Hepatic metabolism during acute ethanol administration: a phosphorus-31 nuclear magnetic resonance study on the perfused rat liver under normoxic or hypoxic conditions

Resveratrol plus ethanol counteract the ethanol-induced impairment of energy metabolism: ³¹P NMR study of ATP and sn-glycerol-3-phosphate on isolated and perfused rat liver

The effects of trans-resveratrol (RSV) combined with ethanol (EtOH) were evaluated by (31)P NMR on total ATP and sn-glycerol-3-phosphate (sn-G3P) contents measured in real time in isolated and perfused whole liver of the rat. Mitochondrial ATP turnover was assessed by using specific inhibitors of glycolytic and mitochondrial ATP supply (iodacetate and KCN, respectively). In RSV alone, the slight decrease in ATP content (-14±5% of the initial content), sn-G3P content and ATP turnover were similar to those in the Krebs-Henseleit buffer control. Compared to control, EtOH alone (14 or 70 mmol/L) induced a decrease in ATP content (-24.95±2.95% of initial content, p<0.05) and an increase in sn-G3P (+158±22%), whereas ATP turnover tended to be increased. RSV (20 μmol/L) combined with EtOH, (i) maintained ATP content near 100%, (ii) induced a 1.6-fold increase in mitochondrial ATP turnover (p=0.049 and p=0.004 vs EtOH 14 and 70 mmol/L alone, respectively) and (iii) led to an increase in sn-G3P (+49±9% and +81±6% for 14 and 70 mmol/L EtOH, respectively). These improvements were obtained only when glycolysis was efficient at the time of addition of EtOH+RSV. Glycolysis inhibition by iodacetate (IAA) evidenced an almost 21% contribution of this pathway to ATP content. RSV alone or RSV+EtOH prevented the ATP decrease induced by IAA addition (p<0.05 vs control). This is the first demonstration of the combined effects of RSV and EtOH on liver energy metabolism. RSV increased (i) the flux of substrates through ATP producing pathways (glycolysis and phosphorylative oxidation) probably via the activation of AMPkinase, and (ii) maintained the glycolysis deviation to sn-G3P linked to NADH+H⁺ re-oxidation occurring during EtOH detoxication, thus reducing the energy cost due to the latter.

A metabolic link between mitochondrial ATP synthesis and liver glycogen metabolism: NMR study in rats re-fed with butyrate and/or glucose

BACKGROUND

Butyrate, end-product of intestinal fermentation, is known to impair oxidative phosphorylation in rat liver and could disturb glycogen synthesis depending on the ATP supplied by mitochondrial oxidative phosphorylation and cytosolic glycolysis.

METHODS

In 48 hr-fasting rats, hepatic changes of glycogen and total ATP contents and unidirectional flux of mitochondrial ATP synthesis were evaluated by ex vivo 31P NMR immediately after perfusion and isolation of liver, from 0 to 10 hours after force-feeding with (butyrate 1.90 mg + glucose 14.0 mg.g-1 body weight) or isocaloric glucose (18.2 mg.g-1 bw); measurements reflected in vivo situation at each time of liver excision. The contribution of energetic metabolism to glycogen metabolism was estimated.

RESULTS

A net linear flux of glycogen synthesis (~11.10 ± 0.60 μmol glucosyl units.h-1.g-1 liver wet weight) occurred until the 6th hr post-feeding in both groups, whereas butyrate delayed it until the 8th hr. A linear correlation between total ATP and glycogen contents was obtained (r2 = 0.99) only during net glycogen synthesis. Mitochondrial ATP turnover, calculated after specific inhibition of glycolysis, was stable (~0.70 ± 0.25 μmol.min-1.g-1 liver ww) during the first two hr whatever the force-feeding, and increased transiently about two-fold at the 3rd hr in glucose. Butyrate delayed the transient increase (1.80 ± 0.33 μmol.min-1.g-1 liver ww) to the 6th hr post-feeding. Net glycogenolysis always appeared after the 8th hr, whereas flux of mitochondrial ATP synthesis returned to near basal level (0.91 ± 0.19 μmol.min-1.g-1 liver ww).

CONCLUSION

In liver from 48 hr-starved rats, the energy need for net glycogen synthesis from exogenous glucose corresponds to ~50% of basal mitochondrial ATP turnover. The evidence of a late and transient increase in mitochondrial ATP turnover reflects an energetic need, probably linked to a glycogen cycling. Butyrate, known to reduce oxidative phosphorylation yield and to induce a glucose-sparing effect, delayed the transient increase in mitochondrial ATP turnover and hence energy contribution to glycogen metabolism.

