Glycolytic support of adenine nucleotides in rat liver flush-preserved with UW or Collins' II. Importance of donor nutritional status

m 6 A-mediated gluconeogenic enzyme PCK1 upregulation protects against hepatic ischemia-reperfusion injury

BACKGROUND AND AIMS

Ischemia-reperfusion (I/R) injury frequently occurs during liver surgery, representing a major reason for liver failure and graft dysfunction after operation. The metabolic shift from oxidative phosphorylation to glycolysis during ischemia increased glucose consumption and accelerated lactate production. We speculate that donor livers will initiate gluconeogenesis, the reverse process of glycolysis in theory, to convert noncarbohydrate carbon substrates (including lactate) to glucose to reduce the loss of hepatocellular energy and foster glycogen storage for use in the early postoperative period, thus improving post-transplant graft function.

APPROACH AND RESULTS

By analyzing human liver specimens before and after hepatic I/R injury, we found that the rate-limiting enzyme of gluconeogenesis, PCK1, was significantly induced during liver I/R injury. Mouse models with liver I/R operation and hepatocytes treated with hypoxia/reoxygenation confirmed upregulation of PCK1 during I/R stimulation. Notably, high PCK1 level in human post-I/R liver specimens was closely correlated with better outcomes of liver transplantation. However, blocking gluconeogenesis with PCK1 inhibitor aggravated hepatic I/R injury by decreasing glucose level and deepening lactate accumulation, while overexpressing PCK1 did the opposite. Further mechanistic study showed that methyltransferase 3-mediated RNA N6-methyladinosine modification contributes to PCK1 upregulation during hepatic I/R injury, and hepatic-specific knockout of methyltransferase 3 deteriorates liver I/R injury through reducing the N6-methyladinosine deposition on PCK1 transcript and decreasing PCK1 mRNA export and expression level.

CONCLUSIONS

Our study found that activation of the methyltransferase 3/N6-methyladinosine-PCK1-gluconeogenesis axis is required to protect against hepatic I/R injury, providing potential intervention approaches for alleviating hepatic I/R injury during liver surgery.

Delayed energy protection of ischemic preconditioning on hepatic ischemia/reperfusion injury in rats

BACKGROUND

Hepatic ischemia/reperfusion (IR) injuries associated with hepatic resections are unresolved problems in the clinical practice. The aim of this study is to elucidate the effect of ischemic preconditioning (IPC) on the energy charge (EC) and related mechanisms at the late phase of hepatic IR injury.

METHODS

30 Wistar rats were randomly divided into sham, IR and IPC groups. The model of partial hepatic IR was used. The rats were subjected to 60 min hepatic ischemia, pretreated by IPC (10/15 min) or not. After 24 h of reperfusion, serum alanine aminotransferase (ALT), nitrite/nitrate (NOx), malondialdehyde (MDA), hepatic tissue arginase activity, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and EC of the liver were measured.

RESULTS

Liver injury reduced by IPC is measured by liver tissue arginase activity and serum ALT. Tissue NOx levels in rats pretreated with IPC were significantly higher than levels in the IR group (p < 0.001). Tissue levels of MDA in the liver of the IPC group were found to be significantly lower than the levels in the IR group (p < 0.001). ATP and EC levels 24 h after hepatic ischemia in rats pretreated with IPC were higher than the levels in the IR (p < 0.05). All groups had similar ADP and AMP levels in the liver tissues. The IPC procedure significantly reduced the hepatic necrosis (p < 0.001).

CONCLUSION

The results of this study demonstrated that pretreatment with IPC improved tissue ATP, EC, and hepatic necrosis at late stages of ischemia reperfusion injury of the liver. Increased nitric oxide, reduced MDA and arginase activity seemed to play a regulatory role in this delayed protective effect of IPC.

Beneficial effects of supplemental buffer and substrate on energy metabolism during small bowel storage

Successful preservation of small bowel (SB) is closely correlated with the maintenance of cellular energetics. This study was designed to assess the ability of a modified UW solution supplemented with buffer and glucose to facilitate ATP production during cold storage. In part A, rats SB (n = 4) were flushed vascularly as follows: Group 1, UW solution (control); Group 2, HUW solution (UW+90 mM histidine). Inclusion of histidine resulted in a >3-fold increase in buffering capacity over the pH range 7.4-6.8. Positive effects of histidine on ATP and energy charge were apparent after 4-10h storage. Examination of the key regulatory enzyme, Phosphofructokinase (PFK), reflected a sustained activation was over 1-4h in the HUW group only. In part B, groups were vascularly flushed as follows: Group 1, HUW solution (control); Group 2, Group 1+20mM glucose; and Group 3, Group 2+luminal flush. Elevated ATP and total adenylates over 2-10h in Group 3 compared to control were a direct consequence of improved glycolytic activity. This data supports the hypothesis that tissue energetics can be significantly improved during cold storage using a histidine-buffered UW solution supplemented with carbohydrate substrate.

