Acetaldehyde selectively stimulates collagen production in cultured rat liver fat-storing cells but not in hepatocytes

Centrilobular distribution of acetaldehyde and collagen in the ethanol-fed micropig

We established a new animal model of alcoholic liver disease in the micropig, a species that consumes ethanol voluntarily in the diet. Ten micropigs were pair-fed diets containing 40% of calories as ethanol or cornstarch with identical amounts of fat, protein and micronutrients for 12 mo. Liver histopathology in the ethanol-fed pigs included steatonecrosis in all five and interstitial and perivenous fibrosis in three. Electron microscopy showed Ito-cell transformation with perisinusoidal collagen accumulation. Acetaldehyde adducts were found by immunofluorescence in the centrilobular region and were focused in perivenous zone 3 of all ethanol-fed animals. Protein and triglyceride levels were increased, whereas vitamin A and iron levels were decreased in liver homogenates from ethanol-fed animals. Thus, in this new animal model of alcoholism, ethanol feeding produced the features of alcoholic liver disease concurrent with hepatic deficiency of selected nutrients. Histological and immunofluorescent studies provide in vivo evidence that perivenous collagen deposition is linked to ethanol metabolism and acetaldehyde production.

Aetiology and pathogenesis of alcoholic liver disease

Until the 1960s, liver disease of the alcoholic patient was attributed exclusively to dietary deficiencies. Since then, however, our understanding of the impact of alcoholism on nutritional status has undergone a progressive evolution. Alcohol, because of its high energy content, was at first perceived to act exclusively as 'empty calories' displacing other nutrients in the diet, and causing primary malnutrition through decreased intake of essential nutrients. With improvement in the overall nutrition of the population, the role of primary malnutrition waned and secondary malnutrition was emphasized as a result of a better understanding of maldigestion and malabsorption caused by chronic alcohol consumption and various diseases associated with chronic alcoholism. At the same time, the concept of the direct toxicity of alcohol came to the forefront as an explanation for the widespread cellular injury. Some of the hepatotoxicity was found to result from the metabolic disturbances associated with the oxidation of ethanol via the liver alcohol dehydrogenase (ADH) pathway and the redox changes produced by the generated NADH, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Exaggeration of the redox change by the relative hypoxia which prevails physiologically in the perivenular zone contributes to the exacerbation of the ethanol-induced lesions in zone 3. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last twenty years have culminated in the molecular elucidation of the ethanol-inducible cytochrome P450IIE1 (CYP2E1) which contributes not only to ethanol metabolism and tolerance, but also to the selective hepatic perivenular toxicity of various xenobiotics. Their activation by CYP2E1 now provides an understanding for the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, 'over the counter' analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Ethanol causes not only vitamin A depletion but it also enhances its hepatotoxicity. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation, with formation of protein adducts, resulting in antibody production, enzyme inactivation and decreased DNA repair; it is also associated with a striking impairment of the capacity of the liver to utilize oxygen. Moreover, acetaldehyde promotes glutathione depletion, free-radical mediated toxicity and lipid peroxidation. In addition, acetaldehyde affects hepatic collagen synthesis: both in vivo and in vitro (in cultured myofibroblasts and lipocytes), ethanol and its metabolite acetaldehyde were found to increase collagen accumulation and mRNA levels for collagen. This new understanding of the pathogenesis of alcoholic liver disease may eventually improve therapy with drugs and nutrients.

Studies of whole blood-associated acetaldehyde levels in teetotalers

We measured whole blood-associated acetaldehyde (WBAA) levels in 225 teetotalers (123 females, 102 males) between the ages of 18 and 86 years. Values were normally distributed, but mean values for females were significantly lower than for males (7.6 +/- 0.6 vs. 7.9 +/- 0.7 microM, p < 0.0001). There was a significant positive correlation with age for the entire group (r2 = 0.149, p = 0.001) and for both sexes. The correlation with WBAA and age was stronger for females. Significant but lesser positive correlations were found between WBAA and other variables that increase with age, including glucose, fructosamine, cholesterol, alkaline phosphatase, serum glutamate pyruvate transaminase (SGPT), gamma glutamyl transpeptidase (GGT), and creatinine in the entire data set. Partial r analyses indicated that the correlations were mediated through the primary association of WBAA and age. We conclude that in individuals who do not consume ethanol there are significant sex differences in whole blood acetaldehyde and that the values increase throughout life.

