Regulation of lipase activities in rat brain in vitro

Regulation of acid and neutral lipase activities in rat brain was examined in vitro. Both activities were decreased by SDS, CuCl2 and ZnCl2 and by delipidation. The neutral lipase activity was also markedly reduced by N-ethylmaleimide and PbCl2. The activity of delipidated preparation was increased by addition of phosphatidyl choline at both pH 5.5 and 7.5 and by phosphatidyl serine at acidic pH value. Pretreatments of the enzyme preparation with phospholipase A and trypsin reduced the lipase activities at both pH values. It is suggested that phospholipids play an important role on lipase activity in brain.

Catabolism of human very low density lipoproteins in vitro: a fluorescent phospholipid method for monitoring lipolysis

The catabolism of human plasma very low density lipoproteins (VLDL) by purified bovine milk lipoprotein lipase has been measured in vitro using a fluorescent phospholipid as a method to monitor lipolysis. Dansyl phosphatidylethanolamine (DPE) was incorporated into VLDL to form DPE-VLDL, and the rate of catabolism was followed by measuring the increase in fluorescence at 490 nm after the addition of the enzyme. The studies were performed with VLDL isolated from 20 normal individuals. In addition, the VLDL from 8 mildly obese subjects with primary hypertriglyceridemia (Type IV phenotype) was studied. With this in vitro system and with a constant amount of lipoprotein lipase, the rate of lipolysis did not differ in normal and in these hypertriglyceridemic subjects. Furthermore, there was no correlation between the rates of hydrolysis and the plasma levels of triglyceride or high density lipoprotein cholesterol.

Studies on cholesterol ester hydrolysis in artificial lipid mixtures

Cholesterol ester is present in lipid deposits in atherosclerotic lesions, such as fatty streaks, fibrous plaques and complicated lesions. The possibility of hydrolysis of cholesterol ester in lipid deposits and its mechanism were examined by studying the effects of the various components of lipid deposits on cholesterol ester hydrolysis. Studies were carried out using artificial lipid samples prepared by sonication of mixtures of the components of lipid deposits. Results suggested that phospholipids, especially phosphatidylcholine, play an important role in the hydrolysis and that alteration of lipid components, other than cholesterol ester, influences cholesterol ester hydrolysis in lipid deposits.

Studies on lipase in rat brain

Lipase activity was measured in homogenates of rat cerebral hemispheres using radioactive glycerol trioleate emulsified with Triton X-100 as substrate. The labeled oleic acid was separated from the ester with a methanol-chloroform-heptane mixture. Under these assay conditions, the activity showed pH optima at about 5.5 and 7.5. The final products of these lipase activities were suggested to be free fatty acid and glycerol.

Preparation and properties of immobilized lipoprotein lipase

Purified bovine milk lipoprotein lipase has been covalently attached to CH-Sepharose with water-soluble carbodiimide. The immobilized enzyme retained enzymic activity and was stimulated 7-fold by the addition of human apolipoprotein C-II. Both [3H]heparin and 125I-labeled apolipoprotein C-II bound to the immobilized enzyme; unlabeled heparin and apolipoprotein C-II competed for binding of their respective labeled compounds. Apolipoprotein C-II did not compete for binding of [3H]heparin and vice versa. Human apolipoprotein C-III did not bind to the immobilized enzyme nor did it compete for apolipoprotein C-II binding. We conclude from these studies that both apolipoprotein C-II and heparin interact with immobilized lipoprotein lipase and that they have different binding sites.

Clinical study of niceritrol on serum lipids in the treatment of hyperlipidemia

The effects of niceritrol, a nicotinic acid derivative, on the levels of HDL-cholesterol (HDL-Ch) and a mixture of VLDL- and LDL-Ch (VLDL- + LDL-Ch) were studied in hyperlipidemic patients. Serum total cholesterol (sTC) and serum triglyceride (sTG) were significantly reduced during niceritrol administration. Lipoprotein electrophoresis showed that niceritrol increased the alpha:beta ratio. HDL-Ch showed a significant increase of 12.5% by the 16th week of therapy. This increase was more marked in patients with lower pre-treatment HDL-Ch levels and significant in patients whose pre-treatment sTG levels were in excess of 200 mg/dl. Females displayed higher pre-treatment HDL-Ch levels (38.5 mg/dl) than males (30.6 mg/dl). However, niceritrol increased HDL-Ch significantly in both groups. At 16 weeks, the VLDL- + LDL-Ch level showed a significant decrease of 9.2%; the HDL-Ch:VLDL + LDL-Ch and HDL-CH:sTC ratios were significantly increased throughout niceritrol administration. Niceritrol is thought to be effective in preventing the development and progression of atherosclerosis because it raises the level of anti-atherogenic HDL-Ch and lowers the level of atherogenic VLDL- + LDL-Ch.