The line asymmetry of electron spin resonance spectra as a tool to determine the cis:trans ratio for spin-trapping adducts of chiral pyrrolines N-oxides: the mechanism of formation of hydroxyl radical adducts of EMPO, DEPMPO, and DIPPMPO in the ischemic-reperfused rat liver

Nonstereospecific addition of free radicals to chiral nitrones yields cis/trans diastereoisomeric nitroxides often displaying different electron spin resonance (ESR) characteristics. Glutathione peroxidase-glutathione (GPx-GSH) reaction was applied to reduce the superoxide adducts (nitrone/*OOH) to the corresponding hydroxyl radical (HO*) adducts (nitrone/*OH) of two nitrones increasingly used in biological spin trapping, namely 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) and 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide, and of 5-diisopropoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DIPPMPO), a sterically hindered DEPMPO analogue. The method offered improved conditions to record highly resolved ESR spectra and by accurate simulation of line asymmetry we obtained clear evidence for the existence of previously unrecognized isomer pairs of cis- and trans-[DEPMPO/*OH] and [DIPPMPO/*OH]. Additional nitrone/*OH generation methods were used, i.e. photolysis of hydrogen peroxide and the Fenton reaction. We developed a kinetic model involving first- and second-order decay and a secondary conversion of trans to cis isomer to fully account for the strongly configuration-dependent behavior of nitrone/*OH. In the reductive system and, to a lower extent, in the Fenton or photolytic systems cis-nitrone/*OH was the more stable diastereoisomer. In various biologically relevant milieu, we found that the cis:trans-nitrone/*OH ratio determined right after the spin adduct formation significantly differed upon the GPx-GSH vs (Fenton or photolytic) systems of formation. This new mechanistic ESR index consistently showed for all nitrones that nitrone/*OH signals detected in the postischemic effluents of ischemic isolated rat livers are the reduction products of primary nitrone/*OOH. Thus, ESR deconvolution of cis/trans diastereoisomers is of great interest in the study of HO* formation in biological systems.

Some processes of energy saving and expenditure occurring during ethanol perfusion in the isolated liver of fed rats; a Nuclear Magnetic Resonance study

Background

In the isolated liver of fed rats, a 10 mM ethanol perfusion rapidly induced a rapid 25% decrease in the total ATP content, the new steady state resulting from both synthesis and consumption. The in situ rate of mitochondrial ATP synthesis without activation of the respiration was increased by 27%, implying an increased energy demand. An attempt to identify the ethanol-induced ATP-consuming pathways was performed using ³¹P and ¹³C Nuclear Magnetic Resonance.

Results

Ethanol (i) transiently increased sn-glycerol-3-phosphate formation whereas glycogenolysis was continuously maintained; (ii) decreased the glycolytic ATP supply and (iii) diminished the intracellular pH in a dose-dependent manner in a slight extend. Although the cytosolic oxidation of ethanol largely generated H⁺ (and NADH), intracellular pHi was maintained by (i) the large and passive excretion of cellular acetic acid arising from ethanol oxidation (evidenced by exogenous acetate administration), without energetic cost or (ii) proton extrusion via the Na⁺-HCO₃^- symport (implying the indirect activation of the Na⁺-K⁺-ATPase pump and thus an energy use), demonstrated during the addition of their specific inhibitors SITS and ouabaïn, respectively.

Conclusion

Various cellular mechanisms diminish the cytosolic concentration of H⁺ and NADH produced by ethanol oxidation, such as (i) the large but transient contribution of the dihydroxyacetone phosphate / sn-glycerol-3-phosphate shuttle between cytosol and mitochondria, mainly implicated in the redox state and (ii) the major participation of acetic acid in passive proton extrusion out of the cell. These processes are not ATP-consuming and the latter is a cellular way to save some energy. Their starting in conjunction with the increase in mitochondrial ATP synthesis in ethanol-perfused whole liver was however insufficient to alleviate either the inhibition of glycolytic ATP synthesis and/or the implication of Na⁺-HCO₃^- symport and Na⁺-K⁺-ATPase in the pHi homeostasis, energy-consuming carriers.

Ethanol perfusion increases the yield of oxidative phosphorylation in isolated liver of fed rats

The question arises as to the effect of ethanol on the actual yield of oxidative phosphorylation in the whole liver because of contradictory results reported in isolated hepatic mitochondria. The adenosine triphosphate (ATP) content of liver isolated from fed rats and perfused in the presence (10 mM) and absence of ethanol was continuously evaluated using 31P Nuclear Magnetic Resonance (NMR). An accurate estimation of mitochondrial ATP synthesis in the whole organ was obtained by subtracting the glycolytic ATP supply from the total ATP production. Simultaneously, the respiratory activity was assessed using O(2) Clark electrodes. The data indicate that ethanol enhanced the net consumption of ATP, leading to a new steady state of the ATP content. ATP synthesis was also found higher under ethanol [1.86+/-0.02 micromol/min g wet weight (min g ww)] than in control [1.44+/-0.18 micromol/min g ww]. However, mitochondrial respiration remained unchanged [2.20+/-0.13 micromol/min g ww] and, consequently, the in situ mitochondrial ATP/O ratio increased from 0.33+/-0.035 (control) to 0.42+/-0.015 (ethanol). The increase of the oxidative phosphorylation yield in the whole liver may be linked to the decrease in cytochrome oxidase activity induced by ethanol [FEBS Lett. 468 (2000) 239]. The significant raise (27%) of the ATP/O ratio was not sufficient to maintain the ATP level following ethanol-increased ATP consumption.

