Boronic acid-containing aminopyridine- and aminopyrimidinecarboxamide CXCR1/2 antagonists: Optimization of aqueous solubility and oral bioavailability

The chemokine receptors CXCR1 and CXCR2 are important pharmaceutical targets due to their key roles in inflammatory diseases and cancer progression. We have previously identified 2-[5-(4-fluoro-phenylcarbamoyl)-pyridin-2-ylsulfanylmethyl]-phenylboronic acid (SX-517) and 6-(2-boronic acid-5-trifluoromethoxy-benzylsulfanyl)-N-(4-fluoro-phenyl)-nicotinamide (SX-576) as potent non-competitive boronic acid-containing CXCR1/2 antagonists. Herein we report the synthesis and evaluation of aminopyridine and aminopyrimidine analogs of SX-517 and SX-576, identifying (2-{(benzyl)[(5-boronic acid-2-pyridyl)methyl]amino}-5-pyrimidinyl)(4-fluorophenylamino)formaldehyde as a potent chemokine antagonist with improved aqueous solubility and oral bioavailability.

Boronic acid-containing CXCR1/2 antagonists: Optimization of metabolic stability, in vivo evaluation, and a proposed receptor binding model

Blockade of undesired neutrophil migration to sites of inflammation remains an area of substantial pharmaceutical interest. To effect this blockade, a validated therapeutic target is antagonism of the chemokine receptor CXCR2. Herein we report the discovery of 6-(2-boronic acid-5-trifluoromethoxy-benzylsulfanyl)-N-(4-fluoro-phenyl)-nicotinamide 6, an antagonist with activity at both CXCR1 and CXCR2 receptors (IC50 values 31 and 21 nM, respectively). Compound 6 exhibited potent inhibition of neutrophil influx in a rat model of pulmonary inflammation, and is hypothesized to interact with a unique intracellular binding site on CXCR2. Compound 6 (SX-576) is undergoing further investigation as a potential therapy for pulmonary inflammation.

Discovery of 2-[5-(4-Fluorophenylcarbamoyl)pyridin-2-ylsulfanylmethyl]phenylboronic Acid (SX-517): Noncompetitive Boronic Acid Antagonist of CXCR1 and CXCR2

The G protein-coupled chemokine receptors CXCR1 and CXCR2 play key roles in inflammatory diseases and carcinogenesis. In inflammation, they activate and recruit polymorphonuclear cells (PMNs) through binding of the chemokines CXCL1 (CXCR1) and CXCL8 (CXCR1 and CXCR2). Structure-activity studies that examined the effect of a novel series of S-substituted 6-mercapto-N-phenyl-nicotinamides on CXCL1-stimulated Ca(2+) flux in whole human PMNs led to the discovery of 2-[5-(4-fluorophenylcarbamoyl)pyridin-2-ylsulfanylmethyl]phenylboronic acid (SX-517), a potent noncompetitive boronic acid CXCR1/2 antagonist. SX-517 inhibited CXCL1-induced Ca(2+) flux (IC50 = 38 nM) in human PMNs but had no effect on the Ca(2+) flux induced by C5a, fMLF, or PAF. In recombinant HEK293 cells that stably expressed CXCR2, SX-517 antagonized CXCL8-induced [(35)S]GTPγS binding (IC50 = 60 nM) and ERK1/2 phosphorylation. Inhibition was noncompetitive, with SX-517 unable to compete the binding of [(125)I]-CXCL8 to CXCR2 membranes. SX-517 (0.2 mg/kg iv) significantly inhibited inflammation in an in vivo murine model. SX-517 is the first reported boronic acid chemokine antagonist and represents a novel pharmacophore for CXCR1/2 antagonism.

Liver transplantation from non-heart beating donors in rats: influence of viscosity and temperature of initial flushing solutions on graft function

BACKGROUND

We evaluated the effect of warm (37 degrees C) versus cold (4 degrees C) solutions as the initial flush for liver preservation from non-heart beating donors in rats.

