Acetaldehyde binds to liver cell membranes without affecting membrane function

Effects of acetaldehyde on hepatocyte glycerol uptake and cell size: implication of aquaporin 9

BACKGROUND

The effects of ethanol and acetaldehyde on uptake of glycerol and on cell size of hepatocytes and a role Aquaporin 9 (AQP9), a glycerol transport channel, were evaluated.

METHODS

The studies were done in primary rat and mouse hepatocytes. The uptake of [(14) C] glycerol was determined with hepatocytes in suspension. For determination of cell size, rat hepatocytes on coated dishes were incubated with a lipophilic fluorochrome that is incorporated into the cell membrane and examined by confocal microscopy. A three-dimensional z scan of the cell was performed, and the middle slice of the z scan was used for area measurements.

RESULTS

Acute exposure to acetaldehyde, but not to ethanol, causes a rapid increase in the uptake of glycerol and an increase in hepatocyte size, which was inhibited by HgCl(2) , an inhibitor of aquaporins. This was not observed in hepatocytes from AQP9 knockout mice, nor observed by direct application of acetaldehyde to AQP9 expressed in Xenopus Laevis oocytes. Prolonged 24-hour exposure to either acetaldehyde or ethanol did not result in an increase in glycerol uptake by rat hepatocytes. Acetaldehyde decreased AQP9 mRNA and AQP9 protein, while ethanol decreased AQP9 mRNA but not AQP9 protein. Ethanol, but not acetaldehyde, increased the activities of glycerol kinase and phosphoenolpyruvate carboxykinase.

CONCLUSIONS

The acute effects of acetaldehyde, while mediated by AQP9, are probably influenced by binding of acetaldehyde to hepatocyte membranes and changes in cell permeability. The effects of ethanol in enhancing glucose kinase, and phosphoenolpyruvate carboxykinase leading to increased formation of glycerol-3-phosphate most likely contribute to alcoholic fatty liver.

Effects of prostaglandins on ethanol damage in primary cultured rat hepatocytes

OBJECTIVES

Several reports demonstrated that ethanol administration impairs the DNA synthesis in rat hepatocytes. Also, it has been demonstrated that prostaglandin (PG) helps prevent membrane damage by hepatotoxic chemicals. In this study, the authors examined PG's effects on the toxicity of ethanol in the primary culture of rat regenerations.

METHODS

We examined two kinds of parameters, i.e., DNA synthesis and lipid peroxidation in the primary culture of rat hepatocytes. Hepatocytes were isolated by the collagenase perfusion method. The rate of DNA synthesis was determined by pulse-labelling cultured cells with [3H]-thymidine. Incorporation of (3H)-thymidine was determined by liquid scintillation spectrophotometer. DNA content was measured by the fluorescence spectrophotometer. The lipid peroxidation was assayed with spectrophotometer.

RESULTS

The results were as follows: 1) PG family (PGA1, PGD2, PGE1, PGE2, PGG2a, PGI2 & Thromboxane B2) stimulated the DNA synthesis of hepatocytes (especially PGD2 and PGE1), 2) ethanol decreased DNA synthesis by clear dose-dependent manner, 3) the combined treatment of PGD2 or PGE1, prevents the decreasing of DNA synthesis, which was induced by ethanol, 4) in ethanol treatment, lipid peroxidation was decreased significantly, but PGD2, PGE1 and PGA1 were not affected, and 5) PGD2, PGE1 and PGA1 decreased lipid peroxidation with ethanol, significantly.

CONCLUSIONS

From these results, we concluded that PG could be useful for the treatment of degenerative liver disease and alcohol-induced liver disease in the assumption that further studies on the action mechanisms of PG will continue.

