In vivo 31P NMR spectroscopic changes during liver regeneration

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.

Biochemical metabolic changes assessed by 31P magnetic resonance spectroscopy after radiation-induced hepatic injury in rabbits

AIM: To compare the features of biochemical metabolic changes detected by hepatic phosphorus-31 magnetic resonance spectroscopy (³¹P MRS) with the liver damage score (LDS) and pathologic changes in rabbits and to investigate the diagnostic value of ³¹P MRS in acute hepatic radiation injury.

METHODS: A total of 30 rabbits received different radiation doses (ranging 5-20 Gy) to establish acute hepatic injury models. Blood biochemical tests, ³¹P MRS and pathological examinations were carried out 24 h after irradiation. The degree of injury was evaluated according to LDS and pathology. Ten healthy rabbits served as controls. The MR examination was performed on a 1.5 T imager using a ¹H/³¹P surface coil by the 2D chemical shift imaging technique. The relative quantities of phosphomonoesters (PME), phosphodiesters (PDE), inorganic phosphate (Pi) and adenosine triphosphate (ATP) were measured. The data were statistically analyzed.

RESULTS: (1) Relative quantification of phosphorus metabolites: (a) ATP: there were significant differences (P < 0.05) (LDS-groups: control group vs mild group vs moderate group vs severe group, 1.83 ± 0.33 vs 1.55 ± 0.24 vs 1.27 ± 0.09 vs 0.98 ± 0.18; pathological groups: control group vs mild group vs moderate group vs severe group, 1.83 ± 0.33 vs 1.58 ± 0.25 vs 1.32 ± 0.07 vs 1.02 ± 0.18) of ATP relative quantification among control group, mild injured group, moderate injured group, and severe injured group according to both LDS grading and pathological grading, respectively, and it decreased progressively with the increased degree of injury (r = -0.723, P = 0.000). (b) PME and Pi; the relative quantification of PME and Pi decreased significantly in the severe injured group, and the difference between the control group and severe injured group was significant (P < 0.05) (PME: LDS-control group vs LDS-severe group, 0.86 ± 0.23 vs 0.58 ± 0.22, P = 0.031; pathological control group vs pathological severe group, 0.86 ± 0.23 vs 0.60 ± 0.21, P = 0.037; Pi: LDS-control group vs LDS-severe group, 0.74 ± 0.18 vs 0.43 ± 0.14, P = 0.013; pathological control group vs pathological severe group, 0.74 ± 0.18 vs 0.43 ± 0.14, P = 0.005) according to LDS grading and pathological grading, respectively. (c) PDE; there were no significant differences among groups according to LDS grading, and no significant differences between the control group and experimental groups according to pathological grading. (2) The ratio of relative quantification of phosphorus metabolites: significant differences (P < 0.05) (LDS-moderate group and LDS-severe group vs LDS-control group and LDS-mild group, 1.94 ± 0.50 and 1.96 ± 0.72 vs 1.43 ± 0.31 and 1.40 ± 0.38) were only found in PDE/ATP between the moderate injured group, the severe injured group and the control group, the mild injured group. No significant difference was found in other ratios of relative quantification of phosphorus metabolites.

CONCLUSION: ³¹P MRS is a useful method to evaluate early acute hepatic radiation injury. The relative quantification of hepatic ATP levels, which can reflect the pathological severity of acute hepatic radiation injury, is correlated with LDS.

Recovery of hepatic function determined by cytochrome P450-dependent drug metabolism lags after compensatory hepatic volume changes after portal vein ligation in rats

BACKGROUND

Clinically, portal vein embolization has been proven to be useful as a preoperative treatment for major hepatic surgeries with impaired liver function. However, its effects on the metabolism and elimination of various drugs after portal vein embolization or ligation remain to be elucidated.

MATERIALS AND METHODS

A portal vein branch that perfuses the central and left lobes of the liver of male Wistar rat was ligated, and changes in the weights of ligated and nonligated lobules as well as hepatic levels and activities of cytochrome P450 (CYP) isoforms, such as CYP3A2 and CYP2C11, were determined. To evaluate in vivo the effect of PVL on hepatic drug metabolism, the narcotic activity (sleep time) of midazolam, a specific substrate for CYP3A2, was measured.

