The use of donor fatty liver for liver transplantation: a challenge or a quagmire?

Journal of’Hepatology 1996; 24: 114-121 Printed in Denmark All rights reserved

Copyright 0 European Association

fir the Srudy of the Liver 1996

Journal of Hepatology

ISSN 0168-8278

Special Article

The use of donor fatty liver for liver transplantation: a challenge or a quagmire?

Franc0 Trevisani, Alessandra Colantoni, Paolo Caraceni and David H. Van Thiel

Liver Disease Program, Oklahoma Medical Research Foundation, Oklahoma City, USA

T E TERM fatty liver identifies a liver in which lipid, mainly triglyceride, accounts for more than 5% of

the wet weight of the liver (1). The finding of a fatty liver is a frequent event, with a reported prevalence ranging from 6% to 24% in most autopsy series (24). Fatty metamorphosis of the liver is caused by a wide variety of common conditions, which include sustained alcohol intake, obesity, malnutrition, parenteral hyperalimentation, metabolic or endocrine diseases such as diabetes mellitus, pregnancy, the use of certain drugs, and hepatitis C as well as a delta virus infection complicating a hepatitis B virus infection. Despite this long list of causes of fatty liver, no etiologic factor can be identified as being responsible for the fatty liver present in a large proportion of cases. Because it is widely held that the accumulation of triglycerides within hepatocytes is not damaging to the liver, steatosis per se is not considered by most physicians as being either a serious or a progressive hepatic disorder.

The excellent survival rates reported after orthotopic liver transplantation (OLT) have increased the demand for liver transplants and have enhanced the disparity between the number of available donor organs and the need for such organs (5,6). Thus, the re- ality of OLT has rekindled scientific interest in the problem of hepatic steatosis. This renewed interest is the result of two factors. First, the prevalence of fatty liver among the potential donor liver population is high, ranging from 13% to 26% (7,8). In this regard, it needs to be remembered that most organ donors are brain-dead accident victims. In a large percentage of cases the accident is a consequence of alcohol consumption. Secondly, fatty livers transplant poorly. As

Correspondence: David H. Van Thiel, M.D., Oklahoma Medical Research Foundation, 825 Northeast 13th Street, Oklahoma City, OK 73104-5046, USA.

a result most steatotic livers with a lipid content ex- ceeding 50% of the hepatic lobule are discarded by transplant surgeons as being unacceptable for use. Many clinical reports indicate that massive fatty infiltration of the liver is an absolute risk factor for the development of primary graft non-function (PNF), a condition defined as failure of an allograft liver to have sufficient function to sustain the life of the allograft recipient (9-l 1). Because lo-30% of the liver allograft candidates on some transplant lists die without being transplanted, considerable effort has been made to increase the use of organs that previously had been thought of as being of “marginal” quality. The prevalence of fatty liver in the donor population is sufficiently high that those interested in clinical liver transplantation are being pressed to identify circumstances and methods whereby a steatotic donor liver might be used successfully. Moreover, a better understanding of the mechanisms responsible for the high rate of PNF with the use of steatotic donor organs should lead directly to the development of treatment options wherein steatosis resolution can be achieved and/or hepatic function can be maintained, despite the presence of excess fat in the donor liver.

Clinical Experience With the Use of Fatty Liver Allografts A key problem relating to the issue of transplantation of fatty livers is to establish the degree of steatosis that makes a donor organ unacceptable. Fatty infiltration of the liver is classified as mild if the amount of steatosis involves less than 30%) of the visualized hepatocytes, as moderate if the steatosis involves 30-60% of the visualized hepatocytes, and severe if it involves more than 60% of the liver cells (12). Donor livers with severe steatosis currently account for 3% of the available donor organs (13). On the basis of experience re-