Insulin in UW solution exacerbates hepatic ischemia / reperfusion injury by energy depletion through the IRS-2 / SREBP-1c pathway

Ischemia / reperfusion (I / R) injury is related to tissue graft energy status. Insulin, which is currently used in the University of Wisconsin (UW) preservation solution with insulin (UWI), is an anabolic hormone and was shown to exacerbate the hepatic I / R injury in our previous study. In this study, the energy status and regulation of metabolism genes by insulin were investigated in liver grafts preserved by UW solution. Insulin could significantly decrease adenosine triphosphate (ATP) level after 3 hours of preservation, as well as total adenine nucleotides (TANs) and energy charge (EC) levels. Energy regeneration deteriorated in the grafts preserved by insulin in terms of ATP and EC levels at 24 hours after transplantation. The insulin signal was transduced through the insulin receptor substrate-2 (IRS-2) pathway and the activity of IRS-2 was decreased gradually at the messenger ribonucleic acid (mRNA) level during cold preservation. Downstream targeting genes such as sterol regulatory element-binding protein-1c (SREBP-1c), glucokinase (GKC), and fatty acid synthase (FAS) genes, as well as phospho-glycogen synthase kinase-3beta (GSK-3beta) were activated and they showed the similar expression profiles during cold preservation. Lipoprotein metabolism was accelerated by insulin through upregulation of the activity of apolipoprotein C-III (Apo C-III) during cold preservation. The insulin-like growth factor-binding protein-1 pathway was inhibited during cold preservation. In conclusion, insulin in UW solution exacerbates hepatic I / R injury by energy depletion as the graft maintains its anabolic activity. The key enzyme activities of the energy-consuming process of glycogen and fatty acid synthesis as well as lipoprotein metabolism were accelerated by insulin through the IRS-2 / SREBP-1c pathway.

Effects of hypothermic machine perfusion on rat liver function depending on the route of perfusion

BACKGROUND AND METHODS

The aim of this study was to evaluate the efficacy of hypothermic machine perfusion (HMP) to preserve rat livers according to the route of perfusion, i.e., via portal vein, hepatic veins (retrograde), or hepatic artery. Livers were preserved for 24 or 48 hr by simple cold storage (SCS) or by HMP. Preservation solution was supplemented with (HMP) or without (SCS) hydroxyethyl starch. After preservation, grafts were reperfused for 2 hr with an oxygenated Krebs-Henseleit bicarbonate buffer.

RESULTS

After 24 hr of preservation, total glutathione concentrations in HMP livers were similar (1287+/-37, 1418+/-118, and 1471+/-62 nmol/g in hepatic artery, portal vein, and hepatic vein HMP livers, respectively) and higher than in the SCS (833+/-118 nmol/g, P<0.05) group. These higher total glutathione values were due to higher reduced glutathione concentrations. ATP concentrations in the liver tissue were similar in HMP groups (0.75+/-0.4, 0.64+/-0.1, and 0.77+/-0.1 micromol/g in hepatic artery, portal vein, and hepatic vein HMP livers, respectively) and higher than in SCS (0.32+/-0.06 micromol/g, P<0.05). After 2 hr of normothermic reperfusion, bile production in the HMP portal and HMP retrograde groups were similar (391+/-29 ml and 372+/-25 ml) and higher than in the HMP artery or SCS groups (275+/-25 ml and 277+/-32 ml, respectively; P<0.05). Aspartate transaminase, alanine transaminase, lactate dehydrogenase, and purine nucleoside phosphorylase release into the perfusate of HMP portal and HMP retrograde perfused livers was similar and significantly lower compared to the HMP artery and SCS groups. At the end of reperfusion, no statistical differences were found for glutathione concentration and energetic reserves in the livers of each group. After 48 hr of preservation, livers from the HMP portal and HMP retrograde groups did significantly better than livers from the HMP artery or SCS groups.

CONCLUSIONS

This study confirms the superiority of HMP over SCS to preserve the liver graft. It shows that retrograde perfusion is similar to PV perfusion and that perfusion by HA is less beneficial.

Metabolic intervention to affect canine pancreas recovery following ischemia during preservation by the two-layer method

