Glycohydrolases as markers of hepatic ischemia-reperfusion injury and recovery

A new index predicts early allograft dysfunction following living donor liver transplantation: A propensity score analysis

OBJECTIVE/AIM

The aim of this study was to identify a new index to predict early allograft dysfunction following living donor liver transplantation.

METHODS

The study enrolled 260 adult living donor liver transplantation recipients. Postoperative laboratory variables were assessed for their association with the prevalence of early allograft dysfunction using the inverse probability of treatment weighting and propensity-score matching (n=93 pairs) analysis.

RESULTS

Forty-seven recipients (18.1%) developed early allograft dysfunction. In multivariable analysis, the alanine aminotransferase and gamma-glutamyl transpeptidase levels on postoperative day 1 were independent predictors of early allograft dysfunction. The alanine aminotransferase to gamma-glutamyl transpeptidase ratio (AGR) was developed. All cases were divided into two groups (Group 1 [AGR≥8.47, n=103] and Group 2 [AGR<8.47, n=157]). AGR≥8.47 (OR 10.345, 95%CI 4.502-23.772, p<0.001), hepatorenal syndrome (OR 3.016, 95%CI 1.119-8.125, p=0.029), and graft to recipient weight ratio <0.8% (OR 2.155, 95%CI 1.004-4.624, p=0.049) were independent risk factors for early allograft dysfunction. The prevalence of early allograft dysfunction was higher in group 1 (after adjusting for inverse probability of treatment weighting [n=39; 37.9% vs n=8; 5.1%] and propensity-score matching [n=33; 35.5% vs n=2; 2.2%]) than that in group 2 (p<0.001).

CONCLUSIONS

The postoperative AGR is a practical index for predicting early allograft dysfunction after living donor liver transplantation.

Novel strategy to decrease reperfusion injuries and improve function of cold-preserved livers using normothermic ex vivo liver perfusion machine

Normothermic extracorporeal liver perfusion (NELP) can decrease ischemia/reperfusion injury to the greatest degree when cold ischemia time is minimized. Warm perfusion of cold-stored livers results in hepatocellular damage, sinusoidal endothelial cell (SEC) dysfunction, and Kupffer cell activation. However, the logistics of organ procurement mandates a period of cold preservation before NELP. The aim of this study was to determine the beneficial effects of gradual rewarming of cold-stored livers by placement on NELP. Three female porcine livers were used for each group. In the immediate NELP group, procured livers were immediately placed on NELP for 8 hours. In the cold NELP group, livers were cold-stored for 4 hours followed by NELP for 4 hours. In rewarming groups, livers were cold-stored for 4 hours, then gradually rewarmed in different durations to 38°C and kept on NELP for an additional 4 hours. For comparison purposes, the last 4 hours of NELP runs were considered to be the evaluation phase. Immediate NELP livers had significantly lower concentrations of liver transaminases, hyaluronic acid, and β-galactosidase and had higher bile production compared to the other groups. Rewarming livers had significantly lower concentrations of hyaluronic acid and β-galactosidase compared to the cold NELP livers. In addition, there was a significant decline in international normalized ratio values, improved bile production, reduced biliary epithelial cell damage, and improved cholangiocyte function. Thus, if a NELP machine is not available at the procurement site and livers will need to undergo a period of cold preservation, a gradual rewarming protocol before NELP may greatly reduce damages that are associated with reperfusion. In conclusion, gradual rewarming of cold-preserved livers upon NELP can minimize the hepatocellular damage, Kupffer cell activation, and SEC dysfunction.

Early elevated serum gamma glutamyl transpeptidase after liver transplantation is associated with better survival

BACKGROUND

Gamma glutamyl transpeptidase (GGT) is a membrane bound enzyme that plays a key role in the synthesis of the antioxidant glutathione. Epidemiological studies have linked high GGT with an increased risk of morbidity and cardiovascular mortality. In contrast, GGT is usually elevated in liver transplant recipients that experience good outcomes.

AIMS

To study if and how GGT is correlated with mortality following liver transplantation.

