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D L Knook

Publications and source records attributed to D L Knook.

At least 37 records · Page 2Linked to original sources
PubMed1995

Role of vitamin A in liver fibrosis.

The relationship between vitamin A and liver fibrosis was studied with a CCl4-induced fibrosis model in rats. Depending on the time of administration, vitamin A can potentiate or reduce fibrosis: when present during CCl4-treatment parenchymal cell damage and fibrosis were enhanced, whereas vitamin A post-treatment strongly reduced fibrosis. Enhanced fibrosis was also found in rats with low hepatic retinoid levels. Administration of beta-carotene during CCl4-treatment reduced several signs of fibrosis. The notion that liver retinoids play an important role in hepatic fibrogenesis is discussed.

Animals↗
PubMed1995

Beta-carotene (provitamin A) decreases the severity of CCl4-induced hepatic inflammation and fibrosis in rats.

Earlier data from experiments in rats have shown that administration of retinyl esters (vitamin A) strongly influences the effects of CCl4 on the liver. The accumulation of collagen was inhibited, but an increase in CCl4-toxicity with high mortality was observed. The present study was conducted to examine the effects of beta-carotene (provitamin A) on CCl4-related general and hepatic toxicity in rats. Oral administration of beta-carotene during CCl4-treatment resulted, biochemically, in a significantly lower increase in the hydroxyproline liver content and, histopathologically, in less severe liver fibrosis as compared with the liver of rats not treated with beta-carotene. The study also showed that beta-carotene administration could prevent the long-term loss of retinoids from the CCl4-injured liver. No significant toxic effects of beta-carotene, as previously found with retinyl esters (vitamin A), were observed. This experimental study suggests that beta-carotene has the therapeutic potential to decrease the severity of liver fibrosis without marked toxicity.

Animals↗
PubMed1994

Morphological characterization of scavenger receptor-mediated processing of modified lipoproteins by rat liver endothelial cells.

Scavenger receptor-mediated processing by rat liver endothelial cells in vivo is studied by using acetylated and oxidized low-density lipoproteins (LDL) as ligands. The cellular localization of acetylated LDL (Ac-LDL) is visualized by both immunohistochemistry and silver enhancement of ultrasmall gold particles conjugated to Ac-LDL. Scavenger receptor-mediated internalization by the endothelial cells only involves coated vesicle formation. Subsequently, three stages of processing are noticed, as represented by (i) large electron lucent vesicles, with ligand in close association to the membrane, (ii) relatively electron-lucent structures, with Ac-LDL dispersed over the vesicular lumen, while tubular membrane extensions did not contain ligand, and (iii) electron-dense vesicles in which the nondegradable gold particles of the conjugate accumulate, while the immunoreactivity for Ac-LDL is low. Addition of chloroquine, an inhibitor of lysosomal degradation, demonstrated that the relatively electron-lucent and electron-dense structures represent subsequent stages of the lysosomal pathway of Ac-LDL, which was also verified by detection of the lysosomal enzyme cathepsin D. Evaluation of the processing of Ac-LDL and oxidized LDL, labeled with different fluorochromes, demonstrated that both ligands follow apparently the same intracellular pathway in the liver endothelial cells, since the fluorescent probes are predominantly localized in the same structures. It is concluded that the scavenger receptor-mediated processing of modified LDL by rat liver endothelial cells involves four morphologically distinguishable stages which represent a highly effective catabolic route, sustaining the important role of the liver endothelial cells in the protection against circulating atherogenic lipoproteins.

Animals↗
PubMed1994

Alcohol in combination with malnutrition causes increased liver fibrosis in rats.

