Abstract:
The present invention relates to new compositions for the preservation of organs prior to implantation comprising hydroxyethyl starch substantially free of ethylene glycol, ethylene chlorohydrin and acetone in a pharmaceutically acceptable organ perfusate.

Description:
This invention was made with Government support under NIH Grant No. AM18624 awarded by the Department of Health and Human Services. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Renal preservation, the ex vivo storage of cadaveric kidneys, is a relatively new field. Preservation of cadaveric kidneys for transplantation is common practice in hospitals; however, advances have been limited to trial and error experimentation. Although this approach has been partially successful from a clinical standpoint, the actual principles behind these successes are not well understood. 
     As renal transplantation has evolved from a strictly research procedure to an esablished clinical therapy for end-stage renal disease, renal preservation has progressed from the laboratory research stage to an established clinical method. At present, the two most commonly used methods for renal preservation are simple hypothermic storage and continuous perfusion. With simple hypothermic storage, the most common method of clinical renal preservation, the organs are removed from the cadaver doner and are cooled rapidly. This is usually achieved by a combination of external cooling and a short period of perfusion to drop the core temperature as quickly as possible. The kidneys are then stored, immersed in a flush-out solution in a simple plastic container, and kept at a temperature of 0° to 4° by immersing the container in ice. The advantages of this method are its simplicity, its low cost, and the ease of transportation of the organs. The composition of the flush-out solution to provide optimum preservation has been extensively studied. 
     The second method of renal preservation which has undergone extensive laboratory investigation, as well as clinical testing, is continuous pulsatile perfusion. The basic ingredients of continuous perfusion are (1) pulsatile flow, (2) hypothermia, (3) membrane oxygenation, and (4) a perfusate containing both albumin and lipids. With minor modifications, all presently used clinical preservation units share these basic principles. There are several advantages to continuous perfusion in clinical transplantation. First, perfusion provides enough time to make cadaveric transplantation a partly elective procedure. Second, it allows viability testing prior to implantation. A significant improvement in the results of cadaveric renal transplantation could be expected if the preservation time could be extended to the 5 to 7 days required for present methods of mixed lymphocyte culture testing. 
     The ability to successfully preserve human kidneys for two to three days by either simple cold storage after initial flushing with an intracellular electrolyte solution or by pulsatile perfusion with an electrolyte-protein solution has allowed sufficient time for histo-compatibility testing of the donor and recipient, kidney sharing among transplant centers, careful preoperative preparation of the recipient, time for preliminary donor culture results to become available, and vascular repairs of the kidney grant prior to implantation. Kidneys preserved for 72 hours using hypothermic pulsatile perfusion with cryoprecipitated plasma proved to be a significant advance for human kidney preservation and is currently the preferred method of preservation. Kidney organ preservation with ice-cold intracellular electrolyte flush solution followed by simple cold storage has been satisfactorily employed for human kidney preservation for up to 61 hours. 
     Serum albumin, in various forms, is used exclusively for clinical organ preservation to produce the necessary oncotic pressure. These forms include cryoprecipitated plasma, plasma protein fraction, human serum albumin, and silica gel-treated plasma. However, because these perfusates are prepared from naturally derived materials, variation is unavoidable. It would be particularly advantageous if a perfusate containing a synthetic colloidal was available. 
     In the past, a large number of synthetic colloidal materials have been experimentally tested for effectiveness in kidney preservation. These colloids include dextrans, polyvinyl pyrrolidine, pluronics, hydroxyethyl starch (HES), Ficoll, gum arabic, and polyethylene glycol. None of these were as effective as serum albumin. However, HES was effective for 24 hours of preservation and in some cases for 72 hours of preservation. These colloidal materials were all tested in saline-based perfusates. Recently, excellent 72-hour preservation of canine kidney was observed with a perfusate containing gluconate anions in place of chloride with human serum albumin (HSA) for colloidal osmotic support. 
     In accordance with the present invention a method of preserving kidneys using a perfusate containing HES in place of human serum albumin is disclosed. 
     As indicated hereinabove, serum albumin (HSA) based perfusates have been the standard for preservation of kidneys both experimentally and clinically for the past 17 years. Unfortunately preservation periods of only three days could be obtained with these types of perfusates. Although both of these methods preserve kidney viability for up to three days, longer preservation times are difficult to obtain consistently. Moreover, even though these methods preserve viability for up to three days, the kidneys are damaged as indicated by the elevated post-transplantation serum creatinine levels and time required to return those elevated levels to normal. Early perfusates were chosen from electrolyte solutions readily available for intravenous infusion and were basically of extracellular composition. 