We have demonstrated that a high adenosine triphosphate (ATP) level in a canine pancreas during preservation by the two-layer method is an important determinant for the ultimate success of pancreatic transplantation. In this study, we investigated (a) the effect of factors that seemed to have an influence on energy metabolism in the canine pancreas at the tissue ATP level and (b) graft viability during preservation by the two-layer method. ATP tissue concentration was determined by high-performance liquid chromatography and graft viability was assessed on the basis of survival rate following autotransplantation. First, the pancreas was harvested from either 72-h-fasted (n = 5) or fed dogs (n = 5) and preserved by the two-layer Euro-Collins solution (EC)/perfluorochemical (PFC) method for 24 h. All the pancreatic grafts were viable in both fed and fasted groups. There was also no significant difference in ATP tissue concentration between the two groups (7.48 +/- 0.55 vs. 7.03 +/- 0.74 micromol/g dry weight, NS). Second, the pancreatic grafts subjected to 60 min of warm ischemia were preserved by either the two-layer (EC/PFC) or (EC + adenosine/PFC) method for 24 h. Without adenosine, ATP tissue concentration did not recover (1.62 +/- 0.26 after warm ischemia vs. 1.56 +/- 0.40 micromol/g dry weight after preservation, NS) and all the pancreatic grafts failed. However, provision of adenosine led to restoration of ATP tissue levels (1.90 +/- 0.53 vs. 7.23 +/- 2.17 micromol/g dry weight, P < 0.01) and four of five grafts functioned immediately and maintained normoglycemia after transplantation. These results clearly demonstrated that the nutritional state of the pancreatic graft before procurement had no influence on ATP tissue level as well as graft viability during 24-h preservation by the two-layer method. On the other hand, provision of adenosine during 24-h preservation enhanced ATP synthesis of the pancreatic tissue, thereby improving viability of the ischemically damaged pancreas.

The role of protein kinase A in anaerobic energy production during liver storage

BACKGROUND/AIM

During cold liver storage in University of Wisconsin solution, glycolysis is inhibited by declining intracellular pH and a reduction in glycogen phosphorylase activity. The current study investigated the effects of a histidine-buffered, modified University of Wisconsin solution with cyclic-AMP analogue plus phosphodiesterase inhibitors to optimize both pH and PK A-mediated limits on glycolytic energy production.

METHODS

In an isolated rodent-liver system, dioctanoyl-cAMP was supplemented with each phosphodiesterase inhibitor (isobutylmethylxanthine, papaverine, Ro 20-1724, dipyridamole). Once the most efficacious combination was determined, a separate group of livers was cold-stored for 24 h and then reperfused at 37 degrees C to examine regeneration of high energy adenylates.

RESULTS

Lactate accumulation in the histidine-lactobionate-raffinose group was 8.7 micromol/g; net increases were greater with all four phosphodiesterase inhibitors with dioctanoyl-cAMP; dipyridamole resulted in a maximum increase of 16.7 micromol/g. ATP was consistently higher in all treatment groups with phosphodiesterase inhibitors throughout 24 h; even after 10-24 h, levels with dipyridamole-treatment were 250-280% higher than with University of Wisconsin (p<0.05). Assessment of glycogen phosphorylase activity in the dipyridamole-treatment group indicated that increased glycolytic activity over the first 4 h was a direct consequence of elevated enzyme levels. However, between 4-10 h, phosphofructokinase underwent a phosphorylation, leading to an inhibition at this point in glycolysis. Upon reperfusion, the higher ATP/ADP and ADP/ AMP ratios found with phosphodiesterase inhibitor treatment suggested that adenylate regeneration was superior with dipyridamole+dioctanoyl-cAMP.

CONCLUSION

Dipyridamole plus dioctanoyl-cAMP treatment achieved increased glycogenolysis throughout 24 h storage by maintaining glycogen phosphorylase in a phosphorylated (active) state; however, a PK A-mediated phosphorylation (inhibition) of phosphofructokinase resulted in decreased glycolytic ATP production between 4-10 h.

Metabolic adaptations of a lower vertebrate to long-term hypothermic hypoxia provide clues to successful clinical liver preservation

This study was designed to determine whether the metabolic adaptations developed by frogs to tolerate natural events of hypothermic hypoxia would precondition its liver for ex vivo organ storage. The metabolic responses of the frog, Rana castabiena, were compared to those of a mammalian system (rat) throughout a prolonged period of organ storage. Livers from rats and frogs were flushed and stored in UW solution at 5 degrees C for periods of 24-96 h. In frog livers, ATP was maintained high and constant over the first 24 h of storage; values ranged from 2.7 to 3.0 micro mol/g. Even after 96 h cold storage, ATP remained > 1.0 micro mol/g. In contrast, ATP levels in stored rat livers dropped rapidly, and by 4 h ATP was 1.2 micro mol/g. In terms of anaerobic endproduct accumulation, lactate levels rose 5.8 micro mol/g in frog liver (over 96 h) and by 8.6 micro mol/g in rat liver (over 24 h). This difference in flux through glycolysis was also reflected in relative rates of carbohydrate catabolism (i.e., glucose + lactate production). The rate of carbohydrate catabolism for frog liver was 0.74 micro mol/g/h compared to 2.26 micro mol/g/h for rat liver; a Q10 value of 6.2 was estimated for livers from R. castabiena. An assessment of glycolytic enzyme activities revealed that key differences in the responsiveness of pyruvate kinase to allosteric modifiers may have been responsible for the marked drop in the rate of anaerobic energy production in frog tissues. Although the concept of depressed metabolism in a lower vertebrate is not new, the data presented in this study demonstrate that a depressed metabolic state can be achieved in isolated livers from R. castabiena simply through cold exposure. With respect to clinical relevance, the results of this study indicate that energetics of stored livers can be maintained effectively through an efficient reduction in energy use in combination with a slow, yet continuous, rate of energy production facilitated by glycolysis.

