Phospholipid metabolism of dog liver under hypoxic conditions induced by ligation of the hepatic artery

Protective effect of propofol on ischemia-reperfusion injury detected by HPLC-MS/MS targeted metabolic profiling

Ischemia-reperfusion injury(IRI), described as tissue damage caused by reversible ischemic injury or hypoxia prior to the blood supply restoration, is a common pathological phenomenon. In recent study, a hypoxia-reoxygenation (H/R) in the presence or absence of propofol posthypoxia treatment (P-PostH) cell model was built to simulate the condition of IRI, and researchers found propofol may protect cells by suppressing autophagic cell death. To investigate the mechanism underling the protective effect of propofol. A metabolomic analysis was performed in this study using ultra performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF- MS) to compare the metabolism during the process of H/R in the presence or absence of P-PostH. A total of 22 metabolites were detected varied after propofol posthypoxia treatment. Pathway analysis revealed these metabolites were mainly involved in the purine metabolic pathway, three carboxylic acid metabolic pathways, alanine, aspartate and glutamate metabolism pathway and lipid metabolism pathway. We measured the level of Hypoxanthine to verify the metabolomics work, for pathway analysis, we detect the level of reactive oxygen species with H/R and P-PostH treatment. Our study achieved a global comparison of metabolism profiling of H/R cell model with or without propofol posthypoxic treatment. The result indicated that propofol can attenuate endothelial injury caused by IRI by reducing oxidative damage.

Calcium and pH in anoxic and toxic injury

The critical events that lead to the transition from reversible to irreversible injury remain unclear. Studies are reviewed that have suggested that a rise in cytosolic free Ca2+ initiates plasma membrane bleb formation and a sequence of events that leads ultimately to cell death. In recent studies, we have measured changes in cytosolic free Ca2+, mitochondrial membrane potential, cytosolic pH, and cell surface blebbing in relation to the onset of irreversible injury and cell death following anoxic and toxic injury to single hepatocytes utilizing multiparameter digitized video microscopy (MDVM). MDVM is an emerging new technology that permits single living cells to be labeled with multiple probes whose fluorescence is responsive to specific cellular parameters of interest. Fluorescence images specific for each probe are collected over time, and then digitized and stored. Image analysis and processing then permits quantitation of the spatial distribution of the various parameters within the single living cells. Our results indicate the following: (1) formation of plasma membrane blebs accompanies all types of injury in hepatocytes; (2) cell death is a rapid event, initiated by rupture of a plasma membrane bleb, and is coincident with the onset of irreversible injury; (3) an increase of cytosolic free Ca2+ is not the stimulus for bleb formation or the final common pathway leading to cell death; (4) a decrease of mitochondrial membrane potential precedes loss of cell viability; (5) cytosolic pH falls by more than 1 pH unit during chemical hypoxia. This acidosis protects against the onset of cell death.

Blood level of mitochondrial aspartate aminotransferase as an indicator of the extent of ischemic necrosis of the rat liver

To assess the severity of ischemic liver injury, we examined release of mitochondrial aspartate aminotransferase (EC 2.6.1.1) and its cytoplasmic isozyme from the ischemic rat liver into the circulation. Their patterns of leakage were quite different: the level of cytoplasmic aspartate aminotransferase reached a peak soon after the circulation to the ischemic liver was restored, while that of mitochondrial aspartate aminotransferase increased slowly, reaching a maximum after more than 10 hr. On anoxic incubation of mitochondria isolated from the normal liver, oxidative phosphorylation capacity was lost within 2 hr, at which time no leakage of matrix enzymes was observed: more than 10 hr after-loss-of-oxidative phosphorylation were needed for the matrix enzymes to leak out of the mitochondrial membrane. Since the viability of cells is considered to depend on the capacity of oxidative phosphorylation, it is highly likely that the delayed appearance of mitochondrial aspartate aminotransferase in blood indicates the postmortem changes of injured cells. In fact, the cumulative activity of mitochondrial aspartate aminotransferase but not cytoplasmic aspartate aminotransferase in circulation after ischemic liver injury correlated fairly well with the decrease of total adenine nucleotides which were monitored to measure viable cells. The difference between mitochondrial aspartate aminotransferase and cytoplasmic aspartate aminotransferase as quantitative indices of hepatic necrosis may be due to the relative stability of the former and significant inactivation of the latter during hepatic ischemia. Therefore, the determination of mitochondrial aspartate aminotransferase in blood may be useful in the assessment of liver necrosis after ischemic injury.

