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M F Sorrell

Publications and source records attributed to M F Sorrell.

At least 91 records · Page 5Linked to original sources
PubMed1991

The chemistry of acetaldehyde-protein adducts.

Acetaldehyde reacts with a variety of proteins to form both stable and unstable adducts. Unstable adducts are readily reversible and are largely represented by Schiff bases. Stable adducts are essentially irreversible products that are characterized by their resistance to various treatments. The structures of stable adducts have not been established, but it appears that the epsilon-amino group of certain lysines and the amino group of N-terminal amino acids participate in aldehyde binding. Stable adducts can form in the absence of a reducing agent, such as sodium cyanoborohydride, and are distinctly different than the ethylated amino groups formed under reductive conditions. Upon prolonged incubation, stable binding of acetaldehyde results in the formation of fluorescent products, and Schiff bases serve as intermediates of these advanced stable products. It is likely that several acetaldehyde molecules and perhaps at least two amino groups participate in the formation of these stable fluorescent products. Such a reaction mechanism could account for both inter-and intra-molecular cross-linking of proteins. Furthermore, it is likely that stable adducts are represented by multiple products whose structures may vary, depending upon the particular target protein. A reaction mechanism involving an aldol condensation and generation of a crotonaldehyde Schiff base is proposed as an essential step in stable adduct formation.

Acetaldehyde↗
PubMed1991

Zonal differences in ethanol-induced impairments in receptor-mediated endocytosis of asialoglycoproteins in isolated rat hepatocytes.

We have shown previously that ethanol-induced defects in receptor-mediated endocytosis of asialoorosomucoid occurred as early as 1 wk after ethanol feeding. This study was undertaken as an initial attempt to establish a possible role of defective receptor-mediated endocytosis in liver injury by investigating whether differences exist in the effects of ethanol on receptor-mediated endocytosis in hepatocytes isolated from different regions of the liver. Perivenule cells, present in the distal half of the liver, are thought to be more susceptible to ethanol-induced liver injury than are the periportal cells located in the proximal half of the liver acini. For these studies, we fed male Sprague-Dawley rats for 7 days with liquid diets containing either ethanol (36% of calories) or isocaloric carbohydrate. Perivenule and periportal hepatocytes were then isolated using a digitonin-collagenase perfusion method. In control animals, cells isolated from the perivenule region bound significantly more ligand than did cells from the periportal region. Amounts of ligand internalized and degraded were also greater in perivenule than in periportal cells in these animals. After ethanol feeding, cells isolated from both the perivenule and periportal regions bound significantly less ligand than their respective controls. This impairment in surface and total binding was more pronounced in perivenule than in periportal cells. Internalization and degradation of the ligand were also more adversely affected in the centrilobular region as shown by decreases of greater than 60% in perivenule cells and by only 20% to 30% in periportal cells of ethanol-fed animals compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effect of chronic ethanol administration on total asialoglycoprotein receptor content and intracellular processing of asialoorosomucoid in isolated rat hepatocytes.

Chronic ethanol administration markedly impairs the process of receptor-mediated endocytosis (RME) of a representative asialoglycoprotein, asialoorosomucoid (ASOR), by the liver (Casey et al. (1987) J. Biol. Chem. 262, 2704-2710). Decreased surface binding was the major defect reported in our initial study, along with impaired internalization and degradation of 125I-ASOR in chronically-fed ethanol animals. In this study, we further characterized these impairments by examining the content of intracellular receptors and by investigating ligand processing directed by these intracellular receptors. Ethanol administration for 5-7 weeks decreased intracellular ASOR receptor content by 40%, a result which was confirmed by using both a ligand-binding assay and an antibody-binding assay. In addition to a decreased number of intracellular receptors, an impairment in intracellular processing of receptor-ligand complexes was identified. In ethanol-fed animals, dissociation of receptor-ligand complexes was decreased during steady-state conditions of endocytosis at 37 degrees C. Impaired receptor-ligand dissociation did not alter the fate of the ligand which was to undergo diacytosis (ligand recycling), but did appear to impair degradation of intracellular ligand. These results indicate that chronic ethanol administration decreases ligand binding due to a decreased number of receptors and impairs intracellular processing of ASOR in hepatocytes.