METHODS

An initial flush was performed just before donor hepatectomy with cold or warm University of Wisconsin solution (UW), UW without hydroxyethyl starch, sodium lactobionate sucrose solution, or lactated Ringer's solution as the control group. A separate group also used as control received no initial flushing. Liver transplantation was performed, and the graft function was determined by survival and assessment of enzyme release. The viscosity of each solution and the vascular resistance of the graft were measured.

RESULTS

The 7-day survival rate was 83% and 100% in the warm and cold sodium lactobionate sucrose solution groups and 60% and 50% in the warm and cold lactated Ringer's solution groups, respectively. In the no-initial-flush group, rats did not survive. The 7-day survival rate was 67% and 0% in the warm and cold UW groups, respectively. Eliminating the hydroxyethyl starch from the cold UW improved the survival to 67%. Serum alanine aminotransferase levels 1 day after transplantation in the no-initial-flush and the cold UW groups were significantly higher than those of the remaining groups. At 4 degrees C the viscosity was higher in the UW (86.2 cp) compared to hydroxyethyl starch-free UW solution (30.9 cp), lactated Ringer's solution (24.5 cp), and sodium lactobionate sucrose solution (32.7 cp). The viscosity of UW at 37 degrees C was 34.7 cp. Vascular resistance correlated well with the viscosity. Livers flushed with solutions with a low viscosity showed lower vascular resistance than those flushed with cold UW and led to better survival.

CONCLUSIONS

These data suggest that the viscosity of the initial flushing solution may play an important role in determining the outcome of organ procurement from non-heart beating donors.

Twenty-four-hour ice storage of rabbit heart

Although cardioplegia is limited to 4 hours of ice storage, University of Wisconsin solution has successfully extended this period to approximately 12 hours. In this study we have substituted polyethylene glycol for hydroxyethyl starch in a simplified University of Wisconsin solution (Cardiosol). Rabbit hearts were ice stored for 24 hours at 0 degrees C in either University of Wisconsin solution or Cardiosol (containing either 5% or 10% polyethylene glycol). Fresh control hearts were tested immediately after cardiectomy. Function was evaluated in an in vitro working heart model for 1 hour with aortic afterload at 100 cm H2O. Total cardiac output or the proportion of hearts reaching 100 cm H2O were compared. Hearts stored in University of Wisconsin solution for 24 hours functioned at 6% of control levels at 15 minutes of observation. None reached 100 cm H2O or deteriorated further with time (p < 0.05). By contrast, hearts stored in 5% Cardiosol showed progressive recovery during the 1-hour observation. Of the 13 hearts, 11 reached 100 cm H2O with a mean cardiac output of 51% of the control value. Increasing the concentration of polyethylene glycol to 10% improved cardiac output at all observation times, reaching 80% of control heart performance at 1 hour (control > 10% > 5% > University of Wisconsin solution [p < 0.05]). We concluded that 10% polyethylene glycol significantly improved 24-hour ice storage and, hence, viability to a functional level that matched our previously reported microperfusion results.

Modification of rejection by polyethylene glycol in small bowel transplantation

The use of polyethylene glycol (PEG) in preservation solutions has been associated with a decreased incidence of rejection in clinical and experimental organ transplantation. In this study, we examined the effect of PEG with different molecular configurations on rejection of small bowel allografts in the rat. Male ACI and LEW rats were used as donors and recipients, respectively. Orthotopic small bowel transplantation was performed using the following preservation solutions: lactated Ringer's solution (n = 7), University of Wisconsin solution (n = 7), University of Wisconsin solution without hydroxyethyl starch (sUW; n = 7), sUW with PEG20M (n = 9), sUW with PEG8000 (n = 6), and sUW with PEG20L (n = 7). No immunosuppression was given. In orthotopic small bowel transplantation, only groups with a high molecular weight PEG, PEG20M and PEG20L, demonstrated longer survival (P < 0.01 and P < 0.001, respectively) and delayed onset of unkempt appearance (P < 0.05 and P < 0.001, respectively). In heterotopic small bowel transplantation, sUW was compared with sUW with PEG20L. Rejection occurred later and its progression was slower in the sUW with PEG20L than in the sUW alone. Our observations suggest that the onset and progression of rejection after small bowel transplantation were influenced by the molecular weight and configuration of the PEG molecule. The mechanism is unclear, but high molecular weight PEG appears to reduce or change the immunogenicity of the small bowel allograft.