Lack of plasma complement activation in severe acute alcoholic hepatitis

To investigate whether complement pathway activation contributes to the clinical and histological features of acute alcoholic hepatitis, we studied the activation of the classical and alternative pathways in patients with alcoholic hepatitis (n = 20), inactive alcoholic cirrhosis (n = 8), heavy drinkers without alcoholic liver disease (n = 10), patients with liver disease of nonalcoholic etiology (n = 11), and healthy control subjects (n = 18). Complement activation was evaluated in the alcoholic hepatitis patients by its correlation with a number of clinical and laboratory features indicative of the severity of liver injury, as well as by comparison of the patient groups. There was no significant difference in circulating C3 [1.02 g/liter, confidence interval (CI) = 0.76-1.28] or C4 (0.25 g/liter, CI = 0.17-0.33) in patients with alcoholic hepatitis when compared with the four control groups. Factor B levels (0.24 g/liter, CI = 0.21-0.27) were higher in the alcoholic hepatitis patients than the control groups (p < 0.01). However, activation of complement (given by the ratios C3d/C3, C4d/C4, and Ba/factor B) was not different in alcoholic hepatitis patients when compared with the control groups. Univariate analysis of a wide range of clinical and laboratory features in the alcoholic hepatitis subjects showed a positive correlation between plasma C3 and serum alkaline phosphatase (r = 0.68, p = 0.0014), AST (r = 0.55, p = 0.015), and gamma-glutamyltranspeptidase (r = 0.47, p = 0.035), but no correlation with clinical or laboratory features associated with high morbidity or mortality. There is no relationship between clinical or laboratory indicators of disease severity and complement activation, and it is unlikely that complement activation contributes to the clinical and histological features of alcoholic liver disease.

Effects of ethanol, acetaldehyde and cholesteryl esters on pancreatic lysosomes

Recent studies indicate that altered lysosomal function may be involved in the early stages of pancreatic injury. Chronic consumption of ethanol increases rat pancreatic lysosomal fragility. The aim of this study is to determine whether the lysosomal fragility observed after chronic ethanol consumption is mediated by ethanol per se, its oxidative metabolite acetaldehyde or cholesteryl esters (substances which accumulate in the pancreas after ethanol consumption). Pancreatic lysosomes from chow fed rats were incubated for 30 minutes at 37 degrees C with ethanol, acetaldehyde or phosphatidylcholine vesicles containing cholesteryl oleate. Lysosomal stability was then assessed by determination of: (a) Latency--that is, the per cent increase in lysosomal enzyme activity after addition of Triton X-100 and (b) Supernatant activity--that is, the proportion of lysosomal enzyme remaining in the supernatant after resedimentation of lysosomes. Acid phosphatase, N-acetyl glucosaminidase, beta-glucuronidase and cathepsin B were assayed as lysosomal marker enzymes. Lysosomes incubated with homogenising medium alone or equivalent volumes of phosphatidylcholine vesicles without cholesteryl oleate were used as controls. Cholesteryl oleate at concentrations of 15 and 20 mM increased pancreatic lysosomal fragility as shown by decreased latency and increased supernatant enzyme. In contrast, ethanol (150 mM) and acetaldehyde (5 mM) had no effect on lysosomal stability in vitro. These results suggest that increased pancreatic lysosomal fragility observed with ethanol may be mediated by cholesteryl ester accumulation rather than by ethanol or acetaldehyde.

Neutrophil elastase activity and superoxide production are diminished in neutrophils of alcoholics

Several lines of evidence indicate that neutrophil elastase and oxidants secreted by phagocytic inflammatory cells play key roles in the development of centrilobular emphysema. A recent report suggests that ethanol consumption may have a protective role against this disease in smokers. The aim of this study was to examine the effect of ethanol consumption on neutrophil elastase activity and superoxide production of peripheral blood neutrophils. These activities were measured in neutrophils from 52 male intoxicated patients and compared to activities in neutrophils from 20 male volunteers. Neutrophils from intoxicated patients contained 31% less elastase activity than that found in controls, 0.99 +/- 0.27 versus 1.44 +/- 0.23 micrograms/10(6) neutrophils (p less than 0.0001) and produced 25 to 27% less superoxide than controls in response to phorbol 12-myristate-13-acetate, 0.90 +/- 0.17 versus 1.2 +/- 0.21 nmol/min/10(6) PMN (p less than 0.0001) or N-formylmethionylleucylphenylalanine, 0.64 +/- 0.19 versus 0.88 +/- 0.24 (p less than 0.001). In follow-up studies of 10 patients admitted for acute alcoholism, elastase activity and superoxide production remained low for 2 to 4 days. After 6 to 10 days, elastase activity and superoxide production were significantly greater than they were at Day 0 and approached normal levels. Neutrophils isolated from blood samples of healthy abstaining donors, which had been exposed to ethanol or to plasma from inebriated patients for 16 to 20 h, showed no loss of elastase activity or superoxide production.(ABSTRACT TRUNCATED AT 250 WORDS)

