Prakash N. Rao

Evidence that small bowel preservation causes primarily basement membrane and endothelial rather than epithelial cell injury

The main site of injury induced during small bowel preservation is perceived to be the basement membrane and the endothelium of the highly vascularized mucosa, an aspect evaluated here in further detail. The effects of preservation were studied using a specific basement membrane stain (laminin antibody), an endothelial cell stain (factor 8 antibody) and standard histology. In addition, mucosal glutaminase activity reflecting entero-cyte integrity was measured as monitor of the extent of preservation injury. Using a rat model, small bowel grafts were harvested, the vascular bed and bowel lumen were flushed, and the grafts were stored (4°C) for 1, 6, 9, and 12 hr and transplanted into syngeneic hosts. After cold storage prior to transplantation, full-thickness small bowel biopsies were obtained for the various tissue preparations. Histologic evaluation at the end of the preservation period revealed separation of the vil-lous epithelium from the lamina propria that increased with extending preservation time. Tissue staining with the laminin antibody disclosed progressive changes with increasing preservation intervals. Staining with the factor 8 antibody demonstrated also progressive changes, but failed to reflect in a gradual fashion increasing endothelial cell injury. Histologic injury became more pronounced after transplantation and reperfusion, then showing destruction of epithelial cells; the extent of injury correlated with the duration of preservation. Glutaminase activity was maintained after cold storage, indicating that the enterocytes remained intact during this period, but when assayed after reperfusion, glutaminase decreased with increasing preservation intervals and increasing histologic mucosal damage. We conclude that cold ischemic injury involves primarily the endothelium and the basement membrane, which progresses to global mucosal impairment with reperfusion.

An improved technique for isolated perfusion of rat livers and an evaluation of perfusates

We have modified the apparatus for isolated rat liver perfusion (IPRL) in order to be able to perform two perfusions simultaneously. In addition, we studied the quality and stability of livers by comparison of five different perfusates: Blood (Group A), Original Krebs Henseleit buffer (Group B), Krebs buffer with glucose (Group C) or bovine serum albumin (BSA) added, (Group D). In a last group (E) albumin, glucose, and taurocholic acid were added to Krebs. After 180 min of perfusion, livers perfused with solutions including 2% albumin (Group D, E) had a significantly higher release of hepatocellular and endothelial cell (purine nucleoside phosphorylase) enzymes and lower bile production as compared to Groups A, B, and C (P less than 0.0001). Increasing levels of purine nucleoside phosphorylase (PNP), a reflection of damage to the microvascular endothelium preceded the increases in hepatocellular enzymes. Histologically, damages of sinusoidal endothelial cells and hepatocytes are appreciated moderate to severe in Groups D and E, slight to mild in Groups A and B, and not significant in Group C. These results suggest that BSA may have toxic effects to the perfused rat liver. These data also confirm that the IPRL modified for simultaneous perfusion of two livers is efficient, and that with this technique the rat liver can be optimally perfused for up to 3 hr with oxygenated Krebs Henseleit buffer without additives (Group B) and without blood. These two improvements should allow those performing studies with perfused rat livers to obtain data in a more efficient, accurate, and inexpensive fashion.

INHIBITION OF FREE RADICAL GENERATION AND IMPROVED SURVIVAL BY PROTECTION OF THE HEPATIC MICROVASCULAR ENDOTHELIUM BY TARGETED ERYTHROCYTES IN ORTHOTOPIC RAT LIVER TRANSPLANTATION

The capacity of specifically targeted erythrocytes to inhibit free radical—mediated injury to the endothelial cell after cold preservation, and improve liver function was studied in two experimental models: An isolated perfused rat liver (IPRL) system and syngeneic orthotopic rat liver transplantation. In the IPRL model, livers were preserved in University of Wisconsin solution for 24 h at 4°C. At the end of the preservation period, livers were flushed with lactated Ringers (control), immunoerythrocytes (IES), or blank intact erythrocytes prior to warm reperfusion for 2 h using an assanguinous Krebs-Henseleit buffer. Production of superoxide (02) anion during warm reperfusion in the IES-treated liver was reduced by 65% as compared with controls (P<0.001) and by 74% (P<0.001) when compared with blank erythrocyte-treated livers. Endothelial cell preservation, as assessed by levels of purine nucleoside phosphorylase (PNP), was much better in the IES-treated group (P<0.001) when compared with untreated livers. Hepatocellular preservation was markedly improved in the IES-treated livers. In the syngeneic liver transplantation model, livers were preserved in UW solution for 24 h at 4°C. Prior to implantation, livers were flushed with 5 ml of cold lactated Ringers or immunoerythrocytes. Survival after three weeks was 60% in the IES-treated group and 30% in the untreated group. Survival in the IES-treated group was not significantly different from a control (no preservation) group.