Use of diethyl(2-methylpyrrolidin-2-yl)phosphonate as a highly sensitive extra- and intracellular 31P NMR pH indicator in isolated organs. Direct NMR evidence of acidic compartments in the ischemic and reperfused rat liver

The novel phosphorylated pyrrolidine diethyl(2-methylpyrrolidin-2-yl)phosphonate (DEPMPH) was evaluated as a (31)P NMR probe of the pH changes associated with ischemia/reperfusion of rat isolated hearts and livers. In vitro titration curves indicated that DEPMPH exhibited a 4-fold larger amplitude of chemical shift variation than inorganic phosphate yielding an enhanced NMR sensitivity in the pH range of 5.0-7.5 that allowed us to assess pH variations of less than 0.1 pH units. At the non-toxic concentration of 5 mm, DEPMPH distributed into external and cytosolic compartments in both normoxic organs, as assessed by the appearance of two resonance peaks. An additional peak was observed in normoxic and ischemic livers, assigned to DEPMPH in acidic vesicles (pH 5.3-5.6). During severe myocardial ischemia, a third peak corresponding to DEPMPH located in ventricular and atrial cavities appeared (pH 6.9). Mass spectrometry and NMR analyses of perchloric extracts showed that no significant metabolism of DEPMPH occurred in the ischemic liver. Reperfusion with plain buffer resulted in a rapid washout of DEPMPH from both organs. It was concluded that the highly pH-sensitive DEPMPH could be of great interest in noninvasive ex vivo studies of pH gradients that may be involved in many pathological processes.

Effects of the mycelial extract of cultured Cordyceps sinensis on in vivo hepatic energy metabolism and blood flow in dietary hypoferric anaemic mice

The beneficial effects of a traditional Chinese medicine, Cordyceps sinensis (Cs), on mice with hypoferric anaemia were evaluated by NMR spectroscopy. Experimental hypoferric anaemia was induced in mice by feeding with an Fe-free diet for 6 weeks. They were then given extract from cultured Cs (200 mg/kg body weight daily, orally) and were placed on an Fe-containing recovery diet (35 mg Fe/kg diet) for 4 weeks. In vivo 31P and 2H NMR spectra acquired noninvasively and quantitatively at weekly intervals were used to evaluate hepatic energy metabolism and blood flow in the mice. During the 4-week Cs-extract treatment, consistent increases were observed in liver beta-ATP: inorganic phosphate value by liver 31P NMR spectroscopy, representing the high energy state, and in blood-flow rate as determined by 2H NMR spectroscopy of deuterated water (D2O) uptake after intravenous injection of D2O. The haematological variables (the packed cell volume and the haemoglobin level) and the hepatic intracellular pH, which was determined from the NMR chemical shift difference between the inorganic phosphate peak and the alpha-phosphate peak of ATP, were not significantly different between Cs-extract-treated and control mice. As blood flow and energy metabolism are thought to be linked, the Cs-extract-increased hepatic energy metabolism in the dietary hypoferric anaemic mice was concluded to be due to increased hepatic blood flow.

31P and 1H NMR spectroscopic studies of liver extracts of carbon tetrachloride-treated rats

NMR spectroscopy was used to examine hepatic metabolism in cirrhosis with a particular focus on markers of functional cellular hypoxia. (31)P and (1)H NMR spectra were obtained from liver extracts from control rats and from rats with carbon tetrachloride-induced cirrhosis. A decrease of 34% in total phosphorus content was observed in cirrhotic rats, parallelling a reduction of 40% in hepatocyte mass as determined by morphometric analysis. Hypoxia appeared to be present in cirrhotic rats, as evidenced by increased inorganic phosphate levels, decreased ATP levels, decreased ATP:ADP ratios (1.72 +/- 0.40 vs 2.48 +/- 0.50, p < 0.01), and increased inorganic phosphate:ATP ratios (2.77 +/- 0.48 vs 1.62 +/- 0.24, p < 0.00001). When expressed as a percentage of the total phosphorus content, higher levels of phosphoethanolamine and lower levels of NAD and glycerophosphoethanolamine were detected in cirrhotic rats. Cirrhotic rats also had increased phosphomonoester:phosphodiester ratios (5.73 +/- 2.88 vs 2.53 +/- 0.52, p < 0.01). These findings are indicative of extensive changes in cellular metabolism in the cirrhotic liver, with many findings attributable to the presence of intracellular hypoxia.

Effect of ethanol and fructose on liver metabolism: a dynamic 31Phosphorus magnetic resonance spectroscopy study in normal volunteers

In vivo 31Phosphorus magnetic resonance spectroscopy (31P-MRS) permits evaluation of dynamic changes of individual phosphorus-containing metabolites in the liver parenchyma, such as phosphomonoester (PME), adenosine triphosphate, and inorganic phosphate (Pi). Intravenous fructose load alters phosphorus metabolites and allows assessment of liver function by 31P-MRS. 31P-MRS data obtained in alcoholic liver disease are however inconclusive. To study the hypothesis that fructose load can be used to investigate metabolic effects of ethanol ingestion, the interaction of different metabolites--i.e., fructose and ethanol--were followed in vivo. Using a 1.5 Tesla magnetic resonance system, six healthy volunteers were examined in three sessions each: a session after administration of (a) fructose only (250 mg/kg) was compared with (b) fructose load after ethanol ingestion (0.8 g/kg). A control experiment (c) was done after ethanol only. Spectra were acquired using one-dimensional chemical shift imaging with a temporal resolution of 5 min. Following a fructose load, the concomitant uptake of ethanol showed drastic changes of individual metabolic steps of the hepatic metabolism (averages +/- standard deviation). While the velocity of the net formation of PME (relative increase 0.46 +/- 0.11 without ethanol vs. 0.61 +/- 0.25 with ethanol) and the use of adenosine triphosphate (-0.13 +/- 0.03 vs. -0.16 +/- 0.03) and Pi (-0.022 +/- 0.009 vs. -0.021 +/- 0.004) were not significantly affected by ethanol uptake, a significant (p < 0.01) reduction of PME degradation (31.3 +/- 9.4 vs. 61.9 +/- 16.9 relative total area) and absence of an overshoot for Pi (10.5 +/- 4.9 vs. -7.1 +/- 5.3 relative area 13 min to 43 min) was observed after ethanol administration. Dynamic 31P-MRS allows the observation of individual steps of hepatic metabolism in situ; fructose metabolism in the human liver is slowed down by concomitant ethanol ingestion after the phosphorylation step of fructose. This could be explained by inhibition of aldolase rather than ethanol-induced changes of the hepatic redox state. Fructose load can be used to study effects of alcohol ingestion and might therefore be useful in patients with alcoholic liver disease.