Identification of connective tissue gene transcripts in freshly isolated parenchymal, endothelial, Kupffer and fat-storing cells by northern hybridization analysis

The aim of the present study was to identify the cell types that express collagen alpha 1(I), alpha 1(III) and alpha 1(IV), fibronectin and laminin B1 genes in normal rat liver. Parenchymal, sinusoidal endothelial, Kupffer and fat-storing (Ito) cells were isolated and purified. Total RNA of the freshly isolated cells was subjected to Northern hybridization analysis. We also compared the steady state levels of specific mRNAs in freshly isolated fat-storing cells to the levels in myofibroblast-like cells obtained from purified fat-storing cells cultured for two passages. The average purity of each cell preparation, and the percentage of contaminating cells, were determined by transmission electron microscopy and by examining the presence of vitamin A-autofluorescent cells. Fibronectin and collagen alpha 1(III) mRNAs were detected in total RNA of purified parenchymal cells. In poly(A)+ enriched RNA, small amounts of collagen alpha 1(I) mRNA were also present. In total RNA of freshly isolated fat-storing cells, collagen alpha 1(III), alpha 1(IV), and laminin B1 transcripts were found, whereas collagen alpha 1(I) and fibronectin mRNAs were not detected. Cultured fat-storing cells, however, did contain high levels of collagen alpha 1(I) and fibronectin mRNAs. The molecular size of the latter transcript was larger than the fibronectin transcript found in parenchymal cells and the whole liver. Endothelial cells contained small amounts of alpha 1(IV) mRNA. Kupffer cells did not contain the investigated transcripts. We conclude that normal parenchymal, fat-storing and endothelial cells each express a typical pattern of connective tissue molecules. When fat-storing cells are allowed to differentiate into myofibroblast-like cells, they express high levels of collagen alpha 1(I) and fibronectin mRNAs, in addition to collagen alpha 1(III) and alpha 1(IV), and laminin B1 chain mRNAs.

Regulation of extracellular matrix synthesis by transforming growth factor beta 1 in human fat-storing cells

BACKGROUND

Fat storing cells (FSC) are nonparenchymal liver cells generally considered the major source of the hepatic extracellular matrix (ECM). Transforming growth factor beta 1 (TGF-beta 1) is a potent regulator of ECM synthesis in various cell types. In this study, the effect of TGF-beta 1 on procollagen types I, III, IV, laminin (Lam), and fibronectin (FN) synthesis in cultured human FSCs was analyzed.

METHODS

FSCs were isolated from wedge sections of normal human livers. Morphological studies were performed by immunofluorescence and electron microscopy. ECM components in human FSC cultures were measured by an enzyme-linked immunosorbent assay. The expression of messenger RNA (mRNA) was evaluated by Northern blot and in situ hybridization.

RESULTS

Cultured human FSCs displayed numerous fat droplets in the perinuclear zone, and immunoreactivity for vimentin and alpha-smooth muscle actin. A weak nonfibrillar staining was observed by using a polyclonal antidesmin antibody. TGF-beta 1 induced a dose-dependent increase of procollagen I, III, and FN accumulation in human FSC cultures, whereas procollagen IV and Lam production was not affected. Furthermore, TGF-beta 1 increased the expression of alpha 1 (I), alpha 1 (III) procollagen, FN and TGF-beta 1 mRNA in human FSC cultures.

CONCLUSIONS

These data indicate that TGF-beta 1 is able to increase the synthesis of procollagen I, III, and FN in cultured human FSCs. Moreover, TGF-beta 1 can induce its own mRNA in the same cells.

Liver collagen of rats submitted to chronic intoxication with acetaldehyde

It was found that chronic intoxication of rats with acetaldehyde results in a distinct, progressive increase of 5-3H-proline incorporation into collagen synthesized by liver. At the same time biosynthesis of other proline-containing (noncollagenous) proteins does not change significantly. On the other hand the collagen content in the rat liver did not increase in the early stage of acetaldehyde administration, but increased when acetaldehyde feeding was continued for 6 months. About 40% increase of total collagen content was found in livers of the intoxicated animals. All the investigated collagen types (I, III, IV and V) grew in the same degree. No changes in proportional relationships between collagens of different types were found.