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ported in the literature, a donor liver with +60% steatosis (severe steatosis) should not be used for transplantation: reports from both sides of the Atlantic have identified an association between macroscopically de- tectable heaptic steatosis (“greasy, yellow graft”) and the subsequent occurrence of PNF (9,lO). In one report, all the recipients of a donor liver with severe fatty infiltration (>66% of hepatocytes involved) developed PNF (7). Similarly, Ploeg et al. reported that the transplantation of livers with >60% steatosis almost in- variably results in primary graft dysfunction and in 80% of the cases PNF (12). This experience has prompted most transplant surgeons to refuse donor livers with severe steatosis (>50% of the liver being steatotic). In a report of Markin et al. (8) a histological evaluation of 385 donors livers resulted in surgeons re- jecting 27 organs. Of these livers 81.4% were rejected because of steatosis involving >45% of the hepatic lobular volume. With the elimination of these overtly steatotic donor livers, the rate of PNF experienced by these authors fell from 8.5% to 1.4% (8).

Clearly, there is much empiric evidence that any degree of hepatic steatosis appears to jeopardize liver transplant outcome by increasing the risk for early graft dysfunction or even non-function (7,8,12,14). These data, however, do not suggest that all fatty do- nor livers must be discarded and not used for transplantation. Pragmatically, the current donor shortage and the high prevalence of fatty livers in the donor population make this “safe” policy unrealistic. Thus, many centers have used “marginal livers”, most of which are steatotic (13). With increasing pressure to use marginal donor organs, it becomes critically important to identify the actual risk of poor initial graft function and primary non-function associated with the use of steatotic donor organs with varying degrees of steatosis. As a starting point, this question can only be answered if a reliable assessment of the severity of steatosis in a given donor organ can be identified and used. Current macroscopic estimates of the severity of steatosis are known to be highly unreliable. The predictive value of such estimates has been assessed to be 71% for massive, 46% for moderate and 17% for mild steatosis (14). Theoretically, an ultrasound investigation of a potential donor liver should be able to reduce the number of unrecognized fatty donor livers being harvested and, potentially, to estimate the intensity of the steatosis (15). Unfortunately, its usefulness in predicting the actual fat content of a given donor liver has been poor, and there are marked differences in the ultrasonographic findings between operators at a given center as well as between different centers.

The development of rapid techniques for the pro-

cessing of frozen-section liver biopsies and the ex- tended preservation periods that exist with current preservation fluids makes it possible to determine the histologic appearance of donor organs not only at the time of harvesting but also just before engraftment. The reported clinical experience for this assessment using routine hematoxylin and eosin-stained sections has been shown to be more useful than oil red 0 stains, because the extent of the steatosis in a liver biopsy tissue appears to be exaggerated using the more specific oil red 0 stain (8).

Because there are no established guidelines for the use of donor livers with mild to moderate steatosis, the clinical judgment of transplant surgeons has been the mainstay for this decision. D’Alessandro et al. reported that only 1 of 26 individuals (3.8%) receiving a donor liver with minimal to moderate steatosis (~66% of the liver being fatty) developed PNF. However, the postoperative period of these 26 cases was characterized by an unusual elevation of the serum transmin- ases, LDH and ammonia levels (7). Markin et al. reported that the postoperative hepatic function of the grafts with steatosis ~15% did not differ from that oc- curring when non-steatotic livers were used, while organs with a fatty infiltration > 15% resulted in signifi- cantly longer prothrombin times and higher ALT levels during the first 5 postoperative days after transplantation. Despite the apparent early graft dysfunction experienced by these steatotic donor organs, the l-year survival rate of the recipients of organs with hepatic steatosis > 15% but less than 50% was not adversely affected. These authors concluded that the use of do- nor livers with mild to moderate steatosis does not add any additional survival risk to the transplantation procedure (8). In the study of Adam et al., the proportion of grafts experiencing a peak SGOT>lOOO IU/l after transplantation was 30% for non-steatotic livers, 50% for mildly steatotic (~30%) and 75% for moderately (30-60%) steatotic organs. Again, the l-month graft and patient survival rates were not adversely affected by the use of steatotic grafts, with less than 60% of the liver being steatotic (14). Finally, in a series of 158 transplants, a multivariate analysis confirmed that moderate donor liver steatosis (30-60%) is an independent risk factor for PNF (12). From these clinical data, it can be concluded that the presence of mild to moderate steatosis in a donor liver, although associated with increased early postoperative graft injury, which appears to be proportional to the degree of fatty infiltration, does not absolutely preclude the use of all steatotic donor organs. Nonetheless, the increased rate of early postoperative injury experienced with the use of such donor organs cannot be ignored categorically, as