METHODS

We analyzed the prognostic relevance of serum GGT levels during the early and late postoperative period after liver transplantation in 522 consecutive adults. We also studied alanine aminotransferase, aspartate aminotransferase, and total bilirubin levels.

RESULTS

Early after transplantation, the peak median (interquartile range) GGT levels were significantly higher in patients who survived more than 90 days compared to non-survivors: 293 (178-464) vs. 172 (84-239) U/l, p<0.0001. In contrast, late after transplantation, GGT levels were significantly lower in patients who survived more than 5 years than those who did not ( p<0.01). The pattern of GGT levels also differed from those of alanine aminotransferase, aspartate aminotransferase, and total bilirubin early after transplantation, while these patterns were congruent late after transplantation. Kaplan-Meier survival analysis showed that early after transplantation the higher the GGT levels, the better the 90-day survival ( p<0.001). In contrast, late after transplantation, higher GGT levels were associated with a lower 5-year survival ( p<0.001).

CONCLUSIONS

  These paradoxical findings may be explained by the time-dependent role of GGT in glutathione metabolism. Immediate postoperative elevation of GGT may indicate a physiological systemic response while chronic elevation reflects a pathological response.

Urinary expression of novel tissue markers of kidney injury after ureteroscopy, shockwave lithotripsy, and in normal healthy controls

BACKGROUND AND PURPOSE

Shockwave lithotripsy (SWL) and ureteroscopy (URS) are minimally invasive treatment alternatives for kidney stones. Although less invasive, SWL subjects the renal parenchyma to a high level of energy and the potential to cause renal injury. The ability to detect renal injury post-SWL in a reliable and noninvasive way would be clinically beneficial. Kidney injury molecule 1 (KIM-1) and N-acetyl-β-D-glucosaminidase (NAG) are two proteins secreted by the kidney into the urine and have been found to be sensitive markers of acute kidney injury in transplant patients. The aim of this work was to measure urinary levels of KIM-1 and NAG in patients with kidney stone who were treated by SWL or URS and in nonstone volunteers.

PATIENTS AND METHODS

Patients with kidney stones who were treated by SWL (n = 50) or URS (n = 10) were recruited. Voided urine samples were collected before and 2 to 3 hours after URS and SWL. In addition, further urinary specimens were collected 2 days and 2 weeks post-SWL treatment. Voided urine samples from healthy volunteers were also collected.

RESULTS

Mean KIM-1 values were increased in patients with kidney stones when compared with volunteers. KIM-1 and NAG levels significantly increased post-SWL and returned to baseline within 2 weeks post-SWL. Poor kidney function was significantly associated with increased biomarker activity both in baseline and post-SWL measurements. There was no significant change in urinary KIM-1 and NAG concentrations before and after URS.

CONCLUSIONS

Kim-1 and NAG levels significantly increased post-SWL treatment suggesting a potential role for these urinary markers in identifying patients at higher risk of tissue injury.

Mechanistic overview of reactive species-induced degradation of the endothelial glycocalyx during hepatic ischemia/reperfusion injury

Endothelial cells are covered by a delicate meshwork of glycoproteins known as the glycocalyx. Under normophysiological conditions the glycocalyx plays an active role in maintaining vascular homeostasis by deterring primary and secondary hemostasis and leukocyte adhesion and by regulating vascular permeability and tone. During (micro)vascular oxidative and nitrosative stress, which prevails in numerous metabolic (diabetes), vascular (atherosclerosis, hypertension), and surgical (ischemia/reperfusion injury, trauma) disease states, the glycocalyx is oxidatively and nitrosatively modified and degraded, which culminates in an exacerbation of the underlying pathology. Consequently, glycocalyx degradation due to oxidative/nitrosative stress has far-reaching clinical implications. In this review the molecular mechanisms of reactive oxygen and nitrogen species-induced destruction of the endothelial glycocalyx are addressed in the context of hepatic ischemia/reperfusion injury as a model disease state. Specifically, the review focuses on (i) the mechanisms of glycocalyx degradation during hepatic ischemia/reperfusion, (ii) the molecular and cellular players involved in the degradation process, and (iii) its implications for hepatic pathophysiology. These topics are projected against a background of liver anatomy, glycocalyx function and structure, and the biology/biochemistry and the sources/targets of reactive oxygen and nitrogen species. The majority of the glycocalyx-related mechanisms elucidated for hepatic ischemia/reperfusion are extrapolatable to the other aforementioned disease states.

