nucleus of the microcapsules according to the present invention. Consequently, this polymer presents a prevalently erodible or gellable nature, according to the viscosity and degree of substitution in the polymeric chain. According to a particularly preferred solution, hydroxypropyl methylcellulose available on the market under the registered trade-mark METHOCEL® E 50 with a molecular weight of 22,000 and with a degree of methoxyl substitution 29 and hydroxypropoxyl substitution of 8.5 is used. The alginates of the bivalent metals forming the microcapsules that form the subject of the present invention are generally those of calcium, strontium, and zinc. The alginates of the trivalent metals are, for example, those of aluminium, iron, and chromium. Preferably, the film of the microcapsules according to the present invention is made up of calcium alginate or zinc alginate. The alginates forming the film of the microcapsules according to the present invention generally present, at 2% in aqueous solution, a viscosity of between 200 cps and 20,000 cps at a temperature of 25°C. The capsules obtained are generally characterized by having a dimension of between 50 micron and 8 mm, preferably of between 100 micron and 5.0 mm, and this enables easy manipulation, transportation and preservation, as well as the use of ordinary catheters for artificial insemination. In step (1) of the process according to the present invention, the diluter for pig seminal material contains glucose in a concentration of preferably between 1.5 and 5 wt%, sodium bicarbonate in a concentration of between 0.05 and 0.8%, potassium chloride in a concentration preferably of between 0.01 and 0.10%, penicillin in a concentration preferably of between 10 4 U.l./l and 10 8 U.l./l, streptomycin in a concentration of between 0.04 and 0.90 wt% or another antibiotic in appropriate concentrations, with the purpose of obtaining a concentration of between 2 x 10 5 and 5 x 10 8 cells/ml. In step (2) of the process that forms the subject of the present invention, the halides of bivalent metals preferably used are calcium chloride or zinc chloride, used in an aqueous solution in a concentration ranging from 0.001 M to 2.5 M, but preferably from 0.01 to 1.0 M. Step (3) is preferably conducted at a temperature of between 10 and 25°C, and the suspension is extruded through hypodermic needles of appropriate size and aperture by means of a peristaltic pump, at a rate such as to produce approximately 20 drops/min. As the metal ions diffuse towards the outer surface, in particular of the drop, they react with the alginate to form a film of alginate of an alkaline earth metal (e.g., calcium alginate), which enables sufficiently rigid microcapsules to be obtained. These are washed a number of times, preferably with a physiological solution, or preferably with the diluter. These microcapsules of a "gelatinous type" may constitute of themselves, without undergoing any further treatment, a first type of material usable for A.I. In step (4), the capsules of a "gelatinous type" prepared as described may undergo cross-linking by means of interface polymerization of the alginate. This procedure brings about the conversion of the gelatinous membrane into a semipermeable rigid membrane of alginate cross-linking with a cross-linked agent of the polyamine type. Preferably these cross-linking agents are selected from: protamine sulphate or phosphate, preferably in the form of an aqueous solution in concentrations of between 0.1 and 5.0% w/v, even more preferably protamine sulphate in a concentration of between 0.5 and 3.0% w/v, polylysine bromohydrate of molecular weight of between 1000 and 800,000 in an aqueous solution at a concentration preferably of between 0.01 and 5.0% w/v, even more preferably of between 0.03 and 3.0% w/v, and polyvinyl amine in a concentration of from 0.001 to 5.0% w/v, even more preferably of from 0.01 to 1.0% w/v. Step (4) is moreover preferably carried out according to the following operating procedure: stirring rate: 5-300 rpm reaction times: 2-180 min. The capsules that are obtained and that may be defined of the "rigid type" are filtered and respectively washed and suspended in the same diluter for pig semen, previously described. The following examples are given to provide illustrations of the preparation of the capsules that form the subject of the present invention. EXAMPLE 1 Preparation of the capsules (GELATINOUS TYPE) Hydroxypropyl methylcellulose (Methocel E50 Premium EP) (4 % w/v) and calcium chloride (0.3 M) is added to a suspension of seminal material of Large White boar with a concentration of 26 x 10 6 cells/ml (motility 90%, acrosomal integrity of over 90%), and the resulting suspension, to which is added the polymeric material, is in turn added to an aqueous solution of sodium alginate (0.5 % w/v), and kept under gentle stirring (30 rpm). The drops are produced by extrusion through hypodermic