Cardiotonic effects of reduced sulfhydryl amines after preservation of rabbit hearts

This investigation was designed to examine the role of glutathione and other reduced sulfhydryl amines during reperfusion of the ischemic rabbit heart. To identify the biochemical features of reduced sulfhydryl amines contributing toward improved myocardial function, we investigated several chemical agents sharing a common property with glutathione (L-leucine, L-glycine, ascorbate, oxidized glutathione, L-cysteine). After a period of 24-hour hypothermic storage of the rabbit heart in a modified University of Wisconsin solution containing polyethylene glycol, the hearts were functionally evaluated on a Langendorff working heart model. The agents were then injected as a bolus (60 mumol/L) during reperfusion, and coronary flow and aortic output were measured. Control hearts were untreated. Reduced sulfhydryl amines (glutathione, L-cysteine) significantly improved coronary flow (p < 0.005) and cardiac output (p < 0.005). Ascorbate, L-leucine, L-glycine, and oxidized glutathione all failed to influence cardiac function.

Significance of terminal rinse for rat liver preservation

A terminal rinse (TR) is standard practice in liver preservation with University of Wisconsin solution (UW) to avoid a potassium load. The fact that sodium lactobionate sucrose solution (SLS) is an effective organ preservation solution with a low potassium provided an opportunity to evaluate rat liver preservation without the TR step. Its importance was investigated in 122 rat liver preservation experiments. In study 1, UW and a hydroxyethyl starch-free, modified UW (UWm) were used for 20-hr liver preservation followed by either no TR or Ringer's lactate TR. The 1-week survival was: UW-TR, 2/14; UW-no TR, 1/6; UWm-TR, 0/6; UWm-no TR, 5/5 (P < 0.01). In study 2, livers were stored for 30 hr in SLS, UW, UWm, and UWm + chlorpromazine 5 mg/L, all without a TR. Nine of 11 rats survived 7 days after SLS, but there were no survivors in the other groups (P < 0.05). Study 3 compared no TR with TR with SLS, Ringer's lactate (RL), or a modified Carolina rinse (CRm) after 30-hr SLS preservation. Survival, serum aspartate aminotransferase and alanine aminotransferase, and histology were assessed. One-week survival of 9/11 rats in no TR was significantly better than in the other groups (3/14 in TR-SLS, 0/8 in TR-RL, and 0/14 in TR-CRm, P < 0.01). The values of aspartate aminotransferase (mean +/- SE) 3 hr after transplantation were 1862 +/- 439 U/L, 3334 +/- 817 U/L, 6591 +/- 1944 U/L, and 7028 +/- 1704 U/L, respectively, in no TR, TR-SLS, TR-RL, and TR-CRm. There were significant differences both in aspartate aminotransferase and alanine aminotransferase between no-TR and each of TR-RL and TR-CRm (P < 0.05). Liver specimens from rats killed 3 hr after OLT showed only mild injury in the no TR group and severe injury in the remaining groups. We conclude that a terminal rinse is harmful in rat liver preservation.

New organ preservation solutions

In 1969 we described a method for kidney preservation that used a brief flush with a new "intracellular" solution followed by ice storage. This paper stimulated research into optimizing solution composition culminating in the UW solution which is now the accepted standard. Further developments in the design of solutions for hypothermic organ preservation have proceeded along several paths, including: (1) modification and simplification of UW solution, (2) investigation of organ specific requirements, (3) addition of pharmacologic agents particularly calcium antagonists to flush solutions, (4) the concept of "microperfusion" for control of acidosis, (5) the use of solutions containing polyethylene glycol, and (6) the use of a terminal rinse solution. Broadly speaking, the results of these studies have shown that it is possible to improve upon the UW solution by simplification, eliminating several of the components, and that sodium variants, and pharmacological additives, such as chlorpromazine, may yield better results in experimental and clinical trials. It has also been found that there are special requirements for individual organs, rendering the concept of a universal solution unlikely. Of the promising new ideas, microperfusion and polyethylene glycol have been found to be very effective for heart preservation yielding for the first time virtually perfect 24-hour preservation. The concept of a terminal rinse to diminish reperfusion injury has strong experimental support and awaits clinical evaluation.