The detection of acetaldehyde/liver plasma membrane protein adduct formed in vivo by alcohol feeding

In order to assess whether acetaldehyde adducts with liver plasma membrane proteins are formed in vivo during alcohol ingestion, liver plasma membranes were prepared from control rats and rats fed on 10% ethanol from weaning and the amino acid constituents of liver plasma membrane proteins were assessed by reversed phase liquid chromatography of an acid hydrolysate of the membranes. The retention time of acetaldehyde/lysine adduct after stabilisation through reduction was determined by chromatography of an acid hydrolysate of polylysine pretreated with acetaldehyde. The presence of a peak with identical retention time to the acetaldehyde/lysine adduct was detected in liver plasma membranes isolated from alcohol-fed rats indicating adduct formation in vivo. The adduct was detectable only when the membranes were prepared by a rapid (Percoll) method, suggesting that the adduct may be unstable. The findings are consistent with the hypothesis that the inflammation of acute alcoholic liver disease may be initiated by the product of acetaldehyde/membrane binding in vivo.

Hepatotoxicity of acetaldehyde in rats

The ability of acetaldehyde to initiate hepatotoxicity as evidenced by enzyme leakage, hepatic fat accumulation and histological alterations was studied in rats. Neither oral nor intraperitoneal treatment with acetaldehyde had any hepatotoxic effect, even following aldehyde dehydrogenase inhibition by disulfiram. This is probably due to the inability of exogenously added acetaldehyde to penetrate liver cell membranes. In contrast, acetaldehyde derived metabolically from ethanol was capable of inducing moderate hepatotoxicity when it accumulated upon pretreatment with disulfiram. Acetaldehyde may thus be partly responsible for alcohol-induced liver damage.

Free radical generation by neutrophils: a potential mechanism of cellular injury in acute alcoholic hepatitis

Liver membrane vesicles were prepared from operative liver biopsies from six patient volunteers undergoing abdominal surgery for non-hepatic disease. Neutrophils were extracted from their blood. The liver membrane vesicles were exposed to 1 mmol/l acetaldehyde with or without reduction of the resultant adducts formed. The production of superoxide anion by the neutrophils upon exposure to the liver membrane vesicles prepared from the same patient was assessed by measuring the rate of cytochrome c reduction before and after the addition of superoxide dismutase. Preincubation with acetaldehyde significantly increased superoxide production in response to both the reduced (from 35.5 +/- 7.1 nmol O2-/10(8) cells/min to 128 +/- 25, mean +/- SEM, p less than 0.01) and the non-reduced liver cell membranes (from 17.2 +/- 4.3 to 81 +/- 17, p less than 0.01); 1 mmol/l acetaldehyde alone caused no superoxide production. Neutrophil free radical production in response to acetaldehyde altered hepatocyte membranes could be an important mechanism of cellular injury in acute alcoholic hepatitis.

Liver disease in the alcoholic

The problem of liver damage in alcoholic patients is widespread. This review discusses hepatic damage on the basis of a histologic classification of increasing severity. In the early stages, or with compensated cirrhosis, clinical and laboratory findings may not accurately reflect hepatic involvement. Furthermore, there exists a group of alcoholic patients in whom liver disease may be caused by factors other than alcohol. Nevertheless, in most patients with liver disease, certain biochemical features help to establish an alcoholic etiology. These features and the use of liver biopsy are discussed, and a practical guideline for diagnosis and follow-up is offered.

Acetaldehyde alone may initiate hepatocellular damage in acute alcoholic liver disease

Acetaldehyde may be the injurious agent in acute alcoholic liver disease. It has been suggested that the mechanism of liver injury in this situation may be immunologically mediated. In the present study acetaldehyde has been bound to human liver plasma membranes. The activation of C3 by the acetaldehyde/membrane product was measured by immunofixation of the separated C3 components. Activation of C3 by acetaldehyde exposed liver plasma membranes was increased to 16.4% compared with 6% by non-exposed membranes (p = 0.004). Human liver plasma membranes bound 212 +/- 18 nmol acetaldehyde per mg membrane protein. The binding constant was 439 +/- 81 microM. It is concluded that acetaldehyde bound to human liver plasma membranes activates the complement sequence and this may be the initial stage in the pathogenesis of acute alcoholic liver disease.