Alcoholism↗
PubMed1990

Chronic ethanol administration impairs receptor-mediated endocytosis of epidermal growth factor by rat hepatocytes.

The effects of chronic ethanol administration on the receptor-mediated endocytosis of epidermal growth factor were studied in isolated rat hepatocytes. In initial experiments, it was demonstrated that significantly less ligand was bound by hepatocytes isolated from rats fed an ethanol liquid diet for 5 to 7 wk than by cells isolated from chow-fed or pair-fed controls. Reduced binding was shown to be primarily caused by a decreased number of surface receptors rather than by changes in receptor affinity. When hepatocytes were incubated at 37 degrees C in the presence of a large saturating concentration of epidermal growth factor (80 nmol/L), intracellular levels of the ligand were significantly lower in cells from the ethanol-fed animals. However, no effect on degradation of the ligand was observed under those conditions. A defect in the initial stages of receptor-ligand internalization was also indicated because less surface-bound ligand was internalized and subsequently degraded in cells from the ethanol-treated rats. When the endocytosis of a lower, more physiological concentration of the growth factor (0.5 nmol/L) was studied, both the uptake of ligand and its degradation were markedly impaired in hepatocytes from the ethanol-fed animals. These results indicate that chronic ethanol administration impairs the receptor-mediated endocytosis of epidermal growth factor by the liver. The major impairment appears to be a reduction of cell surface receptors; however, other steps of the endocytotic pathway also appear to be affected. These altered steps include defective receptor-ligand internalization and changes in intracellular processing of the ligand leading to decreased degradation.

Animals↗
PubMed1990

Orthotopic liver transplantation for graft-versus-host disease following bone marrow transplantation.

Chronic graft-vs.-host disease occurs in 30%-50% of long-term survivors of allogeneic bone marrow grafts, and may eventuate in cirrhosis. In this study, a young woman, originally diagnosed as having acute myelogenous leukemia, underwent successful bone marrow transplantation but later developed graft-vs.-host disease-induced cirrhosis and recurrent variceal hemorrhage. She underwent successful orthotopic liver transplant. Her postoperative course was uncomplicated, with no evidence of rejection or recurrence of graft-vs.-host disease. As bone marrow transplantation is more widely used and survival improves, the number of patients with graft-vs.-host disease or venoocclusive disease resulting in cirrhosis is likely to increase. Hepatic transplantation should be considered for bone marrow transplant patients who develop end-stage liver disease.

Adult↗
PubMed1990

Effects of ethanol on hepatic protein trafficking: impairment of receptor-mediated endocytosis.

Ethanol administration disorders protein trafficking in the liver. The protein secretory and plasma membrane assembly pathways have been shown to be impaired in the liver of ethanol-treated animals; however, traffic along the receptor-mediated endocytosis pathway appears to be especially susceptible to alterations by ethanol. Using asialoglycoproteins as model ligands for studying receptor-mediated endocytosis, we have identified at least three steps of this multi-step pathway that are affected by ethanol treatment. These altered steps are recycling of the receptor, internalization of the receptor-ligand complex and dissociation of the ligand from its receptor in endosomes. Ethanol-induced derangements of endocytosis are more severe in the perivenule region, where alcoholic liver injury starts and predominates, than in the periportal region of the liver. In addition, recent studies have shown that the endocytosis of other ligands, including epidermal growth factor and insulin, are also altered by ethanol treatment. Mechanisms which have been proposed to explain faulty endocytosis include: acetaldehyde adducts to tubulin resulting in impaired microtubule function, improper acidification of endosomes and defective receptor clustering in coated pits. Since receptor-mediated endocytosis by the liver represents an important process by which levels of various hormones, growth factors and other ligands are regulated, and since endocytosis may also be an integral process by which the biological effects of various ligands are elicited, changes in this important process could disrupt numerous metabolic and homeostatic events in the liver and total organism.

Alcohol Drinking↗
PubMed1989

Preferential covalent binding of acetaldehyde to the alpha-chain of purified rat liver tubulin.

