Proton nuclear magnetic resonance spectroscopy of lactate production in isolated rat liver during cold preservation

Potential of in vitro nuclear magnetic resonance of biofluids and tissues in clinical research

Body fluids, cells, and tissues contain a wide variety of metabolites that consist of a mixture of various low-molecular-weight compounds, including amino acids, peptides, lipids, nucleic acids, and organic acids, which makes comprehensive analysis more difficult. Quantitative nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical technique for analyzing the metabolic profiles of body fluids, cells, and tissues. It enables fast and comprehensive detection, characterization, a high level of experimental reproducibility, minimal sample preparation, and quantification of various endogenous metabolites. In recent times, NMR-based metabolomics has been appreciably utilized in diverse branches of medicine, including microbiology, toxicology, pathophysiology, pharmacology, nutritional intervention, and disease diagnosis/prognosis. In this review, the utility of NMR-based metabolomics in clinical studies is discussed. The significance of in vitro NMR-based metabolomics as an effective tool for detecting metabolites and their variations in different diseases are discussed, together with the possibility of identifying specific biomarkers that can contribute to early detection and diagnosis of disease.

N-acetylcysteine decreases lactate signal intensities in liver tissue and improves liver function in septic shock patients, as shown by magnetic resonance spectroscopy: extended case report

Background

N-acetylcysteine (NAC) has been shown to improve splanchnic blood flow in experimental studies. This report evaluates the effects of NAC on liver perfusion and lactate signal intensities in the liver tissue of septic shock patients using proton magnetic resonance imaging and spectroscopy. Furthermore, the monoethylglycinexylidide (MEGX) test was used to investigate hepatic function.

Methods

Five septic shock patients received 150 mg/kg body weight NAC as an intravenous bolus injection over 15 min. Lidocaine was injected both prior to and following NAC administration in order to determine MEGX formation. Measurements (hemodynamics, oxygen transport-related variables, blood samples for lactate, liver-related markers) were performed 1 hour before and 1 hour after NAC injection. In addition to the proton magnetic resonance imaging patients received two proton magnetic resonance spectra, one prior to and one 30 min subsequent to the onset of the NAC infusion at a 1.5 Tesla clinical scanner, for measurement of liver perfusion and liver lactate signal intensity.

Main findings

Following NAC infusion, the lactate signal intensity in the liver tissue showed a median decrease of 89% (11–99%), there was a median increase in liver perfusion of 41% (-14 to 559%), and the MEGX serum concentration increased three times (1.52–5.91).

Conclusions

A decrease in the lactate signal intensity in the liver tissue and an increase in the MEGX serum concentration and in liver perfusion might indicate improved liver function as a result of NAC administration. Patients with compromised hepatosplanchnic function, such as patients with septic shock due to peritonitis, may therefore benefit from NAC therapy.

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

The current shortage of donor organs in liver transplantation has led experienced transplant centers to use more "marginal" grafts. The development of a reliable technique of bile collection gives access to hepatic bile from donors and recipients for bile analysis to characterize the grafts. Proton nuclear magnetic resonance analysis has been applied to the study of bile for more than 30 years, showing encouraging results. This is the first study where proton nuclear magnetic resonance analysis has been applied to hepatic bile from selected liver grafts to evaluate its potential role in graft assessment. Hepatic bile was collected from eight liver donors (four with normal and four with steatotic grafts) during organ retrieval and four transplant recipients (two with good early graft function and two with primary dysfunction) immediately after graft reperfusion. A Varian Unity+ NMR spectrometer, operating at 11.7 Tesla (500 MHz for 1H), was used to obtain the proton nuclear magnetic resonance spectra. The results showed that the hepatic bile from steatotic grafts collected before transplantation had more intense phosphatidylcholine head group resonance than bile from normal grafts. It also showed slower clearance of University of Wisconsin solution in grafts with subsequent primary graft dysfunction, suggesting a slower recovery of bile secretion. These preliminary findings suggest that proton nuclear magnetic resonance analysis might help to differentiate the characteristics of bile acids and biliary lipids from normal and steatotic grafts. The monitoring of the resonance signal of University of Wisconsin solution washout, bile acid, and biliary lipid secretion may help to predict the development of primary graft dysfunction and avoid the need for retransplantation.

Energy metabolism in liver of anoxia-tolerant turtle species (Pseudemys scripta): a model for studying hepatic tolerance to cold hypoxia

We have studied biochemical markers of energy metabolism and glycolysis by enzyme analyses and 1H NMR spectroscopy in livers of the freshwater turtle, Pseudemys scripta, after vascular flush and cold storage. Values for hepatic ATP content and energy charge remained unchanged for 24 h and showed only small declines between 24 and 48 h of cold hypoxia. Lactate and glucose levels increased over the 48-h period, demonstrating, respectively, progressive glycolysis and glycogenolysis. These observations are in contrast to those made in mammalian liver, where ATP levels fall precipitously during the first few hours of cold hypoxia and glycolysis is inhibited. Additional changes suggested by 1H NMR spectroscopy may indicate a role for other metabolic pathways. Isolated organs of species such as Pseudemys may be useful models for studying the biochemical basis of resistance to cold hypoxic damage.

On the correlation between tissue hydration state and proton NMR relaxation rates in experimental liver transplantation

As the tissue hydration state is one of the most important parameters to predict viability cold stored livers before transplantation, we investigated the correlation between the tissue inverse total water fraction, reflecting the hydration state, and proton relaxation times in cold stored rat liver and orthotopic liver transplantation in a pig model. In cold stored rat liver excellent linear correlations between relaxation rates R1 (= 1/T1) and R2 (= 1/T2) and inverse total water fraction 1/Pw were obtained. In pig liver transplants, the slope and intercept obtained from a linear regression model are twice as high for R1 and almost identical for R2; however, correlation coefficients are lower due to increased biological variation and a smaller range in storage conditions, reflected by the range of water content. Proton nuclear magnetic resonance relaxation times measured during the cold storage on the whole organ non-invasively show also linear correlation with the inverse total water fraction, but the method is presently not accurate enough to estimate the hydration state of the liver tissue with sufficient precision. NMR relaxation times obtained from liver biopsies have the potential to predict tissue viability in experimental liver transplantation independent of species, strain and gender, and thus may be useful in estimating the viability of human donor livers (or at least add a new complementary information to the information gained by standard liver selection and function test before and after transplantation).