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Uptake and processing of remnants of chylomicrons and very low density lipoproteins by rat liver. J Lipid Res 1984. [DOI: 10.1016/s0022-2275(20)34458-8] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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52
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Tsujita T, Nakagawa A, Shirai K, Saito Y, Okuda H. Methyl butyrate-hydrolyzing activity of hepatic triglyceride lipase from rat post-heparin plasma. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)90849-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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53
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54
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Chung BH, Segrest JP. Resistance of a very low density lipoprotein subpopulation from familial dysbetalipoproteinemia to in vitro lipolytic conversion to the low density lipoprotein density fraction. J Lipid Res 1983. [DOI: 10.1016/s0022-2275(20)37898-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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55
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Wright PL, Smith KF, Day WA, Fraser R. Hepatic sinusoidal endothelium in sheep: an ultrastructural reinvestigation. Anat Rec (Hoboken) 1983; 206:385-90. [PMID: 6625200 DOI: 10.1002/ar.1092060405] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Following perfusion fixation of livers from fetal, neonatal, and adult sheep, the ultrastructure of the fenestrated sinusoidal endothelium was examined. In contrast to an earlier report which utilized immersion fixation, we found the fenestrae to be unoccluded by diaphragms or basal lamina, thus offering only a discontinuous barrier between the blood and the space of Disse and hepatocytes. This observation was confirmed by perfusing the liver with marker particles. The fenestrae appear, therefore, to have a sieving function, regulating the metabolism of particulate matter such as lipoproteins in sheep in a similar manner to that which has been shown to occur in rats.
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Chajek-Shaul T, Eisenberg S, Oschry Y, Olivecrona T. Metabolic heterogeneity of post-lipolysis rat mesenteric lymph small chylomicrons produced in vitro. J Lipid Res 1983. [DOI: 10.1016/s0022-2275(20)37928-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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57
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Kane JP, Chen GC, Hamilton RL, Hardman DA, Malloy MJ, Havel RJ. Remnants of lipoproteins of intestinal and hepatic origin in familial dysbetalipoproteinemia. ARTERIOSCLEROSIS (DALLAS, TEX.) 1983; 3:47-56. [PMID: 6824496 DOI: 10.1161/01.atv.3.1.47] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We used the low molecular weight form of apolipoprotein B (B-48) as a marker for the identification of remnant particles formed from chylomicrons in the plasma of patients with familial dysbetalipoproteinemia. In the serum of patients fasted 14 hours, the d less than 1.006 g/cm3 lipoproteins of prebeta mobility, separated by starch block electrophoresis, contained only the primary hepatogenous species of apolipoprotein B (B-100), and their lipid composition resembled that of normal prebeta very low density lipoproteins. In contrast, the fraction with beta mobility contained both the B-48 and B-100 proteins; the B-48 protein was found primarily among the largest particles. All fractions of beta mobility were greatly enriched with cholesteryl esters. The beta fraction thus contains remnant particles which appear to originate both from chylomicrons and hepatogenous very low density lipoproteins. It appears that these remnant particles share a common removal mechanism which is impaired in familial dysbetalipoproteinemia.
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58
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Pethick DW, Lindsay DB, Barker PJ, Northrop AJ. The metabolism of circulating non-esterified fatty acids by the whole animal, hind-limb muscle and uterus of pregnant ewes. Br J Nutr 1983; 49:129-43. [PMID: 6821682 DOI: 10.1079/bjn19830018] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
1. The over-all and regional metabolism of non-esterified fatty acids (NEFA) was studied using a combination of isotopic and arteriovenous-difference techniques. 2. There was a common linear relationship, whether stearic, palmitic or oleic acids were used as tracer, between the arterial NEFA concentration and the rates of entry and oxidation. 3. Assuming that the tracer used reflected the metabolism of all the NEFA, the total entry rate in fed and fasted pregnant ewes was (mean +/- SE) 0.44 +/- 0.02 and 0.55 +/- 0.07 mmol/h per kg body-weight respectively. Oxidation of NEFA contributed (mean +/- SE) 34 +/- 5 and 58 +/- 7% to the respiratory carbon dioxide in fed and fasted animals, this accounting for (mean +/- SE) 46 +/- 6 and 59 +/- 3% of the respective entry rates. 4. Hind-limb muscle both utilized and produced NEFA. The mean gross fractional extraction (calculated from isotopic uptake) was (mean +/- SE) 9 +/- 1%. Gross utilization of any NEFA and appearance of 14CO2 across the muscle were linearly related to the arterial concentration of tracer fatty acid, irrespective of whether this was oleate or stearate. The amount of 14CO2 appearing was consistent with (mean +/- SE) 54 +/- 8% of the CO2 produced by the hind-limb being derived from NEFA oxidation. 5. Infused NEFA were partly converted to ketone bodies. Uptake and oxidation in the hind-limb of ketones formed in the liver could account for approximately 20% of the 14CO2 apparently produced in muscle from NEFA. Correction for this reduces the proportion of CO2 derived from NEFA to 43%. There was some indication that ketones were also produced from NEFA in the hind-limb. 6. NEFA were not a significant energy source for the gravid uterus. 7. An over-all view of energy sources for the whole animal and for hind-limb muscle in normal and fasted pregnant sheep was presented.