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early graft dysfunction is not always an innocent tem- porary event but can, at least in some cases, contribute to an increased risk of eventual graft loss as a result of rejection, and a need for retransplantation, clearly increasing total transplantation costs substantially. Thus, most surgeons believe that mild to moderate steatosis (30-60%) is to be considered as a relative risk factor for early graft dysfunction. In other words, it is capable of causing PNF when it occurs in combination with some other risk factors for PNF (11). This view is supported by the finding that the elective engraftment of fatty (85% of them having mild or moderate steatosis) and non-fatty livers produces similar long-term survival results, whereas when the same organs are used under emergency conditions, a marked difference in survival rates becomes evident. Specifi- cally, 44% of the recipients receiving a fatty organ ver- sus 16% of those receiving a non-fatty organ urgently die within 1 month from the transplant (14).

Mechanisms Involved in the Production of a Steatotic Liver Free fatty acids are transported to the liver and utilized by hepatocytes for the synthesis of trigycerides, which are subsequently secreted, combined with specific apo- proteins, as lipoproteins. Hepatic steatosis is an accumulation of fat in parenchymal liver cells, caused either by an increased delivery of fatty acids to the liver in excess of what can be metabolized and excreted, or by the failure of normal synthesis and secretion of hepatic triglycerides and/or apolipoproteins (16). Thus, Sherlock & Dooley classified three main mechanisms for fat accumulation: 1) increased delivery of fat or fatty acids to the liver; 2) increased mitochondrial synthesis of fatty acids or, more likely, reduced mitochondrial oxidation of fatty acids; and 3) impaired export of triglycerides out of the hepatocytes as part of lipoproteins (1). Although alcohol consumption is the most common cause of hepatic steatosis, other rela- tively common conditions are associated with the development of fatty liver, such as malnutrition, obesity, diabetes mellitus, pregnancy and the administration of several drugs. Hepatic steatosis, however, is most com- monly the consequence of chronic alcohol consumption. The mechanisms responsible for the development of an alcoholic fatty liver have been well characterized. High doses of ethanol lead to an increase in circulating levels of epinephrine and norepinephrine, stimulating hormone-related lipolysis in peripheral fat cells and the release of free fatty acids that are taken up by hepatocytes. In the hepatocytes, ethanol metabolism leads to a reduction of the intracellular NADNADH ratio that inhibits both endogenous combustion of

fatty acids in the mitochondria and glycogenolysis. The latter condition promotes an increase in the levels of the free fatty acids and glycerol, precursors of triglycerides. These perturbations in the intermediary metabolism associated with alcohol consumption result in the accumulation of free fatty acids and triglycerides in the parenchymal liver cells that coalesce as macroscopic fatty droplets (17,18).

Mechanisms Whereby a Steatotic Liver Can Contribute to the Problem of Primary Non- function (PNF) A critical clinical point is to identify the answer to the question: why does a fatty liver with apparently normal function in a potential donor fail to function in a liver graft recipient? A mechanical disruption of the hepatic sinusoids is thought by many authors to be the principal cause of PNF with the use of a steatotic do- nor organ. Based on the histologic features of surgical sections of liver graft biopsies, Todo et al. postulated that the key event leading to PNF of a fatty liver allograft is the development of post-reperfusion random hepatocyte rupture resulting in an intravascular co- alescence of small fatty foci into the very large fat droplets that compress and obstruct the hepatic microcirculation. This sequence of events results in enhanced liver cell loss as a direct consequence of mechanical obstruction of the hepatic microcirculation by fat-dis- tended hepatocytes as well as sinusoidal free lipid. Moreover, the release of free lipid into the blood stream (sinusoids) provides a substrate for subsequent enhanced lipid peroxidation during reoxygenation with the formation of oxygen free radicals and a progressive endothelial cell injury that further impairs the hepatic microcirculation and subsequent liver graft function (10). An alternative or additional hypothesis that might explain the increased sensitivity of a fatty liver to cold ischemia may be the solidification of cytosolic triglycerides, phospholipids and fatty acids during cold storage. Such a process would be expected to markedly disrupt liver cell organelle and membrane structure and, as a result, subsequent liver cell function (19). The relative increased proportion of unsaturated fatty acids noted in most experimental models of hepatic steatosis, however, should render hepatic lipids more re- sistant to this process, making this hypothesis and mechanism less likely.

