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J J Lemasters

Publications and source records attributed to J J Lemasters.

At least 199 records · Page 11Linked to original sources
PubMed1984

Is hypoxia involved in the mechanism of alcohol-induced liver injury?

Since alcoholism is a major health problem, mechanisms responsible for various forms of alcoholic liver disease (e.g., fatty liver, alcoholic hepatitis, and cirrhosis) require elucidation. Knowledge of these mechanisms is needed to provide a sound framework to treat alcoholic liver disease, to prevent its occurrence and to identify those most susceptible to it. Israel and co-workers proposed that ethanol-induced necrosis results from hypoxia to centrilobular hepatocytes as a consequence of an alcohol-induced increase in hepatic oxygen utilization (Y. Israel, H. Kalant , H. Orrego , J. M. Khanna , L. Videla , and J. M. Phillips, 1975, Proc. Natl. Acad. Sci. USA, 72(3), 1137-1141). We have employed several new techniques to evaluate this hypothesis. Procedures have been developed to make measurements of hepatic metabolism within the hepatic lobule in the isolated, perfused liver using miniature light guides and oxygen electrodes. By comparing these lobular measurements to global metabolism and to hepatic morphology determined by light and electron microscopy, a coherent, quantitative description of lobular oxygen metabolism is emerging. With these techniques, the lobular oxygen gradient was measured directly in isolated, perfused rat livers. This gradient was elevated in livers from ethanol-treated rats, an effect which was blocked by the antithyroid drug, propylthiouracil. Restriction of oxygen delivery to the isolated liver produced stable, circumscribed zones of virtual anoxia localized around the central vein. Anoxic stress led within minutes to centrilobular injury with complete sparing of periportal areas. Cellular injury was characterized by the formation of membranous blebs on the surface of centrilobular hepatocytes. When hypoxic tissue was reoxygenated , blebs were released into the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Alcohol-induced liver injury. The role of oxygen.

Alcoholism is a major health problem, and one of its primary manifestations is alcoholic liver disease. The mechanisms responsible for the various forms of alcoholic liver disease--fatty liver, alcoholic hepatitis, and cirrhosis--are at present poorly understood. Knowledge of these mechanisms is needed to provide a sound framework for the therapy and prevention of liver disease due to alcohol and for the identification of those individuals most susceptible to develop liver disease from alcohol abuse. These experiments were designed specifically to evaluate the postulate that ethanol-induced pericentral liver damage results from an accentuated gradient of decreasing oxygen tension leading to pericentral hypoxia. Microlight guides were used to detect NADH fluorescence, and miniature oxygen electrodes were employed to measure oxygen tensions from periportal and pericentral regions of the liver lobule from the perfused rat liver. With both techniques, ethanol treatment increased the hepatic oxygen gradient. This increase was blocked by the antithyroid drug propylthiouracil. Thus, these experiments provide evidence in support of the hypothesis that pericentral hypoxia is involved in the mechanism of ethanol-induced liver injury. Furthermore, low-flow hypoxia was shown to cause blebs in the pericentral region of the liver lobule in as little as 15 min. This surface blebbing could represent the mechanism for the well-known release of enzymes by impaired hepatic tissues.

Acetaldehyde↗
PubMed1983

Stimulation of mixed-function oxidation of 7-ethoxycoumarin in periportal and pericentral regions of the perfused rat liver by xylitol.

