Metabolic Changes in Different Stages of Liver Fibrosis: In vivo Hyperpolarized 13C MR Spectroscopy and Metabolic Imaging

The Metabolomic Footprint of Liver Fibrosis

Both experimental and clinical liver fibrosis leave a metabolic footprint that can be uncovered and defined using metabolomic approaches. Metabolomics combines pattern recognition algorithms with analytical chemistry, in particular, 1H and 13C nuclear magnetic resonance spectroscopy (NMR), gas chromatography-mass spectrometry (GC-MS) and various liquid chromatography-mass spectrometry (LC-MS) platforms. The analysis of liver fibrosis by each of these methodologies is reviewed separately. Surprisingly, there was little general agreement between studies within each of these three groups and also between groups. The metabolomic footprint determined by NMR (two or more hits between studies) comprised elevated lactate, acetate, choline, 3-hydroxybutyrate, glucose, histidine, methionine, glutamine, phenylalanine, tyrosine and citrate. For GC-MS, succinate, fumarate, malate, ascorbate, glutamate, glycine, serine and, in agreement with NMR, glutamine, phenylalanine, tyrosine and citrate were delineated. For LC-MS, only β-muricholic acid, tryptophan, acylcarnitine, p-cresol, valine and, in agreement with NMR, phosphocholine were identified. The metabolomic footprint of liver fibrosis was upregulated as regards glutamine, phenylalanine, tyrosine, citrate and phosphocholine. Several investigators employed traditional Chinese medicine (TCM) treatments to reverse experimental liver fibrosis, and a commentary is given on the chemical constituents that may possess fibrolytic activity. It is proposed that molecular docking procedures using these TCM constituents may lead to novel therapies for liver fibrosis affecting at least one-in-twenty persons globally, for which there is currently no pharmaceutical cure. This in-depth review summarizes the relevant literature on metabolomics and its implications in addressing the clinical problem of liver fibrosis, cirrhosis and its sequelae.

In vivo Hyperpolarized Metabolic Imaging to Monitor the Progression of Hepatitis B Virus (HBV)-Related Hepatitis to Liver Fibrosis

PURPOSE

This study aimed to assess metabolic changes to monitor the progression from normal liver to hepatitis B virus (HBV)-related hepatitis and liver fibrosis using hyperpolarized 13C magnetic resonance imaging (MRI).

PROCEDURES

Hepatitis was induced in mice (n = 16) via hydrodynamic injection of HBV 1.2 plasmid (25 μg). Among them, liver fibrosis was induced in the mice (n = 8) through weight-adapted administration of thioacetamide with ethanol. Normal control mice (n = 8) were injected with a phosphate buffer solution. Subsequently, a hyperpolarized 13C MRI was performed on the mouse liver in vivo. The level of hepatitis B surface antigen (HBsAg) in blood serum was measured. Statistical analysis involved comparing the differential metabolite ratios, blood biochemistry values, and body weight among the three groups using the Kruskal-Wallis one-way analysis of variance.

RESULTS

HBsAg was absent in the normal and fibrosis groups, while it was detected in the hepatitis group. The ratios of [1-13C] lactate/pyruvate, [1-13C] alanine/pyruvate, [1-13C] lactate/total carbon, and [1-13C] alanine/total carbon were significantly lower in the normal control group than in the hepatitis and fibrosis groups (p < 0.05). Moreover, these ratios were significantly higher in the fibrosis group than in the hepatitis group (p < 0.05). However, no significant differences were observed in either [1-13C] pyruvate-hydrate/pyruvate or [1-13C] pyruvate-hydrate/total carbon among the three groups.

CONCLUSIONS

The levels of [1-13C] lactate and [1-13C] alanine in vivo may serve as valuable indicators for differentiating between HBV-related hepatitis, liver fibrosis, and normal liver.

Characterization of chemical constituents and metabolites in vivo and in vitro after oral administration of Wuteng tablets in rats by UHPLC-Q/TOF-MS

Waste medicinal plants are widely used in drug production. With the increasing demand for botanical drugs, there is an urgent need to identify new and effective drugs and improve the utilization of medicinal plant resources. Wuteng tablets (WTP) are extracted from the stem of Schisandra chinensis and have a good therapeutic effect on Alzheimer's disease. In this study, a holistic identification strategy based on UHPLC-Q/TOF-MS was developed for the first time to investigate the metabolites and metabolic pathways involved in the in vitro metabolism and liver microsomal incubation and in the in vivo metabolic system of rats after WTP administration. After the oral administration of WTP, 21 metabolites were identified in the serum and 25 metabolites were identified in the urine, of which six were new metabolites; 33 metabolites were inferred from the microsomal metabolites in vitro. The metabolic pathways related to WTP mainly involve demethylation, hydroxylation, dehydroxylation and dehydrogenation. In this study, the metabolites and metabolic pathways of WTP were elucidated via UHPLC-Q/TOF-MS, which provided a basis for an in-depth study of the pharmacodynamic and pharmacotoxicological effects of WTP.