Investigation of a primary requirement of organ preservation solutions: supplemental buffering agents improve hepatic energy production during cold storage

BACKGROUND

This study was designed to investigate the effects of a modified University of Wisconsin (UW) solution supplemented with one of four buffering agents (histidine, bicine [N,N-bis(2-hydroxyethyl)glycine], tricine [N-tris(hydroxymethyl)methylglycine], and Tris) on liver metabolism during cold ischemic storage.

METHODS

Rat livers were flushed and stored for a maximum period of 24 hr at 4 degrees C, and tissue energetics, substrate, and anaerobic end-products were assessed; the group exhibiting the best results during storage was recovered in a 60-min period of warm reperfusion. Relative buffering capacities of the experimental solutions (measured over physiological pH range, in mM H+/L) were: UW, 4.1; histidine+UW, 9.8; Tris+UW, 19.0; bicine+UW, 22.5; tricine+UW, 26.8.

RESULTS

In the UW group, ATP levels dropped rapidly over the first 4 hr; 1.0 micromol/g (40% of initial) remained after 4 hr of storage. By 2 hr, ATP levels in bicine- and tricine-treated groups were 0.5 and 1.1 micromol/g greater than in the UW-stored livers and by 10 hr, ATP in bicine-treated livers was twofold that of the control (UW) group. Total adenylate levels also reflected a superior elevation of cellular energetics; even after 24 hr, quantities were 1.4 and 2.0 micromol/g higher than the UW group in bicine- and histidine-supplemented organs. The increase in energetics occurred as a result of increased flux through the major anaerobic energy-producing pathway, glycolysis. The glycolytic rate was significantly greater at storage times > 10 hr with solutions supplemented with bicine, histidine, and tricine. Final values for net lactate accumulation over the entire 24-hr storage period were: UW, 10.1 micromol/g; histidine, 14.3 micromol/g; bicine, 15.2 micromol/g; tricine, 13.8 micromol/g. Activities of glycogen phosphorylase revealed that the activity of this enzyme dropped by 50% within 2 hr of storage in UW. However, histidine and bicine supplementation resulted in a substantial elevation of phosphorylase "a" over 4 hr and 10 hr, respectively. The best buffer of the four examined in this study was bicine; energetics, glycolytic flux, and patterns of adenylate regeneration upon reperfusion were markedly superior to modified UW solution.

CONCLUSION

The results of this study suggest that supplementing the "gold standard" UW solution with an additional buffering agent (in order of efficacy: bicine>tricine>histidine) may improve the metabolic status of livers during clinical organ retrieval/storage.

Hyperosmolarity associated with diabetes insipidus alters hepatocyte structure and function but not survival after orthotopic liver transplantation in rats

BACKGROUND

This study was designed to evaluate the effect of donor hyperosmolarity secondary to diabetes insipidus, an almost universal occurrence among brain-dead patients, on hepatic function.

METHODS

In vitro (isolated liver perfusion) and in vivo (hyaluronic acid and indocyanine green uptake, arterial ketone body ratio, orthotopic liver transplantation) experiments were conducted using Brattleboro rats, with hereditary hypothalamic diabetes insipidus, and Sprague-Dawley rats, with normal pituitary function. ATP content and recovery after cold preservation were measured during the perfusion.

RESULTS

Cold-preserved livers from hyperosmolar rats were observed to have elevated hepatic enzyme release and decreased bile production compared with normosmolar controls. Moreover, in these livers, the recovery of ATP after cold preservation was completely absent. Transmission electron microscopy of liver biopsies collected from hyperosmolar rats demonstrated profound ultrastructural changes, particularly in the mitochondria, that were not evident in the biopsies from normosmolar rats. All the experimental groups demonstrated similar hyaluronic acid uptake, whereas indocyanine green uptake was markedly impaired in the hyperosmolar group, suggesting that hepatocyte and not sinusoidal endothelial cell function is adversely affected by hyperosmolarity. The arterial ketone body ratio was profoundly compromised by chronic and, to an even greater degree, by acute hyperosmolarity. Survival after transplantation using hyperosmolar donors was not affected in this study.

CONCLUSIONS

These results are an important step toward understanding the mechanism whereby brain death, a complicated pathophysiologic phenomenon, adversely affects the hepatic allograft.