An experimental model of steatosis induced in rats using a diet deficient in both choline and methionine has been used to investigate the behavior of steatotic livers when they are utilized as donor organs. In this model, a fatty donor liver reduces the resistance of the graft to cold ischemic injury. Specifically, the survival

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rate of l&h-preserved liver grafts is 55% for normal livers, but only 37% for fatty livers obtained from do- nor animals after 14 days on the experimental diet and 0% for livers obtained from donors on the diet for 42 days (19). This decreased viability of fatty liver allografts has been attributed to an amplified ischemic in- sult produced as a result of a markedly disrupted hepatic microcirculation (20). Histologically, fat-contain- ing hepatocytes in such donor organs can be shown to compress the sinusoidal network, producing a narrow- ed and irregularly obstructed sinusoid bed that is much smaller than that present in a normal liver. During cold storage of steatotic livers, the sinusoids become obstructed further as a result of white blood cell adhesion to endothelial cells and the protrusion of Kupf- fer cell processes into the sinusoidal lumen. In addition, the phagocytic activity and oxygen free radicals generated by activated Kupffer cells in the hepatic sinusoids are enhanced (19). It is entirely conceivable that the enhanced Kupffer cell activation observed in this situation is the major pathogenetic factor responsible for the disturbance of the hepatic microcirculation seen in steatotic livers, as Kupffer cells are known to produce substances capable of modulating sinusoidal blood flow and highly reactive oxygen species that impair liver cell function by altering macromolec- ular structure and function (20-22). Importantly, in these latter studies, a mechanical obstruction of the hepatic microcirculation by lipid droplets has not been seen. Thus, mechanisms other than sinusoidal obstruction must be responsible for the liver dysfunction noted with the use of these steatotic liver grafts. The formation of oxygen free radicals in the early phases of reoxygenation within the liver after a period of anoxia is currently under intense investigation. Experimental models suggest rather strongly an important role of these high reactive molecules in the pathogenesis of the early transplantation-related liver graft injury (23). Re- cently, it has been observed that an antioxidant- insensitive free radical, is formed during the first 5 min after implantation of a fatty but not a non-steatotic liver graft (24,25).

Finally, a fatty liver may be intrinsically more vul- nerable to warm ischemia-reperfusion injury than is a non-steatotic liver. In this regard, it has been shown that a normothermic ischemic period of 60 min is lethal for rats with fatty liver (>70% steatosis), while 70% of animals with non-steatotic normal livers sur- vive (26). Post-ischemic hepatic hemorrhage, a disruption of the sinusoidal architecture and spotty liver cell necrosis occur in steatotic livers following reperfusion. Despite these rather marked histologic changes, no difference in adenine nucleotides and energy charge be-

tween steatotic and non-steatotic livers before and during ischemia can be demonstrated. Conversely, the re- covery time to achieve a normal energy charge after reperfusion is markedly prolonged when fatty livers are utilized. Thus, it appears that hepatic steatosis does not directly affect the energy metabolism of liver cells during warm ischemia, but rather it reduces the ability of hepatocytes to function and regenerate ATP following reperfusion. Regardless of the specific mechanisms involved, the use of steatotic livers leads to an enhanced rate of microcirculatory and liver cell dysfunction. Recently, Lemasters et al. have reported that the rapid adherence of blood elements along the sinusoidal walls of fatty grafts is accelerated as compared to normal donor organs (27). Obviously this would have a deleterious effect on the subsequent function of a liver allograft by further reducing the effective sinusoidal area and producing microcirculatory failure through- out the organ.