Hyperpolarized carbon 13 MRI in liver diseases: Recent advances and future opportunities

Hyperpolarized carbon-13 magnetic resonance imaging (HP ¹³ C MRI) is a recently translated metabolic imaging technique. With dissolution dynamic nuclear polarization (d-DNP), more than 10 000-fold signal enhancement can be readily reached, making it possible to visualize real-time metabolism and specific substrate-to-metabolite conversions in the liver after injecting carbon-13 labelled probes. Increasing evidence suggests that HP ¹³ C MRI is a potential tool in detecting liver abnormalities, predicting disease progression and monitoring response treatment. In this review, we will introduce the recent progresses of HP ¹³ C MRI in diffuse liver diseases and liver malignancies and discuss its future opportunities from a clinical perspective, hoping to provide a comprehensive overview of this novel technique in liver diseases and highlight its scientific and clinical potential in the field of hepatology.

Identification of potential metabolic biomarkers in predicting esophageal varices needing treatment in patients with liver cirrhosis

The goal of this study was to determine the diagnostic performance of in vivo quantitative proton magnetic resonance spectroscopy (¹H-MRS) to identify the presence of esophageal varices needing treatment (VNT), as well as investigate its correlation with clinical characteristics in patients with liver cirrhosis. Forty cirrhotic patients without VNT showing the negative red color sign, and 40 cirrhotic patients with VNT showing positive red color sign underwent laboratory tests, esophago-gastro-duodenoscopy, and ¹H-MRS with single-voxel localization in the cirrhotic liver parenchyma. The levels of lactate + triglyceride (TG) and choline in cirrhotic patients with VNT were significantly higher than those in cirrhotic patients without VNT. In multivariate analysis, spleen diameter, platelet count, and platelet count/spleen diameter ratio, as well as lactate + TG, and choline were associated with the presence of VNT. Moreover, lactate + TG and choline levels were positively correlated with spleen diameter and negatively correlated with platelet count in the combined group of cirrhotic patients with and without VNT. Our study demonstrated that higher hepatic lactate + TG and choline levels in cirrhotic patients in conjunction with longer spleen diameter, lower platelet counts, and lower ratios of platelet count to spleen diameter were associated with the presence of esophageal VNT and the risk of developing variceal bleeding. Therefore, in vivo ¹H-MRS might be an effective tool for diagnosing and predicting esophageal VNT in patients with liver cirrhosis.

In Vivo Assessment of Metabolic Abnormality in Alport Syndrome Using Hyperpolarized [1-13C] Pyruvate MR Spectroscopic Imaging

Alport Syndrome (AS) is a genetic disorder characterized by impaired kidney function. The development of a noninvasive tool for early diagnosis and monitoring of renal function during disease progression is of clinical importance. Hyperpolarized ¹³C MRI is an emerging technique that enables non-invasive, real-time measurement of in vivo metabolism. This study aimed to investigate the feasibility of using this technique for assessing changes in renal metabolism in the mouse model of AS. Mice with AS demonstrated a significant reduction in the level of lactate from 4- to 7-week-old, while the levels of lactate were unchanged in the control mice over time. This reduction in lactate production in the AS group accompanied a significant increase of PEPCK expression levels, indicating that the disease progression in AS triggered the gluconeogenic pathway and might have resulted in a decreased lactate pool size and a subsequent reduction in pyruvate-to-lactate conversion. Additional metabolic imaging parameters, including the level of lactate and pyruvate, were found to be different between the AS and control groups. These preliminary results suggest that hyperpolarized ¹³C MRI might provide a potential noninvasive tool for the characterization of disease progression in AS.