Rats were malnourished for 12 months with a highly inadequate fat-rich, calorie-sufficient but otherwise poly-deficient liquid diet composed of mashed potatoes with mayonnaise, comparable with the nutritional intake of many chronic alcoholics. When alcohol was incorporated into this diet, administered as whisky in drinking water available ad libitum, the livers of all eight rats showed increased fibrosis and cirrhosis as compared to the livers of the eight non-alcohol-treated, isocalorically fed, paired control rats. Alcohol-treated rats developed fibrosis and cirrhosis on a dietary fat content of 38% of total caloric intake and low blood alcohol levels, ranging from 50 to 126 mg/dl, due to gradual intake over the day and to low absolute intake (mean 11.9 +/- 0.6 g/kg per day). None of the rats died spontaneously. Malnutrition is likely to be an important factor in the development of the fibrosis of alcoholic liver disease, and this rat model may be used to study aspects of the pathogenesis.

Alanine Transaminase↗
PubMed1994

Cholesteryl esters from oxidized low-density lipoproteins are in vivo rapidly hydrolyzed in rat Kupffer cells and transported to liver parenchymal cells and bile.

Human low-density lipoprotein was labeled in its cholesteryl ester moiety with [3H]cholesteryl oleate or [3H]cholesteryl oleoyl ether and oxidized by exposure to 10 mumol/L of cupric sulfate. The in vivo metabolism of cholesteryl esters of oxidized low-density lipoprotein was determined after injection into rats. When oxidized low-density lipoprotein was labeled with [3H]cholesteryl oleoyl ether, a nonhydrolyzable analog of cholesteryl oleate, Kupffer cells contributed to 55.1% +/- 4.1% of the total liver uptake 10 min after injection. When [3H]cholesteryl oleate-labeled oxidized low-density lipoprotein was injected, the radiolabeled cholesterol esters were nearly completely hydrolyzed within 1 hr of injection. Within this time, the Kupffer cell-associated radioactivity declined to 32% of the maximal uptake value. In serum, the highest specific resecreted [3H]cholesteryl (esters) were associated with the serum high-density lipoprotein fraction, suggesting a role for high-density lipoprotein as an in vivo cholesterol acceptor. The kinetics of biliary secretion were studied in rats equipped with catheters in the bile duct, duodenum and heart. One hour after injection of [3H]cholesteryl oleate-labeled oxidized low-density lipoprotein, 4.15% +/- 0.67% of the injected dose was secreted in the bile, mainly as bile acids. Six hours after injection, this value was 19.2% +/- 1.2%. These values are three times higher than those for injected [3H]cholesteryl oleate-labeled acetylated low-density lipoprotein, which is initially mainly taken up by liver endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Fat-storing cells and myofibroblasts are involved in the initial phase of carbon tetrachloride-induced hepatic fibrosis in BN/BiRij rats.

This study on the appearance, distribution and kinetics of fibroblast-like cells (fat-storing cells, transitional cells, myofibroblasts and fibroblasts) after CCl4-treatment was undertaken to delineate further the respective roles of these cell types in liver fibrogenesis. The different cell types were distinguished on the basis of their immunophenotypic pattern with a combination of marker antibodies and on the basis of ultrastructural characteristics. Combined staining for alpha-smooth muscle actin (sma) and desmin (Des) revealed perisinusoidal fat-storing cells (FSC) as d+ sma- and myofibroblasts around the central veins of the normal rat liver as d+ sma+. During the initial phase of CCl4-induced hepatic fibrosis (week 1 and 2), the number of d+ sma+ cells increased in the degenerating area around the central veins and d+ sma+ cells appeared in the very thin fibrotic septa at week 2. Ultrastructural examination of the affected central areas showed the presence of myofibroblasts. These sma+ cells proliferated, as shown by double staining for bromodeoxyuridine (BrdU) and sma. In degenerating parenchymal areas, d+ sma- FSC were present. The FSC in the perisinusoidal space of areas which were not affected by CCl4 intoxification, remained d+ sma-. These immunostaining findings support the electron microscopical results, which show the presence of cells with the typical ultrastructural characteristics of FSC in both the degenerating areas and the perisinusoidal space of unaffected areas. After one week of CCl4-treatment, enhanced deposition of procollagen type III was observed around the central veins. Enhanced deposition of collagen type IV was seen subendothelially along the sinusoids, notably in degenerating parenchymal areas where the septa were later formed. FSC appear to be the principal source of collagen type IV during fibrogenesis. These observations further support and specify the role of FSC in early fibrogenesis. With the progression of the CCl4-induced fibrosis, d+ sma+ myofibroblasts remained localized in the fibrotic septa, but now along their outer edge. The majority of the cells in the septa were formed by d- sma- cells indicating a prominent role of fibroblasts in the septal formation. Septal fibroblasts are not only likely to produce matrix components, but also were shown to degrade collagen, as evidenced by the increased number of collagen-containing vacuoles during the course of fibrosis. In conclusion, myofibroblasts and FSC appear to be the main cell types involved in the initial phase of liver fibrogenesis induced by CCl4. Both myofibroblasts and FSC divide and transform.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Vitamin A deficiency potentiates carbon tetrachloride-induced liver fibrosis in rats.