Effects of brain death and glucose infusion on hepatic glycogen and blood hormones in the pig

We wished to study the effects of intravenous glucose/ insulin infusion to brain-dead pigs on the hepatic glycogen content. Four groups of 40-kg pigs were studied: brain-dead and control pigs given isotonic saline or glucose/insulin (7.5 mg glucose/kg/min, 1.25 mU insulin/kg/ min) (n = 5 to 10 in each group). Brain death was induced by inflating a balloon placed in the epidural space. In brain-dead pigs given saline, liver glycogen decreased from 45 +/- 11 mmol/g DNA (mean +/- SEM) to 7 +/- 3 mmol/ g DNA after 6 hours. Thereafter, it increased to 28 +/- 9 mmol/g DNA after 9 hours (P = .05 compared with the 6-hour measurement). These changes were accompanied by transient increases in plasma adrenaline, glucose, free fatty acids (FFA), and glucagon. Following glucose/ insulin infusion, hepatic glycogen increased steadily and was approximately double after 12 hours (P < .01) in both brain-dead and in non-brain-dead pigs. In brain-dead pigs, the increases in the aforementioned blood measurements were smaller following glucose/insulin infusion than following saline infusion. However, studies of longer duration will be needed to examine these effects on a time scale that is relevant to human organ donors. In conclusion, the decrease in hepatic glycogen content after brain death could be prevented by intravenous glucose/insulin infusion probably because of a reduction of the adrenaline response to the induction of brain death.

Hepatic nucleotide triphosphate regeneration after hypothermic reperfusion in the pig model: an in vitro P-NMR study

The aim of this study was to assess the possibility of regenerating nucleotide triphosphates (NTP) in the pig liver following its harvest and subsequent storage on ice. This study has used a pig model that allowed human donor liver retrieval techniques and methods of storage to be utilized. In vitro phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy was used to evaluate the changes associated with phosphorus containing metabolites such as NTP, phosphomonoesters (PME), phosphodiesters (PDE), and inorganic phosphate (Po). During 4 hr storage NTP levels were reduced to undetectable levels but its regeneration was possible over a period of 2 hr of oxygenated hypothermic reperfusion. Resynthesized NTP reached values that were only 30% reduced from pre-harvest values. There was a corresponding reduction in Pi over the same period. Glycolytic intermediates, 3-phosphoglycerate and 2,3 diphosphoglycerate, both increased significantly during the period of storage and subsequently declined following hypothermic reperfusion. Cellular damage, indicated by the concentrations of glycerophosphorylcholine (GPC) and glycerophosphorylethanolamine (GPE) was minimal during cold storage. However upon hypothermic reperfusion, concentrations of GPC and GPE reduced, indicating a degree of cellular damage caused by reperfusion. This study has shown for the first time that is possible to regenerate high energy phosphate nucleotides following a period of hypothermic reperfusion in a large, clinically related animal model. This technique warrants investigation clinically to improve the outcome of orthotopic liver transplantation. It also provides a method to study the effects of different preservation fluids and methods of storage and organ reperfusion.

Beneficial effect of alanine on metabolic recovery of fasted livers submitted to cold ischemia

The aim of this study was to investigate the possible beneficial effect on perfused mouse liver of alanine as an exogenous substrate for gluconeogenesis. Livers from fed and fasted animals were perfused with oxygenated Krebs' Henseleit buffer for 30 min, then stored at 4 degrees C in University of Wisconsin solution for 48 h. Then reperfusion at 37 degrees C was performed according to two protocols. In the first one, reperfusion with alanine-free Krebs' Henseleit buffer was used for 1 h. 8 mM (3-(13)C) alanine was then added and perfusion was prolonged for a second hour. In the second one, the first hour of perfusion was omitted and the organs were reperfused directly for an hour in the presence of 8 mM (3-(13)C)alanine. 31P NMR was used to measure the NTP recovery of the livers. At the end of the reperfusions, 13C and 1H NMR spectra of perfusates and of glutamine extracted from these perfusates by HPLC were recorded. These data were analysed according to a model of liver metabolism assuming that the only substrate of the liver was (3-(13)C)alanine and endogenous substrates were metabolizable only through pyruvate. It was found that in the absence of initial alanine at reperfusion, livers from fasted mice recovered less NTP than those of fed ones (40 +/- 4% vs 60 +/- 5%, p <0.01), but not if this substrate is present at the beginning of reperfusion (61 +/- 5% vs 60 +/- 5%). This was confirmed by the amount of labelled metabolites produced. However, the dilution of 13C labelled metabolites by unlabelled ones did not indicate a larger concentration of endogenous substrates in livers from fed mice. The conclusion reached was that the lower pyruvate dehydrogenase activity of livers from fasted mice relatively to that from fed mice could be compensated for by the greater pyruvate concentration provided by alanine for the initial production of NTP after cold ischemia and warm reperfusion.

