Covalent binding of acetaldehyde to liver tubulin: a step in the right direction

Inhibition of tubulin assembly and covalent binding to microtubular protein by valproic acid glucuronide in vitro

Acyl glucuronides are reactive metabolites of carboxylate drugs, able to undergo a number of reactions in vitro and in vivo, including isomerization via intramolecular rearrangement and covalent adduct formation with proteins. The intrinsic reactivity of a particular acyl glucuronide depends upon the chemical makeup of the drug moiety. The least reactive acyl glucuronide yet reported is valproic acid acyl glucuronide (VPA-G), which is the major metabolite of the antiepileptic agent valproic acid (VPA). In this study, we showed that both VPA-G and its rearrangement isomers (iso-VPA-G) interacted with bovine brain microtubular protein (MTP, comprised of 85% tubulin and 15% microtubule associated proteins [MAPs]). MTP was incubated with VPA, VPA-G and iso-VPA-G for 2 h at room temperature and pH 7.5 at various concentrations up to 4 mM. VPA-G and iso-VPA-G caused dose-dependent inhibition of assembly of MTP into microtubules, with 50% inhibition (IC(50)) values of 1.0 and 0.2 mM respectively, suggesting that iso-VPA-G has five times more inhibitory potential than VPA-G. VPA itself did not inhibit microtubule formation except at very high concentrations (> or =2 mM). Dialysis to remove unbound VPA-G and iso-VPA-G (prior to the assembly assay) diminished inhibition while not removing it. Comparison of covalent binding of VPA-G and iso-VPA-G (using [14C]-labelled species) showed that adduct formation was much greater for iso-VPA-G. When [14C]-iso-VPA-G was reacted with MTP in the presence of sodium cyanide (to stabilize glycation adducts), subsequent separation into tubulin and MAPs fractions by ion exchange chromatography revealed that 78 and 22% of the covalent binding occurred with the MAPs and tubulin fractions respectively. These experiments support the notion of both covalent and reversible binding playing parts in the inhibition of microtubule formation from MTP (though the acyl glucuronide of VPA is less important than its rearrangement isomers in this regard), and that both tubulin and (perhaps more importantly) MAPs form adducts with acyl glucuronides.

Coagulation protein function. II. Influence of thiols upon acetaldehyde effects

It has been reported that prolonged prothrombin time may be a result of the interaction of acetaldehyde (AcH) with clotting proteins to form alkylated inactive products. The current investigation focuses on the influence of L-cysteine (CysH), DL-homocysteine (HC), D-penicillamine, N-acetyl-L-cysteine (NAC), L-serine and L-alanine at 0.01 M concentrations, lactalbumin hydrolysate (2 mg/ml), and 1.0 mM dithiothreitol (DTT) on clotting time as well as their interaction with AcH. The sulfhydryl amino acids, as well as DTT prolonged clotting upon preincubation with plasma. Cysteine and NAC, upon addition to plasma prior to the addition of AcH, exhibited a prolongation of clotting time compared to that of AcH alone. On sequential addition of serine, alanine, or lactalbumin hydrolysate to plasma followed by the addition of acetaldehyde, a prolongation of clotting time comparable to that of AcH alone was exhibited. When HC and penicillamine were added to plasma prior to the addition of AcH, a prolonged clotting time was observed, which was significantly less than that of AcH alone. Premixing of serine, alanine, and lactalbumin hydrolysate with AcH for 20 min prior to addition to the plasma reduced the effectiveness of AcH in prolonging clotting time as compared to successive additions of the amino acid and AcH. Since CysH and penicillamine have been reported to form cyclic adducts with AcH, it is suggested that a similar possibility exists for penicillamine and for HC. The reversible cyclic adduct formation reported for CysH may explain why cysteine did not lower the prolonged clotting time induced by AcH.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde alters coagulation protein function

Acetaldehyde is the first metabolite of ethanol and has the potential to react with proteins and alter their function. This study evaluated the function of clotting proteins that had been preincubated with acetaldehyde as compared to those incubated with buffer or ethanol as controls. Thrombin, fibrinogen, thromboplastin, or whole plasma were preincubated with 1.8-447 mM acetaldehyde, 1.7-429 mM ethanol, or buffer for varying time periods prior to use in a clotting assay. Clot formation was measured with an automatic fibrometer. Acetaldehyde prolonged the clotting time but ethanol did not. These experiments indicate that circulating acetaldehyde would have the potential to react with proteins of the clotting system and alter their function. Therefore, it is possible that not all of the abnormalities in coagulation in alcohol abusers result from inadequate hepatic synthesis. Perhaps some of the deranged coagulation may be the result of the interaction of acetaldehyde with coagulation proteins.

Effects of ethanol on intercellular communications and polarization of hepatocytes in short-term culture

The formation of intracellular lumina with apical differentiation is observed in several cancerous epithelial cell lines including human hepatocarcinoma. This disorder of cell polarization can be induced by the inhibition of cell-cell communication, a known factor of carcinogenesis. This work was designed to study the effects of ethanol on the differentiation of hepatocytes in short-term culture. Isolated hepatocytes were plated on plastic culture dishes that were 35 mm in diameter (10(6) cells/dish). Three hours after plating, the hepatocytes were incubated in the presence of 20 mmol/L ethanol for 1 hr. Treated cells were compared with controls using morphometric methods after conventional treatment for ultramicroscopy and by measuring cellular dye coupling by the fluorescent Lucifer Yellow CH transfer method. Bile canaliculi formation decreased in alcohol-treated cells (6.5% vs. 9.9%, 2p less than 0.05), whereas intracellular lumina incidence increased (3.1% vs. 0.5%, 2p less than 0.01). In parallel, the dye-coupling capacity decreased significantly when hepatocytes were treated with alcohol (2p less than 0.01). This work shows that short-term ethanol treatment induces significant disturbances of cell polarization and inhibits the reestablishment of cell-cell communication in cultured hepatocytes. These disorders could, at least in part, explain the carcinogenic effects of ethanol.