ADP-dependent platelet function prior to and in the early course of pediatric liver transplantation and persisting thrombocytopenia are positively correlated with ischemia/reperfusion injury

Little is known about the role of platelets in relation to ischemia/reperfusion injury (IRI) of the liver graft especially in children. Thrombocyte function was prospectively analysed in 21 consecutive pediatric liver transplantation (pLT) patients by platelet aggregometry secondary to adenosine diphosphate (ADP), collagen, and the von Willebrand factor activator ristocetin (VWF:rco). Post-OP serum levels of ALT were used to divide patients into groups with high (highHD, n = 8) and low (lowHD, n = 13) hepatocellular damage. Clinically, highHD-patients showed impaired plasmatic coagulation and elevated serum bilirubin levels early after pLT when compared with lowHD-patients. Further, platelet counts markedly decreased between pre-OP and postreperfusion (postrep.) in the highHD group (P = 0.003) and did not recuperate by POD6. In lowHD individuals thrombocytopenia improved from both pre-OP (P < 0.05) and postrep. (P < 0.001) respectively towards POD6. Experimental thrombocyte testing revealed that before graft reperfusion only ADP-dependent platelet aggregation correlated with reperfusion injury, thrombocytopenia and early graft function. During the first 48 h after graft reperfusion, all inducers tested demonstrated elevated platelet aggregation levels in the highHD group. Our data suggest a possible role of platelets and their aggregative status in liver IRI subsequent to clinical pLT. Reperfusion-independent ADP-triggered platelet function may be a determinant for IRI in the pediatric hepatic graft recipient.

Primary graft nonfunction and Kupffer cell activation after liver transplantation from non-heart-beating donors in pigs

More extensive use of non-heart-beating donors (NHBD) could reduce mortality on liver transplantation waiting lists, but this is associated with more primary nonfunction (PNF). We assessed which parameters are involved in the development of PNF in livers from NHBD in a previously validated pig liver transplantation model, in which livers were transplanted after exposure to incremental periods of warm ischemia. The risk of PNF was unacceptably high (>50%) when livers were exposed to >30 minutes' warm ischemia before a short cold ischemic period. This study examined how PNF is affected by Kupffer cell activation (beta-galactosidase), the generation of cytokines tumor necrosis factor alpha and interleukin 6, antioxidant mechanisms (ascorbic acid, alpha-tocopherol, reduced glutathione), circulating redox-active iron, and sinusoidal endothelial cell function (hyaluronic acid clearance). Kupffer cells were more activated in PNF recipients, as suggested by higher beta-galactosidase levels (15 minutes after reperfusion), and secondarily, by higher production of tumor necrosis factor alpha and interleukin 6 (180 minutes after reperfusion). In addition, alpha-tocopherol and reduced glutathione were lower, and ascorbic acid and redox-active iron higher in PNF recipients. Finally, PNF grafts displayed progressively decreasing hyaluronic acid clearance (suggesting sinusoidal endothelial cell dysfunction) and parenchymal edema. Consequently, a reduced-flow phenomenon was documented. In grafts from NHBD that are destined to fail, beta-galactosidase activity (a surrogate of Kupffer cell activation) is higher, proinflammatory cytokines are overproduced, some antioxidant mechanisms fail, and circulating redox-active iron is more rapidly released. A no-flow phenomenon is eventually observed in these failing grafts.

Mechanistic biomarkers for cytotoxic acute kidney injury

Acute kidney injury is a common condition and is associated with a high mortality rate. It has been recognised that routinely used measures of renal function, such as levels of blood urea nitrogen and serum creatinine, increase significantly only after substantial kidney injury occurs and then with a time delay. Insensitivity of such tests delays the diagnosis in humans, making it particularly challenging to administer putative therapeutic agents in a timely fashion. Furthermore, this insensitivity affects the evaluation of toxicity in preclinical studies by allowing drug candidates, which have low, but nevertheless important, nephrotoxic side effects in animals, to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. This review presents the current status of sensitive and specific biomarkers to detect preclinical and clinical renal injury and summarises the techniques used to quantitate these biomarkers in biological fluids.

