James M. Felts

The mechanism of assimilation of constituents of chylomicrons, very low density lipoproteins and remnants - a new theory

Abstract Purified remnant lipoproteins produced from chylomicrons in vivo or in vitro by the action of lipoprotein lipase (LPL) contain firmly bound LPL. The perfused rat liver removes the particulate bound LPL and triglyceride-labeled remnants at exactly the same rate, while purified chylomicrons are not removed. Once remnants are removed by the liver, they are not rereleased into the perfusate. These observations have led to the theory that the LPL attached to the remnant is the signal that allows the liver to “recognize” remnants from chylomicrons. This is followed by fusion of the particle with the cell surface and may be associated with the splitting off a low density lipoprotein particle. The remaining lipids of the remnant are further metabolized by the liver triglyceridase and the cholesterol esterase.

Placental transfer of palmitic acid-1-C14 in rabbits

Abstract The concentration of triglyceride fatty acids in the blood plasma of the fetal rabbit at term is about twice that of the mother. Plasma FFA concentrations are similar (about 0.5 μM per milliliter). After the intravenous injection of palmitic acid-1-C 14 into pregnant rabbits, radioactivity appears in the FFA in fetal plasma within 1 minute and specific activity is maximal in 5 minutes. When compared with previous results obtained in sheep, the data suggest that much more palmitic acid-1-C 14 is transferred across the hemoendothelial placenta of the rabbit than across the syndesmochorial placenta of the sheep. Results of measuring radioactivity in lipids of fetal tissues suggest that the metabolic pathways followed by palmitic acid-1-C 14 in the fetus are similar to those in the adult rabbit. Preliminary data indicate that palmitic acid-1-C 14 is transferred across the human placenta. The possible contribution of placental transfer of FFA to the lipids present in the fetus is discussed.

Apoprotein composition of plasma lipoproteins in uremic patients on hemodialysis.

Abstract Soluble apolipoproteins were isolated from very low density and high density lipoproteins obtained from the plasma of uremic patients on hemodialysis. Quantitative gel electrophoresis was utilized to determine the relative amounts of lipoprotein lipase activator (ApoC-II) and inhibitor (ApoC-III) peptides of very low density lipoproteins from anephric patients, patients with glomerulo-nephritis, polycystic disease and appropriate normal subjects. The relative amounts of A and C apoproteins of high density lipoproteins from anephric patients, patients with glomerulonephritis and normal subjects were also determined. The total protein in very low density lipoproteins was increased by 300–450% and the ApoC-III/ApoC-II ratio increased from 3.4 in normal subjects to 6.2–8.4 in patient groups. The total protein in high density lipoproteins was decreased approximately 30% for all patient groups. There was no difference in the relative percentage of apoproteins A-I and A-II in the high density lipoproteins between the normal and the patient groups. However, the ratio of ApoC-III/ApoC-II was elevated in patients. Our results suggest the possibility that alterations in the composition of the C group of apoproteins of very low density lipoproteins and high density lipoproteins may contribute to the increase in triglyceride concentration by modulating the activity of lipoprotein lipase. Since anephric patients showed patterns identical to other kidney patients, it appears that the uremic state and not a specific kidney disease is associated with the apoprotein alterations.

Diisopropylammonium dichloroacetate (DIPA) and sodium dichloroacetate (DCA): Effect on glucose and fat metabolism in normal and diabetic tissue

Abstract Diisopropylammonium dichloroacetate (DIPA) was found to exert a significant and prolonged hypoglycemic effect in alloxan diabetic rats, but did not alter blood sugar levels of normal rats. It did not affect blood glycerol levels in either the diabetic or nondiabetic group. In order to establish the site of action of DIPA, we carried out a series of in vitro studies. Both DIPA and sodium dichloroacetate (DCA) significantly stimulated glucose-U- 14 C oxidation to 14 CO 2 in isolated hemidiaphragms from diabetic but not from nondiabetic rats. Diisopropylammonium hydrochloride (DIA) was not effective in promoting glucose oxidation in tissues from diabetic or nondiabetic rats. Thus, the effect of the compound in vivo may be due entirely to its acid moiety. DCA (and presumably DIPA) produced no significant changes in glycerol output or on glucose-U- 14 C conversion to 14 C-triglyceride in hemidiaphragms or epididymal fat pads from normal or diabetic rats. In addition, DCA did not alter oleate-1- 14 C conversion to 14 C-triglyceride in muscle or adipose tissue from diabetic animals. However, DCA markedly inhibited oleate-1- 14 C oxidation to 14 CO 2 in muscle from diabetic rats. It is possible that the hypoglycemic activity of DIPA, and presumably DCA, may be due, at least partly, to a suppression of fatty acid oxidation in muscles of diabetic rats. The high levels of circulating free fatty acids and ketone bodies which commonly occur in diabetes increase intracellular concentrations of citrate, a known inhibitor of phosphofructokinase (PFK). By suppressing fatty acid oxidation in muscle, DIPA and DCA may thus reduce citrate levels and reactivate PFK. Such an effect may explain the selective action of both DIPA and DCA on diabetic but not on normal tissue.