A multinuclear MR study of Gd-EOB-DTPA: comprehensive preclinical characterization of an organ specific MRI contrast agent

The characterization of the hepatobiliary contrast agent Gd-EOB-DTPA (gadolinium 3, 6, 9-triaza-3, 6, 9-tris(carboxymethyl)-4-(4-ethoxybenzyl)-undecandicarboxylic acid) in various media (water solution, protein containing solution, phosphorylated metabolites solution, and excised and perfused liver) was performed using different NMR approaches: water 1H nuclear magnetic relaxation dispersion profiles, 2H NMR longitudinal and transverse relaxation rates of labeled complex, water 17O transverse relaxation rates and chemical shifts, 31P relaxation rates and peak area of phosphorylated metabolites. The higher proton relaxivity of Gd-EOB-DTPA in water compared with Gd-DTPA is related to a shorter distance (r) between the water proton and the gadolinium ion and to a longer rotational correlation time (tauR) of the hydrated complex. Although the thermodynamic stability of Gd-EOB-DTPA is identical to the one of Gd-DTPA, its kinetic stability in solutions containing phosphorylated metabolites (ATP, phosphocreatine, and inorganic phosphate) as measured by 31P relaxation rates analysis is higher than for the parent compound. Gd-EOB-DTPA binds noncovalently to serum proteins. Its interaction with human serum albumin is characterized by a dissociation constant of 1-4.1 mM as calculated from proton and deuterium relaxation rates and equilibrium dialysis. This noncovalent interaction involves the subdomain IIA of human serum albumin. 31P spectroscopy of the excised and perfused rat livers was used to monitor the uptake of Gd-EOB-DTPA by the hepatocytes where it enhances the nuclear relaxation of the intracellular metabolites without impairing the adenosine triphosphate metabolism of the cells.

Use of spin-traps during warm ischemia-reperfusion in rat liver: comparative effect on energetic metabolism studied using 31P nuclear magnetic resonance

Detection of free radicals by electron spin resonance (ESR) proves the involvement of reactive oxygen species (ROS) in reperfused organ injuries. Spin-traps are known to ameliorate hemodynamic parameters in an isolated postischemic heart. The effects of 5 mmol/L DMPO (5,5-dimethyl-1-pyrroline-N-oxide) or DEPMPO (5-(diethlphosphoryl)-5-methyl-1-pyrroline N-oxide) on intracellular pH (pHin) and ATP level were evaluated by 31P nuclear magnetic resonance on isolated rat liver submitted to 1 hour of warm ischemia and reperfusion. At the end of the reperfusion period, during which pHin recovered to its initial value (7.16 +/- 0.03) in all groups, the ATP recovery level (expressed in percentage of initial value) was similar in controls and DEPMPO (60% +/- 5%, n = 6 and 54% +/- 4%, n = 6, respectively), but only 37% +/- 1% in DMPO-treated livers (n = 6) (p < 0.05 versus controls and p < 0.05 versus DEPMPO). Oxidative phosphorylation was not affected by an addition of nitrones on isolated mitochondria extracted from livers not submitted to ischemia-reperfusion. In contrast, mitochondria extracted at the end of the ischemia-reperfusion showed an impairment in the phosphorylation parameters, particularly in the presence of DMPO. Mass spectrum of ischemic liver perchloric acid extracts evidenced probable catabolites in treated groups. The differences in the effect of the two nitrones on energetic metabolism may be explained by the production of deleterious catabolites by DMPO as compared to DEPMPO. Even though a specific radical scavenging effect could be operative in the liver, our results indicate that catabolic effects were predominant. The absence of deleterious effects of DEPMPO in contrast to DMPO on the liver energetic metabolism was evidenced, allowing the use of DEPMPO for ESR detection.

Inhibition of gap junction intercellular communications of cultured rat hepatocytes by ethanol: role of ethanol metabolism

BACKGROUND/AIMS

In a previous study, we reported that in cultured rat hepatocytes, ethanol inhibits intercellular communication which is known to play a central role in the regulation of cell growth and differentiation. This work was designed to find out if ethanol exerts a direct action on cell membranes, comparable to other long-chain (C6-C9) alcohols, or an indirect action.

METHODS

Intercellular communication was measured on short-term cultured rat hepatocytes by the fluorescent Lucifer-Yellow CH transfer method. Intracellular pH was measured by spectrofluorimetry and membrane expression of connexin 32 by indirect immunofluorescence.