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Haberbosch W, Poli A, Augustin J. Characterization of human chylomicrons. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 713:398-409. [PMID: 7150620 DOI: 10.1016/0005-2760(82)90259-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Apolipoprotein and lipid composition of differently sized chylomicrons from healthy volunteers was determined. During their intravasal catabolism the chylomicrons lose triacylglycerol and apolipoproteins. Decreasing particle size results in a loss of apolipoprotein C and apolipoprotein E peptides and an increase in apolipoproteins B and A-I, which constitutes more than 20% of the moiety of small chylomicrons. The C peptides do not seem to behave as a functional entity. Apolipoprotein C-III, the inhibitor of lipolytic activities, is catabolized independently of the other C peptides. Albumin constitutes about 15-25% of the protein moiety of all chylomicrons. The different chylomicron fractions were incubated with lipolytic activities of lipoprotein lipase and hepatic triacylglycerol lipase. At lower substrate concentrations the reactions were of first-order. Large chylomicrons were the favored substrate for both enzymes with Michaelis Menten constant Km = 1.1 mM for hepatic triacylglycerol lipase and 0.48 mM for lipoprotein lipase. After incubation with hepatic triacylglycerol lipase or lipoprotein lipase the shape of chylomicrons differs from that of control particles as demonstrated by electron microscopy. C peptides were completely dissociated and found in the infranatant. In the enzyme assay with triolein gum arabic substrate several apolipoproteins showed an influence on the activities of hepatic triacylglycerol lipase and lipoprotein lipase. Apolipoprotein C-III peptides were the most effective inhibitors of both enzymes. Also, apolipoprotein A-II, A-I and apolipoprotein C-I inhibited lipoprotein lipase activity, whereas only apolipoprotein A-II was able to decrease hepatic triacylglycerol activity.
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60
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Reardon MF, Sakai H, Steiner G. Roles of lipoprotein lipase and hepatic triglyceride lipase in the catabolism in vivo of triglyceride-rich lipoproteins. ARTERIOSCLEROSIS (DALLAS, TEX.) 1982; 2:396-402. [PMID: 7126037 DOI: 10.1161/01.atv.2.5.396] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
To define the roles, in vivo, of hepatic triglyceride lipase and lipoprotein lipase in the catabolism of triglyceride-rich lipoproteins, we investigated the relationship between the activities of the above enzymes in postheparin plasma and the fractional removal rates of very low density lipoproteins (VLDL) and VLDL remnant particles. In 22 patients, the fractional removal rates of VLDL and VLDL-remnant particles were determined from analyses of the disappearance of radioiodinated Sf 60-400 and Sf 12-60 lipoprotein B apoprotein. The maximal activities of hepatic triglyceride lipase and lipoprotein lipase were determined in plasma samples drawn 2-60 minutes after heparin injection (60 U/kg). A positive correlation was observed between the fractional removal rate of VLDL and postheparin plasma lipoprotein lipase activity (r = 0.65). When all 22 patients were considered together, no relationship was demonstrable between remnant fractional removal and postheparin plasma lipoprotein lipase activity. However, humans may be subdivided with respect to the way in which they catabolize remnants. In some, all remnant may be catabolized to form LDL. In others, some of the remnant may also be directly removed from the circulation. Those subjects in whom previous studies indicate that all remnant is converted to LDL demonstrated a positive correlation between remnant fractional removal rate and postheparin plasma lipoprotein lipase activity (n = 8, r - 0.83). No correlations between postheparin plasma hepatic triglyceride lipase activity and any of the fractional removal rates were found. These data are consistent with the following: 1) lipoprotein lipase plays a key regulatory role in the catabolism of triglyceride-rich lipoproteins; 2) this role applies only to those catabolic involving the formation of particles of higher density VLDL remnants and low density lipoprotein; and 3) hepatic triglyceride lipase plays no rate-limiting role in the catabolism of VLDL or VLDL-remnant particles.
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61
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Lakshmanan MR, Ezekiel M. Relationship of alcoholic hyperlipidemia to the feed-back regulation of hepatic cholesterol synthesis by chylomicron remnants. Alcohol Clin Exp Res 1982; 6:482-6. [PMID: 6758619 DOI: 10.1111/j.1530-0277.1982.tb05011.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Pairfeeding of ethanol liquid diet for 6 weeks to male Wistar rats resulted in defective extrahepatic as well as hepatic catabolism of rat lymph chylomicrons. Based upon the exponential decay curves of the chylomicrons in the blood compartment it was concluded that chronic ethanol feeding caused 30 and 67% decreases in the rate of degradation of the triacylglycerol and cholesterol moieties, respectively. As a consequence, abnormal chylomicron remnants accumulated in chronic ethanol-fed but not in control animals. These abnormal remnants were not as efficient as the normal remnants in causing the feedback inhibition of cholesterol synthesis in hepatocytes from normal meal-fed rats. Furthermore, the hepatocytes from chronic ethanol-fed animals exhibited defective feedback regulation of cholesterol synthesis by normal chylomicron remnants. The net result of all these abnormalities caused by chronic ethanol feeding would be the delayed clearance of triacylglycerol-rich lipoproteins from the blood compartment and enhanced synthesis and secretion of the triacylglycerol-rich lipoproteins by the liver.
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62
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Frost PH, Shore VG, Havel RJ. Purification of canine post-heparin hepatic lipase. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 712:71-8. [PMID: 7115748 DOI: 10.1016/0005-2760(82)90086-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
A method for the purification of canine hepatic lipase from post-heparin hepatic venous blood plasma was developed and found applicable to mixed venous post-heparin plasma. The method employs sequential (NH4)2SO4 fractionation, heparin-Sepharose chromatography at pH 8.8 and, finally, adsorption to antiserum prepared against dog pre-heparin plasma. The lipase was purified 10,000-fold. The specific activity assayed with Intralipid as substrate was 840 mumol free fatty acid h-1 . mg-1. Enzyme recovery was 20%. Upon electrophoresis of the purified lipase in polyacrylamide gel containing SDS, a major protein-staining band with an apparent molecular weight of 60,000 was consistently found. This component accounted for 85-90% of the protein applied to the gel, and by amino acid analysis appeared to be distinct from canine antithrombin III, a protein thought to contaminate hepatic lipase purified by earlier methods.