Calcium antagonists in sodium lactobionate sucrose solution for rat liver preservation

The effects of the calcium antagonists, chlorpromazine (CPZ), nisoldipine (NIS), trifluoperazine (TFP), and nicardipine (NIC) were compared in rat livers following either 20- or 30-hr ice storage in sodium lactobionate sucrose solution (SLS). Survivals beyond 7 days after orthotopic liver transplantation following 20-hr cold storage were 1/14 in the University of Wisconsin solution, 4/14 in SLS, 4/8 in UW+CPZ, 7/8 in SLS+CPZ. Survivals beyond 7 days after OLT following 30-hr cold storage were 3/8 in SLS+CPZ, 3/8 in SLS+NIS, 2/8 in SLS+TFP, 0/8 in SLS+NIC, and 0/8 in SLS alone. Survival rates were significantly (P less than 0.05) better in both SLS+CPZ and SLS+NIS than in UW and SLS alone. The effluent lactate dehydrogenase (LDH) levels and pH changes were measured at the time of OLT. After 20 hr, LDH levels were 525 +/- 78 IU/L (mean +/- SEM) in UW, 492 +/- 44 in SLS, 322 +/- 35 in UW+CPZ, and 290 +/- 39 in SLS+CPZ. After 30 hr, LDH values were 416 +/- 40 in SLS+CPZ, 450 +/- 25 in SLS+NIS, 448 +/- 21 in SLS+TFP, 573 +/- 18 in SLS+NIC, and 614 +/- 68 in SLS. The LDH levels for SLS+CPZ and SLS+NIS were significantly lower than those of SLS and UW (P less than 0.01). The pH changes in the effluent were significantly less in both the CPZ and NIS groups (P less than 0.01). This study demonstrated improved liver preservation by the use of a simplified colloid-free lactobionate solution containing sodium as the principal cation. The addition of CPZ or NIS to the solution demonstrated the same potency for significant improvement in efficacy of this solution, while NIC was ineffective.

Successful 20-hour rat liver preservation with chlorpromazine in sodium lactobionate sucrose solution

We investigated the effect of the addition of chlorpromazine to a new, simplified organ preservation solution, sodium lactobionate sucrose (SLS), for 20-hour hypothermic rat liver preservation. Survival beyond 7 days after orthotopic transplantation of the stored liver was eight of eight rats in control groups (immediate transplantation, less than 1-hour preservation), one of 14 rats with the University of Wisconsin (UW) solution, four of 14 rats with SLS, seven of eight rats with SLS + chlorpromazine, 1 mg/L, and seven of eight rats with SLS + chlorpromazine, 10 mg/L. The differences is survival between UW and SLS and between SLS and SLS + chlorpromazine were significant (p less than 0.05). Lactic dehydrogenase levels in the effluent after reflushing through the portal vein at the time of transplantation were 145 +/- 20 IU/L (mean +/- SEM) in the controls, 525 +/- 78 IU/L in UW, 492 +/- 44 IU/L in SLS, 290 +/- 39 IU/L in SLS + chlorpromazine, 1 mg/L, 290 +/- 11 IU/L in SLS + chlorpromazine, 10 mg/L. The values for the SLS + chlorpromazine were significantly lower than for SLS and UW (p less than 0.05). The pH of the effluent was 7.10 +/- 0.10 in controls, 6.42 +/- 0.12 in UW, 6.64 +/- 0.18 in SLS, and 7.07 +/- 0.02 in SLS + chlorpromazine, 1 mg/L and 10 mg/L. The pH drop was significantly greater in the groups without chlorpromazine (p less than 0.01). This study shows that superior rat liver preservation was achieved with a simplified lactobionate solution containing sodium as the principal cation, sucrose in place of raffinose, and omitting the colloid and several of the other UW components. The addition of low concentrations of chlorpromazine further enhanced the effectiveness of this solution, without the need for donor pretreatment.

