Showing papers by "Irwin M. Arias published in 1980"

Long-term cultures of normal rat hepatocytes on liver biomatrix.

Abstract: A major stumbling block in liver cell studies has been an inability to maintain functional hepatocytes in vitro for more than a few weeks.’-4 As is typical with most differentiated epithelial or epithelioid cells, hepatocytes either die or dedifferentiate in culture. We have recently proposed that such difficulties are due to the cell culture technique of dissociating a cell type away from the tissue matrix in which exists “socio-cellular” variables critical for the maintenance of the differentiated cell state.‘ These “sociocellular” variables include the components of the extracellular matrix, the basement membrane and ground substance, and the signals from cell-cell interactions (soluble signals). Therefore, to culture differentiated cells and have them retain their differentiated state, we proposed that one must simulate the crucial “sociocellular” variables in vitro. In our initial efforts to ascertain these variables, we have focused upon a ubiquitous and presumably primary cell-cell relationship, the epithelial-mesenchymal relationship. In vivo normal epithelial cells capable of proliferation or long-term survival are attached to a basement membrane which, in turn, is associated with mesenchymally-derived cells, most commonly fibroblasts. The basement membrane, a layer of secretion located between and produced by the epithelium and the mesenchymal cells, is assumed to contain the extracellular, solidstate subset of factors in the interaction. In the early studies, we used mixtures of extracellular matrix components made with purified components. Although a simplistic approach to the problem, these methods indicated that basement membrane components could significantly lengthen the life of certain differentiated cells, insulinoma cells and prostatic epithelial cells.”’ More recently, new procedures have been introduced that supercede the earlier ones and which provide methods for the isolation and use of extracellular matrix components as substrates for cell cultures.6’ The fibrous material isolated by these new procedures is referred to as biomatrix and is a complex mixture of collagens, noncollagenous proteins and carbohydrates. It can be isolated from any tissue although the yields vary significantly from one tissue to another. Tissues such as liver, with small amounts of stroma, give 1-2 gms/100 gms tissue, whereas tissues with extensive stroma or smooth muscle, such as colon or prostate, provide high yields ( 1 5-22 gms/ 100 gms tissue).

Ligandin: an adventure in liverland.

Abstract: Ligandin is an abundant soluble protein which has at 1/2 of 2–3 days, is induced by many drugs and chemicals, and is stabilized in the absence of thyroid hormone. The protein is strategically concentrated in cells associated with transport and detoxification of many endogenous ligands, such as bilirubin, and exogenous ligands, such as drugs and chemicals. The protein is a dimer in rat liver. Whether the dimer is a primary gene product or at least two genes are involved is not known. The protein has broad, low affinity catalytic activity as a GSH-S-transferase for many ligands having electrophilic groups and hydrophobic domains. It catalyzes formation of GSH conjugates, noncovalently binds some ligands prior to their biotransformation or excretion in bile, and covalently binds other ligands, such as activated carcinogens. Recent studies include the possible role of ligandin in chemical carcinogenesis, diagnosis of inflammatory and neoplastic disease of the liver and kidney, and participation in intracellular transport. Although some of the roles that have been outlined are speculative, any single function is important. The GSH-Stransferases are primitive enzymes and non specific binding proteins but “it is precisely their simplistic design that allows such protean serviceability”. Ligandin illustrates a group of hepatic disposal mechanisms which involve bulk transport of ligands. Although specific uptake and transport mechanisms have been described for several hormones which enter the hepatocyte in small quantities and regulate intermediary metabolism and, possibly, cell maturation, bulk transport of ligands into, through and out of the liver involves mechanisms which accomodate many metabolites, drugs and chemicals of diverse structure. The liver is bathed in sewage which contains what we ingest or are injected with and potentially toxic products of intestinal microorganisms. The chemical formulas of the many substances which are metabolized by the liver provide a horror show of potentially reactive and toxic metabolites, mutagens and carcinogens. Despite this alimentary “Love Canal”, we and our livers do remarkably well. These hepatic disposal mechanisms, as exemplified by ligandin, evolved in ancient times. They are present, albeit sluggishly, in insects and ancient elasmobranchs. Hepatic uptake and removal mechanisms of high capacity, modest affinity and broad substrate range permit us to live in what has probably always been a threatening world.

Bilirubin conjugation in the spiny dogfish, Squalus acanthias, the small skate, Raja erinacea and the winter flounder, Pseudopleuronectes americanas

Abstract: 1. 1. Bile pigments from spiny dogfish (Squalus acanthias), small skate (Raja erinacea) and winter flounder (Pseudopleuronectes americanas) were quantitated after chromatography of tetrapyrroles and azopigment analysis. 2. 2. Bilirubin monoglucuronide, unconjugated bilirubin, bilirubin diglucuronide and unidentified pigments were present in decreasing order of abundance. 3. 3. UDPglucuronate glucuronyl transferase and bilirubin glucuroniside glucuronosyl transferase activities were present in all three fish livers, and had temperature optima of 37°C. 4. 4. The distribution of the two enzyme activities were different in liver fractions of the three fish.