Identical catalytic subunit in both molecular forms of hormone-sensitive cholesterol esterase from bovine adrenal cortex

Nafamostat is hydrolysed by human liver cytosolic long-chain acyl-CoA hydrolase

Although the authors recently reported that nafamostat, a clinically used serine protease inhibitor, was mainly hydrolysed by carboxylesterase in human liver microsomes, the involvement of human liver cytosol has not been elucidated. The current study examined the in vitro metabolism of nafamostat with human liver cytosols. Kinetic analysis indicated that the Vmax and Km values in the liver cytosols were 9.82 nmolmin(-1) mg(-1) protein and 197 microM for a liver sample HL-1, and 15.1 nmolmin(-1) mg(-1) protein and 157 microM for HL-2, respectively. The Vmax/Km values in both cytosols were at least threefold higher than those in the corresponding microsomes. The liver cytosolic activity for nafamostat hydrolysis was inhibited by phenylmethylsulfonyl fluoride (PMSF) (43% inhibition at 100 microM), whereas diisopropyl fluorophosphate (DFP) and bis(p-nitrophenyl)phosphate (BNPP) failed to inhibit the activity. Furthermore, the hydrolytic activity was also reduced by palmitoyl-CoA (67% inhibition at 100 microM) but not by acetyl-CoA. Effects of PMSF, DFP and BNPP on cytosolic palmitoyl-CoA hydrolytic activity were comparable with those of the cytosolic nafamostat hydrolytic activity. In addition, the palmitoyl-CoA hydrolytic activity was competitively inhibited by nafamostat with the apparent Ki value of 164 microM for the liver cytosol from HL-2. These results suggest that an isoform of long-chain acyl-CoA hydrolase may be responsible for the nafamostat hydrolysis in human liver cytosol.

Influence of silanated filler content on the biodegradation of bisGMA/TEGDMA dental composite resins

It has been shown that an increase in the content of nonsilanated submicron colloidal silica filler particles within dental composites resulted in the release of more bis-phenol-A diglycidyl dimethacrylate (bisGMA)-derived product, bis-hydroxy-propoxyphenyl propane, following incubation with cholesterol esterase (CE). This work further investigates the enzyme-catalyzed biodegradation of fine composite resin systems, containing silanated micron-size irregular glass fillers, commonly used in clinical restorations. Model composite resin samples (10 or 60% weight fraction silanated barium glass filler, 1 mum average particle size) based on bisGMA/triethylene glycol dimethacrylate (TEGDMA) were incubated in buffer or buffer with CE (pH = 7.0, 37 degrees C) solutions for 32 days. The incubation solutions were analyzed using high-performance liquid chromatography, UV spectroscopy, and mass spectrometry. Both groups were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. In contrast with previous findings for nonsilanated submicron filler systems, the higher filler containing composite showed an increase in its stability with time, following exposure to esterase and when compared to the lower filler content material. As well, the 60% filler composite leached less unreacted monomer TEGDMA. Since the model composite resins studied here were identical and only the filler content varied, the differences in biostability could be specifically associated with the relative amount of resin/filler distribution. The clinical use of different materials in varied dental applications (ranging from fissure sealant to tooth-colored highly filled materials) must consider the potential for different degradation profiles to occur as a function of filler content.

The control by angiotensin II of cholesterol supply for aldosterone biosynthesis

In the adrenal glomerulosa cell, aldosterone is synthesized from cholesterol, which is supplied to the cell and stored under the form of cholesterol esters, then hydrolyzed to be transferred to the mitochondrial outer membrane and finally transported to the inner membrane where the P450 side-chain cleavage enzyme will convert it to pregnenolone. Angiotensin II (AngII), one of the major physiological regulators of mineralocorticoid synthesis, appears to affect most of the steps along this cascade and thus to exert a powerful control over the use of cholesterol for aldosterone production.