Schulte R, Laustsen C. Comprehensive Literature Review of Hyperpolarized Carbon-13 MRI: The Road to Clinical Application

This review provides a comprehensive assessment of the development of hyperpolarized (HP) carbon-13 metabolic MRI from the early days to the present with a focus on clinical applications. The status and upcoming challenges of translating HP carbon-13 into clinical application are reviewed, along with the complexity, technical advancements, and future directions. The road to clinical application is discussed regarding clinical needs and technological advancements, highlighting the most recent successes of metabolic imaging with hyperpolarized carbon-13 MRI. Given the current state of hyperpolarized carbon-13 MRI, the conclusion of this review is that the workflow for hyperpolarized carbon-13 MRI is the limiting factor.

Differentiation of Heterogeneous Mouse Liver from HCC by Hyperpolarized 13C Magnetic Resonance

The clinical characterization of small hepatocellular carcinoma (HCC) lesions in the liver and differentiation from heterogeneous inflammatory or fibrotic background is important for early detection and treatment. Metabolic monitoring of hyperpolarized 13C-labeled substrates has been suggested as a new avenue for diagnostic magnetic resonance. The metabolism of hyperpolarized [1-13C]pyruvate was monitored in mouse precision-cut liver slices (PCLS) of aged MDR2-KO mice, which served as a model for heterogeneous liver and HCC that develops similarly to the human disease. The relative in-cell activities of lactate dehydrogenase (LDH) to alanine transaminase (ALT) were found to be 0.40 ± 0.06 (n = 3) in healthy livers (from healthy mice), 0.90 ± 0.27 (n = 3) in heterogeneously inflamed liver, and 1.84 ± 0.46 (n = 3) in HCC. Thus, the in-cell LDH/ALT activities ratio was found to correlate with the progression of the disease. The results suggest that the LDH/ALT activities ratio may be useful in the assessment of liver disease. Because the technology used here is translational to both small liver samples that may be obtained from image-guided biopsy (i.e., ex vivo investigation) and to the intact liver (i.e., in a noninvasive MRI scan), these results may provide a path for differentiating heterogeneous liver from HCC in human subjects.

Differentiation of Heterogeneous Mouse Liver from HCC by Hyperpolarized 13C Magnetic Resonance

The clinical characterization of small hepatocellular carcinoma (HCC) lesions in the liver and differentiation from heterogeneous inflammatory or fibrotic background is important for early detection and treatment. Metabolic monitoring of hyperpolarized 13C-labeled substrates has been suggested as a new avenue for diagnostic magnetic resonance. The metabolism of hyperpolarized [1-13C]pyruvate was monitored in mouse precision-cut liver slices (PCLS) of aged MDR2-KO mice, which served as a model for heterogeneous liver and HCC that develops similarly to the human disease. The relative in-cell activities of lactate dehydrogenase (LDH) to alanine transaminase (ALT) were found to be 0.40 ± 0.06 (n = 3) in healthy livers (from healthy mice), 0.90 ± 0.27 (n = 3) in heterogeneously inflamed liver, and 1.84 ± 0.46 (n = 3) in HCC. Thus, the in-cell LDH/ALT activities ratio was found to correlate with the progression of the disease. The results suggest that the LDH/ALT activities ratio may be useful in the assessment of liver disease. Because the technology used here is translational to both small liver samples that may be obtained from image-guided biopsy (i.e., ex vivo investigation) and to the intact liver (i.e., in a non-invasive MRI scan), these results may provide a path for differentiating heterogeneous liver from HCC in human subjects.

Metabolic Alterations Associated with Early-Stage Hepatocellular Carcinoma and Their Correlation with Aging and Enzymatic Activity in Patients with Viral Hepatitis-Induced Liver Cirrhosis: A Preliminary Study

