Proton nuclear magnetic resonance analysis of hepatic bile from donors and recipients in human liver transplantation

Prognostic value of endogenous and exogenous metabolites in liver transplantation

Liver transplantation has been widely accepted as an effective intervention for end-stage liver diseases and early hepatocellular carcinomas. However, a variety of postoperative complications and adverse reactions have baffled medical staff and patients. Currently, transplantation monitoring relies primarily on nonspecific biochemical tests, whereas diagnosis of multiple complications depends on invasive pathological examination. Therefore, a noninvasive monitoring method with high selectivity and specificity is desperately needed. This review summarized the potential of endogenous small-molecule metabolites as biomarkers for assessing graft function, ischemia-reperfusion injury and liver rejection. Exogenous metabolites, mainly those immunosuppressive agents with high intra- and inter-individual variability, were also discussed for transplantation monitoring.

Bile Composition as a Diagnostic and Prognostic Tool in Liver Transplantation

Bile secretion and composition reflects the functional status of hepatocytes and cholangiocytes. Bile composition can have a role in the assessment of donor grafts before implantation in the recipient. In addition, changes in bile composition after liver transplantation can serve as a diagnostic and prognostic tool to predict posttransplant complications, such as primary nonfunction, acute cellular rejection, or nonanastomotic biliary strictures. With the popularization of liver machine perfusion preservation in the clinical setting, there is a revisited interest in biliary biomarkers to assess graft viability before implantation. This review discusses current literature on biliary biomarkers that could predict or assess liver graft and bile duct viability. Bile composition offers an exciting and novel perspective in the search for reliable hepatocyte and cholangiocyte viability biomarkers.

Systematic Review: Clinical Metabolomics to Forecast Outcomes in Liver Transplantation Surgery

Liver transplantation is an effective intervention for end-stage liver disease, fulminant hepatic failure, and early hepatocellular carcinoma. Yet, there is marked patient-to-patient variation in liver transplantation outcomes. This calls for novel diagnostics to enable rational deployment of donor livers. Metabolomics is a postgenomic high-throughput systems biology approach to diagnostic innovation in clinical medicine. We report here an original systematic review of the metabolomic studies that have identified putative biomarkers in the context of liver transplantation. Eighteen studies met the inclusion criteria that involved sampling of blood (n = 4), dialysate fluid (n = 4), bile (n = 5), and liver tissue (n = 5). Metabolites of amino acid and nitrogen metabolism, anaerobic glycolysis, lipid breakdown products, and bile acid metabolism were significantly different in transplanted livers with and without graft dysfunction. However, criteria for defining the graft dysfunction varied across studies. This systematic review demonstrates that metabolomics can be deployed in identification of metabolic indicators of graft dysfunction with a view to implicated molecular mechanisms. We conclude the article with a horizon scanning of metabolomics technology in liver transplantation and its future prospects and challenges in research and clinical practice.

Pattern recognition and biomarker validation using quantitative1H-NMR-based metabolomics

The collection of global metabolic data and their interpretation (both spectral and biochemical) using modern spectroscopic techniques and appropriate statistical approaches, are known as 'metabolic profiling', 'metabonomics' or 'metabolomics'. This review addresses 1H-nuclear magnetic resonance (NMR)-based metabolomic principles and their application in biomedical science, with special emphasis on their potential in translational research in transplantation, oncology, and drug toxicity or discovery. Various steps in metabolomics analysis are described in order to illustrate the types of biological samples, their respective handling and preparation for 1H-NMR analysis; provide a rationale for using pattern-recognition techniques (spectral database concept) versus quantitative 1H-NMR-based metabolomics (metabolite database concept); and identify necessary technological and logistical future developments that will allow 1H-NMR-based metabolomics to become an established tool in biomedical research and patient care.

