HK1025477B - Improved storage and maintenance of blood products - Google Patents

Description

Field of the Invention

This invention pertains to a method of improving the storage stability and improved viability, of blood products including, platelets and the like. Specifically, a method for extending the viability of these products, as well as their resistance to membrane damaging agents such as radiation, is provided by storing the products in a suspension including an effective amount of L-carnitine or alkanoyl L-carnitines.

BACKGROUND OF THE INVENTION

Concern has been steadily growing over both the national and worldwide blood supplies. Both the integrity and reliability of existing supplies, and the ability to build larger stocks over time, has been brought into question. One reason for this is the relatively short period of storage stability of blood products. Currently, packed RBCs (red blood cell concentrates, or RCC), the dominant form of blood product for transfusions and the like, are limited to a 42-day storage period. After that time, ATP levels fall substantially, coupled with a significant loss of pH, strongly indicating a lack of viability, or, if viable, an extremely short circulation life upon infusion. In vivo whole blood is not stored for substantial periods. For platelets, the current storage period is even shorter, with the standard being 5-days at 22°C. The difference in storage stability of platelet concentrations (PC) as opposed to RBC, is due to ongoing metabolic reactions in platelets, due in part to the presence of mitochondria in PC, and their absence in RBCs. While both blood products show a drop in ATP, coupled with a drop in pH, over time, accompanied by the production of lactic acid, the presence of mitochondria in PC is likely to exacerbate the problem, due to glycolysis.

Simultaneously, concerns over the reliability and integrity of the blood supply have been raised. In particular, contamination of the blood supply with bacteria, or other microbiological agents or viruses, has been detected repeatedly. Such a situation is even more severe in countries with less sophisticated collection and storage methods. While agents may be added to collected products to reduce contamination, these are not desirable, given the need to transfuse the products back into recipient patients. One desirable alternative is irradiation treatment of the products, after packaging, typically in elasticized vinyl plastic containers. Such irradiation treatment would aggravate RBC and PC storage, resulting in a diminished function of these cells.

Additionally, a small but growing portion of the blood receiving population is at risk of a generally fatal condition known as Transfusion Associated Graft Versus Host Disease (TAGVHD), which is due to the presence of viable allogenic leukocytes. This syndrome is typically associated with immunosuppressed patients, such as cancer and bone marrow transplant patients, but can also occur in immunocompetent persons in the setting of restricted Human Leukocyte Locus A (HLA) polymorphism in the population.

Substantial attention has been devoted to finding methods to extend storage stability. One such method, for extending the storage lifetime of PCs, is recited in U.S. Patent 5,466,573. This patent is directed to providing PC preparations with acetate ion sources, which act both as a substrate for oxidative phosphorylation and as a buffer to counteract pH decrease due to lactic acid production. Such a method does not act directly on the problem of hemolysis, and membrane breakdown. An alternative method is disclosed in the commonly assigned U.S. Patent 5,496,821. In this patent, whole blood is stored in a preparation including L-carnitine (LC) or alkanoyl derivatives thereof. The patent does not describe, however, the effects on blood products such as PC or RBC suspensions, and relies to at least some extent on the impact of LC on plasma characteristics.

As noted above, contamination of the blood supply with microbiological agents or viruses is another problem to be addressed by the medical community. One method of sterilizing the product and improving reliability with respect to contamination, is to irradiate the blood product. In general, gamma irradiation values of about 25 centigray (cG), irradiating the product after it is sealed in a plastic, glass or other container, is desirable. Regrettably, irradiation induces cell membrane lesions, with hemolysis in RBCs. Irradiation of blood products, including whole blood, packed RBCs and PCs continue to pose problems.

Accordingly, it remains an object of those of skill in the art to provide a method to extend the period of viability, and the circulation half-life of RBCs and PCs upon transfusion, beyond the current maximums. Additionally, it remains a goal of those of skill in the art to find a way by which blood products, including whole blood, packed RBCs and PCs can be sterilized by irradiation, without substantial membrane damage and lesions, and hemolysis.

SUMMARY OF THE INVENTION

The Applicant has discovered, through extended research, that the membrane damage experienced by PCs upon storage, or in the face of irradiation, can be substantially delayed and suppressed, by suspending the blood product in a conventional preservation solution, such as AS-3, where the preservation solution further includes L-carnitine or an alkanoyl derivative thereof, in a concentration of 0.25-50 mM or more. Applicant's discovery lies in the recognition that most of the decomposition or blood products, conventionally associated with decreases in ATP levels and pH, can be in fact traced to membrane damage and hemolysis. Membrane maintenance and repair may be effected by lipid reacylation, effected, in part, through L-carnitine, the irreversible uptake of which in PC has been established through the inventive research.