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63
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Black DD, Freeman MR, Sabesin SM. Lipoprotein lipase and hepatic lipase deficiencies associated with impaired chylomicron clearance in D-(+) galactosamine hepatitis. Metabolism 1982; 31:620-6. [PMID: 7078435 DOI: 10.1016/0026-0495(82)90102-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
D-(+) galactosamine (GaIN) produces a reversible from of hepatic injury in the rat, accompanied by alterations in morphology and composition of plasma lipoproteins in the fasting state. Lipoprotein lipase (LPL) and hepatic lipase (HL) activities were measured in fasting control and GaIN rats 24 hr after GaIN injection and initiation of fasting. Significant (p less than 0.001) deficiencies of both enzymes were noted in GaIN animals as compared to controls with LPL activity decreasing to 37.6% and HL activity to 23.2% of control values in GaIN animals. Serial enzyme determinations performed in both GaIN and control animals after gastric fat loading revealed an early persistent HL deficiency (p less than 0.025) at 9 hr after GaIN injection and initiation of fasting which persisted after the fat loading at 15 hr, and a later appearing LPL deficiency (p less than 0.025) was noted at 24 hr after GaIN injection and at 9 hr after fat loading. Serial compositional studies of plasma lipoproteins in pooled specimens after a gastric fat load revealed a marked chylomicronemia in GaIN animals compared to controls which reached a maximum at 12 hr after fat loading. A slight increase in VLDL (very low density lipoprotein) triglyceride and total cholesterol (CH) and a late-appearing (16 hr after fat loading) LDL (low density lipoprotein) CH peak, consisting mostly of unesterified CH, were also noted in GaIN rats as compared to control animals. These data demonstrate a defect in chylomicron (CM) catabolism in GaIN hepatopathy in the rat which is probably secondary to the observed severe LPL and HL deficiencies, although other factors such as activator deficiency, plasma inhibitory substances, and a defective CM particle may be important.
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64
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Quarfordt SH, Hanks J, Shelburne F, Schirmer B. Differing uptake of emulsion triglyceride by the fed and fasted rat liver. J Clin Invest 1982; 69:1092-8. [PMID: 7068847 PMCID: PMC370173 DOI: 10.1172/jci110544] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The recycling perfusion of a fasted rat liver with an apoprotein E-enriched synthetic triglyceride emulsion revealed a significantly greater hepatic uptake of both the apoprotein and the triglyceride than did the liver of a chow-fed animal. This greater hepatic triglyceride uptake by the perfused fasted liver in comparison to the fed was also noted for emulsions containing no added apoprotein or supplemented with both the E and CIII-1 proteins. However, no difference in the uptake of the triglyceride emulsion was seen for the fed and fasted livers when evaluated by a nonrecycling single pass perfusion. The isolated hepatocyte plasma membranes from fasted rats failed to demonstrate enhanced binding of apoprotein or lipid when compared to those from fed animals. If the residual E loaded triglyceride emulsion was recovered from the recycling perfusates of fed and fasted livers and evaluated in a non-recycling single-pass system, the emulsion from the fasted perfusion was cleared as facilely as previously, whereas that from the fed was less actively cleared. The emulsions retrieved from the perfusion of the fed liver contained significantly more protein than did the fasted; in particular apo C. This apparent alteration of emulsion apoproteins by the fed liver possibly results in a less active hepatic retrieval and may be important in downregulating the entry of lipoprotein triglyceride in the postabsorptive liver.
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65
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Iozzo RV, Kushwaha RS, Wight TN, Hazzard WR. Cellular and subcellular distribution of 125I-labeled very low density lipoproteins in the liver of normal and estrogen-treated rabbits. THE AMERICAN JOURNAL OF PATHOLOGY 1982; 107:6-15. [PMID: 6950667 PMCID: PMC1915988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Cholesterol and apo-E-rich very low density lipoproteins (VLDL) are rapidly removed from the circulation by the liver, and estrogen treatment enhances this uptake. The purpose of this study was to determine the cellular site(s) of cholesterol-rich VLDL uptake and the effect of estrogen on the cellular and subcellular distribution of these lipoproteins. (125)I-labeled VLDL, obtained from cholesterol-fed rabbits, were perfused through the isolated rabbit livers for 1/2, 1, 2, and 4 minutes, followed by a 5-minute chase. In both normal and estrogen-treated animals the uptake of VLDL increased linearly with time; however, this uptake was markedly increased by estrogen treatment. Lightmicroscopic autoradiography demonstrated that the majority (70-76%) of the label was localized in the hepatocytes of both normal and estrogen-treated animals. The remaining label was distributed in sinusoidal space (16-20%), littoral cells (6-7%), and bile ducts and large vessels (1-2%). Electron-microscopic autoradiography revealed that at earlier time points (125)I-VLDL were associated with the hepatocyte cell boundary. At later time points the majority of the labeled product (68-72%) was associated with hepatocyte cytoplasm. The estrogen-treated animals at earlier time points, however, had a relatively higher proportion (50%) of grains in the hepatocyte cytoplasm as compared with controls (21%).These findings indicate that 1) the parenchymal cells are primarily responsible for the uptake of cholesterol-rich VLDL, 2) internalization of the labeled product is preceded by its accumulation at the cell boundary, and 3) the mechanism of uptake and processing of the lipoproteins is similar in both normal and estrogen-treated animals but appears to be enhanced in the estrogen-treated animals.
