Localization of the heparin-releasable lipase <i>in situ</i> in the rat liver

Kuusi, Timo; Nikklä, E A; Virtanen, Ismo; Kinnunen, Paavo K.J.

doi:10.1042/bj1810245

Cited by 163 publications

(46 citation statements)

References 15 publications

(16 reference statements)

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“…Tissue fractionation studies have shown that the heparin-releasable enzyme is associated with the plasma membrane fraction of rat liver homogenates [6,14]. In rat [15,16] and chicken [17] liver, the enzyme is synthesized and secreted by the parenchymal cells and subsequently bound to high-affinity binding sites on the non-parenchymal (endothelial) cells [18,19]. Recent experiments have shown that there is only one alkaline lipase in rat liver [ 201.…”

Section: Liver Triacylglycerol Lipasesmentioning

confidence: 99%

Lipolysis of hepatic triacylglycerol stores

et al. 1982

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Section: Liver Triacylglycerol Lipasesmentioning

confidence: 99%

Lipolysis of hepatic triacylglycerol stores

et al. 1982

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“…Hepatic lipase is present in the liver and is believed to play a role in the metabolism of highdensity lipoproteins, intermediate-density lipoproteins and chylo-micron remnants [5][6][7][8][9]. Both lipoprotein lipase and hepatic lipase are synthesized and secreted by parenchymal cells and are bound specifically to the endothelial-cell lining [10][11][12][13][14][15]. It is generally assumed that both hepatic lipase and lipoprotein lipase are bound to heparan sulphates at the endothelium [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Rat liver contains a limited number of binding sites for hepatic lipase

Schoonderwoerd

Verhoeven

Jansen

1994

Biochemical Journal

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The binding of hepatic lipase to rat liver was studied in an ex vivo perfusion model. The livers were perfused with media containing partially purified rat hepatic lipase or bovine milk lipoprotein lipase. The activity of the enzymes was determined in the perfusion media before and after passage through the liver. During perfusion with a hepatic-lipase-containing medium the lipase activity in the medium did not change, indicating that there was no net binding of lipase by the liver. In contrast, more than 80% of the lipoprotein .lipase was removed from the medium. This lipoprotein lipase activity could be recovered into the perfusion medium completely by heparin perfusion of the liver. If livers, first depleted of hepatic lipase by heparin, were subsequent perfused with a hepatic-lipase-containing medium, 90 + 24 m-units of the lipase activity was bound per g of liver (up to 1000 m-units/total liver). However, heparin treatment of the liver decreases the ability of the liver to re-bind hepatic lipase by 80 %. Perfusion of rat livers with 0.3 M NaCl released 60 % of the lipase activity into the medium. Upon subsequent perfusion of these livers with hepatic-lipase-containing media, 541 + 164 munits of hepatic lipase could be bound per g of liver (up to 5000 m-units/total liver). The binding of hepatic lipase was also studied in livers of corticotropin (ACTH)-pre-treated rats. In these rats also, hepatic lipase bound only to livers which had been pre-perfused with heparin or 0.3 M NaCl. After heparin pre-perfusion, 88 + 12 m-units of hepatic lipase could be bound per g of liver, similar to that with livers of control rats not treated with ACTH. After prior salt perfusion, however, the capacity of the livers of ACTH-pre-treated rats to bind hepatic lipase was 212 + 60 m-units/g of liver. This is less than in livers of control rats (541 + 164 m-units/g of liver). These results indicate that in rat liver the binding ofhepatic lipase is heterogeneous in character and consists of heparin-resistant and heparin-sensitive components. The hepatic-lipase binding capacity of the liver is saturable and fully utilized under various conditions. The heparin-sensitive binding capacity is lowered in ACTH-treated rats, whereas the heparin-resistant binding is unaffected. We postulate that the functional hepatic lipase activity can be regulated by changes in the binding capacity of the liver.

