Fatty Liver Tissue Research Articles

Lack of UCP2 reduces fas-mediated liver injury in ob/ob mice and reveals importance of cell-specific UCP2 expression

Fatty liver is vulnerable to conditions that challenge hepatocellular energy homeostasis. Lipid-laden hepatocytes highly express uncoupling protein-2 (UCP2), a mitochondrial carrier that competes with adenosine triphosphate (ATP) synthesis by mediating proton leak. However, evidence for a link between UCP2 expression and susceptibility of liver to acute injury is lacking. We asked whether absence of UCP2 protects ob/ob mice from Fas-mediated acute liver damage. UCP2-deficient ob/ob mice (ob/ob:ucp2-/-) and UCP2-competent littermates (ob/ob:ucp2+/+) received a single dose of agonistic anti-Fas antibody (Jo2). Low-dose Jo2 (0.15 mg/kg intraperitoneally) caused less serum alanine aminotransferase (ALT) elevation and lower apoptosis rates in ob/ob:ucp2-/- mice. High-dose Jo2 (0.40 mg/kg intraperitoneally) proved uniformly fatal; however, ob/ob:ucp2-/- mice survived longer with less depletion of liver ATP stores, indicating that fatty hepatocytes may benefit from lack of UCP2 during Jo2 challenge. Although UCP2 reportedly controls mitochondrial oxidant production, its absence had no apparent effect on fatty liver tissue malondialdehyde levels augmented by Jo2. This finding prompted us to determine UCP2 expression in Kupffer cells, a major source of intrahepatic oxidative stress. UCP2 expression was found diminished in Kupffer cells of untreated ob/ob:ucp2+/+ mice, conceivably contributing to increased oxidative stress in fatty liver and limiting the impact of UCP2 ablation. In conclusion, whereas UCP2 abundance in fatty hepatocytes exacerbates Fas-mediated injury by compromising ATP stores, downregulation of UCP2 in Kupffer cells may account for persistent oxidative stress in fatty liver. Our data support a cell-specific approach when considering the therapeutic effects of mitochondrial uncoupling in fatty liver disease.

Identification of 7‐Hydroperoxycholesterol in Human Liver by Liquid Chromatography‐Mass Spectrometry

A liquid chromatography-mass spectrometry with an atmospheric chemical ionization interface has been developed to identify simultaneously various oxygenated cholesterols in lipid extracts from alcoholic fatty liver. We collected human liver tissues from alcoholic and control subjects at autopsy. We purified the lipid extracts with solid phase extraction and injected them onto a spherisorb ODS column, by using methanol that contained 10 mM ammonium acetate as a mobile phase and a flow rate of 0.7 ml/min. We found the presence of 7-hydroperoxycholesterol and other oxysterols (5-cholesten-3beta-ol-7-one, cholest-5-ene-3beta, 7-diol, and 5, 6beta-epoxy-5beta-cholestan-3beta-ol) in alcoholic fatty liver tissues. We assume that long-term ethanol ingestion leads to excessive oxidative stress and to the accumulation of cholesterol-derived hydroperoxides and oxysterols in alcoholic fatty liver.

Quantitation of lipid in biological tissue by chemical shift magnetic resonance imaging

A method combining several previously used approaches is described for the rapid, accurate quantitation of the fat content of biological tissue based on chemical shift images (CSI) corrected for magnetic field inhomogeneity, and compensated for T1 and T2 effects. The gravimetrically determined lipid content of fatty tissues (pork fat, rabbit and human liver) that had been differentially depleted of lipid by chloroform extraction correlated well (r = 0.99) with the lipid image intensities of the respective tissues. This multi-point CSI method was used to quantitate lipid in fresh fatty human liver tissue (wet and dry) containing varying amounts of lipid. Plots of integrated lipid intensity versus tissue lipid content gave straight parallel lines for hydrated (r = 0.94) and dehydrated (r = 0.98) tissues, permitting determination of a proportionality constant for measuring absolute amounts of lipid present in a specific biological tissue. These results suggest the feasibility of using the method in vivo for absolute quantitation of lipid in tissues of agricultural (e.g. pork, beef) and medical (e.g. human liver) interest.

Proton chemical shift imaging: an evaluation of its clinical potential using an in vivo fatty liver model.