RESULTS

Under our conditions, ethanol (20 mM) inhibited intercellular communication of hepatocytes to the same extent as did octanol and 1 mM. Immunofluorescence semi-quantitative studies of connexin 32 suggested that the observed inhibition was not related to a decrease in the number of gap junction plaques. In contrast with those of octanol, the inhibitory effects of ethanol appeared to be indirect because the inhibition of ethanol metabolism by 4-methyl pyrazole abolished its effects on intercellular communication, while 4-methyl pyrazole did not influence the effects of octanol. Acetaldehyde, the main metabolite of ethanol was without effect on gap junctions.

CONCLUSIONS

This suggests that the inhibition of intercellular communication induced by ethanol may be included among the consequences of intermediary cell metabolism disturbances indirectly due to ethanol oxidation. This may be one of the mechanisms by which ethanol metabolism exerts a hepatotoxic possibly carcinogenic action.

Effects of the mycelial extract of cultured Cordyceps sinensis on in vivo hepatic energy metabolism in the mouse

Mice were given the extract of cultured Cordyceps sinensis (Cs) (200 mg/kg daily, p.o.) for 3 weeks. In vivo phosphorus-31 nuclear magnetic resonance (NMR) spectra of the liver were acquired at weekly intervals using a surface coil. From 1 to 3 weeks, a consistent increase in the ATP/inorganic phosphate ratio, which represents the high energy state, was observed in the Cs extract-treated mice. The intracellular pH of the Cs extract-treated mice was not significantly different from that of the control mice. No steatosis, necrosis, inflammation or fibrosis were observed in the liver specimens from Cs extract-treated mice.

Nicotinamide methylation and hepatic energy reserve: a study by liver perfusion in vitro

BACKGROUND/AIMS

The synthesis of pyridine nucleotides from nicotinamide requires adenosine triphosphate. In man when exogenous nicotinamide is poorly utilized in this synthesis, the excess follows a dissipative metabolic pathway and is excreted in urine as N-methylnicotinamide. In human cirrhosis N-methylnicotinamide serum levels are higher than normal, in basal condition and after nicotinamide oral load. The aim of this study was to verify N-methylnicotinamide production in relation to hepatic content of adenosine triphosphate during in vitro perfusion of rat liver, in normal conditions and after adenosine triphosphate depletion by metabolic stress.

METHODS

"Stress" was obtained by pre-washing with saline for 15 min before the perfusion with nutritive medium.

RESULTS

The adenosine triphosphate decrease in the stressed liver was 38% after pre-washing with saline and 80% at the end of nutritive perfusion. In control liver the corresponding decreases were 1% after pre-washing with nutritive medium and 65% at the end of perfusion with the same medium. The total nicotinamide adenine dinucleotide decreases were 44% and 56% in the stressed liver, and 19% and 52% in the control liver. The output levels of N-methylnicotinamide at 90 min of rat liver nutritive perfusion were 31.50 +/- 4.72 nmol/g for normal liver and 66.40 +/- 13.17 for stressed liver (p<0.001). Liver adenosine triphosphate was inversely related to N-methylnicotinamide production (r=0.93; p<0.001).

CONCLUSIONS

These data suggest that nicotinamide methylation may be enhanced when there is hepatic adenosine triphosphate decrease and energy failure induced by hypoxia or metabolic stress, similar to that obtained in vitro by saline washing before perfusion with nutritive medium. This study shows that the evaluation of N-methylnicotinamide production in man (before and after nicotinamide load) might be useful to explore the energy state of diseased liver.

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.

Compartmentation of inorganic phosphate in perfused rat liver. Can cytosol be distinguished from mitochondria by 31P NMR?

Compartmentation of inorganic phosphate was studied in intact perfused rat liver at 4 degrees C by 31P NMR. It was shown that decreases in cytosolic pH or cytosolic Pi concentration induced the appearance of an additional Pi resonance at low field which was assigned to Pi from an alkaline compartment. Valinomycin (K+ ionophore) induced a further splitting of the lines whereas nigericin (K+/H+ antiport) or potassium cyanide (inhibitor of cytochrome oxidase) had opposite effects. As valinomycin acts mainly on the cytosolic/mitochondrial K+ gradient and KCN on the mitochondrial respiratory chain, it was deduced that the alkaline compartment as revealed by the second Pi resonance was probably mitochondria. Single Pi lines observed on perchloric extracts of livers exhibiting two resonances during cold perfusion confirmed that the split peaks in the intact liver indeed arose from the same molecular species.

Effects of hypoxia and ethanol on xanthine oxidase of isolated rat hepatocytes: conversion from D to O form and leakage from cells

The combined effects of ethanol and hypoxia on the conversion of xanthine dehydrogenase (D form) to xanthine oxidase (O form) and on the leakage of the enzyme from isolated rat hepatocytes was studied. Time-dependent death of cells occurred during incubation in hypoxic conditions. Ethanol (40 mM) had only a moderate effect on viability in aerobiosis, but accelerated the loss of hypoxic cells, which was 96% after 3 h of incubation. In hypoxic conditions, the xanthine oxidase was gradually converted from D into O form. The conversion was complete in 3 h, and was accelerated by 1 mM xanthine or by ethanol, in a concentration-related manner. Hypoxia brought about a progressive leakage of xanthine oxidase from hepatocytes, which was accelerated by ethanol in a concentration-dependent manner. The enzyme found outside hepatocytes was mostly in its O form. The xanthine oxidase of hepatocytes cytosol was converted from D into O form by human plasma or serum. In all cases the conversion could be completely reverted by treatment of the extract with dithiothreitol.

