Hugo O. Jauregui

Trypan blue dye uptake and lactate dehydrogenase in adult rat hepatocytes—Freshly isolated cells, cell suspensions, and primary monolayer cultures

SummaryLeakage of lactate dehydrogenase and staining by the vital dye trypan blue were investigated in adult rat hepatocytes at the time of isolation, in suspensions up to 3 h and in primary monolayer cultures up to 3 d. These two parameters of plasma membrane integrity were found to correlate closely in hepatocyte suspensions, but to a lesser degree in monolayer cultures. Functional activity was demonstrated in culture by glucose consumption and lactic acid production. There was a balance of total lactate dehydrogenase (LDH) activity over time for both hepatocyte suspensions and cultures. Loss of LDH activity in the cell fraction was accompanied by a corresponding increase in enzyme activity in the media fraction. Lactate dehydrogenase activity per dye-excluding hepatocyte was calculated to be 9.2±1.5×10−6 IU assayed at 37°C for 25 preparations of isolated hepatocytes.The results suggest that leakage of cytoplasmic enzyme and vital dye staining are of comparable sensitivity in evaluating hepatocyte preparations. Measurement of LDH leakage offers a less subjective alternative to cell counting procedures and is applicable to both attached and suspended cells.

Gastric adenocarcinoma: Prognostic significance of several pathologic parameters and histologic classifications

Considerable controversy exists about the value of histologic classifications of gastric adenocarcinoma in the prediction of patient survival. Histologic sections of 75 consecutive gastrectomies were used to compare Lauren and Ming classifications with emphasis on clinical stage, size, location of tumor, desmoplasia, inflammatory reaction, and 5-year survival. Both classifications generally correlated and, when combined, proved helpful in defining certain cases. At surgery, about one third of the total cases of intestinal (INT, Lauren) and expanding (ET, Ming) were in early stages, whereas almost all the diffuse (DT, Lauren) and infiltrative (INF, Ming) types were in late stages. When the Lauren classification was applied to preoperative endoscopic biopsies, a 72% diagnostic correlation with the surgical specimens was found. Followup revealed no survivors of the DT and INF and 12 and 11 survivors of INT and ET, respectively, regardless of stage. Inflammatory response was associated with good prognosis. Desmoplasia and size had no prognostic significance. Tumors of the cardia had worse prognoses than those in the body or antrum. Both Lauren and Ming classifications, and especially the degree of inflammation, were significant in predicting survival. Lauren INT and Ming ET should be declared only when they are the sole or predominant features.

Lectin binding to parietal cells of human gastric mucosa.

A light microscopic and ultrastructural analysis of lectin receptors on parietal cells from human gastric mucosa was performed utilizing 12 biotinylated lectins in conjunction with an avidin-biotin-peroxidase complex. Peanut agglutinin conjugated directly to peroxidase was also used. Several fixatives and fixation regimens were evaluated for optimal preservation of parietal cell saccharide moieties. Formalin proved to be the most practical fixative for light microscopic studies. A periodate-lysine-paraformaldehyde (PLP) combination provided good preservation of lectin binding capacity but yielded relatively poor ultrastructure. Conversely, glutaraldehyde provided excellent preservation of ultrastructure but a somewhat diminished lectin binding activity, which was overcome by using long incubation times and high concentrations of reagents. Parietal cells reacted strongly with Bandieraea simplicifolia, Dolichos biflorus, peanut agglutinin, and soybean agglutinin (all specific for galactosyl/galactosaminyl groups) and weakly with Ulex europaeus (specific for fucose). At the light microscopic level a beaded, perinuclear staining pattern was observed which, ultrastructurally, corresponded to an intense staining of intracytoplasmic canaliculi. The membranes of the intracytoplasmic canaliculi were characterized by an abundance of galactosyl residues, a paucity of fucosyl groups, and a lack of mannosyl and glucosyl residues. The biochemical and physiological significance of these findings is discussed.