Angiotensin II activates cholesterol ester hydrolase in bovine adrenal glomerulosa cells through phosphorylation mediated by p42/p44 mitogen-activated protein kinase

In adrenal glomerulosa cells, the stimulation of aldosterone biosynthesis by angiotensin II (Ang II) occurs via activation of the Ca2+ messenger system, increased expression of the steroidogenic acute regulatory protein, and enhanced transfer of cholesterol to the inner mitochondrial membrane. We examined here whether Ang II affects the activity of cholesterol ester hydrolase (CEH), also named hormone-sensitive lipase, the enzyme recruiting cholesterol from intracellular pools, in bovine adrenal glomerulosa cells. In bovine adrenal tissue, CEH activity was detected with characteristics similar to those reported in other tissues (Michaelis constant = 46.3 +/- 6.7 microM, n = 3; maximal velocity = 1 nmol/mg.min). This activity was significantly enhanced in isolated bovine glomerulosa cells challenged for 2 h with 10 nM Ang II (to 149 +/- 11% of controls, n = 3). Similarly, 25 microM forskolin raised CEH activity to 151 +/- 5% of controls (n = 3). This increase in activity of CEH was not due to an increase in the amount of enzyme protein but was associated with an increased phosphorylation of the enzyme to 337 +/- 33% of controls (n = 9, P < 0.0001). Potassium ion (K+) and forskolin also stimulated [32P]orthophosphate incorporation, although to a lesser extent (to 157 +/- 18% and 186 +/- 25% of controls, respectively). On SDS-PAGE, the majority of this radioactivity was associated with a species of 172 kDa, corresponding to a CEH dimer. Both Ang II-induced CEH phosphorylation and pregnenolone production were significantly reduced (to 47 +/- 6% and 50 +/- 8% of controls with Ang II alone, respectively) in the presence of PD098059, an inhibitor of p42/p44 MAPK. Indeed, Ang II challenge led to a rapid 32P incorporation into p42/p44 MAPK. These results demonstrate that, in addition to its known effects on intramitochondrial cholesterol transfer, Ang II also promotes aldosterone biosynthesis by rapidly increasing cholesterol supply to the outer mitochondrial membrane.

Hormonal and stressor-associated changes in porcine adrenocortical cholesterol ester hydrolase activity

Cholesterol ester hydrolase (CEH) activity was characterized in the porcine adrenal gland and experiments conducted to determine the nature of its hormonal regulation. CEH activity was studied in the 14,000 gmax pellet (F4) and in the 192,000 gmax supernatant (F6). Characteristics associated with pH optima, product formation with time, linearity with increasing protein concentration, and equilibration of exogenous cholesterol esters added in acetone with endogenous cholesterol esters were determined. Scatchard analyses of saturation data demonstrated two-site models, which indicated the presence of lower velocity lower Km enzymes (catalytic sites) (L-VKm) and higher velocity higher Km enzymes (catalytic sites) (H-VKm) in both subcellular fractions. Neither ACTH (0.4 micrograms/kg body weight) nor 30-min restraint affected CEH activities at 0.5, 2, and 5 h after injection or initiation of restraint. However, 1 h after a longer restraint period (45 min), F4 H-VKm CEH activity increased concomitantly with decreased F6 L-VKm (P = 0.003). More modest increases in F4 H-VKm (P = 0.03) were still apparent 1 h after the last of nine daily 45-min restraints. Bromocriptine (CB154, a dopamine agonist) administration for 6 days (9.6 mg/daily) reduced plasma prolactin (PRL) by 53% (P < 0.05), but had no effect on CEH activities. ACTH treatment to CB154-induced hypoprolactinemic barrows dramatically reduced F4 (63%) and F6 (49%) L-VKm CEH activity (P = 0.03). These data are the first concerned with regulation of adrenal CEH activity in swine, and are the first to evaluate in vivo treatments on in vitro CEH activity in any species evolutionarily higher than rodents. In vivo regulation of porcine adrenal CEH activity appears complex. Stressor-associated hormonal perturbations apparently must surpass a certain threshold of duration and/or magnitude before they alter CEH activity. Differing Km and Vmax of CEH within and between the two subcellular fractions studied and the differential responses to restraint stressor suggest that as many as four different enzymes with CEH activity are involved. Additionally, the combined effect of ACTH and CB154-induced hypoprolactinemia argues for an interrelated modulatory function of ACTH and PRL (or dopamine) on specific porcine adrenal CEH activities.