Teramoto et al. have reported that 15 and 30 min of warm ischemia result in graft survival rates of 100% and 33% respectively after transplantation of a normal liver, but survival rates of only 57% and 0% when steatotic organs are used (19). Moreover, preliminary data from our laboratory suggest that hepatocytes isolated from fatty livers have an increased sensitivity to warm anoxic injury as compared to liver cells isolated from non-steatotic organs (28). It is worth noting that either normal or steatotic hepatocytes appear to be more sen- sitive to warm than cold ischemia-induced damage (29). This probably reflects the higher metabolic activity of hepatocytes during warm ischemia as opposed to cold ischemia. Anaerobic glycolysis provides the energy for hepatocyte function during warm ischemia. Liver parenchymal cell function is disturbed only if warm ischemia persists for more than 75-90 min, the time limit for the complete utilization of endogenous hepatic glucose reserves. This also means that hepatocytes are more susceptible to warm ischemic injury if it occurs in the presence of glycogen depletion (29). Preliminary data from our own laboratory suggest that hepatocytes isolated from fatty livers have an increased sensitivity to anoxic injury as compared to liver cells isolated from non-steatotic organs (Caraceni et al., un- published observations).

Nonetheless, livers with massive steatosis (>60%) but without focal areas of liver cell necrosis preserved for less than 12 h have been transplanted successfully in rats (19). These authors emphasized the importance of evaluating hepatocyte necrosis as well as preservation time when predicting the outcome of liver transplantation using a fatty donor liver. The clinical evidence that livers with mild or moderate fatty infil-

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tration with minimal liver cell necrosis can be transplanted successfully after a short preservation time, supports this experimental data.

Relevant to the experimental findings of Lemasters et al. (27) it has been reported that one-third of per- ceived “good” donor livers manifest evidence of moderate- to high-grade platelet adhesion to donor endothelial cells when the livers are examined at the end of the harvesting procedure (30). This platelet-associated endothelial cell injury is not associated with any specific histologic feature or biochemical abnormality of the donor liver. Nonetheless, the degree of platelet adhesion predicts the subsequent height of the serum transaminase level and prothrombin time abnormali- ties seen in the recipient in the early postoperative period. Moreover, grafts, whose platelet adhesion grade increases after liver reperfusion, perform less well than do organs in which it remains at a low level. Importantly, the degree of platelet adhesion does not correlate with the amount of fat present in the graft, suggesting that it is yet another independent risk factor for PNF (30). Additional studies are needed to determine whether the degree of platelet adhesion can be used to determine whether or not a given donor liver with or without steatosis should either be used or be discarded.

In summary, the principal cause of reduced hepatic function and primary graft dysfunction when a fatty donor liver is used appears to be an enhanced disruption of the microcirculation, which increases the susceptibility of both liver cells and endothelial cells to ischemic injury.

A very intriguing question is whether the pathogenesis of the steatosis present in a given donor liver influences the post-transplant outcome. Non-alcohol- related nutritional factors such as obesity and hyper- glycemia, alcohol-use-related factors, other metabolic factors, iatrogenic drug use and unknown factors, are all capable of producing hepatic steatosis. In these dis- parate conditions, the specific mechanisms leading to the steatosis are probably different and include a re- sponse to an increased hepatic lipid influx and specific defects in the utilization and export of lipids by the liver (1). Despite the obvious differences in mechanisms responsible for hepatic steatosis, to date no authors have included this aspect of the problem in the analysis of their data.

