Study of the hydrolysis of 4-methylumbelliferyl oleate by acid lipase and cholesteryl oleate by acid cholesteryl esterase in human leucocytes, fibroblasts and liver

Lysosomal Acid Lipase Deficiency in 23 Spanish Patients: High Frequency of the Novel c.966+2T>G Mutation in Wolman Disease

Lysosomal acid lipase (LAL) is a lysosomal key enzyme involved in the intracellular hydrolysis of cholesteryl esters and triglycerides. Patients with very low residual LAL activity present with the infantile severe form Wolman disease (WD), while patients with some residual activity develop the less severe disorder known as Cholesteryl ester storage disorder (CESD). We present the clinical, biochemical, and molecular findings of 23 Spanish patients (22 families) with LAL deficiency. We identified eight different mutations, four of them not previously reported. The novel c.966+2T>G mutation accounted for 75% of the Wolman disease alleles, and the frequent CESD associated c.894G>A mutation accounted for 55% of the CESD alleles in our cohort. Haplotype analysis showed that both mutations co-segregated with a unique haplotype suggesting a common ancestor. Our study contributes to the LAL deficiency acknowledgement with novel mutations and with high frequencies of some unknown mutations for WD.

Caveolin targeting to late endosome/lysosomal membranes is induced by perturbations of lysosomal pH and cholesterol content

Caveolin-1 traffics to late endosomal/lysosomal membranes in response to manipulations of the cholesterol content of cells, suggesting that caveolin functions in the egress of cholesterol from this organelle. Cavicles associate with the periphery of the lysosome as they do with caveosomes, but these are separate organelles.

Caveolin-1 is an integral membrane protein of plasma membrane caveolae. Here we report that caveolin-1 collects at the cytosolic surface of lysosomal membranes when cells are serum starved. This is due to an elevation of the intralysosomal pH, since ionophores and proton pump inhibitors that dissipate the lysosomal pH gradient also trapped caveolin-1 on late endosome/lysosomes. Accumulation is both saturable and reversible. At least a portion of the caveolin-1 goes to the plasma membrane upon reversal. Several studies suggest that caveolin-1 is involved in cholesterol transport within the cell. Strikingly, we find that blocking cholesterol export from lysosomes with progesterone or U18666A or treating cells with low concentrations of cyclodextrin also caused caveolin-1 to accumulate on late endosome/lysosomal membranes. Under these conditions, however, live-cell imaging shows cavicles actively docking with lysosomes, suggesting that these structures might be involved in delivering caveolin-1. Targeting of caveolin-1 to late endosome/lysosomes is not observed normally, and the degradation rate of caveolin-1 is not altered by any of these conditions, indicating that caveolin-1 accumulation is not a consequence of blocked degradation. We conclude that caveolin-1 normally traffics to and from the cytoplasmic surface of lysosomes during intracellular cholesterol trafficking.

Human platelets have cholesteryl ester hydrolytic activity resulting in esterification of [1-14C]oleate to individual phospholipids of platelets

Human platelet cholesteryl ester hydrolytic (CEH) activity was determined toward cholesteryl [1-14C]oleate resulting in esterification of [1-14C]oleate to individual platelet phospholipids: choline-containing phospholipids (PC); ethanolamine-containing phospholipids (PE); phosphatidylserine (PS); phosphatidylinositol (PI); and sphingomyelin (SPH). Liberation of [1-14C]oleate and esterification of [1-14C]oleate to platelet phospholipids was enhanced by 100 nM iloprost (a stable analogue of prostacyclin that increases platelet cyclic adenosine monophosphate (c-AMP)), inhibited by 30 microM H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide)) (a specific c-AMP dependent protein kinase (CADPK) inhibitor) and 500 microM 2',5' dideoxyadenosine (DDA) (an inhibitor of iloprost-induced rise in platelet c-AMP), but unaffected by 150 mM choloroquine diphosphate. These observations suggest that the CEH activity is mediated by a CADPK phosphorylation of an enzyme with the phosphorylated state representing the active form of the enzyme and that the CEH activity is extralysosomal.