RESULTS

Although plasma levels of alanine aminotransferase and hepatic weight returned to basal levels at day 7 after the portal vein ligation, hepatic activities of CYP3A2 and CYP2C11 still remained low (53% and 54% of control levels, respectively), and returned to their initial levels after about day 14. The metabolism of midazolam was prolonged by approximately three times at day 7 after ligation and returned to basal levels at day 14.

CONCLUSIONS

Because hepatic CYP-dependent drug metabolism by CYP isoforms recovered more slowly than the apparent recovery of hepatic volume and plasma alanine aminotransferase levels, the therapeutics of drugs metabolized by the CYP isoforms should be used carefully in patients who receive major hepatectomy with portal vein branch embolization.

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

In the present study we applied proton-decoupled 31P magnetic resonance spectroscopic imaging (MRSI) to noninvasively assess liver metabolism in patients who had undergone a partial hepatectomy (PH). Proton-decoupled 31P chemical shift imaging was performed in 47 patients 2-28 days following major hepatectomy, and the results were compared with those from eight control subjects. All studies were performed on a 1.5T MR imager (General Electric, Milwaukee, WI) equipped with a stand-alone proton decoupler. A 31P-1H resonator pair was used for data acquisition, and 31P data were obtained in 34 min. Liver regeneration was characterized by increases in phosphoethanolamine (PE), and decreases in nucleoside triphosphates (NTP), glycerophosphoethanolamine (GPE), and glycerophosphocholine (GPC). These alterations were most marked 48-72 hr after hepatectomy and returned to baseline within 3 weeks. The level of PE measured by MRSI was also found to depend on the percentage of liver that was removed, while changes in levels of cellular high energy phosphates were independent of the size of liver resection. Implementation of proton-decoupling was critical for assessing individual phosphomonoester and phosphodiester components. This study demonstrates that 31P MRSI can be used to assess metabolic changes in humans during liver regeneration, and may be useful for assessing derangement of the regenerative process or guiding adjuvant chemotherapies.

Monitoring the development of hepatocellular carcinoma in woodchucks using 31P-MRS

The woodchuck is one of the only lab animal models of chronic viral hepatitis infection and the development of hepatocellular carcinoma. Using this model, changes in tissue energetics in the liver due to the development of hepatocellular carcinoma can be monitored by repeated magnetic resonance imaging and localized phosphorus spectroscopy. Age- and sex-matched control (n=5) and chronically infected (n=5) adult woodchucks were imaged four times in a six-month period in a 7-T horizontal-bore magnet. Using a custom-built doubly tunable quadrature volume coil, sagittal and axial FLASH images (128 x 128, slice thickness = 5 mm, TR/TE=1000/4.1, 8 averages) were acquired to locate the largest portion of the liver with the least amount of signal contamination from surrounding abdominal muscle. Two-dimensional 31P chemical-shift imaging (2D-CSI) was acquired (16 x 16 data matrix, 24 x 24 x 2 cm3, 1024 data points, 16 averages) for all animals. The extent of liver injury was determined using serum gamma glutamyltransferase (GGT). The livers of infected woodchucks showed a significant increase (p=0.01) in phosphomonoesters (PME):beta-adenosine triphosphate (NTP). Chronically infected woodchucks had higher levels of serum GGT compared to uninfected woodchucks (p=0.002). An increase in the PME:beta-NTP ratio indicates cellular proliferation within the malignant tumor.

Regenerative activity and liver function following partial hepatectomy in the rat using (31)P-MR spectroscopy