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“…1,2 Human HL is a 476 -amino-acid glycoprotein that is synthesized by hepatocytes and binds to external surfaces of hepatic cells. 3,4 Studies in animal models and HL-deficient humans [5][6][7][8] suggested that HL is involved in the conversion of IDLs to LDLs, and in the catabolism of large lipid-rich HDLs (reviewed in Reference 1). HL also enhances the direct binding and uptake of cholesteryl ester-rich VLDL and chylomicron remnants by hepatocytes.…”

mentioning

confidence: 99%

Overexpression of Human Hepatic Lipase and ApoE in Transgenic Rabbits Attenuates Response to Dietary Cholesterol and Alters Lipoprotein Subclass Distributions

Barbagallo

Fan

Blanche

et al. 1999

ATVB

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Abstract-The effect of the expression of human hepatic lipase (HL) or human apoE on plasma lipoproteins in transgenic rabbits in response to dietary cholesterol was compared with the response of nontransgenic control rabbits. Supplementation of a chow diet with 0.3% cholesterol and 3.0% soybean oil for 10 weeks resulted in markedly increased levels of plasma cholesterol and VLDL and IDL in control rabbits as expected. Expression of either HL or apoE reduced plasma cholesterol response by 75% and 60%, respectively. The HL transgenic rabbits had substantial reductions in medium and small VLDL and IDL fractions but not in larger VLDL. LDL levels were also reduced, with a shift from larger, more buoyant to smaller, denser particles. In contrast, apoE transgenic rabbits had a marked reduction in the levels of large VLDLs, with a selective accumulation of IDLs and large buoyant LDLs. Studies in animal models and HL-deficient humans 5-8 suggested that HL is involved in the conversion of IDLs to LDLs, and in the catabolism of large lipid-rich HDLs (reviewed in Reference 1). HL also enhances the direct binding and uptake of cholesteryl ester-rich VLDL and chylomicron remnants by hepatocytes. 9 Human apoE is a 299 -amino-acid glycoprotein present mainly in triglyceride-rich particles (chylomicrons, VLDLs, and IDLs) and large HDLs. A major role of apoE in plasma lipid transport is to mediate the binding and clearance of remnant lipoproteins and large cholesterol-rich HDLs to receptors in hepatic and peripheral cells. 2,10,11 To determine whether the physiological roles of HL and apoE in plasma cholesterol and lipoprotein metabolism are complementary, we generated transgenic lines of rabbits overexpressing the corresponding human proteins. Rabbits were used because they are naturally deficient in HL and they have relatively reduced levels of apoE compared with other species. 12, 13 We previously found that overexpression of HL in transgenic rabbits resulted in a reduction in IDLs and all subclasses of HDLs in chow-fed rabbits, as well as a 2-fold reduction in plasma cholesterol, in comparison with nontransgenic controls. 14,15 Overexpression of apoE in transgenic rabbits was shown to decrease VLDL levels; this effect was due to an increased affinity of large apoE-rich remnants for the LDL receptor that was related to increased chylomicron clearance rate. 16 Although VLDLϩIDL and LDLs are commonly defined as lipoproteins of density Ͻ1.019 and 1.019 to 1.063 g/mL, respectively, among these intervals it is possible to recognize several heterogeneous subclasses, differing in size, density, flotation rate, electrophoretic mobility, and chemical composition. [17][18][19][20][21][22][23][24][25] We previously used density-gradient ultracentrifugation (DGUC) and electrophoresis in polyacrylamide gradient gels to demonstrate the existence of multiple distinct subclasses of VLDLs and IDLs in humans. 19,20 By injecting human lipoproteins into rats, we documented different met-

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Localization of the heparin-releasable lipase in situ in the rat liver

Cited by 163 publications

References 15 publications

Lipolysis of hepatic triacylglycerol stores

Lipolysis of hepatic triacylglycerol stores

Rat liver contains a limited number of binding sites for hepatic lipase

Overexpression of Human Hepatic Lipase and ApoE in Transgenic Rabbits Attenuates Response to Dietary Cholesterol and Alters Lipoprotein Subclass Distributions

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