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66
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67
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Künnert B, Massmanm J, Wagner J, Wujanz G, Krug H. Cholesteryl esters in pig liver during atherogenic diets and foreign serum protein infusions. EXPERIMENTAL PATHOLOGY 1982; 22:95-102. [PMID: 7140919 DOI: 10.1016/s0232-1513(82)80030-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Eight-month-old pigs were fed a diet supplemented with 15% lard (group II) or 15% lard plus 1.5% cholesterol (group III) for 4 months. Five of the animals fed the high fat and cholesterol diet received two i.v. infusions of foreign serum protein (group IV). One group of animals was treated with the same infusions without dietary fat or cholesterol supplement (group V). Liver lipids and serum cholesterol levels were determined. In group II the concentration and fatty acid composition of hepatic cholesteryl esters showed no marked differences from controls (group I). The same findings were present in 2 of 5 animals of group III; in the other 3 animals higher hepatic cholesteryl ester concentrations and predominantly an elevation of monoenoic acid fraction, in one case also a rise of trienoic acid fraction were obtained. These alterations were found in the liver of all animals of group IV. The reverse was observed in the animals which were given the same serum infusions but only the stock diet (group V): a reduction of hepatic cholesteryl ester concentration and no striking alteration in fatty acid pattern. In cryostat sections of all liver specimens no stainable lipid could be detected. There was no correlation between liver and serum fatty acid composition of cholesteryl esters. The total cholesterol levels in serum showed no increase in group V, a slight increase in group II, a moderate increase in group IV, and a marked, partly large increase in group III. These results are discussed in relation to the effect of cholesterol and fat feeding on cholesterol metabolism and essential fatty acid requirement.
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Zannis VI, Breslow JL, SanGiacomo TR, Aden DP, Knowles BB. Characterization of the major apolipoproteins secreted by two human hepatoma cell lines. Biochemistry 1981; 20:7089-96. [PMID: 6274388 DOI: 10.1021/bi00528a006] [Citation(s) in RCA: 223] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Two newly described human hepatoma derived cell lines, Hep G2 and Hep 3B [Knowles, B. B., Howe, C. C., & Aden, D. P. (1980) Science (Washington, D.C.) 209, 497-499], synthesize and secrete into the culture medium most of the major plasma apoproteins (apoA-I, apoA-II, apoB, apoC-II, apoC-III, and apoE). The synthesized apoproteins were identified by direct two-dimensional gel analysis of the culture medium or by two-dimensional analysis following purification of the apoproteins by ultracentrifugation or immunoprecipitation. We found that the apoA-I synthesized by both of the hepatoma cell lines consists of two isoproteins designated 2 and 3 which are more basic than the major plasma apoA-I isoproteins designated 4 and 5. The apoE synthesized by both cell lines is composed mainly of an array of isoproteins with increasingly higher molecular weights and lower isoelectric points as compared to those of the major apoE isoproteins found in plasma. These precursors of apoE are converted to the major apoE isoproteins upon treatment with Clostridium perfringens neuraminidase and represent sialo apoE isoproteins. ApoA-II, apoC-II, apoC-III-1, and apoC-III-2 correspond to the protein forms present in plasma. The human hepatoma cell lines (Hep G2 and Hep 3B) provide a unique model for studies of the regulation of human apoprotein and lipoprotein synthesis and catabolism.
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69
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Das JB, Joshi ID, Philippart AI. Intralipid intolerance in pancreatitis: the role of hepatic triglyceride lipase in plasma clearance of the lipid emulsion. J Pediatr Surg 1981; 16:1021-8. [PMID: 7338754 DOI: 10.1016/s0022-3468(81)80869-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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70
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Argilés J, Herrera E. Changes in lipid composition of plasma lipoproteins after total hepatectomy in the rat. ARCHIVES INTERNATIONALES DE PHYSIOLOGIE ET DE BIOCHIMIE 1981; 89:461-5. [PMID: 6176203 DOI: 10.3109/13813458109082643] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Lipidic composition of plasma lipoproteins were determined at different times after total hepatectomy in the rat and compared with those in sham-operated animals. After hepatectomy there was a progressive decrease in the plasma triglycerides amounts corresponding to changes in the content of very low density lipoproteins (VLDL) triglycerides. Phospholipid concentrations in both low density lipoproteins (LDL) and VLDL decreased after hepatectomy but theses lipids were unchanged in high density lipoproteins (HDL) which are the main contributors to plasma phospholipid content. Contrary to the other lipid components, plasma cholesterol levels increased after hepatectomy, due mainly to the increment in HDL-esterified cholesterol. Modifications in plasma triglyceride levels after hepatectomy are interpreted as the result of total reduced synthesis and the effect of extrahepatic lipoprotein lipase activity on VLDL-triglycerides. Changes in cholesterol are considered due to its enhanced production by extrahepatic tissues.
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71
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Groot PH, Van Berkel TJ, Van Tol A. Relative contributions of parenchymal and non-parenchymal (sinusoidal) liver cells in the uptake of chylomicron remnants. Metabolism 1981; 30:792-7. [PMID: 7266372 DOI: 10.1016/0026-0495(81)90025-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The relative contributions of parenchymal cells and non-parenchymal (sinusoidal) cells to the in vivo hepatic uptake of chylomicron remnants was measured 30 min after intravenous injection into rats. The chylomicron remnants were labeled with [3H]leucine, which was almost exclusively present in apolipoprotein B. The isolated non-parenchymal cells (a mixture of Kupffer cells and endothelial cells) contained 6.7 times more apolipoprotein B radioactivity per mg cell protein than the isolated parenchymal cells. It was calculated that the contributions of non-parenchymal and parenchymal liver cells to the total hepatic uptake of chylomicron remnants are 35% and 65%, respectively.
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72
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Suri BS, Targ ME, Robinson DS. The removal of partially metabolized very-low-density lipoproteins by the perfused rat liver. Biochem J 1981; 196:787-94. [PMID: 7317016 PMCID: PMC1163099 DOI: 10.1042/bj1960787] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
1. Donor perfused rat livers were used to prepare VLD (very-low-density) lipoproteins, labelled in their triacylglycerol and protein components with [1-14C]oleic acid and L-[4,5-3H]leucine respectively. Partially metabolized VLD lipoproteins, similarly labelled, were obtained from supradiaphragmatic rats injected with the parent VLD lipoproteins. 2. The triacylglycerol and protein components of the partially metabolized VLD lipoproteins were removed by recipient perfused rat livers at rates much higher than those of the parent VLD lipoproteins. No degradation of the partially metabolized VLD lipoproteins to LD (low-density) lipoproteins occurred during the perfusions. 3. Removal of hepatic lipase from the livers did not significantly affect the rate of removal of the partially metabolized VLD lipoproteins.