Earlier studies have shown that retinoid administration suppresses the generation of hepatic fibrosis and stimulates its regression in normal (i.e., vitamin A-sufficient) carbon tetrachloride-treated rats. This study focuses on the possible role of a marginal or deficient vitamin A status on carbon tetrachloride-induced fibrosis. This experimental study in rats shows that vitamin A status, reflected by hepatic retinoid content (retinol and retinyl esters), modulates the development of hepatic fibrosis induced by carbon tetrachloride. In rats with low hepatic retinoid levels (12 +/- 0.9 micrograms/gm liver), carbon tetrachloride-induced liver fibrosis was more pronounced than in rats with sufficient hepatic retinoid levels (1,065 +/- 327 micrograms/gm liver). Enhanced liver fibrogenesis was confirmed both morphologically and by a higher hydroxyproline content of the liver. It was associated with a reduced liver weight and the development of parenchymal regeneration nodules. Furthermore, carbon tetrachloride treatment itself reduced the hepatic retinoid content in rats independently of the liver vitamin A status before treatment and increased serum retinol levels in vitamin A-sufficient rats. The results show that the vitamin A status of the liver plays an important role in hepatic fibrogenesis. Low hepatic vitamin A levels, which can be the result not only of low dietary intake but also of interference with vitamin A metabolism by agents such as ethanol and carbon tetrachloride, may be a risk factor for the development of liver fibrosis. We suggest that retinoids modulate collagen synthesis and deposition irrespective of the degree of hepatocellular necrosis induced by carbon tetrachloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Visualization of the uptake and processing of oxidized low-density lipoproteins in human and rat liver.

The interaction of oxidized human low-density lipoproteins with human and rat liver was analyzed by light and electron microscopy. At the light microscopic level oxidized low-density lipoprotein was visualized by the fluorescent dye 1,1' dioctadecyl 3,3,3',3' tetramethyl indocarbocyanine perchlorate, whereas at the electron microscopic level, an indirect immunolabeling procedure was used that detected the apoprotein B of the oxidized low-density lipoprotein. In rats, oxidized low-density lipoprotein was administered intravenously, and uptake by human liver was studied by perfusion of tissue blocks. Both in human and in rat liver, fluorescently labeled oxidized low-density lipoprotein was mainly found to become concentrated in Kupffer cells and, to a lesser extent, in endothelial cells. In both species the cell association of fluorescently labeled oxidized low-density lipoprotein could be inhibited by preadministration of polyinosinic acid, indicating a scavenger receptor-mediated process. At the electron microscopic level, oxidized low-density lipoprotein was found to bind mainly to areas of the plasma membrane of the Kupffer cells without clathrin coating, although binding to coated regions was also noticed. Internalization of the ligand occurred through coated vesicle formation and through membrane folding of interacting lamellipodia and wormlike structures. No indication for phagocytosis of aggregated oxidized low-density lipoprotein particles was noticed. After internalization, the immunoreactive oxidized low-density lipoprotein was detected in relatively electron-lucent endosomes and, subsequently, in lysosomes. Endothelial cells internalized oxidized low-density lipoprotein solely through coated pits, after which the particles were transferred through endosomes into lysosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Selective uptake of cholesteryl esters from apolipoprotein-E-free high-density lipoproteins by rat parenchymal cells in vivo is efficiently coupled to bile acid synthesis.