The aim of the present study was to determine whether alterations in hepatic energy expenditure following partial hepatectomy (PHx), as documented by in vivo hepatic (31)P-MRS, correlate with standard parameters of hepatic regeneration and/or liver function. In addition, we sought to determine whether changes in hepatic energy levels are proportional to the extent of hepatic resection. Adult male Sprague-Dawley rats (4-7 per group) underwent a 40%, 70%, or 90% PHx or sham surgeries. Magnetic resonance spectroscopy (MRS) examinations were performed on each animal 24 or 48 hours thereafter. After MRS examinations, [(3)H]thymidine incorporation into hepatic DNA, proliferating cell nuclear antigen (PCNA) protein expression, and serum bilirubin determinations were performed on each rat. Twenty-four hours following surgery, rats that had undergone 70% PHx had unchanged adenosine triphosphate (ATP) levels but significantly lower ATP/inorganic phosphate (Pi) ratios (P <.05), whereas, at 48 hours post-PHx, both ATP and ATP/Pi levels were lower than in sham- and nonoperated controls (P <.05). Hepatic regeneration and liver dysfunction mirrored these changes; correlations existed between ATP/Pi ratios and [(3)H]thymidine incorporation (r = -0.61, P <.005), PCNA protein expression (r = -0.62, P <.005), and serum bilirubin (r = -0.49, P <.05). For rats that had undergone graded resections, depleted energy levels 48 hours post-PHx were proportional to the extent of resection, degree of enhanced regenerative activity, and liver dysfunction. In conclusion, (31)P-MRS-generated ATP/Pi index is a noninvasive, robust determination that correlates with standard parameters of hepatic regeneration and function.

Metabolic control patterns in acute phase and regenerating human liver determined in vivo by 31-phosphorus magnetic resonance spectroscopy

OBJECTIVE

To elucidate the metabolic changes occurring within hepatocytes during acute phase reaction and liver regeneration.

SUMMARY BACKGROUND DATA

The metabolic events occurring within the liver during the hepatic stress response are poorly understood. The authors used in vivo 31-phosphorus magnetic resonance spectroscopy to study hepatic metabolism after surgical trauma with and without loss of liver cell mass.

METHODS

Three groups were studied: five patients undergoing partial hepatectomy; five patients in whom laparotomy and colonic resection was performed; and five patients treated by thyroidectomy. Hepatic metabolism was evaluated by 31-phosphorus magnetic resonance spectroscopy before surgery and serially thereafter on postoperative days 2, 4, 6, 14, and 28. Estimation of liver volume by magnetic resonance imaging and blood sampling for biochemistry were performed at the same time points.

RESULTS

The authors found that alterations in hepatocyte phospholipid metabolism occurred after surgery that were correlated with changes in circulating acute phase proteins. Liver regeneration after hepatectomy was also associated with a derangement in energy metabolism, measured by a decrease in the ratio of ATP to its hydrolysis product inorganic phosphate. The depleted energy status was mirrored in biochemical indices of liver function, and restitution paralleled the course of restoration of hepatic cell mass.

CONCLUSIONS

These findings indicate that changes in liver metabolism after surgery reflect the magnitude of tissue injury and the quantity of functioning liver cells. Acute phase responses dominate the initial recovery period at the expense of less important endergonic functions. When liver parenchyma is lost, the acute phase reaction is maintained and further supported by a rapid replenishment of hepatocytes, which can even be considered a continuation of acute phase physiology. Modulation of liver function within the framework of overall hepatic energy economy is one mechanism for matching energy supply with increased demands during these processes.

Long-term observation of in vivo 31P NMR spectra in carbon tetrachloride-intoxicated rabbit liver using implanted wireless surface coil

Phosphorus-31 NMR spectra in rabbit liver were successively observed for more than 5 months in a chronic CCl4 intoxication model using implanted wireless surface coils. The quality of the obtained NMR spectra was satisfactory and there was sufficient time resolution to follow the dynamic changes that occurred during a fructose tolerance test. The implanted coil did not lead to any serious adverse effects such as infection or liver dysfunction. During an 18-week administration of CCl4, the area of the phosphodiester peak significantly decreased. The ratio of P(i)/beta-ATP was transiently elevated and gradually returned to the control level. In the fructose tolerance test, the increase in phosphomonoester and the decrease in P(i) and beta-ATP after i.v. fructose loading were apparent, but the degrees in these changes became smaller during the CCl4 intoxication. This wireless surface coil was useful for consecutive and non-invasive 31P NMR observations of the liver to follow chronically treated animal models over a period of several months.