31P-NMR spectroscopy of perifused rat hepatocytes immobilized in agarose threads: application to chemical-induced hepatotoxicity

A system consisting of isolated rat hepatocytes immobilized in agarose threads continuously perifused with oxygenated Krebs-Henseleit (KH) solution has been found to maintain cell viability with excellent metabolic activity for more than 6 h. The hepatocytes were monitored by phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy at 4.7 Tesla, by measurement of oxygen consumption and by the leakage of lactate dehydrogenase (LD) and alanine aminotransferase (ALT). The data obtained were comparable to those found for an isolated perfused whole liver in vitro. The effects of allyl alcohol (AA), ethanol, and 4-acetaminophenol (AP) were examined. A solution of 225 microM AA perifused for 90 min caused the disappearance of the beta-phosphate resonance of adenosine triphosphate (ATP) in the 31P-NMR spectra, a 7-fold increase in LD leakage and a 70% reduction in oxygen consumption. Ethanol (1.0 M) perifused for 90 min reduced the beta-ATP signal intensity ratio by 20%, the phosphomonoester (PME) signal by 50% and inorganic phosphate (Pi) by 33% (P less than 0.05). AP (10 mM) caused only mild liver-cell damage. The results demonstrate that perifused immobilized hepatocytes can be used as a liver model to assess the effects of a wide range of chemicals and other xenobiotics by NMR spectroscopy.

Phosphorus-31 nuclear magnetic resonance of isolated rat liver during hypothermic ischemia and subsequent normothermic perfusion

The effects of prolonged hypothermic ischemia and subsequent normothermic perfusion on the energetic metabolism and intracellular pH (pHin) of isolated rat livers were studied by phosphorus-31 nuclear magnetic resonance spectroscopy. Nucleoside triphosphate (NTP) depletion and intracellular pH were studied within an 18-h-storage phase, by using the following preservation media: Eurocollins (EC), UW Lactobionate (UW) and Bretschneider's solution (HTK). Values obtained after 8-h ischemia were chosen to estimate the performance of the various media: NTP levels were 37 +/- 7%, 10 +/- 5% and 0% of control levels, respectively, in livers stored in UW, HTK and EC solutions. pHin reached values of 7.15 +/- 0.10 in UW and HTK, and 6.96 +/- 0.10 in EC-stored livers. Ischemic damage was assessed by reperfusing the stored organ with Krebs medium: NTP recovery was around 70 +/- 20% for the three solutions used. Recovery of pHin was near the control value (7.23 +/- 0.08), except for EC solution (7.05 +/- 0.20). The main results are that (i) the rates of NTP and pHin decrease are strongly dependent on the nature of the preservation solution, whereas (ii) NTP recovery is not significantly different during post-ischemic reperfusion. With regard to animal survival, UW solution is at present considered largely superior to EC medium for liver preservation. Thus, our data suggest that the rates of NTP depletion and pHin fall during cold preservation could be both considered as better indicators assessing liver injury than the post-ischemic NTP recovery.

The effects of ethanol concentration on glycero-3-phosphate accumulation in the perfused rat liver. A reassessment of ethanol-induced inhibition of glycolysis using 31P-NMR spectroscopy and HPLC

The dose-dependent effect of ethanol on the hepatic metabolism of the perfused rat liver has been investigated by (a) 31P-NMR spectroscopy for the follow-up of intracellular phosphorylated metabolites and (b) HPLC for compounds released in the effluents. Perfusion of livers from fed rats with ethanol induced an increase in the level of sn-glycerol 3-phosphate and net accumulations of 3.30 +/- 0.33 and 0.69 +/- 0.15 mumol x g-1 wet liver were reached after 20 min, for 70 mM and 0.5 mM ethanol, respectively. sn-Glycerol-3-phosphate accumulation was fully detected by 31P NMR as indicated by comparing quantitations based on NMR and biochemical assays. Ethanol administration up to a concentration of 10 mM induced a dose-dependent decrease in the release of lactate + pyruvate by the liver. Lactate release decreased from 1129 +/- 39 to 674 +/- 84 nmol x min-1 x g-1, while pyruvate decreased from 230 +/- 9 to 6.2 +/- 0.4 nmol x min-1 x g-1, after 20 min of perfusion with 10 mM ethanol. Nevertheless, the flux through 6-phosphofructo-1-kinase, as measured by both the accumulation of sn-glycerol 3-phosphate and release of lactate + pyruvate, was not affected in the early phase of ethanol oxidation. Finally, data obtained from oxygen consumption, the release of acetate and the accumulation of sn-glycerol 3-phosphate do not support the involvement of the microsomal ethanol-oxidizing system in the catalysis of ethanol oxidation, even at high doses of alcohol.