Hepatic ethanol oxidation generates the reactive intermediate acetaldehyde, which binds to proteins. Previous work, using bovine brain tubulin as a model protein, has shown that acetaldehyde preferentially formed stable adducts on the alpha-chain of the heterodimeric molecule. This binding resulted in functional impairment of the tubulin/microtubule system as evidenced by a decreased ability of adducted tubulin to form microtubules. Since tubulin/microtubules are believed to be very important cytoskeletal components of the hepatocyte and results with brain tubulin were interesting, our goal was to extend these studies to liver tubulin. We purified tubulin from rat liver by a polymerization-based cycle method followed by phosphocellulose chromatography. We then characterized the covalent binding of [14C]acetaldehyde to liver tubulin. Naturally forming and cyanoborohydride-stimulated stable adducts formed linearly with liver tubulin in a manner almost identical to that with brain tubulin. We also found that the alpha-chain of the native heterodimeric liver tubulin molecule was the preferred site of adduct formation at low acetaldehyde to protein ratios. These results confirm and extend our previous findings with the brain tubulin model and further suggest that the alpha-chain of tubulin may be a preferential site for acetaldehyde-adduct formation during ethanol oxidation in the liver.

Acetaldehyde↗
PubMed1989

Experimental methods of ethanol administration.

Techniques are reviewed for the experimental feeding of alcohol, including a liquid diet procedure invented 25 years ago. This technique results in much higher ethanol intake than with other approaches. As a consequence, various complications observed in alcoholics can be reproduced in animal models. These include fatty liver, hyperlipemia, various metabolic and endocrine disorders, tolerance to ethanol and other drugs, physical dependence and withdrawal and, in the baboon, liver fibrosis and cirrhosis. Variations of the liquid diet formulation are compared, and adequacy of nutrition in terms of minerals, vitamins, lipotropes, carbohydrates and proteins is discussed. The importance of selecting proper controls is emphasized. The respective advantages of three standardized basic rat formulas are reviewed: (i) an all-purpose (35% fat) diet, comparable to the diet previously referred to as the "Lieber-DeCarli formula" and suitable for most experimental applications, particularly those intended to mimic the clinical situation in which the various effects of alcohol occur in the setting of hepatic changes characterized by a fatty liver; (ii) a low-fat diet comparable in all respects to the preceding diet but with a lower fat content, intended to minimize the hepatic changes, and (iii) a high-protein formula particularly useful in those circumstances in which an oversupply of dietary protein might be recommended (i.e. pregnancy). Variations of this technique, including continuous intragastric infusion, are also discussed. It is concluded that, for most experimental studies of chronic alcohol consumption, the liquid diet technique provides one of the most efficient tools to study the effects of ethanol under controlled nutritional conditions because it allows for alcohol consumption of clinical relevance and offers flexibility to adjust to special experimental or physiologic needs by allowing for various substitutions required for a particular experimental design, including changes in lipids, proteins or other dietary constituents. The technique also facilitates the comparison with controls by simplifying the pair feeding and is the best procedure available for the study of the toxic effects of alcohol and their interactions with deficiency or excess of various nutrients.

Administration, Inhalation↗
PubMed1989

Increased covalent binding of acetaldehyde to calmodulin in the presence of calcium.

The regulatory protein, calmodulin, undergoes major conformational changes in response to changes in intracellular calcium concentration. Furthermore, calmodulin has been reported to have lysine residues which markedly increase their reactivity toward electrophilic substances in the calcium-loaded state. We found that calmodulin formed two to three times more stable adducts with acetaldehyde in the calcium-loaded state as compared to the calcium-free state. Competition-binding studies showed that calmodulin could preferentially compete with albumin for acetaldehyde in the presence, but not in the absence, of calcium. When calmodulin was in the calcium-loaded state, trifluoperazine, an inhibitor of calmodulin activity, significantly decreased the stable binding of acetaldehyde to the protein, whereas in the calcium-free state, minimal effects on binding were observed. Since calmodulin is involved in regulation of multiple important processes in the cell, it is possible that acetaldehyde-calmodulin adducts could contribute to liver injury by perturbation of calcium-dependent homeostatic mechanisms within the hepatocyte.

Acetaldehyde↗
PubMed1989

Preoperative evaluation, preparation, and timing of orthotopic liver transplantation in the adult.