Hypercaloric lipid and glucose infusion reduces the mitochondrial respiratory activity in the regenerating rat liver

In order to evaluate the liver mitochondrial response to an increased energy load, eight groups of rats were studied: a control group (no surgery), a sham-operated group, and 6 groups that had undergone partial hepatectomy (PH). The PH rats either had no infusion following surgery, saline, isocaloric lipid, hypercaloric lipid, isocaloric glucose or hypercaloric glucose infusion. After isolation of liver mitochondria 6, 12, 18 and 24 h after surgery states 3 and 4 of respiration were measured in vitro in the presence of succinate. State 3 and 4 mitochondrial respiration was higher in the sham-operated rats 6 h after surgery than in the control animals, and a gradual decrease towards control values occurred in the 12-24 h period following surgery. Results in mitochondria from PH rats showed variable results, in most cases both State 3 and 4 respiration was higher after PH, while the respiratory control index in general was lower. State 3 respiration was significantly increased in the PH isocaloric lipid and glucose infused groups 6, 12 and 18 h, but not 24 h after partial hepatectomy. The PH hypercaloric glucose and hypercaloric lipid infused rats showed decreases in the liver mitochondrial oxygen consumption after 6, 12 and 18 h of liver regeneration, this was more pronounced after hypercaloric lipid infusion. These results suggest that, in vitro, the surgery tends to increase Status 3 and Status 4 mitochondrial respiration. The hypercaloric parenteral nutrition, both lipid and glucose based, significantly decreased liver mitochondrial oxygen consumption in partially hepatectomized rats, particularly in the first hours of liver regeneration, with restoration 24 h after surgery.

31P NMR assessment of orthotopic liver rejection in a rat model

31P NMR spectroscopy was used serially to study rejecting (ACl-->LEW) and nonrejecting (ACl-->ACl) orthotopic liver transplants in rats. Recipients were evaluated on post-transplant days 1, 3, 5, 7, 9, and 11. The relative changes in phosphomonoester (PME), inorganic phosphate (Pi), high-energy phosphates and pH were studied. The earliest significant difference between the rejecting and nonrejecting groups was a decrease in the alpha-NTP peak area on Day 5. This was followed by significant decreases in beta-NTP and pH, and increases in PME and Pi on Day 7. High-resolution 31P NMR spectra of perchloric acid extracts demonstrated the PME increase to be due mainly to elevated phosphoethanolamine. Using the parameter (Pi + PME)/(alpha + beta + gamma-NTP), rejecting livers were distinguished from nonrejecting livers at a moderate stage of rejection.

Phosphorus-31 nuclear magnetic resonance in vivo spectroscopy of human liver during hepatitis A virus infection

To evaluate the changes in hepatocellular phospholipid metabolism during hepatitis virus infection, 26 patients with acute viral hepatitis A were studied by means of phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy. The spectroscopy of liver showed six signal components in all patients as well as in the normal volunteers. During the early phase of illness, the phosphomonoester (PME)-phosphodiester (PDE) ratios in the patients became markedly greater than the ratios in the controls (P < 0.001). Within six weeks after the onset, the PME/PDE ratios returned to the level of controls. The time course analysis indicated an inverse correlation between the PME/PDE ratio and the period of time after onset (r = 0.738, P < 0.001). The spectral changes of human liver observed in acute viral hepatitis A are similar to those in the regenerating rat liver, indicating that 31P-NMR spectroscopy allows a noninvasive study of cell turnover in human liver disease associated with acute virus infection.

In vivo [31P]NMR assessment of early hepatocellular dysfunction during endotoxemia

Hepatocellular dysfunction, as a result of sepsis or endotoxemia, plays a critical role in the pathogenesis of multiple systems organ failure. Conventional methods to assay hepatic ATP require large tissue samples, making repeat measurements in the same animal impossible, and are unable to detect the minimal changes in metabolism consistent with early or reversible cellular injury. 31P NMR is a modality available for the in vivo measurement of high energy phosphates. Inorganic phosphate (Pi) and phosphomonoester (PME) ratios (markers of cellular metabolism and viability) as well as fractionated ATP may be repeatedly quantitated. To assess the early effects of endotoxemia on hepatic function, phosphorus spectra of the liver were obtained using a 1.7-cm surface coil in six rats after the ip administration of 4 mg/kg Escherichia coli lipopolysaccharide. Conventional assay was performed on 24 matched controls. Pi, PME, alpha-, beta-, and gamma-ATP peaks (expressed as percentage total signal area) were collected over 20 min, integrated, and analyzed. Pi/beta-ATP decreased over time until 6 hr reflecting ongoing uptake of inorganic phosphate and continued cellular metabolism. PME/beta-ATP ratios, which indicate cellular viability, became significantly elevated at 6 hr. Using 31P NMR, beta-ATP best reflected the early subtle energy changes present prior to cell death and subsequent organ failure with significant decreases at 2, 4, and 6 hr. Conventional assay for ATP confirmed similar trends. We conclude that 31P NMR is a valuable tool for the study of reversible hepatic energy changes during early endotoxemia.

