dinitrobenzenes and Liver-Diseases

Petroleum oil enters the coastal marine environment through various sources; marine mammals such as sea otters that inhabit this environment may be exposed to low concentrations of petroleum hydrocarbons through ingestion of contaminated prey. The inability to perform controlled studies in free-ranging animals hinders investigations of the effects of chronic petroleum oil exposure on sea otter morbidity and mortality, necessitating the development of a reliable laboratory model. We examined the effects of oral exposure to 500 ppm bunker C fuel oil over 113-118 days on American mink, a species phylogenetically related to the sea otter. Hematological parameters and organs were examined for fuel oil-associated changes. Hepatic cytochrome P4501A1 mRNA expression and fecal cortisol concentrations were also measured. Ingestion of fuel oil was associated with a decrease in erythrocyte count, hemoglobin concentration (Hgb), hematocrit (HCT), and an increase in mean corpuscular volume (MCV). Total leukocytes were elevated in the fuel oil group from increases in neutrophils, lymphocytes, and monocytes. Significant interactions between fuel oil and antigen challenge were found for erythrocyte parameters, monocyte and lymphocyte counts. Liver and adrenal weights were increased although mesenteric lymph node weights were decreased in the fuel oil group. Hepatic cytochrome P4501A1 mRNA was elevated in the fuel oil group. Fecal cortisol concentration did not vary between the two groups. Our findings show that fuel oil exposure alters circulating leukocyte numbers, erythrocyte homeostasis, hepatic metabolism and adrenal physiology and establish a framework to use mink as a model for sea otters in studying the systemic effects of marine contaminants.

Topics: Animals; Chemical and Drug Induced Liver Injury; Cytochrome P-450 CYP1A1; Dinitrobenzenes; Erythrocyte Count; Feces; Fuel Oils; Hemoglobins; Histocytochemistry; Hydrocortisone; Leukocyte Count; Liver Diseases; Male; Mink; Models, Animal; Organ Size; Otters; Random Allocation; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Water Pollutants, Chemical

In human liver homogenate the formation of bile acid-CoA thioesters is localized both to the microsomal fraction catalysed by an ATP-dependent synthetase and to the peroxisomal fraction catalysed by the thiolase in the last step of the beta-oxidative cleavage of the 5beta-cholestanoyl side chain. The cytosolic bile acid-CoA:amino acid N-acyltransferase catalyse the conjugation of the CoA-activated bile acids with taurine or glycine prior to secretion into bile. The formation of bile acid-CoA esters is considered the rate-limiting step in bile acid amidation. So far, a bile acid-CoA cleaving activity has not been assessed in the research of bile acid amidation in human liver. In this work, a bile acid-CoA cleaving activity has been demonstrated at a rate that may influence the concentration of bile acid-CoA thioesters, free bile acids and amidated bile acids within the hepatocyte. Recently, it was shown that free chenodeoxycholic acid, formed by the thioesterase, is the physiological ligand of the farnesoid X receptor. A multiorganelle distribution of the bile acid-CoA hydrolytic activity was found. In the postnuclear fraction of human liver homogenate, apparent Km and Vmax for the cleavage of choloyl-CoA were 7.7 x 10-5 mol/L and 3.6 nmol x mg-1 x min-1 respectively. The corresponding values for chenodeoxycholoyl-CoA cleavage were 7.1 x 10-5 mol/L and 4.8 nmol x mg-1 x min-1. Hydrolytic activities were detected in the microsomal and the peroxisomal fractions where the bile acid-CoA esters are formed as well as in cytosol housing the N-acyltransferase activity. Compared to the bile acid-CoA synthetase activities, the hydrolytic activities were considerably higher, both in the postnuclear fraction and in the microsomal fraction. The thioesterase activities were in the same range as detected for the N-acyltransferase activities both in the postnuclear fraction and in the cytosolic fraction. The mere presence of thioesterase in microsomes, peroxisomes and cytosol seems counterproductive to bile acid amidation. The thioesterases may have an indirect regulatory function on the bile acid synthesis and are important for the regulation of bile acid synthesis by providing free chenodeoxycholic acid, the most potent activator of the farnesoid X receptor.

Topics: Acyltransferases; Bacterial Proteins; Bile Acids and Salts; Carbon Radioisotopes; Chenodeoxycholic Acid; Cholic Acid; Cysts; Dinitrobenzenes; Enzyme Activation; Humans; Liver; Liver Diseases; Peroxisomes; Protein Binding; Subcellular Fractions; Thiolester Hydrolases