DETAILED DESCRIPTION OF THE INVENTION

This invention employs L-carnitine, and its alkanoyl derivatives, as an agent supporting cell membrane maintenance and repair, and suppression of hemolysis, in blood products. Alkanoyl L-carnitines includes acetyl, butyryl, isobutyryl, valeryl, isovaleryl and particularly propionyl L-carnitine. Herein, reference is made to this family, generically, as LC, and exemplification is in terms of L-camitine. The described alkanoyl L-carnitines, and their pharmacologically acceptable salts, however, may be used in place of L-carnitine.

The addition of LC to blood products, including PCs, requires LC to be present in an amount effective to permit membrane maintenance and repair. The research undertaken, including the examples set forth below, has demonstrated a minimum effective range for the products of most donors of about 0.25 mM-0.5 mM. The upper limit is more practical than physiological. Concentration as high as 50 mM or greater are easily tolerated. Values that are consistent with toxicological and osmological concerns are acceptable. Preferred ranges are 1-30 mM. A range of 1-10 mM or more is suitable with values between 4-6 mM making a marked difference. The effects of this invention, including the prolongation of viability, and the extension of circulation half-life upon transfusion, may be highly donor dependent. Accordingly, generally speaking, an effective concentration of LC is 0.5-50 mM. However, the ordinary artisan in the field may be required to extend that range, in either direction, depending on the particularities of the donor. Such extensions do not require inventive effort.

LC is consistent with conventional support solutions (stabilizing solutions), which are typically prepared to provide a buffering effect. Commonly employed solutions include ACED (citric acid-sodium citrate-dextrose), CPD (citrate-phosphate-dextrose) and modifications thereof, including CPD2/A-3, and related compositions. Typically, the composition includes a carbohydrate, such as glucose or mannitol, at least one phosphate salt, a citrate, and other balancing salts. LC is conventionally soluble and may be added to these compositions freely within the required range.

Suitable solutions, are described in U.S. Patent 5,496,821. However, support solutions other than those conventionally used can be employed, including artificial plasma and other physiologically acceptable solutions provided they comprise LC in accordance with the invention. The important component of the support solution is LC.

The ability of LC, when included in the suspension of PCs, to extend the viable time and therefore shelf length, and the circulation period upon transfusion into the receiving individual, is exemplified below by in vitro and in vivo experimentation. The experimentation employs LC, but other alkanoyl L-carnitines can be employed. Of particular significance is the demonstration, below, that the improved performance is obtained through improved maintenance (including repair) of the cell membrane, and suppression of hemolysis.

IRRADIATION

The problem of contamination of blood products, including PC with bacteria or other microbiological agents or viruses, can be reduced by substantial amount by irradiation. Levels of irradiation necessary for sterilization, and substantially 100% mortality of the aforesaid contaminating agents, have been widely explored.

Additionally, more importantly, leukocytes may be destroyed by similar irradiation. A variety of types of irradiation can be used, including gamma radiation (Cobalt GG, Van de Graf acceleration), UV irradiation, red light irradiation, etc. A close equivalent to about 20-50 cG gamma irradiation is sufficient.

Worldwide, between 60 and 80 million units of whole blood are collected annually and used in the transfusion support of a variety of patient populations. In the underdeveloped countries collection rates per 1000 population are lower and most blood transfusions are given in the treatment of obstetrical and pediatric cases, particularly malaria associated anemia. In the developed countries, collection rates per 1000 population are 50-10 times higher and most transfusions are given in surgery (50%) or in the treatment of patients with cancer associated anemia, bone marrow transplantation, non-malignant gastrointestinal bleeding (Figure 1). There are many potential adverse effects associated with the transfusion of allogenic blood. One particular complication adversely associated with blood transfusion is the rare and usually fatal entity known as Transfusion associated graft versus host disease (TA-GVHD), a complication mediated by viable allogenic immunocytes.

TA-GVHD disease is a rare complication of blood transfusion potentially seen in two types of blood transfusion recipient patient populations. TA-GVHD has a mortality approaching 100% and prevention is the only effective approach at this time. First, in immunocompromised patients, such as patients after bone marrow or other organ transplantation, Hodgkins disease or hereditary deficiencies of the immune system. Second, in nonimmunocompromised patients, when HLA similarity exists between blood donor and blood recipient. This is most often seen in directed donations from close relatives or in populations of more limited HLA polymorphism such as in Japan and Israel. On account of this, it is universal practice to irradiate cellular blood products with gamma irradiation to a mid-plane dose of approximately 25 centigray (cG) in order to destroy the replicating ability of viable immunocytes. It should be noted that TA-GVHD is associated with cellular products which are fresh, i.e. generally less than 15 days. However, "aging" of blood is not as yet an accepted practice in preventing this complication. Although the immunocytes are part of the allogenic leukocyte population, the degree of leukodepletion currently achieved with third generation filters is not considered currently adequate to prevent this complication. Thus, gamma irradiation at this time remains the only accepted prophylactic intervention.