Effect of pantethine on cholesterol ester metabolism in rat arterial wall

The total serum cholesterol level in rats fed on a high cholesterol diet (HCD) for 16 weeks was markedly higher than that in rats fed on a normal diet (ND), but pantethine reduced the increased level in rats fed on HCD (P less than 0.05). Acid cholesterol esterase activity (acid CEase) of arterial wall homogenates from rats fed on HCD was significantly lower than that of rats fed on ND (P less than 0.005). Acid CEase activity in the arterial wall of rats fed on HCD for 8 weeks and then ND for 8 weeks was less than that of rats fed on ND for 16 weeks. Acid CEase activity in the arterial wall was increased in rats fed on pantethine-containing diet. The ratio of cholesterol ester synthesizing activity to neutral cholesterol esterase (neutral CEase) activity was higher in rats fed on NCD than in those fed on ND. The ratio was lower in rats on the pantethine-containing diet than in those on NCD. The relationship between hypercholesterolemia and lipid metabolism in the arterial wall and effects of pantethine are discussed on the basis of these results.

Effects of pantetheine on cholesteryl ester synthesis in the arterial wall of rats on high cholesterol diet

Increase of acyl-CoA synthesis was observed when extracts of rat arterial wall were incubated with pantetheine [D-bis-(N-pantothenyl-beta-aminoethyl)-disulfide]. Cholesteryl ester synthesis from palmitate in the arterial wall extract in vitro was higher with arteries from rats on high cholesterol diet than with those from rats on normal diet, but the synthesis was reduced in the arteries of rats on high cholesterol diet with pantetheine. Triglyceride synthesis was higher with arterial wall extracts of rats on high cholesterol diet than with preparations from rats on normal diet and was not reduced with those of rats on high cholesterol diet plus pantetheine. The value of the effects of pantetheine on lipid metabolism in the prevention of atherosclerosis is pointed out.

Studies of cholesterol esterase in rat arterial wall

Cholesterol esterase activity was estimated in homogenates of rat arterial wall using radioactive cholesteryl oleate incorporated into phospholipid vesicles as a substrate. The labeled oleic acid was separated from the ester by addition of benzene-chloroform-methanol mixture. Under these conditions, two pH optima were found at about 4.5 and 7.5. Most of the activities at pH 4.5 and 7.5 were found in the lysosomal and microsomal fraction, respectively. No enzyme activity was detected when the substrate vesicles were prepared with phosphatidylethanolamine or sphingomyelin, but the activity was higher when the substrate vesicles were prepared with phosphatidylserine and highest when they were prepared with phosphatidylcholine. The relationship between enzyme regulation and lipid deposition in the arterial wall is discussed.

Quantitative and qualitative estimation of urinary kallikrein in a patient with Bartter's syndrome

Urinary kallikrein in a patient with Bartter's syndrome was remarkably higher than normal. Indomethacin treatments increased serum potassium concentration and urinary Na/K ratio, and improved the response of blood pressure to angiotensin II infusion, while it decreased plasma renin activity, plasma aldosterone and urinary kallikrein. The purified urinary kallikrein had one component of the iso-electric point 4.3 by isoelectric focusing using Ampholine system, and its molecular weight was 4.2 x 10(4), which was greater than those of three components of normal human urinary kallikreins (normal HUK). Also Km values with TAME and BAME of urinary kallikrein in our patient with Bartter's syndrome did not correspond to those of normal HUK. Thus it can be said that urinary kallikrein in our patient with Bartter's syndrome was qualitatively different from normal HUK. The present observation might be a reflection of renal tubular dysfunction in this patient with Bartter's syndrome.

Effects of adrenergic blocking agents on lipolysis and adenyl cyclase activity induced by vasoactive intestinal polypeptide (VIP)

VIP stimulates lipolysis and adenyl cyclase activity in the rat adipose tissue. VIP-induced lipolysis and adenyl cyclase activity are not affected by phenoxybenzamine. VIP-induced lipolysis is inhibited by propranolol but VIP-induced adenyl cyclase activity is not.

Studies on the mechanism of action of ACTH on triglyceride synthesis in fat cells

It was found that ACTH greatly reduced lipogenesis in fat cells in the presence of calcium ion, but not in the absence of calcium ion. Of the enzymes involved in triglyceride synthesis from fatty acid in lipid micelle membranes, only acyl-CoA synthetase was inhibited by calcium ion, the apparent Ki value of calcium ion being 4.2 X 10(-4) M. The Km values of the enzyme for palmitate and ATP were 2.0 X 10(-4) M and 2.5 X 10(-4) M, respectively and calcium ion caused non-competitive inhibition with both palmitate and ATP. The acyl-CoA synthetase activity of lipid micelle membranes was inhibited by treatment with phospholipase A or C, but not by treatment with phospholipase D. The mechanism of inhibition of triglyceride synthesis by ACTH is discussed on the basis of these results.