Liver regeneration in humans is characterized by significant changes in cellular phosphorus metabolism: assessment using proton-decoupled 31P-magnetic resonance spectroscopic imaging

Reproducibility of absolute quantification of adenosine triphosphate and inorganic phosphate in the liver with localized 31P-magnetic resonance spectroscopy at 3-T using different coils

Concentrations of the key metabolites of hepatic energy metabolism, adenosine triphosphate (ATP) and inorganic phosphate (Pi), can be altered in metabolic disorders such as diabetes mellitus. 31Phosphorus (31P)-magnetic resonance spectroscopy (MRS) is used to noninvasively measure hepatic metabolites, but measuring their absolute molar concentrations remains challenging. This study employed a 31P-MRS method based on the phantom replacement technique for quantifying hepatic 31P-metabolites on a 3-T clinical scanner. Two surface coils with different size and geometry were used to check for consistency in terms of repeatability and reproducibility and absolute concentrations of metabolites. Day-to-day (n = 8) and intra-day (n = 6) reproducibility was tested in healthy volunteers. In the day-to-day study, mean absolute concentrations of γ-ATP and Pi were 2.32 ± 0.24 and 1.73 ± 0.26 mM (coefficient of variation [CV]: 7.3% and 8.8%) for the single loop, and 2.32 ± 0.42 and 1.73 ± 0.27 mM (CVs 6.7% and 10.6%) for the quadrature coil, respectively. The intra-day study reproducibility using the quadrature coil yielded CVs of 4.7% and 6.8% for γ-ATP and Pi without repositioning, and 6.3% and 7.1% with full repositioning of the volunteer. The results of the day-to-day data did not differ between coils and visits. Both coils robustly yielded similar results for absolute concentrations of hepatic 31P-metabolites. The current method, applied with two different surface coils, can be readily utilized in long-term and interventional studies. In comparison with the single loop coil, the quadrature coil also allows measurements at a greater distance between the coil and liver, which is relevant for studying people with obesity.

Early Postoperative Serum Phosphate Drop Predicts Sufficient Hypertrophy After Liver Surgery

OBJECTIVE

The aim of this study was to assess the impact of postoperative hypophosphatemia on liver regeneration after major liver surgery in the scenario of Associating Liver Partition with Portal vein ligation for Staged hepatectomy (ALPPS) and living liver donation (LLD).

BACKGROUND

Hypophosphatemia has been described to reflect the metabolic demands of regenerating hepatocytes. Both ALPPS and LLD are characterized by an exceptionally strong liver regeneration and may be of particular interest in the context of posthepatectomy hypophosphatemia.

METHODS

Serum phosphate changes within the first 7 postoperative days after ALPPS (n=61) and LLD (n=54) were prospectively assessed and correlated with standardized volumetry after 1 week. In a translational approach, postoperative phosphate changes were investigated in mice and in vitro .

RESULTS

After ALPPS stage 1 and LLD, serum phosphate levels significantly dropped from a preoperative median of 1.08 mmol/L [interquartile range (IQR) 0.92-1.23] and 1.07 mmol/L (IQR 0.91-1.21) to a postoperative median nadir of 0.68 and 0.52 mmol/L, respectively. A pronounced phosphate drop correlated well with increased liver hypertrophy ( P <0.001). Patients with a low drop of phosphate showed a higher incidence of posthepatectomy liver failure after ALPPS (7% vs 31%, P =0.041). Like in humans, phosphate drop correlated significantly with degree of hypertrophy in murine ALPPS and hepatectomy models ( P <0.001). Blocking phosphate transporter (Slc20a1) inhibited cellular phosphate uptake and hepatocyte proliferation in vitro.

CONCLUSION

Phosphate drop after hepatectomy is a direct surrogate marker for liver hypertrophy. Perioperative implementation of serum phosphate analysis has the potential to detect patients with insufficient regenerative capacity at an early stage.

Lactiplantibacillus plantarum AR113 Exhibit Accelerated Liver Regeneration by Regulating Gut Microbiota and Plasma Glycerophospholipid