[3H]Cholesteryl ester-labelled human high-density lipoprotein (HDL) was injected into rats and its decay, intrahepatic cellular distribution and the kinetics of biliary secretion were determined. At 10 min after injection the hepatic uptake of cholesteryl esters from HDL was 3-fold higher as compared with the apolipoprotein. Selective uptake was exerted only by parenchymal cells (5.6-fold more cholesteryl esters than apolipoprotein) and not by liver endothelial or Kupffer cells. The kinetics of biliary secretion of processed cholesteryl esters initially associated with HDL or low-density lipoprotein (LDL) were compared in unrestrained rats, equipped with permanent catheters in bile duct, duodenum and heart. At 72 h after injection of [3H]cholesteryl oleate-labelled HDL, 51.0 +/- 2.5% of the injected dose was recovered as bile acids, which is about twice as high as the secretion of biliary radioactivity after injection of [3H]cholesteryl oleate-labelled LDL. Oestradiol treatment stimulated only liver uptake of LDL cholesteryl esters, and resulted in a 2-fold higher liver uptake than with HDL. However, the rate of radioactive bile acid formation from [3H]cholesteryl oleate-labelled HDL was still more rapid than for LDL. It is concluded that the selective uptake pathway for cholesteryl esters from HDL in parenchymal cells is more efficiently coupled to the formation of bile acids than is the cholesteryl ester uptake from LDL. This efficient coupling may facilitate the role of HDL in reverse cholesterol transport.

Animals↗
PubMed1991

Visualization of the interaction of native and modified lipoproteins with parenchymal, endothelial and Kupffer cells from human liver.

The interaction of low density lipoprotein, acetylated low density lipoprotein and apolipoprotein E-free high density lipoprotein with parenchymal, endothelial and Kupffer cells of human liver was visualized. For this purpose, the fluorescent phospholipid analog 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate was used to label the lipoproteins. The involvement of both parenchymal and nonparenchymal cells in the uptake of 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate-labeled low density lipoprotein and acetylated low density lipoprotein was studied using in vitro perfusion of human liver tissue blocks. In addition, primary hepatocyte cultures were used to visualize the interaction with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate-labeled apolipoprotein E-free high density lipoprotein and (modified) low density lipoprotein. 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate-low density lipoprotein showed a time-dependent and concentration-dependent interaction with both hepatocytes and Kupffer cells, although the intensity of the interaction with parenchymal cells varied strongly among the liver donors. Uptake of 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate-low density lipoprotein by both cell types was strongly inhibited by the presence of excess unlabeled low density lipoprotein in the (perfusion) medium. Methylation and hydroxyacetaldehyde treatment of low density lipoprotein prevented the uptake of low density lipoprotein. This indicated that the uptake of low density lipoprotein by Kupffer and parenchymal cells was mediated by the low density lipoprotein receptor. 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate-acetylated low density lipoprotein was mainly taken up in situ by liver endothelial cells and by a minor population of Kupffer cells. Polyinosinic acid, a known inhibitor of the scavenger receptor, prevented the uptake by liver endothelial cells. Therefore human liver endothelial cells express active scavenger receptors on their surface. Apolipoprotein E-free 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate-high density lipoprotein was found to be associated with the membrane of cultured liver parenchymal cells but was not taken up intracellularly, indicating a cholesterol exchange process occurring extracellularly at the plasma membrane. The cellular localization of lipoprotein receptors and uptake of the various classes of lipoproteins are comparable with the situation in rats.