Optimal cardioplegia and 24-hour heart storage with simplified UW solution containing polyethylene glycol

Recent work has shown that UW may be better than standard cardioplegic solutions for short-term heart preservation. In this study we have used a rabbit heart model to evaluate a simplified UW solution in which penicillin, dexamethasone, insulin, allopurinol, and adenosine were omitted and 5% polyethylene glycol (PEG20M) was substituted for hydroxyethyl starch. The test systems consisted of 4-hr cardioplegic storage at 15 degrees C with repeated flushing every 30 min for 2 hr and 24-hr hypoxic low-flow microperfusion (3 ml/g/24 hr) at 0 degrees C. Control groups were arrested with a 15-25 ml flush in iced saline and immediately tested. Cardiac output (CO)* after preservation was measured in a working heart model using an acellular perfusate at 37 degrees C at an aortic pressure of 100 cm H2O. The CO (ml/g heart wt/min) were as follows--Controls: St. Thomas II 20.5 +/- 8.3 (5), UW 34.7 +/- 11.7 (16), PEG20M 41.8 +/- 4.4 (14); 4-hr cardioplegia: St. Thomas II 17.4 +/- 0.9 (4), Bretschneider HTK 14.9 +/- 7.0 (4), UW 25.2 +/- 11.5 (9), PEG20M 41.1 +/- 7.8 (8); 24-hr microperfusion: UW 25.4 +/- 11.1 (18), PEG20M 37.1 +/- 8.2 (18). Following cardioplegic or microperfusion preservation, PEG20M hearts functioned at control levels (P greater than 0.05) and were significantly superior to all other solutions, with approximately double the CO (P less than 0.05, all other groups). We conclude that for heart preservation, 5 components can be eliminated from UW and substitution of PEG20M for HES appears to have improved its performance.

The pathophysiological effects of brain death on potential donor organs, with particular reference to the heart

Major electrocardiographic, haemodynamic, and histopathological changes take place during the development of brain death; myocardial and pulmonary injury may result. Significant depletion of certain circulating hormones occurs, resulting in an inhibition of mitochondrial function, leading to reduced aerobic metabolic oxidative processes, affecting the body as a whole. Major organ energy stores are therefore diminished, leading to deterioration of function. Replacement of the depleted hormones, in particular triiodothyronine (T3), cortisol, and insulin, leads to rapid replacement of organ energy stores, associated with a return to normal function. T3 alone leads to reactivation of the mitochondria, stimulating aerobic metabolism. Hormonal therapy to brain-dead potential organ donors has been shown to lead to metabolic and haemodynamic stability, resulting in no wastage of organs, and in improved function after transplantation.

Vascular resistance vs. perfusate osmolarity: the short term microvascular effect of hypotonic and hypertonic perfusion in the isolated kidney

Vascular resistance changes were measured in response to alteration in perfusate osmolarity in isolated rabbit kidneys perfused at 10 degrees C. The data obtained were found to fit a simple mathematical model of the vascular resistance of the microcirculation in which it was assumed that variation in this parameter depended solely upon osmotic alterations in the size of the cells within and around the blood vessel walls. The model predicts that the volumetric changes due to the different osmolarities are produced in a tissue layer whose thickness is 30% relative to a fixed outer radius. This result is compatible with the hypothesis that the effects are predominantly due to changes of endothelial cell volume and other perivascular capillary cells. The analysis illustrates the significance of perfusate osmolarity as a determinant of vascular resistance, can be used to investigate the hemodynamic effects that occur during the introduction and removal of cryoprotective agents, and is relevant to the interpretation of results obtained with hypertonic solutions in blood volume restoration after hypovolemic shock.