Extracellular matrix formation in piecemeal necrosis: immunoelectron microscopic study

Immunolocalization of Type I, Type III and Type IV collagens, laminin and prolyl hydroxylase (PH), a key enzyme in collagen synthesis, was examined to clarify the fibrotic process in chronic, active liver disease. In piecemeal necrosis of chronic, active hepatitis (CAH) and active liver cirrhosis (LC), fat-storing cells (FSCs) and transitional cells (TSCs), containing abundant rough endoplasmic reticulum (RER), were increased in number and stained intensely for PH. Immunodeposits of extracellular matrix (ECM) components were found in the RER, Golgi apparatus (GA) and vesicles of these cells, especially in cases with marked inflammation. On the other hand, in the periportal areas of chronic, persistent hepatitis (CPH) or inactive LC, immunoreaction of ECM components was seldom found in the RER of FSCs and TSCs. In the portal tract, immunodeposits of ECM components were seldom found in the organelles of fibroblasts, although ECM was increased there. These findings indicate that FSCs and TSCs in piecemeal necrosis might play a role in the production of ECM components in the progression of fibrosis during the development of chronic active liver disease. In addition, ECM component production by FSCs and TSCs is associated with marked inflammation.

Role of mesenchymal cell populations in porcine serum-induced rat liver fibrosis

The role of liver mesenchymal cell populations in porcine serum-induced rat liver fibrosis were studied morphologically and immunohistochemically. Five-week-old rats were intraperitoneally injected with porcine serum twice a week and examined at various intervals between 3 and 24 wk after the initial injection. At an early phase, numbers of fibroblasts and extracellular matrix increased in the walls of central veins and in portal and capsular connective tissues. In the walls of central veins, the number of "second-layer cells" (i.e., the fibroblasts located at the second layer of the wall) increased. Connective tissue septa, accompanying some fibroblasts, extended from these interstitial tissues into the hepatic parenchyma, and their foremost edges came into direct contact with the perisinusoidal stellate cells. The sinusoids adjacent to the newly formed septa collapsed and later disappeared; this process resulted in the formation of hepatic limiting plates along the septa. At a more advanced stage, the interstitial fibroblasts and septal cells-which were derived from interstitial fibroblasts and the stellate cells-increased and became multilayered, constructing three-dimensional cell networks. These networks, together with increased collagen fibrils and elastic fibers, constitute the fibrotic dense connective tissue. In the control rat, smooth muscle cells were positive on vimentin, desmin and smooth muscle-alpha-actin staining. The stellate cells, second-layer cells, capsular and portal fibroblasts were shown to be vimentin and desmin positive and smooth muscle-alpha-actin negative. In the fibrotic liver, septal(fibroblastic) cells were vimentin and desmin positive and smooth muscle-alpha-actin negative. We conclude that not only the perisinusoidal stellate cells but also the interstitial fibroblasts, including the second-layer cells, play substantial role in the development of porcine serum-induced septal fibrosis in rat liver.

Polyunsaturated lecithin prevents acetaldehyde-mediated hepatic collagen accumulation by stimulating collagenase activity in cultured lipocytes

We recently found that polyunsaturated lecithin prevents ethanol from causing cirrhosis in the baboon. Because transformation of lipocytes to transitional cells plays a key role in hepatic fibrogenesis in vivo, and because this process in alcohol-fed baboons was found to be attenuated by polyunsaturated lecithin, we focused on lipocytes to study the mechanism of the protective effect. Rat lipocytes cultured on plastic undergo spontaneous activation, accompanied by expression of alpha-smooth muscle actin isoform and production of substantial amounts of type I collagen. The latter was further increased on incubation with acetaldehyde. This in vitro model was used here to study how acetaldehyde-mediated collagen production and accumulation can be turned off. Addition of polyunsaturated lecithin (10 mumols/L) was found to prevent the acetaldehyde-induced increase in collagen accumulation by 83% (p less than 0.001). By contrast, a saturated phospholipid (10 mumols/L dilauroyl phosphatidylcholine), a monounsaturated one (10 mumols/L linoleoyl-palmitoyl phosphatidylcholine) or linoleic acid (20 mumols/L bound to albumin) had no such effect. Incorporation of [3H]proline into collagen and the expression of alpha-1 (I) procollagen mRNA were increased by acetaldehyde; the latter was not significantly affected by polyunsaturated lecithin. Polyunsaturated lecithin increased lipocyte collagenase activity by 100% (p less than 0.001), whereas dilauroyl phosphatidylcholine, linoleoyl-palmitoyl phosphatidylcholine and linoleic acid had no such action. We concluded that (a) polyunsaturated lecithin selectively prevents the acetaldehyde-induced increase in collagen accumulation in lipocyte cultures, whereas other phospholipids or linoleate have no such effect; and (b) polyunsaturated lecithin does not modify the acetaldehyde-mediated increase in alpha-1 (I) procollagen mRNA, but it increases collagenase activity, suggesting that the protective effect exerted by polyunsaturated lecithin against alcohol induced fibrosis in vivo is due at least in part to stimulation of collagenase activity, which may prevent excess collagen accumulation by offsetting increased collagen production.