Cells, Cultured↗
PubMed1991

Changes in endotoxin sensitivity in ageing. Absorption, elimination and mortality.

In this paper we describe the influence of ageing on responses to intravenously-injected endotoxin in two rat strains. Old age had no apparent effect on the absorption of 51Cr-labelled endotoxin from either jejunum or colon. Notwithstanding, aged animals appeared much more sensitive than their young counterparts to the lethal effects of intravenously injected endotoxin. Old animals exhibited virtually 100% mortality over the dose range 1-4 mg/100 g body weight while only sporadic deaths were seen in young animals. One consistent feature of dying animals was a profound and progressive hypothermia. At post mortem examination, the major findings were in the liver (leukocyte infiltrates and hepatocellular necrosis) and kidneys (acute tubular necrosis). Ageing was associated with slower removal of endotoxin from the circulation but not to an extent that could reasonably account for the enhanced sensitivity to endotoxin toxicity.

Aging↗
PubMed1991

Chronic administration of ethanol with high vitamin A supplementation in a liquid diet to rats does not cause liver fibrosis. 1. Morphological observations.

Rats of two strains (BN/BiRij and WAG/Rij) were fed the ethanol-containing Lieber-De Carli liquid diet supplemented with high amounts of vitamin A for 16 months. In contrast to Lieber and co-workers, who showed liver fibrosis developing within 9 months on the same diet in Sprague-Dawley rats, we were unable to demonstrate a histological and biochemical increase in liver collagen in either strain. Steatosis was present to a varying degree in both strains in ethanol-treated rats, but also in control animals. Considerable liver inflammation with focal necrosis accompanied by severe systemic inflammation was observed in 60% of the ethanol-treated WAG rats. This suggests that, at least in rats, the main effects of chronic ethanol consumption on the liver may be secondary to interference with host resistance to infections. The ethanol-high vitamin A Lieber-De Carli liquid diet does not necessarily elicit fibrosis or other characteristic histological abnormalities of human alcoholic liver disease.

Animals↗
PubMed1991

Chronic administration of ethanol with high vitamin A supplementation in a liquid diet to rats does not cause liver fibrosis. 2. Biochemical observations.

The inability of the 'ethanol/high vitamin A Lieber-DeCarli diet' to induce liver fibrosis in two different rat strains was further evaluated by determining changes in parameters of liver cell damage and of retinoid and lipid metabolism. In the ethanol/vitamin A-treated group, slight but constant hepatic cell damage, as indicated by elevated alanine aminotransferase, aspartate aminotransferase and glutamate dehydrogenase activities in blood, was already observed at 6 months and maintained until the time of death at 16 months. Serum gamma-glutamyl transaminase activities were not raised. Moderate parenchymal liver cell damage was not accompanied by fibrosis. Hypertriglyceridemia or hypercholesterolemia were observed at 6-16 months of chronic alcohol administration. This response was strain dependent. In ethanol-treated rats of both strains, total liver retinoids and serum retinol concentrations were not altered. Therefore, the hypothesis that interaction between alcohol and retinoids is a major factor in the pathogenesis of alcoholic liver disease, needs to be reconsidered.

Animals↗
PubMed1990

Sinusoidal endothelial cells of the liver: fine structure and function in relation to age.