24-hour rabbit heart storage with UW solution. Effects of low-flow perfusion, colloid, and shelf storage

A new technique for 24-hr cardiac preservation is described utilizing very low flow perfusion (microperfusion) with a cold flush solution. Rabbit hearts were arrested with UW solution and then perfused with the same solution through the aortic root at 0 degrees C at a rate of 3-6 ml/gm heart weight/24 hr. When tested on an ex vivo working heart model, the cardiac output (CO) was 28.72 +/- 7.69 ml/g/min compared with fresh UW flushed controls of 26.48 +/- 2.25 ml/g/min. Both oxygenated highflow perfusion with a more conventional perfusate and 24-hr ice storage with UW led to inferior results. Omission of the colloid, hydroxyethyl starch (HES), from the UW solution or prolonged shelf storage were also significantly detrimental. When a previously untested colloid, polyethylene glycol 20,000, was substituted for HES for microperfusion, excellent cardiac function was obtained. In fact, the mean CO of this group, 31.91 +/- 5.70, was significantly above that of fresh HES-UW unstored controls. The suggestion that the UW solution might be improved by this substitution warrants further study.

Initial experimental experience with a "replaceable" cardiac valve prosthesis

An easily "replaceable" cardiac valve prosthesis has been designed. It consists of two parts: (1) a sewing ring incorporating a circlip and (2) a functioning valve (either mechanical or tissue). The circlip is encased in a sewing ring, which is sutured into the natural valve annulus, and grips the functional part of the prosthesis, thereby preventing dislodgment. A simple instrument has been designed to open the circlip a few millimeters to allow easy removal or insertion of the functional element. This sewing ring/circlip with the functional element of a Björk-Shiley prosthesis was used in 10 baboons undergoing mitral valve replacement. Removal and replacement of the functional element was carried out at a second operation between 1 and 12 weeks later. There were no operative deaths. Baboons were electively killed one day to twelve months after the second operation. There were no complications related to the prosthesis; cardiac catheterization showed normal hemodynamics before and after the second operative procedure.

Pathophysiology of pulmonary edema following experimental brain death in the chacma baboon

Systemic and pulmonary hemodynamics have been studied during the induction of brain death in the chacma baboon. In 11 animals brain death was induced by acute intracranial hypertension. Continuous recording of blood flow through both the pulmonary artery and the aorta was obtained by electromagnetic flow meters placed around these vessels. Mean arterial, central venous, pulmonary arterial, and left atrial pressures were recorded continuously. Systemic and pulmonary vascular resistances were calculated. During the agonal period marked sympathetic activity occurred, with significant increases in circulating catecholamines and systemic vascular resistance. The great increase in systemic resistance resulted in acute left ventricular failure. Mean left atrial or pulmonary capillary wedge pressure rose above the mean pulmonary arterial pressure in 9 animals. As the systemic vascular resistance rose, a significant difference between pulmonary artery and aortic blood flows occurred, leading to blood pooling within the lungs. A mean of 72% of the total blood volume of the animal accumulated within these organs. The increase of left atrial pressure to levels higher than pulmonary artery pressure indicated a state of pulmonary capillary blood flow arrest. This, associated with the blood pooling within the lungs, almost certainly resulted in disruption of the anatomic integrity of the pulmonary capillaries (blast injury); 4 animals developed pulmonary edema, with alveolar septal interstitial hemorrhage.

Improved cardiac function following hormonal therapy in brain dead pigs: relevance to organ donation