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73
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Turner PR, Miller NE, Cortese C, Hazzard W, Coltart J, Lewis B. Splanchnic metabolism of plasma apolipoprotein B: studies of artery-hepatic vein differences of mass and radiolabel in fasted human subjects. J Clin Invest 1981; 67:1678-86. [PMID: 7240415 PMCID: PMC370744 DOI: 10.1172/jci110205] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The metabolism of apoprotein B-containing plasma lipoproteins by human splanchnic tissues has been studied in 29 men undergoing coronary angiography. Before catheterization autologous radio-iodinated lipoproteins were infused into a peripheral vein: 10 subjects received (125)I-labeled Sf 12-60 lipoproteins; 12 received (125)I-labeled Sf 12-60 plus (131)I-labeled Sf 100-400 lipoproteins; and 7 received (125)I-labeled Sf 12-60 plus (131)I-labeled Sf 0-12 lipoproteins. Paired arterial and hepatic vein blood samples were subsequently collected for replicate measurements of apoprotein B (apo B) mass, radioactivity and specific activity in each lipoprotein class. Splanchnic plasma flow was measured with indocyanine green. All studies were conducted after a 14-h overnight fast. Newly synthesized apo B was shown to be secreted by splanchnic tissues as a component of Sf 100-400 lipoproteins, with no detectable uptake of apo B from this class. Sf 12-60 apo B was extracted by the splanchnic bed, with no detectable secretion. After continuous intravenous infusion of (125)I-labeled Sf 12-60 for five or more hours, 41-67% (mean 55%) of extracted Sf 12-60 apo B radioactivity reappeared in hepatic vein Sf 0-12 apo B. There was no detectable splanchnic catabolism of Sf 0-12 apo B. The rates of Sf 100-400 apo B secretion, calculated as the product of artery-hepatic vein concentration difference and splanchnic plasma flow, were greater than the previously reported rates of very low density lipoprotein apo B turnover in fed subjects obtained by kinetic analysis of plasma specific radioactivity decay curves, suggesting that there may be a diurnal variation in hepatic apo B synthesis. They also exceeded the splanchnic extraction rates of Sf 12-60 apo B, suggesting there was some extrasplanchnic catabolism of the apo B of Sf > 60 lipoproteins.
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Shirai K, Barnhart RL, Jackson RL. Hydrolysis of human plasma high density lipoprotein 2- phospholipids and triglycerides by hepatic lipase. Biochem Biophys Res Commun 1981; 100:591-9. [PMID: 7271774 DOI: 10.1016/s0006-291x(81)80217-3] [Citation(s) in RCA: 177] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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76
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Lakshmanan M, Muesing R, LaRosa J. Regulation of cholesterol biosynthesis and 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by chylomicron remnants in isolated hepatocytes and perfused liver. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)69720-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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77
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Nilsson A, Ehnholm C, Florén CH. Uptake and degradation of rat chylomicron remnants, produced in vivo and in vitro, in rat hepatocyte monolayers. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 663:408-20. [PMID: 7213778 DOI: 10.1016/0005-2760(81)90170-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
1. The uptake of small and large chylomicrons in rat hepatocyte monolayer cultures was compared to the uptake of chylomicron remnants prepared either in vitro with pure milk lipoprotein lipase or in hepatectomized rats. 2. Small chylomicrons (Sf less than 400) markedly inhibited remnant uptake and were taken up more efficiently than large ones (Sf greater than 400), indicating that size may be an important factor for the rate of uptake. The Lineweaver-Burk analysis of the data indicated that the V values for the uptake of both small chylomicrons (Sf less than 400) and of remnants prepared either in hepatectomized rats or in vitro was significantly higher than for chylomicrons with Sf greater than 400, whereas the Km values for the different particles did not differ significantly. 3. Preincubation of chylomicrons with serum caused marked changes in their apolipoprotein composition. A loss of apolipoprotein A-I and an increase in apolipoprotein E content was observed by scanning of SDS-polyacrylamide gels. Th preincubation decreased, however, the subsequent uptake of the chylomicrons. In contrast, the uptake of remnants prepared in vivo, or in vitro with serum present, exceeded that of remnants prepared in vitro with albumin or fetal calf serum as the fatty acid acceptor. 4. The data thus indicate that both the decrease in size and the changes in the particle surface during lipolysis with serum present are likely to contribute to the differences seen in the rate of uptake between native chylomicrons and remnants in hepatocyte monolayers.
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78
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Yamada N, Murase T, Akanuma Y, Itakura H, Kosaka K. Ascites chylomicron: a poor substrate for hepatic triglyceride lipase. Clin Chim Acta 1981; 110:45-9. [PMID: 7214713 DOI: 10.1016/0009-8981(81)90298-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A patient with nephrotic syndrome and morbus Kimura (eosinophilic granuloma) showed chylous ascites. Ascites chylomicrons were analyzed and used to study the substrate specificity of lipoprotein lipase and hepatic triglyceride lipase. Ascites triglyceride and cholesterol concentrations were 191 and 12 mg/dl, respectively. Both apo CII and apo CIII content in ascites were approximately one-third of those of plasma from normal subjects. Ascites chylomicrons were incubated with either lipoprotein lipase or hepatic triglyceride lipase, which were prepared from postheparin plasma using heparin-Sepharose affinity chromatography. Lipoprotein lipase hydrolyzed ascites chylomicrons, while hepatic triglyceride lipase did not. These results suggest different functions of these two lipases in chylomicron catabolism.
