Protective effects of trifluoperazine on the microcirculation of cold-stored livers

Nicardipine reverses vasoactivity associated with University of Wisconsin solution in the rat peripheral circulation

BACKGROUND

The rapid uniform delivery of University of Wisconsin solution (UW) to the microcirculation may be compromised by its vasoactivity.

METHODS

In 2 different rodent models, we tested whether UW-mediated vasoconstriction could be reversed with nicardipine.

RESULTS

In the perfused, splanchnic circulation, intravascular control solutions (lactated Ringers [LR], Hextend [HEX], histidine-tryptophan-ketoglutarate [HTK]) or UW (± nicardipine) evoked pressure changes in 3 protocols (series 1; n = 35). In the cremaster muscle, topical control solutions or UW (± nicardipine) evoked vascular responses measured by video microscopy in 4 protocols (series 2; n = 47). In series 1A, 37°C UW increased perfusion pressure, but there was no change caused by LR, HEX, or HTK. In series 1B, 4°C UW caused a similar, albeit transient, increase. In series 1C, nicardipine reversed 37°C UW-mediated vasoconstriction in a dose-related manner. In series 2A, UW caused a 30%-59% constriction that varied with arteriolar branching order. In series 2B, the recovery from UW-induced vasoconstriction varied with duration of exposure, but nicardipine fully reversed residual vasoconstriction. In series 2C, cold and warm UW were equipotent, near maximal, vasoconstrictors. In series 2D, UW potentiated no-reflow.

CONCLUSION

UW causes a potent temperature-independent vasoconstriction by a calcium-mediated mechanism and this effect can be mitigated with nicardipine.

Past and future approaches to ischemia-reperfusion lesion associated with liver transplantation

Ischemia-reperfusion (I/R) injury associated with liver transplantation remains a serious complication in clinical practice, in spite of several attempts to solve the problem. The present review focuses on the complexity of I/R injury, summarizing conflicting results obtained from the literature about the mechanisms responsible for it. We also review the therapeutic strategies designed in past years to reduce I/R injury, attempting to explain why most of them have not been applied clinically. These strategies include improvements in pharmacological treatments, modifications of University of Wisconsin (UW) preservation solution based on a variety of additives, and gene therapy. Finally, we will consider new potential protective strategies using trimetazidine, 5-amino-4-imidazole carboxamide riboside (AICAR), melatonin, modulators of the renin-angiotensin system (RAS) and the phosphatidylinositol-3-OH kinase (PI3K)-Akt and the p42/p44 extracellular signal-regulated kinases (Erk 1/2) pathway. These strategies have shown promising results for I/R injury but have not been tested in experimental liver transplantation to date. Moreover, we will review ischemic preconditioning, taking into account the recent clinical studies that suggest that this surgical strategy could be appropriate for liver transplantation.

Porcine hepatic phospholipid efflux during reperfusion after cold ischemia

BACKGROUND

Cold preservation produces hepatic injury that is difficult to assess during early reperfusion. The value of reperfusion plasma choline phospholipid in predicting subsequent organ function is documented in these studies.

MATERIALS AND METHODS

Livers of female Yorkshire pigs were prepared for transplantation. After 2 h of cold ischemia the reperfusion plasma was evaluated for choline phospholipid and cholesterol. These values were correlated with bile secretion, hepatic hemodynamics, oxygen uptake, and plasma sorbitol dehydrogenase levels.

RESULTS

The isolated porcine liver demonstrates a rapid efflux of choline phospholipids into plasma during early reperfusion after cold preservation. After this initial efflux no subsequent plasma increment occurred. These choline-phospholipid increments were isolated in plasma higher density (d > 1.063) lipoproteins and were not accompanied by equivalent increases in cholesterol. Neither biliary reflux nor lecithin cholesterol acyl transferase abnormalities contributed appreciably to the phospholipid increments in reperfusion plasma. Livers with the largest efflux of choline phospholipids had the most impaired circulatory and bile secretory function at 4 h of reperfusion.