Deterioration of function in brain dead baboons is associated with depletion of both myocardial energy stores and certain circulating hormones, notably thyroxine, cortisol, and insulin. We have therefore investigated the effect of the administration of these three hormones to the brain dead pig; their value has been assessed on both the freshly excised and stored donor heart. Brain death was induced by ligation of the two arteries to the upper part of the body which arise from the aortic arch. Storage of selected hearts was by continuous hypothermic perfusion for 20 to 24 hr. Hearts were biopsied for estimation of adenosine triphosphate, creatine phosphate, lactate, and glycogen, and were subsequently functionally tested. Six groups of pigs were studied. Hearts were tested from control pigs which had not undergone brain death (A1), from brain dead pigs which had received intravenous fluid and inotropic support for 4 hr (B1), and from brain dead pigs which had in addition received 2 hr of hormonal therapy (thyroxine 2 micrograms cortisol 100 mg, and insulin 5-10 IU hourly) (C1). A further 3 groups (A2-C2) underwent management identical to A1-C1, but in addition the hearts were stored for 24 hr. Brain death in pigs was followed by a consumption of myocardial energy stores, despite anaerobic glycolysis; this was associated with reduced myocardial function. The administration of hormones to the brain dead pig led to some replenishment of myocardial energy and glycogen reserves and reduction in lactate, with associated improvement in hemodynamic function. A period of hypothermic perfusion storage appeared to reverse the anaerobic metabolism occurring in the heart in the nonhormonally treated brain dead animal, though not in the hormonally treated animal, and led to replenishment of glycogen reserves in nontreated animals. The observation that both better function and an increase in myocardial energy stores occurred in hormonally treated, stored hearts, even though perfusate lactate dehydrogenase rose to significantly higher levels during hypothermic perfusion storage, and tissue lactate levels remained high, suggests that thyroxine promotes both aerobic and anaerobic metabolism in brain dead animals.

Loss of myocardial viability following hypothermic perfusion storage from contaminating trace elements in the perfusate

Two groups (A and B) of isolated baboon hearts were preserved by continuous hypothermic perfusion storage for 48 hours using perfusates that, according to the manufacturers, differed only in the concentrations of the contaminating trace elements iron, lead, and arsenic. Storage with the perfusate containing the higher concentration of these elements (perfusate B) led to significantly less gain in heart mass, a greater reduction in coronary flow, coronary sinus effluent lactate, and myocardial arteriovenous oxygen difference and a greater increase in coronary sinus effluent lactate dehydrogenase, when compared with perfusate A. Group B hearts totally failed to support the circulation following orthotopic transplantation, whereas group A hearts showed excellent function. Group B hearts had undergone the typical changes of enhanced resting myocardial tension during the storage period (before warm blood reperfusion); we proposed that these changes were brought about by the production of superoxide anions and radicals by the higher relative concentration of iron, or a combination of contaminating trace elements, in perfusate B. To confirm that these perfusates did differ significantly in the concentration of these trace elements, in particular with regard to iron, the superoxide anion activity in both solutions was measured and was found to be significantly higher in perfusate B. The addition of superoxide dismutase to both solutions inhibited superoxide anion activity by more than 80%.

Hyperacute rejection in a discordant (pig to baboon) cardiac xenograft model

Eight freshly excised pig hearts were hemoperfused by baboons in vivo. Cardiac function ceased in six hearts after a mean period of 90 minutes of perfusion (range 30 to 190 minutes). Two hearts continued functioning for the 4-hour study period. On microscopic examination, seven hearts, including one that continued beating, showed histopathologic features of hyperacute rejection. IgG, IgM, and C3 were strongly present on the myocardium in all cases. Hemoperfusion was associated with significant increases in heart mass (p less than 0.002) and circulating polymorphonuclear leukocytes (p less than 0.03) and reductions in coronary blood flow (p less than 0.0001), circulating lymphocytes (p less than 0.03), and C4 (p less than 0.03). Preformed circulating anti-pig antibodies disappeared in all but one baboon. Hyperacute rejection in this discordant xenograft model that used a nonhuman primate as "recipient" differs in few aspects from that seen in other experimental models. Possible methods of prolonging xenograft survival are discussed.

The effects of brain death and 24 hours' storage by hypothermic perfusion on donor heart function in the pig

The effects on the myocardium of the agonal period and subsequent management have been studied in the pig. Acute ischemia of the brain led to major temporary hemodynamic changes. Brain death, with or without hemodynamic support of the circulation, led to a significant reduction in subsequent myocardial function, associated with some depletion of the myocardial high-energy phosphate and glycogen reserves, although the rate of this depletion was reduced by anaerobic glycolysis. Although 24 hours' storage by continuous hypothermic perfusion of hearts taken from control animals led to only a minimal reduction in myocardial function, storage increased the reduction in function associated with brain death when intravenous fluid and dobutamine support had been given to maintain the brain dead pig in a normotensive state. Storage, however, reduced the anaerobic metabolism seen in hearts functioning in hypotensive brain dead pigs and led to replenishment of the glycogen stores.