Liver endothelial cells form a continuous lining of the liver capillaries, or sinusoids, separating parenchymal cells and fat-storing cells from sinusoidal blood. Liver sinusoidal endothelial cells differ in fine structure from endothelial cells lining larger blood vessels and from other capillary endothelia in that they lack a distinct basement membrane and also contain open pores, or fenestrae, in the thin cytoplasmic projections which constitute the sinusoidal wall. This distinctive morphology supports the protective role played by liver endothelium, the cells forming a general barrier against pathogenic agents and serving as a selective sieve for substances passing from the blood to parenchymal and fat-storing cells, and vice versa. Sinusoidal endothelial cells, furthermore, significantly participate in the metabolic and clearance functions of the liver. They have been shown to be involved in the endocytosis and metabolism of a wide range of macromolecules, including glycoproteins, lipoproteins, extracellular matrix components, and inert colloids, establishing endothelial cells as a vital link in the complex network of cellular interactions and cooperation in the liver. Fine structural studies in combination with the development of cell isolation and culture techniques from both experimental animal and human liver have greatly contributed to the elucidation of these endothelial cell functions. Morphological and biochemical investigations have both revealed little changes with age except for an accumulation of iron ferritin and a decrease in the activities of glucose-6-phosphatase, Mg-ATPase, and in glucagon-stimulated adenylcyclase. Future studies are likely to disclose more fully the role of sinusoidal endothelial cells in the regulation of liver hemodynamics, in liver metabolism and blood clearance, in the maintenance of hepatic structure, in the pathogenesis of various liver diseases, and in the aging process in the liver.

Aging↗
PubMed1990

Comparative endotoxin-induced hepatic injury in young and aged rats.

Recent studies have demonstrated that aged rats are more susceptible to the lethal effects of endotoxin (ET) than young rats. The early (15 min to 7 h) hepatic ultrastructural and biochemical changes induced by ET in young (6 months) and aged (24 months) rats were evaluated to elucidate cell populations and/or the mechanisms that may be responsible for the previously observed differential effects. Aged rats given ET had significantly increased numbers of neutrophils in hepatic sinusoids at 30 min and thereafter as compared with ET-treated young rats. Morphologic evidence of coagulation within hepatic sinusoids, including aggregates of fibrin enmeshed among polymorphonuclear leukocytes and platelet aggregates, was frequently observed in ET-treated aged rats but not in ET-treated young rats. In contrast, Kupffer cells of ET-treated young rats frequently contained phagocytized neutrophils and platelets, whereas this phenomenon was rarely observed in Kupffer cells of ET-treated aged rats. Hepatocellular morphologic injury was more pronounced and occurred at earlier time periods in ET-treated aged rats, and was accompanied by significant increase in hepatic transaminases. ET-treated aged rats had an earlier onset and greater severity of endothelial cell injury than did ET-treated young rats. The results of this study indicate a greater aggregation of blood elements in the hepatic sinusoids of aged rats following the intravenous administration of ET, which suggests that a greater diminution in microcirculation was induced in aged rats by ET. Additionally, the increased phagocytosis of inflammatory cells by Kupffer cells of young rats may be a mechanism which affords protection against endotoxin-induced lethality.

Aging↗
PubMed1990

Necessity of the assessment of health status in human immunogerontological studies: evaluation of the SENIEUR protocol.

Disease is frequent in ageing, and the many conflicting results in studies of the ageing process can be due to the presence of factors such as underlying disease or the use of medication. For immunogerontology, a solution to this problem was initiated in 1984 by a working party of EURAGE, the European Community's Concerted Action Programme on Ageing and Diseases. A protocol defining strict admission criteria to studies of ageing, the SENIEUR protocol, was elaborated. This protocol intends to limit the influence of disease and/or medication and to standardize admission criteria to immunogerontological studies. In subjects fulfilling the SENIEUR criteria, we found less immunological defects with ageing than generally stated. This could mean that many studies performed in not-optimally healthy subjects describe defects that are not a consequence of the ageing process, but could be a result of underlying disease or of the influence of medication. For lymphocyte subsets, certain changes are only found in the comparison of SENIEUR groups of young and aged, while other changes are only found when non-healthy groups are compared. The occurrence of monoclonal gammopathies and autoantibodies was increased in ageing, but was also influenced by health status. Experience of other groups, and the objections against the protocol are discussed.

Adult↗