Effect of short-term ethanol feeding on rat testes as assessed by 31P NMR spectroscopy, 1H NMR imaging, and biochemical methods

31P Nuclear magnetic resonance (NMR) spectroscopy and 1H NMR imaging were used to examine the effect of short-term ethanol feeding on the rat testis. Weanling rats were pair-fed for 10 weeks either on ethanol containing liquid diet (36% ethanol of total calories) or a diet in which dextrimaltose was isocalorically substituted for the ethanol of the alcohol-containing diet. In vivo 31P NMR of the testes was used to determine the intratesticular pH and the relative concentrations of various phosphorus-containing metabolites. The integrity of the blood-testes barrier was evaluated using 1H NMR imaging following a gadolinium diethylene tetramine pentaacetic acid derivative (Gd-DTPA) administration as a vascular contrast agent. After the completion of NMR studies, the testis and the liver were freeze-clamped to allow for the assay of their adenosine-5'-triphosphate (ATP) contents. Serum was assayed for its content of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alcohol and testosterone. Ethanol feeding resulted in the following: (a) a reduction in the body weight (p less than 0.05), (b) a reduction in the testicular phosphodiesters (PDE) PDE/ATP ratio (p less than 0.05), (c) an increased change in the testis image intensity difference between pre- and post-iv Gd-DTPA images, (c) a reduction in the testicular and hepatic content of ATP, and (d) increased serum levels of AST and ALT.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy metabolism of the liver in brain dead dogs assessed by 31P-NMR spectroscopy and arterial ketone body ratio

The changes in hepatic energy state were assessed by 31P-nuclear magnetic resonance spectroscopy (31P-MRS) and arterial ketone body ratio (AKBR) in brain dead dogs. 31P-MRS and AKBR were measured before and at 3 hours after brain death. Wiggers' shock model was employed to compare the energy metabolism during hypotension. 1) The brain death model: Systemic blood pressure changed from 178.3/115.0 mmHg (mean) in the control period, to 259.5/162.5 mmHg during Cushing phenomenon (CU period) and to 63.3/51.7 mmHg after completion of brain death (BD period). beta-ATP/Pi increased from 1.27 +/- 0.14 (mean +/- SEM) to 1.46 +/- 0.16 in the early CU period, and then decreased to 1.11 +/- 0.15 at 60 minutes after BD, followed by a gradual increase to 1.33 +/- 0.13 at 3 hours after BD. Intracellular pH (pHi) increased alkaline to the control value. AKBR decreased from 1.10 +/- 0.26 to 0.46 +/- 0.15 in the CU period (p less than 0.05) and then increased to 1.48 +/- 0.25 after BD. 2) Wiggers' shock model: Systemic blood pressure was 190.0/112.5 mmHg in the control period, 83.8/51.3 mmHg during exsanguination (EX period) and 185.0/117.0 mmHg after retransfusion (RT period). beta-ATP/Pi decreased from 1.17 +/- 0.13 to 0.61 +/- 0.10 in the EX period (p less than 0.05) and increased to 1.37 +/- 0.08 in the RT period. The pHi deviated from 7.33 +/- 0.07 to 6.82 +/- 0.14 in the EX period (p less than 0.01) and to 7.51 +/- 0.21 in the RT period. AKBR decreased from 1.00 +/- 0.11 to 0.21 +/- 0.04 in the EX period and increased to 1.08 +/- 0.12 in the RT period. The energy metabolism of the liver was well maintained in the state of brain death in spite of remarkable hypotension, although that was not the case with Wiggers' shock model. It was suggested that the combination of 31P-MRS and AKBR was useful for the evaluation of graft liver viability.