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)

The effects of chronic ethanol consumption on the intact rat liver studied by in vivo 31P NMR spectroscopy

In vivo 31P nuclear magnetic resonance (NMR) spectroscopy provides unique opportunities to study the biochemistry of an organ within the intact animal in a totally non-invasive way. We have used in vivo and in vitro 31P NMR spectroscopy to study steady state changes in the major phosphorus-containing metabolites of the rat liver in control and chronically ethanol-treated rats. Chronic (4 month) ethanol treatment caused a statistically significant increase in the inorganic phosphate and phosphodiester resonances of rat liver in in vivo 31P NMR spectra relative to pair-fed control rats. Phosphomonoester and adenosine 5'-triphosphate resonances, as well as intracellular pH, were not appreciably altered. The effects of chronic ethanol treatment were particularly apparent in the response of the liver to a metabolic challenge of glycerol. Glycerol is phosphorylated almost exclusively in the liver and metabolized predominately via glycolysis and gluconeogenesis. Our in vivo 31P NMR results after administration of glycerol showed a significant increase in the phosphomonoester resonance in the liver of chronic ethanol-treated rats but not for their pair-fed controls. In vitro 31P NMR studies of perchloric acid extracts of liver showed that the increase was due to an accumulation of sn-glycerol 3-phosphate. This effect is due to the NAD(+)-dependent glycerol 3-phosphate dehydrogenase step being inhibited in the chronic ethanol-treated rats. This glycerol test may be useful in assessing the ability of the liver to rapidly regenerate NAD+ in situ and may be a more sensitive indicator of redox imbalance than steady state ratios of redox pairs (e.g., lactate/pyruvate).

Simple cation-exchange high-performance liquid chromatography optimized to the measurement of metabolites in the effluents from perfused rat livers using refractive index and ultraviolet detectors

A high-performance liquid chromatographic method designed to analyse effluents from perfused organs is described. In the case of rat liver, compounds released by the liver are readily separated and quantitated, using a strong cation exchanger (Aminex HPX 87H), two detectors connected in series (ultraviolet detector at 210 nm and refractive index detector), and by optimizing the concentration of sulphuric acid in the mobile phase. Chromatographic conditions described in the present work enable the quantitation, in a single run, of metabolites derived from the tricarboxylic acid cycle, glycolysis, ketogenesis, adenine nucleotides catabolism and ethanol oxidation. The advantage of this method stems from its ease of implementation, sensitivity and flexibility.

Application of reverse-DEPT polarization transfer pulse sequence to study the metabolism of carbon-13-labeled substrates in perfused organs by 1H NMR spectroscopy

Metabolism of 13C-enriched metabolites can be advantageously studied by reverse-polarization transfer methods. In this work an improved reverse-DEPT sequence has been applied for the first time on perfused organs in a 20-mm probe. The metabolic fate of 99% enriched [2-13C]acetate perfused in excised rat liver and heart has been documented.

Study of human liver disease with P-31 magnetic resonance spectroscopy

Liver metabolism and energetics of 24 patients with liver disease were studied using phosphorus-31 magnetic resonance spectroscopy. Significant abnormalities were detected in the majority of these patients. A striking diversity in metabolic patterns was observed. Patients with acute viral hepatitis had low liver phosphodiesters and high phosphomonoesters, possibly phosphocholine and phosphoethanolamine. In alcoholic hepatitis phosphomonoesters were raised. Intracellular inorganic phosphate and inorganic phosphate/ATP ratios were decreased in primary biliary cirrhosis and in some patients with hepatitis. These spectroscopic results were evaluated in respect of the pattern of liver damage and cellular regeneration. Liver tumours had raised phosphomonoesters and also showed evidence for altered spin-lattice relaxation of the phosphorus nucleus in various metabolites. In iron overload the liver ATP resonances were broadened. The line broadening correlated with the degree of iron overload suggesting the potential use of P-31 magnetic resonance spectroscopy for measuring liver iron.

In vitro 31P-NMR spectroscopic studies of rat liver subjected to chronic ethanol administration

31P-NMR spectroscopy of rat liver perchloric acid extracts was utilized to assess hepatic levels of major phosphorylated metabolites with and without ethanol administration from 0 to 51 days. The results are: (1) 3-phosphoglycerate was largely decreased starting from the first day of ethanol ingestion, (2) in ethanol-treated rats, phosphoethanolamine exhibited a significant decrease relative to the control rats until around day 30, (3) glycerophosphocholine and glycerophosphoethanolamine decreased over the entire period of ethanol ingestion, (4) ATP, AMP, Pi and energy charge showed significant changes due to ethanol effects when a 40-50 s exposure to CO2 was used prior to freeze-clamping, but ADP did not change, and (5) the other observable metabolites did not show statistically significant change. Some time-dependent changes in metabolite concentration, although not dramatic, were observed from day 1 to day 51 of ethanol administration. Our results indicate that chronic ethanol ingestion results in an inhibition of glycolysis and gluconeogenesis, a decrease in phospholipid breakdown and a lowering of hepatic energy charge.

Role of xanthine oxidase in ethanol-induced lipid peroxidation in rats

To investigate a possible role of free radical production by xanthine oxidase in the pathogenesis of ethanol-induced hepatic lipid peroxidation, chow-fed rats were given ethanol (5 g/kg) and placed at 32 degrees C for 6 h, which resulted in increased hepatic malondialdehyde levels. Pretreatment with allopurinol in amounts that effectively inhibited xanthine metabolism also significantly decreased ethanol-induced lipid peroxidation, suggesting participation of free radicals produced by xanthine oxidase in the peroxidative process. Both acetaldehyde and purine can serve as substrates for xanthine oxidase. Pretreatment with cyanamide increased hepatic acetaldehyde levels 5-fold, yet this was associated with a decrease in lipid peroxidation, indicating that acetaldehyde is not the xanthine oxidase substrate involved. By contrast, ethanol increased hepatic contents of hypoxanthine and xanthine and enhanced urinary output of allantoin (a final product of xanthine metabolism), incriminating increased metabolism of purines. Ethanol administration also enhanced hepatic nicotinamide adenine dinucleotide (reduced form). A corresponding rise of nicotinamide adenine dinucleotide (reduced form) in vitro inhibited xanthine dehydrogenase activity by 60%-76%. Increased purine degradation, possibly associated with a shift from the dehydrogenase to the xanthine oxidase pathway (secondary to nicotinamide adenine dinucleotide [reduced form]-mediated inhibition of xanthine dehydrogenase activity) is proposed as a possible mechanism for ethanol-stimulated free radical production. Because allopurinol attenuates the associated lipid peroxidation, this agent might be considered for possible therapeutic use in alcohol-induced liver damage.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