     Heretofore, acceptable methods for renal preservation have not been available. Those that have been proven clinically effective are limited to short-term-storage (three days) and significantly reduced viability. The present invention describes the biochemical composition of the perfusate best suited for the hypothermically perfused kidneys and a novel synthetic colloidal osmotic agent that yields significantly improved long-term preservation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a comparison of human serum albumin and hydroxyethyl starch perfusates on renal function after three days of perfusion preservation in accordance with the prior art; 
     FIG. 2 shows the effects of dialysis of hydroxyethyl starch on post-transplant renal function after five days of perfusion preservation in accordance with the present invention, with the creatinine level indicated; 
     FIG. 3 shows the effects of dialysis of hydroxyethyl starch on post-transplant renal function after seven days of perfusion preservation in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In accordance with the present invention the preferred colloid is hydroxyethyl starch having a weight average molecular weight of from about 150,000 to about 350,000 daltons and degree of substitution of from about 0.4 to about 0.7. A more preferred colloid is hydroxyethyl starch having a weight average molecular weight of from about 200,000 to about 300,000 daltons. In accordance with one embodiment of the present invention, the hydroxyethyl starch is dialyzed against distilled-deionized water or otherwise treated to remove several contaminants previously unknown to have an adverse affect on the effectiveness of hydroxyethyl starch preparations. The materials removed by the dialysis process are the very smallest hydroxyethyl starch components, including the ethylene glycol and ethylene chlorohydrin side products of the hydroxyethylation as well as the residual acetone and sodium chloride. Ethylene glycol and ethylene chlorohydrin are known to be toxic. Hence, their removal, even if present in small amount, is desirable. 
     In accordance with the present invention, the kidney perfusate composition includes, but is not limited to, the following: 
     Table 1 
     5% hydroxyethyl starch having a molecular weight of from about 200,000 to about 300,000 and a degree of substitution of from 0.4 to 0.7. 
     25mM KH 2  PO 4   
     3mM glutathione 
     5mM adenosine 
     10mM glucose 
     10mM HEPES Buffer (Sigma Chemical Company) 
     5mM magnesium gluconate 
     1.5mM CaCl 2   
     105mM sodium gluconate 
     200,000 units of penicillin 
     40 units insulin 
     16mg Dexamethasone 
     12mg Phenol Red 
     pH 7.4-7.5. 
     The post-transplant serum creatinine levels in dogs receiving a kidney preserved for three days with the hydroxyethyl starch (HES) perfusate is compared with the albumin (HSA) perfused kidney in FIG. 1 With HES as part of the perfusate, there is a slight elevation of the serum creatine during the first 2-4 days post-transplant followed by a rapid return to normal. 
     Extending the preservation time with this basic perfusate was unsuccessful until the starch was dialized prior to preparation of the perfusate. As shown in FIG. 2, the dialyzed starch gave successful preservation although the kidneys exhibited somewhat elevated serum creatinine values. 
     Seven day preservation of kidneys was accomplished with the HES-based perfusate. As shown in FIG. 3, five of 17 dogs (30%) survived seven day preservation. In all 17 dogs, none showed signs of endothelial damage. Thus, the HES-based perfusate extends the preservation time beyond that which was possible with the HSA perfusate. 
     In addition to the HES, the perfusate is radically different from other commonly used perfusates. Chloride has been replaced with the larger molecular weight (and less permeable) gluconate to suppress hypothermic induced cell swelling. Adenosine and PO 4  are included to stimulate ATP syntheses. Glutathion is added to suppress the loss of glutathione from perfused organs and to act as an antioxidant. The K +  concentration is elevated to 25mM to suppress the loss of intracellular K +   at hypothermia and PO 4  and HEPES are used as buffers. The role of some of these agents have been shown to be beneficial to kidneys during preservation. 
     EXAMPLE 1 
     One hundred grams of hydroxyethyl starch was dissolved in one liter of distilled-deionized water to make a 10% w/w solution. The HES solution was placed in dialysis bags (34 mm×18 inches) having a molecular weight cut-off of 50,000 daltons, placed in a 10-15 liter container of distilled-deionized water, and stirred for 72 hours. The water was changed daily, and the HES was collected and frozen at -20° C. until used. 
     EXAMPLE 2 
     Adult mongrel dogs (15 to 25 kg) were used in all cases. Surgical procedures and hypothermic pulsatile perfusion preservation were performed by conventional procedures. The composition of the perfusate is shown in Table 1. Kidneys were transplanted after 72 hours of preservation followed by immediate contralateral nephrectomy. Serum creatinine level was determined daily after the transplant. 
     Accordingly, the present invention provides extended clinical organ preservation time and, as a synthetic colloid, minimizes the variation which results from perfusates prepared from naturally derived materials. 
     The present invention has been described in detail and with particular reference to the preferred embodiments; however, it will be understood by one having ordinary skill in the art that changes may be made thereto without departing from the spirit and scope thereof.