Hyaluronic acid and purine nucleoside phosphorylase in vascular and luminal effluents of small bowel grafts as parameters of preservation injury.

Reliable parameters reflecting the degree of graft injury after small bowel preservation are currently not established. We investigated hyaluronic acid (HA) and purine nucleoside phosphorylase (PNP) as indicators of preservation injury before small bowel transplantation. In the first part of the study, intestinal grafts were harvested, perfused with saline, and flushed either immediately or after 1, 6, 12, 24, and 48 hr of cold storage (n=6/group). HA and PNP were assayed in vascular and luminal effluents. In the second part of the study, 24 grafts were transplanted after preservation periods of 1, 6, 9, and 12 hr (n=6/group) to assess if HA and PNP are predictors of postoperative graft survival. HA levels in vascular effluents and PNP activities in luminal effluents correlated with duration of preservation time and predicted graft survival. Utilizing both parameters significantly increased the predictive accuracy.

Response of normal and reperfused livers to glucagon stimulation : NMR detection of blood flow and high-energy phosphates

The effects of glucagon on blood flow and high-energy phosphates in control and in rat livers damaged by ischemia were studied using in vivo nuclear magnetic resonance (NMR) spectroscopy. Normal livers and livers which had been made ischemic for 20, 40, and 60 min followed by 60 min of reperfusion were studied. Ischemia led to a loss in adenosine triphosphate (ATP) within 30 min. Reperfusion after 20 min of ischemia led to complete recovery of ATP. 60 min of reperfusion after 40 or 60 min of ischemia led to only a 76% and 48% recovery of ATP, respectively. Glucagon, at doses up to 2.5 mg/kg body weight, caused no changes in the inorganic phosphate (P(i)) to ATP ratio in normal livers as measured by 31P-NMR spectroscopy. In livers which had been made ischemic for 20, 40, or 60 min, glucagon caused an increase in the P(i)/ATP ratio of 18%, 40%, and 40%, respectively. 19F-NMR detection of the washout of trifluoromethane from liver was used to measure blood flow. Glucagon-stimulated flow in the normal liver in a dose-dependent manner, with 2.5 mg glucagon/kg body weight leading to a 95% increase in flow. Ischemia for 20, 40, and 60 min followed by 60 min of reperfusion led to hepatic blood flows which were 63%, 68%, and 58% lower than control liver. In reperfused livers, blood flow after glucagon-stimulation was reduced to 56%, 43%, and 48% of control glucagon-stimulated flow after 20, 40, and 60 min of ischemia. These results indicate that ischemia followed by reperfusion leads to decreases in hepatic blood flow prior to alterations in ATP and the response of the liver to glucagon is altered in the reperfused liver.

A Modified Apparatus for Dual, Sterilized, Isolated Perfusion of the Rat Liver

The isolated perfused rat liver (IPRL) has proven to be a useful model for the study of physiology and pathology of the liver. For research in nonparenchymal cell (NPC) function that includes measurement of cytokine production (eg, TNF), it is necessary to have a sterilized perfusion system. We have modified the IPRL apparatus so as to be able to perform sterile perfusions of two livers simultaneously. The perfusion apparatus is a recirculating closed system in which the oxygenator is a plastic container separated into two chambers by a fenestrated plastic wall. A disposable macropore filter functions as both a bubble trap and perfusate filter. The sterilization process is done by immersing the various components in Benz-All solution. The tubing is disinfected by irrigation with 10% Clorox followed by 0.9% sodium chloride solution. The perfusate used is filter-sterilized Krebs buffer solution containing 0.5 g Mandol/250 mL perfusate. Not only can two organs be conveniently perfused simultaneously, but the entire system can be reliably sterilized for up to 20 consecutive perfusions. Bile production is higher and more stable with less leakage of intracellular enzymes. Many of the components are disposable and can be altered to suit the needs of a particular experiment.