Quantitative analysis in magnetic resonance spectroscopy: from metabolic profiling to in vivo biomarkers

Nuclear magnetic resonance spectroscopy (called NMR for ex vivo techniques and MRS for in vivo techniques) has become a useful analytical and diagnostic tool in biomedicine. In the past two decades, an MR-based spectroscopic approach for translational and clinical research has emerged that allows for biochemical characterization of the tissue of interest either ex vivo (NMR-based metabolomics) or in vivo (localized MRS-single voxel or multivoxel-spectroscopic imaging). The greatest advantages of MRS techniques are their ability to detect multiple tissue-specific metabolites in a single experiment, their quantitative nature and translational component (in vitro/ex vivo-discovered metabolic biomarkers can be translated into noninvasive spectroscopic imaging protocols). Disadvantages of MRS include low sensitivity and spectral resolution and, in case of NMR-metabolomics, metabolite degradation and incomplete recovery in processed samples. In vivo MRS has worse spectral resolution than ex vivo high-resolution NMR due to the inherently wider lines of metabolites in vivo and the difficulty of using traditional line-narrowing methods (e.g., sample spinning). It also suffers from poor time-resolution, therefore offering fewer metabolic biomarkers to be followed in vivo. In the present review article, we provide considerations for establishing reliable protocols (both in vivo and ex vivo) for metabolite detection, recovery and quantification from in vivo and ex vivo MR spectra.

NMR spectroscopy for discovery and quantitation of biomarkers of disease in human bile

Human liver synthesizes bile; bile, containing a large number of metabolites, is transported through the canaliculi and bile ducts, and stored in the gallbladder before entering into the intestine. In the intestine, a large number of bile metabolites are reabsorbed and sent back to the liver for recirculation. Owing to close association of the bile with the gastrointestinal system, the bile metabolic profile is highly sensitive to the onset of numerous gastrointestinal disease processes. A growing number of studies suggest that hepatobiliary disease biomarkers are richly populated in human bile. These studies stress the potential of profiling the human bile metabolome for early diagnostics as well as deeper insights into gastrointestinal disease processes. Once the biomarkers are established reliably using human bile, they can be targeted in easily accessible fluids such as blood and urine or targeted in bile itself using noninvasive methods such as in vivo magnetic resonance spectroscopy. NMR spectroscopy is one of the most powerful bioanalytical tools, which promises profiling of human bile metabolome and exploring early biomarkers for hepatobiliary diseases. Comprehensive analysis of human bile using NMR spectroscopy has lead to identification and quantification of major bile metabolites. This review describes the discovery and quantitation of biomarkers of hepatobiliary diseases in human bile using NMR spectroscopy.

Differences in phosphatidylcholine and bile acids in bile from Egyptian and UK patients with and without cholangiocarcinoma

BACKGROUND

Cholangiocarcinoma (CC) is a fatal malignancy, the incidence of which is increasing worldwide, with substantial regional variation. Current diagnostic techniques to distinguish benign from malignant biliary disease are unsatisfactory. Metabolic profiling of bile may help to differentiate benign from malignant disease. No previous studies have compared the metabolic profiles of bile from two geographically and racially distinct groups of CC patients.

OBJECTIVES

This study aimed to compare metabolic profiles of bile, using in vitro proton magnetic resonance spectroscopy, from CC patients from Egypt and the UK, and from patients with CC and patients with non-malignant biliary disease.

METHODS

A total of 29 bile samples, collected at cholangiography, were analysed using an 11.7-T system. Samples were from eight CC patients in either Egypt (n = 4) or the UK (n = 4) and 21 patients with benign biliary disease (choledocholithiasis [n = 8], sphincter of Oddi dysfunction [n = 8], primary sclerosing cholangitis [n = 5]).

RESULTS

Bile phosphatidylcholine (PtC) was significantly reduced in CC patients. Egyptian CC patients had significantly lower biliary PtC levels compared with UK patients. Taurine- and glycine-conjugated bile acids (H-26 and H-25 protons, respectively) were significantly elevated in bile from patients with CC compared with bile from patients with benign diseases (P = 0.013 and P < 0.01, respectively).

CONCLUSIONS

Biliary PtC levels potentially differentiate CC from benign biliary disease. Reduced biliary PtC in Egyptian compared with UK patients may reflect underlying carcinogenic mechanisms.