Fibrogenesis in cirrhosis. Potential for therapeutic intervention

Liver cirrhosis is an end stage of several diseases that affect the liver chronically. It is characterized, among other things, by excess collagen deposition, distortion of liver architecture, tissue malfunction and hemodynamic alterations. Many of the complications of cirrhosis may result from excess matrix-deposition. Therefore, prevention of collagen accumulation or removal of collagen deposits could ameliorate the disease. In this article we discuss the pathophysiology of liver fibrosis and we describe various compounds with antiinflammatory and antifibrogenic activity. We discuss their possible mechanism of action and we describe animal and clinical studies in which these compounds have been utilized.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic intoxication with acetaldehyde stimulates collagen biosynthesis in rat liver

It was found that chronic intoxication of rats with acetaldehyde results in a distinct, progressive increase of 5(3)H-proline incorporation into collagen synthesized by liver. At the same time, biosynthesis of other proline-containing (noncollagenous) proteins does not change significantly. The effects are similar to those induced by chronic intoxication of rats with ethanol. Since acetaldehyde is an intermediary metabolite formed during ethanol oxidation in liver, it may be concluded that acetaldehyde is a factor responsible for alcohol-induced liver fibrosis.

Hepatic, metabolic and toxic effects of ethanol: 1991 update

Until two decades ago, dietary deficiencies were considered to be the only reason for alcoholics to develop liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition and direct hepatotoxic effects of ethanol were established. Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins, and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) that contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens, and even nutritional factors such as vitamin A. In addition, ethanol depresses hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A is strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Microsomal induction also results in increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin gene-related peptide increases the production of glycosaminoglycans but not of collagen type I and III in cultures of rat fat-storing cells

We investigated whether calcitonin gene-related peptide (CGRP) was able to affect the production of collagen and glycosaminoglycans (GAG) in cultures of rat fat-storing cells (FSC). Rat CGRP (1 nM-1 microM) induced a dose-dependent increase of total GAG production in FSC cultures with an EC50 of 28 nM. One uM human CGRP (8-37) shifted the dose-response curve of rat CGRP to the right (EC50 = 257 nM) without depressing the maximal response. Salmon calcitonin (1 nM-1 microM) did not significantly modify total GAG accumulation in FSC cultures. Collagen type I and III production was not significantly affected by either CGRP or calcitonin in FSC cultures. These findings suggest that peripheral sensory neuropeptides may modulate liver fibrogenesis.

Acetaldehyde-collagen adducts in CCl4-induced liver injury in rats

Circulating AC levels as well as antibodies against AC-protein adducts are increased in non-alcoholic liver injury. To identify the adducts, we used rats with CCl4-induced cirrhosis. Liver subcellular fractions were analyzed by immunochemical staining of protein slot blots and of electrophoretically separated proteins, transferred to nitrocellulose, using AC-protein adduct-specific antibodies. One reactive protein of about 200 kD was detected in the liver soluble fraction and in the cytosol of isolated hepatocytes and, to a lesser extent in the liver microsomes of CCl4-treated rats; in control animals, this reactivity was much weaker. The immunopositive AC adduct co-migrated with the beta 1,2 dimer of rat collagen type I; it was sensitive to digestion by a highly purified collagenase and also reacted with anti-rat collagen type I-specific IgG. In addition, comparison of peptides of the CNBr-digested, immunoprecipitated AC adduct with those of rat collagen type I revealed a high degree of similarity. Thus, AC adduct formation occurs in liver injury of non-alcoholic origin, and a target protein appears to be related to collagen type I, most likely the procollagen precursor.