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79
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Lasunción MA, Llobera M, Herrera E. Morphological and compositional changes of rat plasma triglyceride-rich lipoproteins incubated with adipose tissue. ARCHIVES INTERNATIONALES DE PHYSIOLOGIE ET DE BIOCHIMIE 1981; 89:57-62. [PMID: 6166266 DOI: 10.3109/13813458109069138] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Triglyceride-rich rat lipoproteins (mainly VLDL), purified by ultracentrifugation and dialysis, were incubated for 120 min in the presence of epididymal fat-pad pieces from fed rats in media containing heparin. During this process, the lipoproteins were depleted of triglycerides and proportionally enriched with proteins, causing their increased density. After incubation, electron microscopic study of the triglyceride-rich lipoproteins revealed partially degraded structures, and some particles had atypical discoid flattened form and marked lamellar structure. These findings are in agreement with those of Blanchette-Mackie & Scow (1976) in triglyceride hydrolysed chylomicrons and confirm their observation of monolayers formed by accumulated lipolytic products that move by lateral diffusion, giving rise to a spiral fold between the core triglycerides and the aqueous space.
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80
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Hartiala J, Viikari J, Hietanen E, Toivonen H, Uotila P. Cigarette smoke affects lipolytic activity in isolated rat lungs. Lipids 1980; 15:539-43. [PMID: 7412510 DOI: 10.1007/bf02534227] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Isolated perfused rat lungs liberated fatty acids at a rate of 15 mumol/hr during perfusion of triglyceride-rich medium through the pulmonary vascular bed. About 80% of this activity seemed to result from lipoprotein lipase and 20% to hormone-sensitive lipase. Ventilation of the lungs with cigarette smoke instead of air during the perfusion reduced fatty acid liberation by 23%. Pre-exposure of rats to cigarette smoke for either 1 or 10 days did not cause significant changes in lung lipolytic activity compared to sham-exposed controls.
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81
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Windler E, Chao Y, Havel R. Determinants of hepatic uptake of triglyceride-rich lipoproteins and their remnants in the rat. J Biol Chem 1980. [DOI: 10.1016/s0021-9258(19)70811-4] [Citation(s) in RCA: 207] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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82
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Van Berkel TJ, Vaandrager H, Kruijt JK, Koster JF. Characteristics of acid lipase and acid cholesteryl esterase activity in parenchymal and non-parenchymal rat liver cells. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 617:446-57. [PMID: 6768394 DOI: 10.1016/0005-2760(80)90011-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
(1) Parenchymal and non-parenchymal cells were isolated from rat liver. The characteristics of acid lipase activity with 4-methylumbelliferyl oleate as substrate and acid cholesteryl esterase activity with cholesteryl[1-14C]oleate as substrate were investigated. The substrates were incorporated in egg yolk lecithin vesicles and assays for total cell homogenates were developed, which were linear with the amount of protein and time. With 4-methylumbelliferyl oleate as substrate, both parenchymal and non-parechymal cells show maximal activities at acid pH and the maximal activity for non-parenchymal cells is 2.5 times higher than for parenchymal cells. It is concluded that 4-methylumbelliferyl oleate hydrolysis is catalyzed by similar enzyme(s) in both cell types. (2) With cholesteryl[1-14C]oleate as substrate both parenchymal and non-parenchymal cells show maximal activities at acid pH and the maximal activity for non-parenchymal cells is 11.4 times higher than for parenchymal cells. It is further shown that the cholesteryl ester hydrolysis in both cell types show different properties. (3) The high activity and high affinity of acid cholesteryl esterase from non-parenchymal cells for cholesterol oleate hydrolysis as compared to parenchymal cells indicate a relative specialization of non-parenchymal cells in cholesterol ester hydrolysis. It is concluded that non-parenchymal liver cells in cholesterol ester hydrolysis. It is concluded that non-parenchymal liver cells possess the enzymic equipment to hydrolyze very efficiently internalized cholesterol esters, which supports the suggestion that these cell types are an important site for lipoprotein catabolism in liver.
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83
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Ehnholm C, Schröder T, Kuusi T, Bång B, Kinnunen P, Kahma K, Lempinen M. Studies on the effect of hepatectomy on pig post-heparin plasma lipases. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 617:141-9. [PMID: 7353020 DOI: 10.1016/0005-2760(80)90231-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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84
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TALL ALANR, SMALL DONALDM. Body Cholesterol Removal: Role of Plasma High-Density Lipoproteins1 1Supported by National Health Service Grants HL 18673, HL 07291, and HL 22682, and a Grant-In-Aid from the American Heart Association (316–3070–2286). ACTA ACUST UNITED AC 1980. [DOI: 10.1016/b978-0-12-024917-6.50007-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
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85
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Abstract
The hypothesis that plasma chylomicrons in persons who ingest a cholesterol-rich diet are atherogenic is evaluated. Evidence is presented that in humans, and experimental animals, chylomicron remnants as well as low-density lipoproteins are taken up by arterial cells. In persons who do not have familial hyperlipoproteinemia, atherogenesis may occur during the postprandial period. Research directions that may contribute to the evaluation of chylomicron remnants as a risk factor for atherogenesis are discussed. Lipoprotein studies after administration of a test meal containing fat and cholesterol are urgently needed.