With regard to platelet products, some loss in viability has been reported.

Considerable evidence indicates that gamma irradiation exerts its effects by generating activated oxygen species, such as singlet oxygen, hydroxy, radical, and superoxide anion. These species induce intracellular damage to DNA, thus prevent cell replication, a prerequisite to TA-GVHD. However, these same oxygen species may oxidize platelet membrane, inducing a membrane lesion which reduces the quality (potency) of the cellular product.

L-carnitine is known to play a key role in the transportation of long chain fatty acids across the mitochondrial membrane. Hereditary disorders in which there is a failure of the carnitine system to transport long chain fatty acids results in significant impairment in skeletal muscle function.

L-carnitine or the aforesaid alkanoyl L-carnitines may be used to abrogate or prevent membrane lesions induced by irradiation.

To limit PC susceptibility to membrane lesions and hemolysis, the blood product may be first suspended in a solution including L-carnitine or one of the aforesaid alkanoyl L-carnitines in an amount of 0.25 mM - 50 mM. Cell membrane maintenance and suppression of hemolysis is achieved to a sufficient degree that the sealed product can be irradiated for the purposes of sterilization, and subsequently may enjoy an extended shelf life and circulation half-life after transfusion. Viability on the order of current viabilities can be achieved, with materials more nearly certain to be sterile and unlikely to introduce TA-GVHD, due to irradiation after sealing the blood product suspension. The term blood product, in this connection, is to be interpreted to include PCs.

Variations for the present invention will occur to those of ordinary skill in the art without the exercise of inventive faculty. In particular, alternate stabilizing compositions, blood products, preservatives, inhibitors and the like may be modified, without the exercise of inventive skill. Additionally, specific levels, viability periods and circulation half-lives will vary from donor to donor, and recipient and recipient. Such variations remain within the scope of the invention, unless specifically excluded by the recitations of the claims set forth below.

Claims (10)

1. A method of improving membrane maintenance and suppressing hemolysis on storage of platelet concentrate (PC), comprising suspending said PC in a support solution comprising a carnitine product selected from the group consisting of L-carnitine (LC), alkanoyl L-carnitines or the pharmacologically acceptable salts thereof and mixtures thereof, in an amount effective to improve the ability of said PC to maintain the membrane of said platelets, and to thereby suppress hemolysis, as compared with an identical support solution lacking said L-carnitine, alkanoyl L-carnitines or the pharmacologically acceptable salts thereof and mixtures thereof.
2. The method of claim 1, wherein said L-carnitine, alkanoyl L-carnitines and mixtures thereof is present in a range of 0.25-50mM.
3. The method of claim 2, wherein said L-carnitine, alkanoyl L-carnitines and mixtures thereof is present in an amount of 1-20mM.
4. A sealed container of PC in a stabilizing solution, said stabilizing solution comprising L-carnitine, alkanoyl L-carnitines and mixtures thereof in an amount of 0.25-50 mM.
5. The sealed container of claim 4, wherein said container, subsequent to sealing, has been irradiated to substantially sterilize it and destroy leukocytes therein.
6. A method of substantially sterilizing PC, comprising suspending said PC in a support solution, said solution comprising LC in an amount of 0.25-50 mM, and irradiating said blood product after seating said product within a container, so as to substantially sterilize said blood product.
7. A method of treating PC to suppress leukocytes therein, comprising irradiating said PC in a support solution comprising LC in an amount of 0.25-50 mM, so as to substantially destroy leukocytes in said sample while suppressing damage to membranes of said PC.
8. A method of improving membrane maintenance and suppressing hemolysis on storage of a platelet concentrate (PC) following irradiation of the same for the purpose of destroying immunocytes therein, comprising suspending said PC in a support solution, said support solution comprising a carnitine product selected from the group consisting of L-carnitine, alkanoyl L-carnitines and mixtures thereof, in an amount effective to improve the ability of said PC to maintain the membrane of said platelets, and to thereby suppress hemolysis as compared with identical support solution lacking said carnitine, alkanoyl L-carnitine, and mixtures thereof.
9. The method of claims 1, 2, 3, 6, 7, and 8, wherein the alkanoyl L-carrnitine is selected from the group comprising acetyl, propionyl, butyryl, isobutyryl, valeryl and isovaleryl L-carnitine.
10. The sealed contained of claims 4-5, wherein the alkanoyl L-carnitine is selected from the group comprising acetyl, propionyl, butyryl, isobutyryl, valeryl and isovaleryl L-carnitine.