Human bile as a rich source of biomarkers for hepatopancreatobiliary cancers

Metabolic profiling of biofluids is emerging as an important area with a promising number of applications in clinical medicine, including early diagnosis of numerous diseases that normally remain silent until late in the progress of disease. While blood and urine are more often used to explore biomarkers that distinguish he healthy from disease conditions, human bile is emerging as a rich source of biomarkers specifically for the cancers of the liver (hepatocellular carcinoma), bile ducts (cholangiocarcinoma), gallbladder and pancreas. This is owing to the fact that metabolites linked to the pathways of tumor cell metabolism are rich in bile by virtue of its association or proximity to the pathological source. Recent methodological developments have enabled the identification of a number of bile metabolites that have links with hepatopancreatobiliary diseases. Investigations of human bile are also considered to help the biomarker discovery process in vitro and provide avenues for translational research in detecting and following dynamic variations of biomarkers in clinical settings using noninvasive approaches, such as in vivo magnetic resonance spectroscopy. This article reviews the current status and potential applications of human bile as a source of biomarkers, with emphasis on metabolites, for early detection of cancers associated with the hepatopancreatobiliary system.

Intracellular oxygenation and cytochrome oxidase C activity in ischemic preconditioning of steatotic rabbit liver

BACKGROUND

Mild to moderate steatotic livers are used as marginal donors in liver transplantation. Very little is known about the mechanisms of ischemia reperfusion (IR) injury (IRI) in fatty liver. This study aimed to establish whether cytochrome oxidase C (COX) activity is compromised by IRI in fatty liver and whether ischemic preconditioning (IPC) can protect COX activity.

METHODS

New Zealand rabbits were fed on a high-cholesterol diet for 8 weeks to induce moderate hepatic steatosis. Three groups were tested. The IR group underwent 60 minutes of ischemia, followed by 7 hours of reperfusion. The IPC group (IPC + IR) underwent 5 minutes of ischemia, followed by 10 minutes of reperfusion and then 60 minutes of ischemia and 7 hours of reperfusion. The control group (sham) underwent the same surgical procedure, but ischemia was not induced. Deoxyhemoglobin, oxyhemoglobin, and change in the redox state of COX was continuously monitored in vivo by near-infrared spectroscopy. COX and citrate synthase (CS) activity assays were carried out on liver biopsy specimens in vitro. Bile was collected continuously during the procedure and analyzed using proton nuclear magnetic resonance spectroscopy.

RESULTS

The IR group had decreased COX activity and tissue oxygenation represented by deoxyhemoglobin, oxyhemoglobin, COX, and elevated redox ratios of lactate/pyruvate and β-hydroxybutarate/acetoacetate in vivo and a decrease in COX and CS activity in vitro. The IPC + IR group showed higher levels of all measured parameters in vivo and showed a smaller decrease in COX and CS activity in vitro.

CONCLUSION

This study shows that IRI affects COX activity in fatty livers. This is attenuated by IPC.

Fingerprinting of human bile during liver transplantation by capillary electrophoresis

Increasing rates of success in liver transplantation have increased the number of cases considered. However, liver post-transplant graft dysfunction of liver transplants (TXs) is not fully understood and by applying holistic approaches we can investigate metabolic change deriving from confounding factors such as liver fat content, ischaemia time, donor age, recipient's health, etc. Twenty-six hepatic bile samples taken from liver donors and recipients were retrieved from a total of six TXs, from these one recipient underwent post-graft dysfunction. CE was employed to fingerprint bile collected at 10 min increments in the donors and in the recipients. The electropherograms of these samples were aligned and normalised using correlation optimised warping algorithms and modelled with multivariate techniques. The resulting metabolic signatures were compared; in general donors and recipients showed distinct fingerprints and clustered separately. When a partial least square discriminant analysis (PLS-DA) model was constructed between donor and recipient's samples, a recipient of a 32 year old liver with normal steatosis, and shortest cold ischaemia time showed as the observation nearest to its donor observation, denoting minimal metabolic change. This study proposes CE fingerprinting of human bile as a promising technique to help unravel the complex metabolic pathways involved during transplantation.

Metabolic assessment of human liver transplants from biopsy samples at the donor and recipient stages using high-resolution magic angle spinning 1H NMR spectroscopy