Emerging evidence indicates that probiotics have been proved to influence liver injury and regeneration. In the present study, the effects of Lactiplantibacillus plantarum AR113 on the liver regeneration were investigated in 70% partial hepatectomy (PHx) rats. Sprague-Dawley (SD) rats were gavaged with L. plantarum AR113 suspensions (1 × 10¹⁰ CFU/mL) both before and after partial hepatectomy. The results showed that L. plantarum AR113 administration 2 weeks before partial hepatectomy can accelerate liver regeneration by increased hepatocyte proliferation and tumor necrosis factor-α (TNF-α), hepatocyte growth factor (HGF), and transforming growth factor-β (TGF-β) expression. Probiotic administration enriched Lactobacillus and Bacteroides and depleted Flavonifractor and Acetatifactor in the gut microbiome. Meanwhile, L. plantarum AR113 showed decline of phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidyl serine (PS), and lysophosphatidyl choline (LysoPC) levels in the serum of the rats after the L. plantarum AR113 administration. Moreover, L. plantarum AR113 treated rats exhibited higher concentrations of L-leucine, L-isoleucine, mevalonic acid, and lower 7-oxo-8-amino-nonanoic acid in plasma than that in PHx. Spearman correlation analysis revealed a significant correlation between changes in gut microbiota composition and glycerophospholipid. These results indicate that L. plantarum AR113 is promising for accelerating liver regeneration and provide new insights regarding the correlations among the microbiome, the metabolome, and liver regeneration.

Fast data acquisition techniques in magnetic resonance spectroscopic imaging

Magnetic resonance spectroscopic imaging (MRSI) is an important technique for assessing the spatial variation of metabolites in vivo. The long scan times in MRSI limit clinical applicability due to patient discomfort, increased costs, motion artifacts, and limited protocol flexibility. Faster acquisition strategies can address these limitations and could potentially facilitate increased adoption of MRSI into routine clinical protocols with minimal addition to the current anatomical and functional acquisition protocols in terms of imaging time. Not surprisingly, a lot of effort has been devoted to the development of faster MRSI techniques that aim to capture the same underlying metabolic information (relative metabolite peak areas and spatial distribution) as obtained by conventional MRSI, in greatly reduced time. The gain in imaging time results, in some cases, in a loss of signal-to-noise ratio and/or in spatial and spectral blurring. This review examines the current techniques and advances in fast MRSI in two and three spatial dimensions and their applications. This review categorizes the acceleration techniques according to their strategy for acquisition of the k-space. Techniques such as fast/turbo-spin echo MRSI, echo-planar spectroscopic imaging, and non-Cartesian MRSI effectively cover the full k-space in a more efficient manner per T_R . On the other hand, techniques such as parallel imaging and compressed sensing acquire fewer k-space points and employ advanced reconstruction algorithms to recreate the spatial-spectral information, which maintains statistical fidelity in test conditions (ie no statistically significant differences on voxel-wise comparisions) with the fully sampled data. The advantages and limitations of each state-of-the-art technique are reviewed in detail, concluding with a note on future directions and challenges in the field of fast spectroscopic imaging.

Liver regeneration - mechanisms and models to clinical application

Liver regeneration has been studied for many decades and the mechanisms underlying regeneration of the normal liver following resection or moderate damage are well described. A large number of factors extrinsic (such as bile acids and circulating growth factors) and intrinsic to the liver interact to initiate and regulate liver regeneration. Less well understood, and more clinically relevant, are the factors at play when the abnormal liver is required to regenerate. Fatty liver disease, chronic scarring, prior chemotherapy and massive liver injury can all inhibit the normal programme of regeneration and can lead to liver failure. Understanding these mechanisms could enable the rational targeting of specific therapies to either reduce the factors inhibiting regeneration or directly stimulate liver regeneration. Although animal models of liver regeneration have been highly instructive, the clinical relevance of some models could be improved to bridge the gap between our in vivo model systems and the clinical situation. Likewise, modern imaging techniques such as spectroscopy will probably improve our understanding of whole-organ metabolism and how this predicts the liver's regenerative capacity. This Review describes briefly the mechanisms underpinning liver regeneration, the models used to study this process, and discusses areas in which failed or compromised liver regeneration is clinically relevant.

(90) Y radiation lobectomy: Outcomes following surgical resection in patients with hepatic tumors and small future liver remnant volumes

BACKGROUND

The purpose of this study is to assess operative, post-operative, and long-term outcomes in patients who underwent radiation lobectomy (RL) for tumor control and/or hypertrophy of small future liver remnant (FLR) prior to resection.

METHODS

Right lobar +/- segment 4 radioembolization was performed prior to lobectomy/tri-segmentectomy in patients with hepatic tumor but inadequate FLR. Parenchymal/tumor volumes were calculated from pre/post-RL imaging; FLR/%FLR hypertrophy were determined. Complications were graded by the Clavien-Dindo classification.

RESULTS

Thirteen patients (HCC n = 10, cholangiocarcinoma n = 2, mCRC n = 1) underwent RL prior to resection. The median time between RL and post-RL imaging was 40 days (23-190 days); the median time to resection was 86 days (30-210 days). Median FLR increased significantly [pre: 33% (22-43%); post: 43% (29-69%), P < 0.01] to yield a median %FLR hypertrophy of 30% (4-105%). The median hospital stay after resection was 4 days (3-11 days). Transient hepatobiliary toxicities normalized post-operatively. Ninety-two percent of resected tumors had >50% pathologic necrosis. Median follow up time after surgery was 604 days (144-1,416 days); one death occurred.

