The composition of the liver lipids of sheep and the effect of early sporidesmin poisoning

The cellular and molecular toxicity of sporidesmin

The fungal metabolite sporidesmin is responsible for the hepatogenous photosensitising disease facial eczema in livestock. Toxicity is due to a sulfur-bridged epidithiodioxopiperazine ring that has wide biological reactivity. The ways in which the toxin causes hepatobiliary and other tissue damage have not been established. Hypotheses include direct interaction with cellular thiols including protein cysteine residues or production of reactive oxygen species resulting in oxidative stress. Comparison with the cellular effects of the structurally related compound gliotoxin suggests additional mechanisms including interaction with cell adhesion complexes and possible downstream consequences for regulated necrosis as a response to tissue injury. Revision of hypotheses of how sporidesmin affects cells has the potential to generate new strategies for control of facial eczema including through identification of proteins and genes that are associated with resistance to the disease.

Long-term exposure to chemicals in sewage sludge fertilizer alters liver lipid content in females and cancer marker expression in males

BACKGROUND

The increased incidence of diseases, including metabolic syndrome and infertility, may be related to exposure to the mixture of chemicals, which are ubiquitous in the modern environment (environmental chemicals, ECs). Xeno-detoxification occurs within the liver which is also the source of many plasma proteins and growth factors and plays an important role in the regulation of homeostasis.

OBJECTIVES

The objective of this study was to investigate the effects of ECs on aspects of liver function, in a well characterized ovine model of exposure to a real-life EC mixture.

METHODS

Four groups of sheep (n = 10-12/sex/treatment) were maintained long-term on control or sewage sludge-fertilized pastures: from conception to culling at 19 months of age in females and from conception to 7 months of age and thereafter in control plots until culling at 19 months of age in males. Environmental chemicals were measured in sheep livers and RNA and protein extracts were assessed for exposure markers. Liver proteins were resolved using 2D differential in-gel electrophoresis and differentially expressed protein spots were identified by liquid chromatography/tandem mass spectroscopy.

RESULTS

Higher levels of polycyclic aromatic hydrocarbons (PAHs) and lower levels of polychlorinated biphenyls (PCBs) in the livers of control males compared to control females indicated sexually dimorphic EC body burdens. Increased levels of the PAHs Benzo[a]anthracene and chrysene and reduced levels of PCB 153 and PCB 180 were observed in the livers of continuously exposed females. EC exposure affected xenobiotic and detoxification responses and the liver proteome in both sexes and included major plasma-secreted and blood proteins, and metabolic enzymes whose pathway analysis predicted dysregulation of cancer-related pathways and altered lipid dynamics. The latter were confirmed by a reduction in total lipids in female livers and up-regulation of cancer-related transcript markers in male livers respectively by sewage sludge exposure.

CONCLUSIONS

Our results demonstrate that chronic exposure to ECs causes major physiological changes in the liver, likely to affect multiple systems in the body and which may predispose individuals to increased disease risks.

Separation of some neutral lipids by normal-phase high-performance liquid chromatography on a cyanopropyl column: ubiquinone, dolichol, and cholesterol levels in sheep liver

The normal-phase high-performance liquid chromatographic separation of neutral lipids into molecular classes was carried out on a cyanopropyl (CN) column eluted with isopropanol in hexane. Cholesteryl, retinyl, and dolichyl esters, triglycerides and vitamin E, ubiquinone, dolichol, phytol, and cholesterol eluted as separate peaks with 0.05% isopropanol in hexane. Cholesterol, retinol, diglyceride, and monoglyceride eluted as separate peaks with 0.75% isopropanol in hexane. These separations could not be achieved on a silica gel column. The method was used to assay sheep liver ubiquinone, dolichol, and cholesterol levels, that were determined as 77, 108 and 1864 micrograms/g wet wt, respectively.

Studies of liver lipids in normal, alloxan-diabetic and pregnancy-toxaemic sheep

Triacylglycerols were the major lipid class in the fatty livers from alloxan-diabetic sheep and those suffering from pregnancy toxaemia, with the concentrations increased by 15- and 25-fold, respectively, compared with the normal state. Analysis of the fatty acid composition of total liver triacylglycerols in these animals showed a significant decrease in the proportion of saturated fatty acids, 16:0 and 18:0, and increase in the proportion of polyunsaturated fatty acids (18:2 omega 6, 18:3 omega 3 and 20:4 omega 6), particularly in those with pregnancy toxaemia. In contrast, total liver phospholipids showed a significant increase in the proportion of 18:0 in ewes with pregnancy toxaemia and a significant decrease in a range of polyunsaturated fatty acids in both the diabetic and toxaemic animals. Also, although the concentration of both phosphatidylcholine and phosphatidylethanolamine increased in the diabetic livers the ratio of phosphatidylcholine/phosphatidylethanolamine fell significantly, from 2.22 in the control animals to 1.59. The data suggest that, following the large influx of plasma fatty acids into the ovine liver in diabetes and pregnancy toxaemia, there is a diversion of polyunsaturated fatty acids from phospholipids to triacylglycerols. In diabetic sheep these changes may in turn affect phosphatidylcholine synthesis via the methylation pathway in liver. These changes in lipid composition may, in part, explain the degenerative changes in membrane and subcellular organelle structure and the failure of liver function observed both in advanced diabetes and in severe pregnancy toxaemia.

Fatty acid composition of liver lipids of young lambs

1. The changes in the lipid compositon of livers from lambs receiving either ewe's milk or a reconstituted low-fat milk powder have been studies during the first 8 d after birth.

2. At birth the phospholipid and unesterified fatty acid fractions constituted the major proportion of the liver lipids. In the lambs on the artificial diet the relative concentration of the phospholipid fraction increased and there were corresponding decreases in the relative concentrations of all the other fractions, whereas in the naturally fed lambs the relative concentration of the phospholipids remained similar to that found in the livers at birth.

3. In the liver lipids at birth there were only low concentration of the C18polyunsaturated fatty acids, althoughts there were appreciable concentrations of the higher C20and C22polyunsaturated fatty acids.

4. After birth there was a large increase in the concentration of the C18polyunsaturated fatty acids in the livers of the lambs on the natural diet and a decrease in the 20:3ω9:20:4ω6 (triene:tetraene) ratio. In the lambs receiving the artificial diet the concentration of the C18polyunsaturated fatty acids and the trience:tetraene ration remained similar to that observed at birth.

5. These changes are discussed in relationship to the metabolism of the essential fatty acid in monogastric animals.