Glycogen phosphorylase activity during the cold storage of liver: A limiting effect on glycolytic flux and energy production

This study examined the effects of dibutyryl-cyclic adenosine monophosphate (db-cAMP) and okadaic acid (a specific inhibitor of protein phosphatases 1 and 2A) as additives to a cold storage solution. The effects on levels of glycogen phosphorylase, the resultant effects on flux through the glycolytic pathway, and the consequences of these changes on adenylate (ATP, ADP, and AMP) levels in rat liver during a 24-hr period of cold hypoxia were studied. The rapid transition to anaerobic metabolism was reflected in the increases in lactate levels for all groups. Total lactate accumulation in control livers (flushed and stored with a histidine-lactobionate-raffinose solution) was 9.8 micromol/g. The one notable difference between the control and experimental groups was the total lactate increase in one of the groups treated with db-cAMP; lactate accumulation was 16.0 micromol/g. There was a preferential maintenance of ATP that correlated with the increased flux through glycolysis observed with db-cAMP treatment; levels were 0.4-0.6 micromol/g higher than control group values between 2 and 10 hr of storage. In the control group, levels of glycogen phosphorylase in the active 'a' form began to decrease within 1 hr of exposure to cold hypoxic storage. Values dropped from 86% to 78% within the first 1 hr and by 10 hr, % 'a' was 57%. The separate addition of db-cAMP and okadaic acid resulted in a sustained maintenance of phosphorylase % 'a' throughout the entire cold hypoxic storage period; % 'a' values at 10 hr ranged from 75% to 81%. The major finding of this study was the clear and distinct correlation between phosphorylase % 'a' and total lactate accumulation (index of flux through glycolysis). This relationship was statistically significant after only 1 hr of storage, with a correlation coefficient of r=0.52 (P<0.025); however, the correlation became stronger as the time of storage progressed (by 10 hr, r=0.72; P<0.001). According to the relationship established, the maximum theoretical limit for lactate accumulation with 100% phosphorylase 'a' is approximately 30 micromol/g lactate. This finding suggests that glycogen phosphorylase and not necessarily glycogen content is one major determinant in maintaining anaerobic metabolism and energy production during cold liver storage. Hence, previous experiments that investigated the effects of nutritional status and glycogen content on tissue viability after experimental transplantation need to be reassessed.

Energy status in anoxic rat hepatocytes: effects of isoflurane, solution composition, and hypothermia

Both cold and warm ischemia occur during liver transplantation. Hypothermia and Wisconsin solution preserve adenine nucleotide energy status, which is crucial to hepatic function and viability. The volatile anesthetic isoflurane has been shown to preserve energy status in anoxic isolated hepatocytes in warm Krebs solution. The present study examined isoflurane effects on energy status during incubation also in Wisconsin or Krebs-plus-adenosine solution at 37 degrees or 4 degrees. Hepatocytes were isolated from rat liver after perfusion with Krebs + collagenase. In 25-mL flasks, 12.5 million cells in 2.5 mL of Krebs, Krebs plus 5 mmol/L adenosine, or Wisconsin solution were incubated under an atmosphere of O2/CO2 or N2/CO2 (19:1) +/- isoflurane (3 volumes% = 2ED50), for 30 minutes at 37 degrees C or 4 degrees C. Adenine nucleotides were measured by high-performance liquid chromatography (HPLC), lactate enzymatically. During warm (37 degrees) anoxia, Wisconsin solution preserved energy status; Krebs plus adenosine did not. Isoflurane further protected energy status in all three solutions. Hypothermia (4 degrees) alone greatly decreased anoxic loss of energy status in all solutions. In Wisconsin solution only, energy status tended to be higher in anoxic than in oxygenated cells and was further enhanced by isoflurane, with corresponding increases in lactate. During 30 minutes of either warm or cold anoxia, isoflurane and Wisconsin solution each helped preserve adenine nucleotide energy status in isolated hepatocytes, at least in part through enhanced glycolysis.

Evidence for the detrimental role of proteolysis during liver preservation in humans

BACKGROUND/AIMS

Proteolysis may persist in the liver allograft during cold storage. The aim of this study was to determine the significance of proteolysis within liver allografts stored at 4 degrees C in University of Wisconsin preservation fluid.

METHODS

Thirty recipients of 32 liver allografts were studied prospectively. Amino acid content of the preservation fluid was analyzed at the end of cold storage and was correlated to graft and patient outcome after transplantation.

RESULTS

Analysis of the preservation fluid showed the presence of free amino acids, the profile of which was different from that of stored liver parenchyma. Concentrations of amino acids (alanine, cysteine, leucine, isoleucine, methionine, lysine, ornithine, and threonine) and transaminases (alanine aminotransferase and aspartate aminotransferase) in the preservation fluid correlated with the duration of cold ischemia. Indexes of graft dysfunction (serum alanine aminotransferase and aspartate aminotransferase peaks and prothrombin rate) correlated with concentrations of cysteine, alanine, isoleucine, leucine, methionine, lysine, ornithine, and threonine, whereas enzyme concentrations in the fluid were not predictive of graft dysfunction.

CONCLUSIONS

These data suggest that liver proteolysis occurs during cold storage and may have a detrimental effect on the outcome after transplantation. The measurement of the amino acids in the preservation fluid at the end of the cold storage period could help to identify the most severely damaged organs.

A magnetic resonance study of the effect of nutritional status on cold-preserved murine liver

BACKGROUND/AIMS

Clinical and experimental studies suggest a link between nutritional status and the recovery of hepatic function after hypoxic and hypothermic insults. This study aimed at determining the metabolic pathways involved in such recovery as a function of nutrition.