Human platelets have cholesteryl ester hydrolytic activity toward plasma high density lipoproteins

Human platelet cholesteryl ester hydrolytic (CEH) activity was determined toward high density lipoprotein (HDL) labelled with cholesteryl [1-(14)C] oleate resulting in esterilkation of [l-(14)C] oleate to platelet phospholipid. The observed CEH activity was enhanced by 100 nM prostacyclin (PGI(2)), inhibited by 500 μM 2', 3' dideoxyadenosine (DDA), but unaffected by 100 mM chloroquine diphosphate. The CEH activity may represent a mechanism for delivery of other unsaturated fatty acids from HDL to platelets with subsequent modification of the fatty acid composition of platelet phospholipids and potential modification of platelet reactivity.

Cholesteryl esterase activities in ventricles, isolated heart cells and aorta of the rat

Cholesteryl esterase activities were determined in homogenates of rat heart (ventricles), isolated, calcium-tolerant, cardiac myocytes and aortic tissue and were compared with acid and neutral triglyceride lipase activities in these fractions. Using cholesteryl oleate/phosphatidylcholine/taurocholate emulsions and digitonin pretreatment of the enzyme fractions, acid and neutral cholesteryl esterase activities were measured in all tissue preparations. In contrast to the acid and neutral triglyceridase and acid cholesteryl esterase activity, the neutral cholesteryl esterase activity was subject to substrate inhibition. Upon isolation of cardiac myocytes, and in contrast with the recovery of neutral triglyceride lipase activity, only a small portion of the neutral cholesteryl esterase (6%) was recovered, suggesting that nonmyocyte neutral cholesteryl esterase activity markedly contributes to the relatively high activity detectable in whole ventricular homogenates. The recovery of large amounts of neutral cholesteryl esterase activity in the supernatant of collagenase-digested heart tissue, obtained during the isolation of myocytes, which is also markedly enriched in activities of two endothelial marker enzymes (5'-nucleotidase and angiotensine-converting enzyme) may indicate the predominant contribution of neutral cholesteryl esterase activity from coronary endothelial cells to this activity detectable in ventricular homogenates. Relative to the activity in ventricular and myocyte homogenates, aorta homogenates possessed the highest specific neutral cholesteryl esterase activity. We propose that in addition to coronary endothelium, smooth muscle cells also contribute to the neutral cholesteryl esterase activity in ventricular homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesteryl ester hydrolysis in rat liver lysosomes: different response to female sex hormones

The regulation of the hydrolysis of cholesteryl oleate by female sex hormones was studied in the lysosomal fraction of rat liver. Cholesterol ester hydrolase activity was determined at pH 5.0 with an acetone-dissolved cholesteryl [1-14C]oleate substrate preparation. The administration of a single dose of progesterone decreased the enzyme activity during a 3- to 24-hr period following hormone injection. This effect was not correlated to changes in the lysosomal protein synthesis rate. The lysosomal hydrolysis of cholesteryl esters was also inhibited in a noncompetitive manner by the addition of progesterone at concentrations higher than 100 microM. The esterase failed to respond to the estradiol in vivo as well as in vitro. The findings of the present paper suggest that the lysosomal breakdown of cholesteryl esters in rat liver may be under selective hormonal regulation and that the inhibitory effect of progesterone on the enzyme activity might be, at least in part, responsible for the liver cholesterol ester accumulus produced by the administration of the hormone.

Fluorometric assay for pancreatic cholesterylester hydrolase

A fluorescent cholesterylester analogue, cholesteryl 6-pyrenylhexanoate (ChPH), was used as a substrate for pancreatic cholesterylester hydrolase (CEH, EC 3.1.1.13). The substrate consisted of ChPH in egg phosphatidylcholine stabilized microemulsion with the aqueous phase containing deoxycholate below its critical micellar concentration. Due to the high local concentration of the pyrene moiety in the ChPH phase the fluorescence emission due to monomeric pyrene (IM) is greatly exceeded by the excimer fluorescence intensity (IE). Upon reacting with CEH 6-pyrenylhexanoic acid and free cholesterol are formed. The fluorescent product, 6-pyrenylhexanoic acid, is transferred into the aqueous phase containing deoxycholate, thus resulting in an enhanced fluorescence due to monomeric pyrene. CEH activity can thus be assessed directly by monitoring IM vs. time without product separation. Useful assay conditions were found to be 10 microM ChPH, 0.1 microM egg phosphatidylcholine, 2 mM sodium deoxycholate at 25 degrees C and pH 6.5-7.0.