This work presents the first application of high-resolution magic angle spinning (HR-MAS) 1H NMR spectroscopy to human liver biopsy samples, allowing a determination of their metabolic profiles before removal from donors, during cold perfusion, and after implantation into recipients. The assignment of peaks observed in the 1H HR-MAS NMR spectra was aided by the use of two-dimensional J-resolved, TOCSY and 1H-13C HMQC spectra. The spectra were dominated by resonances from triglycerides, phospholipids, and glycogen and from a variety of small molecules including glycerophosphocholine (GPC), glucose, lactate, creatine, acetate, amino acids, and nucleoside-related compounds such as uridine and adenosine. In agreement with histological data obtained on the same biopsies, two of the six livers were found to contain high amounts of triglycerides by NMR spectroscopy, which also indicated that these tissues contained a higher degree of unsaturated lipids and a lower proportion of phospholipids and low molecular weight compounds. Additionally, proton T2 relaxation times indicated two populations of lipids, a higher mobility triglyceride fraction and a lower mobility phospholipid fraction, the proportions of which changed according to the degree of fat content. GPC was found to decrease from the pretransplant to the posttransplant biopsy of all livers except for one with a histologically confirmed high lipid content, and this might represent a biomarker of liver function posttransplantation. NMR signals produced by the liver preservation solution were clearly detected in the cold perfusion stage biopsies of all livers but remained in the posttransplant spectra of only the two livers with a high lipid content and were prominent mainly in the graft that later developed primary graft dysfunction. This study has shown biochemical differences between livers used for transplants that can be related to the degree and type of lipid composition. This technology might therefore provide a novel screening approach for donor organ quality and a means to assess function in the recipient after transplantation.

Current and future applications of in vitro magnetic resonance spectroscopy in hepatobiliary disease

Nuclear magnetic resonance spectroscopy allows the study of cellular biochemistry and metabolism, both in the whole body in vivo and at higher magnetic field strengths in vitro. Since the technique is non-invasive and non-selective, magnetic resonance spectroscopy methodologies have been widely applied in biochemistry and medicine. In vitro magnetic resonance spectroscopy studies of cells, body fluids and tissues have been used in medical biochemistry to investigate pathophysiological processes and more recently, the technique has been used by physicians to determine disease abnormalities in vivo. This highlighted topic illustrates the potential of in vitro magnetic resonance spectroscopy in studying the hepatobiliary system. The role of in vitro proton and phosphorus magnetic resonance spectroscopy in the study of malignant and non-malignant liver disease and bile composition studies are discussed, particularly with reference to correlative in vivo whole-body magnetic resonance spectroscopy applications. In summary, magnetic resonance spectroscopy techniques can provide non-invasive biochemical information on disease severity and pointers to underlying pathophysiological processes. Magnetic resonance spectroscopy holds potential promise as a screening tool for disease biomarkers, as well as assessing therapeutic response.

N-Acetylcysteine ameliorates the late phase of liver ischaemia/reperfusion injury in the rabbit with hepatic steatosis

Steatotic livers are highly susceptible to I/R (ischaemia/reperfusion) injury and, therefore, the aim of the present study was to evaluate the in vivo effect of NAC (N-acetylcysteine) on hepatic function in the early and initial late phase of warm liver I/R injury in steatotic rabbits. Twelve New Zealand White rabbits were fed a high-cholesterol (2%) diet. The control group (n=6) underwent lobar liver ischaemia for 1 h, followed by 6 h of reperfusion. In the treated group receiving NAC (n=6), an intravenous infusion of NAC was administered prior to and during the 6 h reperfusion period. Systemic and hepatic haemodynamics were monitored continuously. ALT (alanine aminotransferase) activity and bile production were measured. NMR spectroscopy was used to analyse bile composition. Oxidation of DHR (dihydrorhodamine) to RH (rhodamine) was used as a marker of production of reactive oxygen and nitrogen species. Moderate centrilobular hepatic steatosis was demonstrated by histology. The results showed that NAC administration significantly improved portal flow, hepatic microcirculation, bile composition and bile flow after 5 h of reperfusion. NAC administration was also associated with less hepatocellular injury, as indicated by ALT serum activity, and decreased the oxidation of DHR to RH. In conclusion, NAC administration decreased the extent of I/R injury in the steatotic liver, particularly during the late phase of reperfusion.

Metabolomics: the principles and potential applications to transplantation

This review provides a summary of the applications and potential applications of metabolite profiling (i.e. metabolomics) in monitoring organ transplants. While the concept of metabolomics is relatively new to organ transplantation, the idea of measuring metabolites as a quick, noninvasive probe of organ function is not. Indeed, metabolite measurements of serum creatinine have long been used to assess pre- and post-operative organ function. Over the past 10 years, a number of lesser-known, organ-specific metabolites have also been shown to be good diagnostic indicators of both organ function and viability. In general, metabolomics offers a complementary picture to what can be revealed via techniques based on genomics, proteomics or histology. Because metabolic changes typically happen within seconds or minutes after an 'event', whereas some transcript, protein abundance or tissue changes may take place over days or weeks, metabolomic measurements may offer a particularly useful and inexpensive diagnostic tool to monitor donor organ viability or to detect organ rejection. The excitement associated with metabolomics, however, must be tempered by the fact that the technology for rapid metabolite identification is still in its infancy, and that metabolites are but one part of a very complex picture pertaining to organ function.