needles (25G x 5/8") by means of a peristaltic pump (Esapump, Advanced Products, Milan, Italy), at a rate such as to produce approximately 20 drops/min. As the calcium ions diffuse towards the outer surface of the drop, they react with the alginate to form a film of calcium alginate. The capsules thus obtained are filtered, washed three times, and suspended in a physiological solution, and suspended in diluter for pig semen consisting of an aqueous solution containing 2.9% glucose, 0.2% sodium bicarbonate, 0.03% of potassium chloride, 10 6 U.l./l of penicillin, and 0.1% streptomycin. The capsules thus consist of a liquid nucleus containing the suspension of seminal material and hydroxypropyl methylcellulose, and a bio-erodible gelatinous membrane. These capsules (GELATINOUS TYPE) may constitute a first type of material usable for A.I.. Of the preparation obtained in Example 1 Table I gives the results of the determinations of survival time of the seminal material, acrosomal integrity and motility; these latter two parameters are expressed in percentages. EXAMPLE 2 Preparation of the capsules (RIGID TYPE) The GELATINOUS TYPE capsules, prepared as described in Example 1, starting from a suspension of seminal material (26 x 10 6 cells/ml) are suspended in an aqueous solution of protamine sulphate (1% w/v), kept under stirring (30 rpm) for 20 min. By means of this procedure the interface polymerization of the calcium alginate is obtained, and capsules of the RIGID TYPE are prepared. This procedure determines the conversion of the gelatinous membrane into a semipermeable rigid membrane of alginate cross-linked with protamine. The capsules are filtered, washed three times with physiological solution and suspended in diluter for pig semen. The results of the controls carried out are given in Table I. Example 3 Preparation of capsules (RIGID TYPE) The procedure described in Example 2 is used, with the only difference that a suspension of seminal material with a concentration of 52 x 10 6 cells/ml is used. The results of the controls carried out are given in Table I. Code Survival time (h) Acrosomal integrity (%) Motility (%) Fresh spermatic material 96.0 90.0 60.0 Example 1 72.0 35.0 5.0 Example 2 96.0 68.0 20.0 Example 3 48.0 40.0 10.0 From the results reported in Table I, it is evident that the preparation described in Example 2 presents a survival time of the seminal material that is identical to that of the fresh spermatic material, an acrosomal integrity of 75%, as compared to the fresh seminal material, and a good motility as compared to the other preparations.

Claims: Microcapsules comprising: a) a liquid nucleus containing a suspension of pig seminal material and a biodegradable and/or biocompatible polymer, b) a film consisting of a possibly cross-linked alginate of a bivalent or trivalent metal. Microcapsules according to claim 1, characterized in that they are gelatinous and the film of alginate is not cross-linked and is bio-erodible. The microcapsules according to claim 1 of a rigid type, characterized in that the film of alginate is cross-linked. The microcapsules according to any one of claims 1-3, characterized in that the biodegradable and/or biocompatible polymer is chosen from the group consisting of: glucans, scleroglucans, mannans, galactomannans, gellans, carrageenans, chitosans, pectins, xanthanes, polyanhydrides, polyamino acids, poly-(methyl vinyl ethers / maleic anhydride), carboxymethyl cellulose and derivatives thereof, sodium carboxymethyl cellulose, polyvinyl alcohols, hydroxypropyl cellulose with a mean molecular weight of from 2,000 to 4,000,000, hydroxypropyl methylcellulose, carboxyvinyl polymers, alginic acid and derivatives thereof, polyvinyl alcohols, ethylcellulose, methylcellulose and cellulose derivatives in general, starches, derivatives of starches, alpha- beta- gamma-cyclodextrins and derivatives of dextrins. The microcapsules according to any one of claims 1-5, characterized in that said biodegradable polymer is chosen from the group consisting of hydroxypropyl cellulose with a mean molecular weight of between 10,000 and 2,000,000. The microcapsules according to any one of claims 1-4, characterized in that hydroxypropyl methylcellulose with molecular weight between 10,000 and 1,500,000, and degree of methoxyl substitution of between 15 and 30%, and degree of substitution with hydroxypropoxyl of between 4 and 30% is used as biodegradable and/or biocompatible polymer. The microcapsules according to any one of claims 1-6, characterized in that said biodegradable and/or biocompatible polymers are contained in concentrations of between 1.0 and 90% of the total weight of the microcapsule. The compositions according to any one of claims 1-7, characterized in that the said biodegradable polymers are contained in concentrations of between 20 and 80% of the total weight of the microcapsule. The microcapsules according to any one of claims 