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86
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Kuusi T, Kinnunen PK, Nikkilä EA. Hepatic endothelial lipase antiserum influences rat plasma low and high density lipoproteins in vivo. FEBS Lett 1979; 104:384-8. [PMID: 225212 DOI: 10.1016/0014-5793(79)80858-3] [Citation(s) in RCA: 188] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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87
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Deckelbaum RJ, Eisenberg S, Fainaru M, Barenholz Y, Olivecrona T. In vitro production of human plasma low density lipoprotein-like particles. A model for very low density lipoprotein catabolism. J Biol Chem 1979. [DOI: 10.1016/s0021-9258(18)50521-4] [Citation(s) in RCA: 67] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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88
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Fielding CJ. Validation of a procedure for exogenous isotopic labeling of lipoprotein triglyceride with radioactive triolein. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 573:255-65. [PMID: 221031 DOI: 10.1016/0005-2760(79)90059-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A procedure has been developed for the exogenous isotopic labeling of triglyceride-rich lipoproteins (chylomicrons and very low density lipoproteins) using high specific activity radioactive triglyceride in the presence of aqueous dimethyl sulfoxide. The labeled product lipoproteins showed unchanged chemical and physical properties. When the particles had also been labeled biologically by incorporation of unesterified fatty acids into the triglycerides of lipoproteins secreted by liver or intestine, both endogenous and exogenous labels were removed at the same rates in the isolated perfused heart and liver or in intact or functionally hepatectomized rats. These experiments additonally indicated that the triglyceride fatty acid composition of chylomicrons and very low density lipoproteins was unchanged during triglyceride depletion in the peripheral tissues. Using such labeled lipoproteins it has been shown that uptake of remnant lipoprotein cholesteryl ester and triglyceride by the liver is simultaneous. The labeling procedure described should prove suitable for kinetic studies of the disposition of the various lipoprotein non-polar ('core') lipids.
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89
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Kuusi T, Kinnunen PK, Ehnholm C, Nikkilä EA. A simple purification procedure for rat hepatic lipase. FEBS Lett 1979; 98:314-8. [PMID: 421905 DOI: 10.1016/0014-5793(79)80207-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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90
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Carrella M, Cooper AD. High affinity binding of chylomicron remnants to rat liver plasma membranes. Proc Natl Acad Sci U S A 1979; 76:338-42. [PMID: 284350 PMCID: PMC382934 DOI: 10.1073/pnas.76.1.338] [Citation(s) in RCA: 76] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The binding of chylomicron remnants rat liver plasma membranes was studied. Liver membranes bound up to 8 times more remnants than they bound chylomicrons. The remnant particle appeared to bind to the membrane as a unit. Remnant binding was greatest to liver plasma membrane; only one third as much binding was observed with whole liver homogenate, and virtually no binding occurred to erythrocyte membranes or glass. Binding was saturable and had kinetics compatible with the existence of a high affinity site. Half-maximal binding occurred at 27 micron. Competitive binding studies revealed no competition with albumin, a triglyceride dispersion, cholesterol/lecithin vesicles, very low density lipoprotein, or low density lipoprotein. Some displacement of remnant binding was observed with chylomicrons and high density lipoprotein. Binding was decreased by treatment of the membranes with trypsin or the presence of heparin in the incubation medium. These studies suggest that there is a high affinity receptor for the chylomicron remnant on the surface of the hepatocyte.
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91
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Naito M, Wisse E. Filtration effect of endothelial fenestrations on chylomicron transport in neonatal rat liver sinusoids. Cell Tissue Res 1978; 190:371-82. [PMID: 567529 DOI: 10.1007/bf00219553] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The function of endothelial fenestrations in the control of the passage of chylomicrons from the blood to the liver parenchymal cells was studied ultrastructurally in neonatal rats. Measurement of circulating chylomicrons and endothelial fenestrations as well as chylomicrons in the space of Disse at 2--20 h after the onset of suckling revealed a substantial filtration effect of endothelial fenestrations on chylomicrons larger than 250 nm in diameter. Direct uptake of chylomicrons by parenchymal cells was observed to occur by pinocytosis; Kupffer cells endocytosed only very few chylomicrons, and endothelial cells were inactive in this respect.
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92
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Fielding CJ. Metabolism of cholesterol-rich chylomicroms. Mechanism of binding and uptake of cholesteryl esters by the vascular bed of the perfused rat heart. J Clin Invest 1978; 62:141-51. [PMID: 659628 PMCID: PMC371747 DOI: 10.1172/jci109099] [Citation(s) in RCA: 71] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The rate of uptake of cholesteryl ester from chylomicrons has been determined with the isolated perfused rat heart and both intact and functionally hepatectomized rats. Uptake was found to be proportional to the cholesteryl ester content of the particles. Transfer of cholesteryl ester to other lipoprotein classes of the plasma was negligible under these conditions, and loss of cholesteryl ester from the medium was associated with quantitative recovery in the vascular bed. The uptake mechanism was nonsaturable and independent of the lipoprotein lipase binding site. Compared with receptor-dependent uptake of low density lipoprotein cholesteryl ester by heart endothelium, the chylomicron pathway appears to provide a major proportion of cholesteryl ester cleared from the plasma. Uptake was initially heparin dependent, and cleared lipid was released by 10 microgram/ml of heparin; however, lipid taken up rapidly became heparin resistant and was then hydrolyzed slowly with production of unesterified fatty acid. These results are discussed in the context of the possible role of cholesterol-rich chylomicron remnant lipoproteins in atherogenesis.
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93
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Sauar J, Skrede S, Blomhoff JP. Hepatic lipase and lipoprotein lipase in postheparin plasma in liver disease. relations to plasma proteins. Clin Chim Acta 1978; 84:213-23. [PMID: 639306 DOI: 10.1016/0009-8981(78)90497-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Hepatic lipase (HL) and lipoprotein lipase (LPL) in postheparin plasma have been studied in patients with different liver disorders and in a reference group. The dose of heparin (100 I.U./kg body weight) used intravenously to get maximal release of both HL and LPL was the same in patients and in healthy individuals. The release of HL was maximal in healthy controls after 2-5 min, but in patients with liver disease the maximum was not reached until 15 min after heparin administration. The time course of the release of LPL showed the same pattern in patients and controls. The activity of HL was below the lowest observation in the reference group in 8 out of 20 patients with liver diseases, and was not measurable in 3 of them (2 with chronic active hepatitis and 1 with alcoholic cirrhosis). The activity of hepatic lipase was positively correlated with the levels of coagulation factors and with the concentration of prealbumin in the total patient material. The results indicate that low activity of hepatic lipase is a sign of liver parenchymatous injury, and out study gives indirect evidence of the hepatic origin of this enzyme in man.