Prevention of myocardial injury during brain death by total cardiac sympathectomy in the Chacma baboon

In a previous study, structural myocardial damage was found to occur in 60% of baboons after brain death had been induced by a rapid increase in intracranial pressure. In the present study, we attempt to clarify the causative mechanisms involved in the development of such injury. Three groups of baboons were subjected to brain death: group A, the control; group B, those with previous surgical or pharmacological cardiac sympathectomy or cardiac denervation; and group C, those with bilateral vagotomy, incomplete sympathectomy, or bilateral adrenalectomy. Electrocardiographic and hemodynamic responses to brain death were greatly modified in group B baboons compared with responses in groups A and C. Groups A and C showed a high incidence of myocardial necrosis, whereas no myocyte damage was seen in the hearts of group B baboons. The histological appearance of innervated hearts following brain death (groups A and C) may closely resemble that seen during an acute rejection episode following cardiac transplantation. We suggest that myocardial damage occurring during the process of dying may be related to endogenous catecholamine release (possibly resulting in increased calcium uptake by the myocardial cells), inducing various forms of myocyte necrosis. This may result in early failure in a donor heart following cardiac transplantation.

Forty-eight hours hypothermic perfusion storage of pig and baboon hearts

A system has been developed for the continuous hypothermic perfusion of isolated hearts using a clear fluid perfusate. Myocardial viability has been maintained after periods of storage of up to 48 hr. Pig hearts stored in this way showed almost normal hemodynamic performance on subsequent functional testing. Orthotopic allotransplantation or autotransplantation of baboon hearts stored for 48 hr was followed by good immediate and long-term function. Baboons receiving allotransplants survived until rejection. Three of four of those autotransplanted survived until electively sacrificed at 1, 3, and 12 months; all showed normal hemodynamic function on cardiac catheterization and normal myocardial histology.

Impairment of renal slice function following brain death, with reversibility of injury by hormonal therapy

The effects of the agonal period and subsequent donor management on renal slice function, using the K+ - Na+ ratio, have been studied in the pig. Brain ischaemia or death resulted in a reduction in renal slice function, whether the pig was maintained normovolemic or hypovolemic by i.v. fluid and dobutamine therapy. This deterioration in function was, however, reversed or prevented by a period of therapy with thyroxine (T3), insulin, and cortisol. A period of 24 hr storage of the kidney slice in a low ionic strength solution in ice resulted in a further deterioration in slice function in all groups studied.

A successful method of administering cyclosporin A to the chacma baboon

Cyclosporin A (CYA) is a powerful immunosuppressant. Hitherto, it has proved difficult to maintain therapeutic whole-blood levels of the drug in the chacma baboon, making this animal unsuitable for transplantation studies if CYA is used. A successful method of maintaining adequate therapeutic levels after the intramuscular injection of CYA in a mixture of alcohol and Intralipid (Saphar) is described.

An airlift pump device for low pressure perfusion storage of the isolated heart

A portable apparatus for the continuous hypothermic perfusion of the isolated heart is described. The system has been used successfully to store pig and baboon hearts for periods of up to 48 hr, and to store human donor hearts for periods of 7 to 17 hr before being transplanted. The perfusate is both oxygenated and circulated by gas flow from a pressurized oxygen cylinder, using the air-lift pump principle. The apparatus has no moving parts and requires no electrical energy supply; malfunction is, therefore, extremely unlikely. A regulator has been incorporated which can be adjusted to increase or decrease the myocardial perfusion pressure. The system and environmental variables which can affect flow and pressure within the apparatus are discussed. The storage time allowed by this system will enable transportation of donor hearts between most of the world's major cities.