Regulation of steroidogenesis in rat adrenal gland: identification of the bifunctional, hormone-sensitive cholesterol esterase--triacylglycerol lipase enzyme protein and its discrimination from hormone-insensitive lipases

The activities of hormone-sensitive cholesterol esterase and hormone-sensitive triacylglycerol lipase from rat adrenal glands were enhanced about 2-fold by means of ether stress and showed parallel elution profiles on a Sepharose CL-6B column. Both enzymatic activities were inhibited to a similar extent by DFP after separation from hormone-insensitive lipase on heparin-Sepharose. Fractions from the gel filtration column containing the two hormone-sensitive enzymes showed incorporation of tritium-labelled DFP into only one polypeptide of Mr 84 000. From these results we conclude that both hormone-sensitive activities reside on one polypeptide of Mr 84 000, thus providing further support to the concept that the different hormone-sensitive acylester hydrolase activities in steroid-secreting tissues as well as in adipose tissue are performed by the same bifunctional enzyme. In addition to the hormone-sensitive enzyme, rat adrenals contained high amounts of neutral triacylglycerol lipase activity which was not affected by stress. The latter enzyme was resistant to high salt concentrations, was less susceptible to inhibition by DFP, but could be inhibited completely by the addition of antibodies raised against rat liver lipase, thus most probably representing the adrenal liver lipase-like triacylglycerol lipase.

Cholesterol ester hydrolase and sterol carrier proteins

The cholesterol substrate required for sustained adrenal steroidogenesis is largely derived from the endogenous stores of cholesterol esters, which are located in large lipid inclusion droplets in the cytoplasm. In isolated adrenal cells, these esters are hydrolyzed during a variety of stimuli associated with cellular cAMP production. This largely appears to be a response to the action of a neutral cholesterol ester hydrolase, whose activity is modulated by phosphorylation of the enzyme protein, catalyzed by cAMP-dependent protein kinase. Transfer of the resulting unesterified cholesterol to mitochondria can be accomplished in a model system by sterol carrier protein2 (SCP2). This protein is distinct from fatty acid binding protein (FABP), has a Mr of 13,500 and is basic in nature. SCP2 can sequester cholesterol from lipid inclusion droplets in a stoichiometric relationship, and transfer this cholesterol to isolated adrenal mitochondria. SCP2 can also enhance the intermembrane transfer of mitochondrial cholesterol to cytochrome P 450scc, but does not directly affect cholesterol side chain cleavage. The stimulatory effect of adrenal cytosolic preparations on mitochondrial pregnenolone production can be completely abolished by pretreatment with anti SCP2 IgG.

Investigation of the apolipoprotein fraction of isolated rat adrenal and bovine adrenocortical lipid droplets

The lipid droplet fractions from rat adrenal and bovine adrenocortical tissue were isolated by density ultracentrifugation. The droplet fractions were delipidated and the protein components investigated by SDS-polyacrylamide slab gel electrophoresis. The adrenal lipid droplets from both species displayed a qualitatively similar protein profile, and both contained a major apolipoprotein subunit of Mr 40 000. Incubation of intact, non-delipidated lipid droplets with [gamma-32P]ATP in vitro resulted in the phosphorylation of the Mr 40 000 apolipoprotein subunit in the case of rat lipid droplets, but not in the case of bovine lipid droplets. However, following delipidation of the droplets with diethyl ether/ethanol, the Mr 40 000 apolipoprotein subunit was phosphorylated in both cases upon incubation of the delipidated protein fractions with [gamma-32P]ATP in vitro. Labelling with [gamma-32P]ATP and [3H]diisopropyl phosphorofluoridate indicated that the cholesterol ester hydrolase enzyme protein was not a major constituent of the adrenal lipid droplet protein fraction.