Formation of unesterified choline by rat brain

Two preparations of rat brain (ischemic intact brain and homogenized whole brain) formed large amounts of unesterified (free) choline when incubated at 37 degrees C. The accumulation of choline was inhibited by microwave irradiation of brain, or by heating of brain to 50 degrees C, and was maximal at 37 degrees C at pH 7.4-8.5. Choline formation was only observed in subcellular fractions of brain that contained membranes. In homogenates of brain, choline accumulated at a rate exceeding 10 nmol/mg protein per h. There was a significant decrease in brain phosphatidylcholine concentration (of 50 nmol/mg protein) during incubation for 1 h at 37 degrees C. Concentrations of phosphocholine rose (by 2.3 nmol/mg protein), and concentrations of glycerophosphocholine and sphingomyelin did not change during this period. We used radiolabeled phospholipids to trace the fate of phosphatidylcholine and sphingomyelin during incubations of homogenates of brain. Phosphatidylcholine was degraded to form phosphocholine, glycerophosphocholine and free choline. No lysophosphatidylcholine accumulated. Sphingomyelin was degraded to form phosphocholine and a small amount of free choline. Magnesium ions stimulated choline production, while zinc ions were a potent inhibitor. Other divalent cations (calcium, manganese) had little effect on choline accumulation. ATP concentrations in brain homogenates were less than 5 nmol/mg protein (rapidly microwaved brain contained 27 nmol/mg protein). Addition of ATP or ADP to brain homogenates increased ATP concentrations and significantly inhibited choline accumulation. ATP diminished the formation of choline from added phosphatidylcholine, lysophosphatidylcholine, phosphocholine and glycerophosphocholine. The effects of ATP, zinc ion, or magnesium ion upon choline accumulation were not mediated by changes in the rates of utilization of choline for formation of phosphocholine or phosphatidylcholine. In summary, we showed that there was enhanced formation of choline when ATP concentrations within brain were low. This choline was derived, in part, from the degradation of phosphatidylcholine, and we suggest that phospholipase A activity was the primary initiator of choline release from this phospholipid.

Phospholipid alterations and membrane injury during myocardial ischemia

Several independent studies have demonstrated that there is a degradation of membrane phospholipids during myocardial ischemia. At present, most of the data support the initial activation of a phospholipase A pathway of phospholipid degradation. The extent of total phospholipid degradation is in the nanomole per gram wet weight quantity, as opposed to ischemic liver, in which the extent of phospholipid depletion approaches the micromole per gram wet weight level. However, in vitro studies suggest that calcium permeability properties and other myocardial cell membrane functions are sensitive to nanomole levels of phospholipid degradation. Clearly, further work is necessary in intact cell and heart preparations to correlate the degradation of phospholipid with the development of irreversible membrane injury during ATP depletion and hypoxia.

Accumulation of unesterified arachidonic acid in ischemic canine myocardium. Relationship to a phosphatidylcholine deacylation-reacylation cycle and the depletion of membrane phospholipids

Studies in ischemic canine left ventricle have shown that the depletion of membrane phospholipids is a critical event in the development of a sarcolemmal calcium permeability defect and associated irreversible myocyte injury. The mechanism of phospholipid loss is unclear, but may be due to the activation of endogenous phospholipases. Since arachidonic acid is a fatty acid found almost entirely in phospholipid, increases in arachidonate provide evidence for increased phospholipase activity. The present study was designed to examine the temporal relationship of the accumulation of free arachidonate with the onset of phospholipid depletion during fixed ligation of the left anterior descending coronary artery in canine myocardium. The following results were demonstrated in ischemic canine myocardium: (1) the accumulation of unesterified arachidonate is minimal during 10-30 minutes of ischemia, but is significantly increased after prolonging the duration of ischemia to 1-3 hours; (2) significant increases in arachidonate precede the development of a significant decrease in total phospholipid content; (3) the decrease in the arachidonate content of phosphatidylcholine is accompanied by similar decreases in all of the fatty acyl moieties; (4) the arachidonate content of lysophosphatidylcholine and diacylglycerol are unchanged during myocardial ischemia; (5) there is evidence of a deacylation-reacylation cycle in phosphatidylcholine prior to the accumulation of free arachidonate; (6) the fatty acyl specificity of the lysophosphatidylcholine acyltransferase corresponds to the pattern of fatty acyl remodeling of phosphatidylcholine during early myocardial ischemia. These data suggest that the accumulation of arachidonate may be a more sensitive measure of phospholipid degradation than the decrease in total phospholipid content in ischemic canine myocardium. It is postulated that the defective reacylation of arachidonate into phosphatidylcholine may contribute to the net loss of membrane phospholipid during myocardial ischemia.