Rates of O-deethylation of 7-ethoxycoumarin by perfused livers from fasted, phenobarbital-treated rats were 3.7 mumol X g-1 X h-1. Approximately 50% of the product was conjugated. When rates of 7-ethoxycoumarin O-deethylation were varied by infusing different concentrations of substrate, a good correlation (r = 0.91) was found between rates of O-deethylation of 7-ethoxycoumarin and fluorescence of 7-hydroxycoumarin detected from the liver surface. Micro-light guides (tip diameter 170 microns) placed on periportal and pericentral regions on the liver surface were used to monitor the conversion of nonfluorescent 7-ethoxycoumarin to fluorescent 7-hydroxycoumarin. The O-deethylation of 7-ethoxycoumarin to 7-hydroxycoumarin increased fluorescence 64% and 28% in pericentral and periportal regions of the liver lobule, respectively. Rates of 7-ethoxycoumarin O-deethylation estimated from these increases in fluorescence were 5.2 mumol X g-1 X h-1 in pericentral and 2.2 mumol X g-1 X h-1 in periportal regions of the liver. During mixed-function oxidation of 7-ethoxycoumarin, the oxidation:reduction state of NADP(H) was similar in both regions of the liver lobule. Xylitol (2 mM) decreased the NADP+/NADPH ratio and stimulated rates of drug metabolism in both regions of the liver lobule. This indicates that conditions exist where the supply of NADPH is an important rate-determining factor for 7-ethoxycoumarin metabolism in both periportal and pericentral regions of the liver lobule.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1983

Metabolic heterogeneity in the perfused rat liver.

New methods have been developed to monitor metabolic events non-invasively within periportal and pericentral regions of perfused rat livers. These techniques utilize two-fiber micro-light guides and miniature oxygen electrodes positioned on identified lobular regions of the perfused liver based on differential pigmentation of periportal and pericentral areas. Two-fiber micro-light guides detect the fluorescence of native and introduced fluors and are used to monitor redox changes of endogenous pyridine nucleotides and the generation of fluorescent products (e.g., 7-hydroxycoumarin) from exogenous substrates. Changes in fluorescence detected with two-fiber micro-light guides are correlated with changes measured with large, multi-fiber light guides and with whole organ rates of metabolism. Subsequently, local rates are estimated. With these techniques, we show that (a) rates of ethanol and acetaldehyde metabolism are similar in periportal and pericentral regions of the liver lobule; (b) mixed-function oxidation predominantes in pericentral regions in livers from phenobarbital-treated rats; (c) rates of sulfation of 7-hydroxycoumarin are greater in periportal than in pericentral hepatocytes; and (d) oxygen uptake is approximately 3-fold greater in periportal than in pericentral areas of the liver lobule.

Acetaldehyde↗
PubMed1983

Selective increase in pericentral oxygen gradient in perfused rat liver following ethanol treatment.

The oxygen gradient across the liver lobule was measured in isolated, hemoglobin-free perfused livers from control and ethanol-treated rats using micro-light guides and miniature oxygen electrodes. Both techniques yielded similar values for the lobular, periportal and pericentral oxygen gradients. Oxygen uptake increased 33% in livers from rats treated with ethanol for 4 to 6 weeks. In addition, the pericentral oxygen gradient increased by 100%, but the periportal gradient was unchanged. These observations suggest that chronic ethanol treatment may increase the rate of cellular respiration in pericentral regions of the liver lobule selectively. One possible explanation for a region-specific effect of ethanol may be ethanol-induced inhibition of glycolysis which predominates in pericentral hepatocytes.

Alcoholism↗
PubMed1983

Hypoxic hepatocellular injury.

Low flow hypoxia to the isolated, perfused rat liver produced stable, circumscribed zones of virtual anoxia which were confined to centrilobular regions of the liver lobule. As a result, centrilobular hepatocytes were injured while periportal tissue was spared. In hypoxic areas, blebs of hepatocyte plasma membrane cytoplasm protruded into sinusoids through fenestrations of the endothelium, evidently as a result of disruption of the cytoskeleton. Upon resumption of normal flow rates (reoxygenation), blebs disappeared and hepatocytes decreased markedly in volume. Concomitantly, sinusoids widened, endothelial fenestrations dilated, and lactate dehydrogenase activity appeared in the effluent. Filtration of perfusates following resumption of flow yielded cytoplasmic fragments, and it was concluded that blebs were released into the circulation. This shedding of cytoplasmic fragments may represent the cellular basis for the appearance of hepatic enzymes in the sera of patients with liver disease.

Animals↗
PubMed1983

Cell surface changes and enzyme release during hypoxia and reoxygenation in the isolated, perfused rat liver.