PNF has been reported to occur in association with a reduced content of ATP in liver biopsies obtained at the end of the cold preservation period (31). Unfortu- nately, with this endpoint, a great deal of overlap of ATP values exists between grafts with favorable and unfavorable post-transplantation outcomes. Moreover,

the finding of a difference in hepatic ATP contents between successful and unsuccessful grafts has not been confirmed in all studies. Nonetheless a hepatic ATP value above 1.7 pmollg dry tissue weight has been associated with successful engraftment in all cases reported. However, it should be noted that neither study assessing hepatic ATP levels at the time of transplantation or at the time of harvesting was able to demon- strate that a given hepatic ATP level had any prognos- tic value (31,32). The obvious need for special equip- ment to measure the hepatic energy charge and ATP content of the liver in a timely fashion clearly limits the practical usefulness of this particular technique of assessing donor organs for transplant acceptability.

Current Realities Because of the increasing need for organs to be transplanted, it is extremely important to establish reliable criteria for the use of fatty donor organs as grafts. Worldwide, severely steatotic grafts (>60%) are rou- tinely discarded because of the increased rate of PNF and subsequent high mortality of recipients of these organs. The decision to use a mild (~30%) to moderately fatty liver (30-60%) for OLT is a difficult one. From the literature, it is clear that these grafts are associated with an increased risk of PNF and are associated with a decreased survival. Nonetheless, they can be successfully transplanted. However, it needs to be emphasized that, in addition to assessing the histological severity of the steatosis, attention must also be given to the duration of cold and warm ischemia times in each case. Clearly, it is essential to avoid long preservation times if a steatotic liver is to be used for transplantation.

Potential for Increasing the Use of Fatty Livers as Acceptable Donor Organs Any strategy that enables more fatty livers to be used for transplantation must improve the initial function of these organs in their recipients. In theory, this goal can be achieved by either “conditioning” the donor liver during the harvest and preservation procedure to reduce the severity of the ischemia-reperfusion damage or by enhancing the use of hepatocellular triglyceride stores as a hepatic energy source immediately after re- arterialization.

In rats, nutritional repletion of donors limits the damage experienced by both endothelial cells and hepatocytes as a result of cold preservation (33). Simi- larly, in humans, glycogen repletion as a result of intraportal glucose infusions during organ harvesting appears to reduce the amount of ischemic injury experienced by the graft (29). Given the increased sensitivity

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of fatty liver to both cold and warm &hernia (19,20,26), donor glycogen repletion would appear to be a particularly useful means of increasing the use of steatotic organs. Unfortunately, currently no system- atic clinical information is available relating to this simple procedure.

Platelet adhesion to endothelial cells within the sinusoids prior to death and during subsequent organ preservation and engraftment may also be important in initiating and perpetuating the graft vascular injury that produces PNF (30). With reperfusion of the liver, neutrophils can be shown to adhere to the injured endothelial surface (34), further damaging the vascular endothelium. Thus, it is not particularly surprising that two separate studies have reported that prostacyclin, an inhibitor of platelet aggregation, has a beneficial effect on lung preservation that may also extend to hepatic preservation (35,36). The susceptibility of fatty livers to ischemic injury would appear to demand an exploration of the effect of antithrombogenic substances such as prostacyclin on preservation-induced hepatic and endothelial cell injury and early post- transplantation outcome in clinical liver transplantation. In this regard, it is important to note that Prostaglandin El (PGEJ treatment of donors and the addition of PGEi to preservation solutions protects allografts from ischemia, presumably by ameliorating some of the microcirculatory disturbances experienced by the donor organ (37-39). The beneficial effects of PGEi include vasodilatation, inhibition of platelet aggregation and neutrophil activation, improved erythro- cyte deformability, stabilization of lysosomal membranes and stimulation of the regenerative capability of the liver. PGEi treatment of the recipient pre- and post-engraftment may also have a favorable effect on subsequent graft function. This assumption is supported by two findings. First, it has been reported that PGE, infusions started 4-34 h after transplantation, and continued for 4-7 days, are able to reverse PNF in 80% of cases (40). Unfortunately, the his- tology of the livers in this study was not reported. Secondly, in transplanted rats receiving a fatty donor liver, a 4-h intravenous infusion of PGE,, started immediately after transplantation, prevents the initial graft injury that is observed in untreated control animals (41). Based upon these experimental data, an evaluation of the “prophylactic” effect of PGEi in humans receiving a donor fatty liver would appear to be desirable. Moreover, whether treatment of the do- nor with PGEi prior to organ harvesting is a way of conditioning the liver needs to be assessed clinically and experimentally.