Separation of a lipoprotein lipase cofactor from the α1-acid glycoprotein fraction from the urine of nephrotic patients

Abstract Previously, we showed that the α1-acid glycoprotein fraction from the urine of nephrotic patients stimulates triacylglycerol hydrolysis in a lipoprotein lipase assay system. This fraction also accelerates triacylglycerol clearance in vivo in a nephrotic rat model. Based on these observations, we postulated that the hyperlipemia in nephrotic patients may be directly related to the urinary loss of the active α1 -acid glycoprotein fraction which could lead to reduced plasma levels of this lipoprotein lipase cofactor. In the present report we show that the stimulatory activity can be separated from the active α1-acid glycoprotein fraction by DEAE-cellulose chromatography and the conditions necessary for elution (1.0 M NaCl) are indicative of a molecular class of compounds with high negative charge. From additional data, such as precipitation by lysozyme, electrophoretic mobility, toluidine blue staining and the presence of uronic acid, we have concluded that the activity-containing material is a glycosaminoglycan. Gel filtration data suggest that the active α1-acid glycoprotein fraction from urine of nephrotic patients consists of two components: free α1-acid glycoprotein and a glycosaminoglycan- α1-acid glycoprotein complex. This complex can be precipitated by lysozyme leaving free α1-acid glycoprotein in the supernatant. Since the glycosaminoglycan associated with the α1-acid glycoprotein in urine appears to have a cofactor function in the lipoprotein lipase enzyme reaction, we postulate that it is the urinary loss of plasma glycosaminoglycan that may be responsible for the hyperlipemia associated with the nephrotic syndrome.

Activation of Lipoprotein Lipase Comparative Study Of Man And Other Mammals

Injection of heparin into a number of animal species releases lipoprotein lipase into the circulation. We have studied the effect of heparin added in vitro to the lipase activity in post-heparin serum from six mammalian species. With the exception of man, all animals were studied under anesthesia. Our results demonstrate that only post-heparin serum from the rat developed increasing lipoprotein lipase activity when increasing concentrations of heparin were added to the assay system. Heparin decreased activity in the other species. These results prompted us to test the effect of adding rat serum to post-heparin serum from the other species in the presence of increasing concentrations of heparin. Rat serum stimulated lipoprotein lipase activity markedly. In guinea pigs, post-heparin serum activity increased 2,700% at a heparin concentration of 1.0 U/ml in the assay system. This effect may be related to the extremely low level of high-density lipoprotein in the guinea pig and the presence of a unique high-density lipoprotein in the rat.

The effect of α1-acid glycoprotein (orosomucoid) on triglyceride metabolism in the nephrotic syndrome

We have identified α1-acid glycoprotein as a new co-factor in the lipoprotein lipase reaction. We isolated an active form of the compound from nephrotic urine that is effective both in vitro and in vivo. α1-acid glycoprotein increased lipolysis 100% in the presence of C-II apolipoprotein in a lipoprotein lipase assay system. Rats with induced nephrotic syndrome showed a decrease in triglyceride clearance. T12 was increased from 14 min to 43 min. The injection of α1-acid glycoprotein restored the lipid clearance to normal. These findings suggest that elevated plasma triglycerides in human nephrotic patients is the direct result of excessive loss of α1-acid glycoprotein from plasma into urine. We propose that replacement therapy may be possible.

Dispersal of Rabbit Lung into Individual Viable Cells: A New Model for the Study of Lung Metabolism

This new enzymatic method disperses rabbit lung into morphologically intact, viable individual cells. The scattered cells constitute more than 50 percent of the original tissue. At least 90 percent of the cells exclude trypan blue from the nucleus. The dispersed lung cells consumed 6.2 microliters of oxygen per hour per milligram, dry weight. They incorporated [1-14C]palmitate into lecithin.

Kinetics of chylomicron triglyceride removal from plasma in rats: The effect of diet☆

1. 1. The effect of diet upon the kinetics of chylomicron triglyceride removal was studied using an experimental method which allows measurements to be made under optimal physiological conditions. 2. 2. Two groups of rats were fed diets high in carbohydrate or high in fat for 14 days. Another group was fed a standard laboratory chow and fasted 18–20 h before the experiments. From the disappearance of 14C following the end of a 20-min infusion of labeled chylomicrons (0.30–0.35 mg total lipid per min), the apparent half time of removal of chylomicron triglyceride was estimated to be 2.9 ± 0.22 min in the fasted rats, 5.3 ± 0.35 min in the carbohydrate-fed rats, and 2.5 ± 0.39 min in the fat-fed rats. The significantly longer half-time (P < 0.001) found in the carbohydrate-fed rats suggests an impaired mechanism for removing chylomicron triglyceride in these rats.

Lipoprotein spectrum analysis of uremic patients maintained on chronic hemodialysis

It is known that patients maintained on chronic hemodialysis have elevated plasma lipids. In order to establish whether the type of kidney pathology is related to a specific lipoprotein abnormality, we measured plasma lipoprotein in eight patients with glomerulonephritis, two patients with polycystic kidney disease and nine patients that had been surgically nephrectomized. The concentration and composition of plasma very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) in patients were compared to plasma lipoproteins in a control group. In all patient groups, the lipoprotein alterations appeared identical. VLDL were elevated 3 to 4 fold, LDL were decreased 15--35% and HDL were decreased 30--45% when compared to values of our control group. Since no differences in the lipoprotein spectrum were found among the patient groups, it appears that the hypertriglyceridemia of chronic uremia is due to the uremic state per se and is not related to a specific pathology of the kidney.