A comparison of bile composition from heart-beating and non-heart-beating rabbit organ donors during normothermic extracorporeal liver perfusion: experimental evaluation using proton magnetic resonance spectroscopy

BACKGROUND

Organs retrieved from marginal and non-heart-beating donors (NHBDs) have sustained variable degrees of preretrieval damage that result in an increased incidence of complications. Normothermic extracorporeal liver perfusion (NELP) provides an opportunity to evaluate and resuscitate such organs. The aim of this study was to identify markers of ischemic injury in bile during perfusion of livers from heart-beating donors (HBDs) and NHBDs.

METHODS

Livers were retrieved from New Zealand white rabbits. The HBD group (n=4) had no in situ warm ischemia before retrieval and the NHBD group (n=4), 45 minutes of in situ warm ischemia before liver retrieval. After 40 minutes of postretrieval cold ischemia, all livers were dual vessel reperfused, normothermically with oxygenated buffer solution supplemented with rabbit red blood cells, for 6 hours. Bile was collected and examined with 1HMRS.

RESULTS

Perfusion bile from HBD group showed an increased concentration of bile acids, lactate, glucose, and phosphatidylcholine, but a decreased concentration of acetate as compared to retrieval bile. This trend was further enhanced in NHBD group. The mean +/- SD (in micromol/L) were bile acids (10.48 +/- 2.8 vs 26.05 +/- 12.1 vs 44.5 +/- 44.5), lactate (10.66 +/- 4.5 vs 14.66 +/- 5.2 vs 13.22 +/- 1.8), glucose (5.37 +/- 2 vs 21.2 +/- 5.0 vs 29.09 +/- 15.3), phosphatidylcholine (0.21 +/- 0.02 vs 5.57 +/- 1.7 vs 6.42 +/- 0.3), and acetate (1.8 +/- 0.5 vs 0.39 +/- 0.1 vs 0.38 +/- 0.09) for retrieval bile, HBD perfusion bile, and NHBD perfusion bile, respectively. One animal from each group did not produce any bile during perfusion.

CONCLUSIONS

1HMRS of biliary constituents revealed differences with the type of ischemia. These indices may be potential markers of the extent of warm ischemic injury and the functional activity of an extracorporeally perfused liver.

In vivo and in vitro nuclear magnetic resonance spectroscopy as a tool for investigating hepatobiliary disease: a review of H and P MRS applications

Nuclear magnetic resonance (NMR) spectroscopy is a non-invasive technique, which allows the study of cellular biochemistry and metabolism. It is a diverse research tool, widely used by biochemists to investigate pathophysiological processes in vitro and, more recently, by physicians to determine disease abnormalities in vivo. This article reviews the basics of the NMR phenomenon and summarises previous research on the hepatobiliary system using both laboratory-based and clinical methodologies. The role of proton and phosphorus-31 ((31)P) NMR spectroscopy in the study of malignant and non-malignant liver disease and studies of bile composition are discussed. In vivo techniques (magnetic resonance spectroscopy, MRS) can be performed as an adjunct to standard MR examination of the liver. Although still primarily a research tool, the in vivo technique provides non-invasive biochemical information on disease severity and holds promise in its use to gauge response to treatment regimens.

Non-invasive study of human gall bladder bile in vivo using (1)H-MR spectroscopy

The sampling of gall bladder bile for analytical studies remains an invasive procedure. We demonstrate the application of the non-invasive methodology of (1)H-MR spectroscopy to the qualitative and quantitative assessment of human gall bladder bile in vivo. Spectral profiles in vivo are shown in relation to model and porcine gall bladder bile and the quantitation in man of the trimethylamine (choline) and lecithin concentrations were estimated to range from 25.9 mM to 48.4 mM (mean: 35.8 mM, standard deviation: 9.8). The composition of human gall bladder bile together with the quantitation of various constituents can be studied non-invasively in vivo.