In circumstances where the lipid accumulation in the

liver is due to a mobilization of fat to the liver from adipose stores, a reversal of the underlying abnormali- ties responsible for the mobilization of the lipid should either correct or at least ameliorate the problem. Un- fortunately, there is no established pharmacological treatment which is useful for moving triglycerides out of the liver. However, it is known that in normally fed rats, receiving livers with severe steatosis induced by any one of a variety of dietary deficiency paradigms, the fatty accumulation in the liver resolves within 2 weeks (19). The administration of carnitine and coen- zyme A (CoA), which are essential co-factors in the transport of fatty acids into the mitochondria for their subsequent oxidation, to liver recipients of fatty donor organs may be a means of reducing the risk associated with the use of a fatty donor organ by enhancing fatty acid oxidation. In addition to its role in enhancing fat metabolism, carnitine facilitates the removal of potentially toxic acyl groups from mitochondria (42), and is also involved in branched chain aminoacid metabolism, functions that may further contribute to an en- hancement of allograft function in the early postoperative period (43). It is highly likely that the agonal period before death and prior to organ donation is associated with a reduction of the carnitine content of the hepatic tissue. Ischemia has been reported to lower mitochondrial free acetylCoA in heart tissue and probably does so also in the liver (44). If this is in fact the case, it would be reasonable to assess the role of L- carnitine supplementation of donors and/or recipients in enhancing lipid metabolism and energy production by the donor fatty liver immediately after surgical engraftment. The reported pharmacological effects of L- carnitine and CoA administration in experimental models encourages this approach. By restoring the intra-mitochondrial free CoA/acetyl CoA ratio, L-carnitine treatment protects the heart and isolated heart mitochondria against hypoxic damage and improves mitochondrial function and energy production (44,45). The intravenous infusion of L-carnitine in both donor and recipient dogs has been shown to improve the function of transplanted dog lungs (46). Finally, exogenous acetylCoA appears to protect cell membranes and lipoproteins against the peroxidative effects of oxygen-free radicals produced during the reperfusion period (47).

Practical Guidelines and Suggestions for the Future On the basis of this review of the outcome of liver grafting using steatotic livers in experimental and clinical settings, the following principles might be applied to clinical liver transplantation.

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The degree of hepatic steatosis of each and every donor organ should be assessed by histologic means at the time of organ harvesting. The degree of hepatic steatosis of each donor organ should be assessed sonographically prior to organ harvest and the result should be compared against the histological assessment of the same liver. Fatty livers with a fat content involving more than 50% of the hepatic parenchyma should not be used except under highly monitored experimental circumstances. The cold and warm ischemia time and degree of fatty change in donor organs should be accurately recorded and utilized to develop an equation involving each parameter that might be used to predict organ dysfunction. Experimental studies of the role of leukocytes and platelet adhesion molecule antagonists in donors immediately prior to organ harvesting and in the early post-reperfusion period should be initiated. Methods to enhance hepatic utilization of fatty acids in the immediate post-transplant period as a means of reducing the hepatic injury and failure rate associated with the use of steatotic livers should be investigated in experimental models and clinically. Methods to guarantee adequate glycogenation and methods inhibiting free-radical-associated hepatic and Kupffer cell injury during reperfusion need to be assessed experimentally and subsequently clinically.

Conclusions With an understanding of the mechanisms involved in the pathogenesis of the fatty liver and, more particularly, its resolution, it should be possible to return a large number of donor organs that are currently not used back into the usable donor organ pool. This goal is sufficiently important that it should be a major indi- cation for research finding, particularly during the current period when immediate results are considered essential in order to justify expenditure.

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The use of donor fatty liver for liver transplantation: a challenge or a quagmire?