The potential laboratory and clinical utility of proton chemical shift imaging (PCSI) was evaluated by studying fatty liver change in rats, which offered a simple animal model for tissue lipid buildup. There was excellent correlation between lipid group signal intensities from in vivo PCSI studies and liver triglyceride levels obtained from in vitro measurements (R = 0.97). The in vivo T1 relaxation time measurements in fatty liver tissue demonstrated two distinct populations of nonexchanging protons. We explain the reason for the lack of sensitivity in conventional magnetic resonance (MR) imaging studies of fatty liver change and discuss the implications of our findings for MR imaging studies of other tissues. PCSI promises improved diagnostic sensitivity and specificity in studying a wide range of human pathologic conditions.

On the Frequency Dependence of Attenuation in Normal and Fatty Liver

Abstruct-The frequency dependence of the attenuation has been investigated in normal and fatty liver samples in vitro. It was observed that normal liver samples exhibited essentially a linear frequency dependent attenuation, while fatty livers exhibited a power law dependence, where the exponent n was between 1.25-1.4. In order to explain this nonlinear behavior, fatty liver has been modeled as consisting of normal liver tissue which is infiltrated by a large number of tiny fat globules which are 4-10 in size and occasionally coalesce to 100 p, and thus act as Rayleigh scatterers in the diagnostic wavelength range. The addition of these scatterers is consistent with the clinical observation of increased echogenicity in fatty livers. Based on this physical description, the attenuation in fatty liver tissue has been modeled as consisting of a linear absorption term, and a fourthader Rayleigh scattering term. This model predicts that the quantity (n - l) is proportional to the fractional contribution of scattering to the total attenuation. For fatty livers the attenuation contribution due to scatter amounts to 8-13 percent, compared to 21 percent for normal livers.

Lymphocyte Subsets Studied with Monoclonal Antibodies in Liver Tissues of Patients with Alcoholic Liver Disease

In order to determine the nature of T lymphocytes accumulating in hepatic tissues of patients with alcoholic liver disease, we phenotyped these cells in situ, using monoclonal antibodies to lymphocyte surface antigens and the avidin-biotin-peroxidase complex (ABC) technique. In portal areas of cirrhotic livers, a significant increase (p less than 0.001) in T lymphocytes was observed as compared to livers showing only fatty changes and normal liver tissues. The T cells accumulating in cirrhotic livers comprised T helper-inducer (T4) and T suppressor-cytotoxic (T8) subsets with the T4/T8 ratio of 1.4 +/- 0.5 (SD, n = 14). In contrast, the T lymphocytes in the cellular projections which extended into the parenchyma consisted mostly of suppressor-cytotoxic cells. The relative enrichment in T8+ lymphocytes among the cells invading the parenchyma suggests that they may be important in the mediation of a cytotoxic injury of hepatocytes in advanced alcoholic liver disease and in regulating an immunologic challenge possibly initiated in response to alcoholic hyaline.

THE RELATION OF FATTY DEGENERATION TO THE OXIDATION OF PURINES BY LIVER CELLS

These experiments show that it is possible to cause, by the proper use of hydrazine and phosphorus, a very high degree of fatty change in the liver with a minimum of necrosis, involving alike both peripheral and central portions of the lobule and thus eliminating the " factor of safety" or residual normal cells. Nevertheless, it is found that such fatty liver tissue has not lost in the least its power to oxidize uric acid when acting upon it in vitro with abundant air supply, nor is the power to oxidize xanthine to uric acid noticeably diminished. Since these two enzymes, and especially the uricolytic enzyme, are about the last to appear in the development of the animal kingdom and also of the individual mammal, it is to be expected that they will be among the first of the enzymes to be destroyed by injurious agencies, but evidently they are not affected by conditions that lead to the highest degree of fatty metamorphosis of the cytoplasm of the hepatic cells. While these experiments merely prove that extreme fatty degeneration does not destroy or appreciably diminish the power of liver cells to oxidize uric acid and xanthine in vitro, yet they suggest that in general fatty degeneration is probably not essentially incompatible with a high degree of metabolic activity by the affected cells. It is possible that in the living tissue functional activity may be decreased secondarily by fatty metamorphosis, as, for example, by the enlarged fatty cells compressing the capillaries and reducing circulatory activity, or by modification of diffusion through the cell by the fat deposits, independent of any deleterious influence upon the cellular enzymes themselves. Other experiments will be required to determine whether steatogenic poisons leave intrahepatic enzymes other than the uricase equally unaffected, but as it has already been shown by Jacoby that the autolytic enzymes and aldehydase in the liver cells are not destroyed by phosphorus poisoning, and Abderhalden and Schittenhelm* found that peptids are hydrolyzed fully as rapidly by phosphorus livers as by normal livers, it seems probable that extreme fatty metamorphosis is not associated with any serious injury to the enzymes by which the liver cells perform their metabolic functions, with the possible exception of those enzymes concerned with the metabolism of fats.