We examined the effects of hypoxia and reoxygenation in isolated, perfused rat livers. Hypoxia induced by a low rate of perfusion led to near anoxia confined to centrilobular regions of the liver lobule. Periportal regions remained normoxic. Within 15 min, anoxic centrilobular hepatocytes developed surface blebs that projected into sinusoids through endothelial fenestrations. Periportal hepatocytes were unaffected. Both scanning and transmission electron microscopy suggested that blebs developed by transformation of preexisting microvilli. Upon reoxygenation by restoration of a high rate of perfusion, blebs disappeared. Other changes included marked shrinkage of hepatocytes, enlargement of sinusoids, and dilation of sinusoidal fenestrations. There was also an abrupt increase in the release of lactate dehydrogenase and protein after reoxygenation, and cytoplasmic fragments corresponding in size and shape to blebs were recovered by filtration of the effluent perfusate. We also studied phalloidin and cytochalasin D, agents that disrupt the cytoskeleton. Both substances at micromolar concentrations caused rapid and profound alterations of cell surface topography. We conclude that hepatic tissue is quite vulnerable to hypoxic injury. The morphological expression of hypoxic injury seems mediated by changes in the cortical cytoskeleton. Reoxygenation causes disappearance of blebs and paradoxically causes disruption of cellular volume control and release of blebs as cytoplasmic fragments. Such cytoplasmic shedding provides a mechanism for selective release of hepatic enzymes by injured liver tissue.

Animals↗
PubMed1982

Lateral diffusion of ubiquinone during electron transfer in phospholipid- and ubiquinone-enriched mitochondrial membranes.

After fusion of small unilamellar phospholipid liposomes with mitochondrial inner membranes, the rate of electron transfer between membrane dehydrogenases and cytochrome c decreases as the average distance between integral membrane proteins increases, suggesting that electron transfer is mediated through a diffusional process in the membrane plane (Schneider, H., Lemasters, J. J., Höchli, M., and Hackenbrock, C. R. (1980)., J. Biol. Chem. 255, 3748-3756). The role of ubiquinone in this process was evaluated by fusing liposomes containing ubiquinone-10 or ubiquinone-6, with inner membranes. In control membranes enriched with phospholipid only, ubiquinol-cytochrome c reductase and NADH- and succinate-cytochrome c reductase activities decreased proportionally to the increase in bilayer lipid. These decreases were restored substantially in phospholipid plus ubiquinone-supplemented membranes. The degree to which restoration occurred was dependent upon the length of the isoprenoid side chain of the ubiquinone with the shorter chain length ubiquinone-6, always giving greater restoration than ubiquinone-10. It is concluded that electron transfer between flavin-linked dehydrogenases (Complexes I and II) and cytochrome bc1 (Complex III) occurs by independent, lateral diffusion of ubiquinone as well as independent, lateral diffusion of ubiquinone as well as the protein complexes within the plane of the membrane.

Animals↗
PubMed1982

Periportal and pericentral pyridine nucleotide fluorescence from the surface of the perfused liver: evaluation of the hypothesis that chronic treatment with ethanol produces pericentral hypoxia.

Pyridine nucleotide fluorescence made from the surface of the hemoglobin-free perfused rat liver was measured continuously by using a "micro-light guide" placed on selected periportal and pericentral regions of the liver lobule. From the portal oxygen tension at which pyridine nucleotide reduction first occurred in pericentral regions, the oxygen gradient across the liver lobule was estimated in livers from rats treated chronically with ethanol or sucrose. Chronic treatment with ethanol increased the average lobular oxygen gradient from 275 to 400 torr (1 torr = 133 Pa), primarily due to the increase in the oxygen gradient in pericentral regions. Ethanol treatment also increased hepatic oxygen uptake significantly, from 110 to 144 (mumol/g)/hr. Treatment with the antithyroid drug 6-propyl-2-thiouracil reversed the effect of ethanol on O2 uptake and on the lobular oxygen gradient. The oxygen gradients measured with the micro-light guide were confirmed by direct measurement of tissue oxygen tensions in periportal and pericentral areas by using an oxygen electrode. These data are consistent with the hypothesis that chronic treatment with ethanol causes the pericentral region of the liver lobule to become susceptible to hypoxic cellular injury. This may be responsible, at least in part, for the localized hepatotoxic effects of ethanol.