METHODS

Livers from fed and fasted mice were perfused with oxygenated Krebs'-Henseleit buffer (RBKB). After depletion of glycogen, 31P and 13C nuclear magnetic resonance spectra were acquired. Livers were flushed with University of Wisconsin solution and stored at 4 degrees C for 0, 24, or 48 hours. At reperfusion with RBKB, recovery of nucleoside triphosphates (NTP) was followed up. After 45 minutes, [3-13C]alanine was added and substrate consumption and metabolic products assessed.

RESULTS

Livers from fed animals recovered more NTP at reperfusion both after 24 hours (85% +/- 11% vs. 67% +/- 7%; P < 0.01) and 48 hours (61% +/- 10% vs. 36% +/- 10%; P < 0.01, respectively) of cold storage. Gluconeogenesis as reflected by [3-13C]alanine consumption was also higher from fed animals. Hepatic glycogen before preservation was low in both groups. Livers from fasted animals contained increased triglyceride levels, but these did not contribute to NTP production at reperfusion.

CONCLUSIONS

Livers from fed mice show an improved recovery after cold ischemia. Glycogen levels are low in these organs, and NTP synthesis must be from substrates other than fatty acids.

Liver metabolism in cold hypoxia: a comparison of energy metabolism and glycolysis in cold-sensitive and cold-resistant mammals

The effects of cold hypoxia were examined during a time-course at 2 degrees C on levels of glycolytic metabolites: glycogen, glucose, glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, phosphoenolpyruvate, pyruvate, lactate and energetics (ATP, ADP, AMP) of livers from rats and columbian ground squirrels. Responses of adenylate pools reflected the energy imbalance created during cold hypoxia in both rat and ground squirrel liver within minutes of organ isolation. In rat, ATP levels and energy charge values for freshly isolated livers were 2.54 mumol.g-1 and 0.70, respectively. Within 5 min of cold hypoxia, ATP levels had dropped well below control values and by 8 h storage, ATP, AMP, and energy charge values were 0.21 mumol.g-1, 2.01 mumol.g-1, and 0.17, respectively. In columbian ground squirrels the patterns of rapid ATP depletion and AMP accumulation were similar to those found in rat. In rat liver, enzymatic regulatory control of glycolysis appeared to be extremely sensitive to the decline in cellular energy levels. After 8 h cold hypoxia levels of fructose-6-phosphate decreased and fructose-1,6-bisphosphate increased, thus reflecting an activation of glycolysis at the regulatory step catalysed by phosphofructokinase fructose-1,6-bisphosphatase. Despite an initial increase in flux through glycolysis over the first 2 min (lactate levels increased 3.7 mumol.g-1), further flux through the pathway was not permitted even though glycolysis was activated at the phosphofructokinase/fructose-1,6-bisphosphatase locus at 8 h, since supplies of phosphorylated substrate glucose-1-phosphate or glucose-6-phosphate remained low throughout the duration of the 24-h period.(ABSTRACT TRUNCATED AT 250 WORDS)

Can adenine nucleotides predict primary nonfunction of the human liver homograft?

Sixty-eight primary liver grafts were analyzed to see whether adenine nucleotides (AN: ATP, ADP, and AMP) or purine catabolites (PC: adenosine, inosine, hypoxanthine, and xanthine) of tissue or effluent can predict primary graft nonfunction. AN, PC, and nicotinamide adenine dinucleotide, oxidized form (NAD+) of the tissue before (pretransplant) and after graft reperfusion (post-transplant) and of the effluent were analyzed. The graft outcome was classified into two groups (group A: successful, n = 64; group B: primary nonfunctioning, n = 4). No significant differences were observed in pretransplant measurements between groups A and B, whereas ATP, ADP, total AN, total AN + total PC (T) and NAD+, in post-transplant tissues, were significantly higher in group A. Xanthine in the effluent was significantly higher in group B than in group A. ATP, ADP, total AN, T, and NAD+ in post-transplant tissue were significantly associated with primary graft nonfunction by logistic regression analysis.

Study of kidney and liver viability in the rat after exclusive aortic perfusion using intracellular ATP measurement

To find whether the liver can be procured after exclusive aortic perfusion, three organ perfusion models were used in three groups of donor rats. Group 1 underwent liver wash-out via the portal vein; in group 2, the kidneys alone were perfused via the aorta; and group 3 underwent simultaneous aortic perfusion of liver and kidneys. All perfusion flow rates in the three groups were adjusted to physiological values. Harvested organs were transplanted and recipient animals were killed 4 h after transplantation to study liver and kidney viability by using intracellular ATP measurement. Liver ATP was lower (P < 0.005) in the portal perfusion group (group 1: 1.396 +/- 0.412) than in the aortic perfusion group (group 3: 2.181 +/- 0.061). Kidney ATP was comparable in groups 2 and 3:1.066 +/- 0.09 vs 1.059 +/- 0.273 (mumol/g) tissue). Liver cooling was quicker with portal perfusion than with the aortic flush (20 degrees C in 20 s vs 15 degrees C in 60 s). Aortic perfusion at a physiologic flow rate has no detrimental effect on renal viability studied by intracellular ATP measurement. We conclude that liver cooling via the aortic route only is a good alternative to portal perfusion and seems to give good preservation. Application of this observation to emergency procurement in humans is still the subject of controversy.