1-8, characterized in that the film of alginate of a bivalent metal is selected from alginate of calcium, strontium, and zinc; the alginates of the trivalent metals are selected from those of aluminium, iron, and chromium. The microcapsules according to any one of claims 1-9, characterized in that the film consists of alginate of calcium or of zinc. The microcapsules according to any one of claims 1-10, characterized in that they present, in 2% aqueous solutions, a viscosity of between 200 cps and 20,000 cps at a temperature of 25°C. The capsules according to any one of claims 1-11, characterized in that they have dimensions of between 50 micron and 8 mm. The microcapsules according to any one of claims 1-12, characterized in that they have dimensions of between 100 micron and 5.0 mm. Process for preparing the microcapsules according to any one of claims 1-13 comprising the following steps: 1. Pig seminal material is suspended in a suitable amount of solution, consisting of an aqueous solution containing: glucose in a concentration of between 0.5 and 10%, sodium bicarbonate in a concentration of between 0.02 and 4.0 %, potassium chloride in a concentration of between 0.01 and 3.0 %, penicillin in a concentration of between 10 2 U.l/l and 10 10 U.l./L, streptomycin in concentration of between 0.01 and 2.0 %, or other antibiotics normally used for this purpose in suitable concentrations, so as to obtain a concentration of spermatozoa of from 1 x 10 4 up to 5 x 10 10 cells/ml; 2. the biocompatible and/or biodegradable polymer and then an aqueous solution of halides of bivalent metals or halides of trivalent metals is added to the suspension obtained in step (1), 3. the suspension resulting from step (2) is added, drop by drop, to a solution of sodium alginate, keeping the temperature of the entire system within a range of between 5°C and 45°C, and microcapsules of a gelatinous type are obtained, which are subsequently dispersed in the diluter for pig semen described previously; 4. the microcapsules obtained in the foregoing step may possibly be reticulated by means of suspension in an aqueous solution of a cross-linking agent of a polyamine type, which is kept under stirring, to give rise to rigid microcapsules. Process according to claim 14, characterized in that in step (1) the diluter for pig seminal material contains glucose in a concentration of between 1.5 and 5 wt%, sodium bicarbonate in a concentration of between 0.05 and 0.8%, potassium chloride in a concentration preferably of between 0.01 and 0.10%, penicillin in a concentration preferably of between 10 4 U.l./l and 10 8 U.l./l, streptomycin in a concentration of between 0.04 and 0.90 wt%, with the purpose of obtaining a concentration of between 2 x 10 5 and 5 x 10 8 cells/ml. Process according to either one of the claims 14 and 15, characterized in that in step (2), halides of bivalent metals are calcium chloride or zinc chloride, used in an aqueous solution in a concentration ranging from 0.001 M to 2.5 M. Process according to claim 16, characterized in that the concentration of calcium chloride and zinc chloride is between 0.01 and 1.0 M. Process according to any one of the claims 14-17, characterized in that step (3) is conducted at a temperature of between 10 and 25°C, and the suspension is extruded through hypodermic needles of appropriate size and aperture. Process according to any one of the claims 14-18, characterized in that in step (4) the cross-linking agent is selected from: protamine sulphate or phosphate, preferably in the form of an aqueous solution in concentrations of between 0.1 and 5.0% w/v, polylysine bromohydrate of molecular weight of between 1000 and 800,000 in an aqueous solution at a concentration of between 0.001 and 5.0% w/v, and polyvinyl amine at a concentration of between 0.001 and 5.0% w/v. Process according to any one of the claims 14-19, characterized in that in step (4) the cross-linking agent is selected from: protamine sulphate or phosphate, in the form of an aqueous solution in concentrations of between 0.5 and 3.0% w/v, bromohydrate poly l-lysine of molecular weight of between 1000 and 800,000 in an aqueous solution at a concentration of between 0.03 and 3.0% w/v, and polyvinyl amine in a concentration of from 0.01 to 1.0% w/v. Process according to any one of the claims 14-20, characterized in that it is carried out for a time ranging between 2 min and 180 min. The microcapsules according to any one of the claims 1-12 for artificial insemination of pigs.

Inventors: CONTE UBALDO, GIUNCHEDI PAOLO, MAFFEO GIOVANNI, MAGGI LAURETTA, RUSSO VINCENZO, TORRE MARIA LUISA MARINA, VIGO DANIELE, CONTE, UBALDO, GIUNCHEDI, PAOLO, MAFFEO, GIOVANNI, MAGGI, LAURETTA, RUSSO, VINCENZO, TORRE, MARIA LUISA MARINA, VIGO, DANIELE
Applicants: UNI DI PAVIA, UNIV MILANO, UNIVERSITA' DEGLI STUDI DI MILANO, UNIVERSITA DI PAVIA
Application year: 1998
Main classification: A61K9
IPC codes: A61K9, A61K35, A01N1