CONCLUSION

The immediate increase of choline phospholipids, particularly lysophosphatidylcholine, in reperfusion plasma after cold ischemia provides an index of the injury occurring during this interval and correlates with early organ function.

Effect of phospholipase A2 inhibitors on the release of arachidonic acid and cell viability in cold-stored hepatocytes

We investigated the effect of phospholipase A(2) (PLA(2)) inhibitors on PLA(2) activity and cell viability in cold-stored rat hepatocytes. The cells were radiolabeled with [(3)H] arachidonic acid (AA) and cold stored in the University of Wisconsin (UW) solution containing various PLA(2) inhibitors. PLA(2) activity was determined by measuring the total free (cellular + supernatant) AA by thin-layer chromatography after inhibiting reacylation of free AA with inhibitors of energy production (carbonyl cyanide m-chlorophenylhydrazone + iodoacetate). Aristolochic acid, chlorpromazine, and quinacrine in the UW solution showed a significant inhibitory effect throughout 48 h cold storage but only at relatively high concentration. PLA(2) activity was also suppressed (58% of control) by trifluoperazine (50 microM), but its effect was limited to only 24 h. In contrast, pretreatment of the cells prior to hypothermic preservation with trifluoperazine (10 to 100 microM) suppressed PLA(2) activity during 48 h storage. Inclusion of calmodulin antagonist W-7 did not affect PLA(2) activity. Thus, the inhibitory activity of these agents appears unrelated to Ca-calmodulin-phospholipid interaction but to have an inhibitory effect on PLA(2) activity. To study the effects of PLA(2) inhibitors on cell viability, lactate dehydrogenase (LDH) release was measured in the presence or absence of inhibitors upon rewarming cold-stored cells in Krebs-Henseleit buffer for 2 h at 37 degrees C. None of the inhibitors tested improved cell viability after 48 h storage. Thus, although PLA(2) inhibitors blocked PLA(2) activity, there was no suppression of LDH release. PLA(2) may play a minor role in preservation/reperfusion injury to cold-stored hepatocytes.

Phospholipid metabolism of hypothermically stored rat hepatocytes

Isolated rat hepatocytes were suspended and stored in either Liebovitz-15 medium (37 degrees C or 4 degrees C) or University of Wisconsin (UW) solution (4 degrees C) containing [(3)H] arachidonic acid (AA). At varying times, membrane phospholipids were separated by thin layer chromatography. AA labeled phospholipids similarly at both 4 degrees C and 37 degrees C. Analysis of the ratios of [(3)H] AA and [(14)C] glycerol incorporated into phosphatidic acid or other phospholipids in dual-labeled cells indicated that the deacylation/reacylation cycle was the major route of AA incorporation at hypothermia. This was supported by showing that blocking phospholipase A(2) (PLA(2)) activity by trifluoperazine suppressed AA incorporation into phospholipids. PLA(2) activity, measured by determining the release of AA, was slow during 48-hour cold storage, but increased significantly when ATP was depleted by inhibition of mitochondria and glycolysis. In the whole rat liver, there was no significant loss of phospholipids during 48-hour storage (total phospholipids [micromol phosphorus/L/mg] : 0.197 +/-. 001 at 0 hours) unless energy blockers were used (0.155 +/-.005 at 48 hours) or glycogen depleted by fasting the rat (0.167 +/-.001 at 48 hours). This study shows that a net PLA(2) stimulated hydrolysis of phospholipids is seen only when ATP is depleted and its generation from anaerobic glycolysis inhibited. Thus, PLA(2) hydrolysis of phospholipids is not a significant cause of liver cell injury during cold storage when livers are obtained in optimal condition. However, conditions affecting the generation of ATP during cold storage could alter PLA(2) leading to membrane damage.

Oxygen consumption, lactate metabolism, and gastric intramucosal pH in an experimental liver transplantation model

OBJECTIVE

To assess the usefulness of measuring whole-body oxygen consumption (VO2), arterial lactate concentration, and gastric intramucosal pH (pHi) as parameters for evaluating hepatic graft viability in a model of experimental liver transplantation.

