Hydrolysis of lipid monolayers and the substrate specificity of hepatic lipase

Laboda, Henry M.; Glick, Jane M.; Phillips, Michael C.

doi:10.1016/0005-2760(86)90279-1

Cited by 48 publications

(25 citation statements)

References 34 publications

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“…The presumed function of the enzyme is the hydrolysis of triglycerides in intermediate density lipoproteins (IDL) and of phospholipids in high density lipoproteins (HDL2) (5). The capacity ofpurified hepatic lipase to catalyze hydrolysis of phospholipids and mono-, di-, and triglycerides (6,7) is consistent with the putative function. The action of hepatic lipase on HDL2 is presumed to result in the production of HDL3.…”

mentioning

confidence: 59%

Cloning of rat hepatic lipase cDNA: evidence for a lipase gene family.

Komaromy¹,

Schotz²

1987

Proc. Natl. Acad. Sci. U.S.A.

145

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Clones for rat hepatic lipase were isolated by probing a rat liver cDNA library in Agtll with an oligonucleotide synthesized on the basis of a partial peptide sequence. The cloned messenger codes for a protein of 472 amino acids plus a hydrophobic leader sequence of 22 amino acids. The unglycosylated protein has a predicted molecular weight of 53,222 and contains two potential sites for N-glycosylation. The protein bears striking regions of homology with other known lipases and contains peptide sequences that have been implicated in lipid binding. The homologous mRNA is present in liver tissue but no detectable mRNA is observed in the adrenal gland, despite the reported presence of hepatic lipase in both the liver and the adrenal gland. No mRNA was seen in any of a variety of other tissues.Hepatic lipase, localized primarily on the sinusoidal surfaces of the liver, functions in the metabolism of circulating lipoproteins (1). Hepatic lipase activity has also been detected in several extrahepatic tissues, including adrenal gland and ovary (2-4). The presumed function of the enzyme is the hydrolysis of triglycerides in intermediate density lipoproteins (IDL) and of phospholipids in high density lipoproteins (HDL2) (5). The capacity ofpurified hepatic lipase to catalyze hydrolysis of phospholipids and mono-, di-, and triglycerides (6, 7) is consistent with the putative function. The action of hepatic lipase on HDL2 is presumed to result in the production of HDL3. Also, hepatic lipase may participate in the clearance of circulating very low-density lipoproteins (8) and chylomicron remnants (9).Hepatic lipase from rat liver has been purified to homogeneity (7, 10). The enzyme has an apparent molecular weight of53,000 (7,11) cDNA Screening and Analysis. Partial amino acid sequences were determined from the digestion of purified hepatic lipase with subtilisin (11). A single 42-base oligonucleotide probe was constructed on the basis of a 14 amino acid sequence ( Fig. 1) and codon usage tables for mammalian genes (13). In addition to codon usage assumption, G-T base pairing was allowed in designing the probe. A total of 9 x 105 plaques were screened with the end-labeled 42-base oligonucleotide probe. Plaque replicas on nitrocellulose filters were made by the method of Benton and Davis (14). The filters were baked at 80'C for 2 hr and incubated for 3 hr at 370C in 30% (vol/vol) formamide/900 mM NaCl/90 mM trisodium citrate/5 x concentrated Denhardt's solution/50 mM sodium phosphate, pH 6.5, containing salmon sperm DNA at 100 pkg/ml, in a total volume of 200 ml. The 32P-labeled probe (2 x 108 cpm/Ag) was hybridized to the filters for 17 hr at 370C in 200 ml of the same solution. The filters were washed twice at room temperature in 500 ml of 150 mM NaCl/15 mM trisodium citrate/0.1% NaDodSO4 for 30 min per wash, and then six times at 370C in 300 ml of the same solution for 30 min per wash. The filters were exposed to Du Pont Cronex 4 film with Du Pont Hi-Plus intensifying screens at -70'C for 20 hr. DNA from clones t...

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mentioning

confidence: 59%

Cloning of rat hepatic lipase cDNA: evidence for a lipase gene family.

Komaromy¹,

Schotz²

1987

Proc. Natl. Acad. Sci. U.S.A.

145

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“…One possible explanation for the disproportionate delay in clearance of SM compared with PC is that PC may undergo intravascular catabolism because of the actions of hepatic lipase (HL) and LCAT, whereas SM is not a substrate for these enzymes (30,31). To evaluate this possibility, we compared the clearance of PC ethers to SM; PC ethers are also resistant to LCAT and HL (30,32). Thus, [ 3 H]POPC ether and [ 14 C]SMlabeled apoE0-VLDL were injected into apoE0 and Wt mice.…”

Section: Resultsmentioning

confidence: 99%

Increased sphingomyelin content of plasma lipoproteins in apolipoprotein E knockout mice reflects combined production and catabolic defects and enhances reactivity with mammalian sphingomyelinase.