In vivo hepatic energy metabolism during the progression of alcoholic liver disease: a noninvasive 31P nuclear magnetic resonance study in rats

We investigated serially in vivo the ratios of phosphorylated metabolites and the intracellular pH in the livers of rats fed ethanol chronically to evaluate the relation between changes in energy metabolism and the progression of alcoholic liver disease with 31P nuclear magnetic resonance spectroscopy. 31P nuclear magnetic resonance spectra of the liver were acquired noninvasively from rats pair-fed a nutritionally adequate liquid diet containing ethanol or an isocaloric amount of dextrose with an implanted intragastric cannula for up to 24 wk. A high blood alcohol level was constantly maintained. The spectra were obtained using a surface coil combined with a ferrite screen to eliminate nuclear magnetic resonance signals derived from the superficial muscles. Contaminating 31P nuclear magnetic resonance signals arising from abdominal tissues other than the liver were eliminated from the spectra by digital subtraction. Throughout the study the inorganic phosphate/beta-ATP peak area ratio observed in alcohol-fed rats was found to be consistently elevated in comparison with the control rats (at 3 to 5 wk alcohol-fed rats = 1.20 +/- 0.10, control rats = 0.78 +/- 0.04, p less than 0.05.; at 22 to 24 wk alcohol-fed rats = 1.23 +/- 0.10, control rats = 0.81 +/- 0.06, p less than 0.05.; mean +/- S.E.). The phosphomonoesters/beta-ATP ratio tended to be higher in alcohol-fed rats when compared with control rats. The intracellular pH measured by the chemical shift of the inorganic phosphate peak showed no significant differences between alcohol-fed rats and control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical basis for alcohol-induced liver injury

Chronic ethanol ingestion leads to hepatocellular injury and alcoholic liver disease (ALD) only if multiple factors combine to favor centrilobular hepatocellular hypoxia. It is hypothesized that these factors include a shift in the redox state, the induction of the microsomal ethanol oxidizing system (MEOS), a high blood alcohol level (BAL), a high polyunsaturated fat diet and episodic decreased O2 supply to the liver. The shift in the redox state favors a low cellular pH, decreased fatty acid oxidation and increased triglyceride formation. The increased MEOS activity increases O2 consumption and portal-central O2 gradient as well as favors acetaldehyde toxic effects including retention of hepatic lipids and export proteins causing cell swelling. The resultant increase in the concentration of acetaldehyde and lactate may stimulate fibrosis as they stimulate collagen synthesis in vitro. The resultant fatty liver narrows the sinusoids slowing sinusoid blood flow. The combination of events reduces available O2 leading to decreased levels of ATP and cellular pH making the liver vulnerable to episodes of systemic hypoxia. The role of membrane changes are reviewed, i.e., 1) membrane fluidity as related to changes in the species of phospholipids, 2) mitochondrial function as related to the changes in the lipid environment of the electron transport chain, and 3) linoleic acid-prostaglandin metabolism. Acute ethanol in vitro has been shown to affect liver cell metabolism regulation by triggering and increasing protein phosphorylation through the Ca2+-phospholipase C pathway. A high fat diet enhances the liver injury caused by chronic ethanol ingestion.

Liver adenosine triphosphate and pH in fasted and well-fed mice after infusion of adenine nucleotide precursors

Nutrition is a factor which may affect the liver energy charge. Experiments were performed to determine the effect of starvation and of ATP precursors, adenine and ribose on liver energy stores. The 31P NMR spectra of well-fed and starved mice livers were studied in a perfusion system using Krebs-Henseleit buffer (KHB). The ATP precursors, adenine (20 mmol/l) and ribose (80 mmol/l), were then added to determine their effect. Their effect on the ATP dynamics during ischemia and reperfusion were then evaluated. The effects of adenine alone and ribose alone were then determined. The 31P spectra of well-fed mice demonstrated high ATP content relative to Pi, phosphoesters and phospholipids. Animals starved for 24 h showed very low ATP, high Pi and little or no detectable phospholipids. In starved animals, ATP rose steadily to approximately 50% above the baseline level when precursors were added. Pi decreased to 30% of the baseline after 40 min. Little change was noted in well-fed animals. The rate of ATP decay did not change with the onset of ischemia, whether the livers were perfused with KHB alone or KHB with precursors. Upon reperfusion, precursors improved the recovery of ATP (81% vs 49% after 20 min ischemia, 44% vs 34% after 30 min ischemia). Addition of adenine alone produced similar results, but addition of ribose alone did not significantly alter ATP recovery. In conclusion, supplying starved or post-ischemic livers with adenine or ribose and adenine does improve ATP levels.