DESIGN

Experimental, prospective study.

SETTING

Hospital laboratory for experimental surgery.

SUBJECTS

Twenty-eight Landrace-Largewhite pigs: 14 donors and 14 recipients.

INTERVENTIONS

Orthotopic liver transplantation. Two groups were differentiated by graft preservation status: an optimal-graft group (group 1), which received donor livers that had been preserved in Collins solution at 4 degrees C for <4 hrs (n = 7), and an injured-graft group (group 2), which received donor livers that had been preserved in Collins solution at 4 degrees C for >24 hrs (n = 7).

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters, variables related with systemic and hepatic oxygen and lactate metabolism, gastric pHi, and arterial pH were measured at two stages: a) preanhepatic stage; and b) neohepatic stage (60 mins after reperfusion). There were no differences in VO2 between graft groups or stages. In the neohepatic stage, hepatic oxygen extraction and lactate turnover were significantly higher in the optimal-graft group than in the injured-graft group. In the neohepatic stage, gastric pHi decreased significantly and arterial lactate concentrations increased significantly in both groups.

CONCLUSIONS

Changes in hepatic VO2 cannot be detected by VO2 measurements. Optimal-state grafts increased their lactate turnover as a result of substrate overload, but injured grafts did not. Therefore, the evolution of arterial lactate concentrations in the immediate postoperative period may be useful for the early evaluation of transplanted livers. Gastric pHi can be a useful measurement in the immediate posttransplantation period for differentiating between hyperlactacidemia produced by liver dysfunction (normal pHi) and hyperlactacidemia produced by lactate generation as a consequence of inadequate tissue oxygenation or of a mixed origin (abnormal pHi).

[The electrolyte composition of liver preservation solutions for hepatocytes in a model of in vitro preservation and reoxygenation]

The cation and anion content in liver preservation solutions have been investigated in order to justify the use of "intracellular" or "extracellular" electrolyte compositions. Various concentrations of sodium and potassium with chloride or lactobionate as anions and with added calcium and/or magnesium were made up as preservation solutions and incubated with in vitro adherent cultures of pig hepatocytes. In vitro hypoxia and hypothermia (4 degrees C, PO2 < 0.1 mmHg) for 24 h, with reoxygenation for 3 h, in standard culture medium was used as a model for preservation. Measurements of cell viability and detachment rate by light microscopy and of LDH and GOT liberation were used as parameters of cell damage. Cell swelling was estimated in suspension cultures of isolated hepatocytes. When chloride was used as the anion, significant cell toxicity from potassium concentrations over 75 mM was found within 6 h of preservation. Enzyme liberation decreased with increasing content of sodium cations in the preservation solution. Calcium ions had a protective effect at a concentration of 0.8 mM. Addition of magnesium to an "intracellular" ion composition minimized the toxic effect of potassium cations. Using lactobionate as an impermeant anion, there was no difference between the sodium and the potassium salt and the choice of cation had no effect on enzyme leakage or cell volume. An "extracellular" solution with high sodium chloride content and 0.8 mM calcium resulted in better preservation than was obtained with lactobionate solutions. With chloride as the anion, a significant increase in cell swelling was found when potassium replaced sodium in the solutions. Cell swelling decreased with increasing concentration of sodium cations.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of prewarming the donor liver for rat liver transplantation

Cold preservation of donor liver can injure the microcirculation enough to impair the function and survival of the transplanted liver. In this study, prewarming the donor liver to 10 degrees C to 12 degrees C after cold storage prior to implantation significantly increased survival rates in rats 1 week after surgery. Following 6, 8, or 9 hours of cold storage in chilled normal saline, prewarming increased survival rates from 40% to 78.6%, from 0% to 35.7%, and from 0% to 14.3%, respectively. The results suggest that pretreatment of the donor liver with warmth following cold storage and before implantation will improve the survival rate of liver transplanted rats.