PRIMARY CULTURES OF RAT HEPATOCYTES IN HOLLOW FIBER CHAMBERS

SummaryHepatocyte culture may represent an alternative to the use of animals to study drug detoxification by the liver. An ideal in vitro system should closely mimic the in vivo environment by providing continuous media perfusion and oxygenation, and should facilitate sampling of cells and culture media. To meet these criteria, a hollow fiber bioreactor seeded with isolated rat hepatocytes was developed and tested by measuring the formation of three products of the oxidative metabolism of diazepam and the glucuronidation of phenolsulfonphthalein (PSP). To compare the performance of conventional monolayer culture to that of the bioreactor system, diazepam metabolism was studied for 45 days in both systems. The oxygen dependency of diazepam metabolism was evaluated by perfusing the bioreactor in an oxygen-rich atmosphere (30%). Total diazepam metabolism was twofold higher in the O2-rich perfused hollow fiber cultures than in the cultures perfused under normal conditions, reflecting an increase in temazepam and oxazepam production. Diazepam detoxification activity was significantly enhanced by oxygen (P≤0.001) over the life of the perfused cultures. PSP metabolism was similar in all three culture systems. By Day 10, diazepam metabolism in the oxygenated bioreactor system was 44% of the in vivo activity of rat hepatocytes. This activity dropped to 30% by Day 25 of culture. These results justify the use of perfused culture systems for in vitro detoxification studies as an alternative to animal use and emphasize the capacity of a culture device perfused under O2-enriched conditions to maintain long-term P450 activity of rat hepatocytes.

Phenolsulfonphthalein (phenol red) metabolism in primary monolayer cultures of adult rat hepatocytes

SummaryThe sulfonic acid dye, phenolsulfonphthalein (PSP or phenol red), has been incorporated as a pH indicator in many tissue culture media formulations since the emergence of tissue culture methodologies. The present study was designed to examine the pathway, time course, and degree of metabolism of this anionic dye in monolayer cultures of adult rat hepatocytes. Thin layer chromatographic studies coupled with β-glucuronidase studies show that glucuronidation is the major metabolic pathway for PSP in vitro. About 20% of the dye is metabolized in the first 24 h, but this functional activity is decreased by approximately half at 48 h, and even further at 72 h of culture. This metabolic activity was not affected by continuous exposure to the dye. The effect of PSP concentration on its rate of metabolism by the adult rat hepatocyte in culture seemed to be biphasic, and at concentrations of less than 100µM there was indication of a saturable process. Although PSP seemed not to be toxic to hepatocyte cultures, it is partially metabolized by these cells (as opposed to no observed metabolism in human fibroblasts or HeLa cells). Therefore, its incorporation into tissue culture media formulations for use in hepatocyte cultures should be avoided, especially when studying the mechanism(s) of glucuronidation or metabolic pathways thought to be affected by this anionic dye.

A quantitative analysis of lectin binding to adult rat hepatocyte cell surfaces.

SummaryA quantitative evaluation of lectin binding to adult rat hepatocyte cell surfaces was done using cells isolated by two different collagenase perfusion methodologies and cultured as monolayers with two different tissue culture media formulations (protocol I vs. protocol II). The presence of α-D-mannosyl and α-D-glucosyl groups was detected by the binding of Concanavalin A (Con A), Lens culinaris agglutinin (LCA), and Pisum sativum agglutinin (PSA) to freshly isolated cells. Furthermore, β-D-galactose [Ricinus communis agglutinin (RCA)] and sialic acid residues [wheat germ (WGA)] were also found. Protocols I and II served as models for evaluation of: a) the stripping effect of collagenase separation procedures, b) the restoration in culture of collagenase-stripped sugar residues, c) the effect of the culture environment on cell viability [as measured by lactic acid dehydrogenase (LDH) leakage] and the protein content of hepatocytes, and d) the presence of cell surface sugar residues as a function of culture duration. The ultrastructural morphology of freshly isolated and cultured hepatocytes was also evaluated. These studies indicated that a decline in lectin binding invariably occurred earlier than a massive leakage of LDH and a decrease in the protein content of the cells in culture. Ultrastructurally, autophagocytosis was an early phenomenon in cells isolated and cultured by protocol I, which was also inferior to protocol II regarding the preservation of hepatocyte glycocalyces. Sugar residues lost due to the collagenase-stripping effect were restored, as shown by lectin binding, within the first 24 h of culture. This stripping effect was confirmed by quantitative evaluations of lectin binding to hepatocytes in culture after an incubation with collagenase. This study shows that the binding of peroxidase-labeled lectins is a useful tool for quantitative evaluation of the sugar composition of hepatocyte cultures.

Hepatocyte cell surface polarity as demonstrated by lectin binding.

We performed an investigation at the ultrastructural level of the differential distribution of lectin-binding sites among sinusoidal, lateral, and bile canalicular domains of adult rat hepatocytes. Lectin binding to hepatocyte glycocalices was studied in situ or after cellular dissociation by enzymatic (collagenase), chemical (EDTA), and mechanical methods, as well as during cell culture. Using thirteen biotinylated lectins and an avidin-biotin-peroxidase complex (ABC), we have identified lectin-binding sites that are predominantly localized in the bile canalicular [Ricinus communis agglutinin (RCA)] or sinusoidal [Phaseolus vulgaris (PHA)] domains in situ and in mechanically dissociated cells. Lens culinaris (LCA) staining was prominent on sinusoidal surfaces, slight along lateral surfaces, and completely absent in the bile canalicular domain. Concanavalin A (ConA) was unique in binding equally to all domains. Triticum vulgaris [wheat germ agglutinin (WGA)] was also bound to all domains, but most intensely to the bile canalicular region. Cells dissociated via collagenase or EDTA treatment exhibited a spherical morphology characterized by many surface microvilli and absence of morphological domains. Lectin binding to dissociated cells was uniformly distributed over the entire cell surface, suggesting a redistribution of lectin receptors that was independent of the separation procedure. Hepatocytes in culture exhibited a partial restoration of morphological domains, but lectin binding polarity was not re-established.