Liver cirrhosis (LC) can develop hepatocellular carcinoma (HCC). However, noninvasive early diagnosis of HCCs in the cirrhotic liver is still challenging. We aimed to quantify the hepatic metabolites in normal control (NC), cirrhotic liver without HCC, cirrhotic liver with HCC (CLH), and early-stage HCC groups using proton magnetic resonance spectroscopy (¹H-MRS) with a long echo-time (TE) and to assess the potential association between the levels of hepatic metabolites in these four groups and aging and enzymatic activity. Thirty NCs, 30 viral hepatitis-induced LC patients without HCC, and 30 viral hepatitis-induced LC patients with HCC were included in this study. ¹H-MRS measurements were performed on a localized voxel of the normal liver parenchyma (n = 30) from NCs, cirrhotic liver parenchyma (n = 30) from LC patients without HCC, and each of the cirrhotic liver parenchyma (n = 30) and HCC (n = 30) from the same patients in the CLH group. Generalized estimating equations were used to evaluate potential risk factors for changes in metabolite levels. Potential associations between metabolite levels and age and serum enzymatic activities were assessed by correlation analysis. The levels of lactate+triglyceride (Lac+TG) and choline (Cho) in HCC were significantly higher compared to those in LC and CLH. A potential risk factor for changes in the Lac+TG and Cho levels was age, specifically 60–80 years of age. In particular, the Lac+TG level was associated with a high odds ratio of HCC in males aged 60–80 years. The Lac+TG and Cho concentrations were positively correlated with lactate dehydrogenase and alkaline phosphatase activities, respectively. Our findings suggested that ¹H-MRS measurement with a long TE was useful in quantifying hepatic Lac+TG and Cho levels, where higher Lac+TG and Cho levels were most likely associated with HCC-related metabolism in the viral hepatitis-induced cirrhotic liver. Further, the level of Lac+TG in HCC was highly correlated with older age and lactate dehydrogenase activity.

Differentiation of Heterogeneous Mouse Liver from HCC by Hyperpolarized 13C Magnetic Resonance

The clinical characterization of small hepatocellular carcinoma (HCC) lesions in the liver and differentiation from heterogeneous inflammatory or fibrotic background is important for early detection and treatment. Metabolic monitoring of hyperpolarized 13C-labeled substrates has been suggested as a new avenue for diagnostic magnetic resonance. The metabolism of hyperpolarized [1-13C]pyruvate was monitored in mouse precision-cut liver slices (PCLS) of aged MDR2-KO mice, which served as a model for heterogeneous liver and HCC that develops similarly to the human disease. The relative in-cell activities of lactate dehydrogenase (LDH) to alanine transaminase (ALT) were found to be 0.40 ± 0.06 (n = 3) in healthy livers (from healthy mice), 0.90 ± 0.27 (n = 3) in heterogeneously inflamed liver, and 1.84 ± 0.46 (n = 3) in HCC. Thus, the in-cell LDH/ALT activities ratio was found to correlate with the progression of the disease. The results suggest that the LDH/ALT activities ratio may be useful in the assessment of liver disease. Because the technology used here is translational to both small liver samples that may be obtained from image-guided biopsy (i.e., ex vivo investigation) and to the intact liver (i.e., in a non-invasive MRI scan), these results may provide a path for differentiating heterogeneous liver from HCC in human subjects.

Metabolic alterations in acute myocardial ischemia-reperfusion injury and necrosis using in vivo hyperpolarized [1-13C] pyruvate MR spectroscopy

This study aimed to investigate real-time early detection of metabolic alteration in a rat model with acute myocardial ischemia-reperfusion (AMI/R) injury and myocardial necrosis, as well as its correlation with intracellular pH level using in vivo hyperpolarized [1-¹³C] pyruvate magnetic resonance spectroscopy (MRS). Hyperpolarized ¹³C MRS was performed on the myocardium of 8 sham-operated control rats and 8 rats with AMI/R injury, and 8 sham-operated control rats and 8 rats with AMI-induced necrosis. Also, the correlations of levels of [1-¹³C] metabolites with pH were analyzed by Spearman’s correlation test. The AMI/R and necrosis groups showed significantly higher ratios of [1-¹³C] lactate (Lac)/bicarbonate (Bicar) and [1-¹³C] Lac/total carbon (tC), and lower ratios of ¹³C Bicar/Lac + alanine (Ala), and ¹³C Bicar/tC than those of the sham-operated control group. Moreover, the necrosis group showed significantly higher ratios of [1-¹³C] Lac/Bicar and [1-¹³C] Lac/tC, and lower ratios of ¹³C Bicar/Lac + Ala and ¹³C Bicar/tC than those of the AMI/R group. These results were consistent with the pattern for in vivo the area under the curve (AUC) ratios. In addition, levels of [1-¹³C] Lac/Bicar and [1-¹³C] Lac/tC were negatively correlated with pH levels, whereas ¹³C Bicar/Lac + Ala and ¹³C Bicar/tC levels were positively correlated with pH levels. The levels of [1-¹³C] Lac and ¹³C Bicar will be helpful for non-invasively evaluating the early stage of AMI/R and necrosis in conjunction with reperfusion injury of the heart. These findings have potential application to real-time evaluation of cardiac malfunction accompanied by changes in intracellular pH level and enzymatic activity.