Recipient levels and function of von Willebrand factor prior to liver transplantation and its consumption in the course of grafting correlate with hepatocellular damage and outcome*

Von Willebrand factor (vWF) is a major platelet adhesion molecule at sites of vascular injury, such as observed in ischemia/reperfusion injury following orthotopic liver transplantation (OLT). Thirty-three OLT patients were divided into groups with elevated or low markers of hepatocellular damage (high and low-HD). Whole-blood aggregometry was performed to evaluate platelet function. Multimeric analysis was utilized to evaluate functional vWF levels in the course of OLT. Donor and recipient demographics were comparable among groups. Low-HD patients demonstrated better preserved coagulation parameters on POD 1-6 if contrasted to high-HD patients. One year graft survival for the high-HD group was lower than low-HD patients (P = 0.037). Preoperative vWF-dependent platelet aggregation and functional vWF plasma levels correlated directly with alanine transaminase levels early after OLT as did the decrease of functional vWF to reperfusion. In summary, these data suggest that vWF may serve as a significant mediator of platelet recruitment and hepatocellular injury in the graft following reperfusion.

Urinary kidney injury molecule-1: a sensitive quantitative biomarker for early detection of kidney tubular injury

Sensitive and specific biomarkers are needed to detect early kidney injury. The objective of the present work was to develop a sensitive quantitative urinary test to identify renal injury in the rodent to facilitate early assessment of pathophysiological influences and drug toxicity. Two mouse monoclonal antibodies were made against the purified ectodomain of kidney injury molecule-1 (Kim-1), and these were used to construct a sandwich Kim-1 ELISA. The assay range of this ELISA was 50 pg/ml to 5 ng/ml, with inter- and intra-assay variability of <10%. Urine samples were collected from rats treated with one of three doses of cisplatin (2.5, 5, or 7.5 mg/kg). At one day after each of the doses, there was an approximately three- to fivefold increase in the urine Kim-1 ectodomain, whereas other routinely used biomarkers measured in this study [plasma creatinine, blood urea nitrogen (BUN), urinary N-acetyl-beta-glucosaminidase (NAG), glycosuria, proteinuria] lacked the sensitivity to show any sign of renal damage at this time point. When rats were subjected to increasing periods (10, 20, 30, or 45 min) of bilateral ischemia, there was an increasing amount of urinary Kim-1 detected. After only 10 min of bilateral ischemia, Kim-1 levels on day 1 were 10-fold higher (5 ng/ml) than control levels, whereas plasma creatinine and BUN were not increased and there was no glycosuria, increased proteinuria, or increased urinary NAG levels. Thus urinary Kim-1 levels serve as a noninvasive, rapid, sensitive, reproducible, and potentially high-throughput method to detect early kidney injury in pathophysiological studies and in preclinical drug development studies for risk-benefit profiling of pharmaceutical agents.

Non-heart-beating donor porcine livers: the adverse effect of cooling

Normothermic preservation has been shown to be advantageous in an experimental model of preservation of non-heart-beating donor (NHBD) livers, which have undergone significant warm ischemic injury. The logistics of clinical organ retrieval might dictate a period of cold preservation prior to warm perfusion. We have investigated the effects of a brief period of cold preservation on NHBD livers prior to normothermic preservation. Porcine livers were subjected to 60 minutes of warm ischaemia and then assigned to following groups: Group W (n = 5), normothermic preservation for 24 hours; and Group C (n = 6), cold preservation in University of Wisconsin solution for 1 hour followed by normothermic preservation for 23 hours (total preservation time, 24 hours). Synthetic function (bile production and factor V production) and cellular damage were compared on the ex vivo circuit during preservation. There was no significant difference in the synthetic function of the livers (bile production and factor V production). Markers of hepatocellular damage (alanine aminotransferase and aspartate aminotransferase release), sinusoidal endothelial cell dysfunction (hyaluronic acid), and Kupffer cell injury (beta-galactosidase) were significantly higher in Group C. The histology of the livers at the end of perfusion was similar. In conclusion, a brief-period cold preservation prior to normothermic perfusion maintains the synthetic function and metabolic activity but results in significant hepatocellular damage, sinusoidal endothelial cell dysfunction, and Kupffer cell injury. Transplant studies are required to establish whether livers treated in this way are viable for transplantation.