Effects of method of preservation on functions of livers from fed and fasted rabbits

Livers from fed, fasted (48 h) and glucose-fed rabbits were preserved for 24 and 48 h by either simple cold storage (CS) or continuous machine perfusion (MP) with the University of Wisconsin preservation solutions. After preservation liver functions were measured by isolated perfusion of the liver (at 37 degrees C) for 2 h. Fasting caused an 85% reduction in the concentration of glycogen in the liver but no change in ATP or glutathione. Glucose feeding suppressed the loss of glycogen (39% loss). After 24 h preservation by CS livers from fed or fasted animals were similar including bile production (6.2 +/- 0.5 and 5.6 +/- 0.4 ml/2 h, 100 g, respectively), hepatocellular injury (LDH release = 965 +/- 100 and 1049 +/- 284 U/liter), and concentrations of ATP (1.17 +/- 0.15 and 1.18 +/- 0.04 mumol/g, glutathione (1.94 +/- 0.51 and 2.35 +/- 0.26 mumol/g, respectively), and K:Na ratio (6.7 +/- 1.0 and 7.7 +/- 0.5, respectively). After 48 h CS livers from fed animals were superior to livers from fasted animals including significantly more bile production (5.0 +/- 0.9 vs 2.0 +/- 0.3 ml/2 h, 100 g), less LDH release (1123 +/- 98 vs 3701 +/- 562 U/liter), higher concentration of ATP (0.50 +/- 0.16 vs 0.33 +/- 0.07 mumol/g) and glutathione (0.93 +/- 0.14 vs 0.30 +/- 0.13 mumol/g), and a larger K:Na ratio (7.4 vs 1.5). Livers from fed animals were also better preserved than livers from fasted animals when the method was machine perfusion. The decrease in liver functions in livers from fasted animals preserved for 48 h by CS or MP was prevented by feeding glucose. Glucose feeding increased bile formation after 48 h CS preservation from 2.0 +/- 0.3 (fasted) to 6.9 +/- 1.2 ml/2 h, 100 g; LDH release was reduced from 3701 +/- 562 (fasted) to 1450 +/- 154 U/liter; ATP was increased from 0.33 +/- 0.07 (fasted) to 1.63 +/- 0.18 mumol/g; glutathione was increased from 0.30 +/- 0.01 (fasted) to 2.17 +/- 0.30 mumol g; and K:Na ratio was increased from 1.5 +/- 0.9 to 5.3 +/- 1.0. This study shows that the nutritional status of the donor can affect the quality of liver preservation. The improvement in preservation by feeding rabbits only glucose suggests that glycogen is an important metabolite for successful liver preservation. Glycogen may be a source for ATP synthesis during the early period of reperfusion of preserved livers.

Primary culture of adult rat hepatocytes after 48-hour preservation of the liver with cold UW solution

Rat livers were perfused and stored for 48 hr in cold University of Wisconsin solution before dissociation by the two-step collagenase method. At that time, glycogen content was significantly reduced, but no obvious changes in albumin, beta-actin and aldolase B mRNAs and in glutathione levels were observed. Enzymatic perfusion yielded 280 +/- 30 x 10(6) viable hepatocytes vs. 520 +/- 40 x 10(6) viable hepatocytes from unstored organs. Cell viability determined by trypan blue exclusion was 74% and 90%, respectively. Hepatocytes from University of Wisconsin-preserved livers had a 29% reduced adenosine triphosphate content, but glutathione levels did not significantly differ from those found in unstored cells. When put into culture, hepatocytes formed typical monolayers of granular epithelial cells and did not exhibit alteration of their fine structure when compared with cells from unstored organs. After 24 and 48 hr, they showed variations in cytochrome P-450 content and ethoxyresorufin O-deethylase activity similar to those observed with unstored cells. By contrast, overall protein synthesis and albumin secretion rate were 40% and 30% lower, respectively. Hepatocytes from University of Wisconsin-preserved organs could be cryopreserved and further cultured as unstored cells. The University of Wisconsin solution was also used to preserve isolated hepatocytes. Viability of freshly isolated hepatocytes was decreased by only 10% after 48 hr of hypothermic liver storage when assayed by intracellular lactate dehydrogenase content. However, after 4 hr of storage, in contrast with hepatocytes preserved in L15 Leibovitz medium, the cells attached poorly to plastic and exhibited morphological alterations.(ABSTRACT TRUNCATED AT 250 WORDS)