Orthotopic liver transplantation can provide a large number of patients with end-stage liver disease an opportunity for significant improvement in long-term survival and quality of life. Transplantation should not be considered a last-ditch attempt to save a dying patient. Early referral of patients to transplant centers will allow for further improvement in survival of patients after transplantation. Ongoing communication between the referring physician and the transplant team is important in keeping abreast of changes in the patient's status so that optimal timing of the transplant may be achieved.

Adult↗
PubMed1989

Covalent interactions of acetaldehyde with the actin/microfilament system.

The covalent binding of [14C]acetaldehyde to purified rabbit skeletal muscle actin was characterized. As we have found for other cytoskeletal proteins, actin formed stable covalent adducts under reductive and non-reductive conditions. Under non-reductive conditions, individual and competition binding studies versus albumin both showed that the G-form of actin is more reactive toward acetaldehyde than the F-form. When proteins were compared on an 'equi-lysine' basis under non-reducing conditions, G-actin was found to preferentially compete with albumin for binding to acetaldehyde. Time-course dialysis studies indicated that acetaldehyde-actin adducts become more stable with prolonged incubation at 37 degrees C. These data raise the possibility that actin could be a preferential target for adduct formation in cellular systems and will serve as the basis for ongoing studies aimed at defining the role of acetaldehyde-protein adducts in ethanol-induced cell injury.

Acetaldehyde↗
PubMed1989

Ethanol-induced impairments in receptor-mediated endocytosis of asialoorosomucoid in isolated rat hepatocytes: time course of impairments and recovery after ethanol withdrawal.

Chronic ethanol administration markedly impairs the process of receptor-mediated endocytosis (RME) of a representative asialoglycoprotein, asialoorosomucoid (ASOR), by the liver. In this study, we further characterized these impairments by identifying the time of onset for ethanol-induced changes in RME as well as establishing the time course for recovery to normal endocytotic values after ethanol withdrawal. Ethanol administration for 3 days did not alter any aspect of endocytosis examined in this study. After feeding ethanol to rats for 7 days, however, significant decreases in amounts of ligand bound, internalized, and degraded were apparent. These impairments persisted throughout the 5-week feeding study although the effects were somewhat attenuated with more prolonged ethanol feeding. In addition, an accumulation of intracellular receptors was observed in ethanol-fed animals relative to controls after 7 days of ethanol feeding. In all cases, recovery of endocytotic values to control levels was partially completed after 2 to 3 days of refeeding control diet and was fully completed after 7 days of refeeding. These results indicate that ethanol feeding for as little as 7 days profoundly impairs the process of RME by the liver. These impairments can be reversed after refeeding control diet for 7 days.

Animals↗
PubMed1989

Acetaldehyde substoichiometrically inhibits bovine neurotubulin polymerization.

Acetaldehyde is known to form covalent adducts with tubulin and to inhibit microtubule formation. Available evidence indicates that lysine residues are prominently involved in adduct formation. Previous work has shown that lysines on tubulin can be divided into two general classes based upon their reactivity toward acetaldehyde; those of normal reactivity ("bulk" lysines) and a highly reactive lysine (HRL) located on the alpha-polypeptide subunit. We took advantage of the fact that the HRL is unreactive when tubulin is in the microtubule form to differentiate the effects of bulk from HRL adducts on tubulin polymerization. Under conditions where both bulk lysines and HRL formed adducts, 0.2 mol acetaldehyde/mol tubulin caused complete inhibition of polymerization. When we modified bulk lysines, but not HRL, tubulin polymerized essentially normally. Finally, when we first blocked bulk lysines on microtubules (HRL unreactive) using unlabeled acetaldehyde and then measured the amount of [14C]acetaldehyde adduct formed with tubulin after depolymerization (HRL reactive), 0.08 mol acetaldehyde/mol tubulin resulted in completely impaired polymerization. These data show that microtubule formation is very sensitive to even small mole fractions of acetaldehyde-modified tubulin (especially with HRL) and further suggest that small amounts of acetaldehyde adduct could be damaging to cytoskeleton function in the cell.

Acetaldehyde↗