Serum cytosolic beta-glucosidase activity in a rat model of necrotizing enterocolitis

The diagnosis of necrotizing enterocolitis (NEC) is made from a combination of clinical and radiographic findings. There are no useful screening biochemical markers of intestinal injury. The serum concentration of cytosolic beta-glucosidase (CBG), an enzyme found primarily in enterocytes, is markedly elevated in animal models of ischemia and bowel obstruction. We hypothesized that in a rat model of NEC, serum CBG activity would significantly increase before microscopic evidence of severe intestinal injury. Cohorts of 2-wk-old Sprague-Dawley rats (n = 10/cohort) were anesthetized and underwent laparotomy with occlusion of the superior mesenteric artery (SMA). Platelet-activating factor (200 microg/animal) was injected in the proximal duodenum. Serum and intestinal samples were obtained at time 0 (control) and 30, 60, and 90 min of ischemia (I) and after 90 min of I followed by 60 min of reperfusion (I/R). Histopathologic injury was categorized as either no or minimal injury or mural necrosis by two masked investigators and CBG activity was measured by ELISA. Data were analyzed with Fisher's exact test and ANOVA. Only the I/R group had significantly greater mural necrosis compared with the control group (90% versus 0%, respectively, p < 0.001). In contrast, CBG activity was significantly elevated after only 90 min of I and after I/R (15.1 +/- 5.6 and 16.4 +/- 4.3 units/mL, respectively, p < 0.05). We conclude that serum CBG is elevated before transmural intestinal injury in this model and may have utility as an early marker of ischemia in patients at risk for NEC.

Optimisation of an enzymatic method for beta-galactosidase

BACKGROUND

The enzyme beta-galactosidase present in the Kupffer cells of the liver has potential as a marker of liver dysfunction prior to transplantation. Spectrophotometric methods have insufficient sensitivity.

METHODS

Fluorimetric methods have the required sensitivity and we have optimised such a method in a microtitre plate format to improve its utility. beta-galactosidase acts on the substrate 4-methylumbelliferyl-galactoside (MUG) to produce 4-methylumbelliferone (4-MU), detected fluorimetrically with excitation wavelength 355 nm and emission wavelength 460 nm.

RESULTS

Reaction conditions in a citrate-phosphate buffer were optimised to give maximal enzyme activity: pH was optimal at 4.4 (range investigated 3.6-5.0) and substrate concentration at 3.33 mmol/l. A small specimen volume (10 microl) in 80 microl of substrate solution produced adequate fluorescent yield after an incubation period of 30 to 60 min at 37 degrees C. Reaction was terminated by addition of 200 microl of glycine-NaOH, pH 12.8. The assay is linear to 3,000 U/ml. The intra-assay coefficient of variation (CV%) at 50, 502, and 2,012 U/ml was 4.7, 3.1, and 3.4, respectively (n=10). Inter-assay CV% at 51, 496, and 1,986 U/ml was 7.0, 4.0, and 3.9, respectively (n=10).

CONCLUSIONS

The assay has greater practical utility and demonstrated significant differences in the perfusate beta-galactosidase between cold-stored and warm-perfused livers in a porcine model of transplantation.

