Ethionine, an analogue of methionine, induces fatty liver in rats by inhibiting protein synthesis, including that of apolipoproteins in liver. Ethionine was administered to cows to elucidate the participation in fatty liver development of impaired triglyceride secretion from liver attributable to decreased apolipoprotein synthesis. The administration resulted in a significant increase of liver triglyceride contents. Several apolipoproteins were found to have decreased concentrations. In particular, apolipoprotein B-100 in very low-density (0.95 to 1.006 g/ml) lipoprotein and in low-density (1.006 to 1.063 g/ml) lipoprotein fractions was greatly reduced. The decreases of apolipoprotein B-100 concentrations in the 2 lipoprotein fractions were at least partly correlated to the decreased triglyceride concentrations in the respective fractions. Decreased concentrations of apolipoprotein A-I in high-density (1.063 to 1.210 g/ml) lipoprotein were also observed, although not as distinctly as with apolipoprotein B-100. Total cholesterol and phospholipid concentrations in low- and high-density lipoprotein fractions were decreased. The decrease in cholesterol was attributed to reduced concentrations of cholesteryl esters. It was suggested that the impaired lipid secretion from liver attributable to the decreased apolipoprotein concentrations has a role in ethionine-induced fatty liver of cows.

OBJECTIVE To use proteomic analysis to determine the protein constituents of synovial fluid samples from the stifle joints of dogs with and without osteoarthritis secondary to cranial cruciate ligament rupture (CCLR). ANIMALS 12 dogs with clinically normal stifle joints (controls) and 16 dogs with osteoarthritis secondary to CCLR. PROCEDURES A synovial fluid sample was obtained from all dogs. Synovial fluid total protein concentration was determined by the Bradford assay. Proteins were separated by use of a 1-D SDS-PAGE to detect protein bands that differed between dogs with and without osteoarthritis. Those protein bands then underwent trypsin digestion and were analyzed by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry, the results of which were compared with a curated protein sequence database for protein identification. One of the most frequently identified proteins, apoprotein (apo) A-I, was then quantified in all synovial fluid samples by use of a competitive-inhibition ELISA. Results were compared between dogs with and without osteoarthritis. RESULTS Median synovial fluid total protein and apo A-I concentrations for dogs with osteoarthritis were significantly greater than those for control dogs. The most abundant proteins identified in the synovial fluid were albumin and apo A-I. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that quantification of synovial fluid total protein and apo A-I concentrations might facilitate diagnosis of osteoarthritis secondary to CCLR in dogs. Further research and validation of synovial fluid apo A-I concentration as a biomarker for osteoarthritis in dogs are necessary before it can be recommended for clinical use.