Animals↗
PubMed1982

Rates of alcohol dehydrogenase-dependent ethanol metabolism in periportal and pericentral regions of the perfused rat liver.

Infusion of ethanol into hemoglobin-free perfused rat liver caused an increase in NADH fluorescence (366 leads to 450 nm) which was measured with a large-tip (2-mm) light guide placed on the surface of the liver. A linear correlation (r = 0.83) was observed between the increase in NADH fluorescence and rate of ethanol uptake in the concentration range 0.05--2.0 mM. When a micro-light guide (tip diameter 170 micrometer) was placed on periportal or pericentral regions of the liver surface, the maximal fluorescence increase due to ethanol (2 mM) was 31.2 +/- 2.0 and 31.9 +/- 1.7% in periportal and pericentral regions, respectively. The infusion of 4-methylpyrazole (80 microM), an inhibitor of alcohol dehydrogenase, completely abolished the fluorescence increase in both regions, indicating that the changes are entirely attributable to perturbation of cofactor levels due to alcohol dehydrogenase-dependent ethanol metabolism. Using the correlation between the NADH fluorescence increase and rate of ethanol uptake, rates of ethanol metabolism in periportal and pericentral regions were calculated. Values for maximal ethanol uptake were identical in periportal and pericentral regions. Half-maximal ethanol uptake was observed at 0.24 and 0.25 mM ethanol in periportal and pericentral regions, respectively. These results indicate that the rates of alcohol dehydrogenase-dependent ethanol metabolism are similar in periportal and pericentral regions of the liver lobule.

Alcohol Dehydrogenase↗
PubMed1981

Non-equilibrium thermodynamics of oxidative phosphorylation by inverted inner membrane vesicles of rat liver mitochondria.

The relationship of the phosphate potential (delta GP) to the free energy released by the oxidation of NADH (redox potential or delta GR) was studied in suspensions of inverted inner membrane vesicles prepared from rat liver mitochondria. At delta GR values less negative than -52.2 kcal/mol, delta GP was a linear function of delta GR during oxidative phosphorylation at static head. At more negative delta GR, delta GP no longer increased but remained, more or less, at a constant value. At all values of delta GR, delta GP increased as Pi decreased. At high Pi, ATP/ADP was relatively independent of Pi, but at low Pi there was a strong interdependence of ATP/ADP and Pi. The experimental data were analyzed in terms of the theory of non-equilibrium thermodynamics. The degree of coupling, q, averaged 0.8 as estimated from the dependence of respiratory rate on delta GP. From measurements of -delta GR/delta GP at static head and from the estimates of q, an average value of four was calculated for Z, the phenomenological stoichiometry. The results support a 4-proton model of chemiosmotic coupling in which proton stoichiometries are 4H+/site, 3H+/ATPase, and 1H+/translocation of ATP for ADP and Pi. The results further indicate that the site by site reactions of oxidative phosphorylation operate close to thermodynamic equilibrium. This implies that ATP/site ratios are proportional to the redox potentials across each site at static head. Based on the oxidation-reduction potentials of NADH, ubiquinone, and cytochrome c, it follows that the ideal ATP/site ratios of mitochondrial oxidative phosphorylation are 1, 1/2, and 1 1/2, respectively, for sites 1, 2, and 3.

Adenosine Diphosphate↗
PubMed1981

Centrilobular injury following hypoxia in isolated, perfused rat liver.

Hypoxia was produced in isolated, hemoglobin-free, perfused rat liver by reducing the flow rate of oxygen-carrying fluid entering the organ. The procedure caused anoxia in centrilobular regions. In these anoxic areas, structural derangements developed rapidly, characterized by bleb-like protrusions of hepatocyte plasma membrane through fenestrations in the sinusoidal endothelium. Periportal tissue remained normoxic and was completely spared. Cellular injury resulting from localized anoxia may play an important role in the pathogenesis of centrilobular liver disease.

Animals↗