CONCLUSIONS

In this preliminary study, radiation lobectomy was a safe and effective method to achieve remnant liver hypertrophy while providing tumor control. This approach may facilitate safe resection and favorable post-operative outcomes.J. Surg. Oncol. 2016;114:99-105. © 2016 Wiley Periodicals, Inc.

Liver regeneration and energetic changes in rats following hepatic radiation therapy and hepatocyte transplantation by ³¹P MRSI

BACKGROUND & AIMS

Radiation-induced liver damage (RILD) is a poorly understood and potentially devastating complication of hepatic radiation therapy (RT) for liver cancers. Previous work has demonstrated that hepatocyte transplantation (HT) can ameliorate RILD in rats. We hypothesized that RT inhibits generation of cellular ATP and suppresses hepatic regeneration.

METHODS

To study the metabolic changes that occur in RILD with and without HT, (31)P MRSI data were acquired in rats treated with partial hepatectomy (PH) alone, PH with hepatic irradiation (PHRT) or PHRT with HT (PHRT+HT).

RESULTS

Both [γ -ATP] and ATP/Pi (31)P MRSI signal ratio initially decreased and subsequently returned to baseline levels within 2 weeks after PH, which is consistent with other published data. Persistently reduced [γ-ATP] and ATP/Pi (31)P MRSI signal ratio were observed in rats up to 20 weeks after PHRT. However, progressive increases in [γ -ATP] were observed over time in the group of rats receiving PHRT+HT. Normal [γ -ATP] was observed 20 weeks after PHRT+HT (vs. PH alone), although, ATP/Pi levels did not return to normal after PHRT +HT. Ex vivo histological studies were performed to confirm liver repopulation with transplanted hepatocytes and the amelioration of pathologic changes of RILD.

CONCLUSIONS

These findings suggest that (31)P MRSI can be used to monitor the progress of RILD and its amelioration using transplanted hepatocytes to simultaneously restore metabolic function while replacing host hepatocytes damaged by RT.

Hypophosphataemia after major hepatectomy and the risk of post-operative hepatic insufficiency and mortality: an analysis of 719 patients

BACKGROUND

Hypophosphataemia after a hepatectomy suggests hepatic regeneration. It was hypothesized that the absence of hypophosphataemia is associated with post-operative hepatic insufficiency (PHI) and complications.

METHODS

Patients who underwent a major hepatectomy from 2000-2012 at a single institution were identified. Post-operative serum phosphorus levels were assessed. Primary outcomes were PHI (peak bilirubin >7 mg/dl), major complications, and 30- and 90-day mortality.

RESULTS

Seven hundred and nineteen out of 749 patients had post-operative phosphorus levels available. PHI and major complications occurred in 63 (8.8%) and 169 (23.5%) patients, respectively. Thirty- and 90-day mortality were 4.0% and 5.4%, respectively. The median phosphorus level on post-operative-day (POD) 2 was 2.2 mg/dl; 231 patients (32.1%) had phosphorus >2.4 on POD2. Patients with POD2 phosphorus >2.4 had a significantly higher incidence of PHI, major complications and mortality. On multivariate analysis, POD2 phosphorus >2.4 remained a significant risk factor for PHI [(hazard ratio HR):1.78; 95% confidence interval (CI):1.02-3.17; P = 0.048], major complications (HR:1.57; 95%CI:1.02-2.47; P = 0.049), 30-day mortality (HR:2.70; 95%CI:1.08-6.76; P = 0.034) and 90-day mortality (HR:2.51; 95%CI:1.03-6.15; P = 0.044). Similarly, patients whose phosphorus level reached nadir after POD3 had higher PHI, major complications and mortality.

CONCLUSION

Elevated POD2 phosphorus levels >2.4 mg/dl and a delayed nadir in phosphorus beyond POD3 are associated with increased post-operative hepatic insufficiency, major complications and early mortality. Failure to develop hypophosphataemia within 72 h after a major hepatectomy may reflect insufficient liver remnant regeneration.

Systematic review of pathophysiological changes following hepatic resection

OBJECTIVES

Major hepatic resection is now performed frequently and with relative safety, but is accompanied by significant pathophysiological changes. The aim of this review is to describe these changes along with interventions that may help reduce the risk for adverse outcomes after major hepatic resection.