et al. 1998

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Apolipoprotein E knockout (apoE0) mice accumulate atherogenic remnant lipoproteins in plasma. We now provide evidence that these particles are enriched in sphingomyelin (SM), and explore the mechanisms and possible pathophysiological consequences of this finding. The phosphatidylcholine/sphingomyelin (PC/SM) ratio was reduced in all lipoproteins in apoE0 mice compared with wild-type (Wt) mice (2.0+/-0.2 vs. 4.7+/-0.5; 2.8+/-0.5 vs. 5.5+/-0.9; 1.9+/-0. 5 vs. 4.6+/-0.5 for VLDL, LDL, and HDL), reflecting 400 and 179% increases in plasma pools of SM and PC, respectively. Turnover studies using [14C]PC/[3H]SM VLDL or HDL showed that the fractional catabolic rate (FCR) of VLDL-SM and HDL-SM were markedly reduced in the apoE0 mice compared with Wt mice, while the FCRs of VLDL-PC and HDL-PC were similar. By contrast, the FCRs of [3H]PC ether and [14C]SM were identical in apoE0 and Wt mice. The production rates of VLDL-SM and HDL-SM in apoE0 mice were much higher than in Wt mice, while the production rates of lipoprotein PC were similar. To assess the underlying mechanisms, we also measured the PC/SM ratio in VLDL and LDL of LDL receptor knockout (LDLr0) and hepatic LDL receptor-related protein knockout/LDLr0 mice, but found no difference with Wt mice. Using S-sphingomyelinase, an enzyme secreted by macrophages and endothelial cells, we found that VLDL and LDL from apoE0, but not from Wt or LDLr0 mice, were significantly aggregated, and that aggregation was not prevented by adding back apoE. We then enriched the apoE0-VLDL and Wt-VLDL with different amounts of SM, and found that VLDL aggregation was enhanced. Thus, the increased SM content of lipoproteins in apoE0 mice is due to combined synthesis and clearance defects. Impaired SM clearance reflects resistance to intravascular enzymes and delayed removal by a non-LDLr, non-LDLr related protein pathway. The increased SM content in slowly cleared remnant lipoproteins may enhance their susceptibility to arterial wall SMase and increase their atherogenic potential.

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“…27,28 Thus, SM removal from plasma is absolutely dependent on hepatic clearance mechanisms, such as the LDL receptor, the LDL receptor-related protein, or proteoglycan pathways. Because SM is not degraded in plasma, it becomes enriched in remnants of triglyceride-rich lipoproteins.…”

Section: Discussionmentioning

confidence: 99%

Plasma Sphingomyelin Level as a Risk Factor for Coronary Artery Disease

Jiang

Paultre

Pearson

et al. 2000

ATVB

353

259

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Abstract-Only a fraction of the clinical complications of atherosclerosis are explained by known risk factors. Animal studies have shown that plasma sphingomyelin (SM) levels are closely related to the development of atherosclerosis. SM carried into the arterial wall on atherogenic lipoproteins may be locally hydrolyzed by sphingomyelinase, promoting lipoprotein aggregation and macrophage foam cell formation. A novel, high-throughput, enzymatic method to measure plasma SM levels has been developed. Plasma SM levels were related to the presence of coronary artery disease (CAD) in a biethnic angiographic case-control study (279 cases and 277 controls). Plasma SM levels were higher in CAD patients than in control subjects (60Ϯ29 versus 49Ϯ21 mg/dL, respectively; PϽ0.0001). Moreover, the ratio of SM to SMϩphosphatidylcholine (PC) was also significantly higher in cases than in controls (0.33Ϯ0.13 versus 0.29Ϯ0.10, respectively; PϽ0.0001). Similar relationships were observed in African Americans and whites. Plasma SM levels showed a significant correlation with remnant cholesterol levels (rϭ0. 51, PϽ0.0001). By use of multivariate logistic regression analysis, plasma SM levels and the SM/(SMϩPC) ratio were found to have independent predictive value for CAD after adjusting for other risk factors, including remnants. The odds ratio (OR) for CAD was significantly higher for the third and fourth quartiles of plasma SM levels (OR T he association of lipid abnormalities and coronary atherosclerosis is well established. Case-control and prospective epidemiological studies have shown a direct correlation between coronary artery disease (CAD) and serum levels of total cholesterol and LDL cholesterol (LDL-C) and an inverse relationship between CAD and HDL cholesterol (HDL-C) levels. 1 However, compared with plasma cholesterol measurements, very little attention has been given to the relationship between phospholipids and CAD. 2,3 Atherogenesis is initiated by the interaction of cholesterol-rich lipoproteins, such as LDL, with the arterial wall. 4,5 The uptake of lipoprotein cholesterol by macrophages, leading to foam cell formation, is a central event in the initiation and progression of atherosclerosis. 6 However, native LDL is incapable of generating foam cells from macrophages. Thus, it is thought that LDL is modified in the arterial wall by processes such as oxidation, leading to macrophage chemotaxis and the uptake of modified LDL by macrophage foam cells. 7 Retention of lipoproteins on the subendothelial matrix, followed by aggregation, has also emerged as a central pathogenic process in macrophage foam cell formation and atherogenesis. 8 Lipoprotein aggregation in the vessel wall may result from enzymatic modification of LDL, induced by locally produced sphingomyelinase (SMase). 9 It has long been known that sphingomyelin (SM) accumulates in human and animal atheroma and that the major source is plasma lipoproteins. 10 Plasma SM levels are increased in human familial hyperlipidemias, especially in familial hypercholester...

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Hydrolysis of lipid monolayers and the substrate specificity of hepatic lipase

Cited by 48 publications

References 34 publications

Cloning of rat hepatic lipase cDNA: evidence for a lipase gene family.

Cloning of rat hepatic lipase cDNA: evidence for a lipase gene family.

Increased sphingomyelin content of plasma lipoproteins in apolipoprotein E knockout mice reflects combined production and catabolic defects and enhances reactivity with mammalian sphingomyelinase.

Plasma Sphingomyelin Level as a Risk Factor for Coronary Artery Disease

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