Beta-galactosidase as a marker of ischemic injury and a mechanism for viability assessment in porcine liver transplantation

Glycohydrolases are a group of enzymes contained predominantly within lysosomes, which are released during Kupffer cell activation or death. One of these, beta-galactosidase, has been proposed as a marker of ischemia-reperfusion injury in the liver because Kupffer cell activation represents a primary event in the injurious reperfusion cascade. In this study, we compared B-galactosidase with more traditional indicators of liver injury and function in a porcine model of liver preservation. Porcine livers were allocated into two groups: group C (n = 5), preserved in University of Wisconsin solution by standard cold storage for 24 hours, and group W (n = 5), perfused with oxygenated autologous blood on an extracorporeal circuit for 24 hours. Both groups were subsequently tested on the circuit during a 24-hour reperfusion phase. The perfusate was sampled for levels of beta-galactosidase, as well as traditional markers of liver injury and function. A sharp increase in beta-galactosidase levels was seen on reperfusion of cold preserved livers to a level of 1,900 IU/mL. This contrasted dramatically with normothermically preserved livers, in which the level never exceeded 208 IU/mL (P =.002). beta-Galactosidase levels showed much earlier and greater increases compared with transaminase levels in livers injured by ischemia. A rapid elevation in beta-galactosidase levels corresponded well with poor liver function and more liver injury. Measurement of beta-galactosidase is a simple test that quantifies ischemia-reperfusion injury of preserved livers. It is more sensitive than transaminases, with faster and larger increases in levels after ischemic injury. It can be useful in assessing the viability of a liver during machine preservation.

Cell transplantation causes loss of gap junctions and activates GGT expression permanently in host liver

Cell transplantation into hepatic sinusoids, which is necessary for liver repopulation, could cause hepatic ischemia. To examine the effects of cell transplantation on host hepatocytes, we transplanted Fisher 344 rat hepatocytes into syngeneic dipeptidyl peptidase IV-deficient rats. Within 24 h of cell transplantation, areas of ischemic necrosis, along with transient disruption of gap junctions, appeared in the liver. Moreover, host hepatocytes expressed gamma-glutamyl transpeptidase (GGT) extensively, which was observed even 2 years after cell transplantation. GGT expression was not associated with alpha-fetoprotein activation, which is present in progenitor cells. Increased GGT expression was apparent after transplantation of nonparenchymal cells and latex beads but not after injection of saline, fragmented hepatocytes, hepatocyte growth factor, or turpentine. Some host hepatocytes exhibited apoptosis, as well as DNA synthesis, between 24 and 48 h after cell transplantation. Changes in gap junctions, GGT expression, DNA synthesis, and apoptosis after cell transplantation were prevented by vasodilators. The findings indicated the onset of ischemic liver injury after cell transplantation. These hepatic perturbations must be considered when transplanted cells are utilized as reporters for biological studies.

Evaluation of asialoglycoprotein receptor imaging agent as a marker of hepatic ischemia-reperfusion injury and recovery

Protection of hepatocytes from ischemia-reperfusion injury is a clinically important issue. The purpose of this study was to evaluate changes in acute liver damage and recovery after ischemia-reperfusion in rats with asialoglycoprotein receptor (ASGP-R) ligand. Ischemia was induced by clamping the hepatoduodenal ligament for 90 min. At 1, 3, 24, 48 hr, 1 and 2 wk after reperfusion, I-125-GSA was injected. Five min after injection, blood samples were obtained and the liver was removed. Several regions from each lobe were dissected, weighed and counted. Mean uptakes (% dose/g) in the liver and blood samples were calculated. Histologic sections stained with hematoxylin-eosin (H-E) stain showed ischemic damage at 1 and 3 hr, and focal hepatocyte necrosis at 24 hr. Predominant massive necrosis was not seen. The mitotic index with H-E stain and proliferating cell nuclear antigen (PCNA) labeling index were highest at 1 wk, indicating liver regeneration. At 1 and 3 hr, liver uptake was significantly decreased, and blood uptake was significantly increased, indicating decreased tissue blood flow and ischemic damage. Liver uptake showed significant increases at 48 hr and 1 wk, and was the highest at 1 wk, indicating liver regeneration during the convalescence stage. ASGP-R binding may provide valuable information on ischemia-reperfusion injury and recovery.

Effect of magnolol on in vitro mitochondrial lipid peroxidation and isolated cold-preserved warm-reperfused rat livers

BACKGROUND/AIM

A mechanism suggested to cause injury to preserved organs is the generation of oxygen free radicals. Lipid peroxidation is one of the biological damages caused by oxygen free radicals. It is our aim to investigate whether magnolol, a strong antioxidant, suppresses the generation of oxygen free radicals and improves the viability of cold-preserved warm-reperfused rat livers.