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94
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Sherrill B, Dietschy J. Characterization of the sinusoidal transport process responsible for uptake of chylomicrons by the liver. J Biol Chem 1978. [DOI: 10.1016/s0021-9258(19)62331-8] [Citation(s) in RCA: 109] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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95
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Szlam F, Sgoutas DS. Eicosenoic and docosenoic acid incorporation in serum lipoproteins in rats fed rapeseed oil. Lipids 1978; 13:121-7. [PMID: 634044 DOI: 10.1007/bf02533253] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Rats were fed rapeseed oil rich in eicosenoic (20:1) and docosenoic (22:1) acids for 7 days, and the fatty acid composition of the lipid classes of serum and serum lipoproteins was determined. Concentrations of 20:1 and 22:1 acids in the lipid classes were variable, especially among lipoproteins, and were a direct function of the alimentary state of the animal. The results suggest differences in the incorporation of the above acids among the major lipoprotein types and various lipid classes within a given lipoprotein type. The quick partial disappearance of very low density lipoproteins (VLDL) and of low density lipoproteins (LDL) containing 20:1 and 22:1 acids upon starvation and the preferential incorporation of these acids in the triacylglycerols of high density lipoproteins (HDL) are discussed.
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96
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Grundy SM. Cholesterol metabolism in man. West J Med 1978; 128:13-25. [PMID: 204111 PMCID: PMC1237959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Recent investigations on cholesterol metabolism in man have led to new insights into diseases associated with abnormal accumulations of cholesterol in plasma (hypercholesterolemia), arterial tissues (atherosclerosis) and biliary tract (gallstones). Regulation of cholesterol synthesis under the influence of dietary and plasma cholesterol, may play a crucial role in determining biliary and tissue concentrations of this sterol. Plasma concentrations, on the other hand, appear to be controlled by complex mechanisms for secretion, transformation and removal of plasma lipoproteins. The recent identification of specific cellular receptors for uptake of plasma lipoproteins represents a significant advance for the understanding of regulation of both plasma and tissue concentrations, and possibly of the basic mechanisms underlying accumulation of cholesterol in atherosclerotic plaques.
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97
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Berman M, Hall M, Levy RI, Eisenberg S, Bilheimer DW, Phair RD, Goebel RH. Metabolsim of apoB and apoC lipoproteins in man: kinetic studies in normal and hyperlipoproteininemic subjects. J Lipid Res 1978. [DOI: 10.1016/s0022-2275(20)41575-5] [Citation(s) in RCA: 207] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
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98
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Topping DL, Dwyer T, Weller RA. Peripheral vascular disease in cigarette smokers and impaired hepatic metabolism of lipoprotein remnants. Lancet 1977; 2:1327-8. [PMID: 74734 DOI: 10.1016/s0140-6736(77)90371-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The metabolism of very-low-density lipoproteins and chylomicrons includes the extrahepatic hydrolysis of their triglycerides by lipoprotein lipase. This results in cholesterol-rich "remnants" which are further metabolised by the liver. There is experimental evidence that in both patients with type-III hyperlipoproteinaemia and cigarette smokers hepatic-remnant metabolism may be depressed. In type-III hyperlipoproteinaemia the defect is inherited while in smokers it occurs in response to raised blood concentrations of carboxyhaemoglobin. The striking clinical similarity between type-III hyperlipoproteinaemic patients and smokers--namely, a high incidence of peripheral vascular disease--may be due to a common cause, the accumulation of cholesterol-rich remnants in the plasma.
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99
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Florén CH, Nilsson A. Binding, interiorization and degradation of cholesteryl ester-labelled chylomicron-remmant particles by rat hepatocyte monolayers. Biochem J 1977; 168:483-94. [PMID: 204289 PMCID: PMC1183796 DOI: 10.1042/bj1680483] [Citation(s) in RCA: 97] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
1. The cholesteryl ester of isolated chylomicron-remnant particles was efficiently degraded by hepatocyte monolayers. The degradation was sensitive to metabolic inhibitors. 2. With increasing amounts of remnant cholesteryl ester the rate of uptake approached saturation and conformed to a linear double-reciprocal plot. The V(max.) was determined as 80ng of cholesteryl ester/h per mg of protein and the apparent K(m) as 1.4mug of cholesteryl ester per mg of protein. The time course for the uptake and hydrolysis suggested that binding of particles to the cell surface preceded the degradation. 3. Cholesteryl esters of native chylomicrons were degraded to a much smaller extent and their presence had only a small inhibitory effect on the degradation of chylomicron remnants. Intestinal very-low-density lipoproteins were degraded somewhat faster than chylomicrons, and caused more inhibition of remnant degradation. Rat high-density lipoproteins inhibited the hydrolysis of remnant cholesteryl ester by up to 50%, but had less influence on the amount of cholesteryl ester that was bound to the cells. Serum decreased both the uptake and hydrolysis, whereas d=1.21 infranatant had no effect. 4. The cholesteryl ester hydrolysis after the uptake by the cells was inhibited by chloroquine and by colchicine. Only 28-36% of the unhydrolysed cholesteryl ester could be released from these cells by trypsin treatment, indicating that the major portion was truly intracellular. The particles that could be released from the cell surface by trypsin and those remaining in the medium had the same triacylglycerol/cholesteryl ester ratio as the added remnant particles. Significant amounts of denser particles were thus not formed during contact with the cell surface. 5. The presence of heparin, as well as preincubation of the cells with heparin, increased the uptake of chylomicron remnants. This effect was most marked in the presence of serum. A much smaller proportion of the other serum lipoproteins was taken up, and this proportion was not increased by heparin.
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100
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Cooper AD. The metabolism of chylomicron remnants by isolated perfused rat liver. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 488:464-74. [PMID: 901798 DOI: 10.1016/0005-2760(77)90204-1] [Citation(s) in RCA: 77] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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