Characteristics of multiple forms of the acidic triacylglycerol lipase(s) of canine cardiac myocytes

Acidic lipase activity was extracted by digitonin treatment from particulate fractions prepared from isolated adult canine myocytes. Both methylumbelliferyloleate (MUO) and trioleoylglycerol were hydrolyzed with an apparent Km of 13 and 135 microM, respectively. The primary products of trioleoylglycerol lipolysis were oleic acid and 1,2-dioleoylglycerol. Hydrolysis of either MUO or triacylglycerol was stimulated in vitro by the addition of cardiolipin or Triton X-100. Triton X-100 alone was sufficient for maximal stimulation of MUO hydrolysis, but cardiolipin further stimulated triacylglycerol lipolysis in the presence of an optimal concentration of Triton X-100. Cardiolipin increased the Vmax without altering the Km for trioleoylglycerol. Upon gel filtration chromatography the 4-methylumbelliferyloleate and triacylglycerol lipase activities eluted in regions consistent with molecular weights of approx. 47 000 and 55 000, respectively. Chromatofocusing revealed predominantly one form of acidic 4-methylumbelliferyloleate hydrolase (pI approx. 6.3), whereas acidic triacylglycerol lipase activity eluted continuously in the pH gradient from 7.2 to 4.3 with no clearly predominant peak of activity. Two forms of both 4-methylumbelliferyloleate and triacylglycerol lipase were eluted from columns of carboxymethyl Bio-Gel at pH 5.7; one form of each lipase activity was not bound and another form of each lipase was eluted with 50-60 mM KCl. The non-bound forms of each lipase were indistinguishable from their respective carboxymethyl-bound forms on the basis of pH dependency or kinetically (similar Km). The non-bound and carboxymethyl-bound peaks of lipolytic activity differed in the ratios of 4-methylumbelliferyloleate hydrolase to triacylglycerol lipase activity. The results suggest that the cardiac myocyte contains multiple forms of acidic lipase, and that the catalytic units primarily responsible for the hydrolysis of methylumbelliferyl esters and triacylglycerols may not be identical.

Lipids and cholesterol esterifying enzyme changes by Anna Pavala Sindhooram therapy in experimental rat hyperlipaemia

The effect of Anna Pavala Sindhooram (APS), an indigenous drug showing lipid lowering action was tested in experimental rat atherosclerosis induced by feeding an atherogenic diet. APS was found to decrease the levels of serum cholesterol and phospholipids while triglycerides remained unaffected in atherogenic diet fed rats. Lipid levels in the aorta, liver and intestine were also increased by atherogenic diet feeding, and APS administration with diet restriction reversed this trend. Cholesterol ester was lowered. Both cholesteryl ester hydrolase (CEH) and synthetase (CES) activities in the tissues were elevated while the CEH/CES ratio was lowered in atherosclerosis. APS administration led to a decrease in enzyme activities and an increase in the CEH/CES ratio. APS in vitro inhibited both enzyme activities. NMR spectroscopic studies showed that the soluble components of APS bind or modify cholesterol. Iron, copper, magnesium and calcium present in APS may play a role in the removal of cholesterol ester from the aorta and its disposal.

Purification and properties of rabbit liver acid-lipase (4-methylumbelliferyl oleate hydrolase)

An acid lipase was purified from rabbit liver lysosomes by, in sequence, osmotic treatment of the lysosomal fraction, Sephadex LH-20, DEAE-Sephadex A-50, Bio-Gel A-5m, hydroxyapatite and, finally, Sephadex G-200 column chromatography. The substrate was 4-methylumbelliferyl oleate. The enzyme was solubilized by Sephadex LH-20 column chromatography instead of detergents and organic solvents, to obtain an intrinsic macromolecule. 4-Methylumbelliferyl oleate hydrolase, osmotically released from lysosomal particles, had a very high molecular weight (greater than 800 000) which was reduced by gel filtration on a Sephadex LH-20 column; the final molecular weight of the purified enzyme was 58 000. The specific activity of 4-methylumbelliferyl oleate hydrolase increased at almost the same rate as acid cholesterol esterase and triacylglycerol lipase after Sephadex LH-20 column chromatography; the thermal stability of the activity of the three enzymes was almost identical. We also discuss the properties of the enzyme molecule and the interaction between the enzyme and the lysosomal membrane.