Ponceau S: A sensitive method for protein determination in freshly isolated and cultured cells

A protein assay method is described that involves simultaneous dye binding and precipitation of protein. It has a sensitivity comparable to the widely used Lowry and Bradford methods without the chemical interferences sometimes encountered with these methods in tissue culture conditions. The assay uses readily available reagents and is applicable to a variety of cell preparations.

Influence of different substrates in detoxification activity of adult rat hepatocytes in long-term culture: implications for transplantation.

Substrates used to immobilize hepatocytes for transplantation govern attachment and long-term metabolic activity of these cells. The choice of these substrates is based on the familiarity with proteinaceous materials that are constituents of the extracellular matrix. The use of substrates that recognize carbohydrates on the cell surface may provide an alternative method to attach adult mammalian hepatocytes. In this study, immobilized lectins on tissue culture plasticware were used to support hepatocyte attachment. Long-term cultures with these substrates were compared with control cultures seeded on a mixture of collagen types I and III (Vitrogen). To evaluate the attachment efficiency and long-term maintenance of diazepam metabolic activity of hepatocytes seeded on different commercially available plasticware, four different types of polymers (supplied as 60-mm dishes) were tested. Diazepam, a benzodiazepine metabolized by the P450 intracytoplasmic pathway, is associated with a synaptic receptor (GABA-benzodiazepine receptor) which plays an important role in hepatic coma. Polymethylpentene, a derivative of polypropylene treated by plasma discharge, was the best polymer to maintain P450 phenotypic expression, although other polymers provided similar cell attachment efficiencies. The amounts of adsorbed concanavalin A, Arachis hypogaea (peanut), Lens culinaris, and Pisum sativum agglutinin correlate with the percentage values of hepatocyte attachment. Cell attachment to wheat germ agglutinin increased with increased lectin concentrations in spite of constant amounts of adsorbed lectin, whereas hepatocyte attachment to Bandieraea simplicifolia agglutinin was lower and did not change at different lectin concentrations. Long-term cultures of hepatocytes seeded on Vitrogen, concanavalin A, or wheat germ agglutinin showed similar diazepam metabolic activities up to the 10th day, but by day 25, cells seeded on Vitrogen metabolized diazepam at higher values. This study showed that a polymer used for the manufacture of tissue culture plasticware, which permits a better exchange of gases, contributes to the long-term expression of P450 activity. Lectins proved to be nontoxic for hepatocyte survival, maintained hepatocyte viability, and can be used as an alternative substrate to immobilize hepatocytes to be transplanted in animal models of acute or chronic liver failure.

Diazepam Metabolism in Perfused Cultures of Adult Rat Hepatocytes

Recent studies implicating brain benzodiazepine receptors in the genesis of hepatic encephalopathy justify a comprehensive testing of a hollow fiber membrane liver assist device in terms of its capacity to metabolize diazepam in vitro. The detection of diazepam metabolites (temazepam, nordiazepam and oxazepam) indicates an active group of P-450 isoenzymes (b and e in the rat) which are responsible for many detoxification functions and are stimulated by the administration of phenobarbital. After a separation procedure following the Seglen method, 8 × 106 adult rat hepatocytes per ml were seeded on the surface of about 100 polysulfone hollow fibers (W.R. Grace) housed in polypropylene cartridges. The diameter of these fibers is approximately 816 μm. Prior to the seeding procedure, these fibers were coated with Vitrogen (a mixture of collagen I and III). The total capacity of the extracapillary space (the tissue culture chamber) was 5 ml and the total amount of perfused medium (extracapillary space plus reservoir) was 25 ml. The perfusate was a tissue culture medium (CEM)(GIBCO Labs) supplemented with 10% fetal bovine serum (FBS). CEM maintained good diazepam metabolic activities in these hepatocytes attached to hollow fiber membranes. For instance, at 24 hours the combined (nordiazepam, temazepam and oxazepam) activity as measured by HPLC (Waters Chromatography Div.) was 71±13 μg/25 ml media whereas at 48 hours the activity was 27±15 μg/25 ml media. At day 10, the cells still showed an activity of 7 μg/25 ml media.