Improved renal transplant preservation using a modified intracellular flush solution (PB-2). Characterization of mechanisms by renal clearance, high performance liquid chromatography, phosphorus-31 magnetic resonance spectroscopy, and electron microscopy studies

Characterization of improved renal transplant preservation mechanisms using PB-2 flush solution by HPLC assay

Renal flush solutions have been found to be beneficial for extending organ viability, but their mechanisms of action are poorly understood. In order to delineate these mechanisms we studied the addition of mannitol and adenosine to a modified simple hypothermic intracellular flush solution (PB-2), and the relationships of renal adenine nucleotide (AN) concentrations with ischemia, reperfusion and viability. A significant (P < 0.05) and progressive decay in AN and increase in total degradation products (DP; hypoxanthine and xanthine) was noted during warm ischemia. Total AN and AMP were significantly higher after 50 h of cold storage in the PB-2 compared to the C-2 control cold flush group. Viability was associated with a significant (P < 0.01) regeneration of AN within 45 min of reperfusion. HPLC assay indicated that PB-2 cold flush solution enhances renal viability by both diminution of reperfusion injury enabling better reflow and primary preservation of AN. The latter process may appreciably contribute to the former process.

Improved renal preservation with PB-3 flush solution during 72 h of cold storage

Previously, PB-2 flush solution has been found to be superior to Collins 2 solution (C-2) in extending renal viability in the dog. To further characterize preservation mechanisms, we studied mitochondrial oxidative function during 72 h of cold storage comparing PB-3, UW-1, and C-2 flush storage solutions. Complex 1 dependent mitochondrial oxidative phosphorylation (MOP) was found to be significantly less (P < 0.001) at 5 h and 72 h of cold storage (P < 0.001) for the C-2 compared to the other flush groups. Complex 2 dependent MOP had parallel results, having significantly less function (P < 0.002) at 5 h and 72 h (P < 0.02) of cold storage in the C-2 group compared to the other groups. PB-3 and UW-1 solutions were noted to be comparable, suggesting possible equivalent preservation efficacy. Nevertheless the components of PB-3 at the level of MOP contributed significantly to better preservation compared to C-2 solution.

The role of magnetic resonance spectroscopy in the assessment of kidney viability

Renal transplant programmes are seriously limited by the continuing shortage of donor organs. Kidneys from marginal and non-heart-beating donors are increasingly being used, but their viability may be compromised. There is currently no rapid yet accurate method for assessing donor organ viability which can be applied within the window of opportunity between harvesting and implantation. Magnetic resonance spectroscopy (MRS) is a non-invasive technique which is being increasingly applied to delineate biochemical changes in vivo. Studies in animal models and humans now suggest that phosphorus-31 MRS may be useful in the non-invasive assessment of isolated donor kidney viability.

Assessment of preservation induced reperfusion injury via intraoperative renal transplant blood flow and endothelin concentration studies

PURPOSE

We investigated a possible relationship between levels of the vasoconstrictive peptide endothelin and renal transplant reperfusion injury, and modified a technique for measuring renal blood flow with an ultrasonic perivascular transit time flow probe.

MATERIALS AND METHODS

Renal grafts in a swine transplant model were cold flushed with either Collins-2 or University of Wisconsin solution. Renal blood flow and renal vein endothelin levels after reperfusion of transplanted grafts, as well as histological parameters within the transplanted kidney were measured. The 5-minute post-reperfusion renal blood flow was used as the baseline allograft flow. The definition of reperfusion injury was a decrease in flow from baseline with no recovery within 1 hour of reperfusion. In 9 human recipients reperfusion injury was further verified by monitoring subsequent serum creatinine, urine output, graft survival and rejection episodes.

RESULTS

In the swine model and human transplant recipients no evidence of post-reperfusion ischemia was noted by histological examination, supporting that moderate to mild reperfusion injury or ischemic injury cannot be clinically determined with this method. In the swine model the decrease flow from baseline in allograft post-reperfusion renal blood flow was significantly greater in kidneys preserved in Collins'-2 than in University of Wisconsin solution (41.75 +/- 5.69 versus 11.18 +/- 13.99 ml. per minute, p = 0.005), supporting that this technique can assess mild to moderate reperfusion injury. The increase in serum endothelin in the allografts from the swine model and in humans was not significantly different from baseline. Clinically, post-reperfusion renal blood flow changes correlated well with subsequent function. The 4 patients with renal transplant reperfusion injury had significantly higher serum creatinine values and lower urine output 1 week postoperatively than 5 patients with no evidence of injury (serum creatinine: 6.75 +/- 3.03 versus 2.08 +/- 1.28 mg./dl., p = 0.015). Reperfusion injury patients had more rejections (2 versus 1) and less graft survival (75% versus 100%) at 1-year followup compared to the nonreperfusion injury patients.

CONCLUSIONS

Vasoactive factors other than endothelin most likely contribute to reperfusion injury. Furthermore, the ultrasonic transit time flow probe accurately measures post-reperfusion renal blood flow and offers a practical method for assessing acute reperfusion injury, which may help to optimize immunosuppressive strategies to decrease allograft loss associated with delayed graft function.

Improvement of postischemic kidney function by reperfusion with a specifically developed solution (BT01)

Reperfusion is a critical phase of organ preservation. The purpose of this study was to develop a solution specifically for postischemic kidney reperfusion. Unilateral left normothermic kidney ischemia was induced for 60 minutes in two groups of micropigs. In group 1 (control pigs, n = 6) the kidney was reperfused immediately with pure blood at systemic pressure by unclamping the renal artery. In group 2 (test animals, n = 6) the kidney was initially reperfused with an intracellular flush solution enriched with solution BT01 composed of cytoprotectors (natriuretic factor, PGI2), free radical chelating agents (allopurinol, mannitol), and substrates for the mitochondrial respiratory chain (aspartate, glutamate). This solution was mixed immediately before use with blood in a ration of 1:4 parts and injected into the left renal artery with a perfuser at a constant pressure of 60 mm Hg. After 20 minutes, the kidney was reperfused with systemic blood for 100 minutes. Glomerular filtration rate (GFR) was determined by measuring inulin clearance. Kidney blood flow was measured throughout the experiment. After 120 minutes of reperfusion, the kidneys were removed for histologic examination. In the control pigs (group 1) 50% of the animals were anuric. The ratio between GFR measured in the left kidney at the end of perfusion and at equilibrium in the remaining animals was 0.16 +/- 0.01. In test animals (group 2) all animals recovered diuresis. The ratio between GFR measured in the left kidney at the end of perfusion and equilibrium was 0.51 +/- 0.12 (p < 0.001, group 2 vs. group 1). In group 2 postperfusion kidney blood flow was higher than in group 1 (63.0 ml/min vs. 27.4 ml/min; p < 0.05) because of a decrease in renal vascular resistance. Light microscopic examination of kidneys form animals in group 1 revealed tubular necrosis that extended to the parenchyma, with exposure of tubular interstitium. In group 2 only degenerative lesions with edema of tubular cells and disappearance of brush borders were observed. Our findings indicate that flushing the kidneys with BT01 solution mixed with blood improves postischemic kidney function by reducing reperfusion damage.