METHODS

The MEDLINE, EMBASE and CENTRAL databases were searched for relevant literature published from January 2000 to December 2011. Broad subject headings were 'hepatectomy/', 'liver function/', 'liver failure/' and 'physiology/'.

RESULTS

Predictable changes in blood biochemistry and coagulation occur following major hepatic resection and alterations from the expected path indicate a complicated course. Susceptibility to sepsis, functional renal impairment, and altered energy metabolism are important sequelae of post-resection liver failure.

CONCLUSIONS

The pathophysiology of post-resection liver failure is difficult to reverse and thus strategies aimed at prevention are key to reducing morbidity and mortality after liver surgery.

Phosphorus liver MRSI at 3 T using a novel dual-tuned eight-channel ³¹P/¹H H coil

Although phosphorus-31 (³¹P) magnetic resonance spectroscopy holds potential as noninvasive tool to monitor treatment response of liver malignancies, the lack of appropriate coils has so far restricted its use to liver lesions close to the surface. A novel eight-channel phased-array dual-tuned ³¹P/¹H coil that can assess ³¹P metabolism in deeper liver tissue as well is presented in this article. Analysis of its performance demonstrates that this coil can provide good sensitivity across a width of 20 cm, thereby enabling magnetic resonance spectroscopic imaging (MRSI) scans that can fully cover axial views of the abdomen in lean subjects. In vivo results and reproducibility of ³¹P MRSI at 3 T of axial slices covering the full depth of the liver are shown in healthy volunteers. To minimize intrasubject and intersubject data variability, spectra are corrected for coil sensitivities. Methods to maximize the reproducibility of coil placement and spectroscopic planning are discussed. The phosphomonoesters/phosphodiesters ratio calculated in healthy volunteers has an average intrasubject variation of 23% averaged over voxels selected from the entire liver. Finally, the feasibility of using the coil in the clinic is shown by preliminary ³¹P liver MRSI data obtained from a patient with hepatocellular carcinoma.

31P MR spectroscopic imaging detects regenerative changes in human liver stimulated by portal vein embolization

PURPOSE

First, to evaluate hepatocyte phospholipid metabolism and energetics during liver regeneration stimulated by portal vein embolization (PVE) using proton-decoupled (31)P MR spectroscopic imaging ((31)P-MRSI). Second, to compare the biophysiologic differences between hepatic regeneration stimulated by PVE and by partial hepatectomy (PH).

MATERIALS AND METHODS

Subjects included six patients with hepatic metastases from colorectal cancer who were scheduled to undergo right PVE before definitive resection of right-sided tumor. (31)P-MRSI was performed on the left liver lobe before PVE and 48 h following PVE. Normalized quantities of phosphorus-containing hepatic metabolites were analyzed from both visits. In addition, MRSI data at 48 h following partial hepatectomy were compared with the data from the PVE patients.

RESULTS

At 48 h after PVE, the ratio of phosphomonoesters to phosphodiesters in the nonembolized lobe was significantly elevated. No significant changes were found in nucleoside triphosphates (NTP) and Pi values. The phosphomonoester (PME) to phosphodiester (PDE) ratio in regenerating liver 48 h after partial hepatectomy was significantly greater than PME/PDE 48 h after PVE.

CONCLUSION

(31)P-MRSI is a valid technique to noninvasively evaluate cell membrane metabolism following PVE. The different degree of biochemical change between partial hepatectomy and PVE indicates that hepatic growth following these two procedures does not follow the same course.

Noninvasive evaluation of liver repopulation by transplanted hepatocytes using 31P MRS imaging in mice

Hepatocyte transplantation (HT) is being explored as a substitute for liver transplantation for the treatment of liver diseases. For the clinical application of HT, a preparative regimen that allows preferential proliferation of transplanted cells in the host liver and a noninvasive method to monitor donor cell engraftment, proliferation, and immune rejection would be useful. We describe an imaging method that employs the creatine kinase (CK) gene as a marker of donor hepatocytes. Creatine kinase is unique among marker genes, because it is normally expressed in brain and muscle tissues and is therefore not immunogenic. Preferential proliferation of transplanted CK-expressing hepatocytes was induced by preparative hepatic irradiation and expression of hepatocyte growth factor using a recombinant adenoviral vector. CK is normally not expressed in mouse liver and its expression by the donor cells led to the production of phosphocreatine in the host liver, permitting (31)P magnetic resonance spectroscopic imaging of liver repopulation by engrafted hepatocytes. In conclusion, this study combined a noninvasive imaging technique to assess donor hepatocyte proliferation with a preparative regimen of partial liver irradiation that allowed regional repopulation of the host liver. Our results provide groundwork for future development of clinical protocols for HT.

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.