MATERIALS AND METHODS

In vitro lipid peroxidation was induced in rat hepatic mitochondria with ADP and FeSO4. The inhibitory effect of magnolol on lipid peroxidation was measured with oxygen consumption and malondialdehyde (MDA) formation. Subsequently, we preserved and reperfused rat livers in preservation solutions that contained magnolol. The hepatic enzymes and liver MDA were measured to assess the protective effect of magnolol on isolated rat livers.

RESULTS

In rat hepatic mitochondria, magnolol was 470 times more potent than alpha-tocopherol in inhibiting oxygen consumption and 340 times more potent than alpha-tocopherol in inhibiting MDA formation. Addition of magnolol to Ringer's lactate solution had a protective effect, in terms of MDA formation and leakage of hepatic enzymes, on warm-reperfused but not cold-stored liver tissue. Addition of magnolol to University of Wisconsin (UW) solution, a widely used preservation solution, did not modify the effect of this solution on isolated liver tissues.

CONCLUSIONS

We conclude that magnolol is an effective antioxidant and suppresses lipid peroxidation in rat liver mitochondria and can be used as a rinsing solution in protecting transplanted organs from lipid peroxidation during reperfusion, especially for those organs not preserved with UW solution.

Expression of cytosolic beta-glucosidase in guinea pig liver cells

The cytosolic beta-glucosidase of mammalian liver has been implicated in the metabolic transformation of plant glycosides, such as vicine and amygdalin, which are associated with the development of toxic syndromes. We investigated which cell types express cytosolic beta-glucosidase in guinea pig liver, and characterized the contribution of this enzyme to the hydrolysis of aromatic glucosides in cultured cells and in tissue slices. Cytosolic beta-glucosidase was expressed in hepatocytes and not in Kupffer or endothelial cells as determined by enzyme-specific activity and Western blots of liver cell extracts. Intracellular beta-glucosidase activity was visualized using the fluorescent beta-glucosidase substrate, resorufin beta-D-glucoside, and shown to be caused by the cytosolic beta-glucosidase using the inhibitors, conduritol beta-epoxide and dinitrophenol-2-deoxy-2-fluoro-beta-D-glucopyranoside (DNP2FGlc). Staining of fresh liver slices with resorufin beta-glucoside revealed that cytosolic beta-glucosidase is expressed in all hepatocytes, with no significant portal-central gradient. These data indicate that cytosolic beta-glucosidase is a hepatocyte-specific enzyme, and support the hypothesis that cytosolic beta-glucosidase in the liver functions to hydrolyze small glucosides absorbed by the intestine. Furthermore, toxic injury to cultured hepatocytes by CCl4 resulted in release of cytosolic beta-glucosidase in parallel with the hepatocyte marker enzymes alanine transaminase and lactate dehydrogenase. This suggests that acute increases in serum levels of cytosolic beta-glucosidase in animal models of liver injury may reflect direct injury of hepatocytes.

Evaluation of [1-11C]octanoate as a new radiopharmaceutical for assessing liver function using positron emission tomography

[1-11C]Octanoate was evaluated as a new radiopharmaceutical for the evaluation of liver function using positron emission tomography (PET). In biodistribution studies with normal mice, [1-11C]octanoate was rapidly taken up by the liver. [1-11C]Octanoate in the liver was present in the parenchymal cells and was predominantly metabolized via beta-oxidation followed by its rapid clearance. In the CCl4-treated mice, [1-11C]octanoate showed significantly slower hepatic clearance than that in the controls. In PET studies using rats, the time-radioactivity curves in the liver showed a two-phase decrease, and compared with the normal rat, the CCl4-treated rat showed a slower hepatic half-clearance time for the first phase, which is related to beta-oxidation metabolism. A preliminary PET study of [1-11C]octanoate metabolism in a normal volunteer was consistent with these animal studies. The present study showed that metabolism of [1-11C]octanoate in the liver was influenced by beta-oxidation, and it is advantageous to use [1-11C]octanoate clinically as a regional liver-function diagnostic agent in conjunction with PET.